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CHEMISTRY.

BY /? ,

WILLIAM THOMAS BRANDE, D.C.L., F.K..S.L. & E.

OF HER MAJESTY'S MINT.

MEMBER OF THE SENATE OP THE UNIVERSITY OP LONDON, AND
HONORARY PROFESSOR OP CHEMISTRY IN THE ROYAL INSTITUTION OP GREAT BRITAIN i

AND

ALFRED SWAINE TAYLOR, M.D., F.R.S.

FELLOW OP THE ROYAL COLLEGE OP PHYSICIANS OF LONDON,
AND PROFESSOR OP CHEMISTRY AND MEDICAL JURISPRUDENCE IN GUY'S HOSPITAL.

EXPERIMENTIS ET PR^CEPTIS.

SECOND AMERICAN EDITION THOROUGHLY REVISED.

PHILADELPHIA:

HEITETO LEA
1867.

PHILADELPHIA:
COLLINS, PEIATER, 705 JaYNE STREET.

AMERICAN PUBLISHER'S NOTICE,

Dr. Taylor, having kindly consented to give to this
volume a thorough revision, no additions have been found
necessary to adapt it to the wants of the American stu-
dent. The press, however, has been carefully supervised
by a competent chemist, in order to secure the utmost
typographical accuracy ; and it is hoped that the work, in
its present improved condition, will be found worthy a
continuance of the very marked favor with which it has
thus far been received.

Philadelphia, August, ISGt.

CAVSUH

PREFACE

SECOND AMERICAX EDITION

Ix preparing a second edition of the work on Chemistry by tlie
late Professor Brande and myself, I have endeavored to carry out the
principles which influenced us in the selection of subjects and in the
mode of treating them. We felt that there was a large amount of
useful chemical knowledge available for the student, but that it was
too often locked up in elaborate treatises, and incorporated with sub-
jects of no practical interest. Our object in undertaking this work
was to furnish the reader, whether a student of medicine or a man of
the world, with a plain introduction to the science and practice of
chemistry. With this view, we avoided as much as possible the
introduction of questions connected with abstract science or with
chemical philosophy, and we excluded from our pages the formulae
and descriptions of substances which were never likely to be seen
except as rare and curious specimens in the cabinets of professors.
The chemistry of every-day life is quite sufi&cient to give full occu-
pation to a medical student. If, after the completion of his medical
education, he has the time and inclination to devote to the study of
atoms and the numerous and conflicting hypotheses on their combina-
tions in groups and series, there can be no objection to his taking up
the examination of these recondite subjects, but let him make himself
master of what is simple and practical before he occupies valuable
time in studying that which is complex and hypothetical.

The ordinary and well-known notation, based on the equivalent or
combining weights of bodies which was adopted in the first, is
adhered to in this edition. Although not perfect, it is based upon
simple and intelligible principles. The new methods of notation
must be regarded as still upon their trial. Gerhardt's system, which
a few years since was generally adopted by " advanced " chemists, has

yi PREFACE.

now given place to another system, and the extinction of this is
threatened by a third and an entirely different system, recently
propounded by Sir Benjamin Brodie, Professor of Chemistry in the
University of Oxford. Apart from any advantages supposed to be
presented by these new systems, a writer on chemistry, in making a
selection, is bound to consider the present state of chemical literature
and the course which has been adopted by authors of repute. It will
be found that in the best modern works on Chemistry in the English
and French languages and in the great majority of such works, the
ordinary notation is adopted, and the new notation ignored even by
writers who have been or are advocates for a change. In proof of
this, I may refer to the English translation of the Hand-book of
Gmelin, in sixteen volumes ; the Traits de Chimie of Pelouze and
Fremy, in six large volumes, which has already gone through three
editions ; the earlier editions of Dr. Miller's Chemistry ; the works of
Apjohn and Bloxam among recent, and of Eegnault, Mitscherlich,
Graham, Brande, Gregory, and Turner among older publications on
the science. In the Precis d' Analyse Chimique of Gerhardt, pub-
lished eight years after the introduction of his proposed new but now
obsolete system, the ordinary notation was adopted by this author as
more intelligible to the student ; and in the recently published Chimie
Medicale of Professor Wurtz (1867) the new views advocated by the
writer in his Introduction to Chemical Philosophy, are laid aside and
the old equivalents are used. The apology for this is said to be the
necessity of conforming to the official teaching in the Schools of Paris.
This may be true, but it proves that the official teaching in one of the
greatest Chemical Schools of Europe is opposed to these new systems
of notation. With these examples before me, and with a conviction
of the artificial and unsatisfactory nature of the grounds upon which
the new systems are based, I did not feel justified in making any
change in the plan adopted after full consideration by the late Pro-
fessor Brande and myself. Nothing could be gained by laying aside
one system because it is imperfect, for another which at present ofiers
no prospect of stability; for, as Mr. Bloxam justly remarks, "the
different modes of representing chemical changes are almost as
numerous as chemical writers.^

It cannot be denied that a student of chemistry at the present time
has a heavy labor before him. Besides two or more methods of chemi-
cal notation, he will find in English works on the Science, that while
one author employs the continental metrical weights and measures,

» Chemistry, Inorganic and Organic, 1867.

PREFACE. Vll

giving quantities in grammes and cubic centimetres, another adopts
the English system of expressing them in grains and cubic inches. One
describes the barometrical pressures in French millimetres, another in
English inches ; one describes degrees of temperature on the foreign
centigrade scale, another on the ordinary scale of Fahrenheit, and to
add to this want of uniformity, there is a further difficulty that the
same chemical compound may be described under four or five different
names, according to the special views of each writer regarding theo-
ries of atomicity and nomenclature ! This want of agreement among
chemical writers is but little creditable to the science, and is discourag-
ing to a student. Instead of making himself acquainted by actual
experiment with the properties of bodies, so that he may be able to
identify and describe them, he is induced to load his memory with the
formulae of complex organic products, as if chemistry consisted simply
in knowing or calculating the number of atoms in a compound, and
the precise order in which they are grouped. This may be know-
ledge, but it is not true chemical knowledge, and to a medical or general
student, it is not in any sense profitable knowledge. A recent writer
on the Progress and Prospects of Chemistry, justly remarks that "ab-
stract reasoning has thrown more complication round chemical science
than it has ever afforded of satisfactory demonstration. Eecent chemi-
cal works affecting a logical reasoning, are crowded with arguments
and classifications that have in a great measure taken the place of
facts and experiments, and are calculated rather to bewilder than
assist the student. Logic is very well in its own place, but it is easy
to carry it to excess in sciences essentially practical, more especially
when it is built upon assumptions that never have been and perhaps
never will be established as truths. Many of the elaborate systems of
classification now brought forward are more ingenious than useful,
and even their plausibility seems but too often to arise from accidental
circumstances, rather than from any foundation in fact."^

The student who desires to succeed in this branch of science, must
constantly bear in mind that chemistry is essentially based upon ex-
periment, and that work in the laboratory offers a better and surer
road to success than the study of the most ingenious speculations in
the closet.

The revision of the second edition, in consequence of the death of
my lamented colleague, has devolved entirely upon myself. Every
chapter, and indeed every page has been revised, and numerous addi-
tions made in all parts of the volume. These additions have been

• Professor McGauley, Progress and Prospects of Chemistry, 1866.

Viii PREFACE.

restricted chiefly to subjects having some practical interest, and they
have been made as concise as possible in order to keep the book
within those limits which may retain for it the character of a Student's
Manual.

ALFEED S. TAYLOR.

June 29, 1867.

TTiLLiAM Thomas Brande, D. C. L., F. R. S., died at Tunbridge
Wells on the 11th February, 1866. Mr. Brande had been long known
as a skilful chemist and an assiduous cultivator of science. For more
than forty years he was engaged in this metropolis as a lecturer on
chemistry. We have now before us an advertisement of his lectures
in October, 1811. He was then the colleague of the late Sir Benja-
min Brodie in the Medical School of Great Windmill Street. His
lectures subsequently at the Royal Institution, where he was the col-
league of Faraday, gained for him a high reputation. His explanations
of chemical phenomena were lucid, and his experiments ingenious and
well-contrived. The substance of these lectures is incorporated in the
great work by which he acquired a European reputation, namely, the
" Manual of Chemistry." This work was, in its day, one of the most
popular in the English language, and there are few recent treatises, in
chemistry which are not indebted to its pages for much valuable in-
formation. The fact that, owing to its bulk, the manual had gone
beyond the necessities of the medical students, and that it had acquired
an encyclopaedic character led the distinguished chemist to join with
me, in 1863, in preparing the present work in one volume for the
special use of students, and I may here state that the whole of the
chapters on the Metals, excepting those parts which refer to Toxi-
cology, and the larger portion of the section on Organic Chemistry,
were contributed by my friend and coadjutor. For thirty years we
had known each other, and during that time we had been frequently
associated in many important chemical investigations of a public and
private nature. All scientific men who were brought in contact with
Mr. Brande, could not fail to be struck with the accuracy and extent
of his knowledge, the retentiveness of his memory, and the truthful-
ness and honesty of purpose by which he was always actuated. The
friend of Gay-Lussac and Thenard, and the colleague of Davy and
Faraday, he formed a connecting link between the chemists of the
past and the present generation. He lived to see great changes in the

PREFACE. IX

science which he had himself so successfully cultivated, but like his
great contemporaries Guy-Lussac, Th^nard, and Davy, he preferred
demonstration to speculation, and although ready to adopt what was
established by experiment, however it might conflict with his previous
views (proofs of which will be found in the successive editions of his
manual) he was strongly opposed to innovations based upon mere
hypotheses.

In private life it was impossible to meet with a man of more genial
character than Mr. Brande. His conversational powers were great ;
he was full of anecdotes of the scientific and non-scientific celebrities
of his day, and no man could pass an hour in his society without
retaining a pleasing reminiscence of him as a companion.

A. S. T.

CONTENTS.

CHAPTER PAGE

1. Matter and its Properties • . . . . . . 17

2. Crystallization. Dimorphism. Isomorphism . . . . 25

3. Chemical Force. Solution. Electrolysis .... 40

4. Equivalent Weights and Voftimes. Nomenclature and Notation . 64

METALLOIDS.

5. Metalloids and Metals. Properties of Gases and Yapors

6. Oxygen. Oxides. Oxidation ....

7. Oxygen. Incandescence. Combustion. Deflagration

8. Ozone. AUotropic Oxygen. Antozone

9. Hydrogen ......

10. Water. Aqueous Yapor. Ice ....

11. Water. Physical and Chemical Properties. Hydration. Mineral

Waters. Peroxide of Hydrogen

12. Nitrogen. The Atmosphere ....

13. Compounds of Nitrogen and Oxygen. Nitric Acid .

14. Compounds of Nitrogen and Hydrogen. Ammonia and its Salts

15. Chlorine. Compounds with Oxygen and Hydrogen. Hydrochloric

Acid . . .

16. Bromine, Iodine, Fluorine ; and their Compounds

17. Sulphur and its Compounds. Selenium and its Compounds

18. Phosphorus ; its Compounds with Oxygen and Hydrogen

19. Carbon and its Compounds with Oxygen. Carbonic Oxide. Carbonic

Acid . . . . . .

20. Carbon. Compounds of Carbon with Hydrogen, Nitrogen, and Sul

phur ........

21. Boron and Silicon. Boracic and Silicic Acids

78
90
100
110
118
126

139
153
166
178

188
201
212
233

249

269

292

METALS.

22. Physical Properties of the Metals. Eelations to Heat, Light, Elec-

tricity, and Magnetism ...... 307

23. Potassium ........ 312

24. Sodium ......... 328

25. Lithium. Caesium. Eubidum. Thallium .... 341

Zll

CONTENTS.

CHAPTER

26. Barium. Strontium. Calcium. Magnesium .

27. Aluminum. Glucinum. Zirconium. Thorium. Yttrium. Erbium

Terbium. Cerium. Lanthanum. Didymium

28. Qualitative analysis of the Oxides and Salts of the preceding Metals

29. Iron ......••

30. Manganese .......

31. Zinc. Tin. Cadmium ......

32. Copper. Lead .......

33. Bismuth. Cobalt. Nickel. Chromium

34. Vanadium. Tungsten. Columbium. Niobium. Ilmenium. No

rium. Pelopium. Molybdenum. Uranium. Tellurium. Titanium

35. Antimony .......

36. Arsenic ........

37. Mercury ........

38. Silver . . . . . ^ .

39. Photography and its Applications ....

40. Gold. Platinum ......

41. Palladium. Ehodium. Kuthenium. Osmium. Iridium

42. Qualitative Analysis of the most Important Compounds of the pre-

ceding Metals .......

PAGE

346

367
376
380
398
406
417
437

448
459
465
479
492
503
515
526

531

Starch. Gum. Pectose. Gelose-

Alcoholic Liquids

Methylic, Amylic, and other Al

ORGANIC CHEMISTHY.

43. Constitution and Properties of Organic Substanc^. Proximate

Analysis

44. Ultimate or Elementary Analysis

45. Proximate Organic Principles.

Sugar ....

46. Alcoholic or Vinous Fermentation.

47. Alcohol. Aldehyde. Chloroform.

cohols. ......

48. Ether. Oil of Wine. Compound and Double Ethers .

49. Cellulose. Pyroxyline. Wood. Coal. Bitumen. Products of the

Decomposition of Wood and Coal

50. Essential Oils. Camphor. Eesins. Amber. Caoutchouc. Gutta

Percha . .

51. Fats and Fixed Oils. Products of their Decomposition. Spermaceti

Wax. Soaps .

52. Vegetable Acids

53. Alkaloids and Organic Bases. Substances Associated with or De

rived from them

54. Organic Coloring-Matters. Dyeing

55. Neutral Nitrogenous Substances. The Solid Constituents of the

Animal Body, and Substances Derived from them

56. The Fluid Constituents of Animal Bodies, and the Substances De-

rived from them
Appendix
Index

535
545

560
673

583
595

603

613

622
634

657
669

685

706
729
749

CORKIGENDA.

Pago ix, 2d line from top, for " Guy-Liissac" read " Gay Lussac."
" 43,20th " " *• /or " say" reac/" as."

«' 68,15th " " bottom, /or "weights of oxygen" rertrf ''weight of oxygen."
«« 69, 9th and 11th line from top, for «' 1-44" read " 14-4"
« « " line from top, /or « 1-1557" read "1-1057."
« 72, " " " " rfe/e"that"

" " 10th " " " for " aqueou| oxide" read " hydrous oxide."
«' 73,25th " " " /or "no" reac/" an."
«» 75,14th " " bottom,/or"bisulphate" read "bisulphite."
« 93,18th " " top,/or "(NIgO)" read" (MgO)."
" 95, 1st " " " /or "reasons" read " reason."

*' 101, 15th and 16th lines from bottom, for " iodized" read " oxidized."

*' 224, 5th line from bottom, for " 230/' read " 2S202-"

« 710, 22d " " top,/or "Mr. Sorly" read "Mr. Sorby."

«« 744,14th " " " /or "on which" read'" in which."

" 745, table, 4th symbol, 1st column, for " Ce" read " CI."

CHEMISTKY.

CHAPTERI.

MATTER AND ITS PROPERTIES.

Chemistry as a science embraces the whole range of animate an4 inani-
mate nature. By its means, man acquires a knowledge of the special pro-
perties of bodies, and the laws which govern their combinations. By the
application of its principles he can resolve substances into their elementary
constituents, and out of old materials construct new compounds. It confers
on him a species of creative power, by enabling him to unite elements or
compounds, and thus to produce a large number of bodies which have no
independent existence in nature. Either directly or indirectly, Chemistry
as an art lends its aid to the great purposes of civilization. In every civil-
ized country, mining and metallurgy, as well as most branches of manufac-
turing industry, owe their development and progress to the proper cultiva-
tion of Chemistry.

A chemist has to deal with matter, as well as with the forces which are
inherent in and connected with it. Matter may be either simple or compound,
and the forces that control it may be either physical or chemical. Had the
globe been constituted of only one kind of substance or matter, the laws
of physics alone would have sufficed to explain the phenomena of nature.
There are, however, sixty-five different kinds of matter now known to
chemists, and as these are resolvable into no other bodies, they are called
simple substances or elements. But few of these are found in nature in their
simple or elementary condition ; they are in general intimately combined
with each other, constituting the large variety of compounds of which the
crust of the earth is composed. These simple substances not only differ in
properties, but their compounds also differ as much from each other as from
the elements which form them. It is the province of a chemist to define
these differences, to determine the laws by which they are brought about,
and to establish the relations of this with other branches of science.

Chemistry teaches us that matter is in its nature unalterable and inde-
structible : it may change its state, and undergo a change in properties, as
a result of the chemical force, but it may by the same force be restored to
its original state with all its properties unimpaired. Iron and sulphur
possess well-marked characters by which they may be easily known from
each other; but when combined, as in iron pyrites or bisulphide of iron,
these characters are entirely lost, and new properties are manifested. • On
again separating the two elements, each reassumes its original properties.
Chemistry, therefore, is not only a science of properties, but a science of
metamorphoses or transformations.

Recent researches have shown that although elements are not resolvable
into other substances, they are in some instances so altered by chemical and
2

18 ALLOTROPIC STATE. ISOMERISM.

physical forces, that they apparently lose their identity. We have an ex-
ample of this metamorphosis of elementary matter, in that condition which
is called allotropy (axxoc -rponoj, change of state), and no substance presents
it in so remarkable a degree as phosphorus. Common phosphorus is a waxy-
looking solid, melting at or below 111°, and taking fire a little above its
melting point. It is dissolved by sulphide of carbon ; it is luminous in the
dark, evolves an acid vapor in air, producing at the same time ozone, and is
very poisonous. By exposure to a temperature of 460°, under certain con-
ditions, this substance is so completely changed in its properties that it
would no longer be recognized as phosphorus. It presents itself as a hard,
brittle, red-colored solid, which may be heated to about 500° before it melts
or takes fire, is insoluble in sulphide of carbon, does not evolve any lumi-
nous or acid vapors, does not produce ozone, and has no poisonous action
on animals. By the application of chemical reagents and heat, the same
products are obtained from it as from common phosphorus; and as no other
matter or substance can be extracted from it, and each is convertible into
the othgr, we are compelled to ascribe the diflference in properties to mole-
cular changes. Oxygen, sulphur, carbon, boron, and silicon, are bodies
which may also exist in two or more states in which their properties are
widely difierent. This difi'erence is sometimes brought out by physical, and
at other times by chemical agency. These facts show us that the elemen-
tary state of matter is not so simple as has been hitherto supposed, and they
point to the probability that many of the substances now regarded as ele-
ments, may hereafter be proved to be compounds. The allotropic state,
however, is not confined to simple substances. Compound bodies, such as
silicic acid, and the peroxides of iron and tin, present instances of this con-
dition. The physical and chemical properties of these bodies are changed
by heat, or vary with the mode of their production, while their chemical
composition remains unaltered.

When two compounds can be proved to be formed of the same elements in
the same proportions by weight, it would appear to be a reasonable inference
that their properties should be identical ; but chemistry teaches us that this
condition may exist, and yet the substances be wholly difi"ereut in chemical
and physical properties. Bodies which thus resemble each other in atomic
constitution are called isomeric (icro? equal, and fii^o^ part), and isomerism is
the name applied to this condition of matter. The fact is, the properties of
the substance depend not only on the nature of the elements, and the number
of atoms of each, but on the mode in which these elements are grouped or
arranged. Gum, starch, and sugar are isomeric, or are constituted of a like
number of atoms of the same elements, and the difference in their properties
can therefore only be ascribed to a difference of arrangement among these
atoms. Cases of isomerism are much more numerous in organic than in
mineral chemistry, for the reason that organic compounds are composed of a
greater number of atoms of each element, and these admit of a greater
variety of arrangement. In some instances, the atoms are in precisely the
same number, but the bodies which they form are widely diflferent. Thus,
the hydrated cyanate of ammonia is represented by the formula NH3,C2NO,

HO, while the organic compound urea is C^X^OgHj. The properties of
these compounds are widely different. That the differences must depend on
the arrangement of the atoms is proved by the discovery of Wohler, that on
evaporating a solution of the hydrated cyanate of ammonia this salt disap-
peared, and the organic principle urea was produced. Oil of turpentine and
oil of lemons present another instance of similarity of atomic composition
with difierent properties. Each of these oils contains C,^H,„, but no method

PHYSICAL FORCES.

«9

is known by which one can be converted into the other. There is a whole
group of hydrocarbons similarly constituted. Isomeric bodies in which the
atoms are the same in number and relative proportion are called metameric,
in order to distinguish them from another class called polymeric, in which
the relative proportions in 100 parts by weight are the same, while the abso-
lute number of atoms differs. Aldehyd and acetic ether are liquids remark-
ably different in properties, but they are polymeric. Aldehyd is represented
by C^H^O^, and acetic ether by CgHyO^. Two atoms of aldehyd would
therefore be equivalent to one of acetic ether; but 100 parts of each liquid
would yield precisely the same relative weights ftf carbon and hydrogen.
At the same time these liquids are not mutually convertible into each other.
In mineral chemistry, a similar condition presents itself in reference to the
compounds known as ferro and ferri-cyanogen. The former is FejCgNg;
the latter has exactly double the number of atoms, FgjCjaNg. In a state of
combination, their crystalline forms, color, and chemical properties are wholly
different. These facts teach us that the grouping of the atoms, apart from
the chemical composition of substances, has a material influence on their
chemical and physical properties.

While physics relate to those changes, in masses as well as .particles of
matter, which result from the physical forces of gravitation, electricity,
magnetism, light, and heat, chemistry relates to changes produced among the
minute particles of bodies which are the result of one peculiar force — namely,
chemical force, affinity, or attraction.

Physical Forces. — Physical forces are manifested on the same or on different
kinds of matter. The chemical force can be manifested only between different
kinds of matter. As a general rule physical forces produce no permanent
change in the properties of bodies, while it is the special character of the
chemical force, and the leading feature of its existence, that the properties of
the bodies on which it has been exerted are permanently altered. Sulphur
and iron will serve to illustrate the differences here indicated. Gravitation
affects both, but in different degrees. A cubic inch of iron gravitates with
a force equal to that of three and a half cubic inches of sulphur. This is
indicated by a comparison of their relative weights in the same volume or
bulk (specific gravity). If the mass of iron is rubbed with a flannel, and
held near a light substance, such as dry bran, there is no attraction ; when
brought near to a suspended magnet, each end of the magnet is powerfully
attracted ; when heated it does not melt ; under reflected light it has a gray
color and a metallic lustre. A small bar of it held in a flame, allows the heat
rapidly to traverse its substance, and it becomes painfully hot, without under-
going any further change. On the other hand, a mass of sulphur warmed
and rubbed with dry flannel, powerfully attracts bran and all light substances.
Until it has been rubbed it manifests no attraction for the magnet, and after
rubbing, it attracts it only as a result of the frictional electricity produced in
it ; when heated, it readily melts, takes fire, and burns with a blue flame ;
under reflected light it has a peculiar yellow color without any metallic lustre.
Here, then, we have a manifestation of different physical properties in these
two bodies, and we learn that iron is of greater specific gravity than sulphur ;
that while iron is not rendered electric by friction, sulphur becomes highly
electric ; that while iron is powerfully magnetic, there is no magnetism in
sulphur; that as to the effect of heat, while one is infusible and incombus-
tible at ordinary temperatures, the other readily melts and burns ; that the
light reflected by the two is different, and that while iron allows heat to tra-
verse its particles rapidly from end to end, sulphur does not. After having
manifested all these phenomena as a result of physical forces brought to

2$ CHANGES IN MATTER BY THE CHEMICAL FORCE.

bear upon them, the iron and the sulphur resume their original state,
unchanged in properties.

The chemical differences which exist between iron and sulphur are not less
remarkable. If sulphur in fine powder is sprinkled in a jar inverted in a
saucer of water, it may be kept for any length of time without undergoing
any change. If iron-filings are sprinkled in another jar, also inverted in
water, the iron will be oxidized or rusted, and the water will rise in the jar,
showing that a part of its gaseous contents has been removed. The gas thus
removed may be proved by experiment to be oxygen, which, at a low tem-
perature, will combine with iron but not with sulphur.

If we mix together iron and sulphur in the finest powder, in the propor-
tions in which we know they will chemically combine to form iron pyrites
or bisulphide of iron, namely, forty-seven parts of iron and fifty-three of
sulphur, they will remain as a mere mixture, each with its physical properties
unaltered. Owing to the presence of iron the powder will have magnetic
properties, and when placed in water the iron will rust, and remove oxygen
from a vessel of air. If a magnet be drawn over the powder, the iron will
be removed, and the sulphur remain. If examined by a microscope, the
particles of sulphur will be distinctly seen mixed with the particles of iron.

Chemical Force. — When the sulphur and iron are, however, chemically
united in the proportions above-mentioned, as in iron pyrites, they will be
found to have lost their characteristic physical and chemical properties.
This substance is seen in hard cubic crystals ofr a yellow color and of a
metallic lustre. It has no magnetic properties ; it is not, like sulphur,
rendered electric by slight friction, and in the state of fine powder it does
not remove oxygen when placed in a jar of air over water. A magnet drawn
over this powder produces no effect upon it, the iron is not separated from
the sulphur. Neither sulphur nor iron can be seen in the powder, by the
aid of the most powerful microscope. We have, in fact, an entire change of
properties, and the new properties acquired are retained so long as the two
elements are chemically combined. By aid of the chemical force, the two
elements may be separated and procured in a pure state. The iron and sul-
phur will then be found to have re-acquired all the properties, physical and
chemical, which they had lost as the result of their combination.

Physical forces, therefore, produce only temporary changes in bodies,
while the chemical force entirely alters them ; and this alteration continues
until the union of the elements is dissolved. Further, we learn that the
properties of a chemical compound cannot be inferred from the properties of
its constituents. Its physical condition as gas, liquid or solid, and its chemi-
cal and physiological characters, can be determined only by experiment.
Nitrogen and hydrogen are two comparatively inert gases, while carbon is
an innoxious solid. The combination of these three elements produces a
highly poisonous liquid, Prussic acid. Hydrogen has no smell, and sulphur
only a slight smell on friction ; when chemically combined these bodies pro-
duce a most offensively-smelling gas, sulphide of hydrogen. Carbon, oxygen,
hydrogen, and nitrogen, are innoxious agents, and have no taste, but when
combined in certain proportions they form strychnia, remarkable for its
intensely bitter taste and highly poisonous properties. Iron manifests mag-
netism most powerfully, and oxygen is the most magnetic of gases, yet these
two bodies, when combined in the proportions of two of iron to three of
oxygen, produce a compound in which no trace of magnetism can be
discovered.

The properties of substances which are referable to the senses in the form
of taste,_ odor, color, or touch, are called by the French organoleptic, to
distinguish them from physical and chemical properties. They are of some

DIVISIBILITY OF MATTER. ,, 21

importance in chemical analysis, as they often aid the chemist in his search
after minute traces of certain elements or compounds.

Divisibility of Matter. — Matter, in the simple or compound, in the solid
or liquid state, is divisible. Thus, a solid or liquid may, by various pro-
cesses, be reduced into particles so fine that they are no longer perceptible
to the eye. When reduced to the l-500,000th of an inch in diameter, the
particle would be no longer visible under the most powerful microscope
(Mitscherlich) ; but lines closer together than the 100,000th of an inch
admit of no separation by the most powerful modern object-glass. The
minute particles of fine precipitates, such as sulphate of baryta or chloride
of silver, are individually imperceptible : they are only rendered visible to
the eye by aggregation. So of all solids in solution, the particles are so
small that light traverses them. A small quantity of mercury shaken in a
bottle with strong sulphuric acid, is temporarily split into myriads of minute
globules. Mere pressure with the finger will divide this liquid into particles
so small that they become gray and their bright lustre is lost to the eye.
By subliming the metal in a tube, its particles may be so subdivided as to
present only a gray tarnish on the glass. If a solution of chloride of tin is
added to a solution of corrosive sublimate, a grayish-black precipitate is
formed, which, when separated by filtration, appears on the filter in the form
of microscopical globules, so minute that it would be difficult to assign a
weight and size to each. Platinum, in the form of ammonio-chloride, is
converted by nascent hydrogen produced by the action of sulphuric acid on
zinc into a black powder (platinum-black) resembling charcoal. All the
physical characters of a metallic substance are lost by reason of the extreme
tenuity of its particles. Gold admits of still finer subdivision. It has been
reduced to such a state of tenuity that it does not sink in water, but allows
light to traverse it as well as the liquid : its particles giving to the liquid a
blue, green, or ruby color, according to the degree to which they have been
divided by chemical agency. According to Faraday's experiments, the ruby
liquids present metallic gold in the finest state of division ; the blue liquids
hold the gold in a more aggregated form. That they are finely-difi'used par-
ticles of the metal is proved by throwing a cone of sun-rays, either by a lens
or mirror, into the midst of the liquid, when the illuminated cone clearly
proves them to be undissolved bodies. He estimated that a particle in this
state formed 1-500, 000th part of the volume of the fluid. {Proc. Roy. Soc,
vol. 8, No. 24, p. 361.) Muncke has calculated, from the diffusion of a
known weight of gold over silver wire, that one grain admits of subdivision
into ninety-five thousand millions of visible parts, ^. e., visible under a micro-
scope magnifying 1000 times. {Handb. der Naturlehre, 43.) Films of gold,
finer than the finest leaves of the metal, may be obtained by the following
process : Place a thin slice of phosphorus on a surface of a very diluted solu-
tion of chloride of gold. Cover the vessel so as to prevent the access of
light. In the course of twenty-four hours the gold will be reduced to the
metallic state, for a considerable extent around the phosphorus. It will
present the brilliant color of the metal by reflected, but will appear bluish-
green by transmitted light. The metallic film may be raised from the surface
of the solution, by bringing into contact with it a clean surface of glass. It
will adhere iOf and may be dried and preserved upon the glass. Its tenuity
is such, that by mere appearance it is scarcely possible to determine on which
side of the glass it is deposited. It is probably less than the millionth of an
inch in thickness.

The divisibility of matter is of interest to the chemist, inasmuch as it
enables him to speculate on the limits of chemical tests for the detection of
substances. If half a grain of nitrate of silver is dissolved and diffused in

22 COHESIVE FORCE or matter.

100 ounces of distilled water, the presence of the metallic silver throughout
will be indicated by the liquid being rendered opaque, from the production
of chloride of silver, by the addition of a few drops of a solution of common
salt. One grain of silver may here be proved to be split into 138,000 parts.
But Malaguti found in sea-water taken off the French coast, that silver was
dissolved in it as a chloride, in the proportion of one grain in 100,000,000
grains, so that each grain of water would contain only the 100,000,000th of
a grain of metallic silver. No analysis could reveal its presence, except by
an operation on a large quantity. (Quart. Journ. of Chem. Soc. 1851, vol.
8, p. 69.) One quarter of a grain of acetate of lead dissolved and diffused
in 100 ounces of water, will form a solution which is turned of a brown
color by sulphuretted hydrogen, in parts as well as in the mass. The lead
is here converted into sulphide ; and a grain of the metal is actually split
into 336,000 parts. With indigo the divisibility may be carried still further.
One-eighth of a grain of indigo dissolved in sulphuric acid will give a well-
marked blue coly to 300 ounces of water. This is in about the proportion
of a millionth part of a grain in every drop of water. Muncke, vrho has
ingeniously calculated the weight of the minutest visible particle of gold
obtainable from the division of a grain of metal, has endeavored, in reference
to indigo, to determine the size of the minutest particles of this substance
from the dilution of a measured quantity of its solution. He estimates it at
the five hundred billionth of a cubic inch. {Op. cit., p. 44.) Half a grain
of iodine may be easily diffused in vapor, through five gallons of air, con-
tained in a glass vessel. Each millionth of a cubic inch of air contains only
the 1-2, Y10,600, 000th of a grain. In other words, a grain of iodine is split
by diffusion into two thousand seven hundred and seventy millions of parts
— these minute atoms being easily detected throughout the whole of the inte-
rior of the glass vessel by the action of iodine on paper wetted with starch.
Assuming the specific gravity of iodine to be 5, it follows that the size of the
atom of iodine under this divisibility, is less than the three billionth of a
cubic inch.

The divisibility of matter has of late acquired an additional interest in a
chemical point of view, by reason of the discoveries of Kirchoff and Bunsen,
in reference to the diffusion of metals. Their researches tend to show that
sodium, probably in the form of chloride, is a constituent of the atmosphere,
and is diffused as a vapor over the whole of the globe. The divisibility of
sodium to the extent in which it may be detected by prismatic analysis,
utterly defies the balance and the microscope. These chemists have tested
the diffusion of the vapor of sodium from a minute quantity by weight in a
room of known capacity, and they have detected its presence by the prism
when the quantity examined could not have exceeded the 195,000,000th part
of a grain in weight. {Phil. Mag., Aug. 1860, p. 95.) In reference to this
mode of analysis they have also announced the presence of a metal (caesium)
in a mineral water, of which it could not have formed more than the
100,000,000th part.

These results and calculations naturally suggest the question, whether
there can be any limit to the divisibility of matter. Without going into the
metaphysical part of this question, we may state that as bodies in masses
can be proved to combine in definite weights, or weights which are fixed for
each substance, it is probable that the same is true of the minutest particles
of which they are composed. The view most consistent with chemical facts
and theories is, that there is a limit to the divisibility of matter, and to this
limit the term atom (arojuoj, undivided) is applied. It is believed that at
this point matter is no longer divisible-. What that limit is cannot be
defined, and it is unnecessary for practical purposes to inquire. We can

ADHESION AND COHESION. CAPILLARY ATTRACTION. 23

neither calculate nor estimate the size, shape, or absolute weight of atoms,
but we can say that they are infinitely smaller than any particles which we
can weigh in the most delicate balance, or measure in the field of the most
powerful microscope.

Cohesion. — The minute atoms of matter in the solid or liquid state may
be held together by two forces ; first, by the force of cohesion ; and second,
by the force of affinity, or the chemical force. In simple substances cohe-
sion only is exerted. Thus, in sulphur as a solid, and in bromine as a liquid,
the particles of each element are held together by cohesion. In compound
bodies the two forces are in operation. In a mass of lime the particles are
united by cohesio7i; but the oxygen and calcium of which the lime is consti-
tuted, are held together by the chemical force.

The force of cohesion in bodies may be destroyed by physical causes, and
the three states in which matter exists, solid, liquid, and gaseous, depend on
the relative amount of cohesive force exerted among the particles. In a
solid the cohesive force is strong, in a liquid it is comparatively slight, and
iu a gas it ceases to manifest itself. The cohesion of solids is destroyed by
pulverization, but more completely by heat, which operates as an antagonistic
power. Thus many solids are reduced to a liquid, and ultimately to a
gaseous or vaporous state, by the mere effect of heat. Ice, water, and steam,
present familiar examples of these states of matter, in the well-known com-
pound of oxygen and hydrogen. We can see a mass of ice or liquid water,
but no eye, even aided by the microscope, can see the particles of aqueous
vapor into which water is converted above 212°. Some bodies are known
only in the solid state, e. g., lime and carbon ; others only in the gaseous
state, e. g., oxygen ; others, again, only in the liquid and gaseous states, e g.,
alcohol. From recent experiments, there is reason to believe that bodies
hitherto supposed to be of a fixed nature, such as platinum, iron, and even
carbon, are capable of assuming the gaseous or vaporous state under the in-
tense heat of the voltaic battery ; and that their particles may be thus trans-
ferred from one pole to another.

The destruction of cohesion in compounds, whether brought about by
mechanical division or by the effect of heat, does not, as a general rule,
destroy the chemical force by which the atoms are bound together. Calomel
may be reduced to the finest state of powder, or even converted into vapor,
by heat ; but each atom of the compound still consists of chlorine and mer-
cury. In the same manner the invisible particles which constitute aqueous
vapor, contain, in their most extreme division, oxygen and hydrogen. In
some instances, heat applied to solids or liquids, either directly or as a result
of friction or percussion, will dissever atoms united by chemical affinity.
Such effects are seen in the solid iodide and in the liquid chloride of nitrogen ;
but this is the result, not of mechanical division, but of the decomposing
agency of heat on such bodies, brought out by friction or percussion. The
atoms of substances which are once chemically combined, require, as a rule,
the chemical force for their separatiorf.

Adhesion. — Cohesion may take place between substances of different kinds,
but this is by contact of surfaces, and is sometimes called adhesion. An
amalgam of tin and mercury (used in silvering mirrors) adheres closely to
a surface of polished glass. The film of reduced metal in the collodio-iodide
of silver, on which a photographic image has been produced, adheres very
firmly to the glass. Lastly, one metal, platinum, by reason of its expansion
and contraction, when exposed to heat, not differing materially from that of
glass, may be actually welded to this substance, and on cooling it firmly
coheres to it. A platinum wire thus welded into a short glass rod, forms a
useful piece of apparatus for the detection of small quantities of alkaline
bases by combustion.

24 CAPILLARY ATTRACTION.

Capillary Attraction. — Closely allied to cohesion is that mutual attraction
between the surfaces of solids and liquids which gives rise to the phenomena
of capillary attraction, so called from its causing the visible rise of fluids in
tubes of small bore. If a tube with a capillary bore of one-fiftieth of an inch
be dipped at one end into a glass of colored water, the water rises to about
2^ inches, and the rise is great in proportion to the smallness of the bore,
and is greater with water than with any other liquid. If two plates of per-
fectly clean glass be so held as to form a very acute angle with each other^
and their lower edges be then dipped into water colored by sulphate of indigo,
the liquid will rise in the form of a curve (hyperbola) between the plates,
rising highest where the space between them is least. It is in consequence
of this species of attraction that a drop of water upon a solid surface wets
and adheres to it ; and that the surface of water in a clean glass is not truly
level, but a little elevated upon the edges. These phenomena depend upon
the nature of the substances presented to each other ; thus water will not
rise upon greasy glass or wax ; and hence also different liquids rise to differ-
ent heights in the same tube, independently of their specific gravities, and
of their relative degrees of viscidity. Mercury not only does not rise, but
is depressed in the bore of a common glass tube : so that, unlike water, it
presents a convex instead of a concave surface when contained in a glass tube
or vessel, provided the tube or vessel is clean and the mercury is absolutely
pure. The cohesive attraction of the particles of mercury to each other
is greater than of the mercury to the glass : hence they are incapable of
wetting it. This renders mercury well fitted for thermometers of a minute
capillary bore.

The rising of liquids in porous or spongy bodies, the ascent of oil or spirit
in the wicks of lamps, in which the fibres of cotton or asbestos, by reason of
their contiguity, build up small tubes or channels — and the circulation of the
juices of plants, are dependent upon capillary attraction. If a lump of white
sugar is placed on a few drops of diluted sulphate of indigo, the liquid rises
and colors the whole substance of the sugar. A heap of dry sand placed in
contact with water soon becomes damp throughout. If a short piece of cane
is plunged into oil of turpentine, the liquid after a time rises through tbe
fibrous or tubular structure of the cane, and may be burnt as with a wick at
the top. A curious instance of capillary attraction operating with crystal-
lization, is furnished by the following experiment : Let a Florence flask be
half filled with a saturated solution of bisulphate of potash. Plunge into the
liquid a clean deal stick, so that the end may project one or two inches above
the neck of the flask. If kept in a warm and dry place, the liquid will rise
by capillary attraction, and a dense crop of prismatic crystals will after some
days or weeks be formed on the top of the wood. As the small prisms build
up tubes, the liquid is gradually drawn through them, and more crystals are
deposited, until they fall off as a result of their weight.

The effect of capillary attraction is often seen in crystallizing solutions.
The slender prisms deposited at the edge of a vessel where the solution is in
contact with it, draw up more of the crystallizing liquid and another crop is
formed, in a ring or circle above the liquid. These carry the liquid by capil-
lary attraction still further, so that they sometimes creep up the inside of a
vessel and descend on the outside. A prismatic crystallization of carbonate
of soda, nitrate of potash, and sulphate of soda, is often seen on walls, cover-
ing a large surface, as a result of capillary attraction.

This force is remarkable in the fact that, like cohesion, it is more powerful
than gravity. Water and other liquids are lifted perpendicularly in spite of
gravitation. It affects the freezing point of water, which is stated to be
much lower than 32° when the liquid is contained in a capillary tube.

CRYSTALLIZATION. AMORPHOUS BODIES. 25

CHATTEE II.

CRYSTALLIZATION— DIMORPHISM— ISOMORPHISM.

The process by which the cohesive force operates to produce a symmetrical
or regular form in bodies is called crystallization. A crystal (xpvoraxxoj, ice
or crystal) is a polyhedral or many-sided solid, having smooth and bright
surfaces called planes, terminated by sharp edges or angles. This force is
chiefly witnessed in bodies as they are passing from the gaseous or liquid to
the solid state. The study of this subject is of some interest in reference to
analysis. As a peculiar crystalline form is observed in a large number of
mineral and organic compounds, an analyst, when assisted by the microscope,
is enabled to detect many substances in quantities too small, or in mixtures
too complex, for the application of ordinary tests. Thus a crystal of white
arsenic not larger than a 20,000th part of. an inch may be easily identified
by its form.

This force appears to be impressed on the minute atoms of all kinds of
matter. Simple and compound, solid, liquid, and gaseous bodies, all more
or less assume a crystalline form when placed in the conditions necessary to
the process. It appears to be as closely associated with certain kinds of
matter as the force of gravitation itself. Salts not found in nature, but
purely productions of art, acquire crystallizing power in fixed and definite
forms, whenever the union of their atoms takes place in certain chemical pro-
portions. Thus potassium, iron, carbon, and nitrogen, when artificially com-
bined., produce salts which, in one state, form splendid yellow octahedral
crystals with a square base (ferrocyanide of potassium) ; and in another state,
right rhombic prisms of a rich ruby color (ferricyanide of potassium), the
two compounds differing but slightly in the proportions of one of their com-
ponent parts. Crystallization may be regarded as an indication of definite
constitution in certain solids. Thus, among alkaloids strychnia and mor-
phia are obtained perfectly crystalline, but veratria, digitaline, and aconitina
have not been obtained in a crystalline state. It is not improbable that these
oncrystalline substances may consist of the alkaloid associated with other
alkaloids, or principles derived from the vegetable.

The/orm* of crystals are generally characteristic of the substance : thus,
among native or natural crystals, quartz is known by its transparent six-
sided prisms, fluor-spar by its cubes, and Iceland spar by its rhombs.
Among artificial crystals, nitre is known by its long fluted prisms, common
salt by its cubes, and alum by its well-marked octahedra. Some substances,
such as gum, starch, and glass, cannot be made to assume the crystalline
state : they are for this reason called amorphous (from a, priv. and A*opt^,
form). Others, like sulphur, assume it most readily, provided cohesion be
destroyed h^ fusion, sublimation, or solution.

Some bodies, e. g., the metals, can be readily crystallized by fusion ; othets,
as nitre, alum, and the greater number of salts, only by solution ; and others,
again, e. g., calomel, only by sublimation. Corrosive sublimate and white
arsenic may be obtained perfectly crystallized either by sublimation or solu-
tion, and in reference to arsenic the octahedral form is preserved in both

26 STRUCTURE OF CRYSTALLINE SOLIDS.

cases. Hence it follows that if a substance cannot be melted, dissolved, or
sublimed, it will not admit of crystallization.

Crystallization hy Fusion. — If a quantity of pure bismuth is melted in an
iron ladle, and is allowed to cool until a slight crust is formed on the surface,
and two holes are then made in this crust to permit the still liquid metal to
be poured out, a group of cubic crystals of bismuth will be obtained. Sul-
phur melted in a crucible at a low temperature, and treated by a similar
process, will yield a hollow cavity containing numerous prismatic crystals,
intersecting each other in all directions. The crystals thus obtained will be
large in proportion to the quantity of bismuth and sulphur melted, and the
slowness with which the cooling has taken place. The melted substances
should be kept at perfect rest. Groups of crystals thus procured somewhat
resemble the hollow minerals found in different strata called geodes {ys^hri^,
earthy). They are rough-looking globular masses on the exterior, but when
broken are found to be lined with crystals of quartz, fluor, and other mineral
compounds.

Advantage is taken in the arts of this tendency of certain metals to crys-
tallize by fusion, to separate silver from .commercial lead. About six tons
of lead are melted at once. In the act of cooling the lead crystallizes in
octahedra, and is removed from the molten mass by means of a perforated
iron ladle. The melted portion is thereby reduced to about seven hundred
weight; and this consists of a very fusible alloy of lead and silver, in which
the silver is in large proportion, and can be easily separated from the lead
by other processes. The efficiency of this method of separation may be
judged of by the fact that the average quantity of silver contained in lead is
ten ounces to the ton ; and by the crystallization of the lead, the proportion
of silver is brought up to two hundred ounces to the ton.

Structure of Crystalline Solids. — The crystallization of sulphur, bismuth,
and other metals by fusion, shows that crystallizable bodies are made up of
groups of minute crystals, since but for the pouring off of the liquid portion
of bismuth or sulphur, the whole would have set into a confused mass. An
experiment on tin will further illustrate this condition. If a piece of tin-
plate (tinned-iron) is heated, and the surface is then rapidly brushed over
with a liquid consisting of one part of nitric and one part of hydrochloric
acid, with eight parts of water, a very beautiful crystalline structure will be at
once made apparent. This has been called the moiree of tin. The tin in
cooling on the surface of the sheet-iron, assumed a crystalline structure, but
this was concealed by a deposit of amorphous metal which the diluted acid
removes. Spurious tin-foil, i. e., sheet-lead faced with tin, does not present
this crystalline character. When treated with the mixed acids, after a short
interval a dark blue or leaden color appears, and the spurious metal is par-
tially dissolved. Most metals by exposure to weak solvents which act slowly
on the surface, are found to present a crystalline structure. Platinum thus
assumes a crystalline snrface from the action of nitro-hydrochloric acid, and
aluminum may be moireed by the action of a solution of potash or soda.
Wrought iron irnmersed in a weak acid solution of chloride of platinum,
presents a fibrous structure ; and the damasking of steel is produced by wash-
ing the metallic surface with diluted nitric acid.

Many salts which are soluble in water, may be made to present a well-
marked crystalline structure as a result of partial solution. A rough block
of alum placed for a few days in a cold and nearly saturated solution of this
salt, will present upon its surface the planes and angles of numerous octa-
hedra. A crystalline structure is also thus brought out on a mass of bichro-
mate of potash, sulphate of iron, or carbonate of soda. The cohesive force
which holds together the atoms of salt, appears to be stronger in the planes

PLANES or CLEAVAGE. 27

and angles of the crystal than in other directions ; hence these parts resist
solution, and the block is unequally dissolved. Ice may be made to present
a crystalline structure by soaking a block in water at about 32^. This struc-
ture, however, is rendered more apparent by the freezing of thin films of
vapor deposited on glass during winter. The same phenomenon is observed
with respect to most solids which can be dissolved or sublimed. Thus a
rough block of camphor kept in a capacious bottle for some weeks, dimi-
nishes in bulk by reason of a portion being volatilized and deposited in
crystals in the upper part of the bottle, which has been exposed to light.
If the surface of the camphor be now examined with a lens, it will be found
to be composed of the planes and angles of well-defined rhombohedra, as if
it had been artificially carved.

Cleavage. — To the crystalline structure may be i:^ferred the property of
cleavage, whereby crystals can be easily broken only in certain directions,
corresponding to the planes of crystallization. Masses of selenite (sulphate
of lime), Iceland spar, and galena, when struck, will break readily in sharp
angular fragments of different shapes, but presenting bright surfaces. When
these broken surfaces are examined, they are found to correspond to the
planes or layers of the primary form of the crystal, to which each substance
may ultimately be reduced by cleavage. Thus selenite readily splits in two
directions, and in one of these so easily that it may be reduced to the thinnest
plates. By fracture in another direction, the pieces break in the angles of
a rhomb, so as to form rhombic plates. Iceland spar (carbonate of lime)
on the other hand, may be readily cleaved in three directions, so as to produce
a rhomboidal crystal. To this form, the numerous varieties of carbonate
of lime may be finally reduced by cleavage. Galena, or sulphide of lead,
is met with crystallized as a cube, octahedron, or rhombic dodecahedron.
The cubic galena admits of cleavage in three directions, corresponding to
the rectangular form of the cube. If an attempt be made to split the
octahedral or dodecahedral crystal parallel to the planes of those figures, the
crystal will resist the force in these directions, but it may be readily broken
in planes parallel to the cube. These three figures have therefore a direct
relation to each other: they may pass and repass into each other, and they
constitute one of the systems in which crystalline forms are arranged.
Although the diamond is considered to be the hardest substance in nature,
yet as a crystalline body it may be cleaved in four directions parallel to the
surfaces of an octahedron, and when moderate force is applied in either of
these directions, this hard solid readily gives way and may be split into
pieces. The sapphire, although less hard than the diamond, cleaves only in
one direction, and therefore may bear a harder blow without fracture than
the diamond itself. When a rough diamond contains a flaw, it is split into
two at this point, and it then makes two perfect stones. By practical
skill a workman knows how to direct the cleavage and strike the blow.
Tracing the plane, he makes on the exterior a slight nick with another
diamond. He then places a small knife in that nick, gives to it a light tap
with the hammer, and the stone is at once cleaved in two, directly through
the flaw. This operation is daily practised in the diamond works of
Amsterdam. {Pole on Diamonds.) Mr. Pole states that Dr. Wollaston
once made £1250 by purchasing a large flawed diamond at a low price, and
subsequently splitting it into smaller and valuable stones, the principle of
the operation not being then generally known.

• The property of cleavage shows that the force of cohesion in crystals is
stronger in certain directions than it is in others. An amorphous or
uncrystalline solid, like chalk or starch, when struck, will break in any
direction with a dull and uneven fracture. Another curious fact which was

28 CRYSTALLIZING FORCE. PRODUCTION OF CRYSTALS.

discovered by Mitscherlich is, that a great number of crystals, when heated,
expand unequally, i. e., more in certain directions than in others. As a
general rule, solids, when heated, expand equally in all directions. The
crystals belonging to the cubic or regular system (alum, common salt, white
arsenic), also follow this rule ; while in the five other systems of crystallization,
the crystals, when heated, expand unequally in one or more directions.
Thus a rhomb of carbonate of lime, when heated only from 32° to 212°,
undergoes an alteration of shape. The obtuse angles become more acute,
and there is by measurement a difference of 8 J degrees in the inclination of
the planes of the crystal. This can only be ascribed to an inequality in the
cohesive force in two opposite directions. In cooling, the crystal resumes
its original shape.

Crystallizing i^orce.— -The force with which cohesion is exerted in crystal-
lization is very great. In the crystallization of water during freezing, lead,
iron, and glass vessels containing this liquid are liable to burst. This is
owing to the increase of bulk which takes place when water passes into the
solid form of ice. {See Water.) The effects of freezing water on rocks,
earth, and porous stones are well known. Crystallizing solutions, by
penetrating into small cracks or fissures in the vessels which contain them,
often cause their destruction. An alloy of eight parts of bismuth, four of
tin, and five of lead (fusible metal), crystallizes on cooling from a state of
fusion. It expands so as to fill a mould completely, and thus allows a
perfect impression to be taken. For this reason, in the act of crystallizing
it sometimes causes the fracture of a glass vessel in which it is melted. Cast
iron crystallizes on cooling, and expands to such a degree that very accurate
impressions may be taken from moulds. The Berlin iron used for this purpose
contains phosphorus, which increases the fusibility of the metal, and castings
are obtained from this in imitation of the finest filigree work.

Production of Crystals — It follows from what has been stated regarding
the conditions for crystallization, that substances which are insoluble, infusible,
or fixed at a high temperature, cannot be crystallized by artificial processes.
Carbon, sulphate of baryta, silicic acid, and fluoride of calcium, are found
perfectly crystallized in nature, but they do not readily admit of crystallization
by art. The natural crystallization of these bodies is probably due to
the slow operations of nature over very long periods of time, and to the
progressive increase in the size of the crystal by gradual accretion from
without.

In employing boracic acid as a solvent for alumina, magnesia, and oxide
of iron, M. Ebelmen has succeeded in obtaining octahedral crystals identical
in physical and chemical properties with the native spinelle ruby. The
substances in proper proportions were fused with boracic acid, and by
exposing this mixture for some days to the heat of a porcelain furnace, the
solid acid was driven off and hard crystals of spinelle were formed.

When diluted sulphuric acid is added to a solution of nitrate of baryta,
the sulphate of baryta, owing to its great insolubility, falls at once in an
amorphous powder. It shows no tendency to crystallization. When the
same acid is added to a solution of tartrate of potash, a crystalline precipitate
(cream of tartar) is slowly separated. This compound is also produced in
crystals by suspending by a thread, in the midst of a diluted solution of
potash to which a small quantity of alcohol has been added, a large crystal
of tartaric acid. One or two drops of a solution of ammonia added to a
strong solution of oxalic acid in a watch-glass, will slowly lead to the
production of the well-marked prismatic crystallization of oxalate of ammonia.
Metallic lead may be obtained in a beautifully crystalline state by immersing
a piece of clean granulated zinc in a solution of the acetate of lead; acidulated

CRYSTALLIZATION BY SUBLIMATION AND SOLUTION. 29

with acetic acid : — or still better, by the introduction of a piece of clean zinc-
foil into a weak solution of acetate of lead, slightly acidulated with acetic
acid. Tin may also be obtained crystallized in prisms by placing a piece of
granulated zinc in a diluted solution of chloride of tin. When iodide of
potassium is added to a solution of nitrate of lead, a rich yellow precipitate
(iodide of lead) falls down. This precipitate is amorphous ; but if the
supernatant liquid is poured off, and the yellow precipitate is boiled for a
short time in water, a part of the iodide assumes a crystalline state, appearing
under the microscope in triangular or hexahedral plates of a golden color,
with shades of p^reen.

By Sublimation. — Among the bodies which are easily obtained crystallized
by sublimation, i. e., from a state of vapor, may be mentioned benzoic acid,
naphthaline, iodine, white arsenic, and camphor. The last-mentioned sub-
stance is slowly sublimed at ordinary temperatures, in hexahedral plates or
rhombohedral crystals. These are deposited on that side of the glass vessel
containing the camphor which is subject to the greatest amount of cooling
by radiation. The following experiments will illustrate this method of
producing crystals. Place in a small tube about a quarter of a grain of
white arsenic, heat the tube a little above the part where the powder is
deposited, then very gradually warm the powder. At about 3t0° the arsenic
will be volatilized, and if not too rapidly heated, well defined and distinct
octahedra will be deposited on the cold part of the tube. Place in another
tube a few grains of the red iodide of mercury ; heat it until it melts, then
moderate the heat, and the red powder will be sublimed in splendid rhombic
plates.of a brilliant yellow color.

By Solution. — We must here select a salt, such as nitre, alum, or sulphate
of copper, the solubility of which greatly increases with the temperature.
A boiling saturated solution of the salt is made, and the vessel is placed
aside, covered over, and kept undisturbed. The cooling should be allowed
to take place very slowly : 100 parts of water at 212° will dissolve 246 parts
of nitre, but at 60^ this quantity of water will retain only 30 parts of the
salt. Hence 216 parts are deposited on cooling in groups of prisms, which
are large or small according to the quantity of salt dissolved, and the slowness
with which the deposit has taken place. As a general rule, small crystals
are more perfect in form and and more transparent than large crystals. As
the crystals of salts are of greater specific gravity than the liquid in which
they are formed, they are usually deposited at the bottom of the vessel, or
they will adhere to any rough surfaces of wood or string which may be
introduced into the crystallizing solution. Under these circumstances they
increase in size by the spontaneous evaporation of the solution, and a
continued deposit from without, and as they are in the midst of the liquid
they retain a perfect form. We have thus seen produced rhombic prisms of
carbonate of soda of sixteen inches in length, and stalactitic octahedra of
alum of still greater dimensions. If the substance is not very soluble in
water (arsenious acid), the crystals are small but perfect, and are slowly
produced. If the salt is equally soluble in hot and cold water, no crystals
are obtained on cooling the solution. Common salt (chloride of sodium)
presents an example of this kind, and by this singular property it admits of
separation from a large number of salts. It can only be obtained crystallized
from its saturated solution by evaporation, ^. e., by the removal of the
solvent.

The liquid in which crystals are deposited on cooling is a saturated solu-
tion of salt for the temperature ; it is called the mother-liquor. By remov-
ing it from the deposited crystals and carrying the evaporation still further,
i. e., until a slight pellicle appears on the surface, a fresh crop of the same

30 SEPARATION OF SALTS.

crystals may be procured, but not so pure as those first obtained. If a por-
tion of the mother-liquor, cooled to 60°, is placed in a freezing mixture, there
will be a farther deposit of crystals of nitre, this salt being less soluble at
320 than at 60°. "

Crystallization as a result of cooling is witnessed in many liquids, and
becomes a test of their strength on chemical composition. Acetic acid
cooled to below 40"^ sets into a mass of prisms resembling ice. It is hence
called glacial acetic acid. It serves as a test of the strength of the acid, and
represents the strongest form in which this acid can be procured. Sulphuric
acid is liquid at ordinary temperatures. When cooled to below 40° it forms
a solid crystalline mass, like ice, which has a definite constitution of one atom
of acid combined with two atoms of water, a bihydrate. As a liquid at 60°
its specific gravity is 1.78. If the proportion of water is increased or dimin-
ished, it no longer crystallizes at this temperature.

In the deposition of crystals from saline solutions the mother-liquor gene-
rally retains the impurities associated with the salt, and thus by repeatedly
crystallizing a substance in fresh quantities of water, we may bring it to a
state of great purity. In the crystallization of tartar emetic, the arsenic con-
tained in the materials used remains in the mother-liquid ; and according to
Martins, the larger crystals of tartar emetic which are formed principally in
the mother-liquor contain arsenic. {Gmelin, vol. iv. p. 317.) The purifi-
cation of alkaloids by repeated solution in alcohol, ether, or chloroform, is
based on a similar principle.

The more slowly the evaporation takes place, the larger and finer the
crystals. The small and opaque. cubic crystals of common salt are obtained
by rapid evaporation at a boiling temperature. The large crystals of bay
salt are procured by the spontaneous evaporation of brine. A viscid state
of the mother-liquor from repeated evaporations, is a bar to the production
and deposit of fine crystals. Certain alkaloids and other compounds which
do not bear a high temperature are procured perfectly crystallized by allow-
ing the liquids to evaporate in vacuo at a low temperature — a vessel of sul-
phuric acid being placed under the crystallizing liquid, to absorb the aqueous
vapor as it is evolved. ♦

Crystals may be made to grow or to increase in size, by selecting those
which are perfect — covering them with the mother-liquid, and allowing this
liquid to evaporate spontaneously. That the crystals may preserve their
regular form while this increase is taking place, it is necessary that they
should be occasionally turned, otherwise the deposit will be formed chiefly
on the upper parts.

Separation of Salts. — When two or more salts are present in the same
solution, if of different degrees of solubility and not isomorphous, they may
be separated by crystallization. It is observed that the salt which is least
soluble for the temperature is separated first. In the evaporation of sea-
water, sulphate of lime, by reason of its insolubility, is first precipitated and
removed. Chloride of sodium or common salt is then separated, as this is
no more soluble in hot than in cold water, while the other salts associated
with it are much more soluble at a boiling than at a low temperature. When
the water is exhausted of its crystallizable salts, the residue contains chiefly
chloride of magnesium with traces of bromide. It is this chloride which
gives an intensely bitter taste to the liquid, hence the residue is called
I' bittern.'* When two nearly equally soluble salts are present, that which
is in larger quantity is usually separated first.

Deposition of Crystals. — As a general rule all crystals are deposited in the
mother-liquor as the solution cools, but there are solutions of certain salts
which if kept at rest and so covered as to prevent free access of air or dust,

DEPOSITION OP CRYSTALS. 31

will either not deposit crystals on cooling or deposit them only partially. A
hot saturated solution of sulphate of magnesia placed in a vessel secured
with bladder may be cooled at 60°, and yet will only partially deposit crys-
tals. On agitating the cooled liquid, more will be deposited. This property
is more remarkably manifested by sulphate of soda. This salt when dissolved
at a boiling heat in the proportion of two parts by weight of crystals to one
part by weight of boiling water, may be placed in flasks or tubes and cooled
to 60° or below, without depositing crystals, provided the vessels are kept at
rest and the surface of the solution is covered while hot with a stratum of oil,
or the mouth of the vessel is firmly secured by caoutchouc or bladder. Upon
agitating the liquid, or exposing it to air by cutting through the bladder —
by plunging into it a glass-rod or a crystal of the salt, the sulphate immedi-
ately begins to crystallize, either from the surface or around the rod or crys-
tal ; and the whole speedily forms a crystalline mass. If a quantity of this
hot liquid is allowed to cool in a tube about twelve inches long, similarly
secured, the process of crystallization may be easily watched ; the mode in
which a solid mass of salt is built up of myriads of prisms intersecting each
other in all directions, will be then at once made evident to the eye. We
have preserved a solution of this kind, with the process of crystallization
thus suspended, for three years, and the ordinary mechanical causes above
mentioned brought about crystallization in the whole mass after this long
period. From this sudden crystallization of sulphate of soda, we learn that
the production of crystals is attended with the evolution of sensible heat,
light, and even electricity. The phenomenon is considered to be owing to
the fact, that in a hot saturated solution the sulphate of soda is dissolved in
an anhydrous state, and so remains on cooling, until slight mechanical causes
operate on the solution. Agitation, the introduction of a crystal, or expo-
sure to air, causes the formation of the ten-atom hydrate, so that the water
now enters into chemical combination with the sulphate, and the whole sets
into a solid mass. There is also a seven-atom hydrate of the sulphate of
soda. Transparent crystals of this hydrate are frequently deposited in a
flask during the cooling of a saturated solution. They become white on the
surface, probably from a loss of water during the formation of the ten-atom
hydrate. The crystallization of water itself presents a similar phenomenon.
Water kept in a narrow tube and at rest may be cooled to 26°, and yet
remain quite liquid. If shaken, or disturbed by the introduction of a ther-
mometer, a part of the water immediately congeals, and the thermometer
rises to 32°.

The liquid employed in the Storm-glass presents a remarkable instance of
the slight causes which lead to the production and disappearance of crystals
in a solution. Two parts of camphor, one part of nitre, and one part of
chloride of ammonium are dissolved in a minimum of rectified spirit, to which
sufiBcient water is added to dissolve the two salts, the alcohol being just suf-
ficient to retain the camphor. If the solvents are in too large proportion,
the liquid may be brought to the point of saturation by slight exposure to
the air. It should be filtered and placed in a long tube. At temperatures
between 40° and 70° feathery crystals, chiefly of chloride of ammonium, are
produced ; but these disappear at the higher temperature. It is supposed
that their production is also influenced by electrical changes in the atmos-
phere ; but of this there is no proof whatever. The separation of paraffine
from the heavy oil in which it is dissolved, is the eS'ect of a change of tem-
perature. When the oil is cooled to below 4|p, the solid paraflQne crystal-
lizes, and may be separated by pressure from tne liquid.

Interstitial and Combined Water. — Crystals which are deposited in a liquid
necessarily retain a portion of the mother-liquor in their interstices. This

32 INTERSTITIAL AND COMBINED WATER.

has been called interstitial water. It is removed by draining and drying.
The amount contained in any sample of crystals may be determined in the
same manner as hygrometric water. (See Water.)

Many saline substances in crystallizing combine chemically with a certain
proportion of water, which is specially defined for each salt. These are
hydrated salts. Some salts, such as the sulphates of soda and magnesia, form
several hydrates — the number of atoms of water with which they combine
depending on the temperature at which crystallization takes place. Sulphate
of soda may be obtained crystallized in the anhydrous as well as in the
hydrated state. The common sulphate contains ten atoms of water. Sul-
phate of magnesia, crystallized at common temperatures, combines with seven
atoms of water. If crystallized by evaporation at a high temperature, there
are six equivalents of water : and if crystallized from its solutions below 32^,
large crystals containing twelve atoms of water are obtained. {Regnault, 2,
259.) Some crystalline salts contain no combined water ; in other words,
they are anhydrous or dry. The chlorides of sodium and ammonium, and
the nitrate and sulphate of potash are instances of this kind. It is necessary
to observe that as these words are often used synonymously, a dry salt in a
chemical sense does not mean a substance free from moisture or wetness, but
one which contains no water in a state of combination. In a popular sense,
the word " dry" signifies merely the absence of moisture. The want of pre-
cision in the use of these words has led to costly litigation in reference to
patents for procuring colored products from aniline.

Some of these, when suddenly heated, fly to pieces with a cracking noise,
to which the name of decrepitation is given. Common salt and sulphate of
potash possess this property. On the other hand, alum and phosphate of
soda, the sulphates of iron and copper, and the carbonate and sulphate of
soda, are hydrated crystalline solids ; the combined water in some of them
forming more than half the weight of the solid salt. Thus the crystals of
sulphate of soda contain 56 per cent, of water, and those of alum nearly 46
per cent. The combined water is driven off by heat, and the salt is dehy-
drated or rendered anhydrous. If the salt be previously dried, and a given
weight of it be then heated in a platinum crucible, the amount of water may
be determined. The crystalline form, color, and, to a certain extent, the
properties, of the salt are dependent on the presence of this water. The
sulphate, phosphate, and carbonate of soda readily lose a portion of their
combined water at a moderate heat in a dry atmosphere. The sulphate of
soda becomes almost completely dehydrated by exposure ; the crystals lose
their transparency and fall to a white powder. This spontaneous change in
crystals is called efflorescence : it is in general characteristic of the salts of
soda. It may be prevented by preserving the crystals in a damp atmosphere.
On the other ^nd, some salts, such as the chlorides of calcium and mag-
nesium, the nitrates of lime and magnesia, and the carbonate and acetate of
potash, absorb water from the atmosphere, not in definite proportion, but
until they are reduced to a concentrated solution of the respective salts. To
this property the term deliquesce7ice is applied. Many crystals undergo no
change in air ; they are permanent. This is a character possessed by alum,
acetate of soda, and many other salts, as well as by all native crystals.

The chemically combined water in a crystalline solid does not manifest its
presence by da^mpness or humidity when the substance is powdered. The
water, in entering into combination, is in fact solidified in the crystal. Alum
in powder is perfectly dry — m water can be pressed out of it, yet it contains
nearly half its weight of water in a chemically combined state. On heating
crystals of alum, they readily pass to the liquid condition or melt in their
water of crystallization. This is gradually expelled as aqueous vapor by

PEOPERTIES OF HYDRATED CRYSTALS. 33

continuing the heat ; and a light white porous mass is left, in which no ap-
pearance of crystallization can be seen. The residue is anhydrous or burnt
alum. In this state, and by reason of the loss of its water, the salt acts as a
mild caustic. When water is poured over this dry mass the salt recombines
with it, and heat is evolved. Gypsum is the native crystalline state of sul-
phate of lime: it contains about 21 per cent, of water. When roasted at
about 260^ this water is expelled, and the crystalline mass falls to a white
powder known as plaster of Paris. When this powder is mixed with suffi-
cient water to form a cream, it sets in a few minutes into a firm mass, which
by crystallization fills accurately every part of a mould on which it is placed.
The setting of plaster of Paris is therefore due to the resumption of the com-
bined water which had been expelled by heat. The strong tendency which
sulphate of lime has to unite to water in the act of crystallizing, is well illus-
trated by mixing together equal parts of diluted sulphuric acid, and a nearly
concentrated solution of chloride of calcium. When mixed, the liquids set
into a* solid mass owing to the water of the two solutions combining with the
sulphate of lime produced. When powdered sulphate of copper is heated
to a moderate temperature it loses its blue color and forms a white powder.
On pouring water over it it becomes intensely hot, the water again enters
into combination with the white anhydrous sulphate, and the powder acquires
a blue color. The color of the salt therefore appears to depend on the water
of hydration. As a further proof of this, the blue crystals become white when
placed in strong sulphuric acid, as a result of a removal of the water by the
acid. The green crystals of sulphate of iron are also rendered white under
similar circumstances.

The influence of the proportion of combined water on the color of crystals
is more remarkably seen in the platino-cyanide of magnesium than in any
other substance. These crystals are prismatic, and are of a ruby red, with
reflections of an emerald green color. A strong solution of them imparts to
paper a carmine red color, and in this state they contain seven atoms of water.
When water is dropped on the red compound on paper it immediately whitens
the paper, forming a colorless solution of the salt. By gently heating the
red deposit on paper, one atom of water is lost, and the substance becomes
yellow ; at 212^ it loses four atoms of water, and is rendered colorless. If
still more strongly heated, it loses all its water and becomes yellow. These
facts, as well as the discovery of this salt — the type of a remarkable series —
we owe to the late Mr. Hadow, of King's College. We find that the salt is
an admirable test of humidity. If the paper stained with it is rendered yellow
or white by a moderate heat, it rapidly resumes its carmine-red color, as a
result of hydration either in a damp atmosphere or by merely breathing on it.
The chloride of cobalt is another salt which presents changes of color depend-
ent on hydration or dehydration. Paper stained with this Solution has a
light pinkish-red color; when deprived of water by heat it becomes blue, or,
if any iron is mixed with it, green, but it resumes its pink color on cooling.

Freezing Mixtures. — The rapid solution in water, of salts abounding in
water of crystallization, is always attended by a diminution of temperature;
and the more water of crystallization they contain the greater is their cooling
effect during solution. As the water in these salts is solid, their solution
cannot take place without at the same time rendering latent a large amount
of heat. An ounce of crystals of sulphate of soda mixed with x)ne ounce of
water lowers the temperature in consequence of the solid hydrated salt be-
coming itself liquid; but, as it has been above^tated, if an ounce of anhy-
drous sulphate be employed, the addition of water will raise the temperature,
because part of the added water enters into combination with the anhydrous
salt, and the latent heat of the water is set free.
3

34 IRREGULAR FORMS OF CRYSTALLIZATION.

Freezing mixtures may be made by causing the rapid liquefaction of the
combined water of crystalline salts. If to eight parts of crystallized sulphate
of soda we add five parts of strong hydrochloric acid, each being separately
at 50°, the acid takes away water from the sulphate, liquefying it at the same
time, and it thus renders latent so large an amount of heat as to reduce the
thermometer from 50° to 0°. For common purposes, the materials used
need not be weighed. The fresh crystals finely powdered should be drenched
with strong hydrochloric acid. The acid mixed with ice operates in a pre-
cisely similar manner, namely, it causes the rapid liquefaction of the solidified
water, and lowers the thermometer from 32° to 17°. Diluted sulphuric acid
in the proportion of four parts to five parts of the powdered crystals of sul-
phate of soda, produces a mixture in which the thermometer sinks from 50°
to 3°. By taking advantage of these principles, the same substances may
be employed to produce cold or heat. If four parts of broken ice are rapidly
mixed with one part of strong sulphuric acid a freezing mixture results in
which the thermometer falls to 15°. But if four parts of the strong acid
are mixed with one part of ice, the temperature of the mixture rises to 170°
and even higher. In the former case the crystalline solid (ice), is rapidly
liquefied and absorbs heat from all surrounding bodies. In the latter case
the sulphuric acid is in such quantity as to enter into combination with the
water formed producing a hydrate with the evolution of great heat.

Other curious phenomena are dependent on the setting free of the com-
bined water of crystals. Chloride of ammonium contains no combined
water : sulphate of soda contains 56 per cent. These are perfectly dry salts,
but when rubbed together in a mortar in equal parts by weight, for some
time, they form a liquid mass. In fact, they produce by double decomposi-
tion chloride of sodium and sulphate of ammonia. The chloride of sodium
takes no combined water, the sulphate of ammonia requires only 18 per cent.
Thus 38 per cent, of the water of the sulphate of soda is set free as a liquid,
and this causes the liquefaction of the mass. Sulphate of copper and sesqui-
carbonate of ammonia, when triturated together, form, for the same reason,
a semi-liqnid mass.

Although it is commonly, laid down as a principle that no substances will
take on the crystalline state unless they have undergone fusion, sublimation,
or solution, there are some exceptions to this rule among the metals. In
the process of cementation, iron is converted into steel by heating it with
carbon. The iron loses its fibrous character and acquires a crystalline struc-
ture as steel, without fusion. By simple exposure to repeated concussion or
vibratioii, wrought iron is observed to acquire a crystalline structure and to
become brittle. This is a change to which the axles of railway carriages are
subject, and serious accidents have arisen owing to the brittleness acquired
by the iron as a result of its assuming this crystalline condition. Platinum
and silver vessels, frequently heated, undergo, after long use, a similar mole-
cular change, and break with a crystalline fracture. The acquired brittleness
of some kinds of brass wire, containing an undue proportion of zinc, may be
attributed to a similar cause.

Irregular Forms. — Various names are given to the crystalline structure of
bodies when there is an absence of regular form. 1. Fibrous, spicular or
acicular, crystallization is seen in gypsum and sulphide of antimony. 2. A
laminated or foliated structure is observed in mica, petalite, and other mine-
rals. ^ 3. The substance may have a granular structure still presenting bright
but irregular surfaces on ^cture. Loaf-sugar, marble, and alabaster are
examples of this kind. 4. Plumose or feathery crystallization is seen in
chloride of^ ammonium, sulphate of strychnia, and other salts. 5. Stellated
crystallization is seen in the grouping of minute prisms crossing each other

REGULAR FORMS OP CRYSTALLIZATION. 35

at various angles. Strychnia and many other substances often present them-
selves in this form.

Regular Forms. — The external forms of regularly crystalline solids are
subject to great variation. The nature of the solvent, the temperature, and
the presence of other substances in the liquids, modify the form, by creating
new planes or angles, so that the true shape of the crystal may be no longer
recognizable. The octahedral crystals of alum lose their solid angles when
an excess of acid is present, and they become converted into cubes when
alumina predominates. Common salt deposited from an aqueous solution
containing urea, crystallizes in octahedra instead of cubes, its usual form ;
and sal ammoniac under the same circumstances forms cubes, whereas in
pure water its crystals are octahedral. Berzelius states that large crystals of
nitre may be obtained from its solution in boiling lime-water, which has no
other analogous effect upon other salts. Native crystals of the same sub-
stance are met with in great variety. Carbonate of lime is said to present
itself in a hundred varieties of form ; but these are all reducible to one com-
mon figure by cleavage, namely the rhomb. Iron pyrites may be met with
either in cubic, octahedral, or dodecahedral crystals ; but these are forms
which are reconcilable with a systematic arrangement of the molecules around
similar axes.

In order to facilitate the study of this subject, and to reduce the large
variety of forms to a few well-marked classes, chemists now generally agree
in assigning crystals allied in form, to one of six different systems of crystal-
lization, the particles of the substance being supposed to be symmetrically
arranged around certain imaginary axes of the crystal. A system, therefore,
includes all those forms, however varied, which can be referred to the axes
which are peculiar to it. We give on the next page, a table of the special
characters of the six systems of crystallization as described by Weiss, includ-
ing their allied forms and their relations to heat and light.

m

^^^P

36

THE SIX SYSTEMS OF CRYSTALLIZATION.

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DIMORPHOUS BODIES. DIMORPHISM. 87

[To the reader who wishes to pursue this subject, we recommeud the smnll
and concise "Precis -de Cristallogruphie" of M. Laurent. Alodels in wliite
wood, representing the systems of crystallization and the principal allied
forms, may be obtained of dealers in chemical apparatus.]

The student should make himself acquainted with the common external
forms of well-known substances, including the cube, octahedron, and its
derivative, the tetrahedron — the square, hexahedral, oblique, and rhombic
prisuks, and plates. A few drops of a solution of a substance in water or
alcohol, left to spontaneous evaporation on a glass slide, will furnish a group
of crystals, of which the forms can be well determined by a low power of the
microscope. If we have to deal with a soluble solid in fine powder, we
should dissolve a quarter of a grain in a few drops of water or alcohol on a
glass slide, according to the solubility of the substance in either liquid. The
liquid should be warmed, until its circumference acquires a slight but visible
margin of saline matter. The glass may then be placed aside, and the liquid
allowed to crystallize slowly. No crystals are so perfect for microscopical
observation as those which are procured in dry and warm weather by spon-
taneous evaporation. This micro-chemical examination will not only guide
analysis by leading to an immediate suspicion of the real nature of the sub-
stance— but it will sometimes enable a chemist to detect and pronounce an
opinion on the presence of impurities in the substance examined ; and in
medical practice it may suggest the nature of the disease, and point to a plan
for treatment. The sedimentary deposits in urine are now easily recognized
by their crystalline forms, and the presence of urea, uric acid, or cholesterine
in the blood or other liquids, is known by the peculiar crystalline shape
which each assumes.

Dimorphism (6tj and ^itop^i), two forms). — It is a remarkable fact that the
same substance may present itself in crystalline forms belonging to two dif-
ferent systems : such bodies are called dimorphous. This is the case with sul-
phur, which when crystallized by .fusion yields oblique rhombic prisms (5th
system), but is deposited from its solution in sulphide of carbon in octahedra
with a rhombic base (4th system). Carbon, in the form of diamond, crystal-
lizes in octahedra, but as graphite, in hexagonal plates. Carbonate of lime
in calcareous spar has the rhombohedral structure, but in arragonite that of
the rectangular prism ; and there are other analogous instances. It has been
found in regard to these cases of dimorphism, that each form has its peculiar
density ; the specific gravity of calcareous spar, for instance, being 2.71 ; that
of arragonite is 2.94. The temperature too at which the crystals are formed
is another influencing cause : thus when carbonate of lime is precipitated by
adding chloride of calcium to carbonate of ammonia, the grains of the pow-
der are rhombohedral if thrown down at the temperature of 50^, but octa-
hedral if at 150° (G. Rose, Phil. Mag., xiii. 465.)

The iodide of mercury presents a remarkable instance of dimorphism. It
is of a rich scarlet color, and as it is obtained crystallized from a saturated
solution in iodide of potassium, it assumes the form of octahedra, with a
square base. When heated it becomes yellow, forms an amber-colored liquid,
and may be sublimed in rhombic plates of a rich yellow color. In twenty-
four hours these crystals, either partially or wholly, acquire a scarlet color.
Mr. Warington has observed the rhombic plates to break into octahedra with
a square base, as they changed from yellow to scarlet. Hence it is reasonable
to infer that there is a spontaneous change in the molecular condition of this
salt; indicated not merely by change of form but by change of color in the
crystal. The scarlet powder may be crystallized on a card without fusion, by
heating it over a spirit-lamp (thus furnishing an instance of the crystallization
of solids): and if, when cold, the yellow crystalline compound is rubbed

38 ISOMORPHISM.

with a piece of paper, it is reconverted into the red iodide. These differently
colored crystalline forms may be regarded as allotropic states of the sub-
stance.

Dimorphous bodies, or substances crystallizing in the incompatible forms
of two different systems, must be regarded as exceptional to the general law
of crystallization. It is a curious fact, however, that when this condition
exists, the substance frequently presents in its two forms marked differences
in hardness, specific gravity, lustre, solubility, fusibility, optical characters,
&c., thus showing a molecular diff'erence throughout. In addition to the
substances above mentioned, dimorphism has been observed in specular iron
ore, iron pyrites, the carbonates of iron and lead, arsenious acid, oxide of
antimony, the sulphates of magnesia, zinc, and nickel, and in the seleniates
of the two latter metals. It has been noticed with respect to some of these
cases of dimorphism, that the crystal of one system is made up of groups of
crystals of the other system. The sulphate of nickel crystallizes in right
rhombic prisms. Mitscherlich found that when these prisms were heated and
broken up, they were resolved into minute crystals of the second system,
namely, octahedra with a square base. The crystals of sulphur, recently
obtained by fusion, are in the form of oblique rhombic prisms of a yellow
color, transparent and somewhat flexible. In a few days they become opaque
and brittle, and they fall to a powder which, under the microscope, is found
to consist of rhombic octahedra.

Isomorphism (from ?5oj similar, and jwopti? form.) — Although substances may
in general be identified by their special forms, yet diff'erent substances, like
white arsenic and alum, may present themselves in similar forms. Sometimes
a similarity of form is presented by substances which also resemble each other
in atomic constitution, or in the number of atoms of acid, base, or water,
which enter into their composition. In this case it has been found that
such bodies may replace each other, or be substituted for each other in com-
bination, without affecting the crystalline form. Thus the arseniate and bin-
arseniate of soda have the same forms as the phosphate and biphosphate of
soda ; and the arseniate and binarseniate of ammonia resemble the phosphate
and biphosphate of that alkali. Such salts are termed isomorphous. In the
above instances, the equivalents of acid, base, and water of crystallization
correspond ; and a similar correspondence has been traced in the atomic con-
stitution of the acids and bases of the salts. Thus the arsenic and phosphoric
acids each include one equivalent of base and five of oxygen, and are therefore
themselves isomorphous ; so also phosphorus and arsenic are presumed to be
isomorphous — isomorphous compounds, in general, appearing to arise from
isomorphous elements. They have the same garlic odor in the state of vapor,
and combine with the same number of atoms of hydrogen to form gases. So
also in respect to the isomorphism of the sulphates, seleniates, chromates,
and manganates of the same base, each of the acids in these cases contains
three atoms of oxygen to one of the metalloid or metal. In respect to baseSj
similar analogies are observable ; thus the salts formed by magnesia, the
protoxides of zinc, iron, nickel, cobalt, and copper, with a common acid, are
isomorphous ; and alumina and the sesquioxides of chromium, manganese,
and iron, each of which contains two atoms of base and three of oxygen,
replace each other in many combinations without change of crystalline Ibrra.
This is seen in the different varieties of alum. The following is a tabular
Tiew of some isomorphous groups : —

ISOMORPHOUS GROUPS.

39

Chlorine

lodiue

Bromine

Sulphur

Selenium

Chromium

Manganese

Phosphorus

Arsenic

Arsenic

Antimony

Barium

Strontium

Lead

Calcium

Potassium

Sodium

Ammonium

Calcium

Magnesium

Manganese

Iron

Zinc

Cadmium

Cobalt

Copper

Nickel

Aluminum

Manganese

Iron

Chromium

Chloric acid .
Iodic acid
Bromic acid .
Sulphuric acid
Selenic acid .
Chromic acid
Manganic acid
Phosphoric acid
Arsenic acid .

Arsenious acid (unusual form)
Teroxide of antimony .

Their oxides .
(in arragonite)
Their oxides

Their oxides

CIO-

10,

Brb.

SO,

SeOj

CrOj

MnOg

PO,

AsOg

ASO3

Sb03

BaO

SrO

PbO

CaO

KO

NaO

CaO
MgO
MnO
FeO
ZnO
CdO
CoO
CuO
NiO

Their sesquioxides

MU2O3

Common alum consists of sulphate of alumina united to sulphate of potash
with water of crystallization. It crystallizes in well-marked octahedral
crystals. Soda and ammonia are isomorphous with potash, and each may
take the place of this alkali without affecting the form of the crystal. So
again the oxides of manganese, iron, and chromium are isomorphous with the
oxide of aluminum (alumina). Each of these oxides may take the place of
the alumina, the other constituents remaining the same, and the octahedral
form of the compound will be unaltered. A crystal of potassa-alum may
therefore receive a deposit of ammonia-alum in a solution of that salt, and it
has even been found, as a remarkable instance of the tendency of isomorphous
salts to crystallize together, that a white crystal of potassa-alum may be
coated with a layer of deep ruby-red chrome-alum ; and it is stated that if a
solid angle be broken off, chrome alum may be deposited in its place. From
this ready association of isomorphous salts, it is difficult to purify them by
crystallization. Thus all commercial alum contains oxide of iron, which
replaces part of the alumina. Sulphate of magnesia and sulphate of zinc
are isomorphous, and if mixed, they crystallize, more or less, together, so
that other means must be resorted to in order to separate them. This obser-
vation applies also to the sulphates of copper and iron, which belong to the
same system. They are isomorphous in regard to acid and base, and, when
mixed, each crystallizes with seven atoms of water. It is a curious fact, that
pure sulphate of copper, in crystallizing, combines with only five atoois of
water; but if sulphate of iron is present, it will crystallize with seven atoms,
like this sulphate. The two are then isomorphous, and they cannot be sepa-
rated from each other by crystallization. If a large crystal of sulphate of
copper is placed in a nearly saturated solution of sulphate of iron, it will be
increased in size by a deposit of this salt on the outside, and a crystal may

I

40 CHExMICAL FORCE

thus be constructed of successive layers of either salt. Although the carbon-
ates of iron and magnesia are isomorphous, the sulphates of these bases are
not. They contain different quantities of water of crystallization, and when
a solution of the mixed salts is concentrated by evaporation, crystals of each
are separately deposited.

Besides a reliance upon form, the measurement of the angles of crystals
when of similar form, is sometimes necessary for the purposes of mineralogy.
An appropriate and beautiful instrument for this purpose is ihe goniometer of
Dr. Wollaston. Its action depends on the reflection of light from the
polished surface of a crystal, however minute. By rotating a brass circle,
the value of the angle made by any two planes is at once determined ; and as
a vernier is attached to the scale, a very slight difference in the angles of two
similar rhombs may be readily determined, and the identity of each, made
out. Thus the carbonates of lime and magnesia assume the rhombohedral
form, and are alike in cleavage. By the goniometer, however, it is found
that in carbonate of lime the angles formed by the two planes is 105° 5',
while in the rhomb of carbonate of magnesia the angle is 107° 25'. These
measurements supply means of identifying these minerals.

j^. CHAPTER III.

CHEMICALFORC E— S 0 L U T 1 0 N— E LECTROLYSIS.

Chemical Force. — The special characters of the chemical force have been
already explained. While cohesive attraction merely unites the atoms of
similar or dissimilar kinds of matter without altering their properties, the
chemical force leads to the union of dissimilar atoms with a more or less
complete change of properties.

A chemical compound is known, 1. By the substance uniting in definite
proportions by weight — these proportions being called atomic, or equivalent
weights. 2. By their union being attended with the absorption or evolution
of heat, or the evolution of light, electricity, and magnetism. 3. By a
change of properties — thus the density, color, solubility, and crystalline form
of the compound, as well as its reactions on other bodies, are in general
different from those of its constituents.

This force is only manifested between the minute particles of matter.
Place a few grains of powdered iodine in a capacious jar, i. e., of 200 c. t.
capacity. After agitation for a few minutes the particles of iodine will be
found diffused through the whole of the jar. They are quite invisible, but in
a mass they may give a slight pink tinge to the aerial contents. If a long
strip of bibulous paper, soaked in a solution of starch, be now gradually
introduced, the presence of the atoms of iodine, and the formation of a
chemical compound with the starch, will be indicated by the gradual pro-
duction of a purple or blue color in the paper. Although five times the
weight of water, and four thousand times the weight of the air in which
they float, these imponderable atoms clearly indicate their presence and
diffusion by a chemical action on starch. If the paper is now removed, and
a leaf of silver (made to adhere to a glass-plate by breathing on it), is
brought over the mouth of the jar so as to close it, the chemical formation
of iodide of silver will be indicated by the production of circular films on
the metal, of a straw-yellow, purple, blue, and brown color, each of these
films indicating au infinitesimal tenuity of iodide of silver probably less

INFLUENCE OF COHESION. 41

than the 2,000,000th of an inch in thickness. On a thin purple film thus
obtained, an image may be produced by light in the Daguerreotype process.
Influence of Cohesion. — As a general rule, the more perfectly cohesion is
destroyed in substance, the more strongly is the chemical force manifested.
A small block of tin covered with nitric acid in a glass, will show only a
slight amount of chemical action. If an equal weight of tin in the state of
powder is similarly treated, the acid is decomposed with great violence. So
in acting upon equal weights of calcareous spar in lump and fine powder, by
adding to them diluted hydrochloric acid, a striking difference will be
observed in the relative amount of chemical action. The reduction of a
solid to powder operates simply by increasing the surface for chemical action,
which, cseteris paribus, is always proportioned in intensity to the surfaces of
contact between bodies. A cubic inch of a substance exposes only six
square inches of surface ; but if divided into a million parts, that small area
is multiplied into 416 square feet. The finest pulverization of all solids is
therefore a necessary condition for a perfect and rapid chemical combination.
A stream of sulphuretted hydrogen gas may be allowed to fall on a mass
of anhydrous \)xide of iron (hsematite) without producing any chemical
changes. If, however, the gas is passed on the anhydrous oxide in fine
powder, the whole mass becomes speedily red hot, and water and sulphide of
iron are produced. The same gas may be passed into pure water mixed
with coarse fragments of flint-glass without indicating the presence of lead
in the glass ; but if the flint-glass is very finely powdered and is thus treated,
it is rendered brown by the conversion of the oxide of lead contained in it
into sulphide of lead.

Liquids readily combine on mixture ; and some gases combine on contact,
although in the latter case heat or electricity is generally required to bring
about their union. Solution facilitates chemical action by reason of the
infinitesimal division to which a solid is thereby reduced ; and so frequently
is this a preliminary to chemical processes, that the maxim corpora non aguni
nisi soluta is a generally accepted truth. At the same time in reference to
solids which are not easily brought to a state of solution, the operator must
equally bear in mind the rule — corpora non agunt nisi divisa.

The effect of the minute division of solids in accelerating chemical action
is well illustrated in pyrophori — substances which are spontaneously com-
bustible on exposure to air. If finely-powdered Prussian blue is heated
intensely in a glass tube, and then hermetically sealed, the brown-black
powder into which it is converted, instantly takes fire, with bright scintilla-
tions, on exposure to air. If dry tartrate of lead is heated in a tube to a
dull red heat, i. e., sufficient to carbonize the acid (and the tube is hermetically
sealed), the residue, when exposed to air, will take fire and burn. In the one
case, minute atoms of iron, and in the other, of lead are instantly oxidized
with the phenomena of combustion at the ordinary temperature ; although
neither iron nor lead will burn in air under common circumstances. Sulphate
of potassa in powder, strongly heated in a covered crucible, with half of its
weight of lamp-black, is converted into sulphide of potassium, which becomes
so rapidly oxidized on exposure to air, that it will take fire and burn. The
difference between the combustibility of carbon as tinder, and of carbon as
coke or diamond, is also dependent on the different cohesive force and
amount of surface exposed by these substances. Again, thin shavings of
zinc are very combustible in the heat of a spirit-lamp, while a bar of the
metal, or stout foil, resists combustion. There is no case in which this effect
of division and surface is more strongly manifested than in phosphorus. This
substance may be exposed to air in a mass, at a temperature below 60°,
without taking fire. When, however, it has been dissolved in the sulphide

42 CHEMICAL FORCE. INFLUENCE OF WATER.

of carbon, and the solution is poured over a slieet of thin paper, a layer,
consisting of infinitely minute particles of phosphorus, is left upon the paper
by the evaporation of the solvent ; and when dry, these minute particles of
phosphorus on the surface of the paper, burst into a sheet of flame. We are
accustomed to speak of oxygen ae it exists in our atmosphere as passive, but
these facts show us that its passivity is more apparent than real ; and that
were it not for the force of cohesion by which the particles of matter are
held together as solids, many of the metals and metalloids could not possibly
exist in an unoxidized condition.

In some exceptional cases, solids are found to react upon each other.
Potassium placed on ice will decompose it, and burn at the expense of the
oxygen, which is one of its constituents. If powdered iodiue be placed on
a freshly-cut slice of dry phosphorus, mere contact leads to the fusion of the
phosphorus, and to instantaneous combination with combustion. A mixture
of finely-powdered chlorate of potash and allotropic phosphorus explodes
with the slightest friction and with tremendous violence.

Influence of Water. — The influence of water on chemical aflQnity is very
remarkable. In some cases, by its removal, chemical changes are entirely
arrested. Albumen or gelatin, combined with a small quantity of water,
speedily putrefies ; but when desiccated, or deprived of water, these substances
undergo no change. {See Water.) Iron has a great tendency to become
rusted or oxidized on exposure to air ; but if the air is perfectly free from
water, there is no rust or oxidation. A strong solution of nitrate of silver
dried on paper is decomposed in a few days, even when kept from light.
The organic matter of the paper reduces. the silver to the metallic state in
the dark, and the paper becomes discolored. If, however, the paper is
placed in a vessel containing anhydrous chloride of calcium, and kept from
the light, it may be preserved unchanged for weeks and months. Sensitized
papers used in the art of photography, or photographic drawings when once
taken, are thus effectually preserved from change, so long as they are in a
dry atmosphere. Even pure chloride of silver, prepared as white as snow,
by immersing leaf- silver in chlorine gas, undergoes no change on exposure
to light, provided chloride of calcium is placed in the vessel containing it,
and the vessel is accurately closed. We have thus kept the chloride of silver
for six months, with its whiteness unaltered, although during that time it
was exposed to the direct solar rays. Chlorine itself when entirely deprived
of moisture, manifests no tendency to combine with metallic silver in the
state of leaf. The film of iodide of silver, which is used in the collodion
process of photography, may be kept for many months in the dark, with its
sensitive powers undiminished, provided the surplus nitrate of silver is
removed by washing — the film itself is dried and coated with a layer of
albumen or tannic acid, and lime of chloride of calcium is placed in the box
to absorb any moisture. The color of compounds appears to be in some
instances closely connected with the presence of the elements of water. If
Prussian blue is boiled with strong sulphuric acid, it loses its color and
becomes of a dingy white. This change appears to be owing to the removal
of water; for if the white compound is poured into a large quantity of water,
it immediately reacquires its color, but the color is not restored when it is
put into oxygen gas. This proves that the restoration of the blue color
depends on hydration.

In the absence of water we can get no evidence of acidity or alkalinity in
substances. Thus sulphuric acid in the anhydrous state is a fibrous selid,
which has no action on litmus, and no corrosive properties. Solid anhydrous
phosphoric acid has no acid reaction on test-paper; this is only manifested
on the absorption of some water from the air. Boracic acid and silicic acid

INFLUENCE OP WATER. 43

are in the same condition ; in fact, owing to its entire insolubility in the free
state, silicic acid cannot be proved to have any reaction like an acid on
vegetable colors. Dry carbonic acid gas has no action on dry litmus. The
same remark may be made of the gallic, pyrogallic, and other vegetable acids,
whether hydrated or anhydrous. They manifest no acid reaction on test-
paper until water is added. It has been supposed that this apparent
production of acidity by water was a proof that all acids must owe their
acidity to hydrogen, and be really hydracids, hydrides of new radicals, or, as
they are termed, " salts of hydrogen ;" but such an hypothesis is not necessary
for an explanation of the facts. Thus, in reference to the elements of
phosphoric, carbonic, pyrogallic, and other acids, water may simply act as a
solvent to bring the constituents of the acid in contact with the vegetable
color. Anhydrous potassa, soda, ammonia or morphia in the absence of
moisture or water, cannot be proved to exert any alkaline reaction on
vegetable colors ; and to explain this reaction, it is not necessary to suppose
that the potash or soda absorbs another atom of oxygen and becomes a
hydride {see Oxacids, and Oxygen), or to assume therefrom that hydrogen
is the cause of alkalinity. An acid or alkaline reaction, as manifested by
changes in vegetable colors, depends much on the solubility of the substance,
and of the coloring principle employed. Some vegetable acids, say the
tartaric, when dissolved in alcohol, have but a slight effect on litmus paper,
while the solution of the same acid in water has a powerful acid reaction.
Carbonate of potash in water has a strong alkaline reaction on test-paper,
but this salt mixed with alcohol manifests no alkalinity. A solution of pure
potash, whether in water or alcohol, is strongly alkaline. Magnesia manifests
no alkalinity to test-paper when mixed with alcohol, but when mixed with
water it is sufficiently soluble to produce the usual changes of colors
indicative of the presence of an alkali. Solutions of some of the resins in
alcohol give no indication of acidity to test-paper, but when water is added,
to precipitate the resin, there is immediately an acid reaction — litmus paper
is reddened.

The intensity of reaction on vegetable colors, whether acids or alkalies, is
generally in a direct ratio to the solubility of these substances in water.
While tartaric acid acts powerfully on infusion of blue litmus — a solution
of boracic acid barely reddens it — and silicic acid in its ordinary and insoluble
state does not alter the blue color. There is an equally marked difference
of action on vegetable colors, which are affected by alkalies, in reference to
pure potash, lime, and magnesia. Potash is soluble in half its weight of cold
water, ^ime requires 700 times its weight. Magnesia 7000 times its
weight for solution. Potash has an intense alkaline reaction, while magnesia
acts feebly and slowly. Among substances which readily decompose each
other, there is an entire want of action, unless water is present. Thus dry
t&rtaric acid has no action on dry carbonate of soda, even when finely
powdered. In the cases above-mentioned, water as such, may take a share
in promoting chemical action without necessarily undergoing decomposition.
(For other instances see Water.)

In the chemical process of bleaching by chlorine or bromine, it is highly
probable that water is decomposed. Dry chlorine has no bleaching action
on dry vegetable colors. The slightest trace of humidity in the gas or in
the colored material brings about the destruction of color. As hydrochloric
acid is found in a liquid thus bleached, some portion of the water must have
parted with its hydrogen; and oxygen thus liberated in the nascent state
(as ozone) enters into combination with the coloring matter and probably
operates as the direct bleaching agent. The influence of water on the
chemical force is well seen in the production of the so-called amalgam uf

a

44 INFLUENCE OF HEAT.

ammonium. If dry amalgam of sodium is placed in a dry block of chloride
of ammonium, there is no chemical change ; but if water is added, the
mercury speedily increases in size : it becomes soft and compressible, and is
everywhere penetrated with the two gases, liberated by the combination of
the sodium with the chlorine. The whole forms a light spongy mass, which
is rapidly reconverted into mercury, hydrogen, and ammonia. {See Am-
monium.)

Influence of Heat. — Heat plays an important part in reference to the
chemical force. By its agency bodies are united and disunited. Mercury
combines with oxygen at one temperature, and at a still higher temperature
the compound is again resolved into mercury and oxygen. Protoxide of
barium will at one temperature take another equivalent of oxygen, to form
peroxide; but when this compound is more strongly heated, the atom of
oxygen will be expelled, and it will revert to the state of protoxide. Gene-
rally speaking, the effect of heat is to increase the afiBnity of bodies for each
other. The strongest nitric acid has no action on aluminum in the cold, but
when heat is applied, there is a violent action — the metal becoming oxidized.
This action ceases on cooling the acid, and is renewed on again heating it.
Sulphur and charcoal have no tendency to combine with oxygen unless
heated to about 500^ and 1000° respectively, when they both undergo
combustion, and produce gaseous compounds. The inflammation of gun-
powder furnishes an example of the effect of heat on these ingredients. It
is only when this substance is heated in air to a temperature above 500°
that combustion takes place, with the conversion of the solid into a large
volume of gases*

The solubility of substances in water is generally increased by heat : in
some instances, the reverse condition is observed. Lime is twice as soluble
in cold as in boiling water ; hence when a saturated solution of lime is
boiled, a portion of this alkaline earth is deposited. A very diluted solution
of persulphate of iron is decomposed by heat, and a basic salt with excess of
oxide is deposited. The effect of heat on albumen is remarkable. At a
temperature exceeding 110°, the soluble is converted into the insoluble
variety, and the properties of the substance are entirely changed. Heat
destroys temporarily the combination of iodine with starch ; the liquid from
being intensely blue becomes colorless ; but if not too long heated the color
of the liquid will be restored on cooling, by the reabsorption of the vapor of
iodine, which has been temporarily separated from the starch. When this
experiment is performed in a close vessel the colored compound is reproduced ;
but when in an open dish, the iodine is lost by volatilization, and the blue
color is either not restored, or only in a slight degree. A solution of
chloride of calcium, so diluted as to yield no precipitate with a solution of
sulphate of soda, undergoes decomposition when heated, and sulphate of lime
is precipitated, the salt being less soluble in hot than in cold water. Again,
borate of soda produces no precipitation or apparent decomposition of
sulphate of magnesia in the cold, but when a solution containing the two
salts is boiled, an insoluble borate of magnesia is thrown down. A solution
of bicarbonate of soda, or of carbonate of lithia, gives no precipitates with
sulphate of magnesia until the liquids have been boiled. It is unnecessary
to specify additional instances of the influence of heat on chemical affinity.
Illustrations will be found in the history of every element and of most
compounds.

Influence of LigJit.^ThQ influence of light is seen in some combinations
of the gases, as well as in the changes produced in the salts of certain metals,
as silver, mercury, gold, chromium, iron, and uranium. When equal
volumes of chlorine and carbonic oxide are exposed in a glass vessel to solar

INFLUENCE OP LIGHT. 45

light, they combine to form a compound known as phosgene gas. In the
dark they manifest no tendency to unite. When chlorine and hydrogen are
mixed and ex}3osed to the direct rays of the sun, they combine with explo-
sion, and produce hydrochloric acid; in the dark there is no combination ;
and in the diffused light of day the union of the gases takes place slowly,
without explosion. So strictly does this union depend on light, that Bunsen
and Roscoe have made use of such a mixture for the purposes of photometry,
in determining the relative intensity of light. On the other hand, under the
influence of light, aqueous vapor mixed with chlorine undergoes decomposi-
tion, hydrochloric acid and oxygen being the products (supra). Unless a
solution of chlorine is carefully kept in the dark, it is rapidly decomposed,
and the liquid becomes strongly acid from the hydrochloric acid produced.
It is under the influence of solar light that carbonic acid is decomposed by
the leaves of growing vegetables, and the carbon is fixed, while oxy/gen is
liberated.

The influence of light on chemical affinity is especially seen in the changes
produced on the salts of silver. When in contact with organic matter,
nitrate of silver is entirely decomposed by exposure to light. The oxygen
and nitric acid are removed and the silver is reduced to the metallic state.
If moisture is present, chloride of silver is also decomposed by exposure to
light, hydrochloric acid is produced, and metallic silver is deposited. In
reference to these salts, the changes are physical as well as chemical — the
silver is visibly darkened. Other salts of silver, such as the iodide and
bromide, undergo no visible change of color when exposed to light ; but
they are altered in their molecular state. (See p. 52.) This subject will
be more fully considered under Photography. The suboxide of mercury,
exposed to light, is converted into red oxide and metallic mercury. Turpeth
mineral, or the basic sulphate of the peroxide, is darkened by light. The
salts of the peroxide of iron, formed by the citric and oxalic acids in contact
with organic matter, are reduced to proto-salts by exposure to light, a fact
which may be proved by the application of appropriate reagents, e. g., the
chloride of gold. The persalts of uranium and the bichromate of potassa
are also reduced to lower degrees of oxidation by exposure to the solar rays.

The effects above described take place under the influence of ordinary
light; but a closer analysis of the phenomena has established the fact, that
this chemical influence is almost exclusively confined to the more refrangible
rays of the spectrum, namely, the blue and violet. Thus, an intense light
passing through violet or blue glass will cause the immediate explosion of a
mixture of chlorine and hydrogen ; while the same light, traversing yellow
or red glass, has no combining effect on the gases. Although a larger
amount of luminosity exists in the yellow than in the blue light, the yellow
rays are powerless to bring about a chemical union of the gases. This
peculiar effect of colored light is equally observed in reference to the changes
produced on the salts of silver ; but in different degrees in different salts.
The rays which produce these chemical changes are called actinic ; they are
met with even beyond the^visible violet ray. On the undulatory theory of
light, the blue and the violet rays are considered to produce a greater
number of ethereal undulations, in a given time, than the yellow and the red
rays ; and the difference of color is supposed to depend upon the difference
in the number of their undulations. While this theory derives great support
from many physical phenomena, it affords no satisfactory explanation of the
remarkable influence of white or colored light upon the chemical union and
decomposition of bodies.

Influence of the Nascent State. — Gases when once in the free state do not
readily combine with each other. Thus hydrogen will not combine with

46 CHEMICAL COMPOUNDS.

nitroj^en to form ammonia, nor will it combine with sulphur or arsenic in
powder or vapor, to form sulphuretted or arsenuretted hydrog^en ; but
there is a condition, called the nascent state, which is eminently favorable
to the chemical combination of these bodies, either with each other or with
solids. The nascent state simply implies that condition in which a body is
passing from the solid or liquid to the j^aseous state. The ammonia formed
by the putrefaction of substances containing nitrogen, is the result of the
combination of hydrogen and nitrogen, as they are liberated from the
organic solid or liquid. When sulphide of iron is treated with diluted
sulphuric acid, the nascent hydrogen resulting from the decomposition of
water, instantly seizes upon the sulphur of the sulphide to form sulphuretted
hydrogen. When the same acid is poured upon zinc, containing arsenic,
or when the zinc and acid are added to an arsenical liquid, the nascent
hydrogen instantly combines with the arsenic to form arsenuretted hydrogen.
The affinity of hydrogen in the act of liberation from water is so exalted,
that it will combine with and carry over minute traces of carbon, sulphur,
phosphorus, selenium, silicon, arsenic, iron, zinc, and other substances,
although in the state of free gas it has no tendency whatever to combine
with them. The production of silicide of hydrogen, as well as of the tartaric,
acetic, oxalic, and other ethers, depends on the influence of the nascent state
in effecting th? combination of bodies.

Many chemical decompositions in which the results appear to be conflict-
ing, receive an explanation from this theory of a nascent state. A current
of pure hydrogen in a free state, passed through solutions of permanganate
of potash, bichromate of potash, and tartar emetic, produces no chemical
change ; but if the hydrogen is generated in each of these solutions by adding
sulphuric acid to pure zinc, as it is eliminated from the water, it deoxidizes
the dissolved substances. It discharges the color of the permanganate of
potash; it reduces the chromic acid to green oxide of chromium, and it
combines with a portion of metallic antimony escaping from the vessel in
the form of antimonuretted hydrogen. In these cases it matters not how
the hydrogen is produced, so that it is slowly evolved as the result of chemical
decomposition in immediate contact with the substance. An amalgam of
sodium and mercury evolves hydrogen, which equally deoxidizes the per-
manganate of potash. Hydrogen in a free current, when passed into
mixtures of ammonio-chloride of platinum in water and of chloride of silver
in water, produces no chemical changes ; but when the hydrogen is liberated
in the mixture by the reaction of an acid on pure zinc, metallic platinum in
the form of platinum black is thrown down in the one case, and pure silver
in the other. Free hydrogen manifests no reducing power, while nascent
hydrogen has a more intense action and immediately combines with the
chlorine, setting the metals free. Sodium amalgam speedily reduces the
chlorides of gold and platinum, the hydrogen combining with the chlorine
and setting the metals free — the metallic gold entering into combination
with the mercury, forming a gold amalgam. In the rusting of iron, hydrogen
is evolved in the nascent state by the decompqgition of water: it imme-
diately combines with the nitrogen of the air, producing ammonia, which is
formed in most parts of iron rust. When free, hydrogen cannot be made to
combine with nitrogen to produce ammonia. Many other instances might
be cited in illustration of this mode of action. They will be described
hereafter.

What is a CJiemical Compound? — The answer to this question is involved
in the inquiry — How may a chemical compound be distinguished from a me-
chanical^ mixture ? In gun-cotton (pyroxyline) and gunpowder we have
illustrations 'of the two states. Gun-cotton is a chemical compound of the

CHEMICAL FORCE. SOLUTION. 41

offrnnic substance (cotton) as a base with the elements of nitrous or hypo-
nitric acid (NO4). The constituents cannot be separated without an entire
destruction of the substance. Gunpowder is a mechanical mixture of char-
coal, sulphur, and nitre, in certain proportions, the two last beinp^ easily
separable from each other and from the charcoal, by appropriate solvents.
The chemical force is only brought into operation among these ingredients
by heat; while in gun-cotton this force already binds together the nitrous
acid and the cotton, and heat merely produces a new series of combinations.

In spite of these broad distinctions, there are some cases of the union of
substances, of so doubtful a character, that chemists are not. agreed upon
the nature of the force which binds them together. Gelatinous alumina,
shaken with solution of cochineal, removes the color and is precipitated with
it. Charcoal in the same way removes the color of indigo, litmus, cochineal,
and of other vegetable and animal substances. It will also remove the blue
color of iodide of starch, and the red color of permanganate of potavsh,
which are chemical compounds. This is commonly described as a surface
action or an attraction between surfaces, as the properties of the bodies
undergo no change.

When caoutchouc is combined with sulphur at a temperature of about
300°, a compound known as vulcanized rubber is produced. The properties
of this substance are different from those of its constituents. Thus after
vulcanization the rubber is altered in color; its elasticity is remarkably in-
creased ; it does not melt even at the boiling point of mercury, and it does
not become stiff in the cold. It is also quite insoluble in all the liquids which
dissolve rubber. Here then is a change of properties sufficient to justify a
chemist in regarding this as a chemical compound of its two constituents.
On the other hand, the two substances do not combine in definite propor-
tions : the sulphur may be in the proportion of from 10 to 16 per cent., and
it may be removed from the rubber, after incorporation, by the usual sol-
vents, without materially affecting its properties. These conditions are
adverse to the hypothesis of a chemical union, and the result is, that such a
compound can be expressed by no chemical formula. Again, in the phe-
nomena of solution or diffusion, as of hydrated sulphuric acid, or of anhy-
drous alcohol in water, we have evolution of heat and a great alteration of
volume. Is this a chemical union of the liquids with the water, or is it not?
The phenomena accompanying the mixture point to something more than a
mechanical force ; but there is no change of properties, and there is no evi-
dence of union in definite proportions. This subject is, however, of sufficient
importance in a chemical point of view to receive a separate examination.

Solution. — The solution of solids in liquids, whether the solvent be water,
alcohol, ether, benzole, chloroform, or mercury, has been assigned by some
chemists to a species of affinity, and by others to a physical effect of adhe-
sion. By solution we are simply to understand a combination of a solid with '
a liquid, in which the solid itself assumes a liquid form. There is no change
of properties, and here this great feature of chemical force is wanting :
thus common salt dissolved in water possesses all its usual characters. This
observation applies equally to the solutions of other salts, as well as to solu-
tions of acids and alkalies. The best solvents are generally those liquids
which are similar in properties to the solid. Benzole and oil of turpentine
readily dissolve caoutchouc and other solid hydrocarbons ; oils dissolve fats ;
mercury dissolves metals; alcohol dissolves resins; and water, itself a neutral
oxide, dissolves neutral salts and neutral compounds, such as gum, sugar, &c.
Water is the great solvent for chemical purposes, and it is by the use of this
liquid that most chemical changes are produced among solids ; it breaks up

r'W^ t.l

8 SOLUTION OF SALTS.

the cohesion of solids more effectually than pulverization, and thus brings
their particles within the sphere of each other's attraction.

Solution is only influenced by gravitation, when the solid salt is allowed
to remain at the bottom of the water. The lower stratum of liquid then con-
tains a much larger quantity of the salt than the upper portion ; but after a
time it will spread by diffusion, varying in degree with the nature of the salt.
For this reason, solution is always best effected by suspending the solid sub-
stance in the upper stratum of liquid. When the salt is once dissolved and
equally diffused throughout the liquid by agitation, gravitation is not found
to affect it. Thus, although corrosive sublimate has a specific gravity six
times greater than water, yet a solution of it, preserved for many years in a long
tube, was not found to contain any more of this salt in the lower than in the
upper stratum.

Each substance has its own specific solubility which varies with tempera-
ture, and as a general rule heat increases the solubility of solids in water and
other solvents, but there are some exceptions in reference to water. Thus
lime, citrate of lime, sulphate of lime, and sulphate of soda, are less soluble
at the boiling points of their solutions than at lower temperature ; while
chloride of sodium is nearly equally soluble at a high and a low temperature.
The fact that each solid has a special rate of solubility, and that this varies
with temperature is inconsistent with the theory that solution is dependent
on physical force.

A knowledge of the relative solubility of salts in water is of some import-
ance in chemical analysis. Many substances thus admit of separation by
evaporating the solutions, those which are least soluble for the temperature
being first deposited. We subjoin a table of the relative solubility at 60° of
many salts in common use. The figures represent in weight the parts of
salts dissolved by 100 parts of distilled water by weight.

Parts dissolved at 60°.

Parts dissolved in 60°.

Acid tartrate of potash .

. 1

Carbonate of ammonia .

. 33

Oxalate of ammonia

. 4

Nitrate of baryta .

. 35

Alum ....

. 6

Chloride of barium

. 36

Bicarbonate of soda

. 7

Chloride of ammonium

. 36

Sulphate of potash

. 8

Chloride of sodium

. 37

Sulphate of soda .

. 10.5

Sulphate of magnesia .

. 100

Bicarbonate of potash .

. 25

Carbonate of potash

. 100

Phosphate of soda .

. 25

Tartrate of potash

. 100

Phosphate of ammonia .

. 25

Nitrate of ammonia

. 120

Chloride of potassium .

. 29

Iodide of potassium

. 143

Ferrocyanide of potassium

. 33

Chloride of magnesium

. 200

Nitrate of potash .

. 33

Chloride of calcium

. 400

Nitrate of soda

. 33

The term insolubility as applied to a salt has only a'relative signification.
Sulphate of lime is sometimes described as insoluble in water. Compared
with the salts in the preceding list, its solubility in water is very slight.
Thus it requires 400 parts of water at 60° to dissolve one part of the sul-
phate of lime, but it is very soluble when compared with the sulphate of
baryta. Taking the sulphates of lime, strontia, and baryta, their solubility
in water decreases in a decimal proportion. One part of

Parts of water.

Sulphate of lime is dissolved by 400

Sulphate of strontia " « 4^000

Sulphate of baryta « « 40,000

The sulphate of baryta is usually described as quite insoluble, but there
are compounds which are still less soluble than it. Carbonate of lime re-
quires 16,000 parts of water for the solution of one part. The presence of

SOLUTION OP SALTS. 49

free carbonic acid renders it much more soluble. Chloride of silver is the
most insoluble of salts, and is said to require 113 railliou parts of water to
dissolve it.

The comparative insolubility in water of the platina chlorides of the alkali-
metals, enables chemists to separate some of them from each other. The
following table represents the effect of water as a solvent at 60° and at 212°.
One part of

Parts of water

Parts of water

at 60°.

at 21 2--

Platino-chloric

le of potassium is soluble in

108

19

(( «

ammonium "

150

80

Rubidium

u

740

157

Csesium

(<

1,308

261

Thallium

«

15,585

1,948

Parts.

Parts.

58.49

Narcotina

,

,

. 31.17

57.47

Strjclmia

.

,

. 20.19

56.70

Cinchonia

.

,

. 4.31

51.19

Morphia .

.

.

. 0.57

The platino-chloride of thallium, it will be seen, is as insoluble as chalk.

The alkaloids are remarkable for their insolubility in water. Strychnine
is usually described as insoluble : it requires 7000 parts of water for the solu-
tion of one part. The alkaloids are, however, dissolved by alcohol, ether,
benzole, and chloroform in different degrees. The table shows the different
quantities of eight important alkaloids which chloroform will dissolve at 60°.
It may be found useful in the separation of some of these alkaloids from each
other. 100 parts of chloroform by weight dissolve of

Veratria .
Quinia
Brucia
Atropia .

These remarkable differences in the proportion of solids which the same
weight of the solvent is capable of converting into a liquid, render it impos-
sible to admit that solution is a mere physical adhesion of the atoms of one
body to the atoms of another.

The solution of salts in water is sometimes attended with great loss of heat
by reason of the salt rapidly passing from the solid to the liquid state. Some
of the cheapest freezing mixtures, in the absence of ice, are based upon this
property. Thus one part of crystallized nitrate of ammonia, dissolved in one
part of water causes the thermometer to fall from 50° to 4° ; and five parts
of sal ammoniac with five parts of nitre, dissolved in sixteen parts of water,
are nearly equally effective. These are anhydrous salts, so that the result is
the direct effect of solution, and it appears to point rather to chemical com-
bination than mechanical adhesion. Another fact observed by Playfair and
Joule is, that salts containing water of crystallization, when dissolved in water,
add no more bulk to the water than is equivalent to the water of crystalliza-
tion (calculated as ice) with which their atoms are chemically combined.
Thus, when alum is dissolved in water, the increase of volume in the solution
is not in proportion to the bulk of alum used, but to the bulk of combined
water as ice (24 equivalents), contained in it. The atoms of alum have
therefore disappeared, or been received, within the interstices of the atoms
of water ; at any rate they occupy no appreciable space. If these results
are confirmed, it will show that the hypothesis of mechanical adhesion of a
liquefied solid to a liquid is not in all cases sufficient to explain the phenomena
of solution. The effect of heat in increasing or diminishing solubility, the
fixed limit of solubility for different salts, and the decrease or increase occa-
sionally observed in the volume of the solvent, as well as the singular fact
observed by Dr. Gladstone (Proc. R. S., vol. 9, p. 89), namely, the absorp-
4

50 SOLUTION OF SALTS.

live power on light exhibited by strong solutions of salts, are adverse to the
hypothesis of a mere adhesion of atoms.

When a liquid will dissolve no more of a solid, it is said to be saturated-^
in other words, its adhesion or affinity for the solid is exhausted. It is a
curious fact, however, that water which is saturated with one salt has still
the property of dissolving a second and a third salt. Crystals of nitre may
be thus freed from impurities, such a^ chloride of sodium by washing them
with a saturated solution of nitre. A saturated solution of a salt exerts a
powerful attraction on water. If a saturated solution of sulphate of copper
is inclosed in a funnel tube, secured at the larger end by bladder, and the
tube is plunged in a vessel containing water, so that the liquids inside and
outside are on a level, in the course of some hours it will be found that
although some of the copper-salt has passed out through the pores of the
bladder, a much larger proportion of water has passed in. Solutions of
common salt, sugar, and other substances, present this phenomena, to which
the term osmosis (from uiOiu to push) has been applied. The diffusion of
liquids or their relative tendency to mix on contact has been fully examined
by Mr. Graham {Quart. Jour. Cliem. Sac, vol. 3, p. 60) ; and the effect of
porous membranes in allowing liquids or dissolved solids to traverse them,
has also been made the subject of experiment by the same chemist. Mineral
substances, such as arsenic, may thus be separated from organic matter.
He has called this process dialysis. {Proc. R. S., 1861, vol. 11, p. 243.)

The dissolved solid may be separated from the solvent by the addition of
another liquid. Camphor is separated from its solution in alcohol by adding
water — gum from its solution in water by the addition of alcohol — soap from
water by chloride of sodium, and corrosive sublimate and chloride of gold
from water by ether. In the latter case, the metallic salt changes its solvent,
and the compound of mercury or gold is found dissolved in the ether as chloride.

When liquids mix together, they are said to combine by diffusion, accord-
ing to various circumstances. Alcohol and water readily combine with evo-
lution of heat and contraction of volume. If 54 parts, by measure, of alcohol,
are mixed with 50 of water, the reduction in volume on cooling is equal to
about four per cent. {Mitscherlich.) This cannot be regarded as the mere
result of adhesion or any mechanical force, but rather of chemical union,
although the properties of the mixture have undergone no change. If the
alcohol be poured carefully on the water in a long tube, and a piece of white
wax dropped through the spirit, to indicate, by floating, the exact level of
the water, many months may elapse without the position of the wax under-
going a change, and therefore without combination of the two liquids. This
depends on the smallness of the area of contact, and the great difference in
the specific gravity of the two liquids. Water will dissolve or combine with
alcohol in all proportions, but with ether there is a fixed limit : of this liquid
it cannot hold dissolved more than ten per cent, by volume. When water is
added to a mixture of ether and alcohol, the alcohol is entirely dissolved,
but the surplus ether is separated, and floats on the top of the liquid. Chlo-
roform is soluble in alcohol, but only to a limited extent in water ; hence,
for the same reason, water separates it from alcohol.

Some substances appear to be held in water by a kind of suspension resem-
bling solution. Thus starch forms an opaque liquid ; gelatin, gelose, and
certain silicates as well as silicic acid itself, are similarly suspended without
having formed a perfect combination with the water as a solvent. They
appear to constitute hydrates of the respective substances with a large sur-
plus of water. For all practical purposes in chemistry they are regarded
and treated as solutions, although the substances may be ultimately deposited
in an insoluble form. When a chemical change takes^place on the mixture

AMALGAMS. PROOFS OF CHEMICAL CHANGE,

of a liquid and solid, as on the addition of nitric acid to copper or silv
the terra solution is no longer appropriate ; the liquid is decomposed, and
new compound results.

Solutions of metals in mercury are called Amalgams. Some metals are
more soluble in this liquid than others ; thus gold, silver, tin, and bismuth
are rapidly dissolved, while iron, and copper (in its ordinary state), are not
aflfected. Although treated as solution, or the simple adhesion of metal to
mercury, as of salt to water, there is every reason to believe that there is a
chemical union of the mercury with the metal in definite proportions, and
that this compound is dissolved in the large proportion of mercury which
forms a liquid amalgam. Tin and silver combine with small proportions of
mercury to form crystalline compounds. If a large quantity of mercury is
employed, both tin and silver disappear as by solution ; but when a smaller
proportion is used a soft amalgam is formed, which gradually becomes hard
by crystallization. The force which holds the tin to the mercury cannot be
considered the same as that which holds the amalgam of tin and mercury to
a surface of glass. The solution of metals in mercury is sometimes attended
with the production of heat and cold, as well as with a change of state. If
equal parts of sodium and potassium are well mixed by pressure under naph-
tha, and a globule of mercury is poured on the soft alloy, there is instant
chemical union with an evolution of heat and flame, and the production of a
solid amalgam. Melt together 20Y parts of lead, 118 of tin, and 284 of bis-
muth. These form, when cold, a brittle alloy. When this is reduced to a
fine powder, and mixed with 161 T parts of mercury, at a temperature of 60°,
the thermometer falls to \4P. This is owing to the rapid conversion of the
solid metals to the liquid state, and the absorption of heat from surrounding
bodies. It resembles, in effect, the solution of crystallized nitrate of ammo-
nia in water. Mercury, under certain conditions, appears to combine with
the gases hydrogen and nitrogen in th^ proportions of one equivalent of
nitrogen to four of hydrogen, producing the amalgam of ammonium. It
then becomes semi-solid, and assumes a crystalline condition, like that which
it acquires in combining with a large quantity of tin or silver. The union is
only of a temporary nature, and appears to be physical rather than chemical.

Most solids and liquids manifest a tendency to enter into union or combi-
nation. There is, however, one substance which shows a remarkable indif-
ference to conbination of any kind, and from this indifference it has received
the name of parafiine {purum affinis).

Proofs of Chemical Change. — We generally look for certain visible results
as evidence of the chemical union or separation of substances ; but the
chemical force may have acted without causing visible changes ; and on the
other hand the condition of allotropy (see page 31) in elements and com-
pounds, shows us that such changes may take place without reference to the
chemical force. Photographic chemistry furnishes a remarkable instance of
the operation of chemical affinity, without any apparent physical alteration
in the condition of the compound. A dried fihn of pure iodide of silver on
glass, after it has received an impression from light, will retain its surface
unaltered for many hours, or even days ; we should not be able to distinguish
the exposed from the unexposed film ; but if the exposed stirface is washed
with a weak solution of pyrogallic acid or sulphate of iron, the silver is
reduced and blackened only in the parts which have received the luminous
impression, and in a degree precisely proportioned to the intensity with
which the impression has been made. There is perhaps nothing so wonder-
ful in the whole range of chemistry as the fact of thus revealing a dormant
image which has been produced without any apparent physical change in the
iodide of silver by the chemical rays of the spectrum. As a general rule, we

m

52 SINGLE AFFINITY.

cannot trust our senses as furnishing evidence of the chemical force being
brought into operation. We can only arrive at a knowledge of this fact by
a process well known under the name of analysis (ava -kv^, to separate), by
which we separate the component parts of a body. This may be either
qualitative, to determine the nature, or quantitative, to determine the pro-
portions, of the ingredients. Our analytical results may be confirmed by
synthesis {ovv tcOtjixi, to put together), ^. e. , by reconstructing the substance
from its constituent parts. The latter process is not always available, and it
is not indispensable to a correct view of the constitution of a body. It is
suflBcient if we examine the products of chemical combination, and compare
their weights and chemical properties with those of their constituents. The
following experiments will serve as an illustration of the processes of analysis
and synthesis, as applied to elements and compounds. We may analyze or
separate the constituents of hydrochloric acid — namely, chlorine and hydrogen,
by adding zinc to one portion of the acid, and peroxide of lead to another
portion. The zinc liberates the hydrogen, and the peroxide of lead sets free
the chlorine. If we now place a vessel containing chlorine over a jet of
hydrogen burning from a bottle, hydrochloric acid will be immediately
reproduced by synthesis and by the direct union of its elements. Among
compounds which readily admit of analysis and synthesis, is the chloride
of ammonium.

Place in two Florence flasks some of the powdefed chloride. Mix the
chloride of one flask with its bulk of dry lime, and apply a spirit-lamp to the
mixture. Ammonia, as a gas, will escape. Now add to the chloride in the
other flask suflBcient sulphuric acid to moisten the powder. Fumes of hydro-
chloric acid immediately escape. On bringing near to each other the mouths
of the flasks, the gases immediately combine to reproduce, by synthesis in
the air the chloride of ammonium which had undergone analysis, or been
resolved into its constituents in the two flasks.

Single Affinity. — The chemical force is usually studied under the heads of
single and double aflBnity ; and all analytical processes are dependent upon a
knowledge of the laws which govern these operations. In single affinity —
of three substances present, one is found to combine with another in prefer-
ence to a third. Let us assume that the three substances are the base
baryta in solution and two acids — ^. e., the sulphuric and nitric acids diluted
with water. On adding the solution of baryta to diluted nitric acid, there is
no visible change ; the base enters into a soluble combination with the acid,
forming nitrate of baryta. When the baryta is added to sulphuric acid, a
white insoluble precipitate appears (sulphate of baryta). Both the acids
therefore combine with the base, the one to form a soluble, and the other an
insoluble salt. If we now wish to discover which of the acids has the
stronger affinity for the base, we add sulphuric acid to the solution of nitrate
of baryta, and an insoluble sulphate of baryta immediately appears — the
nitric acid being set free. If we treat the precipitated sulphate of baryta
with nitric acid, it will undergo no change. A minute quantity of the pre-
cipitate may be dissolved, but the sulphuric acid still remains, combined with
the baryta. The only conclusion to be drawm from these facts, is, that
sulphuric acid hlis a stronger affinity for baryta than nitric acid, and that it
will take that base to the entire exclusion and separation of the nitric acid.
As a kind of choice is thus manifested, this has also received the name of
elective affinity. The change is represented by the following equation,
BaO,^iO,+S03=BaO,S03 + N05.

'\^\\ii i^vva precipitate has here been employed to indicate chemical change,
and it is desirable to define the proper meaning of a term which so frequently
occurs in chemical language. It is applied by chemists to signify that con-

ORDER OF DECOMPOSITION. 53

dition in which a substance dissolved in a liquid, is thrown down in a solid
form as the result of chemical change or decomposition. If the substance is
not dissolved, but diffused mechanically through the water, its falling to the
bottom is not true precipitation but subsidence, or the mere effect of its
greater specific gravity.

Precipitation always implies that the compound formed is less soluble in
the liquid than the substance which produces it. Sulphuric acid added to
lime-water produces no precipitate, because sulphate of lime is more soluble
than lime. If carbonic acid is employed, there is an immediate precipitate,
the carbonate of lime being much less soluble than lime. Precipitation may
occur rapidly or slowly, according to the solubility of the precipitate. It
may take place as the result of natural causes : thus in petrifying springs,
which owe their properties to carbonate of lime, dissolved by carbonic acid
in the water, a precipitate of carbonate of lime takes place in the form of
stalactite, owing to the escape of carbonic acid. The Geyser water in Iceland
deposits silicic acid, and all chalybeate waters produce, on exposure to air,
ochreous deposits of hydrated peroxide of iron, under similar circumstances.
The quantity of water present influences the production of a precipitate. A
diluted solution of a salt of lime is not precipitated by sulphuric acid, while
an equally diluted solution of a salt of baryta is precipitated, the difference
depending on the relativeinsolubility of the respective sulphates. The great
insolubility of precipitated chloride of silver renders it easy to detect the
minutest traces either of hydrochloric acid or silver. According to Mitscher-
lich, one part of hydrochloric acid diffused through 113 million parts of
water is rendered visible, as a white cloud or precipitate, by the addition of
a salt of silver.

The order of affinity of sulphuric acid for bases, may be Sulphuric Acid.
thus easily determined by experiment ; and upon this prin- ~
ciple, tables of affinity have been constructed, in which the gfj-^t^'a.
substance whose affinities are to be represented is placed at potassa.*
the head of a column, and the bodies with which it combines Soda.
beneath it, in the order of their respective attractions ; thus Lime,
the affinity of sulphuric acid for several bases is shown in the ^lagnesia.
table. From this it would appear that baryta separates sul- Oxidfeof^'ilver
phuric acid from its compounds with all the substances below
it, and that ammonia is separated by all those which are above it. It will
be found, however, by experiment, that if a solution of ammonia is added to
a solution of sulphate of magnesia, there is a precipitate of magnesia. If, on
the other hand, magnesia is boiled in a solution of sulphate of ammonia, the
magnesia combines with the sulphuric acid, and ammonia is evolved as a gas.
Hence the table rather shows the order of decomposition under one set of
circumstances. The relative affinity of the acid for magnesia or ammonia
will depend on the temperature of the mixture. If we take the base soda,
and examine the affinity manifested by it to the three acids — namely, the
boracic, sulphuric, and hydrochloric — we find that this resolves itself also
into a question of temperature.

Soda at 60°. Soda at a Red Heat.

Sulphuric. Boracic.

Hydrochloric. Sulphuric.

Boracic. Hydrochloric.

The result depends on the relative fixedness and solubility of the acid at
the temperature to which the mixture is exposed. If sulphuric or hydro-
chloric acid is boiled with borate of soda — on cooling the liquid, the boracic

w

54

REVERSAL OF AFFINITY.

acid is precipitated by reason of its insolubility in water at a low tempera-
ture ; and sulphate of soda or chloride of sodium remains dissolved. If,
however, the precipitated acid be mixed with the solid sulphate, or chloride
obtained by evaporation, and the mixture is submitted to a full red heat,
borate of soda is reformed, and the more volatile sulphuric and hydrochloric
acids are entirely expelled. The fixedness of boracic acid at a hl^h temper-
ature here causes a reversal of the order of combination.

These tables are of great use in analysis, inasmuch as the exceptional cases
are not numerous, and are easily remembered. They may be made applicable
to elements as well as compounds. We here give tables representing the
order of affinity of lime in solution at 60° for four common acids : also for
some of the combinations of hydrogen with non-metallic bodies, and of
oxygen and chlorine for various metals : —

Lime.

Hydrogex.

Oxygen.

, Chlorine.

Oxalic.

Chlorine.

Hydrogen.

Magnesium.

Sulphuric.

Bromine.

Magnesium.

Zinc.

Acetic.

Iodine.

Zinc.

Lead.

Carbonic.

Sulphur.

Lead.

Tin.

Tin.

Hydrogen.

Copper.

Copper.

Mercury.

Mercury.

Silver.

Silver.

The results thus arrived at are often susceptible of important practical
applications. The liquid in which a salt is dissolved may cause a reversal
of the order of affinity. Thus, if to a strong solution of carbonate of potassa
in water, we add acetic acid, carbonic acid is expelled, and acetate of potassa
is formed and dissolved (KO,C03+Ac=KO,Ac4-C02 in water). If, how-
ever, we pass a current of carbonic acid gas for some time into a saturated
solution of acetate of potassa in alcohol, the gaseous displaces the liquid acid,
and carbonate of potassa is reproduced (KO,Ac + C03=KO,C0^4-Ac in
alcohol). The insolubility of the alkaline carbonate in alcohol, and its im-
mediate removal by precipitation, appear to explain this change in the order
of affinity. If water is added to the alcoholic liquid, the precipitated car-
bonate is redissolved.

Oxide of lead combines readily with carbonic and acetic acids, forming a
carbonate and an acetate of lead. If acetic acid is added to carbonate of
lead, the carbonic acid is displaced, and acetate of lead is formed ; but if a
solution of acetate of lead is exposed to an atmosphere containing carbonic
acid, carbonate of lead is formed and the acetic acid is expelled. The manu-
facture of white lead (carbonate of lead) depends upon this reversal of affinity.
The metal is exposed to the fumes of acetic acid, and the formation of an
acetate is the first step in the production of a carbonate.

This fact appears to support the view of those who believe that chemical
affinity between substances is to some extent governed by the relative pro-
portion or mass of the displacing agent. The changes which chloride of
silver undergoes b^ exposure to light, also tend to corroborate this opinion.
When not absolutely dry, chloride of silver, which is of snow-white appear-
ance, is darkened by exposure to light. In fact it is superficially converted
into subchlorlde (2AgCi=Ag^Cl + Cl). The quantity of chlorine thus set
free is small. Rose found, by using a delicate balance, that there was no
difference in weight between the white and dark chloride. Chlorine water
added to the dark chloride renders it again white.

Decomposition by single affinity may take place, although it is not mani-
fested by the precipitation of a solid or the visible escape of gaseous matter.

PREDISPOSING AFFINITY. DOUBLE AFFINITY. 55

If we boil gold-leaf with some crystals of nitre dissolved in water, there is
no change; if we boil the gold in pure hydrochloric acid, there is no change ;
but if the two are mixed, the gold is immediately dissolved. The solution of
the gold proves that chlorine has been evolved. This could only proceed
from the decomposition of a part of the hydrochloric acid by the nitrate of
potash. Under ordinary circumstances a watery solution of nitre may be
mixed with hydrochloric acid without any perceptible decomposition of either
body.

An interposed animal membrane does not prevent the manifestation of this
force. If a tube containing a weak acid solution of acetate of lead is well
secured at the mouth with a piece of bladder, and the outer surface of the
bladder is then placed downwards on a clean surface of metallic zinc — in
the course of a short time crystals of lead will be deposited on the bladder
inside the tube ; and the solution will contain acetate of zinc, a fact which
proves that the zinc has traversed the bladder either as oxide or metal, and
has displaced an equivalent proportion of lead in the solution. This is
effected by capillary osmosis of a part of the solution of acetate of lead, and
its simultaneous conversion into acetate of zinc.

Predisposing or Concurrent Affinity. — If zinc is covered with hydrochloric
acid it displaces the hydrogen, which escapes, and chloride of zinc is formed;
if covered with water, this liquid is not decomposed until an acid (sulphuric)
is added, when hydrogen immediately escapes, and an oxysalt of zinc is pro-
duced and dissolved. This has been called predisposing affinity, but it should
rather be regarded as concurrent affinity. Two affinities are here brought
into play : there is the affinity of zinc for oxygen, and of the acid for oxide
of zinc, and these are sufficient to decompose the water. This principle is
the basis of many chemical operations. In the manufacture of aluminum,
carbon as charcoal cannot alone remove the oxygen from alumina (the oxide
of aluminum) ; but if chlorine is passed over a mixture of alumina and char-
coal heated to a high temperature, the carbon readily takes the oxygen, and
the chlorine now combines with the aluminum. Platinum cannot be made
to unite to oxygen directly ; but, if caustic potash is fused on the metal, this
is oxidized and destroyed by reason of the tendency of the alkali to combine
with oxide of platinum. Iron does not rust in air free from moisture, ^. e.,
it will not take the oxygen from dry air. Again it will not combine, with
the oxygen of water at common temperatures, except when air is present.
In order that oxidation may take place, it is necessary that air and water
should be present at the same time. It is a well-known fact that gold is not
acted upon, or dissolved by sulphuric acid or nitric aeid, even at a boiling
temperature. But if a drop of nitric acid is added to the mixture of sul-
phuric acid with gold-leaf while boiling, the metal instantly disappears
and enters into some unknown form of combination with the sulphuric acid.
When the acid solution is cooled and added to water the gold is thrown
down as a purple precipitate in the metallic state.

Double Affinity. — In double affinity there is a reciprocal interchange of
elements, or, in reference to salts, of acids and bases, so that two new com-
pounds are produced. One of the simplest cases is seen on the admixture
of hydrochloric acid and a solution of soda. Chloride of sodium and water
result (XaO + HCl = XaCl-f-IIO). Among numerous instances which may
be taken from the class of salts, there is the reaction of sulphate of potash
on nitrate of baryta, by which sulphate of baryta and nitrate of potash are
produced (KO,S03 + BaO,N05==BaO,S03-|-KO,NO.,). In this case one in-
soluble salt only is formed -and precipitated; but two soluble salts may be
changed into two perfectly insoluble compounds, as in adding a solution of
sulphate of silver to chloride of barium (both soluble) when sulphate of

56 DOUBLE AFFINITY. DECOMPOSITION.

baryta and chloride of silver (both insoluble) result. Thus AgOjSOg + Ba
Cl=BaO,SO.j4-AgCl. This decomposition forms one of the steps in the
production of pure peroxide of hydrogen. Double affinity generally furnishes
to the chemist a more perfect method of decomposition than single affinity.
Thus oxalate of ammonia more effectually precipitates lime than oxalic acid.
A solution of arsenious acid does not readily decompose solutions of sul-
phate of copper or nitrate of silver; but if the acid is combined with a small
quantity of alkali (ammonia), the precipitation of insoluble arsenites of the
metals by double affinity is immediate and complete.

In general it may be inferred that two salts will decompose each other,
when, by interchange, an insoluble compound or precipitate can result.
Solubility, however, is a purely relative term, and precipitation must there-
fore often depend on the quantity of water present in the saline solutions.
Nitrate of baryta gives a dense white precipitate with a solution of borate
of soda, provided the two solutions are concentrated. If much water is
present, there Vill be no precipitation on mixture ; a fact also proved by the
re-dissolution of the precipitate on adding a quantity of water. Sulphate
of soda will precipitate a salt of lime, and chloride of platinum a salt of
potassa, provided the respective solutions are concentrated ; but if much
diluted, there will be no precipitate. The platino-chloride of potassium,
although precipitated from potassa or its salts, by a solution of chloride of
platinum, is sufficiently soluble in boiling water to precipitate from their
solutions the salts of rubidium and caesium, the platino-chlorides of which
metals are far less soluble than the corresponding salt of potassium. Tliis,
in fact, is the only available method of separating the salts of the two new
metals from the salts of potassium. While the degree of dilution always
affects the production of a precipitate, it sometimes so completely changes
its character that it might be fairly inferred that two different compounds
were under examination. Thus if nitrate of silver is added to a concentrated
solution of borate of soda, a white borate of silver is precipitated : if the
solution of borate is much diluted, nitrate of silver gives a brown precipitate
resembling oxide of silver. Sulphocyanide of potassium produces, in a con-
centrated solution of a salt of copper, a black precipitate of sulphocyanide,
which slowly becomes gray and white ; in a moderately diluted solution a
gray precipitate is thrown down, and in a very diluted solution a white pre-
cipitate of sub-sulphocyanide is slowly formed.

Precipitates are sometimes readily dissolved by the precipitant : thus the
scarlet iodide of mercury is easily dissolved by a solution of iodide of potas-
sium. This renders it necessary to employ tests with caution, or the pre-
sence of a substance may be overlooked. When the double decomposition
of two salts does not take place in the cold, it may be brought about by
heating the mixture.

Double affinity is liable to be modified by all the causes which affect single
affinity. If a mixture of dry chloride of sodium and sulphate of ammonia
is heated, chloride of ammonium is sublimed, and sulphate of soda remains.
This is one method of manufacturing sal ammoniac from the ammoniacal
liquor of gas-works. When the two salts are intimately mixed with a small
quantity of water, the temperature rises and the mass rapidly dries. There
is a double decomposition, and the sulphate of soda produced absorbs water
of crystallization. Each of the salts alone lowers the temperature during
the act of solution. {Chem. Neivs, Sept. 5, 1860.) But when powdered sul-
phate of soda is well mixed with chloride of ammonium at 60°, there is a
reversal of the affinities — anhydrous sulphate of ammonia and common salt
are produced, while the water of crystallization of the soda-sulphate is set
free, the mass acquiring a liquid consistency. (See page 34.) When solu-

PROOFS OP INTERCHANGE OF ACIDS AND BASES. 57

tions of these two salts are mixed, there is, aocordinp: to SchifiF, an increase
of volume owing to the setting free of water of crystallization.

Salts having the same acid or base do not precipitate each other. Thus a
solution of sulphate of lime does not decompose sulphate of soda or chloride
of calcium. On this principle, the last-mentioned salt is employed to deter-
mine whether the alkalinity of river-water depends on the presence of the
carbonate of potassa or soda, or of the bicarbonate of lime. In the former
case, it gives a precipitate ; in the latter none.

But double affinity may be exerted between two salts in cases in which
there is no visible change or decomposition. AYhen a solution of nitrate of
soda is mixed with chloride of potassium, and this mixture is boiled, chloride
of sodium, or common salt, is separated, because it is the least soluble of the
salts at a boiling temperature, and therefore requires the largest amount of
water to hold it in solution. (See page 30.) If the saturated sc^lutions of
the two salts are kept at a low temperature, nitrate of potassa crystallizes
out of the liquid. In either case there is an interchange of acid and base
dependent on the relative solubility of the salts at a given temperature
(NaCNOj-f KCl=NaCl-f KO,NO/). The process above mentioned has
been employed in Prussia for the manufacture of nitre. The manufacture of
sulphate of magaesia from sea-water is dependent on a similar decomposition.
Sulphate of soda added to a solution of chloride of magnesium or bittern,
produces no visible change ; but when boiled, the compounds are resolved
into chloride of sodium and sulphate of magnesia. The former is separated by
evaporation of the liquid at the boiling-point, the latter by allowing the cold
saturated solution to deposit crystals (NaO,S03-fMgCl=NaCl + MgO,S03).

The production of a color on the admixture of colorless solutions of salts
is evidence of at least a partial interchange of acids and bases. A very
diluted solution of ferrocyanide of potassium added to extremely diluted
solutions of sulphate of copper and persulphate of iron, produces in the one
case a red, and in the other a blue color in the liquid. These results furnish
chemical proofs that the ferrocyanogen of the potassium-salt has, at least in
part, united to the metals of the copper and iron salts. Sulphocyanide of
potassium may be substituted for the ferrocyanide in reference to iron ; and
in this case a blood-red color, but no precipitate, results. Berzelius long
since devised an ingenious experiment by which the interchange of acid and
base in two salts was clearly proved by the peculiar color acquired on mixture.
Of the diluted solutions of the salts of copper, the nitrate and sulphate remain
blue when boiled ; but the diluted chloride, which is blue at 60°, acquires a
bright green color at 212°. This change of color is therefore a distinguishing
test among these salts, of the presence of chloride of copper in a diluted
state. A solution of chloride of sodium is colorless and remains so at all
temperatures. When a diluted solution of nitrate of copper is added to a
diluted solution of chloride of sodium and the mixture is heated, it acquires
a bright green color, thus proving that some portion at least of the nitrate
of copper must have been converted into chloride of copper, and therefore
that an interchange of acids and bases must have taken place. If the two
solutions are highly concentrated, the interchange takes place at 60°, since
the mixture in the cold has a greenish color — the color of the chloride of
copper when in a more concentrated form.

We have hitherto treated the saline compounds as if both were soluble in
water ; but cases of double aflBnity are witnessed, in which one salt is soluble
and the other is insoluble. If insoluble sulphate of baryta or oxalate of
lime is boiled in distilled water with soluble carbonate of potassa for a short
time, and the respective liquids are filtered — it will be found that a partial
interchange of acids and bases has taken place, and while the filtrates (the

58 CATALYSIS.

filtered liquids) will contain two soluble salts (the carbonate of potassa
associated either with the sulphate or oxalate of potassa), the white residues
on the filters will contain, besides sulphate of baryta and oxalate of lime,
the insoluble carbonates of baryta and lime. Four salts are in each case
produced, as represented in the following equation, in which the decomposi-
tion is given only for the sulphate of baryta, 2(BaO,SOJ + 2(KO,C02) =
KO,S03-}-KO,C03andBaO,S034-BaO,CO.,. This mode of decomposition is

^ > ' * '-y '

Soluble. Insoluble.

sometimes resorted to, in order to render an insoluble compound sufficiently
soluble for the purpose of testing. The silicification of chalk or soft lime-
stone is based on this principle. The mineral is soaked in water-glass, or a
solution of silicate of potash or soda, and it is afterwards exposed to the air;
silicate of lime and bicarbonate of potassa or soda result. The surface of the
chalk is thus hardened and rendered impermeable to water. It is probable
that the presence of Epsom salt, or sulphate of magnesia, in spring waters
in certain districts, is dependent on a natural reaction of this kind. Water
containing sulphate of lime flowing over a bed of magnesian rock (carbonate
of magnesia) becomes impregnated with sulphate of magnesia, a portion of
the lime being exchanged for this base. If carbonate of magnesia is agitated
with a solution of sulphate of lime, sulphate of magnesia will soon be found
in the filtered liquid, by appropriate tests.

Double affinity is not prevented by the interposition of animal membrane.
If the mouth of a tube containing sulphate of soda is well secured with
bladder, and inverted in a vessel containing a solution of nitrate of baryta —
or if the nitrate of baryta be secured in a tube, and the soda-sulphate is
placed in an open vessel, double decomposition is observed to take place.
In performing this experiment many times, however, we have noticed that
the white precipitate of sulphate of baryta has been formed in the tube
containing the nitrate, and not in that containing the sulphate of soda.

Catalysis (from xara downwards, and -kvc^ to loosen) is a term which was
first employed by Berzelius, to explain those cases in which two or more
bodies are combined by the presence of a substance which itself takes no
share in the chemical changes. A body is thus supposed to resolve others
into new compounds merely by contact, without gaining or losing anything
itself. When a mixture of oxygen and hydrogen is exposed to the action of
spongy platinum, the gases combine to form water; when alcohol is dropped
on platinum-black under exposure to air, the alcohol is oxidized and con-
verted into acetic acid ; when a ball of spongy platinum, made red hot, is
placed on a mass of camphor, it continues to glow, and causes a slow
combustion of the camphor ; when a ball of platinum is made white hot and
plunged into water, it causes the separation of the constituent gases oxygen
and hydrogen ; and lastly, when fine platinum wire is heated red hot, and
exposed to a mixture of coal-gas and air, it continues to glow, and leads to
a slow combustion of the gas. In these cases the platinum has produced
combination as well as decomposition, but it has undergone no change. We
have witnessed a similar effect with charcoal placed in a mixture of oxygen
and sulphuretted hydrogen. The gases were combined with explosion, but
the charcoal underwent no change. The power of charcoal to absorb and
remove foul effluvia, by leading to their oxidation, may be regarded as a
similar phenomenon ; but all these are simple cases of the absorption and
condensation of gases by the platinum and charcoal, and not referable to
any new force or to any occult effect of contact or presence.

Sulphur, it has been already stated (p. 47), will unite at a high tempera-
ture to India-rubber, and will then produce in it the effects indicated by the

ELECTROLYSIS. 59

term vulcanization — i. e., change of color, infnsibility, great increase of
elasticity, and a resistance to heat and cold. The vulcanized rubber when
boiled in a solution of sulphite of potash is desulphured ; it reacquires its
usual appearance, but it still retains the properties which the sulphur
imparted to it. This has been ascribed to a catalytic action, for the sulphur
itself has undergone no change.

The production of anhydrous chloride of magnesium, according to Mits-
cherlich, turns upon a similar state of circumstances. If hydrochloric acid
is saturated with hydrate of magnesia, and the liquid is concentrated and
cooled, large crystals of chloride of magnesium combined with water are
obtained. If these crystals are heated, like those of other chlorides, in order
to expel the water, the hydrochloric acid escapes and magnesia remains. If,
however, equal weights of hydrochloric acid are saturated with magnesia and
ammonia, and the two solutions are mixed and evaporated to dryness, the
residue, when heated to fusion in a platinum crucible, consists entirely of
anhydrous chloride of magnesium ; the whole of the chloride of ammonium
having been expelled. Here chloride of ammonium causes a fixed combina-
tion of the elements, apparently by a catalytic force.

Catalytic results are obtained with compounds as well as with simple
substances. The production of oxygen at a low temperature, from a mixture
of peroxide of manganese, or of iron with chlorate of potash, has been
referred to an action by catalysis or presence. The facts, however, admit of
another explanation. {See Ozone.) The decomposition of peroxide of
hydrogen by contact with a variety of metals and oxides, was generally
explained by reference to catalysis, until the recent views of Schonbeia had
been made public.

There are many changes in organic compounds which have been referred
to catalysis — e. g., the conversion of gum and starch to sugar, of alcohol to
ether by sulphuric acid, and of sugar to alcohol by a ferment ; but there are
here numerous reactions depending on a variety of causes; and as science
progresses, and these reactions become better understood, the use of this
term may be rendered necessary.

Electrolysis. — (iJiaxT-pov, t-vw, to loosen by electricity.) — This term is
applied to the electro-chemical decomposition of substances as a result of
the electric current. The electric fluid serves to unite as well as to disunite
bodies ; and in producing their disunion or separation there is this remarka-
ble difference from the chemical force — namely, that as current electricity
it transports and collects at particular points, called poles, the elements or
compounds which are separated.

When the electrodes or poles of a voltaic battery are brought near to each
other in certain liquids, such, for instance, as acidulated water and saline
solutions ; or, in other words, when these liquids are made part of the elec-
tric circuit, so that the current of electricity can pass through them, decom-
position ensues ; that is, certain elements are evolved in obedience to certain
laws. Thus water, under these circumstances, yields oxygen and hydrogen ;
and the neutral salts yield acids and alkalies. In these cases, the ultimate and
proximate elements appear at the electrodes or poles — not indiscriminately,
or indifferently ; but oxygen and acids are evolved at the anode, or surface at
which the electricity enters the electrolyte ; and hydrogen, and alkaline bases,
at the cathode, or surface at which the electric current leaves the body under
decomposition.

All compounds susceptible of direct decomposition by the electric current
are called electrolytes ; and when electro-chemically decomposed, they are said
to he electrolyzed. Those elements of the electrolyte which are evolved at
the anode are termed anions, and those which are evolved at the cathode,

60

ELECTROLYSIS.

cations {avlov, that which goes upwards ; xa-tlov, that which goes downwards),
and when these are spoken of together, they are called 'ions : thus when acidu-
lated water is electrolyzed, two 'ions are evolved, oxygen and hydrogen, the
former being an anion, the latter a cation.

In all /?n/wary electro-chemical decompositions, the elements of compounds
are evolved with uniform phenomena either at the anode or cathode of the
electrolyte ; hence their division into electro-negative and electro-positive
bodies, or, into anions and cations. The latter have more recently received
the name of hasylous bodies, as by combining with oxygen they form a large
class of bases. But it frequently happens that the evolution of a substance
at the electrode is a secondary effect; sulphur, for instance, in the decom-
position of sulphuric acid, is evolved at the cathode or negative pole, not by
direct electrolysis, but in consequence of the action of the nascent hydrogen ;
and whenever sulphur is obtained by primary electrolytic action from a com-
pound containing it, it is evolved at the anode, or positive pole ; hence, in
classifying the elements according to their electrical relations, this distinc-
tion must be observed. It is also necessary to guard against the combina-
tion of the substance (or Ion), with the electrode ; hence the advantage of
platinum electrodes, that metal being acted upon by very few of them.

The following table of simple and compou7id ions has been drawn up by
Faraday ; —

ELECTRO-NEGATIVE BODIES OR ANIONS.

Oxygen

Cyanogen

Phosphoric acid

Citric acid

Chlorine

Sulphuric acid

Carbonic acid

Oxalic acid

Iodine

Selenic acid

Boracic acid

Sulphur

Bromine

Nitric acid

Acetic acid

Selenium

Fluorine

Chloric acid

Tartaric acid

Sulphocyanogen.

ELECTRO-POSITIVE BODIES OR CATIONS.

Hydrogen

Tin

Mercury

Strontia

Potassium

Lead

Silver

Lime

Sodium

Iron

Platinum

Magnesia

Lithium

Copper

Gold

Alumina

Barium

Cadmium

Protoxides generally

Strontium

Cerium

Ammonia

Quinia

Calcium

Cobalt

Potassa

Cinchonia

Magnesium

Nickel

Soda

Morphia

Manganese

Antimony

Lithia

■ Alkaloids generally.

Zinc

Bismuth

Baryta

Compounds only undergo electrolysis : and in order to act as electrolytes,
the compound, if a solid, must be in a state of solution or fusion. Electro-
lysis is always definite in amount. Thus the quantity of electricity produced
during the solution of 32 grains of zinc, is equivalent to the decomposition
of 9 grains of water. Electrolytes differ in the facility with which they yield
up their elements to the influence of the electric current, or in the resistance
which they offer to electro-chemical decomposition. The following bodies
are electrolytic in the order in which they are placed, those which are first,
being decomposed by the current of lowest intensity : —

Iodide of potassium (solution) Chloride of zinc (fused)

Chloride of sodium (solution) Chloride of lead (fused)

Sulphate of soda (solution) Iodide of lead (fused)

Chloride of silver (fused) Hydrochloric acid (solution)

Water acidulated by sulphuric acid.

The intensity of the current is in proportion, 1, to the difference in
oxidizing power (by the action of the oxygen and the acid) on the two

PRISMATIC OR SPECTRUM ANALYSIS. 61

metals employed ; 2, to the increase of surface of the metals ; and 3, the
increase of acid on the intensity of chemical action. The first condition is
remarkably illustrated by platinum and magnesium. If a coil of platinum
is placed round a band of magnesium and this is immersed in distilled water,
an electric current is slowly set up, and hydrogen is slowly evolved with-
out the addition of an acid. If a few drops of any acid are added, there
is a rapid evolution of hydrogen partly as the result of chemical, and partly
of the electrical force.

As a result of the chemical force, we may deposit copper on iron or zinc,
by immersing either of these metals in a solution of a salt of copper ; but if
for iron and zinc we substitute silver and platinum, no deposit will take
place, these metals having less affinity for oxygen and acids than copper.
If, however, we wrap a coil of zinc round the bar of silver or platinum, and
then immerse it into a solution of copper; the metal copper will now be
deposited on the silver and platinum as a result of the electric current set
up between the two metals. In this case both the chemical and electrical
forces operate to cause a separation and deposition of metallic copper. By
electrolysis any metal may be thus deposited on any other metal, or on any
organic substance, such as a feather or insect, provided it can receive a
metalline or conducting surface.

Prisinatic or Spectrum Analysis. — Chemists have for many years relied
opon the colors given by the salts of various metals, to the colorless flames
of alcohol, or coal gas, as a useful aid to qualitative analysis. MM. Kirchoff
and Busen, by their researches on the colored flames of metals, have arrived at
an entirely new method, which has enlarged greatly the scope of chemical
reactions, and has led to some important discoveries. This method consists
in not merely relying as, hitherto, upon the color imparted to a flame, but in
decomposing the colored light by a prism ; in other words, in submitting
the colored flame to a minute prismatic analysis. Their observations have
been chiefly directed to the detection of the metals of the alkalies and
alkaline earths. They have employed pure salts of these metals, as well as
various mixtures of them, and they have found that the more volatile the
metallic compound on which they operated, the brighter was the spectrum
which they obtained. A high temperature was generally required: a
coal-gas flame of a Bunsen's burner, of which the heat was estimated at
2350^ C, was found to be sufiBcientfor the alkaline metals, and the colorless
nature of this flame rendered it otherwise well adapted for the spectralytic
observations. The alkaline salt in minute quantity was placed on the end
of a fine platinum wire (bent into a hook and flattened, if for a solution),
and this was introduced into the lower part of the colorless coal-gas flame.
The light of the colored flame was then make to traverse a prism of sulphide
of carbon, having a refracting angle of 60°; and as it issued from the prism
it was examined by a small telescope.

The reader will find a description of this apparatus, and of the method of
employing it, in the Philosophical Magazine for August, 1860, page 91, and
the PharmaceuiicalJournal, February, 1862; but it has since been superseded
by more convenient instruments. The colored flame of each metal, even in
the minutest quantities, was found to give a well-marked and characteristic
spectrum. Compared with the spectrum of solar light, the actual amount
of colored light was very small, and this was distributed without any kind
of order, in a series of bands or stripes of different widths and intensities,
the bands of color taking up the situation of the corresponding spectral
colors. Sodium was observed to give a single or a double line of yellow
light only,, in a position corresponding to the orange rays of the solar
spectrum. Potassium, besides a more diffused spectrum, gave a red line ia

I

C2 DETECTION OF ALKALINE METALS.

the extreme red rays, and a violet line in the extreme violet rajs. Lithium
gave a dark spectrum, with only two bright lines, one a pale yellow
corresponding to the red rays. Strontium, barium, and calcium, the only
three alkaline earthy metals which give spectra (magnesium not being
volatile in this flame), are remarkable for the number and variety of the
colored bands which they present. Strontium presents eight characteristic
lines — six red in the part corresponding to the red rays, one broad orange
band parallel to the orange rays, and at some distance from these a blue
line, in the situation of the blue rays. The spectra of barium and calcium
are distinguished from the others by the number of green bands which they
present, ^wo of these in the situation of the green rays characterize barium.
There are, besides these, three other green bands, and several yellow, orange,
and red lines. Calcium presents one broad green band in the situation of
the yellow-green rays; and a bright orange band near the red rays, besides
several smaller orange lines. The new alkaline metal Ccesium {ccBsius,
sky-color), discovered by Bunsen in the waters of Durckheim and Baden, as
well as in most spring-waters containing chloride of sodium, presents two
distinct grayish-blue lines in the parallel of the blue rays, and no other
colored bands or lines. The other new metal, Rubidium, found by Bunsen
in the waters of Hallein and Gastein, derives its name from the two splendid
red lines in its spectrum ; these are of a low degree of refrangibility.
Thallium gives the most simple spectrum known : it consists of one bright
green band in the situation of the green rays of the solar spectra. The
optical characters of the spectra are constant for each metal, and are equally
well marked in size and position under all varieties of flame, even of that
given by the electric discharge.

Bunsen estimated that the amount of sodium which admitted of detection
by prismatic analysis was the 195,000,000th part of a grain; of lithium, the
10,000, 000th; of potassium the 60,000th; of barium the same; of strontium
the 1,000,000th; and of calcium the 100,000,000th of a grain I

The delicacy of the sodium reaction accounts for the fact that all bodies,
after a lengthened exposure to atmospheric air, show when heated, the sodium
line. Even ignited air and all kinds of dust show the yellow tinge of sodium.
Fine platinum wire or foil, however clean, if exposed to air for a short time,
has been observed to give a yellow color to flame, owing, as it is supposed,
to the deposit upon its surface of sodium derived from the atmosphere.
Three-fourths of the earth's surface are covered with sea-water, and the
niinutely diffused chloride of sodium may, it is supposed, be thus spread
through the whole of the atmosphere. Lithium, which was supposed to be
a rare metal, also appears by this mode of analysis to be very widely
distributed. Bunsen found it in about an ounce and a half of the waters of
the Atlantic Ocean; in the ashes of kelp from Scotland ; the ashes of tobacco,
of vine-leaves, and of plants growing on various soils. It was found in the
milk of animals fed fronj these crops, and it was detected by Dr. Folsvarczny
in the ash of human blood and muscular tissue. It has also been discovered
in the residue of Thames-water, in Stourbridge clay, and in meteoric stones.
It is a curious fact that the intermixture of these alkaline metallic compounds
does not materially interfere with the optical as it does with the common
steps of a chemical analysis. Thus a drop of sea-water shows at first a
sodium-spectrum; after the volatilization of the chloride of sodium — a
calcium-spectrum appears, which is made more distinct by moistening the
platinum wire with hydrochloric acid. By treating the evaporated residue
of sea-water with sulphuric acid and alcohol, potassium and lithium-spectra
are obtained. The strontium reaction is best procured by digesting the
boiler-crust of sea-going steamers in hydrochloric acid, and employing •

DETECTION OF ALKALINE METALS. 63

alcohol as a solvent. By this process of analysis, most mineral waters are
found to contain all the alkalies and alkaline earths excepting the compounds
of barium.

The different degrees of volatility in the alkaline metals are favorable to
their detection in a state of mixture. Thus a solution containing less than
the 600th of a grain of each of the following chlorides — potassium, sodium,
lithium, calcium, strontium, and barium — was brought into the flame. At
first the bright sodium line appeared, and when this began to fade the
bright-red line of lithium was seen, while at some distance from the sodium
line the faint red line of potassium came into view, and with this two of the
green barium lines; the spectra of the potassium, sodium, lithium, and barium
salts gradually faded away, and then the orange and green calcium lines
showed themselves in their usual positions. {Phil. Mag.^ Aug. 1860, p. 106.)
The presence of organic matter in large quantity does not interfere with the
production of simple spectra. Thus it has been found that a portion of the
dried liver of an animal, to which a salt of thallium had been given, yielded,
when burnt, a spectrum, in which the peculiar green line of this metal was
visible. Among other novel applications of this branch of analysis, may be
mentioned the proposal to employ it in the manufacture of cast-steel. In
the new process of melting the metal, it is important to know the exact^^
moment at which to shut down the cover of the furnace ; time must be w #
allowed for the escape of the gaseous products which are injurious to the
steel, but if that time be prolonged, an injurious effect of another kind is ^
produced. To meet this contingency it has been proposed to test the gases
as they fly off, by means of the spectroscope; and as soon as the particular
color is observed, peculiar to the gas, which begins to escape at the moment
the molten metal is in proper condition, the manufacturer will then have an
infallible sign of the proper moment for closing the furnace.

It has been successfully employed for the detection of the coloring matter
of blood. Every red color, mineral or organic, which is soluble in water,
has its peculiar spectrum with special bands of absorption.

An improvement has been recently made in the prismatic apparatus by
which the spectra of two flames may be examined at once. Thus any doubt
respecting the presence of the substance from the colored bands in one
spectrum, may be removed by introducing a portion of the suspected sub-
stance into the second flame, so that the two spectra may be seen side by
side, and compared. In employing this method of analysis, it is often
necessary to compare the solar spectrum with the spectrum of the substance
under examination. A spectroscopic eye-piece has been invented by Mr.
Sorby, which may be adapted to any good microscope. By this invention,
any two spectra may be at once examined and compared. This enables the
observer to determine with accuracy the bands of absorption and their exact
position, compared with the colors of the solar spectrum.

It has been observed that gases ignited by the electric spark from
Ruhmkorff's coil give spectra of a remarkable kind. Thus hydrogen through
which the electric discharge is passed, gives a spectrum having an intensely
red line like that of lithium, and a bright band of green, which can be split
up into a j^umber of thin and beautiful green rays (Roscoe). Spectra of
nitrogen, chlorine, and other gases rendered incandescent, have been obtained
by various observers, and it is not improbable that gases generally and their
complex mixtures may be hereafter qualitatively determined by this method,
like the compounds of alkaline metals.

The platinum poles of a battery, simply ignited, give a violet blue platinum
spectrum ; and if a salt of copper, iron, chromium, nickel, or other metal,
be placed upon them, a spectrum peculiar to each metal is brought out, but

i

i

64 ATOMIC OR COMBINING WEIGHTS.

instead of a few lines of color, as in alkaline metals, they occur in many
hundreds. Dr. Roscoe describes seventy brilliant lines in the iron spectrum,
of all degrees of intensity and breadth. The most prominent of these lines
may, however, be selected for identity. Kirchoff states that he has thus
been able to distinguish the compounds of the rare metals — yttrium, erbium,
terbium, lanthanum, didymium, and cerium. The spectra obtained from a
mixture of the common metals, are not so distinct as those of the alkaline
series. Thus in German silver, the spectrum may show only one of the
constituents (Roscoe). The spectra of the common metals require a much
higher temperature {i. e., the electric spark of Ruhmkorff's apparatus) for
their production, and they are then liable to be mixed with the spectra of
the platinum poles, as well as those of the metalloids, which constitute the
acids or radicals of their salts.

As these discoveries are at present in their infancy, it is difficult to specu-
late upon the practical results to which they may ultimately lead. In
reference to the qualitative analysis of the alkaline salts, they will enable a
chemist not only to detect the respective metals, with great rapidity, in
quantities inconceivably minute ; but they may also enable him to detect
these quantities in mixtures with each other, with a certainty which no other
known analytical process can furnish. On further research they may serve
to. identify, with nearly equal certainty, the salts of other metals, either alone
or in a state of admixture. Quantitative analysis, by the usual processes,
must, however, be still resorted to, in order to determine the proportion of
ingredients by weight in a compound; and as it is impossible to weigh a
smaller quantity than the 1000th part of a grain, chemists may in future be
compelled to assign to a compound many substances which do not admit of
a determination by weight. The extreme delicacy of this photo-chemical
method is likely to create the greatest difficulty in its practical application.
When a mineral-water like that of Baden is thereby shown to contain all the
metals of the alkalies and alkaline earths, excepting barium, besides two
new metals, one of them (the more abundant) existing only in the proportion
of one part in a hundred million parts of the water, the question will really
be, whether there can be any assigned limits to the number of substances
which may be discovered by such a mode of analysis.

CHAPTER IV.

EQUIVALENT WEIGHTS AND VOL UME S— NOM ENC L ATURE
AND NOTATION.

Determination of Equivalent Weights. — It has been already described as a
special character of a true chemical compound, that its constituents combine
in fixed proportions, which are represented by figures, an'd are called equiva-
lent or atomic weights. For the determination of these weights, a series of
careful analyses of the substance are made. To take water as an example,
there is no compound in chemistry of which the constitution has been so
accurately determined, both analytically and synthetically, as of this. In
100 parts by weight, it is found to contain 11.09 of hydrogen, and 88.91 of
oxygen. These proportions reduced to their smallest denomination would
be represented by the figures 1 and 8 ; or if, instead of making hydrogen

CALCULATION OF EQUIVALENT WEIGHTS. 65

unity, we assumed that oxygen combined as 1, then hydrogen would be
represented by the decimal 0125. As, however, this last assumption would
lead to a very inconvenient use of decimals, the standard of unity is assigned,
by most chemists, to hydrogen : and the selection of hydrogen has this great
advantage, that being the lightest body in nature, and combining relatively
in the smallest weight, the figures representing the equivalents of the other
bodies are comparatively low and are easily remembered. The numbers 1
and 8 therefore respectively represent the atomic weights of hydrogen and
oxygen, on the assumption that one atom of each element is contained in
the compound, the atom of hydrogen being equal to a whole volume, and
that of oxygen being considered to represent half a volume of this element.
The weight of the atom of water is, therefore, on this assumption, 9, the sum
of the weights of its two constituents.

All bodies combine either with hydrogen or with oxygen, and the atomic
weight of any body may be therefore found by analyzing its compound with
either of these elements, and determining by the rule of proportion how much
by weight enters into combination with 1 part of hydrogen or with 8 parts
of oxygen. The atomic weight of sulphur may be thus determined. 100
parts of its compound with hydrogen {Sulphide of Hydrogen) are composed
of 941 of sulphur and 5 9 of hydrogen : hence 941 ^5 9=15*9, or, allow-
ing for differences of analysis, 16, the atomic weight of sulphur. Again,
hydrochloric acid consists in 100 parts of 9t'26 chlorine and 274 hydrogen :
hence 97*26-7-2-t4 = 35'49, or, in round numbers, 36, the atomic weight of
chlorine.

It will be understood that these figures do not represent the absolute, but
merely the proportional weights in which bodies combine. We have no
knowledge of the absolute weight of an atom of any substance, and we are
unable to say whether the combining weights thus determined, include one
or more atoms of any element ; but it is convenient to assume that the
figures represent the relative weights of atoms ; and that however the figures
may vary, there is only one atom of each element in the figures which repre-
sent its combining weight. We have thus arrived at two of the laws of
chemical combination.

1. The equivalent or atomic weight of a body represents the smallest
quantity by weight in which it will combine witU one part by weight of
hydrogen or eight parts by weight of oxygen.

2. The equivalent weight of a compound is the sura of the equivalents of
its constituents.

There is a third law which flows from the preceding : —

3. If a simple or compound body combines with more than one propor-
tion of the same substance, the other proportions are multiples, or sub-
multiples, of the first.

Guided by these rules, it is possible to determine the atomic weight of a
substance (fluorine), which has never yet been isolated. The compound of
this body with calcium is a well-known mineral. Assuming that we take a
weighed quantity of fluoride of calcium, we convert it into sulphate of lime
by heating it with sulphuric acid. The weight of the sulphate of lime being
known, the weight of the calcium in the lime is easily determined ; and by
deducting the weight of calcium from the original weight of fluoride employed
in the analysis, the exact amount of combined fluorine is known. The atomic
weight of this unknown element is thus found to be 19.

These laws of combination are of great aid to the analyst. If he can

determine the weight of one constituent of a compound, the weight of the

other may be accurately determined by calculation. If, for instance, in

reference to sulphate of lime — should the weight of sulphuric acid be deter-

5

66 CALCULATION OF EQUIVALENT WEIGHTS.

mined, then as 40 parts of sulphuric acid unite to 28 of lime to form this
salt ; the amount of lime associated with the acid may be readily known by
a simple calculation ; or, conversely, if the weight of lime is determined, the
amount of sulphuric acid which must have been combined with it may be
easily calculated.

It was at first supposed that the equivalents of all simple substances would
be found to be integers or multiples of hydrogen, taken as unity ; but experi-
ence, based on accurate analysis made by Dumas, shows that this rule admits
of application only to those elements enumerated in the subjoined list, and
even the accuracy of the results on which this list is based has been recently
called in question : —

Hydrogen 1.

Oxygen 8. Sulphur 16.

Carbon 6. Phosphorus 32.

Nitrogen 14. Arsenic 75.

Calcium 20.

To this number some chemists have added fifteen other elements. M.
Stas, who has recently investigated this subject, denies the existence of any
multiples of hydrogen among the equivalent weights. He assigns as the
equivalent of nitrogen 14*041, and of sulphur 16'03T1. These differences
are not, however, such as to affect materially any calculations based on the
elements ; and with respect to the equivalent weights of other substances, it
is the common practice among chemists to represent them by whole numbers.
The reason is obvious. No two chemists agree concerning the decimals.
The equivalent of chlorine is given at 35-45, 35*47, and 35*50, by equally
reliable authorities. It is usually taken at 36. Strontium is given by
Stromeyer at 43*67, by Dumas at 43*74, by Rose and de Marignac at 43 77,
by Liebig at 43*80, and by Graham and Pelouze at 43*84. It is usually
taken at the whole number 44. The whole numbers are easily carried in the
memory ; and if great accuracy is required in any investigation it is easy to
substitute for them, the real figures of any selected authority.

Symbols. — It will have been perceived from frequent examples given in
the preceding pages, that a symbolic language has been generally adopted
by chemists. Thus the symbols H, O, S, CI, stand respectively as abbrevia-
tions for hydrogen, oxygen, sulphur, and chlorine. When the initials of
elements are similar, then the first and second, or the first and third letters
of the name of the substance are taken : and in reference to the metals the
corresponding Latin names are similarly used as distinctive symbols. It is
important to bear in mind, however, that these symbols not only represent
the element but the relative weight of it which enters into combination.
Thus the letters HO, not merely represent hydrogen and oxygen, but 1 part
of hydrogen and 8 parts of oxygen ; and the two associated, 9 parts of water.
The number of atoms of each element in a compound is generally indicated
by a figure placed on the right-hand corner. Thus the symbol HOg indicates
2 atoms of oxygen combined with 1 atom of hydrogen (peroxide of hydro-
gen), while 2H0 represents two atoms of water — the figure thus placed on
a line, doubling all that follow it up to the addition sign + , or symbols
included in brackets. Thus KO.SOg, represents sulphate of potassa, but
KO,2S03 represents bisulphate of potassa. Sometimes in order to represent
2 atoms, instead of a figure 2 at the right corner, the symbol is barred, as
thus, -9§-, or O S. These are equivalent to O3 and S3. A collection of sym-
bols constitutes a formula, as in the formula for alum, KO,S03 4-Ala03,3S03
-f24HO. The plus sign is introduced to show that in this compound salt,
the elements are supposed to be arranged as sulphate of potash, sulphate
alumina, and water. It will be perceived from this formula that the atom of
crystallized alum is compounded of 71 atoms, namely, 40 of oxygen, 24 of

SYMBOLS AND FORMULA.

67

hydrop:en, 4 of sulphur, 2 of the metal aluminum, and 1 of the metal potas-
sium ; and the equivalent weight of the compound calculated from this con-
stitution would be 474-6. Formulae when so arranged as to represent
chemical decompositions, constitute an equation^ a term borrowed from
algebra, to represent that the quantities on the two sides are perfectly equal
— 4. e., that the formulae although dissimilar will represent an equal number
of atoms, and therefore, equal atomic weights, as in the reaction of common
salt on a solution of nitrate of silver, NaCl-fAgO,N05=AgCl-f NaO,N05.
The meaning of the word equivalent will be apparent from this equation.
It denotes a quantity of one substance which can exactly replace or be sub-
stituted for another in chemical combination. Thus silver is substituted for
sodium, but in weights which are to each other respectively as 108 to 23, i. e.,
these weights of the metals are equal to each other in the power of satu-
rating the same quantity of chlorine, t. e., 36 : the 8 of oxygen combining
with the sodium, and exactly replacing the 36 of chlorine which have been
transferred to the silver.

The following Table comprises an alphabetical list of the 65 elements now
known to chemists, with their respective symbols, and their atomic or equiva-
lent weights, hydrogen being assumed as unity. In this Table, the non-
metallic elements or metalloids are printed in italics to distinguish them from
the metals.

Table of Elementary Substances, with their Symbols and Equivalent or

Atomic Weights.

ELEMENTS.

05

1

■It

ELEMENTS.

1

•s2

s

CO

-2^

CO

Aluminum

Al

14

Molybdenum ....

Mo

48

Antimony (Stibium) . .

Sb

129

Nickel

Ni

30

Arsenic.

1 As

75

Niobium

Nb

Barium

Ba

69

Nitrogen , '

N

14

Bismuth

Bi

213

Norium

No

Boron

B

11

Osmium

Os

100

Bromine

Br

78

Oxygen

0

8

Cadmium

Cd

56

Palladium

Pd

54

Caesium

C«

123

Phosphorus

P

32

Calcium

Ca

20

Platinum

Pt

99

Carbon

C

6

Potassium (Kalium) . .

K

39

Cerium

Ce

46

Rhodium

Ro

52

Chlorine

CI

36

Rubidium

Rb

85

Chromium

Cr

26

Ruthenium

Ru

52

Cobalt

Co

30

Selenium

Se

40

Columbium (Tantalum) .

Ta

184

Silicon

Si

22

Copper (Cuprum) . . .

Cu

32

Silver (Argentum) . .

Ag

108

Didymium

Di

48

Sodium (Natrium) . .

Na

23

Erbium

Er

?

Strontium

Sr

44

Fluorine . . . .■ , .

F

19

Sidphur

S

16

Glucinum

G

7

Tellurium

Te

64

Gold (Aurum) ....

Au

197

Terbium

Tb

?

Hydrogen

H

1

Thallium

Tl

204

Indium

In

74

Thorium .....

Th

60

Iodine

I

126

Tin (Stannum) . . .

Sn

59

Iridium

Ir

99

Titanium

Ti

24

Iron (Ferrum) ....

Fe

28

Tungsten (Wolfram)

W

92

Lanthanum

La

44

Uranium

u

60

Lead (Plumbum . . .

Pb

104

Vanadium

V

68

Lithium

Li

7

Yttrium

Y

32

Magnesium

Mr

12

Zinc

Zn

32

Manganese

Mn

28

Zirconium

Zr

34

Mercury (Hydrargyrum) .

Hg

100

68 EQUIVALENT VOLUMES.

The equivalent weights have been here placed in integers for reasons
already assigned. The figures, it will be observed, have no relation to the
solid, gaseous, or liquid form of the elements, or to their specific gravity ;
some substances widely different in chemical or physical properties have
similar equivalent weights, while among others, a common difference may be
observed. Thus lithium and glucinum are each represented by 7 ; aluminum
and nitrogen by 14 ; cobalt and nickel by 30 ; iron and manganese by 28 ;
and copper, zinc, yttrium, and phosphorus by 32. Lithium, sodium, and
potassium, have a common difference of 16, these metals being respectively
7, 23, 39. The new alkaline metal, Ccesium, by its high equivalent (123)
disturbs this order. Calcium, strontium, and barium, being strictly 20, 43-8,
and 68"5, have nearly a common difference of 24. Other curious arithmetical
relations may be found in chlorine, bromine, and iodine, as well as in other
groups.

Equivalent Volumes. — In reference to elements and compounds which
exist in the gaseous state, it has been determined by experiment that the
weights correspond in general to very simj)le proportions by volume. Thus
again taking water as an example, it is found that the proportion by volume
in which hydrogen combines is always double that of oxygen ; and further,
that the compound formed, calculated as vapor, is exactly equal to the bulk
of hydrogen which goes to constitute it. Assuming hydrogen as unity, by
volume as well as by weight, it follows that the atomic weight of hydrogen
(1) corresponds to the atomic volume 1 ; and that the above weight of oxygen
(8) corresponds to 0*5, or one-half volume. So in sulphuretted hydrogen 1
equivalent of hydrogen represents 1 volume, but the equivalentof sulphur (16)
in consequence of the great specific gravity of the vapor of this element at
its boiling point corresponds to only l-6th of the bulk of hydrogen, or l-6th
of a volume. This is the greatest deviation from simplicity among all the
gaseous bodies ; but its admission is unavoidable, except at greater inconve-
nience than arises from retaining it. Thus if, to avoid fractional parts of
volumes, sulphur were made unity, ^. e., if 16 parts of sulphur by weight
were assigned to 1 volume of the vapor, then the atomic volume of hydrogen
would be 6, of oxygen 3, and of water 6. Some chemists have compromised
this difficulty by avoiding the fraction for oxygen, but still retaining it for
sulphur ; although why, if retained for one, it should not be retained for both,
does not clearly appear. Thus they represent 1 part by weight of hydrogen
to correspond to 2 volumes of the gas, and 8 parts by weights of oxygen to
1 volume of that gas. They thus adopt hydrogen as unity by weight, but
oxygen as unity by volume. Continental writers reject both of these arrange-
ments ; they take hydrogen at 12-5 by weight, and 100 by volume ; oxygen
at 100 by weight, and 50 by volume.

Water, therefore, stands thus : —

By Weight. By Volume.

Hydrogen
Oxygen .

It will be perceived that these numbers bear an exact ratio to each other.
To us it appears desirable not to depart from the simplicity of ordinary
chemical language, except for some cogent reason. The atomic volume
of hydrogen being 1, the atomic volumes of oxygen, phosphorus, and arse-
nic, are respectively -J, and that of sulphur ^th. With these exceptions there
are no fractional volumes in the gaseous combinations of simple and compound
bodies.

Atomic Fo^wme,— The atomic weight of a gas or vapor divided by the

1 12-5

1 2 100

or

or or

8 100-

I 1 50

NEW NOTATION. ' 69

specific gravity (compared with hydrogen) will give the atomic volume. Thus
the atomic weight of oxygen is 8 : bulk for bulk, it is 16 times heavier than
• hydrogen and 8-r 16 = 0'5, or h the atomic volume of hydrogen. The atomic
weight of sulphur is 16; compared with hydrogen in the same volume, its
weight is 96 (the sp. gr. of its vapor at 900° being 6-63). Thus 16-^-96 =
0*1666, or fractionally Jth of a volume. If we take the ordinary specific
gravity in which air is made the standard, the numbers for the atomic volumes
of gases are in the same proportions. Thus hydrogen has a sp. gr. of
0-0691, and 1 -i-00691 = l-44 ; oxygen, a sp. gr. of M55T, and 8^
l-1057 = 7-2; sulphur vapor at 900° a sp. gr. of 6-63, and 16^6*63 =
2*41. These quotients 1-44, 7 '2, and 2'41 are to each other as 1, J, and
^th respectively, and they equally represent the atomic volumes of these
bodies.

The atomic or equivalent volumes of all solids and liquids, whether ele-
mentary or compound, may be calculated on similar principles — namely, by
dividing their atomic weights respectively, by their specific gravities compared
with watei-, the atomic volume of which is 9-t-l = 9. The sp. gr. of the metal
lithium, the lightest of all solids and liquids is 0 59 : its atomic weight is 7,
and 7 -r- 0*59 = 11 '8, the atomic volume. Platinum, the heaviest of all solids,
has a sp. gr. of 21-5, and its atomic weight is 99, and 99-^21 -5 = 4 6 ; the
atomic volume of this metal. The atomic volume of ice, which, according to
Playfair and Joule, has a sp. gr. of 0-9184, is found on a similar principle
.^y\^ = 9-8. The relative number of atoms in a given volume of any sub-
stance is obtained by an inverse proceeding — namely, in dividing the specific
gravity by the atomic weight.

It appears probable from the researches of Petit and Dulong {Ann. de Ch.
et Phys., X. p. 403), that the atoms of all simple substances have the same
specific heat, for by multiplying the specific heat of any one of the elements
by its atomic weight, in nearly all cases the quotient is the same, or a mul-
tiple or sub-multiple of the figures. There are some remarkable exceptions,
however, as in the case of carbon : and these can scarcely be explained by
any want of accuracy, either in determining the specific heat or the atomic
weight of bodies. Further researches are required to show that there is that
exact relation which has been supposed.

New Notation. — A new system of notation was proposed by Gerhardt,'
with a view to establish a constant relation between the atomic weight of
bodies, their specific gravities, and vapor volumes. In order to carry out
these views, he has suggested that hydrogen should Ije the standard or unit
for the atomic weight, specific gravity, and combining volume, and that, in
order to meet this view, the equivalents of certain bodies should be doubled.
Thus :—

Symbols. Atomic Weights.

Hydrogen H

Oxygen ...... O

Sulphur ...... S

Selenium , . . . . Se

Tellurium Te

Carbon x, . C

The symbols are represented sometimes in Italic capitals, but more cor-
rectly in the Roman capitals barred, to show that they are double the usual
weights. The unitary system creates a difference in the meaning of the terms
atom and equivalent, as hitherto understood. Thus while 8 is the equivalent
weight of oxygen in combining with 1 of hydrogen, 16 is assumed to be the
atomic weight of that element, since this is considered to be the lowest pro-

H

1

0

16

S

32

> Se

79

i Te

128.4

C

12

70 NEW NOTATION.

portion in which oxygen enters into combination with hydrogen or any other
body. Upon this assumption water cannot be formed of less than two atoms of
hydrogen, and it is therefore represented by the formula H^O. So with sul-*
phur the equivalent weight is 16, but under the unitary system the atomic
weight is fixed at 32 — two atoms of hydrogen being here required to form
the compound hydrosulphuric acid, H^S. In reference to chlorine and
bromine, however, hydrogen is supposed to combine with these elements in
the one atom, and thus the equivalent and atomic weights are the same.
Upon this system the various elements have been divided into groups accord-
ing to their assumed power of combining with, or replacing different quan-
tities of hydrogen. We thus have what is called the atomicity of the elements.
Those bodies which combine with or displace one atom of hydrogen are
called monatomic elements, or monads: they include the group of halogens
CI, Br, I and F. In addition to these there are five metals of the alkaline
group, namely, Li, Na, K, Rb, and Cas, with Tl, Ag, and hydrogen itself. The
atomicity is usually indicated by a mark above the letter, thus, H'. The
elements which are assumed to combine with or displace two atoms of hydro-
gen are called Dyads. Among non-metals they include 0, S, Se, and Te, and
among the metals they include those of the alkaline earths Ba, Sr, Ca, Mg,
and eleven of the common metals. Their atomicity is indicated by two marks
above the symbol, thus, 0" S'', &c. The triads, or those which take three
atoms of hydrogen, include among non-metals N P B, and among metals As,
Sb, Bi, Al, Au. This atomicity is expressed by three marks, thus, N'".
The tetrads which are supposed to take or displace four atoms of H, include
C and Si as well as the following metals, Ti, Zn, Sn, Ta, Pd, Pt, Ir, Os.
Their atomicity is thus indicated, C'\ There is a group of Ilexads repre-
sented by the metals, Mo^S V', and W^^', and also a group of nine metals,
of which the atomicity has not been determined, namely, Th, Ro, Ru, G, Yt,
Ce, La, U, and Di, being placed among the tetiads, and the other metals
among the dyads.

This arrangement of the elements is based on certain assumptions which
may or may not be true. With respect to the metals, it is notorious that
they form but few compounds with hydrogen, so that the atomicity must be
determined among them indirectly, ^. e., by their combinations with chlorine.
It places silver in the same group with the alkali metals, and transfers the
alkaline earthy metals to the group which includes copper, manganese, iron,
and mercury.

The doubling of the combining weight of oxygen destroys in some cases
that simplicity which has rendered chemical notation an easy subject to the
student. The compounds of nitrogen with oxygen will illustrate the differ-
ence in the two systems : —

Ordinary Notation

Name. TTnitary Notation.

Name.

NO

Protoxide of nitrogen

NgO

Nitrous oxide

NO.

Deutoxide of nitrogen

NO

Nitric oxide

NO3

Hyponitrous acid

N2O3

Nitrous anhydride

NO,

Hyponitric acid, Nitrous acid

NO2

Nitric tetroxide

NO,

Nitric acid

N2O3

Nitric pentoxide.

Under the ordinary system, in which oxygen is represented by 8, there is
that progressive increase from 1 to 5 atoms, which is in strict accordance
with the simple law of multiple proportions. On the unitary system there
are three compounds vhich it is assumed cannot be formed except by two
atoms of nitrogen entering into combination, while there are two other com-
pounds of these elements which can be produced by one atom of that ele-

NEW NOTATION. 'jl

merit. Owin^ to this arrangement, the oxygen atoms have no kind of
numerical relation. No satisfactory reason can be assigned why one of the
gaseous compounds of these elements should take one atom, and the other
require two atoms of nitrogen for its production. The inconsistency of this
arrangement is still more strikingly displayed in comparing the formulae of
the two systems, which represent the anhydrous nitric and the hydrated
nitric acid.

Ordinary Notation. Name. Unitary Notation. Name.

NOg Anhydrous nitric acid NjOg Nitric pentoxide or anhydride

NO5HO Hyd'd nitric acid HNO3 Hydric nitrate.

The same compound of the two elements is represented on the unitary
system as requiring two atoms of nitrogen for its formation when the elements
of water are not present, and only one atom when the elements of water are
present. No valid reason can be assigned for such an assumption as this,
and it is certainly not in accordance with the simplicity of the laws of chemi-
cal combination. It would be foreign to the purpose of this work to occupy
the pages with controversial matter. It may be sufficient to state, the sup-
posed advantages of the new notation appear to be more than counterbalanced
by the disadvantages which necessarily accompany it. Some of those chem-
ists who use it, frequently violate their principles by retaining the name of
the old system, with which the unitary formula of the compound is wholly
inconsistent. Others with a desire to be consistent, have so completely
changed the names of substances, that they are now scarcely recognizable by
scientific men, and are unknown to and unused by those who are engaged in
pharmaceutical or manufacturing chemistry.

The specific gravity of all gases is referred by Gerhardt to hydrogen as a
standard, instead of atmospheric air. This certainly has the advantage of
representing generally by one set of figures both specific gravities and atomic
weights. Thus oxygen is 16 times heavier than hydrogen. Its specific
gravity would be therefore 16, and, as it combines with hydrogen in the pro-
portion of 8 to 1, this is in the ratio of 16 to 2 ; hence if the atomic weight
of oxygen is 16, it will take two atoms of hydrogen to form water. Thus
hydrogen is supposed to unite not as one, but as two atoms with one atom
of oxygen, in order to meet this duplication of oxygen. This is on the
assumption that equal volumes of gases, under similar circumstances, contain
an equal number of atoms, and that each atom of an elementary gas repre-
sents a volume, and vice versa. Thus a volume of oxygen contains 1 atom
= 16, and a volume of hydrogen contains 1 atom = 1* But water, accord-
ing to this view, cannot be produced by the union of 1 atom or volume
of hydrogen ; hence it would stand thus : —

By Weight. By Volume.

H2 =2 = 2

0 = 16 = 1

= . 1

H2O = 18 = 2

Water would therefore be a suboxide of hydrogen, while the peroxide would
become the oxide (HO). Protoxide of nitrogen would in like manner be a
suboxide NgO, and the deutoxide would become the protoxide (NO). In
respect to this theoretical constitution, it may be remarked that the chemical
properties of water are really those of a neutral oxide, and not of a suboxide.
Faraday considers that the electrolysis of water proves it to be a protoxide,
^. e., a compound of one atom of each element, HO. On the other hand, the
peroxide of hydrogen represented by the unitary system as a neutral oxide,

Y2 . THE UNITARY SYSTEM OF NOTATION.

HO, has none of the characters of a neutral oxide ; but from the facilit}^ with
which it parts with half of its oxygen, it more strikingly resembles a peroxide,
HO,.

The compounds of hydrogen and nitrogen with oxygen serve to illustrate
the inconsistency of the new system of nomenclature. Thus N^O is described
as nitrous oxide, but H^O is described by the same authority as hydric oxide,
or oxide of hydrogen. Again, NO is represented as nitric oxide, while HO
stands as hydric peroxide, or peroxide of hydrogen. It is clear that if this
view is correct, that the compounds are respectively on the unitary system
suboxides and oxides, and water should be aqueous oxide, and oxywater
hydric oxide. This should be the true nomenclature, if the old names of
nitrous and nitric oxide have been properly applied to the analogous com-
pounds of nitrogen with oxygen.

It is stated in favor of this method, that it is better adapted for expressing
the formulae of certain organic compounds than that now in use ; and that,
in reference to compound gases and vapors, the atoms may be so arranged
that they will all yield two volumes — the specific gravities of the compounds,
compared with hydrogen, being then equal to one-half of their atomic weights.
Thus carbonic oxide C 0 forms 2 volumes of gas (the atoms being doubled) ;
the atomic weight is 12 + 16, or 28, and the specific gravity, compared with
hydrogen, equal to one-half, or 13.95. Alcohol is C^IIjiO ; it forms 2 volumes
of vapor; the atomic weight is 24-f 6-|-16— 46, and the specific gravity,
compared with hydrogen, is one-half of this, namely, 23. Chemical facts
are, however, somewhat strained to suit the requirements of this hypothesis.
The specific gravities of arsenic and phosphorus in vapor, compared with
hydrogen, are double their atomic weights, being 152.79 and 63.71 respect-
ively. The atomic weights (75 and 32) therefore represent only half a
volume instead of one volume of each element ; and one volume of arsenic
or phosphorus must represent two atoms. Either, therefore, the system is
inconsistent with itself, and the assumption that the volume of an element
represents one atom, or its atomic weight, is contrary to known facts — or,
in order to bring arsenic and phosphorus within the rule, the atomic weights
of these elements must be doubled on this system of notation. So with sul-
phur— the atomic weight being 32, the specific gravity of the vapor, com-
pared with hydrogen, is 3 times this weight, or 96. Hence, instead of an
atom of sulphur corresponding to one volume, it would be represented by J
of a volume. By ingeniously selecting a specific gravity of sulphur-vapor
calculated for the unusual temperature of 1900'^, in place of the ordinary
specific gravity at 900°, this element is made apparently to fall within the
rule. Oxygen itself only falls within it by doubling the equivalents of all
the bodies with which this element combines.

This system, therefore, introduces duplicate or molecular atoms in place of
the usual single atoms. Elements are supposed to enter into combination
with themselves before they can enter into combination with other elements.
Thus hydrogen does not exist in all cases as H, but on some occasions as
HH or H^; in other words,. it is supposed to form a compound of itself, or
a hydride of hydrogen, and nitrogen is also NN, or a nitride of nitrogen. We
have here not only a departure from simplicity, but from all analogy. Thus

we are told that anhydrous oxide of potassium is j^ [- 0, while the anhydrous

chloride, bromide, iodide, and fluoride, would be represented by one atom of
each, KCl or KBr, &c. The analogy of composition between oxide and
chloride is thus set aside : and the names of compounds are no longer in
accordance with their chemical constitution. The present language has been

NOMENCLATURE OF SALTS. T3

found adequate to explain all chemical changes that are of any importance
and require explanation ; and although in some respects imperfect, it has
this great advantage, that it has taken a deep root not only in the arts and
manufactures of this country, but in medicine and pharmacy.

Nomenclature. Constitution of Salts. — Elementary bodies often take their
names from their peculiar physical properties as chlorine and iodine in refer-
ence to color, and bromine to odor : in some instances the name is derived
from the products of combination, as oxygen, hydrogen, nitrogen, and cyano-
gen. The general principle of nomenclature as applied to compounds, has
been, as far as possible, to indicate the composition of the substance by the
name. Thus sulphate of potash implies at once the constitution of this salt :
it was formerly called the sal de duobus. Its formula is KOjSOg, and herein
its composition is at once announced. The same observation applies to other
salts. In regard to the common metals, the salts receive the name of the
metal, as sulphate of copper CuO,SOg. The acid, however, as in the case of
sulphate of potash, is believed to be combined with oxide of copper, and not
with the metal itself. Among the alkalies the oxides were known long before
the metals, and received specific names, which have been since retained. In
recent times it has been proposed to assimilate the names of metallic salts,
by using a common designation. Thus the sulphate of potash is described
as sulphate of potassium, on the hypothesis that the acids are not combined
directly with the oxides, but with the metals. If, as we believe, this hypo-
thesis is inconsistent with chemical facts, then a retrograde step in nomencla-
ture has been taken, since a name which suggests a direct combination of an
acid or acid radical with a metal, conveys no incorrect idea of the constitu-
tion of salts.

A salt is a compound of an acid and a base. An acid is a compound which
has an acid or sour taste, which reddens the blue color of litmus, and neu-
tralizes an alkali in combining with it to form a salt. But according to some ■
modern chemists, an acid is a salt, and all acids are described as salts of
hydrogen. There are some acids, however, which neutralize alkalies or bases
and form definite salts, but they form no compound with water and are never
found associated with hydrogen in any form. Thus hyponitrousacid (NO3)
forms a well-known class of salts, the hyponitrites — of the alkaline and
metallic oxides. When water is added to the anhydrous acid, this acid is
immediately decomposed. It is the same with hyponitric (nitrou^ acid NO^.
It forms however well-defined nitro-compounds with cellulose, glycerine, and
benzole. It performs all the functions of an acid, but when water is placed
in contact wi^h it, it undergoes decomposition. It enters into no combina-
tion with the elements of water. It is, therefore, impossible to describe an acid
as a salt of hydrogen, except by ignoring the existence of a large class of
substances which have all the characters of acid, except the power of combining
with water or its elements. Even some which combine with water as a
solvent, such as the carbonic and sulphurous acid gases, form no hydrates
or chemical compounds with water. They may be obtained perfectly free
from water or its elements — but they combine with metallic oxides and pro-
duce well-known crystalline salts. Among solids the fused boracic and
silicic acids form a large number of saline compounds by uniting as acids to
bases, wholly irrespective of the presence of water.

The term base is applied by chemists to signify a compound which will
chemically combine with an acid : it includes alkalies (oxides of alkaline
metals, and alkalies of the organic kingdom), oxides of the ordinary metals,
and a variety of complex compounds in the organic kingdom which are not
alkaline and possess none of the characters of metallic oxides. The metals
which form bases are are now called basylous bodies. An alkali is known

74 NOMENCLATURE OF SALTS.

by its having an acrid or caustic taste, by its rendering a red solution of
litmus blue, and by its being neutralized h'j an acid, i. e., having its alkaline
properties entirely destroyed. Further, it has the property of turning yellow-
turmeric to a red-brown color ; the red color of the petals of flowers, and
fruits, to a blue or green ; and the red color of woods and roots to a crim-
son tint. The basic metallic oxides are generally insoluble in water, and
neutral to test-paper ; some have a feebly alkaline reaction.

In reference to Oxacids, or those which contain oxygen, the termination
ic indicates the higher degree of oxidation, while the termination ous im-
plies a lower degree. Thus we have sulphuric (SO J sulphurous (SO^) acids.
When there are more than two acids, a further distinction is made by the
prefix hypo (vrto under) : thus we have hyposulphuric acid to signify an acid
containing a smaller quantity of oxygen than the sulphuric, but a larger quan-
tity than the sulphurous ; and hyposulphurous, indicating a smaller quantity of
oxygen than exists in the sulphurous acid. When an acid has been discovered
containing a still larger amount of oxygen than the highest in a known series,
it receives the prefix hyper (vrtsp above) ; still retaining the terminal ic.
Thus there is manganic acid (MnO^) ; and hypermanganic or permanganic
acid (Mn^Oy), which contains a still larger proportion of oxygen than the
manganic. The salts formed by these acids terminate in ate when the acid
terminates in ic, and in tie when it terminates in ous. The terminations
ic and ous have been employed by Berzelius, and other chemists, to dis-
tinguish the oxides and salts of metals. Thus the protoxide of iron would
be the ferrous oxide, while the peroxide would be the ferric oxide ; so there
ate also ferrous and ferric sulphates — stannous and stannic chlorides and
sulphides.

When there is only one acid formed by the same elements, its termina-
tion is always in ic, as the boracic acid, formed of boron and oxygen, of
which only one compound is known. The class of hydracids includes those
binary compounds in which hydrogen is a constituent ; and the names imply
at once the composition as hydrochloric acid (HCl). Hydrogen, unlike
oxygen, does not form more than one compound with the same element or
radical. These hydrogen acids require no water for the manifestation of
acidity. The term radical, or compound radical, is applied to a compound
which in its order of combination acts like an element. Thus the compound
gas cyanog^ (^CJ is a radical ; it enters into combination with the metals
and metalloids, like chlorine, producing binary compounds called cyanides.
It is a substitute for an element.

When in the composition of salts the atoms of acids preponderate, the
prefix bi or ter is used to indicate the number, as bisulphate of potash
(K02S0,), or tersulphate of alumina (AI3O33SO3). These constitute acid
salts. When the base predominates, the abbreviated Greek prefix di or tri
is employed to designate the surplus atoms of the base. Thus, the triacetate
of lead signifies a compound in which three atoms of oxide of lead are united
to one atom of acid 3PbO,Ac. The terra sesqui is used to signify one and
a half atoms, or avoiding fractions, 3 atoms of base to 2 of acid, as 3PbO,2Ac.
The following Table represents the nomenclature of salts in reference to their
constitution. M stands for anj metal : —

Neutral (normal) salt M0-|- SO3 Bibasic .... 2M04- SO3

Acid MO4-2SO3 Sesquibasic . . . 3MO4-2SO3

Sesquisalt .... 2MO+3SO3 Tribasic .... 3M0-J- SO3

Binary Oompounds.—The Binary System.— ^hm a metalloid is united to
another metalloid or metal, or when a compound radical (salt-radical) is

ON THE CONSTITUTION OF SALTS. 75

united to a metal or metalloid, the combination is called Unary, from its
consisting of two elements. They are generally known by the termination
ide. Thus oxide, chloride, sulphide, carbide, phosphide, and cyanide indicate
compounds of tlie elements or of the, radical (cyanogen) with other elements.
When more than one combination exists, the compounds take the Greek prefix
proto, deuto, trito, or di, to indicate the respective number of atoms of the
constituents. {See Oxygen for the series of Oxides.) The highest combi-
nation always takes the prefix/^er. The binary compounds formed by chlorine,
bromine, iodine, and fluorine, with the alkaline metals, are frequently called
haloid salts, to indicate the marine origin of the radicals (a?.?, ax6?, the sea).
Chloride of sodium furnishes an instance of a binary compound ; and as
nitrate of silver or nitrate of potash equally forms a salt bearing a physical
resemblance to the chloride, it has been suggested that in oxacid salts the
elements may be so arranged as to form hypothetical binary compounds.
Chloride of sodium is NaCl and nitrate of silver is AgOjNOg*, but the
accepted symbolic language would admit of the atomic arrangement AgNOg,
and by this means all decompositions would become mere substitutions of
one metal for another, or for hydrogen. Thus in the production of chloride
of silver we should have in ordinary symbols NaCl4-AgO,N05=AgCl-f
NaO,N05; ^^^ if the oxygen is supposed to be associated with the elements
of nitric acid, forming a compound radical (nitron), then the changes would
be more simply represented thus: NaCl + AgN0f.=AgCl-f-NaN06. If, how-
ever, this view were correct, it should apply to all salts and even to hydrates.
Thus, to take a few examples of compounds which are intelligibly represented
by the present method, we should have, on the binary hypothesis, to make
the following changes : 1. Carbonate of soda, as a type of the carbonates,
NaO,C03 would be rendered Na,C03 ; and for the bicarbonate of soda,
KaO,2CO.^ a new hypothetical radical would have to be created, as NajCgOg
or Na,C03-fC02, neither of which formula would convey the slightest know-
ledge of the composition of the salts. This objection equally applies to all
salts having one atom of base to two or more atoms of acid, as the bisul-
phates, bisulphites, the binarsenates, and others, as well as to all double
salts containing an oxygen acid. 2. In the application of this notation to
hydrates (which could not be fairly expected), hydrate of potash KO,HO
would be KjHOa; but while potassium (K) has a stronger affinity for oxygen
than any other known substance, and peroxide of hydrogen (HOg) so readily
parts with oxygen that the mere contact with metals or metallic oxides is
sufficient for the purpose, it is assumed that the peroxide can remain in com-
bination with potassium without undergoing decomposition. 3. Sulphurous
acid by combining with potash forms KOjSOg. It could not be regarded or
written as KSOg, for this would imply a combination of anhydrous sulphuric
acid with the metal potassium. The bisulphate of potash KO,2S03, would
present an equal difficulty. On the binary system this would be KjSj^O^ —
the sulphur and oxygen, in order to form a salt radical, being here associated
as in hyposulphuric acid, which is a well-known and independent acid of sul-
phur. 4. The anhydrous salts formed of metallic bases and acids could not
be consistently represented on the binary hypothesis ; for there could be no
definite principle on which the oxygen should be wholly assigned to either
metal. Thus chromate of lead is commonly represented as PbO.CrOg, but
as a binary compound it would be either Pb.OrO^, or CrPbO^. Of these
three combinations of elements, those only which are known and separable,
are oxide of lead and chromic acid. The necessary creation of an endless
number of hypothetical radicals, some already conflicting with known com-
pounds, is indeed fatal to the hypothesis. It w^ould add complexity instead
of simplicity to chemical formulae. While NO^, SO3 and COg have a real

76 NEUTRALIZATION AND SATURATION.

and independent existence, the binary radicals NOg, SO^ and COg are mere
assumptions. It has been supposed that the electrolytic decomposition of
salts is in favor of this view ; but although the metal may be separated from
the salt by an electric current, the supposed binary radical has never been
obtained, and the facts are fully explained on the supposition that it is
SO3 + O, and not SO^. On the other hand, ordinary electrolysis favors the
common view of the constitution of salts by acid and base, as the following
simple experiment will show. Provide a piece of glass tube, bent at an angle,
and placed in a wine-glass, to serve for its foot or support. Fill this siphon
with the blue infusion obtained by macerating the leaves of the red cabbage
in boiling water (rendered blue by a little potash), and put into it a few
crystals of sulphate of soda ; then place a strip of platinum foil in each leg
of the siphon, taking care that they do not come into contact at the elbow
of the tube, and connect one of these with the negative and the other with
the positive pole of the pile; in a few minutes the blue color will be changed
to green on the negative side, and to red on the positive side of the tube,
indicating the decomposition of the salt, the alkali or soda of which is col-
lected in the negative, and the sulphuric acid in the positive side. Reverse
the poles, and the colors will also gradually be reversed. In this and ana-
logous experiments, it is found that, whenever a neutral salt is decomposed
by electricity, the oxide or base appears at the cathode, and the acid at the
anode. The bases, therefore, in their electrical relations, rank with hydro-
gen, and are cathions ; and the acids with oxygen, and are anions (see page
59): The least soluble salts may be made to render up their elements m
the same way. If, for instance, we substitute for the sulphate of soda in
the preceding experiment, a little finely-powdered sulphate of baryta
moistened with water, baryta will be evolved at the cathode, and will there
render the liquid green ; while sulphuric acid will appear at the anode, ren-
dering it red.

If the binary hypothesis were adopted, it would be necessary to change
the names of all salts. CO3 is not carbonic acid ; it would be necessary to
invent a new term for this radical, to indicate its composition, e. g.,a teroxy-
carbide, so that dry carbonate of potash K0,C02, would be a teroxycarbide
of potassium KCO3. If names are not to express, as far as may be, the
composition of salts, it would be preferable to return to the old nomencla-
ture based on physical properties, and to designate the sulphate of iron
(FeO,S03) as green vitrol, rather than under the binary hypothesis as the
tessaroxisulphide of iron (FeSOJ. We must bear in mind, in reference to
such changes, that the supposed advantages gained in one part of the science
may be far more than counterbalanced by the disadvantage of using names
which either do not express the nature of the compound, or which express it
in such formulas as to deceive the student of the science. As Dr. Miller has
pointed out, there are four ways in which nitrate of potash may be repre-
sented ; K0,N05; S:,NOe; KNOg; and KNO3; but to only the first of
these is the usual name of the salt applicable. The first, second, and third
formulae are on the ordinary system of notation ; the fourth is on the system
of Gerhardt, which, except by some conventional understanding, cannot
represent the presence of potash or nitric acid in the salt on any reasonable
interpretation.

There are some cases in which the binary theory of salts is inadmissible
not only with respect to oxacids, but to hydracids. The alkalies of the
vegetable kingdom form definite crystallizable salts with the hydrochloric,
sulphuric, and nitric acids. The hydrochlorate and sulphate of morphia
are well-defined salts, in which there is every reason to believe that acid and
base are directly combined. Even in the mineral kingdom, there is some-

DECOMPOSITION OF NEUTRAL SALTS. It

times a want of evidence of this binary condition. Magnesia or alumina
may be dissolved in hydrochloric acid, and it is supposed that soluble
chlorides are formed. In the case of soda and potash there is the strongest
evidence of the production of chlorides by the (act that the binary salts are
obtainable as such by crystallization. On submitting to evaporation the
hydrochloric solutions of magnesia and alumina and applying heat to the dry
residues, no binary compounds are obtained, but simply the bases which
were originally employed. According to some authorities, cobalt forms
both a chloride and hydrochlorate, indicated by a different color in the com-
pounds ; the chloride or binary compound obtained by concentration at a
high temperature being blue, while the hydrochlorate, like the non-binary
compounds nitrate and sulphate, although deprived of water, remain red.

Neutralization^ in reference to salts, must be distinguished from saturation :
the first implies the destruction of the properties of acid and alkali by com-
bination, as manifested on organic colors ; the second the exhaustion of
chemical affinity. Potash is neutralized by combination with one atom of
sulphuric acid. The compound, sulphate of potash, presents neither acid
nor alkaline reaction ; it is a perfectly neutral salt. Potash will however
combine with an additional equivalent of acid forming a bisulphate; in this
compound it is saturated with the acid, but the alkali is more than neutralized ;
it possesses a well-marked acid reaction. Potash in the state of bicarbonate
is saturated with carbonic acid ; it will take no more : but it is not neutral-
ized, for it presents a well-marked alkaline reaction. These terms are often
used as synonymous, but they have a widely different signification. The term
neutral salt is however commonly employed to signify the condition of a
compound without reference to the action of its solution on vegetable colors.
Provided the same equivalent weight of acid is present, the salt is neutral
although the solution may have an acid reaction. The sulphates of copper,
iron, and zinc contain the same proportion of acid to base as the sulphate of
potash, but while the latter is quite neutral, the three former are acid, and
redden litmus. The best test for neutrality is the blue infusion of cabbage,
prepared in the manner elsewhere described (page 76). It is reddened by
an acid, and changed to a green color by an alkali. To avoid confusion from
the use of the term neutral, Gmelin has proposed to call such salts normal.

In the double decomposition of salts it is usual to state that neutral salts
produce neutral compounds. This may be proved by adding to solutions of
sulphate of potash and chloride of barium respectively a small quantity of
blue infusion of cabbage. When mixed, there is a complete interchange of
acids and bases, but the mixed liquids remain blue. Hence there must have
been a complete substitution or replacement of acids and bases in equivalent
proportions ; in other words, the chloride of potassium and sulphate of baryta
are just as neutral as the compounds which form them. If an equivalent of
bisulphate of potash is employed, the blue liquid will be reddened by this
salt, and remain red after mixture, an equivalent of hydrochloric acid being
set free. When solutions of phosphates of soda and chloride of calcium,
colored with blue litmus, are mixed, the compounds, although neutral, so
decompose each other as to set free an acid, and the litmus is reddened.
This is owing to the formation of a basic phosphate of lime, ^. e., a salt in
which the base predominates. An acid and an alkaline salt may by double
decomposition produce neutral compounds. A solution of alum reddened
by infusion of litmus or blue cabbage, when mixed with a due proportion of
a solution of carbonate of potash rendered green by infusion of cabbage,
will give rise to products of a neutral kind (sulphate of potash and hydrate
of alumina), and both liquids will become blue.

78 GASES AND VAPORS.

METALLOIDS OR NON-METALLIC BODIES.

CHAPTER V.

METALLOIDS AND META LS. — PR OPERT IE S OF GASES AND

VAPORS.

Division of Elements. — For the convenience of stndy, elementary bodies
are divided into two great classes, namely, Metalloids or Non-Metals,
and Metals. This division is arbitrary ; hence chemists have taken differ-
ent views of the substances which belong to these two classes. Sulphur may
be regarded as a type of the metalloids, and gold of the metals. Here the
distinctions in physical characters are sufiBciently marked. In some cases,
however, it is difficult to assign the class ; thus arsenic, tellurium, and sele-
nium have been regarded either as metallic or non-metallic. It is difficult
to suggest any broad chemical distinction between the two classes. As a
general rule, non-metallic bodies produce, in combining with oxygen, either
acids or neutral oxides ; they do not form any salifiable base. Water may
be regarded as an exception to the remark : since, although a neutral oxide,
it is believed by most chemists to act, in some instances, the part of a base
to acids, and is known as basic water. Hydrogen therefore ranks with the
metals as a basylous body, and takes the first place as an electro-positive.
On the other hand, the metals, while they produce acids in combining with
oxygen, also produce alkalies, earths, and oxides ; in fact, they are the
chief source of the bases from which salts are formed.

English writers commonly enumerate as non-metallic 13 out of the 65
elementary bodies known to science. They comprise 4 gaseous, 1 liquid,
and T solids, with 1 the physical state of which is unknown. They are con-
tained in the subjoined list : —

Oxygen
Hydrogen
Nitrogen .
Chlorine J

■1

Bromine (liquid)

Phosphorus ]

Fluorine (unknown)

Carbon !

Iodine "j ^

Boron |

Sulphur l S

Silicon J

Selenium J *

l«

The symbols and atomic weights of these bodies will be found at page 67.

Distinction of Gases and Vapors. — The gaseous, liquid, or solid state, is
well known to be a physical condition of matter, depending on the heat
associated with the atoms of the solid or liquid. By heating a solid, we
may cause it to pass through the liquid and vaporous conditions. Thus
camphor placed in a retort and heated to 347° melts or passes to the liquid
state. If the temperature be raised to about 400°, it is rapidly converted
into a transparent vapor or gas, which is deposited in white flocculent masses
on all cold surfaces. Thus distilled from a short retort into a tall jar placed

LIQUEFACTION OF GASES. T9

npright, it forms a beautiful illnstration of the solidification of a vapor by
cooling. Ether, at ordinary temperatures, is a liquid ; if the liquid be heated
to 96°, it is entirely converted into vapor or gas, having at and above this
temperature all the physical properties of gas. The best method of proving
this is to invert in a wide dish of water, heated to above 100°, a small gas-
jar filled with water at this temperature. If a tube containing liquid ether
be opened under the mouth of the jar in the hot water, the ether will pass
into the vessel as gas or vapor, and displace the water. The jar may be
removed, and the contents inflamed by a lighted taper, when it will be seen
to burn like coal-gas. If another jar be similarly filled with the vapor, and
transferred to a basin of cold water, or if cold water be simply poured over
it, the gaseous contents will be condensed, the ether will be liquefied, and
the cold water will rise and fill the jar.

Liquefaction of Gases. — Experiments conducted on these principles led
Mr. Faraday to the discovery that a large number of gases are merely the
condensable vapors of liquids or solids. It is a well-known fact, that when
any gas is submitted to sudden and violent pressure, great heat is given out.
A small volume of air, suddenly compressed, evolves so much heat as to
ignite inflammable substances. Thus a piece of amadon, or German tinder,
may be kindled by the sudden compression of a few cubic inches of air in a
dry and warm glass cylinder. If, therefore, a gas is submitted to pressure,
and at the same time cooled as it is compressed, the conditions are such as
to cause it to pass into the liquid state. On the other hand, when the
liquefied gas again assumes the gaseous condition it absorbs from all
surrounding bodies, a large amount of heat, atid thus produces a great
degree of cold. The freezing of water in a hot platinum crucible is a well
known illustrative experiment. Liquid sulphurous acid is poured in quantity
into a platinum crucible, the temperature of which is suflficient to bring out
a spheroidal condition of the liquid. Water contained in a thin tube
introduced into this liquid is speedily frozen, owing to the rapid evaporation
of the sulphurous acid and its conversion from a liquid into gas.

With some gases no pressure is necessary — mere cooling will be found
sufficient. Sulphurous acid is a gaseous body at all temperatures above
14°. When cooled to this temperature, it is immediately liquefied. If
sulphurous acid gas in a dry state be passed through a tube immersed in a
freezing-mixture of pounded ice and salt, it will be condensed as a liquid in
the bend of the tube, and if the horizontal portions be drawn out in a
capillary form in the first instance, the liquefied gas, when condensed, may
be sealed up and preserved. If the tube be broken, the liquid will rapidly
pass to the gaseous state, producing a great degree of cold. Under
sufficient pressure, the amount of which varies with each gas, some of these
bodies may be liquefied without cooling, and the pressure may be produced
by the gas itself.

The solid crystalline hydrate of chlorine (Cl + IOHO) inclosed in a stout
bent tube sealed, yields, when gently heated, chlorine liquefied by its own
pressure, forming about one-fourth of the liquid obtained in the cool part of
the bent tube. The liquefaction of ammonia may be performed in like
manner, by saturating dry chloride of silver with the gas, and introducing
this into a stout glass tube bent at an obtuse angle and securely sealed. The
amwionio-chloride of silver melts at about 100°. The ammonia is evolved,
and may be condensed to a liquid by cooling the other end of the tube. The
ammonia is reabsorbed by the chloride on cooling, so that this experiment
may be repeated any number of times (Mitscherlich). M. Carrfe has
successfully used liquefied ammonia for producing large quantities of ice for
commercial purposes. The machine consists of two strong iron vessels

80 LIQUEFACTION OF GASES BY COLD AND PRESSURE.

connected in an air-tight manner, with a bent pipe. When it is desired to
procure ice, one of the vessels is charged with a solution of ammonia in
water saturated at 32°. This vessel is heated, and the other acting as a
receiver, is placed in cold water. As the results of the heating the ammonia
is expelled from the water and collects in the cool iron vessel, and when
the pressure amounts to about ten atmospheres, the gas is condensed in a
liquid form. When the greater part of the gas has thus been liquefied, the
arrangement is reversed. The vessel which contained the solution of
ammonia, is cooled, while the water intended to be frozen, is placed in the
hollow interior of the receiver, which holds the liquefied ammonia. By the
evaporation of the ammonia, and its reabsorption by water, so great a degree
of cold is produced that water is rapidly frozen. (RoscoE.) If a substance
like cyanide of mercury, capable of yielding ten cubic inches of gas, is
inclosed in a stout tube of one cubic inch capacity, the gas, when evolved,
will be under a pressure of ten atmospheres (15 x 10), or 150 pounds on the
square inch, a pressure quite sufficient to make it assume the liquid state-
Faraday thus condensed many of the gases by merely exposing them to the
pressure of their own atmosphere. He placed the materials for producing
them in strong glass tubes, bent at a slight angle in the middle, and her-
metically sealed. Heat was then applied to the solid substance; and when
the pressure within became sufficient, the liquefied gas made its appearance
in the empty end of the tube, which was artificially cooled to assist in the
condensation. In these experiments much danger may be incurred from
the occasional bursting of tubes; so that the operator should protect his
face by a mask, and his hands by thick gloves. The greatest caution should
be always observed in performing the experiment. Faraday succeeded in
liquefying the following gases, which, as will be seen, required various
degrees of pressure for the purpose.

Pressure in j-av- Pressure in -p^y...

Atmospiieres. " . Atmospheres. "^'^^^

Sulphurous acid ... 2 at 45° Sulphuretted hydrogen . 17 at 50°

Chlorine 4 "60 Carbonic acid .... 86 " 32

Cyanogen 4 "60 Hydrochloric acid ... 40 " 50

Ammonia 6.5 " 40 Nitrous oxide . . . . 50 " 45

Faraday subsequently succeeded in liquefying defiant gas and fluosilicic
acid, and solidifying hydriodic and hydrobromic acid gases, oxide of chlorine,
and protoxide of nitrogen (P/dl. Trans., 1823 and 1845; also Bunsen.,
Bihliotheque Universelle, 1839, vol. 32, p. 105; and Poggeud. Ann., vol.
12, p. 132).

By employing a bath of solid carbonic acid and ether, Faraday produced
a degree of cold amounting to — 106° in the open air, and — 166° in vacuo.
By simple exposure to a cold of — 106° without any pressure, the following
gases were liquefied: —

Chlorine. Hydriodic acid.

Cyanogen. Hydrobromic acid.

Ammonia. Carbonic acid.

Sulphuretted hydrogen. Oxide of chlorine.

With the aid of powerful condensing pumps, and a cold of — 166°, all the
gases excepting six were liquefied, and those above-mentioned were solidified,
as well as the protoxide of nitrogen. Carbonic acid is, however, readily
obtained in the solid state as the result of the cold produced by the sudden
escape of its own vapor. The six which resisted liquefaction at this low
temperature, and under a pressure varying from 500 to 750 pounds on the
square inch, were the following : —

PHYSICAL PROPERTIES OP GASES AND VAPORS. 81

Oxygen. Nitrogen. Deutoxide of mtrogen.

Hydrogen. Carbonic oxide. Coal-gas. (?)

It will be perceived that of these, three are simple and three are compound
gases. In employing a mixture in vacuo of liquid protoxide of nitrogen and
sulphide of carbon, batterer succeeded in producing a degree of cold equal
to — 220^, without any effect upon these six gases. Dr. Andrews reported
to the British Association (Sept. 1861), that by pressure alone he had
succeeded in reducing oxygen to l-324th of its volume, and by pressure with
a cold of • — 106°, to l-554th of its volume ; and atmospheric air by pressure
and cold to l-675th, in which state its density was little inferior to that of water
(the difference between air and water at 60° being 814). Hydrogen was
condensed by similar means to l-500th, carbonic oxide to l-2T8th, and
deutoxide of nitrogen to l-680th. The gases were compressed in the capillary
ends of thick glass-tubes, so that any physical change they might undergo,
could be easily observed. When thus highly condensed, they were not
liquefied ; hence, although these six gases are probably the vapors of liquids,
they must be regarded at present as perrnanent gases, since cold and pressure
conjoined, and carried to the utmost limits, do not cause them to assume the
liquid condition.

From these facts, we learn that the greater number of gases, simple and
compound, are the vapors of liquids and solids. They differ from ordinary
vapors in the fact, that the boiling points of their liquids are far below
the ordinary temperature of the atmosphere; hence they only admit of
condensation by artificial cooling. A true vapor, like that of ether, is
condensed on its production, because the temperature of the air is below its
boiling-point, 96° : it requires no artificial cooling for its condensation. In
any part of the earth in which the temperature was above 96°, ether would
be a permanent gas, unless kept under pressure ; while in any part where
the temperature was below 14°, sulphurous acid gas would always exist as
a liquid. The difference between vapors and gases is therefore merely a
physical difference dependent on temperature. A gas is permanently, that
which a vapor is temporarily.

The sulphide of carbon as a liquid is stated to resist a very low degree of
cold without solidifying. The intense cold produced by its evaporation is,
however, suflQcient to bring the evaporating liquid to the solid state. Pour
a small quantity of sulphide of carbon into a watch-glass. Place a few fibres
of asbestos on a slip of filtering paper, so that one end may be immersed in
the liquid, and the other passed freely over the edge of the glass. In a few
minutes the projecting end will be fringed with a snow-like crystalline
deposit of a solidified vapor. This may serve as an illustration of the cooling
process by which solid is obtained from liquid carbonic acid.

The laws which govern gases also govern vapors, so long as they have a
temperature above the boiling-points of their respective liquids.

Physical Properties of Gases and Vapors. — Gases have no cohesion.
Their volume is determined by the capacity of the containing vessel ; and it
is remarkably affected by slight changes in temperature and pressure. (The
rules for calculating changes in volume from these causes will be found in
the Appendix.) Unless gases are confined within a closed space, as in
caoutchouc or bladder, or in a gas-jar inverted on water or mercury, we can
have no knowledge of their materiality, or of the fact that they exclude other
bodies from the space which they occupy. When secured in meuibranes, they
manifest remarkable elasticity ; they are easily compressed into a smaller bulk,
but immediately resume their original volume on the removal of the pressure.
They gravitate, and therefore have weight ; but as they are light compared
6

82 GASES, INCREASE OF VOLUME BY TEMPERATURE.

with their bulk, their weights are generally given for 100 cubic inches (nearly
one-third of a gallon). Owing to their great elasticity, their volume is
affected by the height of the column of liquid in which they are standing, as
well as by the density of the liquid itself. Thus a gas admits of accurate
measurement in a graduated vessel, only when the liquid on the outside of the
jar is precisely on a level with the liquid on the inside. If the level on the
inside be higher, the gas is under diminished pressure from the gravitating
force of the column of liquid ; and the contents of the graduated jar, as read
off in cubic inches, appear greater than they really are. If by pressing the
vessel downwards, the level on the inside is below that on the outside, the
gas is under increased pressure, and the contents are less than they appear
to be. The substitution of water for mercury makes a considerable difference
in the volume of a gas. Fill a long stout tube with mercury, and invert it
in a basin containing just enough mercury for this purpose. Allow two or
three cubic inches of air to pass up the tube, and then mark the level of'the
mercury. Now pour into the basin, water covered with litmus, or indigo,
and then raise the tube into the colored water, so that the mercury may flow
out. As it flows out, the water takes its place, and it will be found when
the substitution is complete, that the gas now has only from one-third to
one-half of the volume which it had when over the mercury. The inside
column of mercury gravitates with more force than that of water, and the
expansibility of the gas allows it to occupy a larger space. Over water the
gas contracts nearly to its proper bulk.

The following experiments will illustrate the effects of atmospheric pres-
sure on the volume of gases. Tie securely a piece of thin caoutchouc over
the mouth of a wide short jar. Place it under a receiver on the air-pump
plate, and exhaust the vessel. As the pressure of the air is removed from
the interior, that which is contained in the vessel expands and raises the
caoutchouc considerably. This phenomenon disappears on letting the air
pass into the receiver. — Adjust a small bladder with a leaden weight, so that
it will just sink, in a tall jar of water. Place this under a receiver, as in the
preceding experiment, and withdraw the air. The air in the bladder expands
by removal of pressure from the surface of the water, and the bladder in-
stantly rises to the surface, by reason of the increased volume of its contents.
On letting in the air, it again falls to the bottom of the vessel. — The effect
of heat may be shown by various experiments. Invert a long tube, having
a thin bulb, of about three inches' diameter, at one end, the other, or open
end, being immersed in a solution of litmus contained in a bottle. Heat the
bulb by a spirit-lamp to expel some of the air, wiien, on cooling, the colored
liquid will rise to one-third or one-half the height of the tube. This will
now serve as a delicate air-thermometer. On applying the warm hand to
the bulb, the increase in the volume of air will be at once perceptible by the
descent of the colored liquid in the tube ; and the contraction or diminution
of volume by cold may be shown by pouring a little ether over the bulb.
The cold produced by the evaporation of this liquid, condenses the contained
air, and the colored liquid rises in the tube. — Heated air, by reason of the
increase of volume, is lighter than cold air. Balance on a scale-beam a thin
glass shade of some capacity, with the open end downwards. Place a spirit-
lamp under the shade; the increase in volume and diminution of weight in
the heated air are at once manifested by the rising of the shade. Again, a
small bladder so balanced with lead as just to sink in cold water, will, by
the expansion of air in the bladder, rise to the surface if placed in a jar of
hot water.

Pressure and temperature, with very slight limits, affect all gases equally,
whether compound or simple, however they may differ from each other in

INCANDESCENCE. 83

density. There is, however, a peculiarity in the expansion of gases by heat,
whereby they are distinguished from liquids. The same quantity of heat will
expand a gas, in an equal degree, at a high and a low temperature ; but with
liquids the expansion is, for the same quantity of heat, proportionably greater
at high than at low temperature.

It has been ascertained by Dalton and Gay-Lussac that 1000 measures of
dry air, when heated from the freezing to the boiling point of water, undergo
an increase in bulk about equal to 375 parts ; so that 1000 cubic feet of air
at 32° become dilated to 1375 cubic feet at 212°. Air, therefore, at the
freezing-point expands ^1 o^h part of its bulk for every added degree of heat
on Fahrenheit's scale (for 375-f-180 = 2-08, and 1000^208 = 480). Hence,
assuming that the volume of air is 480 cubic inches, thus,

480 cubic inches, at 32°, become

481 " at 33°,

482 « at 34°, &e.

increasing one cubic inch for every degree. A contraction of one cubic inch
occurs for every degree below 32° : thus,

480 cubic inches, at 32°, become
479 " at 31°,

478 " at 30°, &c.

The volume of air, therefore, at 32° would be doubled at 480°, and tripled
at 960° : the latter temperature being about that of a dull-red heat. Steam,
and all other vapors, when heated out of contact of their respective fluids,
are subject to laws of expansion similar to those of air. It may be remarked,
in regard to the expansion sustained by gases as a result of increase of tem-
perature, that, although great in amount, the actual force which is thus
exerted is small (when compared with that of solids and liquids under the
same circumstances), in consequence of their extreme elasticity : thus,
although the volume of air (or of vapor) is about tripled by red heat, vessels
easily sustain the pressure.

(For the determination of the increase and decrease of volume as a result
of changes of temperature, see Appendix.)

Incandescence. — If is a remarkable fact, that gases which appear of such
an attenuated nature, can, even when brought almost to a state of vacuum,
be rendered incandescent by the high temperature of the electric spark. No
oxygen is present, therefore there can be no combustion. Hydrogen, nitro-
gen, sulphurous acid, and other gases, inclosed in tubes through which the
electric spark from Ruhmkorff's apparatus is discharged, evolve an intense
light as the result of incandescence ; and this light not only presents a
different color for each gas in its vacuous state, but it is resolvable into a
spectrum of colored bands of different degrees of refrangibility. Thus when
pure hydrogen is placed in a tube, which is afterwards brought almost to a
state of vacuum by an air-pump, it is found that under a discharge from the
coil, a fine ruby red light is evolved ; while the nitrogen vacuum,' under
similar circumstances, gives a magnificent violet light (Miller). The
spectra produced by the lights of these gases are singularly contrasted ;
while the nitrogen spectrum includes rays of high refrangibility, that of
hydrogen contains only rays of low refrangibility, and these have scarcely
any action on the collodio-iodide of silver. Attenuated gases thus heated
by the electric discharge, evolve the colors indicated in the subjoined table :

84 SPECIFIC HEAT OF GASES.

Hydrogen, ruby red. Light carburetted

Nitrogen, violet. hydrogen, pale blue.

^Oxygen, greenish-white. Olefiant gas, pale red.

Sulphurous acid, blue. Ammonia, red and violet.
Carbonic acid, violet.

The compound gas ammonia evolves the colors of its constituent elements.

Specific Gravity. — Density. — Gases and vapors vary in specific gravity.
As a general rule, the air is taken as a standard, and all gases are compared
with it under similar circumstances of temperature, pressure, humidity,
dryness, &c. The lightest of all gases is hydrogen, which is 14-4 times
lighter than air. Among the heaviest is the vapor of iodine, which is, bulk
for bulk, nearly 9 times as heavy as air. The greater number of simple and
compound gases are of about the same weight as air, or a little heavier.
(The rules for calculating the specific gravity of gases and vapors will be
found in the Appendix.) It has been proposed to substitute hydrogen as
a standard of comparison instead of the atmosphere, because it is the lightest
of the gases, and it will place the equivalent weights and specific gravities
of these bodies, with few exceptions, in a uniform relation ; but we do not
take naphtha as the standard for the specific gravity of liquids, nor lithium as
the standard for solids ; and the selection of air for gases, and of water for
liquids and solids, has been so confirmed by long use, that any change would
be attended with great inconvenience. A volume of air may be obtained for
the purpose of weighing, with much greater certainty than a volume of pure
hydrogen, not to mention that for equal weights nearly fifteen times as much
hydrogen as air must be taken in one experiment — thus increasing the
chances of error. Gerhardt and others, who have advocated this change to
suit an hypothesis, have entirely forgotten that if the standard is changed for
specific gravity, it will entail a change for specific heat, the refractive power
of gases, the law of diffusion, &c., iu reference to which, air is now uni-
versally taken as a standard.

Specific Heat. — By this it is to be understood the proportional quantity of
heat contained in equal weights of different gases at the same thermometric
temperature. The absolute quantity of heat contained in two gases, as well
as in two liquids, at the same temperature, is very differgnt. A thermometer,
in fact, can only show the relative quantity present. Gases are equally
expanded or increased in volume by equal additions of heat ; but unequal
quantities of heat will be required to raise them to the same degree ; and
for this reason unequal quantities will be given out by them in cooling from
a high to a low temperature.

When equal weights of different gases, heated at 212°, are passed slowly
through a glass tube immersed in cold water, the temperature of the water is
raised while the gas is cooled. The relative heating power of gases has
been thus measured and tabulated — atmospheric air being taken as the
standard of comparison : —

ilydrogen .

. 12340

Air . . .

. 1000

Olefiant gas

. 1576

Protoxide of nitrogen

. 887

Carbonic oxide .

. lOSO

Oxygen

. 884

Kitrogen .

. 1031

Carbonic acid

. 828

These figures represent the specific heat or the capacity for heat of different
gases. As each compound gas has its own speci,fic heat, without reference
to the specific heats of its constituents, it follows that this physical property
of gas€8 may be occasionally applied to distinguish a gaseous chemical
compound from a gaseous mixture. It has been thus applied to the con-
stituents of the atmosphere.

INFLUENCE OF LIGHT, MAGNETISM. 85

Light. — Gases exert a refracting power on lip^ht peculiar to each, and the
refractinf^ power of a compound gas is not equal to the mean refracting
powers of its constituents. Tlie refracting powers of the subjoined gases
were determined by Biot and Arago, and are as follows : — air being the
standard.

Hydrogen .

6614

Nitrogen .

. 1034

Ammonia .

3168

Carbonic acid

. 1004

Carburetter! hydrogen

2092

Air .

. 1000

Hydrochloric acid

1196

Oxygen

. 861

Hydrogen has the highest and oxygen the lowest refracting power among
these gases.

Light like the electric fluid or heat, has in some instances a combining
power over gases. Thus a mixture of chlorine and hydrogen is converted
into hydrochloric acid with explosion, when exposed to the dfirect rays of the
sun or any intense light, as the oxyhydrogen or lime light ; but more slowly
and gradually in diffused light, such as daylight. Bunsen and Roscoe have
ingeniously made the rate of combination a measure of the intensity of light
for photometrical purposes, and have thus been able to institute numerous
comparisons on the relative intensities of artificial lights and the light of the
sun. This combining power resides in those rays of the spectrum which are
near to the raoit refrangible colors, the violet and blue ; although not visible
in the ordinary spectrum, they may be made visible by uranium glass.
When exposed to the yellow, orange, or red rays, the two gases show no
tendency to combine. This is in accordance with the action of light on the
salts of silver.

Magnetism. — Faraday has discovered that there is a difference among
gases, as to their magnetic properties, when secured in glass tubes and deli-
cately suspended in the field of a powerful artificial magnet. Of the follow-
ing gases, four were found to be magnetic, taking up a north and south
position (axial) like the common magnet; while three were diamagnetic,
taking up a position at right angles, or east and west (equatorial). In
measuring the intensity of this power, it was found that a vacuum in the
glass tube was 0*0, and that oxygen manifested the greatest magnetic force.
The following table represents the relative intensities : —

. 0.0

Oxygen

. 17.5 "1 d Carbonic acid

Air .

. 3.4 ■ o Hydrogen .

Oledant gas

. 0.6 ' W5 Ammonia .
. 0.3 J a Cyanogen .

Nitrogen

A vacuum, 0.0.

0.1) .:

0.9)

[The reader will find in the Appendix a Table of the principal gases and
vapors and their compounds, representing in a concise form their combining
volumes, atomic weights, specific gravity, and the weight of 100 cubic
inches.]

Diffusion. — Osmosis. — There is a property oY gases which is known under
the name of diffusion. This implies a power by which they intermingle with
each other in spite of a difference in specific gravity, and when they have no
tendency to combine chemically, and when this intermixture takes place
through membranes or porous partitions it is called osmosis. If we half fill
a bottle with mercury, and pour upon this, ether — it is well known that the
two liquids do not combine chemically, and that there is a great difference in
their specific gravities. Hence, it is hardly necessary to observe, that how-
ever long these liquids may be in contact in a closed bottle, the mercury will
not rise into the ether, nor will the ether descend into the mercury. Further,
if shaken together and thus mixed, they will in a few minutes be completely

86 DIFFUSION OF GASES AND VAPORS.

separated according to their specific gravities. Carbonic acid and hydrogen
among gases have no tendency to form a chemical union, and they differ more
from each other in specific gravity than mercury does from ether. Invert a jar,
well-ground, containing hydrogen, on a similar jar which it will accurately
fit, placed below — containing carbonic acid. After from five to ten minutes'
contact at the ordinary temperature, carbonic acid will be found in the
upper jar (by the appropriate test, lime-water), and hydrogen will be found
in the lower (by the application of a lighted taper and the combustion of the
gas). If this experiment is performed in bottles, it will be found that the
two gases when once mixed will never again separate. If light hydrogen
or coal-gas be thus placed over ajar of air, the light gas will descend, and
render the air explosive. Air is one-third lighter than carbonic acid ; air
will support combustion, and it has no effect on lime-water. If a jar of air
be placed over one of carbonic acid — in a few minutes the heavy carbonic
acid will have risen into the air, a fact proved by lime-water being precipi-
tated white, and a lighted taper being extinguished in the upper jar. This
property of gases applies also to vapors, and it leads to a uniformity of mix-
ture on contact, when there is no tendency among them to combine chemi-
cally. Such mixtures are of a physical nature, and their properties are always
represented by the sum of the properties of their constituents. During
mixture, there is no evolution or absorption of heat, and no increase or con-
traction of volume. The atmosphere itself forms a remarkable example of a
mixture of this kind. There are numerous facts in chemistry illustrative of
this property. That a gas like ammonia, with a specific gravity of O'SST,
should rapidly diffuse itself, and rise through the air is not surprising ; but
it may be proved to fall as well as to rise, or, in other words, to diffuse
itself in all directions. Place a long (stoppered) shade with its open end in
a plate. Suspend from the stopper long strips of dry test-paper for alkalies,
e. g., reddened litmus, turmeric, and rose. Now pour on the plate a few
drops of a strong solution of ammonia, or open a small jar containing am-
monia beneath, the ascent and diffusion of the gas will be indicated by the
progressive change of color in the papers as it ascends. By another method
of proceeding, the diffusion downwards may be proved. Place a similar shade
in a clean plate containing slips of the various test-papers. Remove the
stopper of the shade and place over it a small jar containing a few cubic inches
of ammonia. In the course of a few minutes the descent (or diffusion) of the
light alkaline gas will be indicated by a change of color in the papers. The
specific gravity of sulphuretted hydrogen gas is I 17. A few cubic inches
of this gas will, in spite of its greater density, diffuse itself in the air, and be
perceptible in a few minutes in every corner of a large apartment. The same
is true of other gases which are not perceptible to smell. The vapor of
ether is, perhaps, more remarkable in this respect. Its specific gravity is
nearly 2 6. In spite of this great density, the diffusibility of ether vapor is
so great, that on opening a bottle containing the liquid, the odor of the
escaping vapor will be in a few minutes perceptible over a large space.
Even metallic vapors, such as that of sodium, are observed to have this
diffusible property. Bunsen found that a small piece of sodium burnt in the
corner of a room produced a vapor which was easily detected at the most
distant part of the room by the coloring of an invisible jet of gas, and by
the spectrum obtained from this light (p. 22.) The great natural result of
this property, is to equalize mixtures of gases and vapors, and, in open spaces
to prevent an accumulation of foul efiQuvia in the air.

It must not be supposed, however, that specific gravity has no influence
on diffusion. On the contrary — the heavy carbonic acid escapes slowly by
diffusion from a narrow jar placed with its mouth upwards, while the light

DIFFUSION OF GASES AND VAPORS. 8T

hydrogen also escapes slowly from a similar jar placed with its mouth down-
wards.

A curious fact regarding this property, however, is, that it is manifested
not only when the sole communication between the two gases is by a narrow
tube, but when they are separated by porous partitions, such as dry plaster,
nnglazed porcelain, animal membrane, caoutchouc, cork, or spongy platinum.
To this mode of diffusion the term osmosis is applied, from a Greek word sig-
nifying "to push through," and the terms endosmosis and exosmosis were
applied to those cases respectively in which the gas penetrated into or passed
out of the vessel through the porous septum. Dobereiner first observed the
readiness with which hydrogen escaped through a small crack or fissure in a
glass jar which had been filled with the gas. The water rose three inches in
a jar from which the gas had thus escaped, clearly proving that the hydrogen
had not been replaced by an equal quantity of air passing into the jar. Ac-
cording to Longet, hydrogen will traverse a sheet of writing paper or even
gold leaf. It traverses nnglazed porcelain with great rapidity.

Mr. Graham, on examining Dobereiner's results, observed that while the
hydrogen escaped outwards, a portion of air, amounting to between one-
fourth and one-fifth of the lost hydrogen, penetrated inwards; in fact, that a
volume of air was not replaced by a volume of hydrogen, but by 3.83 volumes.
He also found that every gas had what he calls a diffusion-volume peculiar
to itself, representing the amount in which it was exchanged for a volume of
air — air being considered = l or unity. The diffusion-volume was further
found to depend on the sp. gr. of the gas. Of gases lighter than air, the
diffusion-volume is greater than 1 ; of those which are heavier, it is less than
1. As a general law it may be stated that the diffusion-volumes of gases, or
the volumes in which they replace each other, are inversely as. the square
roots of their densities. The following table represents the diffusion-volume
or the velocity of diffusion among different gases : —

Hydrogen . . . .3.83

Light carb. hyd. (CH2) . 1.34

Carbonic oxide . . .1.01

Nitrogen . . . .1.01

Olefiant gas . . . 1.02

An experiment illustrative of the rapid diffusion and osmosis of gases, may
be performed with hydrogen. Fill a wide-mouthed jar with pure hydrogen,
and secure the mouth (placed downwards) with a piece of thin sheet caout-
chouc. Then place the jar, mouth upwards, under a bell-glass of air immerged
in water. The rapid diffusion and osmosis of hydrogen will be indicated by
the caoutchouc cover being gradually depressed, and after a time it will
burst. This is owing to the place of the hydrogen not being supplied with
sufficient rapidity by the passage of air. If a similar jar is filled with air
and placed in a bell-glass of hydrogen, the caoutchouc will rise up in a con-
vex form, and become so distended that it will finally burst, thus showing that
the gaseous contents of the jar have greatly increased by the rapid osmosis
of hydrogen. A layer of animal membrane (bladder) may be substituted
for caoutchouc with similar results.

The fact that gases will thus traverse membranes which would be imper-
vious to them without rupture under direct piifesure, has an important bear-
ing on numerous chemical and physiological phenomena. The function of
respiration is partly dependent on the exchange of gases by osmosis. The
oxygen of the air is taken into the lungs in all warm-blooded animals, pene-
trates the tine pulmonary membrane, as well as the thin coats of the capil-
laries ; and it there excludes the carbonic acid of the venous blood. Besides

Oxygen

. 0.94

Sulpli. hyd. (HS) .

. 0.95

Protoxide of nit. (NO)

. 0.82

Carbonic acid .

. 0.81

Sulphurous acid

. 0.68

88 . DIFFUSION OF GASES AND VAPORS.

carbonic acid, aqueous vapor containing animal matter is also largely elimi-
nated. Hence the cliief phenomena of respiration are due to an endosmose
of oxygen and exosmose of carbonic acid, which takes its place. Carbonic
acid has been found to escape from blood which was drawn from a vein into
a vessel containing hydrogen ; thus proving that the blood contains carbonic
acid in a free state, and that it is not produced by the combination of oxygen
with carbon in the blood circulating through the lungs.

Gases and vapors which admit easily of detection by chemical tests may
be proved to traverse membranes with great rapidity. If a wide-mouthed
bottle is filled with sulphuretted hydrogen gas, and the mouth is completely
closed by a layer of bladder tied tightly over it, it will be found, by the
application of paper impregnated with a solution of a salt of lead, that the gas
rapidly escapes through the bladder. The paper is turned brown.

If into a similar vessel a small quantity of prussic acid is put, and the
mouth is secured with bladder, the rapid escape of the volatile acid vapor
will be indicated by inverting on the bladder a watch-glass containing a drop
of a solution of nitrate of silver. The solution is whitened in a few minutes,
and crystals of the cyanide of silver will be found in the watch-glass. A
practical application of the property of osmosis of gases, has lately been made
by Mr. Ansell, of the Royal Mint. Light carbnretted hydrogen, the explo-
sive gas of coal mines, comes next to hydrogen in diffusive power. Thus, as
it will be seen by the table, every 100 volumes of air will be replaced by 164
volumes of this gaseous compound. A bladder containing air placed in light
carburetted hydrogen gas, will rapidly become distended. Mr. Ansell has
contrived an instrument to give warning of danger from explosions, based
on this osmotic power of the gas. He says : " For the purpose of indicating
by signal, I use a balloon of thin India-rubber, with its neck tied tightly with
silk, and a piece of linen is bound around the equator of the balloon to pre-
vent expansion. The balloon is placed under a small lever, upon a stand of
wood, so as to exert a gentle pressure upon the lever. If any gas accumu-
lates around the balloon, the lever is pressed, and, raising it, relieves a detent,
by which the poles of a battery are connected, and we thus get telegraphic
communication." " It may be so delicately set," says the author, " as to give
warning if the mixture be still below the explosive point." An ingenious
piece of apparatus for showing the relative osmotic power of gases has also
been invented by this gentleman. It consists of a glass vessel, with a porous
earthenware cover joined to it in an air-tight manner. This vessel forms the
air-chamber. At the lower part it is connected with a thermometer tube,
which bends upwards, and is fastened to a scale. Mercury is introduced into
this tube so as to lie at the lower level of the glass air vessel, and to rise to
a certain height on the thermometer tube where it marks a zero. If ajar,
containing light carburetted hydrogen is now inverted and placed over the
porous glass vessel, care being taken that the earthenware septum is not
wetted, the osmotic force of the gas is immediately manifested by the rapid
rise of the mercurial column in the thermometer tube. This proves that the
light carburetted hydrogen penetrates the air-chamber much more rapidly
than the air passes out. A rise of several inches thus takes place in a few
minutes. A small percentage of the explosive gas has been found to be
sufficient to affect the column^ mercury sensibly. If in place of this gas,
carbonic acid is placed over tM air chamber, a portion of the air contained
in it passes out with greater rapidity than the carbonic acid passes in, and
the mercurial column is depressed. On the removal of the gas-jar, the mer-
cury slowly falls to its level by the whole of the gas which had entered pass-
ing oBF through the porous septum; after some hours, there is nothing but
air in the glass vessel.

PENETRATION OF METALS BY GASES. 89

In some further researches on the property of gases, Mr. Graham has made
the discovery tliat mixed gases, as atmospheric air, for instance, do not tra-
verse septa of caoutchouc in the exact proportions in which their constituents
are known to exist. Thus he found that if one side of the rubber film was
freely exposed to the atmosphere, while the other side was under the influ-
ence of a vacuum, oxygen and nitrogen traversed the septum but in very
different proportions from those constituting the atmosphere. Instead of 21
per cent., the oxygen formed 41.6 per cent., so that the rubber film kept
back one-half of the nitrogen, and allowed the other half to pass through with
all the oxygen. The air was thus dialyzed, and its constituents separated by
the rubber. Its properties were also changed. It kindled into flame, ignited
wood, and, in reference to combination, had all the properties of a mixture
intermediate between air and pure oxygen. {Proc. R. S. 1866.)

Mr. Graham's view is that the gases are liquefied on the surface of the
rubber or membrane ; they thus penetrate its substance as ether or naphtha
would if placed in contact with it, and they again evaporate into a vacuum,
and appear as gases on the other side. The results show that gases are
unequally absorbed and condensed under these circumstances; oxygen twenty-
four times more abundantly than nitrogen, and that they penetrate the rubber
in the same proportion.

Penetration of Metals hy Gases — MM. St. Clair Deville and Troost
found that hydrogen would even penetrate red hot platinum and iron, and it
has been suggested in this case that hydrogen as a metallic vapor is liquefied
and absorbed by the heated metal, and again escapes on the other side. Mr.
Graham /ound that platinum in the form of wire or foil at a low red heat
would take up and hold 3.8 volumes of hydrogen measured cold; but it is
by palladium that the property in question appears to be possessed in the
highest degree. Palladium foil from the hammered metal condensed as much
as 643 times its volume of hydrogen, at a temperature under 212°. The
same metal had not the slightest absorbent power for either oxygen or nitro-
gen. Hence a peculiar dialytic action may reside in certain metallic septa
which may enable them to separate hydrogen from other gases. According
to this gentleman, platinum in the form of sponge will absorb 1-48 times its
volume of hydrogen, and palladium as much as 90 volumes. In the state of
platinum black, the metal absorbs several hundred volumes of hydrogen.
Carbonic oxide is taken up more largely than hydrogen by soft iron, and this
absorption at a low red heat is considered to be the first and necessary stage
in the conversion of iron into steel. The carbonic oxide gives up half of its
carbon to the iron when the temperature is afterwards raised to a consider-
ably higher degree. While heated platinum absorbs hydrogen, silver appears
to have a strong absorbent power over oxygen. It has been long known that
it gives off oxygen in the act of solidifying from the melted state, and gene-
rally in a sudden jet, so as to produce some irregularity on the surface of the
button. Mr. Graham found that the sponge of silver fritted but not fused,
held in one case as much as 7*49 volumes of oxygen.

The first of the metalloids which will require consideration is Oxygen.

OXYGEN. PREPARATION,

CHAPTER YI.

OXYGEN— (0=8)— OXIDES— OXIDATION.

History. — Oxygen, one of tlie six permanent gases, was discovered by
Priestley in the year 1174. He obtained it by heating the red oxide of
mercury. He called it dephlogisticated air ; it was termed empyreal air by
Scheele, and vital air by Condorcet. The name oxygen was given to it by
Lavoisier, from its tendency to form acid compounds (6|i;?, acid, and y^wdoi,
to generate). It is more abundantly diffused throughout nature than any of
the other elementary bodies; it forms eight-ninths of the weight of water,
one-fifth of the bulk of the atmosphere, and a large proportion of the
mineral bodies of which tbe crust of the globe is composed. Oxygen is a
constituent of a large class of acids — the oxacids, which are solid, liquid, and
gaseous compounds. It is a constituent of all the alkalies, excepting am-
monia, and of the alkaline earths ; and it enters largely into the composition
of numerous organic substances belonging to the animal and vegetable
kingdoms.

Preparation. — This gas may be readily procured by heating in an ordinary
retort, by means of a spirit-lamp, a mixture of equal parts of finely-powdered
peroxide of manganese, previously well dried, and of chlorate of potash. The
oxygen is entirely derived from the decomposition of the chlorate, which is
converted into chloride of potassium (KO,CI05=KCl-f08). The gas may
be collected in the usual way over water or mercury. As it is thus procured,
it generally contains traces of chlorine, which may be separated by passing
the gas, during its collection, through a wash-bottle containing a solution of
potash, or by allowing the gas to remain for a short time in contact with
water. One hundred grains of the chlorate will yield thirty-eight grains, ==
about 113 cubic inches of oxygen ; or one ounce will yield nearly two gal-
lons of the gas. This is in the proportion of about twenty-eight gallons of
gas to one pound of the salt. A mixture in fine powder, of ten parts by
weight of chlorate of potash with one part of sesquioxide of iron, has been
recommended by Mr. Ashby as superior to the mixture with manganese, in
the facility with which oxygen is disengaged, and the great economy of heat.
Every grain of this mixture yields a cubic inch of the gas. The result of
our experiments with the mixture is, that the oxygen is liberated too suddenly
and rapidly.

Oxygen may also be procured by heating the chlorate of potash sepa-
rately : but this process requires a much higher temperature, and the employ-
ment of a retort or tube which will not readily fuse. This is, however, the
only method of procuring the gas absolutely pure for chemical purposes ; it
should then be collected over a mercurial bath.

^^ygsn is obtained on the large scale by gradually heating to full redness
in a wrought-iron bottle the black oxide of manganese reduced to a coarse
powder. The bottle should be filled to not more than two-thirds of its capa-
city, and the heat gradually applied. In the first stage of the operation,
aqueous vapor and carbonic acid escape; when an ignited match is kindled
into a bright flame at the mouth of the tube connected with the bottle, the
gas may be collected. The chemical changes which ensue are of a simple

PROCESSES FOR PROCURING OXYGEN. 91

kind (3MnO^=Mn30^-f-Oa). The oxide of manganese, at a full red beat,
parts with one-third of its oxygen. Mitscherlich states that three pounds will
yield a cubic foot (six gallons) of oxygen ; while Dr. Miller assigns five gal-
lons as the quantity obtained from one pound. This difiference probably
depends on the impurities contained in the native oxide. Among these is
carbonate of lime, which contaminates with carbonic acid, the oxygen obtained
from manganese. The carbonate may be removed by previously washing the
mineral with diluted hydrochloric acid ; and if it is subsequently dried before
use, oxygen will be obtained from it in a much purer form. Another method
consists in mixing the peroxide with sulphuric acid in such proportions as to
beoftheconsistencyofcream, and heating the mixture, when oxygen is evolved
(Mn024-S03=MnO,S03+0) ; but there are some inconveniences attending
this process. The bichromate of potash heated with an excess of sulphuric
acid also yields this gas (KO,2Cr03+5(HO,SO,)=KO,HO,2S03+Cr,03
3SO3 + HO + O3), one-half of the oxygen contained in the chromic acid
being evolved in this decomposition. A mixture named oxygenriesis has
been lately much used for the extemporaneous production of oxygen. It
consists of equivalent proportions of peroxide of -barium and bichromate
of potash. Diluted sulphuric acid is added and heat is applied ; oxygen is
liberated, and may be collected from a retort in t^e usual way. The reac-
tion of the acid on the bichromate is as above represented, and on peroxide
of barium as follows : BaO, + S03=BaO,S03+0. The oxygen from the
bichromates comes off as ozone and from the peroxide as antozone. If hydro-
chloric acid is used, some chlorine is evolved. Oxygen may be procured
from the red oxide of mercury by heating it to redness in a retort
(HgO = 0 + Hg). This is an expensive method of procuring the gas, and it
is now seldom resorted to ; but it has an interest to the chemist from its having
been the compound in which this important element was first discovered by
Dr. Priestley.

Among recent processes for procuring oxygen, two are deserving of notice.

1. The first depends on the production and decomposition of the peroxide
of barium. The peroxide is procured by passing a current of air, deprived of
carbonic acid, over baryta heated to low redness in a porcelain tube. If the
air is not too dry, oxygen is absorbed by the baryta at a low red heat, and
the barium becomes peroxidized. The presence of a small quantity of aque-
ous vapor in the air is found to be absolutely necessary to this absorption.
When the peroxidation is completed, the current of air is cut off, the tube is
heated to full redness, and at this high temperature the peroxide is resolved
into oxygen and protoxide, or baryta. The oxygen may be collected, and
the baryta again peroxidized for a fresh supply. According to Boussingault,
a pound of baryta will thus yield about nine gallons of oxygen gas. The
baryta itself remains unchanged during the process. This is the only method
at present known by which pure oxygen, in the gaseous state, can be readily
procured from the atmosphere. 2d. Oxygen has been obtained by causing
the vapor of boiling sulphuric acid to pass through a porcelain tube heated
to full redness. The retort containing the sulphuric acid is filled with pieces
of pumice previously heated with the acid to drive off any chlorides, and the
porcelain tube contains the same material. At a full red heat, the products
obtained are oxygen, aqueous vapor, and sulphurous acid (S03,H0=0 +
HO-fSOa). The sulphurous acid is removed by water or by a solution of
carbonate of soda, through which the gaseous products are passed. Two
useful salts of soda are thus procured — 1, the sulphite employed in the manu-
facture of hyposulphite ; and 2, bisulphite of soda, a salt now much used in
chemistry and the arts for the removal of chlorine. This process has been
carried out on a large scale by MM. St. Clair- Deville and Debray, and it is

92 *" PHYSICAL PROPERTIES OF OXYGEN.

stated, with satisfactory results (Journal de Cliimie, Mai, 1861). M. de
Luca, of Pisa, agrees with these chemists in considering that this is the most
economical process for obtaining oxygen on a large scale. From a fluid
ounce of sulphuric acid M. de Luca states that he procured 360 cubic inches
of oxygen. On the large scale, vessels of platinum must be used {Cosmos,
July, 1861, p. 97).

Properties. — Oxygen gas is insipid, colorless, and inodorous; it is perma-
nently elastic under all known pressures and temperatures. Its specific
gravity compared with air, is as 1-1057 to 1*000. Compared with hydrogen,
its specific gravity is =16, hydrogen being =1. At mean temperature and
pressure, 100 cubic inches weigh 34 24 grains (Dumas and Boussingault).
Its refractive power, in regard to light, is less than that of any of the gases ;
compared in this respect with atmospheric air, it is as 0830 to 1000.
According to De la Roche and Berard, its specific heat, compared with an
equal volume of air, is = 0 9765, and with an equal weight of air, = 0*8848,
that of air being =1 000. According to Tyndall, it has, in reference to
heat, a lower absorbing and radiating power than other gases. Faraday's
researches have shown that it is most magnetic of all gases, its magnetic force
comparedwiththatof the atmosphere being as 17 '5 to 3 4, a vacuum being taken
as 0, or the boundary betvfeen magnetic and diamagnetic gases (see. page 85.)
It occupies, among gases, the place which iron holds among metals, and, as
with iron, its magnetic force is destroyed by a high temperature ; but it
returns on cooling. The magnetic properties of the atmosphere are almost
exclusively due to the oxygen contained in it, and Faraday has suggested that
the diurnal variations of the needle may be referable to the increase or
decrease of the magnetic force in the oxygen of the atmosphere as a result
of solar heat. Oxygen is evolved by electrolytic action at the positive
electrode or anode, and occupies a high position among electro-negative
bodies or anions {see page 60).

It is dissolved by water, but only in small proportion. At 60° 100 cubic
inches of water will dissolve 3 cubic inches of the gas, and at 32°, about 4
cubic inches. All terrestrial waters hold it dissolved in much larger pro-
portion than it exists in the atmosphere-; and in this condition as a solution
of oxygen, it is fitted for the respiration of fish, the blood of these animals,
in circulating through the gills, being aerated by the free oxygen dissolved
in the w^ater. Oxygen in its pure state is neither acid nor alkaline. It is a
perfectly neutral gas ; it does not alter the color of blue or red litmus, and
shows no tendency to combine with acids or alkalies.

Oxygen eminently supports combustion. A lighted wax taper introduced
into this gas is rapidly consumed, with enlargement of the flame and the
production of an intense white light. The wax itself in a melted state, burns
in the gas as well as the wick. If a piece of wax taper three or four
inches long, be lighted and introduced into ajar of oxygen, with the lighted
end downward, it is speedily consumed, and the melted wax burns brightly
as it falls in drops through the gas. A taper (of green wax) with a glowing
wick, (of which the flame has been extinguished) — a slip of wood with the
end ignited, but not burning with flame, or a slip of paper soaked in a
solution of nitrate of potash, dried and ignited — will instantly burst into
flame when plunged into this gas. If the oxygen is pure, the wax taper or
wood may be thus rekindled into flame five or six tinies successively. Tow
saturated with ether or sulphide of carbon, and attached to the end of a
copper wire, if inflamed and plunged into this gas, burns with surprising
intensity, filling the jar with a large volume of flame In most of these
experiments water (HO) and carbonic acid (CO J are the products of com-

COMBUSTION OF CHARCOAL, SULPHUR, AND PHOSPHORUS. 93

bustion, by reasons of the oxygen uniting with the hydrogen and carbon of
the various combustibles.

Charcoal heated to redness and introduced into a vessel of oxygen will
glow more intensely but be consumed without flame. The whole of the
oxygen will be removed and converted into carbonic acid gas, occupying an
equal volume but possessed of widely different properties. If charcoal-bark
is substituted for charcoal, in this experiment, it will be consumed with
bright scintillations traversing the vessel of oxygen in all directions. Sulphur,
which burns in the air with a small blue flame, has the flame enlarged when
it is immersed in ajar of oxygen, and after a time it burns with a beautiful
purple color, dissolving as it were in the oxygen, and converting it into
sulphurous acid gas (SOJ, which is soluble in water. If, in this experiment,
the bell-glass of oxygen be placed in a white plate containing a diluted
solution of blue litmus, the neutrality of oxygen will be indicated in the
first instance by the blue color being unchanged ; and the production of an
acid by the burning of sulphur, will be demonstrated by the blue liquid being
reddened as the sulphurous acid gas is dissolved. Sulphuric acid is not
produced in this experiment. Phosphorus burns with a bright yellowish-
white light in the atmosphere ; but when kindled by a heated wire and
introduced into oxygen, or when kindled in the gas after its introduction,
it will burn with a still brighter light, gradually increasing to a dazzling
whiteness. If the piece be sufficiently large, the phosphorus after a time
will boil, its vapor will be diffused over the whole bell-glass, and burn with
equal intensity in every part. The vessel will become an apparently isolated
source of the brightest light The heat is so great, that the vessel is
frequently broken in this experiment. The yroduct of combustion in this
case is solid phosphoric acid (POs), the highest degree of oxidation of
phosphorus. The acid is seen in dense white vapors which readily dissolve
in water, and produce a strongly acid liquid ; a fact which may be proved by
placing a solution of blue litmus in the plate, as in the preceding experiment.
The production of acids by the union of oxygen with carbon in any form,
with sulphur and phosphorus, led Lavoisier not only to give the name of
oxygen to this body, but induced hira to adopt the hypothesis that the
acidity of compounds always depended on the presence of oxygen. But
oxygen may produce alkalies as well as acids. If potassium or sodium is
heated until it becomes ignited, and it is then introduced into the gas, it is
consumed with a brilliant combustion, and the product is an alkaline solid,
namely, peroxide of potassium (KOJ, in the case of potassium, and ses-
quioxide of sodium (Naj^Og) in the case of sodium. If the experiment is
performed in a bell-glass standing in a white plate, in which there is a
solution of litmus reddened by the product of burning phosphorus, the
formation of an alkaline compound, as a result of the combination of
oxygen with these metals, will be proved by the blue color of the litmus
being restored.

Although the views of Lavoisier respecting the acidifying properties of
oxygen have been proved to be incorrect, there is no non-metallic body with
which the production of acid properties in compounds appears to be more
strongly associated than with oxygen. If a metal combines in various
proportions with this element, the first oxide may show no acid properties,
but act as a base (^. e., it will combine with acids) ; but the other oxides are
often observed to acquire acid properties in proportion to the amount of
oxygen which unites to the metal. This is well illustrated in the oxygen
compounds of the metal manganese {see page 96). Among the common
vegetable acids it is noticed as a general rule, that the number of atoms of
oxygen is in excess of those required to produce water with the hydrogen.

94 OXACIDS. THEIR CONSTITUTION.

Among inorganic or mineral compounds, the oxygen acids or oxacids are
numerous as a class. The hyponitrous, phosphorous, and arsenious acids,
as well as the sulphuric, chromic, boracic, and silicic, contain three atoms of
oxygen ; while the nitric, chloric, bromic, iodic, phosphoric, arsenic, and
antimonic acids contain five atoms of oxygen. Some acids contain only two
atoms, as the carbonic and sulphurous acids, while others contain only one,
as the cyanic. As oxacids for the most part contain an atom of water, and
in the absence of water, they manifest no acidity, it has been supposed that
the oxygen of the water was really a necessary component of the acid, and
that hydrogen was the acidifying principle {see page 43). Thus, instead of
HONO5 representing nitric acid, the acid has been regarded as a hydracid,
i. e., an acid of hydrogen, represented by the formula HNOe. According
to this view, an acid is convertible into a salt of hydrogen, or a compound of
hydrogen with a radical which has not been isolated. But if this be admitted
with respect to inorganic acids, it will equally apply to those of the organic
kingdom. Thus pyrogallic acid (CigHf-Og) is a solid, anhydrous, crystalline
compound, which has no acid reaction, until it is dissolved by water (page
43). Under these circumstances, it must be assumed, either that the acid
now becomes 'RC^JIfij, or the hypothesis is unfounded. Although in com-
bining with chlorine, bromine, iodine, sulphur, and cyanogen, hydrogen
produces gaseous acids free from water, yet acid compounds exist which not
only contain no water, but which are decomposed by that liquid. The
fluoboric acid (BFg) may be taken as an illustration. This body contains
neither hydrogen nor oxygen, and is at the same time as much an acid gas
as hydrocyanic, or any of the hydracid gases above mentioned. But, unlike
these, it is resolved by water into two other acids. A similar observation
may be made with respect to the fluosilicic acid (SiFg). The manganic
(MnOg) and fulminic acids {Cjfi^) combine with bases to form well-defined
salts, but not with water, as no hydrates of these acids are known. The
molybdic, tungstic, silicic, titanic, and other acids, can be obtained perfectly
anhydrous, and in this state they will expel other acids from bases. The
combinations of hydrogen alone prove that there are no sufficient grounds
for adopting this hypothesis of the constitution of acids. Hydrogen com-
bines with nitrogen to form a powerful alkaline base, ammonia ; but when
the three atoms of hydrogen in ammonia are replaced by three atoms of
oxygen, a strong acid is the result; and 'the conversion of the base,
ammonia, into nitric acid and water by simple oxidation, is a matter of daily
experience. Hydrogen differs from oxygen in forming no acid compounds
with metals. The only exception is, its compound with tellurium. It is
also a remarkable fact, that when the hydrogen is replaced by oxygen in
some neutral organic compounds, an acid frequently results. In the acetous
fermentation, the conversion of alcohol to vinegar or acetic acid is the result
of simple oxidation. One-half of the hydrogen is removed — the proportion
of oxygen is increased, and as a result of these changes, the neutral com-
pound, alcohol, is converted into acetic acid. Another remarkable instance
of the acidifying effect of oxidation is furnished by the pure essential oil of
bitter almonds. This liquid, dissolved in alcohol, is perfectly neutral. As
the alcohol evaporates, the oil is oxidized, and is converted into solid crys-
tallized benzoic acid. The only chemical change here is the substitution of
oxygen for hydrogen ; and as this goes on, the neutral is observed to be
converted into an acid compound. Hydrogen has therefore no claim to be
regarded as an acidifying principle in preference to oxygen. The name
given to this element by Lavoisier is fully justified by modern researches,
with the qualification that it is not the only acidifying element. In fact,
acidity, like alkalinity, is a condition or property resulting from the chemical

OXYGEN. OXIDATION. 95

union of bodies; and is not essentially dependent on the presence of any one
substance. There appears to be no good reason, therefore, for converting
the oxygen-acids to hydracids by the supposed decomposition of the water
associated with them.

Oxygen not only produces, as a result of chemical union, acids and
alkalies, but it forms with the greater number of metals, binary compounds
which are quite neutral; and in order to distinguish these from other pro-
ducts, they are called oxides. With some of the metals, when heated to a
high temperature, the phenomena of combustion are splendidly manifested.
Thus zinc in foil or shavings, may be formed into a bundle two or three
inches long (the ends being tipped with a little melted sulphur, for the
purpose of igniting the metal) ; on introducing the ignited zinc into a tall
bell-glass of oxygen, there is a brilliant combustion of the metal. The light
evolved is of an intense greenish white color, and a white flocculent product
results, which is oxide of zinc (ZnO). If in this experiment magnesium
wire is substituted for zinc, a bright white light, almost equal to that of
intense sunlight is produced, and the metal becomes converted into the
alkaline earth, magnesia (NIgO). The finest iron-wire made into a bundle,
tipped with sulphur, ignited, and introduced into a large vessel of the gas in
a pure state, burns with an intense white light, and with scintillations of
fused metal, which sometimes penetrate the substance of the glass. Rounded
masses of the fused iron, oxidized, fall at a white heat (3280°), with hissing
noise, into the water of the vessel in which the gas is placed. The com-
pound produced in this experiment is the magnetic oxide of iron (FgO^, or
FeO -f- Fe^Og). The heat being sufficient to drive off a portion of the oxygen,
which in the first instance produces a peroxide of the metal.

Oxidation. — Oxygen combines with some bodies directly, and at all tem-
peratures. A jar containing deutoxide of nitrogen (NOJ, when exposed to
oxygen gas, or to any mixture containing free oxygen, forms deep ruddy
vapors of an acid nature. The neutral deutoxide is further oxidized, and is
converted to an acid of nitrogen. If iron filings, moistened with water, are
thrown into a jar of oxygen gas, and the particles of metal are diffused by
agitation, so as to adhere to the inner surface of the glass, and the jar is
inverted in a vessel of water, the oxygen is slowly but completely removed
without the evolution of light and heat, while the water rises in the vessel.
The iron takes the oxygen and is converted to peroxide. If this experiment
is performed in a jar containing air, the water rises to about one-fifth of the
capacity of the vessel, thus indicating not only the presence of oxygen, but
the proportion of that element in air. With some substances oxygen will
combine, but only indirectly, or by the aid of complex chemical affinity. As"
examples of this kind may be mentioned chlorine, bromine, and iodine.
Oxygen as a gas has no tendency to unite with these elements. With
fluorine it forms no known combination. In order to combine with oxygen
in a free state most substances require to be heated above the ordinary tem-
perature of the atmosphere. Thus phosphorus has no tendency to form a
compound with pure oxygen below a temperature of 80° ; but when oxygen
is mixed with nitrogen (as in the atmosphere), or with other gases, phos-
phorus will enter into combination with it at 32°, and even at temperatures
below this. The phosphorus is slowly oxidized, being converted into a
deliquescent liquid — phosphorous acid (PO3) ; and, during the oxidation, the
phosphorus appears luminous in the dark. Phosphorus does not commonly
enter into combustion in oxygen below its melting point (112°), while, in
the allotropic state, it may be heated to nearly 500° without taking fire.
Free oxygen, as it exists in the atmosphere, appears to have no tendency to
combine with carbon below a red heat (1000°) — with hydrogen below 600° —

96 VARIETIES OF OXIDES.

with zinc below its vaporizing point (1900°)— or with sulphur below 500°.
This want of action at low temperatures appears to depend less on the
absence of affinity between oxygen and the substance, than on the effect of
cohesion on the substance exposed to the gas. When phosphorus, iron,
and even lead, are reduced to a fine state of division, and exposed to oxygen
at any temperature, they will take fire, and burn with the same brilliancy as
larger masses which have been strongly heated. (See Pyrophori, page 40,
also Combustion.)

In the process of oxidation oxygen may form a gaseous, liquid, or solid
compound, either quiescently or with the phenomena of combustion. A
simple substance may enter into combination with oxygen in various propor-
tions, and it is then found that while the compounds which contain the
smallest proportions of oxygen are neutral oxides, those which contain the
largest proportions have acid properties, and unite with bases like acids to
form salts. The metal manganese (Mn) affords a remarkable instance of this
series of combinations. Thus we have MnO the first oxide or protoxide of
manganese, which combines with acids to form the*alts of this metal — MnOg
the second oxide or deutoxide of the metal. Some have given to this com-
pound the name of binoxide, from the Latin binus, signifying double or twice
as much. This term properly implies that the oxide has twice as much
oxygen as the compound which precedes it. But deutoxides of metals are
not always binoxides in this sense. Peroxide (hyperoxide from vn'sp, higher)
is a term applied to an oxide beyond, or a higher stage of oxidation; this,
without reference to the number of atoms, indicates the maximum degree of
oxidation. Thus while the peroxide of copper has one atom of oxygen
(CuO), and that of iron one and a half atoms (or three to two of metal), the
peroxide of lead has two atoms (Pb02) and that of nitrogen four atoms
(NOJ. The metal manganese furnishes compounds in other stages of oxi-
dation ; thus there is a sesquioxide, Mn^Og, signifying that the oxygen is 1 J
to 1 of the metal, or, to avoid the use of fractions, 3 to 2. There is next
in order a compound of the sesquioxide with the protoxide, called, from its
color, the red oxide of manganese, represented by the formula (MuO,Mny03),
or MuyO^. Beyond this there are two acid compounds, manganic acid MnOg,
and permanganic acid Mn^O^. The compounds of oxygen and manganese,
which represent all the varieties, and at the same time the greatest range
of combinations of oxygen in mineral chemistry, stand as follows : —

Name.

Formulae.

Atoms 0.

Wt. Ox.

At. Mn.

Vrt. Mn.

Protoxide

. Mn 0

1

=

8

1

=

28

Deutoxide

. MnO™

2

r=

16

1

=

28

Sesquioxide .

. MnJO.

3

=

24

2

=

56

Red oxide

. MN3O,

4

=

32

3

=

84

Manganic acid

. Mn O3

3

=

24

1

==

28

Permanganic acid ,

. Mn,0,

7

=

56

2

=

56

There are degrees of oxidation in which the metal is in larger proportion
than the oxygen. These are called suboxides. Thus the suboxide of copper
is represented by the formula Cu^O ; it is a compound of one atom of oxygen
with two atoms of metal.

The tendency of the oxides of metals to combine with acids to form salts
is materially influenced by the stage of oxidation. The protoxide (MO) is
the compound which usually possesses strong basic properties, and which, by
combining with acids, produces the varieties of metallic salts. Chemists
generally fix upon the jjrotoxide by this combining character. If a suboxide
is acted upon by an acid, one atom of the metal is set free, and a protoxide
results, which then forms a salt. Thus, in boiling suboxide of copper with
diluted sulphuric acid, metallic copper is deposited, and a sulphate of the

RANGE OF OXIDATION. 9^

oxide of copper results (Cu.^0 = Cu -f CuO). On the other hand, when a per-
oxide is treated with an acid, an atom of oxygen is given ofif. Thus when
peroxide of barium is treated with sulphuric acid, sulphate of the ])rotoxide
of barium is produced, while oxygen escapes as a gas (Ba03=BaO + 0).
On this principle, as it has been already explained, peroxide of manganese
may be made to yield oxygen by heating it with sulphuric acid. {See page
90.) Sesquioxides may combine with acids to form salts ; this is seen in
the sesquio-xides of iron, aluminum, and chromium ; and as the protoxide,
containing one atom of oxygen, requires one atom of acid for producing a
neutral salt, so the sesquioxide, containing three atoms of oxygen, requires
three atoms of acid to form the class of sesquisalts. The oxides which have
the peculiar constitution of three atoms of metal to four of oxygen, may be
regarded as compounds of two other oxides, and are resolvable into these by
acids. In consequence of this union or mixture, they have been sometimes
called saline oxides — the one oxide being supposed to act as a base to the
other. Examples of these oxygen-compounds occur not only in manganese,
as above stated, but in iron and lead. The magnetic oxide of iron — the
mineral which alone permanently retains magnetic force — is a native oxide of
this description. It is represented by the formula FgO^, which is convertible
into oxide (FeO) and sesquioxide (FegOg) of iron. The substance called red
lead is a compound oxide, having the formula PbgO^, but resolvable by acids
into 2PbO and PbO^. When this oxide is digested in nitric acid, the acid
forms with the protoxide nitrate of protoxide of lead, soluble in water, while
the peroxide is left unacted on as a heavy, dark-brown insoluble powder.

Some metals appear to have no stages of oxidation, in which basic or
neutral compounds are produced. In the lowest degrees of combination with
oxygen they at once form acids. Arsenic furnishes an example of this kind :
this metal combines with three atoms of oxygen to form arsenious acid
(AsOo), and with five atoms of oxygen to form arsenic acid (AsO^). Anti-
mony, which presents so many analogies to arsenic, forms a teroxide with
three atoms of oxygen (SbOg) acting as a base, and an acid with five atoms
antiraonic acid (SbO^). These combine to form a compound which has the
remarkable composition of Sb^Og, and is called antimonious acid.

Reduction. — While the term oxidation implies simply the combination of
oxygen with bodies, the term reduction implies the separation of oxygen from
substances by chemical agency, and the conversion of them into their original
state of metal or combustible. The term regulus was formerly applied to the
metal thus derived from an oxide, and the reguline state, therefore, simply
implies the non-oxidized or metalline state. The word reduction, however,
is equally applied by modern usage to the separation of the metals from
chlorides, sulphides, and similar binary compounds.

Respiration and Combustion. — Oxygen is the great supporter of respira-
tion and combustion, and is largely consumed in these processes; hence air
deprived of oxygen by either process, or by ordinary chemical changes, is
unfit to support animal life, and will not allow of the combustion of other
bodies. If a lighted wax taper is introduced into a jar of air, in which iron
filings have been sprinkled with a little water, it will be found, after some
hours, that the residuary gas will extinguish it ; and any small animal intro-
duced into this residuary gas, would be instantly rendered lifeless. 1. If we
breathe by a wide tube into a bell-glass filled with water, and inverted on a
water-bath, so that the water may be displaced by the expired air as it issues
from the lungs — we shall find on introducing a lighted wax-taper that it will
be instantly extinguished. 2. A lighted taper introduced into a bell-glass
of air, placed over a water-bath (the bell-glass being closed at the top by a
brass plate or stopper), will be extinguished in a few minutes, owing to the
7

i

98 DECAY. EREMACAUSIS. PUTREFACTION,

rapid consumption of oxygen and the absence of any fresh supply. On
removing the extinguished taper quickly and introducing another, lighted,
this will also be extinguished ; and any small animal placed in either of these
mixtures, thus deprived of a large portion of their oxygen, would soon perish.
It must not be supposed, however, that all the oxygen is removed from air,
either by respiration or by ordinary combustion. That there is still some
portion left in the vessels, may be proved by introducing into them a ladle
containing ignited phosphorus. This will continue to burn at the expense
of the residuary oxygen not removed by the lungs in breathing, or by the
wax taper in combustion. Air, therefore, which is deoxidized, or which does
not contain a certain amount of free oxygen, is wholly unfitted to support
life. Respiration and combustion vitiate it by withdrawing oxygen and sup-
plying its place with carbonic acid. As a general rule, an animal cannot
live in air in which a wax-taper will not burn, and a taper will not burn in
an atmosphere, in which there is too small an amount of oxygen to maintain
respiration.

If our atmosphere had consisted of oxygen alone, combustion once set up
would not have ceased until all combustible substances had been consumed,
and the \^ole face of the farth changed. So in regard to animal life,
although oxygen is absolutely necessary to respiration — when this gas is in
a pure state, i. e., unmixed with nitrogen — it operates as a powerful excitant
to the nervous system ; and a small animal confined in an atmosphere of
pure oxygen will die in a few hours, apparently from the excessive stimulus
produced by the gas. Mr. Broughton determined, experimentally, that
rabbits died in six, ten, or twelve hours when confined in oxygen. On exa-
mination after death, the blood was found highly florid in every part of the
body ; and the heart continued to act strongly even after respiration had
ceased. The dilution of the oxygen of the atmosphere with four times its
volume of nitrogen is therefore absolutely necessary to animal life. It is
worthy of notice, however, in reference to this noxious action of pure oxy-
gen, that an animal will live three times as long in this gas as when it is
confined in an equal volume of common air. The reason for the difference
is, that the quantity of oxygen in air available for respiration is not only
four-fifths less, but that which has been consumed by the animal is replaced
by an equal bulk of carbonic acid, which is itself a noxious gas.

Decay. Eremacausis. Putrefaction. — Oxygen takes an important share
in these processes. It is by slow oxidation that organic are converted into
inorganic compounds ; and these again, by means of the vegetable kingdom,
are reconverted into organic substances fitted for the food of animals. In
the slow oxidation of vegetable matter, we have an example of that condition,
which has been called by Liebig eremacausis {rjpiixa slow, xaicrts burning).
If we place in a stoppered bottle containing air, sawdust, tow, jute, or decayed
leaves in a damp state, and expose the bottle for a few days to a temperature
a little above 60°, it will be found that the oxygen of the air in the bottle has
been to a greater or less extent replaced by carbonic acid. A lighted taper,
introduced into the bottle, will be extinguished, and carbonic acid may be
proved to be present by the usual tests. Under these circumstances, there
is no sensible heat or light evolved ; hence the terra combustion, applied to
this kind of oxidation, is not strictly correct. In certain cases, however, the
accumulation of heat as a result of the slow oxidation of some kinds of vege-
table matter is such, that the mass, if easily combustible, may burst into
flame. Hay and cotton in a damp state, stacked or stowed in large quanti-
ties, and under circumstances favorable to the accumulation of heat, acquire
a high temperature, as the result of oxidation. Aqueous vapor is at first
copiously evolved, and when the material is sufficiently dried, unless the

OXYGEN. EQUIVALENT. TESTS. 99

oxidation ceases the orp:anic matter becomes charred and may ultimately
burst into flame. Flax, tow, jute, and other vegetable substances of a porous
nature, in a damp state also acquire a high temperature as a result of oxida-
tion of the fibre. We have found a quantity of damp jute, six feet thick, to
have a temperature of 140°. Aqueous vapor with a small quantity of car-
bonic acid was evolved. Spent tan and manure, and other organic matters
when moist, undergo oxidation and evolve heat. Gutta percha in thin sheets
appears to undergo both physical and chemical changes from the absorption
of oxygen. It becomes altered in color and tenacity by long exposure to
the air ; and although it does not inflame, it may, when exposed in large
surfaces to air, acquire a temperature sufficient to melt it. This is probably
the real cause of the heating of electric cables in the holds of vessels in which
they have been stored. All cases of oxidation are attended with the evolu-
tion of heat, but when the process is slow, the evolved heat is unobserved
and dissipated without accumulation ; in 'Other cases, when the process is
effected in a shorter period, the heat becomes proportionally sensible ; and
when the oxidation is rapid, the whole of the heat being evolved in a much
more limited time, it is proportionably exalted in intensity.

Oxygen takes an important share in the acetous fermentation, as it is by
the oxidation of the elements of alcohol that acetic acid is produced. In
some of its combinations it exerts a deodorizing or disinfecting power. Thus,
as it is set free from a solution of permanganate of potash or soda, it oxidizes
and destroys all the ofl'ensive products evolved in the decomposition of
organic matter, which generally consist of compounds of hydrogen, with sul-
phur, nitrogen, phosphorus, and carbon. -r*

Equivalent. — The equivalent or combining weight of oxygen is taken at 8,4
when compared with hydrogen as unity ; and in reference to its volume-
equivalent in its combinations with other gases, it is one-half of that of
hydrogen, or one-half volume.

Tests. Special Characters. — Oxygen may be known as a gas in the free
state : 1. By its insolubility in water, or in a strong solution of potash. 2.
By its entire solubility in potash to which pyrogallic acid has been added.
3. By its kindling into flame an ignited match or the glowing wick of a
taper. There is only one other gas known which possesses this property,
namely, the protoxide of nitrogen (NO) ; but there are other well-marked
distinctions between this gas and oxygen. 4, Oxygen produces red acid
fumes when deutoxide of nitrogen (NO J is added to it. 5. It changes the
white ferrocyanide of iron to Prussian blue.

When oxygen exists in the uncombined state, but dissolved by liquids,
such as water, its presence may be readily detected by the white proto-ferro-
cyanide of iron. This test-liquid should be made for the occasion. It may
be prepared by shaking in a small bottle a mixture of bright iron filings and
a fresh solution of sulphurous acid gas. After a few minutes the liquid
should be filtered and diluted with water ; a small quantity of a solution of
ferrocyanide of potassium should then be added to it. A milky-white pre-
cipitate of the proto-ferrocyanide is thrown down. This rapidly becomes
blue on the surface by absorbing oxygen, and passing to the state of sesqui-
ferrocyanide of iron, or one variety of Prussian blue. If this liquid is poured
into a jar of oxygen gas, and the jar shaken, it will speedily be converted
into Prussian blue. If poured in a thin sheet on a white plate it will reveal
the presence of oxygen in the atmosphere, by its rapid change of color on the
surface. If we add a little of the test-liquid gradually to eighty or one
hundred ounces of water containing free oxygen, in a tall glass jar, it will be
observed that, as it falls through the water, it will change from white to
blue, by absorbing and fixing the dissolved oxygen.

100 COMBUSTION WITH AND WITHOUT OXYGEN.

The whole of the free oxygen may be removed from a gaseous mixture,
by dissolving pyrogallic acid in a strong solution of potash, and introducing
the mixture into a vessel containing the gas over mercury. In a graduated
vessel the proportion of oxygen present may be thus determined. If car-
bonic acid, or any other acid gas should be present, these may be removed
by first passing a solution of potash only into the tube, and when no further
absorption takes place, the level may be taken, and pyrogallic acid added to
the potash. The further absorption will then indicate the amount of oxygen.
The quantity of free oxygen may be more accurately determined, by adding
to the gaseous mixture its volume of pure hydrogen, and then bringing about
its combination with oxygen, either by the electric spark or by the aid of
spongy platinum. This process will be more fully explained in treating of
the composition of water. Oxygen may also be removed from a mixture of
gases, by causing it to pass throug-h a tube over metallic copper heated to
redness.

CHAPTER VIL

OXYGEN— INCANDESCENCE— COMBUSTION— DEFLAGRATION.

i^ Combustion with and without Oxygen. — Combustion, in its most extensive
^-meaning, may be described as the result of intense chemical combination
between two or more bodies, during which sensible light and heat are
evolved. All ordinary cases of combustion are dependent on the combina-
tion of oxygen with bodies ; and the heat and light are dependent on the
rapidity with which oxidation takes place, as well as on the amount of oxygen
consumed. Levoisier believed that oxygen was the universal supporter of
combustion, and that there was no combustion without it. In this, however,
he was in error. The phenomena of combustion are seen in some of the
combinations of chlorine, bromine, and sulphur with bodies. If phosphorus
is introduced into a jar of chlorine, it speedily melts, takes fire, and burns
with a pale yellowish flame, forming chloride of phosphorus. If thin leaves
of Dutch metal are introduced into chlorine, they burn without flame, pro-
ducing a full red heat, and forming chloride of copper. Freshly-powdered
metallic antimony projected into chlorine gas, burns in scintillations, evolv-
ing much light and heat, and forming white chloride of antimony : if this
metal in fine powder be projected into bromine, it burns, in contact with the
liquid, with bright scintillations, forming bromide of antimony. So with
regard to sulphur ; if this substance is heated in a Florence flask to its
vaporizing point, it forms a dark amber-colored vapor, in which thin pieces
of copper foil, or cuttings of copper, glow and burn with great splendor,
producing sulphide of copper. The metal sodium -heated in air until it
begins to take fire, when plunged into a jar of chlorine, will burn with the
most intense evolution of light and heat, and sometimes with explosive
violence. The ladle holding the metal acquires a red heat as a result of this
combustion. Fine iron wire previously heated to redness also burns with a
deep lurid glow in chlorine. These experiments clearly show that oxygen
is not in all cases necessary to combustion ; and that the phenomena which
attend it, cannot be regarded as dependent upon any peculiar principle or
form of matter ; they must be considered as a general result of intense chemi-
cal union. Each substance, in fact, has its own special properties in refer-

IGNITION. INCANDESCENCE. 101

ence to combustion. Sulphur will not burn in chlorine ; and to cause it to
burn in oxypren, it must be heated to a hii^h temperature. Copper will not
burn in oxygen gas, but it will burn at the lowest temperature in chlorine,
and readily in the vapor of sulphur. Phosphorus will not undergo combus-
tion in oxygen below a temperature of 80° ; but it will take fire in chlorine
at 32°. ^ •

Some compound gases may give rise to the phenomena of combustion with
alkaline metals under certain conditions. Cyanogen gas is a compound of
carbon and nitrogen. If potassium is heated in a current of this gas, the
metal burns, and leaves as a product cyanide of potassium. Again, if sodium
be heated in a flask from which air is entirely excluded, and a current of dry
carbonic acid is passed through the flask, a brilliant combustion will take
place, the oxygen of the carbonic acid being taken by the sodium to form
soda, while carbon is deposited. Magnesium wire ignited and introduced
into carbonic acid, burns with scintillations and gives out an intensely white
light. In most cases, bodies which burn in oxygen are immediately extin-
guished when plunged into carbonic acid.

Oxycomhustion. — Confining our views for the present to combustion as it
takes place in oxygen, it may be remarked that there is no loss of matter bnt
merely a change of state. If a spirit-lamp is accurately balanced in a scale-
pan, and the wick then ignited — as the spirit burns, there will be an apparent
loss of matter, and the counterpoised scale will sink. If we hold over the
burning wick, the open mouth of a gas-jar, we may be able to prove by appro-
priate tests, that the air of the jar is replaced by carbonic acid and aqueous
vapor — the latter being condensed on the inner cold surface of the glass.
These products are formed at a high temperature by the oxidation of the
carbon and hydrogen contained, in the vapor of alcohol. If collected in a
proper apparatus, the weight of these products will be equal to the weight
of alcohol consumed.

If phosphorus is heated in a vessel of pure 'oxygen, all the oxygen dis-
appears, but it is now solidified as phosphoric acid, and the increase in
the weight of the phosphorus would represent exactly the amount of
oxygen consumed. In the burning of carbon there appears to be no loss
of gaseous matter ; but the oxygen in this case is converted into carbonic
acid ; and it will be found, although unaltered in volume, to have acquired
an increase in weight equal to the weight of carbon consumed. Sub-
stances which undergo combustion in oxygen are rendered heavier; the
weight of oxygen taken during combustion, is always added to the original
weight.

When a metal burns in oxygen, it is iodized with the evolution of light and
beat ; but a metal may be iodized without undergoing combustion in the
ordinary sense. Zinc and lead furnish striking instances of the difl'erence.
If zinc is heated in air above its melting point, it will take fire and burn
with a splendid greenish-white light {see page 106) ; but if lead is melted in
air, there is formed on the surface a dirty yellowish-looking film or dross
(oxide of lead), without the evolution of light and heat. Both are instances
of oxidation, but in the latter case there is no combustion.

Ignition. Incandescence. — Combustion always implies chemical action;
either the heat of the combining bodies or that which results from their
combination is set free, and with this, a proportionate quantity of light; but
a body may evolve heat and light without undergoing combustion or any
chemical change. • Thus a platinum wire, some fibres of asbestos, or a piece
of lime, exposed to the strong heat of an invisible flame — e. g., of oxygen
and hydrogen — may be heated to whiteness, so as to evolve both heat and
light of surpassing intensity. To this state the term ignition, or incandes-

1

102 IGNITION. INCANDESCENCE

cence, is applied. The body evolves light as a result of its being intensely
heated, without its particles being materially altered in tlieir physical or
chemical relations. It is not fused at the temperature to which it is exposed ;
and the greater the amount of heat which it is capable of receiving without
a change or its physical condition, the more intense the light which is emitted.
An. ignited body, therefore, serves as a temporary storehouse of heat and
light. The vacuum-light furnishes a remarkable instance of the results of
ignition. The charcoal points, being the terminal poles of a powerful
battery, are inclosed in a glass vessel in which a vacuum has been artificially
produced. The light issues in great splendor as the result of the ignition of
minute particles of charcoal carried between the poles, but the charcoal itself
undergoes no combustion. When platinum poles are used, portions of that
metal are volatilized and so heated as to give out the intense violet-blue light
which characterizes the spark. Mr. Gassiot has observed, that under these
circumstances the negative pole assumes the appearance of being corroded,
owing, as he found, to the separation of particles of this metal and their
deposition on the sides of the vacuum-glass tube. Even gases attenuated to
the highest degree — in fact, almost converted into a vacuum by the air-
pump — are rendered incandescent by the discharge of the spark from
Ruhmkorff's coil {^see page 83). In an absolute vacuum no discharge passes,
as electrical conduction necessarily requires the presence of matter ; but Mr.
Gassiot's experiments have proved that what has been hitherto regarded as
a vacuum, is space filled with highly attenuated matter, capable of being
made incandescent by the electric discharge. The more attenuated the gas
or vapor, the more stratified is the light of the discharge. As the gas is
increased in quantity, the stratifications become closer, until, at a certain
point, the discharge entirely loses its stratified appearance and passes into a
wave line. The vivid luminosity and the varied color of lightning, is pro-
bably dependent on the incandescence of the gaseous and vaporous consti-
tuents of the atmosphere, modified by the density of the stratum in which the
electric discharge takes place.

It is found that the greater number of metals may be converted into vapor,
and that these vapors when rendered incandescent by the current, emit a
light varying in color for each metal. For the purpose of obtaining the
metals in a volatile state, the platinum poles are moistened with the respec-
tive solutions. M. Faye found that zinc gave a blue color in strata or bands ;
antimony, a lilac color : mercury, a pale blue ; cadmium, an intense green ;
arsenic, a magnificent lilac ; and bismuth, a variety of colors, undergoing
rapid changes. {Cosmos, Sept. 20, 1861, p. 321.) It has been further
proved that these colored flames and incandescent vapors present colored
spectra of differently refrangible rays, in some instances characteristic of the
substance. {See page 63.)

Supporters and Combustibles. — Although oxygen, chlorine, and bromine
give rise to the phenomena of combustion with other bodies, they cannot be
made to combine with each other, so as to evolve light and heat ; and hence
they are said to be incombustible. In ordinary language they are called
supporters of combustion, while the bodies to which they unite have been
called combustibles. It is, however, generally admitted that the phenomena
of combustion are dependent on the union of the two bodies; and that the
so-called supporter is consumed as well as the combustible, and aids in
furnishing light and heat. Thus copper and sulphur, at a high temperature,
combine with combustion. Which is the supporter and which is the combus-
tible ? Both must he regarded as combustible substances — for copper burns
in chlorine, and sulphur burns in oxygen. Whether we put phosphorus into
the vapor of chlorine, or chlorine into the vapor of phosphorus, the same

HEAT EVOLVED IN COMBUSTION. 103

kind of combustion equally ensues, and the products are similar. During
the combustion of phosphorus in oxygen the intense and sudden burst of
light which appears after the phosphorus has entered into the boiling state,
arises from the difiTusion of its vapor throughout the oxygen of the vessel,
so that there is a combustion of both at every point of contact. Up to this
time the light and heat may have appeared to proceed from the solid phos-
phorus only ; but it will now be observed to issue equally from all parts of
the vessel containing the oxygen. The oxygen is here as much a combus-
tible as the phosphorus. In fact, the term " combustible" is relative and
arbitrary ; that body which is for the time in larger quantity, or in the gaseous
state, is called the " supporter." Coal-gas burns in oxygen or air only
where it can unite with oxygen ; and it is therefore called a combustible gas.
If we kindle a jet of coal-gas issuing from a bladder, and cause the flame to
be projected into a bell-glass of oxygen, it will burn brilliantly. If we fill
another bell-glass with coal-gas, ignite it at the mouth, and project into it
through the flame a jet of oxygen, this gas will appear to burn, and in fact
does burn, in a jet precisely like the jet of coal-gas; and it' will be found to
give out the same amount of light and heat, and to give rise to similar pro-
ducts. The oxygen and coal-gas burn only where they meet each other at
a high temperature. The oxygen burns in an atmosphere of coal-gas just as
certainly as the coal-gas burns in an atmosphere of oxygen. This experi-
ment may be performed with an ordinary argand gas-burner. A long chim-
ney-glass should be placed over the burner, and all access of air from below
cut off by a cork and a disk of card. If, after allowing the coal-gas to issue
for a few minutes, in order to remove the air, it is ignited at the top of the
chimney-glass, a jet of oxygen may be safely propelled downwards through
the gas-flame, and the oxygen will appear to burn in the glass cylinder con-
taining the coal-gas. These facts show that combustion is really a reciprocal
phenomenon, each body burning, or, in chemical language, combining with
the other body, and, during this combination, evolving light and heat. The
terms combustible and supporter of combustion are, however, convenient for
use, provided we understand by them that each substance shares in the pro-
cess, and that neither is, strictly speaking, passive.

Heat and Light of Combustion. — The results of experiments on some sub-
stances show that the heat of combustion is almost exclusively derived from
the oxygen. Thus it appears, from the researches of Despretz, that the heat
depends, not upon the quantity of the combustible, but upon the weight of
oxygen, consumed. A pound of oxygen, in combining respectively with
hydrogen, charcoal, alcohol, and ether, evolved in each case very nearly the
same quantity of heat, each raising 29 pounds of water from 32^ to 212^.
With respect to the comparative heating powers of equal weights of different
combustibles, he obtained the following results : —

236 pounds of water from 32° to 212°

pound of hydrogen raised .

. 236

" oil, wax

. 90

" ether ....

. 80

" pure charcoal

. 78

" common wood charcoal

. 75

" alcohol

. 68

" bituminous coal .

. 60

" baked wood

. 36

" wood holding 20 per cent.

of water 27

«

it

u

" turf (peat) . . . . 25 to 30 " " "

This table indicates, not the absolute amount of heat evolved, but the
relative heating powers of fuels burnt under similar conditions; and it further
appears to show that, provided the same weight of oxygen be consumed,

104 HEAT EVOLVED IN COMBUSTION.

whatever may be the nature of the fuel, the same amount of heat will be
evolved. In order to produce an intense heat, therefore, the object is not so
much to consume the fuel as to consume the maximum of oxygen, or air with
a minimum of fuel. The heating power of the blowpipe and of the blast-
furnace, especially of the hot blast (to counteract the cooling effect of the
nitrogen associated with oxygen in the air), will now be intelligible on
chemical principles. It is not, kowever, strictly true that the same weight
of oxygen always produces by combination the same amount of heat. Other
experiments performed by Despretz have shown that a pound of oxygen, in
combining with iron, tin, and zinc, could heat nearly twice as much water to
the same temperature as that which in his table he assigns to hydrogen,
carbon, alcohol, and ether ; hence, in reference to these metals, oxygen alone
cannot be concerned in its production. So with regard to phosphorus ; if
this substance is burnt slowly, to produce phosphorous acid, a pound of oxygen
in combining with it evolves the same amount of heat as that assigned to
carbon and hydrpgen ; but if the combustion is so intense as to produce
phosphoric acid, then the heat evolved is twice as great, resembling that
which is given out in the intense combustion of iron, tin, and zinc. There
is another fact which shows that the rule regarding the evolution of heat is
not so simple as Despretz had supposed; namely, that when carbon is in a
state of combination, as in the form of carbonic oxide, the amount of heat
evolved during its combustion and conversion into carbonic acid, is nearly
equal to that which would be evolved by the carbon in a separate state,
although the latter would require twice the amount of oxygen to convert it
to the same product (carbonic acid). {Kane''s Elements of CJiemistry, p.
244.) The later researches of Professor Andrews and other chemists have
shown, that the quantity of heat evolved as a result of the chemical combina-
tion of bodies is definite, and that it has a specific relation to the combining
number of each substance. With a proper supply of oxygen, or air, a given
weight of the substance always produces the same amount of heat.

Hydrogen, carbon, sulphur, and phosphorus are the four principal sub-
stances, with which the phenomena of combustion are witnessed in an
atmosphere containing oxygen. All our ordinary sources of light and heat
for domestic and manufacturing purposes are dependent on the two first-
mentioned elements, associated in variable proportions in coal, wood, and
oil. The following table will show that according to the experiments of
Despretz, hydrogen and carbon, weight for weight, consume the largest
amount of oxygen in undergoing perfect combustion ; and that hydrogen
in uniting to oxygen has more tkan three times the heating power of
carbon : —

1 pound of hydrogen takes

6 pounds of carbon take .
16 pounds of sulphur take .
32 pounds of phosphorus take

Hence by reason of this enormous consumption of oxygen in proportion to
the weight of material burned, hydrogen, and bodies containing it, evolve
the greatest amount of heat. Hence also in the oxy-hydrogen blowpipe, we
have one of the highest sources of heat at present known ; and as an indirect
result of the absorption of this heat by the infusible substance, lime, we
obtain a light which rivals that of the sun in intensity and chemical power.
Lately, by the construction of a close furnace of lime, and the use of the oxy-
hydrogen blowpipe, MM. Deville and Debray have not only been able to
volatilize many of the supposed fixed impurities in commercial platinum ; but

Pounds of Ponnds

Prop, of Coml

Oxygen. of Air.

to Oxygen.

8 or 40 .

,

.1:8

16 or 80 .

,

. 1 : 2.6

16 or 80 .

,

. 1:1

40 or 200 .

,

. 1 : 1.25

#

COMBUSTION. DEGREES OF HEAT. 105

with about 43 cubic feet of oxyj^en they have succeeded in meltifig 25 pounds
of platinum in less than three-quarters of an hour, and casting it into an ingot
in a coke mould. All metals are melted, and many are entirely dissipated in
vapor by the intense heat produced under these circumstances. The lime
itself is unaltered by the heat, and acts as a powerful non-conductor, even
when not more than an inch in thickness. Lime and magnesia appear
hitherto to have resisted fusion, or volatilization as oxides. The heat given
out during the perfect combustion of hydrogen in oxygen was calculated by
Sir R. Kane {Elements of Chemistry, p. 240) to amount to 5478° above the
freezing point; but this estimate falls far below that assigned by the recent
experiments of Bunsen. {See p. 107.) This temperature exceeds the heat
of other artificial sources. It can only be surpassed by the heat of the
electric discharge, or by the concentration of the rays of the sun through a
powerful lens or mirror. When hydrogen is burnt in atmospheric air, the
cooling effect of the nitrogen is such that, according to the same authority,
the heat does not exceed 2739° above freezing; this is nearly equal to the
melting point of cast iron, which is 2786°

Chemists assign different temperatures according to the color emitted by
the incandescent solid. A red, yellow, and white heat are frequently referred
to in chemical processes, bnt the temperatures assigned to these, vary among
different authorities. Lead melts at 620°, and zinc at 773°, but neither of
these metals, at the melting point, is visible in the dark. A red heat seen
only in the dark, is usually taken at about 980°, but this is invisible in day-
light. The iron ladle containing melted lead, heated to this temperature,
shows no color, but if taken into a dark closet, it will be observed that the
iron of the ladle and the molten lead are visibly and equally red, showing that
metals, however they may differ from each other in their melting points,
acquire the power of emitting a similar light at the same temperature.
From 620° to 980°, where a body is strongly, but at the same time is not
visibly heated, is comprised the range of black heat, important in reference to
some chemical processes. The degree for a visibly red heat in day-light has
not been accurately determined. From some experiments made in conjunc-
tion with Dr. Miller, we believe it to be at about the melting point of
antimony, or 1160°. A cherry red is about 1200°, and a white heat, above
the melting point of cast iron (2786°) may be taken at 3000°. We subjoin
a table of high temperatures, based on the researches of Pouillet.

Incipient red heat

Dull red

Incipient cherry red .
Cherry red ....

Bright cherry red . ^ .
Deep orange ....
Bright orange ....
White heat ....
Bright white heat
Dazzling white heat .
Full white heat

In reference to combustion, the improvements made in the use of gas as a
source of heat have depended on the admixture of air or on the free supply of
air by a variety of arrangements ; and in the construction of all furnaces, the
adoption of this principle leads to an economy of fuel, the prevention of
smoke, and the production of the largest amount of heat.

The light evolved in combustion depends — 1, on the intensity of the heat;
and, 2, on the presence of solid non-volatile matter which is capable of

Centigrade.

Fahrenheit

525°

977^

700

1292

. 800

1472

900

1652

1000

1832

1100

2012

1200

2192

1300

2372

1400

2552

. 1500

2732.

. 1600

2912

106 LIGHT FROM COMBUSTION.

receiving thg heat, and of emitting it as light. When combustion takes
place at a low red heat, as in the aphlogistic lamp of Sir H. Davj, there is
bat little light. In fact, this is only visible in the dark. Hydrogen burns
with intense heat ; but as watery vapor is the only product, there is no solid
matter to absorb and emit the heat as light. If platinum wire, or particles
of charcoal lime, asbestos, iron-filings, zinc or magnesium, are introduced into
the flame, they or these products are heated and emit light. The bright
white light emitted by coal-gas is owing to the particles of carbon, set free
during the combustion of the gas, acquiring a white heat, and becoming
incandescent in the flame. The naphthalizing of ordinary coal-gas depends
on the difl'usion through it of a hydrocarbon vapor, which, during com-
bustion, may furnish solid particles of carbon to the flame. In burning
phosphorus in chlorine, a gaseous chloride is produced, and the phosphorus
burns with a pale flame, emitting but little light; but when it is burnt in
oxygen it forms dense solid particles of phosphoric acid, which being strongly
heated emit an intensely white liglit. The difference of light arising from
the products may be shown by raising the phosphorus, which has been
burning in a bell-jar of chlorine, into the atmosphere. The increased
splendor of the combustion from formation of a solid product is at once
manifested, and the eff'ect is increased by plunging a ladle with burning
phosphorus into a bell-jar of oxygen. In burning zinc the same phenomenon is
observed; — the oxide of zinc produced isa solid body, which becomesintensely
heated and emits a large amount of light. If a piece of magnesium wire be
ignited in a Bunsen's jet, a most dazzling white light is evolved, arising from
the fixed particles of the oxide of magnesium becoming strongly heated, and,
as a result of this, evolving a light of the greatest intensity. In some photo-
chemical investigations made by Bunsen and Roscoe, it was calculated that
the light of the sun's disk was only 524 times as great as the magnesium
light, A wire of about the 1-1 00th of an inch in diameter, produced by
combustion as much light as 74 stearine candles. The light, therefore,
arising from combustion, depends to a great extent on the nature of the
combustible, as well as on the product of combustion. Substances like iron
and charcoal, which are fixed, emit a great amount of light in proportion to
the heat produced and the constant renewal of surface leads to continuous
combustion.

The intensity of the light is, caeteris paribus, dependent on the rapidity
with which oxidation takes place, and the amount of material consumed.
The Bude light owes its brightness to the introduction of a current of oxygen
into the centre of the flame. There is in a given time a larger consumption
of the combustible matter, and a consequent increase of light.

The color of the light emitted in combustion, is, to a certain extent,
dependent on temperature. At one degree of keat, the light is red, at
another yellow, and in the highest degree white. These three colors are
well known in chemical processes as forming broad distinctions in the tem-
perature of ignited solids {see page 105.) According to Bunsen, between
the yellow, red, and white heat, the colors of intensely heated bodies pass
through shades of blue to violet, and the white heat is the resultant of all
the spectral colors emitted by the heated substance. Apart from the effects
of temperature, there are colors which are peculiar to the combustible sub-
stance. The light evolved by burning sulphur is of a pale blue color, while
zinc gives a greenish white; potassium, a pale purple or violet; sodium, an
intense yellow; lithium, calcium, and strontium, shades of red; barium,
greenish yellow ; boracic acid, green ; arsenic, a violet blue ; and antimony,
a pale lemon color. It will be perceived, by reference to page 102, that the

HEAT AND OPACITY OF FLAMES. ^^ **lOt

colors which are thus produced during combustion, differ from those which
are emitted as a result of the incandescence of the same bodies.

Among the compound gases, carbonic oxide is known by the blue color of
its flame ; cyanogen gas by a violet flame with a blue halo ; and phos-
phuretted hydrogen gas by the intense yellowish-white light which it emits
during combustion.

Nature of Flame. — Flame arises from the combustion of volatile or
gaseous matter emanating from the heated solid. Those bodies only burn
with flame which, at the usual burning temperature, are capable of assuming
the vaporous or gaseous state. Charcoal and iron burn without flame ;
their particles are not volatile at the temperature at which they burn.
Phospliorus and zinc, on the other hand, are volatile bodies, and therefore
burn with flame. Small particles of each substance are carried up in vapor,
are rendered incandescent by the heat of combustion, and burn wherever
they meet with the atmospheric oxygen ; the more volatile the substance,
the greater the amount of flame.

Flame is hollow — a fact which may be proved by numerous experiments.
If a piece of metallic wire-gauze be depressed over a flame, this will be seen
to form a ring or circle of fire, dark in the centre and luminous only at the
circumference, where the gaseous particles meet with oxygen. The inflam-
mable matter traverses the meshes of the gauze, but is so cooled by the con-
ducting power of the metal that it ceases to burn above. A piece of stiff
paper suddenly depressed on a spirit-flame to about its centre, presents a
carbonized ring corresponding to the circularity of the flame. If a thin
platinum wire be stretched across a wide flame of alcohol, it will be heated
only at the two points, corresponding to the circumference, where combus-
tion is going on, and a thin deal splint will be charred and burnt only at
these two points.

By allowing a jet of gas to issue from a glass cylinder, in the manner
described at page 103, a variety of experiments may be performed to show
the hollowness of flame, and the comparatively low temperature of the gas
or vapor in the interior. A lighted wax taper fixed on wire, introduced
suddenly through the sheet of flame, is extinguished in the interior. Gun-
powder introduced in a ladle may be held in the inner space within the flame
for a long time, and even withdrawn without exploding. Gun-cotton will
not explode under these circumstances if introduced at the end of a copper
wire, while the coal-gas is freely issuing from the chimney-glass, and the jet
is not kindled until after its introduction. That the inner portion of every
cone of flame consists of unburnt gas, or combustible vapor comparatively
cool, may also be proved by placing within it the open end of a glass tube,
supported by wire, and applying a lighted taper at the other end of the tube
which projects out of the flame. The unburnt gas or vapor will be con-
ducted off by the tube, and may be kindled at the end of it, as from an
ordinary jet. Thus, then, all inflammable gases and vapors, when unmixed
with oxygen, have only a surface combustion, which is defined by the access
of oxygen and its contact with the heated gas or vapor.

Flame in all cases consists of matter ignited to a high temperature. Sir
H. Davy assigned a white heat to ordinary flame. Bunsen has recently
examined the temperature of flames by a series of ingenious experiments
{Phil. Mag., Aug., 1860, page 92), and has arrived at the following conclu-
sions : the temperatures here assigned, being those of the centigrade ther-
mometer, of which 5° are equal to 9° of Fahrenheit, plus 32^ for the difference
of the zero.

•

108 COMBUSTION BY OXYGEN SALTS.

Sulphur flame . . 1820° Carbonic oxide flame . 3042°

Sulphide carbon . . 2195 Hydrogen flame (in air) 3259

Coal-gas flame . . 2350 Oxyhydrogen flame . 8061

The heat of the electric flame far surpasses all these temperatures, and is
at present undeterminable in its degree by any known process.

A remarkable announcement has been made by KirchofF and Bunsen,
respecting the colored flames of metals brought to the state of incandescent
vapor, as the result of the heat of combustion or of the electric current —
namely, that they absorb light of the same degree of refrangibility as that
which they emit; in other words, their flames are opaque to their own light.
If the light of the sun, or of the electric current, is allowed to traverse the
flame of a spirit-lamp or that of hydrogen or coal-gas, no shadow is pro-
duced on a white screen placed behind it : the flame is quite transparent, but
the undulating shadows projected for more than a foot above the flame by
the invisible gaseous products of combustion (carbonic acid and water), are
plainly seen. The flame of a common candle produces no shadow when
placed between a screen and the flame of an oil-lamp. The shadow of the
wick only is seen on a white surface. Foucault observed that the intense
light of the electric arc from carbon-points, was so transparent that the
solar rays converged upon it by a lens, completely traversed it, and only a
slight shadow was cast upon the solar light. Bunsen found that the light of
a sodium-flame would not traverse another sodium-flame, or even sodium-
vapor, produced by heating sodium-amalgam in a test-tube much below its
point of luminosity ; and the singular discovery was made, that direct sun-
light, passed through the yellow flame of sodium, changed the yellow spectral
band peculiar to that metal to a dark double line. The red band of lithium
was also changed to a dark band by sunlight. {Phil. Mag., August, 1860,
page 108.) From these results, and from the fact that in the pure solar
spectrum, a dark line appears in the position of the sodium-yellow band,
Kirchoff and Bunsen have inferred that sodium must be a large constituent of
the photosphere of the sun. For a similar reason, chromium, iron, nickel,
and magnesium have also been assigned to this photosphere — and sodium to
the light of the fixed stars. The moon and Venus exhibit lines correspond-
ing with those of the sun. Sirius showed different lines, and Castor others
which were again different. In Procyon the solar line D (sodium), and in
Capella and Betelgeux, the principal star in Orion D (sodium) and b were
found. (Miller.) It is to be observed, however, that the light of platinum,
rendered incandescent by the electric fluid, and the rays of a Drummond
light, equally changed the sodium-yellow into a dark band. Opacity is the
great character of metals : but it is remarkable that, in the state either of
incandescent or non-luminous vapor, this complete opacity to light emitted
by their own flames, should thus exist. If these results are confirmed, this
property of metallic vapors might be made a test of the alleged metalline
nature of certain gases. Incandescent hydrogen gives colored spectral bands
of its own (page 63) ; but these have not been found to possess any absorbent
power at ordinary temperatures. This result is adverse to the hypothesis of
its metalline nature.

Products of Combustion. — The products of ordinary combustion in oxygen
are chiefly water and carbonic acid. They are quite unfitted to sustain com-
bustion, and unless removed as they are produced, they speedily arrest the
process.

Combustion by Oxygen Salts. Defiagration. — It is not necessary that
oxygen should be in the free or gaseous state, in order that combustion
should take place. Salts w%ich abound in oxygen, such as the alkaline per-

• DEFLAGRATION. 109

chlorates, and chlorates, nitrates and bichromates, when mixed with sub-
stances which have a tendency to unite with oxgen — e. g., charcoal, sulphur,
or phosphorus — and heat is applied to the mixture, give rise to combustion
of a most intense kind. The salts above mentioned contain a large propor-
tion of oxgen by weight, and this is readily evolved in contact with a com-
bustible. Even the liquid acids of these salts, in a free state, are capable of
protucing the phenomena of combustion. Dr. Roscoe found that pure' per-
chloric acid, obtained from the perchlorate of potash, was a most powerful
oxidizing agent. A single drop of the liquid brought into contact with
charcoal, paper, wood, alcohol, or other organic substances of the like nature,
caused combustion with explosion, falling not short in violence of that of
chloride of nitrogen.

The sudden conversion of gunpowder into gaseous and vaporous matter is
dependent on the oxygen of the nitre combining at a high temperature with
the charcoal and sulphur. Gun-cotton contains nitrous acid in large propor-
tion. This readily parts with its oxygen at a moderate heat, and the carbon
and hydrogen of the cotton are entirely consumed. If a quantity of nitre is
melted in a flask, and a piece of red-hot charcoal is dropped on the melted
salt, it will continue to glow as a result of combustion, at every point at
which it touches the nitre, until all the charcoal or the nitre has been consumed.
If chlorate of potash is melted in a flask, and a splint of lighted wood is
introduced into the liquefied salt, there is violent and intense combustion,
almost amounting to explosion. A. mixture of finely-powdered charcoal,
with an equal portion of powdered nitrate or chlorate of potash, burns, when
heated, with great violence, giving rise to the phenomena of deflagration.
This process of combustion is occasionally resorted to by chemists for
oxidizing carbon, sulphur, and phosphorus in organic substances, in order
to convert the elements to salts, and determine the presence and proportion
in which they exist. A mixture of twenty-eight parts of ferrocyanide of
potassium, twenty-three parts of white sugar, and forty-nine parts of chlorate
of polash, is known under the name of " white gunpowder.''^ In combustion
it produces a large amount of gaseous matter, consisting of nitrogen, carbonic
acid, carbonic oxide, and aqueous vapor. This is a dangerous compound to
prepare or even to preserve. The materials should be separately powdered,
and then mixed. Mr. Hudson has observed, that when the materials are
ground together with a little water and dried at 150°, the powder is much
more explosive. Even simple friction with a spatula, or slight compression,
was then sufficient to cause a violent explosion. A drop of sulphuric acid
will explode it ; it may also be exploded by percussion. This chemist found
that its explosive force was twice as great as that of common gunpowder.
{Chem. News, Aug. 24, 1861.) It would prove a dangerous substitute for
gunpowder, but it might be serviceable as a composition for shells. An
explosive mixture is also formed by powdering separately, and mixing two
parts of "the black sulphide of antimony with one part of chlorate of potash.
This composition, when dry, is exploded by friction or percussion, by heat, or by
the contact of concentrated sulphuric acid. It furnishes an instance of violent
combustion, at the expense of the oxygen of the chloric acid. The needle-
gun powder of the Prussians has a somewhat similar composition. It con-
sists of five parts of chlorate of potash, three parts of sulphide of antimony,
and two parts of sulphur. These substances are separately reduced to fine
powder, and are then carefully mixed without trituration.

110 CONVERSION OF OXYGEN TO OaONE,

^1*

CHAPTER VIII. •

OZONE. — ALLOTROPIC OXYGEN. — A NTOZONE.

History. — In addition to the ordinary state in which oxygen is known to
chemists, it is believed to exist in another state — that of allotropic oxygen,
or, as it is generally called, Ozone. It had been noticed that a peculiar
pungent odor, resembling that of phosphorus, was sometimes evolved on the
discharge of the electric spark — that litmus paper was reddened — that
starch-paper moistened with iodide of potassium was rendered blue : and
that paper moistened with potash, deflagrated when dry. These efl'ects were
generally referred to the production of nitric acid by the oxidation of the
nitrogen of the air. In 1840, Schonbein of Bale announced that in the
electrolysis of water, this odorous body appeared at the positive pole of the
battery (if of platinum) and that it might be preserved in well-closed bottles.
He considered it to be an electro-negative element, and named it Ozone
(from o^co, to smell.) In the Comptes Rendus for 1850, he described a
method of procuring it from phosphorus and ether, as well as its most
characteristic properties ; and announced that it was produced in the atmos-
phere, especially during winter, as the result of electrical changes.

In a lecture at the Royal Institution, in June, 1851, Mr. Faraday gave an
account of Schonbein's researches, with the results of his own observations.
Fremy and Becquerel in France, and Dr. Andrews and Dr. Tait in this
country {Phil. Trans., 1855-6) have since investigated the subject. [The
reader is also referred to an Essay by Dr. Scoutetten, entitled D Ozone, ou
VOxygene electrise, Paris, 1856 ; and for a more recent account of Ozone
in its medical aspects, to a Paper by Dr. Moffat, read at the British Associ-
ation Sept. 1861.]

The results obtained by different observers tend to show that ozone is
oxygen in an altered state ; and that this conversion may be produced by
the electric spark (when silently discharged into dry oxygen) — by current
electricity in the decomposition of water, and by various chemical processes;
further, that however produced, the properties are the same. The principle
evolved is characterized by a peculiar odor, and by an intensely oxidizing
and bleaching power — so that substances on which common oxygen produces
no effect, are rapidly oxidized on contact with air which contains only a
small portion of this odorous principle.

Preparation. — The most convenient method of procuring ozone, t)r rather
an ozonized atmosphere, is to place in a large bottle of air, which can be
completely closed, a stick o{ phosphorus freshty scraped. Sufficient distilled
water should be poured into the bottle to partially cover the phosphorus ;
the vessel should then be closed with the stopper, and kept in a room at a
temperature between 60° and 70°. The phosphorus is oxidized in the bottle
in the usual way ; and during this process of oxidation, a portion of the
oxygen passes to the state of ozone, and is diffused through the air of the
bottle. It is only in the slow oxidation of phosphorus at a low tempera-
ture that ozone is met with as a product. When this metalloid is oxidized
at a high temperature, as in the production of phosphoric acid by combustion,
no ozone is found. The usual test for the presence of ozone is a slip of

CONVERSION OP OXYGEN TO OZONE. ' 111

pnper jnoistened with a solution of starch and iodide of potassium. {See
page 114.) When ozone is present, this paper, on immersion, acquires a
blue color, owing to the oxidation of the potassium and the production of
iodide of starch. If a similar slip of paper is put into a similar bottle of air,
containing distilled water without phosphorus, no change is produced. In
a warm room, the evidence of the presence of ozone in the bottle is usually
procured in about ten or twelve minutes ; but the maximum quantity of
ozone is found in it in from two to ten hours. Only a small part of the oxy-
gen (from l-50th to l-200th) appears to undergo this change ; and if long
kept, the ozone may be lost by combining with and oxidizing the phos-
phorus : hence the phosphorus should be removed by inverting the bottle in
water so soon as the test-paper is strongly blued. The ozonized air will
then preserve its properties for several days. So if the iodide-paper be left
in the bottle, the blue color will after a time disappear, by the ozone com-
bining with the iodine to form iodic acid. It is not produced in dry oxygen,
nor in humid air or oxygen, when mixed with certain gases or vapors which
prevent the oxidation of phosphorus ; but it appears to be more readily pro-
duced, ceeteris paribus, when oxygen is mixed with nitrogen, hydrogen, or
carbonic acid. By washing and decantation, the ozonized air, which is quite
insoluble in water, may be deprived of the phosphorus-vapor associated with
it, and kept in well-closed bottles. It is speedily lost by diffusion. Graham
found that ozone traversed dry and porous stoneware. Ozone may be pro-
duced on a small scale, by placing a piece of phosphorus with water in a
watch-glass and inverting over this another glass containing the test-paper
or liquid.

Ozone is produced by passing the electric spark silently into pure and dry
oxygen. Fremy and Becquerel found that pure oxygen, contained in a sealed
tube, when treated for a sufficient time with a series of electric sparks, under-
went a complete conversion into ozone, as the whole contents of the tube
when broken were absorbed by a solution of alkaline iodide, in which it was
immersed. In the electrolytic decomposition of water the oxygen at the
positive pole has ozonic properties, provided the poles employed are of gold
or platinum. The hydrogen evolved gave no indication of ozone. Faraday
found that a mixture of iodide of potassium and starch was decomposed at
the positive pole, even after the gaseous oxygen had been made to pass
through a tube containing a layer of cotton soaked in a solution of potash.
The object of this arrangement was to arrest any acid which might be simul-
taneously produced, and thus lead to the decomposition of the iodide. Dr.
Letheby found that the ozone thus evolved at the positive pole possessed the
same power of coloring strychnia or aniline as the oxygen (ozone) liberated
by sulphuric acid from the peroxides of manganese and lead, and from chro-
mic acid.

In 1850, Schonbein found that ozone was a product of the slow combustion
of ether. If a small quantity of ether is poured into a jar or bottle, and a
clean glass rod, or small iron bar, heated to about 500°, is introduced, acid
vapors are given off which redden wetted litmus paper at the mouth of the
jar, and which set free iodine from iodide of potassium, causing the blueing
of starch-paper impregnated with this salt. After the removal of the rod or
bar several strips of paper successively introduced into the jar will undergo
the same change. Clean platinum, and even copper, will produce similar
effects. The residuary ether in the jar at the same time acquires new pro-
perties. It bleaches sulphate of indigo, and converts chromic into blue per-
chromic acid (owing to the presence of antozone or peroxide of hydrogen).
If the rod or metal used in this experiment is too strongly heated, the
ozone formed is reconverted into oxygen ; and if it is not sufficiently heated,

112 OZONIDES AND THEIR PROPERTIES.

no ozone is produced. In either case the tests fail to show the presence of
an oxidizing body. It has been suggested that the results of this experi-
ment are explicable on the supposition that the nitrogen of the air is burnt,
or oxidized at a low temperature, and converted into nitric acid ; but the fact
that they are not observed at temperatures at which ozone cannot, and nitric
acid can, exist ; and further, that the ether itself undergoes changes which
admit of no explanation on this hypothesis, are circumstances adverse to this
view. Asa permanent source of ozone, Boettger has recently suggested that
a mixture should be made of two parts of permanganate of potash and three
parts^f sulphuric acid. The pasty mass thus produced will, he states, con-
tinue to give off ozone for several months. (Chetn. News, Ang. 1861.) The
effects in this case have been referred to the presence of chlorine. {Chem.
News, Oct. 26, 1861.)

Properties. — It has been found that in whatever manner ozone is produced
its properties are the same. It is insoluble in water, alcohol, and ether.
When much diluted with other gases, it is destroyed by agitation with a
large quantity of water. It is readily dissolved by a solution of an alkaline
iodide, converting it into iodate, and it is absorbed by leaf silver in a humid
state. It decomposes the protosalts of manganese (sulphate and chloride),
producing peroxide, and causing a brown stain on paper immersed in these
solutions. Silver leaf, on which common oxygen has no action is, when
wetted and exposed to ozonized air, slowly oxidized, and the ozone disap-
pears. Andrews found that dry silver, whether in leaf or filings, entirely
destroyed ozone when prepared by electrolysis or by frictional electricity,
and that mercury had also the property of absorbing it. Thin films of metal-
lic arsenic and antimony are oxidized by it — the arsenic is rapidly converted
into arsenic acid and disappears. This experiment, which serves to distin-
guish a deposit of metallic arsenic from one of antimony, may be thus per-
formed. Place a watch-glass, containing the deposit of arsenic, over another
containing a clean slice of phosphorus with a few drops of water. In a few
hours the arsenical deposit will entirely disappear, forming arsenic acid.
Peroxides. of manganese, silver, lead, and iron, as well as oxide of copper,
destroy it, or rather convert it into oxygen. Among other reactions, the
sulphides of lead and silver are changed into white sulphates, and cyanide of
potassium into cyanate of potash, while the yellow ferrocyanide is converted
by it into the red ferricyanide of potassium.

Organic substances are variously affected by it. Vegetable colors are
bleached or altered. Blue litmus is bleached without being first reddened.
The color of sulphate of indigo is discharged when the liquid is shaken with
ozonized air. Filtering-paper, soaked in aniline or pyrogailic acid, is rapidly
turned brown. Andrews found that caoutchouc and cork are rendered brit-
tle and destroyed. Besanez noticed that uric acid in water, when shaken
with ozonized air, was dissolved and changed into urea and allantoin. (Hep.
de Pharni., 1859, and Chem. News, 1, 3t.) He also found that ozone readily
entered into combination with tannic acid, and that oxalic acid was a pro-
duct of this union. The milky white precipitate of guaiacum resin produced
by adding a few drops of the tincture to a quantity of distilled water, is ren-
dered blue or of a pale bluish-green color, when shaken with ozonized air.

All these chemical changes are due to oxidation ; and oxides alone result.
In many respects ozone resembles chlorine. It readily displaces hydrogen,
oxidizing it as well as the radical with which it is associated. It will even
combine with nitrogen at common temperatures, when in contact with water
and a base. Ozonized air, placed over lime-water, produced nitrate of lime,
and from this compound, nitre was procured by double decomposition
(Schonbein). It oxidizes ammonia, and sulphuretted hydrogen gas, land

OZONIDES AND THEIR PROPERTIES. 113

converts nitrous and sulphurous, into nitric and sulphuric acids. It acts as
a powerful disinfectant, and its influence in the atmosphere is considered to
be exerted in oxidizing and destroying foul effluvia. It is at any rate diffi-
cult to procure evidence of the presence of ozone in the vicinity of these
effluvia, or in densely populated places ; and it is equally difficult to under-
stand how ozone, in a free state, can be to any extent diffused through the
atmosphere, when its tendency to combine with all oxidizable substances is
proved to be so powerful.

Although ozone is not soluble in water, it appears to be dissolved by cer-
tain liquids. A solution of pure iodide of potassium readily dissolves it,
acquiring a yellow or brown color according to its strength. Iodine is set
free so that this is not a true solution but a removal of ozone by oxidation.
Oil of turpentine, when long kept in contact with air, dissolves and fixes
ozone. If the oil thus changed is mixed with a solution of iodide of potas-
sium, and the mixture is well stirred, it acquires after a time a yellow color,
owing to the ozone combining with the potassium and setting the iodine free.
The vapor of oil of turpentine in contact with phosphorus exposed to air and
w-ater either removes the ozone as it is produced, or prevents its production,
for under these circumstances the oxygen of the air is not ozonized by phos-
phorus. Oil of turpentine containing ozone has a bleaching power. When
shaken with a diluted solution of sulphate of indigo the color is speedily dis-
charged. Other essential oils, such as those of cinnamon and cloves, have also
been found to absorb and fix ozone. Ether long kept in contact with air
contains ozone ; it decomposes a solution of iodide of potassium — bleaches
indigo, and has usually at the same time an acid reaction on test paper.
Ozone appears to be a constituent of the alkaline permanganates, and when
these are dissolved in water it exists potentially in a state of solution. The
destruction of the pink color of the permanganate of potash by organic mat-
ter, is probably owing to the separation of the oxygen as ozone. One drop
of a solution of the permanganate added to a mixture of iodide of potassium
and starch, produces the blue iodide of starch by oxidizing the potassium,
and the precipitated resin of guaiacum is rendered blue by it. Sulphate of
indigo is bleached by this liquid, and foul effluvia are oxidized and lose their
offensiveness. An alkaline permanganate, under the name of ozonized water,
Condy's liquid has been of late much used in medical practice as a deodorizer,
or as an oxidizer. The peroxide of manganese — one of the class of ozonides,
presents similar properties. The peroxide has no action on a solution of
iodide of potassium and starch ; but if a little acetic acid is added, oxygen,
as ozone, is set free, and the liquid immediately acquires a blue color. If
diluted sulphate of indigo is substituted for the alkaline iodide, the color is
discharged. The compounds containing oxygen as ozone are possessed of
similar properties : they are called, by Schonbein, ozonides. The following
are the principal : —

MngO, Pb02 CrOg COgOg MnOg

MnOa AgOj BiOg NigOg

Among these, peroxide of lead appears to have a most energetic action.
Without the addition of any acid, it instantly sets free iodine from iodide of
potassium, and bleaches a solution of sulphate of indigo. When one part of
dry sulphur is rubbed in a warm mortar with five or six parts of dry peroxide
of lead, the oxygen, as ozone, is suddenly given off with combustion of the
sulphur, and formation of sulphide of lead.

Mr. Spencer enumerates the magnetic oxide of iron as one of the com-
pounds of this metal, containing oxygen in the state of ozone. He has
constructed a filter in which this mineral substance is the active material for
8

114 TESTS FOR OZONE IN AIR.

the puriBcation of water, by oxidizing and destroying all organic matters
contained in it.

One of the most remarkable properties of ozone is, that from whatever
source it may be derived — it is reconverted into oxygen by a moderate heat.
If the heat be between 500^ and 600°, the conversion is immediate ; at a
lower temperature (450°) it takes place more slowly. Andrews found that
no water was produced during this conversion, and that only pure oxygen
resulted. Fremy and Becquerel have confirmed this result. This disposes
of the question, whether ozone is a higher oxide of hydrogen. It obviously
contains no hydrogen. Ozonized air passed through a tube heated as above
mentioned, produces the usual reaction on iodide paper on entering the tube,
but has entirely lost this property when it passes out. Hence, while elec-
tricity converts oxygen into ozone — heat reconverts ozone into oxygen.
Electricity, in long-continued sparks, will also bring about this reconversion
into oxygen. Faraday has proved by experiment that when electrical dis-
charges are made through a heated platinum coil, no ozone is produced,
while, when the coil was allowed to cool, ozone reappeared with each spark.
These facts show not only that ozone is oxygen ; but also that the oxidizing
effects attributed to it in the various modes of its production cannot proceed
from the presence of nitric acid, hyponitric acid, or chlorine. A heat of
500° would not destroy the oxidizing action of these compounds.

When peroxide of manganese is heated, oxygen is said to be given off; but
ozone may, in this case, be actually evolved, and converted into ordinary
oxygen by heat. (Schonbein.) Peroxide of manganese, iron, and lead,
absorb ozone, and convert it into oxygen at all temperatures. When either
of these compounds is mixed with chlorate of potash, and heated, it is well
known that oxygen is obtained from the chlorate at a much lower tempera-
ture than when the oxide of manganese or chlorate is separately heated ; but
no oxygen is evolved from the peroxide itself (see page 90). Schonbein
explains this singular phenomenon by assuming that the chlorate is a com-
pound of chloride of potassium and of oxygen as ozone ; and that this com-
bined ozone, like free ozone, is changed by the peroxide into oxygen, and is
thus readily separated from the chloride. The oxygen thus obtained, always
contains chlorine. It has the odor of this gas, bleaches litmus paper, decom-
poses iodide of potassium, and precipitates a solution of nitrate of silver. It
is probable that, in this case, the ozone displaces a portion of the chlorine
from the chloride, and that some manganate of potash is formed.

Peroxide of iron has even a more powerful effect by contact with the
chlorate. A thousandth part of the peroxide mixed with the fused chlorate,
was found to liberate oxygen abundantly ; and with one two-hundredth part,
the oxygen was evolved with great rapidity — the saline mass becoming incan-
descent. A mixture of one part of peroxide with thirty parts of chlorate,
when heated to the point of fusion, brought about an ignition of the mass
with an evolution of the gas almost amounting to explosion. (Pelouze et
Fremy, Op. cit., 1, 194.) In this case, also, chlorine is set free, and probably
some ferrate of potassa is formed.

Tests. — Various methods are employed for testing the presence of ozone
in a gaseous mixture containing it. The iodide of potassium and starch
elsewhere referred to (page 111), is generally employed, and is known as
Schonbein's test. It is thus prepared: One part oi pure iodide (free from
iodate) is dissolved in two hundred parts of distilled water ; ten parts of
starch, finely powdered, are mixed with the solution, and the liquid is gently
heated until it is thickened from the solution of the starch. White unsized
or sized paper is soaked in the liquid : the paper is dried, cut into slips three

OZONE OP THE ATMOSPHERE. 115

inches long by three quarters of an inch wide, and these are preserved in a
stoppered bottle.

When intended for use,^ slip of the prepared paper is exposed to a free
current of air in a spot sheltered as mnch as possible from rain, light, and
foul effluvia, for a period varying from six to twenty-four hours. An inge-
niously construpted box for testing the atmosphere has been contrived by
Mr. Lowe {Proc. R. S., vol. 10, p. 537). By exposure, the paper becomes
brown, and when wetted acquires shades of color, varying from a pinkish
white and iron gray to a blue. A chromatic scale, covering 10°, has been
contrived by Schonbein, with which the changes in the wetted paper may be
compared. Fremy recommends, as a test, white blotting-paper, soaked in
an alcoholic solution of guaiacum, and dried in the dark. By exposure to
an ozonized atmosphere this paper acquires a bright blue color. Houzeau's
test is a s4rip of litmus paper of a wine-red color, of which one-half has been
soaked in a solution of iodide of potassium in water, in the proportion of
one per cent. As a result of exposure to ozonized air, the iodized portion
becomes alkaline, and the paper acquires a deep blue tint. The other por-
tion preserves its normal color ; and by showing an acid or alkaline reaction,
may reveal the presence of vapors in the air, which might otherwise be a
source of error.

As paper is fragile, slips of clean calico (containing starch), dipped in
iodide of potassium, have been substituted by Mr. Lowe. This gentleman
found that twenty-four hours' exposure was required for a satisfactory result.
The calico may be used dry, and wetted after the exposure is complete. The
iodized calico acquires various shades of a brown color, becoming pink, gray,
or blue, when dipped in water. Mr. Lowe observed that the strongest effect
was produced during the night, and at some elevation above the ground ;
also that the months of January, February, and March, gave the largest
amount, both day and night. On a great number of days on which obser-
vations were made, there were no visible traces of ozone. Other observers
have found it to vary according to locality, the season of the year, the hour
of the day, the direction of the wind, and the height of the place above the
level of the sea. It is seldom found in closely inhabited spots. In some
observations made at Brighton; Mr. Faraday procured evidence of ozone on
test-paper exposed to a current of air from the sea, close to the sea-shore,
as well as in the air of the open downs above the town ; but none in the air
of the town itself. Dr. Angus Smith could not detect ozone in the air of
Manchester ; but at a distance, it was easily recognizable when the wind was
not blowing from the town. Some strips of paper, prepared by the process
described (see above), were exposed in Southwark, and at Connemara, in
Ireland. At the former place, there was no change in twenty-four hours ;
while at the latter, the paper acquired a brown color in a few hours ; and on
dipping it into water it became blue. It has been objected to this mode of
testing, that the change in the alkaline iodine under these circumstances,
may be due to free chlorine, bromine, iodine, or to nitric and other acids, or
even to some organic compounds diffused in the athaosphere, and not to
ozone. But it is to be observed, that the test-paper remains unchanged
exactly in those spots where such compounds would be likely to exist («'. e ,
in inhabited towns) ; while the chemical effect is observed to be at a maxi-
mum on open heaths, or downs, on the sea-coast, on the open sea, and on
lofty elevations, more than 20,000 feet above the surface of the earth, where
there is no conceivable source of such impurities in the air. It is possible,
too, as M. de Luca has suggested, that the nitric acid, even if really exist-
ing in the air of those places, may itself be the product of the oxidation of
nitrogen by ozone ; and this may be the source of nitric acid, often found in

116 ANTOZONE AND ITS PROPERTIES.

rain-water, and even in the atmosphere (Comptes Rendus, and Chemical
News, September 7, 1861, p. 136). The absence of any reaction for 118
days out of 365, and the greater effect by night than by day, in wet than in
dry weather, and in winter than in summer, show that these phenomena are
not due to the presence of such impurities in the air as those suggested. At
the same time, the presence of a large quantity of iodate of potassa in the
iodide used, may have been a fertile source of error. A discoloration of the
paper may then be produced by such compounds as sulphurous acid and
sulphuretted hydrogen.

Constitution. — Ozone has been proved to be oxygen in a changed condition.
Andrews found that peroxide of manganese in absorbing it, underwent no
sensible increase of weight although as much as 0*9 gr. were apparently
destroyed ; no water was produced. Hence it was transformed into oxygen,
merely by contact, and it could not have contained any hydrog§n. In its
production by electrolysis, he also noticed that the active oxygen was exactly
equal to the entire weight of the ozone — and was therefore identical with it.
(Proc. R. S., vol. t, p. 476.) But experiment shows that oxygen under-
goes a remarkable condensation in this conversion. There is a reduction to
one-fourth of the bulk, the density of ozone being 4 4224 compared with
that of oxygen as 1. When oxygen has been contracted in bulk by the
electric spark in the production of ozone, peroxide of manganese restores it
to its original volume (vol. 9, p. 608). In fact, the conclusion drawn by
the writer, is in accordance with the results of Schonbein, Faraday, Becque-
rel, and others — that ozone, from whatever source derived, is one and the
same substance, and is not a compound body, but simply oxygen in an altered
or allotropic condition.

Antozone. — While ozone is considered to be active oxygen in a — state
or 0, antozone is active oxygen in a -f state or 0. It is less powerful as
an oxidizer than ozone, and appears to have a neutralizing action in it.

Antozone at present is believed to be a constituent of certain peroxides.
Of these compounds, Schonbein has furnished the following list, under the
name of antozonides : —

HO2 NagO' SrOg.

KO3 Ba O2

In its action on alkaline iodines and in its bleaching properties, antozone
resembles ozone. The differences pointed out by Schonbein are not very well
marked. An ozonide evolves chlorine with hydrochloric acid ; gives a blue
color to the precipitated resin of guaiacum, and turns aniline (on paper)
red brown. It does not produce peroxide of hydrogen. An ozonide (MnOJ,
with sulphuric acid, produces a rich series of purple colors with strychnia.
An antozonide (BaOg) similarly treated does not. Although dealing with
peroxides in both cases, the oxygen, as it is evolved, must therefore be
different in its properties. The oxygen of an ozonide or antozonide,
produces effects which common oxygen does not produce ; and it is further
remarkable that these two oxygens, which appear to be in opposite polar
conditions, have the power of neutralizing each other on contact, and of
evolving ordinary oxygen in a pure state. Thus, when a few crystals of
permanganate of potash or peroxide of manganese is mixed with a solution
of peroxide of hydrogen, oxygen gas with its usual neutral properties, is
given off (Mn03+H0jj=Mn03 + 110 + 0). There is, after the mixture, no
evidence of ozone — of antozone or of allotropic oxygen in any form.
Two tubes filled with peroxide of hydrogen may be inserted over mer-
cury. Into one may be passed peroxide of manganese, and into the
other crystals of the permanganate of potash wrapped in bibulous paper.

ANTOZONE AND ITS PROPERTIES. 117

Oxyfj^en is liberated in both eases, bnt with very prreat rnpidity from the
contents of the tube containino; the pertnanj^anate. When full, the tube may
be removed and the gaseous contents examined. An ignited splint of wood
is liindled into a flame, and starch paper moistened with oxide of potasisiura,
undergoes no change. These mixtures therefore produce neutral oxygen.
If peroxide of barium is substituted in this experiment for peroxide of man-
ganese, no oxygen is evolved.

Peroxide of hydrogen added to a solution of iodide of potassium, sets free
iodine (by oxidation). Peroxide of barium will produce a similar change,
provided a few drops of acetic acid are added in order to set free antozone,
acetate of oxide of barium being formed. Peroxide of manganese produces
the same change on the iodide only after the addition of acetic acid and in a
more intense degree. Permanganate of potash requires no addition of acid
for the oxidation of the iodide. A striking difference between the two classes
of oxides (ozonides and antozonides), is further indicated by the fact that a
mixture of peroxide of barium and acetic acid discharges the color of per-
manganate of potash, while a mixture of peroxide of manganese and acetic
acid has no effect on the permanganate. A mixture of either peroxide with
acetic acid will discharge the color of indigo ; the peroxide of manganese
acting much more rapidly. The permanganate of potash discharges the
color of indigo completely, without requiring the addition of an acid.

One of the new methods of producing oxygen, elsewhere described (see
Oxygen), is based upon this decomposition of an ozonide and an antozonide
in the presence of each other, by means of a diluted acid. The powder
called Oxygennesis, is a mixture of peroxide of barium with bichromate of
potash. The addition of diluted sulphuric acid with the aid of heat, liberates
neutral oxygen.

Antozone in the state of vapor or gas is unknown. Peroxide of hydro-
gen, which will be described in a future chapter, may be taken as the type of
liquid antozone, and peroxide of barium as the type of solid antozone. Per-
oxide of barium, when mixed with solution of iodide of potassium and acetic
acid is added, sets free iodine by oxidizing the potassium. It also bleaches
indigo, but it does not produce a blue color with precipitated guaiacum
resin, and it does not produce the blue or purple colors with strychnia which
are produced under similar circumstances by peroxide of manganese, lead,
and other compounds of the ozonide class

If, according to Schonbein's theory, oxygen is thus reduced from its posi-
tion as an elementary body, and it is really a compound of ozone and anto-
zone, it should follow that whenever ozone is produced antozone must also
be a product. In one of his published papers, Schonbein has stated, that
in the ordinary production of ozone by phosphorus and water, so soon as the
ozone appears, peroxide of hydrogen (HO^, or antozone) may be detected
in the water in which the phosphorus is immersed. By agitating the phos-
phorus with the water, he found that this liquid acquired the property,
which it possesses in common with ozone, of oxidizing potassium, and
setting iodine free from the iodide. In his view, by mere contact with
phosphorus, neutral oxygen is split or decomposed into two oppositely
active conditions — the positive oxygen being absorbed by the water, to form
peroxide of hydrogen, whilst part of the negative oxygen escapes, on
account of its gaseous and insoluble nature, into the atmosphere above the
phosphorus. The greater part, however, combines to form phosphorous acid,
which, like phosphorus itself, can remain in contact with peroxide of hydro-
gen without" abstracting its active oxygen. {Chemisch. Cent. Blatt, Jan.
1860, and Chemical News, Feb. 11, 1860.) When pure oxygen is converted
into ozone by electricity, it is probable that antozone is also produced, and

118 HYDROGEN.

that by continuing the electric sparks, or increasing their intensity, these
bodies are reconverted into ordinary oxygen. When ether-vapor and air
are combined, at a heat below 500°, ozone is produced in the surrounding
air, while antozone (peroxide of hydrogen) is dissolved by the ether, giving
to it bleaching properties, and a power of peroxidizing chromic acid. The
nearest condition to purity in which antozone has been yet found, is in
peroxide of hydrogen, obtained by the substitution of hydrogen for barium
in the peroxide of that metal. (See Peroxide of Hydrogen.) While this
theory appears to account for many curious facts which have hitherto been
vaguely referred to action by contact or presence, it fails to explain satis-
factorily all the phenomena. In the ozonized air obtained by the oxidation
of phosphorus, the antozone is held dissolved by the water ; but the ozone
in ozonized air may itself be converted into oxygen by mere heat above
500°; hence the presence of antozone to produce neutral oxygen is not
always necessary. So the ozone evolved from mixtures of the peroxides of
manganese and iron with chlorate of potash, is converted into oxygen by
heat, without reference to the presence of antozone.

CHAPTER IX.

HYDROGEN (H = l).

History. — In the form of water and aqueous vapor, hydrogen is universally
diffused over the globe. One-ninth part of this liquid by weight consists of
hydrogen ; and it is from this source that the gas is readily and abundantly
procured. The name of the element is derived from the Greek iJScop, water,
and yfvvaQ, to produce. Hydrogen is held with such affinity by oxygen and
other bodies, that it is not found in nature in the free state. Bunsen states
that he found it in a mixture of gases, collected by him in 1846, from the
volcanic district of Nimarljall, in Iceland. It existed in the proportion of
45 per cent. Hydrogen is an important constituent of animal and vegetable
matter, entering largely into the composition of flesh and woody fibre. In
union with carbon, it forms a large number of gaseous, liquid, and solid
compounds, known as the class of hydrocarbons. Associated with carbon
and oxygen, it is a constituent of inflammable substances, such as alcohol
and ether. Hydrogen appears to have been first examined in a pure state
by Cavendish in 1766 {Phil. Trans., vol. 56, p. 44). Previously to this it
had been confounded with several of its compounds, under the name of
inflammable air.

Preparation. — The best method of procuring hydrogen is to place in a
flask, provided with a bent tube ground to fit the neck — one part of granu-
lated zinc, four to five parts of water, and one part of strong sulphuric acid.
There is a brisk effervescence arising from the rapid escape of the gas. Tliis
should be reduced, if too violent, by the addition of more water. It is a
singular fact that, the purer the zinc, the less energetic is the chemical
action ; and, indeed, pure zinc is scarcely affected by the acid. The gas
may be collected in the ordinary water-bath. The first portions are always
contaminated with air, and at least three times the capacity of the flask used,
should be rejected before the gas is collected for experiment. To ascertain
whether the hydrogen is quite free from air, a few bubbles may be passed

Methods of procuring hydrogen. 119

into a jar containing deiitoxide of nitrogen placed over the bath. If no
red fumes are produced, the gas is sufficiently pure for collection. The
chemical changes which take place maybe thus represented, S03,H0-fZn =
ZnOjSOa+H. The hydrogen, which is thus displaced by the metal zinc, is
entirely derived from the decomposition of water, and as the gas is scarcely
dissolved by this liquid, it is readily collected in large quantity. A cubic
inch, or rather more than half an ounce of water by measure, contains
twenty-eight grains of hydrogen, representing 1350 cubic inches, or about
five gallons of the gas. In place of a tubulated flask, a wide-mouthed bottle,
provided with a funnel-tube for pouring in the acid, and a bent delivery
tube for the escape of the gas, may be employed

Other methods have been suggested for procuring hydrogen, but they are
seldom resorted to. Thus, iron has been substituted for zinc, but the gas is
much less pure, and has generally an offensive smell from its producing an
oily volatile compound by uniting with the carbon of the iron ; sulphuretted
hydrogen and other impurities may also be present. 2. Hydrogen may be
obtained by passing the vapor of water over iron-turnings or wire, heated to
redness in a porcelain tube. In this case the iron is converted into magnetic
oxide [3Fe-f4HO = Fe30^ (magnetic oxide) +4H]. 3. It may be obtained
by introducing a ball of sodium or potassium, wrapped in paper, into a stout
jar full of water, placed over the water-bath. Hydrogen is here evolved
without the intervention of an acid, and an alkali is produced (Na-f H0=:
NaO-f-H.). The hydrogen of water may be set free by alkalies as well as
by acids in their reaction on metals. Thus aluminum in a strong solution of
potash liberates the hydrogen and appropriates the oxygen (2Al-f KO^-
3HO=Al,03+KO+3H).

As both zinc and sulphuric acid are frequently contaminated with arsenic
and sulphur, hydrogen, as it is usually obtained, is very impure. The purity
of the materials may be determined by generating the hydrogen in a bulb-
tube, and passing the gas into diluted solutions of nitrate of lead and nitrate
of silver. A brown discoloration of the lead indicates sulphur, while a
brownish-black precipitate in the silver solution indicates arsenic, phos-
phorus, or antimony. In order to determine whether the impurity is in the
zinc, some of the metal should be treated with sulphuric acid of known
purity, and the gas thus produced separately tested. The presence of
arsenic in hydrogen is a dangerous contamination ; the poison is not only
set free during combustion, but if the gas should be accidentally breathed,
it may cause serious symptoms, and even death. A Dublin chemist lost his
life a few years since by inhaling hydrogen thus contaminated with arsenic ;
the purity of the sulphuric acid had not been previously tested. The abso-
lute freedom of hydrogen gas from arsenic, antimony, phosphorus, or sulphur,
may be proved by introducing into ajar, with its mouth downward, a slip of
filtering-paper, moistened with nitrate of silver. The paper should not be
discolored in the gas, if pure.

In order to procure pure hydrogen, pure materials should not only be used,
but the gas should be collected over mercury. Hydrogen may be freed from
all the usual impurities by passing the gas, before collection, through two
U-tubes, both containing broken pumice — in the one tube, impregnated with
a solution of potash, in the other, with a solution of corrosive sublimate. In
the first tube, the compounds of sulphur and carbon are separated, and in
the second, those of arsenic and phosphorus. Hydrogen may be obtained
perfectly dry by causing it to traverse a third tube containing chloride of
calcium, after it has left the purifying apparatus. It is better however to
select pure materials. Very pure distilled zinc may now be procured, and
this should be always employed when the hydrogen is required to be abso-

120 PROPERTIES OF HYDROGEN.

Intely pure, as for the detection of arsenic. Magnesium, which mny now be
procured at a comparatively cheap rate, produces pure hydrogen abundantly,
when put into pure sulphuric acid diluted with a large quantity of water.
It forms at the same time as a product a useful medicinal salt in the sulphate
of magnesia. Magnesium is probably destined at no distant date to take
the place of zinc in many chemical processes, and especially in the construc-
tion of voltaic batteries.

The hydrogen liberated by the electrolysis of water from platinum surfaces
(see Water), may, when dried, be considered as absolutely pure. In this
form, hydrogen has been employed by Mr. Bloxam for the separation of
arsenic and antimony from organic liquids.

Properties. — Hydrogen is a gas which has not yet been liquefied by cold or
pressure : it is not dissolved by water, unless that liquid has been previously
deprived, by long boiling, of common air, in which case 100 cubic inches
dissolve about 1.5 cubic inches of the gas. When perfectly pure it has
neither acid nor alkaline reaction, has no taste, and is inodorous: but as
it is commonly made, it has a slightly disagreeable smell from traces of
foreign matters associated with it. It may be respired for a short time,
although it is fatal to small animals. It does not act as a poison, but causes
death by suffocation, i. e., by the exclusion of oxygen. As a substitute for
nitrogen in atmospheric proportions with oxygen, it has been breathed for
some time without any other effect than that of producing a slight tendency
to sleep. The intensity of sound is greatly diminished in an atmosphere of
hydrogen. Leslie, indeed, found that the sound was more feeble than the
rarity of the gas, compared with air, would have led him to expect. He
placed a piece of clock-work by which a bell was struck every half minute,
under the receiver of the air-pump, and, after exhausting the air, filled the
receiver with hydrogen ; but the sound was then even feebler than in the
highly rarefied atmosphere. (Ann. Philos., 2d series, 4, 172.) It is stated
that sound moves at least three times as fast in hydrogen as in air.

Hydrogen gas is the lightest known form of matter. It is 14.4 times
lighter than air, and 11,000 times lighter than water. In consequence of its
extreme lightness, it is difficult directly to determine its weight with accu-
racy by the common process; but the researches of Berzelius and Dulong,
and of Dr. Prout, lead us to infer that its specific gravity, compared with
oxygen, is as 1 to 16 : 100 cubic inches, therefore, of pure hydrogen gas at
mean temperature and pressure weigh only 2*14 grains, and, compared with
air, its specific gravity would be nearly as 7 to 100, or more correctly as
0*0691 to 1. Boussingault and Dumas have shown that the density of hydro-
gen is between 0-0671 and 0 0695. (Ann. Ch. et Phys., 3d series, 8, 201.)
At a temperature of 32°, 100 cubic inches weigh 2*22756 grains. (Thom-
son.) It has the highest refracting power of all the gases. Compared with
air it is 6614 to 1000. In relation to magnetism, it was found by Faraday
to be diamagnetic ; a vacuum being 0*0, hydrogen was 0 1. In the mag-
netic field, a tube containing it assumed an equatorial position, or pointed
east and west. Its specific heat, compared with an equal weight of air, was
12'340 to 1000. In its electro-chemical relations hydrogen is strongly posi-
tive, and in electrolysis it always appears at the negative pole. It displaces
the metals under these circumstances, and enters into combination with the
oxygen or salt radical. This is one of the facts which is considered to favor
the hypothesis that hydrogen itself is the gaseous state of a metal perma-
nently volatile at the lowest temperature.

The low specific gravity of hydrogen may be illustrated by substituting
it for common air, in soap-bubbles, which then rapidly ascend in the atmo-
sphere, and may be kindled by the flame of a taper. This property led to

COMBUSTION OF HYDROGEN. 121

its employment formerly in the inflation of balloons, but of late years coal-
gas has been substituted. Small balloons, made of gold-beater's skin, or of
collodion, when filled with pure hydrogen, dried by passing it through a
tube containing chloride of calcium, rise in the air, their specific gravity
being inferior to that of the surrounding atmosphere. This gas has a remark-
able penetrating power. It rapidly traverses porous septa of unglazed
earthenware — animal membrane or caoutchouc, and it will pass through tubes
of red-hot platinum. A current of hydrogen issuing from a jet, traverses
white blotting paper as readily as if there were no obstacle to its passage.
Spongy platinum placed on the paper is soon made red-hot by the gas which
passes through the paper.

Hydrogen is itself inflammable, but it extinguishes flame. When pure, it
burns quietly, with a pale yellowish flame at the surface in contact with air ;
but, if mixed with twice its volume of air, it burns rapidly and with
detonation.

The phenomena of its combustion vary according to the mode in which
the experiment is performed, but the product is always water (HO) — the
hydrogen at a high temperature taking the oxygen from the atmosphere. If,
by withdrawing the glass plate from a jar, a slight aperture only is made,
the gas may be kindled without explosion, and by the gradual withdrawal
of the plate it will burn quietly, and with a scarcely visible flame, until all
is consumed. If the gas is kindled, as the cover is suddenly removed, it
always burns with explosion by its rapid admixture with air in its great
tendency to diffuse. If the cover be entirely removed, and the lighted taper
be held six or eight inches above the mouth of ajar, there will be an interval
before combustion takes place, and the gas will tlien burn with a loud explo-
sion. The following experiment may serve as another illustration. Drop a
piece of potassium into a stout jar containing hydrogen gas, having a stratum
of an inch of water at the bottom. The potassium at first decomposes the
water without producing flame ; but, in a few seconds, the air rushes in to
supply the place of a portion of the hydrogen which has escaped, and the
mixture is then kindled by the burning potassium with a loud detonation.
This experiment may be performed with perfect safety in a stout glass jar,
eight inches deep and two or three inches wide. It illustrates the decompo-
sition of water by a metal, and its recomposition by the union of its elements
at a high temperature.

It has been stated that hydrogen extinguishes burning bodies ; in other
words, that it does not support combustion. To prove this, the jar contain-
ing the hydrogen must be inverted. A large jar filled with the gas, having
its open end downward, may be brought over a lighted taper, supported on
a wire. The gas is instantly kindled, and burns at the mouth of the jar.
By depressing the jar over the taper this will become extinguished, and the
blackened wick will be seen in the midst of the hydrogen, which is burning
below. The taper may be relighted by raising the jar, and again extinguished
by depressing it, an experiment which may be repeated several times. There
are other interesting experiments which prove that hydrogen is not a sup-
porter of combustion in the ordinary meaning of these terms. Place a piece
of phosphorus in a small saucer floating in a vessel containing a thin stratum
of water. Kindle the phosphorus, and, when fully burning, cover it com-
pletely with ajar of hydrogen as with an extinguisher. The hydrogen is
inflamed at the mouth of the jar, but, with the flame of the phosphorus, it is
extinguished when the jar is plunged beneath the water. In place of phos-
phorus, a piece of camphor may be employed with like results. Paper im-
pregnated with a solution of nitrate of potash, when dried, ignited, and
introduced into ajar of hydrogen, is extinguished. A certain degree of heat

122 HYDROGEN. EXPLOSIVE PROPERTIES.

is required for the kindling of this gas in air. It is not inflamed by an iron
bar heated to dull redness, but is immediately kindled at a bright red heat.
Daring combustion, hydrogen combines with eight times its weight of oxygen,
producing a more intense degree of heat, weight for weight, than any other
combustible. {See page 106.)

Hydrogen, when mixed with air, and inflamed by a taper or the electric
spark, burns with a loud explosion. Cavendish found that the loudest ex-
plosion was produced by mixing one volume of hydrogen with three of air,
or two volumes with five of air. One of hydrogen with nine of air burned
very feebly, and four of hydrogen with one of air burned without explosion.
{Phil. Trans. , 56.) If, instead of employing a mixture of hydrogen and
atmospheric air, two volumes of hydrogen are mixed with one of oxygen,
and inflamed in a stout jar, the explosion is extremely violent ; but if the
mixture be diluted with eight measures of hydrogen, or with nine of oxygen,
it no longer explodes. The cause of this violent explosion is owing to the
sudden conversion of a large volume of mixed gases into liquid w^ater by con-
densation. As 528 cubic inches of mixed gases produce only 0*4 cubic inch
of liquid water at 60°, there is a diminution in volume to goVuth part. A
vacuum is thus produced, into which the air suddenly rushes, producing a
loud sound. There is, however, in the first instance, expansion by the heat
of combustion, and this is instantly 'followed by a condensation of the pro-
duced steam or aqueous vapor.

The inflammability and low sjDCcific gravity of hydrogen are shown in the
following experiments : Let ajar filled with this gas stand for a few seconds
with its mouth upwards ; on introducing a lighted taper, the gas will be
found to have escaped, and to have been replaced by common air. Place
another jar of the gas inverted, or with its mouth downward ; the gas will
now be found to remain a much longer time in the jar, being prevented from
escaping upwards by the bottom and sides of the vessel. A jar of this gas
may, for the same reason, be removed with its mouth downwards from the
water-bath without a cover, and thus transported to a considerable distance.
It may then be inflamed and burnt, by bringing the open mouth over a
lighted candle. Place a bell-jar having a Harrow neck and containing hy-
drogen, so that the wide open end may rest on three cubes. The jar may be
removed from the bath, as in the previous experiment, without any cover.
Remove the stopper and ignite the gas. It will burn with a fierce flame as
the hydrogen is forced through the neck by the pressure of the external air
beneath, and it will finally produce an explosion, but without any danger,
owing to the last portions of the gas being mixed with the air in explosive
proportions. If a piece of paper dipped in a solution of nitre and dried, is
burnt under the mouth of a jar of hydrogen, it will be found that the smoke
produced will float in a cloud below the gas, owing to the lightness of the
hydrogen. Ajar of air held over another containing hydrogen, from which
the cover is then removed, will catch the hydrogen as it ascends. The ap-
plication of a lighted taper will show its presence in the upper jar and its
absence in the lower jar, in which it was originally contained. Hydrogen
may, in fact, be decanted, as it were, per ascensum, from one jar into another
held above it. Thus, if a light bell-glass be suspended with its mouth down-
wards to one end of a scale-beam, and accurately counterpoised, it will be
found, on placing a jar of hydrogen gas (closed by a plate of glass) under-
neath it, that the hydrogen, on removing the glass plate, will ascend into
the bell, and by its lightness cause the counterpoise to sink ; the hydrogen
may afterwards be inflamed by a taper introduced into the counterpoised
bell. A large bell-glass, suspended, may be filled with hydrogen by dis-
placement— I. e., by opening one or two large jars of the gas beneath it, and

DETECTION OP IMPURITIES IN THE GAS. 123

allowinj;]^ the hydron^en to ascend. If a bell be stru(ik with a hammer in this
atmosphere of hydrogen, it will be at once perceived how much the ordinary
sound is reduced. A small shade, mounted on a handle, and introduced into
this atmosphere of hydrogen, with its mouth downwards, will, after a few
minutes, be filled with hydrogen by displacement. This may be transported
to a distance, and kindled over a Qame. The gas, owing to the admixture
of air, will burn with a slight explosion.

If hydrogen is generated in a bottle, provided with a glass tube drawn
out to a capillary point, it may be burnt in a jet at the end of the tube {the
Philosopher''s lamp) ; but care should be taken not to insert the cork with
the jet until all the air has been removed from the bottle by the free escape
of the gas. The hydrogen burns at first with a long pointed yellowish
flame, which may be proved to be hollow like other flames {see p. 107).
Although the light is feeble the heat is intense. Fine platinum wire is made
white hot in an instant, and sometimes melted. Fine iron wire is rapidly
consumed by combustion with the surrounding air, and glass is speedily
melted. If a cold glass vessel be brought over the flame, the interior is
speedily covered with the condensed vapor of water — the result of combus-
tion ; and, by a condensing tube, the water thus generated may be easily
collected and tested. If, while the gas is burning, a tube from half an inch
to two inches in diameter, and twelve to twenty inches long, open at both
ends, be brought gradually over the flame, the flame becomes elongated,
acquires a bluish tint at the mouth of the jet, and a peculiar sound is heard,
varying according to the diameter of the tube. This forms what has been
called a chemical harmonicon or hydrogen music. It arises from the vibra-
tion of the column of air within the tube, produced as a result of a rapid
succession of slight explosions during the combustion of the gas. The tone
varies in pitch with the length and diameter of the tube; and singular effects
may be produced by employing for the experiment the tube of a broken
retort. If, while the sound is issuing, a tube of larger size is placed at dif-
ferent heights over the tube in which the hydrogen is burning, there will be
remarkable modifications of the sound. A small flame is better fitted for the
production of this phenomenon, but, if too small, the flame may be extin-
guished by the strong current of air passing through the tube.

We may make use of this flame for the purpose of testing the purity of
the gas. If a piece of cold glass or white porcelain be suddenly depressed
on the point of the flame, and the gas is pure, there will be no stain or de-
posit. Nothing but a film of water will be perceived. If there be the
smallest trace of arsenic or antimony in the gas, there will be a brown or
blackish stain, more distinctly visible on the surface of porcelain than on the
glass. By bending the tube at a right angle, and applying a strong red
heat, by means of a spirit-lamp, to the horizontal portion, the presence of
any foreign matters will be revealed. All the gaseous compounds of hydro-
gen are decomposed at a full red heat ; — the gas passes off, and the solid
impurity is deposited in a cold part of the tube. In this way the presence
of the minutest traces of sulphur, arsenic, antimony, phosphorus, or selenium
may be detected. A film or ring of the substance, recognizable by its color
or metallic lustre, will be perceptible. As a proof of the facility with which
hydrogen combines with these contaminating substances, it may be men-
tioned that when the pure gas is allowed to pass through a connecting piece
of vulcanized rubber tubing, it will combine with a portion of sulphur, which
may be re-obtained in a solid state by the method of testing above described.

In discussing the nature of flame, and the causes of its luminosity and
heat, allusion has been made to the high temperature of that of hydrogen.
Tnis gas is occasionally employed for exciting intense heat ; and, when

124 HYDROGEN. COMPOUNDS.

mixed with oxyf2:en, and burned as the mixture issues from a small jet, it
produces a temperature nearly equal to that of the are of flame in the voltaic
circuit. A blow-pipe upon this construction was first made by Newman,
and afterwards improved as to its safety, by Professor Cummin":, of Cam-
bridge. {Journal of Science and the Arts, 1, 67, and 2, 380.) Hemraing's
safety-tube has also been used in these experiments. (See Phil Mag., 3d
series, 1, 82.) An excellent mode of obtaining intense heat by the combus-
tion of oxygen and hydrogen, consists in propelling the two gases, in their
proper proportions to form water, from separate air-holders through a burner
composed of two concentric tubes : a good form of such a burner has been
described by Daniell. {Phil. Mag., 3d series, 2, 57.) The apparatus for
this purpose has been further improved by Maugham, especially as relates to
its application to the solar microscope. {Trans. Soc. Arts, &c. , vol. 50.)
The gases are now forced into a small chamber, terminated by a platinum jet,
from which they are burnt. The heat is such that it is capable of fusing and
even volatilizing platinum ; it causes the melting of rock crystal, as well as
alumina or clay. In this and similar cases where the inflammable gas is
mixed with oxygen, the nature of the flame is materially altered, the com-
bustion being entire throughout the body of the flame, and not limited to
the film in contact with air. Hence, under these circumstances, the quantity
of the combustible consumed, and the quantity of oxygen combining with it in
a given time, are greatly increased. Owing to this perfect mixture of oxygen
and hydrogen, the flame may be described as solid, possessing an intensely
heating and penetrating power. Although scarcely visible in itself, the
flame, when received on lime, asbestos, or platinum, emits an intense light
(see page 101).

Lime was first used by Lieutenant Drummond as a source of light, with
the oxyhydrogen jet, in 1826. {Phil. Trans. 1826, p. 324.) By means of it,
in the Triangulation survey, he successfully connected the opposite shares of
England and Ireland at or about Holyhead, a distance of sixty-four miles.
In Scotland, he obtained a successful result on the summits of Ben Lomond
and Knock Layd, a distance of ninety-five miles. {Gas-Lighting Journal,
Jan. 1860.) Dr. Miller states that the Druminond Light has been seen at a
distance in a right line of 112 miles. Coal-gas, and other inflammable gases
and vapors, when mixed with oxygen in their combining proportions, burn,
for the same reason, with what may be described as solid flames. As coal-
gas, by being overheated in its manufacture, is converted in great part into
hydrogen, it is not only substituted for this gas in aerostation, but also in
producing the lime-light; so that, except for purely scientific purposes, the
more costly oxyhydrogen flame need not be employed as a source of light.

Compounds. — The range of combination of hydrogen is not so extensive
as that of oxygen. It forms with metallic and non-metallic bodies the class
of Hydrides. The hydrides of the metals are few in number, those of arsenic
and antimony being the principal. There are three other metals which form
temporary combinations with hydrogen — namely, potassium, tellurium, and
zinc. Among non-metallic bodies it forms an alkali with nitrogen ; neutral
compounds with carbon and phosphorus ; and acids (the class of hydracids)
with chlorine, bromine, iodine, sulphur, selenium, fluorine, and cyanogen.
These compounds are, for the most part, products of art. At a red heat,
hydrogen is a powerful reducing agent; thus it readily decomposes the
oxides, chlorides, and sulphides of some of the metals, combining with the
oxygen, chlorine, or sulphur, and setting free the metal in a pure and finely-
divided state. A current of dry hydrogen passed over oxide of copper, or
oxide of iron, heated to redness in a tube, takes the oxygen to form water,

EQUIVALENT. TESTS. NASCENT HYDROGEN. 125

which may be collected in a condensing bulb, or tube. The quantity of
oxygen contained in the dry oxides may be thus determined.

Equivalent. — The equivalent, or combining weight, of hydrogen, is, by
most English chemists, taken as unity — 1 : it is the standard with which the
atomic weights of all other bodies are compared. Its volume equivalent in
gaseous combinations is double that of oxygen, and has been variously
assigned as two volumes or one. We can perceive no sufficient reason for
departing from the simplicity of the rule hitherto received, that hydrogen
shall be regarded as representing unity by volume as well as by weight. To
assume that there are two standards, and that hydrogen represents weight,
while oxygen represents volume, presents no advantages in the constructioa
of chemical formulae, or in the explanation of chemical facts.

Tests. Special Characters. — As a gas, hydrogen is easily identified: 1, by
its inflammability, and the production of water as a result of its combustion :
2, by its lightness : 3, by its insolubility in water, in solution of potassa,
and in all liquids : 4, when free from oxygen, by its giving no red vapors
when mixed with deutoxide of nitrogen ; and by the mixture, in equal parts,
burning without explosion, with a greenish-white flame ; 5, by its being
entirely converted into water when mixed with half its volume of pure
oxygen, and the gases are combined by the electric spark, by heat, or by the
action of spongy platinum. For the detection of hydrogen, when in intimate
combination with carbon and oxygen in organic compounds, another process
must be resorted to. Hydrogen, it is well known, at a red heat, decomposes
oxide of copper, and is converted into water {see p. 128). The organic
substance (starch) is first deprived of water by complete desiccation. It is
then mixed with dry oxide of copper, placed in a tube, and heated to redness.
The water produced is collected by passing the products through a balanced
tube containing fused chloride of calcium. The increase of weight in the
chloride represents the total amount of water formed ; and one-ninth part of
this represents the amount of hydrogen contained in the substance under
examination. The process for detecting and separating hydrogen is incb.ded
in that which is employed for the determination of water.

Nascent or Allotropic Hydrogen. — Although the existence of two forms of
hydrogen is unknown, yet as it is evolved from water by electrolysis, or as
it is produced in the nascent state by chemical changes, the gas appears to
have much greater energy in combining, than that whi(;h has been once set
free. It has been long known to chemists, that under these circumstances,
gases frequently display great chemical power. In 1841, Mr. Smee noticed
that porous coke or charcoal, which had formed the negative pole of a battery,
retained a portion of hydrogen, and when placed in a solution of sulphate
of copper, the coke or charcoal was covered with the reduced metal. Free
hydrogen has no power of decomposing a salt of copper, but in this state it
was replaced by the metal. {Elements of Electro- Metallurgy, 1841, p. 37.)
Ozann and Fremy have made similar observations regarding silver. If
hydrogen is received on platinum sponge from the negative electrode of a
battery, until bubbles of the gas begin to appear, it will be absorbed and
condensed by this porous body. When the platinum sponge was washed
and placed in a solution of sulphate of silver, there was immediately a
precipitation of metallic silver. It was also found, that if the hydrogen
evolved from the negative platinum electrode in the decomposition of water,
was conveyed Immediately into a solution of sulphate of silver, the metal was
precipitated. When the gas was conducted into water containing perchloride
of iron, with a trace of ferricyanide of potassium, Prussian blue was formed.
These results could not be obtained with hydrogen gas in its ordinary stale.
When a current of hydrogen is passed into water containing ammouio-chlo-

126 HYDROGExX AND OXYGEN. WATER.

ride of platinum diffused through it, there is no change. If the hydrogen is
generated by zinc and sulphuric acid in the midst of the ammonio-chloride,
there is an immediate decomposition, and finally divided platinum (platinum
black) is set free. (See Nascent State, ante, p. 125.)

If some granulated zinc is placed in diluted sulphate of indigo, and sul-
phuric acid is added in sufficient quantity to generate hydrogen in small
bubbles, the indigo is slowly bleached. If the bleached liquid is exposed to
the air, it will reacquire its blue color. If zinc is placed in a mixture of
diluted sulphuric and nitric acids, few or no bubbles of gas escape; but
ammonia is produced by the hydrogen, in the nascent state, entering into
combination with the nitrogen of the nitric acid. The liquid after some
hours will contain nitrate and sulphate of ammonia. In the rusting of iron
in a damp atmosphere, in the oxidation of tin by nitric acid, in the effect
of heat and of putrefactive changes on nitrogenous matter, ammonia is
produced by nascent hydrogen combining with nitrogen, although hydrogen,
when once free as a gas, shows no tendency whatever to combine with
nitrogen.

These results, if they do not indicate an allotropic state of hydrogen,
demonstrate that the combining properties of this element are widely dif-
ferent in intensity, according to the circumstances under which the observations
are made.

In the electrolytic experiments above described, it has been proved that
hydrogen may displace copper, silver, and other metals. Hence it has been
supposed, that it is itself the vapor of a metallic body. Carbon and phos-
phorus might, however, with equal propriety, be ranked among metals.
Magnesium and zinc readily displace hydrogen from its compound with
chlorine, at ordinary temperatures.

CHAPTER X.

WATER (H0=9). — AQUEOUS VAPOR.— ICE.

History. — Water is an important constituent of the globe. As a liquid it
covers three-fourths of the earth's surface, forming the ocean. In the at-
mosphere it is universally diffused as an invisible vapor, sometimes pre-
cipitated in the solid state as hail or snow, at others assuming the form of
clouds or rain. The surface of the earth is itself covered with large masses
of water, disposed in lakes and rivers. There is scarcely a rock or soil into
which water does not penetrate. All the superficial strata contain it, and it
is found in a great number of minerals, in a proportion varying from two to
twelve per cent, of their weight. It exists in the three states in which
matter is known to us ; 1, as vapor or gas; 2, as a liquid; 3, as a solid. The
range of water as a liquid, is well known to be between 32° and 212°. It
is so abundantly found that there is no need to prepare it artificially ; and it
is easily separated from the foreign ingredients with which it is naturally
associated, by converting it into vapor and subsequently condensing this
vapor.

Water was long regarded as an element, and was supposed to be
convertible into earth, until Lavoisier, in 17Y3, showed the fallacy of this
notion. Cavendish and Watt, in 1781, demonstrated the production of

CHEMICAL COMPOSITION. 121

water by the combustion of oxygen and hydrogen ; and the former, to whom
the important discovery of its composition is strictly due, proved the corres-
pondence in weight of the resulting })roduct with that of the gases used in
its formation. Lavoisier first resolved water into its constituents, and
Humboldt and Gay-Lussac proved that the volume of the oxygen to the
hydrogen was exactly as 1 : 2. The relative weights of these gases were
carefully determined by Berzelios and Dulong, and shown to be very nearly
as 88-9 : ll'l, or 8 to 1.

Chemical Composition. — Viewed in a chemical aspect, water is a perfectly
neutral oxide of hydrogen. The two gases combine in certain proportions
by weight and volume, but only under fixed conditions. If placed in contact,
they simply mix or diffuse with each other. When, however, two volumes
of pure hydrogen are mixed with one volume of pure oxygen, and the mixture
is inflamed in a proper apparatus by the electric spark, they totally dis-
appear, and water, in equal weight to the gases consumed, is formed. Again,
if water is exposed to electrolytic action, it is resolved into two volumes of
hydrogen, disengaged at the negative pole or cathode, and one volume of
oxygen, disengaged at the positive pole or anode ; so that water is thus
proved by synthesis, and by analysis, to consist of two volumes of hydrogen
combined with one volume of oxygen. The specific gravity of hydrogen,
compared with oxygen, is as 1 to 16; these numbers, therefore, represent
the comparative weights of equal volumes of those gases; but as water con-
sists of one volume of hydrogen and half a volume of oxygen ; it is obvious
that the relative weights of these elements in that compound will be as 1 : 8.
The accuracy of these numbers has been determined by the elaborate inves-
tigations of Dumas {Recherches sur la Composition de VEau, Ann. Ch. et Ph.,
Juin, 1843), Regnault, and other chemists.

Atoms. Weights. Per cent. Volumes.

Hydrogen . . . , 1 ... 1 ... 11-09 ... 1-0 2-
Oxygen . . . . 1 ... 8 ... 88-91 ... 0-5 1-

Water . . . . 1 ... 9 ... 100-00 ... 1- 2-

These results nearly correspond to the weights of the two elements, as
deduced from their specific gravities. Thus taking the specific gravity of
hydrogen at 0-0691, and of oxygen at 1*1057, then 0-0691 x 2 = 0-1382
+ 1-1057 (sp.gr. of 0) = 1-2439; and 1-2439 : M057 :: 100 : 88*89. The
specific gravities of the constituents thus give for the composition of water
88 -89 of oxygen, and 11-11 of hydrogen. The specific gravity of aqueous
vapor, compared with air as 1, is found to be 0-622. This corresponds to
one volume of hydrogen and half a volume of oxygen in each volume of
vapor : —

1 volume of hydrogen sp. gr. = 0-0691

^ volume of oxygen " = 0-5528

1 volume of aqueous vapor " = 0-6219

The volume of aqueous vapor formed is always equal to the volume of
hydrogen consumed. At mean pressure, and at the temperature of 212°,
the volume of this vapor is 1689 times that of the water which produces it ;
in other words, a cubic inch, or rather more than half an ounce of water will
be converted at 212°, into 1689 cubic inches, or about six gallons of
vapor— nearly a cubic foot. 100 cubic inches of the vapor weigh, at the
temperature of 212°, and under mean pressure, 14-96 grains, and at 60°,
19-34 grains.

The experiments illustrating the composition of- water and showing the

128 SYNTHESIS OF WATER.

proportions in which its elements are united, may be arranged under synthesis
and analysis.

Synthesis. — If a current of hydrogen is burnt under a funnel-tube connected
with a condenser, the gas unites to the oxygen of the air, producing aqueous
vapor, which may be collected in a receiver. The water thus condensed
frequently has a slightly acid reaction, apparently from the simultaneous
combustion or oxidation of a portion of the nitrogen of the atmosphere, so
that nitric acid is produced. According to Saussure, if the hydrogen is in
excess, the water may contain ammonia. {An7i. de Chim., vol. 71, p. 282.)
This experiment may be modified by burning a small jet of hydrogen under
a tall and capacious bell-glass (provided with a stopper), supplying below,
by another jet connected with a gas-holder, a stream of oxygen equivalent
to half the volume of hydrogen. The bell-glass may be placed in a glass
dish, and the jets may be passed through a perforated cork placed in the
centre of the opening of the bell-glass, and so arranged that they are nearly
in contact. The water produced, as a result of combustion, will trickle
down the sides of the vessel, and may be collected in the dish.

One of the best synthetical processes for the production of water, however,
is that which was employed by Dumas in his experiments on its composition.
It consists in reducing a known weight of dry oxide of copper by pure and
dry hydrogen. The current of hydrogen is purified and dried by the methods
already described. (Page 119.) The oxide is placed in a bulb of hard
glass, which can be maintained at a red heat without fusing, and which is
exhausted of its air before commencing the operation. This is connected
with another glass bulb, kept cool in order to condense and collect the water
produced. When the oxide of copper is heated to full redness, and hydrogen
is passed over it, only so much oxygen is taken by the hydrogen, as will
suffice to form water. Hence the loss of weight in the oxide after the experi-
ment, represents the oxygen consumed, and by deducting this from the weight
of water condensed, the amount of hydrogen combined with the oxygen may
be readily found. By this arrangement, Dumas produced in one operation,
upwards of two ounces of water. The results which he obtained correspond
as nearly as possible to those already given — namely, in 100 parts by weight
— 88888 oxygen, and 11 '11 2 of hydrogen.

If two measures of pure hydrogen are mixed with one of pure oxygen, and
the mixture is detonated by an electric spark, in a graduated glass tube,
standing over mercury, the gases will disappear. If there be any excess of
either gas, the portion in excess will remain unconsumed. At the moment
the explosion takes place, the gaseous mixture becomes greatly expanded,
probably to fifteen times its original bulk (Davy On Flame^ p. 90), and a por-
tion is apt to escape at the bottom of the tube ; hence to prevent any loss,
the experiment should be performed over mercury in a siphon tube.

Oxygen and hydrogen have no tendency to combine when mixed as gases,
but when they are suddenly submitted to violent mechanical compression, the
heat of condensation causes them to unite with combustion, and water is pro-
duced. (Biot.) A red heat, visible by daylight, inflames the mixture ; but
a dull red heat only causes the slow combination of the gases without explo-
sion. Graham states that if a mixture of oxygen and hydrogen be heated
in a vessel containing a quantity of pulverized glass, or any sharp powder,
they begin to unite, in contact with the foreign body, in a gradual manner
without explosion, at a temperature not exceeding 660°.

In the year 1824, Dobereiner found that spongy platinum, procured by
heating the dry ammonio-chloride, on platinum foil, possessed the singular
property of causing the immediate combination of hydrogen and oxygen, with
heat sufficient to render the metal red hot, and to inflame the gases. If

ACTION OF PLATINUM ON OXYGEN AND HYDROGEN. 129

freshly-prepared spongy platinum be held on filtering paper, over a jet of
hydrogen issuing from a small tube into the atmosphere, it will soon become
hot enough to inflame the gas. If a mixture of oxygen and hydrogen, or of
atmospheric air and hydrogen, not in explosive proportions, be submitted to
the action of the platinum, the gases enter into slow combination, water is
gradually formed, and if there is a sufficiency of oxygen, the whole of the
hydrogen will disappear under its influence ; if, on the other hand, there is
an excess of hydrogen, the oxygen will disappear, and the surplus hydrogen
remain. In the analysis of the atmosphere and certain gaseous mixtures,
platinum, in this peculiar state of mechanical division, becomes a valuable
agent. For its more convenient application to such purposes, and to prevent
the danger of explosion, the platinum is mixed with an equal weight of pure
clay, and moulded with a little water into small balls, which, after having
been slowly dried, should be gradually heated to a high temperature in a
Bunsen's jet. For the purpose of manipulation, a small piece of platinum
wire may be fixed in the balls while moist. These balls may be conveniently
introduced into gases standing over dry mercury ; their power is not impaired
by use, for they may always be rendered efficient, or their power restored, by
again heating them red hot. The admixture with clay not only gives cohe-
sion to the platinum, but prevents the rapid heating of the metal, and there-
fore the explosion of the gases. This will be found a convenient method of
analysis. If the gases are pure, and in their proper portions, the whole will
disappear, and the mercury will rise and fill the tube. If there should be a
residue, the amount of oxygen and hydrogen which have combined to form
water, may be easily determined. Two-thirds of the condensed gases will
represent the hydrogen, and one-third the oxygen.

Spongy platinum effects the union of oxygen with several other gases,
such as with carbonic oxide, and, at high temperatures, with olefiant gas ;
it also causes the decomposition of deutoxide of nitrogen by hydrogen,
producing ammonia. (Dulong and Thenard, Ann. de Gh. et Ph., 23, 440.)
It is an essential condition in all cases of the catalytic influence of platinum,
that its surface should be absolutely clean, the slightest film of foreign
matter — a result of mere exposure to air — impairing, or in some instances
preventing the action : hence the advantage derived from carefully heating
in a clear flame, spongy platinum which has become inert. Some other
metals, such as palladium and iridium, operate in the same manner, but less
perfectly than platinum. Spongy platinum placed in hydrogen or in oxygen
gas, separately, has no influence on the gases, and undergoes no change. It
is in the state of mixture, or when one gas can come freely in contact with
the other, that any effect is produced. If freshly-prepared spongy platinum
is placed on mica, on a stand so arranged that the open mouth of ajar of
hydrogen can be suddenly lowered over it, the platinum retains its usual
appearance, and the hydrogen is not absorbed. If, however, the jar is raised
so that the mouth is on a level with the platinum, the metal will become red
hot, and the hydrogen will disappear, owing to its admixture with the oxygen
of the air at this point. The heat is sometimes sufficient to kindle the
hydrogen with a slight explosion. If this experiment is performed on the
mixed gases, they should be in small q&antity, and contained in a stout
glass jar, as the explosion is sudden and violent. Spongy platinum placed
on mica, or platinum foil or gauze, undergoes no change in air, but if a jet
of dry hydrogen be allowed to fall on it from a bladder, it will become red
hot and ignite the gas. In all cases the platinum acts most efficiently when
freshly prepared, or when it has been heated before the performance of the
experiment.

Faraday has found that perfectly clean platinum /oi7 or wire will also cause
9

130 VARIETIES OF WATER.

the combination of oxygen and hydrogen. He refers this phenomenon to a
peculiar attraction between the clean metallic surface and the particles of the
gaseous mixture, resembling that by which bodies become wetted by fluids
with which they do not combine chemically, or in which they do not dissolve;
or the attraction which renders certain bodies hygroraetric, although they
neither dissolve in, nor combine with water. By this surface- attraction, the
particles of oxygen and hydrogen are so approximated and condensed, as to
enter into chemical union ; and, in so doing, to evolve suflBcient heat to raise
the temperature of the metal. It is calculated that platinum in the state of
sponge, will absorb 250 times its volume of the mixed gases, and condense
them to 1-lOOOth of their bulk.

Analysis. — Water may be decomposed, or resolved into its elements, by a
variety of processes. One of these, based on the decomposition of aqueous
vapor, by passing it over iron wire heated to redness in a tube, has already
been referred to, as a source of hydrogen {see page 119). In a carefully
conducted experiment, the iron will be found to have increased in weight ;
and this increase, added to the weight of the hydrogen collected, will be
equal to the weight of the water which has disappeared.

Electrolysis furnishes the best method of analyzing water, in order to
determine its chemical constitution, as well as the volumetric proportions of
its constituent gases. By a simple apparatus, oxygen and hydrogen are
separately collected, and it may be observed, during the action of the battery,
that for every cubic inch of oxygen given off at the positive electrode, there
are two cubic inches of hydrogen collected at the negative electrode. These
gases when mixed over mercury may be recombined in the manner already
described (page 128.) They entirely disappear, and are reconverted into
water. Analytically, and synthetically, therefore, the constitution of water
has been actually determined. Pure water is not easily decomposed by elec-
trolysis ; but its decomposition is readily brought about by the addition of a
tenth part of sulphuric acid. The oxygen evolved possesses some peculiar
properties {see 110).

Varieties of Water. — TTater in its ordinary state, such as spring and river
water, is always so contaminated with foreign substances as to render it
unfit for chemical purposes. Rain-water is more pure, but it frequently
contains small quantities of sulphuric, nitric, and hydrochloric acids, in
combination with ammonia, lime, or other bases, as well as organic matter
of animal or vegetable origin. Rain-water collected near the sea, invariably
shows traces of chlorides ; its impurities vary much with locality. In Paris,
it has been found to contain traces of iodine and phosphoric acid. Even if
collected in clean glass vessels, before it has touched any roof or soil, it is
always found impure in or near inhabited places.

Lalce Water. — Among the purest forms of natural water may be mentioned
lake-water, as it is collected in deep lakes and in slaty and granite districts.
Among pure waters of this kind in Great Britain, is that of Loch Katrine,
in Scotland, containing only two grains of solid matter in the imperial gal-
lon. The waters Loch 2s ess, and of Enerdale Lake in Cumberland, are
nearly equally pure.

JRiver Water is subject to great Variation in quality, according to the nature
of the soil, and other accidental circumstances. It may be regarded as rain-
water holding dissolved, substances derived from the atmosphere and the soil
over which it has flowed. It is this kind of water which is now largely
employed for the supply of towns. The properties of good River water are
— (1) It should be colorless, tasteless, and free from smell. (2) It generally
has an alkaline reaction from the presence of carbonate of lime, held dis-
solved by carbonic acid. This is the principal mineral constituent of river

HARDNESS OF WATER. 131

water in the southern and eastern districts of England. (3) It gives a
slight white precipitate when nitrate of silver is added to it ; this pre-
cipitate is not entirely dissolved by nitric acid (chloride of sodium). (4)
It gives a primrose yellow colored precipitate, with a solution of arsenio-
nitrate of silver. This indicates the predominance of an alkaline carbonate,
generally bicarbonate of lime. The presence of bicarbonate of lime is also
known by an alcoholic solution of logwood striking a violet color with the
water. As the bicarbonates of potassa and soda also produce this change of
color, a solution of chloride of calcium should be added. Bicarbonate of
lime is not precipitated by this salt. (5) It gives, after a time, only a slight
white precipitate, when a solution of nitrate of baryta is added ; this pre-
cipitate being insoluble in nitric acid (sulphuric acid). (6) A white pre-
cipitate when treated with oxalate of ammonia, more abundant than with
any of the other tests (lime). (Y) When boiled, it does not become milky-
looking or turbid, or it presents this appearance only in a slight degree
(precipitation of carbonate of lime). (8) When a standard diluted solution
of permanganate of potassa is added to a few ounces, the pink color is not
discharged (absence of organic matter).

In respect to the last character, it may be observed, that if the color is
discharged, it indicates in the absence of foul effluvia, the presence of organic
matter; and the greater the amount of permanganate decolorized before the
water retains a pink color, the larger the quantity of organic matter present.
If a graduated tube or burette is employed, two waters may thus be com-
pared, in reference to the quantity of organic matter contained in them, or
they may both be compared with an artificial standard. At common tem-
peratures, the organic matter acts very slowly on the permanganate. At a
high temperature, the permanganate itself is decomposed, although no organic
matter is present. M.^onnier found that this change took place at 194°
F., and that if the water were not heated above 160°, a safe inference might
be drawn from the results. In the ordinary employment of this test, it is
not necessary to heat the water or add any acid. A proper solution for the
purpose of testing water may be made by adding one drachm of a cold satu-
rated solution of crystals of permanganate to thirty ounces of fresh distilled
water. One or two drachms of the diluted solution may be added to four
ounces of the water to be tested. If free from oxidizable organic matter,
the pink color imparted to the sample of water should remain unchanged
for an hour or longer. The crystals of the permanganate are soluble in
sixteen times their weight of cold water, hence a drachm of the saturated
solution would contain about four grains, and the standard solution above
mentioned would contain l-3600th part of solid permanganate. Even with
such a dilution the coloring power is very strong.

In relying upon this test as evidence of impurity in water, it must be
remembered that sulphurous acid, sulphuretted hydrogen, protoxide of iron,
as well as other deoxidizing compounds, destroy the color of permanganate
of potash by reducing the permanganic acid to a lower oxide of manganese.
A solution of alum or sulphate of alumina produces in river or spring
water a precipitate of alumina. If the water is free from dissolved impurity
this precipitate will be white ; otherwise, it will be more or less colored.
Alum has been thus employed for the purification of water.

These are the principal chemical reactions of river water. They show the
presence of chlorine, carbonic acid, sulphuric acid, and lime, and generally
indicate the existence of common salt, bicarbonate and sulphate of lime, as
well as of organic matter. Salts of magnesia and potassa, with alkaline
nitrates, oxide of iron, silica, and phosphoric acid are frequently contained

132 ANALYSIS OP RIVER-WATER.

in river water, in smaller proportion ; and they may be easily detected by
other processes applied to the residue left by the water after evaporation.

Among other properties, it may be observed, that river water does not
readily dissolve soap. If a solution of soap in alcohol be added to some
ounces of the water, and the mixture is well agitated, a white curdy sub-
stance is formed (a compound of the fatty acids of soap with the calca-
reous and other bases of the water), and the water is rendered milky-looking ;
but there is no persistent frothiness as with pure water. On this property
is founded the process of determining the hardness or softness of water, by
means of the soap-test. The method of employing this will be presently
explained. The larger the quantity of calcareous and magnesian salts, the
harder the water ; while the more free the water is from any saline matter,
the softer it is. River water, as it is ordinarily constituted, has so little
action on the metal lead, that even after keeping the water in a leaden vessel
for a considerable time, it will either show no trace of lead, or the quantity
is so small that it may be disregarded. The waters of English rivers, how-
ever, vary so much in this respect, that each water should be submitted to a
separate trial, whatever may be its chemical composition. Thus, river
waters which contain soluble nitrates, or chlorides in unusual quantity,
generally act upon lead. This chemical effect depends not merely on the
nature of the salts, but on the proportion in which they are contained in the
water.

The solid residue left by the evaporation of river water varies in weight
from 6 to 50 grains, or more, in the Imperial gallon ; but potable river
waters are generally comprehended between these two extremes. The nearer
the point from which the water is taken to the source of a river, the more
free from saline and other impurities will it be found. The Thames water
formerly supplied to London, yielded from 20 to 2# grains of solid residue,
from the Imperial gallon of tO,000 grains. That which is now supplied
from the river, taken near Hampton, yields only from 15 to 17 grains in
the gallon, varying a little with the season of the year, and the amount of
rain. All foreign substances in water have been described as "impurity."
In a chemical sense this is correct, but the presence of carbonate of lime
(chalk) and chloride of sodium (common salt), in river water, in the small
proportions in which these substances are found therein, is not injurious to
health. The salubrity of districts bears no relation to the greater or smaller
quantity of saline matter in water. If distilled water could be supplied to a
population in millions of gallons daily, it would be neither agreeable nor
wholesome to the general public. The experiments of M. Boussingault
have clearly proved that the calcareous salts of potable waters, in conjunc-
tion with those contained in food, aid in the development of the bony
skeletons of animals. (Pelouze and Fremy, Traitede Chimie, 1860. Yol. i.
p. 234.) Calcareous waters, such as Carrara water, are usefully employed
in medicine. The search after non-calcareous water therefore is based on a
fallacy. If lime were not freely taken in our daily food, either in solids or
liquids, the bones would be destitute of the proper amount of mineral matter
for their normal development.

With respect to the chloride of sodium, which has been wrongly described
as a result of the presence of sewage in river water, it may be safely said
that no natural water taken from the purest sources in the world, has been
yet found without it. All river and spring waters contain it in greater or
less proportion.

The solid contents in the imperial gallon of some principal river waters of
Europe have been found to be as follows : The Thames at Greenwich, 27 '7 9
grains, at Hampton, 15 grains ; the Seine in Paris, 20 grains ; the Rhone at

SPRING WATER. ARTESIAN WELL-WATERS. 133

Lyons, 12-88 grains (Binean) ; the Rhine at Basle, 11-97 grains (Pagenst);
the Garonne at Toulouse, 9-56 grains (Deville) ; the Loire at Mehung, 9-42
grains; the Scheldt in Belgium, 2058 grains; and the Danube, Vienna,
1015 grains (Hauer). The principal salts in these waters are the carbonate
and sulphate of lime, with chloride of sodium.

In conducting an analysis of a potable water, the general course to be
pursued is the following : 1. To determine the solid contents by the slow
evaporation of a gallon, or at least half a gallon of the water, filtered or
unfiltered, according to circumstances. In good river water the residue
thus obtained is white, or of a pale fawn tint; and it will weigh, when dry,
from 6 to 20 grains. 2. The organic or combustible matter is next ascer-
tained by heating the dry residue to a low red heat, and noting the loss of
weight. When a water contains only traces of organic matter, this may be
detected by boiling a pint of it with a few drops of a solution of chloride of
gold, rendered feebly alkaline by potash. If the water is already alkaline,
the addition of potash is not necessary. After a time the water acquires
more or less of a pink color, by reason of the reduction of the gold by
organic matter. This change of color is well seen when the water is boiled
in a white evaporating dish. 3. To determine, by the usual modes of
analysis, the nature and proportion of the salts contained in this residue.
4. To ascertain whether the water has any action on lead. A clean bar of
this metal, exposing an area of from 8 to 12 square inches, should be im-
mersed in the water and the vessel freely exposed to air. In 48 hours the
water may present a railkiness or remain clear. In either case it should be
tested for lead by passing into it a current of washed sulphuretted hydrogen
gas. 5. To determine the relative hardness of the water. A saturated
solution of Spanish soap is made in three parts of rectified spirit (0-830)
and one part of distilled water. After sufficient digestion the solution is
filtered, and it then serves as a soap test. The solution is added from a
graduated vessel to from four to eight ounces of distilled water contained in
a bottle ; and the quantity required to produce a permanent froth in the
water is noted. This forms a standard for comparison. A similar quantity
of river water is treated in another bottle with the same solution of soap ;
and it will be found to require five, six, ten, or twelve times the quantity of
soap-solution to produce an equal amount of permanent froth in it, as in the
distilled water. The river water may thus be described as having 5^, 6°, 10°,
or 12° of hardness, i. e., it will require these additional proportions of soap
to produce in it the same detergent properties, as in a like quantity of dis-
tilled water. Dr. Clark's soap test is based on a different principle. He
makes an artificial solution of chloride of calcium, and uses a weak alcoholic
solution of white curd-soap. His degrees, therefore, are referable to a
different standard.

Spring Water. — Spring waters may be divided into those which are de-
rived from shallow wells, and those which issue from deep springs, called
also Artesian wells. The former are generally within thirty to fifty feet of
the surface, while the latter in the London district are from 400 to 600 feet
in depth, and in Paris they reach a depth of 1800 feet. The water from the
shallow wells of London usually abounds in sulphate and carbonate of lime,
containing generally but little chloride of sodium ; the solid contents of the
gallon are very variable, but sometimes amount to 130 or 140 grains. The
water is very hard, and yields in some cases traces of sewage, gas-liquids,
or ammonia and alkaline nitrates, the products of their decomposition. The
deep (Artesian) wells which penetrate the London clay, and are carried to
different depths into the underlying chalk, vary in the quality of their water
according to the care with which the superincumbent springs have been

134 DISTILLED WATER.

excluded : they contain a larger relative proportion of solid matter than
river water, but less than that found in the surface-wells, and are remarkably
characterized by the abundance of soda salts and by their alkalinity, which
is derived from bicarbonate of soda : like all other spring waters, they hold
more or less carbonic acid. They generally contain from 50.to TO grains of
saline matter in the imperial gallon. The water of the Trafalgar-square
springs, issuing from a depth of 510 feet, contains 68 94 grains of saline
matter in the imperial gallon, including 14 grains of carbonate of soda, 19
grains of sulphate, and 25 grains of chloride of sodium. The well at the
Royal Mint has a total depth of 426 feet. It contains less than 38 grains
of solid matter in the gallon : including 8-63 grains of carbonate of soda,
13 14 grains of sulphate of soda, and 10 53 of chloride of sodium. The
Artesian water supplied to Guy's Hospital issues from the chalk stratum at
a depth of 297 feet, of which 100 feet are in chalk. It contains 47 grains
of solid matter in the gallon, consisting of 1276 carbonate of soda, 10 40
of sulphate of soda, 20-4 of chloride of sodium, and 3*80 of carbonate of
lime with carbonate of magnesia, silica, &c. The organic matter is in very
small proportion: and can be detected only by boiling a pint of this water
with a few drops of chloride of gold. The water of the well at Southampton,
issuing from a depth of 1360 feet, contains 68 grains of saline matter in the
gallon, of which 18 grains consist of carbonate of soda, 8 grains of sulphate,
and 20 grains of chloride of sodium. The Artesian well-water of the Paris
Basin (Grenelle), issuing from a depth of 1794 feet, is much purer than the
London Artesian waters. It contains 20 grains of saline matter in the
gallon, of which nine grains are carbonate of lime, and four grains are
bicarbonate of potassa — the principal saline ingredients. The Artesian
well-waters differ from those of surface wells in containing generally a larger
quantity of phosphates and a smaller proportion of calcareous salts and of
organic matter.

Distilled Water. — When spring or river water is distilled, the solid con-
tents are left in the retort or still. In the chalk district this residue consists
in great part of carbonate of lime, with some sulphate of lime, of carbonate
and sulphate of soda, with magnesia, silica, alumina, and oxide of iron. In
ordinary waters, besides carbonate and sulphate of lime, the insoluble matter
deposited has been found to contain traces of lead, copper, arsenic, and other
metals. The condensed water obtained in the receiver, as it is commonly
distilled, always contains foreign matter. The first portions are frequently
impregnated with ammonia ; these should be rejected, and, when four-fifths
have been distilled, the operation should be stopped. Water distilled in
glass is sometimes alkaline, owing to its dissolving a portion of soda from
the glass. It can be considered perfectly pure only when it has been redis-
tilled at a low temperature in silver or platinum vessels.

Pure water is transparent, and without either color, taste, or smell. It
should be quite neutral. Its neutrality may be tested by adding at least a
pint of it to a small quantity of a strong solution of litmus, reddened to a
port wine tint by tartaric acid. If the water is neutral, the addition of it to
this solution of litmus will not render the liquid blue or more strongly
redden it. Its chemical properties are chiefly negative. It should give no
precipitate with nitrate of silver, nitrate of baryta, oxalate of ammonia, or
ammonia. It should undergo no change of color on passing into it a cur-
rent of sulphuretted hydrogen gas. On adding to some ounces of the water
a few drops of a solution of ammonio-nitrate of silver and exposing the
vessel containing the water to solar light, it should undergo no discolora-
tion. The pink color imparted to the water by a weak solution of per-
manganate of potassa should remain unchanged for some hours. These last

WATER. CONDUCTION OF HEAT AND ELECTRICITY. 135

mentioned tests by their negative results show the absence of organic matter
and foul effluvia. Half a gallon of the water should leave no ponderable
residue on evaporation. Acetate of lead frequently produces in distilled
water a white precipitate owing to the presence of carbonic acid. The pre-
cipitate is soluble in acetic acid, If a brown precipitate is produced by
this test, it indicates the presence of sulphuretted hydrogen. Among other
properties, a solution of soap in alcohol produces no curdiness or opacity in
pure water, but the soap is readily dissolved : on agitation the water
remains clear, and presents a persistent frothy stratum on its surface. If a
piece of clean sheet lead be immersed in pure distilled water, the water
rapidly becomes opaque, from the production of hydro-carbonate of lead.
Distilled water, free from impurity, is indispensable to the chemist. The
water obtained by melting pure ice may be occasionally substituted for it.

In reference to physical properties, pure water is a powerful refractor of
light, but it is a very imperfect conductor of heat and electricity. In reference
to the latter force, pure water so completely resists the passage of a current,
that it has been even doubted whether it was an electrolyte. This resistance
becomes, therefore, a test of the purity of water. The electrolysis of com-
mon water probably depends on the saline matter which it holds in solution.
In such experiments on distilled water, it is necessary to add to it a small
quantity of sulphuric acid. The following experiments will prove that it is
a very imperfect conductor of heat: Fill a long test-tube with distilled water,
and freeze the lower three inches by immersing the end of the tube in a mix-
ture of ice and salt. When the lower part has been thus frozen, the upper
stratum of water may be boiled over a spirit-lamp and kept boiling for a
considerable time without melting the ice below. Lay a thermometer on
the bottom of a shallow porcelain dish ; cover it with a thin layer of water —
pour on this a stratum of ether and ignite it. When the ether is consumed,
although the surface of the water was heated far beyond its boiling point, it
will be observed that the thermometer has scarcely iDcen affected. The sides
of the vessels used in these experiments may, however, conduct heat down-
wards. The experiment may be varied by placing in a jar of water an air-
thermometer, containing colored fluid with the bulb upwards and nearly
touching the surface of the water. Float upon the water a small copper
basin containing ether ; this may be inflamed, and during its combustion,
although the surface of the water is heated to a high temperature, the air-
thermometer will be but slightly affected. Fill a test-glass to two-thirds of
its capacity with water, and place in this a mercurial thermometer, the bulb
resting on the bottom of the glass. Now pour carefully upon the cold water
some, boiling distilled water which has been slightly tinted with blue litmus.
The colored water will float on the cold water in the glass ; but, although at
212°, the thermometer will indicate no change of temperature except by the
heat slowly transmitted downwards by the sides of the vessel. These facts
clearly demonstrate that unlike solids, this liquid cannot transmit heat from
the surface downwards.

The only mode of distributing heat through water and other liquids is by
a kind of diffusion, depending on a change of density. Hot water is lighter
than cold, as one of the above-mentioned experiments proves. If, therefore,
the bottom of a vessel containing water is heated, the liquid will rise as its
specific gravity is diminished, and there will be a series of upward and down-
ward currents until the water has acquired a uniform temperature. This
may be shown by heating water in which are diffused particles of camphor,
precipitated from its alcoholic solution. The motion of these or of any other
light solid diffused through the liquid, will indicate the course of the
currents.

136 PHYSICAL PROPERTIES OF WATER. ICE.

Water is expanded by heat, but its rate of expansion is cceteris panbvs
less than that of other liquids, and the ratio of increase is augmented by the
temperature.

Distilled water is assumed as a standard to which the relative weights of
all solids and liquids may be compared — its specijlc yravity being called
1.000. (In reference to this subject, the reader will find in the Appendix a
description of the methods by which the specific gravities of all solids and
liquids, whether lighter or heavier than water, may be taken. The scale of
Baume, then used on the Continent, is also given in a comparative table )

At the temperature of 62°, which is that to which specific gravities are
usually referred, a cubic inch of water weighs 252-458 grains ; or at 60°, the
cubic inch weighs almost exactly 252'5 grains, and the cubic foot 998'21t
ounces avoirdvpois, which is so near 1000, that the specific gravity of any
substance, in reference to water, is very near the absolute weight of one cubic
foot of such substance in avoirdupois ounces. The specific gravity of gold,
for instance, is 19"3, in reference to water as unity ; and, therefore, a cubic
foot of gold weighs nearly 19,300 ounces. Water is about 815 times heavier
than atmospheric air. At mean temperature, it is assumed as the unit to
which the specific heats of bodies, especially of solids and liquids, are usually
referred.

The density of water varies with the temperature. It attains its maximum
density at 39°-39, or about 40°; hence water expands from this point,
whether the thermometer falls from 40° to 32°, or whether it rises from 40°
to 48. It is a remarkable confirmation of this fact, that the temperature of
the deep sea in all latitudes has been found to fluctuate about 40°.

Water is said to be colorless, but when looked at in a large mass, or what
is better, a tall column, it has a greenish-blue color. This is well seen in
the waters of Matlock and other springs, and in the glaciers of Switzerland.
Most river waters have a slightly yellowish colpr from the presence of organic
and ferruginous substances. A small quantity may show no color, but when
a gallon is examined in a tall glass vessel, placed on a sheet of white paper,
the color may be seen. The purest distilled water presents a color if exam-
ined in a column of sufficient length.

Water is susceptible of compression, as was originally shown by Canton.
Perkins states that a pressure of 2000 atmospheres occasions a diminution
of only l-12th of its bulk. {Phil. Trans., 1820.) According to the experi-
ments of Oersted, and those of Colladon and Sturm {Ann. Ch. et Ph., xxxvi.
140), its absolute diminution of bulk for each atmosphere is not more than
the 51-OOOOOOth of its volume. It is stated by Dessaignes, that when water
is submitted to very sudden compression, it becomes luminous. (Thenard,
Traite de Chimie, i. 432.)

Ice. — At the temperature of 32° water congeals into ice, which, if slowly
formed, produces needles crossing each other at angles of 60° and 120°
forming stars or stellated crystals. The forms are various, but the primitive
figure is that of a regular six-sided prism, belonging to the rhorabohedral
system. Although the freezing of water is commonly said to take place at
32°, yet if the water is contained in a glass tube, one-fourth of an inch in
diameter, it may be cooled to 23° without freezing. When cooled to 21° it
freezes at once. In a capillary tube of l-200th of an inch diameter, Mr.
Sorby found that water did not freeze at 3° ; when, however, it was cooled
to 1° 4, it passed to the state of ice. {Phil. Mag., August, 1859, p. 107.)

The specific gravity of ice varies from 0*918 to 0 950, but the densest ice,
obtained by freezing water deprived of air, is always considerably lighter
than water. According to Bruuner, the contraction of ice by diminution of
temperature exceeds that of any other solid ; its density at 32° being 0918,

FREEZING OF WATER. PROPERTIES OF ICE. 137

at 18° it is 0-919, and at 0°, 0-920, (Ann. Gh. et Ph., July, 1845.) Ice is
a non-conductor, or nearly so, of electricity, and under favorable circum-
stances becomes electric by friction. (Faraday's Exp. Researches, 4th series,
§§ 381 and 419 ) It is a very bad conductor of heat, but it transmits radiant
heat with such facility that Faraday was able to ignite phosphorus by con-
verging the solar rays through an ice-lens. In freezing, w^ater expands, and
with such force as to burst the thick and strong vessels in which it is
confined. The rupture of iron and leaden pipes is a familiar instance of
this power of expansion. The greatest difference observed between the
bulk of water before and after congelation was found to be in the ratio
of 174 : 184. Exposed to the air, ice loses considerably in weight by
evaporation.

The manner in w^hich water frees itself of impurities in the act of con-
gelation, is very remarkable ; by careful freezing, it may be entirely deprived,
not only of common air, but of those gases for which it has a strong affinity,
as well as of all saline matters. In the common mode of freezing water,
the extricated air is entangled in the ice, and renders it more or less porous
and translucent ; but if means be taken to remove the air bubbles, by
agitation or otherwise, the resulting ice is dense and perfectly pellucid, as
we sometimes see in icicles, or, more remarkably, when a thin glass tube
or flask, containing water, is immersed in a freezing mixture, and constantly
agitated by means of a feather, so as to brush off the air and water from
the layer of ice which forms upon the sides of the vessel. The ice is not only
perfectly transparent and free from air-bubbles, but it is also freed from
saline matters, which are therefore contained in excess in the unfrozen water.
This will be found to be the case with common spring water, but a better
illustration consists in thus freezing water colored by sulphate of indigo,
when the ice will not only be quite colorless, but, when rinsed in a little
distilled water so as to cleanse its surface from the adhering mother-liquor,
it will not contain a trace of sulphuric acid. In the same way an aqueous
solution of ammonia, when properly frozen, yields ice which is quite free
from all trace of the alkali. The beautiful masses of perfectly transparent
ice, imported for the use of the table from Norway and from North America
(Wenhara Lake ice), yield perfectly pure water ; they are formed in deep
lakes, as a result of slow and gradual cooling, ending in congelation. It
has long been known that wine and other alcoholic liquors are strengthened
by partial freezing, and that the ice which they deposit is little else than
pure water, and that lemon-juice and vinegar may be similarly strengthened;
but the fact of spring water thus losing the whole of its saline and aerial
contents was first pointed out by Faraday, and in these cases the unfrozen
portion is of course, rendered relatively impure, so that water may be
concentrated by freezing as it is by evaporation. In northern regions,
salt is obtained from sea-water by simply allowing the water to freeze. The
blocks of ice, which are nearly pure water, are removed, and the residuary
liquid is a comparatively strong brine, from which salt may be obtained by
evaporation.

When ice is formed at a temperature a few degrees below the freezing-
point, it has a well-marked crystalline structure, as is seen in water
frozen from a state of vapor, in flakes of snow, or hoar frost. But ice
formed in water at 32^ is a homogeneous mass, breaki!ig with a vitreous
fracture, and presenting no crystalline structure (Graham). The changes
which it undergoes in the movement of glaciers, is a proof that it possesses
some plasticity.

Ice-water produced from the melting of the ice of deep lakes is one of the
purest forms of natural water. We have found in it only minute traces of

138 ICE WATER. AQUEOUS VAPOR.

alkaline chloride. Snow-water is less pure, the fine crystals of snow in their
formation lock up many organic and mineral ingredients which were diffused
through the atmosphere, especially when collected in the neighborhood of
towns. If frequently contains so much organic matter as to show confervoid
vegetation under exposure to light. The amount of air in snow is very
great. We have found that sixty cubic inches of snow, well compressed,
will produce only eight cubic inches of water. To this diffusion of air
among it particles it owes its whiteness. The water derived from melted
snow is generally too impure to be employed for any chemical purposes.

Steam. Aqueous Vapor. — Water gives off a vapor at all temperatures,
even at 32°. In its ordinary state, if exposed to heat in open vessels, it
boils, or is converted at 212*^ into steam, the barometer being at 30 inches ;
but the boiling point of water varies with the pressure, and is influenced by
the air which the water contains, as well as by the vessel in which it is
heated. When quite pure and deprived of air, water may be heated to
about 240° before it reaches the boiling point; at this temperature, however,
it is suddenly converted into vapor with explosive violence. If a piece of
pure ice be heated in a vessel containing oil, the heat may be continued
until the water from the ice has reached a temperature of 240°, when the
whole is converted into vapor with explosion. The tranquil ebullition of
ordinary water at 212° appears, therefore, to be mainly dependent on the
presence of air.

Water generally escapes in vapor unmixed with the solids which may be
dissolved, but during rapid boiling, some portion of the solids is carried
over with the steam. Thus the vapor of a boiling saturated solution of
carbonate of soda has been observed to tinge of a yellow color, lights burn-
ing in the same apartment. This is owing to the combustion of a portion
of sodium from the soda-salt evolved in the aqueous vapor. Even the most
fixed solids may thus escape with steam. Boracic acid is collected in the
lagoons of Tuscany by condensing the aqueous vapor in which it is dissolved;
this vapor, charged with the acid, is continually issuing from the soil. Even
mercury, one of the heaviest metals known, may be carried over with the
vapor of water at 212° (Chem. News, Aug. 24, 1861).

Steam, or aqueous vapor, may be exposed to a full red heat (1000°) by
passing it through iron tubes heated to redness, without undergoing any
decomposition. That which is now called superheated steam, we have
observed to issue from a discharge pipe at a temperature of 460°. In this
highly heated state, the steam is put to various industrial uses without any
danger. The only gas which we have found associated with the steam at
this high temperature, was nitrogen. The decomposition of water by iron
at a red heat appears to be here arrested by the production of the magnetic
oxide of iron, which lines the interior of the tubes, and prevents further chemical
action. Aqueous vapor has been rendered incandescent by the heat of the
electric spark from Ruhmkorff's coil, and a spectralytic examination of the
light has shown that in this state it gives the bright lines due to hydrogen.

When water is placed, in small quantities at a time, in a platinum or
other vessel, heated to full redness, it does not boil, and does not produce
any visible vapor. The liquid assumes what is called the spheroidal state,
and rolls about in a stratum which presents a convexity on all sides, and
nowhere touches the containing vessel. At this temperature, there appears
to be a repulsion between the water and the metal. The liquid has been
found by Boutigny to be a few degrees below its boiling point ; it gradually
diminishes in volume, and at last it evaporates entirely, leaving only the
solid matters which it may have contained. If while the water is in this
spheroidal state, the source of heat is suddenly withdrawn, the metal becomes

WATER. SPECIFIC HEAT. 139

cooled, and at a certain point the water comes in contact with the heated
surface, and a large portion of it is suddenly converted into steam. The
spheroidal state is common to all liquids. It may be well shown in water by
first warming the liquid before pouring it, gradually, on the red hot metallic
surface.

Water may be entirely decomposed into its constituent gases at a full
white heat. Mr. Grove has proved that if a platinum ball, heated to white-
ness, is plunged into water beneath a tube filled with water, the mere contact
of the white hot metal liberates oxygen and hydrogen, which may be col-
lected and exploded in the tube. Heat, like electricity, has therefore not
only a composing, but a decomposing effect, on the elements of water.

CHAPTEK XI.

WATER— PHYSIC AL AND CHEMICAL PRO PERTIE S—H YD RA-
TION—MINERAL WATERS— PEROXIDE OF HYDROGEN.

Relations to Heat. — The relations of water to heat are in many respects
remarkable. Its specific heat, or capacity for heat, is greater than that of
all liquids and solids. By this term we are to understand the relative pro-
portion of heat necessary to raise equal weights of different substances from
some lower to some higher temperature, or more generally, the relative
quantity of heat contained in equal weights of different substances at the
same temperature. This difference was called by Dr. Black the capacity of
bodies for heat. Equal quantities of the same fluid, at different temperatures,
give the arithmetical mean on mixture. Equal measures, for instance, of
water at 70°, and of water at 130°, will give the mean temperature of 100°;
that is, the hot water loses 30°, and the cooler water gains 30°. But if
equal measures of different fluids, as, for instance, water at 70°, and of mer-
cury at 130°, be mixed, the resulting temperature will not be the mean, or
100°, but only 90°. Here, therefore, the mercury loses 40°, while the water
only gains 20°, hence the inference that the quantity of heat required to raise
a given measure of mercury 100°, will only raise the same measure of water
50° : that is (speaking here of equal bulks), the capacity of mercury for
heat is only = half that of water. But the capacities of bodies for heat are
most conveniently referred to equal weights rather than measures ; and if we
thus compare water with mercury, it will be found that a pound of water
absorbs thirty times more heat than the same weight of mercury ; viewed,
therefore, in this way, the capacity of water for heat is to that of mercury
as 30 to 1, or as 1000 to 33, and we generally thus express the capacities of
bodies for heat by a series of numbers, having reference to water as 1000,
such numbers representing their specific heats.

The most accurate determination of specific heat appears to be derived
from the process of cooling, the time required for this purpose being directly
as the specific heats of the bodies, provided they are carefully placed under
similar circumstances : contained, for instance, in a polished silver vessel, in
a vacuum. The following capacities were thus determined by Dulong and
Petit :—

140 SPECIFIC HEAT OF SOLIDS Ax\D LIQUIDS.

Sp. Heat.

Sp. Heat.

Water .

. 1000

Zinc .... 93

Sulphur

. 188

Silver .... 56

Glass .

. 117

Mercury ... 33

Iron

. 110

Platinum ... 31

Copper

. 95

Lead . ... 29

reference

to liquids,

water stands

higher than all others : —

Sp. Heat.

Sp. Heat

Water .

.

. 1000

Oil of turpentine . . 462

Alcohol

. ,

. 620

Sulphuric acid (1-84) 350

Ether .

,

. 520

Nitric acid . (1'36) 630

Olive oil

.

. 438

Hydrochloric acid (1-15) 600

Araon^ liquids, mercury is most easily heated and cooled: hence it is well
adapted for thermometrieal uses ; while water requires a lonp; time to be
brought to a high temperature, and, when once heated, is a long time in
cooling. It is by this property that large masses of water exert an equal-
izing influence on atmospheric temperature.

When solid passes into liquid water — in other words, when ice melts, a
large amount of heat is absorbed, or rendered latent. Ice and water there-
fore contain different quantities of heat, although each may be at the same
temperature, namely 32°. This may be proved by a simple experiment. If
equal weights of water at 32° and 172° respectively, are mixed, the tempe-
rature of the mixture will be the mean of the two — namely, 102°. But if
ice at 32° be mixed with an equal weight of water at 172°, the temperature
of the mixture, instead of 102°, will be only 32°. Thus, in the substitution
of ice for ice-cold water, there is a loss of heat to the amount of 140°.
This expresses the latent heat of water at 32°, compared with that of ice at
the same temperature ; and it follows, that in reconverting the water into
ice, this amount of heat, which was latent in the water (^. e., not appreciable
by the thermometer), must be again set free. Hence, during a thaw, the
temperature of the air near the surface of the earth, is lowered ; while, on
the other hand, in the act of freezing, water gives out a large amount of
heat, which renders the temperature of the air milder.

The production o^ freezing mixtures depends on these principles. Equal
parts of snow or finely-powdered ice and common salt, will lower the ther-
mometer from 32° to 0°. Both solids tend to assume the liquid state ; the
brine which results from their union, remains liquid nearly to zero. Two
parts of snow or ice and three parts of powdered crystals of chloride of cal-
cium, produce a mixture which will lower the thermometer to — 50°, and
thus freeze mercury. Solid carbonic acid and ether are now employed to
produce a maximum of cold {see Carbonic Acid). Whatever causes the
rapid liquefaction of solidified water, produces great cold. Thus, when ice
or snow is mixed in equal weights with diluted sulphuric and nitric acids,
together or separately, cold is produced.

Water may be cooled below 32°, without consolidating into ice ; but the
temperature of water in which ice is melting is always 32°, and does not rise
above that degree so long as any ice remains unmelted. This is the degree
of cold which is really represented as 32° by our thermometers, and as zero
on the scales of Reaumur and Centigrade. Again, when water passes into
steam or aqueous vapor, a still larger amount of heat is absorbed or rendered
latent, so that a small quantity of water in the form of steam is sufficient, by
condensation, to heat a large quantity of cold water. If 100 gallons of water
at 50° be mixed with 1 gallon of water at 212°, the temperature of the whole
101 gallons will be raised by only 1-5°. But, if a gallon of water be con-
densed from the state of steam into a vessel containing 100 gallons of water,

LATENT HI!AT OF VAPORS. 141

the water will in that ease be raised 11°. A gallon of water, therefore,
condensed from steam, raises the temperature of 100 gallons of cold water
9.5° more than the addition of a gallon of boiling water; consequently, if
the heat imparted to 100 gallons of water by 10 pounds of steam could be
condensed in 1 gallon of water, it would raise it to 950° ; and a gallon of
water, (?onverted into steam of ordinary density, contains as much heat as
would bring five and a half gallons of ice-cold water to the boiling point.
The quantity of ice, which is melted by steam of mean density, is seven and
a half times the weight of the steam.

The latent heat of steam and other vapors has been examined by Dulong,
and on his researches the following table is based : —

Water .... 9550-8 Ether .... 1740-6

Alcohol .... 374-4 Oil of turpentine . . 138-6

Hence the vapor of water has a greater amount of latent heat, or a greater
amount of heating power in undergoing condensation, than the vapors of
other liquids.

It is a well known fact that the conversion of water into vapor at any
temperature is attended with the production of cold. The instrument in-
vented by Dr. Wollaston, under the name of cryopJiorus (xpvoj, ice, ^i^nv, to
bear), is constructed on this principle : it establishes the fact that water may
be solidified, as a result of the cold produced by its own vapor. The instru-
ment consists of a tube, having a bulb at each extremity, one of which is
half tilled with water ; the interior of the tube is perfectly deprived of air
by boiling the water in one of the bulbs, until a jet of pure steam issues
through a small opening left at the bottom of the other, which is then sealed
by fusion in the flame of a lamp ; the consequence is, that the water in the
other bulb is greatly disposed to evaporate ; but this evaporation can only
proceed to a certain extent, because the pressure of vapor within the tube
soon prevents its further progress. To get rid of this, to keep up the vacuum,
and to occasion a constant demand upon the water for the fresh formation of
vapor, the empty ball is y)lunged into a freezing mixture, which continually
condenses the vapor within, and so accelerates the evaporation of the water
in the other bulb as to cause it ultimately to freeze.

These peculiar conditions of water in reference to heat have a manifest
tendency to maintain it in a liquid condition, the state in which it is indis-
pensable for animal and vegetable existence.

Water, which has been exposed to the atmosphere, always contains a por-
tion of air, a fact which may be proved by boiling it, or by exposing it
under the exhausted receiver of an air-pump. To separate the air, the water
must be continuously boiled in vacuo, for it is obstinately retained. (Donny,
Ann. Ch. et Ph., Fev. 1846.) It absorbs oxygen gas from atmospheric air
in preference to nitrogen, and, when the air is expelled by boiling, the last
portions contain more oxygen than those first given off. (Humboldt and
Gay-Lussao, Journal de Physique, 1805.) The presence of air or oxygen
in water is known by the addition of protoferrocyanide of iron {see page 99).
If the white compound be added to recently boiled water, the rapid absorp-
tion of oxygen will be indicated by its acquiring a blue color.

Dalton states, that 100 cubic inches of spring water yield about two inches
of air, which, after losing from 5 to 10 per cent, of carbonic acid by the
£fction of lime-water, consists of 38 per cent, oxygen, and 62 nitrogen. {New
System, 271.) Dr. Henry obtained 4*76 cubic inches of gas from 100 of the
water of a deep spring, of which 338 were carbonic acid gas, and 1-38 air,
of the same standard as that of the atmosphere. There can, however, be no

142 INFLUENCE OP WATER ON THE PROPERTIES OF BODIES.

doubt that the gaseous conteuts of different springs vary both in quantity
and quality.

The following table, based on the experiments of various eminent authori-
ties, exhibits the quantity of different gases which water is capable of absorb-
ing or dissolving at a mean temperature and pressure, the water having been
previously deprived of air by long boiling. ,

100 c. i. of

100 c. i. of

■water dissolve

water dissolve

Fluoboric acid .

. 70000 c. i.

Chlorine . . . .

200 c. i.

Hydrochloric acid

. 50000

Protoxide of nitrogen

100

Ammonia .

. 48000

Carbonic acid .

, 100

Fluosilicic acid .

. 35000

Carburetted hydrogen

12-5

HypocMorous acid .

. 20000

Deutoxide of nitrogen

5

Sulphurous acid

. 5000

Oxygen . . . .

4-6

Peroxide of chlorine .

. 2000

Phosphuretted hydrogen .

2-14

Cyanogen .

. 450

Carbonic oxide

ii'6

Hydroselenic acid

. 300

Nitrogen . . . .

2-5

Sulphuretted hydrogen . 300 Hydrogen . . , 1*56

The quantity of each gas dissolved by water is materially dependent on
temperature. While in reference to solids which are soluble in water, the
solubility generally increases with the temperature, that of gases decreases,
so that by heating the water to the boiling point, the gas, unless it has entered
into chemical combination, is expelled. There is an instance of this exQep-
tional condition in hydrochloric acid gas. When a solution of this gas is
boiled, a portion of the acid escapes ; but at a certain point of saturation,
the water and gas are distilled over together.

Water is decomposed by many substances. Some, like chlorine, take the
hydrogen and liberate the oxygen; other substances, like potassium, take
the oxygen and set free hydrogen. With the exceptional case of the decom-
position of this liquid by electrolysis, oxygen is not set free as a gas, but as
it is liberated, it enters into new combinations.

Water plays a most important part in the organic kingdom. It is not only
the medium for conveying soluble matters from the earth and air to the vege-
table structure, but it is essential to the constitution of vegetable and animal,
principles. Thus, it forms from 30 to 80 per cent, of the animal tissues ;
and to its presence the physical properties of these tissues are mainly due.
We have found that muscular fibre contains from QQ to 69 per cent, of water,
and that an oyster contains 81 per cent. Some of the small jelly-fish (acale-
phce) contain 99 per cent, of this liquid. Of the fluids of the body, blood
contains 18, milk 86, and bile 90 per cent of water. Its presence in bodies
is often indispensable to chemical action, and the removal of it, either modi-
fies or arrests chemical changes. Albumen or gelatin, when deprived of
water, may remain unchanged for years ; but when containing only their
normal proportion of water, they rapidly undergo decomposition. Desicca-
tion, or the deprivation of an organic substance of water, may be regarded as
one of the most powerful antiseptic processes. Its remarkable influence on
chemical affinity, and on the chemical properties of compounds, has been
elsewhere pointed out {see page 42). In addition to the illustrations there
given, we may here notice a few others. It is well known that lime has a
strong tendency to combine with carbonic acid ; but unless water is present
as an intermediate agent, caustic lime does not easily combine with carbonic
acid, to form a carbonate. It is generally stated that caustic lime is procured
by heating the carbonate ; but the aflinity of lime for carbonic acid, when
they are once combined, is so strong, that the gas cannot be expelled by
heat — according to Faraday, not even by a white heat, unless water is present.
Hence, water is not only necessary to the combination of acid and base, but

WATER. HYDRATES. HYDRATION. 143

when they are combined, its presence is necessary to bring about their separa-
tion. The combination between a gaseous body and a metal does not readily
take place, unless water is present {see page 42). Thus, while humid chlorine
readily combines with pure silver leaf, to form chloride of silver, the com-
bination takes place only slowly and with great difficulty, if the metal and
the gas^re first thoroughly dried. Phosphorus, it is well known, has a strong
tendency to combine with the oxygen of air, and to produce ozone at ordi-
nary temperatures ; but if the air is perfectly dry, no ozone is formed ; and
it has been observed, that dry oxygen is not ozonized by this metalloid.
These facts, among numerous others, show the important part which water
takes in promoting or modifying the chemical action between bodies, which
are known to have strong affinities for each other.

Hydrates. Hydration. — Water is a general and useful solvent. In this
respect it is indispensable to the chemist, for by its means he cannot only
separate substances, but reduce their particles to that degree of tenuity as a
result of solution, that they can be brought within the sphere of each other's
attraction. Although a perfectly neutral body, it is capable of acting like
an acid or a base, and entering into a large variety of combinations. As the
water is contained in these compounds in definite proportions by weight,
they are called hydrates to distinguish them frpra hydrides, of which the ele-
ment hydrogen is a constituent. In those cases in which the hydrated
compounds are crystalline, the water appears to be essential to the crystal-
line form, and it is therefore called water of crystallization. {See p. 32.)
Those bodies which do not contain combined water, or which have* been
deprived of it by artificial processes, are said to be anhydrous, and are some-
times, although improperly described as anhydrides. They are in fact anhy-
drates. As instances of its combination with gases may be mentioned — 1,
the hydrate of chlorine, a solid compound, consisting of Cl-f-lOHO, which
crystallizes at 32°, and is reconverted to water and chlorine above this tem-
perature ; 2, the crystalline compound produced in the manufacture of sul-
phuric acid, (N04 4-2SOa + 2HO) resolvable by water or steam into sulphuric
acid water and deutoxide of nitrogen. Like an alkali orjj^allj^^xide, water
combines with an anhydrous acid to form a hydrate. It thus unites to anhy-
drous sulphuric, nitric or phosphoric acid ; and in reference to the last
mentioned acid, it produces a change in its chemical properties. In this
state, acting like a base, it is called basic water. When the acid is once
combined with it, the water cannot be again separated by mere heat ; the
acid and the water are distilled over together. The only method of displacing
water in these combinations is to substitute another oxide, such as that of
potassium, and then apply heat. Under these circumstances the water is
entirely expelled, and it is replaced by an atom of metallic oxide. This
replacement sometimes occurs as a simple result of chemical affinity. Thus
the three atoms of water in the terhydrate of phosphoric acid, may be replaced
by three atoms of oxide of silver, forming yellow phosphate of silver. From
these facts it was supposed that water was essential to the acid reaction of a
compound, and that none but hydrated acids could unite to bases, to form
salts. But certain acids which can be made completely anhydrous by heat,
such as the boracic, silicic, and stannic, readily decompose the carbonates,
nitrates and sulphates at a high temperature, displacing their acids, and
forming new salts with the bases, according to the usual laws of affinity.
Anhydrous sulphurous acid will also displace carbonic acid from dry (anhy-
drous) carbonate of soda. (Pelouze et Fremy, op. cit, tom. 2, p. 78.) The
dehydration of some compounds lessens or destroys their solubility in certain
liquids. The silicic and antiraonic acids, as well as the oxides of aluminum
and zinc in the hydrated ^tate, are easily dissolved by alkalies ; but when

144 WATER. HYDRATED SALTS. BASIC WATER.

dehydrated by heat, they become almost insohible, and can tlien only be
united to an alkali by fusion at a high temperature. Water combines with
alkalies without altering or affecting their properties. The hydrate of potassa
is a compound of water and oxide of potassium, and has powerful alkaline
properties. At a high temperature the hydrate is volatile without any loss
of water. In this compound as in the acid hydrates, the water can only be
displaced by adding an acid, snch as the sulphuric or phosphoric acid, and
heating the compound to a high temperature. In some hydrates the water
may be displaced by heat alone, as in the case of silicic acid, linae and mag-
nesia. Water forms hydrates with nearly all the metallic oxides, influencing
their color and solubility in acids. The hydrated oxide of copper is blue, and
the anhydrous oxide is black. The hydrated oxide of this metal when pre-
cipitated by potassa from a solution of sulphate of copper (and the alkali is
added in some excess) is rendered anhydrous, merely by boiling the liquid.
The oxide falls down as a blackish-brown powder. The hydrated suboxide
of copper is yellow, and is produced on warming a mixture of sulphate of
copper, sugar, and potassa. If, however, the liquid is boiled, the suboxide
is rendered anhydrous, and falls down as an insoluble red powder. Up to a
temperature of Qb^ a saturated solution of sulphate of soda deposits on cool-
ing hydrated crystals of this salt. But if heated to the boiling point the salt
becomes less soluble by reason of the formation of the anhydrous sulphate,
the salt being dehydrated by elevation of temperature. In other cases a heat
of 212° appears to be necessary to the production of a hydrate. Precipitate
a solution of alum by potassa, and add enough potash to redissolve the pre-
cipitated alumina ; to this alkaline liquid add a solution of silicate of potassa.
There is no apparent change until the mixture is heated, when the whole of
it sets into a nearly solid hydrated silicate of alumina.

Water combines with the greater number of metallic salts in proportions
variable for each salt, and these are not dependent on any general law.
Occasionally the same salt is observed to combine with diff'erent proportions
of water, according to the temperature of the solution. (See p. 32.) The
color of the salt and its crystalline form are chiefly affected, but its chemical
properties do not appear to be changed. The blue crystals of sulphate of
copper, and the green crystals of sulphate of iron became of a dingy white,
when digested in concentrated sulphuric acid. This is simply the result of
dehydration. The color is restored in each case by the addition of water.
In some salts the water is combined only as water of crystallization, e. g., the
sulphates of iron and copper; in other salts, besides this crystalline water,
another portion exists in a basic form, /. e., intimately combined with the
acid. This is seen in the rhombic phosphate of soda, which contains two
atoms of soda, and one of water as a base, while there are in addition, 24
atoms of combined or crystalline water. The whole of this water can be
expelled by heat, but the basic water with more difficulty than the water of
crystallization. The loss of the basic water completely changes the chemical
properties of this salt : it converts it into pyrophosphate of soda, which pro-
duces a white, in place of a yellow precipitate, with nitrate of silver. It also
gives with a solution of acetate of lead, a white precipitate, which is soluble
in an excess of the pyrophosphate, while the phosphate of lead is insoluble
in the common phosphate of soda.

It has been suggested that some double salts, such as the bisulphate of
potassa, may really be compounds of neutral sulphates with water. Thus the
bisulphate which is commonly represented as KO,2S03,HO may beK0,S03
-fH0,S03. This, however, would be inconsistent with the constitution of
certain analogous compounds not containing water, such as bichromate of
potassa, KO,2Cr03. Chromic acid is isomorphwus with the sulphuric ; and

COMBINED WATER. 145

if the latter can combine in two equivalents to form a bichromate, it is
reasonable to infer that the former can equally combine with two equivalents
of acid to form a bisulphate of the alkali, and not a sulphate of potassa and
basic water.

The phenomena of hydration, as they are witnessed in the combination of
water with acids, oxides and salts, are clearly due to chemical afSnity. When
water is poured on solid sulphuric or phosphoric acid, great heat is evolved,
and steam escapes almost with explosive violence. If a small quantity of
water is poured on a few pieces of dry hydrate of potassa in a glass tube,
the alkali is dissolved, but so much heat is extricated that a small portion of
phosphorus applied to the outside of the vessel will melt and take fire. In
this experiment, a second hydrate of the alkaline oxide is produced by an
additional quantity of water entering into combination. When one part of
water at 32^ is added to three parts of fresh burnt lime at the same tempe-
rature, the water disappears, steam is after a time copiously evolved, the
lime becomes hot, falls to a white powder, and is greatly increased in weight.
The heat given out in the hydration of lime has been estimated at more
than 570° — sufiBciently high to inflame gunpowder. Felletier observed that
in slaking large quantities of lime in the dark, light was evolved as well as
heat. The water forms a solid compound with the lime (slaked lime). In
these experiments it is considered that the late?it heat of water (see page 140)
is set free. This can only be attributed to a direct chemical union of water
in a solid form with the substance. Concentrated sulphuric acid (already
a liquid hydrate) presents some remarkable and apparently paradoxical
results in uniting to an additional proportion of water. If one part of
ice is mixed with four parts of concentrated sulphuric acid, the ice melts —
great heat is evolved as a result of a second hydrate being formed, and
the latent heat of the water being set free. But if one part of sulphuric
acid is rapidly mixed with four parts of ice, in the same or in another
vessel, so intense a degree of cold is produced, that water is frozen in a
lube which is placed in the mixture. This result is in accordance with
what has been already stated, respecting the large amount of heat absorbed
or rendered latent in the liquefaction of ice (p. 140). A hydrate is equally
formed in the latter case : but as the ice greatly preponderates, and
requires much heat for its liquefaction, it not only absorbs that which is
produced as a result of hydration, but much more from all surrounding,
bodies.

With some acids and alkalies water appears to form no hydrates. Thus
the nitrous (NOJ, the fulminic, hydrocyanic, and manganic acids form no-
definite compounds with water, although they combine with certain bases to-
produce salts. On the other hand, the presence of an atom of water is es-
sential to the constitution of oxalic acid (C3O3). When deprived of it, the ,
acid is converted into carbonic acid (COJ and carbonic oxide (CO.) This
atom of water admits only of displacement without the decomposition of the
acid, by the substitution of an atom of a metallic oxide. Carbonic acid as
a gas does not combine with water to form a definite hydrate ; and in the
liquefied state, carbonic acid is quite insoluble in water. Liquid carbonic
acid has no action upon litmus, but when the gas is dissolved in water, it
changes it from blue to red, like other acids. That it forms no acid hydrate
may be inferred from the fact, that the blue color of the litmus is restored
by boiling the reddened liquid. Carbonic acid, therefore, is in the condition
of a gas temporarily dissolved by water. Solution in water appears to be
necessary for the manifestation of acid properties on vegetable colors ; but
for reasons elsewhere assigned, it is not necessary to suppose that the water
undergoes decomposition, and that a new binary compound of hydrogen and
10

146 OSMOSIS AND DIALYSIS. TESTS.

a hypothetical radical is prodnced (p. 94.) Pyrogallic acid, as a solid, has
DO action on litmus ; ^hen dissolved in water it reddens litmus paper, but
when dissolved in absolute ether, and not exposed to air, it has no reddening
action on litmus. In this respect, it resembles liquid carbonic acid dissolved
in pure ether. Among bases, ammonia is remarkable for forming no hydrate
with water. Every particle of water may be removed, without altering the
properties of gaseous ammonia, by simply desiccating it with lime. It has
been supposed, that a binary compound of oxygen and ammonium (NHJ is
formed under these circumstances ; but of this there is a total absence of
proof. (See Ammonium.) Such a view assumes, contrary to all experiments
regarding the relative affinity of bodies, that hydrogen leaves oxygen to
combine with the elements of ammonia, when it is utterly impossible to
cause these bodies to unite ; and when placed in a favorable state for union,
they are rapidly evolved as hydrogen and ammonia.

The phenomena of osmosis have been referred by Graham to the hydra-
tion and dehydration of the membrane forming the septum, or partition,
between two liquids. We have elsewhere referred to the passage of liquids
through animal membrane. The membrane becomes hydrated on the sur-
face which is in contact with the water, but on the side of the saline or
viscid liquid, it is not hydrated. On the contrary, hydration here receives
a check, and some of the water imbibed by the membrane is actually trans-
ferred to the saline liquid, so that there is a continual current inwards or
outwards, according to the relative position of the two liquids. {Phil. Trans. ^
June, 1861.) It is a remarkable fact, that while certain bodies will easily
traverse the membranous partition, others will not. Substances of a viscid,
adhesive, or gelatinous character, whether organic or inorganic {colloid
bodies), of which animal membrane itself may be considered one, retain cer-
tain ingredients, and allow others to pass. It was found by Graham in using
parchment-paper, that on placing urine in a vessel provided with such a
septum, the urea and salts passed out, but the animal principles were
retained. Organic liquids containing small quantities of arsenic, tartar
emetic, and even strychnia, were found to yield the respective poisons to
water, while the organic substances associated with them did not pass. We
have verified this statement by employing a weak solution of arsenic in milk;
these experiments show that pure water iu hydrating substances, may be
tern ployed as a separating agent.

7'estsfor Water. — When water is in a state of chemical union, its presence
is not indicated by any of the usual physical properties of the liquid. Pow-
dered alum contains half of its weight of water, but presents no sign of
moisture. In these cases we must resort to a high temperature, and to
complex .chemical processes, in order to determine its presence and propor-
.tion {see page 32). When water exists uncombined in bodies, it is called
hyyrometric water, and it can be easily detected by gently heating the solid
in a test tube. The water is expelled, and is condensed in globules on the
cold part of the tube. It may be entirely driven off by exposing the
substance to a dry current of air. For this purpose the material is inclosed
in a glass cylinder, immersed in a water-bath at or below the boiling point.
The desiccating apparatus commonly used is connected at one end of the
cylinder with a tube containing broken chloride of calcium, while the other
end of the cylinder is placed in connection with an aspirator. When the
stopcock of this aspirator is opened, air may be made to traverse the whole
of the apparatus, first passing through the chloride of calcium tube, in which
it is dried. It is thus drawn over the substance in a dry state, at the
temperature of the hot water in which it is immersed. When perfectly
desiccated, it ceases to lose weight. If the quantity of water is to be deter-

MINERAL WATERS. SEA WATER. l4t

mined, a TJ tube containing chloride of calcium, accurately balanced, should
be attached to the other end of the desiccating tube, before connecting it
with the aspirator. The increase of weight in this tube, when' the experi-
ment is completed, indicates the weight of hygrometric water contained in
the substance. The chloride of calcium absorbs and fixes the water as it
passes over. In some porous powders the proportion of hygrometric water
is very large, amounting to 12 or 13 per cent. Another method of deter-
mining the amount of free water in liquids or solids, consists in placing them
in a shallow vessel in vacuo, over another vessel containing strong sulphuric
acid. When the receiver is exhausted there is rapid evaporation in the
cold, as the aqueous vapor is absorbed and retained by the sulphuric acid.
The amount of water in albumen, or white of egg, is thus determined, and
is found to be about 80 per cent.

The tenacity with which hygrometric water fixes itself to solids is remark-
able. All fine powders, such as spongy platinum, charcoal, or fine metallic
wire, or gauze, filagree silver, and articles of a porous description are, gene-
rally speaking, strongly hygrometric, and require a continued application of
heat to drive off the water which adheres to them.

Of the tests for liquid water, nothing need be said. It resembles no other
liquid, and the means of determining its purity have been already described
(page 135). The detection of water in certain liquids, "must depend on the
nature of the liquid. In alcohol, water may be detected either by its specific
gravity, or by adding to it, a small quantity of white anhydrous sulphate of
copper. If water is present, the white powder is slowly rendered blue.
Fluosilicic acid gas passed into the liquid, also reveals the presence of water,
by the separation and deposit of white gelatinous silica. The existence of
water in gases, is determined by passing the gas through a vessel containing
chloride of calcium, or if acid, through strong sulphuric acid. Any increase
of weight in the chloride, or acid, is owing to water.

MINERAL WATERS. SEA-WATER.

When the saline and gaseous ingredients of water are in such proportion
as to give to the liquid taste, smell, or medicinal properties, it is called a
mineral water.

Sea-water is a strongly mineralized water ; it may be regarded as the accu-
mulation of all the surface-drainage of the earth. It contains, on an average,
from 3 to 4 per cent, of saline matter, and this amount does not seem to vary
to any great extent, either with the latitude, or with the depth from which
the water is taken. Water collected from the surface of the Gulf of Guinea,
contained 3-5 per cent., and in the same gulf, when taken from the depth of
4000 feet, it is stated to have yielded 4-5 per cent, of saline residue, showing
an increase of only 1 per cent, at this depth. Sea-water taken in N. L.
80^^, sixty fathoms under ice, gave 354 per cent, and in S. L. 20°, 3-9 per
cent.

While carbonate of lime is the principal ingredient in river waters, it exists
sparingly in the sea. The chief saline constituent of sea-water is common
salt, or the chloride of sodium : this forms from one-half to three-fourths of
the solid ingredients. The principal salts associated with it, are chloride
and bromide of magnesium, with sulphate of magnesia, which give the
nauseous bitterness and purgative qualities to the water. Chloride of potas-
sium and sulphate of lime are also found : and as a result of prismatic
analysis, Bunsen has announced the presence of lithium and strontium,
probably existing as chlorides. He detected lithium in less than two ounces
of the waters of the Atlantic, collected off the Azores. Iron, lead, copper,
and silver, have also been found in sea-water. Silver was detected by M.

148 SALINE CONTENTS OF SEA WATER.

Malaguti in water taken off the coast of St. Malo, in the proportion of 1
part in 100,000,000 (Quart. Jour. Chem. Soc, 1851, vol. 3, p. 69), and
Mr. Field has lately announced its presence in the waters of the Pacific
{Proc. R. S., vol. 8, p. 292).

The proportion of saline matter in the waters of some inland seas is very
large. Thus we have found the waters of the Dead Sea in Palestine to con-
tain 24 per cent, of saline matter, of which three-fourths were chloride of
sodium. This is six times as great as the quantity contained in the waters
of the Mediterranean Sea, in the same parallel of latitude. The water of
the river Jordan, which flows into this inland sea, we found to contain no
more than two grains of salt to the Imperial gallon, and only a trace of sul-
phate of lime, while the common salt in the Dead Sea water, amounted to
12,600 grains in the Imperial gallon. This water had a specific gravity of
1-16, and left a considerable incrustation of deliquescent saline matter on
spontaneous evaporation. Every part of the human body, excepting bone,
readily floated on it. The water of the great Salt Lake in the Rocky
Mountains, U. S., is similar to that of the Dead Sea. It has been found to
contain 22 per cent, of saline matter, of which 20 per cent, consists of chlo-
ride of sodium.

The tidal impregnation of river-water with sea-water may therefore be
easily determined, by the discovery in it of a large proportion of the chlorides
of sodium and magnesium. Springs are said to be hracJcish when they
acquire a taste from the presence of these chlorides. Such springs are met
with in countries in which there are vast sandy deserts, also in shallow wells
on the sea coast.

The mean specific gravity of the waters of the Atlantic was found to be
r027 ; of the Mediterranean, between Gibraltar and Malta, r028, and be-
tween Malta and Alexandria, 1-029. The waters of the Red Sea, at the
northern end of the Gulf of Suez, had a specific gravity of 1"039 {Proc. R.
S., Feb. 1855). Admiral King found the waters of the Pacific Ocean to
have a specific gravity of 1*026. The influence of river-water on the specific
gravity and composition of sea-water, is very remarkable. At the estuaries
of all great rivers, the percentage of salt is considerably reduced, and in
approaching the coasts of continents, or even of small islands, there is a great
diminution in the saltness of the sea. The following summary contains the
proportions of saline matter and common salt found, by analysis, in 1000
parts of the waters of various seas : in the North Sea (Heligoland), of saline
matter 30-46 (common salt 23-58) ; British Channel (Schweitzer), saline
matter 35-25 (common salt 28 05) ; Atlantic, saline matter 36-3 (common
salt 25-18) ; the Mediterranean (XJsiglio), saline matter 4373 (common salt
29-42) ; the Black Sea, saline matter 17*66 (common salt 1401) ; the Sea of
Azoff, saline matter 11-87 (common salt 9 65) ; the Caspian Sea, saline
matter 6-29 (common salt 3 67). — (Gobel.) The water of the Mediterranean
Sea contains more lime than that of the Atlantic, and the proportion of mag-
nesian salts in the Mediterranean water diminishes in proceeding from west
to east (Fremy, Op. cit, torn. 1, p. 253). The waters of the Baltic Sea con-
tain but a small proportion of saline matter ; and the water of the Gulf of
Finland is so free from it, that it can be used in place of river-water. The
waters of the great lakes in the plains of Tartary, contain large quantities of
carbonate of soda and sulphate of soda, with common salt; while those of
Thibet contain common salt,' with borate of soda.

Mineral Waters owe their qualities not merely to the quantity of the
ingredients, but to their nature and their intermixture under conditions
which it is difiScult to imitate by artificial processes. The Tunbridge chaly-
beate spring contains only seven grains of mineral matter to the Imperial

MINERAL WATERS. 149

gallon ; it owes its properties to the presence of iron, the proportion of
which is not more than two grains in the gallon. On the other hand, one
of the Yichy springs contains 460 grains of saline matter in the gallon, of
which 333 grains consist of bicarbonate of soda. There are, according to
O. Henry, soluble silicates of soda and alumina in this water, amounting to
forty-four grains in the gallon. In several of the German waters, Bunsen
has detected lithium, strontium, and caesium, in addition to other well-known
ingredients. Mineral waters may vary in their solid contents, as much as
from 7 to 500 grains in the gallon. They are hot or cold, the former being
called thermal. The hot springs in Great Britain are few. They are — the
waters of Bath, 117°; of Buxton, 84°; of Matlock, 60° ; and in Ireland
the waters of Mallow, which have a temperature of 72°. On the Conti-
nent, some of these waters reach a temperature little short of the boiling
point. One of the most remarkable waters for its temperature and com-
position is that of the Great Geyser, in Iceland. Examined in 1846 by
Bunsen, at a depth of sixty-three feet, this water was found to have a tem-
perature of 260°. A sample of this water, collected on the 16th June,
1856, was observed, at the time of collection, to have a temperature. of 190°,
the air being 47°. We fdund this water to contain 106*6 grains of saline
matter in the gallon. Of this 19*53 grains consisted of carbonate of soda,
24'42 of chloride of sodium, 14'65 of sulphate of soda, m^ 48 grains of silica
and insoluble matter. There is no doubt that in this, as in the Vichy and
other waters, the silicic acid is held dissolved by the alkaline carbonate.

Various classifications of mineral waters have been made. We here give
four of the principal varieties, with their special characters : —

1. Carbonated. — These abound in carbonic acid associated with variable
quantities of the alkalies, soda, potassa, or lime, or with traces of oxide of
iron. The waters of Seltzer, Pyrmont, and of Ilkeston, near Nottingham,
are of this kind. They are sparkling, and are characterized by an acidulous
taste and reaction. 1. They redden an infusion of litmus, but the blue
color is restored on boiling. 2. They give a white precipitate with lime-
water (carbonate of lime), but the precipitate is redissolved by an excess of
the water. 3. When a portion is boiled in a retort, and the gaseous con-
tents are passed into lime-water, carbonate of lime is abundantly deposited.
These waters may be alkaline from soda (Vichy), or calcareous from lime
(Bath, Bristol, Buxton).

2. Saline. — These are very numerous. They contain the salts of soda,
potassa, and magnesia. Chloride of sodium is generally a predominating
ingredient, as in some of the Cheltenham waters. This chloride is generally
associated with traces of bromide and iodide of sodium. They are charac-
terized by their taste, and the large quantity of saline matter left on evapo-
ration.

3. Sulphureous. — These are known by their having the offensive odor of
sulphuretted hydrogen gas, and by their tarnishing or discoloring a piece of
silver-leaf, or of glazed card, immersed in them, or by their giving a brown
precipitate (sulphide of lead), with any soluble salt of lead. (Kilburn,
Harrowgate, Aix-la-Chapelle, Bareges.) The sulphuretted hydrogen appears
to be derived from decomposing iron-pyrites, diffused in the strata through
which the water flows. The waters, when fresh, have an acid reaction on
litmus, but this disappears on boiling. After a time they deposit a black
sediment (sulphide of iron), and lose their offensive smell. We have
examined a water of this description from Vancouver's Island, in British
Columbia. These waters discharge the colors of the permanganate of
potash.

4. Chalybeate (;ta^i';3oj, iron.)— Chalybeate waters derive their name from

150 CHALYBEATE WATERS.

the iron which they hold dissolved. There is scarcely a natural water in
which traces of iron may not be found, but the quantity is so minute as not
to affect the taste of the water, although so small a portion of oxide of iron
as l-35000th part of the weight of the water, is sufficient to give the strong
chalybeate taste possessed by the Tunbridge spring. There are two kinds
of chalybeate water — the carbonated and the sulphated. The Tunbridge
and Bath waters belong to the carbonated kind ; they contain but a small
quantity of saline matter (the Tunbridge Chalybeate less than eight grains
in the gallon), and they owe their chief property to protoxide of iron, held
dissolved by carbonic acid. Hence, although clear when freshly drawn,
they become turbid on exposure by the escape of carbonic acid, and they
de'posit a brown ochreous sediment of hydrated peroxide of iron. The
sulphated chalybeates contain a large quantity of sulphate of iron in solu-
tion, derived from the oxidation of iron pyrites in the strata from which
they issue. We have examined one such spring from Horncastle, in Lin-
colnshire, and found it to contain, in the Imperial gallon, 263 grains of solid
matter, of which 169 grains consisted of the sulphates of iron and alumina.
Chalybeate waters abound in the Rhine district, and they are also very
numerous in France. In some of the waters of Aix-la-Chapelle, the iron is
combined with the crenic and apocrenic acids. One curious fact connected
with them is, that t)||p generally contain traces of arsenic. This ingredient
may be found in the mineral water itself, but more commonly in the ochreous
sediment. In France, no fewer than forty-six waters, including the six
springs of Vichy and the waters of Mont d'Or and Plombieres, are impreg-
nated with arsenic. The Vichy water is said to contain the 1 25th part of
a grain of arsenic in a gallon.

The tonic and other medicinal properties of these waters are now con-
sidered to be due, at least in part, to the arsenic which they contain. The
Wiesbaden water, according to Dr. Hofmann, contains one grain of arsenic
in 166 gallons {Chem. News, Aug. 11, 1860). The waters of Spa and Kis-
sengeu are also arsenical. The arsenic is probably in the state of arsenite
and arseniate of iron, and is held dissolved in minute proportions by the
carbonic acid of the water. It is precipitated in the sediment with oxide of
iron. The arsenic has been probably derived from decomposed iron-pyrites
in the strata, and to this cause may be ascribed the presence of arsenic in
some of the river waters of this country. Mr. Church states that he found
arsenic in the water of the Whitbeck, in Cumberland {Ghem. News, Aug. 25,
1860). We have detected it in the water of the Mersey, supplied to a large
town, in the proportion of one grain of arsenic in 250 gallons, and Dr.
Miller discovered arsenic in a potable water from Suffolk. Mr. D. Camp-
bell and ourselves discovered this mineral in the sediment of some small
streams of Derbyshire, and there is but little doubt that if waters traversing
mineral districts were examined by chemists with a view to its detection,
arsenic would frequently be found, either in the water or in the sediment.
We have detected arsenic in two ounces of dry Thames mud. Its alleged
presence in the deposits of boilers may receive an explanation from these
facts. It is not found in all chalybeate waters. We have made two analyses
of 50 and 100 grains respectively of the ochreous deposit of the Tunbridge
water without detecting any trace of arsenic, so that carbonated chalybeate
waters do not necessarily contain this mineral.

A carbonated chalybeate-water is known, 1, by its inky taste ; 2, by its
giving, when boiled, a grayish-green deposit, which becomes ochreous on
standing ; 3, by its acquiring a pink or purple tint when tincture of galls is
added to it; 4, by boiling it with a hw drops of diluted sulphuric acid, and
adding to it a solution of ferrocyanide of potassium, when Prussian blue is

' PEROXIDE OP HYDROGEN. ITS PROPERTIES. ^151

precipitated; 5, paper soaked in an infusion of rose petals, when dipped in
this water, acquires a dark color (tannate of iron). 6. It discharges the
pink color of a solution of the permanganate of potash, and by means of
this test the amount of protosalt of iron contained in the water may be
voluraetrically determined. A sulphated chalybeate water does not dis-
charge the color of permanganate of potash.

A s?/lphurated chidyheate water gives a dense blue precipitate with ferro-
cyanide of potassium (Prussian bhie). It is precipitated by chloride of
barium, the precipitate (sulphate of baryta) being insoluble in nitric acid.
It does not discharge the pink color of the permanganate of potash.

Peroxide op Hydrogen (HO^). — This compound was discovered by The-
nard, in 1818. It was at one time considered to be water, holding an
additional equivalent of oxygen, and was thence called oxygenated water', or
oxy-water. It is, however, a definite compound of oxygen and hydrogen,
although resolvable into water and oxygen under some remarkable conditions.
It has been obtained free from water and in solution in ether; hence it must
be regarded as an independent oxide.

Preparation. — Regnault recommends the following process for its prepara-
tion : Peroxide of barium is rubbed in a mortar, with a sufficient quantity
of distilled water to make a liquid paste; this paste i^ added by small por-
tions to a mixture of one part of hydrochloric acid and three parts of water
placed in a porcelain vessel immersed in a freezing mixture. The liquid must
be kept stirred during the additions. The changes which ensue may be thus
represented (Ba03 + IICl = BaCl + H03). * When the diluted acid is satu-
rated, a fresh quantity of concentrated hydrochloric acid is added, and to
this another quantity of the peroxide of barium. The operation is repeated
until a solution of chloride of barium is obtained, which is saturated for the
low temperature to which the mixture is exposed. If the liquid is now im-
mersed in a mixture of ice and salt, the greater part of the chloride of barium
is deposited, by reason of its insolubility in water at a low temperature. The
small portion dissolved may be precipitated entirely by the cautious addition
of sulphate of silver (BaCl-f AgO,S03=BaO,SO,+ AgCl). The precipi-
tates are separated by filtration and pressed. The filtrate is concentrated by
evaporation in vacuo. For this purpose it should be placed in a shallow
vessel over one containing concentrated sulphuric acid. Another and less
complex method of preparing this compound consists m adding the paste of
peroxide of barium in sufficient quantity to a strong solution of hydrofluo-
silicic acid. The baryta is precipitated by the acid. The liquid containing
peroxide of hydrogen may be separated by filtration, through gun-cotton,
and concentrated in vacuo by the method above described. The peroxide
may be preserved by acidulating it with a small quantity of hydrochloric
acid, which, in the diluted state, is not decomposed by it. The peroxide
should always be kept in a cool place. This compound may be more readily
obtained in solution, or combination with water by passing a current of car-
bonic acid through peroxide of barium finely powdered and diffused in water.
Peroxide of hydrogen and carbonate of baryta result. (BaOo + HO-fCOo^
HO,+BaOCO,).

Properties. — Peroxide of hydrogen is a colorless syrupy liquid of a sp.^r.
of 1-452. When quite free from water it is not solidified at zero. At tempera-
tures above 60° it begins to be decomposed. If heated, the decomposition
takes place rapidly and sometimes with explosion, the compound being con-
verted into water and oxygen (HO^=HO + 0). It sinks in water, but is
dissolved by that liquid in all proportions, and the aqueous solution is not,

152 PEROXIDE OF HYDROGEN. ITS COMPOSITION.

decomposed until it is heated to above 100^. It bleaches the skin and com-
pletely destroys organic colors by its oxidizintr powers. Old paintinf^s whicli
have become coated with a layer of sulphide of lead may have the dingy
sulphide removed by this agent. In photography it has been used of late
for the purpose of oxidizing and destroying any traces of hyposulphate
which may remain in the tissue of the paper. As a cosmetic it has been
used to render dark hair light in color. As it is sold for these purposes it
generally contains some hydrochloric acid. It is a powerful oxidizer. Potas-
sium, sodium, arsenic, selenium and other simple bodies are rapidly oxidized
by it, and the sulphides of copper, silver, antimony, and lead are converted
by it into sulphates. It also oxidizes the hydriodic, hydrosulphuric and
sulphurous acids. This compound is resolved into water and oxygen, not
only by heat but by contact with certain metals or their oxides. It is decom-
posed by platinum, gold, and silver ; and, if the metals are in a finely-divided
state, with explosion. By mere contact with the oxides of these metals, or
with the peroxidesof manganese or lead, or by simple admixture with a solution
of permanganate of potassa, it is resolved entirely into oxygen and water.
It is, however, a remarkable fact that it may remain in contact with phos-
phorus and phosphorous acid without immediately oxidizing these substances.
It has been elsewhere stated (p. 118) that peroxide of hydrogen is con-
sidered to be the ppsitive polar state of oxygen (antozone), while the
oxygen of the peroxides of manganese and lead is ozone, or oxygen in the
negative polar state. The union of the two is supposed to produce neutral
oxygen.

Peroxide of hydrogen has been obtained in solution in ether by Dr. Storer.
For this purpose he employed peroxide of sodium made by heating sodium
cleaned from naphtha, in a platinum dish, and keeping the metal stirred with
an iron rod. The peroxide was introduced in small portions into a mixture
of 1 part sulphuric acid to 24 water, kept cool by ice. After a few additions,
the acid liquid was agitated with successive portions of ether, until the ether
ceased to produce a blue color, with a diluted solution of chromic acid. A
small quantity of the peroxide of sodium was found to give a large quantity

of the compound {Ghem. News, August, 1861, p. 57.) Schonbein has

succeeded in impregnating ether with the peroxide by simply introducing a
coil of red-hot platinum wire, into a bottle of air, containing a small quan-
tity of ether mixed with water. If this experiment be performed several
times, and the liquid sTiaken each time, it will be found to have dissolved
sufficient peroxide, to give a blue color to a solution of chromic acid, and to
evolve oxygen with a solution of permanganic acid, with peroxide of lead,
or with the hypochlorites. At the same time the ether is oxidized by another
portion of oxygen (ozone) which escapes. — {lb., May, 1860, p. 254.)

Composition. — The analysis of peroxide of hydrogen is easily made by
placing a measured quantity of the liquid in a graduated tube over mercury,
and then introducing into it some finely-powdered peroxide of manganese,
wrapped in filtering paper. The liberation of oxygen begins on contact,
and the greater the quantity evolved, the stronger the compound. There is
no substance known which contains so large a proportion of oxygen as this.
It amounts to 94 per cent, by weight, and according to Pelonze, in its maxi-
mii*n of concentration, it will give off 4t5 times its volume of oxygen. Its
constitution is as follows : —

Atoms. Volumes. Weights. In 100 Parts. Pelonze.

Hydrogen H ... 1 ... 1 ... 1 ... 5-9 ... 5-88
Oxygen 0. ... 2 ... 1 ... 16 ... 94-1 ... 94 12

Peroxide of hydrogen 1117 100-0 100-00

METHODS OF PROCURING NITROGEN. 153

Tt is decomposed by electrolysis, and the quantity of oxygen evolved is
twice as great as that separated from water.

There is no other compound of oxygen and hydrogen known.

CHAPTER XII.

NITROGEN — (N=14). — THE ATMOSPHERE.

History — Nitrogen (from vlt^ov, nitre, and y$v»/a«, to produce) was dis-
covered by Dr. Rutherford in 17T2, up to which time it appears to have
been confounded with carbonic acid. It was called Azote by Lavoisier, a
name still retained by the French chemists. This is derived from a, priv.,
and Cw>7, life, owing to the gas rapidly destroying the life of an animal ;
but it is obvious that such a name would be equally applicable to all the
gases. The name assigned to this element by English chemists, is based on
the property which it possesses of producing, with oxygen, an acid which
enters into the composition of nitre. Nitrogen, although found abundantly
in the mineral kingdom, is one of the most important constituents of organic
substances. A large number of animal, and many vegetable compounds
contain it. It forms nearly four-fifths, by weight, of the atmosphere in an
uncombined or free state. Among native mineral substances, nitrate of
potash contains 14 per cent., and nitrate of soda 16 per cent, of nitrogen.
It is a constituent of most fulminating compounds, e. g., the fulminates of
mercury, silver, and gold. Ammonia and all its salts contain it in large
proportion.

Preparation. — Nitrogen may be obtained by burning phosphorus in a
confined portion of atmospheric air. For this purpose, a tall glass jar,
open at the bottom, and provided with a stopc^ock, should be selected : a
small porcelain or metallic cup, containing a sufficiency of inflamed phos-
phorus, is then set afloat in the water-trough and the jar immediately inverted
over it. A quantity of air is at first expelled by the heat : the stopcock is
then closed and the combustion goes on for a few minutes ; when it has
ceased, and the apparatus has cooled, the cup is easily removed by agi-
tating the jar, so as to sink the phosphorus through the water. The resi-
duary gas, which is in nitrogen, should be then thoroughly washed with
lime-water, or with a weak solution of potassa. 2. We may procure it with-
out combustion by placing a stick of phosphorus on a cork or in a porcelain
capsule on water, and inverting over this a capacious jar of air. In about
48 hours the water will have risen in the jar to the extent of one-fifth, and
the residuary gas, when washed with a weak solution of potassa, will be found
to be nitrogen in a pure state. 3. Bright iron filings sprinkled in a jar
wetted on the inside and inverted over a water-bath, will also yield it — the
oxygen in this case being removed by the iron. The residuary gas (nitro-
gen) is not contaminated with any acid, but it may contain a trace of am-
monia, which is easily removed by agitation with water. 4. If, in place of
iron, copper turnings or filings are used, the jar being previously rinsed out
with strong hydrochloric acid, nitrogen will be equally obtained — the oxygen
being entirely removed, while the copper is converted into subchloride.
The gas may be decanted and well washed in water, to remove any acid
vapor. 5. The mode in which nitrogen may be procured perfectly pure is

154 NITROGEN. CHEMICAL PROPERTIES.

the following : Place in a porcelain capsule, floating in a water-bath, some
pyrogallic acid, and pour on the acid a strong solution of potassa. Invert
over the capsule a jar of air. The oxygen will be more or less rapidly
removed, according to the quantity of pyrogallic acid, and the strength of
the solution of potassa. In this case, the carbonic acid as well as oxygen is
absorbed by the liquid, so that the residuary nitrogen contains only aqueous
vapor, which, if necessary, may be removed from it by dry potash. Other
methods for procuring the gas have been suggested, e. g., by passing air
through a tube containing metallic copper, heated to redness. In this experi-
njent the air is deprived of its oxygen, oxide of copper is formed, and the
nitrogen passes over. It has been also recommended to procure the gas by
decomposing a strong solution of ammonia by a current. of chlorine, but
this process is attended with some danger. If the nitrogen is entirely
deprived of oxygen' by any of the above processes, no red fumes will appear
on mixing it with its volume of deutoxide of nitrogen. It is less pure when
produced by the vivid combustion of phosphorus, than when it results from
slow oxidation as in 2.

Properties. — Nitrogen is a permanently elastic, colorless, neutral gas, with
neither smell nor taste : it has no action upon vegetable colors or upon lime-
water. It is not dissolved by water, except that fluid has been deprived of
its ordinary portion of air by long boiling, w^hen it takes up about one and
a half per cent. Its refractive power in regard to light is to that of atmos-
pheric air as 1"034 to 1000. It is rather lighter than atmospheric air,
compared with which its specific gravity is 0967 : 100 cubic inches weigh
at mean temperature and pressure 29*96 grains. (Thompson.) Its specific
gravity in reference to hydrogen is as 14 to 1. The following experiments
will serve to' illustrate the properties of this gas. It does not support com-
bustion : 1. A lighted taper, burning camphor, or a flame of ether, when
plunged into the gas is immediately extinguished. 2. If quite free from
oxygen, inflamed phosphorus will be extinguished in it. These facts prove
that, in ordinary language, it will neither burn nor support the combustion of
other bodies. 3. The neutrality of the gas, if deprived by washing of any
traces of the vapor of phosphorus or of phosphorous acid, may be proved by
pouring into it a solution of litmus ; the blue color will remain unchanged.
4. On shaking the liquid with the gas, its insolubility in water will be
manifested by a lighted taper being as readily extinguished after, as before
the introduction of litmus. 5. If into another jar we introduce a solution
of chloride of lime, colored with litmus, the blue color will not be discharged
— a proof that the gas is not acid. 6. When lime-water is poured into ajar,
and the vessel is shaken, the lime is not precipitated, t. If a solution of
potassa is added to another jar, the gas remains undissolved. 8. A piece of
caustic potassa moistened and placed in a tube of nitrogen over mercury,
produces no absorption or alteration in the volume of the gas. The
extinction of burning bodies is common to nitrogen and carbonic acid ; but
the experiments 3 to 8 serve clearly to distinguish the tw^o gases, and by 8
they may be separated when mixed. Traces of an acid of phosphorus are
sometimes found in the nitrogen obtained by the use of this substance, and
the gas if unwashed may thus appear to have an acid reaction, but as it is
procured by the oxidation of iron, no acid is produced.

Potassium will not burn in nitrogen. Allow a stratum of half an inch of
water to remain in a jar of the gas. Throvv into the jar a piece of potas-
sium ; it will decompose the water, but without combustion.

Although nitrogen is a necessary constituent of atmospheric air, it cannot
be breathed in a pure state without destroying life. It does not appear to
operate as a poison, but when breathed, it simply induces suflfocation, owing

NITROGEN. EQUIVALENT. TESTS. 155

to tlie absence of free oxypcen. If it had any directly noxious effects on the
body, it could not be breathed by animals in the large proportion in which
it enters into the mixture of gases, known as the atmosphere.

Nitrogen is said not to be combustible, but under certain circumstances,
it may be made to undergo a kind of combustion, as when electric sparks
are passed through atmospheric air, or through a mixture of one volume of
nitrogen with two or three of oxygen ; in this case each spark will be
attended by the production of a trace of nitric acid, and after some hundred
sparks, the blue color of litmus will be changed to red. Here combustion
appears to take place in that portion of the gas immediately subject to the
action of the sparks ; but the temperature of the surrounding gas is not
thus sufficiently elevated to enable the combustion to spread beyond the
immediate sparks. This is probably the source of the nitric acid, and of
the nitrates found in rain-water after thunderstorms. The- nitrogen of the
atmosphere is also liable to oxidation, as a result of the action of ozone.
{See page 115.) Some of the eflfects ascribed to ozone, have been set down
to the combustion of nitrogen.

If a mixture of nitrogen with twelve or fourteen volumes of hydrogen, be
kindled as it issues from a small tube, and burned either in common air or in
oxygen, water and nitric acid will be formed ; so that in this case the
nitrogen may be said to undergo combustion by the aid of the elevated tem-
perature of the flame of hydrogen ; but it must be recollected that in these
cases nitric acid could be produced without the presence of water, and that
it may tend to dispose a union which would not otherwise take place. The
formation of a trace of nitric acid, when hydrogen is burned in common air,
is referable to the same cause. Bunsen has found that, by adding to the
mixture of oxygen and nitrogen two volumes of detonating gas (composed
of two volumes of hydrogen and one of oxygen), nitrogen may be easily
oxidized and converted into nitric acid. If the detonating, gas is used in the
proportion of from three to five volumes of the mixed oxygen and nitrogen,
so much nitric acid is produced, that the mercury in the tube is dissolved
with the evolution of deutoxide of nitrogen.

Much discussion has arisen respecting the nature of nitrogen ; and the
question has been agitated, whether it is or is not a simple body ; but
although many ingenious surmises have been published on the subject, and
many analogies suggested in favor of its being a compound, no experimental
proofs have been hitherto adduced. The production of nitrides by combi-
nation with certain metals, and the metallization of ammonia, are considered
by some chemists to favor the view of its compound nature.

Nitrogen is one of those elementary bodies on which the electric current
appears to exert no influence. According to Faraday's researches, nitrogen,
when under the influence of the current, has shown no tendency to pass in
either direction.

Equivalent and Compounds ^^The equivalent weight of nitrogen is 14,

and its volume equivalent is 1. In the free state, it is remarkable for its
neutrality or indifiference to combination. In the nascent state it readily
unites with hydrogen and oxygen, forming ammonia, and, in some cases,
nitric acid. It forms also compounds with carbon, chlorine, and iodine, but
only as a result of complex chemical changes. When combined, it is
remarkable for its instability, since slight physical causes will lead to its
sudden separation with explosion, from many of its combinations. Fulmi-
nating substances frequently owe their properties to the suddenness with
which this element is liberated.

Tests. — Nitrogen-compounds, such as nitric acid and ammonia, are easily
recognized by appropriate tests. The only difficulty connected with the

156 ATMOSPHERE. ITS PROPERTIES.

detection of nitroo^en, is in reference to its presence in organic substances.
It is, however, readily converted into ammonia, and from the production of
ammonia, we infer the existence of nitrogen. For this purpose, the sub-
stance dried and powdered is mixed with its bulk of soda-lime (a mixture
consisting of two parts of hydrate of lime, and one part of hydrate of soda).
On the application of heat to the mixture, ammonia is evolved. This is
known by its odor, and its volatile alkaline reaction on test-paper, as well
as by its special chemical character. {See Ammonia.) Another method
consists in forming a carbon-compound (cyanogen). The substance in
powder is introduced into a narrow test-tube, and a portion of sodium is
introduced, the metal being completely covered with and surrounded by the
powder. Heat is then applied to carbonization, and cyanide of sodium
(NajCgN) is one of the products. When cold, the dark residue is lixi-
viated in water, and the solution filtered. It is of a pale yellow color, and
generally alkaline from the presence of free soda. On adding to it a solu-
tion of green sulphate of iron, there is a turbid dark-green precipitate.
When this is treated with diluted sulphuric acid, oxide of iron is dissolved
and Prussian blue remains. • This is a clear proof that nitrogen was present
in the substance. A small globule of sodium tied in a portion of flannel, and
thus treated, reveals the presence of nitrogen in the albumen of flannel. We
have thus obtaiaed Prussian blue from the nitrogen of the body of a fly.

THE ATMOSPHERE.

It will be understood from the preceding remarks, that the atmospheric air
is a mixture of gases, in which nitrogen predominates. Besides nitrogen,
which forms nearly four-fifths, the other principal ingredient is oxygen,
constituting about one-fifth ; and in addition to these, there are compara-
tively small quantities of carbonic acid, aqueous vapor, sulphurous acid,
ammonia, and other gases, as well as organic matter. The term atmosphere
(from afjiioj, vapor, and o^jatpa, sphere), is applied to the great aerial ocean
which surrounds the earth, and extends, in varying degrees of density, about
forty-five miles from its surface. Large as this may appear, it represents
only 1-1 60th part of the earth's diameter. In a globe of forty feet diameter,
this would be equivalent to a thickness of only three inches. The term
atmosphere is appropriate, inasmuch as it is the receptacle of all the gases
and vapors, organic or inorganic, which are constantly escaping from the
surface of the earth and sea.

Properties. — The physical and chemical properties of the air are those of
its two principal constituents, oxygen and nitrogen ; the active properties of
oxygen being modified by dilution with nitrogen. Air is a transparent,
colorless, elastic, tasteless fluid, and, as its two constituents are permanent
gases, it has not yet been liquefied by cold or pressure. It has been con-
densed to a degree but little inferior to that of water (l-6t5th part of its
original volume), without undergoing any change in its physical condition
(page 81). Heat simply expands it (page 83), and, within certain tempe-
ratures, with great uniformity. The nitrogen has no positive properties ;
oxygen is the principal chemical agent, and is largely consumed iu combus-
tion and respiration (page 95). The oxygen thus consumed is replaced by
an equal volume of carbonic acid, and this in its turn is absorbed and
decomposed by the green parts of vegetables under the influence of solar
light, so that the carbon is fixed in the vegetable structure, and the oxygen
is evolved either in its common or allotropic state. The animal and vegetable
are thus proved, in reference to the atmosphere, to have a compensating
relation to each other. Air is dissolved by water, but the oxygen is taken
up in larger proportion than nitrogen (page 141). It is this which imparts

COMBUSTION IN AIR. 15*7

a fresh aerated taste to water. The proportion of air dissolved, is subject
to variation, but in natural spring waters it is seldom less than two cubic
inches in one hundred of water. It is expelled by boiling, congelation, or
the removal of atmospheric pressure, as by placing a glass of spring water
under the receiver of an air pump and exhausting the vessel. The air is
seen to escape in small bubbles. Owing to the diminution of pressure,
water at lofty elevations is less aerated than at the level of the sea, and, by
reasons of the deficiency of air, the lake-water of high mountainous districts,
is not fitted to support the existence of fish. Air adheres more or less to
all solids, and it is especially contained in porous solids. A stick of charcoal
sunk in water by a leaden weight, and placed in vacuo^ yields a large quantity
of air, which issues in torrents from the broken ends. A piece of pumice,
or an ^^^, sunk in a vessel of water, presents a similar phenomenon. Even
the smooth and polished surfaces of metals may thus be proved to have a
film of air adherent to them.

In comhustion,i\\% oxygen alone is consumed, the nitrogen is set free and
mixes with the carbonic acid produced at the expense of the oxygen. Air
is therefore rapidly contaminated by this process, and in a confined space,
the nitrogen and carbonic acid, as a result of the heat of combustion, ac-
cumulate in the upper part of the vessel or apartment. Neither of these
g:ases is respirable, and neither will support ordinary combustion. The
following experiments will illustrate the d*eterioration of air under these
circumstances. Fix three wax tapers to a stout wire placed upright, and
about three feet in height, so that one is at the upper part, one at the lower,
and the third in the middle. Light the tapers, and invert over them a tall
stoppered shade, leaving a slight space for the entrance of air below. The
accumulation of deoxidized air (nitrogen) and carbonic acid in the upper
part of the shade, will be indicated by the early extinction of the upper and
middle tapers, while the lower one will continue to burn. If, when the
lower taper is burning dimly from impurity of the air, the stopper is removed
from the shade, a current of air is immediately set up, the gaseous products
of combustion are carried off, and the lower taper will burn with a brighter
flame. This experiment establishes the necessity for a rapid removal of the
products of combustion, and the results are equally applicable to the con-
tamination of air by the respiration of animals. Fix in the stoppered
aperture of a bell-jar, by means of a closely-fitting cork, a glass tube, about
an inch in diameter. The tube should rise several inches above the level of
the jar, and should reach on the inside to within two inches of its base.
Mount in a plate two pieces of wax taper, one sufiQciently tall to reach nearly
to the top of the jar when placed over it, the other so short, that when ignited,
the point of the flame only will be inclosed by the open end of the glass tube
fixed in the jar. Light the tapers and invert the jar over them, not pressing
it down closely at the base. The tube should be so adjusted to the short
taper, as to act like a chimney to it, care being taken that it is not touched
by the flame. In a short time, if the cork is well fitted, the tall taper will
be extinguished, but the short taper will continue to burn. In the one case,
the products of combustion are not carried off", in the other they are, and
the supply of air is continually renewed. As a proof of this, if we hold over
the chimney-tube a small gas-jar, the deposition of water on the glass will be
apparent, and, after a time, the presence of carbonic acid may be proved by
pouring lime-water into the jar. (The production of carbonate of lime will
be indicated by a milky appearance of the lime-water.) The principles of
the ventilation of dwellings are based on a proper adjustment of the supply
of pure air for combustion and respiration, and a provision for the complete
removal of the products as they are formed. In the burning of coal-gas the

158 PRESSURE OF THE ATMOSPHERE.

production of sulphurous acid may be an additional source of noxious
impurity.

When combustion takes place in rarefied air, as when a candle is placed
under a receiver from which the air has been partially removed by the air-
pump, the flame is elongated, becomes less luminous, and is soon extin-
guished. According to observations made by Dr. Frankland, in 1859, on
the summit of Mont Blanc, it appears that at this elevation the amount of
combustible consumed is as great as at the level of the sea, although the
light emitted by a burning candle is considerably less.

Air is usually taken as the standard of specific gravity for gases, being,
for this purpose, I'OOO. It is also the standard for refraction, specific heat,
and other properties of gases. One hundred cubic inches of dry air at mean
temperature (60°), and mean pressure (30 inches), are considered to weigh
31 grains. This nearly corresponds to the sum of the weights of the consti-
tuent gases, having regard to the proportions in which they are mixed. Air
is about 815 times lighter than its volume of water, at 60°. Compared with
hydrogen its density is as 14 4 to 1. The weights of 100 cubic inches of any
gas or vapor may be determined by multiplying the specific gravity of the
gas or vapor by 31, the weight of 100 cubic inches of air. Thus : nitrogen
has asp. gr. of 0-967 and 0-967 x 31 =29*98 grains, the weight of 100 cubic
inches of this gas.

Pressure of the Atmosphere. -^Omng to the gravitating force of the atmo-
sphere and the great elasticity of its constituent gases, the lowest stratum —
that which is in contact with the surface of the earth, and in which warm-
blooded animals live, is highly condensed. The pressure of the atmosphere
at the level of the sea, is equal to 15 pounds on every square inch, or about
2216 pounds on each square foot. It is calculated that one cubic inch at
the surface, would expand into 12,000 cubic inches at the extreme limit of
the atmosphere (45 miles). The proportionate increase in volume at differ-
ent elevations, as the result of the decrease of pressure, is given in the sub-
joined table. It will be perceived that at a height of only 2705 miles
(14,282 feet), the atmosphere loses one-half of its density; in other words,
one volume at the surface would expand into two volumes at this elevation.
So rapid is the decrease of density, that while one-half of the mass of the
atmosphere is within three miles of the surface, four-fifths of it are within
eight miles, leaving only one-fifth for the thirty-seven miles above this eleva-
tion. While the height increases in arithmetical progression, the increase
of volume (or decrease of density) follows a geometrical, ratio : —

Height above the

-Volume.

Height above the

Volumt

sea in miles.

sea in miles.

0

. 1

10-820 '.

,

. 16

2-705 .

. 2

13-525 .

,

. 32

5-410 .

. 4

16-230 .

,

. 64

8-115 .

. 8

18-935 .

.

. 128

The temperature of the atmosphere diminishes about 1° for every 350 feet
of ascent, the cause of which is partly referable to the increased capacity of
air for heat in proportion as its density diminishes, and partly to the cir-
cumstance thaji the atmosphere is chiefly heated by contact with the earth.
The line of perpetual congelation gradually ascends from the equator to the
poles. At 0° latitude it is stated to be 15*^,200 feet ; at 60°, 3,818 ; and at
76°, only 1000 feet.

If a tube three feet long is filled with mercury, and inverted in a mercurial
bath, the metal will fall in the tube until its height from the surface of the
bath is equal to about 30 inches. If placed under a receiver and the air is
withdrawn, the mercury will fall in the tube. On readmitting the air it will

PRESSURE OF THE ATMOSPHERE. 159

again rise. It is therefore obvious that this column of mercury is supported
in the tube by the pressure of the atmosphere on the surface of the liquid
metal in the bath. From this experiment it will be easy to calculate the
exact amount of pressure on the lowest stratum of air. This has been already
stated to be equivalent (in round numbers) to 15 pounds avoirdupois on
every square inch of surface. In reality, however, the pressure, assuming
the mean height of the barometer to be 30 inches, is 14*6 pounds on the
square inch — a result which is thus obtained : The weight or gravitating
force of the atmosphere, is proved, by the experiment above mentioned, to be
exactly equal to the weight or gravitating force of a column of mercury thirty
inches in height. A column of this metal, the base of which would be equal
in area to a square inch, would consist of thirty cubic inches. The specific
gravity of mercury being 13 5, the weight of a column of 30 cubic inches
will represent the gravitating force of the atmosphere on the area of a square
inch. A cubic inch of mercury weighs 3408'183 grains (252-458X 13'5 —
the weight of a cubic inch of water multiplied by the specific gravity of
the metal), and therefore 30 cubic inches would weigh (3408*138 x 30=
102245'49 grains or) 14'6 pounds avoirdupois. Hence this may be taken
as the true amount of atmospheric pressure when the barometer is at its
mean height. A column of water 33 feet in height, or a column of air 45
miles in height, each having the area of a square inch, would be equal in
pressure to, a column of mercury 30 inches in height. These diiferent heights
correspond to the respective specific gravities of the liquids.

The influence of this pressure on the volume of gases may be easily proved.
Place a light caoutchouc-ball under the receiver of an air-pump and with-
draw the air. The ball will increase in size as the air is withdrawn — the
air which is confined within the ball acquiring a power of expansion by the
diminution of pressure. If the mouth of a wide glass jar is well secured
with a layer of stout caoutchouc, and the jar is placed under the receiver,
on the removal of the air the membrane will be enormously distended by
the expansion of air in the jar, and may ultimately burst. Invert in a gas-
jar, a graduated tube containing water, colored with sulphate of indigo,
leaving two cubic inches of air at the top. Place this under the receiver.
As the air is withdrawn from the receiver the air in the tube will expand,
and, when the barometer marks 15 inches, it will be found that the two cubic
inches will occupy the space of four, thus showing that by the removal of half
the pressure the air has been doubled in volume. This experiment proves
that the density of the air is in a direct ratio to the compressing force. With
the pressure of half an atmosphere the volume is doubled, and with a pres-
sure of two atmospheres it is reduced to one-half. It is the same for all*
gases and vapors above the boiling point of their liquids), whatever may be
their respective specific gravities.

A well-ground receiver, when the air is removed from the interior, is
pressed with such force to the air-pump plate that it is impossible to move
it. But this pressure may be made visible by th« following experiments.
Close one end of a stout glass-cylinder four or five inches in diameter, with
a strong layer of sheet India rubber, and apply the other end, which should
be well ground for this purpose, to the plate of the air-pump. As the air
is gradually withdrawn, the rubber will be pressed downwards, filling the
interior of the vessel, and it may ultimately burst. If for the rubber we
substitute a layer of wet bladder, and allow this to dry, on placing the glass
oil the air-pump plate, and rapidly exhausting it, the bladder will be burst
with a loud report, as the result of the air rushing into a partial vacuum.
Owing to the great amount of this pressure, receivers and other vessels
intended for exhaustion should be made of stoat glass, and rounded at the

160 EUDIOMETRY. DETERMINATION OF OXYGEN.

top. Fill a short wide jar with carbonic acid. Pour into the jar a small
quantity of water, and add at the same time, but without agitation, several
sticks of fused potash. Tie over the mouth of the jar firmly a stout sheet
of caoutchouc stretched tightly for this purpose. Now agitate the jar, and
as the solid potash is dissolved in the water it removes the carbonic acid
contained in the jar. The universal influence of atmospheric pressure now
shows itself by rendering the caoutchouc concave, and it is so much depressed
that "it sometimes bursts.

As in all fluids, the pressure is equal in all directions. The pressure
downwards is proved by the preceding experiments. The force of the pres-
sure upwards may be proved by the following simple experiment: Fill a
well-ground glass-jar, about twelve inches long and three or four inches wide,
with water. Place over this a square of stout writing-paper, and, pressing
it firmly to the water, suddenly invert the jar. The heavy column of water
will be for a time supported by the atmospheric pressure upwards on the
outer surface of the paper. Make a chemical vacuum by pouring into a
well-ground jar, containing carbonic acid, a small quantity of a strong solu-
tion of potash, and cover the jar immediately with plate-glass. On agitating
the jar, the gaseous contents will be removed, and the cover will be firmly
fixed to the jar by atmospheric pressure. In whatever position the jar may
be held the cover will remain equally fixed, showing equality of pressure in
every direction. From the powerful effects thus produced when the air is
removed from one surface, it may be conceived that nothing could withstand
this pressure unless it were equal in all directions, and thus completely neu-
tralized.

Composition. Eudiometry. — Numerous analyses of the air made by chemists
of repute, show that the proportions of nitrogen and oxygen are not strictly
uniform, either for the same place or for different localities. The proportion
of oxygen varies from 20 to 21 per cent. The amount of oxygen by volume
is readily determined, by the adoption of any of the methods for separating
it described under nitrogen (page 153), provided care is taken to employ
for this purpose an accurately graduated gas tube and a mercurial bath.
Among these, the process described under 5, is preferable to the others.
Phosphorus cast in small balls is sometimes used, but unless the vapor of
phosphorous acid (produced as a result of oxidation) is removed by a ball
of potash, before the volume of nitrogen is read oft", there will be a con-
siderable error in the results. Liebig has advised, in place of phosphorus,
a ball of papier mache, saturated with a concentrated solution of pyrogallate
of potassa. The absorption takes place slowly but completely, particularly
if the ball be once renewed. After this absorption, the gas must be dried
by a ball of potassa, containing as little water as possible. (Bunsen, Gasome-
try, p. 79.) In this case the pyrogallate of potassa, and dry potassa, remove
the oxygen, carbonic acid and aqueous vapor, leaving nothing but nitrogen.
The temperature should be noted both at the beginning and end of the
experiment. #

The ordinary volumetric method of analysis, is based on the admixture of
a quantity of pure hydrogen with air, and its conversion into water, by
any of the usual processes, at the expense of the oxygen contained in the
air under examination. As oxygen represents one-third of the volume of
the combined gases (Water, page 127), the division of the loss by 3 will
at once give the quantity of oxygen present in the air. The air and hy-
drogen, in about equal proportions, are introduced into a graduated glass-
tube placed over mercury, or into a siphon-tube containing mercury, espe-
cially constructed for this purpose ; and the gases are then either detonated
by the electric spark, or are slowly combined by means of a ball composed

DETERMINATION OF OXYGEN. 161

of spongy platinum and clay, introduced through the mercury into the tube.
The gases should be allowed to diffuse thoroughly, before any attempt is
made to combine them. The following experiment on the air of London,
will illustrate the principle of this operation. The air examined amounted
to 35 parts by volume. To this quantity 42 parts of hydrogen were added.
The mixed gases, therefore, amounted to 77 parts. A ball of spongy pla-
tinum was introduced into the mixture, and in two hours combination was
complete. It was found that only 56 parts of gas remained in the graduated
tube. The loss, therefore, as watery vapor was 77 — 55 = 22 ; and one-third
of this must have been oxygen. Therefore 22-^3=7■33 for the proportion
of oxygen in the 35 measures taken : and 35 : 7 33 : : 100 : 20-94 oxygen.
Deducting these figures from 100, the air examined had this composition in
100 parts: oxygen 2094; nitrogen 79-06. The use of spongy platinum
for the combination of the gases, appears to be less liable to fallacy, than
the detonation of the mixture by the electric spark. Bunsen has shown,
that unless great precautions are taken, so much •hitric acid may be formed
in the presence of oxygen and hydrogen by the combustion of the nitrogen,
as to lead to a serious fallacy in calculating the amount of oxygen. (Gaso-
metry, page 60.) On the other hand, the pyrogallate of potassa, as an
absorbing liquid, was found to give very accurate results.

To this kind of analysis the term eudiometry (d, 8iov, and fisrpov, measure
of the purity of the air) has been applied, since the healthiness of localities
was erroneously supposed to depend on the proportion of oxygen present.
Eudiometric tubes, finely graduated and connected with bottles containing
a liquid for the absorption of oxygen, were formerly employed. The air
contained in the tubes was exposed to the eudiometric liquid, and the amount
of absorption was ascertained by opening the bottle under water. A solution
of suli)hide of potassium, or of y)rotosulphate of iron saturated with deut-
oxide of nitrogen, was formerly used for this purpose, ^uch methods of
analysis have been long since abandoned.

As errors frequently arise in reading and correcting the volumes of gases,
owing to the variable influence of pressure, temperature, and other causes,
chemists have given some attention to the discovery of a method for deter-
mining the oxygen and nitrogen by weight, in one operation.

This has been successfully accomplished in the analysis of air, performed
by Dumas and Boussingault. The operation is very simple. Air, deprived
of its carbonic acid, and aqueous vapor, by causing it to pass through a
series of tubes, some of which contain concentrated sulphuric acid, and
others, a saturated solution of potassa, is finally made to traverse a balanced
tube containing metallic copper, heated to redness. It is here entirely
deprived of its oxygen. By opening a stopcock communicating with a large
glass globe in a state of vacuum, the deoxidized air, or nitrogen, is collected
in this vessel, which acts as an aspirator. When filled, the glass globe is
removed and weighed. It is now brought to a state of vacuum, and again
weighed. The difference in weight represents the amount of nitrogen, while
the increase in weight in the balanced tube containing the copper, gives the
amount of oxygen. All the other constituents of air, excepting oxygen and
nitrogen, are excluded by this method of analysis. The results thus obtained
are in close accordance with those determined by other chemists. Air is
thus found to be constituted by volume and weight: —

By Volume. By "Weight.

Oxygen 20-80 23-10

Nitrogen 79*20 76-90

CarhoniCf acid, although in small proportion, is a universal constituent of
11

162 DETERMINATION OF CARBONIC ACID AND WATER.

air. It has been found at all elevations at which it has been sought for,
and may be readily detected by causing a large quantity of air to pass
through a tube or vessel, containing a solution of lime or baryta; or by
simply exposing to the atmosphere, a solution of the alkaline earth in a
shallow glass dish. A white precipitate, or an incrustation of carbonate of
lime or baryta, is obtained after some hours. The presence of aqueous vapor
in the. air is known by the deposition of water on the exterior of a glass-
vessel in which ice has been placed, or by exposing to a current of air, fused
chloride of calcium in a glass tube. In this case the water is absorbed, and
the chloride is thereby increased in weight.

Various methods have been adopted for the purpose of determining the
proportions of carbonic acid and aqueous vapor. In reference to the former,
M. Thenard employed a solution of baryta ; and from the amount of car-
bonate of baryta, obtained by agitating this liquid with a measured volume
of air, he concluded that the proportion was about l-2000th part, or one
cubic inch in two thousand cubic inches of air. The plan more recently
adopted by Boussingault, Regnault, and other chemists, is based on the
separation and weighing of carbonic acid and aqueous vapor in one opera-
tion. By means of a large aspirator, the air is made to traverse a series of
balanced tubes filled with broken pumice, impregnated with concentrated
sulphuric acid, and after having been thus deprived of water, the air traverses
another series of balanced tubes, also filled with pumice strongly impreg-
nated with a concentrated solution of potassa. These tubes arrest the carbonic
acid. Any change of temperature in the contents of the aspirator, during
the performance of the analysis, is accurately noted. It will be obvious, that
by repeatedly filling the aspirator any quantity of air may be thus made to
pass through the balanced tubes, and the first of the series may have a length
of vulcanized tubing so adjusted to it, as to bring the air from any particu-
lar spot. After the completion of the experiment, the amount of aqueous
vapor is known by the increase of weight in the sulphuric acid tubes ; and
the amount of carbonic acid, by the increase in the potassa tubes. Reducing
these quantities to volumes, and dividing the whole amount of air by the
volumes, the proportions of both of these constituents may be determined.

The quantity of carbonic acid amounts to from 3*7 to 6'2 measures in
10,000 : or on an average about l-2000th part by volume. According to
Saussure, the proportion varies with the season. The air in a meadow, in
August, contained 0-000713 ; in January, 0000479 ; in November, in rainy
and stormy weather, 0 000425. Dal ton estimates the carbonic acid at 0 001 ;
Configliachi, the maximum at 0008 ; and Humboldt (probably an excess)
at 0'005 to O'OIS. Saussure and Gay-Lussac found the usual proportion of
carbonic acid in the air from the summit of Mont Blanc, and 4000 feet
above Paris. Beauvais found scarcely a trace of carbonic acid in the air
over the sea off Dieppe, but the usual proportion inland. — (L. Gmelin.)

Carbonic acid is in such small proportion in air, that lime-water indicates
no trace of its presence in 200 cubic inches contained in a closed bottle.
In air taken from low and confined situations, as wells and cellars, the car-
bonic acid may amount to from 3 to 10 per cent. Air suspected to be
strongly impregnated with this gas, may be thus tested. Fill a long, narrow
tube with lime-water, and invert it on the water-bath ; pass up through the
lime- water a few cubic inches of the suspected air. If the carbonic acid is in
undue proportion, this will be made evident by the lime-water acquiring on
its surface a milky appearance, owing to the production of carbonate of lime.
Carbonic acid is stated to be contained in air, in greater proportion in
summer than in winter— at night, than by day— in cloudy, than in fine
weather— in dry, than in wet weather ; but there is no doubt that the amount

AIR, AQUEOUS VAPOR AND AMMONIA. 163

of this gas is kept down partly by its great solubility in water and its
removal by rain ; and partly by vegetation. In the latter case the gas is
decomposed, and oxygen is set free. The great sources of carbonic acid are
combustion, respiration, putrefaction, decay, and fermentation.

The relative quantity of aqueous vapoi- in the atmosphere, is subject to
much variation. From the experiments of Saussure, Dalton, and Ure,
already referred to, it appears that 100 cubic inches of atmospheric air at
57°, are capable of retaining 0-35 grains of watery vapor; in this state, the
air may be considered at its maximum of humidity. It would also appear
that all gases not condensable by water, take up the same quantity of water
when placed under similar circumstances, and that it consequently depends,
not npon the density or composition, but upon the bulk of the gas. From
Dalton's researches, it may be concluded that the vapor forms an independent
atmosphere, mixed, but not combined with air.

The proportion of water diffused as a vapor in a gas depends upon tem-
perature, and not upon the pressure of the atmosphere. The higher the
temperature, and the dryer the atmosphere, the larger the quantity of vapor
taken up. As it is the same at mean temperature, in all gases, the pro-
portions have been tabulated, and will be found in the Appendix. The
quantity by volume contained in air at 52°, is estimated to be 1*42 per cent.,
or about 5 to 12 grains in a cubic foot. In air already saturated with it
there is no evaporation. The presence of aqueous vapor in air, is not only
necessary to vegetation, but is indispensable to the respiration of animals.
Dry air produces an irritative effect on the air passages and lungs.

Ammonia is known to be a constituent of air, but in very small propor-
tion. It is detected by passing a large quantity of air through a vessel
containing hydrochloric acid diluted with water. After operating on a con-
siderable quantity of air, chloride of platinum is added to the acid liquid,
which is then evaporated, and the amraonio-chloride of platinum, after wash-
ing with alcohol to remove any chloride of platinum, is collected, dried, and
weighed. From this weight the proportion of ammonia in air is deduced.
M. Grseger found that the quantity was 0-000,000,333 of the weight of air.
Kemp found a larger proportion, namely, 0 '000,003, 88, and Fresenius
0000,000,133. Horsford, of the United States, has endeavored to de-
termine the proportion in America, and has arrived at the conclusion that a
million parts of air by weight contain from 1 to 42 parts of ammonia, the mini-
mum amount being found in December, and the maximum in August. It is
probable that this constituent, although small, may serve an important pur-
pose in reference to vegetation.

The great variation in these results shows that the proportion of ammonia
cannot be accurately defined. It may be described like some acid vapors,
as existing only in traces.

Organic matter is found in the atmosphere, especially in inhabited locali-
ties, or where animal or vegetable matter is undergoing decomposition. It
is this which gives the foul odor to closely confined rooms, in which many
persons have breathed without due ventilation. Dr. Angus Smith has
endeavored to determine the proportion present in ^air, by noticing how
many measures of air were required to remove the color from a weak stan-
dard solution of the permanganate of soda, or potassa. The larger the
amount of organic matter, the smaller the quantity of air required to cause
the permanganate to lose its characteristic pink color. He has called this
instrument the sepometer. He states that he has found a considerable differ-
ence in the results of experiments on the air of towns, of the country, and
of the sea-coast. The state of ventilation in a room can, according to him,

I

'V"i*"

164 ORGANIC MATTER IN AIR.

be determined by it, and it has enabled him to register degrees of impurity
in air, which could not be detected by the smell.

He found that equal quantities of a standard solution of the alkaline per-
manganate were decolorized by 22 measures of air, from the high ground of
Lancashire — by 9 from an open street in Manchester — by 5-5 from some
small houses on the Medlock — by 2 from a railway carriage full of passen-
gers, and by 1 from the back yard of a house in a low and ill-ventilated
neighborhood.

The results of his experiments show that on some of the Swiss lakes, and
on the German Ocean, sixty miles from land, the sepometer indicated, in the
air, but a small amount of organic matter, or of matter capable of decolor-
izing the test solution. The maximum effects were produced by air from a
house kept close, and from a pigstye recently uncovered. In the subjoined
table we give from Dr. Smith's remarks the relative amount of organic and
oxidizable matters diffused in air taken from different localities. An equal
measure of air showed the following relative quantities in —

Manchester (average of 131 experiments) 52-9

" All Saints, E. wind (37 experiments .... 52-4

" " W. wind, less smoky (33 experiments) . .49-1

" East wind, above 70° Falir. (16 experiments) . . . 58*4

" " below " (21 experiments) . . . 48-6

" In a house kept rather close 60-7

In a pigstye uncovered 109*7

Thames at City, no odor perceived after the warmest weather of 1858 58-4

Thames at Lambeth 43*2

" Waterloo Bridge 43-2

London in warm weather (six experiments) ..... 29*2

" after a thunderstorm . .12*3

In the fields S. of Manchester 13-7

" N. of Highgate, wind from London 12-3

Fields during warm weather in N. Italy 6'6

Moist fields near Milan 18-1

Open sea, calm (German, Ocean 60 miles from Yarmouth) . . . 3*3
Hospice of St. Bernard, in a fog . . . , , . . .2*8

N. Lancashire about same

Forest at Chamouni . . . 2-8

Lake Lucerne . . 1*4

The operation of the permanganate clearly depends on the oxidation of
organic matter, probably as a result of the ozone associated with this salt
(page 112). There can be no doubt that organic matter possesses the
property here ascribed to it, and that in localities where ozone is least to be
detected in air, the largest amount of permanganate will be deprived of its
color. At the same time, the results are open to the objection that sul-
phurous acid, sulphuretted hydrogen, and other volatile deoxidizing com-
pounds, will equally discharge the color of an alkaline permanganate,
whether organic matter is or is not present. Hence provision should be
made for the removal of these agents before the air is submitted to this
method of testing.

The composition of the air, excluding ammonia, organic matter, and other
casual constituents, may be thus stated, for 1000 and 100 parts by volume
respectively : —

In 1000 vols. In 100 vols.

Oxygen 208-0 20-80

Nitrogen 777-0 77-70

Aqueous vapor 14-6 1-46

Carbonic acid 0-4 0-04

1000-0 100-00

AIR. UNIFORMITY OP COMPOSITION. 165

Hie air, not a chemical compound. — The proportions of oxygen and nitro-
gen nearly approach to 1 vol. or 2 eq. of oxygen, and 4 vol. or eq. of nitrogen.
This ratio, however, would give a percentage of 20 of oxygen to 80 of nitro-
gen, proportions that are never found. The gases are therefore not com-
bined in equivalents, either by weight or volume. As an additional proof
that the air is a mere mixture, the following experiments may be adduced.
Remove the oxygen from ajar of air by phosphorus or iron-filings, and then
restore the loss by an addition of pure oxygen. The gases will diffuse or
enter into mixture without any of the phenomena that accompany chemical
union, and a candle will burn in this mixture, as it does in air. There is no
alteration in volume, no evolution of heat or light, and the specific gravity,
magnetism, refractive power, and solubility in water, of this mixture, cor-
respond to the mean specific gravity, and other properties of the constitu-
ents. The solvent power of water is such as would be exercised upon a
mixture, and not upon a chemical compound of the two gases. Thus oxygen
is dissolved in larger proportion than nitrogen, and the difference nearly
corresponds to the difference existing in the solubility of the two gases, in
their separate states. Thus, according to Regnault, of 100 parts of air
dissolved by water, the oxygen is to the nitrogen as 32 to 68, instead of
20*8 to 792 ; while the solubility of each gas gives a calculated proportion
of 31-5 to 68-5. Thus:—

Calciilated Actual

Solnbility. Solubility. Solubility.

Oxygen . . . 0-046 (0 = 0-0092 or 31-5 32

Nitrogen . . . 0-025 (t) = 0-0200 or 68-5 68

Air in water 100- 100

Lastly, metals and metalloids act upon air in the same manner as if the
gases were free. Potassium, sodium, lead in the melted state, phosphorus,
and deutoxide of nitrogen, take the oxygen of air, just as they take oxygen
in the free or uncorabined state.

It has been supposed that the comparative uniformity of composition iu
all parts of the globe, and at all elevations above the sea, could only admit
of explanation on the theory that the two gases were chemically combined.
The laws of diffusion, however, sufficiently account for the uniformity of
mixture (page 85), while at the same time, the ascertained differences in the
proportions of oxygen and nitrogen are not reconcilable with the theory of
their being chemically united. Taking the proportion of oxygen by weight
elsewhere given (page 161), namely, 23 1 parts in 100, the following are
comparative results of the analysis of air in different localities : —

Wt. of 0.

Wt.ofO.

per cent.

per. cent.

Paris (April to Sept. 1841)

23-07

Guadaloupe (W. I.)

. 22-97

" another observation

23-13

Copenhagen

. 23-01

Bern (Switzerland) .

22-95

Elsinore .

. 23-03

Faulhorn (18,800 feet) .

22-98

German Ocean .

. 22-86

Other comparisons may be instituted in reference to its composition by
volume. Assuming the average proportion of oxygen by volume to be
2080, the following results have been obtained :

Vol. of 0. Vol. of 0.

per cent. per cent.

Paris .... 20-93 Mont Blanc (6000 feet) . 20-20

London level of sea . . 20-92 " summit (16,000 ft.) 20-96

" 18,000 ft. elevation 20-88 Simplon (6000 feet) . 19-98

Heidelberg . . . 20-95 Waugen Alp (4000 feet) . 20-45

166 ' PROTOXIDE OF NITROGEN.

Vol. of 0.

Vol. of 0

per cent.

per cent.

Berlin

. 20-90

Aerial ascent (9000 feet) .

. 20-70

Madrid .

. 20-91

In Manchester .

. 20-88

Geneva .

. 20-90

In open places .

. 21-10

Lyons

'. 20-91

In open country

. 21-00

Helvellyn (3000 feet)

. 20-58

In crowded rooms .

. 21-42

Snowdon (3570 feet)

. 20-65

Polar sea ...

. 20-85

During the period of about sixty years, within which accurate analyses of
the atmosphere have been made, there has been no greater difference in the
proportions of its constituents, than that which is above shown to exist
between any two localities at the present time. There has been no apparent
diminution in the amount of oxygen and nitrogen.

Tests for Air. — These are necessarily included in the tests for oxygen and
nitrogen. The presence of nitrogen so affects the combustion of bodies in
air, that the burning of a candle furnishes a good test of the atmospheric
mixture. The red acid vapor produced by adding to air, deutoxide of nitro-
gen, and the entire removal of oxygen by the pyrogallate of potassa, with the
negative properties of the residuary gas, nitrogen, are sufficient to identify
the mixture under all circumstances.

CHAPTER XIII.

COMPOUNDS OF NITROGEN AND OXYGEN. NITRIC ACID.

There are five compounds of nitrogen and oxygen — two neutral gases
and three acids. In these compounds the equivalents of oxygen undergo a
regular arithmetical increase.

They are as follow : —

Nentral. Acid.

Protoxide NO Hyponitrous acid NO3

Deutoxide NOg Nitrous acid NO^

Nitric acid NO.

1, Protoxide of Nitrogen. Nitrous Oxide (NO). — This gaseous com-
pound was discovered by Priestley in 17t6: but its properties were not
fully known until after the researches of Davy in 1800.

Preparation. — The gas may be procured by heating in a glass retort the
crystals of pure nitrate of ammonia. The temperature should not exceed
400°, and the salt, which speedily melts, should be kept in a state of gentle
ebullition. The gas, being very soluble in water, in order to prevent loss,
should be collected in a small water-bath, containing tepid water. In this
case, however, it always becomes mixed with much air on cooling. The salt
is entirely resolved by heat into water and protoxide (NHj,HO,N05,=2NO
-f 4H0). One ounce of the nitrate will give 500 cubic inches, or nearly two
gallons of the gas.

If, during the process, the liquefied salt should be overheated, the gas
comes over with explosive violence, sometimes breaking the retort, or leading
to the production of nitrogen as well as deutoxide, and thereby rendering it
impure. The production of copious white vapors in the retort is a sign
that the proper heat has been exceeded. If the nitrate contains hydro-
chlorate of ammonia, chlorine may be evolved, and impart to the gas its pecu-

PROTOXIDE OF NITROGEN. IGY

liar odor as well as bleaching properties. The presence of hydrochl orate in
the nitrate of ammonia may be known by the solution of this salt giving a
white precipitate with a solution of nitrate of silver. If any deutoxide of
nitrogen is mixed with the gas, this may be detected by the production of
red acid fumes on exposing the gas to the air, or by the dark color imparted
to a fresh solution of protosnlphate of iron when added to a jar of the gas.
If the protoxide is intended for respiration, it is necessary, in the first in-
stance, to test it for these noxious impurities. It may be deprived of any
traces of chlorine and deutoxide by passing it through a solution of potassa
before collecting it.

Properties. — Protoxide of nitrogen is not a permanently elastic gas. It
may be liquefied by great pressure (p. 80). The liquid protoxide mixed
with sulphide of carbon produces, by rapid evaporation, the greatest degree
of cold yet observed ; namely, 220° below the zero of Fahrenheit (p. 80).
The gas itself is solidified at about 150*^ below zero. The cold produced
by the evaporation of the liquid protoxide, placed in vacuo, is sufficient to
solidify it ; under atmospheric pressure it evaporates slowly. Liquid mer-
cury sinks in it and is instantly frozen to a solid. A piece of red-hot char-
coal will at the same time float on it, and burn brilliantly wherever it touches
the liquid. The gas is colorless ; it has a slight odor and a sweet taste. It
is soluble in water, and this solubility leads to a great loss of the gas when
it is allowed to stand in contact with water. Cold water will dissolve about
its own volume, but the gas will be again given out on boiling the solution.
Its admixture with air may thus be known, as the gas should be entirely
removed by its volume of water. It is quite neutral when pure; it neither
reddens nor bleaches litmus.

As it contains half its volume of oxygen it possesses some of the proper-
ties of that gas, modified, however, by the presence of nitrogen. Thus it
supports combustion. A taper burns in it vividly, and is rapidly consumed.
Like oxygen, it kindles into flame a glowing wick, a glowing splint of wood
or ignited nitre-paper. Sulphide of carbon or ether inflamed on tow, and
introduced into this gas, burns with great splendor. In these cases there is
a halo of a peculiar reddish color around the flames, arising probably from
the combustion or incandescence of nitrogen at a high temperature. Sulphur
and phosphorus require to be strongly heated before they will burn in this
gas. Iron does not burn in it, and charcoal only glows in it when intensely
heated, producing carbonic acid. It differs from oxygen — 1st, in its great
solubility in water; and 2d, when free from air, in the fact that it produces
no red fumes when the deutoxide of nitrogen is added to it. This gas is a
narcotic poison, and, when breathed, rapidly destroys the life of an animal.
It may, however, be taken by a human being in limited quantity ; and if the
lungs be emptied before it is inhaled, it rapidly causes a peculiar species of
intoxication, manifested at first by unsteadiness of gait, and subsequently by
violent muscular exertion. There is a brilliant flow of ideas, with, generally
speaking, a great disposition to pugnacity. From the pleasing kind of deli-
rium which it produces it has been called " the laughing or paradise gas."
When breathed, it is rapidly absorbed into the blood, and produces a great
change in that fluid — manifested by a dark-purple color of the lips, and by
a livid or pallid appearance of the face. Some have fallen down at once
powerless, but the greater number are thrown into a state of violent excite-
ment, running swiftly from the spot and scattering everything before them.
Some dance, others sing, and some make speeches of an incoherent kind,
evidently under the impression that they are masters of elocution. An in-
stance is referred to by Sir David Brewster, in which the effects were mani-
fested by an uncommon disposition for pleasantry and mirth, and by extra-

I

168 DEUTOXIDE OF NriROGEN.

ordinary innscular power, in a person of gloomy mind. The effects continued
in a greater or less degree for more than a week. In general the exhilarating
effects pass off in from five to ten minutes, and, with the exception of some
prostration of strength and slight headache, no injurious symptoms have
followed. It is right to state, however, that in certain cases, probably from
idiosyncrasy, the respiration of the gas has been attended with severe head-
ache, giddiness, double vision, and even some delirium, wi^i a feeling of
weakness from exhaustion lasting for several days. It is not to be regarded
as an anaesthetic, like chloroform or ether-vapor. It is a powerful excitent
and stimulant to the nervous system.

Composition. — At a full red-heat this gas is decomposed, and two volumes
of it are resolved into two volumes of nitrogen and one volume of oxygen,
so that it acquires an increase of bulk. The analysis of the gas may be
effected by detonation with hydrogen. When a mixture of one volume of
the protoxide and one volume of hydrogen is fired by the electric spark,
water is produced, and one volume of nitrogen remains (NO 4-11=110 -j-N).
Now, as one volume of hydrogen takes half a volume of oxygen to form water,
the protoxide must consist of one volume or equivalent of nitrogen and
half a volume or an equivalent of oxygen; these being so condensed, in con-
sequence of chemical union, as only to fill the space of one volume. The
decomposition of one volume of the gas, by heating in it the metal potassium,
gives the same results. One volume of nitrogen is left as a residue.

Atoms. Equiv. Per cent. Vol. Sp. Gr.

Nitrogen . . . . 1 = 14 ... 63-6 ... 1-0 ... 0-97
Oxygen . . . .1=8... 36*4 ... 0-5 ... 0-55

Protoxide of nitrogen . . 1 22 100-0 1-0 1-52

The specific gravity and equivalent of this gas are the same as those of
carbonic acid. One hundred cubic inches of it weigh 47 08 grains. It is,
therefore, half again as heavy as the atmosphere. If a lighted taper be
placed at the bottom of a tall jar of air, the gas may be poured into this jar,
and the fact that it falls to the bottom, will be indicated by the increased
brilliancy in the combustion of the taper. If a tall jar containing the gas,
be left uncovered for some time, it will be found, by occasionally introducing
a taper with a glowing wick, that this will be kindled into flame, proving
that, by reason of its density, the gas still remains there. So if ignited
nitre-pajier be brought over a jar of the gas, the smoke, instead of suddenly
falling through it as through air, will float in the form of a dense cloud on
the top of the gas.

This gas enters into no combinations which call for remark. It has been
artificially produced by the slow deoxidation of nitric acid, as where one
part of nitric acid is diluted with from 12 to 16 parts of water, and some
granulated zinc is added to the liquid.

Tests. — The properties already described are sufficient for its identification.
It is known from all other gases, excepting oxygen, by its effects .on com-
bustible bodies, and from oxygen by the negative action of deutoxide of
nitrogen and its insolubility in a solution of green sulphate of iron.

Deutoxide of Nitrogen (NOJ. — Binoxide of Nitrogen. Nitric Oxide.
Nitrous Gas. — This gas was first accurately described by Priestley in 1772.
It may be procured by putting some copper-filings or clippings into a gas-
bottle with nitric acid diluted with two or three parts of water ; the acid is
decomposed, red fumes are produced, and there is a copious evolution of the
gas, which may be collected and preserved over water. In this mode of

PROPERTIES OF THE GAS. 169

obtainiiip: the gas, 3 atoms of copper and 4 of nitric acid produce 3 of nitrate
of copper and 1 of nitric oxide, 4N05 + 3Cu = 3[CuO,XOJ + N02. The
first portions should be rejected, as containing nitrogen and nitrous acid
vapor. The latter being soluble in water is speedily removed. Protoxide
of nitrogen is frequently present in the gas when first prepared. This may
be removed by allowing it to stand for some hours over water.

Properties. — The deutoxide of nitrogen is a colorless, neutral, unliquefiable
gas; its specific gravity compared to hydrogen is as 15 to 1. 100 cubic
inches weigh 32-10 grains ; and, compared with air, its specific gravity is as
10366 to 1000. Under common circumstances, it is permanent over water;
but if agitated with water previously deprived of air by long boiling, it is
dissolved in the proportion of about 1 volume to 20. This solution, when
long kept, is found to contain nitrate of ammonia, resulting from the joint
decomposition of the deutoxide and the water.

It is rapidly fatal to animals; but as it will always meet with a sufficiency
of oxygen in the lungs, to convert a part of it into nitrous acid, the noxious
effects observed may have depended on this acid. When the gas has been
well washed with water, it is not acid, a fact which may be proved by the
color of litmus remaining unchanged by it. The experiment may be thus
performed : After having washed the jar (which should contain no water),
and the plate which confines the gas, introduce it into a basin of blue litmus,
and withdraw the cover. The gas may thus remain in the litmus without
altering the blue color ; but when the jar is raised out of the liquid, so as to
admit a portion of air, red acid fumes are produced, and upon again plunging
it into the litmus, the liquor will be reddened and the acid vapors absorbed.
The red fumes which are formed when the gas is exposed to air are those of
nitrous acid (N02 + 20 = NOJ. They have a peculiar suffocating odor, and
are highly irritating and corrosive. Care should be taken that they are not
breathed, even in a diluted state.

The gas, if free from protoxide, extinguishes the flame of a taper, ignited
camphor, and sulphur. Phosphorus readily burns in it if introduced in
intense ignition; but it is extinguished unless in vivid combustion, and it
may be touched with a hot wire in the gas, without taking fire. Boiling
phosphorus decomposes the gas, nitrogen is evolved, and phosphoric acid
is formed.

If dry nitre-paper is ignited and suddenly plunged into this gas, it will
continue to glow, chiefly at the expense of the oxygen of the nitrous acid,
produced when the jar is uncovered. It is remarkable that this gas should
not support the combustion of a taper, since it contains, in equal volumes,
as much oxygen as the protoxide, and only half the quantity of nitrogen. If
mixed with the protoxide, it will readily support combustion. Potassium
and sodium, when heated to ignition in air, burn in this gas with great splen-
dor : sodium burns with a light which rivals that of phosphorus. The com-
bustion may be effected by throwing a portion of the metal into a jar of the
gas having at the bottom a thin stratum of water. It is decomposed when
passed over charcoal at a red heat— carbonic acid is formed and nitrogen is
set free, NO^+C^N + COa, but neither charcoal nor sulphur will burn in
this gas. If introduced in a state of ignition they are extinguished, but the
vapor of sulphide of carbon mixed with the deutoxide and ignited, completely
decomposes it with the evolution of the most intense light, and the produc-
tion of carbonic and sulphurous acids at the expense of its oxygen, (3NO2+
CSa=2S03+COa+3X). For the performance of this experiment, we may
employ a stout jar, holding 200 cubic inches of deutoxide. About a drachm
of the sulphide should be poured into the jar, which should be agitated, in
order to promote the diffusion or the vapor before the mixture is ignited.

ITO DEUTOXIDE OF NITROGEN. COMPOSITION.

Deutoxide of nitrogen is not altered by a low red heat, but it is decom-
posed when passed and repassed through small tubes heated to bright red-
ness, especially if the heated surface is increased by filling the tubes with
fragments of rock crystal, or by the introduction of platinum wire. It does
not detonate when mixed with two volumes of hydrogen, all subjected to the
electric spark ; a succession of sparks, however, passed through such a mix-
ture, slowly effects the decomposition of a portion. The pure gas is itself
partially decomposed by a succession of sparks into nitric acid and nitrogen.
When mixed in equal volumes with hydrogen, and the mixture is kindled, it
burns with a greenish-white flame and a reddish-colored halo : but there is
no explosion. Water is produced and nitrogen is set free (N03-f2H =
2H04-N) When a mixture of 2 volumes of this oxide and 5 of hydrogen
are passed through a tube containing spongy platinum, and after the expul-
sion of the air, the tube is heated, the platinum becomes ignited, and water
and ammonia are formed (N02,-f 5H = NH3,2HO). An inflamed jet of
hydrogen is extinguished in the gas. Some substances which have a strong
attraction for oxygen, effect a partial decomposition of the deutoxide, and
convert it, at common temperatures, into the protoxide of nitrogen ; such,
for instance, as moist iron-filings, some of the alkaline sulphides, some of
the sulphites, and protochloride of tin ; in these cases two volumes of the
deutoxide produce one of the protoxide. Deutoxide of nitrogen may also
be decomposed, at high temperatures, by the action of some of the metals
which absorb its oxygen. Sir H. Davy decomposed it by heated arsenic
and by the ignition of charcoal. {Elements, 260.) Gay-Lussac decomposed
100 measures of it by the action of heated potassium ; 50 measures of pure
nitrogen remained, and the loss of weight corresponded to 50 measures of
oxygen ; so that two volumes of the gas are resolved into one volume of
oxygen and one volume of nitrogen. Similar results have been obtained
by passing the gas over copper turnings heated to redness in a tube. The
deutoxide then is constituted of one volume of nitrogen and one volume of
oxygen, combined without change of volume ; and its atomic constitution
as well as its specific gravity may be thus represented : —

Nitrogen
Oxygen

Atoms. Equ.

. 1 = 14 .
. 2 = 16 .

. 1 = 30

Per cent.

.. 46-67 .
.. 53-33 .

100-00

Vols.

.. 1 ..
.. 1 ..

2

Sp. Gr.

. 0-4837
. 0-5528

Deutoxide .

1-0365

Pliicker has submitted this gas to spectral analysis, in a quantity so
small as to be scarcely recognizable by the most sensitive balance. The
red band of nitrogen was obtained in great splendor, and near to it was a
bright band derived from the oxygen ; but the latter was gradually extin-
guished. A similar result was obtained with protoxide of nitrogen.

The most characteristic chemical property of this gas, by which it is
immediately distinguished from all other gases, is that of forming red fumes,
chiefly of nitrous acid vapor, when mixed with air or oxygen (^02+20 =
NO4) ; hence these gases are mutually used to detect each other's presence.
As nitrous acid is absorbed by water, oxygen may be abstracted from any
gaseous mixture containing it by the addition of a sufficient quantity of the
deutoxide; and, on the other hand, the deutoxide may be removed by the
addition of oxygen.

Solutions of the protochloride and protosulphate of iron dissolve this gas,
forming a deep greenish-black liquid, having, in reference to the sulphate,
the following composition, (4FeO,S03)-|-N03. These solutions speedily
absorb oxygen when exposed to, or agitated with air, or other mixtures

HYPONITROUS ACID. Itl

containing it. {See page 161.) This property enables us to ascertain the
purity of the deutoxide, which ought wholly to be absorbed by the solution
of iron : some nitrogen or protoxide is thus generally detected in it, by
remaining unabsorbed. According to Peligot {Aim. Ch. et Ph., 54,
17), the proportion of the gas absorbed by protosulphate of iron is
definite, and in the ratio of one equivalent to 4 of the protoxide of iron, in
accordance with the formula above given. By exposure to a vacuum the
gas escapes, and the salt of iron remains unaltered ; but when heated, a
part only of the gas is evolved, and a part is decomposed, while peroxide of
iron and ammonia are formed. When this solution is exposed to air or
oxygen, nitric acid is ultimately produced.

If the deutoxide is perfectly dry, chlorine exerts no action upon it, but
the presence of water causes an immediate change ; it is decomposed, and,
furnishing oxygen to the nitric oxide, and hydfogen to the chlorine, hyponi-
trous and hydrochloric acids are generated. It was the presence of water
which misled those who thought that the red fumes produced by mixing
deutoxide and chlorine over water, resulted from the existence of oxygen in
chlorine. These may, however, arise from the presence of air as impurity in
the chlorine.

Tests. — This gas is known by the red acid fumes which it produces when
brought in contact with air, and by its entire solubility in a solution of
protosulphate of iron.

Hyponitrous Acid (NO3). Azotous Acid. Nitrous Acid. Nitric Ter-
oxide. — This compound is generally designated by continental chemists.
Nitrous acid. Gay-Lussac found by mixing deutoxide of nitrogen and
oxygen in tubes standing over mercury, and containing a little concentrated
solution of potassa, that 400 volumes of deutoxide were condensed under
such circumstances by 100 of oxygen. When, however, he attemped to
decompose the hyponitrite of potassa thus obtained, nitric oxide was evolved,
aud nitrous acid formed. Dulong obtained hyponitrous acid (mixed with
nitrous acid) by passiug a mixture of 1 measure of oxygen with somewhat
more than 4 of deutoxide, first through a tube filled with fragments of
porcelain to insure perfect mixture, and afterwards through a bent tube,
cooled below zero. The acid collected in the tube was a dark -green fluid,
more volatile than nitrous acid, and when distilled leaving a yellow liquid,
which appeared to be nitrous acid. Liebig obtained hyponitrous acid by
heating 1 part of starch in 8 of nitric acid, sp. gr. 1 -25, and conducting the
evolved gases first through a tube filled with fragments of chloride of calcium,
and then into a tube cooled down to 0^ ; ,a very volatile liquid was thus
condensed, colorless at 10^, but green at common temperatures. According
to Fritzsche, hyponitrous acid may be obtained by gradually adding, by
means of a tube drawn out to a fine point, 45 parts of water (5 atoms) to 92
parts of nitrous acid (2 atoms) cooled down to zero, and distilling into a
receiver, surrounded by a freezing mixture, until the boiling-point rises to
82°. The product is of an indigo-blue color. Its vapor is orange-colored,
and its boiling point rises to 82° ; but when distilled, it is partially decom-
posed into deutoxide and nitrous acid. It is very doubtful whether, by any
of these processes, the acid has been yet obtained in an absolutely pure state.
It appears to be generally mixed with nitrous or nitric acid. Its"instability
is so great, that it is decomposed by water (3N03=N054-2N03) into nitric
acid and deutoxide. It is better known in combination with bases, and its
composition has been determined by the analysis of its compound with silver.
It consists of : —

172 NITROUS OR HYPONITRIC ACID.

Atoms. Equiv. Volumes. Volumes.

Nitiocen . .. 1 ... 14 ... 36-8 1 or 2 ) Deutoxide 4

l]=

Oxygen . . . 3 ... 24 ... 63-2 IJ or 3 j ~ Oxygen 1
Hyponitrous acid . 1 38 100-0

Hyponitrites {Nitrites). — When nitrate of potassa, or nitrate of baryta is
strongly heated, the acid loses two atoms of oxygen, and a hyponitrite of the
base is formed : KO,NO.=KO,X034-20. When properly prepared, a small
portion of the fused residue, will give a dense white precipitate, with a solu-
tion of nitrate of silver. If the salt has been overheated, the precipitate will
be brown. Hyponitrite of potassa thus obtained, is a white deliquescent salt,
very soluble in water and alcohol. By its solubility in alcohol, it may be
separated from any undecomposed nitrate. The white precipitate which it
produces with nitrate of silv^, is soluble in nitric acid as well as in a large
quantity of water. It may be obtained in crystals from a hot saturated solu;
tion. By double decomposition with the chloride of any alkaline metal,
other hyponitrites may be obtained. It is impossible to procure hyponitrous
acid in a free state from these salts. When an acid is added to a hyponitrite,
deutoxide of nitrogen escapes, and a nitrate is formed (3KO,N03-f2S03 =
KO,N05+2N03+2KO,S03). If an acid solution of a hyponitrite is warmed,
it becomes a powerful deoxidizer ; thus it discharges the pink color of the
permanganate of potassa, peroxide of manganese being formed. From a
solution of chloride of gold, the metal is precipitated; the color of a solution
of indigo is discharged by it, and a solution of protosulphate of iron acquires
a deep greenish-black color. The hyponitrites are thus easily distinguished
from the nitrates, by the action of acids, and by their reducing agency on
solutions of gold and permanganate of potassa. Some of the hyponitrites
may be produced by the action of deutoxide of nitrogen on the respective
alkaline liquids. Thus when this gas is kept for some weeks in contact with
a strong solution of potassa, it is converted into protoxide, and the potassa-
solution yields on evaporation a hyponitrite (2N03+KO=KO,N03-f NO).
It was this reaction which led Gay-Lussac to the discovery of the acid. 100
volumes of deutoxide left 25 of pi'otoxide : the acid, therefore, which was
absorbed, consisted of 100 volumes of nitrogen and 150 of oxygen. Accord-
ing to Berzelius, several of the hyponitrites are best obtained by boiling
metallic lead in a solution of nitrate of lead, by which a hyponitrite of lead
is formed : this salt may then be decomposed by sulphates, which form sul-
phate of lead, and the hyponitrous acid unites to the base of the original
sulphate. Mitscherlich prepares the hyponitrites by the mutual action of
soluble chlorides and hyponitrite of silver. {See Silver.)

Nitrous Acid (NO^). Hyponitric Acid. Hypoazotic Acid. , Peroxide
of Nitrogen. Nitric Tetroxide. — When 2 volumes of deutoxide of nitrogen
and 1 volume of oxygen, dried by potash, are mixed in an exhausted glass
vessel, the gases combine with the evolution of heat consequent upon their
mutual condensation, and form tiitrous acid vapor, which is condensable into
a nearly colorless liquid at zero, and crystallizes at a somewhat lower tem-
perature. The specific gravity of this liquid is 1 45 ; at 32° it is of a pale
yellow color; but at 60° deep orange : it boils at 82° (Gay-Lussac) ; and
when exposed to the air at common temperature, gradually evaporates in
orange-red fumes. When a mixture of the gases, in the above proportions,
is propelled through a tube cooled to 20°, the liquid acid is at once obtained ;
but at 16° it crystallizes in prisms. If the gases be mixed over water,
hyponitrous acid and nitric acid are formed at low temperatures, (2N0.j=
NOg-fNOJ; and at higher temperatures nitric acid and deutoxide are the
results (3NO^=2N05-f NOJ. The product of the distillation of dry nitrate

NITROUS ACID. 113

of lead appears to be nitrons acid, nearly, if not qnite, pure and anhydrous
(PbO,N05=N044-PbO-fO). The powdered nitrate, previously well dried,
should be put into a small retort, with the beak drawn out, and introduced
into a small tube receiver, which should be immersed in a freezing mixture.
A strong heat is required for the distillation, and when a sufficient quantity
of the liquid acid has been collected, the tube may be sealed by applying the
flame of a spirit-lamp to the elongated neck. It can only be preserved in
sealed tubes.

Properties. — Nitrous acid vapor supports the combustion of phosphorus
and of charcoal, but extinguishes burning sulphur. These experiments may
be performed on the vapor procured by passing a jet of oxygen into a jar,
or bell-glass, filled with deutoxide of nitrogen, until the mixture acquires an
orange-red color. A lighted taper, as well as ignited nitre-paper, glow in
this vapor, and continue to burn. The oxitmiiig properties of the acid
vapor, and its power of destroying foul effluvia, may be shown by inverting
over a jar of it, another containing sulphuretted hydrogen gas. The sulphur
is separated with evolution of great heat (NO^-f 2HS = N03-|-2HO-f 2S).
A solution of iodide of potassium is instantly decomposed by it, an# the
iodine set free. A diluted solution of permanganate of potassa has its pink
color discharged by it as a result of deoxidation.

Its color, like that of the liquid acid, varies with the temperature, becom-
ing darker when heated, and paler when cooled ; it has a peculiar sufi"ocating
odor, which strongly adheres to the hair and to woollen clothing. The
anhydrous liquid has no acid properties, and does not apparently unite with
bases, but forms with them hyponitrites and nitrates (2N04 + 2KO=KO,
K05-l-K0,Is03) ; hence it has been regarded as a peroxide of nitrogen, or a
compound of hyponitrous and nitric acids (2N04=N03+N05). When
passed over baryta or other bases, at a temperature of between 300° and
400°, it is rapidly absorbed with the evolution of heat, and the products are
a nitrate and a hyponitrite. (Gay-Lussac, Ann. Ch. etPh., 1.)

Nitrous acid vapor is constituted of 1 volume of nitrogen, and 2 volumes
of oxygen, condensed into 2 volumes, or, as above stated, 2 volumes of
nitric oxide, and 1 volume of oxygen (NO^j-f 20=N0J. Its specific gravity,
therefore, to hydrogen, will be as 46 to 1 ; to air, as 1-689 to 1. It is
actually found to be 1*7. It is constituted of: —

Atoms. Equ. Per cent. Vols. Sp. Gr.

Nitrogen . . . . 1 ... 14 ... 30-4 ... 0-5 ... 0-4837
Oxjgen . . . . 4 ... 32 ... 69-6 ... 1-0 ... 1*1057

Nitrpus acid ... 1 46 100-0 ... 1- 1-5894

Nitrous acid vapor is not decomposed by a red heat, but it is a powerful
oxidizer, and parts with its oxygen readily to sulphur, phosphorus, and the
metals. When the acid vapor is passed over metallic copper heated to
redness, it gives up its oxygen entirely and nitrogen escapes. By this process,
its composition has been accurately determined. The acid is decomposed by
water, when this liquid is in large proportion, nitric acid being dissolved
and deutoxide of nitrogen escaping (3N0,-f 2H0 =N02+N05,H0).
When the quantity of water is small, although the same products result,
the nitric acid holds the nitrous acid dissolved, and acquires, according to
its specific gravity, a variety of colors. Nitric acid of a high specific gravity
appears to be the proper solvent of this compound, l^ns when saturated
with it, nitric acid of a specific gravity of 1-510 is of a deep orange color,
at 1-410 {aquafortis of commerce), yellow, at 1*320 greenish -blue, at 1-150

174 ANHYDROUS AND HYDRATED NITRIC ACID.

colorless. In the latter case, the quantity of water is so great as to decom-
pose the nitrous acid in solution, and to transform it into colorless nitric acid.

Although this acid does not combine directly with alkaline bases, it forms
a series of remarkable compounds with organic bases. M. Martin's re-
searches have shown that some varieties of gun-cotton, or pyroxyline, are
compounds of nitrous (hyponitric) acid, with this substance as a base. The
fulminating compound contains 5 equivalents of the acid, while the photo-
graphic cotton contains 4. The compound with 3 equivalents of the acid is
of a pulverulent nature, and when dissolved in alcoholic ether, leaves an
opaline residue on evaporation ; while another compound with 2 equivalents
of acid is known by its solubility in water. {Cos7nos,Jmn 28, 1861, p. 769.)
The large amount of oxygen contained in this acid accounts for the great
combustibility of the first of these compounds.

Nitric Acid (NO5)- NiPic Pentoxide. Azotic Acid. — In its monohy-
drated state its formula is H0,N05, or H,N06. The composition of this
acid was first demonstrated by Cavendish, in 1185. He produced it by
passing a succession of electric sparks through a mixture of 1 volumes of
oxy^l^ and 3 of nitrogen. This result has been verified* by Faraday {Ex-
perimental Researches, 3d series, § 324), in reference to the appearance of
minute quantities of nitric acid in the rain water of thunderstorms. Nitric
acid is also formed when deutoxide of nitrogen is slowly added to an excess
of oxygen gas, over water. In this way 4 volumes of deutoxide of nitrogen
are condensed, and they combine with 3 volumes of oxygen. (N02-4-Og=

Anhydrous Nitric Acid. — Nitric Anhydride (NO^) was discovered by
Deville, in 1849. {Ann. Ch. et Ph., 3me ser. vol. 28, p. 241.) He obtained
it by passing dry chlorine over dry nitrate of silver, placed in a U-tube, and
heated to 303°. The temperature is lowered, when chemical action com-
mences to between 136° and 154°. The products are chloride of silver,
oxygen, and anhydrous nitric acid (AgO,N05+Cl=N05+AgCl-|- 0).
Some nitrous acid is at first evolved, but at the low temperature, crystalline
anhydrous nitric acid is volatilized and may be condensed in a second tube,
surrounded by ice. There are many precautions requisite to insure the
success of this operation; no organic matter, such as cork, &c., should be
used in the apparatus.

Anhydrous nitric acid crystallizes in colorless rhombic prisms. The crys-
tals fuse at about 85°: and the liquid boils and is decomposed at 113°.
They dissolve in water, producing great heat, but no gas is disengaged.
The crystals, like those of other anhydrous acids, have no acid reaction until
dissolved {see page 42). They are liable to be decomposed with explosion
at the common temperature, being suddenly converted into oxygen and
nitrous acid.

Hydrated Nitric Acid, Hydric Nitrate. Preparation. — (HO, NO J is
usually obtained by the distillation of purified nitre with sulphuric acid.
The nitric acid of commerce, which is generally red and fuming, in conse-
quence of the presence of nitrous acid, is procured by the distillation of 2
parts of nitre with 1 of sulphuric acid ; these proportions yield about 1 part
of orange-colored nitric acid of the specific gravity of 1-48. Some manu-
facturers employ 3 parts of nitre and 2 sulphuric acid. The British Phar-
macopoeia directstwo pounds (avoirdupois) of nitrate of potash, and seventeen
fluidounces (Imperial measure) of sulphuric acid. In all cases the sulphuric
acid should be in l^ge proportion, if we desire to obtain a colorless product,
and care should be taken that the distillation is carried on at the lowest
possible temperature. Nitrate of soda being cheaper than nitrate of potash,
is frequently resorted to as a source of nitric acid. As nitre generally

PROPERTIES OF NITRIC ACID. 1Y5

contains a little sea salt, the first portions of acid which come over are im-
pure, containing chlorine or hydrochloric acid and nitrous acid, but they serve
to wash quite clean the neck of the retort, ou which some sulphuric acid is
commonly to be found, in spite of all our care, as well as traces of powdered
nitre ; it is best, therefore, to collect the first portion, say one-tenth of the
whole, in a separate receiver, and when the liquid that drops is found to be
free from chlorine (by the test of nitrate of silver), the receiver may be
changed, and the rest of the nitric acid obtained quite pure, or, at most,
slightly tinged by nitrous acid. When 2 equivalents of sulphuric acid (oil
of vitriol) to 1 of nitre are used, the results are 1 equivalent of hydrated
bisulphate of potassa and 1 of monohydrated nitric acid ; KO,N05 + 2[HO,
SOJ=K6,HO,2S03-f H0,N05. When 100 parts of nitre, 96-8 of oil of
vitriol, and 40'45 of water are mixed and distilled, at 2G6° to 270°, nitric
acid, of specific gravity 14, passes over during the whole process. (Mit-

BCHERLICH.)

Oil of vitriol of the sp. gr. 1*84, contains one equivalent of dry sulphuric
acid and one of water ; whereas liquid nitric acid usually contains one equiva-
lent of dry acid and two of water : hence the requisite excess of oil of vitriol,
when colorless and pure nitric acid is to be obtained ; hence, too, the red
color of the acid of commerce, in consequence of the smaller quantity of oil of
vitriol generally used by the manufacturer, the deficiency of water causing
the nitric acid to be resolved into nitrous acid and oxygen.

The nitric acid, or aquafortis of commerce, is always impure, and hydro-
chloric and sulphuric acids may generally be found in it. The former may-
be detected by nitrate of silver, or by boiling in it gold leaf, when if this
impurity exists the gold will be dissolved. Sulphuric acid may be detected
by a diluted solution of nitrate of baryta. If, however, pure nitre and pure
sulphuric acid be employed in its production, and the latter not in excess,
there is little apprehension of impurity in the resulting acid. If the acid is
colored by the presence of nitrous acid, it is rendered colorless by boiling,
which is best performed in a retort, with a loosely-attached receiver ; the
nitrous acid passes off. If it contain hydrochloric acid, this is also decom-
posed by boiling, and chlorine escapes. Iron may generally be detected in
the common acid by the usual test, ferrocyanide of potassium. The acid
should be diluted and neutralized before applying the test. If pure, nitric
acid should leave no residue on evaporation.

Properties. — Pure nitric acid is a colorless liquid, very acid and corrosive,
acting powerfully upon organic substances. Its specific gravity, as usually
obtained, fluctuates between 1-4 and 1-5. At 24*7°, when of the specific
gravity 1-42, it boils and distils over as a hydrate (N0s,4H0) without
change, but the diluted acid is strengthened by boiling ; and the strongest
acid boils at a lower temperature (184°) than that which is of a lower spe-
cific gravity.

At— 40° the concentrated acid is congealed. When diluted with half its
weight of water, it freezes at about — 2°. When the acid of 1-45 is exposed
to the air, it exhales fumes of a peculiar odor, and gradually absorbs water,
so that its bulk becomes increased, and its specific gravity diminished. It
suffers a partial decomposition when exposed to light, becoming yellow and
evolving oxygen, so that it should be kept in a dark place, and especially
excluded from the direct rays of the sun (NO^-j-O). Nitric acid, of the
sp. gr. 1-5, mixed with one-half its bulk of water, occasions an elevation of
temperature in the mixture=:112° : 58 parts of the acid with 42 of water,
both at 60°, give, on mixture, a temperature of 140°. On diluting the red
fuming acid, it assumes a green color— the tint depending upon the quantity
of water added.

176 NITRIC ACID. CHEMICAL PROPERTIES.

Anhydrous nitric acid is composed of—

■

A torn. s.

Nitrogen 1 ..

Oxygen 5 ..

Equ.

. 14

. 40

Per cent.
.. 25 9

... 74-1

(Ueville.)
.. 25-4
.. 74-6

54 100-0 100-0

The liquid nitric acid in its utmost state of concentration (sp. gr. 1*520)
consists of 1 equivalent of anhydrous acid and 1 of water. It is a mono-
hydrate. According to Dr. lire, the acid of a specific gravity of 1*486 con-
tains 1 equivalent of real acid and two of water : —

Sp. Gr.
= 1-520.

Sp. Gr.
= 1-50.

Sp. Gr.
= 1.486.

1 54 75

2 18 25

1 72 100

Sp. Gr.

= 1-424.

1 54 85-72
1 9 14-28

1 54 80
1^ 13-5 20

1 67*5 100

1 54 60
4 36 40

1 63 100-00

1 90 100

Water

The following table, drawn- up by Dr. Ure, exhibits the quantity of dry
anhydrous acid in 100 parts at different densities {Quarterly Journal, 4, 2^7),
the quantity of anhydrous acid in the liquid acid of sp. gr. 1*50 being
assumed=797. The column of dry acid shows the weight which any salifia-
ble base would gain by uniting so as to form an anhydrous salt, with 100
parts of the liquid acid of the corresponding specific gravity.

Specific Dry acid

Specific Dry acid

Specific Dry acid

Specific

Dry acid

gravity. in 100.

gravity. in 100.

gravity. in 100.

gravity.

in 100.

1-5000 79-700

1*4228 60-572

1-3056 41-444

1*1587

22-316

1*4790 73-324

1-3882 54-196

1-2583 35-068

1-1109

15-940

1-4530 66*948

1-3477 47*820

1*2084 28-692

1*0651

9-564

Nitric acid may be decomposed by passing its vapor through a red-hot
porcelain tube ; oxygen is given off, nitrous acid vapor is produced, and a
quantity of diluted acid which has escaped decomposition, passes over into
the receiver ; it is thus proved to consist of nitrous acid, oxygen, and water.
At a white heat, oxygen, nitrogen, and water only are evolved. According
to Faraday, nitric acid does not undergo electro-chemical decomposition, but
the water only. The oxygen at the anode is always a primary result, but the
products at the cathode are often secondary, and due to the reaction of the
hydrogen upon the acid. {Phil. Trans. 1834, p. 96.)

When deuotoxide of nitrogen is agitated with concentrated nitric acid, the
acid is decomposed, and nitrous acid is formed, partly by the acquisition of
oxygen by the oxide, and partly by its loss by the acid (N02-f2N05=3N04).
Hyponitrous acid may also result (NOa+N05=N03 + N04). Various colors
are thus imparted to nitric acid, according to its density {see page 173). If
to a jar holding about 150 cubic inches of deutoxide, an ounce of strong
colorless nitric acid is added, this undergoes an immediate decomposition.
Dense orange fumes fill the jar, and the liquid acquires a deep green or brown
color. Nitric acid is so frequently a mixture of the two acids, that it has
been proposed to call it the Acidum nitrico nitrosum (NO^HOjNO^).

Some of the metals, such as copper, tin, and silver, are at first without
action on concentrated nitric acid, but become vehemently active upon the
addition of a little water. Poured upon hot iron-fillings, or melted bismuth,
zinc, or tin, nitric acid causes a combustion of the metals. In acting upon
those metals which decompose water, nitric acid gives rise to the formation
of ammonia, and nitrate of ammonia may be found by the appropriate tests
among the products. No ammonia is formed during the action of the nitric
acid on copper, lead, antimony, bismuth, mercury, or silver. These metals

NITRIC ACID. CHEMICAL PROPERTIES. lit

remove three-fifths of the oxygen, the deutoxide of nitrogen being evolved.
If the acid is much diluted, zinc and iron take four-fifths, and protoxide of
nitrogen is a product. Tin, which is without action on the concentrated
ocid, deoxidizes it completely when of lower strength, nitrous acid, deutoxide
of nitrogen, and nitrogen being set free. Nitric acid is without action on
gold and platinum at any temperature, and it has no action on aluminum
in the cold. This enables a chemist to detect the common alloys, which
are intended to imitate gold, as nitric acid immediately dissolves them with
the evolution of deutoxide of nitrogen. It is hence called the jeweller's
test. An article of jewelry, such as a ring, may be tested by rubbing it
on a surface of smooth porphyry or other hard stone. One or two drops of
the strongest acid should be added. to the metallic film thus obtained. If
gold it will remain, but if only a base alloy it will disappear. But gold may
be alloyed with nine per cent, of copper, and the acid will not afi'ect it. The
action of protosulphate of iron upon this acid is somewhat remarkable. If
a strong solution of the protosulphate be added to a small quantity of nitric
acid, the liquid acquires a dark, greenish-black color. The nitric acid parts
with three-fifths of its oxygen, and the deutoxide of nitrogen which results,
is dissolved by the sulphate (see page 1*73). The reaction of the oxide of
iron upon the acid may be thus represented, GFeO-fNO.^NOa-f SFeaOg.
The dark liquid has the composition 4(FeO,S03)-j-N03.

The facility with which nitric acid imparts oxygen, renders it a valuable
oxidizing agent. Phosphorus decomposes it at common temperatures, and
sulphur and carbon when aided by heat. A piece of glowing charcoal thrown
upon the surface of the concentrated acid, burns vehemently with the evolu-
tion of red fumes. It acts energetically (often when diluted) upon the greater
number of organic bodies, and mutual decompositions ensue. A drachm of
oil of turpentine, mixed with half a drachm of sulphuric acid, instantly bursts
into flame upon the addition of a drachm of nitric acid. Malic, oxalic, and
carbonic acids are the common products of the action of diluted nitric acid,
upon many vegetable and animal substances ; ammonia and hydrocyanic acid
are also sometimes formed. It tinges many animal substances of a yellow
color, and permanently stains the nails and skin ; it is sometimes employed
in the production of yellow patterns upon woollen goods. Its oxidizing
powers are increased by the presence of nitrous acid (NO^). Pure nitric acid
has no action on a solution of permanganate of potassa, but if it contain
nitrous or hyponitrous acid, the red color of the solution is discharged.

Tests. Nitrates. — Nitric acid is monobasic. There are no acid nitrates ;
the salts are neutral, and are represented by the formula MOjNOg. Among
the metals, there are, however, some basic salts. As the salts of nitric acid
are all soluble in water, neither its presence nor its proportion can be deter-
mined by precipitation. When uncombined, it is recognized : 1. By its
action on copper, and the production of deutoxide of nitrogen. 2. By the
solution of gold when mixed with boiling hydrochloric acid. 3. By its
discharging the color of sulphate of indigo acidulated with sulphuric acid
when the mixture is heated. 4. By its giving a dark olive green color to a
crystal of green sulphate of iron when dropped into it.

Nitric acid, when neutralized by potassa, yields long striated prisms of
nitrate of potassa, and when neutralized by soda, rhombs. Other tests for
this acid are included in those which are required for the detection of a
nitrate. 1. On adding sulphuric acid to a nitrate, colorless fumes of nitric*
acid are given off. 2. On performing this experiment in a small test-tube,
and adding a few copper-filings nitrous acid fumes arc evolved, known by
their odor, their orange-red color, acidity, and the decomposition of a mix-
ture of iodide of potassium and starch. When the quantity of nitrate is
12

178 AMMONIA.

small, this experiment should be performed in a Florence flask — starch paper
wetted with a solution of the iodide of potassium being suspended in the
neck of the flask, which should be corked. 3. Add to the nitrate, dissolved
in a small quantity of water, its volume of sulphuric acid, and when nearly
cool, add a crystal of protosulphate of iron. The crystal is encircled with a
pink or brownish-colored layer of liquid {see page 173). 4. On boiling the
nitrate with a small quantity of hydrochloric acid and a fragment of leaf-
gold, the metal is speedily dissolved. If the gold does not entirely disappear,
the fact that some portion has been dissolved, will be manifested by the liquid
acquiring a purple or dark color on the addition of a few drops of proto-
ehloride of tin. The copper test may fail to reveal the presence of a nitrate
when an alkaline chloride is present. In this case, the gold-test will be
found serviceable. The nitrates are frequently present in potable waters,
and their presence is generally indicative of the infiltration of nitrogenous
matters, and their, subsequent oxidation. They may be easily detected, with-
out separating the other salts, by the application of the gold-test to the
residue left on evaporation. 5. A solution of a nitrate, tinted blue with
sulphate of indigo, acidulated with sulphuric acid, and heated, causes a
destruction of the color.

CHAPTER XIV.

COMPOUNDS OF NITROGEN AND HYDROGEN. AMMONIA
AND ITS SALTS.

It is generally conceded by chemists that there are three compounds of
these elements — Amidogen, NHg; Ammonia, NHg ; and Ammonium, NH^;
Of these, only one has been isolated, namely, ammonia, a gaseous alkali ;
and as the two hypothetical compounds are derived from it, it is this which
will first claim attention.

Ammonia (NH3=1'7). — This is a compound alkaline gas, long known
under the name of volatile alkali. It derives its name from the temple of
Jupiter Ammon, in Libya, in the neighborhood of which sal ammoniac was
at one time manufactured. This gas is found in the atmosphere of towns in
Tery small proportion.

Preparation When nitrogen and hydrogen are mixed in the free state,

they show no tendency to combine ; they diffuse without change, and each
is separable from the other. It is only in the iiascent state that they com-
bine to form ammonia {see page 46). This gaseous compound may be
obtained from a mixture of equal parts of dry quicklime and one of dry
hydrochlorate of ammonia, finely powdered, introduced into a small retort,
and gently heated. It must be collected over mercury. Towards the latter
part of the operation, a little water goes over, which may be arrested in the
neck of the retort by the previous introduction of a piece of blotting-paper,
or of stick potassa, or it may be prevented passing over by filling up the
*bulb of the retort with powdered lime. Hydrochlorate of ammonia is a
compound of hydrochloric acid and ammonia; by the action of the lime
(which is an oxide of calcium) the ammonia is expelled in its pure and
gaseous form : the hydrochloric acid and the lime then mutually decompose

ITS PRODUCTION. PROPERTIES. 179

each other, and water and chloride of calcium are the results : CaO. + NHj,
HCl = CaCl,4-HO+NH3. The gas may likewise be procured by heating
in a retort, a saturated solution of ammonia.

Properties. — Ammonia is gaseous at common temperatures, but it may be
liquefied by a cold of — 40°, or at the temperature of 40° by a pressure of
6 5 atmospheres (Faraday, Phil. Trans., 1823, p. 196). It is most readily
obtained as a liquid by disengaging it by heat, in a sealed tube, from chlo-
ride of silver which has been previously saturated with the gas (page 80).
It forms a colorless transparent liquid, of a specific gravity of ()'76, and with
a refractive power surpassing that of water. When free from water, it does
not conduct electricity. At 103° below 0°, this liquefied ammonia became
a white, translucent, crystalline solid, heavier than the liquid.

Gaseous ammonia has a pungent and suffocating odor : it irritates the
nose, eyes, and throat, and is irrespirable ; but when diluted by mixture
with common air it is an agreeable stimulant. It converts some vegetable
blues to green, yellows to red, and reds to blue or green, properties which
belong to the bodies called alkalies. Ammonia, therefore, has been termed
volatile alkali, and the change of color thus effected by it is distinguished
from that produced by the fixed alkalies by the return of the original tint
when the paper is warmed, or after the ammonia has passed off by exposure.
Dry ammonia has no action on dry vegetable colors (page 43). (K^ne.)
As it is collected in the state of gas, it always holds sufficient water to act
upon vegetable colors. If a small jar of the gas is opened under a large
receiver, in which are suspended strips of paper colored with tincture of
turmeric, infusion of roses, a decoction of Brazil wood, and litmus reddened
by an acid, these will speedily undergo the changes of color which are char-
acteristic of an alkali. Paper stained with the yellow sulphide of arsenic is
bleached in the gas, while that which is wetted with arsenio-nitrate of silver
(mixed solutions of arsenious acid and nitrate of silver) acquires a yellow
color. It combines with the acids, and produces an important class of salts.

The specific gravity of arnmonia, compared with hydrogen, is as 8'5 to 1 ;
compared with air it as 0-5873 to 1 ; 100 cubic inches weigh 1819 grains.
The gas extinguishes flame, but it is partially burned with a yellow flame,
which does not extend to the other portions of the gas. Owing to its light-
ness, this experiment may be performed in a jar inverted. When mixed
with air, it may be burned as it issues from a capillary orifice in an atmo-
spere of oxygen. When mixed with its volume of oxygen it bsrns with a
feeble explosion. Ammonia is abundantly absorbed by chloride of calcium,
as well as by several other chlorides (chloride of silver), with which, and
with the other haloids, it forms compounds. Hence if it be required arti-
ficially to dry the gas, potassa or lime should be used.

Water, at the temperature of 60°, takes up 480 times its volume of ammo-
nia, its bulk is ihcreased (6 measures of water giving 10 of the solution),
and its specific gravity is diminished; that of a saturated solution is 0875,
water being TOOO. A saturated solution of ammonia readily floats on water.
The following table shows the quantity of ammonia in solutions of different
specific gravities (Davy, Chem. Phil, p. 268) : —

100 parts of Sp. gr. Of ammonia. 100 parts of Sp. gr. Of ammonia.
•8750 contain 32-50 -9435 contain 14-53

•9000 " 26-00 -9513 " 12-40

•9166 " 22-07 -9573 " 10-82

•9326 " 17-52 -9692 " 950

The solutions of this gas commonly met with are the three following :—

180 SOLUTION OF AMMONIA.

t

Saturated solu. Common, B. P.

S. G -875 ;..... -889 -959

Ammonia .... 32-3 26 10

Water 67-5 74 90

100- . 100 100

The solubility of the gas in water may be shown by the following experi-
ment. Fill a tube with dry ammonia, and invert it in a basin containing a
small quantity of mercury. Pour into the basin a solution of litmus just
reddened by tartaric acid. Raise the tube containing tne ammonia, so that
the mouth may be immersed in the colored liquid. The liquid will gradually
rise in the tube, and will ultimately fill it if the gas is pure. At the same
time the alkaline nature of the gas will be proved by the red liquid being
turned blue. A lighted taper applied to a small jar of the gas is extin-
guished. If a little water be added, and the jar shaken, the solution of the
gas will be proved by the taper now burning in the jar.

The great solubility of ammonia in water renders it easy to separate this
gas from many others which are insoluble in this liquid. The usual state in
which ammonia is employed is in aqueous solution, both in chemistry and
medicine. This solution {Liquor Ammonice) may be readily obtained by
passing the gas into water in a proper apparatus, or by distilling over the
water and gas together. For this process equal parts of sal-ammoniac and
well-burned quicklime may be employed : the lime is slaked by the addition
of water, and, as soon as it has fallen into powder, placed in an earthen
pan, and covered until quite cold, then mixed with the powdered sal-ammo-
niac and put into a proper retort, and heated as long as it gives out gas,
which should be conducted, by means of a safety-tube, into a quantity of
distilled water, equal to the weight of the salt employed. The specific
gravity of a solution of ammonia so obtained is -936.

Liquid ammonia (as this aqueous solution is sometimes called) should be
preserved in well-stoppered glass bottles, since it loses ammonia and absorbs
carbonic acid when exposed to air. The gas is constantly evolved, and,
when the solution is heated, ammonia is rapidly given off by it ; when con-
centrated, it requires to be cooled to — 40° before it congeals, and then it
is inodorous, and of a gelatinous appearance. If a piece of ice be intro-
duced into a jar of gaseous ammonia standing over mercury, it melts with
great rapidity, and liquid ammonia is produced. This is owing to the strong
affinity of this gas for water.

The solution, when pure, is colorless, and has the pungent odor of the
gas. It is strongly alkaline, irritant, and caustic. It differs from potassa
and soda in redissolving the oxides of copper and silver, precipitated by
alkalies from their solutions. It should leave no residue op evaporation. If
it contains carbonic acid, this may be detected by the addition of lime-water,
or a solution of chloride of calcium, either of which will then cause a white
precipitate of carbonate of lime. The presence of chlorine may be detected
by neutralizing the alkaline solution with nitric acid, concentrating it by
evaporation, and then adding nitrate of silver : if it contains chlorine this
is made evident by the^ppearance of an insoluble white precipitate of chloride
of silver.

Tests. — Ammonia as a gas is recognized by its odor and volatile reaction,
as well as by its producing white fumes of hydrochlorate of ammonia, when
a rod dipped in strong hydrochloric acid, is b.rought near to it. Its solution
is precipitated, 1st, by a solution of tartaric acid, when added in large pro-
portion (acid tartrate of ammonia) ; and 2d, by a solution of chloride of

COMPOSITION OF AMMONIA. 181

platinum, forming a pale yellow ammonio-chloride of that metal, which is
insoluble in alcohol. When existing in solution in very minute proportion,
and the absence of other alkalies has been proved by the entire evaporation
of a portion of the liquid, traces of ammonia may be readily detected by
adding a few drops of the mixed solutions of arsenious acid and nitrate of
silver. Yellow arsenite of silver is produced and precipitated. The solution
of ammonia is an important agent to the chemist. It enables him to precipi-
tate many bodies, and as it is volatile, it can be subsequently expelled by
heat from any mixture to which it has been added.

Composition. — Dr. Henry first observed that a mixture of ammonia and
oxygen might be fired by an electric spark, and this property furnishes a
method of analyzing the gas. When the spark-current from Ruhmkorfif's
induction-coil is discharged through ammonia, the gas is rapidly decom-
posed, and at the same time the liberated gases evolve the light peculiar to
nitrogen and hydrogen. The spectrum produced, results from the super-
position of the spectra for hydrogen and nitrogen. When a succession of
electric sparks has been passed through a quantity of the gas contained in a
tube over mercury, it is uniformly observed to increase to twice its original
volume, and at the same time to lose its alkalinity and solubility in water.
If the gas thus expanded is mixed with from one-third to one-half of its bulk
of oxygen, and an electric spark passed through the mixture, an explosion
takes place, attended by a considerable diminution of volume. Assuming
that in the analysis 4 c. i. of ammonia are expanded to 8 c. i. by the electric
spark, and that 3 c. i. of oxygen are mixed with the 8 c. i. of decomposed
gas, there will be II c. i. of mixed gases. These after detonation are reduced
to 2 c. i., water being produced by the oxygen combining with the hydrogen
of the decomposed ammonia. Two-thirds of the loss, or 6 c. i., represent
hydrogen ( Water, page 128), and the 2 c. i. of residuary gas may be proved
to be nitrogen. Hence ammonia is constituted of one volume or atom of nitro-
gen, and three volumes or atoms of hydrogen, the four volumes being reduced
by combination to two. The changes are represented in the following equa-
tion : 2NH3-|-60^2N'-f 6H0. This method of analysis is open to the ob-
jection that some nitrogen is converted by the electric spark to nitric acid,
which may lead to error in computing the loss after detonation. The follow-
ing plan is not attended with this difficulty. Let 100 c. i. of the gas be
passed through a porcelain tube containing platinum-wire heated to redness ;
it will be doubled in volume and entirely decomposed. The 100 c. i. of am-
monia produce 200 c. i. of mixed gases, of which 50 are nitrogen and 150
may be proved to be hydrogen.

These results are confirmed by ascertaining the sp. gr. of the gas ; but as
the atom of ammonia represents two volumes, the sum of the sp. gr. of the
constituents must be divided by 2. Thus : —

Specific gravity of nitrogen
" hydrogen

. =0-9674
. 0-0691 X 3 = 0-2073

1-1747 -r-2 =

•5873

ind of

Atoms. "Weights. Per cent.
. 1 ... 14 ... 82-35 ..
3 ... 3 ... 17-65 ..

Vols.
1
. 3

Ammonia, therefore, is a compound of

Nitrogen ....
Hydrogen ....

Ammonia 1 17 100-00 2

Ammonia is produced synthetically during the decomposition of many
animal and vegetable substances, or by simply heating nitrogenous matter j

182 SYNTHETICAL PRODUCTION OF AMMONIA.

• it is also formed during the action of nitric acid upon some of the raetals ;
and by moistened iron-filings exposed to an atmosphere of nitrogen of air.
In these cases the nascent gases unite so as to form a portion of ammonia
(Fcg-f 4HO + N=Fe203,HO+NH3). Rust of iron formed by the exposure
of iron to a damp atmosphere, generally contains traces of ammonia. When
^nitric acid is added to a mixture of zinc and dilute sulphuric acid, its nitrogen
' combines with the hydrogen as it is evolved, and ammonia is formed, NO3+
8H=NH3-f 6H0; when, however, the action is violent, some deutoxide of
nitrogen is also evolved. If, after some days, a portion of the liquid is boiled
with a solution of potassa, ammonia will be evolved. The production of this
gas during the rusting of iron may be thus proved. Sprinkle the inside of
a large stoppered bottle with fine iron-filings, adding a small quantity of
water to make the metallic particles adhere to the sides of the bottle. Sus-
pend in the interior from the stopper a slip of litmus-paper, first reddened
by a weak acid. In about twenty-four hours the paper will be rendered blue,
by the ammonia produced in the rusting of iron. In the action of nitric
acid upon tin, ammonia is a product, provided water is present. Add tin-
filings to nitric acid, and then dilute the acid until a violent action com-
mences. The acid and the water are partially deoxidized by the metal, and
the hydrogen of the one unites to the nitrogen of the other, in the nascent
state, to form ammonia (N05+3HO-f-4Sn=NH3-l-4SnO.,). If the residu-
ary oxide of tin be well mixed with water, and some lime stirred into the
mixture, ammonia is immediately evolved. Ammonia, as it is diffused in air
-and water, is liable to become oxidized and converted into nitric acid, as a
result of the action of ordinary or allotropic oxygen, NHg-f 80(Oz)=N05-f
3H0. This oxidation is chiefly observed to occur when fixed bases, with
which the acids can combine, are present. The presence of alkaline nitrates
in large quantity in many well-waters, especially in the neighborhood of
grave-yards, is attributed to the effects of oxidation on the ammoniacal pro-
ducts of putrefaction. On the other hand, it is a curious fact that the nitric
acid of alkaline nitrates is reconverted into ammonia by the nascent hydrogen
evolved from an amalgam of sodium placed in a weak solution of the nitrate
(N03+8H=NH3+5HO).

Ammonia may be synthetically formed by the action of spongy platinum
on a mixture of 2 volumes of deutoxide of nitrogen and 5 of hydrogen. For
such experiments platinated asbestos, formed by dipping that substance
into a solution of chloride of platinum and exposing it to a red heat, may
be used ; while the mixed gases are passing, the platinum should be heated
(x\0,+H,=NH3-f2HO.)

Amidogen (NHg). — Amidogen is presumed to exist in combination with
certain metals, and in some organic compounds. When potassium, or sodium,
is heated in a current of dry ammonia, one equivalent of hydrogen is expelled,
and a solid substance is obtained which, in the case of potassium, is sup-
posed to have the composition KNH3 — an atom of hydrogen having been
replaced by an atom of the metal. This theory is strongly supported by
the fact, that when the substance produced is placed in water, the sole pro-
ducts obtained are potassa and ammonia, KNH3+H0=K0 + NH3. Ami-
dogen is therefore regarded as a hypothetical radical Among the com-
pounds into which it is supposed to enter, may be mentioned those of copper,
CuNHg, and mercury, HgjNHg, the last being the ammonio-chloride of mer-
cury or white precipitate. Inferring from these and other similar cases,
that in ammonia the third atom of hydrogen is less intimately combined
with nitrogen than the remaining two. Sir Robert Kane represents amidogen,
NHg by the symbol Ad, and treats it as the radical of ammonia. Ammonia,

PRODUCTION OF AMMONIUM. 183

therefore, on this view of its constitution, is an amide of hydrogen-='^lS.^,Yl
or AdH.

Ammonium (NHg + II, or NHJ. — AVhen mercary is made the negative
electrode in an aqueous solution of ammonia, it becomes spongy, 'and
assumes the character of a soft amalgam ; oxygen is given off at the positive
electrode, but there is no corresponding evolution of hydrogen on the negative
side until the electric current is interrupted, when the metallic sponge begins
to collapse, and gives out hydrogen and ammonia, leaving a residue of pure
mercury ; but this change may be retarded by cold, and on cooling the
pasty mass to 0°, it is said to yield cubic crystals, which, when decomposed
over mercury, give out ammonia and hydrogen in the respective volumes of
2 to 1. The mercury, therefore, appears to have been combined with a body
represented by NH^, and as the metallic characters of the mercury are un-
changed, it is presumed that NH^ constitutes temporarily a metal which has
been termed ammonium. This phenomenon may be equally observed by
placing an amalgam of potassium or sodium and mercury upon a block of sal
ammoniac, excavated in the form of a cup and containing a small quantity
of water; the amalgam soon increases in size, and forms a soft solid. With-
out water there is no chemical action. It is supposed, in this case, that the
potassium-amalgam, acting upon hydrochlorate of ammonia, gives rise to
chloride of potassium, and the amalgam of ammonium, KHg + NH^HCl
=KCl + HgNH^. The production of this amalgam may be more strikingly
shown by the following experiments. Prepare an amalgam of sodium by
gently warming some mercury in a tube or capsule, and adding at intervals,
small portions of sodium. The amalgam, which should be fluid when cold,
may be preserved for some hours in a well-stoppered bottle. Prepare a few
ounces of saturated solution of chloride of ammonium. Fill a tall glass or
jar to about one-third with this solution at the temperature of 100°, then
pour into it a quantity of the prepared sodium-amalgam. On contact with
the liquid, the amalgam rlapidly enlarges into a spongy mass, sometimes
rising out of the glass and forming a cauliflower excrescence. If kept in
contact with the solution, it retains its spongy state for a short time ; but
the mass slowly collapses : hydrogen and ammonia are evolved, and metallic
mercury remains in the glass, which now contains a solution of the chlorides
of ammonium and sodium. There are other methods of producing this
amalgam. If an alloy of potassium and sodium is made under naphtha by
pressing the two metals together, and a globule of mercury is then added,
an amalgam is immediately formed, with combustion. This amalgam placed
in contact with a warm solution of chloride of ammonium is converted into
the light, spongy amalgam of ammonium.

In the production of the ammonium- amalgam^ while the metal increases
to ten times its volume in the cold, and probably to thirty times its volume
at lOO'^, the hydrogen and ammonia increase its weight only by l*2000th
part. When a portion of the amalgam is placed in water tinted with red
litmus, it is slowly decomposed, minute bubbles of hydrogen escape, and
the solution of the ammonia is proved by the red litmus slowly acquiring
a blue color. If distilled water is used in this experiment, it soon acquires
an impregnation of ammonia and givet a yellow precipitate with arsenio-
nitrate of silver. The evolution of the two gases may be further proved
by filling a long test-tube to two-thirds of its depth, with blue infusion of
cabbage, and the other third with ether. If the amalgam is dropped to the
bottom of the tube, the ammonia, as it escapes, will be dissolved by the
water, and turn the blue cabbage green, while the hydrogen not being soluble
will be seen escaping in numerous minute bubbles through the floating layer
of colorless ether.

134 COMPOUNDS OF AMMONIA AND AMMONIUM.

These facts simply show that hydrogen and ammonia go into the mercury,
and that they are again evolved as such either spontaneously or by contact
with water. Although not, isolated in a combined state, it is assumed — 1,
from the consistency given to the mercury : 2, from the amalgam crystal-
lizing in cubes at zero, that the hydrogen and ammonia are temporarily
>^nited in definite proportions, to form a metal which is dissolved by mercury
nike other metals. At temperatures above zero the tendency of the com-
ponents of this metal to assume the elastic state appears to be so great as
to lead to their evolution under the form of hydrogen and ammonia. It is
remarkable that in the analysis and synthesis of this body the elements are
never arranged as hydrogen and nitrogen, but as hydrogen and ammonia.
There are many difficulties to the admission of the hypothesis that hydrogen
and ammonia, under these circumstances, produce a metal. When the
amalgam is exposed to air, especially in a thin layer, it is speedily resolved
into ammonia, hydrogen, and metallic mercury, and it has been justly asked
why, if ammonium falls apart thus readily in the presence of mercury, should
it ever combine as such with the liquid metal. It is admitted that it is
decomposed in the act of union and resolved into ammonia and hydrogen.
If a liquid amalgam of tin and mercury is compressed between two glass
plates, it retains its metallic character, the amalgam being simply con-
verted into a thin layer. Not so with the amalgam of ammonium ; it requires
bulk in order that it should retain the gases, and thereby its spongy character.
Place a portion of ammonium amalgam on plate-glass, and touch it with a
strong solution of chloride of ammonium. As soon as it begins to enlarge
in size, press it with another glass plate. Instead of forming a continuous
layer, it is immediately split into numerous holes from the escape of ammonia
and hydrogen from all points. It thus looks like a delicate network of metal.
The gases rapidly escape, and nothing but mercury remains. So it has been
found impossible to produce the ammonium amalgam by voltaic electricity,
when the experiment is performed on a thin layer of mercury. The gases
escape as they are produced, a fact which shows that they do not unite in
the mercury to form a metal.

The amalgam of ammonium is produced by acting with the sodium amalgam
npon the chloride, carbonate, or oxalate, but not readily on the nitrate. The
hydrogen and ammonia do not in this case appear to be retained by the
mercury. These experiments may be performed by putting a few drops of
the respective solutions (saturated) upon the sodium amalgam. As water is
essential to this phenomenon, and sodium amalgam alone in water causes
an evolution of hydrogen, soda being at the same time produced, the libe-
ration of ammonia has been ascribed to the reaction of the soda upen the
salts of ammonia. The two gases as they are evolved are for a certain time
retained by the liquid mercury, instead of escaping through it. This may
explain the consistency and lightness acquired by the mercury, without
assuming that the two gases are metallized. The assumption that nitrogen
* and hydrogen might combine with mercury to form a metallic amalgam, is
not inconsistent with chemical doctrines ; but it would be a novelty to assume
that nitrogen and hydrogen first produce ammonia, and that this ammonia
then enters into combination with aliother portion of hydrogen to form the
metal ammonium. There is no fact to show that the products are ever any-
thing more than a mixture of ammonia and hydrogen.

Although this compound metal cannot be separated as such from the
amalgam, chemists have generally agreed to regard its independent existence
as sufficiently established to justify its use in the nomenclature of the salts of
ammonia, thereby assimilating them in some respects to the salts of the other,
alkaline metals. The hypothetical ammonium is, therefore, symbolized some-

COMPOUNDS OF AMMONIA AND AMMONIUM. 185

times as Am, or more commonly by the formula NH^. The salts will stand
thus upou the two theories : —

Potassium series.

Ammonium

series.

Ammonia series.

Metal

K

Am

= NH,

NH3-I-H

Oxide

KO

Am,0

= NH,0

NH3,H0

Chloride

KCl

AmCl

= NH4C1

NH3,HG1

Sulphide

KS

AmS

= ^K^S

NH,,HS

Nitrate

KO,NOg

AmO,N05

= NH,0,N05

nh;ho,no5

Sulphate

K0,S03

AmOjSOg

=:NH,0,S03

NH,,H0,S03

From this comparative table it appears, that while potassium is an alkali-
genous metal, ^. e., a metal producing an alkali by combination with oxygen,
ammonia is a raetalligenous alkali, ^. e., an alkali producing a metal, by com-
bination with hydrogen. While oxide of potassium (KO) is an independent
and well-defined compound, which can be readily obtained either with or
without water, the so-called oxide of ammonium has only a hypothetical ex-
istence. Dry ammonia, like dry potassa, has no alkaline reaction, the presence
of water being required for the manifestation of this property in bodies (p. 43).
There is, however, no reason to suppose that the water is decomposed by
either compound. In reference to ammonia, water acts simply as a solvent,
as it dees on carbonic acid and protoxide of nitrogen. The properties of
the solution are simply those of the gas, ^nd like other soluble gases, ammo-
nia may be entirely expelled by heat. There is no hydrate of ammonia, nor
any condition of this alkali, which shows a chemical union with or reaction
upon the elements of water. Every attempt to extract an oxide has ended
in failure, and even where circumstances were most favorable for its produc-
tion— i. e., in the nascent state — nothing but ammonia and water result.

When perfectly dry ammonia and hydrochloric acid gases are brought in
contact, a solid white crystalline salt is formed, which may be either hydro-
chlorate of ammonia, or chloride of ammonium. On the latter hypothesis,
the affinity of the ammonia for another equivalent of hydrogen is assumed to
be such as to lead to its separation from the chlorine (NH3-|-HC1=NH4,CI).
But the production of this binary compound is not reconcilable with the facts
usually observed in reference to the powerful affinity of chlorine for hydrogen.
Ammonia itself is readily deprived of all its hydrogen by chlorine, as in one
of the processes for obtaining nitrogen (NB[3 + 3Cl=N-f 3HC1). In refer-
ence to the extraction of ammonia by lime, most chemists treat sal-ammo-
niac as hydi'ochl orate of ammonia, and not as chloride of ammonium. Oq
the former view there is simply a displacement of the ammonia by the lime,
and the production of water, NH3,HCl + CaO=NH3-i-CaCl-f HO ; on the
latter view, the decomposition would be, NH^,Cl + Cab=NH3 + CaCl + HO.
Thus synthetically, the ammonia is supposed to be changed into a metal by
a reaction on the elements of hydrochloric acid ; while analytically, the metal
is supposed to be reconverted into ammonia and water by a reaction on the
constituents of lime. It will be perceived that the oxacid salts of ammonia
enumerated in the table cpntain an atom of water, and this is supposed to
furnish the hydrogen for the production of the metal, and the oxygen neces-
sary to constitute its oxide.

While the alkaline metals manifest no basic properties until after they
have entered into combination w^ith oxygen, ammonia, in a dry state, forms
saline compounds with dry sulphurous and carbonic acids, and even with the
anhydrous sulphuric, and phosphoric acids. These compounds have received
the name of Ammonides, to distinguish them from the salts formed with the
hydrated oxacids. Ammonia must therefore be regarded as exceptional in
this respect. The production of a metal, or of the oxide of a metal, is not
necessary for the manifestation of basic properties by this alkali.

186 SALTS OF AMMONIA.

Salts of Ammonia. Nitrate, NHg.HOjNO.. — It is usually obtained by
saturating pure nitric acid with carbonate of ammonia, evaporating and
crystallizing.

This salt was formerly called nitrum jtammans, in consequence of its rapid
decomposition with a slight explosion when heated to about 600^. At 228^
it enters into perfect fusion ; at 356° it boils without decomposition ; at
about 390° to 400° it is decomposed, and is entirely resolved into protoxide
of nitrogen and water (NH3HO,N05=2NO + 4HO). It is deliquescent,
and soluble in less than its weight of water at 60°. Its taste is acrid and
bitter. It indicates free acid after exposure to air, and, like other.' ammo-
niacal salts, it loses its neutrality and becomes acid when its solution has
been boiled.

Hydrochlorate of Ammonia ; Muriate of Ammonia, NH3IICI ; Chloride
of Ammonium, NH^Cl. — This salt may be produced directly, by mixing
equal volumes of dry gaseous ammonia and dry hydrochloric acid, when
entire condensation ensues. The experiment which beautifully illustrates
the solidification of two gases by chemical union, may be thus performed.
Place within a tall, stoppered shade, a small jar containing ammonia. When
the gas has diffused itself, which may be known by a change of color in test-
paper placed at the top of the shade — the stopper may be removed, and a
small jar of hydrochloric acid inverted over the aperture. A dense white
cloud of chloride of ammonium will immediately descend from the top to the
bottom of the shade. Under the name of sal-ammoniac this salt was formerly
imported from Egypt, where it was obtained by burning the dung of camels.
It is now prepared either by saturating hydrochloric acid with carbonate of
ammonia, or by decomposing sulphate of ammonia by chloride of sodium
(NH3,S03,HO + NaCl=NH3,HCl + NaO,S03). When obtained by evapo-
ration from its solution in water, it forms octahedral crystals ; but, in
commerce, it usually occurs, as produced by sablimation, in translucent
fibrous cakes, hard, somewhat elastic, and slightly deliquescent. In this
compact state it requires for solution about an equal weight of water at 212°,
and nearly three times its weight at 60°, cold being produced during its
solution. It is also sparingly soluble in alcohol. When heated it sublimes,
before it fuses, without decomposition, in the form of a white vapor, and may
be even passed through a red-hot porcelain tube without change.

Sal-ammoniac is an anhydrous salt ; it is not volatile at common tempera-
tures, but when exposed to air it becomes slightly acid, in consequence of
the loss of a little ammonia ; the aqueous solution, therefore, of the salt,
often reddens litmus. It is used in the arts for a variety of purposes, especially
in certain metallurgic operations ; it is used in tinning, to prevent the oxi-
dation of the surface of copper ; it is also employed in small quantities by
dyers.

Sesquicarhonate ofAmmo7iia, 2NH3,3CO^,2HO. — This salt is the carbonate
of ammonia of commerce. It is gienerally met with in translucent cakes of a
fibrous fracture, as obtained by sublimation from a mixture of carbonate of
lime and sulphate or hydrochlorate of ammonia. When carbonate of lime
and sulphate of ammonia are used for its production, the results are sulphate
of lime, hydrated sesquicarbonate of ammonia, and free ammonia and water.
3[CaO,COJ + 3[NH3,S03,HC)]=3[CaO,S03] + [2NH3.3CO,,2HO] + NH3,
HO. When sal-ammoniac is substituted for the sulphate we have 3[CaO,
COJ + 3[NH3,HCl]=3CaCl4-[2HN3,3CO„2HO] + NH„HO.

This salt has a pungent odor, a hot and saline taste, and a powerful
alkaline reaction. It may be obtained in an impure state by the destructive
distillation of nitrogenous matter, constituting salts of hartshorn ; but this
and other salts of ammonia are now chiefly procured from the distillation of

SALTS OF AMMONIA. 18t

coal, in the manufacture of gas. Four parts of water at 60° dissolve about
one of this salt, forming the liquor ammonicB sesqnicarhonatis. When
exposed to air, especially in the state of powder, it effloresces into bicar-
bonate of ammonia, and carbonate of ammonia is volatilized. When its
aqueous solution is heated, carbonic acid and a little ammonia is evolved,
and the single carbonate remains dissolved. There is a bicarbonate of
ammonia (NH32CO^MO) on the ammonia theory ; to satisfy the ammo-
nium hypothesis, this must be regarded as a carbonate of ammonia and
carbonate of basic water [HO,C03+NH40,COJ. This difficulty applies
to all the acid salts of ammonia.

Snlphide of Ammonium (NPI^S). — As ammonia is not a metallic oxide, it
is assumed that when hydrosulphuric acid meets with this alkaline gas, the
hydrogen is at once transferred to the ammonia, producing ammonium, with
which the sulphur remains combined. If the dry gases are placed in contact,
a volatile anhydrous crystalline compound is produced, which has the com-
position NH3 + 2HS, or, as it is frequently represented, NH^S-fHS. The
crystals are soluble in water. The sulphide of ammonium, commonly used
as a test, is really the hydrosulphate of the sulphide, and has the composition
above given. The ordinary solution is made by saturating with sulphuretted
hydrogen one-half of a measured quan^ty of a solution of ammonia, and
then adding to it the other half. At first the liquid is pale, but after some
time, and as a result of exposure to air, it acquires a deep yellow color,
owing to the liberation of sulphur and the production of bisulphide of ammo-
nium (NII4S2). A portion of the hydrogen combines with the oxygen of
the air. It is ultimately converted into hyposulphite of ammonia, and sul-
phur is precipitated. If the solution of sulphide is properly prepared, it
should give no precipitate with a solution of sulphate of magnesia. The
liquid, when concentrated, evolves an irritating vapor, which is strongly
alkaline, and has a very offensive odor. It is a convenient test for the
precipitation of numerous metals as sulphides. With some of these it enters
into combination, forming double sulphides.

Persulphide of Ammonium. — This is a compound of sulphuretted hydro-
gen and ammonia, with excess of sulphur. It is probably a bisulphide. It
is obtained by distilling a mixture of about 4 parts of slaked lime, 2 of
hydrochlorate of ammonia, and one of sulphur. In its concentrated state,
this compound exhales white fumes ; hence it was formerly called BoyWs
fumi^ig liquor. It is a deep yellow liquid, smelling like a mixture of
sulphuretted hydrogen and ammonia. It dissolves sulphur.

Characters of the Salts of Ammonia. — They are white, soluble in water,
and are volatilized when heated. With the exception of the carbonate,
they have no odor of ammonia. The solutions are rendered acid by boiling.
In the dry state, a salt of ammonia is known by heating it in powder with
its bulk of quicklime, and in a state of concentrated solution, by boiling it
with a solution of potassa. Ammonia, recognizable by its odor and other
properties, is evolved in both cases.

18S CHLORINE

CHAPTER XV.

CHLORINE (Cl = 36). — COMPOUNDS WITH OXYGEN AND
HYDROGEN. HYDROCHLORIC ACID.

History. — Chlorine is an elementary gas, which was discovered by Scheele
in 1774. For a long time it was supposed, on the authority of Lavoisier,
to be a compound of oxygen and muriatic acid, and it was thence called
Oxymurialic acid gas ; but in the year 1810 it was examined by Davy, and
proved by him to be a simple undecomposable body of highly negative pro-
perties, like oxygen. It derives its name, chlorine, from its greenish-yellow
color (;t^wp6j, green). The alleged presence of oxygen and muriatic acid in
the gas, was explained by its reaction under the influence of light, on the
elements of water — the gas having been examined in the humid state. Under
these circumstances the hydrogen was taken by the chlorine foruiing hydro-
chloric acid and the oxygen was evolved. It is not found free in nature ; its
combining tendencies are so strong, that it could not long exist in the free
state. It is a most abundant element, and is the great constituent of the sea,
as oxygen is of the earth. It is hence called a halogen (ajij, salt). One
pound of common salt (chloride of sodium) contains more than half a pound
of chlorine. This is equivalent to rather more than five gallons of the gas,
for each gallon of sea-water.

Preparaiion Chlorine may be procured by acting on a mixture of sea

salt and black oxide of manganese with sulphuric acid ; but it will be found
more convenient to obtain it directly from hydrochloric acid, which contains
97 per cent, of this gas. The peroxide of manganese, in coarse powder, is
mixed with four parts, by weight, of hydrochloric acid, to which a little water
is added to check the fumes. A flask or retort may be used, but two-thirds
of the capacity of the vessel should be left free, as the mixture swells up
when heated. By the application of a gentle heat the gas will come over
freely. It should be collected in a bath containing but a small quantify of
tepid water. It is very soluble in water, and much is lost by collecting it in
cold water. If hot water is used there is less of the chlorine dissolved, but
on cooling, the gas is liable to become mixed with a large proportion of air.
It must not be allowed to stand over water, or it will entirely disappear.
The jars should stand on accurately fitted glass-plates, and the vessels which
are not ground may be placed in plates containing a small quantity of a
saturated solution of chlorine. The decomposition which ensues in the
above-mentioned process, may be thus represented : 2HCl4-MnO^=Cl4-Mn
CI -f 2H0. From this it will be perceived, that only one-half of the chlorine
is obtained. It may be procured from common salt by heating a mixture of
four parts of chloride of sodium, and three parts of peroxide of manganese,
with seven of sulphuric acid and four of water (NaCH-Mn03-f2S03H0 =
NaO,S034-MnO,S03-fCl + 2HO).

The gas may be procured quite pure and dry, by passing it first through
a wash-bottle containing some distilled water, and afterwards through a
glass tube containing broken chloride of calcium or concentrated sulphuric
acid. As the respiration of even a small quantity of chlorine is highly
injurious to the lungs, the gas should be made only where there is a free

PROPERTIES OF CHLORINE. 189

current of air. The first portions (containing air) should be collected in
jars, and these may be opened under a flue. The gas should not be col-
lected for experiments, until it appears of a rich greenish-yellow color. As
it is very heavy, it may be obtained by displacement. For this purpose the
gas, dried by the process above described, should be conducted by a delivery-
tube to the bottom of a clean dry jar, and when the colored gas is seen to
overflow, the jar may be covered and removed. For common purposes,
chlorine may be speedily dried by placing some strong sulphuric acid at the
bottom of the jar in which it is to be collected, and causing the delivery-
tube to dip into this. The chlorine in passing through the sulphuric acid is
deprived of its water, and if the jar, when filled, is closely covered, and is
allowed to stand for a short time, the gas will be perfectly desiccated.

Properties. — Chlorine gas is of a greenish-yellow color, has a pungent
and suffocating odor, a peculiar and somewhat astringent taste, is highly
irritating when respired, exciting cough and great irritation of the lungs,
even when considerably diluted with atmospheric air. When dry and pure,
it is not affected by light, neither is it altered by a high temperature. But
when the gas in a humid state is passed through a red-hot porcelain tube, it
decomposes the watery vapor, combining with the hydrogen to form hydro-
chloric acid, and liberates oxygen. Although a gas at the ordinary tem-
perature and pressure, chlorine admits of liquefaction by cooling to — 106°,
or by a pressure of four atmospheres at 60°, forming a yellow liquid which
has not been yet solidified. Chlorine readily combines with aqueous vapor
to form a crystalline hydrate of a pale yellowish-green color. A jar of the
gas containing the ordinary amount of vapor, readily yields this hydrate
when exposed to a temperature of 32°. If the temperature rises, the crystals
melt, and the jar will be again filled with the gas, which is set free with
effervescence. This hydrate of chlorine consists of one atom of the gas to
ten atoms of water (Cl + IOHO); it may be obtained in a pure state, by
placing a small quantity of water in a large bottle containing chlorine, and
keeping the bottle in a dark place at or near the freezing point. If these
crystals are introduced into a small bent tube, and the tube is sealed, they
will serve as a source for obtaining the gas in the liquefied state {see page 80.)
On heating the end containing the crystals, and keeping the other end of
the tube cool, a yellow vapor is evolved which is condensed into two distinct
fluids, the upper and lighter being an aqueous solution of chlorine, while
the lower and heavier, which is of a yellow color, is the liquefied gas. When
the tube is broken, the liquid is immediately converted to gaseous chlorine.
The sp. gr. of the liquid gas is 1-33. It is a non-conductor of electricity.

The specific gravity of gaseous chlorine compared with air is 2*4876,
which gives 77 '04 grains as the weight of 100 cubic inches at mean tem-
perature and pressure. Its specific gravity, in reference to hydrogen, may
be considered as 36 to 1. In the electrolysis of its compounds, chlorine,
like oxygen, appears at the positive pole or anode.

At the temperature of 60°, water dissolves twice its volume of the gas.
The solution, saturated at 42°, has a specific gravity of 1-003 ; it is of a
pale greenish-yellow color, has an astringent, nauseous taste, and destroys
vegetable colors ; hence its use in bleaching. The bleaching agency is
explained by the evolution of nascent oxygen, resulting from the decom-
position of aqueous vapor or water. Chlorine itself, when perfectly free
from moisture, has no such action. Thus if a strip of dry litmus-paper be
placed in a jar of chlorine collected by displacement through sulphuric acid
in the manner already described, it will be found that that portion of the
paper which is in the jar retains its blue color, while that which hangs oat
of the jar will be bleached. The mouth of the jar should be closely covered

190 COMBUSTION IN CHLORINE.

by a glass plate, or the moisture in the air wil^cause a bleaching of the
whole of the litmus-paper. The general effect of the humid gas on organic
colors may be thus represented (Cl + HO = HCl + 0). Indigo, litmus,
cochineal, aniline-purple, and other colors, are thus so completely destroyed,
that they cannot be artificially restored.

The bleaching properties of the gas may be shown by passing a few cubic
inches of it into a jar filled with diluted sulphate of indigo, and inverted in
the water-bath. The color of the indigo is destroyed on agitation. Let
some artificial flowers and a bunch of parsley be suspended in a tall shade
filled with water and inverted in the bath. On decanting into the shade
chlorine gas, so as to fill the upper part of it, the colors depending on organic
compounds will be destroyed, while mineral colors, including those depend-
ing on carbon, will remain.

The aqueous solution of chlorine was formerly known as oxymuriatic acid.
It is now called liquor chlori or oqua chlorinii. It has no acid reaction,
unless it has been exposed to light. It is a powerful astringent, and pos-
sesses all the bleaching and oxidizing properties of the gas. It converts
sulphurous into sulphuric acid (Cl-f S03+2HO=HCl-f SO3HO), and the
protoxides of iron and manganese into peroxides. The ferrocyanide of
potassium is changed to ferricyanide by chlorine. This solution gives a
white precipitate with nitrate of silver (AgCl), in nitric acid. When ex-
posed to a temperature of 32*^, the aqueous solution freezes, forming the
crystalline hydrate (page 189), and ice which is free from chlorine. The
aqueous solution of chlorine dissolves gold by the aid of a gentle heat.
When this solution is exposed to the direct rays of the sun, oxygen is
evolved in consequence of the decomposition of the water, the hydrogen of
which unites to the chlorine, and forms hydrochloric acid (Cl-fHO = HCl-f-
O). The same change ensues more slowly in common daylight, but in the
dark, there is no such decomposition ; so that as gaseous chlorine generally
contains aqueous vapor, the bottles in which it is preserved should be care-
fully excluded from light.

Chlorine, and its aqueous solution, are powerful antiseptics, and destroyers
of foul arid noxious efl9uvia. This property depends on its power of decom-
posing the noxious compounds, which generally contain hydrogen, and
resolving them into others which are harmless. For the purposes of fumiga-
tion, chlorine liberated at common temperatures, from black oxide of man-
ganese and hydrochloric acid, or from manganese, salt, and sulphuric acid,
may be diffused through the foul atmosphere. In the same way the offensive
odor of decomposing animal matter, may be removed by sprinkling it with
a solution of chlorine.

When a burning taper is immersed in a jar of this gas, the flame becomes
red, throws oS" dense, black fumes, and is soon extinguished. If a green
wax taper with a glowing wick is suddenly introduced into ajar of the gas,
the flame will be rekindled, and it will continue to burn with the evolution
of much carbonaceous smoke. Tow or cotton, impregnated with ettier, and
introduced in a state of flame into the gas, burns with a dense smoke, chiefly
of carbon. Bibulous paper soaked in hot oil of turpentine suddenly plunged
into a jar of the gas (kept partially covered) frequently bursts into flame, a
large quantity of carbon being given off during the combustion. In all these
cases, chlorine supports combustion, by taking only the hydrogen of the
combustible, and setting free the carbon. That hydrochloric acid is a pro-
duct, may be proved by introducing litmus-paper, which will be reddened —
as well. as a glass rod dipped in strong ammonia, which will cause the evolu-
tion of copious ^^ite fumes of hydrochlorate of ammonia. Some bodies —
Buch as sulphide of carbon, which burn with great splendor in oxygen — are

EQUIVALENT. TESTS FOR CHLORINE. 191

immediately extinguished in this gas. There are, however, many substances,
such as phosphorus and several of the metals, which are spontaneously in-
flamed by chlorine, and burn in it with much energy Phosphorus burns
in the gas at all temperatures (see page 102). In these cases, binary com-
pounds result, some of which, like those of oxygen, are possessed of acid
properties : others are not acid, and are termed chlorides. Brass or copper
leaf, and powdered antimony, serve well to show the intense action of
chlorine upon certain metals. When introduced into the gas, they enter
into immediate combustion, and chloride of copper and chloride of antimony
art formed.

Fill a dry jar with some leaves of Dutch gold, and invert over it a jar of
pure chlorine ; as the gas descends, the metal will undergo combustion,
acquiring a red heat without flame, and the whole will disappear. The com-
bustion of antimony may be shown by sifting the freshly-powdered metal
into ajar of the gas on partially removing the cover. If a piece of sodium,
heated to ignition in air, be introduced into a bell-jar of the gas, it will burn
with great splendor. If a coil of fine iron-wire is made red hot and plunged
into the gas, it will burn with a deep lurid-red flame, evolving copious brown
vapors of sesquichloride of iron. When fine copper or brass wire ignited is
employed, it burns in chlorine with splendid scintillations. Arsenic and
mercury at a high temperature burn in the gas, producing highly noxious
fumes. These experiments should only be performed where there is a free
current of air to carry off the volatile products.

Chlorine displaces bromine and iodine from their metallic and non-metallic
combinations. Paper wetted with a solution of bromide of potassium, and
introduced into chlorine, acquires a yellow color from the liberated bromine.
If iodide of potassium is used, iodine is abundantly set free.

There is no body for which chlorine manifests so strong an afiinity as for
hydrogen. All the hydrogen compounds of carbon, sulphur, phosphorus,
nitrogen, antimony, and arsenic, are decomposed by it: hydrochloric acid is
produced, and the metal or metalloid is liberated. If a jar of chlorine is in-
verted over one containing sulphuretted hydrogen, this gas is decomposed,
sulphur is precipitated, and hydrochloric acid is formed. This may serve as
an illustration of its operation in deodorizing foul and offensive effluvia. The
decomposition of ammonia by this gas has been already referred to. The
whole of the hydrogen is taken and the nitrogen is liberated (3Cl-f 4NH3 =
3(NH.,IICl-f-N) (page 185). The results may be shown in another mode.
Introduce into ajar of chlorine bibulous paper saturated with a strong solu-
tion of ammonia. There is violent combustion with a pale reddish flame
(chloride of nitrogen ?), and dense white fumes of hydrochlorate of ammonia
escape (6Cl-f 4NH3=3(NH3HCl)-f NCI3). Ammonia may be regarded as
the most effectual agent for the removal or neutralization of gaseous chlorine.
Solutions of potassa and soda absorb the gas, producing salts which vary
according to circumstances. A current of the gas passed into a hot and
concentrated solution of potassa, produces chloride of potassium and chlorate
of potassa, which may be obtained by evaporation (6KO + 6Cl=5KCl-h
KOCIO5). If t,he alkaline solution is cold and much diluted, then a chloride
and hypochlorite are produced. (See Hypochlorous Acid.)

Equivalent and Compounds. — The atomic weight of chlorine is usually
taken at 36 (page 66), and its combining volume 1. Like hydrogen, it is
a monatomic gas. Its range of combination is as great as that of oxygen.
It combines with all the metals, and with the greater number of metalloids.
These binary compounds are called Chlorides. It forms only acid compounds
with oxygen and hydrogen.

Tests. — The color, odor, and bleaching properties of this gas are in all

192 HYPOCHLOROUS ACID.

cases sufficient for its identiflcation. In solution \i may be known by these
properties, and by the white curdy precipitate which it gives wth a solution
of nitrate of silver, as well as by its power of decomposing iodide of potas-
sium, and producing a deep-blue-colored compound when the iodide is mixed
with a solution of starck An excess of chlorine destroys this color.

Compounds of Chlorine and Oxygen. — These elementary bodies do not
combine directly. They have but a feeble affinity for each other, and, when
combined, are readily separated by slight causes. There are five compounds
of these elements, four of which are acids : — •

1. Hypochlorous acid, CIO 3. Peroxide of chlorine, CIO4

2. Chlorous acid, CIO3 4. Chloric acid, CIO.

5. Perchloric acid, CIO7.

1. Hypo chlorous Acid (C10=44) When a small quantity of hydrate of

lime is placed in ajar of chlorine, the gas soon disappears, and a compound
of hypochlorite of lime and chloride of calcium is formed (2CaO-f2Cl =
CaO,C10 + CaCl). This is well known as bleaching powder {see Chloride
OF Lime). When a current of chlorine is passed into a cold weak solution
•of soda or potassa, a similar reaction takes place, and an alkaline hypo-
chlorite is formed (2K0 + 2C1=K0,C10 + KC1). If these compounds are
acted upon by acids, they evolve chlorine, and not hypochlorous acid. If,
however, diluted sulphuric acid is added very gradually to chloride of lime,
diffused in water and the mixture is kept stirred, hypochlorous acid is liber-
ated and may be distilled over as a weak solution of the acid in water.
Balard first suggested a method of obtaining pure hypochlorous acid. His
process consists in agitating a mixture of one part of precipitated red oxide
of mercury with twelve of distilled water, in a bottle filled with chlorine ;
the gas is rapidly absorbed. If the proportion of the oxide is insufficient,
the deposited powder is white, and some of the chlorine remains unabsorbed;
but the oxide should be in slight excess, so as to remain red, and entirely
absorb the gas. (2HgO + 2Cl = C10-fHgCl,HgO.)— (6 drachms of red
oxide mixed in .fine powder with an ounce and a half of water, and shaken
in a quart bottle of chlorine, are proportions recommended by Graham)*
When the absorption is complete, the contents of the bottle are poured upon
a filter, and the filtered liquor subjected to distillation in vacuo, by which a
diluted solution of hypochlorous acid is obtained, and this may be concen-
trated by a second distillation.

Tlie gaseous, is obtained from the aqueous acid, by introducing into an
inverted jar of mercury, a quantity of the concentrated liquid, and then pass-
ing into it, through the mercury, small fragments of fused nitrate of lime.
The nitrate abstracts the water and liberates pure hypochlorous acid in the
state of a gas, a little deeper-colored than chlorine, of a strong penetrating
odor, and absorbable by mercury, forming oxychloride, from the contact of
which it is preserved in the above mode of obtaining it, by the layer of solu-
tion of nitrate of lime. A slight elevation of temperature, even the warmth
of the hand, is sufficient to decompose this gas with explosion and evolution
of heat and light, so that it requires careful management. It is not changed
by some hours' exposure to diffused daylight, but direct solar rays decom-
pose it in a few minutes without explosion ; when mixed with hydrogen and
inflamed, it detonates violently, but at common temperatures, the mixture
remains unchanged. Bromine and iodine slowly decompose it; sulphur,
selenium, phosphorus, arsenic, and antimony, decompose it with sudden and
violent detonation ; charcoal also causes it to explode, apparently in con-
sequence of the condensation which the gas suffers in its pores. In these

PEROXIDE OF CHLORINE. 193

cases the elements are pejyjxidized and converted into the higher class of
acids. When placed in contact with iron-61ings, the iron is oxidized, and
chlorine is evolved ; but when silver is substituted for iron, chloride of silver
is formed, and oxygen is evolved. Hypochlorous acid gas may be procured
as a yellow gas, by passing a current of dry chlorine over well-dried oxide
of mercury. The gas must be condensed in a receiver, kept cool by a freez-
ing mixture. In this reaction, the oxygen is simply displaced by the
chlorine (HgO + SCl — C10 + ITgCl),.and corrosive sublimate as well as hypo-
chlorous acid results. In performing this experiment, unless the temperature
is kept low, oxygen only will be liberated. The gas is formed of a volume
of chlorine united to half a volume of of oxygen, these being condensed into
one volume of the compound. The specific gravity of the gas is in accord-
ance with this constitution ; for one half volume of oxygen =0-5528+2'48'76
sp. gr. of chlorine =3'0404. Its specific gravity is, therefore, 3*04, and 100
c. i. weigh 94*16 grains.

According to Regnault, water dissolves at least two hundred times its
volume of this gas, forming a pale yellow-colored liquid. The solution pos-
sesses powerfully bleaching properties ; twice as great in proportion as those
of chlorine. This is probably owing to the nascent oxygen which is evolved
in its decomposition. It is contained with hydrochloric acid in a solution of
chlorine which has undergone chemical changes, and it adds to its bleaching
power. It is decomposed by the non-metallic substances, which act upon
the gas, and is a most powerful oxidizing agent. It will even oxidize the
chloride of potassium, and convert it into chlorate of potassa. It throws
down peroxide of lead from a solution of the chloride of that metal, and
sesquioxide of manganese from the chloride. A solution of chlorine pro-
duces these effects only under the agency of light. (Regnault.) Chloride
of silver exerts upon it a catalytic action, resolving it into its elements
without undergoing any change. A concentrated solution of the gas is
decomposed by hydrochloric acid, and chlorine is evolved (HCl-fC10 =
H0 = 2C1). If the liquids are mixed at a low temperature, a solid crys-
talline hydrate of chlorine is obtained.

2. Chlorous Acid (ClOg=60).— This is a gaseous acid of a greenish-
yellow color, not easily liquefied by cold. It may be procured by mixing 3
parts of arsenious acid with 4 parts of chlorate of potassa and sufficient
water to make a paste, and adding to the mixture in a retort 12 parts of
nitric acid diluted with 4 parts of water. This mixture, distilled in a water-
bath, yields a greenish-yellow colored gas (chlorous acid) of a specific gravity
of 2 64 6. (Regnault.) Water dissolves five or six times its volume : the
solution has a golden-yellow color. The chloric acid is deoxidized by the
arsenious acid, which is converted during the process into arsenic acid. The
gas can be collected only in the dry way, as it is very soluble in water, and
is decomposed by mercury. It is converted by explosion at about 130°
into chlorine and oxygen. Like hypochlorous acid, it oxidizes with explo-
sion many of the non-metallic bodies. It re a powerful bleaching agent,
and is a monobasic acid, forming chlorites with bases. The specific gravity
of the gaseous acid shows that it must contain in each volume one volume of
oxygen and two-thirds of a volume of chlorine— 1 -1057 + 1-6584=2 '764,
which does not widely differ from the specific gravity actually determined.
In reference to its constitution by volume, it is usually considered that two
volumes of chlorine (two atoms), and three volumes of oxygen (six atoms),
are condensed into three volumes or atoms of the compound.
^ 3. Peroxide of Chlorine (010^=68). — This compound, which is some-
times called hypochloric acid, was discovered by Davy, in 1815. It may be
procured by acting on fused chlorate of potassa by concentrated sulphuric

Id

194 CHLORIC ACID.

acid, in the proportion of one part of the salt to three parts of acid. The
materials in small quantity may be heated in a tube-retort by a water-bath,
at a temperature not exceeding 100°. The gas is soluble in water, which
will take up twenty times its volume ; and it is decomposed by mercury,
hence it can be collected only by displacement. The gas is of a yellowish
color, and has a peculiar odor resembling chlorine ; it is not acid in reac-
tion, but it has strong bleaching properties. It is decomposed with explo-
sion at about 140°. Phosphorus produces with it violent combustion even
under water. This experiment may be performed by placing the powdered
chlorate in a tall conical glass with a small quantity of phosphorus, and
covering the mixture with cold water. On pouring concentrated sulphuric
acid into the mixture by a long funnel the peroxide is set free, and the
phosphorus burns with bright scintillations, producing phosphoric acid.
The gas may be readily liquefied by cold and pressure. Although not acid,
it is dissolved by alkaline liquids, but it forms no saline combinations : on
evaporating the alkaline solution, a chlorite and chlorate of the alkali are
obtained (2010^=0103 -I-CIO5). The specific gravity of the gas is 233.
This nearly corresponds to half a volume of chlorine and one volume of
oxygen in each volume (r2438 + 1105t = 2*3495), or in two volumes
there would be one volume of chlorine and two volumes of oxygen.

4. Chloric Acid (0105=16). — This acid was discovered by Gay-Lussac
{Ann. de Chim., xci. 108). It cannot exist independently of an atom of
water, or of some base, so that it has not been obtained anhydrous ; the
hydrated acid, in its state of extreme concentration, being HO,C10,=85.
In depriving it of water it is converted into peroxide of chlorine and oxygen.
Hydrated chloric acid may be prepared by adding diluted sulphuric acid to
a solution of chlorate of baryta, as long as it occasions a precipitate. The
baryta is thus separated in the form of an insoluble sulphr^e, and the chloric
acid remains in aqueous solution. Oare must be taken to add no more sul-
phuric acid than is requisite, for any excess contaminates the chloric acid.
If the exact proportion has been used, the chloric acid is neither rendered
turbid by diluted sulphuric acid nor by chlorate of baryta. If either of these
occasions a precipitate, the solution must be carefully added till the efl'ect
ceases ; the clear liquid may then be decanted or filtered off. It may be
concentrated by evaporation in vacuo until it acquires a syrupy consistency.
It may also be procured by the action of fluosilicic acid on chlorate of potassa.
A hot aqueous solution of ciilorate of potassa is mixed with excess of
fluosilicic acid ; the acid liquid, when cold, is filtered, evaporated below 80°,
and, after two days, filtered through powdered glass.

Hydrated chloric acid is a sour liquid, and of a yellowish tint when highly
concentrated. It deoxidizes permanganate of potassa and destroys its color.
It reddens vegetable blues, and then bleaches them. When added to a
strong solution of potassa, crystals of chlorate of potassa are deposited.
When concentrated, it acts powerfully, and even to ignition, upon paper,
cotton, and some other dry organic bodies; it decomposes alcohol, with the
formation of acetic acid. The most remarkable of its salts, which are now
termed chlorates, were formerly known under the name of oxymuriates, or
hyperoxymuriates. When distilled at a higher temperature than 100°, it
suffers decomposition, and a portion of chlorine and oxygen are liberated,
perchloric acid passing over, but no chloric acid. It is decomposed by
hydrochloric acid into chlorine and water, 5H01 + C105=5HO + 6C1. This
mixture dissolves gold, and is sometimes employed for the oxidation and
destruction of organic matter in toxicological researches. By excess of sul-
phurous acid, it produces sulphuric and hydrochloric acids; 6SOa-fC105,HO
«6S03-fHCl: and by excess of sulphuretted hydrogen it forms water,

PERCHLORIC ACID. 195

hydrochloric acid, and sulphur; 6HS4-C105=5II0, + HC1 + 6S. Those
acids which are already saturated with oxygen, do not act upon it.

Chlorates. — These salts are MO-f-ClO^. They deflagrate powerfully with
combustible matter, and often by mere friction. {See Chlorate of Potassa.)
They are all soluble in water. By heat they are mostly resolved into chlo-
rides and evolve oxygen. The electrolysis of the chlorate, when in igneous
fusion, has been found by M. Gerardin to present an exception to the general
results of the decomposition of salts by current electricity. Thus, in refer-
ence to the salts of potassa and soda, in igneous fusion, it was observed that
the oxygen only was set free at the positive pole, the radicals of both acid
and base appearing at the negative pole. In thus decomposing the fused
chlorate of potassa, however, it was found that the oxygen and chlorine
appeared at the positive pole in a state of mixture, and the potassium at the
negative. This apparent anomaly is probably due to the simultaneous de-
composition of the chloride of potassium produced by the eifect of heat on
the chlorate {Cosmos, Oct. 25, 1861, p. 471.)

A chlorate is easily identified by adding to a small portion in powder a
drop of sulphuric acid. The odor of peroxide of chlorine is immediately
perceived. If a grain or two of white sugar be added to the mixture, there
will be immediate combustion. A solution of a chlorate colored with indigo
has the color discharged in the cold, by the addition of sulphurous acid.
When indigo is mixed with the solution of a nitrate, and sulphurous acid is
added, the color is not discharged until the mixture has been heated.

The euchlorine of Davy, which was produced by the reaction of hydro-
chloric acid on chlorate of potassa, was probably a compound of chlorous
acid and chlorine.

5. Perchloric Add, ClOy, or as hydrate=H0,C107, was discovered by
Count Stadion. It is unknown in the anhydrous state, but it may be pro-
cured as hydrate by distilling perchlorate of potassa with its own weight of
sulphuric acid, diluted with about a fourth part of water. At a temperature
of about 280^, white vapors pass off, which condense in the form of a color-
less liquid.

Another method consists in decomposing a hot solution of chlorate of
potassa with fluosilicic acid, concentrating the chloric acid by boiling, and
subsequently distilling the residue. Dr. Roscoe found that one atom of per-
chlorate of potassa, distilled with four atoms of concentrated sulphuric acid,
also yielded the concentrated hydrate. It is considered to be a more stable
compound than the preceding, as it is not decomposed by sulphuric or
hydrochloric acid. When concentrated, its specific gravity is 16, and it
boils at 392°. By distillation with strong sulphuric acid, it may be obtained
in the solid form and crystallized.

The properties of the concentrated acid have been lately examined by Dr.
Roscoe {Proc. of Brit. Assoc, Sept. 1861). He procured it as a colorlessj
heavy (sp. gr. 1782), oily-looking liquid, fuming, highly corrosive, and
giving off, when heated in air, dense white vapors. It is one of the most
powerful oxidizing agents known ; a single drop brought into contact with
charcoal, paper, wood, alcohol, ether, and other combustibles, caused ex-
plosive combustion resembling that of the chloride of nitrogen. It could
not be kept long, even in sealed glass tubes placed in the dark. It under-
went spontaneous decomposition, blowing the glass vessel to pieces. When
mixed with water, it produced a hissing noise, with the evolution of great
heat forming a crystalline hydrate. It could not be distilled without decom-
position. The acid contains 61 per cent, of oxygen. The solution has a
strongly acid reaction, but no bleaching properties.

Perchlorates. Oxy chlorates.— -These salts have the formula MO + CIO^

196 nYDROCHLORIC ACID.

Although more abundant in oxygen, they are of less explosive tendency, and
less easily decomposed by heat than the chlorates, like which they are
resolved either into chlorides and oxygen gas, or into lower oxides, oxygen,
and chlorine : they are all soluble in boiling water, but the perchlorate of
potassa requires 150 parts of cold water to dissolve it. A perchlorate is
known from a chlorate by the non-production of peroxide of chlorine when
strong sulphuric acid is added to it.

Chlorine and Hydrogen. — There is only one compound of these elements
— an anhydrous gaseous hydracid, known as hydrochloric or muriatic acid
gas. It was discovered by Priestley in 1172.

Hydrochloric Acid (HC1=37). Cfdorhydric ov Muriatic Acid. Spirit
of Salt. — Chlorine and hydrogen, when mixed in equal volumes, combine
directly to produce hydrochloric acid gas. If a lighted taper is applied to
the mixture, or the electric spark is discharged into it, there is immediate
combination, with a violent explosion. This also happens when the mixed
gases are exposed to the direct rays of the sun, the lime-light, or the light of
burning phosphorus. The combination takes place more slowly and gradu-
ally in diffused daylight, and is totally arrested in the dark. A mixture of
the two gases placed in a graduated vessel over water may be employed for
photometrical purposes, the amount of absorption as a result of combination,
indicating the intensity of light.

Preparation. — The gas is generally procured by acting upon common salt
with sulphuric acid ; it must be collected over mercury. The proportions
are one part of salt to two parts of acid. The salt should be fused, coarsely
powdered, and put into a tubulated retort, which may be one fourth filled
with it : the sulphuric acid should barely cover the salt ; the gas is instantly
extricated, and when its evolution slackens, it may be quickened by the
gentle heat of a lamp. It is convenient to put a long strip of blotting-
paper into the neck of .the retort, which absorbs any liquid that may chance
to go over, and prevents its soiling the mercury. Clean and dry bottles may
be filled with this gas by displacement, as it has a high specific gravity.
The chemical changes may be thus represented: NaCl-j-S0„,H0=HCl4-
NaCSOg.

Properties. — Although permanently gaseous at common temperatures and
pressures, Mr. Faraday liquefied this gas by generating it in a sealed tube,
so as to expose it to a pressure of about forty atmospheres at 50°. It was
colorless, and possessed a refractive power inferior to that of water. He
could not succeed in solidifying it. {Phil. Trans., 1823; and 1845, p. 163.)
Hydrochloric acid gas is perfectly irrespirable : it extinguishes the flame of
a taper, and of all combustible bodies, and is itself uninflammable. It irri-
tates the skin ; has a strong attraction for water ; and when it escapes into
the air, it forms visible fumes, arising from its combination with aqueous
vapor. A piece of ice introduced into the gas over mercury, is immediately
liquefied and the gas is absorbed by the liquid. If a tall jar of the gas be
carefully transferred, with its mouth downwards, from the mercurial to the
water-trough, the water instantly rushes in with violence, and fills it. The
gas has no bleaching properties, but it strongly reddens litmus-paper. In
the dry state, it undergoes no change by exposure to heat ; but when mixed
with air and passed over broken pumice, heated to redness, aqueous vapor
and chlorine result. (Pelouze.)

Water takes up 480 to 500 times its bulk of hydrochloric acid gas, at 40°,
and has its specific gravity increased from 1 to 1*210. (H. Davy.) This
may be shown by throwing up a few drops of water into a tall jar of the gas
standing over mercury j the gas disappears, and the mercury fills the vessel.

SOLUTION OF HYDROCHLORIC ACID. 197

There is considerable elevation of temperature during this condensation of
the gas. The experiment maybe performed like that described at page 209,
using a solution of blue in place of red litmus. Entire absorption is a proof
of the purity of the gas.

For saturating water with the acid gas, we may employ a tubulated retort
or flask, connected with a globe receiver from which issues a bent tube at a
right angle, and just dipping below the surface of distilled water contained
in a bottle. The bottle should be closed and the water kept cool, as much
heat is given out during the condensation of the gas. The different joints
of the apparatus may be secured either by grinding, or by well-cut corks
rendered tight by a mixture of drying-oil and pipe-clay. The retort or flask
may be gently heated by a sand-bath. The bottle should be only half filled
with water, as, in dissolving the gas, it increases from one- third to two-thirds
in volume.

Solution. — When gaseous hydrochloric acid is thus dissolved in water, it
forms the liquid hydrochloric acid, commonly called muriatic acid or spirit
of salt, which was discovered by Glauber about the middle of the seventeenth
century. It is generally procured by distilling a mixture of dilute sulphuric
acid and common salt. The proportions directed in the " London Pharma-
copoeia" are two pounds of salt and twenty ounces of sulphuric acid, diluted
with twelve ounces of water. The retort containing these ingredients may
be luted on to a receiver, containing the same quantity of water used in
diluting the sulphuric acid, and the distillation carried on in a sand-bath.
The specific gravity of the product is stated to be 1-160, and 100 grains of
it should be saturated by 132 grains of crystallized carbonate of soda. The
following will be found convenient proportions for procuring the acid — 6
ounces of salt, previously fused, 8| ounces by measure of sulphuric acid (sp.
gr. r65), and 4 ounces of water. An acid of 1-15 sp. gr. is obtained. In
order to procure the acid of greater strength (1 '21) we may employ the
weak acid in place of water and sulphuric acid, in a second distillation with
fused salt. (Gregory.) The quantity of real acid in hydrochloric acid of
different densities may be ascertained by the quantity of pure carbonate of
lime (Carrara marble) which a given weight of the acid will dissolve. Every
fifty grains of the carbonate are equivalent to thirty-seven of real acid.

When this acid is pure and concentrated, it should be colorless, but it has
generally a pale yellow hue arising from particles of cork or lute that may
have accidentally fallen into it, or sometimes from a little iron. The acid of
commerce almost always contains iron, sulphuric acid, and sometimes nitric
acid, as well as common salt. The iron may be detected by the black tint
produced by tincture of galls, in the acid previously diluted and neutralized
by carbonate of soda. If a solution of chloride of barium, dropped into
the diluted acid, occasion a white cloud or precipitate, it announces sulphuric
acid. The presence of nitric acid (and of free chlorine and bromine?) is
shown by boiling some gold-leaf in the suspected hydrochloric acid, and
then dropping into it a solution of protochloride of tin. If nitric acid be
present, this will produce a purplish tint, showing the gold to have been
dissolved, while pure hydrochloric acid has no action upon it. Common
salt and other saline substances may be detected in it by evaporating the
acid to dryness ; when pure, it leaves no residue. Traces of arsenic also
frequently exist in hydrochloric acid. This impurity is derived from the
sulphuric acid used in its formation. It may be deprived of arsenic by dis-
tilling it over a small quantity of sulphide of barium. The presence of
arsenic in this acid may be detected by boiling in the acid diluted with four
parts of water, a small slip of pure copper foil. If the acid contains arsenic,
this is indicated by a dark metallic deposit on the copper. (See Arsenic.)

198 HYDROCHLORIC ACID. CHEMICAL PROPERTIES.

The highly concentrated liquid acid (sp. gr. 1 -20) is very corrosive, emits
copious fumes when exposed to air, and boils, according to Dalton, at a
temperature of about 112^; it freezes at — 60° The boiling-point varies
with the density of the acid ; it is highest (230*^) when it contains between
19 and 20 per cent, of the dry gas. (sp. gr. r094.) The strong acid becomes
weaker, and the weak acid stronger by boiling. It is impossible to expel the
whole of the gas by boiling. At a sp. gr. of r096, acid and water are dis-
tilled over together. When mixed with water, there is a slight elevation of
temperature. It is decomposed by many oxacids, such as the chloric, iodic,
and bromic acids, and several of the metallic peroxides. Its decomposition
by peroxide of manganese, for the production of gaseous chlorine, has already
been referred to (page 188). This may be regarded as a good test for the
presence of the acid.

When metallic zinc is put into strong liquid hydrochloric acid, it is rapidly
decomposed, and hydrogen is copiously evolved. Some peroxide of lead
added to another portion of the acid immediately disengages chlorine, which
may be shown by its bleaching power upon litmus paper; these experiments
well illustrate the separation of the two elements of the acid. On the other
hand, the production of the acid by synthesis may be well illustrated by
bringing a small jar of chlorine over the flame of hydrogen burning from a
jet. The color of the flame is changed to a pale greenish-white, and acid
fumes of hydrochloric acid are copiously formed. Hydrogen may be thus
perfectly burnt in an atmosphere of chlorine. In the voltaic circuit the chlorine
is evolved at the positive electrode or anode, and the hydrogen at the negative
electrode or cathode, so that when thus electrolyzed and tinged with indigo,
a bleaching effect is produced at the anode. Uncombined hydrochloric acid
is not found in nature except in an occasional volcanic product. The acid
is an irritant poison to animals, and its vapors are extremely injurious to
vegetation ; when mixed with 20,000 times its volume of atmospheric air,
it proved fatal to plants, shrivelling and killing all the leaves in twenty-four
hours.

The following table, by Mr. E. Davy, calculated for 40° and a pressure of
30 inches, shows the strength of hydrochloric acid of different densities : —

Sroccific firavitv ^^ grains contain of gnpHflc Gravitv ^^^ grains contain of

bpeciflc bravity. Hydrochloric Gas. bpeciflc Orarity. Hydrochloric Gas.

1-21 42-43 1-15 30-30

1-20 40-80 1-14 28-28

1-19 38-38 1-13 26-26

1.18 36-36 1-12 24-24

1-17 34-34 1-05 10-10

1-16 32-32 1-01 2-02

According to Dr. Thompson, the strongest liquid hydrochloric acid (sp.
gr. 1-208) contains one atom of real acid -j- 6 atoms of water; when this is
evaporated in the air, hydrochloric acid escapes, and it is ultimately reduced
to 1 atom of acid -f 12 of water (sp. gr. 11 19). This hydrate is said to
have a sp. gr. of 1-128 at 58°, and it boils at 223°. When a solution of
hydrochloric acid is distilled, a quantity of gas escapes in the first instance ;
but acid and water soon begin to be distilled together, and the boiling
point remains fixed at 230°. This new hydrate has a sp. gr. of r094, and
it is found to contain 16 atoms of water. There are therefore, according
to Bineau, three hydrates of this acid— HC1,6H0: HCU2H0 : and HCl,
16H0. Pure hydrochloric acid of convenient strength for use in the labo-
ratory may be obtained by diluting the strongest acid with about its volume
of water, so as to reduce its density to about Tl, and then distilling it over
a little chloride of barium. The acid carries over a sufficiency of water for

EQUIVALENT. COMPOSITION. 199

condensation, which may be effected by Liebig's condenser. Acid of this
strength does not fume on exposure to air.

The concentrated acid, at a high temperature, carbonizes and destroys
organic matter. It has, generally speaking, no action on non-metallic
bodies; and among metals it is not decomposed by gold, platinum, mercury,
or silver. If pure, it may be boiled on these metals without change. Its
chlorine is taken by lead, tin, zinc, magnesium, aluminum, and iron, hydrogen
being set free. Its action on copper is peculiar. In the concentrated
state and under a free access of oxygen or air, the acid loses its hydrogen,
which forms water, and oxychloride of copper is produced. By means
of copper and hydrochloric acid, the whole of the oxygen may be removed
from a confined volume of air. {See Nitrogen, p. 154.) It is decomposed
by the alkaline metals, chlorides being formed, and the hydrogen liberated.
Metallic oxides, including the alkalies, decompose it, producing water and
a chloride (K0-fHCl=H04-KCl.) Some bases, however, appear to enter
into direct combination with it — among these may be mentioned magnesia,
alumina, and, according to some chemists, the oxides of chromium and cobalt.
These appear to form both hydrochlorates as well as chlorides. Morphia
and the vegetable alkaloids form hydrochlorates only.

Equivalent and Composition. — When equal volumes of chlorine and hydro-
gen are mixed, and the electric spark is passed through the mixture, the
gases unite, without change of volume, to produce hydrochloric acid, which
is entirely absorbed by water. If exposed to diffused light over water, they
combine and slowly disappear — the water dissolving the compound as it is
produced. By heating potassium in a measured quantity of the gas, the
chlorine is removed and the volume of the gas is reduced to one-half — the
residue being pure hydrtbgen. The specific gravity of the gas is 1*2783.
This is equivalent to one-half of the sp, gr. of chlorine, plus one-half of the
sp. gr. of hydrogen. Hence it is thus constituted : —

Hydrogen .
Chloriue

Atoms.
. 1 ..
. 1 ..

. 1

Weight.
. 1 ..

. 36 ..
37

Per cent.

. 2-7
. 97-3

Volumes.
... 1 ...
... 1 ...

2

Sp. Gr.
0-0691
2-4876

Hydrochloric acid

100-0

2-5567

and 2-556Y-^ 2 = 1-2783. Compared with hydrogen, its sp. gr. is 1-85 ; 100
cubic inches weigh 39-59 grains.

Tests. — The gas is known by its acid reaction, great solubility in water,
the dense fumes which it produces in a humid atmosphere, and the white
fumes of hydrochlorate of ailimonia which are evolved when a glass rod,
dipped in a strong solution of ammonia, is brought near to it. The produc-
tion of a solid compound by the combination of the two gases, may be well
illustrated by placing a small jar of dry ammonia within a tall stoppered
jar. When the ammonia is proved, by its reaction on test-paper, to have
reached, by diffusion, the top of the bell-jar, the stopper may be removed
and a jar of hydrochloric acid gas placed over the opening. The gases
immediately combine, and the hydrochlorate of ammonia formed descends in
a dense white cloud. A solution of hydrochloric acid in the concentrated
state, may be identified by its evolving chlorine when boiled with peroxide
of magnesia. In the diluted state, it is recognized by giving a white-clotted
precipitate with a solution of nitrate of silver (AgCl) which is insoluble in
nitric acid, and becomes slate-colored and ultimately blackens by exposure
to light.

"NiTRO- HYDROCHLORIC AciT). NiTRO-MURiATic AciD. — This term has been
applied to the Aqua Regia of the alchemists. When nitric and hydrochloric

200 NITRO-HYDROCHLORIC ACID.

acids are mixed, they become yellow, and acquire the power of dissolving
gold and platinum, which neither of the acids possesses separately. This
mixture, when heated, evolves chlorine, a partial decomposition of both acids
taking place. Three parts of hydrochloric and one of nitric acid furnish the
most effective mixture ; but a solution having the same general properties,
is obtained by adding nitre to hydrochloric acid, or common salt to nitric
acid. In the mutual decomposition of the two acids by heat, chlorine is
evolved until one of the acids is entirely decomposed. When a metal is put
into nitro-hydrochloric acid, it is not dissolved by either of these acids, but
by the nascent chlorine, the metal combining with it as fast as it is evolved.
The application of heat greatly accelerates this action, but much chlorine
may be lost by employing too high a temperature. The red vapors which
escape on heating the mixture may be condensed by distillation. The con-
densed liquid is known as Chlo7'onitnc Sicid, and has the composition N02Cla.
The reaction by which it is produced may be thus represented: (NO5HO +
3HCl=N02Cl3+Cl + 4HO). Towards the end of the distillation, another
compound, called Chloro-nitrous acid, is produced. This has the compo-
sition NO^Cl, and is thus formed : (N05,II0 + 3HC1=N02C1 + 2C1 + 4H0).
This is a gaseous acid of a deep orange-red color; it may be procured by the
direct union of deutoxide of nitrogen with one-half of its volume of chlorine.
During the solution of metals in this acid, the production of a metallic chlo-
ride and of deutoxide of nitrogen may be thus represented: (3M-fN05+
3HCl=3MCl-f NOa-fSHO). Nitro-hydrochloric acid is the common solvent
of gold and platinum, and may, with proper precautions, be used in the
separation of these metals from silver, which remains as an insoluble chloride.
It furnishes a useful solution of tin; and is employed in the analysis of mine-
rals containing sulphur, to separate and acidify that substance.

Nitrogen and Chlorine. Chloride of Nitrogen; Ter-chloride of
Nitrogen. NCI3. — The gases do not unite directly, but the compound may
be obtained by exposing a solution of nitrate of hydrochlorate of ammonia
to the action of chlorine, at a temperature of 60° or 70°, The chlorine
must be in excess, otherwise nitrogen may be evolved. The gas is absorbed,
and a yellow oil-like fluid, heavier than water, is produced by the union
of the nascent nitrogen (evolved in the decomposition of the ammonia
bf the salt) with the chlorine. NH3,HCl-f 6Cl = 4HCl + NCl3. It was dis-
covered by Dulong, in 1812, and its properties were afterwards investigated
by Davy.

The simplest mode of obtaining this compound consists in filling a per-
fectly clean glass basin with a solution of 1 part of sal-ammoniac in 12 or 15
of water, and inverting in it a tall jar of chlorine. The saline solution is
gradually absorbed and rises into the jar, a film forms upon its surface, and
it acquires a yellow color ; at length small globules of the pure chloride of
nitrogen, looking like a yellow oil, collect upon its surface, and successively
fall into the basin beneath. Balard obtained this compound by suspending
a piece of sulphate of ammonia in a strong solution of hypochlorous acid.

The specific gravity of chloride of nitrogen is 1*65 ; it is not congealed by
cold. Its odor is irritating and peculiar ; it very soon evaporates when ex-
posed to air. It is apparently a non-conductor of electricity. It is danger-
ously explosive, and is decomposed with violent detonation by mere contact
with many combustibles, especially phosphorus, oil of turpentine, and the
fixed oils. In making these experiments, great caution is required. Dulong
lost an eye and the use of a finger, and Sir H. Davy was wounded in the face,
by the effects of its detonation. The explosion takes place with a flash of
light, and the vessel containing the substance is shattered. A leaden basin

BROMINE. 201

should therefore be used for the experiment. At 160° it distils without
chauf^e, but at 212° it explodes, and is decomposed.

The production of light and heat in the decomposition of this compound
does not admit of explanation on any of the ordinary theories of combus-
tion. In combustion bodies unite, and light and heat are the products of
their union and condensation. In reference to this chloride, however, as
well as the oxides of chlorine and the iodide of nitrogen, the light and heat
are the results of the separation of the elements.

The composition of this chloride, although given as NClg, is by some con-
sidered to be NCI4. Its true constitution is not accurately known. From
the researches of Millon it probably contains hydrogen. When mixed with
concentrated hydrochloric acid it forms ammonia, and chlorine is evolved.
It is slowly decomposed by diluted solution of ammonia — hydrochlorate of
ammonia is formed, and nitrogen is evolved. Even when kept in water in
a stoppered bottle it slowly disappears, while nitric and hydrochloric acids
are formed.

Chlorine and carbon form several compounds, but these belong to organic
chemistry.

CHAPTER XVI.

BROMINE — IODINE — FLUORINE; AND THEIR COMPOUNDS.
BROMINE (Br = 78).

History and Preparation. — Bromine was discovered, in 1826, by M. Balard,
of Montpelier, in the uncrystallizable residue of sea-water, commonly called
bittern. A current of chlorine, passed through this liquid, gives to it an
orange tint, in consequence of the evolution of bromine from its combina-
tions (MgBr+Cl=Br4-MgCl). A portion of sulphuric ether is then shaken
up with the colored liquid ; this abstracts the bromine, acquires a reddish-
brown tint, and rises to the surface. The ethereal solution is drawn off and
agitated with a strong solution of potassa, by which a solution of bromate
of potassa and bromide of potassium is formed : the ether floating upon the
surface may be separated and used again; the denser liquid is then evapo-
rated to dryness, and the residue, exposed to a dull-red heat, leaves bromide
of potassium. Purified bromide of potassium is usually employed for pro-
curing bromine ; but the bromide of barium is preferable, as this salt may
be obtained entirely free from chloride. The bromide in fine powder is
mixed with half its weight of peroxide of manganese, and its weight of sul-
phuric acid previously diluted with half its weight of water ; and the mix-
ture is distilled into a cold receiver containing water, and into which the
beak of the retort or condenser just dips. The deep orange-colored vapor
of bromine is condensed, and the liquid bromine, which falls to the bottom
of the vessel, is separated from the water, and is afterwards dehydrated, if
necessary, by distilling it over chloride of calcium [2(S03HO) + KBr-f MnOa
=K0,S03-f MnO,S03 + Br + 2HO]. Should the liquid from which bro-
mine is to be obtained contain iodine, this must be first separated in the
form of subiodide of copper (CuJ), by the addition of a solution of 1 part
of sulphate of copper, and 2J parts of sulphate of iron.

Bromine probably exists in sea-water in the state of bromide of magne-
sium, but its relative proportion is exceedingly minute. One hundred pounds
of sea- water, at Trieste, aflforded only 5 grains of bromide of sodium = 3 3

BROMINE CHEMICAL PROPERTIES

grains of bromine : it is there unaccompanied by iodine ; and the same is the
case, according to Hermbstadt, in the waters of the Dead Sea. In the
Mediterranean, on the contrary, iodine accompanies it. Schweitzer found
bromide of magnesium in the waters of the British Channel. Sea-water
sometimes contains as much as one grain of bromine in a gallon. Bromine
is found in the mineral kingdom combined with silver.

The presence of bromine is recognized either in sea-water or in mineral
springs, by evaporating the water so as to separate its more crystallizable
contents, reducing the remainder to a small bulk, and dropping into it a con-
centrated solution of chlorine. In the absence of iodine, which may be
detected by starch, the appearance of a yellow tint announces bromine. It
has been thus discovered in many saline springs, in the ashes of marine
plants, and in those of some marine animals. Among the saline springs
most abundant in bromine are those of Theodorshal, near Kreutznach, in
Germany ; these are now the chief scource of bromine as an article of com-
merce.

Properties. — At common temperatures and pressures bromine is a deep
reddish-brown liquid, of a pungent disagreeable odor, something resembling
that of oxide of chlorine, whence* its name (ppw^oj, fetor) : its specific
gravity is about 3 (2'96 to 2-99). It emits a heavy brownish-red vapor of
an offensive and irritating nature at common temperatures. This vapor has
a specific gravity of 5-3898, and compared with hydrogen, T8; 100 cubic
inches of it weigh 166*92 grains. It has the color of nitrous or hyponitric
acid. If respired in a diluted state, it causes a sense of suffocation and great
irritation in the nose and throat, producing all the effects of a severe cold,
sometimes lasting for several days. The vapor is so heavy, that it may be
readily poured into and collected in dry jars ; it then appears like an orange-
colored gas. It bleaches litmus-paper as well as solutions of organic colors
(litmus, aniline-red, indigo, and ink) with the same power as chlorine. The
dry vapor, like dry chlorine, does not bleach ; hence the bleaching probably
depends on the decomposition of aqueous vapor and the effect of nascent
oxygen. Its affinity for hydrogen is not so great as that of chlorine. If
the air has been entirely displaced by the vapor, a lighted taper, inOamed
camphor, or ether, introduced into a jar of it, is instantly extinguished.
Bromine vapor, therefore, is a non-supporter of ordinary combustion. The
vapor produces with ammonia dense white fumes of bromide of ammonium.
It decomposes hydriodic acid gas, setting free the purple vapor of iodine
when a small quantity of it is poured into a jar containing that gas. It also
decomposes the solutions of the alkaline iodides ; bromides are formed, and
iodine is separated. Place in a large shallow dish a thin solution of starch,
to which a solution of iodide of potassium has been added. Allow the vapor
of bromine to fall from a bottle containing this liquid, upon the starch ; the
blue iodide of starch will be immediately produced. This experiment, at the
same time, serves to illustrate the great density of the vapor.

If a jar containing bromine vapor is inverted over another containing
sulpharetted hydrogen, the sulphur is precipitated, and hydrobromic acid is
formed. It is almost as effectual as chlorine in destroying foul effluvia, but
its vapor is too noxious and irritating to render it practically useful for
this purpose.

As a liquid, bromine boils at 145°. It is solidified when cooled to — 1-6,
and retains this condition up to 104. (Pelouze.) Its vapor, in spite of
its density, is so diffusive, that one drop of the liquid placed in a large globe
receiver, or jar, will speedily give a color to the whole of the gaseous con-
tents. Bromine is a non-conductor of electricity, and appears in the voltaic
circuit at the positive electrode. It suffers no change by transmission through

HYDROBROMTC ACID. 203

red-hot tubes. It dissolves sparingly in water (1 part in 33), forming an
amber-colored solution of an astringent, but not sour taste, from which the
bromine escapes by exposure, and rapidly by boiling : when long kept,
especially if exposed to light, it becomes acid from the formation of hydro-
bromic acid. It forms, under certain circumstances, a definite hydrate,
which may be obtained by exposing bromine with a small quantity of water
to a temperature of 32^ ; red octohedral crystals of the hydrate of bromine
are then deposited, which continue permanent at the temperature of 50^,
and contain 10 equivalents of water. At a higher temperature they are
decomposed into liquid bromine and an aqueous solution of it. The hydrate
is also obtained by passing the vapor of bromine through a moistened tube
cooled nearly to the freezing-point. Bromine dissolves in alcohol, and more
abundantly in ether and chloroform : — these two liquids readily separate it
from its aqueous solution. It communicates an orange tint to a solution of
starch. Antimony burns in it ; and it combines with potassium and phos-
phorus with explosive violence. Its action on alkaline solutions is analo-
gous to that of chlorine and iodine. It stains the skin of a yellow color,
and irritates it; it acts as a corrosive upon most vegetable and animal
substances, and is fatal to animal life ; a single drop placed in the beak of a
bird will kill it.

Bromio Acid (BrO,). — This is the only known compound of bromine and
oxygen. Bromic acid is obtained by the decomposition of a solution of
bromate of baryta by diluted sulphuric acid : sulphate of baryta is precipi-
tated, and a solution of bromic acid is obtained, which may be concentrated
by slow evaporation ; at a high temperature it is partly decomposed, and
cannot be obtained anhydrous. It is colorless, acid, inodorous, and first
reddens, and then destroys the blue of litmus. It is partially decomposed
by concentrated sulphuric acid, but not by nitric acid. It is decomposed by
sulphurous acid, by sulphuretted hydrogen, and by hydriodic and hydrochloric
acids. From the analysis of bromate of potassa, there can be no doubt
that the bromic acid is analogous in composition and chemical properties
to the chloric and iodic acids. As it is always in the state of hydrate, its
proper formula is BrOa.HO.

Bromates. — These salts are represented by MO+BrOg) they are resolved
at a red heat, either into bromides and 6 atoms of oxygen, or into 5 atoms
of oxygen and 1 of bromine, a metallic oxide being left : they deflagrate with
combustibles like the chlorates. They are recognized by evolving bromine,
when heated with strong sulphuric acid.

Hydrogen and Bromine. Hydrobromic Acid (HBr=Y9). — Bromine
vapor and hydrogen do not combine with each other, either under the influ-
ence of the sun's rays, or by the application of a lighted taper or the electric
spark ; but when they are passed through a tube heated to redness, the
vapor and gas combine, and hydrobromic acid is produced. This gaseous
acid may be procured by gently heating a mixture of 1 part of phosphorus.
12 5 of bromine, and T'8 of bromide of potassium, with a little water,
(MiLLON.) Hydrobromic acid is evolved in dense white fumes when bro-
mide of potassium is decomposed by sulphuric acid; KBr-fS03,H0 =
HBr+K0,S03; but in this case a portion of it is decomposed and bromine
vapor escapes; KBr + 2S0,H0=Br+S0,-f KO,S03+2HO. Phosphoric
acid is not liable to this objection, hence a strong solution of this acid may
be mixed with the bromide of potassium in place of the sulphuric, and the
mixture distilled.

This compound, although gaseous at common temperatures and pressures,

204 HYDROBROMIC ACID.

condenses into a clear, colorless liquid at 100° below 0° : at 124° below 0°,
it is a transparent crystalline solid. As a gas it is colorless, of a pungent
and highly irritating odor, and yields dense acid vapors when mixed with
humid air. It undergoes no change when passed through a red-hot tube,
either alone or mixed with oxygen or iodine ; but chlorine decomposes it,
producing the vapor and drops of liquid bromine, which, being absorbed by
mercury, leaves hydrochloric acid. The attraction of oxygen and of bromine
for hydrogen, is probably nearly equal ; for bromine does not decompose
water at common temperatures, nor does oxygen decompose hydrobromic
acid ; but at a red heat bromine decomposes aqueous vapor, hydrobromic
acid is formed, and oxygen is liberated. Hydrobromic acid gas is not altered
by mercury, but tin and potassium entirely decompose it : the former requires
the aid of heat ; but potassium acts at common temperatures, reducing the
gas to half its bulk, and forming bromide of potassium. Hence it appears
that the constitution of hydrobromic acid is analogous to that of hydrochloric
acid, and that it consists of equal volumes of hydrogen and bromine vapor
combined without condensation. The weight, therefore, of 100 cubic inches
of hydrobromic acid is 84 '53 grains, and the gas consists of —

Atoms. Weights. Per cent. Volumes. Sp. Gr.
Hydrogen '. . . 1 ... 1 ... 1-266 ... 1 ... 0-069
Bromine . . . . 1 ... 78 ... 98-734 ... 1 ... 5-389

Hydrobromic acid . . 1 79 100-000 2 5.458

And 5 '458-:- 2=2 -729 sp. gr. ; compared with hydrogen, its sp. gr. is 39*5.

Hydrobromic acid gas is rapidly absorbed by water ; heat is evolved, and
a fuming liquid acid is obtained, which is colorless when pure, but which
readily dissolves bromine, and acquires a yellow color. The specific gravity
of the densest aqueous hydrobromic acid is 1-486. It boils at 258°*8 and
may be distilled at this temperature. The concentrated acid has the formula
HBr,10HO. The solution is instantly decomposed by chlorine, acquiring a
yellow color from the liberation of bromine. ^Nitric acid also decomposes it,
evolving bromine, and .forming water and nitric acid. This mixture may be
considered a sort of aqua regia, as it dissolves gold and platinum. An
aqueous solution of the acid may be obtained by passing a current of sul-
phuretted hydrogen gas into a mixture of bromine and water; but more
conveniently by decomposing a strong solution of bromide of barium with
sulphuric acid diluted with its weight of water. On distilling the mixture,
hydrobromic acid is procured in the receiver.

"When heated with any of the peroxides of metals, the acid is decomposed,
water is formed, and bromine escapes in vapor. In its reaction on alkalies,
a bromide and water result (KO + HBr=KBr + HO,) except in the case of
ammonia, in which it is supposed that bromide of ammonium is produced :
NH,+HBr=NH,Br.

Bromides — These salts are readily identified, 1st. By heating them with
sulphuric acid and peroxide of manganese, when bromine escapes. 2d.
When dissolved in water — by the solution acquiring a yellow color, and the
odor of bromine when a solution of chlorine is poured into it. Ether or
chloroform may then be used to separate the bromine. 3d. The solution
gives a yellowish-white precipitate with nitrate of silver, insoluble in nitric
acid, and requiring a large quantity of ammonia to' dissolve it. 4th. It gives
an insoluble white precipitate with a salt of lead but no precipitate with a
solution of corrosive sublimate. The insoluble bromides are decomposed by
chlorine and strong sulphuric acid, bromine being set free.

Chloride of Bromine. — By passing chlorine through bromine, and con-

IODINE. PREPARATION. PROPERTIES. 205

densing the resulting vapors at a low temperature, a reddish-yellow liquid is
obtained, having a penetrating odor and disagreeable taste. It is very vola-
tile, emitting a yellow vapor j it is dissolved by water, and the solution
destroys vegetable colors.

IODINE. (1=126.)

History. — ToDiNE was discovered in 1811 by M. Courtois, a chemical
manufacturer at Paris. It derives its name from the Greek labri^ (violet-
colored), from the color of its vapor.

It is chiefly prepared at Glasgow from help, which is the fused ash obtained
by burning sea-weeds, and is principally manufactured on the west coast of
Ireland, and the Western Islands of Scotland. The long stems of the Fucus
palmatus are most productive of iodine. Traces of iodine, in the form of
iodide of sodium, have been discovered in plants growing near the sea, iu
sea-water, in sponge, in many saline springs, in certain kinds of coal, and in
the coarser varieties of common salt. Yauquelin detected it in some silver
ores from Mexico. It has also been found iu cod-liver oil, and in the oil of
the liver of the skate, as well as in the common oyster. The commercial
source of iodine is sea-weed.

Preparation. — For commercial purposes, a lixivium of kelp, containing
chiefly iodide of sodium, is employed for the extraction of iodine. It may
be readily procured by mixing iodide of potassium with half its weight of
peroxide of manganese, and its weight of sulphuric acid, previously diluted
with half its weight of water. The materials may be heated in a short-necked
retort or flask connected with a large globular receiver which must be kept
cool. The changes which ensue may be thus represented : (2S03HO-f KI +
MnO,=KO,S03+MnOS03 + 2HOH-L) The iodine is sublimed, and is de-
posited in a crystalline form in the cool parts of the receiver. The crystals
may be washed out of the receiver by a solution of iodine in water, the liquid
poured off, and the deposit rapidly dried between folds of blotting-paper.
It may be purified by resubliraation at a gentle heat. If the alkaline iodide
in kelp be associated with a large proportion of chloride, the iodine may be
conveniently precipitated as snbiodide of copper (CuJ), by the addition of
a mixed solution of sulphate of copper (one part) and of sulphate of iron
(two and a half parts.) The insolu))le subiodide of copper, when heated
with peroxide of manganese, yields iodine by sublimation.

Properties — Iodine has a gray or bluish-black color, resembling plumbago ;
its lustre is metallic, and its fracture when in a mass, is greasy and lamellar.
It is a non-conductor of electricity. It is not changed by passing its vapor
through a red-hot tube, either alone or over charcoal. It is soft and friable.
Its specific gravity, as a solid, is 4*946. It produces a yellow stain upon
paper and on the skin, without corroding it. Its smell somewhat resembles
that of diluted chlorine ; its taste is acrid. It is extremely volatile, and pro-
duces a pale violet vapor at a temperature of between 60° and 80°. This
vapor may be well brought out by dropping a few grains of iodine into a
large globular glass vessel previously heated. At 120° or 130° it rises more
rapidly in vapor ; at 220° it fuses ; and at 350° it boils and produces dense
violet-colored fumes, which are condensed in brilliant rhombic plates and
octahedra. It may be entirely volatilized by heating it on writing paper.
One hundred cubic inches of iodine vapor weigh 269 64 grains. Its specific
gavity, compared with air, is 8-'7066, and with hydrogen, 126. Like chlo-
rine and oxygen, it is evolved from its combinations at the positive electrode ;
it is very sparingly soluble in water, this liquid not holding more than one
7000th of its weight in solution. The color of this solution is pale brown ;
it gives out no oxygen by exposure to sunshine ; it, however, slowly loses

206 IODINE. PROPERTIES.

its color, and gives rise to the formation of iodic and hydriodic acids.
Iodine is very soluble in alcohol and ether, forming deep brown solutions.
It is soluble in sulphide of carbon, forming a rich crimson-colored liquid.
If in a free state, it may be thus detected and removed from strongly colored
organic liquids. Chloroform also dissolves and separates it from its aqueous
solution, acquiring a rich purple color.

It is said to be destitute of bleaching properties, but this arises from the
small amount of iodine dissolved by water. One ounce of a saturated solu-
tion contains only about one-sixteenth of a grain. If a few grains of iodide
of potassium are dissolved in the water, a much larger amount of iodine is
taken up. This aqueous solution has a dark brown color, and slowly acts
upon litmus and indigo w^hen added in sufficient quantity so as to give them
a light greenish tint. Iodine is very soluble in water containing chloride of
ammonium, nitrate of ammonia, or hydriodic acid. Either as a solid, or in
solution, iodine is an irritant poison.

The violet color of the vapor of iodine, as well as its peculiar odor, is in
many cases a sufficient evidence of its presence ; a more delicate test, how-
ever, is furnished by its property of forming a deep blue compound with
starch. According to Stromeyer, a liquid containing only one 450,000th of
its weight of iodine, receives a reddish-blue tinge when a solution of starch
is added to it, provided too much starch is not present. To insure success,
the iodine should be in a free state, and the solution cold, for heat destroys
the color. When the proportion of iodine is very minute, a few minutes may
elapse before the discoloration ensues. When a very minute quantity of
iodide of sodium or potassium is present in a solution, the addition of chlo-
rine is necessary ; and if a solution of starch be then added, the iodine, set
free by the chlorine, is detected by the blue color. If too much chlorine or
starch is added, the blue color of the iodide is destroyed. One or two drops
of strong nitric acid may be employed as a substitute for chlorine. Any
compound containing common salt and an alkaline iodide, mixed with a solu-
tion of starch, and exposed to voltaic action, yields a blue color at the posi-
tive electrode.

The starch-test may be equally applied for the detection of the vapor.
Place a few grains of iodine in a jar of 200 c. i. capacity , previously warmed,
and allow the vapor to diffuse by agitation. Now introduce into the jar, in
which the vapor is scarcely visible by color, a slip of paper which has been
dipped in a solution of starch. The blue color will speedily appear, and
become stronger as the paper is lowered into the jar. The slow diffusion of
the vapor from the solid may be thus proved. Suspend within a tall bell-jar
a slip of bibulous paper soaked in a solution of starch. Invert the bell-jar
over a saucer containing a few crystals of iodine. After some minutes, the
diffusion of the vapor will be manifested by the blue color acquired by the
paper, the change proceeding from below upwards.

The blue compound obtained by adding a solution of iodine to starch is
not permanently destroyed by heat. Unless the solution has been so long
boiled that the whole of the iodine has been expelled, the blue color will
return as the liquid cools. Iodine acts upon iron, zinc, silver, and some
other metals, by direct contact. It has no solvent power on gold. When
placed on phosphorus, so much heat is evolved that the phosphorus takes
tire and burns. In vapor as well as in solution in water, it decomposes sul-
phuretted hydrogen, and sulphur is precipitated.

Iodine is sometimes adulterated with plumbago, sulphide of antimony, or
peroxide of manganese ; but these adulterations are easily detected by their
insolubility in alcohol, or by the residue left on heating the iodine on mica,
so as to volatilize it. The relative quantity of moisture in iodine may be

PERIODIC AOID. 20t

ascertained by heating it in a tube, with twice its weight of fused chloride of
caleliim, at a temperature not exceeding the boiling-point of the iodine ; the
iodine may be expelled by a current of air, and the increase of weight sus-
tained by the chloride gives the quantity of water.

Iodine and Oxygen. — Of the compounds of these elements only two have
undergone a complete examination, namely, the Iodic and Periodic acids.

Iodic Acid (IO5). — This compound cannot be obtained by the direct
action of oxygen on iodine ; it may be procured by boiling iodine for many
hours with about five times its weight of the strongest nitric acid. The
mixture should be introduced into a flask having a long neck, or into a
retort, in order that the iodine, as it sublimes to the upper part, may be
returned into the acid, until it disappears entirely : on carefully driving off
the nitric acid by heat, the iodic acid remains as a white uncrystalline solid.
It may be dissolved in water, and obtained as a crystalline hydrate. By this
process four parts of iodine yield four and a half parts of iodic acid.

The aqueous solution of this acid, when concentrated by evaporation,
yields a pasty mass, which is hydrated iodic acid, lO^jHO. This may be
crystallized in hexagonal plates, from which some of the water may be driven
off by the careful application of a higher temperature. It then becomes
HO.SlOj (360*^). At about 100^ it fuses, and is decomposed into oxygen
and iodine. Iodic acid acts powerfully upon the metals, and with the oxides
forms a class of salts called iodates. Nitric, sulphuric, -phosphoric, and
boracic acids do not decompose it ; but it is decomposed by hydrochloric,
hydrofluoric, hydriodic, oxalic, sulphurous, arsenious, hydrosulphuric, and
other acids.

When it is mixed with charcoal, sulphur, and some other combustibles, it
forms compounds which deflagrate when heated. The solution of iodic acid
is decomposed by several organic substances, as by morphia, narcotine, gallic,
and pyrogallic acids ; and among salts by the sulphocyanides and hyposul-
phites, as well as by sulphate of iron. Zinc and magnesium liberate iodine.
Iodic acid is analogous to the chloric : it is composed of : —

Iodine ....
Oxygen

oms.

Weights.

Per cent.

1

126

75-9

5

40

24-1

Iodic acid .... 1 ... 166 ... 100-0

Iodates. — The salts are represented by the general formula MOjIOs. By
heat, they either become iodides, losing six atoms of oxygen, or they lose
iodine and five atoms of oxygen, leaving a metallic oxide. Their deflagration
with combustibles is less powerful than that of the chlorates, but they are
decomposed when heated with charcoal leaving metallic iodides. They are
not very soluble in water, and their solutions are decomposed by sulphurous
acid, iodine being set free. This is the best test for their presence.

Periodic Acid (I0,H0).— When a solution of iodate of soda, mixed with
pure soda, is saturated by chlorine, and concentrated by evaporation, a
sparingly soluble white salt is obtained, which is a periodate of soda. This
is dissolved in the smallest possible quantity of diluted nitric acid, and mixed
with nitrate of lead ; a precipitate of periodate of lead is thrown down.
This is collected and decomposed by a small quantity of diluted sulphuric
acid. Periodic acid is not known in the anhydrous state ; it may be obtained
as a crystalline hydrate by filtering the liquid and evaporating it. The

208 HYDRIODIC ACID.

periodaies are less soluble than the iodates, but like them they are decom-
posed at a red heat and evolve oxygen.

Hydriodio Acid (HI). — Hydrogen and iodine do not readily combine
directly ; but when they are passed through a red-hot tube hydriodic acid
gas is produced by their union. The gas may be produced by the following
process suggested by Millon : 10 parts of iodide of potassium are dissolved
in 5 parts of water, and 20 parts of iodine are added to ^the solution in a
retort. One part of phosphorus in small portions is then added and a gentle
heat is applied (2KI-fl3+P + 8HO=HO,2KO,(P05) + THI). Hydriodic
acid passes over, and phosphate of potassa remains in the retort. As it is a
very heavy gas, it may be collected by displacement in dry jars. It is decom-
posed by mercury, and hydrogen is evolved, so that it cannot be be collected
over that metal. •

Hydriodic acid gas is colorless, but fumes strongly in the air, and smells
like hydrochloric acid. It reddens vegetable blues. Its specific gravity,
compared with air, is as 4'3878 to 1 ; 100 cubic inches weigh about 135*89
grains. Compared with hydrogen, its specific gravity is as 63-5 to 1. It
extinguishes flame, and is not itself inflammable. It is liquefiable under
pressure, and becomes a transparent colorless solid at about — 60°. It is
not permanent at a red heat, for, when passed through a red-hot porcelain
tube, it is partially resolved into iodine and hydrogem

Hydriodic acid gas is not decomposed by dry air, but when water is present
the oxygen of the air unites to the hydrogen, and iodine is eliminated and
dissolved. The gas is very soluble in water, but in what proportion has not
been determined. The saturated solution, exposed to a temperature below
260°, becomes concentrated by loss of water ; at about 260° it boils, and
may be distilled. The specific gravity of the strongest liquid acid is 11. It
dissolves iodine. It becomes dark-colored when kept in contact with air,
in consequence of a partial separation of iodine, which colors the liquid. The
aqueous hydriodic acid is best prepared by passing sulphuretted hydrogen
through a mixture of iodine and water : sulphur is deposited, and, on heat-
ing and filtering the liquid, a solution of hydriodic acid is obtained, which
may be concentrated by evaporation. The solution is decomposed by chlorine,
by nitric, sulphuric, arsenic, iodic, and sulphurous acids, and by the proto-
sulphate of iron, the iodine being separated.

When hydriodic acid gas is mixed with oxygen, and is passed through a
red-hot tube, it is resolved into iodine and water. Its decomposition by
chlorine produces hydrochloric acid, sometimes with explosion, and the
purple vapor of iodine is rendered evident, but rapidly disappears in conse-
quence of the formation of chloride of iodine. This decomposition is
beautifully shown by causing hydriodic acid gas to pass into a jar of
atmospheric air, mixed with about a twelfth of its bulk of chlorine; the
violet fumes are then more permanent. On the other hand, mercury takes
the iodine and sets free hydrogen. A little strong nitric acid dropped into
hydriodic acid gas energetically decomposes it, with the evolution of so much
heat that the gas is occasionally inflamed.

The composition of hydriodic acid gas is analogous to that of the hydro-
chloric. It consists of 1 volume of the vapor of iodine and 1 of hydrogen ;
these produce 2 volumes of the acid. When potassium is heated in. the gas
it is reduced to half its volume, which consists of pure hydrogen. It is
therefore thus constituted : —

Hydrogen .
Iodine

Atoms.
. 1 .
. 1 .

Weiglits.
1 .
.. 126 .

127

Per cent,
.. 0-8
.. 99-2

100-0

Volumes.
... 1 ...
... 1 ...

2

Sp. Gr.
0-0345
4-3533

Hydriodic acid .

. 1

4-3878

IODIDES. SEPARATION OF IODINE. 209

Iodides. — These salts may be thus identified: 1. When heated with sul-
phuric acid and peroxide of manganese, iodine is evolved. 2. When dissolved
in water, the iodide (of potassium) is neutral, and has no action on starch.
On adding to the mixture a solution of chlorine, or some nitric acid, a deep
blue color is produced. 3. The solution gives a pale yellow precipitate
with nitrate of silver, insoluble in ammonia: 4, a bright yellow precipitate
with a salt of lead (iodide of lead); and 5, a bright scarlet precipitate with a
solution of corrosive sublimate (iodide of mercury). The presence of an
iodate is detected by adding a solution of tartaric acid : the solution becomes
colored by iodine being set free, as a result of the reaction of iodic oa
hydriodic acid.

The relative insolubility of the silver compounds of chlorine, bromine, and
iodine is indicated by the following experiments. A solution of chloride of
silver in ammonia is precipitated by bromide and iodide of potassium, while
a solution of bromide of silver in ammonia is precipitated by a solution of
iodide of potassium.

Iodide of Nitrogen (NHIJ. — This compound has been shown to contain
hydrogen, as well as nitrogen and iodine. It may be prepared by placing
finely-powered iodine for hfflf an hour in a solution of ammonia. The
liquid portion is poured from the insoluble dark brown powder, which is the
iodide. It should be well washed in water. The compound is dangerously
explosive when dry; hence it should be put in small quantities, while moist,
on filtering paper, and allowed to dry spontaneously on sheet lead. The
slightest contact of a body, or merely dropping the powder through the air
or on the surface of water, causes a sudden and violent explosion, with a
flash of light and the escape of iodine in vapor. Even under water it will
explode by friction. It is slowly decomposed when moist by exposure to
air. Boiling water and solutions of potassa and soda decompose it rapidly.
It is converted into nitrogen, iodic, and hydriodic acids. It is decomposed
by sulphuretted hydrogen, and it loses its detonating properties in the pre-
sence of an excess of ammonia. By numerous experiments, M. Bineau has
proved that its true formula is NHIg.

Chlorine forms two volatile and unstable compounds with iodine, ICl
(liquid) and ICI3 (solid).^

Chlorine, iodine, and bromine are occasionally so associated as to require
separation in analyses. To ascertain the quantity of iodine in the mixed
chlorides and iodides of mineral waters, Rose recommends precipitation by
nitrate of silver; the mixed chloride and iodide of silver thus thrown down
is fused, weighed, and afterwards heated in a tube, and a stream of chlorine
passed over it; the iodine is thus expelled, and the whole converted ioto
chloride of silver; this is weighed again, and a loss is found to have taken
place in consequence of the equivalent of the expelled iodine being greater
than that of the expelling chlorine; this loss, multiplied by 1'4, gives the
quantity of iodine, originally present, which has been replaced by chlorine
for (126— 36 = 90, and 126 -^"90= 1-4) .Schweitzer recommends the adoption
of a similar method for estimating the quantity of iodine when mixed with
bromine ; in this case the mixed iodide and bromide of silver is to be heated
in an atmosphere of bromine vapor, by which the iodine is expelled. The
presence of an iodide, in mixture with a chloride and bromide, may be
detected by considerably diluting the solution with water, and adding to it a
solution of chloride of palladium. Iodine gives with this salt a dense purple
black precipitate of iodide of palladium (Pdl). A diluted chloride or
bromide is not thrown down by this reagent. The mixed sulphates of iron
and copper {see page 205) precipitate the iodine of an iodide in an insoluble
14

210 FLUORINE. HYDROFLUORIC ACID.

form. A chloride is not affected, and a bromide only when the solution is
moderately strong.

Fluorine (F=19).

History and Properties. — Fluorine is a simple body concerning which, in
its pure state, but little is known. It is most abundantly met with in the
mineral known as fluor or fltior- spar, which is a fluoride of calcium (CaF).
Hence the name Jiuo7^ine. In its pure state the fluoride of calcium contains
49 per cent, of fluorine. This mineral is found abundantly in Derbyshire,
Cornwall, and Cumberland. It is well known by its cubic crystals, sometimes
colorless, but more commonly colored purple, yellow, or green. The mineral
cryolite, from which aluminum is extracted, is a compound fluoride of alum-
inum and sodium (AlgFgjSNaF). It is a white translucent fusible substance
found in Greenland. It contains about 42 per cent, of fluorine. Fluorine
is a constituent of the topaz : it is found in some kinds of mica, in fossil
bones and coprolites. It exists in traces in sedimentary rocks, in river,
spring, and sea-water, in recent bones, in teeth, and in many organic substances.

Davy and other chemists have attempted to isolate fluorine by heating dry
fluoride of silver in a current of chlorine. In operating in glass or platinum
vessels, the fluorine instantly entered into combination with the silicon or
platinum, and fluorides of silicon and platinum alone were obtained. It is
stated that fluorine has been procured by the substitution of vessels of fluor-
spar for those of glass and platinum ; but the description of the properties
of the body thus obtained, shows that it was probably a mixture of clilorine
and hydrofluoric acid. One fact, however, has been elicited as a result of
these experiments. When an anhydrous fluoride in a state of fusion is
submitted to electrolysis, there is evolved at the positive electrode a body
which decomposes glass and forms with platinum a fluoride which is decom-
posed by heat. Hence it may be assumed that fluorine, whether gaseous,
liquid, or solid, is an electro-negative metalloid, bearing some analogy to
chlorine, bromine, anfl iodine. It forms no known compounds with these
elements, with, oxygen, or carbon. It unites readily to metals forming
fluorides, and to three non-metallic bodies — namely, hydrogen, boron, and
silicon. The principal compound of fluorine, is that which it forms with
hydrogen — hydrofluoric acid.

Hydrofluoric Acid (HF). — This was formerly called fluoric acid, from
the supposition that it was a compound of fluorine and oxygen. It is a
gaseous anhydrous acid analogous to the hydrochloric. The existence of
this acid was first made known by Scheele, although as he employed vessels
of glass, he did not obtain it in a pure state. Its properties were examined
by Gay-Lussac and Thenard in 1810 {JRecherches Physico-chemiques), and
by Davy(PM. Trans. 1809-1813). When finely-powdered /zfont/e of cal-
cium Qv Jiuor-spar, as it is usually called (carefully selected for its purity and
freedom from silica), is distilled with twice its weight of sulphuric acid, a
highly volatile and corrosive liquid, which is hydrated hydrofluoric acid, is
obtained: CaF-}-S03,HO = CaO,S03-j-HF. It acts powerfully on glass
and on most of metals : the retort employed in the experiment may be of
lead, with a tube and receiver of platinum ; the receiver must be immersed
in a mixture of ice and salt. The product may be preserved in a platinum
bottle, with a well-fitted stopper of the same metal, but gutta-percha bottles
are now commonly employed. In this concentrated state it is a clear,
colorless liquid ; it fumes when exposed to air ; boils at 68°, and flies off in
vapor. Its specific gravity in this state is 10609. It has not been con-
gealed. By the gradual addition of a certain proportion of water it acquires
a considerable increase of density, the mixture having a specific gravity of

PROPERTIES OF HYDROFLUORIC ACID. 211

l'15(HF,4HO). Its attraction for water exceeds that of oil of vitriol ; and
when dropped into water it causes a hissing noise, and great heat is evolved.
Its vapor it dangerously pungent and irritating, and the liquid acid is
eminently active upon organic substances; a minute drop of it upon the skin
produces a painful sore, and in larger quantities malignant ulceration : hence
the vessels containing it require to be handled with great caution. Its most
characteristic property is the energy with which it acts upon glass : its
vapors soon destroy the polish and transparency of all neighboring glass-
vessels, and when dropped upon glass, great heat and effervescence are pro-
duced, and dense fumes are evolved, consisting of hydrofiuosilicic acid.
Diluted with about six parts of water, the acid may be used for etching
upon glass, which it effectually accomplishes in a few minutes. For this
purpose the surface is covered with a thin layer of wax and tallow, and this
is removed from those parts on which it is intended the acid should act.
The diluted acid is then poured on the glass, and after a short time it is
removed. The layer of wax is melted off, and the pattern then appears
corroded on the glass. If a prepared plate is exposed to the acid vapors, a
dull surface is given to the corroded portions.

When the concentrated acid is submitted to electrolysis, hydrogen is
evolved at the negative electrode, and the positive platinum wire is corroded
and converted into a brown compound, probably of fluorine and platinum.
All the metals excepting mercury, gold, silver, platinum, and lead, decom-
pose it with the evolution of hydrogen ; and peculiar compounds result,
Jluorides, consisting of the metal in combination with fluorine. The action
of potassium upon the concentrated acid is very energetic ; it is attended
by explosion, by the liberation of hydrogen, and by the formation of a
peculiar soluble saline compound which is considered as a fluoride of
potassium.

The only metalloids on which it acts are boron and silicon. It has no
action on carbon hence it enables a chemist to distinguish the true from the
false diamonds. Like hydrochloric acid, it acts violently upon zinc, mag-
nesium, and aluminum, setting free hydrogen ; but it has very little action
on copper. When added to solutions of lime, baryta, strontia, magnesia,
and alumina, it throws down insoluble fluorides of the metals. In this
respect it differs from the hydracids of chlorine, bromine, and iodine, which
form soluble compounds with these bases. Nitrate of silver produces with
this acid a white compound, which is soluble in water, which is not affected
by light, and easily decomposed by heat. The chloride, bromide, and iodide
of silver are entirely different in their properties. Its most remarkable
property is that of acting upon silica and all its combinations, even upon
glass — a substance which is not attacked or dissolved by any other acid. A
small quantity of the acid poured upon glass produces immediately an
opaque spot or streak (SiO,+3HF=3HO-f SiFg). The fluoride of silicon
produced when in contact with water undergoes a change by which hydrated
silicic acid or silica is precipitated.

This acid, when mixed with strong nitric acid, and the mixture is heated,
does not dissolve gold or platinum. It forms no aqua regia, like the hydro-
chloric acid.

Composition — Kuhlman's experiments have proved that this is a hydracid ;
he found that pure fluor-spar (fluoride of calcium) was not in the least acted
upon, even at a red heat, by anhydrous sulphuric acid, and that when hydro-
chloric acid was transmitted over fluor-spar at a red lieat, hydrofluoric acid
was disengaged and chloride of calcium formed. It cannot therefore be
doubted that the hydrofluoric, like the hydrochloric acid, is composed of one

212 SULPHUR. ITS PRODUCTION.

atom or volume of each of its elements, and it may be assumed that they are
united without auj condensation.

Atoms.

Weights.

Per cent.

Volumes.

Hydrogen

.

. 1

=

1

5

1

Fluorine.

,

* 1

=

19

95

1

1 20 100 2,

Its atomic weight is derived from the proportion of sulphate of lime
obtained by the decomposition of a known weight of pure fluoride of calcium.

Fluorides. — A soluble fluoride is known by its action on glass. An inso-
luble fluoride may be powdered and covered with sulphuric acid in a platinum
crucible. If the substance is a fluoride, or if any fluoride be present, the
vapor set free will produce a visible change on a glass plate placed over the
crucible.

CHAPTEE XVII.

SULPHUR AND ITS C OMPO U N D S — SE LENIUM AND ITS
COMPOUNDS.

Sulphur (S=16).

This important substance is found native, chiefly in volcanic districts,
either crystallized or amorphous. The Island of Sicily, and the Solfatara,
near Naples are the principal sources of supply. There are large deposits
of sulphur in Spain, also around Hecla, in Iceland, and it occurs more
sparingly in certain gypsum beds in Europe. The well-known mineral, iron-
pyrites, contains about 54 per cent, of sulphur, and readily yields this sub-
stance by distillation. The sulphur thus obtained is, however, less pure than
native volcanic sulphur, and is generally contaminated with arsenic. Although
commonly described as a mineral body, sulphur enters into the composition
of certain animal and vegetable substances. Associated with nitrogen, it is
a constituent of albumen, fibrin, and casein ; it enters into the composition
of silk, hair, horn, nail, and feathers. It is found in gluten, and certain
essential oils — e.g., those of mustard and horseradish.

Preparation. — The native mineral, on which the sulphur is deposited, is
broken up and submitted to distillation in fireclay pots, connected with re-
ceivers. The mineral contains from 30 to 50 per cent, of sulphur. The
greater part of this is separated by the first distillation, the sulphur thus
obtained containing rarely more than 5 or 6 per cent, of earthy impurities.
By a second distillation, the sulphur is obtained pure ; and while in a liquid
state it is poured into wooden moulds of a slightly conical shape. The
sulphur, when cooled, is removed, and it then forms the well-known rolU
sulphur of commerce. By conveying the vapor during distillation into a
large chamber, kept cool, the sulphur is deposited in a pulverulent state,
and is then known as flowers of sulphur. Owing to the combustion of a
portion some sulphurous acid is produced, and thus the powder occasionally
has an acid reaction from this cause. Sublimed sulphur may be purified by
washing it in hot water. Sulphur is obtained from pyrites, by simply dis-
tilling the broken mineral in fireclay, or cast-iron retorts, connected with
receivers. The mineral yields readily from 20 to 25 per cent, of sulphur,

SULPHUR. PHYSICAL AND CHEMICAL PROPERTIES. 213

which frequently has a greenish tint, from the presence of some sulphide of
iron. Sulphur in its purest form generally contains a trace of hydrogen.

Properties. — Sulphur, or brimstone, is a brittle substance, of a pale yellow
color, insipid, and inodorous, but exhaling a peculiar odor when rubbed or
heated. Its specific gravity is 1-970 to 2080. According to Regnault,
the specific heat of crystallized native sulphur is O'lTTG, and of sulphur
recently fused, 0*1844. It becomes negatively electrical by heat and by
friction, and is a non-conductor of heat and electricity. * Sulphur, as a
mineral product, occurs crystallized, its primitive form being an acute octa-
hedron with a rhombic base. In this state its sp. gr. is 2 045, and the
crystals are in a high degree doubly refractive. Crystals of native sulphur,
which have been formed by the condensation of sulphur vapor, as well as
those which are deposited from a solution of sulphur in any menstruum,
possess forms which are either identical or connected by being referable to
the same crystalline axes. Such, on the contrary, as are produced by the
cooling of fused sulphur, belong to a different system of crystallization. One
of the conditions determining the form, is temperature : if the crystal be
formed below 232° it belongs to the right prismatic system ; if at that point,
to the oblique prismatic. This is proved by the influence of temperature on
a crystal of either system ; a crystal of fusion, when first formed, is perfectly
clear and transparent, but kept at common temperatures it soon becomes
opaque, and presents the appearance of the roll sulphur of commerce ; the
same change occurs when a native crystal is placed in a solution of salt which
boils at 232°. The opacity is in both cases produced by a new arrangement
of the particles of sulphur, by which, without any change in the external
form, the internal structure of the crystal is altered. Sulphur, therefore, is
dimorphous. {See p. 38.)

Sulphur has no injurious action on the body : it is insoluble in water, and
snfiFers no change by exposure to air. An invisible vapor is constantly
escaping from it at common temperatures. If leaf-silver be suspended in
the upper part of a bottle containing sulphur, it will, after a few weeks,
become blackened by conversion into sulphide of silver. At about 180^
sulphur is volatilized, and its peculiar odor is strong and disagreeable ; at
about 220^^ it begins to fuse, and between 230° and 2t0^ it is perfectly
liquid, and of a bright amber-yellow color. It may be readily melted by
heating it on writing-paper over a candle. On cooling it sets into a group ,
of prismatic crystals. If melted on a glass-slide, and examined by an inch-
power of the microscope, the phenomena of prismatic crystallization are
beautifully seen. When sulphur is heated to between 300° and 500°, it
becomes viscid, and of a dark brown color, but regains its fluidity When
cooled to 230°. At a higher temperature (out of contact of air) it again
becomes more liquid, and at about 800° it boils, producing an amber-colored
vapor, which may be condensed either in a solid or pulverulent state, accord-
ing to the rapidity of the process and the size of the condensing vessels.
The residue is the sulphur vivum of old pharmacy. If sulphur is heated to
about 450°, and while still viscid, is poured into cold water, it acquires and
retains a certain flexibility and elasticity, having at the same time a dark
color : it hardens slowly. In this state, it is sometimes used to take impres-
sions of gems and medals, or plaster medallions. For this purpose, the
surface of the mould should be oiled before the sulphur is poured on it.
When cold, it has a reddish-brown color, and a specific gravity of 2'3.
When slowly cooled after fusion, sulphur forms a fibrous crystalline mass ;
but it so*raetiraes retains its fluidity, and does not concrete till touched by
some solid body. This state appears somewhat analogous to that of water
cooled in a quiescent state below its freezing-point. (Faraday, Quarterly

214 SULPHUR. ALLOTROPIC STATES.

Journal, 21, 392.) (For the method of procuring crystals of sulphur by
fusion, see page 26.) The following table shows the results of Dumas's
experiments on the influence of temperature upon the color and properties
of sulphur : —

Temperature. Hot Sulphnr. Sulphnr suddenly cooled by immersion in water.

230° . . Very liquid : yellow . . Very brittle : usual color.

284 . . Liquid : deep yellow . . Do. do. .

338 . . Thick : orange yellow . Brittle : ' do.

374. . Thicker: orange . . 5 ^t first soft and transparent, then brittle

^ ^ and opaque : usual color.

428 . . Viscid : reddish . . Soft : transparent : amber color.

464 to 500 Very viscid : brown-red . Very soft : transparent : reddish.

800 boiling Less viscid : brown-red . Do. * do. brown-red.

In order that sulphur may retain its soft or viscid state, it is not necessary,
as sometimes directed, to keep it long in a fused state, but merely to take
care that it has been raised to a due temperature, and then suddenly cooled
by dropping it into cold water; if poured into the water in mass, the
interior cools slowly and reverts to its brittle state. Here, therefore, the
effect of what may be called tempering, is the reverse of that produced
upon steel, and somewhat corresponds with the phenomena presented by
bronze.

The researches of Deville, Berthelot, Magnus, and other chemists, have
shown that sulphur, according to the effect of heat and sudden cooling, may
assume various allotropic conditions. Deville assigns four varieties, and
Magnus six. These are based chiefly on crystalline form, color, and solu-
bility. The hlach sulphur of Magnus is obtained by heating sulphur
repeatedly to near its boiling-point, and then suddenly cooling it in water.
It is characterized not only by its color, but by its insolubility in sulphide
of carbon, and the usual solvents of sulphur. (Pelouze and Fremy, Traite
de Chimie, 1, 200.) The sulphur of commerce occurs in three prevailing
colors, namely, lemon yellow, verging on ^reen, dark yellow, and brown
yellow.; these shades result, partly at least, as the above table shows,
from the different degrees of heat to which it has been exposed during its
fusion or extraction on the great scale — the palest variety having been the
least heated.

For some pharmaceutical purposes, sulphur is precipitated from a solu-
*tion of tersulphide of potassium or pentasulphide of calcium, by hydrochloric
acid, and, when washed and dried, it forms a pale yellowish-gray impalpable
powder; this is the milk of sulphur Qlw^ precipitated sulphur of the Pharma-
copoaia. Thomson considers it to be a compound of sulphur and water — a
hydrate. {System of Chemistry, vol. 1, p. 285.) When dried it gives out no
water, but fuses into common sulphur, always, however, evolving a little
hydrogen.

The purity of sulphur may be judged of by heating it gradually upon a
piece of mica or platinum-foil ; if free from earthy substances, it should
evaporate and leave no residue. It should also be soluble in benzole or
boiling oil of turpentine. According to Ure, sulphur is soluble in ten times
its weight of boiling oil of turpentine at 316°, forming a red-colored solu-
tion which remains clear at 180°. When the solution cools rapidly, or is
rapidly evaporated, prismatic cijstals are deposited. If, however, it is
allowed to evaporate spontaneously, octahedral crystals are formed. The
same phenomena is observed in reference to the solution of sulphur in ben-
zole. The employment of either of these liquids enables a chemist #o deter-
mine whether sulphur is contaminated with its usual impurities, namely,

SULPHUR. COMPOUNDS. TESTS. 215

carbonate and sulphate of zinc, oxide and sulphide of iron, sulphide of
arsenic and silica. These remain undissolved.

The sp. gr. of sulphur-vapor is theoretically 6 "6336, and, supposing it to
exist ^s vapor at mean temperature and pressure, 100 cubic inches would
weigh 205-44 grains. From the experiments of Dumas and Mitscherlich, at
a temperature of 932°, the sp. gr. of the vapor is 6 •654. According to
Bineau, when taken at a temperature of 1832°, the sp. gr. is 2-218. Cora-
pared with hydrogen, the sp.'gr. of sulphur-vapor is as 96 to 1.

Sulphur is not readily dissolved by alcohol, ether, or chloroform. Anhy-
drous alcohol when boiled with it dissolves it in small quantities. The
vapors of these liquids also combine with it. It is very soluble in sulphide
of carbon ; 100 parts of this liquid will dissolve 38 parts of sulphur at the
common temperature, and 73 parts when heated. The sulphide may be use-
fully employed for the separation of sulphur from vulcanized rubber, gun-
powder, &c. If recently fused sulphur is dissolved in the sulphide, and it is
spontaneously evaporated, crystals belonging to the two systems are de-
posited, namely, transparent octahedra, and oblique rhombic prisms, which
are opaque. It is probable that by heat the sulphur has partially undergone
an allotropic change. Among other solvents of sulphur may be mentioned
chloride of sulphur and the alkaline sulphites. The latter are commonly
used for devulcanizing caoutchouc.

When heated in the atmosphere to about 560° sulphur inflames and burns
with a peculiar blue light; at a higher temperature its vapor kindles with a
purple flame ; and in oxygen it burns vividly, with a large lilac-colored
flame. The comparatively low temperature at which sulphur is kindled, is
an important circumstance in reference to its use for the manufacture of gun-
powder, matches, &c. It may be well illustrated by propelling powdered
sulphur into the hot air issuing from an argand lamp-glass; it takes fire at
a great height above the flame. The product of combustion is sulphurous
acid, known by its peculiar odor.

Equivalent and Compounds. — Sulphur combines with the metalloids and
metals, forming the class oi sulphides or sulphurets. The metallic sulphides
generally correspond to the oxides. The range of combination of sulphur
is very great ; it frequently displaces oxygen, converting oxides into sul-
phides, while many sulphides, by simple exposure to air, are converted into
oxides. Its atomic weight, as deduced from its compound with hydrogen, is
16. Hence as sulphur-vapor has a sp. gr. of 96, compared with hydrogen,
each volume of the vapor will correspond to six atoms, or the atomic volume
of sulphur-vapor will be one-sixth of a volume. If the atomic volume of
hydrogen be two, then that of sulphur will be one-third of a volume.

Tests. — The color, fusibility, and combustion with a blue flame, as well as
the odor of the vapor, are sufficient tests for sulphur in a solid state. Its
solubility in sulphide of carbon, and the production of octahedral crystals as
a result of the spontaneous evaporation of the solution, are also characteristic
of the presence of this substance. In many organic solids its existence is
revealed by applying heat, when sulphuretted hydrogen escapes. If sulphur,
or any substance containing traces of it (quill or gluten), be boiled in a solu-
tion of potassa, holding dissolved a small quantity of oxide of lead, the liquid
or the solid acquires a brown-black color from the production of sulphide of
lead. The test is prepared by adding to a solution of potassa a few drops
of a solution of acetate of lead, and then adding a sufficient quantity of po-
tassa to dissolve the white precipitate which is first formed.

SuLPHua AND Oxygen. — Sulphur forms no oxide ; but there are seven
compounds of sulphur and oxygen, all of which rank among the acids. The

216 SULPHUR AND OXYGEN. SULPHUROUS ACID.

most important of these are, 1. Sulphurous acid ; 2. Sulphuric acid ; and 3.
Hyposulphurous acid.

Sulphurous acid

. SO,

Hvposulphuric (dithionic) acid S^Og

Sulphuric acid .

. SO3

Trithionic acid . , . . S3O5

Hyposulphurous acid )

. s,o,

Tetrathionic acid . . . S^Og

Dithiouous acid /

Pentathionic acid . . . S5O5

In the four last compounds, the atoms of oxygen being 5, there is aa
increase of one atom of sulphur in each. Of the seven oxy-compounds here
enumerated, the first three have a special importance to the chemist, and as
they are produced by a conversion or reaction of sulphurous acid, it is this
compound which will first claim our consideration.

Sulphurous Acid (SOg) This is an anhydrous gaseous acid produced by

the burning of sulphur in oxygen. In 1Y74, Scheele pointed out a method
of obtaining it : and about the same time Priestley procured it in the gaseous
form, and ascertained its leading properties. Its atomic composition was
first accurately investigated by Davy, Gay-Lussac, and Berzelius.

Sulphurous acid may be obtained by several processes. It may be pro-
cured directly, by burning sulphur in dry oxygen gas ; or indirectly, by
boiling one part of copper filings or of mercury in three of sulphuric acid
(Cu-fi^[S03,HO] = CuO,S03+2HO + S02): or by heating in a retort a
mixture of three parts of black oxide of manganese in powder and one of
sulphur, S3-HMn02=S03 4-MnS. Charcoal or sulphur boiled with sulphuric
acid, also yields this gas. As water dissolves about fifty times its bulk of
the gas, it should be collected and preserved over mercury. For all the
common purpose of experiment, it may be collected by displacement in dry
jars or bottles. When generated by the action of charcoal, wood, and various
organic matters, upon sulphuric acid, it is mixed with carbonic acid. Sul-
phurous acid may be procured by the combustion of sulphur or sulphide of
carbon in a confined volume of air. Under these circumstances, it is mixed
with nitrogen or carbonic acid.

Properties. — The gas is without color, but it has the suffocating odor of
burning sulphur, and a sour taste. If breathed in a diluted state, it causes
cough and headache ; and in a concentrated form it is fatal to life. It is
highly destructive to all animals. It is very heavy, being more than twice
the weight of air. Its sp. gr. is 2-2112, and compared with hydrogen, 32
to 1 ; 100 cubic inches weigh 68'48 grains. It is one of the most easily
liquefiable of the gases (p. 80). By mere cooling to 14°, it becomes aa
anhydrous limpid liquid.

In the liquefied state it has asp. gr. of 1-45, evaporating with such rapidity
at common temperatures as to generate a great degree of cold, so that by
its aid mercury may be frozen, and chlorine, ammonia, and cyanogen liquefied.
The liquid acid is not an electrolyte. When it is allowed to evaporate in
vacuo, the cold produced is so intense, that the liquid acid is congealed ; it
solidifies at — 105° ; it may also be frozen by the aid of a mixture of solid
carbonic acid and ether ; it then forms a white crystalline mass, denser than
the liquid acid.

When sulphur is burned in pure and perfectly dry oxygen, sulphurous
acid only is produced, without any change in the volume of oxygen, so that
its composition is learned by the increase of weight. Oxygen, when saturated,
is exactly double in weight; hence sulphurous acid consists of equal weights
of sulphur and oxygen. According to Mitscherlich's estimate of the specific
gravity of sulphur-vapor, sulphurous acid consists of 100 volumes of oxygen
gas, and 16 of the vapor of sulphur, condensed into 100 volumes; or one
volume of oxygen combined with one-sixth of a volume of sulphur-vapor
constitute one volume of sulphurous acid.

SULPHUROUS ACID. COMPOSITION. 21T

Atoms, Weights. Per cent. Volume. Sp. Gr.

Sulphur. . . . 1 ... 16 ... 50 ... ^ ... 1-1055

Oxygen . . . . 2 ... 16 ... 50 ... 1 ... 1-1057

Sulphurous acid . . 1 32 100 1 2-2112

As oxyp^en undergoes no chanpje of volume in forming this gas, the num-
ber of volumes of sulphurous acid are indicated by the quantity of oxygen
consumed in the combustion of sulphur.

The gas has a strongly acid reaction. It extinguishes most combustibles
when they are immersed in it in an inflamed state ;. hence burning soot in a
chimney may be extinguished by throwing a handful of sulphur into the fire.
The upper part of the flue should be stopped, and no air allowed to pass
into the chimney except that which traverses the burning sulphur. Air con-
taining only one-third of its volume of this gas does not support ordinary
combustion. The gas vividly maintains the combustion of potassium and
sodium. At mean temperature and pressure, recently boiled water takes up
about 50 volumes of sulphurous acid gas. This solution {aqueous sulphurous
acid), which may be procured by passing the gas into distilled water, has a
sulphurous and somewhat astringent taste, and it bleaches some vegetable
colors. If long kept, sulphuric acid is formed; it acquires a sour flavor,
and reddens vegetable blues. Some coloring matters, such as those of
litmus and cochineal, are not readily bleached by sulphurous acid ; while
those which are bleached may have their colors restored by an acid or an
alkali. If a solution of sulphurous acid is added to infusion of roses or blue
infusion of cabbage, it will redden these liquids, owing to the presence of
free sulphuric acid. By carefully neutralizing this acid with potassa, the
color will entirely disappear. If the liquid thus bleached be now treated
with a strong solution of potassa, it will acquire a green color, while another
portion will be intensely reddened by sulphuric acid. If added to a solu-
tion of azuline there is no change of color, but when a solution of potash is
added to neutralize the sulphuric acid present, the blue liquid becomes color-
less. On adding strong sulphuric acid to this liquid, the blue color is
restored. The bleaching, therefore, depends upon a temporary production
of colorless sulphites. Cotton goods, as well as those of silk, woollen, and
straw, which would be injured by chlorine, are bleached by this acid. The
articles, wetted, are exposed in a close chamber to the fumes of burning
sulphur. They are then well washed, to remove the colorless sulphites, and
are thus eff'ectually bleached. Hops are also bleached by exposure to the
vapor of burning sulphur. Sulphurous acid by its removal of free oxygen
arrests fermentation and putrefaction. When the aqueous solution of sul-
phurous acid is boiled, a great part of the gas escapes, but not when it is
frozen. The specific gravity of the solution at 60°, when it contains 50
volumes of the gas, is 1-04. At a low temperature the concentrated aqueous
solution deposits a crystalline hydrate consisting of SOg+OHO. Alcohol
dissolves sulphurous acid more copiously than water ; one volume taking up
at 60°, 115 volumes of the gas.

Sulphurous acid gas suffers no change at a red heat; but if mixed with
hydrogen, and passed through a red-hot tube, water is formed and sulphur
deposited (2H + S0a=S-f 2H0). Under the same circumstances, it is de-
composed by charcoal, by potassium, and sodium, and probably by several
other metals. It undergoes no change when mixed with oxygen, unless
humidity or water be present, in which case a portion of sulphuric acid is
slowly formed. But a mixture of the dried gases passed over heated spongy
platinum produces anhydrous sulphuric acid. When mixed with chlorine,
and in contact with water, sulphurous acid produces sulphuric and hydro-

218 TESTS FOR SULPHUROUS ACID AND SULPHITES.

chloric acids (SOa+HO + Cl^SOg + HCl) ; but the perfectly dry gases
have no mutual action, except under the influence of bright summer sun-
shine, when a mixture of equal volumes of chlorine and sulphurous acid
yields a liquid of the specific gravity of 1-659 at 68°, which boils at 170°,
the specific gravity of the vapor being 4-67. Its formula is S0^,C1. It
may be compared to sulphuric acid, in which one atom of oxygen has been
replaced by one of chlorine. With water, it evolves heat and yields hydro-
chloric and sulphuric acids. Iodine and bromine are without action on
sulphurous acid unless water is present, when sulphuric acid, and hydriodic
and hydrobromic acids are formed (S034-H04-I=HI-|-S03). The chloric,
bromic, and iodic acids are decomposed by sulphurous acid, with the evolu-
tion of chlorine, bromine, and iodine, and the formation of sulphuric acid.
When gaseous sulphurous acid is mixed with hydrochloric, hydriodic, or
hydrobromic acid gases, they mutually decompose each other ; water, with
chloride, iodide or bromide of sulphur is formed ; but when these acids are
in aqueous solution, they do not decompose each other. In the dry state,
sulphurous acid has no action on hydrosulphuric acid : but when water is
present, or the aqueous sohitions of the two gases are mixed, water is pro-
duced and sulphur is thrown down (S02-i-2HS = 2B[0 + 3S). Sulphur and
pentathionic acid are sometimes products of this mixture. It is probably
by a reaction of this kind that sulphur is naturally deposited at the Sol-
fatara, and in other volcanic districts. Sulphurous acid deoxidizes the
oxacid compounds of nitrogen. Thus, in contact with nitric acid, sulphuric
acid and deutoxide of nitrogen are produced (3S02-fN05,HO=3S03+
NOg+HO). Two atoms of sulphurous acid produce hyponitrous acid, and
one atom produces nitrous acid, both of which are dissolved in the unde-
composed nitric acid, giving to it a bluish green or green color. An excess
of sulphurous acid therefore entirely decomposes the acid compounds of
nitrogen and oxygen. On evaporation of the mixture, nothing but sulphuric
acid is obtained : the deutoxide of nitrogen escaping as a gas. Iodic acid
undergoes a similar deoxidation, (5SO^+IO,=l4-5S03). Iodine is set
free, and may be detected by its odor, or by its action on a solution of
starch. Sulphurous acid gas is entirely absorbed and removed by peroxide
of lead, Pb03 + S03=PbO,S03. In the presence of water or of certain
bases, sulphuric acid and deutoxide of nitrogen combine to form crystalline
compounds. Peroxide of lead, or of manganese, added to the aqueous solu-
tion of sulphurous acid, converts it into sulphuric acid, and destroys its
odor.

Tests. — The best test for sulphurous acid gas is its odor, and acid reaction.
Paper wetted with a solution of protonitrate of mercury is blackened by it.
A mixture of iodic acid and starch in solution, or paper immersed in this
liquid, reveals the presence of the smallest quantity of the acid by the pro-
duction of blue iodide of starch. Zinc is dissolved by the aqueous acid
without any evolution of hydrogen (2Zn + 3S03=ZnO,S,0,+ ZnO,S02).
If hydrochloric acid is added to the mixture, sulphuretted hydrogen is pro-
duced and evolved. Traces of sulphurous acid may thus be found in hydro-
chloric acid. Sulphurous acid may be detected in the smoke of coke and
coal, and it is thus imparted to the atmosphere of places where coal is burnt.

Sulphites and Bisulphites (MO.SO^ and MO,2S03).— The sulphites of the
alkalies when exposed in a moist state to the air, pass gradually, by absorp-
tion of oxygen, into sulphates. Chlorine, nitric acid, and several other
oxidizing agents, produce a similar change. Sulphites destroy the color of
a solution of permanganate of potassa, and reduce the persalts of iron to the
state of protosalts ; added to nitrate of silver they form a white precipitate
of sulphite of silver ;. which is soluble in nitric acid at a boiling temperature.

SULPHURIC ACID. OIL OP VITRIOL. 219

The precipitate given by nitrate of baryta in the solution of a sulphite (free
from sulphate), is also soluble in nitric acid. When an alkaline sulphite is
boiled with nitric acid, fumes of sulphurous acid and nitrous acid are evolved,
and nitrate of baryta will now produce in the liquid a white precipitate of
sulphate of baryta, which is insoluble in nitric acid. A sulphite reduces the
chloride of gold from its acid solution slowly in the cold, but rapidly by heat.
Arsenic acid is converted into arsenious acid by boiling it with a sulphite or
with sulphurous acid. Bisulphite of soda is occasionally used in analysis for
the removal of chlorine from liquids. The solid sulphites evolve sulphurous
acid, when concentrated sulphuric acid is poured on them. This may be
detected by iodic acid and starch.

Sulphuric Acid (SO3). Oil of Vitriol (HOjSOg).

Production. — This acid was first obtained by the distillation of sulphate of
iron, or green vitriol, and was termed from its appearance and consistency,
oil of vitriol. It was formerly procured by the combustion of a mixture of
eight parts of sulphur and one part of nitrate of potassa or soda in a furnace.
During this combustion sulphurous acid and nitric as well as nitrous acid
were evolved. It is now found more convenient to produce the sulphurous
acid by burning sulphur or iron-pyrites under a regulated current of air in
a furnace, and to decompose the nitrate of potassa or soda by means of sul-
phuric acid, in vessels or pots exposed to the heat of the burning sulphur —
or in a separate chamber. The vapors are carried by the flues into capacious
leaden chambers, which are sometimes 100 feet long, 20 to 30 feet wide, and
10 to 16 feet high. On the floor of these chambers there is a stratum of
water; and the decomposition of the gases by which sulphuric acid is pro-
duced, is effected by the occasional introduction of jets of steam. The water
on the floor of the chamber dissolves the products, and gradually becomes
more and more acid : it is converted into diluted sulphuric acid. When it
has thus acquired a specific gravity of 1*2 to 13, it is drawn off into shallow
leaden boilers, where it is evaporated until it reaches a specific gravity of
] 'to. In addition to the loss of water by evaporation, any traces of sulphur-
ous or nitric acid, are then expelled. L% this density the acid would begin
to act upon lead, and the heat required for its further evaporation would
endanger the softening of the metal. At this degree of concentration, there-
fore, the acid is run off into boilers, or into stills of platinum, which are set
upon cast iron, and in which the further boiling down of the acid is continued
until vapors of sulphuric acid begin to appear, or it has attained the specific
gravity of r84. It is then drawn off by a siphon into a platinum cistern or
cooler, and is thence transferred into carboys, or large bottles protected by
basket work, each holding about 100 pounds of the acid. Before the intro-
duction of platinum vessels, the evaporation was finished in glass retorts.

In this process the sulphurous acid derived from the combustion of sulphur
or pyrites is oxidized and converted into sulphuric acid by the agency of
deutoxide of nitrogen and water. The nitric and nitrous acids, set free from
the nitre, are deprived of three and two equivalents of oxygen respectively
apd sulphuric acid and deutoxide of nitrogen result (5SOa+N05 + N04=
5SO3 + 2NO3). As there is air in the chamber, the deutoxide of nitrogen
is immediately converted to nitrous acid (2N0.3+04=2NOJ and thenitrous
acid thus produced is again decomposed by the sulphurous acid. It will be
perceived from this statement, that the deutoxide of nitrogen, once formed,
serves as a medium for transferring the oxygen of air in the chamber to the
sulphurous acid ; and the operation is made continuous by allowing a certain
quantity of air to pass into the chamber with the sulphurous acid. The

290 SULPHURIC ACID. CHEMICAL PROPERTIES.

amount of sulphuric acid produced, depends on the supply of sulphurous
acid. Only a comparatively small proportion of deutoxide is needed for the
chang:e.

Dry sulphurous and nitrous acids have no action on each other. The
presence of a small quantity of aqueous vapor brings about their combina-
tion, and a white crystalline solid is produced. This is decomposed by
water or steam, and while deutoxide of nitrogen is evolved, sulphuric acid is
dissolved in the liquid. The composition of these crystals is viewed differ-
ently by different chemists, but the following equation indicates the changes :
2SO,+NO„ + 2HO=2(SO„HO)-fNO,.

The phenomena connected with the production of sulphuric acid may be
easily witnessed by introducing sulphurous acid with nitrous acid vapor into
a large glass globe, and adding water in a small quantity to produce the
crystals, and afterwards in larger quantity to decompose them. On a small
scale, the reaction of these gases upon each other may be illustrated by
inverting a small jar of moist deutoxide of nitrogen over a jar of sulphurous
acid. A deposit of a white crystalline substance over the interior speedily
takes place. In the working chamber, the crystals are not commonly pro-
duced, as the jets of steam introduced and the abundance of water prevent
their formation. Other methods of forming sulphuric acid have been pro-
posed, but they have not been hitherto applied on a large scale.

Properties. — Monohydrated sulphuric acid is a heavy oily-looking liquid
— limpid, colorless, and inodorous. It gives off no vapor at common tem-
peratures. The specific gravity of the pure acid is 1'842 at 60^ (Pelouze).
Dr. Ure states that he has met with it as high as 1'845, and Dr. Lyon
Playfair has procured it as high as 1*8479. Sulphuric acid boils at a tem-
perature of about 650°, which, therefore, approaches a red-heat, and it may
be distilled over without decomposition. Its boiling-point diminishes with
its dilution; when of the specific gravity of I'YS it boils at 435° ; and at
348° when its specific gravity is 1*63. Owing to the small amount of heat
rendered latent by the vapor of sulphuric acid, it boils with explosive vio-
lence, and gives off sudden jets of vapor. This may be obviated by intro-
ducing into the liquid, broken glass or portions of platinum foil or wire.
The vapor is readily condensed by mere cooling: it is not necessary to place
the receiver in cold water. The concentrated acid freezes at — 30° ; and at
the same time contracts considerably in its volume. When once frozen, it
retains its solid state until the temperature rises to about the freezing-point
of water. Sulphuric acid of the specific gravity of 1*78 (which is a definite
hydrate, containing one atom of anhydrous sulphuric acid, and 2 atoms of
water), freezes at 40°, but if the density of the liquid be either increased or
diminished, a greater cold is required for its congelation.

Sulphuric acid is intensely acrid and corrosive ; it acts speedily upon the
skin, occasioning a biting sensation, and a soapy feel of the part, in conse-
quence of its chemical action on the cuticle ; its taste, even when very largely
diluted, is extremely acid, and it powerfully reddens litmus. It has a strong
attraction for water, so that it absorbs aqueous vapor from the atmosphere
and increases rapidly in bulk ; in moist weather three parts increase to four
in the course of 24 hours, and by longer exposure a larger quantity of water
is taken up, so that it requires to be preserved in well-closed vessels. It is
this property which renders it applicable to the drying of certain gases, and
to the purposes of evaporation and desiccation under the exhausted receiver
of the air-pump. When sulphuric acid is suddenly mixed with water, mutual
condensation ensues, and much heat is evolved. Four parts by weight of
acid, specific gravity 1*84, and one of water at 60^ produce, when thus
mixed, a temperature =300°. According to Dr. Ure, the greatest heat is

SULPHURIC ACID. CHEMICAL PROPERTIES. 221

evolved by mixing 13 of acid with 21 of water. Even a boiling temperature
does not prevent sulphuric acid taking up moisture from the air; hence it
cannot be concentrated so well in an open as in a close vessel ; on which
account retorts, or large platinum stills, are used for the last stage of its con-
centration, by manufacturers. The mixture of sulphuric acid with ice or
snow causes its immediate liquefaction, and as this liquefaction, consistently
with the theory of latent heat, produces cold, while on the other hand the
union of the acid with the water evolves heat, the resulting temperature of
such a mixture depends upon the relative proportions of the substances
mixed. Four parts of acid and one of pounded ice, evolve heat ; but four
parts of ice and one of acid, generate cold. Its affinity for water is so great
that it will dehydrate and render colorless, crystals of sulphate of iron and
sulphate of copper. At the boiling-point it will decolorize Prussian blue ;
but the color is restored on adding water.

Sulphuric acid, under ordinary circumstances, displaces the greater number
of other acids fro'm their combinations ; thus, in the humid way, it decom-
poses the phosphates and the borates ; at a red heat, however, the phosphoric
and the boracic acids, which are comparatively fixed in the fire, expel sul-
phuric acid from its salts. A solution of sulphate of lime is decomposed by
oxalic acid, which forms an insoluble oxalate of lime ; and the tartaric,
racemic, perchloric, and picric acids decompose sulphate of potassa in solu-
tion. In consequence of its strong affinity for water, sulphuric acid chars
most organic substances ; it acquires a brown tinge from the smallest par-
ticles of straw, cement, or dust, that accidentally fall into it; it appears
capable of dissolving small portions of charcoal, and also of sulphur, tellu-
rium, and selenium ; these substances give to it various tints of brown, red,
and green, or blue, and are precipitated when the acid is diluted with water ;
but if heat be applied, they are oxidized at the expense of the acid, and
sulphurous acid and carbonic acid are evolved.

When heated with charcoal, sulphuric acid gives rise to the production
of carbonic and sulphurous acids (C + 2S03=C02+2S03) : with sulphur,
sulphurous acid is the only product (8 + 2803=3803). It is decomposed
by several of the metals, which become oxidized and evolve sulphurous acid,
as shown in the production of this acid by boiling sulphuric acid with copper,
silver, mercury, tin, or lead. Gold and platinum are not affected by the
acid even at the boiling-point. When metals, such as magnesium, zinc, and
iron, are acted on in the cold by diluted sulphuric acid, the water only is
decomposed, its oxygen, being transferred to the metal, forms a metallic
oxide, which unites to the undecomposed sulphuric acid to form a sulphate
of the oxide, whilst the hydrogen is evolved in the gaseous form.

The strength of sulphuric acid is generally determined by its specific
gravity, after its freedom from any solid impurities has been determined by
evaporation. According to Dr. TJre, the proportion of dry acid contained
in 100 parts of liquid acid at different specific gravities is as follows :• —

Specific Dry acid

Specific Dry acid

Specific Dry acid

Specific Dry acid

gravity, in 100.

gravity, in 100.

gravity, in 100.

gravity, in 100.

1-8460 81-54

1-6630 61-97

1-4073 42-40

1-2032 22-83

1-8233 75-02 '

1-5760 55-45

1-3345 35-88

1-1410 16-31

1-7570 68-49

1-4860 48-92

1-2645 29-35

1-0809 9-78

In ascertaining the specific gravity of sulphuric acid, the temperature
requires attention, because from the small specific heat of the acid it is easily
affected, and because it greatly influences the density. When accuracy is
required, the strength of the acid may be determined by its saturating power.
For this purpose, a given weight of the acid is diluted with six or eight parts
of water, and a solution (of known strength) of pure carbonate of soda added

222 ANHYDROUS SULPHURIC ACID. PROPERTIES.

until the solution is exactly neutral (see Alkalimetry). Every 54 parts of
anhydrous carbonate of soda are equivalent to 40 parts of the anhydrous
acid, or to 49 of the liquid sulphuric acid, or oil of vitriol, of the specific
gravity of 1*84. Besides lead and potassa, tin and arsenic are sometimes
found in sulphuric acid : the tin and lead are derived from the leaden cham-
bers, and the arsenic from the sulphur or pyrites. The methods of detecting
these impurities will be described under the respective metals.

Tests. — The concentrated acid. — 1. It carbonizes a splint of wood intro-
duced into it. 2. It evolves sulphurous acid when boiled with metallic cop-
per. 3. Diluted with its volume of water, heat is evolved. The diluted acid.
— In the most diluted state a salt of baryta, added to the liquid, throws
down a white precipitate of sulphate of baryta, which is insoluble in acids
and alkalies. Diluted sulphuric acid does not carbonize organic matter
until the water has been driven off by heat, and the acid is thus concentrated.
A streak of the diluted acid on paper, when heated, produces a black mark
by carbonizing the paper. Pure sulphuric acid should leave no residue on
evaporation.

The presence of nitric or nitrous acid is indicated in sulphuric acid by the
change of color produced on adding a few drops of a concentrated solution
(or a crystal) of protosulphate of iron ; a solution of narcotine is also red-
dened by sulphuric acid containing nitrous acid. Sulphurous acid is detected
by its odor and by discharging the color of permanganate of potassa.

Anhydrous Sulphuric Acid {Sidphuric Anhydride). — When crystallized
green vitriol, or protosulphate of iron, is exposed to a dull red heat, it
crumbles into a white powder, and loses the greater part of its water of
crystallization. In this state, if put into a coated earthen or green glass
retort, and gradually exposed to a full red heat, a dark-colored liquid is
distilled over, of a specific gravity of about 1-89. This has been called
Nordhausen, or Saxon sidphuric acid : it evolves a vapor when exposed to
air, owing to the escape of the highly volatile dry sulphuric acid, which is
united in the brown liquid to a portion of hydrated acid. The brown,
fuming acid is a ready and perfect solvent of indigo. It is resolved by heat
into the common and the anhydrous acid. The changes which take place
in its production may be thus represented: 2(FeO,S03)==S03+S03-{-
FegOg ; but the sulphate of iron is not entirely dehydrated, so that a portion
of hydrated acid is distilled over at the same time. The Saxon acid is
generally supposed to be thus constituted : SOg+SOg.HO ; but the propor-
tion of hydrated acid is subject to variation.

The dry or anhydrous sulphuric acid may be separated from this brown
(or Nordhausen) acid, by a careful distillation from a retort into' a dry and
cold receiver ; it passes over in drops, which concrete, on cooling, into a
tenacious crystalline mass resembling asbestos. The acid is liquid at tem-
peratures above 66°; and at 78° its specific gravity is 1 9t. When it has
once congealed, it is difficult to fuse it, because the first portions heated
become vapor, and propel the rest forward ; by slight pressure, however,
this may be prevented. When kept at a temperature between 75° and 80°,
it gradually liquefies. At a temperature of .110°, it boils and evolves a
colorless vapor, the density of which, according to Mitscherlich, is 3. The
calculated density is 2-77, so that 100 cubic inches would weigh 85'969
grains. In the absence of all moisture, it has no action upon litmus-paper.
Passed through a red hot porcelain tube, anhydrous sulphuric acid is
resolved into one volume of oxygen and two of sulphurous acid. Caustic
lime or baryta, heated in its vapor, becomes ignited, and is converted into
sulphate. The attraction of this anhydrous acid for water is such as to
produce intense heat and a hissing noise when small portions of it are thrown

ANHYDROUS SULPHURIC ACID 223

into that liquid ; and if a sufficient quantity of it be added to such a propor-
tion of water as is required to convert it into hydrated acid, they combine
with heat, light, and explosion. •

Anhydrous sulphuric acid may also be obtained by the action of anhy-
drous phosphoric acid upon monohydrated sulphuric acid. (Barreswill.)
The phosphoric acid is put into a stoppered retort surrounded by ice and
salt, and the oil of vitriol gradually added so as to prevent arise of tempera-
ture, to the amount of two-thirds of the weight of the phosphoric acid ; the
retort is then removed from the freezing mixture, and a receiver placed there,
to which the retort is adapted ; on applying a gentle heat, the anhydrous
sulphuric acid is distilled over, and is condensed in white silky crystals in
the cooled receiver. The principal requisite precaution in this process, is to
keep the acids sufficiently cool, whilst mixing them in the retort {Pharm.
Journ.^ 8, 12T.) It has also been procured by distilling at a high tempera-
ture the dry bisulphate of soda.

It appears, then, that this extraordinary substance, which is thus volatile
and easy of congelation, forms, by combining with water, the fixed and with
difficulty cojigealable oil of vitriol^ and that it contains sulphur and oxygen
in the same proportions as they exist in the acid of the dry sulphates. From
its resolution when passed through a red hot tube, into one volume of sul-
phurous acid and half a volume of oxygen, and likewise from the experiments
of Berzelius upon the direct acidification of sulphur, it appears that the anhy'
drous sulphuric acid consists of: —

Sulphur ....
Oxygen ....

jms.

Weights.

Per cent.

1

16

40

3

24

60

Anhydrous sulphuric acid . . 1 40 100

The sp. gr. of the vapor is found to be 3*01. Assuming that one volume
of sulphurous acid and half a volume of oxygen are condense^ into one
volume of vapor, the sp. gr. would be 2-T64.

The liquid hydrated sidphuric acid, or oil of vitriol, when of the sp. gr.
1*846, consists of: —

Atoms. Weights. Per cent.

Dry sulphuric acid . .1 ... 40 ... 81-64
Water 1 ... 9 ... 18-36

Monohydrated sulphuric acid 1 49 100-00

The compound of sulphuric acid and water of the specific gravity l'T8,
which has been above stated to congeal at 40°, remains solid until the tem-
perature rises to 45° : it is a definite combination of 1 atom of anhydrous
acid +2 atoms of water. The acid of specific gravity 1*632, appears also
to be a hydrate containing 1 atom of anhydrous acid and 3 atoms of water,
for it is to this strength that a diluted sulphuric^^cid, evaporated in vacuo
at 212°, is reduced ; and it is also in these proportions, that sulphuric acid
and water suffer the greatest diminution of bulk in combining. It would
appear, therefore, that there are three definite hydrates of sulphuric acid, of
which the following are the formulae, specific gravities, and boiling-points : —

Monohydrate .
Bihydate .
Terhydrate

Each of these hydrates contains in 100 parts, the following proportions
of dry acid and water : —

Formula;.

Sp. Gr.

Boils at

Congeals at

SO3, HO .

.. 1-846 .

.. 650° .

... —30°

S03,2HO .

.. 1-780 .

.. 435 .

40

S0„3H0 .

.. 1-632 .

.. 348 .

...

224 HYPOSULPHUROUS ACID. HYPOSULPHITES.

Monohyd. Bihyd. Terhyd.

Anhydrous acid . . • . . 81-64 ... 70-94 ... 61-16
Water 18-36 ... 29-06 ... 38-84

According to Dr. L. Playfair, the variation in the sp. gr. of the monohy-
drated acid, as given by Bineau and Marignac — namely, r842 to 1-845 —
may depend upon the temperature at which it has been distilled. Dr. Play-
fair found that from an acid of asp. gr. of r848 (81 62 per cent, of anhy-
drous acid), he obtained a distillate of a sp. gr. of 1840 (80 12 per cent).
This acid, therefore, lost by distillation one and a half per cent, of anhydrous
acid. The weak acid thus obtained, was heated for half an hour to 550*^ ;
and after cooling, it gave an acid of 1847 9 (81*61 per cent, of anhydrous
acid). Hence it follows, that there is a monobydrate which loses anhydrous
acid above 550°, and water below this temperature ; so that a strong acid
is weakened by being heated above 550*^, and a weak acid is strengthened
by heating it to a temperature not exceeding 550°. The different tempera-
tures at which the acid has been concentrated, may thus explain the varia-
tions recorded in its specific gravity and strength. {Cheni. News, vol. 3,
p. 21.)

Sulphates. — These salts in the anhydrous state are represented by the
formula MOjSOg. Among the alkalies, there are some which form acid sul-
phates, such as potassa and soda, in which two equivalents of acid are united
to one of oxide. These are called hisulphates (MO,2S03). These salts
resist a high temperature, but are readily decomposed when heated with two
or three parts of charcoal, sulphides of the metals being produced. They
are converted into sulphides at a still lower temperature, when heated in a
close vessel with cyanide of potassium. An insoluble sulphate, such as that
of baryta, is thus easily recognized by its conversion into a soluble sulphide
of barium. A slight trace of any soluble sulphate, may be detected by the
addition of a salt of baryta to the liquid. If a soluble sulphate is present, a
white precipitate of sulphate of baryta, insoluble in nitric acid, will be pro-
duced.

Hyposulphurous Acid {Dithionotis Acid), {^fi^. — This acid is only
known in the combined state. Its salts, now called Hyposulphites, were
originally described by Gay-Lussac {Ann. de Chim., 85), under the name of
sulphuretted sulphites. Thomson first suggested the term hyposulphurous for
the peculiar acid of sulphur contained in these compounds {Syst. of Chem.,
1817), and they were afterwards examined by Herschel. {Edin. Phil. Journ.)
When an attempt is made to separate the acid from its salts by adding an
acid to the solution, sulphurous acid escapes, and sulphur is precipitated.

(SA=s-fSoj

Hyposulphites. — These salts are formed, 1. "When sulphur is digested, at
a high temperature but without ebullition, in a solution of a sulphite; in
which case the oxygen of the sulphurous acid divides itself between the
original and the newly-adoed sulphur : thus we obtain hyposulphite of soda
by digesting finely-powdered sulphur in a hot solution of sulphite of soda,
KaO,S03,-f S, becoming NaO^SgOg. 2. When sulphurous acid gas is passed
through a solution of an alkaline sulphide, until it no longer precipitates sul-
phur ; thus, we obtain hyposulphite of soda by passing sulphurous acid gas
through a solution of sulphide of sodium ; in which case 2XaS, and SSOg,
become 2NaO,2S02,-|-S. The properties of the acid may be studied in its
salts, and for this purpose the hyposulphite of soda may be selected. This
compound is now manufactured on a large scale for the purposes of photo-
graphy. Hyposulphite of soda dissolves every compound of silver excepting
the sulphide, and that portion of a silver salt which has been decomposed by

HYPOSULPHURIC ACID. HYPOSULPHATES, 225

light. Even the insoluble chloride is easily taken up by it, and the solution
has a sweetish taste. The acid forms soluble double salts with silver and
gold. A hyposulphite precipitates a solution of lead, but redissolves the
precipitate when added in excess. Hyposulphurous acid forms soluble com-
pounds with all the alkalies and alkaline earths, excepting baryta, the salts
of which are precipitated by a hyposulphite. The admixture of a sulphate
is thus easily known : a salt of strontia, which does not precipitate a pure
hyposulphite, throws down any sulphate which may exist in it as impurity.
A hyposulphite dissolves iodine, destroys the blue color of iodide of starch,
and decomposes iodic acid, setting iodine free ; but it has no action on iodide
of potassium. It also decomposes the permanganate of potash.

I'ests. — A hyposulphite may be recognized, 1. By the separation of sul-
phur and sulphurous acid, when its solution is treated with an acid : 2. By
its giving at first a white precipitate with a solution of nitrate of silver, solu-
ble in an excess of the hyposulphite. It dissolves readily the chloride of
silver ; the bromide, iodide and cyanide are also dissolved by it. If nitrate
of silver is added in excess to a solution of a hyposulphite, the white precipi-
tate which is at first formed rapidly undergoes various changes of color, to
yellow, brown, and black — sulphide of silver being ultimately produced ;
3. By its yielding a black precipitate with protonitrate of mercury ; 4. it
gives a white precipitate with a salt of lead (hyposulphite) which is soluble
in an excess of the solution.

It has been shown by Rose {Poggendorffh Annalen, 21), that although
the ratio of the sulphur to the oxygen in this acid is as 16 to 8, its equiva-
lent, or combining proportion,«is not 24, but 48, hence it must be considered
as a compound of

Sulphur . . . 2 32 66-67 )_/ Sulphur . . 1 16 33-33 '.
Oxygen . . . 2 16 33-33 J ~" \ Sulphurous acid 1 32 66-67

Hyposulphurous acid . 1 48 100-00 1 48 100-00

HYPOSULPHURIC Acid {DitMonic Acid) (S^OJ was discovered by Gay-
Lussac and Welther. It is obtained by passing a current of sulphurous acid
through a cold mixture of finely-powdered and pure peroxide of manganese
and water: 2S02H-Mn03=MnO,S205. A solution is obtained, which is
filtered and thoroughly agitated and digested with hydrated baryta, which
must be added in small excess. The sulphuric acid and the greater part of
the oxide of manganese are thus precipitated. The solution is again filtered
and evaporated until it crystallizes, and the crystals of hyposulphate of baryta
are a second time dissolved and obtained by evaporation, in order to pro-
cure them free from manganese ; they are then dried, powdered, weighed,
and dissolved in water ; and to every hundred parts of the dissolved salt,
18'78 parts of sulphuric acid, of the specific gravity of 184, diluted with
four parts of water, are added. The baryta is thus thrown down in the
state of sulphate, and the new acid remains in solution. Having been fil-
tered, it is to be concentrated by exposure under the exhausted receiver of
an air-pump, including a vessel of sulphuric acid, until it acquires a density
of 1'347. If the exposure and evaporation be continued beyond this point,
it is resolved into sulphuric and sulphurous acids (8^05=803 + 803). A
temperature of 212° effects the same change in its composition. It is an
inodorous acid, and reddens vegetable blues. It has not been obtained in
an anhydrous state.

Hyposulphates. — These salts are remarkable for their solubility. When
heated, they are resolved into sulphates, and sulphurous acid escapes. In
the cold, sulphuric acid does not so act upon them as to set free sulphurous
15

226 HYDROSULPHURIC ACID.

acid ; but this acid is evolved on boiling. They do not give a deposit of
sulphur when an acid is added to their solutions.

Trithionic Acid (S.,0.). — If three atoms of bisulphite of potassa in a
saturated solution in water, are digested with two atoms of sulphur, hypo-
sulphite and trlthionate of potassa are produced, as in the following equa-
tion (3[KO,2SOJ + 2S = 2[KOS303] + [KO,S,OJ). The acid may be ob-
tained from the trithionate by adding tartaric acid to the solution, but it soon
undergoes decomposition. It gives no precipitate with the salts of baryta
or lead. When a trithionate is heated, sulphur and sulphurous acid are
given off, and a sulphate of the alkali remains.

Tetrathionic Acid (S^OJ. — This acid was obtained by Fordos and G^lis
(Ann. de Ch. et Ph., Dec. 1842) by carefully decomposing its combination
with baryta by sulphuric acid, so diluted as to avoid elevation of temperature.
The tetrathionate of baryta may be procured by the reaction of iodine on
hyposulphite of baryta 2(BaO,S20j-f I = Bal4-BaO,S^05. The diluted
acid may be boiled without decomposition, but as it becomes concentrated,
it deposits sulphur, evolves sulphurous acid, and the liquid contains sulphuric
atfid. The acid is not affected by dilute hydrochloric or sulphuric acids, but
nitric acid throws down sulphur.

Pentathionic Acid (S5O5). — This compound is produced by the reaction
of sulphuretted hydrogen on a solution of sulphurous acid. Sulphur is
deposited and the two preceding acids are simultaneously produced.

Sulphur and Hydrogen. Hydrosulphuric Acid (HS). Sulphydric
acid. Sulphuretted Hydrogen Gas. — This compound was discoved by Scheele
in 1777: The two elements cannot be made to combine directly under ordi-
nary circumstances ; but when hydrogen is set free in the nascent state, in
contact with a sulphur compound, this gas is immediately produced, and is
recognized by its disagreeable odor. Sulphuretted hydrogen is thus evolved
in the decomposition of many organic substances and in the action of water on
the alkaline sulphides, on iron pyrites, as well as in the decomposition of
water by heated coke containing sulphur.

Preparation. — Protosulphide of iron may be prepared by rubbing a roll
of sulphur on a bar of wrought-iron heated to a full red heat, and collecting
the compound as it melts in a pail of cold water. One part of this sulphide
broken into small fragments may be placed in a retort with four or five parts
of water and one part of sulphuric acid. The heat produced by the mixture
of acid and water is sufficient to liberate the gas copiously. It is dissolved
by water, and acts chemically upon mercury. It should be collected over
a bath holding a small quantity of water, placed near to or under a flue.
The chemical changes which ensue in its production, may be thus repre-
sented : FeS4-S03,HO = HS + FeO,S03. The gas, as it is thus produced,
generally contains a portion of free hydrogen. A mixture of sulphide of
antimony and of hydrochloric acid also evolves, when heated, hydrosulphuric
acid gas.

Properties. — Hydrosulphuric acid is a colorless gas at common tempera-
tures and pressures. Under a pressure of about seventeen atmospheres at
50", it assumes the liquid form : it is then limpid, and apparently possessed
of a refractive power exceeding that of water ; its specific gravity is about
09. When a tube containing it was opened under water, it instantly and
violently rushed forth under the form of gas (Faraday, Phil. Trans., 1823,
p. 92.) When cooled to 122° below 0°, it solidifies, and it is then a white
crystalline translucent substance, heavier than the liquid.

CHEMICAL PROPERTIES. COMPOSITION. 22t

The gas has a peculiarly nauseous, fetid odor, resembling that of rotten
eggs, and so diffusible, that a single cubic inch escaping into the atmosphere
of a large room, is soon perceptible by its smell in every part. 100 cubic
inches weigh 36*38 grains. Its specific gravity compared with air is as
1-1747 to 1 : and compared with hydrogen as 17 to 1. It is inflammable,
burning with a pale blue flame, evolving the odor of burning sulphur.
During its slow combustion, sulphur is deposited, and water and sulphurous
acid are formed (HS-f 03=S0^-|-H0). It extinguishes the flame of a taper.
When respired, it proves fatal ; and it is very deleterious, even though
largely diluted with atmospheric air. Nausea, giddiness, headache, and a
peculiar faintness, with loss of appetite, are the usual symptoms produced,
when an atmosphere even slightly contaminated by sulphuretted hydrogen
has been breathed for any length of time. When its escape into the labora-
tory cannot be prevented, its effect may be counteracted by the diffusion of
a little chlorine, or by sprinkling the room with an aqueous solution of
chlorine or ozonized ether. The gas exists in some mineral waters, which
are thence called sulphureous, such as those of Harrogate. It is also found
in the air and water of foul sewers, and in putrescent animal matter.

Water dissolves three times its volume of this gas at 60°. The aqueous
solution is transparent and colorless when recently prepared, but gradually
becomes opalescent, and if exposed to air it deposits sulphur, while the
hydrogen combines with the oxygen of air to form water. The whole of
the gas is evolved by heat. It is an exceedingly delicate test of the presence
of most of the metals, with which it forms colored precipitates. The colors
of the sulphides produced, when accurately observed, serve to identify the
respective metals. Thus arsenic' and cadmium give a yellow, silver, lead,
and bismuth a black, antimony an orange, and zinc a white sulphide. The
symbols of the different metals may be printed on paper in the respective
metallic solutions, and the paper exposed in ajar containing the gas. The
colors produced by the different metals, are at once indicated by the symbols.
One measure of sulphuretted hydrogen mixed with 200,000 measures of
hydrogen, carburetted hydrogen, or atmospheric air, produces a sensible
discoloration of white lead, mixed with water, and spread upon a piece of
card, or on test-paper impregnated with salt of lead. Cards which have
been glazed with white lead are useful as a test for this gas. In this way
we may ascertain the presence of extremely small quantities of sulphuretted
hydrogen in coal-gas or air. The card or paper acquires a color varying
from a pale brown to black, according to the quantity of the gas present in
the mixture, or the length of exposure. The gas is entirely dissolved by a
solution of potassa and ammonia.

Sulphuretted hydrogen reddens infusion of litmus and moist litmus-paper,
but the blue color is destroyed on boiling the infusion ; it is generally
classed among the hydracids, and is not, therefore, considered to unite
directly with the basic oxides, a metallic sulphide and water being the
usual results of their mutual reaction (HS,MO = MS,HO) ; it combines
certain sulphides (basic sulphides), and forms a class of sulphur salts;
compounds which are analogous to the hydrated oxides, if we substitute
sulphur for oxygen.

When hydrogen becomes sulphuretted hydrogen, its volume is unchanged:
and when one volume of sulphuretted hydrogen is detonated with half its
volume of oxygen, water is formed and sulphur is precipitated (HS-f 0 =
HO -f S), the whole of the mixed gases being condensed. But when a volume
of sulphuretted hydrogen and a volume and a half of oxygen are inflamed in
a deto!iating tube, one volume of sulphurous acid is produced, and water is
condensed. Thus the sulphur is transferred to one volume of the oxygen.

228 HYDROSULPHURIC ACID. DECOMPOSITION.

and the hydrogen to the half volume. This gas, therefore, consists of its
volume of hydrogen pins one-sixth of its volume of sulphur, or 16 parts by
weight.

Atoms. Weights, Per cent. Vols. Sp. Gr.

Sulphur . . . . 1 ... 16 ... 94-1 ... i ... 1-1056
Hydrogen . . . . 1 ... 1 ... 5-9 ... 1 ... 0-0691

Sulphuretted hydrogen . 1 17 100-0 1-00 1-1747

It will be observed that this compound differs from the other hydracid
gases in undergoing condensation : hence its atomic volume, which is always
equal to the hydrogen present, is represented by 1. The hydrochloric,
hydriodic, and hydrobromic acids have an atomic volume represented by 2,
the hydrogen being equal to only one-half of the volume of the gas.
Whether sulphur be considered as representing one-sixth, one-third, or a
whole volume of vapor, the result is the same ; it adds nothing to the volume
of this gas. In constitution this gas resembles water, if we suppose sulphur
to be substituted for oxygen, rather than the hydracid gases of the halogeuous
elements. When a current of the gas is heated to full redness in a glass
tube, it is decomposed, and sulphur is deposited. Spongy platinum does
not effect the combustion of a mixture of sulphuretted hydrogen and oxygen
unless free hydrogen be also present.

Chlorine, iodine, and bromine, in vapor, instantly decompose hydrosul-
phuric acid gas ; when they are not in excess, sulphur is deposited, and
hydrochloric, hydriodic, and hydrobromic acids are formed. Strong nitric
acid poured into the gas occasions a deposition of sulphur, and nitrous acid
and water are formed, with a considerable elevation of temperature, and
occasionally flame. A fold of bibulous paper dipped in the acid may be
safely introduced. An aqueous solution of the gas is also decomposed by
these reagents. When two volumes of this gas are mixed in an exhausted
vessel with one of sulphurous acid, they mutually decompose each other,
occasioning the production of water, and the deposition of sulphur (2HS-|-
S02=2HO-f-3S). If the gases are perfectly dry, the action is slow. Strong
sulphuric acid also decomposes hydrosulphuric acid; the results are water,
sulphurous acid, and sulphur(HS-f-S03=HO-f-S03-f S): but if the acid be
diluted with four or five parts of water, it has no action, and if in that case
it is rendered turbid by the gas, the presence of sulphurous or arsenious
acid may be suspected. Hydrosulphuric acid decomposes chromic as well
as iodic acid, and in the latter case sets free iodine. Sulphur is in these
cases precipitated. Hydrochloric acid has no action on it. It is completely
oxidized and the odor is removed by an alkaline permanganate. Chloride
of zinc decomposes it, and sulphide of zinc is formed. The gas is rapidly
absorbed by charcoal, the hydrogen is oxidized and sulphur is deposited.
If a weak solution of sulphuretted hydrogen is shaken with powdered char-
coal, the smell of the gas rapidly disappears, and on filtering the liquid it
no longer acquires a brown color by the addition of a salt of lead. Owing
to this property. Dr. Stenhouse has recommended the use of a charcoal-
respirator for persons who may breathe the exhalations of sewers.

One of the most efficient metallic compounds for the removal of sulphu-
retted hydrogen either in the gaseous or dissolved form, is the hydrated
peroxide of iron. The substance is now largely employed for the separation
of sulphuretted hydrogen from coal-gas. Black sulphide of iron and water
are formed, and sulphur is set free (Fe203 4-3HS=3HO-f 2FeS-f S). The
change takes place on contact, but more rapidly when aided by heat and
moisture. The sulphide of iron is reconverted into oxide on exposure to

SULPHIDES. CHLORIDES OF SULPHUR.' 2!5$

air [2FeS4-03(air)=Fea03 + S2]. This fact illustrates the facility with
which sulphur and oxygen may replace each other in metallic combinations.

When potassium or sodium is heated in hydrosulphuric acid gas, a
sulphur-salt of the metal is formed with vivid combustion, and pure hydro-
gen is liberated (K4-2HS=KS,HS + H). When tin or lead is heated in
the gas, they all decompose it, and absorb the sulphur, leaving a volume of
hydrogen equal to that of the original gas. Passed over metallic oxides,
water and metallic sulphides are the results : the different oxides effect this
decomposition at very different temperatures.

Tests. — 1. The odor of the gas is sufiBcient to reveal its presence, even
when it forms only 1-200, 000th part of the atmosphere. 2. Paper wetted
with a solution of acetate of lead and dried, or a glazed card, will indicate,
by the appearance of a brown color, the presence of the gas, even when the
proportion is infinitesimal. The same tests apply to the presence of sulphu-
retted hydrogen in water. In addition, a portion of leaf-silver may be
allowed to remain in the water for some hours. If the gas is present, the
silver will be sooner or later tarnished.

Persulphide of Hydrogen. — This is a liquid compound, the composition of
which is not accurately known, but it is supposed to be HSg. It is pro-
cured by adding a solution of persulphide of calcium to diluted hydrochloric
acid. Under these circumstances, sulphuretted hydrogen is not produced,
but the greater part of the sulphur remains united to it, producing a heavy
yellow liquid, which subsides to the bottom of the glass. It has a sp. gr.
of 1-76 ; it is inflammable, and is rapidly decomposed in water or by expo-
sure to air.

Sulphides. — The soluble monosulphides are easily recognized : 1. By the
odor of sulphuretted hydrogen when wetted, or when an acid .is added. 2.
In solution, by the deep brown or black precipitate, which is produced on
adding a salt of lead. 3. By the rich purple or crimson color produced on
the addition of a few drops of a fresh solution of nitroprusside of sodium.
The color produced in this reaction is of a blue or splendid purple tint, when
the alkaline sulphide is in small quantity; and of a rich crimson, in stronger
solutions. The color is slow in appearing in a weak solution of sulphide,
and sooner or later fades. As the nitro-prusside produces no change of
color, in a solution of sulphuretted hydrogen, this reaction enables a chemist
to say whether the solution is or is not mixed with any traces of sulphide.
The monosulphides may be represented by MS, the sulphuretted sulphides
by MS.HS, and a polysulphide by MS^. Solutions of pure monosulphides
are pale, and evolve sulphuretted hydrogen without yielding a precipitate of
sulphur, when hydrochloric acid is added to them. Solutions of persulphides
have a deep orange or amber color, and .when treated with an acid, not only
evolve sulphuretted hydrogen, but give an abundant precipitate of sulphur of
a pale lemon-white color {precipitated sulphur).

Chloride of Sulphur (SCI). — When sulphur is heated in an excess of
dry chlorine, it absorbs rather more than twice its weight of this gas. Ten
grains of sulphur absorb 30 cubic inches of chlorine, and produce a liquid
of a greenish-yellow color by transmitted light, but orange-red by reflected
light. The combination also takes place at common temperatures, and may
e effected by passing an excess of dry chlorine through a tube containing
powdered sulphur. Chloride of sulphur exhales suffocating and irritating
fumes when exposed to the air. Its specific gravity is 1"60. It boils at 146^,
yielding a vapor of the density of 3io.

DiCHLORIDE OF SuLPHUR ; SUBCHLORIDE OF SULPHUR (S^Cl). — When the

preceding liquid is saturated with sulphur, it deposits a portion, often la
crystals, but retains an additional atom of sulphur, forming a yellow-brown

230 SELENIUM. ITS PROPERTIES.

liquid of the specific gravity of 1 686. It boils at 282°. The density of
its vapor is 4 70. It is a powerful solvent of sulphur, and is used in the
cold vulcanization of caoutchouc. It also dissolves phosphorus. Tetra-
hedral crystals of sulphur may be obtained from this liquid, the deposition
of which is much influenced by light. According to Rose {Poggendorffh
Ann., xxxi.), this is the only chloride of sulphur, and the preceding com-
pound is merely a solution of chlorine in this dichloride. When dropped
into water, it gradually yields hydrochloric acid, sulphur, and hyposulphurous
acid, the latter resolving itself into sulphurous acid and sulphur: 2S,C1,
2HO=2HCl,SO„3S.

Sulphur forms compounds with bromine, SBr; with iodine, SI; and nitro-
gen, SgN ; but these present no features of interest.

Selenium (Se=40).

Selenium was discovered in ISlt by Berzelius, during an examination of
certain substances, found in the sulphuric acid, manufactured at Gripsolm,
in Sweden. {Ann. Ch. et Fh.,\x. 160) The sulphur used in these works
is procured from the iron pyrites of Fahlun, and the acid obtained from it
deposits a red matter, which was supposed to contain tellurium, but which
was proved to be a distinct substance, to which its discoverer gave the name
of Selenium, from as%rjv^, the moon. It resembles sulphur, and is generally
placed next to it among the non-metallic bodies.

Preparation. — Selenium may be obtained by the decomposition of selenic
acid, which may be effected by adding hydrochloric acid to its solution in
water, and immersing a plate of zinc in the mixture : a gray or reddish-brown
flocculent precipitate of selenium is then deposited. Selenium may also be
extracted from the native sulphide of iron which contains it, by mixing the
powdered sulphide with eight parts of peroxide of manganese, and exposing
the mixture to a low red heat in a glass retort, the beak of which dips into
water. The sulphur, oxidized at the expense of the manganese, escapes in
the form of sulphurous acid gas, while the selenium is either sublimed ia
vapor or in the state of selenious acid : should any of the latter go over into
the water it would there be reduced to selenium by the sulphurous acid.

Properties — Selenium, when cooled after fusion, has a reddish-brown
color, and a dim metallic lustre; it is very brittle, and its fracture is of a lead-
gray color. Its specific gravity is 4-32, Specific heat=0-083t. Obtained
from its solutions by precipitation upon zinc, it is red, but becomes black
when boiled in water. It has neither taste nor smell. When fused, and
very slowly cooled, its surface is granular, without lustre ; and its fracture
dull, like that of metallic cobalt. It is easily reduced to a powder, which is
red. It is a non-conductor of heat and electricity. Selenium is softened
by heat, becoming semifluid at 212°, and melting at a temperature some-
what higher : it remains for some time soft on cooling, and may be drawn
out into filaments like sealing-wax, which are of a gray metallic lustre by
reflected light, but by transmitted light of a clear ruby-red. Heated in a
tube to about 650°, it boils, and is converted into a yellow vapor, which
condenses into black drops that run together like quicksilver. It is entirely
volatile. It does not, like sulphur, assume a crystalline state on" cooling.
Heated in the open air it rises into vapor, which may be condensed into a
red powder. It is characterized by tinging flame of a light blue color, and
by exhaling, when strongly heated, a peculiarly offensive odor. It is com-
bustible, but when ignited it does not continue to burn, like sulphur. It
evolves no acid vapor resembling sulphurous acid. It is insoluble in water,
and scarcely dissolved by benzole, except at the boiling-point. Its best
solvent is boiling sulphide of carbon, but it is taken up in very small pro-

COMPOUNDS OF SELENIUM. 231

portion, and is left as a red powder by spontaneous evaporation. Powdered
selenium when heated in liquids, even in solutions of alkalies, has a tendency
to agglutinate, forming a mass which the solvent scarcely attacks. Selenium
is considered to exist in two different states — the one vitreous and the other
metallic-looking. The vitreous condition is obtained by the slow cooling of
the melted substance. In this allotroi)ic state, it is insoluble in sulphide of
carbon, while in the other form, it is soluble.

When sulphur is mixed with selenium, they may be separated by defla-
grating the mixture with nitrate and carbonate of potash. Sulphate and
seleniate of potassa are obtained, which may be separated by the process
described under Seleniates.

Assuming the combining volume of the vapor of selenium to be the same
as that of sulphur, and that one volume of selenious acid includes one
volume of oxygen, and one-sixth of a volume of selenium vapor, then the
density of the latter would be by calculation 16 6392 (air==l), and com-
pared with hydrogen 240; 100 cubic inches would weigh 515*8 grains.
Selenium forms three compounds with oxygen — one oxide and two acids.
These compounds are thus constituted : —

Oxide (SeO).

Selenious Acid (SeO,).

Selenic Acid (SeO,).

Selenium .

,

. 83-33

71-06

62-07

Oxygen

.

. 16-67

28-94

37-93

This body differs from sulphur in forming an oxide.

Oxide of Selenium (SeO) is formed by heating selenium in a limited
quantity of atmospheric air, and washing the product to separate a portion
of selenious acid which is at the same time formed. The oxide is sparingly
soluble in water, but it does not redden litmus or combine with alkalies. It
appears to be the source of the peculiar odor, emitted during the oxidation
of selenium.

Selenious Acid (SeOg). — This acid may be obtained in a solid state by
digesting selenium in nitric or nitrohydrochloric acid until entirely dissolved,
and then evaporating to dryness. Its taste is sour and hot : its odor, when
sublimed, acid, but not like that of the oxide. It is very soluble in warm
water, and the solution furnishes crystals of the hydrated acid. The selenious
acid and its salts are decomposed by sulphurous acid — selenium being slowly
separated in red flocculi (SeO,-|-2SO,=Se 4-2803).

Selenic Acid (SeOg). — This acid is obtained by fusing selenium or
selenious acid, or any of its salts, with nitrate of potassa or soda ; an alkaline
seleniate is thus obtained. This may be dissolved in water and decomposed
by nitrate of lead. The insoluble seleniate of lead thus obtained, is diffused
through water, into which a current of sulphuretted hydrogen is passed to
precipitate the lead ; the liquid is boiled, to expel any excess of sulphuretted
hydrogen, and is now diluted selenic acid ; it may be concentrated by careful
evaporation, but the acid cannot be entirely deprived of water without being
decomposed.

Selenic acia, as thus procured, is a colorless liquid, which may be heated
to about 536° without change; but it is partially decomposed at higher
temperatures ; and at 554°, is rapidly resolved into selenious acid and
oxygen (Se03 = SeOa-|-0). When concentrated, by exposure to a tempera-
ture of about 329°, it acquires a specific gravity of 2-524 ; at 513°, it is
2'6 : it may be rendered somewat denser by exposing it to a higher tem-
perature ; but in this case a portion of selenious acid is formed in it. It is
unknown in an anhydrous state. The hydrated acid may be represented by
HOjSeOg. When boiled with hydrochloric acid, selenious acid and chlorine

232 COMPOUNDS OP SELENIUM. SELENIATES.

*

are produced, so that the selenio-hydrochloric acid dissolves gold like the
nitro-hydrochloric (HO,Se03 + HCl = HO,SeO,+HO + Cl). It dissolves
zinc and iron with the evolution of hydrogen ; and copper, with the produc-
tion of seleuious acid. Sulphurous acid, which decomposes selenious acid,
has no action on selenic acid ; so that to decompose selenic acid, it must
first be boiled with hydrochloric acid, which converts it into selenious acid ;
and sulphurous acid, or a sulphite, then effects the separation of selenium.
The affinity of selenic acid for bases is little inferior to that of sulphuric acid.
Seleniates. — The selenic and sulphuric acids are isomorphous, as are the
seleniates and sulphates, as well as the chromates and mangauates. The
seleniates mostly withstand a red heat : they are more easily reduced at
high temperatures by hydrogen, than the sulphates. Heated with sal-
ammoniac, they are decomposed with the separation of selenium. The
seleniates of baryta, strontia, and lead, are insoluble in water, and in dilute
nitric acid. A seleniate boiled with hydrochloric acid dissolves gold. It is
thus distinguished from a sulphate. When a sulphate is mixed with a
seleniate, they may be separated by passing into the solution after boiling,
it with hydrochloric acid, a current of sulphurous acid gas. Selenium is
thrown down in red flocculi, while the alkaline sulphate remains in the
solution.

Seleniuretted Hydrogen ; Hydroselenic Acid (HSe). — This is a color-
less gaseous compound which may be obtained by the action of hydrochloric
acid upon selenide of potassium or of iron. It is readily dissolved by water,
forming a solution at first colorless, but after a time acquiring a reddish hue ;
the solution smells and tastes somewhat like that of sulphuretted hydrogen ;
it reddens litmus, and tinges the skin of a reddish-brown color. Nitric acid
dropped into it occasions no change, and the gas does not readily escapes
from the water; but, when exposed to air, the solution is gradually red-
dened, and deposits selenium, the hydrogen combining with the oxygen of
air. It occasions black or dark brown precipitates in all solutions of neutral
metallic salts, with the exception of those of zinc, manganese, and cerium,
which are flesh-colored. Heated with tin, one volume yields one volume of
hydrogen and selenide of tin. It is decomposed by the joint action of air
and water ; it is absorbed by moist substances, and soon communicates to
them a red color. The selenium is thus remarkably deposited throughout
the texture of organic bodies. A piece of moist paper is penetrated by the
red color. It exerts a noxious action upon the trachea and organs of respi-
ration ; it inflames the eyes, and painfully stimulates the nasal membrane,
destroying for some hours the sense of smell. The gas is inflammable. By
combustion it produces water, and in close vessels leaves a reddish-colored
deposit of selenium.

The specific gravity of seleniuretted hydrogen is 2 '7 95. It contains one
volume of hydrogen and one-sixth of a volume of selenium condensed into
one volume of the compound. Its equivalent or atomic weight is 41. The
gas contains 97*52 per cent, of selenium. Although considered to be a
hydracid gas, it shares the peculiarity of hydrosulphuric acid. Its atomic
volume is equal to the amount of hydrogen, and is not affected by the large
amount of the metalloid which enters into combination with it. Two volumes
of this gas contain two of hydrogen, but two volumes of hydrochloric acid
contain only one of hydrogen.

PHOSPHORUS. PRODUCTION. ^|^

%

CHAPTER XVIII.

PHOSPHORUS (P=32). ITS COMPOUNDS WITH OXYGEN AND

HYDROGEN.

History. — Phosphorus, so termed from its property of shining in the dark
(from 4)wj, light, and ^i^^Biv, to bear), occurs in the three kingdoms of nature,
but most abundantly as a component of the bones and urine of animals : it is
generally present as phosphoric acid, combined with various bases. Although
phosphorus is found in certain phosphates in the mineral kingdom, it is, like
carbon and sulphur, a most important constituent of organic matter. It
exists in albumen, fibrin, and gelatine, in the brain, blood, milk, and other
secretions. It is found in combination with oxygen, united to lime and
magnesia, in the seeds and husks of the cerealia, and in numerous esculent
roots. There is no substance which yields it so abundantly as bone. The
subphosphate of lime forms about eighty per cent, of calcined bone, and
from this source it is now exclusively obtained.

Phosphorus was discovered in 1669, by Brandt, a merchant of Hamburg,
in the solid residue of urine, but no practical use was made of the discovery
until a century later, when a process for preparing this substance from bone,
was first made public by Scheele and Gahn.

Preparation. — On twenty parts of calcined bone, ground to a fine powder,
pour forty of water (by weight) and eight parts of sulphuric acid, previously
diluted with an equal weight of water. These materials are well stirred
together by means of a revolving wooden stirrer, for about six hours, steam
being let into the mixture to promote the chemical changes. The whole is
then put into a conical bag of linen to separate the clear liquor, and the
residuum is washed and pressed until the water ceases to taste acid. Evapo-
rate the strained liquor, and when reduced to about half its bulk, let it
cool. A white sediment will form, which must be allowed to subside ; the
clear solution (superphosphate of lime) must be decanted and boiled to
dryness in a glass vessel. A white mass will remain, which may be fused in a
platinum crucible, and poured out into a clean copper dish. A transparent
substance is thus obtained, consisting of phosphoric acid, with phosphate,
and a little sulphate of lime, commonly known under the name of glass of
phosphorus. It yields phosphorus when distilled at a white heat with one-
fourth of its weight of charcoal. The retort, which is made of the most
refractory fire-clay, should be well and carefully luted, and should have a
wide neck terminating in a copper tube, so bent as to dip perpendicularly
into a bottle of hot water, otherwise it is apt to become plugged up by con-
gealed phosphorus. When cold, it is cut into small pieces, which are put,
with water, into a slightly conical glass tube, and fused by immersion in hot
water : on cooling, the phosphorus is withdrawn in the shape of a stick.

The changes which take place in the various stages of this process, may
be thus described. The subphosphate of lime in bone is 3(CaO),P05. Sul-
phuric acid transforms this salt into acid phosphate (superphosphate) and
sulphate of lime, 3(CaO)P03+2SO,=CaO,2HO,P05+2(CaO,SO,). The
acid phosphate when heated with charcoal is converted into pyrophosphate
(which is not decomposed by carbon) carbonic oxide and phosphorus, a

234 PHOSPHORUS. CHEMICAL PROPERTIES,

portion of the phosphoric acid being set free and deoxidized by the charcoal
at a white heat, 2(CaO,PO,) -f Cs=5CO + 2CaO,P05 + P. Phosphuretted
hydrogen also escapes during the process as a result of the reaction of the
vapor of phosphorus on water.

The phosphorus obtained by the first distillation is commonly of a dirty
red or brown color, owing to the presence of impurities. It is melted in a
solution of ammonia, and is bleached by heating it in a mixture of bichro-
mate of potassa and sulphuric acid. After this it is again melted, and wliile
liquid is strained through chamois-leather. The mechanical impurities are
thus separated, and it is recast into sticks in the manner above described.
This substance is now manufactured in tons, chiefly for the purpose of
making lucifer matches. According to Mr. Gore, about six tons are annu-
ally consumed in Great Britain in the match manufacture — and one pound
will suflfice for 600,000 matches. This manufacture is, however, conducted
on a larger scale abroad. There are two manufactories on the continent,
which consume twenty tons of phosphorus annually.

Properties. — When pure, solid phosphorus is tasteless, but when in solu-
tion, it has a sharp nauseous taste : it is colorless, or of a pale yellow color,
translucent, sectile, and flexible at common temperatures, but at 32° vitreous
and brittle. Exposed to air, it exhales luminous fumes, having a peculiar
odor, distantly resembling that of garlic, and ozone is produced {see page
110). Its specific gravity is 1'826 at 50°. Its specific heat is 0188T
(Regnault). It is a non-conductor of electricity, both in its solid and fluid
state. Phosphorus is insoluble in water, but it is dissolved sparingly by
absolute alcohol, ether, the oils, naphtha, benzole (and other liquid hydro-
carbons, but most abundantly by sulphide of carbon. The chlorides of
sulphur and of phosphorus also dissolve it. When water is added to the
alcoholic solution, phosphorus is separated as a milk-white substance, probably
in the state of hydrate. If the alcoholic solution be poured on hot water
in the dark, there is an evolution of light arising from the slow combustion
of phosphorus. The solution in ether presents similar phenomena. If this
is rubbed over the skin or any warm surface, in the dark, the luminosity of
phosphorus is seen in a pale, bluish-colored, lambent flame, which pro-
duces no sense of warmth. The ethereal solution is decomposed by exposure
to light, and red oxide of phosphorus or red phosphorus is deposited. The
saturated solution in sulphide of carbon, if allowed to evaporate spon-
taneously on paper, leaves a finely-divided residue of phosphorus, which,
when dry, instantly takes fire, and burns in air with a brilliant white light
peculiar to this body. Although phosphorus is not soluble in water, it is
slowly oxidized in this liquid, which is soon found to acquire an acid reac-
tion, and to have the mixed properties of phosphorous and phosphoric acids.
As no hydrogen escapes, it is probable that the air diffused through the
water, furnishes oxygen. Under exposure to light, phosphorus acquires a
reddish color. This was supposed to be caused by oxidation, but as it takes
place in vacuo it is probably owing to a molecular change in phosphorus
itself, a superficial layer of the metalloid being changed into amorphous
phosphorus. The white layer which forms on the surface, when phosphorus
is kept in the dark, has been also ascribed to molecular changes. The
phosphorus in which this change has taken place is very fusible and inflam-
mable.

Phosphorus cannot be readily crystallized by fusion, but it may be crys-
tallized by solution. By slowly cooling some of its hot saturated solutions,
phosphorus has been procured in crystals, having the form of rhombic dode-
cahedra. Crystals of this substance have also been obtained, by melting
under water two parts of phosphorus with one of sulphur : a portion of the

PHOSPHORUS. CHEMICAL PROPERTIES. 235

phosphorus is deposited in regular crystals on cooling. (See Sulphide of
Phosphorus.) Phosphorus melts at about 115°, undergoing an increase of
volume. If suddenly cooled to 32°, after having been heated to 140°, it
sometimes becomes black (Thbnard) ; but if slowly cooled, it remains color-
less. When fused and left undisturbed, it may remain liquid for hours at
the usual temperature, particularly when covered by an alkaline liquid. At
from 550° to 570° in close vessels, it boils and evaporates in the form of a
colorless vapor, the density of which, according to Dumas, is 4*3o5 ; 4 326
(Regnault) ; 100 c. i. weigh 13696 grains. But phosphorus evaporates,
especially if in contact with moisture, at a much lower temperature. The
volatility of phosphorus in conjunction with aqueous vapor, may be shown
by boiling a flask of water containing a piece of phosphorus, over a lamp;
the vapor, as it issues from the flask, is luminous in a dark room. Owing to
its great inflammability, it should always be preserved in water, in a dark
place, and, when required, cut under water.

Phosphorus is a formidable poison ; a few grains of this substance are
sufficient to destroy life. Even the vapors when breathed (as in lucifer-
match making) produce caries and necrosis of the jaws, with wasting disease.

There are some peculiar circumstances connected with the luminosity and
inflammability of phosphorus. When exposed to humid air at temperatures
above the freezing-point, it shines in the dark with a pale blue light, which
increases in intensity with the temperature. This arises from slow combus-
tion, attended by the production of phosphorous acid (PO3) and ozone. If
a streak is drawn on litmus-paper with a stick of dry phosphorus, the paper
is slowly reddened. The luminosity ceases in close vessels as soon as the
oxygen has been absorbed, and it does not take place when the air has been
artificially dried : in this case the formation of phosphorous acid seems to be
prevented. In pure oxygen, phosphorus is not luminous until heated to
between 70° and 80°, above which temperature it becomes strongly luminous,
and soon inflames. Gases, in which phosphorus has been immersed, acquire
its odor, and when mixed with air, they become slightly luminous. If a
piece of phosphorus be introduced into a vessel of pure and dry oxygen gas
over mercury, at a temperature not exceeding 80°, no perceptible absorption
will happen in twenty-four hours ; but if, the temperature remaining the
same, the pressure be diminished to one-eighth or one-tenth of that of the
atmosphere, the phosphorus will be surrounded with white vapors, will
become luminous in the dark, and will absorb oxygen. Graham has shown
that the slow combustion of phosphorus in air is prevented by small addi-
tions of certain gases and vapors. Thus at the temperature of 66°, and
even above this, oxidation is entirely prevented by the presence of small
quantities of sulphurous acid, sulphuretted hydrogen, and of oleflant gas, as
well as by the vapors of sulphide of carbon, ether, creasote, naphtha, and oil
of turpentine. This is probably owing to the oxidation of these vapors,
since it has been noticed that when two oxidable bodies are in contact, one
of them often takes precedence in combining with oxygen, to the entire
exclusion of the other. Potassium is defended from oxidation in air by the
same vapors, though to a less degree. When these oxidable vapors are
absent, there is no better test of the presence of free oxygen, than that
furnished by the luminosity of phosphorus in the dark.

When dry phosphorus is sprinkled with lamp-black, or powdered animal
charcoal, it is apt to inflame ; and, when very thin slices of dry phosphorus
are placed upon dry wood, flannel, wool, lint, fine feathers, or other non-con-
ducting substances, they speedily melt and readily inflame upon the gentlest
friction. It seems as if the slow combustion of the phosphorus produced
heat enough to melt it whilst lying upon a very bad conductor. If several

236 COMBUSTION OF PHOSPHORUS.

pieces of phosphorus be placed upon or near to each other, they are also apt
to inflame.

The actual temperature at which phosphorus inflames has been variously
stated ; but it is generally a little above its melting point. We Kave noticed
that phosphorus coated with a white layer, has melted in air below tO^, and
burst into flame on being touched. Phosphorus easily takes fire by the heat
of the hand and by slight friction, as when rubbed upon a piece of coarse
paper : it requires, therefore, to be handled with the utmost caution. Owing
to the superficial formation of phosphorus and phosphoric acids, when it burns
imperfectly at low temperatures, its further combustion is often prevented :
thus, in rubbing a fragment of phosphorus between two pieces of brown
paper, a momentary combustion ensues, and it often requires considerable
friction to cause it again to inflame. For the same reason it is diSicult to
light a piece of paper by the flame of phosphorus, the paper becoming
covered and protected by the acid produced. So also a small piece of
phosphorus may be fused by the gradual application of heat, but it will not
inflame until the surface is disturbed by touching it with a wire. A frag-
ment gently heated on writing-paper, may be melted and consumed without
igniting the paper. Paper or linen soaked in phosphate of ammonia, is,
for a similar reason, rendered uninflammable by the application of heat;
ammonia is volatilized, and the phosphoric acid liberated, glazes over and
protects the material from combustion.

When in brilliant combustion in the air, phosphorus evolves copious fumes
of phosphoric acid (PO.) : its flame is intensely luminous, and nearly white.
If phosphorus be heated in a confined portion of air, it enters into less per-
fect combustion, and an oxide, a red solid, less fusible than phosphorus, is
produced. The difi*erent products of the combustion of phosphorus are
well shown by heating a fragment of it placed near the centre of a thin glass
tube of about a fourth of an inch diameter, and three or four feet long, and
then gently driving a current of air through the tube ; the fixed and volatile
acids, and the red oxide, are in this way distincly separated.

The vapor of phosphorus explodes with oxygen, and burns violently where
it meets with air. It may be safely produced and burnt at the mouth of a
test-tube, by heating a piece of phosphorus in a small quantity of ether.
The tube becomes filled with ether-vapor, and the phosphorus-vapor burns
only as it issues from the mouth of the tube. Gases in which oxygen is in
a combined state, do not readily part with it to phosphorus, even at the
temperature of combustion. Thus burning phosphorus is extinguished in
pure carbonic acid. It may be melted in deutoxide of nitrogen by a heated
wire without being inflamed ; but when introduced into this gas in a boiling
state, it decomposes it, and unites to the oxygen, producing a vivid com-
bustion. It takes fire spontaneously in chlorine, burning with a pale flame;
and on contact with iodine, the heat of combination is such as to kindle the
phosphorus immediately.

Its great affinity for oxygen is manifested not only by its luminosity in air
at a low temperature, but by its decomposition of the oxides of certain
metallic salts. Small portions of fresh-cut phosphorus suspended in weak
solutions of sulphate of copper, nitrate of silver, chloride of gold, and chlo-
ride of platinum, are speedily coated with layers of the respective metals,
sometimes deposited in a beautifully crystalline state. Phosphorus here acts
as a powerful deoxidizer, and is converted into phosphoric acid P-f5(AgO,
NO,)=5Ag + P05+5NO„ and 5 (CuO,S03) + P=5Cu + P05-f5S03. If
some thin slices of phosphorus be placed on a very diluted solution of chlo-
ride of gold (a grain of chloride to 4000 of water), and covered over, they
will soon be surrounded by thin transparent films of reduced gold, which

ALLOTROPIC, OR AMORPHOUS PHOSPHORUS. 231

may be raised from the fluid by clean and dry plates of glass. There is no
instance in which metallic gold is brought to a finer state of tenuity than in
this experiment. Advantage is taken of this property in the electrotype
art, for coating vegetable and animal substances, insects, seeds, &c., with a
layer of metal, and thus making them conductors. The substance is brushed
over with a small quantity of a weak solution of any salt of gold, silver, or
platinum, and it is then exposed to the vapor of a solution of phosphorus in
alcohol or ether. A thin film of metal is deposited, and this serves as a
conducting surface for a further deposit by the battery. An alcoliolic solu-
tion of phosphorus throws down the metals from solutions of gold and silver.
Phosphorus decomposes solid nitrate of silver and chlorate of potassa with
a violent explosion, when a mixture of the two substances is suddenly struck
with a hammer.

Equivalent. — The atomic weight of phosphorus is in round numbers 32.
As the specific gravity of its vapor, compared with hydrogen is 63 71, it
follows that its atomic volume must be 0'5, or half a volume, so that each
volume of vapor, like that of oxygen, will necessarily contain two atoms.
{See p. 69.) It is diatomic. The hypothesis of Gerhardt, that the atomic
weights of elements in the gaseous or vaporous condition, correspond to
single volumes of their vapors, is therefore wholly inconsistent with the facts
which are known regarding the vapor of phosphorus. Deville did not find
that a heat of 1900° in any way affected the relative volumes of the specific
gravities of phosphorus and oxygen.

Tests. — The smallest fragment of phosphorus, even when mixed with
Other substances, may be sometimes identified by its garlic odor,. and in all
cases by its luminosity in the dark. If the substance suspected to contain
phosphorus is dried and heated in the dark, in a thin layer spread on a
metallic plate, the minutest fragment of phosphorus will appear luminous,
or will burn with a puff of white vapor. The contents of the stomach and
intestines of persons poisoned by phosphorus have been, in some instances,
quite luminous in the dark. If the test of luminosity should fail under these
circumstances, the dried substance should be digested in its volume of
sulphide of carbon for twenty-four hours. The liquid strained off should
be poured into a watch-glass, floating on a surface of hot water in the
dark, when, if phosphorus be present, there will be a luminosity, as the
sulphide evaporates. By evaporation, at ordinary temperatures, small
particles of phosphorus are left as a residue, which may be ignited by a
heated wire.

Allotropic, or Amorphous Phosphorus. — It has been already remarked that
phosphorus, when suddenly cooled from a state of fusion, undergoes certain
changes in its physical properties. As a result of exposure to heat or light,
it acquires a red color, and this red substance, which is allotropic or amor-
phous phosphorus, is possessed of peculiar properties, which have been fully
described by Schrotter and others. {Ann. Ch. et Ph., 3eme ser., 24, p.
406.) Schrotter made the discovery of this variety of phosphorus in 1848.
He obtained it by distilling phosphorus in an atmosphere of nitrogen or
carbonic acid, at a temperature between 460° and 480°. In this case, a
part of the phosphorus assumes the amorphous or red condition, while the
unchanged portion acquires the property, after repeated distillations, of
remaining for a long time liquid, and even sustaining considerable agitation
without congealing. To separate the common, from the amorphous kind,
sulphide of carbon is employed. This dissolves common phosphorus only,
and leaves the allotropic variety, -after having been well purified by washing
with the sulphide, in the form of a red or brownish-red powder. For
commercial purposes, allotropic phosphorus is made by heating phosphorus

238 PROPERTIES OF ALLOTROPIC . PHOSPHORUS.

under water, in an air-tight cast-iron boiler to a temperature of 450°. A
quantity of about 200 pounds of ordinary phosphorus is thus kept heated,
for three or four weeks. When the vessel is opened, the phosphorus
presents itself as a hard, red, briek-like-looking substance, as brittle as
glass. It is broken into small pieces under water, and ground between
mill-stones in a vessel supplied with a small stream of water, which washes
the finer particles into a tank, in which they subside. Any unchanged
phosphorus is then removed by sulphide of carbon. (Gore.) For the
purpose of experiment, this change may be shown by heating a small portion
of phosphorus to a proper temperature, in a tube filled with dry carbonic
acid gas. The change of color produced by heat, and the volatility of
phosphorus at a. still higher temperature, may thus be proved. One end of
the tube should be sealed, and the other end should be plunged into mercury
or water.

Properties. — The color of amorphous phosphorus varies according to the
temperature to which it has been exposed, from nearly black (with a metallic
lustre) to iron-gray, brick-red, crimson, and scarlet. It has no odor. Its
specific gravity at 50° is 1 964 to 214. When dry, it undergoes no change
in air : when moist it is slowly oxidized, but it is not luminous in the dark,
and it produces no ozone. It does not remove oxygen from air, and will
not combine with this gas to produce the phenomenon of combustion under a
temperature of 500°; but it requires to be heated to 570° for its entire
combustion. In vessels filled with carbonic acid or nitrogen, it may be
distilled over as ordinary phosphorus at this temperature. Chlorine acts
upon it, producing heat, but no evolution of light. Chloride of phosphorus
is formed. Iodine has no action upon it; and although it is only phos-
phorus in an altered molecular condition, it has no poisonous properties.
In addition to the characters above described, allotropic phosphorus is quite
opaque, hard, and brittle, and without crystalline structure. It is insoluble
in sulphide of carbon, ether, and all the liquids which dissolve common
phospliorus. It is slightly dissolved by a solution of chlorine. Although it
is considered to be less energetic in its affinities than common phosphorus,
yet when mixed in equal parts with chlorate of potassa, it explodes with
tremendous violence, and with the slightest friction.

From this description it will be perceived that although the two varieties
are easily convertible into each other, they differ as much in properties as
any two metalloids, or metals. The amorphous phosphorus is used in the
manufacture of lucifer-matches, and in some cases a surface of amorphous
phosphorus is employed, on which matches, properly prepared, may be
rubbed.

Phosphorus and Oxygen. — Phosphorus combines with oxygen to form
four different compounds : —

Oxide of phosphorus . PjO Phosphorous acid . PO3

Hypophosphorous acid P 0 Phosphoric acid . . PO5

Oxide OF Phosphorus (PgO) When phosphorus is burnt in air, there

is generally a red residue, which consists in great part of this oxide. If a
large quantity of phosphorus is burned in a confined volume of air, the
oxide is abundantly produced. It may be prepared in quantity, by melting
phosphorus in a conical glass under hot water, and then passing upon it, in
the melted state, a current of oxygen. The phosphorus burns under water,
producing phosphoric acid, which is dissolved, and the red oxide, which is
diffused as an insoluble red powder through the liquid (3P + 60 = PO^-f
PgO). When it has subsided, and the vessel is cool, the water is poured off,

OXIDE OF PHOSPHORUS. HYPOPHOSPHOROUS ACID. 239

and the red compound is digested in snlphide of carbon. This removes any
uncombined phosphorus, and leaves the oxide. The oxide is an insoluble
red solid, not inflammable in air unless mixed with phosphorus, when, if
dry, it will take fire spontaneously. It burns on contact with nitric acid,
and explodes when mixed with powdered chlorate of potassa. It is un-
changed by dry air or oxygen ; but in damp air, it is slowly oxidized. It is
not luminous in the dark ; it is not very inflammable when heated in air ;
but at a red heat, it is converted into phosphoric acid and phosphorus
(5P.^O=P05-f Pg). Like allotropic phosphorus, it is insoluble in sulphide
of carbon, and in all liquids which dissolve phosphorus. It is neutral, and
enters into no combinations.

HYPOPHOSPHOROUS AciD (P0,2H0, or 3H0) is prepared as follows : —
Upon one part of phosphide of barium pour four parts of water, and when
the evolution of phosphuretted hydrogen gas has ceased, pour the whole
upon a filter. To the filtered liquid add sulphuric acid, as long as any
precipitate falls: separate the precipitate, which is sulphate of baryta, and
the clear liquor now contains hypophosphorous acid in solution. When
concentrated by evaporation, a sour viscid liquid is obtained, incapable of
crystallization, and eagerly attractive of oxygen. The concentrated acid is
of the consistency of syrup ; it has not been obtained free from water, with
two, or, according to some, with three equivalents of which, it is always
combined.

In place of the phosphide of barium, bisulphide of barium and phosphorus
may be employed. When these are boiled in water, sulphuretted hydrogen
escapes, and ahypophosphite of baryta is formed (BaS^-f P + 2HO=2HS +
BaO,PO). When potassa, soda, or lime is boiled with phosphorus in water,
phosphuretted hydrogen escapes, and ahypophosphite of the alkali is formed
and dissolved. The salt may be obtained on careful evaporation, although
there is a liability to explosion if it is carried to dryness.

When hydrated hypophosphorous acid is heated, it is decomposed with
the evolution of phosphuretted hydrogen, and the production of phosphoric
acid: 2PO + 3HO = PH3+POs. It is a powerful deoxidizing agent. It
reduces the salts of gold, silver, mercury, and copper to the metallic state
(PO + 4AgO=Ag4+P03). When boiled with sulphuric acid, it decora-
poses it ; sulphurous acid is evolved, and sulphur is deposited. An acid
solution of permanganate of potassa is deoxidized in the cold, and the color
is discharged by this acid. In combination with bases it forms hypophos-
phites ; they are soluble in water, and many of them in alcohol; they are
decomposed by a red heat ; they are mostly deliquescent, and uncrystallizable,
but some are inflammable and even explosive when heated.

Phosphorous Acid (PO3). — The volatile white substance which has been
mentioned as one of the products of the combustion of phosphorus in rarefied
air, consists chiefly of this acid in a dry state. By burning phosphorus in a
tube with a limited access of dry air, and caution as to temperature — as, for
instance, by placing a piece of phosphorus near one end of a tube two or
three feet long, drawn out at the ends, inflaming it, and gently propelling
dry air through the tube — this acid may be collected in the form of a white
volatile powder. It has the odor of garlic, and when exposed to air, rapidly
absorbs moisture as well as oxygen, and is converted into phosphoric acid.
The solid acid may be volatilized by heat in carbonic acid or nitrogen, but
when moderately heated in air, it takes fire and burns, producing phosphoric
acid (5POj,=3P05-|-p2). The slow combustion of phosphorus in air at a
low temperature is attended with the production of this acid (PO3). If
sticks of phosphorus be placed in glass tubes, open at both ends, and

240 ANHYDROUS PHOSPHORIC ACID.

arranged round a glass funnel inserted in the neck of a bottle, the phosphorus
will slowly disappear, as if by deliquescence, and the liquid colleeied in a
bottle will be chiefly a solution of this acid, mixed with some phosphoric
acid. It was formerly called phosphatic acid. When the hydrated acid is
heated, or when its solution is evaporated to dryness, phosphuretted hydro-
gen is evolved, and it is converted into phosphoric acid (4P03+3HO =
PHg + SPOg). It may be obtained hy evaporation in vacuo, as a crystalline
hydrate (POgSHO). The solution in water is not corrosive, but powerfully
acid. When heated with zinc or iron, phosphuretted hydrogen is evolved,
and phosphates of the metals are formed. The solution absorbs oxygen when
exposed to air, and phosphoric acid is produced. It is a powerful deoxidiz-
ing agent. It reduces at a boiling temperature the oxide of mercury, per-
manganate of potassa, and the salts of gold and silver. In reference to the
salts of silver the following changes take place : P054-2AgON03=2Ag +
PO5+XO5. It deoxidizes sulphuric acid, converting it into sulphurous acid,
and this again is decomposed and sulphur is deposited. It also deoxidizes
nitric and arsenic acids, converting the latter into arsenious acid. In these
reactions it is changed into phosphoric acid. The solution of this acid does
not precipitate albumen. Chlorine converts it into phosphoric acid (PO3-I-
2C14-2H0=P034-2HC1).

Phosphites. — The phosphites contain, according to Graham, three atoms
of base to one of acid, the hydrated acid being the tribasic phosphite of
water. Others regard the acid as dibasic — one atom of water being retained
in its combination with two atoms of a metallic oxide. The afQnity of the
phosphorous acid for bases is but feeble. All the phosphites include water,
and when sufficiently heated, are resolved into hydrogen and phosphates,
often with combustion. At common temperatures they do not absorb oxygen
from the air, but they are easily convertible into phosphates by nitric acid,
chlorine, and other oxidizers. They have the characters assigned to phos-
phorous acid.

Phosphoric Acid (POg). — Anhydrous phosphoric acid can only be ob-
tained by the direct combustion of phosphorus in an excess of dry oxygen ;
intense heat and light are evolved, and white deliquescent flocculi line the
interior of the receiver. The acid may be produced by burning phosphorus
under a tall receiver in atmospheric air, the air having been previously 'well
dried by placing under the receiver a saucer containing sulphuric acid. The
receiver should be placed in a glass dish, and should rest upon some thick
pieces of plate-glass. A piece of phosphorus in. a platinum or porcelain
capsule, may be ignited and covered over with the receiver. The phosphorus
burns at first furiously, but the combustion gradually subsides for want of
oxygen, and may be renewed by gently lifting the receiver oflf the glass
plates : thus the whole of the phosphorus may be gradually consumed, and it
forms a quantity of dense vapor, which subsides in the form of white flakes
like snow, some portions adhering to the sides of the glass. A convenient
apparatus has been constructed for burning phosphorus in oxygen, so as to
produce this acid in large quantity. The solid phosphoric acid obtained by
this process, should be transferred as quickly as possible into a dry stopper-
bottle, in which it may be pressed down ; and the portions of acid which
remain adhering to the receiver and dish, may be washed out, and they will
yield a solution of the acid.

In the anhydrous state, phosphoric acid is an extremely deliquescent un-
crystalline white powder, fusible into a vitreous substance, and volatile at
a full red heat. It is inodorous, not acid in the dry state, and not corrosive.
A small quantity of water poured upon the solid acid, dissolves it with a

HYDRATES OF PHOSPHORIC ACID. 241

hissing noise, and great heat is evolved. A solution of the protohydrate of
phosphoric acid is thus obtained. The liquid is sour to the taste, and
powerfully acid in reaction. Chloroform and ether dissolve it, but acquire
no acid reaction on litmus until water is added. Anhydrous phosphoric
acid is occasionally employed in chemistry for the purpose of dehydrating
liquids by distillation. At high temperatures it is decomposed by charcoal,
and by several of the metals. It combines with hydrate of lime to form a
hard cement, which has been used for stopping teeth. The acid consists of: —

Phosphorus

Oxygen ....

Atoms.

Equiv.

Per cent.

. 1

32

44-4

. 5

40

55-6

Phosphoric acid ... 1 72 100-0

Mr. Graham has shown that phosphoric acid occurs in three peculiar or
isomeric conditions, which may be designated, 1. Metaphosphoric acid, or
a phosphoric acid ; aPO^ : 2. Pyrophosphoric acid, or h phosphoric acid ;
6PO5 : 3. Common phosphoric acid, or c phosphoric acid ; cVO^ The first
combines with one, the second with two, and the third with three atoms of
water or base. The acid is regarded, by Graham, as the same in all these
modifications, which are supposed to depend upon the proportion of water
or base with which it is in union : so that c<PO, may become iPOg by the
acquisition of a second atom of water or of base, and cPO, by a third ; and
inversely cPOgby losing an atom of base or of water, becomes hVO^, and this
by the further abstraction of base or basic water, passes into aPOg, and
aPOg losing its single equivalent of water or base reverts to PO5. In ac-
cordance with this view, phosphoric acid intimately combined with one atom
of water, only allows of the replacement, by substitution, of that atom of
water by one atom of base : but if the original acid be similarly united with
two or three atoms of water, these are then replaced by two or three atoms
of base.

PO5HO. Protohydrate or Monobasic Phosphoric Acid; Metaphosphoric
Acid. — Aqueous solutions of any of the modifications of phosphoric acid,
when evaporated and heated until they cease to lose water, yield the proto-
hydrate, in the form of what has been termed glacial phosphoric acid. In
this state it contains 11-2 per cent, of water, which cannot be expelled by
heat. When the acid is kept in solution in water, ^t slowly combines with two
additional atoms and becomes a terhydrate. When phosphate of ammonia,
is heated to expel the alkaline base, this acid remains as a glassy-looking
residue. The white anhydrous phosphoric acid procured by burning phos-
phorus in dry air or oxygen, when dissolved in water forms a solution of the
protohydrate. It is characterized by producing a white precipitate in a,
solution of albumen ; and in solutions of baryta, lime, and oxide of silver, it
gives peculiar white precipitates like soft solids, without crystallization.
These compounds contain one atom of base to one of acid.

P05,2HO. Bihydrate or Bibasic Phosphoric Acid. Pyrophosphoric
Acid. — When a solution of pyrophosphate of soda (obtained by heating the
phosphate to full redness) is precipitated by acetate of lead, and the insoluble
salt of lead is washed and decomposed by sulphuretted hydrogen, an acid
liquid is obtained, which must be left in a shallow basin until the sulphuretted
hydrogen has escaped ; it is then an aqueous solution of pyrophosphoric
acid. It yields the pyrophosphate, when neutralized by carbonate of soda ;
gives a white precipitate with nitrate of silver ; and forms salts, all of which
have two atoms of base. The acid, before neutralization, does not pre-
cipitate solutions of nitrate of silver or of baryta, and it does not precipitate
16

242 PHOSPHORIC AOID. CHEMICAL PROPERTIES.

albumen. A diluted solution of this bihydrate of phosphoric acid may be
preserved without change ; but when it is boiled for some time, it passes
into the terhydrate. Graham and Peligot obtained this acid, not however
quite free from terhydrate, by evaporating the solution of the terhydrate in
a platinum flask, until its temperature attained 416°. It appeared as a soft
glass. Peligot obtained it in opaque imperfect crystals resembling grape
sugar.

POgjSHO. Terhydrate or Trihasic Phosphoric Acid. Common Phosphoric
Acid. — The common phosphate of soda yields this acid, when a solution of
the salt is precipitated by acetate of lead, and the phosphate of lead is
decomposed by sulphuretted hydrogen ; but it is generally procured by
oxidizing phosphorus with nitric acid. The acid must be diluted with
three parts of water in order to prevent too violent an action. Portions of
phosphorus are introduced into a Florence flask and covered with the acid
and water. The mixture is heated carefully, and as soon as red fumes
appear, the heat is reduced, and the action is allowed to proceed (3P-f
5N05=3P05-i-6N02). When the acid is saturated, the liquid is evapo-
rated, and the surplus nitric acid is expelled. It is finally concentrated to
a syrupy state in a platinum dish. When dissolved in water, it forms the
ordinary solution of phosphoric acid, A solution of the terhydrate may be
prepared by boiling the monohydrate in diluted nitric acid. The conversion
is rapid in a diluted solution, and no bihydrate appears to be formed. The
nitric acid in this case appears to act by catalysis (page 58).

In solution, it is very acid, but not corrosive, so that when heated on
paper, the paper is not carbonized. It gives no precipitate with a solution
of albumen or nitrate of baryta, or with a solution of nitrate of silver ; but
when united with a base, it gives with the latter salt, a yellow precipitate.
It precipitates a solution of pure lime, but readily dissolves the precipitate,
if the acid is added in excess. When heated to 400° it loses water, and
becomes a mixture of proto and bihydrate ; but it cannot be made anhydrous
by heat, as it is volatilized in the state of protohydrate below *a red heat.
If kept below this temperature, it is entirely converted into protohydrate.
Conversely, the proto and bihydrate, when kept for some time in solution in
water, take one and two equivalents of water, and are ultimately converted
into the terhydrate. This change is rapid when the aqueous solutions are
weak and submitted to a boiling temperature, or when a little nitric acid is
added. The acid liquid 'will no longer precipitate albumen, and when
neutralized by an alkali, it will give a yellow precipitate with nitrate of
silver. In general, water in combining wuth anhydrous acids in more than
one equivalent, does not alter the properties of the acid. Thus there are
three hydrates of sulphuric acid, but all have similar properties. In reference
to phosphoric acid, the protohydrate, in its reactions on albumen and on a
solution of nitrate of silver, is wholly different from the terhydrate ; and the
bihydrate difl'ers from both.

The only impurity likely to be found in this acid, when made according to
the method above described, is nitric acid. This may be detected by the
usual tests (page 177). If any phosphorous acid is present, it may be
detected by warming a portion with a solution of sulphurous acid. In this
case, there will be a precipitation of sulphur ; and if arsenic is present, it will
be under similar circumstances thrown down as yellow sulphide of arsenic.

The constitution of the three hydrates of phosphoric acid may be thus
represented : —

TESTS FOR SOLUBLE PHOSPHATES. 243

Mouobasic. Bibasic. Tribasic.

Atoms. Weights. Per cent. Atoms. Weights. Per cent. Atoms. Weights. Per cent.

Phosphoric acid 1 72 88-8 1 72 80 1 72 72-72

Water . . 1 9 11-2 2 18 20 3 27 27-2^

1 81 100-0 1 90 100 1 99 100-00

Phosphoric acid has less aflfinity for bases than the sulphuric, at ordinary
temperatures, but as it is more fixed, it will expel the sulphuric acid from
the sulphates at a high temperature.

Phosphates. — Each of the above hydrates of phosphoric acid forms a
distinct class of salts, namely, metaphos^. hates, which are monobasic ; pyro-
phosphates, which are bibasic : and common phosphates, which are tribasic ;
so that the proportion of fixed base with which the acid unites in the humid
way, is dependent upon the proportion of water which the fixed base
replaces. Thus, the metaphosphoric acid, or protohydrate, will only combine
with one, and the pyrophosphoric or deutohydrate with two equivalents of
soda ; and if in either case a larger quantity of base be added, it remains
uncombined : so also in regard to the terhydrate ; if to one equivalent of it
in solution, one equivalent of soda is added, one equivalent only of its water
isdisplacedandtwoare retained: 3(HO)P05 + NaO=NaO,2(HO)P05 + HO.
On the addition of a second equivalent of soda, a second atom of basic water
is displaced, the salt therefore still remaining characteristically tribasic ; for
in this case, NaO,2(HO)P03+NaO, becomes 2(NaO)HO,P05+HO ; and
lastly, the addition of a third equivalent of soda displaces the remaining atom
of water, and we have an anhydrous tribasic phosphate of soda : 2(NaO)HO,
POg + NaO = 3(NaO)P05+HO. So also in regard to the insoluble phos-
phates formed by precipitation : the monobasic, or metaphosphate of soda,
decomposes one equivalent of nitrate of silver, and a white monobasic phos-
phate of silver is thrown down: NaO,P05-f-AgO,NOs=AgO,P05-fNaO,
KO5. On the other hand, the bibasic salt, or pyrophosphate of soda, decom-
poses two equivalents of nitrate of silver to form a white bibasic phosphate
of silver : 2(NaO)P03+2[AgO,N03] = 2(AgO)P05+2[NaO,N03]. And,
lastly, one equivalent of the tribasic phosphate of soda decomposes three
equivalents of nitrate of silver, forming one equivalent of the yellow or common
phosphate of silver, and three of nitrate of soda. 3(NaO)P05-f SfAgO,
NOJ=3(AgO)P03+3[NaO,NO,].

^ The phosphates which are soluble are easily recognized by the addition of
nitrate of silver. A yellow precipitate is thrown down. When acetate of
lead is added to the solution, a white precipitate of phosphate of lead is
formed, and this is not soluble in an excess of the phosphate. For neutral
solutions the following plan may be adopted : Precipitate a solution of sul-
phate of magnesia, and add sufficient chloride of ammonium to redissolve
the magnesian precipitate. This liquid added to the solution of a phos-
phate, even when much diluted, produces a white crystalline precipitate of
phosphate of ammonia and magnesia, insoluble in ammonia and chloride
of ammonium, but soluble in nitric and acetic acids. This precipitate,
when collected, dried, and calcined, is thus constituted : 2(MgO)P05. In
the absence of arsenic acid, it serves for the detection and estimation of
phosphoric acid. In an acid solution of a phosphate the perchloride of iron
is a useful reagent, not merely for the detection, but for the separation of
phosphoric acid. Add to the diluted solution of a phosphate, acetate of
soda and a few drops of a solution of perchloride of iron — a pale reddish-
brown precipitate of phosphate of iron is thrown down. This precipitate is
not soluble in acetic acid, but is dissolved by the hydrochloric and some
othef acids, hence, before the test is employed, it is advisable to nearly

244 COMPOUNDS OF PHOSPHORUS AND HYDROGEN.

neutralize the solutioD. The precipitation is rendered more complete by
boiling the liquid.

An insoluble phosphate (lime) should be first dissolved in diluted nitric
acid. The acid solution gives a gelatinous or flocculent white precipitate of
phosphate of lime, when the acid is neutralized by ammonia. It is insoluble
in alkalies. If nitrate of silver is added to another portion of the acid
liquid, and then a few drops of a weak solution of ammonia, the presence of
phosphoric acid is indicated by the production of a yellow precipitate of phos-
phate of silver. The whole of the phosphoric acid may be obtained from an
insoluble phosphate, by dissolving it in diluted hydrochloric acid, nearly
neutralizing the solution with ammonia, and then adding to it acetate of
soda with a suffijcient quantity of perchloride of iron to give a reddish color
to the liquid. On boiling the liquid, the whole of the phosphoric acid is
precipitated in combination with the oxide of iron.

The Pyrophosphates give white precipitates with solutions of nitrate of
silver and acetate of lead. The lead-precipitate is dissolved by an excess of
the Solution of pyro-phosphate. When a pyrophosphate is added to a solu-
tion of albumen, and the liquid is acidulated with acetic acid, there is no
precipitate. The metaphosphates have the characters assigned to metaphos-
phoric acid (page 241). They precipitate the salts of baryta, lead, and
silver. The white salt of silver is soluble in an excess of metaphosphate,
in which respect it differs from the pyrophosphate.

Phosphorus and Hydrogen. {Phosphide of Hydrogen). — Phosphorus
forms three compounds with hydrogen, one gaseous, PH3 ; one liquid, PHg ;
and one solid, P3H. The gaseous compound is that which is best known as
% highly combustible, and in some cases spontaneously inflammable gas.
This spontaneous inflammability is not, however, a property of the pure gas;
but it depends on the admixture of the vapor of the liquid compound, which
is generated at the same time. It is the spontaneous combustion of this
vapor in air, which renders the phosphuretted hydrogen, associated with it,
inflammable.

The pure phosphuretted hydrogen may be procured by acting on phosphide
of calcium with strong hydrochloric acid. As thus procured, it is a colorless
gas, having a fetid odor resembling that of onions or garlic. Some have
compared it to the small of putrid fish. It is soluble in water and alcohol.
Water will take up about one-eighth of its volume. The gas has no alkaline
reaction. Although combustible at a comparatively low temperature, 212°
(Regnault), it does not burn spontaneously in air, unless it is mixed with
the vapor of the second compound. In this case, it burns with a bright
white light, producing solid phosphoric acid and water.

The mixed compound, containing the inflammable vapor, was for a long
time considered to be the true phosphuretted hydrogen gas. It was dis-
covered by Gengembre, in 1783, while the uninflammable variety was first
made known by Davy, in 1812. The spontaneously inflammable gas is pre-
pared by heating phosphorus in a very strong solution of potassa, a little
ether being placed in the retort, to prevent an accident from explosion, when
the gas is first produced. The gas does not burn in the vapor of ether. The
changes which take place in its production may be thus represented : 3K0-f
4P + 3HO=PH3-f-3(KO,PO). It may be collected over water, and pre-
served in bottles in a dark place for more than a week, still retaining its
property of spontaneous inflammability. If exposed to light, the vapor of
the liquid PH3 undergoes decomposition, and it is resolved into a solid
phosphide of a yellowish color, and into the non-inflammable gas. This
vapor may be separated from the gas, by passing it through a freezing mix-

INFLAMMABLE PHOSPHURETTED HYDROGEN. 245

ture. Tt is also decomposed by hydrochloric acid, and in these cases, the
gas loses the property of spontaneous inflammability.

When a bubble of this gas escapes into the air, it bursts and burns with
the bright white light of phosphorus, producing an expanding wreath of
white phosphoric acid vapor, which, as it slowly dissolves in the air, may be
seen to be composed of numerous smaller wreaths, each rapidly revolving
around a central axis, and at right angles to the expanding horizontal
wreath. This motion appears to be dependent on the heated currents of air
carrying the solid particles of phosphoric acid in their course. PH3,PH3+
0^5=2P05+5HO. Bubbles passed into ajar of oxygen or of protoxide of
nitrogen, burn with a brilliant light. In chlorine, they burn with a pale
bluish light forming perchloride of phosphorus. In nitrogen, deutoxide of
nitrogen, and carbonic acid there is no combustion. When the gas is passed
into a solution of ammonio-nitrate of silver it is absorbed, and the solution
blackened from the reduction of the silver.

A quantity of this gas suddenly exposed, explodes with oxygen or air,
and in the absence of sufBcient oxygen for perfect combustion, red oxide of
phosphorus is deposited in the vessel. The gas is frequently mixed with
free hydrogen. This may be detected by a solution of sulphate of copper,
which dissolves the phosphuretted hydrogen only. It is also absorbed by a
solution of chloride of lime.

It has been long known that whether spontaneously inflammable or not,
the gas had the same composition, a fact which is now intelligible, as the
property is an accidental result of the admixture of another phosphide in
vapor. Gay-Lussac and Thenard found that one volume of this gas, when
decomposed by chlorine, gave three volumes of hydrochloric acid. This
proved that each volume contained one and a half volumes of hydrogen, or
two volumes of the compound contained three of hydrogen. The removal
of the phosphorus from the gas by copper and potassium, establishes the
accuracy of these volumetric proportions. The weight of phosphorus in each
volume is found by deducting one and a half times the specific gravity of
hydrogen from the ascertained specific gravity of the gas. This is as nearly
as possible equal to one-fourth the specific gravity of phosphorus- vapor ;
hence one quarter of a volume of phosphorus-vapor is combined v/ith one
and a half volume of hydrogen, in each volume of phosphuretted hydrogen :
or one half volume with three of hydrogen, in two volumes of the gas.
Some chemists prefer doubling the volumes — thus making one volume of
phosphorus-vapor to be associated with six volumes of hydrogen — the
seven volumes being condensed into four. Its composition will, therefore,
stand thus : —

Atoms. Equiv. Per cent. Vol. Sp. Gr.

Phosphorus . 1 ... 32 ... 91-43 ... J ... 2-1777
Hydrogen . . 3 ... 3 ... 8-57 ... 3 ... 0-2073

1 35 100-00 2 2-3850

The sum of the sp. gr. divided by 2 gives 1*1925. The specific gravity
of the gas is commonly represented to be 1*1850 compared with air; and
com.pared with hydrogen 17 '5. It will be perceived that the gas has some
analogy in its volumetric constitution to ammonia, but it has not the alka-
line properties. It forms, however, solid crystalline compounds with the
hydriodic and hydrobromic acids. The constitution of this gas shows that
the atoms of elements are not necessarily represented by single volumes ;
and those of compounds by two volumes. On the former view, the atomic
volume of phosphuretted hydrogen would be equal to four volumes of the

246 COMPOUNDS OF PHOSPHORUS WITH NITROGEN, CHLORINE,

compound ; and on the latter view, the atom of phosphorus must necessarily
be represented by half a volume {see page 68).

Phosphuretted hydrogen does not change the color of paper impregnated
with a salt of lead ; but it immediately decomposes solutions of silver and
gold, the metals being reduced by it to the metallic state. The gas is ab-
sorbed and decomposed by these solutions. Thus the nitrate of silver
forms a good test for the presence of this compound. When passed through
a tube heated to redness, the gas is decomposed.

Liquid Phosphide of Hydrogen (PHg). — This is procured by distilling
fragments of phosphide of calcium with water only, and collecting the pro-
duct in a receiver, kept cool by a freezing mixture. The phosphide thus
procured is a most inflammable liquid. It takes fire in air, and burns with
a brilliant light. It is colorless, highly refracting, and insoluble in water.
It remains liquid at — 4^ ; is destroyed by a temperature of 86°, and when
exposed to light is resolved into solid phosphide and non-inflammable phos-
phuretted hydrogen : 5PH2=P2H-f 3PH3. When its vapor is mixed with
hydrogen it renders this gas spontaneously inflammable in air. It is decora-
posed by strong hydrochloric acid, and by oil of turpentine. When phos-
phide of calcium is put into water, gaseous phosphuretted hydrogen, with
the vapor of liquid phosphide, escapes, and burns in the air with great
brilliancy. The bubbles of gas are similar to those which are evolved, by
boiling phosphorus in a strong solution of potassa.

Solid Phosphide 0/ Hydrogen (F 2^). — This is analogous in constitution
to the oxide, hydrogen being substituted for oxygen. It may be procured
by exposing to light the liquid compound, or the spontaneously inflammable
gas. It is of a yellow color, has an odor of phosphorus, but is not luminous
in the dark. It is reddened by light. It is insoluble in water and alcohol.
It is not inflamed in air under a temperature of 320°.

Phosphorus and Nitrogen. — A compound of these metalloids was an-
nounced by Rose under the formula N^P. He procured it by saturating
the pure terchloride of phosphorus at a low temperature with ammonia.
The white substance thus obtained, when heated to redness out of contact of
air, left a light white powder insoluble in water, alcohol, and ether. When
excluded from air and moisture, it is fixed and infusible at a red heat,
although its constituents are volatile. When heated in contact with air and
moisture, it evolves white fumes of phosphoric acid, and becomes slowly
oxidized without inflaming. Heated on platinum, it corrodes the metal, and
converts it into a phosphide. According to Gerhardt, it contains hydrogen,
and is in reality an amide of phosphorus, NH^P, or Phosphamide.

Phosphorus and Chlorine. — There are two compounds of these ele-
ments, a terchloride corresponding to phosphorous acid j and a pentachloride
corresponding to phosphoric acid.

Terchloride of Phosphorus (PCI3). — This compound, which is liquid,
is procured by distilling a mixture of phosphorus and chloride of mercury ;
or, by passing the vapor of phosphorus over chloride of mercury heated in
a glass tube, terminating in a cool receiver. This liquid dissolves phos-
phorus, and generally holds a little in solution, which gives to it a reddish
color. When purified by slow distillation, it becomes limpid and colorless ;
it requires to be cautiously excluded from the action of the air. It has a
suff'ocating odor. Its specific gravity is 1*45. Exposed to the air it is vola-
tile, and exhales acid fumes : it does not change the color of dry vegetable
blues, but becomes powerfully acid upon the least acquisition of moisture.

BROMINE, IODINE, AND SULPHUR. 24T

Its vapor is combustible. It has a sp. ^r. of 4*742 ; 3 vols, of chlorine are
combined with 5 vol. of phosphorus to form 2 vols, of the vapor. Chlorine
converts it into pentachloride of phosphorus. It acts upon water with j]rreat
energy, and produces phosphorous and hydrochloric acids, PCl34-3HO =
PO3 + 3HCI.

Pentachloride of Phosphorus (PCI5). — When dry phosphorus is sub-
mitted to the action of chlorine in excess, it burns with a pale yellow flame,
and produces a white, flaky, volatile and deliquescent compound, which
attaches itself to the interior of the vessel, and which is i\iQ pentachloride
of phosphorus. It may be conveniently formed in an exhausted retort, con-
taining phosphorus, to which chlorine is admitted until the phosphorus is
saturated. It was formerly mistaken for phosphoric acid, but its easy
volatility is alone a sufficient distinction, for it rises in vapor at 200^. It is
fusible under pressure, and crystallizable in transparent prisms; it is a non-
conductor of electricity; it reddens dry litmus-paper, in consequence, as
Berzelius supposes, of its acquiring hydrogen and oxygen from the decom-
position of the paper. It fumes in the air, and when brought into contact
with water, a mutual decomposition immediately takes place, and phosphoric
and hydrochloric acids result. PClg-f 5H0 = P05+5HC1. It is combustible,
and produces chlorine and phosphoric acid by its combustion. When passed
through a red-hot porcelain tube with oxygen, phosphoric acid is produced,
and chlorine is evolved ; these facts show that oxygen, at a red heat, has a
stronger attraction for phosphorus than chlorine. Potassium, heated in its
vapor, burns with great brilliancy: with dry sulphuretted hydrogen it yields
hydrochloric acid and chloro-sulphide of phosphorus; PCl5+2HS=PS2Cl3
-i- 2HCI. Metallic oxides decompose it with the production of metallic
chlorides and phosphates. The vapor has a sp. gr. of 3 '66. It consists of
one-half vol. of phosphorus and 5 vols, of chlorine condensed into 4 vols, of
the compound.

There is an oxychloride, PCI3O3, which requires no particular notice.

Phosphorus and Bromine. — There are two bromides of phosphorus — a
liquid and a solid — corresponding to the two chlorides (PBr3,PBr5). The
elements combine on contact with explosive violence, hence great caution
should be used in preparing these compounds.

Phosphorus and Iodine. — Iodine combines with phosphorus on contact,
producing combustion when the mixture is exposed to air. There are two
iodides, a biniodide, PI3, and a teriodide, PI3. They are both solid and
crystalline ; they may be procured by dissolving the constituents in their
equivalent proportions in sulphide of carbon, and cooling the solutions.

Phosphorus and Sulphur. — These elements combine, according to
Pelouze and Fremy, to form five diflferent compounds, four of them corres-
ponding to the four oxygen-compounds of phosphorus — sulphur being
substituted for oxygen. Besides these, there is the persulphide PS^, to
which there is no analogous oxygen compound. Sulphur and phosphorus
may be combined by fusion in an atmosphere of carbonic acid, but great
caution should be used, as with common phosphorus a violent explosion
may occur. The phosphorus should be melted under water, and the sulphur
gradually added in small fragments. Phosphorus will thus combine with a
large quantity of sulphur without losing its liquid state. Sulphur or phos-
phorus may be obtained in crystals from this mixture on cooling, according

248 CARBON.

to whether one or the other happens to be in excess. Amorphous phos-
phorus may be fused with sulphur under these circumstances, without giving
rise to an explosion, although there is a violent action when fusion takes
place. (Kekule.)

CHAPTEH XIX.

CARBON AND ITS COMPOUNDS WITH OXYGEN. CARBONIC
OXIDE. CARBONIC ACID.

The carbon group of metalloids comprises three bodies — carbon, boron,
and silicon. Carbon is the great constituent of the organic, and silicon of
the inorganic kingdom. Boron is not found among organic products, and
is only sparingly diffused in the mineral kingdom. These bodies do not
enter into combination with each other ; but they have certain characters in
common. They exist either in a crystalline or amorphous state ; in the
latter state, they assume the form of black or dark-colored solids, which may
be heated in close vessels without change, but undergo combustion and oxi-
dation when heated in the air. Carbon entirely disappears as a- gaseous
acid (carbonic acid), while boron and silicon are converted into white
fusible solids (boracic and silicic acids). These three bodies cannot be made
to assume the vaporous condition, although they readily combine with other
metalloids to form gaseous compounds. As a summary of their characters,
they are chiefly remarkable for being in the crystalline state intensely hard ;
and in the amorphous state, insoluble, and fixed at the highest temperatures.
Carbon is infusible, but boron and silicon may be fused at a very high
temperature.

Carbon (C=6).

History. — Carbon is found in various states which are considered to be
allotropic modifications of the same elementary substance, but widely
differing from each other in appearance and physical properties. In its
purest form, it constitutes — 1, diamond, which is crystallized carbon. In
a less pure state, it is seen in — 2, plumbago, or graphite; 3, as anthracite ;
and 4, as coke, the carbon of coal. The state in which it is most
commonly seen is — 5, as charcoal, derived either from animal or vegetable
matter.

All these varieties agree in the fact that when heated to a high tempe-
rature in oxygen or air, they undergo combustion and are converted into
carbonic acid. The combustibility, however, varies greatly with the molecular
condition of the carbon. Tinder, the carbon of linen or cotton, is easily
ignitable, and when once ignited, combustion spreads readily throughout the
mass ; but a piece of wood charcoal or coke, if ignited, is soon extinguished
on exposure to air. Animal charcoal, in consequence of its hardness, and
the very large quantity of mineral matter associated with it, burns with
difficulty. Plumbago and diamond, owing to their compact texture, require
to be heated to a very high temperature in pure oxygen, before they will
readily undergo combustion. The diamond finely powdered, may, however,
be burnt by heating it on red-hot platinum ; diamond dust heated with
sulphuric acid and bichromate of potassa, is said to be completely converted
into carbonic acid. (Rogers.)

DIFFUSION OF CARBON. PROPERTIES OF DIAMOND. 249

Carbon is essentially the element of the organic kingdom. All organic
substances, or those which have been produced under the influence of life,
contain it. It constitutes nearly half the weight of the dried animal or
vegetable substance. In the vegetable kingdom, it forms the skeleton of the
plant or tree — a fact which is made evident to us by the perfect preservation
of form, when the substance has been heated out of contact with air. The
detection of carbon in the residues of substances heated to redness in close
vessels, is properly relied upon as the best evidence of the presence of
organic matter. Carbon is, however, an important constituent of the mineral
kingdom. Apart from its crystalline forms in diamond and plumbago, it is
found as anthracite, bituminous coal, and lignite, in vast deposits in the
earth. Limestone, marble, chalk, and coral contain carbon (in a combined
state as carbonic acid) in the proportion of about twelve per cent, of their
weight ; and in the atmosphere, carbonic acid (which contains twenty-seven
per cent, by weight of carbon) is universally found. There is reason to
believe that it is through this medium that carbon finds its way into the
vegetable structure ; and that the oxygen associated with it is restored to
the atmosphere to be again converted by animals into carbonic acid. Carbon
is also present, as carbonic acid, in rain, spring, and river-water.

Diamond (d5a/*aj, signifying hardness). — This substance has been found
in India, Borneo, the Brazils, and Siberia. Diamonds have hitherto been
met with in detached crystals, in alluvial soils, associated with rolled quartz-
pebbles, sand, and a ferruginous clay. They are obtained by simply washing
the soil ; their great specific gravity facilitating their separation from the
light sand and clay. Diamonds are now chiefly procured from the district of
Serra do Frio, in the province of Minas Geraes, in the Brazils.

The primitive form of the diamond is a regular octahedron, each triangular
facet of which is sometimes replaced by six secondary triangles, bounded by
curved lines ; so that the crystal becomes spheroidal, and presents forty-eight
facets. Diamonds, with twelve and twenty-four facets, are not uncommon.
The diamond has been found of various colors; those which are colorless are
most esteemed ; then those of a decided red, blue, yellow, pink, or green
tint. Those which are brown are least valuable. Three-fourths of the
stones found are tinged with some color, mostly pale yellow or yellow
brown.

The fracture of the diamond is foliated, its laminae being parallel to the
sides of a regular octahedron. Although the hardest of bodies, it is brittle,
and is easily broken when struck in its planes of cleavage, which are four,
corresponding to the octahedral sides. Its specific gravity varies from 3 '5
to 3'6 : it is most commonly 3'52. Its specific heat is O'l 192. Itis a non-
conductor of electricity, and acquires positive electricity by friction. It con-
ducts heat so much better than glass, that this property is sometimes employed
as a test, to distinguish the diamond from substances which resemble it.
It exerts a highly refractive power on light : compared with glass or rock-
crystal it is 2 '47 to I'Q. When exposed for some time to strong sunshine,
it becomes, by insolation, luminous in the dark. The strongest alkalies and
acids, including the fluoric acid, whether singly or in mixture, have no effect
upon it. The fluoric acid, however, dissolves and destroys artificial or paste
diamonds. With the exception of oxygen the metalloids, including fluorine,
have no action upon it ; and oxygen will only combine with it at a very high
temperature. Its combustibility was first proved in 1694. It requires a
most intense heat to effect this. It may be burnt in a vessel of pure oxygen
by concentrating upon it the solar rays, or by heating it in the flame of the
oxy-hydrogea blowpipe, and then introducing it into a bell-jar of pure

250 PHYSICAL AND CHEMICAL PROPERTIES OP THE DIAMOND.

oxygen. In the atmosphere, however heated, it will cease to burn so soon
as the current of air is withdrawn. It has been clearly proved that carbonic
acid is the sole product of this combustion, and that equal weights of pure
carbon and diamond yield the same quantity. The diamond, like other kinds
of carbon, deflagrates with melted nitrate of potassa, and produces carbonate
of potassa During its combustion in oxygen, it evolves, without flame, a
bright light, which is even visible in sunshine ; and it occasionally leaves a
slight incombustible residue. Some diamonds have been entirely consumed
in oxygen ; others have left a residue of silica and oxide of iron, varying
from 0"15 to 0*2 per cent, of their weight — a quantity so small, that it may
be regarded as an accidental impurity. The black, or carbonic diamond
{carbona), found at Bahia, in Brazil, in 1843, when burnt, leaves a larger
residue. Three samples left respectively residues weighing 0-24, 027, and
3 03 per cent, of their weight. (Dumas.) The sp. gr. of this variety of
diamond, which is chiefly used for making polishing powder, is from 3"1 to
3 "43. It is the diamond in an amorphous state, quite opaque, and varying
in color from iron-gray to reddish-black. In two years, four thousand ounces
were extracted in Bahia.

When a diamond is heated on charcoal in the arc of fire from a powerful
voltaic battery, it softens, cracks, increases in size, becomes black, and assumes
the appearance of coke. Its sp. gr. is reduced from 3 3 to 2*6. In this
state it is a conductor of electricity : it scratches glass, but is so brittle that
it can be broken between the fingers. The effect of intense heat in thus
destroying the transparency and completely changing the molecular condition
of the diamond, appears to show that this substance, as it is found in nature,
has not been exposed to a high temperature in its production. All attempts
to fuse or crystallize carbon, or to form diamonds artificially, have hitherto
failed. Some suppose that the carbon of diamond is of organic origin ; but
all that we can surmise is, that it has been crystallized from some unknown
solvent, defiant gas, sulphide of carbon and chloroform are colorless com-
pounds of this element, and it is remarkable that the two latter, which are
liquid, have great weight and have a high refracting power with the lustre of
diamond. The sulphide of carbon contains one-sixth of its weight, and
chloroform one-tenth of its weight in combination. The sulphide readily
dissolves sulphur, which may be obtained crystallized from it, but it has no
solvent action on carbon. If sulphur and chlorine could be slowly removed
from these compounds, the carbon might be deposited in crystals. As it is,
when these or other gaseous and liquid compounds are decomposed the car-
bon always assumes the black or amorphous condition of finely-divided char-
coal. There is reason to believe that all crystallized diamonds found native
have been deposited from a state of solution. According to Mr. Lionnet, by
the decomposition of sulphide of carbon by a weak voltaic current in which
platinum and tin were the metals used, he obtained carbon in crystals at the
bottom of the vessel while the sulphur combined with the tin. The diamond
is not always found crystallized in a regular form. Sometimes the substance
has presented only a crystalline structure, at others, as in the black diamond,
it has been found amorphous, having the appearance of intensely hard black
charcoal.

The art of cutting and polishing diamonds, though probably of remote
antiquity in Asia, was first introduced into Europe in 1456, by Louis van
Berquen, of Bruges, who accidentally discovered that, by rubbing two
diamonds together, a new surface or facet was produced. The forms which
are given to the polished diamond are the brilliant and the rose. The bril-
liant form, which has from 56 to 64 facets, was first introduced by Cardinal
Mazarin, in 1650. It is especially calculated to bring out the lustre and

PLUMBAGO. GRAPHITE. BLACK LEAD. 251

refractive powers of the p^em. Thus a well-cut brilliant, held in a beam of
light, reflects nearly the whole of the light which falls upon it, throwing it
out and refracting it in colored rays through the facets in front. With the
exception of one small point of light through the collet, the brilliant forms
an opaque shadow on a screen.

The diamond appears to be unchangeable, and the most indestructible of
substances. The Koh-i-Noor, said to have been discovered in 1550, and now
among the British crown jewels, had undergone no apparent alteration in
brilliancy or polish after the lapse of three hundred years. The weight and
value of diamonds is usually estimated in carats, of which 150 are about
equal to one ounce troy, or 480 grains ; ^. e., each carat is equivalent to 32
grains. The Koh-i-Noor, when first discovered, is stated to have weighed
900 carats. It lost by the first cutting 279 carats, and it has been consider-
ably reduced by its having been recently cut into the shape of a brilliant.
Its weight is now said to be 102 carats. The Russian diamond, the Koh-i-
Toor, weighs 193 carats, but in consequence of its irregular shape, its value
is small in proportion to its weight. Probably the finest diamond in the
world, for its water, shape, and size, is the Pitt diamond, now among the
crown jewels of France. It was discovered in 1702, and was purchased in
the rough state by Mr. Pitt, governor of Bencoolen. In 1717, it was sold
to the Regent Duke of Orleans, during the minority of Louis XV., for the
Bum of 135,000/. It was cut into the form of a perfect brilliant, and proved
to be of the finest water, without color or flaw. It weighed, before cutting,
410 carats, and after cutting, 136. The chips and dust obtained from it
were valued at 8000^. In 1791 a commission of jewellers assigned its value
at 480,000/. It is remarkable that these three large diamonds were found in
the same district of Central India. The cutting and polishing of diamonds
is chiefly carried on at Amsterdam.

Apart from its use in ornamental jewelry, the diamond is employed in
the arts. Owing to its hardness, it is found a useful substance for the pivot-
holes of watches. It has been employed for microscopic lenses, and it is
extensively used for cutting glass. The edge of one of the small curvilinear
crystals is selected for this purpose, as the edges of the crystals formed by
flat planes, only scratch the surface without producing that peculiar fissure
by which the glass can be smoothly cut.

The diamond possesses none of the ordinary properties of carbon, as they
are known in charcoal. This, no doubt, depends on the different molecular
states of the two bodies.

Plumbago, Graphite. Black Lead. — This substance is well known
in the manufacture of pencils, for which purpose it is almost exclusively
obtained from the mine of Borrowdale, at the west end of Derwent Lake,
in Cumberland, where it was first wrought during the reign of Elizabeth.
In a less pure state, it is not an uncommon mineral, occurring in detached
masses, generally in primitive rocks. It is thus found in Germany, France,
India, Ceylon, and North and South America. It is of an iron-gray color,
metallic lustre, and soft and greasy to the touch, producing a leaden mark
on paper. Its specific gravity varies from 19 to 25 ; it occasionally occurs
crystallized in hexagonal plates ; it conducts electricity, and, for this
purpose, is much used in the electrotype process. It is infusible, very
difficult of combustion, and, when mixed with fire-clay, is a useful ingredient
in the manufacture of crucibles and melting-pots intended to withstand high
temperatures. It undergoes no change in air, and is used to cover articles
of iron to prevent them from rusting. When it is burned in a stream of
oxygen gas, it leaves a small quantity of yellow ash, composed chiefly of

252 VARIETIES OF COAL. COKE.

oxide of iron, with silica and titanic acid, but varying in quantity in different
specimens. In good plumbago, the carbon amounts to 96 per cent. Some
specimens from Brazil leave scarcely any residue when burnt. The oxide of
iron is an incidental ingredient, and is not in chemical combination with
carbon. It exists in no definite proportion. The late Mr. Brockedon found
that the dust of plumbago might be forced, under great pressure (like spongy
platinum), into a coherent mass, which might be cut and applied to the same
uses as the pure native substance.

Cast-iron, after corrosion, as a result of long immersion in sea-water,
acquires the softness, greasiness, and some other physical characters of plum-
bago. The cannon-balls and cast-iron guns of the Royal George, sunk
at Spithead, presented this condition after many years' submersion in sea-
water. A mass of cast-iron, which had been immersed some years in a
brewer's vat, had a loose and spongy structure, and was so soft that it could
be cut with a knife. It appears from analysis that, in this transformation,
the greater portion of the iron is removed, and the carbon largely predomi-
nates. The durability of cast-iron piers, sunk in sea-water, may be affected
by this change.

Mr. Brodie has found that plumbago is remarkably altered in its chemical
and physical properties, when it is heated with sulphuric acid and chlorate
of potassa.

Carbon op Coal. — The principal constituent of coal is carbon, associated
with variable proportions of oxygen and hydrogen, as well as with small
quantities of sulphur and nitrogen. The British caking or bituminous coals,
including those of Northumberland, Nottinghamshire, and South Wales,
have a sp. gr'. of about 1*2 ; and according to Dr. Percy, they contain from
"IT to 83"44 per cent, of carbon. The British non-caking coals contain from
72 to 80 per cent, of carbon ; while cannel coals contain 78 to 84 per
cent. (Percy, Metallurgy, p. 99.) All kinds of coal yield an ash consisting
of silica, oxide of iron, and lime. In good coal this varies from one to three
per cent, of its weight. In the bituminous schists, such as the Torbane
mineral, miscalled coal, the ash amounts to 25 per cent of the weight of the
substance.

The chief characters of good coal are that it is a black, brittle, combustible
substance, containing a large amount of carbon, of which it will yield about
half of its weight, under the form of coke, when it is heated out of contact
of air. The amount of mineral ash which is left, after perfect combustion,
is small, and does not interfere with the use of the substance for heating
purposes.

In Lignite, or wood coal, which forms one end of the coal series, the
shape and structure of the wood are preserved. In Bituminous, or pit-coal,
the vegetable structure is in great part lost, probably as a result of heat and
compression. Anthracite, or stone-coal, called also mineral charcoal, contains
a larger proportion of carbon than the other varieties. It is very heavy,
having a specific gravity of 1-4 to 1"8, and has no resemblance whatever to
wood. It is well known as the culm of Wales, and the Kilkenny coal of
Ireland. It has a slight metallic lustre, is very difficult of combustion, so
that it will burn only in a strong current of air ; and when ignited it is
consumed without flame, smell, or smoke. We have found good Kilkenny
anthracite, to leave only 4*4 per cent, of a reddish-brown ash, consisting
chiefly of oxide of iron and silica, so that this coal might be considered as
mineral carbon in a state nearly pure. It constitutes the other extreme of
the coal series.

Coke. — This is the carbonaceous residue of the distillation of pit-coal.

PREPARATION OF CHARCOAL. 253

It is manufactured on a large scale in ovens constructed for the purpose
The bituminous coal of Northumberland yields 66 per cent. ; and that of
Nottinghamshire, 63 per cent, of coke. Non-caking and cannel coals yield
rather less. Coke has a sp. gr. of r6 to 2, but in equal bulks it is about
one-half the weight of coal. It has a porous texture, and sometimes a
metallic lustre. This is owing to the glazing or fusion of the ashes upon the
surface. It is difficult of combustion except in large masses, and under a
rapid current of air. Small pieces, when removed from the fire red-hot, are
soon extinguished. It contains sulphur, and yields, by combustion, sul-
phurous acid. If quenched with water while red-hot, sulphuretted hydrogen
is produced by the decomposition of the water. It exceeds all fuels in the
amount of heat which it evolves by combustion. Next to hydrogen, there
is no body which consumes so large an amount of oxygen as carbon ; but
coke gives a more powerful and steady heat than wood-charcoal, hence it is
largely employed as a fuel in furnaces. It will evaporate 14 times its
weight of water. The harder the coke, the greater is its value as fuel.
Dry coke does not absorb aqueous vapor like charcoal. It will not take up
more than from 1 to 2^ per cent, in a humid atmosphere ; but perfectly dry
coke, placed in water, will absorb this liquid to the extent of half of its
weight. 1000 parts of dry coke, according to Berthier, consists of carbon,
^8; ashes, 115 ; volatile matters, -027. Good coke should not yield more
than 4 or 5 per cent, of ash. Certain hard kinds will yield from 10 to 15
per cent, of their weight.

Charcoal. — Preparation. — Charcoal may be obtained either from vege-
table or animal substances. In order to procure it, it is necessary that the
organic matter should be heated to a high temperature out of contact of air.
If an ordinary splint of wood be burnt in air, the carbon is entirely con-
sumed, and a white alkaline ash remains. If a similar splint ignited, is gradually
lowered into a narrow test-tube, allowing only a slow combustion to go on
at the mouth of the tube, a skeleton of the wood in charcoal will be obtained.
Introduce between two layers of mica a slip of paper, and place a similar
slip on the outside of the mica. When heat is applied beneath, the piece
of paper which is protected from air will be converted into charcoal, while
that which is exposed will be consumed, leaving only a slight ash. If a
sheet of paper, or a portion of lace, impregnated with a solution of phosphate
of ammonia is dried and burnt in air, the carbon of the vegetable matter is
obtained, retaining its perfect form {see page 236). Charcoal may be pre-
pared for chemical purposes, by heating to redness, in a crucible, pieces of
boxwood, covered with sand, and keeping them in that state for about an
hour, or until all volatile matters are expelled. They are thus converted
into a black, brittle, porous substance, which appears to be essentially the
same, from whatever kind of wood it has been procured. The stick of char-
coal, when broken, should be equally black throughout. Sugar and certain
other substances, which neither contain nitrogen nor leave any residue after
combustion, when intensely heated in closed vessels, yield a pure charcoal ;
it always retains, however, traces of oxygen and hydrogen ; thus, Erdmann
and Marchand found in the carbon of sugar obtained at a white heat, 3'1
per cent, of oxyygen, and 0*6 of hydrogen, and even after it had been sub-
jected for three hours to the highest temperature of a blast-furnace, it retained
0*5 per cent, oxygen, and 0*2 hydrogen. In passing the vapors of certain
hydrocarbons, and of oils, alcohol, and ether, through white-hot porcelain
tubes, pure carbon is deposited. A variety of pure carbon is occasionally
found in coal-gas retorts, and in the tubes connected with them, resulting
from the decomposition of the first products of the distillation of coal. It
has a gray color, and often exhibits a laminated texture ; its streak is black,

264 INFLUENCE OF TEMPERATURE.

and it breaks with an earthy fracture : its specific gravity is about IS. It
sometimes happens that the gas escapes through a crack in the retort, in
which case a peculiar carbonaceous deposit is forming upon the surrounding
brickwork, of a stalactitic character, an iron-gray color, and considerable
lustre ; it does not easily burn, nor does it soil the fingers. Some specimens,
from their appearance, might be considered to be metallic ; its specific gravity
is about 1-75.

Common charcoal, employed as fuel, is usually made of oak, chestnut, elm,
beech, or ash-wood, the resinous woods being seldom used. Young wood
afifords a better charcoal than large timber, which is also too valuable to be
thus employed. The billets are formed into a conical pile, which, being
covered with earth or clay, is suffered to burn with a limited access of atmo-
spheric air, by which its complete combustion, or reduction to ashes, is pre-
vented. Another, and a more perfect mode of preparing charcoal, consists
in submitting the wood to a red heat in a kind of distillatory apparatus,
consisting of cast-iron cylinders, from which issue one or more tubes for the
escape of gaseous matters and vapors. This kind of charcoal is preferred
for the manufacture of gunpowder. A third method of charring wood con-
sists in exposing it to the action of highly heated steam, by which, according
to Violette {Ann. Ck. et Ph.^ 3me ser., xxiii. 475), different modifications
of charcoal may be obtained, especially adapted for the manufacture of gun-
powder. In another memoir upon the same subject {Ibid., xxxii. 346), M.
Yiolette arrives at the following conclusions : 1. That the quantity of char-
coal obtained from wood decreases in proportion as the temperature in-
creases. At 482^ the average product of charcoal is 50 per cent. ; at 572^
33 per cent. ; at 752°, about 20 per cent. ; and at the temperature of fusing
platinum about 15 per cent. 2. The quantity of charcoal varies with the
duration of the process of carbonization, and is greatest when the process is
slowly carried on. 3. The normal carbon of the wood is divided during
carbonization into two parts, one of which remains in the charcoal, and the
other escapes with the volatile products. This division varies with the tem-
perature of carbonization ; thus, at 482° the carbon remaining in the char-
coal is double that which escapes : between 572° and 662° the two portions
are equal, and at a high temperature the quantity which escapes is double
that which remains. 4. The charcoal retains a quantity of carbon propor-
tionate to the temperature of carbonization , at 482° it includes 65 per cent,
of carbon ; at 572°, 73 per cent. ; at 752°, 80 per cent. ; and carbonized at
a higher temperature it contains 96 per cent, of carbon, but at no tempera-
ture is the product, carbon, in a state of purity. 5. Charcoal, however pre-
pared, always retains gaseous matter, varying with the temperature of its
preparation ; when made at 482° it amounts to half the weight of the char-
coal ; at 572° to one-third ; at 662° to one-fourth ; at 752° to one-twentieth ;
and at the highest temperatures to about one one-hundredth. The preceding
facts show the great influence of temperature, and of the duration of the
carbonizing process, upon the produce of charcoal from the same wood.
6. When wood is carbonized in perfectly close vessels, the resulting charcoal
retains nearly the whole amount of carbon ; when thus charred, at between
300° and 660°, the percentage of carbon in the charcoal is about 80, which
is thrice that contained in charcoal prepared in the usual way. 7. In ordi-
nary carbonization, the so-called brown charcoal {Charbon ronx) is not ob-
tained under 518°, and the quantity amounts to about 40 per cent ; but in
a perfectly air-tight vessel the quantity obtained is 90 per cent., and the
temperature at which it is formed is 356°. 8. Wood, inclosed in a perfectly
air-tight vessel, and subjected to a temperature of from 572° to 752°, under-
goes a species of fusion ; it agglutinates and adheres to the vessel j on cool-

PROPERTIES OP CHARCOAL

255

ing, it has lost all organic texture, and is a black, shining, porous, fused
mass, exactly resembling pit-coal which has undergone serai-fusion. This
seems to explain the formation of coal. 9. Charcoal made in perfectly close
vessels contains ten times more ash than common charcoal, so that the vola-
tile matters which escape during the ordinary process of carbonization or
distillation, carry with them, either blended or combined, a large proportion
of the mineral substances which constitute the ashes. 10. Charcoal, pre-
pared in the ordinary way, varies much in quality and composition, in con-
sequence of the variation in temperature and time consumed in the process
of charring. The position of the pieces of wood in the cylinders, namely,
whether central or external, in reference to their contents, affects its quality,
a matter of much inconvenience in the manufacture of gunpowder. Char-
coal obtained by the action of highly heated steam, is of a more uniform
character than that which is produced as a result of partial combustion in a
stack.

The quantity and quality of charcoal obtained from different kinds of wood
are liable to much variation, according to the temperature and mode of
charring. The following table shows the produce of charcoal fronii 1000 parts
of several varieties of dense and light woods after exposure to a very high
temperature out of contact of air.

Ebony .

Botany Bay-wood
Brazil-wood .
Eveoas-wood
King-wood .
Tulip-wood .
Satin-wood .

305

281
260
225
220
208
207

Box . . .

202

Fir . . .

181

Lignum-vitae

175

Oak .

174

Mahogany .

157

Beech . . . ,

150

The ashes left by charcoal after complete combustion, vary in quantity
with the kind of wood from which it has been procured. Ordinary charcoal
used as fuel leaves, on an average, 2 per cent, of ashes, consisting chiefly of
carbonate of potash, silica, lime, and oxide of iron. The results of experi-
ments on this subject have shown that 1000 parts of charcoal from the wood
of the lime-tree yield of ashes 50 parts ; the charcoal of the oak, 25 ; of the
birch, 10 ; of the fir-tree, 8 ; of the hornbeam, 26 ; and of the beech, 30
parts. There is a great loss of carbon in the ordinary methods of preparing
charcoal. Thus, assuming that green wood contains 38 '5 per cent, of this
element, the most perfect processes of carbonization do not give a product
greater than 27 or 28 per cent., and the common plan adopted in forests is
so wasteful that not more than 17 to 18 per cent, are obtained. The loss
is occasioned partly by the production of carburetted hydrogen, and, as a
result of combustion, carbonic acid ; and partly by the formation of tar and
acetic acid.

Properties. — Wood-charcoal is a black, amorphous, insoluble, inodorous,
insipid, opaque, and brittle substance. It preserves the form of the wood,
is very porous, containing much air, and has a ringing metallic sound. Its
pores may be injected and made visible by cooling it when red-hot under
mercury. Unlike the diamond, it is a good conductor of electricity, but a
bad conductor of heat, especially when in the state of powder. It is
unchanged by the combined action of air and moisture at common tempe-
ratures. It is easily combustible in oxygen gas. Its specific heat, as
estimated by Regnault, is 0 2411. When pure it is perfectly infusible at
all known temperatures; in the cases in which it was supposed to have been
fused, the fusion was owing to the presence of silicates in the ashes. Under
common circumstances of ignition, it does not appear to volatilize, but it is
not improbable that in the process of steel-making the penetration of iron

256 ABSORPTION OF GASES AND VAPORS BY CHARCOAL.

by carbon may be partly due to its volatility ; and in the voltaic ignition of
charcoal-points, carbon passes from the positive to the negative side in the
arc of flame : so that a concavity is formed upon the surface, when the 4-
electricity emanates, and a deposit of carbon upon the opposite pole. The
intense white light produced in the passage of the electric fluid, is owing to
the incandescence of the minute particles of carbon, transferred from one
pole to the other. In air, there is combustion, but when the experiment is
performed, invacuo, the light is just as brilliant, and in this case, it must be
exclusively due to incandescence. The speciflc gravity of charcoal is about
I'T. It readily floats on water, owing to the large quantity of air within its
pores. If a piece of charcoal, after having been heated to full redness for
some time, is suddenly cooled under water, it will acquire its proper density
and sink. Ordinary charcoal, sunk in a jar of water by attaching to it
sheet-lead, will be found to yield, in vacuo, a large quantity of air, chiefly
from the broken ends. Pieces of charcoal placed in a jar full of water,
inverted in a basin, will give out a large portion of the air which they contain.
When strongly heated out of contact of air, it becomes harder and closer in
texture, and is rendered a better conductor of heat and electricity. AYhea
heated in a current of air, it is consumed, leaving a white or reddish-white
ash {see p. 255). Water, alcohol, ether, hydrochloric acid, and solutions of
chlorine and hydrofluoric acid, have no action upon it. It is slightly
dissolved by strong sulphuric acid, giving to it a brownish color ; and by the
aid of heat it decomposes njtric acid. It is this indifference to chemical
agents, which renders charred wood, such as piles sunk in the earth, inde-
structible. Some of these have been found entire after the lapse of many
centuries.

Newly-raade charcoal has the property of ahsorhing and fixing gases and
vapors, including aqueous vapor. We have found that box-wood charcoal
increased in weight 14 per cent, within 24 hours. The average increase
from this absorption is from 10 to 12 per cent. The researches of Saussure
have proved that different gases are absorbed by charcoal in different pro-
portions, and that the absorption attains its maximum in 24 hours. Damp
charcoal does not absorb gases so readily as that which is dry. If charcoal
is heated red-hot, cooled under mercury, and then introduced into a graduated
tube containing a gas, the results may be easily observed and compared.
Assuming that one cubic inch of charcoal is employed in the experiment,
then, according to Saussure, the number of cubic inches of each gas absorbed
will be represented by the figures in the following table : —

Ammonia

. 90

defiant gas . . .35-

Hydrochloric acid

. 85

Carbonic oxide . . .9-42

Sulphurous acid .

. 65

Oxygen . . . .9-25

Sulphuretted hydrogen

. 55

Nitrogen . . . . 7'5

Protoxide of nitrogen .

. 40

Light carburetted hydrogen 5 •

Carbonic acid

. 35

Hydrogen . . . .1-75

Saussure appears to have employed in his experiments boxwood char-
coal, and charcoals made from hard and dense woods appear to have the
greater absorbing powers. Mr. Hunter experimented with charcoal from
logwood, ebony, boxwood, and the hard-shell of the cocoa-nut. He found
the latter to have the greatest absorbing power. The charcoal is very dense
and brittle, the pores are quite invisible, and when broken the edges present
a semi-metallic lustre. Vapors are also absorbed, but the absorption power
of charcoal ceases sooner in them than in the true gases.

It has been observed that the temperature of the charcoal rises as a gas
is condensed within its pores. When charcoal, already saturated with any

ABSORBING POWER OF CHARCOAL. 251

one g:as, is put into another, it p:ives out a portion of the pras already ab-
sorbed, and takes up a portion of the new gas. It would also appear that
this absorptive quality partly depends upon the mechanical texture of the
charcoal, and consequently varies in the charcoals of different woods. Ac-
cording to Vogel, when recently-ignited charcoal, which has been cooled
under mercury, is put into a jar of atmospheric air, it absorbs the oxygen of
the air to a greater extent than the nitrogen. A piece of well-burned char-
coal, cooled under sand, and then introduced into a mixture of oxygen and
sulphuretted hydrogen gases, rapidly absorbed them ; it then became ignited,
and caused a violent explosion which shattered the bell-jar. In this experi-
ment, which nearly led to a serious accident, a yellow vapor appeared to
issue from the pores of the charcoal, jnst before the explosion took place.
This was owing to the separation of sulphur. It is probable that the sul-
phuretted hydrogen employed w^as mixed with some free hydrogen. Thenard
observed, that when fresh made and dry charcoal was saturated with sul-
phuretted hydrogen, and introduced into oxygen, the gases combined, with
explosion, and water and sulphurous acid were produced. When the oxygen
was mixed with nitrogen, the effect took place more slowly, and the hydrogen
alone was consumed ; there was at the same time a deposit of sulphur.

This property of charcoal is referred to catalysis (p. 58). It resembles
the action of spongy platinum on certain mixtures of gases: but there is
this difference between the two substances : Platinum has not the absorbent
powers on gases which is manifested by charcoal, but it has a greater com-
bininff power. If coarsely-powdered wood-charcoal is boiled in a solution
of chloride of platinum, until it is thoroughly impregnated with the liquid,
and is then heated to redness in a covered crucible, it will retain within its
pores a residue of platinum : this substance is remarkable for its powers of
absorption and combination.

To this property may be ascribed the power which charcoal possesses of
absorbing and removing foul effluvia {see p. 229). A small quantity of
powdered charcoal shaken in a jar of air containing sulphuretted hydrogen
gas, soon removes the smell. If water, containing sul})huretted hydrogen,
is filtered through charcoal, it is speedily deodorized. The gas is first
absorbed, and by a catalytic action, the oxygen of the air unites to the
hydrogen, while sjilphur is deposited. The charring of the interior of a
cask, intended to hold water for use at sea, has a similar influence on foul
water put into it. Sulphuretted hydrogen is so completely removed, that
the usual tests for the gas will fail to indicate its presence. Pans of pow-
dered charcoal placed about a room in which there are foul effluvia, are thus
efficacious in removing them. Putrescent animal matter is deprived of its-
offensiveness by covering it with powdered charcoal. If the charcoal should
lose its power by long use, it may be easily restored by again heating it.

Experiments on a large scale have been performed by Dr. Letheby and
Mr. Haywood, in order to determine how far charcoal could be practically
employed for destroying the effluvia of public sewers. Well-dried charcoal,
broken to the size of a filbert, was placed in trays in the current of air pro-
ceeding from a sewer — it thus acted as an air-filter. The result was most
satisfactory ; the foul effluvia were arrested and destroyed, and the charcoal,
after from nine to twenty months' use, when treated with water, yielded an
abundance of alkaline nitrate, a fact which proved that it had caused the
oxidation of nitrogen in ammonia and other nitrogenous compounds. The
absorbing and oxidizing powers of charcoal were greatly diminished when
it was saturated with water, hence, owing to the absorption of moisture,
the sieves required changing once in three months. If the charcoal is kept
dry, there appears to be no limit to the oxidizing action, of this substauce.
17

258 DEODORIZING POWER OF CHARCOAL.

There can be no doubt from these experiments, that, by a proper use of
powdered charcoal, the noxious effluvia of drains and sewers — the vehicles
of typhoid fever — may be prevented from entering our dwelling. {Report
to Commissioners of Sewers, Feb. 1862.)

But charcoal has not only the power of removing smells ; it will also
remove colors, and even, in some cases, the taste of liquids, where this
depends on the presence of certain organic substances. Introduce into four
bottles containing powdered charcoal, solutions of diluted sulphate of indigo,
of cochineal, of the blue iodide of starch, and of the red permanganate of
potassa. Agitate these liquids for a short time with the charcoal, and on
filtration, it will be found that the colors are entirely removed. Port-wine
may be rendered tawny or light colored by a similar process, thus giving to
it the appearance of age. Impure solutions of sugar and of nitre lose their
colors by filtration through beds of charcoal — animal charcoal being preferred
for this purpose. Other impurities which interfere with the crystallization
of these substances are also removed. The crystallizable vegetable acids
and alkaloids are thus brought to a high state of purity, but not always
without loss. Mr. Warington observed that the sulphate of quinia was
removed from its solution by charcoal, and that the bitterness of the hop
may be entirely removed from ale by this substance, in the attempt, to make
dark-colored ale pale. Strychnia is so completely removed under these
circumstances, that Mr. Graham has recommended it as the basis of a process
for the detection of strychnia in liquids containing organic matter. As a
medium of filtration, therefore, charcoal is eminently qualified to purify water.
It removes color, taste, and smell. Charcoal obtained by the distillation of
peat, or of spent oak-bark, used in tanning, possesses these properties in an
eminent degree.

Charcoal has a great deoxidizing power, even at low temperatures. Por-
tions of fresh-burnt boxwood charcoal, free from ashes, introduced into
nearly neutral and very diluted solutions of gold, platinum, palladium, silver,
and copper, separate the respective metals, which are deposited on the char-
coal in thin films. The deposit of copper, if allowed to remain in the liquid,
soon disappears. At a red heat, charcoal deoxidizes many fixed and volatile
imetallic oxides (arsenious acid), reducing them to the metallic state. It U
tin fact, the great reducing agent of metallurgists. At a white heat, owing
ito its fixedness, it deoxidizes even potassa, soda, and phosphoric acid, setting
free in vapor, potassium, sodium, and phosphorus. It also decomposes
water, producing carbonic oxide and hydrogen (water gas). When the
vvapor of water is passed slowly over charcoal heated to full redness in a
porcelain tube, or when an incandescent piece of charcoal is plunged under
a jar in a water-bath, these gases are evolved, and may be collected : (HO
-4-C = H4-CO). But carburetted hydrogen and carbonic acid are also pro-
ducts of this decomposition. Bunsen found that in 100 parts of this water-
gas, there were 5603 hydrogen; 29'15 carbonic oxide; 14*65 carbonic
acid; and 017 of carburetted hydrogen.

Charcoal produces in the cold a violent explosion with perchloric acid ;
at a red heat, it deoxidizes the chlorates, perchlorates, iodates, and nitrates
with deflagration, producing carbonates with the respective alkaline bases.
At a full read heat it converts most of the sulphates to sulphides. It has no
action on the haloid salts — namely, the chlorides, bromides, iodides, and
.fluorides, and it does not decompose at a high temperature silica, magnesia or
alumina. Its combinations with metals are called Carbides, or carburets.
There is only one of these well known — namely, its compound with iron as
cast-iron. Carbon is found as an impurity in aluminum, and in some other
.metals. Among the metalloids, it enters into direct union only with oxygen

ANIMAL CHARCOAL. 259

and sulphur, and even in reference to these bodies a very high temperature
is required to bring about chemical combination.

Equivalent. Tests The atomic weight of carbon is fixed, by some

chemists, at 6, and by others at 12. As it is unknown in the vaporous con-
dition, its volume is of course hypothetical. For convenience, it is assumed
to be the same as that of hydrogen, and is therefore taken as one or two
volumes, according to the assumed volume-equivalent of that element. When
carbon, as charcoal, is in a free state, it may be identified by its color, inso-
lubility in all menstrua, its fixedness in close vessels, and its combustion and
entire conversion into gaseous matter when heated in air. It may be also
known when existing in any state, by its combustion, as a result of deflagra-
tion in melted nitre or chlorate of potassa, and by the production of car-
bonate of potassa. Carbon may, however, exist in such a form, in organic
compounds, that with the exception of deflagration, these tests are no longer
applicable for its detection. The substance suspected to contain it, should
be well dried and mixed with four parts of dried black oxide of copper, or
dry chromate of lead. The mixture inclosed in a small reduction-tube, bent
at an angle, should be then gradually heated to redness — the mouth of the
tube being immersed in lime-water, contained in a watch-glass. The pro-
duction of a white deposit of carbonate of lime will prove that the substance
under examination contained carbon. The oxjrgen of the oxide of copper,
or chromic acid, here serves as the medium for converting the carbon, present
in the organic matter, into carbonic acid. If the quantity is required to be
determined, then it will be necessary to connect the tube containing the mix-
ture, with another tube, in which is placed powdered chloride of calcium
(for the purpose of drying the carbonic acid), and conduct the products of
combustion into a balanced vessel containing a saturated solution of potassa.
{See Analysis of Organic Substances.) The amount of carbonic acid,
and, by calculation, the amount of carbon, present, may be thereby de-
termined.

Two other forms of carbon require a brief notice.

Animal Charcoal. — Charcoal obtained by the carbonization of animal
substances, such as muscle, horn, or hoof, resembles wood-charcoal in its
general characters ; but instead of retaining the form of the matter from
which it is produced, it appears as if it had undergone fusion, and often has
a peculiar lustre and sponginess. In all animal charcoals, we discover traces
of nitrogen, derived probably from the presence of paracyanogen, or of
mellone ; they also contain the fixed saline and other bodies which existed
in their respective sources. The charcoal obtained by the distillation of
bone, is called bone-black and ivory-black in commerce, and is mixed with a
large proportion of phosphate of lime and other earthy salts contained in
the bone, so that for some purposes it requires to be freed from these salts by-
digesting it in diluted hydrochloric acid, and then washing and drying it.
The special properties of animal charcoal in reference to the destruction of
odors and colors, have already been mentioned. They are due to its mole-
cular state, and not to difference of composition, charcoal being essentially
the same under all its various forms. Of the different kinds of charcoal
used for decoloration, bone charcoal or ivory-black is comparatively feeble,
although it is superior to wood-charcoal. Its decolorizing properties are
nearly doubled by washing it with diluted hydrochloric acid, to remove the
mineral matter, and afterwards with water. For perfect decoloration, the
charcoal, finely powdered, should be allowed to remain for some hours in
contact with the colored liquid, and in certain cases warmed. The charcoal
employed should contain no substances soluble in water or in alcohol. After
a time, animal charcoal loses its efficacy, the surface being covered with the

260 COMPOUNDS OF CARBON AND OXYGEN.

coloring matter and other impurities, but the property may be restored by
reheating it in close cylinders. This renovation is a necessary process in
large sugar-refineries. We have found that a sample of good animal char-
coal contained only 18 per cent, of carbon, leaving as a residue after com-
bustion, 82 per cent, of phosphate and carbonate of lime.

Lamp-hlack is prepared principally by the combustion of refuse and resi-
duary resin, left by the distillation of turpentine, as well as of the tarry oils
obtained in the distillation of coal. These are burned in a furnace, so con-
structed that the dense smoke arising from it may pass into chambers hung
with old sacking, where the soot is deposited, and from time to time swept
off and sold without any further preparation. When lamp-black has been
thus procured and heated red-hot, it may be regarded as a pure form of
charcoal, for it burns entirely away, and leaves no residuary ash, but, it is
found to contain traces of oxygen and hydrogen. A pure form of lamp-
black for chemical purposes, may be obtained by burning camphor, and re-
ceiving the carbon of the smoke in a saucer or basin. When washed with
alcohol this is pure carbon. A substance analogous to lamp-black is obtained
by passing the vapor of certain oils, and of hydrocarbonous compounds,
through red-hot tubes ; at that high temperature they are more or less per-
fectly decomposed, and deposit a quantity of impalpable charcoal, in which,
however, as in lamp-black, traces of hydrogen may be detected. Pure lamp-
black, as it is procured from the carbonaceous smoke of the tarry oils from
coal, is a very light flocculent substance. We found a sample of this carbon
to yield only one per cent, of a white ash, whereas the substance ordinarily
sold as lamp-black, yields an ash containing iron and silica, amounting to 9
per cent, of its weight. It is close and heavy, and appears to be a mixture
of soot and finely-powdered charcoal. One of the principal uses of lamp-
black is in the manufacture of printers' ink. Spanish-black is the carbon of
cork ; Vine-black, that which results from vine-tendrils, and Peach-black from
peach kernels ; the two former have a brownish tint, and the latter a bluish
tint. German or Frankfort-black, is said to be obtained by the carboniza-
tion of a mixture of grape and wine lees, peach kernels, and bone-shavings,
and to be especially fit for copper-plate printing.

Carbon and Oxygen Although a powerful affinity exists between these

bodies, they have no tendency to combine at ordinary temperatures. Carbon
as it exists in certain organic compounds, exposed to the conditions of decay
or putrefaction, will, however, unite with the oxygen of the air to form car-
bonic acid. Thus if damp and decaying woody fibre (sawdust) be kept in a
closed vessel of air for some weeks, it will be found that the air will no
longer support combustion, and that oxygen has been to a greater or less
extent replaced by carbonic acid. It is probable that the union of carbon
and oxygen here takes place as a result of evolution in the nascent state.
When carbon is in a free state, it will not combine with oxygen below a red
heat.

Chemists have enumerated eight compounds of these elements, two of
which are gaseous, and are well known under the name of — 1, Carbonic
oxide (CO) ; and 2, Carbonic acid (COg). The other compounds are — 3,
Oxalic acid (CaOg.SHO), a crystallizable vegetable acid, which will be de-
scribed hereafter, and its derivative, 4, the Mesoxalic acid (CgOJ. In addi-
tion to these, there are four other compounds, possessing at present but
little chemical interest, and therefore requiring only a brief notice. These
are only known in the hydrated or combined state. They are — 5, the Rho-
dizonic acid (C^Oy.SHO), so named from the red color of its salts. The
rhodizonate of potassa is procured by digesting in water the compound of

CARBONIC OXIDE. 261

potassium and carbonic, oxide, produced in the manufacture of potassium,
or as a result of heating potassium in the gas. The acid may be procured
^ from this salt ; it is a solid crystalline acid forming colored salts. 6, Cro-
conic acid (CjO^.HO). Croconate of potassa is a product of the decompo-
sition of the rhodizonate of potassa, when this salt is boiled in water ; the
acid may be obtained from the solution of the croconate, by the addition of
fluosilicic acid. It is a solid crystalline substance, of a yellow color, whence
its name. 7, MeUitic acid (C^Og.HO). This is obtained by a complex
process, from a mineral known as mellilite (honeystone), a mellitate of
alumina. It is a solid colorless acid, crystallizing in prisms, and yielding
by dry distillation, 8, Pyromellitic acid (C5O3) ; also a crystalline body,
remarkable for its solubility in strong nitric and sulphuric acids, without
change.

Carbonic Oxide. Oxide of Carbon (CO). — This gas was discovered by
Priestley, but its real nature was first made known by Cruickshank, in 1802.
It may be procured by gently heating oxalic acid with three times its weight
of strong sulphuric acid, or a sufficient quantity of the acid to drench the
crystals; the mixture effervesces in consequence of the evolution of carbonic
oxide and carbonic acid gases : the latter may be separated by a strong solu-
tion of potassa, and pure carbonic oxide will remain. If the experiment be
performed in a test-tube, the carbonic oxide may be burnt at the mouth of
the tube. In this case the evolution of gases is caused by the abstraction of
water from oxalic acid, which contains, in its anhydrous state, the elements
of one atom of carbonic oxide and one atom of carbonic acid ; but these
can only exist as oxalic acid when in union with water, or with a base.
Crystallized oxalic acid is = C303,3HO, which acted upon by three atoms of
oil of vitriol =:3[S03,HO] become 3[S03,2HO]-f CO^-f CO ; the hydrated
sulphuric acid, darkened in color, remains in the retort. It may also be pro-
cured by heating, in an iron or earthen retort, a mixture of carbonate of
lime (chalk) or baryta, with its weight of iron or zinc tilings. The changes
are as follows: 3BaO,CO,-f 2Fe=3CO + 3BaO + Fe,03» and CaO.CO^-f
Zn = CO + CaO + ZnO. Chalk mixed with finely-powdered charcoal, and
heated to full redness, also yields this gas (CaO,C03-f-C=2CO-i-CaO).
The first portions of gas being mixed with air, should be rejected. In all
cases carbonic acid is also evolved ; this may be separated by causing the
gases to traverse a strong solution of potassa, or a tube containing broken
pumice soaked in potassa. Carbonic oxide is not very soluble in water;
hence it may be collected and preserved over water. The tests of its purity
are that it should not give any precipitate with lime-water, or red fumes with
deutoxide of nitrogen. This gas is a product of the combustion of carbon
when the latter element preponderates, or the supply of oxygen is inade-
quate to the production of carbonic acid. The lambent blue flame which
sometimes plays upon a coke or charcoal fire, or is seen to issue from certain
furnaces, is carbonic oxide, produced by the passage of carbonic acid over
red-hot charcoal, COg+C being converted into 2C0.

Properties. — The specific gravity of this gas compared to hydrogen is as
14 to 1; and to atmospheric air as 0 9674 to I'OOO; 100 cubic inches
weigh 29*96 grains. Carbonic oxide is a powerful narcotic poison. When
breathed it is speedily fatal to animals : it produces before death giddiness
and insensibility, followed by profound coma. According to Bernard, it has
the peculiar property of reddening the blood. There can be but little doubt
that some of the noxious effects hitherto attributed to carbonic acid, have
been due to the action of this gas. It is produced during the combustion
of any form of carbon when this element is in excess, and it may escape

262 PROPERTIES OF CARBONIC OXIDE.

through leaks in stoves or flues. Leblanc found that an atmosphere con-
taining only 1-lOOth of carbonic oxide was as fatal to a bird as one contain-
ing l-25th part of carbonic acid. Boussingault has lately made the discovery,
that this gas, with light carburetted hydrogen, in the proportion together
of 3 or 4 per cent., is eliminated by the green parts of vegetables under the
influence of water, light, and heat. This may arise from the decomposition
of carbonic acid in vegetation, not being so complete as it has been hitherto
supposed to be. If this observation be confirmed, it will show that while
vegetation aids in purifying the air, it leads to the evolution of small quan-
titTes of one of the most deadly gases known to chemists ; and difi'ering from
some other noxious gases in the fact that it cannot be recognized by its
odor, or, in fhe small proportion in which it exists, by any other sensible
properties. Aquatic plants and those growing in swampy places, evolve it
in greater proportion than those growing on a dry soil {Cosmos, Nov. 22,
1861). Is this gaseous poison the secret cause of the unhealthiness of such
localities ?

Carbonic oxide extinguishes flame and burns with a peculiar blue light
when mixed with, or exposed to, atmospheric air. Thus, then, it is a com-
bustible gas, but a non-supporter of combustion. When consumed in air it
emits no odor, and there is no deposit of solid matter. Its volume is also
unchanged ; each cubic inch of carbonic oxide being converted into a cubic
inch of carbonic acid (C0 + 0 = C03). Its conversion into carbonic acid by
combustion, may be proved by adding lime-water to a jar of the gas while it
is in the act of burning. Sir H. Davy found that the temperature of an iron
wire heated to dull redness was sufficient to inflame it. It has no taste, and
little odor, and when pure, it occasions no precipitate in lime-water and
does not redden a solution of litmus. If burned under a dry bell-glass of
air or oxygen, no moisture whatever is deposited, showing that it contains
no hydrogen.

Carbonic oxide suffers no change by being passed and repassed through a
red-hot porcelain tube ; it is not decomposed at high temperatures by phos-
phorus, sulphur, nor even, according to the experiments of Saussure, by hy-
drogen (Journal de Physique, Iv.), although it is stated, upon other authori-
ties, that at high temperatures, hydrogen does decompose it. When one
volume of carbonic oxide is detonated with one of protoxide of nitrogen,
there result one volume of carbonic acid and one of nitrogen (CO-|-NO =
COg-l-N). None of the metals exert any action upon this gas, except potas-
sium and sodium, which, at a red heat, burn in it by abstracting its oxygen,
and carbon is deposited. In the nascent state, itYorms a solid compound
with potassium, from which rhodizonic and croconic acids may be obtained
(p. 260). It appears to combine with this metal at a temperature not ex-
ceeding 176°. At the melting-point of potassium the gas is absorbed form-
ing a black mass, which is spontaneously inflammable in air (Liebig).

Carbonic oxide is one of the few compound gases which has not yet been
liquefied by the most intense cold and pressure (p. 81). The gas is a per-
fectly neutral oxide. If pure, it neither reddens nor turns green, the blue
infusion of cabbage. Water dissolves about 6 per cent, of the gas by
volume : it is not soluble in a strong solution of potassa. Berthelot found
that the gas was slowly dissolved by hydrochloric acid, or by ammonia hold-
ing in solution subchloride of copper. Carbonic oxide is a powerful deoxi-
dizing agent, inasmuch as it always has a tendency, at a high temperature,
to be converted into carbonic acid. It thus plays an impoi'tant part in blast-
furnaces in the smelting of iron. At a red heat, it converts the alkaline and
alkaline-earthy sulphates to sulphides, CaO,S03 + 4CO = 4C03-f CaS.' Le-
vol has recommended a solution of chloride of gold as a test for the gas,

CARBONIC ACID. 263

inasmuch as it reduces this metallic compound at common temperatures ;
bat sulphurous acid has also this property. Oxalate of lime, for a similar
reason, serves as a flux for the reduction of arsenious acid. When carbonic
oxide is added in an equal volume, to a mixture of hydrogen and oxygen
gases in explosive proportions, it prevents spongy platinum from causing
detonation ; but the gases slowly react upon each other, and form water and
carbonic acid.

Coynposition. — The composition of carbonic oxide is determined by the
result of its combustion with oxygen, with which it forms carbonic acid.
When two volumes of carbonic oxide and one of oxygen are acted on by the
electric spark, detonation ensues, and two volumes of carbonic acid are pro-
duced : hence it follows, that carbonic oxide is unchanged in volume by this
conversion, and that it contains half as much oxygen, and the same quantity
of carbon, as carbonic acid. Hence, assuming carbonic oxide to be a prot-
oxide of carbon, it will consist of —

Atoms. Weights. Per cent. Vols. Sp. Gr.

Carbon . . 1 ... 6 ... 42-85 ... 1 ... 0-4146
Oxygen . . 1 ... 8 ... 57-15 ... ^ ... 0-5528

1 14 100-00 1 0-9674

The volume of carbon-vapor which has not been determined experiment-
ally, is here assumed to be equal to that of hydrogen. As carbonic oxide
has a sp. gr. of 0*9674, and it contains half its volume of oxygen, then, 0 9674
— 0-5528(l-1057H-2) = 0-4146, the hypothetical sp. gr. of carbon-vapor.
From this result, the percentage of carbon and oxygen contained in the gas,
may be easily deduced; for 0*9674 : 0 4146 : : 100 : 4285 per cent, of car-
bon. The difference will represent the oxygen. Carbonic oxide has the
sp. gr. and equivalent of nitrogen.

Chlorocarbonic Acid; Phosgene Gas{CO,(j\). — This gas may be obtained
by exposing to solar light a mixture of equal volumes of chlorine and car-
bonic oxide : hence its name (^w?, light, y? fi-aw, to produce). It is also formed
by exposing the mixed gases to ordinary daylight, but several hours are
required for the purpose. When perfectly excluded from light, the gases
have no tendency to combine. In the sunshine the mixture diminishes in
bulk to one-half of its original volume, and forms a compound of a peculiar
and pungent odor, but not disagreeable when considerably diluted. It red-
dens litmus, and is resolved by water into carbonic and hydrochloric acid
gases. Alcohol and pyroxylic spirit absorb it, and form ethereal compounds.
The specific gravity of chlorocarbonic acid compared with hydrogen is as
50 to 1, and with common air as 3 425 to 1. In reference to the theory of
substitutions this compound has been regarded as carbonic acid, in which 1
equivalent of oxygen has been replaced by I of chlorine.

Carbonic Acid. Fixed Air ; Aerial Acid; Garhonic Anhydride (COj. —
This compound was first described by Dr. Black, in 1757, under the name
of fixed air, a name which it derives from its being a constituent of limestone.
Its composition was first determined by Lavoisier. It is produced by burn-
ing carbon, either pure charcoal, graphite, or the diamond, in oxygen gas ;
the oxygen, in thus becoming converted into carbonic acid gas, suffers no
change of volume. When charcoal is burned in a jar of oxygen gas the
phenomena of combustion depend upon the nature of the charcoal, which, if
well made, and of a dense wood, glows with intense heat without flame, and
gradually disappears ; but if of a lighter wood, and especially if covered with
portions of the bark, it throws off jets of brilliant sparks. These scintilla-
tions are especially brilliant and beautiful, when a small piece of the charred

264 CARBONIC ACID. PREPARATION. PROPERTIES.

bark of oak or elm is used; it should be attached to a copper wire, and in-
troduced into a sufficiently capacious air-jar filled with pure oxygen ; the
combustion may thus be made to last for some minutes. If only the quiet
combustion of charcoal is required for the purpose of showing the conversion
of oxygen into carbonic acid, the best kind of carbon which can be used for
this purpose is that obtained from box, lignum vitae, or other hard and
dense woods.

Carbonic acid is, like sulphurous acid, an anhydrous oxacid gas producing
no hydrate acid, having less affinity for bases than sulphurous acid, so that
it may be expelled from the dry alkaline carbonates by means of this gas. It
is a natural constituent of the atmosphere, of which it forms from ^^Vo^^ to
^^i__th part : it is a result of the decomposition of animal and vegetable sub-
stances, and is the chief gaseous product of combustion, respiration, and the
vinous fermentation.

Preparation. — Carbonic acid constitutes about half the weight of carbonate
of lime or marble. It is readily procured by adding to one part of broken
marble one part of hydrochloric acid diluted with three parts of water. The
gas is instantly evolved, producing the phenomenon known as effervescence
(CaO,CO,+HCl = CO,+CaCl-|-HO). A flask or retort may be used in
the experiment. The gas should not be collected until a few bubbles of it,
thrown into a jar containing deutoxide of nitrogen, cease to produce ruddy
fumes. It may be collected in a water-bath, although, owing to the solu-
bility of the gas in water, there is considerable loss. One grain of pure
marble will give nearly a cubic inch of the gas.

Properties. — This gas is colorless, of a slightly sour taste, and much heavier
than atmospheric air, its specific gravity being about 152. Compared with
hydrogen, its sp. gr. is as 22 to 1. 100 cubic inches weigh 47 '087 grs. at
mean temperature and pressure. When so far diluted with air as to admit
of being received into the lungs, carbonic acid operates as a narcotic poison,
producing drowsiness, entire loss of muscular power, rapidly followed by
insensibility and coma. When the gas is respired into the lowest poisonous
proportion, the symptoms come on very gradually, and the transition from
life to death is usually tranquil. This gas is the fatal chohe-damp of coal
mines. It is a product of the combustion of light carburetted hydrogen
(fire-damp), and is the common cause of death to miners who are not at once
killed by the explosion.

It is not combustible, and immediately extirrguishes other bodies which
are in a state of combustion. This may be proved by successively introducing
into ajar of the gas a burning taper, ignited camphor, and a large flame of
ether, on cotton or tow. The flames of these substances are instantly extin-
guished. We have found that a candle will burn in mixtures of carbonic
acid and air until the proportion of the gas reaches 20 per cent. ; but such
mixtures would be noxious to breathe : hence, although the extinction of a
candle in wells or cellars is a proof of danger, the fact that it continues to
burn must not be regarded as an indication of safety. We have also found
that the presence of a large proportion of oxygen completely counteracts
this effect of carbonic acid. In a mixture of equal parts of oxygen and car-
bonic acid a taper burns as brilliantly as in oxygen ; and the presence of
carbonic acid would not be suspected in the mixture but for the effect pro-
duced by the addition of lime-water and other tests. Carbonic acid cannot,
however, replace nitrogen in air. When it forms four-fifths of the mix'ture,
combustion is no longer supported, and animals are killed.

This gas possesses well-marked acid properties. If blue infusion of
litmus is added to ajar of the gas, it is speedily reddened. If the red'liquid
is boiled, the blue color will be restored, thus showing that the reaction

I

CARBONIC ACID A PRODUCT OF COMBUSTION. 265

depended on a gaseous acid. If to jars of the gas, solutions of lime,
baryta, or subacetate of lead, are separately added, dense white precipitates
of the respective carbonates of these bases will be produced. Lime-water
is the usual test for this gas, but a solution of the subacetate of lead is more
delicate in its reaction. Lime-water will be found to be alkaline to test-
paper before pouring it into the gas, but it will entirely lose its alkalinity
afterwards. Air containing one per cent, of carbonic acid produces a white
precipitate in lime-water, hence in an atmosphere containing a noxious
proportion of carbonic acid, lime-water is instantly rendered turbid, even by
a small portion of the air collected in a bottle. If the precipitated carbonate
of lime be transferred to another jar of carbonic acid, it will be found after
a time to be re-dissolved. Carbonic acid is absorbed by alkalies. If a
saturated solution of potassa is put into a jar of the gas, and well shaken,
the plate-glass cover of the jar is fixed as if by a vacuum. On removing
the cover and introducing a lighted taper, this will be found to burn as in
air. Introduce into a wide jar, containing carbonic acid, some solid hydrate
of potassa with a small quantity of water. Cover quickly the mouth of the
vessel with a stout layer of caoutchouc, and then agitate the liquid. As the
carbonic acid is absorbed by the dissolved potassa, the atmospheric pressure
forces down the elastic caoutchouc cover, just as in a vessel exposed to the
vacuum of an air-pump. The most perfect vacua known, are now produced
by gently heating hydrate of potassa in tubes filled with pure carbonic acid,
hermetically sealed.

Solution. — Water takes up its own volume of the gas at common tempera-
ture and pressure, and acquires a slight increase of specific gravity (about
r0018). Under increased pressure a much larger quantity is absorbed.
Thus, water may be made to take up five or six times its volume by pressure.
It then becomes brisk and acid, and reddens vegetable blues. If litmus-
paper, thus reddened, be exposed to the air, the blue color returns as the
acid evaporates. By freezing, boiling, or exposure to the vacuum of an air-
pump, the gas is given off, and it gradually makes its escape when exposed
to air, collecting in small bubbles upon the sides of the containing vessel,
and passing off with especial rapidity when any foreign substances are
thrown in, or when any substance is dissolved in the water ; thus it is, that
sugar added to soda-water, cider, champagne, or other similar carbonated
liquors, occasions in them an immediate and abundant effervescence. The
effervescent qualities of many mineral waters, as well as of fermented liquids,
are referable to the presence of this gas. Artificially aerated waters are
prepared on a large scale by condensing carbonic acid under pressure, into
water holding dissolved alkaline or saline substances. Carbonic acid may
be thus made to dissolve lime, magnesia, and the protoxide of iron. A solu-
tion of carbonic acid in water, precipitates lime-water, but re-dissolves the
precipitate when added in larger quantity.

Carbonic acid forms no hydrate with water ; and when liquefied, or solidi-
fied by cold, it will not combine with water. Some English chemists have
given to it the name of Carbonic anhydride. As this term is applied to
acids which are capable of forming definite hydrates with water, in order to
distinguish the anhydrous from the hydrated state, it is singularly inappro-
priate to apply it to an acid which forms no hydrate whatever. The words,
too, imply, not the absence of water, but the absence of hydrogen. Nitrogen
and carbonic oxide would, in either point of view, have an equal claim to be
called anhydrides. Long established usage has fixed the name of carbonic
acid in chemical nomenclature, and no sufficient reason has been adduced for
the adoption of this innovation.

As all common combustibles, such as coal, wood, oil, wax, and tallow,

266 CARBONIC ACID OF RESPIRATION.

contain carbon as one of their component parts, so the comhustion of these
bodies is always attended by the production of carbonic acid. Float a lighted
taper, fixed in a cork, on lime-water, contained in a glass dish ; and invert
over the taper a bell-glass of air or exygen. After a time tlie tai)er will be
extinguished, and the surface of the lime-water will be covered with a white
film of carbonate of lime. Hold a large jar so that its mouth shall be
slightly above a jet of burning gas, or the flame of a spirit-lamp. After a
few minutes remove it, and pour lime-water into the jar. This will be
rendered milky by the carbonic acid which has resulted from combustion.

This gas is also produced by respiration ; hence it is detected, often in
considerable proportion, in crowded and illuminated rooms which are ill-
ventilated. The symptoms produced by the respiration of such a con-
taminated atmosphere, are difficulty of breathing, giddiness, and faintness.
Its expiration from the lungs is easily shown, by blowing the expired air
through lime-water by means of a small tube ; the liquid becomes milky and
soon deposits carbonate of lime. The same fact is also strikingly shown by
allowing expired air to pass into a solution of chloride of lime, colored blue
by litmus. The color is soon destroyed by the carbonic acid discharged
from the lungs decomposing the chloride, and setting free chlorine. An
apparatus has been contrived, by which the air inspired, is made to traverse
lime-water without producing any change in it, while the air expired
through the same liquid produces carbonate of lime. If lime-water is
placed in a large jar, and the air of the jar is breathed two or three times,
taking care that the air, as it is expired, is returned into the jar, the lime
water, which was unaffected by the air contained in the vessel, will be
rendered milky from the production of carbonate of lime. Inspired air
contains only from l-2000th to l-2500th part of carbonic acid, but expired
air contains (on the assumption that 3 per cent, only are present) sixty times
as much carbonic acid, or l-33d part by volume. Dr. Prout assigns the
proportion of carbonic acid in expired air at from 3*3 to 4-1 per cent., and the
average at 3 43 per cent. It varies at different periods of the day, according
to the state of health, and other conditions. On this estimate, however, 16
cubic inches, representing 4 grains of solid carbon, are thrown out of the
lungs of an adult every minute — a quantity amounting to about 12 ounces of
carbon in 24 hours 1 According to Dr. Brinton {Food and its Digestion),
the carbonic acid daily given off from the adult healthy body may' be esti-
mated at n cubic feet, or about two pounds in weight. Allowing that half
a cubic foot (about an ounce) is eliminated through the skin, the remainder
is exhaled from the lungs. The quantity of carbon or charcoal by weight, to
which this amount of carbonic acid would correspond, is nine ounces. In
making this estimate Dr. Brinton assumes l-2500th part of carbonic acid as
the proportion present in inspired, and l-25th part as the proportion con-
tained in expired air.

Carbonic acid retards the putrefaction of animal substances. It favors the
growth and development of vegetables in air and water. Most plants thrive
in an atmosphere containing as much as a tenth or twelfth part of carbonic
acid ; and under certain circumstances they decompose it, appropriate the
carbon, and evolve the oxygen.

At high temperatures, carbonic acid is decomposed by carbon and several
of the metals, and is converted into carbonic oxide. The influence of ignited
carbon in effecting this decomposition is seen in an ordinary coal-fire. The
oxygen of the air in passing between the bars below, produces carbonic
acid : and this is deoxidized by the red-hot coke (CO,-f C=2C0) the car-
bonic oxide thus produced, burning at the top of the fire with a flickering
blue flame. Potassium and sodium, when heated intensely, burn in the gas,

CARBONIC ACID. COMPOSITION. 267

and are converted into potassa and soda, whilst the carbon of the gas is
separated in the form of charcoal. There are some other substances, which,
at hipjh temperatures, are capable of decomposing carbonic acid, and ab-
stracting part of its oxygen ; thus, if a mixture of 2 parts of hydrogen and
1 of carbonic acid by volume, be passed through a red-hot tube, water and
carbonic oxide, with the excess of hydrogen, escape.

Carbonic acid is not affected by heat alone : it may be passed through a
red-hot porcelain tube unchanged ; but it is partially converted by a succes-
sion of electric sparks into carbonic oxide and oxygen. It is worthy of
remark, as illustrative of the variable effects of the electric spark, that by
means of it, a mixture of carbonic oxide and oxygen may be suddenly con-
verted into carbonic acid. Iron, zinc, and manganese, at a high temperature,
deprive the gas of half of its oxygen, and convert it into carbonic oxide.

Equivalent and Tests. — The equivalent or atomic weight of carbonic acid
is 22, and its volume-equivalent is I. The tests for its presence are — 1, the
extinction of a burning taper; 2, the production of a milky precipitate of
carbonate of lime, when lime-water is added to a jar containing the gas ;
3, entire absorption and removal by potassa. For this purpose, the carbonic
acid should be collected in a tube over mercury, and some portions of solid
potassa, with a small quantity of water, introduced. The carbonic acid
slowly disappears, and if the gas is pure, there will be no residue. A
strong solution of potassa, or portions of alkali, moistened, and placed in an
appropriate apparatus, previously balanced, will separate carbonic acid from
most neutral gases ; and by the increase in the weight of the potassa, a
chemist will be enabled to determine the weight or volume of carbonic acid
present.

Composition. — As oxygen, in being converted into carbonic acid by the
combustion of carbon, undergoes no change of volume, it is evident that
the weight of carbon present must be equal to the difference between the
specific gravities of carbonic acid and oxygen =0-4145 (1'5202 — 1"1057).
Assuming that this represents one volume of carbon-vapor, then the weight
of carbon in 100 parts of carbonic acid is equal to 27 22 (I 520 : 0*4145 : :
100 : 27*22), and the oxygen will be, 72-78. These elements are obviously
in the proportions of 3 to 8, or 6 to 16, as found by Stas and Dumas in the
burning of pure carbon in oxygen, and in taking directly the weight of the
resulting carbonic acid. The composition of this gas will therefore stand as
follows : —

Atoms. Weights. Per cent. Vols. Sp. Gr.

Carbon . . 1 ... 6 ... 27-22 ... 1 ... 0-4145
Oxygen . . 2 ... 16 ... 72-78 ... 1 ... 1-1057

1 22 100-00 1 1-5202

As the weight of carbon is added to that of the oxygen without altering
its bulk, this gas is very heavy ; hence it accumulates temporarily in wells,
cellars, or other excavations in the soil : but unless constantly produced, it
will soon disappear by the law of diffusion (p. 86). The following experi-
ments will serve to prove how much denser it is than air. Balance a glass
shade in a scale pan, allow a current of carbonic acid gas to pass into it from
a bottle, taking care that the tube conveying the gas reaches nearly to the
bottom of the shade. It will collect and displace the air, and the shade will
now preponderate by reason of the greater weight of the gas, A lighted
taper lowered within the shade is extinguished. Dry nitre paper ignited,
will also be extinguished when introduced, but the smoke produced as a
result of its combustion will float upon the heavy stratum of carbonic acid.
A soap-bubble, or a small collodion balloon of air, will also float upon the gas.

268 LIQUID AND SOLID CARBONIC ACID.

If a small jar or glass-beaker is lowered into the shade, it will, in a few
minutes, be filled (by displacement) with carbonic acid, which may be
removed to a distance and tested by a lighted taper, as well as by lime-water.
Remove the covers from two small jars containing the gas, taking care that
one is placed with its mouth upwards and the other with its mouth down-
wards. After a few minutes, a lighted taper may be applied to the two. It
will be found that the gas has fallen out of the jar with its mouth downwards,
and that the taper will burn brightly in it ; whereas it will be immediately
extinguished in the other jar, and will not entirely escape from it for a quarter
of an hour, or longer. Smoke produced by the combustion of nitre-paper
at the mouth of the jar, will float like a cloud upon it. The falling of the
gas from one vessel to another may be easily demonstrated by allowfng a
taper to burn at the bottom of a jar of air, and then gradually inverting
over it another jar containing carbonic acid : the taper will be extinguished
in the jar which contained air, while in that which contained the carbonic
acid it will now continue to burn. This experiment may be varied by placing
three lighted tapers at dififerent levels in a glass basin about eight inches
wide, and five or six inches deep. If a large jar of carbonic acid is brought
over the mouth of the basin, at the part corresponding to the lowest taper,
and the cover gradually raised, the gas will fall through the air in the basin,
and as it rises it will successively extinguish the three tapers. The Grotta
del Cane, near Naples, is an excavation on the side of a hill, in which carbonic
acid collects, owing to the basin-like form of the floor of the grotto. The
gas is always issuing from fissures in the soil, and thus the accumulation goes
on faster than the diffusion. Dogs are asphyxiated by being held within
the stratum of gas, which rises to about the height of the knee. On gra-
dually lowering burning straw and phosphorus in this grotto, we found that
the level of the gas was accurately determined by the extinction of the flame
and the floating of the smoke. These well-known facts regarding the specific
gravity of carbonic acid, have led to the erroneous supposition that, under
all circumstances, the gas will accumulate, and remain on the floor or soil.
The law of diffusion, however, prevents such accumulation, unless there is
a constant source from which the gas can proceed.

Liquid and solid Carbonic Acid. — Carbonic acid may be liquefied by
great pressure, aided by a low temperature (page 80). It is usually liquefied
by its own pressure — i. e., by liberating it in a wrought-iron vessel, the
capacity of which is very small compared with the amount of gas which can
be set free by the action of an acid on bicarbonate of soda. It may be
Uquefied by mere cooling to 106^ without pressure. The liquid is colorless,
very soluble in alcohol, ether, and essential oils. It will not mix or combine
with water, but floats on that liquid. It does not redden the solid extract
of litmus. It dissolves camphor and iodine. Although it has no solvent
action on gutta-percha or caoutchouc, it penetrates into these substances,
and whitens them. It is a strong insulator of electricity, and is deoxidized
only by the alkaline metals. (Oore, Proc. R. S., 1861, No. 43, page 85.)

By allowing liquefied carbonic acid to escape through a perforated metallic
box, the cold produced is so intense that a portion of the gas is solidified,
and presents the appearance of a snowy-looking mass. Solid carbonic acid
has a temperature of at least 100° below zero, but it is surrounded in the air
with a gaseous atmosphere, which prevents immediate contact with bodies,
and it rapidly disappears as gas, when exposed. This solid acid may be
borne in the hand without any particular sensation of coldness or pain ; but
when mixed with ether, it produces an intense degree of cold, which would
destroy at once the vitality of any part of the body with which it was in
contact. A small portion placed on stout plate-glass produced no effect

CARBON AND HYDROGEN. 209

until ether was poured upon it, when, owing to the intense cold suddenly
produced, the glass was broken to pieces. A sheet of paper was folded so
as to make a long trough, or cavity, into which liquid mercury was poured ;
the metal was then covered with solid carbonic acid, and ether was poured
upon it. The mercury was instantly frozen into a long bar of metal, the
temperature of the air being at the time above 60° Medals of mercury
have thus been made, and preserved for some time in the cold bath of car-
bonic acid and ether. Gases may be liquefied and solidified by means of this
bath. In vacuo the cold produced by it has been calculated by Faraday
to reach to — 166°, or 198° below the freezing-point of water. From the
experiments of Tyndal it appears that ice contains sufficient heat to liquefy
and boil solid carbonic acid.

Carhonates, — These salts are represented by the formula MO, COg, and the
bicarbonates by MO.SCOa. Among the alkaline carbonates those of potassa,
soda, ammonia, and iithia, are alone soluble in water, and have an alkaline
reaction. Those of lime, magnesia, protoxide of iron, and manganese, are
dissolved by water containing much carbonic acid. A soluble carbonate gives
a white precipitate with the solutions of lime, or baryta, or with their salts.
This precipitate is dissolved with effervescence (escape of carbonic acid) by
the acetic and other acids. The precipitate given by sulphate of magnesia
is soluble in hydrochlorate of ammonia, containing free ammonia ; that given
by lime is not. A soluble bicarbonate gives no precipitate with sulphate of
magnesia, and a yellowish (becoming slowly a red) precipitate, with a solu-
tion of corrosive sublimate. This test at once precipitates a soluble car-
bonate, excepting that of Iithia, of a deep-red color. A solution of a
carbonate added to a strong acid, effervesces strongly, /^so/wi/e carbonates
are identified by their dissolving with effervescence in nitric acid. The gas
which escapes is invisible, and without smell. It precipitates lime-water.

CHAPTER XX.

CARBON. COMPOUNDS OF CARBON WITH HYDROGEN,
NITROGEN, CHLORINE, AND SULPHUR.

Carbon and Hydrogen. — These elements, although they form a large
number of compounds chiefly belonging to the organic kingdom, cannot be
easily made to unite directly. When a voltaic current of a very powerful
kind is established in an atmosphere of hydrogen by means of charcoal points,
a peculiar hydrocarbon is, however, formed as a result of direct combination.
This is called (Mtyllne. It is represented by the formula C^HgOr CgH. Carbon
and hydrogen form gaseous, liquid, and solid compounds, among which it is
sometimes difficult to distinguish those which ought to be considered as defi-
nite, from others which are mere mixtures. These compounds are generally
termed hydrocarbons, or carbo-hydrogens. Amongst them are some striking
illustrations of that species of isomerism, which has been called polymerism
(page 19) — that is, of compounds differing, often essentially, in their physical
or chemical properties, or both, and yet apparently produced by the union
of the same elements in similar proportions. Among these compounds may
be mentioned the oils of lemon, turpentine, juniper, and savin ; naphtha,
naphthaline, and benzole ; all remarkable for their inflammability and their
combustion with a yellowish-white smoky flame. As these hydrocarbons are
of a complex nature, and are for the most part educts, or products, of organic

2Y0 LIGHT CARBURETTED HYDROGEN. PROPERTIES.

substances, they will be the subject af consideration hereafter. The three
which now require notice are, the light carburetted hydrogen, CHg, olefiant
gas, CgH^, and oil gas, C.H^.

Light Carburetted Hydrogen (CH.J. Marsh-gas. Fire-damp This

gas is considered to be diffused in very small proportion in the atmosphere.
It is the well-known Fire-damp of coal-mines, rushing out occasionally in
enormous quantities in " blowers" from seams of coal, owing to its being
probably contained in the strata under high pressure. It derives its synonym
of marsh-gas from the fact that it is formed in stagnant pools in hot wither,
during the spontaneous decomposition of vegetable matter. It may be pro-
cured by stirring the mud, and collecting the gas as it rises in bubbles, in a
glass-jar filled with water and inverted. In this state it is mixed with nitro-
gen and carbonic acid ; the latter may be separated by washing the gas in
lime-water or in a solution of caustic potassa. The gas procured from a
Mower in a coal mine, after having been washed with lime-water, furnishes
tljis compound in a pure state. It may also be obtained by the decomposi-
tion of certain acetates, when heated in a retort with an excess of alkali.
Dumas recommends for this purpose 40 parts of crystallized acetate of soda,
40 of caustic potassa, and 60 of powdered quick-lime. They should be
strongly mixed and well heated, the use of the lime being to prevent the
action of the alkali upon the glass. At a heat approaching to dull redness,
the gas is evolved, and may be collected over water ; the action is determined
by the affinity of the alkaline bases for carbonic acid, and the instability of
the acetic acid at high temperatures ; an atom of acetic acid and an atom of
water produce carbonic acid, which combines with the soda and potassa ;
while light carburetted hydrogen passes off; (C^HgOg-f HO) yielding 2CO2,
and 2CH2.

Properties. — The specific gravity of this gas is 0*552, and compared with
hydrogen it is as 8 to 1. It is the lightest known body next to hydrogen,
and like that gas it has resisted all attempts to liquefy it by cold and pres-
sure. 100 cubic inches weigh 17*12 grains. It is a colorless gas. Its re-
fractive power is 2097, air being 1*000. When breathed in a pure state, it
is fatal to life, but it is not very noxious when mixed with air, even when it
forms from 8 to 10 per cent, of the mixture. It is sparingly soluble in water,
and is not dissolved by fuming sulphuric acid. It does not support combus-
tion, but is inflammable, burning with a pale yellowish flame, and producing
carbonic acid and water CH^-f 0,==CO,-f 2H0 ; it has, when quite pure,
neither odor nor taste. It is decomposed Iby a succession of electric sparks,
the carbon being deposited and hydrogen left in double the volume of the
original gas. When passed through a white-hot tube, it deposits a portion
of its carbon, CH2=C + H2. When chlorine is mixed with the pure gas,
there is no immediate action ; but when 1 volume of the gas and 3 of chlorine
are mixed and exposed to diffused light, a violent explosi«p soon ensues,
hydrochloric acid is formed, and carbon is deposited. One' volume of the
gas with two volumes of chlorine, produce the strongest effect (CH^-f 2C1 =
2HC1 + C), and the combination is immediately effected by the electric spark.
When the gas is previously mixed with, its volume of carbonic acid, the
chlorine may be added without danger. If exposed to light, carbonic acid
is produced, and an oily liquid is deposited, which is chiefly bichloride of
carbon (C,Cl2). In the dark, there is no combination. When the gas is
passed with chlorine through a red-hot tube, carbon is deposited, and hydro-
chloric acid is formed. When mixed with twice its volume of oxygen, and
the mixture is detonated, it produces its volume of carbonic acid, and water
IS at the same time condensed. From these results, its constitution may be
determined. One volume of oxygen is contained in each volume of carbonic

COAL GAS.

211

acid ; and as two volumes are required for the perfect combustion of the gas,
the other volume of oxygen must combine with two volumes of hydrogen to
form water, or

1 vol.

O4

2 vols.

= CO,

1 vol.

+

2H0

2 vols.

hence one volume of carbon-vapor and two volumes of hydrogen must be
contained in each volume of the light carburetted hydrogen. Its specific
gravity is in accordance with this constitution : —

Carbon
Hydrogen .

Atoms.

1 .

2 .

Weights.
.. 6 ..
.. 2 ..

Per cent.
. 75 ..
. 25 ..

Vol.
. 1 ..
. 2 ..

Sp. Gr,
. 0-4146
. 0-1382

100

0-5528

The ascertained specific gravity is very nearly in accordance with this view,
being 0556.

The production of the gas in marshy localities, is owing to the decay of
vegetable matter, and the decomposition of woody fibre, in contact with the
elements of water. The water simply furnishes hydrogen and oxygen to the
carbon of the decaying vegetables.

Coal Gas. — Gas procured by the distillation of bituminous coal in iron
retorts is a mixture of gases and vapors, but consists chiefly of light carbu-
retted hydrogen. 100 parts of coal, distilled at a high temperature, yield
the following solid, liquid, and gaseous products by weight : —

Coke.

68-93

defiant gas . . 0-78

Tar .

12-23

Sulphuretted hydrogen 0-75

Water

7-40

Hydrogen . . . 0-50

Liglit carb. hydrogen

7-04

Ammonia . . . 0-17

Carbonic oxide .

1-18

Nitrogen . . . 0-03

Carbonic acid .

1-07

(BUNSEN AND PlAYFAIR.)

The more bituminous the coal the larger the amounts of gas yielded by-
distillation. A ton of ordinary coal yields from 8000 to 11,000 cubic feet of
gas, but a ton of cannel coal will yield 15,000 cubic feet. The liquid and
watery products are condensed : the carbonic acid is removed from the
gaseous mixture by passing it through lime, and the sulphuretted hydrogen
by causing it to traverse beds of hydrated oxide of iron and sawdust (page
228), and the ammonia by water. The purified coal gas, thus obtained,
when not overheated, was found to consist in 100 parts of 825 parts of light
carburetted hydrogen and 13 of olefiant gas, with 3'2 parts of carbonic oxide
and 0 8 of nitrogen. Its sp. gr. was 0"65. These were the proportions in
the early stage of the process. The gaseous mixture collected after five
hours' working; when the tubes had become strongly heated, contained a
larger proportion of free hydrogen, derived from the decomposition of the
light carburetted hydrogen. It then consisted in 100 parts, of 56 parts of
light carburetted hydrogen and 7 of olefiant gas, 11 of carbonic oxide, to 7
of nitrogen and 21-3 of hydrogen. Its sp. gr. was 050. After ten hours'
distillation, the olefiant gas had entirely disappeared — the light carburetted
hydrogen amounted to only 20 parts, carbonic oxide 10, nitrogen 10, and
hydrogen 60, the sp. gr. being as low as 0345. (MiTSCHERLicn.) The con-
stitution of the coal gas varies, therefore, greatly with the temperature of
distillation.

Coal gas is colorless, and has commonly a strong odor of naphtha vapor.
A taper plunged to the bottom of a jar containing it is extinguished ; but

2Y2 COAL GAS. PROPERTIES.

the gas burns, where it -meets with air, with a yellowish flame. Aqueous
vapor is condensed on the sides of the jar, and carbonic acid may be proved
to be a product of its combustion, by pouring lime-water into the jar, while
the gas is burning ; or by holding the mouth of a clean jar of air over a jet
of gas in combustion, and then adding lime-water : the presence of carbonic
acid will be indicated by a white precipitate. This gas may be kindled ia
air by a full red heat without flame. Apply a red-hot bar of iron tS a jar of
the gas, or to a current of gas, as it issues from a jet, and it will be found
that the iron, although visibly red, will not inflame the gas unless the metal
is heated to bright redness. If fine platinum wire is made red-hot in a gas-
flame, as it is burnt with air from a wire-gauze burner, and the flame is sud-
denly extinguished, the wire will continue to glow in the current of unignited
gas, causing the slow combustion of the gas and air without inflaming the
mixture, until some portions of the wire acquire a white heat: the mixture is
then suddenly kindled with a slight explosion. This gas is so light that the
series of experiments described under hydrogen (page 121) may be readily
performed with it. A jar of the gas may be removed from the water-bath,
with its mouth downwards, without a cover, to a distance, and there ignited.
It rapidly escapes from jars which are open with their mouths upwards. A
jar of air held over ajar of the gas, suddenly uncovered, will thus receive it
in the act of ascending. The contents may be exploded, while the jar which
originally contained the gas, will contain air. Nitre-paper burnt at the
mouth of an inverted jar of the gas will produce smoke, which will remain at
the lowest level, the gas floating on the top of it. A jar opened under a
balanced shade, inverted, will cause the opposite scale to preponderate, the
air being displaced by the light gas which rises to the upper part of the
shade. Soap-bubbles blown with this gas, on collecting it by pressure from
an ordinary jet, will ascend in air, and balloons of goldbeater's skin filled
with it acquire great buoyancy, thus illustrating the principles of aerosta-
tion. As this gas is only half the weight of air, and only one-third the
weight when partially decomposed by overheating, it is now exclusively
employed for the purposes of aerostation — the larger size of the balloon com-
pensating for the higher specific gravity of the gas compared with hydrogen.
Coal gas should have no acid reaction on infusion of blue litmus. If it con-
tains sulphuretted hydrogen, it will give a brown discoloration to paper
wetted with a salt of lead : if ammonia is present, this will be indicated by
its restoring the color of faintly reddened litmus-paper. When these im-
purities coexist, the gas will give a bluish or pinkish red color to a solution
of nitro-prusside of sodium. In spite of all ordinary methods of purifica-
tion, coal gas, in burning, evolves an acid vapor, which is found to be sul-
phurous acid. This proceeds from a minute portion of sulphide of carbon
vapor, which the common purifiers do not remove.

The illuminating power of coal gas is increased by saturating it with coal
naphtha. The gas is simply passed through a box in which the vapor of
naphtha is diffused, and it is speedily saturated with it.

The effect produced by the presence of this vapor may be illustrated by
generating hydrogen in a two-necked vessel provided with glass tubes which
can be fixed into the necks by corks. One of these tubes should have in it a
few fibres of asbestos soaked in naphtha or benzole. The gas may be then
ignited as it issues from the two jets. In one the flame will be scarcely
visible ; in the other there will be a luminous smoky flame. The effect on
coal gas may also be illustrated by burning it from a tube in which asbestos
with naphtha is placed.

Acetylene CjHaC^H,. This is usually found in coal gas. It is a gaseous
body having a disagreeable odor, and burning with a luminous smoky flame.

EXPLOSIONS IN COAL MINES. SAFETY LAMP. 273

Light carburetted hydrogen and the vapor of alcohol, when passed through
a red-hot tube, yield acetylene as a product. It appears to be produced in
all cases in which there is an incomplete combustion of carbon compounds.
It is characterized by giving a red precipitate with an aramoniacal solution
of subchloride of copper. It combines directly with chlorine and bromine.

In reference to explosions in coal-mines, two important chemical questions
present themselves for consideration — 1st, the proportion per cent, of light
carburetted hydrogen, which forms the most dangerous explosive mixture
with air; and 2d, the temperature at which such a mixture is liable to be
kindled. It is here assumed that the gas is pure, and that it contains no
admixture of olefiant gas or carbonic oxide. In the experiments which
Davy performed on this subject, he found that the greatest explosive power
was manifested when the gas v^as in the proportion of one volume to seven
or eight volumes of air, or when it formed from 12 to 14 per cent, of the
mixture. As two volumes of oxygen are theoretically required, and these
correspond to ten volumes of air, it will be seen that the maximum explosive
effect takes place with a smaller proportion of oxygen than theory indicates.
When the gas was in the proportion of 20 per cent, of the mixture, there
was combustion without explosion. When it amounted to rather less than
T per cent., there was no explosion, but an enlargement of the flame of a
candle; and this enlargement, but in a diminishing ratio, was observed in
mixtures gradually reduced to 3 or 4 per cent, of the gas. From these
results, which have been since confirmed by the observations of others, it is
obvious that long before the point of danger is reached, a warning is given
by an elongation of the flame of a lamp or candle.

As to the temperature required for the explosion of a mixture of fire-
damp and air, Davy observed that well-burned charcoal, ignited to the
strongest red heat, did not explode any mixture of air and of the fire-damp;
and a fire made of well-burned charcoal, i. e., charcoal that burned without
flame, was blown up to full redness by an explosive mixture containing the
fire-damp, without producing its inflammation. An iron rod at the highest
degree of red-heat, and even at the common degree of white-heat, did not
inflame explosive mixtures of fire-damp ; but, when in brilliant combustion,
it produced this efl'ect. Flame of any kind exploded a mixture of fire-damp
and air. In reference to combustibility, therefore, this compound difl'ers
from the other common inflammable gases. Davy found that olefiant gas
which explodes when mixed in the same proportion with air, is fired by
both charcoal and iron heated to redness. Carbonic oxide, which explodes
when mixed with two parts of air, is likewise inflamed by red-hot iron and
charcoal ; and hydrogen, which explodes when mixed with three-sevenths of
its volume of air, takes fire at the lowest visible heat of iron and charcoal ;
this also occurs with a mixture of air and sulphuretted hydrogen.

The safety-lamp contrived by Davy for the prevention of accidents by
explosion in coal-mines, consists of a cylinder of metallic wire-gauze con-
taining from 700 to 900 meshes in the square inch. This presents a large
metallic surface favorable for the cooling of flame, and of reducing its
temperature below that required for kindling explosive mixtures. The
principle of its qperation may be illustrated by various experiments. Flame
is nothing more than gaseous or vaporous matter, heated to a very high
temperature, and requiring a high temperature for its continuance. {See
page 107.) The following experiments will serve as illustrations: Place
a lump of camphor on a sheet of wire-gauze like that which is used for the
safety-lamp. The camphor may be inflamed from beneath, and it will there
be consumed, but the inflammable vapor of the camphor will not be ignited
above the gauze — the heat conducted by the metal having lowered the tem-
18

5lt4 CONSTRUCTION OP THE SAFETY LAMP.

peratnre far below that required for its combustion. Tow or cotton soaked
in ether or alcohol may be substituted for the camphor with like results.
There will be no ijrnition of the vapor of either liquid above the gauze, while
it will burn readily below. Into a small cylinder of wire-gauze (closed at
the bottom with a layer of gauze, but open at the top) throw a miss of tow
soaked in alcohol and inOamed. The cylinder may now be placed in a saucer
containing alcohol. The whole of the spirit will be drawn in and consumed
within the cylinder ; but there will be no communication of flame to that
which is on the outside. Let the same cylinder be fitted closely to a wire-
stand supporting a wax taper, so that when the taper is kindled, it may be
completely enclosed by the gauze cylinder. If a jar of hydrogen or coal-gas,
or a mixture of either with air, is brought over the cylinder inverted, and
very gradually lowered, the inflammable gas will traverse the gauze and burn
with flame, but without explosion, in the interior of the cylinder, and there
will be no kindling of the explosive mixture on the outside of the cylinder.
In this manner the whole of the inflammable gas may be consumed without
being inflamed in the jar ; whereas, if any such mixtures were brought over
the lighted taper, not covered by the gauze cylinder, there would be instanta-
neous inflammation and explosion.

The safety-lamp consists of an ordinary oil-lamp, to which a gauze cylinder
is so secured as to allow of combustion only by the air which traverses the
meshes of the gauze. As a test of the eflBcacy of the lamp, it may be lighted
and suspended within a large gas-jar, to the bottom of which, a current of
coal-gas is conducted by a vulcanized rubber tube. The efl'ects produced
by mixtures of coal-gas and air, in various proportions, can thus be ob-
served. If there is a deficiency of oxygen, the lamp will be extinguished;
if the quantity of gas is in very small proportion, combustion will be con-
tinued with an elongated flame. In explosive proportions, the mixture will
penetrate the lamp and burn in the interior of the gauze-cylinder, tempo-
rarily extinguishing the flame. If suddenly raised into the air, the flame will
sometimes be re-kindled ; but in no case, if the wire-gauze is in a sound
condition, wil-l the flame be communicated to the gaseous contents of the jar.
If a full stream of coal-gas mixed with air is allowed to play at diflerent
distances upon the flames of a Davy lamp, all the phenomena described will
be witnessed. According to the proportions of gas and air the flame
will be lengthened or the gas burnt inside, but if the lamp is sound, there
will not be any kindling of the gas on the outside as it issues from the jets.
The wick of the lamp is frequently re-kindled when the jet of gas is with-
drawn.^ If the jet is brought close to the wire, there is so much'gas and so
little air that combustion can no longer go on, and the lamp is extinguished.

In the use of this lamp in coal mines the cylinder should be locked or
securely fastened to the lamp, and on no pretence removed while it is em-
ployed for mining purposes. The real object of this invention has been, to
a great extent, defeated by ignorance and carelessness. Davy's experiments
have shown that the state of the flame will alwavs give warning of danger.
The lamp is admirably adapted to test with safety the condition of the air in
the shafts and galleries of coal mines, and to warn the miner of the spots
where it would be unsafe to commence, or continue work, until the fire-damp
had been removed by proper ventilation. As the explosive mixture is not
noxious to breathe, miners continue to use the lamp long after it has indi-
cated danger. The gauze may become red-hot by the continued combustion
of the mixture within the lamp ; the flame may be driven through the meshes
by a strong current of the gas from Mowers, or a small particle of coal-dust
may strike upon the outside of the red-hot wire and be kindled into flame,
when the whole mixture will be exploded, with a great destruction of life,

OLEFIANT GAS, PREPARATION. 216

arising from burning, from serious mechanical injury, or from suffocation as
a result of the carbonic acid produced in the explosion. The accidents which
have almost annually led to a great destruction of life in coal mines have
been wrongly attributed to the use of the lamp. They have been rather due
to its abuse. The removal of the gauze-cylinder — or, when locked, the per-
foration of it for obtaining more light — the use of tobacco, lucifer matches,
and gunpowder in coal mines, are the principal causes of these accidents,
when it has been possible to trace them. In the late fatal accidents, 1866-t,
lucifer matches and pipes were found in the pockets of some of the miners
who had been killed by the explosion.

The fire-damp, being very light, ascends and collects in hollows or recesses
at the upper parts of the workings ; so that while the lower part or floor
may be ventilated and free from danger, a light brought near to the roof
might lead to a dangerous explosion. For the prevention of accidents a
better system of ventilation is required, and a more strict supervision of the
modein which safety-lamps are used by miners. A very ingenious instru-
ment has been lately devised by Mr. Ansell, called the Fire-damp Indicator,
the object of which is to show when there is an undue accumulation of gas
in coal mines. Its action depends on the law of diffusion and on the great
diffusive powers of coal-gas. If a vessel covered with a porous membrane or
with unglazed porcelain, containing air is brought into a mixture of light
carburetted hydrogen and air, the gas penetrates rapidly into the interior,
and either distends the elastic membrane, or, if unglazed porcelain is used,
causes a pressure upon a column of mercury which immediately begins to
rise. By movements thus obtained the wires of a voltaic battery may be
brought into communication and a signal given, or, where the instrument is
in the form of an aneroid barometer the degree of mixture may be read by an
index affixed. The presence of one or two per cent, of the gas in air is said
to be indicated by some of these instruments. (See Chem. News, 1867, v. 15,
p. 13.)

Explosions in houses from an accumulation of coal-gas and its admixture
with air are equally formidable, and depend on similar chemical principles.
There is, however, always ample warning in these cases by the powerful
odor which announces the escape of coal-gas, long before it has reached its
explosive proportion. Instead of opening doors and windows, and keeping
at a distance all lights, until the smell has disappeared, the ordinary practice
is to ap[)ly a light for the purpose of ascertaining where the leakage has
occurred. The whole of the air in a room may be in an explosive state, but
the coal-gas has a great tendency to accumulate at the upper part. Hence
it is this part which should be thoroughly ventilated. A lighted candle may
burn on the floor of a room, but, if raised a few feet above it, it may cause
a violent explosion. In no case, however, can this accumulation occur with-
out full warning being given by the odor of the gas, which is perceptible
when mixed with 500 times its volume of air. {See, on the subject of gas-
explosions in houses, a paper in the Medical Gazette, vol. xlii. p. 343.)

Olefiant Gas. Elayle. Elhelene. Carburet of Hydrogen. Bicarhu'
retted Hydrogen (CallJ. — This gas was discovered in 1796, by the Dutch
chemists, who gave to it the name which it commonly bears, owing to the
property which it possesses of forming an oily compound with chlorine.

It is usually obtained by the decomposition of alcohol by concentrated
sulphuric acid. For this purpose, about two parts of the acid and one of
alcohol (by measure) are put into a capacious retort, and heated by a lamp ;
when the mixture boils, the gas is evolved with sulphurous and carbonic
acids J and a carbonized mass remains in the retort. It may be collected

276 CHEMICAL PROPERTIES. COMPOSITION.

over water, and should be well washed with lime-water, or with a solution of
potassa, in order to remove carbonic and sulphurous acids ; it also retains
a little ethereal vapor, which may be remove by agitating it with vteak alcohol
and afterwards with water. During the distillation, the black carbonaceous
mass is apt to fill the retort and pass over into the bath. To prevent an
accident of this kind, the heat should be applied around the body of the
retort by a circular jet of gas, and sand or broken glass may be mixed with
the liquids before the heat is applied.

The changes which take place in the production of this gas may be thus
represented : Alcohol is C^HgO^,, a constitution which is equivalent to two
volumes of olefiant gas 2(C2,H2) and two volumes of aqueous vapor 2(H0).
By the action of sulphuric acid, at a temperature of about 320° the alcohol
is resolved, by a catalytic action (p. 58), into these compounds, while the
water is retained by the acid in the receiver (C4Hg02+ 803X10 = 2C2H2-f
S03,3HO). There are other and more complicated changes in the latter
stage of the distillation, as the carbon of the alcohol then decomposes part
of the sulphuric acid, forming the two gaseous acid products which contami-
nate the gas : these changes will be considered at another time.

Properties. — Olefiant gas is colorless, and neutral in reaction. It has been
liquefied by pressure, and cooling to — 166°, but not solidified. Even when
purified, it retains a slight ethereal odor. It acts like a narcotic poison
when breathed. Water dissolves about 12*5 per cent, of its volume. It is
dissolved more freely by fuming sulphuric acid, and by the ammoniacal solu-
tion of the subchloride of copper. It extinguishes all burning bodies, but
is itself highly combustible, burning with a bright white flame, similar to
that of burning oil, tallow, wax, or a coal-fire. It evolves much light during
combustion : the particles of carbon, of which it contains a large quantity,
being rendered incandescent by the combustion of the hydrogen. A portion
of this carbon is deposited on any cold surface introduced into the flame.
When mixed with a large proportion of air it burns with a pale flame, the
carbon being then entirely consumed as well as the hydrogen. If a taper is
suddenly plunged to the bottom of a jar of the gas it will kindle the gas, but
be itself extinguished. If the taper is withdrawn, and a quantity of water
is poured through the burning gas so as gradually to fill the jar, the gas will
be brought to the surface, and burnt in a large sheet of flame. If lime-water
is "added to another jar, during its combustion, this liquid will be rendered
milky, showing the production of carbonic acid. This may also be proved
by burning the gas from a jet under a jar of air, and afterwards testing the
contents of the jar with lime-water.

When mixed with three times its volume of oxygen, and the mixture is
exploded, either by flame or the electric spark, it is converted, with a violent
detonation, into carbonic acid and water :

C2H2 4- Og (15 vols, air) = 2CO2 -f 2H0

1 vol. 3 vols. 2 vols. 2 vols.

Its composition may be deduced from these results :— the 2 vols, of car-
bonic acid represent 2 vols, or equivalents of carbon, with 2 vols, of oxy-
gen ; while 2 vols, of aqueous vapor represent 2 vols, of hydrogen, and 1
vol. of oxygen : —

Atoms. Weights. Per cent. Vols. Sp. Gr.

Carbon. . . 2 ... 12 ... 85-7 ... 2 ... 0-8292
Hydrogen . . 2 ... 2 ... 14-3 ... 2 ... 0-1382

14 100-0 1 0-9674

CARBON AND NITROGEN. 2*77

The specific gravity of olefiant gas is therefore about 0'96*74, and, com-
pared with hydrogen, it is 14 to 1. 100 cubic inches weigh 29-96 grains.
Its refractive power is 1818, air being =1000: — its specific heat, com-
pared with that of air, 1-53 (Dulong), being greater than that of any
other gas. As it is usually prepared, it is often associated with other hydro-
carbon vapors, which may affect its physical properties. A mixture of this
gas with oxygen is converted into acetic acid by spongy platinum, and its
solution in sulphuric acid has, by agitation in water and mercury, produced
alcohol. (Berthelot). When passed through a tube heated to redness,
it deposits one-half of its carbon, and is changed into light carburetted
hydrogen. If, however, the tube is heated to whiteness, all the carbon is
deposited, and each volume of the gas yields two volumes of hydrogen.

The action of chlorine on olefiant gas is remarkable. When the gas is
mixed with chlorine, in the proportion of 1 to 2 by volume, the mixture,
when inflamed, produces, without explosion, hydrochloric acid, and black
amorphous carbon is abundantly deposited. If the gases be well mixed,
and then inflamed in a tall and narrow glass jar (about 2 feet high and 4
inches in diameter), placed with its mouth upwards, the experiment is very
striking ; a deep-red flame gradually descends through the mixture, and a
dense black cloud of carbon rise's into the atmosphere ; fumes of hydrochloric
acid are at the same time formed, and a peculiar aromatic odor is evolved
(C3H2+2C1=2HCI + 2C). The hydrochloric acid maybe detected by its
effect on litmus-paper, and the production of white fumes with ammonia.

Chloride of Olefiant Gas (CgHj^Cl) ; Dutch Liquid ; Chloric Ether. —
If chlorine and olefiant gases be merely mixed, in equal volumes, over water,
or in a clean and dry glass globe, exhausted of air, they act slowly upon
each other, and a peculiar liquid is formed, which appears like a heavy yel-
low oil : hence the term olefiant gas, applied to this hydrocarbon by the
Dutch chemists, and Elayle (from l-Kauov, and v-kri, the source of an oil) by
Berzelius. It may also be formed by allowing a current of each gas to meet
in a proper receiver ; but there should always be an excess of olefiant gas,
for if the chlorine is in excess, the liquid will absorb it. To purify it, it
should be washed in water, and then carefully distilled over fused chloride
of calcium.

This compound is a transparent and colorlcvss liquid ; its taste is sweet,
and somewhat acrid ; its odor fragrant. Its specific gravity is 1-2. It boils
at 180°. According to Gay-Lussac, the specific gravity of its vapor is 3-45.
It burns with a green flame, evolving hydrochloric acid, and depositing car-
bon. It is decomposed when passed through a red-hot tube, and is converted
into acetylene and hydrochloric acid. It has been employed as an anaesthetic,
but has been found too stimulating. Olefiant gas forms a similar compound
with the vapor of bromine.

Oil Gas (C4HJ. — This is a gaseous compound, containing in each volume,
as its vapor density proves, double the proportions of carbon and hydrogen
existing in olefiant gas. It was obtained by Faraday as one of the products
of the destructive distillation of oil. He called it bicarburetted hydrogen.
As a gas, it has a sp. gr. of 1-9264 ; it burns with a brilliant, white, smoky
flame. It is not dissolved by water, but is soluble in alcohol and the oils.
When cooled to zero, it is condensed into a colorless, light liquid, having a
sp. gr. of 0-627.

Carbon and Nitrogen. — These elements cannot be made to combine
directly, but they form three different compounds ; a gaseous body, cyano-
gen, NCa) and two solids, paracyanogen, N^C^, and mellone, N^Cg.

2Y8 CYANOGEN. CHEMICAL PROPERTIES.

Cyanogen (NCg, or Cy=26). Bicarhuret of Nitrogen. — This gaseous
componnd was discovered, in 1815, by Gay-Lussac, and terml^d cyanogen
(from xvaroj, blue, and yiwdoi, to generate), in consequence of its being essen-
tial to the production of Prussian blue. It is sometimes formed by the
direct action of nitrogen upon carbon in the presence of bases, as where
nitrogen or air is passed over a mixture of charcoal and carbonate of potassa,
heated to redness. Under these circumstances, cyanogen is produced, and
enters into combination with the metal potassium (KOjCO^ + C^-f N=K,NCg
-f SCO). Cyanide of potassium is thus sometimes produced and deposited
in the crevices of the walls of blast-furnaces. When an organic substance
containing nitrogen and carbon is heated, these elements will not unite
directly; but if heated with the alkaline metals, potassium or sodium, in a
glass tube, out of contact of air, they instantly combine to form cyanogen,
and this body unites with the metal, to produce a metallic cyanide. This
conversion has already been described as one of the best methods of detect-
ing nitrogen in organic matter (p. 156). In the destructive distillation of
coal, the nitrogen and carbon combine to form cyanogen, which is found in
the solid products in combination with ammonia and lime. Sulphocyanogen
is also produced under these circumstances, as the cyanogen combines with
a portion of the sulphur of coal.

Preparation. — Cyanogen may be obtained in the gaseous state by heating
well-dried cyanide of mercury in a small retort to dull redness. The gas
readily comes over, and, as it is dissolved by water, it should be collected,
and preserved over mercury. Although cyanogen and mercury are both
volatile bodies, it is impossible to obtain more than one-third of the cyano-
gen present in the cyanide [3HgCy=NC2(cyanogen)4-N4C4(paracyanogen)
H-3Hg]. Mercury sublimes, but there remains in the retort a brownish-
black, spongy-looking solid, which from its composition has been called />«m-
cyanogen. It is equivalent to two atoms of cyanogen, and is polymeric with
it (2NC3=N2C4). When strongly heated in air, this residue yields carbonic
acid, and leaves CN ; but it is very difBcult of combustion. Cyanogen is so
easily decomposed by the elements of water, that great care should be taken
to dry the cyanide of mercury thoroughly before it is submitted to heat ; and
no moisture should be present in the jars in which the gas is collected.

Properties. — Cyanogen is a colorless neutral gas, of a pungent odor, irri-
tating to the eyes, and highly poisonous if breathed even in a diluted state.
Its specific gravity when compared with hydrogen is as 26 to 1 ; and with
common air, as 1-796 to 1; 100 cubic inches weigh 55-64 grains. It sustains
a high temperature in porcelain tubes without decomposition. Under a
pressure of between three and four atmospheres at the temperature of
45°, Faraday condensed cyanogen into a limpid colorless liquid, of a specific
gravity of about 0 9, and a refractive power rather less than that of water.
When a tube containing it was opened, the expansion within appeared incon-
siderable, and the liquid slowly evaporated, producing intense cold. It
does not conduct electricity. At temperatures below —30°, it becomes a
transparent crystalline solid.

It extinguishes a lighted taper, but takes fire and burns with an inner
rose-red flame, surrounded by a blue flame. As it is very heavy, the jar
Bhould be slightly inclined for its complete condensation, or water should be
poured into the jar while it is burning. Carbonic acid and nitrogen are the
sole products of this combustion. Four equivalents or two volumes of
oxygen are required for its entire combustion (NC3 + 0,=2CO,-fN). In
these proportions the mixture is explosive by heat or electricity. ' A red-hot
platinum wire, or the electric spark, will kindle the gases instantly. The
production of carbonic acid as a result of its combustion, may be proved by

COMPOUNDS OF CYANOGEN. 279

burning the gas from a jet under a jar of air, and subsequently adding lime-
water to the contents of the jar. All ordinary combustibles are extin(z;uished
in it. Alkaline metals may, however, be burnt in it as readily as in chlorine.
Potassium or sodium heated to ignition and introduced into the gas, under-
goes vivid combustion, and the cyanogen combines directly with the metal to
form a metallic cyanide. It is this property of entering into combination
like an element, and the fact that with hydrogen it forms a hydracid in every
respect analogous to those produced by the halogens, which have induced
chemists to designate cyanogen as a compound radical, and to associate it
with chlorine, bromine, and iodine. Its existence shows that a body may
have all the ordinary chemical properties assigned to an element, and yet be
of a compound nature.

Cyanogen does not bleach organic colors. Water will dissolve 4*5 volumes
of the gas; alcohol will dissolve 23 volumes; and it is also taken up by
ether and oil of turpentine. Its aqueous solution is rapidly decomposed
by exposure to light ; it acquires at first acid and afterwards alkaline pro-
perties, cyanic acid and ammonia being products of this reaction. Oxalate
and carbonate of ammonia, formate of ammonia, urea, and paracyanogen, are
also products, in different stages of decomposition, of the aqueous solution.
Iodine, sulphur, and pliosphorus may be sublimed in the gas without change.
Dry chlorine has no action on dry cyanogen ; but when moist and exposed
to light, a yellow oil is produced, which appears to be a mixture of chloride
of carbon and chloride of nitrogen (Serullas), furnishes another proof of
the importance of water to bring about chemical changes in bodies {see pages
42 and 145).

The gas is readily dissolved by alkaline liquids ; and, as with the halogens,
a cyanate of the alkali and cyanide of the metal are produced. Oxide of
mercury in a humid state, also absorbs the gas, forming a soluble cyanide.

Composition. — Cyanogen may be passed through a porcelain tube intensely
heated without undergoing any change ; but if passed through a red-hot iron
tube, carbon is deposited, and a volume of nitrogen*, equivalent to the cyanogen
employed, is set free. If one volume of this gas is mixed with two volumes
of oxygen, and the mixture is detonated by the electric spark over mercury,
two volumes of carbonic acid and one volume of nitrogen result; hence,
deducting the oxygen employed, each volume of this gas must consist of two
volumes of carbon vapor, and one volume of nitrogen condensed into a single
volume of the gas.

Atoms. Weights. Per cent. Vols. Sp. Gr.

Nitrogen . . 1 ... 14 ... 53-85 ... 1 ... 0-9G74
Carbon . . 2 ... 12 ... 46-15 ... 2 ... 0-8292

1 26 100-00 1 1-7966

Test. — The colored flame of the gas during combustion, and an examina-
tion of the products, carbonic acid and nitrogen, are sufficient to identify it.

Compounds. — Cyanogen combines directly with metals, like an element,
forming cyanides of metals analogous to oxides and chlorides ; it forms acids
with oxygen and hydrogen, and compound radicals with sulphur and iron,
which also combine with hydrogen to form acids, and with metals to form
peculiar classes of salts. The metallic cyanides are remarkable for the readi-
ness with which they produce double salts. The subjoined list comprises the
principal derivative compounds of cyanogen : —

280 CYANIC ACID. CHEMICAL PROPERTIES.

Cyanogen Cy Cyanide MCy

Cyanic acid Cy, 0 Cyanate ^^^'^^?..^

Fulminic acid Cy2,02 Fulminate S^202,2MO

Cyanuric acid Cyg.Og Cyanurates Cy.Og.SMO

Hydrocyanic acid HCy + MO = Cyanide MCy, (HO)

f H Hvdrosulphocyanic acid
Sulphocyanogen bgf^y | j£ Sulphocyanide

j H, Hydroferrocyanic acid
Ferrocyanogen teLy^ \ Mg Ferrocyanide

f H3 Hydroferricvanic acid
Femcyanogen i^e^Ly^ \ M3 Ferricyanide

„ „ „^ f H, Nitroliydrocyanic acid

Nitroferricyanogen Fe^CygNO^ JmJ Nitroprusside

Mellone (N^Cfi). — The third compound of carbon and nitro^jen is a solid
substance of a yellow color, produced in the destructive distillation of sul-
phocyanogen. It may be heated to dull redness without change, but at a
higher temperature it is resolved into three volumes of cyanogen and one of
nitrogen (N4C6=3NC24-N). It is a compound radical, and combines directly
with metals to form Mellonides. According to Gerhardt, it always contains
hydrogen.

Cyanogen and Oxygen. — These bodies form three homologous acids,
the cyanic (CyO), the fulminic (CygOJ, and the cyanuric (CygOg). They
are monobasic, bibasic, and tribasic, respectively.

Cyanic Acid (CyO). — When cyanogen is passed into an alkaline solution,
a cyanide and a cyanate are formed (2BaO + 2Cy = BaCy-fBaO,CyO), and
so far the action of cyanogen corresponds to that of chlorine : but the ex-
treme tendency of the cyanates so formed, to decomposition, prevents their
separation. A permanent cyanate may be obtained by the following process:
six parts of ferrocyanide of potassium and two of carbonate of potassa,
both carefully dried (anhydrous), are intimately mixed in fine powder with
eight parts of pure and dry peroxide of manganese: this mixture is heated
for some time to dull redness, until a portion cooled and dissolved in water,
does not give a blue precipitate with a persalt of iron. The contents of the
crucible are then allowed to cool, reduced to powder, and boiled for fifteen
minutes in alcohol, sp.gr. 'SSO. The liquid is filtered while hot, and on cooling
it deposits crystals of cyanate of potassa. The alcohol is poured from the
salt and again boiled with the residue, so long as further portions of cyanate
can be thus obtained. The salt should be well dried by pressure in filtering
paper, and afterwards in vacuo over sulphuric acid; it must be preserved out
of contact of air and moisture, otherwise it will soon pass into ammonia and
carbonate of potassa. Although the cyanic acid may thus be obtained in
union with a base, any attempt to set it free by means of another acid, is
attended by its immediate decomposition into carbonic acid and ammonia.
Wohler endeavored to procure the acid in a pure state, by decomposing
cyanate of silver by dry hydrochloric acid. The product, however, was hy-
drated cyanic acid with one equivalent of hydrochloric acid gas ; hence,
when brought into contact with water, it was immediately resolved into
hydrochlorate of ammonia and carbonic acid. Cyanic acid, in the presence
of water, cannot be separated from its salts without undergoing immediate
decomposition. Liebig found that it might be procured in a concentrated
form as hydrate, by heating cyanuric acid in an air-tight retort, connected
with a receiver surrounded by ice. These acids contain the same elements,
and are mutually convertible the one into the other ; but cyanic acid is a
simple atom, while cyanuric acid is a complex atom.

Properties.— "Yhx^ acid in its concentrated state (HO, CyO) is a limpid
colorless liquid. It is intensely corrosive and strongly acid. Its vapor is

FULMINIC ACID. 281

very pungent, like that of the stronp^est acetic acid, and It is very irritating
to the eyes and nose ; but it is not inflammable. Wiien diluted with a little
water and retained at 32°, its odor is like that of acetic acid, but it soorf
begins to change ; carbonic acid is evolved, carbonate and cyanate of ammo-
nia are formed, and, by evaporation, crystals of urea may be obtained. In
this case one atom of cyanic acid and three of water, at first yield one atom
of bicarbonate of ammonia; C2N,0 + 3HO=NH3,2C03 : but the cyanic,
being a stronger acid than the carbonic, the undecomposed cyanic acid com-
bines with the ammonia and expels carbonic acid ; and, on evaporation, the
cyanate of ammonia combines with an atom of water to form urea ; NH3,
HO,C,NO = C,H,OA.

Hydrated cyanic acid, as obtained by the method above described, when
it has cooled to 60°, becomes turbid and milky-looking ; it acquires heat
spontaneously, begins to boil, and then passes into a pasty-looking solid,
while there are sudden evolutions of gas with explosions, from the unchanged
portion of the acid. It is ultimately converted into a dry, solid, uncrystal-
line white substance, which is called Gyamelide (Liebig). These remarkable
changes take place rapidly at the common temperature, and quite independ-
ently of air and moisture. They also take place at the freezing-point, but
more slowly, and no gas is evolved under these circumstances.

Cyamelide is insoluble in water, nitric acid, and hydrochloric acid, either
separately or mixed as aqua regia. It is dissolved by potassa with evolution
of ammonia, and cyanurate of potassa is obtained by evaporation. Concen-
trated sulphuric acid dissolves it when the mixture is moderately heated, with
escape of carbonic acid and the production of sulphate of ammonia. The
products of its decomposition are therefore the same as those of cyanic acid
in water, and when cyamelide is distilled by itself it is reconverted into hy-
drated cyanic acid. It is therefore an isomeric solid condition of this acid.

Cyanates. — The cyanates of the alkalies alone are soluble in water, and
are not decomposed by a red heat. When an aqueous solution of an alkaline
cyanate is heated, carbonic acid and ammonia are produced (NC.30 + 3HO =
NH3+2COij). The nitrates of lead, silver, and mercury give with the solu-
tion of a cyanate white precipitates. When mixed with sulphate of ammonia,
and evaporated to dryness, a solution of a cyanate yields urea. When hy-
drated cyanate of ammonia is gently heated either in the dry state or in solu-
tion, it is converted into urea (Wohler). These substances are metameric
(seepage 19). When an acid is added to a cyanate, either solid or in solu-
tion, there is eflfervescence, owing to the production and escape of carbonic
acid. The strong pungent odor of hydrated cyanic acid will be perceptible,
and a salt of ammonia is formed in the liquid. Hence a cyanate cannot be
mistaken for a carbonate.

FuLMiNio Acid 2(C3N)03 or {(^yfi^. — Under the articles Mercury and
Silver, the process for preparing detonating compounds of these metals, by
acting upon their nitric solutions by alcohol, will be described. The oxides
are united to an acid containing the same elements, and in the same relative
proportions, as the cyanic acid, to which, in that particular state of combi-
nation, the term Falminic Acid has been applied ; but the equivalent of the
fulminic acid is exactly double that of the cyanic. This acid has not been
isolated : it is known only in combination with bases.

Fulminic acid, therefore, cannot be obtained as such from the bases with
which it is combined ; at the moment of its separation by a stronger acid,
it is resolved into hydrocyanic acid and other products. Hence we have ia
this compound an acid in which the metal cannot be replaced by hydrogen
{see page 75).

Fulminates. — These are bibasic salts containing either two atoms of fixed

282 CYANOGEN AND HYDROGEN. HYDROCYANIC ACID.

base (neutral fulmitiates), or one atom of fixed base and one atom of water.
The two atoms of fixed base may be represented by two atoms of the oxide
of an easily reducible metal, or by two atoms of the oxides of two different
metals, also easily reducible. There are no fulminates of two alkaline bases.
The fulminates explode by concussion, friction, heat, or contact with concen-
trated sulphuric acid. They evolve hydrocyanic acid when treated v/ith
hydrochloric acid.

Cyanuric Acid (CgNgOa or CygO.). — This acid may be obtained in com-
bination with three atoms of water, as SHO + Cy^Og. Scheele first described
it under the name of pyro-uric acid. He procured it by the destructive dis-
tillation of uric acid. It exists in the hydrated and anhydrous states. It
is dissolved by strong sulphuric or nitric acid without change, and is pre-
cipitated by water. The alkaline cyanurates evolve, when heated, hydrated
cyanic acid, cyanate of ammonia, carbonic acid, and nitrogen, leaving a
residue of cyanate.

The cyanic, fulminic, and cyanuric acids, although composed of similar
proportions of the same elements, are widely different in properties — a fact
which appears to show that, in compounds of a quasi-organic character, the
properties of bodies are more dependent on molecular arrangement than on
atomatic constitution. The cyanuric acid alone can exist in the anhydrous
state, and remain unchanged in contact with water and other acids. This
acid alone is soluble in alkalies without change, and may be separated from
its alkaline solution by acids in an unaltered state. Cyanurate of silver will
bear a temperature of 300°, without undergoing decomposition. At this
temperature, cyanate of silver is decomposed with ignition and evolution of
carbonic acid and nitrogen (Liebig), while fulminate of silver under the
same circumstances is decomposed with detonation, a double amount of car-
bonic acid and nitrogen being produced. Although fulminic acid is the
intermediate compound, it cannot be procured either by the intermixture of
the cyanic and cyanuric acids, or by the action of any chemical reagents
upon them. In this respect these three compounds somewhat resemble the
hydrates of phosphoric acid, the first being converted at once into the third,
without the production of the second hydrate (p. 242). In phosphoric acid,
the difference arises from an increase in the atoms of water of hydration : in
these acid compounds of cyanogen, the first and last members of the series
only are hydrated ; and there is an increase in the proportion of the elements
as well as of the atoms of water. In reference to fulminic acid, it is worthy
of note that, as in an isolated state, it will not combine with the elements of
water, its existence proves, among other facts, that acids are not necessarily
salts of hydrogen {see p. 94).

Cyanogen and Hydrogen. Hydrocyanic Acid. Oyanhydric Acid,
Prussic Acid.—{R,^G, or HCy) — This compound was first obtained by
Scheele in 1782. It was not, however, until the discovery of cyanogen by
Gay-Lussae, in 1815, that its real nature was understood, and its compo-
nents accurately determined. Cyanogen and hydrogen have no tendency
to direct combination, but by the action of certain acids on metallic cyan-
ides, hydrocyanic acid is produced by double decomposition : in this way it
is obtained by the action of hydrochloric acid on dry cyanide of mercury or
silver (AgCy + HCl=AgCl4-HCy). The mixture may be distilled in a
sand-bath, and the product collected in a receiver kept cool by a freezing
mixture. In order to obtain anhydrous hvdroeyanic acid, the following pro-
cess 18 preferable. Introduce the dry cyanide of mercury into a long glass
tube, terminating at one extremity in a receiver immersed in a freezing mix-
ture, and then, from a proper apparatus, pass over it a stream of pure and

COMPOSITION OF HYDROCYANIC ACID. 283

well dried sulphuretted hydrogen, the sulphur of which combines with the
mercury to form sulphide of mercury, while the hydrogen unites to the
cyanogeu to form hydrocyanic acid (HgCy + HS = HgS + HCy). The vapor
of the acid may be driven, by the application of a gentle heat, into the cold
receiver, and there condensed. The ordinary process of obtaining this acid,
consists in distilling by a gentle heat 10 parts of 6nely powdered ferrocyanide
of potassium, with a mixture of 5 parts of sulphuric acid and 14 of water:
the product should be collected in a well cooled receiver. The acid may be
concentrated by digesting it with chloride of calcium. Any Prussian blue
may be separated from it by re-distillation. The hydrocyanic acid thus pro-
cured, should be preserved in a well-stopped phial. In this process, the
cyanide of potassium of the ferrocyanide, is decomposed by the hydrated
sulphuric acid. KCy-f HO,S03=KO,S03-f HCy. Cyanide of potassium
may be substituted for the ferrocyanide. Hydrocyanic acid forms no definite
hydrate with water: hence, according to Millon, it may be obtained anhy-
drous from the most diluted solution with as little trouble as absolute alcohol.
He submits the diluted acid to fractional distillation, collecting the distillate
between 120° and 212°. After two or three distillations, he passes the
vapor through two Woulfe's bottles, containing dry chloride of calcium, and
condenses it in a receiver, placed in a freezing mixture. The heat of distilla-
tion in the last stage is not allowed to exceed ITG^.

Properties. — Anhydrous hydrocyanic acid is a colorless liquid : its vapor
when diffused in air has an odor resembling that of bitter almonds. Its
taste, when diluted with water, is warm and acrid, and it is highly poisonous,
so that the utmost care should be taken to avoid the inhalation of its vapor.
The respiration of a small quantity of this vapor, even in a diluted state,
produces an acrid sensation in the nose and throat, dizziness, sense of weight
in the head, and insensibility. It is irritating to the eyes. The vapor
readily traverses by osmosis, paper, animal membrane, and even caoutchouc.
The anhydrous acid is the most powerful poison known, whether we regard
the smallness of the dose or the rapidity of its operation. Less than a grain
of the acid has destroyed the life of an adult in twenty minutes. The anhy-
drous acid volatilizes so rapidly as to freeze itself, when a drop of it is placed
on a glass plate. Its specific gravity at 64° is 0*696 : and the specific
gravity of its vapor, as experimentally determined by Gay-Lussac, is 09476 ;
it boils at 80°, and congeals at 3°, or 4° above 0° in its ordinary state ; but
when it is perfectly anhydrous, it remains liquid according to Schultz at
— 40°. It burns with a bright flame. It scarcely affects the blue of litmus.
It is very liable to spontaneous decomposition, especially under the influence
of light, becoming brown, evolving ammonia, and depositing paracyanogen,
changes which are prevented by the presence of minute portions of other
acids, but are accelerated by traces of ammonia or other bases. The pure
anhydrous acid is decomposed spontaneously, whether kept in the light or
dark, whether in open or closed vessels. If highly concentrated, it solidifies
into a brownish-black jelly-like mass. When mixed with strong hydro-
chloric acid, it soon solidifies into a pure crystalline mass of hydrochlorate
o*f ammonia. Millon found that the anhydrous acid forms other compounds,
which are only stable, so long as water is excluded. Moisture destroys
them, and formate of ammonia is produced. The effect of ammonia upon
this liquid is remarkable : a few bubbles of the gas were found to solidify
several ounces of the anhydrous acid. Dilution with water delayed, but did
not prevent this result. The preservative effects of acids, appear to depend
on the neutralization of ammonia or the prevention of its production. When
water is present, the concentrated inorganic acids resolve it into ammonia
and formic acid : 3 atoms of water and 1 of hydrocyanic acid include the

284 DILUTED HYDROCYANIC ACID^

elements of 1 atom of formate of ammonia; 3H0-f H,NC3=H,NC3 + XH3.
It is resolved by dry chlorine, under the influence of the sun's rays, into
hydrochloric acid and chloride of cyanogen. The changes produced by acids
in the constitution of hydrocyanic acid, show that an excess of hydrochloric
or sulphuric acid employed in its preparation may lead to its decomposition
and contamination with formic acid. As a singular fact connected with this
conversion, Leibig has noticed that when formate of ammonia is transmitted
through a glass tube, heated to dull redness, it is decomposed and is recoa-
verted into hydrocyanic acid and water.

CgH -I- N = 1 atom of hydrocyanic acid.
O3 -j- H3 = 3 atoms of water

1 atom of formic acid. 1 atom of ammonia.

The easily reducible oxides (of mercury and silver) decompose hydrocyanic
acid, and yield water and a metallic cyanide. When lime or baryta is heated
to redness in hydrocyanic acid vapor, they afford cyanides and cyanates,
and hydrogen is evolved.

In the voltaic circuit, hydrocyanic acid yields hydrogen at the negative,
and cyanogen at the positive electrode, but the aqueous solution of this
acid, when pure, is a very bad conductor of electricity. When its vapor
is mixed with oxygen it may be exploded by the electric spark, in which
case 2 volumes of hydrocyanic acid vapor require for perfect combustion 2
volumes and a half of oxygen : the results are water, 2 volumes of carbonic
acid, and 1 volume of nitrogen (H,NC3-f05=2C03-f-HO + ^^). When
potassium is heated in its vapor, cyanide of potassium is formed, and
hydrogen, equal to half the volume of the acid is liberated: it appears,
therefore, that there is the strictest analogy between the hydrocyanic and
the other hydracids, and that 1 volume of cyanogen and 1 of hydrogen form
2 volumes of the vapor of hydrocyanic acid. It contains in each volume,
half a volume of hydrogen and half a volume of cyanogen.

Atoms. Weights. Per cent. Vols. Sp. Gr.

Hydrogen . . 1 ... 1 ... 3-70 ... 1 ... 0-0691
Cyanogen . . 1 ... 26 ... 96*30 ... 1 ... 1-7966

1 27 100-00 2 1-8657

And 1 -8657 -^2=0-9328, the sp. gr. of hydrocyanic acid vapor. The ex-
perimental result of Gay-Lussac makes it rather higher. 100 cubic inches
of the vapor weigh 2889 grains; compared with hydrogen, hydrocyanic
acid vapor has a sp. gr. of 13-5. The anhydrous acid is miscible in all pro-
portions with water, alcohol, and ether.

This acid forms no definite hydrate, but in various states of dilution it is
used in medicines as a sedative, and certain processes are recommended for
at once obtaining it of a convenient strength for pharmaceutical purposes.
The Pharmacopoeial hydrocyanic acid contains 2 per cent, of anhydrous acid,
while that which is sold under the name of Scheele^s acid contains from 4 t9
6 per cent. A dose of Scheele's acid exceeding 20 drops, and an equivalent
portion of any of the other solutions of the acid, would generally suffice to
destroy life. Diluted hydrocyanic acid of the sp. gr. 0*982 at 54°, con-
tains 10-53 per cent, of anhydrous acid (Trautwein). The process for
preparing diluted hydrocyanic acid for officinal purposes, consists in the
decomposition of ferrocyanide of potassium (FeCy,2KCy), by diluted sul-
phuric acid. The proportions are somewhat different from those above
described, but the process is similar.

Liebig recommends for obtaining dilated hydrocyanic acid, the distillation

DILUTED HYDROCYANIC ACID. 285

of a mixture of equal parts of cyanide of potassium and sulphuric acid ; the
cyanide being dissolved in twice its weigiit of water, and the acid diluted
with three times its weight of water ; these solutions are to be gradually
mixed, and the mixture cautiously distilled. This acid is a product of the
distillation of the bitter almond, the kernels of the peach, nectarine, and
other seeds of the like nature. It may also be procured by distilling the
young shoots of laurel.

As pure hydrocyanic acid, even in a diluted state, is still liable to decom-
position, it should be prepared in small quantities, and preserved in well-
stopped phials out of the presence of light : or a very minute addition of
diluted sulphuric or hydrochloric acid may be made to it, by which its ten-
dency to change is prevented.

When diluted hydrocyanic acid is pure, it leaves no residue on evapora-
tion, and only slightly and transiently reddens litmus : if it contains any of
the stronger acids, its action on vegetable blues is very decided. Under
these circumstances, also, it throws down red iodide of mercury from the
solution of the double salt of iodide of potassium and cyanide of mercury ;
but in using this test no alcohol must be present, as it would retain the
cyanide of mercury in solution. (Geoghegan, Ph, Mag. and Journ., vii.
400.)

Officinal hydrocyanic acid may contain, as impurity, hydrochloric or sul-
phuric acid, and occasionally Prussian blue. The latter substance is de-
posited on standing, or readily separated by careful distillation. In order to
detect hydrochloric acid, ammonia is added, and the liquid is concentrated
by evaporation. The hydrocyanate of ammonia is volatilized, while the
hydrochlorate of ammonia remains in prismatic crystals. A solution of these
crystals may be tested by the addition of nitrate of silver. The chloride of
silver with its characteristic property of insolubility in nitric acid, is thrown
down. A solution of borax, free from chloride of sodium, may be employed
instead of ammonia. This fixes the hydrochloric acid alone. Sulphuric
acid may be detected by the addition of nitrate of baryta ; if present, a white
precipitate of sulphate of baryta, insoluble in nitric acid, is deposited.

Hydrocyanic acid is a weak acid : it will not decompose the alkaline car-
bonates, or set free carbonic acid from these salts ; but it separates silicic
acid from the soluble alkaline silicates. It dissolves the oxide of mercury,
and this solution is not precipitated by alkalies (Hg04-HCy=--HgCy + H0).
It decomposes a solution of subnitrate of mercury, giving a gray precipitate
of the reduced metal (HCy + Hg30=HgCy + Hg+H0). It has no action
on solutions of the chloride and nitrate of mercury. Among other chemical
properties, it gives a white cyanide, insoluble in cold nitric acid, with a
solution of nitrate of silver (AgO,N054-HCy=AgCy-fHO,N05). Unless
it contains sulphuric acid, it does not precipitate a salt of baryta. It does
not affect a persalt of iron, and it does produce with it Prussian blue when
an alkali is added to precipitate the oxide. It does not precipitate a solu-
tion of the green sulphate of iron, but produces Prussian blue on the addition
of an alkali, by a reaction of its elements on the mixed oxides of iron which
are precipitated. This may be proved by adding diluted hydrochloric acid
to the mixture : the oxide of iron is dissolved, and Prussian blue remains.
It does not affect a solution of copper until potassa is added, when white
subcyanide of copper, insoluble in hydrochloric acid, is produced. When
the sulphate of copper is previously mixed with a small quantity of sulphurous
acid, the white subcyanide of copper (CugCy) is formed, and slowly deposited.
Hydrocyanic acid destroys the color of iodine in aqueous solution, as well as
the blile color of iodide of starch.

However carefully diluted hydrocyanic acid may have been prepared, its

286 TESTS FOR HYDROCYANIC ACID.

real strength should always be determined by experiment, for the specific
gravity is no adequate criterion. Neither the proportions of materials used,
nor the specific gravity of the product, can convey any accurate knowledge
of the strength of the acid. The strength of the medicinal acid may be ob-
tained by precipitating a given weight of it by nitrate of silver, v^^liich throws
down an insoluble cyanide of silver, of which 134 parts are equivalent to 27
of anhydrous hydrocyanic acid ; so that if the weight of the precipitated
cyanide of silver (well washed, and carefully and perfectly dried,) be divided
by 5, or multiplied by 0-2015 (2t-M34) the product will almost exactly
represent the quantity of real acid. One hundred grains of officinal acid, of
'a strength of 2 per cent., should therefore give 10 grains of dry cyanide of
silver ; and 100 grains of Scheele's acid should give from 20 to 25 grains of
dry cyanide. From the result of such an analysis it is easy, by the addition
of water, to reduce a strong acid to any assignable strength.

Tests for Hydrocyanic Acid. Analysis in cases of Poisoning. — The pecu-
liar odor of the acid is perceptible in liquids, unless other strong odors are
present. 1. Nitrate of Silver. This throws down a heavy white precipitate
(cyanide of silver) unchanged by exposure to light. It is insoluble in cold
nitric acid. When well dried and heated in a small reduction-tube it melts,
and evolves a gas which burns with the rose-red and blue-colored flame of
cyanogen. — 2. Sulphate of Iron. Add to the liquid a few drops of a solu-
tion of green vitriol, followed by a solution of potassa, and agitate the mix-
ture. It will acquire a dark bluish-green color. After a short time add
diluted hydrochloric or sulphuric acid ; oxide of iron will be dissolved, and
Prussian blue (having a greenish tint if much iron is present) will be left.
Prussian blue is known by its color and insolubility in diluted acids. This
test will reveal the presence of prussic acid even when mixed with alkaline
chlorides and other salts. — 3. Sulphide of Ammonium. Add to the liquid
one or two drops of yellow or bisulphide of ammonium, and evaporate to
dryness on a sand-bath. The hydrocyanic acid is converted into sulpho-
cyanide of ammonium (NH.S^-f HCy + 0(air)=NH,S,Cy-f HO). And this
is at once proved by the deep red color imparted to the white residue by the
addition of a persalt of iron. {London Medical Gazette, vol. xxxix. p. 765.)

These tests may be applied to detect the vapor of hydrocyanic acid, as it
escapes from any simple or complex liquid which contains it. The suspected
liquid is placed in a small jar, or beaker, the top of which admits of being
covered by a watch-glass. A drop of nitrate of silver in the hollow of the
glass, when inverted over a liquid containing prussic acid, will be whitened,
owing to the production of cyanide of silver: if slowly formed, the deposit
will be found under the microscope to consist of well-defined oblique rhombic
prisms. A drop of a solution of bisulphide of ammonium may be added to
the deposited cyanide of silver, and the mixture warmed. Persulphate of
iron will produce a red color in the liquid notwithstanding the presence of
black sulphide of silver. This will prove the presence of cyanogen, if the
cyanide is in too small a quantity to yield evidence by combustion. In em-
ploying the iron-test for the detection of the vapor, a solution of potassa
should be placed in the watch-glass, and, after sufficient exposure of the
alkali to the vapor, the sulphate of iron, followed by diluted hydrochloric
acid, should be added to the alkaline liquid. These tests will fail if the liquid
contains sulphuretted hydrogen; but in this case, the sulphur-test will be
available. The bisulphide of ammonium, placed in a watch-glass, absorbs
the vapor completely, and, on evaporation to drvness, the residue will be
found to contain sulphocyanide of ammonium by th*e iron-test. These vapor-
tests may be thus readily applied to the detection of the poison in food', in the

ANALYSIS OF THE CYANIDES. 28T

contents or coats of the stomach or intestines, in blood, and in the substance
of the heart and liver.

In order to obtain the acid from the coats of the stomach, or its contents,
in cases of poisoning, the substance, cut in small pieces, should be mixed
with cold distilled water, and distilled by a water-bath at a low temperature
(170°), the distillate being collected in a cooled receiver. If the liquid
suspected to contain the poison is alkaline, a small quantity of tartaric acid
may be added to neutralize it. The colorless distillate in the receiver may
then be examined for its odor, and tested by the action of the three tests
above described. If the liquid of the stomach is acid, it should be neu-
tralized; as, if ferrocyanide of potassium was present, any excess of acid,
would produce hydrocyanic acid from this salt. In the dead body, hydro-
cyanic acid is converted by putrefaction into sulphocyanide of ammonium,
which may be dissolved out by alcohol, and tested. {See Sulphocyanides.)

Cyanides. — The salts formed by hydrocyanic acid are similar to those of
the halogens. Thus, in contact with diluted alkaline solutions, water and a
cyanide are produced (KO-f HCy=H04-KCy). If the alkaline solution is
concentrated, then as with the concentrated acid in the presence of water,
hydrocyanic acid is resolved into formic acid and ammonia {see page 284).
The cyanides of the alkaline and alkaline earthy metals are very soluble,
producing strongly alkaline solutions, which evolve an odor of hydrocyanic
acid from the action of the carbonic acid of the air. They are powerful
poisons. They are readily distinguished from other salts by the fact that the
weakest acid decomposes them, and sets hydrocyanic acid at liberty. This
may be detected by the vapor-tests. The metallic cyanides, excepting that
of mercury, are insoluble in water, and are not readily decomposed by oxacids.
Hydrochloric and hydrosulphuric acids decompose them, and liberate hydro-
cyanic acid. Many of the metallic cyanides are soluble in, and form double
salts with, cyanide of potassium. Nitrate of silver throws down from solu-
tions of the cyanides, white cyanide of silver, possessing the characters
above described. A solution of green sulphate of iron followed by a diluted
acid, produces with a soluble cyanide, Prussian blue. When heated to
redness, out of contact of air, the cyanides of potassium and sodium undergo
no change, but if heated with exposure to air, or in contact with sub-
stances containing oxygen, cyanates of the alkalies are produced. They
are powerful deoxidizers. Cyanide of potassium, owing to its fusility, and
its deoxidizing action, has been usefully employed in the arts for the soldering
of metals. It removes every particle of oxide, and produces a clean surface
for the solder.

Cyanogen and Chlorine. — These bodies unite to form gaseous, liquid
and solid compounds, which are isomeric. The gaseous compound (Cy.Cl)
may be obtained by placing a small quantity of powdered cyanide of mercury,
moistened with water, in a vessel of chlorine, taking care that it is kept la
the dark. In a few days the chlorine will be replaced by the gaseous chlo-
ride. On cooling the vessel to zero, the chloride is desposited in crystals,
which are soluble in water. (Serullas.) The odor of this gas is pungent
and irritating. It does not redden litmus, or precipitate a solution of nitrate
of silver. (Pelouze.) After some time it is spontaneously decomposed into
carbonic acid and hydrochlorate of ammonia. This gas is composed of a
volume of each of its constituents, which unite without condensation. The
specific gravity is 2'1244, which nearly corresponds to the sum of the specific
gravities of chlorine and cyanogen, 2*4876+1 "7966 -r-2 = 2'l 421.

Liquid Chloride (CygClJ. — This is obtained from the same substances as
the previous compound j but in this case the vessel must be exposed to sun-

288 SULPHOCYANIC ACID.

light. This chloride is a heavy, yellow, oily-looking liquid, insoluble in
water, but soluble in alcohol.

Solid Chloride (CygClg). — This is a white solid crystalline substance at
common temperatures. It is not very soluble in cold water, and is decom-
posed by boiling water into hydrochloric and cyanuric acids. It may be
procured by adding a small quantity of hydrocyanic acid to a vessel of dry
chlorine, and exposing it to the solar rays. These compounds are deadly
poisons.

Bromide of Cyanogen (CyBr) is a colorlevSS solid of a pungent odor, ob-
tained by the reaction of bromine on cyanide of mercury.

Iodide of Cyanogen (Cyl) is a volatile solid resembling the bromide. It
is obtained by the action of iodine on the cyanide of mercury. Both are
poisonous.

Cyanogen and Sulphur. Sulphocyanogen (NC3S2=CyS3). — Liebig
obtained this compound radical by saturating a concentrated solution of
sulphocyanide of potassium with chlorine, as well as by boiling a soluble
metallic sulphocyanide in diluted nitric acid. It falls in the form of a
yellow precipitate, which preserves its color when dry ; it is insoluble in
water, alcohol, and ether, but soluble in hot sulphuric acid, from which it is
again thrown down by water. It is decomposed by concentrated nitric acid ;
when heated with potassium — sulphide, cyanide, and sulphocyanide of po-
tassium are formed; subjected to dry distillation, it yields sulphide of carbon,
and ultimately nitrogen and cyanogen.

SuLPHOCYANio AciD. JTydrosiilpJiocyanic Acid (CyS^,!!). — The aqueous
solntion of this acid may be obtained by decomposing basic sulphocyanide
of lead by diluted sulphuric acid, taking cace to leave an excess of the salt of
lead, which may be afterwards removed by sulphuretted hydrogen. It is
also formed when sulphocyanide of lead or of silver, diffused through water,
is decomposed by a current of sulphuretted hydrogen gas.

The hydrated hydrosulphocyanic acid is colorless, easily decomposed by
exposure to air or heat, yielding, among other products, a peculiar yellow
insoluble powder {Mellotie, see page 280). Chlorine and nitric acid abstract
its hydrogen, and evolve sulphocyanogen ; by their prolonged action, cyanic
and sulphuric acids are formed, and ultimately ammonia. It reddens the
solutions of persalts of iron. It exists in a combined state in the seeds of
certain cruciferous plants (mustard), and in the saliva of man and the sheep.

Sulphocyanides. — This is a monobasic, and the salts are procured by neu-
tralizing sulphocyanic acid with the respective bases, or by the action of
hydrocyanic acid on polysulphides. The alkaline compounds are soluble in
water and alcohol. They are identified by the deep red color which is pro-
duced, when a persalt of iron is added to their aqueous solutions. This
reaction is employed for the detection of hydrocyanic acid (p. 286). The
red color is destroyed by solutions of corrosive sublimate and chloride of
gold. They give white precipitates with the salts of silver, and lead, and a
gray precipitate with subsalts of mercury. The sulphocyanide of silver
readily changes by light; it is not soluble in nitric acid, which gives a reddish
color to the liquid, but it is dissolved by an excess of the alkaline sulpho-
cyanide. Chloride of sodium produces no precipitate in this solution. The
sulphocyanide of lead is soluble in nitric and acetic acids. With a salt of
copper, a concentrated sulphocyanide gives a black precipitate : when diluted
a white sulphocyanide of the metal is slowly formed. When heated to a high
temperature, a sulphocyanide is decomposed, yielding nitrogen, sulphide of
carbon, and a metallic sulphide. The sulphocyanide of mercury undergoes

FERROCYANOGEN. BISULPHIDE OF CARBON. 289

combustion producing a bulky porous residue of a smoke-like form and color
{Pharaoh's serpents). •

FERROCYANOGEN (FeCy3=Cfy) and Ferricyanogen (FegCyn.ssCfdy) are
compound radicals, in which metallic iron is an important constituent.
These will he again referred to in the description of that metal. Ferrocij-
anides. — The compounds formed with the alkalies are soluble in water, the
others are insoluble. The soluble salts are yellow in the hydrated, and while
in the dehydrated state. The persalts of iron give, with the soluble ferro-
cyanides, a deep blue precipitate (Prussian blue) 3Cfy,4Fe. The pure pro-
tosalts of iron give a white precipitate (protoferrocyaoide of iron) becoming
blue by exposure to air, oxygen, or chlorine. This has already been described
as a valuable test for oxygen in water (page 99). Sulphate of copper gives,
with a ferrocyanide, even in an extremely diluted state, a reddish-colored
precipitate, ferrocyanide of copper (Cfy2Cu). The alkaline/em oy ferrid-
cyanides are crystalline salts of a ruby-red color. They are recognized by
the action of a protosalt of iron, which produces with them a blue precipitate
(2Cdfy,3Fe). A persalt of iron darkens the solution, but there is no pre-
cipitate of Prussian blue. A crystal of an alkaline ferricyanide produces,
with a mixture of strychnia and concentrated sulphuric acid, a splendid
blue, passing to a purple and red color. No such results are produced
when a portion of an alkaline ferrocyanide is employed.

Nitroprussides. — By the action of nitric acid on ferrocyanide of potas-
sium, among other products, salts known as the nitroprussides are formed.
This acid, like the ferrocyanic, is bibasic {see page 280.) The salt of sodium
(NagFeaCysjNOg) crystallizes in long red-colored prisms. It is soluble in
water, but the solution is decomposed by light, Prussian blue being deposited.
The test for a nitro-prusside, is a soluble alkaline sulphide, the smallest
quantity of which produces a rich purple or crimson color, which, however,
is not permanent (p. ^9). The solution, although decomposed, is not
colored by sulphuretted hydrogen alone.

Melam (CiaNi^HJ is a product of the decomposition of sulphocyanide of
ammonium.

Melamin (CgN(.H(,), Ammelin (CgNgH^Og), and Ammelid (CigNgHgOg) are
products of the decomposition of melam. They possess but little chemical
interest.

Carbon and Sulphur. Bisulphide of Carbon. Sulphocarbonio Acid
(CSJ. — This is a liquid compound which was discovered in 1796 by Lam-
padius, while distilling a mixture of pyrites and charcoal ; he termed it alco-
hol of sulphur. It may be obtained either by passing the vapor of sulphur
over red-hot charcoal in a porcelain tube, or by distilling about six parts of
yellow iron pyrites (bisulphide of iron) with one of charcoal. The charcoal
should be in small fragments heated to full redness — the sulphur vapor
slowly passed through it, and the refrigerator and receiver should be cooled
to 32°, or even below. Vessels of porcelain and coated earthenware answer
best, although it is difficult to prevent loss by the escape of the vapor ; iron,
at the high temperature which is required, too easily combines with the sul-
phur to render it conveniently available. The product is sometimes con-
veyed by a glass tube into ice-cold water.

When purified by redistillation at a low temperature with chloride of cal-
cium, the bisulphide is a transparent, colorless liquid, insoluble in water,
but soluble in alcohol and ether. It should leave no residue on evaporation,
its refractive and dispersive powers on light are very considerable. Inclosed
in a prismatic bottle it serves for the spectral analyses of the alkaline and
19

290 CARBON AND SULPHUR. SULPHOCARBONIC ACID.

Other metals. Its specific gravity is 1-272. It boils at 110° and does not

freeze at 60^. It is very volatile and inflammable, and has a pungent

taste and peculiarly fetid odor. The liquid poured on paper and inflamed,
commonly burns with a blue flame without igniting the paper. When poured
on water, a portion sinks in globules like a heavy oil, while another portion
floats. This may be ignited, and in the pale flame, iron-wire burns with
great brilliancy. If burnt on blue infusion of litmus, this liquid is reddened.
The cold which it produces during evaporation is so intense, that by exposing
a thermometer bulb, covered with fine lint, and moistened with it, in the
receiver of an air-pump, the temperature sank, after exhaustion, to 80^.
When a mercurial thermometer was used the metal froze. The intensity of
the cold is such that it appears to have the power of freezing a portion of the
liquid {see page 75). Asbestos or filtering paper placed in the liquid, soon
acquires as a result of capillary attraction, a deposit of the solidified vapor.
It is soluble in fixed and volatile oils, and it dissolves camphor, sulphur,
phosphorus, and iodine. The readiness with which phosphorus dissolv'es in
the bisulphide of carbon is remarkable, and the amount considerable — one
part of the bisulphide taking up twenty parts of phosphorus. The solution
is occasionally used to give a thin film of phosphorus to delicate articles
intended to be coated with metals : they are dipped into it, and then into a
solution of silver or copper, by which a film of the metal is reduced upon
the surface : upon this other metals may be precipitated by the electric cur-
rent. The solution of phosphorus is a powerful and often useful deoxidizer
(page 236). When the vapor of bisulphide of carbon is passed over heated
lime or baryta, it produces ignition, and carbonates of these bases, together
with sulphides of calcium and barium are formed. It is also decomposed by
copper, and iron. At a red heat potassium and sodium float on it without
decomposing it at ordinary temperatures. If while the sodium is floating on
the sulphide, in a test-tube, a few drops of water are added, hydrogen is
evolved, and after a time the sodium takes fire tnd burns with explosive
violence, a cloud of yellow vapor at the same time escaping. Sulphide of
sodium is found in the liquid residue. Under the influence of dry chlorine,
it yields chloride of sulphur and perchloride of carbon.

The vapor of this liquid is very heavy, and may be decanted from one
vessel into another. Pour the vapor into a small jar containing a solution
of blue litmus, and ignite it : it will burn with a pale blue flame, producing
sulphurous acid — known by its peculiar odor — and the litmus will be reddened.
If a mixture of starch and iodic acid is placed in another jar, into which
the vapor is poured and ignited, blue iodide of starch will be produced (page
218).^ The vapor is not decomposed by mere heat, but at a temperature of
600° it takes fire in air, and burns with explosion. Pour a small quantity
of the liquid sulphide into ajar of 200 c. i. capacity, and after a few minutes,
when the vapor is diffused, apply a lighted taper to it : the vapor will burn
with a slight explosion, producing a deposit of sulphur. It requires three
volumes of oxygen for its perfect combustion ; and sulphurous and carbonic
acids are the only products (CS^-f 60 = COa-j-2SO,). As it is burnt in a
jar, sulphur is deposited, the air not being in sufficient quantity to consume
it. Lead water indicates the production of carbonic acid, and iodic acid
and starch the presence of sulphurous acid.

Bisulphide of carbon appears to be frequently formed during the produc-
tion of gas from coal, and to be retained in the state of vapor by the coal-gas
after its purification by lime. This impurity gives a sulphurous smell to the
gas when burned, although so perfectly deprived of sulphuretted hydrogen
as not to discolor carbonate of lead. The Rev. Mr. Bowditch has found
that when coal-gas containing this vapor is passed over hydrate of lime.

BISULPHIDE OP CARBON. COMPOSITION. 291

heated below the melting-point of lead, sulphide of calcium is produced, and
sulphuretted hydrogen is set free; this gas maybe subsequently separated
by the hydrated oxide of iron. When the vapor of the bisulphide is burned
with pure oxygen, it forms carbonic and sulphurous acids. It consists of

Atoms. Weights. Per cent. Vols. Sp. Gr.

Carbon . . ' . . 1 ... 6 ... 15-79 ... 1 ... 0*4145
Sulphur . . . . 2 ... 32 ... 84-21 ... ^ ... 2-2112

Bisulphide of carbon . 1 38 100-00 1 2-6257

The specific gravity of the vapor was found by Mitscherlich to be 2 '640,
which does not difi'er widely from that above given as the sum of the calcu-
lated specific grnvities of its constituents. Compared with hydrogen, the
vapor has a specific gravity of 38. It is analogous to carbonic acid, the
two atoms of oxygen being replaced by two atoms of sulphur. Mr. Gore,
who has compared the properties of the bisulphide with those of liquid car-
bonic acid, finds that in solvent powers and general properties they are
analogous. * The bisulphide is a more powerful solvent of fatty substances.
The chemical constitution of this compound may be easily determined by
evaporating a portion to dryness, with sodium in a test-tube, and afterwards
igniting the residue. On digesting this in water, and throwing it on a filter,
the carbon is left in the filter as a black powder, and the sulphur, combined
with sodium, will be found by the usual tests in the filtrate.

The vapor has been employed as an anaesthetic, but unsuccessfully. It is
a narcotic poison. The liquid sulphide is manufactured on a large scale,
and is extensively employed as a solvent of sulphur and caoutchouc, in the
manufacture of vulcanized rubber. It is also used for the separation of
phosphorus and iodine from organic substances in cases of poisoning. It
will not combine with alkalies, but it forms a class of salts with the alkaline
sulphides known as suJphocarhojuites, represented by MS,CS3. These re-
semble the carbonates which are MO,COa. It is obvious that if, according
to the views of certain writers, a carbonate should be represented as MjCOg,
the sulphocarbonate would stand as M,CS3, a change for which no suflBcient
reason has been offered. The vapor of this liquid furnishes a most powerful
means of sulphuration. At a red heat, nearly all oxides are converted by it
into sulphides (Fremy).

Tests. — The odor of the liquid, and the inflammability of the vapor, with
the nature of the products of combustion, are sufficient to identify it. If
pure, it should evaporate without leaving any residue. When the liquid is
boiled with potassa containing oxide of lead dissolved, the presence of sulphur
is indicated by the copious formation of brown sulphide of lead. It thus
serves as a test for detecting the presence of oxide of lead as an impurity in
a solution of potassa.

PREPARATION OF BORON.

CHAPTEE XXI.

BORON AND SILICON. BORACIC AND SILICIC ACIDS.
BORON (B = ll).

Boron is a solid metalloid found only in combination with oxygen, as
boracic acid. It was discovered by Davy as a constituent of this acid in
1807. Unlike carbon, it is an element which is but sparingly dij0fused, and
is only found in the mineral kingdom. In the Lipari Islands and Tuscany
it is deposited in the form of boracic acid; but in most cases it is associated
with alkaline or alkaline earthy bases, either in mineral deposits or as a con-
stituent of the waters of lakes and springs. Borate of soda or tincal is found
in the waters of certain lakes in Ceylon, Thibet, and Tartary. Borate of
lime, or datholite, is found in Norway, Sweden, and in South America, while
borate of magnesia, or horacite, is met with in Holstein. The South Ameri-
can mineral is a compound borate, being a mixture of borate of soda and
borate of lime (NaO,2BO3+2CaO,3BO3 4-10HO). It is found in Peru in
white kidney-shaped masses, called tiza, associated with the deposits of
nitrate of soda. Borax has lately been discovered in certain lakes in Cali-
fornia.

Preparation. — Boron may be procured in an amorphous state by heating
anhydrous boracic acid finely powdered, to a temperature of about 300°,
with twice its weight of potassium or sodium. The experiment may be per-
formed in a copper or iron tube (B03 + 3K=3KO-f B). This substance is
also obtained by melting in a cast-iron crucible, a mixture of 10 parts of
anhydrous boracic acid, with 6 parts of sodium, and 4 or 5 parts of common
salt. The salt aids the chemical changes, and forms an easily removable
flux. The fused matter is washed out of the tube or crucible with water,
and the whole put upon a filter. The boron remains in the form of a dark-
colored, insipid, insoluble powder. The product is at first washed with
diluted hydrochloric acid and then with water. Berzelius obtained boron by
decomposing the borofluoride of potassium. This compound, in the state of
dry powder, may be heated in a porcelain crucible with potassium; the re-
duction goes on quietly, and the fused mass may be triturated with water,
by which the boron is separated. It is then washed upon a filter with a
solution of hydrochlorate of ammonia, and afterwards with alcohol.

Wohler and Deville obtained boron in a crystallized state, by heating, to
a high temperature, in a plumbago crucible, for five hours, 8 parts of alumi-
num in large pieces, with 10 parts of anhydrous boracic acid. Boron and
vitrified borate of alumina are produced. The metallic portion of the mass
is treated with a boiling concentrated solution of soda, w^hich removes the
undecomposed aluminum; hydrochloric acid is subsequently added to re-
move the iron, and, lastly, nitrohydrofluoric acid to remove any silicon. In
this process, aluminum passes to the state of alumina at the expense of the
oxygen of the boracic acid (BOg-f 2Al=Al,03-j-B). The boron thus ob-
tained may, by repeated fusions with aluminum in exctss, be obtained in
hard crystals. These, however, retain both carbon and aluminum. By this
process, Wohler and Deville procured three varieties of crystallized boron :
1, black and opaque brittle laminae, which have the lustre and nearly the

BORON. CHEMICAL PROPERTIES. 293

hardness of the diamond; these crystals consist of 97*60 of boron, and 2*40
of carbon ; 2, long prismatic crystals, perfectly transparent and as brilliant
as diamond, but not so hard as the first variety; these crystals contain 89-10
boron, 6*T0 aluminum, and 4*20 of carbon ; 3, minute crystals of a chocolate-
red or pale yellowish color, of a sp. gr. of 2*68. These are boron diamonds.
They are as hard as the diamond, and will scratch its surface.

Properties. — Amorphous boron is a deep olive-colored substance, infusible,
inodorous, insipid, and a non-conductor of electricity. Its specific gravity
exceeds 2. It is not acted upon by air, water, either hot or cold (at least
after it has been heated to redness), alcohol, ether, or the oils. In the state
of hydrate, it long remains diffused through pure water, especially if free
alkali is present, and it even passes through filters ; but its precipitation is
accelerated by saline solutions (sal ammoniac). It undergoes no change
when heated in close vessels ; but when nearly red-hot in the air (600°), it
takes fire and burns with difficulty into boracic acid, chiefly on the surface.
According to Despretz, it becomes denser and more closely aggregated at a
full red heat ; and under a powerful galvanic battery, it has been fused into a
black bead. It is more easily oxidized by the action of nitric acid ; the pure
hydracids at common temperatures have no Action upon it, but nitrohydro-
chloric acid converts it into boracic acid, and nitrohydrofluoric acid into
fluoride of boron. At a high temperature, it rapidly decomposes nitre with
explosive violence ; under the same circumstances, it also decomposes and
deflagrates with the hydrate and carbonate of potassa : in the former case
water is decomposed, and hydrogen evolved ; in the latter, carbonic oxide is
evolved in consequence of the decomposition of carbonic acid ; in both cases
borate of potassa is the result.

A boiling solution of potassa or soda has no action on boron. At a high
temperature, boron deoxidizes most oxides and metallic salts. It inflames
and burns in deutoxide of nitrogen, forming boracic acid and nitrate of boron.
It burns in chlorine, when slightly heated, and also in vapor of bromine, pro-
ducing a chloride and bromide of boron. With hydrochloric acid it also
produces a chloride, with the evolution of light and heat. At a full red heat
it decomposes aqueous vapor, forming boracic add and setting hydrogen
free ; a portion of the boracic acid is at the same time vaporized with water.
Boron forms no compound with hydrogen, but it readily combines with nitro-
gen to form a nitride. This may be produced by heating the metalloid in a
current of ammoniacal gas ; hydrogen rs liberated. When boron is heated
in the vapor of sulphur, the two bodies combine to form sulphide of boron.
The production of boracic acid in some of the hot springs of Tuscany, has
been ascribed to the decomposition of sulphide of boron issuing with aqueous
vapor from the volcanic soil. Boracic acid and sulphuretted hydrogen are
among the products (BS3-}-3HO=B03-f 3HS). When boron is strongly
heated with boracic acid or borax, it fuses with the substance, producing a
vitreous compound of a black or brown color, resembling smoky quartz.
When very strongly heated in a close vessel, it acquires a chocolate-brown
color, and closely resembles, in appearance, amorphous silicon. (Wohler
and Devillb.) Crystallized or adamantine boron has been heated to the
temperature at which iridium melts, without undergoing any change. Its
sp. gr. is 2-68. It resists the action of oxygen at very high temperatures ;
but at the degree of heat at which diamond will enter into combustion, the
boron diamond will burn in oxygen. Owing to the surface becoming rapidly
covered with a layer of melted boracic acid, the combustion soon ceases.
Chlorine combines with it at red heat ; and when a crystal of boron is heated
between layers of platinum-foil, it combines with and causes the fusion of
the metal.

294 BORACIC ACID. CHEMICAL PROPERTIES.

Boron and Oyygen. Boracic Acid (BO,). — This acid, which is a crys-
talline solid, is the only known compound of boron and oxyp^en. It was
first obtained by Homberg, in 1702, and was used in medicine under the
name oi sedative salt. Its composition was demonstrated by Davy in 1807.
It is usually obtained by dissolving one part of borax in four parts of hot
water, and subsequently adding half its weight of sulphuric acid. As the
solution cools, white scaly crystals appear, which, when washed with cold
water, are nearly tasteless ; they consist of boracic acid combined with about
40 per cent, of water : they retain a portion of the acid employed, which may
be driven off at a red heat. A hot saturated solution of borax may also be
decomposed by hydrochloric acid (NaO,2B03 + HCl=XaCl4-HO + 2B03) :
the hydrated boracic acid, which falls as the liquid cools, should be washed
in very cold water and dried. When it is heated in a platinum crucible, it
fuses into a hard transparent glass, and by being thus heated, it loses any
traces of hydrochloric acid which may be mixed with it. The following
proportions will be found convenient for the production of the acid : 4 parts
of borax dissolved in ten parts of boiling water may be decomposed by 2|
parts of concentrated hydrochloric acid.

The specific gravity of the 'acid before fusion is 1 -48, and after fusion
1-837. At a white heat, this acid slowly sublimes when exposed to air. It
sometimes happens, that flashes of light are observed during the spontaneous
cracking of a mass of fused boracic acid.

The crystallized hydrate of boracic acid (BO^.SHO) is soluble in about 25
parts of cold, and 3 of boiling water. The latter solution, as it cools, de-
posits the acid in pearly scales ; it is also soluble in pure alcohol, to the
flame of which it communicates a beautiful green color. It is dissolved by
several of the strong acids, especially the sulphuric. It has little taste, and
feebly reddens vegetable blues ; it renders turmeric brown like an alkali.
The anhydrous acid (BOg) becomes opaque when exposed to air; it is very
fusible, and forms with many of the metallic oxides a glassy-looking sub-
stance variously colored ; it is often used as a flux, and in the soldering of
metals. Ebelmen has in this way employed it as a solvent of certain metallic
oxides, which have afterwards been obtained from it in the form of crystals,
so as to imitate native mineral products (Ann. Ch. and Ph., 3eme ser. xxii.
211), such as the ruby and emerald. When boracic acid is perfectly pure,
and is slowly depoisted from its aqueous solution, it forms small prismatic
crystals ; it is more commonly seen in scaly crystals.

Composition. — Boron, when burned, or acidified by nitric acid, combines
with about 68 per cent, of oxygen ; and with this proportion the theoretical
estimate of Berzelius coincides. There is, however, a difference of opinion
as to the atomic constitution of boracic acid, and the equivalent of boron.

Boracic acid is generally represented as BO,, and the equivalent of boron
will thus be 10-8. Adopting 11 as the equivalent, anhydrous boracic acid
will be constituted of

Boron

Oxygen . .

Atoms.

Weights.

Per cent.

, 1 .

.. 11 ..

. 31-43

3 .

.. 24 ..

. 68-57

Boracic acid 1 35 100-00

The crystallized hydrate will consist of 56 4 anhydrous acid and 43 6 per
cent of water. The crystals of the acid, when dried at 212°, lose half their
water.

Boracic acid is a feeble acid. It produces a wine red color with infusion
of litmus, becoming rather sombre red on boiling. This arises from its slight
solubility. It readily decomposes the solutions of the alkaline carbonates

TESTS FOR BORACIC ACID AND BORATES. 295

when moderately heated, and expels carbonic acid ; but concentrated
solutions of borates are decomposed by nearly all other acids, even the
acetic. Owing to the fixed nature of the boracic acid, it expels at a full red
heat, the sulphuric and phosphoric acids from the sulphates and phosphates.
It has no action on the alkaline chlorides, unless water is present, in which
case a borate of the alkali is formed, and hydrochloric acid is set free. Ily-
dro<2jen and carbon have no action upon the acid at the highest temperatures,
unless chlorine is present. Under these circumstances the acid is decom-
posed and carbonic oxide and chloride of boron are produced (BOg-f 3C-f-
3Cl=BCl3H-3CO). It is deoxidized at a Tiigh temperature by potassium,
sodium, and aluminum. The chief supply of boracic acid is from the district
of Monte Cerboli and Sasso, in Tuscany. It is much employed as a flux for
colors in the manufacture of porcelain.

I'ests. — Boracic acid may be identified : 1. By its fusibility and fixedness
at high temperatures ; 2. J3y its sparing solubility in water and its entire
solubility in boiling solutiohs of alkalies and alkaline carbonates, in the latter
with effervescence; and 3. By its rich green color which it communicates to
the flame of strong alcohol. Oxide of copper gives a similar tint, but this
may be easily excluded.

Borates. — 1. The alkaline borates are soluble in water, and have an alka-
line reaction. 2. When the solution is concentrated by evaporation if neces-
sary, hydrochloric acid will throw down scaly crystals of, boracic acid. 3. A
salt of baryta throws down a white precipitate, soluble in nitric acid and
even in an excess of water. 4. Nitrate of silver gives, with a soluble borate,
if concentrated, a white precipitate, soluble in nitric acid; if diluted, a brown
precipitate (oxide of silver). Arsenio-nitrate of silver gives a yellow pre-
cipitate with a borate, whether the solution is concentrated or diluted.
These precipitates are soluble in nitric acid. 5. Sulphate of magnesia does
not precipitate a concentrated solution of a borate in the cold ; but white
borate of magnesia is thrown down on boiling the mixture. 6. Add sul-
phuric acid to the borate, and then a small quantity of alcohol, ignite the
mixture, and the appearance of a green flame will show the presence of
boracic acid. This acid may be expelled from all minerals, by heating the
powdered solid with a mixture of sulphuric and hydrofluoric acids. It
escapes as fluoboric acid gas. A borate melts and forms a glassy-looking
substance at a high temperature.

Nitride op Boron (BN) has been already referred to. It is an amor-
phous white light powder. It was discovered in 1842 by Mr. Balmain,
who gave it the name of Ethogen. It is most readily obtained by heating
to bright redness, in a platinum crucible, a mixture of two parts of dried
sal ammoniac and one part of anhydrous borax, or an equivalent proportion
of boracic acid. A white porous substance remains, from which the
chloride of sodium may be removed by washing It may also be procured
by calcining a mixture of borax and ferrocyanide of potassium in a covered
crucible.

The nitride of boron is an amorphous powder, insoluble, infusible, and
fixed. It has neither taste nor smell. It burns under the blowpipe with
a brilliant flame of a greenish-white color. When heated in a current of
aqueous vapor, it produces ammonia and boracic acid (borate of ammonia).
Heated with hydrate of potassa it yields ammonia. It is a powerful deox-
idizer at a high temperature. Its most remarkable property is, that when
calcined with dry carbonate of potassa, it yields borate and cyanate of potassa,
so that it decomposes carbonic acid, the carbon of which unites with the
nitrogen to form cyanogen (BN + 2(KO,COJ=KO,B03-f KO,NC,0) ; if

296 CHLORIDE AND FLUORIDE OF BORON.

excess of the nitride is used, cyanide of potassium will also be formed. This
appears to be the compound from which native boracic acid is sometimes
formed in volcanic districts. Mr. Warinp:ton examined a substance brouf^ht
from Ynlcano, one of the Lipari Islands, and found it to possess all the pro-
perties of the artificial nitride of boron. Boracic acid was found'condensed
like drifted snow, within the crater of this volcano, and at a few inches
below the surface, there was a mass of sal ammoniac. As ammonia is com-
monly found associated with native boracic acid, it is not improbable that
these are products of the decomposition of nitride of boron by aqueous vapor
(BN+SHO^BOg+NH^).

Chloride of Boron (BCl,). — This is a volatile liquid compound of the
two elements. It may be procured by passing dry chlorine over heated
boron, or over a mixture of dry boracic acid and charcoal heated to redness.
The vapor is here mixed with carbonic oxide (BOg-f 3C + 3Cl=BCl3 + 3CO).
The chloride is a highly refracting liquid of sp. gr. 1-35, boiling at a tem-
perature of 59°. Its vapor has a density of 4 07. It is resolved by water
into boracic and hydrochloric acids (BCl3 + 3HO=3HCH-B03). There is
a liquid bromide (BjBi^) resembling the chloride.

Fluoride of Boron. Fluoboric Acid (BF.J. — This is a gaseous com-
pound, which may be obtained by heating a mixture of vitrified boracic acid
and fluor-spar (fluoride of calcium) to w^hiteness ; fluoboric acid passes over
as a gas, and biborate of lime remains in the tube (TBOg-f 3CaF = 3[CaO,
2B03] + BF3). The gas may also be procured by heating in a glass retort,
over a lamp, a mixture of 1 part of vitrified boracic acid, 2 parts of finely
powdered fluor-spar, and 12 parts of sulphuric acid ; but in this case, it is
generally contaminated by fluosilicic acid gas, derived from the glass. It
must be collected over dry mercury (BOg-fSCaF-f 3(S03,HO) = 3(CaO,S03)
+ 3HO-fBF3).

Fluoboric acid gas has a specific gravity of 2 31 ; it is colorless, of a
pungent, suffocating odor, highly deleterious when breathed, and it ex-
tiuguishes flame. The gas strongly reddens litmus ; and when bubbles of it
are allowed to escape into the air, they produce remarkably dense white
fumes, in consequence of their eager attraction for, and combination with
aqueous vapor. It is thus a good test of humidity. Water takes up 700
times its volume of the gas, increasing in volume and density, and forming
a caustic and fuming solution, in which Berzelius found boracic and hydro-
fluoric acids in combination {horohydrofltioric acid) : it would seem, there-
fore, that fluoboric acid gas decomposes water, and that the hydrogen of the
water unites to the fluorine to form hydrofluoric acid, and the oxygen to the
boron, to form boracic acid (BFg-f 3HO=3HF-j-B03). When the solution
is concentrated, the hydrofluoric and boracic acids again decompose each
other, and the original compound is reproduced. Neither the gas nor the
liquid acid act upon glass, but they speedily decompose almost all organic
substances : a piece of paper introduced into the gas standing in a tall jar
over mercury, causes its rapid absorption, and becomes charred as if burned,
in consequence of the abstraction of the elements of water. When potas-
sium is heated in fluoboric acid gas, it burns, and a brown compound results,
consisting of boron and fluoride of potassium : the latter may be dissolved
in water, and pure boron remains. .The gas gives a green color to the
flame of alcohol. It forms in equal volumes a solid white volatile compound
with ammonia, both gases being in the anhydrous state. This compound
is decomposed by water, and is converted into hydrofluate and borate of
ammonia.

PREPARATION OP SILICON. 297

As the vapor densities of fluorine and boron are unknown, it is impossible
to assi^ni the volumetric constitution of the fluoride. The gas contains in 100
parts, by weisj:ht, 16- 17 of boron and 83'83 of fluorine, or one atom of boron
and three atoms of fluorine.

SILICON (Si=22).

Silicon, like boron, may be obtained in the amorphous or crystalline state.
It so closely resembles boron in one of its crystalline modifications (the
graphitic), that the two metalloids cannot be distinguished by their appear-
ance. In 1824, Berzelius first procured pure amorphous silicon, by decom-
posing, at a high temperature, the silico-fluorideof potassium with an excess
of the metal. Wohler and Deville have since improved upon his process ;
and they have first brought to the knowledge of cliemists, that silicon might
be procured in two, or, according to them, in three allotropic conditions —
namely, the amorphous, graphitic, and the regular crystalline forms.

Freparation. — Amorphous or pulverulent silicon may be obtained by
heating in an iron tube, a mixture of one part of the double fluoride of
silicon and potassium (3KF,2SiF3) (or the hydrofluosilicate of potassa),
with nine parts of potassium. (The double fluoride is itself obtained by
saturating hydrofluosilicic acid with a strong solution of potassa, washing
the precipitate, and drying it thoroughly below a red heat ) In heating the
mixture, the mass becomes suddenly incandescent, and the following changes
take place: (3KF,2SiF3+6K=9KF + 2Si). The residue, when cooled,' is

treated with cold water, some hydrogen escapes from the decomposition of
a portion of silicide of potassium, formed in the process, and silicon is pre-
cipitated in an insoluble form. After the liquid, used in washing the pre-
cipitate, ceases to be alkaline, hot water is employed in order to remove any
undecomposed double fluoride; and the silicon remains as a dark brown
powder. The decomposition of the vapors of the fluoride and chloride of
silicon, in passing them through a heated tube containing potassium or so-
dium, furnishes other methods of procuring this metalloid.

The most economical process for obtaining crystallized silicon, according
to Caron, is to project quickly into a red-hot crucible (provided with a
cover, also kept red-hot) a mixture of 30 parts of dried silico-fluoride of
potassium, with 40 parts of pure granulated zinc, and 8 parts of sodium, in
small pieces. The mass is removed from the crucible when cooled ; and
while the lower part contains the ingot of zinc, the crystallized silicon will
be found adhering to the upper portion of this metal. The greater part of
the zinc is run out by raising the mass to its melting-point; and the small
quantity which adheres to the silicon, and any iron that may be present, are
removed by digesting the mass in concentrated hydrochloric acid. If lead
is present, this should be removed by nitric acid ; the pure silicon which
remains, may be washed and dried. The silicon thus obtained may be
melted by mixing it with the double fluoride and coarsely-powdered glass,
and heating the mixture in a double' crucible to the melting-point of iron.
A globule of silicon is formed in the midst of the glass and slag. These
substances may be removed mechanically, and any adhering traces, by im-
mersing the silicon in concentrated hydrofluoric acid, which has no action on
this substance.

The scaly crystals, or graphitic silicon, were obtained by Deville in de-
composing the dry double fluoride by aluminum, at the melting-point of
silver: silicide of aluminum was produced. This compound, treated first
with boiling hydrochloric acid, and afterwards with hydrofluoric acid, left
pure silicon in scales resembling graphite: the aluminum and the silica pro-

298 SILICON. CFIEMTCAL PROPERTIES.

duced beinof completely removed by the two acids. 100 parts of alnminara
gave by this process from 30 to 80 parts of silicide, containing from 65 to
75 per cent, of its weight of silicon. The aluminum appears to determine
the crystalline form of the silicon, under these circumstances, just as cast-iron
affects carbon, in producing artificial graphite. In decomposing the vapor
of chloride of silicon by aluminum in a vessel containing hydrogen, Wohler
and Deville obtained silicon in hard hexahedral prisms of an iron-gray color,
and of a reddish tint, by reflection. These crystals, like diamond, had the
property of scratching glass, and even cutting it.

Properties. — Amorphous silicon is a dark brown powder, less fusible than
boron, but still capable of being melted between the poles of a powerful
voltaic battery, or by fusion, as in the process above described. It is inso-
luble in water, hot or cold. It is a non-conductor of electricity. Nitric,
hydrochloric, and sulphuric acids, whether separately or mixed, have no
action upon it, even when boiled. It may be exposed to a very high tem-
perature in close vessels, without any other change than an increase of hard-
ness and density ; but if heated in air or oxygen before it has been thus cal-
cined in close vessels, it will take fire, and burn superficially, the silicic acid
formed melting and protecting the residuary silicon from continued combus-
tion. A full red heat in a covered platinum crucible, appears to produce an
allotropic change isj this substance. Pulverulent silicon, in the amorphous
state, decomposes cold hydrofluoric acid, as well as a concentrated hot solu-
tion of potassa, hydrogen being liberated in both cases, and silicon dissolved.
A fluoride is formed with the acid, and a soluble silicate with the alkali.
Silicon, heated to full redness, acquires so great a density that it sinks in
sulphuric acid ; and it loses the property of burning in oxygen or air, even
when heated in the flame of the blowpipe. Hydrofluoric acid and a boiling
solution of potassa are not decomposed by it; but nitro-hydrofluoric acid
alone dissolves it, with the evolution of deutoxide of nitrogen. (Fremy.)

When heated with an alkaline carbonate at the temperature of fusion, a
silicate of the alkali is formed, carbonic acid is decomposed, and carbonic
oxide escapes. If the silicon is in large proportion, this gas is even deoxi-
dized, and carbon is set free. This shows that silicon has a stronger aSinity
for oxygen than carbon, and that its deoxidizing powers are equal to those
of the alkaline metals. It does not decompose nitrate of potassa at a dull
red heat, unless this salt is mixed with a portion of carbonate, when deoxi-
dation takes place with explosive violence. At full redness decomposition
is produced without the addition of the carbonate. It is oxidized by the
hydrated alkalies in the melted state, but it has no action on boracic acid or
borax, at the temperature of fusion. When heated in a current of chlorine,
it undergoes combustion and forms a volatile chloride. It fuses with plati-
num, when melted in this metal, or as it is evolved in the nascent state. It
combines with hydrogen, to form a gaseous silicide of hydrogen. This gas
is spontaneously inflammable in air, like phosphide of hydrogen, burning
with a bright white flame, and producing wreaths of vapor of white silicic
acid. The gas is decomposed at a red heat, silicon being deposited, and it
detonates violently when mixed with chlorine. Its constitution has not been
determined.

Crystallized silicon in the graphitic state, possesses most of the chemical
properties assigned to amorphous silicon which has been intensely heated.
It has the color and lustre of iodine, is very hard, and has a specific gravity
of 2 49. It IS a good conductor of electricity. It is insoluble in all acids
excepting the nitro-hydrofluoric. It decomposes fused carbonate of potassa
at a red heat; and, at the same temperature, burns in chlorine, forming a
chloride. ' o

VARIETIES OF QUARTZ AND ROCK CRYSTAL, 299

Silicon and Oxygen. Silicic Acid (SiOg). Silica. — This is an abun-
dant natural product. It is a constituent of every soil, and is found more
or less in all spring, river, and sea-waters. Under the form of sand and
sandstone, it covers a large portion of the surface of the earth, and it is found
in all rocks, from the most ancient to the most recent. Granite, felspar, and
all the varieties of natural clays, contain a large proportion of silicic acid in
combination with alumina, oxide of iron, lime, magnesia, and other bases.
While carbon, the first member of this group of metalloids, is the main con-
stituent of the organic, silicon, in the form of silicic acid, is the chief con-
stituent of the inorganic kingdom. It is, however, not an unimportant
constituent of organic matter. The cuticle or epidermis of the grasses, and
of the husks of grains, is constituted of silicic acid. The cuticle and scaly
hairs of DeiUzia contain a large quantity of this substance. In the Equi-
setacece, the whole structure of the vegetable is so penetrated by it, that a
complete skeleton of the vegetable structure in silicic acid, maybe obtained.
Silica is found, more or less, in the ashes of all vegetables, especially of
those which grow on sandy soils. In some species of plants it forms 13 per
cent., and in others 50 per cent, of the ash. According to Johnston, it
forms 65 per cent, of the ash of wheat-straw, and 74 per cent, of that of
rice-straw. In the bamboo {Bamhusa arundinacea) silica is often collected
at the joints in masses ; and to these the name of tahasheer is given. The
long, slender, and hollow stems of the grasses, derive their strength from
their silicious covering. The silica is generally deposited in plates, grains
or needles: on the leaves of deiitzia scahra, it is deposited in a stellated
form.

It is but sparingly diffused in the bodies of man, and the higher orders of
animals ; but it constitutes the skeleton of whole tribes of infusoria. The
substance called mineral flour, or mountain-meal {Bergmehl), is almost en-
tirely constituted of the silicious skeletons of infusoria. A specimen of this
substance, obtained by Dr. Traill from Swedish Lapland, and analyzed by
him, was found, in the dry state, to consist of 7 1 '13 parts of silicic acid, 22
of organic matter, 5'31 of alumina, and 015 of oxide of iron. The cells of
the Diatomacce have silicious coverings, which enable them to retain their
form, even after digestion in strong acids.

The following are the principal minerals which contain silicic acid (silica),
pure, or nearly so.

Rock-crystal, or quartz, which may be considered as pure anhydrous silicic
acid (silica). It crystallizes in the form of a six-sided prism, terminated by
six-sided pyramids. Some varieties are perfectly transparent and colorless ;
others white (milk-quartz) and more or less opaque. Its specific gravity is
2-6. It is so hard as to give sparks when struck with steel, and is nearly
infusible. The primitive Crystal, which is rare, is an obtuse rhomb, the
angles of which are 94° 24', and 85° 36'. The finest and largest specimens
of quartz are brought from Madagascar, the Brazils, and the Alps. The
small and perfectly transparent crystals found near Bristol and in Cornwall,
are sometimes called Bristol and Cornish diamonds. The finest crystals are
cut into ornaments, and are used as a substitute for glass in spectacles ; they
are then termed pebbles ; they are harder and do not so readily become
scratched as glass. iThe refractive power of rock-crystal is the same as that
of glass, being about 1*6. Water is 1-3, and the diamond 2-47. Owing to
this difference, the lustre and brilliancy of rock-crystal is far inferior to
that of diamond. Quartz is also of lower specific gravity, and although hard
enough to scratch glass, its surface is easily scratched by the diamond, as
well as by the topaz and ruby. Brown and yellow crystals of quarts are .
found in great beauty in the mountain of Cairn Gorm, iu Scotland. This

300 SILICIC ACID. OPAL. JASPER. AGATES.

variety of quartz is sometimes called Scotch topaz ; it varies in color from a
pale yellow to a deep amber tint. The color may be due to the presence of
traces of carbon or silicon. The hrown quartz varies much in shade from a
smoky to a very deep tint : the color is probably due to a similar cause.
Fine samples of smoky quartz are found in Switzerland. Purple quartz, or
amethyst, is found in India, Ceylon, and Persia: it owes its color to traces
of iron and manganese. Rose-quartz derives its color from manganese.
Prase, or green quartz, is colored with oxide of iron ; and chrysoprase is
tinged of a delicate apple-green by oxide of nickel. Aveniurine is a beauti-
ful variety of quartz, of a rich brown color, which is filled with bright span-
gles of golden mica ; the finest specimens are from Cape de Gatte in Spain.
The artificial aventurine is a variety of glass, containing tetrahedral crystals
of metallic copper produced by fusion. Small crystals of quartz, tinged
with iron, are found in Spain, and have been termed hyacinths of Corapo-^
Stella.

Chalcedony, Carnelian, Onyx, Sardonyx, and Blood-stone, or Heliotrope,
and the numerous varieties of Agates, are principally composed of quartz,
with various tinging materials, chiefly oxide of iron. Flint owes its black
color apparently to organic matter. When heated in a current of air to a
very high temperature, it yields white amorphous silicic acid, nearly pure,
with a trace of oxide of iron.

Opalh among the most beautiful productions of the mineral world ; it is
a compound of about 90 silicic acid and 10 water, and is distinguished by its
very brilliant play of iridescent colors. The finest specimens come exclu-
sively from Hungary. There is a variety of opal called hydrophane, which
is white and opaque until immersed in water ; it then resembles the former.
The proportion of water with which silica is combined in the different varie-
ties of opal, is liable to so much variation, that they can scarcely be re-
garded as definite hydrates.

Common opal is usually of a dirty white color, and does not exhibit the
colors of the noble opal; it contains silicic acid and water, with a little oxide
of iron, and is not of unfrequent occurrence. Wood-opal is opaque, of a
brown color, and of a ligneous appearance. Jasper is a perfectly opaque
variety of silica, containing oxide of iron, and of a red, brown, or green color ;
these colors often alternating and giving a striped appearance to the sub-
stance. Black jasper, or Lydian quartz, forms the touchstone of jewellers.

The term chalcedony, from Chalcedon in Bithynia, near to which it is
found in large quantity, is applied to a variety of bluish and translucent
stalactitic quartz, sometimes of a milk-white or a gray color. The milk-
white variety forms white carnelian, and the red variety forms red carnelian.
When brown and opaque-white chalcedony occurs in alternate layers, it con-
stitutes the 07iyx. If the color is of a deep bro\fnish-red, or by transmitted
light, blood-red, the stone is termed sard. Alternate layers of sard and
milk-white chalcedony, constitute Sardonyx. Heliotrope has a deep green
color : it derives its name of blood-stone from the bright red spots of per-
oxide of iron scattered through it. It is found in Siberia and Iceland.
(Thomson.) Mocha-stone is chalcedony containing dendrites, usually of a
black or brown color ; but sometimes green, and resembling certain mosses.
Hence the term moss-agates. The filaments which ha^e the appearance of
vegetable fibres appear to be owing to the infiltration of iron, manganese,
or their compounds. Mocha-stone is chiefly brought from Arabia. Agate
has a basis of chalcedony, with sometimes crystals of quartz or amethvst in
the centre. It consists of alternate layers of chalcedony, quartz, jasper,"'helio-
trope, or opal, the layers being occasionally disposed in an angular form
(fortification agates) and variously colored. It is found in Saxony, Bohemia,

PREPARATION OF SILICIC ACID. 301

Siberia, Iceland, and the Isle of Skye. This substance is useful to the chemist,
as it is turned into mortars for grinding hard substances. The order of
hardness usually adopted by mineralogists is as follows; 1. talc; 2. gypsum;
3. calcareous spar ; 4. fluor-spar ; 5. phosphate of lime ; 6. felspar ; t.
quartz ; 8. topaz ; 9. sapphire and ruby ; 10. diamond. The diamond can
only be powdered in hard steel mortars. When once reduced to fragments
by cleavage, its own powder serves for its further trituration.

Obsidian is a glassy-looking substance, of a greenish or brownish-black
color. It is found in the Lipari Islands and Iceland. It is volcanic-glass.
It contains from 12 to 78 per cent, of silicic acid combined with alumina,
potassa, and soda. It owes its color to oxide of iron. Pumice is a porous
fibrous substance of a gray color. It contains 'Zt'S per cent, of silicic acid.
It is found chiefly interstratified with obsidian in the islands of Lipari and
Ponza. In Lipari, there is a hill {Capo Bianco) 1000 feet high, constituted
entirely of pumice.

Tripoli contains 90 silicic acid, T alumina, and 3 of oxide of iron. It was
formerly brought from Tripoli in Africa, whence its name. It is found in
Bohemia and Tuscany. When finely levigated by trituration with water, it
is much used for polishing metals, marble, glass, and other hard bodies.

Preparation. — Silicic acid may be obtained for chemical purposes* by the
following process. Heat colorless rock-crystal to redness, quench it in
water, and reduce it to a fine powder ; in this state it is silicic acid, almost
perfectly pure. Fuse 1 part of this powder with 3 parts of a mixture con-
sisting of equal parts of carbonate of soda and carbonate of potassa, in a
silver or platinum crucible. Dissolve the resulting mass in vrater, add a
slight excess of hydrochloric acid, and evaporate to dryness. Wash the dry
mass in boiling distilled water upon a filter, and the white substance which
remains is silica. This is the usual process. The silica obtained by simply
reducing the colorless rock-crystal to powder is nearly pure ; it sometimes
contains traces of oxide of iron and manganese, as well as of alumina. Pure
silica may also be obtained, by the fusion of fine white sand, or powdered
rock-crystal, with carbonate of lime; the resulting compound of lime and
silica may be decomposed by dilute hydrochloric acid, and the product, after
having been duly washed, is silica in the form of a light powder. When
gaseous fluoride of silicon (fluosilicic acid) is passed into water, the silicic
acid which is precipitated, after having been washed and dried, is also pure,
and in a state of extreme mechanical division.

At a high temperature, steam carries off silica in the state of vapor, thus
establishing an analogy between the silicic and boracic acids. While
boracic acid is fusible at a red, and volatile at a white heat, silicic acid,
according to Deville, is less fusible than platinum, but is volatile at this
temperature in a current of gas or vapor.

Properties. — Silicic acid exists in two states, the amorphous and crystalline.
The acid obtained by precipitation in the processes above described, is the
amorphous variety ; while the native rock-crystal represents the crystalline
form. They are difl'erently affected by reagents. Amorphous silicic acid,
as it is precipitated from its solutions, is supposed to be a hydrate, repre-
sented by the formula, Si03,H0. — When dried at 21 2°, it is said to lose
half its water, and to become 2(Si03)HO. According to Mitscherlich,
there is no definite hydrate of silicic acid. It loses a variable quantity of
water in drying, and absorbs water in a damp atmosphere. When the pre-
cipitate is heated to 370°, it loses the whole of its water, and forms the
insoluble variety of amorphous silicic acid (SiOg). In this state, it is a
white, tasteless powder, insoluble in water, and not forming with it a cohesive,
plastic mass, like alumina. It has no action on vegetable colors, and is

302 SILICIC ACID. CHEMICAL PROPERTIES.

infusible except under the intense heat of the oxyhydrogen blowpipe, in the
flame of which it melts, forming a transparent colorless globule. Its sp. gr.
is, like that of the crystalline variety, 2 66. It is not dissolved by any of
the oxacids, either separately or in mixture, even at a boiling temperature.
When a very diluted solution of a silicate is treated with sulphuric, hydro-
chloric, or nitric acid, the silicic acid is not precipitated, but appears to be
dissolved by the water as a hydrate. When the acid solution is, however,
concentrated by evaporation, or the acid is at once added to a concentrated
solution of a silicate, the hydrate is precipitated in a gelatinous form, and
when dried and strongly heated it forms the insoluble variety.

Solubility of Silicic Acid. — The solubility of silicic acid in water has been
hitherto doubted or denied by chemists. Some have admitted that pure
water would dissolve only a thousandth part of its weight of recently pre-
cipitated or gelatinous silica. Mr. Graham has, however, by the process of
dialysis, succeeded in procuring a solution of silica varying from 5 to 14 per
cent, of the weight of the water. He added hydrochloric acid to a solution
of silicate of soda, and placed the mixture in a dialyser (p. 146). In a few
days the chloride of sodium and hydrochloric acid were entirely removed,
while silica and water alone remained in the dialyser. He calls this colloid
silicic acid. The liquid, when left to itself, slowly deposited silica in a gela-
tinous and insoluble form : hence it cannot be regarded as a solution in its
proper chemical signification (pp. 47 — 51). Lime-water, or a solution of
carbonate of potassa, added to it, rapidly caused the separation of silicic
acid in a gelatinous form. These facts may account for the temporary solu-
bility and deposit of silica, under circumstances which have hitherto appeared
difficult of explanation.

Amorphous silicic acid, either in the state of gelatinous hydrate, or in
powder dried but not heated, is readily dissolved in the cold by concentrated
hydrochloric, nitric, or sulphuric acid. A strong solution of potassa or soda
will dissolve it, but with more difficulty. In evaporating alkaline solutions
in glazed porcelain dishes, a portion of the silica of the glaze is frequently
dissolved. The alkalift? also dissolve silica from flint glass.

Silicic acid which has been strongly calcined, is as insoluble in alkalies
and oxacids as the anhydrous native silicic acid — rock-crystal. Among
hydracids, the hydrofluoric is the only one which dissolves silicic acid,
forming water and fluoride of silicon (Si03H-3HF=3HO + SiF3). The
rapidity of this action is in proportion to the concentration of the acid. If
the silicic acid is in fine powder, if it has not been calcined, and if a sufficient
quantity of hydrofluoric acid is employed, it is readily dissolved. Insoluble
silicates, such as the varieties of glass, are similarly attacked and dissolved
by this acid ; but crystalline silicic acid, or native rock-crystal, resists its
action.

In the precipitation of silicic acid from its alkaline solutions by acids,
alumina may be associated with it. If the residue is brought to dryness,
moistened with strong hydrochloric acid for half-an-hour, and then boiled in
water, alumina, as well as oxide of iron, magnesia, and other bases present,
will be entirely dissolved, while the silic acid alone will remain utidissolved.
Its quantity may thus be determined.

Silicic acid is precipitated from its concentrated solutions by nearly all
acids, even the carbonic and hydrocyanic. When its solutions are long
kept, or are exposed to air, the silicic acid is deposited as an opaque white
mass. The silica thus precipitated is readily dissolved by strong acids, but
n-ot readily by alkaline solutions, even at a boiling temperature. When dry
silicic acid is fused with the hydrates of potassa, soda, or baryta, it readily
enters into combination, forming silicates. In the anhydrous state, at a

SILICIC ACID. CHEMICAL PROPERTIES. 303

high temperature, it expels carbonic acid from alkaline carbonates (KO,COa
-f-Si03=KO,Si03+ COJ. It is worthy of. remark, that in this decompo-
sition, there is no substitution of a metallic oxide for water, but a displace-
ment of one anhydrous acid by another. It is impossible to regard silicic
acid as a salt of hydrogen. It is an anhydrous oxacid, capable of displacing
other oxacids at a high temperature, without the intervention of the elements
of water.

Silicic acid is unaffected at the highest temperatures by hydrogen, carbon,
phosphorus, or chlorine. When, however, it is heated and exposed to the
combined action of chlorine and carbon, oxide of carbon and a volatile chlo-
ride of silicon are produced. When heated with carbon in contact with
iron or platinum, it undergoes decomposition : carbonic oxide escapes, and
silicides of the metals result. Platinum vessels may be thus destroyed by
nascent silicon.

Although silicic acid, as it is commonly met with, is not soluble in water,
yet there is scarcely a river or spring-water in which traces of it may not
be found. It appears to be held in solution either by alkalies or their car-
bonates. The Geyser springs of Iceland contain a large quantity of silicic
acid. We have found as much as 48 grains in a gallon of the water of the
Great Geyser (1856) : the solvent here appears to be carbonate of soda, the
efi'ect of which is probably aided by the high temperature as well as the
pressure to which the heated column of water is subjected. The silicic acid
is precipitated from the water in a hard crystalline form on all the sur-
rounding rocks. It has been already stated that hydrated silicic acid may
be volatilized with aqueous vapor at a high temperature, like hydrated
boracic acid (p. 301).

Composition. — The amount of oxygen contained in 100 parts of silicic
acid, has been variously estimated at from 51*98 (Mitscherlich) to 52 93.
Assuming the former proportion to be correct, and silicic acid to contain 3
atoms of oxygen united to 1 atom of silicon (SiOg), then (51 "98 : 24 : :
4802 : 22-1) the equivalent of silicon would be 22. This is in accordance
with the views of Berzelius and the majority of British and foreign chemists,
including the most recent writers on the subject, Pelouze and Fr^my. It
is also consistent with the atomic constitution of boracic acid, to which
such acid bears a much stronger analogy in chemical and physical proper-
ties, than it does to the oxygen compound of carbon (COj. It has, how-
ever, been proposed to alter the equivalent of silicon, by making the formula
of silicic acid SiOg ; but there are no valid reasons for making this change.
Col. York, in experimenting with silicic acid on different alkaline salts and
bases, obtained such widely different results, that he could draw no satis-
factory conclusion. Thus, in calculating by the amount of carbonic acid
expelled by silicic acid from fused carbonate of potassa, the mean result of
four experiments gave as the equivalent of silicic acid 30*7, corresponding
to the formula SiOg. Seven experiments with the carbonate of soda, how-
ever, gave an equivalent of 21-3, represented by SiOg. Carbonate of lithia
gave the number 1499, nearly agreeing with the formula SiO. The fusion
of silicic acid with hydrate of potassa gave a result corresponding to that
derived from the carbonate, 30*8 ; but hydrate of soda gave 172, a result
approaching to that obtained by carbonate of lithia. Such results furnish
no grounds for changing the equivalent of silicic acid. On the other hand,
in experimenting with other substances, this gentleman found that boracic
acid only gave results similar to those obtained with silicic acid. Proc,
JR. S., Vol. 8, JS'o. 25, p. 441.) As this acid is admitted to have the formula
of BO3, this simple fact justiQes the retention of the generally accepted
formula, SiOg. Apart from other strong analogies between boron and

304 ANALYSIS OF SOLUBLE AND INSOLUBLE SILICATES.

silicon, a change in the formula of silicon would be, therefore, inexpedient
and inconsistent.

The experiments of Scheerer {Chem. Neius, March 30, 1861, 205) show
that, in fusing silicic acid with carbouate of soda, various silicates may be
produced, and variable amounts of carbonic acid expelled. The result
depends on the temperature of fusion, the duration of the fusion, the relative
proportions of silicic acid and base, and the chemical relations of carbonic
acid to the base at a high temperature. From his results, Scheerer con-
siders the formula SiOg to be correct.

Silicates. — These salts form a numerous class of substances, in some of
which the acid, and in others the base, predominates. All are insoluble in
water, excepting those of potassa and soda. The polysilicates of these
alkalies constitute varieties of glass. The aqueous solution of a soluble
•silicate is alkaline. It gives a white precipitate with ammonia, or carbonate
of ammonia, which is not dissolved by a cold solution of potassa, or by
chloride of ammonium (A precipitate given by carbonate of ammonia in a
salt of alumina is dissolved by a cold solution of potassa.) A silicate is
distinguished from the alkaline-earthy and all other salts, by the fact that an
acid (even the acetic) will precipitate the silicic acid from a concentrated
solution, as a gelatinous hydrate. The white powder obtained on drying and
heating this precipitate, may be identified as silicic acid, by its insolubility
in all menstrua excepting hydrofluoric acid. It is dissolved by this acid,
and if the silicic acid contains no impurity, the whole of it may be vola-
tilized as fluoride of silicon, by heating the solution in a platinum capsule.

Among other chemical characters of a soluble silicate, may be mentioned
.the following: Nitrate of silver gives with the solution a brown, and the
arsenio-nitrate a yellow precipitate. It is precipitated in a gelatinous form
by all the salts of ammonia, and by all acids, including even the hydrocyanic
and carbonic. Nitrate of baryta also produces in it a gelatinous precipitate
which is not dissolved by nitric acid ; but this could not be mistaken for a
sulphate, inasmuch as nitric acid alone produces a dense gelatinous precipi-
tate in a solution of a silicate.

The analysis of the insoluble silicates is attended with some difficulties.
Some of these in which the base predominates, as in certain slags, may be
entirely decomposed, and the silicic acid set free in a gelatinous form, by
digesting the finely-powdered silicate in a strong acid, such as the sulphuric,
hydrochloric, nitric, or even the acetic. The bases are found in soluble
combination with the acid, which should be selected accordingly. The
greater number of native silicates admit, however, of being correctly analyzed
only by fusion. The silicate, very finely powdered, may be mixed with four
times its weight of a mixture consisting of equal parts of the carbonates of
potassa and soda, and fused in a platinum crucible for half an hour. When
cold, the residuary mass may be digested in an excess of hydrochloric acid,
and geutly heated. If the decomposition of the silicate has been complete,
no insoluble gritty matter will remain. When the whole is dissolved, the
acid liquid is evaporated to dryness, the residue moistened with concentrated
hydrochloric acid, and after a time boiled in water. The solution is filtered;
the silicic acid, collected on the filter, is well washed and dried. The bases
associated with the silicic acid will be found in the filtered liquid. The
hydrates of potassa or soda act more readily by fusion, but the process
cannot be carried on in platinum. If the silicic acid is combined with
potassa or soda, the powdered silicate may be fused either with pure baryta,
or the carbonate or nitrate of this alkaline earth. All the insoluble silicates
fuse at a high temperature, and more readily when mixed than when
separate.

CHLORIDE AND FLUORIDE OF SILICON. 305

Silicic acid is often associated with titanic acid. In order to separate
this, the silicate may be fused in a platinum crucible, with bisulphate of
potassa. The titanic acid may be dissolved out of the residue by water,
while the silicic acid will remain undissolved. (Will.)

Wohler and Buff have described a hydrated sesquioxide of silicon (Si^Og,
2H0) as a light, white, amorphous substance, oljtained by the action of
water on the hydrochlorate of the chloride of silicon.

Chloride of Silicon (SiClg). — Silicon burns when heated in a current of
dry chlorine, producing this gaseous compound. It may be produced by
passing dry chlorine over silicon heated to redness, or by passing the dry
gas over a mixture of silicic acid and charcoal similarly heated (SiOg+SC
-f 3Cl = SiC]3+3CO). The chloride is a yellowish fuming liquid of a sp.
gr. of 1-52, boiling at 122°, and converted by water into hydrochloric and
silicic acids (SiCl3-f-3riO = Si03 + 3HCl). Its vapor has a density of 5-939.
Each volume contains two volumes of chlorine. There is also a Bromide of
Silicon (SiBrg).

Fluoride op Silicon (SiFg). Fluosilicic Acid, — The only body which
acts energetically upon silicic acid is the hydrofluoric acid : the result of
this action is a gaseous compound. To obtain the gaseous fluoride of sili-
con, four parts of pulverized fluor-spar and three of powdered glass, or two
of silica finely powdered, are well mixed in a retort with about five parts of
oil of vitriol ; the gas evolved is to be collected over mercury, and when its
production slackens, it may be accelerated by a gentle heat. The mercury
and the glass vessels employed must be quite dry, for if in. the least damp,
they acquire an adhering film of silica. This decomposition depends upon
the evolution of hydrofluoric acid and its action upon the silica, water and
•fluoride of silicon being the ultimate results (SiO.^-f 3HF = SiF3-f 3H0).
The hydrofluoric acid is derived from the action of the aqueous sulphuric
acid on the fluoride of calcium; CaF-f S03,HO = HF + CaO,S03.

Fluoride of silicon is a colorless gas ; its odor is acrid, somewhat resem-
bling that of hydrochloric acid ; its taste very sour ; its specific gravity is
3*6 compared with air; 100 cubic inches we;gh nearly 112 grains. It
extinguishes the flame of a taper, and all combustible bodies ; it has no
action on glass ; it may be liquefied and solidified by cold. It produces
white fumes when in contact with damp air; ,and when exposed to water it
is absorbed, and a soluble compound of silicic with hydrofluoric acid is
formed. The changes may be thus represented : 3SiF3-J-3HO=3HF,2SiF3
H-SiOg. The hydrofluosilicic acid, 3HF,2SiF3, is dissolved in the water^
while the silicic acid, SiOg^ is precipitated in a gelatinous state. If the beak
of a retort from which the gas is issuing is plunged into a basin of water, it
will be soon choked by a copious deposit of hydrated sifica, which sometimes
forms tubes through the water, by which the gas escapes directly into the
air. Water will dissolve 350 volumes of this gas, and when it is intended
to make a solution, or to produce gelatinous hydrate of silica, the conducting
tube or beak of the retort should be so fixed as to plunge just below the
level of a small quantity of mercury in a conical glass. Water may be care-
fully poured on the mercury, until the glass is filled, and the distillation then
safely carried on. As each bubble of the fluoride of silicon escapes through
the mercury and rises into the water, it becomes invested with an envelope
of the hydrate of silica, owing to the decomposition above described.

This gas is dissolved by alcohol, but if the alcohol is hydrated there, is a
separation of silicic acid. The decomposition of this gas by water, enables
a chemist to detect the slightest trace of silicic acid in any mineral. The
20

8(H5 HYDROFLUOSILICIC ACID.

mineral should be powdered and mixed with powdered fluor-spar (free from
silica) and sulphuric acid. The mixture should be heated in a platinum
vessel, and the vapors carried by a platinum tube into water. If siHca is
present in the mineral, there will be a separation of the gelatinous hydrate,
on contact with the water. The whole of the silicic acid may be thus
expelled.

When a streak is made on paper with a solution of fluosilicic acid, the
paper is not carbonized when heated. If sulphuric acid is present as an
impurity, the paper will be carbonized.

Hydrofiuosilicic Acid (3HF,2SiF3). — This is a product of the decom-
position of the fluoride above mentioned, in contact with water. The acid
may be procured by separating the gelatinous silica, by means of a linen
filter, and filtering the liquid through paper. It is also produced when
diluted hydrofluoric acid is saturated with silica.

The liquid has a strongly acid reaction. It may be evaporated in a pla-
tinum vessel without change, but it corrodes glass ; and, when highly con-
centrated, it is converted into hydrofluoric acid, and silica, which is deposited.
Although its solution has no direct action on glass, it slowly acts upon the
alkaline bases, potassa, soda, lime, and oxide of iron existing in glass, and
forms a white deposit of a hydrofluosilicate of the base. Its action on
alkalies and their salts is remarkable. It precipitates in an insoluble form
as hydrojiuosilicates or double silicofluorides (3MF,2SiF3), potassa, soda,
and baryta. Pure lime and strontia are not precipitated from their solutions
in water. Ammonia in excess and carbonate of ammonia decompose the
acid and throw down gelatinous silica. Concentrated solutions of the salts
of potassa, soda,, lithia, baryta, and alumina are also precipitated; those of
potassa so completely, that the alkali may be thus separated from the acid.
In this manner chloric acid may be obtained by adding hydrofluosilicic acid
to a strong solution of chlorate of potassa (p. 194). In these cases the
hydrogen of the acid is simply replaced by the metal. A solution of the
acid precipitates a salt of strontia, but much more slowly than a salt of
baryta. These precipitates, like those given by sulphuric acid in the solu-
tions of the alkaline-earthy salts, are insoluble in nitric acid, and might be
mistaken for sulphates. When calcined, they leave a fluoride, which may be
identified by its action on glass. A sulphate is only decomposed when
heated with charcoal, or cyanide of potassium, and a sulphide then results.

Silicon forms compounds with nitrogen and sulphur, SiXaC?), and 8183.

PHYSICAL PROTERTIES OF THE METALS

30t

METALS.

CHAPTER XXII.

PHYSICAL PROPERTIES OP THE METALS. RELATIONS TO
HEAT, LIGHT, ELECTRICITY, AND MAGNETISM.

The metals constitute a numerous and important class of elementary
bodies ; they are characterized by a peculiar and distinctive lustre, by their
opacity, and by their high conducting powers in regard to heat and electricity.
They are also marked by a high specific gravity. Their oxides form bases
as well as acids. They combine with each other to form alloys, and some of
them combine with mercury to form amalgams. In the following table
they are enumerated in the order in which they will be described. A table
of their symbols and equivalents will be found at page 67.

POTASSIUM

SODIUM

LITHIUM

CESIUM

RUBIDIUM

THALLIUM

BARIUM
STRONTIUM
CALCIUM
MAGNESIUM

ALUMINUM

GLUCINUM

ZIRCONIUM

THORIUM •

YTTRIUM

ERBIUM

TERBIUM

Two which are but imperfectly known — namely, Norium, and Pelopium —
are excluded from this list. Altogether, the number of metals known is 54.
Of these metals only 19 are commonly met with, and among these about 12
comprise the greater number employed in medicine and in the arts and manu-
factures.

The first six ofjhe metals in the above list are distinguished as the metals
of the alkalies ; fneir oxides are powerfully alkaline; they have an intense
aflanity for oxygen, and decompose water at all temperatures. The four
metals in the following group are the bases of the alkaline earths ; with the
exception of magnesium, they also decompose water at all temperatures.
The ten succeeding metals, with the exception of aluminum, have been but

CERIUM

NIOBIUM

LANTHANUM

ILMENIUM

DIDYMIUM

MOLYBDENUM

URANIUM

IRON

TELLURIUM

MANGANESE

TITANIUM

ZINC

ANTIMONY

INDIUM

ARSENIC

TIN

CADMIUM

MERCURY

COPPER

SILVER

LEAD

GOLD

BISMUTH

PLATINUM

COBALT

PALLADIUM

NICKEL

RHODIUM

CHROMIUM

RUTHENIUM

VANADIUM

OSMIUM

TUNGSTEN

IRIDIUM

COLUMBIUM

308 HARDNESS. MALLEABILITY. DUCTILITY. TENACITI.

im#>erfect]y examined ; they are generally designated as the bases of the
earths. The following twenty-three metals have been sometimes divided
into those which form basic oxides, and those which form acids ; and they
have been separated into other distinctive groups, having reference to the
action of acids upon them, to their action upon water at high temperatures,
and to the isomorphism of their salts ; these characters, however, are not
sufficiently definite; and as regards the basic or the acid character of their
compounds with oxygen, several of them form compounds belonging to both
classes. The last nine metals have been particularly designated as noble
metals ; they are not changed by air or by water, and their affinity for oxygen
is comparatively feeble : to some of these properties, however, osmium forms
an exception.

Physical Properties. — A high degree of lustre is one of the leading
physical characters of the metals, the color of the light which they reflect
varying with the nature of the metal and the number of reflections to which
it has been subjected. In most cases it is nearly w^hite, gray, or bluish ;
•from gold it is yellow, and from copper, red ; but the intensities of these
colors may be greatly increased by repeated reflections.

The opacity of metals is such, that when in very thin leaves they transmit
no light. Gold is so far an exception, that when beaten into leaves of one
two-hundred-thousandth of an inch in thickness it transmits green light, and
if alloyed with silver, blue light. There are also other means by which ex-
tremely thin metallic films may be obtained, and which often exhibit a cer-
tain amount of transparency.

Hardness; Brittleness. — Few of the metals, when pure, are very hard;
they are generally softer than steel. Lead may be scratched by the nail ;
and potassium at 60° is softer than wax. Some, such as antimony, arsenic,
and bismuth, may be easily pulverized ; others are brittle at one temperature,
but malleable and ductile at another. Zinc, for instance, which at common
temperatures is comparatively brittle, may be rolled and drawn into wire
when heated up to 300°.

MaUeahility, or the capacity of being extended by hammering or rolling,
belongs to some of the metals in a very remarkable degree. Common gold-
leaf, for instance, is not more than a 200,000th of an inch in thickness; and
3 grains of the metal are sufficient to cover a square foot. Silver, copper,
and tin, also admit of great extension under, the hammer. In hammering
and rolling, some of the metals become so hard and brittle as to require
occasional annealing; in these cashes they give out much heat. The follow-
ing is the order of malleability — gold, silver, copper, aluminum, tin, cadmium,
platinum, lead, zinc, and iron.

Ductility. — The malleable metals are also ductile ; that is, they admit of
drawing out into wire. In this respect, gold, silver, platinum, and iron,
stand at the head of the list. A grain of gold may be drawn into 500 feet
of wire. A wire of platinum, not exceeding a 30,000th of an inch diameter,
fcas been obtained by placing it in the axis of a small cylinder of silver, and
then drawing the compound wire in the usual way, and afterwards dissolving
off the silver by nitric acid. The order of ductility is as follows : gold,
silver, platinum, iron, copper, aluminu-m, zinc, tin, and lead.

Tenacity, or the power of supporting a weight without breaking, is an
important property of the metals. Iron is at the head of the list, and lead
at the bottom ; but the respective tenacities are much*influenced by the
temperature at which the comparisons are made, the manner in which they
are tested, and more especially by the process of annealing. A wire of
unannealed iron, which sustained a weight of 26 lbs. only bore 12 lbs. after
having been annealed ; and a wire of copper which sustained 22 lbs. before

SPECIFIC GRAVITY OP THE METALS.

309

annealing:, was broken by 9 lbs. after annealing. The following metals are
arranged in the order of their tenacities : iron, copper, palladium, platinum,
silver, gold, zinc, tin, lead. The tenacity of iron compared with lead is as
25 to 1.

In the following table the figures represent the number of pounds required
to break wires one. tenth of an inch in diameter : —

Lead, 27-7 Zinc, 100-8 Silver, 187-1 Copper, 302-2

Tin, 34-7 Gold, 159-7 Platinum, 274-3 Iron, 549-5

AssnnfUg the tenacity of lead to be represanted by unity, then, according to
Wertherius' results, the tenacity will be represented by the following numbers : —

Lead . . . .1* Silver . . . .8-9

Cadmium . . .1-2 Platinum . , . 13*

Tin 1-3 Palladium . . .15-

Gold . . . .5-6 Copper. . . .17*

Zinc . . . .8- Iron . . . •26-

The tenacity of a metal, with few exceptions, decreases in proportion as
its temperature increases ; but iron, though less tenacious at 212° than at
32°, is more so at 890° than at 212°.

Crystallization Metals are susceptible of assuming the crystalline form.

With many, this may be effected by fusion and slow cooling, and especially
by suffering the melted metal to concrete externally, and then perforating
the solid crust, and pouring out the liquid interior. The cavity so formed
will be then lined with crystals : this mode of proceeding answers extremely
well with bismuth, which furnishes a singular congeries of cubic crystals
(page 26). When the metals are precipitated by each other, they often
crystallize during their deposition, as in the precipitation of silver by mer-
cury, and in that of lead by zinc. A stick of phosphorus immersed in a
solution of silver becomes incrusted with metallic crystals (p. 236). Gold
is occasionally deposited in a crystalline form, from its ethereal solution.
During the electrolysis of metallic solutions, especially when low powers are
employed, beautiful crystals are also occasionally obtained.

The crystalline structure of a metal materially affects some of its other
physical properties. Copper, silver, and even gold, become comparatively
hard and brittle when in a crystalline condition ; and the most brittle metals
are those which most readily assume the crystalline form, such as bismuth
and antimony. Even iron, which in one condition is fibrous, tough, and
tenacious, becomes relatively brittle, when it assumes even an approach to
a crystalline structure ; and this change in its condition is sometimes the
result of changes of temperature, and shows itself in bars and axles which
have been subjected to protracted friction and vibration.

Specific Gravity. — The specific gravities of the metals, or their relativp
densities, as compared with distilled water at the temperature of 60°, are
shown in the following table ; they include the lightest and the heaviest

solids.

The metal lithium is lighter than all known solids and 1

Osmium . .

. 21-40

Platinum

. . 21-15

Iridium . .

. 21-15

Gold . . .

. 19-3

Tungsten . .

. . 17-6

Mercury . .

. . 13-5

Rhodium . .

. . 12-0

Thallium . .

. . 11-9

Palladium .

. . 11-8

Ruthenium .

. . 11-3

Lead . , .

. . 11-4

Silver . . .

. . 10-5

Bismuth . .

. . 9-8

Cobalt 8-9

Copper 8*9

Nickel 8-8

Molybdenum . . . 8-6

Cadmium .... 8-6

Manganese .... 8*0

Iron 7-8

Iridium 7-2

Tin 7-2

Zinc 7-1

Columbium ... 6-9

Antimony .... 6-7

Tellurium

Arsenic .

Chromium

Titanium

Aluminum

Strontium

Glucinum

Magnesium

Calcium

Sodium .

Potassium

Lithium

quids :-

5-9

5-9

5-3

2-6

2-5

21

1-7

1-5

0-97

0-86

0-59

310 RELATION OF METALS TO HEAT

[The reader is referred to the Appendix for the rules to be observed in
taking the specific gravity of metals and other solids.]

' Relation OF Metals TO Heat. Expansion; Conduction. — The changes
of bulk which metals undergo vi^ith changes of temperature are relatively-
greater than those of other bodies, but each metal has its peculiar rate of
expansion, as shown in the following table, in which 1,000,000 parts of each
metal are supposed to be heated from 32° to 212° : —

Increase Increase 1 Increase ^ Increase

in length. fn bulk. in length. ^ in bulk.

Platinum . . . 1 in 1131 ... 1 in 377 ! Copper . . . . 1 in 5^2 ... 1 in 194

Palladium . . 1 in 1000 ... 1 in 333 | Silver . . . . 1 in 524 ... 1 in 175

Antimony . . 1 in 923 ... 1 in 307 Tin 1 in 516 ... 1 in 172

Iron . . . . 1 in 846 ... 1 in 282 Lead . . . . 1 in 351 ... 1 in 117

Bismuth . . . 1 in 718 ... 1 in 239 Zinc 1 in 340 ... 1 in 113

Gold . . . . 1 in 682 ... 1 in 227 I

The expansion of glass is nearly the same as that of platinum, hence wires
of this metal may be welded into fused glass without inconveuience, but if
we substitute a wire of another metal, its different rate of contraction tends
to break the glass as it cools. So also a compound bar of iron and copper,
or of platinum and silver, formed by riveting strips of the metals to each
Other, though it remains straight at the temperature at which they were
riveted, becomes warped or curved when heated or cooled. The metallic
thermometer, d;nd the compensation pendulum or balance-wheel as applied
to clocks and watches, are illustrations of the same principle. The force
exerted in this act of metallic expansion is so considerable as often to pro-
duce injurious effects when not adequately provided for, as in railways,
bridges, water and gas-pipes, and in the beams, columns, and roofs of
buildings.

That the metals are excellent condnctors of heat is proved by the rapidity
with which heat passes from one end to the other of a metallic bar ; and that
the different metals thus transmit heat with different degrees of facility, is
shown by comparative experiments. If, for instance, two similar bars of
silver and of platinum be heated at one end, the silver will be more rapidly
heated throughout than the platinum. Gold, silver, and copper are among
the best conductors ; then come iron, zinc, and tin ; and lastly, lead. A
consequence of this property of the metals is, that they communicate and
abstract heat more readily than other bodies ; that they feel hotter and colder
than wood, or other bad conductors, though of the same temperature. If
the thermo-conducting power of gold be assumed as = 100, that of silver
will be about 98, of copper 90, of iron 38, of zinc 36, of tin 30, and of lead
Qnly 18.

The polished metals are remarkable for their low power of emitting and of
receiving radiant heat. A polished metallic vessel filled with hot water, is a
long time in cooling ; and such a vessel containing cold water, and placed
before the fire, is a long time in acquiring heat. When the polish is taken
off, the radiating and receptive powers of such vessels are increased ; but
under all circumstances the metals are bad radiators. If we compare the
radiating power of a surface coated with lamp-black, with that of polished
gold, silver, copper, or tin, it is nearly as 100 to 12 ; and all tarnished metals
radiate better than those which are bright and clean.

Fusibility.— "ThQ metals are all susceptible of fusion by heat, but the tem-
peratures at which they liquefy are extremely various. At higher temperatures
than those required for their fusion, the metals are volatih, and many of them
may be distilled in close vessels. Mercury is volatile at temperatures above

RELATIOX OP METALS TO ELECTRICITY AND MAGNETISM. 311

40^. A piece of gold leaf suspended over it in a stopped b(^tle becomes
slowly whitened by amalgamation. Cadmium, potassium, sodium, tellurium,
and zinc, are volatile at a red heat, and arsenic below a red heat. Gold and
silver are converted into vapor when exposed to intense heat; and most of
the other metals evaporate under similar circumstances.

Although the melting-points will be described under the heads of the
respective metals, it will be convenient to give in this place a table showing
how some of the more important metals differ from each other, in regard to
the temperature at which they pass from the solid to the liquid state. The
metals are here arranged in two groups : 1, those which are fusible helow
a red heat (1000°) ; and 2, those which are fusible above this temperature.
The metals not included in this list can be readily fused only under the oxy-
hydrogen blowpipe — one only is described as infusible, namely osmium : —

FUSIBLE BELOW A RED HEAT.

Mercury .... — 40O Lead 620O

Potassium . . . .150

Sodium

Lithium

Tin .

Cadmium

Bismuth

Thallium

200
356
442
442

497
550

Zinc ....

. 773

Red heat in the dark .

. 980

Calcium

. 1000

Magnesium

. 1000

Antimony .

. 1160

Red heat in the daylight

. 1160

lED HEAT.

Gold ....

. 2016O

Cast-iron .

. 2786

FUSIBLE ABOVE A

Aluminum .... 1750O

Silver 1873

Copper .... 1996

Specific Heat of the Metals. — By the term specific heat is meant the
quantity of heat required to raise similar quantities of different substances to
the same temperature. If we thus compare oil and water, it will be found
that the quantity of heat required to raise the temperature of a pound of oil
from 32° to 212° is only half that which is required to produce the same
'change of temperature in water ; hence the specific heat of water being = 1,
that of oil is 0-5 (p. 132). If we thus compare water with mercury we find
that the specific heat of water being = I'OOO, that of an equal weight of
mercury is only 0-033. The specific heat of water, therefore, or, in other
words, its capacity for heat, is very great compared with that of the metals,
as shown in the following table; from which it will also be seen that the
specific heat of bodies increases with their temperatures, so that it requires
more heat to raise them a given number of degrees when they are at a high
than when at a low temperature. The specific heats are in all cases com-
pared with water, as = 1 : —

Between

Between

Between

Between

320 and 212=^.

32^ and 572°.

323 and 212^.

32^ and 572°.

Iron .

. 0-1098 .

.. 0-1218

Antimony

. 0-0507 .

. 0-0547

Zinc .

. 0-0927 .

.. 0-1015

Platinum

. 0-0335 .

. 0-0355

Copper

. 0-0949 .

.. 0-1913

Mercury

. 0-0330 .

. 0 0350

Silver

. 0-0557 .

.. 0-0611

When the specific heat of the elementary bodies is multiplied into their
atomic weights, the product is (with some exceptions) nearly the same (p. 69).

RELATION OP THE METALS TO ELECTRICITY AND MAGNETISM.

In respect to electrical conduction, silver is the best, and mercury the worst
conductor. Assuming the electro-conduction of silver as = 100, that of cop-
per is about 92, gold 65, zinc 24, tin 14, iron 12, lead and platinum about
8, and mercury 2. Professor McGauley gives the relative conducting power

312

POTASSITTM.

of the differ^t metals in reference to their actual efficiency in the battery in
the following order : —

Silver .

. 100-

Magnesium

. 25-47

Coppef

. 74-74

Iron

. 14-44

Gold

. 55-15

Tin .

. 11-45

Sodium .

. 37-43

Platinum

. 10-53

Aluminum

. 33-76

Lead

. 7-77

Potassium

. 28-85

Mercury .

. 1-63

Zinc

. 27-39

These conducting powers are remarkably influenced, in some cases, by
temperature. Thus, in reference to tin, if its conducting power at 32^ be =
16, at 212° it will only be = 10 ; so that, in general, the lower the tempera-
ture of the metal, the higher its elertro-conducting power. Metals which
are bad conductors of electricity become most heated by an electric current,
as is well shown by transmitting a current of electricity through a wire com-
posed of alternate lengths of platinum and silver ; the platinum only becomes
red-hot. The presence of the metalloids interferes with the conducting
power. Thus the conductivity of copper is greatly reduced by the presence
of arsenic as an impurity.

Magnetism. — The peculiarities of iron in respect to magnetism have been
long known, as also its permanent retention by steel. When a bar of iron
is suspended between the poles of a magnet, it is equally attracted by each,
and places itself parallel to the magnetic axis. .Some metals are similarly
affected, though in an inferior degree ; bnt there are others which appear to
be repelled by the magnetic poles, and which, when properly suspended be-
tween them, assume a direction at right angles to the magnetic axis, placing
themselves eqiiatorially. Faraday, who first observed these phenomena,
terms such substances diamagnetics. He has shown that various solids,
liquids, and gases, include magnetic and diamagnetic substances (p. 85) ;
and that, as far as the metals are concerned, they may be arranged in the
following order : —

Magnetic.

Diamagnet

ic.

Iron

Cerium

Bismuth

Silver

Nickel
Cobalt

Titanium
Palladium

Antimony
Zinc

Copper
Gold

Manganese

Platinum

Tin

Arsenic

Chromium

Osmium

Cadmium

Uranium

Sodium

Iridium

Mercury
Lead

Tungsten

CHAPTEE XXIII

POTASSIUM (K = 39).

Potassium (Kalinra) was discovered by Davy in 1807. He obtained it
by submitting caustic potassa to the decomposing action of voltaic electri-
city : the metal was slowly evolved, together with hydrogen, at the negative
pole. By this process, however, it could only be procured in small quanti-
ties, and -other methods have since been devised : that which is now usually
adopted consists in subjecting a mixture of carbonate of potassa and charcoal
to a high temperature, in a wrought-iron distillatory apparatus, to which a

OXIDES OF POTASSIUM. 313

proper receiver is adapted. The potassium which first passes over requires
to be purified by a second distillation, to free it from a quantity of bkick
matter which is of an explosive nature, and consists of a compound of potas-
sium with carbon and carbonic oxide. In these distillations, the contact of
the metal with air must be carefully guarded against : for this purpose it is
usually received into, and preserved under, naphtha, or some liquid hydro-
carbon, upon which it has no action. In this process the carbon deprives
the carbonate of potassa of its oxygen, forming carbonic oxide, which abun-
dantly escapes during the distillation ; and if such decomposition were entire,
69 parts of the carbonate should yield 39 parts of potassium. It would be
as follows : KO,C02+C2=K + 3CO. T3ut the actual product of potassium
falls far short of this result ; and in consequence of some of the potassa
escaping decomposition, and of the formation of carbide and oxicarbide of
potassium, not more than one-fourth of the potassium contained in the mix-
ture subjected to distillation, is usually obtained.

Potassium is a silvery-white metal of great lustre. It instantly tarnishes
and acquires a bluish-white film by exposure to air, and is gradually con-
verted into an oxide. At 60° it is of the consistency of soft wax. Its sp.
gr. is 0*86. It is most conveniently preserved in naphtha, in a well-stopped
phial. It fuses at 150° ; and at a bright red heat, in close vessels, it boils,
and rises in green vapor. At 32° it is brittle, and of a crystallized structure.
If heated in air, it burns with a brilliant flame. It is a good conductor of
electricity and heat, and its lustre is well shown by fusing it under naphtha,
through which it is seen as brilliant as mercury ; or by flatting a clean slice
of it by pressure between two plates of glass. A drop of water placed upon
it causes it instantly to take fire and burn with a violet flame.

Potassium, when placed on alcohol or ether, is rapidly oxidized without
combustion. In reference to alcohol, hydrogen .is evolved, and ethylate
of potash is dissolved. The metal simply displaces part of the hydrogen.
If we place potassium on a layer of ether (in a test-tube) floating on water
colored blue with the infusion of cabbage, the potassium will rapidly disap-
pear, hydrogen being ^evolved ; but the oxide of potassium formed is not solu-
ble in ether. On inverting the tube, and agitating the liquid after the
oxidation of the metal, the alkali will be dissolved by the water producing a
green color in the infusion, while the ether will float to the surface in a clear
and transparent stratum. In this experiment, although the metal is heavier
than ether, it is buoyed up by the hydrogen, and floats upon the surface.
Potassium has no action on chloroform or sulphide of carbon. Mr. Gore
found, on bringing it into contact with anhydrous hydrochloric acid gas,
liquefied under pressure, that no gas was evolved, and it did not dissolve.
{Proc. R. S., May, 1865, p. 208.)

Potassium and Oxygen. — There are three oxides of potassium, namely, a
suboxide =Kfi, a protoxide =K0, which in the state of hydrate constitutes
caustic potassa =KO,HO, and superoxide =K03.

.Suboxide op Potassium (K^O) is formed by heating potassium in a
limited portion of air, or by heating i part of potassium with \\ of iiydrate
of potassa; while hot it is reddish, but gray when cold: it is fusible and
inflammable, taking fire when gently heated. Water converts it, without
combustion, into potassa, hydrogen being evolved.

Protoxide op Potassium. — Anhydrous Potassa (KO) is most readily
obtained by heating 1 atom of potassium =39 with one of hydrate of potassa
=56: hydrogen is evolved, and 2 atoms of protoxide are formed (K+KO,

81^ CAUSTIC POTASSA.

H0=2K0 + H). When 1 atom of potassium acts upon 1 atom of water
oiiUof the contact of air, it is also produced (K4-H0=K0 + H). When
peroxide of potassium is intensely heated, it loses oxygen and leaves prot-
oxide. It is a hard, gray, brittle substance, fusible at a bright red heat, sp.
gr. about 2 65 ; extremely caustic and alkaline.

The composition of this oxide is learned by the action of potassium upon
water; when the metal is placed upon water, or even upon ice, it inflames,
with the evolution of hydrogen, and burns with a violet-colored flame, pro-
ducing a small globule of fused potassa, which, in combining with water,
produces so much heat as to cause a slight explosion. If the potassium is
plunged under water the decomposition ensues with explosive violence. By
carefully employing a small quantity of the metal, wrapped in blotting paper,
and introducing it under a tube inverted in water, the evolved hydrogen may
be collected. It thus becomes the indicator of the quantity of Oxygen taken
by the potassium, 100 parts of which are thus found to combine with 20*51
of oxygen: and 20*51 : 100 :: 8 : 39; so that the equivalent of potassium
thus deduced is 39. When a portion of the metal is laid upon a solution of
red litmus it burns, and the oxide, as it dissolves, turns the red litmus blue.
In an atmosphere of nitrogen, hydrogen is simply liberated without combus-
tion.

Hydrated Protoxide of Potassium; Caustic Potassa (K0,H0) is
procured in decomposing carbonate of potassa by lime. The process con-
sists in boiling in a clean iron vessel pure carbonate of potassa, with half its
weight of pure quicklime, in not less than 7 or 8 parts of water. The lime,
previously slaked, is gradually adiled to the boiling alkaline solution, which
is kept constantly stirred, and towards the end of the operation it is tested
by filtering a small portion, and pouring it into two or three times its bulk
of strong nitric acid; if there be no effervescence, sufificient lime has been
used; but if carbonic acid escapes, the ebullition with lime must be con-
tinued, taking care to keep up the original quantity of water, until the tested
portion shows no signs of carbonic acid. The whole is then allowed to
remain quiet, that the carbonate of lime and excess of the hydrate of lime
may subside ; the clear liquor, or lye, may then be siphoned or poured off,
concentrated by evaporation, strained through a clean calico filter, and set
by in a well-stopped bottle till it admits of being decanted from any sedi-
ment. When the lye is evaporated in a polished iron or pure silver vessel,
it assumes the appearance of an oily liquid, and concretes on cooling. When
cast into sticks it is employed in surgery as a powerful and rapidly-acting
caustic: in this state it generally contains some peroxide and other impuri-
ties, and evolves oxygen and deposits a sediment when dissolved in water.
It is sometimes further purified by boiling it in a silver basin with highly-
rectified alcohol for a few minutes, and then setting it by in a stopped phial ;
when the impurities are deposited, the alcoholic solution may be poured off
and rapidly evaporated to dryness in a silver vessel ; or if the quantity of
alcohol be considerable, it may be distilled off in a silver alembic with a glass
head: the heat may then be raised so as to fuse the potassa, which on cool-
ing shoAild be broken up and preserved in well-closed phials ; if, however,
pure materials and due care are employed, the alcoholic purification may be
dispensed with, for even when so prepared the product contains traces of
carbonate, and sometimes of acetate of potassa.

The pure hydrated oxide is white and somewhat crystalline in texture : its
sp. gr. 2*1. It is fusible at a heat below redness, and evaporates from an
open vessel at a bright-red heat, in the form of acrid fumes. A platinum
wire, dipped into potassa and heated, communicates a characteristic violet

CAUSTIC POTASSA. 315

tint to a colorless flame. At a white heat it is decomposed by charcoal,
and carburetted hydrofren, carbonic oxide, and potassium are the pro-
ducts. It quickly absorbs moisture and carbonic acid from the air, and is
solul)le in half its weio;ht of cold water. When reduced to a powder and
slijz^htly moistened it forms a crystallized combination which is a terhydrate
(K0,3H0). By keeping a stronj]^ aqueous solution of potassa at a low tem-
perature in a stopped phial, crystals may be obtained which are a penta-
hydrate (K0,5H0).

Caustic potassa is highly alkaline, reddening turmeric, and changing
several vegetable blues to green. It acts energetically upon the greater
number of organic products, and saponifies the fat oils. When touched
with moist fingers it has a soapy feel, in consequence of its action upon the
cu.ticle, and it then exhales a peculiar odor: this is also perceptible in the
solution of potassa, and is probably referable to the formation of ammonia,
arising from traces of organic matter accidentally present. In the fused
state, it produces heat when dissolved in water ; but in its crystallized state
it excites considerable cold, especially when mixed with snow. It dissolves
sulphur and several sulphides, and silica and alumina. The oxides of several
of the other metals are also soluble in an aqueous solution of potassa.
* When a solution of caustic potassa is required to be filtered, it is apt to
act upon the filter and to absorb carbonic acid, so that filtration should as
far as possible be avoided, and the liquor obtained clear by subsidence. Oa
the large scale, linen strainers are generally used ; upon the small scale, the
absorption of carbonic acid may be prevented, by covering the funnel with
a plate of glass, and receiving it into a bottle as nearly air-tight as possible.

A solution of potassa acts gradually upon flint glass, which contains oxide
of lead ; hence green glass vessels are preferable ; but when the alkaline
solution is to be exposed to heat, or evaporated to dryness, even these com-
municate impurity, and in such cases vessels of pure silver must be used, for
almost all other metals, platinum not excepted, are more or less acted upon.

The solution of caustic potassa is frequently impure from the presence of
carbonic acid, silica, alumina, lime, oxide of lead, and sulphuric or hydro-
chloric acid. If an effervescence is produced when the solution is dropped
into nitric acid, it indicates the presence of carbonic acid ; if a gelatinous
precipitate is formed, not soluble in a slight excess of acid, it is silica ; if
soluble, it is alumina. The presence of lime is shown by adding oxalate of
ammonia to the solution previously neutralized by nitric acid ; in the same
solution nitrate of silver will indicate hydrochloric acid, or chlorine ; and
nitrate of baryta, sulphuric acid, or sulphates. Freedom from metallic
impurities is shown by sulphide of ammonium., which should occasion no
precipitate or change of color.

The following table shows the quantity of anhydrods potassa contained in
aqueous solutions of different specific gravities. The boiling point of a
saturated solution, sp. gr. 1-68, is 329°; of the officinal solution, sp. gr.
1-OG, 2130

Specific Potassa Specific Potassa Specific Potassa Specific Potassa

gravity, per ceat. gravity, per cent. gravity, per cent. gravity, per cent.

1-68 51-2

1-60 46-7

1-52 42-9

1-47 39-6

1-44 36-8

1-42 34-4

1-39 32-4

1-36 29-4

1-33 26-3

1-28 23-4

1-23 19-5

1-19 16-2

1-15 13-
1-11 9-5
1-06 4-7

Alkalimetry. — One of the most simple methods of determining the strength
of a solution of potash is to find, by the use of a graduated burette, the
number of measures of a standard sulphuric acid required to neutralize a
given weight of hydrate of potash. A convenient strength of acid for this

316 HYPOCHLORITE OF POTASSA.

purpose may be made by mixing about one part of the monohydrated sul-
phuric acid by weight with six parts of water. The sp. gr. of an acid thus
used was 1-1268, and three measures of it from the burette were found to
neutralize ten grains of pure hydrate of potash.

As an illustration, a flnidounce of a solution of potash, weighing 500
grains, was colored of a faint blue with litmus infusio.n. The standard acid
was poured from the burette, and the liquid kept well stirred until the
faintest reddening of the liquid begins to show itself. It was found that
eleven measures of the acid had been required to completely neutralize this
quantityof the alkaline liquid. Hence, 3 : 10 : : 11 : 36'6 ; and 36 6^ 5=
T'32 per cent, of hydrate of potash in the alkaline solution. This corre-
sponds to 6' It per cent, of anhydrous potash.

•

Peroxide op Potassium (KO3) is formed when potassium is burned with
free access of air, or in oxygen gas ; it is a yellow fusible substance, which,
on cooling, acquires a crystalline apj:Jearance. It has some singular pro-
perties; it supports the combustion of most of the inflammables, .and, when
heated in hydrogen, diminishes the bulk of the. gas, and forms water; it
decomposes ammonia under the same circumstances. When put into water,
oxygen is evolved, and a solution of potassa obtained. When hydrated'
potassa is fused in an open crucible, a portion of its water is disengaged, and
oxygen is absorbed, so as to form this peroxide ; hence it is that common
caustic potassa almost always gives out oxygen when put in water.

Potassium and Chlorine; Chloride of Potassium (KCl). — Potassium
burns brilliantly in chlorine, especially if introduced into the gas in the state
of fusion, as, otherwise, a crust of chloride is apt to form and protect the
interior from further action. When potassium is heated in gaseous hydro-
chloric acid, chloride of potassium is formed, and hydrogen evolved :
K4-HC1=KC1 + H. It is also formed by dissolving potassa or its carbonate
in hydrochloric acid, and evaporating to dryness. The affinity of potassium
for chlorine exceeds that for oxygen ; so that potassa heated in chlorine,
loses oxygen, and yields chloride of potassium : hence, also, potassium heated
with other chlorides, evolves their bases and forms chloride of potassium.
When chlorine is passed over iodide of potassium at a red heat, iodine is
expelled, and chloride of potassium formed.

Chloride of potassium dissolves in three parts of water at 60°. One part
of the powdered salt stirred into four parts of cold water, produces a de-
pression of temperature of between 20° and 25°, whereas chloride of sodium
under the same circumstances only depresses the thermometer between 2° and
3° : hence it has been proposed to estimate the relative proportions of these
chlorides when mixed, by the depression of temperature resulting from their
solution. Chloride of potassium crystallizes in cubes ; its taste is saline and
bitter. Its sp. gr. is 1-9. In old pharmacy it was called digestive salt of
Sylvius. It is insoluble in alcohol. When intensely heated in open vessels,
it evaporates in the form of white fumes. This salt is a residue of several
chemical and pharmaceutical processes, and is sometimes found in rough
saltpetre ; it is also contained in kelp, and in the juices of many plants.
The crystals, which occur in old pharmaceutical extracts, are usually of this
salt. The manufacturers of alum occasionally employ it as the source of
potassa in that salt.

Hypochlorite of Potassa (K0,C10), called also chloride of potassa, and
chlorinated potassa has only been obtained in solution by adding aqueous
hypochlorous acid to a solution of potassa. When chlorine is passed into a

CHLORATE OF POTASSA. 31Y

solution of carbonate of potassa so as not quite to saturate the alkali, car-
bonic acid is evolved, and a solution of hypochlorite of potassa is obtained,
provided the liquor be kept cold. If heated, or if more than one atom of
chlorine to one of potassa be used, the hypochlorite is decomposed, and part
of the bleaching power of the solution destroyed. A solution of hypochlo-
rite of potassa is also obtained by double decomposition, when solution of
hypochlorite of lime is mixed with carbonate of potassa. It is colorless,
powerfully bleachinj?, and antiseptic. When chlorine is passed over slightly
moistened carbonate of potassa, a bleaching salt mixed with bicarbonate is
the result.

Chlorate of Potassa (KOjClOj is formed- by passing excess of chlorine
through a strong solution of potassa: chloride of potassium is one of the
results, the other is chlorate of potassa, a salt in brilliant rhomboidal tables
(formerly called oxymuriate of potassa). By concentrating the liquid, the
chlorate of potassa, which is much less soluble in cold water than the chloride
of potassium, is deposited on cooling. The action of chlorine upon a solution
of carbonate of potassa at first produces bicarbonate of potassa, which, by
the continued action of chlorine, is decomposed, the whole of the carbonic
acid expelled, and hypochlorite of potassa and chloride^of potassium are then
formed; 6K0 + 6C1 = 3KC1 + 3[K0,C10] : the hypochlorite is itself after-
wards resolved into chlorate and chloride: 3[KO,C10]=KO,C105+2KCl:
so that the ultimate result may be thus represented: 6K0-f GCl=5KCl-^-
KO,C105.

The following is the most economical process for the preparation of this
chlorate : One equivalent of carbonate of potassa and one of hydrate of
lime are mixed and exposed to a current of chlorine ; the mass becomes hot,
and evolves water during the absorption of the gas : when saturated, it is
gently heated to complete the decomposition. No oxygen is evolved, the
action being such that 6[K0,C0J, and 6[CaO,HO], acted on by 6C1, yield
5KCl4-6[CaO,COJ + KO,C103; whilst 6H0 are evolved. By the action
of water, the soluble salts are separated from the carbonate of lime, and
the chloride and chlorate by crystallization.

Chlorate of potassa is an anhydrous salt of a cooling taste. It forms tabu-
lar crystals of a pearly lustre. Its specific gravity is 19. When pure, its
aqueous solution is not rendered turbid by nitrate of silver. When tritu-
rated, it appears phosphorescent. It decrepitates and fuses at a temperature
between 400^ and 500°: at a higher heat it effervesces, and gives out nearly
40 per cent, of oxygen, and chloride of potassium remains {see p. 90). It is
soluble in 18 parts of cold, and in 25 of boiling water; and in about 120
parts of alcohol. , It acts energetically upon many inflammables, and when
triturated with sulphur, phosphorus, and charcoal, produces inflammation
and explosion. A mixture of three parts of this chlorate with one of sulphur,
detonates loudly when struck with a hammer, and even sometimes explodes
spontaneously. When sulphuric acid is dropped upon mixtures of this salt
and combustibles, ignition ensues, in consequence of the evolution of peroxide
of chlorine. A mixture of sugar and the chlorate thus treated, is immedi-
ately kindled; and a mixture of sulphide of antimony and the salt, suddenly
deflagrates with a bright puff of flame and smoke ; the latter mixture requires
to be cautiously made, as it often takes fire by gentle trituration. When
mixed with finely-powdered metallic antimony or zinc, and a little starch or
sugar, it causes, on the application of heat or of sulphuric acid, a violent
combustion of those metals with oxidation. Two parts of finely-powdered
magnesium with one of chlorate, ignited by he||, produce the instantaneous
light employed in photography. This light has great actinic power. The

318 IODIDE OF POTASSIUM.

fulminating compound used in the Prussian needle-gun consists of five parts
of chlorate of potash, three parts of sulphide of antimony, and two parts of
sulphur — the ingredients being finely powdered, and mixed together by
sifting. .

Perchlorate of Potassa; Oxychlorate of Potassa (K0,CI07). — This
salt is formed when chlorate of potassa is heated in a porcelain crucible till
it fuses, and by giving out a portion of oxygen, becomes thick and pasty ;
the cooled mass, dissolved in hot water, deposits perchlorate of potassa on
cooling, which may be purified by recrystallization. The chloride of potas-
sium and undecomposed chlorate remain in solution. The action of heat on
2 equivalents of the chlorate forms one of chloride of potassium, and 1 of
perchlorate ; while 4 of oxygen are evolved; 2(KO,C105)=KCl + KO,CI07
-fO^. This salt forms anhydrous rhombic crystals, soluble in 65 parts of
water at 60 ; at a high temperature it is resolved into oxygen and chloride
of potassium.

Iodide of Potassium (KI). — Iodine and potassium act upon each other
very energetically, and often with explosion, and a white, fusible crystalline
compound is obtained. When hydriodic acid is saturated with potassa,
and the solution carefully evaporated, anhydrous crystals of the iodide are
obtained. The usual mode of procuring this compound consists in dissolving
iodine in solution of potassa till it begins to assume a brown color ; on evapo-
rating to dryness, and fusing the residuary salt at a red heat, iodide of potas-
sium remains, generally mixed, however, with a little iodate ; if a little
charcoal is added previous to fusion, the decomposition is complete. If,
instead of fusing the products, the solution be evaporated nearly to dryness,
and alcohol poured upon it, the iodide is dissolved, and iodate of potassa
remains, which, at a red heat, evolves oxygen, and becomes iodide of potas-
sium. The action of iodine upon the alkali corresponds with that of chlorine ;
that is 6K0, and 61, produce 5KI, and KO,IO, ; and then, by the application
of heat, K0,I05 becomes KI, and 60 are given off. Iodide of potassium
is also prepared by decomposing a solution of iodide of iron or of zinc, by
carbonate of potassa, and filtering and evaporating the resulting solution;
Fel + KCCOg become KI, and FeO,CO,.

Iodide of potassium forms cubic crystals, of an acrid saline taste ; they
are anhydrous, and slightly deliquescent in damp air. 100 parts of water at
65° dissolve 143 of this salt, and a considerable depression of temperature
is produced during the solution. It should be purchased in crystals, which
ought not to be very deliquescent, and should dissolve in six or eight parts
of alcohol, sp. gr. -836. They generally redden turmeric, from the presence
of a little carbonate of potassa. The usual impurities in the iodide, are
chloride of potassium and sodium, iodate of potassa, and water. To detect
chlorine, the iodide may be decomposed by nitrate of silver, and the washed
precipitate digested in a strong solution of ammonia; if the filtered solution,
acidified by nitric acid, gives a white precipitate, it is chloride of silver. To
detect iodate of potassa, add to the solution of iodide a solution of tartaric
acid. If a yellow or brown color is produced, this indicates the presence of
iodate. When starch is added, the liquid acquires a deep blue color. The
aqueous solution of iodide of potassium dissolves a considerable portion of
iodine ; this solution, under the name of ioduretted iodide of potassium, is
used in medicine. Iodide of potassium is decomposed by chlorine, and even
When largely diluted, a minute quantity of chlorine discolors the solution ;
sulphuric or nitric acid (coiltaining nitrous acid) also decomposes it. Chlo-
ride of palladium reddens a solution containing only a 12,000th of the iodide ;

nitrIte of potassa. 319

and protonitrate of mercury produces a yellow cloud, where only a CO, 000th
is present. Paper which has been bleached by chlorine is generally dis-
colored by iodide of potassium; and if characters are written or figures drawn
with a solution of iodide of potassium, they are rendered visible, in the manner
of sympathetic ink, by the slightest breath of chlorine. When paper imbued
with a mixed solution of starch and iodide of potassium is exposed to the air
in certain situations, it sometimes becon)es more or less discolored in conse-
quence of the presence of ozone (p. 114); there are other causes, however,
which may occasionally produce this change. Ozonized ether and oil of tur-
pentine decompose it and set free iodine.

loDATE OF Potassa (KO.TOJ is one of the products of the action of
iodine on a solution of potassa ; after evaporation the iodide of potassium
maybe separated from the iodate by digestion in alcohol sp. gr. -810, which
leaves the latter salt undissolved. Iodate of potassa requires about 14 parts
of water at 60° for its solution ; it is insoluble in absolute alcohol. Its
crystals are small cubes, permanent in the air ; at a red heat it gives out.
between 22 and 23 per cent, of oxygen, and is converted into iodide of potas-
sium, no periodate being intermediately formed. Its aqueous solution is
decomposed by sulphuretted hydrogen, and by sulphurous and arsenious
acids.

Bromide of Potassium (KBr). — Potassium and bromine act intensely
upon each other, evolving heat and light, and producing explosion. When
bromine is dropped into a solution of potassa, the mixture evaporated, and
the residue heated to redness, bromide of potassium is also obtained. Its
sp. gr. is 2*4 ; it is white, fusible, and crystallizes in cubes, easily soluble in
water, and slightly so in alcohol. It is sometimes prepared for medicinal
use by decomposing bromide of zinc or bromide of iron, by carbonate of
potassa ; it should be purchased in crystals, as it is otherwise apt to be
impure.

Nitrate of Potassa ; Nitre ; Saltpetre (K0,N05). — This salt is prin-
cipally brought to this country from the East Indies, where it is produced
by lixiviation from certain soils ; but the mode or cause of its formation is
not well understood ; it is probably connected with the oxidation of ammonia.
The greater part of the rough nitre imported from the East Indies is in
brqJven-down crystals, wliich are more or less deliquescent ; exclusive of other
implrities, it often contains a considerable portion of common salt, which,
reacting upon the nitre, sometimes induces the production of nitrate of soda
and chloride of potassium ; it also usually contains sulphate of lime and
traces of organic matter. In Germany and P'rance, it is artificially produced
in what are termed nitre-beds. The process consists in lixiviating old plaster
rubbish, which, when rich in nitre, affords about five per cent. Refuse animal
and vegetable matter, which has putrefiefl in contact with calcareous soils,
produces nitrate of lime, which affords nitre by mixture with carbonate of
potassa.

Nitre crystallizes in anhydrous, six-sided prisms, usually terminated by
dihedral summits. Its sp. gr. is about 2. The solubility of nitre varies
extremely with temperature : at 32°, 100 parts of water dissolve 13 2 of the
salt; at 77°, 38 parts; at 132°, 97 parts ; at 176°, 169 parts; and at 212°,
246 parts. During the solution of 1 part of powdered nitre in 5 of water,
the temperature sinks from 50° to 35°. It is insoluble in pure alcohol. The
crystals of nitre, though the salt is anhydrous, generally contain interstitial
water ; so that they appear moist when powdered, and lose weight on drying.

3$0 gunpowder!

The taste of nitre is cooling and peculiar. At a temperature of about 600°,
nitre fuses without undergoing change of composition, and congeals on cool-
ing. Sometimes it is cast into small balls or cakes, called sal prunella . At
a red heat, nitre is slowly decomposed ; and highly heated in an earthen re-
tort, or gun-barrel, it affords oxygen gas, mixed with a portion of nitrogen.
In this decomposition, the nitre is first converted into byponitrite of potassa,
which is somewhat deliquescent; potassa is the final result.

Nitre is rapidly decomposed by charcoal at a red heat, and the results are
carbonic oxide and acid, nitrogen, and carbonate of potassa, sometimes
called wJiite flux. These mixtures of nitre and charcoal form the basis of a
variety of compositions used for fireworks, the rapidity of the combustion
being modified by the relative proportion of the charcoal. When phosphorus
is thrown upon nitre, and inflamed, a vivid combustion ensues, and a phos-
phate of potassa is formed. Sulphur sprinkled upon hot nitre burns, and
produces a mixture of sulphate and sulphite of potassa. Many of the metals,
when in filings or powder, deflagrate and burn when thrown on red-hot nitre.
A mixture of 3 parts of nitre, 2 of dry carbonate of potassa, and 1 of sul-
phur, fovm^ fulminating powder. If a little of this is heated to about 330°,
it blackens, fuses, and explodes with violence, in consequence of the rapid
action of the sulphur upon the nitre, and the sudden evolution of nitrogen
and carbonic acid, the residue being chiefly sulphate of potassa, 3[K0,N0J
-f2[KO,COJ + 5S=5[KO,S03] + 3N4-2CO,. The action of sulphuric
acid on nitre has been already described (p. 175). When nitre and hydro-
chloric acid are heated together, chlorine and nitrous acid are evolved, and
on evaporation to dryness, chloride of potassium remains.

Gunpowder consists of a mixture of nitre, sulphur, and charcoal, the pro-
portions varying according to the uses made of it, as follows : —

Common

Shooting

Shooting

Miners'

gunpowder.

powder.

powder.

powder.

Saltpetre .

. 75-0

78

76

65

Charcoal .

. 12-5

12

15

15

Sulphur .

. 12-5

10

9

20

Per cent.

101

75-0

16

11-8

18

13-2

The explosive force of gunpowder depends upon the sudden formation of
nitrogen and carbonic acid gases, which, at the high temperature at which
they are evolved, may be considered as amounting to about 1500 times the
volume of the powder employed. Supposing the combustion perfect, and
the powder to consist of : —

Per cent. ^

1 equivalent of nitre ....
1 " sulphur ....

3 " carbon ....

135 100-0

the resulting products may be thus* represented : K0,N03-f S-f C3=3CO.,-f
N-fKS, the only residue being sulphide of potassium, which gives the fetid
odor to the washings of a gun-barrel. The temperature required for the
explosion of gunpowder, is a black heat between 500° and 600°. Below
600° the sulphur is volatilized from the other ingredients. The presence of
nitrate of soda is as a rule injurious, owing to its tendency to absorb moist-
ure from the air, but as it is cheaper than nitre it is sometimes added to gun-
powder for blasting purposes. A powder of this kind had the composition
of sulphur 10 parts, charcoal 15 parts, nitrate of potash 56 parts, and
nitrate of soda 18 parts.

In the manufacture of gunpowder, the nitre and sulphur should be pure,

NITRITE or POTASSA. 321

the charcoal carefully selected and prepared, and the whole perfectly mixed
in fine powder. This mixture is moistened, ground and pressed into a cake ;
it is then granulated, dried, and polished by attrition in revolving barrels.
The granular form of the powder increases the rapidity of its combustion, by
enabling the flame so to penetrate it as to kindle every grain nearly at the
same time ; but this combustion, though very rapid, is by no means instanta-
neous, for in that case scarcely anything would resist its power, and its
explosion would more resemble that of fulminating mercury or silver, and
would burst the gun instead of propelling the ball. A cubic foot of good
gunpowder should weigh about 58 pounds ; and 2 ounces of it when ex-
ploded in a mortar 8 inches in diameter, and placed at an angle of 45°,
should throw a 68 lb. shot about 270 feet. Gunpowder is sometimes tried
by placing two heaps of about sixty grains each upon clean writing-paper,
three or four inches asunder, and firing one of them by a red-hot wire ; if
the flame ascends quickly with a good report, sending up a ring of white
smoke, leaving the paper free from specks and not burnt into holes, and if
no sparks fly from it so as to set fire to the contiguous heap, the powder is
good. Mr. Gale has lately patented a process for rendering gunpowder un-
explosive. It consists in mixing 4 parts of finely-powdered glass with 1
part of powder. When thoroughly mixed, the gunpowder does not explode
on applying a red heat, but it burns with deflagration. The glass is incom-
bustible and non-conducting : and it acts by preventing the communication
of the flame from one particle to another. The difiBculty arises, however, in
rapidly separating the glass completely, unless the gunpowder is made very
coarse — the large proportion of glass used would increase the bulk for storage
enormously, and in transport by sea or rail the gunpowder would have a ten-
dency to separate from the glass. On the whole, the process is not practi-
cably available for insuring safety without rendering the gunpowder useless.
Analysis. — Weigh off 100 grains of the powder, and dry it at 212° to
estimate the moisture ; then wash it upon a filter with boiling water, which
dissolves out the whole of the nitre ; dry the washed residue, and digest it
in bisulphide of carbon, which abstracts the sulphur and leaves the charcoal.
The aqueous solution, if the nitre be pure, should not be affected by nitrate
of silver or nitrate of baryta.

Action op Potassium on Ammonia ; Potassiamide. — When potassium is
heated in gaseous ammonia, hydrogen is evolved, and an olive-colored sub-
stance is obtained, of a crystalline fracture. It burns in oxygen, producing
hydrated potassa, and nitrogen ; exposed to air, it deliquesces, and evolves
ammonia; water acts upon it, producing potassa and ammonia. The volume
of hydrogen evolved by this action of potassium on ammonia, is the same as
that which it would have evolved from water ; so that when 1 atom of potas-
sium acts upon 1 of ammonia, 1 of hydrogen is evolved, and the remaining
elements of the ammonia (namely, 1 atom of nitrogen and 2 of hydrogen)
combine with the potassium. As 1 of nitrogen and 2 of hydrogen constitute
amidogen, the resulting compound has been termed />o«as5^«m^G?e, its formula
being KjNHg-, an atom of the hydrogen of the ammonia being replaced by
an atom of potassium. Heated in hydrogen, potassium absorbs a portion of
that gas, and forms a gray hydride, which is very inflammable: it is decom-
posed by the contact of mercury ; it is said to consist of 1 atom of hydrogen
combined with 4 of potassium.

Nitrite op Potassa. Hyponitrite of Potassa: Potassium Nitride (KO,
NOg). — This salt is obtained by heating nitrate of potassa so as to expel two
atoms of oxygen. It is thus procured as a white neutral deliquescent solid,
21

322 SULPHIDES OF POTASSIUM.

very soluble in water. It is also soluble in alcohol, and it may thus be dis-
tinguished and separated from the nitrate. It may be obtained crystallized
from the hot aqueous solution. Its solution is precipitated white by nitrate
of silver, and the hyponitrite of silver thus obtained may be decomposed by
any alkaline chloride and other hyponitrites produced. The silver salt is
soluble in a large quantity of water and in nitric acid. Stahlschmidt has
found that when finely-divided zinc is boiled with a solution of nitrate of
potassa, the salt is reduced to hyponitrite. A saturated solution of nitrate is
gently heated with one-tenth of its volume of ammonia, and zinc in powder
is added. At from 80° to 100° there is a rapid action which may be reduced
if necessary by cooling the liquid. In half an hour the reduction is so far
complete, that on adding to the liquid twice its volume of alcohol there is no
precipitation of nitrate. The free potassa in the solution may be neutralized
by nitric acid and separated by crystallization. Any oxide of zinc formed
may also be removed.

The hyponitrite of potassa has many useful reactions. Sulphuric acid added
to the dry salt sets free deutoxide of nitrogen, producing in the air the usual
ruddy fumes of nitrous acid. In this respect the hyponitrite is strongly dis-
tinguished from the nitrate. In the following experiments with the solution of
hyponitrite, a small quantity of diluted sulphuric acid should be added. When
a solution of hyponitrite is added to a diluted solution of chloride of gold and
the liquid is warmed, metallic gold is precipitated ; when added to a solution of
permanganate of potash the pink color is discharged — to iodide of potassium,
iodine is set free — to freshly-precipitated resin of guaiacum, a beautiful blue
color is produced — to a solution of sulphate of indigo the color is discharged;
and lastly, when added to a solution of green sulphate of iron, the liquid
becomes of a dark brown color, owing to the deutoxide of nitrogen producd
being dissolved by a portion of the undecomposed sulphate. In some of
these reactions the hyponitrite acts by removing, and in others by imparting
oxygen. Hence the acid of this salt is an oxidizer and deoxidizer.

Sulphides of Potassium. — When sulphur and potassium are heated in
an exhausted tube, vivid combustion ensues, and if atomic proportions are
observed, a protosulphide of potassium is formed =KS. So also when a
stream of hydrogen is passed over heated sulphate of potassa, water and the
protosulphide are the results: (KO.SO^-f 4H=KS-f 4H0). If a mixture
of 2 parts of sulphate of potassa and 1 of lamp-black is heated out of the
contact of air, a pyrophorus is formed, which is a mixture of the protosul-
phide and charcoal. A solution of this protosulphide is obtained by dividing
a solution of caustic potassa into two equal parts, and saturating one of
them with sulphuretted hydrogen, by which the compound KS,HS is formed,
and which, when mixed with the other half of the solution, is converted into
protosulphide: KS,HS,+K0=2KS-f HO. When this solution is evapo-
rated, it yields a nearly colorless crystalline product, acrid and alkaline, and
evolving sulphuretted hydrogen when an acid is added : thus (with sulphuric
acid) KS4-S03HO=KO,S03-f HS. It absorbs oxygen when exposed to
air, and becomes yellow.
^ Bisulphide of Potassium (KS,) is formed by heating four parts of potas-
sium with three of sulphur ; or by exposing an alcoholic solution of KS,HS
to the air, till it begins to deposit sulphur, and then evaporating in vacuo ;
it is an orange-colored fusible substance. Tersulphide of Potassium (KS3) is
formed by passing the vapor of bisulphide of carbon over carbonate of potassa
at a red heat ; carbonic oxide and carbonic acid are evolved ; 2(K0,C0J -f
3CS.=C02-|-4CO,-f 2KS3. The substance formerly known under the name
of Liver of Sulphur, is a mixture of this tersulphide with sulphate of potassa ;

CARBONATE OF POTASSA. 323

it is obtained by heatinp: 70 parts of carbonate of potassa with 40 of sulphur ;
carbonic acid is evolved and 3KS3+KO,S03 is produced. Tetrasulphide of
Potassium (KSJ is formed by passing the vapor of sulphide of carbon over
heated sulphate of potassa. Pentasulphide of Potassium (KS^) is formed
when solutions of the preceding sulphides are boiled with excess of sulphur ;
or when a solution of caustic potassa and excess of sulphur are boiled
together. In this case, 3 equivalents of potassa and 12 of sulphur, yield 2
equivalents of the pentasulphide and 1 of hyposulphite of potassa; 3K04-
12S=2KS,+KO,SA.

Sulphate of Potassa (KOjSOg). — This salt is the result of several
chemical operations carried on upon a large scale in the processes of the
arts. It is the sal de duohus of the old chemists. Its taste is bitter and
saline. It crystallizes in short six-sided prisms, terminated by six-sided
pyramids. They are anhydrous, and soluble in about 12 parts of water at
60^, and insoluble in alcohol. This salt is thrown down when sulphuric
acid is added to a moderately strong solution of potassa. When about 2
parts of sulphate of potassa and 1 of lamp-black, intimately mixed in jBne
powder, are heated to redness in a coated phial, and great care taken to
exclude the air during cooling, the product takes fire on exposure to air.
It appears to contain a compound of potassium, which powerfully attracts
oxygen, and thus evolves heat enough to inflame the charcoal and sulphur.

BisuLPHATE OF PoTASSA (KO,HO,2S03) is formed by heating in a pla-
tinum crucible 87 parts of sulphate of potassa with 49 of sulphuric acid.
When one atom of sulphate is dissolved in from 3 to 5 atoms of the acid,
and evaporated to crystallization, an anhydrous bisulphate first forms in
acicular crystals, but in a few days it liquefies and is converted into rhora-
boidal hydrated crystals. This salt is not decomposed below redness ; at a
red heat it gives out sulphuric acid, sulphurous acid, and oxygen, and is
converted into the neutral salt. It is soluble without decomposition in
about half its weight of boiling water, but by large quantities of water it is
resolved into neutral sulphate and acid. Bisulphate of potassa is also formed
by the distillation of 1 atom of nitre and 2 of sulphuric acid, as in the pro-
cess for obtaining Nitric Acid. Under the old name of sal enixum, it is
used for cleansing metals.

Carbonate of Potassa (KO.COJ is a salt of much importance, and
known in different states of purity under the names of wood-ash, pot-ash,
pearl-ash, subcarbonate of potassa : it was formerly known as salt of tartar.
It may be obtained directly, by passing carbonic acid into a solution of
potassa, till saturated, evapol^ting to dryness, and exposing the dry mass to
a red heat ; or indirectly, by burning purified tartar (bitartrate of potassa),
lixiviating the residue, and evaporating to dryness. A mixture of purified
tartar and nitre projected into a crucible heated to dull redness, also affords
carbonate of potassa, which may be obtained by lixiviation as the preceding.
When succulent vegetables are dried and burned, their potassa-salts are for
the most part converted into carbonate, hence the term vegetable alkali ;
and particular plants a'fford it in larger quantities than others. The younger
branches of trees afford more than the old wood, hence their selection as a
source of wood-ash.

Carbonate of potassa is generally derived from two sources, namely, from
the carbonate of commerce, or from the bicarbonate. The carbonate of
potassa of commerce is purified by lixiviating it with its weight of cold
water ; being more soluble than the salts which usually accompany it, these

324 CARBONATE OF POTASSA.

remain undissolved, and the solution, poured off, strained or filtered if ne-
cessary, and evaporated, leaves the carbonate of potassa. Or the crude
carbonate may be dissolved in water, filtered, evaporated till the solution
acquires the sp. gr. 1-52, and set aside in a cold place, when the greater
part of the foreign salts are deposited, and the solution of the carbonate
may be poured off; with every precaution, however, when thus obtained, it
is still impure. When required pure, it is obtained by heating the crys-
tallized bicarbonate to a temperature below redness, but sufficient to expel
its water and half of its carbonic acid. When equal parts of bitartrate and
nitrate of potassa are burned in successive portions in an iron crucible, the
residuary carbonate was formerly called white flux: when 2 parts of tartar
are used to 1 of nitre, the whole of the charcoal is not consumed, and the
product was called black flux ; these compounds being used in fusing or
fluxing metallic ores.

Carbonate of potassa is fusible without decomposition, at a red-heat; its
sp. gr. is 2 24 : it is very soluble in water, which at 55° takes up nearly its
own weight. It deliquesces by exposure to air, forming a dense solution,
formerly called oil of tartar. Its taste is alkaline, and it has a strong alka-
line action upon test-papers. It is insoluble in absolute alcohol. A satu-
rated solution of carbonate of potassa in water contains about 48 per cent,
of the salt, and has a sp. gr. of \h. When this solution is evaporated till
its sp. gr. becomes 1*62, it yields deliquescent crystals which include 2 atoms
of water. The solution will commonly be found to contain traces of sulphate
and chloride, as well as oxide of lead dissolved from the glass. These im-
purities may be detected by their appropriate tests. As carbonate of potassa
is usually derived from the ashes of vegetables, its production is limited to
countries which require clearing of timber, or where there are vast natural
forests. If vegetables growing in a soil not impregnated with sea-salt are
burned, the residue, which is in the form of a brown saline mass, contains a
large relative proportion of this carbonate, and is commonly called rough, or
crude potassa. If it be again calcined so as to burn away the carbonaceous
matter, it becomes a white mass, generally termed poarlash.

The pearlash of commerce contains a variety of impurities, which render
it of variable value. In general, its purity may be judged of by its easy
solubility in cold water, 2 parts of which should entirely dissolve 1 part of
the salt; the residue consists of impurities. The quantity of acid of a given
strength, requisite to saturate a given weight, may also be resorted to as a
criterion of its purity. Now 355 grains of diluted sulphuric acid of the
specific gravity of 1-141 neutralize 100 grains of pure carbonate of potassa.
Hence, if we dissolve 100 grains of the alkali to be examined, in six or
eight parts of .water, and gradually add the test sulphuric acid till we find,
by the application of proper test-papers, that the alkali is exactly neu-
tralized, we may deduce, from the weight of the acid consumed, the propor-
tion of real carbonate present: for as 355 is to 100, so is the weight of the
test-acid employed, to that of the pure carbonated alkali present. To save
trouble, the acid properly diluted may be put into a glass tube so graduated
as to show directly the value of the alkali by the quantity consumed in its
saturation. Thus we find, by reference to the scale of equivalents, that 100
parts of carbonate of potassa are saturated by 70 of sulphuric acid, specific
gravity 1-84. If, therefore, we put 70 grains of such acid into a tube divided
into 100 parts, and fill it up with water, it follows that the quantity of car-
bonate of potassa existing in any sample of pearlash under examination, will
be directly shown by the measure of such diluted acid required for saturation ;
100 grains of the sample, if pure carbonate, would require the whole 100
measures of acid ; but if only containing 50 ^er cent, of pure carbonate, the

CYANIDE OP POTASSIUM. CYANATE OP POTASSA. 325

100 grains would be saturated by 50 measures of the test-acid, and sq on.
Such graduated tubes are called alkalimeters, and are to be obtained from
the makers of chemical apparatus, together with practical directions for
using them.

Bicarbonate op Potash (K0,H0,2C02) is formed by passing carbonic
acid into a solution of the carbonate, or by subjecting the moist carbonate
to excess of gaseous carbonic acid. It may also be obtained by the action
of sesquicarbonate of ammonia on carbonate of potassa, in which case pure
ammonia is evolved. Bicarbonate of potassa forms hydrated prismatic crys-
tals, which are not deliquescent, and taste slightly alkaline. Thej require
for solution about four parts of water at 60°. Boiling water dissolves
nearly its own weight, but during the solution a portion of carbonic acid is
evolved, and by long boiling, the salt is said to become a sesquicarbonate,
or even carbonate. The solution has an alkaline reaction, and possesses
most of the chemical properties of the carbonate. It is distinguished from
the carbonate — 1, in giving no precipitate in the cold, with a solution of
sulphate of magnesia: and 2, in producing a pale yellowish precipitate
with a few drops of a solution of corrosive sublimate. A solution of the
carbonate gives immediately a brick-red precipitate of oxychloride of mer-
cury. Bicarbonate of potassa is nearly insoluble in absolute alcohol. Exposed
to a red heat, it evolves carbonic acid and water, and carbonate of potassa
remains. This salt is generally pure, or very nearly so, and may be con-
veniently resorted to for the preparation of the carbonate and other salts,
when purity is required.

Cyanide op Potassium (KNCg or KCy) is obtained by heating to red-
ness, in a covered crucible, a mixture of 8 parts of dry ferrocyanide of
potassium, and 3 of dry carbonate of potassa, till it no longer gives off gas ;
the iron subsides, and the fused product, when poured off, concretes into a
white mass, which is a mixture of the cyanide and of cyanate of potassa, the
reaction being as follows : 2(K,FeCy3)-f 2(KO,CO,)=5(KGy) + KO,CyO +
Fe2+2C02. The formation of the cyanate maybe prevented by adding to
the mixture before fusion an eighth of its weight of powdered charcoal ; the
fused mass may then be digested in boiling alcohol, from which the cyanide
of potassium crystallizes on cooling.

Cyanide of potassium should be carefully preserved out of the contact of
air and water: it may be fused without decomposition, provided air be
excluded, and is not changed by a red heat ; but with the access of oxygen
it becomes cyanate of potassa: KCy + 20=KO,CyO. Its taste is pungent
and alkaline, accompanied with the flavor of hydrocyanic acid, and it is very
poisonous. It is very soluble in water, and may be obtained from its solu-
tion, in anhydrous cubic crystals : it is but little soluble in cold alcohol,
which throws it down from its recent and cold aqueous solution : exposed to
air, it becomes moist and smells of hydrocyanic acid. It is a powerful
reducing agent, as respects oxides and sulphides, and as such, is used in
mineral analysis : the oxides of copper, and those of tin, iron, and lead, are
immediately reduced when sprinkled into the fused cyanide. When cyanide
of potassium effervesces with acids, it contains either cyanate or carbonate
ef potassa ; a yellow tint indicates the presence of iron : if it blackens when
calcined, it is contaminated by formate of potassa.

Cyanate op Potass (KO,CyO). — The \)reparation of this salt has been
described under Cyanic Acid (p. 280). It is decomposed both by water
and acids, which convert the cyanic acid into carbonic acid and ammonia ;

326 FERROCYANIDE OF POTASSIUM.

in fact, by exposure to air, it exhales ammonia, and becomes bicarbonate of
potassa. It crystallizes in small plates ; tastes like saltpetre ; is anhydrous ;
and in close vessels excluded from air and moisture may be fused without
decomposition.

SuLPHOCYANiDE OF POTASSIUM (K.NCaS^) may be formed by boiling 2
equivalents of finely-powdered sulphur in a solution of 1 equivalent of cya-
nide of potassium : it yields prismatic crystals which are of a cooling bitter
taste, deliquescent, and anhydrous. In close vessels this salt fuses and con-
cretes on cooling into an opaque crystalline mass : heated in the air, it is
decomposed, and if moisture be present, carbonate of ammonia and sulphide
of potassium are formed. For the chemical characters of this and other
sulphocyanides, see page 288.

Ferrooyanide OF Potassium. Prussiate of Potassa (K3,Fe,Cy3).—
When iron filings are digested in a solution of cyanide of potassium, and
the mixture is exposed to air, oxygen is absorbed and this compound is
produced. If air is excluded, the water is decomposed, and hydrogen is
liberated. On evaporation a salt is obtained which has the formula (Kg
FeCy3,3HO). A mixture of sulphide of iron and cyanide of potassium also
forms the ferrocyanide, and sulphide of potassium. When Prussian blue is
boiled with potassa it is decomposed, oxide of iron is separated, and on
filtering and evaporating the solution, crystals of the ferrocyanide are obtained.
This salt is largely prepared as an article of commerce, chiefly for the use of
calico-printers, by calcining at a red heat, in a globular iron vessel, a mix-
ture of carbonate of potassa with animal matters, such as horns and hoofs,
woollen rags, or parings of leather. The fused mass takes a portion of
iron from the iron vessel, and this forms prussiate cake. When cold it is
lixiviated, and the evaporated solution yields an impure product, which, when
redissolved and slowly crystallized, furnishes the purified salt. In this
operation the cyanogen derived from the nitrogen and carbon of the organic
matter combines with the potassium and iron to produce the ferrocyanide.

Ferrocyanide of potassium forms permanent yellow, tabular, and octahe-
dral crystals (=K2Fe,Cy3,3HO), of the specific gravity of 1'83: they are
insoluble in alcohol. Water at 60^ takes up about one-third, and at 212^,
its own weight of this salt. It has a bitter, saline, and sweetish taste, and
is not poisonous. When moderately heated it loses color, and crumbles
into powder, parting with about 13 per cent, of water. By a red heat it is
converted with the escape of nitrogen, into carbide of iron and cyanide of
potassium : and in the presence of air the latter salt becomes cyanate of
potassa, and the iron is oxidized. Boiled with dilute sulphuric or hydro-
chloric acid, hydrocyanic acid is given out, and a white precipitate is formed
similar to that which the salt produces in a solution of protosulphate of iron.
By nitric acid or by chlorine it is converted into ferricyanide of potassium.
The action of concentrated sulphuric acid upon this salt is attended by the
evolution of carbonic oxide. Neither sulphuretted hydrogen, the hydrosul-
phates, the alkalies, nor tincture of galls, produce any precipitate in solu-
tions of this salt. Red oxide of mercury decomposes it at a moderate heat,
peroxide of iron and metallic mercury are precipitated, and qyanide of mer-
cury is formed ; so that the iron is peroxidized at the expense of the oxide
of mercury. When a solution of this salt forms insoluble precipitates in
metallic solutions, the nature of the metal present may often be judged of
by the character and color of th^ precipitate. This is white or nearly so,
with the salts of manganese, zinc, tin, cadmium, lead, bismuth, antimony,
protosalts of iron, mercury and silver ; yellowish-green with those of cobalt j

TESTS FOR POTASSA. 321

reddish-hrown, with tliose of copper and uranium ; blue, with the persalts of
iron, and pea-green, with the salts of nickel. It, therefore, forms a good
eliminating or general test for many metals. It is also employed as a re-
ducing agent for arsenic and its sulphides. When a mixture of ferrocyanide
of potassium with dilute sulphuric acid is subjected to distillation, hydro-
cyanic acid is evolved, and a ferrocyanide, represented by the formula K,
FCyCyg, and known as Everitt's yellow salt, is among the products (page
283).

Ferricyanide of Potassium (Kg.Feg.Cyg). — When chlorine is passed
through a solution of ferrocyanide of potassium till the liquor ceases to pre-
cipitate Prussian blue from the persalts of iron, and then filtered and slowly
evaporated, it furnishes right rhombic prismatic crystals, which, purified by
a second solution, assume a ruby-red color ; they are anhydrous, and require
3'8 parts of cold water for solution, and are nearly insoluble in alcohol.
They burn with brilliant scintillations, and when heated in close vessels, give
off cyanogen and nitrogen, and leave ferrocyanide of potassium and carbide
of iron. When dissolved in water, this salt is decomposed by sulphuretted
hydrogen, sulphur and cyanide of iron are precipitated, and hydrocyanic acid
and ferrocyanide of potassium formed. This salt occasions no precipitate in
solutions of iron containing the peroxide only, but it is a most delicate test
of the protoxide, with which it forms a blue precipitate. In its formation
the chlorine abstracts one-fourth of the potassium of the ferrocyanide, pro-
ducing chloride of potassium and ferricyanide, 2(K2,Fe,Cy3) + Cl,=KCl-f
K3,Fe.3,Cyg). There is a remarkable difference between the ferri and ferro-
cyanide of potassium which it may here be proper to point out. The ferri-
cyanide acts like an ozonide on strychnia, and has been proposed by Dr.
Davy as a test for that alkaloid. When a crystal of ferricyanide of potassium
is brought in contact with strychnia previously mixed with strong sulphuric
acid, a series of colors are produced, commencing with a sapphire blue and
passing through various shades of purple to a light red. They are similar to
those given under the same circumstances by the peroxides of manganese
and lead and by bichromate of potash. If the ferrocyanide of potassium is
employed, these colors are not produced.
•

Silicates of Potassa. — When silica and potassa are fused together they
combine in various proportions and produce a series of silicates, differing in
solubility and fusibility, according to the preponderance of the base or of
the acid. When the alkali is in excess, the product is soluble in water ; but
with excess of silica it is insoluble, and constitutes a species of glass {see
Silicate of Soda). When finely-divided silica is added to fused carbonate
of potassa, carbonic acid is evolved, and by using atomic proportions, a
compound may be obtained represented by KO.SiO,, in which 47 parts of
potassa are united to 46 of silica. When 1 part of silica and 4 of caustic
potassa are fused together and slowly cooled, a part of the compound may be
poured out of the crucible before the whole has solidified, and pearly crystals
are formed in the residuary portion.

Tests for Potassa and its Salts. — A solution of pure potassa is charac-
terized— 1. By a strong alkaline reaction on test-paper ; 2. By its giving a
brown precipitate with a solution of nitrate of silver (oxide of silver). This
distinguishes it from solutions of carbonate and bicarbonate of potassa, both
of which give a yellowish-white precipitate (carbonate of silver). 3. The
solution give.s a crystalline precipitate of acid tartrate of potassa, when a
large excess of a concentrated solution of tartaric acid is added to it. The

328 SODIUM.

solution must not be too dilute. The precipitate is soluble in 180 parts of
water, and is readily dissolved by mineral acids and by alkaline solutions.
The addition of a small quantity of alcohol promotes this reaction. The
production of the alkaline oxide from the metal is at once indicated by plae-
inp: a globule of potassium on a solution of tartaric acid in a glass : 4,
Chloride of platinum gives with the solution a yellowish precipitate of plati-
nochloride of potassium (KCl.PtCla) (100 parts of this precipitate, when
dried, correspond to 16'03 of potassium, 19-33 of potassa, and 40*39 of
platinum); 5. A clean platinum wire dipped into the solution, and introduced
into a smokeless flame, gives a pale violet color to it. This color traverses
a solution of indigo or a layer of blue glass. A small quantity of the liquid,
burnt with alcohol in a platinum capsule, will give a similar color. This
color is produced in flame by all the salts of potash. The spectral analysis
of the flame shows the presence of two bright lines, one in the red and an-
other in the violet portion of the spectrum. Most of the other colors occur.

The solution of potassa is precipitated by solutions of the picric, per-
chloric, and fluosilicic acids. The last is frequently employed for separating
the acid from its salts (page 306).

The solutions of the salts of potassa, when sufficiently concentrated, give
precipitates with tartaric acid and chloride of platinum, similar to those
obtained with the solution of the pure alkali. In the smallest quantity on
platinum wire, they tinge flame of a pale violet color. This color is per-
ceptible through blue glass, or a diluted solution of sulphate of indigo. In
using chloride of platinum to detect potassa-salts, the absence of ammoniacal
salts must be previously ascertained, as they produce analogous effects upon
this reagent; or the platinum-test may be applied after the salt has been
subjected to a red heat, by which the salts of ammonia will have been decora-
posed or evaporated. When chloride of platinum is used in quantitative
analysis, it should be added in excess to the potassa-solution, together with a
drop or two of hydrochloric acid, and the mixture evaporated at 212°. The
residue should then be washed with a mixture of equal parts of proof spirit and
water, which removes everything except the platino-chloride of potassium.

CHAPTER XXIV.

SODIUM (Na=23).

This metal, called also Natrium, was discovered by Davy in 1808. He
procured it by the decomposition of the oxide under a powerful voltaic cur-
rent. It is most abundantly diffused as chloride in the earth, air, and sea.
Four gallons of sea water contain about a pound of the chloride, and this is
equivalent to about half a pound of sodium. As potassium is the terrestrial,
sodium may be regarded as the marine metallic element. The metal is now
obtained from carbonate of soda by a process similar to. that for potassium.
A mixture of carbon and carbonate of soda, derived from the calcination of
the acetate of soda in close vessels, is employed. To this, charcoal is added,
and the mixture is distilled. As this metal does not combine with carbonic
oxide, it is obtained more readily than potassium. One pound of the cal-
cined acetate will yield from five to seven ounces of sodium. Sodium is now
made in large quantity for the manufacture of aluminum and magnesium and
for preparing sodium amalgam. It may be obtained at the low price of six

HYDRATE OP SODA. 329

shillino^s per pound. It is soft, malleable, and easily sectile : it does not,
like potassium, become brittle at 32°, but even at this low temperature
several globules may be welded toj]^ether by pressure. In color it somewhat
resembles silver, but rapidly tarnishes on exposure to air. Its sp. gr. is 0 97.
It softens at about 122° ; it fuses at about 200°, and is volatile at a white
heat, its vapor being colorless. It burns with a yellow flame when heated
in contact with air, and requires the same cautions to preserve it from oxida-
tion as potassium. Sodium, when placed on a large surface of cold water,
does not take fire and burn like potassium. It decomposes cold water with-
out combustion. If, however, one or two drops of water are placed on a
fresh-cut slice of sodium, the heat is so intense that it immediately takes fire
and burns with a yellow flame. If wrapped in a small muslin bag, and
placed on water, or even on ice, the metal will also take fire and burn with
a yellow flame. It also takes fire and burns on hot water. If a globule of
sodium is wrapped tightly in copper gauze and dropped into ajar of water,
a copious stream of hydrogen issues from it, rising in bubbles through the
water. By inverting a jar of water and holding the sodium in the gauze
beneath, the hydrogen may be collected. If the jar is filled with a solution
of litmus, the production and solution of an alkali is indicated by the red
litmus being turned blue.

Sodium and Oxygen; Protoxide op Sodium; Soda; (NaO). — The
affinity of sodium for oxygen appears to be somewhat less than that of potas-
sium. It is more slowly oxidized on exposure to air ; but the protoxide is
the result of the action of air or water. Anhydrous soda is obtained in the
same way as anhydrous potassa, and resembles it in appearance, but is less
fusible and less volatile.

Peroxide op Sodium (Na^Og). — By heating sodium in oxygen, it burns
vividly, and a yellowish-green peroxide is formed, which, by the action of
water, evolves oxygen, and produces a solution of the protoxide.

Hydrate of Soda ; Caustic Soda (NaO, HO) is obtained from the car-
honate, by the action of lime, as described under the head of Potassa. It is
now obtained as a product in the manufacture of magnesium. Pure hydrate
of soda is white, opaque, brittle, and deliquescent ; its sp. gr. is 2*0 ; it re-
quires a red heat for fusion ; and when intensely heated evaporates and
tinges the flame yellow. It has the same general characters as hydrated
potassa ; like it, it retains water at a red heat, and is deprived of it by the
same means.

The following table shows the proportion of anhydrous soda in solutions
of ditferent specific gravities : —

pecific gravity

Dry soda per cent

Specific gravity

Dry soda per cent.

of solution.

by weight.

of solution.

by weight.

1-85

63-6

1-36

26-0

1-72

53-8

1-32

23-0

1-63

46-6

1-29

19-0

1-56

41-2

1-23

16-0

1-50

36-8

1-18

13-0

1-47

34-0

1-12

9-0

1-44

31-0

1-06

4-7

1-49

29-0

Hydrated soda is distinguished from hydrated potassa by forming an efflo-
rescent paste when long exposed to the atmosphere: potassa under the same
circumstances remains deliquescent. The chemical properties of the solution

330 CHLORIDE OF SODIUM.

of soda as an alkali, are similar to those of potassa, bat from the trouble of
procuring it, it has been much less used than potassa. Hydrate of soda is
now, however, abundantly produced in the manufacture of magnesium ; and
its solution is likely to take the place of the solution of potassa for many
chemical purposes. The impurities liable to be found in the solution of soda
are similar to those described under potassa; thus oxide of lead is frequently
present in it, as the result of a chemical action on the glass. This impurity
is detected by the addition of sulphuretted hydrogen or sulphide of ammo-
nium, either of which will give a brown color to the liquid, if lead should be
present.

Chloride OF Sodium; Sea Salt; Muriate of Soda; (NaCl). — Sodium,
when heated in chlorine, burns vividly, and produces this compound. It
exists abundantly in nature both as a solid fossil (sal gemme), and in the
ocean, and in brine springs. Extensive beds of it occur in Cheshire, where
it is known under the name of rock-salt. From these sources the immense
demands are supplied ; that is, either by evaporating brine-springs, or sea-
water, or quarrying it from the mine. In sea-water it amounts to about 2*7
per cent., or to about 4 ounces in the gallon. When heated, chloride of
sodium decrepitates. At a red heat it fuses without undergoing decomposi-
tion, and on cooling concretes into a white mass ; at a bright-red heat it
sublimes, and tinges flame of a blue color. It is insoluble in absolute alcohol,
but dissolves in proof spirit. It is taken up nearly in the same proportion
by cold and by hot water; 100 of water dissolving 37 of salt; or 1 of salt
to 3*7 of water. Concentrated hydrochloric acid precipitates chloride of
sodium from its concentrated aqueous solution. When pure, chloride of
sodium does not alter by exposure to air, though it is generally more or less
deliquescent, from containing chlorides of magnesium and calcium. Obtained
by slow or spontaneous evaporation, it crystallizes in solid cubes ; but when
procured at a boiling heat, by removing its crystals from the surface of its
solution, it forms hollow quadrilateral pyramids. The crystals are anhy-
drous, though they often include interstitial water. Their specific gravity
is 2-557.

Chloride of sodium is decomposed by moist carbonate of ammonia ; bi-
carbonate of soda, sal-ammoniac and free ammonia are formed ; with moist
carbonate of potassa, it yields chloride of potassium and carbonate of soda.
In the process for obtaining hydrochloric acid it is decomposed by sulphuric
acid. In this decomposition, the oxygen of the water of the sulphuric acid
is transferred to the sodium of the salt, the chlorine of which combines with
the hydrogen of the water to produce hydrochloric acid, and the oxide of
sodium unites with the dry sulphuric acid to produce sulphate of soda
(NaCl + S03,HO=NaO,S03+HCl). Chloride of sodium is also decom-
posed by nitric acid : effervescence ensues, chlorine tinged with nitrous acid
is evolved, and, provided a sufficiency of nitric acid has been used, nitrate of
soda remains on evaporation to dryness. When chloride of sodium is tritu-
rated with oxalic acid and heated, hydrochloric acid is evolved, and oxalate
of soda formed, so that when the residue is heated to redness, carbonate of
soda remains. When chloride of sodium and ferruginous clay are heated
together, the silica and alumina of the clay are vitrified by the soda of the
salt, and its chlorine combines with the iron ; it is upon this principle that
salt is used as a glaze for stoneware ; when thrown into the furnaces in
which the articles are baked, it is volatilized, and decomposed upon their
surfaces, producing silicate of soda, which forms the glaze to the stoneware.
This principle has been applied by Mr. Gossage, of Warrington, in a new
process for procuring hydrate and carbonate of soda from salt. A lofty

NITRATE OP SODA. 331

tower of fire-brick is filled with layers of flint or balls of sand, so arranpred as
to receive the heat of several gas-furnaces placed at the lower part of the
tower. Two other furnaces, constructed in a similar manner, supply steam
and common salt in a state of vapor to the heated flints. Hydrochloric acid
and silicate of soda are the products. The latter, dissolved by the water,
flows down through the flints, leaving a fresh surface for chemical action.
The silicate of soda is afterwards decomposed by lime to produce the hydrate
of soda, or by a current of carbonic acid to form the carbonate of soda.
{Laboratory, No. 3, 1867, p. 42.) It is of most extensive use as a preserva-
tive of food ; as a condiment ; as a source of soda, of hydrochloric acid, and
chlorine ; and for various agricultural and horticultural purposes.

Hypochlorite of Soda. Chloride of Soda. — These names have been
applied to a compound formed by passing chlorine into a cold and dilute
solution of caustic soda, or by decomposing chloride of lime by a solution of
carbonate of soda. It is powerfully bleaching, and smells of chlorine : ex-
posed to air, it absorbs carbonic acid and evolves chlorine. When heated
it undergoes changes similar to those produced by passing chlorine into a
solution of soda, that is, chlorate of soda and chloride of sodium are formed.

Laharraque's disinfecting liquid, which is essentially a hypochlorite, is
made by passing chlorine into a solution of carbonate of soda {see page 335).

Bromide of Sodium (NaBr). — Sodium and bromine act upon each other
with much intensity; the result is a fusible compound, soluble in water and
in alcohol, und crystallizing at 86° in anhydrous cubes, but at lower tem-
peratures in hexagonal tables, containing 26 37 per cent, of water.

Iodide of Sodium (Nal). — Iodine and sodium act upon each other with
the same phenomena as in the case of potassium. Iodide of sodium may
also be formed by adding iodine to a solution of caustic soda, evaporating to
dryness, and fusing the residue. It is contained in the mother-liquor of
kelp, in the ashes of burned sponge, and in the oyster. {See Iodine, p. 205.)

Nitrate op Soda (NaO.NOj). Chili, or South American Nitre This

salt, which was formerly called cubic nitre, may be obtained by neutralizing
carbonate of soda by dilute nitric acid. It crystallizes in rhomboids, solu-
ble in 3 parts of water at 60°. It has a cool sharp flavor, and is somewhat
deliquescent in damp air, and therefore unfit for the manufacture of gun-
powder. A mixture of 5 parts of nitrate of soda, 1 of charcoal, and 1 of
sulphur, burns more slowly than a similar mixture with nitrate of potassa:
its flame is yellow. Large quantities of native nitrate of soda occur in Peru,
formi-ng a stratum covered with clay and alluvium, of many miles in extent,
and it is now a considerable article of trade. It may be employed in fire-
works, and used as a substitute for nitre (it being cheaper) in the manufac-
ture of nitric acid, of sulphuric acid, and in other cases in which nitre is
consumed. It has been hitherto found too expensive as a source of soda.
It is frequently employed as a manure. At a red heat it is decomposed with
results similar to those of nitrate of potassa, and is ultimately resolved into
soda, nitrogen, and oxygen. As nitrate of soda is comparatively a cheap
article. Dr. Wagner has proposed to procure nitric acid from it without sul-
phuric acid, and to utilize the products. He found that when the salt
was heated with hydrate of alumina, nitric acid was evolved with some
hyponitric acid, and the residue, which consisted of aluminate of soda,
when treated with carbonic acid, formed the useful compound carbonate of

332 SULPHATE OF SODA.

soda, and left the alumina in the state of hydrate for further use. This
ingenious process has not yet been carried out on a large scale.

Sodium and Sulphur. — The account of the action of sulphur on potas-
sium and potassa, and of sulphuretted hydrogen upon solution of potassa,
applies generally to sodium and soda, and their corresponding compounds.

Hyposulphite of Soda (NaO.SgOg). — This salt may be procured by the
various processes which have been described at page 301. It is now manu-
factured on a large scale for the purpose of photography, and is usually
seen in prismatic crystals. It is very soluble in water. Its solution has a
bitter, nauseous taste. It is decomposed by heat. Its chemical properties
have been elsewhere fully described (p. 224). Owing to its being a ready source
of sulphurous acid, the hyposulphite of soda admits of being employed as a
bleaching agent. M. Artus has used it for the bleaching of sponges. The
sponge is well washed in a weak solution of soda ; the all^ali is entirely
removed by washing in water, and the sponge is then transferred to a weak
solution of hyposulphite of soda and diluted hydrochloric acid. In a short
time it is bleached. The hyposulphite may be thus used for bleaching all
articles of which the color is removed by sulphurous acid.

Sulphite op Soda (NaO.SOg) is obtained in the same way as sulphite of
potassa : it is crystallizable in prisms, soluble in four parts of water at 60°.
The crystals contain 8 atoms of water. There is also a crystallizable bisul-
phite of soda, obtained by passing a current of sulphurous acid gas through
a solution of carbonate of soda till fully saturated ; it yields, on evaporation,
four-sided rectangular prisms, having a sulphurous taste and smell, and red-
dening vegetable blues.

Sulphate of Soda; Glauber^ s Salt; Sal Mirahile (NaO,S03) ; is abun-
dantly produced in various processes of the arts, by the action of oil of
vitriol upon chloride of sodium : S03,HO, + NaCl = NaO,S03 + HCl. An-
hydrous sulphate of soda may be obtained by drying the common hydrated
crystals upon a sand-heat; they fall into a white powder, which reabsorbs
water with the evolution of heat. When a hot concentrated solution of
sulphate of soda is suffered to deposit crystals (at a temperature between
90° and 100°) they are anhydrous rhombic octahedra. 100 of water at 57°
dissolve 10*58 of this anhydrous salt, and the solution, set aside to cool and
crystallize, gives the common decahydrated crystals. The ordinary crystals
(decahydrated sulphate of soda) are deposited from solutions cooled to com-
mon temperatures; they are large transparent striated prisms. They are
efflorescent, and by due exposure to dry air, lose their water, crumbling
into powder, which, however, in damp air, reabsorbs water, with increase of
bulk. When gently heated, the crystals fuse, and at the same time deposit
anhydrous sulphate ; their taste is saline and slightly bitter ; they are inso-
luble in alcohol. The solubility of sulphate of soda in water follows a sin-
gular law. After having increased rapidly to about the temperature of 92°,
where it is at its maximum, it diminishes to 215°, and at that temperature
the salt is nearly of the same solubility as at 87°. This salt mixed with
starchy matters has been largely employed for giving weight to cotton
fabrics.

BisuLPHATE OF SoDA (NaO,2S03) ^s obtained by adding sulphuric acid to
a hot solution of sulphate of soda. It crystallizes in rhombic prisms, soluble
in twice their weight of water at 60°, and containing water of crystallization.

PHOSPHATES OP SODA. 333

By adding half an equivalent of oil of vitriol to sulphate of soda, and evapo-
rating the solution, crystals of a sesquisulphate, 2NaO,3S03, are deposited.

Phosphates of Soda. 1. Trihasic Phosphates. — There are three phos-
phates of soda belonging to the tribasic class : they have been usually dis-
tinguished as common or rhombic phosphate, subphosphate and biphosphate.
The ammoniophosphate also belongs to this class.

Common or Rhombic Phosphate, 2(NaO),HO,P05+24HO.— This salt (the
sal perlatum of old writers) is obtained by saturating the phosphoric acid
prepared from calcined bones by sulphuric acid, with carbonate of soda : the
liquor is filtered, evaporated, and set aside to crystallize. The crystals are
alkaline to test-paper, superficially efflorescent, and soluble in about 4 parts
of cold water. This salt has a slightly saline and alkaline flavor, and has
been used in medicine as an aperient. The crystals, when moderately heated,
fuse in their water of crystallization ; at a dull red-heat, the salt runs into a
clear glass, which becomes opaque on cooling {pyrophosphate). When a
solution of this phosphate is dropped into nitrate of silver, it forms a yellow
precipitate (p. 242).

Subphosphate of Soda, 3[NaO]P05+24HO. — When excess of caustic
soda is added to a solution of the preceding salt, it yields on evaporation
slender six-sided prisms, which are permanent in the air, soluble in 5 parts
of water at 60°, and undergo watery fusion at 1*10°. The solution of this
salt absorbs carbonic acid, and is deprived of one-third of its alkali by the
weakest acid. This salt continues tribasic after exposure to a red heat.

Biphosphate of Soda, NaO,2(HO),P05-f 2H0, is obtained by adding ter-
hydrated phosphoric acid (p. 291) to a solution of the common phosphate,
till it ceases to precipitate chloride of barium. The solution in cold weather
affords crystals, which are very soluble, and have a distinctly acid reaction.
It precipitates nitrate of silver of a yellow color.

Ammoniophosphate of Soda (NaO,NH40,HO,P05-f 8H0).— This salt ex-
ists in urine, whence it was procured by the early chemists under the names
of microcosmic and fusible salt. It may be formed by dissolving in water 5
parts of crystallized rhombic phosphate of soda with 2 of crystallized phos-
phate of ammonia, and evaporating. It forms transparent prisms of a
saline and cooling taste, very soluble, and which effloresce and lose ammonia
in a dry atmosphere.

2. Bibasic Phosphates. Pyrophosphates. — There are two phosphates of
soda belonging to this class, commonly called i\\Q pyrophosphate and bipyro-
phosphate. Pyrophosphate of Soda [2(NaO,) POj-f lOHO] is obtained by
heating the common phosphate to redness, when it loses its basic water and
water of crystallization, and becomes anhydrous pyrophosphate, =2[NaO,]
POj. Dissolved in hot water, this anhydrous salt yields permanent prismatic
crystals on cooling, containing 10 atoms of water; these crystals are less
soluble than those of the common phosphate, and their solution precipitates
nitrate of silver white, and has an alkaline reaction. The insoluble pyro-
phosphates, with the exception of that of silver, are soluble to a certain
extent in the solution of pyrophosphate of soda. The pyrophosphates of
ammonia and of potassa exist in solution, but when they crystallize they pass
into tribasic salts (p. 242).

Bipyrophosphate of Soda (NaO,HO,P05). — This salt is formed by the
application of a graduated heat to the biphosphate of soda ; its solution has
an acid reaction, and does not crystallize. It throws down white pyrophos-
phate of silver from nitrate of silver.

3. Monobasic Phosphates; Metaphosphate of Soda (NaO,POs). — When
any of the preceding phosphates which contain only 1 equivalent of fixed

334 PHOSPHATES OF SODA. CARBONATE OF SODA.

base (soda) are heated to redness, they afford metaphosphate : when bipyro-
phosphate is used, the properties of the resulting salt vary with the tempera-
ture to which it has been subjected ; thus if heated to 500°, it becomes neu-
tral, but still retains the characters of a pyrophosphate. At a temperature
somewhat higher, but below redness, it becomes very difficultly soluble, and
only feebly acid ; when evaporated, its solution does not give crystals, but
dries into a transparent pellicle like gum, which retains at the temperature
of the air somewhat more than a single equivalent of water. Added to
neutral and not very dilute solutions of earthy and metallic salts, metaphos-
phate of soda throws down insoluble hydrated metaphosphates, of which
the physical condition is remarkable ; they are all soft solid or semifluid
bodies, the metaphosphate of lime having the degree of fluidity of Venice
turpentine (p. 241).

Carbonate of Soda (NaO,C02). — This important salt was formerly ob-
tained by the combustion of marine plants, the ashes of which afforded by
lixiviation the impure alkali called soda. Two kinds of rough soda were
known in the market, barilla and kelp ; besides which, some native carbonate
of soda was also imported from Egypt. Barilla is the semifused ash of the
salsola soda. Kelp is the ash of sea- weeds, collected upon many of the
rocky coasts of Britain. It seldom contains more than 5 per cent, of car-
bonated alkali, and about 24 tons of sea-weed are required to produce 1 ton
of kelp. The best produce is from the hardest deep-sea /i<cz, such as the
serratus, digitalis nodosus and vesiculosus.

Kelp is now chiefly important as a source of iodine, the large commercial
demands for carbonate of soda being supplied by the decomposition of sul-
phate of soda. The process consists, 1. In the conversion of chloride of
sodium into sulphate of soda or salt cake. 2. In the production of black ash,
by heating sulphate of soda with chalk and coal. 3. In the extraction of
carbonate of soda from the black ash. The furnace in which the chloride of
sodium is decomposed consists of an iron vessel of the shape of a flattened
sphere, having two openings, one in front, for the introduction of the charge,
and the other opposite to it, through which the charge is thrust out into the
roaster. From the upper part of the decomposing pan a pipe issues for the
conveyance of the hydrochloric vapors into the condenser^ which consists of
two or more lofty turrets communicating with each other and filled with
large pebbles, or with fragments of coke, and through each of which a stream
of water is allowed slowly to flow (from a reservoir at the summit), which
having absorbed the hydrochloric gas, runs off at the bottom into a receiver.
The gases or vapors enter the first tower at its base, and passing upwards,
are conveyed by a pipe of communication, into the upper part of the second
tower, through which they pass downwards. The hydrochloric acid is thus,
removed, and the uncondensable gases pass off into a lofty chimney with
which the base of the second tower is connected by a flue ; in this way a
current of air is constantly drawn from the decomposing pans, and from the
part of the furnace called the roaster^ which is also supplied with a separate
pipe communicating with the condensing towers. In the decomposing pans,
the original charge of sulphuric acid and salt is converted into a mixture of
bisulphate of soda and undecomposed chloride ; but when the charge is
pushed on into the second division of the furnace, or roaster, the decomposi-
tion is completed by the higher heat, and the bisulphate of soda, acting on
the undecomposed chloride, converts the whole into neutral sulphate, or salt
cake. In the next step of the process, this rough sulphate of soda is mixed
with its weight of bruised chalk or limestone, and somewhat less than its
weight of small coal. This mixture is heated and ultimately fused in a proper

CHLORINATED CARBONATE OP SODA. 335

furnace, during which it gives out jets of inflammable gas; and when these
cease, the charge is raked out into iron barrows, and in this state it is called
hall soda or black ash. This is then broken up and lixiviated with warm
water, so as to extract all that is soluble ; the solution is allowed to settle,
and then evaporated in shallow pans, and the product so obtained is mixed
with sawdust and roasted in a reverberatory furnace ; it thus yields the crude
carbonate of soda known under the name of soda ash, and from this the puri-
fied crystallized carbonate is obtained. The chemical changes concerned in
the above operations are chiefly these ; when, as in the preparation of black
ash, sulphate of soda is fused with carbon and carbonate of lime, carbonic
oxide is evolved and sulphide of sodium formed ; this and the carbonate of
lime then react on each other so as to form carbonate of soda and sulphide
of calcium, the latter being combined with excess of lime so as to be insolu-
ble in water. 1 equivalent of sulphate of soda, 1 of carbonate of lime, and
4 of carbon, would thus produce 1 of carbonate of soda, 1 of sulphide of cal-
cium, and 4 of carbonic oxide, NaCSOg-f CaOjCOg-f 4C=NaO,C03+
Ca^ + 4C0. The changes are, however, more complex than these formula
would imply. According to Dr. Roscoe, about 200,000 tons of common salt
are annually consumed in the alkali-works of Great Britain for the prepara-
tion of nearly the same weight of soda ash, of which the value is about two
millions sterling. Some other processes for the production of carbonate of
soda from common salt have been proposed, but none have hitherto super-
seded the above.

The usual form of the common crystallized carbonate of soda is a rhombic
octahedron. It is soluble in twice its weight of water at 60^, and in less
than its own weight at 212°. Its taste and reaction are alkaline. It fuses
readily in its water of crystallization, and on pouring oif the fused salt, a
portion of monohydrated carbonate remains. Exposed to a dry atmosphere,
the crystals effloresce, and at a red heat lose the whole of their water.
When the vapor of a boiling solution of carbonate of soda is introduced into
a flame, it gives it a yellow color, in consequence of traces of the salt passing
ofi" with the aqueous vapor. Crystals containing smaller proportions of
water may be obtained, but these rarely occur, and the usual crystals are,
NaO,CO2,10HO. The principal impurities contained in carbonate of soda
are detected as follows : 1. Sulphate of soda. A precipitate by chloride of
barium when the solution is supersaturated with hydrochloric acid. 2. Chlo-
ride of sodium. By a precipitate with nitrate of silver in the solution super-
saturated by nitric acid. 3. Salts of potassa, by chloride of platinum, or
tartaric acid. 4. Lime, by oxalic acid. Carbonate of lime is rendered
soluble to a certain extent by carbonate of soda, and such a solution cooled
to 32° deposits a white crystalline powder composed of the two carbonates.
Oxide of lead from flint glass is detected by the solution giving a brown
precipitate with sulphide of ammonium.

Chlorinated Carbonate of Soda. — By proper management, chlorine
may be combined with a solution of carbonate of soda ; the resulting combi-
nation has been termed Labarraque^s disinfecting liquid. It is obtained as
follows : 2800 grains of crystallized carbonate of soda are dissolved in r28
pints of water, and the chlorine slowly evolved from a mixture of 967 grains
of salt with 750 grains of black oxide of manganese, and 967 grains of sul-
phuric acid, previously diluted with 750 grains of water, is carefully passed
into it. No carbonic acid escapes, and a pale yellow liquid is the result ;
its taste is sharp, saline, and astringent, and it at first reddens, and then
bleaches turmeric paper. It is but little changed by a boiling heat, and
gives out no chlorine. By careful evaporation, it furnishes crystals which

336 BORATE OF SODA.

produce the original liquid when redissolved ; but exposed to the air, and
suffered to evaporate spontaneously, the chlorine escapes, and crystals of
carbonate of soda are obtained.

Bicarbonate of Soda (NaO,HO,2C03) is formed by passing carbonic
acid through a strong solution of the carbonate : a granular or crystalline
powder is deposited, which, when carefully dried at common temperatures,
is composed as above. This salt may also be obtained by condensing car-
bonic acid upon crystals of the carbonate ; a portion of the water of the latter
salt separates, and when the gas ceases to be absorbed, it is found converted
into a porous and friable bicarbonate, which must be carefully dried at a low
temperature, otherwise it loses a portion of its carbonic acid. Bicarbonate
of soda has a slight alkaline taste and reaction. It is much less soluble than
the carbonate, requiring 10 of water at 60°. The crystals of this bicarbonate
are rectangular prisms. It loses carbonic acid if moistened and left in the
vacuum of an air-pump ; the gas is also evolved when 1 part of the salt is
boiled with 4 of water. In these cases it is converted into a sesquicarbonate.
When long exposed to damp air, it is converted, after some months, into
pentahydrated monocarbonate (NaO,C03,5HO). Its solution gives no pre-
cipitate with sulphate of magnesia, while a solution of the carbonate is im-
mediately precipitated.

Sesquicarbonate of Soda (2NaO,.3C02). — This carbonate of soda occurs
native in the Soda Lakes of Hungary; also in Africa, near Fezzan, where
the natives call it Trona ; it is in hard striated crystalline masses, not altered
by exposure to air ; a productive soda lake also exists in South America, at
Maracaibo.

Carbonate op Soda and Potassa (NaO,C03+KO,C02) is obtained by
fusing the salts in single atomic equivalents : the double salt is much more
fusible than its components, and is therefore conveniently used in many cases
of mineral analysis by fusion, as in the analysis of insoluble silicates (page
304). When dissolved in water the component carbonates separate.

Borate of Soda ; Borax ; Biborate of Soda ; (NaO,2B03). — This salt,
formerly imported from India, under the name of Tincal, is now manufac-
tured by combining soda with the native boracic acid procured from Tuscany.
Common borax crystallizes in transparent prisms, slightly efflorescent. Its
taste is cooling and alkaline ; it has an alkaline reaction upon turmeric. It
is soluble in 12 parts of cold, and 2 of boiling water. When heated it loses
water of crystallization, and becomes a porous friable mass, called calcined
borax. At a red heat it runs into a transparent glass, which, by exposure
to air, becomes opaque and pulverulent upon the surface. The common
crystallized borax is a decahydrate =NaO,2BO3,10HO. This salt is decom-
posed by the greater number of the acids. (See Boracic Acid, page 294.)
It is often used as a blowpipe flux for vitrifying metallic oxides, and forming
beads of different colors : violet with manganese ; green with iron, chromium
and copper ; blue with cobalt ; and slightly yellow with some of the colorless
oxides. In the reduction of the metals by charcoal, borax is often useful as
forming a medium through which the globules fall and collect into a button,
being at the same time protected from the air. At the potteries it is used
in the glazes applied to the better kinds of earthenware, and to porcelain.
Alone, or mixed with phosphate of ammonia or soda, borax *nay be employed
to render muslin, paper, wood, and other materials, to a certain extent in-
combustible ; this it does by covering them with a vitrifiable glaze by which

SILICATES OF SODA. 33T

the access of air is prevented. Borax is also used in the process of solder-
ing ; when, for instance, two surfaces of cojiper are to be soldered together,
they are scraped or rubbed clean, sprinkled with a mixture of powdered
borax and solder-filings, and heated till the solder fuses so as to alloy with
the copper and make a perfect joint : the borax not only prevents the contact
of air, and consequent oxidation of the metals, but dissolves any oxide acci-
dentally formed, and so retains the surfaces in that perfectly clean state which
is requisite for their union. An aqueous solution of borax dissolves several
of the resins, and some of these solutions, especially that of lac, form good
vehicles for coloring materials.

Octahedral Borax (NaO,2B03,5HO). — This salt contains 5 instead of
10 atoms of water, and is obtained by dissolving common borax in boiling
water, till the solution has a specific gravity of 1*26 ; it is then allowed to
cool slowly, and between the temperatures of 174° and 145° it deposits
octahedral crystals ; below that temperature, the ordinary prismatic crystals
are formed. Octahedral borax is harder than the prismatic, and is preferred
for brazing and soldering.

•

Silicates of Soda. — The atomic constitution of these silicates is as inde-
finite as those of potassa. By the fusion of one equivalent of anhydrous car-
bonate of soda with 1 of silica, 53-f 46, a silicate is formed, which when dis-
solved in a small quantity of water yields crystals of a silicate containing 6
and 9 atoms of water. When 100 parts of silica are fused with 40 of caustic
soda, the resulting glass is transparent; but if slowly cooled exhibits crystal-
line points. When 8 parts of dry carbonate of soda, 15 of fine white sand
or powdered flint, and 1 part of powdered charcoal are well mijfed and fused,
a glass is obtained which is soluble in about 6 parts of boiling water : this
solution has been used to diminish the combustibility of wood, canvas, and
similar materials, and more especially of theatrical scenery : it prevents its
burning with flame, by forming a glaze upon the surface. Silicate of soda
may also be procured by decomposing nitrate of soda at a high temperature
with fine sand. Wagner has suggested this as a cheap source for procuring
nitric acid, the silicate produced being a valuable commercial article. Silicates
of soda always have a greenish or bluish tint, however pure the materials
used in their production, and this is an obstacle to the substitution of soda
for potassa in certain kinds of glass.

Manufacture of Glass. — Glass is a compound of silica with potassa or
soda, other substances, or silicates, more especially those of lead, lime, or
iron, being occasionally added; transparency and insolubility in water being
among its most essential qualities. It should also resist the action of other
solvents, such as acids and alkalies, and for many purposes, it should not
fuse or even soften at a red heat. The insolubility of glass depends much
upon its aggregation, for if reduced to fine j)6wder, it reddens turmeric
paper when moistened, restores the blue color to red litmus, and gives a
yellow precipitate with arsenio-nitrate of silver. A portion of the alkali is
frequently abstracted from glass which has been long exposed to the action
of air and water. The varieties of glass which contain oxide of lead are
readily discolored by sulphuretted hydrogen, when in powder and difl"used in
water, although they long resist its action in their ordinary state. The more
fusible glasses, containing excess of alkali, of oxide of lead, or of lime, are
also apt to be acted on by acids and alkalies, and are unfit for the retention
of such solutions. All glass is more or less disintegrated by the action of
water at very high temperatures.

As the varieties of glass are mixtures rather than definite compounds of

338 MANUFACTURE OF GLASS.

their component silicates, they scarcely admit of being represented by for-
mulae, though in some cases the proportion which the oxygen of the bases
bears to that contained in the silica may be usefully stated. The large pro-
portion of oxide of lead in flint-glass gives it a high refractive power and
brilliancy when cut, but renders it soft, easily fusible, and liable to be acted
on by many chemical agents. In plate-glass the predominance of silicate of
soda gives a more liquid combination than potassa, and enables- it to be
poured out of the crucible in which it is melted, upon a cast-iron table, and
rolled into sheets, which, after careful annealing, are ground to a level sur-
face with emery, and ultimately polished with colcothar. Large quantities
of the waste and broken glass of former operations are frequently melted
up (under the name of cullet) with the materials in the crucible. The
remarkable tenacious viscidity of glass, when in a fit state for the operations
of the glass-house, and the facility with which it is shaped, by blowing,
moulding, and other manipulations, into its infinitely various forms, can only
be understood by personal inspection.

The following table will give a notion of the relative proportions of the
components of several kinds of glass in common use, but these vary to such
an extent as not to admit of being r^resented by any satisfactory formulae.
A glass composed of borate and silicate of lead has been used by Faraday
for some optical purposes, and the borosilicate of zinc has been similarly
applied by Maez and Clemandot.

Plate. Crown. Flint. Bottle. Tube. Optical.

Silica .

. 78

63

52

59

73

43

Potassa

. 2

22

14

2

12

12

Soda .

. 13

...

10

3

Lime . *

. 5

a

...

20

11

"i

Alumina .

. 2

3

i

2

1

Oxide of lead

.

33

44

Oxide of iron

"i

...

■» '"

100 100 100 100 100 100

All glass requires to be carefully annealed — that is, suffered to cool very
slowly — otherwise it becomes liable to fly to pieces upon the slightest touch
of any substance hard enough to scratch its surface. Small unannealed
flasks, blown from samples taken from the pot, for the purpose of ascertain-
ing the quality of the glass, and known in the glass-house under the name
of proofs, will show this. When a fragment of flint is dropped into them
they immediately crack ; and if melted bottle-glass be dropped into water,
so as to form what are called RuperVs drops, the instant that their thin end
is broken off they crumble into powder with a kind of explosion. This
probably arises from the unequal tension of the layers of glass in consequence
of the sudden cooling of the exterior, whilst the interior remains dilated, or
even red-hot. When large masses of glass are slowly cooled, crystallized
nodules are sometimes formell, more or less opaque, and imbedded in the
transparent glass. These appear to arise from the formation of definite
silicates.

When glass, imbedded in sand, is heated up to a point a little below that
of fusion, and allowed to cool slowly, it is converted into Reaumer's porce-
lain : It has become hard, white, opaque, and somewhat less fusible ; changes
which have been referred to the formation of certain definite crystallizable
silicates, more especially those of lime and alumina. These phenomena of
devitrification are best shown with common green bottle glass. A peculiar
glass IS used for the manufacture of artificial gems, called strass or paste,
containing a large quantity of oxide of lead, and frequently borate of lead :
It IS easily fusible, highly refractive, and very soft

MANUFACTURE OF GLASS. 339

The art of coloring glass depends upon its power of dissolving certain
metals, metalloids, or metallic oxides. The principal metals thus employed
are, 1. Gold; it imparts various shades of red or pink, inclining to purple,
but here there is reason to believe that the gold is in the metallic state. 2.
8^7^'er /oxide, chloride, or phosphate of silver, give a yellow color. 3. Iron,
The oxides of iron produce blue, 'green, yellow, or brown, dependent upon
the state of oxidation and quantity. The protoxide gives various shades of
green ; the peroxide of brownish yellow. 4. Manganese. The protoxide
leaves the glass colorless, but the peroxide gives it various tints of violet,
and, if added in excess, renders it black. This oxide was formerly called
glass soap, from its property of destroying the green tint communicated by
protoxide of iron, derived from the use of impure materials ; this it effects by
converting the protoxide of iron into peroxide, which, in small proportions,
does not materially affect the color of the glass ; whilst the peroxide of man-
ganese, losing oxygen, becomes protoxide, and in this state is also not inju-
rious. A little nitre is sometimes used for the same purpose. 5. Copper.
The protoxide gives a rich green, and the dioxide a ruby red. The glitter-
ing appearance of aventurin glass is due to the dissemination of minute tetra-
hedral crystals of metallic copper, produced by the fusion of a mixture of
iron and copper scales in the glass. This glass has been hitherto manufac-
tured at Venice, and cut into ornaments. It is so called from its resemblance
to aventurine quartz, which is a variety of rock crystal, being, interspersed
through it — minute scaly crystals of golden mica which reflect light in
various directions. 6. Cobalt, in the state of oxide, gives beautiful blues of all
shades ; in large quantity black, t. Chromium produces greens and red,
depending upon its state of oxidation. According to Pelouze, a beautiful
aventurine glass may be made by fusing together 250 parts of sand, 100
parts of carbonate of soda, 50 parts of carbonate of lime, and 40 parts of
bichromate of potash. The resulting glass, which is very hard, contains from
6 to 7 per cent, of chromium, partly combined with the glass, giving to it a
greenish-yellow color, and partly distributed through it in brillfant crystalline
scales. 8. Uranium is the source of the peculiar opalescent yellowish-green
glass. 9. Tin, in the state of bioxide gives the varieties of opalescent glass,
terminating in opaque white enamel, in which there is also a little oxide of
of lead. An alloy of 1 part of tin and 2 of lead is calcined for the produc-
tion of the oxides, and these are mixed with powdered glass. When sur-
faces are to be enamelled, this mixture is applied with a brush, and then
fused by exposure to heat in a muffle. The colors used in enamel painting
are derived from the metals above enumerated. A species of enamel is
sometimes applied to iron saucepans and other vessels ; it is a vitrifiable
mixture of powdered flint with carbonate of soda, borax, and Cornish clay,
with a little oxide of tin ; this is brushed over the surface, then carefully
dried, and heated in a muffle to bright redness; 10. Arsenic. Arsenious
acid is much employed for giving an opal tint to glass. This glass is trans-
lucent, of a pale bluish-white color, with a reddish hue when viewed in cer-
tain lights. On powdering this glass, and applying the usual tests for
arsenic, the presence of this substance may be readily detected. Arsenious
acid, in small quantity, by peroxidizing iron, which usually gives a green
tint, tends to render glass colorless. The metal arsenic is volatilized in
this process ; hence arsenic is not found in glass-tubing, or in ordinary
chemical glass. 11. The Metalloids. Some of these have the property of giving
a color to glass. Carbon imparts various shades of yellow or straw yellow.
Sulphur gives a yellow color, and Selenium, in the proportion of one per
cent., communicates to glass a beautiful orange tint, resembling that of some
varieties of topaz and zircon-hyacinth. (Pelouze.)

340 TESTS FOR SODA.

Sodium and Potassium form an alloy whicli, if composed of 1 part of
potassium, and 3 of sodium, remains fluid at 32^. Equal parts of the metals
form a brittle crjstallizable alloy. When added to a small quantity of mer-
cury they form a solid amalgam, with the production of great heat and a
partial combustion of the alkaline metals.^

Tests for Soda and its Salts — Pure soda and its carbonates, like pure
potash and its carbonates, have, in solution, an alkaline reaction, and pro-
duce with a solution, of nitrate of silver similar precipitates. The differ-
ences between these alkalies are chiefly of a negative kind. Thus a solution
of soda gives no precipitate with a solution of chloride of platinum : but the
platino-chloride of sodiurii possesses a property not observed in the platino-
chloride of potassium. Dr. Andrews has found that the sodium salt in the
minutest traces produces a brilliant display of prismatic colors when under
the action of polarized light, and he has thus been enabled to detect the
100,000th of a grain of soda. The potassium salt has no action on polarized
light. Soda and its salts are not precipitated by picric or perchloric acid.
When nelitralized by nitric acid and crystallized, soda yields rhombic plates,
while, under the same circumstances, potassa yields long prisms. The essen-
tial character of soda is that in the smallest quantity it will give a well-
marked yellow color to the flame of alcohol, either when burnt with a small
portion of that liquid, or when a minute film of the alkali, on a fine platinum
wire, is introduced into the flame of a spirit-lamp. This color is very pow-
erful, and tends to conceal the pale violet tint given by potassa. Unless
the soda flame is very intense, it will, however, be intercepted by blue glass,
or a diluted solution of indigo ; so that if potassa is mixed with soda, the
pale violet color of the potassa flame only will be seen through this colored
medium. It is thus easy to determine the fact of the admixture of their alka-
lies when no other chemical means are available for this purpose. In a
colorless flame an intense yellow color is at once produced by imponderable
quantities of 'sodium. When this colored flame is submitted to spectral
analysis, the spectrum of sodium is characterized by a fine bright double line
which is identical in position with the dark solar line called D. This alka-
line metal gives a monochromatic light : all the other colors are absorbed,
and tUe spectral space is black. A portion of sodium-salt less than the
1-180,000, 000th of a grain can be detected in the atmosphere by the produc-
tion of this line. Dr. Roscoe observes that every substance which has been
exposed to the air for a moment, gives the soda line in a colorless flame.
The cleanest platinum wire touched by the finger removes sufficient chloride
of sodium from the skin to give the yellow color and the yellow spectral
line. Thus sodium may be detected in the atmosphere and in all kinds of
impalpable dust. The salts of soda are very soluble in water ; they give the
same negative results with tests as the pure alkali. They are readily distin-
guished by the strong yellow light imparted to flame.

LITHIUM. LITHIA. 341

CHAPTER XXV.

LITHIUM. CESIUM. RUBIDIUM. THALLIUM.

LITHIUM (Li = t).

LiTHiA, which is the oxide of this metal, was discovered by Arfwedson, in
ISIT. To obtain lithium, its chloride may be decomposed by an electric
current. The metal is reddish-white, softer than lead, and admits of welding
and of being pressed into wire : it is the lightest known solid, its specific
gravity being 0*594, so that it floats on naphtha ; it fuses at 356°, but is not
volatile at a red heat. Lithium is ductile : it may be formed into wire by
strong compre'ssion when in a heated state through an aperture in a close
metallic box. It decomposes water without combustion, setting free hydro-
gen. It burns when placed on strong nitric acid. It forms only one oxide.
When heated in air it burns with an intensely white light, forming lithia.

LiTHiA (LiO) has only been found in a few minerals ; and, by spectral
analysis, in minute quantities in the sea and many mineral waters. By this
delicate method of research, traces of it have been detected in the Thames
water, fireclay, and a variety of other substances — Lepidolite, triphane, and
petalite, are the principal minerals from which it has been obtained, in pro-
portions varying from 3 to 6 per cent. The mineral, in very fine powder, is
intensely heated in a covered platinum crucible, with about twice its weight
of lime for half an hour. The resulting mass is then digested in diluted
hydrochloric acid, and the whole evaporated to dryness ; when this residue
is dissolved in dilute sulphuric acid, and the solution is treated with oxalate
of ammonia to separate lime, and with baryta water to separate sulphuric
acid, it yields, on filtration and evaporation, hydrate of lithia.. — Hydrate of
Lithia (LiO, HO) is less soluble in water than potassa or soda; its solution
has an acrid taste, and a powerful alkaline reaction. It is sparingly soluble
in alcohol. It does not deliquesce by exposure, but absorbs carbonic acid
and becomes opaque. At a high temperature it attacks platinum in its pure
and carbonated state, and hence must be fused in a silver crucible. — Chloride
of Lithium (LiCl) differs from the chlorides of potassium and sodium, in
being very deliquescent and soluble in absolute alcohol ; it being decomposed
when strongly heated in the open air ; when it loses chlorine, absorbs oxygen,
and becomes alkaline ; it being with difficulty crystallizable, and in tinging
the flame of alcohol of a crimson-red color. — Nitrate of Lithia (LiO,N05)
is a very soluble and deliquescent salt : it crystallizes in rhombic and acicular
prisms, and is dissolved by alcohol. — Sulphate of Lithia (LiO,S03). The
anhydrous salt is white and with difficulty fusible, unless sulphate of lime is
present, when it fuses below redness ; its taste is saline, but not bitter ; it
crystallizes in rhombic prisms, which are slightly efflorescent and soluble in
alcohol. — Phosphate of Lithia may be obtained by adding phosphoric acid to
sulphate of lithia ; no precipitate is at first formed, but upon adding excess
of ammonia and warming the liquid a white insoluble phosphate of lithia
falls. This property enables us to separate lithia from potassa and soda.
The phosphate of lithia may be decomposed by dissolving it in acetic acid,
and adding acetate of lead: acetate of lithia remains in solution. By heat-
ing this, carbonate of lithia may be procured. — Carbonate of Lithia (LiO,

342 CESIUM.

CO^). When a strong solution of carbonate of ammonia is added to a con-
centrated solution of sulphate of lithia and the mixture is heated, a white
precipitate of carbonate is formed. It requires at least 100 parts of water
at 60° for its solution, and is insoluble in alcohol. It is fusible at a full red
heat, but does not lose carbonic acid. The aqueous solution has a strong
alkaline reaction. Carbonate of lithia is rendered more soluble in water by
carbonic acid. Some Bohemian mineral springs contain lithia in this state.
An artificial water of this description has lately been employed in medicine
under the name of Aerated lithia water.

Tests for Lithia and its Salts. — Lithia is characterized by the splendid
crimson-red color which it imparts to flame, as well as by the peculiar spectrum
which the colored flame produces (p. 62). The carbonate of lithia is less
soluble in water than the carbonates of potassa and soda ; but much more
soluble than the carbonates of the four alkaline earths. 1. A solution of the
carbonate is strongly alkaline, and gives a yellowish- white precipitate with
nitrate of silver. 2. It gives a dense white precipitate with the salts of
baryta, strontia, and lime, as well as with the aqueous solutions of these
three alkaline earths. 3. It gives no precipitate with sulphate of magnesia
until boiled ; and only slowly precipitates a solution of corrosive sublimate.
(In these respects it resembles the bicarbonates of potassa and soda.) A
small portion of the carbonate on platinum wire imparts a crimson-red color
to the flame of alcohol. A concentrated solution of lithia is precipitated
by solution of ammonia ; but the precipitate, which is hydrate of lithia, is
redissolved when heated.

The other salts of lithia possess these general characters. 1. Carbonate
of potassa will slowly give, with their solutions if concentrated, a precipitate
of carbonate of lithia. The precipitation is accelerated by heat. 2. Phos-
phate of soda slowly precipitates them in the cold, but immediately when
heated. 3. Chloride of platinum, and diluted sul|>tiuric as well as oxalic
acid, produce no change in the solution. 4. Ammonia gives no precipitate
in a solution of a salt of lithia, and, when diluted, the addition of phosphate
of soda causes only a slow precipitation. If the mixture is boiled, a pre-
cipitate is formed immediately. 5. The solubility of the chloride in abso-
lute alcohol, enables a chemist to separate this base from potassa and soda.
6. The crimson-red color given to flame by all the salts, is characteristic of
lithia. This color traverses blue glass or blue solution of indigo. The red
is sometimes concealed by the presence of soda, but the yellow of soda is
absorbed by the blue medium. The spectrum of lithium is characterized by
one bright red line whereby the smallest traces of its salts may be easily
detected. Dr. Roscoe states the six millionth part of a grain of lithium may
thus be detected. Although lithium is a rare metal in reference to quantity,
and has been hitherto found in only four or five minerals, it is proved by
spectrum analysis that it is very widely diffused but in minute quantities.
Thus it has been detected in almost all spring waters, in Artesian waters
issuing from a great depth in chalk ; in tea, tobacco, milk, and blood.

CESIUM (C8e=133).

This alkaline metal was discovered hy Bunsen and Kirchoff in 1860, by a
spectral analysis of the residue of the mineral water of Durckheim (p. 62).
A ton of the water was estimated to yield not more than three grains of
chloride of caesium. The metal derives its name from the Latin ccssius,
signifying grayish blue, this being the color of the two lines produced in its
spectrum. It exists in small quantity in the mineral water of Kreuznaeh,
forming not more than l-3,000,000th part of the solid contents. Bunsen
obtained about 250 grains of the platinum salt of cassium from the residue

RUBIDIUM. 343

of twenty tons of this water. The residue of 9000 gallons of the Durckheini
water yielded about an ounce of the pure chloride. Coesium was procured
in tlie state of amalgam with mercury by the electrolysis of the fused chlo-
ride. The first step in the process was to separate from the residue of the
water, the salts of all other ali^alies, excepting those of potassa and soda.
Chloride of platinum was then added. Compounds of potassa and cassia
(KCl,PtCla,C8eCl,.PtCla) were thrown down. The platino-chloride of potas-
sium was separated from that of caesium by boiling distilled water, in which
the latter is biJt little soluble.

The metal coesium decomposes water, setting free hydrogen, and forming
a strongly alkaline solution of protoxide of caesium (CaeO), or cassia. The
hydratQ of caesia (CaeO, HO) is soluble in alcohol, corrodes platinum like
lithia, and is volatile at a high temperature. The carbonate is soluble in
water and alcohol, is highly alkaline, deliquescent in air, absorbs carbonic
acid, and forms a bicarbonate which crystallizes in prisms. The nitrate
and sulphate are anhydrous crystalline salts, soluble in water : the latter forms
an alum with sulphate of alumina. The chloride (CieCl) crystallizes in cubes,
which are deliquescent, in which respect it resembles chloride of lithium,
and differs from the chlorides of potassium, sodium, and rubidium. It is
fusible and volatile.

Caesium is always found associated with rubidium. It appears to be
extensively diffused, but exists only in traces ; and probably but for spectral
analysis, it would have remained undetected. This is at present the only
available method of determining its presence in the residues of water. The
1-70, 000th part of a grain of caesia may be thus detected.

RUBIDIUM (Rb = 85).

This metal derives its names from two intensely red lines which its spec-
trum produces near the extreme end of the less refrangible rays. It requires
about the 30,000th of a grain of the chloride to render the lines visible
(see p. 62.) Rubidium is commonly found associated with caesium, but
it appears to be more abundant. Thus, a ton of the Durckheim water
gave about four grains of chloride of rubidium. Bunsen estimates the pro-
portion of rubidia in the Durckheim spring, at 1-2,000,000 part of the
weight of the water. Sea-water contains 1-400,000, and the lepidolite of
Moravia l-2,000th of its weight of the oxide of this metal.

For the separation of the mptal, about 300 pounds of lepidolite are em-
ployed in one operation. The lithia is separated by the usual process (p.
341), and the residue, concentrated by evaporation, is precipitated by chloride
of platinum. The platino-chloride of potassium (KCl,PtCl2) is separated
by successive quantities of hot water, by which the rubidium salt, like the
caesium salt, is not readily dissolved. It requires 158 times its weight of
boiling water for solution, while the potassium salt requires only 19 times
its weight. (According to Bunsen, 100 parts of boiling water will dissolve
5-18 of the potassium salt, 0*634 of the rubidium salt, and 0'37V of the
caesium salt.) The platino-chloride of rubidium (RbCl,PtC1.2) is decomposed
by hydrogen, and chloride of rubidium is obtained. When the chloride is
fused and submitted to electrolysis, the metal is obtained at the negative pole.

Rubidium is a volatile metal, and may be obtained by distilling a mixture
of carbonate of rubidia and carbon. Calcined bitartrate of rubfdia yields
it ; 75 parts of this salt give 5 of rubidia. Rubidium is a white metal
having a specific gravity of 152. Its melting point is stated to be as low
as 101°. Like potassium, it decomposes water with great violence, and
burns when placed in contact with it. Under these circumstances, hydrogen
is liberated, and an oxide is formed having a powerful alkaline reaction

344 THALLIUM.

(RbO). It is, according to Btinsen, a powerful base, and is more electro-
positive than potassium, llubidia forms a hydrate soluble in water and
alcohol. Like hydrate of potassa, it is fusible, and when exposed to air
absorbs water and carbonic acid. The carbonate of rubidia (RbO,CO,^,nO)
is fusible, deliquescent, and soluble in water, producing a strongly alkaline
liquid. It is not soluble in absolute alcohol ; and as the carbonate of cJBsia
is soluble in this liquid, alcohol furnishes a method of separating the two
alkalies. The sulphate and bisulphate are similar to those of potassa. The
chloride (Rb,Cl), like that of potassium, is colorless and crystaflizes in cubes:
it is not deliquescent, but it is fusible and volatile.

Rubidia and csesia resemble potassa in giving precipitates with chloride
of platinum, which are less soluble than the platino-chloride of potassium.
They also give crystalline precipitates with tartaric acid, and uncrystalline
precipitates with fluosilicic acid. These new alkalies are therefore liable to
be mistaken for potassa. Irrespective of the ditference in the solubility of
the chlorides, the only certain method of distinguishing them is that by
which they were discovered, namely, spectral analysis.

Rubidium and caesium have been found in nearly all mineral waters abound-
ing in salts of potassa, soda, and lime, and only in infinitesimal quantities.

THALLIUM (Tl = 204).

This metal, which in some of its properties resembles lead, and in others
silver, is here placed with the alkaline group, for the following reasons. It
is rapidly oxidized by exposure to air, forming a soluble oxide having strongly
alkaline properties. This oxide resembles potassa in taking carbonic acid
from the air and forming a soluble carbonate, in producing with chloride of
platinum an insoluble platino-chloride, and in forming an octahedral alum
with sulphate of alumina. Like lead, thallium gives a white precipitate with
hydrochloric acid and alkaline chlorides, and a brown or black precipitate
with sulphuretted hydrogen and alkaline sulphides. Like silver, it forms a
soluble and crystallizable sulphate and an insoluble chloride.

Thallium was discovered by Mr. Crookes in 1861, and its discovery was
one of the results of spectral analysis. Thallium and its salts have the
property of producing a splendid bright monochromatic green line in the
spectrum, from which the metal has received its name (6>a>.xta, a bud or germ),
the green color being similar to that of the buds of leaves in spring. The
position of this line corresponds to Ba 8 of Kirchoff. It exists in small
proportion, associated with sulphur in place of arsenic, in certain kinds of
pyrites. Spanish pyrites are a favorable source of it, but even in these it
forms no more than one or two grains in a pound.

The flue-dust from the combustion of pyrites consists of sulphur containing
thallium : the sulphur is burnt away, oxide of thallium is left, and the metal
is obtained from this by the ordinary process of reduction by flux. Various
other sources of thallium have been recently announced. Mr. Scott states
that he has found it in the violet and red sands of Alum Bay to the extent
of 0-3 to 0*4 per cent. An alloy of copper, silver, and thallium, containing
as much as lY per cent, of the latter metal, is stated to have been found in
Norway. Mr. Crookes did not find it in any ore in larger proportion than
ten ounces to the ton.

Properties. — Thallium is a white metal with the lustre of tin. It is very
heavy, having a specific gravity of 11-9. It melts at 550° is volatile at a
full red heat, and when strongly heated in oxygen it takes fire and burns
with a bright green flame. It is one of the most diamagnetic bodies known,
and in electric conductivity is but little inferior to lead. It is soft, and can
be easily drawn into wire. It produces a mark on paper like lead, but it is

THALLIUM. 345

SO rapidly oxidized in air that if the mark is made on paper stained with
turmeric or red litmus, and the part is wetted, it will show a strong alkaline
reaction. The metal^does not decompose water, but it is rapidly oxidized
and tarnished in acids, acquiring a dark incrustation of oxide (TIO). This
may be dissolved off by water, especially if boiling, and the bright white
surface of the metal will then appear. When the solution takes place slowly,
it brings out a crystalline structure. It is ductile and can be drawn into
wire, but it has no great tenacity.

Thallium forms two oxides, TIO and TIO3. The protoxide Thallia is
obtained by simple exposure of the metal to the air, or by the decomposition
of its salts. It resembles potassa in many of its properties. It is soluble in
alcohol and water. Its aqueous solution has an alkaline reaction, and, like
potassa, gives a brown precipitate with nitrate of silver, and a yellow precipi-
tate with the arsenio-nitrate. The solution is not precipitated by carbonate
of potassa. On exposure to air, it combines with carbonic acid and forms a
soluble carbonate. This requires, however, 25 parts of water for its solution.
The metal or its oxide rapidly deoxidizes permanganic acid, and destroys
the color of a solution of permanganate of potassa.

The sulphate and nitrate of thallium are white crystal lizable salts soluble
in water. Nitric acid is the best solvent of the metal, but it decomposes
and is dissolved by concentrated boiling sulphuric acid. The sulphate of
thallium thus formed may be obtained crystallized in six-sided prisms. It
combines with sulphate of alumina to form an octahedral alum, thus replacing
potash, soda, and ammonia. The chloride is not very soluble in water. The
metal is precipitated from its solutions by magnesium and zinc.

Tests for Thallium and its Salts. — A wire of platinum warmed and
drawn over the surface of the metal, or dipped in a solution of the oxide or
any of the salts, and introduced into a colorless flame, imparts to it a brilliant
bright green color. This traverses a solution of indigo or blue glass of a
pale green color, thus revealing the metal when mixed with potash or soda.
The green color given to flame is unlike that imparted by oxide of copper,
boracic acid or a salt of baryta. The green color given to flame by thallium
has been hitherto considered to be monochromatic in its character. Dr. Mil-
ler found, on exposing thallium to the flames of burning hydrogen and of the
oxyhydrogen jet, that as the temperature increased in intensity, the brilliancy
of the thallium green line increased also, but no new lines made their appear-
ance. When the induction coil was employed, and the sparks were examined
by the spectroscope, besides the intense line in the green, five others were
observed : 1, a very faint one in the orange ; 2, two of nearly equal intensity
in the green, more refrangible than TIO, with a third much fainter, the three
lines in the green being nearly equidistant; there was also a well-defined line
in the blue. When examined photographically, the spectrum resembled those
of cadmium and zinc more than that of lead.

A solution of any of the salts has the following reactions : 1. Chloride of
platinum gives a yellowish-colored precipitate in the most diluted solution.
It requires 15,585 parts of water to dissolve it. 2. Iodide of potassium
gives a yellow precipitate which is not dissolved by a solution of potassa.
3. Chromate of potassa also gives a yellow precipitate not soluble in a solution
of potassa, 4. Sulphuric acid does not give a precipitate, except in a strong
solution. 5. Hydrochloric acid, or an alkaline chloride, throws down an
insoluble white chloride even in a very diluted solution. 6. The solution is
not precipitated by potassa or its carbonate. T. Sidphuretted. hydrogen, or an
alkaline stdphide, gives a brown or black precipitate (TIS). Thallium is
slowly thrown down from its solutions in a crystalline state or as a black
powder by zinc and magnesium. The platino-chloride, acidulated with sul-

346 BARIUM, STRONTIUM, CALCIUM, MAGNESIUM.

phuric acid and treated with zinc, yields thallium in the form of a black
powder.

This metal and its salts have not yet been put to any use. They are at
present too costly. Experiment has shown that the salts have a poisonous
action on animals. They produce griping pains, with trembling of the limbs
and a state of paralysis. Less than two grains has sufficed to kill a dog.
A curious application has been made of spectrum analysis in reference to
this substance. The presence of absorbed thallium in the body of an animal
has been proved by drying and burning a portion of the liver. The mono-
chromatic green band in the spectrum showed the presence of thallium.

CHAPTER XXVI.

BARIUM, STRONTIUxM, CALCIUM, MAGNESIUM.

BARIUM (Ba=69).

This metal was discovered in 1808 by Davy, who obtained it by the voltaic
decomposition of its oxide. It may also be procured by passing potassium
in vapor over baryta heated to redness in an iron tube, or in decomposing
the fused chloride by an electric current. Barium is of a gray color, and
rapidly absorbs oxygen ; when gently heated, it burns with a red light. It
is not fusible at the melting point of glass. Its sp. gr. is 4 5 (Pelouze).
It decomposes water without combustion, evolving hydrogen, and forming
a solution of baryta ; its properties, however, have not been accurately
ascertained.

Oxide of Barium ; Baryta (BaO) is obtained by exposing pure nitrate
of baryta to a bright red heat in a porcelain crucible; some iron filings
facilitate the decomposition. It acts upon platinum, and if a silver crucible
be employed, the heat required is such as to endanger its fusion. Baryta
may also be obtained by subjecting artificial carbonate of baryta to an
intense white heat, thoroughly mixed with about 10 per cent, of finely-
powdered charcoal. Baryta is generally in the form of a porous mass, or
gray powder, and, when pure, is very difficult of fusion. Its specific gravity
is about 4, hence the name Baryta, as being the heaviest of the substances
usually called earths (from jSipvj, heavy). It is very poisonous. It has a
strong alkaline taste, and reaction on vegetable colors. It is insoluble in
alcohol. It eagerly absorbs water, heat is evolved, and a white hydrate is
formed. After long exposure to air it becomes white, and is a mixture of
the hydrate and carbonate.

Hydrate op Baryta (BaO.HO).— When pure baryta is sprinkled with
water it becomes intensely hot, and crumbles into a bulky white powder,
which fuses, but does not give out water at a red heat. It dissolves in 20
parts of cold and in 3 of boiling water, forming a solution which is a very
delicate test of the presence of carbonic acid, and which speedily becomes
covered with a film of carbonate of baryta when exposed to air. A saturated
solution of baryta in hot water deposits hexagonal prisms as it cools, con-
taining 10 equivalents of water.

CHLORIDE OF BARIUM. 347

PERO^tiDE OF Barium (BaOg) is obtained when dry oxygen gas is passed
over baryta heated to dull redness in a glass or porcelain tube : it may also
be formed by adding 1 part of chlorate of potassa to 4 of baryta, previously
heated to redness in a platinum crucible ; the oxygen of the chlorate com-
bines with the baryta, and, by the action of cold water, the remaining
chloride of potassium may be washed out, and a hydrated peroxide of barium
remains. When the anhydrous peroxide, which is of a gray color, is put
into cold water, it does not evolve heat, but becomes a white, pulverulent,
and insoluble hydrate (BaO^jOHO) ; but if this is boiled in water, it will give
out an equivalent of oxygen, and revert to the state of protoxide, which is
soluble. When peroxide of barium is heated in hydrogen it becomes incan-
descent, emitting a greenish flame, and absorbing the gas ; protohydrate of
baryta is the product. Peroxide of barium is also formed when dry air is
passed over heated baryta: the temperature required for this absorption of
oxygen is a dull red heat: at a bright red heat not only is no oxygen
absorbed, but the peroxide is itself decomposed, and giving off 1 atom of
oxygen, reverts to the state of protoxide, which may thus be used to absorb
and evolve oxygen by turns: this has been proposed as an economical source
of oxygen, but independently of the diEBculty in the due adjustment of the
heat, the capacity of baryta for absorbing oxygen gradually decreases by
repeated use (p. 92). Peroxide of barium, when treated with hydrochloric
acid, does not evolve chlorine, like peroxide of manganese, but it produces
peroxide of hydrogen, the barium combining with the chlorine, and being
replaced by hydrogen. Any acid added to this compound, diffused in water,
produces peroxide of hydrogen. When a current of carbonic acid is used,
the baryta is precipitated as carbonate, and peroxide of hydrogen is con-
tained in the liquid.

Nitrate of Baryta (BaO,N05) may be produced by dissolving the native
carbonate in dilute nitric acid, evaporating to dryness, redissolving and
crystallizing; or by decomposing a solution of sulphide of barium by dilate
nitric acid. It forms permanent octahedral crystals, which are anhydrous,
and taste acrid and astringent. It is soluble in 12 parts of cold and 4 of
boiling water. It is insoluble in alcohol. If a moderately strong iolution
of nitrate of baryta is added to nitric acid, a precipitation of the nitrate of
baryta takes place, in consequence of the difficult solubility of the nitrate in
the dilute acid ; in the concentrated acid the nitrate is insoluble ; hence, in
using nitrate of baryta as a test of the presence of sulphuric acid in nitric
acid, the latter should be considerably diluted, lest the precipitated nitrate
of baryta be mistaken for sulphate.

Chloride of Barium (BaCl). — This compound may be obtained by heat-
ing baryta in chlorine (in which case oxygen is evolved, to the amount of
half a volume for every volume of chlorine absorbed) ; or in hydrochloric
acid gas, when it becomes red hot, and chloride of barium and water are the
results. It is generally formed by dissolving carbonate of baryta in diluted
hydrochloric acid, evaporating to dryness, and fusing the residue in a covered
platinum crucible. Chloride of barium, after it has been thus fused, is
translucent and of a grayish color ; sp. gr. 3*8 ; its taste is acrid ; it is not
deliquescent, but absorbs moisture and becomes opaque, increasing in weight
after a few days to the amount of 13 to 14 per cent. ; when moistened it
evolves heat : 100 parts of water at 32^ dissolve between 32 and 33 parts of
this anhydrous chloride : it is insoluble in absolute alcohol, but imparts a
pale greenish-yellow color to its flame during combustion. Its aqueous
solution yields, when evaporated, flat four-sided crystals =BaCl,2H0, which

348 TESTS FOR BARYTA AND ITS SALTS.

effloresce in dry air. At 212° the water is expelled, and anhydrous chloride
remains. 100 parts of water at 60° dissolve about 43 parts of these crystals.

Sulphide of Barium (BaS) is formed, 1. By passing sulphuretted hydro-
gen over red-hot baryta in a coated glass or porcelain tube, as long as water
is formed; it yields a gray granular compound: BaO + HS=BaS + HO.
2. By passing hydrogen over finely- powdered sulphate of baryta at a bright
red heat : BaO,S03 + 4B[=BaS + 4HO. 3. By the action of charcoal upon
ignited sulphate of baryta ; BaO,S03 + 4C=BaS + 4CO. Mix sulphate of
baryta, in fine powder, into a paste, with an equal volume of flour, place it
in a covered crucible, and expose it to a white heat for an hour or two. On
pouring hot water on the product, the sulphide of barium is dissolved, and
may be separated from undecomposed sulphate and excess of charcoal, by
filtration. Sulphide of barium is readily soluble in hot water, and the solu-
tion on cooling out of the contact of air, deposits hydrated crystals. By
exposure to air, it absorbs carbonic acid and oxygen, yielding carbonate and
hyposulphite of baryta. It dissolves sulphur, forming a pentasulphide.
When its solution is boiled with oxide of copper till it ceases to blacken
acetate of lead, and filtered whilst hot, it yields on evaporation, pure baryta.

Sulphate of Baryta (BaOjSOg) is an abundant natural product known
under the name of heavy spar ; it is insoluble in water, hence the solutions
of baryta are accurate tests of the presence of sulphuric acid and the soluble
sulphates. Recently precipitated sulphate of baryta is sometimes very
obstinate in subsiding from water, and not only long remains suspended, but
adheres to the glass, and even passes through filtering-paper : heat, and a
little excess of acid, greatly facilitate its deposition. It may be heated to
redness without change, and hence the filter containing it, in some cases of
quantitative analysis, may be conveniently burned away ; but the carbon of
the paper converts a minute portion of the sulphate into sulphide. 100
grains of the incinerated sulphate correspond to 65 63 grains of baryta.

Carbonate of Baryta (BaO,C03). — This salt falls in the form of a white
powder,, when the soluble salts of baryta are precipitated by carbonate of
ammonia. It is so nearly insoluble, that water at 60° only takes up about
l-4300th part. Water saturated with carbonic acid dissolves l-820th. It
has no alkaline reaction on vegetable colors. Native carbonate of Baryta,
or Witherite, is found crystalline and massive. Its density is 4-33. It is
useful as a source of pure baryta and its salts. Though scarcely soluble in
water, it is poisonous, probably in consequence of its solubility in the acids
of the stomach. It dissolves more sparingly in solution of carbonic acid
than the precipitated carbonate, and is not so easily decomposed. Sulphate
and carbonate of baryta are largely employed for mixing with white lead,
although they are far inferior to the latter for the purposes of a pigment.
This practice of adulterating white lead appears to be carried on to a great
extent, and thus we find that the minerals of baryta raised in 1865, in the
United Kingdom amounted to 6768 tons.

Tests for Baryta and its Salts— A solution of baryta has an alkaline
reaction: and it gives a brown precipitate with nitrate of silver. It differs
from the solutions of potassa and soda in acquiring a white incrustation (car-
bonate of baryta) on exposure to air. It is immediately precipitated as a
white carbonate, by a current of carbonic acid, or by the addition of a few
drops of a solution of carbonate or bicarbonate of potassa, soda, or ammonia.

There are two soluble barytic salts, the nitrate and the chloride. They

NITRATE OF STRONTIA. 349

are characterized by the following properties: 1. The solution is neutral; 2.
It gives a white precipitate with alkaline carbonates and bicarbonates ; 3.
It is precipitated white by sulphuric acid and all soluble sulphates, even by
the sulphates of lime and strontia. This precipitate, sulphate of baryta, is
insoluble in diluted acids and alkalies; 4. It gives a white precipitate with
fluosilicic acid ; and 5. A white precipitate with an alkaline hyposulphite;
6. It gives a yellowish-white precipitate with a solution of chromate of pot-
assa; 7. Oxalic acid does not precipitate the solution of either of these salts
unless they are highly concentrated, and then after a time a crystalline pre-
cipitate of binoxalate of baryta may be formed ; 8. When a small portion of
the salt is introduced into the flame of alcohol, it produces a pale greenish-
yellow color, which when viewed through a solution of indigo, appears bluish-
green. The spectrum produced by this flame presents a variety of well-
marked colors (p. 62), and is distinguished from all, excepting that of calcium,
by numerous green bands.

In reference to the insoluble salts, the carbonate may be dissolved by nitric
acid, and the sulphate converted into sulphide (p. 348), and this compound
into chloride by hydrochloric acid. They may then be tested.

Strontium (Sr=44).

Strontia was first discovered in the state of carbonate at Strontian in Ar-
gyleshire, and was supposed to be a carbonate of baryta : it was first shown
to contain a peculiar earth by Dr. Hope, in 1*792. It is a substance of rare
occurrence. The existence of strontium, as the metallic base of the earth,
was first demonstrated by Davy in 1808. It is a fixed metal of a gray color
with a reddish reflection. It has been recently obtained, but in small quan-
tities, by Bunsen and Matthiessen. The fused chloride was decomposed by
electrolysis, iron being employed for the poles of the battery. The strontium
which adhered to this metal was removed, and preserved in naphtha, in which
it could be moulded. It was rapidly oxidized on exposure to air ; it decom-
posed water without combustion, setting free hydrogen, and forming a solu-
ble protoxide. The metal has a sp. gr. of 2*5, it therefore sinks in water.

Protoxide of Strontium. — Strontia (SrO) may be obtained from the
nitrate, the carbonate, and the sulphate of strontia, by processes similar to
those directed in regard to baryta. It is a grayish-white porous substance :
its specific gravity is 3 9; it is extremely infusible, not volatile, has an acrid
taste, and an alkaline reaction.

Hydrate of Strontia (SrO, HO). — When strontia is sprinkled with
water it becomes heated and falls to powder, forming a white hydrate, which,
when subjected for a long time to a high temperature, gradually becomes
anhydrous. It is insoluble in alcohol. It dissolves in about 60 parts of
water at 60°. Boiling water dissolves it more abundantly, and on cooling
deposits crystals containing lOHO.

Nitrate of Strontia (SrO,N05) is obtained by processes similar to those
for obtaining nitrate of baryta: it crystallizes in octahedra, soluble in 5 parts
of water at 60°, and in half its weight of boiling water. It is insoluble in
anhydrous alcohol. Its taste is pungent and cooling. At a red heat the
acid is evolved and decomposed, and strontia remains. It is used in the red
fire employed at the theatres, which consists of 40 parts of fused nitrate of
strontia, 13 of powdered sulphur, 5 of chlorate of potassa, and 4 of sulphide
of antimony. The chlorate and sulphide should be separately powdered and

350 TESTS FOR STRONTIA AND ITS SALTS.

cautiously mixed with the other ingredients. This mixture, if kept in quan-
tity in a dry place, is liable to spontaneous combustion. When nitrate of
strontia is linely powdered and mixed with alcohol, it communicates a beau-
tiful red tint to the flame.

Chloride of Strontium (SrCl) is obtained by dissolving carbonate of
strontia in hydrochloric acid, evaporating to dryness, and fusing the residue.
It is of a gray color and an acrid taste; its sp. gr. is 2-8. The aqueous
solution of the chloride when concentrated furnishes white prismatic crystals,
which are deliquescent. The chloride is soluble in alcohol. These proper-
ties enable a chemist to distinguish baryta from strontia, and to separate
the two bases when in the state of chloride. Chloride of barium crystallizes
in quadrangular plates, which are not deliquescent, and are insoluble in
alcohol.

Sulphate of Strontia (SrO,S03) is of very sparing solubility, 1 part
requiring 3600 of water. It is distinguished from sulphate of baryta by
being slowly soluble in solution of chloride of sodium. It is insoluble in
solution of sal-ammoniac. It is soluble in boiling sulphuric acid, but falls
upon dilution. When heated with charcoal, its acid is decomposed, and
sulphide of strontium formed. Native sulphate of strontia is sometimes of a
blue tint, and has hence been called ccelestine. The finest crystallized speci-
mens are accompanied with native sulphur, from Sicily.

Carbonate of Strontia (SrO,C03), when artificially formed, is a white
powder, soluble in 1586 parts of hot water. Native Carbonate of Strontia^
or Strontianite^ is a rare mineral. It has a greenish tint, and occurs in
radiated masses, and sometimes in acicular and hexahedral crystals.

Tests for Strontia and its Salts. — A solution of strontia resembles
that of baryta in alkaline reaction — in giving a brown precipitate with
nitrate of silver, and producing a white incrustation of carbonate by expo-
sure to air, or on the addition of a solution of an alkaline carbonate. The
solutions of baryta and strontia may be thus distinguished: 1. Sulphuric
acid gives a white precipitate, immediately with baryta, slowly with strontia.
2. Sulphate of lime precipitates baryta, but not strontia. 3. Fluosilicic
acid precipitates baryta, but not strontia. 4. Oxalic acid precipitates both ;
a slight excess of the acid will redissolve oxalate of baryta, but oxalate of
strontia is insoluble in the acid.

The principal sohible salts are the nitrate and chloride. They are
neutral. Like those of baryta, they are precipitated white by alkaline car-
bonates and bicarbonates. The difl"erences are: 1. Sulphuric acid and
alkaline sulphates precipitate strontia slowly, but baryta immediately.
2. Sulphate of 'strontia produces no precipitate in them. 3. Fluosilicic
acid precipitates a concentrated solution of a salt of strontia very slowly.
4. They are not precipitated by an alkaline hyposulphite, or by chromate
of potassa. 5. Oxalic acid produces slowly a white granular precipitate.
6. A salt of strontia gives to the flame of alcohol a rich red color, which
traverses a stratum of solution of indigo, and appears of a deep crimson
tint. By spectral analysis this color is resolved into eight lines or bands-
red, orange, and blue, but there are no green lines (p. 61).

Calcium (Ca=20).

The existence of calcium, as the metallic base of lime, was first demon-
strated by Davy in 1808. Like strontium, calcium has been obtained by
the electrolysis of its chloride, iron poles being employed with the battery.

OXIDE OF CALCIUM. LIME. 351

«

(BuNSEN.) This metal has a yellowish color, is harder than lead, malleable,
fusible at a red heat, but not volatile, and is only slowly oxidized when
exposed to humid air. It burns with scintillations, producing a bright white
light when heated in the air, and it undergoes vivid combustion in chlorine,
and in the vapor of bromine, iodine, and sulphur. Its specific gravity is
1 '57 ; it sinks in water, and rapidly decomposes it without combustion,
hydrogen being liberated, and lime (protoxide of calcium) being dissolved
by the water.

Oxide of Calcium ; Lime ; QuicUime (CaO). — Lime may be obtained in
a state of considerable purity by exposing humid carbonate, or nitrate of
lime, to a white heat for an hour, in an open crucible (p. 142). Pure lime
is white, acrid, caustic, and alkaline ; its specific gravity is 3 08. It is infu-
sible, but remarkably promotes the fusion of some other oxides, and is,
therefore, used in several metallurgic processes, as a flux. When intensely
heated — as, for instance, by the oxyhydrogen blowpipe — it is remarkable for
its luminosity, and at this very high temperature a minute quantity is vola-
tilized (p. 124). It is an essential ingredient in mortar and other cements.
Exposed to air, it absorbs water and then carbonic acid, and, losing its
causticity, becomes partially converted into carbonate of lime ; so that when
used for agricultural purposes, it should, generally speaking, be speedily
ploughed in, and not left in heaps upon the surface so as to acquire carbonic
acid. In its caustic state, it is most active in the destruction of vermin, and
in effecting chemical changes upon the organic and inorganic constituents of
the soil. Its powerful affinity for water renders it useful in various cases of
dehydration, as in drying certain gases, and abstracting water from alcohol
and some other liquids ; in the state of hydrate, or diffused through water
(cream and milk of lime), it is also used as an absorbent of carbonic acid;
when perfectly dry or anhydrous it does not absorb that gas.

Lime-burning. — Although all carbonates of lime may, by burning, be
brought to the state of quicklime, chalk and compact limestone are alone
used for this purpose in the large way. The limekiln at present almost uni-
versally employed in this country, is a cup-shaped concavity, in a solid mass
of masonry, open at top and terminated at bottom by a grate, immediately
above which is an iron door. This simple furnace is first charged with fuel
(either wood, or coal and cinders), upon which is afterwards laid a stratum
about a foot thick, of chalk or limestone, broken into pieces not larger than
the fist ; to this succeeds a charge of fuel, and so on alternately, keeping the
kiln always full. The pieces of limestone descend towards the bottom of the
kiln in proportion as the fuel is consumed, being in the meantime kept at a
pretty full red heat. At this temperature the water and carbonic acid are
driven off; and by the time the limestone arrives at the bottom of the kiln,
which happens in about forty-eight hours, it is rendered perfectly caustic.
The door above the grate is then opened, and the lime below the next
descending stratum of fuel is raked out; the remaining contents of the fur-
nace sink down, and a fresh charge is laid on the top. The compact lime-
stone, after having undergone this process, though lighter and more porous
than before, still retains its figure unaltered; hence it is readily separable
from the ashes of the fuel, and is sufficiently hard to be carried from place
to place without falling to pieces.

Hydrate of Lime; Slaked Lime; (CaO, HO). —When a small quantity
of water is poured upon lime, a rise of temperature ensues from the solidifi-
cation and combination of a portion of the water, and a bulky white powder
is obtained, which is a hydrate. The rise of temperature is so great, when

352 CHLORIDE OF LIME.

large heaps of good lime are suddenly slaked, as to scorch wood (p. 145).
Hydrate of lime may be obtained in a crystalline form, by placing lime-water
under the receiver of an air-pump, containing another vessel of sulphuric
acid. The water is thus slowly evaporated, and six-sided crystals (CaO,HO)
are formed.

Lime-water. — At a temperature of 60°, 150 parts of water are required for
the solution of one part of lime. Boiling water, however, does not dissolve
so large a quantity ; 1 part of lime requiring 1280 parts of water at 212^^ for
its solution ; at 32°, 1 part of lime is soluble in 656 of water. When lime-
water is boiled, a portion of the lime is therefore precipitated in small crys-
talline grains. Lime-water is limpid and colorless ; its taste is nauseous and
alkah'ne, and it has an alkaline reaction ; and although the quantity of lime
which it contains is relatively small, its alkaline reaction is very marked. It
is usually prepared by pouring warm water upon powdered lime, and allowing
the mixture to cool in a close vessel ; the clear part is then decanted from
the remaining undissolved portion. When lime-water is exposed to the air,
a pellicle of carbonate of lime forms upon its surface, which, if broken, is
succeeded by others, until the whole of the lime is thus separated.

Chloride of Calcium; Muriate of Lime; (CaCl). — This compound
occurs in sea-water and in some saline springs, where it is sometimes accom-
panied by traces of bromine and of iodine. It is formed by dissolving car-
bonate of lime in hydrochloric acid, evaporating to dryness, and exposing
the residue to a red heat in close vessels. It soon deliquesces when exposed
to air, and is frequently employed, after it has been fused, to deprive gases
of aqueous vapor ; but when thus used, its absorptive powers in regard to
some gases must not be overlooked. It is also used as a means of depriving
alcohol, ether, and other liquids, of water, for which purpose they are gene-
rally distilled off dry chloride of calcium. Its taste is bitter and acrid. One
part of water at 66° dissolves four parts of this chloride ; its solubility, how-
ever, is greatly influenced by temperature, for at 82° one part of water will
not dissolve more than two of the salt, and at 212° it takes up nearly any
quantity. It is copiously soluble in alcohol, and heat is evolved during the
solution, which in cold weather affords crystals containing about 60 per cent,
of alcohol, instead of water of crystallization. By the solubility of this chlo-
ride in alcohol, lime may be separated from potassa, soda, and baryta.
While hydrated hydrochloric acid and lime react upon each other powerfully,
it appears from the experiments of M. Gore that hydrochloric acid gas lique-
fied under great pressure, may be brought in contact with caustic lime
without any chemical change taking place between the hydrogen acid and
the oxygen base. The solid porous lime was everywhere penetrated by the
liquefied acid, but there was no chemical action between them; thus affording
another proof that for the neutralization of bases by acids, and the produc-
tion of salts, water is necessary. {Proc. JR. S., May, 1865, p. 213.)

Chloride of Lime; Hypochlorite of Lime. — This important bleaching
material is made by passing chlorine into chambers containing hydrate of
lime in fine powder, by which the gas is copiously absorbed. It is a dry
white powder, smelling feebly of chlorine, and having an acrid taste ; it is
partially soluble in water, and the solution is used under the name of bleach-
ing-liquor. Exposed to air, it slowly evolves chlorine and absorbs carbonic
acid ; ultimately some chloride of calcium is formed, and it deliquesces.
When heated, it gives off oxygen, and chloride of calcium results, an expe-
riment which shows the superior attraction of calcium for chlorine as com-
pared with oxygen, the latter being expelled from the lime.

CHLORIDE OF LIME. 353

The solution obtained by digesting bleaching-powder in distilled water
has a strong alkaline reaction upon most of the usual tests, and its bleaching
power is only slowly developed unless some acid is added, when it is power-
ful and immediate ; thus it is that calico-printers produce white figures upon
colored ground, by printing the pattern intended to be brought out upon
the colored calico, in citric or tartaric acid thickened with starch or gum ;
the goods are then rapidly wound through a properly-adjusted solution of
chloride of lime, and the bleaching power only shows itself where the acid
pattern had been previously applied. In the same way a solution of the
chloride may be colored blue by litmns, or green by red cabbage, or brown
by turmeric, and on the addition of a few drops of acid the color disappears.
By exposure to air, the absorption of carbonic acid effects the same change ;
and the evolution of that acid in respiration is well shown, by tinging a
weak solution of chloride of lime blue by litmus, and then breathing through
it by means of a tube, when the blue color gradually disappears.

The best samples of commercial chloride of lime contain on an average
about 30 per cent, of chlorine ; and when chlorine is passed over hydrate of
lime in an experiment upon the small scale, it cannot be made to absorb
more than about 40 per cent. ; but if hydrate of lime is diffused through
water, it will absorb its own weight of chlorine, and a solution containing 1
equivalent of lime (or of hydrate of lime) and 1 of chlorine (which is the true
atomic compound) is obtained. In its ordinary state, bleaching-powder may
be regarded as containing : —

Chlorine ... 1 36 32-72

Hydrate of lime . . 2 74 67-28

Bleaching-powder . . 1 110 100-00

When put into water, 1 atom of hydrate of lime remains undissolved, and
the solution contains 1 atom of lime and 1 of chlorine (p. 192). Some have
considered bleaching-powder as containing a hypochlorite of lime, and repre-
sent its formation as follows: 2CaO-f 2Cl=CaCl + CaO,C10. But when
properly prepared, it yields no chloride of calcium when digested in alcohol,
and it is not deliquescent. When used as a bleaching agent for calico, the
goods are in the first instance washed, and then boiled in a weak solution of
soda to cleanse them of greasy and other impurities ; they are then put into
a weak solution of the chloride of lime, and afterwards into water slightly
acidulated by sulphuric acid. These operations are repeated if necessary,
and the process is completed by thoroughly washing the goods in running
water. When employed as a disinfectant, cloths soaked in a solution of the
chloride are suspended in the apartments, where they slowly evolve chlorine
in consequence of the action of the carbonic acid of the air. Or, if a larger
and more sudden evolution of chlorine is required, dilute sulphuric acid is
added to the powder or its solution.

The quality of chloride of lime may be determined either by testing its
bleaching power by means of a standard solution of indigo, or by determin-
ing the quantity of protoxide of iron in acid solution, which is convertible
into peroxide by a given weight of the powder; in this case, supposing- pro-
tosulphate of iron to be used, 07ie equivalent of chlorine will convert two
equivalents of that salt into one of persulphate of iron. (Graham.)

Fluoride of Calcium. Fluor-Spar (CaF). — This compound may be pro-
duced by saturating dilute hydrofluoric acid with carbonate of lime, or by
precipitating a neutral salt of lime with a soluble fluoride : in this case it,
forms a gelatinous mass, the precipitation of which is accelerated by the
23

354 SULPHIDES OF CALCIUM.

addition of caustic ammonia. Native fluoride of calcium, or fluor-spar, is a
mineral found in many parts of the world, but in great beauty and abundance
in England, and especially in Derbyshire, where it is commonly called blue
John. It occurs in cubic crystals, which may be cleaved into octahedra and
tetraheda. Its colors are various. Its specific gravity = 3. It phospho-
resces when exposed to heat, and at a high red heat it fuses, and is some-
times used as a flux for promoting the fusion of other minerals. It generally
occurs in veins : in the Odin mine at Castleton, it is found in detached masses,
from an inch to more than a foot in diameter ; their structure is divergent,
and the colors, which are various, disposed in concentric bands. It is the
only variety which admits of being turned in the lathe into vases and
other ornamental articles. Compact fluor is a scarce variety ; the finest
specimens come from the Hartz. A third variety is cldoro2)hane, so called
from the beautiful pale-green light which it exhibits when heated. The
nature of the coloring-matter of blue and green fluor-spar is not understood:
it is liable to fade, and the blue varieties become red and brown by heat.
Fluoride of calcium exists in small quantity in bone : it has been found in
coprolites, and in some fossil bones, to the extent of 10 per cent. Pure
fluoride of calcium is slowly decomposed by cold sulphuric acid, forming
with it a viscid mixture. At a temperature of abo^t 100° its decomposition
is rapid, sulphate of lime is formed, and hydrofluoric acid is evolved. If the
fluor-spar contain silica, sulphuric acid immediately acts upon it, evolving
white fumes of fluosilicic acid. Fused with carbonate of potassa, carbonate
of lime and fluoride of potassium are produced.

Nitrate of Lime (CaO,N05). — This is a deliquescent salt soluble in
one-fourth its weight of water at 60°. It is found in old plaster and mortar,
from the washing of which nitre is procured by the addition of carbonate of
potassa. It sometimes occurs in spring and river water. It may be crys-
tallized by very low evaporation. It is soluble in alcohol. When exposed
to heat it fuses, and on cooling concretes into a phosphorescent substance
called Balduin's phosphorus. At high temperatures the acid is driven off,
and pure lime remains.

Sulphide of Calcium (CaS) is formed by passing sulphuretted hydrogen
over red-hot lime, when water is evolved: CaO + HS=CaS-f HO. It is
also formed by the action of charcoal, or of hydrogen, upon sulphate of lime
at a red heat. It is slowly acted upon by water, forming a colorless solu-
tion. When freshly prepared it is phosphorescent {Canton'' s phosphorus).

Bisulphide of Calcium (CaS^).— When sulphur and hydrate of lime, in
about equal weights, are boiled together in water, and the solution cooled,
yellow prismatic crystals form, which, after having been dried in vacuo, are
permanent : their taste is alkaline and sulphurous ; they contain 1 atom of
calcium, 2 of sulphur, and 3 of water : when gently heated in vacuo they
become anhydrous, and the bisulphide remains. The yellow liquor, from
which the crystals are deposited, retains hyposulphite of lime in solution :
6S + 3CaO=CaO,S302-l-2CaS2. By exposure to air it becomes colorless, in
consequence of its conversion into hyposulphite.

Pentasulphide of Calcium (CaS,).~When excess of sulphur is boiled
in water with quicklime, a compound of 5 atoms of sulphur with 1 of calcium
is formed, which is not crystallizable : it is soluble in alcohol ; and when
its aqueous solution is evaporated in vacuo, it leaves a yellow mass contain-

SULPHATE OF LIME. 355

ing about 80 per cent, of sulphur. By heat it loses sulphur, and becomes
protosulphide.

• Hyposulphite op Lime (CaO.SgOJ. — When crystals of hydrated bisul-
phide of calcium are ground in a mortar with sulphurous acid, it loses its o^or,
and when filtered it is found to be a solution of hyposulphite of lime. By
passing sulphurous acid through the yellow liquor obtained by boiling lime
and sulphur in water, the same product is obtained ; and if the solution be
filtered and evaporated, at a temperature not exceeding 140°, it furnishes
hexagonal crystals (CaO,S302, + 6HO), which at the temperature of ebul-
lition are decomposed into sulphite of lime and sulphur. The crystals are
little altered by air, very soluble in water, and insoluble in alcohol. This
salt is occasionally employed in photography as a means of removing the
salts of silver from drawings, so as to render them permanent when exposed
to light.

Sulphite of Lime (CaO,SO„) is formed by passing sulphurous acid into
a mixture of lime and warm water. It is a white powder of a slightly sul-
phurous taste ; it requires about 800 parts of water at 60° for solution : it
is rendered soluble by excess of sulphurous acid, and then separates in hex-
angular prisms, of difficult solubility, efflorescent, and passing into sulphate
of lime by exposure to air.

Sulphate of Lime (CaO.SOg) occurs native in selenite, gypsum, and
plaster-stone. It is formed artificially by decomposing a solution of a soluble
salt of lime, by sulphuric acid or by a soluble sulphate. When slowly
deposited, it forms silky crystals soluble in 350 parts of water. When these,
or the native crystallized sulphate (CaO.SOgSHO), are exposed to a heat of
about 300, they lose 20 per cent, of water, and fall into a white powder
{plaster of Paris), which, made into a paste with water, soon solidifies, and,
when in large quantity, with very sensible increase of temperature : hence
its use in taking casts for busts, figures, and ornaments : it is also the basis
of stucco, and scagliola or artificial marble, which is made by mixing plaster
of Paris, colored in various ways, with size and water; when it has indurated,
its surface is polished. It is a useful cement for joining substances which are
liable to be exposed to heat. Mixed with alum its cementing properties are
said to be improved for joining metals to glass and similar purposes. When
sulphate of lime is exposed to a red heat, but short of its fusing-point, it
loses this property of recombining with water. The sp. gr. of anhydrous
sulphate of lime (artificial) is 2-927. It requires about 500 parts of water
at 60°, and 450 parts at 212°, for its solution. Like other sulphuric salts,
it is slowly decomposed when its solution is subjected to the action of decay-
ing vegetable matter, in which case the odor of sulphuretted hydrogen
becomes apparent. As sulphate of lime is more soluble in water than pure
lime, sulphuric acid affords no precipitate when added to lime-water. Nearly
all spring and river waters contain traces of this salt, and in those waters
which are called hard it is often abundant; it renders them unfit for washing
and for culinary purposes. At a very high temperature sulphate of lime is
fusible, but suffers no decomposition ; heated with charcoal it is converted
into sulphide of calcium. It dissolves in dilute nitric and hydrochloric acids,
and separates from these solutions in silky crystals. It is decomposed by the
alkaline carbonates. Sulphate of lime is sometimes employed as a manure,
and, when sprinkled over the land in small quantity, is said to improve
certain soils, especially for the growth of clover : is used for many purposes
in the arts.

356 PHOSPHATE OF LIME.

Native sulphate of lime occurs in various forms. The crystallized or
hydrous variety, CaO,S03,2HO, is called selenite ; the fibrous and earthy,
gypsum; and the granular or massive, alabaster. The primitive form of
selenite is a rhomboidal prism. The crystals are commonly transparent, of
a s^cific gravity of 2 32, and may be scratched by the nail. A beautiful
fibrous variety, called satin gypsum, is found in Derbyshire, applicable to
ornamental purposes. Massive and granular gypsum is found in the sand-
stone accompanying the salt-deposits in Cheshire. It abounds in the strata
of Montmartre, near Paris. In the Tyrolese, Swiss, and Italian Alps, it is
found upon the primitive rocks. It is turned in the lathe, and sculptured
into a variety of beautiful forms. There is a variety of sulphate of lime
which has been called anhydrous gypsum or anhydrite, in reference to its
containing no water. It is harder and denser than selenite, its specific
gravity being 2*96 : it sometimes contains common salt, and is then called
muriacite. It is rarely crystallized. It has been found in Derbyshire and
Nottinghamshire, of a pale-blue tint ; sometimes it is pijik or reddish, and
often white. A compound of sulphate of lime and sulphate of soda is found
in the salt mines of New Castile, which mineralogists have described under
the name of Glauherite, and which may be formed artificially by fusing the
two salts.

Phosphide of Calcium (CaP). — By passing the vapor of phosphorus
over lime heated to dull redness, a brown compound is produced, which de-
composes water with the evolution of phosphuretted hydrogen, and consists
of the phosphide of calcium and phosphate of lime ; the oxygen of the lime
at this temperature converts a portion of the phosphorus into phosphoric
acid, and the evolved calcium combines with another portion of phosphorus
to form phosphide. In a damp atmosphere this substance crumbles into a
brown powder, and in this state does not produce a spontaneously inflamma-
ble gas when put into water. It is rapidly decomposed by the dilute acids.
{See Phosphides of Hydrogen, p. 244.)

Hypophosphite of Lime (CaO,PO,2HO) may be obtained by carefully
boiling phosphorus in a thin cream of lime, filtering the solution, and pass-
ing carbonic acid through it, to separate excess of lime. It is also formed
by the action of boiling water on phosphide of calcium, and treating the
clear liquor in the same way. The solution evaporated in vacuo, furnishes
rectangular prismatic crystals of the hypophosphite, which are nearly
equally soluble in hot and cold water, and quite insoluble in alcohol : they
contain from 18 to 22 per cent, of water of crystallization. This salt is used
in medicine.

Phosphates of Lime. — There appears to be several definite combinations
of lime with phosphoric acid, but the following is the most important.

Common Phosphate of Lime ; Tribasic Phosphate of Lime ; Bone
Phosphate ; (3(CaO),POs).— This salt occurs abundantly in bone-ash, and
is found as a mineral product. On adding chloride of calcium to the tribasic
phosphate of soda, a corresponding phosphate of lime precipitates. When
a solution of bone-earth in hydrochloric or nitric acid is boiled to expel all
carbonic acid, and decomposed by caustic ammonia, the bone-phosphate
separates in the form of a bulky precipitate, which, when perfectly dried, is
white and amorphous. When bone-phosphate is digested in dilute sulphuric
acid, it is resolved into sulphate of lime and (if a sufficiency of sulphuric
acid be used) phosphoric acid: 3(CaO),P05-f 3S03=3[CaO,SOJ + P05.

CARBONATE OF LIME. 351

If less sulpliiiric acid be used, an acid phosphate of lime is formed. Hydro-
chloric and nitric acids readily dissolve bone-phosphate. Acetic acid, and
water saturated with carbonic acid, also dissolve it. Caustic ammonia
added to these acid solutions throws down the original phosphate. It is
also slightly soluble in solutions of ammoniacal salts, and of chloride of
sodium ; and when recently precipitated, it is slightly soluble in water.
Water containing starch or gelatine in solution, dissolves it somewhat more
freely.

Native phosphate of lime (bone phosphate) occurs in apatite, associated
with fluor-spar its primitive form is a six-sided prism: it also occurs in some
volcanic products. Crystallized apatite is found of great beauty in Cornwall
and Devon, and the massive varieties in Bohemia and in Spain. This is one
of the most beautiful of the phosphorescent minerals. When fragments of it
are placed upon iron heated just below redness, they emit a brilliant pale
green light. In these minerals the phosphate is generally associated with
fluoride of calcium, the formula of apatite being 3[3CaO,P05]-fCaP. The
substances known under the name of coprolites, and which appear to be the
excrements of fossil reptiles, also abound in phosphate of lime. On the shore
at Lyme Regis, and in the lias of the estuary of the Severn, they are singu-
larly abundant. They occur throughout the lias of England, and in strata
of all ages that contain the remains of carnivorous reptiles ; in external form
they resemble oblong pebbles, varying in size with the cells of the intestines
which have produced them. They contain fluoride of calcium. Phosphate
of lime occurs in small quantities in some varieties of chalk, and in certain
schists and other rocks. It is present in all fertile soils, and in the vegeta-
bles they produce, through which it is conveyed to the animals that feed
upon them. These facts bear importantly upon agriculture, and give great
interest to the economy of bone-manure, and other sources of the phosphates.
Minute quantities of phosphate of lime and phosphate of iron have been
detected in the water of the deep wells of London.

Carbonate of Lime (CaOjCOJ is the most abundant compound of this
alkaline earth ; it exists in river and spring water, and consequently in the
ocean, and is an essential ingredient in fertile soils. When lime-water is
exposed to air, it becomes gradually covered with an insoluble film of car-
bonate of lime ; hence its use as a test of the presence of carbonic acid ; but
excess of carbonic acid redissolves it, producing a supercarbonate. It follows,
therefore, that if lime-water be added, in equivalent proportion, to water
holding carbonate of lime in solution by excess of carbonic acid, the whole
of the lime may be thrown down in the form of an insoluble carbonate, and
the water will remain pure. Carbonate of lime is also precipitated by the
carbonated alkalies, from solutions of calcareous salts. It is a tasteless white
powder, insoluble in pure water, and having no alkaline reaction. Exposed
for a sufficient time, in a humid state, to the joint action of a red heat and
current of air, the whole of the carbonic acid escapes, to the amount of 44
per cent, and quick-lime is obtained. Cream of lime gradually absorbs
carbonic acid to the amount of half an equivalent when exposed to the air, and
forms a definite compound of hydrate and carbonate. It also appears, that
in burning lime, one-half of the carbonic acid escapes more easily than the
other, indicating the existence of a dicarbonate=2(CaO),C03.

Native carbonate of lime occurs in great abundance and in various forms.
The primitive form of the crystallized carbonate or calcareous spar, is an ob-
tuse rhomboid. Its specific gravity is 2*72. It occurs in every kind of rock,
and its secondary forms are more numerous than those of any other substance.
What is termed Iceland spar is this substance in its primitive form, and of

358 MORTARS AND CEMENTS.

extreme purity ; it is highly doubly refractive when 'transparent. Some of
the varieties are opaque or translucent, snow-white, or tinned of different
hues. It is recognized by its rhomboidal fracture and moderate hardness,
being scratched by fluor-spar ; before the blowpipe it loses carbonic acid,
and becoming lime, is intensely luminous. Carbonate of lime sometimes
forms stalactites and stalagmites, of which some of the caverns of Derbyshire
furnish magnificent specimens; it is there deposited from its solution in water
containing carbonic acid, and substances immersed in this water become
incrusted by carbonate of lime when the excess of acid flies off. A fibrous
carbonate of lime, called satin-spar, is found in Cumberland.

A peculiar variety of carbonate of lime, originally found in Arragon, ia
Spain, has been termed Arragonite ; it often occurs in six-sided crystals of a
reddish color, and is harder than the common carbonate. There is also an
acicular or fibrous variety, found in France and Germany.

All the varieties of marble and limestone consist essentially of carbonate of
lime : of these, white granular limestone, or primative marble, is most
esteemed ; there are, also, many colored varieties of extreme beauty. The
most celebrated statuary marble is that of Paros, and of Mons Pentelicus,
near Athens ; and of Carrara, or Luni, on the eastern coast of the Gulf of
Genoa ; it is milk white and less crystalline than the Parian. Many beautiful
secondary marbles for ornamental purposes are quarried in Derbyshire, and
especially the black marble. Westmoreland and Devonshire also afford
varieties of ornamental marble ; and in Anglesea, a marble intermixed with
green serpentine is found, little inferior in beauty to the verd antique. Among
the inferior limestones, we enumerate many varieties, such as common marble ;
bituminous limestone, abundant upon the Avon, near Bristol, and known
under the name of swinestone, or stink-stone, from the peculiar smell which
it affords when rubbed ; Oolite, or Roestone, of which the houses of Bath
are built ; Portland-stone ; Pisolite, or pea-stone, consisting of small rounded
masses composed of concentric layers, with a grain of sand in the centre ;
an lastly, chalk and marl.

All these substances are more or less employed for ornamental or useful
purposes ; they afford quicklime when burned, and in that state are of great
importance in agriculture, and as ingredients in the cements used for
building.

Silicates of Lime. — There are several native silicates of lime ; apophylite
is a hydrated potassio-silicate, and datolite and botryolite are hydrated boro-
silicates of lime. Silicate of lime is also an ingredient in many varieties of
glass, and in the slags of iron-furnaces. Silica and lime have been combined
by fusion, but this requires a very high temperature, and the results "have not
been minutely examined ; the most common silicate of lime is that in which
the oxygen in the base is to that in the acid as 1 : 3 (CaO,Si03).

Mortars. — Lime and silica are the principal components of mortars and
cements, but common mortar is a mixture rather than a compound. When
lime, made into a paste with water, is applied to the surface of porous stones,
or bricks, the greater part of the water is absorbed, and a layer of hydrated
lime adheres to the surface : but this adhesion is much greater if the lime be
previously mixed with two or three parts of silicious sand, and more espe-
cially if the too rapid absorption of the water be prevented by previously
wetting the surface of the brick or stone to which the mixture is applied.
Much of the excellence of the mortar depends upon the selection of the sand,
which should be clean, sharp, and rather coarse-grained, and upon the quality
of the lime, and the care with which they are blended ; and it should be
spread thinly, and not allowed to dry too rapidly. Under these circum-
stances it adheres firmly to the surfaces to which it is applied ; and as it

TESTS FOR LIME AND ITS SALTS. 359

dries, it absorbs carbonic acid when exposed to the air, and a strong adhe-
sion ensues between the lime and sand, in consequence, probably, of the
formation of a thin layer of silicate of lime upon each grain of the latter.
But although good mortar is excellent for all common purposes, it is soon
disintegrated under water ; and where buildings are to resist such action,
peculiar kinds of limstones are required, so as to constitute what are called
hydraulic cements. There are several substances more or less effective in
imparting to mortar the valuable property of hardening under water. Lime-
stone containing alumina, silicate of alumina, carbonate of magnesia, or
oxide of iron, are of this class ; and consequently, meagre limes as they are
called, or limestones containing c^a^^, afford, when burned, an hydraulic lime ;
and artificial mixtures of particular kinds of clay, with chalk or other lime-
stones, and a proportion of sand, when duly calcined in properly constructed
kilns, are employed for this important manufacture. Portland cement and
Roman cement, are hydraulic mortars or cements of this description ; the
former, when dry, resembling Portland stone ; and the latter, being a substi-
tute for the cements containing puzzuolana, a volcanic product found at
Puzzuoli, near Naples, and long celebrated as conferring hydraulic proper-
ties on common lime : it contains the silicates of alumina, lime, and soda.
The rapidity with which these cements harden in damp places, or when
exposed to water, varies with their composition : 10 or 12 per cent, of clay
confers hydraulic properties, but the cement requires about twenty days to
harden. With 20 to 30 per cent, of clay, it sets in two or three days ; and
with 25 to 35 per cent, it is hard in a few hours. The last mixtures are
those in common use for facing buildings, and when the cement is of good
quality and very carefully prepared, it is extremely durable and weather-proof,
and admits of elaborate moulding. A mixture of hydraulic mortar with
coarse gravel, or broken flints, is largely used under the name of concrete,
for the foundations of buildings ; it soon hardens and becomes impermeable
to moisture.

Tests for Lime and its Salts. — A solution of litne (lime-water) is
alkaline, and has the general properties of solutions of baryta and strontia,
in reference to the action of nitrate of silver, and precipitation by carbonic
acid, or any alkaline carbonate. It is distinguished from a solution of baryta,
it not being precipitated by diluted sulphuric or fluosilicic acids ; also by the
fact that the precipitate given by oxalic acid in the solution is not dissolved
by an excess of the acid. In the last-mentioned character, lime resembles
strontia; but the non-precipitation of lime by sulphuric acid furnishes a
sufficient distinction. Of the three alkaline-earthy solutions, lime-water is the
only one which yields a deposit when boiled.

The soluble salts of lime are neutral. They are precipitated — 1. By
alkaline carbonates and bicarbonates. ^ 2. When the solutions are diluted,
they are not precipitated by sulphuric acid or alkaline sulphates ; 3. They
are not precipitated by a solution of sulphate of lime, or chromate of potassa.
4. They are precipitated by oxalic acid, and oxalate of ammonia. The
oxalate of lime is insoluble in oxalic and acetic acids, but is dissolved by
mineral acids. The oxalate of ammonia will detect one part of lime in
50,000 of water ; it is generally resorted to for the quantitative determination
of lime. 73 parts of oxalate of lime carefully dried at 212°, indicate 28 of
lime ; or the oxalate may be converted, by a very low red heat, into carbonate
of lime, or by a higher heat into quicklime. They are mostly soluble in
nitric and hydrochloric acids. 5. When chloride of calcium is burnt in the
flame of alcohol, it imparts to it an orange-red color. This is resolved by
spectral analysis into green and orange bands (p. 62), no other alkaline
metal giving a green color, excepting barium. There are no blue rays in the

360 MAGNESIUM.

calcium spectrnm. Those salts of lime which are insohihle in water are
nearly decomposed when boiled in solution of carbonate of soda or potassa,
and so afford carbonate of lime.

Magnesium (Mg=12).

Magnesium was first obtained by Davy in 1808, by passing the vapor of
potassium over white-hot magnesia, but was not accurately examined till
1830, when Bussy prepared it by heating anhydrous chloride of magnesium
•with sodium. Bunsen and Matthiesen have recently procured this metal, by
electrolyzing the fused chloride of magnesium. It is a white ductile mallea-
ble metal resembling silver in appearance, sometimes tough and at others
brittle. It is hard, but is readily softened by heat, and in this state it may
be forced by hydraulic pressure through a small orifice. It issues like a
solid stream of silver into wire. It is fusible at about 1000° and volatile at
a still higher temperature. When strongly heated in air, it burns with great
brilliancy, evolving an intensely white light, and produces anhydrous oxide
of magnesium, a solid innocent product. Its light is almost insupportable
when the metal is burnt in oxygen. The intensity of its light is calculated
to be about l-225th of that of the sun, but its active power is much greater
in proportion, amounting according to some experiments to l-36th of that
of the sun. Magnesium burns when once ignited in carbonic acid. It also
burns when heated in chlorine and bromine. Its specific gravity is 1*74. It
is not readily changed by dry air, but in damp air it loses its lustre, being
slowly oxidized. It may be boiled in a solution of potash without under-
going any change, and in this respect it differs strikingly from zinc and
aluminum, both of which decompose water in alkaline solutions and set free
hydrogen.

Magnesium is now manufactured on a large scale by the reaction of sodium
on chloride of magnesium and the magnesium, is afterwards purified by dis-
tillation. It may be obtained in plates or wire at the rate of about eight
shillings an ounce. The pure or distilled metal is now substituted for zinc
in toxicological researches, and it has the advantage over zinc that it is never
likely to contain arsenic or antimony. The weakest acid causes the libera-
tion of hydrogen when added to water in which a bar of pure magne-
sium has been placed : hence dilated acids which are entirely free from arsenic
may be employed with the magnesium. Pure zinc is with difficulty acted on
by hydrochloric acid, while in reference to magnesium hydrogen is liberated
from the most diluted solution : M. Roussin has investigated the properties
of this metal and his researches show that it is an important agent in the hands
of the chemist. If solutions of the proto and persalts of iron, of zinc, of prot-
oxide of cobalt, or of nickel slightly accidulated are brought in contact with
pure magnesium, there is an escape o/ hydrogen and the different metals are
precipitated in a metallic state. These metals w^hen washed and dried
acquire by compression great metallic brilliancy, and they entirely dissolve
in acids. Iron, cobalt, and nickel so obtained are highly magnetic : zinc
takes the form of a large spongy mass which the least compression renders
brilliant. Magnesium equally precipitates solutions of platinum, gold, mer-
cury, lead, copper, tin, cadmium, bismuth, and thallium. It does not readily
combine with mercury to form an amalgam, and it does not precipitate alumi-
num in a metallic state from its acid solutions. Arsenic and antimony pass
off chiefly with the hydrogen in the form of gas. We have, however, obtained
deposits of metallic arsenic on this metal and subsequently procured crystals
of arsenious acid by sublimation. Powdered magnesium at a high tempera-
ture readily reduces arsenious acid and gives a sublimate of metallic arsenic.

OXIDE OF MAGNESIUM. 361

The absence of any ordinary metal from a solution may now be inferred if
there is no deposit or precipitate on the addition of magnesium, or no escape
of a metal in the form of gas. As it adds only a salt of magnesia to the
liquid, it does not interfere with any further analysis that may be required.

Although magnesium does not decompose water like the other metals of
the allialine earths, very slight causes bring about its oxidation by the decora-
position of water. Thus a band of platinum-foil wound round a bar of
magnesium produces a slight electric current when the metals are immersed
in pure water, but sufficient to cause the slow decomposition of the liquid.
The most diluted acids added to water in which magnesium is placed causes
its decompositionandaliberationofthehydrogen. A weak solution of common
salt, of chloride of ammonium, or of chloride of platinum, has the same effect.
As distilled magnesium contains no silicon or carbon, the hydrogen liberated
from water is quite pure. Magnesium, unlike silver, is not tarnished by sul-
phur-vapors, and its bright silvery lustre may be preserved by covering its
surface when polished, with a thin layer of shell-lac, in spirit. It is perhaps
the only metal which occurs in commerce in a state of absolute purity. It
forms alloys with other metals, but they are for the most part very brittle and
have a great tendency to tarnish. The most permanent is that which it
forms with zinc, but this has not yet been found applicable to any useful
purpose. Mr. Parkinson states that when these two metals are heated
together in air or under a flux, the reaction is violent and explosive. He
found it necessary to combine them under a current of hydrogen. The alloy
with bismuth containing 10 per cent, of magnesium, was found to have re-
markable properties. Thus it deliquesced when exposed to air, and the
action of moist air was so great that the alloy hissed when held in the hand.
{Proc.Chern. Soc.) Magnesium does not readily amalgamate with mercury,
but if, as in the case of zinc, the metal is shaken in a bottle with a mixture
of mercury and diluted sulphuric acid an amalgam is formed. This amalgam
decomposes water violently and nascent hydrogen is copiously evolved. It
is more powerful in this respect than sodium amalgam.

Oxide of Magnesium. Magnesia (MgO). — This, which is the only
compound of magnesium and oxygen, is procured by exposing carbonate of
magnesia to a red heat. It forms a bulky white insipid powder, sp. gr.
about 3*4, nearly insoluble in water, and having an alkaline reaction upon
vegetable colors. Notwithstanding its great insolubility, the alkalinity of
the oxide may be clearly proved by mixing a portion of it with blue infusion
of cabbage or red litmus. The former is turned green, and the blue of the
latter is restored. If the oxide is diffused in water, and a solution of sul-
phuretted hydrogen added, followed by a few drops of a solution of nitro-
prusside of sodium, a rich rose-pink color is brought out. Its basic character
and power of displacing metallic oxides are also proved by mixing it with a
solution of nitrate of silver ; brown oxide of silver is separated. If arsenio-
nitrate of silver is used, a yellow precipitate of arsenite of silver is produced.
Magnesia is almost infusible, and a mixture of lime and magnesia is scarcely
more fusible than the separate earths. It does not absorb carbonic acid, or
moisture, when exposed to air, nearly so rapidly as the other alkaline earths;
and scarcely any heat is produced by pouring water upon it, but it is con-
verted into a hydrate (MgO, HO). When thrown down from its solutions
by potassa, collected upon a filter, and dried at 212°, it still retains water;
but at a temperature below redness, it becomes anhydrous. It is insoluble
in solutions of potassa and soda, but it should be entirely dissolved on boil-
ing it with diluted sulphuric acid. It forms bitter saline compounds with
the acids ; and is readily distinguished by the solubility and bitter taste of

362 CHLORIDE OP MAGNESIUM.

its sulphate. The attractions of magnesia for the acids correspond, in most
instances, closely with those of ammonia, which is in some cases displaced
by, and in others displaces, magnesia. Native hydrate of magnesia is found
in the serpentine rocks of Hoboken, in New Jersey ; and in Unst, one of the
Shetland Isles. It has a pale greenish hue, and a soft lamellar texture ; sp.
gr. 2*3. Sometimes it forms prismatic crystals.

Nitrate of Magnesia (MgO,N05). — This salt may be procured by
digesting carbonate of magnesia in diluted nitric acid, and evaporating to
produce crystallization. It is very deliquescent, and is obtained crystallized
with difficulty, in rhomboidal prisms. It is soluble in half its weight of
water, and in nine parts of alcohol. It has a cooling and bitter taste. It is
decomposed at a red heat, leaving anhydrous oxide of magnesium. St. Clair
Deville found that when this was mixed with water it was converted into a
compact crystallized hydrate. When made into a paste with chalk or pow-
dered marble, it soon became extremely hard, making a kind of artificial
marble. Magnesia in this form appears to have good hydraulic properties.
Nitrate of magnesia is occasionally found in the saline residue of river or
spring water. Its presence causes a fallacy in determining the amount of
organic matter by heating the residue, the nitrate beginning to undergo
decomposition and evolving nitrous acid fumes below redness.

Chloride of Magnesium (MgCl). — Hydrochloric acid, when combined
with water, has a powerful action on this metal. It is rapidly dissolved as
chloride of magnesium, and hydrogen is evolved. M. Gore found, however,
that bright magnesium, when placed in liquefied hydrochloric acid gas, be-
came dull without any visible evolution of gas. Magnesium cannot separate
chlorine from hydrogen except in the presence of water. If magnesia or its
carbonate is treated with hydrated hydrochloric acid, chloride of magnesium
is formed ; but on attempting to procure it in the solid state, the whole of
the hydrochloric acid is expelled and magnesia remains. The chloride may,
however, be obtained by dissolving 1 part of magnesia in hydrochloric acid,
and then adding 3 parts of sal-ammoniac, and evaporating the mixed solution
to dryness. The resulting double salt (NH4,Cb2MgCl) is then decomposed
by a red heat in a covered platinum crucible. When the sal-ammoniac is
expelled, chloride of magnesium remains, and concretes on cooling ; it forms
a crystalline mass, which evolves heat when acted on by water. It cannot
be obtained by simply evaporating its aqueous solution to dryness, for in
that ease hydrochloric acid escapes, and magnesia remains. This magnesia
has the same properties as that obtained from the decomposition of the
nitrate. When a concentrated solution of chloride of magnesium is exposed
to a cold atmosphere, it yields prismatic hydrated crystals (MgCl,6H0),
deliquescent, very soluble in water and alcohol, and of a bitter and biting
taste. This salt is found in a few saline springs, and in the water of the
ocean, forming a principal ingredient in the liquid which remains after the
separation of sea salt, and which is usually called bittern (p. 147). Chloride
of magnesium is now largely manufactured from it as a source for procuring
magnesium. Bromide of magnesium is also a constituent of sea- water.

Chloride of Magnesia. Hypochlorite of Magnesia.— Hhh compound may be
produced by a process similar to that employed for the hypochlorite of lime.
It appears to be a weaker base than lime, and much more readily parts with
its chlorine, hence it has been recently recommended as a more rapidly
bleaching agent than the lime compound. Bolley states that it is a good
bleacher for straw.

SULPHATE OF MAGNESIA. 363

Sulphate OF Magnesia (MgO,SOJ. — The commercial demands for sul-
phate of mag:nesia are chiefly supplied from sea-water, and from magnesian
limestone. When sea-water is resorted to, the greater part of the common
salt is first removed by evaporation, and the remaining bittern, consisting
chiefly of a solution of chloride of magnesium and sulphate of magnesia, is
boiled down with the addition of sulphuric acid, or with sulphate of soda, by
either of which the chloride is ultimately decomposed and converted into
sulphate. The bittern may be also decomposed by hydrate of lime, and the
resulting precipitate afterwards treated by sulphuric acid, by which sulphate
of magnesia and sulphate of lime are obtained. When magnesian limestone
is used as a source of sulphate of magnesia, it is calcined, and reduced to
powder by sprinkling it with water ; it is then diffused through water, and
sulphuric acid is added, and as sulphate of magnesia is so much ftiord soluble
than sulphate of lime, it is easily separated. According to Mr. Swindells,
the manufacture is carried on on a large scale, as the salt is in great demand
for the use of warp-sizers, to add weight to the cloth and thereby give a
false impression of its value. The qy^ntity thus disposed of in Manchester
alone amounts, according to him, to 150 tons per week, and he sets down-
the annual production in this country at 12,000 tons. The salt is of course
removed in the first washing of the cloth. It gives a greater stiffening- pro-
perty to starch. (Chem. Hews, April, 186t.)

A solution of sulphate of lime may be also decomposed by carbonate of
magnesia, as is sometimes seen, where water holding sulphate of lime in solu-
tion, filters through strata of magnesian limestone. The sulphate of magnesia
from bittern is sometimes preferred as a source of magnesia, or of carbonate
of magnesia, in consequence of the absence of iron, traces of which are always
discoverable in the sulphate obtained from magnesian limestone ; but as the
latter is free from chloride of magnesium, and consequently not deliquescent,
and may be obtained nearly pure, it is generally preferred for medicinal use.

There are some saline springs, or mineral waters, in which sulphate of
magnesia is the leading ingredient, as those of Seidlitz, Seydschutz, Egra,
and formerly those of Epsom in Surrey, whence the name of Epsom salt ; it
is also largely obtained in some alum works. It not unfrequently occurs as
a fine capillary incrustation upon the damp walls of cellars and new buildings.
It has been found native, constituting the hair salt of mineralogists. It
appears to be produced, in some springs, by a reaction of sulphate of lime
in the water, on carbonate of magnesia in the soil.

Crystallized sulphate of magnesia (MgOjSOg.THO) forms, at ordinary
temperatures, four-sided prisms with reversed dihedral summits ; or four-
sided pyramids. When the crystals are produced at about 70° to 80°, they
contain 6H0 : at 32° they are large and contain 12 HO. Their density is
1*7. Exposed to air, the salt has, when pure, a slight tendency to efflores-
cence, but the salt of commerce is often deliquescent from the presence of
chloride of magnesium. Its taste is saline and bitter. The crystals are
soluble in about their own weight of water at 60°, and in three-fourths their
weight of boiling water. When exposed to heat, they readily lose six equiva-
lents of water, but retain one equivalent, up to 500. At a red heat this
salt becomes anhydrous, and at a higher temperature it runs into a white
enamel. The anhydrous salt regains water from the atmosphere, and when
sprinkled with water evolves much heat. The aqueous solution of sulphate
of magnesia furnishes a precipitate of hydrated carbonate, upon the additioQ
of carbonate of potassa, or of soda ; but carbonate of ammonia does not
even render it turbid, unless heat be applied, in which case a precipitate of
hydrated carbonate is also thrown down. The alkaline bicarbonates occa-
sion no precipitate when added to a cold solution of sulphate of magnesia,

364 CARBONATE OP MAGNESIA.

but after some hours crystals of hydrated carbonate of magnesia are de-
posited.

Sulphate of magnesia forms compound sulphates with the sulphates of
potash, soda, and ammonia.

Phosphates of Magnesia. Trihasic phosphate of magnesia and water
(2(MgO)HO,P05-f 14:H0). — This phosphate is formed by mixing a solu-
tion of two parts of crystallized sulphate of magnesia in 32 of water, with
a solution of three parts of common crystallized phosphate of soda in 32 of
water : after twenty-four hours, acicular crystals are deposited, having the
above formula. They effloresce in the air, and are sparingly soluble in
water, but readily soluble in dilute acids. At a red heat this salt becomes
a 'pyrophospiiate=^{M.gQ)VOr.

Phosphate of Ammonia and Magnesia (2(MgO)NHp,P05+12HO). —
This salt, formerly designated triple phosphate, is produced when ammonia,
or an ammoniacal salt, is added to a mixture of common phosphate of soda
with any magnesian salt. Thus on adding ammonia or carbonate of ammonia
to a mixed solution of phosphate of soda, and sulphate of magnesia, the
ammonia-magnesian phosphate falls in the form of a white granular precipi-
tate, insoluble in the liquid from which it is thrown down, but sparingly
soluble in pure water, so that it cannot be washed upon the filter without
loss. It is readily soluble in the greater number of diluted acids. If bicar-
bonate of ammonia is used in its formation, it falls slowly, but its appearance
is accelerated by drawing lines with a glass rod upon the surface of the glass
or basin containing the mixed solutions, when the double phosphate pre-
sently appears upon those lines. When this phosphate is heated, it loses
water and ammonia, and at a red heat glows like tinder, and leaves a phos-
phate of magnesia =2MgO,PO-, containing therefore 35't per cent, of mag-
nesia. It is often resorted to for the determination or the presence, and of
the quantity of magnesia.

This salt is frequently deposited from urine, in the form of white sand, or
as a superficial crystalline film, especially in cases where the natural acidity
of the urine is diminished by diet, medicine, or morbid action, constituting
what has been termed the phosphatic diathesis ; it frequently forms urinary
calculi ; and it occurs in intestinal concretions. The presence of phosphate
of magnesia in the husk of grain, in the potato, and other plants, is im-
portant to the agriculturist, and shows why phosphoric acid and magnesia
are contained in fertile soils : its existence in urine, and almost all animal
manures, contributes therefore to their efiBcacy : it has been said especially to
promote the growth of potatoes. It may be detected, in considerable quan-
tity, in good malt liquor.

Carbonate op Magnesia.— This term is applied to the precipitate
obtained by adding carbonate of soda to a solution of sulphate of magnesia,
and edulcorating and drying it : it is generally obtained from boiling solu-
tions, and great attention should be paid to the purity of the water employed
m washing the precipitate, and to the method of drying it. It usually con-
tains from 40 to 43 per cent, of magnesia, 36 to 37 of carbonic acid, and
from 20 to 22 of water ; so that it may be regarded as =5MgO,4C02,6HO :
or 4 atoms of monohydrated carbonate, in combination with 1 atom of bin-
hydrate of magnesia. A light and a heavy carbonate of magnesia are pre-
pared for pharmaceutical use, dependent upon the strength and temperature
of the solutions from which they are precipitated : if these be dilute, it is
light and bulky ; if more concentrated, the product is more dense. When

BORATES OF MAGNESIA. SILICATES OF MAGNESIA. 365

a current of carbonic acid is passed through a mixture of water and car-
bonate of magnesia, under pressure, a clear solution is obtained, which has a
bitter taste, and which, when surcharged with carbonic acid, affords a useful
medicinal preparation ; but a crystallized hicarhonate of magnesia cannot be
obtained. When magnesia is precipitated by carbonate of soda, a portion of
a double soda salt is formed, unless the liquid is boiled. An excess of sul-
phate of magnesia easily dissolves the precipitated carbonate.

There is a carjbonate of lime and magnesia in the mineral known under the
name of hitter spar; it consists of one atom of each of its component car-
bonates. The mineral called Dolomite or magnesian limestone is similarly
constituted, being MgO,C03+CaOC02. There is a band of this mineral
extending from Sunderland to Nottingham, a distance of about ninety miles.
It is of various shades of ochre or light brown color, owing to the presence
of oxide of iron, and in some districts it is hard, in others soft. The hard
variety forms a good building stone. This mineral is the principal source
of magnesia and magnesian compounds. When calcined at a low red heat,
and made into a paste, it is said to form under water a stone of extraordinary
hardness. It has long been known to produce a good hydraulic cement. If
calcined at too high a temperature, its hydraulicity is destroyed. The cal-
cined mineral should be very finely ground to act as a cement. Dr. Calvert
states from his experiments that the strength of the cement is in proportion
to the amount of magnesia present.

Native Carbonate of Magnesia has been found in Piedmont and Moravia,
and at Hoboken, in North America, in veins in a serpentine rock, accom-
panying the native hydrate. A variety of native carbonate of magnesia has
also been brought from India.

Some of the magnesian limestones are well adapted for rough sculpture,
and building materials ; but when porous, or granular, they are subject to
decay, especially in a London atmosphere, where the rain always brings down
some sulphate of ammonia, a salt which acts on the magnesian limestone,
forming carbonate of ammonia, and sulphate of magnesia and lime : these
sulphates, by crystallizing in the pores of the stone, tend to its gradual dis-
integration. It has been attempted to check this crumbling, by washing the
surface first with a solution of silicate of soda, and then with chloride of
calcium, so as to form an insoluble silicate of lime in the pores of the stone,
which tends to cement and indurate it, and trials of this kind are now being
made at the Palace of Westminster : how far it may be possible to arrest
the decay unfortunately going on in many parts of that building remains to
be proved.

Borates op Magnesia. — Several of these salts have been described, but
the only one of interest is Boracite. It is found in Holstein. It sometimes
contains lime. Its sp. gr. is 2-95: it is with difficulty fusible before the
blowpipe, insoluble in water, and slowly soluble in acids. It consists of 3
atoms of magnesia combined with 4 of boracic acid. Sulphate of magnesia
does not give a precipitate with borax until the mixture is boiled.

Silicates of Magnesia. — These compounds are difficult of fusion, but
become less so by the addition of silicate of lime : the neutral silicate, MgO,
SiOg, may be melted in a blast-furnace. Native silicates of magnesia are
abundant : the varieties of serpentine are silicates combined with hydrates of
magnesia. 7a/c, steatite, soap-stone, French-chalk, and meerschaum, are also
magnesian silicates. Viennese meerschaum is an artificial compound pre-
pared by mixing 100 parts of silic.ate of soda with 60 parts of carbonate of
magnesia and 80 parts of native meerschaum or of pure alumina. The

366 TESTS FOR MAGNESIA AND ITS SALTS.

mixture is finely powdered and sifted, mixed with water, boiled for ten
minutes, and then poured into moulds from which the water can easily drain
away. Jade, so extensively used for ornamental purposes by the Chinese, is
a silicate of magnesia and lime. Olivine, or chrysolite, and peridot, found in
igneous rocks, and occasionally accompanying meteoric iron, is a silicate of
magnesia and iron. Many other double magnesian silicates are common
mineral products.

Tests for Magnesia and its Salts. — The oxide of magnesium, or mag-
nesia, is distinguished from the other alkalies and alkaline earths, by its
insolubility in water. With this exception, it has the usual properties of an
alkali in its action on vegetable colors, and on a solution of nitrate of silver.
It is dissolved by acids, forming the salts of magnesia, which are neutral and
characterized by a bitter taste.

The aqueous solutions are precipitated : 1. By potassa or soda, the pre-
cipitate being soluble in hydrochloric, nitric, and sulphuric acids, and in
hydrochlorate, nitrate, and sulphate of ammonia, but not in potassa or soda.
2. Ammonia throws down only part of the magnesia from a diluted solution,
and forms a double salt. The precipitated hydrate of magnesia is soluble in
hydrochlorate of ammonia. Ammonia does not precipitate the solutions of
any other alkali or alkaline earth. 3. Carbonate of potassa or soda throws
down only a part of the magnesia, unless the solution is heated, when nearly
the whole is precipitated. Sal-ammoniac redissolves this precipitate, and
when previously added to the magnesian solution, no precipitate ensues on
adding the alkaline carbonates, unless the liquor is heated. 4. The carbo-
nate of ammonia and bicarbonates of potassa and soda give no precipitate
in magnesian solutions, unless boiled. These tests distinguish a magnesian
salt from the salts of baryta, strontia, and lime, which are precipitated in the
cold. 5. Common phosphate of soda only precipitates concentrated magne-
sian solutions, but if ammonia or carbonate of ammonia is added, the mag-
nesia is precipitated in the form of ammonio-magnesian phosphate, insoluble
in hydrochlorate of ammonia, and diluted ammonia. Moistened with acetate
of cobalt, and heated before the blowpipe, the magnesian salts give pale
rose-colored compounds : the tint is only distinct on cooling, and never
very intense. 6. Sulphuric acids and the alkaline sulphates, oxalic acid and
the oxalates, give no precipitate in a solution of a salt of magnesia. 7. A
magnesian salt, if pure, gives no color to the flame of alcohol. The light of
magnesium, burning in oxygen or air, produces a spectrum similar to that
of solar light. The colors are perfect, and of the most intense description.
It thus shows the colors of all objects.

^ In quantitative analysis, magnesia is almost always precipitated by a solu-
tion of phosphate of soda, to which ammonia or its carbonate has been pre-
viously added ; it is collected and washed with the precautions above men-
tioned, and ignited so as to be weighed in the state of pyrophosphate.
Every 100 parts of ammonio-magnesiura phosphate, dried at 60°, indicate
16-26 of magnesia: every 100 parts of its residue, after ignition, indicate
35 T parts of magnesia, and 64-3 of phosphoric acid.

OXIDE OF ALUMINUM. 36t

CHAPTEE XXVII.

ALUMINUM — G LUC INUM — ZIRCONIUM — THORIUM — YTTRIUM
— E R B I U M— T E R B I U M— C ERIUM— LANTHANU M— D I D Y M I U M .

Aluminum (AI = 14).

Aluminum is obtained on decomposing the chloride of aluminum by
sodium at a high temperature : intense ignition ensues, and the jeduced
aluminum forms metallic globules in the midst of the chloride of sodium,
which is removed by water. (Al3Cl3+3Na=2Al+3NaCl). The mineral
called cryolite (a double fluoride of aluminum and sodium) has also been used
as a source of the metal, and is decomposed when heated with sodium,
yielding globules of aluminum, imbedded in fused fluoride of sodium, which
is easily dissolved by water. The changes which take place may be thus
represented : Al,F3,3NaF+3Na = 2Al + 6NaF.

Aluminum is a bluish white malleable and ductile metal, of about the
hardness of silver ; its specific gravity, when rolled, is about 2-67, and when
cast 2-56. Its point of fusion is, according to Deville, 1750^. It is not
acted upon by air or water at common temperatures, but damp air slowly
tarnishes it. When intensely heated in a current of air, it suffers only slight
oxidation : heated to redness in an atmosphere of steam, it is slowly oxid-
ized. It is readily acted upon by hydrochloric acid, which evolves hydro-
gen and forms chloride of aluminum : neither sulphuric nor nitric acid
affects it at common temperatures, but when boiled in the latter, it is oxidized
only so long as the heat is maintained. These acids, when diluted, do not
affect it, and it may be boiled in acetic acid without undergoing any chemi-
cal change. Hydrofluoric acid is decomposed by it, hydrogen is set free,
and fluoride of aluminum, a constituent of the topaz and of cryolite, is pro-
duced. Weak alkaline solutions of potash and soda slowly act upon and
dissolve it, giving to the surface a frosted appearance ; but when the solu-
tions are concentrated, it is oxidized, and hydrogen is liberated. This action
is increased when the alkaline solution is heated. It forms alloys with many
of the other metals, but does not combine with mercury. It is not affected
by sulphur or sulphuretted hydrogen, or by solutions of the alkaline sul-
phides. The metal is now largely manufactured in England and France,
and is much used for ornamental and other purposes. Its lightness is a
great recommendation. Under the same bulk it has only about one-fifth of
the weight of silver. It forms a golden-colored alloy with copper in the
proportion of 90 parts of very pure copper to 10 of aluminum — called
aluminum bronze — the specific gravity of which is 7 "689. It has, when fresh
polished, a deep golden lustre, but is rapidly tarnished. There is a white
alloy with silver, but this has not been much used.

Oxide op Aluminum. Alumina (Al^OJ. — To obtain alumina we de-
compose a solution of alum by excess of carbonate of ammonia, wash the
precipitate with repeated portions of hot distilled water until all soluble
matters are removed. In this state alumina is obtained as a white gelati-
nous hydrate. When dried and heated to redness, it forms anhydrous
alumina. This may be at once obtained by igniting pure ammonia-alum,

368 HYDRATES OF ALUMINA.

sulphate of ammonia evaporates, and alumina remains, perfectly white, and
soft to the touch, but almost insoluble in acids.

Alumina is a colorless, insipid, and insoluble powder, without any action
upon vegetable colors ; in other words, a perfectly neutral compound. It
does not set free oxide of silver from a solution of nitrate ; and when dif-
fused in water, it produces no change of color with sulphuretted hydrogen
and a solution of nitro-prusside of sodium. Its specific gravity is 2, but
after exposure to an intense heat, about 4. By the oxy hydrogen blowpipe
it may be fused into a colorless globule. It has a strong attraction for
moisture, which it rapidly absorbs from humid air, to the amount of one-
third of its weight. When mixed with water, alumina is characterized by
the plasticity of the mixture ; and if the paste be dried in the air, and then
heated, it shrinks considerably in consequence of the loss of water, but it
retains its form. Alumina has a strong affinity for various organic com-
pounds, and its use in the arts of dyeing and calico-printing depends upon
its attraction for different coloring- principles, and for woody fibre. If am-
monia is added to a solution of alum in infusion of cochineal, or of madder,
the alumina falls in combination with the coloring-matter, and the super-
natant liquor remains colorless. Colors thus prepared are called Zcd-es.
A small quantity of hydrate of alumina added to hard and impure water,
tends to purify it. The alumina is slowly deposited with the organic impu-
rities. A few drops of a solution of alum, added to water containing calca-
reous or soda salts, operates in a similar manner, alumina being precipitated
and acting as a clarifier to the water. Moist hydrate of alumina is readily
soluble in most of the concentrated acids; but after the expulsion of its
water by heat, it is dissolved with more difficulty, and may be con^dered
insoluble. It is sparingly soluble (when moist) in caustic ammonia ; but
potassa and soda readily dissolve it ; it is also soluble, to a small extent, in
the aqueous solutions of baryta and strontia. It forms no combination with
carbonic acid. The fixed alkaline solutions of alumina are decomposed by
the acids, and by ammoniacal salts.

Alumina, like other sesquioxides, is a comparatively feeble base ; none of
its salts are, in fact, neutral, but have an acid reaction ; and in respect to
the more powerful basic oxides, it has been represented as performing the
part of an acid, so that such compounds have been termed Aliuninates.
Many of these combinations exist native. Alumina in the state of hydrate
is recognized by its solubility in caustic potassa; by the formation of octa-
hedral crystals of alum on evaporating its sulphuric acid solution»with the
addition of sulphate of potassa ; by the astringent sweetness of this sul-
phate ; by the octahedral crystals of alum deposited on evaporation ; and by
the blue color which it affords when moistened with nitrate of cobalt and
strongly heated.

Native alumina constitutes the sapphire, which occurs either colorless or
pale-bkie, is extremely hard, and occasionally crystallized; its specific
gravity is about 3-5. The oriental ruby and the oriental topaz are red and
yellow varieties of sapphire. Corundum adamantine spar, and emery, also
consist chiefly of alumina, with less than 2 per cent, of oxide of iron, and a
trace of silica : the specific gravity of corundum is about 4. All these sub-
stances are extremely hard, being, in that respect, second only to diamond.
They are aluminous minerals, and consist chiefly of anhydrous alumina
slightly colored.

Hydrates of Alumina.— Alumina, precipitated from its solutions, and
dried at between 70^ and 80°, retains about 60 per cent, of water; but its
physical characters vary, dependent upon the strength of the solution from

SULPHATE OF ALUMINA AND POTASSA. 369

which it is precipitated. When thrown down from a saturated solution of
alum, it is pulverulent ; but from a dilute solution, gelatinous : the pulveru-
lent hydrate loses its water at a red heat. Diaspore and Gihbsite are native
hydrates of alumina.

Chloride of Aluminum (Al^Clg). — This compound may be obtained as
follows : Alumina is mixed into a paste with powdered charcoal, oil, and
sugar, and this is heated in a covered crucible till the organic matter is
decomposed : an intimate mixture of the alumina with charcoal is thus
obtained, which is introduced, whilst hot, into a porcelain tube, placed in a
convenient furnace ; dried chlorine is then passed through it into a receiver
attached to the other end of the tube, and the air being thus expelled, the
tube is heated red-hot, and chlorine gradually passed into it ; carbonic oxide
is disengaged, and chloride of aluminum formed, which chiefly collects
within the tube, and ultimately plugs it up. This was chiefly made for the
extraction of aluminum. Alumina is mixed with charcoal, and chlorine is
passed over the mixture when heated to a high temperature. The volatile
chloride of aluminum distils over. It is a volatile yellow-colored solid;
it fumes and deliquesces when exposed to air; it is energetically acted upon
by water, and is very soluble in alcohol ; it may be preserved in naphtha.
When a solution of alumina in hydrochloric acid is evaporated, a deliques-
cent hydrated chloride remains, which at a higher temperature evolves hy-
drochloric acid and leaves alumina.

Sulphate of Alumina (Al.^Og.SSOg) is formed by digesting hydrate of
alumina in sulphuric acid diluted with an equal bulk of water; the solution
is evaporated and alcohol added, which throws down the tersnlphate. It
dissolves in 2 parts of water, and forms small lamellar crystals, of a sweet
and astringent taste, which include 18 atoms of water. When excess of hy-
drated alumina is boiled in the diluted acid, and the solution filtered, and
evaporated in vacuo over sulphuric acid, it congeals into a soft, white, semi-
transparent mass, which may be dried on blotting paper, and is not altered
by the air. When ammonia is added to a solution of sulphate of alumina,
a white powder falls, which is not decomposed by excess of ammonia, and
which, when well washed and carefully dried, has the formula of a basic
sulphate (AlgOajSOajOHO). It exists native, forming the mineral called
aluminite.

Sulphate of Alumina and Potassa ; Common Alum; Potassa Alum

(K0,S03; Al3,03,3S03 ; 24HO) This useful salt is manufactured upon an

extensive scale. Aluminous slate, or shale, which is an argillaceous slaty
rock containing sulphide of iron, is roasted so as to oxidize the iron and
acidify the sulphur ; on lixiviating the roasted ore, a sulphate of alumina is
obtained, which, with the addition oi sulphate of potassa, yields alum. The
shales or wastes of old coal mines, which fall down in a decomposing state,
yield, on lixiviation, especially after prolonged exposure to air and moisture,
considerable quantities of sulphate of alumina and sulphate of iron ; the
solution of these salts is evaporated, and, when sufficiently concentrated, is
run out into coolers, where the sulphate of iron crystallizes, and the sulphate
of alumina, being more soluble, remains in the mother-liquors. TJo these,
when heated, sulphate, or chloride of potassium is added, and they then yield
crystals of alum, not at first pure, but rendered so, and obtained in beauti-
fully-perfect octahedra, by recrystallization. When chloride of potassium is
used, it decomposes the sulphate of iron of the alum-liquors, forming chloride
of iron and sulphate of potassa; the latter salt goes to the formation of alum,
24

370 SULPHATE OF ALUMINA AND AMMONIA

leaving the chloride of iron in solution. There are other methods of manu-
ifacturing alum, such as by the decomposition of clay by sulphuric acid, and
by the lixiviation of certain alum stones, as they are called, which are pro-
ducts of the joint action of sulphurous acid and oxygen upon volcanic rocks
containing alumina and potassa.

Ordinary alum has a sweet and astringent taste, accompanied by some
degree of acidity ; its sp. gr. is ri2 : it reddens vegetable blues : it dissolves
in about 16 parts of cold water, and in less than its weight of boiling water.
The crystals are permanent in the air, or only very slightly efflorescent in a
dry atmosphere ; when heated, they fuse in their water of crystallization, and
when this is expelled the dry (anhydrous) alum becomes opaque and spongy,
and in this state is termed roche alum, or burnt alum. At a temperature of
140°, alum gradually loses 18 atoms of its water of crystallization. When
long retained in fusion it loses 18'95 percent, of water, and ultimately forms
a vitreous mass, which retains 14 atoms of water: if in this state it be kept
at a temperature of 248° for 12 hours, the loss of water amounts to about
38 per cent., and it forms a porous mass retaining 5 atoms of water ; it then
remains unchanged up to 320° ; but at 856 it sustains a farther loss of water,
amounting on the whole to 43 5 per cent., so that the residue only retains
one atom of water, which is not expelled under a temperature approaching
to redness. Anhydrous alum gradually absorbs water from the atmosphere.
When freshly prepared, and put into water, it appears almost insoluble, and
remains for a long time nearly unchanged ; but if previously exposed to the
atmosphere, it dissolves more readily. At a red-heat, alum first loses that
portion of its acid belonging to the alumina, and ultimately the sulphate of
potassa is itself decomposed under the influence of the alumina, which com-
bines with the potassa forming an aluminate and displaces the sulphuric acid.

If the quantity of carbonate of soda necessary to neutralize a portion of
alum be divided into three equal portions, and added in a gradual manner
to the aluminous solution, it will be found that the alumina first precipitated
is redissolved upon stirring, and that no permanent precipitate is produced till
nearly 2 parts of alkaline carbonate are added. It is in the condition of this
partially-neutralized solution that alum is generally applied as a mordant.
When this solution is concentrated, alum crystallizes from it, generally in the
cubic form, hence the name cubic alum, and the excess of alumina is precipi-
tated. Alum is a salt of extensive use in the arts, especially for the prepara-
tion of mordants employed by the dyer and calico-printer ; it is also employed
in preparing and preserving skins ; in pharmacy it is used as an astringent
and a styptic. When potassa-alum is ignited with charcoal, a spontaneously-
inflammable compound results, which has long been known under the name
of Homberg^s pyrophorus. The potassa is decomposed in this process, as
well as the acid of the alum ; the pyrophorus is probably a compound of
sulphur, charcoal, potassium, and aluminum. Potassa is not readily disco-
vered in potassa-alum until the alumina has been removed. Thus neither
fluosilicic acid nor tartaric acid will precipitate potassa from a concentrated
solution ; and chloride of platinum produces after a time only a slight tur-
bidness. Potassa-alum may, however, be easily identified by the lilac color
given to flame when a small portion of the powder is heated beyond fusion
on fine platinum wire ; soda-alum gives under the same circumstances a yel-
low color; and ammonia-alum, if free from these two bases, imparts no color
to flame.

Sulphate of Alumina and Ammonia. Ammonia' Alum (XH^0,S03 ;
AlaOg.SSOg ; 24FIO). — This salt is obtained exactly as the preceding, only
sulphate of ammonia is substituted for sulphate of potassa : its atomic con-

SILICATES OF ALUMINA. 371

stitution also resembles that of potassa-aliira ; and it is so similar in other
respects, that, as far as mere appearance and more obvious properties are
concerned, the two salts are not readily distinguished. It is recognized by
evolving ammonia, when triturated with lime or potassa. This variety of
alum is manufactured on a large scale with the sulphate of ammonia derived
from gas-works. It has no ammoniacal odor. When heated it loses water,
then ammonia, and at a very high heat, its acid, the residue being pure
alumina.

Sulphate of Alumina and Soda. Soda-Alum (NaO.SOg ; Al^Oa.SSOa;
24HO). — This salt is formed when the sulphate of potassa of common alum
is replaced by sulphate of soda ; it crystallizes in octahedra, which are less
hard, smooth, and regular, than those of potassa-alum ; they efiSoresce in dry
air, and at 110^ to 120° become opaque and gradually lose their water of
crystallization, the whole of which is expelled at a red heat. They dissolve
in 214 of water at 55°, and in their own weight at 212°.

The three alums are isomorphous, and the bases may replace each other
without altering the crystalline form. So the alumina may be replaced by
isomorphous oxides — e. g., the sesquioxides of iron, chromium, and manga-
nese ; hence the following may be taken as a general formula for the alums ;
KO(NH,0,NaO,C£eO,RbO)S03,Al,03(FeA»CrAMnA)3S03,24HO. (p.

Sulphate of Alumina and Lithia. Lithia Alum (LiO,S03 ; AI2O3,
3SO3; 24HO). — When an aqueous solution of sulphate of lithia and sulphate
of alumina is subjected to spontaneous evaporation at a temperature not
exceeding 52°, it yields octahedral and rhombic dodecahedral crystals solu-
ble in 24 parts of cold, and 0*87 of boiling water.

The new alkalies, caesia and ruhidia also form alums with sulphate of alu-
mina, similar in constitution and form to potassa-alum.

Phosphates of Alumina. — Common phosphate of soda gives a gelatinous
precipitate with solution of alum, which dries into a white insipid powder,
insoluble in water, and in solution of sal-ammoniac, but soluble in acids and
in solution of potassa. The mineral known under the name of Wavellite is a
hydrated phosphate of Alumina, SAlgOg", 2P03,12HO. Turquois or Galaite
is a phosphate of alumina =2(Al303)P05-f-5HO, colored by oxide of copper.
Amhligonite is a phosphate of alumina and lithia, and Lazulite contains phos-
phate of alumina with phosphate of iron.

Alumina does not combine with carbonic acid.

Silicates of Alumina. — All the varieties of clay are silicates or hydrated
silicates of alumina; they are frequently largely mixed with other substances,
but their important uses in agriculture and the arts are referable to the above
silicate. Several minerals are definite crystalline silicates, which by disin-
tegration or decomposition, contribute to the formation of clay; common
felspar is a silicate of alumina and potassa ; Al^Og; 3Si03+KO,Si0.j: it is
one of the constituents of granite, and some of its varieties crumble, when
exposed to the joint action of air and water, int(5 a white clay : Cornish clay,
and the Kaolin of China, are clays so formed, and may be represented as
Al2,03; SSiOg-f 2H0. Other clays are less pure, from the admixture of
sand, oxide of iron, or carbonate of lime, substances which importantly
modify their properties. The varieties of marl are calcareous clays ; and
the colored clays generally derive their various tints from the oxides of
iron. The presence of these and some other extraneous matters, renders

312 POTTERY AND PORCELAIN.

some clays very fusible : the pure aluminous silicates are nearly infusible,
but when lime, maprnesia, or oxide of iron, is present, they become more or
less fusible or vitrifiable, in proportion to tlie quantity of these bases present
in the cla!f. The varieties oti fire- day used for lining furnaces, and other
similar purposes, are nearly pure silicates =Al2, 03,88103, with mere traces of
alkaline bases and oxide of iron. The different red and yellow ochres, and
boles, are mixtures of clay and hydrated peroxide of iron ; some of them con-
tain oxide of manganese. FuUer^s earth, used for the capillary absorption of
greasy matters, is also a porous silicate of alumina. Clay has some remark-
able distinctive properties ; it exhales a peculiar odor when wetted or breathed
upon, and when dry and applied to the tongue, it adheres to it, in consequence
of the rapidity with which it absorbs moisture; it readily absorbs ammonia,
and many other gases and vapors generated in fertile and manured soils ;
hence its agricultural value. The important quality o{ plasticity, upon which
the manufacture of porcelain and pottery depends, belongs exclusively to
aluminous combinations in their humid state, so that they admit of being
turned in the lathe or upon the potter's wheel, or of being moulded into the
infinite variety of useful and ornamental products of the ceramic art. These
forms are rendered permanent by careful drying, and subsequent exposure to
high temperatures.

Tests for the Salts of Alumina. — These salts have an astringent,
sweet, and subacid taste, and redden litmus. 1. They are precipitated by
potassa or soda, the precipitate being redissolved when the alkalies are added
in excess, but the alumina is ag«in precipitated by hydrochlorate of ammonia.

2. The precipitate produced by ammonia is not soluble to any extent in
excess of that alkali, and it is not dissolved by hydrochlorate of ammonia.

3. The carbonates and bicarbonates of potassa, soda, and ammonia, throw
down hydrated alumina, with the escape of carbonic acid, and the precipitate
is nearly insoluble in an excess of the precipitants. 4. Sulphate of potassa,
with a little sulphuric acid, added to an acid solution of alumina, deposits,
by concentration, a crystalline compound, which is alum. 5. Phosphate of
soda produces a flocculent precipitate of phosphate of alumina. 6. When
aluminous substances are heated by the blowpipe with nitrate of cobalt, they
acquire a blue color, which is only distinctly seen by daylight after the mix-
ture has cooled. T. Hydrosulphate of ammonia gives a precipitate which is
gelatinous hydrate of alumina — sulphuretted hydrogen being set free. This
result is owing to the action of ammonia — as sulphuretted hydrogen produces
no precipitate (of sulphide) in the solutions. The gelatinous hydrate is
readily dissolved by a solution of potassa. This test serves to distinguish
a solution of alum from one of magnesia, since unless the hydrosulphate
contain free ammonia, it will give no precipitate with a salt of magnesia. If
a precipitate is formed (by reason of the presence of ammonia) it is recog-
nized as hydrate of magnesia by its being dissolved by hydrochlorate of
ammonia. Hydrate of alumina is insoluble in this liquid. Ferrocyunide of
potassium has no action upon a salt of alumina.

Pottery and Porcelain —The better kind 0^ pottery, called in this country
Staffordshire ware, is made 'of a mixture of alumina and silica ; the former
obtained in the form of a fine clay, from Devonshire chiefly, and the latter,
consisting of chert or flint, heated red-hot, quenched in water, and then re-
<3uced to powder. Each material, carefully powdered and sifted, is diffused
through water, mixed by measure, and brought to a due consistency by
evaporation : it is then highly plastic, and may be formed upon the
potter's wheel and lathe in circular vessels, or moulded into other forms,

POTTERY AND PORCELAIN. 3T3

which, after having been dried in a warm room, are inclosed in baked clay
cases, called seggars ; these are ranp^ed in a kiln so as nearly to fill it, leaving
only space enou«?h for the fuel ; here the ware is kept red hot for a consider-
able time, and thus brought to the state of biscuit. This is afterwards glazed^
which is done by dipping the biscuit-ware into a tub containing a mixture of
about 60 parts of litharge, 10 of clay, and 20 of ground flint, diffused in
water to a creamy consistence, so that when taken out, enough adheres to the
piece to give an uniform glazing when heated. The pieces are then again
packed up in the seggars, with small bits of pottery interposed between
each, and fired in a kiln as before. The glazing-mixture fuses at a moderate
heat, and gives an uniform glossy coating, which finishes the process when
it is intended for common white ware. The presence of lead in glazes is often
objectionable, and may be dispensed with by using borax, which, however,
is too expensive for common use. 100 parts of silica, 80 pearlash, 10 nitre,
and 20 lime, fused, and then finely powdered, form a good glaze.

Glazed cast-iron vessels for culinary and other purposes are manufactured,
in which the absence of lead in tlie glaze is important : those manufactured
at Wolverhampton are glazed with a mixture of borax, potter's clay, and
pulverized flints, to which powdered plate, or crown glass (free from lead),
and a little carbonate of soda, are added. These ingredients are fused
together; and the mass, reduced to a fine powder, is mixed with water and
applied to the clean surface of the iron, upon which it is dried, and vitrified
by exposure to heat in a muffle.

The patterns upon ordinary earthenware, which are chiefly in blue, in con-
sequence of the facility of applying cobalt, are generally first printed off
upon paper, which is applied to the plate, or other article, while in the state
of biscuit ; the color adheres permanently to the surface when heat is properly
applied. In the manufacture of porcelain, the materials are so selected that
the compound shall remain perfectly white after exposure to heat, endure a
high temperature without fusing, and at the same time acquire a semivitreous
texture, and a peculiar translucency and toughness. These qualities are
united in some of the Oriental porcelain, or China, and of the French, Eng-
lish, and German porcelain. The Berlin porcelain, so justly esteemed in
the laboratory, consists of about 71 silica, 24 alumina, 2 potassa, 1*5 pro-
toxide of iron, and 1*5 lime and magnesia. The colors employed in painting
porcelain, are the metallic oxides which are used for coloring glass ; and in
all the more delicate patterns they are laid on with a camel-hair pencil, and
generally previously mixed with a little oil of spike-lavender or of turpen-
tine. When several colors are used, they often require various tempera-
tures for their perfection ; in which case those that bear the highest heat
are first applied, and subsequently those which are brought out at lower
temperatures. This art of painting on porcelain, or in enamel, is of the
most delicate description : much experience and skill are required in it, and
with every care there are frequent failures. The gilding of porcelain is
generally performed by applying finely-divided gold mixed up with gum-
water and borax; upon the application of heat the gum burns off, and the
borax vitrifying upon the surface, causes the gold firmly to adhere ; it is
afterwards burnished.

Crucibles composed of one part of good clay mixed with three of coarse
sand, slowly dried and annealed, resist a very high temperature without fusion,
and generally retain metallic substances ; but when the metals oxidize, there
are few which do not act upon earthen vessels ; and when saline fluxes are
used, the best of them suffer. Whenever silica and alumina are blended,
the compound softens, and the vessel loses its shape if exposed to a white
heat ; this is even the case with Hessian crucibles. The most refractory of

374 GLUCINUM. ZIRCONIUM.

all vessels are those made entirely of clay, coarsely-powdered burned clay
being used as a substitute for sand : these resist saline fluxes longer than
others, and are therefore used for the pots in glass-furnaces. Plumbago is a
good material for crucibles, and applicable to many purposes ; when mixed
with clay, it forms a very difficultly fusible compound, and is protected from
the action of the air at high temperatures.

Liites. Under this term, a variety of compounds are used for securing the

junctures of vessels, or protecting them from the action of heat. Slips of
wetted-bladder ; linseed meal made into a paste with gum- water ; white of
e^g and quicklime ; glazier's putty, which consists of chalk and linseed oil ;
2knd fat lute, composed of pipeclay and drying-oil, are useful for retaining
vapors ; but to withstand the action of a high temperature earthy compounds
are required. Loam, or a mixture of clay and sand well beaten into a paste
and then thinned with water, and applied by a brush in successive layers, to
retorts, tubes, &c., enables them to bear a high temperature ; if a thick coating
is required, care should be taken that the cracks are filled up as the lute
dries ; a little tow mixed with it renders it more permanent. If the lute is
intended to vitrify, as, for instance, to prevent the porosity of earthenware at
high temperatures, a portion of borax, or of red-lead, may be mixed with it.

Glucinum (G='7).

Glucinum is obtained in decomposing its chloride by means of sodium.
•It is a gray malleable metal, sp. gr. 2-1. Its fusing point is a little below
that of silver: it is not altered by exposure to air, and is difiQcult of oxida-
tion, even in the flame of the blowpipe.

Oxide op Glucinum or Glucina (GaOg), was first discovered in the beryl:
it also exists in the emerald, in euclase, in the chrysoberyl, in phenakite, and
in a few other rare minerals. It is white, insipid, and insoluble in water;
it has no action on vegetable colors ; its specific gravity is 2-97. It dis-
solves, especially in the state of hydrate, in solution of caustic potassa and
soda, but not in ammonia. It differs from alumina in being soluble, when
freshly precipitated, in carbonate of ammonia. With the acids it forms
saline compounds of a sweetish astringent taste. From these solutions the
carbonates of potassa and soda throw it down in the form of a bulky hydrated
carbonate.

Characters of the Salts of Glucina. — These salts are astringent and sweet ;
they are precipitated by the caustic fixed alkalies, and the precipitate is re-
dissolved by their excess, and sparingly by their carbonates : it is not solu-
ble in caustic ammonia, but readily so in carbonate of ammonia, and the
oxide is again precipitated on boiling the liquid. A characteristic property
of glucina is, that when a warm solution of it is mixed with a warm solution
of fluoride of potassium, till a precipitate begins to appear, and the mixture
is then suffered to cool, a difiBcultly soluble double salt separates in the form
of lamellar crystals. Sulphate of glucina does not form a erystallizable
double salt (like alum) when mixed with sulphate of potassa.

Zirconium (Zr=34).

Zirconium is obtained by acting upon the potassio-fluoride of zirconium
by potassium at a red heat. When cold the product is thrown into water,
and the zirconium separates in the form of a black powder, having the appear*
ance of plumbago. Troost obtained it in a crystallized state, by heating
the double fluoride, of zirconium and potassium with aluminum. After
heating the mixture to a temperature equal to that of melted iron, crystal-

TIIORINUM, OR THORIUM. 375

line plates of zirconium, lyin^^ close tof^ether, like the leaves of a book, were
found upon the surface of the alurainura. Some zirconium combines with
the aluminum and at the temperature of melted silver only an alloy of the
two is obtained. Troost considers zirconium to belong to the carbon group
and places it between silicon and aluminum. {Quart. Journ. of Science,
1865.) It is not easily soluble in acids, with the exception of the hydro-
fluoric, which readily dissolves it, evolving hydrogen. Heated in the atmos-
phere it burns into zirconia.

Oxide of Zirconium ; Zirconia {7i\\0^) is of rare occurrence, having
only been found in tlie Zircon or Jargon, and a few other scarce minerals.
Zircon, when colorless and transparent, ranks among the gems : when
colored brown or red, it is termed hyacinth. This mineral contains between
60 and 70 per cent, of zirconia, combined with silica and a little oxide of iron.
Zirconia is obtained by fusing finely powdered zircon with soda, saturating
the product with hydrochloric acid, evaporating the solution to dryness, re-
dissolving in water, and precipitating by excess of ammonia: the precipitate
is then washed, dried, and ignited. Zirconia is a white infusible substance,
insoluble in water; specific gravity 4*3: it gives intense luminosity to the
blowpipe flame. After having been heated to redness it resists the action
of the acids, with the exception of the sulphuric. It is insoluble in caustic
alkalies. Chloride of Zirconium forms efflorescent acicular crystals, soluble
in water and in alcohol.

The Salts of Zirconia have an astringent taste. They are precipitated by
caustic potassa, and the precipitate is nofr soluble in excess of the alkali.
When boiled with sulphate of potassa, a sparingly soluble subsulphate of
zirconia subsides. Infusion of galls produces in them a yellow precipitate ;
and phosphate of soda throws down a white phosphate of zirconia. The
recently precipitated carbonate of zirconia is soluble in excess of bicarbonate
of ammonia or of potassa.

Thorinum, or Thorium (Th=60).

By passing a current of dry chlorine over a mixture of thorina and char-
coal-powder, a crystalline chloride of thorinum is obtained, which is easily
decomposed by potassium, and the product is thorinum. It is of a gray
color, metallic lustre, and apparently malleable. It is not oxidized by water,
but when heated in the air it burns into thorina. It is feebly acted on by
sulphuric acid, and scarcely by nitric acid ; it is not attacked by the caustic
alkalies at a boiling heat. Hydrochloric acid dissolves it, with the evolu-
tion of hydrogen.

Oxide of Thorinum : Thorina (ThO). — This oxide, hitherto only found
in a rare Norwegian mineral, Thorite, is white, and insoluble in the acids,
with the exception of the sulphuric. When thrown down in the state of
hydrate it dissolves more readily, and exposed to the air absorbs carbonic
acid.

Thorina is distinguished from the other oxides by the following proper-
ties : from alumina and glucina, by its insolubility in pure potassa ; from
yttria, by forming with sulphate of potassa a double salt, which is insoluble
in a cold saturated solution of sulphate of potassa; from zirconia, by the
circumstance that after being precipitated from a hot solution of sulphate
of potassa, it is almost insoluble in water and the acids. Thorina is precipi-
tated also by ferrocyanide of potassium, which does not separate zirconia
from its solutions. Sulphate of thorina is more soluble in cold than in hot

376 YTTRIUM. ERBIUM. CERIUM. LANTHANUM. DTDYMIUM.

water, so that a cold saturated solution becomes turbid when heated, and, on
cooling, recovers its transparency.

Yttrium (Y=32).

Yttrium is obtained by decomposing its chloride by potassium : it is gray,
brittle, and resists the action of air and water.

Oxide of Yttrium, or Yttria (YO), was first discovered in Gadolinite, a
mineral found at Ytterby, in Sweden ; it also occurs in a very few other rare
minerals.

Erbium. Terbium.

According to Mosander, Yttria is always accompanied hy Erhia and Terhia,
the oxides of two distinct metallic bases. Erbia Is pale yellow, and Terbia
pale red ; but none of these substances have been adequately examined or
identified.

Cerium (Ce=46).

By heating chloride of cerinm with potassium, an alloy is obtained which
evolves hydrogen when put into water, and leaves cerium in the form of a
gray metallic powder. Heated in the air it burns into an oxide, and it is
soluble in the weakest acids with the evolution of hydrogen.

Cerium forms two oxides : the protoxide (CeO), which forms colorless
salts; and the sesquioxide (Ce203), which forms red salts. Cerium has
hitherto been found in a few minerals only, and it seems doubtful how far the
properties ascribed to its oxides and salts, are not more or less dependent
upon the presence of other bodies. Its most characteristic salt is the double
sulphate of cerium and potassa. The oxalate of cerium has been lately
employed in medicine.

Lanthanum (La=44).

This metal is associated with Cerium. All its salts are said to be color-
less. When the oxalate is heated, it leaves a white carbonate, which at a
higher temperature, is converted into a light brown anhydrous oxide : the
white hydrated oxide attracts carbonic acid so rapidly, that it cannot be
completely washed upon a filter without conversion into carbonate.

Didymium (Di=48).

Didymium accompanies lanthanum and cerium in the minerals containing
the latter metal. It appears to form one oxide only, of a brown color ; and
all its sorts are colored, some being pink, others violet. The sulphate and
nitrate are rose-colored ; the hydrated oxide, carbonate, and oxalate are
violet, and when ignited leave a dark-brown anhydrous oxide, readily soluble
in dilute acids, and absorbing carbonic acid from the air.

The atomic weights attached to these metals are of doubtful accuracy.
(Watts's Jour. Ghera. Soc, ii. 131.)

CHAPTER XXVIII.

QUALITATIVE ANALYSIS OF THE OXIDES AND SALTS OF
THE PRECEDING METALS.

The oxides of the metals described in the preceding chapters form three
well-marked groups. 1. The Alkalies, comprising potassa, soda, lithia,

CHEMICAL CHARACTERS OF ALKALIES AND EARTHS 3TT

coesia, rubidia, and thallia (Tlo), to which may be added ammonia, the
chemical characters of which have been considered at paj^e 181. 2. AlknUne
earths, baryta, strontia, lime, and magnesia ; and 3. The Earths, of which
only one is selected as a type of the others, namely, alumina.

The bases comprised in these three groups, whether in acid or neutral
solutions, are not precipitated by a current of sulphuretted gas. One of
them, alumina, is precipitated from its solution as hydrated oxide by a solu-
tion of sulphide of ammonium.

1. The Alkalies. — This name is applied to the oxides of those metals
which are soluble in water and alcohol ; they are marked by the following
characters : 1. They have an acrid caustic taste. 2. Tiiey are corrosive to
organic matter. 3. They neutralize acids, and form salts. 4. They com-
bine with the oily acids to form soaps. 5. They exert a peculiar action on
vegetable colors. As it is by the last-mentioned character that their pre-
sence is commonly recognized in analysis, it may be stated that an alkali
restores the blue color to red litmus ; that it renders blue infusion of cabbage
green, and yellow tincture of turmeric red-brown. Blue litmus-paper, red-
dened by a weak acid, turmeric-paper, or rose-paper (paper impregnated
with a strong infusion of red roses), may be employed in the preliminary
testing for alkalies. Well-made rose-paper is nearly colorless, and it
acquires a bright green color as the result of the action of a diluted alkali.
If the alkaline solution is concentrated, the coloring matter is destroyed, and
the rose-paper acquires a brownish-yellow tint. Blue infusion of cabbage,
the method of preparing which has been elsewhere described (p. t6), is
admirably adapted for a test-liquid. It acquires a red color from an acid
solution, a green color from an alkaline solution, and it remains blue if the
solution is neutral. The nitro-prusside of sodium is also a delicate test of
alkalinity in a liquid. In order to employ it, a small quantity of sulphu-
retted hydrogen is passed into the suspected solution, and a few drops of
nitro-prusside of sodium are added. A magnificent rose, purple, blue, or
crimson color speedily manifests itself, according to the strength of the alka-
line solution. The color soon disappears. This test thus indicates alka-
linity in weak solutions of the phosphates, borates, carbonates, and even
among the least soluble oxides, such as lime and magnesia (p. 361).

2. The Alkaline Earths. — These oxides have the general properties of
alkalies, but they are specially marked by the following characters: 1. They
are insoluble in alcohol, and much less soluble in water than the alkalies:
one of them (magnesia) is nearly insoluble in water. 2. They form insolu-
ble compounds with carbonic and phosphoric acids.

3. The Earths. — These oxides differ from the two preceding groups, in
the following points : They are white tasteless powders. 2. They have no
alkaline reaction. 3. They are insoluble in water and alcohol. 4. As
hydrates, they combine with acids and alkalies to form salts ; and 5. Their
oxides are not reducible at a red heat by hydrogen or carbon.

Acids, as contrasted with alkalies, have the property of rendering vege-
table blues (litmus and cabbage) red. They neutralize alkalies and form
salts. They exist in the gaseous, liquid, and solid state, sometimes soluble
in water, at other times only sparingly so, as the boracic and arsenious
acids; and in some instances quite insoluble, as calcined silicic acid. Those
which are soluble are characterized by a sour taste, and sometimes by a
strongly corrosive action on organic matter. Those only which are dis-
solved by water redden blue litmus-paper ; this is the indication of acidity
on which a chemist chiefly relies. The special tests for the principal acids
have been already described in the first part of the work.

Under each of the metals in the preceding chapters, the tests for its saline

378 QUALITATIVE ANALYSIS OP BASES.

combinations have been given in detail. It will now, therefore, only be
necessary to select a few of the more important of these tests, in order to
show how the presence of a base belonging to one of the three groups of
oxides may be determined.

In this summary, we include among the alkalies, ammonia. Although
not an oxide (page 182), it bears in its chemical properties the strongest
analogies to potassa and soda, which are oxides of metals. Among the
earthy bases, we select alumina as the only one which will probably present
itself in the ordinary course of analysis. The bases selected will be there-
fore the following: potassa (KO), soda (NaO), ammonia (NH.,), lithia
(LiO), baryta (BaO), strontia (SrO), lime (CaO), magnesia (MgO), and
alumina (AlgOg), It will be necessary to consider them (I) in the uncom-
hined or free state, as bases ; and (2) in the combined or saline state, as salts.
The elements, radicals, and acids with which the metals or their oxides are
supposed to be combined, have been already described in the chapters on
the Metalloids ; and to these the reader is referred for a description of the
characters of each class of salts, in so far as they depend on the acid.

Bases. — Out of the nine bases selected, three may be at once recognized;
ammonia by its odor and volatile reaction ; and magnesia and alumina by
their insolubility in water. The two latter may be dissolved in hydrochloric
or sulphuric acid with certain precautions, converted into salts, and tested
as such, in the combined state ; but when uncombined, they are easily dis-
tinguished by a solution of nitrate of silver. Magnesia separates the brown
oxide of silver, while alumina has no effect upon the solution of nitrate. If
the bases are diffused in water, and to each of them a small quantity of sul-
phuretted hydrogen and nitro-prusside of sodium are added, the magnesia
imparts a pale rose-color to the liquid, and the alumina produces no change
whatever.

In the following table, P signifies precipitated, and D dissolved.

If the oxides are presented in a solid form, their physical properties will
serve in a great measure to identify them. It may be assumed, however,
that they are dissolved in water. In this case the solution will have a strong
alkaline reaction, and nitrate of silver will give with all of them a precipitate
of hrown oxide of silver.

Not P. by Carbonate of Potassa. P. by Carbonate of Potassa.

KO NaO LiO BaO SrO CaO

P. by chloride of Not P. by chloride of P. by sulphuric Not P. by sul-

platinum. platinum. acid. phuric acid.

Rapidly. Slowly.

5 g o 'i Lilac. Yellow. Crimson. ^ ,. .,

° S o Oxalic acid.

BaO SrO CaO

P. soluble. P. insoluble.

* i r

o I ( Greenish- Red. Orange-

3 ?a I yellow. red.

Salts. — The following table refers to the qualitative analysis of the solu-
ble salts of the following bases : KO, NaO, NH3, LiO, BaO, SrO, CaO, MgO,
AI2O3. Many of these are neutral : some have an acid and others an alkaline
reaction. All are fixed at a high temperature, excepting those of ammonia;

QUALITATIVE ANALYSIS OF SALTS.

S79

hence an amraoniacal salt is excluded, after the dry residue of evaporation
has been strong^ly heated. For the purposes of this analysis, it is assumed
that the salt is dissolved in water.

Not P. by Carbonate of Potassa.

P. by Carbonate of Potassa.

KO, NaO, NH3, LiO

BaO, SrO, CaO MgO Al^Og

P. on boiling if
concentrated.

P. by Chloride of Platinum.

D.byNH.CL D. by KO.
Not D. by Not D. by
KO. NH^Cl.

Sulphate of Lime.

KO NH3

BaO SrO CaO

1. Salts fixed by 1. Salts volatile.

heat.

2. Lilac flame to 2. Boiled with KO,

alcohol. ammonia evolved.

Precipitated Not P.
Chromate of Potassa.

Not P. by Chloride of Platinum.

BaO SrO CaO

NaO LiO

P. P. only if Not P.
concentrated.

Oxalic Acid.

Not P. by alkaline P. by alkaline
phosphate and phosphate and
ammonia. ammonia on
boiling.

BaO SrO CaO

S S -S i Yellow. Crimson.

Not P. Precipitated.
Hyposulphite of Lime.

BaO SrO CaO

P. Not precipitated.

Solution of Ammonia.

BaO

SrO

CaO

MgO

ALO.

2 07^ r

} yellow.

Not precipitated.-

Oqa OS [

Red.

Orange-
red.

Precipitated.
P. soluble in P. insoluble in

chlor. chlor.

ammonium. ammonium.

NotD.byKO., D. byKO.

The salts of magnesia and alumina impart no color to the flame of alcohol.
When strongly heated in the blowpipe flame with a solution of nitrate of
cobalt, magnesia acquires a pale-red color, and alumina a bright-blue color.
In the compound sulphates of magnesia and alumina with potassa and soda,
the peculiar colors given by these alkalies to flame announce their presence.

It will be observed, in considering these groups, that the alkalies are linked
to the alkaline earths by lithia, and the alkaline earths to the earths by mag-
nesia. Thus carbonate of lithia may be precipitated from the concentrated
solutions of that alkali by carbonate of potassa or soda ; but the carbonate
of lithia is at the same time sufficiently soluble in water to throw down car-,
bonates of baryta, strontia, and lime from the salts of these bases. The
phosphate of lithia occupies also this intermediate position, in respect to
solubility. Magnesium and its oxide (magnesia) approach closely to alumi-
num and alumina in properties. Magnesium is not readily oxidized by ex-
posure to air ; it does not decompose water. It forms one oxide, which is nearly

380 IRON.

insoluble in water. Its salts are precipitated by ammonia and lime-water.
No sulphide of the metal can be obtained by boilinj? its oxide with sulphur, and
DO chloride by digesting its oxide in hydrochloric acid, and evaporating to
dryness. In these respects the resemblances to alumina, and the differences
from the bases with which magnesia is usually associated, are very remark-
able.

In dealing with a mixture of the salts of the first and second groups, car-
bonate of ammonia may be selected as the precipitant. If this reagent,
mixed with a small quantity of ammonia and chloride of ammonium, is added
to the liquid, and the liquid is warmed, baryta, strontia, and lime only will
be precipitated. The filtrate will contain potassa, soda, and magnesia.
The latter may be precipitated by adding phosphate of ammonia. When
this is separated by filtration, potassa, and soda will remain in the filtrate.
This is evaporated to dryness, and sharply heated : all the surplus ammoniacal
salts are driven off, and salts of potassa and soda only remain for subsequent
testing. The base of the third group (alumina) is precipitated with the
alkaline earths by carbonate of ammonia. Alumina may be removed from
the alkaline earthy carbonates by a solution of potassa.

CHAPTER XXIX.

Iron (Fe=28).

Iron is found largely diffused in the state of oxides and carbonate ; it is
also found combined with sulphur, and with several acids, and is a constitu-
ent in greater or lesr? proportion of a large number of minerals. It occurs
in small quantity in some animal and vegetable bodies, and mineral waters,
and it enters largely into the composition of many meteoric stones. It is
one of the most abundant metals on the earth, but is never found in a pure
state. It is chiefly seen under the forms of cast-iron, wrought-iron and steel.
{See Nickel.)

Manufacture of Iron. — The argillaceous iron ore of the coal-measures is
the principal source of British iron. It occurs in nodules and seams, alter-
nating with coal, shale, and limestone, and contains from 70 to 80 per cent.
of carbonate of iron, the remainder being chiefly clay and carbonate of lime.
It is first roasted, either in kilns or heaps, and, mixed with coke and lime-
stone, is subjected to the intense heat of the blast-furnace ; these materials
being successively thrown in from the top, and gradually descending till they
reach the lower or hottest part. In their descent the iron is reduced, and in
combination with a portion of carbon, falls through the fused slags to the
bottom of the furnace, whence it is withdrawn at intervals, by opening the
tap-hole, while the slags are allowed to run off by an aperture left for the
purpose: they consist chiefly of the silicates of lime and alumina, with
smaller proportions of the silicates of magnesia, manganese, and iron. The
smelting or blast furnaces are usually about 50 feet high, and 15 feet in the
.widest part of their internal diameter; they are constructed of strong
masonry and brickwork, and lined with the most refractory fire-stone. They
are worked day and night for several successive years, air being supplied to
them by powerful blowing machines, generally so constructed as to throw it
in m a heated state, or as a hot blast, and to the amount of about six tons'
weight per hour. It is estimated that by the use of hot instead of cold air,

CAST AND WROUGHT IRON. 381

a very large saving of fuel is effected. With the cold blast, about eight tons
of coal are consumed in the production of a ton of iron ; whereas with the
hot blast, less than three tons are sufficient, and with it, coal may be substi-
tuted for coke. These furnaces are usually tapped night and morning,
furnishing from eight to ten tons of metal daily, and requiring an hourly
supply of about a ton and a half of the mixture of roasted ore, limestone,
and coal or coke. The melted metal is suffered to run into rough moulds of
sand, and in this state constitutes the cast or pig iron of commerce.

Cast Iro7i. — There are several varieties of cast iron, but they are commer-
cially distinguished as 1. gray, 2. mottled, and 3. white. They are all carbides^
and the gray and mottled varieties include a portion of graphite diffused
through them, which remains undissolved and unchanged after the action of
dilute sulphuric acid, and, whilst the greater part of the combined carbon
unites to the hydrogen, forming hydrocarbons. Cast iron also contains
silicon, phosphorus, manganese, and traces of calcium, aluminum, and sul-
phur. Gray cast iron is soft and somewhat tough ; it admits of being bored,
and turned in the lathe. When immersed in dilute hydrochloric acid it
leaves a black insoluble residue ; its texture resembles bundles of small
needles. Mottled iron is coarser grained, and small particles of graphitic
carbon may be discerned in its fracture. White cast iron is very hard and
brittle ; acids act but slowly upon it, and develop a lamellar rather than a
radiated texture : it sometimes contains as much as 5 per cent, of carbon, so
that it is nearly represented by Fe^C, and may be regarded as iron saturated
with carbon. When small articles of cast iron are imbedded in oxide of
iron, such as powdered haematite, and kept for some hours at a red heat,
they are to a great extent decarbonized, and so far softened as to resemble
wrought iron, especially when they are slowly cooled. In this operation
the carbon of the bar of cast iron appears to be gradually removed, in the
form of carbonic oxide, at the expense of a part of the oxygen of the oxide
in which they are imbedded.

Wrought, or malleable iron is the metal in a comparatively pure state,
though it retains traces of carbon and of some of the other impurities of
cast iron. To effect the conversion of cast into wrought iron, the cast metal
is in the first instance refined, by subjecting it to the action of air at a very
high temperature, in a kind of forge furnace ; much of the carbon is thus
burned off ; and the silicon, converted into silica, forms a fusible slag with
the oxide of iron, which tends to the further purification of the mass. The
fused metal is then ruH off, and formed into cakes, which are rapidly cooled
by the affusion of water. The silicate of iron formed in this process is
partly derived from the rough cast iron, and partly from added sand ; it
approaches the composition 3(FeO)Si03, and itself performs a part, in
cleansing the metal, by acting as an oxidizing agent. The further, and final
purification of the metal, is effected by a process called puddling, carried on
in a reverberatory furnace, which admits of the fusion of the refined iron by
a current of intensely heated air and flame, without direct contact with the
fuel ; here the metal is well stirred, so that the superficial oxide may be
mixed in the mass, which soon begins to heave and emit jets of carbonic
oxide, and gradually growing tough and less fusible, becomes at length pul-
verulent ; the fire is then urged so that the particles again agglutinate at a
welding-heat, and admit of being made up into globular masses, or blooms,
and in that state of intense heat are subjected to the shingling -press, or to
rollers by which extraneous matters are squeezed out in the form of slag, and
the density of the metal increased ; it now admits of being rolled into bars,
which are cut into convenient lengths, placed in parcels in a very hot rever-
beratory furnace, and again rolled. The metal is now tough, flexible, and

382 PROPERTIES OF IRON.

malleable, but less fusible, and is, in fact, nearly pure, retaining not more
than one two-hundredth part of carbon, and mere traces of other matters.
A new process for saving the time wasted in puddling and refining has been
brought out by Mr. Bessemer. The carbon and silicon of cast iron are
burnt off by passing a blast of atmospheric air at a great pressure through
the molten metal, and such a quantity of pure cast iron is then added to the
wrought iron, produced by this process, as at once to convert the whole
mass into steel, which is then cast in the usual way. This process has
answered with some kinds of iron, e. g., that reduced by charcoal, but not
with other varieties. In these it is said to have led to a great w^aste of
metal. Dr. Roscoe states that by the Bessemer process, six tons of cast iron
can at one operation be converted into steel in twenty minutes. Iron is now
largely manufactured by this process into railway axles and rails.

The slags formed in the ordinary operations of refining and puddling,
containing about 60 per cent, of iron, are reduced in the blast furnace, in
the same way as the original ore, but the iron so produced is cold short; it
admits of working at a red heat, but is brittle when cold, a quality supposed
to depend upon the presence of phosphide of iron, derived from phosphate of
iron existing in the slag. Iron is also occasionally red short, that is, brittle
at a red heat, though malleable when cold ; this quality has been ascribed to
traces of arsenic and copper. Various processes have been suggested for
hardening iron. M. Goudin found that a small quantity of boron gave
hardness to the metal, and that cast iron fused with phosphate of iron and
peroxide of manganese acquired great hardness. The mixture could not be
forged, but admitted of being cast. A still harder material for making
cutting tools hgis been produced by the addition of tungsten.

Properties. — Pure iron has a bright white color, and when polished a great
lustre. It is fusible at a white heat, but with great difficulty when perfectly
pure. It requires the highest heat of a wind-furnace to run down soft iron
nails into a button, and therefore a temperature equal to about 3300^. Its
sp. gr. is 7 "8. Its texture varies with the method of working; in bars or
wires it appears longitudinally fibrous, but when long kept at a red heat it
acquires a crystalline texture, and a tendency to cuboidal fracture. It is
the hardest and toughest of the ductile metals : it may be drawn into very
fine wire, but its malleability is not so great as its ductility. Sheets have
been obtained equal to 42 square inches of surface, and have weighed only
69 grains. It is stated that the thinnest sheets yet produced had a surface
of 69 square inches and weighed only 49 grains. They were of about the
two thousandth of an inch thick and only about half the thickness of the
thinnest tissue paper. {Scientific Review, June, 1866, p. 54.) Iron is very
tenacious, even in the thinnest wire. At a bright red or orange heat it
admits of being welded or joined by hammering to another piece of red hot
metal. In the state of wrought iron the metal has a fibrous structure, and
its value depends greatly upon this. When uniformly hammered or sub-
mitted to vibration, it acquires a granular crystalline structure. It has now
lost its toughness and become brittle. Accidents have occurred from the
breaking of railway axles, owing to the wrought iron originally used having
(as the result of vibrating motion) assumed thi^ crystalline and brittle state.
Iron slowly decomposes water at common temperatures when acid and car-
bonic acid are present. Water simply filtered through iron filings acquires
a chalybeate (inky) taste, and a dissolved salt of iron (carbonate) may be
proved to be present in it by the usual tests. When the vapor of water is
passed over iron heated to redness, the iron takes the oxygen and hydrogen
is evolved.^ At this high temperature the iron appears to pass to the state
of magnetic oxide. In iron pipes heated to redness through which super-

OXIDES OF IRON. 383

heated steam is passed, the first effect is to set free hydrogen, but when a
layer of magnetic oxide has been once formed, there is no further decom-
position of water. The gas associated with superheated steam is chiefly
nitrogen derived from the air in water.

One of the special characters of iron is that it is attracted to the magnet,
but it does not retain magnetism when pure. Iron is thus readily detected,
although it may be completely covered by zinc, tin, and other metals. At a
bright red heat, iron loses all its magnetic power, but this returns when it is
cooled to a black heat.

According to the Mineral Statistics of the United Kingdom, published by
M. Hunt, it appears that in 1865 the iron ore raised amounted to 9,910,045
tons. This yielded 4,819,254 tons of pig iron. Of this quantity 543,018
tons were exported, and the remainder was converted into finished iron.

To obtain pure iron, fine iron wire or filings of the best bar-iron are mixed
with about one-fifth their weight of pure peroxide of iron, and exposed
(covered with pounded glass quite free from lead) in a well-closed crucible,
for about an hour, to the strongest heat of a forge. Another method con-
sists in exposing the peroxide of iron heated in a tube to a high temperature
to a current of pure hydrogen. The oxide is reduced and water is formed.
The iron is left in a state of fine powder {ferrum redactum), and unless re-
tained in an atmosphere of hydrogen until quite cold, it is liable to take fire
on exposure to air and become oxidized. Iron in this state readily dissolves
in an acid with the evolution of hydrogen. If it is in the state of oxide, it
dissolves without any escape of hydrogen.

Exposed to heat and air, iron becomes superficially converted into a fusible
oxide; when exposed to a damp atmosphere, it becomes incrusted by a brown
rust. When in a state of extreme division its aflBnity for oxygen is such,
that it becomes heated, and may even be ignited, on exposure to air ; this is
the case with the metal as obtained by the action of hydrogen upou red-hot
oxide of iron, and when thus reduced, at a temperature not sufficient to cause
the adhesion of the particles of the metal, and suffered to cool in an atmos-
phere of hydrogen, it requires the same precautions for its preservation as
potassium. A spontaneously combustible form of iron is also obtained by
the ignition of Prussian blue. In a dense mass, iron is not afi*ected by dry
air, and it even retains its polish when immersed in pure water which has
been deprived of air ; but in common water, or in water exposed to air, it
soon rusts. This oxidation by water is prevented by the alkalies ; and in
lime-water, or in a weak solution of ammonia, potassa, or soda, the metal
keeps its lustre, probably owing to the entire exclusion of free carbonic acid.

Oxides of Iron. — Iron is susceptible of four definite degrees of oxidation
forming a protoxide (FeO), which has not been isolated, but which is the
bases of a seriqs of well-defined salts ; a sesquioxide (FegOg), generally termed
red oxide or peroxide; a Mack intermediate oxide, known also under the
name of magnetic oxide (FegOJ ; and a hyperoxide, called /erne acid (FeOg),
but which, like the protoxide, has not been isolated.

Protoxide of Iron ; Ferrous Oxide (FeO). — When a solution of potassa
is added to a solution of a pure protosalt of iron, every precaution being
taken to exclude oxygen, a white precipitate falls, which is a hydrated prot-
oxide ; it is difficult to wash and dry it under entire exclusion of air ; but
when this is done, it is pale green, not magnetic, and absorbs oxygen when
exposed to air, and is converted into peroxide ; it rapidly absorbs carbonic
acid, and dissolves in the dilute acids. The pure protosulphite of iron for
this purpose may be obtained by shaking in a stoppered bottle, for a few

884 OXIDES OF IRON.

minutes, a mixture of clean iron filings with a fresh and strong solution
of sulphurous acid. On filtering and adding potash, a white hydrated
oxide of the metal is procured, which, however, rapidly absorbs oxygen from
the air and passes to the state of peroxide. The salts of this oxide, when
crystallized or hydrated, are mostly greenish-blue. The green tint is owing
to the admixture of some yellow persalt with the blue protosalt. The crys-
tals become white or nearly so when anhydrous. Thus crystals of the green
protosulphate are whitened by immersion in strong sulphuric acid. In
aqueous solution they have an inky taste, and are very prone to pass into salts
of peroxide. The fixed alkalies throw down this oxide as hydrate. With
ammonia, only half the oxide is precipitated, and a green solution is formed,
which, on exposure, becomes covered with a brown film. Carbonates of
potassa and of soda, and sesquicarbonate of ammonia, throw down a white
protocarbonate of iron, which soon becomes brown, and which, if solution
of sal-ammoniac be added, is re-dissolved. Bicarbonates of potassa and soda
produce the same preci[)itate, unless the solution be very dilute, in which
case the mixture is clear, but deposits protocarbonate of iron if boiled, and
when exposed to air it gradually lets fall hydrated oxide. The protosalts of
iron act as powerful deoxidizers. Nitric acid is decomposed by them, and
deutoxide of nitrogen is set free, which is dissolved by a portion of protosalt,
and forms a dark olive-green solution (p. 110). The protosalt is at the same
time converted into persalt. When added to solutions of chloride of gold or
nitrate of silver, gold and silver are separated in the metallic state. It
deoxidizes a solution of permanganate of potassa; hence, a standard solution
of permanganate is used volumetrically to determine the quantity of prot-
oxide in a liquid.

Sesquioxide of Iron ; Peroxide of Iron ; Ferric Oxide (FegOg). —
When a protosalt of iron is boiled with nitric or nitro-hydrochloric acid, it
becomes peroxidized, and on adding ammonia a brown hydrated precipitate
falls, which, when washed and ignited, is the sesquioxide. When protosul-
phate of iron is decomposed by a very high temperature a red powder re-
mains, which is also the peroxide, and which was formerly called colcothar,
and is used as a red paint, and for polishing glass and metals. The color of
peroxide of iron varies according to the mode of its formation and the tem-
perature to which it has been subjected : it is generally a reddish or yellow-
brown powder, which acquires a darkened hue by a moderate heat, and is not
magnetic except when it has been overheated: in this case it appears to under-
go partial reduction. This oxide is a weak base, or what has sometimes been
called 'dn indifferent oxide : its salts generally have a brown color and an acid
reaction ; and, when very dilute, their solutions are decomposed by boiling,
in which case the acid of the salt combines with the water, and the peroxide
or a basic salt is precipitated. In some cases this oxide acts as an acid. It
is thrown down from its solutions by ammonia, potassa, and soda, in the form
of a bulky brown hydrate, and in this state is easily redissolved by acids ;
but when it has been dried, and exposed to a full red heat for some time, it
is difficultly soluble. It is also partly converted into magnetic oxide by
losing oxygen, 3Fe,03=2Fe30, + 0. The best solvent for this oxide is the
hydrochloric acid. When dried at 212°, it is 2Fe^03 + 3HO; at 400° it
becomes Fe.Oa-j-HO. A temperature exceeding 500^ is required to drive
ofl' the whole of the water. When produced under exposure to air, it almost
always contains traces of ammonia. When precipitated by excess of the
fixed alkalies, or their carbonates, it carries down a portion of the alkali,
which cannot be entirely removed by washing ; and if the alkali be not in
excess, the precipitated oxide is not free from the acid, or from a subsalt :

OXIDES OF* IRON. 385

hence the necessity of precipitating by excess of ammonia, when the result-
ing hydrated oxide may be deprived, by heat, both of water and of excess of
the precipitant. When certain organic substances are present in solutions
of this oxide they prevent its precipitation by the alkalies. This is the case
with hot solutions of gelatine, starch, gum, and sugar. Tartaric, citric, and
some other acids, produce the same effect. This oxide of iron is reduced by
hydrogen at a temperature even below redness. When gently heated with
charcoal it is converted into magnetic oxide, and at a high temperature is
reduced.

The salts of this oxide are changed into those of the protoxide by adding
sulphurous acid or bisulphite of soda, and warming the liquid ; or by adding
to the warm liquid pure zinc, in which case hydrogen is generated, and the
persalt is converted into a protosalt. A standard solution of permanganate
of potassa, which is not affected by a persalt, may be employed voluraetri-
cally, to determine by the discharge of color the amount of protoxide, and
by calculation of the peroxide present. Care should be taken that all the
sulphurous acid is expelled from the liquid before adding the solution of per-
manganate. A current of sulphuretted hydrogen will also reduce the per-
salts to the protosalts, but in this case there is a separation of sulphur.

Black Oxide of Iron ; Magnetic Oxide of Iron; Ferrosoferrio Oxide
(FcaOj ; or FeO,Fe203) This oxide is formed by passing steam over red-
hot iron. The scales of iron obtained from the smith's forge, the oxide
formed when iron is burned in oxygen gas, and the black powder formed by
the action of air on moistened iron filings, and formerly called Martial
Ethiops, are also allied to this oxide; but in these the protoxide or peroxide
may occasionally predominate. A solution of this oxide in hydrochloric acid
has the properties of the proto and persalts of the metal.

A hydrate of this oxide may be obtained by dissolving equal weights of
protosulphate of iron in two separate portions of water, boiling one of them
with a sufficiency of nitric acid to peroxidize it, and then mixing it with the
other, and pouring the mixture into a solution of potassa or soda, sufficient
in quantity and strength to decompose the whole : the precipitate at first
consists of a mixture of protoxide and peroxide of iron, but when boiled for
a few minutes they combine, and the black oxide fails in the form of a dense
crystalline powder, very obedient to the magnet, and readily soluble in hy-
drochloric and in nitric acid. The salts of this oxide are mixtures of those
of the two oxides. Magnetic iron ore is a native black oxide.

Ferric Acid (FeOg). — Ferric acid is only known in combination with
bases : it is one of those acids which cannot be separated without undergoing
decomposition. When sesquioxide of iron is mixed with four parts of nitre,
and exposed for an hour to a full red-heat in a covered crucible, it forms a
deliquescent reddish-brow^n mass, which should be powdered while warm,
and put into a stopped phial; this {^ferrate of potassa: its solution in water
has an amethystine tinge so deep as to be nearly opaque, and gradually
evolves oxygen, and deposits sesquioxide of iron ; this decomposition is im-
mediate and perfect at 212^^. A solution of ferrate of potassa yields red in-
soluble precipitates in solutions of baryta, strontia, and lime, which are
easily decomposed by acids.

Native Oxides of Iron. — These constitute an extensive and important class
of- ores. They vary in color, depending upon mere texture in some cases ;
in others, upon the degree of oxidizement. Some are magnetic, and those
which contain least oxygen are attracted by the magnet. The following are
some of their principal mineralogical varieties : 1. Magnetic iron ore, which
25

386 CHLORIDES OF IRON.

is generally black, with a slight lustre. It occnrs massive and octahedral,
and is often powerfully magnetic ; its specific gravity is 4-5. It is abundant
in Sweden, where it is manufactured into a bar-iron much esteemed for
making steel. 2. The specular and micaceoiis iron ore. It is found crystal-
lized, of singular beauty, in Elba, and occasionally among volcanic products.
Its specific gravity is 5-0 to 5*2 ; it yields a reddish powder. 3. Hcematite,
or red ironstone, occnrs in globular and stalactitic masses, having a fibrous
and diverging structure. It is sometimes cut into instruments used for bur-
nishing; its density is 4*8 to 5. It abounds in Lancashire. Sometimes it
is of a brown, black, or ochraceous color. This, as well as the iron-glance,
is a sesquioxide, and does not affect the magnet. There are also several
varieties of hydrated peroxide of iron, such as the fibrous haematite, the
granular and pisiform iron ore, and certain varieties of ochre and umber.
4. A fourth variety of oxide of iron is known under the name of Bog ore,
found in low marshy places, and generally of recent origin.

Iron and Chlorine. — There are two chlorides of iron, corresponding in
composition to the protoxide and sesquioxide. Protochloride of iron (FeCl)
may be obtained by passing dry hydrochloric acid gas over red-hot iron wire;
or by digesting iron filings in hydrochloric acid, in which case, as in the
former, hydrogen is set free ; or by employing protosulphide of iron instead
of metallic iron, when sulphuretted hydrogen is evolved ; in both cases a
green solution is obtained, which, evaporated out of the contact of air, leaves
a residue which is to be exposed to a red heat. Protochloride of iron is of
a gray color, and after fusion acquires a foliated crystalline texture ; it is
volatile at a high red heat, and may be condensed in pale gray crystals.
When heated with access of air, sesquichloride of iron sublimes, and peroxide
of iron remains (6FeCl + 30 = 2[Fe2Cl3]-f Fe^Og). When the vapor of water
is passed over it at a dull red heat, hydrochloric acid and hydrogcFi are
evolved, and black magnetic oxide remains : (3FeCl-f 4HO=Fe304 4-3HCi
H-H). Hydrated Protochloride of Iron. — Dissolved in water free from air,
and evaporated in vacuo, this chloride furnishes a crystallizable hydrate.
When a saturated solution of iron in hydrochloric acid is evaporated, air
being excluded, it yields blue rhombic crystals, which become green and
effloresce in dry air, into a white powder. Their formula is FeGl,4H0.
They are soluble in alcohol, and when heated in the air, leave peroxide.

Perchloride of Iron ; Sesquichloride of Iron (FegClg). — When fine
iron wire, heated to redness, is introduced into a bell-jar of chlorine, it burns
with a lurid red light and much red-brown smoke, and this compound is
formed. A mixture of equal weights of chloride of calcium and calcined
sulphate of iron, heated to redness, also afi'ords a sublimate of sesquichloride.
Sesquichloride of iron forms brilliant and iridescent brown crystals, volatile
at a temperature below redness.

Hydrated Sesquichloride of Iron. — Sesquichloride of iron is deliquescent
and very soluble in water ; when the solution is evaporated in the air, hydro-
chloric acid passes off, and peroxide of iron remains. A solution of this
chloride is obtained by dissolving peroxide of iron in hydrochloric acid ; it
forms a deep brown liquid, which, when concentrated and exposed to cold,
yields crystals, the form of which varies with their respective quantities of
water : when they form acicular and radiating tufts, they include about 40
per cent, of water, being Fe2Cl3,12HO ; but when they form larger tabular
crystals, they contain about 22 per cent, and are Fea,Cl3,5IIO ; these latter
are best obtained by placing the former over a surface of oil of vitriol under
-a bell-glass ; they deliquesce into a thick fluid, which gradually passes into

NITRATES OP IRON. 38t

a mass of the crystals containing 5 atom^ of water. When a current of chlo-
rine is passed through a solution of protochloride of iron, or when nitric acid
is gradually added to it when heated, it is converted into sesquichloride. If
a dilute solution of the protochloride be exposed for some days to the atmo-
sphere in a tall jar, and a few drops of ammonia be then introduced at dif-
ferent depths, by means of a glass tube, the precipitate near the surface will
be green ; a little lower, blue ; still lower, gray ; then of a dirty white ; and
at the bottom, quite white, provided the solution has not been so long ex-
posed as to have become oxidized throughout. The sesquichloride is soluble
in alcohol and ether.

Ammonio- chlorides of Iron. — Protochloride of iron absorbs ammonia and
forms a bulky white powder, which is resolved by water into hydrochlorate
of ammonia and hydrated oxide of iron. If iron-filings are boiled in a satu-
rated solution of sal-ammoniac, hydrogen and ammonia are evolved, and the
liquor deposits green crystals of hydrated protochloride of iron and ammonia.
When sesquichloride of iron is exposed to ammonia it is slowly absorbed,
and the compound furnishes a clear red solution with water ; it contains
about 9 per cent, of ammonia, being (NHajFe^Clg). A mixed solution of
sal-ammoniac and sesquichloride of iron evaporated in vacuo over oil of
vitriol, furnishes brown crystals which are =(2NH4Cl,Fe2Cl3,2HO). When
hydrochlorate of ammonia and sesquioxide of iron are mixed and heated,
a yellow sublimate is obtained, which is the Ferri ammonio- chloridum of ipheiv-
macy.

Protiodide of Iron (Fel) is formed by digesting iron-turnings, or wire,
with iodine in water, taking care to have excess of metal present ; a green
solution is obtained, which, by evaporation out of contact of air, leaves a
gray fusible protiodide of iron. It is soluble in water and alcohol, but the
solution absorbs oxygen and deposits peroxide, unless metallic iron is present ;
so that to preserve it unchanged, some pieces of clean iron wire should be
immersed in it. By careful evaporation i7i vacuo crystals of a hydrated
protiodide of iron, including 5 atoms of water, may be obtained. This salt
is used medicinally, and its oxidation is prevented by mixing it with syrup.
It is employed in the production of iodide of potassium. There is also a
Bromide of iron (FeBr).

Nitrates of Iron. Protonitrate. — This compound is formed by digesting
iron filings on very dilute nitric acid (specific gravity 1'16). But little gas
is evolved, and the liquid assumes an olive-brown color from the nitric oxide
which it contains, but when exposed to the air it becomes pale-green incon-
sequence of the escape of this gas. Alkalies produce a green precipitate
in this solution ; the salt cannot be obtained in crystals by the usual process,
and passes into pernitrate by exposure to air. It may, however, be crystal-
lized by evaporation in an exhausted receiver over sulphuric acid ; it then
forms crystals of a light green color =FeO,NO,,7HO. When protosulphide
of iron is dissolved in dilute nitric acid sulphuretted hydrogen escapes, and
a green solution of protonitrate is obtained, which, when gently heated,
speedily becomes brown, in consequence of the formation of peroxide. Pro-
tonitrate of iron is also formed when solutions of protosulphate of iron and
nitrate of baryta are mixed in atomic prpportions. The solution of the neu-
tral protonitrate is decomposed near the boiling temperature, with the evo-
lution of nitric oxide, and the abundant precipitation of a subnitrate of the
peroxide. Iron turnings may be dissolved in cold and highly concentrated
nitric acid, so as to produce ammonia and protonitrate of iron, without the
extrication of gas (8Fe,-fl0NO5-t-4HO=8[FeO,NOjH-NH,O,NO5). Per-
nitrate of Iron; ISesquinitrate of Iron. — Nitric acid, diluted with a little
water, acts violently on iron and peroxidizes it ; a large quantity of gas is

388 SULPHIDES OF IRON.

generated, consisting of nitrous and nitric oxides, and a solution is formed
of a reddish-brown color, containing pernitrate of iron, and affording a brown
precipitate with the alkalies. \Yhen this solution is evaporated, a brown
deliquescent mass remains, soluble in water and alcohol ; it is decomposed
at a red heat, and peroxide of iron remains. If this solution be mixed with
excess of carbonate of potassa, the precipitate at first thrown down is redis-
solved by the alkali, and a deep-brown liquid obtained {Liquor ferri alka-
lini.)

Passive condition of Iron, in respect to the action of Nitric Acid. — In ordi-
nary cases nitric acid of the specific gravity 1-35 acts powerfully upon iron,
but under certain circumstances the metal becomes inert. This state is
brought about: 1. By slightly oxidizing the extremity of an iron wire by
holding it in the flame of a spirit lamp, and when cold dipping it gradually
into the acid, taking care to introduce the oxidized end first. 2. By dipping
the end of the wire into strong nitric acid, and washing it in water. 3. By
first introducing a platinum wire into the acid, and then the iron wire in
contact with it, which contact may, however, afterwards be broken. 4. An
iron wire already rendered passive acts as the platinum wire, and renders
other wires passive in the same way.

Protosulphide of Iron (FeS). — When sulphur is dropped upon red-hot
iron wire, or fused with iron filings, a compound is obtained, which, after
having been heated to expel excess of sulphur, is soluble in dilute sulphuric
acid, with the evolution of sulphuretted hydrogen, and is a protosulphide of
iron. So also, when a bar of wrought iron is heated nearly to whiteness,
and the surface is rubbed with a roll of sulphur, the protosulphide melts
from the surface of the metal, and may be collected in a vessel of cold water.
It should be perfectly dried. Protosulphide of iron is of a dark-bronze
color, and influences the magnet. It is much more fusible than iron ; it
loses no sulphur, even at a white heat, out of contact of air ; when pure, it
is soluble without residue in dilute acids, with the evolution of sulphuretted
hydrogen and the formation of a protosalt of iron. It is much employed,
with diluted sulphuric acid, for the purpose of obtaining sulphuretted hydro-
gen gas. When heated in air or oxygen, sulphurous acid and oxide of iron
are formed. When the moist hydrated protosulphide is exposed to air, the
iron becomes oxidized, and sulphur separates, and more or less sulphurous
and sulphuric acids are often formed with heat enough to produce inflamma-
tion. The formation of this sulphide, by the action of sulphuretted hpdrogen
upon hydrated peroxide of iron, has already been mentioned (p. 228).

Bisulphide of Iron (FeSg) is formed when the protosulphide is well
mixed with half its weight of sulphur, and subjected to a high temperature,
which, however, should be below redness ; a bulky, dark-yellow metallic
powder is the result, not attracted by the magnet, and insoluble in dilute
sulphuric and hydrochloric acids. Bisulphide of iron is the occasional result
of the slow decomposition of a solution of sulphate of iron by organic matter.
Thus, the bones of some mice, which had accidentally fallen into a solution
of the sulphate, were found incrusted with bisulphide. Its presence in
masses of wood found in clay, or in coal, may be explained upon similar
principles.

Native Sidphides of Iron. — Magnetic pyrites is a protosulphide of iron,
and common or yellow pyrites a bisulphide. Common pyrites is found mas-
sive, and crystallized in a variety of forms; it often occurs in radiated nodules,
which, when rolled amongst the shingles upon the sea-beach, are sometimes
called thunder-holts; it is of different shades of brass yellow. It is used in
the formation of sulphate of iron, or green vitriol, for which purpose it is
gently roasted and exposed to air and moisture. The cubical bisulphide is

PROTOSULPHATE OF IRON. 389

very permanent, but some of the prismatic varieties spontaneously pass into
sulphate, and when in large masses generate heat enough to produce igni-
tion ; in this way beds of coal have been set oh fire in consequence of the
absorption of oxygen by their contained pyrites. Pyrites has also been used
as a source of sulphur, and as a substitute for sulphur in the production of
sulphuric acid. This article is now an important article in British manufac-
tures. In 1865, according to Mr. Hunt, the quantity of iron-pyrites raised
in the United Kingdom amounted to 114,195 tons, and of this quantity the
county of Wicklow in Ireland yielded 81,993 tons.

Sesquisulphide OF Iron (Fe^S.^). — This compound is formed either by
passing sulphuretted hydrogen over sesquioxide of iron at a temperature not
exceeding 212^, or by the action of the same gas upon the hydrated sesqui-
oxide, at common temperatures. It is formed in the humid way by adding
neutral persulphate of iron drop by drop, to a solution of an alkaline hydro-
sulphate ; it then falls as a black powder, which cannot be dried in the air
without change.

Hyposulphite of Protoxide op Iron (FeOjS^Og) is obtained together
with sulphite, by digesting finely-divided metallic iron in sulphurous acid
(2Fe + 3S02=FeO,SA-f FeO,SOJ. When sulphuric or hydrochloric acid
is added to its solution, sulphurous acid is evolved, and sulphur precipitated.
This solution furnishes a perfect protosalt of iron ; and by keeping a few
filings of iron in it, it may be retained in this state. It gives a white pre-
cipitate with ferrocyanide of potassium, becoming blue by exposure to oxygen
or air. Infusion of galls does not immediately discolor its solution.

Protosulphate of Iron (FeO,S03) \s the copperas and green vitriol o^
commerce, and is often prepared by exposing roasted pyrites to air and
moisture, in which case the salt is impure. It is usually formed by dissolving
iron in dilute sulphuric acid, filtering and evaporating the solution, and
setting it aside to crystallize. It is also obtained, free from persulphate, by
acting upon protosidphide of iron by dilute sulphuric acid. This salt forms,
when pure, bluish-green crystals in the form of oblique rhombic prisms,
soluble in about 2 parts of water at 60°; of a styptic taste, reddening vege-
table blues, and including T atoms of water (FeO,SO,^,*7HO). When chlorine
is passed through an aqueous solution of protosulphate of iron, hydrochloric
acid is formed, and the iron becomes peroxidized, so that water is decom-
posed. Protosulphate of iron is insoluble in alcohol, and in sulphuric acid,
both of which deprive the crystals of water, and precipitate the salt in the
form of a white powder. The green vitriol of commerce usually contains
persulphate, and has a grass-green color. Exposed to dry air, this salt
effloresces, and in moist air absorbs oxygen, becoming of a rusty or reddish
color, whence the French term couperose, applied to it, corrupted into cop-
peras. When heated in close vessels, it fuses, and at 238° loses 6 equiva-
lents of water, but retains 1 equivalent till heated above 535° : this may be
driven off at a higher temperature, arfd the salt is then white, pulverulent,
and anhydrous. At a higher temperature the anhydrous protosulphate is
converted into an anhydrous persulphate, and sulphurous acid is at the same
time evolved: 2[FeO,S03] = Fe303,S034-S02 ; and at a full red-heat the
persulphate is itself decomposed, and leaves peroxide, while the sulphuric
acid partly passes off in an anhydrous state, and is partly resolved into sul-
phurous acid and oxygen (Saxgn acid). The residuary oxide is of a deep-
red color, and was formerly known under the name of colcothar, or caput
mortuum vitrioli. It is in consequence of this decomposition that sulphate
of iron is often used as a substitute for sulphuric acid, to separate w^eaker
acids from their bases, at high temperatures. Native green vitriol is fre-
quently found associated with pyrites, and produced by its decomposition.

390 PHOSPHATES OF IRON.

Persulphate op Iron (FeaOg.oSOp is made by adding 1 equivalent of
sulphuric acid to a solution of 2 equivalents of protosulphate, boiling, and
then dropping in nitric acid as long as red fumes are evolved ; a buff colored
deliquescent mass is obtained on evaporation, slowly soluble in water, and
which, when carefully heated, leaves an anhydrous salt : it is decomposed at
a red heat. In this compound the number of atoms of acid are equal to the
number of atoms of oxygen combined with the metal. Persulphate of iron forms
double salts with the sulphates of ammonia and of potassa, which, in form
and composition, resemble alum. The formula of the ammonia-salt is NH^O,
SO.^+FegO^.SSO^-f 24HO, and that of the potassa-salt KO.SOg+Fe^Og,
3803+24110. It is sometimes found associated with sulphate of alumina in
chalybeate waters.

Phosphide of Iron (Fe^P) is formed by dropping phosphorus into a
crucible containing red-hot iron wire : it is a brittle gray compound, and
acts upon the magnet. It may also be procured by the ignition of a mixture
of iron filings, phosphoric acid, and charcoal powder ; or of a phosphate of
iron and charcoal. It is not readily dissolved by acids. A small portion of
this compound is said to be present in cold-short iron ; it is injurious to the
quality of the metal when contained in it to the amount of 1 percent. Phos-
phorus increases the fusibility of iron. The fine thread-like Berlin castings
are said to be produced from iron containing the phosphide.

Protophosphate of Iron (2(FeO)HO,P03) is insoluble in water. It
may be formed by adding a solution of common phosphate of soda to proto-
sulphate of iron. It is at first white, but becomes blue by exposure : it fuses
and forms a crystalline bead before the blowpipe ; it is soluble in most of
the acids, from which it may be again precipitated by ammonia, but it is
soluble in excess of ammonia. When it has acquired a full blue tint, it is
probably analogous to the 7iative phosphate, and is a hydrated compound of
the phosphate of the protoxide with phosphate of the peroxide. This blue
phosphate may be produced by adding phosphate of soda to the solution of
the mixed sulphates of iron ; it is not changed by exposure to air ; its
formula is HO,2(FeO)P03+2(Fe,03)r'03. The analyses of the crystal-
lized and amorphous native phosphates agree with the formula 3(FeO)P05
+ 8H0.

Perphosphate of Iron is a white insoluble compound which is precipi-
tated on adding common phosphate of soda to persulphate or perchloride of
iron ; -or by adding phosphoric acid to a mixture of acetate of soda and a
persalt of iron. The precipitate is rendered brown by solution of ammonia,
but is not soluble in ammonia unless excess of the phosphate of soda is
present, when it forms a brown solution, which remains clear with ferro-
cyanide of potassium till an acid is added, when Prussian blue is thrown
down. It is also dissolved by a large excess of peracetate of iron. Owing
to the insolubility of the perphosphate in acetic acid, an aliialine phosphate
forms a valuable test for this metal (page 397), and enables a chemist to
separate iron from the alkaline earths, as well as the peroxide from the prot-
oxide of the metal.

Iron and Carbon. Carbide of Iron. — It is doubtful how far any defi-
nite carbide of iron can be separately obtained, but these compounds have
important bearings upon the properties of cast iron and steel. The deter-
mination of the quantity of carbon in them ie usually effected by mixing
from 50 to 100 grains of the sample in very fine filings, with about tea
times its weight of chromate of lead, heating the mixture in a combustion-
tube, such as is used in organic analyses, to a red-heat, and passing over it
a stream of pure and dry oxygen : in this way the iron and carbon are both
burned, and the carbonic acid formed by the latter, when absorbed by a

MANUFACTURE AND PROPERTIES OF STEEL. 391

solution of potassa, becomes the indicator of the quantity of carbon present.
But cast iron contains carbon mechanically mixed, as well as chemically
combined ; and to ascertain their relative proportions, the iron may be dis-
solved in hydrochloric acid, when the chemically combined carbon goes off
in the form of hydrocarhons, while the graphite or other forms of carbon,
which were mechanically mixed, remain, together with silica, and may be
separated by filtration, washed, and dried. This residue, wiien properly
burned, so as to consume the carbon, leaves the silica, and the loss of weight
gives the quantity of carbon.

MoMufacture of Steel. — Steel is generally regarded as a compound of iron
with a quantity of carbon, varying from one to two per cent. ; but the exact
nature of this valuable substance is perhaps scarcely understood. In some
samples the proportion of carbon has been found below 0 2 per cent. ; in
others, nitrogen has been detected ; and under the supposition that these
small quantities of foreign matters cannot confer upon steel the remarkable
properties upon which its value depends, it has been assumed that it may
be an allotropic condition of iron. Traces of silicon, manganese, phos-
phorus, arsenic, and aluminum, have also been discovered in steel of good
quality.

Steel combines the fusibility of cast, with the malleability and ductility of
bar or wrought iron ; its texture varies, some of the varieties being granular
or lamellar, and others exhibiting a silky fracture ; but it is never fibrous,
like the iron from which it is obtained. After it has been highly heated,
and then suddenly cooled, it acquires extreme hardness, and becomes more
or less brittle, and very elastic ; but if, after having been heated to redness,
it be allowed to cool very slowly, it becomes nearly as tough and soft as
pure iron. But the most characteristic quality of steel is, that it may be
brought to any intermediate degree of hardness between these extremes, by
the process called tempering, to which we shall presently advert. Steel is
also distinguished from iron by-its permanent retention of magnetism. Steel
may be obtained from the purer varieties of cast iron, or from some of the
native oxides of iron, by so modifying the process of reduction as to leave
the iron in combination with no more carbon than is requisite ; and, in that
case, it has been termed natural steel. Iron may also be converted into
steel by passing carburetted hydrogen over the bars at a full red heat ; but
it is generally made by a process called cementation, which consists in heating
to full redness bars of the purest iron, in contact with charcoal, to which a
little common salt and wood-ash is usually added. This process requires
from 6 to 10 days, according to the thickness of the iron bars, which, when
removed from the furnace, exhibit a blistered surface, arising, as has been
supposed, from the production of carbonic oxide. When blistered steel is
drawn down into smaller bars, and forged by the tilt hammer, it forms tilted
steel; and this, when broken up, and again welded and drawn into bars, forms
shear steel. Cast steel is prepared by fusing blistered steel with a carbonaceous
and vitrifiable flux, and casting it into ingots, which are afterwards hammered
or rolled into bars. It has a more uniform texture and composition than the
other varieties, and is used in the manufacture of superior cutlery, and for
the matrices, punches, and dies of the medal engraver and coiner. The best
cast steel seldom contains less than 99 per cent, of iron, the remaining 1 per
cent, being made up of carbon, silicon, phosphorus, manganese, and occa-
sional traces of the other substances found in cast iron.

Case-hardening is an operation performed upon cast or wrought-iron, by
which it is superficially converted into steel : the article is for this purpose
either heated to redness in contact with charcoal powder ; or sometimes, if
small and delicate, is wrapped round with leather, and then gradually heated

392 MANUFACTURE AND PROPERTIES OF STEEL.

to redness, and kept iu that state till its surface is duly carbonized. Ferro-
cyanide of potassium is also a valuable material as a case-hardener, and in
various operations connected with the management of steel.

Hardening and Tempering Steel — When steel is heated to a cherry-red
color, and then plunged into cold water, it becomes so extremely hard and
brittle, as to be unfit for almost any practical purpose. To reduce it from
this extreme hardness it is subjected to the process of tempering, which is
effected by again heating the steel up to a certain fixed point. The surface
being a little brightened, exhibits, when thus heated, various colors depend-
ing upon the formation of thin films of oxide, which constantly change as
the temperature is increased, and by these colors it is customary to judge of
the temper of the steel. But a more accurate method is to use a bath and
thermometer; the bath may be of oil, mercury, or fusible metal. Into this
the articles to be tempered are put, together with the bulb of a thermometer
graduated to the boiling point of mercury. The corresponding degrees at
which the various colors appear are from 430° to 600°. The first change
is about 430°, but this is very faint. At 460° the color is straw, at 500°,
brown ; this is followed by a red tinge, then purple, and at nearly 600°, it is
hlue. Lancets, certain surgical instruments, and razors, are tempered between
430° and 460° ; penknives, and fine cutlery, at 460° to 500 ; table and carv-
ing-knives at 500° to 530° ; and sword-blades, saws, and articles requiring
great elasticity, at 530° to 600°.

When a mass of steel, a die, for instance, has been heated red-hot, and
suddenly quenched in cold water, it retains when cold, the bulk that it had
when heated ; the consequence is, that its particles are thrown into a state
of very unequal tension, so that it frequently cracks off or flies to pieces. Its
specific gravity is also diminished. The specific gravity of a plug die of the
best cast-steel, weighing about 2600 grains, after having been well annealed,
was 7 "8398 ; after having been indented by a punch in a fly-press, its specific
gravity was T*8605; it was then hardened by heating it to bright redness
and plunging it into water at 55°. By this process its sp. gr. was reduced
to 7-1525.

The quality of steel is sometimes tested by washing its clean surface with
dilute nitric acid, which ought to produce a uniform gray color ; if the steel
is imperfect, and contains veins or pins of iron, they become evident by their
difference of color. When some particular kinds of iron or steel are thus
tested; a mottled appearance is produced, as if it were composed of layers
or wires of iron and steel welded together ; hence is supposed to arise the
peculiar character of the celebrated Damascus sword-blades. According to
Rinman {Chem. News, April, 1867), tempered steel dissolves in hot or cold
hydrochloric or sulphuric acid without leaving any carbonaceous residue :
untempered steel dissolves in hot acid, without, and in cold acid with, a car-
bonaceous residue. Iron dissolved in acid sets free carbon in three states —
as graphite in pig-iron, as ferrocarbon in untempered steel, and as hydro-
carbon in tempered steel.

Alloys of Steel — Attempts have been made to improve the quality of steel
by alloying it with manganese, silver, and some other metals, but none of
these combinations have been found, after due experience, to be superior to
the best ordinary steel.

Protocarbonate of Iron (FeO,C03).— When a solution of a pure proto-
salt of iron is precipitated by carbonate of potassa or soda, a white hydrated
protocarbonate of iron falls, which, if washed and dried, with all the requisite
precautions for excluding oxygen, forms a greenish tasteless powder, contain-
ing from 24 to 30 per cent, of carbonic acid ; it may therefore be considered
as FeO,C02,IIO. When air is not excluded, the white precipitate presently

CYANIDES OF IRON. 393

passes through various shades of green, and if exposed to air becomes brown,
losing carbonic acid, and passing into hydrated peroxide. When carbonic
acid in aqueous solution is digested with iron filings, a colorless solution of
the protocarbonate is obtained. It is not an uncommon ingredient in mineral
waters, where it is held in solution by excess of carbonic acid. The most
celebrated springs of this kind in England are those of Tunbridge Wells.
These waters have an inky flavor, are blackened by vegetable astringents ;
and wlien boiled, or when exposed to air, deposit hydrated peroxide of iron.
Chalybeate waters seldom contain as much as a grain of carbonate of iron
in a pint ; the chalybeate springs in and about Tunbridge Wells contain
from 2 to 3 grains in the gallon (p. 150).

Native Protocarbonate of Iron, or Spaihose Iron Ore {VeO,CO,^) occurs in
rhombic crystals. Its color is yellowish, or brownish-gray. It generally
contains manganese, lime, and a trace of magnesia; it slowly dissolves in
hydrochloric acid, evolving carbonic acid. The clai/ iron ore of our coal
districts, from which British iron is chiefly obtained, is an impure protocar-
bonate of iron, usually containing from 30 to 40 per cent, of oxide (p. 380).
Carbonic acid does not form a definite or permanent compound with per-
oxide of iron.

Iron and Cyanogen. — These substances give rise to several important
compounds, in which they exist either combined in various proportions or as
a compound radical or base, in union with other bodies. Protocyanide of
Iron (FeCy) is obtained, in the form of a gray powder, by gently heating
ammonio-cyanide of iron (ferrocyanide of ammonium) out of the contact of
air. It is also formed by digesting recently- prepared Prussian blue in a
well-stopped phial with a saturated solution of sulphuretted hydrogen ; it
becomes white, and the solution contains hydrocyanic acid. When solutions
of cyanide of potassium and protosulphate of iron are mixed, an abundant
reddish precipitate falls, which is redissolved by excess of the cyanide, and
then forms ferrocyanide of potassium. But it is doubtful whether a jyure
protocyanide of iron has been isolated. According to Pelouze, a combina-
tion of cyanogen and iron (FcgCyJ, corresponding to the magnetic oxide, is
obtained by passing a current of chlorine into a boiling solution of ferrocy-
anide of potassium ; a green powder precipitates, which is to be boiled in 8
or 10 parts of concentrated hydrochloric acid, by which peroxide and cyan-
ide of iron are dissolved, and a green powder remains, which, when washed
and dried in vacuo, constitutes this intermediate combination =FeCy+
FcgCyg + ^HO. Heated to 355°, it loses water, cyanogen, and a little hydro-
cyanic acid, and acquires a deep purple color. By a solution of caustic
potassa, it is converted into peroxide of iron, and a mixture of the ferro and
ferricyanides of potassium.

Percyanide of Iron ; Sesquicyanide of Iron (FCgCyg). — This compound
has not been isolated. It is obtained in solution when ferricyanide of potas-
sium is decomposed by silico-fluoride of iron, forming a brown astringent
liquid, but on evaporation it deposits Prussian blue. The varieties of Prus-
sian blue are compound cyanides of iron.

Ferrocyanides and Ferricyanides. — The cyanides of iron combine with
other cyanides and produce two classes of salts, which have been termed
ferrocyanides ^w^ ferricyanides , the former Q,oxii^\mx\^ferrocyanogen =FeCy3,
and the latter ferricyanogen =Fe2Cyg. Neither ferrocyanogen nor ferricya-
nogen has been isolated, but the hypothesis of their existence as distinct
radicals is so convenient, as to have led to its general adoption. Ferrocya-
nogen, Fey, containing 1 atom of iron and 3 of cyanogen, is dibasic. Fer-
ricyanogen, Fdcy, containing 2 atoms of iron and 6 of cyanogen, is tribasic.
The ferrocyanide of potassium, for instance, is K^jFcy, and the ferricyanide,

394 MANUFACTURE OF PRUSSIAN BLUE.

Kg.Fdcy ; the ultimate elements of the former being KaFeNgCg ; and those
of the latter, KgFegNeC.a. They are isomeric (p. 19).

Ferrocyanide of Hydrogen ; Ferrocyanic Acid; Hydroferrocyanio
Acid (H3,Fcy=H3Fe,Cy3). — {Ferrochyazic acid o^ Porret, by whom it was
discovered in 1818.) — This acid maybe obtained by the following processes:

1. Dissolve 58 grains of crystallized tartaric acid in alcohol, and pour the
solution into a phial containing 50 grains of ferrocyanide of potassium dis-
solved in 3 drachms of warm water ; the potassa is precipitated in the state
of bitartrate, and the hydroferrocyanic acid remains dissolved in the alcohol,
from which it may be obtained, by careful evaporation, in small crystals. 2.
Mix a cold saturated solution of ferrocyanide of potassium with one-fourth
of its volume of strong hydrochloric acid, and agitate it with half its volume
of ether ; a white crystalline substance separates, which, when washed with
ether and dried, or, if necessary, dissolved in alcohol, and again precipitated
by ether, is hydroferrocyanic acid. In this decomposition, 1 atom of ferro-
cyanide of potassium and 2 of hydrochloric acid yield 1 of hydroferrocyanic
acid and 2 of chloride of potassium. Hydroferrocyanic acid thus obtained,
is soluble in water and alcohol, and powerfully acid : it decomposes the alka-
line carbonates with effervescence, forming ferrocyanides of their bases. It
is inodorous, and not poisonous : it is permanent in the dry state, but when
moistened and exposed to air it forms Prussian blue.

Ferrocyanogen, regarded as a bibasic radical, forms two sets of salts, com-
bining, namely, with 2 atoms of the same metal, as in the ferrocyanide of
potassium, F^Fcy ; or with 2 atoms of different metals, as in the ferrocyanide
of potassium and calcium, K,Ca,Fcy ; and when these salts are formed by
the hydroferrocyanic acid, the 2 atoms of its constituent hydrogen are
replaced by 2 atoms of the same or of different metals. The ferrocyanides
are decomposed by heat with various phenomena. 1. The ferrocyanogen
evolves nitrogen and becomes converted into carbide of iron, which remains
mixed with the basic cyanide ; this is the case with ferrocyanide of potassium.

2. The cyanogen of both the cyanides is decomposed, nitrogen evolved, and
metallic carbides of iron and of the basic metal are formed ; as with ferro-
cyanide of lead. 3. The basic cyanide evolves cyanogen, and is reduced ;
as in the case of ferrocyanide of silver.

Ferrocyanide of Iron. — When ferrocyanide of potassium is added to a
pure protosalt of iron, a whitish precipitate falls, which becomes blue by
exposure, and is =K,Fe3,Cy3. The same salt is thrown down on adding
hydrochloric acid to a solution of ferrocyanide of potassium. Representing
this salt by the formula KFe,Fcy, it comes under the class of ferrocyanides
with two basic metals.

Prussian Blue. — This pigment was accidentally discovered by Diesbach,
a color-maker at Berlin, in the year ITIO. It is largely consumed in the
decorative arts, in dyeing, and calico-printing : it is used in making some
of the varieties of what is called stone-blue, and is sometimes added to starch,
though for this purpose, as well as for covering the yellow tint of paper,
smalt or cobalt blue is preferable. Prussian blue is prepared of different
degrees of purity, by precipitating solutions of peroxide of iron by ferrocy-
anide of potassium, various additions being made according to the purposes
for which it is required.

Pure Prussian blue is obtained by adding a solution of ferrocyanide of
potassium to persulphate of iron, thoroughly washing the precipitate, first
with water slightly acidulated by sulphuric acid, and then with pure water,
and ultimately drying it in a warm place. Prussian blue is of a peculiarly
rich and intense blue, with a copper tint upon its surface ; it is insipid, in-
odorous, insoluble in water, in alcohol, and in dilute acids, and is not poison-

PERRICYANOGEN. FERRICYANTDES. 395

ous. Concentrated snlphnrio acid forms with it a white pasty mass by dehy-
drating it, from which water again separates it as Prussian blue ; nitric acid
decomposes it ; concentrated hydrochloric acid ultimately abstracts part of
its iron. Sulphuretted hydrogen, and nascent hydrogen, gradually destroy
its color. The alkalies decompose it into soluble ferrocyanides and oxide
of iron, hence, as a dyeing material, it does not resist the action of soap.
Boiled in water with peroxide of mercury, it forms cyanide of mercury, and
an insoluble compound of cyanide and oxide of iron. A^ccording to Chevreul,
Prussian blue becomes white in the direct rays of the sun, but regains its
blue color in the dark. It is occasionally used in the composition of writing
fluids. It is hygrometric, and after having been well dried, speedily attracts
moisture. When subjected to destructive distillation, it yields a little water
with hydrocyanate of ammonia, and then carbonate of ammonia ; a black
pyrophoric carbide of iron remains.

Prussian blue is regarded as a compound of cyanogen and iron, but various
views have been taken of its atomic constitution, according as it has beea
considered to contain, or not to contain, the elements of water. When an-
hydrous, it contains 7 atoms of iron and 9 of cyanogen ; or 4 atoms of iron
and 3 of ferrocyanogen ; but it is generally admitted that it cannot practi-
cally be obtained in this state, and that it always contains water, or the ele-
ments of water, which cannot be expelled without the decomposition of the
compound ; if so, it is probably a hydroferrocyanate of the sesquioxide of
iron.

Ferrocyanide of Potassium and Iron. — It has already been observed that
the white precipitate resulting from the action of ferrocyanide of potassium
upon a protosalt of iron, contains 1 atom of potassium, 2 of iron, and 3 of
cyanogen, and is identical with the salt produced by the action of sulphuric
acid upon ferrocyanide of potassium ; it is therefore a ferrocyanide, in which
1 atom of potassium is replaced by an atom of iron =K,Fe2Cy3 ; or*it may
be regarded as a compound of 1 atom of ferrocyanide of potassium with 3 of
cyanide of iron =(K2,Fe,Cy3)H-3FeCy=2(K,Fe^,Cy3). When this white com-
pound is exposed to air, it absorbs oxygen and becomes blue, forming what
has been termed soluble or basic Prussian blue, a compound of Prussian
blue with peroxide of iron =(Fe7,Cyg+Fe303). When washed with water,
the ferrocyanide is first washed away, but if the washing be continued, the
whole of the precipitate is gradually dissolved, furnishing a dark-blue liquor,
which maybe evaporated to dryness without decomposition. The blue liquor
is not precipitated by alcohol, but when solution of sulphate of potassa (and
certain other salts) is added, a blue precipitate falls, which is again perfectly
soluble in pure water.

Ferricyanogen (Fe3Cy8=Fdcy). — This assumed tribasic salt radical is
isomeric with ferrocyanogen, being formed by the coalescence of 2 atoms of
that compound.

Ferricyanide of Hydrogen. Hydroferricyanic Acid (Il3,Fe^Cye or Hg,
Fdcy). — This acid is prepared by decomposing recently precipitated ferricy-
anide of lead by dilute sulphuric acid, or by sulphuretted hydrogen : on fil-
tration a yellow liquor is obtained, which by very slow spontaneous evapora-
tion deposits crystals ; if heat be used, a brown powder remains : the aqueous
solution gradually decomposes, especially if heated, and deposits a blue crys-
talline powder. This acid, in combining with metallic oxides, produces water
and metallic ferricyanide, its hydrogen being replaced by the metal ; its com-
pounds with the metals of the alkalies and alkaline earths are soluble in
water; the others are insoluble, and are formed by the reaction of a soluble
ferricyanide upon solutions of the metallic salts (p. 289).

Ferricyanide of Iron (FesCyg=Fe3,Fdcy). — This is the precipitate

396 TESTS FOR THE SALTS OF IRON.

formed by adding solution of ferricjanide of potassium to a protosalt of iron;
it is produced by the substitution of 3 atoms of iron for 3 of potassium ; it is
known in commerce as TiirnhulVs blue (K3,Fdcy) + 3(FeO,S03) = (Fe3,Fdcy +
3KO,S03). It may also be prepared by adding to a protosalt of iron a mix-
ture of ferrocyanide of potassium and chloride of soda, to which hydrochloric
acid has been previously added. It is distinguished from common Prussian
blue by its action on ferrocyanide of potassium, for when boiled in a solution
of the latter salt it decomposes it into ferricyanide, which is dissolved, and
into an insoluble gray residue of ferrocyanide of iron and ferrocyanide of
potassium.

Hydronitroprussic Acid and Nitroprussides. — When binoxide of nitrogen
is passed through an aqueous solution of hydroferricyanic acid, one of the
products is hydronitroprussic acid, the formula of which is H2,Fe.3Cy5,N03 :
it forms a well-defined series of salts, discovered by Dr. Playfair {Phil.
Trans. 1848). One of the most characteristic of these is the nitroprusside
of sodium: Na2,Fe3Cy5,N03-|-4Aq. It is obtained by the action of 5 parts
of nitric acid (diluted with its bulk of water) upon 2 parts of pulverized fer-
rocyanide of potassium ; cyanogen and hydrocyanic acid are evolved, and,
when the effervescence has ceased, the solution is heated in a water-bath till
it produces a gray (instead of a blue) precipitate with a protosalt of iron :
it is then set aside, and crystals of nitre, with some oxamide, are deposited ;
these being removed, the solution is neutralized by carbonate of soda, which
throws down a greenish-brown precipitate, and, on filtering and evaporating
the liquid, crystals of the nitroprusside and of the nitrates of potassa and
soda are obtained : the former are picked out and purified by another crys-
tallization. Nitroprusside of sodium forms red prismatic crystals, soluble in
about 2|- parts of water. The solution, when exposed to light, deposits
Prussian blue, and evolves nitric oxide; when an alkaline sulphide is added
to it, ev?n in a most diluted state, it assumes a deep and characteristic purple
color, which, however^ soon disappears (p. 288). Nitroprusside of Barium
(Ba.-5,FeeCy5,N03-f-6Aq) forms red octahedral crystals.

Alloys of Iron. — These compounds are not of much importance, except
perhaps those of zinc and tin, as far as they are concerned in the production
of zinced and tinned iron, which are mentioned under those metals.

Tests for the Salts of Iron. Protosalts. — The solutions of these salts
have a. greenish color, and a peculiar metallic inky taste. 1. Sulphuretted
hydrogen gives no precipitate in a solution of a protosalt, provided it is
acid. 2. Hydrosulphate of ammonia gives a precipitate of greenish black
sulphide, part of which is dissolved, and imparts a green tint to the alkaline
liquid. When exposed to the air, this precipitate is converted into a red-
dish-brown basic salt of the peroxide. 3. Potassa and soda throw down a
white hydrated oxide, insoluble in the alkali. This, by exposure to air,
rapidly becomes green, and ultimately brown (hydrated peroxide). When
precipitated under similar circumstances, the oxide of manganese becomes
brown, but without passing through any shade of green. 4. Ammonia gives
a similar precipitate, which is partly dissolved by an excess, forming a green-
ish colored liquid ; but on exposure, the solution or precipitate undergoes
similar changes. 5. Alkaline phosphates and arsenates throw down white
precipitates (phosphate and arsenate) which pass through similar changes.
The precipitated phosphate of the protoxide is soluble in acetic acid. 6.
Ferrocyanide of potassium gives a white precipitate (p. 394), which, by the
rapid absorption of oxygen, acquires a dark blue color (Prussian blue).
Hence this white precipitate forms a useful test for free oxygen (p. 99). T.
The ferricyanide of potassium gives a rich blue precipitate (p. 289). The
precipitates given by this and the preceding test are insoluble in strong

SEPARATION AND ESTIMATION OP THE OXIDES OF IRON. 39T

hydrochloric acid. If the solution is alkaline, they are not produced, since
alkalies decompose them. 8. Tincture of galls (tannic acid) produces no
change of color in the solutions of pure protosalts, but by the absorption of
oxygen, and the oxidation of the protoxide, the liquid soon acquires, on the
surface, a pink, purple, blue, or even black tint, according to the quantity
of peroxide of iron produced. Sulphocyanide of potassium and succinate
and benzoate of ammonia produce no precipitate or change of color.

Persalts of Iron. — The solutions are generally brownish-yellow and very
acid. The more neutral they are, the deeper the color. 1. Sulphuretted
hydrogen gives with the solution a milky-white precipitate of sulphur — the
persalt being converted to a protosalt (Fe,033S034-HS=2(FeOS03) + HO,
SOg-j-S). 2. Hydrosidphate of ammonia gives a black precipitate of sul-
phide of iron (FeS) with a separation of sulphur. This precipitate is soluble
in hydrochloric acid. It becomes brown by exposure to air. 3. Foiassa,
soda, and ammonia, as well as their carbonates and hicarhonates, throw down
brown hydrated peroxide, insoluble in an excess of the alkalies or their salts,
as well as in chloride of ammonium. Some organic substances, if present,
will interfere with this action of the alkalies (p. 385). In this case hydro-
sulphate of ammonia should be employed. 4. Phosphate or arsenate of soda
gives, in a diluted and nearly neutral solution of a persalt, a whitish or pale
brown precipitate of phosphate or arsenate of iron, insoluble in acetic acid,
but dissolved by mineral acids ; this precipitation is promoted by boiling.
Peroxide of iron may thus be separated from the alkalies and alkaline earths,
as well as from any protoxide of iron which may be present: these bases are
held in solution. 5. Ferrocyanide of potassium produces, even in a very
diluted solution, a blue precipitate (Prussian blue, p. 394) which is insoluble
in hydrochloric acid. 6. Ferricyanide of potassium gives a deep emerald
green color to the liquid, but no precipitate of Prussian blue is formed, t.
Sidpliocyanide of potassium gives a blood-red tint even when the persalt is
largely diluted. This color is destroyed by heat and by solutions of chloride
of gold and corrosive sublimate. 8. Tincture of galls (tannic acid) gives
immediately a blue-black color, which is destroyed by strong mineral and
some vegetable acids. 9. Succinate and benzoate of ammonia (if the solution
is not too acid) throw down pale reddish-brown precipitates (persuccinate
and perbenzoate of iron). The protosalts of iron and the salts of manganese
are not precipitated by these two reagents.

The protoxide may be separated from the peroxide of iron by various
processes. 1. The solution of the two salts, nearly neutralized, may be
treated with acetate of soda, and a small quantity of phosphoric acid then
added. The perphosphate of iron alone is precipitated, especially when the
liquid is boiled, the protophosphate remaining dissolved in the acetic acid.

2. The mixed oxides should be dissolved in hydrochloric acid, and the
liquid warmed. If carbonate of baryta is then added to this liquid in a
covered vessel, the hydrated peroxide of iron only is precipitated. On
warming the acid liquid, the protosalt is obtained in solution in the filtrate.

3. A solution of permanganate of potassa loses its red color by admixture
with the proto, but not with the persalts, hence the proportions of the mixed
oxides may be determined volumetrically. Dissolve the oxides in hydro-
chloric acid and dilute the liquid until it is colorless. A standard solution
of permanganate of potassa, of which a certain number of measures corre-
spond to a grain of protoxide, is now added. When the color is ho longer
discharged, the operation is stopped, and the number of measures, repre-
senting grains of protoxide, read off. It has been hitherto the custom to
estimate iron by precipitating it by ammonia as peroxide from a persalt.
The precipitate is simply washed with warm water, dried, calcined, and

398 MANGANESE.

weighed. The volumetric method, however, is preferable. If a few zinc
filings are placed in the acid liquid, warmed, or a little sulphite or bisulphite
of soda is added to it, the persalt is rapidly converted into protosalt, and in
this state the proportion present admits of speedy determination by the use
of permanganate of potassa. The zinc should contain no iron, and the whole
of the sulphurous acid should be removed by boiling. 36 parts of anhydrous
protoxide are equal to 40 parts of anhydrous peroxide. Iron may be readily
separated, as peroxide, from all the alkalies, as well as from baryta, strontia,
and lime, by adding to the acid solution, ammonia and hydrochlorate of
ammonia. It may be separated from magnesia, the protoxide of manganese,
nickel, and cobalt, by diluting the liquid containing the persalt of iron, and
adding a solution of carbonate of soda, until it has acquired a brownish-red
color. If acetate of soda is then added and the liquid boiled, the hydrated
peroxide of iron is precipitated (Will). A very delicate test for the
presence of a protosalt in a persalt, is to boil the diluted liquid with chloride
of gold. If a trace of protosalt is present, metallic gold is deposited, other-
wise not.

The only metals which precipitate iron in a metallic state are magnesium,
zinc, and cadmium : they effect an imperfect precipitation from some of its
protosalts, in vessels excluded from the access of air. Before the blowpipe,
peroxide of iron produces with microcosmic salt, or borax, in the exterior
flame, a glass which is blood-red while hot, but yellow when cold. The
protoxide forms a green glass, which, by increasing the proportion of the
oxide, passes through bottle-green to black, and is opaque. The glass from
the peroxide which is reddish-colored in the exterior, becomes green in the
interior flame : it is there reduced to protoxide, and becomes attractable by
the magnet.

The native compounds of iron may be dissolved by hydrochloric or nitro-
hydrochloric acid. The silicates containing iron should be fused with four
times their weight of- the mixed carbonates of potassa and soda. The iron
then becomes entirely soluble in hydrochloric acid.

CHAPTER XXX.

MANGANESE (Mn = 28).

The common ore of manganese is the black, or peroxide ; it is found in
considerable abundance, and is of great importance as a source of oxygen,
and for the production of chlorine from seasalt, and as a chemical agent in
various arts and manufactures. Manganese also occurs in several mineral
compounds, and traces of it are found in the ashes of some plants, in a few
animal products, and in some spring waters. To obtain metallic manganese,
carbonate of manganese, mixed into a paste with oil, is subjected to a heat
gradually raised to redness, in a close vessel. The carbonaceous mixture
thus obtained is then rammed into a good crucible, filled up with charcoal-
powder, and submitted for two hours to a white heat : a metallic button is
thus obtained, which is manganese, containing a little carbon and silicon,
from which it may be freed, by fusion with borax in a crucible coated with
charcoal ; it is doubtful, however, whether in this case it does not retain
boron or sodium.

OXIDES OF MANGANESE. 399

Properties. — Manganese is a hard gray metal of a reddish white color,
with a granular or slightly crystalline fracture. Sp. gr. 8-013. It is best
preserved in naphtha, for in the air it tarnishes by oxidation and crumbles
into powder ; it undergoes the same change in water, with the evolution of
hydrogen. When handled with moist fingers, it exhales a disagreeable odor,
and when acted on by acids, the purest specimens afford traces of carbon.

Manganese and Oxygen. — There are five compounds of manganese and
oxygen, three of which are oxides, and two acids; together with two inter-
mediate oxides, namely, the red oxide, and the mineral called Yarvicite.
Their formulae are as follows : —

Protoxide ......... Mn 0

Sesquioxide Mn^Oj

Binoxide (Peroxide) ....... Mu O2

Red oxide (Hausmannite) MiigO^^

Varvicite ......... Mn^O^

Manganic acid ........ Mn O3

Permanganic acid MngO^

Protoxide op Manganese ; Manganous Oxide, (MnO), is obtained by
passing a current of dry hydrogen over carbonate of manganese, in a porce-
lain tube, exposed to a red heat. It should be allowed to cool before re-
moval from the tube, otherwise it is apt to absorb oxygen. It is of a dingy
green color ; when heated in the air it is converted into sesquioxide ; and at
a temperature of about 600° burns sometimes like tinder. It is soluble in
the dilute acids, and is the basis of the ordinary manganesian salts, which
are soluble in water, and are nearly colorless when pure, but often have a
slightly pink hue. When ammonia is added to solutions of this oxide, the
whole is not precipitated, but a double salt is formed, as with magnesia :
thus 2[MnO,S03] + NH3=[MnO,NH32S03] + MnO. When the salts of
this oxide are decomposed by potassa or soda, a bulky white precipitate falls,
which is hydrated protoxide of manganese ; it speedily becomes brown by
exposure to air, absorbing oxygen and a little carbonic acid ; and, when col-
lected and washed upon a filter, it gradually becomes a hydrate of the sesqui-
oxide. A similar change is immediately produced by solution of chlorine or
chloride of lime, by which a hydrate of the sesquioxide, or of the binoxide
is formed. The recently precipitated and moist hydrate of the protoxide is
soluble in ammonia, but not in potassa or soda.

Sesquioxide of Manganese; Manganic Oxide; (MuaOg). — When
protoxide or carbonate of manganese is exposed for some time to a red heat
in an open vessel, it absorbs oxygen, and is converted into a deep-brown
powder. An oxide similarly constituted is also obtained by heating the pure
peroxide in a platinum crucible till it ceases to give out oxygen at dull red-
ness. By exposing protonitrate of manganese to a red heat, the sesquioxide
remains as a black powder ; and this is the most certain way of obtaining it.
The characters of this oxide, in respect to solvents, differ with its state of
aggregation; its acid solutions, which are at first red, become colorless when
heated, when exposed to air and light, or in contact with organic matter,
and deposit peroxide, while a portion of protoxide remains in solution.
They are rendered colorless by sulphuretted hydrogen, by sulphurous acid,
and some other deoxidizers. Heated with hydrochloric acid, it evolves
chlorine ; and with sulphuric acid, oxygen ; and a protochloride and proto-
sulphate of manganese result. Digested with nitric acid, protonitrate and
peroxide are formed. As a base, this oxide is isomorphous with sesquioxide
of iron (FCaOg), and with alumina {A\fi^). It may replace either of these

400 OXIDES OP MANGANESE.

oxides by formino^ a manganese alum. It gives a violet, or, in small quan-
tity, a pink tinge, to glass, and appears to be the coloring principle of
amethyst. It constitutes the mineral called hraunite, which occurs in octa-
hedral crystals.

Hydrated Sesquioxide of Manganese (Mn203+HO).is obtained by exposing
the hydrated and moist protoxide to the action of air; or by passing chlorine
through water holding protocarbonate of manganese in suspension, and
leaving excess of the latter ; for if the chlprine be in excess, hydrated
binoxide is formed. It is a common natural product (the manganite of
mineralogists), occurring crystallized and massive, sp. gr. 4-3, and so closely
resembling the peroxide, that it is often difficult to distinguish them ; the
powder of the hydrated sesquioxide is, however, generally brown, that of the
peroxide hlach; the former, heated in a tube, gives off water and little
oxygen ; the latter little moisture and much oxygen.

Binoxide OF Manganese ; Peroxide of Manganese (MnOg). — This is
the oxide which most frequently occurs native. It is common in Devonshire,
Somersetshire, and Aberdeenshire. It is found in a variety of forms : com-
pact and massive, pulverulent and crystallized. Many of the latter varieties
have a gray metallic lustre, and are found acicularly radiated, and in rhom-
boidal prisms. Its specific gravity varies between 4*8 and 49. It is the
pyrolusite of some mineralogists. Under the name of manganese it is met
with in commerce, and is largely consumed in the manufacture of bleaching
compounds. In the laboratory, it is resorted to as a source of oxygen gas
(2Mn02=Mn203 + 0), for which purpose it should be well dried before it is
heated. Carbonate of lime, silica, oxide of iron, and some other substances,
are not unfrequently associated with it. In the arts it is used to give a
black color to earthenware, and to remove the green color which glass
derives from protoxide of iron ; in this case MnO^, acting on 2FeO, produces
MnO and FcgOg, neither of which in small quantity gives color to glass. A
little excess of the oxide of manganese is apt to give the pink tint which is
sometimes seen in plate-glass windows. This oxide is a good conductor of
electricity. It forms no combinations with the acids ; but such of them as
appear to dissolve it, reduce it to the state of protoxide. Gently heated
with hydrochloric acid, chlorine is liberated, in consequence of the decompo-
sition of the acid by the oxygen of the oxide (Mn03+2HCl = MnCl + 2HO
-f CL) The chloride in solution has all the properties of the protosalts of
manganese. Boiled with sulphuric acid, oxygen is evolved, and a soluble
sulphate of the protoxide is formed, [MnO„4-S03=:MnO,S03 + 0]. This
is one of the methods of procuring oxygen, but it is an objectionable pro-
cess, on account of the hard cake of sulphate of manganese produced. This
is liable to break the retort. Winkerlius suggested the use of bisulphate of
soda, the residue left on distilling common salt with hydrochloric acid, as a
substitute for sulphuric acid. He finds that a mixture of three parts of
bisulphate and one of manganese answers well. The mixture fuses under
the heat of a spirit-lamp, and remains liquid to the end, oxygen being gently
given off. The acid sulphate of potash, a waste residue left on distilling
nitre with sulphuric acid, would also answer the purpose. Nitric acid has
no action on peroxide of manganese unless it contains sesquioxide, or some
deoxidizing agent is at the same time present. Many vegetable acids
decompose it by the aid of heat.

The commercial value of this oxide may be said to depend upon the pro-
portion of chlorine which a given weight of it will evolve when heated with
hydrochloric acid ; or, in other words, the quantity of oxygen which it con-

MANGANIC ACID. MANGANATES. 401

tains beyond that contained in the protoxide. The usual mode of deter-
mining this excess of oxygen, is founded upon the mutual action of the oxide
and oxalic acid in the presence of free sulphuric acid, when protosulphate of
manganese and carbonic acid are formed.

A hydrated peroxide, =Mn02, + H0, is formed by precipitating proto-
chloride of manganese by chloride of lime. In this state it is brown, while
the anhydrous oxide is black. The soft black mineral known under the name
of IVad, is also a hydrate of this peroxide.

Jied Oxide of Manffanese {Mn.fi^). — This oxide exists native, constituting
the mineral termed Hausmannite . It is said to be formed when the hydrated
protocarbonate of manganese, after having been dried, is exposed in the air
to a red heat. Varvicite (Mn^Oy). — This name has been given to a peculiar
oxide of manganese from Warwickshire. It is harder and has more lustre
than the native peroxide.

Manganic Acid (MnOg). — This acid is met with only in a state of com-
bination with alkaline bases. It may be obtained as manganate of potassa
by fusing equal parts of peroxide of manganese in fine powder, and hydrate
of potassa, with a small quantity of nitrate, in a covered crucible; a greenish
black mass results, which with water affords a deep green solution of manga-
nate of potassa. This is permanent with excess of alkali, but otherwise it
becomes blue, purple, and ultimately red on exposure to air, in consequence
of the formation of permanganate of potassa by the absorption of oxygen
{chameleon mineral). At the same time it deposits a brown powder, which
is hydrated peroxide of manganese, and free alkali is separated : (3[K0,
Mn03]=KO,MnaOy4-Mn03+2KO.) Nitric acid or chlorine added to the
liquid, changes the green into the red compound. When set free from the
base, manganic acid is resolved into hydrated peroxide and oxygen.

Manganate of Potassa (KOjMnOg), may be obtained in a purer state as
follows : Mix 4 parts of finely-powdered peroxide of manganese with 3| of
chlorate of potassa, and add them to 5 parts of hydrate of potassa dissolved
in a small quantity of water. The mixture is evaporated to dryness, pow-
dered, and then ignited in a platinum crucible, but not fused, at a low red
heat. Digested in a small quantity of cold water, and filtered through as-
bestos, this affords a deep emerald green solution of the alkaline manganate,
which may be obtained in crystals of the same color by evaporating the solu-
tion over sulphuric acid in the air-pump. The crystals are isomorphous with
the sulphate and chromate of potassa. They are anhydrous. They are
soluble in a moderately concentrated solution of potassa, forming an intensely
green solution, and are again deposited without change when evaporated in
vacuo. The changes of color which the compound undergoes may be well
illustrated by placing a quantity of the manganate in powder in a capacious
jar, and very gradually adding to it a large quantity of water which is aerated.
As the oxygen is absorbed by the manganic action, it changes in color from
emerald green to blue, violet, purple, and at length remains of a ruby or
amethyst red. It is now permanganate of potassa. This conversion is im-
mediately brought about by the addition of an acid, even by acetic acid.
Acids operate by removing the base. The change is also rapidly effected by
boiling, showing that the manganic is a very unstable acid. It is reduced to
the state of hydrated peroxide by many kinds of organic matter, especially
if in a decomposing state. It is instantly decomposed and rendered colorless
by sulphurous, phosphorous, and nitrous acids. Arsenious acid also reduces
it. The tendency of this acid therefore is to pass either to a lower or higher
state of oxidation..
26

402 PERMANGANIC ACID.

Permanganic Acid (Mn^Oy). — When the green solution of manganate of
potassa in water, moderately diluted, is boiled, it rapidly becomes purple by
conversion into the permanganate of potassa (KOjMn^Oy). As the solution
is decomposed by contact with organic matter, it must be filtered through
asbestos, and concentrated by evaporation. Deep ruby-colored crystals are
thus obtained, which are soluble in 16 parts of water at 60°, and possess an
intense coloring power ; one or two grains will give a deep amethyst red
tint to a large quantity of water.

The solution of this salt is now much employed in volumetric analysis. It
readily parts with its oxygen to organic matter and deoxidizing bodies
generally ; it loses its color, and brown hydrated peroxide of manganese is
deposited. Thus the color of the permanganate is discharged by sulphurous,
phosphorous, nitrous, and arsenious acids, as well as by their salts when an
acid is added. Sulphuretted hydrogen, a protosalt of iron, thallium and
its oxide, grape-sugar, aiid nicotina immediately deoxidize it. Iodide of
potassium converts a concentrated solution to green manganate, but deoxi-
dizes entirely a weak solution. Ammonia is slowly oxidized by the solution:
when the decolorized permanganate, to which ammonia has been added, is
filtered and evaporated, it has been observed that on the addition of an acid to
the dry residue, red fumes have been evolved showing the presence of some
nitrite or hyponitrite of potash. A diluted solution of permanganate is not
affected in the cold by magnesium, zinc or aluminum ; but mercury agitated
with it is converted into suboxide, and the solution loses its color. The
action takes place more strongly if the metal is boiled in the solution, but in
this case some oxide of mercury is formed. A standard solution of the
permanganate has been employed for determining the presence of organic
matter in air and water, (pp. 131, 163). It has been erroneously supposed
that it would determine the precise amount of organic matter present in a
given volume of water, but experiment shows that different kinds of organic
matter require different quantities of the permanganate, and therefore no
reliance can be placed upon quantitative results, unless we are aware of the
nature of the organic matter which is present in the water. Dr. Frankland
found on dissolving three grains of each of the following organic substances
in distilled water, and testing by a standard solution of permanganate, that
the following quantities were indicated : —

Of Gum acacia .

. -082

Creatine

,

. -064

Cane sugar .

. -051

Alcohol

,

. -074

Starch .

. -114

Urea .

^

. -074

Gelatine

. -634

Oxalic acid

.

. 2-998

The only result approaching to correctness was given by oxalic acid, the
standard deoxidizer used. The determination of the weight of oxidizable
organic matter by means of this test is therefore based on a pure fallacy.
At the same time it is a safe guide in forming an opinion of the freedom of
water from decomposing organic matter. If six or eight ounces of water
retain a pink color for several hours from the addition of a few drops of a
weak solution of permanganate, it may be inferred that the water is com-
paratively pure and free from any undue amount of decomposing organic
matter and gaseous impurities. Foul water may be thus purified, and after
filtration rendered fit for drinking purposes. For the preparation of the
purest water. Star recommends that permanganate of potash should be added
and the mixture distilled. Rain water may be thus purified.

Under the name of Condifs Disinfecting Liquid, a solution is generally
sold in a concentrated form in the state of green manganate, but it becomes
converted into purple or red permanganate by the necessary dilution with

CHLORIDES OP MANGANESE. 403

water. As it is a fixed compound, it can operate only as a deodorizer by
direct contact with the liquid or solid, emitting offensive effluvia. Linen
wetted with it, and suspended in a foul atmosphere, removes the effluvia
from that portion of air which comes in contact with it, but it does not, like
chlorine, diffuse itself through the apartment so as to destroy the noxious
matter in all parts. For this purpose ozonized ether is preferable to the
permanganate. The acid loses three atoms of oxygen during this process,
and is reduced to hydrated peroxide which causes stains on linen. Per-
manganate also operates as a bleacher by oxidation. Thus a few drops of
the solution added to a solution of indigo discharges the color. This salt
has become a most useful substance in the laboratory. A solution of it is
sold under the name of Ozonized water. When used as a lotion, it removes
the smell of fetid breath, of offensive ulcers, and also of effluvia from the
hands.

If a solution of nitrate of silver is added to a hot concentrated solution
of permanganate of potassa, red crystals of permanganate of silver are
deposited on cooling. By double decomposition with the chlorides, per-
manganates of the alkaline earths may be obtained. If a concentrated solu-
tion of potassa is poured into a diluted solution of permanganate, the liquid
becomes first violet and by very gradual additions of the alkali, passes through
various shades of purple to emerald green. Manganate of potassa is formed,
and a double quantity of base enters into combination (KO,Mn207+KO =
2(KO,Mn03)-fO) : the oxygen being retained in the liquid. A perman-
ganate is more stable in water than a manganate, since it may be boiled
without being decomposed. The acid is, however, slowly changed by ex-
posure to air, into peroxide of manganese. Permanganic acid may be
obtained in combination with water, by decomposing permanganate of baryta
with diluted sulphuric acid. Its formula is MO,^i\fi^. The solution is of
a red color. It is rapidly decomposed even at common temperatures. A
portion of the oxygen in this acid is supposed by Sch'onbein to be in an
allotropic state, as ozone (p. 113).

PROTOCHLORIDE OF MANGANESE (MnCl). — When peroxide of manganese
is heated with hydrochlorate of ammonia, a solution of chloride of manganese
may be obtained from the residue, which furnishes transparent pinkish crys-
tals of hydrated chloride. The same salt is obtained by dissolving carbonate
of manganese in diluted hydrochloric acid, and evaporating the solution.
The higher oxides of this metal, when treated with hydrochloric acid, give off
chlorine, and are converted into protochloride of manganese. Thus a man-
ganate, treated with an excess of hydrochloric acid, acquires the usual chemi-
cal properties of the protosalts.

Exposed, out of the contact of air, to a red heat, the hydrated crystals
of the protochloride lose water to the amount of about 40 per cent., and
leave a lamellar anhydrous chloride of manganese ; heated in the contact of
air, the chloride is decomposed and converted into an oxide, like the cor-
responding chloride of magnesium. 100 parts of water at 60° dissolve
about 40 parts of the anhydrous salt : alcohol dissolves half its weight, and
the solution, when evaporated in vacuo, affords a crystalline alcoate, contain-
ing two equivalents of alcohol. When ammonia is added to a solution of
the chloride, half of the manganese is thrown down in the state of hydrated
protoxide, and the remainder forms a double salt. When a recently precipi-
tated hydrated protoxide of manganese is digested in a solution of sal-
ammoniac, the double chloride is formed. A large quantity of this chloride,
in an impure state, is obtained as a waste product in the manufacture of
chloride of lime.

1$

404 SULPHATES OF MANGANESE.

Sesquichloride or Manganese (Mn^Clg) is formed when the sesquioxide
is dissolved at a low temperature in hydrochloric acid; a dark brown
solution is obtained which, with a slight elevation of temperature, evolves
chlorine.

Perchloride of Manganese (MngCly) is produced by adding fused chlo-
ride of sodium to a solution of permanganate of potassa in sulphuric acid ;
the compound passes off in the form of a green vapor, condensible at 0°
into an olive-colored liquid. If the vapor be conveyed into a moistened
flask, it acquires a red tint, and hydrochloric and permanganic acids are
generated.

Nitrate of Manganese (MnOjNOg). — Dilute nitric acid dissolves moist
protoxide or protocarbonate of manganese, and forms a protonitrate, which
may be obtained by evaporation in vacuo, in hydrated prismatic crystals, de-
liquescent, very soluble in water and in alcohol, and of a bitter taste ; their
alcoholic solution burns with a green flame.

Sulphide of Manganese (MnS). — When dried protosulphate of manga-
nese is ignited with one-sixth its weight of finely-powdered charcoal, or when
a current of sulphuretted hydrogen is passed over the protocarbonate or
protosulphate heated to redness, a sulphide of manganese is obtained. It
has a gray metallic lustre, and is soluble in dilute sulphuric and hydro-
chloric acid, with the evolution of sulphuretted hydrogen. It is identical
with the native sulphide of manganese, a rare ore, found in Cornwall and
Transylvania.

Sulphate of Manganese (MnO,S03) 's formed by dissolving the prot-
oxide or protocarbonate in dilute sulphuric acid, or by mixing peroxide of
manganese into a paste with sulphuric acid, and heating the mixture to dull
redness ; in the latter case oxygen is evolved. The dry residue washed with
water affords a solution of the sulphate of the protoxide, which may be
crystallized by evaporation. This salt is used in dyeing and calico-printing.
When cloth is passed through its solution, and afterwards through a caustic
alkali, protoxide of manganese is precipitated upon it and rapidly becomes
brown in the air; or it is at once peroxidized by passing the cloth through
a solution of chloride of lime. This color is called manganese hrown.
Sulphate of manganese, as it is obtained by gentle evaporation from the
neutral solution, forms rhombic prisms which contain 4 atoms of water.
When the crystals are formed between 45° and 68° they contain 5 atoms of
water ; when formed under 42° they include 7 atoms of water ; and when a
concentrated solution of sulphate of manganese is mixed with sulphuric
acid, it yields on evaporation small granular crystals containing only 1 atom
of water. The solubility of sulphate of manganese varies with its water of
crystallization ; the anhydrous salt is soluble in 2 parts of water at 60°, and
in its own weight at 212°. It is insoluble in alcohol. The taste of sul-
phate of manganese is styptic and bitterish, and the crystals have generally
a slight tinge of rose-pink. At 240°, they lose 3 atoms of water, but retain
1 until heated above 400° ; at a red heat the salt becomes anhydrous. This
compound forms double salts with potassa and ammonia.

Sesquisulphate of Manganese (Mn^Og-f SSOg) is formed by dissolving
the sesquioxide in sulphuric acid : the solution is of a crimson color. When
heated it gives off oxygen and becomes colorless : it is instantly bleached by
sulphurous acid or any deoxidizing agent. Its most important property is
that of forming, with sulphate of potassa or of ammonia, double salts crys-
tallizing in octahedra, which are manganese alums, similar in constitution to
ordinary alum, but with AI3O3, replaced by Mn^Og (p. 369). 1 part of per-
oxide of manganese mixed with 13 of oil of vitriol, and gently heated till

r
TESTS FOR THE SALTS OP MANGANESE. 405

half the quantity of oxygen thus separable has escaped, yields a mass from
which water extracts the sesquisulphate ; 1 part gives a red color to 1280
parts of water.

Carbide of Manganese is probably always contained in the metal reduced
by charcoal. The quality of steel is said to be improved by the presence in
it of carbide of manganese. The plumbago-like substance called kish, occa-
sionally produced in iron furnaces, contains this carbide.

Carbonate of Manganese (MnOjCOJ is white, insipid, and insoluble in
water. It is precipitated as a hydrate, by alkaline carbonates, from the pro-
tochloride or protosulphate : it becomes brown by drying in the air. Car-
bonate of manganese constitutes the spathose manganese of mineralogy, and
often accompanies spathose iron.

Tests for the Salts of Manganese. — The proto-saltsare soluble in water.
The solution is either colorless or slightly pink, and has an acid reaction.
It has a bitter astringent taste, and becomes brown and turbid when long
exposed. 1. Sulphuretted hydrogen produces no precipitate, but hydrosul-
phate of ammonia throws down a flesh-colored sulphide, which is easily dis-
solved by acetic acid. The precipitates become brown by exposure to air.
2. Potassa or soda throws down a white hydrated oxide, which rapidly
becomes brown on exposure, owing to its conversion into sesquioxide. Before
undergoing this change the precipitate is soluble in hydrochlorate of ammonia :
it is insoluble in potassa or soda. 3. Ammonia also precipitates partially a
white hydrated oxide, which becomes brown when exposed. 4. Carbonates
and hicarhonates of potassa, soda, or ammonia, throw down a white carbo-
nate, which is dissolved by hydrochlorate of ammonia, and becomes slowly
brown by exposure. 5. Ferrocyanide of potassium produces a white precipitate,
with a shade of blue if iron is present, and red if copper is present. 6. Fer-
ricyanide of potassium gives a brownish-red precipitate. T. Chlorine produces
no effect on the solution, but when any alkali is added, brown hydrated per-
oxide of manganese is precipitated. Chloride of lime immediately gives a
brown precipitate. 8. Heat a few grains of minium in a few drops of strong
nitric acid; and add to the liquid a small quantity of the peroxide of manga-
nese. Permanganic acid is produced, which may be recognized by the pink
color of the solution, as soon as the oxide of lead has subsided. 9. On a loop
of platinum wire melt some carbonate of soda with a little nitre. If a mere
trace of oxide of manganese be fused with the mixed salts in the inner flame
of the blowpipe, or of a Bunsen's jet, manganate of soda is produced,
known by its greenish color (if the manganese is not in excess). If the
wire is placed in a few drops of water in a tube, an emerald green solution
is obtained, which, when diluted and warmed, or an acid is added, is converted
into a pink solution of permanganate of potassa. This is probably the most
delicate test for manganese, whether in a soluble or in an insoluble form.

The peroxide of manganese as well as the manganic and permanganic acids
belong to this class of ozonides. They readily part with a portion of their
oxygen which is supposed to be evolved in the form of ozone. Thus, when
placed in contact with strychnia moistened with sulphuric acid, they produce
blue, violet, purple, and red colors, and serve as tests for that alkaloid.
When added to freshly-precipitated tincture of guaiacum, they impart to it a
beautiful blue color, a result of the oxidation of the precipitated resin.

406 ZINC AND OXYGEN.

CHAPTER XXXI.

ZINC — INDIUM — TIN — CADMIUM.

Zinc (Zn=32).

The Zinc of commerce is produced from the native sulphide {blende) or
carbonate {calamine). The ore is picked, broken into small pieces, submitted
to a dull red heat in a reverberatory furnace, by which carbonic acid is driven
off from the calamine, and sulphur from the sulphide. It is then washed,
ground, and thoroughly mixed with about one-eighth of its weight of powdered
charcoal. This mixture is put into large earthen pots, not unlike oil-jars,
six of which are usually placed in a circular furnace. Each pot has an iron
tube passing from its lower part, through the floor of the furnace, and
dipping into water; they are everywhere else firmly luted. Upon the ap-
plication of a full red heat, the metal distils through the tube into the water
beneath, whence it is collected, melted, and cast into cakes. This process is
called distillatio per descensum. Commercial zinc generally contains traces
of sulphur, iron, and arsenic. In 1865 the products of the mines of the
United Kingdom in blende and calamine amounted to 1*1,842 tons, yielding
4,460 tons of metallic zinc.

Properties. — Zinc is a bluish white metal, with considerable lustre, rather
hard, of a specific gravity of about 6-8 in its usual state, but when drawn
into wire, or rolled into plates, its density is augmented to 7* or 7 1. It has
a peculiar odor when breathed upon, or handled with moist fingers. In its
ordinary state and at common temperatures it is tough, but becomes brittle
when its temperature approaches that of fusion, which is about 773°. At a
temperature a little above 212°, and between that and 300°, it is ductile and
malleable, and may be rolled into thin leaves or drawn into wire. If slowly
cooled after fusion, its fracture is very crystalline. It is volatile at a bright
red heat, and admits of distillation, but if its vapor be exposed to air, it
burns with intense brilliancy.

When a surface of clean and polished zinc is exposed to dry air, it remains
bright; in damp air it tarnishes, and then remains unchanged. Under
water it becomes enfilmed with hydrated oxide, or with a hydrated basic
carbonate if carbonic acid be present. At common temperatures it does not
decompose water, but does so at a red heat, or in the presence of acids. In
pure water, from which air has been carefully excluded, it remains bright.
The energy with which zinc is acted on by dilute sulphuric acid is greatly
dependent upon the purity of the metal ; when perfectly pure the action is
feeble, but when it contains minute portions of other metals, it becomes
rapid: this is apparently owing to a galvanic action ; and when a piece of
pure zinc is wound round with platinum wire an equivalent effect is produced.
Zinc and all its compounds, excepting blende, are soluble in hydrochloric
acid ; hydrogen is evolved, when the metal is employed. A strong solution
of potassa, or soda, when heated, also dissolves the metal with the evolution
of hydrogen. If the zinc contains arsenic, the hydrogen evolved, whether
as the result of the action of an acid or an alkali, are mixed with arsenuretted
hydrogen. This may be inferred when the gas blackens paper impregnated
with a solution of nitrate of silver. Phosphorus combined with hydrogen

OXIDE OF ZINC. SULPHIDE OF ZINC. 40T

will produoe a similar action op nitrate of silver. If the hydrogen contains
sulphur, this will be indicated by tlie discoloration of paper impregnated with
a salt of lead. Zinc, in consequence of its lightness and cheapness, is much
used for roofing, gutters, and chimney-tops; but it should not, as is some-
times the case, be riveted with copper or iron nails, the contact of which
with the zinc accelerates the destruction of the latter by electric action;
indeed, any of the common metals in metallic contact with zinc, tend to pro-
duce its oxidation.

Zinc and Oxygen. — The high attraction between zinc and oxygen is
shown by the facility with which many of the other metallic oxides, in solu-
tion, are reduced to the metallic state by its means. Its important electro-
generative power in Voltaic arrangements, is also referable to this cause.
As the zinc compounds are now easily reduced by magnesium, this metal is
likely to take the place of zinc for electrical and other purposes so soon as
it can be cheaply manufactured. By exposing zinc to the joint action of
heat and air, at a temperature just sufficient to fuse it, it is converted into a
gray powder, which is probably a mere mixture of metallic zinc and oxide of
zinc, although by some it is regarded as a true suboxide, Zn^O.

Oxide of Zinc (ZnO). — This is the only salifiable oxide of zinc ; it is
obtained by intensely heating the metal exposed to air, when its vapor takes
fire, burns with a very bright flame, and forms a white flocculent substance,
formerly called 7iihtl album, philosopher^ wool, and flowers of zinc. When
this combustion goes on with violence, the oxide, though in itself not volatile,
is carried up in flocculi by the current of air, which are so light as to remain
for a long time floating about the atmosphere. A piece of zinc-leaf may
also be inflamed by a spirit-lamp, and will continue to burn brilliantly even
when removed from the flame ; if inflamed and plunged into oxygen, the
combustion is as vivid as that of phosphorus — indeed, the splendor of the
flame probably arises in both instances from the same cause, namely, the
ignition of finely-divided solid incombustible matter (p. 102). The oxide of
zinc, as prepared by combustion, generally contains small particles of the
metal, which render it gritty : it may also contain other impurities, so that
for pharmaceutical use it should be procured by decomposing a solution of
pure sulphate of zinc at a boiling heat by its equivalent of carbonate of soda.
The precipitate well washed, dried, and exposed to a dull-red heat, is a pure
oxide ; or the cold solution of the sulphate may be decomposed by carbonate
of ammonia, and the precipitate washed and dried as before. Traces of sul-
phuric acid, or of soda, may be detected in the oxide from cold solutions
when carbonate of soda has been used, and if a hot solution be precipitated
by carbonate of ammonia, the oxide will retain sulphuric acid.

Oxide of zinc obtained by the combustion of the metal, or by passing steam
oyer red-hot zinc, is sometimes crystalline; its specific gravity is between
5*6 and 5-7. It is commonly met with in the form of a white powder, which
at a high temperature acquires a yellow tint, but again whitens as it cools.
It has been used as a pigment, both with oil and water ; and is employed in
medicine as a tonic, and as an external application. Oxide of zinc is readily
soluble in acids ; it also dissolves, especially in the state of hydrate, in the
caustic fixed alkalies, and in pure and carbonated ammonia. The strong
ammoniacal solution becomes turbid when dilute, and deposits the oxide
when boiled. When a solution of alumina in caustic potassa is mixed with
an ammoniacal solution of oxide of zinc, a definite combination of the two
oxides is thrown down, containing 6 atoms of alumina and 1 of oxide of zinc,
being identical in composition with the mineral called Gahnite.

Nitrate op Zinc (ZnO,N05,6HO) is a deliquescent salt, which crystal-

408 CARBONATE OF ZINC.

lizes with difiBculty in four-sided prisms: it, is very soluble in water and in
alcohol.

Chloride of Zinc (ZnCl) is formed by heatinp: leaf-zinc in chlorine ; or
by evaporating a solution of zinc in hydrochloric acid to dryness, and heating
the residue to dull redness. It is a white translucent substance, extremely
deliquescent, fusible at 300°, and volatile at a bright-red heat: its vapor
condenses in acicular crystals. It has a nauseous styptic taste, and is power-
fully emetic. It was formerly called hitter of zinc. It is readily soluble ia
water, and the solution gives on evaporation a crystallizable but deliquescent
hydrate (ZnCl, HO), which, when heated in the open air, partly sublimes ia
the form of chloride, and is partly resolved into hydrochloric acid and oxide
of zinc. Sir William Burnett's disinfectant liquid, and preservative against
dry-rot, is a strong solution of chloride of zinc ; its sp. gr. is 1'019. Chlo-
ride of zinc forms several double salts, with the chlorides of the alkaline
metals. Zinc combines directly with bromine and iodine to form a bromide
and an iodide.

Sulphide op Zinc (ZnS) may be formed by heating oxide of zinc with
excess of sulphur; it is also produced by heating a mixture of zinc filings
and sulphide of mercury. When a salt of zinc is precipitated by an alkaline
sulphide, a white compound is obtained, which is probably a monohydrated
sulphide of zinc* Native sulphide of Zinc, or Blende, occurs in crystals
which are brittle, soft, and of different shades of brown and black. Its
primitive form is the rhomboidal dodecahedron. It usually contains traces
of iron and lead. It is an abundant mineral, and important as a source of
the metal, which is obtained by roasting the ore, and afterwards exposing it
to heat in proper distillatory vessels, mixed with charcoal. The English
miners call the sulphide from its color black jack. It is dissolved by nitro-
hydrochloric acid.

Sulphate of Zinc (ZnO,S03). — Zinc is readily oxidized and dissolved by
dilute sulphuric acid, and hydrogen is given off; the zinc so decomposes
water that an atom of zinc is substituted for an atom of hydrogen : HO,
S03 4-Zn=ZnO,S03 4-H ; and a solution of sulphate of zinc results, which
by evaporation affords crystals =ZnO,S03,'7HO, in the form of right rhombic
prisms. This salt is soluble at 2-5 parts of water at 60°. The crystals are
slightly efflorescent: at 212° they lose 6 atoms of water, retaining I till
heated nearly to dull redness. The anhydrous sulphate is white and friable ;
exposed to humid air it gradually resumes 7 atoms of water ; it heats when
sprinkled with water ; at a high temperature it evolves sulphuric and sul-
phurous acid and oxygen, and at a white heat is decomposed, leaving oxide
of zinc. It is soluble in hydrochloric acid without decomposition. White
vitriol, or the sulphate of zinc of commerce, is often obtained by the oxida-
tion of blende, and is impure ; it generally contains a sulphate of zinc,
together with the sulphates of iron, copper, cadmium, alumina, and some-
times lead : it usually occurs in amorphous masses. The sulphate, like the
chloride of zinc, forms double salts with the sulphates of the alkalies.

Carbonate of Zinc. — The precipitate formed by adding carbonate of
potassa to sulphate of zinc is a mixture of carbonate and hydrated oxide,
analogous to the magnesia alba, its formula being 2(ZnO,C03) + 3(ZnO,HO,)
or when precipitated in the cold, ZnO,CO.,+2(ZnO,HO). Native Carbonate
of Zinc, or Calamine, occurs both crystallized and massive. It is often found
investing carbonate of lime, which has sometimes been decomposed, and the
calamine remains in pseudo-crystals. It abounds in Somersetshire, Flint-
shire, and Derbyshire. A beautiful variety colored by carbonate of copper
is found at Matlock. The variety of calamine known by the name of electric

TESTS FOR THE SALTS OF ZINC. 409

calamine, from its property of becorain,2^ electrical when gently heated, con-
sists of oxide of zinc in combination with silica.

Zinced Iron; Galvanized Iron. — If plates of hot iron be dipped into
melted zinc, they acquire the appearance of tin-plate, for which they are a
valuable substitute, inasmuch as the zinced iron is prevented from oxidation
and rusting, by the electrical relations of the metals ; the zinc, it is true, is
more subject to oxidation than tin, but so long as any of it remains, the iron
is protected, and when covered by a coat of paint is extremely durable.
Hurdles, fences, and all out of door iron-work, as well as implements used in
damp situations, and employed in contact with water, may be thus defended.
The wires of electric telegraphs are generally of zinced iron, and their sec-
tion, when exposed to air and water, sometimes exhibits a fresh deposition
of zinc, arising from the galvanic precipitation of small portions of dissolved
zinc upon the electro-negative iron. The zincing of iron is generally per-
formed by dipping the iron, previously well cleaned, into melted zinc, the
surface of which is kept carefully covered with sal-ammoniac to prevent
oxidation, and so enable the iron to become thoroughly wetted, as it were,
and superficially combined with the zinc. The zinc is fused in large wrought
iron vessels, placed over proper furnaces, and after the frequent dippings of
the iron articles, there is ultimately found at the bottom of the melted metal,
a quantity of a granular alloy of zinc and iron. The process is not appli-
cable to the generality of vessels used for culinary purposes, in consequence
of the contaminations by oxide of zinc which would often ensue, especially
with acidulous or saline liquids. In using zinced iron, care should be taken
that where nails or rivets are required, they should also be coated with zinc.

Tests for the Salts of Zinc. — They are mostly soluble in water ; the
solutions are colorless, and have an astringent and metallic taste. 1. Potassa,
soda, and ammonia, form white precipitates, soluble in excess of the alkali,
and in dilute sulphuric acid. In this case the precipitate is distinguished
from alumina by its solubility in excess of ammonia, as well as in chloride of
ammonium. 2. The precipitate formed in solutions of zinc by the carbonates
of potassa. and soda is not soluble in excess of these carbonates, but when
carbonate of ammonia is employed, the precipitate produced is again dis-
solved. Zinc is thus separated from oxide of lead, alumina and the alkaline
earths. 3. Sulphuretted hydrogen throws down a white hydrated sulphide of
zinc in neutral solutions, but not in those which are acid or alkaline. 4.
Hydrosulphate of ammonia produces a white, or yellowish-white precipitate.
5. Ferrocyanide of potassium gives a white bulky precipitate, and ferricya-
nide a brownish precipitate. The soluble phosphates, oxalates, and borates,
produce white precipitates soluble in acids and alkalies. The salts of zinc
which are insoluble in water, dissolve in dilute sulphuric acid, and are pre-
cipitated by ammonia, but are redissolved by an excess of acid or of precipi-
tant. Metallic zinc is readily thrown down from its solutions by magnesium
and in some exceptional cases by iron.

The special characters of a salt of zinc are, that the oxide is soluble both
in potassa and ammonia, and that from the alkaline solutions it is precipitated
as a white sulphide by sulphuretted hydrogen, but it is not precipitated from
them by chloride of ammonium. By these characters it is distinguished from
alumina and other oxides which are soluble in potassa. Zinc is the only
metal which forms a white sulphide with sulphuretted hydrogen.

Before the blowpipe, or on platinum foil, oxide of zinc becomes yellow
when heated, but whitens as it cools. A small proportion forms with borax
a clear glass, which becomes opaque on increasing the quantity of oxide. If
a drop of nitrate of cobalt is added to the oxide, and this is dried and ignited,
it becomes green. With soda, in the interior flame, oxide of zinc is reduced,

410 INDIUM. TIN.

and the metal burns with its characteristic flame, depositing its oxide upon
the charcoal. Mixed with oxide of copper, and reduced, the ziuc will be
fixed and brass obtained.

Indium (In=35-9).

This metal, the result of investigations by spectral analysis, was discovered
in 1863 by Richter and Reich, chemists of Freiburg. It was discovered by
them in the Freiburg zinc blende, which contains it in small proportion. It
received the name of Indium from the fact that it imparted a beautiful blue
color to a colorless flame, and gave in its spectrum a well-marked indigo-
blue line. It may be obtained from the Freiburg zinc by operating on the
dark-colored residue which is left undissolved by diluted hydrochloric acid.
This consists of lead, iron, arsenic, cadmium, and indium, but lead is the
principal ingredient. The metals are separated from indium by a series of
chemical processes, and the metal indium is ultimately obtained in decompos-
ing its oxide by a current of hydrogen or heating it with cyanide of potassium.
It is a white metal with the lustre of cadmium. It is so soft that it may be
cut with a knife : it is ductile and malleable : it melts at about the same
temperature as lead, and is volatile at a bright red heat. Heated to this tem-
perature in air, it burns with a blue flame, producing a powdery yellow oxide
which is deposited. It is volatile at a high temperature and has a peculiar
odor. It is not readily tarnished on exposure to air. Its specific gravity in
the hammered state is 7*27. It is easily attacked by most acids. One oxide
is only known (InO) : This by combining with acids forms colorless salts.
The precipitated oxide is insoluble in ammonia, and is thus distinguished and
separated from oxide of cadmium. The special character of the salts of
indium is that they readily impart a blue color to a smokeless flame, and in
the spectrum there is a deep blue line.

The atomic weight has been variously given at 79, 74, and 35-9. The
two first numbers are calculated on the scale of oxygen being 16.

Indium is a rare and costly metal. Its present price is about two shillings
per grain. In the French Exhibition for 1867, two ingots were showing
weighing together 7700 grains. Their value was estimated at £370.

Tin (^n=50).

Tin (Jupiter 2J_ of the alchemists) has been known from remote ages, and
was obtained at a very early period from Spain and Britain by the Phoeni-
cians. It occurs most abundantly in Cornwall, the mines of which afford
about 3000 tons annually : it is also found in Germany, Bohemia and Hun-
gary ; in Chili and Mexico ; in the Peninsula of Malacca ; and in India, in
the Island of Banca. The native peroxide is the principal ore of tin : the
metal is obtained by heating it to redness with charcoal or culm, and a little
lime ; the first product is impure, and is returned into the furnace, and care-
fully heated so as to fuse the tin, which runs off into an iron kettle, while
the principal impurities remain unmelted ; in the kettle the tin is kept in
fusion, stirred, and agitated by plunging wet charcoal into it, by which a
quantity of impurities collect upon the surface, and are removed by a skim-
mer : thus refined, the metal is cast into blocks of about three cwt. each.
The common ores are known under the name of mine tin, and furnish a less
pure metal than that obtained from stream tin. The purest tin is known
under the name of grain tin, a term formerly applied exclusively to the metal
obtained from the stream ore : block tin is less pure, and is the produce of
the common ore. The peculiar columnar fracture which pure tin exhibits
when broken, is given by heating the ingot till it becomes brittle, and then
letting it fall from a height upon a hard pavement.

OXIDES OF TIN. 411

Tin has a silver-white color, with a slight tint of yellow, and when so
viewed as to exclude the white light reflected from its surface, it is decidedly
yellow : it is softer than gold, but harder than lead : it is malleable, though
imperfectly ductile. What is termed tin-foil is the metal beaten out into
thin leaves. The malleability of the metal is such that it may be beaten into
leaves of only the 1-1 000th of an inch in thickness. It has a slightly yellow-
ish reflection. A spurious foil, under the name of patent tin-foil, is largely
sold and used as a substitute for pure tin. It is nothing more than lead with
a thin facing of tin. It is more easily oxidized than pure tin, and produces
a poisonous salt of lead. It is much used for wrapping children's food,
articles of confectionery, &c., and we have found food thus superficially con-
taminated with carbonate of lead, the spurious foil being eaten into holes by
chemical changes. The spurious foil has a dark bluish reflection, and when
treated with diluted nitrohydrochloric acid, the tin is removed and a grayish,
blue layer chiefly consisting of lead is left. The genuine tin-foil thus treated
presents a crystalline surface of a bright lustrous appearance. Traces of
arsenic are sometimes found in tin. The sp. gr. of the metal fluctuates from
t*28 to 7 6, the lightest being the purest metal. When bent, it occasions a
peculiar crackling noise ; and when rapidly bent backwards and forwards
several times successively, it becomes hot. When rubbed, it exhales a pecu-
liar odor. It melts at 442°, and slightly contracts on consolidation. By
exposure to heat and air it is gradually converted into protoxide ; but if the
heat is continued till metallic tin no longer remains, the protoxide passes
into peroxide. Placed upon ignited charcoal under a current of oxygen gas,
it enters into rapid combustion, forming the peroxide ; and if an intensely-
heated globule of the metal be thrown upon a slieet of dark-colored paper,
it subdivides into small particles, which burn very brilliantly, and leave lines
of white oxide. It volatilizes at a very high temperature. When a polished
surface of tin is heated it becomes yellow and iridescent, in consequence of
superGcial oxidation. A preparation, under the name of powdered iin,^ is
sometimes made by shaking the melted metal in a wooden box rubbed with
chalk on the inside. When it has become solid it is in the state of fine
powder. By diffusion in water the coarser particles are readily separated ;
the tin powder is then made into a paste with glue, and is applied in any
desired pattern to steel, iron, or other articles. When dry it is burnished
and afterwards varnished. It acquires and retains great brilliancy. Pure
tin is not readily oxidized by exposure to air. It retains its lustre for a
considerable period. We have seen in the Bodleian Library at Oxford, a
missal of the ninth century of the date of Alfred, in which the margin of the
page- had been illuminated with tin laid on in fine powder or foil, and bur-
nished. It retained the white lustre of the metal but little diminished,
although a thousand years had probably elapsed since it was first laid on the
vellum. Tin putty or putty powder used for polishing plate is made by
levigating the crusts of oxide that form on melted tin. It is often injuriously
mixed with mercury, an adulteration which may be discovered by heating a
portion in a reduction tube, when the mercury will sublime in globules. The
quantity of tin ore produced from our tin mines in Cornwall and Devonshire in
1865 amounted to 15,686 tons, from which 10,039 tons of metallic tin were
obtained. {HunVs Mineral Statistics of the United Kingdom, 1866.)

Protoxide of Tin ; Stannous Oxide (SnO) is obtained by precipitating
a solution of protochloride of tin by ammonia ; it falls in the state of hydrate:
when dried, out of the contact of air, it is of a dark color. When the pro-
tochloride is decomposed by a carbonated alkali, the precipitate is also a
hydrated protoxide, retaining no carbonic acid. It is obtained anhydrous^
by heating it in a glass tube, passing a current of dry carbonic acid over it

412 CHLORIDES OF TIN.

till the water is carried of, and suffering it to cool out of the contact of air.
The specific gravity of this oxide is 6-6. It forms a dark-gray or black
powder, which, on the contact of a red-hot wire, burns like tinder into per-
oxide. In the hydrated state it dissolves readily in sulphuric, hydrochloric,
and dilute nitric acids, as well as in caustic potassa and soda, but not in am-
monia, nor in the alkaline carbonates. It is soluble in lime-water, and in
baryta-water. Its alkaline solution, when long kept, deposits metallic tin in
arborescent crystals, and becomes a solution of the peroxide.

Sesquioxide of Tin (Sn^Oa). — When a solution of protochloride of tin is
mixed with moist hydrated sesquioxide of iron and boiled, an interchange
of elements takes place, by which protochloride of iron and sesquioxide of
tin are formed: in this case, 2(SnCl) and Fefi.^, become Sn203 and 2(FeCl).
The solubility of this oxide in ammonia distinguishes it from protoxide ; and
its giving a purple precipitate with chloride of gold from peroxide. It is
soluble in concentrated hydrochloric acid. It may be represented as a stan-
nate of the protoxide by the formula SnO.SnOg.

Peroxide op Tin ; Binoxide of Tin (SnO^). — This is the common ore of
tin : in its crystalline form it is insoluble in acids, but when heated with
potassa or soda it forms a soluble compound. There are two remarkable
varieties of the hydrate of this oxide, which have been distinguished as stan-
nic and metastannic acid. Stannic acid (SnO^HO) is obtained by precipi-
tating a solution of bichloride of tin by ammonia, and washing and carefully
drying the precipitate : it is soluble in acids, and in solutions of potassa and
soda, but not in ammonia. When heated to about 300°, it passes into
metastannic acid. Stannate of Potassa is formed when peroxide of tin is
heated with potassa : the' product, when dissolved and evaporated, yields
crystals (KO,Sn03,4HO). Their aqueous solution is alkaline, absorbs car-
bonic acid, and is precipitated by most of the salts of potassa, soda, and
ammonia. Stannate of soda (NaO,Sn02,4HO) may be similarly prepared
and crystallized : it is largely used as a mordant by dyers and calico-
printers.

Metastannic acid is the result of the action of nitric acid upon tin : in its
most concentrated form this acid does not immediately act, but on the addi-
tion of a few drops of water violent effervescence ensues, much heat is
evolved, together with nitric oxide and nitrous acid vapor ; some nitrate of
ammonia is also formed (p. 182) ; and the metastannic acid remains in the
form of a white insoluble powder : it may be purified by washing, and dried
at a dull-red heat. When dried in the air it consists of Sn50io,10E[0 : dried
at 212° it loses 5H0, and at a red heat becomes anhydrous, and acquires a
pale buff color. Hydrated metastannic acid is insoluble in nitric acid : it
dissolves in sulphuric acid, forming a compound soluble in water, but decom-
posed by boiling. It dissolves in solutions of potassa and soda and their
carbonates, but not in ammonia. The metastannates are not crystallizable.
When the hydrated acid is moistened with protochloride of tin it forms a
characteristic yellow metastannate of tin.

Native Peroxide of Tin is generally gray, brown, or black, and sometimes
transparent or translucent ; its specific gravity is T : its primitive crystal is
an obtuse octahedron, of which the modifications are extremely numerous.
In some of the valleys of Cornwall it is found in nodules mixed with pebbles,
and is called stream tin. A modification of stream tin, in small banded frag-
ments or globular masses, is called wood tin.

Protochloride of Tin (SnCl) is obtained by subjecting a mixture of
equal weights of calomel and of an amalgam of tin and mercury to distilla-
tion, in a retort gradually raised to a dull-red heat; or a mixture of 1 part
of tin filings and 2 of corrosive sublimate may be treated in the same way.

CHLORIDES AND SULPHIDES OF TIN. 413

When hydrochloric acid gas is passed over heated tin in a glass tube, the
protochloride is also formed and hydrogen given off. When tin is dissolved
in hydrochloric acid, the solution evaporated, and the dry residue carefully
heated to incipient redness in a small tube retort, so as to exclude air, the
protochloride of tin remains nearly pure. It is in the form of a gray solid,
fusible and volatile'at a high heat (Butter of Tin). When its solution in a
small quantity of water is evaporated it yields prismatic crystals, which
include 3 atoms of water, of which the greater part may be expelled at 212°.
When a large quantity of water is poured upon these crystals they are partly
decomposed, hydrochloric acid is separated, and a white powder formed,
which is an oxicJdoride of tin =SnO,SnCl,2HO. The protochloride of tin,
or salt of tin of commerce, is made by putting 1 part of granulated tin into
a basin upon a sand-bath, and pouring upon it 1 part of hydrochloric acid,
so that when heated it may be exposed to the joint action of the acid and
air ; after some hours 3 parts more of the acid are added, and the mixture
stirred and digested till a saturated solution is obtained. During the pro-
cess, fetid hydrogen gas is given off, and the greater part of the tin is dis-
solved ; when the clear liquor is poured off it is set aside to crystallize ; the
mother-liquors are again evaporated as long as they afford crystals, and the
residue is afterwards employed for conversion into bichloride.

In consequence of the decomposition above mentioned, the aqueous solu-
tion of protochloride of tin is turbid, but becomes clear on the addition of
hydrochloric acid. This acid solution quickly absorbs oxygen, and, when
added to certain metallic solutions, it revives or deoxidizes them. It preci-
pitates sulphur from sulphurous acid. It reduces the persalts of iron to pro-
tosalts, and converts arsenic acid into arsenious acid, and chromic acid into
oxide of chromium. With a weak solution of corrosive sublimate it forms a
gray precipitate of metallic mercury. Added to a dilute solution of chloride
of platinum it changes its color to a deep blood-red. With solution of gold
it produced a purple precipitate used in painting porcelain, and known under
the name of Purple of Cassius. With infusion of cochineal it produces a
purple precipitate ; and it is much used to fix and alter colors in dyeing and
calico-printing.

Perchloride of Tin (SnClg). — If tin is heated in excess of chlorine, or
if a mixture of 1 part of tin filings and 4 of corrosive sublimate is distilled,
the perchloride will pass over. It is a transparent colorless fluid, formerly
called Lihavius^s Fuming Liquor: it exhales copious fumes when exposed
to moist air ; and with one-third its weight of water it forms a crystallized
hydrate =(SnCl25HO). It does not congeal at — 20^. Its boiling point
is 250°; and the density of its vapor is 919. It is instantly decomposed
by metallic zinc, forming chloride of zinc and a precipitate of metallic tin.
A solution of perchloride of tin much used by dyers, is made by dissolving
tin in a mixture of 2 measures of hydrochloric acid, 1 of nitric acid, and 1
of water. The perchloride forms double salts with the chlorides of ammo-
nium, potassium, and sodium.

Protosulphide of Tin (SnS) may be formed by heating tin with sulphur.
A hydrated protosulphide of tin is precipitated from the salts of the prot-
oxide, by sulphuretted hydrogen ; it is of a brownish-black color, and
loses water when heated. Sulphide of tin is a brittle black compound,
soluble in hydrochloric acid with the evolution of sulphuretted hydrogen.

Sesquisulphide op Tin (Sn^Sa) is obtained by heating the protosulphide
with one-third its weight of sulphur : it is of a yellowish-gray color, metallic
lustre, and when digested in hydrochloric acid gives out sulphuretted hydro-
gen, and leaves a yellow residue of bisulphide.

Bisulphide of Tin (SnSJ is obtained as follows ; Take 12 oz. of tin

414 ALLOYS OF TIN.

and amalgamate it with 6 oz. of mercury ; reduce it to powder, and mix it
with 7 oz. of sublimed sulphur and 6 oz. of sal-ammoniac, and put the
■whole into a glass matrass placed on a sand-bath. Apply a gentle heat till
the white fumes abate, then raise the heat to redness, and keep it so for a
due time. On cooling and breaking the matrass, the bisulphide of tin is
found at the bottom. The use of the mercury is to facilitate the fusion of
the tin and its combination with the sulphur, while the sal-ammoniac pre-
vents such increase of temperature as would reduce the tin to the state of
protosulphide. A hydrated bisulphide of tin is formed by decomposing a
solution of perchloride of tin by sulphuretted hydrogen. The precipitate
becomes a dingy yellow when dried, and has a vitreous fracture.

The extraordinary golden lustre of the bisulphide of tin, and its flaky
texture, rendered it an object of great interest to the alchemist : it was
termed aurum musivum, and mosaic gold. When well made, it is in soft
golden flakes, friable and adhering to the fingers; sp. gr. 4-4 to 4*6. It is
insoluble in acids, except in nitrohydrochloric acid ; it is soluble in caustic
potassa, but not without partial decomposition. It dissolves in sulphide of
sodium, and the concentrated solution yields crystals of a hydrated double
sulphide, the formula of which is 2NaS+SnS2H-12HO. It is used for
ornamental work, under the name of hronze-powder^ especially by the manu-
facturers of paper-hangings: it is chiefly imported from Holland and Germany.

Tin pyrites is a rare mineral composed of the disulphides of copper and
iron with bisulphide of tin, =2(Fe2,S)SnS,+ 2(Cu„S)SnS2.

Sulphates of Tin. — When excess of the tin is boiled in sulphuric acid, a
solution is obtained which deposits white acicular crystals of protosulphate
of tin. Protosulphate of tin is also precipitated by pouring sulphuric acid
into protochloride of tin. When tin is boiled in excess of sulphuric acid, a
persulphate is formed.

Alloys. — Tin-plate is a most useful alloy of tin and iron, in which iron
plate is superficially combined with tin, and to the surface of which a quan-
tity of tin further adheres, without being in combination. It is made by
dipping cleansed iron plates into a bath of melted tin. An objection to
such combinations is, that in consequence of the electrical relations of the
metals, the iron, if anywhere exposed, has an increased tendency to oxida-
tion : for although the surface of the tin itself is sufficiently durable, no
sooner is any portion so abraded as to denude the iron, than a spot of rust
appears and rapidly extends : hence the superiority of iron plate covered
by zinc instead of tin, zinc being electro-positive, whereas tin is electro-nega-
tive in regard to iron, under the influence of common oxidizing agents.

Moire metallique is tin plate which has been superficially acted on by an
acid, so as to display, by reflected light, the crystalline texture of the tin :
the tin plate being best suited for the purpose is that which has rather a
thick coating of pure tin. It should first be well cleansed by washing its
surface with a little caustic potassa, then in water, and drying it. The acid
employed is always some modification of the nitrohydrochloric, more or less
diluted ; a mixture of 8 parts of water, 2 of nitric, and three of hydrochloric
acid, generally answers well. The plate should be slightly heated, and then
quickly sponged over with the acid, so as to bring out the moire ; it should
then be immediately dipped into water containing a little potassa dissolved
in It, well washed, and perfectly dried. If the acid has blackened or oxidized
the surface, a weak solution of caustic potassa will generally clean it. The
crystals on the unprepared tin .plate are usuallv large and indistinct, so that
It IS often modified expressly for the purpose, by heating it up to the point
of the fusion of the tin, powdering it over with sal-ammoniac to remove the
oxide, and then plunging it into cold water ; in this way the crystals are

TESTS FOR THE SALTS OP TIN. CADMIUM. 415

generally small. By sprinkling the surface of the heated plate with water,
or by only partially fusing the tin by holding the plate over the flame of a
spirit-lamp, or running a blowpipe flame over it, various modifications of
the crystalline surface may be obtained, or different devices sketched as it
were upon it. The plates are generally finished by a coating of transparent
or colored varnish.

The tinning of pins is effected by boiling them for a few minutes in a
solution of 1 part of bitartrate of potassa, 2 of alum, and 2 of common salt,
in 10 or 12 of water, to which some tin filings, or finely-granulated tin are
added ; they soon become coated with a film of tin, and are then taken out,
cleaned and dried. The pins are made of brass wire, and require to be per-
fectly clean before they are put into the tinning liquor. Tin medals, or casts
in tin, are bronzed by being first well cleaned, wiped, and washed over with
a solution of 1 part of protosulphate of iron, and 1 of sulphate of copper,
in 20 of water : this gives a gray tint to the surface ; they are then brushed
over with a solution of 4 parts of verdigris in 11 of distilled vinegar; left
for an hour to dry ; and polished with a soft brush-and colcothar.

Tests for the Salts of Tin. — The protosalts are colorless and acid ; they
are generally represented by protochloride : 1. Sulphuretted hydrogen, 2i\\di
hydrosulphate of ammonia, give a deep brown precipitate of protosulphide
(SnS). This is dissolved by an excess of the hydrosulphate, and is con-
verted into bisulphide (SnSg). Acids throw it down yellow from this solu-
tion. 2. Potassa gives a white precipitate (hydrated oxide), soluble in an
excess of the alkali, and in hydrochlorate of ammonia. 3. Ammonia, and
alkaline carbonates and bicarbonates produce, in diluted solutions, white pre-
cipitates, insoluble in an excess of the reagents as well as in hydrochlorate
of ammonia. 4. Corrosive sublimate gives a white precipitate, becoming
gray or black when heated, provided the salt of tin is in excess. This is
owing to the separation of metallic mercury. 5. Chloride of gold gives,
with a diluted solution, a red-brown color, which becomes of a deep purple
red when heated. 6. When heated with a salt of copper, the salt is reduced
to white dichloride, which is precipitated on the addition of water. A piece
of granulated zinc, placed in the diluted liquid acidified, separates tin in crys-
tals. The jyer5a/^5 of tin (perchloride) : 1. Sulphuretted hydrogen 2.w.^ hydro-
sulphate of ammonia give a dingy yellow precipitate of bisulphide of tin,
which is soluble in an excess of the hydrosulphate. 2. Potassa gives a white
precipitate soluble in an excess of the alkali, but insoluble in hydrochlorate
of ammonia. 3. Ammonia, and all alkaline carbonates give a white pre-
cipitate, insoluble in an excess and in the hydrochlorate of ammonia. 4 and
5. Corrosive sublimate and chloride of gold produce no change in the solution.
In a mixture of proto and persalts, chloride of gold, in small quantity, gives
a deep ruby-red color, or precipitate.

Cadmium (Cd=56).

This metal was discovered in 1811 by Stromeyer ; he called it Cadmium^
from xaSjufto, a term formerly applied both to calamine and to the substance
which sublimes from the furnace during the manufacture of brass. It is con-
tained in certain ores of zinc, and being more volatile than zinc, passes over
with the first portions of distilled metal, from which it may be separated by
dissolving it in dilute sulphuric acid, and passing sulphuretted hydrogen
through the solution : the sulphide of cadmium thus precipitated, is then
dissolved in hydrochloric acid, and precipitated by carbonate of ammonia.
This precipitate, after having been washed and dried, is mixed with char-
coal, and reduced in an earthen retort ; the cadmium passes over at a dull
red heat.

416 CADMIUM.

Cadmium, in its physical properties, much resembles tin, but it is rather
harder and more tenacious : it crackles when bent. Its sp. gr. is from 8-60
to 8-69. It fuses at about the temperature required by tin (442°), and distils
over a heat somewhat below redness, condensing into metallic globules : its
vapor is inodorous. Air scarcely acts upon it except when heated, when it
forms an orange-colored oxide, not volatile, and easily reducible. Owing to the
production of this fixed oxide, the metal cannot be volatilized except in
close vessels or tubes of narrow bore. A portion is always converted into
yellow oxide during sublimation.

Oxide of Cadmium (CdO). — Cadmium slowly dissolves in diluted sulphu-
ric or hydrochloric acid, with the evolution of hydrogen. The oxide is best
obtained by dissolving the metal in dilute nitric acid, and precipitating it in
the state of carbonate, which is then washed, dried and ignited. It is of a
reddish-brown or orange color, neither volatile nor fusible ; but when mixed
with carbonaceous matter it appears to be volatile, in consequence of its easy
reduction, and the oxidation of the separated cadmium. When thrown down
from its solutions by alkalies, it forms s,^\\\iQ hydrate, which absorbs carbonic
acid from the atmosphere, and is soluble in excess of ammonia, but insoluble
in potassa and soda.

Nitrate of Cadmium (CdO,N054HO) forms radiated acicular crystals,
which are deliquescent, and soluble in alcohol.

Chloride of Cadmium (CdCl) is formed by dissolving the hydrated oxide
in hydrochloric acid : on evaporation, small prismatic crystals are obtained,
very soluble in water ; they readily fuse, and, losing water, concrete into a
lamellar crystalline mass of anhydrous chloride, which, at a very high tem-
perature, is volatile, and condenses in the form of a nacreous sublimate. It
forms double salts with the alkaline chlorides.

Bromide of Cadmium (CdBr). — This may be procured by digesting in a
tubulated retort connected with a receiver, 2 parts of cadmium in fine shav-
ings, 1 part of bromine, and 10 of water. When the reaction has ceased,
and the liquid is colorless, it may be filtered, and concentrated in a porcelain
vessel. White, silky-looking prismatic crystals are deposited ; they are
readily dissolved by water, alcohol, and ether.

Iodide of Cadmium (Cdl). — The iodide may be procured directly by a
process similar to that above described for the preparation of the bromide.
The proportions are, 2 parts of cadmium in fine shavings, 4 parts of iodine,
and 10 parts of water. The operation is continued until the liquor is color-
less. It is then evaporated, and the iodide is deposited on cooling, in wiiite
scaly crystals of a nacreous appearance. It is soluble in water, alcohol, and
ether. This salt is remarkable for its fixedness, whether solid or in solution.
With the bromide, it is largely used in photography. Collodion, prepared
with iodide or bromide of cadmium, retains its properties unchanged for a
long period.

Sulphide of Cadmium (CdS) is obtained in the form of a bright yellow
powder, insoluble in ammonia and in the fixed alkalies, by precipitating the
solutions of the metal with sulphuretted hydrogen, or an alkaline sulphide.
It dissolves, with the evolution of sulphuretted hydrogen, in hydrochloric
acid, and is not volatile at a white heat. It furnishes a yellow pigment, which
mixes well with other colors, and closely resembles sulphide of arsenic.

Sulphate of Cadmium (CdO,S03,4HO) yields transaprent prismatic
colorless crystals, very soluble in water, and forming a double salt with sul-
phate of potassa.

Carbonate of Cadmium (CdOjCOJ is a white anhydrous powder, which
loses its acid at a red heat.

MANUFACTURE OF COPPER. 41T

Tests for the Salts of Cadmium. — 1. Sulphuretted hydrogen gives a
bright yellow, passing to an orange-yellow precipitate, even in acid solutions.
This precipitate is insoluble in potassa and ammonia, but is dissolved by
strong hydrochloric acid. By these properties, the sulphide of cadmium is
easily distinguished from that of arsenic. 2. Hydrosulphate of ammonia
gives a yellow sulphide, insoluble in an excess of the reagent. 3. Potassa
throws down a white oxide, insoluble in an excess of the alkali, and in hydro-
chlorate of ammonia. 4. Ammonia, a white oxide, soluble in excess, not
precipitated by hydrochlorate of ammonia, but thrown down as yellow sul-
phide by sulphuretted hydrogen. 5. Carbonate of ammonia and other
alkaline carbonates, a white precipitate, insoluble in excess. The carbonate
of zinc is soluble in the precipitant, so that by this test zinc and cadmium
may be distinguished and separated from each other. 6. Ferrocyunide of
potassium, gives a white precipitate, insoluble in hydrochloric acid ; and the
ferricyanide a brownish-yellow precipitate, soluble in a large excess of hydro-
chloric acid. Magnesium and zinc precipitate cadmium in a metallic state
from its solutions.

CHAPTER XXXII.

COPPER AND LEAD.

Copper (Co =32).

Copper, Cuprum, or Venus, of the alchemists (9), was known in the early
ages of the world, and was the principal ingredient in the manufacture of
domestic utensils, and instruments of war, previous to the discovery of malle-
able iron. The word copper is derived from Cyprus, the island where it was
first wrought by the Greeks. It is found native, and in various states of
combination. The sulphides are its most abundant ores, and from them,
commercial demands are almost exclusively supplied.

Manufacture of Copper. — The ore, having been picked and broken, is
heated in a reverberatory furnace, by which arsenic and sulphur are in great
part driven off. It is then transferred to a smaller reverberatory, where it
is fused, a large portion of the sulphide of iron having been converted into
oxide, which, by the addition of silicious sand, forms a vitreous slag. When
the iron is thus separated, the sulphur begins to burn out of the sulphide of
copper, and the copper becoming oxidized, is reduced by the carbonaceous
matter. The impure metal is then granulated by letting it run into water:
it is afterwards remelted and granulated two or three times successively, in
order further to separate impurities, which are chiefly sulphur, iron, and
arsenic ; and it is ultimately cast into oblong pieces called pigs, which are
broken up, roasted, ai>d melted with a portion of charcoal in the refining-
furnace. Malleability is here conferred upon the copper, and its texture
improved, by stirring the metal with a pole of green wood : assays are occa-
sionally taken out, and the metal, originally crystalline and granular when
cold, now becomes fine and close, so as to assume a silky hue when the
assays are half cut through and broken. The metal is then cast into cakes.
The whole process of refining copper, and toughening it bj poling, requires
much care ; and if it be over-poled, the metal is even rendered more brittle
than in its original state. The effect of poling has not been satisfactorily
explained : it may consist in the separation of a small portion of oxide of
2Y

418 IMPURITIES IN COPPER.

copper ; and the effect of over-poling may possibly depend npon the combi-
nation of the copper with a portion of carbon. Copper for brass-making is
granulated by pouring the metal through a perforated ladle into water ;
when this is vvarm, the copper assumes a rounded form, and is called bean-
shot ; but if a constant supply of cold water is kept up, it becomes ragged,
and is called feathered shot. Another form into which copper is cast, is in
pieces of the length of six inches, and weighing about eight ounces each :
the copper is dropped from the moulds, immediately on its becoming solid,
into a cistern of cold water, and thus, by a slight oxidation of the metal, the
sticks acquire a rich red color on the surface. This is called Japan copper.

Copper may be obtained by the voltaic decomposition of a solution of the
sulphate ; or by dissolving the copper of commerce in nitric acid, with the
addition of a little sulphuric acid ; the solution is diluted, and a plate of iron
is immersed, upon which the copper is precipitated; after having been pre-
vipusly washed in dilute sulphuric acid, to separate a little adhering iron, it
may be fused into a button.

The usual impurities in ordinary copper are traces of arsenic, antimony,
tin, lead, iron, oxide of copper, and carbon. From recent researches it
appears that all English " refined" copper, whether in the state of foil or the
finest wire, contains a notable proportion of arsenic. This impurity does not
affect the ductility or malleability of copper to the extent alleged by some
chemical writers ; but, according to Dr. Mathiessen's experiments, it
diminishes to a considerable extent the conducting power of the metal in
reference to electricity, so that such interference might almost be made a test
of the presence of this impurity. Copper free from arsenic cannot be
obtained, except with the greatest difficulty. The presence of arsenic in
small quantity is easily overlooked, and thus samples which contain it are
frequently sold as pure. The Burra Burra copper, as well as about forty
samples of copper, British and foreign, which we have examined, contained
arsenic in variable proportion. The arsenic is associated in the ore with
the sulphides of iron and copper, and- cannot be expelled from the metal
by heat, or in the ordinary process of refining. Some coppers from
America, obtained from native carbonates, have been found free from arsenic.
Dr. Percy {Metallvrgy, Yol. I., p. 381) takes exception to the statement
here made respecting the presence of arsenic in all the copper used in com-
merce, the arts, and chemistry, yet our experience since the publication of
the former edition of this work has only tended to confirm its correctness.
Having procured, by Dr. Percy's recommendation, some of what he describes
as " best selected copper," and from sources recommended by him, we have
tried experiments on this, and found as much arsenic in it as in ordinary
copper. Dr. Percy does not state that he has ever found a sample without
arsenic, but an inference might be drawn from his remarks which would lead
to the use of arsenical copper for toxicological purposes and thus give rise
to serious mistakes. Non-arsenical copper may be procured of special dealers
at the cost of about one guinea a pound. It is deposited by a voltaic current
from a solution of the pure sulphate, and afterwards undergoes certain re-
fining processes. It is to be obtained in the form of a fine powder or foil.
Neither the refined nor the "best selected" can be trusted as free from arsenic.
We have, under Oxide op Copper (p. 420), given a process for obtaining
this metal pure ; and under Subchloride of Copper (p. 422), we have de-
scribed a method for the detection of arsenic in copper. Native copper
occurs in a variety of forms; massive, dendritic, granular, and crystallized
in cubes or octahedra. It is found in Cornwall, Siberia, Saxony, Hanover,
Sweden, America, Cuba, and Australia. The copper mines of Great Britain

OXIDES OF COPPER. 419

and Ireland produced, in 1865, 198,298 tons of copper ore, yielding 11,888
tons of metallic copper.

Properties. — Copper is the only metal which has a red color : it has much
lustre, and is very malleable, ductile, and tenacious: it exhales a peculiar smell
when warmed or rubbed. It melts at a temperature intermediate between
the fusing-points of silver and gold, = 1996^ Fahr., and when in fusion
absorbs small quantities of oxygen, which again escape when the metal
solidifies, occasioning a spirting out of portions of the liquid copper. At a
very high temperature, copper emits fumes which condense upon cold surfaces
into minute globules of protoxide with a metallic nucleus. Its specific
gravity varies from 8t88 to 8958; the former being the least density of
cast copper, the latter the greatest of rolled or hammered copper. The sp.
gr. of some samples of copper, containing a little of the protoxide, does not
exceed 8-5, and such copper is of inferior ductility. When copper is in a
state of extreme division, it burns like tinder ; under a flame urged by oxygen
gas, it burns with a green light. Exposed to damp air, copper becomes
covered with a thin greenish crust of hydrated oxide and carbonate. If
heated and plunged into water, a quantity of reddish scales separate, con-
sisting of an imperfect oxide. The same scales fly off, during cooling, from
a plate of the metal which has been heated red-hot. Copper does not
decompose water at a red heat. It deoxidizes nitric acid (sp. gr. 1*5)
rapidly in the cold. It has no action on sulphuric acid, except at a boiling
temperature, when it deoxidizes this acid, and sets free sulphurous acid.
Hydrochloric acid exerts no action on it in the cold, unless the metal is at
the same time exposed to air ; but if heated, chloride of copper is formed,
and hydrogen escapes. Hydrogen, however, is only slowly eliminated, even
under these circumstances, and it is commonly combined with arsenic or
antimony.

Copper and Oxygen. — There are two oxides of copper, a suboxide or
dioxide, Cu^O, and a protoxide, CuO : the latter is the basis of the staple
and common salts of copper. The dioxide combines directly with only a few
of the acids, and is in most cases resolved by them into metallic copper and
the oxide: (CuaO = Cu + CuO).

Suboxide of Copper; Dioxide of Copper (Cu^O). — This oxide maybe
formed by adding to an aqueous solution of equal weights of sulphate of
copper and sugar, a sufficiency of soda to redissolve the first precipitate, and"
then boiling the resulting blue liquor: the suboxide falls as a red powder,
which, when washed and dried, is permanent in the air. By boiling a
solution of acetate of copper with a sufficiency of grape-sugar, it is readily
obtained without the addition of caustic alkali. It is yellow or orange-
colored in the hydrated state, as it is at first precipitated ; but it becomes
anhydrous and of a deep red color, by continued boiling. This oxide
occurs native as Ruby copper, crystallized in octahedra. When dioxide of
copper is heated in the air, it passes into oxide. The dilute acids mostly
decompose it and separate metallic copper. It dissolves in concentrated
hydrochloric acid ; it also dissolves in ammonia, forming a colorless solution
when kept from air; but it is not soluble in solutions of potassa or of soda.
Its salts are frequently formed by the action of deoxidizing agents on the
protosalts.

Copper vessels, such as tea-urns, and medals, are often superficially coated
with oxide, or bronzed; it gives them an agreeable appearance, and prevents
tarnish. For this purpose two processes are resorted to. 1. The copper
surface is cleaned, and then brushed over with peroxide of iron (generally
colcothar) made into a paste with water, or with a very dilute solution of
acetate of copper ; heat is then cautiously applied in a proper furnace or

.480 OXIDES OF COPPER.

muflQe, till it is found, on brushing ofif the oxide, that the surface beneath has
acquired its proper hue. 2. Two parts of verdigris and one of sal-ammoniac
are dissolved in vinegar : the solution is boiled in a pipkin, skimmed, and
diluted with water until it only tastes slightly of copper and ceases to dej^osit
a white precipitate : it is then poured into another pipkin or copper pan,
and rapidly brought to boil, and the medal, previously rendered perfectly
clean, is dipped into the boiling solution, which may be most conveniently
done by placing it in a small perforated copper ladle. The surface of the
medal becomes at first black or dark blue, and, in about five minutes, acquires
the desired brown tint ; it must then be instantly withdrawn and washed in
a stream of water, and lastly, carefully wiped and dried. The medal is
generally perfected by afterwards giving it one gentle pinch between the dies.
When there are many medals, each must be bronzed separately ; they must
not be allowed to touch each other, and care should be taken to rest them
upon as few points of contact as possible. The bronzing-liquid must not be
suffered to concentrate by evaporation, but must be diluted if necessary, so as
to keep it in a proper state, and especially to avoid all appearance of a white
precipitation in it. A weak solution of chloride of gold forms a good bronz-
ing liquid for copper.

Oxide of Copper. Protoxide (CuO). — When sheet copper is exposed in
the* air to a red heat, black scales form upon it, which are thrown off on
plunging it into water, or which fly off as it cools, in consequence of the
comparatively rapid contraction of the metal. Wlien these scales are re-
duced to powder, and stirred in contact with air at a red heat, they yield the
oxide. When nitrate of copper is exposed to heat gradually raised to red-
ness, it fuses and is decomposed, and ultimately this oxide remains as a
Telvety black powder. The oxide may be at once prepared in large quantity,
by dissolving copper in one part of nitric acid and two parts of water,
evaporating to dryness, and heating the residue to redness in a platinum
dish. The arsenic contained in "refined" copper is converted into arsenic
6cid. It may be separated from the black oxide by boiling it in distilled
water, until nitrate of silver no longer gives a red color with the residue of
the evaporated water. When the purified oxide is dissolved in sulphuric
acid, and the metal is precipitated by voltaic electricity, it is free from arsenic,
and may be regarded as pure copper. Thus procured, it is brittle, and admits
of lamination with difficulty. It requires frequent annealing to reduce it only
to a moderately thin sheet.

Oxide of copper is black; its specific gravity is 6-4. Before the blow-
pipe, it fuses when intensely heated in the point of the flame, upon charcoal :
in the interior of the flame it affords a globule of metal. Heated alone, it
is not decomposed at the highest temperature, but it is easily and rapidly
decomposed at a dull red heat, or even below it, by hydrogen or carbon. It
is also decomposed when heated in contact with organic substances, con-
verting their hydrogen into water, and their carbon into carbonic acid ; hence
• its use in their analysis : it is hygrometric, and if weighed whilst hot, aug-
ments in weight^ after cooling, in consequence of the absorption of aerial
moisture. It is insoluble in water, but it dissolves in the greater number of
the acids, and is the basis of all the common salts of copper. When alkalies
are dropped into its solutions, they throw it down as a bulky blue hydrate,
which, however, is not permanent at a boiling heat, but becomes black and
anhydrous whe;i boiled in an excess of the alkaline liquid. This oxide of
copper is not soluble in the liquid fixed alkalies, except in the presence of
sugar, tartrate of potassa, albumen, caseine, lactose, glycerine, and some
other substances. With grape-sugar and an excess of the alkaline liquid,
the hydrated oxide of copper forms a rich sapphire-blue solution, which

CHLORIDES OF COPPER. 421

reduces the protoxide to suboxide slowly in the cold but rapidly when
heated. This constitutes Trommer''s test for sn^rar. Other reducing agents
operate in a similar manner. Thus, if arsenious acid is present, potassa
forms with the oxide, a blue solution which, when boiled, yields, like su^ar,
a hydrated or anhydrous suboxide of copper. When carbonate of potassa
or of soda is fused with it, it expels carbonic acid, and combines to form a
blue or green compound. Its combination with ammonia will presently be
noticed. It communicates a green, and sometimes a blue tint to vitreous
compounds; and is the basis of certain colors used by the aticients, which
had been supposed to contain cobalt. The dioxide gives a beautiful ruby
red color to glass.

Hydrated Oxide of Copper (CuO,HO), as thrown down from a solution of
sulphate of copper by dilute potassa or soda, is at first blue, but soon changes
to green, especially if it be dried : it sustains, when dry, a temperature of
212° without decomposition, but a little above that it becomes discolored.
When boiled in the liquor from which it has been precipitated, or when a
solution of copper is added to a boiling solution of soda or potassa, it
becomes anhydrous and nearly black.

Nitrate op Copper (CuO,NOg,3HO). — Nitric acid diluted with 3 parts
of water, rapidly oxidizes copper, evolving nitric oxide, and ultimately form-
ing a bright-blue solution, which affords deliquescent prismatic crystals, of
a fine blue color, very soluble in water and in alcohol. They liquefy at a
temperature below 212° ; at a higher temperature they lose water and acid,
becoming a subnitrate, and are entirely decomposed at a red-heat, leaving
protoxide of copper. At low temperatures this salt crystallizes in rhora-
boidal plates, which contain 6 atoms of water, but these effloresce into the
terhydrate in vacuo over oil of vitriol. Potassa forms, in the solution of
this nitrate, a bulky blue precipitate of hydrated oxide of copper, which, as
already observed, when boiled in potassa or soda, becomes black from the
loss of its combined water. When nitrate of copper is coarsely powdered,
sprinkled with a little water, and quickly rolled up in a sheet of pure tinfoil,
there is great heat produced, nitrous gas is rapidly evolved, and the metal
often takes fire. Ammonia added to a solution of nitrate of copper, occa-
sions a precipitate of the hydrated oxide; but if added in excess, the pre-
cipitate is redissolved, and an ammonia-nitrate is produced.

Ammonia and Oxide of Copper. — When copper filings are digested in
aqueous ammonia exposed to air, the solution soon becomes blue : if air be
then excluded, it gradually loses color, but again acquires a blue color on
the contact of air: in the blue liquor the copper exists as oxide ; in the
colorless liquor as dioxide. If a tall glass be filled with liquid ammonia and
a few drops of solution of suboxide of copper (subchloride) are added, the
surface becomes blue, but it remains colorless below. The solution of the
oxide of copper in ammonia is obtained by exposing copper filings in solu-
tion of ammonia to air, or by dissolving the hydrated oxide in ammonia : it
is of a splendid deep-blue color.

Copper and Chlorine. — Gaseous chlorine acts upon finely-divided copper
with great energy, producing the phenomena of combustion ; two chlorides
are the result of this action ; the one a comparatively fixed fusible substance,
which is the subchloride : the other a yellow substance, which is a chloride.

Subchloride of Copper. — Bichloride (Cu^CI) may be obtained by ex-
posing copper filings to the action of chlorine, not in excess : or by evapo-
rating the solution of dioxide of copper in hydrochloric acid, and heating
the residue in a vessel with a very small orifice; or by heating the proto-
chloride in the same way. It is also precipitated, on adding protochloride
of tin no a strong solution of the chloride. It is insoluble in water, but

422 SULPHIDES OF COPPER.

soluble in ammonia — a solution employed in eudiometry. It is also dissolved
by hydrochloric acid, from which potassa throws down the hydrated dioxide :
when water is added to its hydrochloric solution, it is thrown down in the
form of a white granular or crystalline hydrate, the crystals having sometimes
a tetrahedral form : its color varies, being brown when fused, but if slowly
cooled, it is yellow, translucent, and crystalline ; when in fine division it is
nearly white : it must be preserved out of contact of air. If moistened and
exposed to air, it acquires a green color, and becomes converted into a
hydrated oxy chloride, which has been termed suhmuriate of copper, or Bruns-
wick green ; the same compound may be formed by adding hydrated oxide of
copper to a solution of the chloride : or by exposing to the atmosphere slips
of copper partially immersed in hydrochloric acid. In this case, the follow-
ing changes first take place : HCl + 2Cu-f-0(air) = Cu2Cl-j-nO. A portion
of the metal becomes oxidized, and the oxychloride results. A mixture of
this kind was employed by Gay-Lussac in the analysis of the atmosphere,
and it serves as a process for obtaining nitrogen (p. 153). After 24 hours
the acid liquid in which the copper has been partially immersed, acquires a
dark greenish-brown color from the production of dichloride. In this state,
if the liquid is submitted to distillation at a moderate temperature, any
arsenic present in the copper will be distilled over with hydrochloric acid, as
chloride of arsenic {see Arsenic). By evaporating this subchloride to dry-
ness, the whole of the arsenic may be driven off ; and by further exposure in
contact with pure hydrochloric acid, pure oxychloride of copper may be
obtained. As these precautions are not taken in practice, the. oxychloride,
as it is generally prepared, contains arsenic.

Chloride op Copper (CuCl) may be formed by heating copper filings in
excess of chlorine, or by dissolving oxide of copper in hydrochloric acid, and
evaporating to dryness by a heat below 400°. Chloride of copper is brown
when anhydrofs, but becomes blue by exposure to air; it is soluble in water
and alcohol, and very difficultly crystallizable. The prismatic crystals are
CuCl, 2110. The concentrated aqueous solution is green ; when diluted,
blue; but the solution again becomes green when heated to 212°. Exposed
to a red heat in a tube with a small orifice, chlorine is expelled, and it
becomes a subchloride. When acted upon by potassa not added in excess,
and only so as partially to decompose it, a green oxychloride is thrown
down.

Oxychloride of Copper, 3(CuO)CuC],4HO, is found native m Peru and
Chili, sometimes in the form of green sand, and sometimes massive and crys-
tallized. The green sand was first found in the desert of Atacama, sepa-
rating Pern from Chili. Chloride of copper has also been found upon some of
the lavas of Vesuvius.

Subiodide of Copper ; Diniodide of Copper (CuJ).— When iodide of
potassium is added to a solution of the protosulphates of copper and iron,
both in crystals, in the proportion of 1 to 2^, the protoxide of iron takes the
oxygen of the oxide of copper, and the iodine the metallic copper, with
which it forms a white precipitate of the insoluble subiodide ; it may be
dried in close vessels. In the manufacture of iodine the mixed sulphates are
sometimes employed for precipitating the iodine from the iodides in kelp
(p. 205). When iodide of potassium is added to a salt of oxide of copper,
iodine is set free, and a brown subiodide falls.

Copper and Sulphur ; Disulphide of Copper (Cu^S) may be formed by
heating a mixture of 8 parts of copper fillings and 3 of sulphur : as soon as
the latter melts the copper becomes red-hot, undergoes combustion, and a
black brittle compound is formed. It is soluble in hydrochloric acid with
the evolution of sulphuretted hydrogen. Vitreous copper is a native ^isul-

SULPHATES OF COPPER. 423

phide ; it occurs crystallized and massive in Cornwall and Yorkshire. It has
a gray color, a metallic lustre, and a sp. gr. of about ST. Sulphide (CuS)
occurs native, associated with the disulphide. It is thrown down from solu-
tions of salts of copper by sulphuretted hydrogen, as a dark-brown hydrate,
insoluble in alkalies and diluted acids. Ferrosulphides ; Copper pyrites, or
yellow copper ore is the ore from which commercial copper is chiefly derived.
It is a compound of sulphur, copper, and iron, the proportions of the sul-
phides being subject to variation, but commonly represented by CugSjFCaSa,

Sulphate OF Copper; Roman Vitriol; Blue Vitriol (CuO,S03). — This
salt is formed by boiling copper in sulphuric acid, a process which furnishes
an abundance of sulphurous acid (Cu4-2S03=CuO,S03-f SOg). It is also
made by exposing roasted sulphide of copper to air and moisture ; thus ob-
tained, it is impure, generally containing iron and arsenic and often zinc,
and it is obtained in large quantities, and nearly pure, in certain processes,
afterwards to be described for refining gold and silver. Sulphate of copper
forms rhomboidal crystals containing 5 atoms of water, (CuO.SOgjSHO) :
sp. gr. 2-27. The crystals are sometimes very large, of a beautiful sapphire-
blue color, and slightly efflorescent in a dry atmosphere ; they are soluble in
4 parts of cold water. This salt has a peculiarly nauseous metallic taste.
When heated to 212°, it loses 4 atoms of water of crystallization, and crum-
bles down into a pale powder; heated to 400° it becomes white and anhy-
drous ; in this state it slowly reabsorbs water from the air, and regains its
blue color ; or if sprinkled with water heat is evolved, and the salt crumbles
down into a blue hydrate. By a continued high red or white heat, sulphuric
acid, and some sulphurous acid and oxygen, are evolved, and black oxide of
copper remains. Anhydrous sulphate of copper, by reason of its great affin-
ity for water, removes it from liquids, such as alcohol, ether, chloroform, and
pyroxylic spirit. It is occasionally used in dehydrating these liquids by
distillation. The powder changes in color from white to blue. When the
blue crystals of the salt are digested in concentrated sulphuric acid, they are
dehydrated and become white. This salt (the Vitriol, or Salt of Venus, of
the alchemists) is much used as a source of several blue and green colors.
It is employed by dyers and calico-printers, and is an ingredient in some
kinds of writing-ink. It has been used to prevent smut in corn, by steeping
the grain in a dilute solution of the salt. It appears to operate by coagulat-
ing the albumen of the seed. It is also employed for the same reason to
prevent dry rot by steeping timber or planks in its solution; and it is a power-
ful preservative of animal substances. The commercial sulphate sometimes
contains sulphate of iron as impurity. In order to detect this, ammonia may
be added to the diluted solution of sulphate in sufficient quantity to redis-
solve the whole of the oxide of copper which is at first precipitated. As
oxide of iron is not permanently dissolved by ammonia, this after some hours
will be deposited as hydrated peroxide at the bottom of the tube. There is,
however, a more serious impurity — namely, the presence of arsenic — not only
in the commercial but the officinal sulphate. This may be detected by distil-
ling the powdered crystals with strong hydrochloric acid. Chloride of arsenic
passes over into the receiver {see Arsenic). Several basic sulphates of
copper have been described.

Sulphates of Ammonia and Copper. — 1. Ammonio-sulphate of copper.
Anhydrous sulphate of copper rapidly absorbs gaseous ammonia, heats, and
forms a bulky blue powder soluble in water,— 5XH3,-f2(CuOS03). 2. Gupro-
sulphate of ammonia. When a solution of sulphate of copper is supersatu-
rated by ammonia so as to redissolve the precipitate at first formed, and
crystallized by evaporation, dark blue transparent crystals are obtained,
soluble in 1-5 of cold water, but insoluble in alcohol, = CuO,S03-f2NHgHO.

424 ALLOTS OF COPPER.

The crystals, when exposed to air, lose ammonia, becoming at first opaque
and pale blue, and then crumble into a green powder, which is a mixture of
sulphate of ammonia and basic sulphate of copper. When the aqueous solu-
tion of this salt is largely diluted, it deposits basip sulphate of copper. 3.
Sulphate of ammonia and copper. (NH,0,SO, + CuO,S03 + 6HO). This
salt crystallizes out of the mixed solution of sulphate of ammonia with sul-
phate of copper ; it effloresces in dry air. The solution of the ammonio-
sulphate of copper is used as a test for arsenic.

Carbonates OF Copper. — When hot solutions of copper are precipitated
by the carbonated fixed alkalies, carbonic acid is evolved, and a bulky green
hydrated dicarlonate of copper falls, = 2(CuO),C02,HO. Its tint is im-
proved by repeated washing with boiling water. It is prepared as a pigment,
under the name of mineral green, or greeii verditer. When a cold dilute
solution of sulphate of copper is decomposed by carbonate of soda, a blue
precipitate falls, which, by careful drying, retains its color, and is known
under the name Uue verditer. It differs from the green carbonate in contain-
ing more water. There is an inferior pigment, also called verditer, which is
a mixture of subsulphate of copper and chalk. Native Carbonates of Cop-
per ; Malachite (na^dxr;, 7nalloio, from its color), or the green hydrated car-
bonate,=2{CnO),CO^,IIO, is found in various forms, but never regularly
crystallized, the octahedral variety being a pseudo-crystal derived from the
decomposition of the red oxide : it occurs in great beauty in a stalactitic
form in Siberia, and in Australia; it is rarely found in Cornwall. It is of
various shades of green, and often cut into small slabs, or used as beads and
brooch-stones. The pulverulent variety has been termed chrysocolla, and
moimtain-green. The blue hydrated car6on«;e, = 3(CuO)C0.2,IIO, is found
in great perfection at Chessy, near Lyons. It occurs crystallized in rhom-
boids and imperfect octahedra ; it is also found in small globular masses.
The earthy variety is sometimes called copper-azure or mountain-blue. The
dioptase, or copper emerald, a rare mineral, hitherto found only in Siberia, is
a hydrated silicate of copper ; some of the varieties of malachite also appear
to contain a silicate of copper.

Cyanide of Copper. — Hydrocyanic acid, and cyanide of potassium, throw
dowm a white curdy precipitate in a solution of dichloride of copper, = Cu2,
Cy. It combines with other metallic cyanides, forming a class of cuprocya-
nides. When cyanide of potassium is added to sulphate of copper, a brown
precipitate, =CuCy is formed, which by giving otf cyanogen passes into a
double cyanide,=Cu2,Cy4-CuCy. When CuCy is digested in excess of
cyanide of potassium, it forms two cuprocyanides, CuCy,KCy, and CuCy,
3KCy.

Alloys of Copper. — Many of these are of great use in the arts, especially
those with zinc and tin, and with silver and gold.

Brass. — This important alloy of copper with zinc was formerly made by
mixing granulated copper with calamine and charcoal, and exposing the
mixture to a heat sufficient to reduce the calamine and melt the alloy. It is
now usually prepared by melting granulated copper with about half its weight
of zinc, but the relative proportions of the two metals vary in the different
kinds of brass ; and some contain a little lead and tin. An alloy of 54 parts
of zinc and 46 of copper is white and crystalline, but it assumes the yellow
color of brass when the zinc is increased, as well as when it is diminished.
Ordinary brass contains about 64 per cent, of copper. The new Austrian
gun metal is stated to have the following composition : Copper 55 04 : zinc
42 36 : iron 1-77 and tin 0-88 in 100 parts. Maniz^s patent sheathing metal^
which has been found an excellent substitute for copper in the sheathing of
ships, is an alloy of about 60 copper and 40 zinc : it admits of being rolled

ALLOYS OP COPPER. BRASS. BRONZE. BELL-METAL. 425

hot, whereas the common varieties of brass generally split under such circum-
stances, and are therefore rolled cold, which requires more time.

Brass is very malleable and ductile (when cold), and its color recommends
it for many purposes of the arts : it specific gravity varies from 7 9 to 8-9,
and exceeds the mean of its components. Tutenag, Tombac, Dutch gold.,
Similor, Prince RuperVs metal, Pinchbeck and Manheim gold, are alloys
containing more copper than exists in brass, and consequently made by fusing
various proportions of copper with brass. An alloy of 570 parts of copper,
69 of tin, and 48 of brass, is equal to brass in hardness, and may be worked
with the same facility ; it has been used for standard measures, as being less
liable than brass to oxidation when exposed to air. Brass containing 25
per cent, of zinc melts at about 1750^, and its fusibility is increased by a
larger proportion of zinc. The malleable alloy known as Dutch leaf gold is
a compound of 15*4 of zinc and 84 6 of copper. Its malleability is sucli that
it may be beaten into leaves of the l-50,000th of an inch in thickness. It is
frequently used as a substitute for gold leaf, but it rapidly tarnishes when
exposed to damp air. Gold paper hangings are usually prepared with this
alloy — the fine dust being laid on a yellow adhesive ground. The alloy is
immediately dissolved by nitric acid, forming blue nitrate of copper. When
platinum is added in a certain proportion to the alloy, it resists the nitric
acid test and may be mistaken for gold. {See Gold Alloys.) Speculum
metal is an alloy of copper and tin, with a little arsenic ; about 6 copper, 2
tin, 1 arsenic. The Earl of Rosse employed copper and tin only in the spec-
ulum of his large telescope ; the proportions he used were 126*4 of copper,
to 58 9 of tin (about 4 atoms of copper to one of tin).

Bronze ; Bell-metal. — These are alloys of copper and tin ; they are harder
and more fusible, but less malleable than copper. The specific gravity of
bronze exceeds the mean of its component metals, when carefully hammered
and free from air-blebs : but bronze castings are apt to be porous unless
considerable care and skill have been used in fusing and pouring the metal,
and in the construction of the mould ; and in large castings, owing to the
gradual cooling of the mass, there is often a want of uniformity in the com-
position of different parts of it ; that portion containing the least tin being
the first to solidify, while the more fusible portion to a certain extent sepa-
rates, and is sometimes projected from the mould. In large bronze castings,
SQch as statutes, porosity and bubbles require carefully to be avoided : where
they exist so as' to deface the appearance of the work, they are sometimes
filled up with substances which are only temporarily durable, or which, \h
metallic, give rise to electrical effects which time renders prejudicially evi-
dent, For this reason, the different pieces of a large statue should be fused
together, or united by bronze, and not by a more fusible solder ; and iron
bars, and leaden junctions for the support or fixing of the work, should,
upon the same principle, be avoided, as they are themselves liable, under
such circumstances, to corrosion, and this may affect the stability or safety
of the statue, independently of other influences. Of the difficulty of casting
a large and perfect bell in bronze, the Great Bell at Westminster has fur-
nished a memorable instance. When bronze is frequently renielted it gradu-
ally loses tin by oxidation, so that in such cases fresh additions of tin may
sometimes be requisite ; and it is apparently this oxidation of the tin which
tends to deteriorate the texture of remelted bronzes, and renders them more
subject to bubbles and porosity when recast, an effect which may be prevented
by the action of carbonaceous fluxes, or by the operation of poling, as in the
case of copper.

Tempering produces upon bronze an effect directly opposite to that upon
steel J and in order to reader bronze malleable, it must be heated to redness

426 TESTS FOR TflE SALTS OF COPPER.

and quenched in water. The alloy which thus acquires the greatest tenacity
is that of 8 of copper and 1 of tin, and this is consequently preferable for
medals ; the advantage of bronze over copper for these purposes being hard-
ness, and resistance to oxidation ; the former quality resists friction, and the
latter has handed down to us the works of the ancients with little deteriora-
tion, though buried for ages in damp soil, or immersed in water. The small
value of bronze, as compared with gold and silver, is also another important
consideration, as affecting the preservation of such works of art. The alloy
employed in the recent bronze coinage is composed of 95 copper, 4 tin, 1
zinc. The pound avoirdupois is coined into 48 pence, each piece weighing
145-83 grains; into 80 halfpence, each weighing 87 50 grains; into 160
farthings, each weighing 43 75 grains. Analysis made of ancient Roman
coins by M. Commaille have shown that they consist of copper nearly pure,
with small quantities of tin, lead, and silver. Cadmium and gold have been
found in some of them. In certain coins ten per cent, of tin and as much as
28 per cent, of lead have been detected. The coins of Vespasian and Mar-
cus Aurelius consisted of copper with traces of tin — and those of Titus con-
tain 2'Tl per cent, of zinc. The Roman AS was found to be composed of
copper 69'65 : of lead 2437, and of tin 5*98. We have found arsenic in
these ancient coins and in the ancient alloys of copper and zinc : used for
sepulchral brasses.

The analysis of brass is best effected by the action of nitric acid. The
solution may be tested for the presence of lead by sulphuric acid : if tin is
present it is converted into an insoluble oxide : the clear nitric solution eva-
porated to dryness leaves nitrate of copper and nitrate of zinc : this residue,
redissolved, may be decomposed by a slight excess of caustic potassa, and
boiling, by which the oxide of copper is thrown down. The oxide is col-
lected on a filter, washed, dried, and gently ignited, the clear filtrate holds
the oxide of zinc in solution : it may be neutralized by hydrochloric acid,
and precipitated by carbonate of soda ; the precipitate, after washing, dry-
ing, and ignition, is oxide of zinc.

Tinned Copper. — Vessels of copper for culinary purposes are usually
coated with tin, to prevent the food being contaminated by copper. Their
interior surface is first cleaned, then rubbed ^ver with sal-ammoniac : the
vessel is then heated, a little pitch spread over the surface, and a bit of tin
rubbed over it, which instantly unites with and covers the copper. Much
care is requisite in the manipulations of this process, and independently of
Jhe tin permanently adhering to and combining with the surface of the cop-
per, there is generally a portion in excess, which fuses off, the first time the
pan is used for frying. Lead is sometimes added to the tin used in tinning,
and sometimes a small quantity of mercury, but these are very objectionable
additions.

Tests for the Salts of Copper.— The solutions of these salts have either
a blue or green color, and an acid reaction. 1. Sulphuretted hydrogen and
hydrosulphate of ammonia give, even in acid solutions, a brownish-black
precipitate, not soluble in the precipitants, in alkalies, or diluted acids. 2.
Ammonia, when added in excess, produces a deep blue solution. 3. Ferro-
cyanide of potassium produces a deep red-brown precipitate in strong solu-
tions, but a red color in those which are very dilute. This may be regarded
as a most delicate test for copper. The blue ammoniacal solution above
mentioned under 2, when rendered feebly acid by the addition of dilute sul-
phuric acid, will give a red precipitate with the ferrocyanide. Thus two of
the most important tests may be applied to the same portion of liquid. 4.
A polished needle, or any clean surface of iron, is coated with a layer of
metallic copper of its usual red color, when immersed or suspended in the

LEAD. EXTRACTION OF LEAD. 4^t

solution slightly acidified with diluted sulphuric acid. The deposit takes
place .slowly when the solution of copper is very dilute. The needle, with
the red deposit, when washed and placed in a reduction tube with a small
quantity of solution of ammonia, imparts a blue color to the liquid by the
production and solution of the oxide. A coil of fine steel wire may be used
in place of a needle.

Before the blowpipe, black oxide of copper is not altered by the exterior
flame, but becomes red suboxide in the interior. With borax it forms a
green glass, while hot, which becomes blue-green as it cools. When strongly
heated on charcoal in the interior flame, the metal is reduced.

Analysis in cases of Poisoning. — A colored liquid containing organic
matter, and suspected to contain copper in solution, may be thus treated :
Place a portion of the liquid, acidified with dilute sulphuric acid, in a plati-
num capsule; touch the platinum through the liquid with a piece of zinc
foil; a bright layer of metallic copper,*of a red color, will be deposited on
every part of the platinum touched by the zinc. Wash out the capsule with
distilled water ; dissolve the film of deposited metal in a few drops of nitric
acid and water ; expel any excess of acid, and add ammonia,- and subse-
quently ferrocyanide of potassium (p. 426). The blue and red colors will
at once indicate the presence of copper. This is the best method of pro-
ceeding in cases of poisoning ; as the metal is first obtained and converted
into a salt, when the tests give the results described, there can be no doubt
of the presence of copper.

In order to procure a solution of the metal, the organic matter may be
dried, incinerated in platinum, and. the ash digested in 1 part of nitric acid
and 2 of water. Pickles or fruits suspected to contain copper may be
treated by the 'following process : Pass a bright needle through the sub-
stance ; if it is impregnated with copper, there will be a deposit of this
metal upon the iron. It will be proper to state in this place, that as copper
and, generally speaking, all its salts, may contain arsenic, this poison may
be found in an organic liquid, or in a cupreous medicine, as the result of im-
purity.

Lead (Pb=104).

Lead has been known from the earliest ages. The alchemists gave to it
the symbol and name of Saturn, \, which is the symbol of Jupiter or Tin
inverted. The native compounds of lead are numerous, but the most import-
ant is the sulphide known under the name of galena, from which the greater
proportion of commercial lead is obtained.

Extraction of Lead. — The reduction of galena upon the large scale is
eflfected by heating and raking the prepared ore, mixed with a little lime, in
a reverberatory furnace ; a large proportion of the sulphur is in this way
burned off, and a mixture of oxide, sulphate, and sulphide of lead obtained ;
the temperature is then so raised as to fuse this mixture, when the substances
further react upon each other, and metallic lead separates from the mass.
If it contains tin or antimony, it is further refined by fusing it in a shallow
vessel, when those metals, being more easily oxidized than lead, are removed
from the surface. If the lead contains silver in such proportion as to render
it worth separating, this is effected by dipping into the fused metal, during
cooling, a large perforated iron ladle, whereby the lead, which is the first to
separate in crystals, is removed. The granular crystals are ladled out, and
are nearly pure lead (p. 26), the silver being retained in the more fusible
portion. By a repetition of this process of desilvering the melted lead, the
silver gradually accumulates in the latter, from which it is subsequently
separated by cupellation. Six tons of lead thus treated, were desilvered by

428 ACTION OP AIR AND WATER ON LEAD.

this process in about two hours, the weight of the argentiferous alloy left in
the melting-pan being seven hundred weight. The iron ladle employed held
about one hundred weight of liquid metal. The amount of silver in the lead
was increased twentyfold, one tou of the alloy containing as much silver as
twenty tons of the original lead. In the factory at Newcastle, in which we
witnessed this operation, 60 tons of lead were desilvered weekly, producing
about 600 ounces of silver. In 1858, it was calculated that the quantity of
silver thus extracted from lead in this country was not less than 600,000
ounces per annum. This valuable process was discovered by the late Mr.
H. L. Pattinson, of Newcastle. The lead, thus deprived of its silver, is
improved in quality, and is cast into the oblong masses, or pigs, in which it
occurs in commerce. The total quantity of lead ore raised in the United
Kingdom in 1865 was 90,452 tons, from which were obtained 67,181 tons
of metallic lead and 724,856 ounces of silver.

When lead containing silver is exposed at a high heat to a current of air,
the lead is converted into protoxide, and may be run off in a fused state from
the surface; whilst the silver, which, under these circumstances, resists oxida-
tion, ultimately remains upon the cupel. This operation closely resembles
that which is conducted upon a small scale by the assayer, and will again be
adverted to in the chapter on Silver. The proportion of silver contained
in argentiferous galena varies very considerably. The average is about ten
ounces in the ton : when it amounts to 120 ounces to the ton, it is considered
very rich ; but silver may be profitably extracted when as low as from 3 to
4 ounces to the ton. The English lead-mines afford an annual produce of
from 60,000 to 70,000 tons of metal, froju the greater part of which the
silver is extracted by the process above described.

Perfectly pure lead may be obtained either by reducing pure nitrate of
lead by charcoal, at a red heat, or by heating oxalate of lead in a covered
crucible. Its color is bluish-white : it has much brilliancy, is remarkably
flexible and soft, and leaves a dark streak on paper ; when handled it exhales
a peculiar odor. Its specific gravity is 1 1 "4. It admits of being rolled into
thin sheets, and drawn into moderately fine wire, but its tenacity is so low
as to render the latter operation difficult. It melts in about 620^^, and by
the united action of heat and air is readily oxidized. In perfectly close
vessels it does not sublime at a bright red heat ; but before the oxygen blow-
pipe it boils when heated to whiteness, and is dissipated in copious fumes of
oxide. When slowly cooled it forms octahedral crystals, and contracts
during solidification; in bullets, therefore, and in castings of lead rapidly
cooled, there is generally a cavity which interferes with the rectilinear pas-
sage of the ball.

At common temperatures, and in its ordinary state, lead undergoes little
change; but when in a state of very fine division, as it is obtained by ex-
posing tartrate of lead to a red heat in close vessels, it takes fire when
brought into contact with the air; so also the finely-divided lead obtained
by the reduction of the oxide by hydrogen at a temperature insufficient for
its fusion, burns when gently heated in the air. It is generally considered
that water is not decomposed by lead, but Stolba asserts that on boiling pure
water witli a relatively large quantity of lead in foil or granulated, hydrogen
was evolved, and a strongly alkaline fluid remained in the flask. {Quar.
Jour, of Science, 1865,) In distilled water, free from air, and in close ves-
sels, a clean surface of lead remains bright ; but in open vessels it tarnishes,
and small crystalline white scales of hydrated oxide of lead are formed, a
portion of which dissolves in the water, and is again slowly precipitated in
the form of oxycarbonate. This oxycarbonate is itself very insoluble, so
that if water holding a little oxide of lead in solution be exposed to air, the

OXIDES OF LEAD. LITHARGE. 429

more soluble oxide passes into the state of the less soluble oxycarbonate ;
and after a few hours, if the water be Altered, it will be found almost abso-
lutely free from lead in solution, pure water not dissolving more than about
one four-millionth of its weight of this oxycarbonate, or about one-sixteenth
of a grain in a gallon. The action of water upon lead is much modified by
the presence of saline substances. It is increased by chlorides and nitrates,
and diminished by carbonates, sulphates, and phosphates, and especially by
carbonate of lime, which, held in solution by excess of carbonic acid, is a
frequent ingredient of spring and river water. But water highly charged
with carbonic acid may become dangerously impregnated with lead, in the
absence of any protecting salt, in consequence of its solvent power over car-
bonate of lead. In general, water which is not discolored by a current of
sulphuretted hydrogen gas, may be considered as free from lead ; but there
are very few waters which have passed through leaden pipes, or have been
retained in leaden cisterns, in which a minute analysis will not detect a trace
of the metal ; and were it not for the great convenience of lead, iron pipes
and slate cisterns would, in a sanitary point of view, be in all cases preferable.
Another cause of contamination of lead may arise from electric action, as
where iron, copper, or tin is in contact with, or soldered into lead : and in
these cases, owing to the action of alkaline bases as well as of acids upon
the lead, danger may occur when it is thrown into an electro-negative as
well as an electro-positive state. Cisterns are sometimes corroded, and their
bottoms are perforated by pieces of mortar having dropped into them, the
lime of which has caused the oxidation of the metal and a solution of the
oxide.

Oxides of Lead. — There are four definite combinations of lead and oxy-
gen, namely, suboxide or dioxide (PbgO) ; a protoxide (PbO) ; an interme-
diate oxide generally known as red oxide (PbgOJ ; and a peroxide (PbOg).
Of these, the protoxide only is salifiable.

Suboxide of Lead; Dioxide of Lead (PbgO). — When oxalate of lead h
carefully heated to about 570° in a small retort, carbonic oxide and car-
bonic acid are evolved, and this oxide remains in the form of a gray powder,
which is resolved by acids into protoxide and metallic lead.

Protoxide of Lead (PbO) is formed, 1. By raising the temperature of
melted lead to a white heat, when it burns with a brilliant flame, and forms
copious fumes of protoxide. 2. By exposing the gray powder which
gradually collects upon the surface of melted lead, to the further action of
heat and air, until it acquires an uniform yellow color. 3. By exposing
nitrate or carbonate of lead to a dull red heat out of contact of air, and
taking care to avoid fusion; 4. When a solution of acetate of lead is
dropped into a solution of ammonia, the white crystalline powder which
falls is a hydrated oxide. When this oxide is heated it has a red color, but
in its ordinary state it is lemon or orange-yellow, according to the mode in
which it has been prepared, and is known under the name of Massicot, At a
high red heat, it fuses and forms, on cooling, a lamellar vitreous mass of a
reddish-brown color : this is often obtained in scales, under the name of
Litharge {xiOo^ dpyvpov, silver stone), which, when red from the presence of
minium, was called Litharge of Gold, the paler varieties being termed Litharge
of Silver. Protoxide of lead is a salifiable base, forming neutral salts with
the acids; and, in many instances, subsalts which have an alkaline reaction ;
it absorbs carbonic acid from the atmosphere, and gradually acquires the
property of dissolving in acids with effervescence. It is soluble in potassa
and soda, forming yellow liquids, which after a time gradually deposit crystals
of anhydrous oxide of lead : it combines with baryta, strontia, and lime,
forming compounds of sparing solubility, and easily decomposed even by the

430 RED OXIDE OF LEAD. PEROXIDE OF LEAD.

weakest acids. A paste or wash containing hydrate of lime mixed with 80
to 90 per cent, of oxide of lead, is used to blacken hair, which it does in
consequence of the formation of a black sulphide arising out of the combi-
nation of the sulphur in the hair with the metal of the oxide, while the lime,
by its action on the organic matter, promotes the effect. The use of this
compound is liable to give rise to an attack of lead palsy.

When oxide of lead is fused with the earths and metallic oxides, it forms
vitreous, and in some cases very fusible compounds, hence its use in the
manufacture of glass (p. 337) ; hence also the readiness with which it corrodes
common crucibles when kept in fusion in them. Heated with charcoal, this
and the other oxides of lead are easily reduced to the state of metal ; they
are also reduced when heated in hydrogen or coal gas. The white or hydrated
oxide, when dried at about 100°, is a soft crystalline powder, =3(PbO)HO :
it is slightly soluble in pure water, and the solution has an alkaline reaction ;
it loses water and gradually becomes anhydrous when heated to about 160°.
The influence of carbonic acid and minute portions of saline substances upon
the solubility of this hydrate, has been above noticed.

Red Oxide of Lead ; Minium ; Red Lead (?hfi^). — This substance,
which is well known as a red pigment, is made by exposing protoxide of
lead to heat and air so as to oxidize without fusing it, the temperature
required for this purpose being between 570° and 580° ; it gradually acquires
a fine red color, the splendor of which, however, goes off by exposure to
light. The minium of commerce is of variable composition, and generally
contains excess of protoxide, which may be separated by very dilute acetic
acid, or by digestion in solution in acetate of lead. When exposed to a tem-
perature above that required for its formation, minium gives off oxygen, and
reverts to the state of protoxide. The most brilliant minium is obtained by
heating and stirring pure carbonate of lead in a current of air at a tempera-
ture a little short of 600°. Minium has a sp. gr. between 8 6 and 9. It is
decomposed by acids ; nitric acid resolves it into insoluble peroxide, while a
soluble nitrate of the protoxide is at the same time formed. Hydrochloric
acid, in small quantity (2 atoms to 1 of minium), produces with it chloride
and peroxide of lead, and water— PbgO^-f 2HCl = 2(PbCl) + PbO,4-2HO :
in larger quantity, the products are, chloride of lead, water, and free chlorine ;
Pb30^+4HCl=3PbCl + 4HO + Cl. With an aqueous solution of chlorine
it affords chloride and peroxide of lead ; (Pb30,+Cl=PbCl-f 2PbO,).

Peroxide of Lead; Binoxide of Lead-, Plumhic Add (PbOj.— This
oxide is obtained in the form of an insoluble brown powder, by digesting
minium in cold nitric acid ; or by heating salts of lead with chloride of soda
or lime; or by passing chlorine through minium diffused in water, or through
a solution of acetate of lead, and thoroughly washing the product in hot water
to remove the chloride of lead. The first is the best process, if the minium
and nitric acid are pure ; the resulting oxide only requires to be boiled in
very dilute nitric acid, then washed, and dried at 212°.

This oxide is a conductor of electricity. At a red heat it gives off oxy-
gen, and is converted into protoxide. By the continued action of light, or
of a gentle heat, it is resolved into oxygen and minium. Digested in liquid
ammonia, a mutual decomposition takes place, and water and nitrate of lead
are formed. Triturated with a fifth of its weight of sulphur, it inflames spon-
taneously; or with half its weight of sulphur when touched with oil of vitriol.
It is also decomposed, with the evolution of heat, when rubbed with an
eighth part of its weight of sugar ; or with its weight of crystallized oxalic
acid, with which it forms water, carbonic acid, and carbonate of lead. With
hydrochloric acid, it furnishes chlorine and chloride of lead. When boiled
in nitric or sulphuric acid, oxygen is evolved and salts of the protoxide are

NITRATE AND CHLORIDE OF LEAD. 431

formed. It absorbs sulphurous acid gas with the evolution of much heat,
or even with ignition, and forms sulphate of lead ; hence its occasional use
in the analysis of gaseous mixtures, to separate sulphurous from carbonic
acid gas. It is supposed to contain the second equivalent of oxygen in the
form of ozone (p. 113). It decomposes a solution of iodide of potassium
and bleaches sulphate of indigo. It oxidizes the resin of guaiacum, turning
it blue, and it gives blue and purple colors with strychnia when used with
sulphurous acid.

Plumhate of Potossa. — When potassa, moistened with a little water, and
peroxide of lead are heated for a short time in a silver crucible, a compound
is obtained which, dissolved in a small proportion of water and slowly evapo-
rated, yields crystals =KO,PbOa,3HO : they are deliquescent rhomboids,
soluble without decomposition in solution of potassa, but resolved by water
into hydrated peroxide of lead, and a brown solution of hiplumhafe of potassa.
Phimbate of Soda may be obtained in the same way, but it is little soluble
in water. The insoluble plumbates are formed by heating mixtures of the
bases with protoxide of lead, in the air, when oxygen is absorbed. Plumhate
of lime and of baryta are so formed. Under this aspect minium is a plumbate
of lead, =2(PbO),PbO,.

Metallo- chromes. — When solutions of the salts of lead are electrolyzed, they
deposit the peroxide on the positive electrode. When thin films of peroxide
of lead are thus formed upon polished steel plates, they give rise to the
prismatic tints described under the above name.

Hyponitrite of Lead {Tetranitrite of Lead). — When 1 part of neutral
nitrate of lead and 2 of metallic lead are boiled together for 12 hours in a
large quantity of water, the filtered solution yields red crystals, alkaline to
tests, soluble in about 1200 parts of cold and 34 of boiling water =4(PbO),
NO„HO.

Nitrite of Lead. — When 166 parts of neutral nitrate of lead, and 156
of metallic lead, are boiled in a large proportion of water, the yellow filtrate
yields orange-colored crystals^ soluble in 1250 of cold, and 34 of boiling
water =7(PbO),2N04,2HO. When 166 parts of neutral nitrate of lead
and 104 of lead (I atom and 1) are digested together in water at about 160,
the solution deposits yellow crystals, acid to litmus, soluble in 80 parts of
water at 77° =2(PbO),NO„HO.

Nitrate of Lead (PbO,NOg) is obtained by dissolving the metal (or
better, litharge) not in excess, in hot nitric acid diluted with two parts of
water, and evaporation. It crystallizes in octahedra, which are white, anhy-
drous, translucent, and of a styptic taste ; they decrepitate when heated, and
give out nitrous acid and oxygen, and protoxide of lead remains: they are
soluble in between 7 and 8 parts of water at 60° : they are insoluble in
alcohol and in nitric acid. Soft wood, or paper, impregnated with this salt,
burns like a slow match, with slight deflagration. Nitric acid forms with
oxide of lead a dinitrate, trisnitrate, and a sexbasic nitrate.

Chloride of Lead (PbCl). — When laminated lead is heated in chlorine,
the gas is absorbed, and a chloride of lead results. The same substance is
obtained by adding hydrochloric acid, or a solution of chloride of sodium, to
a concentrated solution of nitrate of lead, washing the precipitate in cold
water, and drying at 212°; it is also formed when the oxides of lead are
digested with heat in hydrochloric acid. It is white and fusible, and, on
cooling, forms a yellow horn-like substance {phimhum corneum). It does not
absorb ammonia. It volatilizes at a high temperature, provided air has access,
in which case a portion of oxide of lead is also formed. It dissolves in about
40 parts of water at 212°, separating, as its solution cools, in small anhy-
drous acicular crystals, unchanged by exposure to air, and of a sweetish

432 IODIDE, BROMIDE, AND SULPHIDE OF LEAD.

taste. Its solubility in water is greatly diminished by the presence of a little
hydrochloric acid, yet it is soluble in strong hydrochloric acid, and is
precipitated on dilution. It dissolves rather copiously in solutions of potassa
and soda, and of the alkaline hyposulphites. It is insoluble in alcohol.

Native chloride of lead occurs amongst the products of Vesuvius, in small
acicular crystals ; a dichloride of lead (PbgCl) has been found in the Mendip-
hills, in Somersetshire ; it forms fibrous yellow crystalline masses, upon a black
ore of manganese ; a native oxychloride of lead has also been found in the
same locality.

Oxychloride of Lead. — When chloride of lead is heated in the air till it
ceases to give off fumes, a compound remains =PbCl + PbO; it may also be
formed by fusing together atomic equivalents of chloride and oxide, or
chloride and carbonate of lead : it is a yellow crystalline compound. A
hydrated compound of chloride and oxide of lead is obtained by acting upon
a solution of common salt by litharge ; solution of soda, and oxide and
chloride of lead are formed ; this insoluble residue, when rendered anhydrous
by fusion, is known under the name oi patent yellow, Tumer^s yellow, or Cas-
sel yellow, =PbCl + 7PbO. A similar compound may be obtained by fusing
together 1 part of chloride with 4 or 5 of oxide of lead, or by heating sal-
ammoniac with oxide of lead.

Iodide of Lead (Pbl) may be formed by heating leaf-lead with iodine ;
but it is most readily obtained by adding iodide of potassium to a solution of
nitrate of lead, in equivalent proportions ; it then falls in the form of a bright
yellow powder, soluble in about 1250 of cold and 200 parts of boiling water,
and separates, as this solution cools, in brilliant flakes, which are hexahedral,
or derivatives of the hexahedron. In this crystalline state it retains its color,
but the pulverulent iodide becomes pale by exposure to light. When gently
heated it becomes deeper colored, and even brown, but again yellow on cool-
ing : at higher temperatures it fuses, and volatilizes at a strong red heat.
It is soluble in aqueous solutions of potassa and soda, forming colorless double
salts: boiled with carbonate of potassa, it forms carbonate of lead and iodide
of potassium. It becomes white when digested in caustic ammonia, forming
the compound, =NH3,PbI ; the same compound is obtained by the action of
gaseous ammonia upon the iodide. Iodide of lead is soluble in hydrochloric
acid, and if concentrated by heat, the solution as it cools deposits radiated
prismatic crystals of a yellow color, composed of iodide and chloride of lead.
It dissolves in concentrated solutions of the alkaline iodides, and in the ace-
tates of potassa, soda, and ammonia. An iodide of lead and sodium is thus
formed by adding slight excess of iodide of sodium to a hot solution of iodide
of lead, and placing the liquid in a warm place; it separates in yellow shin-
ing laminae =NaI,2PbI. It forms a similar crystallizable double salt with
iodide of potassium.

Bromide of Lead (PbBr) is precipitated from a solution of lead by hydro-
bromic acid or bromide of potassium : it is white, crystalline, fusible, and
concretes on cooling into a yellow mass. It is sparingly soluble in water,
and its boiling solution deposits shining acicular crystals.

Fluoride of Lead (PbF) is almost insoluble, and obtained by adding
hydrofluoric acid to a nitrate of lead, when it fivlls in the form of a white
powder, soluble in nitric and hydrochloric acids.

Sulphide of Lead (PbS) may be formed by fusion; when the lead melts,
it suddenly combines with the sulphur with ignition. Its lustre and color
much resemble pure lead, but it is brittle, and requires a bright red heat for
fusion. Its specific gravity is 7 58. Boiled with hydrochloric acid, chloride
of lead and sulphuretted hydrogen are formed ; by nitric acid it is converted
into sulphate of lead. Sulphide of lead may be obtained in the humi'd way,

SULPHATE AND CARBONATE OF LEAD. 433

by precipitating any salt of lead by sulphuretted hydrogen : the precipitate
is black, or brown if the solution is dilute : this is so delicate a test of lead,
that a solution containing the three hundred-thousandth part of the metal is
discolored by it, provided no excess of acid be present. Native sulphide of
lead, or galena, is the principle source of the commercial demands of the
metal. It occurs massive, and crystallized in cubes and their modifications.
When galena is finely powdered and heated with strong nitric acid, it is con-
verted into sulphate of lead, the other metals associated with it (copper and
silver) being dissolved as nitrates. When the nitric acid is diluted, some
nitrate of lead is formed and dissolved, and a portion of sulphur is pre-
cipitated.

Sulphite of Lead (PbOjSOJ is formed by digesting protoxide of lead
in aqueous sulphurous acid ; or by adding the acid to nitrate of lead. It is
white, insoluble in water, and tasteless.

Sulphate of Lead (PbO.SOa) — Cold sulphuric acid has but little action
upon metallic lead ; when the metal is boiled in the concentrated acid, sul-
phurous acid is evolved, and sulphate of lead is formed. The purer the lead
the more readily is a chemical action set up between it and sulphuric acid.
It is easily produced by adding dilute sulphuric acid, or a soluble sulphate,
to a solution of nitrate of lead, when it falls in the form of a dense white
powder : hence the applicalnon of the soluble salts of lead, especially the
nitrate, as tests of the presence of sulphuric acid and sulphates. After hav-
ing been dried at 400°, it may be heated to redness without losing weight.
Heated on charcoal by the blowpipe, it is ultimately reduced. Sulphate of
lead is insoluble in water and in alcohol. It is sparingly soluble in excess
of sulphuric acid, and separates from it in small prismatic crystals. It is
soluble, when recently precipitated, in hydrochloric acid, the fixed alkalies,
and sparingly so in their carbonates, and in some of the salts of ammonia,
especially the acetate. Its acid is expelled by the action of silica and of
alumina at a red heat, hence its decomposition when fused in earthen cru-
cibles. This compound is found native, crystallized in rhombs in Angle-
sea, Scotland, and other localities.

Phosphate OF Lead. — Each modification of phosphoric acid gives a white
precipitate in the soluble salts of lead, which is soluble in nitric acid. —
Native phosphate of lead. The mineral usually so called is a compound of
phosphate and chloride of lead, in which 3 atoms of the tribasic phosphate
are combined with 1 of chloride (9PbO,3PO,-|-PbCl). It has been found
in the mines of Cumberland, Durham, Yorkshire, and of Wanlock Head in
Scotland, and in many of the foreign mines. Its color is various shades of
green, yellow, and brown. It usually occurs in six-sided prisms, semitrans-
parent and brittle.

Carbonate OF Lead. Ceruse; White Lead. (PbO,COa). — This impor-
tant compound is extensively employed as an oil-pigment : it is chiefly made
in London and at Newcastle-on-Tyne, to the annual quantity of about 16,000
tons. There are many processes by which it may be obtained, and much in-
genuity has been displayed in their modification and improvement, the great
objects being to obtain it in such a state that it shall form the most opaque
and densest body as it is called, when ground up with linseed, or other dry-
ing oil, and shall at the same time be of a pure and perfect white.

The following is an outline of the several methods by which this carbonate
may be formed. 1. By the precipitation of soluble salts of lead by alkaline
carbonates. A solution of nitrate or acetate of lead is thus decomposed by
carbonate of soda; it yields a dense white precipitate, which, when washed
and dried, is of a pure white, but when examined by a magnifier, is found to
consist of minute crystalline grains, a circumstance which interferes with its
28

434 MANUFACTURE OF WHITE LEAD.

body or opacity to such an extent as to render it unfit for oil-paint : it is
also' a pure or neutral carbonate, and it will appear that the most esteemed
white lead generally contains more or less oxide or hydrated oxide of lead.
It varies in texture according as the carbonate is added to the nitrate, or the
nitrate to the carbonate ; the latter mode of precipitation, with properly
diluted solutions, furnishes the most impalpable powder. When the carbonate
has once acquired a crystalline texture, no grinding or mechanical comminu-
tion is capable of conferring upon it the qualities which fit it for an oil pig-
ment. 2. When carbonic acid gas is passed through a hot solution of sub-
nitrate of lead, carbonate of lead is thrown down, and the solution reverts
to the state of neutral nitrate ; this is reconverted into subnitrate by boiling
with protoxide of lead (powdered litharge), and the precipitation continu-
ously repeated. 3. Subacetate of lead is decomposed by passing through it
a current of purified carbonic acid gas. The celebrated white lead of Clichy
is thus prepared. 4. Finely-powdered litharge is moistened, mixed with a
very little acetate of lead (about a hundredth part), and submitted during
constant stirring to a current of heated carbonic acid : in this process a sub-
acetate of lead is successively formed and decomposed ; a small quantity only
of the original acetate therefore is required. 5. In the Dutch process lead
is cast into plates or bars, or into the form of stars, or circular gratings of
six or eight inches in diameter, and from a quarter to half au inch in thick-
ness : five or six of these are placed one above another in the upper part of
a conical earthen vessel, something like a garden-pot, in the bottom of which
there is a little strong acetic acid. These pots are then arranged side by
side, on the floor of an oblong brick chamber, and are imbedded in a mixture
of new and spent tan (ground oak-bark as used in the tanyard). The first
layer of pots is then covered with loose planks, and a second range of pots
imbedded in tan is placed upon the former ; and thus a stack is built up so
as entirely to fill the chamber with alternate ranges of the pots containing
the lead and acetic acid, surrounded by and imbedded in the tan. Several
ranges of these stacks occupy each side of a covered building, each stack
containing about 12,000 of the pots, and from 50 to 60 tons of lead. Soon
after the stack is built up the tan gradually heats or ferments, and begins to
exhale vapor, the temperature of the inner parts of the stack rising to 140^
or 150°. The acetic acid is slowly volatilized, and its vapor passing readily
through the gratings or folds of lead, gradually corrodes the surface of the
metal, upon which a crust of subacetate is successively formed and con-
verted into carbonate, there being an abundant supply of carbonic acid fur-
nished by the slow fermentative decomposition of the tanners' bark. In the
course of from 4 to 6 weeks the process is completed, and now, on unpack-
ing the stacks, the lead is found to have undergone a remarkable change :
the form of the castings is retained, but they are converted, with consid-
erable increase of bulk, into carbonate of lead ; this conversion is sometimes
entire, at others it penetrates only to a certain depth, leaving a central skele-
ton of metallic lead, the conversion being unequal in different parts of the
stack, and varying in its perfection at different seasons, temperatures, and
states of the atmosphere. The stacks are so managed that they are succes-
sively being built up and unpacked. The corroded and converted gratings,
or cakes, are then passed through rollers, by which the carbonate of lead
(white lead) is crushed and broken up, and the central core of metallic lead
(blue lead), if any remain, is easily separated : the white lead is then trans-
lerred to the mills, where it is ground up into a thin paste with water, and
is ultimately reduced, by the process of elutriation, or successive washings
and subsidences, to the state of an impalpable powder; it is then dried ia
wooden bowls placed upon shelves in a highly-heated stove, and thus brought

CARBONATE OF LEAD. 435

to the state of masses easily rubbed between the fingers into a fine powder,
in which the microscope does not enable us to discern the slightest traces
of crystalline character. If intended for the use of the painter, it is next
submitted to grinding with linseed oil ; and it is found that a hundred
weight of this white lead is formed into a proper consistence with 8 pounds
of oil, whereas precipitated white lead requires 16 pounds of oil for the
same purposes ; the one covering the surface so much more perfectly, and
having so much more body than the other. It is sometimes supposed that
in this process the oxygen and carbonic acid required to form the carbon-
ate of oxide of lead are derived from the decomposition of the acetic acid ;
but this is evidently not the case, for not more than 100 pounds of real
acetic acid exists in the whole quantity of the dilute acid contained in the
several pots of each stack ; and in 100 pounds of acetic acid there are not more
than 4t to 48 pounds of carbon, whereas 6740 pounds would be required
to furnish the carbonic acid which should convert 50 tons of lead (the
average weight of that metal in each stack) into carbonate of lead. Tiiere
can be no doubt then that the carbon or carbonic acid must come from
the tan, and that the oxygen is partly derived from the same source, and
partly from the atmosphere : the principal action of the acetic acid, there-
fore, is to form successive portions of subacetate of lead, which are suc-
cessively decomposed by the carbonic acid: the action is, however, of a very
remarkable description, for even masses of lead, such as blocks of an inch
or more in thickness, are thus gradually converted through and through
into carbonate, so that if due time is allowed, there is no central remnant
of metallic lead. The original texture of the lead is much concerned in
the extent and rapidity of the conversion. Rolled or sheet lead will not
answer, and the gratings, coils, and stars which are employed, are all of cast
lead. The purest metal is also required; for if it contain iron, the resulting
white lead acquires a tawny hue ; and if a trace of silver, it acquires a per-
ceptible dinginess when subjected to the action of liglit.

Sulphate of baryta is frequently added to commercial white lead, by
which its valuable properties are proportionately deteriorated ; the adultera-
tion is easily detected by digesting the sample in dilute nitric acid, which
dissolves the carbonate of lead, but leaves the sulphate of baryta ; the
articles known under the name of Venice white, Hamburgh white, and Butch
white, are avowedly mixtures of sulphate of baryta with carbonate of lead.
Clichy white, Krems or Kremnitz white, and Silver white, are pure white lead.
A minute addition of indigo or of lamp-black is sometimes made to white
lead, to give it a slight bluish shade.

Carbonate of lead is usually in the form of a heavy white powder, insolu-
ble in water, and very sparingly soluble in aqueous carbonic acid ; its specific
gravity varies from 6*4 to 6 75. It entirely dissolves with effervescence in
acetic and in dilute nitric acid. It is immediately discolored and ultimately
blackened by sulphuretted hydrogen, whence the necessity of the cautious
exclusion of all sources of that compound in white-lead works. When care-
fully heated in contact of air carbonate of lead loses carbonic acid, and
furnishes by proper management a beautiful minium. The usual composi-
tion of commercial white lead, prepared by the Dutch process, is represented
by Phillips {Journ. Ghem. Soc, iv. 170) as 2(PbO,COJ-f PbO,HO. It
loses the whole of its water at 300°, and at 350° the carbonic acid begins to
be evoKed.

Native Carbonate of Lead is one of the most beautiful of the metallic
ores ; it occurs crystallized, and fibrous, the former transparent, the latter
generally opaque. It is soft and brittle, and occasionally tinged green with
carbonate of copper, or gray by sulphide of lead.

436 TESTS FOR THE SALTS OF LEAD.

Cyanide of Lead (PbCy) falls in the form of an insolnble white powder
when cyanide of potassium is added to a solution of nitrate of lead, or when
hydrocyanic acid is dropped into acetate of lead : heated to redness in a
glass tube, it gives out nitrogen, and leaves a pyrophoric carbide of lead.

Borate of Lead is precipitated in the form of a white powder when
borate of soda is mixed with nitrate or acetate of lead : it fuses into a color-
less glass, and probably consists of 2 atoms of boracic acid and 1 of protoxide
of lead. Boracic acid and oxide of lead may be fused together in all pro-
portions ; 112 of oxide and 24 of acid give a soft yellow glass, sp. gr. 6*4 ;
with 48 of acid the glass is less yellow and harder ; and with Y2 of acid it
is colorless, as hard as flint glass, and highly refractive.

Alloys of Lead. — With tin, lead forms several useful alloys, which are
somewhat less dense than the mean. Common pewter consists of about 80
parts of tin and 20 of lead. Equal parts of lead and tin constitute plumbers^
solder. When pieces of copper are thrown into red-hot melted lead, they
soon disappear, and form a gray, brittle, and granular alloy. In coating
iron with lead, the surface of the metal is first cleaned with hydrochlorate of
ammonia : it is then dipped into melted zinc, and afterwards into a bath of
melted lead.

Tests for the Salts of Lead. — The salts are for the most part white,
and those which are soluble form colorless solutions. They have a sweetish
metallic taste. 1. Sulphuretted hydrogen gives a brownish discoloration
even when less than 1-300, 000th part of a salt of lead is present. In ordi-
nary solutions, it throws down a brown-black precipitate (sulphide of lead),
insoluble in alkalies and in diluted mineral acids, but decomposed by strong
nitric acid. 2. Hydrosidphate of ammonia gives a similar precipitate, not
soluble in an excess of the reagent, and having the other properties of the
sulphide. The insoluble salts of lead, such as the sulphate and phosphate,
are decomposed by this liquid, and a soluble salt of the acid is formed.
3. Diluted mlphuric acid throws down a white precipitate, slowly in acid
solutions. This precipitate is soluble in potassa and strong hydrochloric
acid. 4. Potnssa and soda throw down a white precipitate, soluble in excess
of the alkaline liquid. 5. Ammonia precipitates a white hydrated oxide,
not soluble in an excess of the alkali. 6. All the alkaline carbonates throw
down white precipitates, insoluble in an excess. 7. Iodide of potassium
gives a yellow precipitate, soluble in potassa and in hydrochloric acid.
8. Chloride of sodium gives a white precipitate, partly dissolved when
boiled, and readily dissolved by potassa or strong nitric acid. The lead-
precipitates dissolved by alkalies are thrown down black by sulphuretted
hydrogen or hydrosulphate of ammonia. 9. Ferrocyanide of potassium
gives a white precipitate.

The salts insoluble in water are dissolved by soda and potassa, or by nitric
acid, when the metal is rendered manifest by sulphuretted hydrogen and
other tests. When these salts are boiled with carbonate of soda, they afford
carbonate of lead, which may be dissolved in acetic or dilute nitric acid, and
subjected to the usual tests. Heated by the blowpipe upon charcoal, with
carbonate of soda or cyanide of potassium, they afford a globule of metal.
Lead is precipitated from its solutions, in the metallic state, by magnesium
and zinc. All the soluble, as well as the insoluble, salts of lead may be
decomposed and reduced, by mixing them with dilute nitric acid, and im-
mersing a plate of either of these metals in the liquid.

When solutions of the salts of lead are filtered through charcoal, which
is sometimes done for the purpose of decoloration, part or even the whole of
the oxide of lead, if it only amount to about one-twentieth of the charcoal
employed, will be abstracted by the charcoal. This renders charcoal in

OXIDES OF BISMUTH. 43*7

coarse powder most useful in the construction of the filters for domestic pur-
poses. Any casual imprei!::nation of water by lead may thus be removed,
and the water rendered wholesome. So small a quantity as one grain of
lead in a gallon of water has been known to produce the effects of lead-
poisoning.

CHAPTER XXXIII.

BISMUTH — COBALT — NICKEL — CHROMIUM.

Bismuth (Bi=213).

This metal was first described by Agricola, in 1529. It is sometimes
called marcasite. It is neither of common occurrence, nor very abundant.
Native bismuth is found in Cornwall, and in Saxony, Transylvania, and
Bohemia ; and it has been recently discovered in South Australia. It is
readily extracted from its ores by fusion. Bismuth is a brittle white metal,
with a slight tint of red. It fuses at 497°, and expands and crystallizes on
cooling. Its sp. gr. is 9 8. To obtain fine crystals, it should be purified
by fusion with nitre, and when thus refined, carefully melted and poured into
a heated mould, and suffered slowly and quietly to cool. When the surface
has solidified, the crust is pierced, and the liquid metal poured out from the
interior : the mould is then suffered to cool, ai\d the superior crust carefully
removed, when the cavity is found lined with iridescent cubical crystals (pp.
25 and 309). Arsenic, iron, copper, nickel, silver, and other metals, are
frequently found in the bismuth of commerce. To purify it, it may be dis-
solved in nitric acid, and the clear solution poured off into water, which
occasions a precipitation of a subnitrate of bismuth, easily reducible by fusion
with charcoal or black flux in an earthen crucible.

Bismuth and Oxygen There are two well-defined oxides of bismuth, a

teroxide =Bi03, and an acid oxide =Bi05. A third oxide has been described
as a compound of these =Bi03,Bi05.

Oxide of Bismuth; Teroxide of Bismuth (BiOg). — When bismuth is
exposed at a white heat to a current of air, it burns, and produces an abun-
dant yellow smoke, which condenses in the form of a yellowish-white subli-
mate. The readiest mode of obtaining this oxide consists in dissolving
bismuth in nitric acid, precipitating by dilution with water, edulcorating the
precipitate, and heating it, when dry, nearly to redness. Owing to imperfect
washing, it frequently contains traces of arsenic acid. At a red heat, this
oxide fuses, and when in fusion it acts upon other oxides much in the same
way as oxide of lead. It forms, on cooling, a yellow vitreous mass of a spe-
cific gravity of 8*2. It is easily reduced by hydrogen, charcoal, and several
of the metals. It combines with water, forming a white hydrate, which is
best obtained by digesting the precipitate formed by pouring the nitric
solution of bismuth in water, into caustic potassa or soda, and after washing,
drying it at 80°. It is insoluble in excess of the alkalies (and their car-
bonates) ; and when boiled with them becomes yellow and anhydrous. It
is also insoluble in tartaric acid, by which it is known from the antimonial
precipitate in water. Native oxide of bismuth is a rare mineral, found in
Cornwall and Saxony : it is the bismuth ochre of some mineralogists.

Peroxide of Bismuth ; Bismuthic Acid (BiO^). — This oxide is obtained
by dropping nitrate of bismuth into a solution of caustic potassa. The pre-

438 SALTS OF BISMUTH.

cipitate should be boiled in the alkaline liquor, washed, and, while moist,
diffused through a solution of potassa into which chlorine is passed. A red
precipitate is thus formed, which consists of bismuthic acid and teroxide, and
which is to be digested in nitric acid of sufficient strength to dissolve the
oxide. The remaining acid, which is a hydrate, is to be well washed, and
dried at 100°; it is a red powder, becoming brown and anhydrous when
dried at 266° ; at higher temperatures it begins to lose oxygen. It is de-
composed by sulphuric acid, and by hot nitric acid.

Nitrate of Bismuth (BiOg.SNOjjOHO). — When nitric acid is poured
upon powdered bismuth, the action is intensely violent. Nitrate of bismuth
is usually made by dissolving the metal to saturation in 2 parts of nitric acid
and 1 of water; nitric oxide is copiously evolved, and the solution affords
prismatic crystals, which may be dissolved in a small quantity of water; but
if the solution, even when acid, is poured into a large quantity of water, it
is decomposed, and affords a white and somewhat crystalline precipitate,
commonly called sahnitrate of bismuth^ and formerly known as magistery of
bismuth, pearl white, and blanc cfEspagiie ; it is insoluble in water, and when
dried in the air is =Bi03,N05,H0 ; but becomes anhydrous when adequately
dried. This compound is used in medicine : it frequently contains arsenic
in the form of arsenic acid, owing to imperfect washing of the precipitate.
Out of five druggist's samples, we have found arsenic in three. The presence
of this impurity may lead to a serious error. It may be detected by boiling
the subnitrate in some ounces of distilled water, filtering, evaporating the
liquid to dryness, and then adding to the residue a few drops of a solution
of nitrate of silver. A brick-red stain or precipitate indicates the presence
of arsenic acid.

The nitrate is not so completely decomposed by water as the chloride :
hence, in order to procure the complete decomposition of the nitrate, some
hydrochloric acid should be added to the solution, and this should be after-
wards concentrated by evaporation. The addition of a large quantity of
water to the residue will then produce a copious white precipitate. {See
Chloride.)

Chloride of Bismuth ; Terchloride. (BiClg) is procured by gently heat-
ing the metal in chlorine ; it burns, and forms a gray compound. This ter-
chloride may also be prepared by heating 2 parts of corrosive sublimate with
I of powdered bismuth, and expelling the excess of the former by heat ; or
by evaporating the solution of oxide of bismuth in hydrochloric acid to dry-
ness, and heating the residue in close vessels. It was formerly called Butter
of Bismuth. It is of a gray color, and fuses at about 480°. When exposed
to air it deliquesces. It is decomposed by a large quantity of water. A
solution of the chloride may be obtained by dissolving pure teroxide of bis-
muth, or the pure sulphide, in hydrochloric acid, and evaporating the liquid.
. When added to a large quantity of water, a white oxychloride of the metal
is precipitated (3BiCl3+6HO=BiCl3,2Bi03+6HCl). A small quantity of
oxide of bismuth is, however, retained by the acid liquid. This precipitate
has also received the name of pearl lohite.

Sulphide of Bismuth (BiSg) is of a bluish and metallic lustre ; it is less
fusible than bismuth. It may be formed by fusion ; and also by precipitating
the salts of bismuth by sulphuretted hydrogen, when it forms a black or
dark-brown precipitate (hydrated), which, when dried and heated, acquires
a metallic lustre.

Sulphate of Bismuth (Bi03,3S03) is obtained by heating powdered bis-
muth in sulphuric acid. It is a white compound, insoluble in, but decom-
posed by water, which converts it into a subsulphate and supersulphate.
Carbonate of Bismuth is thrown down from the nitrate by carbonated

TESTS FOR THE SALTS OF BISMUTH. COBALT. 439

alkalies; it is a white powder, insoluble in water and in carbonic acid, and
soluble in nitric acid with effervescence.

Alloys of Bismuth. — Those with tin and lead are remarkable for the low
temperature at which they enter into fusion, and for the extraordinary irre-
gularities of expansion and contraction which they exhibit with changes of
temperature. An alloy of 2 parts of bismuth, I of lead, and 1 of tin, fuses
at 200°. The alloy of 8 parts of bismuth, 5 of lead, and 3 of tin, fuses at
a little below 212° : the addition of 1 part of mercury or of cadmium renders
it still more fusible. It may be employed for taking casts from medals, and
even from the surface of wood and embossed paper : some beautiful casts of
the internal ear have also been made in this alloy, showing the complexities
of its bony cavities. When the alloy is poured upon a marble slab, and
broken as soon as it is cool enough to be handled, its surfaces are bright and
conchoidal, and the whole extremely brittle ; after this it becomes hot, and
loses its brittleness, its fractured surface becoming granular and dull.

Tests for the Salts of Bismuth. — Many of them are resolved by water
into a soluble acid salt, and a less soluble or insoluble and more basic com-
pound. 1. In the clear acid solutions of oxide of bismuth, potassa, soda,
and ammonia, and their carbonates, produce white precipitates, insoluble in
excess of the alkali, or its carbonate, and insoluble in hydrochlorate of am-
monia. 2. Hydrosulphate of ammonia and sulphuretted hydrogen produce
brown or black precipitates, insoluble in the precipitants, but soluble in
boiling nitric acid, and easily reduced to metallic bismuth when mixed with
soda, and fused in the inner flame of the blowpipe. 3. Chromate of potassa
gives a golden-yellow precipitate, soluble in nitric acid, but insoluble in
potassa. 4. Iodide of potassium gives a purple-brown precipitate. 5. Sul-
phuric acid does not precipitate the solution ; and by this reagent lead may
be detected in, and separated from, bismuth. 6. Ferrocyanide of potassium
gives a greenish-white precipitate, and ferricyanide a similar precipitate, but
of a deeper color. T. The acid solutions of bismuth are decomposed by
magnesium, zinc, lead, tin, and cadmium. When a salt of bismuth is boiled
with polished copper in diluted hydrochloric acid, there is a deposit of white
metal on the copper, but this is not volatilized by heat. A piece of zinc in-
troduced into a solution of a salt of bismuth, the surface is soon covered with
a black uncrystalline deposit of reduced bismuth, which protects it from the
further action of the acid. All the compounds of bismuth give a metallic
button on charcoal under the blowpipe flame. The metal is surrounded with
a yellow border of anhydrous oxide.

Bismuth may be mistaken for antimony from the fact that its salts, espe-
cially the chloride, produce v/hite precipitates when added to a large quan-
tity of water, provided too much of the acid is not present. The white preci-
pitate from bismuth is not soluble in tartaric acid, and is blackened by sul-
phuretted hydrogen ; that from antimony is easily dissolved by tartaric acid,
and acquires a deep orange-red color from the gas.

Cobalt (Co=30).

The native combinations of cobalt are the oxide, and compounds of the
metal with iron, nickel, arsenic, and sulphur. The ore called glance cobalt
is a sulpho-arsenide. The red ore is an arseniate.

Cobalt is never employed in the metallic state, so that the processes for
its reduction are generally carried on upon a small scale, and confined to the
experimental laboratory ; but there is much difficulty in obtaining it pure.
It is a metal of a reddish-gray color, brittle, and difficultly fusible. Its sp. gr.
is 89. It forms two oxides, a protoxide and a sesquioxide, and these com-
bine with each other.

440 COBALT : OXIDES, CHLORIDES, AND SULPHIDES.

Protoxide of Cobalt (CoO), formed by adding potassa to the nitrate
and washing and drying the precipitate out of contact of air, appears nearly
black. By exposure to heat and air it absorbs oxygen, and is converted
into peroxide. The protoxide, when recently precipitated and moist, is blue ;
if left in contact of water, it becomes a red hydrate ; it then absorbs oxygen,
and acquires a green tint. It may also be obtained by heating the carbon-
ate of cobalt out of contact of air ; it is then of a greenish-gray color. It
is recognized by the facility with which it imparts a blue tint to vitrifiable
compounds, and to white enamel. When hydrogen is passed over it at a red
heat, it is decomposed, and porous metallic cobalt remains, which is some
times pyrophoric.

Peroxide of Cobalt; Sesquioxide of Cobalt (Co^Og). — When the prot-
oxide is heated in the air, it absorbs oxygen, and acquires a dark-brown
color, forming an oxide intermediate between the peroxide and protoxide,
= €'0304. When chlorine is passed through a mixture of the hydrated prot-
oxide and water, or when a solution of chloride of cobalt is decomposed by
chloride of lime, a black precipitate falls, which is the hydrated peroxide
(Co^Og.SHO), and which may be deprived of water by cautious drying ; it is
then black, and insoluble in dilute acids ; it does not form salts ; when acted
on by hydrochloric acid it evolves chlorine, and yields a protochloride.

Nitrate of Cobalt (CoOjNOJ. — With nitric acid the oxide of cobalt
furnishes a brownish-red deliquescent salt, in rhombic crystals, consisting
of CoO,N05,6HO. Characters written with it upon paper become pink in
dry air, and disappear in a damp atmosphere. It thus forms a red sympa-
thetic ink.

Chloride of Cobalt (CoCl). — When oxide of cobalt is dissolved in hydro-
chloric acid, evaporated to dryness, and the residuum heated to redness out
of the contact of air, a substance of a blue color a?id micaceous texture is
obtained, which is anhydrous chloride of cobalt. When this chloride is dis-
solved in water, it yields a pink solution, which, if written with, becomes
invisible when dry ; but if gently heated, the writing appears in brilliant blue
(auhydrous chloride), which soon vanishes as the paper cools, in consequence
of the salt absorbing aerial moisture (hydrochlorate of the oxide, p. T6) ; if
overheated, the writing blackens. This solution has been termed sympatlietic
ink. When evaporated, it forms red crystals, composed of 1 atom of the
chloride and 5 of water.

Protosulphide of Cobalt (CoS) is yellowish-gray ; it fuses at a red-heat,
and is easily soluble in acids.

Sesquisulphide of Cobalt (Co^Sg) is obtained by decomposing sulphate
of cobalt by sulphuretted hydrogen at a red heat. It is dark gray, and occurs
native.

Sulphate of Cobalt (CoO,S03) forms oblique rhombic prisms, soluble in
24 parts of water at 60°, and insoluble in alcohol. It may be made by dis-
solving the newly-precipitated protoxide or carbonate of cobalt in sulphuric
acid diluted with its bulk of water. When dried at a temperature of 500°
the crystals fall into a blue powder, which in a red heat fuses, but does not
give off acid except at a very high temperature. When 1 part of sulphate
of cobalt and 2 or 3 of sulphate of zinc are dissolved together and precipitated
by carbonate of soda, a precipitate falls which, when washed and calcined,
has been used as a pigment, under the name of Rinmami's green.

Phosphate of Cobalt (3CoO,PO,) may be formed by adding phosphate
of soda to chloride of cobalt; it is insoluble in water, of a lilac color, and
soluble in excess of phosphoric acid. When phosphate of cobalt is mixed
with pure and moist alumina, and exposed to heat; it produces a blue com-
pound, which has beeu employed as a substitute for ultramarine, under the

TESTS FOR THE SALTS OF COBALT. 441

name of Thenard^s Blue. A pure salt of cobalt free from nickel, and pure
alumina free from iron, are essential to the production of a fine l)lne.

Carbonate of Cobalt. — When nitrate, chloride, or sulphate of cobalt,
is decomposed by carbonate of soda, a purple powder is precipitated, be-
coming pink when dried, and soluble with effervescence in the acids. Heated
in close vessels it gives off carbonic acid, and a gray protoxide remains : it
is a mixture of carbonate and hydrated oxide =5CoO,2C02,4HO.

Ammonia Compounds of Cobalt. — Several of the salts of cobalt form
double salts with those of ammonia. When hydrated oxide of cobalt is dis-
solved in an ammoniacal solution of sal-ammoniac, it absorbs oxygen from
the air, and acquires a purple color ; and if excess of hydrochloric acid be
then added, and the mixture boiled, a crimson precipitate falls, leaving the
liquor colorless. When this precipitate is dissolved in hot water, acidulated
by hydrochloric acid, it deposits red octahedral crystals, insoluble in hydro-
chloric acid, and which, at a red heat, lose ammonia and hydrochlorate of
ammonia: their composition is 3(NII^Cl-f 2(CoO)NH3).

CoBALTOCYANiDES. — When cyanide of potassium is added to a solution of
cobalt salt, a brown precipitate (CoCy) falls, which, dissolved in an excess
of cyanide of potassium, yields a double cyanide =KCy,CoCy. When this
salt is exposed to the air, or when a solution of hydrated oxide of cobalt in
potassa is supersaturated with hydrocyanic acid, a salt is formed =K3,Co2,
Cyg. It corresponds to the ferricyanide of potassium. Similar salts, with
sodium and other bases, have been obtained.

Borate of Cobalt. — Solution of borax occasions a pink precipitate in
solution of chloride of cobalt, which is a borate of cobalt, and which produces
a beautiful blue glass when fused.

Uses of Cobalt. — The chief use of cobalt is in the state of oxide as a
coloring material for porcelain, earthenware, and glass; it is principally im-
ported from Germany in the state of zaffre, and smalt, or azure. Zaffre is
prepared by calcining the ores of cobalt, by which sulphur and arsenic are
volatilized, and an impure oxide of cobalt remains, which is mixed with
about twice its weight of finely-powdered flint. Smalt and azure blue are
made by fusing zaffre with glass, or by calcining a mixture of equal parts of
roasted cobalt ore, common potassa, and ground flint. In this way a blue
glass is formed, whicil, while hot, is dropped into water, and afterwards re-
duced to impalpable powder. Thenard's blue is a valuable pigment, and
has been substituted for smalt in the manufacture of paper, though it is said
not to be so effectual in covering the yellow tint of the paper. There was
formerly a large addition of smalt made to bank-note paper, and consequently
the ash obtained by the periodical combustion of notes at the Bank, often
assumed by fusion the appearance of a deep blue glass : so also the blue-
tinted writing-papers leave a fine blue ash when burned, and often exhale an
aliaceous odor from the presence of arsenic in the smalt. Smalt generally
contains traces of arsenic, and this substance may be thus transferred to
starch and paper. In paper-making, there is some difficulty in keeping the
smalt uniformly suspended in the pulp, so that the under side of the sheet is
generally bluer than the upper. The manufacturers of paper-hangings also
use smalt and Thenard's blue for all brilliant and durable blues.

Tests for the Salts of Cobalt. — The salts are generally blue in the
anhydrous state, as well as in concentrated acid solutions. If diluted, they
have a crimson or pink-red color. 1. Sulphuretted hydrogen does not pre-
cipitate an acid solution. If acetate of soda is added to the liquid, a dark-
brown precipitate (CoS) falls. 2. Hydrosidphate of ammonia produces a
dark-brown or black precipitate, which is quite insoluble in an excess of the
reagent. 3. Ammonia gives a bluish precipitate, soluble in an excess of the

442 NICKEL AND ITS OXIDES.

alkali : the precipitate, on exposure to air, rapidly acquires a green, and
finally a brown color. 4. Potassa throws down a deep blue precipitate,
which, when boiled without exposure to air, becomes rose-red. The blue
precipitate exposed to air becomes olive-green, and finally brown. 5. Alka-
line carbonates give a light-red precipitate of basic carbonate. This preci-
pitate is dissolved by carbonate or hydrochlorate of ammonia, forming a rich
crimson-red solution. 6. Ferrocyanide of potassium produces a deep green,
and Ferrocyanide of potassium, a red-brown colored precipitate.

The salts of cobalt which are insoluble in water are dissolved by hydro-
chloric and sulphuric acids. The hydrochloric solution on paper is identified
by the red spot or streak acquiring a rich blue color when dried by a mode-
rate heat, and by its resuming the ordinary red color when exposed to damp
air (p. 76). Before the blowpipe, borax and raicrocosmic salt acquire a
blue color from cobalt and the compounds containing it.

Nickel (Ni=30).

Nickel was discovered by Cronstedt, in 1751. Its commonest ore was
termed by the German mm^vs, kupfernichel, or " false-co|)per :" it is au
arsenide of nickel. The common commercial source of nickel is an impure
fused arsenide, known under the name of Speiss ; it generally contains be-
tween 50 and 60 per cent, of nickel. The pure metal may be obtained from
this arsenide by roasting it, dissolving the product in a mixture of equal
parts of nitric and hydrochloric acids, and evaporating the solution to dry-
ness, so as to expel excess of acid ; then redissolving the residue in water,
passing a current of sulphuretted hydrogen through the solution, and filter-
ing. A little nitric acid is added to the filtrate, and after boiling it, an
excess of caustic ammonia is added ; it is again filtered, and solution of pot-
assa added until the blue color of the liquid nearly disappears ; this produces
a green precipitate, which, when thoroughly washed with boiling distilled
water, dried, and exposed to a red heat in a current of hydrogen gas, leaves
the nickel in a finely-divided state. It may be obtained in the form of a
button by fusion at a white heat.

Properties. — Nickel is a white, ductile, and malleable metal, nearly as
difficult of fusion as iron : it is magnetic, but its magnetism is more feeble
than that of iron, and vanishes at a heat somewhat below redness. It is
not oxidized at common temperatures, but when heated it acquires various
tints, like steel, and at a red heat becomes coated with a gray oxide. Its
sp. gr. is 8*8. It is slowly soluble in dilute sulphuric and hydrochloric
acids, evolving hydrogen, and producing protosalts : nitric acid is its best
solvent.

Protoxide of Nickel (NiO) is obtained by adding potassa to the solution
of the nitrate or sulphate; a green precipitate falls, which is a hydrated
protoxide ; this, heated to redness, affords a gray protoxide. The carbonate,
oxalate, and nitrate of nickel, when heated to redness, also afford the prot-
oxide in the form of a gray powder : when intensely heated out of contact
of air, the oxide becomes green. It is not magnetic. This oxide, in the
state of hydrate, dissolves in ammonia, forming a sapphire-blue solution, a
property made use of to separate oxides of nickel and iron, the latter (per-
oxide) being insoluble in ammonia.

Peroxide of Nickel Sesquioxide of Nickel (Ni^Og).— When nitrate
or carbonate of nickel is carefully heated nearly to redness, a black powder
remains, which is this oxide. It may be obtained as a hydrate by passing
chlorine through the hydrated protoxide diffused in water, in which case a
solution of protochloride is obtained, and peroxide is formed (3NiO-f Cl=

SALTS OF NICKEL. 443

NiCl + NiaOa). It may also be formed by the action of a warm solution of
chloride of lime upon the hydrated protoxide. When this hydrated oxide
is carefully dried, it is =Ni.jO,^,3IIO. It does not combine with acids.

CfiLORiDE OF Nickel (NiCl). — When finely-divided nickel is heated in
chlorine, it burns, and a golden-colored chloride results. This compound
may also be obtained by dissolving the oxide in hydrochloric acid, evaporating
to dryness, and heating the residue to redness in a glass tube : it then
remains in the form of a yellow lamellar substance, volatile at a high red
heat, which dissolves in hot water, and leaves on evaporation a confusedly
crystalline mass of an apple-green color, and sweetish taste =NiCl,9B[0. —
Ammonio- chloride of Nickel. 100 parts of anhydrous chloride of nickel
absorb 74 8 of ammonia, becoming a bulky white powder =3(NH3),NiCl,
which yields a blue solution with water.

Nitrate of Nickel (NiO,N05,5IIO). — Nitric acid acts upon nickel with
disengagement of nitric oxide, and a bright green solution of protoxide is
obtained, which yields prismatic crystals : exposed to heat, part of the acid
may be driven off so as to leave a green insoluble subnitrate, and this at a
higher temperature is decomposed, peroxide, or ultimately protoxide, of
nickel remaining. The crystals of nitrate of nickel effloresce in dry air, but
deliquesce in a damp atmosphere ; they are soluble in 2 parts of water a 60°,
and also in alcohol.

Sulphide of Nickel (NiS) may be formed by heating nickel filings with
sulpliur; they combine with ignition; also by heating oxide of nickel with
sulphur ; or by passing sulphuretted hydrogen over the heated oxide. It is
yellow, and resembles pyrites.

SuPHATE OF Nickel (NiO.SOg.THO) is formed by dissolving the oxide
or carbonate of nickel in diluted sulphuric acid : it yields emerald-green
prismatic crystals, soluble in about 3 parts of water at 60°, and efflorescent
by exposure; its taste is sweet and astringent; it is insoluble in alcohol and
in ether. Exposed to heat, the crystals crumble down into a yellow powder :
at a white heat the acid is expelled, and protoxide remains. When the
ordinary crystals (containing 7 atoms of water) are exposed to the sunshine,
or when long kept, they become a congeries of small octahedral crystals,
which are opaque, but retain the original quantity of combined water.

Sulphate of Ammonia and Nickel. — (NH^O,NiO,2S03,5HO) Js obtained
by evaporating a mixed solution of sulphate of ammonia and sulphate of
nickel ; it forms four-sided prismatic crystals, of a blue-green color, soluble
in four parts of cold water. Anhydrous sulphate of nickel absorbs gaseous
ammonia, evolving heat, and forming a bulky pale blue powder, which gives
a blue solution in water, and deposits green hydrated oxide : the amount of
ammonia absorbed is about 56 per cent., so that the compound may be re-
presented as 3(NH3)NiO,S03. Sulphate of Potassa and Nickel (K.O,'N\0,
2S03,6HO) is obtained by evaporating the mixed solution of sulphate of
nickel and sulphate of potassa. It forms pale green rhomboidal crystals,
isomorphous with the corresponding magnesian salt. Double sulphates of
nickel and iron, and of nickel and zinc, may also be obtained.

Phosphate of Nickel 3(NiO)P05, being nearly insoluble, is precipitated
upon adding phosphate of soda to a solution of nickel. It is of a pale-green
color, and sometimes forms a crystalline powder.

Carbide of Nickel occasionally remains in the form of a shining powder,
when a button of the metal which has been fused for a long time in contact
with carbon is dissolved in nitric acid.

Carbonate of Nickel (NiOjCO^) falls as a crystalline powder when a
solution of nitrate of nickel is dropped into a solution of bicarbonate of
soda. There is also a basic carbonate.

444 CHR0311UM AND ITS OXIDES.

Cyanide of Nickel (NiCy) is thrown down as a green precipitate when
a soluble cyanide is added to a solution of nickel, or when hydrocyanic is
mixed with acetate of nickel.

PoTASSio-CYANiDE OF NiCKEL (KCy,NiCy). — When freshly-precipitated
cyanide of nickel is dissolved in a solution of cyanide of potassium, yellow
rhombic prisms are obtained on evaporation, which are this double cyanide
with 1 atom of water. Similarly constituted salts may be obtained with the
cyanides of ammonium, calcium, and barium.

Alloys of Nickel. — An alloy of nickel and iron forms a principal metallic
ingredient in most aerolites or meteoric stones, and in the masses of native
iron found in various parts of the world, in which the proportion of nickel
varies from TS to 8 "5 per cent. With copper, nickel forms a hard white alloy.
The lohite copper of the Chinese, or Pakfong, consists of 40 '4 parts of copper,
3r6 of nickel, 25*4 of zinc, and 26 of iron. A similar alloy is often used
as a substitute for silver, or for plated articles, under the name of German
silver ; it should consist of 8 parts of copper, 3 to 4 of nickel, and 3j of
zinc. A variety of articles are now plated with nickel by electrolytic pre-
cipitation from a solution of sulphate of nickel, the process Being similar to
that in which copper is used.

Tests for the Salts of Nickel. — The salts of nickel are green in the
hydrated, and yellow in the anhydrous state. Their solutions have a green
color and an acid reaction. 1. Sulphuretted hydrogen produces no precipitate
in an acid solution ; but if acetate of soda is added to the liquid in small
quantity ; there is a dark-brown or black precipitate. 2. Hydrosulphate of
ammonia gives a similar precipitate, which is only partially dissolved by an
excess of the reagent. 3. Ammonia gives, in neutral solutions, a pale
greenish precipitate, which is dissolved by an excess of the alkali, forming a
blue solution. The precipitate is also soluble in hydrochlorate of ammonia.
4. Potassa gives a pale green precipitate of hydrated protoxide, insoluble in
an excess of the alkali, but dissolved by hydrochlorate of ammonia. Potassa
in excess gives a pale green precipitate in the blue solution formed by
ammonia with a salt of nickel (3). The blue solution of a salt of copper in
ammonia is not affected by the addition of potassa. 5. Alkaline carbonates
give a similar precipitate soluble in an excess of carbonate of ammonia,
forming a blue solution. 6. Ferrocyanide of potassium gives a pale greenish
precipitate even in the ammoniacal solution of nickel. This test forms a clear
distinction between nickel and copper. The Ferricyanide gives a greenish-
yellow precipitate. Before the blowpipe, these salts give with borax a
reddish-yellow bead, which becomes paler as it cools, and which, in the
reducing flame, yields grayish particles of reduced nickel.

Chromium (Cr=26).

Chromium was discovered by Yauquelin in 179t. Its two native combi-
nations are the chromate of lead, and the chromite of iron, a compound of the
oxides of chromium and iron.

Metallic chromium may be obtained by intensely igniting its oxide witli
about a tenth of its weight of charcoal, but the reduction is difficult and
imperfect. Its color resembles that of platinum ; it scratches glass, and
takes a good polish. Its sp. gr. is 5-9. It has also been obtained by the
action of potassium on chloride of chromium, and is then pulverulent, burns
when heated, into an oxide, and is energetically acted on by most of the
acids; whereas, when obtained by the usual modes of reduction, it is com-
paratively fndiflferent to the action of powerful reagents.

Chromium and Oxygen. — There are four oxides of chromium — namely,

CHROMIC AND PERCHROMIC ACIDS. 445

protoxide, CrO ; a sesquioxide, Cr^O. ; an intermediate oxide, OvO,Qv,p.^',
and lastly, chromic acid, CrOg. In addition to these, a perchromic acid has
been announced, having the formula Crfij.

Protoxide of Chromium (CrO) is obtained in the form of a brown
hydrate, by the action of potassa on the corresponding protochloride : it is
unstable, and passes by the action of air or water into the intermediate oxide,
which is isomorplious with the magnetic oxide of iron.

Sesquioxide of Chromium (CrgOJ is obtained by heating chroraate of
mercury, or chromate of ammonia, to dull redness; it is also formed by the
action of a red heat upon bichromate of potassa : in this case neutral chromate
of potassa is formed, which may be removed by washing the product. This
oxide is of a green color, and not changed by heat, and is much used in
enamel and porcelain painting ; it also forms an ingredient in the pink color
of common earthenware, which is prepared by heating a mixture of 1 part
of cliromate of potassa with 30 of peroxide of tin, and 10 of chalk, to a
red heat, and then washing the finely-powdered product with dilute hydro-
chloric acid. In its hydrated state this oxide is obtained by precipitation
from its acid solutions : for this purpose a solution of bichromate of potassa
may be strongly acidulated with sulphuric or hydrochloric acid, and boiled
with the addition of a little alcohol, by which the red salt is deoxidized, and
a green solution obtained, from which ammonia throws down a bulky greenish
precipitate, which, when washed and dried in the air, is CryOg.lOHO. When
this hydrate has been heated, it shrinks, and is difficultly soluble. At a
temperature a little below a red heat it suddenly becomes incandescent. It
is a weak base, and forms green and purple solutions ; the former do not
crystallize, but the latter readily yield crystallizable salts. Native Sesquioxide
of Chromium has been found in the form of a green incrustation. It is the
coloring matter of the emerald, and exists in a few other minerals, such as a
diallage and some varieties of serpentine.

Chromic Acid (CrOJ. — This acid is most readily obtained by mixing 4
measures of a cold saturated solution of bichromate of potassa with 5 of
sulphuric acid : the chromic acid separates, as the liquid cools, in crimson
needles, which may be dried upon a porous tile, under a bell-glass. The
crystals are very soluble in water, but sparingly soluble in sulphuric acid of
the specific gravity of 1'55 : they are anhydrous, and become of a very dark
color when heated, but resume their scarlet tint on cooling ; they fuse at
about 400°, and when more highly heated become incandescent, giving off
oxygen, and yielding sesquioxide. They taste sour and metallic. Chromic
acid dissolves in alcohol, and the solution gradually deposits green oxide.
It is a powerful oxidizing and bleaching agent, yielding half its oxygen to
oxidizable bodies, and being reduced to sesquioxide ; (2Cr03=Cr203-f O3) :
hence a mixture of bichromate of potassa and sulphuric acid is frequently
resorted to as a means of oxidizing organic bodies. It oxidizes and turns
blue the precipitated resin of guaiacum. It decomposes a solution of iodide
of potassium, and sets free iodine, producing the usual blue color when
starch is added to the mixture. It is considered to be an ozonide.

Perchromic Acid {Qvjd^). — When chromic acid is agitated with peroxide
of hydrogen, the liquid acquires a beautiful blue color (pp. 118, 153) ; and
by means of ether, the blue-colored compound may be separated from the
watery solution. It has not been obtained in an isolated state, or in com-
bination with bases, but it is supposed to be chromic acid in a higher stage
of oxidation ; and its formula is assumed to be similar to that of the per-
manganic acid.

Chromate of Potassa (KOjCrOg) is prepared by exposing a mixture of
4 parts of powdered native chromite of iron with 1 of nitre, to a strong heat

446 CHROMATE AND BICHROMATE OP POTASSA.

for some hours, and washing out the resulting soluble matter : The process
is repeated until the ore is decomposed. The washings yield chromate of
potassa by evaporation. This process is now generally conducted so as to
yield a bichromate, by heating the pulverized chrome-iron ore with carbonate
of potassa and a little nitre in a reverberatory furnace, and constantly stirring
the mixture, to complete the oxidation : the product is then digested in
water, and the yellow solution is supersaturated by nitric acid, which throws
down silica, and by abstracting a portion of potassa leaves bichromate.
Chromate of potassa forms yellow prismatic crystals of a disagreeable
metallic taste, soluble in about twice its weight of water, and insoluble in
alcohol. When heated to 400° it acquires a crimson color, but becomes
again yellow on cooling. When fused it crystallizes on cooling, but is not
decomposed except in contact of carbonaceous matter, when carbonate of
potassa and oxide of chromium are produced.

Bichromate of Potassa (KOjSCrOg) is obtained by adding a sufficiency
of sulphuric or other acid to a solution of the chromate to give it a sour
taste, and setting it aside for a day or two, when deep orange-colored or red
crystals are de})osited ; the acid abstracts half the potassa, and if sulphuric
acid is used, there is some difficulty in separating the sulphate from the
chromate ; nitric acid is preferable. The crystals are anhydrous prisms,
permanent in the air, of a metallic taste, soluble in 10 parts of water at 60°,
and much more soluble in boiling water. At a red heat they fuse into a
transparent liquid, which congeals into a crystalline mass on cooling, and
then falls to powder. At a white heat, half the acid of the salt is decom-
posed, forming a mixture of oxide of chromium and neutral chromate of
potassa. When 3 parts of bichromate of potassa are gently heated with 4
of sulphuric acid, potassio-sulphate of chromium is formed, and oxygen
evolved: (KO,2Cr03-|-4(S03,HO) = [KO,S03-f CrA,3SOJ-(-4HO + 30).
Both the chromate and bichromate have a deleterious action on the system
when their solutions are brought much in contact with the skin, causing
sores which are difficult to heal. Paper impregnated with these salts has
photographic properties. The effect of light is to reduce the soluble chromic
acid to the state of insoluble sesquioxide of chromium. The drawing is
fixed by simply removing the unchanged portion of salt by washing in water.
Paper impregnated with the bichromate of potash and dried burns like
tinder, undergoing a species of deflagration. When the bichromate of
ammonia is used, the ash produced is of a dark-greenish black color, and it
assumes the form of dried green tea leaves. Chromic acid is an ozonide,
possessing powerful bleaching properties. When sulphuric acid is added to
it, it forms a mixture in which various substances can be bleached. A
mixture of this kind is used for bleaching phosphorus. They have been era-
ployed for bleaching phosphorus and other substances.

Bichromate of Chloride of Potassium (KCl,2Cr03).— When 2 atoms
of chromic acid and 1 of chloride of potassium are dissolved in hydrochloric
acid, crystals of this salt may be obtained in the form of flat prisms, having
the color of the bichromate. This salt is permanent in the air, and may be
dissolved without decomposition in dilute hydrochloric acid ; but by pure
water it is resolved into hydrochloric acid and bichromate. Similar bichro-
mates of the chlorides of sodium, calcium, magnesium, and ammonium have
been formed.

Chromate OF Soda (NaO,Cr03) crystallizes in oblique rhombic prisms of
a fine yellow color, very soluble in water, and sparingly so in alcohol.

Bichromate of Soda (NaO,2CrO,) is more soluble than the preceding :
it forms prismatic and tabular crystals.

Chromate op Lead (PbO.CrOa).— When chromate of potassa is added

THE SALTS OF CHROMIUM. 447

to any of the soluble salts of lead, a fine yellow powder falls, which is the
neutral chromate : it is insoluble in water, but soluble in nitric acid, and in
solution of potassa : solution of carbonate of potassa fornis with it carbonate
of lead and chromate of potassa. It is decomposed by sulphuric acid, sul-
phate of lead is formed, and chromic acid set free. Native Chromate of
Lead is of a deep orange-red color ; it occurs crystallized in prisms, some-
what translucent and brittle. Specific gravity, 6.

DiCHROMATE OF Lead ; SuBCHROMATE OF Lead, 2(PbO),Cr03, is formed
by digesting the neutral chromate in a dihite solution of caustic potassa; it
is of a scarlet color. These chromates of lead are valuable pigments, and
used both as oil and water colors, and in calico-printing and dyeing. The
mineral called Vauquelinite is a double chromate of lead and copper, having
the formula 2(PbO)CuO,3Cr03. The dark-red mineral, which has been
termed melanochroit, is a sesquichromate of lead, =3PbO,2Cr03.

Protochloride of Chromium (Or CI) is formed by passing hydrogen
over the sesquichloride at a dull red heat, when a white crystalline mass
remains, which at a higher heat fuses, and on cooling presents a fibrous
texture.

Sesquichloride of Chromium (Cr^Clg) is formed along with the proto-
chloride in the process just described : it is also obtained by evaporating to
dryness the hydrochloric solution of the sesquioxide, and heating the residue
intensely in a retort, or in a stream of chlorine ; it forms a crystalline pink
sublimate, which yields a green solution with water.

OxYCHLORiDE OF CHROMIUM; Chromate of Terchloride of Chromium;
Chlorochromic Acid (CrCl3,2Cr03). — This compound is obtained by heating
a mixture of chromate of potassa, chloride of sodium, and sulphuric acid ;
sulphate of potassa and sulphate of soda remain in the retort, and the oxy-
chlorite of chromium distils over': 3(KO,Cr03)+3NaCl-f-6S03=3(KO,803)
-f 3(NaO,S03) + (CrCl3,2Cr03). It is a fuming liquid of a deep red color:
it decomposes water, forming chromic and hydrochloric acids. When passed
through a red hot tube, it is resolved into oxygen, chlorine, and sesquioxide
of chromium: 2(CrCl3,2Cr03) = 3(Cr,03)-f03-+-Cl8.

Terfluoride OF Chromium (CrFg) is obtained by distilling 4 parts of
chromate of lead, 3 of powdered fluor-spar, and 8 of sulphuric acid, in a
platinum retort : the vapor which passes over may be condensed by cold
into a red liquid, which is converted by the moisture of the air into chromic
and hydrofluoric acids : CrF3+3UO, = Cr03+3HF.

Sesquisulphide of Chromium (Cr^^Sa) is formed by passing the vapor of
sulphide of carbon through a red-hot porcelain tube containing protoxide
of chromium : it is of a dark-gray color, and when heated in the air it burns
into oxide. It is a weak sulphur base, and forms a few sulphur salts.

Sulphate of Chromium. — When a solution of 8 parts of hydrated oxide
of chromium in 9 of sulphuric acid is exposed to the air in a covered basin
it concretes in a few weeks into a blue-green crystalline mass; when this is
dissolved in water, and alcohol added, a blue crystalline compound falls,
soluble in about its weight of water at 60° : it consists of Crjj03,3S03,15HO.
With sulphate of potassa it forms a beautiful double salt, which crystallizes,
in green and purple octahedra, and has been termed chrome alum, its formula
being K0,S03, H-Cr203,3S03, + 24HO. It also forms a similar aluminoid
compound with sulphate of ammonia, =NH40,S03+Cr303,3S03,H-24HO.
This blue sulphate, when heated to 212°, becomes green, losing 10 atoms of
water, and though soluble, is no longer crystallizable. If either of these
sulphates is heated to about 700°, a red insoluble anhydrous salt remains
= Cr303,3S03, which, however, by long digestion in water, reverts to the
soluble varieties.

448 VANADIUM AND ITS COMPOUNDS.

Tests for the Compounds of Chromium. — The sesquisalts of this metal
are of various shades of green, blue, or purple, and their solutions are usually
red by transmitted light. 1. With potassa and soda, and their carhonates,
they give green precipitates, soluble in an excess of the precipitant, forming
green solutions, but again thrown down as anhydrous oxide on boiling the
liquid. 2. Ammonia and the hydrosulphate of ammonia throw down a bluish-
green hydrated oxide, partially soluble in excess of ammonia, forming a pink
solution. Carbonate of ammonia acts in a similar manner. The salts of the
protoxide soon absorb oxygen, and are decomposed, or pass into sesquisalts.

The chromates are all deeply colored : they are decomposed when boiled
with deoxidizing agents (grape-sugar, arsenious acid, alcohol, wood-spirits),
and the sesquioxide is formed. A solution of chromate of potassa gives a
characteristic yellow precipitate with the soluble salts of lead, orange with
those of mercury, and red with those of silver. A compound of chromium
fused at a high temperature, with a mixture of carbonate of soda and chlorate
of potassa, forms a soluble chromate of the alkali, producing a yellow solu-
tion in water, which may be tested in the manner above described. Before
the blowpipe, they color borax green in the interior, and yellow or red in
the exterior flame.

CHAPTER XXXIV.

VANADIUM — TUNGSTEN— CO LUMBIUM — NIOBIUM — I LMENIUM
— NORIUM — PELOPIUM— MOLYBDENUM — URANIUM— TELLU-
RIUM—TITANIUM.

Vanadium (Y=68).

This metal was discovered in 1830, and named after Vanadis, a Scandi-
navian deity. It occurs in certain iron and lead ores. Mr. Riley states that
he has found this rare metal in the Wiltshire oolitic iron-ore, and in the pig-
iron, smelted from it. This will yield it readily, as it contains more vanadium
than that obtained from the Taberg ore of Sweden. Vanadium is procured
by decomposing chloride of vanadium by a current of dry ammonia, in a glass
tube heated over a spirit-lamp ; sal-ammoniac sublimes, and metallic vana-
dium remains. It may also be obtained by heating vanadic acid with
potassium.

Vanadium has a silvery lustre, is brittle, and not acted upon by air or
water at common temperatures; at a dull red heat it burns into a black
oxide ; it is not acted upon by'sulphuric or hydrochloric acid, but nitric and
nitrohydrochloric acids yield with it dark-blue solutions.

Oxides of Vanadium. — There are three compounds of this metal with
oxygen ; two oxides, and an acid. — Protoxide of Vanadium ( VO). When
a stream of dry hydrogen gas is passed over heated vanadic acid, water is
formed, and a black substance remains, which is infusible, and which, when
heated in the air, is converted by slow combustion into the binoxide. It is
not salifiable. — Binoxide of Vanadium: Vanadious Acid {YO,^). This is
the only salifiable oxide : it may be obtamed in the state of hydrate, by pre-
cipitation from its acid solutions by carbonate of soda in very slight excess.
It yields blue solutions with the acids, and dissolves in caustic potassa and
in ammonia, forming brown liquids.— Vanadic Acid (VO3). When vanadate
of ammonia is heated in an open vessel it acquires a red color, and leaves

TUNGSTEN AND ITS COMPOUNDS WITH OXYGEN. 449

vanadlc acid: heated in a close vessel, the hydrogen of the anitnonia deoxi-
dizes the acid, and the binoxide is the product. Vanadic acid, when fused,
is red, but when in powder, brown : it fuses at a dull red heat, and in the
act of cooling it contracts in bulk, and becomes incandescent. It undergoes
no change by heat, provided deoxidizing agents are excluded ; but when com-
bustible matter is present it passes into oxide : it is tasteless, insoluble in
alcohol, and nearly* so in water — Vanadates, These compounds are gene-
rally yellow, but sometimes are produced colorless, without apparent change
of composition, and give a blue solution, distinctly opposed to the green of
chromium. The soluble vanadates are deoxidized by alcohol, sulphuretted
hydrogen, and sulphurous acid. Vanadic acid dissolves and forms colored
compounds with the binoxide : they are formed when the binoxide in water
is exposed to air; it gradually forms vanadic acid, and the solution becomes
blue, green, yellow, and red, according to the extent of acidification.

Vanadium combines with chlorine, bromine, iodine, sulphur, and cyanogen.
— Chloride of Vanadium. When dry chlorine is passed over a red-heated
mixture of protoxide of vanadium and charcoal, in a glass tube, a yellow
liquid is obtained, which when acted upon by water yields hydrochloric and
vanadic acids : it is therefore a terchloride (VC1.J. — Sulphide of Vanadium.
By passing sulphuretted hydrogen over the binoxide heated to redness, a
hisidphide if formed. When sulphuretted hydrogen is passed through vana-
dic acid in water, a mixture of hydrated binoxide and sulphur is precipitated ;
but when a solution of vanadic acid in hydrosulphate of ammonia is acidu-
lated by hydrochloric acid, a brown hydrated tersulphide subsides.

Tungsten (W=92).

This metal, called also Wolframium, was discovered in 1781. It derives
its name tungsten from two Swedish words, signifying heavy stone. Its
native' sources are wolfram, which is a tungstate of iron and manganese, =^
MnO,W03, + 3(FeO,W03), and tungstate of lime, CaO.WOg. It is obtained
by passing hydrogen over ignited tungstic acid mixed with charcoal. It is
very difficult of fusion, hard, brittle, and of an iron-gray color. Its specific
gravity is It 6. It is oxidized by the action of heat and air, and by nitric
acid. It is also oxidized and gradually dissolved by a solution of potassa,
with the evolution of hydrogen, and tungstate o{ potassa is produced^ — Oxide
of Tungsten ; Binoxide of Tungsten (WO^). This oxide may be obtained by
mixing finely-powdered wolfram with twice its weight of carbonate of potassa,
and fusing it in a platinum crucible. Tungstate of potassa is thus formed,
which is dissolved in hot water with half its weight of sal-ammoniac, evapo-
rated to dryness, and heated red hot in a Hessian crucible. The mass is
then well washed in boiling water, and digested in a weak solution of potassa.
The residue is oxide of tungsten. Thus prepared, the oxide is black, and
when heated to redness it suddenly ignites and burns into tungstic acid. It
does not combine with acids. When a current of hydrogen is passed over
heated tungstic acid, it is partially deoxidized and converted into a chocolate-
colored oxide, which neither combines with acids nor bases, and which is
identical in composition with the above. If the action of hydrogen be con-
tinued, the oxide itself is reduced.

A compound of this oxide with soda is obtained by adding as much tung-
stic acid to fused tungstate of soda as it will dissolve, and then passing hy-
drogen over the compound at a red heat ; on washing out the undecomposed
tungstate with water, a golden-colored substance remains, in cubes and scales-
of a metallic lustre, and insoluble in caustic alkalies and in nitric, sulphuric,
and nitrohydrochloric acids, but soluble in hydrofluoric acid.
29

459 COLUMBIUM.

TuNGSTic Acid (WO,) is obtained when the oxide is heated red hot, and
stirred in an open vessel. When finely-powdered native tnngstate of lime is
boiled for some hours in nitric acid, tungstic acid is separated, in the form of
a yellow powder, which may be freed from adherinf? nitric acid by dissolving
it in ammonia and heating the tungstate of ammonia to redness. Tungstic
acid is a yellowish powder, insoluble in water, but soluble in the caustic alka-
lies, when in its hydrated state ; after it has been heated it is difficultly acted
upon by solvents, but most of its compounds may be obtained by fusion at a
red heat. The tungstate of soda is employed for the purpose of rendering
cotton and linen unintiammable. The most delicate lace impregnated with
a weak solution of this salt dried and burnt, is converted into carbon without
inflaming.

Chloride of Tungsten (WClg). — When tungsten is heated in chlorine,
it forms a red crystalline compound, fusible, and volatile, which becomes blue
in water. — Perchloride of Tungsten (WCI3). When sulphide of tungsten is
heated in chlorine, it forms a perchloride, which condenses in red crystals.
This chloride is resolved by the moisture of the air into tungstic and hydro-
chloric acids.

Sulphide op Tungsten. — When sulphuretted hydrogen is passsd over
tungstic acid heated highly in a porcelain tube, a black powder is obtained,
which is a bisulphide =WS2.

Characters of the Compounds of Tungsten. — Before the blowpipe,
tungstic acid becomes upon charcoal at first a brownish-yellow, is then reduced
to a brown oxide, and lastly becomes black without melting or smoking.
With microcosmicsalt, in the internal flame, and in small proportion, it forms
a blue-colored-glass ; if iron is present the color is blood-red.

The tungstates of the alkalies are colorless, and form colorless solutions.
When a little hydrochloric acid is added, and a bar of zinc is placed in the
solution, the liquid soon acquires a rich blue color from the production of
oxide of tungsten. The presence of this metal in any mineral may be thus
easily recognized. The substance should be powdered, and fused with four
times its weight of carbonate of soda mixed with some nitre. A soluble
tungstate is thus produced, which may be tested by the process above described.
Mineral acids, excepting the phosphoric, precipitate tungstic acid from solu-
tion of tungstates, in an insoluble form.

CoLUMBiUM (Ta=184).

This metal, called also Tantalum, was discovered in 1801, in a mineral
from North America (Columbia). It was afterwards found in the minerals
called tantalite, yttro-tantalite, and Fergusonite. Columbiura has been obtained
by heating potassium with the potassio-fliwride of columbium, and washing
the reduced mass with water. It remains in the form of a black powder ;
by pressure it acquires the lustre and color of iron ; it burns at a red heat
into whitish oxide. It is insoluble or nearly so, in most acids. Heated to
redness, it burns into columbic acid.

Oxide of Columbium ; Tantalous Acid (TaO^).— When columbic acid is
intensely heated in a charcoal crucible, it is superficially reduced to a metallic
state, but the interior portion is a dark-gray oxide, becoming brown when
pulverized ; it is insoluble in the acids, but may be peroxidized by fusion
with potassa.

Columbic Acid ; Tantalic Acid (TaOg) is obtained by fusing finely-
powdered tantalite with caustic potassa ; a soluble columbate of potassa is
formed, from which columbic acid may be precipitated, as a white hydrate,
by acids. After having been ignited, it is nearly insoluble in acids, but solu-
ble in potassa. The hydrated acid (Ta03,3HO) dissolves in potassa, in

OXIDES OF MOLYBDENUxM. 451

nitric, hydrochloric, hydrofluoric, sulphuric, tartaric, citric, and oxalic acids.
It is dissolved by a solution of birioxalate of potassa, but scarcely at all by
bitartrateof potassa. It is ap:ain precipitated from its acid solutions by alka-
line carbonates. Ferrocyanide of potassium produces a yellow ; infusion of
galls an orange; and the hydrosulphates a white precipitate in the oxalic
solution. Tantalic acid is precipitated by water from its solution in sul-
phuric acid, and when this precipitate is dissolved by diluted hydrochloric
acid, and a bar of zinc is introduced, the liquid at first acquires a blue color,
and afterwards becomes brown. (Will )

Niobium. Ilmenium. Norium. Pelopium. — Among these rare metals,
the two first-mentioned have been announced as associated with colurabium
in some varieties of tantalite, but their distinctive characters have been as yet
very imperfectly ascertained. Niobium is considered by some chemists to be
columbium, while the metal pelopium has no independent existence, the pe-
lopic and niobic acids being identical. Yon Kobell has announced another
metal of this series, to which he has given the name of Dianium. He states
tiiat it exists in the columbite of Tammela, in euxenite, and other minerals.
Rose and St. Clair Deville, who have examined these minerals, affirm that
the supposed dianic acid is hyponiobic acid. Dianium, therefore, is identical
with Pelopium and Columbium {Cosmos, Janvier, 1862, p. 28).
•

Molybdenum (Mo=48).

This metal derives its name from the Greek fio-Kv^^atva (a mass of lead),
owing to the res'emblance of the native bisulphide to lead. It was discovered
in 1782. The bisulphide is its principal ore; there is also a native molyh-
date of lead. To procure molybdenum, the pulverized native sulphide is
roasted in a muffle, so as to burn off the sulphur ; a gray powder remains,
which is digested in ammonia, and the solution filtered and evaporated to
dryness : the dry residue is then dissolved in nitric acid, and again evapo-
rated to dryness, when pure molybdic acid is left. If this be made into a
paste with oil and charcoal, and intensely heated, the metal remains. It
may also be obtained by passing hydrogen over molybdic acid at a red heat
in a porcelain tube.

Molybdenum is a whitish, brittle, and very difficultly-fusible metal ; when
intensely heated in the air, it produces a white crystalline sublimate of mo-
lybdic acid. It forms three compounds with oxygen, two of which are sali-
fiable, and the third an oxide.

Protoxide of Molybdenum (MoO) is obtained by dissolving molybdic
acid in hydrochloric acid, and putting a piece of zinc into the solution : the
liquid changes to blue, red, and black ; excess of ammonia is then added, by
which protoxide of molybdenum is thrown down in the form of a black
hydrate, whilst the oxide of zinc is retained in solution. In the state of
hydrate, this oxide is soluble in the acids, but when anhydrous, it is almost
insoluble. It is not dissolved by the caustic and carbonated alkalies, but
the recently-precipitated hydrate is soluble in carbonate of ammonia.

Deutoxide of Molybdenum (MoOJ. — This oxide is obtained by heating
a mixture of sal-ammoniac and molybdate of soda in a platinum cruoible
until the fumes cease: the residue is well washed, digested in caustic potassa
to separate any molybdic acid, and again washed with boiling water. The
oxide remains in the form of a black powder, becoming dark-brown when
dry, and purple when exposed to the sun's rays. Although zinc reduces
molybdic acid to the state of protoxide, copper only brings it down to deut-
oxide; if therefore, copper, molybdic acid, and hydrochloric acid are put
together, the molybdic acid disappears, and the liquid, which contains the
chlorides of copper and molybdenum, acquires a deep-red tint. When au

452 MOLYBDIC ACID. MOLYBDATES.

excess of ammonia is added to the liquid, the dentoxide of molybdenum is
thrown down, and the oxide of copper is retained in solution ; the precipi-
tate is cleansed by washing with solution of ammonia, and when carefully
dried in vacuo over sulphuric acid, is the hydrated deutoxide. It is brown,
slightly soluble in water, and insoluble in saline solutions and in caustic
alkalies, but soluble in their carbonates. When heated in vacuo, it becomes
dark brown, and loses its solubility.

Molyhdous Acid. — When metallic molybdenum and molybdic acid are
boiled together in water, a blue solution is formed, which has sometimes
been termed molyhdous acid, and regarded as a distinct stage of oxidation,
but which appears to be a compound of molybdic acid with the deutoxide,
and consequently a molybdate of oxide of molybdenum =Mo02, + Mo03.
When a current of hydrogen is passed over molybdic acid at a dull red heat,
it acquires a blue color, and becomes converted into molyhdous acid. Tliis
compound is soluble in water, and yields a rich blue solution, which becomes
colorless on moderate dilution: it is insoluble in a solution of sal-ammoniac;
it is immediately converted into molybdic acid by nitric acid and chlorine;
and, on the other hand, deoxidizing agents, such as protochloride of tin, or
tin filings and hydrochloric acid, convert molybdic acid into this blue com-
pound.

Molybdic Acid (M0O3) The production of this acid has alreai^r been

described. It is a white, difl&cultly-soluble powder. Heated to redness in
an open vessel, it slowly sublimes, and condenses in yellowish scales. It
dissolves in hot sulphuric acid, forming a solution which is colorless while
hot, but on cooling acquires a blue color, which is heightened by the addi-
tion of soda. Its hydrochloric solution is pale yellowish-green, but becomes
blue when neutralized by potassa. It dissolves in the alkalies, forming solu-
tions which are colorless, and from which the molybdic acid is at first pre-
cipitated, but afterwards dissolved, by the stronger acids. It unites with
bases and forms neutral and acid salts. The molybdic acid has been lately
recommended by F. Frohde as a more reliable test for morphia than nitric
acid. The molybdic acid is dissolved in strong 'sulphuric acid, and a drop
of this solution is added to morphia or any of its salts (in a dry state), when
a violet color is produced; this passes to a blue, aud afterwards to a dingy
green, leaving a nearly colorless spot.

Molybdate of Ammonia (NHp,Mo03). — This salt is obtained by dis-
solving molybdic acid in excess of ammonia, and leaving it to spontaneous
crystallization : it forms square prisms, of a pungent metallic taste. When
the ammoniacal solution is boiled down, it atfords, on cooling, a crystalline
mass of himolyhdate of ammonia, which, by spontaneous evaporation, may be
obtained in rhombic crystals of a pale bluish-green color, and difficultly solu-
ble in water. A solution of this salt is occasionally employed as a test for
phosphoric acid. The suspected solution of phosphate is acidulated with
nitric acid, and the molybdate is then added. If a phosphate is present
the liquid becomes yellow, and in boiling it a yellow crystalline precipitate
is obtained, the insoluble phospho-molybdate of ammonia. The phospho-
molybdic acid is used as a precipitant for the alkaloids, but it has no advan-
tage over the iodo-hydrargyrate of potash, which does not form an insoluble
compound with ammonia, or precipitate that alkali.

Protochloride of Molybdenum (MoCl).— When the vapor of bichloride
of molybdenum is passed over molybdenum heated nearly to redness, a deep
red compound is obtained, which yields a crystalline sublimate when heated
in an open tube : it is insoluble in water, but is decomposed by a solution of
potassa, yielding hydrated protoxide of molybdenum. This chloride forms
double salts with sal-ammouiac and with chloride of potassium.

• TESTS FOR TFIE SALTS OF MOLYBDENUM. URANIUM. 453

Bichloride of Molybdenum (MoClo) is formed by heatin/? metallic mo-
lybdenum in dry chlorine; the metal burns, and a red vapor fills the retort,
which condenses into crystals resembling iodine ; they are fusible, volatile,
and in the air first fume, and then deliquesce into a black liquid, which
changes color in proportion to the water it absorbs, becoming blue-green,
green-yellow, dark red, rose-colored, and lastly, yellow. This chloride forms
a double ammonio-chloride of molybdenum with sal-ammoniac, but does not
combine with the chlorides of potassium or sodium.

Chloromolyhdic Acid. — When a current of chlorine is passed over gently-
heated binoxide of molybdenum, a yellowish crystalline sublimate is formed,
and molybdic acid remains in the tube: this compound is less volatile than
the bichloride. It readily dissolves in water, and alcohol. It is a com-
pound of molybdic acid with perchloride of molybdenum =MoCl3,2Mo03.

There are three Sulphides of Molybdenum, two of which correspond
with the deutoxide and with molybdic acid, and the third contains 4 equiva-
lents of sulphur ; no protosulphide corresponding with the protoxide has
been formed. — Bisulphide of molybdenum (MoS^) is produced artificially by
intensely heating a mixture of molybdic acid and sulphur, out of the contact
of air. It forms the native sulphide. — Tersulphide of Molybdenum (M0S3) is
obtained by saturating a strong solution of a molybdic salt with sulphuretted
hydrogen, and then adding hydrochloric acid; a dark-brown precipitate
falls, which becomes black on drying, and which, when heated in close
vessels, gives off sulphur, and becomes bisulphide. The sulphide combines
with the sulphides of the alkaline bases, and produces a class of sulphur-
salts, which may be called molybdo-tersulphides, some of which form beautiful
iridescent crystals. — Persulphide of Molybdenum (MoS^) is obtained by satu-
rating bimolybdate of potassa with sulphuretted hydrogen, and boiling the
solution for some hours in a retort : when it cools, a black powder and red
scales are deposited, which must be separated as far as possible : the red
deposit is then washed upon a filter with water, till the washings no longer
afford a red (not a brown) precipitate with hydrochloric acid ; the residue
upon the filter is then treated by boiling water, and the dark-red solution
which filters through is decomposed by excess of hydrochloric acid : a brown
precipitate falls, which, when washed and dried, is the quadrisulphide.

Tests for the Salts of Molybdenum. — 1. The protosalts give brown
precipitates with the alkalies and their carbonates, soluble in excess of car-
bonate of ammonia, but not of the alkali. 2. Sulphuretted hydrogen gives
a brown precipitate, soluble in hydrosulphate of ammonia. 3. The salts of
the deutoxide give brown precipitates with ammonia, and with ferrocyanide
of potassium. 4. The molybdates are characterized by the blue color pro-
duced on the addition of a few drops of protochloride of tin, and by the blue
color produced by zinc in their solutions, when acidulated with hydrochloric
acid. This, after a time, becomes green, and ultimately black. When a
mineral containing molybdenum is fused with carbonate of soda and nitre, a
soluble molybdate of the alkali is obtained. Molybdic acid is precipitated
from its solutions by a mineral acid, but the precipitate is soluble in an ex-
cess of the acid. This forms a distinction between the molybdic and tungstic
acids. The oxides of molybdenum give to microcosmic salt in the inner
flame of the blowpipe a green color, and to borax a brown-red color.

Uranium (XJ==60).

Uranium (named from the planet Uranus) was discovered in 1789, in a
mineral called pitchblende, which is an impure oxide, and from which the
metal and its compounds are almost exclusively obtained. It also occurs, in
the form of a double phosphate of lime and uranium, in uranite, a rare mica-

454 SALTS OF URANIUM.

ceons mineral ; and in a similar mineral of a green color, called chalcolite, in
which the lime is replaced by oxide of copper.

Uranium is obtained by the decomposition of its chloride by sodium, the
process being similar to that by which majGrnesium is obtained : it is white,
slightly malleable, and unchanged by air and water at common temperatures;
when heated in air, it undergoes combustion and is converted into an oxide.

Oxides of Uranium. — Uranium forms four oxides — namely, a protoxide,
a sesquioxide, and two intermediate oxides. — Protoxide of Uranium (^0)
is formed by heating the peroxalate out of contact of air : it is brown, and,
when in the state of hydrate, dissolves in the acids, forming green salts.
"When heated to redness, and suddenly cooled, it becomes the hlack oxide
(U4OJ, which is used in porcelain painting for the production of an intense
black. — Green Oxide of Uranium (U3O4) is obtained by evaporating an
ethereal solution of nitrate of uranium, and exposing the residue to a red
heat. — Per or Sesquioxide of Uranium (U2O3). Uranium and its inferior
oxides pass into peroxide when acted upon by nitric acid, forming a yellow
solution, from which the alkalies throw down compounds of the peroxide
with the precipitants. A pure hydrate of the peroxide nray, however, be
obtained by evaporating the alcoholic solution of the pernitrate until it
effervesces in consequence of the escape of nitrous ether; the yellow residue,
washed first with cold and then with hot water, leaves the hydrate, assuming,
when dried at 212°, the form of a yellow powder =UyO.„HO, but if dried in
vacuo =U20o,2HO. At a high temperature (about 570°) it becomes anhy-
drous, and afterwards loses oxygen, and leaves a brown mixture of protoxide
and green oxide : in its anhydrous state it is red.

The salts of the peroxide of uranium are best formed by the action of
nitric acid upon the salts of the lower oxides. They are yellow, and mostly
soluble in water, and are reduced to protosalts by sulphuretted hydrogen,
and by alcohol and ether under the influence of solar light. Peroxide of
uranium unites to bases ^oxxnmg uranates ; those of the alkalies are obtained
by precipitating the uranic salts with them. The uranates of baryta, lime,
and magnesia are formed by mixing their salts with those of the uranic oxide,
and adding ammonia, but a portion of uranate of ammonia in these cases
goes down with them. They are yellow or orange-colored compounds.

Nitrate of Uranium (U203,N05,6H0). — This is the common crystallized
nitrate of uranium obtained by evaporating the nitric solution of any of the
oxides: it forms yellow prisms, efflorescing in a warm atmosphere into a ter-
hydrate. When heated it fuses in its water of crystallization, becoming
orange-colored ; and at a red heat leaves green oxide. It is very soluble in
water, alcohol, and ether. When its alcoholic solution is gently heated, it
effervesces and evolves nitrous ether, depositing hydrated peroxide. Its
ethereal solution, exposed to the sun's rays, deposits green oxide, nitrous
ether, and a green solution of protoxide being at the same time formed.
When crystallized nitrate of uranium is carefully heated until it becomes
orange-colored, a yellow insoluble subnitrate separates : this, at a red heat,
passes first into UgO^, and then into UyOg. This solution sometimes con-
tains lead as an impurity; this will affect the action of tests. The ammonio-
nitrate of uranium is of a golden-yellow color, soluble in boiling water with
loss of ammonia, but not very soluble in cold water. It is easily dissolved
by diluted nitric acid when heated. The solution is rendered pale by an
excess of acid.

The nitrate of uranium has been employed, under the name of Wothlytype,
for taking photographic drawings. Paper impregnated with a strong solu-
tion of this salt (I part to 5 parts of distilled water) is dried and exposed in
the usual manner. After several minutes' exposure in direct sunlight, a not

TESTS FOR THE SALTS OF URANIUM 455

very vigorous imajye is obtained. Tt is subsequently developed by the use of
a silver or gold developer, and fixed by simply washing the drawing in
water. The advantages of this process are said to be that it dispenses with
the use of hyposulphite of soda or any chemical fixing agent. It is to be
observed, however, that either silver or gold is employed for the necessary
purpose of developing the images, and it is well known to be extremely
difficult to remove these metals entirely from the tissue of paper except by
the aid of some chemical solvent.

pROTOCHLORTDE OF Uranium (UCl) IS obtained by passing dry chlorine
over a mixture of oxide of uranium with one-fourth its weight of carbon
heated to redness in a porcelain tube : red vapors of the chloride are formed,
which condense into dark-green crystals : they dissolve rapidly in water,
furnishing a dark-green solution, and, when exposed to air, evolve fumes of
hydrochloric acid.

Sulphates of Uranium. — A sulphate of protoxide of uranium (UO.SOg)
is formed by adding sulphuric acid to the concentrated aqueous solution of
the protochloride : it forms green hydrated crystals, which do not become
anhydrous till so highly heated as to begin to lose acid, and which, in a large
quantity of water, are resolved into a green acid solution, and a deposit of
basic sulphate =2(XJO),S03,2HO, when dried in vacuo. This salt forms a
crystallizable double sulphate with sulphate of ammonia =NH^0,S03,+
U0,S03. Sulphate of green oxide of uranium is formed by dissolving the
green oxide in sulphuric acid, and expelling the excess of acid by heat : it is
a pale-green mass =1X30^,2803. When heated to redness it evolves sulphu-
rous acid, and leaves a pale yellow sulphate of the peroxide : 2(1X30^,2803)
^8(1X203,803) + 80^. Sulphate of peroxide of uranium (1X303,803) is ob-
tained by oxidizing the solution of the green oxide in sulphuric acid by nitric
acid, or by adding sulphuric acid to a solution of the nitrate, evaporating to
dryness, so as to expel the excess of acid, dissolving the residue in water,
and concentrating the solution by evaporation to the consistency of syrup; it
is slowly and difficultly crystallizable in small yellow prisms =IX,^03S03,3HO:
dried at 212°, they lose 2 atoms of water, and become anhydrous at 600°.
A phosphate and carbonate of the peroxide of uranium may be obtained by
double decomposition. There is also an ammonio-phosphate, which is very
insoluble.

Tests for the Salts of Franium The salts of the peroxide form yellow

solutions ; an excess of acid renders them pale. 1. Sulphuretted hydrogen
produces no precipitate. 2. Hydrosulphate of ammonia throws down a dark-
brown sulphide. 3. Potassa or ammonia throws down an orange-yellow:
uranate, insoluble in an excess of the reagent, and in hydrochlorate of
ammonia. 4. Alkaline carbonates (soda and potassa) give a pale yellowish-
green precipitate, not soluble in an excess. The precipitate is dissolved by
alkaline bicarbonates, and by carbonate of ammonia, but is re-deposited on
boiling the liquid. 5. Ferrocyanide of potassium gives a deep red-brown
precipitate, or color : ammonia destroys this color, forming a nearly colorless
liquid. The color of the precipitate closely resembles that which is produced
in a solution of copper ; but the ferrocyanide of copper, dissolved by am-
monia, produces a blue liquid. This furnishes a sufficient distinction between
the two metals. The carbonate of an alkaline earth (baryta) precipitates
the sesquioxide of uranium from its solutions as it does the sesquioxide of
iron. With borax the oxide gives, under the blowpipe, a bead which is
green in the inner and yellow in the outer flame. With microcosmic salt the
color from the outer flame is yellow-green.

Peroxide of uranium is used to give a yellow or a greenish yellow color
to glass. The green oxide is employed to produce a black color on porce-

456 TELLURIUM AND ITS COMPOUNDS WITH OXYGEN.

lain. The protosalts of urauium are green, and are rapidly converted into
yellow persalts either by exposure to air, or by the action of nitric acid.

Tellurium (Te=G4).

Tellurium was discovered in 1T82. It derives its name from tellus, the
earth. Its ores are rare, and generally contain it in combination with other
metals, especially with gold, silver, lead, copper, and bismuth.

Tellurium is of an iron-gray color, hard, brittle, fusible at a temperature
a little above melting lead, and volatile at a full red heat, its vapor condens-
ing in metallic-looking opaque globules in- the cold part of the tube. The
vapor is yellow, resembling that of selenium. It is partially oxidized and
converted into a white uncrystalline oxide, which is deposited around the
condensed globules of the metal. It gives a metallic ring resembling some-
what that of arsenic ; but it is so much less volatile than arsenic, that it re-
quires for its volatilization, the full heat of Bunsen's jet. Its oxide is not
deposited in transparent octahedral crystals. When warmed with sulphuric
acid, it imparts to that liquid a splendid amethyst-red color, which is not
permanent. If heated on platinum it rapidly melts, combines with, and de-
stroys that metal, forming a very fusible crystalline alloy. When heated on
mica, it melts and burns with a bluish flame, having a greenish margin, and
it evolves a thick white acid smoke. The color of the flame resembles that
of selenium, but has a greenish tint. It traverses a solution of indigo, giving
a pale blue light. Although closely resembling selenium, yet it difters in
readily forming a fusible alloy with platinum, and in evolving no reddish-
colored fumes when heated in air. Its sp. gr. is 6*2 to 6*8. It is crystalli^
able, and, for a metal, it appears to be a bad conductor of heat and electricity :
indeed, it may be said, in some respects, to form a connecting link between
sulphur or selenium and the metals. By some chemists it is placed among
the metalloids, between selenium and phosphorus.

BiNOXiDE OF Tellurium ; Tellurous Acid (TeOg). — Exposed to heat and
air, tellurium fuses and burns, exhaling a peculiar sour odor, and forming a
white oxide. This oxide is thrown down as a white hydrate when a recently
made solution of tellurium in nitric acid is poured into water. In its anhy-
drous state it is difficultly soluble, but when hydrated, it readily dissolves in
most of the acids, forming colorless solutions of a nauseous 'metallic taste :
they afford metallic tellurium in a black powder when acted on by phospho-
rous acid, or sulphurous acid, as well as by zinc, iron, tin, lead, copper, and
some other metals. Most of the solutions of this oxide in the mineral acids
are decomposed by copious dilution with water, provided there is no great
excess of acid; with the alkalies and their carbonates they give precipitates
of hydrated oxide soluble in excess of the precipitant, especially when aided
by heat: they are precipitated white by phosphate of soda; dark-brown by
sulphuretted hydrogen and alkaline hydrosulphates ; and yellow by tincture
of gall ; they are not affected by ferrocyanide of potassium, nor by oxalic
acid. The basic combinations of tellurous acid, or tellurites, are obtained :
1. by dissolving the hydrated acid in the alkalies; 2. by double decomposi-
tion ; or 3. by fusion. The alkaline tellurites are soluble in water : those of
baryta, lime, and strontia with difficulty ; most of the other compounds are
insoluble in water; but they are nearly all soluble in hydrochloric acid.

Peroxide of Tellurium ; Telluric Acid (TeOg) may be obtained by pass-
ing chlorine through the solution of tellurous acid in excess of potassa till
it is fully saturated, and the first precipitate is redissolved. The filtered
liquor is then neutralized by ammonia, and chloride of barium added, which
occasions a precipitate of tellurate of baryta; this, digested with a fourth of
its weight of sulphuric acid (diluted with water), yields a solution, which,

TESTS FOR THE SALTS OF TELLURIUM. 457

when filtered and carefully evaporated, affords crystallized hydrated telliirio
acid =TeO.„3IiO, from which adherin<^ sulphuric acid may be removed by
alcohol. This hydrate loses its water by heat, and the anhydrous ncid, of a
lemon-yellow color, remains. This acid is readily procured as a tellurate by
fusinj::^ tellurium with nitre, and when this is calcined with charcoal and car-
bonate of potassa, telluride of potassium is obtained. Anhydrous telluric
acid is insoluble in water ; but the crystallized acid dissolves in boiling water.
When boiled with hydrochloric acid it forms tellurous acid, and like selenic
acid, sets free chlorine (p. 232). Dried at 320°, the crystals lose 2 atoms of
water, and become anhydrous at a temperature a little below redness. The
tellurates of the alkalies are moderately soluble in water ; those of the alkaline
earths are sparingly soluble; and many of the other tellurates are insoluble.
When tellurium is heated in chlorine it burns, forming a dark liquid, which
by an excess of chlorine becomes yellow, and concretes on cooling into a
white deliquescent crystalline bichloride, =TeCl3. If this is heated witjj
pulverized tellurium, a dark purple protochloride is formed, =TeCl, more
volatile than the bichloride, and giving a vapor resembling that of iodine.

Telluretted Hydrogen (TeH). — When an alloy of tellurium and tin, or
zinc is acted on by hydrochloric acid, telluretted hydrogen gas is evolved ; it
reddens litmus, dissolves in water, and possesses the general properties of
sulphuretted hydrogen, which it also resembles io odor. Its sp. gr. is 4*48.

There appear to be two sulphides, which act as sulphur acids ; they are
obtained by the decomposition of tellurous and telluric acids by sulphuretted
hydrogen.

. Tests for the Compounds op Tellurium The solutions of tellurium in

mineral acids are decomposed by the immersion of zinc, tin, lead, copper, or
cadmium, and the metal is precipitated in the form of a black powder. Tel-
lurous acid and its salts are decomposed when an excess of hydrochloric
acid is present, by boiling them with sulphurous acid, or alkaline sulphites,
by protosulphate of iron, and protochloride of tin, which occasion a brown
or black flocculent precipitate of tellurium. Sulphuretted hydrogen throws
down a black bisulphide of tellurium, which is soluble in hydrosulphate of
ammonia. The telluride of potassium procured by the method above de-
scribed blackens silver and evolves telluretted hydrogen when treated with
acids.

Titanium (Ti=24).

Titanium was first detected in a mineral, found in the form of a black sand,
in the vale of Menachan, in Cornwall, consisting of the oxides of titanium
and iron. In the state of titanic acid it exists in the minerals called Rutilite,
Anatase, and Oysanite. Titanite is a silicate of titanium and lime : it occurs
in quartz and granite, and it sometimes transverses rock-crystal in brown
hair-like filaments. Titanium, as titanic acid, is frequently found in clays
and sands, associated with silica and oxide of iron. It is also found in the
slags of some iron furnaces ; they contain small copper-colored cubic crys-
tals, of a sp. gr. of 5'3 ; insoluble in the acids, but oxidized by fusion with
nitre. They appear to be a combination of nitride with cyanide of titanium,
and contain about 18 per cent, of nitrogen and 4 of carbon. Another
nitride is obtained in form of copper-colored scales by passing ammonia
over the ammonio-chloride of titanium heated to redness. These nitrides
were formerly regarded as pure titanium. To obtain titanium, the potassio-
fluoride is decomposed by potassium, when the metal remains in the form of
gray particles, which burn brilliantly if heated in oxygen.

Protoxide of Titanium (TiO). — When titanic acid is subjected to a
white heat in a charcoal crucible, it is superficially reduced: but the interior

458 TITANIUM AND ITS COMPOUNDS WITH OXYGEN.

is in the state of a black powder, which is the protoxide. When a plate of
zinc is immersed in a solution of chloride of titaiiinm, a purple powder is
obtained, which is a hydrated sesquioxide (Ti.^O^.HO).

Peroxide of Titanium ; Titanic Acid (TiOg) may be obtained from riiti-
lite, by fusing it, in fine powder, in a platinum crucible, with thrice its weight
of carbonate of potassa : a gray mass is obtained, which, after having been
washed with water, is dissolved in hydrochloric acid, and on diluting with
water, and boiling the solution, the greater part of the titanic acid is pre-
cipitated; it may be collected and washed with very dilute hydrochloric acid.
The acid is more perfectly precipitated by adding sulphite of soda and
boiling the liquid. Titanic acid is white, infusible, and very difficult of
reduction : its sp. gr. is 3 93. When calcined it becomes yellow, and is then
dissolved only by concentrated hydrofluoric or sulphuric acid. When recently
precipitated, it dissolves in some of the acids, but becomes nearly insoluble
aJ'ter it has been ignited ; and like oxide of tin, it is susceptible of two iso-
meric modifications. When its solution in hydrochloric acid is heated to the
boiling-point, a part of the titanic acid is thrown down ; but by slow evapo-
ration a soluble chloride remains. It is precipitated by the pure and carbo-
nated alkalies, including ammonia and its carbonate, in a gelatinous form :
infusion of galls and ferrocyanide of potassium throw it down of a charac-
teristic red-brown color, and the precipitate is soluble in an excess of the
solution of the ferrocyanide. Sulphuretted hydrogen produces no precipi-
tate in the hydrochloric solution. Titanic acid which has been rendered
yellow by ignition is sometimes used in enamel and porcelain painting, to
give a yellow color. Titanic acid is thrown down from its solution in hydro-
chloric acid, by alkalies arid the alkaline carbonates, and the precipitates are
insoluble in an excess of the reagents. The precipitates are, however, dis-
solved by strong acids.

Bichloride of Titanium (TiCl.^) is obtained bypassing dry chlorine over
metallic titanium, or over a mixture of titanic acid and charcoal heated to
redness. It is a dense, transparent, and colorless fluid, fuming when exposed
to air. It boils at 277^ ; the density of its vapor is 6'836. With a small
quantity of water it forms a crystalline hydrate, which, by the further addi-
tion of water, deposits titanic acid.

BiFLuoRiDE OF TiTANiuM (TiFg). — Titanic acid readily dissolvcs in hydro-
chloric acid. When this solution is saturated with potassa and evaporated,
a titanofiuoride of potassium is the result.

Bisulphide of Titanium (TiS^) is obtained by passing the vapor of sul-
phide of carbon over ignited titanic acid. It has a dark-green or bronze
color, and a metallic lustre.

None of the other metals appear so to combine with titanium as to form
definite alloys ; but when it is blended with some of them by fusion, it is
susceptible of oxidation, and is then soluble in acids which do not otherwise
act upon it.

Tests for the Salts of Titanium. — Titanium is not thrown down in the
metallic state by any other metal. The orange-red precipitate, which its
solutions afford with infusion of galls and with ferrocyanide of potassium,
is very characteristic. When titanic acid is fused on charcoal with carbonate
of soda and cyanide of potassium, it does not, like tin, yield any metallic
globule. In ordinary analyses of silicates, titanic acid is liable to be pre-
cipitated with, and estimated as, oxide of iron, or to be weighed as silica.
The best method of separation is probably the following : Fuse the mineral
containing titanic acid with four times its weight of carbonate of soda, and
remove all that can be dissolved by cold water. The residue will be a
titanate of the alkali and oxide of iron. Digest this in concentrated hydro-

ANTIMONY AND ITS COMPOUNDS WITH OXYGEN. 459

chloric acid, by which the iron and titanic acid are dissolved ; then boil the
sohition, diluted with water, with sulphite of soda — titanic acid alone is pre-
cipitated. This may be redissolved in hydrochloric acid, and a bar of zinc
introduced into the liquid. If titanic acid is present, it is reduced to the
8tate of sesquioxide, which is dissolved, and p^ives a blue color to the liquid.
By a continuance of the action it is still further reduced, and the oxide of
titanium is precipitated as a violet-colored powder.

CHAPTEE XXXV.

Antimony (Sb = 129).

Antimony, or stibmm, was first made known towards the end of the fif-
teenth century. It is found native, but its principal ore is the sulphide, the
stibium of the ancients. Antimony is obtained from the sulphide by mixing
8 parts of it in fine powder, with 6 of tartar, and 3 of nitre, and pro-
jectiuf^ it by spoonfuls into a red-hot crucible. The sulphur is oxidized by
the nitre, and the metal collects at the bottom. If the metal is required
perfectly pure, the p-ure oxide must be reduced by charcoal.

Antimony is of a bluish-white color, brittle, and crystalline, so that when
broken it exhibits splendid facets, and the surface of the ing;ot as it has
cooled in the crucible is often stellated. It fuses at about 1160^, or at a dull
red heat : it is slowly volatile at a white-heat and in the absence of air, but
in a stream of hydrop:en it'may be distilled. Itssp. gr. is 6-7. Placed upon
ignited charcoal, under a current of oxygen, antimony burns with great bril-
liancy, throwing off a dense yellow smoke ; and if a globule of the intensely-
heated metal be thrown upon the floor, or upon a black board, it subdivides
into numerous smaller globules, which burn as they roll along, and leave a
series of white or yellowish lines of oxide. The metal is not dissolved by-
hydrochloric acid, but readily by nitrohydrochloric acid. It is oxidized
when heated with nitric acid, leaving a white residue, insoluble in nitric but
soluble in tartaric acid.

Antimony and Oxygen. — There are two well-defined compounds of anti-
mony with oxygen, a ternxide, SbOg, and antimonic acid, SbOg. A third
oxide is sometimes described under the name of antimonioits acid, SbO^, but
it should rather be regarded as an antimoniate of oxide of antimony (SbOg,
SbO,).

Teroxide of Antimony (SbOg) is formed by heating the metal in air to
its point of combustion, when the vapor burns with a bluish flame ; and by
placing the crucible in an inclined position, acicular crystals of the oxide
are deposited in its. upper part, fornaing ih^fiores antimonii And nix stihii of
the older chemists. It may also be formed by adding 50 parts of finely-
powdered metallic antimony to 200 of sulphuric acid, boiling the mixture to
dryness, and washing the dry mass, first in water, and then in a weak solution
of carbonate of soda : a white powder remains, which, when thoroughly
washed with hot water, is the teroxide. Teroxide, or, as it is sometimes
called, protoxide of antimony, is white, fusible, and volatile at a high red
heat, undergoing no change in close vessels, but condensing in acicular and
octahedral crystals ; after fusion it concretes into a silky crystalline mass :
if air be present, it burns like tinder, and passes into a higher state of oxida-
tion. It is soluble in hydrochloric and tartaric acids, and it forms emetic

#

460 ANTIMONIOUS AND ANTIMONTC ACIDS,

tartar when boiled with a solution of bitartrate of potassa. It occurs native^
forming: the white ore of antimony.

Teroxide of antimony forms compounds with many bases, and in various
atomic proportions : most of them are decomposed by water, which becomes
milky from the deposition of a subsalt. These compounds have been termed
antimonites. The teroxide is precipitated from its solution in hydrochloric
acid by potassa as a white hydrate, which is dissolved by an excess of the
alkali. If to this alkaline liquid, nitrate of silver is added, a black antimo-
nide of silver (Agg.Sb), quite insoluble in ammonia, isthrovyn down. When
chloride of gold is added, there is a dark purple precipitate of reduced gold.
The teroxide, when heated in a reduction tube, melts into a yellow liquid,
and is only partially volatilized in octahedra by the heat of a spirit-lamp.
The analogous compound of arsenic is entirely volatilized in brilliant octa-
hedral crystals without melting.

Antimonious Acid, or Antimoniate of Antimony (SbOgSbOj, or 2Sb04),
is the result of the above-mentioned combustion of the protoxide : it is also
obtained by exposing antiraonic acid to a red heat. It is white in its ordi-
nary state ; and it is fixed and infusible in the fire. It is thus distinguished
from the teroxide. It also differs from this oxide in being less soluble in
hydrochloric acid. Antimonious acid differs from antimonic acid by its re-
mainiug white when heated in a close vessel or tube, and by its not evolving
oxygen under these circumstances.

Antimonic Acid ; Peroxide of Antimony (SbOj) is procured by acting
for a considerable time upon the finely-powdered metal by an excess of hot
nitric acid, and exposing the product to a heat not exceeding 500^. It is
of a pale yellow color, tasteless, and insoluble in water. It neither fuses nor
volatilizes at a bright red heat, but loses oxygen, and becomes antimonious
acid. It does not decompose the alkaline carbonates in the humid way, but
at a red heat it expels their carbonic acid, and combines with the base. It
dissolves, but not readily, in a boiling solution of caustic potassa, from which
it is thrown down by an acid in the form of a white hydrate, SbOs,4HO.
In this state it reddens litmus and dissolves in hydrochloric acid, and in the
alkalies. In the anhydrous state it is only partially dissolved by hydro-
chloric acid. An acid solution of this oxide is precipitated by a current of
sulphuretted hydrogen, as an orange-yellow pentasulphide of antimony. No
precipitate is produced by this gas in an alkaline solution of hydrated anti-
monic acid ; and if free from teroxide it does not reduce the salts of silver
and gold.

Antimoniates. — Antimonic acid in combination with bases forms neutral
and acid salts. Antimoniate of potassa is formed by heating 1 part of pow-
dered metallic antimony with 4 of nitre, in an earthen crucible, and washing
the pulverized product with water. Its formula is 2(KO),Sb05. When this
salt is boiled for some hours in water, it is partly converted into a soluble
hydrated antimoniate, and an insoluble hiantimoniate =KO,2Sb05. A solu-
ble biantimoniate, supposed to contain a modified acid {metantimonic acid),
is obtained by deflagrating antimony with nitre, washing, and boiling the
product so as to convert it into the state of soluble antimoniate, and evapo-
rating this solution in a silver basin to the consistence of syrup : caustic
potassa is then added, and the evaporation is continued till a drop of the
solution, placed upon a cold piece of glass, crystallizes ; it is then set aside
to cool, and the crystallized salt dried upon a porous tile. This himetanti-
moniate of potassa has the formula KO,HO,Sb03=6Aq. It has been used
as a test for soda, with which it furnishes an insoluble precipitate ; but its
indications are very uncertain, and the test itself, when kept for a few days in
solution, passes into the neutral antimoniate, which does not precipitate soda.

ANTIMONIURETTED HYDROGEN. 4G1

The insoluble himetnntimoniate of sodaH represented as ]S'aO,HO,Sb03,(>Aq.
Considerable uncertainty hangs over the nature of these modifications of the
antimonic acid and the antimoniates, the difference in their properties pro-
bably depending upon peculiarities of molecular constitution, which confer
distinct characters upon compounds similarly constituted.

Antimony and Hydrogen. — Antimonurettedhydrogen yas (SbHg) is formed
by the action of dilute sulphuric or hydrochloric acid on an alloy of zinc and
antimony; or by adding an acid solution of oxide of antimony to zinc. The
gas is colorless, nearly inodorous (if free from arsenic), and is decomposed
when passed through a tube heated to dull redness, depositing a brilliant
coat of metallic antimony. It burns in the air with a pale greenish-white
flame, producing a white smoke consisting of oxide of antimony, and if the
flame be in contact with glass or porcelain, metallic spots are formed some-
what resembling those produced by a similar combustion of arseniuretted
hydrogen. It instantly decomposes the salts of silver, precipitating a black
antimonide of silver (SbIl3+3AgO=Ag3Sb-|-3HO), but it produces no
change of color in paper impregnated with a solution of a salt of lead. In
contact with water the gas rapidly undergoes decomposition, and deposits
metallic antimony in the form of a black powder. {See Arsenuretted Hy-
drogen, p. 472.)

Antimony and Chlorine ; Terohloride op Antimony (SbClg). — Anti-
mony takes fire when thrown in fine powder into gaseous chlorine, and a
mixed chloride is formed with combustion. The terchloride is usually ob-
tained by the distillation of 3 parts of powdered metallic antimony with 8 of
corrosive sublimate (Sb + 3HgCl = SbCl3,-|-3Hg), or by dissolving oxide of
antimony in hydrochloric acid, and evaporating to dryness out of the contact
of air. It is a soft solid at common temperatures, but becomes liquid by a
gentle heat, and crystallizes as it cools. It is the butter of antimony of old
writers. It deliquesces by exposure to air. When water is added to it a
mutual decomposition ensues, and hydrated oxychloridc of antimony and
hydrochloric acid result (6SbCl34-15HO=15HCl + SbCl3,5Sb03). This
white basic compound resembles that of bismuth in its mode of production
and insolubility. It is distinguished from the bismuthic precipitate by its
being entirely dissolved by tartaric acid.

Perchloride of Antimony ; Pentachloride of Antimony (SbClg), is
formed by passing dry chlorine over heated antimony, or by exposing the
terchloride to a stream of dry chlorine. It is a volatile transparent liquid,
which emits fumes when exposed to air. When heated it becomes terchlo-
ride by the evolution of chlorine. By exposure to air it becomes a crystalline
hydrated perchloride, vi\nQ\i\% deliquescent and soluble without decomposition
in hydrochloric acid. — Oxychloride. When chloride of antimony is mixed
with a large quantity of water, a precipitate falls, (5(Sb03)SbCl3) which was
formerly used as an emetic, under the name of AlgarottVs poivder, or Mercu^
rius vitae. The same compound is formed on diluting a solution of antimony
in nitro-hydrochloric acid. When first thrown down it is white and curdy,
but afterwards assumes a yellowish-gray color and becomes pulverulent or
crystalline. By continued washing with hot water, and by the action of
alkaline carbonates, it leaves the oxide of the metal. Antimony combines
with bromine and iodine, forming compounds analogous to the chlorides.

Tersulphide of Antimony (SbSg). — This compound may be formed by
fusing the metal with sulphur. Its color is dark-gray and metallic ; its
specific gravity 4*66 : it closely resembles the native sulphide. When exposed
under a muffle to a dull red heat, it gradually loses sulphur, aud absorbs
oxygen, being converted into a gray powder, which consists of a mixture of
oxide and sulphide. If the heat be increased, this fuses into a transparent

462 SULPHIDES OF ANTIMONY.

substance formerly called Glass of antimony. Compounds of the oxide with
larger quantities of the sulphide, have been termed Saffron of antimony or
Crocus metallorum, and Liver of antimony.

Hydrated tersulphide of antimony h thrown down in the form of a reddish-
brown or orange-colored precipitate, when sulphuretted hydrogen is passed
through antimonial solutions, and when carefully dried it retains its color,
but if it be heated it darkens, and becoming anhydrous, assumes a metallic
appearance. It dissolves in solutions of the sulphides of the all<aline metals,
which take it up largely when heated, and deposit a portion of it on cooling;
it is thrown down from these solutions by acids. Hydrochloric acid dis-
solves it with evolution of sulphuretted hydrogen, producing a colorless ter-
chloride. A hot solution of sulphide of antimony in caustic or carbonate of
potassa, deposits a brown powder on cooling, formerly called Kermes mineral;
it is sulphide mixed with oxide of antimony, retaining a little of the alkali.
If hydrochloric acid be added to the filtrate, after the deposition of the
Kermes, sulphuretted hydrogen escapes, and the remaining sulphide of anti-
mony is thrown down, with some excess of sulphur, and a variable proportion
of oxide of antimony. This compound is the golden sulphide of antimony of
pharmacy, but, like Kermes, it is .of uncertain composition. The red ore of
antimony is a native oxysulphide, =2SbS3-j-Sb03.

Native sulphide is by far the commonest ore of antimony. It occurs in
prismatic and acicular crystals. It was known to the ancients, and used by
the Asiatic and Greek ladies as a pigment for the eyelashes : it was called
stimmi {atiixfxi) and stibium (art/St). It is known in commerce as crude anti-
mony, and is usually met with in conical masses or loaves, presenting a
dark-gray crystalline fracture; its powder is nearly black, and its melting-
point somewhat above that of the pure metal : it is seldom pure, frequently
containing the sulphides of lead, iron, copper, and arsenic, the arsenical
impurity forming sometimes 1-33 per cent,

Pentasulphide of Antimony ; Sulphantimonic Acid (SbSg) is formed
by passing sulphuretted hydrogen through pentachloride of antimony dis-
solved in aqueous tartaric acid. It is an orange-colored powder, which
when heated out of contact of air, loses 2 atoms of sulphur ; it dissolves in
warm aqueous ammonia, and in potassa and soda, and combines with the
basic sulphides, forming compounds which have been called sulphantimo-
niates. One of the most remarkable of these is the tribasic suljihantimoniate
of sodium, (3NaS,SbS5+ I8Aq) : it is obtained by mixing 18 parts of finely-
powdered tersulphide of antimony, 22 of dry carbonate of soda, 13 of quick-
lime, and 3 5 of sulphur, triturating this mixture with.a little water, and then
putting it into a well-closed bottle filled with water, and allowing it to digest,
with frequent agitation, for twenty-four hours ; the clear liquor is then filtered
and evaporated m vacuo over sulphuric acid ; it crystallizes in transparent
tetrahedra. ,

Alloys of Antimony. — With potassium and sodium antimony forms white
brittle compounds. The alloy of potassium and antimony may be procured
by heating to redness in a covered crucible a mixture of equal parts of finely-
powdered antimony and tartar for about three hours. By substituting tar-
trate of soda for common tartar, the alloy of sodium and antimony may be
obtained ; and a mixture of soda-tartrate of potassa and powdered antimony
yields the triple alloy of antimony, potassium, and sodium. When these
alloys are reduced to powder, and exposed to air, they heat, and take fire
like pyrophori (p. 41), and if blended with excess of carbon they burst into
sudden ignition on exposure, especially on the addition of a few drops of
water. Antimony and iron combine by fusion, and form a white alloy : 2
parts of sulphide of antimony fused with 1 of iron, yield a slag of sulphide

TESTS FOR THE COMPOUNDS OP ANTIMONY. 463

of iron, and an alloy formerly called Martial regulus. This alloy may be
recognized by its magnetic properties. Zhic and antimony form a hard
brittle alloy. Antimony and tht may be fused together in various propor-
tions : an alloy of 1 atom of each is brittle and pnlverizable : 1 part of anti-
mony and 10 parts of tin form a ductile compound, which a little lead renders
brittle. A fine pewter is said to consist of 12 parts of tin and 1 of antimony,
with a small addition of copper. An alloy of 1 of antimony and 3 of copper
is lamellar and brittle, but takes a good polish. When there is excess of
antimony the alloy is white. Type metal is a compound of 4 parts of lead
and 1 of antimony ; its hardness is such as to resist the pressure to which in
the printing press the type is necessarily subjected : it is readily fusible, and
takes a very sharp impression from the matrix or mould in which the letter
or stereotype plate is cast. A good white metal, used for spoons and tea-
pots, called Britannia metal, is composed of 100 tin, 8 antimony, 2 bismuth,
and 2 copper. Antimony readily combines and forms a fusible alloy with
platinum.

Tests for the Compounds of Antimony. — 1. The compounds of anti-
mony, when dissolved in water, or in an acid, are decomposed by the immer-
sion of a plate of zinc ; the metal is thrown down in the form of a black
powder, and when hydrogen is evolved a portion of antimony escapes with
this gas. 2. iSulphuretted hydrogen produces a distinctive brownish-red or
dark orange precipitate in salts of antimony with excess of acid, but if
they are neutral, their color is only changed, and the precipitate does not
ensue until an acid (tartaric) is added. 3. The alkaline hydrosulphates pro-
duce a similar precipitate, which is soluble in an excess of the precipitant,
especially when aided by heat. The precipitate is insoluble in ammonia,
but is dissolved by potassa. 4. Many of the combinations of antimony are
decomposed when largely diluted with water, and a basic salt is thrown down :
this decomposition is prevented by the presence of an excess of tartaric acid.
{Distinction from Bismuth, see p. 43y.) 5. Ammonia and the carbonate of
ammonia throw down teroxide of antimony completely from its solutions as
a white precipitate, insoluble in an excess of either precipitant. 6. Potassa
throws down a white hydrated oxide, soluble in an excess of the alkaline
liquid. Nitrate of silver added to this alkaline solution of the oxide, pro-
duces a black precipitate, insoluble in ammonia ; and chloride of gold pro-
duces in it a purple-black precipitate. 7. Ferrocyanide of potassium gives a
white precipitate, having frequently a bluish tint from the presence of iron.

These results are not obtained in a solution of tartar emetic, or the double
tartrate of antimony and potassa. 1. Sulphuric, nitric, and hydrochloric
acids produce white precipitates (basic salts) in a solution of the double
tartrate. These precipitates are readily dissolved by an excess of tartaric or
hydrochloric acid. 2. The alkalies and alkaline carbonates do not precipitate
the solution except at a boiling temperature. 3. It is not precipitated by
ferrocyanide of potassium. 4. It is not readily precipitated by sulphuretted
hydrogen until an acid is added, and for this purpose the tartaric acid is pre-
ferable : an orange-red precipitate, characteristic of oxide of antimony, is
thrown down. This precipitate is distinguished from many other sulphides
by its solubility in sulphide of ammonium, and in solution of potassa — as
well as by its insolubility in ammonia. If collected and dried, it may be dis-
solved by heat in a small quantity of strong hydrochloric acid ; and when all
the sulphuretted hydrogen has escaped, it will be found that, on adding this
solution to water, a white oxychloride of antimony is precipitated, possessing
the characters elsewhere described (p, 461). A portion of the sulphide, dis-
solved in hydrochloric acid may be introduced with zinc and sulphuric acid
into Marsh's apparatus. The gas which escapes at the jet produces a deep

464 ANALYSIS IN CASES OP POISONING.

black deposit on paper impregnated with a solution of nitrate of silver ; bnt
unless sulphur is present it produces no change on paper impregnated with a
salt of lead. When ignited the gas burns with a pale yellowish-white flame,
producing white fumes of teroxide of antimony (p. 461). Porcelain, or
glass, depressed on the flame receives a black deposit of finely-reduced metallic
antimony, with grayish-colored layers of oxide at the circumference. There
is no metallic lustre, such as is produced by arsenic under similar circum-
stances ; but on examining the reverse side of the glass, a metallic lustre
will be perceptible. If a current of the gas is heated to redness in a tube,
a ring of metallic antimony of a tin-like lustre will be deposited close to the
heated spot. This is much more fixed than the deposit of arsenic, and can-
not, like it, be resolved into a white sublimate of transparent octahedral
crystals. If the gas is made to pass through a small quantity of fuming
nitric acid containing nitrous acid, it is decomposed, the antimony is per-
oxidized, and may be obtained as a white, insoluble residue, on evaporation.
A solution of nitrate of silver produces no change in this deposit; but if
one or two drops of ammonia are added, there is a black deposit of anti-
monide of silver (AggSb). Compounds of antimony heated with carbo-
nate of soda or cyanide of potassium in the reducing flame of the blowpipe,
yield globules of metal, surrounded by a white incrustation on the charcoal.

Analysis in Cases of Poisoning. — The suspected liquid, if clear, may
be acidulated with tartaric acid, and a current of sulphuretted hydrogen
passed into it. The precipitated sulphide may be easily identified by the
characters above described. The contents of the stomach, or the coats of
the organ, may be boiled in hydrochloric or tartaric acid, and the filtered
liquid subsequently decomposed by the gas.

The following method of detecting antimony, when dissolved in any organic
liquid, is based upon the principle by which copper and other metals may
be detected under similar circumstances (page 427). Acidulate a portion
of the suspected liquid with hydrochloric acid, and place it in a shallow pla-
tinum capsule. Touch the platinum, through the acid liquid, with a piece
of pure zinc foil. Wherever the metals come in contact, metallic antimony
in the state of a black powder, is deposited upon the surface of the platinum.
The liquid should be poured off, and the capsule thoroughly washed with
distilled water. This may be effected without disturbing the deposit. A
small quantity of hydrosulphate of ammonia poured on the black deposit
speedily dissolves it (if antimony) by the aid of heat, and on evaporation, an
orange-red sulphide of antimony remains. This may be dissolved by a few
drops of strong hydrochloric acid, and on adding the acid liquid to water,
hydrated oxychloride of antimony is precipitated. By this process antimony
in small quantity may be detected in any liquid containing organic matter.
Some portion of the metal escapes with the hydrogen. The quantity of anti-
mony may, however, be so small, or the metal may be so ditfused through
the animal substance (in the tissues), that this process will yield no evidence
of the presence of antimony. The parts should then be finely cut up, and
boiled in a mixture of one part of hydrochloric acid, and five parts of water.
After some time, the liquid may be tested by introducing into it a slip of
polished copper foil free from antimony. If antimony is present in small
quantity, the copper will acquire a violet-colored deposit on its surface : if
in large quantity, the deposit will be gray with a metallic lustre, or sometimes
in the state of a black powder. When the copper with the deposit is heated
in a reduction tube, no crystalline deposit can be obtained from it as in the
case of arsenic. Having obtained deposits on several slips of copper foil,
these may be washed, dried, and heated in a strong solution of potassa (free
from lead), with occasional* exposure to air, until the metallic deposit is re-

ARSENIC. ITS DIFFUSION. 465

moved. The antimony is thereby oxidized and dissolved by the potassa.
A current of sulphuretted hydrogen gas may then be passed into the alkaline
liquid. This will throw down any lead tliat may be accidentally present.
Filter the alkaline liquid and acidulate with hydrochloric acid: the orange
sulphide of antimony is deposited, and may be collected and examined by
the methods above described.

Zinc separates metallic antimony, in the form of a black powder, from the
acid solutions of its oxides. This is one of the difficulties attendant on the
use of Marsh's process for the detection of antimony. The greater part of
the metal is deposited in the tube as a black flaky precipitate, and in the
course of a short time, barely a trace of antimony will be found issuing with
the hydrogen from the jet. Tin also separates antimony under certain cir-
cumstances, and it may be usefully employed in qualitative testing. Any
liquid suspected to contain antimony should be concentrated by evaporation
to the smallest possible bulk, and one-tenth part by volume of pure hydro-
chloric acid should then be added to it. A slip of pure tin-foil half an inch long
and one-eighth of an inch wide may be immersed in the suspected liquid and
allowed to remain for 24 hours. If antimony is present the tin will have
acquired a black deposit which is quite soluble in a solution of sulphide of
ammonium. If there is no deposit it may be concluded that no antimony is
present. Under similar circumstances arsenic is not deposited on tin.

The following method admits of the se[)aration of antimony from organic
substances when the metal is in mere traces. Coil a portion of pure zinc
foil round a portion of clean platinum foil, and introduce the two metals
into the hydrochloric-acid decoction of the tissues, sufficiently diluted to
prevent too violent an action on the zinc. Warm the organic liquid, and
suspend the coils in it. Sooner or later, according to the quantity of anti-
mony present, the platinum as well as the zinc will bs coated with an adher-
ing black powder of metallic antimony. Wash the platinum foil, and digest
in strong nitric acid. So soon as the antimony is dissolved from its surface,
the platinum may be removed. Add a few drops of hydrochloric acid, and
evaporate the acid liquid to dryness. The residue, redissolved in hydro-
chloric acid, and the solution diluted and treated with a current of sulphu-
retted hydrogen, will yield an orange-red sulphide of antimony. The black
deposit is readily dissolved by sulphide of ammonium, yielding an orange-
red sulphide of antimony, and it is also soluble in nitrohydrochloric acid, but
not in hydrochloric acid alone. When kept for a few days in contact with
water and air, the black metallic deposit is converted into white oxide of anti-
mony. Magnesium may be employed with advantage in this experiment in.
place of zinc. In this case the liquid need not be so strongly acidulated.
The magnesium, as it dissolves, does not impart to the liquid any substaoae
which can be precipitated by sulphuretted hydrogen.

CHAPTER XXXVI.

Arsenic (As='75).

The distinct metallic characters of arsenic were fir&t noticed in 17t3, but
some of its combinations (the sulphides) were known before the Christian era.
Its name is derived from the Greek apaevixov (orpiment). Its chemical rela-
tions are such as to place it rather among the simple acidifiable substances than
30

r

466 CHEMICAL PROPERTIES OP ARSENIC.

among the metals : it, however, has the lustre and opacity of a metal, and
conducts electricity. It occurs native, and in form of native oxide ; and there
are many native arsenates : it also occurs as a sulphide, and is frequently
found in combination with other sulphides, especially with sulphide of iron,
constituting arsenical pyrites =Y^'^^,YqA^. It is owing to its presence in
pyrites that arsenic is found in coal and lignite. It has been detected in the
coal of Northumberland and Nottingham. The coal of Sarrebriick was
found to contain 0 003 per cent, of arsenic, and in a variety of French coal
from Ville, as much as 0*0415 per cent, of arsenic was detected (Percy's
Metallurgy, p. 106). During the roasting of the arseniferous sulphides of
copper, iron, cobalt, and nickel, large quantities of oxide of arsenic are
formed, and from such sources, commercial demands are supplied. The
amount of white arsenic obtained in Cornwall in 1865, and separated from
other metallic ores was 826 tons.

Traces of arsenic are found in many minerals, and consequently in some
of their products, as in sulphur and sulphuric a«id, in zinc, in sulphide of
antimony, and occasionally in phosphorus. It w^as at one time supposed
that arsenic entered into the composition of the flesh and bones of animals
as a normal constituent, but it has been clearly proved that it is never found
in the tissues, either of animals or vegetables, except when it has been intro-
duced into them by accident or design. It is thus remarkably contrasted
with phosphorus, which is an essential constituent of organic matter. On
the other hand, the chemical analogies between these elements are in some
respects striking. In vapor, they have a similar odor : they form solid acids
with oxygen, similar in composition (AsOg, POg and AsO,, PO5), and
similar gaseous compounds with hydrogen (AsHg, PH3). Their volume
equivalents are the same, the atomic weight of each element being represented
by half a volume of vapor.

Arsenic may be obtained from the purified white arsenic of commerce, by
mixing it with its weight of black flux, and introducing the mixture into a
flask or small retort, gradually raised to a red heat : a brilliant metallic
sublimate of arsenic collects in the upper part of the flask or retort. The
volatility of white arsenic pr.events its easy reduction by charcoal alone ;
but the potassa in the flux enables it to acquire a temperature sufficient for
its reduction. Dried ferrocyanide of potassium is a good reducing agent
in all cases where it is desired to obtain the metal from arsenious acid.
Arsenic may also be obtained by heating the ore called native arsenic
in coarse powder in a retort ; the metal sublimes, leaving the impurities
behind.

Properties. — Arsenic is of a steel-gray color, crystalline texture, and very
brittle. Its sp. gr. is 5-75. It volatilizes when heated, and in close vessels
may be sublimed at a temperature lower than its fusing point; this is
generally stated to be about 400, but according to Fischer it does not rise
in vapor below a dull red heat. The density of arsenic-vapor is about 10*39.
Metallic arsenic tarnishes on exposure to air, falling to a grayish-black
powder (suboxide ?). It gives off no vapor. It does not decompose water,
and is not dissolved by that liquid, although it is slowly oxidized by air and
w^ater. It has no taste and no odor at ordinary temperatures ; but in the
state of metallic vapor, as it is liberated by heating its oxide with carbon,
it has an odor resembling that of garlic. When boiled in water with a
Btrong solution of potassa, arsenite of potassa is formed and hydrogen is
jJUfiliberated. It is not soluble in strong hydrochloric acid : but it is rapidly
^■^ oxidized and converted into arsenic acid by nitric and nitrohydrochloric
acids. Diluted nitric acid transforms it into arsenious acid. It combines
directly with chlorine, iodine, bromine, and other elementary bodies. It is

ARSENIOUS ACID. 467

rapidly oxidized by an ozonized atmosphere, and is converted into arsenic
acid (p. 112). When heated in a close tube, it sublimes unchanged : but
when heated in air, it is oxidized and converted into arsenious acid, which
is deposited in octahedral crystals.

Native arsenic usually occurs in rounded masses, or nodules, of a foliated
lamellar texture, and is often associated with the ores of silver, cobalt, lead
and nickel. Its color in the fresh fracture is nearly tin-white, but it speedily
tarnishes.

Arsenic and Oxygen. — There are two compounds of arsenic and oxygen,
namely, arsenious acid and arsenic acid.

Arsenious Acid (AsOa) ; White Arsenic; White Oxide of Arsenic. —
This is the best known, and most commonly occurring compound of arsenic.
It is formed by the combustion of the metal ; but is generally procured by
the joint action of heat and air on certain arseniferous ores. Arsenious acid
occurs in white translucent vitreous masses, often of a slight buff tint, and
occasionally transparent, especially when first removed from the subliming
vessel : on breaking the more opaque pieces, a translucent glassy nucleus is
often found within them. When slowly sublimed in a current of air, as in a
tube open at both ends, the vapor condenses in regular octahedral crystals ;
but if rapidly sublimed it forms a white powder, which, however, under the
microscope, is evidently crystalline. The massive arsenious acid of com-
merce is generally pure, but when in powder it is sometimes adulterated with
the sulphate of baryta or lime. The temperature at which arsenious acid rises
in vapor is below that at which it fuses, and appears to be about 360°. The
density of its vapor is 13*85, and it is inodorous. When heated under pres-
sure, or when suddenly and highly heated, it fuses, and concretes on cooling
into an amorphous vitreous solid. Arsenious acid is almost tasteless. In
fine powder it has been described as having a rough or astringent taste.
The specific gravity of the opaque arsenious acid is about 3 6, that of the
transparent vitreous and fused acid is about 3 8. The solubility of arsenious
acid in water has been variously stated, and it appears in some measure to
be dependent upon its isomeric modifications ; 100 parts of water at 60° dis-
solving 0*96 of the vitreous, and 1-25 of the opaque acid ; and at 212°, 9 68
of the former and 11-47 of the latter. When these solutions are cooled
down to 60°, r78 of the vitreous and 2-9 of the opaque are retained.

We have found by experiment that hot water cooling from 212° on the
opaque variety in fine powder, does not dissolve more than l-400th part of
its weight. Water boiled for an hour and allowed to cool, will hold dis-
solved l-40th part of its weight, or twelve grains to an ounce. If boiled for
a shorter time not more than l-80th part is retained in the cold solution.
Cold water does not dissolve more than from l-400th to 1-1 000th of its
weight. When mixed with water the powder partly floats, forming a film
on the surface. A saturated solution of arsenious acid has a slightly acid
reaction on litmus-paper. It is dissolved by alcohol and oils, but only to a
slight extent. When a concentrated solution of the vitreous acid in boiling
hydrochloric acid is suffered to cool, the crystals which it deposits have the
properties of the opaque acid, and this transition from the one aliotropic
modification to the other is attended by the evolution of light ; but if the
opaque acid is used, or if the deposited crystals are redissolved, those which
are subsequently deposited from the hydrochloric solution are formed without
any luminous appearance. ^^

Arsenious acid is decomposed at a dull red heat by hydrogen, and many ^B
of the metals. Its aqueous solution is rendered yellow by a current of sul- ^^
phuretted hydrogen, and when the solution is acidulated by hydrochloric
acid a yellow precipitate of tsrsulphide of arsenic falls; AsOg, + 3113 =

468 CHEMICAL PROPERTIES OF ARSENIOUS ACID.

AsSg+SHO : a yellow tint is observed, even when only a 10,000th part of
arsenious acid is dissolved. Hydrosulphate of ammonia does not precipitate
a solution of arsenious acid unless an acid is added, when the tersulphide
falls. Sulphate of copper and nitrate of silver give no precipitates in the
solution until an alkali is added, when the former produces a green, and the
latter a yellow precipitate. For the further action of tests upon this com-
pound in the solid as well as in the dissolved state, see page 476.

Hydrochloric acid is a powerful solvent of arsenious acid, but by the con-
tinued application of heat much of the arsenic escapes as chloride. A copper
wire introduced into this acid solution, moderately heated, is instantly coated
with a layer of metallic arsenic of an iron-gray color. (As03+3HCl4-3Cu =
As-fSHO-fSCuCl). On this reaction Behisch^s process for the detection of
arsenic is based (page 477). When placed in contact with nascent hydro-
gen, as by adding zinc or magnesium to the hydrochloric acid solution, or
any soluble compound of arsenic to zinc or magnesium and sulphuric acid,
water and arsenuretted hydrogen are produced (As03 + 6H=AsH3-j-3HO).
On this reaction, Marshes process for the separation of arsenic is founded
(page 477). Unlike antimony, the metal is not separated from its solutions
by tin. Thus a strip oi pure tin-foil, placed in a solution of arsenious acid
containing one-tenth of its volume of hydrochloric acid, remains untarnished:
no metallic arsenic is deposited. In a solution containing antimony, this
metal under similar circumstances is rapidly separated in the cold, and is de-
posited on the tin in the form of a black powder. A boiling solution of
potassa readily dissolves arsenious acid without change. If a strong alkaline
solution is employed in excess, and pure zinc is added to the liquid, arsenu-
retted hydrogen escapes (K0 + 6Zn-f 3HO+As03=AsH3H-KO,(5ZnO).
Fleitmann has recommended this process for the detection of arsenious acid
when mixed with organic matter.

When arsenious acid is mixed with rather more than its bulk of dry acetate
of potassa or soda, and the mixture is strongly heated in a closed tube, it
undergoes fusion, a portion of metallic arsenic is sublimed, and the oxide of
the compound radical cacodyle, recognized by its offensive odor, is set free
(2C4H303-i-As03=C4H60,As+4CO,). It is decomposed by carbon and
all carbonaceous flues, the metal being volatilized (As03 + 3C=As-l-3CO).
The cyanide of potassium, mixed with a little carbonate of soda to prevent
fusion, and the ferrocyanide of potassium, heated with arsenious acid,
decompose it, and metallic arsenic is sublimed: 2As03-f 3KCy=2As-f 3K0,
CyO. Powdered metallic magnesium also acts as a good reducing agent
(AsOg-|-3Mg=As + 3MgO). Arsenious acid operates as a deoxidizer.
When boiled with a solution of chromate of potassa, green oxide of chromium
is produced. It decolorizes a solution of permanganate of potassa, reduces
chloride of gold to the metallic state, and reduces the black oxide, of copper
to red oxide, when a few drops of the sulphate are added to a solution of
arsenious acid in caustic potassa, and the liquid is boiled. Chlorine, or a
mixture of hydrochloric acid with chlorate of potassa, as well as an alkaline
nitrate or chlorate, by fusion, convert it into arsenic acid and arsenate of

Traces of arsenious acid are not unfrequent in various chemical and phar-
maceutical preparations : it has been detected in sulphuric, hydrochloric,
nitric, acetic, and phosphoric acids, in phosphate of soda, and in emetic tar-
tar. The preparations of bismuth and copper frequently contain it ; and it
is sometimes found associated with the hydrated oxide of iron, in the ochreous
sediments of spring and river waters (page 150). This acid is used in many
of the arts, especially in color-making, dyeing, and calico-printing ; it is also
used in medicine, and in a variety of preparations for the destruction of ver-

ARSENITES. SCHEELE'S GREEN. 469

min. It is much em[)loyed in the steeping of seed-corn for the purpose of
destroyini]^ the spores of fungi. In the small quantities in which it is com-
monly sold to the public it is directed to be colored with indigo or soot, a
circumstance which must be borne in mind in searching for it in cases of
poisoning. It is a powerful irritant poison, and has destroyed the life of
an adult in the small dose of two grains. It is rapidly absorbed into the
blood, and is equally fatal whether it is taken by the mouth or applied to a
wound.

Arsenites. — These salts, when strongly heated, either evolve arsenious
acid or metallic arsenic : in the latter case they are converted into arsenates;
thus, 5(AsOj=3(AsOJ-}-2As: when heated with charcoal, or cyanide of
potassium, metallic arsenic sublimes. The alkaline arsenites, when in solu-
tion, are decomposed by lime and the salts of lime, and a white precipitate
of arsenite of lime falls, 2(CaO)As03: they are precipitated green by solu-
tions of copper, 2(CuO)As03, and yellow by nitrate of silver, 2(AgO)As03.
They are not precipitated by sulphuretted hydrogen, except when an excess
of a stronger acid is present : in this way the hydrochloric solutions of those
arsenites, which are insoluble in water, may also be .decomposed. The
arsenites of ammonia, potassa, and soda, are easily soluble, but are uncrys-
tallizable : they are formed by dissolving the acid in the respective alkaline
solutions. The supposed crystals of arsenite of ammonia deposited by the
solution of arsenious acid in ammonia are quite destitute of ammonia, and
consist only of arsenious acid. When arsenious acid is dissolved in the
alkaline carbonates, it is deposited unaltered by evaporating the solution, so
that it has been doubted whether this acid expels carbonic acid in the humid
way.

The arsenites of lime, baryta, strontia, and magnesia, are with difiBculty
soluble in water, but readily soluble in hydrochloric acid : there are two
arsenites of lime — one basic, =2(CaO)As03; the other neutral, CaO,As03.
Arsenite of potassa is the active ingredient in the Liquor arsenicalis of the
Pharmacopoeia, and in Fowlerh mineral solution, or tasteless ague-drop. A
mixture of arsenious acid with carbonate of potassa, or soft-soap, is used as
a wash for killing the fly in sheep. Another mixture, used by naturalists for
preserving animals, consists of 32 parts of white soap, 32 of arsenious acid,
12 of dried carbonate of potassa, and 4 of powdered quicklime, with 1 part
of camphor. Arsenuretted hydrogen is said to be slowly evolved from this
composition.

Arsenite op Copper, 2(CuO) AsOg, Scheele^s green ; Aceto- Arsenite op
Copper, SchweinfUrth green 3(CuO,As03) + (CuO,C^H303) are green pig-
ments much used in the arts. The latter, known also by the name of Emer-
ald green, from its rich green color, containing 59 per cent, of arsenious
acid. It is much employed in the coloring of paper-hangings and various
articles of dress, as well as in the coloring of confectionery. When an alka-
line arsenite is mixed with a solution of sulphate of copper, a precipitate of
an apple-green color falls (Scheele^s green), used as a pigment : it is prepared
by dissolving 2 parts of sulphate of copper in 44 of hot water, and gradually
adding it to a solution of 2 parts of carbonate of potassa and 1 of arsenious
acid in 44 of hot water, the whole being well stirred during mixture : the
arsenite of copper, in the form of a fine green powder, is gradually deposited,
and is to be washed and dried at 212^. A similar preparation, known under
the name of SchweinfUrth green, is made as follows : 50 lbs. of sulphate of
copper and 10 of lime are dissolved in 20 gallons of vinegar, and a boiling-
hot aqueous soljition of 50 lbs. of arsenious acid quickly stirred into it ; the
precipitate is dried and reduced to a fine powder. This green pigment, by
reason of its being very loosely laid on paper-hangings is liable to be diffused

470 CHEMICAL PROPERTIES OP ARSENIC ACID.

in the air of a room, and under these circumstances it has in some cases given
rise to the usual well-marked symptoms of chronic poisoning. Its employ-
ment on articles of dress and confectionery has been attended with more
serious consequences. The following is a simple method of detecting arsenic
in the colored substance. Cover a portion of the green paper with a solu-
tion of ammonia. The green pigment is dissolved and forms a blue solution
with the ammonia, owing to the oxide of copper with which the arsenic is
combined. Place a few crystals of nitrate of silver in a porcelain capsule,
and pour upon them a few drops of ammoniacal solution. If arsenic is
present, the crystals will acquire a superficial yellow color by the production
of yellow arsenite of silver (see page 476). A small portion of the green
powder, when heated in a reduction-tube, yields a sublimate of octahedral
crystals, which may be easily identified as arsenious acid.

In the solutions of lead, antimony, and bismuth, arsenite of potassa forms
white precipitates; added to nitrate of cobalt, it forms a pink precipitate ;
and bright yellow, with nitrate of uranium. With nitrate of silver it forms
a yellow precipitate, very soluble in ammonia. All these precipitates are
probably arsemtes of the respective metals, and, heated by a blowpipe on
charcoal, they exhale the smell of arsenic. They are decomposed when
boiled in solution of carbonate of potassa or of soda ; they are mostly soluble
in an excess of arsenious acid, and are readily dissolved by nitric acid, and
such other acids as form soluble compounds with their bases. Native arse-
nite of lead is found in France, Spain, a!id Siberia, and the mineral called
Condurrite appears to be an arsenite of copper.

Arsenic Acid (AsOg) is obtained by distilling a mixture of 1 part of hy-
drochloric, 12 parts of nitric, and 4 parts of arsenious acid : nitric oxide gas
is given oif, and when the contents of the retort have acquired the consist-
ency of a thin syrup, they are poured into a porcelain dish, and evaporated
by a moderate heat ; suddenly, the arsenic acid (which is anhydrous) con-
cretes into an opaque white mass, which should be put, whilst warm, into a
well-stopped phial. The hydrochloric acid is only useful in promoting the
solution of the white arsenic, which otherwise adheres to the retort, and
occasions irregular ebullition.

Arsenic acid is a white deliquescent compound ; it forms several crystalli-
zable hydrates : it fuses in close vessels at a heat approaching to redness, and
concretes on cooling into a vitreous mass ; at a higher temperature it is
decomposed, oxygen is evolved, and arsenious acid sublimes (As05=As03-f
20). Its specific gravity is about 3 '7. It requires for solution 6 parts of
cold and 2 of boiling water ; its solution reddens vegetable blues, and has
an acid and metallic taste. When water is poured upon the solid acid, part
only is immediately dissolved, and another portion, as is the case with phos-
phoric acid, remains undissolved, but after a time, upon agitating the solution,
the whole is taken up. Arsenic acid gives with lime-water a white precipi-
tate, and with ammonio-sulphate of copper a pale greenish-blue precipitate.
It is converted by sulphurous acid into arsenious acid, and by the bisulphite
or hyposulphite of soda into arsenite of soda (AsOg-f 2SOa=As03-f 2SO3).
It^exerts no reducing action on chloride of gold, permanganate of potassa,
or the salts of copper and chromium. When the solid acid is boiled with
aniline in certain proportions, it produces a purple dye. When heated with
hydrochloric acid, and copper is introduced into the liquid, metallic arsenic is
only slowly deposited ; and there is no deposit unless the arsenic acid is in com-
paratively large proportion. Sulphuretted hydrogen very slowly affects it, and
throws down after a time a pale yellow pentasulphide (As03-t-5HS = AsSg-f
HO). To effect its complete precipitation, it should be firs? converted into
arsenious acid by warming the solution with sulphurous acid. Another method

CHEMICAL CHARACTER OF THE ARSENATES. 4U

consists in acidulating the liquid with hydrochloric acid, then adding a solu-
lution of hyposulphite of soda, and boiling the mixture. Tersulphide of
arsenic is precipitated (AsS.,). With nitrate as well as with the amraonio-
nitrate of silver, arsenic acid gives at once a red-brown precipitate. It is
decomposed by nascent hydrogen like arsenious acid, and yields arsenuretted
hydrogen. When the solid acid is heated to redness with carbon or cyanide
of potassium, the arsenic is reduced to the metallic state, and is sublimed.

Arsenates are produced by the union of this acid with metallic oxides ;
those which are insoluble may be formed by adding arsenate of potassa to
their respective solutions. The normal arsenates are constituted like the
phosphates, of 1 atom of acid with 3 of base, and there are also salts with
1 and 2 atoms of basic oxide, in which the deficient base is replaced by 1
and 2 atoms of water ; but there appear to be no modifications correspond-
ing to the pyrophosphates and metaphosphates. The arsenates which are
insoluble in water, are soluble in dilute nitric acid and in such other acids as
do not form insoluble compounds with their bases: ammonia, precipitates
them from these solutions. They are readily decomposed by charcoal at a
red-heat ; but many of them, when heated alone, are unchanged even at a
higher temperature. They are decomposed when boiled in solutions of the
fixed alkaline carbonates. The soluble arsenates generally give a white pre-
cipitate with lime-water 2(CaO)HO,AsO-; they are not immediately preci-
pitated by a solution of sulphuretted hydrogen : with protosulphate of iron
they give a white precipitate (or yellowish if arsenious acid be at the same
time present). They give white precipitates with solutions of lead and zinc ;
yellow with the persalts of uranium and mercury ; red with the solutions of
salts of cobalt; green with those of nickel ; pale greenish-blue with those of
copper 2(CuO)HO,AsO„ and reddish-brown with those of silver 3(AgO)
AsO.. The last reaction is the most characteristic: hence nitrate of silver
is alone sufficient for the detection of an arsenate. These precipitates are
mostly soluble in hydrochloric acid, and in solutions of ammoniacal salts.
Arsenate of potassa gives a yellow precipitate with persulphate of uranium
when the solution is so diluted as to contain only a 10,000th part of arsenic
acid ; and with protosulphate of iron a white cloud is perceptible under the
same state of dilution. All the arsenates, when dissolved in water or la
dilute nitric acid, give a white precipitate with acetate of lead, which fuses
and emits arsenical fumes when heated on charcoal before the blowpipe.

The salt commonly called Binarsenate of potassa =K0,As03, may be
formed either by adding excess of arsenic acid to a solution of potassa, and
evaporating ; or by heating to redness, in a Florence flask, a mixture of equal
parts of nitre and white arsenic. During the latter operation much nitrous
gas is evolved, and on dissolving the residue in water, filtering, and evapo-
rating, prismatic crystals are obtained, resembling those of the corresponding
phosphates of ammonia and potassa; they are soluble in 5-3 parts of water
at 40^, and insoluble in alcohol; their formula is KO,2(HO),As05. Mac-
quer was the first who procured this salt ; hence it is termed Macquerh Ar-
senical salt. «It is not easily decomposed by heat alone, and may be fused
and kept red-hot without undergoing other change than losing a little water ;
but when mixed with about an eighth of charcoal powder and distilled,
metallic arsenic rises, and carbonate of potassa, mixed with a part of the
charcoal, remains in the body of the retort. This salt as well as the arsenite,
is used in medicine. It is a delicate test of the presence of silver, in solu-
tions of which it occasions a red-brown precipitate ; it is also sometimes
used to separate iron from manganese ; it produces in the persalts of iron a
white precipita'te, whilst the arsenate of manganese remains in solution. Ar-
senate of soda is extensively used in calico-printing. When dissolved iu

4Y2 ARSENATES OF IRON. ARSENURETTED HYDROGEN,

water and mixed with sugar, it is sometimes employed as a fly-poison. Paper
impregnated with this liquid, and dried, is sold under the name of Papier
Moure. The arsenates of the alkaline earths are not soluble in water. When
a solution of an arsenate is acidulated with hydrochloric acid, and boiled
with hyposulphite of soda, tersulphide of arsenic is precipitated. {See p.
4n.)

Arsenic acid forms a nearly insoluble compound salt with ammonia and
magnesia, resembling the ammonio-magnesian phosphate. When phosphoric
acid or a phosphate is not present, arsenic may be thus separated, and its
quantity determined. If a solution of sulphate of magnesia is mixed with
a solution of arsenic acid; and if ammonia, with chloride of ammonium, is
then added, an insoluble crystalline precipitate of arsenate of ammonia and
magnesia is slowly produced. This is not only a test for arsenic acid, but
it serves to distinguish it from arsenious acid, as this forms no similar com-
pound salt. The precipitate, when dried at 212°, has the composition NH,,
HO,2(MgO)AsO.,HO. It contains 62*9 per cent, of arsenic acid. It does
not, like the corresponding phosphate, admit of calcination, as a portion of
arsenic would be expelled at a high temperature.

Arsenates op Iron. — The protosalts of iron give a white precipitate with
arsenate of ammonia, which gradually becomes green on exposure to air;
it appears from Chenevix's analysis to be 3(FeO),As05,6HO. When solu-
tions of perchloride of iron and bibasic arsenate of soda are mixed, a white
perarsenate of iron falls : 2Fe,Cl3-f 3[2NaO, As05] = 2Fe203,3As05-f 6NaCl.
This salt, when dried at common temperatures, retains about 18 per cent, of
water (=12 atoms) which it loses when heated, and becomes red, and at
higher temperatures it glows and acquires a yellow color. It is insoluble in
water; hence hydrated peroxide of iron has been used as a chemical anti-
dote in poisoning by arsenic. This oxide precipitates both arsenious and
arsenic acid when these are in solutioti in water. The arsenates of the other
metallic oxides call for no special notice.

Arsenic and Hydrogen ; Arsenuretted Hydrogen Gas. Hydride of
Arsenic (AsHg). — When nascent hydrogen comes into contact with arsenic,
or any of its soluble compounds, a portion of the metal is carried over in a
state of combination with the hydrogen. If arsenious acid is added to
dilute sulphuric acid, and magnesium or zinc is dissolved in the mixture, the
liberated hydrogen is rich in arsenic ; but free hydrogen is also evolved.
Pure arsenuretted hydrogen is best obtained by the action of hydrochloric
acid upon a pulverized alloy of zinc and arsenic, obtained by fusing together
equal parts of these metals. This gas is colorless : it has a nauseous odor
resembling garlic, and is so poisonous that extreme caution must be observed
in dealing with it. It has proved fatal to three chemists, who were engaged
in experiments upon it. The gas blackens paper impregnated with nitrate
of silver, but it produces no change of color on paper impregnated with a
salt of lead.

Arsenuretted hydrogen may be collected and retained over water, which,
however, absorbs it to the amount of about one-fifth of its volnme, and, if it
contain air, a dark-colored film of arsenic is gradually deposited ; it is not
absorbed by alkaline solutions, nor by alcohol or ether, but oil of turpentine
absorbs it largely. It is liquefied, under atmospheric pressure, when cooled
down to — 40°. Faraday could not solidify it at 166° below 0°. Arsenu-
retted hydrogen is decomposed at a full red heat, arsenic is deposited, and 2
volumes of the gas afford 3 volumes of hydrogen. When mixed with an
insufficient quantity of air or oxygen for its perfect combustion it deposits
metallic arsenic in burning; but with excess of oxygen it explodes with
violence, and forms water and arsenious acid. It burns in contact with air

CHLORIDE OF ARSENIC. 473

with a pale blue frame, forminnr water and arsetiions acid, and depositing
arsenious acid upon the sides of the jar as the flame descends (AsH^ + ^Oss
3H04-AsO.J. These are the products of its combustion when burnt from a
jet. If a clean glass plate, or a surface of porcelain, is held above the point
of the flame, arsenious acid and water only are deposited ; if held so as to
bisect the flame a deposit is obtained, consisting of metallic arsenic in the
centre, and of white arsenioVis acid at the circumference. When deposited
on glass the central portion is opaque if viewed by transmitted light, but by
reflected light it has a strong metallic lustre. The deposit is of a hair-brown
color at the circumference. It possesses the following additional chemical
characters: 1. It is entirely dissolved by fuming nitric acid, and leaves, on
evaporation, arsenic acid. 2. It is readily dissolved by a fresh solution of
chloride of lime, and leaves, on evaporation, some arsenate of lime mixed
with chloride. 3. It is not readily dissolved by hydrosulphate of ammonia ;
on evaporation it leaves a yellow residue of sulphide of arsenic. The anti-
monuretted hydrogen, produced under similar circumstances, has widely
different properties. In addition to those elsewhere described (page 461)
the following may be noticed in contrast with the characters of an arsenical
deposit : 1. It is not dissolved by a solution of chloride of lime. 2. It is
readily dissolved by hydrosulphate of ammonia, leaving, on evaporation, an
orange-red sulphide of antimony.

The sp. gr. of arsenic in vapor is 10*39, and the sp. gr. of arsenuretted
hydrogen is 2'695. As in the analogous compound of phosphorus — half a
volume of the vapor of arsenic =75, is combined with three volumes of
hydrogen =3, the 3z volumes being condensed into 2 volumes of the gas
(pp. 72 and 245).

Atoms. Weights. Per cent. "Vols. Sp. Gr.

Arsenic . . 1 ... 75 ... 96-15 ... J ...* 5-195
Hydrogen . . 3 ... 3 ... 3-85 ... 3 ... 0-207

1 78 100-00 2 5-402

The sum of. the sp. gr. of the constituents, divided by 2 (5*402 -r 2), is
equal to 2'701, which is but little in excess of the sp. gr. determined by
Dumas. Compared with hydrogen, the sp. gr. is one-half of the equivalent
weight, namely, 39. The observation occurs with this as with respect to the
phosphorus-compound : one volume of the vapor of arsenic is equivalent to
two atoms of this elementary substance.

Arsenuretted hydrogen gas is instantly decomposed by chlorine ; and if
chlorine is suffered to ascend into a jar containing it, while standing over
water, each bubble inflames, producing hydrochloric acid, whilq brown fumes
of arsenic are produced and deposited ; if the arsenuretted hydrogen is sent
up in the same way into chlorine, when this gas is in great excess hydro-
chloric and arsenious acids are immediately formed. The gas is similarly
decomposed by iodine and bromine. Agitated with a solution of sulphate
of copper, the gas is absorbed, and arsenide of copper and water are formed.
3(CuO,S03)-f AsH3=Cu3As4-3HO + 3S03. This action furnishes a means
of testing the purity of the gas, for any uncombined hydrogen remains un-
absorbed. It reduces the salts of silver, gold, platinum, and rhodium, to
the metallic state, and arsenious acid remains in solution : thus, with nitrate
of silver, the results are silver, arsenious acid, water, and nitric acid. 6(AgO,
NOJ-f AsH3=6Ag-f As03-h3HO-f6N05. We find by experiment that
there are no liquids which so completely arrest and decompose this gas as a
saturated solution of nitrate of silver and fuming nitric acid.

Arsenic and Chlorine ; Terchloride of Arsenic (AsClg). — This com-
pound may be formed : 1. By throwing finely-powdered arsenic into chlo-

474 SULPHIDES OF ARSENIC. REALGAR.

rine ; the metal burns and produces a volatile liquid ; or by passinj^ dry
chlorine over arsenic placed in a tube, and gently heated : the resulting vapor
of the chloride should be condensed in a receiver cooled by ice, and may be
purified by redistilling it with a little powdered arsenic. 2. Distil 6 parts
of corrosive sublimate with 1 of powdered arsenic ; the chloride passes into
the receiver in the form of an unctuous fluid, formerly called butter of arsenic.
3. 1 part of arsenious acid with 10 parts of sulphuric acid, are put into a
tubulated retort, and the temperature raised to about 212°. Fragments of
fused common salt are then thrown in by the tubulature ; by continuing the
heat, and successively adding the salt, chloride of arsenic is obtained ; it
distils over, and may be condensed in cold vessels. Yery little hydrochloric
acid is disengaged, but towards the end of the operation, a portion of
hydrated chloride of arsenic is produced, which floats upon the pure
chloride, and appears more viscid and colorless. Mixed with a large quan-
tity of w^ater, the chloride of arsenic is decomposed, and arsenious acid is
formed, hydrochloric acid being at the same time produced. On this reaction
Schneider, in 1852, founded a process for procuring arsenic by distillation in
cases of poisoning. When fused chloride of sodiuiu is employed, this should
always be kept in excess, as if the sulphuric acid is in excess, the arsenious
acid will be retained by it in the retort. If the mixture of arsenious and
hydrochloric acids is saturated with chlorine, or chlorate of potassa, the
arsenic is converted into arsenic acid, and barely a trace passes over as
chloride.

Chloride of arsenic, when concentrated, is a dense oleaginous transparent
liquid : it does not freeze at 0°; it boils at about 270°, the density of its
vapor being 6'3 : it exhales vapor when exposed at common temperatures to
the air. With a small quantity of water it forms what has been termed
hydrated chloride of arsenic : this is probably a hydrochloric solution of
arsenious acid ; [AsCl34-3HO = As03 + 3HCl], and when more largely
diluted, arsenious acid is deposited ; but when a solution of arsenious acid
in excess of hydrochloric acid is heated, the whole is volatilized, and there
is no residue ; so that when hydrochloric acid containing arsenious acid is
distilled, the product which passes over is always arseniferous ; and when
any arseniferous acid acts upon common salt, the hydrochloric acid which is
evolved carries arsenic with it. On this reaction is based a method of sepa-
rating arsenic from mineral and organic substances [see page 465). A diluted
solution of chloride of arsenic reduces a solution of gold to the metallic
state. When heated with metallic copper, arsenic is deposited on the metal ;
and when a rod of zinc or magnesium is introduced into the liquid, the arse-
nic rapidly escapes as arsenuretted hydrogen.

There is no pentachloride of arsenic; ^. e., no chloride corresponding to
arsenic acid. When arsenic acid is distilled with hydrochloric acid, terchlo-
ride only appears to be produced to a limited, extent. The greater part of
the arsenic acid remains unchanged in the retort. The chloride of arsenic
is a powerful poison, as it is very readily absorbed. A quantity equivalent
to the tenth part of a grain has produced serious symptoms.

A.RSENIC AND Sulphur. Bisulphide of Arsenic. • Red Sulphide of Ar-
senic. Realgar (AsS^). — By slowly fusing a mixture of metallic arsenic
and sulphur, or by heating 15 parts of arsenious acid with 8 parts of sulphur,
a red sulphide of arsenic is obtained. It is crystallizable, and of a vitreous
fracture : its specific gravity is 34 to 3-5. It is easily fusible, and may be
sublimed unaltered in close vessels. It is usually known under the name
of Realgar, and occurs native. It is used in the preparation of the pyro-
technical compound, called White Indian Fire, which consists of 24 parts
of saltpetre, 7 of sulphur, and 2 of realgar, finely powdered and well mixed.
The mixture burns with a splendid white flame of great brilliancy.

ORPIMENT. ALLOYS OF ARSENIC. 4t5

Tersulphide of Arsenic. Orpimeyit. Sulpharsenious Acid (AsSg)

When snlphnretted hydrofj^en is passed through a solution of arsenious acid
in dilute hydrochloric acid, this sulphide is formed. It is also procured by
subliming a mixture of sulphur and arsenious acid, or arsenic, in proper
proportions. It is fusible, and sublimes in close vessels without change : it
has a rich golden-yellow color, and assumes a lamellar texture on cooling.
Heated in air, it burns with a pale-blue flame, producing fumes of sulphurous
and arsenious acids. Its specific gravity is 3*45. It is soluble in caustic
alkaline solutions ; it is insoluble in diluted acids, but is decomposed by
nitric and nitro-hydrochloric acids, forming arsenic and sulphuric acids.
These sulphides are decomposed by fusion with potassa ; sulphide of potas-
sium and metallic arsenic in the form of a sublimate, are the results.

As this sulphide is commonly met with, it contains undecomposed arse-
nious acid in variable proportions. This may be separated by boiling the
compound in water, in which the sulphide is insoluble. Although the sul-
phide is not very soluble in strong hydrochloric acid, yet under continued
heaj;, chloride of arsenic and arsenuretted hydrogen are produced. It is
only the hydrated precipitated sulphide that is readily dissolved by strong
solutions of potassa, soda, or ammonia. By its solubility in ammonia sul-
phide .of arsenic may be separated from sulphide of antimony. For the
complete reduction of this sulphide. Otto recommends that it should be
heated with ten parts of a mixture consisting of 1 part of cyanide of potas-
sium, and 3 parts of carbonate of soda, finely-powdered and well-dried :
Bulphocyanide of potassium is formed and metallic arsenic is sublimed (2As
S3+3KCy=3KCyS,+ 2As).

An ammoniacal solution of this sulphide has been employed as a dye-stufif.
Orpiment is the basis of a pigment called King^s Yellow. Native Orpiment
(the auripigmentum of the ancients) is of a bright lemon or golden color. It
is generally massive and lamellar. This, and the preceding sulphide, act as
sulphur acids, and form salts (Arsenio-sulphides), with sulphur bases.

Persulphide of Arsenic. Sulpharsenic Acid (AsS,). — When sulphuret-
ted hydrogen is passed through a concentrated solution of arsenic acid, a
pale yellow precipitate very slowly falls, which may be sublimed, without
change, in close vessels. It is fusible, and soluble in alkaline solutions, but
insoluble in boiling water. The same compound is obtained when sulphu-
retted hydrogen is passed through a concentrated solution of arsenate of
potassa, and the resulting sulpho-salt is decomposed by hydrochloric acid
(p.^ 4T0). This compound reddens litmus-paper. Its reactions are those of
a sulphur acid. Thus, it combines with alkaline and metallic sulphides to
form sulphur salts, and it expels carbonic acid from the carbonates. The
sulphides of arsenic are poisonous, but in a less degree than arsenious acid.
Common orpiment, owing to its containing arsenious acid, is a virulent
poison.

There is a native sulphide of arsenic and iron diffused with ordinary py-
rites (FeAs,FeSjj). It is of a more silvery color than common pyrites.
When heated, it exhales an odor of arsenic. It is called arsenical pyrites,
or mispickel. It is an abundant source of arsenious acid. By the decora-
position of arsenical pyrites, under exposure to air and moisture, insoluble
compounds of the acids of arsenic and oxide of iron are diffused through
certain soils, and are contained in the sediments of spring and river waters.

Alloys of Arsenic ; Arsenides. — Arsenic unites with most of the metals,
forming compounds which are generally brittle and comparatively fusible.
Arsenic and iron form compounds which are more brittle, hard, and fusible
tlian iron : iron containing only 2 or 3 per cent, of arsenic becomes very
brittle when heated. Native arsenide of cobalt occurs in cubic, octahedral,

476 TESTS FOR ARSENIOUS ACID.

•

and dodecahedral crystals, sp. s^r. 6*78, of a tin white color; it contains
about 20 per cent, of cobalt and 80 of arsenic, and is therefore Co^ASg. The
ore known in Germany as speiskohalt is an arsenide of cobalt, iron, and
nickel. Arsenide of nickel is gray and brittle. Kupfermckel is a native
arsenide ^ AsNij ; and the white arsenical nickel, or nickel pyrites, is AsNi.
When copper is heated to redness with excess of arsenic, a gray arsenide is
formed ; it has been called lohite tomhac. Arsenide of lead is obtained by
heating lead with excess of arsenic or of arsenions acid ; it is of a gray, crys-
talline, brittle compound. A very minute quantity of arsenic (less than 1
per cent.) is always contained in common lead shot; it gives the lead the
property of spherical granulation when the fused metal is passed through a
sieve and suffered to fall through the air till it solidifies. Arsenide of anti-
mony is brittle, hard, and very fusible : it occurs native^ containing about 36
per cent, of antimony ; this ore therefore is SbASg.

Tests for Arsenic ; Analysis in Cases of Poisoning. — Arsenious acid,
or arsenic, as it is commonly called, is a white crystalline powder. 1. When
heated on platinum foil, or mica, it is entirely volatile at a moderate heat,
without undergoing fusion. It escapes in a white smoke, which has no odor.

2. When gently heated in a small reduction-tube, closed at one end, it sub-
limes without fusing, in well-defined transparent octahedral crystals, or deri-
vatives of the octahedron, sometimes visible without the aid of a microscope.

3. A small portion on a loop of platinum-wire introduced into a Bnnsen's
jet, burns with a pale blue flame, emitting dense white fumes. 4. When a
solution of hydrosulphate of ammonia is poured upon the powder it under-
goes no immediate change of color ;*but by exposure to heat, or by sponta-
neous evaporation of the liquid, it is converted into an orange-yellow sul-
phide of arsenic, which is dissolved by ammonia, but not by hydrochloric
acid. 5. The powder is not easily dissolved by water, ^ven at a boiling
temperature. It is, however, readily dissolved by potassa without change, and
by hydrochloric acid which converts it into volatile chloride of arsenic. A
small quantity of hydrochloric acid in water renders arsenious acid much
more soluble. 6. When heated with 3 or 4 parts of soda-flux (prepared by
calcining acetate of soda in a close platinum-crucible) it yields a dark iron-
gray sublimate of metallic arsenic. In the absence of soda-flux, powdered
ferrocyanide of potassium may be used as a reducing agent. The sublimate
of metallic arsenic may be identified by the following characters. When
the glass with the metal is gently heated in a larger tube, the metal is
oxidized and volatilized in the form of a white crystalline sublimate of ar-
senious acid. When treated with strong nitric acid containing nitrous acid,
and evaporated to dryness, it leaves a residue of arsenic acid,' which is known
by the brick-red color, or stain produced on the addition of a few drops of
nitrate of silver. Cadmium, tellurium, selenium, and mercury produce sub-
limates ; but when heated, or acted on, by nitric acid, the results are wholly
different.

A solution of arsenious acid in water is tasteless, and feebly acid to litmus-
paper. 1. Ammonio-nitrate of silver produces with it a yellow precipitate
of arsenite of silver. 2. Ammonio-sulphate of copper givesagreen.precipi-
tate. This precipitate, when collected, dried, and heated in a tube, yields a
sublimate of arsenious acid in octahedral crystals. The green precipitate,
dissolved in a few drops of solution of ammonia, and treated with a crystal
of nitrate of silver, produces on the surface of the crystal a layer of yellow
arsenite of silver. 3. A current of sulphuretted hydrogen produces a yellow
precipitate, which is completely thrown down on acidulating the liquid with
a few drops of diluted hydrochloric acid. This yellow precipitate (sulphide
of arsenic) is known from all others of a similar color. I. By its insolubil-
ity in hydrochloric acid ; 2. By its dissolving in ammonia, forming a pale

ANALYSIS IN CASE OF POISONING. 477

colorless solution ; and 3. By its yielding a sublimate of metallic arsenic
when heated with 2 or 3 parts of powdered ferrocyanide of potassium.

Arsenic Acid. — This compound is easily recognized. 1. By its fixedness
when heated. 2. By its great solubility in water, and the strong acid reac-
tion which it imparts to water. 3. By the color of the precipitate given by
a solution of nitrate or ammonio-nitrate of silver. When the arsenic acid
is in a very diluted state, the precipitate is of a pale brownish color, becom-
ing of a deeper and browner red in proportion to the quantity present.
Metallic arsenic and arsenious acid may be readily identified by these pro-
perties when converted into arsenic acid by the action of fuming nitric acid.

When arsenic is contained in organic liquids it may sometimes be separated
in lumps, or powder, by washing ; or if dissolved, it may be precipitated as
sulphide by sulphuretted hydrogen, and this may be tested in the manner
above described. i^mzscA's jorocess furnishes a useful trial test under these
circumstances. The suspected liquid, which should not contain nitric acid,
or any chlorate or nitrate, must be acidulated with pure hydrochloric acid
(its purity having been previously determined) in the proportion of 1 part
of acid to 6 or 7 parts of the liquid. The acid liquid is then brought to the
boiling point, and a slip of bright copper-wire, or foil (free from arsenic) is
introduced. If the quantity of arsenic is minute, the copper will acquire a
metallic deposit of a bluish or purple color, passing to gray or iron-gray, in
proportion to the quantity of arsenic present. The coated copper, washed
and dried, will, when heated in a small reduction tube, yield a sublimate of
octahedral crystals of arsenious acid. If there is no tarnish or deposit on
the copper after some minutes' boiling, it may be inferred that arsenic is
either not present, or that the proportion is exceedingly small. On the other
hand, there may be a deposit, but insufficient to yield crystals of arsenious
acid. In this case the following process may be resorted to : —

The solid or tissue, previously dried and divided into small portions, or
an extract of the suspected liquid, may be placed in a flask or retort with a
sufficient quantity of pure and concentrated hydrochloric acid to render the
mass quite liquid. The receiver should contain a small quantity of distilled
water. If a globular flask is used, this may be connected with the receiver
by means of a long narrow tube, kept cool by wetted blotting-paper folded
round it. The distillation should take place slowly, by means of a sand-
bath, and be carried nearly to dryness. A distillate is thus obtained con-
taining either the chloride of arsenic, or a mixture of hydrochloric and
arsenious acids. If this is colored, or mixed with organic matter, it should
be submitted to a second distillation. When any oily matter has distilled
over, this should be separated by passing it through a wet filter. In some
cases, as where the substance has not been thoroughly dried, a second dis-
tillation, with a fresh portion of hydrochloric acid, may be required to remove
the whole of the arsenic ; but with ordinary care this is not necessary. One-
third of the liquid distillate (diluted with water if too acid) may now be
heated with a slip of polished copper foil (^Reinsch^s process). If ar-
senic is present, even to the l-4000th of a grain, the copper will indicate
this by a change of color — the metallic lustre being retained. By using
other portions of copper successively, the whole of the arsenic may be ex-
tracted. The remaining two-thirds of the liquid should then be submitted
to Marsh'' s process with the following modifications. The distillate, if very
acid, should be so diluted that its action on zinc may not be too violent.
The most convenient form of apparatus is a tube, about an inch in width and
six or eight inches in height, provided with a well-fitted cork, through which
passes a safety-funnel tube on one side, and an exit or delivery-tube, bent at
a right angle, on the other side. The exit-tube should be connected by

478 DETECTION OF ARSENIC IN CASES OF POISONING.

corks with a short wide tube, containing fragments of fused chloride of cal-
cium, for the purpose of drying the gas. To the other end of the drying-
tube there should be fitted a long tube of hard glass (free from lead), about
one-quarter of an inch in diameter, and provided with two or three capillary
contractions. This tube should be bent at a right angle, so that the end of
it may dip into a solution of nitrate of silver.

Pure zinc or magnesium having been placed in the apparatus, the acid dis-
tillate is poured upon it through the funnel. After a short time, if arsenic is
present, the bubbles of hydrogen, as they escape, will darken the solution
of nitrate of silver. The liquid will first become of a pale brown color,
gradually deepening to black, according to the amount of arsenic present.
When the silver solution has undergone this change, the horizontal glass
tube may be heated to redness, about an inch before each capillary contrac-
tion. The arsenuretted hydrogen will be thereby decomposed, and a dark
mirror of metallic arsenic, in the form of a ring, will be deposited in the con-
tracted portion of the tube. By this arrangement, three or more metallic
deposits of arsenic, corresponding to each contraction, may be procured.
When the gas has spent itself in the silver solution, this may be removed.
The end of the delivery tube should then be washed, and allowed to dip into
a small quantity of fuming nitric acid containing nitrous acid. This com-
pletely arrests and decomposes the arsenuretted hydrogen.

The chemist has now before him all that is necessary to identify the sub-
stance as arsenic. The glass tube is detached from the apparatus, and the
metallic sublimates are obtained separately by melting the glass in the con-
tracted portions. One may be sealed up and preserved ; one may be tested
by applying a gentle heat to the metallic deposit, when a brilliant ring of
colorless octahedral crystals may be obtained, plainly visible under the micro-
scope. With respect to the other tube, the portion of glass containing the
metallic deposit may be separated by a file, broken into fragments, and di-
gested in a small porcelain capsule, in a few drops of fuming nitric acid.
On evaporating to dryness and adding a solution of nitrate of silver, a red-
dish-colored precipitate, entirely soluble in ammonia, indicates that arsenic
acid was present, and that the metallic deposit was arsenic. It is here
assumed that the chemist is obliged to rely exclusively upon the results
obtained by decomposing the arsenuretted hydrogen gas by heat. In gen-
eral, however, it will be found that the silver solution and the nitric acid
which have been employed to receive the surplus gas, will yield satisfactory
evidence, and render a special analysis of the metallic deposits unnecessary.

1. The darkened solution of nitrate of silver is filtered, in order to sepa-
rate the metallic silver. The filtrate contains arsenic in the state of arseni-
ous acid, mixed with nitrate of silver undecomposed. The addition of ammo-
nia to this liquid produces immediately a yellow precipitate of arsenite of
silver.

2. The fuming nitric acid into which the gas has been passed, may be
evaporated to dryness on a sand-bath in a clean porcelain capsule. A white
deliquescent acid residue is thus obtained. On adding to this residue a
few drops of nitrate, or of ammonio-nitrate of silver, a brick-red precipitate
of arsenate of silver is immediately produced. (For the further details of this
process see Guyh Hospital Reports, Oct. 1860, p. 253.) It will be per-
ceived that by this method, arsenic if present is obtained in the state of
metal and of its two oxides arsenioas and arsenic acids. Hence no further
demonstration is required.

The usual method of detecting arsenic in the tissues or organs of the body,
consists in rendering the arsenic soluble in the midst of a large quantity of
carbonized organic matter, which, in spite of every care, will more or less

MERCURY. 479

accompany it. By the process of distillation as originally sn«?p^ested by
Schneider, the arsenic is removed from the organic matter, and thus sepa-
rated from a large number of metals which do not form volatile chlorides at
a low temperature. The residue in the retort, after the complete separation
of arsenic, may be analyzed for mercury, antimony, and other metals. "This
process does not interfere with the carbonization of the residue by sulphuric
acid, if necessary. In the state of chloride, arsenic is distingui*shed from all
metals excepting antimony, by its ready conversion into a gaseous hydride,
and by the entire decomposition of this hydride by heat. Lastly, by means
of the hydride the arsenic may be reproduced, 1st, as metal ; 2d, as arsenious
acid ; and 3d, as arsenic acid, beyond which it is unnecessary to carry the
analysis. The processes of Marsh and Reinsch are not here resorted to until
after the arsenic has been separated from other substances by distillation.
These processes should corroborate each other ; and the only caution required,
is that pure zinc and copper, as well as pure hydrochloric and nitric acids,
should be employed. These substances should each be separately tested in
the apparatus on a sufficient scale, before the analysis is commenced. Mag-
nesium is preferable to zinc, from its absolute purity.

In reference to antimony, there are characteristic differences, which have
been already described (p. 465). The only method by which the quantity of
arsenic can be approximately determined in these researches, is by condensing
the whole of the arsenic obtained from a given weight of the material, in
fuming nitric acid, and precipitating the arsenic so obtained as arsenate of
ammonia and magnesia (p. 472). A hundred parts of this precipitate, dried
at 212°, are equivalent to 54 -14 of arsenious acid.

If the organic substance submitted to examination, should be in a state of
putrefaction, sulphuretted hydrogen may be found in the distillate. This
may be removed by the addition of chlorine, and heating the liquid, or by
exposing the liquid to air- for 24 hours. Sulphur is deposited and may be
separated by filtration. If the quantity is small, the sulphuretted hydrogen
may be stopped by placing lead-paper in the first portion of the drying-tube.
When sulphuretted hydrogen comes over with arsenuretted hydrogen, the
metallic deposit, obtained by heating the current of gas is, in part at least,
converted into yellow sulphide of arsenic. If arsenic acid is present, this
should be converted into arsenious acid by sulphurous acid before submitting
it to distillation. If sulphide of arsenic or orpiment is present, this should
be converted into arsenic acid by fuming nitric acid, and then submitted to
distillation as above described. By the process above described, minute
traces of arsenic have been separated from Thames mud, the ochreous deposits
of rivers, and from the salts of copper as well as from animal solids and fluids
of various kinds iu cases of poisoning.

CHAPTEE XXXVII.

Mercury (Hg=100).

The principal ore of this metal is the sulphide or natii'>e cinnabar, from
which mercury is separated by distillation, either with quick-lime or iron-
filings, or by simply burning off the sulphur. Mercury occurs native, in small
globules, generally dispersed through the sulphide. It is also found as a

I

4B0 OXIDES OP MERCURY.

chloride, iodide, and selenide, but these are rare ores: in combination witji
silver it constitutes native amalgam.

Mercury is a brilliant silvery-white fluid-metal, whence the terms hydrar-
gyrum (liScop apyvpoj) and quicksilver. It has been known from remote ag:es.
It is liquid at all common temperatures, solid at — 40^, and contracts at the
moment of congelation. Its characters, when frozen, vary with the tempera-
ture, being flexible when verging towards liquefaction, but brittle at lower
temperatures. It boils at about 660*^. It emits vapor at all temperatures
above 40^, but no api)arent spontaneous evaporation goes on from it when
below that temperature. Its great lustre and opacity may be well seen by
compressing a globule between two clean glass plates. If pure, it assumes
when placed on surfaces of glass or porcelain a rounded spherical form capa-
ble of subdivision by pressure into minute and scarcely visible globules. It
flows also readily as a globule over the surface : when mixed with lead, tin,
or other metals, it coheres to surfaces, and the globular form is no longer
seen. It may be deprived of these impurities by careful distillation, but it
has been found better before distilling the impure mercury, to add to it about
one-twelfth of its weight of nitric acid, allowing a slight digestion in the
cold and then applying a moderate heat. The mercury is decanted and dis-
tilled. The nitrates formed by the action of the acid may be evaporated
to dryness, and the dry residue distilled with the mercury (Lacassin). Its
sp. gr. at 60° is 13 56, but in the solid state it exceeds 14. The specific
gravity of mercurial vapor is 6 97 6. When mercury is pure, it is not affected
by agitation in contact with air ; but when impure, it becomes covered with
a gray powder, which is a mixture of the foreign metallic oxide and finely-
divided mercury. When pure mercury is shaken with water, ether, sulphu-
ric acid, or oil of turpentine, or rubbed with sugar, chalk, lard, conserve of
roses, &c., it is reduced to a gray powder, which consists of minute mercu-
rial globules, blended with the foreign body; and when this is abstracted
they again unite into running mercury. In well made mercurial ointment
these globules are not discernible by the naked eye. The extent to which
this division may be carried, is well illustrated in the preparation termed
precipitated mercury ; obtained by precipitating a solution of corrosive subli-
mate by protochloride of tin : the liberated mercury forms so fine a precipi-
tate that it is perfectly black, and requires several hours to subside. There
are two oxides of mercury, both of them salifiable : a dioxide or suboxide,
HggO, and an oxide, HgO.

Suboxide op Mercury. Dioxide of Mercury ; Black Oxide of Mercury ;
Mercurious Oxide (Hg^O). — This oxide (formerly termed protoxide) is
obtained when finely-levigated dichloride of mercury -(calomel) is triturated
with excess of lime-water ; it must be carefully washed with cold water, and
dried at common temperatures, under exclusion of light. It is a black or
brownish-black powder, sp. gr. 10 6, easily resolved by light, or by heat into
metal and oxide. The salts of this oxide are generally obtained either by
its direct solution, or by digesting excess of mercury with the acids, or with
the salts of the red oxide, or by double decomposition : they are usually
yellow when basic, but otherwise colorless, soluble in water, redden litmus,
and taste metallic ; some of them are resolved by the action of water into an
insoluble basic, and a soluble acid salt. They give black precipitates, with
the caustic alkalies. With carbonate of potassa they afford a brownish-
yellow, and with bicarbonate a yellowish-white precipitate, sparingly soluble
in an excess of the bicarbonate, and becoming black and losing carbonic acid
when boiled. With carbonate of ammonia the precipitate is at first white,
but blackens on adding it in excess. With hydrochloric acid and soluble
chlorides these salts give a white precipitate of subchloride of mercury,

SUBCHLORTDE OF MERCURY. CALOMEL. 481

which is immediately blackened by the alkalies. With sulphuretted hydro-
gen, and the hydrosulphates, the precipitate is black ; with phosphate of
soda, white ; with iodide of potassium, greenish-yellow, darkened by an
excess of the precipitant ; with hydrocyanic acid, mercury is precipitated,
and a cyanide of mercury formed : Hg,,0 + HCy=Hg-fHgCyH-HO.

Oxide of Mercury. Red Oxide ; Peroxide ; Mercuric Oxide (HgO). —
This oxide is produced by heating mercury in a long-necked flask, open to
the air, nearly to its boiling-point. It becomes slowly coated with reddish-
brown scales and crystals, and is ultimately converted into a red crystalline
substance, called in old pharmaceutical wovV^,, precipitatum per se, or calcined
mercury. It may also be obtained by heating nitrate of mercury, so long as
fumes of nitrous acid are evolved ; the resulting oxide is in the form of an
orange-red crystalline powder. This oxide is also thrown down in the form
of a yellow powder, when potassa of soda is added to a solution of corrosive
sublimate, or of nitrate of mercury. In this precipitated state it possesses
certain properties in regard to solvents, which distinguish it from the crystal-
line oxide, of which it is considered an allotropic modification. Oxide of
mercury has a metallic taste, and is poisonous ; it is slightly soluble in water,
and the solution, which is feebly alkaline, when exposed to air becomes
gradually covered with a brilliant film. Its specific gravity is 11 '0^4. When
heated, it blackens, but becomes again red on cooling; at a red heat it
evolves oxygen, and is reduced to the metallic state; it was thus that
Priestley first obtained oxygen gas. When long exposed to light it becomes
black upon the surface. It should be entirely volatilized when placed upon
a red-hot iron, for it is sometimes adulterated with red lead. This oxide of
mercury is decomposed by sulphur, phosphorus, and several of the metals :
when mixed with sulphur and heated, it explodes ; and with phosphorus it
explodes by the blow of a hammer. It combines with acids, and like the
suboxide forms compounds, several of which are resolvable into salts with
excess of base, and salts with excess of acid. There is also a great tendency
to the formation of double salts among the haloid mercurial compounds.
The salts of the red oxide are, generally speaking, more active and poisonous
than those of the black oxide; they mostly redden litmus, and are reduced
first to the state of salts of suboxide, and then to metal, by several deoxi-
dizing agents, such as phosphorous and sulphurous acids, protochloride of
tin and sugar.

Mercury and Chlorine combine in two proportions, and form a sub-
chloride or dichloride, and a chloride or perchloride of mercury, compounds
corresponding with the oxides, and formerly called protochloride and bichlo-
ride ; the old terms calomel and corrosive sublimate applied to these chlorides
are distinctively convenient, and are not liable to cause mistakes in dispensing
mercurial preparations.

SUBCHLORIDE OF Mercury; Dichloride of Mercury. Mercurious Chloride.
Calomel (Hg3,CI). — This compound is first mentioned by Crollius early in
the seventeenth century. The first directions for its preparation are given
by Beguin in 1608. There are several processes by which calomel may be
obtained: one of these consists in triturating 4 parts of corrosive Sublimate
with 3 of mercury (and a little water to prevent the dust rising), till the
whole forms a gray powder, which is introduced into a proper subliming
vessel, gradually raised to a red heat : the subchloride sublimes, mixed with
a little of the chloride, which may be separated by reducing the whole to fine
powder, and washing it in large quantities of hot distilled water. In this
process the chloride is reduced to the subchloride by the addition of mer-
cury (HgCl + Hg, = Hg2,Cl). Subchloride of mercury may also be formed
by precipitating a soFution of subnitrate of mercury by a solution of common
31

482 CALOMEL AND CORROSIVE SUBLIMATE.

salt: Hg20,N054-NaCl=Hg:2Cl,-f NaO,N05. Calomel is generally manu-
factured upon the large scale, for pharmaceutical purposes, by sublimation,
from a mixture of the sulphate of the suboxide with common salt : (Hg^O,
S03,-|-NaCl, = IIgaCl + NaO,S03). The calomel vapor is received into a
capacious condenser, in which it is deposited in a pulverulent form : it is
afterwards most carefully triturated, levigated, and washed in large quanti-
ties of distilled water, till it becomes perfectly tasteless, and till the water
filtered from the washed powder is not discolored by sulphuretted hydrogen.

The form in which calomel sublimes depends much upon the dimensions
and temperature of the vessel in which its vapor is condensed. In small
vessels it generally condenses in a crystalline cake, the interior surface of
which is often covered with prismatic crystals : in this state it acquires, by
rubbing into powder, a pale buff tint. If, on the contrary, it is sublimed
into a capacious and cold receiver, it falls in an impalpable white powder.
By a modification of the process, it may be suffered, as it sublimes, to fall
into water. But in whatever way calomel is obtained, it requires cafeful
washing, and extreme care as to its state of minute mechanical division. To
detect corrosive sublimate in calomel, we may digest the calomel in warm
ether for a few hours, pour off the liquid or filter it and evaporate to dryness.
Any corrosive sublimate will be kft in prismatic crystals, which will acquire
a red color when moistened with a solution of iodide of potassium.

Calomel is tasteless, and insoluble in water. Its sp. gr. is 7 '14. At a
beat somewhat below redness, it rises in vapor, without previous fusion ; but
it fuses when heated under pressure. The density of its vapor is 8 -2. By
hot hydrochloric acid it is resolved into mercury and corrosive sublimate;
but when boiled in dilute hydrochloric acid a portion is dissolved without
decomposition. By nitric acid it is converted into corrosive sublimate and
pernitrate, with the evolution of nitric oxide (3Hg2CI + 4N05=3HgCl-h3
[HgOj^^Ogj + NOg). Sulphur, phosphorus, and several of the metals de-
compose it. Boiled with copper and water, chloride of copper and metallic
mercury are procured. Triturated with iodine and water, corrosive subli-
mate and iodide of mercury are formed : Hg2ClH-I=HgCl + HgI. With
aqueous hydrocyanic acid calomel yields metallic mercury, and cyanide of
mercury and hydrochloric acid are found in solution ; HggCl-|-HCy=Hg-|-
HgCy + HCl. Native Suhchloride of Mercury or Mercurial Horn Ore, has
been found crystallized, and sometimes incrusting and massive : it is rare.

Chloride of Mercury. Perchloride. Bichloride. Mercuric Chloride.
Oxymuriate of Mercury ; Corrosive Sublimate (HgCl). — When mercury is
boiled and introduced into chlorine, it burns with a pale flame, and a white
volatile substance rises, which is this chloride. When oxide of mercury is
heated in a current of chlorine, oxygen is expelled ; HgO + Cl=HgCl4-0 :
and when the oxide is gently heated in hydrochloric acid gas, water and the
chloride are the results; HgO-f HCl = HgCl + HO. The ordinary process
for making corrosive sublimate consists in exposing a mixture of chloride of
sodium and sulphate of mercury to heat in a proper subliming vessel ; corro-
sive sublimate rises, and sulphate of soda is the residue : HgO,S03+NaCl=
NaO,S03wMIgCl.

Chloride of mercury has an acrid nauseous taste, leaving a permanent
metallic and astringent flavor upon the tongue : it is a powerful corrosive
poison. It evaporates to a small extent at common temperatures. Its spe-
cific gravity is 5'4. It is usually met with either in the form of heavy white
semi-transparent and imperfectly crystallized masses, or in powder. It fre-
quently exhibits prismatic crystals upon the inner surfaces of the sublimed
cakes. It is soluble in about 16 parts of cold, and 3 of boiling water; and
as the solution cools, it deposits quadrangular prismatic crystals. It dis-

CHLORIDES OP MERCURY. 483

solves in 3 parts of alcohol and in 4 of ether. "When heated, it fuses, boils,
and entirely evaporates in the form of a dense white vapor, powerfully
afifecting the nose an(\ mouth : the density of this vapor is 9*4 : it is condensed
in prismatic crystals on cold surfaces in tubes. Corrosive sublimate is nearly
insoluble in concentrated nitric and sulphuric acids. Hydrochloric acid of
the specific gravity 1"158, at the temperature of 60°, dissolves about its own
weight, and the solution, when cooled to about 40°, concretes into a mass
of crystals; there appear to be two or three of these hydro chlorates of chloride
of mercury ; they are partially decomposed when added to a great excess of
water, and resolved into free hydrochloric acid and chloride. Corrosive
sublimate is either decomposed by, or combines with, many organic bodies ;
some of them convert it into calomel, others enter into combination with it,
forming permanent compounds. The applications of it to the preservation
of anatomical preparations, and to the prevention of dry rot, illustrate these
actions. The efiBcacy of a mixture of white of ^.gg and water, in preventing
or mitigating the poisonous effects of this substance, depends upon its direct
combination with albumen.

Oxichlorides of Mercury. — There are three of these compounds produced
by the action of corrosive sublimate on bicarbonate of potassa ; and each
of them is said to be susceptible of allotropic modifications. If a saturated
solution of the bicarbonate is added to 8 times its bulk of a saturated solution
of the chloride, a red precipitate falls, which is 2(HgO)HgCl ; but with one
volume of the alkaline solution, and two of the sublimate, the precipitate is
black and crystalline, but of the same composition. When the solutions are
mixed in equal volumes, the precipitate, which is at first yellow, is 3(HgO)
HgCl ; and when the solution of sublimate is added to a large excess of that
of the bicarbonate, carbonic acid is evolved, and brown crystalline crusts are
deposited, which are 4(HgO)HgCl.

Action of Ammonia on Chloride of Mercury. — When corrosive sub-
limate is heated in a stream of ammonia, a white crystalline, volatile, and
fusible compound is obtained, which is not soluble in water without decom-
position : it is an ammonio- chloride =NH3,2HgCI. A solution containing
1 atom of sal-ammoniac and 1 of corrosive sublimate in a small quantity of
water, yields rhombic prisms, permanent in the air, but which, when dried
at 212°, become opaque, and lose about 5*5 per cent, of water. They con-
stitute the sal alemhroth of the old chemist =NH4Cl,HgCl. When 1 atom
of sal-ammoniac and 2 of corrosive sublimate are mixed and heated, a com-
pound = NH^Cl + 2HgCl sublimes: when the same salts are dissolved in water,
the solution yields, on evaporation, silky crystals =NH4C1 -f-2HgCl-f HO.

Amidochloride of Mercury ; White Precipitate (HgNH3,HgCl) is ob-
tained by adding a slight excess of ammonia to a solution of corrosive
sublimate, washing the precipitate with cold water, and drying it by a gentle
heat: 2HgCl + 2NH3=HgNH„HgCl-f NH.Cl. It is a white powder,
which, when boiled in water, is partly converted into sal-ammoniac, which is
dissolved, and partly into an almost insoluble yellow powder, which is a com-
pound of amidide, chloride, and oxide of mercury : 2(HgNH2HgCl)-f 2H0
= NH,Cl + (HgNH3 4-HgCl + 2HgO). When white precipitate is highly
heated, a red crystalline compound remains, which is represented by the
formula 2(HgCl)HgN. White precipitate is more chalky-looking than
calomel, and not so heavy. Like calomel it is insoluble in water; but while
alkalies turn calomel black, they produce no change of color in this compound.
When boiled in a solution of potash, white precipitate gives off ammonia,
and the residue becomes yellow. Calomel is blackened and evolves no
ammonia. White precipitate, owing to imperfect washing, generally con-
tains some corrosive sublimate. This may be detected by the process

484 IODIDES OF MERCURY.

recommended for its detection in calomel. Ammonio-chloride of mercury is
an active poison. In medicine it is used only for external application.

Hydrargochlorides. — Chloride of mercury forms a numerous series of
double salts with chlorides of the other metals, which are obtained by dis-
solving the salts in proper proportions, and allowing them to crystallize.

Iodides of Mercury. — There are two iodides of mercury, corresponding
to the chlorides.

SuBioDiDE (HgJ) is obtained, 1. By triturating together 200 parts of
mercury and 128 parts of iodine, moistened with alcohol. 2. By adding
iodide of potassium to a very dilute solution of acetate or nitrate of suboxide
of mercury : Hg20,N05+KI = Hg2l-fK0,N05. 3. By digesting in boiling
water 236 parts of calomel with 166 of iodide of potassium : Hg2Cl + KI=
Hggl-f KCl. 4. By triturating together 1 equivalent of mercury with 1 of
iodide of mercury, moistened with alcohol. Subiodide of mercury is a dingy
greenish-yellow powder : specific gravity 7 "7 : it is nearly insoluble in water,
and insoluble in alcohol. When rapidly heated in a glass tube it fuses, and
sublimes unaltered : gently heated, or long exposed to light, it is resolved
into mercury and iodide.

Iodide. — Periodide of Mercury (Hgl) is obtained, 1. By triturating 1
equivalent of mercury with 1 of iodine (100 mercury and 127 iodine)
moistened with a little water or alcohol. 2. By the mutual decomposition
of corrosive sublimate and iodide of potassium : HgCl4-KI=HgI + KCl.
When a strong solution of iodide of potassium is gradually added to one of
corrosive sublimate, a red precipitate forms, which redissolves on agitation ;
forming a soluble compound of chloride and iodide of mercury ; on the
further addition of iodide of potassium a pale reddish and permanent pre-
cipitate is obtained, which is also a compound of chloride and iodide,
containing, however, more of the latter ; this precipitate, on continuing the
addition of the iodide of potassium, becomes of a brilliant scarlet, and this
is iodide of mercury, but if excess of iodide is added, it disappears, and a
colorless solution of hydrargoiodide of potassium is formed ; so that to
obtain a pure iodide of mercury the relative atomic equivalents must be
strictly preserved. When heated it becomes yellow, and fuses into an amber-
colored fluid, giving off vapor which condenses in yellow rhombic plates;
these, if scratched or ruptured, resume a scarlet color (p. 36). Crystalliza-
ble double salts {hydrargoiodides or iodo-hydrargyrates) are formed by the
combination of iodide of mercury with the alkaline iodides. The iodide is
soluble in the chlorides of the metals of the alkalies, but does not form
crystallizable compounds with them. When a hot solution of corrosive sub-
limate is saturated with iodide of mercury, it deposits crystals on cooling
=HgI,2HgCl. A combination of this kind forms a useful precipitant of
the alkaloids, producing with the true alkaloids, when the solution is not too
acid, an insoluble white compound containing an insoluble hydriodate of the
alkaloid. This test is made by dissolving 16 grains of corrosive sublimate
and 60 grains of iodide of potassium in 4 ounces of water. Small quantities
of morphia, veratria, and strychnia are thus easily detected in mixtures which
do not contain much alcohol or acid (acetic). If no precipitate is produced,
the absence of an alkaloid may be fairly inferred. Albumen gives a pre-
cipitate with the test, but this organic principle may be separated by boiling
the liquid and filtering it before adding the test. It is not affected by
ammonia, but gives a precipitate of yellow oxide of mercury with potash or
soda.

Subbromide of Mercury (Hg^Br) is obtained when 1 atom of mercury
and 1 of bromide of mercury are mixed and heated ; it forms a crystalline

BROMIDES. SUBNiTRATES OF MERCURY. 485

sublimate of a pale yellow color: it is also thrown down in the form of a
white powder, on mixing^solutions of bromide of potassium and nitrate of
suboxide of mercury. It is insoluble in water, fusible, and volatile at a dull
red heat.

Bromide 'OF Mercury (llgBr) is formed by triturating mercury with bro-
mine, or when bromine and mercury are shaken together in water. It is
deposited from its aqueous solution in lamellar crystals, fusible and volatile.
It is soluble in 100 parts of cold water, and in 4 or 5 of boiling water. It
is very soluble in alcohol and in ether. An oxyhromide of mercury =HgBr,
3HgO, is formed by boiling bromide and oxide of mercury together in water ;
it is a yellow crystalline powder, sparingly soluble in boiling water. There
are several compounds of bromide of mercury with basic bromides (Jiydrar-
gobromides), some of which are crystallizable.

Mercury and Nitrogen. Xitride of Mercury (IlggN). — This com-
pound is formed by passing ammonia over oxide of mercury till saturated ;
it is then heated to 300°, and the current of ammonia continued as long as
water is formed: 3HgO -f NH3=Hg3N,-|-3HO. The product is always
contaminated by a little metallic mercury, which may be abstracted by cold
dilute nitric acid. Nitride of mercury is a brown powder, which explodes
when struck with a hammer, or when suddenly heated.

Mercury and Nitric Acid. Nitrates of Mercury. — There appear to
be three nitrates of the suboxide of mercury — namely, a neutral and two
basic salts. 1. The neutral Nitrate of suboxide of Mercury =HggO,N05, is
formed by digesting excess of mercury in cold dilute nitric acid till short
prismatic crystals are formed, which include 2 atoms of water. (If these are
left in the solution they gradually give place to larger crystals of a sesqui-
salt.) They are entirely soluble in a small quantity of warm water ; by a
large quantity of water they are resolved into an acid and basic salt : the
acid salt is at once obtained by dissolving this, or the subnitrates, in dilute
nitric acid. This salt is resolved by heat into red oxide {Hydrargyri nitrico-
oxidum), a,nd nitrous acid; (Hg30,NOg=2E[gO + N04). 2. Sesquinitrate
of suboxide of Mercury (3IIg30,2N03). — When the first formed crystals of
the preceding salt are left in the mother-liquor, they gradually dissolve, and
are replaced by large transparent prisms having the formula 3B[g20,2N05,
3H0. They are soluble without decomposition in a little water ; in much
water they pass into a yellowish subsalt and a soluble supersalt. — 3. Bibasic
nitrate of suboxide of Mercury (2(Hg20)N05) is formed by repeatedly
washing either of the preceding salts with cold water : it remains as a yellow
crystalline powder.

Nitrates of the red oxide of Mercury ; Pernitrates of Mercury. — 1. There
is no crystallizable monobasic tiitrate of red oxide of Mercury =HgO,N05.
When peroxide of mercury is dissolved in nitric acid, or when mercury is
boiled in strong nitric acid, a dense liquor is obtained on evaporation, which
stains the cuticle brown ; on further, evaporation acid escapes, and crystals
of dipernitrate are formed. 2. Bibasic nitrate of red oxide of Mercury.
Dipernitrate of Mercury 2(HgO)N05. This salt, which crystallizes out of
the preceding solution, is deliquescent, decomposed by water, but soluble
without change in water acidulated by nitric acid : its crystals are 2(HgO)
N05,2HO. 3. Tribasic nitrate of the red oxide of Mercury =(3HgO)N05,
HO, remains in the form of a yellow hydrated powder when the preceding
salt is drenched with cold water as long as it runs off sour. — Sexbasic nitrate
of red oxide of Mercury, 6(HgO)N05, is formed by the continuous action of
boiling water on the yellow tribasic salt. The nitrates of mercury are some-
times used for the purpose of dressing the fur on the skins of animals such

486 NITRATES OF MERCURY SULPHIDES.

as hares and rabbits. Workmen engaged in this occupation have suffered
from the usual symptonas of mercurial poisoning.

Action of ammonia on the Nitrates of Mercury. 1. Ammonio-nitrate of
suboxide of Mercury. Hahnemannh Soluble Mercury (3Hg.^0,H-NH^d,
NO5). — This compound is obtained by precipitating a very dilute cold aqueous
solution of nitrate of suboxide of mercury by a weak solution of ammonia;
the mixture should be constantly stirred, the ammonia not added in excess,
and the precipitate washed as quickly as possible upon a filter, and dried in
the shade at ordinary temperature. It is a grayish-black powder. — 2. Nitrate
of ammonia and of suboxide of Mercury. By evaporating a mixed solution
of nitrate of suboxide of mercury and nitrate of ammonia, prismatic crystals
are formed, the aqueous solution of which gives a gray precipitate both with
ammonia and with carbonate of potassa. — 3. Basic a. mi do -nitrate of Mer-
cury (HgNHg-f 5(HgO)N05). Tliis compound appears to be sometimes
formed when excess of ammonia is added to a concentrated nitrate of per-
oxide of mercury : it is a pale yellow powder containing about 85 per cent,
of mercury.

Mercury and Sulphur. Subsulphide of Mercury ; Disulphide of Mer-
cury (HgaS). — When 1 part of mercury is triturated for some time with 3
of sulphur, a black tasteless compound is obtained, which was called in old
pharmacy, Ethiops mineral ; when boiled in solution of potassa, sulphur is
taken up, and sulphide, (HgS) remains, so that it is probably a mixture of
sulphur and sulphide. When sulphuretted hydrogen is passed through a
dilute solution of nitrate of suboxide of mercury, or through a mixture of
very finely divided calomel and water, a black powder is thrown down, which
is a true subsulphide.

Sulphide OF Mercury ; Bisulphide; Vermilion; Cinnabar (HgS). — This
sulphide is obtained anhydrous and of a red color by the following process :
6 parts of mercury are mixed in an iron pot with 1 of sulphur, and made to
combine by a moderate heat, and constant stirring : the mixture is then
transferred to a subliming-vessel, and heated to redness in a sand-bath.
Mercury and sulphur evaporate, and a steel-gray sublimate forms, which is
removed, and rubbed or levigated into a very fine powder (vermilion). If
mercury and sulphur are heated together in large quantities, the action is so
intense at the moment of their combination, as to occasion an explosive
ignition. When solution of corrosive sublimate is decomposed by the pro-
longed action of an excess of sulphuretted hydrogen, or of an alkaline
sulphide, the precipitate which falls is hydrated sulphide of mercury : it is
black, until warmed in the sulphuretted liquor, when it gradually reddens, as
a result of dehydration. The principal points to attend to in procuring this
pigment of its most perfect hue, are in the first place the careful selection
and cleansing of the first crystalline gray sublimate, so that there may not
be the smallest remaining admixture of the black pulverulent amorphous
compound; ajid secondly, the perfection of the pulverization and elutriation,
so as to render the powder as impalpable as possible. Cinnabar is not
altered by exposure to air or moisture ; when heated to a dull redness in an
open vessel, the sulphur forms sulphurous acid, and the mercury escapes in
vapor. The metal is thus procured from its ores (p. 479). In close vessels
it sublimes before it fuses. It is decomposed by distillation with fixed alka-
lies, lime, and baryta, and by several of the metals. When adulterated with
red lead or with colcothar, it is not entirely volatile. It is insoluble in caustic
alkaline solutions, and in nitric and hydrochloric acids; but nitrohydrochloric
acid acts upon, and decomposes it, even in the cold. Boiled in sulphuric
acid, sulphurous acid is evolved, and a sulphate of mercury is formed. Native
Cinnabar is the principal ore of mercury : it occurs massive and crystallized.

SULPHATES OF MERCURY. 4S7

It is of various colors, sometimes appearine^ steel-prray, at otliers bright-red.
Native mercury, and native amalg:nm of silver, sometimes accompany it.

Chlorosulphide of Mercury (2(rigS)IIgCl). — AViien sulphuretted hy-
drogen is passed through a solution of corrosive sublimate a white precipitate
is first formed ; if the action of the gas is continued, this white compound
blackens and becomes hydrated sulphide of mercury. The same white com-
pound is formed by digesting moist and recently precipitated sulphide of
mercury, in a solution of corrosive sublimate. It may be washed and dried
without decomposition. Corresponding compounds of the sulphide have
been obtained with iodide and bromide of mercury. Sulphide of mercury
also combines with other metallic sulphides.

Sulphide of Suboxide of Mercury (Hg.,0,S03). — When 1 part of mer-
.cury is digested in a moderate heat with \^ of sulphuric acid, sulphurous
acid gas is evolved, and a white mass is obtained, which, washed with cold
water, affords a difficultly soluble white salt, which is a sulphate of suboxide
of mercury. The same salt is thrown down, when sulphuric acid is added to
a solution of nitrate of suboxide of mercury : it is also formed by triturating
equivalent proportions of mercury and persulphate, and heating the mixture.
In this way it is prepared for the manufacture of calomel. Sulphate of sub-
oxide of mercury requires 500 parts of cold, and 300 of boiling water for
its solution : it crystallizes in prisms.

Sulphate of Peroxide of Mercury; Persulphate of Mercury (HgO,
SO3). — This salt is formed when two parts of mercury and three of sulphuric
acid are boiled down to dryness. Sulphurous acid escapes in consequence
of the decomposition of a portion of the acid (Hg + 2S03=HgO,S03+SOjj).
Thi« sulphate is decomposed in the humid way by the hydracids, and free
sulphuric acid is found in solution. It is resolved by water into a soluble
acid salt and an insoluble basic salt: the former may be obtained in white
deliquescent acicular crystals. — Tribasio Sulphate of Peroxide of Mer-
cury ; Subsulphate of Mercury (3(HgO)S03). This sa-k, long known
under the name of Turpeth mineral (so called from a similarity in its medi-
cinal effects to those of the root of the Convolvulus Terpethum, which is
cathartic and emetic), is obtained in the form of an almost insoluble yellow
powder by the action of boiling water upon the preceding sulphate ; when
gently heated, its color gradually deepens to orange, but reverts to lemon-
yellow as it cools. Sulphate of Mercury forms a double salt with sulphate
of ammonia =NH^0,S03-f HgOjSOg, which is difficultly soluble, and falls
in the form of a white powder on mixing solutions of the component sul-
phates.

Phosphates of Mercury. — When solution of common phosphate of so"da
is dropped into a solution of suboxide of mercury, a white crystalline pre-
cipitate falls (2(Hg30)HO,PO.) ; when the solution of the phosphate is
added to pernitrate of mercury, a dense white insoluble powder is thrown
down=2(HgO)HO,P05.

Carbonates op Mercury. — Carhonate of Suboxide of Mercury (Hg^O,
CO^) is thrown down when solution of carbonate of soda is dropped into
solution of nitrate of suboxide of mercury, in the form of yellow powder.
Carbonate of Peroxide of Mercury (4( HgO) CO J. — Solution 'of nitrate of
mercury affords a reddish-brown precipitate with carbonate of soda, which
is slightly soluble in excess of the alkaline solution, and in aqueous car-
bonic acid.

Mercury and Cyanogen. Cyanide of Mercury (HgCy). — There are
several processes for obtaining this compound. (I.) By boiling 1 part of
finely-powdered peroxide of mercury with 2 of Prussian blue in 8 of water,
a solution is obtained, which if filtered while hot, deposits crystals of the

488 FULMINATING MERCURY.

cyanide. (2.) When peroxide of mercury is brought into contact with the
vapor of hydrocyanic acid they act intensely upon each other, and water and
cyanide of mercury are formed. (3 ) Peroxide of mercury may be digested
in aqueous hydrocyanic acid. (4.) To a solution of 2 parts of ferrocyanide
of potassium in 15 of boiling water, add 3 parts of dry persulphate of mer-
cury ; boil for 15 minutes and filter off the clear liquid whilst hot ; as it cools
cyanide of mercury crystallizes, which must be purified by a second crystalliza-
tion; (K,FeCy3+3(HgO,S03)=3HgCy-f2KO,S03, + FeO,S03). Cyanide
of mercury forms anhydrous prismatic crystals, nearly colorless, or of a pale
buff color, at first transparent, permanent in the air, poisonous, and of a
nauseous metallic taste ; they dissolve in 8 parts of water at 60°, and are
sparingly soluble in alcohol. This salt is decomposed by heat, as in the
process for obtaining cyanogen, and a brown or black matter remains in the
retort, which \s> paracyanogen (p. 218) If distilled with hydrochloric acid,
hydrocyanic acid and chloride of mercury are produced: it is also decomposed
by hydriodic acid and by sulphuretted hydrogen, an iodide and a sulphide of
mercury, and hydrocyanic acid, being formed (p. 282). Nitric acid dis-
solves it without decomposition. It is decomposed when heated with sul-
phuric acid. The alkalies do not act upon this cyanide.

Fulminating Mercury ; Fulminate of Mercury ; (2(Hg30)Cy202). —
This compound is prepared by dissolving 100 grains of mercury in a measured
ounce and a half of nitric acid, aided by heat. This solution is to be poured,
when cool, into two measured ounces of alcohol in a porcelain basin, and
gently warmed : it soon effervesces and evolves ethereal vapor, and if the
action is too violent, it must be quelled by cooling the vessel, or by the
addition of a little cold alcohol. During this action a gray precipitate
falls, which is to be immediately separated by decantation and filtration,
washed with small quantities of distilled water, and carefully dried at a heat
not exceeding 100°. The above quantity of mercury should yield about 120
grains of the powder. If the product is mixed with metallic mercury, it
may be purified by solution in boiling water, from which it is deposited in
silky acicular crystals. This dangerous compound is now in considerable
demand for the manufacture of percussion caps. It is introduced into the
caps, closely compressed, moistened with a resinous varnish, and subsequently
carefully dried. When fulminating mercury is heated to about 300°, it
explodes suddenly with a bright flame : it also detonates by friction or per-
cussion, especially when placed in contact with particles of sand or glass ;
by the electric spark, and by contact of concentrated sulphuric and nitric
acids ; the gases evolved by its explosions are carbonic acids, nitrogen, and
the vapor of mercury.

Alloys of Mercury. Amalgams. — Mercury combines with most of the
other metals, forming a class of compounds which are called amalgams.
Many of these are definite and crystallizable, and may be separated, by
gentle pressure, from the excess of mercury in which the definite compound
is suspended or dissolved. They are generally brittle or soft. The extra-
ordinary phenomena connected with the amalgam of ammonium, and the
probable nature of that substance, have already been discussed (p. 183).
An amalgam of sodium is now in great demand for procuring gold and silver,
as well as for many useful purposes in chemistry and the arts. One part of
potassium with 70 of mercury produces a hard brittle compound. If mer-
cury is added to the liquid alloy o^ potassium and sodium, an instant solidi-
fication ensues, and heat enough to inflame the latter metals is evolved.
Iron and mercury may be combined by triturating together clean iron filings
and zinc-amalgam, and adding a solution of perchloride of iron ; by rubbing
and heating this mixture, the iron and mercury form a bright amalgam.

AMALGAMS OF MERCURY. 489

Under common circumstances, iron resists the action of mercnry so perfectly,
that tiie latter metal is usually kept in iron bottles; and mercurial troughs
and barometer cisterns are made of iron. An amalg:am of zinc is used for
the excitation of electrical machines. 8 parts of mercury and 1 of zinc form
a white brittle compound ; 5 of mercury and 2 of zinc form a crystal I izable
amalgam. Amalgam of tin is easily formed by triturating the metals to-
gether, or by fusion at a gentle heat : it is largely used for silvering looking-
glasses. This beautiful process is performed as follows : A single and perfect
sheet of pure tinfoil, of proper thickness, and somewhat larger than the plate
of glass, is spread upon a perfectly plane table of slate or stone : mercury is
then poured upon it, and rubbed upon its surface by a hare's foot, or a ball
of flannel or cotton, so as to form a clean and bright amalgam; upon this,
an excess of mercury is poured, until the metal has a tendency to run off.
The plate of glass, previously made quite clean, is now brought horizontally
towards the table, and its edge so adjusted, as, by gradually and steadily
sliding it forward, to displace some of the excess of mercury, and float the
plate as it were over the amalgam, the dross upon its surface being pushed
onwards by the edge of the glass, so that the mercury appears beneath it
with a perfectly uniform, clean, and brilliant reflecting surface. Square iron
weights, of 10 or 12 lbs. each, are then placed side by side upon the surface
of the plate, so as entirely to cover it, and press it down upon the amalga-
mated surface of the tin ; in this way the excess of mercury is partly squeezed
out, and the amalgam is made to adhere, by crystallization, firmly to the
glass (p. 23). The mercury, as it runs off", is received into a channel on the
side of the table, which is slightly inclined to facilitate the drainage, and in
about 48 hours the weights are taken off and the plate is carefully lifted from
the table and set nearly upright, by which the adhering mercury gradually
drains off, and the brilliant amalgam remains, perfectly and uniformly ad-
hering to the glass. Amalgam of copper may be made as follows : to a
hot solution of sulphate of copper add a little hydrochloric acid and a few
sticks of zinc, and boil the mixture for about a minute ; the copper will be
precipitated in a metallic state, and in a finely-divided spongy form ; take
out the zinc, pour off the liquor, wash the copper with hot water, and pour
upon it a little dilute nitrate of mercury, which will instantly cover every
particle of copper with a coating of this metal ; then add mercury to the
amount of two or three times the weight of the copper, and a slight tritura-
tion will so con>bine them that the completion of the process may be effected
by heating the mixture for a few minutes in a crucible. Lead and mercury
readily combine in all proportions : 3 parts of mercury and 2 of lead form a
crystallizable amalgam. Bismuth amd mercury readily unite : a mixture of
3 parts of mercury, 1 of lead, and 1 of bismuth forms a fluid amalgam used
for silvering the inside of hollow glass spheres. When mercury is adulterated,
it is with these metals ; but the facility with which it then oxidizes, and the
imperfect fluidity of its small globules, render the fraud easy of detection.

Tests for the Salts of Mercury. — The soluble salts of the suboxide are
mostly white : some of them, when neutral, are resolved by water into basic
and acid salts. 1. With phosphorous and sulphurous acids, and protochlo-
ride of tin, they give precipitates of metallic mercury ; 2. The caustic alka-
lies throw down a black, and the carbonated alkalies a yellow or brown pre-
cipitate ; 3. The alkaline phosphates, a white precipitate, even in very dilute
solutions; 4. Sulphuretted hydrogen and the hydrosulphates, black; 5.
Hydriodic acid and the iodides, dingy green or yellow in very diluted solu-
tions ; 6. Hydrochloric acid and the chlorides, white and curdy precipitates;
the alkaline chromates, red ; ferrocyanide of potassium, white ; the oxalates,
white, even when very dilute. The soluble salts of the red or peroxide of

490 TESTS FOR THE SALTS OF MERCURY.

mercury are mostly white when neutral, yellow when basic, and are often re-
solved by .water into acid and basic salts. 1. Protochloride of tin gives a
black precipitate, which, when boiled, thrown on a filter, and dried, runs
into small globules of metallic mercury. 2. Caustic alkalies, when added
in small quantity, give a reddish-brown, and in large qnantity, a yellow pre-
cipitate of the hydrated oxide of mercury. 3. Ammonia and carbonate of
ammonia produce white precipitates in their solutions. 4. Iodide of potas-
sium gives a red, and infusion of galls an orange precipitate. Unless in con-
centrated solutions they are not affected by hydrochloric or oxalic acid. Me-
tallic mercury is precipitated from all of its solutions by a plate of clean
copper, or by the addition of protochloride often, and boiling the liquid.
The insoluble mercurial salts are mostly volatilized at a red heat ; and both
soluble and insoluble salts are decomposed, with the production of metallic
mercury, when heated in a glass tube with 2 or 3 parts of dry carbonate of
soda, or of ferrocyanide of potassium.

Analysis in Cases of Poisoning. — Oxide of Mercury may be identified
by its red color, its insolubility in water, and by its yielding a sublimate (in
globules) of metallic mercury, when dried and heated in a glass tube. It is
dissolved by nitric acid, and the solution possesses the characters assigned
above to the persalts of the metal. White precipitate. This is a white chalky-
looking powder, not soluble in water, but partly converted into a yellow
basic salt by boiling water: 1. Ammonia does not change its color. 2.
Nitric acid readily dissolves it (by these two characters it is distinguished
from calomel) ; in the acid solution, chlorine may be found by the addition
of nitrate of silver. 3. When boiled with a solution of potassa, ammonia is
liberated. 4. When digested with protochloride of tin, it is darkened, and
metallic mercury is set free. 5. When heated with dry carbonate of soda, it
yields a sublimate of metallic mercury.

Corrosive Sublimate. — This is the principal poison of mercury. It is
usually seen in heavy crystals, or in the form of a white crystalline powder.
As a solid, 1. When the powder is heated on a platinum foil or mica, it
melts, and is volatilized in a white vapor without leaving any residue. 2.
When heated in a close tube, it melts and forms a sublimate, consisting of
prismatic crystals sometimes stellated. 3. The powder is changed in color
by the following reagents: iodide of potassium produces a bright scarlet,
potassa a yellow, and hydrosulphate of ammonia a black precipitate ; ammo-
nia does not alter it. 4. The mercury and chlorine may be discovered by
one process. Mix the powder with 3 parts of dry carbonate of soda, and
heat it until the residue in the tube fuses and becomes white. A sublimate
of metallic mercury in globules will be obtained. Detach by a file the end
of the tube containing the fused residue, which is chloride of sodium with
some undecomposed carbonate. Digest it in water with nitric acid, and
apply heat until it is entirely dissolved : then add to the solution, nitrate of
silver. A white precipitate of chloride of silver, insoluble in nitric acid will
be at once produced. The solid is thus proved to contain both mercury and
chlorine, and the only compound of these elements soluble in water is cor-
rosive sublimate. In solution in water. 1. Protochloride of tin added to a
solution of corrosive sublimate, produces a black precipitate which, after it
has been boiled, is resolved into globules of metallic mercury. 2. Sulphu-
retted hydrogen and hydrosulphate of ammonia produce, after a time, a black
sulphide, not soluble in alkalies or diluted acids. 3. If the liquid is acidu-
lated, and bright copper foil, wire, or gauze, is plunged into it, the copper
acquires a silvery-white deposit, even in the cold, but more rapidly by heat.
When the copper with the metallic deposit is heated in a tube, globnles of
mercury are obtained.

DETECTION OF MERCURY IN CASES OF POISONING. 491

In Organic Liquids. — The liquid should be separated by filtration from
any insoluble portion. The latter should be pressed, dried, and set aside
for a separate analysis. A slip of bright copper foil or gauze may be em-
ployed as a trial test in the manner above described. In place of copper,
a small galvanic combination, made by twisting a layer of gold-foil round a
layer of zinc foil, may be introduced. The liquid should be slightly acidu-
lated with hydrochloric acid and warmed. The metals may be suspended in
the liquid for some hours. If the mercurial poison is present, the gold will
sooner or later lose its color and become silvered while the zinc will be wholly
or in part dissolved. The slip of gold foil may be washed in water, and
afterwards in ether, and dried. It should be divided into two equal portions.
One should be submitted to heat in a tube, when globules of mercury will
be obtained ; the other should be heated in concentrated nitric acid, until
the gold has reacquired its yellow color. On evaporating the excess of acid,
and adding a solution of protochloride of tin, a dark gray precipitate of
metallic mercury is thrown down. It may be remarked that sublimed mercury
is wholly unlike any other volatile substance. Globules of the 8000th part
of an inch in diameter may be easily recognized by the aid of a microscope.
Their perfect sphericity, their silvery whiteness by reflected, and complete
opacity by transmitted light, at once identify them as metallic mercury.

In the event of a doubt existing respecting their mercurial nature, the
following experiment will remove it. Cut off by a file the portion of glass
in wliich they are deposited : introduce this into a wide short tube, with a
few drops of hydrochloric, and half the quantity of nitric acid. Heat the
acid liquid, and carry it to dryness on a sand-bath. White prismatic crys-
tals of corrosive sublimate will remain if the sublimate was of a mercurial
nature, and too great a heat has not been applied. On touching the white
residue cautiously with a drop of solution of iodide of potassium, the crystals
will acquire a scarlet-red color.

Another method of analysis may be sometimes usefully resorted to. Place
the suspected organic liquid in a small golden capsule. Acidulate it slightly
with hydrochloric acid, and touch the gold, through the acid liquid, with a
slip of pure zinc foil. Mercury will be deposited in a white silvery stain on
the gold, wherever the two metals have come into contact. Wash out the
capsule with distilled water, and add a few drops of strong nitric acid. Per-
nitrate of mercury is thus obtained, which may be tested by the processes
above described for the detection of the persalts of mercury.

The insoluble compounds of mercury may be dissolved by strong nitric
acid, and the solution tested for the metal. If none is found, the dried solid,
mixed with dried carbonate of soda or ferrocyanide of potassium, may be
heated in a tube, when mercury, if present, will be volatilized. The tissues
may be dried and dissolved in 1 part of hydrochloric acid and 4 parts of
water. The metal may be separated from the concentrated liquid, either by
copper-gauze or by gold and zinc.

The processes above described reveal only the presence of mercury. When
the quantity of corrosive sublimate in an organic liquid is moderately large,
it may be removed by means of ether. Place the filtered liquid supposed to
contain the poison, in a stoppered tube ; add to it, its volume of pure ether,
and agitate the liquid at intervals for half an hour. Allow the liquid to
subside, pour off the ether into a dial-glass, and submit it to spontaneous
evaporation. As the ether passes off, the corrosive sublimate wMll be de-
posited in white silky-looking prisms. These may be purified by solution in
water, if necessary, and the solution again crystallized. If mercury and
arsenic are associated in a poisonous mixture, the arsenic may be entirely
separated by distillation (page 479).

492 PRODUCTION OF SILVER FROM ITS ORES.

CHAPTER XXXVIII.

Silver (Ag=108).

This metal, the Luna or Diana of the alchemists (D), was known at a
very remote period : it is found native, and in a variety of combination, the
most common of which is the sulphide. Native Silver occurs massive, arbor-
escent, capillary, and, sometimes, crystallized. It is seldom pure, but con-
tains other metals, which affect its color and ductility.

Silver is not unfrequently obtained in considerable quantities from argen-
tiferous sulphide of lead, which is reduced in the usual way, and the argen-
tiferous lead is then fused in a shallow dish, placed in a reverberatory furnace,
with a current of air constantly passing over its surface ; in this way the lead
is converted into oxide or litharge, and the silver is left in the metallic state.
The litharge which results from this operation is afterwards reduced by
charcoal, and furnishes lead which is free from silver ; the ordinary lead of
commerce generally contains a trace of the latter metal, and is consequently
unfit for certain purposes of the arts, especially for the manufacture of white
lead.

The sulphides of silver are reduced by amalgamation. The ore, when
washed and ground, is mixed with a portion of common salt, and roasted :
during this operation arsenic and antimony are expelled, the copper and the
iron are converted into oxides, chlorides, and sulphates, and sulphate of soda
and chloride of silver are formed. The product is powdered, and agitated
with mercury, water, and filings or fragments of iron ; in this operation the
chloride of silver is decomposed, chloride of iron is formed which is washed
away, and the silver and mercury combine into an amalgam, from which the
excesss of mercury is first squeezed out in leather bags, and the remainder
driven off by distillation. The old process of eliquation is now scarcely
used : it consisted in fusing alloys of copper and silver with lead ; this triple
alloy was cast into plates which were placed in a proper furnace upon an
inclined plane of iron with a small channel grooved out, and heated red-hot,
during which the lead melted, and in consequence of its attraction for silver,
carried that metal with it, the copper being left behind in a reddish-black
spongy mass. The separation of silver from lead by the process of crys-
tallization has been already noticed (page 26).

Pure Silver may be procured by dissolving the standard silver of com-
merce in nitric acid, diluted with an equal measure of water. Immerse a
plate of clean copper in the filtered solution, which occasions a precipitate
of metallic silver ; collect it upon a filter ; wash it with a weak solution of
ammonia, and then with water, and fuse it into a button. It may also be
procured by adding to the above solution of standard silver a solution of
common salt ; collect, wash, and dry the precipitate, and gradually add it
to twice its weight of fused carbonate of potassa mixed with carbonate of
soda, in a red-hot crucible. Metallic silver is separated, and may be fused
into a button. Again the chloride may be dissolved in ammonia, and a slip
of copper foil introduced : or the chloride diffused in water may be decom-
posed by nascent hydrogen derived from zinc and sulphuric acid or from
sodium amalgam. By any of these processes silver may be procured pure.

PROPERTIES OF SILVER. OXIDES OF SILVER. 493

Properties. — Silver is of a more pure white tban any other metal : it has
considerable brilliancy, and takes a high polish. Its specific gravity varies
between 10*4, which is the density of cast silver, and 10'5 to 10'6, which is
the density of rolled or stamped silver. It is harder than gold, and after
gold the most ductile of metals. One grain of the pure metal may be drawn
into wire 400 feet in length, finer than a human hair. It is less malleable
than gold, but it may be beaten into leaves which are not more than
1-150, 000th of an inch in thickness. They are not, however, so thin as to
be translucent. When alloyed with gold the malleability is increased, and
the leaves transmit a violet colored light. Silver is regarded among metals
as the best conductor of heat and electricity. Silver melts at a bright red
heat, estimated at 18t3° of Fahrenheit's scale, and when in fusion appears
extremely brilliant. It resists the action of air at high temperatures for a
long time, and does not oxidize, but it is readily oxidized by a current of
moist air containing ozone. The ordinary tarnish of silver is occasioned by
sulphuretted hydrogen ; it takes place very slowly upon the pure metal, but
more rapidly upon the alloy with copper used for plate, especially in a damp
atmosphere. Pure water has no effect upon the metal ; but, if the water
contains organic matter, it is sometimes slightly blackened. If an electric
discharge is passed through fine silver-wire, it burns into a black powder.
In the Voltaic circle it burns with a fine green light, and throws off abundant
fumes. Exposed to an intense white-heat in the open fire it boils and
evaporates, but in close vessels it is not sensibly volatile. If suddenly
cooled, it crystallizes during congelation, often shooting out like a cauli-
flower, and spirting or throwing small particles of the metal out of the
crucible. This arises from the escape of oxygen, which the metal absorbs
and retains whilst fluid, but suddenly gives off when it solidifies : this curious
property of absorbing oxygen is prevented by the presence of a small quan-
tity of copper.

Oxides of Silver. — There are three oxides of this metal — a suboxide,
AgijO ; a protoxide, AgO ; and a binoxide, AgO^. Of these, the protoxide
only forms permanent and definite saline combinations. 1. Suboxide of
Silver (Ag^O). This oxide is obtained by the action of hydrogen on citrate
of silver, at the temperatcPre of 212^; the protoxide loses half its oxygen,
and the suboxide remains combined with half of the acid. The solution in
water of the suboxide salt is dark-brown, and the suboxide is precipitated
black from it by potassa ; when the solution of the subsalt is heated, it be-
comes colorless, and metallic silver appears in it. Some other salts of silver
containing organic acids, may be substituted for the citrate. 2. Oxide of
Silver (AgO) may be obtained by adding lime-water or a diluted solution of
soda to a solution of nitrate of silver, washing the precipitate, and drying it
at 212°. It is of a dark olive color, tasteless, but soluble to a small extent
in pure water ; and, like oxide of lead, it has when in solution an alkaline
reaction : this solution is reddened by exposure to light, and is rendered
turbid by a little carbonic acid, but again becomes clear with an excess.
When heated to dull redness this oxide is reduced to the metallic state ; long
exposure to light also reduces it, converting it into a black powder, which
is either silver or its suboxide. It is reducible by hydrogen at a tempera-
ture of about 212° ; and also by phosphorous and sulphurous acids. It
imparts by fusion a yellow color to glass, and is employed in enamel and
porcelain painting. Oxide of silver dissolves in aqueous ammonia, forming
a colorless liquid, which becomes coated with a film of suboxide by exposure
to air; and when kept for some months in a stopped bottle, acquires a film
of metallic silver. Berthollet's fulminating silver is also formed by the action
of ammonia on the oxide. The best process for preparing it is to pour a

4'&4 CHLORIDE OP SILVER.

small quantity of strong aqueous ammonia upon the oxide ; a portion is dis-
solved, and a black powder remains, which is the deto.nating compound ; it
should be cautiously dried on bibulous paper. It explodes with tremendous
violence when gently rubbed or heated ; nitrogen and water are evolved, and
the silver is reduced. It should only be prepared in small quantities, and
handled with caution, for it occasionally explodes while wet. It is soluble
in an excess of ammonia, and this solution sometimes deposits it in small
brilliant opaque crystals. There is some doubt respecting the real nature
of this compound : it is probably a nitride of silver, =Ag3N. The composi-
tion usually assigned is 3(AgO)NH3 ; when exploded, it is converted into
3Ag + N-f3HO.

Peroxide of silver (AgOg). — By electrolyzing a weak solution of silver,
acicular crystals of this peroxide are formed at the positive pole. Ammonia
energetically decomposes it, and acids convert it into the protoxide. When
mixed with phosphorus or sulphur, and struck with a hammer, it detonates.
There is reason to believe that the second equivalent of oxygen is in the
state of ozone, and is evolved as such. If introduced in a sealed tube into
a stoppered bottle containing dry chlorine, and the tube is then broken by
agitating the bottle, it will be found after a short time that the chlorine has
disappeared and is replaced by oxygen.

Chloride op Silver (AgCl). — Silver does not decompose hydrochloric
acid even on boiling, so that no chloride can be formed by digesting the
metal in the acid. If the surface of the silver is tarnished by sulphuretted
hydrogen, the sulphuret is entirely decomposed and the discoloration removed
by the acid. Silver and chlorine may, however, combine directly on contact.
When silver leaf is acted upon by gaseous chlorine in a humid state, it is
gradually converted into this compound, and if sufficiently thin, a leaf of
white chloride of silver is obtained in a few hours ; otherwise the action is
superficial. Chloride of silver is usually procured by adding a solution of
common salt to a solution of nitrate of silver. It falls in the form of a white
curdy precipitate, which, by exposure to light, becomes violet-colored, brown,
and ultimately black. This happens even in diffused daylight; but in sun-
shine the change is rapid, especially if organic matter or moisture is present.
This property of the chloride has led to its eraifloyment in photography.
When a small quantity of subchloride of mercury is precipitated along with
the chloride of silver, the blackening effect of light is greatly diminished.
Chloride of silver is so insoluble in water, that the minutest portion of hydro-
chloric acid, or of any chloride in aqueous solution, may be detected by it.
It is insoluble in nitric acid, and in cold sulphuric acid ; but when boiled in
sulphuric acid, it is slowly decomposed, with the formation of sulphate of
silver. It is soluble to a small extent in boiling hydrochloric acid, and in
strong solutions of the chlorides of the alkaline metals, forming with them
erystallizable double salts. It is abundantly soluble in solutions of ammonia,
cyanide of potassium, and the alkaline hyposulphites.

When dry chloride of silver is heated to dull redness in a silver crucible,
it does not lose weight, but fuses, and, on cooling, concretes into a gray
semitransparent substance (sp. gr. 5-45), which has been called horn silver^
or luna cornea. If slowly cooled, it has a tendency to octahedral crystalli-
zation. Heated to a bright red or white heat in an open vessel, it volatilizes
in dense white fumes. If fused with potassa or soda, or their carbonates,
chloride of silver is decomposed, and metallic silver is obtained; (AgCl-|-
K0=Ag4-KClH-0). Moist chloride of silver is also decomposed when
triturated with, and boiled in a solution of caustic potassa; a dense black
oxide is produced, and if sugar is added, it is reduced to metallic silver. If
diffused in water acidulated with dilute sulphuric or hydrochloric acid, and

IODIDE, BROMIDE, AND NITRATE OF SILVER. 495

a rod of magnesium or zinc is introduced into the mixture, hydrogen is
liberated and the silver is completely reduced (AgCl4 H = AgH- HCl). Tri-
turated with fine zinc filings, and moistened, the heat produced is considera-
ble. The fused chloride, exposed to ammonia, absorbs a considerable portion
of the gas, which is again given off by heat. If the chloride, thus saturated
with ammonia, is thrown into chlorine, the ammonia spontaneously inflames.

Chloride of silver is said to require 113,000,000 partsof water to dissolve it.
It may therefore be considered as insoluble in water. Hence a salt of silver
is employed in quantitative analysis, as a means of determining the propor-
tion of chlorine. In these cases some excess of the precipitant should be
used, and the precipitate allowed to subside previous to separating it upon
the filter : if the supernatant liquor becomes perfectly clear, the whole of the
silver has fallen ; if it remains opalescent, a portion is probably still retained.
When the precipitate remains long suspended, its deposition may be accele-
rated by heat, by agitation, or by adding a little nitric acid. The chloride
should be perfectly dried before weighing it. 100 parts of the dried and
fused chloride, are equivalent to 24*67 parts of chlorine and 75 33 of silver.
Native Chloride of Silver has been found in most of the silver-mines : it occurs
massive and crystallized.

Iodide of Silver (Agl). — When silver-leaf is put into a bottle containing
a little iodine it is speedily tarnished, and in the course of a few days con-
verted into a film of yellow iodide. Iodide of silver is precipitated upon
adding a soluble iodide to a solution of nitrate of silver. It is of a yellowish
color, insoluble in water, and decomposed when heated with potassa.
Chlorine also decomposes it. It is nearly insoluble in ammonia. When
fused it acquires a red color. It dissolves in solutions of the alkaline
cyanides and hyposulphites, and in a saturated solution of nitrate of silver :
it is also dissolved by iodide of potassium and other alkaline iodides Native
Iodide of Silver has been found in some of the Mexican ores, associated with
native silver, sulphide of lead, and carbonate of lime.

Bromide of Silver (AgBr) is an insoluble yellowish substance, thrown
down upon the addition of bromine, or the soluble bromides, to nitrate of
silver : it dissolves in an excess of a strong aqueous solution of ammonia,
and readily in alkaline cyanides and hyposulphites : it is fusible, and con-
cretes on cooling into a yellow corneous mass. Chlorine converts it into
chloride of silver : it is sparingly soluble in solutions of bromide of potas-
sium and sodium, and more abundantly so in a solution of sal-ammoniac :
the compounds which it forms with the alkaline bromides are decomposed
when diluted. Native bromide of silver has been found in Mexico and Chili,
in small yellowish cubic crystals ; and a native chlorobromide (3Ag'Cl,2Ag
Br) from Chili has been described by Colonel Yorke.

Nitrate of Silver (AgO,N05). — Nitric acid diluted with 3 parts of
water readily dissolves silver, with the disengagement of nitric oxide : if the
silver contains copper, the solution is bluish ; or if gold, that metal remains
undissolved in the form of a black powder. The solution of nitrate of silver
should be clear and colorless ; it is caustic, and tinges animal substances at
first of a yellow color, becoming, by exposure to light, purple or black. On
evaporation, the solution yields anhydrous tabular crystals, which have a
bitter metallic taste, and are soluble in about their own weight of water at
60°, and in half their weight at 212°: they are insoluble in nitric acid.
Alcohol dissolves about one-fourth its weight of this salt at its boiling-point,
but deposits nearly the whole as it cools. Nitrate of silver, when mixed
with organic matters, blackens on exposure to light ; and when thus acted
upon, it is no longer perfectly soluble in water, owing to the separation of a
portion of metallic silver; but if cautiously excluded from the contact of

0Kk AMMONIO-NITRATE OF SILVER.

organic matter, light alone does not discolor it. When heated in a silver
crucible, it fuses into a gray mass, and if cast into small cylinders, forms the
lunar caustic of pharmacy. It may be fused at the end of platinum wire.
When nitrate of silver is exposed to a red h-eat, the acid is partly evolved
and partly decomposed, and metallic silver is obtained. Sulphur, phospho-
rus, charcoal, hydrogen, and several of the metals, decompose this nitrate.
A few grains mixed with a little sulphur, and struck upon an anvil with a
heavy hammer, produce a detonation : phosphorus occasions a violent ex-
plosion when about half a grain of it is placed upon a crystal of the nitrate
and struck sharply with a hammer ; if heated with charcoal it deflagrates,
and the metal is reduced.

A stick of phosphorus or charcoal introduced into a weak solution of
nitrate of silver, soon becomes incrusted with crystals of silver. A plate of
copper also occasions a precipitation of crystalline silver. Arborescent
crystals of silver may be produced on glass by the following process : Coat
a glass plate with collodion in the usual way, immerse it in the bath of nitrate
of silver to produce a complete penetration. Then lay it, with the coated
surface downwards, on a triangle or quadrangle made of fine copper wire,
and keep it in the dark. The silver will be slowly reduced at each point of
contact with the wire, and will spread in a thin crystalline film over the
surface. When dried, the crystals may be protected by another glass plate
placed over the surface. Mercury introduced into a solution of nitrate of
silver causes a crystalline deposit of silver, called the arbor Diaiice. Proto-
sulphate of iron throws down metallic silver when added to a solution of the
nitrate ; protochloride of tin forms a gray precipitate.

When some of the solutions of silver are reduced by certain essential oils,
or by grape-sugar, a brilliant film of the metal may be so thrown down upon
glass as to furnish a substitute for the amalgam of tin usually employed for
mirrors: the coating is not to be depended upon for durability, but it has
the advantage of being applicable to curved surfaces and the interior of
spherical vessels. Pelouze and Fremy describe the process as follows : 600
grains of nitrate of silver are dissolved in 1200 grains of water; to this are
added, 1st. 75 grains of a solution composed of 10 grains of sesquicarbonate
of ammonia, 10 of solution of ammonia, sp. gr. 0980, and 25 of distilled
water ; 2d. 30 gains of solution of ammonia, sp. gr. 0 980 ; 3d. 1000 grains
of alcohol, sp. gr. 0-850 : this mixture is left at rest to become clear, it is then
decanted, and a mixture of equal parts of alcohol and of oil of cassia is
added, in the proportion of 1 part of this essence of cassia to 15 parts of the
solution of silver : this mixture is shaken and left to settle for some hours,
and then filtered : just before applying it to the glass to be silvered, it is
mixed with l-78th of its bulk of essence of cloves, cooiposed of 1 part of oil
<^ cloves and 3 of alcohol. The glass to be silvered is first thoroughly
cleansed, then covered with the silvering solution and warmed to about 100^,
at which temperature it is kept for 2 or 3 hours: the liquid is then decanted
and may be used for other glasses. The deposit of silver is then washed,
dried, and varnished.

Nitrate of silver is employed for writing upon linen, under the name of
indelible or marking ink : and it is an ingredient, with gallic or pyrogallic
acid, in some of the liquids sold for the purpose of changing the color of
hair : the black stain of any of these preparations of silver may be removed
by cyanide of potassium. When taken internally, a bluish-black discolora-
tion of the skin often ensues, so that the whole surface of the body, and
especially the parts exposed to light, acquire a leaden-gray color. Among
organic compounds which deoxidize a solution of nitrate of silver, may be
noticed the freshly-precipitated resin of guaiacum. This is white, but on

SULPHIDE AND HYPOSULPHITE OF SILVER. 497

adding it to a small quantity of nitrate of silver and warming the liquid, it
becomes of a deep-blue, a result of oxidation of the resin. On boiling the
Cquid the color changes and metallic silver is separated in the form of a dark
powder. Gallic acid slowly reduces the metal in the cold, but pyrogallic
acid rapidly decomposes it, the silver being precipitated as a black powder.

Solution of the nitrate of silver is a valuable test of the presence of chlo-
rine, hydrochloric acid, and the soluble chlorides, with all of which it forms
a white cloud when very dilute, but a flaky precipitate when more concen-
trated ; the precipitate is soluble in ammonia, but insoluble in nitric acid.
Heat, agitation, or the addition of a few drops of nitric acid, so as to render
the liquid acid, facilitates the deposition of the precipitate. The hydriodic,
hydrobromic, and hydrocyanic acids also occasion in a solution of nitrate of
silver, precipitates which become slightly darkened by exposure to light.

Ammonio-Nitrate of Silver. — Ammonia is rapidly absorbed by nitrate
of silver, with the production of heat sufficient to fuse the compound, which
consists of 100 parts of the nitrate, and 295 parts of ammonia. An ammo-
nio-nitrate of silver is also obtained when ammonia is added to a solution of
nitrate of silver until the first-formed precipitate is redissolved. This solu-
tion when colored with a little Indian ink forms a good marking ink, but the
stains of all these compounds may be removed by cyanide of potassium : or
by steeping the linen in chlorine water until the stain is whitened, and then
applying ammonia or a solution of hyposulphite of soda to dissolve and wash
out the chloride.

Sulphide of Silver (AgS). — Silver readily combines with sulphur, and
produces a gray crystallizable compound, more fusible and softer than silver.
It may be obtained by heating finely-divided silver, or plates of silver, with
sulphur. Its density is about 7. Sulphuretted hydrogen and hydrosulphate
of ammonia occasion a copious black precipitate of sulphide of silver when
added to solutions of the metal : sometimes a portion of the silver is at the
same time reduced to the metallic state. It is the presence of sulphur in the
atmosphere (generally sulphuretted hydrogen) which occasions the tarnish
upon silver, and which is a great obstacle to many applications that might
otherwise be made of this beautiful metal.

Native Sulphide of Silver, or vitreous silver, is found massive and crystal-
lized. It is soft and sectile. A triple combination of silver, antimo7iy, and
«M//?A?/r, = 3(AgS)SbS3, constitutes the red, or ruby silver-ore ; it is some-
times accompanied by the brittle sulphide, or silver glance, and by antimonial
silver (AggSb).

Hyposulphite of Silver (AgO,S203,5HO) is formed by dropping a weak
solution of nitrate of silver into a solution of hyposulphite of soda : a white
cloud is produced, which redissolves on agitation : on adding more of the
precipitant, the cloud reappears and aggregates into a gray precipitate of
hyposulphite of silver. When the nitrate is in excess, the precipitate rapidly
changes from gray to yellow, brown, and black, being ultimately converted
into sulphide of silver. Hyposulphite of silver is also produced when chlo-
ride of silver is dissolved in any of the hyposulphites; the solution has a
sweetish taste. This solubility of argentine compounds in alkaline hyposul-
phites, has led to the important application of them to the photographic art.
{See Photography, p. 511.) Hyposulphite of silver is very prone to de-
composition, especially on boiling, being resolved into sulphate of oxide of
silver, and sulphide of silver. Doable salts of the hyposulphites of ammonia,
potassa, and soda, with silver, have been formed.

Sulphite of Silver (AgOjSOg) is obtained in white crystalline grains
by adding an alkaline sulphite to a solution of silver. It produces double
salts witb the sulphites of the alkalies.
32

498 SULPHATE, PHOSPHATE, AND CYANIDE OF SILVER.

Sulphate op Silver (AgO,S03) is deposited when sulphate of soda or
dilute sulphuric acid is mixed with nitrate of silver. It is also produced by
boiling silver with its weight of sulphuric acid. It forms a white salt solu-
ble in about 90 parts of water at 60°; in boiling water it is more soluble,
and is deposited, as the solution cools, in small anhydrous crystals : it dis-
solves in sulphuric acid, but on moderate dilution, the greater part of the
salt again falls down. By leaving a strong sulphuric solution of silver in a
dark place, it gradually absorbs water, and octahedral crystals of the sulphate
are deposited. Upon the large scale, small portions of gold are separated
from large quantities of silver, by heating the finely-granulated alloy in sul-
phuric acid : the gold remains in the form of a black powder, and the sul-
phate of silver may be decomposed by the action of metallic copper, which
precipitates metallic silver, and forms sulphate of copper. Sulphate of
silver absorbs ammonia, and by saturating a strong and warm solution of
ammonia with sulphate of silver, prismatic crystals =2(NH3),AgO,S03, are
obtained.

Phosphate of Silver 3(AgO)P05. — When a solution of common phos-
phate of soda, 2(NaO)HO,P05, is added to nitrate of silver, a yellow anhy-
drous tribasic phosphate of silver falls, and free nitric acid is found in the
supernatant liquor: 3(AgO,N05)-f2(NaO)HO,P05=3AgOP05+2(NaO,
N05)-fH0,N05). If the solution of nitrate of silver is precipitated by
anhydrous tribasic phosphate of soda, 3(NaO)P05, the supernatant solution
remains neutral. This phosphate of silver fuses at a red heat. It is soluble
in nitric, phosphoric, and acetic acids, as well as in ammonia and carbonate
of ammonia.

Pyrophosphate op Silver, 2(AgO)P05, is the white precipitate thrown
down from nitrate of silver by pyrophosphate of soda: in this case the super-
natant liquid remains neutral [2(AgO,N05)-f 2(NaO)P03=2(AgO)P05-f-
2(NaO,N03)].

Metaphosphate of Silver (AgO,P05) is a white gelatinous precipitate,
thrown down by a solution of nitrate of silver by metaphosphate of soda ;
boiling water resolves it into an acid and a basic salt.

Carbonate of Silver (AgOjCOg) is precipitated in the form of a pale
yellow powder, by adding carbonate of potassa to nitrate of silver. It
blackens by exposure to light, and is easily decomposed by heat. Moist
oxide of silver absorbs carbonic acid from the air.

Cyanide of Silver (AgCy). — Hydrocyanic acid, or solution of cyanide
of potassium, causes a white precipitate in solution of nitrate of silver, which
is cyanide of silver, and which, when heated, fuses, and, at a high tempera-
ture, gives out cyanogen. It is insoluble in water and in fixed alkalies, but
soluble in ammonia. It is decomposed by hydrochloric acid, and by sulphu-
retted hydrogen ; nitric acid scarcely acts upon it, unless concentrated and
heated. Sulphuric acid, diluted with its volume of water, decomposes it
when boiling, with the escape of hydrocyanic acid and the formation of sul-
phate of silver : in this way cyanide may be separated from chloride of silver.
It dissolves in a strong solution of nitrate of silver, and forms a compound
which is decomposed by water. It is soluble in the alkaline chlorides, in
hyposulphite of soda, and in cyanide of potassium. Argento-cyanides. — Cya-
nides of the alkaline bases form soluble double salts with cyanide of silver :
they are insoluble in alcohol, which throws them down from their aqueous
solutions. The argento-cyanide of potassium (KCy,AgCy) yields plumose
colorless crystals : it produces precipitates in many of the metallic solutions,
which are insoluble argento-cyanides. A solution of oxide or chloride of
silver in cyanide of potassium, forms a useful liquid for silvering metals by
immersion, especially when aided by electricity. It is thus employed in

FULMINATE OF SILVER. 499

electro-plating : 1 part of cyanide of potassiam may be dissolved in 10 parts
of water, and 50 or 60 grains of oxide or chloride of silver dissolved in each
pint : the oxide and chloride should be in a moist state. Cyanide of potas-
sium is also useful for removing the tarnish from old^ silver. It decomposes
and dissolves the sulphide.

Cyanate of Silver (AgO,CyO). — This monobasic salt falls in the form
of a white powder when cyanate of potassa is added to nitrate of silver.

Fulminate of Silver; Fulminating Silver, 2(AgO)Cya02. — This dan-
gerous compound is prepared as follows : 100 grains of fused and finely-
powdered nitrate of silver are added to an ounce of warm alcohol in a large
basin ; an ounce of nitric acid is then added, and presently effervescence
ensues and a powder falls : as soon as this appears white, cold water is added,
and the powder collected upon a filter, washed, and carefully dried at a tem-
perature of 100°. In collecting and handling this powder the utmost caution
is requisite ; it should be made in small quantities only, and not touched
with anything hard, for it has exploded upon the contact of a glass rod under
water. The feather of a common quill serves to collect it ; and it should be
kept either under water, or if dry, in a wide-mouthed vessel covered by
paper, and not in a stoppered or corked phial. Fulminating silver is a gray
crystalline powder ; it acquires a dingy hue by exposure to light ; it dissolves
in from 30 to 40 parts of boiling water, and as the solution cools, nearly the
whole is again deposited in minute crystals. It detonates with great violence
when heated, or when touched by any hard substance ; placed upon a piece
of rock-crystal and touched in the slightest manner by another crystal, it
explodes violently ; it also detonates upon the contact of sulphuric acid, and
by the electric spark. In the formation of fulminic acid, a portion of the
alcohol is oxidized so as to form aldehyde, and formic and oxalic acids : this
is effected at the expense of the oxygen of the nitric acid, which passes into
hyponitrous acid, and this, reacting upon another portion of the alcohol,
forms hyponitrous ether, fulminic acid, and water ; 1 atom of hyponitrous
ether and 1 of hyponitrous acid containing the elements of 1 atom of fulminic
acid and 6 of water.

Hyponitrous Ether -f- Hyponitrous Acid = Fulminic Acid + Water
' C^H.OjNOg ' ' NO3 "" '~ C4N2O2 "" 5H0

When fulminating silver (2(AgO)Cy30a) is digested in a solution of
potassa, half of the oxide of silver is precipitated, and on filtering and
evaporating the solution, a crystallizable salt is obtained =AgO,KO,Cy303.
It is dangerously explosive. In this salt one atom of oxide of silver is
replaced by one atom of potassa. Corresponding compounds may be ob-
tained with other basic oxides.

Cyanurate of Silver. — If nitrate of silver is added to cyanurate of
potassa, a white precipitate is obtained, which consists of 1 atom of cyannric
acid combined with 2 of oxide of silver and 1 of water ; 2(AgO)HO,Cyg03.
This salt, heated in the dry state, evolves hydrated cyanic acid. If a solution
of silver be added to a boiling solution of cyanurate of ammonia, containing
ammonia in excess, the cyanurate with 3 atoms of oxide of silver, is formed :
3(AgO)Cy303.

Ausenite of Silver, 2(AgO)As03, is precipitated in the form yf a pale
yellow powder, soon becoming deeper yellow, gray, and brown, by the addi-
tion of arsenite of potassa, to nitrate of silver. Arsenious acid only produces
a white cloud in solution of nitrate of silver, but the yellow arsenite falls on
the subsequent addition of a small quantity of alkali. This salt retains its
yellow color when carefully dried, but becomes brown on exposure to light.

500 SALTS OF SILVER. ALLOYS OF SILVER.

Arsenio -nitrate of Stiver. — This is obtained in solution by mixing one part
of a saturated solution of nitrate of silver with five or six parts of a saturated
solution of arsenious acid. It should give a yellow precipitate when a small
quantity of any alkali is added to it. If the precipitate is brown more
arsenious acid must be added. It is a useful solution for the detection of
alkalies or alkaline liquids.

Arsenate op Silver, 3(AgO)As05, is thrown down from nitrate of
silver by arsenic acid, and by the soluble arsenates, of a reddish-brown
color. It is insoluble in water, but soluble in aqueous ammonia; it dis-
solves in nitric acid, and in acetic acid.

Chromate of Silver, AgO.CrOg, is precipitated of a crimson-red color
by mixing solutions of chromate of potassa and nitrate of silver. It soon
loses its brilliant tint and becomes brown.

Bichromate of Silver, AgO,2Cr03 is precipitated by adding bichromate
of potassa to an acid solution* of nitrate of silver. When boiled in water it
is resolved into dark green neutral chromate, and an acid solution, which, on
cooling, again deposits crystals of bichromate.

Alloys of Silver. — The compounds of silver with potassium, sodium,
and other light metals, have not been examined. When silver and steel are
fused together, an alloy is formed, which appears perfect while in fusion, but
globules of silver exude from it on cooling, which shows the weak attraction
of the metals. At a very high temperature, the greater part of the silver
evaporates, but a portion equal to about 1 in 500 remains, forming an alloy
known as silver-steel, and said to be well adapted to the formation of cutting
instruments, but subject to rust from galvanic action. Silver readily com-
bines with zinc, producing a brittle bluish-white granular alloy. With tin
silver forms a white, hard, brittle alloy. The alloy with copper constitutes
plate and coin. By the addition of a small proportion of copper to silver,
the metal is rendered harder and more sonorous, while its color is scarcely
impaired. When the two metals are in equal weights the compound is
white : the maximum of hardness is obtained when the copper amounts to
one-fifth of the silver. The standard silver of this country is composed of
92-5 silver+T"5 copper ; that of France, of 90 silver -|-10 copper; and in
that of Prussia, the alloys amount to 25 per cent. The specific gravity of
British standard silver is 10"3. The silver coins of the ancients, and many
Oriental silver coins, are nearly pure ; they only contain traces of copper
and of gold. When silver alloyed by copper, such as standard silver, is
exposed to a red heat in the air, it becomes black from the formation of a
superficial film of oxide of copper ; this may be removed by immersion in hot
diluted sulphuric acid, and a film of pure silver then remains, of a beautiful
whiteness : this is called blanched, dead, or frosted silver. The blanks for
coin are treated in this way before they are struck, whence the whiteness of
new coin, and the darker appearance of the projecting portions occasioned
by wear, in consequence of the alloy showing itself beneath the pure surface ;
articles of plate are often deadened, matted, or frosted by boiling in bisul-
phate of potassa (sal enixum), which acts in the same way as dilute sul-
phuric acid. Lead and silver form a very brittle dull-colored alloy, from
which the lead is easily separated by cupellation. When fused lead con-
taining silver is suffered to cool slowly, the lead, which first concretes, forms
granular, crystals, and is nearly pure, while almost the whole of silver is
contained in the liquid portion ; in this way the separation of the two metals
may to a certain extent be efi'ected, especially upon the large scale (p 26).
Antimony iovm?. a brittle white alloy. With Bismuth, [he alloy is brittle
and lamellar. When silver and arsenic are fused together, an alloy is formed,
which is gray, brittle, and granular. Silver amalgamates easily with mer-

ASSAY OP SILVER. 501

cury : when red-hot silver is thrown into heated mercury it dissolves, and
when 8 parts of mercury and 1 of silver are thus combined, a granular
crystalline soft amalgam is obtained. "When a solution of this amalgam in
liquid mercury is squeezed through chamois leather, the excess of mercury,
retaining only a trace of silver, goes through, and the solid amalgam is left
behind. Amalgam of silver is sometimes employed for plating; it is applied
to the surface of copper, and the mercury being evaporated by heat, the
remaining silver is burnished. The better kind of plating, however, is per-
formed by the application of a plate of silver to the surface of the copper,
which is afterwards extended by rolling. A mixture of chloride of silver,
chalk, and pearlash, is employed for silvering brass : the metal is rendered
very clean, and the above mixture, moistened with water, rubbed upon its
surface. Plating by metallic precipitation from ammonio-chloride of silver
is also frequently resorted to, but electro-plating with cyanide of silver, now
supersedes the other methods.

Assay of Silver. — The analysis of alloyed silver is in continual practice
by refiners and assayers. It may be performed in the humid way by dis-
solving the alloy in nitric acid, precipitating with hydrochloric acid or chlo-
ride of sodium, and either reducing the chloride, or estimating the quantity
of silver which it contains ; every 100 parts of the carefully dried chloride
indicating 75-33 of silver.

But a modification of this method is now generally resorted to, especiatty
applicable in cases where the quality of the alloy is approximately known :
it depends upon the precipitation of the silver by a standard solution of com-
mon salt, each 1000 grains of which contain a sufficient quantity of salt to
precipitate 10 grains of silver; so that, supposing the silver and the salt to
be pure, 10 grains of silver dissolved in nitric acid, would be entirely pre-
cipitated by 1000 grains of the standard solution. To effect this, each 1000
grains of the standard solution must contain 5 55 grains of pure chloride of
sodium ; this is equivalent to 388 grains in each gallon of such solution ; but
as commercial salt is not absolutely pure, the exact strength of the standard
solution must be experimentally adjusted by dissolving 10 grains of perfectly
pure silver in nitric acid, precipitating it by 1000 grains of the solution, and
adding either salt or water, as may be required. Having thus prepared this
standard solution of salt, 1000 grains of it are put into a convenient counter-
poised burette, or dropping-bottle ; 10 grains of the sample of silver to be
assayed are then placed in a stoppered bottle capable of holding about 6
ounces of water, and dissolved in about 2 drachms of nitric acid of sp. gr.
1'25. Such portion of the solution of salt is then added as will be required
to throw down nearly the whole of the silver ; the bottle is then well shaken
for about a minute, and the precipitated chloride allowed to subside. When
the liquid above it has become clear, a drop or two more of the standard
solution is added, and if it occasions any precipitate, the bottle is again
shaken, and, when clear, more of the standard solution is very cautiously
added, as long as it occasions any turbidity. When no cloud is produced,
the weight of the standard solution which has been added is ascertained by
re-weighing the burette, and the number of grains so employed indicates the
quantity of pure silver in the sample : if this be of the fineness of English
standard silver, 925 grains of the standard solution will have been used,
indicating the composition of the alloy to be 9 25 silver and 0*75 copper : if
the sample be of the French standard, 900 grains of the salt solution will
have been required, indicating an alloy of 9 silver and 1 copper. This pro-
cess of humid assaying was introduced into the French Mint by Gay-Lussac,
who has described it in detail, together with the apparatus required for car-
rying it out, and the precautions necessary to insure accuracy. A full

502 CUPELLATION. TESTS FOR THE SALTS OF SILVER.

description of this method, by Mulder, will be found in the Chemical News,
1861, vol. 2, pp. 137—204.

Assayers generally determine the value of silver bars by the process of
cupellation. Of the useful metals, three resist the action of air at high tem-
peratures— namely, silver, gold, and platinum ; the others, under the same
circumstances, become oxidized ; it might, therefore, be supposed, that alloys
of the first three metals would suffer decomposition by mere exposure to
heat and air, and that the oxidizable metal would burn into oxide. This,
however, is not the case : for if the proportion of the latter be small, it is
protected by the former ; or, in other cases, a film of infusible oxide coats
the fused globule, and prevents the further action of the air. These diffi-
culties are overcome by adding to the alloy some easily oxidizable metal, the
oxide of which is fusible. Lead is usually selected for this purpose. Sup-
posing, therefore, that an alloy of silver and copper is to be assayed, or
analyzed by cupellation, the following is the mode of proceeding : A clean
piece of the metal (about 20 grains) is laminated, and accurately weighed.
It is then wrapped in the requisite quantity of pure sheet-lead, apportioned
by weight to the quality of the alloy, and placed upon a small cupel, or
porous shallow crucible, made of bone-earth. The whole is then placed
within the muffle, heated to bright redness : the metals melt, and, by the
action of the air which plays over the hot surface, ihe lead and copper are
oxidized, and their fused oxides are absorbed by the cupel, and, if the opera-
tion has been skilfully conducted, a button of pure silver ultimately remains,
the completion of the process being judged of by the cessation of the oxida-
tion and motion upon the surface of the globule, and by the brilliant appear-
ance assumed by the silver when the oxidation of its alloy ceases. The
button of pure silver is then suffered to cool gradually, and its loss of weight
will be equivalent to the weight of the alloy which has been separated by
oxidation, a certain allowance being made for a small loss of silver, which
always occurs, partly by evaporation, and partly by the metal being carried
off with the oxides which are absorbed by the cupel. To perform this pro-
cess with accuracy, certain precautions are requisite, which can only be
learned by practice, so as to enable the operator to obtain uniform results.

Tests for the Salts of Silver. — 1. The soluble salts of silver give with
hydrochloric acid, and with soluble chlorides, a white curdy precipitate,
which is readily soluble in ammonia and in hyposulphite of soda, but insolu-
ble in nitric acid : it darkens by exposure to light. 2. With solutions of
potash and soda brown precipitates are produced, insoluble in an excess of
the alkali. 3. With ammonia the precipitate is also brown, but readily
redissolves in an excess of the precipitant. 4. With sulphuretted hydrogen
and hydrosulphate of ammonia, the precipitate is black and insoluble.
5. Protosulphate of iron throws down metallic silver. 6. A yellow precipi-
tate with common phosphate of soda, and arsenite of potassa, — a brick-red
precipitate with arsenate of potassa, — a crimson with chromate of potassa,
and a white with ferrocyanide of potassium, are further characteristics. The
silver salts insoluble in water are mostly soluble iu ammonia, and in nitric
acid. These salts, excepting those containing colored acids, are either white
or of a pale yellow color, provided they have not been exposed to light, to
sulphuretted hydrogen, or deoxidizing agents. Many of the metals, especially
copper, tin, and lead, separate metallic silver when immersed in its solutions.
Before the blowpipe the silver salts are easily reduced, especially when
mixed with carbonate of soda.

PHOTOGRAPHY. 503

CHAPTER XXXIX.

PHOTOGRAPHY AND ITS APPLICATIONS.

The Chemistry of Light.

The art of photography is based on the chemical changes which the salts
of silver undergo, when exposed to light. Silver is not the only metal which
is affected by light. Solutions of gold in contact with organic matter, yield
metallic gold of a defep purple color. The compounds of mercury, chromium,
uranium, iron, and molybdenum, are either reduced to a lower state of oxi-
dation by light, or, as in the black oxide of mercury, the metal is set free.
But there are no metallic salts which are so favorable for the practice of
photography as those of silver ; hence they are almost exclusively employed
for this purpose.

In some cases, a pure binary compound of the metal, Agl, or AgBr, is
used on a surface of metallic silver, as in the daguerreotype process : in others,
a binary salt, obtained by double decomposition, associated with pyroxyline,
is selected, as in the collodion process. The silver-compound used with dry
collodion, is the same as that of the daguerreotype, namely, Agl, or AgBr,
and is frequently a compound of the two ; while with the wet collodion, there
are not only these two salts, but free nitrate of silver. In the ordinary
paper process, the chloride of silver (AgCl) is employed ; but there is asso-
ciated with this, free nitrate of silver ; and when the surface of the paper is
albumenized, an organic compound of albuminate of silver.

All the salts of silver are more or less affected by light. In some instances
they undergo a visible change, being rendered dark in proportion to the
intensity of the light and the length of exposure. This is well seen in the
white chloride of silver when in a humid state ; and in the nitrate and am-
raonio-nitrate in contact with organic matter. It is less apparent in the
sulphocyanide, the hyponitrite, and pyrophosphate of silver, and is scarcely
visible in the cyanide, even after long exposure. The iodide and bromide
of silver do not darken by exposure to light* but they undergo instantane-
ously a remarkable molecular change, which renders them especially adapted
for photography.

The conditions necessary for these changes are light and moisture. When
the salt of silver is in contact with albumen or gelatine, the reduction is not
only accelerated, but it takes place with greater uniformity and depth. A
decomposable salt of silver in contact with organic matter, will spontaneously
change in the dark in a humid atmosphere ; and thus it is well known that
paper employed in photography, when once sensitized, or impregnated with
a silver solution, cannot be preserved unless certain precautions are taken.
The albuminate and chloride of the metal, formed upon the surface of the
paper in the act of sensitizing it, are decomposed, and the paper is slowly
darkened. The effect of a dry atmosphere in preserving the salts Of silver
from change has been elsewhere described (p. 42). As pure chloride of
silver undergoes no change of color when exposed to light in an atmosphere
artificially dried by chloride of calcium, the presence of water or moisture
appears to be necessary to the change ; but the presence of organic matter
is not absolutely necessary. In contact with water alone, the chloride

504 ACTION OF LIGHT ON THE SALTS OP SILVER.

changes from a snow-white to a pink, violet, brown, and finally a dark
bronze-black color ; and during this conversion, hydrochloric acid is pro-
duced. Hence the chemical change may be thus represented : AgCl + HO
=Ag-}-HCl-f O. According to Mitscherlich, the precipitated chloride,
well dried, inclosed in a tube, and exposed to light, is decomposed, and
chlorine only liberated : AgCl=Ag-fCl. The darkening of a layer of the
precipitated chloride is superficial ; if the darkened surface is removed, the
chloride beneath will be found quite white. When the chloride is precipi-
tated on paper for photographic purposes, the change, after long exposure,
extends more or less into the substance of the paper. If ammonia is poured
upon the precipitated chloride which has been exposed to light, that portion
which has not undergone the change, is dissolved, while the dark substance
(^. €., the reduced silver) remains undissolved. If a strong solution of chlo-
rine is added to the darkened chloride, it is again rendered white, by reason
of the metallic silver recombining with this element ; and the white chloride,
when covered with a solution of chlorine, does not readily undergo the
change. A solution of common salt or hydrochloric acid in excess, also
retards the change ; but when the solution of nitrate of silver is in excess, it
takes place with very great rapidity. We have preserved paper prepared
with chloride of silver, but containing an excess of chloride of sodium, for a
period of twenty-two years. Under strong solar light it retained, after this
long interval, sufficient unchanged chloride to yield an impression from a
collodion negative.

Nitrate of silver undergoes no change by exposure to light, except wheu
in contact with organic matter : the nitric acid and oxygen are then liberated,
and the silver is reduced; AgO,N05=Ag + 0-fN05. The oxygen is pro-
bably taken by the hydrogen and carbon of the organic matter. The in-
soluble chloride, iodide, and bromide of silver are not so readily decomposed,
when in contact with organic matter in the dark, as the soluble nitrate, or
the ammonio-nitrate of silver. If mixed with the nitrate, however, they
rapidly undergo a change : hence, for the perfect preservation. of plates or
paper covered with iodide of silver, it is necessary that every trace of the
nitrate of silver should be removed. On this principle is founded the dry-
plate process in photography. The dry and pure iodide of silver, free from
nitrate, will receive an impression on exposure, just as certainly, although
not so rapidly, as the wet iodide mixed with nitrate. Among the facts which
prove that the chloride and nitrate of silver are reduced by light to the
metallic state, are the following : 1. That substance which has been darkened
by light is insoluble in ammonia and the alkaline hyposulphites ; while that
portion of the salt of silver which has not undergone the change, is readily
dissolved by these reagents. 2. When the reduction of the chloride or
nitrate has taken place on paper, the surface has been found to conduct
electricity. 3. When paper which has thus been darkened by light is intro-
duced into a weak solution of chloride of gold, rendered slightly alkaline,
metallic gold is slowly deposited of a dark purple color, in place of the re-
duced silver; an efi'ect similar to that produced by metallic silver when
immersed in a solution of gold. The well-known process of toning photo-
graphs, depends on this property of chemically replacing metallic silver by
metallic gold : and there is but little doubt that the impressions are thus
rendered much more durable. It is an ascertained fact, that this replacement,
or substitution, does not occur except in those portions of a drawing, in
which the silver has been completely metallized or perfectly reduced by light.

There is another circumstance connected with this metallization of silver,
under the influence of light, which is deserving of notice. When all other
conditions are favorable, the rays of the spectrum afi'ect the salts of silver

EFFECT OP COLORED LIGHT ON THE SALTS OF SILVER. 505

unequally. If paper, containing the albuminate and chloride of silver, is
covered with plates of glass variously colored, and is then exposed for an
equal time to light, it will be found that under some of the dark-colored
plates the change has been nearly as great, as if colorless glass had been
employed, while under the lighter-colored plates, it has been retarded. Ex-
periments of this nature have clearly proved that the dark or more refrangi-
ble rays of light, violet, indigo, and blue, allow the chemical changes to take
place rapidly ; while the less refrangible rays, red, orange, and yellow, retard
them. Of all the colors, the blue produces, witfein a given time, the greatest,
and the red, the least amount of chemical action. Thus the sensitized paper
is intensely blackened under blue glass, while it remains nearly white under
red glass. The chemical rays, however, do not appear to be completely
intercepted ; for a long exposure to light through colored glass will slowly
lead to a change of color in the paper. The chemical action of light is
therefore determined by the difference between the accelerating and retarding
rays, of which white light is constituted. Colorless light, however, produces
caeteris paribus, a more rapid and complete change than the isolated blue
rays of a colored medium.

From these facts it will be perceived that the two ends of the solar spec-
trum do not neutralize each other in reference to this force ; for the actinic
or chemical rays predominate, and are found to operate sooner or later
through every color. Nothing but the absolute withdrawal of light will
entirely arrest the chemical changes. Hence the salts of silver may be em-
ployed for photometric observations. They serve to measure, not only the
relative intensity of light, but by the changes induced on sensitized paper,
they are made available for numerous important purposes in science and the
arts. We have thus seen this art successfully applied to the diurnal registra-
tion of the amount of rain-fall ; the electrical tension of the atmosphere, and
the force and direction of the wind. It has also furnished important evidence
in courts of law, and has been usefully employed to illustrate various sub-
jects in medicine, natural history, archaeology, ethnology, and astronomy.

Other conditions connected with these phenomena are worthy of notice.
The chemical changes produced in the salts of silver are not in proportion
to the illuminating power of the rays of the spectrum. The greatest amount
of light is in the yellow rays, and the least amount in the blue and violet ;
but the latter possess the chemical power in its greatest intensity. The
salts of silver, it is well known, are decomposable by heat : but in reference
to these chemical changes, it is found that the calorific rays (red) have the
least influence in producing them. Hence, this photochemical force is not
in proportion to the light or heat of the solar rays, but to other rays which
are called actinic; and the force itself is therefore called actinism. In refer-
ence to the spectrum, it is at its maximum when the violet and blue rays
predominate, and at its minimum when the yellow and red rays are. most
abundant. Hence, if red or yellow rays abound, as in a glowing sunset, or
occasionally in a foggy state of the atmosphere, however clear an image may
appear to the eye, the actinic power is lost, and an impression cannot be
taken.

The salts of silver differ from each other in respect to the changes produced
by colored light : thus while the maximum effect on the chloride paper is in
the blue rays, that produced on the iodized paper is in the extreme violet,
while the bromized paper is affected more or less throughout the whole spec-
trum, even in the yellow and red rays. These remarkable effects produced
by the colored rays of the spectrum have not received any explanation on
the unduhatory theory of light: and it seems difficult to understand how an
undulation, or any mechanical vibration, producing a violet color, should

506 PHOTOGRAPHY ON SILVER. DAGUERREOTYPE.

break up ^ the chemical composition of chloride of silver, while that which
produces a yellow or red ray should have little or no effect upon this salt.

The colored rays of the spectrum are represented on prepared paper by
degrees of darkness, or a blackening of the exposed portions, and not by the
reproduction of color. It has been hitherto found impossible to procure and
fix by the chemical agency of light the colors Of external objects, except to
a very limited extent. We have in one instance seen the iridescent colors of
the opal transferred to a surface of silver, by the daguerreotype ; but they
entirely disappeared on the preservation of the impression. Further, the
unequal action of white light as it is reflected from white surfaces, as well as
from shadows and shades of various degrees, is so great, that it is difficult,
if not impossible, to attain the even gradation of tone which gives harmony
to all natural objects. White light acts with such disproportionate rapidity,
and the light of shadows so slowly, that the most finished impressions of
objects are generally left with extremes of light and shade. While the lights
are unnaturally intense, the shadows are generally black, without that grada-
tion which in nature serves to reveal the most minute details. There is a
want of aerial perspective. To a certain extent this defect is, however,
remediable by art.

With a knowledge of the principles above described, a chemist may pro-
duce, and render permanent, images which have been impressed by light on
a salt of silver. He may select a medium of metallic silver, glass, or paper,
and he may produce the image on the prepared surface, either by refraction
with a camera obscura, or by superposition and simple exposure to dififused
light. In either case he may obtain, directly or indirectly, an image in
metallic silver, in those parts in which the metal has been reduced ; while
the undecomposed salt of silver remains in those spots in which there has
been a deficiency or entire absence of light. A solvent is selected for the
removal of the unchanged salt, and the drawing is thus preserved.

The fact that images of objects might be impressed by light on paper, im-
pregnated either with the chloride or nitrate of silver, had been proved
experimentally by Davy and Wedgwood in 1802 ; but they could discover
DO method of fixing or preserving them. It was not until 1816 that the
solvent properties of the alkaline hyposulphites on the salts of silver were
first made known by Herschel ; but so slow was the progress of this subject,
that even in 1839 Mr. Fox Talbot, in announcing his discovery, could sug-
gest no better means for the preservation of his drawings than the use of
strong solutions of alkaline chlorides, iodides, and bromides, which were
soon proved to be quite inefficient.

1. Daguerreotype. Photography on Silver. — This branch of the art has
received its name from the discoverer, Daguerre, who first announced his
process in the year 1839. This may be regarded, in a chemical point of
view, as photography in its most simple, and for delineation of details its
most perfect, form, A highly polished plate of silver is exposed to the
diluted vapor of iodine, in a dark box. A colored film of iodide of silver
(Agl) is thus produced by direct combination, and this, at a certain stage,
is found to possess a high degree of sensitiveness to light. The use of
bromine in addition to iodine was suggested by Dr. Goddard in 1840. A
compound film of bromo-iodide of silver was thus produced; and this is found
to give more satisfactory results than the iodide alone. The plate is then
transferred from the dark room to a camera, and in from five to ten seconds
it is removed. In this stage nothing is visible on the plate. The film has
the same bronze-yellow color as when it was placed in the camera ; but a
molecular change may be proved to have taken place. When the plate is
exposed in a box, at a moderate temperature, to the vapor of mercury, an

PHOTOGRAPHY ON GLASS. COLLODION PROCESS. 507

image will immediately appear, the metallic vapor fixing itself closely (by
amalgamation) only on those parts which have received the luminous im-
pression, the mercury lying loosely on the other portions without entering
into chemical combination. When a strong solution of an alkaline hypo-
sulphite is poured over the plate, the image appears in full relief, with a con-
trast of light and shade, and with the most delicate details. The portions
of bromo-iodide of silver not acted on by light are dissolved by an alkaline
hyposulphite ; and the highly polished silver beneath forms the deep shades,
which give blackness to the picture. The mercury imparts a dull white
appearance to those parts of the metal with which it is chemically combined
or amalgamated, and thus constitutes the lights.

The action of light on the bromo-iodide of silver probably consists in
displacing the bromine and iodine, wholly or in part, and thus leaving
a metallic surface favorable for combination with the vapor of mercury
(Ag,Br=Ag-f-Br). Mercury does not combine with the salts of silver:
hence the film of undecomposed bromo-iodide in those parts which were not
exposed to light is sufficient to prevent any direct union between the mer-
cury and the silver beneath. After the undecomposed salt of silver has been
removed by the alkaline hyposulphite, the plate simply requires washing.
A film of gold may be then spread over it by heating upon its surface a
layer of a very diluted solution of chloride of gold in hyposulphite of soda;
and another washing completes the operation.

Owing to the highly polished surface of the metal, the daguerreotype is
admirably adapted to bring out the minutest details of objects. In 1846 we
obtained by this process a copy of the 10,000 letters of the Greek inscription
on the Rosetta stone of the British Museum, within the space of two square
inches. The drawing is still preserved, and the Greek letters are easily
legible by the aid of a lens. The process, however, has these disadvantages :
the film is so thin that the polish of the silver prevents the image from being
clearly seen in all lights; and, as with all silver-surfaces, the plate is exposed
to tarnishing by sulphuration. These drawings, therefore, can only be pre-
served by completely preventing the access of air. The film of sulphide of
silver, which after a time obscures the drawing, may, however, be removed
by washing the plate with a weak solution of cyanide of potassium.

2. The Collodion Process. Photography on Glass. — The application of
pyroxyline, or gun-cotton, to the purposes of photography, was discovered
by Mr. Archer, in 1850. It is used either in the wet or dry state; and as it
is employed on glass, it may be applied either for the production of positive
images, with the light and shade correct, or of negative images, in which
the light and shade are reversed. Positive impressions on paper may be
procured from the latter. Collodion is a solution of pyroxyline in a mixture
of ether and alcohol. {See Pyroxyline.) There are several compounds
known under the name of gun-cotton, but one of these only appears to be
well fitted for photographic purposes (p. 174). It is what is called a substi-
tution-compound, in which, assuming cotton to be Ga^HgpOjjo, four equivalents
of nitrous acid are substituted for four of hydrogen, thus bringing the
formula of photographic cotton to Ca4[H,p4(NOJ]0.^. The proportion of
cotton to the mixed solvents varies according to circumstances. From 5 to
6 grains of cotton may be used to an ounce of a solvent consisting by measure
of one part of alcohol (sp. gr. 0830) and two parts of ether (sp. gr: 0724),
the latter being diminished, and the former increased, in hot weather. When
the collodion is required for use, it is necessary to add to it an alcoholic
solution of an iodide, either of potassium, cadmium, or ammonium, or a
mixture of these. The proportion of iodide required is from 4 to 6 grains
to each ounce of collodion. Pure iodide of potassium, free from iodate {see

508 COLLODION PROCESS. CHEMICAL CHANGES.

page 318), is commonly selected for immediate use; and the iodide of cad-
mium when the liquid is required to be preserved. A mixture of equal parts
of the two, i. e., 2^ grains of each iodide, dissolved in 2 drachms of alcohol,
will be found convenient. This quantity may be added to 6 drachms of the
prepared collodion. A mixture of the iodides of potassium, ammonium, and
cadmium is frequently employed with advantage ; and an addition of the
bromide of either metal to the iodide renders the film more sensitive to the
less refrangible rays of light (yellow and red) (page 505). In using a
bromide, the proportion should not exceed 1 to 3 or 4 parts of the iodide.
Reynaud advises for each ounce of collodion 5*3 grains of iodide to 15
grains of bromide, as producing the most sensitive film. The bromides of
ammonium and cadmium are, according to him, preferable for this purpose.

When collodion thus prepared, has been rendered perfectly clear by sub-
sidence, it is poured rapidly from a wide-mouthed vessel over a freshly
cleaned and dry surface of plate-glass ; and as soon as it is set into a cohe-
rent layer, the glass is plunged into a bath containing a solution of nitrate
of silver, in a darkened room.

This bath is prepared by dissolving 480 grains of neutral crystallized
nitrate of silver in 2 ounces of water, and adding to the solution 4 grains of
iodide of cadmium or potassium, dissolved in a small quantity of water.
Iodide of silver is thus formed, and dissolved by the concentrated nitrate.
The solution may be then made up to twelve fluidounces, by the addition of
distilled water. After standing some hours, it should be filtered to separate
the precipitated iodide of silver. The solution, when filtered, should neither
be alkaline nor neutral. If acid, a little oxide of silver may be used to cor-
rect this ; and when corrected, it may be very slightly acidulated, either
with a few drops of glacial acetic acid, or of strong nitric acid (containing
nitrous acid) properly diluted. If the bath is neutral, the pictures are not
clear; if too acid, the sensitiveness of the film is impaired. To avoid a
"fogging" of the impression, it has been lately suggested that a few drops
of an alcoholic solution of iodine should be added to the bath-liquid, until
it has acquired an orange-yellow color. (Reynaud.)

The result of the immersion of the plate in this bath for a few minutes, or
until the oily appearance of the film is removed, is the production on it, of
a primrose-colored layer of iodide of silver, while nitrate of soda or cadmium
is dissolved in the bath: (AgCNO^-f KI(CdI)=AgI + KO(CdO)N03).
If, when taken from the bath, the opaque yellow film is well washed with
distilled water, to remove all traces of free nitrate of silver, it may be dried,
and the dry plate preserved in a sensitive state in a dark box (containing
some quick-lime) for many weeks, or even months. We have thus obtained
impressions on dry plates after four or five months' preservation. The ab-
sence of moisture and the entire withdrawal of light are, however, essential
conditions for the preservation of the plates. Yarious liquids, such as tannic
acid, albumen, and a solution of chloride of sodium, have been employed as
varnishes for covering and preserving the film, containing the precipitated
iodide of silver.

The plate with the iodide of silver on its surface, may be exposed in the
camera for a few seconds if wet, and for a longer period if dry. When
removed, no image is perceptible ; but on pouring over the film of iodide,
a solution of a protosalt of iron mixed with a few drops of a weak solution
of nitrate of silver, of gallic or pyrogallic acid, the image will appear, slowly
or rapidly according to the nature and strength of the developer, the degree
of exposure, and the intensity of light. We have found the following pro-
portions to be well fitted for bringing out the image : Green sulphate of
iron, 150 grains; glacial acetic acid, two fluidrachms and a half; alcohol,

DEVELOPMENT OF THE IMAGE. 509

five fluidrachms ; distilled water, ten ounces. When all the minute de-
tails are visible, the surface of the film should be well washed with water to
remove the whole of the iron developed. The silver thus reduced and
deposited in the parts aflFected by light, is not sufficiently dense, but its
density and opacity may be increased by the use of the following (intensify-
ing) solution : Pyrogallic acid, 40 grains; citric acid, 100 grains; distilled
water, 8 ounces. The plate having been covered with this solution, a few
drops of a solution of nitrate of silver (thirty grains to the ounce) are added
to it, and it is again poured on the plate, and moved about until the dark
portions appear sufficiently opaque. If a dry plate is used, this should be
breathed upon, or wetted with distilled water, before the developing solution
is poured over it, in order that the latter may be readily diffused over the
whole surface. The illuminated portions of the picture will appear, under
the action of the reducing liquid, more or less black, while the shaded por-
tions will retain the yellow color of the iodide. When the details of the
shaded portions appear, the acid liquid is washed off, and the development
is arrested. The surface of the plate is then well washed, and the plate
introduced into a bath containing a saturated solution of hyposulphite of
soda. After a few minutes, it will be found that .the yellow iodide of silver,
where it has not been affected by light, will be dissolved ; and only the
reduced or metallized portions of silver will remain : these appear more or
less opaque when viewed by transmitted light. The plate now requires the
most complete washing with water to remove every trace of hyposulphite of
soda, or the film of reduced silver will be subsequently cracked and de-
stroyed by the crystallization of traces of this salt beneath.

The changes which take place in the production of the image on the
iodide of silver, have been variously explained. All agree that the effect of
the impingement of light, is to produce only a molecular change in the com-
pound. There is no perceptible alteration in the film after exposure to
light. There is no loss of iodine, or the iodide would be darkened like the
chloride. The film retains its chemical properties, and whether on paper or
on silver, it is still easily dissolved by the alkaline hyposulphites. In refer-
ence to the Daguerreotype, a molecular change in the iodide, is proved to
exist, by the vapor of mercury fixing itself only on those parts which have
been exposed to light, excluding the iodine and combining directly with the
metallic silver. In regard to the collodio-iodide, it may be inferred from
the effect of reducing agents, that the changes consist in a deoxidation of
the nitrate and a deiodization of the iodide of silver. It is a singular fact,
that while a molecular change is produced in the iodide by the agency of
light only, the actual production of the image depends on the presence of a
small quantity of nitrate of silver, either on the plate itself in the wet pro-
cess, or by an addition of it to the reducing liquid in the dry process.

The effects produced by reducing agents, such as the gallic and pyro-
gallic acids, on the oxysalts of silver, are somewhat remarkable. Gallic
acid reduces a solution of the nitrate very slowly at common temperatures:
pyrogallic acid reduces it instantaneously, throwing down black metallic
silver by taking the oxygen from the oxide: (AgO,N05+C,3Hg08=Ag-f
NOg-f-C^gHgOgjO). A solution of the sulphate of silver is scarcely changed
in color by the gallic, and is only slowly decomposed by the pyrogallic acid.
When acetic or citric acid is mixed with the pyrogallic, the reducing actioa
is retarded, much more by the citric than by the acetic acid. It is in order
to prevent a too rapid decomposition, by which the plate would be speedily
covered with precipitated silver, and the picture rendered indistinct, that
one or other of these acids is added to the reducing liquid. Either of them
has the property of lowering the reducing power of the pyrogallic even to

510 CHEMICAL CHANGES PRODUCED.

that of the gallic acid. On the other hand, the presence of any alkali leads
to the instantaneous decomposition of a salt of silver. Thus, when pyro-
gallic acid is added to a solution of the ammonio-nitrate of silver, the metal
is immediately reduced and precipitated. It has been elsewhere stated that
a solution of pyrogallic acid in potassa has the property of entirely removing
oxygen from air (p. 154). Neither the gallic nor the pyrogallic acid
exerts any reducing action on the chloride, bromide, or iodide of silver,
except in the presence of an excess of nitrate, when both the oxysalt and
haloid compound are decomposed. The decomposition appears in all cases
to commence with the nitrate and to extend to the iodide ; but unless the
iodized film has been exposed to light, it resists the action of pyrogallic acid,
even in the presence of nitrate of silver. The proportion of nitrate in the
reducing liquid, is commonly greater than that of the pyrogallic acid era-
ployed. It is another curious feature of these changes, that when once the
silver has been reduced as a result of the impression of light, a continued
reduction of the nitrate of silver by a further employment of this salt mixed
with pyrogallic acid, does not obscure the image, or produce a loose deposit
over the whole surface of the plate. The fresh portions of silver as they are
set free by the pyrogallic acid, fix themselves upon the metal already re-
duced, add to its thickness, and thus increase the intensity of the darkened
portions. The fact is well illustrated in the process of intensifying a nega-
tive, in which the reduced metal forms a basis for an increased deposit of
metallic silver from the nitrate. This depends on the well-known principle,
that like particles attract each other in preference to unlike. The reduced
silver coheres to the metallic silver of the film, but not to the layer of unde-
composed iodide.

Pyrogallic acid rapidly deoxidizes strong nitric acid, but it has no action
on it in the very diluted state in which the latter is here liberated ; and it
has no tendency to decompose the iodide of silver alone ; but assuming that
the molecular condition of the iodide has been broken in the parts which
have received an impression from light, it is probable that the iodine is
thereby placed in a state for removal by very slight causes. As the result
of the application of the reducing agent is the same, whether it is employed
immediately or after eighteen hours (if the plate has been kept in the dark),
it is clear that this molecular displacement of the atoms of silver and iodine
is not of a temporary kind, or the power of bringing out the image would
be speedily lost. The iodide on the plate, in the parts affected by light, may
be decomposed by the metallic silver which is liberated from the nitrate by
pyrogallic acid, so that the same compound may be decomposed by light,
and reformed by the reducing agent. If the compound on the plate after
the action of light is represented by Agl, and the silver liberated from the
nitrate by the pyrogallic acid be regarded as Ag, then the change would be
as in the following equation, AgI^-\^Ag=A^I-\-Ag. The iodine is removed
from the iodide, and it must be removed either as iodide of silver (Agl), or
(on the assumption that water is decomposed) as hydriodic acid (HI), the
oxygen of an atom of water being taken by another portion of the pyrogallic
acid. The last view is entirely opposed to the fact that pyrogallic acid with
water has no decomposing action on the iodides, whether soluble or insoluble
in water. A solution of iodide of potassium is not decomposed by pyrogallic
acid. A solution of iodine in water does not lose its color by the addition
of this acid, although it is so changed that starch will no longer render it
blue. Hence, under the most favorable circumstances, water is not decora-
posed by pyrogallic acid in the presence of a metallic iodide.

Mr. Carey Lea has shown that light acts on neutral iodide of silver, since
he produced an action on silverized glass by merely covering it with a sola-

PRESERVATION OF THE IMAGE ON GLASS. 511

tion of iodine, but this fact had already been established by the results ob-
tained in the Daguerreotype. According -to this gentleman, there are four
pictures or impressions on an ordinary negative : 1st, by that produced by
the physical action of light on the iodide of silver; 2d, by the reduction of
iodide to subiodide, if the exposure has been sufiBciently long ; 3d, one pro-
duced by light in connection with the organic matter of the film ; and 4th,
the reduction of the chloride and bromide, if present. With respect to the
demonstration of the third, an ordinary bromo-iodized plate was treated with
pernitrate of mercury. The bromide and iodide of silver were dissolved,
and the film left clear as glass. When it had been well washed and the
developer added, an image appeared.

The protosulphate of iron is now almost universally employed as a re-
ducing agent in place of pyrogallic acid. The protosulphate passes to the
state of persulphate at the expense of the oxide of silver. 3(FeO,S03)4-
AgO,N05=Ag+Fe303,3S03+FeO,N05. It is employed in the propor-
tion of 14 grains to the ounce of water, acetic acid and alcohol being
added in the proportions above given. This reducing agent produces less
dense negatives : the reduced silver has a tendency to assume a white crys-
talline or frosted state, and the more acid the sulphate from the presence of
free sulphuric or nitric acid, the stronger is this effect. There is another
evil attending its use — the silver is frequently reduced to a metallic film on
the surface of the liquid ; this falls on the collodion-negative, and cannot be
removed by mere washing. The image is thus obscured. The sulphuric
may be replaced by the acetic acid, as in adding acetate of lead or acetate
of baryta to a solution of the protosulphate of iron, and filtering the liquid.
Nitrate of baryta has been employed for a similar purpose, and in this case
nitric acid is set free. The iron-developer should always be strongly acid
(with acetic acid) in order to prevent a too rapid reduction of the salt of
silver. • The addition of acetic ether and hyponitrous ether has been found
to operate effectually in a similar manner. Like the pyrogallic acid, the
protosulphate of iron has no action on the iodide of silver unless free nitrate
is present, and unless the iodide has been exposed to light. It does not
decompose either the soluble or insoluble iodides, and it does not discharge
the color of a solution of iodine, or prevent the formation of the usual blue
compound on the addition of a solution of starch.

The reduced silver on the'plate is insoluble in a solution of hyposulphite
of soda, but the undecomposed iodide is dissolved by it. It forms a com-
pound salt with the iodide: its action may be thus represented: Agl-|-2
(NaO,S303)=NaI-f NaO,AgO,2S30a. The glass plate thus preserved may,
according to the degree to which the image has been brought out, be em-
ployed as 2i positive, by placing it on a dark background, in which case those
portions that are opaque to light, or in which the silver is deposited, will
reflect light, and furnish the lights of the picture ; while those which are
transparent, and on which the light did not act, will appear black from the
nature of the background, and these will represent the shadows of the pic-
ture. In the Daguerreotype the picture is inverted when finished, while in
the collodion positive it appears non-inverted. In a further stage of devel-
opment the image may be so strongly defined that the deposited silver will
more or less completely intercept the light, producing a negative impres-
sion, from which a non-inverted image, or positive drawing, may be procured
on another sensitized surface. In order to protect the film on the plate from
injury it is necessary to varnish the collodion side with amber or resinous
varnish. The former is preferable, as it is not softened by solar heat in
taking a positive drawing.

512 PHOTOGRAPHY ON PAPER.

3. Photography on Paper. — In 1839, Mr. Fox Talbot first published a
method of procuring images on paper with the salts of silver, and of so pre-
serving them that from the negatives positive drawings (in which the light
and shade were correct) might be taken by superposition and exposure. He
used the chloride, iodide, or bromide of silver; and various saline solutions
as preservatives. He gave to one modification of his process for producing
the image the name of Calotype. In this the image was received on paper
impregnated with iodide of silver, and afterwards developed by a mixture of
gallic acid and nitrate of silver. It would be impossible here to describe
the numerous modifications which the so-called paper-process has assumed
since it was first discovered. Owing to imperfect methods of preservation,
nearly all the drawings which were taken at an early period have perished.
Paper impregnated with wax, with one part of wax to four parts of paraffin,
with gelatin, albumen, and other substances, has been used, and admirable
drawings of large size have been procured from transparent wax-negatives :
but the paper-process is now chiefly confined to the procuring of positive
impressions from collodion negatives on glass ; and the salt of silver which
is preferred for this purpose is the chloride (AgCl), with or without albu-
men, but always accompanied with free nitrate of silver. The chloride,
although the cheapest and most convenient, is not the most sensitive com-
pound. Experiments on this subject, performed by Mr. Wright, have given
the following results, in which the action of light on chloride of silver is
taken as a standard : —

Paper prepared with chloride of silver

. 1-000

" " chloriodide of silver .

. 1-078

« " bromide of silver

. 2-396

" " chlorobromide of silver

. 4-022

« " bromiodide of silver .

. 4-060

Preparation of the Paper. — Paper manufactured for photographic use
should be floated for five minutes on a solution containing from 10 to 12
grains of chloride of sodium or ammonium to an ounce of water. When
dried, it should be floated in a dark room for another five minutes, on its
salted surface, on a solution of nitrate of silver, consisting of from 60 to 80
grains to the ounce of water. When dry, it is fit for use. Paper prepared
with a surface of albumen and impregnated with chloride of sodium may be
readily procured. This may be sensitized in a similar manner. A positive
impression is taken by placing the collodion side of a negative plate, on
which there is a fixed image, in contact with the dry sensitive side of the
paper, and exposing it to light in a pressure-frame until the lights of the
drawing are of a pale lilac hue, and the shades are of a deep bronze color.
It is afterwards soaked in successive portions of tepid water, until the water
is no longer rendered milky by the production of chloride of silver. It is
then transferred to a toning bath, which is thus prepared : Acetate of soda
and bicarbonate of soda, of each 20 grains : dissolve in ten fluidounces of
distilled water, and filter the solution. Add, at the time required, one
fluidrachm of the following solution : chloride of gold eight grains, distilled
water one ounce. The soda liquid should be kept in a stoppered bottle
covered with black paper. It may be used any number of times, the quan-
tity lost being made up by a fresh quantity of a similar solution ; and as the
gold is removed by each process of toning, an additional quantity may be
added to the soda liquid. The toning liquid should be prepared a few hours
before it is used, and warmed to a temperature of about 70^ or 80° by
placing it before a fire. As there is occasionally a deposit in it, the solution
before use should be poured off clear, or filtered.

PHOTOGRAPHY ON PAPER. 513

The positive paper drawings, before immersion in the toning bath, should
be first well soaked in a weak solution of acetate of soda, and afterwards
^'ashed in two or three waters until all traces of chloride of silver disappear.
Under these circumstances, there is only reduced silver on the surface of the
paper, and some portion of chloride in the tissue of the paper. The draw-
ings, which are now reddish-colored, are introduced separately into the toning
liquid, the face upwards, and are kept in motion until they begin to darken.
The silver is replaced by gold, and the drawing passes through shades of
brown, purple-black, blue-black, and black, and, if left too long, a kind of
bleacliing takes place, and the sharpness and delicacy of the drawing are
destroyed. As a rule, they should be removed when the color is of a deep
purple-black. Those drawings which are feebly printed will not acquire any
depth of color; they either become more faint, or retain a brown color. In
fact, it is only in those parts in which the silver has been completely reduced
by light, and has a bronze color from overprinting, that this toning effect
takes place. The auro-chloride of sodium, in the proportion of ten grains
to one ounce of distilled water, forms also a good toning solution, as a sub-
stitute for pure chloride of gold. All the operations above described, except
that of salting the paper, must be carried on in a darkened room. The
drawing, after toning, should be washed in cold water, to remove any traces
of the gold-bath, and then plunged for a quarter of an hour into a solution
of hy|)Osulphite of soda, containing one ounce of the salt to eight ounces of
water. Any chloride of silver contained in the substance of the paper is
thereby removed, while in a perfect drawing the color is but little changed,
unless it is allowed to remain too long in the bath. No more of the solution
of hyposulphite should be employed than is necessary for the number of
drawings to be preserved. The hyposulphite, after use, should be thrown
away. If used more than once, it is liable to cause stains in the drawings
subsequently made. The drawing is now soaked in a large quantity of
water, occasionally renewed, for twenty-four hours, with a view to remove all
the compound hyposulphite of soda and silver. The last drainings of the
drawing may be tested for any traces of hyposulphite, either by a solution
of nitrate of silver, or of acid subnitrate of mercury. If any hyposulphite is
still contained in the washings of the drawing, the former will give a brown
color to the liquid, and the latter will produce a gray, or even a black pre-
cipitate. Albumenized paper, owing to the greater uniformity of chemical
action, facility for toning the smoothness of surface, and tenacity which it
possesses, is now almost universally employed for positive photography. It
is, however, open to this serious objection : the albuminate of silver which
is formed on the surface is not soluble in an alkaline hyposulphite, and is
therefore irremovable. The lights of the drawing therefore retain a quantity
of silver salt, which slowly tarnishes, not merely from the sulphur vapors
diffused through the atmosphere, but by reason of the sulphur contained in
the albumen itself, and which, by decomposition, has a tendency to produce
brown sulphide of silver and cause a yellow or brown discoloration of the
drawing. Attempts have been made to correct this evil by pressing, rolling,
ironing, and waxing the drawings, but only with partial success. These
objections do not apply to the plain paper drawings, but it is a matter of
great difficulty to procure paper of this kind which will give clear details,
that will resist the necessary processes of toning, treating with chemical
solvents, and frequent washing. Paper prepared with collodion in place of
albumen has been employed, and with success, but it is more difficult to
prepare.

In February, 1839, soon after the announcement of Mr. Fox Talbot's
method of impregnating paper with chloride of silver, we found that a solu-
33

514 CHEMICAL CHANGES IN THE PAPER PROCESS.

tion of ammonio-nitrate of silver gave greater certainty and uniformity in
the results. The solution then called Photogenic liquid was prepared by
dissolving 4 drachms of nitrate of silver in 6 ounces of water. Strong am-
monia wa^ added to the liquid until the oxide of silver at first precipitated
was entirely redissolved ("On the Art of Photogenic Drawing," Jeffery.
London, 1840, p. 6). The liquid was laid on the paper with a brush, the
paper being selected according to the dark and even tone which it acquired
when prepared with the silver solution and exposed to light. Drawings
taken by this process in July, 1839, and preserved by the hyposulphite of
lime, have undergone but little change in twenty-eight years. The lights
and shades are still well defined, but the color of the shades is brown, as a
result of the action of hyposulphite and the absence of toning. By allowing
the drawing to remain in a very diluted solution of gold for twenty-four
hours, the silver is replaced by a purple deposit of gold. The lines of the
drawing at first disappear, and are afterwards restored in precipitated gold.
The paper should be well washed afterwards, in order to remove any traces
of chloride of gold. In salting paper for the ammonio-nitrate of silver, the
quantity of chloride of ammonium or sodium used should be less than that
employed for the nitrate. It was thought that such a solution would be
dangerous for use, by giving rise to the production of fulminating silver;
but an experience of many years showed that this was an error. The addi-
tion of a small quantity of alcohol and a few drops of nitric acid to the liquid
has been found to render it adapted for albumenized paper, the proportion
of nitrate of silver employed being about 70 grains to an ounce of water.
The objection to the use of the ammonio-nitrate on plain paper is the diffi-
culty of giving a good permanent color by toning with gold. A drawing
may be well taken on plain paper, but the processes of toning and preserving
by hyposulphite destroys its sharpness.

The chemical changes which take place in the various stages of the paper
process may be thus described: Chloride of silver is produced in sensitizing
the paper, NaCl-hAgO,N05=AgCl + NaO,N05. The chloride is by this
method of preparation evenly precipitated over the surface of the paper; but
it is always mixed with free nitrate of silver, which accelerates and increases
the chemical changes. When albumenized paper is used, in addition to the
two preceding salts, an organic salt (the albuminate) is also produced. The
three salts are decomposed by light, but in difl'erent degrees: the nitrate
produces a brown-black, the chloride tends to produce a purple-black, and
the albuminate a reddish-brown color, which is not easily darkened by the
gold-bath. A deficiency of nitrate of silver in the silver-bath (as it is rapidly
replaced by nitrate of soda), an undue proportion of chloride of sodium in
the paper, or too short a contact with the sensitizing liquid, will affect the
results. Exposure to light causes a reduction of the silver in the exposed
parts to the metallic state: AgCl = AgH-CI, and AgO,N05=Ag-f 0-f NO^;
but only a very small portion of the silver salts on the paper is thus metal-
lized. When the recent drawing is washed with acetate of soda and placed
in water containing an alkaline chloride, there is an abundant milky deposit,
owing to the production of chloride of silver from the undecomposed nitrate
in the paper. This should be removed as rapidly as it is formed, but the
body of the paper will still hold a quantity, which surface-washing with water
will not remove. When the drawing is now placed in an alkaline solution
of gold, the gold is deposited either upon or in substitution of the metallic
silver, giving to it a purple-black in place of the red-brown color (3Ag-}-
AuCl3=Au-H3AgCl), and rendering it better fitted to withstand the action
of the hyposulphite of soda. A compound hyposulphite of gold and soda,
which may be made by adding a weak solution of the chloride of gold to a

GOLD. DISTRIBUTION AND PRODUCTION. 515

concentrated solntion of the hyposulphite, has been found preferable for the
toning of drawings on plain salted paper. In this case it is, however, pro-
bable that the more perishable sulphide of silver still exists in the drawing,
with precipitated gold. The perfect preservation of the drawing is based
on two conditions : 1. The entire removal from the substance of the paper
of any chloride of silver by the hyposulphite of soda: AgCl4-2(NaO,SaOa)
=NaCl + NaO,AgO,2S202. Hence the drawing should be left sufficiently
long in this liquid, and it should be of a sufficient strength, but not greater
than is required, for the removal of the chloride. If very strong, it injures
the finer parts of the impression by dissolving the reduced silver. It is
better, therefore, to employ a solution of the minimum strength for the
removal of the chloride. If the solution is too weak, it produces in the
substance of the paper spots of brown sulphide of silver. 2. The second
condition is, that the whole of the compound hyposulphite thus produced
should be removed from the paper, otherwise it will undergo spontaneous
decomposition, especially in a damp atmosphere. Brown and yellow stains
sooner or later appear in the drawing, and thus destroy it. They arise from
the decomposition of the hyposulphite of silver, which passes through a
series of changes until it is resolved into sulphide of silver, and ultimately
this appears to be itself resolved into sulphate of silver (AgO,S203=AgO,
S02+S = AgS + S03). The sulphuric acid probably reacts upon another
portion of hyposulphite, forming sulphate of silver, and setting free sulphur
and sulphurous acid.

There are many points connected with the art of photography which can
be acquired only by long practice. The causes of failure in every stage of
the process are numerous, and are sometimes difficult of explanation.

CHAPTER XL.

GOLD. PLATINUM.

Gold (Au=19t).

Gold has been known from the remotest ages : it is the Sol of the alche-
mists, who represented it by the circle O, the emblem of perfection. It
occurs in nature in a metallic state alloyed with silver or copper, and is called
native gold. It is found disseminated in primitive or igneous rocks, or in
the beds of rivers, and in alluvial deposits. The largest supplies have been
derived from Australia and California; from Brazil, Mexico, and Peru; from
the Ural Mountains ; and from some parts of Africa. The rivers of Hun-
gary, Transylvania, and^Piedraont, have also yielded the metal ; and it has
been found in Cornwall, Wicklow, and North Wales. The gold quartz from
the Welsh Hills, near Dolgelly, produced in 1862, 5299 ounces of gold; in
1863, 552 ounces ; in 1864, 2336 ounces ; and in 1865, only 1663 ounces.
Gold has also been found in the refuse slags of sulphuric acid works, when
pyrites has been used as a source of sulphur. Although it generally occurs
in small nodules and granules, nuggets are sometimes found weighing many
pounds. It is usually separated from the matrix by grinding and washing,
or by amalgamation with mercury. The latter process has been to a great
extent superseded by the employment of sodium amalgam as suggested by
Mr. Crookes. The product in gold has been thereby increased threefold.

516 • PROPERTIES or GOLD.

Messrs. Johnson and Matthey found, by direct experiment on the same
sample of California mineral, that while by ordinary amalgamation a toQ
yielded only 2 oz. 16 dwts of gold, by the sodium amalgam the yield was a
few grains more than t ozs., while an assay of the mineral showed that it
contained 7 ozs. 9 dwts. per ton. (See Chem. News, Oct. 12, 1866, p. 170 )

Gold may be obtained pure by dissolving standard gold in nitro-hydro-
chloric acid, evaporating the solution to dryness (by a gentle heat towards
the end of the process), redissolving the dry mass in distilled water, filtering,
acidulating with hydrochloric acid, and adding a solution of protosulphate of
iron. A brown powder falls, which, after having been washed with hydro-
chloric acid and distilled water, affords on fusion with a little borax or other
suitable flux, a button of pure gold; (6(FeO,S03) + AuCl3=2(Fe203'3S03) +
FeaCl^+Au). If the solution from which the gold is precipitated is ex-
tremely dilute, it acquires on the first addition of the salt of iron a beautiful
blue tint, when viewed by transmitted light, and appears reddish by reflection.

Properties. — Gold is of a deep and peculiar reddish-yellow color. It melts
at a bright-red heat, equivalent to al3out 2016° of Fahrenheit's scale, and
when in fusion appears of a greenish color ; as it solidifies it contracts in
bulk. Its specific gravity, in its least dense state, after fusion, is 192 ; by
hammering and rolling it may be brought up to 193 or 19'4. It is so
malleable, that it may be beaten into leaves which do not exceed the
1-200, 000th of an inch in thickness ; a single grain may be extended over 56
square inches of surface. In this state of tenacity the metal is translucent
and admits of the passage of the green rays of light. No alloy can be thus
attenuated, for the alloys of gold are generally harder and less ductile and
malleable than pure gold. The green color transmitted by the leaf is there-
fore a test of purity. It may be at once observed by breathing on a glass
plate, or mica, and pressing it on the leaf. It will readily cohere. The
metal undergoes no change by exposure to air or water at any temperature.
Pure gold never tarnishes, but some of its alloys are readily tarnished by
oxidation or sulphuration. The ductility of gold is such that a grain may
be drawn out into 500 feet of wire. An inch of this wire would weigh only
l-6000th part of a grain.

Gold may be kept for several hours in fusion without perceptible loss of
weight; but when subjected to an intense heat it affords evidence of vola-
tility. The concentrated mineral acids have separately no action upon pure
gold ; neither has sulphur nor sulphuretted hydrogen. Chlorine, iodine, and
bromine, on the contrary, are capable of acting upon it; the agent com-
monly resorted to for dissolving it, is chlorine, generally in the form of nitro-
hydrochloric acid, or aqua regia. If a small portion of leaf-gold is added to
a freshly-made solution of chlorine, and the mixture is heated, the gold is
speedily dissolved, forming a yellow-colored liquid. Any silver that may be
present, will remain in dark-colored particles undissolved. Bromine water
also dissolves gold. When gold is boiled with hydrochloric acid, and a small
quantity either of peroxide of manganese, or of an alkaline seleniate is added
to the liquid, the metal is immediately dissolved. Chlorine is set free in both
cases (pp. 188 and 232). Hydrofluoric acid has no action on gold. When
mixed with strong nitric acid and boiled, the gold immersed remains un-
changed. No fluoride is formed under the circumstances. Sulphuric acid
and nitric acid used separately have no action on the metal. Thus gold-leaf
boiled in strong sulphuric acid remains unchanged, but if a drop of nitric
acid is added, the gold is entirely dissolved. It does not appear that any
salt is formed, for when added to water the gold is precipitated in the metallic
state as a purple black powder. If the sulphuric solution is simply exposed
to air, the gold is deposited in a similar state so soon as the acid absorbs

PERCHLORIDE OF GOLD. 517

water. The remarkable fact is that so small a quantity of nitric acid should
confer this solvent property on sulphuric acid. If hydrochloric acid is sub-
stituted for nitric acid in this experiment, the p^old is not dissolved.

There are two oxides of j?old, a protoxide and b, peroxide.

Protoxide op Gold. Atirous Oxide (AuO) is obtained by precipitating
a solution of the protochloride by a weak solution of potassa. It is of a dark
color, and is converted by hydrochloric acid into metallic gold and perchlo-
ride ; potassa and soda dissolve a little of it ; with ammonia it forms a de-
tonating compound.

Peroxide of Gold. Auric Oxide ; Auric Acid (AuOg). — The best pro-
cess for obtaining peroxide of gold consists in the decomposition of the
perchloride by magnesia or oxide of zinc washing the precipitate with dilute
nitric acid, and drying it at a low heat. It is of a brown color, and is re-
duced by the action of light, or when heated to 480^. It dissolves in sul-
phuric and in nitric acids, but the solutions are decomposed by dilution with
water. It is soluble in the hydrochloric acid, and combines, when hydrated,
with alkaline bases, forming salts which have been called Aurates. It is not
dissolved by hydrofluoric acid. With ammonia it forms a fulminating com-
pound. It explodes at 290°.

Protochloride of Gold (AuCl) is obtained by exposing the perchloride
to a temperature not exceeding 350° : it loses chlorine, and is converted into
a pale-yellow protochloride, which is very unstable, and is decomposed by the
action of boiling water.

Perchloride of Gold (AuClg). — The common solvent of gold, for the
purpose of obtaining the chloride, is the nitrohydrochloric acid. Six grains
of pure gold (dentist's foil) may be dissolved in -J a drachm of pure nitric
and \\ drachms of pure hydrochloric acid. A gentle he-at should be em-
ployed, and the acid liquid concentrated by evaporation on a sand-bath, until
it is reduced to one-third of its bulk. It may then be set aside for crystalli-
zation, or at once mixed with a quantity of water, in proportion to the
strength of the solution required. The chemical changes may be thus repre-
sented : (Au-hN05+3HCl=AuCl3 + 3HO + NO,). By evaporating a satu-
rated solution, prismatic crystals of a deep orange color are obtained. These
are very deliquescent, fusible, and readily decomposed by heat, yielding, at
first the protochloride, and ultimately, pure gold. The solution, even when
much diluted, has a rich yellow color. It is decomposed by phosphorus,
charcoal, sulphurous and gallic acids, and many of the metals and their
compounds. Even silver will slowly displace gold. Silver leaf allowed to
remain in a diluted solution of chloride of gold, acquires a dark metallic
film upon the surface. , In the toning of photographs by immersing the
paper with reduced silver in a solution of chloride of gold, the gold is de-
posited either in the place of or in contact with the reduced silver. A diluted
solution of chloride spread over a surface of clean [copper gives a good
bronzing effect to that metal by the deposition of gold. Leather washed
over the diluted chloride, and exposed to light, acquires a golden-brown film
of the reduced metal. If a sheet of paper or gelatin is soaked in the diluted
chloride and exposed to light, the gold is deposited of various shades of
green-purple or ruby color. This compound of gold has been used for
photographic purposes in place of the salts of silver. Like the latter, it is
only reduced by light in the presence of organic matter. When the solution
of chloride, with a small quantity of soda or potash, is boiled in a liquid
containing organic matter, the gold is rapidly reduced and precipitated la
the form of a purple powder. Protosulphate of iron throws down the
metal in a finely-divided state, and in this condition it is used for gilding
porcelain, and other purposes (p. 516).

518 PERCHLORIDE AND SULPHIDE OF GOLD.

Perchloride of gold dissolves in alcohol and in ether : the latter solution
is obtained by agitating the aqueous solution of gold with ether, after which
the mixture separates into two portions ; the superior is yellow, and is an
ethereal solution of chloride of gold *, the inferior is colorless, being water
and hydrochloric acid. Polished steel dipped into this ethereal solution
acquires a coating of gold, and it has hence been employed for gilding deli-
cate cutting instruments. When long kept, it often slowly deposits films of
metallic gold, in arborescent crystals. The ruby gold is here in the metallic
state as in Bohemian glass.

Purple of Cassius. — When a dilute mixed solution of protochloride and
perchloride of tin is gradually added to a dilute solution of perchloride of
gold, this purple compound is precipitated ; and if a piece of tinfoil be im-
mersed in a dilute solution of the chloride, the same purple powder is thrown
down. The purple of Cassius, so called from its discovery by Cassius of
Leyden, is used in enamel and porcelain painting, and also for tinging glass
of a fine ruby tint. It retains its color at a high red heat: it is insoluble
in solutions of potassa and soda; but if, whilst in its hydrated state, it is
washed with ammonia, a bright purple liquid is obtained. This compound
is regarded as a hydrated stannate of gold and tin (AuO,Sn03+SnO,SnOa4-
4Aq).

Auro-Perchlorides. — These are compounds in which the chloride of
gold is combined with certain electro-positive chlorides, such as those of the
alkaline bases, potash and soda ; they consist of 1 atom of perchloride of
gold, and 1 atom of the other chloride, and may be formed of their respec-
tive chlorides in such proportions. Some of them have been long known :
they mostly form prismatic crystals, and include water of crystallization. It
is in consequence of the formation of these soluble double salts, that a solu-
tion of perchloride of gold in hydrochloric acid, yields no precipitates with
the alkalies, even when added in excess. Different aurochlorides, obtained
by adding salts of potassa, soda, ammonia, and other bases, to the chloride,
are employed in gilding copper trinkets, buttons, and other articles. It may
be here observed that most metals are readily deposited from acid solutions
only. In reference to gold the deposition of the metal does not readily take
place except from an alkalinic solution.

Iodides and Bromides of gold, corresponding to the chlorides, have been
formed. They also produce double salts with the electropositive iodides and
hromides.

Sulphide of Gold (AuS.AuSg) is produced by passing sulphuretted
hydrogen through a cold and diluted aqueous solution of perchloride of gold.
It falls in the form of a black powder, and is resolved by heat into gold and
sulphur. It is soluble in alkaline sulphides. A double sulphide of gold and
potassium is formed, when sulphide of gold is digested in a solution of sul-
phide of potassium ; or when gold, sulphur, and potassa are fused together;
the compound is soluble in water. Sulphide of gold is used in the Potteries
as a source of the preparation of gold with which a dingy gilding is given
to porcelain. When sulphuretted hydrogen is passed through a boiling
solution of chloride of gold, the metal is precipitated: 4AuCl3+3HS-f
9HO=4Au+12HCl + 3S03.

Protocyanide of Gold (AuCy) falls in the form of a yellow crystalline
precipitate on adding a solution of cyanide of potassium to a dilute solution
of perchloride of gold. Its most important compound is that with cyanide
of potassium, which may be formed by dissolving either cyanide of gold, or
the compound obtained by precipitating a solution of perchloride of gold by
ammonia, in a solution of cyanide of potassium. Its concentrated solution

ALLOYS OF GOLD ANALYSIS. 519

gives crystals =KCy,AuCy. It is used for gilding silver and copper, and
especially for electro-plating.

Percyanide of Gold (AuCy.,) is formed by mixing a solution of caustic
potassa, to which excess of hydrocyanic acid has been added, with perchlo-
ride of gold free from uncorabined acid. It yields crystals =AuCy3 + 6Aq.
It forms double salts with the cyanides of the alkaline bases.

Alloys of Gold. — The most important are those with copper, mercury,
and silver. With copper, gold forms a ductile alloy of a deeper color, harder,
and more fusible than pure gold; this alloy, in the proportion of 11 gold to
1 copper, or 91*67 gold, 8 33 copper, constitutes standard gold; its density
is 17 "157, being a little below the mean. One troy pound of this alloy is
coined into 46|f sovereigns, or 20 troy pounds into 934 sovereigns and a
half. The pound was formerly coined into 44 guineas and a half. The
standard gold of France consists of 9 parts of gold and 1 of copper.
Standard gold is not affected by nitric acid ; but the inferior alloys which
are made to imitate gold, consisting chiefly of copper and zinc, immediately
decompose this acid, and set free deutoxide of nitrogen. Standard gold
containing nearly 9 per cent, of copper is not affected by nitric acid. The
inferior copper alloys, as a rule, decompose the strong acid, and are dissolved
as nitrates. There is an alloy consisting of 16 parts of copper, 7 of platinum,
and 1 of zinc, which resists the action of the nitric acid test, and it has, at
the same time, the color of 16 carat gold. In testing small articles of jewelry
the following plan may be adopted. The metal may be rubbed upon a
smooth surface of blood-stone or jasper, so as to transfer a portion to the
stone. One or two drops of strong nitric acid are then placed on the
metallized surface of the stone. If the article is a base alloy, the metallic
appearance is speedily destroyed, and the metal is dissolved : if gold, it
remains unaffected. Base alloys are frequently plated with gold, and in this
case the only method of judging of the quality of the metal, is by taking the
specific gravity, which should be at least 17 for standard gold. Trinket-gold
is seldom above 15 ; and the so-called gold chains ordinarily met with vary
from 11 to 13. Common gilt articles vary from 7 to 9.

Mercury and gold combine readily on contact, especially when heated, the
mercury then taking up a considerable proportion of gold without loss of
fluidity : when rich in gold, the amalgam is of a buttery consistency, and
may be separated from the more liquid portion by pressure through leather.
It consists of about two parts of gold and one of mercury : the amalgam
used for gilding bronze contains about one-eighth of gold. Silver and gold
mix readily in all proportions, when the fused metals are stirred together.
The standard gold at present coined, is for the most part alloyed with copper
only ; previous to the year 1826, the alloy consisted in part of silver, hence
its paler color. To separate the silver from gold, the alloy is melted with a
great excess of silver, granulated, and boiled in sulphuric acid, by which the
silver is oxidized and converted into sulphate, and the metallic gold remains
in the form of a dark insoluble powder, which is afterwards collected, washed,
and fused into a button or ingot. In the same way, the small quantity of
gold contained in silver coin, which used to pass unheeded, is extracted by
sulphuric acid; the recently coined silver will accordingly be found, in most
cases, destitute of those traces of gold which are contained in our coin of a
date anterior to 1826. When gold and silver are parted by the action of
nitric acid, it is necessary, as in the case of sulphuric acid, that the silver
should be in great excess (three-fourths of the weight of the alloy) ; it is
otherwise protected from the solvent power of the acid.

Assay of Gold. — Tiie quantity of standard or other gold used for assay
is generally about 8 grains : to this, about three times its weight of pure

520 TESTS FOR THE SALTS OF GOLD. PLATINUM.

silver, ton^ether with the proper proportion of lead is added, and the whole
subjected to cupellation, as already described (page 502). The silver and
gold are thus thoroughly combined, while the oxides of lead and copper are
absorbed by the cupel. The auriferous button is then flattened under the
hammer, and after having been annealed, is passed between a pair of small
rollers, so as to extend it into a thin ribbon : it is then again annealed, and
coiled up so as to form what is called a cornet, which is put into a flask or
matrass containing about an ounce of hot nitric acid, sp. gr. 1-180, and
boiled for about ten minutes, by which the silver is entirely dissolved, and
the gold, retaining the form of the cornet, remains : this is again boiled for
about twenty minutes in somewhat stronger nitric acid, and then carefully
washed and transferred to a small crucible, in which it is heated to redness.
When cold, the loss upon the original weight of the sample, is carefully
ascertained. The weight of the alloy operated upon is always represented
as =1000, and the weights used are so adjusted as to give the value of the
alloy in thousandths. In the process of gold-assaying, as in that of silver,
various errors have to be compensated for, more especially in reference to
the traces of copper, lead, and silver which may have been left in the gold.

Tests for the Salts of Gold. — Such of these as are soluble are distin-
guished by the peculiar purple precipitates which they afford with the mixed
chlorides of tin. All the compounds of gold are decomposed by heat, and
the residuary gold is easily recognized. The following reactions are pro-
duced in a diluted solution of chloride of gold by the under-mentioned tests:

1. Potash 2Lndi soda give no precipitate, but form soluble, double aurates.

2. Protosulphate of iron gives a precipitate which may be blue or green,
with a ruddy appearance on the surface, from reduced gold. 3. Sulphurous
acid throws down metallic gold slowly. in the cold, rapidly when the mixture
is heated. 4. Oxalic acid the same. 5. Tincture of galls the same.

6. Arsenious add. This produces, on boiling, a similar decomposition.

7. Guaiacum resin, freshly precipitated, produces a bluish green color.
On warming the mixture, metallic gold is precipitated. Tannic acid, gallic
acids also, throw down metallic gold. The compounds of gold are decom-
posed by light in contact with organic matter, and metallic gold, of various
shades of purple color, is deposited.

Platinum (Pt=99).

This metal was first made known in 1741. Its name is derived from
platina, a diminutive of the Spanish word plata, silver.

Platinum is found in the metallic state, in small grains, confined to streams
and alluvial strata, chiefly in Brazil and Peru, and in the Uralian mountains
of Siberia. The grains, besides platinum, contain generally gold, iron, lead,
palladium, rhodium, iridium, 'and osmium, and often oxide of titanium and
chromate of iron. Rounded masses of the metal occasionally occur among
them ; these are rarely larger than a pea or a small marble, though some
have been found of the size of a pigeon's egg. The usual mode of obtaining
pure platinum consists in digesting the ore in nitrohydrochloric acid, decant-
ing the clear solution from the black insoluble residue, and mixing it with
a solution of sal-ammoniac; a yellow double chloride of ammonium and pla-
tinum falls (NH^CIjPtCy, which, when well washed and heated to redness,
leaves a spongy mass of finely-divided metal ; this is triturated with water,
and subjected to powerful pressure in a brass mould, so as to form a porous
ingot, which is gradually raised to a white heat and carefully hammered at
its ends, until it forms a coherent bar.

Malleable platinum has lately been manufactured by the following process,
contrived by Deville and Debray. The prepared ore is fused with its weight

PLATINUM- ITS COMPOUNDS WITH OXYGEN. 521

of sulphite of lead and half its weight of metallic lead ; some of the impuri-
ties are thus separated in combination with sulphur, while the platinum forms
an alloy with the lead, which is freed from the scoriae, and subjected to the
joint action of heat and air, until the greater part of the lead is oxidized into
lithar<re, so that the residuary alloy only retains about 5 per cent, of lead.
It is then subjected to the intense heat of an oxyhydrogen flame in a furnace
of chalklime, where the rest of the lead (together with any gold, copper, and
osmium) is driven off in fumes : the remaining platinum is cast into any
required form. This process, which has furnished ingots of more than 50
pounds in weight, leaves some rhodium and iridium in combination with the
platinum ; but these metals do not affect its useful applications, neither ren-
dering it more fusible nor more liable to the action of acids. In the Inter-
national Exhibition of 1862,. Messrs. Johnson exhibited a mass of pure
platinum, prepared by Deville's process, weighing 230 pounds, and valued at
3840/. It had been cast in a mould of lime. In the production of this
enormous mass of a metal hitherto regarded as infusible, the operator was
nearly killed by the fumes of osmic acid evolved.

The color of platiaum is white — between that of iron and silver. When
pure it scarcely yields in malleability to gold and silver : it is excessively
ductile and tenacious, and takes a good polish : it is harder than copper,
but softer than iron. Its hardness is increased by the presence of iridium.
Platinum is more ductile than malleable. It may be drawn into the finest
wire, but cannot be beaten into such thin leaves as gold and silver. It
undergoes no change by exposure to heat, and can only be melted by the
oxyhydrogen jet. It cannot be oxidized at any temperature. Its rate of
expansion and contraction by heat is so similar to that of glass, that it
admits of being welded with or fused into glass. The specific gravity of
platinum fluctuates between 21 and 22. Its extreme difficulty of fusion, and
the perfect manner in which it resists the action of almost all acids, at a
boiling or even at a red heat, render it importantly useful in many of the
arts, and indispensable in the laboratory. The curious catalytic action of
clean surfaces of platinum on wire and foil of pulverulent and spongy plati-
num, and platinum black, upon gaseous mixtures, especially in determining
the combination of oxygen and hydrogen, has rendered this metal useful in
gaseous analyses. Bibulous paper, or fibres of asbestos, saturated with a
strong solution of chloride of platinum, dried, and ignited, yield an ash
which exhibits the properties of a finely-divided platinum in perfection.
This catalytic action of platinum appears increased in proportion to the
mechanical division of the metal and the perfect cleanliness of its surface.

Platinum- Black. — Platinum-black may be prepared by dissolving proto-
chloride of platinum in a strong hot solution of caustic potassa, and adding
alcohol : the hot mixture is stirred till the effervescence, arising from the
escape of carbonic acid ceases; this is so violent as to require the use of a
capacious vessel. The platinum falls in the form of a black powder, from
which the supernatant liquor is poured off; the powder is then boiled suc-
cessively in alcohol, in hydrochloric acid, and in solution of potassa, and
lastly, in four or five portions of distilled water. If the alcohol is not
entirely removed, the powder ignites on drying, and loses its catalytic power.
It is dissolved by a solution of chlorine. When dry, it looks like lamp-
black, but acquires a metallic aspect after having been heated white-hot.
This form of platinum is also obtained by heating an aqueous solution of
.4 parts of bichloride of platinum, 10 of crystallized carbonate of soda, and 1
of grape-sugar to 212^, stirring the liquor till the whole of the black pre-
cipitate has fallen, which is then well washed and dried : it is improved by

522 PROTOXIDE OF PLATINUM,

boiling it first in nitric acid, and then in solution of potassa, and finally
washings and drying:.

A much more simple method of procuring platinum-black consists in
decoraposino^ the ammonia or potash chloride of platinum by zinc. The
yellow compound is diffused through water acidulated with diluted sulphuric
acid, and a bar of zinc is introduced. As the hydrogen is evolved the pla-
tinum is separated as a black powder, and simply requires washing. Mag-
nesium is equally effectual, and being purer than zinc, leaves, when dis-
solved, no metallic residue to contaminate the platinum. Sodium amalgam
also throws down platinum-black still more rapidly. Pure mercury only
very slowly precipitates a solution of the chloride. Iron, and some other
metals, throw down platinum in a very finely-divided state.

Spongy Platinum. — Spongy platinum is readily procured by heating, on
platinum foil, the dry ammonio-chloride of platinum until the yellow color
has disappeared, and nothing but a gray spongy-looking metallic substance
remains. Care should be taken not to overheat it. It is platinum in a less
finely-divided state than platinum-black. Its properties are remarkable :
these have been elsewhere described (see Catalysis). It condenses certain
gases when they are in contact with it, and causes their union, although the
metal itself undergoes no change. That condensation is said to be equal to
250 times the volume of the platinum. In the presence of hydrogen it con-
denses oxygen, and vice versa; and produces water by causing the combina-
tion of the two. At a moderate heat it condenses hydrogen and deutoxide
of nitrogen, producing ammonia and water. Although it does not appear to
absorb or condense oxygen when alone, yet it acts upon the freshly precipi-
tated resin of guaiacum like the ozonides, or those bodies which easily part
with oxygen in the nascent state. It oxidizes the resin, and imparts to it a
blue color. During these combinations the platinum passes to the state of
full red heat, but undergoes no change of weight or properties.

Although pure platinum is infusible in an ordinary wind furnace, it softens
so as to admit of welding and forging. In the arc of flame of the voltaic
current, and before the oxyhydrogen blowpipe, in a lime-furnace, it not only
admits of being fused, but when very intensely heated it is said to give off
vapor. Platinum is insoluble in nitric acid, yet when alloyed with certain
other metals soluble in this. acid, it is taken up ; as for instance, with silver.
It is attacked at high temperatures by the alkalies, especially by baryta,
lithia, and potassa, which cause its oxidation and destruction. Nitre and
the alkaline persulphides have a similar action. Platinum readily fuses with
phosphorus, but it is not affected by sulphur unless in the spongy state. It
combines with the greater number of the metals, and with many of them—
such as lead, antimony, and tin — forms very fusible compounds ; these actions
show the necessity of caution as to the substances which are ignited or fused
in platinum crucibles, and as to the fuel with which they are brought into
contact.

The affinity, of platinum for oxygen is, like that of gold, extremely feeble ;
it shows no disposition to become an oxide by exposure to air or oxygen at
any temperature, and although a strong electric discharge, when transmitted
through a fine platinum wire, dissipates it into black dust, this, as in the
analogous case of gold, is probably finely-divided metal, and not the result
of oxidation. Two oxides of platinum have been satisfactorily identified.

Protoxide of Platinum (PtO).— When protochloride of platinum is
gently heated in a solution of caustic potassa, a black oxide is formed, part
of which is dissolved, and part precipitated: it may be thrown down from its
alkaline solution by diluted* sulphuric acid. It is easily reduced by heat,

OXIDES AND CHLORIDES OF PLATINUM. 523

and slowly dissolves in the acids, most of which decompose it, and resolve
it into peroxide and metal.

BiNoxiDE OF Platinum ; Peroxide of Platinum (PtOJ is obtained by-
decomposing nitrate of platinum by carbonate of soda, so as to leave the
nitrate in excess. It falls in the form of a brown hydrate, which, when
heated, first gives out water and becomes black ; at a higher temperature it
evolves oxygen, and is reduced : it has a feeble attraction for the acids, but
combines with many salifiable bases, and dissolves in the caustic and car-
bonated alkalies. It forms a fulminating ammoniacal compound, similar to
fulminating gold.

Protochloride of Platinum (PtCl) When perch! oride of platinum is

exposed in a porcelain capsule to a temperature not exceeding that of melt-
ing tin (about 400°), and stirred so long as it evolves chlorine, it is con-
verted into a gray powder, insoluble in water, and not decomposed by sul-
phuric or nitric acid, but soluble in boiling hydrochloric acid. This is the
protochloride of platinum. It forms crystallizable double salts with the alka-
line chlorides. It is decomposed at a red heat, leaving a residue of metallic
platinum.

Bichloride of Platinum; Perchloride of Platinum (PtClg). — A solution
of chlorine has no action on ordinary platinum foil or wire, but when in the
finely-divided state of sponge or as platinum black, chlorine, especially by
the aid of heat, slowly combines with the metal to form a bichloride. The
usual process for making this salt consists in digesting fine platinum wire foil or
grains in one part of nitric and three of hydrochloric acid with three parts of
water (to keep down iridium.) The solution is accelerated by heat and is
evaporated to two-thirds of its volume after saturation with platinum. When
so evaporated, it affords a deep-brown liquid which shoots into prismatic crys-
tals, consisting of hydrated perchloride of platinum and hydrochloric acid ;
on further evaporation it yields a brown saline mass, which becomes deeper
colored upon the expulsion of its combined water. It is then a perchloride
of platinum, yielding a deep yellow solution in water, and soluble in alcohol
and in ether. If still further heated, it loses all its chlorine, and metallic
platinum remains as a dull gray film which acquires a metallic lustre by bur-
nishing. It was by this method that earthenware and china were at one
time platinized. The bichloride of platinum combines with the alkaline
chlorides forming an extensive class of double salts known as PlatinO'
chlorides. More frequently the name of the alkali is used as a prefix.
Among these may be mentioned the compounds with potassium, rubidium,
coBsium, ammonium, and thallium. These are all more or less insoluble in
water. The salts of potassium, rubidium, caesium and ammonium are isomor-
phous and crystallize in cubes. The sodium salt is quite soluble in water
and crystallizes in prisms.

The Ammonio- Bichloride of Platinum (NH^CIH- PtClg) is the yellow
powder which falls when solutions of bichloride of platinum a"nd sal-ammoniac
are mixed. When exposed to heat, it loses a little water, and at a red heat
it evolves nitrogen, hydrochloric acid, and sal-ammoniac, without undergoing
fusion, and the platinum remains in the peculiar state known as spongy or
reduced platinum. It requires 150 parts of water at 60^^ and 80 parts of
boiling water to dissolve one part of this salt. This ammonio-chloride is
insoluble in alcohol and in cold hydrochloric acid, but it falls as a crystalline
powder from its solution in hot hydrochloric acid. It is almost entirely in-
soluble in solution of sal-ammoniac.

The action of ammonia ow the two chlorides of platinum gives rise to a
series of compound bases which have much theoretical, but little practical in-
terest, and which have hitherto been only imperfectly examined as to pro-

524 SALTS OF PLATINUM.

perties and preparation. Any condensed notice of these, compatible with
the limits of this work, would be useless to the student.

Potassio- Bichloride of Platinum (KC],PtCl2) — This is thrown down in the
form of a yellow powder, when concentrated solutions of chloride of potassium
and of bichloride of platinum are mixed. It is soluble in 108 parts of water at
60° and in 19 parts of boiling water, and is deposited from its boiling solu-
tion in small octahedral crystals. It is insoluble in alcohol. The difficult
solubility of this compound renders bichloride of platinum a useful test of
the presence of the salts of potassa, as well as of the salts of rubidium and
caesium. The platino-chlorides of these two metals, however, are much less
sohible than the platino-chloride of potassium : hence a solution of the latter
gives a dense yellow precipitate in a salt of caesium or rubidium. Sodio-
Bichloride of Platinum (NaCbPtCl^). — Chloride of sodium occasions no
precipitate with bichloride of platinum, but the mixed solutions yield on
evaporation prismatic crystals, of a deep orange color, soluble in water and
in alcohol, and which, when heated, lose 6 atoms of water of crystallization,
leaving the anhydrous double salt. A variety of other analogous double
salts have been described ; they are generally made by mixing the two
chlorides in atomic proportions. The Bihromide and Biniodide of platinum
are sparingly soluble in water, and are obtained by the decomposition of the
bichloride, by bromide and iodide of potassium.

Protosulphide of Platinum (PtS) may be formed by heating finely-
divided platinum with sulphur, or by the decomposition of protochloride of
platinum by sulphuretted hydrogen. It is a gray or black powder, unaltered
by air or water, scarcely attacked by the boiling acids, but decomposed when
heated in the air. Bisulphide of Platinum (PtSj falls in the form of a
brownish powder, when the sodio-bichloride of platinum is precipitated by
sulphuretted hydrogen : at a red heat it is decomposed, and leaves metallic
platinum.

Protosulphate of Platinum (PtOjSOa) is obtained when a solution of
protoxide of platinum in caustic potassa is saturated with sulphuric acid, the
liquid poured off, and the precipitate dissolved in diluted sulphuric acid ;
the concentrated solution is black ; diluted with water it becomes red, and
passes into persulphate. Persidphate of Platinum (Pt03,2S03) is obtained
hy acidifying the sulphur of the sulphides of platinum by nitric acid. It is
deep brown, and soluble in water, alcohol, and ether; with soda, potassa,
and ammonia, it forms double salts.

Cyanide of Platinum forms a series of double cyanides, some of which are
extremely beautiful. The platino-cyanide of potassium (KCy,PtCy) or
(K,PtCy2) formed by dissolving protochloride of platinum in a solution of
cyanide of potassium, forms prismatic crystals, yellow by transmitted, and
blue by reflected light. They contain 3 atoms of water. The platino-
cyanide of magnesium forms crystals which exhibit various shades of red,
blue, and green (p. 33). When chlorine is passed through a solution of the
platino-cyanide of potassium, crystals are deposited which are green by trans-
mitted light, but of a copper color by reflected light. This salt, termed
sesquiplatino-cyanide of potassium, has the formula (K3,Pt2Cy3,6Aq).

Alloys of Platinum. — Iron and platinum in equal parts form a crystal-
line alloy, which takes a fine polish. Platinum dissolves in fused zinc ; the
alloy is bluish-white, brittle, and hard. Zinc heated in Diatinum-foil before
the blowpipe burns vividly and even with explosion. Tin and platinum
form alloys more or less brittle and fusible. When tin-foil and platinum are
wrapped together and heated by the blowpipe, they combine with incan-
descence. With its weight of nickel platinum forms a pale yellow alloy,
susceptible of a high polish. Copper and platinum form alloys, the ductility

TESTS FOR THE SALTS OF PLATINUM, 525

and color of which vary with the proportions : platinum easily destroys the
color of copper : an alloy of 1 platinum, 16 copper, 1 zinc, resembles gold
in color. Lead and platinum form brittle alloys. Platinum and lead-foil
folded together and heated before the blowpipe, combine with elevation of
temperature. Antimony and platinum readily enter into ignition in the
flame of a spirit lamp when they combine, in the same manner as tin and
zinc. Arsenic and platinum form a dark-gray brittle alloy. When particles
of arsenic are placed upon red hot platinum-leaf, they immediately fuse a hole
in it. Mercury amalgamates difficultly with platinum : spongy platinum
forms the readiest combination, especially when rubbed with the mercury in
a hot mortar. Silver and platinum form ductile alloys. Gold^w^ platinum
require a strong heat for combination, and the color of the gold is greatly
deteriorated.

The perfection with which vessels of platinum resist the action of heat,
and of most acids, renders them peculiarly valuable in many of their applica-
tions ; but its high price is against its general adoption. In the employ-
ment of platinum-vessels, the following precautions must be attended to : 1.
They must not be subjected to the action of compounds which evolve chlo-
rine. 2. Nitre, and the alkalies, must not be fused in them. 3. No metallic
reductions must be performed in them ; nor compounds of phosphorus de-
composed, so as to evolve that substance. 4. When metallic oxides are
heated in a platinum crucible, the heat must not be raised to redness if the
oxide is easily decomposed. 5. The immediate contact of the fuel (charcoal
should always be used) with the crucible should be avoided, especially at
very high temperatures ; for by combining with silicon platinum is rendered
brittle and unsound.

Tests for the Salts of Platinum. — The color and the difficult solubility
of the ammonio and potassio-chlorides of platinum, and the solubility of the
corresponding soda-compound, are very characteristic of this metal. All the
metals which reduce the chloride of gold, with the exception of palladium,
act similarly upon chloride of platinum, but its complete separation in the
metallic state is slow : iron, zinc, cadmium, and copper, are its most eGfective
precipitants ; they separate it as a black powder, which sometimes adheres in
films to the glass. Protosulphate of iron, tincture of galls, oxalic, sulphur-
ous, and arsenious acids occasion no precipitates in a solution of perchloride
of platinum, a circumstance which distinguishes this metal from gold, silver,
and palladium.

A solution of a salt of platinum has the following special characters: 1.
Potash and ammonia throw down yellow precipitates. 2. The Chlorides of
potassium and ammonium also throw down yellow precipitates (platino-chlo-
rides). 3. The solution evaporated to dryness, and heated, yields metallic
platinum.

The chloride of ammonium from the insolubility of the platino-chloride
formed, has been usually selected as the test for this metal, the precipitation
being aided by the addition of a little alcohol or diluted hydrochloric acid.
The discovery of the salts of thallium, however, by Dr. Crookes has made
known a still more delicate test for the compounds of platinum. A solution
of nitrate of thallium will throw down a platino-chloride of that metal, in a
solution in which chloride of ammonium produces no change. The platino-
cliloride of thallium requires 15,585 parts of water to dissolve it.

In a mixture of gold and platinum, the gold may be precipitated and sepa-
tated by boiling the solution with sulphate of iron or arsenious acid, or the
platinum may be precipitated by chloride of ammonium or nitrate of thallium,
rreshly-precipitated guaiacum resin, when added to a solution of gold, .pro-

526 SALTS OF PALLADIUM.

duces a greenish-blue color; with chloride of platinum it produces no parti-
cular effect. On boiling the solutions the gold is completely reduced and
deposited, but the platinum solution remains unchanged. The salts of plati-
num, unlike those of gold and silver, are not affected by light.

CHAPTER XLI.

PALLADIUM. RHODIUM. RUTHENIUM. OSMIUM, IRIDIUM.
Palladium (Pd=54).

Palladium was discovered by Wollaston in 1803 : it is associated with
the other metals mentioned in the last section as constituting the ore of pla-
tinum. It has also been found alloyed with gold.

Palladium is separated from the ore of platinum by the following process.
Digest the ore in nitrohydrochloric acid, neutralize the redundant acid by
soda, throw down the platinum by sal-ammoniac, and filter : to the filtered
liquor add a solution of cyanide of mercury : a yellow flocculent precipitate
of cyanide of palladium is soon deposited, which yields palladium on expo-
sure to heat. This metal has a dull-white color, is malleable and ductile, but
hard. It fuses at a temperature above that required for the fusion of gold,
and when intensely heated by the oxyhydrogen blowpipe, it is dissipated in
sparks. When heated over the flame of a spirit-lamp, it acquires various
shades of blue upon its surface, in consequence of superficial oxidation. It
is acted on by the greater number of the acids when aided by heat, and also
by potassa and nitre : it has a strong affinity for cyanogen.

Protoxide of Palladium (PdO). — This oxide is the base of the salts of
the metal. Thus, when nitrate of palladium is precipitated by an alkali, the
red or dark-orange powder which falls is a hydrated oxide. In this state, it
is soluble in acids, yielding red and brown salts of an astringent taste. It
becomes black and anhydrous at a dull red heat. Binoxide of Palladium
(PdOg) is obtained as a brown hydrate, by the action of a solution of potassa
on the potassio-chloride of palladium.

Protochloride op Palladium (PdCl) is obtained by digesting palladium
in hydrochloric acid with a little nitric acid, and evaporating to dryness : it
forms a brown powder, which is nearly black when anhydrous. It forms
double salts with the basic metallic chlorides, which are soluble in water and
in alcohol. With ammonia it forms a series of compounds resembling those
of platinum. Bichloride of Palladium ; Perchloride of Palladium
(PdCy is only known in solution. It forms red double salts with the alka-
line chlorides.

Nitrate of Palladium. — Palladium, when aided by heat, dissolves slowly
in nitric acid, forming a brown solution which leaves a brown subnitrate on
evaporation. Nitrate of protoxide of palladium forms a double salt with
ammonia.

Sulphide of Palladium (PdS) is formed by .fusing sulphur with palla-
dium ; it is white, hard, and fusible, and when long exposed to heat and air,
it loses its sulphur. It is thrown down in the form of a black powder by
the action of sulphuretted hydrogen upon the salts palladium.

Protosulphate of Palladium (PdO,S03) is obtained by boiling the pro-
tonitrate to dryness with sulphuric acid ; or by boiling the metal in sulphuric

SALTS OF RHODIUM. 52Y

acid, when sulphurous acid is evolved, and a brown solution is obtained,
which deposits the sulphate in red crystals. This salt, dissolved in aqueous
ammonia, yields two ammonio-sulphates =:NH3,PdO,S03 and 2(NH3,)PdO,
SO,.

Carbide of Palladium. — Palladium acquires brittleness when fused in
contact with charcoal. When a plate of palladium is long held in the flame
of alcohol, carbonaceous excrescences gradually form upon it, which, when
burned, leave palladium. This property of precipitating charcoal from flame,
and combining with it, is peculiar to palladium ; platinum and iron only show-
slight indications of it.

Cyanide of Palladium (PdCy) is formed when a solution of cyanide of
mercury is added to a neutral solution of palladium: it falls in olive-colored
or dingy yellow flakes; this furnishes a method of separating palladium from
other metals which are incapable of decomposing the cyanide of mercury.
It dissolves in cyanide of potassium, and forms palladio-cyanide of potassium.
There is also a corresponding ammoniacal salt.

Tests for the Salts of Palladium. — The fixed alkalies throw down red
or orange precipitates from the solutions of palladium, sparingly soluble in
excess of the alkali. Ferrocyanide of potassium gives an olive-green preci-
pitate ; and sulphuretted hydrogen one of a dark-brown color. Protochloride
of tin occasions a brown precipitate in the neutralized solutions of palladium;
when dilute, the mixture becomes green. Protosulphate of iron throws down
metallic palladium. Cyanide of mercury forms a precipitate in all the salts
of palladium, when the acid is not in excess. Iodide of potassium occasions
a black precipitate of iodide of palladium in very diluted solutions. Chloride
of palladium added to a solution of 1 part of iodide of potassium in 400,000
of water produces a brown tint. It is therefore a delicate test for an alkaline
iodide.

As the iodide of palladium is slightly soluble in iodide of potassium the
latter must not be in excess. Chloride of palladium is not only a delicate
test for an alkaline-iodide, but it enables the chemist to separate iodide from
chlorine and bromine. The palladium salt gives no precipitate in solutions
of an alkaline-chloride or bromide unless in the latter case the solution is
very concentrated.

Rhodium (R=52).

After the platinum and palladium have been separated from the nitrohy-
drochloric solution of the crude ore, by sal-ammoniac and cyanide of mercury,
and any excess of the cyanide has been decomposed by the addition of hydro-
chloric acid, chloride of sodium is added, and the liquor evaporated to dry-
ness, the residue is then digested in alcohol, which leaves a red insoluble
double chloride of sodium and rhodium. When this is dissolved in water,
and a plate of zinc immersed, metallic rhodium is thrown down ; or the
double chloride may be at once decomposed by heating it in a current of
hydrogen. Rhodium, discovered by Wollaston in 1108, is a white metal
very difficult of fusion, and extremely hard and brittle. When pure, the
acids do not dissolve it, but they act upon several of its alloys. It may be
oxidized by ignition either with nitre or with bisulphate of potassa, and,
when heated with the latter, a double sulphate of peroxide of rhodium and
potassa is produced. It may be oxidized by the joint action of heat and air,
but the protoxide =R0, has not been examined in an isolated state. The
salifiable oxide is R^Og.

Sesquioxide of Rhodium (RaOg). — This oxide is obtained by heating
finely-divided rhodium with caustic potassa and a little nitre to redness in a

S9^ COMPOUNDS OF RUTHENIUM AND OSMIUM.

silver crucible, washing the product, and digesting it in hydrochloric acid :
a greenish-gray hydrated oxide remains, which is insoluble in acids.

Protochloride of RhodiUxM (RCl) is- obtained by passing dry chlorine
over heated protosulphide of rhodium : it is reduced when heated in hy-
drogen.

Sesquichloride of Rhodium (R^Clg) is obtained by adding fluosilicic
acid to an aqueous solution of rhodiochloride of potassium, filtering, evapo-
rating, dissolving the residue in water, and evaporating again with the addi-
tion* of hydrochloric acid. This is a dark-brown compound, which deli-
quesces on exposure to air, and forms a red solution with water, and with
alcohol. This chloride combines with many other chlorides to form double
salts {Rhodiochlorides), which are of a red color : hence the name of the
metal.

Rhodiochloride OP Ammonium; Ammonio-sesquichloride of Rhodium
(2(NH^Cl)R2Cl3), is obtained by evaporating a mixed solution of chloride
of rhodium and sal-ammoniac : it forms brilliant garnet-colored prisms,
which, when decomposed by heat, leave 31 per cent, rhodium.

Protosulphide of Rhodium (RS) is obtained by heating the ammonio-
chloride with sulphur : when heated in the air it leaves spongy rhodium.

Sesquichloride OF Rhodium (Rj^Sg) is thrown down in the form of a
brown hydrate, by adding hydrosulphate of ammonia to a hot solution of
rhodio-chloride of sodium.

Characters of the Salts of Rhodium. — The salts of the sesquioxide
are mostly red ; they are reducible by hydrogen and by zinc ; sulphuretted
hydrogen occasions a brown, and ammonia a yellow, precipitate in them. A
hydrated oxide of rhodium, of a red-brown color, is thrown down by lime-
water from a solution of the sesquichloride of rhodium in hydrochloric acid.

Ruthenium (Ru=62).

This is one of the raetals remaining in that portion of the ore of platinum
which resists the reaction of aqua regia : it has been imperfectly examined,
but is stated to be hard, brittle, infusible in the oxyhydrogen flame, but
readily oxidized by fusion with nitre, and furnishing four oxides. Of these,
the peroxide, or Ruthenic acid (RuOg), is produced when the other oxides
are heated with nitre. The sesquioxide (Ru^Og) is obtained by heating the
metal in the air : it forms soluble yellow salts with the acids, from which the
alkalies throw it down in the form of a brown hydrate.

When a solution of sesquichloride of ruthenium is decomposed by sulphu-
retted hydrogen, a brown sulphide falls, and the supernatant liquid retains a
protochloride in solution, and is of a bright blue color : this is the most
marked character of the metal.

Osmium (Os=100).

Osmium and iridium, discovered by Tennant in 1803, are also contained
in the residue of the action of nitrohydrochloric acid upon the ore of plati-
num. This residue, when fused with potassa and washed, furnishes a yellow
alkaline solution of oxide of osmium, which, when saturated by sulphuric
acid and distilled, yields a colorless solution of this oxide, from which almost
all the other metals thfow down metallic osmium. When thus obtained by
precipitation, osmium is in the form of a black powder, which acquires a
metallic lustre by friction. Osmium is the heaviest of all known metals ; its
specific gravity being 21-4. Lithium, also a metal, occupies the other end
of the scale ; its sp. gr. being 059, thus showing that in equal bulks osmium
is 36 times as heavy as the lightest metal. Osmium has not yet been melted.

COMPOUNDS OF OSMIUM. 529

When heated in the air osmium burns into an oxide, and exhales poison-
ous fumes having a peculiar odor, somewhat like that of chlorine ; hence the
name of the metal (from 6(T;u?J, odor), and most of its compounds may be re-
cognized by exhaling this odor when heated with a little carbonate of soda
before the blowpipe. It forms five oxides.

Protoxide of Osmium (OsO) is obtained by the action of pure alkalies on
the protochloride : it falls in the forms of a nearly black hydrate, obstinately
retaining a portion of alkali ; it dissolves slowly in the acids, forming deep-
green or greenish brown solutions. Sesquioxide of Osmium (Os^Og) has
not been isolated, but is produced when the peroxide is heated with excess
of ammonia. Binoxide of Osmium (OsOy). — When a solution of bichloride
of osmium is heated with carbonate of soda, the binoxide falls in the form of
a dark gray powder. Teroxide of Osmium (OsOg) is assumed to exist in
certain salts of this metal, but it has not been isolated. It has the proper-
ties of a weak acid. *

Peroxide of Osmium ; Osmic Acid (OsOJ is the volatile oxide above
adverted to, and is obtained by the combustion of the metal in oxygen, by
the action of boiling nitric acid, or by the fusion of osmium with nitre or
with potassa. When osmium is heated, and a current of oxygen passed
over it, yellowish crystals of the anhydrous peroxide are formed : these dis-
solve slowly in water, and readily in alcohol and ether ; the solutions stain the
skin black, and gradually deposit metallic osmium. It is reduced by sulphu-
retted hydrogen, and sulphide of osmium is formed. It has no acid reaction,
but it combines with alkalies, and forms compounds which are permanent at
high temperatures. When infusion of galls is dropped into its aqueous
solution, a characteristic blue color is produced.

Chlorides of Osmium — Four chlorides of this metal have been described.
When chlorine is transmitted over heated osmium, a dark green sublimate
of protochloride of osmium \^ i\iQ result. This is succeeded by a red subli-
mate, which is the bichloride. The sesquichloride and perchloride have not
been obtained in a separate state, but form double salts with chloride of
potassium.

Sulphides of Osmium. — Sulphur and osmium apparently combine in
several proportions, for sulphuretted hydrogen precipitates it from all its
solutions.

The remaining compounds of this remarkable metal have not been minutely
examined, but the characters of its salts will be sufficiently obvious from the
preceding statements.

Iridium (Ir=99).

Iridium is found associated with platinum and gold. It gives great hardi-
ness to both metals, and its presence (alloyed with osmium) in Californtia gold
coined at the United States Mint is said to have caused the destruction of
some valuable dies, and this led to its detection and removal.

The alloy of Iridium and Osmium remaining after the ore of platinum has
been digested in aqua regia, may be decomposed by fusing it with chloride
of sodium, and passing chlorine over the mixture, in a tube heated to dull
redness ; the resulting product is then digested in boiling water, and the
filtered solution concentrated, mixed with nitric acid, and distilled ; osmic
acid passes over, and iridio- chloride of sodium remains, which, by the addi-
tion of sal-ammoniac, yields a precipitate of iridio-chloride of ammonium :
this double salt is decomposed by heat, and metallic iridium remains.

Iridium is a hard, white, brittle metal, extremely difficult of fusion. It is
not acted upon by acids, but its alloy with platinum is soluble in aqua regia^.
34

530 COMPOUNDS OF IRIDIUM.

and it is oxidized when fused with nitre. When in a very finely-divided
state, it has properties resembling those of platinum black.

Oxides of Iridium. — There are three oxides of this metal, the solutions
of which are of various colors : hence the name Iridium (from Iris, the rain-
bow) applied to it. The protoxide is thrown down by the action of potassa
on the protochloride, in the form of a black powder, nearly insoluble in acids,
but yielding, with potassa, a blue or purple solution. The sesquioxide is
formed by fusing iridium with nitre. In its hydrated state, it is soluble in
hydrochloric acid, giving a blue solution, which becomes green, and brown
when heated. The hinoxide falls as a blue hydrate, when a solution of bi-
chloride of iridium is boiled with potassa.

Chlorides of Iridium. — ^\\% protochloride h formed by heated iridium in
chlorine : it is of a dark olive color, and forms double salts with the alkaline
chlorides. The sesquichloride, formed by dissolving the sesquioxide in
hydrochloric acid, also produces double salts. The bichloride also forms
double salts with other chlorides, many of which resemble the corresponding
platinum compounds. The iridio-bi chloride of ammonium is remarkable for
the intense brownish-red color of its solution : it is said to communicate a
decided tint to 40,000 parts of water.

Alloys of Iridium. — The greater number of these alloys, when digested
in nitric acid, leave iridium ; but nitrohydrochloric acid dissolves them when
the proportion of iridium is not considerable. The native alloy of iridium
and osmium forms small crystals of much lustre, harder than steel, and as
refractory as iridium. It has lately been found in Canada. A fused alloy
of platinum and iridium has been employed by Messrs. Johnson and Matthey
for making the touchholes for cannon. One of these, used in a Whitworth
gun for more than 3000 rounds, showed scarcely any signs of wear. The
hardness and durability, as well as infusibility of this alloy, render it better
fitted for vent-pieces than any other metal or metallic alloy.

In consequence of the difficult fusibility of iridium, and of the native alloy,
grains of it are sometimes diffused through ingots of gold, and remain after
a number of successive fusions. In coined gold moneys, it occasionally hap-
pens that one or more of these grains may be discerned ; and where large
quantities of gold are melted, they sink to the bottom of the crucible, so that
dn great gold coinages at the Mint, it has occasionally happened that several
-ounces of the ore of iridium have been thus accumulated.

There are some peculiarities belonging to the six preceding metals —
namely, platinum and its associates — which deserve notice, in reference to
•their atomic weights and their specific gravities, and which have led to their
^division into two groups of three each, as follows : —

Sp. Gr.

Atom. Wt.

Sp. Gr.

Atom. Wt.

Platannm .

. 21-15

99

Palladium .

. 11-8

54

Iridium .

. 21-15

99

Rhodium .

. 12-0

52

Osmium .

. 21-40

100

Ruthenium

. 11-3

52

It will be observed that the specific gravities and atomic weights of the
'first group are almost identical ; so also are those of the second group, the
specific gravities and atomic weights of which are almost precisely one-half
of those of the first group.

QUALITATIVE ANALYSIS OF METALLIC COMPOUNDS. 531

CHAPTEH XLIT.

QUALITATIVE ANALYSIS OF THE COMPOUNDS OF THE
PRECEDING METALS.

In giving a summary of the methods of detecting the salts of the metals,
not included in the 28th chapter, we propose making a selection of those
which are more likely to fall in the way of a student. They may be repre-
sented by the following eighteen bodies : iron, manganese, zinc, tin, cadmium,
lead, copper, bismuth, cobalt, nickel, chromium, uranium, antimony, arsenic,
mercury, silver, gold, and platinum. They are here given in the order in
which they have been treated in this volume. Referring in this place to the
solutions of their salts, and to those compounds which are soluble, we may
observe that many may be at once recognized by their peculiar colors, even
when the liquids are much diluted. These are the salts of iron, manganese,
copper, cobalt, nickel, chromium, uranium, gold, and platinum.

The reagents which may be selected for the qualitative analysis of these
metals are, sulphuretted hydrogen, hydrosulphate of ammonia, iodide of po-
tassium, hydrochloric acid, ammonia, and ferrocyanide of potassium.

Among the general reagents employed in the analysis of metals, there is
none so useful as sulphuretted hydrogen. The gas should be washed, and
passed in a current into the suspected liquid, previously acidulated with
hydrochloric acid. It produces in the liquid either a change of color or a
colored precipitate (sulphide), which may be then easily identified by certain
special characters.

The following metallic oxides are precipitated as sulphides from their solu-
tions, of the colors mentioned below.

Yellow. Orange red.

AsOg CdO SbOg

AsOj SnOg SbOg

Arsenious acid is precipitated of a golden-yellow color, immediately ;
arsenic acid of a paler yellow color, slowly ; oxide of cadmium is thrown
down of a sulphur-yellow color ; and a peroxide of tin of a yellowish-brown
color. The two arsenical sulphides are recognized by their entire solubility
in ammonia, or in its hydrosulphate, as well as in a solution of potassa ; and
by their insolubility in strong hydrochloric acid. The sulphide of cadmium
is insoluble in ammonia, potassa, and hydrosulphate of ammonia, but is dis-
solved readily by strong hydrochloric acid. The sulphide of tin is not soluble
in ammonia, but is dissolved by the hydrosulphate, and by hydrochloric acid.
The hydrosulphate of ammonia may be at once employed to divide the four
oxides, which produce yellow sulphides, into two groups. For this purpose
no hydrochloric acid should be added to the suspected liquids. The hydro-
sulphate produces no precipitate in solutions of arsenious and arsenic acids,
but it precipitates at once the oxide of cadmium, and peroxide of tin. The
sulphide of tin is distinguished from that of cadmium, not only by a striking
difference of color, but by the fact that it is quite soluble in an excess of the
hydrosulphate, while the sulphide of cadmium is insoluble in that liquid.
The means of distinguishing arsenious from arsenic acid have been elsewhere

532 QUALITATIVE ANALYSIS OF METALLIC COMPOUNDS.

fully explained (pages 416, ill). An orange-red precipitate is peculiar to
antimony, whether the oxide is combined with a mineral or a vegetable acid.
The precipitated sulphide is insoluble in ammonia. The antimonial com-
pounds are similarly precipitated by hydrosulphate of ammonia, the orange-
red sulphide being soluble in an excess of reagent.

The acid solutions of the following metals are precipitated or colored by
a current of sulphuretted hydrogen : —

Precip. bi-own or black by Sulphuretted Hydrogen.

Hg 0 PbO SnO

HggO CuO AuOg

Ag 0 BiOg PtOg

The persalts of mercury are thrown down at first of a yellowish color :
the precipitate becomes black, only when the sulphuretted hydrogen has been
passed into the liquid in large excess. Lead is not readily precipitated from
very acid solutions ; a solution of platinum is deepened in color by the gas,
and only slowly precipitated.

Among the metallic oxides in this list, a salt of copper would be recog-
nized by its blue color, a compound of gold by its rich yellow, and of pla-
tinum by its red-brown color. The application of ammonia, or the ferrocy-
anide of potassium, would serve to identify a cupreous salt. {See Copper,
page 426.) A solution of potassa would precipitate platinum, and not gold ;
while a solution of protosulphate of iron would precipitate gold (in a metal-
lic state), and would not affect a solution of platinum.

The solutions of the remaining metallic oxides are colorless. One of these
(bismuth) may be distinguished by the solution giving a white precipitate
when added to a large quantity of distilled water. This precipitate is soluble
in nitric acid, but it is not dissolved by a solution of tartaric acid. {See
Bismuth, p. 439.)

The solutions of the other metals, much diluted, may be treated with a
solution of iodide of potassium : they are then precipitated as iodides, of
the following colors : Subsalts of mercury, yellow (insoluble in hydrochloric
acid, and in potassa) ; persalts of mercury, scarlet (soluble in an excess of
the reagent) ; salts of silver, pale yellow (insoluble in, but rendered white
by ammonia) ; of lead, bright yellow (soluble in hydrochloric acid, and in
potassa) ; the salts of protoxide of tin, pale yellow (soluble in hydrochloric
acid and potassa) ; the salts of bismuth produce a brown precipitate soluble
in an excess of the iodide.

Although the solutions of copper, gold, and platinum, have been already
excluded from the group, by color and their chemical properties, it may be
desirable to place here the results produced by the addition of iodide of
potassium to their diluted solutions. With a salt of copper, the iodide pro-
duces a yellow-brown precipitate of subiodide of copper ; with gold, a yel-
low-green precipitate, iodine being set free ; and with platinum, a deep wine-
red colored liquid, which, on being heated, deposits platinum in a metallic
state. The whole of the metals in this group are precipitated by hydrosul-
phate of ammonia, as brown or black sulphides. Of these, three only, the
protoxide of tin, and the peroxides of gold and platinum, are dissolved by
an excess of the reagent. The sulphide of tin requires a large excess for
solution. Hydrochloric aaWalso serves as an eliminating test for the color-
less metallic solutions of this group : —

Precipitated white. Not Precipitated.

HggO AgO PbO HgO BiOg SnO

QUALITATIVE ANALYSIS OP METALLIC COMPOUNDS. 533

The white precipitate given by lead is soluble in boiling water : it is also
dissolved with or without the aid of heat, by a solution of potassa, and by
strong hydrochloric acid. The white precipitates, given by suboxide of mer-
cury and oxide of silver, are insoluble in water, potassa, and in hydrochloric
acid. The precipitated subchloride from suboxide of mercury is not soluble
in ammonia, but is blackened by that alkali. The precipitated chloride of
silver is quite soluble in ammonia, forming a colorless solution. Of the three
not precipitated by the acid, a persalt of mercury is recognized by the black
precipitate of metallic mercury given on the addition of a protosalt of tin ;
and a protosalt of tin by a similar precipitate being produced when a per-
salt of mercury is added to its solution. Bismuth may be recognized by the
precipitate which it gives on the addition of water (p. 439.)

We have thus disposed of eleven metals of the selected group. The re-
maining seven are not precipitated by a current of sulphuretted hydrogen^ in
solutions acidulated with hydrochloric acid.

Not precipitated by Sulpliuretted Hydrogen.

Fe O NiO MuO

FegOg CoO U2O3

Cr O3 ZnO

When sulphuretted hydrogen is passed into a solution of peroxide of iron,
the persalts are reduced to the state of protosalts, and there is a milky- white
deposit of sulphur. In the salts of chromic acid a green color is produced
from the production of green oxide of chromium, which is dissolved in the
acid liquid, and sulphur is separated.

Hydrosulphate of ammonia precipitates the whole of these metallic solu-
tions : —

p. black or brown. Green. White. Reddish-white.

r-

Fe 0 CoO CrOg ZnO MnO

FeA U2O3

NiO

Black sulphide of iron is produced by this test in gaits of the protoxide
and peroxide, a small quantity being suspended, and giving a greenish color
to the liquid. When exposed to air, these precipitates are rapidly converted
into reddish-brown hydrated peroxide of iron. In undergoing this rapid
change by exposure to air, they are distinguished from the sulphides of nickel
and cobalt. These precipitates are not soluble in an excess of the reagent.
The other three metallic oxides are sufficiently characterized by the colors
of their sulphides.

The ferrocyanide mid ferricyanide of potassium may be here employed as
useful eliminating reagents. The protosalts of iron are precipitated white
or bluish-white by ferrocyanide, and deep blue by ferricyanide of potassium.
The persalts are precipitated of a deep blue color by ferrocyanide, but not
by ferricyanide of potassium ; this liquid merely imparts to them a deep
greenish tint. Ferrocyanide of potassium produces in the salts of nickel a
pale green precipitate, in the salts of cobalt a dingy olive-green precipitate,
and in the salts of peroxide of uranium, a deep red color or precipitate,
resembling that produced in solutions of salts of copper. The cupreous pre-
cipitate is dissolved by ammonia with the production of a blue color, while
the uranium precipitate is dissolved by this alkaline liquid, with the produc-
tion of a pale yellow color. The action of this test upon the other members
of this group may be thus described. Oxide of zinc gives a white, and oxide
of manganese a reddish-white precipitate. The presence of copper or iron,

63 i

QUALITATIVE ANALYSIS OP METALLIC COMPOUNDS.

as an impurity, in these liquids, will of course affect the colors of the preci-
pitates. A chroraate is neither changed in color nor precipitated : a bichro-
mate acquires a darker color.

Ferrocyanide of potassium is also useful as a general test. We subjoin a
table of its reaction on the eighteen metals which have been here selected
for qualitative analysis. The greater number of these metallic solutions are
precipitated white, or of shades of white : some are not precipitated ; while
a few are thrown down of peculiar colors, by which they may in general be
identified.

Not precipitated by ferrocyanide of potassium.

AS03

ASO5
Pre

SbOg

CrOj

AUO3

PtO^

With tartaric acid. Emerald green Pale green

color. color.

cipitated white by ferrocyanide of potassium.

SbOg

SbOg

Ago
Reddish-white.

HgO

Hg^O

PbO

Claret red.
"cuO U^O^

BiOg

SnO
SnOg

Blue.

FeO
ZnO
CdO

Pale-green.

MnO

NiO CoO

The oxides of antimony combined with organic acids are not precipitated
by this test.

The insoluble compounds of the metals may be brought into solution with
hydrochloric or nitric acid ; and the solutions, properly diluted, may then be
submitted to the action of the tests here described.

The object of these rules is to point out the base, or oxide of the metal.
"When this has been indicated, the tests of special kind, which are described
under each metal, may then be applied.

ORGANIC SUBSTANCES. 535

ORGANIC CHEMISTRY.

CHAPTER XLIII.

CONSTITUTION AND PROPERTIES OF ORGANIC
SUBSTANCES. PROXIMATE ANALYSIS.

Organic Chemistry is that branch of the Science which refers to the
properties and composition of organized products, or of substances which
have been formed in vegetables and animals, under the influence of life.
These products differ remarkably in physical and chemical characters from
bodies which belong to the Mineral or Inorganic kingdom ; and they may,
in many cases, be at once distinguished by external appearance. In refer-
ence to chemical composition, they are also widely different. While they are
constituted of a smaller number of elements, the atoms of each element are
in general numerous, and are, at the same time, grouped in more complex
forms, building up frequently intermediate compounds or proximate princi-
ples. The greater number of vegetable substances are constituted of only
three elements. Carbon^ Hydrogen, and Oxygen, of which carbon is the prin-
cipal. Some organic substances contain only ^2^0 elements, CH or CO, the
compounds of HO being inorganic ; but in these cases, the atoms of each are
more numerous than in the mineral compounds of the same elements. One
of the most simple in atomic constitution among organic substances, is pro-
bably anhydrous oxalic acid. It contains only two elements, and but a
small number of atoms of each, being represented by the formula C3O3. In
this simple state, however, it includes an atom of each of the inorganic com-
pounds of the same elements, CO (carbonic oxide), and COg (carbonic acid).
The alkaloids, or vegetable alkalies, are at the other end of the scale. The
most complex contain four elements, of which nitrogen is one ; and with the
exception of this, the atoms of each element are very numerous. Thus mor-
phia, one of the alkaloids of opium, is represented by the following complex
formula: CgsHgoOgN, and its equivalent or combining weight is 292. The
low saturating power of these organic bases will account for the high num-
bers by which they are represented. Thus, 292 parts of morphia are only
equivalent to 41 of potassa, 31 of soda, and IT of ammonia. Other bodies,
such as the neutral vegetable organic principles, gum, starch, and sugar,
occupy an intermediate position. They consist of three elements, carbon
hydrogen, and oxygen, of which the oxygen and hydrogen are in the propor-
tions to form water. Thus, cane-sugar and gum are Oi^^fi^j and starch,
dextrine, and cellulose are C^gH^jOio the differences among these bodies
consisting chiefly in the presence or absence of one or more atoms of water.
This curious relationship of the oxygen to the hydrogen in these bodies, long
since attracted the notice of chemists, and it entered into one of the early
systems of classification. It is not, however, peculiar to neutral substances,

536 ISOMERIC CONDITIONS.

but is found occasionally among vegetable acids. Thus anhydrous acetic acid
is C4H3O3, and pyroffallic acid is C^gHgOg. It is a mere accident of consti-
tution to which no importance can be attached, inasmuch as there is no rea-
son to suppose that these elements are combined as water; and it is quite
certain that the neutral properties of a compound do not depend upon any
uniformity in the proportions of oxygen and hydrogen.

Isomeric Conditions. — The fact that two substances so different in phy-
sical and chemical properties as gum and sugar, are represented by the same
number of atoms of the three elements, C,H,0, at once points to a peculiar
character among organic products — namely, the frequent occurrence of iso-
merism among them. The meaning of this term has elsewhere been fully
explained (p. 18) ; and illustrations of its two principal modifications, poly-
merisra and metamerism, have been given. The word merely expresses the
fact of a similarity of atomic proportions among different bodies ; and the
reasonable inference from the existence of this condition is, that the proper-
ties of organic compounds are referable to a different arrangement of their
atoms, .and not to their relative proportions. The atoms of carbon, oxygen,
and hydrogen in gum are so numerous, that they admit of being arranged in
a variety of groups ; and, according to the order of grouping, so may the
properties vary. Analysis might, therefore, show that two substances were
identical in composition, while they were at the same time entirely different
in properties. We agree with the observation of Pelouze and Freray, that
in the present state of science, the molecular constitution of bodies and the
mode of arrangement of their elements, are problems yet unsolved, even with
respect to the most simple organic substances ; and d fortiori^ unsolvable
with regard to those which are complex. {Traite, de Ghimie, 1861, ii. p.
463.)

The non-oxygenated oils of the vegetable kingdom, present a remarkable
isomeric series. In their ultimate constitution they consist of hydrogen and
carbon, forming the series of hydrocarbons. Thus oil of turpentine, one of
the series, has the formula CgoHie- ^^^ ^^^^ ^^ lemons, oranges, bergaraot,
camomile, cloves, and thyme are represented by the same formula (Cy„Hig) ;
and the differences existing among these oils can only be referred to a dif-
ferent molecular arrangement of the carbon and hydrogen.

This complex atomic constitution leads to results which may be regarded
as peculiar to organic chemistry — namely, the variety of artificial .products
which may be obtained from them by different methods of treatment. Thus,
in reference to the effects o^ heat, some are volatilized without decomposition
(benzoic acid) ; others are entirely decomposed, as gum, starch, and sugar,
yielding compounds which vary in their nature, according to the temperature
applied ; while a third class, at a heat below redness, are converted into new
and stable compounds, simply by the loss of the elements either of water or
of carbonic acid. When gallic acid is converted into pyrogallic acid by
heating it to about 410^, carbonic acid is evolved, and the new acid is sub-
limed in crystals : —

Gallic acid. Pyrogallic acid. Carbonic acid.

Again, when pyrogallic acid itself is heated to a still higher temperature
(482°), it is resolved into water, and a black amorphous insoluble compound,
which is called metagallic or gallulmic acid : —

C.aHeOe = 2H0 + C,2H40,

Pyrogallic acid. Metagallic a^id.

ORGANIC CHEMISTRY. EDUCTS AND PRODUCTS. 53t

So, when malic acid is converted by heat into maleic acid, water is evolved.
Thus—

jCgHeO.o = CgH.Og + 2H0

Malic acid. Maleic acid.

The organic acid is thus entirely transformed, partly into a new pyrogenous
acid, and partly into water or carbonic acid, without leaving, in a carefully
conducted experiment, any trace of carbon in the retort. (Pelouze.) The
influence of heat in causing the re-arrangement of the elements of hydrated
cyanate of ammonia, and its conversion into a neutral organic base, urea, has
been already pointed out (p. 18). The conversion of starch and gum into
sugar, and the transformation of cane-sugar into grape-sugar, when these
substances are heated, or merely agitated with diluted acids, furnish other
illustrations of the facility with which a new arrangement of atoms is pro-
duced, and tend to confirm the correctness of chemical views regarding the
isomeric constitution of these bodies. The production of oxalic acid by
treating sugar with nitric acid, or by acting on sawdust (woody-fibre) with
potassa at a low temperature, proves not only the facility of change, but the
very difl*erent chemical methods by which this change may be brought about.
It would be easy to multiply instances of this kind, by referring to the
action of some of the metalloids, as well as of their compounds, on organic
substances. The range of organic chemistry has been of late years almost
infinitely extended to the application of this simple method of research.

Educts AND Products. — The products, ov those substances which result
from artificial processes, are far more numerous than the educts, or proximate
principles of which organic compounds are considered to be formed. These
educts, which, as their name implies, may be extracted in an unaltered state,
are the immediate or proximate principles of the vegetable or animal struc-
ture ; and the means Of separating them, or determining their proportion,
constitutes an important branch of chemical research, known &8 proocimate
analysis. The elementary analysis of wood would merely indicate the pre-
sence of carbon, hydrogen, and oxygen (C,H,0) : but its principal proximate
constituents, or the educts, which may be extracted from it without change
of properties, are gum, resin, and woody fibre, each of which would yield
the same elements as the original wood, but in proportions varying slightly
with each substance. If we compare Boussingault's analysis of the grain of
wheat and of wheat-straw, we shall find but little difference in the proportion
of the elements, although the former contains nutritious principles in the
form of starch, gluten, dextrine, and sugar ; while the latter consists chiefly
of woody fibre, and contains but little nutrient matter.

Grain of wheat. Wheat-straw.

Carbon 46-10 48-40

Hydrogen 5-80 5-30

Oxygen 43-40 38-95

Nitrogen 2-30 0-35

Ash . 2-40 7-00

100-00 100-00

Educts, when separated, are possessed of peculiar physical and chemical
properties by which they may be identified, and it is to the accurate study
of these, as well as a knowledge of their elementary composition, that we
owe the numerous additions which have been made to this branch of science.
To take a simple illustration, gum is an educt ; its constitution is similar to
that of cane-sugar (CjaHjiO^J. When 1 part of gum is boiled with 4 parts

538 CHANGES PRODUCED IN ORGANIC SUBSTANCES.

of nitric acid (sp. gr. IBS) and 1 part of water, it loses 3 atoms of hydrogren,
acquires 3 atoms of oxyp^en, and is transformed into a white uncrystalline
and comparatively insoluble substance — mucic acid (C^3HgOj4,2HO). This
compound, when moderately heated, is converted, like gallic acid, into a
volatile pyrogenous acid, while carbonic acid and water escape.

+ 2CO2 + 6H0

Mucic acid. Pyromucic acid. Carbonic acid. Water.

When the isomeric compound, cane-sugar (C^Ji^^O^^), is similarly treated —
t. c, when 1 part of sugar is boiled in 8^ parts of nitric acid (sp. gr. 1*38),
and the liquid is concentrated — an acid of a totally different nature is ob-
tained, namely, the oxalic (Cfi^). Both gum and cane-sugar are convertible
into grape-sugar, C^^K^fli^, or C^Jl^fi^^2J10, by the same process, i. e., by
beating them in diluted sulphuric acid. In this conversion, three atoms of
water are fixed. From gum, therefore, as an educt, we may obtain mucic
acid, pyromucic acid, and grape-sugar, as products ; and from cane-sugar,
oxalic acid, and grape sugar. By slightly varying the methods of treatment,
other products may be obtained. Thus woody fibre, or cellulose (Ci^H^oOjo),
when heated with potassa, is converted into oxalic acid ; but when treated
with cold sulphuric acid it is transformed into grape-sugar. Under the
action of nitric acid, water is produced at the expense of a part of the hy-
drogen ; and for each atom of hydrogen lost, one atom of nitrous acid (NOJ
enters into combination. Gun-cotton is the result of this chemical substitu-
tion of nitrous acid for hydrogen.

Some bodies which exist naturally in the vegetable structure, and are re-
garded as educts, may be artificially produced by a reaction of mineral on
organic substances. In all cases, however, either an organic substance, or a
body derived from the organic kingdom, is indispensable to this conversion.
Hydrocyanic aeid may be regarded as an organic product. The materials
for its production, on contact with water, exist in the bitter almond, the
kernels of the peach, the seeds of the apple, and other fruits of a similar
kind, as well as in the root of the plant from which tapioca is obtained
(Jatropha manihot), and in the shoots and leaves of the laurel and bay-trees.
The principal sources of hydrocyanic acid are, however, certain metallic
cyanides (page 282). But these compounds have an organic origin : they
are the products of a reaction of organic upon inorganic substances ; hence
the production of hydrocyanic acid by their decomposition furnishes no ex-
ception to the remark above made. Under this point of view, the production
of artificial urea from hydrated cyanate of ammonia is simply a conversion -
of cyanic acid (a derivative of an organic substance) into another organic
compound. By no processes yet known, can gum, starch, or sugar, be pro-
duced from their elementary constituents (CHO) ; and, by the production of
alcohol from a mixture of sulphuric acid, oleBant gas, and water, Berthelot
has merely proved that a hydrocarbon of organic origin, or one derived from
organic matter, is capable of being converted into another organic product.
Olefiant gas is obtained by a reaction of sulphuric acid on alcohol (page 275),
and Berthelot's ingenious experiment proves that when olefiant gas is dis-
solved in sulphuric acid, and this is mixed with water and distilled, alcohol
is reproduced. This is a simple case of synthesis. Another source of ole-
fiant gas is coal ; but of the organic origin of this substance no doubt can
be entertained.

There appears to be scarcely a limit to this power of transforming one
organic substance into another, and thus producing compounds analogous
to educts, or those which are formed by nature. Oxalic acid is a natural

ORGANIC CHEMISTRY. 539

coTivStituent of the leaves of sorrel and of the rhubarb plant {Rheum rhapou'
ticum) ; but, as above stated, it is an artificial product of the reaction of
potassa on woody fibre, and of nitric acid on sugar. The formic acid,
which exists naturally in the body of the red ant, and as there is reason to
believe in the poison of the wasp and bee, is readily procured by the action
of sulphuric acid and peroxide of manganese on gum, starch, sugar, or tartaric
acid. It may also be procured by a reaction of peroxide of lead on tartaric
acid. Glucose, or grape-sugar, which exists in the grape and other fruits, is
prodnced in large quantity by the reaction of diluted sulphuric acid on starch.
By other processes, succinic acid, which is naturally contained* in amber, is
produced by the action of nitric acid on certain fatty substances : butyric
acid is a product of the fermentation of grape-sugar ; and lactic acid is pro-
duced by the fermentation of grape sugar and sugar of milk.

The instability which characterizes organic products seems in a great
measure to arise out of the peculiarities of their atomic constitution ; and
accordingly we find that, under circumstances in which inorganic compounds
remain unchanged, organic substances are subject to a variety of changes,
the tendency of these being generally such as to terminate in the production
of binary compounds. The complicated phenomena of fermentation, putre-
faction, and decay (page 98) will illustrate these tendencies; and the very
existence of organization is intimately dependent upon them. In these causes
several intermediate stages are often passed through, but the principal ulti-
mate results are the production of carbonic acid, water, and ammonia.
These form the chief food of vegetables ; and when absorbed either from the
atmosphere or from the soil, they furnish carbon, hydrogen, oxygen, and
nitrogen, again to be elaborated into " proximate organic principles" by the
vital powers of the plant. It is only under such conditions, that vegetables
can assimilate the materials of which their fabrics are built up ; and, in fact,
so combine them as to form the proximate components of the animal frame ;
while, on the other hand, the animal functions work in an opposite direction,
and produce the above-mentioned binary compounds. Thus the animal and
vegetable kingdoms are found to work in diametrically opposite directions.
Strictly speaking, however, the two kingdoms may be regarded as supple-
mentary to each other ; that which the vegetable ejects, is necessary to
animal existence ; and that which the animal eliminates, is necessary to the
vegetable. No plant could grow and thrive without carbonic acid and water,
and no animal could live without oxygen. The vegetable, therefore, lives
by a process of deoxidation, and the animal by a process of oxidation. The
vegetable may be regarded as the living chemical laboratory which prepares
the food for the animal. Water and chloride of sodium appear to be the
only mineral substances which are employed as food by animals. Other sub-
stances used as food, are derived either from plants or animals.

Spontaneous Changes. — Probably there is no greater difference between
organic and inorganic substances than that spontaneous tendency to change
which is manifested by the former, and to which the term fermentation is
somewhat loosely applied. By exposure to air, and at a moderate tempera-
ture, in the presence of a body which is called 2, ferment, sugar is spontane-
ously converted into alcohol and carbonic acid ; and alcohol into acetic acid
and water. There are other remarkable conversions of an analogous kind,
by which gallic, lactic, butyric, and hydrocyanic acids are produced from
substances which either do not originally contain them, or contain them
only in small quantity. These changes frequently consist in the simple
absorption or fixation of oxygen. Thus the essential oil of bitter almonds
is converted, by exposure to air, into benzoic acid (page 94) ; ether, from
being neutral, is partially changed into acetic acid, and acquires an acid

540 METAMORPHOSES. ACTION OF FERMENTS.

reaction. The gallic and pyrogallic acids, when dissolved in water and
exposed to air, rapidly absorb oxygen, and are converted into dark-brown
oxidized compounds. This change takes place with great rapidity when
the acids are mixed with an excess of any alkaline base. Chemists employ
a solution of this kind as a ready method for absorbing oxygen (page 100).
When pyrogallic acid is dissolved in neutral ether, it has no acid reaction if
kept from air ; but when oxygen has free acces to it, litmus-paper moistened
with the liquid, becomes reddened by the absorption of this element, show-
ing that an acid is produced, although in the absence of pyrogallic acid, the
liquid simply evaporates without reddening the paper. Woody fibre is
transformed by oxidation into a brown insoluble compound called humus,
and carbonic acid is evolved, constituting that condition which has been
described as eremacausis (page 98). In place of the oxygen entering into
combination with the new compound, or being evolved as carbonic acid, it
may operate by removing part of the hydrogen and producing water. The
transformation of white to blue indigo by exposure to air, is considered to
be dependent on a change of this kind : —

C.gHAN + 0 = HO + C.eHAN

White indigo. ' Blue indigo.

The operation of the ferment, in some of these metamorphoses, appears to
be of a catalytic kind (p. 58). It takes no absolute share in the changes,
but it induces an altered molecular arrangement in other bodies. In refer-
ence to the oxidation of bodies, the ferment may even be replaced by a
mineral substance — platinum-black — which has the power, under a moderate
access of air, of rapidly transforming alcohol into water and acetic acid
{C^^fi^-\-0^=^^0-\-Cfi^O^] and of converting wood-spirit into water
and formic acid (C2H,02-+-0^=3H0 + C3H03). These facts show that a
ferment, in certain cases, operates, like platinum-back, merely as a medium
for transferring oxygen.

The living animal body furnishes numerous illustrations of the facility with
which certain organic sul3stances pass and repass into each other. Among
these, there is probably none more striking than the conversion of benzoic
acid (Cj^HgOg.HO) into hippuric acid (Cj8Hg05N,H0). A small quantity
of benzoic acid, when taken into the system, is eliminated in the urine as
hippuric acid. The hippuric acid naturally contained in the urine of the
horse slowly disappears, and is spontaneously changed, by a species of fer-
mentation, into the benzoic. The condition of the animal appears to favor
the production of one or the other acid, according to circumstances. Thus
when the animal is kept at rest, hippuric acid is abundant ; but when violently
exercised, this is replaced by the benzoic. This transformation, whether
viewed as the result of changes in the living animal, or of fermentation out
of the body, is the more remarkable, inasmuch as the two acids have no
isomeric relations, and appear to have no analogous composition. In some
instances we obtain a key to this conversion, and can imitate the process.
When a mixture of gelatinous starch is heated for a few minutes to a tem-
perature of about 90^, with a small quantity of saliva, or of the vegetable
principle diastase, it will be found that the starch has become partially con-
verted into grape-sugar by a fixation of the elements of water. It is worthy
of remark that sulphurous acid and sulphites have a tendency to prevent
these changes, probably by absorbing and removing oxygen. It has been
long known that sulphurous acid had the power of arresting the conversion
of sugar into alcohol, and of alcohol into acetic acid ; but it operates with
equal effect in preventing the conversion of starch into sugar by saliva and

MINERAL CONSTITUENTS OF VEGETABLES. 541

diastase. Some of these spontaneous changes are of a complex character,
and take place in close vessels irrespective of the absorption of oxygen.
Thus pyroxyline (gun-cotton or paper) is sometimes resolved, without any
apparent cause, into nitrous and hydrocyanic acids.

Proximate Analysts An organic substance frequently contains a cer-
tain proportion of water as well as of mineral matters. The leaves of plants
contain from 80 to 85 per cent, of water, and the soft animal tissues contain
a very large quantity (p. 142) : to the presence of this water their physical
properties are mainly due. The driest vegetable powders contain a certain
percentage of it, which must be removed before a correct analysis can be
made. The methods of removing water, and determining the quantity pre-
sent, have been elsewhere described (p. 146).

The mineral substances are sometimes in large proportion in the vegetable
and animal structure. Bone contains about 67, and the teeth 70 per cent.
of mineral matter, in the form of phosphate and carbonate of lime. Shells,
and other solid structures of the like nature, are chiefly constituted of car-
bonate of lime, cemented by animal matter. In certain infusoria, silica is
very abundant : this substance is also an important constituent of the epi-
dermis of the reeds and grasses. It forms from 13 to 50 per cent, of the
ashes of some species of plants (p. 299). It is associated with oxide of iron,
and sometimes with traces of manganese. Certain salts of lime, potassa, soda,
and magnesia are the principal mineral constituents of organic substances.
The alkalies are generally found in the ash, combined with carbonic acid (a
product of the combustion of organic acids) and with sulphuric acid ; or in
the state of chlorides, iodides, and bromides of the respective metals. The
alkaline earths are also found as carbonates, but frequently associated with
the phosphoric, sulphuric, and silicic acids. Lime and oxide of iron exist
more or less in the ashes of all organic substances ; and the metals iron and
manganese (the latter rarely) are found in the residue of combustion, as
oxides. These mineral ingredients, although generally small when compared
with the weight of the organic constituents, appear to be of essential im-
portance to the life of plants, and to the structure of the skeleton in animals.
They serve, in the vegetable kingdom, to build up the cell-walls for the
reception of the organic principles, and they give firmness and strength to
the vegetable structure. Potassa and soda are found abundantly in succulent
plants. These alkalies exist more or less in combination with vegetable acids
in all plants ; and it is to the presence of their carbonates that the alkaline
reaction of the ashes of vegetables is due. Potassa is more abundant in
inland, and soda in marine plants ; certain vegetables, such as the Armeria
maritima, Gochlearia officinalis, and Plantago maritima, produce chiefly
potassa when they grow in inland districts, and soda when near the sea-coast.
It is probable that soda is never entirely absent from the ashes of vegetables.
Although it cannot be detected by ordinary processes of analysis in the
ashes of many inland vegetables, including the foliage of trees, its presence
has been revealed in every instance by the photo-chemical process of Bunsen
and Kirchoflf. A quantity of sodium, amounting to less than the 20,000th
part of the weight of the ash, readily admits of detection by spectral analysis.
Soda is the principal alkali of animal compounds : as chloride of sodium, it
is found in the ashes of most animal solids and liquids. Lime in combination
with phosphoric acid is found in all the cereal grains, as well as in potatoes,
turnips, chicory, and other roots. The oxalate and carbonate of lime, in a
crystalline state, are found sometimes in the cells of plants, constituting
raphides. Crystals of oxalate of lime are found abundantly in the root of
rhubarb, and in certain cactuses. Iodine and bromine exist as iodides and

542 MINERAL COMPOUNDS IN ORGANIC SUBSTANCES.

broraide8, not only in marine, but in many land plants; and fluorine has been
detected as a constituent of scurvy-grass {Cochlearia officinalis), and in otiier
plants growing near the sea. The only vegetables which, according to Mul-
der, yield no mineral ash or residue, are the mould-plants, formed in saccha-
rine and acid liquids. They consist of cellulose with nitrogenous substances.
Like the acalephce, or jelly-fish, of the animal kingdom, they are chiefly con-
stituted of water, and yield, on drying, merely a trace of solid matter. The
proportion of mineral matter contained in an organic substance varies with
its nature. We have elsewhere given the proportions of ashes yielded by
different kinds of wood (p. 255). By reference to the analysis of wheat and
straw (p. 537), it will be seen that the proportion in the straw is threefold
that of the grain. Certain educts, when separated from the vegetable by
artificial processes, may be obtained so pure that, on incineration, they leave
no mineral matter — e. g., starch and sugar; others, such as gum, are always
associated with a large quantity of lime, as well as oxide of iron. The
mineral matters found in vegetables are considered to have a telluric origin ;
«. e., they are supposed to be derived from the soil. Sulphur and phosphorus,
in combination with oxygen, united to bases, as sulphates and phosphates,
are found in the earth; and chlorine, combined with sodium, is present in all
soils and in all waters. It is probable that plants growing near the seaside
derive a large portion of the soda which they contain from the diffusion of
the chloride in watery vapor in the atmosphere. Marine plants and animals
derive this salt, chloride of sodium, carbonate of lime (as coral or shell), as
well as the iodides and bromides of the alkaline metals, directly from sea-
water. The following list comprises the principal inorganic constituents of
vegetable and animal substances: Sl'SO^), PCPOg), Si(Si03), Ca(CaO),
Mg(MgO), K(KO), Na(NaO), CI, I, Br, F, Fe(FeA), and Mn(xMnO).

The chloride of rubidium has been detected by M. Grandeau in the saline
waters derived from beet-root, associated in minute quantity with chloride of
potassium. It has also been found in the ashes of tobacco, tea, coffee, aud
in the crude tartar derived from the grape. The colza, cacao, and sugar-
cane, contained none, although some of the ashes were rich in potassium. By
spectral analysis, lithium has been detected in the ashes of seaweed, of the
vine, tobacco, and of numerous other plants growing on the granitic soil of
Germany. It is stated that it has also been found in the ashes of milk,
blood, and muscular tissue. Dr. Cameron did not detect it in cereal plants,
and in some fuci which he examined ; but he found that when lithia was
added to the soil, the ashes of barley contained this alkali, which had been
apparently substiti^ted for soda in the plant {Chemical News, May 31, 1862).
It^ is remarkable that alumina (AlgOg) which is a large constituent of every
soil, is rarely found in the ashes of vegetables, except as an accidental
ingredient. The analyses hitherto made show that alumina is not an essen-
tial constituent of plants, and that it is very rarely present.

Although plants appear to have generally a power of rejecting noxious
ingredients, yet in certain cases, substances of a poisonous nature are taken
from the soil by the roots, and are distributed through their tissues. The
metals thus absorbed, appear to be deposited there, without injuring the
growth or vitality of the plant. We have found by direct experiment that
the seeds of mustard and cress, grown on a soil containing the disintegrated
slag of old lead-works, took up a sufficient quantity of lead to allow its
presence to be readily determined in the grown plants. We also found lead
in the ashes of many plants and shrubs, and of the grass growing on lead-
slag, in the valleys of the Mendip hills. Care was taken to remove any
particles of the soil adhering to the plants. Dr. Cameron states that he
invariably found lead in the plants grown near lead-smelting works at Bally-

ESTIMATION OF WATER AND MINERAL MATTER. 543

corns, county of Dublin {Cliemical News, June, 1862, p. 315). Dr. Wilson
has made a similar observation ; and further, that herbage thus impregnated
with lead, may be a cause of lead-poisoning in cattle {Edinhurgh Monthly
Medical Journal, 1852, vol. xiv. p. 386). The question has been raised
whether plants can thus imbibe arsenic from the soil ; and this is of some
importance, inasmuch as arsenical sulphuric acid is largely employed in the
manufacture of certain manures. The only recorded instances of the
absorption of this mineral, are in some observations made by Dr. Davy and
Mr. Horsley. They found that turnips and other vegetables grown on soils
on which arsenicated manures had been placed, acquired an impregnation of
arsenic {Philosophical Magazine, August, 1859, p. 108). Some of the
lower kinds of plants (confervae) readily grow in certain metallic solutions,
which are poisonous to animals. A solution of tartar emetic exposed to air
becomes speedily covered with confervoid growths of a peculiar kind.
Mould-plants are observed to flourish in solutions of tartaric, citric, gallic,
and tannic acids, and their compounds, but not in a solution of oxalic acid.

With respect to the inorganic elements found in the animal kingdom, if
we except the zoophytes and marine mollusca, these elements may be traced
to the food of the animal, and not to the medium in which they live. Thus
all terrestrial animals derive their support either from other animals or from
vegetables ; hence, except from accidental circumstances, the inorganic com-
pounds found in animals are the same as those which exist in vegetables.

The separation of mineral matters from an organic substance may be
effected by burning a known weight in a platinum crucible. The carbon,
oxygen, and hydrogen, are thus removed, and the residue, which is a light,
porous, white, or (if iron is present) reddish-colored ash, can be readily
weighed. It will probably be found to contain salts, some of which are solu-
ble in water, and others only dissolved by acids. The larger proportion of
the ash is generally insoluble in water. Thus of 100 parts of the ashes of
the oak, only 15 parts are dissolved by water ; of the ashes of the box, 24
parts; and of the ashes of the fir, 17 parts. The acids and bases may be
sought for by the rules laid down at pp. 276 and 531. It has been suggested
that nitric acid should at once be employed for the removal of these mineral
substances from the vegetable. In a few cases this may be resorted to ; but
the most certain method of separation is that of incineration. The presence
of mineral matter in any organic substance may be readily detected by heat-
ing a portion of it on thin platinum foil, or in a platinum capsule. If there
is any difiBculty in consuming the carbon, it may be finely powdered, mixed
with its weight of red oxide of mercury, and heated either in a glass tube or
porcelain capsule. The proportions of water, mineral, and organic matter,
in 100 parts of the fresh leaves of the lettuce and nettle, and of the lime,
ash, and elm-trees, are derived from recent experiments : —

Water

Mineral matter ,

Organic matter .

Lettuce.
. 96-6 ..
. 0-6 .,
. 2-8 ..

Nettle.
,. 79-60 .
,. 2-96 .
. 17-44 .

Lime.
.. 80- ..
.. 2- ..
.. 18- ..

Ash.

,. 75-83 .
. 1-66 .
,. 22-51 .

Elm.

.. 70-
.. 2-

.. 28-

100-0 100-00 100- 100-00 100-

The water was determined by spontaneous desiccatioTi and subsequent
drying at 212°; and the ash by careful incineration in platinum ; the ash in
each case was nearly white. It was more or less alkaline, and was found to
contain carbonic, sulphuric, and traces of phosphoric acid, chlorine, potassa,
lime, magnesia, and oxide of iron. The elm and nettle leaves contained the
largest, and the lime and ash leaves the smallest proportion of lime and

544 PROXIMATE ANALYSIS.

oxide of iron. The greatest amount of phosphoric acid was found in the
nettle, associated with lime. The color-test to flame gave not the slightest
indication of the presence of soda in any of the leaves. Probably by spec-
tral analysis both sodium and rubidium might have been found.

The proximate analysis of an organic substance may be generally effected
by various solvents, such as ether, alcohol, or water, successively applied ;
and occasionally sulphide of carbon, benzole, oil of turpentine, or chloroform
may be employed as substitutes for ether. Ether, which should be used first,
is a solvent of fatty and waxy substances, as well as of resins, camphor, and
some essential oils. Alcohol is a solvent of resins, and of a variety of bodies,
upon which ether has but little action ; while water, either cold or hot, is an
important solvent of many neutral vegetable principles, such as gum, sugar,
or starch. Vegetable alkalies may be dissolved by diluted acetic, hydro-
chloric, or sulphuric acid; and are thus obtained in a state for further
separation by potassa, ammonia, or lime. Vegetable acids admit of separa-
tion by potassa, lime, oxide of silver, or lead ; and from the compounds thus
produced the acid may be procured by a diluted mineral acid, or by the
decomposition of a vegetable salt of lead by sulphuretted hydrogen. The
solvents above mentioned often remove several substances at one time.
Those which are of a crystalline nature may be separated either by cooling
or concentrating the solution to different degrees, or by varying the solvent.
The new process of dialysis may be also employed for the separation of salts
from organic matter diffused in water (pp. 50, 146).

Fractional distillation, as applied to volatile liquids, admits of a more or
less perfect separation of these liquids, by collecting the products which are
condensed at a fixed temperature, or within a range of a few degrees. Thus,
rectified coal-naphtha consists of a series of volatile oils which boil at tem-
peratures varying from 1 40*^ to 342*^. By condensing the vapors evolved at
different temperatures, at which the thermometer remained fixed, Mansfield
found that this liquid might be resolved into five oils, having different boiling-
points, and possessed of different properties. The oil which boils at 176°,
and is condensed below that temperature, is well known as an important
product, under the name of benzole (CjaHg). To this method of separation
we owe the production of paraffine from the tarry oils obtained by the dis-
tillation of coal or bituminous schist at a low temperature. These remarks
apply to the preliminary separation of substances for a further analytical
investigation. It would be impossible to lay down any general rules for the
qualitative and quantitative examination of the bodies thus obtained in solu-
tion, or as a result of distillation. The properties of each organic compound
must be separately studied, and the tests for its detection, and the processes
required for its separation, must be well understood, before a successful
proximate analysis can be made. The difficulties with which a chemist has
to contend are, that organic substances are liable to undergo changes by
mere contact with simple chemical reagents, and that the means of perfect
separation by precipitants are much more limited than in mineral chemistry.

ORGANIC CONSTITUENTS OF VEGETABLES. 545

CHAPTER XLIV.

ULTIMATE OR ELEMENTARY ANALYSIS.

Organic Constituents. — Assuming that the hygrometric water has been
removed from an organic substance, and that the proportion of mineral mat^r,
if present, has been determined, the next stage is to ascertain the nature and
proportion of the organic constituents. These are, in the vegetable, chiefly
three, represented by carbon, hydrogen, and oxygen, occasionally associated
with nitrogen, sulphur, and phosphorus. In the animal they are commonly
four — carbon, nitrogen, hydrogen, and oxygen; and, more frequently than in
the vegetable, associated with sulphur and phosphorus. Carbon is the only
element which appears to be essential to an organic compound. Gmelin has
justly observed that each of the other elements may be absent from particular
compounds; but no compound, which, in all its relations, deserves the name
of organic, is destitute of carbon. Further, organic compounds are distin-
guished from the carbon compounds of the inorganic kingdom, by containing
more than one atom of this element. The atoms of carbon in organic formulae
are in pairs, or in even numbers. The carbon is frequently in such propor-
tion as to be equal to the combined weights of oxygen and hydrogen : it is
generally in large excess, and is estimated to form from one-half to two-thirds
of the weight of dried organic matter. It constitutes 42 per cent, of sugar,
52 per cent, of the weight of alcohol, and 87 per cent, of the weight of oil
of turpentine. The great source of carbon to the vegetable is the carbonic
acid diffused through the atmosphere (p. 162). Although the proportion
present in air is relatively small, it is very great when the bulk of the
atmosphere is regarded. This gas is absorbed by the leaves of plants, and^
while carbon is partly retained, oxygen, carbonic oxide, and carburetted
hydrogen (in the proportion of 1*11 c. i. to 100 of oxygen) are eliminated
(p. 262). Boussingault found that when air was passed over the fresh leaves
of the vine, the carbonic acid was absorbed. The influence of light appears
to be necessary for the elimination of these gases. The roots of plants also
take up a portion of carbonic acid in a state of solution in water.

Test for an Organic Compound. — In determining the question whether a
substance is of an organic or inorganic nature, a chemist seeks for the
presence of carbon. No organic substance contains a sufficient quantity of
oxygen to consume the whole of its carbon and hydrogen ; hence, if the
suspected solid is heated in a close vessel, so that air can have no access, a
black or carbonized residue will remain. The experiment may be readily
performed by heating the substance in a small glass tube. If organic — e. g.,
starch — it will be carbonized: if inorganic — e.g., sulphate of lime — it will
remain unchanged. Volatile bodies — such as the oxalic and benzoic acids,
alcohol, ether, and acetic acid — require a different method of treatment.
Some are entirely, and others are only partly, volatile. Anhydrous oxalic
acid, too, presents this peculiarity : the oxygen is in sufficient quantity to
transform the carbon into carbonic acid and carbonic oxide, but as an inde-
pendent acid it always contains an atom of water. No inorganic compound
leaves a residue of carbon when heated under similar circumstances.

Sulphuric acid is sometimes employed as a medium for testing the organic
35

546 DETECTION AND SEPARATION OF CARBON AND HYDROGEN.

natnre of an unknown solid. When the substance is heated with an excess
of the acid, the mixture is blackened by the liberation of the carbon, and
sulphurous acid is .evolved as a result of the decomposition of a part of the
acid employed. Sulphuric acid, however, produces peculiar effects with
many organic products; it dissolves indigo, forming a blue solution; and
gallic acid, forming a rich crimson-colored liquid ; it produces red-colored
compounds with veratria, certain resins, and oil of bitter almonds ; and while
it carbonizes many bodies, it dissolves others, such as citric acid, with
scarcely any change of color. On the whole, the effect of heating the com-
pound in a close vessel furnishes the most reliable evidence of its organic
nature.

Carbon. — If we have satisfied ourselves, by the production of a carbona-
ceous residue, that the substance is organic, we may next proceed to deter-
mine, by an accurate chemical method, not only the presence, but the
proportion of carbon present. The substance well dried and finely powdered,
is mixed with dried chromate of lead, or black oxide of copper, and intro-
duced into a tube which is connected with two balanced tubes, the first
containing broken chloride of calcium for drying the gaseous products, and
the second a strong solution of potassa, either by itself, or diffused through
dry pumice (p. 162). When the mixture is strongly ignited, the carbon of
the organic substance is entirely converted into carbonic acid: this is dried
by the chloride of calcium, and the gas itself is absorbed by the potassa.
The increase of weight in the potassa indicates the amount of carbonic acid
present. 100 parts of carbonic acid represent 27 "2 parts by weight of
carhon (C). The chromate of lead is preferable to the oxide of copper, as
at a high temperature it fuses and incloses the organic matter, thus insuring
the complete oxidation of the carbon present. The changes which take
place will be readily understood. The oxide of copper is simply deoxidized,
2CuO + C = C03-|-2Cu ; but the chromate of lead is reduced to subchromate
and sesquioxide of chromium, 4(PbO,Cr03) = 4PbO,2Cr03+Cr203 4-03.
The oxygen liberated is taken by the carbon. Unlike the black oxide of
copper, this compound evolves oxygen by the mere effect of heat.

The oxide of copper or chromate of lead is deoxidized, not only by the
•carbon, but by the hydrogen of the organic matter : and carbonic acid and
•water are produced. The water is absorbed by the chloride of calcium.
'The production of carbonic acid under these circumstances, furnishes of itself
a good test of the presence of organic matter. Thus, in place of heating
the organic compound in a close vessel, it may be mixed with oxide of copper
and heated at once in a small tube bent at an angle and drawn out in a
capillary form at the open end. This may be broken off and dipped into a
small quantity of lime-water contained in a tube or watch-glass. If carbon
is present, carbonic acid is produced, a fact indicated by a milky precipitate
in the lime-water. A mere trace of carbon in a substance thus easily admits
of detection.

Hydrogen — This element is commonly in small proportion by weight ; but
there is a large class of organic compounds wtiich are formed entirely of hy-
drogen and carbon, the carbon always preponderating. Hydrogen forms
about 6 per cent, of sugar, and 13 per cent, of alcohol and oil of turpentine,
the latter being a pure hydrocarbon. There is no direct test for the pre-
sence of this element in organic matter. The proof of its presence in a dried
organic substance is derived from the production of water, either by simply
heating the solid to a certain temperature, or by igniting it in a tube with
black oxide of copper or chromate of lead. In this case the deoxidation is
•effected by hydrogen as well as by carbon, and if the substance has been

DETERMINATION OP OXYGEN. 547

properly dried at 212°, and the oxide of copper or chroraate of lead has beea
well dried, all the water carried over and condensed in the chloride of cal-
cium tube will represent the amount of hydrogen in the organic substance.
The chromate of lead, when it has been fused and powdered, is much less
absorbent of water than the oxide of copper ; hence it gives more correct
results for hydrogen.

Inflammable liquids containing hydrogen, such as alcohol and ether,
produce a large quantity of water by combustion in air. The method of
determining the presence and amount of hydrogen has been described above
under Carbon, and additional details will be found at pp. 125 and 146. The
increase of weight in the chloride of calcium tube, which arrests the water,
divided by 9, indicates the amount of hydrogen present. Thus, 100 parts of
water are equivalent to 11 "1 H.

The hydrogen existing in vegetable substances is, no doubt, chiefly derived
from the deoxidation of water, either as it is diffused in vapor through the
atmosphere, or taken up from the soil. This element is never found in the
atmosphere in a free state, but some of its compounds — namely, ammonia
and light carburetted hydrogen — have been detected in air in small quanti-
ties; and some portion of the hydrogen of the vegetable structure may be
derived from these sources, the nitrogen and carbon being at the same time
appropriated. The vital power which can separate hydrogen from oxygen
can also separate this element from nitrogen and carbon : the oxygen elimi-
nated from the decomposed water is supposed to be ozonized, like that which
is set free by the electrolysis of water.

Oxygen. — This element, next to carbon, is the principal constituent by
weight of organic matter. In some compounds, as in vegetable acids, it is
in greater proportion than carbon. It constitutes 66 per cent, of anhydrous
oxalic acid, 52 per cent, of sugar, and 34 per cent, of alcohol. In the case
of oxalic acid, it is associated with carbon only : but in sugar, alcohol, and
the greater number of vegetable principles, it is combined with hydrogen,
and sometimes with nitrogen and sulphur. Some of the alkaloids, acids,
and neutral compounds contain none — e. g., nicotina, aniline, hydrocyanic
acid, and oil of turpentine. There is no direct test for the presence of oxy-
gen in organic substances, if we except the production of carbonic acid and
water by heating them out of contact of air. The oxygen is then consumed
by the hydrogen of the substance, and water is produced as well as carbonic
acid. The general principle on which the determination of the presence and
amount of oxygen is based consists in the separation and quantitative esti-
mation of the other constituents, and in the deduction of the sum of these
from the amount of dry organic matter employed in the experiment. If the
substance examined was perfectly dry and pure, and the other elements have
been accurately weighed, this method will give a sufficiently correct result ;
but any errors on these points will add to or diminish the amount of oxygen.
When the substance consists of carbon, hydrogen, and oxygen only, the
results are generally satisfactory ; but when nitrogen, sulphur, and phosphates
are present, there is greater difficulty attending the correct estimation of the
oxygen. The oxygen found in organic substances is probably derived, not
only directly from the atmosphere, but indirectly from the oxidized products
— carbonic acid and water — which are diffused through it.

. Nitrogen. — This element, although most abundantly found in animal sub-
stances, is an important constituent of many vegetable compounds. Albu-
men, fibrin, gluten, and casein of both kingdoms contain it in a large
proportion. It exists in the sap and juice of vegetables: it is present in
many alkaloids, in indigo, in bases such as aniline and nicotine ; also in
amygdaline, in hydrocyanic and carbazotic acids, and in a great variety of

548 DETECTION OF NITROGEN.

artificial products. Compounds of nitrogen and hydrogen, or of nitrogen
and oxygen, are not met with among organic substances. Ammonia, which
is constituted of nitrogen and hydrogen, is not an organic substance, but
the product of the decomposition of organic matter. Nitrogen is associated
with carbon in cyanogen and its compounds, with sulphur in oil of mustard,
and with sulphur and phosphorus in albumen, fibrin, and other organic
principles.

Organic substan-ces which contain this element and a sufficient quantity of
moisture, undergo changes to which the term putrefaction is applied. One
of the most abundant products is ammonia, which is derived from the nitro-
gen uniting with hydrogen in the nascent state.

The presence of nitrogen may in general be determined by heating the
dried substance in a close tube : ammonia, in combination with carbonic or
hydrosulphuric acid, is distilled over with water among the first products.
The alkaline gas may be identified by its pungent odor, and by its reaction
on test-paper placed in the mouth of the tube, or by any of the usual tests.
The substance may be heated in a tube, with hydrate of potassa or calcined
soda-lime, finely powdered: in either case the nitrogen present is entirely set
free as ammonia. The alkaline bases operate by fixing any acid that may
be produced. For another method of detecting this element, see p. 156.
Even a diluted solution of potassa, at a moderate heat, will in some cases
destroy the substance and produce ammonia. Among alkaloids, strychnia
and morphia resist the action of a solution of potassa which is sufl[icient to
decompose atropia, aconitina, and hyoscyamia. Morphia or strychnia, when
heated alone, evolves ammonia, showing that nitrogen is a constituent of
these alkaloids"; but their salts give ofi' no ammonia when heated, unless they
are mixed with 4 or 5 parts of hydrate of potassa or dry soda-lime. Caout-
chouc, when heated in a reduction-tube, evolves ammonia ; gutta-percha does
not. When nitrogen is absent, the organic solid commonly evolves an acid
(acetic), the vapor of which reddens litmus-paper. Thus dextrine, gum, or
woody fibre, when heated strongly in close vessels, evolves acetic acid. Non-
nitrogenous are thus distinguished from nitrogenous substances : If we heat
in a tube a small quantity of Russian isinglass, ammonia is copiously evolved ;
but if we substitute for this the substance called Japanese isinglass {Gelidium
corneum) an acid vapor escapes. This substance contains no nitrogen, while
the Russian isinglass contains it in large proportion. Another method of
detecting nitrogen in organic substances consists in converting it into cyan-
ogen. For this purpose a fragment of sodium is heated with the organic
substance in a tube of narrow bore. A black alkaline residue is obtained,
which is dissolved in water. The solution will contain free soda as well as
carbonate, and if nitrogen was present, cyanide of sodium. The liquid
nearly neutralized by a dilute acid, is treated with a small quantity of a solu-
tion of green sulphate of iron and is well stirred. It was now acidulated
with diluted sulphuric acid — oxide of iron is dissolved, and if nitrogen was
present in the organic substance Prussian blue will be produced. The non
production of Prussian blue, under these circumstances, shows that nitrogen
is not a constituent of the substance examined.

The vegetable is supposed to derive its nitrogen chiefly from ammonia
diffused through the atmosphere, or carried by rain into the soil. The very
small proportion of ammonia found in air may appear to be insufficient as -a
source of nitrogen for plants ; but vegetables have the power of extracting
and appropriating their elements, even when diffused in such minute traces
as not to be revealed by ordinary reagents. Rubidium has been detected
in the salts obtained from beet-root, but none has hitherto been found in the
soil. A similar fact has been noticed with regard to marine plants ; they

DETECTION AND SEPARATION OF SULPHUR. 549

have a power of accumulating and fixing iodine in their tissues ; but iu the
sea-water in which they flourish, it is difl&cult to detect, by chemical tests,
any traces of iodine, even when a large quantity is made the subject of ex-
periment. Although nitrogen is an alaundant constituent of the atmosphere,
there is no evidence that vegetables procure it directly from this source. As
hyponitrite or nitrate of ammonia (the result of the oxidation of the elements
of air and aqueous vapor by ozone or electricity), nitrogen in a combined
state is not only diffused in the atmosphere, but carried by rain into the soil.
• According to Schonbein, a plant in the act of growth, by causing a reaction
of the elements of air upon aqueous vapor, is a generator of nitrate (hypo-
nitrite) of ammonia, and thus prepares a part of its own nitrogenous food.
On this theory, the nitrogen of vegetables is derived indirectly from the con-
stituents of the atmosphere. The quantity of nitrogen in an organic com-
pound, may be determined either by separating the element in the gaseous
state, or by converting it into ammonia, and precipitating this alkali by
chloride of platinum. These methods will be presently described.

Sulphur. — Sulphur is frequently associated with nitrogen. The nitroge-
nous principles of the animal and vegetable kingdom — albumen, fibrin, gluten,
and casein — contain it abundantly. Gelatine and indigo contain nitrogen
but no sulphur; gutta-percha contains a trace of sulphur but no nitrogen ;
while caoutchouc contains both. Sulphur is an important constituent of
certain essential oils. In dried organic solids, it may be detected by heating
the substance in a small tube : the vapor evolved, containing sulphuretted
hydrogen, blackens a slip of glazed card, or of paper impregnated with a salt
of lead. Dried gluten, bread, caoutchouc, flannel, hair, horn, or feathers,
evolve a quantity of a sulphur compound under these circumstances. If the
substance also contains nitrogen, ammonia is produced, and hydrosulphate
of ammonia comes over with aqueous vapor. The detection of the hy-
drosulphate and therefore of the presence of nitrogen and sulphur, in the
compound, is readily effected by one experiment. Paper wetted with a
solution of nitro-prusside of sodium, acquires immediately a rich purple or
crimson color. Unless the sulphur is in combination with an alkali, this
change does not take place.

There are other methods of detecting sulphur. The substance may be
boiled in a solution of potassa containing a small quantity of oxide of lead
dissolved ; if sulphur is present, the substance is either blackened or the
liquid acquir.es a dark color from the production of sulphide of lead. A
portion of flannel or silk thus tested by a potassa-solution of oxide of lead,
will be completely blackened ; but if mixed with cotton the fibres of the latter
will remain white, as this substance contains no sulphur. A small portion
of flour thus treated is also blackened by reason of the gluten contained in
it. Pure starch is simply dissolved, as this contains no sulphur. Owing to
the occasional presence of lead as an impurity in a solution of potash, most
sulphur compounds, when boiled with the alkali, impart to it a dark color.
Liquid compounds of sulphur which are dissolved by potassa undergo a
similar change. As an alkaline sulphide is produced by the reaction of the
potassa on the sulphur of the organic matter, the nitroprusside of sodium
may be made available for the detection of this element. If a small quantity
of hair, woollen, or silk is boiled in a solution of potassa, the presence of
sulphur will be indicated by the alkaline liquid acquiring a reddish or crimson
tint when a few drops of nitroprusside of sodium are added. For this pur-
pose, potassa, free from lead, should be selected. When the organic sub-
stance is dry the following simple process will enable a chemist to determine
the presence of sulphur and nitrogen at one operation : The substance is
heated iu a narrow tube, with a small quantity of sodium, and the residue

550 PHOSPHORUS, CHLORINE, BROMINE, AND IODINE.

lixiviated. A sulphide of the metal is formed, and the presence of this may
be discovered by the addition of nitroprusside of sodium, which produces a
crimson color, or of acetate of lead when a brown precipitate results. Should
there be much cyanide present, white cyanide of lead is thrown down, and
this conceals to some extent the dark sulphide. A few drops of diluted
nitric acid removes the cyanide, and the characteristic precipitate of sulphide
of lead is then seen of its proper color. If we add to another portion of the
liquid a solution of persulphate of iron, we obtain a red precipitate, the sul-
phocyanide of iron, thus indicating the presence of sulphur and nitrogen in
the substance treated with sodium. No sulphocyanogen could be found unless
both of these elements were present.

In some cases, the molecular condition of the substance interferes with the
application of this test. Thus caoutchouc contains much sulphur, but in
order to detect it, the substance should either be digested in strong nitric
acid containing nitrous acid, or deflagrated in a silver crucible with pure
hydrate of potassa and nitre, until it has become white. The sulphur is
oxidized and converted into sulphuric acid or sulphate of potassa, and the
quantity of acid produced may be determined by precipitating a neutralized
solution of the residue in water, with baryta or one of its salts.

Phosphorus. — This is not unfrequently associated with nitrogen and
sulphur in organic compounds, and exists sometimes in large proportion in
animal products. In the state of phosphoric acid combined with soda, lime,
or magnesia, it is an abundant mineral constituent of animal and vegetable
matter, and is readily obtained by incineration. Its presence and proportion
may be determined, by deflagrating the dried organic substance with a mix-
ture of equal parts of pure nitrate of potassa and bicarbonate of potassa in
fine powder. The experiment may be performed in a platinum crucible :
the saline residue is dissolved in water, and the solution neutralized with
acetic acid. Any soluble phosphate that is present may be precipitated by
the methods described at pages 243 and 390. In the first case aramonio-
phosphate of magnesia is produced, 100 parts of which when dried and
ignited, are equivalent to 28 '57 parts of phosphorus, and in the second an-
insoluble perphosphate of iron is thrown down.

The sulphur and phosphorus of the vegetable kingdom are chiefly derived
from a deoxidation of the sulphates and phosphates contained in the soil.

Chlorine, Bromine, and Iodine. — In all natural compounds these elements
are found associated with alkaline metals, and are readily separated by the
process of incineration. Artificial compounds, containing them in such a
form as to yield no precipitate on the addition of nitrate of silver, may be
analyzed by passing the vapors through a combustion-tube containing a
mixture of three parts of hydrate of lime and one part of hydrate of soda,
the purity of which has been previously ascertained. A chloride, bromide,
or iodide of the alkaline metal is thus procured. After the tube has cooled,
the lime is dissolved in very diluted nitric acid ; and nitrate of silver is added
to the. filtered solution. A precipitate, consisting of chloride, bromide, or
iodide of silver, or a mixture of these salts, is thus obtained, and the propor-
tion of each element may be determined by the process described at page
208. Volatile compounds of these elements are introduced into the mixture
in small glass bulbs.

When the substance for analysis consists of carbon in combination with
hydrogen or oxygen, or with both of these elements, the proportions in 100
parts may be at once determined by the use of the Gombustdon-tube.

The tubes used in these analyses should be made of green glass free from
lead, or of hard Bohemian glass. They are generally about four-tenths of an
inch in diameter, and from 15 to 18 inches in length, sealed, and either drawn

ESTIMATION OF THE RESULTS. 551

into a point or rounded at the sealed end; the open extremity should be
smoothed by fusion, so as to receive a cork without danger of cracking. It
is sometimes necessary to protect the tube, by rolling a strip of copper-foil
spirally round it, tied at each end by a piece of wire. The tube may be
heated, either by a lamp-furnace or over charcoal, in a trough of sheet-iron
constructed for the purpose.

When the substance to be analyzed is solid, from 3 or 4 to 8 or 10 grains
of it, properly dried, are carefully mixed with about 200 grains of the dried
oxide of copper, and introduced into the combustion-tube, into the end of
which is previously placed about half an inch in length of small copper-
shavings superficially oxidized. These shavings should occupy about two
inches of the tube above (or, as it lies horizontally, before) the organic mix-
ture, the object being to keep the whole contents of the tube in a loose or
porous condition, so that the gaseous products may escape from it without
impediment. .The mixture of oxide of copper and the organic substance
should be placed about the centre of the combustion-tube, some pure oxide
of copper being placed before and behind it. If the organic substance under
examination is a ternary compound of hydrogen, carbon, and oxygen, it is
obvious that the products will be only loater and carbonic acid. In order to
ascertain the weight of the former, and thence the weight of the hydrogen
required to form it, the products, as they escape, are carried through a tube
containing fragments of fused chloride of calcium, and accurately weighed.
The vapor of water is absorbed, and the increase in the weight of the tube
and its contents, will indicate its quantity. The juncture of the combustion-
tube with the chloride of calcium tube, should be made air-tight by a per-
forated cork.

The carbonic acid, deprived of water, is conducted from the extremity of
the chloride of calcium tube, into a light glass tube blown into five bulbular
enlargements, containing a strong solution of caustic potassa, and accurately
balanced. The bulb apparatus is then connected with the chloride of calcium
tube, by short lengths of caoutchouc piping.

After the abstraction of the water in the chloride of calcium tube, the car-
bonic acid passes on into the solution of caustic potassa, through which, by
properly inclining the bulb apparatus, it may be made to pass in divided
bubbles, and under some pressure, so as to insure its total absorption. When
the experiment is completed, the apparatus is allowed to cool, and in order
to prevent any portion of the alkaline solution retrograding into the
chloride tube, the tip of the combustion-tube is broken off, and any residuary
carbonic acid may then be drawn into the alkaline solution, by applying
gentle suction at the end, or by the use of an aspirator. The weight of the.
evolved carbonic acid, and therefore of the carbon, is ascertained by accu-
rately determining the increase in the weight of the condenser with its alka-
line solution.

In order to illustrate the mode of operation, we may assume that 10
grains of pure starch have been thus decomposed by oxide of copper in the
combustion-tube, and that the chloride of calcium tube has acquired an
increase of weight equal to 5 94 grains (water), and the potassa. apparatus
has increased in weight 16 24 grains (carbonic acid). As pure starch is
known to contain only carbon, hydrogen, and oxygen, the proportions of
each element in 100 parts may be thus determined. Hydrogen forms one-
ninth part of water : hence 5-94-f-9 = 0 66 H. In 22 parts, by weight, of
carbonic acid, there are 6 parts of carbon : hence 22 : 6 : : 1624 : 443 C.
The oxygen, if these results are correct, may be determined by deducting
the sum of the weights of hydrogen and carbon from the weight of the starch

552 SEPARATION OP NITROGEN AS AMMONIA.

employed in the experiment, 0'66 + 4'43 = 5*09 : and 10 — 509 = 4-91 0.
Hence these results show that pure starch consists of: —

In 10 parts. la 100 parts.
Carbon . . . . , 4-43 44-3

Hydrogen .... 0*66 6-6

Oxygen . . . . . 4 91 49-1

10-00 100-0

When nitrogen is a constituent of the organic matter under examination,
the mixture with oxide of copper is made as usual, but the contents of the
fore part of the combustion-tube must now consist of a mixture of shavings
or filings of metallic copper with the oxide, and great care must be taken slowly
to conduct the evolved gases through this mixture, rather highly heated, in
order to effect the complete evolution of the nitrogen, and to decompose the
various compounds which that substance might possibly form with the
oxygen, carbon, or hydrogen. The nitrogen then escapes as a gas with car-
bonic acid. The gases may be collected in a proper mercurial apparatus,
and the carbonic acid removed afterwards by a few fragments of fused
hydrate of potassa, when the nitrogen will remain, and its weight may then
be deduced from its volume. Deutoxide of nitrogen is an occasional product
of the decomposition of a nitrogenous compound by oxide of copper. It is
most readily formed when chromate of lead, or a current of pure oxygen, is
employed in the combustion-tube. It is produced in larger quantity, cceteris
paribus, when the temperature is high, than when the combustion takes place
slowly.

The quantitative determination of nitrogen may be more accurately ob-
tained by converting it into ammonia, and in this form combining it with
chloride of platinum, so as to weigh it in the state of ammonio-chloride.
(Varrentrapp and Will, Ann. der Ghem. und Pharm., 39, 257.) For this
purpose the azotized organic product, to the amount of 4 or 5 grains, is
thoroughly blended in a warm mortar with a mixture of 1 part of dry hydrate
of soda, and 2 of lime, in such quantity as to fill the combustion-tube to
within about 3 inches of its open end. Attached to the combustion tube is
a three-bulbed apparatus, containing pure hydrochloric acid sp. gr. 1130.
Heat is then applied to the combustion-tube, beginning at the anterior
extremity; and when the whole length has been so heated that the substance
has become quite white, air is drawn through it as in the case where oxide
of copper is used, and the contents of the bulb-apparatus poured into a basin,
the bulbs being afterwards washed, first with a mixture of alcohol and ether,
and then with water, from an ounce to an ounce and a half of liquid being
used for that purpose. A solution of pure chloride of platinum is then
added in excess to the mixture of the hydrochloric solution and washings,
and the whole evaporated to dryness : the residue is treated with a mixture
of two volumes of alcohol and 1 of ether ; if this affords a yellow solution,
excess of chloride of platinum has been added, and the remaining washed
ammonio-chloride of platinum may be collected on a filter, dried at 212°,
and weighed. In order to control the weighing, the ammonio-chloride should
be calcined, and the resulting metallic platinum also weighed. 100 parts of
the dried ammonio-chloride, are equivalent to 6-22 of nitrogen and 44 parts
of metallic platinum. All substances containing nitrogen, under these cir-
cumstances, evolve this element in the form of ammonia, excepting nitric acid.
If any soda-lime is carried over it does not affect the result, as these alkalies
are not precipitated by chloride of platinum. Any excess of chloride of
platinum is completely removed by the mixture of alcohol and ether.

The soda-lime, before use, should be ignited and finely powdered. In its

SEPARATION OP NITROGEN AS AMMONIA. 553

reaction on organic matter at a high temperature, it is probable that the
carbon unites with the oxygen of the water of the hydrates, forming carbonic
acid, which unites to the bases, while the hydrogen which is set free combines
with the nitrogen of the organic substance to produce ammonia. Three
parts of hydrogen are sufficient for the entire conversion of fourteen parts of
nitrogen. If the nitrogenous compound is a liquid, it may be introduced
into bulbs and heated with soda-lime in the manner in which organic liquids
are heated with black oxide of copper. Some nitrogenous organic substances
do not evolve ammonia under these circumstances, but a volatile organic base
on which soda-lime has no action. Thus, indigo yields aniline, and other
substances produce other bases containing no oxygen. They all form, how-
ever, insoluble compounds with chloride of platinum and the amount of nitro-
gen present admits of easy determination by incinerating the salt and obtain-
ing the platinum in the metallic state. 99 parts of platinum are equivalent
to 14 of nitrogen or 100 parts to 14'4.

If the substance for analysis is a volatile organic liquid (alcohol), it may
be collected in a small balanced bulb of glass, and its weight accurately de-
termined after sealing the capillary end of the bulb. It may then be dropped
into the midst of the oxide of copper in the combustion-tube, the small ca-
pillary end being previously broken. After the oxide has become full heated
in the fore-part of the tube, the portion containing the bulb is heated, and
as the va^or of the liquid escapes, it is immediately decomposed by the ig-
nited oxide of copper. Two of these bulbs, containing together from 6 to 8
grains of the liquid, may be employed in one operation, provided that several
inches of the oxide are interposed between them. If the liquid has a high
boiling-point and is rich in carbon, it will be found better to subdivide the
quantity among three bulbs. Substances of a viscid or fatty nature may be
introduced into the combustion-tube in small glass tubes, or in trays of pla-
tinum foil.

In the analysis of hydrocarbons, it is sometimes necessary to use a current
of pure oxygen, in order to consume the carbon Completely. Occasionally
chlorate of potassa is mixed with oxide of copper, in order to insure a copious
supply of oxygen. Chromate of lead, as a source of oxygen, has some advan-
tages over oxide of copper. After it has been fused, it is but little hygro-
metric ; and if the substance which is to be analyzed contains chlorine or
sulphur, the lead retains these elements, while with oxide of copper a volatile
chloride of that metal is formed, as well as sulphurous acid. This last-men-
tioned compound is not absorbed by chloride of calcium, but it readily com-
bines with potassa, and thus adds to the apparent amount of carbon. In
order to avoid this source of error, a tube containing finely-powdered peroxide
of lead, should be placed between the chloride of calcium tube, and the
potassa-apparatus. This completely arrests any sulphurous acid that maiy
be produced. With the use of chromate of lead, however, the tube contain-
ing peroxide is seldom required.

Sulphur can be estimated only by the process described at p. 549. Nitric
acid is not always efficient in completely oxidizing the sulphur of organic
compounds. Liebig advises that the substance should be gradually fused in
a silver crucible with an excess of a mixture of 8 parts of hydrate of potassa
and 1 part of nitre. If the mixture should not become colorless when heated,
a little more nitre may be added. The white residue is dissolved in water
acidulated with hydrochloric acid, and this solution is precipitated by chloride
of barium. The sulphate, after it has been washed, dried, and ignited, may
be weighed : 100 parts of dried sulphate of baryta are equivalent to 13-8 of
sulphur. Volatile organic liquids containing sulphur may be vaporized, and

554

EQUIVALENTS OP ORGANIC SUBSTANCES.

the vapor passed through a tube containing a mixture of nitre and bicar-
bonate of potassa or soda, strongly heated.

[For further information on the analysis of organic substances, the reader
is referred to Fresenius's Quantitative Analysis, p. 385, and Liebig's Hand-
hook of Organic Analysis.']

Equivalents of Organic Substances. Formula. — The results obtained
by the use of the combustion-tube merely represent the weights of the ele-
ments in 100 parts. There can be no doubt that these elements are com-
bined in equivalent proportions, and the principles on which the atomic
weight of an organic compound is calculated, are therefore similar to those
described for mineral substances (p. 66). We may take for illustration an
alkaloid, an acid, and one or more neutral substances.

1. An Alkaloid. — One hundred parts of morphia yield by combustion : of
carbon, 71-91; of hydrogen, 6 85; of oxygen, 16 44; and of nitrogen, 4*80.
The hydrochlorate of this base may be readily obtained anhydrous, and it is
found that 100 grains of the anhydrous salt contain 8875 of morphia and
11*25 of hydrochloric acid. Assuming this analysis to be correct, the atomic
weight of the alkaloid will be 292 (11'25 : 88 75 : : 37 : 292). The weight
of each element contained in this quantity of the alkaloid is easily deduced
from the elementary analysis of 100 parts. Thus —

100

71-91 :

: 292 :

209-97 Carbon

100

6-85 :

: 292 ■

20-00 Hydrogen

100

16-44 :

: 292

48 00 Oxygen

100

4-80 :

: 292 .

14-01 Nitrogen

If the w^eight of each element, contained in an equivalent of morphia, is
divided by its atomic weight, the products will represent the number of atoms
contained in each atom of morphia: —

Parts.

Equiv.

Atoms.

Atoms.

209-97

■— 6 ==

34-99

or 35 of Carbon

20-00

-^ • 1 =

20-00

or 20 of Hydrogen

48-00

4- 8 =

G-00

or 6 of Oxygen

14.00

-^ 14 =

1.00

or 1 of Nitrogen

The formula for morphia is, therefore, C35H2o06N=292. When it is required
to calculate the percentage composition of the alkaloid from its formula, we
adopt an inverse method. Thus : —

Parts.
210 Carbon

20 Hydrogen

48 Oxygen

14 Nitrogen

<
and —

100 71-91 Carbon
100 • 6-85 Hydrogen
100 16-44 Oxygen
100 4-80 Nitrogen

Alkaloids which form double chlorides by combining with chloride of pla-
tinum, may have their equivalents determined by a calculation based, 1st, on
the weight of the platinum salt in the dry state, and 2dly, on the weight of
the metallic platinum obtained as a result of its combustion.

2. An Organic Acid. — For the purpose of illustration, we may take Oxalic
acid. This and other acids are first combined with oxide of silver or oxide

Atoms.

Equ

35

X 6

20

X 1

6

X 8

1

X 14

292

210

292

20

292

48

292

14

FORMULiE OF ORGANIC ACIDS. 555

of lead, takinp^ care that the compounds are neither basic nor hydrated.
The oxalate of lead, dried at 212°, consists of 24*32 of oxalic acid, and
7568 of oxide of lead, or 36 parts of the acid are required to form a definite
salt with 112 parts (or one equivalent) of oxide of lead. This acid contains
no hydrogen, so that in burning the dry lead-salt with well-dried oxide of
copper, no water is formed, and the only product is carbonic acid : 100 grains
of Oxalic acid, (0), are thus found to contain 33 33 parts of carbon and

0

0

100 :

; 33-33 :

: 36 ;

: 11-99 Carbon

100

: 66-67 :

: 36 :

; 24-00 Oxygen

66-61 of oxygen: and 11-99^6=1 99, or 2C, and 24-^8=30: hence anhy-
drous oxalic acid is represented by Cfi^ : and from this formula, its cen-
tesimal composition may be deduced as in the case of morphia.

Alkaloids and acids which either crystallize, or form crystallizable salts,
frequently combine with water to form hydrates. To avoid error in this
respect, it is sometimes advisable to ascertain the atomic weight of an alka-
loid by determining, by precipitation, the proportion of acid (sulphuric or
hydrochloric) contained in a weighed quantity of the crystallized salts. In
reference to crystallizable acids, the amount of water combined with the
crystals of Oxalic acid may be thus determined : 63 grains of the acid dis-
solved in water, and precipitated by acetate of lead, yield 148 grains of dry
oxalate of lead. Deducting the weight of the oxide (148 — 112 = 36), we
obtain the weight of dry acid which has combined with lead. As 63
grains of crystallized acid were used in the experiment, then 63 — 36=21,
or three equivalents of water must have been combined with them. Hence
crystallized Oxalic acid has the formula C303,3HO, or, as it cannot exist
without an atom of water, CaOgHO -f 2H0.

3. Neutral Bodies. — In reference to neutral substances which do not enter
into combination with mineral compounds of which the equivalents are known,
there are great difficulties in assigning a correct atomic constitution. In
some cases they combine with oxide of lead, and from this combination, a
formula may be deduced : gum, sugar, and starch are bodies of this kind :
on the other hand, some, such as mannite, enter into no known combination.
The general rule regarding organic substances of this nature, is to divide
the quantity of each element contained in 100 parts, by its equivalent. The
quotients thus show the relations which the elements bear to each other in
atoms or equivalents, and if fractional, these may be converted into integers
by multiplication.

Cane-sugar may be combined with oxide of lead ; and, by analysis, it is
found that this compound contains in 100 parts, 59'3 of oxide of lead and
40 1 of sugar. If an atom of sugar were united to an atom of oxide of lead,
then the equivalents would be 76-81 for (59 3 : 40-1 : : 112 : 16-81), but
there is great reason to believe that 2 atoms of oxide of lead replaced 2
atoms of water which are contained in crystallized sugar ; and therefore that
the equivalent of anhydrous sugar is 153 ; (16-81x2=153-14). One hun-
dred parts of crystallized cane-sugar give by combustion : —

Atoms.
Carbon . 41-50 -f- 6 = 6-92 1-064 = 11-7 or 12

Hydrogen 6-45 -^ 1 == 6-45 0-993 = 10-9 or 11

Oxygen . 52-05 -f. 8 = 6-50 1-000 = 11-0 or 11

The figures in the fourth column are obtained by making oxygen the unit
and divisor,— thus,69-2-i-6-50 = l-064 ; 6-45-f-6-50=0-993; and 6-50^6-50
= 1. The quotients multiplied by 11 give the results in atoms at HI, 109,

556 CALCULATED FORMULuE OF, SUGAR AND MANNITE.

and 11 respectively, or, in round numbers, C^^K^^O^^. Deducting the 2
atoms of water which are known to exist in crystallized cane-sugar, the for-
mula would stand thus : C^'gHyOg-f 2H0. When sugar combines with oxide
of lead, the two atoms of water are replaced by two of this oxide, so that
saccharide of lead would be Cj5jHgOg,2PbO, or 153 parts of sugar (1 atom)
to 224 parts of oxide of lead (2 atoms). The formula here given is well
adapted to explain the conversion of sugar into alcohol, as well as various
other chemical changes of this compound. If, from the formula of crystal-
lized cane-sugar (C,aHijOii), we desire to calculate the centesimal composi-
tion, so as to compare the theoretical with the ascertained results, the differ-
ences will be no greater than might be explained by slight errors in analysis.
This will be evident from the following figures : —

Atoms. Calculated. Found.

Carbon. . . 12 x 6 = 72 or 42-11 41-50

Hydrogen . . 11 x 1 = H or 6-43 6-45

Oxygen . . 11 X 8 = 88 or 51-46 52-05

Mannite is a compound of three elements. In 100 parts it consists of : —

Carbon . 39-54
Hydrogen 7-73
Oxygen . 52-73

6 = 6-59 1-00 X Q = Q

1 = 7-73 1-17 X 6 = 7

8 = 6-59 1-00 X Q = &

The atoms of carbon, hydrogen, and oxygen, as deduced from the cen-
tesimal composition, are as the respective numbers, 659, 773, 659. If the
figures in the third column are divided by the amount of oxygen as unity,
quotients are obtained which, when multiplied by 6, give a series of atoms in
integers, namely, CgHyOg. These figures, therefore, merely express the pro-
portions of the elements in reference to their atomic weights. They convey
a better knowledge of the composition of bodies than the arithmetical pro-
portions in 100 parts ; and are so far convenient for use. At the same time
formulae thus derived, are purely empirical.

Volatile Liquids. — When the organic compound is a volatile liquid, its
vapor-density will serve to control the results of an analysis. In the series
of isomeric liquid hydrocarbons, it is chiefly by the vapor-density of each
liquid, that the number of atoms which should enter into the respective
formulae, can be accurately determined. The degree of condensation of the
elements is therefore a material point in considering their atomic constitu-
tion, and in constructing their formulae. 100 parts of Alcohol yield by the
combustion-tube : —

Atoms.
Carbon . . 52-65 -j- 6 = 8-92 8-92 -f- 4-30 = 2

Hydrogen . 12-90 -^ 1 = 12-90 12-90 -^ 4-30 = 3

Oxygen . . 84-45 -j- 8 = 4-30 4-30 -i- 4-30 = 1

The sp. gr. of the vapor of alcohol is 1"61 : hence, if this analysis be cor-
rect the specific gravities of the elements in these atomic proportions should
correspond. With respect to carbon, the volume of its vapor, compared
with hydrogen, cannot be determined experimentally. It is assumed that
one volume or atom is represented by the sp. gr. 0*4146. Oxygen has a sp.
gr. of 1-1057, and hydrogen a sp. gr. of 0*0691, hence : —

Atoms. Sp. gr.

Carbon ... 2 (0-4146 x 2) = 0-8292

Hydrogen ... 3 (0-0691 x 3) = 0-2073

Oxygen ... 1 (1-1057 -r- 2) = 0-5528

Sum of specific gravity . . . 1-5893

CALCULATED FORMULAE FROM VAPOR-DENSITIES. 557

The sp. gr. of the vapor of alcohol is therefore nearly in accordance with
that which should be found in one volume of a vapor of which the consti-
tuents are 2 atoms (or volumes) of carbon, 3 atoms (or volumes) of hydro-
gen, and 1 atom (or half a volume) of oxygen. The most simple formula
for alcohol would therefore be C^Uft. Alcohol has neither acid nor basic
properties, and forms no definite compounds with bodies. Hence its equi-
valent might be taken at twice, three times, or even four times the numbers
of the atoms above given. The theory of the production of sulphovinic
acid and of ether by there action of sulphuric acid on alcohol, is rendered
much more simple by doubling the numbers obtained by analysis, and making
them C^HgOg. In this case the atom of alcohol would correspond to two
volumes of its vapor ; and its specific gravity compared with air would be as
161 to I'GO and with hydrogen as 23 to 1. The conversion of alcohol into
aldehyde and acetic acid by processes of oxidation, is rendered more intelli-
gible by the adoption of the formula above given.

Rectified Oil of turpentine yields by analysis in 100 parts : —

Carbon
Hydrogen

Its formula as thus deduced, would be, in its most simple form, 5 atoms of
carbon and 4 of hydrogen (C5HJ. But it might also be C,oHg or CgoHjQ.
The ascertained specific gravity of the vapor compared with air is 4*76. A
constitution represented by C5H4 would give for the specific gravity, only
one-half of this density, or 2-35. C^JI^ would give a density of 4*70, re-
sembling so closely that which has been determined by experiment, that it is
impossible not to conclude that 10 atoms of carbon and 8 atoms or volumes
of hydrogen are included in each volume of the vapor of oil of turpentine.
The oil, however, combines with some of the hydracids, including the hydro-
chloric. With the latter it forms a solid artificial camphor, represented by
C^oH,gHCl. The formula for the oil of turpentine should be, therefore, Cgo
H^g, unless it be supposed that 2 atoms of the oil ^iC^oR^) are combined
with 1 of hydrochloric acid. The former is selected by reason of its greater
simplicity and its agreement with the formulae of other hydrocarbons. One
atom of oil of turpentine, like one atom of alcohol, therefore corresponds to
two volumes of vapor: hence the specific gravity would be about 4 '7 : —

Atoms.

88-24 -^ 6 = 14-70

1-25 or 5

11-76 -7- 1 = 11-76

1- or 4

Atoms, Vol.

Carbon .

• ,

. 20 or 20 = 0-4146

X 20 ...

... 8-292

Hydrogen

.

. 16 or 16 = 0-0691

X 16 ...

... 1-105

9-397

Vapor-density of oil of turpentine .... 4-698

Chloroform is considered to have the constitution represented by the for-
mula C.jH,Cl3. The specific gravity of its vapor is 4'20. This is in accord-
ance with the view, that each atom of the compound corresponds to two vol-
umes of the vapor : —

Carbon .
Hydrogen
Chlorine

Atoms.
. 2 ..
. 1 ..
. 3 ..

Vol.

2

.... 1
.... 3

2

jhlorofoi

m

Sp. gr.

0-4146 X 2 ...
0-0691 X 1 .-.
2-4876 X 3 ...

Sp. gr.
... 0-8292
... 0-0691
... 7-4628

1

8-3611

isity of (

. 41805

558 EMPIRICAL AND RATIONAL FORMULA.

As a general rule the vapor-density shows the proportions in which the
elements combine, but the atomic weight can be correctly determined only
by calculation from some definite compound. In the case of chloroform no
such compound is known. This and other instances prove that in the vapors
of organic liquids, the gaseous elements undergo an enormous condensation.

When the formula of an organic substance merely expresses the number
of atoms of each element, as C^HgOg (alcohol), or C^H^O^ (hydrated acetic
acid), it is called empirical. It expresses the relative proportions of the
elements, without reference to the mode in which they are combined, or to
the atomic weight of a body. A rational formula implies one which pro-
fesses, upon certain hypotheses, to define the mode of union or actual arrange-
ment of atoms in a compound, of which the equivalent has been determined
by experiment.

We here necessarily enter into a region of speculation. Thus, out of an
atom of alcohol a variety of rational formula may be constructed, according
to the hvpothesis which the chemist may adopt. The empirical formula of
alcohol '(C.,He03) may be expressed by C^H30 + H0, or 2C,H,-f2HO, or
2CO-f2CH2, + H3. The empirical formula of hydrated acetic acid (C^H^J
may, according to the radical theory, be converted into the rational formulae
(C,H303-fHO, or2(C,H,)-fOJ.

Compound Radicals. — In inorganic chemistry, radicals are represented, by
simple substances which enter into combination with oxygen, chlorine, and
other electro-negative bodies. Sulphur (S) is the radical of sulphuric acid
(SO3), and sodium (Na) is the radical of chloride of sodium (NaCl). In
order to assimilate organic to inorganic chemistry, it has been suggested that
some of the atoms of organic substances may be so arranged as to form
compound radicals, which are assumed to combine with the electro-negative
elements, 0, CI, and S, to form biliary compounds, like those met with in
inorganic chemistry. Cyanogen is a well marked instance of a compound
radical. It is represented by the formula C^jN and it acts in all respects
like an element. It combines with hydrogen and all the metals like an
electro-negative body, and with oxygen and chlorine like an electro-positive
body. A compound radical, therefore, is simply a body which combines,
like an element, with other elementary bodies. It may also enter into combi-
nation with other compound radicals. In the cyanide of cacodyle (KdCy,
or C^HgAs-fCaN) we have an instance of two compound radicals combining
like elements.

Organic radicals, a few of which have been isolated, while the greater
number have only an hypothetical existence, may consist of two, three, or
more elements. When they contain carbon and hydrogen only, they generally
terminate in yle, and are represented by a symbol, like elements. Thus, the
radical of alcohol (C^H^) is called Ethyle, and is represented by the symbol
Ae. Ether would therefore be an oxide of ethyle (C^Ht3,0, or AeO). For-
myle (Cgll) (Fo) is the radical of formic acid, and this acid is C2H,03, oxide
of formyle, or F0O3. Methyle (Me) is CgHg ; Acetyle (Ac) C JI3. Cacodyle,
which consists of carbon, hydrogen, and arsenic, is C4H(;As, and has the
symbol Kd. This view of the constitution of organic compounds has been
generally adopted. While it is open to some objections, there can be no
doubt that it has greatly facilitated the study and classification of organic
substances.

Substitutions. — As in mineral chemistry, one negative element may be sub-
stituted for another, HO becoming HCl by the substitution of chlorine for
oxygen, so in reference to organic radicals, a similar change may be observed.
Formic acid is converted into chloroform by the substitution of three atoms
of chlorine for three atoms of oxygen, the radical remaining the same : thus

COMPOUND RADICALS. SUBSTITUTION- COMPOUNDS. 559

C3H+O3 becomes C^H-f CI3; and whole series of compounds may be thus
constructed, in which one negative element simply replaces another negative
element, according to the usual laws of equivalent proportions. There is,
however, anotlier remarkable character in organic compounds, to which the
term substitution is specially applied — namely, where the electro-negative may
take the place of an electro-positive body, the compound remaining unaltered
in its type ; ?'. e., the elements being otherwise in the same number, propor-
tion, and, as it is supposed, molecular arrangement, differing in fact only in
equivalent weight. Hydrated acetic acid (C4H303,HO) may have its hydro-
gen replaced by chlorine, to form chloracetic acid (C^ClgOgjHO), the electro-
negative chlorine being substituted for the electro-positive hydrogen. A
similar substitution is observed in the conversion of chloride of methyle into
chloroform by chlorine: C,H3C1 + 4C1 = C3H,C13 + 2HC1.

In the production of pyroxyline from cellulose (p. 607), a certain number
of atoms of nitrous acid (NOJ are substituted for an equal number of atoms
of hydrogen, the other constituents remaining unchanged. Benzole (Ci^Hg)
is in like mann-er converted by nitric acid into nitro-benzole (Ci3H5[NOJ),
by the removal, of an atom of hydrogen, and the substitution of an atom of
nitrous acid, as in the following equation : —

C.^HsH -f NO5 = C,2H,(N0,) -f- HO

Benzole. Nitric acid. Nitrobenzole. Water. ^

Water is a product of this reaction : and, when we compare the chemical
and physical properties of benzole with those of nitrobenzole, there is pro-
bably no more remarkable change in organic chemistry, than that which this
substitution effects.

Nitrobenzole admits of a still further change, by a removal of its oxygen,
and the addition of two atoms of hydrogen : it is thereby transformed into
Aniliiie, and becomes the source of an extensive series of most valuable
dyes : —

C,2H5(N04) 4- 2H0 -f 4Fe = C.^R^^ + 2PeA

Nitrobenzole. Water. Iron. Aniline. Sesquioxide

of iron.

By simple distillation with water and metallic iron, this remarkable meta-
morphosis is brought about ; and by assuming that aniline contains an atom
of the compound radical, Phenyle (C13H3), this base is frequently described
as a compound ammonia, in which one atom of phenyle is substituted for one
atom of hydrogen. Thus ammonia being NH3, aniline (Ci3Hy,N) may have
its atoms thus arranged on the type of ammonia (C13H5) NH^. It is ques-
tionable how far the application of the names of well-known chemical sub-
stances, possessed of entirely different properties, to compounds of this
nature, is beneficial to science. It rests entirely on assumption ; for the
atomic arrangement of the elements is insusceptible of proof; and although
the doctrine of substitutions affords some ground for the view, it tends to
produce in the mind of a student a confusion of hypothesis with fact. The
terra ammonia is in these cases employed 'in an entirely new sense: it is
intended to signify, not the well-known gaseoUs compound of nitrogen and
hydrogen, of defined properties and composition, but a substance wholly dif-
ferent, and having only an hypothetical resemblance to it in chemical consti-
tution. Thus, a body which contains one atom of nitrogen, associated with
one or more atoms of hydrogen, and a group of atoms which is supposed to
replace the deficient hydrogen, is designated an '' ammonia. ^^ This may be
better illustrated by the following table, in which the composition of ammonia

560 PROXIMATE ORGANIC PRINCIPLES.

is given, and the atomic constitution of the radical, substituted for the hy-
drogen, is also represented. It should be observed that Phenyle (Cj^Hj)
has only an hypothetical existence, while Methyle (C3H3) and Ethyle (C^H^)
have been isolated.

Radical substitute for 1 atom
of hydrogen.

Ammonia . . . N H H H

Methylamiue . . N H H Me Me = C^Hg

Ethylamine . . N H H Ae Ae = C^'H.

Diethylamine . . N H Ae Ae 2Ae = CgHjQ

Triethylamine . . NAeAeAe 3Ae = ^vi^ts

Aniline . . . N H H Ph Ph = C.^H^

These are all considered to be ammonias, or substitution-compounds of
ammonia. They agree in constitution, in having 1 atom of nitrogen, asso-
ciated with 3 atoms of hydrogen, or with 1, 2, or 3 atoms of the compound
radical. In accordance with this hypothesis it has been proposed to call
aniline Phenylamine ; but there appears to be no good reason for changing
a universally received name upon purely hypothetical grounds. Ammonia
itself might, with an equal disregard of custom and utility, be called Nitra-
mine, just as arsenuretted and antimonuretted hydrogen have been recently
designated Arsenamine and Stibamine. The latter are described as " ammo-
nias" of arsenic and antimony, because they happen to be constituted of one
atom of a metallic radical (replacing nitrogen), and three atoms of hydrogen.
The terms alcohol, aldehyde, ether, urea, &c., hitherto restricted to well-known
special bodies, have been thus vaguely applied by some chemists to com-
pounds presenting certain hypothetical resemblances of constitution. As
nothing is really known of the atomic constitution of compounds, such a
system of nomenclature, if recognized, must necessarily lead to perpetual
changes, and to endless confusion. Aniline has already borne the names of
Kyanol, Phenylamide, Phenylia, and Benzidam. Its present designation
points to its original source from indigo. It involves no hypothesis of con-
stitution, and is therefore not liable to be changed by the progress of dis-
covery. While there can be no objection to any new organic compound
being designated according to the fancy of its discoverer, there is a serious
objection to the application of old and well-known names to new substances,
or to the use of such names in a sense entirely different from that in which
they have been hitherto universally accepted.

CHAPTEE XLV.

PROXIMATE ORGANIC PRINCIPLES. STARCH. DEXTRINE
INULINE. GUM. PECTOSE. GELOSE. SUGAR.

The proximate principles of the vegetable and animal kingdoms often
bear a close resemblance to each other. Thus sugar, oil, albumen, and
coloring matter, are found in both. Gum appears to be of purely vegetable
origin, but starch, which has been hitherto considered to be vegetable, has
been found, according to some authorities, in a modified condition in the
organs of animals. Urea is peculiar to the animal kingdom. In this and
the following chapters we shall group together those substances which
possess analogous properties, whether of vegetable or animal origin.

STARCH.

561

Rice ....

70-85

Beans .

Dried potatoes

83-8

Maize .

Wheat ....

. 60-80

Potatoes

Aerated bread .

68

Turnips

Barley ....

60

Beet- root

Fermented bread

53-3

Parsnips

Oats ....

50

Carrots .

Peas ....

42-6

Starch (C.^'R.fiJ,

Starch (Fecula amylum) is an organized substance most extensively
diffused in the vegetable kingdom. It is found in the seeds, tubers, roots, and
woody portions of plants, and is generally associated with gum, sugar,
woody fibre, and other vegetable principles. It is especially abundant in
the seeds of the cerealia. Wheat and rice contain the largest proportions.
It is contained in solid granules in the cells of the seed, and is separated by
a simple mechanical process. The proportions contained in 100 parts of
different seeds and roots, is as follows : —

42

28.4

15-20

15

13-14

9

3

Starch is usually seen as a white, and especially in the seeds of the cerealia,
somewhat glistening powder, of a specific gravity of about 1*5, which, when
pressed, produces a peculiar cracking sound, and feels somewhat elastic.
Under the microscope it is seen to consist of small spheroidal granules,
differing in size and shape ; the largest, and those best adapted to micro-
scopical examination, are obtained from the rhizome of the Canna coccinea,
known under the name of Tous les Mois : they are about one-260th of an
inch diameter ; they appear wrinkled, and as if made up of concentric layers,
and a fissure (htlum) may generally be observed upon some part of the grains,
which has been regarded as the spot where they adhered to the cell contain-
ing them. Examined by polarized light, these granules present a black
cross, the centre of which appears to correspond with the hilura. In wheat
starch this cross is not easily observed, but in potato-starch it is distinct, so
that it has been resorted to as a means of detecting the adulteration of
wheat starch with the cheaper varieties. The granules of potato-starch are
remarkable for their large size and peculiar shape. Some of them have a
diameter of one-250th of an inch, and have a clam-shell shape, the lines or
workings spreading in zones around the hilum, which is at the smaller end.
The granules of wheat-starch have about the 1- 1000th of an inch in diameter,
and are of an irregularly rounded form. These granules are accompanied
by others, which are much smaller. The granules of rice-starch are small
and irregular ; they have about the l-3000th of an inch in diameter. The
granules of starch are contained in cells, and are separated mechanically by
breaking up these cells in cold water. Starch is chiefly procured from wheat
and the tubers of potatoes, by simple maceration of the pulp in cold water —
the acetic acid produced by fermentation of the aqueous liquid removing the
gluten. It is procured from rice by dissolving the gluten, by means of a
weak alkaline solution of soda. 100 parts of rice yield from 70 to 80 parts ;
100 parts of wheat, from 33 to 45 parts ; and 100 parts of fresh potatoes,
from 10 to 12 parts of starch.

Starch is generally represented as insoluble in cold water ; and indeed the
usual mode of obtaining it, which consists in diffusing the rasped or ground
vegetable in cold water, and washing and collecting the deposit, seems to
justify such a conclusion ; but if potato-starch is triturated with water at
60^, and the mixture poured upon a filter, the filtrate contains starch : and
if a dilute solution of starch in hot water is cooled to 60° and filtered, there
is starch in the filtered liquid, but it is probably in a state of fine suspen-
36

562 STARCH,

sion. As starch is an organized substance, and cannot be obtained in that
state of purity which belongs to crystallized products, and, as it is easily
convertible into gum and sugar, it may be doubted how far some of the
properties ascribed to starch actually belong to this body in its pure form.

Starch is rapidly disintegrated by hot water : when 1 part of it is gradu-
ally heated in 15 parts of water to about 130°, it begins to change its appear-
ance, and at 140° or 150° the whole acquires a pasty consistence, and the
microscope shows that in this state the granules are swollen and broken : if
the paste is dififused through water, a large portion of them subsides, and the
supernatant fluid retains some starch, in a modified state, but this appears
to be after a time deposited. Dialysis shows that this substance is not really
soluble in water : it will not traverse the dialysing septum. We have found
that 5000 parts of water will not dissolve one part of starch. It may be for
a longer or shorter time suspended in a transparent form in water, but even
when aided by long boiling the starch appears to be only mechanically dif-
fused through the water, and not perfectly dissolved. Various salts dis-
solved in water, facilitate this deposition of starch. If starch-paste is sub-
jected, under pressure, to a temperature of about 300°, a solution is obtained
which, on cooling, deposits minute spherical granules of about one-4000th
of an inch diameter, and having the leading chemical characters of the origi-
nal starch ; so that in this way the varieties of starch may be brought to the
same physical condition. — (Jacquelain.) Starch is insoluble in alcohol and
ether. It forms a tenacious paste with weak solutions of potassa or soda,
but not with ammonia.

With iodine it forms a characteristic blue compound, which, provided the
iodine is not in excess, loses color when heated to about 160°, but regains it
on cooling ; it is also decolored, with the production of hydriodic acid, by
exposure to light. This property renders iodine a valuable test for starch,
and starch for iodine, but it is open to many fallacies. In a warm solution
no color is produced, and the blue color formed in a cold solution of starch
is destroyed by chlorine and bromine, by corrosive sublimate, by all alkalies,
by sulphurous acid and arsenious acid, and by all bodies which can enter
into combination with free iodine. When iodine is in a combined state, it
has no action on starch. Thus iodide of potassium has no effect until nitric
acid, chlorine, or some oxidizing agent is added ; and iodic acid produces no
change in starch until some deoxidizing substance is added, e. g., sulphurous
acid. Vegetable acids (acetic, oxalic, and tartaric) have no effect upon the
compounds of starch and iodine, but gallic acid or tannic acid in excess
prevent its production and destroy the blue color when produced. Paper
imbued with a mixed solution of starch and iodide of potassium is imme-
diately blued by free chlorine and bromine, and ia paper of this kind is used
as a test for atmospheric ozone (p. 115).

The ultimate elements of pure wheat-starch, dried at 212°, are represented
as CigHinOio, but when in combination with oxide of lead the compound
appears to be C^aHgOgjPbO, so that the more correct formula for starch is
CigHgOg+HO ; but starch, in its ordinary state, retains a larger propor-
tion of water, and it varies in the different varieties of starch. When 1 part
of starch is dissolved in 150 of boiling water, and precipitated by ammoni-
acal acetate of lead, the composition of the precipitate is CiaHg09+2PbO.
This compound, which is called the Amylate of lead, is also produced by
the addition of subacetate of lead added to starch, in a state of suspension or
solution in water. Starch mixes readily with a solution of sulphate of copper,
but on adding an alkali the oxide is precipitated in combination with starch.
It is not redissolved by adding an excess of alkali, and no suboxide is pre-
cipitated on boiling. Starch, when gelatinized by weak solutions of potassa

USES OF STARCH. 563

or of soda, may be thrown down from these alkaline liquors by neutralizing
them with acetic acid, and then adding alcohol. A cold solution of starch
is precipitated by tannic acid or infusion of galls, and starch may be thus
separated from gum. The tannate of starch is redissolved at a boiling tem-
perature. The mineral acids have a peculiar effect upon starch, according
to their degree of concentration and the proportion in which they are used.
Strong nitric acid heated with starch, oxidizes it and converts it into oxalic
acid. Diluted nitric acid converts it into dextrine. Strong sulphuric acid,
in the cold produces slowly with starch a pink color, but when heated the
mixture is carbonized. Diluted sulphuric acid produces various changes in
this principle. When starch is mixed with hot water and sulphuric acid is
added to the mixture in the proportion of a few thousandths of its weight,
the globules swell and burst, and the more soluble portions are transformed
into what is called soluble starch, the liquid not having its usual opacity,
but being more or less transparent. The article called Glenjield starch
appears to have undergone this change. It is employed for stiffening net
and fine fabrics generally, and it does this without rendering them opaque.
If the proportion of acid is slightly increased and the heat is continued for
a short time, the starch undergoes another molecular change : the liquid
becomes of a pale yellow color, and now gives a wine-red in place of a bright
blue color with iodine. The starch is converted into dextrine. If the liquid
with the acid is boiled for some hours, it produces no change of color with
iodine, but is converted into starch sugar, a variety of glucose (p. 569).
The Greenfield starch occasionally undergoes transformation to this extent,
for we have found it to possess the property, like glucose, of reducing the
oxide of copper in a solution of potash.

The principal commercial varieties of starch are, 1. Wheat-starch ; 2.
Potato-starch ; 3. Rice-starch ; 4. Arrowroot-starch, obtained from the
tubers of the Maranta arundinacea; 5. Sago, from the stems of certain palms,
and which is usually granulated ; 6. Tapioca, the starch of the Jatropha
manihot; t. Tons les raois, from the rhizome of the Canna coccinea ; 8.
Otaheite arrowroot, from Canna pinnatifida ; 9. Portland arrowroot, from
the tubers of Arum maculatum.

Uses of Starch. — Starch is not only largely consumed in the manufacture
of dextrine, but is in common use for stiffening various fabrics and articles
of wearing apparel ; and for this purpose a slight blue tinge is generally
given to it by a little artificial ultramarine. Thin and cheap calicoes are
often largely imbued with starch and sulphate of soda or magnesia to make
them appear of greater substance than they really are. Lozenges, and
various articles of confectionery, consist partly of starch. Cheap sugar-
plums are composed of refuse starch, with chalk, gypsum, and other trash :
a spurious refined liquorice is also made upon the same principle. Stone-
blue is a compound of indigo, or Prussian blue, and the inferior kinds of
starch. Among the substances used to adulterate starch, porcelain-clay was
at one time prevalent. Considered as an article of food, as a part of the
diet of children and of invalids, and as a component of our most nutritious
vegetables, starch is very important. Bu-t, although eminently adapted to
form part of our food, it is not fitted for exclusive nutriment ; and this is the
case with all vegetables deficient in nitrogen.

When starch is carefully heated to about 300° it becomes anhydrous, and
at about 400° it darkens in color and is converted into a substance called
torrefied starch, British gum, or Dextrine, It is now soluble in cold water,
forming a brown gummy solution, the properties of which will be hereafter
described. If the heat is carried still higher the starch becomes carbonized,

564 DEXTRINE.

and in the air it undergoes combustion. It leaves a carbonaceous residue,
but this may be entirely burnt away, if the starch is pure. Smalt or mineral
blue is sometimes used to give a slight color to starch, and in this c4se the
coloring matter will be left as a residue.

Dextrine (C^^H.^OJ.

This may be regarded as an isomeric condition of starch. It differs, how-
ever, remarkably in its properties. The term dextrine has been given to
this substance from the property which its solution possesses of turning the
plane of polarization to the right when acting on polarized light, while gum,
which it resembles in chemical properties, turns the plane of polarization to
the left. A solution of starch also rotates the plane to the right, but not iu
such a marked degree as a solution of dextrine. According to Roscoe, the
deviation produced by dextrine is equal to -f 138° 7'. It has been stated
that starch is easily convertible into dextrine by a heat of about 400° ; but
there are other means of effecting this change ; amongst which the most re-
markable is that produced by a peculiar azotized principle called diastase
(from 8uatt]fii, to separate), and which is formed in germinating seeds and
growing buds. It occasions the change of the amylaceous part of the seed
into gum and sugar, during a certain period of its growth ; and it is in con-
sequence of its presence in malt that the brewers' sweet worts are produced,
and that the addition of a little malt to unmalted grain changes a large pro-
portion of its starch into saccharine or fermentable matter. It is a remarka-
ble fact that saliva has also the property of converting starch into sugar. If
a small quantity of starch in water is gently warmed with saliva, and a few
drops of a solution of sulphate of copper with an excess of potash are added
and the liquid is boiled, a precipitate of suboxide of copper is produced, as
with grape-sugar. Hence starchy matters are more or less saccharined
during the process of mastication.

Diastase may be obtained from carefully prepared malt, by bruising and
digesting it in water at 70° to 80° : the pasty mixture is then pressed, and
the liquor which runs from it filtered, heated to about 170°, and again
filtered : this filtrate retains the diastase, and may be used for many purposes
as a solution of that substance, but it also retains other matters which may
be separated by absolute alcohol : this throws down the diastase. It is a
white flocculent substance, soluble in water, insoluble in alcohol, tasteless,
and easily decomposed : its effects upon starch are destroyed at a boiling
heat : its ultimate composition has not been determined, but as certain other
organic products effect similar changes upon starch, such as gastric juice,
animal membrane, yeast, &c., its claims to be considered a distinct principle
have been doubted. Its power of changing starch into dextrine and sugar
is such that 1 part of it is capable of thus modifying 2000 parts of starch :
its effect may be well shown by adding a little of it to a thick starch paste,
heated to about 180° ; it immediately becomes fluid, gummy, and sweet.

When starch-paste is warmed with water acidulated by sulphuric acid, it
also passes into dextrine. The same change may be effected by very dilute
nitric acid : Payen's method consists in moistening 10 parts of starch with 3
of water, containing one-150th part of nitric acid, and drying it in thin lay-
ers in a stove heated to about 240°. In two hours the conversion is com-
plete.

Dextrinfe is a brownish colored powder, nearly tasteless, uncrystallizable,
soluble in water, hot or cold, insoluble in alcohol, and of the same composi-
tion as starch and gum ; it is not blued but reddened by iodine, and differs
from gum in forming a deep blue liquor with a solution of sulphate of cop-
per, which deposits suboxide of copper when boiled. With acetate of lead

INULINE. LICHENINE. GUM. 565

and ammonia it gives a precipitate =C^Jl^fi^(,'2iFhO. Tannic acid produces
with the solution in water a slight turbidness. Unlike gum, it does not form a
gelatinous compound with the persalt of iron. It is most easily convertible
into sugar on boiling it with a dilute acid, and it appears to be the transi-
tion stage between starch and sugar. When heated with nitric acid it pro-
duces oxalic and not mucic acid.

An aqueous solution leaves by drying a shining streak on paper resembling
gum in appearance, but differing from it in the red color produced by the
addition of iodine water. It is this substance which is used as the adhesive
material for postage stamps. It is used also for adhesive bandages, as a
local application in burns and scalds, and in fixing colors in calico printing.

Although dextrine has been here treated chiefly as an artificial compound,
it appears to exist in certain grains or seeds and roots as well as in the
shoots of young plants. In these cases it is probably starch partially con-
verted by natural processes.

Inuline (C^B.^ft2i)'

This principle is seen in the form of a light brown powder, and may be
obtained from the roots of the Inula Hellemum, the dahlia, colchicum, dan-
delion, and chicory. It is not very soluble in cold water, but it is dissolved
by boiling water. It is insoluble in alcohol. It does not present the form
of independent granules under the microscope. The aqueous solution is
neutral. It is not blued by iodine, but is turned of a deeper yellow color.
Tannic acid renders the solution slightly turbid. A solution of subacetate
of lead gives with it a dense precipitate, and the same is formed by adding
ammonia to a mixture of acetate of lead with the solution. The lead com-
pound has the composition of Cg^Hg^OgiPbO. When heated with diluted
acid it is converted into sugar, and with strong nitric acid it produces
oxalic acid, not mucic. Like gum, its solution turns the plane of polariza-
tion to the left — it is laevorotatory. From this description it will be seen
that the properties of this substance are a mixture of those of gum and
starch.

LiCHENINE.

A decoction of Iceland moss contains a principle soluble in boiling water.
It resembles starch in being turned of a dark purple by iodine water, and in
being precipitated in the cold by a solution of tannic acid. The precipitate
is soluble on boiling.

Gum (C^H,,0,,).

Several modifications of a distinct proximate principle of vegetables are
included under the term gum : they are not organized, like starch, nor are
they crystal lizable, like sugar : they either readily dissolve in water, hot or
cold, or swell up into a viscid mass when moistened ; and they are tasteless,
and insoluble in alcohol and in ether. They are generally the inspissated
juices of certain plants, and ooze naturally from the tree ; but in commercial
language the term gum is loosely applied to substances which resemble it in
external appearance, such as resins. Caoutchouc and gutta percha are also
sometimes called gums. In a chemical sense a gum is characterized by
solubility in cold water and insolubility in alcohol : it is -infusible and not
very combustible. The principal varieties of gum may be described as Ara-
bine and Bassorine.

Arahine, as represented by Gum Arabic, is the produce of various species
of Acacia; its sp. gr. is from 1'30 to 1*50. It is soluble in water, hot or

666 PECTOSE.

cold, and it forms a viscid, tasteless mucilage with it, which, even when
fresh, slightly reddens litmus, and leaves a transparent glaze or varnish when
it dries. Alcohol throws down a white hydrated gum from its solution : it
produces a rotation to the left of a polarized ray of light. The alkalies
and alkaline earths form soluble compounds with arabine, but with several
metallic oxides {e.g.^ lead and iron) it produces definite, insoluble precipi-
tates, which have been called Arahi?iates : thus, with subacetate of lead the
white compound which falls is PbO,C,3HiiOii. It is not precipitated by a
solution of neutral acetate of lead until ammonia is added, but it is thrown
down by neutral persulphate of iron, with which it forms a red jelly, and
nitrate of mercury. When potassa is added to a solution of gum and
sulphate of copper, a blue arabinate falls, which is not decomposed by boil-
ing : this distinguishes arabine from dextrine. "When heated with concen-
trated sulphuric acid, gum is carbonized, but when boiled with very dilute
sulphuric acid it is gradually changed into dextrine and glucose. It absorbs
chlorine and produces a peculiar acid : it also absorbs hydrochloric acid.
Nitric acid converts it into Mucic acid {Q^^Jd^fiKO.) Bromine and
iodine are without action upon it. Oxalate of ammonia indicates the pre-
sence of lime in a solution of gum arable. When dried at 212°, gum loses
from 12 to It per cent, of its weight, and it becomes hard, brittle, and
pulverizable, forming a white powder. When heated to 300° in air, it
swells up, but does not melt or burn. At a higher temperature it gives otF
an acid vapor and burns, leaving an ash containing much lime.

An aqueous solution undergoes no change of color by the addition of
iodine, and it is not precipitated by tannic acid. A good solution of gum
for adhesive purposes may be made by dissolving one ounce of gum acacia
in three ounces of boiling water, and adding to the solution two drachms of
glycerine and a few drops of a solution of carbolic acid. The latter pre-
vents the production of mould. A small portion of camphor may be sub-
stituted for carbolic acid.

Bassorine. Tragacanthine. — Gum Tragacanth may be taken as the type
of this modification of gum. It is the produce of difi'erent species of Astra-
galus. When steeped in water it swells into a bulky mucilaginous mass,
which, when long boiled, acquires the general properties of arabine. Cherry-
tree gum, or Gerasine, and the gum which exudes from peach and apricot
trees, and other species of prunus, seems to be a mixture of arabine and
bassorine. There is also a number of mucilaginous substances, such as those
derived from quince-seed, linseed, marshmallow root, etc., which closely
resemble the varieties of gum. The term- mucilage is given to the aqueous
solutions of these seeds. A cold solution of bruised linseed has an acid re-
action. It undergoes no change of color on the addition of iodine, and is
precipitated by alcohol, as also by a solution of subacetate of lead.

Pectose.

Vegetable Jelly — A gelatinous principle has long been recognized as one
of the proximate components of vegetables : it is derived, according to
Fremy, from the presence of Pectose {rtrjxfbi, coagulated), a substance usually
associated with the cellular tissue, and which is insoluble in water, alcohol,
and ether, but which, under the influence of acids, aided by a gentle heat,
becomes converted into a soluble gelatinous substance, Pectine, represented
by the formula CfgiH^oOsg. Pectine is found ready formed in the juices of
ripe fruits, in consequence of the action of their acids upon the original
pectose. It may be obtained from the expressed juice of ripe pears or apples
(after the lime which it contains has been precipitated by oxalic acid, and
the albumen by a strong solution of tannin), by means of alcohol, which

PECTIO ACID. GELOSE. 50T

throws it down in gelatinous filaments. When pure, it is white, neutral, not
crystallizable, soluble in water, but insoluble in alcohol and in ether : it is
precipitated by subacetate, but not by neutral acetate of lead. When its
aqueous solution is long boiled, it loses viscosity, and is changed mto para-
pectine, which precipitates neutral acetate of lead ; and if boiled with a dilute
acid, it is further modified into metapectine, which is distinguished by pre-
cipitating a solution of chloride of barium.

Pectic Acid (C.jgH2o023,2HO). — Pectine and its modifications are changed
into pectic acid by the action of weak alkaline solutions ; and the soluble
pectates thus formed may be decomposed by other acids. Pectic acid is
generally obtained by boiling the pulp of certain roots, of carrots, for
instance, with a very weak solution of an alkaline carbonate, and precipi-
tating by chloride of calcium ; the precipitate, after having been well washed,
is decomposed by dilute hydrochloric acid, which leaves the pectic acid in
the form of a jelly, insoluble in cold water, but which, when long boiled in
water, is changed into parapectic acid, which is soluble in water, sour, and
is precipitated from its solutions by baryta water : its formula is (C^^HigO^i,
2110). Under the influence of powerful acids, or alkaline bases, pectine
and its modifications are further changed into metapectic acid (CgH507,2HO),
which forms soluble salts with all bases.

Pectic Fermentation. — Pectose is always associated with a substance
which Fremy calls Pectase, having a special action upon it (as diastase has
upon starch), and which he represents as the ferment of the gelatinous pro-
ducts. It is obtained by adding to fresh carrot-juice, alcohol, which throws
it down in an insoluble form, but it retains its characteristic properties. It
transforms pectine (at a temperature between 80° and 90°) into a substance
insoluble in cold water (Pectosic acid), and subsequently into Pectic acid, as
above described. None of these pectic compounds exert any rotatory action
on polarized light.

Gelose.

There are many Algae, Fuci, and Lichens, which abound in a peculiar
gelatinizing principle. One of the most remarkable is the Gelideum cor-
neum, from which an article is prepared known commercially as Japan Isin-
glass. The gelideum corneum contains 58 per cent, of substances soluble in
boiling water. The dried gelatinous compound obtained from it is insoluble
in cold, but soluble in hot water. It sets into a firm jelly on cooling, even
when it forms only one-120th part of the weight of the water. One part of
isinglass (animal gelatin) produces a similar jelly with about 80 parts of
w^ater. The vegetable jelly is neutral, tasteless, and imputrescible. It is
insoluble in alcohol, ether, and weak acids. Like woody fibre it is con-
verted into glucose by sulphuric acid. Unlike animal jelly, it is not precipi-
tated in solution by tannic acid, and it is not altered by a solution of iodine
or subacetate of lead. It has been proposed to substitute it for the varie-
ties of animal gelatine, but it is destitute of nitrogen, having the formula
C24H21O24 {Eep. de Pharm., Jan. 1860). The edible birds'-uests, esteemed
as a delicacy in China, are constructed by a species of swallow, of the Plo-
caria Candida. In some of these Alg88, however, Dr. Davy has found from
2 to 4 per cent, of nitrogen, and it is probable that researches directed to
the use of these allied vegetables as food, would greatly extend the number
of edible species. Many of them abound also in a modification of sugar
(Majinite), and they are extensively used as manures and as sources of
iodine.

The Chondrus crispus (Irish, or Carrageen moss) contains nearly 80 per
cent, of a gelatinous principle which has been called Carrageenin {O^^^q

St

568 PROCESS OF SUGAR REFINING.

O^o)? ^"^ in the Cetraria Islandica Berzelius found from 40 to 50 per cent,
of a mucilaginous matter which he compares to starch. {See "Stanford on
the Economic applications of Seaweed," Journ. Soc. of Arts, Feb. 1862.)

Sugar.

There are two leading varieties of sugar. Cane-Sugar (Sucrose) and
Grape-Sugar (Glucose). To these some writers have added Fruit Sugar,
an uncrystallizable principle called Fructose or Levulose.

Cane-Sugar (C^^fi^.^HO) is chiefly obtained from the sugar-cane,
each gallon of its juice yielding about a pound : it is also derived from beet-
root, which yields from 4 to 6 per cent. ; from the sap of the sweet maple,
and from some other sources, especially from the stalks of Indian corn or
maize, the juice of which is nearly as rich in sugar as that of the cane.
Several of the palm tribe, such as the date and cocoa-palm, are also import-
ant sources of this kind of sugar.

The general characters of cane-sugar, and its ordinary commercial varie-
ties are well known. Its sp, gr. is about 1*6 ; it dissolves in one-third its
weight of water at 60° producing a viscid syrup, which affords, by sponta-
neous evaporation, prismatic crystals of candy. A solution saturated at
230°, concretes into a granular mass or tablet ; but when boiled down until
it acquires a tendency to vitreous fracture on cooling, or till a portion
thrown off from a stirrer, concretes, or feathers as it falls, it congeals into a
transparent amorphous mass (barley-sugar) which, however, has a tendency
to become opaque, and pass into a granular crystalline texture, exhibiting* a
case of dimorphism : this change is prevented by the addition of a little
vinegar or tartaric acid. Absolute alcohol dissolves about one-80th of its
weight of this sugar at its boiling-point, nearly the whole of which separates
in small crystals on cooling. If equal parts of strong syrup and of alcohol
are mixed, a quantity of small brilliant crystals of sugar is soon deposited.
Pure cane-syrup is not prone to change ; but certain substances, when pre-
sent only in very minute proportions, materially affect the stability of the
solution, and lead to a series of curious changes which will be adverted to
under the head of Fermentation.

When a thin cane-syrup is long-boiled, it gradually grows less viscid, and
slowly passing into a modified state, ultimately becomes brown and uncrys-
tallizable ; so that, where saccharine liquids are concerned, the protracted
application of heat should be avoided ; and if mere traces of acid or alkali
be present, these changes are promoted, and new products result, some of
which form insoluble compounds with the majority of basic bodies, and have
been termed melassic and melassinic acids; others resemble ulmic and humic
acid (sachulmine).

Refining of Sugar. — The process of refining sugar, or of converting the
varieties of raw, brown, or Muscovado, into white loaf-sugar, is extensively
carried on in London and Liverpool. The sugar is first dissolved in lime-
water, by the aid of steam, in a metal tank called the blowing-up pan, and
a portion of bullock's blood, technically termed sfice, is usually added, the
albumen of which, as it coagulates, entangles many impurities, carrying
them to the surface, and so enabling them to be skimmed off, together with
some insoluble products of the action of the lime. The liquor, thus far cla-
rified, is then transferred to a series of cotton filtering bags, till it runs
through them quite bright, but still of a dark color. To decolor it, it is
passed through bone-back, or other varieties of charcoal, contained in verti-
cal metallic cylinders, the effect of which is to render the dark-colored syrup
nearly colorless and bright. In this condition, and of proper strength, it is
transferred into the vacMMW ^aw, and boiled down under diminished pres-

GRAPE SUGAR. 569

sure, and at a temperature of about 150°, till of sufficient density to be
drawn off into a vessel now termed the heater, but which when, as formerly,
the syrup was boiled down over an open fire, and at a temperature of not
less than 230°, was called the cooler. Here the temperature of the syrup,
now inclined to crystallize, is raised to about 175°, under constant stirring,
and it becomes a kind of magma, which is filled out into proper conical
moulds of copper, zinced iron, or earthenware, the orifice at the apex of
each mould being plugged by a paper stopper. As soon as this magma ha3
consolidated upon the upper surface (or the base of the cOne) it is well
stirred up again, and in due time the stoppers are removed, so as to allow
the uncrystallized liquid to drain away into vessels placed for its reception.
The loaves are now submitted to a peculiar washing or cleansing operation,
sometimes called claying, which consists in the application of a thick mortar
or magma of sugar and water (now used instead of clay) to the base of the
loaf, portions of the fluid from which gradually percolate the loaf, carrying
the dark-colored syrup, or treacle, before them. Finally, an operation
termed liquoring is resorted to ; that is, a dense and very pure syrup is
poured upon the base of the loaf, previously smoothed by a bottoming trowel,
and as this filters through the cone, it deposits a portion of its sugar in its
way, and at the same time washes out the relics of colored syrup. When
this process is completed, and all percolation has ceased, the loaf is knocked
out of the mould, and if above 16 pounds' weight, is truncated by cutting
off the apex, so as to form what is called a lump, or titler ; or if intended for
a loaf proper, a new apex is given to it by a conical cutter or nosing ma-
chine. Finally, the loaves are papered, and deposited on trellised shelves in
a room called the stove, heated to about 130°, till dry throughout. By
another process, which is now largely worked at Bristol, the crystallizable
syrup is placed in a perforated cylinder or sieve, which is made to revolve
with great rapidity in another vessel. The treacle or fluid portion is by
this method at once separated from the small crystals of sugar. This is
known in commerce as centrifugal sugar. It is remarkably pure.

Grape-Sugar; Glucose (C,,H,,0,„ or C,,H^0,,+2H0).— This modifi-
. cation of sugar abounds in grapes, figs, plums, and other fruits : it is also
the result of the action of diastase, and of dilute acids upon starch. In good
seasons the expressed juice of grapes yields from 30 to 40 per cent, of solid
matter, the greater part of which is this kind of sugar. When obtained
from fruits, it is accompanied by more or less of an uncrystallizable sugar
(Fruit-sugar or Fructose, Q^Jiifit^^ which, however, by assimilating the
elements of water, passes into the condition of grape-sugar, or glucose. The
conversion of starch into this kind of sugar has been adverted to. It is a
process extensively carried on as a commercial manufacture, especially in
France. (It is used in the making of beer and in the adulteration of sugar
and honey.) Potato-starch and sago are principally used for this purpose :
they are saccharized by the action of dilute sulphuric acid (10 parts of acid
to 1000 of water and 500 of starch). The dilute acid is heated by steam,
and the starch, previously mixed with water of a temperature between 112°
and 130°, is suffered gradually to dribble-in under constant stirring ; its con-
version into dextrine is immediate : in about two hours and a half the whole
of the starch is added, and in from 15 to 25 minutes afterwards, the sacchari-
fication is complete ; the steam is then shut off, and the liquor transferred to
another vat, in which the acid is saturated with chalk. When the sulphate
of lime has subsided, the clear liquid is drawn off and evaporated to the sp.
gr. of about 1-26. The resulting syrup is then left to deposit the sulphate
of lime separated during evaporation, and afterwards drawn off perfectly
clear. In this state it may be used as a source of alcohol, or for sweeten-

510 ACTION OF BASES ON SUGAR.

ing colored liqnors ; but it requires, for the greater number of purposes, to
be deprived of color, which is done by filtering it through animal charcoal.
When required in its solid state, the syrup is evaporated in a steam vat till
of a sp. gr. of about r4 and then poured into coolers, where it concretes.

Glucose, or grape-sugar, differs from sucrose, or cane-sugar, in being less
soluble in water, and more soluble in alcohol, so that the two may be to
some extent separated by the action of alcohol. The sweetening power of
glucose is also greatly inferior to that of sucrose, 2 parts of the latter being
in this respect equivalent to about 5 of the former. They both deoxidize
and discharge the color of a solution of permanganate of potash, but glucose
acts more rapidly and perfectly than sucrose. Sucrose easily crystallizes in
prisms, but glucose forms tubercular concretions, or fibrous acicular groups,
= Ci3H^20,3,2HO. Both these sugars form definite crystallizable compounds
with chloride of sodium.

When cane-sugar is heated to about 320° it melts, and at about 400° be-
comes brown, deliquescent, and slightly bitter, losing water (2 atoms), and
passing into Caramel, = G^JI^Oq. In this state it is used for coloring wines
and spirits : it is soluble in water, but is thrown down from its solution by
excess of alcohol. It combines with certain bases, such as baryta and oxide
of lead, forming insoluble compounds. Heated to about 500°, melted sugar
bursts into flame, and leaves a porous mass of nearly pure charcoal.

When grape-sugar is heated to 212° it softens, and loses 2 atoms of water
becoming (C^^H^fi^^) ; at 284° it passes by further loss of water into caramel,
CigllgOg, and at a higher temperature is entirely decomposed. Solutions of
cane and of grape-sugar produce a right-handed rotation upon a ray of
polarized light.

Concentrated sulphuric acid acts energetically upon cane-sugar, evolving
water, carbonic and formic agids, and charcoal. It is a striking experiment
to mix about equal bulks of oil of vitriol and strong syrup : the mixture,
when stirred, becomes brown and black, then suddenly heats, boils up, and
passes into the state of a bulky black magma : the acid appears suddenly to
abstract the elements of water from the sugar, leaving charcoal. The action
of sulphuric acid upon grape-sugar is very different : it merely renders it
brown, and a new compound, sulphosaccharic acid, is produced, characterized
by forming soluble salts with lime and baryta.

Boiled with very dilute sulphuric, hydrochloric, or tartaric acid, cane-
sugar becomes fruit or grape-sugar, by the assimilation of an atom of water ;
and under the influence of yeast {see Alcoholic Fermentation) there is a
similar transition of the one species of sugar into the other ; but the con-
verse change, namely, that of grape or fruit-sugar into cane-sugar (glucose
into sucrose), cannot be effected. Nitric acid changes the varieties of sugar
into saccharic and oxalic acids. In the presence of decomposing casein and
chalk, sugar forms lactic acid, and under the influence of certain substances
occasionally present in raw sugar, it passes into a ropy mucilage and into
mannite.

Action of bases upon Sugar. — When lime or baryta is boiled with sugar-
and water a bitter solution is formed, which is said to contain a definite
saccharide (2CaO, or 2BaO,4-C^s,HgOg). Freshly precipitated oxide of lead
is similarly dissolved, and on cooling, a white compound falls, which, after
having been dried at 212°, is = 2PbO-fC,3Hg09. Alcohol does not pre-
cipitate sugar from its solution in water, and tannic acid and iodine water
have no effect upon it. The aqueous solution gives no precipitate with a
salt of lead, but on adding ammonia the sugar combines with and is precipi-
tated with oxide of lead. Many of these compounds are soluble in excess
of alkalies, and hence the presence of sugar sometimes prevents the precipi-

TESTS FOR SUGAR. 571

tation of metallic oxides from their salts. In other cases sugar tends to
reduce the oxides. The compounds o^ glucose with bases are less stable than
the preceding, this sugar gradually passing into glucic acid (C^aHgOgjSHO),
which under the influence of heat becomes apoglucic acid (CigHQ0g,2H0) :
and ultimately melassic acid is formed. Grape-sugar is distinguished from
cane-sugar by boiling it in a solution of potassa. The former alone darkens
as the result of the formation of glucic acid. This is commonly known as
Moor eh test.

Tests f 07^ Sugar. — The deoxidizing property of glucose above mentioned
is the foundation of a valuable test of its presence ; and inasmuch as the
other varieties of sugar are transformed into glucose by the joint action of
very dilute acids and heat, the same mode of testing is applicable to sugar
generally. Certain salts of copper and of platinum are especially applicable
to these purposes. When a little cane-sugar is added to a dilute solution of
copper, and the mixture heated, little immediate change ensues ; but with
grape-sugar the blue color of the liquor is presently changed to green, it
then becomes yellowish or reddish-brown, and suboxide of copper or metallic
copper falls: these changes are more rapid when a little alkali has been
added to the solution. Thus if a few drops of a very diluted solution of
sulphate of copper are added to a solution of either sugar a slight color is
imparted. A small quantity of a solution of potash causes in the mixture
a precipitate of blue hydrated oxide of copper. An excess of the alkaline
liquid dissolves this precipitate, forming a sapphire-blue solution. When
this is heated the grape-sugar causes rapidly the changes above mentioned —
the yellow precipitate formed being the hydrated suboxide and the red pre-
cipitate the anhydrous suboxide. Pure cane-sugar thus treated does not
easily decompose the salt of copper. It requires long boiling to produce
any decomposition. With grape-sugar it usually takes place upon slightly
warming the liquid and before it has reached the boiling point. One form
of the copper test as it is sometimes employed for the detection of sugar is
the soda tartrate of copper, obtained by dissolving recently precipitated
tartrate of copper in a solution of soda or of carbonate of soda : it is imme-
diately reduced when boiled with a trace of glucose ; used quantitatively, it
will be found that 15 parts of the precipitated or red suboxide of copper are
equivalent to about 5 of cane-sugar, and to about 5'1 of grape-sugar. The
copper test for sugar has been long known under the name of Trommerh test.
Some precautions are required in its employment. If sugar is not present
potash has no solvent action on the precipitated oxide of copper, and on
boiling the colored liquid, black or anhydrous oxide of copper only is
thrown down. On the other hand, a solution of the precipitated oxide by
an excess of alkali does not indicate the presence of sugar. In the presence
of albumen, casein, glycerine, mannite, or any alkaline tartrate, potash re-
dissolves the precipitated oxide, forming a blue or purple-blue liquid : but
on boiling the liquid, there is no reduction of the oxide of copper, and no
red suboxide is produced. If chloroform is present, even in small quantity,
the oxide of copper is not redissolved by an excess of potash, but it under-
goes a complete reduction to suboxide on boiling it. Here the non-redissolu-
tion would distinguish chloroform from sugar. On the other hand, arsenious
acid or an alkaline arsenite, when present, forms a clear blue liquid with a
salt of copper and an excess of potash ; and on boiling the solution, the red
suboxide of copper is precipitated as if sugar were really present. The test
when properly employed is with proper precautions adequate to the detection
of sugar under all circumstances. Although the presence of pure cane-sugar
is not readily indicated by the test, yet on warming the solution for a short

5t2 HONEY. MANNITE.

time, with a few drops of tartaric or very dilute sulphuric acid, the cane is
converted into grape-sugar, and it will then immediately respond to the test.

A hot solution of nitrate of suboxide of mercury is immediately blackened
by glucose, and finely-divided mercury falls: in the same way a boiling
solution of corrosive sublimate deposits calomel, which is afterwards partially
reduced : red oxide of mercury is also reduced when boiled in the saccharine
solution. Solutions of nitrate of silver and of chloride of gold, when boiled
with glucose, afford precipitates of silver and gold : when in these cases,
excess of .carbonate of soda is present, the effect is more rapid, and in this
way the chlorides of platinum and palladium are reduced. A delicate test of
glucose is the soda-chloride of platinum formed by adding excess of a solution
of carbonate of soda to a moderately dilute solution of chloride of platinum.
When this solution is boiling, a small portion of cane-sugar dropped into it
produces no effect, but it is instantly discolored, and ultimately blackened,
by the smallest trace of grape-sugar. Where these tests are used, the absence
of other organic matters likely to effect their decomposition, must be insured.

The ultimate components of the preceding varieties of sugar are as fol-
lows : —

SUCROSE,

GLUCOSE.

Atoms.

Equiv.

Per cent.

Atoms,

Equiv.

Per cent.

C 12

... 72 ..

. 42-11

C 12

... 72 ..

. 36-36

H 11

... 11 ..

6-43

H 14

... 14 ..

7-08

0 11

... 88 ..

. 51-46

0 14

... 112 ..

. 56-56

1- 171 100-00 1- 198 100-00

Fructose or Levulose exists chiefly in fruits, but it does not appear to be
an independent sugar, although the formula 0^^^f>^^ is usually assigned to
it. It is not crystallizable : it is quite soluble in alcohol, and turns the plane
of the polarization to the left : hence it is sometimes called inverted sugar.
After a time it seems to be spontaneously converted into crystallized grape-
sugar or glucose. Thus white fresh grapes contain fructose, the dried raisins
contain glucose.

Honey. — The substance secreted in the nectaries of flowers is converted
by the bee into honey and wax : the portion not required for their food is
returned into the combs in the form of a yellow syrup, the qualities of which
differ according to the flowers whence it has been derived. In its original
liquid state it probably resembles uncrystallizable sugar of fruits, &c. (Fruc-
tose, 0^2^130^2) ; but when kept for some time, a large portion of it passes
into a granular form, identical with glucose = C^gHj^O^^. But honey also
contains a little wax, gum, coloring matter, and mannite.

Diabetic Sugar, or that which is formed in a diseased state of the animal
system (diabetes), has all the properties of grape-sugar or glucose. It may
be separated from the extract of diabetic urine by boiling alcohol.

Mannite; Manna-Sugar (CgH^Og). — This substance is most abundant in
manna, but it is also found in the beetroot, celery, asparagus, onions, and
probably in other sweet plants : it is also contained in the sap of the larch, and
other species of pinus (Manna Brigantina). It has been detected by Dr.
Stenhouse in Laminaria Saccharina, and some other fuci. Manna exudes
from several species of ash, especially from the Fraxinus ornus and rotundi-
folia. Mannite is obtained by boiling manna in alcohol, from which it
crystallizes on cooling in acicular prisms. It forms about four-fifths of the
best manna; the residue being chiefly common sugar, and a peculiar ex-
tractive matter, in which the aperient quality of the manna is said to reside.
Mannite is also an occasional product of the viscous fermentation.

Mannite is very soluble in water, but is not susceptible of vinous fermen-

FERMENTATION. 513

tation, so that it may in this way be separated from the other varieties of
sugar ; for, when mixed with them, it remains undecomposed in that process.
Nitric acid converts it into saccharic and oxalic acids, without any trace of
mucic acid. Its aqueous solution precipitates basic acetate of lead, forming
a compound in which 2 equivalents of water are replaced by two of oxide of
lead, = CaIl50^,2PbO. It reduces chloride of gold and nitrate of silver.
With precipitated oxide of copper it forms a clear blue liquid on the addition
of an excess of alkali, but there is no decomposition or reduction on boiling.
When a solution of mannite is boiled with an excess of a solution of potash
DO glucic acid is produced, and the liquid does not darken. When heated
with diluted acids, mineral or vegetable, it is not converted into glucose. It
combines with Sulphuric acid, forming sulphomannitic acid, =^CqB.^O^, 2SO3.

Glycyrrhizine {Q^^^fi^^ is the sweet principle of Uquorice-root : it forms
with many acids and bases compounds which are not very soluble, and it is
not susceptible of vinous fermentation.

There are some other substances allied to these modifications of sugar,
which do not require detailed notice, such as Melitose and Eucalyn, the pro-
duce of the Eucalyptus munnifera ; Sorbine, from the berries of the mountain-
ash ; Quercite, from acorns.

CHAPTER XLVI.

ALCOHOLIC OR VINOUS FERMENTATION. ALCOHOLIC

LIQUIDS.

By fermentation, we are to understand the conversion of an organic
substance into one or more new compounds, in presence of a body called
a ferment. , Hence there are various kinds of fermentation, designated
according to their products — vinous or alcoholic, lactic, butyric, acetous, &c.
In vinous fermentation su^ar is resolved into alcohol and carbonic acid.
Sugar itself is not absolutely necessary to the process ; for starch, dextrine,
or any substance capable of being easily converted into sugar, under the
circumstances, may be substituted, and similar products obtained. The
conversion of the substance into sugar appears to be, however, an essential
preliminary condition for the establishment of the process. It is well known
that a portion of malt or saccharized barley, mixed with unmalted grain, will
produce alcohol — the starch and dextrine of the unmalted grain being con-
verted into sugar during the process. In the same way alcohol may be pro-
duced in large quantity, by the mixture of the starchy pulp of the potato with
a portion of treacle. The fermentation of dough in the making of bread
appears to depend on similar principles ; apportion of the starch is converted
into sugar, and, in the presence of a ferment, the sugar is immediately
resolved into alcohol and carbonic acid.

Pure sugar, extracted from the vegetable and dissolved in water, has no
tendency to undergo this remarkable change. A solution of pure cane-
sugar is slowly converted into grape-sugar, but there the change stops : no
alcohol is produced. The saccharine juices of vegetables, however, readily
ferment, owing to the presence of a nitrogenous principle with which they
are usually associated. This is called o, ferment It is an organic compound

574 FERMENTATION. PRODUCTION OF FERMENTS.

containing nitrogen, and is readily susceptible of change by simple exposure to
air. In this state it possesses the property of rapidly inducing changes in any
saccharine liquid. Gay-Lussac observed long since, that when fresh grape-
juice was collected in a vessel containing carbonic acid, and placed over
mercury, no fermentation took place, although all other circumstances, were
favorable to this process. When the juice was exposed to air and a proper
temperature, it rapidly fermented, and when once this fermentation had com-
menced, it continued until the saccharine matter was entirely decomposed.
If to the nnfermented juice, placed over mercury, a few bubbles of air or
oxygen were admitted, the same change took place, and continued until the
sugar was exhausted, a large quantity of carbonic acid being at the same
time evolved, while the liquid was found to have lost its saccharine, and to
•have acquired a spirituous or alcoholic flavor. These facts prove that there
is present in grape-juice a substance which, by contact with oxygen, under-
goes a change, and becomes a ferment ; and further, that the saccharine
juices of fruits do not ferment, because the access of free oxygen is cut oflf by
the epidermis of the fruit.

A saccharine solution of malt, called wort, will undergo similar changes,
by reason of the nitrogenous principles contained in the grain. The custom
is, however, to add to the liquid, for the purpose of accelerating the change,
a quantity of a nitrogenous compound called yeast, or harm, derived from a
previous fermentation. This constitutes the ferment. It produces a rapid
conversion of the saccharine matter into alcohol and carbonic acid ; and at
the same time causes the separation of the nitrogenous principles of the wort
in the form of additional ferment or yeast. The quantity of new yeast thus
procured, amounts to seven or eight times the quantity of that which has
been added to the wort.

It has been shown by Mitscherlich {Poggend. Ann., iv. 224), that the
actual contact of the particles of the yeast with the dissolved sugar is
essential. He suspended a wide glass tube, the bottom of which was closed
with bibulous paper, in a jar of a solution of sugar, the tube being itself filled
with the same solution. Some yeast was then put into the syrup contained
in the tube, where it soon induced fermentation, and the alcohol there formed,
passed through the pervious bottom, and, together with carbonic acid,
diffused itself in the surrounding liquor : but the actual phenomena of fer-
mentation— namely, the decomposition of the sugar and the formation of
alcohol and of carbonic acid — were limited to the syrup in the tube contain-
ing the ferment, and the sugar in the outer vessel remained unchanged.
Quevenne found that yeast which had been deprived of all matter soluble in
water, still retained its power of exciting fermentation. The active part of
yeast is composed of minute vesicles, or globules, and during fermentation
these germinate in the saccharine liquor, producing a microscopic fungus, the
Torvla or Mycoderma cerevisise. The plant, according to one theory of the
process, is supposed to grow at the expense of the sugar, giving out carbonic
acid, and leaving alcohol. According to Andral and Gavarret {Ann. Gh. et
Ph., Seme ser., viii. 399), there are two species of vegetable seeds contained
in yeast, which may be separated by diluting it with water : in a few days
globules fall to the bottom of the vessel, forming a gray pulverulent deposit
which is extremely active in producing alcoholic fermentation when added to
saccharine solutions ; but at the same time a film forms upon the surface of
the liquid, which consists of germs (of Penicidlum glaucum) having no
power to excite fermentation : these latter germs make their appearance in
all acid albuminous liquids, and h^comQ jilamentous, while the true producer
of alcoholic fermentation always retains its globular form. According to

CONDITIONS WHICH INFLUENCE FERMENTATIONS. 515

Mitscherlich, the active part of yeast which remains after it has been washed
with water, consists of;

Before fermentation.

After fermentation.

Carbon .

. 47-0

47-6

Hydrogen

... 6-6

7-2

Nitrogen

. 10-0

5.

Oxygen .

. 35-8

Sulphur

. .. 0-6

Of this yeast (in the dry state) from 2 to 3 parts are required for the
decomposition of 100 parts of sugar: and if there is excess of sugar, it
remains unchanged after the fermentation. That portion of the yeast which
remains in the form of a deposit after fermentation is over, is inefficient as a
ferment ; it appears, when examined under the microscope, to consist of the
ruptured cells, and is not susceptible of vegetation ; so that during the
fermentation of sugar, a certain portion of the yeast-plant dies, and is decom-
posed, the living plant being required to sustain the fermentative process.
If more yeast be present than is required for the decomposition of a certain
quantity of sugar, the deposit which is in that case formed, consists partly
of broken and partly of entire cells, and the latter retain their power of
inducing fermentation. It further appears that that portion of the yeast
which has become inert as a ferment, has lost the greater part, if not the
whole, of its nitrogen ; and certainly, one of the results of the changes which
ensue during saccharine fermentation, appears to be the formation of ammo-
nia, which may, although so small in quantity as generally to elude observation,
be easily detected amongst the gaseous products.

For the formation of artificial yeast or ferment, the requisites appear to
be the presence of sugar, of an azotized principle, water, and exposure to
air at a moderate temperature. Any nitrogenous substance partly decom-
posed may act as a ferment. Thus gluten, albumen, casein, or fibrin, of the
vegetable or animal kingdom, provided it be in a state of change or partial
decomposition, may act as a ferment to saccharine liquids. To obtain a
ferment, in the first instance, a quantity of ground malt may be made into a
thick paste by the addition of some concentrated wort, at a temperature of
about 70° to 75°, so as to convert the starch into sugar ; a little alcohol is
then added, and after a few days, when the violence of the fermentation has
subsided, a deposit of ferment is formed. An artificial yeast may be thus
prepared : A small handful of ordinary wheat flour is made into a thick paste
with cold water, covered with paper, and left seven days in a warm room,
being occasionally stirred (Fownes).

The yeast-cells, when treated with an aqueous solution of iodine, are found
to consist of a colorless envelope, of the nature of cellulose, containing a
fluid which acquires a brown color from the iodine. If yeast is dried in
vacuo, or at a low temperature, it is converted into a hard, hOrny, translucent
substance. It reacquires its property of exciting fermentation when digested
for some time in cold water. German yeast appears to be a partially dried
mass of cells. It has undergone washing to free it from the impurities of
the fermented liquid, and is then dried at a low temperature. This yeast
is chiefly obtained from the distilleries of Holland, and is now largely
imported into England. Boiling water destroys the fermenting properties
of yeast ; but unless boiled so long as to have its chemical nature entirely
changed, it reacquires a fermenting power on exposure to air. As the
yeast-cells are composed of a cellulose envelope, containing an albuminous
liquid, these properties are destroyed by chemical reagents; thus alcohol,
common salt, strong acids and alkalies, destroy its fermenting power. Weak
vegetable acids appear to accelerate fermentation. Yeast is generally acid,

5Y6 ALCOHOLIC FERMENTATION. CHEMICAL CHANGES.

and this state of acidity probably operates favorably by converting any
cane-sugar present in the fermenting liquid, into grape or fruit-sugar, which
more easily undergoes fermentation.

The temperature which is found to be most favorable for vinous fermenta-
tion is about 70°, but it will take place at all temperatures between 40^ and
80°. The lower the temperature the slower the process. At a high tem-
perature the alcoholic rapidly passes into the acetous fermentation. The
process appears to be so identified with sugar, that it has been employed as
a test for this principle ; and the amount of carbonic acid obtained has been
employed as a measurer of the quantity of the sugar present. A strong
solution of sugar will not, however, ferment ; it requires a certain state of
dilution with water, in order that the process should take place. Further,
sugars differ among each other in the readiness with which they take on this
property. Pure cane-sugar {sucrose, Q^fi^fi^^ does not readily ferment :
grape-sugar {glucose, C^^^fi^^ is easily fermented, but the process takes
place most readily in fruit-sugar {fructose), represented by G^Jl^S)^^. The
examination of the solutions of these sugars by polarized light, during fer-
mentation, renders it highly probable that both cane and grape-sugar are
converted into fruit-sugar before they undergo the change. These two
sugars belong to the crystallizable variety, and their aqueous solutions are
dextrogyrate under polarized light — ^. e., they turn the polarized ray from
left to right. The fruit-sugar, which is uncrystallizable, is Isevogyrate,
turning the rays from right to left. Cane-sugar ferments slowly, because
some time elapses before it is perfectly converted into fruit-sugar by the
acids contained in the ferment. In this stage its rotatory power on polarized
light is inverted. Cane-sugar also requires for its conversion a much larger-
quantity of ferment than other sugars. When fermentation is complete,
100 parts of fruit-sugar are resolved into 51 '12 of alcohol and 4888 of
carbonic acid, so that the ferment adds nothing to and removes nothing from
the elements of sugar. In fact, it appears, by a catalytic action, simply to
resolve the sugar into these two compounds. The changes may be thus
expressed : —

C,2H„0„

+

HO =

Water.
C,2H,20,2

Fruit-sugar.

C 13^12^12

Cane-sugar.
C,2H„0,4 •

Fruit-sugar,
-f 2H0

Grape-sugar.

Water.

An atom of cane-sugar combines with the elements of water to produce
fruit-sugar, while an atom of grape-sugar, by losing two atoms of water,
becomes at once converted into fruit-sugar. 1 atom of this compound is
resolved by fermentation into 4 atoms of carbonic acid, and 2 atoms of
alcohol : —

Fruit-sugar. Carbonic acid. Alcohol.

How does the ferment operate to effect this remarkable change ? Yital,
chemical, and dynamical theories have been suggested in order to explain
the phenomena. The vital theory assigns the cause to the growth of a
fungus derived from the yeast-cells. This is said to become developed at
the expense of the sugar ; but the objection to this view is, that the ele-
ments of the sugar are not removed by the fungus : they merely assume a
new arrangement. Since the discovery of the fact that the ferment practi-
cally takes no direct share in the changes, no chemical theory has been sug-

PRODUCTS OF FERMENTATION. 5Yt

gested, which can adequately explain this conversion. The dynamical
theory, advocated by Liebig, involves the assumption that the molecules of
the ferment are in a state of motion, arising from their partial decomposi-
tion ; and that this motion is mechanically communicated to the atoms of
sugar, which thenceforth arrange themselves in the form of more stable
compounds. This hypothesis, however, fails to explain why the particular
compounds in question are invariably produced, or how the motion of atoms
(if it exists) can bring about such remarkable chemical changes.

The phenomena of fermentation may be experimentally demonstrated by
dissolving in a quart of water at a temperature of 70^, half a pound of trea-
cle and half a pound of brown sugar, adding to the solution one pound and
a half of bruised raisins, and a pint of fresh yeast. This mixture may be
placed in a capacious glass globe, provided with a cork, and exposed to a
temperature of from 70° to 80°. In about an hour fermentation will com-
mence : the liquid will appear to be in continual motion, by reason of the
bubbles of carbonic acid, as they are evolved, rising to the surface, and car-
rying with them portions of the yeast and the husks of the raisins. The gas
there escapes, and as the solids again sink they gradually acquire a fresh
coating of bubbles, which they carry up as before ; and in this way that
motion of the whole mass of liquor is produced which is so characteristic of
active fermentation, and which, provided a sufficiency of ferment be present,
is maintained so long as any sugar remains to be decomposed. The process
is attended by a considerable elevation of temperature, and when complete,
the liquor clears, the yeast falls to the bottom, the sugar has vanished, and
is replaced by alcohol. A trace of ammonia also at the same time makes its
appearance.

Air or oxygen is not necessary to these changes : they go on readily in a
close vessel. Too free an exposure of the liquid to air would cause a loss
of alcohol, or the conversion of a part of this product into acetic acid.
Although the ferment takes no direct part in the changes, a portion of it,
equivalent to about 2 per cent, of the weight of the sugar, invariably disap-
pears during the process. There is a certain relation between the propor-
tions of sugar and ferment, which must be observed, in order to obtain the
most satisfactory results. Kegnault found that 4 parts of cane-sugar dis-
solved in 16 parts of water, required for their complete fermentation 1 part
of fresh yeast. If the proportion of yeast Is too small, it is decomposed
before the entire conversion of the sugar, a portion of which remains
unchanged in the liquid. If, on the other hand, the yeast is in too large a
quantity, the sugar is entirely decomposed, and the residuary ferment after-
wards undergoes the usual spontaneous changes. If more sugar be added,
this will be converted into alcohol and carbonic acid until the ferment is
exhausted. If in any case the sugar is in too large a proportion, the pro-
cess is less active : and in a saturated solution of sugar, fermentation is alto-
gether arrested. It was formerly believed that the ferment itself was not
decomposed, but experiment has shown that there is invariably a consump-
tion of it, although this is small in proportion to the sugar which is decom-
posed by it.

The properties of the products thus obtained from sugar may be easily
demonstrated. If a lighted taper is introduced into the globular vessel
when fermentation is complete, it will be extinguished : if a portion of the
gaseous contents of the vessel is poured into a jar containing lime-water,
and the vessel agitated, the liquid will become white from thfe production of
carbonate of lime. If the gas is poured from the globe into another jar
containing a solution of chloride of lime colored blue by litmus, the color
will be destroyed on agitation, thus showing the presence of a gaseous acid..
37

678 WINE. CHEMICAL PROPERTIES OF VINOUS LIQUIDS.

If during fermentation the aperture of the vessel is made air-tight, and con-
nected by a bent glass tube with a jar full of water, and inverted over a
water-bath, the carbonic acid may be collected as it issues in bubbles. The
quantity which escapes is very large : it amounts to nearly half the weight
of the sugar, 180 parts of fruit-sugar are converted into 92 parts of alcohol,
and 88 of carbonic acid. Three drachms of fruit-sugar, when completely
fermented, yield 187 cubic inches of this gas. One grain of fruit-sugar thus
produces rather more than a cubic inch. In order to produce these quanti-
ties of alcohol and carbonic acid, there are required of grape-sugar 198
parts, and of cane-sugar 171 parts. When the sugar is derived from malted
grains, the liquid product of fermentation is called beer; when from the juice
of the grape, it is called wine.

Beer. — This liquid consists chiefly of water and alcohol, with sugar, dex-
trine, coloring matter, essential oil, carbonic acid, and saline matters. Hop%
impart to it, as a result of the volatile oil and other principles contained in
them, an aromatic bitter flavor, and an agreeable odor. They also diminish
the tendency to subsequent fermentation. The color of beer depends on the
temperature to which the malt has been exposed. Pale malt, i. e., malt which
has not been exposed to a temperature above 140^, is in the best condition
for the production of beer ; but more color and flavor are imparted by malt
which has been dried at a higher temperature. To a good beer brewed from
pale malt, any depth of tint may be imparted by a careful use of roasted
malt. Caramel or burnt sugar is sometimes employed as a coloring sub-
stance. The average amount of absolute alcohol, by measure, in the varie-
ties of ale, is from 6 to 9 per cent. ; less than six in common ale ; in porter
about 5 per cent. ; and in small beer 1 to 2 per cent. Some of the stronger
ale contains as much as 9 per cent. The method of determining the propor-
tion will be described hereafter.

Wine. — The grape-sugar, or glucose, contained in the ripe grape, the
juice of which is called must, is the source of the alcohol of wine. Besides
water and alcohol, the fermented juice contains sugar, gum, coloring matter,
malic and tannic acids, the bitartrate of potassa, tartrate of lime, and other
salts, as well as volatile oil and oenanthic ether. Red wines contain much red
coloring matter, which is derived chiefly from the red husks of the grapes.
The husks also impart tannic acid, which gives astringency to port and simi-
lar red wines. The pale yellow or brown color of white wines arises from
the fermentation of the juice only, or from fermentation over nearly colorless
husks. The deep brown color of some wines (Tent wine) is more commonly
produced artificially by the addition of caramelized grape-sugar. The dark-
colored varieties of sherry frequently owe their tint to burnt sugar, or caramel.

All wines have an acid reaction, arising from the presence of the acid tar-
trate of potassa or lime, as well as of acetic acid, derived from a partial
oxidation of the alcohol after the vinous fermentation is completed. In
sparkling wines the acidity is partly due to carbonic acid. Malic acid is
frequently present ; and sulphuric acid, derived from the sulphuring of the
juice to arrest fermentation, is also a cause of acidity. This may be found
in comparatively large proportion in most sherry wines. The amount of acid
in wines may be determined volumetrically by the use of a standard diluted
solution of ammonia, and a graduated burette. Some portion of the acid is
volatile, and may be separated by distillation.

In all wines there is more or less of an odorous principle, partly derived
directly from th'e grape, and partly formed during fermentation ; it has the
characters of an essential oil ; it constitutes the perfume or bouquet of the
wine, and in some wines is evanescent and small in quantity, in others more
persistent and abundant. It does not exceed the forty-thousandth part of

DETERMINATION OP ALCOHOL IN WINES. 579

the wine. This odorous substance, which is formed in the process of fer-
mentation, is represented by Pelouze and Liebig (Ann. Ck. et Ph., liii. 115,
and Ixii. 439) as a true ether, that is, as a combination of oxide of ethyle
with oenanthio acid. The formula Ci^HjgOa is represented as that of oenan-
thic acid, which 4-C4H50 gives CigH^gOa as the composition of cenanthic
ether. Deleschamps first separated this ether from the wines of Burgundy,
and it was afterwards recognized, together with amylic alcohol (potato-spirit
oil), in the products of the distillation of the grapestalks of Montpellier.

(Enanthic ether (from ohoi, wine), which is considered to be identical with
pelargonic ether, may be obtained by agitating the oil derived from brandy
or from grain-spirit (Weinfuselol), which is a mixture of cenanthic acid and
cenanthic ether, with a solution of carbonate of soda, till the free acid is neu-
tralized ; heat is then applied, and the cenanthic ether separates upon the
surface, and may be dehydrated by chloride of calcium.

According to some, this ether exists ready formed in unfermented grape-
juice. It is a colorless oily liquid, of a strong vinous odor, sp. gr. 0-862,
boiling at 440*^, soluble in alcohol and ether, but insoluble in water. A
small quantity, however, passes over with the vapor of water during distilla-
tion. It has a strong taste and odor, as well as intoxicating properties. It
imparts a powerful aroma, which is very persistent in any bottle or vessel
that has contained wine : the odor is soon perceived over a very large apart-
ment. Butyric, caprylic, acetic, and other ethers, are sometimes associated
in wine with the cenanthic. The bouquet or perfume of wine is much affected
by age. In some wines there is a fixed non-nitrogenous principle which has
been called cenanthin.

During fermentation the acid tartrate of potassa becomes less soluble, by
reason of the production of alcohol ; and the acidity of the wine, if dependent
on the presence of this salt, diminishes, while its strength increases. This is
deposited in the cask or bottle, either colored or colorless, according to the
nature of the wine. It is well, known under the name of crude tartar, or
argol. Some wines which contain much sugar are observed, after a certain
period, to become viscid or ropy. This has been called the viscous fermen-
tation. It appears to arise from a spontaneous conversion of grape-sugar
into an isomeric mucilaginous or gummy compound. Mannite is said to be
a product, and hydrogen is evolved under these circumstances. Wines which
contain much tannic acid are not liable to this change ; and this acid, when
added to wine thus affected, precipitates the mucilaginous compound. We
have observed this change to take place in ale, arising probably from an
excess of sugar and a deficiency of tannic acid in the hops.

Wines which are bottled before alcoholic fermentation is completed undergo
this process still further ; the carbonic acid accumulates in the liquid, and
gives to the wine a sparkling character. An albuminous compound in the
husk of the grape serves as a natural ferment to the juice. If the fruit-sugar
is in excess, the wine will remain sweet after fermentation (Liqueur wines).
If the ferment is in excess, the whole of the sugar will be decomposed and
the wine will be slightly acid (Rhenish wines). If the sugar and ferment
are equal, the wine is neither acid nor sweet (Burgundy). {Mulder on Wine,
139.) When the sugar and ferment are thus equally balanced, the sugar
almost entirely disappears, and a dry wine is the result. If, during fermen-
tation, the alcohol reaches about 20 per cent, of the wine, the process is
arrested, and any undecomposed sugar remains. In some of the Rhenish
wines Fischern found the sugar so completely removed that, while it amounted
to 21 7 per cent, of the grape-juice, it constituted only 01 per cent, of the
wine (Liebfrauenmilch), the alcohol amounting to 9*9 per cent, and the dry
extract to 4*1.

580 COMPOSITION OP WINE.

The quantity of alcohol contained in different wines is variable ; the best
mode of determining it consists in carefully distilling four ounces of the wine,
until from one-half to three-fourths have passed over, having previously neu-
tralized the acid of the wine by a little soda, potassa, or lime, A quantity
of distilled water is then added to the portion of the alcoholic liquid which
has gone over, so as accurately to make up the original volume of the wine :
the mixture is well shaken and set aside for a day or two in a stoppered
bottle, so that it may obtain its maximum density. Its specific gravity may
then be taken in the usual way at 60°, and from this datum the proportion
of alcohol may be determined by reference to tables which show the quantity
of absolute alcohol contained in diluted alcohol of different densities {see p.
586). There is, of course, no direct relation between the original density of
the wine and its alcoholic contents, inasmuch as some of the most alcoholic
wines are also those which have the highest specific gravity, in consequence
of the sugar, extract, and other substances which they hold in solution.
Thus we have found some very strong wines to have a greater sp. gr. than
water, the solid contents of the wine being in larger proportion.

Another method consists in gently distilling the wine until one-half is
obtained in the receiver. The sp. gr. of the distillate may be at once taken
without admixture with water. In this case, as there is only half of the ori-
ginal quantity, the distilled spirit will have twice the strength : hence the
proportion of alcohol is determined by dividing the quantity per cent, by 2.
Thus, four ounces of sherry yield two ounces of spirit, which, when mixed
with two ounces of water, will have a sp. gr. of 0-9753 = l'r per cent, of
alcohol. The distiUed spirit, before the addition of its bulk of water, has a
sp. gr. of 0-9511=34 per cent, of alcohol, and 34-^2=17 per cent, of alco-
hol contained in the wine. These methods of determining the alcoholic
strength of wines are applicable to ale, beer, and other weak alcoholic liquids.

Independently of the proportion of alcohol, the analysis of wine is directed
to the amount of dry extract, the quantity of mineral matter, and the nature
of the inorganic salts. The presence of tannic acid, grape-sugar, and other
inorganic ingredients, may be determined by their appropriate tests. The
following represents the analysis of a sample of dry sherry. The sp. gr. of
the entire wine was 0*994. The alcohol, obtained by distillation from a
measured quantity, when made up to its original bulk with distilled water,
had a sp. gr. of 0*978 at 60°. According to the tables, this is equivalent
to 15 per cent, by weight of absolute alcohol. The dry extract obtained by
the evaporation of the wine amounted to 3*75 per cent, of its weight. This
consisted chiefly of grape-sugar, coloring matter, acid tartrate of potassa, and
tartrate of lime. The dry extract, when incinerated, left a white ash, which
weighed 0*45 grains. The ash was slightly alkaline : it contained potassa,
soda, lime, and a trace of alumina, with carbonic and sulphuric acids. In
the entire wine, besides grape-sugar and coloring matter, tartaric, tannic,
and sulphuric acids were found — the latter in comparatively large proportion,
owing to the use of burning sulphur, for checking undue fermentation in the
wine-manufacture. The constitution of this wine would therefore be, in 100
parts, as follows : —

Sp. gr. in the entire state 0-994

Alcohol 15-00

Dry saccharine extract 3-30

Mineral ash ' . 0*45

Water, oil, ether, and volatile products . . 81-25

100-00

ANALYSIS OP WINES. 581

•

The comparison of weight with measure may be thus made. The sp. gr.
represents in grains ihe weiglit of eighteen fluidrachms of the wine at 68°,
namely, 994 grains, the same volume of water weighing nearly 1000 grains
at this temperature. The mixture of the distillate with the residue in the
retort, however carefully the distillation may have been conducted, will not
reproduce the wine with its original odor and flavor. This is owing to the
loss or decomposition of the volatile oily matters and oenanthic ether during
distillation.

The quality of wine, although for financial purposes estimated by its alco-
holic strength, does not depend on the amount of alcohol, or of dry residue
in one hundred parts, although the finest wines contain, generally speaking,
a large proportion of solid matter. It depends chiefly upon the peculiar
flavor imparted by the grape during fermentation, and the effects of age in
improving and heightening this flavor. The amount of alcohol will depend
on the quantity of fruit-sugar in the grape-juice, on the addition of starch-
sugar, or glucose, to the must during fermentation, or of brandy after that
process. The solid contents are generally small, except in sweet wines. Dr.
Christison states, from his observation, that in Port and Sherry, when fit for
drinking, the solid seldom exceeds three per cent, in Bordeaux wine they
amount to about two and a half, and in Hock and Moselle to two per cent,
only.

Te results of analysis will be affected by the age of the wine, the degree
to which fermentation has taken place, and other circumstances. The fol-
lowing table represents, chiefly as the result of recent analyses, the constitu-
tion of many wines which are now consumed in this country. The alcoholic
strength is given by weight in absolute alcohol (sp. gr. •'794 at 60°). At
this temperature and specific gravity, 49 parts of alcohol by weight are
equivalent to 100 parts of proof spirit, by weight (sp. gr. '920), or to 102*57
parts by measure. The alcoholic strength of vinous liquids is sometimes
calculated in alcohol of a sp. gr. of '825. At this sp. gr., however, alcohol
is combined with 11 per cent, of water.

TABLE OF ANALYSIS OF WINES.

Specific

Alcohol in

Dry extract in

Ash in 100

'

gravity.

100 by weiglit

. 100 by weight.

by weight.

Port, 1820 (Muspratt)

. 0-9945

... 18-01

... 5-14 ...

Port, 1844 .

. 0-9977

... 17-00

... 6-20 ...

0-30

Sherry

. 0-9960

... 17-30

... 5-70 ...

0-70

Sherrj (dry)

. 0-9940

... 15-00

... 3-75 ...

0-45

Tarragona .

. 1-0154

... 16-00

... 10-80 ...

0.50

Gelopiga ,

. 1-0547

... 15-00

... 20-70 ...

0-20

Bucellas .

. 0-9934

... 16-00

... 3-30 ...

0-40

St. Estephe

. 0-9930

... 10-00

... 2-00 ...

0-30

11

. 0-9933

... 10-00

... 2-47 ...

0-23

Haut. Brion

. 0-9940

9-00

... 2-30 ...

0-25

St. Emilion

. 0-9960

9-00

... 2-44 ...

0-32

Beaujolais

. 0-9930

... 10-00

... 2-00 ...

0-20

Sauterne .

. 0-9955

7-50

... 1-32 ...

0-10

Chablis .

. 0-9212

9-00

... 1-60 ...

0-10

Roussillon .

. 1-0076

... 13-00

... 7-10 ...

0-40

Steinberg \ /^ei^er^
Riidesheim / ^^^^S^^)

. 1-0025
. 1-0025

... 10-87
... 12-65

... 9-94 ...
... 5-39 ...

Tokay (Richter)

. 1-0201

... 12-10

... 10-60 ...

Malaga (Mayer)

. 1-0570

... 12-24

... 18-40 ...

Tent wine .

. 1-1150

7-00

... 32-60 ...

O'Aiy

Champagne

. 1-0290

... 11-70

... 0-30 ...

traces

In comparing the bulk of the wine with the weight, it may be observed
that the sp. gr. represents the weight in grains and tenths of grains, of 18
fluidrachms, or 65 cubic centimetres. Thus, this quantity of port wine

582 STRENGTH OF SPIRITUOUS LIQUIDS.

(1820) weighed 994*5 grains, the same volume of water weigTiing 1000
grains. In calculating the percentage of alcohol as proof spirit at 918, the
amount in absolute alcohol should be doubled. Thus, 18 01 absolute alcohol
in port wine (1820) are equivalent to 36 75 of proof spirit per cent.

Spirituous Liquids. — Brandy, rum, gin, and whiskey are spirituous liquids
which contain about half their weight of alcohol, and are therefore nearly in
the condition of proof-spirit. They are obtained by distilling various fer-
mented liquors. They chiefly consist of alcohol and water, with a very small
proportion of solid matter : they owe their peculiar odors and flavors to the
presence of certain oily and ethereal products of fermentation. When genuine,
they are neutral, and leave only a slight residue on evaporation. Brandy is
the result of the distillation of wine ; and its qualities vary with the kind of
wine from which it is obtained, and the precautions with which it is distilled.
It is frequently strongly colored with caramel. — Rum is distilled in the East
and West Indies from a fermented mixture of molasses and water, with the
skimmings of the sugar boilers, and the lees or spirit-wash of former distil-
lations— Gin, or Geneva, is prepared from difi'erent kinds of corn-spirit: it
was originally largely imported from Holland, and was known as Holland or
Hollands' gin. Its flavor is derived from juniper-berries, or from the essen-
tial oil of juniper, which contributes to its diuretic quality. Calamus aro-
maticus, or sweet flag, and other flavoring articles, are occasionally used in
its manufacture. The great gin-distillers sell it to the trade at about 20 per
cent, over proof, but the retailers afterwards dilute and generally sweeten it.
Yarious chemical substances are employed in its adulteration. — Whiskey (a
term said to be derived from the Irish usquebaugh^ is also a corn-spirit, and,
when genuine, derives its characteristic flavor from the malt used in its manu-
facture having been dried over peat or turf fires ; but this odor and flavor
of burned turf, or peat-reek, is frequently given to raw corn-spirit by im-
pregnating it with peat-smoke. — Arrack, or Rack, is a spirituous liquor
prepared in various parts of India from the fermented juice of the cocoa-nut,
and also from fermented infusion of rice. It has a peculiar flavor and odor,
but in other respects closely approaches in its characters to rum. It is said
that a genuine arrack may be very well imitated by dissolving 10 grains of
benzoic acid in a pint of rum.

There are many other alcoholic liquors, the preparation of which is pecu-
liar to diJBferent places — Kirschwasser is obtained in Switzerland, and in
some parts of France, from bruised black cherries, fermented and distilled.
— Maraschino is a similar liqueur prepared also from a peculiar kind of cherry
growing in Dalmatia — Noyau and several analogous liqueurs are flavored with
an essential oil containing more or less hydrocyanic acid, and often with that
derived from bitter almonds, the kernels of peaches, apricots, &c., or from
the leaves of laurels. Some of these compounds come under the denomina-
tion of tinctures; such, for instance, as Curagoa, which is prepared by digest-
ing orange-berries (the immature fruit) and bitter orange-peel with cloves
and cinnamon in brandy : when this tincture is distilled, and afterwards
sweetened, it constitutes white Curagoa. These compounds are frequently
called Ratafias, a term derived, like the word ratify, from ratum and fio, to
make firm, or confirm. By ratafia, therefore, was originally meant a liquid
drunk at the ratification of an agreement.

In the analysis of these spirituous liquids the distillation for the separa-
tion of alcohol must be carried on at a low temperature until nearly the whole
of the liquid has passed over. The following table represents the results of
recent analyses, the alcohol being estimated by weight and volume as abso-
lute.

ALCOHOL.

Alcohol in

Dry extract in

Ash in 100

Name.

Sp. grav.

100 by weight.

100

by weight.

by weight.

Whiskey .

. 0-9208

... 50-00

...

0-10 ..

trace

Gin .

. 0-9440

... 45-00

0-20 ..

. 0-10

Brandy, Cognac

. 0-9300

... 46-00

...

1-40 .

. 0-20

" common

. 0-9483

... 36-00

...

0-60

. 0-05

Rum .

. 0-9260

... 48-00

...

0-90 .

. 0-10

583

^ But two of these compound are introduced into pharmacy, whiskey, Spi-
ritus Frumenti (U. S. P.), and brandy under the classical name of Spiritus

Vini Gallici.

CHAPTER XLVII.

ALCOHOL. ALDEHYDE. CHLOROFORM. METHYLIC,
AMYLIC, AND OTHER ALCOHOLS.

Alcohol. Ethylic Alcohol {Q^fi^.

The word alcohol signifies in Arabic a liquid or solid brought to its utmost
perfection. By the careful distillation of any of the spirituous fermented
liquids described in the preceding chapter, the alcoholic portion may be sepa-
rated from the less volatile matters, and the product is known in commerce
as Rectified Spirit of Wine. Its sp. gr. is usually about 0*840 to 0 850,
and it consists of alcohol combined with about from It to 20 per cent, of
water : it generally contains traces of oily matters, and of some other impuri-
ties. The distillers commonly prepare a liquor called wash, for the express
purpose of producing from it rectified spirits. Instead of using pure malt,
they employ chiefly raw grain, mixed with a small quantity only of malted
grain. The water employed in the mash-tub is generally at a lower tempe-
rature than that adopted in brewing beer, and the mashing is longer con-
tinued. The wort is afterwards fermented with yeast, and then distilled for
the production of proof- spirit and alcohol. In this state the product is called
malt-spirit. Its specific gravity is from '914 to '936, and it contains about
half its weight of alcohol. The oily products which are combined with the
spirit and render it impure, are mostly less volatile than alcohol, so that when
the process of rectification is carefully performed, they remain with the resi-
duary water in the still or retort. Many precautions are requisite, both in
conducting the distillation, and in the management and construction of the
stills, so as to produce what is techanically known as clean spirit. Rectified
spirit thus obtained, varies in sp. gr. from "835 to '884, and contains from 85
to 65 per cent, of alcohol.

To obtain pure or absolute alcohol, rectified spirit is usually dehydrated,
by distilling it with certain substances which have a strong affinity for water.
Although the boiling points of alcohol and water greatly differ, it is impos-
sible to separate the water from aqueous alcohol by distillation at a low tem-
perature. The vapors of both pass over and are condensed together so soon
as the liquid reaches a sp. gr. of 0-825. Among the substances used for
dehydration, are carbonate of potassa, chloride of calcium, quicklime, and
anhydrous sulphate of copper.

When common spirit of wine is employed, the first portions of water may
be abstracted by adding to it dry carbonate of potassa until that salt ceases
to be dissolved ; the mixture is then frequently shaken, and when allowed to

684 RECTIFIED SPIRIT.

stand at rest, it soon separates into two portions, the uppermost being alco-
hol (of sp. gr. 0'825) and the lowermost an aqueous solution of the car-
bonate. The former is drawn oflF and poured upon a quantity of powdered
quicklime, amounting to about half the weight of the alcohol, and previously
introduced into a tubulated retort. This mixture may be left to digest for
a day or two, and then slowly distilled in a water-bath, at a temperature of
about 200°. Fresh-burnt lime alone may be used without the previous
employment of carbonate of potassa, the water being then absorbed and
retained by the lime as hydrate. In place of lime an equal weight of fused
chloride of calcium may be employed. Any color or odor possessed by the
rectified spirit may be removed by the use of finely-powdered animal char-
coal.

Properties of Alcohol. — Alcohol is a limpid colorless neutral liquid of an
agreeable odor, and a strong pungent taste. It is quite neutral, and is not
liable to undergo any change by keeping. The specific gravity of absolute
alcohol is 0 794 at 60°. When spirit of wine is as far as possible dehydrated
by simple distillation, its specific gravity is 0-825 at 60° ( = 89 per cent, of
alcohol). The rectified spirit of the Pharmacopoeia is directed to have a sp.
gr. 0*838. It contains 16 per cent, of water, and is employed for making
certain tinctures. The quantity of absolute alcohol contained in these and
other commercial forms of alcohol and spirit of wine, will be seen by refer-
ence to the table given at p. 542. According to Despretz, the specific heat
of alcohol is 0 52. Alcohol has never been frozen. Faraday exposed it to
a temperature of 166° below 0°; it thickened considerably, but did not con-
geal {Phil Trans., 1845, p. 158). According to Mitchell, alcohol of 0-798
becomes oily at — 130°, and at — 146° flows like melted wax ; and alcohol
of sp. gr. 0-820 entirely congeals in a bath of solid carbonic acid and ether
(—166°). The boiling-point of alcohol of sp. gr. 0-7947 is 173° (Barom.
29-5). When of the sp. gr. 0-825 it boils at a temperature of 176° under
the same pressure. In the vacuum of an air-pump, alcohol boils at common
temperatures. The specific gravity of the vapor of alcohol (in reference to
air = 1-000) was experimentally found by Gay-Lussac to be 1-6133: this
nearly corresponds to its calculated specific gravity. The latent heat of the
vapor of alcohol is to that of the vapor of water as 332 to 531 (Despretz).

Absolute alcohol has so strong an affinity for water as to absorb it from
the atmosphere ; it requires, therefore, to be kept in well-stopped bottles, as,
after exposure, it undergoes a sensible increase of specific gravity ; it is
even apt to absorb a small quantity of water during its distillation. Anhy-
drous sulphate of copper is not rendered blue by strong alcohol, and potas-
sium decomposes it without combustion and without imparting to it a dark
color. Alcohol does not appear to form any definite hydrate : for even the
water, which passes over with it by distillation at a sp. gr. of 0*825, may be
entirely separated by lime, carbonate of potassa, or any substance which
combines with or dissolves in water. It may be mixed, in all proportions,
with water without change, and while heat is evolved, a diminution of bulk
(or increase of specific gravity) ensues. When alcohol and snow are mixed,
there is, on the other hand, a diminution of temperature, as a result of the
sudden liquefaction of the snow. The contraction in volume which ensues
on mixing alcohol with water has been already described (p. 50) : it is
always attended with an increase of temperature. Thus equal measures of
alcohol (sp. gr. 0*825) and water, each at 50°, afford, when suddenly mixed,
a temperature of 70° ; and equal measures of proof spirit and water, each at
50°, give, under similar circumstances, a mixture of the temperature of 60°.
The greatest amount of heat and condensation is produced by the admixture

PROOF SPIRIT.

585

of 1 equivalent (53-74 parts) of alcohol and 6 equivalents (49*84) of water.
The mixture is reduced on cooling to 100 parts, and has a sp. gr. of 0-227.
Proof Spirit. — This is a weaker form of alcohol than rectified spirit. It
is employed in reference to Excise regulations, and in pharmacy {Spiritus
tenuior). In the latter, the sp. gr. is fixed at 0 920. It consists by weight
at 60° of 49 parts of alcohol and 51 parts of water. The British Pharma-
copoeia directs that it should be made by mixing five pints of rectified spirit
(0*838) with three pints of distilled water. It is employed for making the
greater number of medicinal tinctures. The sp. gr. of Excise proof-spirit
at 60^ is 0*916. This corresponds nearly to equal parts by weight of alco-
hol and water. Such a mixture, according to Gilpin's tables, should have
a sp. gr. of 0*917. The term proof, appears to be derived from the old
gunpowder-test. Spirit was poured over gunpowder and the vapor in-
flamed: if it fired the gunpowder it was over-proof; if it burnt without
igniting the powder, owing to the residuary water rendering the powder
damp, it was said to be under-proof. The weakest spirit capable of firing
gunpowder was the proof-spirit of pharmacy, sp. gr. 0*920. Drinkwater
gives the following table, showing the results of his experiments upon the
composition of proof -spirit.

Alcohol and water.

Specific gravity
at 60° F.

Bulk of mixture of 100
measures of alcohol

By weight

By measure.

+81-82 water.

Alcohol. Water.

100 4- 103-09
or in 100
49-24 + 50-76

Alcohol. Water.
100 4- 81-82
or in 100
54 4- 46

•91984

175-25

The strength of such spirituous liquors as consist of water and alcohol, is
ascertained by their specific gravity, and for fiscal purposes it is determined
by the hydrometer ; but the only correct mode of ascertaining the specific
gravity of liquids is by weighing them in a delicate balance, against an
equal volume of pure water of the same temperature. For this purpose a
thousand-grain bottle may be employed. Small hydrometers are constructed
to indicate, by flotation, proof-spirit, and a certain number of degrees above
and below proof.

Alcohol is extremely inflammable, and burns with a pale bluish flame,
scarcely visible in bright daylight ; but the heat of its flame is very intense,
as may be shown by suspending in it a coil of fine platinum wire, which
soon becomes white-hot. It produces no smoky deposit upon cold sub-
stances held over it. The products of the combustion of alcohol are carbonic
acid and water, the weight of the water considerably exceeding that of the
alcohol consumed. According to Saussure, jun., 100 parts of alcohol afl'ord,
when burned, 136 parts of water, the production of which may be shown by
holding a glass-jar over the flame until it is extinguished. Water is depo-
sited on the sides of the jar, and carbonic acid is collected within it, a fact
which may be proved by the addition of lime-water. The flame of alcohol
may also be burned under a condensing-apparatus, the exit-tube at its ex-
tremity being turned down into a glass-jar. It will then be found that a
current of carbonic acid passes out of it : this may be rendered evident by
lime-water, and the extinction of a taper. When alcohol is burned at a
lower temperature than that required for its inflammation, as by the action
of spongy or finely-divided platinum, or by a hot platinum wire, as described
at p. 54, the products of its combustion are diS'erent ; the proportion of
carbonic acid is less, and aldehydic and acetic compounds are formed.

586

TABLE OF THE PERCENTAGE OF ALCOHOL.

The following table by Fownes represents the specific gravities of mix-
tares of alcohol and water. The proportion of absolute alcohol is given by
weight.

Sp.gr.

Percentage

Sp. gr.

Percentage

Sp. gr.

Percentage

at 60°.

of alcohol.

at eo^".

of alcohol.

at 60=.

of alcohol.

•9991

0-5

•9511 ..

34

•8769

... 68

•9981

1

•9490 ..

35

•8745

... 69

•9965

... 2

•9470 ..

36

•8721

... 70

•9947

... 3

•9452 ..

37

•8696

... 71

•9930

4

•9434 ..

38

•8672

... 72

•9914

5

•9416 ..

39

•8649

... 73

•9898

... 6

•9396 ..

40

•8625

... 74

•9884

... 7

•9376 ..

41

•8603

... 75

•9869

... 8

•9356 ..

42

•8581

... 76

•9855

9

•9335 ..

43

•8557

... 77

•9841

... 10

•9314 ..

44

•8533

... 78

•9828

... 11

•9292 ..

45

•8508

... 79

•9815

... 12

•9270 ..

46

•8483

... 80

•9802

... 13

•9249 ..

47

•8459

... 81

•9789

... 14

•9228 ..

48

•8434

... 82

•9778

... 15

•9206 ..

49

•8408

... 83

•9766

... 16

•9184 ..

50

•8382

... 84

•9753

... 17

•9160 ..

51

•8357

... 85

•9741

... 18

•9135 ..

52

•8331

... 86

•9728

... 19

•9113 ..

53

•8305

... 87

•9716

... 20

•9090 ..

. 54

•8279

... 88

•9704

... 21

•9069 ..

55

•8254

... 89

•9691

... 22

•9047 ..

56

•8228

... 90

•9678

... 23

•9025 ..

57

•8199

... 91

•9665

... 24

•9001 ...

. 58

•8172

... 92

•9652

... 25

•8979 ..

59

•8145

... 93

•9638

... 26

•8956 ..

. 60

•8118

... 94

•9623

... 27

•8932 ..

. 61

•8089

... 95

•9609

... 28

•8908 ..

. 62

•8061

... 96

•9593

... 29

•8886 ..

. 63

•8031

... 97

•9578

... 30

•8863 ..

. 64

•8001

... 98

•9560

... 31

•8840 ..

. 65

•7969

... 99

•9544

... 32

•8816 ..

. QQ

•7938

... 100

•9528

... 33

•8793 ..

. 67

Bleached bees-wax is sometimes employed as a test for the strength of
spirits. It has a sp. gr. of '960, and in spirits of this sp. gr., representing
29 per cent, of absolute alcohol, this substance indififerentiy floats or sinks.
If the sp. gr. is lower, and the alcohol is therefore in greater proportion, it
sinks : if, on the contrary, it is higher, and the water is in larger quantity, the
wax floats. If a tube is half filled with water, and half with alcohol, the
wax will sink through the latter, and float on the former, indicating its
level. The slow diffusion of these liquids, under such circumstances, will
be proved by the wax maintaining its level for many weeks or months, pro-
vided the contents of the tube are not disturbed.

Graham has shown that alcohol may, in some instances, be combined with
certain saline bodies, such as chloride of calcium, nitrate of magnesia, nitrate
of lime, chloride of zinc, and chloride of manganese. The alcohol appears
to be substituted for water of crystallization. Such combinations have been
called alcohates. They are obtained by dissolving the substances by heat in
absolute alcohol, and the compounds, more or less regularly crystallized, are
deposited as the solution cools. . They appear to be definite compounds, and
in some of them, the alcohol is retained h^ an attraction so powerful, that it
is not evolved at a temperature of 400° or 500°.

Alcohol dissolves nearly all the acids, mineral and organic, giving rise to
an important and varied class of compounds. When a little sulphuric acid

CHEMICAL PROPERTIES OF ALCOHOL. 58T

is mixed with alcohol, the mixture has no action upon any neutral carbonate,
and yet it decomposes acetate of potassa, evolving acetic acid. A mixture
of alcohol and hydrochloric acid does not act upon carbonate of potassa, but
it decomposes the carbonates of soda, lime, strontia, and magnesia. A
mixture of alcohol and nitric acid is without action upon carbonate of
potassa, but it acts powerfully on the carbonates of lime and strontia, and
slowly on the carbonates of soda, baryta, and magnesia. Alcoholicsolutious
of acetic and tartaric acid decompose none of the carbonates : a similar
solution of citric acid decomposes the carbonates of potassa and joagnesia,
but not the carbonate of baryta, strontia, or lime ; while an alcoholic
solution of oxalic acid decomposes carbonates of strontia, lime, and mag-
nesia, but not carbonate of potassa. The addition of a small quantity of
water does not affect these mixtures, for when a saturated solution of
carbonate of potassa is mixed with an alcoholic solution of acetic acid, the
carbonate is precipitated without effervescence (p. 54) ; an alcoholic solution,
therefore, may appear neutral to certain tests, whilst, in reality, it is strongly
acid.

Alcohol dissolves a small quantity of sulphur, especially at its boiling
temperature, but the greater portion is deposited, on cooling, in small
brilliant crystals. It also dissolves phosphorus, taking up about a 240th
part at its boiling-point, and retaining a 320th part when cold. This
solution is luminous in the dark on exposure to air, and produces a beautiful
pale bluish flame, when poured upon hot water. Alcohol dissolves sulphide
of carbon, and the solution is decomposed by the alkalies. Alcohol is an
important agent in organic analysis : it dissolves benzole, chloroform, ether,
the resins, and a large number of the alkaloids, the vegetable acids, camphor,
and all the essential oils. It dissolves some of the fatty acids, but not
readily the fixed oils, excepting castor oil. It dissolves grape and fruit-
sugar, but does not readily dissolve cane-sugar, and has no solvent action
on starch and gum. It deoxidizes slowly a solution of permanganate of
potassa, but rapidly when the mixture is heated, or some hydrochloric acid
is added. It has no reducing action on the salts of silver or gold, or on
precipitated oxide of copper when mixed with potassa. It readily reduces
chromic acid to green oxide of chromium, when set free from a chro.mate
by an acid (hydrochloric), and the mixture is heated. A solution of a
chromate, rendered alkaline by potassa, is not reduced when heated with
alcohol. As this alkaline solution is readily reduced by grape-sugar, the
presence of grape-sugar in an alcoholic liquid may be determined by this, as
well as by the copper-test.

Potassium decomposes rectified spirit, if much water is present, with the
ordinary phenomena of combustion. With strong spirit there is no com-
bustion; and when sodium or potassium is placed on anhydrous alcohol,
hydrogen is given off, and the metal disappears without combustion. A
crystallizable compound is obtained from the liquid, which has been called
sodium or potassium alcohol, or ethylate of soda or potassa. When
potassium or sodium is heated with alcohol, carburetted hydrogen is evolved
among the products.

Potassa and soda are soluble in alcohol, hence this liquid is sometimes
resorted to for the purification of these alkalies. After a time, however,
they begin to act upon each other, and complicated changes ensue ; a car-
bonate of the alkali is formed, and carbonaceous matter is evolved on the
application of heat; by their slow mutual action, acetic acid, a resin, and a
species of brown extractive, appear to be formed. Ammonia and its
carbonates are soluble at common temperatures in alcohol : it also absorbs
in various proportions several other gases. Lithia, baryta, strontia, and

588 COMPOSITION OP ALCOHOL. TESTS.

lime, are almost insoluble in alcohol, even in their hydrated states ; so als®
are the fixed alkaline carbonates : but their sulphides are dissolved. The
greater number of the chlorides, iodides, and bromides, which are soluble in
water, are soluble also in alcohol, and with many of them, the definite
alcoholized compounds above mentioned are produced : but the sulphates
are almost all insoluble ; hence the use often made in the analysis of mixtures
of salts, of the separative power of alcohol.

The uses of alcohol in the arts, and its applications to various economical
purposes,, are extremely numerous : to the chemist it is a most valuable
species of fuel. Alcohol coagulates albumen and corrugates fibrin. It
removes water from organic matter, and is employed as an antiseptic.

Composition. — When alcohol-vapor and oxygen are mixed in certain
proportions, and the mixture is fired by an electric spark, a violent explosion
ensues, and carbonic acid and water are the results : 2 volumes of alcohol-
vapor, or 1 equivalent, require 6 volumes of oxygen, or 12 equivalents, for
their perfect combustion ; and 4 volumes of carbonic acid and 6 volumes
of aqueous vapor result {Q^B.fi^-\-\^0=iQ0^ + ^110).

The analysis of absolute alcohol by oxide of copper gives results in ac-
cordance with these experiments. The following is the composition of this
liquid : —

Atoms.

Equiv.

Per cent.

Dumas.

Vol.

Carbon .

. 4 ..

.. 24 ..

,. 52-65 ..

,. 52-17 .

.. 4

Hydrogen

. 6 ..

6 ..

. 12-90 ..

. 13-31 .

.. 6

Oxygen

. 2 ..

. 16 ..

. 34-45 ..

. 34-52 .

.. 1

Anhydrous alcohol 1 46 100-00 100-00 2

For the calculated vapor-density of alcohol, see p. 556.

The equivalent 46, which is here assigned to alcohol, is generally adopted
by chemical authorities. Some have proposed to double it, and others to
quadruple it, upon hypothetical considerations ; but no sufficient reasons
have been advanced for these changes.

Tests. — The chief adulterating ingredient is water, the amount of which
may be determined by distilling the liquid and taking the sp. gr. of the dis-
tillatjB. Alcohol is entirely volatile, and any residue will indicate the amount
of impurity. The odor and taste of the liquid will enable a chemist to de-
termine whether any essential oil, resin, or methylated spirit, is mixed with
it. It burns with a pale blue flame, and should deposit no smoke upon cold
surfaces brought in contact with it. Absolute alcohol should not give a
blue color to the white anhydrous sulphate of copper, and should yield no
precipitate of silicic acid when a current of fluosilicic acid gas is passed
into it {see p-. 305). In cases of suspected poisoning, the liquid should be
distilled by a water-bath, and the product rectified with fresh lime or car-
bonate of potassa. The alcohol, if present, may be drawn off by a few fibres
of asbestos and burnt. If in sufficient quantity, it will be detected by its
odor, and by its solvent power on camphor. If in very small quantity, the
heated vapor should be conducted through a tube containing a few fibres of
asbestos moistened with a mixture of bichromate of potassa and strong
sulphuric acid. If only a trace of alcohol is present, green oxide of chro-
mium will be precipitated on the asbestos. Ether and pyroxylic spirit
produce a similar decomposition ; but these liquids are detected by their
peculiar odors.

Other alcohols are enumeratd: the Propylic (0^fi,liO)\ the Butylic
(C,HaO,HO) ; the Caproic CC^aHj^Oa), and the Caprylic {Q^.ILJd^). These
are occasional products of the vinous fermentation, but are more abundantly
produced in the fermentation of the marc or residue of the grape. Like

ALDEHYDE. 589

araylic alcohol, these alcohols, which are colorless volatile liquids, do not
readily combine with water, in which, among other properties, they differ
remarkably from ordinary or ethylic alcohol. They form an homologous
series of compounds : each contains two equivalents of oxygen ; and the
equivalents of hydrogen always exceed by two, the equivalents of carbon.

Aldehyde (C^H^Og).

This compound, which is also called Acetic Aldehyde, derives its name
from the words alcohol dehydrogenatus, inasmuch as alcohol becomes alde-
hyde by the loss of 2 atoms of hydrogen. Aldehyde is one of the products
of the decomposition of alcohol or ether, in passing the respective vapors
througha red-hot tube, or in burning mixtures of ether or alcoholic-vapor
and ox/^n, at a comparatively low temperature without flame.

C^HgOa + 02= C^H.O^ + 2H0

Alcohol. Aldehyde.

It is best obtained in its pure state by the following process (Ltebig,
A7171. Ch. et Ph., lix. 289) : a mixture of 4 parts of alcohol (sp. gr. 0*844),
6 of oil of vitriol, 4 of water, and 6 of pulverized binoxide of manganese, is
introduced into a capacious retort, and distilled through a condenser into a
large receiver cooled by ice. When about 6 parts have passed over, or
when the distillate has become acid, the process is stopped, and the product
is put into a small retort with its own weight of chloride of calcium, and re-
distilled ; this process is repeated, so as to yield about 3 parts of dehydrated
aldehyde. The distillate, however, still contains acetal, ether, and alcohol ;
to free it from these, it is mixed with about twice its volume of ether, and
saturated with dry gaseous ammonia, when a crystalline compound of
aldehyde and ammonia gradually separates, which is insoluble in ether, and
which may be dried in the air. Two parts of this compound are then dis-
solved in their weight of water, and the solution mixed with 3 parts of sul-
phuric acid previously diluted with 4 of water, and distilled. Considerable
effervescence ensues during the evolution of the aldehyde, which requires to
be passed through a good condensing apparatus ; the distillate is fiualiy de-
hydrated by the careful addition of a little chloride of calcium, and distilled
at a temperature of about 87°.

Pure aldehyde is a volatile colorless liquid, of a peculiar ethereal, and at
the same time suffocating odor : when its concentrated vapor is respired, it
produces spasm of the glottis. Its sp. gr. is 0*79 at 65° : its boiling point
is 68°, and the density of its vapor is 1-53. It mixes in all proportions with
water, alcohol, and ether, and may be separated from its aqueous solution by
means of chloride of calcium. It is neutral to test-paper, but acquires
acidity on exposure to air, in consequence of the absorption of oxygen and
the formation of acetic acid, a change which is very rapid under the influence
of platinum-black {C^^fi^-\-0^=G^B.p^,B.O). Heated with dilute nitric
acid, it is also acetified, and nitrous acid is formed. With another atom of
oxygen, it forms aldehydic acid (C^H^Og). An aqueous solution of aldehyde
heated with oxide, or a salt of silver, reduces the metal in the form of a bril-
liant film, and aldehydate of silver is found in solution {2AgO-\-C^fifi=
AgOjC^HPg+Ag). This result and the odor are the best tests of its pre-
sence. Aldehyde is found in the distillation of wines dissolved in the alcohol.
When its vapor is passed over a heated mixture of hydrate of potassa and
quicklime, acetate of potassa is formed, and hydrogen gas disengaged. The
term aldehyde is now applied to analogous compounds obtained from the
imperfect combustion of other alcohols. They are named after the acids

590 CHLORAL. CHLOROFORM.

which they produce, as the result of the absorption of 2 atoms of oxygen ;
hence the compound above described is sometimes called acetic adelhyde.

Chloral (C^ClgHOJ

Is a transparent, colorless, oily liquid, obtained by the reaction of dry
chlorine on anhydrous alcohol and by subsequent distillation. Its sp. gr. is
1-5; its boiling point 206°, and the density of its vapor is 5. It has an
irritating odor, is soluble in water, and its solution is not affected by nitrate
of silver. It is sometimes called chloric ether, a name which is also applied
to hydrochloric ether, chloride of hydrocarbon, and to a solution of chloro-
form in alcohol.

Chloroform (C2HCI3). ^

Chloroform may be procured by distilling chloral with lime and water, or
with solution of potassa. It is more readily obtained by distilling in a capa-
cious retort, a mixture of 1 part of alcohol with 24 parts of water and 6
parts of dry chloride of lime. The temperature should not exceed 180°.
The distillate consists of water and chloroform, and the process is arrested
when about two parts have passed over. The chloroform is in the lowest
stratum. It is separated from the water, shaken with sulphuric acid to purify
it, and rectified by a second distillation. In addition to chloroform, the pro-
ducts of this reaction are formate of lime, chloride of calcium, and water.
The process recommended in the British Pharmacopoeia is as follows :
Chloride of lime 10 pounds, rectified spirit 30 fluidounces, water 3 gallons,
slaked lime a sufficiency. The water and spirit are mixed and brought to a
temperature of 100° in a large retort. The chloride of lime mixed with five
pounds of the slaked lime is then added. A heat sufficient to cause distilla-
tion is applied, the product being condensed in the usual way. So soon as
distillation is well established, the heat is withdrawn and the process is
stopped, when the product in the receiver amounts to 50 ounces. This is
well washed in successive quantities of water, agitated with an equal volume
of sulphuric acid, and afterwards by a water-bath distilled off 2 ounces of
chloride of calcium mixed with half an ounce of slaked linie, which should be
perfectly dry. The product, which is pure chloroform, should be preserved
in a cool place in a well-stopped bottle. Wood-spirit may be employed
instead of alcohol, but the product is not so pure.

Properties. — Chloroform is a colorless, transparent, heavy, neutral liquid,
having, when its vapor is diluted, a pleasant odor resembling that of apples.
It has a sweet taste, slightly pungent. Its sp. gr. , when pure, is 1 -5 : it
boils at 140°, and the density of its vapor is 4 2. It is not readily inflam-
mable, but it may be burnt on bibulous paper, producing a greenish colored
smoky flame. When its vapor is respired, more or less diluted with air, it
soon induces insensibility, in the same way as, but more rapidly and effec-
tually than ether-vapor ; hence its use in the performance of surgical opera-
tions and in obstetric practice as originally suggested by Dr. Simpson, of
Edinburgh. {Pharm. Journ., vii. 277 and 313.) When a few drops of
chloroform are placed upon the hand, it speedily evaporates, and produces a
great degree of cold. If pure, it leaves no residue and no unpleasant odor.
When poured upon water, the greater part of the liquid sinks in globules,
which are of a milk-white appearance if the chloroform is not perfectly free
from alcohol. Chloroform is so little soluble in water, that three drops
added to nine ounces of distilled water, and well shaken, did not wholly dis-
appear, although they imparted a strong odor to the liquid. With alcohol
and ether it readily forms transparent solutions, which burn with a yellow
smoky flame. Water added to the alcoholic solution causes a separation of

CHLOROFORM. 591

the chloroform, which falls to the bottom of the vessel. If to the alcoholic
solution potash is added, and the mixture boiled, the chloroform is resolved
into chloride of potassium and formate of potash.

Chloroform readily combines with oil of turpentine, and with sulphide of
carbon. It easily dissolves camphor, and the solution burns with a yellow
smoky flame, having a green edge or border. It speedily softens and dis-
solves caoutchouc. It dissolves wax, cantharidine, amber, copal, and all the
common resins. With red or black sealing-wax it makes a strong varnish.
It has but a slight solvent action on sulphur and phosphorus. It dissolves
iodine and bromine, forming deep red solutions. A few drops of chloroform
shaken with an aqueous solution of iodine or bromine will remove either of
these bodies, and the chloroform falls to the bottom of the vessel, acquiring
a red color, the depth of which is proportioned to the quantity of either sub-
stance present. Chloroform is usefully employed either alone or in combi-
nation with ether, as a solvent for many alkaloids. 100 parts of chloroform
dissolve of veratria, 58*49 parts: quina, 57'47: brucia, 56"70: atropia, 51*19:
narcotina, 31-17 : strychnia, 2019 : cinchonia, 4*31, and of morphia, 0-57.

Chloroform floats on concentrated sulphuric acid, which is only darkened
by it at a boiling temperature, when the chloroform is rapidly dissipated in
vapor. It slowly decomposes nitric acid in the cold, but at a high tempera-
ture deoxidation is rapid, and nitrous acid is abundantly evolved. It scarcely
afi'ects a solution of iodic acid, which acquires, after a time, only a faint pink
color. It has no bleaching properties : it does not decompose iodide of
potassium, nor does it dissolve gold, either by itself or when boiled with
concentrated nitric acid. When nitrate of silver is added to it, there is no
precipitate, the chloroform merely acquiring that milky opacity which it has
when dropped into distilled water. The chlorine is therefore not in the same
state of combination as in the soluble chlorides of mineral compounds.
Chloroform has no action on a salt of copper until a solution of potash is
added in excess and the liquid is boiled. The copper is then reduced to the
state of suboxide, as if glucose was present. There is, however, this marked
difference : in the presence of chloroform potash does not redissolve the pre-
cipitated oxide of copper, so as to form the clear blue solution which is pro-
duced when grape-sugar is present.

The alkaline metals potassium and sodium have no action upon pure
chloroform. It may be distilled over them without undergoing any change.
If, however, to a mixture of chloroform and sodium a small quantity of
water is added, the nascent hydrogen produced brings about a chemical
change. The temperature rises, the sodium burns, and, after a short time,
with explosive violence, a large amount of carbon being set free. The
liquid, which is blackened by the amorphous carbon, is strongly alkaline
from the presence of soda, and is copiously precipitated by nitrate of silver,
showing the production of a soluble chloride of the metal — the oxide being
readily separated from it by nitric acid. Two of the constituents of chloro-
form— chlorine and carbon — are thus proved to be present in this liquid.

Chloroform is occasionally observed to undergo spontaneous changes —
chlorine and hydrochloric acid being set free. It appears that a free ex-
posure to light favors this decomposition. It also takes place more readily
when a little moisture is present than when it is quite free from water.
Alcohol added to it in small quantity tends, on the other hand, to preserve it.

When the vapor of chloroform is passed over copper or iron, heated to
redness, it is decomposed, a metallic chloride results, and carbon is deposited ;
but, according to Liebig, no inflammable gas is evolved. When the vapor
of chloroform is passed through a glass tube heated to full redness, it is re-

593 PYROXYLIC SPIRIT OR METHYLIC ALCOHOL

solved into chlorine and hydrochloric acid, but no carbon is deposited. On
this is founded a process for its detection in the blood and other liquids.

Chloroform is represented by the formula CgHClg, and is considered to be
a terchloride of the compound radical formyle (C^H). When the 3 atoms
of chlorine are replaced by 3 of oxygen, formic acid is produced : hence the
name chloroform. The liquid contains 89 per cent, of chlorine, but, unlike
an ordinary chloride, it gives not the slightest indication of the presence of
this element by the usual test.

Methylic Alcohol (C^Hfi^).

This compound has been long known under the name of Wood-spirit,
Wood-naphtha, or Pyroxylic spirit. It derives its present name from vidv,
wine, and v-kti, wood.

It is not a product of fermentation, but it is produced in the destructive
distillation of wood. In this process there is formed, besides tar, acetic
acid, and other products, a variable portion, but not amounting on an
average to more than about 1 per cent, of an inflammable and volatile
liquid. This may be separated, to a certain extent, from the water and
acetic acid, by distillation and separation of the first products ; these, redis-
tilled and rectified over quicklime, afford the pyroxylic spirit, or methylic
alcohol of commerce. If it contain ammonia, it should be neutralized, by
sulphuric acid, previous to its last rectification.

To obtain perfectly pure pyroxylic spirit, an excess of chloride of calcium
is added, and the mixture is distilled in a water-bath so long as any volatile
matter goes over. A compound of wood-spirit with chloride of calcium re-
mains in the retort, to which a quantity of water, equal to that of the original
spirit, is added, and the distillation is then continued. The product which
is now obtained, and which is pure pyroxylic spirit diluted with a little
water, may be dehydrated by a final distillation off quicklime, or anhydrous
sulphate of copper.

Properties. — Pyroxylic spirit is the alcohol of the methylic series. When
pure it is a limpid colorless liquid, of a penetrating odor, partaking of that
of alcohol and acetic ether, with an aromatic taint which has been compared
to peppermint. Its taste is hot and pungent. Its sp. gr. at 60^ is 0*838.
It is highly inflammable, and burns with a pale flame resembling that of
alcohol. Its vapor will take fire at some distance from the liquid, and the
flame spreads with great rapidity. It boils at about 150° ; if heated in a
retort, even in a water-bath, the sudden escape of its vapor is troublesome :
this may be prevented by the presence of a little mercury, which equalizes
the distribution of heat. The density of its vapor is 1'125 (1*20 at 212°).
When pure it is not altered by exposure to air or light, but when subjected
to the slow action of platinum-black, it yields, together with other products,
formic acid ; not acetic acid, as is the case with alcohol. If pure it is quite
neutral, and mixes in all proportions with water, alcohol, and ether, without
becoming turbid ; it does not form a black precipitate with protonitrate of
mercury. Like alcohol, it is a powerful solvent for resins, and is now much
used in the form of methylated spirit. The odor of its vapor is disagreeable,
and*when breathed it produces nausea and headache. It rapidly deoxidizes
a- solution of permanganate of potash and of chromic acid, producing in the
latter case green oxide of chromium. When potassium or sodium is placed
on it, it undergoes decomposition, hydrogen is evolved without combustion,
and the liquid is rendered alkaline. When methylic alcohol is mixed and
distilled with four parts by weight of sulphuric acid, decomposition takes
place, and methylic ether, water, and carbonic and- sulphurous acid are
among the products. It is strikingly distinguished from ethylic alcohol by

METHYLATED SPIRIT. AMYLIC ALCOHOL. 593

the fact that a compound homologous to olefiant gas has not been produced
by the action of sulphuric acid upon it.

Chlorine acts less powerfully on pyroxylic spirit than on alcohol, and accord-
ing to Dumas and Peligot, heat is required to accelerate their mutual action :
it then gives rise to the production of two liquids of very different degrees
of volatility ; that which is least volatile forms a crystallizable compound
with ammonia. According to Kane, the action of chlorine on this spirit,
under the influence of light, is violent, and even attended by inflammation ;
in the absence of light, the gas is quietly absorbed under the abundant pro-
duction of hydrochloric acid, and a thick liquid is formed, composed of
CflHgOgCla. Chloride of lime acts upon pyroxylic spirit as it does upon
alcohol, and methylic chloroform is one of the products. Its solvent powers,
in regard to salts closely resemble those of alcohol, and it has been stated
that it may be substituted for alcohol in the preparation of fulminating
silver, although the action is less violent, and the product smaller in quantity;
but according to Dumas and Peligot, the product is really oxalate, and not
fulminate of silver ; so also it converts nitrate into oxalate of mercury. Sul-
phur and phosphorus are to a small extent soluble in it. It dissolves the
resins, and may be used as an excellent substitute for alcohol in almost all
varnishes ; indeed, its superior volatility renders it preferable ; but its offen-
sive odor is objectionable. It is a powerful antiseptic, and has been found
an effectual preservative of animal matter. Pyroxylic spirit has the formula
of C,H,Oa, or as hydrated oxide of raethyle of C,H30,H0, or MeO,HO.

Methylated Spirit. — A mixture of 90 per cent, of alcohol and 10 per cent,
of methylic alcohol, is much used in the arts and manufactures, as well as in
medicine and chemistry, as a substitute for rectified spirit.

Methyle Me(C2H3) is a gaseous body of a sp. gr. of r036. It is produced
by decomposing iodide of methyl with zinc. It forms an oxide analogous
to ether in composition. — Methylic ether, CgHgO. This oxide is a colorless
gas of an ethereal odor, and has a sp. gr. of 1'59. It burns with a pale blue
flame. In elementary composition it is isomeric with alcohol, for 2(C3H30)
are equal to C^HgOg. Methylic ether is procured by distilling 1 part of
wood-spirit with 4 parts of sulphuric acid. The gas may be collected over
mercury, and the carbonic and sulphurous acids mixed with it, may be
removed by potassa. Methyle forms a chloride, iodide, and bromide, as well
as various other compounds, with the oxacids, analogous to those of ethyle.

Pyroxanthine (CgiHgO^) is a yellow crystalline solid, which was dis^
covered by the late Mr. Scanlan, as a product of the reaction of potassa on
wood-spirit. It is insoluble in water, but is dissolved by boiling alcohoh
The crystals melt at 291°. Its most remarkable property is that of forming
a rich purple compound with strong sulphuric acid, which slowly becomes
blue and black.

Amylic Alcohol {O^^^fiy)

Amylic Alcohol, or Hydrated Oxide of Amyle (C,oHjj,04-HO ; or AylO)
has long been known under the name of oil of potato-spirit; it is i\\Q fusel-
oil of the Germans. It is now considered to be the alcohol of the amylic
series, the base of which is amyle (C,oH,i). It has hitherto been exclusively
obtained as a product of fermentation, especially from potato-brandy.
Balard {Erdmann and Marchand^s Journ., xxxiv. 123) found it, accompa-
nying cenanthic ether, in the volatile oil obtained from brandy ; it has also
been detected in the spirit afforded by the fermentation of beet-root treacle.
It> is abundantly obtained from corn-spirit, in the process of its rectification
upon the large scale (Medlock, Journ. Chem. Soc, i. 368). It is chiefly
produced during fermentation iu neutral or alkaline liquids, not in acid.
3»

594 • AMTLE. AMYLENE.

liquids : it is formed by the decomposition of the starch — hence its name,
amyJic alcohol. In wines containing tartaric and citric acids, or acid salts,
it is not readily formed. The presence of hops also prevents its production,
since it is not found in ale or beer. The high temperature at which it boils
renders it easy to separate other volatile liquids from it.

When potato-brandy is distilled, and after the greater part of the alcohol
has passed over, a milky liquid is obtained, which deposits the crude potato-
oil. It is similarly obtained among the less volatile products of the distilla-
tion of corn-spirit of all kinds. This crude oil is purified by washing it
with water, then drying it by means of chloride of calcium, and redistilling it;
the portion which passes over at about 268° or 270°, is pure amylic alcohol

It is a colorless liquid of a peculiar, nauseous, suffocating, and most per-
sistent odor. It has an acrid, hot taste ; it burns with a blue flame, but is
not very easily inflammable, differing strikingly from ethylic alcohol in this
respect. Its sp. gr. is OSIS at 70°; it boils at 270°; the density of its
vapor is 3-14. At 4° it forms a crystalline solid. It is sparingly soluble
in water, floating upon it like an oil, but dissolving in all proportions in
alcohol, ether, and in fixed and volatile oils. It dissolves iodine, sulphur,
and phosphorus. It is a good solvent of the alkaloid morphia, and deposits
it from a hot solution in well-defined prismatic crystals. It separates mor-
phia, when uncombined, from an aqueous solution. When acted upon by
oxidizing agents it yields Valeric or Valerianic acid. According to Ca-
hours, it is resolved when exposed to air, under the influence of platinum-
black, into this acid and water. Its formula is Q^^H^Jd^, or CjoHj^O-f HO.
When amylic alcohol is heated with sulphuric acid, it does not yield an
ether like ethylic alcohol. If it is decomposed, the mixture blackens, and
sulphurous and carbonic acids are evolved. When treated with a larger
proportion of sulphuric acid it does not produce a gas homologous with
defiant gas. It also differs from ethylic alcohol in its action on the ray of
polarized light. It exerts a rotatory power to the left, while alcohol does
not alter the position of the ray. It very rapidly discharges the color of
permanganate of potash by deoxidizing the permanganic acid. When so-
dium or potassium is placed upon it, hydrogen is evolved without combus-
tion, and the liquid which becomes alkaline, is speedily darkened on ex-
posure to air.

Amyle, Ayl (CjoH,,), has been isolated by Frankland {Journ. Chem. Soc,
iii. 30). He obtained it by the action of zinc-amalgam upon iodide of
amyle, under pressure. Amyle is a colorless pellucid liquid of an ethereal
odor and burning taste; cooled down to 18° it becomes thick and oily, but
does not solidify: its sp. gr. at 52° is 0-7704: the density of its vapor is
4-9062 (= 5 vols, carbon vapor, 4-1461 ; + 11 vols, hydrogen, 0-7601). It
boils at 310°. It does not ignite at ordinary temperatures, but on being
heated its vapor burns with a white smoky flame. It is insoluble in water,
but mixes in all proportions with alcohol and ether. It is not affected by
fuming sulphuric acid, but is slowly oxidized by fuming nitric acid, or by a
mixture of nitric and sulphuric acids, when it acquires the odor of Valerianic
acid. Amyle forms a hydride (C,oHjjH).

Amylene (CjoHjo). — When amylic alcohol is distilled with anhydrous
phosphoric acid, amylene passes over as a colorless oily liquid. It is lighter
than water; its boiling-point is about 102°. It is a hydrocarbon, isomeric
with olefiant gas and etherine ; but the density of its vapor is 5*5, which is
5 times that of olefiant gas ; each volume of it therefore contains 10 volumes
of hydrogen in combination with 10 atoms of carbon. Its vapor has been
used, but unsuccessfully, as a substitute for chloroform in anaesthetic surgery ;
it has caused death in several instances.

ETHER. ITS PRODUCTION. 695

CHAPTER XLVIII.

ETHER. OIL OF WINE. COMPOUND AND DOUBLE lETHERS.

Ether (CJlfl). Ethylic or Yinic Ether.

The term Ether is applied to a highly volatile liquid obtained by the
action of sulphuric acid upon alcohol This liquid is usually procured either
by distilling a mixture of sulphuric acid and alcohol, or by allowing alcohol
to drop gradually into the heated, and somewhat diluted acid.

Sulphuric acid, water, and alcohol, at a certain temperature, are necessary
for the production of ether. Concentrated sulphuric acid mixed with diluted
alcohol, or diluted sulphuric acid mixed with absolute alcohol, will equally
produce ether, provided certain proportions are observed, and a certain
temperature is maintained. The following process has been found to yield
satisfactory results : A mixture of 8 parts by weight of concentrated sul-
phuric acid, and 5 parts of rectified spirit of wine of sp. gr. 0'834, is intro-
duced into a large flask, connected with a proper condensing apparatus and
receiver, and the mixture is heated by means of a lamp until it attains a
temperature of 300°. The rectified spirit is then allowed to drop into the
heated mixture through a long funnel, and by adjusting its quantity on the
one hand, and regulating the degree of heat on the other, the temperature
of 300° is maintained as steadily as possible, taking care at the same time
that the liquid in the flask is kept in rapid ebullition. Under these circum-
stances the bulk of this liquid may be maintained unchanged for several
hours, and every drop of alcohol which falls into it is instantly converted
into ether and water, the mixed vapors of which pass through a tifce into a
condenser. The receiver is ultimately filled with water and ether, the latter
floating upon the former.

The principal point to be attended to in this process, is the maintenance
of a steady temperature at or about 300°, and of rapid or even violent ebul-
lition. The limits of the ether-producing temperature are between 260°
and 310°, and the success of the operation is well insured by the use of oil
of vitriol and spirit of wine, in the above proportions and of the described
strength. If more alcohol, or a weaker acid be used, so as to occasion the
boiling-point to fall below 260°, little else than unchanged alcohol distils
over ; and if, by the employment of too much oil of vitriol, the boiling-point
rises up to or above 320°, in place of ether, oil of wine and olefiaut gas are
generated, together with variable quantities of other products.

The proportions recommended by Mitscherlich are, 100 parts of concen-
trated sulphuric acid (which already contains 18-5 of water) diluted with
20 parts of water, and mixed with anhydrous alcohol, in the proportion of
50 parts to every 100 of concentrated acid. To this mixture heat is ap-
plied, and it is kept boiling until the thermometer within the flask indicates
284° : two strips of paper are then pasted upon opposite sides of the flask
containing the mixture, to indicate exactly the bulk of its contents, by
showing the level of the liquid within it ; alcohol is then allowed to flovv in
by a funnel-tube, the supply being so regulated as to maintain the boiling-
point at 284°. The temperature for etherification, according to Mitscher-
lich, is between 284° and 302° The distillate obtained by this process,

CM RECTIFICATION 'OP ETHER. WASHED ETHER.

separates into two parts, the lighter stratnm being ether with a little alcohol
and water ; and the heavier, water with a little alcohol, and ether. If the
process has been carefully conducted, the weights of the water and ether
exactly correspond to that of the alcohol consumed. In an experiment on
a large scale, the proportions obtained in the distillate were 65 ether, 18
alcohol, and 17 water. Careful manufacturers obtain from 100 parts of rec-
tified spirit, containing 76 parts, by weight, of absolute alcohol, 60 parts of
ether, of the sp. gr. 0 727 ; according to calculation, they should obtain
58 parts of ether of 0 '724.

The ether of commerce almost always contains alcohol, which materially
affects its density ; sometimes it also contains water, which is the case with
what is termed washed ether ; and if ether has been long prepared, it is often
slightly acid, and leaves a peculiar odor when rubbed upon the hand. In
order to procure from the distillate perfectly pure ether, it must be well shaken
in a close vessel with about twice its bulk of water, and allowed to separate
npon the surface of the mixture ; it is then poured off, and a suflScient quan-
tity of well-burned lime added to it, by which the water which it had
acquired by the agitation, is abstracted. The mixture of ether and lime is
then distilled by a water-bath, care being taken to prevent all escape of
vapor, and to keep the condensing-receivers cold : the first third that distils
over may be considered as pure ether, free from alcohol and water. Com-
mercial ether may be purified by agitating it with milk of lime, and then
distilling it from a water-bath by a gentle heat ; the first distillate is then
shaken with water to separate alcohol, and the resulting aqueous either sub-
sequently dehydrated by distilling it off quicklime, chloride of calcium, or
anhydrous sulphate of copper.

The chemical changes which take place in the production of ether have
been variously described. The alcohol is entirely resolved into ether and
water {GJifi^=Gfifi-{-HO), but sulphuric acid does not operate by sim-
ply abstracting the elements of water, since ether is equally produced at the
proper temperature (284° to 302*^) by the reaction of diluted sulphuric acid
on absolute alcohol. One theory assumes that by the admixture of sulphuric
acid and alcohol in certain proportions, Sulphovinic acid is produced ; and
that at a certain temperature, this acid is simply resolved into ether and a
mixture of sulphuric acid and water. Sulphovinic acid has been regarded
by Liebig as a bisulphate of alcohol (C4Hg022S03), and by Regnault as a
bisulphate of ether with 2 atoms of water (C,H50,2S03 + 2HO). Which-
ever view is adopted, it is obvious that this compound contains all the ele-
ments necessary to the production of ether, when the mixture is exposed to
the temperature required for its decomposition. The researches of Graham
have, however, proved that the production of sulphovinic acid is not neces-
sary to the formation of ether. When a mixture of oil of vitriol and alcohol
is exposed in a sealed tube to a temperature ranging from 284° to 302°, no
charring occurs, but the liquid divides itself into a light stratum which is
nearly pure ether, and a heavy stratum consisting of alcohol, water, and sul-
phuric acid {Journ. Chem. *Soc.,iii. p. 24). These results confirm the origi-
nal view of Mitscherlich, that alcohol is, under certain fixed conditions,
simply resolved into ether and water by a catalytic, or polymerizing, action
of sulphuric acid. The acid which remains in the retort is unchanged in
properties, and unaltered in quality. A certain proportion of acid is neces-
sary in the process, in order to maintain the liquid in the retort or flask at
the requisite temperature. Sulphuric acid exerts a similar catalytic action
on oil of turpentine : it splits this oil into two other hydrocarbons — terebene
andcolophene — one of which has a higher boiling point and a greater vapor
density than oil of turpentine. This product, as in the case of ether, does

PROPERTIES OP ETHER. 597

not form any combination with the acid. As an additional proof that ether
is produced independently of the conversion of alcohol into sulphovinic acid,
it may be stated that the proportions of alcohol and sulphuric acid, which
yield the greatest amount of sulphovinic acid, do not yield the largest pro-
portion of ether. One part of sulphuric acid to 6 or 8 parts of alcohol,
yields the largest quantity of ether and but little sulphovinic acid : the pro-
portion of sulphuric acid must be greatly increased, in order to produce sul-
phovinic acid.

Other acids act in a similar manner. Thus, .when alcohol is heated to a
high temperature with a concentrated solution of phosphoric acid, it is split
into water and ether. In this case the water is retained by the acid, and
when this is sufficiently hydrated, its decomposing action on alcohol ceases.
Certain chlorides and fluorides also produce this conversion. The anhy-
drous chloride of zinc dissolves to a great extent in alcohol. When this
solution is distilled, alcohol first passes over, and as the temperature rises,
ether and water are obtained as products in the receiver.

Properties. — Ether is a highly volatile, transparent, colorless, limpid liquid,
of a peculiar penetrating odor, and a pungent and sweetish taste. It is
highly exhilarating, and produces a remarkable species of intoxication when
its vapor is respired mixed with air ; by the proper management of the in-
halation, a continuous insensibility to pain may be maintained. This appli-
cation of ethereal vapor was at one time resorted to in the performance of
surgical operations ; but as an anaesthetic for breathing, the vapor of chlo-
form is now preferred. In the form of a fine spray, ether has been lately
much used as a local anaesthetic. Thus a jet of finely-divided ether directed
against a portion of the skin annuls sensibility so much that severe surgical
operations may be performed without causing pain. Ether is neither acid
nor alkaline ; it has a highly refractive power in regard to light, and is a
non-conductor of electricity. It should not redden litmus when pure. The
evaporation of this liquid produces intense cold. When a few drops of
ether covering a drop of water are blown upon by a blowpipe the water
freezes, in consequence of the rapid evaporation of the ether. The vapor
has been employed for the artificial production of ice on a large scale, the
evaporation of the liquid being accelerated by means of an air pump. In
vacuo this liquid boils at the lowest temperature. A mixture of it with
solid carbonic acid causes the thermometer to sink to — 166°. The sp. gr.
of ether varies greatly with the temperature. We found, at a temperature
of 60°, that absolute ether, washed and distilled over quicklime, had a sp.
gr. of 0-113. It is more commonly met with of a sp. gr. of 0720. This
liquid is so affected in its volume by temperature that 1000 parts at 96° are
reduced to 968-2 at 60°, and to 948' at 330.

At mean pressure, ether boils, according to Gay-Lussac, at 96 5. Ether
of the sp. gr. of 'T20 may be said to boil, under a pressure of 30 inches, at
98°. Upon this subject, however, authorities vary a little, in consequence
of variations in the density of the ether, and also of barometical pressure,
circumstances which easily influence the boiling-point of this liquid. Pure
anhydrous ether does not freeze. Faraday failed in congealing this liquid,
although he exposed it to a temperature of 166° below zero. {Phil. Trans.,
1845, p. 158.) The extreme volatility of ether renders it impossible to pour
it from one vessel to another without losing a portion by evaporation, and
its vapor, in consequence of its density, may be seen to fall from the liquid :
it is this which renders it so dangerous to expose ether near to, and espe-
cially above, the flame of a candle. The sp. gr. of the vapor, at mean pres-
sure and temperature, is 25860 in reference to air as=l. At the tempera-
ture of 21^o, 1 volume of ether gives 212 volumes of vapor. The density of

598 PROPERTIES OF ETHER.

the vapor may be well shown by clipping a §ock of cotton into ether, and
placing it within a glass tube of about an inch diameter, and 18 or 20 inches
long ; the vapor will descend and escape from the lower end of the tube,
where it may be inflamed by a lighted taper, but none rises to the upper end
of the tube. If the lower end of the tube be drawn into a point and bent
upwards, the ether vapor may there be burned in the manner of a gas-light.
The vapor of ether, poured from a wide-mouthed bottle through a long
funnel, will readily fall, and, when ignited, burn at the end of the funnel. If
two or three drachms of eth^r are placed in a quilled receiver on a stand,
and the vessel is slightly inclined, the ether vapor will fall out of the long
narrow tube, and may be burnt like a jet of gas. Its density is shown by
depressing the tube, when the flame will be much increased. If raised, the
flame is diminished, and ultimately extinguished. This proves the gravi-
tating power of the vapor. The elastic force of the vapor may be shown by
letting a drop or two of ether pass into the vacuum of a barometer, when it
instantly depresses the mercury several inches, more or less according to the
temperature : hence also, when thrown up into gases standing over mercury,
it greatly augments their bulk. The great inflammability of the vapor may
be shown by boiling two or three drachms of ether violently in a Florence
flask, and igniting the vapor as it issues. It burns in a large column of
flame, with a light like that of coal-gas. Ether may be poured upon a large
surface of water, and its vapor burnt on this liquid in a sheet of flame.

When ether is inflamed it burns with a bright and slightly sooty flame,
leaving no residue, and producing carbonic acid and water (C4lI.O-fl20.=
4CO2+5HO). These products may be collected by holding the mouth of a
clean jar over a flame of burning ether. Water is condensed on the sides of
the jar, and carbonic acid is collected in the interior. When lime-water is
poured into the jar the presence of carbonic acid is proved by the liquid
becoming milky white. Aldehyde and water, as well as acetic acid, are
among the products of combustion at a low temperature (C4H5O + 2O —
C4H4O3+HO). By passing ether into a jar or bladder supplied with a jet
and stopcock, placed in warm water, its vapor may be burned at the jet.
If its vapor is mixed with about 10 volumes of oxygen, it explodes violently
by an electric spark ; but with smaller quantities of oxygen, or with air, this
combustion is only imperfect. If a little ether is poured into a bladder full
of air, supplied with a stopcock and jet, the mixture of air and ether vapor
may be burned at the jet with a brilliant flame, without risk of explosion.

Exposed to air and light, as in bottles which are frequently opened, ether
absorbs oxygen as strong ozone : it acquires bleaching properties, and is
less capable of dissolving fixed oils. As one of the results of this absorp-
tion of oxygen, acetic acid is produced. The presence of this acid is not at
first apparent, because it forms acetic ether, but it gives to the ether a
peculiar odor, and in time it becomes acid to tests. Ozonized, or, more
correctly, antozonized ether may also be produced by pouring a quantity of
liquid ether into a glass jar, and when the vapor is thoroughly diffused with
air at the mouth of the jar, introducing a bar of iron at a black heat and
moving it about for a short time. The temperature of the metal should not
be sufficiently high to inflame the vapor. Ozone is produced which is readily
detected in the air and escapes with it, while antozone enters into combina-
tion with the ether. Ozone is not soluble in ether, and the name given to
this liquid should therefore be antozonized ether. Besides its bleaching
properties, it oxidizes and destroys offensive effluvia, and is in this respect
a useful deodorizer. It sets free iodine from the iodide of potassium, but it
does not, like ozone, render precipitated guaiacum resin blue. When added
to chromic acid, or to an acid solution of diluted bichromate of.potash, it

PROPERTIES or ETHER. 59,9

bring^s out a beautiful blue color from the formation of perchromie aoid,
which is dissolved by the ether, and this liquid floats with it, forminj^ a blue
stratum on the surface. Ether not containing antozone slowly reduces the
acid chromate, forming green oxide of chromium. The decomposition is
accelerated by heat. Bodies containing ozone only do not produce per-
chromie acid under the circumstances. Another difference has also been
pointed out. It is well known that peroxide of manganese added to an
antozonide causes the evolution of ordinary oxygen, and the properties of
ozonide and antozonide are destroyed. A small quantity of peroxide of
manganese added to what is called ozonized ether, destroys its peculiar
properties, thus proving that it contains antozone, or positive oxygen. Dr.
John Day, of Geelong, Australia, and Dr. B. W. Richardson, have intro-
duced the antozonized ether as a valuable agent in medical practice. Ether
long kept in a bottle containing air generally acquires the properties of an-
tozone. When added to permanganate of potash the pink color is only
slowly discharged by pure and fresh ether; but if it contains antozone the
permanganate is very rapidly deoxodized and loses its color.

If ether vapor is passed over red-hot platinum wire, or if red-hot platinum
wire is plunged into a bottle of air containing a little ether vapor diffused in
it, the metal continues to glow, and acetic and aldehydic acids are produced.
When a stout rod of platinum, copper, iron, or glass, is heated short of
redness, and introduced into the mixture, ozone and antozone are produced
at the expense of a part of the oxygen.

The best method of preserving ether is to keep it in well-stopped bottles,
quite full, and in a dark place. In contact with alkaline bases, this conver-
sion of ether into acetic acid takes place more rapidly. Ether is soluble in
alcohol and chloroform in all its proportions, but has only a limited solubility
in water. Nine parts of water dissolve one part of ether. On this difference
is based the separation of alcohel from ether, as well as the detection of that
liquid in commercial samples. When a mixture of alcohol and ether is
shaken with water the mixture separates into two layers, each of which con-
tains the three liquids. The upper layer contains a large excess of ether,
the lower a large excess of water, with the greater part of the alcohol with
which the ether was mixed. By repeated washing, the whole of the alcohol
may be removed. Ether which has thus been washed retains about a tenth part
of water ; or, according to Liebig, 36 parts of pure ether dissolve one part
of water. From this it may be freed by distillation with quicklime, anhydrous
sulphate of copper or dry chloride of calcium. A mixture of alcohol, ether,
and ethereal oil is known under the name of Hoffmannh anodyne liquor, or
spirit of ether. Such a mixture is employed in photography as a solvent for
pyroxyline.

Ether dissolves a small quantity of sulphur (l-80th), which is not thrown
down by the addition of a little water; the solution smells of sulphuretted
hydrogen, and by slow evaporation deposits regular crystals of sulphur.
Ether dissolves n;iore than 2 per cent, of phosphorus (l-37th); the solution
when concentrated by evaporation, deposits crystals of phosphorus : it is
luminous in the dark when in contact of air, and if poured upon hot water
produces a brilliant column of luminous vapor. Exposed to air, this solu-
tion becomes acid, and phosphorus is precipitated when it is mixed with
water or alcohol ; i^ gradually deposits red phosphorus when exposed to
light. Ether does not dissolve potassa or soda, or their carbonates.

The fixed and volatile oils, many of the resins, caoutchouc, various forms
of extractive, the alkaloids, and some other vegetable principles, are more
or less soluble in ether ; hence ether is often employed in the analysis of
organic. products, as a means of separating their proximate principles from

6.00 CONSTITUTION OF ETHER. ETHYLE.

each other. When mixed with chloroform, its solvent power on certain
alkaloids is much increased. Such a mixture is employed as a solvent for
strychnia. Many metallic salts are soluble in ether, and especially the
chlorides of gold, platinum, iron, and uranium ; the property which ether
has of abstracting these salts from their aqueous solutions, has been adverted
to under the history of the respective metals. Potassium and sodinra are
converted into potassa and soda by contact with ether, and hydrogen is
disengaged without combustion, the metals floating in the liquid.

A small quantity of sulphuric acid added to ether produces no effect, but
a mixture of equal parts of ether and the acid blackens, and yields, on dis-
tillation, oil of wine, olefiant gas, acetic and sulphurous acids, and water ; it
leaves a resinous matter and charcoal. Anhydrous sulphuric acid decom-
poses ether, and produces, according to Liebig, " isethionic and althionic
acids, oil of wine, and sulphate and bisulphate of oxide of ethyle ; if heat
be used, these products are decomposed, and sulphate of oxide of ethyle, oil
of wine, water, and ether, together with acetic, formic, and sulphurous acids,
carbonic oxide, and olefiant gas, pass over." Heated with nitric acid, ether
yields, according to Liebig, carbonate, acetic, formic, and oxalic acids, as
well as aldehyde.

When a little ether is introduced into chlorine, the gas is absorbed, and
peculiar compounds result. When bubbles of chlorine are passed into ether,
they often cause inflammation, and when a small quantity of ether is poured
into a jar of gaseous chlorine, and a lighted taper is applied, hydrochloric
acid is formed, and carbon is set free, sometimes with explosion. Iodine
and bromine are soluble in ether, and gradually react upon and decompose
it. The solution of iodine in ether is dark brown, and soon gives rise to
the production of hydriodic acid. When ether is saturated with bromine,
and the mixture is left for ten or twelve days, it is entirely decomposed; the
products are, 1, formic acid(?); 2, hydrobromic acid ; 3, hydrobromic ether;
4, heavy bromic ether ; 5, bromal. The first four products may be separated
by distillation, and the bromal remains (C^HOjjBrg) : it may be purified by
mixture with water, and in the course of twenty-four hours crystals of hy-
drate of bromal are formed. When this hydrate is boiled with an alkaline
solution, 2 atoms are resolved into 2 atoms of formic acid, 2 of bromoform,
and 6 of water.

Composition. — The vapor of ether, when passed through a red-hot tube,
is decomposed : carbon is deposited, and water and aldehyde are among the
products. When the vapor is analyzed by passing it through red-hot oxide
of copper, the results furnish the following elementary composition : —

Carbon
Hydrogen .
Oxygen

Ether ... 1 37 100-00 1^ 2-5567

The specific gravity of ether vapor compared with air is 2 5573, and its
calculated density is in accordance with this result. Compared with hydro-
gen, the sp. gr. of ether vapor is 37 ; its volume equivalent is 1. If oxygen
is assumed to be 16, the equivalent of ether must be doubled. Its relations
to alcohol and other bodies would thus be disturbed, and the formulae for the
various ethers would be rendered unnecessarily complex.

Tests. — Ether may be identified by its odor and inflammability, as well as
by the color of its flame and the products of combustion.

Ethyle. — Ether is commonly regarded as an oxide of the compound radical
Ethyle (C^HJ. With an atom of water it forms alcohol, which is therefore a,

Atoms.

Weights.

Per cent.

Vols.

Sp. gr.

. 4

... 24 ..

. 64-87 .

.. 4 ..

. 1-6584

. 5

5 ..

. 13-51 .

.. 5 ..

. ^-3455

. 1

8 ..

. 21-62 .

.. h -

. 0-5528

HEAVY OIL OP WINE. NITRIC ETHER. 601

hydrated oxide of ethyle. Ethyle combines with the halogens and ether, as
its oxide combines with the oxacids. Dr. Frankland isolated this radical
by the action of zinc on iodide of ethyle. {Journ. of Chem. Set., ii. p. 263.)
He describes it as a colorless gas, of a slightly ethereal odor, burning with
a brilliant white flame, and of a sp. gr. =200394. It is not liquefied at 0°,
under atmospheric pressure, but under a pressure =225 atmospheres, at
37°, it becomes a colorless, transparent, mobile liquid ; it is absorbed by
alcohol, which evolves it again on dilution. In Frankland's experiments,
the theoretical result of the decomposition of the iodide of ethyle, namely,
C4H5l4-Zn = ZnI + C4H„ was never attained, but a portion of the ethyle
was always resolved into elayle and methyle, CJH^^C^H^+C^B.^', so that
the action of the zinc upon the iodide of ethyle, at the temperature required
for its decomposition, namely 302°, may be represented as follows : —

2[C,H3l] + 2Zn, = 2ZnI, + C,H,+ CA+C,H3.

The anhydrous does not readily pass to the state of hydrated oxide of
ethyle. Thus, ether may be shaken with water, and kept long in contact
with this liquid, without producing alcohol. The dehydration of the oxide
(alcohol) is also effected in a remarkable manner by sulphuric acid, and this
acid does not combine with the oxide as it is produced. The anhydrous
oxide and water are distilled over together.

Heavy Oil op Wine. Sulphatic Ether. Oleum ^thereum. — When the
distillation of a mixture of sulphuric acid and alcohol is carried beyond the
point at which ether ceases to come over, a liquid, looking like oil, is ob-
tained, to which the above names have been applied ; when washed, it has a
bitter aromatic flavor. It has long been known under the name of oil of wine,
and was formerly regarded as analogous in composition to the volatile oils.

It may be prepared by distilling a mixture of 1 part of alcohol and 2-5
parts of concentrated sulphuric acid. The oil in the distillate is separated
from the water, and is purified by placing it in vacuo with two vessels, the
one containing hydrate of potassa, and the other strong sulphuric acid. Its
formula is C^HjOjSOg. It is therefore, in constitution, a sulphate of the
o^ide of ethyle, or sulphuric ether. The oil is of a yellow color, has a pene-
trating aromatic odor, and a sp. gr. of 1133 ; it is soluble in alcohol and
ether, but not in water. It cannot be distilled without decomposition ; at
270° it is converted into alcohol, sulphurous acid, and olefiant gas. When
long boiled with water, it is converted into sulphovinic acid and alcohol,
and an oily hydrocarbon which floats on water. This is light oil of wine, or
etherole; it resembles olive oil, and has a sp. gr. of 0-920.

Numerous ethers are produced by the action of a variety of acids upon
alcohol. These are called compound ethers.

Hyponitrous Ether.— iWVroMS Ether (C^HPjNOg).— This is procured
by mixing and carefully distilling, at a gentle heat, equal weights of alcohol
(0-820) and of nitric acid (1*30). One hundred parts of this mixture yield
10 parts of rectified ether. It is a highly volatile inflammable liquid, sp. gr.
0-947 at 60° : it boils at 70°, and its vapor has a sp. gr. of 2 627. It is
neutral, but by exposure to light, in contact with water, it becomes acid.

Nitric Ether (C^H^O.NOs).— A mixture of nitric acid and alcohol, when
heated, or even allowed to stand, invariably produces hyponitrous ether, with
a violent action. In order to prevent the formation of hyponitrous acid,
about one per cent, of nitrate of urea is added to equal weights of nitric
acid (1-4) and alcohol (0 842). The mixture is gently heated, and seven-
eighths are distilled over. The nitrate of urea is unchanged, and may be
repeatedly used. The rectified product has an agreeable odor, distinct from

602 ACETIC, HYDROCHLORIC, AND HYDRIODIC ETHERS.

that of hyponitrous ether. It has a sweet and slightly bitter taste : its sp.
gr. is ril2, and it boils at 185°. It is insoluble in water, but soluble in
alcohol, from which it is again precipitated by water.

Acetic Ether (CJlfl,Ac). — When an acid does not directly resolve
alcohol into water and ether, the conversion may be effected, and a new ether
produced by distilling one of the salts of the acid with alcohol and sulphuric
acid. Thus three parts of acetate of potassa, three of absolute alcohol, and
two of sulphuric acid, distilled to dryness, yield a product which, when
rectified by redistillation with sulphuric acid and by the action of lime and
chloride of calcium, is called acetic ether. This liquid boils at about 165°.
Its sp. gr. is 0'89, and the density of its vapor is 3 03. It has a peculiarly
agreeable odor, and appears to exist in and contribute to the odor and flavor
of certain wines. It burns with a yellowish flame, and acetic acid is de-
veloped by its combustion. Water dissolves about one-seventh of its weight
of this ether, and the solution is decomposed by potassa, giving rise to an
acetate and to alcohol. Ammonia has no action upon it. It is soluble in
all proportions in alcohol and in ether.

Hydrochloric Ether (C^H^CI). — Muriatic Ether. Chloride of Ethyle. —
This may be obtained by subjecting to careful distillation a concentrated
solution of hydrochloric acid gas in alcohol ; or a mixture of 1 part of
alcohol, 1 of sulphuric acid, and 2 of fused and finely-powdered chloride of
sodium. In all these cases the ether passes over : it should first be trans-
mitted into warm water, by which its adhering acid and alcohol are abstracted,
and its vapor may then be condensed by conducting it through a cold tube,
and receiving it in a bottle surrounded by ice and salt. Hydrochloric ether
is a limpid, neutral, colorless liquid, of a peculiar penetrating odor, and a
sweetish acrid taste. Its specific gravity is 0-874 at 42°; it boils at about
60°; and the specific gravity of its vapor is 2'219. When cooled down to
— 10°; it crystallizes in cubes. It is soluble in about 50 parts of water, and
in all proportions in alcohol and ether. It dissolves sulphur and phosphorus,
as well as the fixed and volatile oils.

Iodine and Bromine produce with alcohol, ethers analogous to the hydro-
chloric. They have the formula C4H5I and C^H^Br.

Hydriodic Ether, or Iodide of Ethyle, is obtained by the distillation of a
mixture of alcohol, iodine, and phosphorus. It is a colorless liquid of a
penetrating ethereal odor, of a sp. gr. of 1*94 at 61°. It boils at 148° ; the
sp. gr. of its vapor is 5 '4. It is not inflammable, but when dropped on red-
hot charcoal it gives off a purple vapor. It is decomposed at a red heat.
It is dissolved by alcohol, but not readily by water. This liquid possesses
an interest as being the source of the compound radical ethyle. Hydrohromic
Ether is prepared by a similar process. Fluorine, cyanogen, sulphocyanogen,
and even sulphur, form compounds with ethyle of the nature of ethers. These
are obtained by various complex processes. Hydrosulphuric Ether or Mer-
captan (C^H^S-f HS), is procured by distilling a concentrated solution of
hydrosulphate of sulphide of barium with sulphovinate of baryta. It is a
colorless liquid, of a strong odor, resembling that of garlic. It is not very
soluble in water, but is dissolved by ether and alcohol in all proportions.
Its sp. gr. is 0*832 : it boils at 97°, and the density of its vapor is 2"14.
It has a powerful affinity for mercury : it decomposes corrosive sublimate,
forming mercaptide of mercury : hence the name mercaptan (mercurium
captans).

Other ethers are formed by the combination of oxide of ethyle with many
anhydrous acids — e. g., the perchloric, silicic, boracic, oxalic, carbonic,
arsenic, cyanic, hydrocyanic, formic, benzoic, succinic, tartaric, and citric
acids. These aye for the most part procured by distilling a mixture of

CELLULOSE. WOODY FIBRE, OR LIGNINE. G03

alcohol and hydrochloric or sulphuric acid with the respective acids of their
salts.

Double ethers are those in which the elements of ordinary ether are com-
bined with the ethers of the amylic or methylic series.

Compound ethers are found ready formed in plants and fruits, and to the
presence of these, their odors and flavors are frequently due. They may he
artificially imitated. When dissolved in a large quantity of alcohol, these
ethers lose their offensive odor, and form various essences for giving perfume
and flavor. l^h\i% pine- apple oil is butyric ether, 041130,0811703. It may be
produced by agitating two parts of alcohol and two parts of butyric acid
with one part of sulphuric acid diluted with its bulk of water. On standing,
the butyric ether rises to the surface and may be purified by agitating it
with water in which it is almost insoluble. It is afterwards deprived of any
water by chloride of calcium. It is the alcoholic solution of the ether which
forms what is called pine-apple oil. It is also a product of the reaction of
alcohol on impure glycerine. Essence of melons is ether combined with one
of the acids of cocoa-nut oil, and essence of quinces is pelargonic ether,
O^HgOjOjgH^^Oa. This is considered to be identical with oenanthic ether,
which gives the bouquet to wine (page 579). Pear-oil is an alcoholic solu-
tion of the acetate of amyl, OjoHj^O.C^HgOg, and apple-oil is the valerianate
of the same radical, 0^oH„0,Cj^Hg03. The oil of winter-green is the sali-
cylate of methyl, C2H30,C,,HA-

CHAPTER XLIX.

CELLULOSE. PYROXYLINE. WOOD. COAL. BITUMEN. PRO-
DUCTS OF THE DECOMPOSITION OF WOOD AND COAL.

Woody Fibre. Cellulose. Lignine.

The term cellulose has been applied to the pure base of woody fibre.
The varieties of woody matter differ in color, texture, and hardness or
toughness ; but when freed from various foreign matters, they leave a white
translucent residue, insoluble in water, alcohol, and ether, and convertible,
by sulphuric acid, into a substance having some of the characters of starch,
and then into dextrine or sugar. Oertain piths, linen, cotton, filtering
paper, and some other allied substances, are nearly pure cellulose. Weak
acids and aliialine liquids, and a weak solution of chlorine, have scarcely
any action on this principle, but they change, combine with, or decompose
it when concentrated, and some of these reactions are very important : when,
for instance, clean linen or cotton rags are acted on by cold sulphuric acid,
a magma is formed, which if immediately saturated by carbonate of baryta,
or lead, yields insoluble sulphates, together with soluble sulpholignates.
These salts appear identical with those of the sulphoglucic or sulphosaccharic
acid, derived from the action of sulphuric acid on glucose. This magma is
also blued by iodine. If it be much diluted and boiled, it yields dextrine,
and ultimately glucose. By this action of sulphuric acid upon paper, a useful
material now known as vegetable parchment, is obtained. It is prepared by
steeping thick unsized paper in a mixture of equal parts of sulphuric acid
and water, at a temperature of BO'^y then washing it well in cold water and
drying it. It is translucent, tough, and nearly impermeable to water, form-

604 PYROXYLINE. GUN-COTTON.

ing a useful substitute for common parchment or vellum. The following is
another method of preparing this parchment : two parts, by measure, of the
strongest sulphuric acid are mixed with one part of water. These propor-
tions are material : if the acid is weaker, the fibre of the paper is converted
into gum, if stronger it is corroded. White blotting-paper is thoroughly
soaked in the mixed acid and water, and immediately removed. It is then
transferred to a large quantity of water containing a little ammonia, and
after thorough washing it is dried. In this conversion the fibre undergoes
no chemical change. The molecular condition of the paper is simply altered
by the pores being filled up. The influence of a slight increase in the water
may be thus shown. If the unsized paper is wetted in spots before it is
immersed in the acid mixture, the wetted parts are destroyed while the
remainder of the paper is parchmented. The substance is now put to many
important uses in the arts.

Pyroxyline. Gun- Cotton.

This remarkable substance, discovered in 1846 by Schoenbein, is prepared
by dipping clean carded cotton, well dried, into a mixture of 3 volumes of
nitric acid (sp. gr. 1-5) with 5 of sulphuric acid. The concentrated com-
mercial acids answer the purpose : the mixture is allowed to cool, and small
portions of cotton should be used at a time, and completely immersed, so as
to avoid elevation of temperature : in 10 or 20 minutes the cotton may be
withdrawn (the excess of acid pressed out), and thoroughly washed in water
containing a little ammonia; it is then cautiously dried, at a temperature
not exceeding 200^. 100 parts of cotton thus treated yield about 170 of
dry gun-cotton. Clean paper, the purer varieties of sawdust, and other
forms of ligneous matter, produce similar compounds. Pyroxylic paper is
remarkable for the intensity of its electricity when slightly rubbed. Well
prepared pyroxyline resembles the original cotton in appearance, but is more
harsh and brittle to the touch, and highly electric ; its extreme combusti-
bility is remarkable ; inflamed in the open air it flashes off without smoke,
smell, or residue ; it takes fire at about 325°, which is about 200° below the
temperature required for the ignition of gunpowder, and its combustion is
more rapid. In consequence of its whiteness it is not so easily inflamed by
a solar lens as gunpowder, unless it is tinged with indigo or carmine, or
covered with a little charcoal. Burned in a tube it produces red fumes,
having the odor of nitrous acid. When substituted for gunpowder in fire-
arms, the extreme suddenness of its explosion is apt to burst the barrel, but
it is a powerful projectile agent. For mining purposes it is preferable to
gunpowder, in producing less noxious fumes ; and it is not deteriorated in
damp air, or even (when subsequently dried) by immersion in water ; and ,
weight for weight, its explosive force is between 3 and 4 times greater than
that of gunpowder. The extreme rapidity of its combustion is well shown
by placing a flock of it upon a small heap of gunpowder, where it may be
exploded by a hot wire without kindling the powder. Exclusive of the traces
of nitrous acid above adverted to, prussic acid, aqueous vapor, carbonic
acid, and nitrogen, are the products of its combustion. Pyroxyline, as
above prepared, is insoluble in dilute acids ; it dissolves in methylic and
acetic ethers, and in acetone. It is very slightly soluble in mixtures of ether
and alcohol.

Gun-cotton for medical purposes is prepared by keeping the cotton for
about two hours in a mixture of 2 parts of powdered nitre, and 3 of sulphuric
acid ; after washing and drying, it is digested in a mixture of about 90 parts
of ether, and 10 of alcohol {Collodion). Spread upon silk this solution fur-
nishes a good sticking-plaster. A solution of potassa dissolves and decom-

GUN cotton: manufacture, properties. 605

poses gnn-cotton ; ammonia also dissolves it, and leaves it, on evaporation,
in a pulverulent form. Sulphuric acid dissolves pure gun-cotton and is not
discolored by it, unless it contains portions of unchanged cotton. It is
scarcely affected by cold nitric acid, but, if heated, nitrous acid vapor is
evolved ; and on adding water, a white inflammable powder falls, which re-
sembles that obtained by a similar process from a nitric solution of starch —
called xyloidine.

The production of nitrous acid by the combustion of pyroxyline may be
shown by exploding a portion on blue litmus-paper, or on starch-paper, im-
pregnated with a solution of iodide of potassium. The former is reddened,
and the latter acquires a deep-blue color. The production of prussic acid,
or a cyanogen compound, is shown by exploding a portion in a jar, and then
inverting over its mouth a watch glass moistened with a few drops of a solu-
tion of nitrate of silver. White cyanide of silver is speedily produced. Gun-
cotton is liable, when long kept, to spontaneous changes ; it becomes soft
and pasty, contracts greatly in volume, and the red vapors of nitrous acid
as well as the vapors of prussic acid are evolved. The solid residue con-
tains a principle which like glucose reduces oxide of copper in a solution
of potash. This has been ascribed by some chemists to the presence of pec-
tose. According to M. Abel the presence of a small quantity of carbonate
of soda in gun-cotton prevents these spontaneous changes in it.

The pyroxyline used in photography requires many precautions for its pre-
paration. Its qualities are materially affected by the proportions of the
acids; their sp. gr., the temperature of the mixture, and the period of time
during which the cotton is immersed. Mr. Nicol recommends the following
formula: Ten ounces, by measure, of sulphuric acid (1*840), and 5 ounces,
by measure, of nitric acid (1'370), are to be well mixed, and 2 fluidrachms
of water added. When the mixture has cooled to about 130°, place in it,
tuft by tuft, well pulled out, 5 drachms of clean cotton. Each tuft should
be penetrated by the acid, as it is immersed. The cotton should be kept
immersed ten minutes, then removed, washed, and dried. If it appear to
dissolve while immersed in the acids, this may be prevented by pressing the
cotton together with glass rods. We have found this compound to be very
soluble in a mixture of alcohol and ether. It leaves, on evaporation, a smooth
transparent film. It is not very explosive, but completely combustible. Thei
following is another formula : Powdered nitre, 925 grains, sulphuric acid
(1-8), 1389 grains. When the nitre is entirely dissolved in the acid, plunge
in, by separate portions, 62 grains of clean cotton. Immerse for ten minutes,
then remove and wash the product. Generally speaking, the longer the
cotton is left in the acid mixture, the less soluble it becomes. A sample of
gun-cotton prepared according to this formula, was preserved for five years in
a perfect state. It was very combustible and explosive when dry, and very
soluble in a mixture of ether and alcohol, forming a good collodion.

The composition of pyroxyline no doubt varies, according to the mode in
which it is prepared. There are at least four varieties known. In all cases
it must be regarded as the nitrite of an organic base. The formula for
photographic cotton is (C^Hie(NOJ,0.^). It is a substitution-compound in
which 4 atoms of hydrogen are replaced by 4 atoms of nitroUs acid. Accord-
ing to Pelouze and Fr^my {Chim. Organ., vol. i. p. 950), the formation of
pyroxyline is as follows : —

2(C,2H,oO,o) -f 5(N0,H0) = lOHO -f (^mH^O.s^SNO^)
Cellulose. Pyroxyline.

The composition of cellulose, or pure woody fibre, might be represented as

606 LIGNINE. WOOD. DRY ROT.

CgHsOg : but a higher equivalent is better adapted to its combinations, and
its most convenient formula is C^ll.^0^

LiGNiNE. Wood. — The varieties of wood have cellulose, as their basis,
with other substances superadded, giving special characters to the several
varieties. In some of the hard and white woods, these foreign matters are
nnimportant; but in others, as in the resinous, colored, and astringent woods
and barks, they materially affect their durability and uses. The average sp.
gr. of wood is 1-5, but it generally floats, in consequence of theair it includes,
though there are a few woods — such as guaiacum, ebony, and box — which
sink in water. Green wood includes from 30 to 40 per cent, of water; in its
ordinary state of dryness, it retains about 25 per cent. : but when artificially
dried, as when used for fuel, in. which case its humidity greatly diminishes
its heating powers, it should not retain more than 10 or 12 per cent.

The durability of woods depends upon their state of hardness, and upon
the extraneous matters, such as resin and tannin, which they contain ; but by
long exposure to air and moisture, they are all more or less liable to decay
{dry rot) in consequence chiefly of the presence of a nitrogenous principle
which seems to act as a ferment ; the attacks of insects and the growth of
fungi and lichens also contribute to these changes. This decay may be to a
great extent prevented, by imbuing the timber with certain oils, tars, oxides,
and salts, but especially with carbolic acid; and ropes, sailcloth, &c., may be
similarly treated. Alum, sulphate, and pyrolignate of iron, sulphate of
copper, corrosive sublimate, and chloride of zinc are some of the substances
which have been thus applied as preservatives; they act by combining with
the wood or fibre ; but when large dense pieces of timber are operated on,
there is a difficulty in causing them to be permeated by the solution. In
some cases this has been efl"ected by placing the wood and preservative liquor
in a vessel admitting of being exhausted, so that the interstitial air of the
wood has been pumped out, and the metallic solution forced in on restoring
the air's pressure. Another mode of effecting a more entire penetration, con-
sists in rendering the natural functions of the tree available : the force with
which the sap rises from the roots to the leaves, is well known, and accord-
ingly, if a tree in full leaf be cut through just above the root, and the cut
surface immersed in the metallic solution, this will be carried upwards and
transmitted even to the smaller branches. Even a hole bored into the body
of the tree, or a section into it by a saw, may be resorted to as means of pre-
senting an absorptive surface to which the protective liquor may be applied.
It has also been proposed to apply this system to coloring and perfuming
woods, by causing them to absorb colored liquors, or metallic solutions,
which by reacting upon each other would cause the deposition of colored
precipitates : Prussian blue, chromate of lead, tannate of iron, ferrocyanide
of copper, and other similar metallic colors, have thus been formed by double
decomposition in the ligneous texture, and it has been similarly pervaded by
certain essential oils. (Boucrerie, Ann. Ch. et Ph., Ixxiv. 113.) Silicious
solutions, and solutions of certain phosphates, have also been thus employed,
with the twofold object of preservation from decay and protection from fire.

Products of the Decay of Wood. — When wood is kept dry, or when sub-
merged in deep water, it is little prone to change. In dry mummy-cases, in
the roofs of some old buildings, in the piles of bridges and in submerged
forests, wood has remained for centuries in good condition ; but under the
protracted influence of air and moisture it undergoes a series of changes, the
rapidity of which, as well as the results, will depend upon the texture of
the wood and the quantity and nature of the foreign matters associated with
it. Some of these promote and others retard decay ; among the former,
certain azotized or albuminous matters are apparently most active. Car-

BITUMINOUS COAL. LIGNITE AND ANTHRACITE. 60T

bonic acid and water are always evolved during the decay of wood, and
a variety of intermediate compounds are among the solid products, more
especially the brown matter found in soils or mould, and to which the terms
geine, humus, and ulmine, have been applied. These or analogous com-
pounds are obtained by the action of alkalies upon several organic principles
including wood. They are compounds of carbon, hydrogen, and oxygen in
various proportions, and may be regarded as so many steps in those processes
of decomposition in which wood, by the loss of water and carbonic acid gradu-
ally passes into the modification of coal. These brown extractive matters
combine with alkalies, and have been described as geic acid (C^oHj^OjJ,
humic acid (C^oHj^O,.^), and ulmic acid (C^oH^^O^.^). The dark brown exuda-
tion on the barks of certain trees, and especially of the elm, contains a similar
substance, combined with potassa, and allied products have been found in
the ferruginous deposits of certain mineral waters, and have been termed
Crenic and Apocrenic acids.

Coal. — Pit coal and many of its allied products are obviously of veget-able
origin ; but the circumstances under which they have been formed, and
deposited in their present localities, are very imperfectly understood.

Lignite, as its name imports, generally retains its ligneous structure; some-
times it resembles indurated peat, and contains brown extractive matter and
resin. When heated, it exhaleaw, bituminous odor, and burns with a bright
flame. It is found in tertiary strata.

Bituminous coal constitutes our common fuel ; but there are many varie-
ties of it, differing in color and structure, in their manner of burning, and in
the quality and quantity of the gas and coke which they yield on distillation
(see p. 271). The geological position in which this coal occurs, is between
the New and the Old Red Sandstones, forming the coal-measures.

Cannel coal and Parrot coal are distinguished by their slaty and conchoidal
fracture, their clean dull surface, and by their yielding a large proportion of
gas of high illuminating power, and leaving about half their weight of coke.
There is a variety of coal intermediate between that which is highly bitumi-
nous and the anthracites, called steam coal and Welsh coal: it burns well,
does not cake, gives little smoke, and yields a porous coke. It is a useful
fuel for many closed stoves, when the draught is insufficient for the combus-
tion of anthracite.

Anthracite (av^pal, coal) is more difficult of combustion, yields little vola-
tile matter, and therefore burns without flame. Some of its varieties are
very compact, and split into small fragments when heated.

The essential ultimate constituents of coal are carbon and hydrogen ; but
it also includes oxygen, nitrogen, sulphur, and various mineral matters, con-
stituting the incombustible residue or ash, which is chiefly composed of sili-
cious matter and unburnt charcoal, with carbonate of lime and oxide of iron.
100 parts of several varieties of coal, previously dried at 212°, gave the fol-
lowing results. (Yaux, Journ. Chem. Soc, i. 328.)

Carbon
Hydrogen .
Oxygen
Nitrogen .
Sulphur .
Ash

Newcastle.
. 81-41
. 5-83
. 7-89
. 2-05
. 0-75
. 2-07

Staffordshire.

... 78-57
5-23

... 12.88
1-84
0-89
1-03

Wigan Cannel.
... 80-07 ...
5-53 ...
8-09 ...
2-12 ...
1-50 ...
2-70 ...

1-276 ...

Anthracite.
90-89
3-28
2-97
0-83
0-91
1-61

Specific gravity .

. 1-276

1-278

1-392

Approximate formula C27H,,02

C26H.0O3

C^oHgO

608 BITUMEN. ASPHALT. PETROLEUM. ROCK-OIL.

Bitumen, Asphalt, Petroleum. — These, and several allied substances,
are closely connected with coal, in reference especially to the products of
their destructive distillation. Many of the varieties of coal may be regarded
as carbonaceous matters impregnated with bitumen, and the Bituminous
Schists are earthy compounds, chieiy alumino-silicious, similarly impreg-
nated. The bituminous shales of Dorsetshire, and of Bathgate, near Edin-
burgh {the Torhane Mineral), leave little carbonaceons matter, and nothing
in the form of coke, but from 20 to 25 per cent, of earthy matter or ash.
When distilled in close vessels, their volatile products, on the other hand,
are very abundant, and vary in character and composition with the tempera-
ture to which they are subjected. If rapidly distilled at a high temperature,
gases of high illuminating power abound; if at a lower temperature, liquid
oily hydrocarbons in great variety are obtained, and among these, paraffine
and its congeners.

Asphalt, or Mineral Pitch, in its purest form, may be taken as the type
of the Bitumens : it occurs on the shores of the Dead Sea (the Asphaltic
Lake^, in Barbadoes and Trinidad, in Albania, and nearly pure at Coxitarabo
in South America. It formed a leading ingredient in the celebrated Greek
fire of the middle ages. Pure asphalt is black, or dark brown, has a slight
bituminous odor, a resinous fracture; sp. gr. 1 to TI ; it softens when
heated, and burns with a smoky flame. Itois insoluble in water, sparingly
so in alcohol, but abundantly in ether and in benzole. Asphalts and bitu-
mens of various degrees of purity, and from various sources, are used in
combination with lime, chalk, sand, &c., for pavements and cements. Two
of the proximate components of asphalt have been termed Asphaltene
(0«H3,0«) and Petrolene (C,oH,,).

Petroleum, Naphtha. Rock- Oil. Mineral Tar. (Cj^H^^). — Inflammable
oily bodies, issuing often in large quantities from fissures in connection with
coal strata, and in other localities, have been long known. The purer varie-
ties are nearly colorless, and burn without residuum {native naphtha). Others
are brown, and leave asphalt when distilled. The Burmese petroleum or
naphtha has long been celebrated : it issues from a sandy loam resting upon
bituminous shale and coal strata : it is used in lamps, and mixed with earth
for fuel. Enormous quantities of rock-oil have been lately imported from
the United States and Canada. In the former country, according to Mr.
Hunt, the wells are chiefly found in New York, Pennsylvania, and Ohio.
Those of Mecca (Ohio) have been sunk from 30 to 200 feet in a sandstone,
which is saturated with the oil. Of 200 wells which have been sunk, a dozen
or more yield from five to twenty barrels of oil daily. The wells of Pennsyl-
vania vary in depth from 70 to 300 feet, and the petroleum, or rock-oil, is
met with throughout. The oil varies considerably in color and thickness.
Its sp. gr. is from 0"830 to 0'890. The oil-wells in the United States are
for the most part sunk in the sandstones of the Devonian series ; but those
of western Virginia and southern Ohio rise through the coal-measures which
overlie the Devonian strata. In Canada the oil is found in shales and lime-
stones. At one of the Canadian wells the oil rises from a depth of 234 feet
at the rate of 25 barrels, or about 1000 gallons, per hour, and much of it is
allowed to run to waste from the inadequacy of the supply of barrels, and
of other means to store it. At another well the supply is alleged to have
poured forth about 70,000 gallons a day uninterruptedly, except when the
opening was plugged, for several months. A third well exists of similar capa-
city; and the other wells which require labor or machinery for pumping are
innumerable. The American rock-oil may be regarded as a compound of

COAL-TAR. NAPHTHA NAPHTHALINE. 609

various hydrocarbons boiling: at different temperatures, and possessing differ-
ent degrees of inflammability. Some of these oils evolve a vapor which is
exceedingly inflammable and dangerously explosive when mixed with air.
An act of the legislature prevents the storage of petroleum, except in limited
quantities, where it is proved that it is liable to give off a vapor at or below
100°, which will ignite on the application of flame and produce combustion
of the liquid. This kind of inflammable oil has been sold for the purposes of
burning in lamps, and owing to the evolution of inflammable vapor has led
to fatal accidents. An oil is easily tested by placing a portion in a beaker
immersed for a few minutes in water, at a temperature of 100°, and bring-
ing a lighted taper near the mouth of the beaker. If the vapor should
ignite, and cause the ignition of the liquid oil, it is exceedingly dangerous,
and it can hardly be regarded as reasonably safe, if it evolves an inflammable
vapor at this temperature, although the flame may not be communicated
to the liquid oil below. As a rule, all oils intended for burning should only
be capable of burning by the aid of a wick. All these mineral oils, when
subjected to fractional distillation, yield products more or less resembling
those similarly obtained from coal naphtha, and are available for similar com-
mercial purposes. A heavy inflammable liquid distilled from Petroleum is
known under the name of Kerosine.

Coal-tar, as produced in the gas-factories, is a very complex substance :
it is always alkaline, from the presence of ammonia : it contains aniline and
numerous other bases, as well as carbolic and acetic acids. When distilled,
fetid ammoniacal compounds pass over, and a hght oil {Coal naphtha), suc-
ceeded by small portions of a heavier oil (dead oil), containing a little
paraffine, and by naphthaline : the residuary pitch, or asphalt, is used for
common black varnishes. By a careful fractional distillation of the rectified
naphtha, the following products are obtained — 1, An oil of an alliaceous
odor, boiling between 150° and 160°; 2, an oil boiling at 170°, identical
with benzole, CjaHg ; 3, an oil consisting chiefly of toluole, C„Hg, boiling at
240° ; 4, an oil boiling between 240° and 290°, having the proportions of
Cumole, C,sHj2 ; and 5, an oil between 330° and 340°, and resembling
Cymole, CgoHj^ (Mansfield, Quarterly Journ. Chem. Soc./\. 252). Naphtha
therefore is a mixture of several apparently definite hydrocarbons. Amongst
them benzole is the most important.

Naphthaline (CgoHg). — In a pure state this is a white substance in lami-
nated crystals, obtained by subjecting coal-tar to distillation. It passes
over after the coal-oils, and is produced when the vapors of coal-tar are passed
through a red-hot tube. It may be purified by sublimation with powdered
charcoal. Naphthaline has a faint odor, which has been compared to that
of the narcissus, and a slightly aromatic taste; its sp. gr. is 1*05; it is
unctuous to the touch, and evaporates slowly at common temperatures ; it
fuses at about 176°, and crystallizes as it cools; it boils at 420°; the sp.
gr. of its vapor is 4*5. It burns with a lurid smoky flame. It is insoluble
in water, but alcohol, ether, and some of the oils dissolve it readily ; it is
deposited from its alcoholic solution in lamellar iridescent crystals. Tbe
alkalies have no action upon it.

When gently heated with sulphuric acid it produces a red crystalline com-
pound which when saturated with carbonate of baryta, yields insoluble sul-
phate, and a soluble sulphonaphthalate of baryta. The formula of sulpho-
naphthalic acid is supposed to be HO,C2oH7S,05- Naphthaline combines
with chlorine, producing two chlorides, Cj^HgCl.,, and CaoH^Cl,. the properties
and reactions of which have been studied by Laurent : it also combines with
39

610 BENZOLE. CARBOLIC ACID OR PHENOL.

bromine. From these chlorides and bromides a numerous series of substitu-
tion-compounds have been derived. By the protracted action of nitric acid
on naphthaline, naphthalic or pthalic acid is formed ^{'2{M0),C^^lfi^),
which when distilled with lime yields benzole and carbonate of lime. This
acid is also one of the products of the action of nitric acid on alizarine.

Paranaphthaline. — Under this terra Dumas and Laurent {Ann. Gh. et
Ph., 1, 187) have described a hydrocarbon resembling? naphthaline, but yield-
ing a vapor having the density of 6*78. Paranaphthaline is less volatile
than naphthaline, and, therefore, when coal-tar is distilled, it is among the
latter products. According to Reichenbach {Poggend. Ann., xxviii. 484),
paranaphthaline is a mixture of naphthaline and paraffine. The term anthra-
cene has been applied to paranaphthalilie, and it has been represented as
CgoHjg. Among the last portions of the distillation of coal-tar, a yellow
crystalline solid is found, fusing at 455°, and insoluble in most liquids ; it
has been termed chrysene, and its formula is said to be CiaH^ : it is accompa-
nied by a more fusible substance, pyrene =C3oH^.

Benzole (Ci^Hg) ; Benzine. — Benzole was first discovered by Faraday, in
the products of the destructive distillation of whale-oil ; and Mitscherlich
obtained it by heating benzoic acid with excess of hydrate of lime ; but it is
now procured from coal naphtha, the more volatile products of which when
cooled to 32°, deposit it in a solid form. It fuses at 40°, boils at 170°, and
burns with a very smoky flame. It is insoluble in water, but soluble in alcohol
and in ether ; it dissolves fats and oils, and is a useful solvent of wax,
caoutchouc, gutta percha, sulphur, and numerous resins.

When benzole is exposed to sunlight in contact with chlorine, it produces
a crystalline chlorobenzole, =Cj2HgClg; and a hromohenzole, =Ci4HgBrg, may
be similarly obtained. With anhydrous sulphuric acid benzole produces a
crystallizable compound, which, acted upon by water, yields sulphobenzide,
=013113803, in which therefore an atom of hydrogen is replaced by an atom
of sulphurous acid : suJphobenzolic acid, =012115803 -f HO, SO3 is at the same
time formed : but amongst these reactions, those with nitric acid are the most
interesting. If benzole is gradually added to red fuming nitric acid, gently
heated, there is a considerable action, and on diluting the product, a heavy
yellow oil separates, which is nitrobenzole, =(j^^fi^ \ it boils at 415°, and
may be distilled without decomposition ; it smells like bitter-almond oil, tastes
sweet, and is used by perfumers and confectioners under the name of essence
of Mirbane, or bitter almonds. When an alcoholic solution of nitrobenzole
is mixed with caustic potassa, and distilled, a red oily liquid passes over,
which deposits crystals of- azobenzole (O^^H^N) ; the liquid contains aniline.
By the action of a mixture of nitric and sulphuric acids upon benzole, a
crystalline product, binitrobenzole, is obtained, =:C^fifiJl^ci. I" these
derivatives of benzole, one and two atoms of its constituent hydrogen are
respectively replaced by one and two atoms of NO^ (p. 559). M. Berthelot
has succeeded in producing benzole synthetically from acetylene (O^Hj,
with which it is isomeric. In passing acetylene through a red-hot tube, he
obtained, by condensation, a yellowish-colored liquid, more than one-half of
which was benzole. He therefore regards benzole as triacetylene 3C^H2=
CjaHg. The fact is interesting, inasmuch as acetylene may be produced by
the direct union of carbon and hydrogen.

Carbolic Acid. Phenol, Phenyh'c, or Phenic Acid {C^^I{QO^,='RO,G^,^
H^O) — When those portions of the acid of coal-tar which distil over between
.300° and 400°, are mixed with a strong and hot solution of caustic potassa.

PARAFPINE. 611

a crystalline mass is obtained, which is resolved by the action of water into
a light oil, and a heavy alkaline liquid ; when the latter is neutralized by
hydrochloric acid, the impure carbolic acid separates in the form of a light
oil : it requires to be distilled off chloride of calcium, exposed to a low tem-
perature, and freed from the remaining liquid. The pure acid forms a color-
less deliquescent crystalline mass, which fuses at 95°, and passes into vapor
at 37 0°. It has a smoky odor, an acrid taste, and the antiseptic properties
of kreasote. It is much used as a deodorizer. It does not redden litmus,
but produces a transient greasy stain upon the paper. Its sp. gr. is 1062.
When heated in a sealed tube with ammonia it yields aniline and water :
CiA02+NH3=C,,H,N + 2HO). When carbolic acid is distilled with
perchloride of phosphorus, one of the results is chloride of phenyle (C^^Hfil),
a fragrant liquid, boiling at 277°, and a crystallizable phosphate of phenyle
is at the same time formed. A numerous class of substitutional phenylic
compounds, in which chlorine, bromine, and nitrous acid replace one or
more of the hydrogen atoms, has also been formed ; they mostly constitute
monobasic acids, and many of their salts are of a definite character.

Paraffine (CH) (parum affinis) was originally discovered by Reicben-
bach, among the products of the distillation of wood-tar, but it has more
recently been abundantly obtained from the oils derived from the distillation
of bituminous schists, and other bituminiferous minerals : it exists in large
proportion in some petroleums, in that of Rangoon : it is also contained, in
small qantities, in common coal-tar. It is a crystalline solid, without taste,
smell, or color. It is not greasy ; its sp. gr. is about 0*87 ; it melts at 112°,
and may be distilled. over unchanged at a higher heat. Its name is derived
from its inertness, or want of affinity, for it resists the action of acids, alkalies,
and chlorine ; but it unites by fusion with stearine, stearic acid, cetine, wax,
and resin, and it dissolves in naphtha, benzole, oil of turpentine, and chloro-
form : it is soluble in hot ether, but the solution concretes on cooling ; it
also separates in crystalline flakes from its solution in hot alcohol. The
density of its vapor and its true composition have not been satisfactorily
determined, but it is a hydrocarbon of the olefiant type. The substance
known as Fossil wax^ and tallow, Ozohei^te, and Hacheiine^ which occur in
the coal-formations, closely resemble paraffine.

The product known as Paraffine Oil is one of the associated hydrocarbons
contained in the least volatile portions of the bituminous oils. Together
with paraffine it is largely obtained from the bituminous schists accompanying
the coal-measures at Bathgate, near Edinburgh, and known under the name
of Boghead Cannel mineral. This valuable substance yields nearly three-
fourths its weight of volatile matters, leaving an aluminous ash, and some-
times not more than 6 per cent, of carbon ; and no real coke, in which respect
it is eminently distinguished from ordinary coal, which yields from 50 to 60
per cent, of porous coke, and only from 1 to 2 per cent, of an ash contain-
ing little or no alumina. When wetted, the mineral has the well-known
earthy smell of ordinary clays, and any hard substance produces on it a
brown streak.

The sp. gr. of the Boghead mineral is from 1 199 to 1*32. When dis-
tilled at a high temperature it produces a large quantity of highly illumi-
nating gas, and it is largely employed for the making of gas. When
distilled at a low temperature (a low red heat), it produces solid and liquid
hydrocarbons, and a smaller proportion of gas. The following results were
obtained as an average : From 100 parts of the mineral —

612 WOOD TAR. KREASOTE. EUPION.

"^ater, 3-0 ) ^^i,.M^ >

Oils and Tar, 45-9 \ Zf^^^};^,, } 59-11

Gas, 10-2 ) products ;

Coke or Carbon, 16*8 ^ ,., v

100-0 100-00

From one ton of this earthy mineral, about eighty gallons of crude oil are
obtained, and from this, 57 gallons of refined oil, yielding by a cooling
process 16 pounds of paraffine, and 13 pounds of pitch and tar. The 57
gallons of refined oil, by further distillation, yield 38 gallons of light oil
fitted for burning, and 19 gallons of a thick viscid oil employed as a lubri-
cant for machinery.

The melting point of paraflQne is so low that it too readily fuses, and it
burns with a very smoky flame. It is not materially improved in these re-
spects, by mixing it with less fusible fat or wax, for beyond a certain pro-
portion the compound becomes more fusible than the mean would represent.
The oil requires a peculiar lamp for its combustion. I^ike other hydrocarbon
oils, paraffine oil cannot be employed for the manufacture of soap. It will
not combine with alkalies.

Wood Tar. — When wood is subjected to destructive distillation as in the
process for the manufacture of gunpowder, and of pyroligneous acid, a large
quantity of tar is among the products, from which, as well as from common
Stockholm tar^ a variety of hydrocarbons and oxyhydrocarbons may be ob-
tained. The processes, by which these are separated and purified, are mostly
tedious and complicated ; they have- been especially de*scribed by Reichen-
bach. Paraffine is amongst them ; but he has also discovered several other
definite compounds, such as kreasote, eupion, tapnomor, pittacal, picamar^
and cedriret.

Kreasote (xpcaj, fleshy aca^a, to preserve) appears to be the principal
source of the peculiar odor and of the antiseptic and preservative qualities
of wood-smoke. When properly purified it is a colorless oily-looking liquid
of great refractive and dispersive power, of a penetrating smoky odor and a
burning taste: itssp.gr. is about 1*04; it remains fluid at 17^^; it burns
with a sooty flame ; is sparingly soluble in water, and is neutral to test-paper.
It dissolves readily in alcohol, ether, benzole, and acetic acid ; and forms a
crystalline compound with potassa. It coagulates albumen ; and a solution
of it, containing not more than 1 per cent., preserves meat from putrefac-
tion. The efficacy of crude pyroligneous acid, as a preservative of provi-
sions, and the peculiar smoky flavor which it confers upon them, appear to
be due to kreasote. It is an irritant poison when undiluted, but when largely
diluted it has been found effectual in checking vomiting, and as an appli-
cation in toothache for the destruction of the nerve. It appears to be closely
related to phenic (carbolic) acid, and the formula C^eHioOa has been assigned
to it.

EuPiON is a light oil of a peculiar greasy character (fv, and ftiutv, greasy)
resembling paraffine oil. It has the formula CJIq, and is regarded by Frank-
land as hydride of amyl, C^oHj^.H. Kapnomor (xanvbi, smoke, fioipa part)
is a pungent oil, sp. gr. 0*9. The formula CgoH^^Og has been assigned to
it. Pittacal is characterized by affording a blue color with baryta-water.
Picamar appears to be the hitter principle of wood tar, and is contained in
the heavy oil. Cedriret is a crystallizable product, soluble in kreasote, but
insoluble in water and alcohol.

ESSENTIAL OILS. THEIR USES. 613

Picric Acid. Carhazotic Acid (Ci3Ha(N0,)30,H0).— This is a solid
crystalline, and of an intensely bitter taste. It was formerly procured by
the action of nitric acid upon indigo, and it is also a product of the reaction
of that acid on silk, salicine, and some resinous substances. It is now manu-
factured chiefly by boiling carbolic acid in strong nitric acid. The crystals
are deposited from the solution on cooling. They are of a pale yellow color,
in the form of prisms with a rhomboidal base. When slowly heated, the
crystals swell, and the acid is partly sublimed without change. If heated
in air, it kindles without explosion and burns, leaving a carbonaceous
residue ; when quickly heated it detonates. Hydrochloric, nitric, and sul-
phuric acids have no action upon it. The acid is soluble in alcohol, ether,
and benzole. Ether appears to be the best solvent.

The crystals are not very soluble in water, requiring 80 parts of cold
water for their solution. They nevertheless give to the water an intense
yellow color, even when much diluted. The acid has remarkable tinctorial
properties, and is used as a yellow dye. It stains all nitrogenous organic
matter yellow, and is thus employed as a dye for silk or woUen. It does not
give a permanent color to cotton or flax ; and it thus serves to detect the admix-
ture of cotton with silk. The article is plunged into a strong and hot solu-
tion of the acid, and is afterwards washed in water. The silk only retains
the color. The picrate of potash is very sparingly soluble in cold water,
so that the acid is sometimes used as a test for that alkali.

CHAPTER L.

ESSENTIAL OILS. CAMPHOR. RESINS. AMBER. CAOUT-
CHOUC. aUTTA PERCHA.

Essential Oils.

The essential or volatile oils may be regarded as the odorous principles of
vegetables, and are generally obtained by distilling the plant with water,
either in its fresh, salted, or dried state. In some cases the oils are pressed
out of the cellular structure, as from orange and lemon peel. They are
obtained from all parts of plants, though usually most abundant in the leaves
and flowers ; and they sometimes differ in different parts of the same plant ;
thus, with regard to the orange-tree, the leaves, flowers, and fruit, each yield
a distinct oil. Some of them are so delicate and evanescent as to require a
peculiar mode of treatment, such as those of the flowers of jasmine, tuberose,
narcissus and mignonette : these flowers are stratified with layers of cotton,
or wool, imbued with some inodorous fixed oil, which by slight pressure
absorbs the perfume of the flowers. When the oil is saturated with the
essence, it is digested in alcohol, which abstracts the essential from the fixed
oil, and an odoriferous essence is obtained. Sometimes the cotton is distilled
with water or alcohol to separate the odorous essence, but the fragrance is
always more or less impaired by these processes. {See Piesse, On Perfumes.)

The essential oils are applied to many useful purposes ; some in the manu-
facture of paints and varnishes, some for burning in lamps ; others in pharmacy
and medicine, and others in perfumery. They are mostly ready formed in
the plant, but they are in some cases generated by the action of water upon
peculiar principles, as in the production of bitter-almond oil j and there are

614 ADULTERATIONS. CLASSIFICATION.

a few instances of their artificial production, as in that of oil of spircea by
the oxidation of salicine. When fresh and pure, these oils are mostly colorless,
or nearly so ; a few are green or blue, and some, after having acquired color,
lose it under the influence of li^ht. Their odors resemble those of the plants
yielding them, but are less agreeable, partly in consequence of concentration,
for they become more pleasant when diffused in the air, or attenuated by
solution in some inodorous vehicle. Their odors arS also influenced by their
chemical relations to air and water : there are some, such as those of turpen-
tine, lemons, and juniper, which, when distilled off quicklime, out of contact
of air are nearly inodorous, but which acquire their characteristic odors
when spread upon paper.

The sp. gr. of the essential oils fluctuates between 0*840 and 1-100, and
when subjected to a careful fractional distillation, they are mostly resolvable
into products differing in sp. gr. and in composition ; one of which is
frequently a hydrocarbon, and the other an oxyhydrocarhon, which is some-
times concrete, constituting a species of camphor. The terras elaioptene
and stearoptene have been applied to these liquid and solid products (from
fXatov, oil, or atiap, fat, and Titfjvhe, volatile). Their boiling points are very
variable, and so are the temperatures at which they congeal, these being
often dependent upon the relative proportions of their component oils.
They are sparingly soluble in water, to which, as in the medicated waters
of the Pharmacopoeia, they communicate odor and flavor ; most of them are
copiously soluble in absolute alcohol and in ether, and in fixed oils and
liquid hydrocarbons. In consequence of the high price of many of these
oils, they are sometimes adulterated with alcohol, with fixed oils, or with
cheaper essential oils. Alcohol may generally be separated by shaking the
adulterated oil with water, and its quantity determined by the diminution
in the bulk of the original oil ; it may also be abstracted by fused chloride
of calcium. Moreover the pure volatile oils dissolve, for the most part, in
the fixed oils, without interfering with their transparency ; but when adul-
terated with alcohol they produce turbidness. The admixture of a Jixed oil
is shown by the greasy stain which remains on evaporating a drop of the oil
before the fire, from a piece of blotting-paper : some of the genuine oils
leave a stain, but it is rather resinous than greasy, and admits of being written
upon with a pen and ink, or removed by alcohol ; the feel of the fixed oil
between the finger and thumb is also greasy, and when it is distilled with
water, the fixed oil remains in the retort. The adulteration of a high priced
with a cheap essential oil is often difficult of detection, and requires experi-
ence in the odor and qualities of the genuine article. When oil of turpentine
is so used, its characteristic odor is often covered, until the adulterated oil
is dissolved in a little alcohol, and water, added, when the odor and flavor
of the turpentine are manifest. The taste of the oil in these cases is often
a good guide ; oil of lemons is frequently adulterated with turpentine, but
its taste is very different from that of the genuine oil. The difference
between the indices of refraction of the adulterated and genuine oils has
been proposed as a means of detecting falsifications, and Dr. Wollaston
suggested an instrument for the purpose (Phil. Trans., 1802); but the
refractive power of the genuine oil varies too much to render this method
satisfactorily available.

The action of chlorine, bromine, and iodine upon the essential oils, gives
rise to an infinity of new compounds, resulting from the substitution of one
or more atoms of these elements, for a corresponding number of the hydro-
gen atoms of the oil ; and in some cases, direct combinations ensue. With
some of them iodine causes fulraination. Nitric acid acts violently upon
most of them ; they are more quietly decomposed by sulphuric acid. They

ESSENTIAL OILS. OX YH YDROCARBONS. '615

are not saponifiable by the alkalies. When their vapors are passed over
heated potassa, or soda, hydrogen is sometimes evolved, and an acid cora-
poand with the base is formed.

For the purpose of chemical description, the essential oils may be arranjred
under three divisions: 1, Those composed of carbon and hydrogen; 2, of
carbon, hydrogen, and oxygen; 3, those containing sulphur.

1. Hydrocarbons. — The elementary composition of this group may be
represented by C^H^ : it includes many isomeric compounds of which oil of
turpentine may be assumed as the type. Oil of turpentine, G^K^^ {camphene ;
camphyle), is obtained by distilling the turpentine of commerce with water.
There are many varieties of turpentine ; but that principally resorted to as
a source of the oil, is derived from different species of pinus, and chiefly
imported from North America. The first product is purified by redistilla-
tion. The original turpentine is thus resolved into the volatile oil, and into
residuary resin ; which, when retaining a portion of water, is known as yellow
rosin; or, as colophony, after fusion at a higher temperature.

Oil of turpentine, or turps, as the common oil is usually called, is a color-
less and very mobile liquid; sp. gr. 0*8()5, boiling at 312°, and yielding a
vapor of the density of 4'764 (p. 557). It has a characteristic odor, a hot
pungent taste, and burns with a large sooty flame : it is almost insoluble in
water, but soluble to some extent in alcohol and in ether. Under the name
of Camphene it was at one time largely used as a source of light, and when
carefully burned in a properly constructed lamp, gives a brilliant light; but
if the oil is not fresh, and h^s been exposed to air, it clogs the wick, and
smokes. Its use has lately been superseded by rock-oil and other modifica-
tions of naphtha. When oil of turpentine which has been agitated with
water is kept for some time at a temperature of 120°, it deposits crystals
^CaoHjg-f HO. When the oil and water are left together at common
temperatures, another hydrate, =C2„H^6,6HO, is produced. A crystalline
compound of hydrochloric acid and oil of turpentine has long been known
under the name of artificial camphor =G,^B.^q-\-11CI Corresponding hydro-
bromates and hydriodates have also been formed. The decomposition of
these, and other terebinthic compounds, has led to the discovery of several
isomeric hydrocarbons, principally distinguished by their action on polarized
light, some causing left-handed and others right-handed rotation of the ray.
Oil of turpentine is a great solvent of ozone. When exposed to air it
absorbs oxygen and acquires some of the properties of ozone. Thus it will
bleach organic colors and oxidize iodide of potassium, setting free iodine.

The oils of lemon, hergamot, orange Juniper, and many others, are isomeric
with turpentine oil.

2. OxYHYDROCARBONS. — The essential oils containing oxygen are very
numerous, and include Camphor and its modifications. Bitter-almond oil
and Spircea oil are elsewhere noticed, and there are others which have been
the subjects of minute investigation. Some of these, when distilled, are
separable into a more volatile hydrocarbon and a less volatile oxyhydro-
carbon, but the nomenclature applied to these compounds is often confused
and unsatisfactory ; in some cases a hydrocarbon, and in others an oxyhydro-
carbon, having been assumed as the radical of the series.

Oil of Cumin, for instance, may be resolved into a hydrocarbon =2oHi4,
which has been called Cymol, and an oxyhydrocarbon =^G.^^B.,p., called
Cuminol But cuminol has also been represented by the formula C^oH,,
O -f-H, and has been described as a hydride of a radical called Cumyle, C,o
H O . Oil of Aniseed is similarly separable into a hydrocarbon, isomeric

616 ESSENTIAL OILS CONTAINING SULPHUR.

with oil of turpentine, and an oxyhydrocarbon (the concrete portion of the
oil), C20HJ2O2; but this is sometimes represented as containing a radical
= CjgH70^, to which the terra anisyl has been applied, and from which a
Toluminous series of substitution and other compounds has been obtained.

Analogous radicals or bases have been obtained from many of the other
essential oils, or have been assumed as existing in them ; and it has often
been found convenient, in theory, to represent the oils as hydrides of these
radicals ; thus, oil of cinnamon is represented as a hydride of chinamyl,
by the formula CisHyOg+H, another of its products, cinnamic acid, being

Camphor (CgoH^gOJ. — Common camphor is the produce of the Laums
Camphora of Japan, China, and Java. It is extracted, by distillation with
water, from the roots and wood of the tree, and refined by sublimation. It
is tough, white, translucent, of a peculiar odor and flavor, and evaporates at
ordinary temperatures, gradually subliming in close vessels, and attaching
itself, in hexahedral and prismatic crystals, to the surface most exposed to
cooling. Its sp. gr. is 0*987 to 0'996*, but after long immersion in water,
this is so affected by changes of temperature, that this substance floats on
water above 50°, but sinks at a lower temperature. It fuses at 370°, and
boils at 400°, when it may be distilled without decomposition. When a clean
fragment of camphor is placed upon water, it acquires a rotatory motion,
which is rapid in proportion to its smallness. This appears to depend upon
the evolution of vapor, and the reaction of this upon the water. The light-
ness of the camphor and the absence of all friction favor this motion. It
does not take place on water already saturated'with camphor, nor when any
good solvent of camphor is added to the water. Thus the motions of the
fragments are immediately arrested by the addition of oil of turpentine to
the water. Camphor is so little soluble in water that it requires about 1000
parts for its solution, but is very soluble in alcohol, ether, chloroform, acetone,
acetic acid, and sulphide of carbon. It burns with a white smoky flame,
depositing much carbon. By the protracted action of hot nitric acid cam-
phor is converted into camphoric acid, CgoHj^Og or 2(HO)CaoHj408, which
crystallizes in acicular prisms, rendered anhydrous by sublimation, and
sparingly soluble in water.

A variety of camphor, known as Borneo camphor, the produce of the
Dryahalanops Camphora, contains two equivalents more of hydrogen than
common camphor: it is associated with a hydrocarbon {Borneen) = Q^H^^,
identical, therefore, with oil of turpentine. Camphor is contained in several
of the essential oils ; and substances resembling it are found in the Inula
Helenium, in Assarabacca, and in some of the Anemones.

3. Essential Oils containing Sulphur, — There are several essential oils
which contain nitrogen and sulphur, amongst which the oil of black mustard-
seed, garlic, assafcetida, and horseradish are the most remarkable.

Oil of Black Mustard-seed. — To obtain this oil, the cake of the seed, after
the fixed oil has been expressed, is made into a paste with water, which after
some hours is subjected to distillation, in the same way as bitter-almond oil
is distilled from the almond-cake. As in that case the oil is formed by the
action of emulsine upon amygdaline in the presence of water, so in this
instance the volatile and pungent mustard-oil is formed by the action of a
substance analogous to emulsine, which has been termed myrosine, upon a
peculiar substance existing in the black mustard-seed, and which has been
termed xnyronic add, sulphosinapisine, and sinapine. The oil which first
passes over, when dehydrated by means of fused chloride of calcium, is an
acrid, colorless liquid, soluble in alcohol and ether : it boils at 290°, and the

RESINS AND GUM RESINS. 61t

density of its vapor is 3"44. Its altimate elements are CgHgNSg; so that it has
been regarded as the sulphocyanide of a hydrocarbon, = C6H3, to which the
terra Allyl has been applied, and which has been isolated by the action of
sodium upon iodide of allyl (CgH^I). This iodide, under the name of iodized
propylene, was obtained by Berthelot {Ann. Ch. et Ph., xliii. 257) as a result
of the action of biniodide of phosphorus upon glycerine : it has been assumed
as the basis of numerous derivatives, included in what has been termed the
allyle series.

Oil of Garlic is a fetid sulphuretted product, which appears to consist of
oxide and sulphide of allyle (CeHsO + CgH^S), both of which have been
isolated.

Kesins.

These substances are found as proximate constituents of many plants :
those which have been principally examined are such as either flow naturally
from fissures in the bark or wood, or are obtained from incisions in the trees
and shrubs which produce them. They are almost always in the first instance
mixed with variable proportions of essential oil, which either evaporates on
exposure to air, or becomes resinified by the action of oxygen. Mixtures
of essential oil in large proportion with resin are called balsams: although,
strictly speaking, this term is applied to those mixtures of essential oil and
resin which contain benzoic or cinnamic acid, as the balsams of benzoin, tolu,
storax, and Peru. Balsams of copaiba and Canada are resins mixed with an
essential oil which is isomeric with oil of turpentine. The so-called Canada
balsam is the nearly colorless liquid resin of the Pinus halsamea.

Resins are generally soluble in alcohol, benzole, and chloroform. Some
are soluble in ether. The alcoholic solution, when mixed with water, gives
a whitish precipitate, which has frequently an acid reaction. This is the
pure resin in the state of hydrate. If an alcoholic solution of a resin is
poured upon a surface of glass, an opaque layer of resin is left upon drying :
if the glass is first heated, the resin is deposited in a transparent form, and
closely adheres to the surface. Many resins are dissolved when heated in a
solution of potash or soda. They form in this case a species of soap, and
give frothiness to the water when agitated.

Resins, when pure, are inodorous ; a few of them are crystallizable ; they
are usually of a pale yellow or brown color, opaque or transparent. They
become electric by friction. The greater number of them are heavier than,
and insoluble in water, and have little taste. They are generally softened,
or even fused, when boiled in water. In the air they melt and burn .with a
sooty flame. They are thus distinguished from gums. When subjected to
dry distillation, they yield resin-oil, volatile liquids, and inflammable gases.
Many of the natural resins are mixtures of two or more resinous substances,
separable by the action of alcohol. There are many of them which, when
in alcoholic solution, redden litmus, and combine with alkalies; others are
indifferent, and some have been regarded as basic.

Gum-resins are natural mixtures of gum and resin in variable proportions.
They sometimes contain an essential oil which gives to them a powerful odor.
They are the milky juices of plants solidified by exposure. While a pure
gum is insoluble in alcohol, and a pure resin is insoluble in water, a gum-
resin is characterized by its forming a milky emulsion with water, the solution
of the gum suspending the fine particles of resin with which it is associated.
Ammonium, Myrrh, Gamboge, and Assafoetida are gum-resins.

There are a few of the resins, and their allied substances, which require
especial notice. , -n • <• *

Colophony; Common i?o5iw.— This is the residue of the distillation ot tur-

618 SILVIO AND PINIC ACIDS. GUAIACUM.

pentine (p. 615). It is brittle, tasteless, of a smooth shining resinous frac-
ture; sp. ^r. 1 080; softens at about 180°, and fuses at 275°. According to
Unverdorben, it includes two distinct acid resins, which he designates pinic
acid and silvic acid, the former preponderating. As respects the composi-
tion of these acids, it appears that they are isomeric, and have the formula
ascribed to colophony {Q^Jl^fi.^,'RO).

Silvic acid is obtained by mixing an alcoholic solution of colophony with
an alcoholic solution of oxide of copper, drying the precipitate, and digest-
ing it in alcohol, which dissolves the silvate, but leaves the pinate of copper.
Sulphuric acid is added to the alcoholic solution, and it is then precipitated
by water, which throws down silvic acid, and which, dissolved in alcohol,
yields crystals on evaporation.

Pinic Acid. — When pinate of copper is dissolved in boiling alcohol acidu-
lated by hydrochloric acid, and water is added to the mixture, pinic acid is
precipitated in the form of a colorless resin. This substance is not crystal-
lizable, but in other respects resembles silvic acid. The pinates are less
soluble in ether than the silvates, and pinate of magnesia is insoluble in
alcohol, whereas the silvate is soluble.

When colophony is heated somewhat above its point of fusion, it acquires
a dark color, and is less easily soluble in alcohol : in this state it has been
called colopholic acid. Distilled over an open fire, colophony is resolved
into carbon, water, and colophene; there is also formed a liquid hydrocarbon
= C,„Hg, having the properties of terebene. But these products vary with
the mode of distillation, for Fremy represents them as consisting of water,
together with a thick yellow oil, which he terms resineine, and represents as
= 0^0^2302; and by distilling in the same way a mixture of 1 part of resin
and 8 of powdered quicklime, he obtained two liquids, which he calls resi?io?ie,
= C,„HyO, and resineone, ssCggllagO, carbonic acid being at the same time
formed.

A resin isomeric with colophony is obtained from the turpentine of the
pinus maritima, and has been distinguished as pimaric acid. All these
resins readily combine with the alkalies, and enter largely into the composi-
tion of common yellow soaps. Elemi, Anime, Sandarac, or juniper resin,
and Mastic, each contain two distinct resins, separable to a great extent by
the alternate action of cold and hot alcohol, and dififering slightly in compo-
sition (Johnston, Phil. Trans., 1840).

Guaiacum. — This is a hard, brittle, greenish-brown resin, obtained from
the Guaiacum officinale. It is very soluble in alcohol, and its solution
gives a white precipitate with water, which absorbs oxygen, and is colored blue
or green according to the quantity of resin and the degree of exposure. The
change appears to be due entirely to oxidation, for the precipitated resin,
inclosed in a hermetically-sealed glass tube, was unaltered in color after two
months' exposure to light. The powdered resin, exposed to air, slowly
becomes green, and in order to make a pure tincture for experimental pur-
poses, the minor portions only of the resin should be taken. According to
Deville, the resin consists of two distinct resinous acids, one of which,
guaiacic acid, has the following formula: HOjCj^HyOg. Deville has pro-
cured this from the resin in a crystallized state.

Chlorine, bromine, and nitric acid rapidly oxidize the precipitated resin,
turning it of a green color. Nitric acid has the same effect on the powdered
resin and on guaiacum wood. Bodies containing ozone, e. g., a solution of
manganate or permanganate of potash, or even insoluble peroxide of man-
ganese, give a rich azure-blue color to the resin — the last-mentioned com-
pound somewhat slowly. Peroxide of lead operates in a similar manner.
Paper soaked in the tincture, and dried and kept from air, has been recom-

RESINS. LAC. 619

mended by Schonbein as a test for ozone. The paper is bloed when ex-
posed to an ozonized atmosphere, but ordinary oxygen also appears to have
a similar action upon it, although a longer time is required by the produc-
tion of the blue color. A solution of a salt of iron, whether of the prot-
oxide or peroxide, also produces a blue color with the precipitated resin.
This bluing takes place under circumstances which it is not always easy to
explain. Thus the fresh pulp of potato, flour, and gluten in any form, pro-
duce a similar change in the resin. Peroxide of hydrogen does not change
the color, and peroxide of barium only produces a blue color with the resin
after the addition of an acid (acetic) to the mixture. On this negative
action of peroxide of hydrogen depends the guaiacum test for the detection
of blood.

Copal, the resin of the Hymencea verrucosa, is characterized by its diffi-
cult solubility in alcohol; but when powdered and exposed for some months
to the air, it becomes more soluble. It is the basis of some excellent var-
nishes, and is generally fused before it is dissolved in oils or spirit. Lac is
also a valuable ingredient of varnishes, rendering them, like copal, tough
and durable : its secretion appears to depend upon the puncture of a small
insect (the Coccus Jicus) , made for the purpose of depositing its ova upon
the branches of several plants growing chiefly in India, more especially the
Mcus Indica, Ficus religiosa, and Rhamnus Jujuba. The twig soon becomes
incrusted with a dark reddish-colored substance, constituting slick-lac, which,
when washed and coarsely pulverized, forms seed-lac; and this, formed into
thin plates by fusion at a low temperature, is called shell-lac. It consists of
about 90 per cent, of a peculiar resin, which appears to be a mixture of
three or four distinct resinous products. Lac is an important ingredient in
varnishes and lacquers, and is largely used in the manufacture of hats, and
of sealing-wax. The varnish commonly called lacquer, employed for color-
ing brass, and protecting it from the oxygen and sulphur of the atmosphere,
is made by mixing lac with half its weight of sandarach and a small quantity
of Venice turpentine. These are dissolved in ten or twelve parts of alcohol.
Marine glue is a solution of caoutchouc in coal-naphtha, to which some
shell-lac is added.

Red sealing-wax is made by carefully fusing a mixture of 48 parts of shell -
lac, 19 of Venice turpentine, and 1 of Peru balsam, to which 32 parts of
finely-levigated cinnabar and some sulphate of lime are afterwards added.
In the cheaper kinds of red sealing-wax, red lead is substituted for vermilion,
and there is a large addition of common rosin, which causes the wax to run
into thin drops when fused. Black sealing-wax is made of 60 parts of shell-
lac, 10 of Venice turpentine, and 8 of finely-levigated ivory-black.

Varnishes. — The principal substances used in varnishes as solvents are the
oil of nuts, linseed, and turpentine, as well as alcohol, ether, chloroform,
and benzole. The solids employed are amber, copal, mastic, sandarac, lac,
dammara, anime, benzoin, and colophony. They are sometimes colored with
various vegetable coloring principles.

Asphaltum is an ingredient in Japan or black varnish, and caoutchouc in
those which are required .to be elastic and waterproof. The best photo-
graphic varnish is a solution of amber in chloroform. The characters of a
good varnish are, that it should firmly adhere to the surface to which it is
applied, that it should not change color or lose lustre, by exposure to light
and air ; and that it should not be long in drying. Varnishes are distin-
guished as spirit and oil varnishes; the former are the most brilliant, but
most brittle, the best spirit varnishes being those containing lac or copal.
The article known as French polish is an alcoholic solution of shell-lac, a
little linseed oil being added at the time of its application : it is laid ou by

620 AMBER. CAOUTCHOUC.

a ball of cotton-wool, and then rapidly rubbed in the direction of the fibres
of the wood : it is ultimately finished off, after drying, by friction with tripoli
and oil. The varnishes prepared with oil of turpentine (or benzole) are less
brittle than those in which alcohol only is used. A common varnish for oil-
paintings, and paper previously sized, is made with 24 parts of mastic, 3 of
Yenice turpentine, and 1 of camphor. These are mixed with 10 parts of
pounded glass, and dissolved in 72 of rectified oil of turpentine (Miller).

Amber. — This substance, usually regarded as a fossil resin, is chiefly
brought from the southern coast of the Baltic, where it is thrown up on the
beach ; it is found on the coast of Norfolk ; it also occurs in beds of brown
coal or lignite in superficial strata. It has not been found in bituminous
coal drawn from great depths. It is generally of a peculiar yellow color,
pale or deep, transparent or translucent, slightly heavier than water, and
becoming very electric by friction. It is only soluble to a small extent in
alcohol and in ether. Subjected to dry distillation it fuses, giving off water,
oily matters, and succinic acid ; the latter derived apparently from the de-
composition of that portion of resin which is soluble in ether; and the oils,
from the insoluble and apparently bituminous part. Sixteen ounces of
amber, carefully distilled, yield about an ounce of impure acid, three ounces
of oil, and ten of a torrefied resin, fit for the preparation of varnish. The
empyreumatic oil thus obtained by distillation is the product of the decom-
position of the bituminous portion of amber which is not soluble in alcohol
or ether. Amber is dissolved by chloroform, forming a useful varnish. It
is also dissolved by strong nitric acid, and may be crystallized from the solu-
tion when it is concentrated. If the liquid portion is distilled, a substance
resembling camphor passes over.

Succinic acid, (2HO),C8H^Og, is a product of the action of nitric upon
stearic acid. It is also formed by fermentation, from asparagine, and from
malic acid. It crystallizes in rhombic plates, soluble in five parts of cold,
and two of boiling water ; it may be obtained anhydrous, by distillation with
anhydrous phosphoric acid. If the crystals are heated to 450°, they lose a
portion of their water, and a monohydrated acid sublimes. The succinic, is
a very stable acid ; it resists the action of chlorine and of boiling nitric acid.
When fused with caustic potassa it yields oxalic acid, and an inflammable
gas. The soluble succinates produce a bulky reddish-brown precipitate in
the neutral and basic salts of peroxide of iron, and they have been used as
a means of separating it from oxide of manganese. When heated with
bisulphate of potassa, they give a sublimate of succinic acid.

Caoutchouc {Indian Rubier, Gum Elastic) was first brought to this
country at the beginning of the last century, moulded into the shape of bot-
tles and animals, and used for rubbing out pencil marks : it has since been
applied to a variety of important purposes, and many tons of it are annually
imported from South America and the East Indies. The trees which yield
it are the Jatropha and Urceola elastica, and several others, and it is found
in small proportion in the poppy, lettuce, euphorbium, and other plants
having a viscid milky sap. The fresh juice of the tree is a yellow, milky
fluid, which, when exposed to warm air, forms an elastic deposit, retaining
albumen and other impurities which are found in the commercial article.
This is frequently of a dark color, and has a sp. gr. varying from 0"926 to
0"960. Pure caoutchouc is a hydrocarbon, being, according to Faraday,
CJIj, although other authorities give it C^H^ ; thus making it isomeric with
oil of turpentine. The remarkable elasticity of this substance, and its chemi-
cal peculiarities, have led to a multitude of important applications of it in

VULCANIZED RUBBER. GUTTA PERCHA. 621

the industrial arts. (Hancock on Caoutchouc, &c. ; Muspratt^s Chemistry,
Art. Caoutchouc, &c.)

In its ordinary state it becomes hard at low temperatures, but never brit-
tle ; it is soft 'and very elastic when warmed ; and when heated to about
260°, melts into a viscid mass, which, on cooling, never regains its former
characters. It burns with a smoky flame and exhales a peculiar odor. Sub-
jected to destructive distillation, it affords a mixture of various hydrocarbons,
gaseous and liquid ; the latter, under the name of Caoutchine CgoH^g, having
a peculiarly penetrating, greasy, and disagreeable odor. Caoutchouc is in-
soluble in water, alcohol, dilute acids, and alkalies. Ether, chloroform,
bisulphide of carbon, rectified oil of turpentine, benzole, coal-naphtha, and
some other hydrocarbons, soften and dissolve it; some of these solvents
leaving it on evaporation in its elastic condition. In this dissolved state,
it is extensively used for water-proofing and other purposes. The processes
by which the commercial caoutchouc is purified, kneaded, moulded into
blocks, cut into sheets, ribbons, and thread, are almost exclusively mechani-
cal, but are necessary preliminaries to its most important applications, many
of which are dependent upon a process which has been termed Vulcanization,
and which consists in subjecting it, by heat or solution, to the action of
sulphur. By this process it becomes so far modified as to resist the action
of its ordinary solvents, and of the greasy oils, and to retain perfect pliancy
and elasticity at the low temperatures which harden, and at the high tem-
peratures which soften common India rubber. When a sheeti of rubber is
immersed in melted sulphur, it absorbs a portion of it, without any material
change ; but if heated in this sulphurized state, to about 300"^, the vulcani-
zation is effected. So also if sulphur is added to the solution of the rubber
in turpentine or naphtha, it retains its ordinary properties after the evapo-
ration of these solvents^ until heated to the vulcanizing temperature (270°
to 300°). Sulphur is sometimes imparted to rubber by dipping it in thin
sheets into a solution of chloride of sulphur. A hard compound of sulphur
and rubber, heated to a high temperature and for a longer time, is called
Ebonite,

The cause of the change effected by vulcanization is not well understood ;
but it is generally supposed that the rubber retains about two per cent, of
sulphur in chemical combination, inasmuch as all beyond that quantity may
be removed by appropriate solvents (alkaline sulphites). It has also been
surmised that the process of vulcanization has conferred an allotropic condi-
tion upon the rubber, and that the Whole of the sulphur may be withdrawn,
still leaving it in its altered condition. The removal of sulphur is effected
on the large scale, by boiling the vulcanized rubber in a solution of sulphite
of potassa. A large quantity of silicate of magnesia, in fine powder, is
sometimes incorporated with the rubber before vulcanization, to give it a
smooth and non-adherent surface. An article known as marine glue is made
by dissolving a mixture of caoutchouc and shell-lac in coal-naphtha : it is of
extreme adhesiveness.

GuTTA Percha is closely allied to caoutchouc in composition and in its
general chemical characters: it was first brought into notice in 1846, and
has now become an important article of commerce : it is the produce of the
Isonandra percha, a forest tree abounding in the islands of the Eastern
Archipelago. It exudes as a milky juice. It is a tough, unyielding, fibrous
substance, generally met with in black or brown masses. It melts at 250°.
When immersed in boiling water, it softens, and admits of moulding into
any requisite shape, but hardens again on cooling, retaining the shape which
has been given to it. It becomes powerfully electric by friction, and is an

629

FATS AND FIXED OILS.

excellent insulator. It is applied to a variety of iisefnl and ornamental pur-
poses, in many of which it is advantageously substituted for leather. It is
not elastic like caoutchouc, but is much more tough. It is insoluble in
water and alcohol, but is dissolved by chloroform, benzole, and sulphide of
carbon. When heated in air, it melts, takes fire, and burns with a smoky
flame. It forms no combination with sulphur, like vulcanized rubber.
After long exposure to air in thin sheets it acquires a yellow color, is very
brittle, and is now soluble in alcohol. It appears to be resinified as a result
of oxidation. It rapidly absorbs and removes ozone.

Gutta percha consists of a distinct principle, gutta^ associated with two
resinous compounds. The gutta is represented by the formula C^oHgg, and
is a pure hydrocarbon. The resins have the same formula, with an addition
of two and four atoms of oxygen respectively. Gutta percha contains neither
sulphur nor nitrogen.

CHAPTER LI.

FATS AND FIXED
SITION.

OILS. PRODUCTS OF THEIR DECOMPO-
SPERMACETI. WAX. SOAPS.

Fats and Fixed Oils.

These substances are common to animals and vegetables ; they vary in
consistence from thin oil (olive oil) to hard fat (suet). When pure, they
are neutral ; they leave a greasy spot upon paper, which does not disappear
when moderately heated. They are insoluble in water, but more or less
soluble in alcohol and ether, and are insipid and inodorous. In vegetables
they chiefly occur in the seed, and pericarp of the fruit (olive), and are
generally obtained by pressure, with or without the aid of heat.

The following table shows the proportion of oil per cent, yielded by a
Tarifety of seeds : —

Walnuts .

. 64-8

Croton seeds

. 43-4

Hazel-nuts

. 59-4

Hemp

. 35-5

Sweet almonds .

. 55-4

Mustard

. 31-8

Bitter almonds .

. 520

Laurel berries

. 31-8

Poppy

. 49-4

Linseed

. 29-6

Cacao

. 47-4

Mace

. 25-5

Castor

. 46-0

Cotton seed

. 18-4

The residue left by compression is well known under the name of oil-cake.
It contains, besides vegetable fibre, various nitrogenous principles, chiefly
albuminous, and it is largely employed as food for cattle.

It has been found that a large quantity of oil is left in these residues, and
as this cannot be extracted by compression, a new plan has been adopted to
remove the whole of the oil. Sulphide of carbon is employed for this pur-
pose. This liquid penetrates the cake of the oleaginous seed or the pulp of
the olive, and rapidly and completely extracts the residuary oil, from which
it is afterwards separated by distillation. This process is carried on largely
in France, and it is stated that from thirty to thirty-five tons of oily sub-
stances are thus extracted at each operation.

In animals the oil is deposited in a cellular membrane, as in the blubber
of the whale. The separation of the oil here takes place by simply treating

8TEARINE. STEARIC ACID. (523

the fatty substance with boiling water. The adipose cells are rnptured

the oil escapes and collects upon the water in which the crude fat is boiled.
The. melting points of oils and fats vary from about 20° to 140°. At high
temperatures (500° to 600°) they do not distil unchanged, but evolve acrid
products, and are resolved, at a red heat, into inflammable gases and vapors,
of high illuminating power. Their specific gravity, which is below that of
water, varies much with temperature : the sp. gr., for instance, of hog's lard
at 60° is 0-9.38 ; in its fluid state at 122° it is 0-892 ; at 155° it is 0'881 ;
and at 200°, 0'863. Some of these oils are little aflfected by exposure to air,
but gradually become rancid ; others absorb oxygen, and form a resinous
varnish ; they are known as drying oils ; and when their surface is much
extended, as in greasy rags and cotton-waste, this change is sometimes
attended by spontaneous combustion. The drying quality of these oils is
generally increased by heating them with oxide of lead or manganese.

When the solid fats are subjected to pressure between folds of bibulous
paper, they afford more or less of fluid oil ; and when the liquid oils are
cooled to about 32°, they deposit more or less of a concrete matter. The
liquid portion is termed oleine or elaine (fXuiiov, oil), and the solid, stearine
(otiapjfat), with which a variable portion of margarine (fiapyafiov, a pearl,
from its pearly lustre) is associated, each of these being compounds of a
distinct fattg acid, with a sweet principle, glycerine (yxvxvj sweet). These
acids are the oleic, the stearic, and the margaric ; so that oleine is an oleate,
stearine a stearate, and margarine a margarate, of glycerine. Besides these,
many fats contain distinct volatile acids, such as butyric, capric, and caproic
acids, in butter ; hircic acid in goat's fat, phocenic acid in fish-oil, etc.
Oleine may be more or less separated from stearine by ether or oil of turpen-
tine, in which liquids it is much more soluble than stearine.

In the process of saponification, the fatty bodies are heated with hydrated
alkalies, generally with soda, by which they are decomposed, the glycerine is
set free, and oleates, stearates, and margarates of the alkaline bases are
formed.

Fat or oil

c, . ( Stearic acid

Stearme {(Glycerine

„ . ( Marffaric acid

Margarine | eHyeerine

^, . ( Oleic acid

1^ Oleine |ai^cerine

These combinations (soaps) are in their turn decomposed by the greater
number of other acids, and the fatty acids are separated. These acids are
insoluble in water, but soluble in alcohol and in ether, and are less fusible
than the original fats. They are soluble in oil of turpentine and in benzole,
and when free from volatile products, are insipid and inodorous. The soaps
of alkalies are soluble, but those of the alkaline earths, and of most of the
other metallic oxides, are insoluble in water; hence it is that hard waters are
unfit for washing, in consequence of the earthy salts which they contain, and
which give rise to the production of insoluble soaps.

Stearine (Ci,^H,,oO,b) {Stearate of Glycerine) is best obtained from mutton
suet, by boiling it in ether, and filtering the hot solution ; as it cools, it
deposits stearine, which, after having been pressed in bibulous paper, may
be purified by a second solution, and cooling. Its fusing point is about
140°. It is insoluble in water, but soluble in boiling alcohol and ether,
which, however, deposit nearly the whole of it as they cool.

Stearic Acid (HO,C3eH3,03).— When stearine is saponified, it is resolved
into stearic acid and glycerine, a change which may be represented by the
following equation : —

624 STEARATES. MARGARIC AND OLEIC ACIDS.

C,„H„oO^ + 6H0, = ^^^,0,^ + 3(HO,C3eH3,03)

Stearine. Glycerine. Stearic acid.

This acid may be obtained by decomposing a soluble stearine soap by tartaric
acid, and purifying the product by solution in boiling alcohol, from which it
separates in crystalline flakes ; it may be further purified by solution in ether.
It is white, inodorous, and tasteless, but it reddens litmus : it fuses at about
160°, and may be distilled in vacuo, but when highly heated in the air it
undergoes more or less change. Stearic acid may be distinguished from
stearine by its ready solubility in a boiling solution of potassa, by its acid
reaction and crystallizing properties.

Stearates. — Stearic acid forms monobasic and bibasic salts (neutral and
acid). The stearates of the alkalies are soluble in water, alcohol, and ether ;
but when the aqueous solutions of the neutral compounds are largely diluted,
they deposit flakes of the acid stearate. The stearates of the alkaline earths
may be obtained by double decomposition, from bistearate of potassa : they
are insoluble. Stearate of potassa is the basis of soft soap, and stearate of
soda of the principal hard soaps : these stearates are separated from their
solutions in water by excess of alkali, and also by chloride of sodium and
some other salts. Stearate of lead is the basis of lead-plaster.

3Iargarine (CiogHjo^O^g) {Maryarate of Glycerine). — This substance is
found in some animal fats, but it is best obtained from olive oil, by cooling
it to 32°, pressing out the oleine, and dissolving the residue in boiling
alcohol, from which the margarine separates in pearly crystals. It is re-
solved by the alkaline bases into glycerine and margaric acid.

Margaric Acid (HO.Cg^HggOg) is obtained by decomposing the soap of
olive-oil and potassa, by acetate of lead or chloride of calcium: an insoluble
margarate and oleate of lead or lime is formed, from which the oleate may
be abstracted by cold ether ; the remaining margarate may then be decom-
posed by dilute hydrochloric or nitric acid, when the margaric acid separates,
and may be purified by crystallization from its alcoholic solution : it fuses at
about 140°; in other respects it resembles stearic acid, and the margarates
closely resemble the stearates. According to Heintz, margarine is a mixture
of stearine and palmitine (found in palm-oil), and consequently margaric
acid is not an independent acid, but a mixture of stearic and palmitic acids.

Oleine {G^^Jl^^fi^^ {Oleate of Glycerine). — Oleine is the chief ingredient
in the fat-oils which remain fluid at common temperatures. It may be pro-
cured by separating the margarine and stearine from a fat oil, by cold and
pressure, dissolving the liquid portion in ether, evaporating, and digesting
the residue in cold alcohol, which dissolves the oleine, and leaves margarine
and stearine undissolved. Oleine is colorless, inodorous, and tasteless ; its
sp. gr. is about 0*9. It is insoluble in water, but abundantly soluble in
alcohol and in ether. It remains fluid at and below 32°.

Oleic Add (CggHggOg) is obtained by saponifying almond oil with potassa,
and decomposing the soap by hydrochloric acid, which separates a mixture
of oleic and margaric acids: this, by digestion with oxide of lead, is con-
verted into oleate and margarate of lead, and by digesting these in ether,
an acid oleate of lead is dissolved. The ethereal solution is mixed with its
bulk of water and decomposed by hydrochloric acid, which throws down
chloride of lead, and leaves the oleic acid in solution, from which it is
obtained by evaporation. The crude oleic acid, produced by pressure in
the manufacture of stearine candles, may be similarly purified. Oleic acid
is colorless, concretes at about 50°, and reddens litmus ; it is insoluble in
water, but abundantly soluble in alcohol and in alkalies. The neutral oleates
have litMe tendency to crystallize. The soluble alkaline oleates are soft

glycerine: its properties. 625

fusible compounds, more soluble in alcohol than in water, and are decom-
posed, by excess of water, into free alkali and acid compounds. It is a
solution of the pure oleate of soda in the proportion of one part to fifty parts
of water, mixed with two-thirds of its bulk of pure glycerine, which forms
what is called the glycerine liquid for producing persistent soap-bubbles.
Bubbles of large size blown with this liquid will retain their form for eighteen
or twenty-four hours. M. Plateau found that Marseilles soap, in a fresh or
moist state, may also be used for this purpose in the proportion of one part
dissolved in forty parts of distilled water at a moderate heat. When the
solution has cooled it is filtered, and to three volumes of it two volumes of
pure glycerine are to be added, and the whole well shaken and allowed to
remain for several days. It is then submitted to a cooling process, and is
filtered to separate any deposit. {Ghem. News, Dec. 1866, p. 291.)

Glycerine (CgHgOg) {y7.vxvi, sweet). — This substance was discovered by
Scheele. It is obtained by boiling equal parts of hydrated oxide of lead
and olive oil with water : the solution thus formed, freed from lead by sul-
phuretted hydrogen, filtered, evaporated to the consistency of syrup, and
then exposed in vacuo over sulphuric acid until it no longer loses weight,
leaves the glycerine. It is now produced in large quantities by soap and
candle-makers, and has been applied to many useful purposes in medicine
and the arts.

Glycerine is a colorless, neutral, inodorous liquid, of a sweet taste and
syrupy consistency, sp. gr. 1-28, soluble in all proportions in water and in
alcohol, but nearly insoluble in ether. It does not dry by exposure to air.
It is slightly volatile at 212°, but when heated in air to a high temperature,
it gives off an inflammable vapor and burns with a luminous flame. It is
usually described as uncrystallizable, and when pure and exposed to a tem-
perature of zero, it has not solidified but has apparently become more viscid.
A large quantity imported from Germany during the severe winter of 186(5-7
was found by Mr. Crookes to have assumed a solid and a crystalline condition.
The original glycerine was of a pale brown color. The solid glycerine had
separated in* crystalline colorless masses resembling sugar candy. The
crystals were brilliant and apparently of an octahedral form. The liquid
which drained from them was of a dark-brown color. They melted slowly
retaining a temperature of 45°. When fused the liquid had all the proper-
ties of pure glycerine (Chem. News, 1867, i. 26). It dissolves baryta, lime,,
oxide of lead, and many salts. When mixed with a solution of caustic
potassa, it readily dissolves hydrated oxide of copper, forming a deep blue
solution, which, however, produces no suboxide when boiled. When boiled
with a solution of potassa, no glucic acid is produced, and the liquid does
not become dark-colored like glucose under similar circumstances. In order
to detect syrup in glycerine the liquid may be warmed with a small quantity
of tartaric acid and ther*opper test then applied. If cane-sugar syrup is
present the red oxide of copper will be formed and precipitated. Sulphuric
acid does not carbonize it in the cold : it is thus distinguished from sucrose..
When heated in a retort, part passes over and part is decomposed, producing
the pungent vapors of acrolein; but it may be distilled without decomposi-
tion in a current of superheated steam, at a temperature between 400° and.
500°. It is not susceptible of vinous fermentation, but when left for some
months in a warm place, mixed with a little yeast, it produces propionic acid.
Impure glycerine digested with alcohol produces butyric ether. Distilled
with dilute sulphuric acid and peroxide of manganese, it yields carbonic and
formic acids. Mixed with twice its weight of sulphuric acid there is con-
siderable elevation of temperature, and after the mixture has cooled, if it be
40

626 NITRO-GLYCERINE, NITROLEUM, AND GLONOINE.

diluted, saturated by milk of lime, and filtered, it yields, on evaporation,
crystals of a salt of lime containing sulphoglyceric acid, =Q^fl,-\-'^^0^.
A corresponding Phosphoglyceric acid is said to exist in the brain, and in
yelk of Ggg.

In combination with the fatty acids, glycerine produces the various fats
and oils, but they appear to combine in various proportions: assuming stearic
acid as CggHgjOg, stearine will be a terstearate of glycerine : —

Glycerine. Stearic acid. Stearine.

and oleine a teroleate of glycerine : —

^ CeHA 4- 3(C3eH3303) = C,^H„^

Glycerine. Oleic acid. Oleine.

and so with regard to other fatty acids. Berthelot has synthetically repro-
duced the fats by the union of their acids with glycerine, and has pointed
out the existence of analogous combinations, in which 1 and 2 equivalents
of the respective acids are similarly combined with glycerine, producing
distinct fatty bodies {Ann. Ch. et Ph., 3eme ser., xli. p. 216).

Nitro-glycerine, Nitroleum, Glonoine, CeH.(NO^)30f5, a substitution com-
pound, in which three equivalents of the hydrogen of glycerine are replaced
by three equivalents of nitrous acid. It is procured by adding glycerine in
small quantities to equal measures of the strongest nitric and sulphuric
acids, previously well mixed and cooled. If the mixture became heated, the
glycerine would be decomposed, and oxalic and carbonic acids would be
produced. The combination is completed in five or ten minutes : the acid
mixture is then added to five or six times its volume of cold water and well
agitated : the nitroglycerine is precipitated as a heavy oily-looking liquid,
so that it may be easily separated from the diluted acids by decantation, and
washed. The chemical changes which take place may be thus represented : —

^CeHgOe + 3(H0,N0,) = CeH^CNOJaOe ^ + 6H0

Glycerine. Nitric acid. Nitroglycerine. Water.

Nitroglycerine is an oily-looking liquid, of a pale brownish color, becoming
•Bolid at 40°, sp. gr. 1*6, not soluble in water, slightly soluble in alcohol, but
easily dissolved by ether and wood-spirit. The last-named liquid is said to
counteract its explosive properties, and to render its transport safe. It may
be separated from these solutions by water. Although more violent than
:gunpowder and guncotton in its explosive power, it is not so easily exploded
by heat as either of those compounds. When flame or a red heat is applied
to it openly, it burns without explosion ; but when* placed in a closed vessel,
it will explode at 360°. It most readily explodes by percussion, as when
sharply struck in a hard and resisting surface. In blasting rockis, a fuse
charged with gunpowder is employed for the purpose of exploding it : it has
ten times the rending force of an equal weight of gunpowder. Like gun-
cotton, it is apt to undergo spontaneous changes, and the evolution of gas as
a result of decomposition has probably been the primary cause of the serious
accidents which have occurred from the transport of this liquid. It has a
sweet and aromatic taste, and is said to be poisonous both as a liquid and
vapor. When breathed in small quantities, it is stated to have produced
violent headache and other unpleasant symptoms. It has lately been manu-
factured on a large scale for use in the blasting of rocks.

ACTION or SULPHURIC ACID ON PATS AND OILS. 62*7

Action of Sulphuric Acid on Fats and Oils — This acid generally so com-
bines with the proximate principles of the fatty bodies as to form a series of
distinct acid products, such as sidphostearic, sulphomargaric, and sulpholeic
acids; the glycerine at the same time yielding sulphoglyceric acid; but when
sulphuric acid is heated with the fatty bodies, the glycerine is decomposed,
and the fatty acids are set free. This process is resorted to upon the large
scale, for the production of the fatty acids for the manufacture of candles.
The tallow is mixed with about a sixth part of oil of vitriol in large copper
vessels, and subjected to a temperature of about 350°, by means of highly
heated steam ; sulphurous and carbonic acids are abundantly evolved, in
consequence of the action of the sulphuric acid upon the glycerine. The
liberated fatty acids, after having been well washed, are distilled in a current
of steam, heated to between 500° and 600° by transmission through a red-
hot pipe ; the fatty acids are carried over, leaving their impurities in the
form of a black residue, and are then subjected to pressure, so as to squeeze
out the more fluid oleic portions, and leave the stearic acid in a fit condition
for candle-making. But the decomposition of the fats by highly heated steam
only, has lately been carried to such perfection, as not only to yield the fatty
acids, but also the glycerine, in a very pure state, a process which will pro-
bably entirely supersede that by sulphuric acid.

Action of Nitric Acid on Fats and Oils. — These products may be divided
into two classes : 1. Those which are volatile, and pass over in distillation ;
and 2. Those which are comparatively fixed, and remain in the retort ; they
are as follows : —

)latile acids.

Volatile acids.

Fixed acids.

Formic

(Enanthjlic

Succinic

Acetic

Caprylic

Adipic

Butyric

Pelarganic

Pimelic

Valerianio

Capric

Suberic

Caproic

Sebacic

These products are obtained by gradually dropping oleic acid into a retort
containing nitric acid, heated to about 130° : violent action ensues, and the
distillate consists of water holding the most volatile and soluble acids in
solution, such as formic, acetic, and butyric, covered by an oily layer of the
valerianic and other acids. On pouring off the oil, agitating it with baryta-
water, and submitting the solution to successive crystallizations, caproate
of baryta is first obtained — then oenanthylate, caprylate, pelargonate, and
caprate, and, lastly, valerianate. The more fixed acids are dissolved in water,
and the solution saturated with carbonate of soda : on evaporation, crystals
of acetate of soda separate, and on adding sulphuric acid to the mother-
liquor, an oily layer, consisting of butyric and metacetonic acids is formed.
(Regnault.) There are other modes of obtaining these and the other fixed
acids, which are elsewhere noticed.

Suberic Acid, CigHj^Og, is one of the products of the action of nitric
acid on oleic acid ; it was originally produced by the action of nitric acid
upon cork. When pure, it is a difficultly soluble crystalline powder; suberates
of the alkaline bases are soluble; they give white precipitates with the salts
of lead and silver, =2,{M0,)G,QB.^fiQ.

Butyric Acid (C3H703,H0).— Butter includes several fatty bodies {see
Milk), amongst which are butyrin, caproin, and caprylin, to which its pecu-
liar smell and taste have been referred : these may be resolved by saponifica-
tion into glycerine, and butyric, caproic, and caprylic acids. Butyric acid,
obtained by the decomposition of butyrate of lime by hydrochloric acid, is
a volatile oily body, sp. gr. 0963, and boiling at 315°: it has the odor of
rancid butter, a pungent taste, and is soluble in water, alcohol, and ether :

628 CAPRIC AND VALERIANIC ACIDS.

its salts are mostly soluble and erystallizable. It is among the products of
the action of nitric acid upon olein, and of certain oxidizing agents upon
fibrin or casein, and is found in some fruits. The readiest mode of obtaining
it is that of Pelouze and Gelis, and is as follows: a solution of sugar of the
sp. gr. 1*064, is mixed with powdered chalk amounting to half the weight
of the sugar, and to this a portion of casein or curd is added, equal to 8 or
10 parts for every 100 of sugar, and the mixture kept at a temperature of
about 80°; viscous and lactic fermentations ensue, carbonic acid and hydro-
gen are evolved, and after some weeks hutyrate of lime is formed in the liquor:
in this case the lactic acid which is first formed passes, by loss of carbonic
acid and hydrogen, into butyric acid.

2(HO),C„H,oO,p = ^ H0,CgH,03 + 4C02+4H
Lactic acid. Butyric acid.

This acid appears to be formed in the stomach in certain disordered states
of digestion, and, by mixing with oily or fatty matters, to produce the acrid
liquid which gives rise to heartburn or cardialgia. Dr. Lared found, in
experiments on himself, that heartburn could be produced by swallowing
butyric acid. Pastry and substances of the like nature contain butyric acid
or the elements required for forming it, and these, it is well known, produce
the disorder in question. The remedy consists in the administration of a
mild alkali, either carbonate of ammonia or soda. Cod-liver oil also relieves
it by mixing with the butyric acid and dissolving it.

Capric Acid (CgoH^gOgjHO) is among the products of the action of nitric
acid on oleine, and is one of the results of the saponification of butter, but
it is most readily procured by the oxidation of the oil of Rue by nitric acid
(Gerhardt), and has hence been termed Rutic acid. It is obtained pure by
the decomposition of caprate of baryta by sulphuric acid : it forms acicular
crystals fusible at 86°, of a sour acrid taste, and goat-like odor.

Caprylic Acid {RO,C^^^fi^ is liquid at temperatures above 60°, little
soluble in water, boils at 258°, and has a nauseous odor.

Caproic Acid (H0,C,gE[jj03) is a liquid of a sour odor and taste, boiling
at 390°, and sparingly soluble in water.

Valerianic Acid ; Valeric acid (HOjCjoHgOg). — The volatile oil, obtained
by distilling the root of valerian with water, is a mixture of a hydrocarbon
=CioH2, with an oxygenated oil convertible into valeric acid. This acid has
also been obtained from angelica root, and from the berries and bark of the
Guelder-rose ( Viburnum opulus) : it is an occasional product of the oxidation
of fatty bodies, and is artificially produced by the action of oxidizing agents
(chromic acid) on amylic alcohol {fusel-oil). It is a colorless liquid, smelling
strongly of valerian, and of a sour pungent taste. It boils at 270°, and the
density of its vapor is 3 55. It is soluble in about 30 parts of water, but
may contain 20 per cent, of water without losing its oily appearance. The
Valerianates, when pure and dry, are nearly inodorous, but generally have a
valerianic odor and sweetish taste ; they smell strongly of valerian when
moistened with a dilute acid ; some of them have been used medicinally.
Acted upon by chlorine, valerianic acid furnishes two compounds in which 3
and 4 atoms of its hydrogen are replaced by chlorine, the chlorovalerisic and
chlorovalerosic acids ; and by the protracted action of nitric acid a part of
it is converted into nitrovalerianic acid, =HO,CjoHg07N. The valerianates
of soda and zinc are used in medicine. They are produced by replacing an
atom of water with an atom of the oxide of either metal.

Valerianate of Soda (XaO,C,oH903). — The characters of this com-
pound, as described in the British Pharmacopoeia are, that it is in dry white

LINSEED AND OTHER FIXED OILS. 629

masses without any alkaline reaction. It should be entirely soluble in recti-
fied spirits, and give out a powerful odor of valerian when moistened with
diluted sulphuric acid. The Valerianate of Zinc (ZnCCjoHgOa) is made
by double decomposition, equal weights of valerianate of soda and sulphate
of zinc being dissolved in a sufficiency of distilled water and then mixed.
This salt is obtained in brilliant white tabular crystals of a pearly lustre.
They have a slight odor of valerianic acid, and a metallic taste. The salt
is scarcely soluble in cold water or ether, but is dissolved by hot water or
alcohol, and the hot aqueous solution is not precipitated by a solution of
chloride of barium. When heated to redness, oxide of zinc remains, which
when dissolved in diluted sulphuric acid gives the usual reaction of that
metal.

Fixed Vegetable Oils.

In adverting to the general nature and properties of the oils and fats, we
may select a few more for special notice ; taking linseed-oil as a specimen of
the drying oils, — olive-oil of the non-drying or greasy oils, and palm-oil of
the concrete oils or vegetable butters. The fixed oils are generally of a pale
yellow color : they may be bleached by exposure to light. They should be
neutral, but they frequently have an acid reaction. They are insoluble in
water and not very soluble in alcohol. They are soluble in benzole and
chloroform. When exposed to air they gradually assume resinous charac-
ters, as a result of the absorption or fixation of oxygen. According to re-
cent observations on the drying of oils by oxidation, some volatile products
are given off, consisting chiefly of the formic, acetic, butyric, acrolic, and
carbonic acids, while the fixed residue consists of margaric and oleic acids
associated with a resinous acid. The glycerine also disappears. The greasy
and concrete oils become rancid, principally in consequence of mucilaginous
and albuminous impurities which gradually react upon them. This is espe-
cially observed in olive oil.

When cooled to a low temperature the fixed oils thicken or solidify, —
olive oil at about 36° — colza oil at 22° — linseed oil at a temperature near
zero, and almond oil at some degrees below zero. They may be heated to
about 500° without undergoing decomposition, but they do not admit of
distillation without decomposition ; they are said to boil, but are really de-
composed at about the boiling point of mercury 650°. Owing to this fixed-
ness at high temperatures, a fixed oil may be used as a bath for many useful
purposes. Thus in the manufacture of vulcanized rubber, the melted sulphur
is kept heated to a proper temperature for vulcanization by means of an oil-
bath. The tempering of some articles of hardened steel may also be more
readily effected by employing heated oil, than in judging by the color ac-
quired by the polished surface of the metal. Thus when the oil begins to
smoke, the temper is that of a straw color, or 450°. A darker and more abun-
dant smoke indicates a brown color, 500°. A purple temper, about 530°,
is shown by a still more abundant and black smoke. A blue temper is
reached when the oil takes fire on the application of a flame, but ceases to
burn on its removal, a temperature of about 580°. The usual temper for
springs is found to be when the oil takes fire and continues to burn.

Linseed oil, obtained by expression from the seeds of the Linu7n usitatis-
simum, or common flax, remains fluid until cooled down to about 0°, when
it gradually solidifies.. It is largely used for paints and varnishes, and for
these purposes its drying quality is increased by heating it with a little
litharge. It is an important component of Printers^ Ink, for which it is first
heated and then set fire to, and allowed to burn for some time, when it is
extinguished, and the heating continued till a film forms upon it } m this

630 OLIVE, ALMOND, CASTOR, AND PALM OILS.

state it is called varnish, and is easily raiseible with fresh oil, or with tur-
pentine, or other matters required for thinning or tempering it, and about a
sixth or eighth part of fine lamp-black is then added. Silk and leather are
varnished and enamelled with similar preparations of linseed-oil. Walnut,
hemp, and poppy-oil also rank with the drying oils, but are inferior to linseed-
oil.

Olive-oil, IS expressed from the fleshy part of the fruit of the olive tree. It
varies in quality according to the mode of obtaining it. What is termed
virgin-oil is obtained by gentle pressure at common temperatures : it has a
very slight nutty flavor, and is long in becoming rancid. Its sp. gr. at 60^
is about 0"915. This oil is unrivalled for culinary use, and being less apt
than most other oils to thicken by exposure to air, it is preferred for greas-
ing delicate machinery, especially watch and clock-work. In order to pre-
pare it for this purpose, the finest and purest cold-drawn oil is first selected :
it is then cooled, and the more liquid portion poured ofl'from the fatty deposit ;
a piece of sheet-lead or some shot are then immersed in it, and it is exposed
in a corked phial to sunshine ; a white matter separates, after which the oil
becomes clear and colorless, and is poured off for use.

Almond-oil is prepared from sweet and bitter almonds ; the purest is cold-
drawn, by gentle pressure, from coarsely-powdered almonds: when hot-
pressed, it has a deeper color, and becomes sooner rancid.

Colza oil is an inodorous yellowish oil obtained from cabbage-seed {Bras-
sico oleifera). It has a sp. gr. of '915. It is most extensively used as a
cheap and good burning oil.

Oil of Ben, from the seeds of the Moringa aspera, separates soon after
expression into oleine and margarine ; the former is much esteemed for oil-
ing watch- work, as it neither becomes viscid nor rancid ; hence also its excel-
lence for certain scented oils, as of jasmine and tuberose flowers.

Castor-oil is obtained from the seeds of the Ricinus communis. This is
the heaviest of the fixed oils, its sp. gr. being 0*969. It is a thick, viscid,
colorless oil ; when cooled to 0^ it congeals into a transparent mass. Although
not a drying oil, it hardens by exposure to air. It dissolves in all propor-
tions of alcohol and ether, and thus differs from other fixed oils. It forms
a thick tenacious mass when mixed with collodion. This singular compound
has been called Parkapine, from its discoverer, M. A. Parks. Castor oil is
much used as a hair oil, and medicinally as a mild aperient. The products
of its saponification are peculiar ; and when acted on by nitrous acid it pro-
duces a concrete fatty substance, the palmic or ricinelaidic acid.

In the subjoined table we have given the specific gravities of good sam-
ples of the principal fixed oils : —

Sperm oil

. -8750

Southern whale

. -9225

Colza

. -9156

Poppy .

. -9254

Olive (flask) .

. -9158

Cod-liver .

. -9285

Olive (jar)

. -9171

Linseed .

. -9362

Olive (cask)

. -9174

" boiled .

. -9506

Almond ,

. -9214

Castor

. -9674

Palm-oil and Cocoa-nut oil are good specimens of vegetable butters. Palm-
oil is chiefly produced from the fruit of the Elais Guineensis ; it is orange-
colored, but admits of bleaching, and has the violet odor of orris-root. It
is used in the manufacture of soap, candles, and a composition for greasing
the axles of railway carriages, in which it is combined with soda. Cocoa-
nut oil, from the Cocos nucifera, fuses at about 70*^ ; but its stearine, mixed
with a portion of the stearic acid of tallow, forms a good and cheap candle.
By saponification it afl'ords several distinct acids. Chocolate-nut oil, ex-
pressed from the seed of the Theobroma Cacao, gives greasiness to Chocolate,

MANUFACTURE OF SOAPS. 631

which is made by torrefying the bean, and grinding it into a fine paste in a
hot mill or mortar. The varieties of cocoa are derived from the same source.
Nutmeg butter, the concrete oil of the nutmeg, and Laurel-oil, the fat of the "
bay berry, belong also to this class, and when saponified yield mynstic and
lauric acids, and glycerine.

^ Animal fats are generally contained in the adipose membrane or cellular
tissue, which is chopped up and heated so as to liquefy the fat : the remain-
ing membranes are rendered crisp by the heat, and when the fat has been
pressed out of them are sold in the form of flat cakes, called greaves or crack-
lings, used as a coarse food for dogs, as a manure, and in the manufacture of
ferrocyanide of potassium. Whale-oil, when saponified, yields fatty acids
and glycerine, and traces of phocenic acid. Spermaceti-oil deposits the pecu-
liar white fatty crystalline matter, Spermaceti. The oil itself is an oleate of
glycerine. It is the lightest of the fixed oils, having a sp. gr. of 0-878. It
is of a yellow color, and when cooled to about 45° assumes a semi-solid
state. Spermaceti, or Cetine, when saponified, affords no glycerine, but in
its place a distinct base termed jEtkal,=G^fl^fi^. Pure spermaceti (C8,H„^0J,
fuses at about 120° ; its sp. gr. is 0 940 ; it dissolves in boiling anhydrous
alcohol and in ether, but falls on cooling. When subjected to destructive
distillation it is resolved into a liquid hydrocarbon, ce^ewe, = Cg^Hg.^, and ethalic
or palmitic acid (CggHg^OaHO). Ethal fuses at about 118°, and is deposited
from its hot alcoholic solution in white flakes. When distilled with anhy-
drous phosphoric acid it yields cetene. When oxidized by the protracted
action of boiling nitric acid, spermaceti yields succinic, oenanthylic, pimelic,
and adipic acids.

Beeswax consists, according to Brodie {Phil. Trans., 184T-49), of three
substances separable by boiling alcohol : namely, of Myricin (Cg^Hg^Oj,
which is insoluble.; Cerin {G^^^fi^, which is deposited in crystals as the
solution cools ; and Cerolein, which is retained in solution. Their relative
proportions vary, but in ordinary beeswax there appears to be about 73
per cent, of myricin, 22 of cerin, and 5 of cerolein. The Myrica cerifera,
and some other trees, yield vegetable wax. White wax melts at 140°. Its
specific gravity is "960.

Soaps. ^

Common hard soaps are chiefly made with tallow and soda, they are there-
fore stearates, margarates, and oleates of soda. The sp. gr. of the solution
of caustic soda is about 1*15, and is prepared in the usual way by the action
of lime upon carbonate of soda. When the lye is raised to its boiling-point
the tallow is gradually added so long as the lye saponifies it, and in this way
a liquid is obtained, which holds the soap and glycerine in solution : to
separate the former, common salt is added ; soap being insoluble in brine, is
thus brought to float upon the surface, and, if the brine is concentrated, the
soap separates nearly in an anhydrous state ; but as this is not the object of
the manufacturer, the quantity of salt employed is only such as to effect the
separation of the soap without dehydrating it. New soap is said to contain
about 50 per cent, of water, and to retain above 30 per cent, when compara-
tively hard and dry. The alkali amounts to from 5 to 7 per cent. There
is, therefore, a manifest advantage to the consumer in purchasing dry and
old soap, while the object of the vendor is to sell the soap as humid as
possible, and to prevent its d'esiccation, which is effected by keeping it in
damp cellars. The following analyses represent the comparative composition
of some well-known varieties of soap : —

632 MANUFACTURE OF SOAPS.

BEST YELLOW.

BEST MOTTLED.

Tallow acids .

. 50-00

Bone-tallow acids .

. 62-40

Water .

. 31-50

Water .

. 30-00

Caustic soda .

. 6-50

Caustic soda .

. 7-60

Resin

. 12-00

MARINE.

BLUE MOTTLED.

Cocoa-oil acids

. 23-00

Palm and cocoa-acids

. 50-00

Water .

. 59-60

Water .

. 41-20

Caustic soda .

. 2-70

Caustic soda .

. 7-30

Chloride of sodium

. 14-70

Salts

. 1-80

{Laboratory, No. 10, June, 1867, p. 176.) In the glycerine soap a large
proportion of glycerine is incorporated with the fatty salts. Soap is some-
times colored, mottled, or maj*bled, by the addition of coloring matters : the
mottling is produced by oxide of manganese. Sometimes a solution of
sulphate of iron is used, which being decomposed, causes the diffusion of
oxide of iron through the soap ; in these cases the mottling is originally
black, but becomes red or brown or variegated upon the exterior of the bars
in consequence of the action of the air. A considerable quantity of common
rosin is added to the yellow soaps of commerce. There are also other
additions made to soap, some of which are supposed to improve its detergent
quality ; but, generally speaking, they deteriorate the article, and are princi-
pally resorted to as adding to the weight of the soap by the substitution of
cheap materials ; sand, clay, fuller's earth, alkaline silicates, sulphate of soda,
Cornish clay, aluminate of soda, starch, flour, and many other substances,
have been employed. The use of such substances as these in the manufacture
of soap can only be regarded as a fraud upon ihe public, often legalized by
the granting of a patent to the manufacturer ! Excepting the alkaline sili-
cates, which of course only operate by their alkalinity, the other ingredients
have no detergent action whatever. The presence of a large percentage of
water artificially kept in the soap and the addition of a large quantity of
silica in the form of silicate add greatly to the weight of the soap, and 'pro
tanto reduce its value as a detergent compound. Silicic acid is not so
costly as the fatty acids ; hence the addition is in favor of the manufacturer.

Curd soap is usually manufactured from tallow only, but sometimes lard or
olive oil is added. Common yellow soap is made from tallow, palm oil, and
common rosin. The latter being acid, combines with the alkali to form a
saponaceous compound.

The soaps known in commerce as Spanish soap (Sapo durus) and Marseilles
soap are soda-soaps of olive-oil. Palm-oil and cocoa-nut oil are also largely
nsed as sources of soap, and mixtures of these with the animal fats and bone-
grease are employed as the basis of scented and other toilet soaps. Bone
grease is manufactured in enormous quantities by the bone-boilers in and
around London : in addition to its use in the production of the finest toilet
soaps, it is employed in the manufacture of scented and colored pomatums,
and of an article commonly sold under the name of Beards grease. Soaps
are perfumed with various essential oils. Nitro-benzole under the name of
Essence of Mirhane is largely employed as a cheap substitute for the essential
oil of bitter almonds.

The soaps of potassa are distinguished from those of soda by remaining
soft (Sapo mollis). Common soft soap is frequently made with fish-oil.
Naples soap is a perfumed potassa-soap made with lard. Transparent soap
is obtained by dissolving soap in alcohol, which is afterwards distilled off, so
as to leave a soft brown transparent residue, which is dried in moulds or balls.
The soaps of potash, soda, and ammonia are soluble in water, but those of the
alkaline earths and metallic oxides, which are produced by double decompo-

MANUFACTURE OF SOAPS. ACROLEINE. 633

sition, are insoluble in water, and float upon it, forming a curd. A good
soda soap forms a thick viscid liquid with distilled water — the solution is
frothy when shaken : it has an alkaline taste and reaction. A solution of
pure oleate of soda with glycerine is remarkable for the tenacity which it
gives to water, and has been much employed for producing soap-bubbles of
large size and remarkable for their preserving their form for a long time.
Soap is soluble in alcohol, but its best solvent is a mixture of one part of
water with three parts of alcohol. An alcoholic solution of soap is employed
as a soap-test for determining the relative degrees of hardness in river or
spring water. For this purpose Castile or Spanish soap is preferable, as
the solution is less liable to spontaneous changes. A solution of soap is
decomposed by all acids and earthy salts, especially by the salts of lime and
magnesia. Acids take the alkaline base and set free the fatty acids of the
soap, while the calcareous and magnesian salts form insoluble white curdy-
looking compounds, which float on water. When heated, soap melts and
gives off a combustible vapor, leaving an ash either of soda or potash, and
sometimes consisting of a mixture of the alkalies in the state of carbonate.

When the fats and oils are decomposed by oxide of lead, the resulting
combinations of the fatty acids with that oxide, is known under the name
of Lead plaster. {Emplastrum plumhi ; Diachylon.)

AcROLEiNE (CeH^Og).— When the ordinary fatty bodies are subjected to
destructive distillation, the oleic acid is partially converted into sebacic acid,
the stearic into margaric acid, and the glycerine into acroleine. When
glycerine is distilled with anhydrous phosphoric acid, water and acroleine are
the products, and the latter may be dehydrated by rectification over chloride
of calcium. Glycerine contains the elements of acroleine with four equiva-
lents of water, hence under the dehydrating action of phosphoric acid, the
conversion. is readily effected: —

CeHgOe = C^HA + 4H0

^ — . ' » — . — ' -—^-' ^gjgj

Glycerine. Acroleine. Water. "^^Bl

Fatty bodies which contain no glycerine do not yield acroleine by distillation.
Thus while tallow produces it, stearic acid does not. Some have regarded
acroleine as the aldehyde of glycerine. Pure acroleine is a limpid colorless
liquid of a highly irritating odor, lighter than water, boiling at about 125°,
and burning with a bright flame ; it is soluble in alcohol and ether, but only
sparingly so in water. It soon undergoes spontaneous changes, depositing
an isomeric white substance, disacryle, and a resinoid body ; and when ex-
posed to air, or more especially when oxidized by oxide of silver, it is con-
verted into acrylic add=(RO,Q^B.^O^), a portion of the oxide being at the
same time reduced; CflH,0,+3AgO,=(AgO,C6H303)+2Ag-|-HO.

634 VEGETABLE ACIDS. TARTARIC ACID.

CHAPTER LII.

VEGETABLE ACIDS.

The acids of the regetable kingdom are very numerous as a class. About
lYO are now known. They are for the most part solid and colorless, and
many are crystalline. They are combined with potassa, soda, or lime, and
are thus contained as salts in the juices of plants. Some are educts, i. e.,
they exist in the vegetable structure, and are separated by simple processes.
The tartaric, citric, malic, gallic, and tannic acids are instances of this class.
Others, like the pyrogallic, mucic, and picric acids, are products of art.
These are the most numerous, and their number is annually increasing.
Others, again, as the oxalic and benzoic acids, are both educts and products.

The vegetable acids are soluble in water and in alcohol : they form with
bases various classes of well-defined crystalline salts. By reason of their
superior affinity, they sometimes displace mineral acids from their saline
combinations. Thus oxalic acid separates lime, and the oxides of silver and
copper, from the solutions of the salts of these bases ; and picric acid sepa-
rates potassa from the salts of that alkali. Tannic acid precipitates the
salts of lead, antimony, and other metals. This acid generally forms pre-
cipitates (insoluble compounds) with most of the alkaloids, and separates
them from their mineral acid combinations. Some of these acids have a
simple constitution, being formed of three elements C H O : one (the oxalic
acid) is formed of C 0 only. Others, especially those of artificial origin,
are much more complex : thus picric, or carbazotic acid, has the composition
of (C,2H20(NO^)3,HO). When dissolved in water, some, such as the tartaric,
citric, and gallic acids, undergo decomposition, and vegetable mould results.
Others, such as the oxalic and acetic, show no tendency to decomposition.
All are decomposed by heat in close vessels : some are volatile when heated
to a moderate temperature in air (benzoic, formic, acetic) ; others are fixed,
and are decomposed when strongly heated, either being entirely burnt, or
leaving a residue of carbon. When the salts of these acids are heated in close
vessels, carbon and a carbonate of the base result. The equivalents of these
acids are high : they are easily determined by the rules already explained.

Tartaric Acid (C8H,0,o2HO=T).

This acid is found free, and in combination, in many vegetables. It is
found in the grape, mulberry, tamarind, and pine-apple ; but its principal
source is the juice of the grape, in which it exists in the form of tartar, or
bitartrate of potassa (KO,HO,C8H40io)- This salt is decomposed as follows :
4 parts of it in fine powder, are well mixed with one part of powdered chalk,
and the mixture thrown, by small portions at a time, into 10 parts of boiling
water ; when the effervescence is over, the whole is stirred and left to subside ;
the liquid, which is a solution of neutral tartrate of potassa, is then poured
off the sediment, which is tartrate of lime, and a solution of chloride of
calcium is added to it. This throws down an additional portion of tartrate
of lime, which is mixed with the first, and having been well washed, is de-
composed by dilute sulphuric acid ; this forms sulphate of lime, while the
tartaric acid remains in solution, and is obtained by slow evaporation. The

TARTARIC ACID. THE TARTRATES. 635

first crystals require to be redissolved, and digested with a little purified
animal charcoal until the liquid is colorless ; it is then again evaporated and
crystallized. Tartar may be similarly decomposed by carbonate of baryta
and chloride of barium; the resulting sulphate of baryta falls more rapidly
than the sulphate of lime, and may be used for white paint.

Crystallized tartaric acid is very sour: its sp. gr. is 1-74; it is translucent,
and of complicated forms, derived from an oblique rhombic prism. It acquires
electric polarity by heat. It is permanent in a dry atmosphere : water dis-
solves about 1-5 its weight at 60°, and more than twice its weight at 21 2^.
It is also soluble in alcohol. The dilute aqueous solution soon becomes
mouldy. It is converted into oxalic and acetic acids by fusion with potassa.

^C8H,0,o,2HO] + 3 [KO,HO] = [KO.C^HgOa] + 2[KO,C203] + 6[H0]

Tartaric acid. Potassa. Acetate of potassa. Oxalate of potassa. Water.

It is transformed by the action of peroxide of manganese, or of lead, into
formic and carbonic acids.

[C8H,0,o,2HO] + eCPbOJ = 2[PbO,C2H03] -f 4[PbO,C02] + 4[H0]

Tartaric acid. Peroxide of lead. Formate of lead. Carb. of lead. Water.

Tartaric acid is distinguished by the white granular precipitate which it
produces when added in excess to solutions containing potassa. If these
solutions are very dilute, the crystalline precipitation is accelerated by the
addition of alcohol. It produces a white precipitate, soluble in an excess of
the acid, in lime, baryta, and strontia- water, and in acetate of lead. It is
used in calico-printing, and is much employed as a cheap substitute for citric
acid in lemonade and in effervescent solutions. In the laboratory it is used
as a test for the salts of potassa, and to prevent the precipitation of certain
oxides, as the oxide of antimony, and titanic acid.

The tartaric acid of commerce is apt to be contaminated by traces of sul-
phuric acid and of lead. To detect sulphuric acid, chloride of barium may
be used : if added in excess, or if the solution of tartaric acid is concentrated,
tartrate of baryta will fall ; but the presence of sulphuric acid in the precipi-
tate is recognized by its insolubility in hydrochloric acid, which acid dissolves
tartrate of baryta. Sulphuretted hydrogen is the test for the presence of lead.
If lead is present this gives a brown discoloration to the solution. This
impurity is derived from the leaden pans in which crystallization takes place.

Pasteur has shown that there are two modifications of crystallized tartaric
acid. The crystals of one variety, when dissolved in water, turn the polar-
ized ray to the right — dextro-tartaric, or the common tartaric acid. Other
crystals selected from the same mass, when dissolved in water, turn the ray
to the left — Icevo-tartaric add. Both sets of#rystals are unsymmetrical, but
the absence of symmetry is exactly in opposite directions. It is remarkable
that when equal parts of the two acids are mixed, crystals are deposited from
the mixture, which appear to be identical in properties with racemic acid :
they have no action on a ray of polarized light. As racemic acid diflfers in
chemical properties from the tartaric, these facts show a singular relation
between the crystalline forms and the chemical and optical properties of
bodies.

The tartrates are mostly crystallizable, and are either neutral or acid. In
the neutral tartrates 2 atoms of base are combined with 1 atom of acid, as in
neutral tartrate of potassa, which is 2(KO),C8H^O,o, or in tartrate of potassa
and soda =KO,NaO,CsH^Oio. In the acid tartrates (or bitartrates) 1 atom
of water replaces 1 of the bases, as in bitartrate of potassa, which is KO,

636 METALLIC TARTRATES.

HOjCgH^Ojo. There is also an important class of tartrates in which one of
the bases is a protoxide and the other a teroxide, the salt being neutral,
as in the tartrate of potassa and antimony (emetic tartar), which is KO,Sb
03,C8H^Oio. Lastly, there are tartrates in which one of the bases is replaced
by a weak acid, as in the boro-tartrate of potassa =KO,B03,C8H^Oio.

Tartrate of potassa^ 2(K0),T, used as an aperient under the name of solu-
hie tartar, forms prismatic crystals of a saline and bitter taste, soluble in two
parts of water. Most of the acids occasion a precipitate of the acid tartrate
in the aqueous solution of this salt, by abstracting an atom of potassa.

Acid Tartrate. Bitartrate of Potassa. Tartar (KO,HO,T). — This salt
exists in the juice of the grape, and is deposited in wine-casks in the form of
a white or red crystalline incrustation, called argol, or crude tartar. It is
purified by dissolving it in boiling water, with one-twentieth of its weight of
pipeclay, which absorbs the coloring matter, and falls as a sediment, the
crystals of tartar separating afterwards upon the surface of the liquor, and
upon the sides and bottom of the boiler; the term cream of tartar was origi-
nally applied to the imperfectly crystallized superficial crust. The acid tar-
trate of potassa is also formed by adding excess of tartaric acid to a solution
of potassa : the mixture presently deposits crystalline grains, and furnishes
an example of diminution of solubility by increase of acid in the salt. Upon
this the use of tartaric acid as a test for potassa depends ; for soda forms an
easily soluble supertartrate, and affords no precipitate.

The crystals of this salt, which are rhombic prisms, include one equivalent
of water, which is not separable at a heat much below that at which the acid
of the salt begins to be decomposed. They are hard, gritty, and subacid ;
sp. gr. 1-95. This salt is soluble in 184 parts of water at 68° ; and in 18
parts at 212°. It is rendered much more soluble by the addition of boracic
acid or of borax; 2 parts of borax and 5 of tartar are soluble in about six
times their weight of boiling water; on evaporating the solution, the residue
concretes into Le Fevreh soluble cream of tartar, or sal-gummosum. When
exposed to heat in a close vessel, tartar fuses, blackens, and is decomposed,
and carbonate of potassa, mixed with charcoal (black flux) remains. It is
an excellent flux in the reduction of metallic ores, upon a small scale, its
alkali promoting their fusion, and the carbonaceous matter tending to reduce
the oxides. Tartar is sometimes adulterated with pounded quartz or calca-
reous spar; the former is detected by its insolubility, the latter by efferves-
cence with dilute hydrochloric acid. Tartrate of lime is often present in
purified tartar ; it separates in tufts of acicular crystals from a hot solution
of the salt.

Tartrate of soda (2(NaO),T+4HO) forms acicular crystals, soluble in
about their own weight of w%ter. When their aqueous solution is mixed
with half their weight of tartaric acid, it yields small prismatic crystals of
acid tartrate of soda, =NaO,HO,T,2HO, of an acid taste, soluble in 8 parts
of cold and 1-8 of boiling water. Tartrate of soda is formed extempora-
neously by dissolving equal parts of powdered tartaric acid and of bicar-
bonate of soda, in separate portions of water, and then mixing the solutions ;
it forms a refreshing saline and slightly aperient draught.

Tartrate of potassa and soda (KO,NaO,T + 8HO) is prepared by satu-
rating the excess of acid in tartar, with carbonate of soda : it is the Soda
tartarizata of pharmacy ; it forms fine transparent prismatic crystals. This
salt has long been used as a mild aperient, under the name of Rochelle Salt,
and Sel de Seignette, having been first prepared at Rochelle by an apothecary
of the name of Seignette. The crystals are soluble in about 3 parts of cold
water.

ACTION OF HEAT ON TARTARIC ACID. 637

Tartrate of lime is often found as a hard crystalline deposit in light white
wines. It falls on dropping tartaric acid into lime-water, and is soluble in
excess of the acid.

Tartrates of iron — The prototartrate falls as a whitish crystalline powder
on adding tartaric acid to protosulphate of iron. When recently prepared
and moist peroxide of iron is dissolved in tartaric acid, an uncrystallizable
salt is produced, which is not precipitated by the alkalies.

A pertartrate of iron and potassa is formed by digesting hydrated peroxide
of iron with tartar and water : made into balls, and dried, it forms the
glohuli martiales, or Boules de Nancy, of old pharmacy.

Tartrate of copper forms a bluish green crystalline precipitate in a mixture
of tartrate of soda and sulphate of copper : if the solutions are very dilute,
the salt is long in falling, but on striking the glass, or drawing lines upon it
with a glass rod, it soon appears. Dissolved in a solution of soda, this salt
forms a deep blue liquid, useful as a test for grape-sugar.

7hrtrate of lead is a white crystalline powder thrown down by tartaric
acid, or a tartrate, from a solution of nitrate of lead. After having been
heated in a glass tube to dull redness, it leaves a pyrophorus, which inflames
when shaken out into the air, in consequence of the rapid oxidizement of
the finely-divided lead.

Tartrate of potassa and antimony; Emetic tartar (KO,Sb03,C8H^Ojo,HO),
is obtained by boiling any of the forms of SbOg with tartar and water. It
is a white salt, of a nauseous styptic taste, slightly efflorescent, soluble in
about 14 parts of cold, and in less than 2 parts of boiling water. Its solu-
tion is rendered turbid by hydrochloric, nitric, and sulphuric acids, but not
by the fixed alkalies : the fixed alkaline carbonates, and lime-water, decom-
pose it. Ammonia throws down oxide of antimony, especially when aided by
beat. Infusion of galls and many other vegetable bitter and astringent infu-
sions form a precipitate in a solution of emetic tartar, which is generally
said to be inactive, and hence decoction of bark has been recommended as
an antidote to its poisonous effects. It is not precipitated by a solution of
ferrocyanide of potassium. A solution of sulphuretted hydrogen precipi-
tates only strong solutions of emetic tartar ; weaker solutions are merely red-
dened by it : it is also decomposed by hydrosulphate of ammonia ; in these
cases the precipitate is sulphide of antimony. Heated to redness, out of the
contact of air, it furnishes a highly-pyrophoric residue, which contains an
alloy of potassium and antimony.

Action of Heat on Tartaric Add. — When common crystallized tartaric
acid is heated to about 350°, it fuses without losing weight, and congeals on
cooling into a vitreous mass, which has the same saturating power as the
original acid, but which produces salts differing in crystalline form, and more
soluble than the common tartrates. If the heat exceed 360^, the acid
becomes monobasic, but still without loss of weight, and is represented by
CsHgOji.HO: it forms* with potassa an uncrystallizable, deliquescent salt.
These isomeric modifications have been designated metatartaric and isotar-
taric acids : when solutions of their salts are boiled, they gradually revert to
common tartrates. When the common acid is kept in fusion at about 372°,
it loses half an equivalent of water, and is changed into tartralic acid. The
tartralates are quite distinct from the tartrates : those of lime, baryta, and
strontia are soluble in water, and there is no difficultly soluble potassa salt.

When the temperature of the fused tartaric acid is raised to 392^ it loses
an equivalent of Vater, and becomes tartrelic acid: in this state it forms a
peculiar syrupy precipitate with the acetates of lime, baryta, and strontia,

638 . RACEMIO ACID. CITRIC ACID.

and produces neutral salts with one equivalent of base. The tartralates are
converted into tartrates, when boiled with water.

By carefully continuing the action of heat on tartaric acid, it may be ob-
tained anhydrous ; it is then white, amorphous, and insoluble in cold water:
but by the protracted action of water, or by boiling, it reverts to its ordinary
condition, by the resumption of two atoms of water.

Characters of Tartaric Acid. — 1. When heated on platinum foil, it melts
and burns with a reddish flame, evolving a peculiar odor. It leaves a slight
residue of carbon. 2. Its aqueous solution is precipitated by lime-water,
the white precipitate (tartrate of lime) being dissolved by a slight excess of
acid, or by a large quantity of water. 3. A concentrated solution of the
acid is precipitated by a solution of potassa, provided the acid is in excess.
A small quantity of alcohol facilitates the precipitation. 4. Nitrate of silver
produces no precipitate in a diluted solution. When the acid is neutralized
by potassa, nitrate of silver throws down a white precipitate, which is black-
ened and decomposed when heated to 212°. 5. A few drops of the acidr
solution evaporated on a glass-slide, leave prismatic crystals, which assume a
plumose form.

Racemio Acid: Uvic Acid; Paratartaric Acid. — This acid, formerly
considered as peculiar to the grapes of certain districts, has been found
generally in the juice of sour grapes. It is obtained by saturating the juice
with carbonate of soda : the double tartrate is allowed to crystallize, and
the double racemate, being more soluble, remains in the mother-liquor ; it is
decomposed by carbonate of lime, and the racemate of lime (treated as the
tartrate) affords crystals of racemic acid, in the form of oblique rhombic
prisms. It may be obtained anhydrous ; and in this state as also in the
intermediate states of hydration, it resembles tartaric acid, but it is distin-
guished by its inferior solubility in alcohol, and by furnishing a precipitate
with nitrate and sulphate of lime, as well as with chloride of calcium.

The relations of the anhydrous tartaric acid to its several hydrated modi-
fications are as follows : —

Anhydrous tartaric acid .... CgH^Ojo

Crystallized tartaric acid .... CgH^Ojg 2H0

Metatartaric acid ..... CgH^OiQ 2H0

Isotartaric acid ..... Cj^HgO,, HO

Tartralic acid 2(CgH40,o)3HO

Tartrelic acid C8H40,o HO

Racemic acid C8H40,o 2H0

Pyruvic Acid ; Pyrotartaric Acid. — When tartaric acid is subjected to
distillation at about 400*^, it furnishes, among other products, a liquid and a
crystalline acid. The former produces a characteristic red color with pro-
tosalts of iron, and is monobasic : its formula is HO,CgH305. The latter is
bibasic : it forms soluble salts with baryta, strontia, and lime : its formula is
2(HO),C,oHeOe.

Citric Acid (C^H50,„3HO=Ci).

This acid, discovered by Scheele in 1784, is found in several fruits, but is
especially abundant in lemon-juice. To obtain it, the juice, clarified by
heating it with a little white of Qgg, is saturated with chalk added in small
portions, so long as it occasions effervescence : this throws down citrate of
lime ; but a portion of acid citrate remains dissolved, which may be neu-
tralized by hydrate of lime. When the liquid no longer reddens litmus, the
precipitated citrate is washed, and decomposed by dilute sulphuric acid,
which forms sulphate of lime, and the citric acid is retained in solution ; it
is filtered off and evaporated until a crystalline pellicle appears on the surface :

CITRIC ACID. ITS CHEMICAL PROPERTIES. 639

crystals of citric acid are deposited, which are purified by repeated solntion
ana crystallization. (The practical details of the process are given in
Parks' Chemical Essays.) A gallon of good lemon-juice yields about 10
ounces of pure acid. Citric acid crystallizes in rhoraboidal prisms, which
are dissolved by their weight of cold water, and are soluble in alcohol, but
not in ether. It is considered as tribasic, the formula of the ordinary citrates
being 3(MO),C,aH50i^. The ordinary crystals deposited from a hot saturated
solution are 3(HO),Ci2HgO„+HO ; but those obtained from spontaneous
evaporation, from a cold solution, are 3(H0),Cj.^H.0ii-f 2H0. The former
neither lose weight nor transparency at 212°, but the latter, dried at 212°, lose
their adventitious water, and become 3(H0),Cj.^H.0ii. Anhydrous citric acid
has not been isolated. When the crystals are highly heated, inflammable gas
and vapor are disengaged, and a yellow residue obtained which is aconitic acid.
Citric acid is used in the preparation of acid drinks, and in pharmacy, as a
substitute for lemon-juice. When mixed with tartaric acid, the adulteration
may be detected by adding to the acid, dissolved in cold water, a solution of
acetate of potassa, which occasions the precipitation of acid tartrate of
potassa. When citric acid is added to lime-water, the liquid remains clear
until heated : it then becomes turbid, and deposits citrate of lime. This
character distinguishes it from several other vegetable acids. Heated with
sulphuric acid, citric acid is resolved into carbonic oxide, carbonic acid,
acetic acid, and water. The action of sulphuric acid on this acid and tar-
taric acid is diflferent. When tartaric acid is heated with sulphuric, the
mixture is intensely blackened ; when citric acid is thus treated, the liquid
acquires only a pale-yellow color. The presence of tartaric acid in citric
would be indicated by a considerable darkening. The deoxidizing or re-
ducing powers of citric acid are less than those of tartaric acid. Thus when
a tew drops of solutions of the acids or their soluble salts are added to a small
quantity of a solution of green manganate of potash rendered strongly alka-
line, and the liquids are heated, the color is rapidly discharged by tartaric
acid as a tartrate, but not by citric acid as a citrate. The dififereuce is so
marked that the manganate of potash may be employed to detect the adulte-
ration of citric with tartaric acid. When citric acid is decomposed by fusion
with caustic potassa, it yields oxalic and acetic acids, and water.

Citrates. — The citric, like other tribasic acids, forms neutral and acid
salts: they are mostly soluble in water, and when lime-water is added to
their solutions, they become turbid when boiled, but again clear on cooling.
The citrates of potassa and of soda are used medicinally. Citrate of lime is
the usual source of the pure acid.

Action of Heat on Citric Acid. — When carefully heated, citric acid loses
2 atoms of water, and is transformed into aconitic acid (equisetic or citricic
acid), an acid found in the varieties of aconite, and in the equisetums ; —

Citric acid. Aconitic acid.

SHOjCjaHgO,, = CiaHgOja + 2H0

Under the continued influence of heat, aconitic acid yields carbonic acid,
and an oily distillate which crystallizes on cooling, and is a mixture of two
isomeric acids, one much less soluble than the other, the itaconic (pyrocitric
or citricic acid), and the eitraconic acid; their formula is '•1)10^^^)1^^.

Aconitic acid. Itacouic acid.

C„HeO„ = C,oH,0, -f 2C0,

. Characters of Citric Acid.^l. When heated on platinum, it melts, and
burns with a yellow flame, leaving scarcely any carbon. 2. Its aqueous solu-

646 MALIC ACID. TANNIC ACID.

tion is not readily precipitated by lime-water until it is boiled, when citrate
of lime is thrown down, 3. A concentrated solution of the acid is not pre-
cipitated by potassa. On this is founded a method of detecting the adul-
teration of citric with tartaric acid. Cover a glass plate with a layer of solu-
tion of potassa, and drop on the liquid the powdered acid. If pure, the
citric acid simply dissolves : if tartaric acid is present, stellated prisms of
acid tartrate of potassa are formed in groups, and remain. 4. Nitrate of
silver produces in the solution no precipitate. When the acid is neutralized
by potassa, nitrate of silver throws down white citrate of silver, which is
only slightly discolored and partially decomposed when heated to 112^^. 5.
A few drops of the acid evaporated slowly on a glass slide, leave small cir-
cular groups of prismatic crystals radiating from a centre.

Malic Acid. SorMc Add (C8H,08,2H0=Ma).

The existence of a distinct acid in apple-juice was first proved by Scheele,
in 1784: it was thence called Malic acid. In 1815 Donovan found it in
the berries of the mountain-ash (Sorbus aucuparia). It occurs in other
vegetables, especially (with oxalic acid) in the stalks of garden rhubarb. It
is obtained from the clarified juice of ripe mountain-ash berries, by adding
to it acetate of lead, washing the precipitate with cold water, then pouring
boiling water upon the filter, and allowing it to pass through the precipitate
into glass jars : after some hours, crystals of malate of lead are deposited,
which are to be boiled with 2-3 times their weight of dilute sulphuric acid,
sp. gr. 1'09; the clear liquor then poured off, and while still hot, sulphu-
retted hydrogen passed through it to precipitate the remaining lead ; the
liquid, after having been boiled and filtered, is a solution of nearly pure
malic acid. It crystallizes with difficulty in deliquescent prisms. The malates
are either acid or neutral, the acid being bibasic. They are mostly soluble
in water, and insoluble in alcohol. Lime-water is not rendered turbid by
malic acid, but on evaporating the solution, crystalline malate of lime sepa-
rates, which is redissolved by boiling. These characters distinguish malic
acid from oxalic, tartaric, racemic, and citric acids. The peculiar and
brilliant crystalline appearance which recently precipitated malate of lead
assumes when left in the liquid, is characteristic of this salt. A mixture of
malate of lime and water, with a little yeast, gradually ferments ; carbonic
acid is given off, and succinic and acetic acids are found in the residue.

Malic acid. Succinic acid. Acetic acid.

3(C8H408,2HO) = 2(C8H305.3HO) + (C,H303,HO) -f AGO, -f 2H0.

Action of Heat on Malic Acid. — When this acid is heated up to about
400°, it is resolved into water and a crystalline sublimate of Maleic Acid (p.
634); but if the heat is carefully maintained between 270° and 280°, the
product is Fumaric or Paramaleic Acid, an acid found in Fumitory, and
isomeric with maleic acid : it is especially characterized by the insolubility
of the fumarate of silver : according to Dessaignes, a liquid containing one-
200,000th of fumaric acid, gives a precipitate with nitrate of silver.

Tannic Acid ; Tannin ; Quercitannic Acid ; Gallotannic Acid
(C«H,A4,=Qt)-
There are many vegetable substances containing a principle which confers
upon them an astringent taste, and which has the property of forming a pre-
cipitate in a solution of gelatine, and of striking a dark-blue or black pre-
cipitate with solutions of the persalts of iron. These properties are pos-

TANNO-GALLATES. INK. GALLIC ACID. 641

sessed in a remarkable degree by an infusion of gall-nuts — the excrescences
which form upon the branches and shoots of the Quermis infectoria^ being
produced by the puncture of the female of the Cynips gallae tinctorice. The
insect deposits its ovum in the puncture, and occasions the excrescence, or
gall, within which the larva is developed, and when the insect is perfect, it
eats its way out. The best galls, known as hlack or blue halls, are gathered
before the insect has escaped ; the white galls are those from which the insect
has departed, and are consequently perforated with a small circular hole.
To obtain tannic acid, powdered galls are digested in about an equal weight
of washed ether, containing about 10 percent, of water, which, when poured
off, separates into two portions, the heavier of which, when carefully evapo-
rated, leaves tannic acid. It is an uncrystallizable scaly substance, of a pale
buff color, very astringent, and soluble in water, alcohol, and ether : it red-
dens litmus, and remains unchanged when dry, but when moist it soon
absorbs oxygen, and passes into gallic acid. Some of the acids and several
salts precipitate its aqueous solution ; and when boiled with dilute hydro-
chloric or sulphuric acid, it is converted into gallic acid and sugar.

C54H22O3, + lOHO = SCC.^HgO.o) + C,2H„0,4

Tannic acid forms insoluble compounds with the greater number of bases,
as well as with many organic substances, and especially the vegetable alka-
loids. Combined with gelatin, it forms leather, and in combination with
peroxide of iron it is the basis of black dyes and writing-ink. No immedi-
ate precipitate is occasioned by tannic acid in very dilute solutions of pure
protosalts of iron : but when the solutions are concentrated, a white gelati-
nous precipitate falls. If excess of tannic acid is added to a solution of
persulphate of iron, a black precipitate is formed ; and a similar precipitate
falls in a solution of the protosulphate after due exposure to air.

The following, according to Dr. Miller, furnishes a good writing-ink :
Digest three-quarters of a pound of bruised galls in a gallon of cold water,
then add six ounces of sulphate of iron with an equal weight of gum arable,
and a few drops of creasote. Let this mixture digest at ordinary tempera-
tures for two or three weeks, with occasional agitation, then let it settle, and
decant for use. The tannoferric inks are liable to fade with age ; but the
writing may generally be restored by washing it with a weak acid, and then
applying an infusion of galls, logwood, or ferrocyanide of potassium.

Characters of Tannic Acid. — 1. When heated in air it melts, and burns-
like a resin. 2. It is precipitated by a solution of gelatin or albumen. 3..
It gives a black precipitate or color in a solution of a neutral persalt of iron.
4. An excess of lime-water gives with it a dirty blue precipitate which
rapidly becomes greenish colored. 5. The acid has a peculiarly astringent
taste. It may be detected in all vegetable infusions or decoctions by their
acquiring a dark color on the addition of a few drops of a persalt of iron.

Gallic Acid (Cj^H^Oio).

This acid was discovered in 1786 by Scheele : it is one of the results of
the decomposition of tannic acid. It may be obtained by mixing powdered
galls into a thin paste with water, and exposing it some weeks to air, occa-
sionally adding water to prevent desiccation ; the powder swells, becomes
mouldy, and evolves carbonic acid, in consequence of a species of fermenta-
tion, during which gallic acid is formed. The magma is then pressed, the
residue boiled in water, and the solution filtered while hot : on cooling, it
deposits crystals of the acid, which may be purified by redissolving and boil-
ing them with a little animal charcoal, when the filtered solution deposits
white silky crystals of gallic acid. This acid is soluble in 100 parts of cold
41

642 CHARACTERS OF GALLIC AND PYROGALLIC ACIDS.

and in 3 of boiling water ; readily soluble in alcohol, and sparingly so in
ether. According to Strecker, it is a tribasic acid, represented in its anhy-
drous state by C^^H^Oy, and forming 3 classes of salts, represented by MO, 2
(H0),C,,H30,, 2(MO),HO,C,,H30,, and 3(MO),Cj,H30,. When 1 part of
gallic acid is triturated with 5 of sulphuric acid, gently heated, and dropped
into water, a red crystalline substance falls {RufigaUic aaW,=2(H0),Cj^H^
Og), which produces on mordanted calico a dye resembling madder-red.

Characters of Gallic Acid. — 1. It is white and crystalline, soluble in water
and alcohol. When heated in air it melts, and burns like a resin. 2. It
produces an inky blue color with a persalt of iron. 3. It is not precipitated
by nitrate of silver until boiled, when the silver salt is reduced. 4. It gives
DO precipitate with a solution of gelatin or albumen. 5. With an excess of
lime-water it gives a white precipitate, which in air rapidly passes through
shades of a blue and purple color. 6. When ammonia is poured on the
crystals, they acquire a rich red color. T. When the crystals are heated
with a small quantity of sulphuric acid, they produce a rich crimson com-
pound.

Pyrogallic Acid (Ci^HgOg).

This acid is now largely manufactured for the purposes of photography.
It is obtained by sublimation from gallic acid, which, at a temperature
between 410^ and 420°, obtained by an oil-bath, is resolved into pyrogallic
and carbonic acids.

Gallic acid. Pyrogallic acid. Carbonic acid.

The changes which this acid is disposed to undergo under the influence of
a dry heat, account for the great loss as a result of this process. Thus while
theoretically 74 per cent, of pyrogallic acid should be obtained, the pro-
duct is barely more than one-third of this, namely, 25 per cent. Hence the
costliness of this acid. By the application of moist heat a saving of 50 per
cent, has been effected. The gallic acid, with 2 or 3 parts of water, is sub-
jected in a close bronze boiler to a temperature of from 392° to 410° ; and
after it has been kept at this temperature for about half an hour, the liquid
is allowed to cool. The pyrogallic acid is treated with animal charcoal,
filtered and evaporated. The crystals are deposited on cooling. At a
higher temperature pyrogallic acid is converted into water and a brown
amorphous product insoluble in water, but soluble in the alkalies, called
metagallic acid.

Pyrogallic acid forms white acicular and lamellar crystals, feebly acid, of
an astringent bitter taste. The crystals melt at 257°, and sublime at about
400°. The acid is very soluble in water, alcohol, and ether. It is perma-
nent when dry, but in aqueous solution soon becomes brown, as a result of
oxidation, and under the influence of a free alkali, it rapidly absorbs oxygen.
It does not precipitate the pure protosalts of iron, but tinges them of a
characteristic blue ; it reduces most of the salts of mercury, silver, gold, and
platinum. Dropped into milk of lime it produces a purple tint, which soon
becomes brown. It is an important photographic agent.

Characters of Pyrogallic Acid. — These have been described at p. 510. Its
most characteristic property is the instant reduction of silver to the metallic
state, from a solution of the nitrate. It differs from gallic acid in many
respects. When the crystals are heated with a small quantity of sulphuric
acid, a black compound results from some decomposition of the acid.

OXALIC ACID. MANUFACTURE FROM SAWDUST. 643

Ellagic Acid (C^HjO^SHO) is produced, together with gallic acid,
during the exposure of moistened jyalls to air : it is a gray crystalline powder,
insoluble in water but soluble in the alkalies, with which it forms sparingly
soluble salts. This acid has been found in the intestinal concretions called
Oriented Bezoars.

Oxalic Acid (CPaHO).

This acid was discovered by Scheele in 1776 : it is found in some fruits,
in the juice of wood-sorrel'and of common sorrel (Oxalis acetosella; Rumex
acetosa), in the varieties of rhubarb, especially the Rheum rhaponticum, or
pie-plant, and in several other plants : in these it is generally combined with
potassa or lime. Certain lichens growing upon calcareous rocks contain
half their weight of oxalate of lime. It occasionally occurs in urine, as oxa-
late of lime, forming one variety of urinary calculus. The mineral called
Humholdtite is a peroxalate of iron. The commercial demands for oxalic
acid are, however, supplied from artificial sources. When 1 part of sugar
is mixed with 4 of nitric acid and 2 of water, nitric oxide and carbonic acid
are evolved ; after distilling off the excess of nitric acid, and pouring the
residue into a shallow vessel, crystals of oxalic acid are deposited, and on
further evaporation of the mother-liquor, a second crop is obtained. The
product is purified by solution in water and recrystallization. According
to L. Thompson {Pharm. Journ., viii. 117), one atom of sugar =C,gHjjOn,
and 7 atoms of nitric acid =7N05, are thus resolved into 7N03,6COa,2HO,
and SCCaOgSHO). These proportions, he observes, do not greatly differ
from those employed by the wholesale makers, who use 112 lbs. of sugar,
560 lbs. of nitrate of potassa, and 280 lbs. of oil of vitriol, to produce 135 lbs.
of crystallized oxalic acid, and 490 lbs. of sulphate of potassa.

Oxalic acid is now, however, chiefly manufactured from sawdust. It is
thus produced of good quality, in large quantity, and at a much cheaper
rate than in the process by the action of nitric acid on sugar. It has been
long known that when woody fibre was heated to a moderate temperature
with caustic potassa, the products were ulmic acid and hydrogen. At a
higher degree of heat, oxalic acid replaces the ulmic as a product, and at a
still higher degree, in which destructive distillation takes place, carbonic
acid and hydrogen result. The principle of this new manufacture, therefore,
is to heat the woody fibre with alkali, to a degree sufiBcient to produce
oxalic, and neither ulmic nor carbonic acid. The sawdust is mixed with a
solution of two equivalents of hydrate of soda and one of hydrate of potassa,
having a sp. gr. of 1*25. Soda alone is not found to answer the purpose.
The sawdust acquires a dark brown color from the action of the alkalies, and
is rendered soluble in water. The mixture is heated to about 400^ in
shallow cast-iron pans for some hours, care being taken to avoid charring.
The heat is then cautiously raised, and the result is a residue, containing a
large quantity of the mixed oxalates of potassa and soda. A solution of
carbonate of soda passed through the mixed oxalates on a filter, transforms
the oxalate of potassa to oxalate of soda, the carbonate of potassa passing
through the filter. The oxalate of soda is converted by lime to oxalate of
lime, and this compound is decomposed by an equivalent of sulphuric acid.
Oxalic acid remains in the liquid, and after two or three crystallizations is
obtained in a pure state in large crystals. Two pounds of sawdust thus
yield one pound of oxalic acid. Messrs. Dale and Roberts, of Manchester,
who have perfected this process, manufacture nine tons of oxalic acid weekly
for the purposes of calico-printing, dyeing, and bleaching.

The ordinary crystals of oxalic acid (CA,H0 + 2H0) are transparent
four-sided prisms. They are intensely sour, and dissolve in about 12 parts

644 OXALATES. OXAMIDE.*

of water at 60^, their solubility increasing rapidly with the increase of
temperature ; at 212° they fuse in their water of crystallization. They are
less soluble in alcohol than in water, and still less soluble in ether : at a
temperature of 100°, they gradually fall into powder, and lose about a third
of their weight : after having been deprived of 2 equivalents of water, they
sublime when heated to about 320° ; and the sublimate contains 1 atom of
water, from which the acid cannot be parted without being entirely decom-
posed. When the ordinary crystals are rapidly heated to about 350°, water,
carbonic acid, carbonic oxide, and formic acids are the results. Unlike other
vegetable acids, oxalic acid is a powerful poison. A dose of it has destroyed
life in ten minutes. It ranks among the most active irritant poisons, and
the resemblance of its crystals to those of Epsom salt, has given rise to many
fatal accidents. The antidotes are chalk or magnesia.

Hydrochloric acid dissolves oxalic acid without decomposition. It is not
decomposed by dilute nitric acid, but when heated with concentrated nitric
acid, it is converted into carbonic acid. Mixed with about 2 parts of sul-
phuric acid, and gently heated, it is rapidly resolved into equal volumes of
carbonic acid and carbonic oxide, whilst the water of the crystals remains
combined with the sulphuric acid. The intensity of the acidity of oxalic
acid is such, that 1 part in 200,000 of water reddens litmus. It abstracts
lime from sulphuric acid when added ,to a solution of sulphate of lime, but
oxalate of lead is decomposed by sulphuric acid ; so that its affinity for bases
appears to be about equal to that of sulphuric acid. When a solution of
oxalic acid is boiled with the peroxides of manganese, lead, cobalt, or nickel,
or with chromic acid, these oxides are partially reduced, carbonic acid is
evolved, and oxalates are formed. When it is boiled with chloride of gold
it throws down metallic gold, and carbonic acid passes off.

Oxalates. — In the neutral oxalates, the oxygen of the base is to that of
the acid as 1 : 3, their formula being M0,C203 ; and if the oxygen of the
base be added to the acid, the result is a metal and carbonic acid, or
M,2[C02]. Some oxalates, when heated, give this result : thus oxalate of
silver yields, when heated, metallic silver and carbonic acid ; AgO,C203=
Ag-f2[C03]. Sometimes carbonic oxide and carbonic acid are given off,
leaving a protoxide of the metal ; this is the case with oxalate of manganese ;
MnO,C203=MnO,-fCO-fC02; and sometimes the carbonic oxide thus
evolved reacts on the metallic oxide, and reduces it ; thus with oxalate of
cobalt, CoO-,C203=CoO + C04-C02; and CoO, + CO = Co + C02. When
the oxalates are heated with sulphuric acid, they are decomposed, and yield
carbonic oxide and carbonic acid. In the acid oxalates, the quantity of acid
is either twice, or four times, that contained in the neutral oxalates.

Oxalate of Ammonia (^^fi,(jfi^,-[-B.O) is obtained by saturating a hot
solution of oxalic acid with carbonate of ammonia, and crystallizing. It
forms prismatic crystals, soluble in 28 parts of cold water. They are insolu-
ble in alcohol. Added to any soluble compound of lime, this salt produces
an insoluble oxalate of lime, provided no excess of acid is present ; hence its
use as a test of the presence of lime. The crystals contain two atoms of
water. There is a binoxalate as well as a quadroxalate, but these are unim-
portant salts.

Oxamide (CgO^NHg). — When oxalate of ammonia is subjected to dry dis-
tillation, it fuses, boils, is decomposed, and volatilized, leaving a little carbon
behind; the liquid which passes over contains a flocculent substance, which
also lines the neck of the retort, and to which Dumas gave the name of
oxamide; it may be separated by washing and filtration, 100 parts of the
oxalate yielding about 5. The other products of the decomposition are
ammonia, water, carbonic acid, carbonic oxide, and cyanogen. Oxamide is

OXAMIC ACID. OXALATES OP POTASSA AND LIME. 645

also formed by the action of ammonia on oxalic ether ; and of boiling nitric
acid upon ferrocyanide of potassium. Oxamide forms a granulated powder,
without taste or smell, and having no action on test-papers. It is volatile
when carefully heated : it is scarcely soluble in water at 60°, and a saturated
solution at 212° deposits it in flocculi. It is insoluble in alcohol. Boiled
with potassa, or soda, oxamide evolves ammonia, and the carbon and oxygen
remain in the state of oxalic acid. Dilute sulphuric, nitric, and hydrochloric
acids convert it into oxalic acid, and form ammoniacal salts. Boiled with
concentrated sulphuric acid, oxamide affords sulphate of ammonia, and equal
volumes of carbonic acid and carbonic oxide are disengaged: concentrated
nitric acid converts oxamide into nitrate of ammonia and carbonic acid.

Referring to the ultimate elements of oxamide, Dumas regards it as an
amide of carbonic oxide, or as containing the hypothetical radical amidogen,
NH,.

Oxamic Acid (C^HgOgN). — This compound is one of the results of the
careful destructive distillation of binoxalate of ammonia, which at a tempera-
ture of about 450° leaves a residue of oxamide and oxamic acid ; the latter
is soluble in water, and when added to a soluble salt of lime or baryta, it
gives a crystalline precipitate, which is an oxamate of the base, and may be
decomposed by sulphuric acid. Oxamic acid is a yellowish powder, which
when boiled in water is reconverted into binoxalate of ammonia, CJIgOgN
-f2H0,=NHp,CA,H0.

Oxalates of Potassa. — There are three of these oxalates : the neutral salt
is with difficulty crystallizable. The binoxalate forms rhombic prisms, in-
cluding 3 atoms of water, one of which is basic : it has a very sour taste,
and is prepared in some parts of Germany and Switzerland from the juice of
the wood-sorrel : it is often used for the removal of ink-stains and iron-
moulds from linen under the name of essential salt of lemons. The quadroxa-
late is formed by the action of hydrochloric acid on the binoxalate, which
abetracts half the potassa : it crystallizes in octahedra.

Oxalate of lime exists in many plants, and is found in such quantities in
some lichens (especially Variolaria communis^ Indium corallinum, Psora
Candida), that the soil upon the spots on which they have grown and de-
cayed, and trunks of trees upon which they have flourished, abound in it.
The bodies called raphides, found in the cellular tissue, and floating occa-
sionally in the juices of vegetables, are composed of oxalate of lime ; this
salt also exists occasionally in the human urine, and forms calculi, which,
from their nodular exterior and reddish-brown color, are called Mulberry
calculi. On adding oxalate of ammonia to any solution of lime, oxalate of
lime is precipitated in octohedral crystals : it is insoluble in water in excess
of oxalic acid, and in acetic acid, but dissolves in hydrochloric and nitric
acids : hence, in testing acid solutions for lime by oxalate of ammonia, an
excess of acid should be previously neutralized. It is decomposed by sul-
phuric acid. When oxalate of lime is digested in a solution of a carbonated
alkali,*carbonate of lime and an alkaline oxalate are formed. When rendered
dry upon a sand-heat, this salt becomes singularly electrical on friction, and
platinum and other metals rubbed against the powder become negative, the
powder positive ; it appears to stand at the head of the substances which
become positive by friction. (Faraday.) At a red heat it is converted
first into carbonate and then into quicklime. When well washed, and dried
at 212° till it ceases to lose weight, it is G2^0,YL0,Cfi^, and contains 38'4
per cent, of lime. i ui •

Of the other oxalates those of lithia, strontia, and alumina, are soluble m
water ; those of baryta, lead, and silver, are nearly insoluble in water, but
are dissolved by a solution of sal-ammoniac. The double oxalate of potassa

646 ACETIC ACID.

and chrominra forms crystals of an intense blue color. The oxalate of
copper, unlike the tartrate and citrate, is not soluble in an excess of potash.
Characters of Oxalic Acid. — Tests as a poison: 1. This acid crystallizes
in well-defined quadrilateral prisms. 2. When the crystals are heated on
platinum, they melt, and are volatilized without combustion, and without
leaving a carbonaceous residue : any mineral residue may be regarded as im-
purity. 3. Lime-water, or a solution of sulphate of lime, produces a white
precipitate, not soluble in any vegetable acid, but it is dissolved by nitric
acid. 4. A solution of the acid gives a white precipitate with nitrate of
silver (oxalate of silver), soluble in an excess of the acid. This precipitate
may be boiled without undergoing decomposition. When collected in a filter,
washed, dried, and heated, it is decomposed, with slight detonation, into
carbonic acid and metallic silver, AgO + C203=Ag + 2C02. The crystalline
form and volatility, the action of sulphate of lime and nitrate of silver, are
the most reliable tests in cases of poisoning. By reason of its solubility in
alcohol, oxalic acid may be separated from many organic substances. The
aqueous solution of the acid, acidulated with acetic acid, should be precipi-
tated by a solution of acetate of lead, rendered acid with acetic acid : the
oxalate of lead collected, and this compound decomposed by a current of
sulphuretted hydrogen. By this process, oxalic acid may be obtained in a
crystalline state on evaporating the aqueous filtrate.

Acetic Acid (C,H,0„ or C.HgOg.HO).

There are two principal sources of acetic acid, namely, 1. Acetous fermen-
tation, and 2. The destructive distillation of wood. Comparing the ultimate
composition of alcohol with that of acetic acid, it appears that 1 equivalent
of alcohol, by taking 4 equivalents of oxygen, is resolved into 1 equivalent
of acetic acid and 2 of water.

C4H6O2 -f O4 = C^H.O^ 4- 2H0.

Alcohol. Acetic acid.

This is the theory of the formation of vinegar by the action of air on
wine, beer, and similar fermented liquors. The first stage of conversion,
however, is most probably into aldehyde : —

CAO2 -f O2 = C.H.O^ 4- 2H0.

Alcohol. Oxygen. Aldehyde. Water,

oxygen the aldehyde is co

20 = C^H.O^

By taking two other equivalents of oxygen the aldehyde is converted into
acetic acid.

Aldehyde. Oxygen. Acetic acid.

Alcohol itself, except in the presence of oxidizing agents (platinum black),
does not undergo the change, and a mixture of alcohol and water does not
produce acetic acid, unless some nitrogenous substance as a ferment is present.
The acetic acid of a previous fermentation operates as a ferment to convert
alcohol into acetic acid, provided tfie alcohol is diluted with a certain pro-
portion of water, and there is a sufficient access of air to supply the neces-
sary oxygen.

Vinegar (from vin aigre), or the dilute acetic acid chiefly used for domestic
purposes, varies in quality according to the sources whence it is obtained.
The best French vinegar is made by putting wine into a cask already con-
taining a little vinegar, and to which air has due access, the temperature of
the factory being maintained at about 80°. In this country, beer, or a wort

PROPERTIES or VINEGAR. 647

prepared for the purpose, is used as a source of vinegar. A good extempo-
raneous vinegar may be* prepared by dissolving 1 part of sugar in 6 of water,
with 1 part of brandy, and a little yeast : this mixture is put into a cask,
with the bunghole open, and kept at a temperature of between 70° and 80^:
in from four to six weeks, the clear vinegar may be drawn off. Lieljig re-
commends 120 parts of water, 12 of brandy, 4 of brown sugar, 1 of tartar,
and ^ of sour dough, left for some weeks in a warm place, as ingredients for
the production of a good vinegar. Various modes of accelerating acetifica-
tion have been suggested by the extension of the surface of the liquid. As
far back as 1743, Boerhaave recommended that a mixture of 1 part of alcohol
and 9 of water should be made to trickle slowly through beech-shavings,
previously soaked in vinegar, and lying loosely in a cask perforated with
holes : the best proportions are, 1 part of alcohol (sp. gr. 0848) with 4 to
6 of water, and a thousandth part of ferment, honey, or extract of malt.
This mixture, previously heated to about 80°, is made to trickle through
the shavings steeped in vinegar ; the temperature, as a result of the oxida-
tion of the liquid, soon rises to 100° or 104°, and remains stationary if all
goes on favorably. When the liquid has been passed through the shavings
three or four times, it is completely acetified : this may occupy from 20 to
36 hours. If the supply of air is deficient, part of the alcohol remains in
the state of aldehyde, which escapes, and occasions a loss of acetic acid.
The presence of essential oils, or of pyroligneous acid, prevents the acetifi-
cation.

Vinegar is apt to be infested hjjlies {Musca cellarus), and by animalcules,
commonly termed eels ( Vihriones aceti) ; these may be destroyed by passing
the vinegar through a spiral tube immersed in boiling water, or by heating it
in a hot-water bath. When vinegar is exposed to air, it gradually becomes
turbid, or mothery, losing its acidity, and depositing a gelatinous conferva,
the vinegar-plant, which, by reason of holding vinegar like a sponge, causes
acetous fermentation in saccharine liquids. The vinegar becomes weak and
mouldy as these changes go on, and they are rapid in proportion to its
weakness.

The adulteration of vinegar by sulphuric or by hydrochloric acid may be
detected by nitrate of baryta and nitrate of silver, the precipitates being
insoluble in nitric acid; but traces of sulphuric acid are found in all vinegars
(from sulphates in the water), and their presence must be allowed for in
nsing the barytic test. If nitric acid is present in vinegar, it destroys the
color of an acid solution of sulphate of indigo, when boiled with it. In
order, as it is said, to prevent vinegar becoming mouldy, it is allowed by law
to contain one-thousandth part of its weight of sulphuric acid.

The specific gravity of vinegar depends more upon the foreign matters
which it contains, than upon its actual strength, so that its value cannot be
judged of by that criterion: the density of the best vinegar is about 1-020
to 1-025. To ascertain the proportion o^ real acetic acid which it contains,
it must be cautiously neutralized by carbonate of soda, the quantity of this
salt requisite for the purpose, indicating the proportion of real acetic acid
present, 53 parts of dry carbonate of soda being equivalent to 51 of anhy-
drous acetic acid. The equivalent of carbonate of lime, which is 50, .is so
near that of acetic acid, as to furnish a ready mode of ascertainmg the value
of vinegar or other dilute acetic acid. For this purpose a piece of clean
white marble is selected and accurately weighed : it is then suspended by a
thread in a proper quantity of the vinegar to be examined, which is 0(3ca-
sionally cautiously stirred, so as to mix its parts without chipping the marble ;
this when it is no longer acted on, is removed, washed, dried, and weighed ;
its loss in weight is equivalent to the weight of acetic acid present. Another

648 DISTILLED VINEGAR. PYROLIGNEOUS ACID.

mode of ascertaining the strength of vin^egar consists in neutralizing it by
hydrate of lime ; acetate of lime is extremely soluble*, so that the quantity of
acetate of lime formed and dissolved, is directly as the quantity of acid pre-
sent, and the density of the resulting solution of acetate of lime is in the same
ratio. {See J. and P. Taylor on an Acetometer, Quart. Joum., vi.) "An
ounce of good vinegar should saturate about 30 to 32 grains of pure and dry
carbonate of potassa : such vinegar contains about 5 per cent, of anhydrous
acetic acid, and its density is from I'Ol to 1*03." (Liebig.)

Distilled Vinegar. — When vinegar is carefully distilled, the first portion
which passes over usually contains a little alcohol ; this is followed by dilute
acetic acid, which, towards the end of the process, often acquires an empy-
reumatic odor; the residue is brown, acid, and has a burned flavor. Accord-
ing to R. Phillips (on the London Pharmacopoeia), when the best English
malt- vinegar, of the specific gravity of 1*024 is distilled, the first eighth part
which passes over is of the specific gravity 0-99712, so that it contains a
little alcohol ; a fluidounce of it, = 0-8047 cubic inches, dissolves from 4*5
to 5 grains of precipitated carbonate of lime : the next six-eighths have the
specific gravity 1-0023, and a fluidounce dissolves 8-12 grains of the carbonate ;
a fluidounce of the acid, of specific gravity TOOT, dissolves 15 to 16 grains
of precipitated carbonate of lime, or 138 grains of marble.

Distilled vinegar is colorless, and it has not the agreeable flavor and odor
of the original vinegar ; it contains a trace of alcohol and of acetic ether,
and also a peculiar organic matter. When distilled from a copper-still
through a pewter worm, it becomes discolored by sulphuretted hydrogen
from the presence of traces of copper, lead, or tin, so that silver or earthen
condensers are used by the wholesale distillers.

Pyroligneous Acid. — The production of vinegar by the destructive dis-
tillation of wood, was one of the numerous discoveries of Glauber ; and a
large quantity of acetic acids, of all strengths, is now derived from this source.
The wood is heated in iron retorts, connected with a proper condensing
apparatus, and the inflammable gaseous products are conducted into the fur-
nace, so as to serve as fuel. The hard woods, such as beech, oak, birch, and
ash, are selected, and previously dried: The liquid products are water, wood-
spirit or naphtha, tar, and acetic acid : these are drawn off from the floating
tar, and distilled, when the wood-spirit first passes over, and afterwards the
acetic acid, still, however, very impure from the presence of tar and other
matters. This impure acid is then saturated either by soda or by chalk, and
the acetate so formed is carefully heated, so as to decompose or expel the tarry
matters without decomposing the salt, which is then further purified by solu-
tion and crystallization, and ultimately decomposed by distillation with sul-
phuric acid diluted with about half its weight of water. The acetic acid
which passes over is purified by redistillation. The sulphate of soda resulting
from this process may be used to convert the crude acetate of lime to acetate
of soda and sulphate of lime, when chalk has been used for the saturation of
the crude acid. The purest acetic acid, obtained by the decomposition of an
acetate by sulphuric acid, contains an atom of water (HO, Ac), which in the
formation of the neutral acetates is replaced by an atom of base.

For our knowledge of the anhydrous acid (C^HgOg), we are indebted to
Gerhardt. It may be obtained by distilling 8 parts of dry acetate of potassa
with 3 of oxychloride of phosphorus ; the distillate is returned upon the resi-
due and redistilled, and the product again rectified.

Anhydrous acetic acid, sometimes represented as the teroxide of the com-
pound radical acetyle (C^H^), is a colorless liquid, of a peculiar odor; (sp.
gr. I'OT); its boiling-point is 280°, and the sp. gr. of its vapor is 3 47.

HYDRATED ACETIC ACID. 649

When dropped into water, it falls to the bottom like heavy oil, but soon
dissolves on agitation ; it readily absorbs moisture when exposed to air.
Acted upon by potassium it evolves hydrogen, and forms acetate of potassa,
and an oily product of an agreeable odor. It dissolves chloride of phos-
phorus, producing phosphorous acid and oxychloride of acetyle.

Monohydrated Acetic Acid, or Glacial Acetic Acid (C^H303HO). — This is
obtained by distilling 1 equivalent of fused acetate of soda with 2 equivalents
of sulphuric acid, and placing the distillate in ice; the congealed product
is then suffered to drain, by inverting the bottle, and in that frozen state it
is the pure monohydrated acid. Its crystals are plates or tufts, which fuse
at about 50°. It has a strong pungent odor, agreeable when diluted, and is
powerfully acid and caustic, reddening and blistering the skin. It boils at
243°, and its vapor is inflammable : it absorbs moisture from the air, and
dissolves in all proportions in water. The sp. gr. of the liquefied crystal-
lized acid is 1-0635 at 62°, and this density increases on dilution, until the
acid contains 1 equivalent of anhydrous acid to 3 of water, when it is 1-073 ;
on further dilution, its density diminishes, and when it consists of about equal
weights of the acid and water, its sp. gr. is 1-063, or the same as that of the
undiluted acid. The monohydrated acid does not attack carbonate of lime
until it is diluted ; and when mixed with alcohol, it neither reddens litmus
nor decomposes many of the carbonates (p. 585.) It is partially decomposed
by passing it through a red-hot porcelain tube, yielding acetone, carbonic
acid, and water.

2(C,HA) = CeHeO^ + SCO^ -f 2H0

Its entire decomposition is only effected at a very high temperature ; but
when its vapor is passed over heated platinum-black, it is resolved into equal
volumes of carbonic acid and light carburetted hydrogen (C^H^O^=s2C02 4-
2CH2). Pure acetic acid acts only slowly upon a solution of permanganate
of potash, but when acetic acid contains tarry matters, sulphurous acid or
organic matter, such as is found in vinegar, the permanganate is rapidly
decomposed and the color is discharged.

When chlorine is passed through a mixture of 2 parts of glacial acetic acid
and 1 of water (taking care to exclude the direct rays of the sun), it is slowly
absorbed, and a compound is formed which has been termed chloracetic acid,
=HO,C^H203Cl: it is stated to produce definite salts, in which, when dilute,
nitrate of silver gives no precipitate. This chloracetate of silver forms shining
scales, soluble in water, and decomposed by light.

When glacial acetic acid is exposed to the action of gaseous chlorine,
under the influence of the sun's rays, white deliquescent flocculi are formed
=110,0^01303. This compound has been termed trichloracetic acid; in it
the hydrogen of the anhydrous acetic acid is replaced by chlorine, but the
reaction is more complex, inasmuch as chlorocarbonic, carbonic, and oxalic
acids are at the same time formed. This acid forms salts which are soluble
in water, and which when heated, evolve chlorocarbonic acid and carbonic
oxide, and leave a chloride.

M0,C,Cl303 = MCI -f 2(C0,C1) -f 2C0

Sulphacetic JaU— When acetic acid is acted on by anhydrous sulphuric
acid, it loses 2 atoms of watei^and a new acid =C4Ha02,2S08,2HO, results :
it forms deliquescent crystals,^nd bibasic salts.

Acetates.— These salts are very numerous, and many of them of much
importance in the arts. The neutral acetates, =M0,C,H303, are all soluble
in water : acted on by sulphuric acid they evolve acetic acid, recognized by

650 ACETATES OF COPPER AND LEAD,

its odor. They are raostly reddened by perchloride of iron. They are de-
composed by a red heat, some of them giving off the acid and leaving the
metal, such as the acetates of copper and of silver ; some give off acetone
and leave a carbonate, and some, which require a higher temperature for
decomposition, afford acetone and other more complex products.

Acetate of Ammonia, obtained by neutralizing distilled vinegar by
ammonia, has long been used in medicine, under the name of Spirit of
Mindererus. When boiled, ammonia passes off and a hinacetate is formed.
These salts are very soluble in water and in alcohol, and are crystallized with
difficulty. — Acetate of Potassa is very deliquescent; soluble in its weight of
water at 60°, and in twice its weight of alcohol. When carefully fused, it
concretes into a lamellar mass on cooling, the terra foliata tartari, or febri-
fuge salt of Silvius, of old pharmacy. It is present in the sap of many
vegetables, and is a source of the carbonate of potassa found in their ashes.
The aqueous solution of this acetate is not decomposed by carbonic acid ;
but a current of that gas passed through its alcoholic solution, precipitates
carbonate of potassa, and sets free acetic acid. Like the acetate of soda, it
is decomposed when heated with caustic potassa or lime, and resolved into
carbonate of potassa and Marsh gas. Acetate of soda is largely manufac-
tured as a source of acetic acid, by the action of sulphate of soda on acetate
of lime (NaO,S03, + CaO,Ac=NaO,Ac, + CaO,S03). It crystallizes in
rhombic prisms with 6 atoms of water. It bears a dull red heat without
decomposition. — Acetate of haryta forms efflorescent crystals with 1 atom
of water, if obtained at 80°, but 3 if at 32°. By heat this salt is resolved
into carbonate of baryta and acetone, 2(BaO,C^H303) =2(BaO, CO^) -f- CgHgOa.
Acetate of lime forms silky prisms, soluble in water and in alcohol. When
heated to about 230° and triturated, it is phosphorescent. — Acetates of alu-
mina, prepared by decomposing solutions of sulphate of alumina or of alura
by acetate of lead, are extensively used as mordants, by calico-printers.
These acetates have been minutely examined by Mr. Crum {Q. J. Chem.
Soc, vii.) — Protacetate of iron, obtained by the action of acetic acid on the
protosulphide, out of contact of air, forms white silky crystals. The pera-
cetate, made by digesting iron turnings in the acid exposed to air, is a deep
red solution, not crystallizable. It is used by dyers and calico-printers.

Acetates of Copper These constitute the varieties of verdigris. The

common verdigris of commerce is a hydrated dibasic salt =2(CuO),Ac,
3H0 : it is prepared by exposing plates of copper to the action of acetic
acid. The method now practised consists in alternating plates of copper
with pieces of woollen cloth steeped in acetic acid ; they gradually become
covered with verdigris, which is removed in the form of a blue-green powder,
and the operation repeated as long as the plate lasts. Sometimes husks and
stalks of grapes or raisins, in a state of acetous fermentation, are employed
to act upon the copper, as is the case with some of the French verdigris.
This article is commonly packed in leather, and frequently adulterated with
a mixture of chalk and sulphate of copper. Pure diacetate of copper forms
small silky crystals of a greenish-blue color, which when heated to 212°,
become green, and lose water : when moistened, this salt crumbles, and is
only partially soluble in water, by which it is resolved into tribasic and
neutral acetates. The neutral acetate of copper (^crystallized verdigris) is
made by dissolving common verdigris in a^fetic acid, and allowing it to
crystallize upon twigs or pieces of string : it f(frms blue-green prisms, soluble
in 5 parts of boiling water and sparingly in alcohol. When its dilute solu-
tion is boiled, it deposits a tribasic salt : if boiled with sugar, a crystalline
precipitate of suboxide of copper is formed. Acetates of lead. — When oxide

ACETATES OF LEAD. TESTS FOR ACETIC ACID. 651

of lead is dissolved in excess of acetic acid, prismatic crystals are obtained
on evaporating the filtered solution =PbO,C^H303,3HO. This salt, known
as sugar of lead, generally occurs in the form of a crystalline mass, slightly
efflorescent, soluble in less than two parts of water, and in about 8 parts of
alcohol. When heated, it first becomes anhydrous, then fuses, and at a
higher temperature is converted into a subsesquiacetate =3(PbO),2(C^H3
Og), soluble in water and alcohol, and having an alkaline reaction. When
7 parts of litharge and 10 of sugar of lead are boiled together in 30 parts
of water, a solution of a trihasic acetate =3(PbO),C^H303 is formed,
known in pharmacy as Goulard's extract of lead; this salt may be obtained
in acicular crystals, having an alkaline reaction. Its decomposition by car-
bonic acid is one of the processes for making white lead, and has been elsewhere
noticed. This subacetate is a delicate test for the presence of carbonic acid,
which it absorbs from the atmosphere, or from any liquid containing it :
even distilled water is seldom so free from carbonic acid as not to be rendered
turbid by the addition of a few drops of this salt, and with all spring and
river water it forms a more or less turbid white mixture. When excess of
minium is heated in glacial acetic acid to about 105°, the solution deposits
prismatic crystals on cooling, composed oi peroxide and acetate of lead ; they
are very unstable, and on attempting to dry them are decomposed into per-
oxide of lead and acetic acid. Acetate of suboxide of mercury (Hg20,Ac,)
is formed by mixing solutions of acetate of potassa and nitrate of suboxide
of mercury ; it forms micaceous crystalline plates requiring 600 parts of cold
water for solution. The acetate of the red oxide is readily soluble. Acetate
of silver is deposited in lamellar crystals when acetic acid is added to a strong
solution of nitrate of silver; and it is abundantly precipitated from the
nitrate by acetate of soda. This, and the preceding, are the only neutral
acetates not easily dissolved in water. Acetate of uranium forms a series of
double salts with basic acetates, which have been described by Wertheim.
{Ann. Ph. et Ch., 3feme ser. xi. 49.)

Characters of Acetic Acid and the Acetates. — 1. Acetic acid at ordinary
temperatures is liquid, and has a powerful and peculiar odor. 2. It is
entirely volatile if pure, and the vapor of the concentrated acid is combusti-
ble, burning with a pale reddish flame. 3. It is not precipitated by lime-
water, acetate of lead, or nitrate of baryta or silver, if free from sulphuric
and hydrochloric acids.

An acetate may be identified by boiling it with sulphuric acid : the vapor
of acetic acid is evolved. This may be recognized by its odor, volatility,
and acid reaction. Acetic acid sometimes contains lead, silver, or copper,
as an impurity. The first may be detected by sulphuretted hydrogen, pro-
ducing a brown color : the second by the action of the gas, and the produc-
tion of a white precipitate by hydrochloric acid : the third by the action of
ammonia. Acetate of soda may be present in the acid : this is detected by
the yellow color imparted to flame.

Acetone (CgHgO^). — This product is obtained when acetate of lime is
distilled with excess of quicklime, or when 2 parts of acetate of lead and 1
of lime, well mixed, are heated in an iron retort connected with a proper
condensing apparatus. The distillate is rectified, and finally redistilled from
a water-bath. Pure acetone is a colorless liquid of a peculiar aromatic
odor and pungent taste. Its sp. gr. 0*792 ; it boils at 132° ; the sp. gr. of
its vapor is 2-022; it dissolves in all proportions in water, alcohol, and
ether ; but chloride of calcium and caustic potassa separate it from its aque-
ous solution. It is very inflammable and burns with a bright flame. _ By
the action of chlorine upon acetone, three substitution-products are obtained,
in which 2, 3, and 4 atoms of its hydrogen are replaced by chlorine.

652 FORMIC ACID. FORMATES.

Formic Acid (CaH,03,H0)

was first noticed, iu 1670, in the body of the red ant {Formica rufa), and was
obtained by distilling the bruised insects with water. It may be artificially
produced by many processes founded upon the oxidation of various organic
products. Dobereiner procured it by the distillation of 10 parts of starch,
3*7 of peroxide of manganese, 30 of water, and 30 of sulphuric acid, until 30
parts had passed over : or by distilling a mixture of 10 parts tartaric acid,
3 of peroxide of manganese, 3 of sulphuric acid, and 3 of water. In these
cases, capacious retorts must be used, to allow of the great effervescence which
ensues. The acid distillate, which is very dilute, is saturated with carbonate
of lead, and the resulting formate of lead purified by crystallization during
the cooling of its solution in boiling water; it is then decomposed, either by
an equivalent of sulphuric acid, or by the action of sulphuretted hydrogen.
Formic acid has also been obtained by distilling a mixture of oxalic acid and
anhydrous glycerine at a temperature of about 212°; in this case, the oxalic
acid is resolved into formic and carbonic acids.

2(H0,CA) = (H0,C,H03) + 2(C0,).

The reaction between the two bodies commences at about 127°, and attains
its maximum at 194°. By distillation, an aqueous fluid mixed with formic
acid passes over into the receiver and is condensed. The glycerine remains
unchanged, provided the heat is not allowed to exceed 220°. A fresh quan-
tity of oxalic acid, added to the mixture some time after the evolution of
carbonic acid has ceased, causes the decomposition to recommence, and a
fluid containing a larger proportion of formic acid is obtained. Successive
additions of oxalic acid may thus be made. The oxalic acid yields more
than half its weight of formic acid containing 56 per cent, of the anhydrous
acid. The action of the glycerine appears to be of a catalytic kind, like
that of sulphuric acid in splitting alcohol into ether and water.. The
commencement and termination of this process of conversion are indicated
by the evolution of carbonic acid. Monohydrated formic acid may be pro-
cured by this process by heating formic acid of 70 per cent, with anhydrous
oxalic acid. The decomposition begins at 122°.

There is reason to believe that the poison of the wasp and bee, as well as
that of the vesicles surrounding the bases of the hairs on the leaf of the
stinging-nettle ( Urtica dioica), is formic acid in a concentrated state.

Monohydrated formic acid is a very acrid fuming liquid, of the sp. gr.
1-22; crystallizable below 32°, boiling at about 220°, and yielding an in-
flammable vapor, the density of which is 2'125. The anhydrous acid has
not been isolated. It is easily converted by oxidation into carbonic acid and
water : when boiled, either with oxide of mercury or oxide of silver, this
oxide is reduced, with the escape of carbonic acid (2AgO, + C2H20^,=2Ag,
-f 2C02,4-2HO). Chlorine converts it into carbonic and hydrochloric acids
(C2H20^,-f2Cl,=2C03-f 2HC1). Formic acid is frequently represented as
the teroxide of the compound radical /ormy/e (CgH-f O3). Its elements are
in the proportions to form two atoms of carbonic oxide and one of water
(C,H03=2CO + HO).

Formates. — The neutral formates are =(MO,C2H03). They are all soluble:
when heated with excess of sulphuric acid, they yield carbonic oxide and
water ; and with caustic potassa they evolve hydrogen and are changed into
carbonates. Formate of ammonia, when heated to about 400°, is resolved
into hydrocyanic acid and water, NH40,C2H03=(C^N,H)4-4HO. Formate
of lead, when heated to about 375°, evolves carbonic acid and hydrogen,
and leaves metallic lead : it requires 40 parts of cold water for solution, but

PROPERTIES OP BENZOIC ACID. 653

is very soluble in boiling water. Formate of copper crystallizes in lar^e blue
prisms : it forms double salts with the formates of baryta and of strontia.

Characters of Formic Acid. — This acid may be identified by its odor, vola-
tility, and its reducing power on the salts of silver and gold.

Benzoic Acid (C,^H503,H0).

This substance is found ready formed in benzoin, the resinous exudation
of the Styrax lenzoin, a tree growing in Sumatra, Borneo, and Java. Tolu
and Peru Balsam also contain it, in common with Cinnamic acid; and it is
a product of the oxidation of hitter-almond oil. It is found in the pods of
the Vanilla. It is generally obtained from benzoin, either by sublimation,
or in the humid way, by the action of bases : the amount of the product is
various, depending upon the quality of the benzoin, upon the process selected,
and the care with which it is conducted ; it fluctuates from 4 to 10 per cent.
The process usually resorted to consists in coarsely pulverizing the benzoin,
and heating it in a shallow vessel, over which a sheet of coarse blotting-paper
is stretched, surmounted by a cone of thick paper, or by a wooden receiver,
if the operation is carried on upon the large scale. The layer of benzoin
should not be more than two or three inches in thickness, and the heat
gradually and regularly applied, so as slowly to sublime the acid, the vapor
of which, passing through the bibulous diaphragm, condenses in a crystalline
form in the cone or recipient, empyreumatic oil at the same time evolved, is
retained and absorbed by the paper. (Mohr.) Benzoic acid may also be
obtained by triturating benzoin with half its weight of hydrate of lime, and
adding 10 parts of water; after the mixture has digested for some hours, it
is boiled and filtered : the filtrates are then concentrated, and saturated,
whilst hot, by hydrochloric acid ; on cooling, benzoic acid is deposited, which
must be again dissolved and crystallized. (Scheele.)

Benzoic acid is inodorous ; but, as it is obtained by sublimation, it has
an agreeable odor, derived from a trace of volatile oil j it generally forms
acicular crystals. It has a slightly sour and acrid taste. It melts at about
250°, and, on cooling, congeals into a crystalline mass. At about 295° it
sublimes : about 460° it boils, and forms an acrid vapor, the sp. gr. of which
is 4-26. This acid requires 200 parts of water at 60°, and 30 parts at 212°,
for its solution ; the saturated boiling solution concretes on cooling into a
crystalline mass. It dissolves in about twice its weight of alcohol, and is
precipitated on dilution with water. It also dissolves in ether, and in fixed
and volatile oils. In its usual crystalline form it contains an atom of water,
its equivalent being 122 ; that of the anhydrous acid is 113.

It has been found convenient, in reference to the numerous compounds of
the benzoic series, to regard them as derived from a compound radical, to
which the term Benzoyle has been applied ; and which has been obtained, in
the form of an oil, by the dry distillation of benzoate of copper ; its formula
is C,,H.02,=Bz. It is obvious that benzoic acid {G^^Rfi^+O) may be
regarded as an oxide, and bitter- almond oil (C.^H^O^+H) as a hydride of
this radical, and that it may be assumed as the basis of the numerous deriva-
tives of those bodies. But the term Benzoyle, or Benzule, is perhaps more
appropriately confined to the fundamental hydrocarbon (Ci^H^) of the series.

Anhydrous benzoic acid has been obtained by the action of oxychloride
of phosphorus on anhydrous benzoate of soda ; it is insoluble in water, but
soluble in boiling alcohol and in ether : by continuous boiling in water it
reverts to the ordinary hydrate.

Benzoates.^ThQ^Q salts are represented by the general formula MU,Oi^
H.Og : they are mostly soluble in water and in alcohol. Benzoate of lime
dissolves readily in boiling water. Basic benzoate of peroxide of iron is so

654 ESSENTIAL OIL OP BITTER ALMONDS.

little soluble in water that an alkaline benzoate has been used to precipitate
iron, "and to separate this metal from some other oxides.

Chlorolenzoic acid is the result of the action of the sun's rays on benzoic
acid in dry chlorine. In it an atom of hydrogen is replaced by one of
chlorine, giving Ci^H^03,Cl. There are also two other of these chlorine
compounds, in which 2 or 3 atoms of hydrogen are displaced by a similar
number of atoms of chlorine. A similar bromine compound has also been
obtained.

Sulphohenzoic acid is the product of the action of anhydrous sulphuric on
benzoic acid : it is dibasic, and is represented as 2(HO),Ci4H^S^03.

Nitrohenzoic acid (HOjCi^H^g.NOJ is a compound in which an atom of
hydrogen is replaced by an atom of nitrous acid. The nitrobenzoates are
mostly crystallizable and soluble in water and alcohol : when suddenly
heated they deflagrate.

Benzamic acid. Carhanilic acid. Amidobenzoic acid. — This is one of
the results of the action of sulphuretted hydrogen upon an alcoholic solution
of nitrobenzoate of ammonia : it is represented as benzoic acid, in which an
equivalent of hydrogen is replaced by an equivalent of amidogen (Ci^H (N
H,)03).

Hydride op Benzoyle. Essential oil of hitter almonds (Cj^HgOa-f H, or
C^^HgOg). — Bitter almond oil is obtained by macerating the pulverized bitter-
almond cake, after the fixed oil has been expressed, in water heated to about
100°, for 24 hours, and then distilling; it passes over with the vapor of
water, and condenses in the form of a heavy oil, the supernatant water hold-
ing a portion of it in solution. This oil is combined with hydrocyanic acid,
and is therefore, as well as the bitter almond water, very poisonous. It may
be obtained also from the peach, plum, cherry, and apricot kernels, from the
leaves and young shoots of the laurel {Prunus lanrocerasus), and from the
bark of the wild cherry (Prunus padus). To free it from hydrocyanic acid,
the oil may be agitated with milk of lime and a solution of protochloride of
iron, and redistilled.

Pure bitter-almond oil is a colorless liquid of a peculiar and agreeable
aromatic odor and a pungent flavor. It is not very poisonous when freed
from prussic acid, but as it is much used in confectionery and cookery, care
should be taken that for such purposes its purification has been adequately
performed. Its boiling-point is about 350°. It is much heavier than water,
its sp. gr. being 1*043. It is easily inflammable, and burns with a bright
sooty flame. It is soluble in about 30 parts of water, and in all proportions
in alcohol and ether. Its alcoholic solution constitutes the Essence of bitter-
almonds commonly sold for culinary purposes; it usually consists of one part
of the oil dissolved in seven of alcohol. When this oil is exposed to air
it absorbs oxygen, and is converted into crystallized benzoic acid : C,.HbO„
-fO„ = C,AO,

Neither bitter-almond oil nor hydrocyanic acid exists ready formed, in the
almond or sources whence they are obtained, but they are produced by the
mutual agencies of certain azotized substances, under the influence of water
and a due temperature ; these substances are amygdaline, and emulsin or
synaptase.

Amygdaline (C^oHgyOgaN) is found in bitter-almonds, in the leaves and
berries of the cherry laurel, and the bitter kernels of the species of amygdalus
and prunus. To obtain it, the pulverized cake of bitter-almonds which re-
mains after the expression of the fixed oil, is boiled in repeated portions of
alcohol of sp. gr. 0-820. These alcoholic liquids are then distilled in a
water-bath, till the residue acquires a syrupy consistence, when it contains
little else than amygdaline and sugar ; to get rid of the latter, the liquor is

ACTION OP EMULSINE UPON AMYQDALINE. 655

diluted with water, and a little yeast having been added, it is placed in a
warm situation, to ferment; when the fermentation has ceased, the liquor
is filtered, and again evaporated to the consistence of syrup ; excess of cold
alcohol is then added, which throws down the amygdaline in the form of a
white crystalline powder. From three to four per cent, of the principle is
thus obtained from bitter-almonds. Amygdaline is readily soluble in water,
and the crystals deposited from its saturated aqueous solution are transpa-
rent prisms, containing 10-57 per cent, of water (= 6 atoms). It is in-
odorous and slightly sweet and bitter. When acted on by fixed alkalies, it
evolves ammonia and forms amygdalic acid.

^A-,022^^ + KO,HO 4- HO = KO,C,oH3,0,, + NH,

Amygdaline. Amygdalate of potassa.

The action of emulsine upon amygdaline in the production of bitter
almond oil, was first explained by Wohler and Liebig. When a solution of
10 parts of amygdaline in 100 of water is mixed with a solution of 1 part of
emulsine in 10 of water, the mixture becomes opalescent, acquires the odor
of bitter almonds, and, when distilled, yields hydride of benzoyle and hydro-
cyanic acid ; these changes ensue most rapidly at a temperature between 85*^
and 105°. Boiling water and boiling alcohol destroy the action.

When expressed bitter-almonds are moistened and triturated with water,
the same reaction ensues ; and if water enough be present to dissolve the
oil as it is formed, the whole of their amygdaline disappears : to obtain the
full proportion of oil, 1 part of bitter-almond cake should be macerated for
24 hours in 20 parts of water, at about 100°, and then subjected to distilla-
tion. Seventeen grains of amygdaline dissolved in an ounce of emulsion of
sweet almonds, yield a solution containing 1 grain of anhydrous hydrocyanic
acid.

In the fermentative changes which ensue during the mutual action of
emulsine and amygdaline under the conditions above stated, bitter-almond
oil and hydrocyanic acid ^re'not the only products; sugar and formic acid
are also formed. The general result may be represented as follows : —

1 atom of amygdaline,

C^nHg-OooN

1 atom of hydrocyanic acid . Cg H

2 " hydride of benzoyle CjgHjjO^

i " sugar • CgHeOg

2 " formio acid . . . C4 Hg Og

6 " water H. 0.

Action of Ammonia on Hydride of Benzoyle.— 'By agitating bitter-almond
oil with ammonia and heating the mixture, a crystalline compound is formed,
hydrohenzamide (C^H^gNJ ; it is changed by the action of potassa into an
isomeric basic body, henzoHne or amarine, the salts of which are intensely
bitter. Some other azotized compounds are similarly produced.

When crude bitter-almond oil (retaining hydrocyanic acid) is digested
with an alcoholic solution of caustic potassa, it is converted into a crystal-
line product, which has been termed Benzoine, represented as =0,811^304,
and therefore isomeric with the hydride of benzoyle ; but it is inodorous and
tasteless. When its vapor is passed through a red hot tube, it is resolved
into bitter-almond oil. This curious product has beeb represented by the
formula C^^H^.O^H, as the hydride of a radical, =C^H„0,, called 5^.%^
For further details in reference to these, and many other compounds derived
from or connected with bitter-almond oil, we must refer to Laurent (Ann.
de Chim. et Ph., I. 291, 3feme SQr.) and to Gerhardt {Chim. Organ.).

656- HIPPURIC AND MECONIC ACIDS

HippuRic Acid (C,3H30,1S', + H0).

This acid is contained in a combined state chiefly in the urine of herbivo-
rous maramifera, forming? about TS per cent. It is present in small quantity
in human urine, in which it may be produced artificially by the use of ben-
zoic acid. Benzoic acid, in passing through the system, is converted into
hippuric acid. It may be obtained by adding milk of lime to fresh cow's
urine, boiling, filtering, neutralizing the filtrate with hydrochloric acid, and
evaporating it to about one-eighth of its bulk ; excess of hydrochloric acid
is then added, which throws down impure hippuric acid. It may be puri-
fied by dissolving it in boiling alcohol, which on cooling deposits it in color-
less, long, four-sided prisms with pointed terminations. It requires about
400 parts of water at 60° for its solution : it is abundantly soluble in boil-
ing water and in alcohol, but less so in ether. It fuses when heated, and
concretes into a crystalline mass on cooling. If distilled at a high tempera-
ture it gives, among the products, benzoic and prussic acids. When long
boiled with dilute nitric or hydrochloric acid, it yields benzoic acid and
gelatine-sugar (glycocol or glycocine). When boiled for half an hour in a
strong solution of potash, it is converted into benzoic acid, forming a ben-
zoate of the alkali, 100 parts of hippuric acid thus produce 68 parts of
benzoic acid. This conversion also takes place in the urine of the horse,
as a result of spontaneous changes after it has been voided ; and thus urine
which has been long kept, yields benzoic in place of hippuric acid. Boiled
with peroxide of lead, carbonic acid, benzoic acid, and benzamide (C^4H5
OjNHg) are formed. Hippurates. — Those of the alkalies and earths are
soluble and crystallizable ; they give white precipitates in solutions of lead,
mercury, and silver, and a brown precipitate with persalts of iron.

Meconic Acid (Cj^HO.ijSHO).

The existence of a distinct acid in opium was announced by Seguin in
1804, and shortly afterwards by Sertuerner, wlio gave it the above name
(from ^ijxcov, poppy). This acid has not been found in any other plant. It
may be most conveniently extracted from the precipitate obtained by adding
chloride of calcium to infusion of opium, in the process for procuring
morphia. This precipitate is washed first in water, and then with hot
alcohol, and mixed with ten times its weight of water, at 195° ; hydrochloric
acid is then gradually added, so as to dissolve the meconate of lime (which
forms the bulk of the precipitate) and leave the sulphate of lime ; the solu-
tion is filtered, and on cooling deposits crystals of bimeconate of lime: these
are again dissolved in hot dilute hydrochloric acid, by which the lime is-
abstracted, and crystals of meconic acid obtained, which, if pure, should
leave no residue when burned : they must be redissolved in the acid, and
recrystallized, till they are obtained in this state, but care must be taken to
keep the temperature of their solutions below 212°.

Meconic acid Crystallizes in transparent and micaceous scales of an acid
taste, soluble in 4 parts of hot water, and in alcohol. The crystals are per-
manent in the air, but when heated to 212° they lose 21 -5 per cent, of water :
they then sustain a temperature of 240° without decomposition ; but if a
strong aqueous solution of the acid is boiled, it becomes dark colored, car-
bonic acid is evolved, and oxalic acid and comenic {metameconic) acid are
formed, together with a brown product. Boiled in hydrochloric acid, me-
conic acid is resolved into carbonic and comenic acid.

One of the principal characters of this acid and of its salts, is that of
forming a compound with the peroxide or iron of an intensely red color,
very similar to that of the sulphocyanide of iron, but dififerin^ in the fact

ALKALOIDS AND ORGANIC BASES. 657

that a solution of corrosive sublimate does not destroy the red color ; hence
a persalt of iron is an excellent test of its presence, and by it, opium may
sometimes be recognized, when the quantity is so small as to render the mor-
phia very difficult of detection. The red color is destroyed by heat, by sul-
phurous acid, and by protochloride of tin. Meconic acid in solution gives
a yellowish-white precipitate with acetate of lead, and this precipitate is not
dissolved by acetic acid. The acid may be detected in any opiate liquid by
adding to it a mixture of a solution of acetate of lead with acetic acid, and
, boiling the liquid. The meconate of lead is precipitated in an insoluble
form, and may be obtained by filtration. When dry, this precipitate, if
warmed with diluted sulphuric acid, yields a solution of meconic acid ; its
presence in the filtrate is readily detected by the addition of a persalt of iron.

CHAPTER LIII.

ALKALOIDS AND ORGANIC BASES. SUBSTANCES ASSO-
CIATED WITH OR DERIVED FROM THEM.

These are for the most part solid and crystallizable compounds. Some
are volatile : others are fixed, and are readily decomposed when heated, or
when brought in contact with chemical reagents. They generally contain an
atom of nitrogen as one of their ultimate elements ; they have a bitter taste,
are sparingly soluble in water, more soluble in alcohol, but readily soluble
in most of the dilute acids as well as in ether, chloroform, and benzole. With
an excess of iodic acid, they generally produce precipitates. They are sali-
fiable bases, and their compounds with the acids are- decomposed and pre-
cipitated by the alkalies. The aqueous solutions of those which are true
bases, and form crystallizable salts, give white flocculent precipitates with
solutions of tannic acid; the chloriodide of potassium and mercury, and iodide
of potassium with iodine. Of these, the chloride of potassium and mercury,
or the iodo-hydrargyrate of potassium, is the most reliable. The liquid
should not be acid or contain much alcohol. Ammonia is not precipitated
by this solution, but potash and soda give a yellowish precipitate with it.
The test for alkaloids is prepared by dissolving sixteen grains of corrosive
sublimate, and sixty grains of iodide of potassium in four ounces of water.
As it gives a precipitate with albumen, this when present should be first re-
moved by boiling and filtering the liquid to be tested. Although this solu-
tion precipitates an alkaloid even when in small quantity, there is no easy
process by which the alkaloid can be extracted from the precipitate in a
pure state. Bouchardat has proposed another precipitant of the alkaloids
which is very effectual in throwing down many of them in an insoluble form.
The solution which he employs is a strong solution of iodide of potassium
with iodine. The proportions by weight are 5 parts of iodide of potassium,
and 1 part of iodine, dissolved in 20 parts of water. A small quantity of
this solution added to a solution of an alkaloid throws down a red brown
precipitate. Some alkaloids are effectually precipitated by it, e. g., strychnia,
others only partially.. The precipitate is quite insoluble in water, and admits
of frequent washing even in water which is feebly acid without material loss.
The precipitate is diffused in water acidulated with dilute sulphuric acid,
and some iron filings are added to produce a slow evolution of hydrogen.
42

658 MORPHIA.

The precipitate disappears, and the liquid becomes nearly colorless. When
hydrogen is no longer evolved, a solution of ammonia is added, and a com-
pound precipitate of oxide of iron, and the alkaloid is thrown down. This
is well washed on a filter, dried, and treated with alcohol by W'hich the alka-
loid is removed from the oxide of iron. This process is said to be very effi-
cacious for discovering and separating small quantities of some alkaloids.
It would not answer on the large scale. Other and more simple methods
must here be resorted to.

The alkaloids are for the most part crystallizable, and are represented by
very high equivalent numbers. These solutions restore the blue color to
reddened litmus. They are found in plants united to certain acids, and
usually forming neutral or acid salts, which, as well as their artificial com-
binations, are decomposed in the voltaic circle, and the base is evolved at
the negative pole. Many hypotheses have been built upon the ultimate
composition of these alkaloids, and some curious analogies pointed out
respecting them by Liebig, Dumas, and others. In consequence of the
analogy that pervades these principles, one general method of separating
them is applicable to all, though each may require peculiar modifications of
it. The substance which contains them is boiled in water acidulated by
an acid, the decoction is filtered and neutralized by ammonia, lime, or mag-
nesia, when the alkaloid is precipitated, and afterwards separated and puri-
fied by alcohol or ether. Much of the history of these bodies is connected
with Materia Medica. We shall here examine them simply in reference to
their chemical properties.

Morphia (C35H,o06N+2HO=M+2HO).

In order to procure this alkaloid, a filtered solution of opium in tepid
water is mixed with acetate of lead in excess ; the precipitated meconate of
lead is separated by a filter, and through the solution, containing acetate of
morphia, now freed to a considerable extent from color, a stream of sul-
phuretted hydrogen is passed. The filtered, and nearly colorless liquid,
from which the lead has been removed, may be warmed to expel the excess
of gas, once more filtered, and then mixed with a slight excess of caustic
ammonia, which throws down the morphia and narcotine ; these may be
separated by boiling ether, in which the latter is soluble. The meconate of
lead, well washed, suspended in water, and decomposed by sulphuretted
hydrogen, yields solution of meconic acid. The quantity of morphia
obtained from opium is variable ; the produce is greatest from Turkey opium,
and least from the East Indian and Egyptian. The average is generally
estimated at about 1 oz. from the pound. Good opium is considered to
contain ten per cent, of morphia.

Morphia^ when obtained from its alcoholic solution, is in small brilliant
and colorless crystals : they are generally six-sided prisms, with dihedral
terminations, but their form is a right rhombic prism. When gently heated
they become opaque and lose water : at a higher temperature morphia fuses
into a yellow liquid, which becomes white and crystalline on concreting. In
the air it burns with a bright resinous flame. When heated in a close tube
it yields ammonia. Morphia, though apparently nearly insoluble in cold
water, has a bitter taste : boiling water dissolves not more than a hundredth
of its weight, but the solution is alkaline to delicate tests. It dissolves in
40 parts of cold, and 30 of boiling anhydrous alcohol. . It is almost insolu-
ble in ether and benzole, and is only sparingly dissolved by chloroform ;
hence one of the methods of separating it from narcotina, which is readily
soluble in ether. Amylic alcohol readily dissolves morphia at a moderate
temperature, and deposits it in well marked crystalline prisms on cooling.

ALKALOIDS IN OPIUM. CODEIA. 659

It also has the property of removing at least a portion of morphia from au
aqueous solution when the alkaloid is set free by the addition of ammonia.
The amylic alcohol also dissolves a portion of organic matter and becomes
colored. On drawing off the alcohol with a pipette, and allowing it to
evaporate spontaneously, a film or crystalline deposit may be obtained suffi-
cient to give the reactions of the tests for morphia as mentioned below.
Morphia is soluble in potassa and soda ; hence the necessity of avoiding the
use of these alkalies in its precipitation. Ammonia dissolves it sparingly,
so that this alkali ought not to be used in excess.

The tests for morphia are: 1. Nitric acid, which when dropped upon
crystallized morphia, forms a bright-red solution. 2. Neutral persulphate of
iron, which produces a very characteristic blue color when added to morphia,
or to its salts, provided the test is neutral and the solutions are not very
dilute. 3. Iodic acid; when this is added to morphia either solid or in solu-
tion of morphia it produces a reddish-brown color, and the odor of iodine is
immediately perceptible. The minutest quantity of morphia has the property
of decomposing iodic acid, but in cases where very small quantities are pre-
sent, a solution of starch may be employed to detect the free iodine. A
solution of iodic acid is decomposed by a great variety of substances ; its
chief use, therefore, is to distinguish morphia from other alkaloids which do
not decompose it, rather than to detect the presence of morphia in liquids of
unknown composition. 4. Sulpho-molyhdic add, this test for morphia has
been lately suggested by Frobide. A small quantity of molybdic acid or of
a raolybdate is dissolved by heat in concentrated sulphuric acid. If morphia
or any of its salts is touched with a drop of this compound acid, it produces
a beautiful reddish violet color passing to a deep sapphire blue at the margin
of the spot. The blue color results from the partial deoxidation of the
molybdic acid by the morphia, whereby a molybdate of molybdenum or
molybdous acid is produced. Many kinds of organic matter will sooner or
later produce the blue compound tint, but the reddish violet or purple color
is considered to be characteristic of morphia. The reaction is very delicate
for the smallest visible portion of morphia will be indicated by the change
of color.

CoDEiA (CgsHaoO.N-f 2H0).

This alkaloid was discovered by Robiquet, in 1832, in the hydrochlorate
of morphia. On dissolving the mixed hydrochlorates in water, and pre-
cipitating the morphia by ammonia, the codeia remains in solution and
crystallizes by subsequent evaporation : it may be also separated by ether,
in which it is soluble. According to Pelletier, 100 pounds of opium yield
6 ounces of codeia.

Codeia crystallizes in acicular, or flat prisms, colorless and transparent.
It fuses without decomposition, when heated in a tube to about 300°, and
the mass crystallizes on cooling. In the air it burns away with a smoky
flame. Water at 60° dissolves 1*26 per cent., and at 212°, 59 per cent.
When it is present in larger proportions than the boiling water can dissolve,
the excess fuses, and remains at the bottom of the solution. ^ Its solution is
sensibly alkaline to tests. Codeia is soluble in alcohol and in ether, and in
the dilute acids, and forms distinct and easily crystallizable salts. It is
distinguished from morphia, by its greater solubility in water and in ether,
by its insolubility in fixed alkalies, by its not being reddened by nitric acid,
nor blued by perchloride of iron.

Narceia {Q^B.Jd^^^), Thebaia (C^H,A^^)» Papaverine (C^HatOgN),
and Meconine (CjoH.Oj, are other crystalline principles found in opium.

660 NARCOTINA. CINCHONIA. QUINIA.

Narcotina (C^gHg^OjgN).

This well-defined and distinct principle appears to exist in opium in a free
state : it may be obtained from powdered opium by digesting it in warm
ether, which takes up little else than narcotina, and yields it in crystals.
When caustic potassa is added to an aqueous solution of opium, so as just to
saturate the free acid, the matter which falls consists chiefly of resin and
narcotine. When all the soluble parts of opium have been extracted by
water, as in making extract of opium, and in the preparation of morphia,
the residue, digested in dilute hydrochloric acid, also yields narcotina.

Narcotina is insipid when pure. It fuses at 268°, and when slowly cooled
concretes into a crystalline mass. It is deposited from its alcoholic or ethe-
real solution in well-defined rhombic prisms, insoluble in cold, and sparingly
soluble in hot water; 100 parts of boiling alcohol (sp. gr. 0*825) dissolve
about 5 parts of narcotina, 4 of which crystallize on cooling : boiling ether
dissolves about 3 or 4 per cent., of which it deposits more than one-half, on
cooling. It is soluble in the volatile and fat oils, but insoluble in alkaline
solutions. It does not render a solution of a persalt of iron blue, nor is it
reddened by nitric acid. This acid turns it yellow. Sulphuric acid, con-
taining a mere trace of nitric acid, immediately reddens it most intensely :
but when mixed with pure sulphuric acid, it acquires a yellow color. A
particle of an alkaline nitrate added to the mixture brings out a blood-red
color. It does not decompose iodic acid. Heated on paper over a candle,
it produces a greasy-looking stain. As it does not affect vegetable colors,
it is easily distinguished from morphia and codeia. It is readily soluble in
dilute acids, forming salts which are very bitter, and with difficulty obtained
in the crystalline state, for when evaporated they are mostly decomposed into
acid and narcotina, and crystals of the latter only separate. This is espe-
cially the case with the acetate of narcotina, and furnishes a means of
separating it from morphia, for the latter substance is retained in permanent
combination and solution.

+
CiNCHONiA. Cinchonine (CgoH,30N=Cin).

This alkaloid is obtained from the principal varieties of pale or gray
Peruvian bark. It is usually in the form of white semi-transparent crystals,
requiring about 2500 parts of water at 212° for their solution, and are
almost insoluble in cold water. They have little taste, but become intensely
bitter upon the addition of almost any acid. They restore the blue color
of reddened litmus. They are sparingly soluble in cold alcohol, ether, and
fixed oils ; but more abundantly soluble in boiling alcohol : the solution
deposits crystals on cooling, and becomes milky when dropped into water.
It forms with acids a large number of salts.

QuiNiA. Quinine {QJiiS^^,=(l).

Quinia is generally obtained from yellow hark. It almost always contains
more or less cinchonia : these alkaloids may be separated by solution in
alcohol, which, when duly evaporated, deposits the cinchona in crystals,
while the quinia, being more soluble, remains in solution : by one or more
repetitions of this process, it may be freed from cinchonia. If they are con-
verted into sulphates, the sulphate of quinia, being less soluble than the
sulphate of cinchonia, crystallizes, and leaves the latter salt in solution.

Sulphate of quinia, which is abundantly prepared for medicinal use, is the
most ready source of the alkaloid : it is obtained by adding ammonia to a
solution of that salt, when it falls in white flakes, which unless very carefully

SALTS OF QUINIA. STRYCHNIA. 661

dried, are apt to become brown. Quinia is very difficult of crystallization,
but it has been obtained in crystals by slowly evaporating its alcoholic solu-
tion by exposure to dry cold air.

Quinia has a decided alkaline action; it is intensely bitter; very sparingly
soluble, even in boiling water, of which it requires about 200 parts for its
solution. It is readily soluble in boiling alcohol, and the solution, when
evaporated, leaves it in the form of a viscid mass, which indurates and
acquires a resinous aspect on exposure to air. It is more soluble than cin-
chonia in chloroform and ether. It forms distinct salts with the acids.
When anhydrous quinia is heated in a tube, it fuses, becomes thick, viscid,
and dark-colored, an oily liquid evaporates, ammoniacal and hydrocyanic
vapors follow, and a bulky carbonaceous matter remains.

The Salts of quinia are for the most part crystallizable, and are generally
less soluble in water, and more bitter than the salts of cinchonia ; they are
also soluble in alcohol. The aqueous solution has a peculiar bluish opaline
appearance, as a result of fluorescence. They are liable to acquire a yellow
or brown tint by long exposure to solar light. In this altered state they
form the substance called quinoidine — a mixture of several basic compounds,
including quinidine {Q^^Jd^c^-^iB-O), isomeric with quinine. It is ex-
tracted by ether. These different bases of Peruvian bark are combined in
the plant with a peculiar crystallizable acid, called the Cinchonic or Kinic
acid (CyH^O^HO).

Strychnia (C^^Ha^O^NJ.

The following is Merck's process for the extraction of this alkaloid. The
seeds of nux vomica are boiled for 24 or 36 hours in a closed boiler, with
water enough to cover them, acidulated by one-eighth of its weight of sul-
phuric acid ; they are then bruised and beaten into a paste, and the liquor
well expressed. Excess of caustic lime is then added to it, and the precipi-
tate, having bee«i pressed, is boiled in alcohol of sp. gr. -850, and filtered
hot ; strychnia and brucia are deposited together in a colored and impure
state, and may be separated by cold alcohol, which dissolves the brucia.
The remaining strychnia is then boiled in alcohol with a little animal char-
coal, and the solution filtered boiling hot ; on cooling, the strychnia crystal-
lizes. The same process is applicable to the Ignatius' beans.

Strychnia is a powerful poison, de^roying life in the dose of half a grain.
It is a white crystalline solid, neither fusible nor volatile, but easily decom-
posed by heat, yielding ammonia, in close vessels. It requires 7000 parts
of cold and 2500 of boiling water for solution : the intensity of its bitterness
is such, that an aqueous solution which does not contain more than a forty-
thousandth of its weight of strychnia is sensibly bitter. It is soluble in
common alcohol, especially at its boiling temperature, and readily crystallizes
in quadrangular prisms and octahedra from this solution. Absolute alcohol
and ether scarcely dissolve it when quite free from acid. It is dissolved by
chloroform and benzole, and separated from water by these solvents when an
alkali is added to a solution of a salt of strychnia. It is dissolved by the
acids, forming colorless and crystallizable salts. It is not soluble in the
alkalies. Nitric acid does not color strychnia or its salts, if free from brucia ;
but it frequently reddens them, owing to the presence of traces of brucia.

When a minute quantity of strychnia is moistened with a drop of concen-
trated sulphuric acid, the strychnia is dissolved without any peculiar color,
but if a minute quantity of the peroxide of lead or manganese, of bichromate
of potassa, or ferricyanide of potassium, is added, a fine blue tint is developed,
which passes into violet and red, and after some hours into a pale reddish
yellow color. This reaction is characteristic of strychnia. The peroxide

662 BRUCIA.

of manganese in small quantity is preferable for this experiment. A strong
solution of strychnia gives crystalline precipitates with sulphocyanide and
ferricyanide of potassium, as well as with chromate of potash. The ferricy-
anate and chromate of strychnia, when touched with sulphuric acid, acquire
the blue, violet, and purple colors which characterize strychnia. To these
may be added the sulpho-molybdic acid (see Morphia), which produces a
peculiar reaction with strychnia. When first added there is no change of
color. The border of the acid liquid soon begins to show a fringe of a pale
blue or azure color. This gradually extends by exposure to the whole of
the liquid', until it is uniformly of a light azure blue, without any of the deep
blue tint observed in morphia and other alkaloids.

This alkaloid perfectly neutralizes the acids, and forms soluble and very
bitter and poisonous salts : they are mostly crystal lizable. The caustic
alkalies throw down from their solutions a white precipitate of strychnia,
which may be dissolved and removed by agitating the liquid with twice its
bulk of ether or chloroform. This is the process usually pursued for the
extraction of strychnia in cases of poisoning. The liquid is acidulated,
concentrated in a w^ater-bath, rendered alkaline by potassa, and then shaken
with two volumes of ether. The ethereal liquid poured off, and sponta-
neously evaporated, leaves strychnia. The salts of strychnine are precipitated
by tincture of galls (tannic acid).

Brucia (C,,H,30,N,).

This alkaloid is most abundantly procured from the bark of the Strychnos
nux-vomica, common\y C2i\\Q^ false angustura. This bark is coarsely pow-
dered, and, having been previously digested in ether to free it from fatty
matter, is treated with alcohol, the alcoholic solution evaporated, and the
residue dissolved in water saturated with oxalic acid, and evaporated to
dryness. Alcohol digested upon this residuum dissolves coloring matter,
and leaves pure oxalate of brucia, which may be decomposed by lime, and
the brucia dissolved out by boiling alcohol, from which, by slow evaporation,
it is obtained in crystals.

Brucia forms either prismatic or foliated crystals, according as it has been
slowly or rapidly deposited : it is soluble in about 850 parts of cold, and in
500 of boiling water. Sometimes, on precipitating a salt of brucia by
ammonia, the alkaloid separates in the form of an bi\, which after a time
concretes, if left in contact with water. The taste of brucia is strongly and
permanently bitter : its poisonous action resembles that of strychnia, but it
has only one-sixth of the strength. It is very soluble in alcohol, but insolu-
ble in ether, and in the fat oils : it is sparingly soluble in essential oils. It
forms soluble salts with the acids, which are mostly crystallizable ; they are
bitter, and are decomposed not only by the alkalies, but by morphia and
strychnia, both of which precipitate the brucia. Brucia is strongly reddened
by nitric acid, and the color changes to violet when the liquid is warmed
and protochloride of tin is added. It is distinguished from strychnia by its
not producing the blue and purple colors when mixed with sulphuric acid
and peroxide of manganese. It is also known from this alkaloid by the
different effect produced upon it when it is touched with a drop of sulpho-
molybdic acid. A flesh or pale red color is first produced — the spot becom-
ing of a dingy olive-green color in the centre. By long exposure the whole
of the spot acquires a deep sapphire-blue color.

Strychnia and brucia, as they exist in the vegetable structure, are com-
bined with a peculiar acid, called the strychnic or igasuric.

COLCHIOIA. ATROPIA. 063

YERATRTACCg^H^eOgN).

This alkaloid is contained in the seeds of the Veratrum sahadilla, and in
the roots of the Veratrum album, or white hellebore, united with gallic acid.
Commercial veratria is not crystallizable ; it has a pungeut but not a bitter
taste, and powerfully irritates the nostrils, causing the most violent sneezing.
A small dose produces nausea and vomiting. It is a poison. It fuses at a
temperature of 122°, and concretes, on cooling, into a translucent yellow
mass. Boiling water does not take up more than a thousandth part' of its
weight, but it is readily soluble in alcohol, and somewhat less so in ether.
Chloroform dissolves it in large quantity. Yeratria is characterized by its
producing, when warmed with diluted sulphuric acid, an intense crimson
color. If strong sulphuric acid is used a greenish-yellow color is first pro-
duced, which becomes slowly dark red by exposure, but rapidly acquires a
most intense blood red color when heated. As sulphuric acid reddens a
great variety of organic substances, e. g., salicine, cholesterine, gallic acid,
etc., the last alone is not sufficient. Chloride of tin evaporated with vera-
tria leaves a reddish colored-residue. Nitric and hydrochloric acids produce
in it a characteristic change. The sulpho-molybdic acid produces with it
at once a dingy olive-green color, which passes after a time to a rich sapphire-
blue.

CoLCHiciA. Colchidna.

This substance, originally confounded with veratria, has been shown by
Geiger and Hesse to exist in the Golchicum autumnale, as a distinct alkaloid,
but it has not been analyzed, nor has its atomic weight been determined. It
exists in the bulb and flowers gathered in July, but is best obtained from the
pulverized seed, which is digested in alcohol acidulated by sulphuric acid ;
lime is then added to the liquor, which is filtered, saturated by sulphuric
acid, and the alcohol expelled by distillation. The remaining concentrated
aqueous solution having been decomposed by excess of carbonate of potassa,
the precipitate is dried and digested in absolute alcohol. The alcoholic
solution of the alkaloid is then decolorized by animal charcoal, filtered, and
gently evaporated : the product is afterwards purified by repeated crystalli-
zations.

Colchicia is a powerful poison. It crystallizes in colorless needles, which
have a bitter taste and are very poisonous ; it causes purging and vomiting
in very small doses. It is slightly alkaline and easily fusible. It is rendered
deep violet blue by concentrated nitric acid, becoming afterwards olive-colored
and yellow ; sulphuric acid renders it brown. It is soluble in water, alcohol,
and ether, and its aqueous solution is precipitated by tincture of iodine, by
solution of chloride of platinum, and by infusion of galls. It neutralizes the
acids, and forms salts which are mostly crystallizable, permanent in the air,
and very bitter and acrid. They are soluble in water and alcohol, and their
aqueous solutions are acted upon by reagents similarly to colchicia. When
not too dilute, the alkalies precipitate the alkaloid.

Atropia. Hyoscyamia. Daturia. Piorotoxia.
Atropia is the poisonous alkaloid of the Atropa Belladonna, or Deadly
Nightshade; Hyoscyamia, of the Hyoscyamus niger; Daturia, of the Datura^
Stramonium; and Picrotoxia, of Cocculus Indicus. Aconitina and Digitaline
are extracted respectively from Aconitum napellus and Digitalis purpurea.
These are all active poisons. Their composition has not been accurately
determined. There are other alkaloids of less interest, which require no
particular notice in a chemical point of view.

664 NICOTINA. CONTA.

The bases hitherto considered contain oxygen. There are two volatile
alkaloidal bodies, Nicotina and Conia, which contain no oxygen.

NiCOTINA (C^oH^N).

Kicotina is obtained by boiling dry tobacco-leaves in water acidufeted by
snlphuric acid, and evaporating the decoction; the residue, digested in alco-
hol, yields a solution of sulphate of nicotina, which, when concentrated and
distilled with quicklime, furnishes a solution of ammonia and nicotina. Ether
abstracts nicotina from this solution, and when a sufficiently concentrated
ethereal solution has been thus obtained, it must be deprived of water by agi-
tation with chloride of calcium, decanted, and distilled; the nicotina remains
in the retort.

Pure nicotina is a colorless, limpid, oleaginous liquid, having a slight odor
of stale tobacco ; when it contains ammonia, this odor is very intense. At a
temperature below 475° it may be slowly distilled, but at that temperature it
is decomposed; its sp. gr. is 1-048. It is powerfully alkaline to test-papers;
it is very inflammable, and burns with a smoky flame. When dissolved in
water, caustic potassa separates it in the form of oily drops. Ether abstracts
it from its aqueous solution. It dissolves in all proportions in alcohol and
in oils. It is decomposed when heated with hydrate of potassa. Exposed
to air, it becomes brown and resinous: it is decomposed by chlorine, iodine,
and nitric acid. It is eminently poisonous, but does not occasion dilatation
of the pupil : half a drop killed a rabbit ; one drop was fatal to a dog ; a
tenth of a grain applied to the eye of a cat, occasioned violent convulsions
and paralysis of the hind-legs, which lasted for an hour. Nicotina neutralizes
the acids and forms salts which do not easily crystallize, but are very soluble
in water and alcohol. When it is slightly supersaturated by hydrochloric acid,
nicotina gives no precipitate with bichloride of platinum, but the mixture,
after some hours, deposits acicular crystals. If the nicotina contains am-
monia, it occasions an immediate precipitate. The solution of nicotina pro-
duces a white precipitate with corrosive sublimate.

Conia. Conidna (C,eH,6N).

It appears from the experiments which have been made upon hemlock,
that its active principle resides in a volatile and uncrystallizable alkaloid; its
properties have been investigated by Geiger, and by Dr. Christison {Edin.
Phil. Trans., 1836, p. ^3). When the seeds or leaves of hemlock are dis-
tilled with water, the fluid which passes over has the odor of the plant, but
is not poisonous ; but when caustic lime or potassa is previously added to
the green seeds or leaves, and these are distilled with water at as low a tem-
perature as possible, the liquid which then passes over is both alkaline and
poisonous. When 10 or 12 pounds of the seeds are worked at once, an oily
matter comes over at first, which is nearly pure conia, but the greater part
of the alkaloid is dissolved in the distilled water ; if this be redistilled, it
loses a little of its strength ; but if previously neutralized by an acid, such as
the sulphuric, the poisonous principle becomes fixed, and water alone distils
over. The residue consists of sulphate of conia, sulphate of ammonia, and
resin, the latter being produced by the decomposition of part of the conia.
To obtain the conia, the above residue is digested in a mixture of 2 parts of
•alcohol and 1 of ether, which leaves the sulphate of ammonia ; and then, the
alcohol and ether being carefully distilled off, the remaining sulphate of conia
is heated gently with a little water and caustic potassa, when there is obtained
in the receiver a watery solution of conia in the lower part, and floating on
this a layer of nearly pure hydrate of conia, containing a trace of ammonia;

ANILINE. CG5

the water ^raay be abstracted by chloride of calcium, and the ammonia by
exposure i7i vacuo.

Conia thus obtained has the appearance of a colorless volatile oil, lighter
than water, of a powerful diffusible odor, somewhat like that of hemlock, and
when diluted resembling the smell of mice : it is intensely acrid to the taste.
It has a strong alkaline action on reddened litmus and on turmeric. It is
readily soluble in diluted acids, which it neutralizes, but its salts have not
been crystallized. It is sparingly soluble in water, ant combines with about
a fourth of its weight of water to form a hydrate.

Conia is a deadly poison to all animals : it first paralyzes the voluntary
muscles, then the respiratory muscles and the diaphragm, thus producing
death by asphyxia. The heart continues to act after other signs of life are
extinct. Few poisons equal it in subtlety or swiftness ; a drop put into the
eye of a rabbit killed it in nine minutes ; three drops, in the same way, killed
a strong cat in a minute and a half; two grains of conia, neutralized with
hydrochloric acid, and injected into the femoral vein of a young dog, produced
almost instant death : in two seconds, or three at farthest, and without the
slightest warning struggle, respiration had ceased, and with it all external
signs of life. If conia be present in an extract or other preparation, it may
be detected by triturating either the solid or liquid with a solution of potassa,
upon which the odor of mice will be strikingly perceptible.

Aniline. Phenylia (C^aHyN).

This is an artificial base which contains no oxygen. It has been already
referred to as a product of the distillation of coal. It may be procured by
distilling indigo with a strong solution of potassa. It is now obtained in
large quantities, for dyeing and other purposes, by distilling nitrobenzole
with a mixture of acetic acid and zinc, or iron, in which case this liqnid is
decomposed by nascent hydrogen, and aniline is a product. The proportions
employed are 10 parts of nitrobenzole, 6 parts of commercial acetic acid,
and 15 parts of pounded iron-turnings.

Aneline when pure is a colorless or oil-like liquid, possessing a very high
refractive power : it has a strong disagreeable odor, and a hot aromatic
flavor. It boils, according to Hofmann, at 360°, but it evaporates rapidly
at common temperatures, and the greasy spot which it produces on paper
quickly disappears; it remains perfectly fluid at 0°; its sp. gr. at 60- is
1020. We have found it in two samples to be 1'023 and 1*024 respectively.
It is soluble to a slight extent in cold water, the greater part falling in oily
globules : the solution becomes turbid when heated ; it is soluble in all pro-
portions, in alcohol, ether, wood-spirit, aldehyde, acetone, sulphide of carbon,
and in fixed and volatile oils. It has no alkaline reaction on turmeric or on
reddened litmus. When a glass rod dipped in hydrochloric acid is held
over its aqueous solution, white fumes are produced, resembling those formed
by ammonia. Aniline dissolves sulphur when aided by heat, and on cooling,
deposits it in prismatic crystals ; it also dissolves phosphorus, camphor, and
colophony, but not copal or caoutchouc ; like creasote, it coagulates
albumen.

When aniline is exposed to air, it absorbs oxygen, and becomes yellow,
brown, and resinous. A few drops of fuming nitric acid added to anhydrous
aniline produces a fine blue color, which on slightly heating the mixture
passes into yellow, and violent action ensues, sometimes followed by explosion ;
otherwise, the liquor passes through various hues, and crystals of picric acid
are formed in it. When aniline is added to a solution of permanganate of
potassa, peroxide of manganese is thrown down, and oxalic acid and ammo-
nia are formed. When treated with a solution of chloride of lime, a beauti-

666 EMETINA AND OTHER BASES

ful violet-color is produced, which is reddened by the addition of an "acid;
this reaction is very characteristic of aniline. When chlorine is passed into
aniline, it assumes the consistence of tar, and on distilling this product, a
compound passes over, composed of CiaHgNCl. When heated with corro-
sive sublimate, it produces a splendid red dye. It is now largely employed
in the manufacture of the coal-tar colors.

Aniline forms a series of crystallizable salts with different acids.

The production of^niline from nitrobenzole furnishes an apt illustration
of the complexity wTiich it is proposed to introduce into chemical formulae,
in place of the simple system which is now generally employed. When
nitrobenzole is distilled with a mixture of iron-filings and acetic acid, it is
converted into aniline, as a result of the evolution of nascent hydrogen ; and
the simple equation which represents this change is : —

C,2H,(N0,)

Nitrobenzole. Hydrogen. Aniline.

The following represents the changes, according to Dr. Hofmann, on what
is called the unitary system : —

(C6H5)NOO + HH 4- HH -f HH

(CeH,))

Nitrobenzole. Hydrogen. Water. Aniline.

Emetina, Caffeine, Theine, and other Bases.

Emetina {C^'E.^^0^^. — This term is applied to the active or emetic princi-
ple of Ipecacuanha. It is a white, inodorous, and almost insipid powder,
alkaline to test-paper, and sparingly soluble in cold water. It is more solu-
ble in alcohol ; but ether, the essential oils, and the caustic alkalies, scarcely
act upon it ; it fuses at about 120^. Concentrated nitric acid converts it in
the first instance into a bitter yellow resinoid substance, and ultimately into
oxalic acid. It neutralizes the acids, and forms salts which are not crystal-
lizable except with excess of acid. Emetina has a powerful emetic action.
In a dose of three or four grains it acts as a poison.

Piperine (Cj^H^gOgN). — This substance is obtained from hlach pepper. It
is generally a pale straw color, and crystallizes in the form of four-sided
prisms, insoluble in cold, and slightly soluble in hot water; readily soluble
in alcohol, and less so in ether. When quite pure, it is inodorous and taste-
less. It fuses at a little above 212°, and is not volatile, but when more
highly heated, yields ammoniacal products. It is regarded as a feeble alka-
loid.

Asparagine {C^Jd^^-\-^^0). — This principle exists in asparagus. It
is best obtained from the expressed juice of asparagus, evaporated to the
consistency of syrup, and set aside ; it deposits crystals, which are purified
by solution in water and recrystallization. Asparagine forms transparent
prismatic crystals, which are hard, brittle, of a cooling and somewhat nau-
seous taste, neither alkaline nor acid ; soluble in 58 parts of cold water, and
more soluble in hot ; insoluble in anhydrous alcohol, and in ether. When
asparagine is long boiled with hydrated oxide of lead, magnesia, or other
bases, it is resolved into ammonia and into an acid, called Aspartic acid.

Caffeine. Theine. (CgH.O^Ng). Guaranine. This important compound
is found in coffee (the seed of Goffea Arahicd) and in tea, the leaves of Thea
Chinensis : it is also said to occur in the leaves of Guarana officinalis or
Paullinia Sorbiiis, and in Ilex Paraguayensis (^Paraguay tea). It is re-

THEINE. THEOBROMINE. SALICINE. GOT

mark^le that one and the same principle, and that belonging to the class of
azotized basic bodies, should be found in two such dissimilar vegetables as
tea and coffee, infusions of which are used over the greater part of the known
world.

^ Caffeine naay be procured as a crystalline sublimate in considerable quan-
tity in the roasting of large quantities of coffee ; it sublimes in an impure
form, but is easily deprived of its adhering impurities. The process gene-
rally recommended for its preparation is that of Runge\ it consists in making
a strong aqueous infusion of ground raw coffee, adding to it a solution of
sugar of lead, which occasions a green precipitate, and leaves the superna-
tant liquid colorless : the excess of the salt of lead in this liquid is then pre-
cipitated by sulphuretted hydrogen, it is filtered, and evaporated ; the caf-
feine remains, and must be treated by animal charcoal to whiten it, and re-
crystallized. Caffeine (or theine) forms white silky crystals, soluble in boil-
ing water and alcohol, and deposited in crystalline filaments as these solu-
tions cool : it has no alkaline reaction, yet it appears capable of combining
definitely with some of the acids, especially with hydrochloric acid.

TJieine is thus prepared : a decoction of tea is first treated with a slight
excess of acetate of lead, which throws down the tannic acid and almost all
the coloring matter it contains ; it is then filtered whilst hot, and the clear
liquid is evaporated to dryness. It forms a dark yellowish mass, which is
to be intimately mixed with a quantity of sand, and introduced into Mohr's
subliming apparatus aud moderately heated for 10 or 12 hours. The theine
sublimes in beautifully white anhydrous crystals, deposited upon the paper
diaphragm which runs across the apparatus. The only point to be observed
is that the temperature should never rise too high, as the more slowly the
operation is conducted, the finer are the crystals and the greater their quan-
tity. From a pound of coffee, Stenhouse obtained an average produce of
15 grains of theine, sometimes not so white as that made from tea, but ren-
dered so by a second sublimation. From hyson tea (green), Stenhouse ob-
tained r05 per cent, of theine; from Congou (black) 1*02 per cent. ; from
Assam (black) r2t, and from Tonkay (green) 0-98. But Peligot, guided
by the large proportion of nitrogen evolved in the ultimate analysis of tea,
was led to suspect a larger proportion of theine, and obtained the following
quantities, namely, from hyson, 2*56 to 3*40 per cent, and from gunpowder
tea 2-20 to 4' 10 per cent.

Theohromine (Cj^HgO^^J is a base which is contained in the cacao-nut
{Tlieohroma cacao). It is but little soluble in water, alcohol, and ether. It
has a bitter taste, and forms crystallizable salts with acids.

Salicine (CaBHjgO^). — This is a crystalline substance which is extracted
from the bark of the willow. It is soluble in water and alcohol : its solu-
tions have a bitter taste : they are laevo-gyrate with regard to polarized
light. Salicine is characterized by the deep red color which is produced
when the crystals are moistened with strong sulphuric acid. When salicine
is boiled with dilute sulphuric acid, glucose or grape-sugar is a product.
Nitric acid converts it into oxalic and carbazotic acids. When distilled with
bichromate of potassa and dilute sulphuric acid, salicylous acid or hydride
of salicyl {C^^Ufi^,W) is obtained in the distillate. This is identical with
the essential oil of Meadow-sweet {Spirsea uhnaris). Salicine yields about
one-fourth of its weight of the hydride. When fused below redness with
three parts of hydrate of potassa, a salicylate of the alkali is obtained, from
a solution of which salicylic acid is precipitated by the addition of hydro-
chloric acid.

A solution of a salicylate is characterized by its striking a violet-hlMQ color
with a persalt of iron. Certain insects which feed upon willow bark, oxidize

668 ORGANO-METALLTC BASES.

salicine in their bodies. If placed on paper impregnated with a persalt of
iron, and they are irritated, they eject a liquid which produces a blue or
violet-colored spot on the paper.

The oil or essence of winter-green ( Gaultheria procumhens) is a salicylate
of the oxide of methyle (CgllgO + C^HgOg). It has a strong agreeable odor,
and acquires a violet color on the addition of a persalt of iron.

Phloridzine {G^^^O^,i^O) is a crystallizable principle obtained from
the bark of the apple and pear trees, by simply boiling the decoction in
water, and allowing the liquid to cool. When boiled with diluted acids,
grape-sugar is one of the products. Salicine, phloridzine, and some other
principles of a similar kind, which thus yield grape-sugar, under such simple
conditions, have received the name of Glucosides.

Organo-metallic Bases.

We have elsewhere referred to the compounds of zinc with the organic
radicals methyle (p. 593), amyle (594), and ethyle (600) : but there is pro-
bably no compound more remarkable for its constitution and range of
combination, than that which was discovered and isolated by Bunsen under
the name of Kakodyle.

Kakodyle (C4HgAs=Kd). — This is a compound of metallic arsenic with
carbon and hydrogen : it derives its name from its highly offensive odor.
Bunsen procured this radical by decomposing anhydrous chloride of kakodyle
with pure zinc, and distilling the product. Owing to its spontaneous com-
bustion in air, and its highly poisonous nature, great precautions are required
in its preparation. It is a clear colorless liquid (sp. gr. 1'48); the density
of its vapor being 7 "2. When cooled to 20° it crystallizes in square prisms.
When exposed to air, oxygen, or chlorine, it burns, forming with oxygen,
water, carbonic and arsenious acids. It is resolved at a red heat into arsenic,
light carburetted hydrogen, and olefiant gas ; and by these results its exact
constitution has been determined (C4HgAs=As-f-2CHa + C2H3).

Kakodyle, like cyanogen, combines with oxygen, sulphur and chlorine.
It also combines with cyanogen. Oxide of kakodyle (KdO) is known under
the names of Alkarsine and CadeVs fuming liquor. It is procured by distilling
at a red heat, a mixture of equal weights of arsenious acid and dry acetate
of potassa. The vapor has an offensive odor resembling that of garlic, and
is very poisonous. The oxide is a colorless liquid (sp. gr. 1*64). It is
insoluble in water, but dissolves in alcohol and ether. Another oxygen
compound (KdOgjHO) is known under the name of Kakodylic acid or Alkar-
gen. It is procured by mixing red oxide of mercury with oxide of kakodyle
under water. TJhis acid may be obtained crystallized in prisms. Although
it contains 56 per cent, of arsenic, 6 or 7 grains of it, according to Bunsen,
produced no ill effect on a rabbit. The chloride is procured by distilling
the oxide with corrosive sublimate and hydrochloric acid ; and the cyanide
by distilling the oxide with concentrated hydrocyanic acid.

The preparation of any of these compounds is attended with great danger
to the operator. Bunsen states, that in distilling the oxide, an explosion is
very likely to occur, if the glass bulb above the level of the liquid becomes
too hot. " Should a drop of the liquid, during ebullition, fall on that part,
the whole of the apparatus is shattered to pieces, and an arsenical flame
several feet high rises up, covering everything near it with a black offensive
layer of arsenic." Of the cyanide of kakodyle he says, that "the vapor
diffused in the smallest quantity through the atmosphere, produces a sudden
cessation of muscular power in the hands and feet, giddiness and insensibility,
which end in total unconsciousness !"

ORGANIC COLORING MATTERS. $$9

CHAPTER LIV.

ORGANIC COLORINa MATTERS. DYEING.

Under this head a variety of substances are included, of very different
character and composition. Many of them are important in the arts : they
are used as pigments, and extensively employed by dyers and calico-printers.
Others are of so fugitive a nature as not to admit of this application, and are
chiefly known as giving variety and beauty to flowers, or as communicating
to vegetables in general, those infinitely varied shades of color which charac-
terize this division of the organic creation. By far the greater number of
these substances are educts of vegetable origin, or products of the decom-
position of vegetable substances. The coloring-matters derived from animal
substances are comparatively few.

A colored compound is a frequent product of chemical changes in colorless
organic compounds. When gallic acid is dissolved by heat in strong sul-
phuric acid, a rich crimson-colored liquid is produced. On dissolving essen-
tial oil of bitter almonds in the same acid, a ruby-red liquid is produced,
which becomes yellow on exposure to air. Pyroxanthine gives with sulphuric
acid in the cold, splendid purple and crimson compounds, which gradually
darken by exposure. When crystallized cane-sugar in powder is mixed with
arsenic acid and water, so as to form a thick paste, the mixture slowly
acquires, by exposure to air at a temperature of about Y0°, a splendid
crimson color, which gradually darkens. When arsenious acid is employed
no colored compound results. The substitution of aniline for sugar, and the
application of heat to the mixture of aniline and arsenic acid, has been
recently made the subject of various patents for the production of permanent
purple dyes. The action of sulphuric acid and bichromate of potassa on
strychnia and aniline, in producing blue, purple, and crimson-colored com-
pounds, furnishes other instances of the production of splendid colors from
colorless organic substances. A small quantity of a solution of gallic acid
added to lime-water produces a white precipitate, which speedily becomes
blue, purple, and ultimately olive-green. Bile produces with sulphuric acid
and sugar, aided by heat, a splendid purple color, and with nitric acid a rich
green color. In most of these cases, it may be proved that color is produced
as a result of the oxidation of the organic substance ; and in reference to
many of the coloring matters described in this chapter, it will be found that
they do not exist ready formed in the living plant, but are products of the
oxidation of certain principles contained in the sap or vegetable fil3re.
Chemical compounds which impart oxygen, e. g., chromic acid, the peroxides
of manganese and lead, and arsenic acid, produce color ; while those which
have reducing properties, such as nascent hydrogen,- sulphuretted hydrogen,
alkaline sulphides, and the protoxides of manganese and iron, render the
colored compounds temporarily colorless. Organic colors are easily destroyed
by exposure to light. This, which is called fading, may be due to the effect
of nascent oxygen or ozone. That nascent oxygen has a powerfully destruc-
tive influence, is seen in the action of ozone, and of chlorine. Humid chlo-
rine completely destroys all organic colors. Sulphurous acid also bleaches
them either by removing oxygen, or by forming with the coloring matter,

670 PRODUCTION OF COLORS

colorless compounds, which are soluble in water, and admit of removal by-
washing. Acids and alkalies sometimes restore the color when sulphurous
acid has been used, but not when chlorine has been employed.

Some coloring principles, although neutral in reaction, appear to act like
acids in combining with bases. Thus alumina and the oxides of tin and
iron, form insoluble compounds with organic colors, and at the same time
modify the color. Hydrate of alumina precipitates most organic colors
which are soluble in water, rendering the liquid colorless. Charcoal in
powder has a similar effect : it removes the color without altering it. Ani-
mal and vegetable fibres also remove and fix these colors by a powerful
attraction, and they are sometimes employed for the purpose of separating
the coloring principle in a pure state (see Carthameine). As a general rale,
wool appears to have the strongest attraction for coloring substances ; silk
comes next to it, then cotton, and lastly hemp and flax.

The art of dyeing and calico-printing consists in the application of these
organic colors to animal or vegetable fibre, such as silk, wool, linen, or cotton.
It is based on simple chemical principles. In the first place, the articles
require to be thoroughly cleansed from all foreign matters and colors : this
is effected by washing and bleaching. The simple operation of dyeing is
generally performed upon animal fibre, such as wool and silk; whilst the more
refined operation of printing in patterns and devices of various colors is
chiefly, though by no means exclusively, conducted upon cotton, or, as it is
usually termed, calico. Some colors are of such a nature as to combine with
the fibre without any medium; and when this is the case, they constitute
what have been termed substantive colors. Other colors require the inter-
vention of a base or mordant^ and they are then called adjective colors. The
mordants which are most frequently resorted to are the salts of alumina,
iron, and tin. Albumen, as well as the alkaline phosphates and arsenates,
are also employed as mordants in calico-printing. The substance to be dyed,
is first impregnated with the mordant, and then passed through a solution
of the coloring matter, which is thus fixed in the fibre, and its tint is often
modified or exalted by the operation. A considerable portion of the mordant
is retained in the fibre of the calico or cloth which is dyed. Ure found that
100 parts of the ashes of Turkey-red calico (dyed by an alum mordant)
afforded between 16 and H parts of alumina, whereas the ashes of white and
washed calico afforded only a trace of that earth.

Calico-printing, which is a more refined and difficult branch of the art, is
a species of topical dyeing. In this process adjective colors are almost
always employed. The mordants, the principal of which are acetate of
alumina and acetate of iron, and albumen, are first applied to the calico by
means of wooden blocks or copperplates, or cylinders, upon which the requi-
site patterns are engraved. When albumen is used as a mordant, this is
fixed by exposure to a steam-heat. The stuff is then passed through the
coloring bath, and afterwards exposed on the bleaching-ground, or washed.
The color flies from those parts which have not received the mordant, and is
permanently retained on those parts to which the mordant has been applied.
A variety of colors is produced by employing various mordants, and different
coloring materials, and by using them in various states of dilution and com-
bination. Instead of first applying the mordant, and afterwards the color-
ing material, they are occasionally both printed together, but in these cases
particular management is requisite in the selection of the substances em-
ployed, and in the mode of their application ; when this method is resorted
to, the color is ofi^w fixed by the application of steam. Thus in the employ-
ment of albumen, either of Qg^ or blood, or of lactarine (the curd of cheese),
the coloring-matter is at once mixed with the organic principle, and the

PRODUCTION OP INDIGO, gYl

colored compound is printed in a pattern on the cloth. When the cloth has
been subjected to the steaming process, the color and the albumen mixed
with it are rendered insoluble, and remain fixed on the fibres of the stuff.
Cottons, which receive dyes with more difficulty than silk or wool, are thus
effectually dyed. By the aid of albumen or lactarine, insoluble mineral
colors, such as ultramarine, or Scheele's green, may be imprinted on the
finest fabrics.

We shall here consider the principal coloring matters which are employed
in chemistry and the arts.

Indigo. — Indigo, as it occurs in commerce, is usually in the form of cubi-
cal pieces, or cakes, friable, and more or less brittle, and of various shades
of a peculiar deep blue. When rubbed with a hard body, it acquires, like
Prussian blue, a coppery-red color, but always furnishes a deep-blue powder ;
it is tasteless, nearly inodorous, and almost insoluble in water, alcohol, and
ether. The masses of indigo have a dull conchoidal fracture, and the finest
samples are those which are lightest and most copper-colored. The plants
resorted to as a source of indigo, are different species o{ Indigofera ; it is
also obtained from other genera, as Nerium, Isatu, Marsdenia, Polygonum^
and Asclepias. Indigo appears to exist in the juices of these plants, in the
form of a colorless soluble compound ; and it is generally obtained by fer-
menting the bruised plant, during which ammonia is evolved, and a yellow
liquid obtained. This liquid, on the addition of lime-water, and exposure to
air, deposits the blue indigo in the form of a flocculent precipitate. Its chief
sources are India and South America.

Indigo-hlue. Indigoiine (CigH-OgN). — It is this coloring matter which
gives the commercial value to indigo, of which it forms about 50 per cent.
In order to obtain the pure coloring principle, the indigo of commerce is
successively treated with hydrochloric acid, weak solution of potassa, and hot
alcohol, to remove any foreign substances. It is then thoroughly mixed with
twice its weight of freshly-slaked lime, and the mixture put into a bottle
capable of holding 150 times the quantity of indigo operated on ; the bottle
is then filled with boiling-hot water, and 4 parts of crystallized protosulphate
of iron added for every 3 of indigo; it is then securely stopped so as to be
air-tight, and having been well shaken, is set aside for several hours. In this
way the indigo-blue, which is insoluble, is converted into indigo-white, which
is soluble in the solution of lime, producing a yellow liquid. This yellow
liquor is then poured off, mixed with dilute hydrochloric acid, and left for a
long time exposed to air ; the acid retains the lime and other substances in
solution, while the indigo-blue is deposited, and may be freed from hydro-
chloric acid and chloride of calcium, by washing with water.

Indigotine is volatile, without decomposition, at a low temperature. If
powdered indigo is carefully heated in a tube through which a current of
hydrogen is passing, the indigotine sublimes in a violet-colored vapor resem-.
bling that of iodine, and is deposited in purple crystals in the form of fine
needles. If overheated, or heated in air, it is decomposed. The sublima-
tion takes place readily at about 550° : the melting-point of this substance,
its point of volatilization, and that at which it is decomposed, are very near
to each other. The sp. gr. of sublimed indigo-blue is 1*35. When the
crystals are heated in an open vessel, they sublime without residue, in a
reddish-violet vapor ; in close vessels, as the heat advances, the vapor
acquires a scarlet tinge, and then becomes orange-colored; a small quantity
of aniline is formed, and charcoal is deposited.

Heated upon platinum-foil, indigo-blue gives a purple smoke, and if the
heat be rapidly augmented it fuses, boils, and burns with a bright flame,

6t2 CHEMICAL PROPERTIES OF INDIGO.

giving off much smoke, and leaving a carbonaceous residue, which may be
entirely consumed. Indigo-blue is insipid and inodorous, and neither basic
nor acid. It is insoluble in water, alcohol, ether, and the oils. Dilute acids
and alkaline solutions have no action upon it.

Indigo-white. Indigogene (CigHgOgN). — If the yellow solution, obtained
by the action of lime and protosulphate of iron upon indigo and water, is
decomposed by an acid under the cautious exclusion of oxygen, a white pre-
cipitate is formed : this is indigo-white. It may be obtained by siphoning
the yellow liquor into a stopper bottle previously filled with hydrogen or
carbonic acid gas, and containing some acetic or dilute hydrochloric acid,
the siphon itself being previously filled with water deprived of air. Under
these circumstances a white, flocculent, and often somewhat crystalline pre-
cipitate falls: it should be most carefully excluded from all contact with air,
and allowed to subside ; the supernatant liquor must then be decanted, the
precipitate collected upon a filter in an atmosphere of hydrogen or of carbonic
acid, washed with water freed from air, pressed in folds of bibulous paper,
and dried in vacuo.

Indigo-white, when dried, has always a greenish or bluish tint, though it
probably would be perfectly white, if quite pure. It has a silky fracture, is
destitute of taste and odor, and shows no acid reaction. It is not volatile,
and when heated in vacuo it gives off a little water, while indigo-blue sub-
limes, and carbon remains : no permanent gas is evolved. It is insoluble in
pure water, and in dilute acids. It forms a yellow solution in alcohol and
in ether, and these solutions, when exposed to air, gradually deposit indigo-
blue. When moist, it speedily passes into indigo-blue under the influence
of air; and even when dry, it slowly acquires a blue color : this change goes
on even in vacuo, in consequence probably of the air retained in the pores
of the substance being sufficient to communicate to it a blue tinge. When
it is gradually heated in air, the whole mass suddenly acquires a dark-purple
color, being converted into indigo-blue.

Although a neutral principle, indigo-white acts in the manner of an acid
in respect to bases. It forms yellow solutions with the alkalies and alkaline
earths, which, when exposed to air, become immediately covered with an
iridescent copper-colored film of indigo-blue, whilst the liquid underneath
acquires at first a peculiar reddish-green tint, and then gradually passes into
blue. Hence the liquid containing it, is an admirable test for free oxygen,
either as a gas, or as it is contained in water.

Indigo-white was originally regarded as deoxidized indigo, or as a lower
oxide of the base of indigo-blue; the processes, therefore, by which indigo-
white is obtained, were considered as cases of deoxidation, and it was sup-
posed that simple oxidation was the cause of the change of the white into
the blue oxide. But Dumas has shown that in passing into white indigo,
blue indigo acquires an additional atom of hydrogen, the proportion of
oxygen remaining the same in both.

Sulphindigotic Acid; Sulphindylic Acid ([CigH^OgN-f SgOJ + HO). —
When 1 part of indigo-blue is digested for three days with 15 parts of oil
of vitriol, in a stoppered bottle, at a temperature between 120^ and 140°,
a deep blue solution is obtained, without any evolution of sulphurous acid.
This solution mixes perfectly with water, and if the preceding proportions
have been adhered to, there is no sediment ; it is a solution of sulphindigotic
acid. The Nordhausen or Saxon sulphuric acid forms a better solvent than
common oil of vitriol. When evaporated to dryness, the acid remains in
the form of a dark blue substance, which is deliquescent, and has a peculiar
odor; it forms a dark blue solution with water and alcohol, of a sour and
somewhat astringent taste. If woollen cloth be immersed in the diluted

SULPHOPURPURIC ACID. LICHEN-BLUES. 673

blue liquor, it becomes effectually dyed, and the liquid is entirely deprived
of color. By digesting the blue wool in a solution of carbonate of ammo-
nia, a solution of sulphindigotate of ammonia is obtained, with which several
other salts of the blue acid may be prepared.

When zinc or iron is put into the aqueous solution of this acid, it loses
its color, but regains it by long exposure to air. Sulphuretted hydrogen
does not affect it at common temperatures; but when heated to 120°, sulphur
is thrown down, and the blue color disappears. Protochloride of tin, and
all those substances which convert indigo-blue into indigo-white, act simi-
larly upon this acid. When protosulphate of iron is dissolved in a solution
of a neutral sulphindigotate, the color is not destroyed, nor is it affected
when part of the oxide of iron is thrown down by an alkali, but the moment
that the whole of the oxide is precipitated and an excess of alkali is preserjt,
decoloration ensues ; on again adding an excess of acid, the blue color
returns.

Sulphopurpuric Acid ([Cg^H.oO^N.-f 2803] + HO). —When 1 part of
indigo is triturated with 7 or 8 parts of oil of vitriol (or better, with fuming
sulphuric acid), the mixture, upon the addition of water, deposits sulpho-
purpuric acid in the form of a purple powder, which must be immediately
washed upon a strainer with water acidulated by hydrochloric acid, until all
traces of free sulphuric acid are removed, and then carefully dried in vacuo.
This acid is soluble in pure water and in alcohol. By digestion in oil of
vitriol, it passes into the sulphindigotic acid. It saturates only 1 atom of
base.

Isatine (CigHgO^N). — This compound is the result of the oxidation of
indigo by chromic or nitric acid. A diluted aqueous solution of chromic
acid is gradually added to pulverized indigo ; the mixture is heated nearly,
but not quite, to its boiling-point, and a brown solution is obtained. The
chromic acid should only be of such strength as freely to dissolve the indigo ;
if it is too strong, carbonic acid is evolved, oxide of chromium is precipi-
tated, and isatine is not formed. The brown solution should be filtered
whilst hot, and the isatine crystallizes as the liquor cools.

Isatine forms brilliant reddish-brown prismatic crystals, inodorous,
sparingly soluble in cold, but more abundantly in hot water, and readily
soluble in alcohol, but less so in ether. The alcoholic solution communicates
a peculiarly unpleasant and permanent odor to the cuticle. When isatine
is heated in a tube, a portion of it sublimes, but the greater part is decom-
posed, leaving carbon, which is with difficulty combustible. Heated in air
it fuses, exhales a suffocating vapor, burns with a brilliant flame, and leaves
a carbonaceous residue. By the action of chlorine and bromine, it forms
chlorisatine, hichlorisatine, bromisatine, and hibromisatine. It dissolves in
solutions of ammonia, potassa, sulphuretted hydrogen, and sulphide of amnao-
nium, producing peculiar compounds. Isatine may be regarded as indigo
-f 2 atoms of oxygen ; or CeH.OgN+Oa. Isatinic add (CjeHeOgN-f-HO)
is procured by the action of a solution of potassa upon isatine.

Isatyde (CigHgO.N^ is a white crystalline compound which may be obtained
by adding a little sulphide of ammonium to a hot alcoholic solution of isatine
*n a close vessel. * • j-

Aniline and Picric acid are also products of the decomposition of indig#-
by potassa and nitric acid. These compounds are elsewhere described.

Lichen-blues. Archil ; Litmus.— These substances are prepared from

various lichens, amongst which Roccella tinctoria and corallina, Lecanora

tartarea, Variolaria lactea, and dealbata have been especially resorted to.

The lichens are principally collected from rocks adjoining the sea : tney grow

43

674 ORCINE ANB ITS PROPERTIES.

abundantly on the Canary and Cape Yerd Islands ; and there is a general
similarity in the mode of treatinpr them for the manufacture of the above
mentioned colors. They are cleaned, and ground into a pulp with water;
ammoniacal liquids, derived chiefly from gas-works, or occasionally from
urine, are from time to time added, and the mass is frequently stirred so as
to expose it as much as possible to the action of air. Peculiar substances
existing in the lichens are, during this process, oxidized by the joint action
of air and water, in the presence of ammonia, thereby generating the coloring
matter. When the color is extracted, the mass is pressed, and chalk, plaster
of Paris, or alumina, is added, so as to form it into a consistent paste. In
this state, it is of a pnrple or violet-red tint, and constitutes the archil of
commerce, frequently called Cudbear (from Cuthbert, one of the manufac-
turers of the article at Leith) ; it is the orseille and persio of the French
and Germans. The other variety, called litmus, or, in France and Germany,
tournesol and lacmus, is generally made up into small cubes, and has a fine
violet color. The lichens which are proper for the manufacture of these
colors may be recognized by moistening them with a little solution of
ammonia, and setting the mass aside in a corked vial ; if of the proper
kind, the lichen and the liquid will acquire a purple tint in the course of a
few days.

The following substances have been discovered in these coloring princi-
ples : —

Lecanorine ; Lecanoric or OrselHnic Acid (CigHgO^-l-HO). — This com-
pound exists in different species of lecanora. It is obtained by exhausting
the lichen with ether, which is then distilled oflf, and leaves a residue contain-
ing lecanoric acid, mixed with resinous and fatty matter, and some substances
soluble in water. Lecanoric acid forms inodorous and tasteless stellated
groups of silky acicular crystals, insoluble in water, but soluble in hot alcohol
and ether. Subjected to dry distillation, it is resolved into orcine and car-
bonic acid ; and it undergoes the same change when moistened with sulphuric
acid and left in a damp place ; or when boiled in a solution of ammonia or
potassa.

1 atom of Ipoanoric acid C H 0 — ^ ^ ^^^^ ^^ °^^^"^ * * ^'e^A
1 atom Of lecanoric acia, I., gUgUg — ^^ u carbonic acid Cg O4

Orcine (C,eHgO^-|-HO). — This substance is one of the principal sources
of the coloring-matter derived from lichens. It is found ready formed in
Lichen roccella, parellus. deustus, tartarius, dealbatus, etc., and is produced
by various processes from lecanorine. It is obtained by exhausting the
dried and pulverized lichen in boiling alcohol, and filtering while hot. The
alcoholic extract dissolved in water, deposits long, brown, brittle needles,
which may be redissolved in water, treated with animal charcoal, filtered,
and again crystallized. Orcine crystallizes in a flat four-sided prism, with
dihedral summits ; it has a sweet but somewhat repulsive taste, and it is
perfectly neutral. When dried at 212°, it loses a portion of its water of
crystallization; at about 550°, it rises in vapor, may be distilled, and con-^
densed in crystals, which contain 1 atom of water. It is soluble in watef
find in alcohol.

If orcine is exposed to air, it gradually reddens, especially when the sun
occasionally shines upon it. W^hen subjected to the action of chlorine, it
heats, fuses, and hydrochloric acid is produced. Nitric acid acts upon orcine
with the evolution of nitrous gas, and a red solution is formed, which deposits
a resin-like substance. The fixed alkalies convert it into a brown substance.
Gaseous ammonia is absorbed by orcine, and on exposure to air it again

LITMUS-PAPER. MADDER. GARANCINE. ALIZARINE. 675

escapes ; but when water is present, the oxygen of the atmosphere is
absorbed, and a colored azotized body is the result, to which the name of
orceine or orceic acid has been pjiven.

Orceine; Orceic Acid (CmHj,0„N, + HO). — This substance may be ob-
tained by placing pulverized orcine in a capsule, together with a saucer of
solution of ammonia, under a bell-glass; the orcine becomes brown, but on
exposure to air the excess of ammonia escapes, and on adding a little water,
and a few drops of ammonia, a purple liquid is obtained, from which acetic
acid throws down orceine, or, as Berzelius terms it, orceic acid. Sul-
phuretted hydrogen decolors the purple liquid, not by deoxidation, but by
entering into combination with orceic acid, for the color reappears on expo-
sure to air, on saturating the sulphuretted hydrogen by an alkali. A solu-
tion of litmus, when kept in a close-stopped vessel for some time, acquires a
dirty-brown color, and smells offensively. When exposed to air, it rapidly
assumes a purple and blue color. In the preparation of blues from lichens,
orceic acid is produced under the influence of ammonia. It is not itself a
permanent dye-stuff, but is a valuable auxiliary in the production of other
blues and purples.

Erythrine ; Erythryline ; Erythric Acid{Q^^fi^^. — These are probably
identical with, or, at all events, closely related to, lecanorine.

Litmus-paper. — The lichen blues are much used for the preparation of
litmus-paper. In order to prepare this paper for chemical purposes, an ounce
of litmus, finely powdered, should be infused in half a pint of boiling water
in a covered vessel for an hour. The clear liquor should then be poured
off, and fresh quantities of hot water added until the color is exhausted.
White, unsized paper, containing but little mineral matter, cut into conve-
nient lengths, should then be dipped into the infusion and allowed to dry.
It should have a full blue color. Paper thus prepared, if not tinted of too
deep a color, forms the best tests for acids, either gaseous or liquid. It is
sooner or later reddened. Red litmus-paper forms a very delicate test for
alkalies, as the blue color is restored by alkaline liquids. In order to pre-
pare it, the blue litmus-paper should be exposed in a jar to the diluted vapor
of acetic acid or to a damp atmosphere. In order to act with delicacy as a
test for an alkali, the reddish tint thus artificially imparted to it, should be
barely perceptible. These test-papers should be cut in strips of three inches
by half an inch, and kept in well stopped bottles in a dark closet. Light
destroys the color, and exposure to air reddens the paper by the action of
carbonic acid and other acid vapors diffused through the atmosphere. A
paper prepared from an infusion of the best cudbear, without the addition
of either alkali or acid, has a purple color, and is affected both by acids and
alkalies ; it is convenient in alkalimetry, being already too red to be affected
by carbonic acid, while it is distinctly reddened by mineral acids.

Madder; Garancine; Alizarine; Alizari.^The plant which furnishes this
valuable dye-stuff {Eubia tinctorum) is common in the South of Europe and
in many parts of the Levant, where it is known under the name of alizan :
it is also largely cultivated in Holland. It has a long spreading fibrous root,
which is the part used in dyeing. In the living plant, the sap is yellowish
colored : and contains no red coloring principle. This appears to be de-
yeloped in the woody fibre, during the act of drying, and by exposure to air.
Madder-root contains three coloring principles, named respectively xanthine,
alizarine, and purpurine. By digesting the root repeatedly in cold water,
the xanthine, or madder-yellow, is removed, as this principle is very soluble
in water. When the residue is treated with half its weight of sulphuric acid
at 21 2°, the woody fibre is in great part destroyed, and may be removed by

6Y6 CARTHAMINE.

further dij^estion with water. A brown pulverulent residue is left, which is
known under the name of garancine. This contains a red coloring-matter,
Alizarine (CaoHgOg), which may be obtained in orange-colored crystals by
digesting the garancine in boiling alcohol, or by subjecting it to superheated
steam. It is scarcely soluble in water, hot or cold, but is readily dissolved
by alcohol and alkaline solutions. The latter change the red to a violet
color. It gives a bluish precipitate with solutions of lime and baryta, thus
acting like a weak acid. Sulphuric acid dissolves it, forming a brown liquid,
but it is again precipitated unchanged on dilution with water.

Purpurine (CjgHgOe), or madder-purple, is a red coloring principle, which
may be procured by digesting the washed root in a boiling saturated solution
of alum, in which alizarine is insoluble. On adding sulphuric acid to the
decoction, the purpurine is slowly deposited. It may be obtained as a deep
red powder, by repeated digestion in alcohol and ether. It is not dissolved
by cold water, but it is soluble in hot water. It is also soluble in alcohol
and ether. When a solution of carbonate of soda is added to a decoction of
madder-root in alum, there is an abundant precipitate of the red coloring
matter with alumina, constituting what is called madder-lake.

Carthamine. Carthameine. — This is the coloring principle of Safflower,
the petals of the Carthamus tinctorius, or Bastard saffron. It is cultivated
in Spain, and in many parts of the Levant, whence it is chiefly imported ;
but on account of its price it is seldom used, except to give the finishing hue
to some silks, and in the preparation of the article called rouge. Safflower
contains a red coloring-matter which is insoluble in water, and a yellow
soluble substance. The former has been distinguished as carthameine, and
appears to be derived from the oxidation of a peculiar principle existing in
the petals, which has been called carthamine.

Carthamine (C26Hg05+2HO) is obtained from the flowers, after all soluble
matters have been extracted by water, by digesting them in a weak solution
of carbonate of soda. It crystallizes in small white prismatic needles of a
bitterish taste, not very soluble in water, but more soluble in alcohol ; it is
not volatile, but fuses when heated, exhales a pungent odor, and burns away
without residue. When exposed to the air, it gradually acquires a yellow
color. When an alkaline solution of carthamine is left in contact with
oxygen, it becomes first yellow, and then red, and on saturating this red
liquor with citric acid, red carthameine is thrown down. W^hen air is ex-
cluded, the alkaline solution remains colorless.

Carthameine. Carthamic Acid (CgeHgO^). — This is the product of the
oxidation of carthamine, under the influence of alkaline bases : it exists in
the safflower, from which it may be extracted by digesting it, after the yellow
matter has been removed by water, in a solution of carbonate of soda, and
then precipitated by citric acid. It forms a dark-red powder, insoluble in
water and in acids, and sparingly soluble in alcohol, to which it communi-
cates a fine red color ; it is also sparingly soluble in ether. It is not volatile,
but is decomposed by dry distillation. It forms salts from the alkalies, from
which it is thrown down by organic acids, of a bright rose-red color.

The afl&nity of carthameine for cotton and silk is such, that when it is
recently precipitated, these substances immediately combine with it, become
at first rose-colored, and afterwards of a fine red, so that they may be thus
dyed without the intervention of a mordant. The stuffs so dyed are rendered
yellow by alkalies, and the color is, to a certain extent, restored by acids.
Carthameine is never used in dyeing wool. When it is precipitated from
concentrated solutions, it furnishes a liquid paint, which, evaporated upon
saucers, leaves a residue of a somewhat greenish metallic lustre, used as a

BRAZILINE. SANTALINE. ANCHUSINE. 677

pink dye-stuff, and which, mixed with finely-powdered talc, and dried, con-
stitutes common rouge.

HiEMATOXYLiNE. Hcemateine. — These substances are extracted from log-
wood, a dye-stuff of considerable importance : it is the heartwood of the
Hcematoxylon Campechianmn, and is imported from Campeachy, Honduras,
and Jamaica, in hard and dense logs, about three feet long, and of a dark-
red or purple color. In the dye-house it is used for the production of certain
reds and blues, but its chief consumption is for blacks, which are obtained of
various intensities, by means of iron and alum bases.

EcematoxyUne (CigHyOg.HO), which has also been called hcematine, is pro-
cured by digesting the aqueous extract of the wood in alcohol. The alcoholic
tincture, when submitted to spontaneous evaporation, deposits crystals of this
substance. An aqueous solution of these crystals does not become colored
by exposure to air, but the addition of a few drops of ammonia causes the
liquid to assume an intense-red color. By this reaction the hsematoxyline is
converted into hcemateine (C^gHgOg), which may be procured in crystals of a
purple-black color with a metallic lustre. The crystals dissolve in water,
giving to the liquid, when concentrated, a deep purple tint. This compound
differs from ha^matoxyline in containing one atom less of hydrogen.

Braziline (CggH^^Oj^) is the red-coloring principle of Brazil-wood. It
may be procured in small prismatic crystals, which are soluble in water,
alcohol, and ether. A decoction of the wood is of a reddish-brown color ;
it acquires a rich purple hue by the addition of alkalies. The coloring prin-
ciple, Brazilme, when treated with ammonia and exposed to air, is converted
into a new compound, brazileine, which is of a deep purple color. An
alcoholic solution of braziline is a delicate test for the presence of alkalies ;
and paper which has been dipped in a decoction of Brazil-wood and dried,
is sometimes employed for this purpose. The red color given by the Brazil-
wood is very fugitive.

Brazil-wood is distinguished from logwood by its paler hue, and by the
precipitates which its infusion forms with acetate of lead, protochloride of
tin, and lime-water : these are crimson, instead of being violet-colored as
with logwood. The infusions of both woods are rendered yellow by a drop
of sulphuric or hydrochloric acid. Red ink is usually made by boiling about
two ounces of Brazil-wood in a pint of water for a quarter of an hour, and
adding a little gum and alum.

Santalinb. ^awto/eme.— Red Sanders is the name given in this country
to the wood of the Pterocarpus santalinus, a large tree which grows upon the
Coromandel coast, and in other parts of India, especially Ceylon. The
coloring principle of this wood is Santaline, a white crystalline powder,
which speedily reddens on exposure to air. It is instantly reddened by
alkalies, and furnishes red solutions with the greater number of the dilute
acids. It dissolves in water, alcohol, and ether, and when its aqueous
solution is long boiled under exposure to air, it is converted into santa^ne,
which is a dark red crystalline substance. Its probable formula is L.^hi^U^,
but the composition of this substance and of santaline has not been accurately
determined.

ANCHUSINE. Anchusic Acid.— These terras have been applied to the
coloring matter of the root of Alkanet {Anchusa tinctoria), a species olbugtoss,
which is a native of the warmer parts of Europe, and is cultivated in our
gardens. Large quantities are raised in Germany and France. Anchusme

678 COCHINEAL. GUANO-COLORS.

(CjyHjoOJ has the characters of a resin ; it is of a dark red color and of a
resinous fracture, softened by heat, insohible in water, soluble in alcohol, and
very soluble in ether and in fat and volatile oils, to all which it communicates
a bright red color.

Lac — This is a resinoid substance, the production of which appears to
depend upon the puncture of a small insect (the Coccus ficus), made for the
purpose of depositing its ova, upon the branches of several plants, especially
the Ficus religiosa and Indica. The coloring matter of lac is prepared in
India, and is extensively used as a scarlet dye-stuff, for the production of
which it is a most efficient substitute for cochineal. Two forms of it are im-
ported, called lac-lake and lac-dye. These substances contain about 50 per
cent, of the red coloring matter, mixed with more or less of the resin, and
with earthy matters, said to consist chiefly of chalk, gypsum, and sand.

CocHiNEAL-RED. Carmine. — The substance known in commerce as cochi-
neal^ consists of the dried female insects of a species of coccus. It is imported
from Mexico and other countries. The insects, when powdered, yield a deep
reddish-black substance, which, when boiled in water, forms a dark-red
solution that speedily undergoes decomposition. If to the fresh-filtered
liquid a solution of alum or acid tartrate of potassa is added, a precipitate
is slowly formed, which consists of the coloring principle of the insect, united
to some animal matter. This is commercial carmine. In general the pigment
is prepared by boiling cochineal in a weak solution of carbonate of potassa
or soda, and adding to the filtered liquid, a solution of alum and cream of
tartar. The coloring principle is then slowly precipitated with alumina,
forming carmine-lake. The precipitation is sometimes accelerated by the
use of gelatine or albumen. The purest form of the coloring principle is
obtained by the following process : The powdered insects are boiled in
ether, to separate fatty matter. They are then boiled in alcohol, until this
liquid is saturated with color, and from the alcoholic decoction, the carmine
is deposited on cooling. This principle is soluble in water, forming a rich
red solution, which is heightened by acids, and changed to a deep red crimson
by alkalies. It is also soluble in alcohol, but not in ether. A variety of
carmine now prepared is scarcely dissolved by water ; but when a few drops
of ammonia are added, it forms a splendid red solution with a slight crimson
tint. Its composition has not been accurately determined. A substance
procured from cochineal by Pelletier, by a process similar to that which has
been above described, is known under the name of Carmeine or Cocdnelline,
and its composition is represented as CgaHggOjjoN. Carminic acid, which is
obtained by precipitating an aqueous decoction of cochineal by acetate of
lead, and decomposing the washed precipitate by sulphuretted hydrogen, has
the composition of CggHj^Oig.

GuANO-coLORS. Murexlde (from Murex, a shell-fish, the supposed source
of Tyrian purple.) — This is commonly known as the purpurate of ammonia
of Prout : it is an animal-red of a rich purple shade. It is procured by the
reaction of nitric acid on uric acid, and has been lately largely manufactured
from guano as a dye-pigment. The guano is first digested in hydrochloric
acid to remove foreign substances ; the residue, consisting of acid and sand,
is treated with soda; this dissolves out the uric acid, which may now be
readily procured by neutralizing the liquids with hydrochloric acid. Nitric
acid converts uric acid, in the cold, into alloxan ; and dilute nitric acid
heated, converts it into alloxantine. When uric acid is dissolved in nitric
acid of a sp. gr. of 1-40, and the solution is heated, the color is brought out

ANNOTTO. QUERCITRINE. 6t9

by adding to the acid liquid when cold, ammonia or its carbonate, until a
slight aramoniacal odor is imparted to it. Dr. Gregory advises that seven
parts of alloxan and 4 parts of alloxantine should be dissolved in 240 parts
of boiling water, and this solution added while hot to 80 parts of a cold
saturated solution of carbonate of ammonia. The liquid becomes opaque,
owing to the intense purple color produced, and crystals of murexide are
deposited on cooling.

The crystals are square prisms. Like rosaniline, carthamine, and some
other reds, they have a rich green color like that of beetles' wings by re-
flected, but are purple-red by transmitted light. They are but slightly solu-
ble in cold water, which, however, acquires a strong color ; they are soluble
in boiling water, and are insoluble in alcohol and ether. The color is de-
stroyed by ammonia and sulphuretted hydrogen. Potassa dissolves murexide,
forming a rich purple solution, but the color is destroyed on boiling. When
to this colorless solution, an excess of dilute sulphuric acid is added, murexan
is precipitated. This is considered to be identical with uramile and the
purpuric acid of Dr. Prout. A solution of murexide is precipitated by the
solutions of various metallic salts. In dyeing silk with murexide, corrosive
sublimate is used as a mordant; in dyeing cotton, a salt of lead, and in dye-
ing woollen, a double chloride of tin and ammonium.

There is no agreement among chemists respecting the formula of murexide ;
and the discrepancies which exist appear to be at present utterly irrecon-
cilable. The chemical changes which take place in its production cannot be
represented, therefore, by any correct equation.

The vegetables which afford the different shades of yellow used as pig-
ments, and in the arts of dyeing and calico-printing, are very numerous, but
definite crystallizable principles have been only in a few instances obtained
from them.

Annotto. — This substance is derived from the pulp of the seeds of the
Bixa Orellana, a shrub which is native in South America, but cultivated in
Guiana and St. Domingo, and also in the East Indies. It is usually met
with in a pasty form, of a deep orange-red color, nearly tasteless, and of a
disagreeable odor. It is but little soluble in water, but alcohol and ether
act upon it more readily, forming solutions, which, when evaporated, leave
the coloring-matter in the state of powder. It is soluble in the alkalies and
their carbonates, forming dark-red liquids, in which the acids occasion
orange-red precipitates. Annotto contains a yellow and a red coloring-
matter; the former soluble in water and in alcohol, and slightly soluble in
ether, and giving a yellow dye to silk and wool mordanted with alumina ;
the latter little soluble in water, but soluble in alcohol and ether, as well as
in the alkalies, and rendered blue by sulphuric acid. Annotto is chiefly
used as a dye for silk, giving various shades of orange. The color which it
imparts is less affected by soap, acids, and chlorine, than most other similar
dyeing materials, but it does not well resist the joint agency of light and air.
In Gloucestershire and Cheshire it is used to color cheese, and sometimes
butter and milk. It is employed as a color in varnishes.

QUERCITRINE. — This is the coloring principle of the inner bark of quercit-
ron (Quercus nigra or tinctoria). It may be obtained from the aqueous de-
coction of the bark. It has a sweetish-bitter taste, and is soluble in water,
alcohol, and ether. On exposing its aqueous solution to air, it becomes
deep yellow and deposits a yellow precipitate : if this solution is boiled in a
shallow basin, it becomes turbid, and deposits a quantity of yellow acicular

680 PERSIAN BERRIES. EUXANTHINE.

crystals of quercitreine. Quercitrine forms yellow solutions with the dilate
mineral acids. With the alkalies, its solution, if exposed to air, is dark
brownish-yellow. With acetate of lead the precipitate is white, and may be
dried without change of color, provided air is excluded. According to
Preisser, the formula of quercitrine is CggllijO^; and that of quercitreine,
when dried at 212^, Q^Jl^^O^^, A decoction of quercitron bark deprived of
its tannic acid, by a little gelatin, produces a fine yellow upon fabrics mor-
danted with alumina, and various shades of olive with iron mordants. It is
much used in calico-printing.

Fustic. — This dye-stuflf is the wood of the Morus tinctoria, a large tree
which grows in Brazil, Jamaica, and most of the West Indian Islands.
When a concentrated decoction of fustic cools, it deposits a yellow crystal-
line matter, to which Chevreul has given the name of morine.

Weld. — This, which is the gaude or vaude of the French, consists of the
dried leaves and stem of the Reseda luteola, a plant indigenous in Britain
and other parts of Europe. The whole herb is gathered when in seed, at
which period its dyeing power is greatest. There are two kinds of weld, the
cultivated and the wild ; the former is richest in coloring matter. The
decoction of this plant has a slightly acid reaction and a greenish yellow
color, which is deepened by alkalies, and rendered paler by dilute acids. It
contains a coloring principle called luteoline.

Persian Berries. — Under this name, the berries of the Rhamnus tinctoria
are known amongst painters and calico-printers. They contain a coloring
principle called rhamnine. This is obtained from an ethereal tincture of the
berries. It is an almost colorless crystalline powder, of a bitter taste, and
soluble in water, alcohol, and ether. These solutions soon acquire a yellow
color by exposure to air, the rhamnine passing into rhamnmie. Nitric and
chromic acids, bichromate of potassa, and other oxidizing agents, immedi-
ately produce the same change; and under the influence of alkalies, the
liquids acquire, on exposure to air, a dark-brown color.

Cfhrysorhamnine, or Rhamneine, and Xaiithorhamnine, are yellow coloring
principles, also obtained from these berries.

Turmeric. — This is the root of the Curcuma longa, a plant which is a
native of the East Indies, and much cultivated about Calcutta, and in all
parts of Bengal ; also in China and Cochin-China. The tubers of this plant,
commonly called turmeric, contain a coloring principle called curcumine.
It is obtained by treating the watery extract of turmeric by boiling alcohol
of sp. gr. 0'80, and evaporating the filtered tincture. The residue is digested
in hot ether : this dissolves the curcumine, which is deposited, on the evapo-
ration of the ether, in the form of an inodorous, transparent, reddish sub-
stance, not crystalline, and acquiring a fine yellow color when rubbed to
powder. It fuses at 105^, and is scarcely soluble, even in hot water, but
readily soluble in alcohol and ether, and in fat and volatile oils. It there-
fore approaches in its characters to the resins.

Turmeric paper for chemical use is best prepared with a strong tincture of
turmeric in proof-spirit.

EuxANTHiNE. — A substancc under the name of Purree, or Indian yellow,
is imported from India and China; its origin has not been well ascertained,
but it is supposed by Stenhouse to be the juice of some unknown plant,
mixed with magnesia. It has an odor somewhat resembling that of castor,

COAL-TAR COLORS. 681

and was therefore suspected to be of animal origin, derived probably from
the gall of the elephant or camel. The crystallizable principle which it
contains, and which may be conveniently termed euxanthine (LowiG, i. 888),
may be separated by boiling the crude purree in water, and treating the
residue, which is of a fine yellow color {euxanthate of magnesia), with hot
dilute hydrochloric acid. The euxanthine crystallizes as the liquid cools,
and may be purified by dissolving the washed crystals in alcohol, and recrys-
tallizing. Euxanthine is readily soluble in ammonia, potassa, and soda,
forming yellow solutions, which yield crystalline compounds, soluble in water,
but insoluble in solutions of the alkaline carbonates. When euxanthine is
dissolved in a hot solution of carbonate of ammonia, potassa, or soda, car-
bonic acid escapes, and crystalline euxanthates are formed. These salts are
soluble in alcohol. Euxanthine has the composition of 04311^8033.

Coal-tar Colors. — The use of many of the coloring matters described in
the preceding pages, has been in a great measure superseded by the discovery
of various simple methods of producing almost every variety of color, in its
highest perfection, from the tarry oils obtained in the distillation of coal.
These discoveries are among the most remarkable of modern chemistry. We
can here only advert to them in general terms. The gaseous and liquid
products of the destructive distillation of coal have been already referred to,
(p. 271). Although coal itself is simply a compound of five elements, C.H.
O.N.S., yet, according to the mode in which it is treated, the gaseous and
liquid substances obtained from it amount to no fewer than fifty-one, some
of these having a most complex composition. Aniline is found among them,
but the quantity contained in coal-tar oil is too small to render its extrac-
tion for the manufacture of colors practically available. In addition to
aniline, the tarry-oils contain benzole (p. 610) and phenole, or carbolic acid
(p. 610), which are the principal substances employed in this manufacture.
They may be separated from the other products by fractional distillation, and
from each other by the chemical processes.

Aniline-purple. Mauveine (CgyHjgNg). — Among the various methods of
procuring aniline-purple may be mentioned that adopted by Messrs. Dale, of
Manchester. Their process is based upon the fact that salts of aniline, when
heated with a solution of chloride of copper, completely reduce it to the
state of subchloride, with the simultaneous formation of a black precipitate,
containing aniline-purple. One equivalent of a neutral salt of aniline ia
dissolved in water, and boiled for several hours with six equivalents of chloride
of copper, a mixture of alkaline chlorides and copper salts being employed
for this purpose. When the reaction is completed, the mixture is filtered,
the black precipitate well washed and dried, and afterwards digested repeat-
edly in dilute alcohol, in order to dissolve out the coloring-matter, which it
contains in a remarkably pure state. By heating adhydrous hydrochlorate
of aniline with nitrate of lead to 360°, a bronze-like brittle mass is obtained,
which contains aniline red mixed with aniline-purple. The red may be
separated from the purple by boiling water ; one grain of it will strongly
color a gallon of water. These coloring matters are fixed on cotton by a
new mordant; the goods are prepared with a solution of the color and
tannic acid, and are then passed through a bath containing tartar emetic.
The tannate of antimony produced serves to fix the dye.

By methods already described, benzole is easily converted into nitrobenzole,
and this product into aniline (p. 559). When bichromate of potassa is added to
a mixture of aniline and sulphuric acid (sulphate of aniline), a splendid purple
dye is produced, which may be procured as a dark-red colored solid. When
dissolved in water, this substance forms a dye of a rich purple color, known

682 PRODUCTION OF ANILINE-RED. ROSANILINE.

under the name of Mauve or aniline purple. This important discovery was
made by Mr. Perkins. Aniline purple is not very soluble in cold water, but
it is dissolved more readily by hot water, or by water slig:htly acidulated. It
is thrown down from its solution by alkalies. It is decomposed and de-
stroyed by strong nitric acid and chlorine. Alcohol dissolves it, and its
tinctorial power is said to be such, that one- tenth of a grain of the solid dye
will form a rich violet-colored solution with a gallon of alcohol (Hofmann).
The exact constitution of aniline-purple is not known. It forms insoluble
blue and purple precipitates with corrosive sublimate and tannic acid.
Tannic acid is used as a mordant for fixing the dye on cotton, the aniline-
purple being dissolved in acidulated water. In calico-printing, the color is
mixed with gum and fixed by albumen, according to the method already
described (p. 670). Wool and silk are readily dyed by an aqueous solution
without a mordant, at a temperature of about 120'^.

Aniline-red. Magenta. — Aniline yields red colors with various chemical
reagents. Thus, when mixed with sulphuric acid and treated with peroxide
of lead, it yields a rose-colored compound, which has been called Roseine ;
and when heated with bichloride of tin, corrosive sublimate, nitrate of mer-
cury, arsenic acid, or indigo, it produces a crimson compound, known under
the name of Fuchsine. The production of color from a colorless organic
compound, is remarkably shown in the reaction of corrosive sublimate on
aniline. The white mineral solid and the aniline form by mixture a colorless
paste : but when this is heated, it acquires an intense crimson color. From
this colored product, which appears to be a salt, Mr. Nicholson succeeded in
procuring a colorless crystalline body, Rosaniline {G„^.^^^0), which acts
the part of a base, and which, on entering into combination with acids at a
moderate heat, produces the well-known crimson dye {Magenta). The salts
of rosaniline may be obtained on evaporation, perfectly crystalline. The
acetate crystallizes in splendid octahedral crystals, which have by reflected
light the metallic greenish color of beetles' wings; but when dissolved in
water, they form a solution of an intense crimson color. Silk and woollen
readily take this dye, without the aid of a mordant. Cotton and linen
require to be mordanted with albumen. When aniline is heated with bichlo-
ride of tin to a high temperature in a close vessel, a rich blue dye is produced,
which is known under the name of Bleu de Paris.

The colors which are obtained by these processes, depend on the oxida-
tion of aniline, and they vary with the degree of oxidation. Thus the same
ingredients yield a violet, purple, or red color, according to the proportions
in which they are used. Mr. Price found that aniline-red (roseine) was
produced by boiling together, 1 equivalent of aniline, 1 equivalent of sul-
phuric acid, and 2 equivalents of peroxide of lead; and aniline purple (pur-
purine) was the product, when 2 equivalents of aniline, 2 equivalents of
sulphuric acid, and 1 equivalent of peroxide of lead were employed. The
redness of the tint appears to increase with the degree of oxidation. Girard
discovered that 10 parts of aniline, added to a mixture of 12 parts of arsenic
acid in 12 parts of water, gradually heated to about 248° and not above
320°, yielded a rich aniline-red with a slight violet tint. When the same
quantity of aniline is used with 24 parts of arsenic acid in 24 parts of water,
an aniline purple or violet color is obtained. Of all the processes yet sug-
gested, it appears that there is none which, for economy and perfection of
color, surpasses that originally devised by Mr. Perkins. In this, the oxida-
tion of aniline is effected by bichromate of potassa. The selection of a
proper mordant materially affects the results. Of all the mordants yet pro-
posed for the aniline dyes, the stannate of soda appears to be the most
efficient.

COLORING MATTER OF FLOWERS. 683

Aniline-yellow, Chrysaniline (C,oHj,N3)._-This is a yellow powder ob-
tamed as a secondary product in the manufacture of aniline red. It is nearly
insoluble in water, but is soluble in alcohol. It combines with acids like a
base, forming well-defined salts. These are for the most part soluble, ex-
cepting the nitrate.

A yellow dye is obtained by the reaction of strong nitric acid on phenole
or carbolic acid {see p. 610). The product is picric or carhazolic acid, the
properties of which have already been described. Silk or flannel, when im-
pregnated with alum, acquires a rich yellow color by immersion in a solu-
tion of this acid. Various shades of green may be obtained by the admixture
of the yellow of picric acid, with indigo and other blues.

Aniline blue. — When the acetate or hydrochlorate of rosaniline is boiled
with an excess of aniline, this blue compound is produced. It is of a
brown color, not soluble in water, but dissolved by alcohol, forming a rich
blue solution. M. Clanel renders the blue-dye soluble in water by dissolving
it in fuming sulphuric acid, diluting the solution considerably, and passing
into it steam. The addition of common salt to the cooled liquid threw
down the blue pigment in flocculi soluble in water free from saline matter.
{Quart Jour, of Science, April, 1864, 322.)

One variety of coal-tar blue, called azuline, is seen in bronze-colored crys-
tals, which are dissolved by water, forming an intense sapphire blue solu-
tion, even in the smallest quantity. A small quantity of ammonia added to
the solution renders it colorless. This liquid when treated with a strong
solution of potash or soda is reddened ; while on adding an acid, hydrochloric
or sulphuric, it acquires again an intense blue color. The color can be
imparted to paper, and this may be used as test-paper. It is the converse
of litmus; it is reddened by a fixed alkali, and rendered blue by an acid;
ammonia iDleaches it.

A green dye is manufactured by acting on aniline with a mixture of hydro-
chloric acid and chlorate of potash, or on magenta with aldehyde, while an
aniline black has been obtained by the use of similar reagents.

CoLORiNG-MATTER OF Flowers. — These are principally blue, {Antho-
cya7iine) ; red, {Anther ythrine) ; and yellow, {Anthoxanthine) : they have as
yet been imperfectly examined ; many of them are very fugitive, change con-
siderably in tint, and are often altogether destroyed, on drying; others are
comparatively permanent. According to Thompson, the expressed juice of
most red flowers is blue, whence he infers that the coloring-matter in the
petals is reddened by carbonic acid, which escapes on exposure. The violet
is colored by a blue matter which is changed to red by acids, and first to
green and then to yellow by alkalies, the green probably resulting from the
mixture of blue and yellow. The petals of the red rose, when triturated
with a little chalk and water, yield a blue liquid which is rendered green by
alkalies and their carbonates, and restored to red by acids. The same blue
coloring-matter as that of the violet, exists in many other flowers, and seems
also to form the most usual red of the red flowers, in which it is apparently
reddened by an acid, for many of these reds become blue when cautiously
neutralized by an alkali, and green and yellow by an excess of alkali. This
is also the case with the red of the red cabbage and of the radish. Some of
these reds become blue merely on being bruised, and give blue infusions with
water. The color of yellow flowers is generally more permanent than that
of the blue or red ; it is rendered paler by acids, and deeper by alkalies.
Most of the coloring-matters of the petals of flowers are extremely suscep-
tible of the bleaching influence of sulphurous acid and chlorine. The color-
ing-matter of yellow flowers is partly soluble and partly iusoluble in water

684 COLORING MATTER OF LEAVES.

and spirit. The red petals of Papaver rhceas yield a red solution with lime-
water or carbonate of soda ; potassa renders it green, and hydrochloric acid
pale red : the color of red rose-leaves is brightened by acids, and rendered
green by alkalies.

A strong infusion of the petals of the French rose imparts a faint reddish
tint to bibulous paper; and paper thus fully impregnated and dried, forms
a useful test-paper. It indicates alkalies by the production of a green color ;
acids by a deeper red tint ; and as it contains tanno-gallic acid it is dark-
ened by the persalts of iron.

The application of spectrum analysis to the red coloring-matters of
flowers and prints shows that they bear no resemblance to the red coloring-
matter of blood. None of them give any absorption bands in the green.
Mr. Sorley states, as the result of his spectralytic observations, that many
flowers contain four or five different-colored substances.

Coloring-matter op Leaves. Cfhlorophylline. Xanthophylline. ErythrO'
phylline. — Chlorophyll or Cltlorophylline (CjgHjjOgN), from which leaves and
herbage derive their green color, may be procured by digesting the crushed
leaves in renewed portions of alcohol or ether; this tincture is then evaporated
on a water-bath, and the deposit which is formed is separated, dried, and
digested in alcohol so long as any green soluble matter is abstracted. Chlo-
rophylline appears as a dark-green substance, which is grass-green when
reduced to powder. It fuses at about 390°. When moist, it is slightly
soluble in alcohol, with a grass-green color; when dry, it is less soluble, and
the color of the solution is bluish-green. It is similarly soluble in ether,
and it communicates a green color to oil of turpentine and to fat oils. It is
insoluble in water. When the ethereal solution of chlorophylline is long
exposed to light, it acquires a yellow color, and, on evaporation, leaves a
residue having all the characters of xanthophylline.

Xanthophylline is a term applied to the coloring-matter extracted from the
yellow leaves which fall in autumn. It was obtained from the leaves of a
pear-tree by Berzelius, by digesting them for several days in a bottle entirely
filled with alcohol of sp. gr. 0'833, and well stopped, so as to exclude air;
for when it is in contact with the leaves under these circumstances; they
change from yellow to brown. On distilling off the alcohol from the tincture
thus prepared, and allowing the residue to cool slowly, the xanthophylline,
together with a little resinous and fatty matter, was deposited. It is a dark-
yellow substance, fusible at about 110°, and becoming transparent on cooling,
it is insoluble in water, sparingly soluble in alcohol, and readily soluble in
ether or benzole.

Erythrophylline. — It was remarked by Berzelius that all trees and shrubs,
the leaves of which redden in autumn, bear red fruit or berries. (Sorbus
aucuparia, Prunus cerasus, Pibes grossularia, &c.) He obtained this red
coloring-matter from cherry and red-currant leaves, by digesting them, when
in a proper condition, in alcohol, and distilling the red tincture. The
changes of color which the leaves of many forest-trees undergo in autumn,
passing from green to red, and from red to yellow, have been ascribed by
Macaire-Prinsep to the action of certain chemical agents upon a single
coloring-matter. {Ann. Gh. et Ph., xxviii. 415.) Spectral analysis has
thrown some light upon these changes and upon the coloring principle of
leaves. By this optical method. Prof. Stokes has found in the spectrum of
chlorophylline of land plants two distinct greens and two yellows. Accord-
ing to Mr. Tichborne, the yellow, brown, and red coloring-matters exist in
leaves quite independently of the green coloring principle {chlorophylline),
which in the presence of moisture and atmospheric oxygen is very sensitive

NEUTRAL NITROGENOUS SUBSTANCES. 085

to light. It has a characteristic spectrum when examined in an alcoholic
solution, and this chlorophyll spectrnra, which is marked by a broad band in
the red rays, is always present in leaves when in an active state of vegetation,
whatever color the leaf may be, and however it may be modified by the
presence of other substances. In a leaf or other green part of a plant,
chlorophyll is constantly being deposited, and as fast as it is being deposited
it is being converted into yellow, brown, or reddish products of decom-
position— a fact demonstrated by spectral observations ; but during active
growth the chlorophyll is being deposited much more rapidly than it is de-
composed. Ordinary leaves fall when the chlorophyll is no longer formed,
their existence being then at an end. The autumnal tints of leaves may be
ascribed to the slower deposition of the leaf-green. In dark-colored leaves,
although the natural color may be disguised to the eye, the bands charac-
teristic of chlorophyll will be found well marked in the spectra. The change
in the leaves of the Virginian creeper, observed at the close of autumn, shows
that they have a power of vitality for some time after the deposition of chlo-
rophyll has ceased, or is proceeding very slowly. The general conclusion
drawn by Mr. Tichborne from his observations is that chlorophyll is directly
concerned in, if not actually the medium for the elaboration of the crude
pieces of the plant, and that it is intimately connected with the amylaceous
series of vegetable products. {Laboratory, June, 1867, 194.)

CHAPTER LV.

NEUTRAL NITROGENOUS SUBSTANCES. THE SOLID CON-
STITUENTS OF THE ANIMAL BODY; AND SUBSTANCES
DERIVED FROM THEM.

Neutral nitrogenous substances are found in the vegetable and animal
kingdoms : in the former they are represented by gluten, albumen, casein, or
legumin: and in the latter by fibrin, albumen, casein, and gelatin. In
addition to carbon, hydrogen, and oxygen, they all contain nitrogen, and
the greater number contain variable quantities of sulphur and phosphorus :
animal gelatin contains neither of these elements. These principles are
important as articles of food to animals, and they are frequently described
as yesh^forming substances, in order to distinguish them from the neutral
compounds of the three elements C.H.O., starch, gum, and sugar, which,
according to modern theory, are only heat-producing. Although their
elementary composition is well known, yet, as they form no definite com-
binations with other bodies, no correct rational formulae have yet been con-
structed to represent their constitution. There is no material diflference in
the composition of these substanqes, whether they are derived from the
vegetable or the animal. It has been suggested that, with the exception ot
gelatin, they are derivatives from a common principle, to which the name ot
Iroteini^ given (^pcotevo, to take the first place) ; and that this consists of a
definite number of atoms of carbon, hydrogen, oxygen, and nitrogen : hence
they are sometimes described as proteinaceous substances. Their centesimal
composition, as furnished by the combustion-tube, is given in the tollowing
table. From this it will be perceived that the differences in elementary
constitution are slight, and that differences in properties are probably due
to molecular arrangement.

686

NIT

ROGENOUS PRINCIPLES. PUTREFACTION.

Albumen.

Emulsin.

Casein.

Legumin.

Gluten.

Fibrin.

Protein.

Carbon

. 54-8

50-9

54-9

50-7

55-2

54-6

55-0

Hydrogen

. 7-1

6-8

7-1

6-8

7-5

6-9

6-9

Oxygen .

. 21-2

23-4

22-2

24-9

21-4

22-8

22-0

Nitrogen .

. 16-9

18-9

15-8

17-6

15-9

15-7

16-1

In the above analyses, the sulphur and phosphorus are included in the
amount of oxygen. The proportion of sulphur and phosphorus, according
to Mulder and Scherer, is on an average about 1 per cent. : in seralbunien it
was found to be 1*1 ; in ovalburaen, 0*82 ; and in the fibrin of ox-blood it
varied from 1-31 to 1*59 per cent. In casein the proportion is less than in
albumen. Owing to their complex constitution, and as a result of the loose
attraction of their elements out of the living body, these principles, when
exposed in a moist state to air at a proper temperature, undergo spontaneous
changes, and are ultimately converted into water, ammonia, carbonic acid,
and other inorganic compounds. In the stage of transition, noxious and
offensive effluvia, consisting of compounds of nitrogen, sulphur, and phos-
phorus, with hydrogen, are evolved ; and to this stage the term putrefaction
is applied. The conditions necessary for this process are the following : —

1. Temperature. — Putrefaction occurs at any temperature above 50°. That
which is most favorable varies from 70° to 100°. It most probably acts by
increasing the affinity of the elements for each other. Too high a tempera-
ture coagulates or dries the substance, and thus arrests decomposition, while
too low a temperature also prevents it. The greater number of animal
substances may be indefinitely preserved at or below the freezing point, and
when slowly thawed, they generally regain their original characters : it is in
this way that supplies of animal food are kept in a fresh state in many parts
of the north of Europe, and that fish is preserved for the London market.
A remarkable instance of the preservative power of cold was exhibited in
the discovery of an ancient elephant, in a mass of ice, at the mouth of the
river Lena, in Siberia. {Mem. Imp. Acad. iSt. Fetersb., and Quart. Journ.
of Science, &c., viii. 95.) The Laplanders preserve reindeer's milk in a
frozen state, and when thawed, after the lapse of several months, it perfectly
retains its original characters.

2. Moisture is a condition essential to putrefaction. When flesh is care-
fully and thoroughly dried, either by a current of warm and dry air, or by
other methods which do not alter its composition, it resists decay. It has
thus occasionally happened that corpses have been preserved for long periods
by accidental desiccation ; and animal substances which are either naturally
dry, or rendered so by art, retain their nutritive powers, and resume their
former appearance when cautiously moistened. The various forms of gelatin
and albumen, when desiccated, are imperishable; whilst in aqueous solution,
or in their original humid state, they are the most perishable of all animal
proximate principles.

3. Air, or at least oxygen, if not absolutely essential to, is a powerful
promoter of putrefactive changes, and, uifter certain circumstances, its ex-
clusion indefinitely retards them. Hence, the rapidity of putrefaction in pure
oxygen ; and its retardation in gases, which either do not contain oxygen,
or in which it is held by superior attractive power. Thus, in deutoxide of
nitrogen, which contains more than half its weight of oxygen in an intimately
combined state, and which absorbs all free oxygen brought in contact with
it, we have kept pieces of beef perfectly fresh, in one experiment for 126,
and in another experiment for 224 days. Even under water, when oxygen is
strictly excluded, putrefaction is greatly retarded, and modified in its results.
Meat immersed in water previously boiled to expel air, and then covered by
a layer of oil, to prevent its subsequent absorption, may long be kept fresh.

CONDITIONS FOR AND RESULTS OF PUTREFACTION. 687

In the putrefaction of animal matter, if there is not a suflBeient supply of
air to oxidize the products, ammonia and sulphuretted hydrogen abound.
Thus, in bodies buried in coffins, we have found these products even after
six years' interment. If water has had access to the body, a singular change
takes place. The flesh and all the organs become sodden, white, and
unctuous to the touch, and the soft parts are so coherent, that although the
animal substance is preserved, the organs can no longer be recognized. On
boiling this white substance in water a large quantity of oil rises to the
surface, and ammonia escapes : the oily matter solidifies on cooling. This
substance has been called adipocere, from its supposed resemblance to a
mixture of wax and fat ; and its formation has been ascribed to the reaction
of ammonia, evolved during putrefaction, on the fatty acids, '^hereby a soap
of margarate, stearate, and oleate of ammonia is produced. We have
examined a body thus metamorphosed, after eight years' burial. The result
was that, while the fatty parts of the body had undergone this change, the
muscular tissue still preserved a fibrous character. It was simply altered
fibrin, in which the ordinary course of decomposition had been modified, by
constant immersion in water and want of free access of air.

In the process for the preservation of animal and vegetable food, the
substances are heated and hermetically sealed in tin canisters, the included
oxygen is converted into carbonic acid, or enters into other combinations.
The partially boiled or roasted meat (free from any tainted portions), with
half-dressed vegetables, and soup, are introduced into a canister, which is
then soldered up, with the exception of a small hole left in the lid: the
canister is placed in a salina bath, heated to a few degrees above the boiling-
point of water, and when steam is copiously issuing from the aperture, it is
dexterously soldered up, so that the canister is not only hermetically sealed,
but a vacuum is created within it: it should be strong enough to resist
atmospheric pressure. The success of the process is indicated by the ends
of the canister, when sealed, being concave as a result of atmospheric pres-
sure. When the substances have undergone putrefaction, owing to the
failure of the process, the ends of the canister bulge out, if the gases pro-
duced cannot escape. In 1846 we examined one of the canisters that had
formed part of the stores of the Blonde frigate, which was dispatched to
the Sandwich Islands in 1826, and circumnavigated the globe. Although
twenty-years had elapsed, the contents were found good and wholesome :
they were readily consumed by persons who were not aware of the long time
during which they had been preserved. In April, 1867, a similar canister
having been part of the stores of the same ship was opened before a Com-
mittee of the Society of Arts and the contents examined chemically and
microscopically (see Journal of Society of Arts, May 3, 1867, p. 379).
Although forty^one years had elapsed, the fibrous character of the meat
(beef) was still retained. It was of a red color, but became brown by expo-
sure to air. It had not undergone putrefaction, but was soft and tasteless.
The coloring matter of the blood, fibrin, and gelatin were detected in it.
Even the striped character of the muscular fibre was perceptible. This fact
proves for what a long period animal matter partially cooked may be pre-
served, provided the access of air is cut off. Oil, butter, suet, and such
substances, are sometimes effectual as preservatives of food; and potted
meats, when covered with a film of fatty matter, which if freed from mem-
brane is not prone to change, are thus preserved from the contact of air.
Paraffine has been employed by Mr. Redwood on the same principle, the
meat being thoroughly impregnated with paraffine.

For the preservation of animal substances for scientific purposes, we have
found the following solution, recommended by Mr. Goadby, to be very effi-

638 ALBUMEN AND ITS VARIETIES.

cacious: bay-salt, 4 ounces; alum, 2 ounces; corrosive sublimate, 2 grains;
water, 1 quart. The preparation should be first well soaked in a portion of
the liquid, and then transferred to a vessel containing a fresh solution
filtered. We have preserved in this liquid for upwards of sixteen years, the
entire body of a bird, as well as hen's eggs deprived of their shells by immer-
sion in dilute acetic acid.

Various chemical liquids have been recommended as antiseptics. For the
purpose of embalming, solutions of arsenic and chloride of zinc have been
used. Carbolic acid combined with an alkali has been found to possess
strongly preservative properties ; but its offensive odor is adverse to its
employment for anatomical purposes.

Albumen.

This terra is applied to an organic principle which is soluble in cold water,
but when its solution is heated to about 160^, it becomes more or less
opaque, and deposits white flakes, or if concentrated, forms a coagulum ; and
when thus coagulated, it is insoluble in water. It is the most widely diffused
of all the principles in the animal body. It exists as a liquid in lymph, chyle,
milk, and in the blood, of which it forms about *l per cent., in the salivary
and pancreatic fluids, the humors of the eye and brain. In certain forms of
disease it is found in the bile and urine. As a solid it is a constituent of
skin, of the brain, nerves, glands, and cellular membrane, and it is the chief
component of horn, hair, nail, feathers, wool, flannel, and silk. Albumen in
a s6luble form occurs in solution in the sap or iuices of most vegetables, as
of the potato, carrot, turnip, cabbage, asparagus, &c. : it is a constituent of
the seeds of the cereal grasses, and of almonds, fiUoerts, and most of the oily
nuts ; it abounds in the juice of the common houseleek, and in the shoots of
young plants. The properties of albumen are best studied in the white of
Q^g (ovalbnmen), or in the serum of the blood (seralbumen), so that we shall
first consider its characters as derived from these sources, and afterwards
advert to its existence in other animal and vegetable products, where it is
found both in the liquid and solid state.

Ovalhumen. — The albumen of the white of ^^^ is contained in a delicate
membranous texture {o'dnin), from which it may be separated by agitation or
trituration with three or four parts of water, when the cellular membrane is
gradually deposited, and the albumen remains in solution. It is difficult to
obtain it in a clear solution unless it is very dilute, in which case it passes
the filter : a drop or two of caustic potassa added to the white of 2g^
dissolves the membrane, and then the solution may be more easily filtered.
When carefully dried by a gentle heat, or by evaporation in vacuo, in a
vessel containing chloride of calcium, ovalbnmen is obtained in the form of a
brittle transparent yellow substance, inodorous, insipid, and when triturated
with cold water, resuming its original glairiness. When heated, it exhales
the nsual products of azotized organic bodies, and a residue of carbon
remains, which is very difficult of incineration. It leaves about 6 or 7 per
cent, of saline matter, composed of carbonate, phosphate, and sulphate of
soda, phosphate of lime, and chloride of sodium, with traces of potassa and
magnesia. 100 parts of ovalbnmen, when evaporated in vacuo, leave a resi-
due of from 10 to 15 parts of albumen and salts. Direct experiment shows
that in the white of egg (globidin), the solids amount, on an average, to 12
per cent. ; and in the yelk (vitellin) to 37*1 per cent. In the latter there is
a large quantity of yellow oil containing phosphorus, which appears to give
color to the yelk. This oil may be removed by alcohol or ether.

PROPERTIES OF ALBUMEN. . 689

The following Table, based on direct experiments, shows the solid contents
of the principal albuminous liquids in 100 parts:

White of egg. Yelk. Serum (blood). Serum (milk). Serum (Anasarca).

Sp-gr 1-041 1-030 1-027 1-009

Dry organic matter 10-8 35-1 7*0 4-5 1-1

Ash 1-2 2-0 2-0 1-1 0-6

Water .... 88-0 62-9 91-0 94-4 98-3

White of egg ....

10 to 13

Liquor amnii (4th month)

10-77

(5th month)

7-07

" (6th month)

6-67

" (9th month)

0-82

100-0 100-0 100-0 100-0 100-0

The average proportions of albumen per cent, in various animal liquids
are given below.

c««„r« fliuman . . . 6-3 to 7

S^^^^^i animal ... 6-7

Chyle 3 to 6

T„^„T,i human ... 0-43

I^y^^P^t horse . . . 0-39

Seralbume7i,. .»^The albumen of the serum of blood resembles that of white
of egg ; in reference to chemical properties, they may be considered as iden-
tical. They are both slightly alkaline, and are miscible with water in all
proportions. When evaporated to dryness at a low temperature, reduced
to powder, and digested in cold water, the albumen of serum is difficult of
solution, unless a small quantity of potassa or soda is added.

A moderately strong aqueous solution of albumen (white of egg, or serum)
is without taste or odor : it is adhesive, and when dried in a streak on paper,
it presents a varnished surface. Like a solution of gum (arabine), it exerts
a left-handed rotation on polarized light. It is insoluble in and precipitated
by alcohol. It appears to be converted into coagulated or solid albumen
by this reagent, as it is no longer soluble in water. Heat. — When the solu-
tion is heated to about 150° it becomes opalescent, and at about 170° it
coagulates, forming a white, translucent, and somewhat elastic substance,
with which we are familiar in the white parts of a hard-boiled egg ; and when
in this state, it is cautiously dried, it no longer remains soluble in water, but
becomes tough and horny ; so that there is this, a characteristic distinction
between albumen which has, and that which has not undergone previous
coagulation. As this coagulation ensues in close as well as in open vessels,
it may be concluded that the proportion of water in the recent and in the
concrete albumen is the same. Two parts of white of egg and one of water
entirely coagulate or set into a solid when duly heated, but equal parts remain,
under the same circumstances, semifluid ; a mixture of 1 part of white of egg
and 10 of water becomes opaque, but is not coagulated ; and a milkiness is
perceptible when the white of egg forms only a thousandth part of the heated
solution. Hence, heat furnishes the best test for the detection of this prin-
ciple. Albumen thus coagulated or solidified has the chemical properties of
fibrin. When a new-laid egg is immersed in boiling water, the white does
not so readily coagulate as in an old egg, a distinction, perhaps depending
upon the egg having, in the latter case, lost a portion of water by evapora-
tion through the shell, and being therefore in a somewhat less diluted state
than in the fresh egg. When diluted albumen is boiled, it coagulates and,
though heavier than water, becomes blended with air, and forms a scum,
which rises to the surface, and is effectively used in the clarification of certain
liquids.

The cause of the coagulation of albumen by heat has not been explained.
44

690 CHANGES DURING INCUBATION.

** It is," says Dnraas, " probably a simple isomeric modification of this body,
analogous to that by which cyanic acid is converted into cyanuric acid ; so
that it would be interesting to determine whether the atomic weight of
coagulated albumen is not double or triple that which belongs to liquid
albumen" (p. 622). When coagulated albumen is boiled in water for several
hours, it becomes horny, communicating to the water traces of organic and
saline matters.

Acids. — A clear aqueous solution of serum or of white of egg may be
neutralized by acetic acid, without coagulation ; hence it is inferred that the
solubility of albumen does not depend on the presence of free alkali. Among
vegetable acids the acetic, tartaric, oxalic, and gallic acids have no action
upon the solution ; but it is precipitated in an insoluble form by tannic acid
(tannate of albumen). When a moderately strong solution is boiled with
acetic acid, it is not coagulated; but a gelatinous compound results, which
dissolves in an excess of acetic acid and water.

An acetic solution of albumen is precipitated by sulphuric, nitric, and
hydrochloric acids, as well as by a solution of ferrocyanide of potassium. It
is also precipitated slowly in the cold, but rapidly, when warded, by solutions
of neutral salts, e. g., chloride of sodium, nitrate of potassa, and sulphate of
soda. It is remarkable that the solutions of these salts have no action on
a solution of albumen, and do not prevent its coagulation by heat ; but when
acetic acid is present, albumen is thrown down, at even a low temperature,
in an insoluble form.

It is probable that by some chemical change analogous to this, soluble is
converted into insoluble albumen in the living body. All that is required is
the presence of a free acid (lactic, acetic, or hydrochloric) and chloride of
sodium. A temperature of 98°, which would not alone suffice for the trans-
formation, would in the presence of these substances, bring about the con-
version.

It is less easy to explain the metamorphoses of soluble into insoluble
albumen, during the process of incubation. The temperature to which the
egg of the hen is submitted at intervals for a period of three weeks, is about
104°. Having examined a freshly-laid egg, and another which had reached
the 22d day of incubation, we found the following differences : in the recent
egg the albumen was entirely soluble in cold water, and on incineration, iron
and phosphate of lime were found both in the albumen of the white and the
yelk. In the incubated egg, there was a perfectly developed chicken, the
albumen of the yelk being contained within its abdomen. The soluble
albumen of the white, had assumed the insoluble condition, and existed in
the form of feathers, beak, claws, cellular membrane, and of the soft organs
generally, the blood retaining a portion in the liquid state. There was no
diflference in the amount of iron and phosphate of lime. The shell was
thinner and more brittle. This metamorphosis cannot be explained on
purely chemical principles. These might show how one form of albumen
passes into another ; but no chemical theory can account for the conversion
of one portion of insoluble albumen into feathers, and another portion into
cellular membrane. We have here an illustration of organization, or the
arrangement of matter, not according to physical and chemical laws, but by
a force wholly dififerent from them. Boerhaave, writing in 1727, says, in
reference to this subject : "All the parts of a chick — as the blood, flesh,
bones, etc. — are formed out of the bare white of egg ; for nothing but this
is consumed during the time of incubation of the hen, the yolk all the while
remaining entire." The results of incubation show that soluble is not only
converted into insoluble albumen, but that it is convertible into fibrin, as
muscular fibre is formed, and into gelatinous tissues, as it exists in the bones

ACTION OF ALKALIES ON ALBUMEN. 691

of the chicken. Farther, althoufrh the soluble albumen is, chemically speak-
ing, the same in the eggs of the chicken and the duck, and although the
physical conditions to which the eggs are exposed are the same, it is invari-
ably found that the albumen is converted into beak, claws, feathers, muscles,
and bones of a bird resembling that of the animal which produced the e»;g.
The chicken's beak and feathers are not produced from the albumen of the
duck's egg, or vice versa. Those chemists who look upon the vital force in
organic bodies as a myth, have failed to explain these facts by any reasonable
suggestion based on the laws of chemistry or physics.

Concentrated sulphuric acid precipitates an aqueous solution of albumen
immediately, but redissolves the precipitate. Hydrochloric acid acts in a
similar manner; when these acids are diluted, no immediate precipitate
ensues ; but after some hours there is a white flocculent deposit.

Albumen, even in the coagulated state, like other protein-compounds,
dissolves slowly in concentrated hydrochloric acid, at a boiling temperature,
forming a reddish or purple liquid. When albumen has been thrown down
by hydrochloric acid, it generally becomes reddish after washing and expo-
sure to the air. This tint is somewhat characteristic of the varieties of
albumen ; quill, horn, &c., exhibit it when boiled in the strong acids; almonds,
cocoanut, chestnuts, and other substances containing vegetable albumen,
become similarly tinted.

Nitric acid is the most effectual precipitant of albumen, and is generally
employed as a test for its presence. Even in a diluted state, it throws down
a white precipitate from an aqueous solution ; but this precipitate is quite
soluble in a large excess of water. It may be, however, again thrown down,
when strong nitric acid is added to the liquid. Phosphoric acid produces
different effects on an aqueous solution of albumen, according to its state of
hydration. The monohydrated acid throws it down in white flakes; the
terhydrated acid, not only does not precipitate it, but redissolves the former
precipitate : hence albumen serves as a test to distinguish these acids.

Alkalies. — Albumen is soluble in aqueous ammonia, potassa, and soda.
Alcohol added to the cold potassa solution, produces no precipitate ; and
when the alkaline solution is boiled, the liquid becomes yellow, but the
albumen is not coagulated. This alkali, even in the cold, however, alters
the chemical characters of liquid albumen. Under common circumstances,
acetic acid does not precipitate aqueous albumen : but when to the potassa-
solution, a few drops of acetic acid are added, a dense precipitate is imme-
diately produced. When a concentrated aqueous solution of albumen is
mixed with a strong solution of caustic potassa or soda, a gelatinous com- ■
pound is the result, which is soluble in water ; and if this aqueous solution
is evaporated at a gentle heat, pellicles like those which form on boiled milk,
gradually collect upon the surface. If the strong alkaline solution is boiled,
ammonia is evolved, and an alkaline sulphide is produced which blackens a
salt of lead. A portion of coagulated white of egg boiled with a diluted
alkaline solution of oxide of lead, speedily blackens from evolved sulphur,
and in this way sulphur may be detected in quill, wool, hair, in the almond,
and many other vegetable substances. Lime, baryta, and strontia form
combinations with albumen, which harden on drying. The compound
obtained by mixing slaked lime with white of egg, is used as a lute ; it
resists to a great extent the action of acid fumes.

Serum and the white of egg are coagulated by the greater number of
metallic salts. Those of iron, copper, lead, mercury, silver, and antimony
yield precipitates which are compounds of albumen and the metallic oxides,
hence albumen is a valuable antidote in cases of poisoning by metallic salts.
The precipitate is usually soluble in an excess of serum or white of egg, and

602 PROPERTIES OF COAGULATED ALBUMEN.

sometimes in the salt which produces it. Thus sulphate of copper readily
dissolves the precipitate, which it first produces in albumen. When excess
of potassa is added to a mixture of albumen and hydrated oxide of copper,
a transparent solution of a splendid violet color is obtained ; it may be
produced by adding the alkaline solution (either potassa or soda) to a mix-
ture of serum and solution of sulphate or acetate of copper. The oxide of
copper is not reduced to the state of suboxide on boiling this liquid. The
subacetate of lead is a perfect precipitant of all the forms of albumen : one
part of fresh albumen of egg in 2000 of water, is rendered turbid by this
reagent. Subnitrate of mercury is also an effectual precipitant of this
principle. Corrosive sublimate is a delicate test of the presence of albumen ;
a liquid containing only a two-thousandth part of solid albumen is precipi-
tated by it. The white precipitate formed, is an insoluble compound of the
salt with the organic substance. Albumen, it is well known, is the antidote
which is employed in this form of poisoning.

Kreasote and carbolic acid cause copious precipitates in a solution of
albumen. It is not affected by solutions of rennet, which copiously coagu-
late milk. Ether rather gelatinizes than coagulates the white of egg, when
the two are shaken together ; after a time, a yellow liquid separates, which
is not coagulated by heat, and a spongy albumen remains. When serum is
similarly treated, no such precipitation ensues ; the mixture separates into
two portions, and the ether which floats upon the surface, holds the oil of
the blood in solution.

The best tests for liquid or soluble albumen, are the application of heat,
the action of nitric acid, and the nse of ferrocyanide of potassium and acetic
acid.

Coagulated Albumen. — Albumen, coagulated by heat, presents itself as a
white solid ; it dries, by exposure, to a horny-looking substance. It is in
this state identical in chemical properties with horn, hair, nail, quill, wool,
and tortoiseshell. It is quite insoluble in water, alcohol, and weak acids: it
is dissolved by strong acids and concentrated solutions of alkalies. Acetic
acid added to the alkaline solution, throws down the substance called Protein.
The alkali is supposed to abstract sulphur and phosphorus ; while a previous
digestion in water, alcohol, ether, and diluted hydrochloric acid, serves to
remove all soluble matters contained in the albumen. However carefully
prepared, we have still found sulphur in the precipitate ; and the so-called
protein, appears to be nothing more than the original albuminous principle
somewhat altered in its properties, by the variety of chemical processes to
which it has been subjected.

When protein or its compounds are boiled in a moderately strong solution
of potassa, until ammonia is no longer disengaged, and the liquid, after it
has cooled, is saturated by sulphuric acid, sulphate of potassa is formed,
the greater part of which may be separated by crystallization. If the re-
maining solution is poured off and evaporated to dryness, and the residue is
boiled in repeated portions of alcohol, this dissolves the organic products,
and leaves sulphate of potassa : as the alcoholic solution cools, it deposits a
brown oleaginous matter {erythroprotide), and afterwards, by spontaneous
evaporation, it deposits leucine (CiaH^aO^N), and retains protide, mixed
with formate of potassa in solution. We have here illustrated the produc-
tion of protein and its derivatives, by the conversion of albumen ; but these
compounds may be equally obtained by treating in a similar manner, fibrin,
casein, or horny tissue.

Albumen presents itself in a variety of modifications in the animal body.
Under the name of globulin, it partly constitutes the transparent humors of
the eye, including the crystalline lens. The same principle associated with

PROPERTIES or CASEIN. 693

coloring-matter, or hgematosine, forms the mass of the globules of the blood.
It is soluble in acetic acid and alkalies ; and is precipitated when either
solution is brought to a state of neutrality. Ptyalin is a modi6cation of
albumen existing in saliva. A remarkable property which characterizes this
principle, is its power of rapidly transforming starch and dextrine into
glucose or grape-sugar. If starch paste is heated for a short time to 100°
with saliva, it is converted into sugar. Pyin is an albuminous principle
found in pus ; Mucin, in mucus ; and Echidnine, in the viper-poison. In
general, the differences are slight, but in pyin and echidnine formidable
poisons are produced.

Oysters, snails, and the bodies of molluscous animals generally, are com-
pounds of modified albumen and chondrin. An analysis of oysters shows
that they consist, in 100 parts, of water, 80-11 ; dry organic matter (albumen
and chondrin), 18*69; and of saline matter, 1-2. In the saline residue,
besides chloride of sodium, traces of the iodide of sodium were found.

Vegetable Albumen. Emulsin. — Albumen in the vegetable kingdom is
generally associated with one or more of the following principles — gum,
sugar, starch, or oil. It may be procured by macerating the succulent shoots
of young plants (turnips), or bruised seeds, like those of the almond, in cold
water, allowing the liquid to clear itself by subsidence, and then filtering it.
The cake of the almond, after the oil has been pressed out of it, yields it
abundantly. The liquid coagulates by heat, and is precipitated by nitric
acid, tannic acid, and a solution of corrosive sublimate, precisely like animal
albumen. It has all the properties of a weak solution of ovalbumen. It
contains sulphur and nitrogen. When the pulp of almond is boiled with
strong hydrochloric acid, it is reddened like ordinary albumen : when boiled
in a solution of potassa holding oxide of lead, it is blackened, thereby show-
ing the presence of sulphur. The albumen of the almond, and of some other
seeds, has been called, Emulsin, from its property of forming a white or
milky emulsion in water with the oil of the seed. Emulsin is stated to differ
from albumen in several points. Thus, its solution, like that of casein, is
precipitated by acetic acid : it is coagulated by rennet, and is thrown down
by the terhydrate of phosphoric acid, which has no action on albumen. The
term Synaptase has been applied to emulsin by Robiquet (from ovj/arttw,
adsum) in consequence of its necessary presence in the conversion of amyg-
daline into hydrocyanic acid and hydride of benzoyle.

Casein. Legumin.
This term is applied to the coagulable principle of milk, as it is this which
forms cheese {caseus). A similar substance is occasionally found in the
blood, and in the pancreatic liquids of the ox and sheep : it occurs also m
vegetables. It is not found except in the liquid state, and according to
Robin and Yerdeil the only liquid in which its presence has been clearly
demonstrated, is the milk of the human being and of animals of the class
mammalia. It is therefore a principle not found at all ages, nor in the male
sex, except under certain abnormal conditions. 100 parts of milk contain
the following proportions of casein in admixture with a small quantity ot
albumen : —

Average human
" inferior
Colostrum
Cows' milk
Dog

. 3-5 Asses . . . 1-9 to 2-3

, 2-7 Mares . . • * I

. 4-0 G«'at . . • 4-5 to 6-0

3 to 7-0 Ewe . . • • 15-3

11-3

0)94 PROPERTIES OF CASEIN.

The proportion is subject to variation according to food and other circum-
stances. Casein is in a state of solution in milk, and raay be procured nearly
])ure by coagulating well-skiraraed milk heated up to 150° or 160°, by a
few drops of acetic acid. The curd thus obtained is thoroughly washed,
pressed, and digested in boiling alcohol, or in ether, to deprive it of oil, and
then carefully dried. As it is thus procured, casein presents itself in white
opaque masses (curds), resembling coagulated albumen, but much less firm.
It is without odor or taste, is insoluble in water, alcohol, and ether, and
when dried at a low temperature, presents itself in yellow horny-looking
masses. It dissolves in weak solutions of the alkalies and their carbonates,
and is thrown down from these solutions by acids : the precipitate is a com-
pound of the acid and casein, and is soluble in an excess of the acid. Casein
is also soluble in some saline solutions, as of common salt, sal-ammoniac,
and nitre. Its compounds with the earths and metallic bases are insoluble
in water: hence, milk may be beneficially used as an antidote in poisoning
by many metallic salts. The casein of milk is precipitated by sulphate of
copper. The caseate of oxide of copper is redissolved by potassa, forming
a violet-blue solution : the oxide is not reduced to suboxide on boiling the
liquid, unless sugar is present.

Casein, or a principle analogous to it (legtimin), is contained abundantly
in peas, beans, and the seeds of leguminous plants ; it is there associated
with starch, and in the oily seeds, with albumen and emulsin. It may be
obtained by digesting coarsely-powdered peas in cold or tepid water for two
hours, allowing the starch and fibrous matter to subside, and then filtering
the liquid. It forms a clear viscid solution, which is not coagulated by heat,
unless albumen is also present ; but like emulsin, and unlike albumen, it is
precipitated by acetic acid. It is coagulated by lactic acid, also by alcohol ;
in the latter case the precipitate is redissolved by water. Casein is distin-
guished from albumen by its not coagulating when heated in a dilute solu-
tion, and by being precipitated from its solution by acetic acid. On boiling
milk in air the casein appears to become oxidized and rendered insoluble,
forming a kind of skin on the surface of the milk. Like albumen, it is pre-
cipitated by tannic acid. The fact that it is coagulated by rennet (the lining
membrane of the fourth stomach of the calf), as in the process of curd and
cheese-making, is also one of its distinctive characteristics. It contains
sulphur, to the amount of 0'36 per cent. (Mulder), but no phosphorus —
not at least in the peculiar state of combination in which that substance is
found in albumen and fibrin ; but it appears to be intimately combined with a
certain proportion of phosphate of lime. The sulphur may be easily detected
in it, by boiling the casein in a solution of oxide of lead in potassa. Like
albumen and fibrin, casein is dissolved by strong hydrochloric acid at a boil-
ing temperature, forming a reddish-purple-colored solution.

Casein is stated not to be coagulable by heat : but it is found in practice,
that heat greatly facilitates the separation of the curd from milk when
rennet or acids are employed. (See Milk, p. til.) Thus, in procuring
curd by rennet for the manufacture of cheese, the milk is heated to a tem-
perature of 77° to 86°, and at the same time agitated. The casein separates
in a mass, with more or less oil, according to the richness of the milk. The
curds are pressed into masses, salted, and allowed to undergo a species of
fermentation, by which peculiar flavors are brought out. A rich cheese
abounds in oil, a poor cheese in casein. The casein is generally colored of
a pale-yellow to an orange-red color by annotto. The method of obtaining
cream in Devonshire and Cornwall, furnishes another proof of the influence
of heat in aiding the separation of casein. After the cream has risen to the
surface, in a pan of milk, instead of removing this by skimming or otherwise

PROPERTIES OF LEGUMIN. GLUTEN. 695

disturbing it, the pan is carefully heated over a charcoal fire, until bubbles
of vapor begin to appear in the liquid, below the surface. A serai-solid
mass is thus produced, consisting of the cream, with a very large proportion
of casein. The milk which remains is of course proportionably impoverished.

Legumin is the name specially applied to the azotized caseous principle
of peas, beans, and many similar seeds : it is considered to be identical with
casein by Liebig and Wohler (Liebig, Chim. Organ., iii. 220), and with
emulsin by Dumas and Cahours {Ajin. Ch. et Ph., 1842). A solution of it
may be obtained from ground peas by the process above described. Acetic
acid, diluted with 8 or 10 parts of water, is carefully dropped into the filtered
solution and the legumin is precipitated : an excess of the acid should be
avoided, as this would dissolve the precipitate. It falls in the form of white
flakes, and after having been washed on a filter, it should be dried, pul-
verized, and freed from adhering fat, by digestion in ether. Legumin may
be obtained from lentils with the same facility as from peas ; but it is less
easily procured from beans (haricots), in consequence of their containing a
gummy matter, which interferes with its precipitation, and with the filtra-
tion of the liquids. The chemical properties of legumin are identical with
those of casein.

Liebig supposes that grape-juice, and other vegetable juices which are
deficient in albumen, derive their fermentative power from soluble legumin.
This principle is soluble in tartaric acid, and to its presence he ascribes the
tendency of sugar to form alcohol and carbonic acid, instead of mucilage and
lactic acid.

Gluten.

Vegetable Fibrin. — The term gluten is applied to the opaque, white, tena-
cious, and somewhat elastic substance which is obtained by subjecting
wheaten flour to the continuous action of a current of water. The best
mode of proceeding is to tie up the flour in a coarse cloth, and knead it
under a stream of water until the starch and soluble matters are entirely
washed out, and the water runs off clear. The residuary gluten should give
no blue color with iodine water. According to some chemists, it consists of
three distinct substances, of which Vegetable fibrin forms the largest pro-
portion. Gluten, as it is thus extracted, is a white tenacious substance,
capable of being drawn into long fibres. When dry, it becomes hard, horny
and brittle, so thaf it is easily pulverizable. Macaroni is nearly pure gluten
in a dry state, but generally associated with a little starch. Gluten when
pure, undergoes no change of color on the addition of iodine. It is quite
insoluble in water, but is dissolved by acetic acid, and a strong solution of
potassa. It is again precipitated, when the acid and alkaline liquids are
exactly neutralized. It contains sulphur, and is blackened when boiled in
a potassa-solution of oxide of lead. It acquires a dark-red color when
boiled in strong hydrochloric acid. Bread and macaroni, which chiefly
owe their nutritious qualities to gluten, undergo similar changes. In a
partially decomposed state, it forms yeast, and induces alcoholic fermentation
in saccharine liquids. It also separates casein in milk at a boiling tempera-
ture. In most of the chemical characters here described gluten bears a close
resemblance to fibrin.

Gluten, like certain ozonides, has the remarkable property of rapidly
oxidizing the resin of guaiacum, and a solution of this resin in alcohol may
in some cases be employed as a useful test of the presence of this principle.
If a solution of guaiacum in alcohol (tincture of guaiacum) is poured upon a
substance containing gluten, such as wheat flour, a beautiful azure-blue color

696 PROPERTIES OF GLUTEN.

is speedily brought out, even when the flour is largely mixed with other
organic or mineral substances. It produces no change of color in starch if
free from gluten, in gum, or sugar. A small quantity of macaroni in powder,
moistened with the tincture of guaiacura, rapidly acquires a deep indigo-blue
color. If the macaroni is previously soaked in cold water, an intense blue
color is produced immediately on the addition of the tincture. The gluten
appears to Jose this property of oxidizing guaiacum by exposure to a high
temperature: thus tincture of guaiacum, when added to boiled gluten (boiled
macaroni), produced no change of color either by itself or on the addition of
a solution of peroxide of hydrogen. When the tincture was applied to the
crumb of aerated bread, it produced no blue color until after the addition of
a small quantity of peroxide of hydrogen.

The tenacious properties of dough, or the paste of flour, are mainly owing
to gluten. It is more abundant in wheat and in rye than in other cereals,
and in these grains the gluten has a greater tenacity than in others : hence,
they are better fitted for making bread. Calculated in the dry state, gluten
forms from T to 14 per cent, of wheat flour, that of Odessa containing the
largest proportion (Duma's). Wheat grown in Algeria and other hot coun-
tries contains a larger proportion of gluten than wheat grown in England or
countries still colder. The hard, thin-skinned wheat contains more gluten
than the softer varieties. The proportions of gluten in 100 parts of different
seeds are as follows : —

Algerian wheat .

. 16

Danzig wheat

. 9

Odessa wheat .

. 15

Barley

. 6

South Carolina wheat

. 14

Oats .

. 6

English wheat .

. 10-7

Rye .

. 5

Canadian wheat

. 9-8

Peas .

. 4

The nutritious properties of the grain are in proportion to the amount of
gluten.

Gluten, as it is extracted from wheat flonr, does not appear to be a pure
vegetable principle. It contains cellulose and fatty matter ; the latter may
be removed from it by boiling alcohol or ether. It has been also supposed
to contain another principle, analogous to albumen, called Olutin : but all
chemical analogy is destroyed in the process by which it is extracted. If
gluten is digested first in concentrated and afterwards in weak alcohol, in
which albumen is quite insoluble, a yellow-colored liquid is obtained, which
deposits a substance said to resemble casein, called vegetable casein. 'When
the alcoholic liquid is poured off and evaporated, a yellowish viscid extract
is obtained, to which the name of gliiti7i has been given. It may be precipi-
tated as a white substance by the addition of water to the alcoholic liquid.
It still contains the oily matters which existed in the original gluten. In
this process the greater part of the gluten remains unaffected by the alcohol,
and this insoluble residue is called Vegetable Jibrm. It is this substance
which has the chemical properties of animal fibrin, that gives to the dough
or paste of wheat flour the peculiar tenacity which allows it to be converted
into wholesome bread. This tenacity is especially observed in the dough or
paste made from wheat and rye : hence these grains are better fitted than
other cereals for the making of bread. Gluten is exclusively a vegetable
product : it abounds in nitrogen, and thus resembles an animal principle.
It is the basis of flesh in herbivorous feeders, and is particularly abundant in
hay. There is reason to believe that it is a complex compound, the chemical
characters of which have been as yet but imperfectly ascertained. Dumas
and Cahours have proved by their analysis that the undissolved gluten has
the same chemical composition as dissolved glutin ; the latter is, therefore,
probably only a small portion of altered gluten removed by alcohol.

properties of fibrin. g9t

Fibrin.
Under this name a principle has been described common to animals and
Tegetables. Animal fibrin is obtained by agitating blood, as it flows from
the vessels, with a rod, to the twigs of which it adheres in the form of fibrous
filaments, which may be cleansed of coloring and other soluble matters by
repeated washings in fresh portions of water. The essential character of
this principle, as it is contained in blood, is its power of spontaneous coagu-
lation. From a fluid state in this liquid, when removed from the living
vessels, it speedily passes into a solid and insoluble condition, assuming a
fibrous or reticulated form. It undergoes this change in from ten to twenty
seconds when blood comes in contact with threads and thin rods, or with a
sponge or dust which can absorb water. In the dead body it takes place
slowly. There have been many hypotheses on the cause of this solidification
of fibrin or coagulation of the blood, but none of these can be regarded as
furnishing a satisfactory explanation of it. It has been supposed that the loss
of a small quantity of ammonia was the cause, and that it was the presence
of one or two thousandths of ammonia in the blood of the living body which
caused it to retain the fluid state. It has been shown, however, by Dr.
Davy and others, that healthy blood contains no appreciable quantity of
ammonia, and that ammonia added to fresh blood, in any quantity, did not
prevent the. fibrin from assuming the solid state. (See Ed. Monthly Journal,
1859, vol. xlv. p. 537.) When ammonia has been found in blood, it has
been probably the result of incipient decomposition. It is also a curious
fact that ammonia is the only one of the common alkalies which has no
solvent action on fibrin when it has once solidified. The real question
appears to be, not what causes the solidification of fibrin out of the living
body, but what causes its state of liquidity in the body. Whether the blood
is exposed to heat or cold, whether it is at rest or in motion, whether
exposed to air or not, the fibrin will solidify and the blood coagulate. The
only conclusion to which the ascertained facts lead is this : In order that
fibrin should retain a liquid state, it must be kept in motion in a living
bloodvessel at or about a temperature of 98°. If the motion is stopped by
two ligatures applied to a vessel, the blood will coagulate between them : it
coagulates if effused into the living textures, although it does not escape
from the body. It has been successfully injected by transfusion from the
vessels of one living body into those of another ; but if injected into the
vessels of a dead body artificially heated to 98°, it would still coagulate.
No chemical or mechanical forces well explain this phenomenon : it furnishes,
like the reparative power which manifests itself in the living body just when
it is required, an irrefragable proof of the presence and incessant operation
of a vital force.

Fibrin is found in two other fluids of the body, chyle and lymph, and from
these it separates as a solid when the liquids are removed and exposed. The
proportion of fibrin contained in healthy venous blood has been variously
stated by different chemists. The average is about 2 parts in 1000, and it
seldom exceeds 3 parts, except in certain diseases.

Proportion of Jihrin in 1000 parts

Of venous blood (Lehmann) 1-9 to 2-8

« « « (Scherer) 2-03 to Z b6

" " " (Denis) 2-20

" (Lecanu) ^f

" " " (Reguault) n ^n * n ro

" lymph (humai)' o'-IS '' '*'

" " (horse) l^fl

chyle (horse)

" (eow) \g

♦* (cat) -^ ^"

((

698 PROPERTIES OF FIBRIN.

Andral and Gavarret found that the proportion of fibrin was increased in
some diseases and diminished in others. Assuming the normal average in
healthy blood at 3 parts in 1000, they give the following as the results of
their observations : —

Acute rheumatism

. 5 to 10

Acute diseases —

Pneumouia

.

. 5 to 10

Phlescmasiae

5

Bronchitis

,

. 6 to 9

Phthisis .

. 4

Pleuritis .

.

. 5 to 6

Advanced phthisis .

. 5

to 6

Peritonitis

,

. 5 to 7

Eruptive fevers

. 1

to 4

Typhoid fever .

. 0-9

to 1

Properties. — Viewing this principle in its chemical relations, it may be
observed that in a humid state it holds about 75 per cent, of water, which
may be removed by drying. It may be purified by digestion in ether, by
which fatty matter is removed, and when dried, at 240° it is yellowish-gray,
translucent, and horny. It is insoluble in water, but when long boiled, traces
of ammonia are evolved, and a liquid is obtained which, when evaporated,
leaves a substance having the smell of boiled meat : it does not gelatinize,
but is precipitated by infusion of galls. The insoluble portion resembles
coagulated albumen. When fresh fibrin is covered with water, it becomes in
a few days viscid, and acquires the odor of old cheese : it produces ammo-
niacal salts, and then the mixture gradually liquefies : in this state it is
coagulated by heat, by the addition of alcohol, or of solution of corrosive
sublimate, resembling, in these respects, serum. Immersed in sulphuric acid
diluted with five or six parts of water, it shrinks, and a compound of the
acid with fibrin is formed.

When fibrin is digested in nitric acid, nitrogen is evolved, and a yellow
substance is produced, which has been termed Xanthoproteic acid (Mulder).
Hydrochloric acid at first gelatinizes fibrin, and afterwards forms with it a
blue or purple liquid, which, on dilution with water, lets fall a white hydro-
chlorate of fibrin. When fibrin is immersed for about 12 hours in water
slightly acidulated with hydrochloric acid, it becomes gelatinous, and when
this jelly is triturated with water, it yields a solution which coagulates by
heat, is precipitated by ferrocyanide of potassium, and affords a precipitate
on the addition of hydrochloric acid, not soluble except in an excess of this
acid. These facts have some bearing upon the theory of digestion. Accord-
ing to Dumas and Cahours, water containing a millionth part of hydrochloric
or hydrobromic acid, gelatinizes fibrin, and if a few drops of gastric juice
(pepsin) be then added, it is entirely dissolved in a couple of hours at a
temperature of 96° to 100°. Rennet produced the same effect. Phosphoric
acid with 1 atom of water acts upon fibrin in the same way as sulphuric acid.
The acid with 3 atoms of water converts fibrin into a gelatinous mass, which
is soluble in water, and the solution is not affected by an excess of the acid.
Fibrin is rapidly penetrated by concentrated acetic acid, and converted by
it into a thick jelly soluble in hot water. When another acid (sulphuric) is
added to this solution, a precipitate is formed, composed of fibrin and the
added acid. On the addition of an alkali (potassa), the fibrin is at first
precipitated, but it is redissolved by an excess of the alkali. The fibrin of
young animals is more easily acted on by acetic acid than that of old ones,
BO that there is in this respect a material difference between the fibrin of veal
and of beef. (Dumas )

Fibrin is soluble in weak solutions of potassa and soda, first becoming
gelatinous, and then forming a yellowish liquid which blackens silver and
oxide of lead, and exhales the odor of sulphuretted hydrogen on the addition
of an acid. Caustic ammonia seems to act upon fibrin in the same way as
the fixed alkalies, but its solvent action is less energetic. The fibriu of blood

NUTRIENT POWERS OP NITROGENOUS PRINCIPLES. 699

as it issues from the living body, i. e., before it has coagulated, is soluble in
from 6 to 8 parts of fresh serum, and also in a saturated solution of sulphate
of soda. All liquids which dissolve this principle (solutions of potash, soda,
and acetic acid) prevent the coagulation of the blood.

Ferrocyanic and ferricyanic acids combine with fibrin; the compounds are
obtained in the form of white and yellow precipitates, by adding solutions
of ferrocyanide and ferricyanide of potassium to the acetic solution of fibrin.
The white precipitate is insoluble in the dilute acids, but the alkalies decom-
pose it, and forming ferrocyanides, separate the fibrin in a gelatinous form.
The yellow precipitate (obtained by the ferricyanide) is more soluble than
the preceding.

An alkaline solution of fibrin yields precipitates with several of the
metallic salts — e. g., sulphates of iron and copper, and corrosive sublimate.
They are compounds of the respective oxides with the organic principle,
which, owing to this combination, loses all tendency to undergo putrefac-
tion. Tannic acid precipitates fibrin from its solutions, and the compound
(tannate of fibrin) is imputrescible.

The three nitrogenous principles, alhmneii, Jihrin, and casein, are the con-
stituents of animal food ; and the fact that principles of a precisely similar
nature are found in the vegetable kingdom, shows that, chemically speaking,
there is not that broad distinction between animal and vegetable food which
some have imagined. The constituents of flesh, i. e., fibrin and albumen,
exist in vegetables, and from these vegetable principles, the flesh of herbivora
must be formed. These two principles find their way directly into the blood
through the medium of the chyle, the liquid product of digested food.
Gelatin is not found in the blood, but it is no doubt formed from it in the
living body. With reference to the human body, it can be properly nourished
only by a variety of food, to suit the variety of textures of which it is con-
stituted. A theory was formerly propounded to the effect, that the body
could be supported by any one of these nitrogenous principles, excepting
gelatin ; but a Commission of the French Academy reported, upon due
inquiry, that this observation was equally applicable "to albumen, fibrin, or
casein, if employed alone ; and that neither animals nor man should be re-
stricted to any course of diet which does not contain all the proximate
principles of the frame." (Todd and Bowman.) These four principles,
under the influence of life, appear to be convertible into each other. This
is proved to some extent by the process of incubation. The recently laid
Q^^ contains only soluble albumen and oil. When incubation is complete,
fibrin and gelatin are found in the muscles and soft parts of the young bird,
and a large proportion of the soluble albumen has passed into the insoluble
state. Casein,' as it is contained in milk, is necessarily converted in the
living body into the other principles.

It is calculated that the human body wastes daily about one-twenty-fourth
part of its entire weight, and another physiologist has drawn the conclusion,
that the body will lose in substance unless it has supplied to it daily one-
twenty-third part of its weight. These averages must of course be materially
afi'ected by exercise, temperature, age, and state of health. The daily waste
compared with the weight of the body appears to increase in all animals in
an inverse ratio to the size. The smaller the animal the greater the pro-
portionate waste.

Gelatin.

This principle is abundantly diffused in the animal kingdom. It derives
its name from the fact that a hot solution of it, on cooling, sets into a jelly.
A principle similar to it in gelatinizing properties is found among vegeta-

TOO FISH GELATIN. ISINGLASS.

bles, especially in certain kinds of algae and fuci. Vegetable gelatin (gelose),
which has already been described, is, however, eminently distinguished from
that of the animal kingdom, by the absence of nitrogen, and by a difference
in its chemical properties. Animal gelatin is not included among the pro-
teinaceous principles. When dissolved in potassa, no protein-compound is
precipitated from the solution, on the addition of acetic acid. In constitu-
tion, also, it differs from the other principles considered in this chapter.
When freed from all impurities, it contains no sulphur. Owing to these
marked distinctions, it has been theoretically supposed to be deficient in
nutritive power, and to have no claim to be regarded as a flesh-forming prin-
ciple. There are no facts, however, to support this theory; on the contrary,
experience shows that gelatin may be a source of nutriment to animals,
although in a less degree than the fibrin and albumen.

Gelatin is characterized by its insolubility in cold and solubility in hot
water. It has been supposed that this principle had no independent exist-
ence in the animal body ; but it is found abundantly in all young animals,
in a state quite distinct from albumen, casein, and fibrin, which cannot be
converted into gelatin by boiling water. It constitutes exclusively the middle
portion of the air-bladder of the sturgeon and other fish, requiring only
water for its solution ; and it exists ready formed in skin, in a condition to
produce tanno-gelatin, or leather, by simple immersion in a solution of tannic
acid. Cold acetic acid will also dissolve gelatin from skin. There is, there-
fore, no ground for the statement that it is generated by the action of boil-
ing water upon the membranous tissues. In some instances, owing proba-
bly to its molecular condition, it requires a long application of heat for its
perfect extraction by water ; but in all cases, it must be regarded as an
educt and not as a product. The term gelatin was long indiscriminately
applied to all the gelatinous substances, obtained by the action of boiling
water on bone, cartilage^ and ligament, until Mtiller pointed out the pecu-
liarities of the product derived from cartilage, and appropriated to it the
name of Chondrin. {Poggend. Ann., xxxviii. 305.)

To obtain common gelatin, the substances affording it, such as the clip-
pings of hides, hoofs, horns, calves' feet, cows' heels, sheep's trotters, are
cleansed in cold water, and then subjected to the action of boiling water.
The solution so obtained is freed from fat, and from any deposit, by skim-
ming and straining, and allowed to gelatinize on cooling : the jelly so formed
is more or less colored and impure. It is cut into slices and dried.

Fish Gelatin. — Isinglass (probably a corruption of hasenhlase, bladder of
the sturgeon). This is a variety of commercial gelatin which is largely con-
sumed as an article of food, and is chiefly prepared in Russia, from the air-
bladders and sounds of certain species of Acipenser, or sturgeon. The blad-
ders are cleansed, dried, and scraped, so as to separate from them the exter-
nal and internal membranes ; and without further preparation, the residue
forms leaf isinglass. Isinglass was formerly picked into shreds, but is now
usually cut into delicate filaments by machinery. It should be colorless, ino-
dorous, and tasteless ; soluble in hot water after a short maceration in cold
water : and when incinerated, it should leave only traces of phosphate of
soda and of lime. There are many varieties of isinglass. The Beluga leaf,
from Astrachan, is the best, while the Brazilian isinglass is of the worst
quality. All kinds of commercial isinglass contain a certain amount of in-
soluble albuminoid matter, which is precipitated on cooling the hot solution.
We have found this to amount to 2 per cent, in the best quality, and to as
much as 20 per cent, in the worst. When any of the varieties of isinglass
are refined, they yield the pure principle gelatin, which is identical with that

SKIN GELATIN. BONE GELATIN. TOl

obtained from the fresh skins of calves and bullocks by the process mentioned
below.

Skill Gelatin. — A very pure form of gelatin sold under the name of Pateyit
Refined Isinglass is manufactured from glue-pieces, or the cuttings of the
skins of calves and bullocks. These are cleansed of fat and dirt by washing
in lime-water : they are then sliced and digested in water, at a temperature
of about 200^. The gelatinous liquid, strained through flannel, is allowed
to cool until it has acquired a proper consistency. It is then poured on a
slab of wet slate, and when nearly set, the sheet of gelatin is transferred to
an open network for the purpose of drying. It is subsequently damped,
rolled into thin sheets, and cut by a machine into fibres of various degrees
of thickness. This process applied to Brazilian and other impure kinds of
commercial isinglass, yields equally pure gelatin. A cheaper form of gelatin,
but improper as an article of food, has been manufactured, under a patent,
by digesting glue-pieces in an alkaline liquid, and afterwards boiling down
the whole of the tissues.

Bone Gelatin. — This is obtained by heating ground or rasped bones with
water, under pressure, to a temperature of 250^ to 270° ; the liquor gelati-
nizes on cooling, and the jelly may be purified as in the previous cases.
But the gelatin thas procured always retains an offensive odor when moist,
and a disagreeable flavor, in consequence of the high temperature employed.
Another mode of obtaining bone jelly consists in digesting the bones, pre-
viously boiled in water to remove the fat, in dilute hydrochloric acid, so as to
abstract the phosphate of lime. The animal part of the bone is thus left,
having the appearance of a tough flexible cartilage : this is thoroughly
washed in water, steeped in lime-water, or in a weak solution of carbonate
of soda, and again washed and dried. The dried bone-gelatin may then be
made into glue or size by boiling, gelatinizing, and drying, as with the other
forms of gelatin. It has been sold as an article of food in thin sheets, and
sometimes colored to conceal its impurity, under the name of French gelatin.
It is a variety of glue.

From whatever source obtained, pure gelatin is colorless, transparent, ino-
dorous, and insipid : it may have no smell in the dry state, and therefore
it should be tested by immersing a small quantity in boiling water. The
agglutinated mass, if a bad sample, will have the ofi'ensive odor of glue.
The fibre of pure gelatin is translucent, and when wetted, more or less
elastic, tough, and resisting. It at the same time nearly retains its trans-
parency. The fibre of isinglass, in which gelatin is always associated with
albuminoid matter, becomes quite opaque when wetted, is inelastic, and with-
out cohesion. Gel.atin is heavier than water. When heated it softens, then
shrinks, and exhales a peculiar odor, burning with difficulty, and exhaling
the ammoniacal odor of burned horn or feathers. Subjected to destructive
distillation, it yields an abundance of carbonate of ammonia, together with
the other products of azotized organic matters, and leaves a bulky carbon
difficult of incineration.

In cold water, gelatin gradually softens and swells, but scarcely dissolves
until gently heated, and on again cooling the solution, it forms a more or less
firm jelly. By its solubility in hot water it is distinguished and separated
from fibrin and albitmen. According to Bostock I part of isinglass dissolved
in 100 of water, gelatinizes on cooling; but in 150 of water it remains
liquid. We have found that 1 part to 80 of water, was required to produce
a moderately firm jelly. This eff'ect, as is well known, varies much with tem-
perature, so that jellies are more easily prepared in winter than in summer.
The stiffness of the jelly is also greatly dependent upon the source whence

T02 CHEMICAL PROPERTIES OF GELATIN.

the gelatin was originally obtained ; the skins and tissues of old animals
yielding a stronger and firmer jelly than that derived from young animals.
The gelatinous mass cannot be regarded as a definite hydrate. The water
slowly evaporates or may be imbibed by porous substances, and the gelatin
then remains in a dry state with its original properties. The gelatinous con-
dition is owing to physical causes and is common to organic and mineral
matter. Silica, alumina, and starch, as well as the coagulum of blood, may
be obtained in a gelatinous state.

When a solution of gelatin is repeatedly warmed and cooled, especially if
boiled, it gradually loses its tendency to gelatinize, and it becomes more and
more soluble in cold water. In spite of this well-known fact, some have
asserted that when a hot decoction is made of any animal matter and it does
not set into a jelly on cooling, no gelatin is present. But the proportion of
gelatin may be too small for this purpose, or it may have been exposed to
heat for too long a time — or too strongly heated. If the substance is dis-
solved by hot water — if the solution is precipitated by tannic acid, corrosive
sublimate, chloride of platinum, and subnitrate of mercury, these facts estab-
lish that the animal matter so dissolved is of a gelatinous nature, although
when cooled it may have a thin pasty or even fluid consistency. The so-called
extract of meat {extractum carnis) consists chiefly of altered gelatin with
kreatine, osmazome, and other soluble principles of flesh. It is obvious
from the mode of preparation, that they cannot contain either fibrin or
albumen, the principal nutritious constituents of meat. The proportion of
nutritious solids thus obtained is small : 34 pounds of flesh, containing nearly
24 pounds of water, yield only 1 pound of extract, and a large percentage
of this is water.

In close vessels, jelly may be kept in cool weather for some days without
change ; but in open vessels, it soon becomes mouldy. It then putrefies and
exhales a disagreeable ammoniacal odor. A little acetic acid considerably
retards these changes without materially affecting gelatinization. The fresh -
made aqueous solution is neutral, and should have no smell or taste. A
solution of isinglass commonly has a slight fishy odor and taste. Gelatin is not
soluble in absolute alcohol ; and when alcohol is added to a warm and strong
aqueous solution, the gelatin separates in the form of a white viscid substance.
It is insoluble in ether, and in fixed and volatile oils. It is dissolved by
acetic acid.

Gelatin is soluble in all the dilute acids, excepting the tannic, diflfering
essentially in this respect from albumen ; of these, the acetic solution only
gelatinizes on evaporation. Gallic acid gives no precipitate with it. When
the dilute nitric solution of gelatin is evaporated, nitrous gas is evolved, and
the residue deflagrates just before dryness ; with strong nitric acid, oxalic
acid is formed. The action of strong sulphuric acid on gelatin is attended
by the formation of leucine, and of a peculiar saccharine product, which is
known under the names of glycocol or glycocine. It is gelatin-sugar.

The dilute caustic alkalies, and ammonia, do not prevent the gelatinization
of gelatin, but they often throw down a portion of phosphate of lime. When
gelatin is dissolved in a dilute solution of caustic potassa, and exactly neu-
tralized by acetic acid, the evaporated liquid does not gelatinize on cooling.
When boiled with caustic potassa, ammonia is evolved, and leucine and
gelatin-sugar are formed. Gallic, acetic, and nitric acids produce no pre-
cipitate in an aqueous solution of gelatin. The addition of common salt or
other neutral salts, or of ferrocyanide of potassium, to the acetic solution,
does not cause the precipitation of gelatin. When gelatin is dissolved in
a weak solution of potassa, acetic acid does not affect the liquid. When a

TANNO-GELATIN. LEATHER. LEUCINE. 703

solution of chloride of lime is added to gelatin in acetic acid, a turbidness
is produced.

A solution of gelatin is not precipitated either by the neutral acetate, or
by subacetate of lead. With protochloride of tin it gives a flocculent pre-
cipitate, but none with the perchloride. With sulphate of copper there is
no precipitate. A solution of gelatin is not precipitated by a solution of
corrosive sublimate; if a cloud is formed, it soon disappears. Gelatin
is not precipitated by solution of silver or of gold, but chloride of platinum
precipitates it and the sulphate of platinum throws it down in brown viscid
flakes, which blacken and become brittle when dried on a filter. E. Davy
recommends this as a delicate test for gelatin, detecting it in solutions too
weak to be affected by tannic acid, and not liable to be interfered with by
the presence of albumen. {Phil. Trans., 1820, p. 119.) Subnitrate of mer-
cury added to a solution of gelatin produces a dense white precipitate.
Neither sulphate of alumina nor alum occasions any precipitate in a solution
of gelatin ; but a mixture of chloride of sodium and alum, or a solution of
chloride of aluminum, form a white precipitate : this compound exists in
taived leather.

Tannic acid or cold infusion of galls is a most delicate test of the presence
of gelatin ; when it is added to a solution of 1 part of gelatin in 5000 of
water a cloud is evident, and on dropping tincture or fresh infusion of galls
into a strong solution of gelatin, a dense white curdy precipitate of tanno-
gelatin falls, which becomes gray when dried, is insoluble in water, and not
putrescible. Mulder has described two definite combinations of tannic acid
with gelatin: 1, one containing 1 atom of gelatin and 1 of tannic acid,
which is thrown down when a great excess of the latter is used ; and "2, one
containing 3 atoms of gelatin and 2 of tannic acid, formed when the latter is
not added in excess. According to Davy, when gelatin is precipitated by
infusion of oak-bark, 100 parts of the precipitate contain 54 of gelatin and
46 of tannin. Schiebel found that when a solution of 100 parts of gelatin is
precipitated by a great excess of an infusion of 1 part of oak-bark in 9 of
water, it combines with 118 parts of tannin; but when a weak solution of
extract of oak-bark is added to a solution of gelatin, so as not to precipitate
the whole of the latter, the precipitate which slowly falls contains 100 of
gelatin and 60 of tannin. As albumen is also precipitated by tannic acid,
when this acid is used as a test for gelatin, the absence of albumen should be
previously ascertained. Tanno-gelatin is identical with leather. In the
manufacture of leather, the precipitate is formed in the skin itself, by
immersing it first in a weak and afterwards in a strong infusion of oak-bark.
The albumen of the skin is also at the same time converted into tannate of
albumen.

A solution of fish-gelatin (isinglass) has the same properties as that of
skin-gelatin ; the latter is not so rapidly dissolved by hot water, but it
dissolves entirely, leaving no sediment, like isinglass. A solution of bone-
gelatin differs from both of these in the fact that as phosphate of lime is
soluble in gelatin, oxalate of ammonia produces a turbidness in its solution.
As isinglass is frequently adulterated with bone-gelatin, oxalate of ammonia
occasionally produces a turbidness in its aqueous solution. Under polarized
light a filament of moistened isinglass when examined by an analyzer, gives
a spleadid display of iridescent colors owing to its peculiar organic structure.
A filament of gelatin similarly treated and examined, gives a uniform band
of color which is the complementary color of the ground on which it is placed.
Leucine {C.JI^fi,!^), so called from its white appearance. This com-
pound, which bears some resemblance to cholesterine, may be procured by
boiling gelatin in sulphuric acid, diluted with 4 parts of water. It is also

T04 GLYCOCINE SIZE. GLUE. CHONDRIN.

obtained with tyrosine, when dry casein is fused with its weight of hydrate
of potassa. Tyrosine (CigH^^OgN) may be precipitated from the lixivium
by the addition of acetic acid. Leucine melts at 350°, and undergoes de-
composition. This substance is also known under the names of Gaseous oxide
and Aposepedine. It may be obtained from the fibrin of muscle, from gluten,
and other nitrogenous principles.

Glycocine (C^HgO^N), Glycocol. Gelatin- sugar. — This is another product
of the reaction of dilute sulphuric acid on gelatin at a boiling temperature.
It is also procured as a result of the action of hydrochloric acid, at a boiling
temperature, on one of the organic acids of bile, or on hippuric acid. It
assumes a crystalline form, is not very soluble in water, and is insoluble in
alcohol and ether. It has a sweet taste, but differs from sugar in not under-
going vinous fermentation. When treated with nitric acid, no oxalic acid is
formed ; but a new acid, called the Nitro-saccharic, is produced. The interest
attached to this product, lies in the variety of sources from which it may be
obtained, and in the numerous compounds which are derived from it.

Various formulae have been assigned to gelatin. That which is now
generally admitted represents its constitution as Ci3lIioO^N2. It contains
a large proportion of nitrogen, but no sulphur. When pure gelatin is dis-
solved by boiling it in a solution of potassa, containing oxide of lead, no
discoloration is produced. The contrary statement appears to have arisen
from the application of this test to commercial isinglass, which always con-
tains a certain proportion of albuminoid tissues. When these have been
separated by refining the isinglass, the resulting gelatin produces no effect in
a potassa-solution of oxide of lead.

Sizt is usually sold in the form of a stiff tremulous jelly : it is obtained
chiefly from the waste of vellum, parchment, and from the skins of horses,
cats, dogs, and rabbits, and sometimes from fish. It is largely employed in
the manufacture of paper, and by whitewashers, painters in distemper, paper--
stainers, and gilders. Size has usually a putrid odor and taste, and a brown
color.

Glue is an important article of manufacture, and differs in price and quality
according to its source. It is extracted from bones, muscles, tendons, liga-
ments, membranes, and skins, the latter yielding the best glue, especially
when from old animals. The parings of hides and pelts from tanners and
furriers, the hoofs and ears of horses, oxen, calves, sheep, etc., are employed
in the manufacture of glue. They are first digested in lime-water, washed,
laid in a heap to drain, and boiled in soft water ; the impurities are carefully
skimmed off, and the liquid is then strained, clarified with a little alum, and
allowed to settle. The solution is poured off from the sediment, and boiled
down to a proper consistence, so as to concrete on cooling : the glue is then
cut by a wire into slices, which are dried upon netting. Good glue is hard,
brittle, of a uniform brown translucency, and when immersed for some time
in cold water, it becomes soft and gelatinous, but requires to be heated, in
order to dissolve and fit it for use. It should be heated over a gentle fire,
or in a water-bath, and it may then be applied to the moistened wood by a
stiff brush : it will not harden in a freezing temperature ; the adhesion de-
pends upon the absorption and evaporation of the superfluous water.

Cfhondrin. — This variety of the gelatinous principle constitutes cartilage,
as it exists in the windpipe, nose, and ear, as well as in the cornea of the
eye, in the ribs, and at the ends of the long bones. It is found abundantly
in the flesh and cartilaginous skeletons of fish, and from fish-bones ; it may
be readily extracted by boiling water. If sufficiently concentrated, the solu-
tion sets into an opaque jelly on cooling. It is not so soluble in hot water

COMPOSITION OF THE SOFT SOLIDS AND OP BONES. 105

as gelatin. An aqneoiis solution of chondrin is precipitated by acetic acid,
but the precipitate is dissolved by an excess of the acid. It is precipitated
by nitric and tannic acids, as well as by sulphate of copper and acetate of
lead. It is not affected by caustic alkalies. Its formula is Cg.^U.jgOi^N^.

The nitrogenous principles which we have here considered, build up the
animal body. The soft solids of animals are chiefly formed of fibrin, albu-
men, and gelatin.

Fibrin enters largely into the composition of muscle or flesh ; thus,
assuming that the proportion of water varies from 71 to 74 per cent., the
fibrin in muscle, averages from 19 to 22 per cent., and the gelatin from 5 to
7 per cent. In addition to these constituents, muscle consists of cellular
tissue (albumen), nerves, vessels, and fat. Dry muscle yields, by ultimate
analysis, the same elements as blood. In the juice of flesh, which is always
acid, crystalline nitrogenous principles exist, which may be separated by
complex processes. Among these may be enumerated Kreatine (CgH5,O^N3
-I-2H0) and Kreatinine (CgH^OaNg) : this is also a product of the decom-
position of kreatine. Inosinic or Inosic acid {Q^^fi^^^^ + llO) and Sar-
cosine (CgH^O^N) are other principles, the former being an educt of the
juice of flesh, and the latter a product of the decomposition of kreatine.
Inosin {C^Jl^^fi^^-^^YiO), a variety of sugar, has been found in the juice of
the involuntary muscles. Osmazome (dafiij, odor, and ^wjwos, broth) is not a
definite compound, but an alcoholic extract of the residue left by a watery
extract of flesh.

Albumen enters into the composition of muscle, of the brain, spinal cord,
and nerves. It is 1 constituent of cellular tissue, and of the soft organs, such
as the liver, spleen, lungs, and kidneys. The substance of the brain consists
of 80 per cent, of water, with 7 per cent of albumen in a soluble form. It
contains two acids, a solid white fatty acid (the cerebric), and an oily liquid,
the oleophosphoric, acid. The cerebric acid contains phosphorus. The waxy
secretion of the ear {Cerumen) is a compound of albumen with an oily matter,
and a yellow bitter extract, which is soluble in alcohol.

Gelatin enters into the composition of the skin, tendons, ligaments, and
the white fibrous tissue generally, as well as of bone, cartilage, ivory, and
the teeth of animals. 100 parts of dry human bones contain about 33-3 of
organic matter (gelatinous tissues), and 66 6 of earthy matter, consisting
chiefly of subphosphate of lime with carbonate of lime and phosphate of
magnesia. Fluoride of calcium is found only in fossil bones. The propor-
tions of organic and inorganic matter vary slightly in the bones of different
animals, and in the different bones of the same animal. ^ The proportions of
mineral and organic matter also vary at different periods of life. Thu*,.
according to the analysis of Schreger, in the child, the earthy matter forms
nearly one-half of the weight of the bone (48 48 per cent.) : in the adult
three-fifths (74-84 per cent.), and in old age seven-eighths (84.10 per cent.).
The bones, at this period of life, contain much oily matter. The mode in
which the organic and inorganic constituents are blended in the skeleton, is
worthy of remark. When a fresh bone, e. g., the scapula, is digested in dilute
hydrochloric acid, all the mineral matter is removed : but the bone perfectly
retains its shape. The residue consists of flexible and elastic gelatinous
tissue. If a similar bone is carefully heated to a high temperature, under a
free access of air, a white brittle mineral substance is obtained which retains
the perfect shape of the bone. This consists of phosphate and carbonate ot
lime. These results show that every atom of mineral is- associated with au

45

70fi PROPORTION OF FLUIDS AND SOLIDS IN ANIMAL BODIES.

atom of organic raatter. Bones contain, not merely in their hollow interior
{cancelli), but in their substance, a large quantity of oily matter which is
profitably extracted by simply boiling crushed bones in large caldrons of
water. It rises to the surface like an oil, and is removed in a solid cake
when the liquid has cooled. Bone fat, or grease, is now manufactured
weekly by tons in this metropolis. Its composition does not differ from that
of other animal fats, and it contains the same principles, but rather a large
proportion of oleine. Bone fat is soft, inodorous, and easily fusible. It is
largely used in the manufacture of pomatum, "bear's grease," and other
cosmetics, and is employed for some of the finer kinds of toilet soaps, in
preference to other animal fats. When bones are heated in close vessels,
they leave a porous charcoal, which is usefully employed in chemistry and
the arts, under the name of animal charcoal.

Ivory has a composition similar to that of bone. The dentine or bony
part of the teeth, contains from 68 to 70 per cent, of mineral matter ; while
the enamel contains 74 per cent, with 6 per cent, of gelatin. Pearls and
mother-of-pearl contain 66 per cent, of carbonate of lime and 34 of organic
matter. Shell, coral, and madrepore are chiefly composed of carbonate of
lime cemented with animal matter. The shell of the egg contains 98 per
cent, of carbonate of lime, and 2 per cent, of organic raatter. The effect of
incubation is to render it thin and brittle.

In the shell of the lobster and crab, the mineral matter appears to be
cemented by another organic principle, Chitin (C^^H^^Oj^N). It is insoluble
in water, but soluble in strong acids. It enters into the composition of the
elytra of certain insects, e. g., the cockchafer, cockroach, and beetles.

CHAPTER LVI.

THE FLUID CONSTITUENTS OF ANIMAL BODIES, AND THE
SUBSTANCES DERIVED FROM THEM.

Although water is commonly regarded as a compound belonging to the
inorganic kingdom, it is a most abundant, and certainly a most important,
constituent of animal bodies. At least two-thirds of the weight of the human
body are represented by water. If we except the bones, this liquid forms
three-fifths of the solid organs and textures, and about four-fifths of the fluid
■constituents. The flexibility, softness, elasticity, and tenacity of the tissues
are due to the presence of water. Fibrin and albumen, when deprived of it,
lose their most important physical properties as parts of a living structure ;
and it is a matter of demonstration, that without it, vital action cannot con-
tinue. At p. 544 we have given the results of recent analyses, whereby it is
proved that some vegetables contain 96 per cent, of this liquid ; and at p.
142 we have referred to the constitution of the AcalephcB, animals which con-
tain 99 per cent., and which might almost be described as living water.
From calculations based upon the analysis of bone, and of the solid and fluid
constituents of the human body, we find that the body of a male adult, weigh-
ing 150 pounds, consists of water 100 pounds ; dry organic solids 34 pounds;
earthy or mineral matter, chiefly the phosphate and carbonate of lime and
chloride of sodium, mixed with small quantities of other earthy and alkaline
salts, and oxide of iron, 9 pounds ; and of oil, or fat, 7 pounds. The amount

ANIMAL LIQUIDS. THE BLOOD. 707

of mineral mntter Ims been deduced from the actual weighing of dry adult
skeletons; and the fat from the calculations of Burdach, who estimates it at
about 5 per cent, of the weight of the body. The ordinary analyses of the
solid and fluid constituents, furnish the remaining elements of this calcula-
tion. It is pyobable that the proportion of water is even greater than that
which is here assigned ; as it is, it amounts in an adult to 100 pounds or ten
gallons ! If we carry this inquiry into the proportions of the elements, as
they are known to constitute the dry organic solids and the oil or fat, we
arrive at the following results : Of the 41 pounds of the dry solids and of oil
or fat, carbon forms 23 pounds ; oxygen 8 pounds ; nitrogen 6 pounds ; hy-
drogen Bj pounds; and sulphur and phosphorus together (the former pre-
ponderating), half a pound. This is exclusive of the oxygen, hydrogen,
carbon, and phosphorus, which exist in the water and mineral matter.

The fluids of the animal body may be divided, according to their principal
chemical characters, into, 1. Those which are at the same time fibrinous and
albuminous ; 2. Those which are albuminous ; and 3. Those which are non-
albuminous. Gelatin is not found in any of the fluids : it exists in the body
only as a component of the solid tissues. All the fluids in a healthy state
contain albumen, excepting the bile and urine. In certain diseased states
of the body, albumen is found in the last-mentioned liquid. Casein exists
chiefly in the milk, a secretion peculiar to the class mammalia. Thejibrinous
and albuminous liquids are the blood, chyle, and lymph.

The Blood.

In mammiferous animals, the blood is of a red color ; florid and approach-
ing to scarlet in the arteries, and of a deep purple in the veins. Its sp. gr.
varies between 1*049 and 1 057, and its temperature in the healthy human
body is between 98° and 100°. It has an unctuous or somewhat soapy feel,
a slightly nauseous odor and saline taste, and an alkaline reaction. It
appears homogeneous, or uniform, whilst circulating in its vessels, or imme-
diately upon its removal from them ; but when examined by a microscope, it
is seen to consist of numerous red particles or cells, varying from one-three
thousandth to oae-six thousandth of an inch in diameter, floating in a color-
less transparent fluid ; the former having been termed the red corpuscles, the
latter the liquor sanguinis.

The corpuscles of blood are mechanically diffused in the serum, in which
the fibrin is dissolved. Under ordinary circumstances, the blood, after it
has been drawn from its vessels, gelatinizes, or coagulates ; and the jelly,
or coagulum, gradually separates into two parts, a liquid serum, and a soft
clot or crassamentum. In the act of coagulation, the corpuscles apparently
coalesce and give to the clot a uniformly red color. This arises from the
tendency of fibrin, when removed from a living bloodvessel, to assume the
solid and insoluble state. The particles of fibrin cohere in a sort of fibrous
network, retaining the red corpuscles in the interstices. The proportion
which the clot bears to the serum is variable, and is partly dependent upon
the shape of the vessel in which the blood is contained. According to
Lecanu, in 1000 parts of healthy blood, there are 869 parts of serum and
131 of clot, which he describes under the general name of "globules." The
mode of procuring fibrin and its chemical properties have been already
described (p. 698). The corpuscles consist of an envelope or membrane
holding a liquid of an albuminoid nature {globulin, p. 692), deeply tinged by
a very small proportion of an organic coloring-matter (hamatosme, C^jH.jg
NgOfiFe). The proportion of fibrin in recent healthy blood is from 2 to 3

T08 H^MATOSINE. RED CORPUSCLES. COLORING- MATTER.

parts in 1000 by weight, and the proportion of coloring principle (Jisematosine)
is rather less than this. The clot (or globules of Lecanu) may therefore be
considered to be thus constituted in 1000 parts of blood : —

Fibrin 2-948

Hsematosine (coloring matter) .... 2-270
Globulin (albumen) 125-627

130-845

Arterial blood has not been found to contain more fibrin than venous
blood, but capillary blood contains less than either. With the exception of
color, there is no marked physical or chemical difference between arterial
and venous blood. If blood freshly drawn is bottled and well secured, it
may be kept for many years without undergoing any material change in
color. It loses its power of spontaneous coagulation, but the red coloring
matter when diluted with water retains its bright red color, and its usual
chemical properties. No corpuscles could be seen under the microscope.
In opening a bottle after keeping it for some years, there was a slight smell
of sulphuretted hydrogen.

Hcematosine. Coloring -matter. — This consists of small corpuscles, blad-
ders, or flattened cells, containing a red coloring principle combined with
globulin. It is to their great number and aggregation, that the blood owes
its red color. In the mammalia, they are not spherical, hence the term
globule is inappropriate. They are disks of the shape of a circular double
concave lens, being thicker at the circumference than in the centre. In the
Camel tribe, they are of an oval form, but, in these, as in other mammalia,
there is no nucleus. In birds, reptiles, and fishes, they are of an oval shape,
and have a nucleus in the centre. Their size bears no proportion to the size
of the animal. They have the same size and form in the human being at all
stages of growth ; but the average size varies in different animals. They
are larger in man than in most domestic animals, while they are smaller in
the sheep and goat than in the pig, hare, and rabbit. In man, they have
an average diameter of 1-3500 of an inch : in the goat of l-6366th of an
inch. A cubic inch of blood weighing about half an ounce, contains about
sixty-four thousand millions of these blood-cells or corpuscles.

Miiller found that these corpuscles were so large in the blood of a frog
(1-27 45th of an inch), that they might be separated by filtration. The
liquor sanguinis passed through the filter, and the fibrin separated sponta-
neously from the albumen, in' a colorless state. In the blood, there are also
colorless nucleated corpuscles of a spherical form which are rather larger than
the red corpuscles. They are similar to the nucleated particles found in
lymph and chyle.

The red corpuscles in human blood have a sp. gr. of 10885, and as the
sp. gr. of serum, in which they are diffused, is 1-030, they have a tendency
to sink in this liquid. The corpuscles may thus be collected and examined
in serum, which does not dissolve the coloring-matter, as it is contained in
them. The coloring -matter is an organic principle containing nitrogen and
iron in some unknown state of combination. It has an intense coloring
power; and on the breaking of the outer membrane of the corpuscles, the
red color is diffused and communicated to water or other liquids. The pro-
portion of iron has not been accurately determined, but it is supposed to
form from 0*43 to 05 per cent, of the dried corpuscles, or 6 per cent, of the
pure coloring-matter. The albuminous principle, glolaulin, is dissolved by
water, hence an aqueous solution of the coloring-matter always contains a
portion. It may be separated by a mixture of alcohol and sulphuric acid,

ANALYSIS OP VENOUS BLOOD. 709

hy which globulin is coagulated, while the coloring-matter, as it is supposed,
is unaffected.

An aqueous solution of the coloring-matter, when recent, has an intensely
red color, and a peculiar odor : it is quite neutral. When the solution is
heated to about 150°, the haematosine is coagulated and destroyed, the
liquid assuming a muddy brown color. It is now rendered quite insoluble
in water. Nitric acid and chlorine destroy the red color, turning the liquid
brown and greenish brown. Weak alkalies (ammonia) in small quantity,
have no effect upon the color. In excess they darken it. Neutral salts pro-
duce no change in it. Alcohol and tannic acid render the solution turbid,^
but do not destroy the red color.

The serum of blood is a pale straw-colored albuminous liquid, of a slightly
alkaline reaction. Its sp. gr. is 1*030: it contains about 90 per cent, of
water. It sets into coagulura when heated to about 160°. Its properties
have been already described under the head of seralbumen (p. 689).

The blood contains fatty and saline matters, the latter consisting chiefly
of alkaline chlorides and phosphates. Its composition concisely stated
would therefore stand thus, according to recent analysis (Regnault) : —

ANALYSIS OF VENOUS BLOOD IN 100 PARTS.

Clot or crassamentum .... 13-0
Serum 87'0

100-0

(Fibrin 0-30

Clot -< r^, , , ( Hgeraatosine .... 0*20
I Globules lenobulin .... 12-50

13-00

f Water 79-00

. cj ! Albumen 7-00

Serum \ ^^.^^ ^^ ^^^^^ matters .... 0-06

t^ Chloride of sodium and other salts . . 0-94

100-00

The use of the blood is to maintain, by its incessant distribution to all
parts of the body, the life of an animal. It has been described as "liquid
flesh" (BoRDEu) : it contains the animal solids in a state of solution ; and
analysis shows that blood and flesh yield as nearly as possible, the same
elements in the same proportions. The daily waste of the blood is supplied
by the chyle. With the exception of chyle and lymph, all the fluids and
solids of the body are formed by the blood, and at the expense of its con-
stituents. On the other hand, in the formation of the body of the young
bird, during the process of incubation, blood, with its usual constituents,
fibrin and hsematosiue, is actually produced from soluble albumen. That
such widely different products as milk, bile, and urine, should be produced
in the living body from the constituents of this fluid, with such remarkable
uniformity and regularity, is one of those marvels of vital chemistry which
science cannot explain. , . .« ,

Tests for 5/oorf —Blood-stains on articles of clothing may be identihed
—1 By their peculiar crimson-red color. 2. By the shining and raised
surface of the stain or spot (dried albumen and fibrin). 3. By their ready
solubility in water, to which they give a red color. The water under these
circumstances contains albumen, as well as haematosine. ^^^f.'^/"'!"?!*
does not change the red color to a blue, green, or crimson tint. When
boiled, the albumen and hsetnatosine are both coagulated, and the red co or
is entirely destroyed ; a muddy brown coagulum subsides, which is quite m-

TIO ANALYSIS OF VENOUS BLOOD.

soluble in water and alcohol. For the examination of small stains in a dry
state, an inch power of the microscope will be found convenient.

By employing a small quantity of water on a glass slide in order to dissolve
the stain, the clot may be broken up and the red corpuscles separated. These
may be examined by a qunrter-inch power under the microscope. When
detected, the evidence of the presence of blood is placed beyond doubt.
Xo other red coloring-matter, vegetable or animal, owes its color to cor-
puscles or cells. A small quantity of glycerine added to the water which is
used as a solvent, prevents it from drying too rapidly. The red coloring-
matter of the blood differs from all other red coloring-matters, animal and
vegetable. It is very soluble in water as it issues from the corpuscles, and
has an intense tinctorial power, so that a few drops of blood will give a red
tint to a large quantity of water. When exceedingly diluted, the water has
a very pale red color. Even in this diluted state its optical and chemical
properties are highly characteristic. When such a solution is examined by
a spectroscopic eye-piece attached to the microscope, two black and well-
defined absorption bands appear, one of them at the junction of the yellow
with the green, and the other traversing the green ray about its centre.
By acting on blood with sulphate of iron and other chemicals, other bands
characteristic of blood may be made to appear. No other red coloring-
matters produce spectra with bands similar in number or position to those
observed in the blood. Mr. Sorley, of Sheffield, has brought this branch
of science to a very perfect state, and has been able to prove, by a series of
ingenious experiments, that even when other red coloring-matters are mixed
with blood so as to conceal the blood-spectra, these may be again brought
out by the use of an alkaline sulphite which destroys the foreign coloring-
matter without materially affecting the optical properties of blood.

Another remarkable property of the red coloring-matter of blood is mani-
fested in its action on the precipitated resin of gnaiacum. A small quantity
of blood added to the precipitated resin of gnaiacum, produces no change
of color. A solution of peroxide of hydrogen treated with the red coloring-
matter of blood, or with a drop of the tincture of gnaiacum separately, pro-
duces no other effect than a slight reddish tint in the liquid ; but if to a
mixture of coloring-matter of blood with gnaiacum resin we add a few drops
of peroxide of hydrogen, or any liquid containing it, a beautiful blue color
is brought out as a result of the speedy oxidation of the resin. For the
production of this change the three substances must be together, but it
matters not in what order they are mixed. So delicate is this test, that a
quantity of blood in water, not suflBcient to give a red stain to paper or
linen, will be indicated by the production of a blue color under these cir-
cumstances. Other red coloring-matters — e. g., cochineal, the red color of
rose-leaves, red wine. Brazil-wood, &c. — produce no such effect on the addi-
tion of peroxide of hydrogen. The persulphocyanide of iron blues the resin,
hut this is owing to the iron salt, and the bluing takes place without requiring
the addition of peroxide of hydrogen. The peculiarity of this mode of test-
ing depends on the fact that neither blood nor peroxide, used separately,
has any effect upon the resin ; but when used together, they bine it. Other
substances turn it blue, but they produce this change of color at once, and
without the addition of peroxide of hydrogen. On the other hand, the cochi-
neal and vegetable red coloring-matters, so far as they have been examined,
have no coloring action upon the resin, even when peroxide of hydrogen is
added to the mixture. This mode of testing was first suggested by Van
Pi'cu, and he recommended the ozonized oil of turpentine. Dr. Day, of
Geelong, recommended and first successfully used ozonized ether, and proved
that this really contained antozone; but, when jt can be procured, a solution

COMPOSITION OF CHYLE AND LYMPH. 711

of pure peroxide of hydrogen will be found a better liquid for employment.
It is remarkable that when the colorino;.iuatter has undergone the action of
glacial acetic acid and chloride of sodium to produce crystals, it still ])os-
sesses the power of bluing a mixture of resin and peroxide, although much
more slowly.

It would carry us far beyond the limits of this work if we entered into
more minute details on the chemistry of the blood. No treatise on the
science can supply the special information now required by students of medi-
cine on the physiological and pathological chemistry of this important fluid.
We therefore advise the reader who desires further information to consult one
of those numerous monographs which have been published on the subject.

Chyle.

This is a milky-looking liquid which is found in the thoracic duct. It has
an alkaline reaction. It appears to consist of oily matter in a state of emul-
sion, with an albuminous liquid. Under the microscope, oil-globules and
colorless nucleated globules (chyle-globules) are visible. A fibrinous clot,
which amounts to from 1 to 6 per cent, of the liquid, separates by sponta-
neous coagulation, as in the blood, and no doubt owing to the same cause —
^. e., the natural tendency of this principle, when not in free motion in a
living vessel, to assume a solid and insoluble state. An analysis made by
Dr. Rees shows that 100 parts of healthy chyle consist of 7 '08 albumen,
with traces of fibrin, extractive matters (undefined), 1'08; fatty matters,
0-92; chloride of sodium and other salts, 0-44; water, 90-48. The chyle
conveys the elements of nutrition immediately into the blood by means of
the thoracic duct.

Lymph.

The fibrin and albumen in this liquid, as it is circulated in the lymphatics,
are generally stated not to exceed 1 per cent. In an analysis of lymph made
some years since, we found the liquid, which was feebly alkaline, to consist
of albumen and fibrin, 2 ; saline matters, 2 ; water, 96.

The albuminous liquids are very numerous, and comprehend all the secre-
tions of the body, excepting bile. They are either alkaline or neutral,
generally the former, and their principal saline ingredients are chloride of
sodium, carbonate of soda, and the phosphates of soda and lime. The most
important of these liquids is the milk, which is secreted from the blood by
the mammary glands, and is necessary to the nourishment of the young of
the class mammalia.

Milk.

This is an opaque white liquid consisting of water, casein with some albu-
men, sugar (lactine) with lactic acid, oil (butter), and salts. When examined
by the microscope, it is found to contain oil-globules of various sizes, floating
in a clear liquid (serum or whey). These globules are remarkable for their
perfect sphericity in all respects, as well as for the brightness of their middle
portions in contrast with the dark circumference, an optical effect depending
probably on the refractive power of the oil, which appears to be containea
within a transparent membrane. The opacity of milk is owing to the number
and diffusion of these oil-globules, which vary in duameter from ^^u l^ to

^ th of an inch They give to the liquid the character of an emuU on,
llirL pi^dilced when tL'pulp of the alJ^ond is mixed with wate. When
milk is allowed to stand, it separates spontaneously into two P«''tions. 1 he
oil-globules, by reason of their low specific gravity, collect upon the surface,

712 ANALYSIS OF MILK. ITS COXSTITUENTS.

forming cream. The richness of milk is determined by the relative thickness
of this stratum, and for this purpose the milk is placed in a graduated tube
called a lactometer, by means of which the proportion of cream may be at
once determined.

The oil-globules are not dissolved by ether on simple agitation with milk.
If a little acetic acid is added, and the liquid boiled, the membrane is dis-
solved by the acid, and the oily portion, as it is set free, is dissolved by the
ether. Butter is the result of the aggregation of the oil-globules. The
separation of the oil in this form is commonly effected by the process of
churning, which consists in the mechanical agitation of the cream at a
moderate temperature. The milk of all animals is, in its normal state,
neutral ; although it very soon exhibits acidity when exposed to air, in con-
sequence of the formation of lactic acid. This, after a time, causes the
separation of casein in the form of coagulura. The sp. gr. of milk varies ;
that of the cow is generally about 1-030. It fluctuates in different animals,
according to Brisson, from 1 0203 to r0409; but as it is affected by the
presence of the butter on the one hand, which diminishes, and by the casein
and salts on the other, which increase its density, it is difficult to estimate a
mean. According to Berzelius, the sp. gr. of skimmed milk is 1-033 ; that
of cream, 1-024.

Some of the principal properties of milk are due to the presence of casein^
the chemical peculiarities of which have already been described (p. 637).
Fresh milk does not coagulate when boiled, A firm and coherent pellicle
forms upon the surface when it is boiled in air, as the result of the oxidation
of a part of the casein; and on the removal of this, a fresh pellicle is
formed ; but there is no coagulum. In this form, casein is insoluble in water.
By direct analysis, we found that 100 parts of good cow's milk yielded of
water 86"4, organic matter 12-6, and saline matters 1. The proportions of
oil, casein, and sugar are subject to great variation in different animals, as
well as in the same animal, according to its state of health and the substances
on which it feeds. The milk is sometimes a source of elimination of noxious
substances which may have been taken in the food. According to Regnault,
the following represents the constitution of 100 parts of this liquid in various
animals : —

Cow.

Ass.

Goat.

Mare.

Bitch.

Human Fern,

Water 87-4

90-5

82-0

89-6

6(J-3

88-6

Oil or butter . . . .4-0

1-4

4-5

traces.

14-0

2-6

Lactine and soluble salts . 5-0

6-4

4-5

8-7

2-9

4-9

Casein, albumeu, and fixed salts 3-6

1-7

9-0

1-7

16-8

3-9

100-0 100-0 100-0 100-0 100-0 100-0

The salts of the milk are here chiefly included in the weight of the casein
and albumen. They amount to only 0 37 per cent., of which 018 are phos-
phate of lime, and 0 1 35 chloride of sodium. The phosphates of magnesia,
soda, and iron are found in traces, as well as carbonate of soda. It is stated
by some authorities that casein contains no phosphorus ; but it is certain
that phosphates are rather abundantly obtained in the ash.

The colostrum, or milk as it is first secreted, is thicker than milk, and of a
yellowish color. Under the microscope, it presents oil-globules, mucus, and
granules of an irregular shape. It contains 17 per cent, of solid matters,
including casein. The analysis of cream shows that it consists of about
equal parts of butter and casein, with a variable quantity of serum or whey.
The adulteration of milk chiefly consists in the addition of water. It may
be discovered by the lowering of the specific gravity, and by the deficiency
of oil-globules under the microscope.

MILK. LACTINE. LACTIC ACID. V13

The casein of milk may be separated by warmiiif^ the liquid and addin<r a
few drops of acetic or any other acid : in this case the casein combines whh
the acid (p. 693). The action of rennet is remarkable. This substance,
which consists of the inner membrane of the fourth or dij^esting stomach of
the calf, when added to 1800 parts of milk heated to 122°, causes a perfect
separation of the whole of the casein in flaky masses, a pale and yellowish
watery liquid remaining, which is the whey or serum, sometimes entirely
deprived of the casein. This is probably effected by the action of the
organic principle, pepsine.

The watery portion, or whey, i. e., the serum of milk, is neutral, but some-
times acid. It is rendered opaline by heat, owing to the presence of albumen ;
also by acetic acid, if any casein remains. It has a specific gravity of 1 02T,
and contains 94 4 per cent, of water. It is abundantly precipitated by
tannic acid and by other compounds which act on albumen. Oxalate of
ammonia generally throws down a precipitate of oxalate of lime, owing to
the presence of phosphate. The butter, or oil, which is remarkable for its
fusibility at a low temperature (70°), is a compound of various fatty princi-
ples, which have been already described (p ()2T). By saponification, these
principles form fatty acids, including butyric acid.

The fact that milk is the food of all young mammalia in the first stage of
life, and that the growth of the body depends on the principles contained in
this liquid, are sufficient proofs that casein, in the living body, can be trans-
formed into fibrin and albumen in all their modifications; the phosphate of
lime contained in milk, being appropriated for the skeleton, and the oil of
milk for the production of fat.

Lactine(CJI.,fi^„ or G^Jl^fi.g-i-b'HO): Sugar of Milh; Lactose.— \t\%
this substance which gives the sweet taste to fresh milk. It is procured in
large crystalline masses by the evaporation of the whey of fresh milk, after
the separation of the casein and oil. It is prepared in Switzerland from
whey, in the manufacture of Gruyere cheese. It is white, hard, and gritty,
only slightly sweet to the taste, soluble in about 6 parts of cold and 2 parts
of -boiling water. It does not form a syrup. It is insoluble in alcohol and
ether. Its aqueous solution turns the polarized ray to the right. Dilute
acids convert it into glucose. Nitric acid produces with it oxalic as well
as mucic acid. Lactine differs from other sugars, and resembles gums, in
producing the last-mentioned acid with nitric acid. It does not reduce an
alkaline solution of oxide of copper, until, by the agency of an acid, it has
been converted into glucose. Under these circumstances it darkens when
boiled with a solution of potassa, as a result of the production of glncic
acid. It readily undergoes fermentation, the casein and albumen in milk
being sufficient ferments. Thus at a temperature of 104° the lactine of
fresh milk is converted into alcohol and carbonic acid, by the alcoholic fer-
mentation : if the milk has been exposed to air for some time, a change is
induced in the casein, by which lactic acid is produced, as a result of the
lactic fermentation. This is seen in the spontaneous souring of milk when
long kept, the casein being separated in curds by the lactic acid, either im-
mediately or when slightly warmed. Under other conditions milk passes
through the butyric fermentation, and butyric acid is a product. Lactine is
represented as consisting of equal equivalents of carbon, hydrogen, and
oxygen ; but at 248° it loses 2 atoms of water, and at 302° it loses 3 atoms
water. According to Regnault, in combination with oxide ofjead, it loses
5 atoms of water : hence its formula in the anhydrous state is C,,n,„0,g. In
the hydrated state it corresponds to 2 of fructose or uncrystalhzable sugar,
for C,,H,,0,, are =2(C,,H,.Pj,). .,,.,• • i

Lactic Acidic fi,0„ or C«HA + HO).-This acid, which gives an acid

'714 LACTIC ACID. SALIVA. PTYALIN.

reaction to milk, is a product of the fermentation of lactine, of beet-root
juice, and otiier substances. It may be procured from the whey of sour
milii. Sour whey is evaporated to one-sixth of its original weight and
filtered : lime is added to the filtrate, to precipitate phosphoric acid, and any
excess of lime is removed by oxalic acid and subsequent filtration. The
liquid is concentrated, and the lactic acid may be dissolved out by alcohol,
and subsequently purified. It is a colorless liquid of the consistency of
syrup, miscible in all proportions with water and alcohol. It dissolves
phosphate of lime, decomposes the acetates, and coagulates albumen. It
produces no change in cold fresh milk, but the presence of a small trace of
this acid in boiling milk causes coagulation. It is supposed to be present
in the sweat and in many of the fluids of the body. Lactic acid is simply an
isomeric condition of lactine, for 4.(CQRfi^.) = C.^^H^^0^^. Lactic acid con-
tains 1 atom of water, hence its usual formula is CeH^O^jHO.

Saliva.

This is a transparent viscid liquid, secreted by the salivary glands. Its
sp. gr. is LOOS. It is generally mixed with the mucous secretions of the
mouth : these are acid, and when they predominate, give an acid reaction to
the saliva, but this secretion, in a pure state, is always alkaline (Andral).
The alkalinity probably depends upon the presence of phosphate of soda,
which with chloride of sodium and phosphate of lime, forms the bulk of the
mineral matter, found in this secretion. Saliva commonly presents itself as
a ropy, opaline liquid, depositing, on standing, threads or flakes of opaque
mucus. Under the microscope it presents mucous globules and epithelial
scales. Alcohol precipitates from the clear liquid an albuminoid principle
{ptyalin), which forms, with the mucus, from 1 to 2 per cent, of saliva. The
mucus which gives the ropiness to saliva may be separated by acetic acid.
The ptyalin precipitated by alcohol is redissolved by the addition of water.
The liquid is rendered more opaline on boiling, or by the action of nitric
acid. Tannic acid and subacetate of lead also throw down the ptyalin. The
addition of a drop of neutral persulphate of iron imparts a deep red color
to saliva, which disappears on the addition of a solution of corrosive subli-
mate. This indicates the presence of a trace of an alkaline sulphocyanide,
which is found in all healthy saliva. The solid contents of saliva vary. We
have found by experiment that the solid residue does not exceed 2 per cent.
The ptyalin and mucus, according to Lehmann, are generally below 1 per
cent. The saliva of tobacco-smokers, according to Gmelin, contains from
1'14 to 1-19 percent, of solid matter, which leaves, when burned, 0-25 of
ash. The tartar which is deposited on the teeth, and salivary calculi, con-
sists of the salts of the saliva, chiefly phosphate of lime cemented with
animal matter.

The ptyalin of saliva differs from albumen in its power, at a temperature
of 100°, of rapidly transforming starch and dextrine into glucose. The use
of the saliva is to aid in the reduction of the food to a perfectly soft state,
so that it may not only be more easily swallowed, but that when it -reaches
the stomach, it may be more completely penetrated by the gastric juice.

Serpent-poison: Echidnine (from ^x'-^voeihr^i, viperous). — The secretion
from the poison-glands of the viper and other serpents, is a clear viscid fluid,
of a slightly yellow color, and neutral in its reaction. It contains albumen,
mucus, fatty matter, a yellow coloring principle ; and among its salts, phos-
phates and chlorides. There is associated with the albumen, a peculiar
nitrogenous body resembling ptyalin and pepsine, which is called echidnine,
and which appears to be the active poisonous principle of this fluid. It3

GASTRIC JUICE. PEPSINE. PANCREATIC FLUID 115

exact constitution is unknown (Bernard). Echidnine is soluble in alcohol :
and may be separated from the other principles by the employment of this
liquid, and subsequently evaporating the solution in vacuo. The fatty matter
may be removed by ether. Echidnine thus obtained, is in colorless white
uncrystalline scales, resembling; tannic acid. It is neutral, and has neither
odor nor taste. When heated with potassa, it evolves ammonia : it is solu-
ble in water, hot and cold. The precipitate which is first produced in the
aqueous solution by alcohol, is redissolved by an excess. It is not precipi-
tated by acetate of lead. It acts upon the blood of animals like the serpent
poison. De Blainviile considers it to be analogous to ptyalin, and that the
fluid containing it is a peculiar kind of saliva. The poison-bag of the viper
seldom contains more than one grain and a half of this liquid : l-250th of a
grain is sufficient to kill a small bird. This poison produces no injurious
effects when swallowed (Dumeril).

Salamandrine. — The poison of the salamander, according to Zalesky, is a
creamy liquid strongly alkaline and possessing a bitter taste. It contains
an active principle which is precipitated by phospho-molybdic acid. He has
given to this principle the name of Salamandrine and assigns to it the follow-
ing formula, C^aHaoNgOio. {Quarterly Journal of Science, Jan. 1867.)

Gastric Juice.

This is a secretion from the mucous membrane of the stomach. When
separated from mucus by filtration, it presents itself as a colorless limpid
liquid, of an acid reaction, from the presence of lactic or hydrochloric acid,
the former being probably derived from starch or sugar, taken as food. It
contains from 96 to 98 per cent, of water, the residue consisting of organic
matter and salts, of which chloride of sodium and alkaline sulphates are the
principal. The acid mucus of the stomach is associated with a nitrogenous
principle {pepsine), to which its solvent properties are due. It has been
precipitated and extracted from the fluid portion by alcohol and acetate of
lead, but probably in an altered condition. Its constituents cannot, there-
fore, be accurately determined. Fibrin or coagulated albumen plunged into
this liquid, at the temperature of the body, swells up, and becomes gradually
disintegrated and dissolved. This property of dissolving fibrin and analo-
gous substances has been verified by experiments on animals : and in one
remarkable instance in a human being, in whose stomach there was a fistulous
opening. Pepsine loses this solvent property at a temperature above 120°.
From the researches of Dr. Robiuson on the human foetus, it appears that
no gastric juice is secreted in the stomach, until the act of respiration has
been performed. He found that the contents of the stomach before birth
consisted chiefly of the liquor amnii, mixed with an albuminous matter and
saliva. There is no proper digestion, and only an imperfect process of

chymification. ^u • * • c

Medicinal pepsine consists of the dried mucus escaped from the interior ot
the stomachs of animals (the sheep and the pig). It is sometimes incorpo-
rated with starch. The soluble pepsine consists of this substai.ce dissolveU
in a solution of chloride of sodium. It is supposed to supply additional
digestive power to those whose stomachic secretions are deficient m pepsine.

Pancreatic Fluid.

This is a colorless viscid liquid, which is secreted by the pancreas. It is

always alkaline, and is rendered frothy by agitation. It yields from 8 to 9

per cent, of a solid residue, of an albumiuoid nature When heated it .ets

into a solid like ovalbumen : but xM. Robin found that if sulphate of mag-

716 MUCUS. PUS. SYNOVIA.

nesia was first added to the liquid it gave no eoagulura when heated. Sul-
phate of magnesia added to a solution of albumen does not prevent it from
coagulating by heat. Like albumen it is precipitated from its aqueous solu-
tion by alcohol ; but an excess of water redissolves the precipitate, even after
it has been dried. When the solid residue is incinerated, the ash yields
chloride of sodium, with phosphate and carbonate of soda. The nature of
the organic principle is not well understood. It appears to resemble, in
some respects, ptyalin (the albumen of saliva) and casein, but its character-
istic property is to assimilate oily matters. It forms an emulsion with all
oils and fats, when mixed with these substances, and the mixture is heated
to about 100° — the temperature of the body. Chemically speaking, this
appears to be a process of saponification, glycerine is produced, and the
fatty acids are set free.

Mucus.

This is a viscid tenacious liquid, secreted by mucous membranes in the
healthy state. It is white, yellow, green, and sometimes almost black. It
is thrown out from the membranes of the nose, mouth, and air-passages, as
well as from the whole tract of the alimentary canal. It is sometimes opaque,
at others transparent, ropy, or gelatinous, according to the part which
secretes it. Mucus generally has an alkaline reaction. It is heavier than
water, and insoluble, but diffusible in tliis liquid : it is not coagulated by
heat. It is precipitated from its aqueous mixture by acetic acid and alcohol.
It appears to be a modified state of albumen {mucin). Under the microscope,
mucus presents nucleated globules and epithelial scales, which vary in shape
with the situation of the membrane from which they are thrown off.

Pus.

Pus is a morbid or diseased secretion from mucous membranes, ulcers, or
abscesses. It is a creamy-looking liquid, of a yellowish-white color. Its
sp. gr. is 1'030. When in a normal state it is alkaline; and, according to
Andral, it is never acid until it has been exposed to air. It contains 867
water, 7 '4 albumen, dissolved, forming a serous liquid, and 5 9 of fatty
matter, including salts. Examined microscopically, pus presents numerous
white nucleated globules, mixed with oil-globules, floating in a serous liquid.
When diffused in water, the serum dissolves, and the wliite mucous globules
subside. The aqueous solution is coagulated by heat, and possesses the
other properties of diluted albumen. By this character, and the presence of
oil-globules, pus may be distinguished from mucus. It appears to be serum
in which colorless globules of a special character are developed. If pus is
mixed with a solution of potassa, it forms a jelly resembling bronchial mucus.
The albuminous principle existing in pus is called joym. When absorbed
into the blood, pus appears to act as a powerful poison. In diseased states
of the body, it forms a vehicle for some of the most virulent animal poisons,
such as that of glanders and smallpox.

Synovia.

Synovia is a glairy yellowish-white fluid : it derives its name from ovv, cum,
(Ibv, ovum, owing to its resembling the white of an egg in its viscidity. It is
secreted by the lining membranes of joints, only in sufficient quantity to keep
the surface lubricated. It is an alkaline fluid, containing albumen and salts,
which consist chiefly of the phosphates of lime and soda.

LIQUOR AMNII. PULMONARY EXHALATION. tlT

Liquor Amnil

The organic principle in this liquid is albnmen, associated with chloride
of sodiiira and phosphate and carbonate of lime. It is remarkable that tlie
proportion of albumen varies according to the period of gestation. At the
4th month in the human female, it amounts to 1077 per cent.; at the 5th
to 7-67 ; at the 6th to 6 67 ; and at the 9th to 0-82. In the latter stage of
gestation, it contains merely traces of albumen and saline matter.

Cutaneous Secretion.

Pulmonary Exhalation. — The sudoriparous glands of the skin secrete a
liquid which is constantly escaping in the form of vapor, and is speedily
condensed on cold surfaces. Under violent exercise, or in a temperature at
or above 100°, it is deposited on the skin in a liquid form : in this state it
has an acid reaction. It is said to contain from 05 to 1-25 per cent, of a
solid albuminous substance, including saline matter, principally consisting of
the chlorides of sodium and ammonium, with alkaline phosphates. As it is
secreted from the axillae, it has a peculiar odor. It produces in drying a
yellowish stain on linen. An aqueous solution of the dried excretion is
neutral : like albumen, it is rendered opaline by boiling, and is coagulated by
nitric acid. A large quantity of chloride of sodium is continually eliminated
from the skin by this excretion, when the body is in a healthy state. If the
hands, when perfectly clean, are dipped for a short time in distilled water, it
will be found, on adding a solution of nitrate of silver to the water, that it
produces a whitish precipitate, indicative of the presence of alkaline chloride
derived from the skin. This excretion is sometimes acid, owing to the
presence of lactic and acetic acids : it easily undergoes decomposition, and
sulphur compounds with ammonia and other offensive effluvia are produced.
In these chemical changes of the condensed liquid, we have probably one of
the sources of noxious exhalations in closely inhabited dwellings.

The halitus^ or aqueous vapor which escapes in respiration, also contains
nitrogenous animal matter, which is liable to decomposition. Ammonia is
said to be thus eliminated, but we have not found this alkali present in
expired air in a healthy person. When extricated from the lungs, from the
blood, or from the skin, it is probably a result of the decomposition of nitro-
genous matter. This exhalation generally contains noxious volatile vapors,
which have been absorbed into the blood. Thus, alcohol, ether, chloro-
form, and prussic acid have been recognized by their odors, in the vapor
expired by persons who were laboring under their effects.

Humors of the Eye. — The crystalline lens, of which the refracting index
compared with that of water is 1-339 to 1336, contains 359 percent, of
the albuminoid principle globulin. The vitreous humor consists of albumen
0-18, chloride of sodium and extractive (?) 1'43, water 98 40. The aqueous
humor is water, with traces of animal matter and common salt.

Tears. "flie liquid secreted by the lachrymal glands and poured from the

eye under powerful emotion, is chiefly water, with a trace of albumen and
chloride of sodium. The Liquor Pericardii and Cerebrospinal fluid are
also of an albuminous nature.

The two principal non-albuminous fluids produced from the blood, are the
Bile and Urine— WiQ one secreted by the venous blood of the liver, the other
by the arterial blood of the kidneys.

18 BILE. CHOLIC ACID.

Bile.

This is a ropy, viscid, and saponaceous liquid of a greenish-yellow color
in man, greenish-brown in the ox, and emerald or grass-green in birds, rep-
tiles, and fish. It has an offensive odor and a bitter taste. Its sp. gr. is
1 024. It has a slightly alkaline reaction, and it mixes in all proportions
with water, giving a yellow color to this liquid, and rendering it viscid and
frothy.

The bile contaios no albumen : it is not coagulated by heat. Alcohol
renders it turbid by precipitating the mucus. Alkalies readily mix with it ;
\Snt acids, including the acetic, tlirovv down a dense precipitate, consisting of
the organic acids of the bile with mucus and coloring-matter. 100 parts of
oX'bile evaporated on a water-bath left a residue of 9 2 parts solid matters,
and this residue, when incinerated, yielded a strongly alkaline ash, weighing
1-2 grains. It contained a large proportion of soda.

The bile essentially consists of the salts of two peculiar organic acids, in
which soda is the base, namely, the chelate and chuleate of soda, of cholesterine,
and fat, as well as mucus and coloring-matter. The cholic and choleic acids
are of the nature of the resinous and fatty acids ; hence they were formerly
included under one substance, which was called biliary matter, or resin of
the bile. They give, by the presence of their salts, a saponaceous character
to the liquid : it is well known that ox-gall is a powerful detergent, and is
much used as such, in the arts and manufactures.

By digesting the dried extract of bile in alcohol, all is dissolved excepting
the mucus, the cholate and choleate of soda being soluble in this liquid.
Cholic acid is a nitrogenous acid, while choleic acid not only contains nitro-
gen, but all the sulphur which is found in the bile. The cholic acid is in
much larger proportion than the choleic.

Cholic Acid {C^Jl^^O^^^). Glycocholic, Glycocholalic Acid. — This acid
may be procured by mixing the filtered solution of bile in absolute alcohol,
with three or four parts of ether. This causes a crystalline deposit of cholate
of soda. By digesting this deposit in dilute sulphuric acid, crystals of cholic
acid are obtained. They are very soluble in alcohol, but are not readily dis-
solved by water or ether. If the coloring matter of the bile has been pre-
viously removed by animal charcoal, the crystals may be obtained quite white.
Cholic acid is what has been termed a conjugated compound of a nitroge-
nous substance, Glycocine or gelatin sugar (p. 587), and a non-nitrogenous
acid called the cholalic When cholic acid is boiled in a solution of potassa,
these compounds result, two atoms of water being required to effect the de-
composition : —

^5,H,30,2N^ 4- 2H0 = ^C,gH,,0,^ -f JC^H^N

Cholic acid. Water. Cholalic acid. Glycocine.

When cholic acid is boiled with hydrochloric or other acids,- glycocine is
set free ; but a new acid appears, namely, the choloidic (C^gHggOg). This is
an isomeric compound of the anhydrous cholalic acid ; in the hydrated state,
the latter acid contains one equivalent of water. The choloidic acid is an
uncrystalline resinous-looking substance, insoluble in water and soluble in
alcohol, like a resin. This was no doubt the resin of the bile as described
by former writers. Cholalic acid, when long boiled with hydrochloric acid,
is itself decomposed : it loses three equivalents of water, becoming Dyslysine

Choleic Acid (CgyH^gOi^SyN). Tauro-cholic. Tauro-cholalic Acid. — This
acid is procured from the choleate of soda, by adding acetate of lead to a

CHOLEIC ACID. CH0LE8TERINE. 719

solution of bile in 10 or 15 parts of water, and afterwards a little ammonia.
The resulting precipitate is gently heated ; the liquid is then poured from it,
and it is triturated and washed with a little water, and afterwards treated
with boiling alcohol, which dissolves an acid salt, leaving a bnsic salt, and
a compound of coloring-matter and oxide of lead. The alcoholic solution,
decomposed by sulphuretted hydrogen, filtered, and evapornted to dryness,
leaves a brown resinous magma, from which fatty matters (margaric acid and
cholesterine) must be separated by ether : it is then redissolved in cold weak
alcohol, filtered and evaporated to dryness : the remaining choleic acid is
slightly contaminated by soda, sulphur, and margaric acid. (Demarcay.)
It has not yet been obtained in a pure state ; but its constitution may be
inferred from the compounds into which it is resolved, when boiled with
alkalies, namely, taurine and cholalic acid. Two equivalents of water are
required to bring about this change, when choleic acid is boiled iu a solution
of potassa : —

^52H,50,4S2N^ 4- 2H0 = C,8H,oO,o ^ + C^H.OeS.N

Choleic acid. Water. Cholalic acid. Taurine.

It is remarkable that in this breaking-up of choleic acid, all the sulphur
and nitrogen should go into the taurine. Acids produce a similar change,
but they convert the cholalic into choloidic acid ; and this, by further boil-
ing, into dyslysine. It appears that when the bile is spontaneously changed
by putrefaction, taurine and cholalic acids are products of the decomposi-
tion of the cholic and choleic acids. The impure cholic and choleic acids, as
they are obtained in combination with soda, by the evaporation of bile, form
a greenish-brown resinous-looking substance, which melts like a resin, burns
with a smoky flame, and leaves a carbonaceous ash, in which soda may be
abundantly detected. It was formerly called Bilin.

Taurine (C^H-OnS^N) —This principle is obtained directly from bile, by
boiling it with hydrochloric acid until the liquor, at first turbid, becomes clear:
the choloidic acid is separated by decantation, and the liquid is evaporated
until the greater part of the chloride of sodium has been deposited. Five or
six parts of alcohol are then added to the mother-liquor, when the taurine
gradually falls in acicular crystals, which may be purified by washing with
alcohol, solution in boiling water, and recrystallization. Pure taurine forms
colorless four-sided prisms, which are inodorous and nearly tasteless, neutral,
permanent in the air, soluble in water, but insoluble in absolute alcohol.
The presence of a large amount of sulphur in taurine (and in bile) is im-
portant in reference to chemical physiology, and the functions of the liver.
A variety of other products have been described as derivatives from bile, but
they have not been adequately defined or examined. Some of them appear
to be the preceding substances in an impure state, or mixtures of them.

Cholesterine (C3,H,,0, + 2HO).— This is a solid fatty principle, found in
traces only in the bile : according to Berzelius, it does not form more than
one-10,000th part of this liquid. It cannot be readily extracted trom bile,
but it may be procured from gallstones. These consist of cholesterine
ixo-Kn, bile, and oteap, fat), or inspissated bile, with mucus and more or less
coloring matter. These stones are lighter than water, of various colors,
generally brittle, friable, with flat surfaces and angles. When heated they
melt and burn. To obtain cholesterine. the gall-stone is finely powdered,
and the powder boiled in alcohol. The liquid is filtered while hot and on
cooling, the cholesterine is deposited in pearly scales. Cholesterine has been
found in the brain, in yelk of egg, and in some morbid secretions

Pure cholesterine is seen in colorless scales, which are lighter than water,

'120 TESTS FOR BILE.

and fusible at 293^ into a colorless liquid, which does not concrete until
cooled at 240°. It is insoluble in water, and scarcely soluble in cold alco-
hol; it dissolves in boilings alcohol, ether, wood-spirit, and in oils. In close
vessels, it may be sublimed unchanged. It is not acted upon by the alkalies
even when long boiled in their solutions. In addition to the cholesterine,
there is a peculiar fatty matter in bile in combination with soda. It exists
as margarate and oleate of soda.

LithofelUc Acid (C^oHgjOy.HO). — This compound resembles cholesterine
in its properties. It is found in the form of brown concretions in the intes-
tines of certain animals in eastern countries. Tht concretions are known
under the name of bezoars.

Amhreine {Q^^YL^^O). — This is obtained from ambergris, which is a diseased
concretion from the intestines of the spermaceti whale. It is a fat-like
matter, amounting, in some specimens, to 60 per cent., and, according to
Chevreul, it resembles cholesterine. Benzoic acid has been found in some
specimens of ambergris ; in others, equally genuine, there are no traces of it.
Musk, castor, and civet, exclusive of their peculiar and odorous principles,
contain distinct species of fat.

Tests for Bile. — 1. The chelates and choleates maybe distinguished by
the peculiar action of sulphuric acid and grape-sugar upon their solutions,
moderately heated. (Pettenkofer.) If to half an ounce of diluted bile one
drop of a solution of sugar is added, and sulphuric acid is gradually dropped
into the mixture, a brownish precipitate is at first formed ; but this is dis-
solved on the addition of more acid, and the liquid acquires a rich red,
gradually passing into a purple color. It is brought out by warming and
agitating the mixture, taking care that the temperature does not exceed 120°.
The color is s'trikingly shown by heating the mixture in a white plate.

2. The coloring-matter of bile, when diluted with water, appears yellow :
it imparts a yellow stain to organic substances. Strong nitric acid produces
with it a green color, passing through shades of blue, violet, and red, under
exposure to air, the intensity of the colors depending on the quantity present.
Nitric acid dropped on bile, rendered a little alkaline, produces a red and
bluish, followed by a green color. One mode of testing for diluted bile in
liquids is dependent on this reaction. Add a small quantity of nitric acid
to the liquid and allow it to stand. The liquid slowly acquires a greenish
color if the coloring-matter of bile is present. The green color is strikingly
brought out by adding strong hydrochloric acid to the colored liquid, and
boiling the mixture for a short time. The production of a green color by
acids, merely indicates the presence of the coloring-matter — not of the bile
itself. The only true test for bile is that of Pettenkofer : the production of
a red color by the action of sulphuric acid and sugar, indicates the presence
of cholic and choleic acids. It has been noticed, in certain cases, that the
urine contained the coloring-matter only : it was turned green by nitric acid,
but as it gave no results with the sulphuric acid and sugar tests, the main
constituents of the bile were absent.

We subjoin, in a concise form, an analysis of 100 parts of the bile of the
ox, sp. gr. 1024 : —

Cholic and choleic acids, with mucus and fat . . 8-0
Mineral matter containing much soda . . . . 1-2
Water 90-8

100-0

The action of the bile in chymification in the living body does not admit
of ♦any satisfactory chemical explanation. It assists in some manner to con-

ANALYSIS OF URINE. 721

vert the chyme (digested food) into chylous matter, rendering it proper for
absorption and for being carried into the blood.

The mecomum which collects in the intestines during foetal life has been
found to consist chiefly of excreted bile with intestinal mucus.

Excrementitious Matter. — This has been supposed to consist, in great part,
of biliary matter ; but from analyses which have been made, it appears that,
except under the violent action of purgative medicines or in disease, the
amount of bile actually discharged is very small. The portion which is ex-
creted consists chiefly of the coloring and fatty matters, and does not amount
to more than one-sixteenth part of the weight of the secretion. Hence the
organic acids of the bile are probably reabsorbed into the system in an
altered condition. The proportion of water in feculent matter is about 70 to
75 per cent., and the residue is made up of unassimilated food, woody fibre,
and nitrogenous matters. Dr. Marcet has extracted from faeces a crystalline
principle which he calls Excretine.

An analysis made by Berzelius gives the following results : Water, 73 3 ;
soluble organic matters, including bile, albumen, and salts, 5-7 ; insoluble
residue of food, 7*0; insoluble matters from the intestines, with mucus, 14.
The salts are chiefly phosphates and chlorides.

The Urine.

In animals which have no urinary bladder, and in which the ureters open
into the rectum, the urine is solid. This is the case with reptiles. In ani-
mals provided with a urinary bladder, it is liquid. Liquid urine is found
throughout the whole of the class mammalia. It differs a little in the car-
nivorous, herbivorous, and omnivorous varieties. The urine of the carnivora
is a clear, transparent, light-colored liquid, possessing an acid reaction and
rarely yielding any deposit on cooling. The urine of the herbivora is a
dark-colored liquid, with a strong alkaline reaction and depositing a copious
sediment. The urine of the omnivora has characters between the two ; it is
clear, slightly acid, and only occasionally yields a deposit on cooling. The
urine of carnivora contains in combination uric acid, of the herbivora hip-
puric, and in omnivora both of these acids are found. This liquid, as
secreted by the kidneys in the human body, carries off several substances
from the blood, which may be termed excrementitious, and which would be
injurious if retained : these substances, for the most part, abound in nitrogen.
According to Dr. Thudichum, the average quantity of urine produced in a
healthy human adult in 24 hours amounts to from 49 to 56 fluidounces, at a
specific gravity of 1*020. The mean amount of solids excreted is from 850
to 1020 grains, and the water varies from 47 to 54 fluidounces. The solids
are thus apportioned by weight in grains : —

Grains.
. 154
. 23.
. 56.
. 19
. IjO

The urine when first voided is limpid, and of various tints of yellow,
inclining in health to a pale straw-color. Its taste is saline and bitterish.
Its odor is peculiar, urinous. Its sp. gr. ranges from 1*015 to 1'030. It is
usually about 1*020; but in some forms of disease it is found to be much
higher, and in others, mach lower. Its solid contents may in general be
estimated at between 5 and 8 per cent. Recent healthy urine almost always
has more or less of an acid reaction. According to Andral, the urine is acid
46

Grains.

Urea

Uric acid .

Creatine .

Creatinine

Hippuric acid .

. 463 to 617
7.5
4-5
7-
7-5

Chloride of sodium
Sulphuric acid
Phosphoric acid
Earthy phosphates
Ammonia

Y22 ANALYSIS OP URINE. EXTRACTION OP UREA.

in health and disease ; and is only alkaline when the mucous membrane
secretes pus. After it has stood in an open vessel for a few hours, the
acidity gradually becomes less apparent, and it generally deposits a little
mucus, containing traces of acid urate of ammonia. It is extremely prone
to complicated changes ; and in warm weather it begins in the course of a
few hours to putrefy and to acquire new properties. It becomes alkaline,
acquires a disagreeable odor, and lets fall a whitish sediment, consisting
chiefly of ammonio-magnesian phosphate, and phosphate of lime ; it becomes
afterwards ammoniacal, and is found to hold carbonate of ammonia in solu-
tion. Similar changes may be effected by continued boiling : they are chiefly
referable to the decomposition of the characteristic ingredient of the urine,
namely, urea, a substance which is easily resolved during putrefaction into
carbonate of ammonia.

The principal constituents of healthy urine are urea, uric add, fixed salts ^
coloring -matter, organic matters, and mucus. As the urine varies in sp. gr.,
so do these substances vary in quantity ; and in the same individual, at dif-
ferent hours of the day, the urine presents very different proportions of solid
contents. The late Dr. Bird obtained the following results, in examining
1000 parts of the urine of a healthy person after ten hours' fasting {urina
sanguinis), and the urine after dinner in the evening {urina cihi) : —

Analysis of urine. After fasting. After eating.

Specific gravity 1-016 1-030

Water 962-72 930-10

Solids 37-43 69-90

Urea 14-30 24-40

Uric acid 0-23 1-33

Fixed salts, chiefly chlorides, sulphates,) ^.-.q q.qq

and phosphates . . . . )

Organic matter, kreatine, kreatinine, color- 1 17. 80 34-27

ing matter, and volatile salts . . j

The acidity of fresh healthy urine has been variously ascribed to the pre-
sence of uric acid, of hippuric acid, of lactic acid, and superphosphates. It
is most probable that the acid reaction is due to the presence of the acid
phosphates of soda and lime. Robin and Yerdeil have found both the
neutral and acid phosphate of soda in urine. It is well known that the urine
of herbivora contains the carbonates in large, and the phosphates in small
proportion. The vegetable salts in the food of herbivora have chiefly for
their acids, the tartaric, malic, and oxalic, and these are easily transformed
into carbonates which are excreted with the urine. In carnivora, the food
is rich in phosphates, and contains but a small proportion of salts capable of
being turned into carbonates ; hence it imparts to the urine more phosphorus
than carbonates. It is a remarkable fact, that while the acidity of the urine
chiefly depends on acid phosphates, the alkalinity of the blood depends on
the presence of basic phosphates, or, as it has been shown by Liebig, these
may be replaced by alkaline carbonates.

The properties and composition of the salts found in the urine, have
already been described in other parts of the work. The chemical properties
of urea, and of uric acid, bodies which peculiarly characterize urine, remain
to be noticed.

Urea {Q^fi^^. — This is the principle which confers upon the urine
its chief peculiarities. It may be procured by the following processes :
(1.) Evaporate urine by the gentle heat of a water-bath (never exceeding
200^) to the consistence of a thin syrup, filter, and add to the filtrate an

EXTRACTION OF UREA PROPERTIES. 723

equal volume of colorless nitric acid (sp. gr. 1 35), which should be perfectly
free from nitrous acid. A brisk effervescence ensues, and there is at the
same time a copious deposition of crystallized and nearly pure nitrate of
urea, this compound not being dissolved by an excess of strong nitric acid.
If the evaporated urine is allowed to cool before the acid is added, the crys-
tals are very brown. The nitrate of urea is separated from the acid liquid,
dissolved in a small quantity of water, and treated with carbonate of baryta
or of potassa, until rendered neutral : on evaporating the clear solution,
crystals of nitrate of baryta (or nitrate of potassa) are first obtained, and
then those of urea. The latter are purified by redissolving them in alcohol,
which takes up the urea, and yields it in crystals, when evaporated. If the
urea is colored, a little permanganate of potassa may be added to its aqueous
solution, which has no action on urea, but destroys the coloring matter.
Any color communicated by an excess of permanganate, is instantly de-
stroyed by a few drops of alcohol, and the filtrate then yields colorless crys-
tals of urea. (2.) The concentrated urine may be saturated by oxalic acid,
which yields crystals of oxalate of urea ; these, dissolved in water, decolored
by animal charcoal, and decomposed by digestion with carbonate of lime,
yield a solution from which colorless crystals of urea may be obtained. (3.)
From cyanate of ammonia. 28 parts of dried ferrocyanide of potassium,
and 14 parts of binoxide of manganese, are mixed in powder, and calcined
upon an iron plate, heated to dull redness ; the mixture takes fire, but is
gradually extinguished, and must be stirred, while cooling, to prevent agglu-
tination. The cold mass is then powdered and digested in cold water, which
takes up the cyanate of potassa; this solution is filtered off and set aside;
the remaining powder is then washed with a second portion of cold water
and again filtered, and in this filtrate, 205 parts of sulphate of ammonia are
dissolved, and the solution. added to the first filtered solution of the cyanate.
A large quantity of sulphate of potassa is deposited, which is strained off,
and the filtered liquor, now containing, with some sulphate of potassa, all
the cyanate of ammonia, is evaporated to dryness, during which process the
cyanate of ammonia is transformed into urea (p. 18). The dry mass is di-
gested in alcohol, which dissolves only the urea, and yields it pure, on
evaporation. (Liebig, Annalen der Pharm., xxxiii. 108.) In all of these
processes the urine is first concentrated by evaporation at a comparatively
high temperature, and this causes an unavoidable loss of urea, which is easily
decomposed by heat. In order to prevent this loss, and to procure urea in
the purest possible state, Dr. Thudichum has suggested another method
which he has found to yield a better result. It is as follows : A quantity
of urine is mixed with one-half of its volume of a solution of baryta (consist-
ing of two volumes of saturated solution of baryta or baryta water and one
volume of a saturated solution of nitrate of baryta), or a quantity of that
solution sufiBeieut to precipitate the sulphuric and phosphoric acids. The
fluid is then filtered from the precipitate, neutralized with nitric acid, and
evaporated to dryness in a water-bath. The residue is extracted with alco-
hol. The alcoholic extract is again evaporated and exhausted a second time
with absolute alcohol. The last solution contains the urea very pure, so
that it crystallizes out in colorless needles.

Urea crystallizes in flattened four-sided prisms ; they generally resemble
nitre in appearance, and have a similar cooling saline taste: they are ino-
dorous. They are soluble in their own weight of cold water, and in every
proportion in hot water; they dissolve in 45 of cold, and in 2 parts of
boiling alcohol ; but they are insoluble in ether, and in an excess of strong
nitric acid. Their solution is neither acid nor alkaline; but urea belongs
to the class of neutral organic bases, and forms crystallizable compounds

124 NITRATE AND OXALATE OF "UREA.

with several of the acids. Pure urea is permanent in the air ; at 250° it
fuses into a colorless liquid ; at a higher temperature it yields ammonia,
cj'anate of ammonia, and dry solid cyanuric acid. When heated in her-
metically sealed vessels to between 428° and 464°, it is entirely converted
into carbonate of ammonia. Alkalies do not evolve ammonia by their action
upon urea, unless aided by heat; but when fused with them it is resolved
into carbonic acid and ammonia. An aqueous solution of urea remains long
without change ; but the addition of proteiniferous substances resolves it
more rapidly into carbonate of ammonia. In this case 1 atom of urea, and
2 atoms of water, yield 2 atoms of carbonate of ammonia : C3H40|N2, + 2HO,
=2(NH3,C02). Urea produces no precipitate in a solution of nitrate of
silver; but when nitrate of silver and a little potassa are added to a cold
solution of urea, a compound of oxide of silver with urea, is thrown down.
If the mixed solution of urea and silver is evaporated at about 120°,
nitrate of ammonia and cyanate of silver are the results ; an atom of urea
containing the elements of an atom of cyanic acid, an atom of ammonia, and
an atom of water : C3H,02N2=NC20,+NH3. + HO.

Nitrate of Urea (CaH^O^N^.NO^HO). — This is prepared by the process
above described. It crystallizes in rhombic plates. The crystals are soluble
in 8 parts of cold water. Heated above 212°, nitrate of urea is decomposed,
evolving carbonic acid and nitrogen. At 284° it is resolved, according to
Pelouze, into carbonic acid and nitrous oxide, in the proportion of 2 volumes
to 1, and the residue is nitrate of ammonia; at a higher temperature, water,
nitrous oxide, carbonic acid, and ammonia, are the products. Nitrous acid
immediately decomposes urea ; equal volumes of carbonic acid and nitrogen
are evolved, and nitrate of ammonia is formed: (C3H^02N3+2N04=2C03
-f 2N + NH,0,N05). (MiLLON, Ann. Ch. et Ph., Seme ser. viii. 233.)

Oxalate of Urea {Cfifi^l^^^-Cfi^-^YL0).—'Yh\^^2At is thrown down in
short flattened prismatic crystals, on mixing strong aqueous solutions of
oxalic acid and urea : it is less soluble than the nitrate. The production of
the nitrate and oxalate can be well observed under the microscope with an
inch power, on adding the respective acids to concentrated urine. Sal-am-
moniac crystallizes from an aqueous solution containing a little urea, in
cubes instead of octahedra ; while common salt, under the same circumstances,
crystallizes in octahedra instead of cubes : these crystals contain only a trace
of urea.

The proportion of urea contained in urine is subject to great variation.
Sometimes it can scarcely be detected, ovping to the large amount of other
organic matters which are present (diabetes). It is deficient in hysteria.
It is generally in larger quantity in the urine of males than in that of females,
and is more abundant in youth than in old age. It is the great medium for
the elimination of nitrogen, of which it contains 28 per cent. It is found
in the healthy blood in small quantity, so that it appears to be simply elimi-
nated, and not secreted by the kidneys. When these organs are extensively
diseased, the urea accumulates in the blood, and is found in large quantity
in this and other fluids of the body. It then produces a form of narcotic
poisoning, known under the name of urcemia.

In a state of health, human urine does not contain sufficient urea to be
indicated by a deposit of crystals, on the addition of its volume of nitric
acid ; but if fresh urine is gently evaporated in a watch-glass to about one-
third of its bulk, and an equal volume of strong colorless nitric acid is then
added, there should be, after a time, a deposit of crystallized nitrate of urea
in rhombic plates.

Uric Acid (C,oH,06N,=C,oH20,N,-f 2H0). Lithic Acid. Urylic Acid.
— This acid forms but a small proportion of the solid contents of urine. It

URIC ACID. "[25

is not in a free state, but combined with soda or other bases forming urates,
hence to prove its presence, it is necessary to add to a large quantity of
urine (ten or twelve ounces) a few drops of hydrochloric acid, and allow the
acid liquid to stand. In about 24 hours small crystals of uric acid, generally
colored by a dark red coloring-matter, will be found deposited and adhering
to the sides of the glass vessel. The quantity of this acid in healthy urine,
in the combined state, is too small to allow the chemist to procure the acid
readily from this liquid. Free uric acid is considered to be only an acci-
dental or pathological constituent of the urine of man and of that of the car-
nivora and omnivora. It has been found in the urine in gout, in articular
rheumatism, and in some inflammatory diseases. It constitutes the most
common variety of urinary calculus (hence it is called lithic acid), and it is
probably slowly separated from the urates in this case, by lactic acid. Uric
gravel is another morbid state in which the acid is found in the bladder. It
is not present in the urine of herbivorous animals: but it exists in large
quantity in a solid and combined state in the urine of serpents, of birds of
prey, and of those which feed upon fish and animal matter. The substance
called Guano, which is used as a manure, is the decomposed excrement of
aquatic birds ; it contains a large proportion of uric acid. The excrement
of birds generally consists of a white chalky mass which is a compound of
uric acid and lime. The excrement of the boa-constrictor and other large
snakes is chiefly composed of urate of ammonia ; it is voided in the form of
a gray semi-fluid mass, which, on drying, forms a whitish, friable, chalky-
looking substance.

In order to procure pure uric acid, the dry-excrement of the boa-constrictor
should be reduced to powder and boiled, first in alcohol, and then in water,
to remove all matters soluble in these liquids ; it may then be treated with
dilute hydrochloric acid to remove phosphate of lime, washed, and digested
in a hot solution of caustic potassa. The liquid is then poured off or filtered,
more of the solution of potassa is added to it, and it is concentrated by evapo-
ration, when the urate of potassa, which is not soluble in the strong alkaline
liquid, separates, while the coloring matters are retained. On cooling, the
whole concretes into a pasty mass, which must be pressed out and washed
with cold water. The urate of potassa which remains, is then dissolved in
boiling water, and the hot solution poured into hydrochloric acid, when a
white gelatinous precipitate falls, which soon assumes a crystalline aspect,
and when washed and dried, is pure uric acid. Uric acid may be also ob-
tained by boiling the excrement of the snake in 30 or 40 parts of a weak
solution of caustic potassa, until the odor of ammonia is no longer perceived ;
the solution is then filtered, and hydrochloric acid is added.

Uric acid is a soft white crystalline powder ; it is insipid and inodorous ;
it slightly reddens moistened litmus-paper. It is almost insoluble in cold
water, requiring 10,000 parts to dissolve it, but soluble in between 1800 to
1900 parts of boiling water ; it is insoluble in alcohol and in ether. Sul-
phuric acid dissolves it, but it is again precipitated as a hydrate on adding,
water. It is dissolved by potassa and soda, but not by their carbonates.
When dried at 212°, this acid retains two atoms of water, being bibasic ;
C oH 0 N -f 2H0. When heated on platinum foil, the acid is decomposed,
leaving^only a slight residue of carbon. If heated in a close tube, it evolves,
among other products, ammonia.

Owing to the small quantity present in urine, it is not easily detectea m
this liquid. It may, however, be discovered by the use of the microscope.
As it exists in the urine in a combined state, an acid must be employed for
its separation. Two or three ounces of urine should be warmed and poured
into a conical test-glass ; a few drops of hydrochloric acid are added, and

T26 TESTS FOR THE ACID.

the liquid stirred. After some hours, either a dark-colored pellicle forms on
the surface, or small reddish-brown crystals are deposited. These, when
examined microscopically, have a rhombic or fascicular form. They are com-
bined with much coloring matter. Uric acid has been found, as urate of
soda, in the blood of gouty persons. It is observed that the proportion of
uric acid is diminished in the urine, immediately before a paroxysm of gout.
Tests for the Acid — In addition to the chemical characters above men-
tioned, uric acid may be identified by the peculiar action of nitric acid.
The powdered acid dissolves with effervescence in nitric acid. The solution
is gently evaporated at a low temperature, and when the excess of nitric
acid has been expelled, and the yellowish-colored residue has been exposed
to the vapor of ammonia, the rich purple color of purpurate of ammonia, or
murexide, appears. {See p. 678.)

Urates. — All the urates are sparingly soluble in cold water, and they are
mostly white insipid powders. By dry distillation they yield carbonate and
hydrocyanate of ammonia, cyanic acid, and an erapyreumatic oil ; and those
with alkaline bases leave cyanides. They are more soluble in boiling
water. Acid Urate of Ammonia (NH^O.HO.CjoH^O^Nj. — When uric
acid is digested in a solution of caustic ammonia, it becomes warm, and in-
creases in bulk, forming, when dried, a white, amorphous salt, scarcely solu-
ble in cold water. It may be obtained in minute acicular crystals, by adding
excess of ammonia to a boiling mixture of uric acid and water, and when
dried at 100*^, has the above composition. It requires 1608 parts of water
at 60° for its solution. When long boiled in water, it is decomposed, ammo-
nia is evolved, and the pure acid remains. This compound forms one variety
of urinary calculus (stone), and is frequently deposited from urine as a red-
dish-brown sediment, soluble in the hot liquid, but precipitated on cooling.
Urate of Soda. — The neutral urate of soda exists in the urine of carnivora ;
it exists also in the urine of herbivora, when they are deprived of food. It
has been found in blood in gout, and is often deposited mixed with urates of
lime and ammonia, in persons laboring under fever. It constitutes what are
called chalk-stones, which are deposited in the joints of the fingers in gouty
persons. Its alleged production from neutral nitrogeneous matters by a
species of combustion, is not consistent with the fact that it is not usually
found in the urine of herbivora, although there is much nitrogen in their
vegetable food.

The action of nitric acid upon uric acid is attended with the production
of some remarkable compounds. When 1 part of uric acid is added by
small portions at a time to 2 parts of nitric acid (sp. gr. 1-41 to 1*45), care
being taken to prevent the heating of the mixture, nitrogen and carbonic
acid (in equal volumes) are evolved, and the mixture becomes a crystalline
magma, from the formation of alloxan (CgH^OioNg). Nitrate of urea is pro-
bably first formed, which is decomposed by the evolved hyponitrous acid,
and nitrate of ammonia, carbonic acid, and nitrogen are produced. If the
nitric acid, instead of being concentrated, is very dilute, the uric acid dis-
solves with effervescence, and alloxantiiie (CgHgOjoNJ, nitrate of ammonia,
and nitrate of urea, are found in solution. If uric acid is dissolved in
moderately strong nitric acid, and the liquid is evaporated until gas is no
longer evolved, the alloxan originally produced is decomposed ; and crystals
of par abanic acid (CfiHgOfiNa) are formed. When the solution of parabanic
acid is supersaturated with ammonia and evaporated, it combines with the
elements of water to form oxaluric acid, =CgH40gNg. If the nitric solution
of parabanic acid, instead of being saturated with ammonia, is further eva-
porated, it continues to evolve carbonic acid, and ultimately yields crystals
of nitrate of urea. When a solution of uric acid in very dilute nitric acid,

HIPPURIO ACID. COLORING-MATTER. 727

is evaporated until the alloxantine which it contains crystallizes, and the
residue is' saturated with ammonia, the liquid acquires a purple color, and
deposits murexide, together with a red powder, which is uramile (C„H,0«NJ.
(p. 678.) V 8 5 6 a;

Hippuric Add. Uro-benzoic Acid (C,^Y{fig'N).—The properties of this
acid and the method of procuring it have been elsewhere described (p. 655).
It appears to have been for a long time mistaken for benzoic acid in the
urine of the cow, horse, and other herbivora. It has been observed that in
a horse at rest in a stable hippuric acid is produced, but in a horse after
violent exercise it is replaced by benzoic acid. It will be only necessary
here to describe the method of detecting the acid in urine. A few ounces
should be evaporated to a small bulk and an equal bulk of hydrochloric acid
then added. A mixture of hippuric and uric acids slowly falls mixed with
coloring-matter. The supernatant liquid being decanted, the deposit should
be boiled in alcohol, in which hippuric acid alone is soluble. As it is ob-
tained from the alcoholic solution, it presents itself in four-sided prisms with
pointed terminations.

The Coloring-matter of the urine has not been separated in a distinct
form. Heller has called it Uroxanthin. The late Dr. Bird suggested a test
for this principle. A small quantity of urine is heated in a tube to the
boiling-point, and a few drops of hydrochloric acid are added. The color
produced varies from a pale lilac to a deep crimson, according to the amount
of coloring-matter present. A substance analogous to indigo has been
occasionally found in this liquid : we have in one instance seen the urine of
a deep purple-black color. In hysteria the coloring-matter is frequently in
very small proportion.

Mucus. — This presents itself in healthy urine as a faint cloud subsiding
after some hours to the bottom of the vessel. It may be separated by
filtration.

Kreatine and Kreatinine. — Kreatine, which has been already described
with fibrin as a constituent of flesh, is found in urine and also in the blood.
It appears to be formed in the muscles, passes into the blood, and is thence
thrown out through the kidneys. Kreatinine is also found in urine, and has
been detected in the blood, but it has not been discovered in the muscles.
(Robin and Verdeil.) For the detection of these principles in the urine the
following process may be adopted : Evaporate an ounce of urine and allow
it to cool. Decant the fluid extract from the deposited salts. Dissolve in
the extract, a portion of chloride of zinc about the size of a pea, and set the
whole aside for twenty-four hours. When the residue is examined by the
microscope, radiating crystals like minute zeolites, will be observed, con-
sisting of a triple compound of zinc and chlorine with kreatine and kreati-
nine. Their crystalline form is more distinctly seen, by dissolving them in a
drop of water on a glass slide over a spirit-lamp, and allowing the solution
to evaporate spontaneously.

In reference to the fixed salts, it may be observed that ammonia or lime-
water added to urine, produces a white precipitate, by neutralizing the
excess of acid and throwing down the earthy phosphates. A salt ot baryta
(with nitric acid) gives a dense precipitate indicative of the presence ot
much sulphuric acid: nitrate of silver (with nitric acid) throws down an
abundance of chloride (chlonne), and oxalate of ammonia precipitates Ume

728 SALTS. ABNORMAL INGREDIENTS. URINARY CALCULI.

from the lime-salts dissolved in the liquid. Under the microscope, this
deposit, if slowly formed, appears in the shape of octahedral crystals with a
square base {oxalate of lime). The ash of urine indicates by the usual tests,
the presence not only of lime, but of soda, which exists chiefly as chloride of
sodium. The presence of magnesia in urine is indicated by the stellated
crystals of phosphate of ammonia and magnesia, which are seen under the
microscope, on adding ammonia to a few drops of urine on a microscopic
slide. By evaporating the urine (after fasting) chloride of sodium may be
seen in the form of crosses and daggers mixed with plumose crystals of phos-
phate of soda.

The abnormal ingredients in the urine are very numerous. Albumen may
be detected by the turbidness or coagulum produced on heating the liquid,
as well as by the action of nitric acid. Albuminous urine is frothy and of
low specific gravity. Sugar may be detected by evaporating the urine to a
syrup, digesting the residue in boiling alcohol, and testing the alcoholic
extract by the copper test. (See p. 571.) Pus may be detected in the sedi-
ment, by the presence of oil-globules, also of albumen in the urine, and by
the production of a jelly-like mass, on adding to the sediment an equal
volume of solution of potassa. Blood may be distinguished by a smoky
color, if in small quantity, or by a reddish color, if in large proportion. The
urine also contains the albumen of serum. The coloring matter of blood
may be readily detected in urine, either by the guaiacum test or by spectral
analysis. When tincture of guaiacum is added to urine not containing blood,
the resin is simply precipitated of a dingy white, and on the addition of per-
oxide of hydrogen there is no alteration of color. If, however, blood is
present, even in so small a quantity as to be barely perceptible by a smoky or
pale red color, the addition of tincture of guaiacum and peroxide of hydrogen
to the urine produces a beautiful blue color. When a portion of the urine,
containing blood in small quantity, is spectrally examined by the microscope,
the black bands in the yellow and green rays are also perceptible up to an
extreme state of dilution. They are more faint as the red color of blood is
more diluted by the urine. The guaiacum test, however, indicated the pre-
sence of the red coloring-matter when no dark bands could be detected by
the spectroscope.

Urinary Calculi. — These usually include — 1. Uric acid ; 2. Urate of am-
monia ; 3. Oxalate of lime ; 4. Phosphate of lime, and 5. Phosphate of
ammonia and magnesia. The first two may be distinguished by the action
of nitric acid. {See p. 726.) For the method of detecting insoluble phos-
phates, see p. 243 : and for the analysis of oxalate of lime, p. 645.

WEIGHTS AND MEASURES. ^29

APPENDIX

WEIGHTS AND MEASURES.

The two systems of weights called Troy and Avoirdupois have no coramon
integer except the grain. Although the names, pound, ounce, and drachm
are common to both systems, they denote different quantities in each. The
English Troy pound is subdivided into twelve ounces, and each ounce is
equal to 480 grains. The subdivisions of the Troy ounce, called Apothe-
caries^ weight, are into 8 drachms, each drachm into 3 scruples, and each
scruple into 20 grains. The Troy ounce is also divided into 20 penny-
weights, of 24 grains each. For philosophical purposes, ambiguity is most
easily avoided by employing the grain as integer : and the Laboratory should
be provided with good sets of weights, from 1000 grains downwards ; the
grain should be decimally subdivided into tenths, hundredths, and thou-
sandths.

apothecaries' weight.

Pound.

Ounces.

Drachms.

Scruples.

Grains.

French grammes.

1

= 12

= 96

= 288

=

5760

=5

372-96

1

= 8

= 24

=

480

=

31-08

1

= 3

—

60

3-885

1

=

20

1

=

1-295
0-0647

AVOIRDUPOIS WEIGHT.
Pound. Ounces. Drachms. Grains. French grammes.

1 =16 =256 = 7000 = 458-25

1 = 16 = 437-5 = 28-328

1 = 27-343 = 1-77

The avordupois ounce and pound being the weights practically used in the
sale of medicines and generally in commercial transactions, were substituted
for Apothecaries' or Troy weight in the British Pharmacopoeia of 1864, and
they are still retained in the edition of 1867. The grain is a convenient
unit, and it is a weight which is well understood in this country and well
adapted for estimating the weight of medicines. There is no weight between
the grain and the avoirdupois ounce of 437 5 grains, which it will be per-
ceived is not a multiple of the grain. To remedy this inconvenience the
scruple and the drachm, representing respectively twenty and sixty grains,
are retained for the purpose of prescribing. In the measurement of liquids,
the Imperial measure is used for the higher denominations, and the fluidounce
and its subdivisions into fluidrachms and minims for the lower denominations
of volume.

Measures of Volume. — Weights are connected with measures by the sub-
divisions of the Imperial gallon. The weight of an Imperial gallon of
absolutely pure water, at 30 inches pressure, and 62°, is tea Avoirdupois

ISO FRENCH METRICAL SYSTEM.

pounds, or 70,000 grains. It is equal to 277 2T4 cubic inches. It is one-
fifth more than the old Wine gallon, i. e., 30 Imperial are = 36 Wine gallons.
A cubic foot of water represents 6*23 Imperial gallons.

IMPERIAL MEASURE.

Gallon.

Pints.

Fluidounces. Fluidrachms.

Minims.

1 =

8

= 160 =

1280

= 76800

1

= 20 =

160

.= 9600

1 =

8

1

= 480
= 60

RKT.ATION OF MEASURES TO WEIGHTS.

Weight of water at 62°.

Measure.

Cubic inches.

Grains.

1 Gallon

= 277-274

sss

70,000

1 Quart

= 69-318

=

17,500

1 Pint

= 34-659

^s

8,750

16 Fluidounces

= 27-727

z=s

7,000

1 Fluidounce

= 1-732

=:

437-5

1 Fluidrachm

= 0-216

=

54-7

1 Minim

= 0*0336

=

0-91

The weight of owe cubic inch of distilled water at 62° is 252*458 grains.
The Troy ounce of distilled water, which contains 480 grains, is equal to
1'8047 cubic inches. The wine-pint corresponds to 28-875, and the Imperial
pint to 84-65 cubic inches at 60°. 100 cubic inches are equal to 57 fluid-
ounces.

The Metrical System. — The French metre is equal to 39-370788 English
inches. The metre is in France the integer of the measure of length, and
from it all measures of surface, capacity, and weight, are derived. The
integer of the measure of capacity is the litre, which is the cubed decimetre,
and is equal to 35'275 fluidounces, or 1-763 Imperial pints. The integer of
the measure of weight, is the gramme, = 15 434 English grains. It is
exactly equal to the weight of a cubic centimetre of water weighed in vacuo,
at its maximum density (39°-38). The cubic centimetre is employed by
French chemists in all measurements of gases in place of our cubic inch. It
is equal to 0*061 of a cubic inch. It corresponds to about 17 minims, and
weighs 1 gramme or 15 4 grains. Two fluidounces by measure are equal to
58 cubic centimetres. The weight of the cubic centimetre of water is to
the cubic inch of water as 15 434 to 252*458 : hence there are 16 34 cubic
centimetres to an English cubic inch.

This rule is sufficiently correct for practical purposes. It is to be observed,
however, that the French take the weight of the cubic centimetre of water at
39*38 in vacuo: the English take the weight of the cubic inch (252-458
grains) at 62° in air. Assuming the sp. gr. of water at 32°, to be 1 000000,
the sp. gr. at 39°*38 is to the sp. gr. at 62°, as 1-000099 to 0999000. The
French measures increase and decrease in decimal proportions. For the
increase, a prefix is used, derived from the Greek deca, hecto, kilo, and myria;
the integer, whether metre, litre, or gramme, being multiplied by 10, 100,
1000, and 10,000 respectively. To indicate the decrease, the prefixes deci,
centi, and milii, derived from the Latin, are employed. In this case the
integer is suppovsed to be divided by 10, 100, or 1000.

Various plans have been devised for converting the French weights and
measures into their English equivalents. The following Tables will be found
useful for this purpose : —

METRICAL EQUIVALENTS.

731

MEASURES OF LENGTH.

MEA8DBE8 OF VOLUME.

English inches.

Cubic Inches.

Millimetre . . = '03937

Millilitre .

= 'OeiOS

Centimetre . = -39371

Centilitre .

= -61028

Decimetre . . = 3-937(t8

Decilitre .

= 6-1028

MHre . . . = 39-37079

Litre . . .

= 61-028

Decamfetre . . = 393-70788

Decalitre .

. = 610-28

Hectometre . = 3937*0788

Hectolitre .

= 6102-8

Kilometre . . = 39370-788

Kilolitre

= 61028-

Mjriametre . = 393707-88

Myrialitre .

= 610280-

MEASURES OP WEIGHT.

English grains.

Milligramme .

. =

•0154

Centigramme .

. =

•1543

Decigramme .

—

1-5434

Gramme

. =

15-434

• Decagramme .

=s

154-34

Hectogramme

. =

1543-4

Kilogramme ....,. = 15434-
Myriagramme = 154340-

A kilogramme is equal to 22046 pounds Avoirdupois, and 1000 kilo-
grammes are equal to an English ton. The quintal, or 50 kilogrammes, is
equal to an English cwt. With respect to the equivalents of French and
English weights and measures, some slight differences will be found among
English writers. These arise from the calculations being based on the em-
ployment of a larger or smaller number of decimal figures.

The gramme is the French unit of weight, and is much too high for many
purposes, as it represents 15"43 grains of our ordinary" weight. A deci-
gramme corresponds to about one grain and a half of our weight. There is
no weight corresponding to our well-known and highly convenient unit of
one grain. It is rather less than seven centigrammes,* being represented by
the decimal 0-0648 grammes. The Troy or Apothecaries' ounce corresponds
to 31 08 grammes, while the Avoirdupois ounce is represented by 28 328
grammes. A cubic centimetre is the unit of French liquid measure, and,
compared with our cubic inch, is as much too small as the gramme is too
large for convenient use. It corresponds to nearly 17 minims, and it weighs
one gramme, or 15" 4 grains. In reference to these metrical weights, what-
ever trouble they may save to advanced chemists in calculating the results
of their analyses, the introduction of tliem into pharmacy would have led to
serious if not fatal mistakes in the preparation and dispensing of medicines.
The habits of a profession or of the population of a country cannot be sud-
denly changed in this respect, nor can such a change as the metrical system
would effect be only partial. It must include weights, measures, depths,
heights, distances, and square as well as long measure. However the scien-
tific physician may admire, in the abstract, the rigorous simplicity of the
gramme, the metre, and the litre, he would not venture to prescribe medi-
cines in centigrammes or cubic centimetres; nor would a scientific chemist,
wishing to make his processes intelligible in the arts and manufactures, adopt
the metrical system of weights and measures without giving side by side a
translation of quantities for the information of his English readers. The
constructors of the British pharmacopoeia may well have shrunk from the
responsibility of imposing on the profession a system of weights and measures
which not one dispenser in five hundred would understand or know hov7
to use.

As, however, an attempt has been made to force this system on students
of chemistry by its adoption in some English works on the science, it will be
well to insert here the tables showing the relation of some of the common
weights to those of the metrical system.

732

BAROMETRICAL EQUIVALENTS.

RELATIONS OF THE WEIGHTS OF THE BRITISH PHARMACOPCEIA TO THE METRICAL WEIGHTS.

1 Pound
1 Ounce
1 Grain

= 543*9525 grammes.
= 28-3495 "
= 0-0648 "

1 Gallon .
1 Pint

1 Fluidounce
1 Fluidrachm
1 Minim .

MEASURES OP CAPACITY.

= 4-543487 litres. .

= 0-567936 " or 567-936 cubic centimetres.

= 0-028396 " " 28-396 " "

== 0-003549 " " 3-549 " "

= 0-000059 " " 0-059 " "

Surfaces and Capacities. — Surface of a Sphere : diameter squared x
3"141593. Capacity of a Sphere: diameter cubed X 0-5236. Area of a
Circle: diameter squared x 0'785938. Area of Rectangle, Square, Rhom-
hus, and Rhomboid : base X by the height. Capacity of the Prisfh or Cylin-
der (rule for calculating the capacities of cylindrical vessels used for Gases) :
area of the base x by height.

Barometric Scale in Millimetres and Inches.

In foreign scientific works, and in some recent English works on chemistry,
the barometrical pressure, whether for meteorological or other scientific pur-
poses, is represented in millimetres. The subjoined Table gives the corre-
sponding equivalents in English inches : the pressure to which gases are
submitted may be thus easily ascertained without resorting to calculation :
762 mm = 30 incljes mean pressure.

Mm.

In.

Mm.

In.

Mm.

In.

700

=

27-560

7.30

=

28-741

760

=

29-922

701

r=

27-599

731

^

28-780

761

=

29-961

702

=

27-638

732

=

28-819

*762

=

*30-000

703

=r

27-678

733

=

28-859

763

=

30-040

704

=

27-717

734

=

28-898

764

=r

30-079

705

=

27-756

735

=3

28-938

765

=

30-119

706

=

27-796

736

=s

28-977

766

=

30-158

707

=

27-835

737

=:

29-016

767

=

30-197

708

=

27-876

738

=

29-056

768

=

30-237

709

=

27-914

739

=

29-095

769

=

30-276

710

27-953

740

_.

29-134

770

^

30-315

711

=

27-992

741

=

29-174

771

=

30-355

712

=

28-032

742

=

29-213

772

=

30-384

713

=

28-071

743

=

29-252

773

=

30-434

714

=

28-111

744

=

29-292

774

=:

30-473

715

=

28-150

745

=

29-331

775

=

30-512

716

=

28-189

746

=

29-371

776

=

30-552

717

=

28-229

747

=

29-410

777

:^

30-591

718

s=

28-268

748

=

29-449

778

=:

30-631

719

=

28-308

749

=

29-489

779

=

30-670

720

_

28-347

750

__

29-528

780

30-709

721

=

28-386

751

=

29-567

781

=

30-749

722

==

28-426

752

=

29-607

782

=

30-788

723

r^

28-465

753

=

29-646

783

=

30-827

724

=

28-504

754

s:=

29-685

784

^=.

30-867

725

=

28-543

755

=

29-725

785

=:

30-906

726

=

28-583

756

s=:

29-764

786

=

30-945

727

=s

28-622

757

s=

29-804

787

=

30-985

728

=:

28-661

758

=

29-843

788

=

31-024

729

=

28-701

759

=

29-882

789

=

31-063

THERMOMETRICAL EQUIVALENTS,

•733

THERMOMETRICAL EQUIVALENTS.

Rules for converting Degrees of Fahrenheit's, Centigrade, and Reaumur's
Thermometers into each other.

The space between the two fixed points of temperature— namely, the
freezing and boiling of water, is divided by Fahrenheit into 180°, by Centi-
grade into 100°, and by Reaumur into 80°:

W = 9. »2"o° =5. |g = 4 : therefore 9 F. represents 5 C. and 4 R.

5 X 1-8 = 9

1-8:

} therefore ^[i^'.^Z^'.

The zero of C. and of R. is at the freezing of water: the zero of F. is 32°
F. below the zero of C. and of R.

Therefore — L For temperatures above the zero of C. (32° F.)
Rule. Examples.

F. — 32 -r- 1-8 = C 40OF. — 32(=8)-|-l-8=4o-44C.

C. X 1.8+32 =F 40-44C. X 1-8 (=8)4- 32 = 400 F.

2. For temperatures helow the zero of C. (32°), but not below the zero of

F. (— n°-t C.)

Rale. Examples.

F. ~ 32 -i- 1-8 = C. . . 20OF. -32 (=12)-M-8 = — 60-66C.
~C. X 1-8-32 =F. . . 60-66C. Xl-8 (=12)~32 = 20OF.

3. For temperatures helow the zero of F. ( — 17°'t C.)

Rule. Examples,w

— F. + 32 -1. 1-8 = — C. . . 20OF. + 32 (=52) -r- 1-8 = —280-8 C.
— C. X 1-8-32 =— F. . . 280.8C. xl-8(=52)— 32 = — 20OF.

To convert Fahrenheit and Reaumur into each other, use the above roles,
only substituting for C. 1-8, R. 2-5 i// = 2-5

As the Centigrade thermometer is employed by all French and German
writers and by a few English writers on Chemistry, we subjoin for convenient
reference a Table of the equivalent degrees of Centigrade and Fahrenheit
between the freezing and the boiling points of mercury.

Cent.

Fahr.

Cent.

Fahr.

Cent.

Fahr.

Cent.

Fahr.

Cent.

Fahr.

—40°

—40-0°

—18°

— 0-4°

4°.

. 39-2°

26°..

. 78-8°

48°..

. 118-4°

—39

—38-2

—17

4- 1-4

5 ..

. 41-0

27 ..

. 80-6

49 ..

120-2

—38

-36-4

—16 .

.. 3-2

6 .

. 42-8

28 ..

. 82-4

50 ..

122-0

—37

—34-6

—15 .

.. 5-0

7 .

. 44-6

29 ..

. 84-2

51 ..

123-8

—36

-32-8

—14 .

.. 6-8

8 .

. 46-4

30 .

. 86-0

52 ..

125-6

—35

-30-0

-13 .

.. 8-6

9 .

. 48-2

31 ..

. 87-8

53 ..

127-4

—34

—29-2

—12 .

.. 10.4

10 ..

. 50-0

32 ..

. 89-6

54 ..

129-2

—33

—27-4

—11 .

.. 12-2

11 ..

. 51-8

33 ..

. 91-4

55 ..

1310

—32

-25-6

—10 .

.. 14-0

12 ..

. 53-6

34 ..

. 93-2

56 ..

132-8

—31

-23-8

— 9 .

.. 15-8

13 ..

. 55-4

35 ..

. 95-0

57 ..

134-6

—30

-22-0

— 8 .

.. 17-6

14 ..

. 57-2

36 ..

. 96-8

58 ..

136-4

—29

-20-2

— 7 .

.. 19-4

15 ..

. 59-0

37 ..

. 98-6

59 ..

138-2

—28

-18-4

— 6 .

.. 21-2

16 ..

. 60-8

38 ..

. 100-4

60 ..

140-0

—27

—16-6

— 5 .

.. 23-0

17 ..

. 62-6

39 ..

. 102-2

61 ..

141-8

—26

-14-8

— 4 .

.. 24-8

18 ..

. 64-4

40 ..

. 104-0

62 ..

143-6

—25

-13-0

— 3 .

.. 26-6

19 ..

. 66-2

41 ..

. 105-8

63 ...

145-4

—24

-11-2

— 2 .

.. 28-4

20 ..

. 68-0

42 ..

. 107-6

64 ...

147-2

—23

— 9-4

— 1 .

.. 30-2

21 ..

. 69-8

43 ..

. 109-4

65 ...

149-0

—22

— 7-6

0 .

.. 32-0

22 ..

. 71-6

44 ..

. 111-2

66 ...

150-8

—21

— 5-8

+ 1 •

.. 33-8

23 ..

. 73-4

45 ..

. 113-0

67 ...

152-6

—20

— 4-0

2 .

.. 35-6

24 ..

. 75-2

46 ..

. 114-8

68 ...

154-4

—19

— 2-2

3 .

.. 37-4

25 ..

. 77-0

47 ..

. 116-6

69 ...

156-2

734

THERMOMETRICAL EQUIVALENTS.

Cent.

Fahr.

Cent.

Fahr.

Cent.

Fahr.

Cent.

Fahr.

Cent.

Fahr.

70°..

158-0°

129°...

264-2°

188°...

370-4°

247°..

476-6°

306°

.. 582-8°

71 ..

159-8

130 ...

266-0

189 ..

372-2

248 ..

478-4

307 .

.. 584-6

72 ..

161-6

131 ...

267-8

190 ..

3740

249 ..

480-2

308 .

.. 586-4

73 ..

163-4

132 ...

269-6

191 ...

375-8

250 ..

482-0

309 .

.. 588-2

74 ..

165-2

133 ...

271-4

192 ..

377-6

251 ..

483-8

310 .

.. 590-0

75 ..

167-0

134 ...

273-2

193 ..

379-4

252 ..

485-6

311 .

.. 591-8

76 ..

168-8

135 ...

275-0

194 ..

381-2

253 ..

487-4

312

.. 593-6

77 ..

170-6

136 ...

276-8

195 ..

383-0

254 ..

489-2

313

.. 595-4

78 ..

172-4

137 ...

278-6

196 ..

384-8

255 ..

491-0

314

.. 597-2

79 ..

174-2

138 ...

280-4

197 ..

386-6

256 ..

492-8

315

.. 599-0

80 ..

176-0

139 ...

282-2

198 ..

388-4

257 ..

494-6

316

.. 600-8

81 ..

177-8

140 ...

284-0

199 ..

390-2

258 ..

496-4

317

.. 6026

82 ..

179-6

141 ...

285-8

200 ..

392-0

259 ..

498-2

318

.. 604-4

83 ..

181-4

142 ..

287-6

201 ..

393-8

260 ..

500-0

319

.. 606-2

84 ..

183-2

143 ..

289-4 '

202 ..

395-6

261 ..

501-8

320

.. 608 -0

85 ..

185-0

144 ..

291-2

203 ..

397-4

262 ..

503-6

321

.. 609-8

86 ..

186-8

145 ..

293-0

204 ..

399-2

263 ..

. 505-4

322

.. 611-6

87 ..

188-6

146 ..

294-8

205 ..

401-0

264 ..

. 507-2

323

.. 613-4

88 ..

190-4

147 ..

296-6

206 ..

402-8

265 ..

. 509-0

324

.. 615-2

89 ..

192-2

148 ..

298-4

207 ..

404-6

266 ..

. 510-8

325

.. 617-0

90 ..

194-0

149 ..

300-2

208 ..

406-4

267 ..

. 512-6

326

... 618-8

91 ..

195-8

150 ..

302-0

209 ..

. 408.2

268 ..

. 514-4

327

... 620-6

92 ..

197-6

151 ..

303-8

210 ..

. 410-0

269 ..

. 516-2

328

... 622-4

93 ..

. 199-4

152 ..

305-6

211 ..

. 411-8

270 ..

. 518-0

329

... 624-2

94 ..

. 201-2

153 ..

307-4

212 ..

. 413-6

271 ..

. 519-8

330

... 626-0

95 ..

. 203-0

154 ..

309.2

213 ..

. 415-4

272 ..

. 521-6

331

... 627-8

96 ..

. 204-8

155 ..

. 311.0

214 ..

. 417-2

273 ..

. 523-4

332

... 629-6

97 ..

. 206-6

156 ..

312.8

215 ..

. 419-0

274 ..

. 525-2

333

... 631-4

98 ..

. 208-4

^57 ..

%58 ..

314.6

216 ..

. 420-8

275 ..

. 527-0

334

... 633-2

99 ..

. 210-2

. 316.4

217 ..

. 422-6

276 ..

. 528-8

335

... 635-0

100 ..

. 212-0

159 ..

. 318.2

218 ..

. 424-4

277 ..

. 530-6

336

... 636-8

101 ..

. 213-8

160 ..

. 320-0

219 ..

. 426-2

278 ..

. 532-4

337

... 638-6

102 ..

. 215-6

161 ..

. 321-8

220 ..

. 428-0

279 ..

. 534-2

338

... 640-4

103 ..

. 217-4

162 ..

. 323-6

221 ..

. 429-8

280 ..

. 536-0

339

... 642-2

104 ..

. 219-2

163 ..

. 325-4

222 ..

. 431-6

281 ..

. 537-8

340

... 644-0

105 ..

. 221-0

164 ..

. 327-2

223 ..

. 433-4

282 ..

. 539-6

341

... 645-8

106 ..

. 222-8

165 ,.

. 329-0

224 ..

. 435-2

283 ..

. 541-4

342

... 647-6

107 ..

. 224-6

166 ..

. 330-8

225 ..

. 437-0

284 ..

. 543-2

343

... 649-4

108 ..

. 226-4

187 ..

. 332-6

226 ..

. 438-8

285 ..

. 545-0

344

... 651-2

109 ..

. 228-2

168 ..

. 334-4

227 ..

. 440-6

286 ..

. 546-8

345

... 653-0

110 ..

. 230-0

169 ..

. 336-2

228 ..

. 442-4

287 ..

. 548-6

346

... 654-8

Ill ..

. 231-8

170 ..

. 338.0

229 ..

. 444-2

288 ..

. 550-4

347

... 656-6

112 ..

. 233-6

171 ..

. 339-8

230 ..

. 446-0

289 ..

. 552-2

348

... 658-4

113 ..

. 235-4

172 ..

. 341-6

231 ..

. 447-8

290 ..

. 554-0

349

... 660-2

114 ..

. 237-2

173 ..

. 343-4

232 ..

. 449-6

291 ..

. 555-8

350

... 662-0

115 ..

. 239-0

174 ..

. 345-2

233 ..

. 451-4

292 ..

. 557-6

351

... 663-8

116 ..

. 240-8

175 ..

. 347-0

234 ..

. 453-2

293 ..

. 559-4

352

... 665-6

117 ..

. 242-6

176 ..

. 348-8

235 ..

. 455-0

294 ..

. 561-2

353

... 667-4

118 ..

. 244-4

177 ..

. 350-6

236 ..

. 456-8

295 ..

. 5630

354

... 669-2

119 ..

. 246-2

178 ..

. 352-4

237 ..

. 458-6

296 ..

. 564-8

355

... 671-0

120 ..

. 248-0

179 ..

. 354-2

238 ..

. 460-4

297 ..

. 566-6

356

... 672-8

121 ..

. 249-8

180 ..

. 356-0

239 ..

. 462-2

298 ..

. 568-4

357

... 674-6

122 ..

. 251-6

181 ..

. 357-8

240 ..

. 464-0

299 ..

. 570-2

358

... 676-4

123 ..

. 253-4

182 ..

. 359-6

241 ..

. 465-8

300 ..

. 572-0

359

... 678-2

124 ..

. 255-2

183 ..

. 361-4

242 ..

. 4«7-6

301 ..

. 573-8

360

... 680-0

125 ..

. 257-0

184 ..

. 363-2

243 ..

. 469-4

302 ..

. 575-8

126 ..

. 258-8

185 ..

. 365-0

244 .

. 471-2

303 ..

. 577-4

127 ..

. 260-6

186 ..

. 366-8

245 ..

. 473-0

304 ..

. 579-2

128 ..

. 262-4

187 ..

. 368-6

246 ..

. 474-8

305 .

. 581-0

RULE FOR CALCULATING CHANGES OF VOLUME IN GASES BY PRESSURE.

The mean height of the barometer is to the observed height as the ob-
served volume to the volume required, or the mean pressure (30 inches) is to

CHANGES OF VOLUME IN GASES BY TEMPERATURE. 735

the observed pressure. Hence, assuming 100 cubic inches of gas to be at 28
inches pressure : required the volume at 30 inches pressure.

Mean pr. Obs. pr. Observed volume. Required volume.

30 : 28 :: 100 : 93-33

Thus 100 cubic inches are condensed to 9333 cubic inches by the baro-
meter rising two inches, from 28 to 30. The increase of pressure is l-15th.
and the diminution of volume is in the same proportion.

The increase in the weight of 100 cubic inches of gas at different pressures,
may be determined by the following rule: if 100 cubic inches of gas weigh
30 grains, when the barometer is at 29 inches — required the weight at 30
inches.

Obs. pr. Mean pr. Observed weight. Required weight.

29 : 30 : : 30 : 31-03

The pressure to which a gas, standing over mercury, is submitted, is indi-
cated by the height of the barometer, when the mercury on the inside and
outside of the vessel has the same level : but if the mercury on the inside be
higher than on the outside, the difference, in inches must be deducted from
the height of the barometer, in order to obtain the exact pressure to which
the gas is subjected.

RULE FOR CALCULATING CHANGES OF VOLUME IN GASES BY TEMPERATURE.

According to the researches of Gay-Lussac, 1000 volumes of air at 32°
are increased to 1375 volumes at 212°. Hence the increase is f||, or 2*08.
for each degree between 32° and 212°: and 1000H-2-08=480. Hence the
increase for each degree, is equal to l-480th part of the volume at 32° ; or,
assuming that the volume of gas at this temperature is 480 cubic inches,
there will be an addition of one cubic inch for every degree of increase in
temperature up to 212°. By taking this as the proportionate increase at
any two temperatures, it will be easy to calculate the change of volume for
any other temperature. The mean temperature is taken at 60°, and 480
cubic inches at this temperature would become (60 — 32 + 480) 508 cubic
inches. If the observed temperature be 70°, then 480 cubic inches at this
temperature would be (70—32 + 480) 518 cubic inches. The number 32 is
deducted from the temperatures because it is from this degree (32°) that the
rate of expansion, on which the calculation is based, commences. It is
obvious that it matters not whether the number 32 is deducted from the two
temperatures, or from the number 480, as the sura will be the same in the
two cases ; but it makes this important difference in the calculation, that
480—32=448 furnishes a constant, which needs only to be added to each
temperature, in order to produce the proportionate numbers. This constant
is easily remembered, by the fact that the last figure of the three is produced
by the addition of the two figures that precede it, each being equal to one-
half of the sum.

The rule for correction is, therefore, as follows: The increase at the
T)bserved temperature (70°) is to the increase at the mean temperature (60°)
as the observed volume of gas (100 cubic inches) to the volume required, or

Obs. temp. Mean temp. Obs. vol. Required vol.

448 + 70° : 448 + GO*' : : 100 : 98-069

Thus 100 cubic inches of gas at 70° are reduced in volume to 98-069
cubic inches by cooling 10°, i. e., from 70° to 60°. The rule may be repre-
sented under the following simple equation : —

136

SPECIFIC GRAVITY OP LIQUIDS.

448 + t' X V
448 + t

t' Mean temperature,
t Observed temperature.
V Observed volume.

100 cubic inches at 40°. Required the volume at 60°. Answer : 448 +
60x100-^448 + 40 = 1041.

With an alteration in volume there is an alteration in weight, and thus the
difference at any two temperatures may be found by the following rule, in
which observed weight is substituted for observed volume: Thus 100 cubic
inches of air weigh 31 grains at 60°. Required the weight at 212°.

Obs. temp.
448 + 212=

Mean temp.
448 + 60

Grs. obs. weight.
:: 31

Required weight.
23-86

AQUEOUS VAPOR IN GASES.

The subjoined Table represents the proportion hy volume of aqueous vapor
which exists in any gas, standing in contact with water at the corresponding
temperatures and a mean barometric pressure. This must be deducted from
the measured volume in order to determine the actual volume of any gas.
(Faraday.)

Temp.

A. V. by vol.

Temp.

A. V. by vol.

Temp.

A. V. by vol

40° .

•00933

54°

•01533

68° .

•02406

41

•00973

55

•01585

69

•02483

42

•01013

56

•01640

70

•02566

43

•01053

57

•01693

71

•02653

44

•01093

58

•01753

72

•02740

45

•01133

59

•01810

73

•02830

46

•01173

60

•01866

74

•02923

47

•01213

61

•01923

75

•03020

48

•01253

62

•01980

76

•03120

49

•01293

63

•02050

77

•03220

50

•01333

64

•02120

78

•03323

51

•01380^

65

•02190

79 .

•03423

52

•01426

QQ

•02260

80

•03533

53

•01480

67

•02330

SPECIFIC GRAVITIES.

All bodies on the surface of the earth are attracted towards its centre by
gravitation. The comparative force with which gravitation acts on different
bodies, is called their relative weight. Equal masses of the same substance
gravitate equally ; that is, have equal weights : but equal masses of different
substances gravitate unequally ; or, in other words, each species of substance
has its own peculiar force of gravitation. Specific gravity, therefore, is the
relative gravitating power (or weight) of equal volumes of different sub-
stances.

In determining specific gravities, two processes are necessary : first, that
the substances compared should be reduced to equal volumes ; secondly,
that the comparative weight of these equal volumes should be found.

Specific Gravity op Liquids. — All liquids are easily reduced to equal
volumes by filling the same bottle at the same temperature successively with
each of them, and weighing it when so filled. These different weights,
minus that of the bottle, are the comparative specific gravities of the liquids
experimented on. The specific gravity of water, is the unit to which that of
all liquids and solids is adjusted. The volume of liquids varies with their
temperature, and that of 62° F. is generally adopted in this country as the
standard.

BAUME'S HYDROMETERS.

737

Light glass bottles with perforated stoppers are sold, with a counterpoise,
for the purpose of taking the specific gravities of liquids and small solids.
They are so made that when counterpoised at 62°, they are calculated to hold
from 100 to 1000 grains of pure (distilled) water. The specific gravity of a
liquid is then at once determined by its weight. Thus the 1000-graiu bottle
would hold 796 grains of absolute alcohol (0*796), and 1846 grains of concen-
trated sulphuric acid (1-846). In delicate experiments it is always advisable
to take the exact weight of water which the counterpoised bottle will hold ;
as slight differences in the volume, and therefore in the weight of water,
arise in fluctuations in temperature. Thus, according to the temperature,
the bottle will sometimes hold more and sometimes less than 1000 grains.

In pathological researches, it is occasionally required to take the sp. gr.
of a very small quantity of liquid. A light glass tube about three inches
long, and about three-eighths of an inch in diameter, may be employed for
this purpose. It may be fixed in a hole in a cork, and accurately balanced.
It should be marked in horizontal lines, at different levels, by a diamond ;
and the weight of distilled water at any one of these levels being ascertained,
the weight of the liquid at the same level may be afterwards determined.
The two weights will, by the rule of proportion, give the specific gravity.

Baume's hydrometer is much used on the Continent. We subjoin a Table,
in which the degrees of this hydrometer are compared with the ordinary
range of the specific gravities of liquids.

FOR LIQUIDS HEAVIER THAN WATER.

jgrees.

Sp. gravity.

Degrees.

-Sp. gravity.

Degrees.

Sp. gravity.

Degrees.

Sp. gravity

0 .

. 1-000

20 ..

. 1-152

40 .

. 1-357

60 .

. 1-652

1 .

. 1-007

21 ..

. 1-160

41 .

. l-3b'9

61 .

. 1-670

2 .

. 1-013

22 ..

. 1-169

42 .

. 1-381

62 .

. 1-689

3 .

. 1-020

23 ..

. 1-178

43 .

. 1-395

63 .

. 1-708

4 .

. 1-027

24 ..

. 1-188

44 .

. 1-407

64 .

. 1-727

5 .

. 1-034

25 ..

. 1-197

45 .

. 1-420

65 .

. 1-747

6 .

. 1-041

26 ..

. 1-206

46 .

. 1-434

66 .

. 1-767

7 .

. 1-048

27 ..

. 1-216

47 ..

. 1-448

• 67 .

. 1-788

8 .

. 1-056

28 ..

. 1-225

48 .

. 1-462

68 .

. 1-809

9 .

. 1-063

29 ..

. 1-235

49 .

. 1-476

69 .

. 1-831

10 .

. 1-070

30 ..

. 1-245

50 .

. 1-490

70 .

. 1-854

11 .

. 1-078

31 ..

. 1-256

51 ..

. 1-505

71 .

. 1-877

12 .

. 1-085

32 ..

. 1-267

52 .

. 1-520

72 .

. 1-900

13 .

. 1-094

33 ..

. 1-277

53 .

. 1-535

73 .

. 1-924

14 .

. 1-101

34 .

. 1-288

54 .

. 1-551

74 .

. 1-949

15 .

. 1-109

35 ..

. 1-299

55 .

. 1-567

75 .

. 1-974

16 .

. 1-118

36 .

. 1-310

56 .

. 1-583

76 .

. 2-000

17 .

. 1-126

37 .

. 1-321

57 .

. 1-600

18 .

. 1-134

38 .

. 1-333

58 .

. 1-617

19 .

. 1-143

39 .

. 1-345

59 .

. 1-634

FOR LIQUIDS LIGHl

'ER THAN WATER.

agrees.
10 .

Sp. gravity.
.. 1-000

Degrees.
23 .

Sp. gravity.
. 0-918

Degrees,
36 .

Sp. gravity.
. 0-849

Degrees.
49 .

Sp. gravity;
. 0-789

11 .

.. 0-993

24 .

. 0-913

37 .

. 0-844

• 50 .

. 0-785

12 .

.. 0-986

25 .

. 0-907

38 .

. 0-839

51 .

. 0-781

13 .

.. 0-980

26 .

. 0-901

39 .

. 0-834

52 .

. 0-777

14 .

.. 0-973

27 .

. 0-896

40 .

. 0-830

53 .

. 0-773

15 .

.. 0-967

28 .

. 0-890

41 .

. 0-825

54 .

. 0-768

16 .

.. 0-960

29 .

. 0-885

42 .

. 0-820

55 .

. 0-764
. 0-760

17 .

.. 0-954

30 .

. 0-880

43 .

. 0-816

56 .

18 .

.. 0-948

31 .

.. 0-874

44 .

. 0-811

57 .

. 0-757
. 0-753

19 .

.. 0-942

32 .

. 0-8(59

45 .

. 0-807

58 .

20 .

.. 0-936

33 .

.. 0-864

46 .

.. 0-802

59 .

. 0-749

21 .

.. 0-930

34 .

.. 0-859

47 .

.. 0-798

60 .

. 0 745
. 0-741

22 .

.. 0-924

35 .

.. 0-854

48 .

.. 0-794

61 .

47

738

SPECIFIC GRAVITY OF SOLIDS.

Twaddell's hydrometer is employed by English Chemical manufacturers.
The degrees on Tvvaddell are readily converted into equivalent specific
gravities, by multiplying them by 5°, and adding 1000. Thus 8° Twaddell,
8x5 = 40 + 1000 = 1040. We subjoin a Table of their equivalents.

rees

Sp. gravity.

Degrees.

Sp. gravity.

Degrees.

Sp. gravity.

Degrees.

Sp. gravity

1

... 1-005

8

.. 1-040

15 .

.. 1-075

22 .

. 1-110

2

... 1-010

9

.. 1-045

16 .

.. 1-080

23 .

. 1-115

3

... 1-015

10

.. 1-050

17 .

.. 1-085

24 .

. 1-120

4

... 1-020

11

.. 1-055

18 .

.. 1-090

25 .

. 1-125

5

... 1-025

12

... 1-060

19 .

.. 1-095

26 .

. 1-130

6

... 1-030

13

... 1-065

20 .

.. 1-100

27 .

. 1-135

7

... 1-035

14

.. 1-070

21 .

.. 1-105

28 .

. 1-140

Specific Gravity of Powders or Small Solids. — The sp. gr. of solids
in powder or in small pieces may also be conveniently determined by a bottle.
Thus : weigh the powder, pour it into the bottle, and fill it with water at
62° F., taking care to dislodge all adhering bubbles of air. Then weigh it
and deduct the known weight of the bottle : the remainder is the conjoint
weight of the powder and water. Deduct from this last sum the found
weight of the powder, and the difference is the weight of the water ; deduct
this difference from the known weight of water, required to fill the bottle,
and the remainder is the weight of a volume of water, equal to the volume
of the solid in powder; then, as this is to the known weight of water, required
to fill the bottle : : sp. gr. water : sp. gr. powder.

We subjoin an example in reference to native platinum in grains : —

Weight of water in the bottle

Weight of native platinum grains (in air) .

Weight of water and platinum in bottle

Grains.
1000
40

1040
1037-5

Difference =: vol. of water displaced ... 2-5

40 -r- 2-5 =: 1 6 sp. gr. of native platinum.

The sp. gr. of mercury, or any liquid or solid, not dissolved by water, may
be obtained by the same rule. When the substance is soluble in water,
another liquid of known sp. gr., which does not act upon the solid, must be
employed. Alcohol, oil of turpentine, or olive oil, may be used, or, in some
cases, the substance may be coated with varnish. ^ ssuming that the sp. gr. of
sugar is required, and the liquid selected is oil of turpentine, sp. gr. 0-870 ;
the sugar is first weighed in air, and then in the oil ; the difference gives the
weight of an equal bulk of the oil ; then, if the weight of the sngar in air
be 400 grains, and its weight in oil of turpentine 182 '5, the weight of an
equal bulk of the oil will be'400— 182-5=217 '5. Then 0*870 : 1000 : : 217-5
: 250, and 400-7-250=1-6, which is the sp. gr. of the sugar.

Specific Gravity of Solids Heavier than Water. — Weigh the solid
in air, then suspend it by a fine thread to one arm of a balance; exactly
counterpoise it, and immerse the solid so counterpoised in distilled water at
62*^ F. , and note how much less it weighs now than when weighed in air.
The difference between the two is the weight of a volume of water exactly
equal to that of the immersed solid. Divide the weight of the solid in air
by this difference, and the result is the sp. gr. of the solid. Thus, in re-
ference to a small bar of aluminum : —

SPECIFIC GRAVITY OF GASES. 739

Grains.

Weight of aluminum in air 46 "3

Weight of aluminum in water . . . .29-0

Difference = volume of water .... 17*3
46-3 -f- 17*3 = 2-6 sp. gr. of aluminum.

A portion of bone in air weighed 90*6 grains: in water 45'6. Differ-
ence = 45 grains ; and 90-6-^45=2'01 sp. gr. of hone. A portion of muscle
weighed in air 91-2 grains : in water 7*2 grains. Difference = 84 grains ;
and 91'2-^84 = 1'085 sp. gr. of muscle.,

A knowledge of the specific gravity of solids enables a chemist to deter-
mine the weight of bodies from their volume. A cubic foot of water con-
tains 1728 cubic inches, and weighs 1000 ounces (strictly, 997*145 ounces
or 62'4 pounds Av.) ; hence a cubic foot of sulphur (sp. gr. 1-957) would
weigh 1957 ounces, and a cubic foot of marble (sp. gr. 2-5) would weigh
2500 ounces. A cubic foot of ice weighs 937 '6 ounces, or 58'6 pounds Av. ;
a cubic foot of air weighs 535*161 grains.

Specific Gravity of Solids Lighter than Water. — 1. Find the weight
of the solid {a) in air. 2. Take a piece of metal heavy enough to make a
sink in water, and find its weight in air and in water. 8. Tie together a and
the metal, and find the weight of the compound mass in water. The differ-
ence between the weight of the metal in air and in water is the weight of a
volume of water, equal to that of the metal ; deduct this from the difference
between the weights in air and in water of the compound mass, and the
remainder is the weight of a volume of water equal to a. We divide the
weight of a by the remainder, and obtain the sp. gr. Thus with reference
to beef-fat : —

Grains.

Weight of the fat in air 117-3

Add brass weight to sink it 1000-0

Weight of compound mass in air . . . . 1117-3

Grains.

Loss of weight by the compound mass in water . 245-5

" brass weight (1000) " . 119-4

Weight of the water displaced by the fat . . 126-1
Hence 117-3 -f- 126-1 = 0-930 sp. gr. of beef-fat.

Specific Gravity of Gases. — The principles are the same as those above
described for determining the specific gravity of solids and liquids. The
weighing of the air and gas should take place at the same temperature and
pressure, or a calculation should be made according to the rules already
given (p. 735). In reference to Gases and Vapors, air is taken as the
standard of unity (pp. 84 and 743).

Gases.— A light glass flask, of about 40 or 50 c. i. capacity, is employed.
This is capable of being screwed to the air-pump plate, and of being sus-
pended to a scale-beam and accurately balanced. The flask is exhausted,
balanced, filled with dry air, and again balanced. The increase in weight
represents the weight of the volume of dry air in the flask, at the pressure
and temperature at which it was filled. The experiment is repeated with
the dry gas, the sp. gr. of which is proposed to determine. The following
is an example of the sp. gr. of Carbonic acid : —

•740 SPECIFIC GRAVITY OF VAPORS.

Grains.
Weight of the flask with drj air . . . . 2033-8
Weight of the flask exhausted .... 2021-4

Weight of dry air in the flask .... 12*4

Grains.
Weight of the flask with dry carbonic acid . . 2040-24
Weight of flask exhausted . • . . 2021-40

Weight of dry carbonic acid in flask . . . 18-84
Hence 18-84 -J- 12-4 = 1-520 sp. gr. of carbonic acid.

When the sp. gr. of a gas has been ascertained, the weight of 100 cubic
inches is determined by multiplying the sp. gr. of the gas by the weight of
100 cubic inches of air = 31 grains (pp. 158 and 143). Thus, 100 cubic
inches of dry carbonic acid are found by experiment to weigh 41 '08 grains,
and its sp. gr. (r520x31=4t'l) gives 471 grains for the weight of 100
cubic inches, calculated by this rule. Conversely, when we have ascertained
the weight of 100 cubic inches of a gas, we can determine its sp. gr. by
dividing this weight by 31. Thus 4t"l-i- 31 = 1-520. The sp. gr. of a gas,
of which the atomic weight is known, may also be determined, by multiplying
the atomic weight by the sp. gr. of hydrogen. Thus the atomic weight of
carbonic acid is 22, and 22 x "0691 = 1*5202, the sp. gr. of carbonic acid.
On the other hand, if the sp. gr. is known, the atomic weight may be de-
termined by dividing the sp. gr. of the gas, by the sp. gr. of hydrogen, thus
1-502 "7- -0691=22, the atomic weight of carbonic acid. When however the
atomic weight of a gas corresponds to 2 volumes then the quotient must be
divided by 2, to obtain the real sp. gr. Thus in reference to ammonia, the
atomic weight is lY, and 17x-0691 = l*1747. As the atom of ammonia
corresponds to 2 volumes, then l'1747-^2='5873, sp. gr. of ammonia.

A knowledge of the sp. gr. of gases, enables a chemist to control the
results of an analysis of a compound gas. Thus if 2 volumes of ammonia
consist of 1 volume of nitrogen and 3 volumes of hydrogen, it follows that
the sum of the specific gravities of its constituents, divided by 8, should
exactly represent the sp. gr. of the gas. {See p. 158, also p. 743.)

Specific Gravity of Yapors. — The determination of the sp. gr. of
vapors is attended with greater practical difficulties, but the principle of the
operation is the same. We compare the weights of equal volumes of the
vapor and air under the same temperature and pressure. A thin glass globe
of about three inches diameter is drawn out at its neck to a narrow tube, six
or seven inches long, the point of the tube being cut across with a file, but
not sealed. The globe is then weighed, and the temperature and pressure
at the time are observed. In order to introduce the volatile liquid, the globe
is warmed so as to expel a portion of its air, and the end of the tube is then
dipped into the liquid. As the globe cools, the air within contracts, and
the liquid is forced into it by atmospheric pressure. When a suflScient quan-
tity (from 100 to 150 grains) of liquid has entered, the globe is firmly
inclosed in a wire holder, and immersed in a bath of water, oil, or other
'medium, heated to 50° or 60° above the boiling-point of the liquid in the
globe. Under these circumstances, a stream of vapor rushes rapidly through
the orifice, carrying with it the air of the globe. When this ceases, the
point of the tube is sealed by a blowpipe flame, the temperature of the bath
being observed at the same moment. The globe is removed from the bath,
and when cool is cleaned and weighed.

The next point to be determined is the capacity of the globe. For this

SPECIFIC GRAVITY OP VAPORS. Y41

purpose the neck is broken under the surface of water or mercury, when the
cold fluid enters the globe and fills it completely, if the operation has been
properly conducted, and all the air has been expelled by the vapor. By
pouring out the water or mercury into a graduated vessel, the capacity of
the globe is accurately ascertained. We thus obtain the data necessary for
the calculation.

1. The weight of the globe full of air at the common temperature and
pressure.

2. The weight of the globe, and of the vapor filling it at the temperature
of the bath, and under the same pressure.

3. The capacity of the globe. Having these results, we obtain by calcu-
lation—

4. The weight of the empty globe.

5. The weight of the vapor filling the globe at the temperature of the
bath, as well as its volume at this or any other temperature that may be
required.

Let it be assumed that the object is to determine the specific gravity of
the vapor of Chloroform. 1. The weight of the globe full of air at 60°
and bar. 30, is found to be 2012-4 grains. 2. The liquid chloroform having
been introduced into the globe, in the manner described, the globe is main-
tained at a temperature of 200° in the bath, until nothing but vapor remains
in the interior. The aperture of the small tube is then sealed. The globe,
when dry, and cooled at 600, is found to weigh 2040 grains. This gives
the weight of the globe and vapor together. 3. The capacity of the globe
is determined by breaking the point of the tube under water. The liquid
rushes in and entirely fills the vessel. When this liquid is poured into a
graduated glass, it is found that at 60° there are 40 cubic inches ; hence, 40
cubic inches of air were contained in the globe at common temperature and
pressure. 4. The weight of this air would be 12-4 grains (100 c. i. : 31
grs. : : 40 c. i. : 12-4 grs.) : and as the globe and air weighed together 20124
grains, then 2012'4 — 12*4=2000 grains, the weight of the empty globe.
5. The weight of the vapor filling the globe may now be determined. The
globe was found to weigh, on cooling, 2040 grains, hence, 2040 — 2000=40
grains, the weight of the vapor. It is now necessary to determine either
the weight of air which would fill the globe at the temperature of the bath,
or the volume of vapor which by calculation would be contained in the globe
when cooled at 60°. The reduction of the volume by cooling from 200° to
60° is the more simple process. Thus, 40 cubic inches of vapor at 200°
would be reduced to 30-78 cubic inches at 60° (648 : 508 : : 40 : 30-^8) (p.
136). Hence, assuming that chloroform vapor was cooled to 60°, and
could still exist as a vapor at that temperature, it is obvious that its specific
gravity would be determined by ascertaining the weight of 30*78 cubic inches
of air at the same temperature and pressure. 100 cubic inches of air weigh
31 grains, hence 100 : 31 : : 30*78 : 9*54. Hence, at the same temperature,
60°, 30-78 cubic inches of chloroform vapor would weigh 40 grains, while an
equal volume of air would weigh only 9-54 grains; and 40-^9-54=4*19,
which is nearly the specific gravity of the vapor of chloroform, as determined
by calculation from its elementary composition. We subjoin a summary of
these results ; —

Capacity of the globe at 60O = 40 cubic inches.
Weight of the globe with dry air = 2012*4 grains.
Weight of the air by calculation = 12*4 grains.
Weight of the globe without air = 2000 grains.
Weight of the globe with chloroform vapor =2040 grains.
Weight of the chloroform in vapor = 40 grains.

•742 SPECIFIC GRAVITY OF VAPORS.

40 c. i. of air or vapor at 200O, reduced to 30-78 c. i. at 60O.

Weight of 30-78 c. i. of air at 60O =: 9-54 grains.

Weight of 30-78 c. i. of chloroform vapor at 60O =40 grains.

Hence —

Wt. of air.

Wt. of chlor, V.

Sp. gr. air.

Sp. gr. chlor.

9-54

: 40 ::

1-000

4-192

It may be observed that the ascertained sp. gr. of chloroform -vapor is
4*20, and the sp. gr. of the vapor calculated from its elementary composition
is 4"1805, differences which^re comparatively unimportant (p. 755).

The relations of sp. gr. to weight and volume are the same with vapors
as with gases. In fact, all the conditions which affect gases equally affect
vapors, so long as these bodies have a temperature above the boiling points
of the liquids which produce them.

The weight of 100 cubic inches of the vapor of water may be determined
from its sp. gr. by the rule already given (p. 739). Thus 0.6129 x 31 = 19-27
grains. The sp. gr. of the vapor of arsenic being 10-39, 100 cubic inches
of this vapor would weigh 32209 grains (1039x31).

A determination of the specific gravity of vapors or of vapor-density is of
considerable importance in the analysis of volatile organic liquids. There
are many liquid hydrocarbons which, so far as centesimal composition is
concerned, yield precisely similar weights of hydrogen and carbon, by the
combustion-tube. The specific gravity of their vapors, however, differs ;
and this difference often enables a chemist to apportion with great accuracy
^their atomic constitution. The specific gravity of a compound vapor must
always be the sum of the specific gravity of its constituent elements, or a
multiple of them. We need not go further into this subject, as the reader
will find several examples given at page 556.

TABLE OF GASES AND VAPORS.

743

TABLE OF SIMPLE AND COMPOUND GASES AND VAPOBS.

Gases and vapors.

Symbols.

Atom,
vol.

Atomic
weight.

Sp. gr. of
airl.

Sp. gr. of
hydrogen'

Weight of

100 c. i. iu

grains.

Air

1-000

14-48

31-00

Hydrogen

H

*i*

"i

0-0691

1-

2-14

Oxygen

0

h

8

1-1057

16-

34-24

Nitrogen

N

1

14

0-9674

14-

29-96

Chlorine

CI

1

36

2-4876

36-

77-04

Bromine

Br

1

78

5-3898

78-

166-92

Fluorine

F

1?

19

19-

Iodine .

I

1

126

8-7066

126-

269-64

Sulphur

S

^

16

6-6336

96-

205-44

Selenium

Se

i.

40

16-6390?

240-

515-80

Phosphorus .

P

^

32

4-3555

64-

136-96

Carbon

C

1?

6

0-4146

6-

12-84?

Tellurium .

Te

k

64

4-4190

38-4

136-98

Arsenic

As

^

75

10-3900

150-

322-09

Aqueous vapor

HO

1

9

0-6219

9-

19-26

Protox. of nitrogen

NO

1

22

1-5202

22-

47-08

Deutox. of nitrogen

NO,

2

30

1-0365

15-

32-10

Nitrous acid

NO,

1

46

1-5890

1.

49-15

Ammonia

NH3

2

17

0-5873

18-19

Hypochlorous acid

CIO

1

44

3-0404

44.

94-16

Peroxide of chlorine

CIO.

2

68

2-3494

34-

72-76

Hydrochloric acid

HCI

2

37

1-2783

18-5

39-59

Hydrobromic acid

HBr

2

79

2-7294

39-5

84.53

Hydriodic acid

HI

2

127

4-3878

63-5

135-89

Hydrofluoric acid

HF

2?

20

10-

Sulphurous acid .

SO,

1

32

2-ini

32-

68-48

Hydrosulphuric acid

HS

1

17

1-1747

17-

36-38

Hydroselenic acid

HSe

1

41

2-7950

41-

86-64

Phosph. hydrogen

PH3

2

35

1-1925

17-5

36-96

Terchlor. of phosph.

PCI3

2

140

4-7420

70-

147-00

Pentachl. of phosph.

PCI5

4

212

3-6600

53-

113-46

Carbonic oxide

CO

1

14

0-9674

14-

29-96

Carbonic acid

CO2

1

22

1-5202

22-

47-08

Light carb. of hydroger

CH2

1

8

0-5528

8-

17-12

defiant gas .

CoHo

1

14

0-9674

14-

29-96

Cyanogen .

NC/

1

26

1-7966

26-

55-64

Hydrocyanic acid

HCy

2

27

0-9328

13-5

28-89

Tellur. hydrogen .

TeHj

1

65

4-4881

65-

139-11

Arsen. hydrogen .

AsHg

2

78

2-7010

39-

83.73

Alcohol

C4 HgOj

2

46

1-6100

23-

49-91

Ether .

C H^O'

1

37

2-5567

37-

80-25

Chloroform .

C2 HCI3

2

121

4-1805

60-5

129-59

Oil of turpentine .

^^20^ 16

2

136

4-6980

68-

145-63

[The reader is referred to page 67 for a table of the symbols and equivalent weights
of the Elements. Tables showing the proportion per cent, of dry acids and alkalies,
as well as of alcohol with water, will be found in their proper places in the body of
the work.]

OLD AND NEW NOTATIONS.

In Chapter lY. a table of the elements has been given, representing their
symbols and the equivalent weights in which they combine with each other.
By many chemists of repute they have been and are still regarded as syno-
nymous with atomic weights. An atom, however, in the opinion of many
eminent chemists, is the smallest quantity of an element, indivisible by
chemical means, which can exist in a compound body ; and a molecule is a

744 OLD AND NEW NOTATIONS.

group of atoms, either of simple or compound bodies, forming the smallest
quantity which can exist in a free state, or can take part in a chemical
reaction. The words "smallest quantity" are left undefined. On the old
notation the smallest quantity of oxygen which enters into combination with
one part of hydrogen to form water is 8, and this is taken to represent the
equivalent or combining weight or atom of oxygen. On the new systems,
which, however, are based on the old system of Berzelius, the smallest quan-
tity of oxygen which can go to constitute water is 16. The atom of oxygen
is thus made to represent two equivalents, but this requires the admission of
the assumption that one atom of hydrogen cannot possibly form water, that
a molecule or double atom is required for this purpose (H^), and that hydro-
gen cannot combine with oxygen until after it has combined with itself to
form a hydride of hydrogen.

In 1848 Gerhardt introduced a system of notation on which the equiva-
lents of a certain number of elements were doubled. Various modifications
have been introduced since his time, which have completely changed the
aspect of chemistry as represented by its symbolic language. Great differ-
ences of opinion and many conflicting theories have been introduced by these
frequent changes. I agree with Mr. Bloxam in thinking that the advantages
in adopting, the new notation is chiefly seen in speculative chemistry, and
that the new formulae are likely to be of less service in practice than those
based on the doctrine of equivalent or combining weights. {Bloxam's Che-
mistry, 1867.) Dr. Apjohn, after showing that the exceptions to the propo-
sitions on which the new system is founded are such as to render them
inadmissible in a purely experimental science, asserts that the existing
method (the ordinary notation) is entitled to preference, from its compara-
tive simplicity, and from its resting exclusively on experimental evidence.
(On the Metalloids, 1864.)

Sir Benjamin Brodie, who at one time adopted Gerhardt's notation, has
remarked recently, in introducing his own views to chemists under the name
of " Ideal Chemistry," that " system has followed system and doctrine has
followed doctrine, but these systems and doctrines have one after another
fallen to the ground." {Chemical Neivs, June 14, 1867.) This gentleman,
considering that the present systems of notation, whether old or new, are
utterly inadequate to deal with the complicated chemical facts brought to
light by modern discoveries, proposes to abolish the whole of those now in
use, and to substitute for them an entirely new symbolic language in which
Greek letters are employed to indicate elements and compounds based upon
a certain definite quantity assumed as unity. According to this, the newest
view, a unit of ponderable matter is that portion of ponderable matter which
in the condition of a perfect gas at the temperature of 0° C, and under the
pressure of 760 millimetres, occupies the space of 1000 cubic centimetres.
The unit of space is 1000 cubic centimetres of space, divested of all matter
whatever, represented by the symbol 1 ; hence 1=0. Translated into Eng-
lish, this implies a volume of matter occupying at a temperature of 32° and
under a pressure of 30 inches, 612 cubic inches. One of the difficulties
which must attend all calculations based on volume, or in reasoning from
volume to weight, is that the volume of a large number of substances must
be purely speculative. Carbon, silicon, and boron, and most of the metals,
are not convertible into perfect gas or vapor, so as to be made the subject
of measurement. We may conceive a unit of space represented by 61*2
cubic inches, but there is no method of determining by experiment the por-
tion of ponderable matter, in the shape of gaseous carbon or diamond, which
would till that space at 32° under a pressure of 30 inches. These views,
however, have not at present been fully brought before the public.

OLD AND NEW NOTATIONS.

T45

TABLE OF SYMBOLS AND EQUIVALENT AND ATOMIC WEIGHTS ACCORDING TO VARIOUS

SYSTEMS OP NOTATION.

Equivalent Gerhard t's

Atomic

Equivalent

Gerhardt's

Atomic

Symbols.

weights,

new nota-

weights,

Symbols.

weights,

new nota-

weights,

old nota-

tion.

new nota-

old nota-

tion.

new nota-

tioa.

tion.

tion.

tion.

H . . .

1

1

1

Mu . . .

27-5

27-5

55

0

8

16

16

Cr .

26-7

26-25

53-5

N

14

14

14

U .

60

60

120

Ce

35-5

35-5

35-5

Fe .

28

28

56

Br

80

80

80

Co .

29-5

29-5

59

I ,

127

127

127

Ni .

29-5

29-5

59

F

19

19

19

Zn .

32-6

32-6

65-2

S

16

32

32

Cd .

56

56

112

Se

39-7

79-5

79-5

Cu .

3] -7

31-75

63-5

Te

64

129

129

Pb .

103-5

103-5

207

P

31

31

31

Bi .

210

210

210

As

75

75

75

Sn .

59

56

118

C

6

12

12

Ti .

•

25

137-32

50

B

10-9

11

11

Wo.

92

92

184

Si

14

...

28

Mo .

48

48

96

Zr

44-8

...

89-6

Va .

68-5

48

137-2

K

39

39

39-1

Sb .

122

122

122

Na

23

23

23

Hg .

100

100

200

Li

7

7

7

Ro .

52

...

104-4

Ag

108

108

108

Pd .

53-3

...

106-6

Ba

68-3

68-5

137

Pt .

98-7

98-5

197

Sr

43-8

43-75

87-5

Ir .

99

98-5

198

Ca

20

20

40

Ru .

52-2

...

104-4

Mg

12

12

24

Os .

99-5

199-2

Al .

13-7

13-75

27

Au .

197

...

196-98

This table has been compiled from the tables published by Wurtz {Intro-
duction to Chemical Philosophy, translated by Crookes, 1867). In this small
volume the reader will find a good exposition of the various systems of nota-
tion now in use. For an account of Sir B. Brodie's new views on " Ideal
Chemistry," I would refer the reader to his published lecture in the Labora-
tory, No. 11, June 15, 1867, or Chemical News, June 14, 1867.

746

OLD AND NEW NOTATIONS.

TABLE OF THE ORDINARY AND UNITARY FORMULA OF SOME OF THE MORE IMPORTANT
CHEMICAL COMPOUNDS.

Names of the compounds.

Ordinary or dualistic
formula.

Unitary formulae.

Water

HO

H2O

Potash

. KO

K2O

Hydrate of Potash

KO,HO

HKO

Oxide of Silver

AgO

Ag^O

Hydrochloric Acid .

HCl

HCl

Chloride of Potassium .

KCl

KCI

Ammonia

NH„

NH3

Nitrous Oxide

NO

N2O

Nitric Oxide ....

NO,

NO

Hyponitrous Acid .

N03^

NA

Hyponitric Acid

NO,

NO.

Anhydrous Nitric Acid .

NO.

N2O,

Hydrated Nitric Acid

HO,NO.

NO3H

Nitrate of Potash .

KO.NO,

NO3K

Carbonic Acid

*

CO,

CO,

Carbonate of Potash

K0,C02

K2C03

Bicarbonate of Potash .

HO,KO,2C02

HKC03

Anhydrous Sulphuric Acid

SO3

S03

Hydrated Sulphuric Acid

H0,S03

S0,H2

Sulphate of Potash

K0,S03

S0,K2

Bisulphate of Potash .

KO,HO,2S03

SO.KH

Sesquioxide of Iron

FeA

Fe,03

Chromic Acid

0

Cr03

Cr203

Chromate of Potash

K0,Cr03

K2Cr04

Bichromate of Potash^ .

KO,2CrO,

K2Cr04,Cr203

Phosphoric Acid (anhydrous)

PO,

P2O5

Terhydrate

3H0,P0,

H3PO4

Tribasic Phosphate of Soda

HO,2NaO,P05

HNagPO^

Pyrophosphate of Soda .

2NaO,P05

Na.P^O,

Metaphosphate of Soda .

NaO,P05

NaP03

Cyanogen

C^NCCy)

CN(Cy)

Cyanide of Potassium .

KC2N

KCN

Ferrocyanide of Potassium

K,FeCy3

K.FeCye

Ferricyanide of Potassium

KgFe.Cye

KsFeCy^

Sulphocyanide of Potassium

KCyS,

KCyS

Hydrated Acetic Acid .

HO,C,H303

C2HA

Alcohol ....

C^HeO^

C2HgO

Ether ....

cI<o'

C4H.0O

In making his election between these two systems, the student of chemistry
will do well to bear in mind the following judicious remarks by Dr. Miller,
in the second edition of his Elements of Chemistry, Part 2, p. 861. After
observing that the notation in common use has many advantages over that
proposed by Gerhardt, he says : —

• " 1. The ordinary system is known to every one who has made the science
of chemistry his study. 2. All the memoirs, with the exception of a few in
later years, are written in accordance with this system, and a change of nota-
tion would at once render these memoirs less easily accessible and intelligible.
3. The new notation is not in harmony with the language of chemistry.

' It is difficult to give any consistent unitary formulas to the chromates. Those chemists
who adopt the new notation do not agree either in the arrangement of the atoms or molecules,
or in the nomenclature. Thus, while the composition of this salt is plainly indicated in the
ordinary system as Bichromate of Potash, KO,2Cr03, it is described by Dr. Koscoe as Potas-
sium Anhydro-chromate, with the formula KaCrOi.CrOa, and by Dr. Williamson as Potassic
dichromate, with the formula CraOiKa ; while according to Gerhardt the same salt has the
formula K2Cr204,Cr203. Another recent chemical writer, Dr. S. Macadam, adopts Williamson's
formula, but places the symbols in an inverted order, KaCraO,.

OLD AND NEW NOTATIONS. Y4t

NO, for example, would (or ought to) be called binoxide of nitrogen, but
written as a protoxide.* 4. The present system of notation is capable of
expressing all the later theories with perfect precision, while it is applicable
to the older views ; but the new notation is not applicable to many of the
older views. By the ordinary notation, nitrate of potash, for instance, may
be represented either as a compound of potash and nitric acid (KO.NO^), or
as a combination of potassium with nitrion (K,NOfl), or as an aggregation
of particles without indicating any specific mode of combination (KNOg) ;
whereas in the new notation, unless its principle is abandoned by doubling
the formulae, it is impossible that KNO3 should be represented as formed of
potash and nitric acid. It would, therefore, be a retrograde step thus to
exclude from our notation the power of indicating the constitution of a large
class of compounds upon a view which has long been more or less prevalent.
5. Any extensive change of nomenclature or of notation, while the truth of
the theory upon which it rests is still under discussion, cannot but lead to
serious inconvenience. If such a practice were admitted, every new theory
would be privileged to introduce a new language, which, in a continually
progressive science like chemistry, would soon give way to an equally transi-
tory successor. Chemistry, it must be remembered, is not merely a science :
it is also an art which has introduced its nomenclature and its notation into
our manufactories, and, in some measure, even into daily life : it is therefore
specially necessary to beware of needless innovation in its terms and symbols.'
Any system of notation, it must also be borne in mind, is a mere artificial
contrivance to represent to the mind certain changes or certain hypotheses ;
and to argue for a system of notation as though it were anything more, as
has sometimes been done, shows a want of true appreciation of its meaning.

"The question to be considered is not simply — What is, in the abstract,
the best mode of notation ? but What, considering all the circumstances of
the science, possesses the greatest advantage ? That system of notation
which is consistent with itself, and which lends itself most completely to the
various theories and aspects of the science which have been maintained or
may be maintained, is therefore, philosophically speaking, the best.^ And
such grounds, it appears to me, exist for continuing to use the system hitherto
generally adopted. This question of notation, it must be observed, is entirely
independent of Gerhardt's theory of the atomic constitution of the elements
to which he proposes to apply it. Even those who admit the truth of his
hypothesis may still express the molecular constitution of compounds, as he
did himself in his Traite, by the ordinary mode of notation."

It is impossible to advance stronger or better reasons against these new
systems of notation than those here given in detail by Dr. Miller. Although
published in 1860, his objections to the proposed change are as valid now as
they were then. The objection under 5 is indeed unanswerable. If a sweep-
ing change is to be made, it must not be to a system which is still upon its
trial, but to one which is really based on experiment, and which will, above
all, command the assent of all inquirers after truth. A. S. T.

"■ This difficulty has been evaded by going back to the old name which the compound bore
half a century ago— nitric oxide ; but, in adopting this course, there is no longer any relation
between the name and composition of the gas. ^ j xv *

^ This remark equally applies to weights and measures, and the barometer and thermometer.
Unless we succeed in deanglicizing the nation, it is vain to expect that articles will be sold by-
kilogrammes, medicines prepared by centigrammes or cubic centimetres, or that the rise and
fall of the barometer and thermometer will be indicated by mUlimetres and centigrade degrees.

A. b. 1.

INDEX.

A.

A.ciT>—cont.

PAGE

kcir)—cont.

PAOB

PAGE

chlorocarbonic

263

hydronitroprussio

396

ACALEPH^

142, 706

chlorochromic

447

hydrosulphocyanic

289

Acetates

649

chloromolybdic

453

hydrosulphuric

226

Acetic acid

646

chlorous

193

hypoazotic

172

anhydrous

648

chlorovalerisic

628

hypochlorous

192

glacial

649

chlorovalerosic

628

hyponitric

172

monohydrated

649

cholalic

718

hyponitrous

171

Acetification

646

cholic

718

hypophosphorotis

239

Acetometer

648

choleic

718

hyposulphuric

225

Acetone

651

choloidic

719

hyposulphurous

224

Acetyle

648

chromic

445

inosinic

705

Acetylene

269, 271

cinchonic

661

iodic

207

Acid, acetic

646

cinnamic

653

isatinic

673

aconitic

639

citraconic

639

isethionic

600

acrylic

633

citric

638

isotartaric

637

adipic

627

citricic

639

itaconic

639

aerial

263

citridic

639

kakodylio

668

aldehydic

689

cobaltocyanio

441

kinic

661

althionic

600

colopholic

618

lactic

713

amidobenzoic

654

columbic

450

lauric

631

amygdalic

655

comenic

656

lecanoric

674

anchusic

677

crenic

607

lithic (uric)

724

antimonic

460

croconic

261

lithofellio

720

antimonious

460

cyarihydric

282

maleic

640

apocrenic

607

cyanic

280

malic

640

apoglucic

571

cyanuric

282

manganic

401

arsenic

470

dithionic

225

margaric

624

arsenious

467

dithionous

224

meconic

656

aspartic

666

ellagic

642

melassinic

668

auric

617

equisetic

639

mellitic

261

azotic

174

ethalic

631

mesoxalic

260

azotous

171

ferric

385

metameconic

656

benzaraic

654

fluoboric

296

metagallio

641

benzoic

653

fluoric

210

metapectic

667

bismuthic

437

fluosilicio

305

metaphosphoric

241

boracic

294

formic

662

metastannic

412

borohydrofluoric

298

fulminic

281

metatartaric

637

bromic

203

fumaric

640

molybdic

452

butyric

627

gallic

641

molybdous

462

camphoric

616

gallotannic

640

mucic

666

capric

628

geic

607

muriatic

196

caproie

628

glucic

571

myristio

631

caprylic

628

glycocholalio

718

myronic

616

carbanilic

654

glycocholic

718

naphthalic

610

carbazotic

613

hippuric

656, 727

nitric

174

carbolic

610

humic

607

nitrobenzoio

654

carbonic

263

hydriodic

208

nitrohydrochloric

199

carminic

678

hydrobromic

203

nitromuriatic

199

carthamie

676

hydrochloric

196

nitroso-nitrio

176

cerebric

705

hydrocyanic

282

nitrous

171

ehloracetic

649

hydroferricyanic

395

cenanthic

679

chlorbydric

196

hydroferrocyanic

394

oleic

624

chloric

194

hydrofluoric

210

oleophosphoric

705 ,

chlorobenzoic

654

hydrofluosilicic

306

orceic

675

750

INDEX.

Acid — co7it.

PAGE

Acid — cont.

PAGE

Alcohol— cojj^ page

orsellinic

674

sulphomolybdic

659, 662

ethylic

583

osmic

529

sulphonaphthalic

609

latent heat of vapor of

141

oxalic

643

sulphopurpuric

673

methylic

692

oxamic

645

sulphosaccharic

570

properties of

684

oxaluric

726

sulphostearic

627

propylic

688

palmic

630

sulphovinic

696

solvent powers of

586

palmitic

631

sulphuric

219

sp. gr. of, table of

■ 586

parabanic

726

sulphurous

216

tests for

588

paramaleic

640

sulphydric

226

uses of

588

parapectic

667

tannic

640

Alcoholic fermentation

673

paratartaric

638

tantalic

450

liquors, strength of

683

pectic

567

tantalous

450

Aldehyde

689

pectosic

567

tartaric

634

Ale

579

pelargonic

627

tartralic

637

Alembroth, salt of

483

pentathionio

226

tartrelic

637

Algaroth, powder of

461

perchloric

195

taurocholalic

71-S

Alizarine

674

perehromic

445

taurocholic

718

Alkalies defined

73

periodic

207

telluric

456

Alkaline reaction, influ-

permanganic

402

tellurous

456

ence of water on

43

phenic, or phenylic

610

tetrathionic

226

Alkaloids, organic

657

phocenic

631

titanic

458

formulae of

554

phosphatic

240

trichloracetic

649

solubility of, in chloro-

phosphoglyceric

626

trithionic

226

form

49

phosphoric

240

tungstic

450

tests for 484

, 657

phosphorous

239

ulmic

607

Alkalimetry

315

picric

613

uric

724

Alkanet

677

pimaric

618

uro-benzoic

727

Alkargen

668

pimelic

627

valerianic

628

Alkarsin

668

pinic

618

vanadic

448

Allotropic carbon

248

propionic

625

xanthoproteic

698

hydrogen

126

plumbic

430

Acid reaction, influence of

oxygen

110

prussic

282

water on

43

phosphorus

237

pthalic

610

Acids, constitution of 93

sulphur

214

purpuric

679

defined

73

Allotropy

18

pyrocitric

639

dibasic

241

Alloxan

726

pyrogallic

509, 641

monobasic

241

Alloxantin

726

pyroligneous

648

nomenclature of

74

Alloys of steel

392

pyromellitic

261

organic

554

Allyl

017

pyrophosphorio

241

vegetable

634

Alum

369

pyrotartaric

638

Aconitina

663

chrome

447

pyruvic

638

Acrolein

625, 633

varieties of

270

quercitannic

640

Actinism

505

Alumina

367

racemic

638

Adamantine spar

368

acetates of

650

rhodizonic

260

Adhesion

23

hydrates of

368

ricinelaidio

630

of air

157

oxalates of

645

rutic

628

Adipocire

687

phosphates of

371

salycilic

667

Aeration of water

141

silicates of

371

eebacic

627

Aerolites

444

sulphates of

369

selenic

231

Affinity

62

tests for

372

selenious

231

single

52

Aluminates

368

silicic

299

double

55

Aluminite

369

silicofluoric

306

predisposing

55

Aluminum

367

silvic

618

Agate

300

chloride of

369

sorbic

640

Air, atmospheric

156

fluoride of

367

stannic

412

fixed

263

Amalgam 51

488

stearic

623

thermometer

82

for electrical machines

489

suberic

627

weight of

158

of ammonium 43

, 183

succinic

620

Alabaster

356

Amalgamation of silver

492

sulphacetic

649

Albumen

688

Amarin

655

sulphantimonic

461

vegetable

693

Amber

620

sulpharsenic

475

use of iij dyeing

670

Ambergris

720

sulpharsenious

475

Albuminates

691

Ambligonite

371

sulphindigotic

672

Alcohates

586

Ambreine

720

sulphindylic

672

Alcohol

583

Amethyst

300

sulphobenzoic

654

absolute

584

Amides

182

sulphobenzolic

610

butylio

588

Amidogen

182

sulphocyanic

488

caproic

588

Ammelid

289

sulphoglyceric

627

caprylic

588

Ammeline

289

sulpholeic

627

composition of

588

Ammonia

178

sulphomannitic

573

equivalent of.

deter-

acetate of

650

sulphomargaric

627

mined

556

alum

370

INDEX.

751

Ammonia — cont. page

analysis of 181

aqueous 179

carbonates of 186

decomposition of 181

formate of 652

hydrochlorate of 186

hydrosulphate of 187

metallization of 183

muriate of 186

nitrate of 186

oxalates of 644

proportion in air 163
in water 130

salts of 186

tests for 180

sp. gr. of solution 180
Ammonias, hypothetical 659

Ammonium 183
amalgam of 43, 183

chloride of 186

sulphides of 187

Amorphous bodies 25

phosphorus 237

Amygdaline 654

Amyle 694

oxide of 594

hydrated 693

Amylene 594

Amylic alcohol 593

Amylum 561

Analysis 62
prismatic, or spectrum 61

proximate organic 641
qualitative, of metal-
lic compounds 376, 531

ultimate organic 545
of organic compounds 550

Anatase 457

Anchusine 677

Anhydrates 143

Anhydrides 143

Anhydrite 357
Anhydrous compounds 143

salts 32

Aniline 665

colors from 681

Animal fluids 706

Anions and cations 60

Annotto 679

Anode 59

Antherythrine 683

Anthocyanine 683

Anthoxanthine 683

Anthracene 610

Anthracite 607

Antimonial poisoning 464

Antimoniates 460

Antimony 459

acids of 460

alloys of 462

butter of 461

chlorides of 461

golden sulphur of 462

oxides of 459

sulphides of 461

tests for 463

Antiseptic liquids 688

Antozone 116

Apatite 357

Apophyllite 358

Aposepedine (leucine) 704

1

PAGE

Attraction— coM^

PAGE

Apple oil

603

electrical

19

Aqua chlorinata

190

gravitative

19

Aqua fortis

174

magnetic

19

regia

199

varieties of

22

Aqueous vapor

138

Atropia

663

in air

163

Aurates

517

in gases

735

Aurochlorides

617

Arabinates

666

Auripigmentum

475

Arabine

665.

Aurum musivum

414

Arbor Diange

496

Aventurine

300

Archil

673

Axes of crystals

36

Argento-cyanides

498

Azobenzole

610

Argol 679

, 636

Azote

153

Arrack

583

Arragonite

358

Arrowroot

663

B.

Arsenamine

660

Arsenates

471

Balduin's phosphorus

354

Arsenic

465

Ball soda

335

acid

470

Balsam of Peru

653

alloys of

475

tolu

653

butter of

474

Balsams

617

chlorides of 473

,474

Barilla

334

extraction of

466

Barium

346

in coal

466

chloride of

347

in copper

418

nitroprusside of

396

in mineral waters

150

oxides of

346

in vegetables

543

sulphide of

348

Marsh's test for

477

Barley sugar

568

native

466

Barometer,con8truction of 158

oxides of

467

uses of

159

properties of

465

(water)

159

Eeinsch's test for

477

French scale of

732

sulphides of

474

Baryta

346

tests for

476

acetate of

650

white

467

carbonate of

348

Arsenical pyrites

466

nitrate of

347

Arsenides

475

oxalate of

645

Arsenious acid

467

plumbate of

431

Arsenites

469

sulphate of

348

Arsenuretted hydrogen

472

sulphonaphthalate of

609

Artesian well water

133

tartrate of

635

Artificial camphor

615

tests for

348

Ashes of vegetables

641

Bases, alkaline and

estimation of

643

earthy, tests for

378

Asparagin

666

defined

73

Asphalt 608

619

organic

657

Asphaltene

608

Basic water

144

Assay of gold

629

Bassorine

566

of silver

601

Beans

694

Atacamite

422

Bear's grease

706

Atmosphere

156

Beeswax

631

ammonia in

163

Beer

578

analysis of _ 160

165

Bell -metal

425

aqueous vapor in

163

Benzine

610

composition of

164

Benzoic acid (anhydrous)

663

density of

158

Benzole

610

height of

158

Benzyle

653

magnetism of

92

Benzoates

553

organic matter in

163

Benzoin

653

physical properties of

156

Benzoine

655

pressure of

158

Benzoline

655

uniform constitution of 165 |

Benzoyle

653

Atomic theory

65

hydride of

654

volumes

68

Bergmehl

399

weights

67

Beryl

374

Atoms, size and weight of

22

Bessemer process

382

Attraction, adhesive

23

Bezoars 643

720

capillary

24

Bibroraisatine

673

chemical

20

Bicarbnretted hydrogen

276

cohesive

23

Bichlorisatine

673

152

PAGE

Bile

718

tests for

720

Biliary calculi

719

Bilin

719

Binary compounds

74

Binitrobenzole

610

Bismuth

437

alloys

439

arsenic in

438

butter of

438

chloride of

438

nitrates of

438

oxides

437

sulphate of

438

tests for

439

Bisulphide of carbon '

289

Bitter-almond oil

654

spar

305

Bittern

363

Bitumen

608

Bituminous coal

607

schist

608

Black ash

334

flux

324

Jack

408

lead

251

Blanc d'Espagne

438

INDEX.

PAGE

Bristol diamonds

300

Britannia metal

463

Bromal

600

Bromates

203

Bromides

204

Bromine

201

chloride of

204

in organic bodies

550

Bromisatine

673

Bromobenzole

610

Bronze

425

castings

425

coinage

426

Bronzing medals

419

tin

415

Brucia

662

Brunswick green

422

Bude light

106

Butter

712

of antimony

461

of bismuth

438

of tin

413

Butyrates

628

Butyric fermentation

628

Bleaching 189, 217, 332

Bleaching-powder 352

Blende 408

Bleu de Paris 682

Blood 707

coloring-matter of 708

corpuscles 707

tests for 709

Bloodstone 300

Blowers in coal mines 270 j

Blowpipe, oxhydrogen 124 |

Blue dyes 671 |

John 354 i

Prussian 394 :

Thenard's 441

vitriol 423

Boghead coal 611

Bog iron ore 386

Boiling-points 138

Bone 705

weight of in adult 707

gelatine " 701

Bone earth 356

Bone grease 632, 706

Boracite 365

Borates 295

Borax 336

Borneen 618

Borneo camphor 618

Boron 292

chloride of 295

fluoride of 296

nitrate of 295

Botryolite 358

Boules de Nancy 637

Bouquet of wines 578

Boyle's fuming-liquor 187

Brain 705

Brandy 582

Brass 425

analysis of 426

Brazilwood 677

Braziline and Brazileine 677

Bread 696

Cadet's fuming-liquor 668

Cajsium 343

Cadmium 415

chloride of 416

oxide of 416

salts of 416

tests for 417

Caffeine 666

Cairngorm stones 300

Calamine 408

Calcareous spar 357

Calcedony 301

Calcium 350

chloride of 352

fluoride of 353

oxide of 351

phosphide of 351

sulphide of , 354

Calculi, biliary 719

salivary 714

urinary 728

Calico-printing 670

Calomel 481

Calotype 612

Camphine 615

Camphor 616

artificial 615

Borneo 616

Camphyle 615

Cane-sugar 668

Cane-coal 607

Canton's phosphorus 354

Caoutchine 620

Caoutchouc 620

vulcanized 59, 621

Capillarity 24

Capillary tubes 24

Caput mortuum 389

Carrageenin 667

Caramel 670

Carbazotates 613

Carbides 258

PAGE

Carbolic acid 610

Carbon 248
antiseptic powers of 257

amount of, expired 267

bisulphide of 289

estimation of 546

gaseous oxide of 261

of coal 252
. source of, in organic

bodies 645

Carbonated waters 149

Carbonates 269

Carbonic acid 263

quantity expired 267

decomposed by

plants 266, 645
decomposition of 266
liquefaction of 268
present in air 161
properties of 264
solidification of 268
sources of 264
tests for 267
Carbonic anhydride 266
Carbonic oxide 261
Carburet hydrogen 275
(light) 270
Carmeine 624
Carmine 623
Carnelian 300
Carre's freezing apparatus, 79
Carthamic acid 676
Carthamein 676
Carthamine 676
Cartilage 700
Casehardening 391
Casein 637
Cassel yellow 432
Cassius, purple of 518
Cast iron 381
Castor 720
Castor oil ^0
Catalysis 68
Cathode 69
Cations 60
Cedriret 612
Cellulose 603
Cementation 391
Cements 359
Cerasin 666
Cerebro-spinal fluid 717
Cerin 631
Cerolein 631
Cerium 376
Cerumen 705
Cetene 631
Cetine 631
Chalcolite 454
Chalk 358
Chalk-stones 726
Chalybeate waters 149
Charcoal 253
absorption of gases by 256
animal 259
ashes of 255
antiseptic powers of 257
catalytic power of 257
combustion of in oxy-
gen 92
decoloring power of 258
filters 258

INDEX,

753

ChAECOAL — C07lt. PAGE

preparation of 253

properties of 255

quantity from various

woods 255

Cheese 638

Chemical analysis 52

change, proof of 51

compounds defined 46

equivalents 64

force 20, 40

nomenclature 73

notation 69

and physical properties 20

Chemistry defined 17

China 374

Chitin 706

Chloracetates 649

Chloral 589

Chloric ether 275, 590

Chlorides 191

Chlorimetry 353

Chlorine 188

aqueous 190

combustion in 190

in organic bodies 550

oxides of 192

properties of 188

tests for 191

Chlorisatine 673

Chlorites 192

Chlorobenzole 610

Chloroform 590

formula of determined 557

Chlorophyllin 684

Chlorophane 354

Chocolate 630

Choke-damp 264

Cholesterine 719

Chondrin 704

Chromates 445

Chrome-alum 447

yellow 446

Chromic acid 445

Chromium 444

chlorides of 447

fluoride of 447

oxides of 444, 445

sulphates of 447

tests for 448

Chromomolybdic acid 453

Chrysene 610

Chrysoberyl 374

Chrysocolla 424

Chrysolite 366

Chrysoprase 300

Chrysorhamnine 680

Chyle 711

Chinchonia 660

Cinnabar 486

Cinnamyle 616

Citric acid, characters of 638

Citrates 539

Civet 720

Clay 371

Clay — iron-stone 380

Cleavage of crystals 27

Clot of blood 707

Coal 607

analysis of 607

bituminous 607

b oghead cannel 611

48

Coal — cont. page
cannel 607
carbon of 252
gas 271
composition of 271
measures 607
mines, fire-damp of 273
naphtha 609
oil 609
origin of 607
parrot 607
products of its distilla-
tion 271
steam 607
tar 609
colors from 631
Welsh 607
Cobalt 439
ammonia compounds of 441
arsenate of 439
arsenide of 439
borate of 441
carbonate of 441
chloride of 440
cyanides of 441
glance 439
nitrate of 440
oxides of 439, 440
sulphate of 440
sulphides of 440
tests for 441
uses of 441
Cobaltocyanides 441
Coccinelline 678
Cochineal 678
Cocoa 630
Cocoa-nut oil 630
Codeia 659
Coffee 666
Cohesion 23
influence of, on chemi-
cal force 41
Coke 252
Colchicia 663
Colcothar 389
Cold, production of 33
Collodion 507
process in photography 607
Colophene 618
Colophony 618
Color of the blood 707
of flowers and leaves
of light 107
of gases 102
of incandescent gases 84
solids 105
of salts influenced by
water 144
Coloring matters 669
of blood 708
influence of water on 42
Colors, production 669
substantive and adjec-
tive 670
Colostrum 712
Columbium 450
Combination, laws of 65
Combustibles defined 103
Combustion defined 103
in air 153
in oxygen 92, 100
in rarefied air 158

Combustion— ro??f. page
heat and light evolved

in 103

products of 108

without oxygen 101

Combustion-tube 550
Compound radicals 74, 558

Compounds, binary 74
Compressibility of liquids 136

Concrete 359
Concussion, influence of

on crystallization 34
Conduction, electric, by

metals 311
by water 135
of heat, by metals 310
by water 135
Condy's disinfectant 402
Confectionery, poisonous 470
Congelation, line of per-
petual 158
Conia 664
Constitution of salts 73
Conversion of heat 135
Copal 619
Copper 417
alloys of 424
acetates of 650
azure 424
ammonio-sulphate 423
bronzing of 419
carbonates of 424
chlorides 421
cyanides 424
emerald 424
formate of 652
iodide of 422
manufacture of 417
nitrate of 421
ores of 419, 423
oxides of 419
use in organic analysis 546
poisoning by 427
pyrites 423
silicate of 424
sulphate of 423
sulphides of 422
smelting of 417
tartrates of 637
tests for 426
tinned 426
Copperas 389
Coral 706
Cornish clay 371
diamonds 299
Corpuscles of the blood 708
Corrosive sublimate 482
tests for 490
Corundum 368
Crassamentum 707
Cracklings 631
Cream 702
of tartar 636
Creasote (see Kreasote) 612
Crocus of antimony 462
Crucibles ' 373
Cryolite 367
Cryophorus 141
Crystalline solids 28
structure 26
Crystallization 26
by fusion 26-

Y54

INDEX.

PAGE

Crystallization — cont.

by sublimation 28

salts separated by 30

by solution 29

systems of 35

theory of 35

Crystals, axes of 36

artificial mineral 28

biaxial 36

cleavage of 27

deposition of 30

double refracting 36

forms of 25

microscopic 37 ,

production of 28 i

structure of 26

unequal expansion of 28

uniaxial 36 '

Weis's system of 35

Cudbear 674

Camole 609

Cupellation 427, 502

Curagoa 582

Curcumine 680

Curd 694

Cyamelide 281

Cyanates 281

Cyanides 287

tests for 287

Cyanogen 278

bromide of 288

chlorides 287, 288

iodide of 288

sulphide of 288

tests for 278

Cyanurates 282

Cymol 609

Daguerreotype

Datolite
Daturia
Decay
of wood

506
358
663
98
606

Decomposition, electric 59

of salts 59

Decrepitation 32

Definite proportions 40

Deflagration 108

Deliquescence 32

Dentine 706

Deoxidation 97

Derbyshire spar 354

Dextrine 664

Diabetic sugar 572

Diachylon 632

Dialysis 50, 146

Diamagnetic bodies 312

Diamond 249

cleavage of 27

combustion of 249

valuation of 251

Diaspora • 369

Diastase 564

Diatomacse 299

Didymium 376

Diffusion of gases 85

law of 87

of metallic vapors 86

Diffusion — cont. page

of liquids 50

of vapors 86

volume 87

Digestion 715

Digitalia 663

Dimorphism 37

Dipples oil (acroleine) 632

Disacryle 633

Distillation — fractional 644

Distilled vinegar 648

water 134

Divisibility of matter 21

Dolomite 365

Double affinity 55

Dough 696

Dry rot 606

Drummond's light 124

Ductility 308

Dutch gold 425

liquid 277

white 435

Dyeing 670

Dyslysine 718, 719

E.

372
621
714
537

688

Earthenware
Ebonite
Echidnine
Educts, organic
Efflorescence
Eggs, white of

yelk of ess

Elaine 623

Elaioptene 614

Elayle 275

Electric flame, heat of 108

Electrodes 69

Electrolysis 59

Electro-negative bodies 60

Electro-plating 501

Electro-positive bodies 60

Elements 17

arrangements of 78

relative proportions of

in animals 706

table of 68

Elementary analysis 545

Emerald 374

Emerald-green 469

Emery 368

Emetic tartar 637

Emetina 666

Emulsin 654

Enamel 339

of teeth 704
Endosmose and exos-

mose 50, 87, 146

Epsom salt 363

Equivalent weights 64

volumes 68

Equivalents chemical 65

tablfe of 67

of organic bodies 554

barometrical 732

thermometrical 733

Erbium 376

Eremacausis 98

Erythrine 675

PAGE

675
684
692
613
614
631
595
602
698
602
602
603
602
279
602
602
595
602
602
602
602
602
602
601
latent heat of its vapor 141
muriatic 602

nitric 601

nitrous 601

cenanthio 579, 603

ozonized 698

pelargonic 603

perchloric 602

phosphoric 597

production of 595

products of its combus-

598

Erythrylene
Erythrophylin
Erythroprotide
Essential oils

adulteration of
Ethal
Ether

acetic

antozonized

benzoic

boracic

butyric

carbonic

chloric

citric

cyanic

formation of

formic

hydriodic

hydrobromic

hydrochloric

hydrocyanic

hydrosulphuric

hyponitrous

tion
silicic
succinic
sulphatic
sulphuric
tests for

602
602
601
595
600

theory of its formation 596

washed 696

Etherification, theory of 596

Etherole 601

Ethers, compound 603

double 603

Ethiops mineral 486

Ethogen 295

Ethylamine 560

Ethyle 601

bromide of 602

chloride of 602

cyanide of 602

iodide of 602

Ethyle, sulphide 602

Ethylic alcohol (Alcohol) 683

Ethylene 275

Eucalyn 673

Euchlorine 195

Euclase 374

Eudiometry 160

Eupion 612

Euxanthates 681

Euxanthin 681

Expansion of gases 82

liquids 136

metals 310

solids 310

Excrement 721

Excretine 721

INDEX,

T55

PAGE

Explosions in coal mines 274
Eye, liquids of the 717

F.

Fats, general properties

of 622
Fatty acids 623
Fecula 560
Felspar 299
Fergusonite 450
Fermentation 573
acetic 646
alcoholic 573
butyric 628, 713
lactic 628, 713
panary 573
pectic 567
viscous 579
Fermented liquids 578
Ferments 573
Ferrates . 385
Ferric acid 385
Ferricyanogen 289
Ferricyanides 289
Ferrocyanogen 289
Ferrocyanides 289
Ferrum redatum 383
Fibrin 697, 705
tests for 699
vegetable 695
Fire-clay 372
Fire-damp 270, 274
indicator 275
Fixed air 263
oils 622
stars, light of 108
Flame, nature of 107
temperature of 107
Flesh, juice of 705
Flint 300
Flowers, colors of 681
scents of 613
Fluoborio acid 296
Fluorides 212
Fluorine 210
Fluor-spar 353
Food of animals 539
preservation of 687
Force, chemical 20
physical 19
Formates 652
Formulae, chemical 67
from vapor densities 656
empirical 558
in organic analysis, 654
rational 558
Formyle 652
Fowler's mineral solu-
tion 469
Fractional distillation 544
Freezing mixtures 33
by evaporation 79
French chalk 366
polish 619
Fructose 569, 672
Fruits, sugar of 669
Fuchsine 682
Fuller's earth 371
Fulminating mercury 488
powder 320

PAGE

Fulminating silver 499

Fulminic acid 281

Fuming liquor of Boyle 187

of Cadet 668

of Libavius 413
Functions of vegetables

and animals 266

Fusel oil 593

Fusibility of metals 310

Fusible metal 439

Fustic 680

G.

Gadolinitb 376

Galena 433

Gallates 642

Gall-nuts 641

Gall-stones 719

Gallic acid 641

Galvanized iron 409

Garancin 675

Garlic, oil of 617

Gas explosions 274

in mines 273

Gaseous diffusion 85

Gases 78

and vapors defined 78
bulk of, at different

temperatures 83

desiccation of 146

diamagnetism of 85

diffusion of 86

expansion of, by heat 83

incandescence of 83

liquefaction of 79

magnetism of 85
measurement of 82, 734
passage of, through

diaphragms 87

physical properties of 81

refractive powers of 85
specific gravities of 84, 677

specific heat of 84

solidification of 80

solubility of, in water 141
effect of pressure and

temperature on 734, 735

aqueous vapor in 736

Gastric juice 715

Geine 607

Geodes 26

Gelatin 699

offish 700

of skin 701

of bone 701

sugar 704

tests for 703

Gelose _ 667

Gems, artificial 28

imitations of 338

Gerhardt's notation 69

German silver 444

Geyser water 303

Gibbsite 369

Gilding by amalgam 619

Gin 682

Glass, analysis of 338

aventurin 339

Bohemian 650

bottle 338

Glass, colored
crown
devitrified
expansion of
flint

PAOB

339
338
338
310
338

Glass, manufacture of 337

optical 338

plate 338

soliible 304

Glauberite 356

Glauber's salt 332

Glaze for iron pots 339, 373

for earthenware 373

Globulin 692, 717

Glonoine 626

Glucina, salts of 374

Glucinum 374

Glucose 660

Glucosides 668

Glue 704

Gluten 696

Glutin 695

Glycerine 625

Glycocine 704

GlydocoU 704

Glvcyrrhizine 673

Gold 515

alloys of 51»

amalgam of 519

assay of 519

bromide of 618

chlorides of 517

coin 619

cyanide of 518

iodides 518

oxides of 517

pure 516

quality of, ascertained 619

separation of, from

silver 620
standard 519
sulphides of 518
tests for 620
trinkets 519
use of, in photography 512
Goniometers 40
Goulard's extract of lead 651
Granite 299
Grape-sugar 669
Graphite 251
Gravity influences solu-
tion 48
specific 736
Greaves 631
Green paper-hangings 469
Scheele's 469
vitriol 389
Guaiacum 618
Guano 725
colors from 678
Gum 665
elastic 620
resins 617
Gun-cotton 604
photographic 605
Gunpowder 320
for needle-gun 109
unexplosive 321
Gutta-percha 622
Gypsum 365

756

INDEX.

H.

Hydrogen — cont. page

Iron — co7it.

page

pIge

light carburetted

270

bog, ore of

386

H^MATEINE

677

nascent

125

bromides of

387

Hsematosine

708

penetrating power of

121

carbonates of

392

Haematite

386

peroxide of

151

carbides of

390

Haematoxylin

677

persulphide of

187

cast

381

Hair

688

preparation of

118

change of structure

Halogens

188

properties of

120

of

34, 382

Haloid salts

75

sulphuretted

226

chlorides of

386

Hamburgh-white

435

telluretted

457

cold short

382

Hardening of steel

392

Hydrophane

300

combustion of, in

3xy-

Hardness of minerals

301

Hydrosulphuric acid

226

gen

95

of metals

309

Hyoscyamia

663

cyanides of

393

Harmonicon chemical

123

Hydrometers

585

ferricyanide of

395

Hartshorn, salt of

187

Baume's

737

ferrocyanide of

393

Hatchetine

611

Twaddell's

738

galvanized

409

Hausmannite

401

Hygrometric water

147

gray cast

381

Heat, conduction of 135

310

Hyponitrites

172

hot-short

382

convection of

135

Hypophosphites

239

hyposulphite

389

influence of on chemi-

Hyposulphates

225

iodide of

387

cal force

44

Hyposulphites

224

magnetic oxide of

385

expansion by 136

310

Hyposulphuric acid

224

magnetism of

383

latent

140

Hyposulphurous acid

224

malleable

381

specific

139

manufacture of

380

Heating powers of differ-

I.

meteoric

444

ent combustibles

103

mottled

381

Heavy spar

248

Ice

136

native

444

Heliotrope

300

crystalline texture of

137

nitrates of

387

Hellebore

663

expansion of

137

ores of

385, 393

Hippuric acid

656

specific gravity of

132

oxides of

383

Hippurates

656

Ice water

137

passive state of

388

Hoffmann's anodyne

599

Iceland spar

357

persalts of

397

Homberg's pyrophorus

370

Igasuric acid

662

phosphates of

390

Honey

572

Ignition

101

phosphide of

390

Hops, use of, in beer

578

temperature of

105

protoxide of

383

Horn

688

in vacuo

102

pure

382

Horn-lead

431

voltaic

102

pyrites

388

silver

494

Ilmenium

451

reduced

383

Hot blast

104

Incandescence 33

, 101

refining of

381

Humboldtite

643

Incubation, changes of

separation of the oxides 397

Humic acid

607

the egg in

690

smelting of

380

Humors of the eye

717

Indian fire

474

specular ore of

386

Humus

603

rubber

620

succinate of

620

Hyacinth

375

yellow

680

sulphates of

389

Hydracids

43

Indigo

671

sulphides of

388

Hy drargochl orides

485

Indigogene

672

tartrates of

637

Hydrargyroiodides, test

Indigotine

671

tests for

396

for alkaloids

484

Indium

410

welding of

382

Hydrate of soda from salt 330

Ink, marking

496

wrought

381

Hydrated salts

32

printing

629

zinced

409

Hydrates

143

sympathetic

440

Isatide

673

Hydraulic lime

359

writing

641

Isatine

673

Hydrie nitrate

174

Inuline

665

Isinglass

700

Hydrides

124

lodates

207

Japan

567

Hydrobenzamide

655

Iodides

209

. patent

701

Hydrocarbons

269

Iodine

205

Isomerism

18, 536

analysis of

653

chloride of

209

Isomorphism

38

oily

615

in organic bodies

550

Isomorphous bodies

38,39

Hydrochloric acid

196

tests for

206

Ivory

706

Hydrocyanic acid

281

Ions

60

tests for,

286

Ipecacuanha

666

Hydrogen

118

Iridium

629

J.

allotropic

125

salts of

630

Jade

386

a metallic vapor

126

Iron

380

Japan isinglass

567

antimonuretted

461

acetates of

650

varnish

619

arsenic in

119

alloys of

396

Jargon

375

arsenuretted

472

alum

390

Jasper

300

compounds of

124

ammonio-chloride of

387

estimation of, in or-

arsenates of

472

K.

ganic analysis

546

bar

382

high temperature of its

benzoate of

654

Kakodylb

668

flame

123

black oxide of 383

385

Kaolin

371

INDEX.

157

PAGE

Kapnomor

612

Kelp

324

Kermes-mineral

462

Kerosine

609

King's yellow

475

Kinic acid

661

Kirschwasser

582

Kreasote

612

Kreatine

705, 727

Kreatinine

705, 727

Krems white

435

Kupfernickel

442, 476

Kyanol (aniline)

665

L.

Labarraque's disin-
fectant 331, 335

Lac 619

dye 678

lake 678

sulphuris 214

Lacmus 673

Lacquer 619

Lactarine 670

Lactic fermentation 628

Lactine 713

Lactose, op lactine 713

Lakes 368

Lake water 130

Lampblack 260

Lanthanum 376

Laquers 619

Lard 623

Latent heat 140

of steam 140

of vapors 141

Laughing gas 167

Laws of combination 65

Lazulite 371

Lead 427

acetates of 650
action of air and water

on 428

alloys of 436

amylate of 562
borate of . 436

bromide of 432

black 251

carbonate of 433

chloride of 431

chromates of 446

cupellation of 428

cyanide of 436

desilvering of 427
extraction of, from

ores 427

fluoride of 432

formate of 652

hyponitrite of 431

iodine of 432

in vegetables 542

nitrates of 431

oxichloride of 432

oxides of 429

phosphates of 433

pyrophoric 41

saccharide of 570

sugar of 651

sulphate of 433

Lead — cont. page

sulphide of 432

sulphite of 433

tartrate of 637

tests for 430

white 433

Leather 703

Leaves, colors of 628

Lecanorine 674

Legumin 695

Lepidolite 341

Leucine 703

Levulose 5 1 2

Lichenine 565

Lichens 567

colors from 673

Light, chemical action of

446, 455, 503
and heat of combustion 103
chemistry of 503
color of, in gases 102
emitted in crystalliza-
tion 467
evolved in combustion 105
influence of, on com-
bination 85
influence of, on chemi-
cal force 44
polarized 570
refraction of, by gases 85
carburetted hydrogen 270
Lightning, color of 102
Lignine 606
Lignite 607
Lime 351
acetate of 650
benzoate of ■ 653
carbonate o 357
chloride oi 362
citrate of 639
hypochlorite of 352
hypophosphite of 356
hyposulphite of 355
meconate of 656
muriate of 352
nitrate of 354
oxalate of 645
phosphates of 356
plumbate of 431
silicates of 358
sulphate of 355
sulphite of 355
tartrate of 637
tests for 359
water 352
Lime-kiln 351
Lime-light 124
Limestones 358
Liquation 492
Liquefaction, cooling by 33
of gases 79
Liquors 582
Liquids, compressibility of 136
conduction of heat by 135
convection of heat by 135
expansion of 136
spirituous 682
Liquor amnii

pericardii
Liquorice sugar
Litharge
Lithia

48*

PAGB

Lithia, oxalate of

645

salts of

341

tests for

342

Lithium

341

in organic bodies

642

Litmus

673

paper

674

Liver of antimony

462

of sulphur

322

Loam

374

Logwood

677

Lozenges

563

Luna cornea

494

Lunar caustic

495

Luteolin

680

Lutes

374

Lymph

711

717
717
573
429
341

Macaroni 695
Macquer's arsenical salt 471
Madder 675
Madrepore 706
Magenta dye 682
Magistery of bismuth 438
Magnesia 361
ammonia-phosphate of 364
borate of 365
carbonates of 364
chloride of 362
euxanthate of 681
hydrate of 361
hypochlorite of 362
nitrate of 362
phosphates of 364
silicates of 365
sulphate of 363
tests for 366
Magnesian limestone 365
Magnesium 360
bromide of 362
chloride of 362
combustion in oxygen 95
in chlorine 101
oxides of 361
platino-cyanide of, 33, 524
Magnetic iron ore 385
Magnetism of the atmo-
sphere 92
of metals 312
of gases 85
Malachite 424
Malates 640
MalleabUity 308
Malt 678
Malt-spirit 678
Manganates 401
Manganese 398
carbide of 405
carbonate of 406
chlorides of 403
nitrates of 404
oxides of 399
sulphate of 404
sulphide of 404
tests for 405
, Manganic acid 401
I oxide 399
I Manganite 400

758

INDEX.

PAGE

Manganous oxide 399

Manheim gold 425

Manna 572

Mannite 572
formula of, calculated 556
Manure 357, 725

Maraschino 682

Marble 358

Marcasite 437

Margarine 624

Marking-ink 496

Marl 358

Marsh gas 270

Marsh's arsenic test 477

Martial Ethiops 385
Mass, influence of, on

aflBnity 54

Massicot 429

Matter, properties of 17

divisibility of 21

Mauve dye 681

Meadowsweet, oil of 667

Measures and weights 729

Meconine 659

Meconium 721
Medals, bronzing of 415, 419

Meerschaum 365

Viennese 365

Melam 289

Melamine 289

Melitose 573

Melinite 261

Mellone 280

Melon, essence of 603
Membranes traversed by

gases and vapors 87

Mercaptan 602

Mercurius vitas 461

Mercury 479

acetate of 651

amalgams of 488

amidochloride of 483

amidonitrate of 486

bromides of 484

carbonates of 487

chlorides of 481

chlorosulphide of 487

cyanide of 487

detection of, in cases of

poisoning 490

freezing of 480

fulminating 488

iodides of 484

nitrates of 485

nitride of 485

ores of 479

oxides of 480

phosphates of 487

purification of 480

sulphates of 487

sulphides of 486

sulphocyanide of 288

tests for 489

Metalochromes 431

Metalloids 78
Metallic compounds, quali-
tative analysis of 376, 531

Metals 307

diamagnetism of 312

ductility of 308
electro-coflduction by 312

Metals— cont. page

expansion of 310

fusibility of, 310

general properties of 308

hardness of 308

lustre of 308

magnetic 312

magnetism of 312

malleability of 308

penetration of, by gases 89

specific gravity of 309

specific heat of 311

table of 307

tenacity of 308

Metameric compounds 19

Metantimoniates 460

Metaphosphates 244

Metastannates 412

Meteoric stones 444

Methylamine 560

Methylated spirit 693

Methyle 593

salicylate of 603

Methylic alcohol 692

ether 693

Metre 730

Metrical system 730

equivalents 731

Mica (talc) 365

Microcosmic salt 333

Milk 693, 711

Mindererus's spirit 650

Mineral cameleon 401

green 424

oil 608

pitch 608

tar 608

waters 148

Minium 430

Mirbane, essence of 610

Mirrors, silvering of, 489

by silver 496

Mispickel 475

Mocha-stone 300

Moire metallique 414

Molybdates 452

Molluscous animals 693

Molybdenum 451

chlorides of 452

oxides of 451

sulphide of 453

tests for 453

Mordants 67

Morine 680

Morphia 658

formula of, determined 454

tests for 452, 659

Mortars and cements 358

Mosaic gold 414

Moss-agate 300

Mother-liquors 29

Mountain blue 424

green 424

meal 299

Mucilage • 566

adhesive 566

Mucin 693

Mucus 716

Multiple proportions 96

Muntz's metal 424

Murexan 679

Murexide 678

Muriacite

Muscle

Musk

Mustard, oil of

Myricin

Myrosin

N.

PAGE

356
705
720
616
631
616

Naphtha, coal

609

native

608

wood

592

Naphthalin

609

Narceia

659

Narcotina

660

Nascent state

45, 125

Natrium

328

Needle-gun powder 109
Negative photographs 607
Neutralization 77
Neutral nitrogenous prin-
ciples 685
Nickel 442
alloys of 444
carbonate of 443
carbide of 443
chloride of 443
cyanide of 444
nitrate' of 443
oxides of 442
phosphate of 443
potassio-cyanide of 444
pyrites 442
sulphate of 443
sulphide of 443
tests for 444
Nicotina 664
Nihil album 407
Niobium 451
Nitrates 177
Nitre 319
Nitric acid, tests for 177
oxide 168
pentoxide 174
tetroxide 172
tritoxide 171
Nitrides 155
Nitro-benzole 610
Nitrogen 153
bicarbide of 278
binoxide of 168
chloride of 200
deutoxide of 16.8
estimation of, in organic

analysis 552

iodide of 209

in the atmosphere 156

oxides of 166

peroxide of 172

phosphide of 246

preparation of 153

properties of 154

protoxide of 168

tests for • 155

Nitro-glycerine 626

Nitro-muriatic acid 199

Nitro-prussides 289

Nitrous gas 168

oxide 166

Nitrum flammans 186

INDEX.

"[59

PAGE

Nomenclature, chemical 73

of organic compounds 569

Non-metallic bodies 78

Nordhausen sulphuric acid 222

Norium 451

Normal salts 77

Notation, chemical 64

Gerhardt-s 69

old and new 745

unitary 69

Notations compared 70

Noyau 582

Nutmeg butter 631

Nutrition of animals 685, 699

plants 539

Nux vomica 661

Obsidian 301

Ochre 372

(Enanthic ether 679

(Enanthin 579

Oil-gas 277

Oil of almonds 630

ben 630

bitter almonds 654

castor 630

chocolate-nut 630

cocoa-nut 630

coal -tar 609

cod-liver 630

colza 670

Dippel's (acrolein) 632

hemp 630

laurel 671

linseed 629

meadow-sweet 667

nutmeg 671

olive 670

palm 630

poppy-seed 630

rock 608

sperm 630

turpentine 615

walnut 630

whale 630

of vitriol 219

of wine 601

Oils, drying 629

essential 613

fixed 629

specific gravity of 630

volatile . 618

Oil-bath 629

Oleates 624

Olefiant gas 275

chloride of 277

Oleine 624

Oleum sethereum 601

Olivine 366

Onyx 300

Oolite 358

Oonin 688

Opacity of metals 308

Opal 300

Opium 668

Orceine 675

Orcine 674

Organic chemistry 535

Organic analysis
bodies, test for
coloring matters
elements
equivalents
metamorphoses
principles
radicals

PAGE

541
645
669
356
554
640
356
658

substances, tests for 645
Organoleptic properties 20
Organo-metallic bases 668
Orpiment 475

Orseille 674

Osmazome 705

Osmium 528

compounds of 529

Osmosis 50, 87, 146

Ovalbumen 688

Oxacids, constitution of 93
Oxalates 644

Oxalic-acid, manufacture
of 643

properties of 643

tests for 646

ultimate analysis of 545
Oxamic acid 645

Oxamide 644

Ox-gall 718

Oxidation 95

Oxides defined 96

nomenclature of 96

reduction of 97

Oxychlorates 195

Oxygen 90

allotropic 110

deodorizing power of 99
in the atmosphere 160

equivalent of 99

magnetism of 92

preparation of 90

properties of 92

determination of in or-
ganic analysis 547
refractive power of 92
specific heat of 92
tests for 99
Oxygennesis 91
Oxyhydrogen blowpipe 124
Oxymuriatic acid 188
Oxy water 151
Oysanite 457
Oysters ' 693
Ozokerite 611
Ozone 110
bleaching power of 112
constitution of 116
in the atmosphere 115
from ether 111
in oil of turpentine 113
in permanganates 113
reconverted into oxygen 114
tests for 114
Ozonides 113
Ozonized water 403
Ozonometry 115

Pakfovg
Palladium

444
526

PAGE

Palladium, carbide of

527

oxides of

626

■ salts of

526

tests for

527

Pancreatic fluid

715

Papaverine

669

Papier Moure

472

Paracyanogen

278

Paraffine

611

oils

611

Paranaphthaline

610

Parchment, vegetable 603

Patent yellow 432

Pear-oil 603

Pearl-ash 323

Pearl-white 439

Peas 695

Pea-stone 358

Pectase 667

Pectic acid 667

fermentation 667

Pectine 566

Pectose 566

Pelargonic ether 603

Pelopium 451

Pepper 666

Pepsine 716

Perchlorates 195

Perchromic acid 445

Percussion caps 488

Periodates 208

Permanganates 402

Peroxide of hydrogen 151

Persian berries 680
Persistent soap-bubbles

625, 633

Persulphide of hydrogen 187

Peru balsam 653

Petalite 341

Petrolene 608

Petroleum 608

Pettenkofer's test for bile 720

Pewter 436, 463

Pharaoh's serpents 289

Phene (benzole) 610

Phenakite 374

Phenol 610

Phenylia (aniline) 665

Phenalamine (aniline) 560

Philosopher's lamp 125

wool 407

Phloridzine 668

Phosgene gas 263

Phosphamide 246

Phosphates 243

tests for 243

Phosphides of hydrogen 244

Phosphites 240

Phospbori solar 354

Phosphorus 233

acids of 239

allotropic 237

amorphous 237

Balduin's 350

bromides of 247

Canton's 354

chlorides of 246

deoxidation by 236

in organic bodies 550

iodides of 247

nitride of 246

t60

INDEX.

Phosphorus — cont. page

oxide of 238

sulphide of 247

tests for 237

Phosphorized alcohol 234, 587

ether 254, 597

oils 234

Phosphuretted hydrogen 244

Photographic pyroxyline 605

Photography 603

collodion process in 507

on glass 507

on paper 512

Photometry 196

Physical forces 19

Picamar 612

Picric acid 613

tinctorial properties of 6 1 3

Picrotoxia 663

Pine-apple oil 603

Pinchbeck 425

Pink saucers 676

Pins, tinning of 415

Piperine 666

Pisolite 858

Pitch 608

Pitch-blende 453

mineral 608

Pittacal 612

Plants, functions of 547

nutrition of 539

Plaster of Paris 355

lead 633

Plaster-stone 355

Plating . 498

Platino-chlorides 623

Platinocyanides 624

Platinum 620

alloys of 625

ammonio-chloride of 623

black 621

bromides of 524

catalytic 58, 522

chlorides of 523

condensation of gases

by 128, 522
cyanide of 624
fulminating 523
iodides of 624
malleable, manufac-
ture of 620
ore of 620
oxides of 522
potassio-chloride of 524
sulphate of 524
a test for gelatin 703
sulphide of 524
tests for 525
Plumbago 251
Plumbates 431
Poling of copper 417
Polymeric compounds 19
Porcelain 374
Reaumur's 338
Porter 678
Portland arrowroot 563
cement 359
stone 358
Pot-ash 323
Potassa • 313
acetate of 650
alum 369

Potassa — cont. page
antimonio -tartrate of 637
bicarbonate of 325
bisulphate of 323
bitartrate of 636
carbonates of 323
chlorate of 317
chlorinated 316
chromates of 445
cyanate of 325
hydrates of 314
hypochlorite of 316
hyponitrate of 320
in organic bodies 641
iodate of 319
nitrate of 319
nitrite ;i21
oxalates of 645
oxychlorate of 318
perch 1 orate of 318
plumbate of 431
silicates of 327
sodio-tartrate of 636
solutions, sp. gr. of 315
Stan n ate of 412
sulphates of 323
tartrates of 636
tests for 327
Potassiamide 321
Potassio-tartrate of anti-
mony 637
of iron 637
of soda 636
Potassium 312
bromide of 319
chloride of 316
cobalto-cyanide of 441
cyanide of 325
ferricyanide of 327
ferrocyanide of 326
iodide of 318
iodohydrargyrate of 657
nitride 321
oxides of 313, 314
sulphides of 322
sulphocyanide of 326
Potato-spirit 693
Pottery 374
Prase 300
Precipitate, signification of 53
per se 481
white 483
Precipitation ' 53
Predisposing affinity 66
Preservation of animal

substances 687
Prince Rupert's metal 425
Printer's ink 629
Prismatic analysis 61
Products, organic 637
of combustion 108
Proof-spirit 685
Proofs of chemical change 51
Propylene 617
iodized 617
Proteic compounds 686
Protein 685
Protide 692
Proximate organic ana-
lysis 641
principles 560
Prussian blue 394

Prussian blue — cont. page

soluble 395

TurnbuU's 396

Prussic acid 282

tests for 286

Ptyalin 693, 714

Puddling of iron 381

Pulmonary exhalation 717

Pumice 301

Purple of Cassius 517

Purpurutes 679

Purpuric acid 679

Purpurine 676

Purree 681

Pus 716

Putrefaction 98

animal 686

Puzzuolana 359

Pyin 693, 716

Pyrene 610

Pyrites, arsenical 475

copper 423

iron 388

Pyrogallic acid 642

use of, in eudiometry 160

in photography 508

Pyroligneous acid 648

Pyrolusite 400

Pyrophori 41

Pyropborus, Homberg's 370

of lead 637

Pyrophosphates 243

Pyroxanthine 693

Pyroxylic spirit 692

Pyroxyline 604

photographic 606

Q.

Quartz 299

Quercite 573

Quercitron bark 679

Quercitrine and quer-

cifcreine 679

Quicklime 351

Quinces, essence of 603

Quinia 660

sulphate of 660

Quinidine 661

Quinoidine 661

R.

638

Racemates

Racemic acid 638

Rack 682

Radicals, hypothetical 74

organic 658

simple and compound 74

Range of oxidation 96

Raphides 641

Ratafia 582

Rays, actinic 505

chemical 505

Realgar 474

Reaumur's porcelain 338

Rectified spirit of wine 583

Red dyes 676

glass 339

ink 677

lead 430

INDEX

701

Red — co7it. PAGE

ore of antimony 462

ore of silver 497

Sfinders wood 677

Reduction of oxides 97

of iron 383

Regains of a metal 97

Reinsch's arsenic test 468

Rennet 694, 713

Resins 617

Respiration 97

of animals 267

of plants 539

Rhamnine and rhamneine 680

Rhodium 527

oxides of 527

salts of 528

sulphides of 528

Rhubarb, acid of 643

River water 130

Rochelle salts 636

Rock-crystal 299

Rock-oil 608

Rock-salt 330

Roestone 358

Roman cement 359

Rosaniline (Roseine) 682

Rosin 615

Rouge 677

Rubidum 343

in vegetables 542

Ruby 368

silver ore 497

Rue, oil of 628

Rutic acid 628

Rupert's drops 338

metal 425

Ruthenium 628

Rutilite 457

S.

Sacchulmine

568

Safety lamp

273

Safflower

676

Sago

563

Sal alembroth

483

ammoniac

186

de duobus

323

enixum

323

gummosum

636

mirable (Glauber's)

332

prunella

320

Salicine

667

Salicyle

667

Salicylic acid

667

Saline waters

149

Saliva

714

its action on starch

562

Salivary calculi

714

Saltpetre

319

Salt of sorrel

645

Salt of tartar

323

Salt, spirit of

196

Salts, acid

74

anhydrous

32

basic

74

binary

74

constitution of

73

decrepitation of

32

defined

73

Salts — cont. page

deliquescent 32

eiflorescent 32

electric decomposition of 76

haloid 75

hydrated 32

nature of 73

neutral 77

nomenclature of 74

normal 77

Sandstone 299

Santaline and santaleine 677

Saponification 631

Sapphire, oriental 368

Sarcosine 705

Sardonyx 3^0

Satin spar 368

Saturation defined 50, 77

Saturn 427

Sawdust, oxalic acid from 643

Saxon sulphuric acid 222

Scheele's green 469

Schists, bituminous 608

Schweinfiirth green 469

Scotch topaz 300

Sealing-wax 619

Sea-salt 330

Sea-water 147

sp. gr. of 148

saline contents of 148

Sea-weed 567

Sedative salt 294

Seignette's salt 636

Seleniates 232

Selenite 366

Selenium 230

Seleniuretted hydrogen 232

Seralbumen 689

Serpentine 366

Serpent-poison 714

Serum of blood 689

Sheathing of metal 424

Shell- lac 619

Shells 706

bherry, analysis of 680

Shot 476

Silica 299

in plants 299

Silicates 304

Silicic acid 299

Silicon 297

bromide of 306

chloride of 306

fluoride of 306

nitride of 306

sulphide of 306

Silk 613

Silver 492

acetate of 650

alloys of 500

amalgam of 600

ammonio-nitrate of 497

arsenate of 500

arsenio-nitrate 600

arsenite of 499

assay of 601

bromide of 495

carbonate of 498

chloracetate of 649

chloride of 494

chromates of 500

coin 600

Silver — cont.
cupellation of
cyan ate of
cyanide of
cyanurate of
electro-plating of
extraction of
frosted
fulminate of
fulminating
German

hyposulphite of
iodide of
in lead
nitrate of
ores of

reduction of
oxides of
phosphates of

PAGE

602
499
498
499
499
492
600
499
499
444
497
495
428
495
492
492
493
498

salts of, their characters 602

effects of light on 503

use of, in photography 603

standard 600

steel 600

sulphate of 498

sulphide of 497

tests of 502

Silver-white 435

Silvio acid 618

Silvius, febrifuge salt of 650

Similor 425

Sinapine 617

Single affinity 52

Size 704

Slags, iron 380

Smalt 441

Smelting of copper 417

iron 380

lead 427

silver 492

Snow 138

Soap ^ ^ 631

composition of 631

Soap-bubbles, persistent

625, 633

Soap-stone 366

Soap-test for water 132

Soda 329

acetate of 650

alum 371

ash, manufacture of 334

bicarbonate of 336

bisulphate of 332

borate of 336

carbonate of 334

chloride of 331

chlorinated, carbonate

of 335

chromate of 446

hydrates of 329

hypochlorite 331

hyposulphite of 332
use of in photography 506

metantimoniate of 461

muriate of 330

nitrate of ^ 331

in organic bodies 641

phosphates of 333

plumbate of 431

silicates of 337

solutions, sp. gr. of 329

spectrum of 340

762

INDEX.

Soda — cont. page

stanuate of 412

sulphates of 332

sulphites of 332

tartrates of 636

tests for 340

Soda-alum 371

Soda-lime 552

Sodium 328

bromide 331

chloride of 330

in the photosphere of

the sun 108

iodide of 331

nitroprusside of 396

oxides of 329

sulphides of 332

Solder 436

Solidification of gases 80

Solubility of gases in

water 142

of salts 48

specific 48

Soluble tartar 636

Solution defined 47

Sorbine 573

Sound in hydrogen gas 123

Spathose iron ore 393

Specific gravity 736

of gases 84, 739

liquids 736

metals 309, 738

solids 738

vapors 84, 740

Specific heat 139

of liquids 140

metals 311

gases 84

solids 140

Spectrum-analysis 61

solar 505

actinic rays of 505

chemical actions of 505

in manufacture of steel 63

photographic influence

of 505

Specular iron ore 386

Speculum metal 425

Speiss 442

Spermaceti 631

oil 631

Spheroidal state of liquids 138

Spirit, methylated 593

Mindererus's 650

of salt 197.

of turpentine 616

of wine 683

of wood 692

pyroxylic 592

Spirituous liquids 582

Spongy platinum 522

action of 129

Spring-water 133

StaflFordshire ware 272

Stalactite 358

Stalagmite 358

Standard gold 519

silver 500

Standards of weight and

measure 729

Stan nates 412

Stannic acid 412

PAGE

Starch 561

analysis of 551

granules of 561

in animals 560

metamorphoses 562

potato 563
proportions of in seeds

and roots 561

rice 663

sugar

tests of

uses of

varieties of

wheat
Steam

latent heat of

sp. gr. of

superheated
Stearates
Stearine
Stearopten
Steatite
Steel

alloys

blistered

cast

natural

shear

tempering of

tilted
Stibamine
Stibium
Stick-lac
Stilbyl
Stinkstone
Stone-blue
Stoneware
Storm-glass
Stream tin
Strontia

oxalate of

salts of

tests for
Strontium

chloride of

oxides of

569
562
563
562
562
138
140
127
138
624
623
614
366
391
392
391
391
391
391

391, 392
391
560
459
619
655
358
566
372
31
410
349
645

349, 350
350
369
350
349

Structure of minerals 34

Strychnia 661

salts of 662

poisoning by 661

tests for 327, 661

Suberates 627

Sublimate, corrosive, tests

for 490

Sublimation 29

Substitutions, chemical 558

Succinates 620

Sucrose 568

Suet 622

Sugar 668
action of, on polarized

light 570

beet-root 568

composition of 668

cane 668

diabetic 572

fermentation of 573

formula of 555

fruit 569

grape 669

of lead 661

Sugar— cow*.

PAGE

manufacture of

568

maple

568

milk

713

refining of

568

starch

669

of gelatin

704

tests for

671

varieties of

572

Sulphantimoniates

462

Sulpharsenates

476

Sulpharsenites

476

Sulphates

224

Sulphatic ether

601

Sulphides

229

Sulphites

218

Sulphobenzide

610

Sulphobenzolic acid

610

Sulphocarbonates

291

Sulphocyanides

288

sulphocyanogen

288

Sulphoglyceric acid

627

Sulphonaphthalates

609

Sulphosjnapsine

618

Sulphovinic acid

646

Sulphur

212

allotropism of

214

bromides of

230

chlorides of

229

compounds of, with oxy-
gen 215
density of vapor 215
estimation of, in organ-
ic bodies 653
flowers of 213
iodide of 230
liver of 322
modifications of 213
nitride of 230
precipitated 214
tests for 215
Sulphuretted hydrogen 226
Sulphureous waters 149
Sulphurets 229
Sulphuric acid 219
anhydrous 222
densities of 221
its action on organic

bodies 545

manufacture of 219

Nordhausen 222

tests for 222

Sulphurous acid 216

Sun, light of 108

Supporters of combustion 102

Sweat 717

Sweet-wort 663

Swinestone 358

Symbols, chemical 66

old and new compared 745

Synaptase 654, 693

Synovia 716

Synthesis 52

Systems of crystallization 36

Table of absorption of
gases by charcoal 256

of aqueous vapor in
gases 736

of crystalline forms 36

INDEX.

7G3

Table — coyit. page |

PAGE

PAGE

of affinities 53

, 54

Talbotype

512

Tombac

425

albuminous liquids

639

Talc

365

Toning photographs

612

of anions and cations

69

Tallow

631

Topaz, Oriental

368

of atomic weights

67

fossil

611

Scotch

300

of atmospheric pres-

Tannin

640

Tortoise-shell

693

sures

158

a test for gelatin

703

Touchstone

300

of composition of air

165

Tanning, process of

703

Tous les mois

563

of coal

607

Tantalite

450

Tragacan thine

666

of glass

338

Tantalum

450

Triacetyline

610

of proof spirit

585

Tapioca

563

Triphane

341

of cyanogen compounds

280

Tar, Coal

609

Tripoli

301

of elementary substances 67

mineral

608

Trommer's sugar-test

421

of difiFusion volume

87

wood

643

Trona

336

of equivalents

67

shale

608

Tungstates

480

of heating powers of

Tartar

634, 636

Tungsten

449

combustibles

103

cream of

636

chlorides of

450

of hydrates of phospho-

soluble

636

oxides of

449

ric acid

243

emetic

637

sulphides of

450

of isomorphous bodies

39

soluble

636

tests for

450

of liquefaction of gases

80

of the teeth

714

Turmeric

680

of magnetics and dia-

Tartaric acid

634

paper

680

magnetics

312

Tartrates

635

Turner's yellow

432

of magnetism of gases

85

Tartralates

637

Turpentine

615

of metals

307

Tartrelates

638

oil of

615

their expansion

310

Taurine

719

its formula deter

.

of fusibility of metals

311

Tawed leather

703

mined

557

specific gravity

309

Tea

666

latent heat of its

va-

specific heat of metals

311

Tears

657

por

141

tenacity of metals

308

Teeth

646

Turpeth mineral

487

of non-metallic ele-

Telluretted hydrogen 457

Turquois

371

ments

78

Tellurium

456

Turps

615

of simple and compound

tests for

457

Tutenag

425

gases and vapors

743

Tempering of steel

392

Type-metal

463

of produce of charcoal

Tenacity

308

Tyrosin

694

from different woods

259

Terbium

376

of proportions of oil

Terebene

618

U.

from seeds

622

Terra foliata tartari

650

of protein compounds

686

Test-papers

675, 680

Ulmine

607

of refractive powers of

Thallium

344

Ultimate analysis

645

gases

85

oxides of

345

Unitary notation

69

of solubility of gases in

salts of

345

Uramile

679

water

142

tests for

345

Uranite

453

of salts in water 48,49

Thebaia

659

Uranium

463

of alkaloids in chlo-

Thein

666

acetate of

651

roform

49

Thenard's blue

441

oxides of

454

of specific gravity of

Theobromine

667

salts of

454

fixed oils

630

Thermometers

733

tests for

465

of gases and vapors

743

equivalents of

733

Urates

726

of metals

309

Thorina

375

Urea

722

of spirituous liquors

586

Thorinum

375

artificial

281, 723

of alcoholic mixtures 586

Thorite

375

compounds of

722, 724

of solutions of ammo-

Tin

410

tests for

724

nia

179

alloys of

414

Uric acid

724

of hydrochloric acid

198

amalgam of

489

tests for

726

of nitric acid

176

butter of

413

Urinary calculi

728

of potassa solutions

315

chlorides of

413

deposits

726

of soda solutions

329

foil

411

Urine

721

of sulphuric acid

221

ores of

410

of animals

721, 727

of wines

581

oxides of

411

albuminous

728

of specific heats

140

stream

410

saccharine

728

of gases

84

sulphides

413

Usquebaugh

582

of liquids

140

tests for

414

of metals 311

531

Tin-plate

414

V.

of solids

140

Tinned copper

426

of symbols

67

Tinning of pins

415

Vacuum-light

102

of starch in seed anc

Titannic acid

458

Valerianates

628

roots

561

Titanite

457

Valerianic acid

594, 628

of temperatures of

Titanium

457

Valeric acid

594

flames

108

Tobacco

664

Vanadates

649

tests for metals

378

Tolu balsam

663

Vanadium

448

weights and measures

730

Toluole

609

chloride of

449

7G4

INDEX.

Vanadium — cont.
oxides of
sulphides of

Vapor, aqueous
densities

PAGE

448
449
138
656

"Water— co7^i.
density of
distilled
estimation of
electrolysis of

page
186
134
146
130

Vapors and gases defined 78

diffusion of 85

physical properties of 85

table of 743

specific gravity 739, 740

Varnishes 619

Varvicite 401

Vegetable albumen 693

alkaloids 657

parchment 603

Vegetables, functions of 547

Venice-white 435

Veratria 663

Verd antique 358

Verdigris 650

Verd iter 424

Vermilion 486

Vinegar 646

adulterations of 647

distilled 648

manufacture of 646

strength of 647

of wood 648

Vinous fermentation 573

Viper-poison 693, 714

Viscous fermentation 679

Vitellin 688

Vitriol, blue 423

green 389

oil of 219

white 408

Voltaic light 102

current 69

Volumes, atomic 68, 743

equivalent 68

Vulcanized caoutchouc 621

W.

Wad

401

Wash

583

Water

127

analysis of

130

anomalous expansion of 136

barometer 159

basic 143

boiling of 138

capacity of, for heat 139

color of 136

combined 31

composition of 127

compressibility of 136
conduction of electri-

• city by 135

of heat by 135

convection of heat by 13»

decomposition of 130

explosive ebullition of 138
freezing of 136
hard and soft 132
hygrometrio 146
influence of, on chemi-
cal force 42, 142
influence of, on color 42
on reaction 43
in crystals 144
in organic substances 142
interstitial 31
maximum density of 136
of crystallization 32
of lakes 130
of rivers 130
of springs 133
organic matter in 164
physical properties of 135
proportion of, in ani-
mals 706
sea 147
synthesis of 128
soap test for 132
solid contents in the

gallon of 132

specific gravity of 136

specific heat of 139

spheroidal state of 138

tests of its presence 146

tests of its purity 132

varieties of 130

weight of 136

Waters, aerated 266

arsenicated 150

carbonated 149

chalybeate 150

mineral 147

sulphurous 149

silicated 303

Wavelite 371

Wax 631

fossil 611

vegetable 631

weights, atomic 67

Weights and measures 729

Weld 680

Welding 382

Whey 712

Whisky 582

White arsenic 467

White copper 444

White fire 474

White flux 320, 324

White lead 433

White precipitate 483

White vitriol 408

Wine 678

acid in 578

WixE — cont. PAGE
anal^^sis of 581
composition of 680
perfume of 678
solia contents»of 680
strength of 581
varieties of 578
Winter green, oil of 603, 606
Witherite 348
Wolfram 449
Wood 606
decay of 606
preservation of 606
products of its distil-
lation 612
Wood-ash 323
Woody fibre 603
Wood-opal 300
Wood-spirit 692
Wood-tar 612
Wood-vinegar 612
Wort 574, 583
Wothly-type 454
Writing ink 641

Xanthine 675

Xanthorhamnine 680

Xanthophylline 684

Xyloidine 605

Y.

Yeast, artificial 575
change of, in fermen-
tation 575
composition of 575
German 575
growth of 574
Yellow dyes 679, 681
Yttria 376
Yttrotantalite 450
Yttrium 376

Z.

Zapfre

441

Zinc

406

amalgam of

489

carbonate of

408

chloride of

408

combustion of, in oxy-
gen 95
flowers of 407
oxide of 407
nitrate of 407
sulphate of 408
sulphide of 408
tests for 409
white 407
Zircon 375
Zirconia 375
Zirconium 374

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MEDICAL LEXICON; A Dictionary of Medical Science: Con-
taining a concise explanation of the various Subjects and Terms o^ Anatomy, Physiology,
Pathology, Hygiene, Therapeutics, Pharmacology, Pharmacy, Surgery, Obstetrics, Medical
Jurisprudence, and Dentistry. Notices of Climate and of Mineral Waters; Formulae for
OfiRcinal, Empirical, and Dietetic Preparations ; with the Accentuation and Etymology of
the Terms, and the French and other Synonj-mes; so as to constitute a French as well as
English Medical Lexicon. Thoroughly Revised, and very greatly Modified and Augmented
In one very large and handsome royal octavo volume of 1048 double-columned pages, in
small type; strongly done up in extra cloth, $6 00; leather, raised bands, $6 75.
The object of the author from the outset has not been to make the work a mere lexicon or
dictionary of terms, but to afford, under each, a condensed view cf its various medical relations,
and thus to render the work an epitome of the existing condition of medical science. Starting
with this view, the immense demand which has existed for the work has enabled him, in repeated
revisions, to augment its completeness and usefulness, until at length it has attained the position
of a recognized and standard authority wherever the language is spoken. The mechanical exe-
cution of this edition will be found greatly superior to that of previous impressions. By enlarging
the size of the volume to a royal octavo, and by the employment of a small but clear type, on
extra fine paper, the additions have been incorporated without materially increasing the bulk of
the volume, and the matter of two or three ordinary octavos has been compressed into the space
of one not unhandy for consultation and reference.
It would be a work of supererogation to bestow a . It is undonbtedly the most complete and useful

word of praise upon this Lexicon. We can only
wonder at the labor expended, for whenever we refer
to its pages for information we are seldom disap-
pointed in finding all we desire, whether it be in ac-
centuation, etymology, or definition of terms. — New
York MediealJournal, November, 1S65.

It would be mere waste of words in us to express
our admiration of a worli which is so universally
and deservedly appreciated. The most admirable
work of its kind in the English language. As a book
of reference it is invaluable to the medical practi-
tioner, and in every instance that we have turned
over its pages for information we liave been charmed
by the clearness of language and the accuracy of
detail with which each abounds. We can most cor-
dially and confidently commend it to our readers. —
Glasgoio Medical Journal, January, 1866.

A work to which there is no equal in the English
language. — Edinburgh Medical Journal.

It is something more than a dictionary, and some-
thing less than an encyclopaedia. This edition of the
well-known work is a great improvement on its pre-
decessors. The book is one of the very few of which
it may be said with truth that every medical man
should possess it. — London Medical Times, Aug. 26,
1S6.5.

Few works of the class exhibit a grander monument
of patient research and of scientific lore. The extent
of the sale of this lexicon is sutticient to testify to its
u-efulness, and to the great service conferred by Dr.
Robley Dunglison on the profession, and indeed on
others, by its issue. — London Lancet, May 13, 1865.

The old edition, which is now super.seded by the
new, has been universally looked upon by the medi-
cal profession as a work of immense research and
great value. The new has increased usefulness ; for
medicine, in all its brancl^es, has been making such

medical dictionary hitherto published in this country.
— Chicago Med. Examiner, February, 1S65.

What we take to be decidedly the best medical dic-
tionary in the Euglish language. The present edition
is brought fully up to the advanced state of science.
For many a long year "Dunglison" has been at our
elbow, a constant companion and friend, and we
greet him in his replenished and improved form with
especial satisfaction.— Paei/ic Med. and Surg. JouT'
nal, June 27, 1865.

This is, perhaps, the book of all others which the
physician or surgeon should have on his shelves. It
is more needed at the present day than a few years
back. — Canada Med. Journal, July, 1865.

It deservedly stands at the head, and cannot be
surpassed in excellence.— .Bw/ato Med. and Surg.
Journal, April, 186.5.

We can sincerely commend Dr. Dunglison's work
as most thorough, scientific, and accurate. We have
tested it by searching itit pages for new terms, which
have abounded so much of late in medical nomen-
clature, and our search has been successful in every
instance. We have been particularly struck with the
fulness of the synonymy and the accuracy of the de-
rivation of words. It Is as necessary a work to every
enlightened physician as Worcester's Euglish Dic-
tionary is to every one who would keep up his know-
ledge of the English tongue to the standard of the
present day. It is, to our mind, the most complete
work of the kind with which we are acquainted. —
Boston Med. and Surg. Journal, June 22, 1865.

We are free to confess that we know of no medical
dictionary more complete; no one better, if so well
adapted for the use of the student ; no one that may
be consulted with more satisfaction by the medical
practitioner. — Am. Jour. Med. Sciences, April, 1S65.

The value of the present edition has been greatly
enhanced by the introduction of new subjects and

progress that many new terms and subjects have re

cently been introduced : all of which may be found

fully defined in the present edition. We know of no

other dictionary in the English language that can , a a ■ u]

bear a comparison with it in point of completeness of ^"^„^^f^"'^^^®

subjects and accuracy of statement. — N. Y. Drug'

gists' Circular, 1S65.

For many years Dunglison's Dictionary has been
the standard book of reference with most practition-
ers in this country, and we can certainly commend

this work to the renewed confidence and regard of I in the English language for accuracy and extent
our readers. — Cincinnati Lancet, April, 1865. I references. — London Medical Gazette,

terms, and a more complete etymology and accentua-

o'therircti7nk"rrrQ''the" EnTlishTanguagTthat'c^^ ! tion, which renders the work not only satisfactory

•' -.-•■'.- o » - - I and desirable, but indispensable to the physician.—

Chicago Med. Journal, April, 1865.

No intelligent member of the profession can or will
be without it. — St. Louis Med. and Surg Journal,
April, 1865.
It has the rare merit that it certainly has no rival

prOBLYN {^RICHARD D.), M.D.

A DICTIONARY OF THE TERMS USED IN MEDICINE AND

THE COLLATERAL SCIENCES. A new American edition, revised, with numerous
additions, by Isaac Hay.s, M.D., Editor of the "American Journal of the Medical
Sciences." In one large royal 12mo. volume of over 500 double-columned pages; extra
cloth, $1 50 ; leather, $2 00.
It is the best book of definitions we have, and ought always to be upon the student's tdiblQ. —Southern
Med. and Surg. Journal.

Henry C. Lea's Publications — (Manuals).

^EILL {JOHN), M.D., and ^MITH [FRANCIS G.), M.D.,

Prof, of the Institutes of Medicine in the Univ. of Penna.

AN ANALYTICAL COMPENDIUM OF THE VARIOUS

BRANCHES OF MEDICAL SCIENCE ; for the Use and Examination of Students. A
new edition, revised and improved. In one very large and handsomely printed royal 12mo.
volume, of about one thousand pages, with 374 wood cuts, extra cloth, $4 ; strongly bound
in leather, with raised bands, $4 75.

The Compend of Drs. Neilland Smith is incompara-
bly the most valuable work of its class ever published
ia this country. Attempts have been made in various
quarters to squeeze Anatomy, Physiology, Surgery,
the Practice of Medicine, Obstetrics, Materia Medica,
and Chemistry into a single manual; but the opera-
tion has signally failed in the hands of all up to the
advent of" Neill and Smith's" volume, which is quite
a miracle of success. The outlines of the whole are
admirably drawn and illustrated, and the authoi-s
are eminently entitled to the grateful consideration
of the student of every class. — N. 0. Med. and Surg.
Journal.

This popular favorite with the student is so well
known that it requires no more at the hands of a
medical editor than the annunciation of a new and
improved edition. There is no sort of comparison
between this work and any other on a similar plan,
and for a similar object. — Nash. Journ. of Medicine.

There are but few students or practitioners of me-
dicine unacquainted with the former editions of this
unassuming though highly instructive work. The
whole science of medicine appears to have been sifted,
as the gold-bearing sands of El Dorado, and the pre-
cious facts treasured up in this little volume. A com-
plete portable library so condensed that the student
may make it his constant pocket companion. — West-
ern Lancet.

To compress the whole science of medicine in less
than 1,000 pages is an impossibility, but we think that
the book before us approaches as near to it as is pos-
sible. Altogether, it is the best of its class, and has
met with a deserved success. As an elementary text-
book for students, it has been useful, and will con-
tinue to be employed in the examination of private
classes, whilst it will often be referred to by the
country practitioner. — Va. Med. Journal.

I As a handbook for students it is invaluable, con-
taining in the most condensed form the established
facts and principles of medicine and its collateral
sciences. — N. H. Journal of Medicine.

In the rapid course of lectures, where work for the
students is heavy, and review necessary for an exa-
mination, a compend is not only valuable, but it is
almost a sine qua non. The one before us is, in most
of the divisions, the most unexceptionable of all books
of the kind that we know of. The newest and sound-
est doctrines and the latest improvements and dis-
coveries are explicitly, though concisely, laid before
the student. Of course it is xiseless for us to recom-
mend it to all last course students, but there is a class
j to whom we very sincerely commend this cheap book
I as worth its weight in silver — that class is the gradu-
I ates in medicine of more than ten years' standing,
I who have not studied medicine since. They will
perhaps find out from it that the science is not ex-
! actly now what it was when they left it off. — The
I Stethoscope.

I Having made free use of this volume in our exami-

! nations of pupils, we can speak from experience ia

I recommending it as an admirable compend for stu-

j dents, and especially useful to preceptors who exam-

j ine their pupils. It will save the teacher much labor

by enabling him readily to recall all of the points

upon which his pupils should be examined. A work

of this sort should be in the hands of every one who

takes pupils into his office with a view of examining

them ; and this is unquestionably the best of its class.

Let every practitioner who has pupils provide himself

with it, and he will find the labor of refreshing his

knowledge so much facilitated that he will be able to

do justice to his pupils at very little cost of time or

trouble to \i\ms.eM.— Transylvania Med. Journal.

J^VDLOW {J.L.), M.D„

A MANUAL OF EXAMINATIONS upon Anatomy, Physiology,

Surgery, Practice of Medicine, Obstetrics, Materia Medica, Chemistry, Pharmacy, and
Therapeutics. To which is added a Medical Formulary. Third edition, thoroughly revised
and greatly extended and enlarged. With 370 illustrations. In one handsome royal
12mo. volume of 816 large pages, extra cloth, $3 25; leather, $3 75.

The arrangement of this volume in the form of question and answer renders it especially suit-
able for the office examination of students, and for those preparing for graduation.

We know of no better companion for the student
during the hours spent in the lecture-room, or to re-
fresh, at a glance, his memory of the various topics
crnrnmed into his head by the various professors to
whom he is compelled to listen. — Western Lancet.

As it embraces the whole range of medical studies
it is ueceasarily voluminous, containing 816 large
duodecimo pages. After a somewhat careful exami-
nation of its contents, we have formed a much more
favorable opinion of it than we are wont to regard
such works. Although well adapted to meet the wants

of the student in preparing for his final examination,
it might be profitably consulted by the practitioner
also, who is most apt to become rusty in the very kind
of details here given, and who, amid the hurry of his
daily routine, is but too prone to neglect the study of
more elaborate works. The possession of a volume
of this kind might serve as an inducement for him to
seize the moment of excited curiosity to inform him-
self on any subject, and which is otherwise too often
allowed to pass unimproved. — St. Louis Med, and
Surg. Journal.

JiANNER ( THOMAS HA WKES), M />.,

A MANUAL OF CLINICAL MEDICINE AND PHYSICAL DIAG-

NOSIS. Third American, from the second enlarged and revised English edition. To
which is added The Code of Ethics of the American Medical Association. In one band-
some volume 12mo. (^Preparing for early publication.)

This work, after undergoing a very thorough revision at the hands of the author, may now be
expected to appear shortly. The title scarcely affords a proper idea of the range of subjects em-
braced in the volume, as it contains not only very full details of diagnostic symptoms propeply
classified, but also a large amount of information on matters of every day practical importance,
not usually touched upon in the systematic works, or scattered through many different volumes.

J

Henry C. Lea's Publications — {Anatomy).

QRAY {HENRY), F.B.S.,

Lecturer on Anatomy at St. George! 8 Hospital, London.

ANATOMY, DESCRIPTIVE AND SURGICAL. The Drawinirs by

H. V. Carter, M. D., late Demonstrator on Anatomy at St. George's Hospital ; the Dissec-
tions joii^tly by the Author and Dr. Carter. Second American, from the second revised
and improved London edition. In one magnificent imperial octavo volume, of over 800
pages, with .388 large and elaborate engravings on wood. Price in extra cloth, $6 00 ;
leather, raised bands, $7 00.
The author has endeavored in this work to cover a more extended range of subjects than is cus-
tomary in the ordinary text-books, by giving not only the details necessary for the student, but
also the application of those details in the practice of medicine and surgery, thus rendering it both
a guide for the learner, and an admirable work of reference for the active practitioner. The en-
gravings form a special feature in the work, many of them being the size of nature, nearly all
original, and having the names of the various parts printed on the body of the cut, in place of
figures of reference, with descriptions at the foot. They thus form a complete and splendid series,
which will greatly assist the student in obtaining a clear idea of Anatomy, and will also serve to
refresh the memory of those who may find in the exigencies of practice the necessity of recalling
the details of the dissecting room; while combining, as it does, a complete Atlas of Anatomy, with
a thorough treatise on systematic, descriptive, and applied Anatomy, the work will be found of
essential use to all physicians who receive students in their offices, relieving both preceptor and
pupil of much labor in laying the groundwork of a thorough medical education.

Notwithstanding its exceedingly low price, the work will be found, in every detail of mechanical
execution, one of the handsomest that has yet been offered to the American profession ; while the
careful scrutiny of a competent anatomist has relieved it of whatever typographical errors existed
in the English edition.

Thus it is that book after book makes the labor of I and with scarce a reference to the printed text. The
the student easier than before, and since we have surgical application of the various regions is also pre-
seeu Blanchard & Lea's new edition of Gray's Ana- sented with force and clearness, impressing upon the
tomy, certainly the finest work of the kind now ex- stndent at each step of his research all thelmportant
tant, we would fain hope that the bugbear of medical j relations of the structure demonstrated. — Cincinnati
students will lose half its horrors, and this necessary ' Lancet.

foundation of physiological science will be much fa- j This is. we believe, the handsomest book on Ana-
cilitated and advanced. — N. 0. Med. News. tomy as yet published in our language, and bids fair

I to become in a short time the standard text-book of
The various points illustrated are marked directly 1 our colleges and studies. Studeuts and practitioners
on the structure; that is, whether it be muscle, pro j will alike appreciate this book. We predict for it a
cess, artery, nerve, valve, etc. etc. — we say pach point bright career, aud are fully prepared to endorse the
is distinctly marked by lettered engravings, so that statement of the London Lancet, that "We are not
the student perceives at once each point described as ! acquainted with any work in any language -which
readily as if pointed out on the subject by the de- 1 can take equal rank with the one before us." Paper,
monstrator. Most of the illustrations are thus ren- ' priuting, binding, all are excellent, aud we feel that
dered exceedingly satisfactory, and to the physician a grateful profession will not allow the publishers to
they serve to refresh the memory with great readiness [ go unrewarded. — Aashville Med. and Surg. Journal.

^MITH [HENRY B.), M.D., and TJORNER ( WILLIAM E.), M.D.,

Prof, of Surgery in the Univ. of Penna., &c. Late Prof, of Anatomy in the Univ. of Penna., Ac-

AN ANATOMICAL ATLAS, illustrative of the Structure of the

Human Body. In one volume, large imperial octavo, extra cloth, with about six hundred

and fifty beautiful figures. $4 60.
The plan of this Atlas, which renders it so pecu- 1 the kind that has yet appeared; and we must add,
liarly convenient for the student, and its superb ar- | the very beautiful manner in which it is "got up"
tistical execution, have been already pointed out. We is so creditable to the country as to be flattering to
must congratulate the student upon the completion our national pride.— .American MedicalJournal.
of this Atlas, as it is the most convenient work of I

ff"

RNER [WILLIAM E.), M.D.,
SPECIAL ANATOMY AND HISTOLOGY. Eighth edition, exten-

sively revised and modified. In two large octavo volumes of over 1000 pages, with more
than 300 wood-cuts ; extra cloth, $6 00.

OHARPEY ( WILLIAM), M.D., and Q VAIN [JONES Sr RICHARD).
HUMAN ANATOMY. Revised, with Notes and Additions, by Joseph

Leidv, M.D., Professor of Anatomy in the University of Pennsylvania. Complete in two
large octavo volumes, of about 1300 pages, with 511 illustrations; extra cloth, $6 00.
The very low price of this standard work, and its completeness in all departments of the subject,
should command for it a place in the library of all anatomical students.

A

LLEN [J.M.), M.D.

THE PRACTICAL ANATOMIST; or. The Student's Guide in the

Dissecting Room. "With 266 illustrations. In one very handsome royal 12mo. volume,
of over 600 pages; extra cloth, $2 00.
One of the most useful works upon the subject ever written. — Medical Examiner.

Henry C. Lea's Publications — (Anatomy).

JYILSON {ERASMUS), F.R.S.

A SYSTEM OF HUMAN ANATOMY, General and Special. A new

and revised American, from the last and enlarged English edition. Edited by W. H. Go-
BRECHT, M.D., Professor of General and Surgical Anatomy in the Medical College of Ohio.
Illustrated with three hundred and ninety-seven engravings on wood. In one large and
handsome octavo volume, of over 600 large pages; extra cloth, $4 00; leather, $5 00.
The publisher trusts that the well-earned reputation of this long-established favorite will be
more than maintained by the present edition. Besides a very thorough revision by the author, it
has been most carefully examined by the editor, and the efforts of both have been directed to in-
troducing everything which increased experience in its use has suggested as desirable to render it
a complete text-book for those seeking to obtain or to renew an acquaintance with Human Ana-
tomy. The amount of additions which it has thus received may be estimated from the fact that
the present edition contains over one-fourth more matter than the last, rendering a smaller type
and an enlarged page requisite to keep the volume within a convenient size. The author has not
only thus added largely to the work, but he has also made alterations throughout, wherever there
appeared the opportunity of improving the arrangement or style, so as to present every fact in its
most appropriate manner, and to render the whole as clear and intelligible as possible. The editor
has exercised the utmost caution to obtain entire accuracy in the text, and has largely increased
the number of illustrations, of which there are about one hundred and fifty more in this edition
than in the last, thus bringing distinctly before the eye of the student everything of interest or
importance.

J^Y THE SAME AUTHOR. ^

THE DISSECTOR'S MANUAL; or, Practical and Surgical Ana-

, TO MY. Third American, froxn the last revised and enlarged English edition. Modified and
rearranged by William Hunt, M. D., late Demonstrator of Anatomy in the University of
Pennsylvania. In one large and handsome royal 12mo. volume, of 582 pages, with 154
illustrations; extra cloth, $2 00.

TTODGES, {RICHARD M.), M.D.,

J-L Late Demonstrator of Anatomy in the Medical Department of Harvard University.

PRACTICAL DISSP:CTI0NS. Second Edition, thoroughly revised. In

one neat royal 12mo. volume, half-bound, $2 00. {Just Issued.)
The object of this work is to present to the anatomical student a clear and concise description
of that which he is expected to observe in an ordinary course of disseefcions. The author has
endeavored to omit unnecessary details, and to present the subject in the form which many years'
experience has shown him to be the most convenient and intelligible to the student. In the
revision of the present edition, he has sedulously labored to render the volume more worthy of
the favor with which it has heretofore been received.

31

ACLISE {JOSEPH).

SURGICAL ANATOMY. By Joseph Maclise, Surgeon. In one

^ volume, very large imperial quarto; with 68 large and splendid plates, drawn in the best

style and beautifully colored, containing 190 figures, many of them the size of life; together
with copious explanatory letter-press. Strongly and handsomely bound in extra cloth.
Price $14 00.
As no complete work of the kind has heretofore been published in the English language, the
present volume will supply a want long felt in this country of an accurate and comprehensive
Atlas of Surgical Anatomy, to which the student and practitioner can at all times refer to ascer-
tain the exact relative positions of the various portions of the human frame towards each other
and to the surface, as well as their abnormal deviations. The importance of such a work to the
student, in the absence of anatomical material, and to practitioners, either for consultation in
emergencies or to refresh their recollections of the dissecting room, is evident. Notwithstanding
the large size, beauty and finish of the very numerous illustrations, it will be observed that the
price is so low as to place it within the reach of all members of the profession.

We know of no work on surgical anatomy which
can compete with it. — Lancet.

Tlie work of Maclise on surgical anatomy is of the
highest value. In some respects it is the best publi-
cation of its kind we have seen, and is worthy of a
place in the libiary of any medical man, while the
student could scarcely make a bptter investment than
this. — The Western Journal of Medicine and Surgery.

No such lithographic illnstrations of surgical re-
gions have hitherto, we think, been given. While
the operator is shown every vessel and nerve where
an operation is contemplated, the exact anatomist is

refreshed by those clear and distinct dissections,
which every one must appreciate who has a particle
of enthusiasm. The English medical press has quite
exhausted the words of praise, in recommending this
admirable treatise. Those who have any curiosity
to gratify, in reference to the perfectibility of the
lithographic art in delineating the complex mechan-
ism of the human body, are invited to examine our
specimen copy. If anything will induce surgeons
and students to patronize a book of such rare vulne
and everyday importance to them, it will be a survey
of the artistical skill exhibited in these fac-similes of
nature. — Boston Mtd. and Surg. Journal.

PEASLEE {E. R.), M.D.,
Professor of Anatomy and Physiology in Dartmotith Med. College, N. H.

HUMAN HISTOLOGY, in its relations to Anatomy, Physiology, and

Pathology; for the use of medical students. With four hundred and thirty-four iII«Btra-
tions. In one handsome octavo volume of over 600 pages, extra cloth. $3 75.

Henry C. Lea's Publications — {Physiology).

rjARPENTER [WILLIAM B.), M.D., F.R.S.,

Examiner in Physiology and Comparative Anatomy in the University of London.

PRINCIPLES OF HUMAN PHYSIOLOGY; with their chief appli-

cations to Psychology, Pathology, Therapeutics, Hygiene and Forensic Medicine. A new
American from the last and revised London edition. With nearly three hundred illustrations.
Edited, with additions, by Francis Guhney Smith, M. •., Professor of the Institutes of
Medicine in the University of Pennsylvania, &c. In one very large and beautiful octavo
volume, of about 900 large pages, handsomely printed; extra cloth, $5 50 ; leather, raised
bands, $6 50.

The highest coinpliment that can he extended to
this great work of Dr. Carpenter is to call attention
to this, another new edition, which the favorahle
regard of the profession has called for. Carpenter is
the standard authoiity on physiology, and no physi-
cian or medical student will regard his library as
complete without a copy of \i.— Cincinnati Med. Ob-
server.

With Dr. Smith, we confidently believe "that the
present will more than sustain the enviable reputa-
tion already attained by former editions, of being
one of the fullest and most complete treatises on the
subject in the English language." We know of none
from the pages of which a satisfactory knowledge of
the physiology of the human organiKm can be as well
obtained, none better adapted for the use of such as
take up the study of physiology in its reference to
the institutes and practice of medicine. — Am. Jour.
Med. Sciences.

A complete cyclop ajdia of this branch of science.—
N. Y. Med. Times.

We doubt not it is destined to retain a strong hold
on public favor, and remain the favorite text-book iu
our colleges. — Virginia Medical Journal.

We have so often spoken in terms of high com-
mendation of Dr. Carpenter's elaborate work on hu-
man physiology that, in announcing a new edition,
it is unnecessary to add anything to what has hereto-
fore been said, and especially is this the case since
every intelligent phy.siciau is as well aware of the
chai-acter and merits of the work as we ourselves are.
— St. Louis Med. and Surg. Journal.

The above is the title of what is emphatically the
great work on physiology ; and we are conscious'that
it would be a u.seless elfort to attempt to add any-
thing to the reputation of this invaluable work, and
can only say to all with whom our opinion has any
influence, that it is our authority. — Atlanta Med.
Journal.

The greatest, the most reliable, and the best book
on the subject which we know of in the English lab-
guage. —Stethoscope.

JDT THE SAME AUTHOR.

PRINCIPLES OF COMPARATIVE PHYSIOLOGY. New Ameri-

can, from the Fourth and Revised London Edition. In one large and hjindsome octavo
volume, with over three hundred beautiful illustrations Pp. 752. Extra cloth, $5 00.
As a complete and condensed treatise on its extended and important subject, this work becomes

a necessity to students of natural science, while the very low price at which it is offered places it

within the reach of all.

B

Y THE SAME A UTHOR.

THE MICROSCOPE AND ITS REVELATIONS. With an Appen-

dix containing the Applications of the Microscope to Clinical Medicine, &c. By F. G.
Smith M. D. Illustrated by four hundred and thirty-four beautiful engravings on wood.
In one large and very handsome octavo volume, of 724 pages, extra cloth, $5 25.

rpODD [ROBERT B.), M.D. F.R.S., and JDOWMAN [W.), F.R.S.
THE PHYSIOLOGICAL ANATOMY AND PHYSIOLOGY OF

MAN. With about three hundred large and beautiful illustrations on wood. Complete in
one large octavo volume of 950 pages, extra cloth. Price $4 75.

practitioner can consult relating to physiology. — N.
Y. Journal of Medicine.

The names of Todd and Bowman have long been
familiar to the student of pl)ysiology. In this work
we have the ripe experience of these laborious physi-
ologists on every branch of this science. They gave
each subject the most thorough and critical examina-
tion before making it a matter of record. Thus, while
they advanced tardily, apparently, in their publica-
tion, the work thus issued was a complete exponent
of the science of physiology at the time of its final
appearance. We can, therefore, recommend this
work as one of the most reliable which the student or

To it the rising generation of medical men will
owe, in great measure, a familiar acquaintance with
all the chief truths respecting the healthy structure
and working of the frames which are to form the
subject of their care. The possession of such know-
ledge will do more to make sound and able practi-
tioners than auything else. — British and Foreign
Medico- Chirurgical Review.

K

IRKES [WILLIAM SENHOUSE), M.D.,

A MANUAL OF PHYSIOLOGY. A new American from the third

and improved London edition. With two hundred illustrations. In one large and hand-
some royal 12mo. volume. Pp. 586. Extra cloth, $2 25 ; leather, $2 75.
By the use of a fine and clear type, a very large amount of matter has been condensed into a
comparatively small volume, and at its exceedingly low price it will be found a most desirable
manual for students or for gentlemen desirous to refresh their knowledge of modern physiology.

It is at once convenient in size, comprehensive in lent guide in the study of physiology in its most ad-
design, and concise in statement, and altogether well vauced and perfect form. The author has shown
adapted for the purpose designed. — St. Louis Med. himself capable of giving details sufilciently ample
and Surg. Journal. in a condensed and concentrated shape, on a science

in which it is necessary at once to be correct and not
The physiological reader will find it a most excel- Lengthened.— JSdm&itry/t Med. and Surg. Journal.

Henry C. Lea's Publications — (PKysiology).

9

T)ALTON [J. a), M.D.,

-^-^ Professor of Physiology in the College of Physicians and Surgeons, New York, See.

A TREATISE ON HUMAN PHYSIOLOGY, Designed for the use

of Students and Practitioners of Medicine. Fourth edition, revised, with nearly three hun-
dred illustrations on wood. In one very beautiful octavo volume, of about 700 pages, extra
cloth, $5 25 ; leather, $6 25. {Now Ready.)

From the Preface to the New Edition.
** The progress made by Physiology and the kindred Sciences during the last few years has re-
quired, for the present edition of this work, a thorough and extensive revision. This progress
has not consisted in any very striking single discoveries, nor in a decided revolution in any of
the departments of Physiology; but it has been marked by great activity of investigation in a
multitude of different directions, the combined results of which have not failed to impress a new
character on many of the features of physiological knowledge. ... In the revision and
correction of the present edition, the author has endeavored to incorporate all such improve-
ments in physiological knowledge with the mass of the text in such a manner as not essentially
to alter the structure and plan of the work, so far as they have been found adapted to the wants
and convenience of the reader. . . . Several new illustrations are introduced, some of them
as additions, others as improvements or corrections of the old. Although all parts of the book
have received more or less complete revision, the greatest number of additions and changes were
required in the Second Section, on the Physiology of the Nervous System."

The reputation which this work has acquired, as a compact and convenient summary of the
most advanced condition of human physiology, renders it only necessary to state that the author
has assiduously labored to render the present edition worthy a continuance of the marked favor
accorded to previous impressions, and that every care has been bestowed upon the typographical
execution to make it, as heretofore, one of the handsomest productions of the American press.

The advent of the first edition of Prof. Dalton's
Physiology, about eight years ago, marked a new era
in the study of physiology to the American student.
Under Dalton's skilful management, physiological
science threw off the long, loose, ungainly garments
of probability and surmise, in which it had been ar-
rayed by most artists, and came among us smiling
and attractive, in»the beautifully tinted and closely
fitting dress of a demonstrated science. It was a
stroke of genius, as well as a result of erudition and
talent, that led Prof. Dalton to present to the world
a work on physiology at once brief, pointed, and com-
prehensive, and which exhibited plainly in letter and
drawings the basis upon which the conclusions ar-
rived at rested. It is no disparagement of the many
excellent works on physiology, published prior to
that of Dalton, to say that none of them, either in
plan of arrangement or clearness of execution, could
be compared with his for the use of students or gene-
ral practitioners of medicine. For this purpose his
book has no equal in the English language. — Western
Journal of Medicine, Nov. 1S67.

A capital text-book in every way. We are, there-
fore, glad to see it in its fourth edition. It has already
been examined at full length in these columns, so that
we need not now further advert to it beyond remark-
ing that both revision and enlargement have been
most judicious.— 2/owd6»» Med. Times and Gazette,
Oct. 19, 1867.

No better proof of the value of this admirable
work could be produced than the fact that it has al-
ready reached a fourth edition in the short space of
eight years. Possessing in an eminent degree the

merits of clearness and condensation, and being fully
brought up to the present level of Physiology, it is
undoubtedly one of the most reliable text-books
upon this science that could be placed in the hands
of the medical student. — Am. Journal Med. Sciences,
Oct. 1867.

Prof. Dalton's work has such a well-established
reputation that it does not stand in need of any re-
commendation. Ever since its first appearance it has
become the highest authority in the English language ;
and that it is able to maintain the enviable position
which it has taken, the rapid exhaustion of the dif-
ferent successive editions is sufficient evidence. The
present edition, which is the fourth, has been tho-
roughly revised, and enlarged by the incoi'poratioa
of all the many important advances which have
lately been made in this rapidly progressing science.
—N. Y. Med. Record, Oct. 15, 1867.

As it stands, we esteem it the very best of the phy-
siological text-books for the student, and the most
concise reference and guide-book for the practitioner.
—N. Y. Med. Journal, Oct. 1867.

The present edition of this now standard work fully
sustains the high reputation of its accomplished au-
thor. It is not merely a reprint, but has been faith-
fully revised, and enriched by such additions as the
progress of physiology has rendered desirable. Taken
as a whole, it is unquestionably the most reliable and
useful treatise on the subject that has been issued
from the American press.— CViica^ro Med. Journal,
Sept. 1867.

-nUNGLISON [ROBLEY], M.D.,

J-^ Professor of Institvies of Medicine in Jefferson Medical College, Philadelphia.

HUMAN PHYSIOLOGY. Eighth edition. Thoroughly revised and

extensively modified and enlarged, with five hundred and thirty-two illustrations. In two
large and handsomely printed octavo volumes of about 1500 pages, extra cloth. $7 00.

TEHMANN {G. G.)

PHYSIOLOGICAL CHEMISTRY. Translated from the second edi-
tion by George E. Day, M. D., P. R. S., Ac, edited by R. E. Rogers, M. D., Professor of
Chemistry in the Medical Department of the University of Pennsylvania, with illustrations
selected from Funke's Atlas of Physiological Chemistry, and an Appendix of plates. Com-
plete in two large and handsome octavo volumes, containing 1200 pages, with nearly two
hundred illustrations, extra cloth. $6 00.

' THE SAME AUTHOR.

MANUAL OF CHEMICAL PHYSIOLOGY. Translated from the

German, with Notes and Additions, by J. Chbston Morris, M. D., with an Introductory
Essay on Vital Force, by Professor Samuel Jackson, M. D., of the University of Pennsyl-
vania. With illustrations on wood. In one very handsome octavo volume of 336 pages
extra cloth. $2 25.

10

Henry C. Lea's Publications — {Chemistry).

DRANDE ( WM. T.), D. C.L,, and J^AYLOR [ALFRED S.), M.D., F.R.S.
CHEMISTKY. Second American edition, thorongbly revised l\y Dr.

Taylok. In one handsome 8vo. volume of 764 pages, extra cloth, $5 00 ; leather, $6 00.
{Now Ready.)

From Dr. Taylor's Preface.

"The revision of the second edition, in consequence of the death of ray lamented colleague,
has devolved entirely upon myself. Every chapter, and indeed every page, has been revised,
and numereus additions made in all parts of the volume. These additions have been restricted
chiefly to subjects having some practical interest, and they have been made as concise as possible,
in order to keep the book within those limits which may retain for it the character of a Student's
Manual " — London, June 29, 1867.

A book that has already so established a reputa-
tion, as has Brande and Taylor's Chemistry, can
hardly need a notice, save to raentiou the additions
and improvements of the edition. Doubtless the
work will long remain a favorite text-book iai the
school.-', as well as a convenient book of reference for
all.— iV. r. Medical Gazette, Oct. 12, 1S67.

For this reason we hail with delight the republica-
tion, in a form which will meet with general approval
and command public attention, of this really valua-
ble standard work on chemistry — more particularly
as it has been adapted with such care to the wants of
the general puhlic. The %vell known scholarship of
its authors, and their extensive researches for many
years in experimental chemistry, have been long ap-
preciated in the scientific world, but in this work they
have been careful to give the largest possible amount
of information with the most sparing use of technical
terms and phraseology, so as to furnish the reader,
"whether a student of medicine, or a man of the
world, with a plain introduction to the science and
practice of chemistry." — Journal of Applied Chem-
istry, Oct. 1867.

I This second American edition of an excellent trea-
tise on chemical science is not a mere republication
from the English press, hut is a revision and en-
I largement of the original, under the supervision of
' the surviving author. Dr. Taylor. The favorahle
opinion expressed on the puhlication of the former
\ edition of this work is fully sustained by the present
: revision, in which Dr. T. has increased the size of
the volume, by an addition of sixty -eight pages. — Am.
JOurn. Ated. Sciences, Oct. IStJT.

' The H.tNUBOOK in Chemistry of the Student. —
For clearness of language, accuracy of description,
extent of information, and freedom from pedantry
and mysticism, no other text-book comes into com-
petition with it. — Tlie Lancet.
I The authors set out with the definite purpose of
' writing a book which shall be intelligible to any
educated man Thus conceived, and worked out in
the most sturdy, common-sense method, this book
gives in the clearest and most summary method
possible all the facts and doctrines of chemistry. —
Medical Times.

nOWMAN [JOHN E.),M. D.

PRACTICAL HANDBOOK OF MEDICAL CHEMISTRY. Edited

by C. L. Bloxam, Professor of Practical Chemistry in King's College. London. Fourth
American, from the fourth and revised English Edition. In one neat volume, royal 12mo.,
pp. 351, with numerous illustrations, extra cloth. $2 25.

The fourth edition of this invaluable text-book of
Medical Chemistry was published in England in Ocio-
ber of the last year. The Editor has brought down
the Handbook to that date, introducing, as far as was
compatible with the necessary coDcisene.ss of such a
work, all the valuable discoveries in the science

which have come to light since the previous edition
was printed. The work is indispensable to every
student of medicine or enlightened practitioner. It
is printed in clear type, and the illustrations are
numerous and intelligible. — Bo-iton Med. and Surg.
Journal.

DY THE SAME A UTHOR.

INTRODUCTION TO PRACTICAL CHEMISTRY, INCLUDING

ANALYSIS. Fourth American, from the fifth and revised London edition. With numer-
ous illustrations. In one neat vol., royal 12mo., extra cloth. $2 25. {Just Issued.)

One of the most complete manuals that has for a
long time been given to the medical student. —
Atlienceurn.

We regard it as realizing almost everything to be
desired in an introduction to Practical Chemistry.

It is by far the best adapted for the Chemical student
of any that has yet fallen in our way. — British and
Foreign Medico-Ghirurgical Review.

The best introductory work on the subject with
which we are acquainted. — Edinburgh Monthly Jour.

QRAEAM [THOMAS], F.R.S.

THE ELEMENTS OF INORGANIC CHEMISTRY, including the

Applications of the Science in the Arts. New and much enlarged edition, by Henry
Watts and Robert Bridges, M. D. Complete in one large and handsome octavo volume,
of over 800 very large pages, with two hundred and thirty-two wood-cuts, extra cloth.

$5 60.

Part II., completing the work from p. 431 to end, with Index, Title Matter, &c., may be had
separate, cloth backs and paper sides. Price $3 00.

From Prof. E. N. Horsford, Harvard College.

It has, in its earlier and less perfect editions, been
familiar to me, and the excellence of its plan and
the clearness and completeness of its discussions.
have long been my admiration.

No reader of English works on this science can

afford to be without this edition of Prof. Graham's
Elements. — Silliman^s Journal, March, 185S.

From. Prof. Wolcott Gibbs, N. Y. Free Academy.

The work is an admirable one in all respects, ana
its republication here cannot fail to exert a positive
influence upon the progress of science in this country.

Henry C. Lea's Publications — (ChemiHfn/^ Pharmacy^ &c.). 11

rpOWNES {GEORGE), Ph. D.
A MANUAL OF ELEMENTARY CHEMISTRY; Theoretical and

Practical. With one hundred and ninety-seven illuptrations. Edited by Robert Bridges,
M. D. In one large royal 12mo. volume, of 600 pages, extra cloth, $2 00; leather, $=2 60.

We know of no treatise in the language so well
calculated to aid the student in becoming familiar
with the numerous facts in the intrinsic science on
which it treats, or one better calculated as a text-
book for those attending Chemical lectures. * * * *
The best text-book on Chemistry (hat has issued from
our press. — American Medical Journal.

We again most cheerfully recommend it as the
best text-book for students in attendance upon Chem-
ical lectures that we have yet examined. — III. and
Ind. Med. and Surg. Journal.

A fii"st-rate work upon a first-rate subject. — St.
Louis Med. and Surg. Journal.

No manual of Chemistry which we have met
comes so near meeting the wants of the beginner. —
Western Journal of Medicine and Surgery.

We know of none within the same limits which
has higher claims to our confidence as a college class-
book, both for accuracy of detail and scientific ar-
rangement.— Augusta Medical Journal.

We know of no text-book on chemistry that we
would sooner recommend to the student than this
edition of Prof. Fownea' work. — Montreal Medical
Chronicle.

A new and revised edition of one of the best elemen-
tary works on chemistry accessible to the Araericaa
and English student. — N. Y. Journal of Medical and
Collateral Science.

We unhesitatingly recommend it to medical stu-
dents.— N. W. Med. and Surg. Journal.

This is a most excellent text-book for class instruc-
tion in chemistry, whether for schools or colleges. —
Silliman's Journal.

ABEL AND BLOXAM'S HANDBOOK OF CHEMIS-
TRY, Theoretical, Practical, and Technical. In one
vol. Sro. of 662 pages, extra cloth, $1 50.

GARDNER^S MEDICAL CHEMISTRY. 1 vol. 12mo.,
with wood-cuts ; pp. 396, extra cloth, $1 00.

KNAPP'S TECHNOLOGY ; or Chemistry Applied to
the Arts, and to Manufactures. With American
additions, by Prof. Walter R. Johnson. In two
very handsome octavo volumes, with 500 wood
engravings, extra cloth, $6 00.

JpARRISH [ED WARD\

Professor of Materia Medica in the Philadelphia College of Pharmacy.

A TREATISE ON PHARMACY. Designed as a Text-Book for the

Student, and as a Guide for the Physician and Pharmaceutist. With many Formulae and
Prescriptions. Third Edition, greatly improved. In one handsome octavo volume, of 850
pages, with several hundred illustrations, extra cloth. $5 00.
The immense amount of practical information condensed in this volume may be estimated from
the fact that the Index contains about 4700 items. Under the head of Acids there are 312 refer-
ences ; under Emplastrum, 36 ; Extracts, 169 ; Lozenges, 25 j Mixtures, 55 ; Pills, 56 ; Syrups,
131 J Tinctures, 138 ; Unguentum, 57, &c.

We have examined this large volume with a good
deal of care, and find that the author has completely
exhausted the subject upon which he treats ; a more
complete work, we think, it would be impo.ssible to
find. To the student of pharmacy the work is indis-
pensable ; indeed, so far as we know, it is the only one
of its kind in existence, and even to the physician or
medical student who can spare five dollars to pur-
chase it, we feel sure the practical information he
will obtain will more than compensate him for the
outlay. — Canada Med. Journal, Nov. 1864.

The medical student and the practising physician
will find the volume of inestimable worth for study
and reference. — San Francisco Med. Press, July,
1864.

When we say that this book is in some respects
the best which has been published on the subject in
the English language for a great many years, we do
not wish it to be understood as very extravagant
praise. In truth, it is not so much the best as the
only book. — The London Chemical News.

An attempt to furnish anything like an analysis of
Parrish's very valuable and elaborate Treatise on
Practical Pharmacy would require more space than
we have at our disposal. Thi.s, however, is not so
much a matter of regret, inasmuch as it would be
ditflcult to think of any point, however minute and
apparently trivial, connected with the manipulation
of pharmaceutic substances or appliances which has

not been clearly and carefully discussed in this vol-
ume. Want of space prevents our enlarging further
on this valuable work, and we must conclude by a
simple expression of our hearty appreciation of its
merits. — Dvhliri, Quarterly Jour, of Medical Science,
August, 1864.

We have in this able and elaborate work a fair ex-
position of pharmaceutical science as it exists in the
United States ; and it shows that our transatlantus
friends have given the subject most elaborate con-
sideration, and have brought their art to a degree of
perfection which, we believe, is scarcely to be sur-
passed anywhere. The book is, of course, of more
direct value to the medicine maker than to the physi-
cian ; yet Mr. Parrtsh has not failed to introduce
matter in which the prescriber is quite as much
interested as the compounder of remedies. In con-
clusion, we can onlyexpress our high opinion of the
value of this work as a guide to the pharmaceutist,
and in many respects to the phy.sician, not only in
America, but in other parts of the world. — British
Med. Journal, Nov. 12th, 1864.

The former editions have been sufllciently long
before the medical public to render the merits of the
work well known. It is certainly one of the most
complete and valuable works on practical pharmacy
to which the student, the practitioner, or the apothe-
cary can have diCCQ^s.— Chicago Medical Examiner,
March, 1864. y

J^VNGLISON {ROBLEY), M.D.,

Professor of Institide^ of Medicine in Jefferson Medical College, Philadelphia.

GENERAL THERAPEUTICS AND MATERIA MEDICA; adapted

for a Medical Text-Book. With Indexes of Remedies and of Diseases and their Remedies.
Sixth edition, revised and improved. With one hundred and ninety-three illustrations. In
two large and handsomely printed octavo vols, of about 1100 pages, extra cloth. $6 50.
■DY THE SAME AUTHOR.

NEW REMEDIES, WITH FORMULAE FOR THEIR PREPARA-
TION AND ADMINISTRATION. Seventh edition, with extensive additions. In one
very large octavo volume of 770 pages, extra cloth. $4 00.

12 Henry C. Lea's Publications — {Mat. Med. and Therapeutics).

O

RIFFITH [ROBERT E.), M.D.

A UNIVERSAL FORMULARY, Containing the Methods of Pre-

paring and Administering Officinal and other Medicines. The whole adapted to Physicians
and Pharmaceutists. Second edition, thoroughly revised, with numerous additions, by
Robert P. Thomas, M.D., Professor of Materia Medica in the Philadelphia College of
Pharmacy. In one large and handsome octavo volume of 650 pages, double-columns.
Extra cloth, $4 00 ; leather, $5 00.

In this volume, the Formulary proper occupies over 400 double-column pages, and contains
about 5000 formulas, among which, besides those strictly medical, will be found numerous valuable
receipts for the preparation of essences, perfumes, inks, soaps, varnishes, <fec. &c. In addition to
this, the work contains a vast amount of information indispensable for daily reference by the prac-
tising physician and apothecary, embracing Tables of Weights and Measures, Specific Gi'avity,
Temperature for Pharmaceutical Operations, Hydrometrical Equivalents, Specific Gravities of some
of the Preparations of the Pharmacopoeias, Relation between different Thermometrical Scales,
Explanation of Abbreviations used in Formula3, Vocabulary of Words used in Prescriptions, Ob-
servations on the Management of the Sick Room, Doses of Medicines, Rules for the Administration
of Medicines, Management of Convalescence and Relapses, Dietetic Preparations not included in
the Formulary, List of Incompatibles, Posological Table, Table of Pharmaceutical Names which
diflFer in the Pharmacopoeias, Officinal Preparations and Directions, and Poisons.

Three complete and extended Indexes render the work especially adapted for immediate consul-
tation. One, of Diseases and their Remedies, presents under the head of each disease the
remedial agents which have been usefully exhibited in it, with reference to the formulae containing
them — while another of Pharmaceutical and Botanical Names, and a very thorough General
Index aflFord the means of obtaining at once any information desired. The Formulary itself is
arranged alphabetically, under the heads of the leading constituents of the prescriptions.

This is one of the most useful books for the prac-
tising physician which has been issued from the press
of late yeai's, containing a vast variety of formulas
for the safe and convenient administration of medi-
cines, all arranged upon scientific and rational prin-
ciples, with the quantities stated in full, without
signs or abbreviations. — Memphis Med. Recorder.

We know of none in our language, or any other, so
comprehensive in its details. — London Lancet.

One of the most complete works of the kind in any
language. — Edinburgh Med. Journal.

We are not cognizant of the existence of a parallel
work. — London Med. Gazette.

OTILLE (ALFRED), 31. D.,

A^ Professor of Theory and Practice of Medicine in the University of Penna.

THERAPEUTICS AND MATERIA MEDICA; a Systematic Treatise

on the Action and Uses of Medicinal Agents, including their Description and History.

Third edition, revised and enlarged. In two large and handsome octavo volumes. {Nearly

Ready.)
Owing to the author's engagements, this work has been for some time out of print. It is now,
however, passing rapidly through the press, and its publication may be expected at an early
moment. That two large editions of a work of such magnitude should be exhausted in a few
years, is sufficient evidence that it has supplied a want generally felt by the profession, and the
unanimous commendation bestowed upon it by the medical press, abroad as well as at home,
shows that the author has successfully accomplished his object in presenting to the profession a
systematic treatise suited to the wants of the practising physician, and unincumbered with de-
tails interesting only to the naturalist or the dealer.

We have placed first on the list Dr. Stille's great j than formerly. Wecancordiallyrecommendtotho.se
work on Therapeutics. When the first edition of this i of our readers who are interested in Therapeutics a
woi-k made its appearance nearly five years ago, we | careful perusal of Dr. Still6'swork. — Edinburgh Med.
expressed our high sense of its value as containing a I Journal, 1865.

full and philosophical account of the existing state [ An admirable digest of our present knowledge of
of Therapeutics. From the opinion expressed at that , Materia Medica and Therapeutics. — Am. Journ. Med.
time we have nothing to retract; we have, on the Sciences. July, 1860.

contrary, to state that the introduction of numerous I Dr. Stillfe's splendid work on therapeutics and ma-
additions has rendered the work even more complete I teria medica. — London Med. ^imes, April 8, 1865.

J^LLIS [BENJAMIN), M.D.

THE MEDICAL FORMULARY: being a Collection of Prescriptions

derived from the writings and practice of many of the most eminent physicians of America
and Europe. Together with the usual Dietetic Preparations and Antidotes for Poisons. To
which is added an Appendix, on the Endermic use of Medicines, and on the use of Ether
and Chloroform. The whole accompanied with a few brief Pharmaceutic and Medical Ob-
servations. Eleventh edition, carefully revised and much extended by Robert P. Thomas,
M. D., Professor of Materia Medica in the Philadelphia College of Pharmacy. In one
volume 8vo., of about 350 pages. $3 00.

frequently noticed in this Journal as the successive
editions appeared, that it is sufficient, on the present
occasion, to state that the editor has introduced into
the eleventh edition a large amount of new matter,
derived from the current medical and pharmaceutical
works, as well as a number of valuable prescriptions
furnished from private sources. A very comprehen-
sive and extremely useful index has also been sup-
plied, which facilitates reference to the particular
arti^e the prescriber may wish to administer; and
the language of the Formulary has been made to cor-
respond with the nomenclature of the new national
Pharmacopoeia. — Am. Jour. Med. Sciences, Jan. 186-L

We endorse the favorable opinion which the book
has so long established for itself, and take this occa-
sion to commend it to our readers as one of the con-
venient handbooks of the oflBce and library. — Cin-
cinnati Lancet, Feb. 1864.

The work has long been before the profession, and
its merits are well known. The present edition con-
tains many valuable additions, and will be found to
be an exceedingly convenient and useful volume for
reference by the medical practitioner. — Chicago
Medical Examiner, March, 1864.

The work is now so well known, and has been so

Henry C. Lea's Publications — (3Iat. 3Ied. and Therajwutics), 13

pEREIRA [JONATHAN), M.D., F.R.S. and L.S.

MATERIA MEDICA AND THERAPEUTICS; being an Abridg-

ment of the late Dr. Pereira's Elements of Materia Medica, arranged in conformity with
the British Pharmacopoeia, and adapted to the use of Medical Practitioners, Chemists and
Druggists, Medical and Pharmaceutical Students, &c. By F. J. Faure, M.D., Senior
Physician to St. Bartholomew's Hospital, and London Editor of the British Pharmacopoeia;
assisted by Robert Bentlev, M.R.C.S., Professor of Materia Medica and Botany to the
Pharmaceutical Society of Great Britain; and by Robert Warington, F.R.S., Chemical
Operator to the Society of Apothecaries. With numerous additions and references to the
United States Pharmacopoeia, by Horatio C. Wood, M.D., Professor of Botany in the
University of Pennsylvania. In one large and handsome octavo volume of 1040 closely
printed pages, with 236 illustrations, extra cloth, $7 00; leather, raised bands, $8 00.
\Ji(st Issued.)

pceia, none will be more acceptable to the student
and practitioner than the present. Pereira's Materia
Medica had long ago asserted for itself the position of
being the most complete worlc on the subject in the
English language. But its very completeness stood
in the way of its success. Except in the way of refer-
ence, or to those who made a special study of Materia
Medica, Dr. Pereira's worli was too full, and its pe-
rusal required an amount of time which few had at

The task of the American editor has evidently been
no sinecure, for not only has he given to us all that
is contained in the abridgment useful for our pur-
poses, but by a careful and judicious embodiment of
over a hundred new remedies has increased the size
of the former work fully one-third, besides adding
many new illustrations, some of which are original.
We unhesitatingly say that by so doing he has pro-
portionately increased the value, not only of the con-
densed edition, but has extended the applicability of I their disposal. Dr. Farre has very judiciously availed

the great original, and has placed his medical coun-
trymen under lasting obligations to him. The Ame-
rican physician now has all that is needed in the
shape of a complete treatise on materia medica, and
the medical student has a text-book which, for prac-
tical utility and intrinsic worth, stands unparalleled.
Although of considerable size, it is none too large for
the purposes for which it has been intended, and every
medical man should, in justice to himself, spare a
place for it upon his book-shelf, resting assured that
the more he consults it the better he will be satisfied
of its excellence.— iV. Y. Med. Record, Nov. 15, 1866.

It will fill a place which no other work can occupy
in the library of the physician, student, and apothe-
cary.— Boston Med. and Surg. Journal, Nov. 8, 1866.

We have here presented, in a volume of a thousand
pages, that which we sincerely believe the best work
on materia medica in the English language. No phy-
sician, no medical student, can purchase this book,
and make anything like a proper use of it, without
being amply rewarded for his outlay. — The Cincin-
nati Journal of Medicine, November, 1866.

The American editor can very justly say, then, that
•'his ofiice has been no sinecure." The result, how-
ever, of the labors of the different gentlemen engaged
on the work has been to give us a compendium that

himself of the opportunity of the publication of the
new Pharmacopoeia, by bringing out an abridged edi-
tion of the great work. This edition of Pereira is by
no means a mere abridged re-issue, but contains ma-
ny improvements, both in the descriptive and thera-
peutical departments. We can recommend it as a
very excellent and reliable text-book. — Edinburgh
Med Journal, February, 1866.

The reader cannot fail to be impressed, at a glance,
with the exceeding value of this work as a compend
of nearly all useful knowledge on the materia medica.
We are greatly indebted to Professor Wood for his
adaptation of it to our meridian. Without his emen-
dations and additions it would lose much of its value
to the American student. With them it is an Ameri-
can \)no^. — Pacific Medical and Surgical Journal,
December, 1866.

Altogether, the work is a most valuable addition to
the literature of this subject, and will be of great use
to the practitioner of medicine and medical student.
The work, as issued by the American publisher, is a
handsome volume of 10.30 pages, most amply illus-
trated, the wood-cuts being of superior finish, and
clearly impressed. — Ca,nada. Med. Journal, Nov. 1866.

Only .592 pages, while Pereira's original volumes
included 2000, and yet the results of many years' ad-

is admirably adapted for the wants and nece-ssities-of , ditional research in pharmacology and therapeutics
the student. We willingly concede to the American | ^re embodied in the new edition. Unquestionably

editor that we have rarely examined a work that,
the whole, is more carefully and laboriously edited
than this ; or, we may add, that is more improved in
the process of editing. — New York Medical Journal,
December, 1866.

Of the many works on Materia Medica which have
appeared since the issuing of the British Pharmaco-

Dr. Farre has conferred a great benefit upon medical
students and practitioners. And in both respects we
think he has acted very judiciously. And the work
is now condensed — brought fully into accordance with
the pharmacological opinions in vogue, and can be
used with great advantage as a handbook for exami-
nations.— The Lancet, December, 1865.

fl ARSON [JOSEPH], M.D.,

vy Professor of Materia Medica and Pharmacy in the University of Pennsylvania, &c.

SYNOPSIS OF THE COURSE OF LECTURES ON MATERIA

MEDICA AND PHARMACY, delivered in the University of Pennsylvania. With three
Lectures on the Modus Operandi of Medicines. Fourth and revised edition, extra cloth,
$3 00. {Now Ready.)

ROYLE'S MATERIA MEDICA AND THERAPEU-
TICS; including the Preparations of the Pharma-
copoeias of London, Edinburgh, Dublin, and of the
United States. With many new medicines. Edited
by Joseph Carson, M.D. With ninety-eight illus-
trations. In one large octavo volume of about 700
pages, extra cloth. $3 00.

CHRISTISON'S DISPENSATORY; or. Commentary
on the Pharmacopoeias of Great Britain and the
United States; comprising the Natural History,
Description, Chemistry, Pharmacy, Actions, Uses,
and Do.ses of the Articles of the Materia Medica.
Second edition, revised and improved, with a Sup-
plement containing the most important New Reme-
dies. With copious additions, and two hundred
and thirteen large wood-engravings. By R. Eoles-
FELD Grfffitit, M. 1). In one very handsome octavo
▼olume of over 1000 pages, extra cloth, i^i 00.

CARPENTER'S PRIZE ESSAY ON THE USE OF
Alcoholic Liquors in Health and Disease. New
edition, with a Preface by D. F. Condie, M.D., and
explanations of scientific words. In one neat 12mo.
volume, pp. 178, extra cloth. 60 cents.

De JONGH ON THE THREE KINDS OF COD-LIVER
Oil, with their Chemical and Therapeutic Pro-
perties. 1 vol. 12mo., cloth. 75 cents.

MAYNE'S DISPENSATORY AND THERAPEUTICAL
Remkmbraxcer. With every Practical Formula
contained in the three British Pharmacopoeias.
Edited, with the addition of the Formulae of the
U. S. Pharmacopoeia, by R. E. Griffith, M. D. la
one 12mo. volume, 300 pp., extra cloth. 75 cents.

14

Henry C. Lea's Publications — {Pathology).

QROSS [SAMUEL D.), M. D.,

Professor of Stirgery in the. Jefferson Medical College of Philadelphia.

ELEMENTS OF PATHOLOGICAL ANATOMY. Third edition,

thoroughly revised and greatly improved. In one large and very handsome octavo volume
of nearly 800 pages, with about three hundred and fifty beautiful illustrations, of which a
large number are from original drawings ; extra cloth. $4 00.
The very beautiful execution of this valuable work, and the exceedingly low price at which it
is offered, should command for it a place in the library of every practitioner.

Charles-

To the student of medicine we would say that we
know of no work which we can more heartily com-
mend than Gross's Pathological Anatomy. — Southern
Med. and Surg. Journal.

The volume commends itself to the medical student ;
it will repay a careful perusal, and should be upon

the book-shelf of every American physician.
ton Med. Journal.

It contains much new matter, and brings down our
knowledge of pathology to the latest period. — London
Lancet.

J

ONES [C. HANDFIELD), F.R.S., and SIEVEKING [ED, H.), M.D.,

Assistant Physicians and Lecturers in St. Mary's Hospital.

A MANUAL OF PATHOLOGICAL ANATOMY. First American

edition, revised. With three hundred and ninety-seven handsome wood engravings. In
one large and beautifully printed octavo volume of nearly 750 pages, extra cloth, $3 50.

Our limited space alone restrains us from noticing
more at length the various subjects treated of in
this interesting work; presenting, as it does, an excel-
lent summary of the existing state of knowledge in
relation to pathological anatomy, we cannot too
strongly urge upon the student the necessity of a tho-
rough acquaintance with its contents. — Medical Ex-
aminer.

We have long had need of a hand-book oT patholo-
gical anatomy which should thoroughly reflect the
present state of that science. In the troritise before
us this desideratum is supplied. Within the limits of
a moderate octavo, we have the outlines of this great
department of medical science accurately defined.

and the most recent investigations presented in suffi-
cient detail for the student of pathology. "We cannot
at this time undertake a formal analysis of this trea-
tise, as it would involve a separate and lengthy
consideration of nearly every subject discussed ; nor
would such analysis be advantageous to the medical
reader. The work is of such a character that every
physician ought to obtain it, both for reference and
study. — N. Y. Journal of Medicine.

Its importance to the physician cannot be too highly
estimated, and we would recommend our readers to
add it to their library as soon as they conveniently
can. — Montreal Med. Chronicle.

T>OKITANSKY [CARL), M.D.,

Curator of the Imperial Pathological Museum, and Professor at the University of Vienna.

A MANUAL OF PATHOLOGICAL ANATOMY. Translated by

W. E. SwAiNE, Edward Sieyeking, C. H. Moore, and G. E. Day.
bound in two, of about 1200 pages, extra cloth. $7 50.

Four volumes octavo,

GLUGE'S ATLAS OF PATHOLOGICAL HISTOLOGY.
Translated, with Notes and Additions, by Joseph
Leidy, M. D. In one volume, very large imperial
quarto, with 320 copper-plate figures, plain and
colored, extra cloth. $i 00.

SIMON'S GENERAL PATHOLOGY, as conducive to
the E^'tablishnient of Rational Principles for the
Prevention and Cure of Disease. In one octavo
volume of 212 pages, extra cloth. $1 2.3.

y^lLLIAMS [CHARLES J. B.), M.D.,

Professor of Clinical Medicine in University College, London.

PRINCIPLES OF MEDICINE. An Elementary View of the Causes,

Nature, Treatment, Diagnosis, and Prognosis of Disease ; with brief remarks on Hygienics,
or the preservation of health. A new American, from the third and revised London edition.
In one octavo volume of about 500 pages, extra cloth. $3 50.

The unequivocal favor with which this work has
been received by the profession, both in Europe and
America, is one among the many gratifying evidences
which might be adduced as going to show that there
is a steady progress taking place in the science as well
as in the art of medicine.— /S<. Louts Med. and Surg.
Journal.

No work has ever achieved or maintained a more
deserved reputation. — Virginia Med. and Surg.
Journal.

One of the best works on the subject of which it
treats in our language.

It has already commended itself to the high regard
of the profession ; and we may well say that we
know of no single volume that will afford the source
of so thorough a drilling in the principles of practice
as this. Students and practitioners should make
themselves intimately familiar with its teachings —
they will find their labor and study most amply
repaid. — Cincinnati Med. Observer.

There is no work in medical literature which can
fill the place of this one. It is the Primer of the
young practitioner, the Koran of the scientific one. —
Stethoscope.

A text-book to which no other in our language is
comparable. — Charleston Med. Journal.

The lengthened analysis we have given of Dr. Wil-
liams's Principles of Medicine will, we trust, clearly
prove to our readers his perfect competency for the
task he has undertaken — that of imparting to the
student, as well as to the more experienced practi-
tioner, a knowledge of those general principles of
pathology on which alone a correct practice can be
founded. The absolute necessity of such a work
must be evident to all who pretend to more than
mere empiricism. We must conclude by again ex-
pressing our high sense of the immense benefit which
Dr. Williams has conferred on medicine by the pub-
lication of this work. We are certain that in the
present state of our knowledge his Principles of Medi-
cine could not pos.sibly be surpassed. While wo
regret the loss which many of the rising generation
of practitioners have sustained by his resignation o
the Chair at University College, it is comforting to
feel that his writings must long continue to exert a
powerful influence on the practice of that profession
for the improvement of which he has so assiduously
and successfully labored, and in which he holds so
distinguished a ^os.iiioD..— London Jour, of Medicine

Henry C. Lea's Publications — {Practice of Medicine).

15

TILINT [AUSTIN], M.D.,

J~ Professor of the Principles and Practice of Medicine in Bellevue Med. College, N. T.

A TREATISE ON THE PRINCIPLES AND PRACTICE OF

MEDICINE ; designed for the use of Students and Practitioners of Medicine. Second
edition, revised and enlarged. In one large and closely printed octavo volume of nearly
]000 pages; handsome extra cloth, $6 50; or strongly bound in leather, with raised bands,
$7 60. {J?ist Issued.)

From the Preface to the Second Edition.
Four months after the publication of this treatise, the author was notified that a second edition
was called for. The speedy exhaustion of the first edition, unexpected in view of its large size,
naturally intensified the desire to make the work still more acceptable to practitioners and
students of Medicine; and, notwithstanding the brief period allowed for a revision, additions
have been made which, it is believed, will enhance the practical utility of the volume.

We are happy in being able once more to commend
this work to the students and practitioners of medicine
who seek for accurate information conveyed in lan-
guage at once clear, precise, and expressive. — Amer.
Journ. Med. Sciences, April, 1867.

Dr. Flint, who has been known in this country for
many years, both as an author and teacher, wlio has
discovered truth, and pointed it out clearly and dis-
tinctly to others, investigated the symptoms and na-
tural history of disease and recorded its language and
facts, and devoted a life of incessant study and
thought to the doubtful or obscure in his profession,
has at length, in his ripe scholarship, given this work
to the profession as a crowning gift. If we have spoken
highly of its value to the profession and world ; if we
have said, all considered, it is the very best work
upon medical practice in any language; if we have
spoken of its excellences in detail, and given points
of special value, we have yet failed to express in any
degree our present estimate of its value as a guide in
the practice of medicine. It does notcontain too much
or too little ; it is not positive where doubt should be
expressed, or hesitate where truth is known. It is
philosophical and speculative where philosophy and
speculation are all that can at present be obtained,
but nothing is admitted to the elevation of established
truth, wiiliout the most thorough investigation. It
is truly remarkable with what even hand this work
has been written, and how it all shows the most care-
ful thought and untiring study. "We conclude that,
though it may yet be susceptible of improvement, it
still constitutes the very best which human knowledge
can at present produce. "When knowledge is in-
creased," the work will doubtless be again revised;
meanwhile we shall accept it as the rule of practice.
— Buffalo Med. and Surg. Journal, Feb. 1867.

He may justly feel proud of the high honor con-
ferred on him by the demand for a second edition of
his work in four months after the issue of the first.
No American practitioner can afford to do without
Flint's Practice. — Pacific Med. and Surg. Journal,
Feb. 1867.

Dr. Flint's book is the only one on the practice of
medicine that can benefit the young practitioner. —
Nashville Med. Journal, Aug. 1866.

We consider the book, in all its essentials, as the
best adapted to the student of any of our numerous
text-books on this subject. — AM' 3ied. Journ.. Jan.'Gl .

Its terse conciseness fully redeems it from being

ranked among heavy and common-place works, while
the unmistakable way in which Dr. Flint gives his
own views is quite refreshing, and far from common.
It is a book of enormous research ; the writer is evi-
dently a man of observation and large experience ;
his views are practically sound and theoretically
moderate, and we have no hesitation in commending
his magnum opus to our readers — Dublin Medical.
Press and Circtdar, May 16, 1866.

In the plan of the work and the treatment of indi-
vidual subjects there is a freshness and an originality
which make it worthy of the study of practitioners
as well as students It is, indeed, an admirable book,
and highly cre4itable to American medicine. For
clearness and conciseness in style, for careful reason-
ing upon what is known, for lucid distinction betweeu
what we know and what we do not know, between
what nature does in disease and what the physician
can do and should, for richness in good clinical ob-
servation, for independence of statement and opinion
on great points of practice, and for general sagacity
and good judgment, the work is most meritorious.
It is singularly rich in good qualities, and free from
faults. — London Lancet, June 23, 1866.

In following out such a plan Dr. Flint has suc-
ceeded most admirably, and gives to his readers a
work that is not only very readable, interesting,
and concise, but in every respect calculated to meet
the requirements of professional men of every class.
The student has presented to him, in the plainest
possible manner, the symptoms of disease, the prin-
ciples which should guide him in its treatment, and
the difficulties which have to be surmounted in order
to arrive at a correct diagnosis. The practitioner,
besides having such aids, has offered to him the con-
clusion which the experience of the professor has
enabled him to arrive at in reference to the relative
merits of different therapeutical agents, and different
methods of treatment. This new work will add not
a little to the well-earned reputation of Prof. Flint as
a medical teacher.— A^. ¥. Med. Record, April 2, 1866.

We take pleasure in recommending to the profession
this valuable and practical Avork on the practice of
medicine, more particularly as we have had oppor-
tunities of appreciating from personal observation
the author's preeminent merit as a clinical observer.
This work is undoubtedly one of great merit, and we
feel confident that it will have an extensive circula-
tion.— The N. 0. Med. and Surg. Journal, Sept. 1866.

jnUNGLISON, FORBES, TWEEDIE, AND CONOLLY.

THE CYCLOPEDIA OF PRACTICAL MEDICINE: comprising

Treatises on the Nature and Treatment of Diseases, Materia Medica and Therapeutics,
Disea.ses of Women and Children, Medical Jurisprudence, &e. <fec. In four large super-royal
octavo volumes, o 13254 double-columned pages, strongly and handsomely bound in leather,
$15; extra cloth, $11,
*^* This work contains no less than four hundred and eighteen distinct treatises, contributed
by sixty-eight distinguished physicians.

The most complete work on practical medicine
extant, or at least in our language, — Buffalo Medical
and Surgical Journal.

For reference, it is above all price to every practi-
tioner.— Western Lancet.

One of the most valuable medical publications of

the day. As a work of reference it is invaluable. —
Western Journal of Medicine and Surgery.

It has been to us, both as learner and teacher, a
work for ready and frequent reference, one in which
modern English medicine is exhibited in the most ad-
vantageous light. — Medical Examiner.

BARLOW'S MANUAL OF THE PRACTICE OF
MEDICINE. With Additions by D. F. Condie,
M. D. 1 vol. Svo., pp. 600, cloth. $2 50.

HOLLAND'S MEDICAL NOTES AND REFLEC-
TIONS. From the third and enlarged English edi-
tion. In one handsome octavo volume of about
500 pages, extra cloth. $3 50.

16

Henry C. Lea's Publications — {Practice of Medicine).

TTARTSHORNE [HENRY], M.D.,

•^^ Profesfsor of Hygiene in the University of Pennsylvania.

ESSENTIALS OP THE PRINCIPLES AND PRACTICE OF MEDI-
CINE. A handy-book for Students and Practitioners. In one handsome royal ]2mo.
volume of about 350 pages, clearly printed on small type, cloth, $2 38 j half bound, $2 63.
{Jtist Issued.)
The very cordial reception with which this work has met shows that the author has fully suc-
ceeded in his attempt to condense within a convenient compass the essential points of scientific
and practical medicine, so as to meet the wants not only of the student, but also of the practi-
tioner who desires to acquaint himself with the results of recent advances in medical science.

nearly than any similar manual lately before us the
standard at which all such books should aim — of
teaching much, and suggesting more. To the student

As a strikingly terse, fiiU, and comprehensive em-
bodiment in a condensed form of the essentials in
medical science and art, we hazard nothing in saying
that it is incomparably in advance of any work of the
kind of the past, and will stand long in the future
without a rival. A mere glance will, we think, im-
press others with the correctness of our estimate. Nor
do we believe there will be found many who, after
the most cursory examination, will fail to possess it.
How one could be able to crowd so much that is valu-
able, especially to tbe student and young practitioner,
within the limits of so small a book, and yet embrace
aad present all that is important in a Avell-arrauged,
clear form, convenient, satisfactory for reference, with
so full a table of contents, and extended general index,
with nearly three hundred formulas and recipes, is a
marvel. — Western Journal of Medicine, Aug. 1867.

The little book before us has this quality, and we
can therefore say that all students will find it an in-
valuable guide in their pursuit of clinical medicine.
Dr. Hartshorne speaksofitas "an unambitious eflbrt
to make useful the experience of twenty years of pri-
vate and hospital medical practice, with its attendant
study and reflection." That the effort will prove suc-
cessful we have no doubt, and in his study, and at
the bedside, the student will find Dr. Hartshorne a
safe and accomplished companion. We speak thus
highly of the volume, because it approaches more

can heartily recommend the work of our transat-
lantic colleague, and the busy practitioner, we are
sure, will find in it the means of solving many a
doubt, and will rise from the perusal of its pages,
having gained clearer views to guide him in his daily
struggle with disease.— i>w6. Med. Press, Oct. 2, 1S67.

Pocket handbooks of medicine are not desirable,
even when they are as carefully and elaborately com-
piled as this, the latest, most complete, and most ac-
curate which we have seen. — British Med. Journal,
Sept. 21, 1S67.

This work of Dr. Hartshorne must not be confound-
ed with the medical manuals so generally to be found
in the hands of students, serving them at best but as
blind guides, better adapted to lead them astray than
to any useful and reliable knowledge. The work be-
fore us presents a careful synopsis of the essential
elements of the theory of diseased action, its causes,
phenomenal and results, and of the art of healing, as
recognized by the most authoritative of our profes-
sional writers and teachers. A very careful and can-
did examination of the volume has convinced us that
it will be generally recognized as one of the best man-
uals for the use of the student that has yet appeared.
— American Journal Med. Sciences, Oct. 1S67.

Tm TSON ( THOMAS), M. D., ^c.

LECTURES ON THE PRINCIPLES AND PRACTICE OF

PHYSIC. Delivered at King's College, London. A new American, from the last revised
and enlarged English edition, with Additions, by D. Francis Condie, M. D., author of
•' A Practical Treatise on the Diseases of Children," &c. With one hundred and eighty-
five illustrations on wood. In one very large and handsome volume, imperial octavo, of
over 1200 closely printed pages in small type; extra cloth, $6 60; strongly bound in
leather, with raised bands, $7 50.
Believing this to be a work which should He on the table of every physician, and be in the hands
of every student, every effort has been made to condense the vast amount of matter which it con-
tains within a convenient compass, and at a very reasonable price, to place it within reach of all.
In its present enlarged form, the work contains the matter of at least three ordinary octavos,
rendering it one of the cheapest works now offered to the American profession, while its mechani-
cal eixecution makes it an exceedingly attractive volume.

DICKSON'S ELEMENTS OF MEDICINE ; a Compen-
dious View of Pathology and Therapeutics, or the
History and Treatment of Diseases. Second edi-
tion, revised. 1 vol. Svo. of 750 pages, extra cloth.
$1 00.

.WHAT TO OBSERVE AT THE BEDSIDE AND AFTER
Death in Medical Cases. Published under the
authority of the London Society for Medical Obser-

vation. From the .second London edition. 1 vol.
royal 12rao., extra cloth. $1 00.
LAYCOCK'S LECTURES ON THE PRINCIPLES
AND Methods of Medical Observation and Re-
search. For the use of advanced students and
juQior practitioners. In one very neat royal 12mo.
volume, extra cloth. $1 00.

-nARCLAT {A. W.), M. D.
^A MANUAL OF MEDICAL DIAGNOSIS; being an Analysis of the

Signs and Symptoms of Disease. Third American from the second and revised London
edition. In one neat octavo volume of 451 pages, extra cloth. I|i3 50.
A work of immense practical utility. — London \ The book should be in the hands of every practice
Med. Times and Gazette. , man. — Dublin Med. Press.

JPULLER [HENRY WILLIAM), M. D.,

-*• Physician to St. George^ s Hospital, London.

ON DISEASES OF THE LUNGS AND AIR-PASSAGES. Their

Pathology, Physical Diagnosis, Symptoms, ard Treatment. From the second and revised
English edition. In one handsome octavo volume of about 500 pages, extra cloth, $3 50.
{Now Ready.)

Dr. Fuller's work on diseases of the chest was so ; accordingly we have what might be with perfect ju.s-
favorably received, that to many who did not know j tice styled an entirely new work from his pen, the
the extent of his engagements, it was a matter of won- ! portion of the work treating of the heart and great
der that it should be allowed to remain three years j vessels being excluded. Nevertheless, this volume is
out of print. Determined, however, to improve it, of almost equal size with the first. — London Medical
Dr. Fuller would not consent to a mere reprint, and I Times and Gazette, July 20, 1867.

Henry C. Lea's Publications — {Practice of Medicine).

IT

J^LINT {A USTIN), M. D.,

-*■ Professor of the Principles and Practice of Medicine in Bellevue Hospital Med. College, N. Y.

A PRACTICAL TREATISE ON THE PHYSICAL EXPLORA-
TION OF THE CHEST AND THE DIAGNOSIS OF DISEASES AFFECTING THE
RESPIRATORY ORGANS. Second and revised edition. In one handsome octavo volume
of 595 pages, extra cloth, $4 60. {^Just Issued.)
Premising this observation of the necessity of each
student and practitioner making himself acquainted

with auscultation and percussion, we may state our
honest opinion that Dr. Flint's treatise is one of the
most trustworthy guides which he can consult. The
style is clear and distinct, and is also concise, being
free from that tendency to over-refinement and unne-
cessHry minuteness which characterizes many works
on the same subject. — Dublin Medical Press, Feb. 6,
1S67.

In the invaluable work before us, we have a book
o^ facts of nearly 600 pages, admirably arranged,
clear, thorough, and lucid on all points, without pro-
lixity; exhausting every point and topic touched; a
monument of patient and loug-coutinued observation,
which does credit to its author, and reflects honor on

American medicine. — Atlanta Med, and Surg. Jour-
nal, Feb. 1867.

The chapter on Phthisis is replete with interest;
and his remarks on the diagnosis, especially in the
early stages, are remarkable for their acumen and
great practical value. Dr. Flint's style is clear and
elegant, and the tone of freshness and originality
which pervades his whole work lend an additional
force to its thoroughly practical character, which
cannot fail to obtain for it a place as a standard work
on diseases of the respiratory system, — London
Lancet, Jan. 19, 1867.

This is an admirable book. Excellent in detail and
execution, nothing better could be desired by the
practitioner. Dr. Flint enriches his subject with
much solid and not a little original observation. —
Banking's Abstract, Jan. 1867.

B

Y THE SAME A UTHOR.

A PRACTICAL TREATISE ON THE DIAGNOSIS, PATHOLOGY,

AND TREATMENT OF DISEASES OF THE HEART. In one neat octavo volume of
nearly 500 pages, with a plate ; extra cloth, $3 50.

We question the fact of any recent American author
in our profession being more extensively known, or
more deservedly esteemed in this country than Dr.
Flint. We willingly acknowledge his success, more
particularly in the volume on diseases of the heai't, in

makingan extended personal clinical study available
for purposes of illustration, in connection with cases
which have been reported by other trustworthy ob-
servers.— Brit, and For. Med.-Chir. Review.

ffff AMBERS [T. K.), M. D.,

^ Consulting Physician to St. Mary's Hospital, London, &c.

THE INDIGESTIONS ; or, Diseases of the Digestive Organs Functionally

Treated. Second Edition, revised. In one handsome octavo volume of over 300 pages,

extra cloth, $3 00. {Now Ready.)

and practical skill — that his success as a teacher or
literary expositor of the medical art consists; and the
volume before us is a better illustration than its au-

He is perhaps the most vivid and brilliant of living
medical writers ; and here he supplies, in a graphic
series of illustrations, bright sketches from his well-
stored portfolio. His is an admirable clinical book,
like all that he publishes, original, brilliant, and in-
teresting. Everywhere he is graphic, and his work
supplies numerous practical hints of much value. —
Edinburgh Med. and Surg. Journal, Nov. 1867.

Associate with this the rare faculty which Dr.
Chambers has of infusing an enthusiasm in his sub-
ject, and we have in this little work all the elements
which make it a model of its sort. We have perused
it carefully; have studied every page; our interest
in the subject has been intensified as we proceeded,
and we are enabled to lay it down with unqualified
praise.— A^. Y. Med. Record, April la, 1867.

It is in the combination of these qualities — clear and
vivid expression, with thorough scientific knowledge

thor has yet produced of the rare degree in which
those combined qualities are at his command. Next
to the diseases of children, there is no subject on
which the young practitioner is oftener consulted, or
on which the public are more apt to form their
opinions of his professional skill, than the various
phenomena of indigestion. Dr. Chambers comes most
opportunely and effectively to his assistance. In fact,
there are few situations in which the commencing
practitioner can place himself in which Dr. Cham^
bers' conclusions on digestion will not be of service.
— London Lancet, February 23, 1867.

This is one of the most valuable works which it
has ever been our good fortune to receive. — London
Med. Mirror, Feb. 1867.

B

RINTON [WILLIAM), M.D., F.R.S.

LECTURES ON THE DISEASES OF THE STOMACH; with an

Introduction on its Anatomy and Physiology. From the second and enlarged London edi-
tion. With illustrations on wood. In one handsome octavo volume of about 300 pages,
$3 25. {Just isstied.)

The most complete work in our langiiage upon the
diagnosis and treatment of these puzzling and impor-
tant diseases.— £o6-<o?i Med. and Surg. Journal, Nov.
1865.

extra cloth.

Nowhere can be found a more full, accurate, plain,
and instructive history of these diseases, or more ra-
tional views respecting their pathology and therapeu-
tics.—^m. Joum. of the Med. Sciences, April, 1865.

H

H

ABERSHON [S. 0.), M.D.

PATHOLOGICAL AND PRACTICAL OBSERVATIONS ON DIS-
EASES OF THE ALIMENTARY CANAL, (ESOPHAGUS, STOMACH, C^CUM, AND
INTESTINES. With illustrations on wood. In one handsome octavo volume of 312
pages, extra cloth. $2 60.

UDSON (A.), M.D., M. R.LA.,

Phy,9ieian to the Meath Hospital.

LECTURES ON THE STUDY OF FEYER. In one vol. 8vo.

lishing in the "Medical News and Library" for 1867 and 1868.)

(Pub-

18

Henry C. Lea's Publication& — {Practice of Medicine).

'DUMSTEAD [FREEMAN J.), M.D.,

•J-^ Lecturer on Materia 3fedica and Venereal Diseases at the Col. of Phys. and Surg., New Yorlt, &c.

THE PATHOLOGY AXD TREATMENT OF YENEREAL DIS-

EASES. Including the results of recent investigations upon the subject. A new and re-
vised edition, with illustrations. In one large and handsome octavo volume of 640 pages,
extra cloth, $5 00. {Lately Issued.)
During the short time which has elapsed since the appearance of this work, it has assumed the
position of a recognized authority on the subject wherever the language is spoken, and its transla-
tion into Italian shows that its reputation is not confined to our own tongue. The singular clear-
ness with which the modern doctrines of venereal diseases are set forth renders it admirably
adapted to the student, while the fulness of its practical details and directions as to treatment
makes it of great value to the practitioner. The few notices subjoined will show the very high
position universally accorded to it by the medical press of both hemispheres.

Well known as one of the best authorities of the i which has long been felt in English medicalliterature.

present day on the subject. — British and For. Med.-
Ghirurg. Review, April, 1866.

A regular store-house of special information. —
London Lancet, Feb. 24, 1866.

A remarkably clear and full systematic treatise on
the whole subject. — Lond. Med. Times and Gazette.

The best, completest, fullest monograph on this
subject in our language. — British American Journal.

Indispensable in a medical library. — Pacific Med.
and Surg. Journal.

We have no doubt that it will supersede in America
every other treatise on Venereal. — San Francisco
Med. Press, Oct. 1864.

A perfect compilation of all that is worth knowing
on venereal diseases in general. It fills up a gap

— Brit, and Foreign Med.-Chirurg. Review, Jan., '6.5.

We have not met with any which so highly merits
our approval and praise as the second edition of Dr.
Burastead'swork. — Glasgow Med. Journal, Oct. 1S61.

We know of no treatise in any language which la
its equal in point of completeness and practical sim-
plicity.— Boston Medical and Surgical Journal,
Jan. .30, 1S64.

The book is one which every practitioner should
have in his possession, and, we may further say, the
only book upon the subject which he should acknow-
ledge as competent authority. — Buffalo Medical and
Surgical Journal, July, 1864.

The best work with which we are acquainted, and
the most convenient hand-book for the busy practi-
tioner — Cincinnati Lancet, July, 1864.

(lULLERIER [A.), and

^ Surgeon to the Udpital du Midi.

"DUMSTEAD [FREEMAN J.),

J~^ Professor of Venereal Diseases in the College of

Physicians and Surgeons, N. Y.

AN ATLAS OF VENEREAL DISEASES. Translated and Edited by

Freeman J. Bumstead. To be issued in five parts, at Three Dollars each, making a large
imperial 4to. volume, with 26 plates, containing about 150 figures, beautifully colored, many
of them the size of life. (Parts I. and II. noiv ready.)
In charge of the celebrated Ilopital du Midi, where M. Eicord gained his immense experience,
M. Cullerier is known as one of the most profound syphilographers of the present day. This
work presents the results of his observations and reflections on the whole round of venereal acci-
dents and afiFections, and is illustrated with a complete series of colored plates, more minute and
extensive than anything of the kind that has yet been laid before the profession. The translator
and editor. Dr. Bumstead, is so well known in this country as an authority on the subject, and
as a clear and elegant writer, that his connection with the work is suflBcient guarantee that its
value will be increased in passing through his hands.

*^* A specimen of the plates and text sent free by mail, on receipt of 25 cents.

BUCKLER ON FIBRO-BRONCHITIS AND RHEU-
MATIC PNEUMONIA. In one octavo vol., extra
cloth, pp. 1.50. *1 2.5.

FISKE FUND PRIZE ESSAYS.— LEE ON THE EF-
FECTS OF CLIMATE ON TUBERCULOUS DIS-
EASE. AND WARREN ON THE INFLUENCE OF
PREGNANCY ON THE DEVELOPMENT OF TU-
BERCLES. Together in one neat octavo volume,
extra cloth, $1 00.

HUGHES' CLINICAL INTRODUCTION TO AUS-
CULTATION AND OTHER MODES OF PHYSICAL
DIAGNOSIS. Second edition. One volume royal
12mo., extra cloth, pp. 304. $1 2.5.

WALSHE'S PRACTICAL TREATISE ON THE DIS-
EASES OF THE HEART AND GREAT VESSELS.
Third American, from the third revised and much
enlarged London edition. In one handsome octavo
volume of 420 pages, extra cloth. $3 00.

J^A ROCHE [R.), 31. D.

YELLOW FEYER, considered in its Historical, Pathological, Etio-
logical, and Therapeutic.nl Relations. Including a Sketch of the Disease as it has occurred
in Philadelphia from 1699 to 1854, with an examination of the connections between it and
the fevers known under the same name in other parts of temperate as well as in tropical
regions. In two large and handsome octavo volumes, of nearly 1500 pages, extra cloth, $7 00.
jyT THE SAME AUTHOR.

PNEUMONIA ; its Supposed Connection, Pathological, and Etiological,

with Autumnal Fevers, including an Inquiry into the Existence and Morbid Agency of
Malaria. In one handsome octavo volume, extra cloth, of 500 pages. $3 00.

J^YONS [ROBERT D.), K. C. C.

A TREATISE ON FEYER; or. Selections from a Course of Lectures

on Fever. Being part of a Course of Theory and Practice of Medicine. In one neat octavo
volume, of 362 pages, extra cloth. $2 25.

CLYMER ON FEVERS; THEIR DIAGNOSIS, PA-
THOLOOY AND TREATMENT. In OQe octavo volume
of 600 pages, leather. $1 75.

TODD'S CLINICAL LECTURES ON CERTAIN ACUTE
DisEA!!ES. In one neat octavo volume, of 320 pages
extra cloth. $2 50.

Henry C. Lea's Publications — {Practice of Medicine).

19

IJOBERTS ( WILLIAM), M. D.,

-*• ^ Lecturer on Medicine in the Manchester School of Medicine, &c.

A rilACTICAL TREATISE ON URINARY AND RENAL DIS-

EASES, including Urinary Deposits. Illustrated by numerous cases and engravings. In
one very handsome octavo volume of 516 pp., extra cloth. $4 50. {^Just Issued.)

In carrying out this design, he has not only made
good use of his own practical knowledge, but has
brought together from various sources a vast amount
of information, some of which is not generally pos-
sessed by the profession in this country. We must
now bring our notice of this book to a close, re-
gretting only that we are obliged to resist the temp-
tation of giving further extracts from it. Dr. Roberts
has already on several occasions placed before the
profession the results of researches made by him on
various points connected with the urine, and had thus
led us to expect from him something good — in which

sive work on urinary and renal diseases, considered
in their strictly practical aspect, that we possess in
the English language. — British Medical Journal^
Dec. 9, lS6r>.

We have read this book with much satisfaction.
It will take its place beside the best treatises in our
language upon urinary pathology and therapeutics.
Not the least of its merits is that the author, unlike
some other book-makers, is contented to withhold
much that he is well qualified to discuss in order to
impart to his volume such a strictly practical charac-
ter as cannot fail to render it popular among British
readers. — London Med. Times and Gazette, March
17, 1SH6.

expectation we have been by no means disappointed
The book is, beyond question, the most comprehen

J^^, " Bird on Urinary Deposits," being for the present out of print, gentlemen will find in the
above work a trustworthy substitute.

MORLAND ON RETENTION IN THE BLOOD OF
THE ELEMENTS OF THE URINARY SECRE-
TION. 1 vol. 8vo., extra cloth. 75 cents.

BLOOD AND URINE (MANUALS ON). By J. W.

Griffth, G. 0. Reese, and A. Markwick. 1 vol,
12mo., extra cloth, with plates, pp. 460. $1 25.
BUDD ON DISEASES OF THE LIVER. Tliird edition.
1 vol. 8vo., extra cloth, with four beautifully colored
plates, and numerous wood-cuts. pp. 500. $4 00.

jyUGKNILL [J. a),M.D., and

-*-'' Med. Superintendent of the Devon Lunatic Asylum.

T^ANIEL H. TDKE,M.D.,

-^-^ Visiting Medical Officer to the York Retreat.

A MANUAL OF PSYCHOLOGICAL MEDICINE; containing the

History, Nosology, Description, Statistics, Diagnosis, Pathology, and Treatment of In-
sanity. With a Plate. In one handsome octavo volume, of 536 pages, extra cloth. $4 25.

TONES [G. HANDFIELD), M. D.,

^ Physician to St. Mary's Hospital, &c.

CLINICAL OBSERVATIONS ON FUNCTIONAL NERVOUS

DISORDERS. In one handsome octavo volume of 348 pages, extra cloth, $3 25.

{Just Issiced.)

Taken as a whole, the work before us furnishes a 1 We must cordially recommend it to the profession

short but reliable account of the pathology and treat- ' of this country as supplying, in a great measure, a

ment of a class of very common but certainly highly j deficiency which exists in the medical literature of

obscure disorders. The advanced student will find it ! the English language. — New York Med. Journ., April,

a rich mine of valuable facts, while the medical prac-
titioner will derive from it many a suggestive hint to
aid him in the diagnosis of "nervous cases," and in
determining the true indications for their ameliora-
tion or cure. — Amer. Journ. Med. Sci., Jan. 1S67.

1867.

The volume is a most admirable one— full of hints
and practical suggestions. — Canada Med. Journal,
April, 1867.

HARRISON'S ESSAY TOWARDS A CORRECT
THEORY OF THE NERVOUS SYSTEM, In one
octavo volume of 292 pp. $1 50.

SOLLY ON THE HUMAN BRAIN: its Structure,

Physiology, and Diseases. From the Second and
much enlarged London edition. In one octavo
volume of 500 pages, with 120 wood-cuts; extra
cloth. *2 50.

OMITH {EDWARD), M.D.
CONSUJMPTION; ITS EARLY AND REMEDIABLE STAGES.

one neat octavo volume of 254 pages, extra cloth. $2 25.

gALTER {H. H.), M.D.

ASTHMA ; its Pathology, Causes, Consequences, and Treatment.

one volume; octavo, extra cloth. $2 50.
gLADE [D. D.),

In

In

M.D.

DIPHTHERIA; its Nature and Treatment, with an account of the His-
tory of its Prevalence in various Countries. Second and revised edition. In one neat
royal 12mo, volume, extra cloth. $1 25. {Just issued.)

ALLEMAND AND WILSON.

A PRACTICAL TREATISE ON THE CAUSES, SYMPTOMS,

AND TREATMENT OF SPERMATORRHCEA. By M. Lallemand. Tran.«lated and

edited by Henry J. McDougall. Fifth American edition. To which is added ON

DISEASES OF THE VESICUL^ SEMINALES, and their associatrd organs. With
special reference to the Morbid Secretions of the Prostatic and Urethral Mucous Membrane.
By Mauris Wilson, M.D. In one neat octavo volume, of about 400 pp., extra cloth, $2 76.

20

Henry C. Lea's Publications — (Diseases of the Skin).

T^ILSON {ERASMUS), F.R.S.,

ON DISEASES OF THE SKIN. The sixth American, from the fifth

and enlarged English edition. In one large octavo volume of nearly 700 pages, extra
cloth. $4 60. Also—

A SERIES OF PLATES ILLUSTRATING "WILSON ON DIS-
EASES OF THE SKIN;" consisting of twenty beautifully executed plates, of which thir-
teen are exquisitely colored, presenting the Normal Anatomy and Pathology of the Skin,
and embracing accurate representations of about one hundred varieties of disease, most of
them the size of nature. Price, in extra cloth, $5 50.
Also, the Text and Plates, bound in one handsome volume, extra cloth. Price $9 50.
This classical work has for twenty years occupied the position of the leading authority on cuta-
neous diseases in the English language, and the industry of the author keeps it on a level with the
advance of science, in the frequent revisions which it receives at his hands. The large size of the
volume enables him to enter thoroughly into detail on all the subjects embraced in it, while its
very moderate price places it within the reach of every one interested in this department of practice.

Such a work as the one before us is a most capital
and acceptable help. Mr. Wilson has long been held
as high authority in this department of medicine, and
his book on diseases of the skin has long been re-
garded as one of the best text-books extant on the
subject. The present edition is carefully prepared,
and brought up in its revision to the present time In
this edition we have also included the beautiful series
of plates illustrative of the text, and in the last edi-
tion published separately. There are twenty of these
plates, nearly all of them colored to nature, and ex-
hibiting with great fidelity the various groups of
diseases treated of in the body of the work. — Cin-
cinnati Lancet, June, 1863.

No one treating skin diseases should be without
a copy of this standard work. — Canada Lancet.
August, 1863.

We can safely recommend it to the pi-ofession as
the best work on the subject now in existence in
the English language. — Medical Times and Gazette.

Mr. Wilson's volume is an excellent digest of the
actual amount of knowledge of cutaneous diseases;
it includes almost every fact or opinion of importance
connected with the anatomy and pathology of the
skin. — British and Foreign Medical Review.

These plates are very accurate, and are executed
with an elegance and taste which are highly creditable
totheartisticskillofthe American artist who executed
them. — St. Louis Med. Journal.

The drawings are very pei'fect, and the finish and
coloring artistic and correct ; the volume is an indis-
pensable companion to the book it illustrates and
completes. — Charleston Medical Journal.

JDY THE SA3IE AUTHOR.

THE STUDENT'S BOOK OF CUTANEOUS MEDICINE and Dis-

EASES OP THE SKIN. In One very handsome royal 12mo. volume. $.3 50. {Now Ready.)
This new class-book will be admirably adapted to I Thoroughly practical in the best sense. — Brit. Med.
the necessities of students. — Lancet. \ Journal.
DF THE SAME AUTHOR.

HEALTHY SKIN; a Popular Treatise on the Skin and Hair, their

Preservation and Management. One vol. 12mo., pp. 291, with illustrations, cloth. $1 00

ISJELIGAN [J. MOORE), M.D., M.R.I.A.,

A PRACTICAL TREATISE ON DISEASES OF THE SKIN.

Fifth American, from the second and enlarged Dublin edition by T. W. Belcher, M. D.

In one neat royal 12mo. volume of 462 pages, extra cloth. $2 25. {Just Issued.)
Of the remainder of the work we have nothing be- ! This instructive little volume appears once more,
yond unqualified commendation to offer. It is so far Since the death of its distinguished author, the study
the most complete one of its size that has appeared, : of skin diseases has been considerably advanced, and
and for the student there can be none which can com- [ the results of these investigations have been added
pare with it in practical value. All the late disco- by the present editor to the original work of Dr. Neli-
veries in Dermatology have been duly noticed, and !gan. This, however, has not so far increased its bulk
their value justly estimated; in a word, the work is as to destroy its reputation as the most convenient
fully up to the time.*, a,nd is thproughly stocked with manual of diseases of the .skin that can be procured
most valuable information. — Mw York Med. Record, by the student. — Chicago Med. Journal, Dec. 1866.
Jan. 15, 1867. | » «

j^F THE SAME AUTHOR.

ATLAS OF CUTANEOUS DISEASES. In one beautiful quarto

volume, with exquisitely colored plates, Ac, presenting about one hundred varieties of
disease. Extra cloth, $5 50.

The diagnosis of eruptive disea.se, however, under
all circumstances, is very difficult. Nevertheless,
Dr. Neligan has certainly, "as far as possible," given
a faithful and accurate representation of this class of
diseases, and there can be no doubt that these plates
will be of great use to the student and practitioner in
drawing a diagnosis as to the class, order, and species
to which the particular case may belong. While
looking over the "Atlas" we have been induced to
examine also the "Practical Treatise," and we are
Inclined to consider it a very superior work, com-
bining accurate verbal description with sound views

of the pathology and treatment of eruptive diseases.
It possesses the merit of giving short and condensed
descriptions, avoiding the tedious minuteness of
many writers, while at the same time the work, as
its title implies, is strictly practical. — Glasgow Med.
Journal.

A compend which will very much aid the practi-
tioner in this diflicult branch of diagno.sis. Taken
with the beautiful plates of the Atlas, which are re-
markable for their accuracy and beauty of coloring,
it constitutes a very valuable addition to the library
of a practical m^n.— Buffalo Mid. Journal.

TJILLIER [THOMAS), M.D.,

-^-^ Physician to the Skin Department of University College Hospital, &e.

HAND-BOOK OF SKIN DISEASES, for Students and Practitioners,

In one neat royal 12mo. volume of about 300 pages, with two plates; extra cloth, $2 25.
{Just Issued.)

Henry C. Lea's Publications — (Diseases of Children).

21

ftONDIE [D, FRANCIS), M. D.

A PRACTICAL TREATISE ON THE DISEASES OF CHILDREN.

Sixth edition, revised and augmented. In one large octavo volume of nearly 800 closely,
printed pages, extra cloth, $5 25 ; leather, $6 25. {Now Beady.)

it are based, as all practice should be, upon a familiar
knowledge of disease. Tlie opportunities of Dr. Con-
die for the practical study of the diseases of children
have been ji;reat, and his worlc is a proof that they have
not been thrown away. He has read much, but ob-
served more ; and we think that we may safely say
that the American student cannot find, in his owa
language, a better book upon the subject of which it
treats. — Am. Journal Medical Sciences.

Dr. Condie's scholarship, acumen, industry, and
I»Tactical sense are manifested in this, as in all his
numerous contributions to science. — Dr. Holmes's
Report to the American Medical Association.

Taken as a whole, in our judgment. Dr. Condie's
treatise is the one from the perusal of which the
practitioner in this country will rise with the great-
est satisfaction. — Western Journal of Medicine and
Surgery.

In the department of infantile therapeutics, the work
of Dr. Condie is considered one of the best in the Eng-
lish language. — The Stethoscope.

As we said before, we do not know of a better book
on Diseases of Children, and to a large part of its re-
commendations we yield an unhesitating concurrence.
— Buffalo Medical Journal.

The work of Dr. Condie is unquestionably a very
able one. It is practical in its character, as its title
ln^)ort8 ; but the practical precepts recommended in

We pronounced the first edition to be the best work
on the diseases of children in the English language,
and, notwithstanding all that has been published, we
still regard it in that light. — Medical Examiner.

The value of works by native authors on the dis-
eases which the physician is called upon to combat
will be appreciated by all, and the work of Dr. Con-
die has gained for itself the character of a safe guide
for students, and a useful work for consultation by
those eng^ed in practice. — N. Y. Med. Times.

'^/'EST [CHARLES), M.D.,

Physician to the Hospital for Sick CJiildren, &c.

LECTURES ON THE DISEASES OF INFANCY AND CHILD-

HOOD. Fourth American from the fifth revi.'sed and enlarged English edition. In one
large and handsome octavo volume of 656 closely-printed pages. Extra cloth, $4 50 ;
leather, $5 50. {Just issued.)

This work may now fairly claim the position of a standard authority and medical classic. Five
editions in England, four in America, four in Germany, and translations in French, Danish,
Dutch, and Russian, show how fully it has met the wants of the profession by the soundness of its
views and the clearness with which they are presented. Few practitioners, indeed, have had the
opportunities of observation and experience enjoyed by the Author. In his Preface he remarks,
"The present edition embodies the results of 1200 recorded cases and of nearly 400 post-mortem
examinations, collected from between 30,000 and 40,000 children, who, during the past twenty-
six years, have come under my care, either in public or in private practice." The universal favor
with which the work has been received shows that the author has made good use of these unusual
advantages.

Of all the English writers on the diseases of chil-
dren, there is no one so entirely satisfactory to us as
Dr. West. For years we have held his opinion as
judicial, and have regarded him as one of the highest
living authorities in the difficult department of medi-
cal science in which he is most widely known. His
writings are characterized by a sound, practical com-
mon sense, at the same time that they bear the marks
of the most laborious study and investigation. We
commend it to all as a most reliable adviser on many
occasions when many treatises on the same subjects
will utterly fail to help us. It is supplied with a very
copious general index, and a special index to the for-
mulae scattered throughout the work. — Boston Med.
and Surg. Journal, April 26, 1866.

Dr. West's volume is, in our opinion. Incomparably
the best authority upon the maladies of children
tliat the practitioner can consult. Withal, too — a
miaor matter, truly, but still not one that should be
neglected — Dr. West's composition possesses a pecu-
liar charm, beauty and clearness of expression, thus
affording the reader much pleasure, even independent
of that Avhich arises from the acquisition of valuable
truths. — Cincinnati Jour, of Medicine, March, 1866.

We have long regarded it as the most scientific and
practical book on diseases of children which has yet
appeared in this country. — Buffalo Medical Journal.

Dr. West's book is the best that has ever been
written in the English language on the diseases of

infancy and ♦hildhood. — Columhus Review of Med.
and Surgery.

To occupy in medical literature, in regard to dis-
eases of children the enviable po.sition which Dr.
Watson's treatise does on the diseases of adults is
now very generally assigned to our author, and his
book is in the hands of the profession everywhere as
an original work of great value. — Md. and' Va, Med.
and Surg. Journal.

Dr. West's works need no recommendation at this
date from any hands. The volume before u.s, espe-
cially, has won for itself a large and well-deserved
popularity among the profession, wherever the Eng-
lish tongue is spoken. Many years will elapse before
it will be replaced in public estimation by any similar
treatise, and seldom again will the same subject be
discussed in a clearer, more vigorous, or pleasing
style, with equal simplicity and power. — Charleston
Med. Jour, and Review.

There is no part of the volume, no subject on which
it treats which does not exhibit the keen perception,
the clear judgment, and the sound reasoning of the
author. It will be found a most useful guide to the
young practitioner, directing him in his management
of children's diseases in the clearest pos.sible manner,
and enlightening him on many a dubious pathological
point, while the older one will find in it many a sug-
gestion and practical hint of great value.— i?ri/. Am,
Med. Journal.

r)EWEES [WILLIAM P.), M.D.,

-*-^ Late Professor of Midwifery, &c., in the University of Pennsylvania, &c.

A TREATISE ON THE PHYSICAL AND MEDICAL TREAT-
MENT OF CHILDREN. Eleventh edition, with the author's last improvements and cor-
rections. In one octavo volume of 548 pages. $2 80.

22

Henry C. Lea's Publications — (Diseases of Women).

rPHOMAS [T. GAILLARD), M. D.,

-*- Professor of Obstetrics, d-c in the College of Physicians and Surgeons, N. Y., d^c.

A COMPLETE PRACTICAL TREATISE ON THE DISEASES OF

FEMALES. In one large and handsome octavo volume of over 600 pages, with 219 illus-
trations, extra cloth, $5; leather, $6. {Now Ready.)
In this work Professor Thomas has endeavored to supply the want of a complete treatise on
Gynaecology, embracing both the medical and surgical treatment requisite to the diseases and
accidents peculiar to women. The investigations and improvements of the last few years have
worked so great a change in this important department of practical medicine that a work like the
present, thoroughly on a level with the most advanced condition of the subject, can hardly fail
to possess claims on the attention of every practitioner.

To show the scope of the work, a very condensed summary of the contents is subjoined.

Chapter I. History of Uterine Pathology. — II. Etiology of Uterine Diseases in America. — III. Diagnosis
of Diseases of Female Genital Organs. — IV. Diseases of the Vulva. — V. Diseases of the Vulva (conAinued).
VI. Vaginismus. — VII. Vaginitis. — VIII. Atresia Vaginse. — IX. Prolapsus Vaginae. — X. Fistulae of the
Female Genital Organs. — XI. Fecal and Simple Vaginal Fistulse. — XII. General Remarks on Inflammatiou
of the Uterus. — XIII. Acute Endo-Metritis and AcuTe Metritis. — XIV. Cervical Endo-Meti'itis. — XV. Chronic
Cervical Metritis. — XVI. Chronic Corporeal Endo-Metritis and Metritis. — XVII. Ulceration of the Os and
Cervix Uteri. — XVIII. General Considerations on Displacements of the Uterus. — XIX. Ascent and Descent
of the Uterus. — XX. Versions of the Uterus. — XXI. Flexions of the Uterus — XXII. Inversion of the Ute-
rus.—XXIII. Peri-Uterine Cellulitis. — XXIV. Pelvic Peritonitis.— XXV. Pelvic Absces.s.— XXVI. Pelvic
Hseraatocele. — XXVII. Fibrous Tumors of the Uterus. — XXVIII. Uterine Polypi. — XXIX. Cancer of the
Uterus.— XXX. Cancroid Tumors of the Uterus —XXXI. Epithelial Cancer of the Uterus. — XXXII. Dis-
eases resulting from Pregnancy. — XXXIII. Dysmenorrhcea. — XXXIV. Menorrhagia and Metrorrhagia. —
XXXV. Amenorrhoea. — XXXVI. Leucorrhoea.— XXXVII. Sterility. — XXXVIII. Amputation of the Cer-
vix Uteri.— XXXIX. Diseases of the Ovaries —XL. Ovarian Tumors. — XLI. Ovariotomy. — XLII. Ovarian
Tumors (continued). — XLIII. Diseases of the Fallopian Tubes.

Jj^EIGS {CHARLES D.), M. D.,

Late Professor of Obstetrics, dec. in Jefferson Medical College, Philadelphia.

WOMAN: HER DISEASES AND THEIR REMEDIES. A Series

of Lectures to his Class. Fourth and Improved edition. In one large and beautifully
printed octavo volume of over 700 pages, extra cloth, $5 00 ; leather, $6 00.

Every topic discussed by the author is rendered 80
plain as to be readily understood by every student :
and, for our own part, we consider it not only one of
the most readable of books, but one of priceless value
to the practitioner engaged in the practice of those
diseases peculiar to females. — N.Am,. Med.-Chir. Re-

That this work has been thoroughJy appreciated
by the profession of this country as well as of Europe,
is fully attested by the fact of its having reached its
fourth edition in a period of less than twelve years.
Its value has been much enhanced by many impor-
tant additions, and it contains a fund of useful in-
formation, conveyed in an easy and delightful style.

J^Y THE SAME AUTHOR.

ON THE NATURE, SIGNS, AND TREATMENT OF CHILDBED

FEVER. In a Series of Letters addressed to the Students of his Class. In one handsome
octavo volume of 365 pages, extra cloth. $2 00.

QHURGHILL [FLEETWOOD), M. D., M. R. L A.

ON THE DISEASES OF WOMEN; including those of Pregnancy

and Childbed. A new American edition, revised by the Author. With Notes and Additions,
by D. Francis Condie, M. D., author of '* A Practical Treatise on the Diseases of Chil-
dren." With numerous illustrations. In one large and handsome octavo volume of 768
pages, extra cloth, $4 00; leather, $5 00.
As an epitome of all that is known in this depart- I fullest and most valuable in the English language,
ment of medicine, the book before us is perhaps the | — Dublin Medical Pre^ss.

J^Y THE SAME AUTHOR.

ESSAYS ON THE PUERPERAL FEVER, AND OTHER DIS-
EASES PECULIAR TO WOMEN. Selected from the writings of British Authors previ-
ous to the close of the Eighteenth Century. In one neat octavo volume of about 460
pages, extra cloth. $2 50.

'^RO WN (ISAAC BAKER), M. D.

ON SOME DISEASES OF WOMEN ADMITTING OF SURGICAL

TREATMENT. With handsome illustrations. One volume 8vo., extra cloth, pp. 276.
$] 60.

ASHWELL'S PRACTICAL TRE.\.TISE ON THE DIS-
EASES PECULIAR TO WOMEN. Illustrated by
Cases derived from Hospital and Private Practice.
Third American, from the Third and revised Lon-
don edition. In one octavo volume, extra cloth,
of r>2S pages. $3 uO.

EIOBY ON THE CONSTITUTIONAL TREATMENT
OF FEMALE DISEASES. In one neat royal 12mo.
volume, extra cloth, of about 250 pages. $1 00.

DEWEES'S TREATISE ON THE DISEASES OF FE-
MALES. With illustrations. Eleventh Edition,
with the Author's last improvements and correc-
tions. In one octavo volume of 536 pages, with
plates, extra cloth, $3 00.

COLOMBAT DE L'ISERE ON THE DISEASES OP
FEMALES. Translated by C. D. Mfeios, M. D. Se-
cond edition. In one vol. 8vo, extra cloth, with
numerous wood-cuts. pp. 720. $3 75.

Henry C. Lea's Publications — (Diseases of Women).

23

JJODGE {HUGH L.), M.D.

OX DISEASES PECULIAR TO WOMEN;, including Displacements

of the Uterus. With original illustrations. Second edition, revised. In one beautifully

printed octavo volume of about 500 pages. {Preparing.)

Indeed, although no part of the volume is not emi- the day — one which every accoucheur and pliysiciHn

nently deserving of perusal and study, we think that j should most can^fully read: for we are persuaded

the nine chapters devoted to this subject are espe- that he will^rise from its perusal with new ideas,

ill

cially so, and we know of no more valuable mono-
graph upon the symptoms, prognosis, and manage-
ment of these annoying maladies than is constituted
by this part of the work. We cannot but regard it as
one of the most original and most practical works of

which will iWlnct him into a more rational practice
in regard to many a suffering female who may have
placed her health in his hands.— .Br#i*ft American
Journal, Feb. ISGl.

l^EST {CHARLES), M.D.

LECTURES ON THE DISEASES OF WOMEN. Third American,

from the Third London edition. In one neat octavo volume of about 550 pages, extra
cloth. $3 75; leather, $4 75. {Now Ready.)
The reputation which this volume has acquired as a standard book of reference in its depart-
ment, renders it only necessary to say that the present edition has received a careful revision at
the hands of the author, resulting in a considerable increase of size. A few notices of previous
editions are subjoined.

The manner of the author is excellent, his descrip-
tions graphic and perspicuous, and his treatment up
to the level of the time— clear, precise, definite, and
marked by strong common sense. — Chicago Med.
Journal, Dec. 1861.

We cannot too highly recommend this, the second
edition of Dr. West s excellent lectures on the dis-
eases uf females. We know of no other book on this
subject from which we have derived as much pleasure
and instruction. Every page gives evidence of tlie
honest, earnest, and diligent searcher after truth. He
is not the m«re compiler of other men's ideas, but his
lectures are the result often years' patient investiga-
tion in one of the widest fields for women's diseases —
St. Bartholomew's Hospital. As a teacher. Dr. West
is simple and earnest in his language, clear and com-
prehensive in hi^ perceptions, and logical in his de-
ductions.— Cinc^nati Lancet, Jan. 1862.

We have thus embodied, in this series of lectures,
one of the most valuable treatises on the diseases of
the female sexual system unconnected with gestation,
in our language,aHd one which cannot fail, from the
lucid manner in which the various subjects have
been treated, and the careful discrimination used in
dealing only with facts, to recommend the volume to
the careful study of every practitioner, as affording
his safest guides to practice within our knowledge.
We have seldom perused a work of a more thoroughly
practical character than the one before us. Every
page teems with the most truthful and accurate infor-
mation, and we certainly do not know of any other
work from which the physician, in active practice,
can more readily obtain advice of the soundest cha-
racter upon the peculiar diseases which have been
made the subject of elucidation. — British Am. Med.
Journal.

T>T THE SAME AUTHOR. —

We return the author our grateful thanks fdr the
vast amount of instruction he has afforded us. His
valuable treatise needs no eulogy on our part. His
graphic diction and truthful pictures of disease all
speak for themselves. — Medico-Chirurg . Review.

Most justly esteemed a standard work It

bears evidence of having been carefully revised, and
is well worthy of the fame it has already obtained,
— Duh. Med. Quar. Jour.

As a writer. Dr. West stands, in our opinion, se-
cond only to Watson, the "Macaulay of Medicine;"
he possesses that happy faculty of clothing instruc-
tion in easy garments; combining pleasure with
profit, he leads his pupils, in spite of the ancient pro-
verb, along a royal road to learning. His work is one
which will not satisfy the extreme on either side, but
it is one that will please the great majority who are
seeking truth, and one that will convince the student
that he has committed himself to a candid, safe, and
valuable guide. — N. A. Med. -Chii-urg Review.

We must now conclude this hastily written sketch,
with the confident assurance to our readers that the
work will well repay perusal. The conscientious,
painstaking, practical physician is apparent on every
page. — .A^. Y. Journal of Medicine.

We have to say of it, briefiy and decidedly, that it
is the best work on the subject in any language, and
that it stamps Dr. West as the facile princeps of
British obstetric authors. — Edinburgh Med. Journal.

We gladly recommend his lectures as in the highest
degree instructive to all who are interested in ob-
stetric practice. — London. Lancet.

We know of no treatise of the kind so complete,
and yet so compact. — Chicago Med. Journal.

AN ENQUIRY INTO THE PATHOLOGICAL IMPORTANCE! OF

ULCERATION OF THE OS UTERI. In one neat octavo volume, extra cloth. $1 25.

s

IMPSON {SIR JAMES F.), M.D.

CLINICAL LECTURES ON THE DISEASES OF WOMEN. With

numerous illustrations. In one octavo volume of over 500 pages. Second edition, preparing.
'DENNET {HENRY), M.D.

A PRACTICAL TREATISE ON INFLAMMATION OF THE

UTERUS, ITS CERVIX AND APPENDAGES, and on its connection with Uterine Dis-
ease. Sixth American, from the fourth and revised English edition. In one octavo volume
of about 500 pages, extra cloth. $3 75. {Recently Issued.)
From the Author'' s Preface.
During the past t'wo years, this revision of former labors has been my principal occupation, and
in its present state the work may be con.sidered to embody the matured experience of the many
years I have devoted to the study of uterine disease.

Indeed, the entire volume is so replete with infor-
mation, to all appearance so perfect in its details, that
we could scarcely have thought another page or para-
graph was required for the full description of all that
is now known with regard to the diseases under con-
sideration if we had not been so informed by the au-

thor. To speak of it except in terms of the highe.st
approval would be impossible, and we .gladly avail
ourselves of the present opportunity to recommend
it in the most un<i'ialiQed manner to the profession.
—Dublin Med. Press.

24

Henry C. Lea's Publications — {Midwifery).

JJODGE {HUGH L.), 31. D.,

Late Professor of Midwifery, &c.

the University of Pennsylvania, &c.

THE PRINCIPLES AND PRACTICE OF OBSTETRICS. Illus-
trated with large lithographic plates containing one hundred and fifty-nine figures from
original photographs, and with numerous wood-cuts. In one large and beautifully printed
quarto volume of 550 double-columned pages, strongly bound in extra cloth, $14. {Lately
published. ) ^

The work of Dr. Hodge is something more than a
simple presentation of his particular views in tlie de-
partment of Obstetrics; it is something more than an
ordinary treatise on midwifery ; it is, in fact, a cyclo-
pjedia of midwifery. He has aimed to embody in a
single volume the whole science and art of Obstetrics.
An elaborate text is combined with accurate and va-
ried pictorial illustrations, so that no fact or principle
is left unstated or unexplained. — Am. Med. Tirn.es,
Sept. 3, 1S64.

We should like to analyze the remainder of this
excellent work, but already has thi.s review extended
beyond our limited space. We cannot conclude this
notice without referring to the excellent finish of the
work. In typography it is not to be excelled ; the
paper is superior to what is usually afi'orded by our
American cousins, quite equal to the best of English
books. The engravings and lithographs are most
beautifully executed. The work recommends itself
for its originality, and is in every way a most valu-
able addition to those on the subject of obstetrics. —
Canada Med. Journal, Oct. 1864.

It is very large, profusely and elegantly illustrated,
and is fitted to take its place near the works of great
obstetricians. Of the American works on the subject
it is decidedly the best. — Edinb. Med. Jour., Dec. *64.

*** Specimens of the plates and letter-press will be forwarded to any address, free by mail,
on receipt of six cents in postage stamps.

We have examined Professor Hodge's work with
great satisfaction ; every topic is elaborated most
fully. The views of the author are comprehensive,
and concisely stated. The rules of practice are judi-
cious, and will enable the practitioner to meet every
emergency of obstetric complication with confidence.
— Chicago Med. Journal, Aug. 186-4.

More time than we have had at our disposal 8hic«
we received the great work of Dr. Hodge is necessary
to do it justice. It is undoubtedly by far the most
original, complete, and carefully composed treatise
on the principles and pi*actice of Obstetrics which has
ever been issued from the American press. — Pacific
Med. and Surg. Journal, July, 1S64.

We have read Dr. Hodge's book with great ple^
sure, and have much satisfaction in expressing our
commendation of it as a whole. It is certainly highly
instructive, and in the main, we believe, correct. The
great attention which the author has devoted to tha
mechanism of parturition, taken along with the con-
clusions at which he has arrived, point, we think,
conclusively to the fact that, in Britain at least, the
doctrines of Naegele have been too blindly received.
— Glasgow Med. Journal, Oct. 1864.

JfANNER [THOMAS H), M. D.,

ON THE SIGNS AND DISEASES OF PREGNANCY. Vmt American

from the Second and'Enlarged English Edition. With four colored plates and illustrations
on wood. In one handsome octavo volume of about 600 pages, extra cloth, $4 25. {Now
Heady.)
The reputation of Dr. Tanner as a correct observer and skilful teacher is so widely known that
anything from his pen necessarily commands the attention of the profession. The present work
is one to which he has devoted especial attention in the hope of rendering it a useful guide to
practitioners in the important subjects of which it treats. In the systematic treatises on obstet-
rics and the diseases of females so little space is usually accorded to the disorders and aflfections of
the gravid state that a treatise devoted to them exclusively would seem to be a necessary addition
to the library of every working practitioner. The scope of the work may be judged from the
subjoined condensed

SUMMARY OF CONTENTS.
Chapter I. General Observations on the State of Pregnancy.— II. The Signs and Symptoms of Pregnancy.
— III. The Diseases which Simulate Pregnancy. — IV. The Duration of Pregnancy. — V. The Premature Ex-
pulsion of the Foetus. — VI. The Examination of Substances Expelled from the Uterus, &c. — VII. Extra-
Uterine Gestation — VIII. Superfoitation— Missed Labor. — IX. The Diseases which may coexist with Preg-
nancy and their Reciprocal Influence. — X. The Sympathetic Disorders of Pregnancy. — XI. The Diseases of
the Urinary and Generative Organs. — XII. The Displacements of the Gravid Uterus.

lj^0NTG03IERY [W. F.), M. D.,

Professor of Midwifery in the King's and Queen's College of Physicians in Ireland.

AN EXPOSITION OF THE SIGNS AND SYMPTOMS OF PREG-

NANCY. With some other Papers on Subjects connected with Midwifery. From the second
and enlarged English edition. With two exquisite colored plates, and numerous wood-cuta.
In one very handsome octavo volume of nearly 600 pages, extra cloth. $3 75.

M

ILLER [HENRY), M.D.,

Professor of Obstetrics and Diseases of Women and Children in the University of Louisville.

PRINCIPLES AND PRACTICE OF OBSTETRICS, &c.; incliidmg

the Treatment of Chronic Inflammation of the Cervix and Body of the Uterus considered
as a frequent cause of Abortion. With about one hundred illustrations on wood. In ond
very handsome octavo volume of over 600 pages, extra cloth. $3 75.

EIGBT'S SYSTEM OP MIDWIFERY. With Notes
and Additional Illustrations. Second American
editioa. One volume octavo, extra cloth, 422 pages.
$2 50.

DEWEES'S COMPREHENSIVE SYSTEM OF MIIV
WIFERY. Twelfth edition, with the author's last
improvements and corrections. In one octavo vol-
ume, extra cloth, of 600 pages. $3 50.

Henry C. Lea's Publications — {Midwifery).

25

lifEIGS {CHARLES D.), M.D.,

-*^" Lately Professor of Obstetrics, &c , in the Jefferson Medical College, Philadelphia.

OBSTETRICS: THE SCIENCE AND THE ART. Fifth edition,

revised. With one hundred and thirty illustrations. In one beautifully printed octavo
volume of 760 large pages. Extra cloth, $5 50; leather, $6 50. {Now ready.)
The original edition is already so extensively and
favorably known to the profession that no recom-
mendation is necessary; it is sufficient to say, the

present edition is very much extended, improved,
and perfected. Whilst the great practical talents and
unlimited experience of the author render it a most
valuable acquisition to the practitioner, it is so con-
densed as to constitute a most eligible and excellent
text-book for the student.— /Sow</ier?i Med. and Surg.
Journal, July, 1S67.

It is to the student that our author has more par-
ticularly addressed himself; but to the practitioner
we believe it would be equally serviceable as a book
of reference. No work that we have met with so
thoroughly details everything that falls to the lot of
tlie accoucheur to perform. Every detail, no matter
how minute or how trivial, has found a place, —
Canada Medical Journal, July, 1867.

This very excellent work on the science and art of
obstetrics should be in the hands of every student and

practitioner. The rapidity with which the very large
editions have been exhausted is the best test of its
true merit Besides, it is the production of an Ame-
rican who has probably had more experience in this
branch than any other living practitioner of the coun-
try.— St. Louis Med. and Surg. Journal, Sept. 1867.

He has also carefully endeavored to be minute and
clear in his details, with as little reiteration as possi-
ble, and beautifully combines the relations of science
to art, as far as the different classifications will admit.
— Detroit Review of Med and Pharm., Aug. 1867.

We now take leave of Dr. Meigs. There are many
other and interesting points in his book on which we
would fain dwell, but are constrained to bring our ob-
servations to a close. We again heartily express our
approbation of the labors of Dr. Meigs, extending over
many years, and culminating in the work before us,
full of practical hints for the inexperienced, and even
for those whose experience has been considerable. —
Glasgow Medical Journal, Sept. 1867.

J^AMSBOTHAM {FRANCIS ff.), M.D.

THE PRINCIPLES AND PRACTICE OF OBSTETRIC MEDI-

CINE AND SURGERY, in reference to the Process of Parturition. A new and enlarged
edition, thoroughly revised by the author. With additions by W. V. Keating, M. D.,
Professor of Obstetrics, Ac, in the Jeiferson Medical College, Philadelphia. In one large
and handsome imperial octavo volume of 650 pages, strongly bound in leather, with raised
bands ; with sixty-four beautiful plates, and numerous wood-cuts in the text, containing in
all nearly 200 large and beautiful figures. $7 00.

To the physician's library it is indispensable, while
to the student, as a text-book, from which to extract
the material for laying the foundation of an education
on obstetrical science, it has no superior. — Ohio Med.
a.nd Surg. Journal.

When we call to mind the toil we underwent in
acquiring a knowledge of this subject, we cannot but
envy the student of the present day the aid which
this work will afford him. — Am. Jour, of the Med.
Sciences.

We will only add that the student will learn from
it all he need to know, and the practitioner will find
It, as a book of reference, surpassed by none other. —
Stethoscope.

The character and merits of Dr. Ramsbotham's
work are so well known and thoroughly established,
that comment is unnecessary and praise superfluous.
The illustrations, which are numerous and accurate,
are executed in the highest style of art. We cannot
too highly recommend the work to our readers. — St.
Louis Med. and Surg. Journal.

QHURCfflLL {FLEETWOOD), M. D., M. R. L A.
ON THE THEORY AND PRACTICE OF MIDWIFERY. A new

American from the fourth revised and enlarged London edition. With notes and additions
by D. Francis Condie, M. D., author of a "Practical Treatise on the Diseases of Chil-
dren,'' &c. With one hundred and ninety- four illustrations. In one very handsome octavo
volume of nearly 700 large pages. Extra cloth, $4 00; leather, $5 00,
In adapting this standard favorite to the wants of the profession in the United States, the editor
has endeavored to insert everything that his experience has shown him would be desirable for the
American student, including a large number of illustrations. With the sanction of the author,
he has added, in the form of an appendix, some chapters from a little "Manual for Midwives and
Nurses," recently issued by Dr. Churchill, believing that the details there presented can hardly
fail to prove of advantage to the junior practitioner. The result of all these additions is that the
work now contains fully one-half more matter than the last American edition, with nearly one-
half more illustrations ; so that, notwithstanding the use of a smaller type, the volume contains
almost two hundred pages more than before.

These additions render the work still more com-
plete and acceptable than ever; and with the excel-
lent style in wliich the publishers have presented
this edition of Churchill, we can commend it to the
profession with great cordiality and pleasure.— Cm-
cinnati Lancet.

Few works on this branch of medical science are
equal to it, certainly none excel it, whether in regard
to theory or practice, and in one respect it is superior
to all others, viz., in its statistical information, and
therefore, on these grounds a most valuable work for
the physician, student, or lecturer, all of whom will
find in it the information which they are seeking. —
Ba'it. Am. Journal.

The present treatise is very much enlarged and
amplified beyond the previous editions but nothing

has been added which conld be well dispensed with.
An examination of the table of contents shows how
thoroughly the author has gone over the ground, and
the care he has taken in the text to present the sub-
jects in all their bearings, will render this new edition
even more necessary to the obstetric student than
were either of the former editions at the date of their
appearance. No treatise on obstetrics with which we
are acquainted can compare favorably with this, in
respect to the amount of material which has been
gathered from every source. — Boston Mtd. and Surg.
Journal.

There is no better text-book for students, or work
of reference and study for the practising physician
than this. It should adorn and enrich every medical
library. — Chicago Med. Journal.

26

Henry C. Lea's Publiications — {Surgery).

QROSS {SAMUEL D.), 31. D.,

Professor of Surgery in the Jefferson Medical College of Philadelphia.

A SYSTEM OF SURGERY: Pathologiccal, Diagnostic, Therapeutic,

and Operative. Illustrated by upwards of Thirteen Hundred Engravings. Fourth edition,
carefully revised, and improved. In two large and beautifully printed royal octavo volumes
of 2200 pages, strongly bound in leather, with raised bands. $15 00.
The continued favor, shown by the exhaustion of successive large editions of this great work,
proves that it has successfully supplied a want felt by American practitioners and students. Though
but little over six years have elapsed since its first publication, it has already reached its fourth
edition, while the care of the author in its revision and correction has kept it in a constantly im-
proved shape. By the use of a close, though very legible type, an unusually large amount of
matter is condensed in its pages, the two volumes containing as much as four or five ordinary
octavos. This, combined with the most careful mechanical execution, and its very durable binding,
renders it one of the cheapest works accessible to the profession. Every subject properly belonging
to the domain of surgery is treated in detail, so that the student who possesses this work may be
said to have in it a surgical library.

It must long remain the most comprehensive work
on this important part of medicine. — Boston Medical
and Surgical Journal, March 23, 1S65.

We have compared it with most of our standard
■works, such as those of Erichsen, Miller, Fergusson,
Syme, and others, and we must, in justice to our
aiithor, award it the pre-eminence. As a work, com-
plete in almost every detail, no matter how minute
or trifling, and embracing every subject known in
the principles and practice of surgery, we believe it
stands without a rival. Dr. Gross, in his preface, re-
marks "ray aim has been to embrace the whole do-
main of surgery, and to allot to every subject its
legitimate claim to notice ;" and, we assure our
readers, he has kept his word. It is a work which
we can most confidently recommend to our brethren,
for its utility is becoming the more evident the longer
it is upon the shelves of our library. — Canada Med.
Journal, September, lS6o.

The first t^o editions of Professor Gross' System of
Surgery are so well known to the profession, and so
highly prized, that it would be idle for us to speak in
praise of this work. — Chicago Medical Journal,
September, 1S65.

We gladly indorse the favorable recommendation
of the work, both as regards matter and style, which
we made when noticing its first appearance. — British

tioner shall not seek in vain for what they desiue.—
San Francisco Med. Press, Jan. 1S6.5.

Open it where we may, we find sound practical in-
formation conveyed in plain language. This book is
no mere provincial or even national system of sur-
gery, but a work which, while very largely indebted
to the past, has a strong claim on the graiiiude of the
future of surgical science.— Edinburgh Med. Journal,
Jan. 1S65.

A glance at the work is sufficient to show that the
author and publisher have spared no labor in making
it the most complete "System of Surgery" ever pub-
lished in any country— 5^ Louis Med. and Surg.
Journal, April, 186.5.

The third opportunity is now ofiered during our
editorial life to review, or rather to indorse and re-
commend this great American work on Surgery.
Upon this last edition a great amount of labor has
been expended, though to all others except the author
the work was regarded in its previous editions as so
full and complete as to be hardly capable of improve-
ment. Every chapter has been revised ; the text aug-
mented by nearly two hundred pages, and a con
siderable number of wood-cuts have been introduced.
Many portions have been entirely re-written, and the
additions made to the text are principally of a prac
tical character. This comprehensive treatise upon

and Foreign Medico-Chirurgical Review, Oct. 1865. | surgery has undergone revisions and enlargements.

The most complete work that has yet issued from
the press on the science and practice of surgery. —
London Lancet.

This system of surgery Is, we predict, destined to
take a commanding position in our surgical litera-
ture, and be the crowning glory of the author's well
earned fame. As an authority on general surgical
subjects, this work is long to occupy a pre-eminent
place, not only at home, but abroad. We have no
hesitation in pronouncing it without a rival in our
language, a«d ♦qual to the best systems of surgery in
any language. — N. Y. Med. Journal.

Not only by far the best text-book on the subject,
as a whole, within the reach of American students,
hut one which will be much more than ever likely
to be resorted to and regarded as a high authority
abroad. — Am. Journal Med. Sciences, Jan. 186.).

The work contains everything, minor and major,
operative and diagnostic, inclndiag mensuration and
examination, venereal diseases, and uterine manipu-
lations and operations. It is a complete Thesaurus
of modern surgery, where the student and piacti-

keeping pace with the progress of the art and science
of surgery, so that whoever is in possession of this
work may consult its pages upon any topic embraced
within the scope of its department, and rest satisfied
that its teaching is fully up to the present standard
of surgical knowledge. It is also so comprehensive
that it may truthfully be said to embrace all that is
actually known, that is really of any value in the
diagnosis and treatment of surgical diseases and acci-
dents. Wherever illustration will add clearness to the
subject, or make better or more lasting impression, it
is not wanting; in this respect the work is eminently
superior. — Buffalo Med. Journal, Dec. 1864.

A system of surgery which we think unrivalled in
our language, and which will indelibly associate his
name with surgical science. And what, in our opin-
ion, enhances the value of the work is that, while the
practising surgeon will find all that he requires in it,
it is at the same time one of the most valuable trea-
tises which can be put into the hands of the studeut
seeking to know the principles and practice of this
branch of- the profession which he designs subse-
quently to follow.— T/ie Brit. Am. Journ., Montreal.

jyT THE SAME AUTHOR.

A PRACTICAL TREATISE OX THE DISEASES, INJURIES,

AND MALFORMATIONS OF THE URINARY BLADDER, THE PROSTATE GLAND,
AND THE URETHRA. Second edition, revised and much enlarged, with one hundred
and eighty-four illustrations. In one large and very handsome octavo volume, of over nine
hundred pages, extra cloth. $4 00.
Whoever will peruse the vast amount of valuable I guage which can make any just pretensions to he it«

practical information it contains will, we think, agree equal. — N. Y. Journal of Medicine.

with us, that there is no work in the English Ian- |

DY THE SAME AUTHOR.

A PRACTICAL TREATISE ON FOREIGN BODIES IN THE

AIR-PASSAGES. In one handsome octavo volume, extra cloth, with illustrations,
pp. 468. $2 75.

Henry C. Lea's Publications — (Surgery),

21

PRICHSEN {JOHN),

J-^ Professor of Surgery in University College, London.

THE SCIENCE AXD ART OF SURGERY; being a Treatise on Sur-

gical Injuries, Diseases, and Operations. New and improved American, from the Second
enlarged and carefully revised London edition. Illustrated with over four hundred wood
engravings. In one large and handsome octavo volume of 1000 closely printed pages; extra
cloth, $6; leather, raised bands, $7.

We are bound to state, and we do so without wish- as one of the very best, if not the best text-book of
ing to draw invidious comparisons, that the work of surgery with which we were acquainted, permits us
Mr. Erichsen, in most respects, surpasses any that to give it but a passing notice totally unworthy of its
has preceded it. Mr. Erichsen's is a practical work, merits. It may be confidently asserted, that no work
combining a due proportion of the "Science and Art on the science and art of surgery has ever received
of Surgery." Having derived no little instruction more universal commendation or occupied a higher
from it, in many important branches of surgery, we position as a general text-book on surgery, than this
can have no hesitation in recommending it as a valu- treati!=e of Professor Erichsen. — Savannah Journal of
able book alike to the practitioner and the student. Medicine.
-^Dublin Quarterly. j Jq fulness of practical detail and perspicuity of

Gives a very admirable practical view of the sci- style, convenience of arrangement and soundness of
ence and art of surgery. — Edinburgh Med. and Surg, discrimination, as well as fairness and completeness
Jcnirnal. i of discussion, it is better suited fo the wants of both

We recommend it as the best compendium of sur- ! student and practitioner than any of its predecessors,
gery in our language. -ion^o« Lancet. -^"^- 'Journal of Med. Sciences.

It is, we think, the most valuable practical work I ^fter careful and frequent perusals of Erichsen's
on surgery in existence, both for young and old prac- ^^}'^Sevy,we^^e at a loss tul y to express our admira-
titioners.-iVa.57m«e Med. and Surg. Journal. t^«^ «f '^- Jhe author's style is enainently didactic,

" and characterized by a most admirable directness,

The limited time we have to review this improved clearness, and compactness. — Ohio Med. and Surg.
edition of a work, the first issue of which we prized Journal.

jyY THE SAME AUTHOR. (Ready in June.)

ON RAILWAY, AND OTHER INJURIES OF THE NERA^OUS

SYSTEM. In small octavo volume. Extra cloth, $1 00.

We welcome this as perhaps the most practically
useful treatise written for many a day. — Sledical
Times.

It will serve as a most useful and trustworthy guide

to the profession in general, many of whom may be
consulted in snch cases; and it will, no doubt, take
its place as a text-book on the subject of which it
treats. — Medical Press.

JlflLLER {JA3IES),

-^Kl. Late Professor of Surgery in the University of Edinburgh, &c.

PRINCIPLES OF SURGERY. Fourth American, from the third and

revised Edinburgh edition. In one large and very beautiful volume of 700 pages, with
two hundred and forty illustrations on wood, extra cloth. $3 75.

B

T THE SAME AUTHOR.

THE PRACTICE OF SURGERY. Fourth American, from the last

Edinburgh edition. Revised by the American editor. Illustrated by three hundred and

sixty-four engravings on wood. In one large octavo volume of nearly 700 pages, extra

cloth. $3 75.

It is seldom that two volumes have ever made so I acquired. The author is an eminently sensible, prac-

profound an impression in so short a time as the | tical, and well-informed man, who knows exactly

"Principles" and the "Practice" of Surgery by Mr. what he is talking about and exactly how to talk it. —

Miller, or so richly merited the reputation they have | Kentuclcy Medical Recorder.

piRRTE ( WILLIAM), F. R. S. E.,

-*- Professor of Surgery in the University of Aberdeen.

THE PRINCIPLES AND PRACTICE OF SURGERY. Edited by

John Neill, M. D., Professor of Surgery in the Penna. Medical College, Surgeon to the
Pennsylvania Hospital, <fec. In one very handsome octavo volume of 780 pages, with 316
illustrations, extra cloth. $3 75.

^ARGENT [F. W.), M.D.

ON BANDAGING AND OTHER OPERATIONS OF MINOR SUR-

GERY. New edition, with an additional chapter on Military Surgery. One handsome royal
12mo. volume, of nearly 400 pages, with 184 wood-cuts Extra cloth, $1 76.

We cordially commend this volume as one which
the medical student should most closely study ; and
to the surgeon in practice it must prove itself instruct-
ive on many points which he may have forgotten. —
Brit. Am. Journal, May. 1862.

Exceedingly convenient and valuable to all mem-
bers of the prot'essiou.— Chicago Medical Examiner,
May, 1862.

The very best manual of Minor Surgery we have
Been. — Buffalo Medical Journal.

MALGAIGNE'S OPERATIVE SURGERY. With nu-
merous illustrations on wood. In one handsome
octavo volume, extra cloth, of nearly 600 pp. $2 50.

SKEY'S OPERATIVE SURGERY. In one very hand-
some octavo volume, extra cloth, of over 650 pagee,
with about 100 wood-cats. $3 25.

28

• Henry C. Lea's Publications — {Surgery).

JJRUITT {ROBERT), M.R. C.S., Sfc

THE PRINCIPLES AND PRACTICE OF MODERN SURGERY.

A new and revised American, from the eighth enlarged and improved London edition. Illus-
trated with four hundred and thirty -two wood-engravings. In one very handsome octavo
volume, of nearly 700 large and closely printed pages. Extra cloth, $4 00 ; leather, $5 00.

Besides the careful revision of the author, this work has had the advantage of very thorough
editing on the part of a competent surgeon to adapt it more completely to the wants of the Ameri-
can student and practitioner. Many illustrations have been introduced, and every care has been
taken to render the mechanical execution unexceptionable. At the very low price affixed, it will
therefore be found one of the most attractive and useful volumes accessible to the American
practitioner.

All that the surgical student or practitioner could
desire. — Dublin Quarterly Journal.

It is a most admirable book. We do not know
when we have examined one with more pleasure. —
Boston Med. and Surg. Journal.

In Mr. Druitt's book, though containing only some
seven hundred pages, both the principles and the
practice of surgery are treated, and so clearly and
perspicuously, as to elucidate every important topic.
The fact that twelve editions have already been called

theoretical surgical opinions, no work that we are at
present acquainted with can at all compare with it.
It is a compendium of sargical theory (if we may use
the word) and practice in itself, and well deserves
the estimate placed upon it. — Brit. Am. Journal.

Thus enlarged and improved, it will continue to
rank among our best text-books on elementary sur-
gery.— Coltimbun Rev. of Med. and Surg.

We must close this brief notice of an admirable
work by recommending it to the earnest attention of

for, in these days of active competition, would of every medical student. — Charleston Medical Journal

itself show it to possess marked superiority. We and Review.

have examined the book most thoroughly, and can '

say that this success is well merited. His book,

moreover, possesses the inestimable advantages of
having the subjects perfectly well arranged and clas-
sified, and of being written in a style at once clear
and succinct. — Am. Journal of Med. Sciences.

Whether we view Druitt's Surgery as a guide to
operative procedures, or as representing the latest

A text-book which the general voice of the profes-
sion in both England and America has commended as
one of the most admirable "manuals," or, "vade
mecum" as its English title runs, which can be
placed in the hands of the student. The merits of
Druitt's Surgery are too well known to every one to
need any further eulogium from us. — Nashville Med.
Journal.

TJAMILTON [FRANK n.l M.D.,

Professor of Fractures and Dislocations, &c. in BeJZevue Hosp. Med. College, New York.

A PRACTICAL TREATISE ON FRACTURES AND DISLOCA-

TIONS. Third edition, thoroughly revised. In one large and handsome octavo volume
of 777 pages, with 294 illustrations, extra cloth, $5 75. {Jttst Issued.)
The demand which has so speedily exhausted two large editions of this work shows that the
author has succeeded in supplying a want, felt by the profession at large, of an exhaustive treatise
on a frequent and troublesome class of accidents. The unanimous voice of the profession, abroad
as well as at home, has pronounced it the most complete work to which the surgeon can refer for
information respecting all details of the subject. In the preparation of this new edition, the
author has sedulously endeavored to render it worthy a continuance of the favor which has been
accorded to it, and the experience of the recent war has aflforded a large amount of material which
he has sought to turn to the best practical account.

In fulness of detail, simplicity of arrangement, and American professor of surgery; and his book adds

accuracy of description, this work stands unrivalled.
So far as we know, no other work on the subject in
the English language can be compared with it. While
congratulating our trans-Atlantic brethren on the
European reputation which Dr. Hamilton, along with
many other American surgeons, ha.« attained, we also
may be proud that, in the mother tongue, a cla8s^ical
work has been produced which need not fear compa-
rison with the standard treatises of any other nation.
— Edinburgh Med. Journal, Dec. IStitj.

The credit of giving to the profession the only com
plete practical treatise on fractures and dislocations
in our language during the present century, belougs

one more to the list of excellent practical works which
have emanated from his country, notices of which
have appeared from time to time in our columns du-
ring the last few montiis.— London Lancet, Dec. 15,
1S66.

These additions make the work much more valua-
ble, and it must be accepted as the most complete
monograph on the subject, certainly in our own, if
not even in any other language.— .dTnertcan Journal
Med. Sciences, Jan. 1867.

This is the most complete treatise on the subject in
the 'E,nf(i\sh.\-An.s,\x?ige.— Ranking' s Abstract, Jan.lS67.

A mirror of all that is valuable in modern surgery.

to the author of the work before us, a distinguished Richmond Med. Journal, Nov. 1S66,

'DARWELL [RICHARD), F.R.C.S.,

"^ Assistant Surgeon Charing Cross Hospital, &c.

A TREATISE ON DISEASES OF THE JOINTS. Illustrated with

engravings on wood. In one very handsome octavo volume of about 500 pages ; extra cloth,
$3.

BRODIE'S CLINICAL LECTURES ON SURGERY.
1 vol. 8vo., 350 pp.; cloth, $1 25.

COORER ON THE STRUCTURE AND DISEASES OF
THE Testis, aito on the Thymus Gland. One vol.
imperial 8vo., extra cloth, with 177 figures on 29
plates. $2 50.

COOPER'S LECTURES ON THE PRINCIPLES AND
Practice of Surgery. In one very large octav-o
volume, extra cloth, of 750 pages. $2 00.

GIBSON'S INSTITUTES AND PRACTICE OF SUR-

OERY. Eighth edition, improved and altered. With
thirty-four plates. In two handsome octavo vol-
umes, about 1000 pages, leather, raised bands. $6 50.

29

Henry C. Lea's Publications — (Surgery).
rpOYNBEE {JOSEPH), F.R.S.,

-*- Aural Surgeon to and Lecturer on Surgery at St. Mary^s Hospital.

THE DISEASES OF THE EAR: their Nature, Diagnosis, and Treat-

ment. With one hundred engravings on wood. Second American edition. In one very
handsomely printed octavo volume of 440 pages ; extra cloth, $4.

The appearance of a volume of Mr. Toynbee's, there-
fore, in which the subject of aural disease is treated
in the most scientific manner, and our knowledge in
respect to it placed fully on a par with that which
we possess respecting most other organs of the body,
is a matter for sincere congratulation. We may rea-
sonably hope that henceforth the subject of this trea-
tise will cease to be among the opprobriu of medical
science. — London Medical Review.

The work, as was stated at the outset of our notice,
is a model of its kind, and every page and paragraph
of it are worthy of the most thorough study. Con-
sidered all in all — as an original work, well written,
philosophically elaborated, and happily illustrated
with cases and drawings— it is by far the ablest mo-
nograph that has ever appeared on the anatomy and
diseases of the ear, and one of the most valuable con-
tributions to the art and science of surgery in the
nineteenth century. — N. Am. Med.-Chirurg. Semew.

TA URENCE [JOHN Z.), F. R. G. S., and llfOON [ROBERT C.\

■^ Editor of the Ophthalmic Review, &c. ^^ -£f'^«*« Surgeon to theSoidhwark Oph-

thalmic Hospital, &c.

A HANDY-BOOK OF OPHTHALMIC SURGERY, for the use of

Practitioners. With numerous illustrations. In one very handsome octavo volume, extra
cloth. $2 50. {Jttst Isstted.)

No book on ophthalmic surgery was more needed.
Designed, as it is, for the wants of the busy practi-
tioner, it is the neplus ultra, of perfection. It epito-
mizes all the diseases incidental to the eye in a clear
and masterly manner, not only enabling the practi- vember, 1S66
tioner readily to diagnose each variety of disease, but
affording him the more important assistance of proper
treatment. Altogether this is a work which ought
certainly to be in the hands of every general practi-
tioner.— Dublin Med. Press and Circular, Sept. 12, '66.

We cordially recommend this book to the notice of
our readers, as containing an excellent outline of
modern ophthalmic surgery. — British Med. Journal,
October 13, 1S66.

Not only, as its modest title suggests, a "Handy-
Book" of Ophthalmic Surgery, but an excellent and
well-digested risumi of all that is of practical value
in the specialty.— iVezo York Medical Journal, No-

This object the authors have accomplished in a
highly satisfactory manner, and we know no work
we can more highly recommend to the "busy practi-
tioner" who wishes to make himself acquainted with
the recent improvements in ophthalmic science. Such
a work as this was much wanted at this time, and
this want Messrs. Laurence and Moon have now well
supplied. — Am,. Journal Med. Sciences, Jan. 1867.

TAWSON [GEORGE), F. R. C. S., Engl

-*^ Assistant Surgeon to the Royal London Ophthalmic Hospital, Moorfields, &c.

INJURIES OF THE EYE, ORBIT, AND EYELIDS: their Imme-

diate and Remote Effects. With about one hundred illustrations. In one very hand-
some octavo volume, extra cloth, $3 50. {Now Ready.)
This work will be found eminently fitted for the general practitioner. In cases of functional
or structural diseases of the eye, the physician who has not made ophthalmic surgery a special
study can, in most instances, refer a patient to some competent practitioner. Cases of injury,
however, supervene suddenly and usually require prompt assistance, and a work devoted espe-
cially to them cannot but prove essentially useful to those who may at any moment be called upon
to treat such accidents. The present volume, as the work of a gentleman of large experience,
may be considered as eminently worthy of confidence for reference in all such emergencies.
It is an admirable practical book in the highest and fulness of practical knowledge. We predict for Mr

best sense of the phrase. Copiously illustrated by
excellent woodcuts, and with well-selected, well-
described cases, it is written in plain, simple lan-
guage, and in a style the transparent clearness and
frankness, so to speak, of which, add greatly to its
value and usefulness. Only a master of his subject
could so write ; every topic is handled with an ease,
decision, and straightforwardness, that show the
skilful and highly educated surgeon writing from

Lawson's work a great and well-merited success.
We are confident that the profession, and especially,
as we have said, our country brethren, will feel
grateful to him for having given them in it a guide
and counsellor fully up to the most advanced state of
Ophthalmic Surgery, and of whom they can make a
trusty and familiar friend.— London Medical Times
and Gazette, May 18, 1867.

J

ONES [T. WHARTON), F.R.S.,

Professor of OpMhalmic Med. and Surg, in University College, London.

THE PRINCIPLES AND PRACTICE OF OPHTHALMIC MEDI-
CINE AND SURGERY. With one hundred and seventeen illustrations. Third and re-
vised American, with Additions from the second London edition. In one handsome octavo
volume of 455 pages, extra cloth. $3 25.

llfA CKENZIE [W.), M. D.,

jLfJ- Surgeon Ocxdist in Scotland in ordinary to her Majesty, &c,

A PRACTICAL TREATISE ON DISEASES AND INJURIES OF

THE EYE. To which is prefixed an Anatomical Introduction explanatory of a Horizontal
Section of the Human Eyeball, by Thomas Wharton Jones, F. R. S. From the fourth
revised and enlarged London edition. With Notes and Additions by Addinell Hewson,
M. D., Surgeon to Wills Hospital, «tc. Ac. In one very large and handsome octavo volume
of 1027 pages, extra cloth, with plates and numerous wood-cuts. $6 50.

30 Henry C. Lea's Publications — (Surgery).

jyA^^^ {PHILIP S,), M. D., Surgeon U. S

iV.

MECHANICAL THERAPEUTICS: a Practical Treatise on Surgical

Apparatus, Appliances, and Elementary Operations : embracing Minor Surgery, Band-
aging, Orthopraxy, and the Treatment of Fractures and Dislocations. With six hundred
and forty-two illustrations on wood. In one large and handsome octavo volume of about
700 pages: extra cloth, $5 75; leather, $6 75. {Now Ready.)
The author has attempted in this volume to supply a want which has been generally felt by
Btudents and practitioners of a work which should present, minutely, but concisely, the various
details in surgical operations, which are apt to be passed over in systematic treatises. It falls
to the lot of comparatively few surgeons to perform the major operations, but every physician,
especially in the country, is liable at any moment to be called upon to remedy some accident or
to prevent some deformity, and the aim of the present treatise is to present that kind of informa-
tion with such detail that it may be regarded as an unfailing book of reference. The very com-
plete series of illustrations renders the whole easy of comprehension by the student, while the
author's practical experience in the naval service, and the care with which he has collected the
results of the latest authorities, at home and abroad, give assurance of the value of his teachings.
A very condensed summary is subjoined of the

COnSTTEISTTS.

PART I. Op the Apparatus? op Dressing.

Chap. I. Of the Instruments of Dressing. — II. Of the First Pieces of Dressing. — III. On the
Use of some Topical Remedies. — IV. On the Use of Water in Surgical Dressings and Inju-
ries.— V. Injections. — VI. On the Use of Gases and Vapors. — VII. Bandages. — VIII.
Special or Regional Bandaging.
PART II. Mechanical Bandages and Apparatus.

Chap. I. Apparatus for Remedying Loss of Parts. — II. Apparatus for Remedying Loss of
Function. — III. Apparatus for Remedying Loss of Symmetry.
PART III. Fractures; their Reduction, Dressing, and Apparatus.

Chap. I. General Consideration of Fractures. — II. Fractures of Particular Bones.
PART IV. Dislocations; their Reduction, Dressing, and Apparatus.

Chap. I. Sprains or Strains. — II. Dislocations in General. — III. Particular Dislocations.
PART. V. The Minor Operations op Surgery.

Chap. I. Rubefaction. — II. Vesication. — III. Cauterization. — IV. Moxa. — V. Issues. — VI.
Setons. — VII. Acupuncture and Electropuncture. — VIII. Puncturing. — IX. Vaccination.
— X. Incisions. — XI. Bloodletting. — XII. Extraction of Teeth. — XIII. Catheterism —
XT;V. Removal of Foreign Bodies. — XV. On the Modes of Arresting Hemorrhage. — XVI.
On the Dressings of Wounds. — XVII. Anaesthesia.

The adoption of this work for use in both the Army and Navy of the United States is a guffi-
cient guarantee of its usefulness to the practitioner.

A

SHTON {T. J.)
ON THE DISEASES, INJURIES, AND MALFORMATIONS OF

THE RECTUM AND ANUS; with remarks on Habitual Constipation. Second American,
from the fourth and enlarged London edition. With handsome illustrations. In one very
beautifully printed octavo volume of about 300 pages. $3 25. {Jnst Issued.)

The short period which has elapsed since the ap-
pearance of the former American reprint, and the
numerous editions published in England, are the best
arguments we can oflfer of the merits, and of the u.-^e-
lessne.ss of any commendation on our part of a book
already so favorably known to our readers. — Boston
Med. and Surg. Journal, Jan. 25, 1866.

We can recommend this volume of Mr Ashton's in
the strongest terms, as containing all the latest details
of the pathology and treatment of diseases connected
with the rectum. — Canada Med,. Jnurn., March, 1S66.

One of the most valuable special treatise** that the
physician and surgeon can have in his library. —
Chicago Medical Examiner, Jan. 1S66.

JirORLAND [W. W.), 31. D.

DISEASES OF THE URINARY ORGANS; a Compendmm of their

Diagnosis, Pathology, and Treatment. With illustrations. In one large and handsome
octavo volume of about 600 pages, extra cloth. $3 50.
Taken as a whole, we can recommend Dr Morland's I of every medical or surgical practitioner. — Brit, and
compendium as a very desirable addition to the library | For. Med.-Chir. Review, April, 18.59.

rtURLING [T.B.), F.R.S.,

Surgeon to the London Hospital, President of the Hunterinn Society, &c.

A PRACTICAL TREATISE ON DISEASES OF THE TESTIS,

SPERMATIC CORD, AND SCROTUM. Second American, from the second and enlarged
English edition. In one handsome octavo volume, extra cloth, with numerous illustxa-
tions. pp. 420. $2 00.

Henry C. Lea's Publications — {Medical Jurisprudence^ &c.). 31

rPAYLOR [ALFRED S.), M.D.,

•*- Lecturer on Med. Jurisp. and Chemistry in Guy's Hospital.

MEDICAL JURISPRUDENCE. Sixth American, from the eighth

and revised London edition. With Notes and References to American Decisions, by Cle-
ment B. Penrose, of the Phihidelphia Bar. In one large octavo volume of 776 pages,
extra cloth, $4 50 ; leather, $5 60. {Now Ready.)
Considerable additions have been made by the editor to this edition, comprising some important
Bections from the author's larger work, " The Principles and Practice of Medical Jurisprudence,"
as well as references to American law and practice. The notes of the former editor, Dr. Harts-
horne, have likewise been retained, and the whole is presented as fully worthy to maintain the
distinguished position which the work has acquired as a leading text-book and authority on the
subject

A new edition of a work acknowledged as a stand-
ard authority everywhere within the range of the
English langurtge. Considering the new matter intro-
duced, on trichiniasis and other subjects, and the
plates representing the crystals of poisons, etc. , it may
fairly be regarded as the most compact, comprehen-
sive, and practical work on medical jurisprudence
which has issued from the press, and the one best
fitted for students. — Pacific Med. and Surg. Journal,
Feb. 1857.

The sixth edition of this popular work comes to us
in charge of a new editor, Mr. Penrose, of the Phila-
delphia bar, who has done much to render it useful,
not only to the medical practitioners of this country,
but to those of his own profession. Wisely retaining
the references of the former American editor. Dr.
Hiirtshorne, he has added many valuable notes of his
own. The reputation of Dr. Tnylor's work is so well
e^stablished, that it needs no recommendation. He is
now the highest living authority on all matter.s con-
nected with forensic medicine, and every successive
edition of his valuable work gives fresh assurance to
his many admirers that he will continue to maintain
his well-earned position. No one should, in fact, be
without a text-book on the subject, as he does not
know bat that his next case may create fur him an

elaborate treatises. — New York Medical Record, Feb.
LO, 1867.

The present edition of this valuable manual is a
great improvement on those which have preceded it.
Some admirable instruction on the subject of evidence
and the duties and re.>sponsibilities of medical wit-
nesses has been added by the distinguished author,
and some fifty cuts, illustrating chiefly the crystalline
forms and microscopic structure of «ubstaaces used
as poisons, inserted. The American editor has also
introduced several chapters from Dr Taylor's larger
work, "The Principles and Practice of Medical Juris-
prudence," relating to trichiniasis, sexual malforma-
tion, insanity as affecting civil responsibility, suicidal
mania, and life insurance, &c., which add cou.siderably
to its value. Besides this, he has introduced nume-
rous references to cases which have occurred in this
country. It makes thus by far the be.-^t guide-book
in this department of medicine for students and the
general practitioner in our language. — Boston Med.
and Surg. Journal, Dec. 27, 1866.

Taylor's Medical Jurisprudence has been the text-
book in our colleges for years, and the present edi-
tion, with the valuable additions made by the Ameri-
can editor, render it the most standard work of the
day, on the peculiar province of medicine on which

emergency for its use. To those who are not the for- ' it treats. The American editor. Dr. Hartshorne, has
tuuate possessors of a reliable, readable, interesting, t done his duty to the text, and, upon the whole, we
and thoroughly practical work upon the subject, we ! cannot but consider this volume the best and richest
would earnestly recommend this, as forming the best ^ treatise on medical jurisprudence in our language. —
groundwork for all their future studies of the more i Brit. Am. Med. Journal. ^

TYIiVSLOW [FORBES), Mly~D.C.L., fcT

ON OBSCURE DISEASES OF THE BRAIN AND DISORDERS

OF THE MIND; their incipient Symptoms, Pathology, Diagnosis, Treatment, and Pro-
phylaxis. Secpnd American, from the third and revised English edition. In one handsome
octavo volume of nearly 600 pages, extra cloth. $4 25. {Jiist Isstied.)
Of the merits of Dr. Winslow's treatise the profes- 1 our conviction that it is long since so important and
Biou has sufftciently judged. It has taken its place in { beautifully written a volume has issued from the
the front rank of the works upon the special depart- British medical press. The details of the manage-
ment of confirmed cases of insanity more nearly in-
terest tho.se who have made mental disea-ses their
special study; but Dr. Winslow's masterly exposi-
tion of the early symptoms, and his graphic descrip
tions of the insidious advances of incipient insanity,
together with his judicious observations on the treat-
ment of disorders of the mind, should, we repeat, be
carefully studied by all who have undertaken the
responsibilities of medical practice. — Dublin Medical
Press.

It is the most interesting as well as valuable book
that we have seen for a long time. It is truly fasci-
nating.— Arn. Jour. Med. Sciences.

Dr. Winslow's work will undoubtedly occupy an
unique position in the medico-psycli^ilogical litera-

ment of practical medicine to which it pertains. —
Cincinnati Journal of Medicine, March, 1866.

It is an interesting volume that will amply repay
for a careful perusal by all intelligent readers —
Chicago Med. Examiner Feb. 1866.

A work which, like the present, will largely aid
the practitioner in recognizing and arresting the first '
insidious advances of cerebral and mental disease, is j
one of immense practical value, and demands earnest
attention and diligent study on the part of all who i
have embraced the medical profession, and have |
thereby undertaken responsibilities in which the j
welfare and happiness of individuals and families j
are largely involved. We shall therefore close this \
lirief and necessarily very imperfect notice of Dr

Winslow's great and classical work by expressing j ture'of this country. — London Med. Review.

EA [HENRY C.)

' SUf'ERSTITlON AND FORCE: ESSAYS OX TRE WAGER OF

LAW, THE WAGER OF BATTLE, THE ORDEAL, AND TORTURE. In one hand-
some volume royal 12mo., of 406 pages; extra cloth, $2 50.

a humor so fine and good, that he makes us regret it
was not within his intent, as it was certainly within
his power, to render the whole of his thorough work
more popular in manner.— At/antic Monthly, Feb. '«7.
This is a book of extraordinary research. Mr. Lea
has entered into his subject con am ore ; and a more
striking record of the cruel superstitions of our un-
happy Middle Ages could not possibly have been com-
piled. ... As a work of curious in«5|Uiry on certain
outlying points of obsolete law, "Superstition and
Force" is one of the most remarkable books we have
me; yv'xih..— London At/ienceum, Nov. 3, 1866.

The copious collection of facts by which Mr. Lea has
illustrated his subject shows in the fullest manner the
constant conflict and varying success, the advances
*id defeats, by which the progress of humane legisla-
tion has been and is still marked. This work fills up
with the fullest exemplification and detail the wise
remarks which we have quoted above. As a book of
ready reference on the subject it is of the highest
value. — Westminster Review, Oct. 1867.

When — half in spite of himself, as it appears — he
sketches a scene or character in the history of legalized
©iTor and cruelty, he betrays so artistic a feeling, and

32

Hexry C. Lea's Publications.

INDEX TO CATALOGUE,

Abel and Bloxam's Handbook of Chemistry
Allen's Dissector and Practical Anatomist
American Journal of the Medical Sciences
Abstract, Half-Yearly, of the Med, Sciences
Anatomical Atlas, by Smith and Horner
Ashton on the Kectum and Anus .
Ashwell on Diseases of Females .
Brinton on the Stomach
Barclay's Medical Diagnosis .
Barlow's Practice of Medicine
Barwell on the Joints ....
Bennet (Henry) on Diseases of the Uterus
Bowman's (John E.) Practical Chemistry
Bowman's (John E.) Medical Chemistry
Brande & Taylor's Chemistry
Brodie's Clinical Lectures on Surgery .
Brown on the Surgical Diseases of Women
Buckler on Bronchitis ....
Bucknill and Tuke on Insanity
Budd on Diseases of the Liver
Bumstead on Venereal ....
Bumstead and Cullerier's Atlas of "Venereal
Carpenter's Human Physiology .
Carpenter's Comparative Physiology .
Carpenter on the Microscope
Carpenter on the Use and Abuse of Alcohol
Carson's Synopsis of Materia Medica .
Chambers on the Indigestions
Christison and Griffith's Dispensatory
Churchill's System of Midwifery .
Churchill on Diseases of Females
Churchill on Puerperal Fever

Clyraer on Fevers

Colombat de I'lsere on Females, by Meigs
Condie on Diseases of Children .
Cooper's (B. B.) Lectures on Surgery .
Cooper (Sir A. P.) on the Testis, &c' .
Cullerier's Atlas of Venereal Diseases
Curling on Diseases of the Testis .
Cyclopedia of Practical Medicine .
Daltou's Human Physiology .
De Jongh on Cod-Liver Oil .
Dewees's System of Midwifery
Dewees on Diseases of Females .
Dewees on Diseases of Children .
Dickson's Practice of Medicine
Druitt's Modern Surgery
Dunglison's Medical Dictionary .
Dunglison's Human Physiology .
Duuglison on New Remedies
Dunglison's Therapeutics and Materia Medica
Ellis's Medical Formulary, by Thomas
Erichsen's System of Surgery
Erichsen on Nervous Injuries
Flint on Respiratory Organs .

Flint on the Heart

Flint's Practice of Medicine .
Fownes's Elementary Chemistry .
Fuller on the Lungs, &c.
Garduer's Medical Chemistry

Gibson's Surgery

Gluge's Pathological Histology, by Leidy
Graham's Elements of Chemistry .

Gray's Auatomy

Griffith's (R. E.) Universal Formulary .
Griffith's (J. W.) Manual on the Blood, &c.
Gross on Urinary Organs
Gross on Foreign Bodies in Air-Passages
Gross's Principles and Practice of Surgery
Gross's Pathological Anatomy
Hartshorne's Essentials of Medicine .
Habershon on Alimentary Canal .
Hamilton oq Dislocations and fractures
Harrison on the Nervous Systei.. .
Hoblyn's Medical Dictionary

Hodge on "Women

Hodge's Obstetrics

Hodge's Practical Dissections
Holland's Medical Notes and Reflections
Horner's Anatomy and Histology
Hudson on Fevers, ....

Hughes on Auscultation and Percussion
Hillier's Handbook of Skin Diseases

PAGE

11

6

1

3

6

30

22

17

16

15

18
30
15

9
13
24
22
21
16
28

4

9
11
11
12
27
27
17
17
15
11
16
11
28
14
10

6
12
19
26
26
26
14
16
17
28
19

4
23
24

7
15

6
17
18
20 i

Jones's (T. "W.) Ophthalmic Medicine and Surg.

Jones and Sieveking's Pathological Anatomy

Jones (C. Handfield) on Nervous Disorders

Kirkes' Physiology ....

Knapp's Chemical Technology

Lea's Superstition and Force

Lallemand and "Wilson on Spermatorrhoea

La Roche on Yellow Fever .

La Roche on Pneumonia, &c.

Laurence and Moon's Ophthalmic Surgery

Lawson on the Eye ....

Laycock on Medical Observation .

Lehmann's Physiological Chemistry, 2 voli

Lehmann's Chemical Physiology .

Ludlow's Manual of Examinations

Lyons on Fever

Maclise's Surgical Anatomy .

Malgaigne's Operative Surgery, by Brittan

Markwick's Examination of Urine

Mayne's Dispensatory and Formulary

Mackenzie on Diseases of the Eye

Medical News and Library .

Meigs's Obstetrics, the Science and the Art

Meigs's Letters on Diseases of Women

Meigs on Puerperal Fever

Miller's System of Obstetrics

Miller's Practice of Surgery . »

Miller's Principles of Surgery

Montgomery on Pregnancy .

Morlaud on Urinary Organs .

Morland on Uraemia ....

Neill and Smith's Compendium of Med. Science

Neligan's Atlas of Diseases of the Skin

Neligan on Diseases of the Skin .

Prize Essays on Consumption

Parrish's Practical Pharmacy

Peaslee's Human Histology .

Pirrie's System of Surgery .

Pereira's Mat. Medica and Therapeutics, abridged

Quain and Sharpey's Anatomy, by Leidy

Ranking's Abstract ....

Roberts on Urinary Diseases .

Ramsbothara on Parturition .

Reese on Blood and Urine

Rigby on Female Diseases

Rigby's Midwifery

Rokitansky's Pathological Anatomy .

Royle's Materia Medica and Therapeutics

Sargent's Minor Surgery

Sharpey and Quain's Anatomy, by Leidy

Simon's General Pathology .

Simpson on Females ....

Skey's Operative Surgery

Slade on Diphtheria ....

Smith (H. H.) and Horner's Anatomical Atlas

Smith (Edward) on Consumption .

Solly on Anatomy and Diseases of the Brai

Still6's Therapeutics ....

Salter on Asthma

Tanner's Manual of Clinical Medicine .
Tanner on Pregnancy ....
Taylor's Medical Jurisprudence .
Thomas on Diseases of Females .
Todd and Bowman's Physiological Anatomy
Todd on Acute Diseases ....
Toynbee on the Ear ....
Wales on Surgical Operations
Walshe on the Heart ....
Watson's Practice of Physic .
West on Di8ea.«es of Females
West on Diseases of Children
West on Ulceration of Os Uteri .
What to Observe in Medical Cases
Williams's Principles of Medicine
Wilson's Human Anatomy . . . ,

Wilson's Dissector

Wilson on Diseases of the Skin .
Wilson's Plates on Diseases of the Skin
Wilson's Handbook of Cutaneous Medicine
Wilson on Healthy Skin
Wilson on Spermatorrhoea .
Winslow on Brain and Mind

I

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^QV24199/

12,000(11/95)

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