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UC-NR

John Sv;ett

1. Solar Spectrum.

2. Spectrum of Potassium

3. Spec ir
4 Spec

Harpe

H Hi

150 160. , 170

93 100 110 120 130 140 150 160 HO

lllllllllllllllil.lltlllllllllllllllllllllllllllliilllllllillllllllllllllllllll'llllll

100 110 120 130 140 150 If

110 120 130 140 150 160

100 110 1ZO 130 140 ISO 160 170

100 11C 1ZO 130 140 150

TL of Sodium,
of Strontium.

Brother s .TfewYork .

5. Spectrum, of Calcium.

6. Spectrum of Barium.

See page 286.

SCIENCE

FOB THE

SCHOOL AND FAMILY.

PART II.

CHEMISTRY.

WORTHINGTON HOOKER, M.D.,

PROFESSOR OF THE THEORY AND PRACTICE OF MEDICINE IN YALE COLLEGE,

AUTHOR OF "HUMAN PHYSIOLOGY," "CHILD'S BOOK OF NATURE,"
"NATURAL HISTORY," ETC.

Ellustrateti b$ Numerous

SECOND EDITION,
REVISED AND CORRECTED.

NEW YORK:
HARPER & BROTHERS, PUBLISHERS,

FRANKLIN SQUARE.
1876.

,UCATION £

By DR. WOETHINaTON HOOKER.

THE CHILD'S BOOK OF NATURE.

For the Use of Families and Schools ; intended to aid Mothers and Teachers in
training Children in the Observation of Nature. In three Parts. Engravings.
The Three Parts complete in one vol., small 4to, Cloth, $1 CO ; Separately, Part,
L, 60 cents ; Parts II. and III., 65 cents each.

PABT L PLANTS.

PABT IL ANIMALS.

PABT IIL AIK, WATER, HEAT, LIGHT, &o.

FIRST BOOK IN CHEMISTRY.

For the Use of Schools and Families. Engravings. Square 4to, Cloth, 90 cents.

NATURAL HISTORY.

For the Use of Schools and Families. Nearly 300 Engravings. 12mo, Cloth, $1 50.

SCIENCE FOR THE SCHOOL AND FAMILY.

PART I. NATURAL PHILOSOPHY. Engravings. 12mo, Cloth, $1 50.
PABT II. CHEMISTRY. Engravings. 12mo, Cloth, $1 50.

PABT III. MINERALOGY AND GEOLOGY. Engravings. 12mo, Cloth,
f!50.

Published by HARPER & BROTHERS, Franklin Square, ff. T.

B^P* HABPEK & BEOTm?ns will send any of the above works by mail, postage prepaid,
to any part of the United States or Canada, on receipt of the price.

Entered according to Act of Congress, in the year 1875, by HARPER & BROTHERS, in the Office of the
Librarian of Congress, at Washington.

PREFACE TO THE FIRST EDITION.

THIS book differs from all other text-books on Chemistry in several
particulars.

1st. It includes only that which every well-informed person ought to know
on the subject, and excludes whatever is of value only to those who are to
be chemists, or who intend to apply chemistry to specific branches of busi-
ness, as medicine, metallurgy, etc. For the extended and specific knowl-
edge required for such purposes other books can be studied afterward, this
book being suitable for a preliminary preparation. I will give a single ex-
ample of the sort of selection I have practiced in carrying out my plan. I
exclude the consideration of the tests of the presence of arsenic in cases
of poisoning, because the application of them is so complicated that none
but a professed chemist can make the investigation. On the other hand,
I notice very particularly the chemical action of the whites of eggs upon
corrosive sublimate, because, as poisoning with this substance is quite fre-
quent, and promptness in the use of the antidote is all-important, every one
ought to know what the antidote is, and he will certainly be the more
prompt to apply it if he understand its modus operandi.

2d. I recognize fully the distinction between a book for reference and a
book for study. The pupil should have his book specially adapted for
study ; and the teacher should have, in addition to this, books for refer-
ence, so that his knowledge may be wider than that included in the text-
book, in order that he may meet any inquiries that may arise, or add to the
facts and illustrations which the text-book furnishes, as occasion may offer.
Most text-books are too extensive, because the distinction referred to is not
observed. The attempt sometimes made to draw the line between the mat-

541767

JV PEEFACE.

ter for the pupil to learn and other matter not so essential by a difference
in type is always awkward, and is not fully effectual.

3d. While most books on Chemistry are illustrated chiefly from phenom-
ena developed in the laboratory of the chemist, I have taken great pains to
have abundant illustrations from common every-day phenomena, so that
this book is largely a Chemistry of Common Things. As an illustration of
the general neglect on this point, I find that very few of all who have
studied ordinary chemical books, or have attended lectures, can explain the
chemistry of so very common a thing as striking fire.

4ith. The arrangement of topics is entirely different from that of any
other text-book on Chemistry. It is such that the most simple and inter-
esting topics come first, and each page enables the pupil to understand bet-
ter the pages that follow. I begin with making the pupil familiar with the
four grand elements, oxygen, nitrogen, carbon, and hydrogen, and their
combinations with each other. This brings out fully those most interesting
of chemical subjects, combustion, water, and the chemistry of the atmos-
phere. I then pass to the combinations of these four elements with other
elements, and the combinations of these latter with each other. In this
portion of the book I notice first the metals and their compounds with oxy-
gen— the oxides ; then the metalloids sulphur, phosphorus, etc., and their
combinations with oxygen — the oxygen acids, and also the hydrogen acids.
Then in natural sequence come to view the salts formed by the union of
these acids and oxides, and in connection with these the salts of the chlorine
family. Now follows a development of the laws of chemical affinity, the
examples being taken from the facts already brought out, so that we have
here in part a review of what is gone before, which is of great advantage to
the student. In this connection I introduce the consideration of chemical
equivalents, symbols, and the atomic theory. All of this is commonly in-
troduced into the first part of Chemistry, and hence is generally but par-
tially understood, and is very diy and uninteresting ; but on the plan which
I have adopted the pupil easily comprehends it, and is interested at every
step. Then comes in. naturally the influence of the modifiers of chemical
affinity — heat, light, electricity, and magnetism — which before have been al-
luded to here and there, but now are fully treated of. The hook concludes
with the consideration of Organic Chemistry.

PBEFACE. V

The only text-book which has any resemblance to this in its plan is
Stb'ckhardt's, and the resemblance touches only a few points. The coinci-
dence, so far as it goes, gave me great gratification when my attention was
called to it by a friend to whom I was developing my plan.

A large proportion of the experiments can be tried with very simple ap-
paratus, and a few dollars' worth of materials obtained from the druggist ;
but it will be well for the teacher to purchase a few articles — such as re-
torts, a retort-stand, thin flasks, glass tubes, etc. — at some chemical shop,
and also such materials as druggists do not usually have — as potassium,
sodium, oxide of manganese, phosphorus, etc. A pneumatic trough can be
easily made by any tinman or cabinet-maker from the teacher's directions,
or he can even construct one himself by fixing a perforated shelf in a small
tub. At the same time, it may be said that the book can be profitably read
or studied with only trying such experiments as the most common materi-
als and apparatus which any household may furnish, because the illustra-
tions are drawn so abundantly from ordinary phenomena within the obser-"
vation of all. There are around us, and even within us, chemical reactions
which are the counterpart of a large proportion of the experiments which
the chemist performs in the laboratory.

Questions are appended for the use of teachers if they desire them, and
also a full Index. There is a glossary, or rather a list of terms, with the
numbers of the sections where their explanation may be found.

With the present degree of instruction in natural science in our general
system of education, this book is rather too far advanced for the oldest
scholars in common schools, though it would not be if they had gone
through with the previous books of the series* which I have prepared. Until
the different gradations which I have aimed at in this series are fairly intro-
duced, the proper place for this book and Part III. is the High School and
the Academy, while Part I. is within the comprehension of the next grade
below. But it is to be hoped that the time will very soon come when nat-
ural science shall have its due prominence during the whole course of edu-
cation, and then the books of this series, or other similar books, will find

• All the books of this series are mentioned in the Preface of Part I. See also
back of the title of the present volume.

VI PEEFACE.

their appropriate places; and thus those pupils who in so large numbers
stop short of the High School and Academy, will not go out into the world,
as they now do, destitute of that knowledge which not only embraces the
principles lying at the basis of the arts and trades into which many of them
will enter, but will add greatly to their usefulness and happiness, even if
their business be such as to call for no practical application of this knowl-
edge.

W. HOOKER.
November, 1863.

PREFACE TO THE SECOND EDITION.

THE rapid progress made by Chemistry within the last decade, and the
changes in the methods of instruction, hare necessitated a new edition of
this standard work. The alterations deemed advisable have been chiefly
of four kinds — omission of sections, insertion of new ones, introduction
of the latest nomenclature and chemical formulae throughout, and a com-
plete rearrangement of the matter. A rearrangement of the chapters re-
lating to Organic Chemistry on a strictly scientific basis was found imprac-
ticable, consequently the empirical plan adopted by the author has been re-
tained, while the editor has endeavored to point out the desirable method
of classification of organic bodies in Chapter XXTV.

The sections relating to Chemical Philosophy, especially in Chapters II. t
III., and IV., have been entirely rewritten ; the chapter on Galvanism in
the first edition has been omitted, the subject being now treated in connec-
tion with Physiqs ; a brief chapter on Spectrum Analysis has been added ;
and, lastly, the Metric System of Weights and Measures and the Centigrade
Thermometer have been adopted as standards throughout the work. Tables
explaining these standards are given in an Appendix.

Many wood-cuts have been added, and nearly all are new. The intro-
duction of two sizes of type may aid the teacher in the instruction of young-
er scholars. The questions in this edition are placed at the end of each
chapter, instead of being collected at the end of the book.

Finally, the editor expresses the hope that he has not entirely obliterated
the pleasant, familiar manner of treating the subject so happily adopted by
the author and so successfully carried out.

H. CAKBINGTON BOLTON, Ph.D.

SCHOOL OF MINES, COLUMBIA COLLEGK, )
September, 1ST5.

CONTENTS.

CHAPTW *AO«

^ I. INTRODUCTORY 11

IL CONSTITUTION OP MATTER 23

III. LAWS OF CHEMICAL COMBINATION. — NOTATION 30

IV. CHEMICAL PHILOSOPHY (CONTINUED) 42

V. OXYGEN AND OZONE 49

VI. NITROGEN AND ITS OXIDES 61

VII. CARBON AND CARBONIC ANHYDRIDE 76

VTII. THE CHEMISTRY OF THE ATMOSPHERE 92

IX. THE CHEMISTRY OF WATER.— HYDROGEN 110

X. COMBUSTION 131

XI. CHLORINE, BROMINE, IODINE, AND FLUORINE 158

XH. SULPHUR 172

XTTTV PHOSPHORUS 184

XIV. SILICON AND BORON 190

XV. METALS 197

XVI. GROUP I. POTASSIUM AND SODIUM 206

XVH. GROUP II. BARIUM, STRONTIUM, CALCIUM. — GROUP m.

ALUMINIUM, ETC. — GROUP IV. MAGNESIUM AND ZINC. 222
XVUI. GROUP V. MANGANESE, IRON, COBALT, NICKEL, CHROMI-
UM.— GROUP VI. TIN 240

XIX. GROUP VH. ARSENIC, ANTIMONY, AND BISMUTH. —

GROUP Vm. COPPER AND LEAD 253

XX. GROUP IX. MERCURY, SILVER, GOLD, AND PLATINUM.. 264

XXI. CHEMICAL INFLUENCE OF LIGHT 274

XXTT. SPECTRUM ANALYSIS 282

XXill, ORGANIC CHEMISTRY 29(^

XXIV. CLASSIFICATION OF ORGANIC SUBSTANCES 301

XXV. CONSTITUENTS OF PLANTS, ETC 313

X CONTENTS.

CHAPTER PAGE

XXVI. CONSTITUENTS OP PLANTS (CONTINUED) 327

XXVII. VEGETATION 341

XXVIII. SOILS AND MANURES 350

XXIX. OILS AND FATS 364

XXX. FERMENTATION 380

XXXT. ANIMAL CHEMISTRY 394

APPENDIX.— METRIC SYSTEM OF WEIGHTS AND MEASURES.. 415

INDEX.. . 419

CHEMISTRY.

CHAPTER I

INTRODUCTORY.

1. Difference between Chemistry and Natural Philosophy.
— Chemistry treats of the composition of substances, while
in Natural Philosophy, or Physics, their mechanical con-
ditions and relations alone are regarded. For example, in
Natural Philosophy we look at the laws governing the
pressure and movements of water, while in Chemistry we
inquire of what water is composed, and into the composi-
tion of what substances it enters. And so of other sub-
stances— solid, liquid, and gaseous.

2. Elementary Substances. — In making its investigations,
chemistry decomposes such substances as are composed of
two or more things. When any substance is found that
can not be decomposed or separated into two or more
things, it is termed an element, or an elementary substance.
On the other hand, all those substances which can be de-
composed are called compound. Iron is an element, for it
can not be decomposed : it is one thing. But iron rust is
a compound substance composed of three things, for water
and a gas called oxygen, existing in the air, unite with iron
to form rust.

12 v ..,,:; CHEMISTRY.

3. Idea ^ of Elements among the Ancients. — The ancients
<?uj»£0ae(! tji£ittth£i-e were only four elements — viz., air, wa-
ter, fire, and earth. But the science of chemistry has shown
us that these are not elements. We could see this to be
true of earth without any chemical experiments, for what
we commonly call earth is very different in different places.
Then water, simple as it appears to be, is composed of two
gases, one of which is the lightest of all substances. Air is
neither an element nor a compound, but a mere mixture of
gases. And what we call fire is merely a result of some
changes that take place in various substances under certain
circumstances. When wood or oil or gas, or any thing
burns, the result that we see we call fire. Fire, then, is not
only not an element, but it is not even a thing. It is not
a substance at all, but it is merely a phenomenon or ap-
pearance.

4. Number of Elements. — Chemists have discovered six-
ty-three elements. More may yet be discovered; and, on
the other hand, some which are now considered elements
may hereafter be found to be compounds. Seventy years ago
several substances were supposed to be elements that have
since been decomposed by chemists. Potash, for example,
formerly supposed to be an element, was discovered by Sir
Humphrey Davy to be a compound composed of a gas and
a metal.

Here is a list of the Elementary Substances, with their
Symbols and Atomic Weights. What these symbols and
numbers mean we will explain in another chapter. The
most important elements in this table are printed in CAPI-
TALS, the next in importance in italics, and those which are
very rare in ordinary type. Do not try to commit these
long names to memory all at once; you will get familiar
with them by degrees.

INTRODUCTORY.

ELEMENTAEY SUBSTANCES,

THEIR SYMBOLS AND ATOMIC WEIGHTS.

ALUMINIUM

..Al

27.5

MERCURY

200

..Sb

122

..As

Nickel.

.Ni

Barium

..Ba

137

NITROGEN

14 ""

Bismuth...

..Bi

210

Osmium

199

B or o n

OXYOEN

16 "

< BROMINE

..Br

Palladium

106.5

..Cd

112

PHOSPHORUS

31 -

..Cs

133

Platinum .

197 1

CALCIUM.. .

POTASSIUM

39 1

^CARBON

Rhodium

.Ro

104 3

..Ce

85 3

^CHLORINE...

..Cl

35.5

Ruthenium

T?n

104.2

..Cr

52.5

Selenium

79.5

Cobalt

SILICON

..Cb

SILVER

108 '

^ COPPER

..Ctt

63 5

SODIUM

Nfl

Didymium

..Di

87.5

..E

112.6

SULPHUR

~SF L U O R I N E

Tantalum

182

Glucinum

..G

9 5

Tft

129

^GOLD

196 6

Thallium

.Tl

204

*** HYDROGEN

Thorinum

238

Indium

75 6

TIN

118

^ IODINE.

Titanium

Indium.

197 1

Tungsten

184

\IRON

120

Lan thanium

51.3

^"LEAD

207

Yttrium

61.7

ZINC

Mff

24 3

Zirconium . .

89 5

""MANGANESE..

..Mn

5. Classification of the Elements. — The elements are di-
vided into two great classes — metallic and non-metallic.
The latter are often termed by chemists metalloid's, which

14 CHEMISTRY.

means substances having some resemblance to metals, the
affix old being derived from a Greek word meaning like;
since, however, the non- metallic bodies are not at all like
metals, we will not use the term metalloid, but say non-
metals. In the preceding table the non-metals are indicated
by being printed in spaced type.

Some of the elements, as arsenic, antimony, etc., seem to
possess a character intermediate between the metals and
non-metals ; sometimes chemists reckon them in one class,
and sometimes in the other. Of the sixty-three elements,
forty-nine are accounted metals and fourteen as non-met-
als. Of the latter, five are gases — oxygen, nitrogen, chlo-
rine, fluorine, and hydrogen ; the solid non-metals are sul-
phur, phosphorus, carbon, iodine, silicon, boron, and the rare
bodies selenium and tellurium. There is but one liquid
non-metal, bromine, as there is but one liquid metal, mer-
cury. Although hydrogen is put among the non-metallic
elements in all treatises on chemistry, yet there are some
reasons for regarding it as a metal in a gaseous state.
Only fourteen of the elements are quite abundant, and of
these the great bulk of our earth, including its water and
air, is composed, the remaining forty-nine existing only in
small quantities, some of them exceedingly small com-
pared with those which are abundant. Of the forty- nine
metals, only ten are quite familiar to most people — viz.,
iron, copper, lead, tin, zinc, silver, gold, mercury, arsenic,
and bismuth. Most of the remainder are known only to
the chemist, and are very rare.

6. The Elements as Found in Nature. — Generally the ele-
ments are found in nature in combination one with anoth-
er. But some of them, as gold and platinum, are always
found uncombined. Others are sometimes combined and
sometimes not. Thus carbon in wood, in alcohol, and in
starch is combined, but in the diamond and in graphite it

IXTEODUCTOBT. 15

is nncombined. So, also, nitrogen and oxygen are com-
bined in nitric oxide, but uncombined in the air, as that is
a mere mixture of these gases. Some elements, as you will
see in a future chapter, are never found in an nucombined
state, but are obtained in this state only by processes in the
laboratory of the chemist.

7. Variety in their Combinations. — There is very great va-
riety in the combinations of many of the elements, in form,
in color, and in other qualities more essential than these.
You will hereafter learn, in Chapter VI, that nitrogen and
oxygen form five combinations very different from each
other. And then one of these compounds, nitric acid, forms
a vast variety of combinations with many of the metals.
Take the compounds of mercury as another example. Oxy-
gen forms with it two oxides — a gray oxide and a red oxide.
Sulphur also forms with it two compounds — one a black
powder, and the other black also till it is sublimed, and
then it ia red, and constitutes the pigment called vermil-
ion. Besides these, there are various compounds of mercury
with nitric acid, sulphuric acid, etc. As we proceed with
our investigations in future chapters this variety will be
developed to you, and the examples which I have given
will suffice for the present. By far the greatest variety, as
you will see, is shown in organic substances. Here, for the
most part, there are only four elements, sometimes but three,
as stated in § 407. With these few elements, what an end-
less variety of forms, colors, odors, tastes, and other quali-
ties is. presented by vegetable and animal substances !

8. Difference in Form between Mineral and Organized Sub-
stances.— The forms which the combinations of the elements
assume in organized or living substances are very different
from those which they have in substances which are not liv-
ing. In the former the tendency is to curved lines, but in
the latter, with few exceptions, to straight lines and angles.

16 CHEMISTRY.

The subject of the crystallization of minerals belongs to min-
eralogy, and will be fully treated in Part Third. I shall
barely allude to it here. You see the tendency spoken of
in almost every mineral, and it never fails in its operation
except from opposing circumstances. You can often see it
in the rudest stone, especially if you call to your aid the
microscope. The angles and edges and faces of the half-
formed crystals can be seen huddled together. In the rocks
and mountains we see this crystalline tendency roughly ex-
hibited in lamina and pillars. The most common exhibi-
tion of it is furnished us in water as it solidifies into snow
and frost and ice.

9. Relations of Heat to the Forms of Substances. — Most
substances, whether elementary or compound, like mercury
and bromine, exist in different forms at different temper-
atures. We are accustomed to speak of them in the form
in which they usually appear to us, with the idea that this
is their natural condition. And yet this condition depends
wholly upon circumstances. Alter the temperature vari-
ously, and you may have them solid, liquid, or dissipated in
the form of vapor. Thus we speak of iron as a solid, and
mercury as a liquid ; but you can heat iron so as to make
it a liquid, and you can cool mercury so as to make it a solid.
Indeed, in some parts of the earth, the extreme arctic re-
gions, the natural condition of mercury is that of a solid.
Then, too, you can by heat turn mercury, heavy as it is, into
a vaporous or gaseous condition. Water exists in the three
different forms, solid, liquid, and gaseous, according to the
degree of heat. Some substances can exist in only one
form, so far as we know. This is the case with some of the
gases. Some substances can exist in but two forms. Thus
alcohol can be only in the liquid and gaseous forms, the
severest cold which man has ever produced not having
been able to make it solid.

INTRODUCTORY. 17

10. No Chemical Action in the Changes Noticed above. —
In the alterations of form above alluded to there is no chem-
ical change — that is, no change in composition. When iron
is melted, it is still iron ; when mercury freezes, it is still
mercury ; and when water freezes or is vaporized, it is still
simply water. The change that occurs in such cases is mere-
ly in the arrangement of the particles, and not in their qual-
ities. The change when the liquid, water, is converted into
the vapor that we call steam is a

great change. The particles are
very much separated from each oth-
er, as you may realize by observing
the alteration in bulk as represent-
ed iitFig. 1. Here the large cube
represents the quantity of steam
produced from a quantity of wa-
ter of the bulk of the small cube. Yet with this immense
change there is no alteration of the composition of the water.
Let the steam be condensed, and it will be simply water.

11. Forma of Matter as Affected by Chemical Causes. —
Though many of the changes in the form of matter are un-
attended by any chemical action, there are also many others
which are produced by chemical causes. One of the most
striking examples of this we have in water. This liquid is
composed wholly of two gases chemically united. As a
large volume of steam condensed forms but a little water,
so the bulk of the gases required to form a small amount of
water is very great. So, too, there must be great conden-
sation when the three gases of which nitric acid is composed
unite to form that liquid. On the other hand, in some chem-
ical combinations there are great expansions of matter.
When any solid, for example, enters into the composition
of a gas, it must be expanded into a very large volume.
Thus when the solid, carbon, unites with the gas, oxygen,

1 8 CHEMISTRY.

to form carbonic anhydride, in becoming invisible it must
be made exceedingly thin, and therefore occupy a very
large space. Many solid substances are formed by the union
of a large bulk of some gas with a comparatively small bulk
of some solid. Thus when iron rusts or any metal tarnishes,
it is by the union of the solid with a large volume of the
oxygen of the atmosphere. In a pound of iron rust there
have been nearly twenty-seven gallons of oxygen condensed
in the union of this gas with the iron. In quicklime we have
a union of this same gas with a metal. There is a great
number of these metallic compounds, called oxides, from the
oxygen that is in them. Animal and vegetable substances
generally are composed, to a great extent, of this and cer-
tain other gases ; and the gases that result from combustion
and decay fly off in the atmosphere only to appear again in
the living forms that we see around us. This agency of
gases in forming solid substances is always surprising to a
beginner in the study of chemistry, and he can hardly credit
the supposition of chemists that oxygen gas constitutes full
one third of the solid crust of the earth.

1 2. Extent and Variety of Chemical Action. — Some of the
elements are very busily at work producing changes every
where. When any thing burns we see an exhibition of the
chemical action of elements upon each other. The rusting
of a metal is the uniting of two elements. The effects of
manure, compost, lime, etc., in the soil come from chemic-
al action effecting compositions and decompositions. Air
and water are every where busy helping to produce these
changes in the soil. The operations of life, both in vegeta-
bles and in animals, are in part chemical, and those which
occur when death comes to either are wholly so. The sap
of vegetables and the blood of animals are made up of
chemical compounds of elements. Even the heat of the
body is produced by a chemical process, which is like com-

INTKODUCTOBY. 19

bastion, except that there is no flame. The air which we
breathe into our lungs acts chemically upon the blood, and
life is very soon destroyed if this chemistry of the respira-
tion be stopped. Chemistry, to a great extent, makes and
prepares our food. The grains are made by a union of ele-
ments which the plant sucks up from the ground and takes
from the air through the pores of its leaves ; and the mak-
ing of bread is in part a chemical process, upon the due per-
formance of which the goodness of the bread depends. In
these examples of chemical action you see the wide range
and the practical character of the interesting subjects which
chemistry presents to your view.

13. Changes in the Rocks. — In the midst of the chemical
changes so extensively and constantly taking place there
are some things which are nearly the same from year to
year, and even from age to age. The rocks of " the ever-
lasting hills" seem to remain unchanged. But it is not so ;
there is some change even in them. Heat, air, and water
are continually at work upon them, and some portions are
thus worn away even from the hardest of them to mingle
with the earth. And then, by means of chemical action,
these particles from stones and rocks are used in the growth
of both plants and animals. The flint that gives strength to
the stalks of grain and grass, the lime that is in the shells
of eggs and in the bones of animals, and the iron that is in
the blood, all came originally from the rocks.

14. The Sun's Agency. — In this chemistry, which is at
work so universally, heat is one of the chief agents. And
as the sun is the great source of heat, we may think of it
not only as giving us light and warmth, but as constantly
stimulating to the changes which are taking place among
the elements that are within and around us. Not only so,
but, as you will see in the course of our investigations, there
is a special chemical force bound up with the light and heat

20 CHEMISTRY.

that come to us in the rays of the sun, so that every ray is
a bundle of three forces united together — an illuminating, a
calorific, and a chemical. The sun, therefore, with its light
diffused every where, is the greatest of all the chemical
agents in our earth.

15. Summary. — The chief characteristics by which chem-
ical changes are distinguished are briefly summed up in the
statement following :

1st. Heat is evolved during chemical combination.

2d. A more or less complete change of physical and chemical properties.

3d. A chemical compound can not be broken up by simple mechanical
means.

4th. No weight is lost in chemical combination.

5th. Chemical combination takes place only in certain definite propor-
tions by weight.

The significance of the fifth point will appear fully in
Chapter III.

16. Analysis and Synthesis. — When a substance is sepa-
rated into the parts of which it is composed by means of
physical or chemical forces brought to bear upon it, the op-
eration is called analysis, or a "loosening again," from two
Greek words — ana, " again," and luein, " to loosen." Chem-
ical analysis forms an important branch of practical chem-
istry of immense value in determining the composition of
bodies. Synthesis, or a " putting together," also from the
Greek, is the opposite of analysis — it is the basis of a large
portion of chemical manufactures, which, however, pertain
to both branches.

17. Nomenclature. — There is no science that has so ap-
propriate and accurate a nomenclature as chemistry has at
the present time. It is in direct contrast with that loose
and unscientific nomenclature which was in vogue before
the time of Priestley and Scheele and Lavoisier. The old
names were given from some quality of the substance, or

INTEODUCTOEY. 21

from some fanciful idea of its nature. Thus nitric acid was
called aqua fortis (strong water), because it is a liquid of
such powerful acid properties ; and sulphuric acid was
named oil of vitriol, because it flows like oil, and was ob-
tained from what was called green vitriol. Then the sul-
phates of iron, copper, and zinc were respectively named
green, blue, and white vitriol, because, from their translu-
cency, they somewhat resemble glass of these colors. Oth-
er examples might be given, but these are sufficient. In
chemical books all these old names have given place to the
new nomenclature introduced by Lavoisier and his com-
peers, though a few of them are yet retained in common
language. This nomenclature, which, though it has been
extended with the progress of chemical discovery, has not
been essentially altered since it was first promulgated, is
worthy of admiration for its beautiful clearness and simplic-
ity. There is nothing arbitrary but the names of the ele-
ments. All the compounds have names which indicate their
ingredients ; and if any new compound be discovered, the
discoverer gives to it a name which expresses its chemical
character in accordance with the general plan of the nomen-
clature. Examples of the method of naming compounds
will be given in the next paragraph ; and as we proceed in
the examination of various substances, you will have con-
stant illustrations of this language of chemical science.

1 8. Naming of Chemical Compounds. — The names of com-
pound bodies are derived from the elements of which they
are composed ; many of these names have been anticipated,
but some explanation is necessary. In general, when two
elements unite, the name of the compound is formed by
writing the name of one element in full and placing the name
of the other element after it, giving to the latter the termi-
nation ide. Usually the non-metallic element follows the
metallic ; thus potassium and oxygen form potassium oxide;

22 CHEMISTRY.

barium and sulphur, barium sulphide; sodium and chlorine,
sodium chloride. Sometimes two sets of bodies are formed
by the same elements ; in such cases the name of the first
component receives the termination ous or ic, according to
the quantity of the second element combining with it. Thus
nitrogen and oxygen form two compounds, nitrous oxide
and nitric oxide — the former containing more nitrogen than
the latter, or, if you please, the latter containing more oxy-
gen than the former. Further explanations of the methods
of naming compounds will be given in connection with the
section on oxides (§ 62), and on acids, bases, and salts (§ 79).

QUESTIONS.

[The numbers refer to the sections.]

1. What is the difference between Chemistry and Natural Philosophy ?
Illustrate it by an example. — 2. What is the difference between element-
ary and compound substances ? — 3. What were the four elements accord-
ing to the ancients ? Show the error of this idea. — 4. How many ele-
ments are there ? What is said of the possibility of some of them being
compounds? Name some of the most important elements. — 5. Into what
two classes are the elements divided ? How many gases ? How many
liquids? How many metals? Name the best-known metals. — 6. How do
the elements occur in nature ? Give examples. — 7. What is said of the variety
of their combinations ? — 8. What differences in form are noticed between
mineral and organized bodies ? — 9. State in>full what is said of the influ-
ence of heat on the forms of substances. — 10. Illustrate the fact that no
chemical changes accompany the changes of form just mentioned. — 11.
Give examples of the nature of chemical changes. What is iron rust ? Do
gases unite with solid substances ? What are oxides ? — 12. State in full
what is said of the extent and variety of chemical action. — 13. What is
said of changes in the rocks ? — 14. What of the sun's agency in chemical
changes? — 15. Sum up the five characteristics of chemical change. — 16.
What is meant by analysis and synthesis? — 17. Contrast the old and
modern systems of nomenclature. Who introduced the present method ?
How are new compounds named? — 18. On what principles are names of
compound bodies formed ? Give examples — sulphur and sodium ? barium
and chlorine ? What do the terminations ous and tc signify ?

CONSTITUTION OF MATTER. • 23

CHAPTER II.

CONSTITUTION OF MATTER.

[Note to the Teacher. — In pursuing a logical arrangement of matter, the
principles of chemical philosophy appropriately precede the descriptive por-
tion of chemistry, and yet to some minds abstract ideas are exceedingly
difficult of comprehension, and can best be grasped after having acquired
a number of facts and phenomena with which to connect them. It is hard-
ly to be expected, then, that all young pupils will be able to intelligently
learn many parts of this and the two succeeding chapters ; it is recommend-
ed, therefore, that these chapters be carefully reviewed after having com-
pleted the study of the first ten chapters. Nomenclature and notation
should, however, be dwelt upon on the first perusal until the pupil is per-
fectly familiar with the systems employed. — EDITOR.]

19. Constitution of Matter. — You have already learned in
Part I, p. 17, that matter is in the abstract any thing which
is perceptible by the senses, but that we do not know any
thing of its nature ; we can only observe its phenomena and
learn its properties. In order to interpret facts and to aid in
their classification, theories have been formed regarding the
nature of matter, and one of these is of importance to us.
Theories, you should bear in mind, are not to be considered
as having the same weight of authority as facts, but as mere
matters of convenience, which are liable to be supplanted
by other and new theories so soon as the old ones prove in-
sufficient. We do not propose to trouble you with meta-
physical speculations, but will explain the so-called atomic
philosophy simply and briefly, both because it is interesting
and apparently true, and also because its consideration will

24 CHEMISTRY.

serve to impress upon your minds more strongly some of
the great principles and facts of chemistry.

20. Molecules. — The atomic philosophy assumes that mat-
ter can not be infinitely divided — that is, you may cut and
pulverize any thing as fine as you please, and you may then
think the smallest attainable particles divided again and
again, smaller and smaller, until you reach a certain limit,
beyond which matter can not be subdivided. Hence bod-
ies consist of an immense number of little particles called
molecules — literally, little masses. These molecules do not
touch each other, but are separated by empty spaces, and
these void spaces are very large compared with the dimen-
sions of the molecules themselves. These little particles
are held near each other by some force, or attraction, as it is
often called, and this force varies considerably in power in
the three different states of matter with which you are fa-
miliar. It is supposed that if it were not for the fact that
these molecules do not touch each other, we would be un-
able to cut any substance into pieces, for the small parti-
cles of matter are considered to be impenetrable ; and when
a knife-edge is forced into a body, it simply enters the void
spaces between the molecules and makes them separate — it
does not penetrate the substance of the molecules them-
selves. It seems strange at first to think of hard substances
like iron and silver as made up of particles which do not
touch each other; but this is a way of regarding them which
you will find easier to accept the longer you study. Do not
for an instant think that these little particles are ever visible
to any one, even with the aid of a most powerful microscope.
They are so small that we can only think them. "What we
do see are immense numbers of these molecules aggregated.
To give you a faint idea of the littleness of these particles,
we will tell you that philosophers have conjectured that fifty
million million molecules placed in a row would occupy the

CONSTITUTION OF MATTER. 25

space of one inch, and the weight of a million million mole-
cules of hydrogen gas (the lightest substance known) is
supposed to be equal to about three pennyweights. Or, if
you prefer another way of looking at it, imagine a drop
of water the size of a pea magnified to the size of the earth,
then the molecules in it increased in the same proportion
would be coarser than fine shot, but probably not so coarse
as cricket-balls. These speculations may seem rather extrav-
agant ; but three trains of thought have led philosophers
to nearly similar conclusions. These molecules are con-
ceived to be continually in motion, so that the interior of a
body presents to our imagination some resemblance on a
small scale to the vast system of the universe. In fact, we
see in the latter case stars held in certain positions deter-
mined by the law of universal attraction, and revolving one
about another. Repeating briefly what we have told you
in this section, masses of matter are made up of excessively
small particles, called molecules, separated from each other
by void spaces, mutually attracting and constantly in mo-
tion.

21. Advantages of this Theory. — We have already alluded
to the fact that this theory enables us to explain intelli-
gently the divisibility of matter, bftt besides this it accounts
in a satisfactory manner for many of the facts of physical
science. When you heat iron, it expands ; this you remem-
ber was explained fully in Part I., just as we do now by
saying that the particles are put farther apart by the heat,
which is really but an increase of motion imparted to them.
When any thing is cooled down, on the other hand, it con-
tracts — that is, the particles approach each other. This
theory, then, accounts for the changes of volume caused by
changes of temperature. Then, again, the very existence of
three states of matter — solid, liquid, and gaseous — depends
on the relative position of the molecules. In solid bodies,

26 CHEMISTRY.

force is required to move the molecules and separate them ; in
liquid bodies the relative position of the particles is no long-
er permanent — they glide past each other with perfect ease,
and less force is required than in the case of solids ; in gases
the mobility of the molecules is still greater than in liquids,
and the molecules tend constantly to recede from each other.
In Fig. 2 you have a rough representation of the way
molecules are separated from each other by heat.

o e

• e

Fig. 2.

22. Atoms. — As minute and intangible as these mole-
cules are, they are believed to be composed of still smaller
particles called atoms. We have already alluded to the
difference between Chemistry and Physics (or Natural Phi-
losophy), but this difference is now clearer when we state
that physical phenomena affect mainly the molecules, while
chemical science deals with atoms. Thus the physical
properties of an object refer to its condition, whether solid,
liquid, or gaseous ; crystalline form, color, hardness, specific
gravity, transparency or opacity, and the relations of the
body to heat, light, and electricity, are physical properties.
These you have studied in Part I.

CONSTITUTION OF MATTEE. 27

The phenomena of combustion, fermentation, putrefaction,
decomposition, etc., belong to the science of chemistry. In
short, all the phenomena in which the molecule remains un-
changed belong to the science of physics, while the phenom-
ena in which the molecule is changed or modified in its nat-
ure belong to the science of chemistry.

23. Illustration. — If you examine a piece of iron from a
purely physical point of view, you may describe it as black
or steel gray, opaque, hard, of a specific gravity of 7.8 — i. e.,
nearly eight times as heavy as water — and a fair conductor
of heat, as you will find on heating one end red-hot. Be-
sides these qualities, it is a conductor of electricity, and may
be converted into a magnet possessing the power of attract-
ing and repelling other pieces of iron. It is also fusible,
malleable, ductile, elastic, capable of crystallization. In all
this, however, its nature is not changed — it still remains iron,
its molecules are intact. Again, here you have some sul-
phur : it is, physically considered, yellow, brittle, electric,
easily fusible, readily crystallized, soluble in certain liquids,
etc., etc. Now take some iron filings having the physical
qualities named, and mix these with powdered sulphur
having its own properties ; mix and pulverize as fine as you
please ; each grain of the mixture will contain a particle of
iron and a particle of sulphur. The iron may be withdrawn
by a magnet, and the sulphur may be dissolved out in car-
bon disulphide. Examined under a powerful microscope,
each particle will be seen to consist of two distinct substan-
ces, iron and sulphur. Now apply heat to this mixture, and
thus set chemical force at work : the mass glows, a kind of
combustion takes place, and on cooling you have a dark sub-
stance which possesses physical and chemical properties of
its own. The iron has disappeared, the sulphur has gone,
each has united with the other, atom to atom. The magnet
will not now withdraw the iron, nor can the sulphur be dis-

28 CHEMISTRY.

solved out ; the microscope reveals a homogeneous mass, and
the whole is soluble in acids, evolving a very disagreeable
odor. The new substance, while containing iron and sul-
phur, is neither iron nor sulphur ; chemists call it sulphide
of iron.

24. Two Kinds of Molecules. — Molecules may be com-
pound or simple. Simple molecules are made up of atoms
of one and the same substance. By exposing the sulphide
of iron to the action of other substances, with the agency of
heat and chemical force it may be resolved into its constit-
uents, iron and sulphur ; sulphide of iron, then, is a com-
pound molecule composed of atoms of iron and atoms of
sulphur. Iron is not capable of being decomposed, nor is
sulphur — that is, their molecules are simple, or compounded
only of like atoms. They are elementary bodies, as you
were told in the first chapter ; but you now learn to regard
the elements from another and peculiar point of view.

25. Further Properties of Atoms. — These atoms, it is sup-
posed, can not be destroyed or altered or divided, but have
remained precisely the same since their first creation. The
atoms of some elements have been continually uniting with
the atoms of others, changing from one kind of combination
to another, and yet, after myriads of such changes, they
have not altered in shape or character. Take oxygen for
example. When its atoms unite with those of hydrogen
to form water, it is not by any change in the atoms them-
selves that a fluid so different from each of these gases
is produced, but it is only by some arrangement of these
atoms. So when potassium is thrown upon water, and pro-
duces fire and smoke, amid all the commotion and burn-
ing not an atom of either the potassium or oxygen or hy-
drogen is lost or injured, but they simply form new associ-
ations. The disturbance is the mere result of the eagerness
of the atoms of oxygen and potassium to unite together.

CONSTITUTION OF MATTER. 29

So, too, when a mixture of oxygen and hydrogen explodes
on the application of a light or electricity, the atoms of the
two gases merely unite in a very hurried manner, forming
water, and none of them experience the slightest change.
These ultimate atoms unite together to make molecules or
particles, which, unlike the atoms, can be both changed and
divided if the atoms composing them be of two or more
kinds, and can at least be divided if their atoms are of one
kind alone.

26. Weight of Atoms. — A most important attribute of
atoms has not yet been mentioned, viz., weight. Every ele-
mentary body is supposed to be made up of atoms of ex-
actly the same size and weight in the same body. The
weight of the atoms of different elements varies greatly ;
if we call the weight of the hydrogen atom l,then that of
oxygen is 16, while mercury is 200, gold 19 7, carbon 12, etc.
How it is that chemists are able to determine that the
atoms of the various elements differ in weight we can not ex-
plain to you in this work, but you must not imagine that sin-
gle atoms are ever weighed, only immense numbers of them
taken together. Nor is there any thing absolute with ref-
erence to their weight — it is merely relative ; that is, the
figures for hydrogen and oxygen named, viz., 1 and 16,
do not stand for any particular quantity, say pounds or
grammes, but they signify that if the hydrogen atom weighs
1 gramme or 1 pound, then the oxygen atom, being sixteen
times as heavy, weighs 16 grammes or 16 pounds. Any
other unit than hydrogen might be taken; and actually
many years ago oxygen was placed equal to 100, and the
weights of the other atoms were proportionally heavier —
hydrogen becoming 12.5, since 8 : 100 = 1 : 12.5. All the fig-
ures representing the relative weights of the atoms were
then 12.5 times heavier. Chemists now universally adopt
hydrogen as the standard, and make it unity.

30 CHEMISTEY.

QUESTIONS.

19. What is the use of theories ? — 20. What is said of the divisibility of
matter ? What are molecules ? Give the reason for their not touching
each other in masses. State what is given as the probable size of mole-
cules ? Are molecules motionless? — 21. What are the advantages of this
theory ? Why do bodies expand by heat ? — 22. Of what are molecules
made up ? Show the difference between Chemistry and Physics ? — 23. De-
scribe the illustration of this difference in the example given. What is
sulphide of iron ? — 24. Explain the nature of elements with reference to
the atomic theory. — 25. What other properties are ascribed to atoms ? Is
any thing lost or destroyed when burned up ? — 26. What is the most im-
portant attribute of atoms ? Are these absolute weights ? What is the
standard now adopted ?

CHAPTER III.

LAWS OF CHEMICAL COMBINATION. — NOTATION.

27. Law of Definite Proportions. — Chemists have made
innumerable experiments and analyses by which it is proved
that elementary bodies unite in definite proportions by
weight. Thus, if you take 32 pounds of sulphur and heat
it with iron filings to make sulphide of iron, as in the experi-
ment noticed in § 23, you will require just 56 pounds of iron,
no more and no less. If you should take 32 pounds of sul-
phur and GO pounds of iron, you will have four pounds of
iron left over, i. e., uncombined ; or if you take 50 pounds of
sulphur and 56 of iron, you will have 18 pounds of sulphur
too much. While, therefore, there may be great indefinite-
ness in mere mixtures, there is none in the formation of
compounds. Every compound always has exactly the same
composition. No matter under what circumstances the
compounds are produced, this exactness is preserved. The
carbonic anhydride formed by combustion, by respiration,

LAWS OP CHEMICAL COMBINATION. — NOTATION. 31

by fermentation, or by the explosion of gunpowder, always
possesses the same definite composition. This is one of the
four great laws governing chemical combination, and is
known as the Law of Definite Proportions. Before taking
up the study of the other laws you must understand the
meaning of chemical symbols.

28. Chemical Symbols. — Now turn to the table on page
13, and we will tell you how to use it. First you have a list
of all the elementary substances, and opposite each name
you find letters placed, which are either the first two letters
of the full name or some other abbreviation, the meaning of
which you will now learn. These letters are the symbols
used so much in chemistry, and we will explain some of them.
Take those elements whose names begin with S. We call
sulphur S, and we must therefore designate the others in
such a way as to distinguish them from this and from each
other. "We call, then, silver Ag, from Argentum, the Latin
for silver ; and sodium N"a, from an old Latin name for soda,
Natrium. Phosphorus is set down as P, being a prominent
element with a name beginning with that letter. Then Po-
tassium is designated by K, from JTalium, an old Latin
name for potash. Several of the elements take their sym-
bols from their Latin names. Thus the Latin for Antimony
is Stibium, Sb ; for Mercury, Hydrargyrum, Hg; Lead,
Plumbum, Pb ; Copper, Cuprum, Cu ; Gold, Aurum, Au ;
Iron, Ferrum, Fe ; and Tin, Stannum, Sn. Generally those
which are most important are represented by a single let-
ter; as, for example, the four grand elements, oxygen, ni-
trogen, carbon, and hydrogen. We use these symbols as a
kind of short-hand for expressing chemical reactions, and it
is necessary to become familiar with this method of writ-
ing from the very outset. Thus, instead of writing Potas-
sium in full, we write K, or in place of Hydrogen we write
H. This is not all they signify, however : each letter stands

32 CHEMISTRY.

for one atom of the element it represents. IT, then, means
one atom of hydrogen — no more and no less. If we want to
express two, three, or more atoms, we place a little 2 or 3 to
the right hand of the symbol ; thus Na2 stands for two
atoms of sodium, and O3 means three atoms of oxygen.
Sometimes large figures are placed in front, as 5N, which
means five atoms of nitrogen. Now unlike atoms unite to
form molecules of new bodies, and to represent this we write
the symbols alongside of each other. Thus HC1 will signify
the body having one atom of hydrogen united to one atom
of chlorine ; you will learn farther on that this body is call-
ed hydrochloric acid.

29. The Symbols in Formulae. — The example given in the
last paragraph, HC1, is called the formula of the body. In
place of writing "one atom of hydrogen united to one atom
of chlorine," we say "HC1," which is certainly much short-
er. In the same way CO stands for a gas called carbonic
oxide, containing as you see one atom of carbon and one
atom of oxygen. ISTaCl signifies chloride of sodium; CaO,
oxide of calcium. These examples anticipate of necessity
the method of forming the names of compounds, which you
will learn more fully in the section on nomenclature. In
the examples we have taken so far, only one atom unites
with one atom of another substance; it frequently happens,
however, that several atoms of an element unite with one
of another element, and to show this we use the little figure
referred to in § 28, and which is called a coefficient. Thus
water is made up of two atoms of hydrogen and one of oxy-
gen, hence it is written H2O ; marsh gas is CH4, sulphuric
acid is H2SO4, etc., etc. Interpreting the last formula, we
would say that two atoms of hydrogen, one of sulphur, and
four of oxygen, held together by chemical attraction, make
one molecule of sulphuric acid. Potassium nitrate is KNO3,
gypsum is CaSO4, sodium carbonate is N"a2CO3. If a snb-

LAWS OF CHEMICAL COMBINATION. NOTATION. 33

stance crystallizes with water, we usually write the mole-
cules of water separately, thus : Xa2CO3 . 10H2O, a period
separating them ; in place of a period, a plus sign is some-
times used. CaSO4-f 2H2O is the formula, then, of crystal-
lized gypsum, the sign + indicating that the connection be-
tween the gypsum and the water is not so close as that of
the remaining elements. We know this to be a fact, because
if crystallized gypsum containing water be heated red-hot,
the water is driven off, but the C, the S, and the O4 are not
thus separated. Notice that the 10 prefixed to the H2O in
the case of sodium carbonate, and the 2 prefixed to the
H2O in the other formula, multiplies the O as well as the
H2 ; it is the same as if w^e had written H20O10, or H4O2, and
means that ten and two molecules of water respectively are
taken.

From what we have said about formulae, it is plain that a
group of atoms constitutes a molecule, and that the number
of atoms in a molecule varies considerably; in HC1 we have
two, wrhile in Fe2(SO4)3, for example, there are seventeen.
In the chapters on organic chemistry, you wTill learn that
frequently the organic bodies contain a much larger num-
ber of atoms in a molecule.

30. Further Explanation of Symbols. — Since the atoms
have definite weights, and elementary bodies unite in fixed
proportions by weight, these symbols stand not only for
the atoms of the respective elements, but also for definite
weights of the elements. The third column in the Table
on page 13 gives these weights. S, then, means not only
one atom of sulphur, but also 32 parts by weight. Na
stands for 23 parts by weight of sodium, and so on. In this
light, formulae have a new significance. HC1 means 1
part by weight of hydrogen, and one atom or 35.5 parts by
weight of chlorine. In sulphuric acid, or H2SO4, we have
the following composition :

34 CHEMISTRY.

2 atoms of hydrogen, or II2, weigh 2

1 atom of sulphur, or S, weighs 32

4 atoms of oxygen, or O4, weigh 64

1 molecule of sulphuric acid, or HSSO4, weighs 98

You notice that we have drawn a line under the weights of
the atoms and added them together, obtaining the weight
of a molecule of sulphuric acid. Atoms, you remember,
unite to form molecules, and here you see that the sum of
the atomic weights of the elements composing the mole-
cule of a body gives the weight of a molecule of that body.
This is called the Law of Molecular Weights.

Take another example : Common limestone, you will learn
farther on, is a compound of calcium, carbon, and oxygen,
in the proportions represented by the formula CaCO3 :

1 atom of calcium, or Ca, weighs 40

1 atom of carbon, or C, weighs 12

3 atoms of oxygen, or O3, weigh 48

1 molecule of calcium carbonate, or CaC03, weighs 100

The molecular weight of crystallized gypsum can be cal-
culated in like manner, the weight of two molecules of
water (2H2O = 36) being added to that of one molecule, of
gypsum. Use the Table on page 13 to make this calcula-
tion. These examples also make the Law of Definite Pro-
portions much clearer.

31. Other Laws of Chemical Combination. — In explaining
the meaning of symbols, we have somewhat anticipated the
other laws of chemical combination. The Law of Multiple
Proportions may be thus stated: When one body com-
bines with another in several proportions, the higher propor-
tions are multiples of the first or lowest. This results from
the fact that one, two, three, or more atoms of one element
often unite with a single atom of some other element, form-
ing three or more bodies having very different properties.

LAWS OF CHEMICAL COMBINATION. NOTATION. 35

Examples of this law are abundant; to take the case
most familiar to us, iron and sulphur unite not only in the
proportions of atom to atom, but also of one atom of iron to
two atoms of sulphur — consequently in the ratio of 56 parts
by weight to twice 32 parts. This is shown in the follow-
ing manner :

. i unites with \ ... (to make >

1 atom iron, weighing

Fe, 56, , gj

/ unites with \ ... (to mane \
J 1 atom sulphur, i ™Shin* J a molecule, i
( S, i 32' I FeS, )

1 atom iron, weighing j sulphur, i weighing]

Fe> 56' I S2, i <*• I FeS2, ) —

When there are two elements forming different com-
pounds, generally one remains the same in all the combina-
tions, while the other is varied, not irregularly, but regular-
ly. When two elements unite to form a series of com-
pounds, this law of multiples is very noticeable. Oxygen
and nitrogen furnish such a series, which you will find on
page 63. Sometimes the series is complete, as in the case
of the combinations of hydrogen with oxygen and chlorine,
which may be stated thus :

Composition by weight

Names. Formulae. Hydrogen. Chlorine. Oxygen.

Hydrochloric Acid HC1 1 35.5

Hypochlorous " HC1O 1 35.5 16X1=16

Chlorous " HC1O2 1 35.5 16X2=32

Chloric " HC1O3 1 35.5 16X3=48

Perchloric " HC1O4 1 35.5 16x4=64

Here the proportions of oxygen, 16 xl, 16 x 2, 16x3, 16x4,
are respectively the multiples of 16 — viz., 32, 48, and 64.

The remaining law is that of Reciprocal Proportions,
which may be thus stated: If two bodies combine with a
third, the proportions in which they combine with that
third body are measures or multiples of the proportions in
which they may combine with each other.

36 CHEMISTRY.

Referring again to the Table of Atomic Weights, we
find that 32 parts by weight of sulphur combine with 56
parts by weight of iron and with 16 parts by weight of
oxygen, consequently 56 parts by weight of iron combine
with 16 parts by weight of oxygen. Or, using less wordy
language, since one atom of sulphur (32) combines with one
atom of iron (56) and with one atom of oxygen (16), these
bodies, iron and oxygen, combine with each other atom,
to atom (56 and 16). Actually the relation is not quite so
simple, for oxygen and sulphur combine usually in the
proportion of two atoms of the former to one of the latter,
and this necessitates the use of the word " multiples " in
the law as just stated.

We might in a similar way go through the whole list of
elements, showing that their atomic weights express their
value in satisfying the demands of each other in their com-
binations.

32. Summary. — We will sum up in four propositions the
facts which we have developed in this chapter in regard to
the combinations of substances. l.When substances com-
bine with each other, it is always in certain fixed and in-
variable proportions. In other words, every compound al-
ways has precisely the same composition. This is called
the law of definite proportions. 2. When two substances
unite in more proportions than one, these proportions bear
a simple arithmetical relation to each other. This is called
the law of multiple proportions. Commonly, as you have
seen, one of the substances remains the same, while the
other is in different proportions, usually as 1,2, 3, etc.
Sometimes the relation is as 1 J, 2-J-, 3J, etc.; but this we shall
speak of in another place. 3. When several substances,
B, C, D, etc., unite with a substance, A, the proportions in
which they unite with it are expressed by numbers, which
represent the proportions in which they unite with each

LAWS OF CHEMICAL COMBINATION. — NOTATION. 37

other. This is called the law of equivalent or reciprocal
proportions. 4. The molecular weight of a compound is
the sum of the atomic weights of its constituents. This
is the law of molecular weights.

33. Chemical Equations. — Returning to the symbols, there
is a further great advantage to be derived from their use
which we have not yet mentioned. By writing formulae in
a particular way, they place before the eye in small com-
pass the exact changes which occur when chemical action
takes place between two substances. We will give only
very few examples here, but you will become familiar with
them as you progress.

The formula for water, you know, is H2O; now potassium
is simply K. In Chapter XVI. you will learn that potassium
decomposes water, forming potassium hydrate, and setting
half the hydrogen free ; this is expressed in symbols thus :

Potassium and Water yield Potassium hydrate and Hydrogen
K + II 2O KHO + H

The plus sign between potassium and water signifies
" mixed with " or " in contact with," or " acted upon by,"
and not " combined with." The sign of equality means
" yields " or " produces," and has not the precise meaning
of " equal to " as when used in algebra. Notice particu-
larly that you have the same elements on both sides of the
equation, viz., O, H2, and K,but they are arranged different-
ly. K+H2O expresses the condition of the substances be-
fore they come in contact, and KHO-fH their condition
after the chemical action.

The most important meaning conveyed by the chemical
equations remains still to be explained. Bearing in mind
that the symbols stand for definite weights of the bodies
they represent (referred to hydrogen as unity), the equa-
tions give the actual proportion by weight of the elements

38 CHEMISTRY.

concerned, and of the bodies produced by the chemical

change. This is shown thus :

Potassium

Water yield hydrate

H2O KHO

39.1

(1)2 + 16 = 39.1 + 1 + 1G

Hydrogen
+ H

57.1 57.1

The 39.1 stands for so many grammes, pounds, tons, etc.,
of potassium, the 18 (obtained by adding the weights of the
atoms) for so many grammes, pounds, tons, etc., of water;
now when chemical action takes place, nothing is lost, so we
must find just as many grammes or pounds of these ele-
ments taken together, viz., 57.1, on one side of the equation
as on the other. That this is the case is evident ; only the
atoms are arranged differently — on the right-hand side we
have 56.1 grammes, pounds, or tons of potassium hydrate,
and 1 pound, etc., of hydrogen.

34. Combination by Volume. — "We have hitherto considered only
the laws governing combination by weight, but the elementary bodies which
exist in a gaseous state combine by volume in simple ratios, and the vol-
ume of the resulting body bears a simple ratio to the volume of its constit-
uents. A full examination of the laws of combination by volume can not
be entered upon in this work. We can give you only a few illustrations to
show that the volume relations of gaseous compounds are very simple.

Thus one volume of H and one volume of Cl unite to form two volumes
of hydrochloric acid, two of H and one of O form two of water, three of II
and one of N form two of ammonia, and, finally, four of H and one of C
form two of marsh gas. This, you will see, is in direct connection with the
atomicity of the elements explained in § 44. Now there is a law in physical
science that all molecules in the gaseous state occupy the same volume ; and
taking the volume of an atom of hydrogen as unity, the volume occupied
by molecules is two. Chemical formulae, then, dealing with molecules of
bodies, as well as the atoms, represent the volumes of the constituents as
well as the weights. If we represent the volumes by squares, as on the next
page, this will be somewhat clearer ; we take for examples the formation
of the bodies HC1, H2O, NH3, and CII4, just mentioned :

LAWS OF CHEMICAL COMBINATION. — NOTATION. 39

H + ci = H Cl or H + C1 = HC1 (hydrochloric acid).

-1 + I O I = HlO or H,+O = H2O (water).

I H I '— ' — l— '

2LI _

H | + | N | = I N'H3| or H3+N = NH3 (ammonia).

1"!

= C HJ or H<+C = CH4 (marsh gas).

35. Significance of Equations. — Every chemical equation
expresses a great deal in an exceedingly condensed manner.
It shows :

1st. What and how many elements are concerned in the reaction.

2d. How these elements are combined before and after the chemical
change has taken place.

3d. The proportion by weight of every constituent in the compounds.

Iii the case of gases a fourth point is shown, to which we
have just alluded, viz., the proportion by volume.

We will give you one more example to study; try to
determine the application of the three points above named.
The names of the bodies are not familiar, but that need not
be a source of confusion :

Calcium Hydrochloric Calcinm Carbonic

Carbonate. Acid. Chloride. Water. Anhydride.

CaCO3 + 2HC1 = CaCl2 + H2O + CO2
40 + 12 + (1GX3) 2(1+35.5) 40+(35.5X2) (1X2) + 16 12+(16x2)

100 73 "Til 18 44

~17Z~ ~173

40 CHEMISTRY.

36. Mathematical Calculations.— You have already obtained some
insight into the numerical relations of the atoms ; the calculations made
from the atomic weights and molecular weights of bodies belong to a special
branch of chemical philosophy called stoichiometry, a word made up of two
Greek words meaning "an element" and " a measure." These mathemat-
ical calculations are of the greatest importance both to the scientific and
manufacturing chemist ; the former is enabled to determine the composi-
tion of new bodies, or the purity of known substances ; the manufacturer is
enabled to estimate how much of any given material it is necessary to use
in order to manufacture a certain product. A knowledge of a few simple
rules, seldom requiring higher arithmetic than Proportion, properly ap-
plied to questions of practical import in manufacturing chemical products,
saves the capitalist thousands of dollars, and dollars and cents are items of
no small consideration. We can not explain all these calculations to you,
nor is it necessary for any one except a working chemist to master them,
but you should endeavor to realize their importance. We will give only
a single case, and illustrate it by two examples. Turn to page 38 ; you
find there an equation for the reaction of potassium in water, with the nu-
merical values of each atom and molecule attached. Now suppose this was
a good method for manufacturing potassium hydrate (or caustic potash, as
it is commercially known), and we should want to know how much of it
can be made from 10 pounds of metallic potassium, the question would be
solved thus :

From the equation cited it is evident that one atom of potassium yields
one molecule of potassium hydrate ; but one atom, or K, weighs 39.1, and
the molecule KHO weighs 56.1, therefore we have the proportion :

Atomic oecuar The number

39.1 : 56.1 :: 10 : the answer;

56 1x10
whence ' — ~-. — =14.3; consequently 10 pounds of potassium would

oJ. 1

furnish 14.3 pounds of potassium hydrate.

Supposing, again, that this was an economical method for manufactur-
ing hydrogen gas, how much potassium is required to make 100 grammes
of hydrogen ? By examining the equation on page 38, you will find as
before that one atom of potassium weighing 39. 1 takes place in the re-
action setting free one atom of hydrogen weighing 1 , hence the propor-
tion :

LATVS OF CHEMICAL COMBINATION. — NOTATION. 41

( A • ^ ( A^m-« 1 f The given "\ C Number of ^

A ) -k-T^V • * 5 • M f I ^ -a 3 number of f ... } grammes off
As -< weight of > is to 4 weight of s so is •< CTamraes of ( to ^ potassium T
(hydrogen) (potassium,) (ghyd™Jeu ) ( required. )

1 : 39.1 :: 100 : the answer ;

whence - - =3910 grammes of potassium. Such calculations are

very useful as a discipline for students, impressing on their minds the four
great laws of chemical combination, particularly the law of definite pro-
portions. Examples may be multiplied at the discretion of the teacher,
employing from time to time the equations given in different parts of the
book. The questions of percentage composition and of volume relations
can not be entered upon in an elementary work.

QUESTIONS.

27. How do elementary bodies unite ? Illustrate by taking iron and sul-
phur. What is the first great law governing chemical combinations? — 28.
Explain the nature of symbols ? How are they used ? What do they sig-
nify ? Write five atoms of nitrogen. How are molecules expressed ? — 29.
What is a formula of a body ? What is the formula for common salt ?
What of sulphuric acid ? Explain the small figure in the latter formula.
What is the use of the period ? AVhat of the plus sign ? How are several
molecules of one substance written ? Do molecules ever contain several
atoms ? — 30. What else do the symbols stand for ? Explain the law of
molecular weights. (The teacher should place examples on the black-
board.)— 31. Give the law of multiple proportions. Illustrate with iron and
sulphur. What is the law of reciprocal proportions ? Explain by referring
to a Table of Atomic Weights. — 32. Recapitulate the four laws. — 33. Give
in your own language the use of chemical equations. Write the action of
water on potassium. Explain this equation. — 34. How do the elements
combine as regards volumes ? — 35. What three points are expressed by
equations ? — 36. What is stoichiometry ? Calculate how many pounds of
caustic potash can be made from 100 pounds of potassium. How many
grammes of potassium are required to make 100 grammes of hydrogen ?
Explain the calculation.

42 CHEMISTRY.

CHAPTER IV.

CHEMICAL PHILOSOPHY (CONTINUED).

37. Forces. — The force which binds unlike molecules to-
gether is called cohesion; it is this power which gives rigid-
ity to solid bodies, and which, though weaker in fluids, pre-
serves their particles in contact. The attraction exerted be-
tween unlike molecules is called adhesion; this is the force
which makes water adhere to solid bodies, and which you
Lave already studied in Part I. The power which unites
atoms within the molecule is called chemical attraction^
though sometimes spoken of as affinity. To illustrate these
different forces, we may say that the molecules of a pane of
glass are held together by cohesion ; dip the pane in water,
and the water sticks to it by adhesion ; while the atoms of
silicon, calcium, potassium, and oxygen (of which the mole-
cules of glass are composed) are held together by chemical
attraction. Observe that in the attraction of adhesion and
of cohesion the particles are merely held together, without
producing any change in the nature of the substances which
attract each other, however different they may be. But
when two substances attract each other chemically, in the
union that occurs a change is produced in both. Moreover
ordinary attraction operates at all distances, in masses as
well as in particles, while chemical attraction operates only
when the particles of substances are intimately mingled —
as we usually say, in actual contact. Note, also, that chem-
ical attraction has nothing in common with electrical or
magnetic force about which you studied in Part I, for the

CHEMICAL PHILOSOPHY. 43

latter produce no change in the actual constitution of the
metals themselves.

38. Chemical Affinity. — There is great variety in the range
and degrees of chemical attraction. Between some sub-
stances there appears to be no disposition to unite under
any circumstances: thus no compound of fluorine and oxy-
gen is yet known. We say yet known, for such a compound
may be discovered to-morrow, as we have no proof of the
absolute impossibility of the union taking place. In a gen-
eral way substances which are alike are not eager to unite ;
thus the metals form few definite compounds, their alloys
being mainly mixtures. Bodies belonging to the same
group, and therefore chemically similar, as chlorine, io-
dine, and bromine, are not very prone to form definite com-
pounds.

The widest range of aflinity is possessed by oxygen ; it
unites with every known element except fluorine, as just
stated. Sulphur has a very wide range of attraction, unit-
ing with nearly all the metals, forming an important class
of bodies called sulphides. Oxygen and nitrogen show a
marked contrast in this respect, the latter having very lit-
tle tendency to enter into combination, particularly in its
free state, as it exists in the atmosphere.

Chemical attraction varies much in its degrees, or power,
between different substances. This is seen strikingly in the
affinity of oxygen for the various metals. At one end we
have the so-called noble metals, gold, platinum, etc., uniting
with oxygen only under compulsion ; while at the other ex-
treme we have potassium, sodium, etc., so eager to unite
with oxygen that they are never found uncombined in nat-
ure. Between these two extremes at various points we
have iron, zinc, copper, lead, etc. The same variation in the
degrees of the attraction of oxygen is shown in relation to
other substances besides the metals ; we shall learn how

44 CHEMISTRY.

this is the case with sulphur, phosphorus, and carbon far-
ther on. Oxygen lias a great attraction for hydrogen,
and is continually uniting with it, on every hand produc-

ing water.

Some substances can be made to unite with each other
only under the most extraordinary circumstances. This is
the case with oxygen and nitrogen. No degree of heat to
which we may subject them together can force them to
unite. Lightning does it to a small extent, as it shoots
through the atmosphere, forming nitric acid. And the pow-
er of this and many other analogous compounds consists, at
least for the most part, in the looseness of the affinity which
holds their constituents together. They destroy by falling
to pieces, their elements uniting with other substances for
which they have an affinity. This is the explanation of the
action of all caustics — they do not eat and themselves re-
main whole, but they are decomposed in the destruction
which they cause. So, too, the efficacy of gunpowder de-
pends upon looseness of affinity in the nitre, and the conse-
quent readiness with which it furnishes one of its elements,
oxygen.

39. Providence Seen in Affinity. — The various degrees of
affinity between different substances are adjusted by the
Creator, as all other forces in nature are, with an obvious
reference to the comfort and welfare of man. Take, for ex-
ample, the different degrees of affinity which oxygen has
for hydrogen and nitrogen. With hydrogen it is uniting
every where and continually to form water. This is done,
as you will see, in all ordinary combustion. Now if oxy-
gen united with nitrogen with the same ease — if the heat
of ordinary combustion could cause them to combine, form-
ing nitric anhydride — with the great abundance of these
gases in the air the most disastrous effects would result
every where. So, also, if sulphur had the same degree of

CHEMICAL PHILOSOPHY (CONTINUED). 45

affinity for oxygen that phosphorus has, the abundance of
this substance in the earth would occasion wide-spread con-
flagrations. Examples illustrating the same truth could be
cited to any extent, but these will suffice.

40. Modifiers of Chemical Attraction. — The force of chem-
ical attraction varies not only with respect to the different
substances between which it is exerted, but it is greatly
influenced by certain circumstances independent of the sub-
stances themselves. Solution has so much influence upon
affinity, or the disposition of substances to act chemically
upon each other, that it has given rise to a maxim set
down by the older chemists, " Coipora non agunt nisi sint
soluta" — substances do not act unless dissolved. A famil-
iar illustration of this we have in the mixture of common
soda powders. If the powders of tartaric acid and sodium
carbonate be mingled dry, there will be no action ; but if
each be dissolved before they are mixed, the action will be
immediate, producing a brisk effervescence. There are two
reasons for this : First, the particles are brought nearer to-
gether in solution than they can be mixed in powder, how-
ever finely they may be pulverized ; and, secondly, they
are free to move about among each other. Water, aside
from the chemical actions which itself produces, exerts a
very great agency as a solvent in the chemical changes
ever going on in all parts of the earth ; and not only so,
but it acts as a distributor, often bringing substances to-
gether which otherwise could never have come within the
range of each other's chemical action.

41. Influence of Heat. — Alteration of temperature is an-
other of the causes which modify the attractive force ex-
erted between atoms. Both composition and decomposi-
tion are effected by the influence of heat. How this can
be we will explain. Heat expands all bodies, or, in other
words, spreads the molecules farther apart; but, as you

46 CHEMISTRY.

have already learned, it is necessary that the particles of
different substances should be in immediate contact, or ex-
ceedingly near to each other, in order that they may exert
their combining power. Now if any substance is heated
so hot that the atoms of which it is composed are separated
so widely that they pass beyond the range of their attrac-
tion, and new molecules form by a re-arrangement of the
atoms, the body is said to be decomposed by heat.

42. Influence of the Nascent State.— When the molecules of a
body are acted upon by any force which separates its constituent atoms, the
latter momentarily possess unusual attractive force, and are said to be in
the nascent state, or just born. The reason that a gas is so active in its
nascent state is supposed to be that at the very instant of its production
from some solid or liquid it is for that instant in a highly concentrated
state, not yet having expanded to the dimensions which it has in the gas-
eous state. Many gases which will not show any affinity for each other
under ordinary circumstances, if at the instant of their production, the mo-
ment of their birth, they are in immediate neighborhood of each other,
unite at once. The particles of the two gases thus produced are, in their
momentary concentrated state, so pressed in among each other that they
must unite if they have any affinity at all. When they are expanded there
is none of this pressure to bring the particles within the range of their at-
traction— in other words, they are removed too far apart to exert a chem-
ical attraction upon each other. This being so, perhaps some one might
think that if a mixture be made of two gases, and great pressure in some
way be exerted upon it, these gases could be made to unite as they would do
in their nascent state. But the difficulty would be that no artificial press-
ure can bring them into so concentrated a state as they are in at the mo-
ment that they are produced in some fluid or solid. The state of conden-
sation in which gases are, as forming a part of solids or fluids, is far be-
yond any thing which mere pressure can produce. There are twenty-seven
gallons of oxygen in a single pound of iron rust. Is there any pressure
which man can produce in any way that can condense such a body of gas
into so small a space ?

43. Catalysis — Dissociation.— There are other circumstances which
influence chemical attraction, among which should be mentioned what is
termed catalysis. This word is derived from two Greek words, viz., kata
"down," and luein, "to loosen," and is applied to the peculiar power ex-

CHEMICAL PHILOSOPHY (CONTINUED). 47

erted by some substances which assist chemical action without themselves
undergoing any chemical change. Dissociation is another term applied to
a special kind of chemical change effected by heat alone. But a full dis-
cussion of these points is here out of place.

44. Atomicity.— After you have become familiar with the multitude
of compounds formed by the union of the elementary bodies, it will appear
that there is a large class of elements which invariably combine with each
other in the proportion of one atom to one atom. Hydrogen, chlorine,
bromine, iodine, sodium, potassium, and silver belong to this class ; there
are such bodies, for example, as HC1, Agl, KBr, NaCl, etc., in which the
elements are combined in the simple ratio of one to one. Moreover, chem-
ists are not able to make any such bodies as H2C1, or HC12, or NaCl2, or
KaBr3 ; hence it is supposed that this class of bodies are monatomic, and
are said to possess only one bond of affinity.

There is a second class of elements which are prone to unite with two of
these monatomic elements, and are hence called diatomic, and are said to
have two bonds or tint to of affinity. Oxygen, sulphur, calcium, etc., belong
to this class ; thus water contains two atoms of H to one of O, and is writ-
ten, as you know, H2O. We have other examples in the following bodies,
CaCl2, H2S, K2O, Na2O. These diatomic elements may also unite with
two dissimilar monatomic elements, giving rise to such bodies as KHO,
NaHS, etc. ; in this case, however, hydrogen is generally one of the mon-
atomic elements.

Besides these monatomic and diatomic elements, there are several other
classes— the tri-, tetr-, pent-, and hex-atomic — which combine respectively
with three, four, five, and six monatomic elements. A triatomic element
may unite with one monatomic element and one diatomic ; a tetratomic
element may combine with two diatomic elements, or with one triatomic
and one monatomic element, etc. This combining capacity, or atom-Jixing
power, is generally believed to point to a real difference of chemical power ;
it has nothing to do with the atomic weights, nor with the combination by
volume.

This idea of atomicity is represented in symbols by a very simple
method ; a single stroke attached to the symbol, thus H' or H-, signifies
that the element named has only one bond of affinity, or is monatomic.
T\vo strokes connected with a symbol, thus O'', or -O-, or O=, represent
a diatomic element; three, N'" or XN', a triatomic ; four, Civ or -C-, a tetr-
atomic, etc. You may, if you please, regard these strokes as so many arms
stretched out to grasp some other element. Water is often represented

CIIEMISTEY.

thus, H-O-H, which is the same thing as H2O, only it shows the rel-
ative atomicity of its constituent elements. The atom-Jixiny power of
the elements is not a fixed quantity for each element; nitrogen, for
instance, may be pentatomic or triutomic ; sulphur may be hexatomic,
tetratomic, or even diatomic, according to circumstances ; the maximum is
generally taken as the true atomicity of the element. This variation is in-
geniously accounted for by supposing that in the lower powers the bonds
are neutralized by self-saturation, or by combining with themselves ; thus,

if in pentatomic nitrogen, ^N^, two of the bonds unite, it may become
triatomic, ,N> The bonds are said to be saturated when joined to them-

V X

selves or to the bonds of some other element.

It scarcely ever happens that an element possessing an even atomicity
can assume an odd atomicity, nor can the reverse take place, consequently
the elements are divided into two great classes — those of even atomicity,
called artiads, and those of odd atomicity, called perissads. The following
table embraces all the commonly occurring elements which are thus grouped.
The symbols only are given, in order to familiarize you with them. This
whole subject of atomicity is a theory which is as yet only in its infancy, and
is so replete with exceptions to the rule that the longer it is studied the
more unsatisfactory it becomes. We have only sketched its fundamental
principles, and we do not propose to apply them in the body of this work,
notwithstanding they have been of great advantage to the progress of the-
oretical chemistry.

In the following table the monatomic elements are called monads; the
triatomic, triads; the diatomic, dyads, etc., in accordance with custom.

TABLE OF ATOMICITY.

PERISSADS.

ARTIADS.

Monads.

Triads.

Pentads.

Dyads.

Tetrads.

Hexads.

OXYGEN AND OZONE. 49

QUESTIONS.

37. Explain the difference between cohesion and adhesion. What is
chemical attraction? Illustrate these forces. — 38. What is said about the
variety of chemical attractions? What element has the widest range of
affinity ? What about the compounds of oxygen with the metals ? Under
what circumstances do oxygen and nitrogen combine? — 39. What advan-
tages result to mankind from the various degrees of affinity? — 40. How
does solution affect chemical attraction ? Give an example. How does
water act on the earth? — 41. How does heat modify the attractive force?
— i2. What is meant by the nascent state ? Why are gases active in this
condition ? — 43. Name two other circumstances which influence chemical
attraction. — 44. What are monatomic bodies? Give examples of com-
pounds of monatomic elements. What other classes are named? How
do these mono-, di-, tri-, and tetr-atomic elements combine ? How is at-
omicity expressed in symbols ? What is said of the variableness of this
atom-fixing power ? Explain the division into artiads and perissads. What
is the atomicity of oxygen ? what of phosphorus ? what of hydrogen ?

CHAPTER V.

OXYGEN AND OZONE.

45. Composition of the Air. — The air is composed chiefly
of two ingredients, oxygen and nitrogen, which are ele-
mentary substances, gaseous in form. These are not united
chemically in the air, but are only mingled together. The
atmosphere is a mere mixture of gases, just as alcohol and
water form a fluid mixture. We will now study oxy-
gen at some length, and then take up nitrogen in the next
chapter.

46. Abundance and Importance of Oxygen. — Oxygen is
the most abundant of all substances. It forms nearly one
half the whole bulk of material substances in our earth.
It constitutes by weight nearly one fourth of the atmos-
phere, eight ninths of the waters of the earth, and about

CHEMISTRY.

one third of the earth's solid mass. It is one of the chief
components, also, of all vegetable and animal substances.
It enters into more combinations with other substances
than any other element. There is but one element with
which it does not combine. This is not true of any other
of the sixty-four elements. Oxygen, therefore, may be said
to be the most important substance in nature. This will
be still more apparent when we come to consider its agency
in the chemical operations every where going on, especially
in those of living substances.

47. One Way of Obtaining Oxygen. — Oxygen can be read-
ily obtained from many substances which have a great
deal of it in them. The red oxide of mercury, formerly
called red precipitate, is one of these. This is mercury
united with considerable oxygen ; its formula is HgO. By

heating this oxide the ox-
ygen can be made to leave
the mercury. One way in
which this can be done is
shown in Fig. 3. We have
here a glass vessel full of
mercury, containing the mer-
curic acid at the top, stand-
ing in the mercury in the
dish, B. The heat applied is
that of the sun's rays con-
Fig, s. cent-rated by a burning-glass,
C. The result is the decomposition of the red substance,
the oxygen of which accumulates in the upper part of the
glass vessel, pushing the mercury down before it.

Expressed in symbols, the decomposition is very simple :
Mercuric Oxide. Mercury. Oxygen.

HgO Hg O

48. Discovery of Oxygen.— The above was the original ex-

OXYGEN AND OZONE. 51

periment by which Dr. Priestley, an English chemist, made
the discovery of this gas a little more than a hundred years
ago, on the 1st of August, 1774. It was discovered also by
Scheele, a Swedish chemist, shortly after, he not having
heard of the discovery by Priestley. The gas was called
by Priestley dephlogisticated air, for reasons which we will
explain to you. Very crude and fanciful notions prevailed
at that time, and among others that of Stahl, a German
chemist, who maintained that all combustible substances
burn in consequence of an element in them which he called
phlogiston. Now as this gas, while it makes other things
burn brightly, does not burn itself, Priestley considered it
as destitute of phlogiston, or dephlogisticated. Some years
after, the investigation of the qualities of this gas having
in the mean time been diligently prosecuted, Lavoisier, a
French chemist, gave it the name which it has retained to
this day, and which it probably always will retain — viz.,
oxygen. It is derived from two Greek words, oxus, acid,
and gennao, I give rise to. His idea was that this gas
is a component of all acids. This has since been found
not to be true ; but the name is nevertheless retained.

49. Another Mode of Obtaining Oxygen. — A more easy
and convenient way of obtaining oxygen from oxide of mer-
cury than that described in § 47 is represented in Fig. 4
(p. 52). Here the oxide is put into a retort, a, where it is
heated by the flame of a spirit-lamp. You see also a re-
ceiver, b, from which a bent tube, c, passes under the water
in the pneumatic trough, g, where its end is directly under
the open mouth of a glass jar. The heat of the lamp de-
composes the oxide, so that in place of this compound sub-
stance we have two elements, mercury and oxygen. But
the mercury, as it separates from the oxygen, is, on account
of the heat, in the form of vapor, and therefore passes on
with the oxygen gas through the tube of the retort. By

52 CHEMISTRY.

Fig. 4.

the time, however, that it arrives at the end of the tube it
is so far cooled as to become liquid, and drops into the
receiver, b. But the gas moves on through the tube, c, and
goes up the glass jar, forcing the water in it down as fast
as it collects.

50. Difference between Gases and Vapors. — You see in
the above process what the difference is between a gas and
a vapor. The mercury rises in vapor with the oxygen
gas, and both are invisible as they pass mingled together
through the tube of the retort. This is because the parti-
cles of the mercury are so much separated from each other
by the action of heat, just as it is with water when it is
converted into steam. But these particles are condensed
or brought near together again, and appear in the liquid
form in the receiver, b. Meanwhile the gas, though cooled
equally with the mercury, retains its gaseous form, and
passes on. You see that the vapor has its gaseous form
dependent upon a certain range of temperature, but the gas
retains it under all temperatures. No degree of cold (that
is, diminution of heat) can condense the gas into a liquid
form. The form of the gas, then, is not accidental and
temporary, but permanent. The range of temperature in
which vaporization can take place is different in different
substances. Water can evaporate at all temperatures, while

OXYGEN AND OZONE. 53

mercury will not evaporate under 40°. The space above
the mercury in a barometer or a thermometer is spoken of
as a vacuum ; but it is not strictly so, for there is some
little of the vapor of mercury diffused through that space.

While it is proper, then, to speak of substances appearing,
under certain circumstances, in the form of vapor as being
gaseous or aeriform, they can not properly be called gases.
This name belongs only to those substances which main-
tain this state under all circumstances ; or perhaps we
should say under all ordinary circumstances, for some of
the gases under extraordinary circumstances have been
made to take on another form, either solid or liquid.

51. Obtaining Oxygen from Oxide of Manganese. — The
chemist does not now get his oxygen from mercuric oxide,
for there are other compound substances that contain more
of it, and furnish it more readily and abundantly. One of
these is an oxide of a metal called manganese ; there are
several oxides of this metal containing different propor-
tions of oxygen ; the one used for the preparation of oxy-
gen is called the dioxide, MnO2. Manganese dioxide oc-
curs native as a mineral, and when ground fine it is a con-
venient and cheap source of oxygen ; it is not now so much
used as formerly, for
still better methods
have been invented. In
obtaining oxygen from
it great heat is em-
ployed ; it must there-
fore be heated in an
iron retort, such as you
see in Fig. 5, placed in
a furnace. Only one Fig. 5.

third of the oxygen in the dioxide is driven off, leaving
behind the red oxide of manganese. The dioxide is of a
dark color, and is commonly called the black oxide.

54 CHEMISTRY.

52. Preparation of Oxygen from Potassium Chlorate. — The
most common way of obtaining this gas is by heating a
substance called potassium chlorate. This contains a large
quantity of oxygen. In every hundred grammes of it there
are thirty-nine grammes of this gas. This is more than four
times as much as there is in the mercuric oxide, the sub-
stance from which Priestley obtained the oxygen for his
experiments. Over a gallon and a half of oxygen can be
obtained from an ounce of potassium chlorate. There is only
a little more of this gas in this substance than in the diox-
ide of manganese ; but the former gives up all its oxygen
on being heated, while the latter, as we told you in § 51, gives
up but a third part of what it contains. And, besides, the

potassium chlorate
needs to be heated
but little compared
with the manganese
dioxide to evolve
the gas. The heat
of a spirit lamp or
of a Bunsen burner
is sufficient. Fig. 6
shows the method
of generating and
collecting the gas.

53. Explanation of the Process. — The potassium chlorate
is composed of three elements — the two gases, oxygen and
chlorine, and the metal potassium, in the proportion KC1O3.
The oxygen is driven off by heat, and the chlorine remains
united with the potassium, making what we call potas-
sium chloride. Expressed in formulae thus: KClO3+heat
— KCl-f-O3. Of chlorine and potassium we shall speak par-
ticularly hereafter. There is some danger of explosion in
obtaining oxygen from potassium chlorate alone, because

OXYGEN AND OZONE. 55

large quantities of the gas are apt to be set free suddenly.
This danger is prevented by mixing with it an equal weight
of manganese dioxide. What is singular is that the diox-
ide does not part with any of its oxygen, and yet it regu-
lates and renders more easy the separation of the oxygen
from the potassium chlorate. Less heat is required than
when the chlorate is used alone, and the gas is driven off
gradually and yet very readily.

54. Other Methods of Preparing Oxygen. — There are many
other ways of preparing oxygen gas, and by some of them we
obtain it indirectly from the atmosphere. One way in which
this is done is (1) by passing air over a heated mixture of
manganese dioxide and sodium hydrate, and then (2) heat-
ing the materials hotter while a current of steam is passing
over them. In the first part of the operation sodium man-
ganate is formed ; this gives up its oxygen in the second
part of the operation, thus reproducing the original materi-
als, when the process is repeated. This method was invent-
ed by a Frenchman named Tessie du Hotay, and has been
tried on a very large scale.

Oxygen can also be prepared by decomposing sulphuric
acid, by heating barium dioxide, and in other ways of less
value. Oxygen gas is now a commercial article in great
cities, being manufactured for use in the arts.

55. Properties of Oxygen. — Oxygen gas is heavier than
that mixture of oxygen and other gases which we call air.
If we take 1 as representing air, oxygen would be repre-
sented by 1.106. This is said to be the specific gravity of
oxygen, air being the standard in reckoning the weight of
all the different gases. Oxygen is, like the air, transparent,
and without color, odor, or taste.

56. Oxygen a Supporter of Combustion. — It is this ingre-
dient of the atmosphere which, to use common language,
ordinarily makes things burn. If any thing that is burning

56 CHEMISTRY.

be introduced into a jar filled with oxygen, it will burn
much more briskly and brilliantly than in the air. For the
same reason, if a candle or taper be blown out, it will
at once be rekindled if put into ajar of oxygen, though
there be only a slight spark on the wick. This may
be done many times in the same jar of oxygen. After
a while this effect will not be produced, because the
oxygen is used up ; for every time the candle is in-
troduced some of the oxygen unites with the wick
and the tallow. It is this union that produces the
phenomenon which we call combustion. A very con-
venient way of introducing a taper or a candle into
.r. jars filled wjth gas is represented in Fig. 7.

57. Charcoal Burned in Oxygen. — If a piece of charcoal
be ignited in the air, it will exhibit only a dull red color ;
but the moment that it is introduced into oxygen gas it
burns brilliantly, casting off sparks with great rapidity, as

seen in Fig. 8. Charcoal made from bark is
better for this experiment than that made from
wood. In this case, as in that mentioned in
56, the oxygen is used up by uniting with
the burning substance. In doing this it forms
with the charcoal or carbon carbonic anhy-
dride, a gas which we shall speak of particularly in the
next chapter. This union is very simple : C + O2=CO2.

58. Phosphorus Burned in Oxygen. — One of the most
splendid experiments with oxygen is the burning of phos-
phorus in it. On introducing the ignited
phosphorus into a vessel filled with oxygen,
Fig. 9, thick white fumes arise, illuminated
by a most intense brightness. In the combus-
tion here the oxygen unites with the phospho-
rus to form phosphoric anhydride, the parti-
Fig. 9. cles of which make the fumes that you see.

In this case we have P2+O3=:P2O5.

OXYGEN AND OZONE. 57

59. Combustion of Steel in Oxygen.— Some things which
will not burn at all in common air will do so in oxygen
gas. This is the case with even so hard a substance as
steel. Take an iron wire, or, better, a steel watch-spring,
which you can get at any jeweler's, melt a little sulphur and
drop it on one end of the spring, ignite the

sulphur, and introduce it into the oxygen in
the manner represented in. Fig. 10. The com-
bustion will at once be communicated to the
wire, and it will go on, throwing off sparks of
intense brightness till most of the oxygen is
united with the iron. The experiment will
be very brilliant if the steel spring be coiled. Fig< 10*
The result of the combustion in this case is a solid, for the
oxygen unites with the iron to form an oxide of iron. The
sparks which fly from the red-hot iron struck by the black-
smith's hammer are the same, being formed by the union
of the oxygen of the air with some of the iron. But there
is this difference : The sparks emitted from the iron in the
oxygen are much hotter, because the combustion is more
brisk and perfect. Some of the iron falls in small burning
globules, which are so intensely hot as to be imbedded in the
glass, or they may even go through it if it be thin. We have
spoken of iron as not burning at all in air. This is not
strictly true, for every time that we strike fire with a steel
and flint, or with the heel of the shoe upon the sidewalk, we
set fire to a particle of steel. It is not only an exceedingly
little fire, but it is also momentary. It would be continuous
if the air were all oxygen, and the shoes on our feet would
be constantly taking fire from this cause.

60. Oxygen Essential to Life. — As ordinary combustion
can not go on without oxygen, so also is its presence essen-
tial to the continuance of life. It is the oxygen of the air
that supports life in all breathing animals, and no other gas

58 CHEMISTRY.

can take its place in that respect. Cut off the supply of
oxygen to our lungs for only a minute or two, and life is
extinct. When death occurs by drowning, it is because
oxygen is shut out from the lungs.

61. Oxides. — Among the most common chemical com-
binations are the oxides of metals. Most metals have such
an affinity for oxygen that they readily unite with it and
form oxides, some much more readily than others. Ex-
posed to the air, they tarnish, that is, unite with oxygen.
Gold, silver, mercury, and platinum do not oxidize in this
way, and therefore are called the noble metals. Gold and
platinum are so reluctant, as we may express it, to be
united with oxygen, that when the chemist by certain
processes forces them to a union with it, they very easily
part with the oxygen and return to their metallic state.
Such oxides are said to be unstable compounds. On the
other hand, there are some metals which have so strong
an affinity for oxygen that they are never found native,
and can only be obtained by separating them from the ox-
ygen with which they are combined. Such are the metals
of which lime, potash, and soda are oxides.

62. Different Degrees of Oxidation. — While some of the
metals have but a single oxide, most of them have two or
more, made by having different amounts of oxygen united
with the metal. Thus while there is but one oxide of
zinc, lead has three, mercury two, copper three, etc. If
there be two or more oxides of a metal, they are named
thus: Monoxide, dioxide, trioxide, etc., the prefixes being
derived from Greek words meaning one, two, three, etc.
Thus the dioxide has twice as much oxygen as the mon-
oxide, the trioxide three times as much, and so on, the rel-
ative amount of the metal being the same in all cases.

In some cases another system of nomenclature is em-
ployed, as mentioned in § 18. Thus we have nitrous oxide,

OXYGEN AND OZONE. 59

nitric oxide, and nitric peroxide, according to the propor-
tion of oxygen in them, as you will learn in the next chap-
ter. A peroxide, is an oxide having the highest amount of
oxygen, or at least a higher amount than the nitric oxide
in the series named. In the case of the compounds of ox-
ygen with the metals, sometimes an oxide is discovered
containing less oxygen than the monoxide, and this is call-
ed a suboxide, the prefix sub being the Latin for under.
Some metals form compounds having one and a half times
as much oxygen as the monoxide ; or, what is the same
thing, since we can have no half atoms, these compounds
contain two atoms of metal to three of oxygen ; they are
then called sesquioxides, the prefix sesgui being the Latin
for one and a half. Iron gives us an example of this, form-
ing Fc2O3, which you see is a sesquioxide.

63. Ozone. — This is oxygen gas in a peculiar condi-
tion, distinguished from common oxygen by its pungent
smell and its very active chemical properties. You may
perceive the peculiar smell when an electrical machine is
in action, owing to the partial conversion of the oxygen
of the air into ozone. The easiest way of effecting this
change is by means of phosphorus. Place a clean stick of
phosphorus in a corked flask having a little water in the
bottom, and let the flask stand half an hour. Remove the
phosphorus with a pair of pincers, and notice the peculiar
odor of the gas in the flask. The phosphorus very slowly
oxidizes and induces the formation of a little ozone. Pure
ozone has never been made — it is always mixed with much
oxygen. Ozone when breathed irritates the lungs, and
corrodes organic matter. It immediately oxidizes metals
which ordinarily unite with oxygen at high temperatures
only.

64. Experiment. — Boil as much starch as will cover the
point of a penknife with about fifty cubic centimeters of

60 CHEMISTRY.

water, and add a very little potassium iodide. Now steep
some slips of paper in the mucilage thus prepared, and you
have a test-paper for ozone. Place a strip of this paper in
the flask containing ozone prepared by phosphorus, and
it will soon turn blue, owing to the action of the ozone.
The explanation is this : Ozone first decomposes the potas-
sium iodide, setting iodine free ; now free iodine forms a
blue substance with starch, called iodide of starch, and
hence the color produced. Ordinary oxygen will not act
thus. Traces of ozone are found in the atmosphere, partic-
ularly in the country, and it is tested for with this same
iodine-starch paper.

Ozone has strong bleaching properties, and advantage
has been taken of this to bleach sugar on a large scale, the
ozone being formed by electricity.

65. Nature of Ozone. — Exactly how phosphorus or elec-
tricity act in converting oxygen into ozone is not under-
stood by chemists. But it has apparently to do with the
question of the arrangement of atoms, for the mere arrange-
ment of atoms in the molecule of a substance has much to
do with the production of the various qualities presented
by different substances. Thus in oxygen we have two
atoms in one molecule, arranged thus, O=O, the two lines
indicating the supposed points of union ; but in ozone
we have three atoms of oxygen to a molecule, and ar-
ranged thus, / \ You will meet with other cases of allo-

tropism, as this is called, where a fuller explanation will be
attempted.

QUESTIONS.

45. Of what does air consist? — 46. What is the most abundant of ele-
ments ? — 47. Describe one way of obtaining oxygen. Write the equation
and explain its significance.— 48. What makes this method of making ox-

NITEOGEN AND ITS OXIDES. 61

ygen of interest ? — 49. Describe a more convenient way of obtaining oxy-
gen from the same material. — 50. How do gases and vapors differ ? What
is a permanent gas? — 51. How is oxygen prepared from manganese di-
oxide?— 52. How from potassium chlorate? — 53. Explain the process.
Why is there danger of explosion ? How is explosion avoided ? Write
and explain the equation. — 54. Name two other methods of making oxy-
gen. Who invented a commercial process ? — 55. What are the properties
of oxygen ? — 5G. What is said of oxygen as a supporter of combustion ? —
57. What of burning charcoal in it ? What becomes of the oxygen in this
case ? — 58. What forms when phosphorus burns in oxygen ? — 59. How may
steel be burned in oxygen ? What is striking fire ? — CO. Why is oxygen
essential to life ?— 61. What are oxides? Mention an unstable oxide. — 62.
What is said of metals uniting with oxygen in different ratios ? What is
a peroxide? What a suboxide? What a sesquioxide? — 63. How may
ozone be prepared ?— 64. How does ozone act on potassium-iodide-starch
paper ?— 65. What are the properties of ozone ? What is said of its nat-
ure?

CHAPTER VL

NITROGEN AND ITS OXIDES.

66. Abundance of Nitrogen and its Combinations. — Nitro-
gen gas forms about four fifths of the atmosphere. It is one
of the elements in all animal substances, constituting about
one fifth of the flesh of animals when dried — that is, when
freed from the water that is in it. It enters also into the
composition of many of the vegetable substances that are
designed for food for animals. It forms some important
substances by uniting with oxygen and other elements, as
nitric acid, ammonia, etc. It does not enter into any thing
like the number of combinations that oxygen does. For
example, while oxygen makes with the metals a multitude
of substances called oxides, there are very few compounds
of the metals with nitrogen.

66 «. How Nitrogen can be Obtained. — Nitrogen gas can

62 CHEMISTRY.

be readily obtained from common air in the mode represent-
ed in Fig. 11. Let a cork, with a
cup-shaped piece of chalk on it for
the reception of a bit of phosphorus,
float in a pneumatic trough, d. Aft-
er igniting the phosphorus, hold over
it a glass jar, a, keeping the edge of
its mouth immersed in the water.
After a little time there is nothing
Fig. 11. -n tne jar kufc nitrogen gas nearly

pure. The explanation is this : As the phosphorus burns, it
unites with the oxygen of the air in the jar, thus making
phosphoric anhydride, as phosphorus burned in pure oxy-
gen does (§ 58). This rises in fumes, and is mingled with
the nitrogen. We have then nitrogen "and phosphoric an-
hydride in the jar. How do we get the nitrogen separate ?
Wait a little, and the fumes disappear, for the phosphoric
anhydride dissolves readily in the water in the pneumatic
trough, leaving the nitrogen alone in the jar. The nitrogen
occupies less space by one fifth than the air in the jar did,
for the oxygen that has disappeared was one-fifth part of
the air. The cork, therefore, rises somewhat in the jar during
the process, being pushed up by the water to take the place
of the oxygen. The water now contains phosphoric acid.

67. Properties of Nitrogen. — Nitrogen is lighter than air,
its specific gravity being .972. Like oxygen, it is transpar-
ent, without color, taste, or smell. But it is very different
from oxygen in some of its properties. Nothing will burn
in it. The contrast between the two gases in this respect
can be very prettily shown if you have two jars filled with
them. If you let a lighted taper down into the jar of ni-
trogen, it will go out. If now you introduce it quickly into
the jar of oxygen, it will light up again and burn brilliant-
ly ; and you can pass it back and forth from one jar to the

NITROGEN AND ITS OXIDES. 63

other many times, producing the same results. The brill-
iancy of the lighting-up will diminish each time, because
the combustion of the taper uses up the oxygen.

68. Nitrogen in Respiration. — As nitrogen can not sup-
port combustion, so it can not support life. If we put an
animal — a mouse, for example — into ajar of nitrogen, it will
die speedily. But nitrogen does not act as a poison. The
air which animals take into their lungs is four fifths nitro-
gen, but it does them no harm. The reason that animals
can not live in nitrogen alone is simply that they can not
live without having some oxygen in the air which they
breathe. Because this gas can not support life it is some-
times called azote, from two Greek words — «, privative,
and zoe, life.

69. Compounds of Nitrogen with Oxygen. — Nitrogen forms
five compounds with oxygen. Those which are of the most
interest to us are nitric anhydride, which unites with water
to form nitric acid (formerly called aqua fortis, the Latin for
strong water), and nitrous oxide, the so-called laughing-gas.

The following table shows us the names and formulae of
these five oxides of nitrogen :

Names. Formulae. Composition.

1. Citrous oxide (or laugh-) __

ing-gas) . . . ; N'° 28 Parts N' 16 PartS °'

2. Nitric oxide NaOa(orNO)* 28 " " 32 " "

3. Nitrous anhydride NaO3 28 " " 48 " "

4. Nitric peroxide N2O4(or N0a)* 28 " " 64 " "

5. Nitric anhydride N2O3 28 " " 80 " "

This table illustrates the regularity in proportions which
prevails in all chemical combinations, explained in Chapter
III.

In order to learn all about these oxides of nitrogen, you

* For reasons which we can not explain here, the formula? of these bod-
ies are of necessity halved as indicated.

CIIEMISTKY.

will understand them best by taking up nitric anhydride
first, and then following the others in the order given above.

70. Nitric Anhydride, N2O5. — This body is a great curios-
ity even to a chemist ; it is difficult to obtain, and hard to
keep when prepared ; and, since it has no good uses, you do
not care to learn much about it. When, however, we have
this substance united with water, we get the very impor-
tant acid known as nitric acid. We will give you the
reaction, although nitric acid is never prepared in this
manner, as you will presently see :

N205+H20=2(HNO3).

One molecule of nitric anhydride unites with one of wa-
ter, forming two molecules of nitric acid.

71. Preparation of Nitric Acid. — Potassium nitrate, com-
monly called either nitre or saltpetre, and sodium nitrate, are
the chief sources of nitric acid ; they are natural products,
but may also be made artificially, as you will learn hereafter.
Nitrate of sodium, heated with sulphuric acid — also called
oil of vitriol — gives us nitric acid and sodium sulphate :

Sodium nitrate.
2NaNO3

Sulphuric acid.
H2SO4

Sodium sulphate.

Nitric acid.
2HNO3

The process is
represented in Fig.
12. In the retort,
A, are the saltpetre
and the sulphuric
acid. The heat ap-
plied serves the
double purpose of
facilitating the
chemical change,
and of driving the
nitric acid as it is generated over into the receiver, B, in

Fig. 12.

NITEOGEN AND ITS OXIDES. 65

the form of vapor. There it is condensed into the liquid
form. To produce this condensation the receiver is kept
cool by a stream of water flowing from the pipe, *, over
its surface, a netting being spread over it to distribute the
water evenly. As the water accumulates in the vessel, c c,
in which the receiver rests, the waste runs off by the pipe, I.

72. Properties of Nitric Acid. — This is a nearly colorless
fluid, intensely acid, and very corrosive. It stains the skin
yellow the moment that it touches it, and if it continue to
be applied, it eats the skin, as it is commonly expressed, or,
in chemical language, decomposes it. It also attacks and
dissolves most metals. These active properties result from
the quantity of oxygen in nitric acid, and the readiness
with which it parts with a portion of it. What we call the
strength, then, of this substance is really its weakness — that
is, the weakness with which it holds on to one of its in-
gredients. If it held on to its oxygen strongly, instead of
parting with a portion of it readily, it would not produce
such powerful effects upon other substances. We will pro-
ceed to illustrate this explanation of its power by its action
on metals, and on certain combustible substances.

73. Action of Nitric Acid on Metals. — If you put a bit of
copper (a copper cent will answer) in a saucer, and pour
upon it some nitric acid, it will at once begin to dissolve
the copper. But you do not really get a mere solution, as
salt is dissolved in water. The copper acted upon by the
nitric acid is no longer copper. It is chemically changed.
What the change is we will explain. The acid immediately
in contact with the copper lets go a portion of its oxygen,
which unites at once with the copper, forming an oxide of
copper. The acid that does this is of course no longer nitric
acid, for it has lost a portion of one of its ingredients. It
becomes nitric oxide, and passes off in fumes. Observe now
what becomes of the oxide of copper that is formed. This

66 CHEMISTRY.

does not remain an oxide. It is immediately laid bold of
by some of the acid, and they together make a substance
called nitrate of copper and water. And so the process
goes on, some of the particles of nitric acid constantly giv-
ing oxygen to the copper, and other particles as constantly
seizing upon the oxide of copper thus formed, till the cop-
per is all changed to nitrate of copper. This lengthy ex-
planation is conveniently abridged in the following equa-
tions :

Copper. Nitric acid. Oxide of copper. Nitric oxide. Water.
3Cu + 2HNO3 = 3CuO + 2NO + H2O

Oxide of copper. Nitric acid. Nitrate of copper. Water.
3CuO + 6HNO3 = 3(Cu(N03)2) + 3H2O

The hydrogen of the acid takes to itself oxygen and
forms water in each case. It is this action of nitric acid
upon the oxides of metals which makes it so useful in
cleansing the surface of instruments or vessels made of
metals, as brass and copper, when they have become oxi-
dized from exposure or any other cause. The acid dissolves
the oxide, forming a salt with it, and thus makes the sur-
face bright.

74. Exceptions. — Most of the metals are acted upon in
the same way by nitric acid. The action upon tin and an-
timony is different from that which we have described in the
case of copper. Only one step of the process is taken with
these metals. The nitric acid merely parts with a portion
of its oxygen, and forms oxides of these metals. No solu-
tion is made, but we have the oxides in the form of a white
powder. Gold and platinum are not acted upon at all by
this acid. The reason is that they are not oxidizable, and
so the acid keeps all its oxygen to itself.

75. Nitrates. — These bodies are formed either by direct
union of nitric acid with the oxides or by the action of the

NITROGEN AND ITS OXIDES. 67

acid upon the metals themselves. In the latter case the
acid in immediate contact with the metal gives some of its
oxygen to the metal forming an oxide, and the moment that
this is done another portion of the acid seizes this oxide,
forming with it the nitrate ; and this double process goes
on continually until the action stops. You see, then, that
a part of the acid is decomposed in order to provide an ox-
ide to unite with the other part. In this decomposition, the
acid losing a portion of its oxygen, fumes of nitric oxide
pass off.

We will study the nitrates of the metals in connection
with the metals themselves.

F6. Combustion by Nitric Acid. — As this acid so read-
ily parts with some of its oxygen, it can set fire to certain
substances oh being applied to them. If you heat some
powdered charcoal, on pouring nitric acid upon it combus-
tion will at once take place. The cause is the rapid union
of the charcoal with the oxygen, which it takes from the
nitric acid. The reason that it is necessary to heat the
charcoal is that the union would not be sufficiently rapid
to produce a fire without the aid of heat. So, too, if you
pour some of the acid upon warmed oil of turpentine, the
oxygen which the turpentine takes from the acid sets it all
ablaze. Some caution is required in trying this experiment.
The test-tube containing the acid should be fastened to the
end of a stick a yard long, so that the experimenter may
be at some distance from the turpentine
as he pours the acid upon it. Phospho-
rus, if thrown upon some nitric acid in a
plate, will be set on fire, as seen in Fig.
13. The bits of phosphorus must be very
small, or some harm will be done by the
violence of the combustion. If the acid
be rather weak, as that which is bought at the shops often

68 CHEMISTEY.

is, it may be necessary in this experiment to heat it before
dropping the phosphorus upon it. In all these cases oxides
of the bodies named are formed.

77. Nitric Acid in the Atmosphere. — Nitric acid can not
be made by mixing together its ingredients, oxygen, hydro-
gen, and nitrogen. No degree of heat, however severe, will
make them unite to form the acid. Accordingly they ex-
ist together in the air without uniting, except under ex-
traordinary circumstances. If they could be made to unite
readily, producing every now and then nitric acid in con-
siderable amounts, the most destructive effects would result
from the corrosive acid as it descended in showers upon the
earth. As it is, there is only one agent that can cause them
thus to unite, and that is electricity. Even this does it, as
we may say, with difficulty. It is only when this agent
acts with violence that the effect is produced. Nitric acid
is, therefore, generated in the air only in small quantity,
and it is carried down by the rain into the earth, where
it answers a valuable purpose in vegetation, as you will
see in another part of this book. Its formation then,
small as the quantity is, is not a mere accident, but a
provision of Providence for a special purpose of a marked
character.

78. Acids. — Nitric acid being the first acid you have
studied, we can now tell you about the class of bodies called
acids. But first make a simple experiment. Purple cab-
bage, certain lichens, and other vegetables, when boiled
with water, furnish blue infusions. Paper steeped in this
strong blue solution, and dried, gives us a test-paper for
acids which is very useful. The substance usually em-
ployed is called litmus, and the paper, prepared as above,
litmus paper. Now this blue coloring matter is turned red
by the action of even a very small quantity of acid. Dip
some litmus paper in a very weak solution of acetic, sul-

NITROGEN AND ITS OXIDES. 69

phtiric, nitric, or any other acid, and you find the blue paper
will turn red. This is a characteristic property of acids.
Another and important distinction is this : all acids contain
hydrogen. Nitric anhydride, which has just been men-
tioned, contains no hydrogen, as its very name indicates ;
when, however, it comes in contact with water, a new body
is formed containing hydrogen, and this is nitric acid. The
hydrogen in acids may be replaced, as it is termed, by
metals forming new bodies called salts, as you will further
learn in § 80. All the non- metallic elements, except hy-
drogen and fluorine, unite with oxygen, forming anhydrides,
which, dissolved in water, yield acids.

79. Names given to Acids. — Just as we have ous and ic
compounds of oxygen, so we have ous and ic acids named
in like manner from the proportion of oxygen in them (see
§ 62). Thus nitric anhydride gives us nitric acid, while
nitrous anhydride gives us nitrous acid. The compounds
of sulphur and oxygen are similar ; sulphurous anhydride
yields sulphurous acid, and sulphuric anhydride yields sul-
phuric acid. The prefix hypo is used to name certain acids
having less oxygen than the ic or ous acid — as hypophos-
phorus acid.

When the acids combine with the metals with elimina-
tion of hydrogen, we have bodies whose names correspond
in a certain way to the acids whence they are derived.
The rule is as follows : Compounds of acids ending in ic are
indicated by names ending in ate, and compounds of acids
ending in ous are distinguished by names terminating in
ite. More concisely stated : ic acids form ates, ous acids
form ites. Examples are abundant : nitric acid forms ni-
trates, nitrcws acid forms nitrites; chloric acid forms chlo-
rates, chlorous acid forms chlorates. The termination ite
must never be confounded with the ending ide, as sulphide,
chloride, etc. ; these bodies contain no oxygen.

70 CHEMISTRY.

Acids containing one atom of hydrogen are said to be mono-basic ; when
they contain two or three atoms of hydrogen, they are called di-basic or tri-
basic. Thus nitric acid, HN03, is mono-basic, and sulphuric acid, H2S04,
is di-basic.

80. Bases and Salts. — You have seen that blue litmus is
turned red by acids ; now there is another class of bodies
which turns reddened litmus to blue again. These bodies,
chemically opposed to the acids, are called bases. They
are either oxides or hydrates of the metals. Thus sodium
oxide, Na2O, and potassium hydrate, KHO, and calcium hy-
drate, CaH2O2, are bases. The soluble hydrates are called
alkalies, and possess strong caustic properties. Now when
the hydrogen of an acid is exchanged for a metal, or when
the acids act upon these bases, a third class of bodies is pro-
duced, called salts. Thus the hydrogen in nitric acid may
be replaced by silver, forming silver nitrate, which is a salt.
When the hydrates or the oxides are acted upon by acids,
water is formed at the same time with the salts, as shown
in the two examples below :

Potassium hydrate, Nitric Potassium nitrate, Water.

A base. Acid. A salt.

KHO + HN03 = KNO3 + II30

Calcium oxide, Nitric Calcium nitrate, Water.

A base. Acid. A salt.

CaO + 2HNO3 = Ca(NO3)a + H2O

Having in the second example taken a dyad metal and an acid contain-
ing only one atom of hydrogen, two molecules of the acid are necessary to
complete the equation and form the salt.

When an acid acts upon a base to form a salt, a remark-
able change in the properties of both the acid and the base
takes place ; the acid loses its corrosive, acid properties,
and the base loses its alkaline and caustic nature, the re-
sulting body being neutral. Neither reddened nor blue
litmus are affected by neutral salts.

XITEOGEX AXD ITS OXIDES.

Some acids contain two or more atoms of hydrogen, which may be re-
placed successively by a metal ; if only one atom of hydrogen is thus
exchanged, an acid salt is formed ; if both atoms of hydrogen are ex-
changed for two atoms of a monad or one atom of a dyad metal (see § 44),
a neutral salt results. You will observe this in the study of sulphuric
acid.

81. Nitrous Oxide, or Laughing-Gas. — This gas is the com-
pound of oxygen and nitrogen, which has the smallest pro-
portion of oxygen. It is obtained by heating ammonium
nitrate in a re-
tort or flask,
a. Complete
decomposition
ensues; the gas
is washed in
the flask, b, and
collected in
the receiver, c.
"We obtain two
substances en-
tirely different
from each oth-

Fig. 14.

er and from the substance from which they come, viz., water
and the nitrous oxide gas :

Ammonium nitrate.
NH4N03

Nitrous oxide.
NSO

Water.

The vapor of the water and the gas pass together into the
second flask ; but there the vapor is condensed into water,
and the gas bubbles up into the glass jar set in the trough
to receive it. Some caution is necessary in preparing this
gas, or it may be impure, and therefore injurious to those
who may inhale it. To avoid this the material must be
pure, the heat must not be so great as to cause fumes to
rise in the retort, and the gas should be passed through

CHEMISTRY.

solutions of potassium hydrate and ferrous sulphate before
collecting it in a receiver.

82. Properties of Laughing-Gas. — The nitrous oxide gas is
as colorless and transparent as air, and has a sweetish taste.
A lighted taper burns almost as brightly in it as in oxygen,
and if there be but a spark on the wick, on introducing it
into a jar of this gas it lights up instantly. When breathed,
it occasions no irritation in the lungs, but produces a sin-
gular excitement, a delicious intoxication, which lasts but
two or three minutes. Individuals under the influence of
it act variously. Some dance, some laugh, some declaim,
some fight, etc. The excitement is very commonly of a
pleasant kind, and hence this gas is called in common lan-
guage laughing-gas. It also possesses the property of
causing insensibility to pain, and is now much used by den-
tists.

83. Nitric Oxide. — This is a colorless gas which has just
twice as much oxygen in it as the nitres oxide. It can be
obtained from nitric acid and copper in the apparatus rep-
resented in Fig. 15.
Bits of copper and
nitric acid, some-
what diluted, are in-
troduced into a flask.
The gas passes out
through the tube,
and may be collect-
ed in the usual way
in jars in the pneu-
matic cistern. The
first gas that passes
over will be orange-
colored, and we must

not begin to collect till the gas is colorless. The object of

NITROGEN AND ITS OXIDES. 73

the funnel is to enable us to add more nitric acid as the ac-
tion moderates.

Copper. Nitric acid. Nitrate of copper. Nitric oxide. Water.
3Cu + 8HNO3 = 3(Cu(NO3)2) + 2NO + 4H3O
Though this gas is colorless, the moment that it is ex-
posed to the air it is changed into orange fumes. This is
very prettily shown if a jarful of this gas be raised out of
the water in the pneumatic trough. The air, entering the
jar, diffuses an orange-red color in every part of it. The
explanation is this : The oxygen of the air unites with the
nitric oxide, converting it into a mixture of nitrous anhy-
dride and mtric peroxide, 3(NO) + O2=N2O3+NO2. You
can now understand why the first gas that rises in the flask
is colored. There is some air in the flask, and when the
gas begins to rise-it takes the oxygen from this air, and be-
comes nitrous anhydride. When this is driven off the ni-
tric oxide will come along pure.

In making these experiments you must be very careful
not to breathe the reddish fumes of nitrous anhydride mixed
with nitric peroxide, for they irritate the lungs. Indeed,
they smell so horribly we think you will not need to be
warned.

84. Explanation of a Former Experiment. — You will see
that in the above process the same materials are used as in
the experiment given in § 73. Nitric oxide was formed in
that experiment, as well as in this process, and yet reddish
fumes arose from the copper and the acid. The nitric ox-
ide at once united with the oxygen of the air, and so was
changed into nitrous anhydride and nitric peroxide, as ex-
plained in § 83. In the process for obtaining the nitric oxide
we prevent this change, as you see, by shutting out the air.

85. Air and Nitric Oxide Contrasted. — The two great in-
gredients of air are those which compose nitric oxide. And
yet how entirely opposite these two substances are in their

74 CHEMISTEY.

qualities! — one being one of the blandest of all substan-
ces, flowing into the lungs without irritating in the least
the delicate air-cells, while the other is powerfully acid,
and dangerous to breathe. The chief reason of this differ-
ence is that the air is a mere mixture of oxygen and nitro-
gen, and therefore partaking of the properties of both of
these gases, while nitric oxide is a compound, a new sub-
stance formed by the chemical union of the two gases.
You have here illustrated in a striking manner the grand
difference between mixtures and compounds, the mixture
having properties intermediate between those of its ingre-
dients, while the compound generally has properties differ-
ing widely from those of either of the substances of which
it is composed.

86. Nitrous Anhydride. — This is a thin, mobile, blue liquid
at a very low temperature, otherwise it is an orange-red gas.
Dissolved in water, it combines with it and forms nitrous
acid, which is of no great importance, though some of its
compounds are useful in the arts ; they are called nitrites.

87. Nitrous Anhydride in Nitric Acid.— It is the nitrous
anhydride that gives the yellow color which nitric acid so
commonly has. But how is this gas generated in the nitric
acid ? The explanation is easy. Nitric acid, we have told
you, is very ready to part with a portion of its oxygen.
Even exposure to light will make it do this ; so that if we
wish to preserve the acid pure, we must keep it in a dark
place or in dark-colored bottles. As we commonly see it,
a portion of it has become, by a loss of one fifth of its oxy-
gen, nitrous anhydride, which, readily dissolving in the nitric
acid, gives it a yellow color. Sometimes the oxygen which
is disengaged in this decomposition of the nitric acid, to-
gether with some of the nitrous anhydride, forces out the
stopper of the bottle.

88. Nitric Peroxide. — To obtain this substance in a liquid

NITROGEN AND ITS OXIDES.

form you can heat nitrate of lead in a glass retort and col-
lect the deep red fumes
in a tube surrounded
by a freezing mixture.
At a low temperature
the fumes condense to
a red liquid. The proc-
ess is represented in
Fig. 16. It also forms
in the gaseous state by
exposing nitric oxide Fitr 1(J

to the oxygen of the
air. This does not form an acid on dissolving in water.

QUESTIONS.

66. Where does nitrogen occur in nature ? — 66 a. How can it be obtained?
— 67. What are the properties of nitrogen? — 68. WTiat are its relations to
life ?— 69. How many and what are the compounds of nitrogen with oxy-
gen ? Wrhat are the proportions of these elements in laughing-gas ? What
in nitric oxide ?— 70. What is said of nitric anhydride ? What does it
form when dissolved in water ? — 71. Describe the preparation of nitric acid.
— 72. What are its properties ?— 73. Explain the action of nitric acid on met-
als.— 74. What metal does not dissolve in nitric acid ? WTiy ?— 75. What
are nitrates ?— 76. Give an example of combustion produced by nitric acid.
— 77. What is said of the formation of nitric acid in the air ? — 78. What is
the action of acids on blue vegetable solutions ? How do anhydrides form
acids ? — 79. Explain the method of naming acids. What does the prefix
* ' hypo " mean ? How are bodies derived from acids by replacement of hydro-
gen named ? — 80. WThat are bases ? How do they act on reddened litmus ?
What is a salt ? What do nitric acid and potassium hydrate form by com-
bining ? What is a neutral salt ? WThat an acid salt ? — 81. How is nitrous
oxide prepared ? — 82. WTiat are its properties ? — 83. How is nitric oxide
obtained ? — 84. What are the reddish fumes given off when copper is put
into nitric acid ? — 85. What is said of the contrast between air and nitric
oxide ? What does this illustrate ? — 86 and 87. What is nitrous anhydride ?
How does it occur in nitric acid ? — 88. How is nitric peroxide obtained ?

76 CHEMISTRY.

CHAPTER VII.

CARBON AND CARBONIC ANHYDRIDE.

89. Abundance of Carbon. — The two elements which we
have described to you in Chapters V. and VI. are gaseous.
Carbon, the element which we are now to consider, is a solid.
This is present almost every where. It forms nearly one half
of all the solid part of all vegetable and animal substances.
The different varieties of coal are nearly pure carbon. This
element is one of the ingredients of all limestones and mar-
bles. All shells are composed in part of it. It is present
every where in the air, united with oxygen to form a gas,
carbonic anhydride, which we shall speak of particularly in
the latter part of this chapter.

90. Charcoal. — One of the most common forms in which
we see carbon is charcoal. Before hard coal was introduced
into use it was the most common form ; and it is for this
reason that the word charcoal is often used as being syn-
onymous with carbon. Charcoal is ordinarily made from
wood ; or, to speak more correctly, it is obtained from wood,
for no new substance is formed, but there is merely a sep-
aration of the components of the wood. All the compo-
nents except the carbon are driven off, for the most part.
This is done by a smothered and imperfect combustion.
The wood is piled together and covered over with turf. It
is then set on fire from below, and suitable openings are
kept in the covering to allow the proper degree of combus-
tion. Figs. 17 and 18 (p. 77) illustrate the manner of piling
the wood and conducting the operation. Some of the car-

CARBON AND CARBONIC ANHYDRIDE.

bon is lost in this process, for it unites with the oxygen of
the air that is admitted in the openings, forming a gas, and
so passes out at the
upper openings with
the other matters that
are driven off by the
heat. About 40 per
cent, of the wood is
carbon, and the char-
coal obtained is from
20 to 25 per cent., so
that the loss of carbon
is nearly, often quite,
one half. The best
charcoal is made by
heating wood in tight
iron vessels till all the
vapors and gases are
driven off. The proc-
ess of making char- Fi°- 1S-
coal can be illustrated by holding a burning slip of wood in
a test-glass, as represented in Fig. 19.
The portion within the glass, not hav-
ing a free access to air, is subjected
to a partial smothered combustion,
and therefore becomes charcoal.

91. Soot. — In burning wood there is
more or less smoke. This arises from
the imperfection of the combustion,
and is dense in proportion to that im-
perfection. If the combustion were
Fig. 19. perfect, there would be nothing visi-

ble, for the substances passing off in the air would be, as you
will learn more particularly in another chapter, vapor and

78 CHEMISTRY.

gases only, and all that would be visible is the ashes. But, as
it is, there pass upward in this body of vapor and gas solid
particles of carbon that failed to be burned, and it is these that
you see and call smoke. These accumulate to some extent in
a chimney upon its sides. The soot thus formed is not pure
carbon, for there are some other substances — creosote, etc. —
mingled with it. The reason that we do not have smoke and
soot from hard coal is that the combustion is more perfect
than in the case of wood. So, too, there is more of smoke,
and therefore soot, from green wood than there is from dry
wood. For this reason green or wet wood is used in smok-
ing meat. When a lamp smokes from having the wick too
high, it is because the carbon of the oil is furnished in too
large quantity for the oxygen that is in the air around the
wick. Whatever this smoke touches has soot deposited
upon it. When the combustion is perfect, all the carbon,
as it rises in the heated wick, is made by the heat to unite
with the oxygen of the air, and form carbonic anhydride,
which passes upward unseen.

92. Lampblack. — This substance, so much used in making
printing-ink, is a fine kind of soot
made from pitch or tar. In Fig. 20
is represented an apparatus for mak-
ing lampblack. In the iron pot, a,
some pitch or tar is heated to boil-
ing, and, as a little air is admitted
through small openings in the brick-
work around the pot, an imperfect
combustion takes place. The carbon
of the tar passes in a dense cloud of
smoke into the chamber, b c. In this

hangs a cone of coarse cloth, the height of which may be
regulated, as you see, by a pulley. The lampblack or car-
bon is deposited in powder on the cone and on the sides of

CARBON AND CARBONIC ANHYDRIDE. 79

the chamber, which are lined with leather. There are two
objects in having the cone — one to prevent the smoke from
passing upward too rapidly, and the other to present a
large surface for the deposition of the powder in addition
to that of the walls of the chamber.

93. Bone-Black. — Bone or ivory black is a powdered char-
coal prepared from bones. It is far from being pure char-
coal, as you will see as we explain its preparation. A bone
is composed of two parts mingled together, a mineral and
an animal part. These can be obtained separate from each
other, as has been fully shown in the " First Book of Physi-
ology." It is the animal part alone that really furnishes
charcoal ; but in the preparation of bone-black both parts
are used together. The bones are heated in iron vessels,
and the heat, driving off all the volatile ingredients of the
animal part, leaves the carbon mingled with the mineral
portion — the phosphate of lime. The advantage of this form
of charcoal is that the carbon is very minutely divided by
being thus mingled with the mineral powder. Besides other
uses soon to be noticed, bone-black is used in the manufact-
ure of blacking, being mixed for this purpose with oil of
vitriol and sirup.

94. The Carbon in Animal Substances. — As there is car-
bon in the animal part of bone, so it is in all animal sub-
stances. It exists in combination with other elements, and
therefore does not appear as carbon. It is only by some
chemical process which separates it from these combina-
tions that it can be made manifest, and combustion is one
of the processes that can do this. When animal skin or
flesh is charred — that is, partially burned — the charcoal that
appears is produced essentially in the same way that it is
when made from wood. It is not really made, but it is sepa-
rated by the heat from the substances with which it is com-
bined, the heat for the most part driving these off into the

80 CHEMISTEY.

air. Whenever meat is overcooked in roasting, some of the
outside exhibits this separation of carbon by chemical de-
composition.

95. Properties of Charcoal. — Although charcoal is so com-
bustible, it is in some respects a very unchangeable sub-
stance, resisting the action of a great variety of other sub-
stances upon it. Hence posts are often charred before be-
ing put into the ground. Grain has been found in the ex-
cavations of Herculaneum which was charred at the time
of the destruction of that city, 1800 years ago, and yet the
shape is perfectly preserved, so that you can distinguish
between the different kinds of grain. While charcoal is
itself so unchangeable, it preserves other substances from
change. Hence meat and vegetables are packed in char-
coal for long voyages, and the water is kept in casks which
are charred on the inside. A ham was kept, by a friend of
the author, packed in charcoal-dust eight years, and on be-
ing cut was found as fresh and sweet as when first put
in. Charcoal is also a great purifier. Tainted meat can
be made sweet by being covered with it. Foul and stag-
nant water can be deprived of its bad taste by being fil-
tered through it. Charcoal is a great decolorizer. Ale
and porter filtered through it are deprived of their color,
and sugar-refiners decolorize their brown sirups by means
of charcoal, and thus make white sugar. Animal charcoal,
or bone-black, is the best for such purposes, although only
one tenth of it is really charcoal, the other nine tenths be-
ing the mineral portion of bone. Other substances besides
those which give color are often extracted by charcoal.
Thus brandy is rendered pleasanter in taste and smell by
being filtered through charcoal, because an acrid volatile
oil, called fusel-oil, is extracted. So charcoal takes away
from beer not only its color, but that which causes its bitter
taste.

CARBON AND CARBONIC ANHYDRIDE. 81

96. Absorbing Power of Charcoal. — Most, if not all, of the
effects above mentioned are attributed to the absorbing
power of charcoal. This power is very great. Charcoal
will absorb of some gases from eighty to ninety times
its own bulk. This constitutes a protection to substances
which are covered with charcoal, for gases are the grand
agents in decay. Absorbed by the charcoal, they are put
out of the way ; and not only so, but they constitute a part
of the wall of defense together with the charcoal, filling up
as they do all its spaces. Charcoal thus saturated with
gases defends the substance that it covers from access of
the air. When decay has already begun before the char-
coal is applied in the work of purification, it absorbs all the
gases tli at have been produced in the decay, and thus puts
a stop to the process.

97. Explanation. — The question arises as to what gives
this power of absorption to charcoal. It is generally sup-
posed that it is owing to its great porosity. Charcoal is
full of minute spaces, and is therefore intersected by num-
berless partitions. If these were spread out they would con-
stitute a surface perhaps a thousand times larger than the
external surface of the charcoal. As every point of this sur-
face is a point of attraction, it is supposed to account for
the enormous accumulation of gases in the spaces of the
charcoal. But this accounts for it only in part. If it were
the only cause of the absorption, there should not be such a
great difference in absorbing different gases. Of some gases
it absorbs nearly fifty times as much in bulk as it does of
some others. When great quantities of gases are absorbed,
there must be great condensation, and this would hardly
come from mere common attraction. There must be some
peculiar power in the charcoal to change in some way the
condition of a gas of wrhich it absorbs ninety times its own
bulk. And, besides, it seems to show some sort of affinity

D 2

82 CHEMISTEY.

for certain substances in separating the'm from others, as,
for example, in separating the coloring substance from ale,
and also that which gives it its bitter taste.

98. Coal. — All the different varieties of coal — anthracite,
bituminous, etc. — are carbon, more or less mixed with
compounds of hydrogen and carbon called hydrocarbons.
Anthracite burns without smoke, and when fully ignited
without flame, for it is destitute of the volatile hydrocar-
bons that are present in bituminous coal. The reason of
the difference is that these volatile substances have been
driven off by heat in the formation of the anthracite. When
the anthracite is burned the carbon all passes upward, unit-
ed with the oxygen of the air, forming carbonic anhydride.
The impurities combined with this carbon in the coal fall
below, making the ashes. The bituminous coal is used in
making illuminating gas. What is left after the volatile
matters are driven off is a very impure charcoal called coke.

99. Graphite. — Graphite, or plumbago, sometimes called
black-lead, contains not a particle of lead, but is crystallized
carbon, having commonly a very little iron mingled with
it. It is a grayish black substance having a metallic lus-
tre. It is used for making the so-called lead-pencils, and for
giving a polish to stoves and other iron articles. When
powdered it is so soft and lubricating that it is added to
grease for the prevention of friction in wheels and machin-
ery. It is a very incombustible article, and therefore the
coarser kinds are manufactured into crucibles, or melting-
pots. There are famous mines at Cumberland, in England,
and in Siberia, which furnish very fine graphite for pencils.
It is quite a common mineral in this country, appearing in
many localities. At Ticonderoga, in New York State, an
extensive deposit occurs, most of which is worked up into
crucibles and stove-polish.

100. The Diamond. — In the diamond we have pure carbon

CARBON AND CARBONIC ANHYDRIDE. 83

crystallized, but differently from what it is in graphite. It
is the hardest of all substances. It has not the least resem-
blance to coal, yet it can be burned up in oxygen, car-
bonic anhydride being the result, as in the burning of coal
and other forms of carbon. It was discovered to be carbon
in this way by Lavoisier, a French chemist. He threw the
sun's rays, concentrated by a large lens, upon a diamond in
a vessel of oxygen gas. It was consumed, and carbonic an-
hydride alone resulted, showing that the substance that had
thus united with the oxygen was nothing but carbon. No
one has ever yet been able to convert coal into diamonds.
The difficulty seems to be that coal can neither be dissolved
nor melted, for, in order to crystallize any substance, it must
first be in a liquid state. It is indeed stated that a French-
man, M. Despretz, has with a galvanic battery melted and
crystallized carbon, and thus made diamonds; but they
were so small as to be visible only with a microscope.

101. Allotropism. — You have learned that the elementary
body carbon appears under three very different forms — dia-
mond, graphite, and charcoal — varying in color, hardness,
specific gravity, and other physical properties. "We can
not explain exactly how and why this is so, but we know
that some other elements appear in two or more distinct
forms, and the peculiarity is not confined to carbon. Bear
in mind that, chemically, diamond, graphite, and charcoal
are one and the same, but they differ in their physical as-
pects. Bodies having this power of taking different forms
are said to be allotropic, and the phenomenon is called allo-
tropisra. These words are made up from two Greek words,
allos," other," and tropos, "way," because the body exists in
some "other way." When we say that carbon exists in
three allotropic forms, we do not explain any thing; we
rather conceal our ignorance of the truth by employing a
high-sounding word coined for that purpose.

CHEMISTRY.

102. Carbonic Anhydride. — Having given you an account
of the element carbon, we will now notice a gas formed by
the union of this element with oxygen, viz., carbonic anhy-
dride.* This is formed whenever carbon is burned in oxy-
gen, as in the experiment in § 57. So, also, when a diamond
is burned in oxygen, this, being pure carbon, unites with the
oxygen to form carbonic anhydride. This gas is one of the
products of all ordinary combustion, the result of the union
which takes place between the oxygen of the air and the
carbon in the combustible substance. Thus the carbon
of wood, oil, tallow, illuminating gas, etc., unites, in the
act of burning, with the oxygen of the air, and forms this
gas.

103. Common Mode of Obtaining Carbonic Anhydride. —
Put into a flask, Fig. 21, some small bits of chalk or marble,

Fig. 21.

and pour upon them some hydrochloric acid. The gas will
bubble up, and, forcing out the air before it, will pass through

* This gas used to be called carbonic acid, but chemists have decided
that it is not a true acid because it contains no hydrogen, hence it is now
known as carbonic anhydride.

CARBON AND CARBONIC ANHYDRIDE. 85

the bent tube, and so can be collected in jars in the pneu-
matic cistern. The explanation is this : The chalk and mar-
ble are two forms of the same substance, calcium carbon-
ate, which contains carbonic anhydride united to the oxide
of calcium, commonly called lime. Now the hydrochloric
acid decomposes the calcium carbonate, forming water, the
gaseous carbonic anhydride, and a new body, calcium chlo-
ride, which remains dissolved in the water. We do not see
the water formed, for it mixes with that in the flask ; nor
do we see the calcium chloride, for it is very soluble, and
remains in the water ; we can easily prove it is there, how-
ever, by evaporating the watery solution, when we will ob-
tain a white solid mass. The carbonic anhydride set free
is seen as it bubbles up through the water. Expressing
this in symbols, we write thus :

,, ., Hydrochloric Calcinm \xr^a Carbonic

Marble- ' acid. chloride. Water* anhydride.

CaCO3 + 2HC1 = CaCl3 + HsO + COa

Sodium carbonate, potassium carbonate, or any other car-
bonate, will serve equally well; so, also, sulphuric or nitric
acid may be used instead of hydrochloric.

104. Properties of Car-
bonic Anhydride. — This
gas is, like air, transparent
and without color. It has
a slightly acid and agreea-
ble taste. Its specific grav-
ity is 1.527 — that is, it is
about one and a half times
as heavy as air. Because it
is so much heavier than air
it can be collected by dis- Fis- 22-

placement, as it is termed. This is represented in Fig. 22.
The gas produced in the flask passes over in the tube and

CHEMISTRY.

displaces the air in the jar, pushing it upward as water
would oil. In order that it may do this quietly and ef-
fectually, the jar is so placed that the end of the tube is
near the bottom. So, also, we can pour this heavy gas from
one vessel into another, the same displacement of air taking
place in this case. The comparative weights of air and this
gas may be shown by the experiment represented in Fig.
23. An empty beaker — that is, a glass vessel full of air —
is first balanced on a scale; then carbonic anhydride is
poured into it, of course causing the beaker to go down.

Fig. 23.

105. Liquefaction and Solidification of Carbonic Anhydride.
— By an apparatus which subjects carbonic anhydride to
great pressure and cold this gas can be made fluid, and even
solid. As a solid it is a very peculiar substance, of a white
color, appearing much like dry snow. If held in the hand
it will destroy the skin like red-hot iron. The enormous
degree of pressure required to liquefy carbonic anhydride
is shown by the fact that the apparatus once exploded
in Paris, killing an assistant engaged in the experiment.

CARBON AND CARBONIC ANHYDRIDE.

106. Carbonic Anhydride not a Supporter of Combustion.
— A lighted taper introduced into a jar of this gas is extin-
guished as quickly as it would be if it were dipped into wa-
ter. This is simply because oxygen is absolutely necessary
to the continuance of the combustion. There is, it is true,
a sufficient quantity of oxygen in the carbonic anhydride,
but it is so thoroughly united with carbon that not a par-
ticle will quit it to unite with the carbon of the taper. A
very pretty way of showing that this gas is not a support-
er of combustion, and at the same time that it is heavier
than air, is to pour it, as seen in Fig. 24,

from one jar down into another in which
there is a lighted taper. Notwith-
standing that carbonic anhydride does
not support ordinary combustion, a few
substances having a great attraction for
oxygen will burn in it. A piece of
magnesium wire lighted and plunged
into a jar of the gas burns brilliantly,
taking the oxygen to itself and leaving
the carbon, which appears as a black
powder on the sides of the glass jar.
The decomposition of the carbonic anhydride is thus ex-
pressed :

Carbonic anhydride, Magnesium, Carbon, Magnesium oxide,
CO2 " + 2Mg C + 2MgO.

107. Effects of Carbonic Anhydride when Respired. — As it
is with nitrogen (§ 68), so with this gas — no animal can live
in it. But it destroys life not merely because, like nitrogen,
it shuts out oxygen from the blood in the lungs, but it acts
also as a positive poison. It produces an effect upon the sys-
tem similar to that of some narcotics. Nitrogen is constant-
ly taken into the lungs in large quantities without doing any
harm, for about four fifths of the air is nitrogen; but if car-

Fig. 24.

88 CHEMISTRY.

bonic anhydride be present in the air to the amount of one
tenth of the whole, its poisonous influence is very manifest.
And even when it is present only in the small quantity of
one or two per cent., bad effects show themselves on breath-
ing such an air for some little time. This gas is always
present in the atmosphere, but in so very small amount, as
you will see in the next chapter, that it produces no effect
as a poison.

108. Carbonic Acid in the Stomach. — While this gas is thus
a poison in the lungs, it is far otherwise in the stomach.
It produces an agreeable tonic effect there, as it is intro-
duced in effervescing drinks. The chemistry of these two
organs is different. The lungs can use oxygen chemically
to advantage ; while carbonic anhydride, which is a deadly
poison to the blood in the lungs, is beneficial in the stomach,
or at least is not injurious there.

109. Absorption of Carbonic Anhydride by Liquids. — Wa-
ter readily absorbs or dissolves about its own bulk of car-
bonic anhydride. By means of pressure it can be forced to
absorb more than this, the amount absorbed being in propor-
tion to the amount of pressure. Thus " soda-water " is com-
monly only water into which a large quantity of carbonic
anhydride has been forced, and the effervescence is owing to
the escape of this gas on taking off the pressure. The wa-
ters of many natural springs have considerable of this gas,
which, being generated under pressure in the earth, is there-
fore largely dissolved in the water, and, escaping from this
pressure as the water issues forth, causes an effervescence.
In beers and sparkling wines the carbonic anhydride is
made by the fermentation of the liquid as it is confined.
The bursting of bottles, which sometimes occurs, is pro-
duced by the generation of too large an amount of this gas,
or by its undue expansion by exposure to heat.

110. No True Carbonic Acid. — Carbonic anhydride is one

CARBON AND CARBONIC ANHYDRIDE. 89

of a class of bodies which unite with water to form acids.
You have learned in § 70 that nitric anhydride combines
with water, forming nitric acid ; thus N2O5-f-H2O=2HNO3.
But carbonic acid does not seem to have any definite ex-
istence ; the solution of CO2 in H2O may be regarded as
H2CO3, but the acid, if it exist at all, is decomposed at ordi-
nary temperatures, and quickly by boiling. Although car-
bonic acid has a doubtful existence, the carbonates derived
from it are a most important and numerous class of bodies.
From these carbonates the stronger acids, hydrochloric and
nitric, for example (or even acetic), do not drive out carbon-
ic acid, but carbonic anhydride, and the reaction is accom-
panied by the formation of water.

111. An Apparent Inconsistency. — Notwithstanding the
comparative weakness of carbonic acid, it adheres to its
union with some substances in spite of the most intense
heat. No degree of heat can drive off the carbonic acid
from potassium or sodium carbonates. Why this is we
know not, neither do we know why lime will take carbonic
acid away from potash. It would seem from this that car-
bonic acid has a stronger attraction for calcium than for
potassium, and yet, from the effect of heat upon carbonate
of lime, we should make exactly the opposite inference.
This is one of the apparent contradictions in affinity which
we can not explain, though the object which the Creator
had 'in making such differences is generally quite obvious.

112. Carbonic Oxide. — This is a gas which has but half
as much oxygen in it as carbonic anhydride, its formula be-
ing CO. It is a transparent colorless gas, and burns with
a beautiful blue flame, which you have often seen playing
over the surface of an anthracite fire as it kindles. The ex-
planation of its formation in this case is this : The closely
packed coal does not get sufficient oxygen from the air to
make carbonic anhydride, and so carbonic oxide is formed.

CHEMISTRY.

When, however, it emerges into the air, if the heat be suffi-
cient to inflame it, it takes from the air an additional quan-
tity of oxygen, and thus becomes carbonic anhydride.
When the whole body of the coal has become thoroughly
ignited, there is no more carbonic oxide formed, but only
carbonic anhydride, and hence there is no longer any flame.
When charcoal burns without a good supply of air, carbonic
oxide is produced, mingled with carbonic anhydride. This
gas is very poisonous, much more so than the carbonic an-
hydride. It is the mixture of the two gases that produces
such injurious effects when charcoal is burned in a chafing-
dish or an open furnace in a close room. We have known
similar effects produced when a damper of an anthracite coal-
stove was closed before the coal was well ignited, thus pre-
venting the carbonic oxide as it rises from being fully con-
verted into carbonic anhydride, and forcing some of both
of these gases out into the room.

113. Preparation of Carbonic Oxide. — This gas is common-
ly obtained from oxalic acid, the acid which gives the sour
taste to sorrel. This is composed of carbon, oxygen, and hy-
drogen, the same ingredients which we have in carbonic an-
hydride and
carbonic ox-
idephts water,
but in differ-
ent propor-
tions. The
chemist by
means of sul-
phuric acid
splits up, as
we may say,
the oxalic acid
into these two

CARBON AND CARBONIC ANHYDRIDE. 91

gases, and then, by taking away the carbonic anhydride, he
has the carbonic oxide by itself. The way in which he
does this is represented in Fig. 25 (p. 90). The oxalic acid
and the sulphuric acid are put into the flask, a, and on the
application of gentle heat the two gases, carbonic anhydride
and carbonic oxide, are produced, and pass over through the
tube into the bottle, b. Here there is a solution of potassium
hydrate; and as the gases pass into it the carbonic anhy-
dride unites with the potassium to form potassium carbon-
ate, and the carbonic oxide goes on alone into the jar, c, where
it is received for experiments.
114. Experiment. — If you
take a jar of this gas, Fig. 26,
and apply a lighted taper to
its mouth, the gas will burn
with a beautiful blue flame.
You can make the flame very
large by pouring water in, for
this forces the gas out rapidly.
As it burns it becomes carbonic
anhydride by taking oxygen
from the air. Fig. 20.

Carbonic oxide. Oxygen. yield Carbonic anhydride.
CO + O = CO2

QUESTIONS.

89. In what forms does carbon occur in nature ? — 90. How is charcoal
made? How illustrated?— 91. What is soot? What is said of imperfect
combustion ? Why do lamps smoke when the wick is too high ? — 92. How
is lampblack made ?— 93. What is bone-black ? What does it contain be-
sides charcoal ? What are some of its uses ?— 94. What is said of the pres-
ence of carbon in animal substances ? What is the chemical explanation
of the charring of flesh and skin ? What is said of overcooking meat ? —
(>."). What of the unchangeably of charcoal ? What of its preservative
power? What of its purifying and decolorizing powers? What other

92 CHEMISTRY.

effects does it produce ? — 9G. What is said of its absorbing power ? — 97.
How is this power to be explained? — 98. What is the difference between
anthracite and bituminous coal ? What is coke ? — 99. What is said of
black-lead? — 100. What of the diamond? — 101. What is meant by allo-
tropism ? Whence is the word derived ? — 102. State various cases in which
carbonic anhydride forms ? — 103. Describe and explain the common mode
of obtaining it? Write the equation given. — 104. What are the properties
of carbonic anhydride? How is it collected? Show it has weight. — 105.
What is said of converting gases into solids ? — 106. What effect does car-
bonic anhydride have on combustion? Illustrate this. — 107. What effect
on respiration ? How does it differ from nitrogen in this respect ? — 108.
How does carbonic anhydride act on the stomach?— 109. What is "soda-
water?" — 110. Why is there no true carbonic acid? — 111. State what is
said of an apparent inconsistency. — 112. What is the composition and nat-
ure of carbonic oxide? Where do we often see it burning? Explain its
production and burning in this case.— 113. How may it be prepared ? Why
will it burn when forced out of a jar by pouring in water ? Is it poisonous ?

CHAPTER VIII.

THE CHEMISTRY OP THE ATMOSPHERE.

115. Ingredients of the Atmosphere. — The air is a mixture
of three gases — oxygen, nitrogen, and carbonic anhydride.
The proportions of these ingredients are changed by cir-
cumstances, as you will soon see, and yet wherever the air
is free the proportions are always the same. About one
fifth of the air is oxygen, and
the remaining four fifths nitrogen.
The amount of carbonic acid is
very small, there being only 4 vol-
umes in every 10,000 volumes of
air. These proportions are repre-

sented to the eye in Fig. 27, the

largest square representing the nitrogen, the one at its side
the oxygen, and the smallest the carbonic anhydride.

THE CHEMISTRY OF THE ATMOSPHERE. 93

116. Quantity of Carbonic Anhydride in the Atmosphere. —
As the air encircling the earth is from 45 to 50 miles in
height, the quantity of carbonic acid, although proportion-
ably small, is really in the whole very great. It has been
estimated that there is seven tons' weight of this gas over
every acre of the earth's surface.

117. Chief Use of Nitrogen in the Air. — Oxygen, you have
seen, is a very active substance, supporting life and com-
bustion every where. It is so active that it needs to be
diluted in the air with four times its bulk of nitrogen gas.
If it were not thus diluted the world would be one vast
scene of continued conflagrations. Combustible substances
would take fire five times as easily as now, and when once
on fire it would be difficult to put them out. Iron would burn
as readily as wood now does. So also the operations of
life would be attended with five times the amount of heat
that they now are, and the tendency in every animal would
be to fever and inflammation. As oxygen is so stimulat-
ing, it has sometimes been used successfully in reviving
persons who have been drowned or suffocated. In such
cases, the more of this gas you can introduce into the lungs
for a little while the better. It is easily introduced by a
pipjB from a bladder filled with it. The remedy, however,
has seldom been used, because it is not at hand unless the
accident occur near the laboratory of a chemist.

118. Analysis of the Air. — We will describe two modes of analyz-
ing the air. The first is this : A certain volume of air is allowed to pass
slowly through a tube containing potassium hydrate. This has a very
strong attraction for one of the ingredients of the air, carbonic anhydride,
and has none for either the oxygen or nitrogen. It takes, therefore, the
carbonic anhydride, and the weight of the tube compared with its weight
before the experiment shows how much there is of this ingredient in the
volume of air employed. And now the air, thus deprived of its carbonic
anhydride, is made to pass through a tube filled with red-hot copper-filings.
The copper in this state attracts to itself the oxygen, but having no tendency

CIIEMISTEY.

to unite with the nitrogen, this passes on. The weight of this tube com-
pared with its weight before the experiment shows the amount of oxygen
in the air. Then subtracting the sum of the weights of the oxygen and
carbonic anhydride from the weight of the air examined, we have the
weight of the nitrogen.

Another mode which ascertains the proportionate volumes of the gases
as well as their weights is represented in Fig. 28. We
have here a tube, a b c, with a very minute opening at
a, a bulbous enlargement at 6, and its larger orifice, c,
made to fit air-tight in the top of the vessel, d. This
vessel is filled with mercury, and is graduated, as you
see. There is a cock at e, by which you can let the
mercury run out in as small a stream as you please.
Before fitting the tube, a ft c, to the vessel, it is filled
with loose cotton having bits of phosphorus scattered
in it, which, by warming, is spread over the fibres of
the cotton, and then the tube is accurately weighed.
Fitting the tube to the vessel, the cock, e, is now slight-
Fig. 23. ]y opened. AS the mercury flows slowly out, air pass-
es in at a to take its place, and in passing in it loses all of its oxygen, for
the phosphorus which it finds every where in the cotton takes it, forming
with it phosphorous anhydride, which remains in the cotton. We have
therefore nitrogen alone in the vessel, </, to take the place of the mercury
that runs out. When the volume of air employed is used up we close the
stop-cock at e. We can ascertain the volume of the nitrogen by the grad-
uation on the vessel, or more accurately by measuring the mercury which
has run out, for this, of course, exactly equals in bulk the nitrogen that
has taken its place. And from its volume we know its weight, because the
specific gravity of the gas has been ascertained by chemists. Then we find
the weight of the oxygen, by weighing the tube, and comparing its weight
with that which it had before the experiment ; and its volume is found from
its specific gravity. In this process you see that no account is taken of the
carbonic anhydride that is in the air. It is indeed so small in amount
(§ 115) that it would make but little difference in the result. There is al-
ways moisture in air, and this must be got rid of in order to make the an-
alysis accurate. This can be done by letting the air to be analyzed first
pass through a tube containing some substance which has a great affinity
for water, as the fused calcium chloride.

119. The Gases of the Air Obedient to Gravitation. — You

THE CHEMISTRY OF THE ATMOSPHERE. 95

learned in Part L, Chapter VI., that the atmosphere is held
as a robe around the earth by the attraction of gravitation.
Now it is with the gases as with solid and liquid substan-
ces— each is attracted to the earth in the proportion of its
specific gravity, the heaviest always taking the lowest posi-
tion— that is, getting the nearest to the earth. As mercury,
therefore, gets below water, and water below oil, so car-
bonic anhydride tends to get below oxygen, and oxygen
below nitrogen. See what would be the consequence if
this tendency were allowed to be carried out unopposed.
The carbonic anhydride would be accumulated beneath all
the oxygen and nitrogen, filling up all the valleys, and lying
along upon all the plains. And as this gas is a deadly poi-
son, no animal could live except upon elevated places, hills,
and mountains. But even there life would be short, and
attended with suffering ; for the nitrogen, being lighter than
oxygen, would be above it, so that animals would breathe
air that would be too stimulating, producing fevers and in-
flammations, and the extreme readiness with which every
thing would burn would occasion constant trouble.

120. Disposition of Gases to Mingle Together. — The in-
fluence of gravitation upon the gases is counteracted to a
great extent by a disposition which we find in gases to
mingle with each other, and thus the disastrous consequences
above alluded to are prevented. The following experiment
beautifully exhibits this diffusion, as it is termed : Let a bot-
tle (Fig. 29, p. 96) be filled with carbonic anhydride, having
a long tube fitted into the cork. At the upper end of the
tube place a bottle of hydrogen gas. As the carbonic an-
hydride is twenty-two times heavier than hydrogen, gravi-
tation tends strongly to keep the carbonic anhydride in the
lower bottle, the hydrogen of course remaining in the upper
one. But observe what happens. If the apparatus be left
to stand for an hour or two, it will be found that there is a

CHEMISTRY.

mixture of carbonic anhydride and hydrogen
in both bottles. A part of the carbonic anhy-
dride has gone up into the upper one, and a
part of the hydrogen has come down into the
lower. This is because, for some reason, there
is a strong disposition in the two gases to
mingle — strong enough to overcome the force
of gravity which tends to keep them separate.
And notice that in this case gravity must op-
erate very strongly indeed, for hydrogen is the
lightest of all substances, while carbonic an-
hydride is a very heavy gas. If, then, the dis-
position of gases to mingle overcomes so readi-
ly in this case the force of gravity, much more
readily will it do so when we have carbonic
anhydride with oxygen and nitrogen, as in the
air, where the difference in specific gravity is
so much less.

121. An Analogy- — There are some liquids
which have a disposition to mingle together in
the same way that gases do. Thus water min-
gles readily with alcohol, with the various
acids, etc. Alcohol is lighter than water, as
oxygen is lighter than carbonic anhydride, and
therefore, in obedience to gravitation, the water
inclines to keep below the alcohol, and would
do so if the disposition to mingle were not
stronger than the influence of gravity. In the case of oil
and water there is no disposition to mingle, and therefore
gravitation acts without any impediment, keeping the water
under the lighter oiL Agitation promotes the mingling of
both liquids and gases. Alcohol can be poured so quietly
upon water that it will remain for some little time. This can
be made obvious by having the alcohol colored. They will

THE CHEMISTRY OF THE ATMOSPHERE. 97

mingle intimately in a little while, but will do so at once if
shaken or stirred together. So it is with the gases. If in
the experiment in § 120 we shake the apparatus, the two
gases will not require an hour or two to mingle, as is the case
when they are still, but will do so at once. So the constant
motion of the atmosphere causes the gases that compose it
to mingle together most perfectly, so that the carbonic an-
hydride, heavy as it is, though constantly produced in vari-
ous ways, as you will soon see, at the bottom of the atmos-
pheric sea that envelops the earth, is readily diffused
throughout that sea though it be fifty miles high. This is
not done merely by violent winds, but equally — nay, more —
by the slighter motions which are every where and always
going on in the air.

122. Grotto del Cane. — There are some localities where the
carbonic anhydride does, however, lie along under the other
gases of the atmosphere. Such a locality is the Grotto del
Cane in Italy, so called because the layer of gas on the
floor of the grotto is only high enough to destroy dogs that
enter it — cane being the Italian for dog. There are two
reasons for this accumulation of carbonic anhydride. One
is, that the gas is produced at the locality in very great
abundance from some chemical operations in the earth;
that is, it is produced so rapidly that it is not all readily
diffused. Another is, that the locality is so sheltered as to
shut out in some good degree the common agitation of the
air.

123. Carbonic Anhydride in "Wells. — Sometimes this gas
is generated in wells and deep pits. When this is the case,
the diffusion must be slow, the air being confined, and so
prevented from being agitated. The gas will therefore ac-
cumulate, being mingled with air toward the mouth of the
well, but not so at the bottom. If a light then be lower-
ed, it will burn more and more dimly as it goes down, and

98 CHEMISTBY.

at length will go out. It is prudent always to use this test
before going down into a well or a pit. It is to be remem-
bered that if the light merely burn dimly on coming near
the bottom, there is danger, as you will understand by re-
calling what is said in § 107. There are various means re-
sorted to for ridding wells of this gas. One is to lower
into the well a pan of recently heated charcoal. This will
absorb into its pores 35 times its own bulk of this gas. An-
other is to burn a bundle of straw held to one side in the
well. The fire occasions an upward current in the gas, the
air going down on the other side to take its place. An-
other expedient is to bail out the gas with a bucket. This
can be done owing to its great specific gravity. The bucket
comes up to the mouth of the well apparently empty, but
actually full of the gas, as you might find by trying with a
lighted candle.

124. Fumes of Burning Charcoal. — If charcoal be burned
in a chafing-dish or open furnace in a close room, we have
the production of carbonic anhydride under circumstances
similar to those attending its production in a well. The air
in the room is comparatively still, and it is shut in. Life
has often been destroyed in this way. It is not carbonic
anhydride alone that does this, for, as stated in § 112, there
is produced with this more or less of a still more deadly
poison — carbonic oxide. The grand remedy, when we find
persons suffering from the fumes of burning charcoal, is to
open all the doors and windows, so that these gases may
be speedily diffused in the gases of the atmosphere, and the
reviving pure air from without be introduced into the lungs
of the sufferers.

125. Carbonic Anhydride Discharged from the Lungs. —
Every time that we breathe out we add to the carbonic an-
hydride in the atmosphere around us. That this gas is thus
discharged from the lungs can be proved by a very simple

THE CHEMISTRY OF THE ATMOSPHERE.

experiment. All that you require for it is a tumbler of lime-
water and a tube. If you breathe through the tube into the
lime-water it will soon become milky ; and if you let the
tumbler remain for a little time a fine powder will settle on
the bottom.* This is calcium carbonate, or chalk, formed
by the union of the carbonic anhy-
dride that came from your lungs with
the calcium hydrate, or lime-water.
The experiment can be made more
striking by using the simple appara-
tus represented in Fig. 30. You can
either draw in air through the tube
A, and thus let the air that goes into
your lungs come through the lime-
water, or you can force the air out of
your lungs through the lime-water

by the tube B. If you draw air through the lime-water, it
will take a very long time
to make it milky, because
there is so very little car-
bonic anhydride in the air
that you breathe in, as you
saw in § 115 ; but if you
throw the air from your
lungs into the lime-water
by the tube B, it will re-
quire only a few breaths
to make it decidedly
milky. The experiment
can be tried in still anoth-
er form, as represented in
Fig. 31. Here we have lime-water in both vessels. You

* When a substance thus foils as a sediment in any chemical process, it
is said to be precipitated, or is termed a precipitate.

100 CHEMISTRY.

see by the arrangement of the tubes that the air which is
breathed in must come through the vessel at the left hand,
while that which is breathed out must pass out through the
other. In this latter, of course, will be seen the milky ap-
pearance. The reaction in these experiments is thus ex-
pressed :
Lime-water, Carbonic anhydride, Calcium carbonate, Water,

CaH3O3 + COa CaC03 + H2O.

126. Ventilation. — The importance of free ventilation in
our apartments, and especially in lecture - rooms, public
halls, churches, etc., results from this production of carbon-
ic anhydride in our respiration. Wherever breathing is
going on there will be an accumulation of this gas, unless
there be suitable facilities for its diffusion in the atmos-
phere. Where there are only a few persons in a room, the
escape of this gas and the introduction of fresh air are ef-
fected sufficiently by means of the crevices here and there,
together with the occasional opening of the doors, and a
thorough ventilation once a day by opening the windows.
But when many are gathered together, other means are re-
quired. It costs something to have good air in thronged
places of concourse, not merely from the apparatus required,
but from the additional fuel necessary to maintain warmth
with the afflux of cold air from without. But it must be re-
membered that good air is a valuable commodity. The bad
influence of imperfect ventilation upon the health is not ap-
preciated because it is so gradual. Multitudes are constant-
ly undermining their health by sleeping in small chambers
with no proper means of ventilation, and occasionally tak-
ing an extra dose of the poison into their lungs in crowded
assemblies. While the community are struck with horror
at the sudden destruction of a few lives in such a case as
that of the Black Hole of Calcutta, the slow and constant
destruction of multitudes by the gradual introduction of

THE CHEMISTRY OF THE ATMOSPHERE* . , * ,101

the same poison — tbe poison of human breaths — -j
but little attention. The bad effects of impevfec
tion in places crowded with people do not depend alone on
the carbonic anhydride which accumulates, but are due in
large measure to a sort of effluvium which is given off from
the surface of the bodies of human beings. The precise nat-
ure of this miasmatic emanation is not known, but it is
shown to be largely organic by the fact that it is destroyed
by passing through a flame. The importance of ventilation
in rooms which are lighted by gas can not be too strongly
insisted upon. When we come to study the chemistry of
combustion, you will learn that carbonic anhydride and wa-
ter are the chief products of the burning gas. In fact, it is
calculated that even two candles of six to the pound pro-
duce as much carbonic anhydride per hour as would be gen-
erated by the respiration of a man of ordinary size.

127. Sources of Carbonic Anhydride in the Atmosphere. —
Carbonic anhydride is constantly poured forth into the at-
mosphere chiefly from three sources. 1. All fires and lights
produce it. 2. It is breathed out by all animals, from the
greatest to the smallest. 3. It is one of the products of de-
cay. The two first-named sources we have already noticed.
The third will be particularly noticed in another part of this
book. You will observe in regard to the first two that
while carbonic anhydride is formed the oxygen of the air is
at the same time diminished. Indeed, in ordinary combus-
tion the carbonic anhydride is made by a union of the oxy-
gen of the air with the carbon of the burning substance ;
and in respiration the lungs absorb oxygen from the air at
the same time that they give out carbonic anhydride.

128. Chemistry of Leaves. — We have stated in § 115 that
all free air is composed of the same proportions of oxygen
and nitrogen and carbonic anhydride; and yet there are
processes, as you saw in the last paragraph,which constantly

102 CHEMISTEY.

o the carbonic anhydride, and take from the oxygen
of tlieaiiv If there were nothing in opposition to these proc-
esses, there would of course be a gradual accumulation of
carbonic anhydride and lessening of the oxygen, rendering
the air very shortly incapable of maintaining life. But there
is provided an effectual counteracting process, and the seat
of it is in the leaves of plants and trees. Upon their out-
spread surfaces are countless pores which take in carbonic
anhydride, and at the same time discharge oxygen into the
air. Each of these pores is a real chemical laboratory, and
the number of them in a single leaf is immense. " On a
single square inch of the leaf of the common lilac," says
Johnston, " as many as 1 20,000 have been counted ; and the
rapidity with which they act is so great that a thin cur-
rent of air passing over the leaves of an actively growing
plant is almost immediately deprived by them of the car-
bonic anhydride it contains." Here, then, we have a sort
of chemical barter between lungs and fires on the one side,
and leaves on the other. Lungs and fires give carbonic an-
hydride to the leaves, and take from them oxygen in return.
In this operation leaves may be regarded as the lungs of
plants, having a chemistry, however, which is opposite to
that of the lungs of animals; and the carbon which is thus
introduced into the plant by the leaves is just as necessary
for its life and growth as the oxygen introduced into the
animal by its lungs is necessary for its life and growth.

129. Agency of the Sun. — It is only under the influence
of the sun's light that the chemistry of the leaves is carried
on. At night all the little laboratories cease their labor,
and then with the first gleams of the morning sun begin
again to pour out the oxygen and take in the carbon. Pro-
fessor Draper, of IsTew York, has made an interesting dis-
covery in regard to this influence of light. Of the several
colors which combined make up common white light, as you

THE CHEMISTRY OF THE ATMOSPHERE. 103

learned in Part I, Chapter XIV., he found that the yellow
ray is that portion which is the peculiar stimulus of the
chemistry of the leaves.

130. Priestley's Experiment. — This chemical action of the
leaves was first demonstrated by Priestley, the discoverer
of oxygen (§48). The exper-
iment by which he demon-
strated it is represented in

Fig. 32. Some green leaves
were placed in a bell-jar filled
with water well charged with
carbonic anhydride, and the
bell-jar was then inverted, as
you see, in a vessel of water.
Placing the apparatus in the Fig. 32.

sun, he saw bubbles of gas arise continually from the sur-
face of the leaves, and soon quite a quantity of this gas was
collected in the upper part of the bell-jar, forcing of course
a part of the water downward. This gas, on being tested,
was found to be oxygen, and an examination of the water
showed that the carbonic anhydride in it had disappeared.
The conclusion was clear, then, that the leaves had absorbed
carbonic anhydride, and at the same time had given out
oxygen.

131. Wonderful Balancing of the Chemistry of the Atmos-
phere.— Free air, we have told you, is everywhere composed
of its three ingredients in the same proportions. Climate
makes no difference. A gallon of air taken from the torrid
zone, where the rank vegetation is breathing out such quan-
tities of carbonic anhydride, and taking in from the air so
much of its oxygen, on being examined by the chemist,
shows the same proportions of nitrogen, oxygen, and car-
bonic anhydride that a gallon of air does which has been
taken from the icy regions of the North, where all vegeta-

104 CHEMISTRY.

tion is covered up in its wintry toinb. This is certainly
very wonderful when we consider the constant changes
which are going on in two of these ingredients, oxygen and
carbonic anhydride. An exact balance is maintained by the
Creator in the opposing chemical operations that we have
noticed, under circumstances in which there would appear
to be a liability to great and sudden variations. Leaves
might give out more oxygen than would be used by lungs
and fires, and then there would be an increase of the oxy-
gen of the air, rendering every thing more combustible,
and producing in animals fevers and inflammations. Or
more carbonic anhydride might issue from lungs and fires
and decaying matters than the leaves could absorb, and
then carbonic anhydride would accumulate in the air, de-
stroying life and extinguishing fires. But so accurately
does the Creator adjust these opposite chemical operations,
that production and consumption in the case of each sub-
stance exactly balance each other. World-wide are these
operations, and they are carried on under circumstances
which are not only various, but exceedingly variable ; but
an Almighty Power so controls them that the air, amid all
its changes, preserves those proportions which exactly adapt
it for the respiration of the myriads of animals, great and
small, that swarm on the earth's surface.

132. Nitrogen in the Chemistry of the Air. — Although ni-
trogen constitutes four fifths of the atmosphere, it is not at
all affected in most of the chemical changes which we have
noticed in the preceding paragraphs. The oxygen and car-
bonic anhydride of the air are continually changing, but not
so with the nitrogen. It goes into the lungs of the animal,
and comes out unchanged, though the oxygen that went in
with it is much lessened, and the carbonic anhydride is
much increased. So also in combustion, however hot may
be the fire, the nitrogen of the air comes out of it unchanged.

THE CHEMISTRY OP THE ATMOSPHERE. 105

It goes into the fire with the oxygen, but parts compa-
ny with that gas as it unites with the combustible sub-
stance. There is only one of the processes that we have men-
tioned, that of decay, which affects the quantity of nitrogen
in the air, and this it does very slowly. Nitrogen, there-
fore, may be considered, in comparison with oxygen and
carbonic anhydride, almost a fixed constituent of the air.
So far as we know as yet, the only way in which the nitro-
gen of the air is lessened is by the occasional formation of
nitric acid by electricity, the result of a union effected by
this agent between some of the oxygen and nitrogen of the
air in the presence of moisture. Only minute quantities of
this powerful acid are produced in this way, and chemists
have to use very delicate tests to detect it. It is useful in
the promotion of vegetation, as you will see in another part
of this book ; and it is supposed that this is the purpose of
its production, it being brought down by the rain as it falls,
to soak with it into the earth. But comparatively little of
the great bulk of the nitrogen can be used in this way, and
this small diminution is met by a supply from the processes
of decay.

133. Air in "Water. — There is always more or less air in
water. It is dissolved in it, for it is wholly hidden from
view among the particles of the water, and does not ap-
pear in bubbles except in the act of escaping
from its dissolved condition. This can be shown
by a very pretty experiment. Place a vessel of
water under the receiver of an air-pump, Fig.
33. You can see no air in it, and yet on ex-
hausting the air from the receiver multitudes of
small bubbles will arise, as represented. This Fig. 33.
is because the pressure is taken off from the surface of the
water, and the air, therefore, which is dissolved in it, ex-
pands and escapes, its particles huddling together in bub-

106 CHEMISTRY.

bles as they pass upward. So, also, if water be boiled, the
air that is dissolved in it escapes, being expanded by the
heat, and rising with the steam.

134. Composition of the Air that is in Water.— The ail-
that is dissolved in water is not of the same composition
with the atmosphere. The ingredients are the same, but
the proportions are different. There is a larger proportion
of oxygen in the air that is in water. The reason is that
oxygen is more soluble in water than nitrogen, and there-
fore water absorbs or dissolves more of the former from the
air than it does of the latter. Here is a marked and ob-
vious provision of Providence for the benefit of the inhab-
itants of the waters. As fishes and other animals that live
in the water get so little air compared with animals that
live out of the water, it is necessary that the air they breathe
should have a larger proportion of that ingredient which is
essential to the purposes of life.

135. Experiment with Snow. — What we have just stated
furnishes the explanation of an experiment which was for-
merly a great puzzle to philosophers. The experiment is
this : Let a glass bottle be filled with snow, and, corking it
tightly, let the snow melt. You will, of course, have in the
bottle water and the air which escaped from the snow as it
melted. On examining this air it will be found to contain
much less oxygen than common air does; and yet the air
which was in the interstices of the snow was common air
which became mingled with it as it fell. The question is,
what has become of the missing oxygen. The answer is
easy. A part of the air in the snow has been dissolved in
the water; but since water dissolves a larger proportionate
quantity of the oxygen of the air than of its nitrogen, the
air which is not dissolved will contain a larger proportion
of nitrogen.

1 36. Oxygen Supplied to Fishes by Water-Plants. — Fishes

THE CHEMISTRY OF THE ATMOSPHERE. 107

are not wholly dependent upon the air for their oxygen.
Plants that grow under water continually discharge oxygen
from their leaves, just as is done from leaves in the air; and
there is the same chemical commerce between animals and
plants under water that there is in the air, though it is not
so extensive. The fishes and other animals give carbonic
anhydride to the plants, and take from them oxygen in re-
turn. The oxygen can often be seen gathered in globules
on the surface of water-plants, waiting to be dissolved by
the water. A suitable regard to this exchange between
plants and animals under water suggests the presence of
water-plants in an aquarium as a necessary part of the ap-
paratus, they getting from the lungs of the animals carbon
for their growth, and breathing back to them from the pores
of their leaves oxygen in return.

137. "Water in the Air. — As water dissolves air, so air dis-
solves water when the latter is in a gaseous state. There
is always water in the atmosphere, even when it seems to
be perfectly dry. It is invisible because it is in its vapor-
ous form, and so its particles are intimately mingled with
the gaseous particles of the air. This solution of water in
air is like the solution of some solids in water. If alum, for
example, be dissolved in water, it disappears, and so does
the water dissolved in air. And as warm water will dis-
solve more alum than cold water, so will warm air dissolve
more water than cold air. There is therefore more water
in the air in summer than in winter. Sometimes there is as
much as one gallon of water to every sixty gallons of the
air. The analogy can be traced farther. If warm air be
chilled in any way, it can not hold as much water in solu-
tion, and some of it, therefore, is separated from the air — that
is, taken out from that intimate union which constitutes so-
lution. This separated part of the water may appear as fog
or cloud, or be deposited as dew or frost, or fall as rain,

108 CHEMISTRY.

snow, or hail. So, likewise, if you dissolve as much as pos-
sible of alum in hot water, and then let it cool, the water
can not then hold as much alum in solution, and some of it
will be separated and deposited.

138. How the Air is Freed from Impurities. — Impurities
that rise in the air and become mingled with it become dif-
fused widely, as the air is so continually in motion. If they
were not thus diluted and dissipated they would do great
harm to health, especially in cities. The falling rain is the
chief means of ridding the air of them. Water is here, as
every where, the grand purifier. The shower-bath which
the air receives whenever it rains brings down most of these
impurities, as it does the nitric acid formed by the lightning
(§ 132), and mingles them with the earth, where they are
used in vegetation.

139. Proofs that the Air is a Mixture. — You are now pre-
pared to appreciate fully the proofs that air is a mixture. It
was the prevalent doctrine, even for a long time after Priest-
ley and Scheele had by their discoveries placed chemistry
upon a rational basis, that air is a compound. This opinion
was based chiefly upon the fact that the proportions of the
ingredients are always the same in all free air. Then, be-
sides, it was thought that if the air were merely a mixture
of the gases composing it, they would be very prone to obey
the influence of gravity, the oxygen taking its place under
the nitrogen, and the carbonic anhydride under the oxygen.
The disposition of gases to mingle together (§ 120) had not
then been demonstrated and illustrated, or this ground of the
doctrine would have been abandoned. At the present time
all chemists regard the air as a mixture, and the proofs are
briefly these : The ingredients of the air are separated from
each other too easily to warrant the belief that it is a chem-
ical compound. Then again, though the composition of all
free air is always the same, the proportions of the ingredients

THE CHEMISTRY OF THE ATMOSPHERE. 109

are varied under certain restricting circumstances. For ex-
ample, the air in a close room where there are many per-
sons has its oxygen lessened, and its carbonic anhydride in-
creased, and still it is air — a mixture, but with the propor-
tions of its ingredients altered. So, also, when air is dis-
solved in water, the proportions of its ingredients are not
the same as before it was dissolved (§ 134). Then, again, the
qualities of air are not wholly different from its constituents,
as is the case with compounds (§ 85), but they are midway be-
tween those of oxygen and nitrogen. And, lastly, if we min-
gle these two gases in the same proportions that occur in air,
the mixture has nearly all the properties of the atmosphere.

QUESTIONS'.

115. What are the ingredients of the atmosphere, and in what propor-
tions ? — 116. How large is the total amount of carbonic anhydride in the
air? — 117. What is the chief use of nitrogen in the air? What would
happen if all the air were oxygen ? — 118. Explain the two methods of ana-
lyzing the air. How is the moisture removed in the second operation ? —
119. What is said of the influence of gravitation on gases? What would
result if there were nothing tending to counteract this ? — 120. Describe
an experiment illustrating diffusion. — 121. State fully the analogy between
liquids and gases in regard to mingling. — 122. What is said of the Grotto
del Cane ? — 123. What of the accumulation of carbonic anhydride in wells?
How can it be removed ? — 124. What two gases are produced by the burning
of charcoal ? Which is the most destructive ? What is to be done when
persons are suffering from the fumes of charcoal? — 125. How can you show
that carbonic anhydride is discharged from the lungs ? What is a precipi-
tate? Explain the experiments to illustrate this exhalation. — 126. Why
is the bad influence of poor ventilation not commonly appreciated? Are
the bad effects of imperfect ventilation due to the carbonic anhydride sole-
ly?— 127. What are the sources of carbonic anhydride in the air ? — 128. De-
scribe the chemistry of the leaves.— 129. What influence has the sun upon
the chemistry of leaves ?— 130. State Priestley's experiment.— 131. State in
full what is said of the wonderful balancing power of the chemistry of the
atmosphere.— 132. How is nitrogen in contrast with the other ingredients

110 CHEMISTRY.

of the air in respiration ? How in contrast with oxygen in combustion ?
How is the nitrogen of the air lessened ? What is said of the nitric acid
formed in the air? — 133. How can you show that air is contained in water?
— 134. What is said of the composition of the air that is in the water? —
135. Describe the experiment with snow. — 13G. What is said of the chem-
ical exchange between plants and animals in water? — 137. What is said
of the moisture in the air ? Trace the analogy between this and the solu-
tion of solids in a liquid. — 138. What is said of the diffusion of impurities
in the air? How is it purified from them? — 139. For what reasons was
the air formerly thought to be a compound ? What are the proofs that it
is a mixture ?

CHAPTER IX.

THE CHEMISTRY OF WATER. — HYDROGEN.

140. Constituents of Water. — "Water, though a fluid, is
composed of two gaseous elements. With the properties
of one of these, oxygen, you have already become well ac-
quainted. The other gas is hydrogen, so called because
when chemically united with oxygen it produces water, the
name being derived from two Greek words — hudor, water,

and gennao, I form. In form-
ing water, two volumes of
hydrogen unite with one vol-
ume of oxygen, or two parts
2 vols. + 1 vol. = 2 vols. ^7 weight of the former with

Oxygen 88.9 per cent. Sixtee" PartS ** Wci?ht °f

Hydrogen 11.1 «* " ™ie wtjMT. All this is pre-

Water Tooo sented to the eye in the di-

PI& ^ agram, Fig. 34 — the spaces

representing the proportions

of the two ingredients in bulk, and the figures their propor-
tionate weights. You will notice that owing to the con-
traction which takes place, two volumes of water result

H2O 18

THE CHEMISTRY OF WATER. — HYDROGEN.

Ill

from the combination of three volumes of the component
gases.

141. Decomposition of Water. — Water may be decom-
posed—that is, resolved into the two gases of which it is
made — in a variety of ways, both physical and chemical.
We will first describe a method in which electricity is used,
and then give you some chemical methods.

A current of electricity from a galvanic battery, gener-
ated as explained in Part I, decomposes water very readily.
By employing the apparatus, Fig. 35, the gases may be col-

rig. 35.

lected separately. Through the bottom of a glass dish are
introduced, water-tight, two platinum wires, a c and a b.
Over each of these wires a tube, with its upper end closed,
is placed. The tubes and the dish are filled with water,
which is slightly acidulated in order to make it a bet-
ter conductor. If now the wire a c be connected with
the positive pole of a battery, and the wire a b with its
negative pole, some of the water will be decomposed, and
the resulting gases, oxygen and hydrogen, will collect in
the tubes e and / respectively, driving the water down

112 CHEMISTRY.

in them. You see that there is twice as much gas in /, the
tube containing the hydrogen, as there is in e, the tube con-
taining the oxygen; this confirms what we have just stated,
viz., that two volumes of hydrogen unite with one volume of
oxygen. If, when there is a sufficient amount of the gases
collected, you cautiously remove the tube e, closing its mouth
with your finger, and, turning it upside down, introduce into
it a slip of wood with a spark on the end, the wood will burst
into a flame — showing that the gas is oxygen. If now you
remove/, and apply a light to its mouth, the gas will rush
out, burning as it comes. Or, if you mingle with it an equal
quantity of atmospheric air, and then apply the light, you
will have an explosion. These phenomena are characteris-
tic of hydrogen, as you will presently learn.

The above experiment may be varied. Thus, let P
and N, Fig. 36, be tubes with their lower ends open,
and having wires of platinum passing through their
sealed upper ends. The wine-glasses, the curved tube
connecting them, and the two tubes, P and N, are filled
with acidulated water. On connecting P with the pos-
itive pole, and N with the negative, oxygen gas will
collect in P and hydrogen in N, and as readily as they
would if the tubes were in one vessel.

This physical method of decomposing water by a
current of electricity has received the name of electrolysis of water. Many
substances, particularly liquids, both inorganic and organic, may be decom-
posed by submitting them to electrolysis.

142. Mode of Obtaining Hydrogen. — Hydrogen can be ob-
tained by a process represented in Fig. 37 (p. 113). A gun-
barrel filled with clean iron turnings is placed across the
fire in a furnace. Steam, or more properly water-gas, is
made to pass through the barrel by means of a glass tube,
which conducts from a flask where water is boiling by means
of a gas-burner. The water-gas — that is, the water in the
form of vapor — passing among the iron turnings, is decom-

THE CHEMISTRY OF WATEE. — HYDROGEN.

113

Fig. 37.

posed by reason of the attraction of oxygen and iron for
each other. The oxygen of the water unites with the iron,
forming an oxide of iron. This leaves the other constitu-
ent of water, hydrogen, to pass on alone. It issues at the
other end of the barrel, and is conducted off by a bent tube,
to be collected in jars in the usual manner. This reac-
tion, expressed in the symbolic language of chemistry, is
written thus : 4H2O+Fe3=Fe3O4+8H. Hydrogen would
not be formed if water were merely poured through the
barrel. Neither would it if steam pass through, unless the
iron turnings be heated to a high degree. You see, then,
that a very great heat is required to make the iron decom-
pose the water, or, in other words, to make the oxygen quit
the hydrogen and unite with the iron. The object of hav-
ing iron turnings in the barrel is to allow the steam to come
in contact with a very extensive surface of iron. Bundles
of knitting-needles are sometimes used, and, instead of a
gun -barrel, a piece of iron gas -pipe. If the barrel were
empty, but little of the steam would be decomposed. As it
is, some steam may pass through unchanged ; but if it does
it is condensed in the water of the pneumatic trough, and
does not pass on with the hydrogen into the receiving jar.

114 CHEMISTRY.

We have in this experiment an illustration of both decomposition and
composition produced by the agency of heat. The water is decomposed,
its two elements, oxygen and hydrogen, being separated from each other ;
and there is composition, for the oxygen, as it leaves the hydrogen, unites
with the iron to make an oxide of that metal. The oxidation, which is
produced slowly in ordinary temperatures, is here produced quickly by heat.
It is a curious fact that precisely the reverse of this action may be made to
occur. If hydrogen gas be passed through a gun-barrel heated red-hot, and
containing oxide of iron, it will take the oxygen from the iron, forming wa-
ter, which will issue in steam from the barrel. In the former experiment
you have steam entering one end of the barrel and hydrogen issuing from
the other, and the iron in the barrel is oxidized ; in the latter you have hy-
drogen entering at one end, and steam discharged from the other, and the
oxide of iron in the barrel is deoxidized.

143. A Better Method. — You can obtain hydrogen from
water without having this great amount of heat applied,
and therefore with a less cumbrous apparatus, as seen in
Some bits of zinc or of iron are put in water in a

Fig. 38.

bottle, and sulphuric acid is poured in through the funnel
tube. An effervescence at once appears, occasioned by the
gas as it is produced from the water ; and you must be care-
ful not to pour in too much, lest the heat generated by mix-
ing the strong acid with the water crack the glass bottle,

THE CHEMISTRY OF WATER. — HYDROGEN. 115

and lest effervescence be violent. When the effervescence
slackens, more of the acid can be added. The gas passes
out through the tube, which, like the funnel tube, is fitted
in the cork, and is received in the jar standing in the pneu-
matic trough. The first portion of the gas must be al-
lowed to escape, as it has the air which is in the flask and
tube mingled with it, constituting an explosive mixture.
The explanation of the process is this: The acid makes the
oxygen of the water unite with the metal to form an oxide,
and so the hydrogen is set free and rises in effervescence.
This union does, indeed, take place when there is no acid
present, but it is very slow ; while the acid causes a rapid
union, and therefore sets free at once a large amount of hy-
drogen. But this is not all. The acid not only turns the
metal into an oxide, but it unites with that oxide, making
with it a substance called zinc sulphate, which dissolves in
the water. Observe the effect of this on the production of
the gas. If the acid merely occasioned the formation of an
oxide, this would make an insoluble coating over the metal,
preventing the acid from acting farther upon it, and so,
though there would be considerable gas formed at the first,
very soon the process would stop. But as it is, the acid
takes away the oxide as fast as it is formed, so that a fresh
surface of the metal is constantly present for it to act upon.
Sometimes a different sort of explanation is given; and the
hydrogen is considered to come from the acid rather than
from the water ; the zinc replaces the hydrogen of the sul-
phuric acid, forming zinc sulphate, and the hydrogen is set
free. This way of regarding the matter is shown in the
following equation :

Zinc. Sulphuric acid. Zinc sulphate. Hydrogen.

Zn + HaS04 ZnS04 + H2

144. Forming Water by Uniting Oxygen and Hydrogen. —
As the oxygen and hydrogen that constitute water may be

116 CHEMISTRY.

separated from each other, as just described, so, on the other
hand, water may be formed by uniting these gases. But
they will not unite by merely being mixed together. Some
force must be brought to bear on them to effect their union.
Heat will do it when sufficient to produce combustion. Ac-
cordingly, when combustion takes place where there is hy-
drogen, the oxygen unites with the hydrogen, forming wa-
ter; and this occurs very generally in most cases of what
we call combustion, as you will see in the next chapter.
Electricity, also, will do it. If a charge of electricity be
passed through a mixture of the two gases, they will unite,
and water will be formed.

To show this experiment an apparatus called a Eudiometer is employed.
It consists of a strong- glass vessel containing two platinum wires soldered
into the glass and nearly touching at their points. The glass vessel is filled
with two volumes of hydrogen and one volume of oxygen, and closed tightly
with a well-fitting stopper. An electric spark is then passed between the
wires, so that as it jumps from one end of a wire through the mixed gases to
the other wire, the gases are intensely heated and unite with explosive vio-
lence. If the eudiometer is cooled and opened under water, water will rush
in to fill the space left by the condensation of the gases. If, however, the
eudiometer is placed in a vessel heated by steam to 100° C., the water-gas
will be found to occupy two thirds of the volume of the mixed gases, pro-
vided they were measured at the same temperature and pressure. This
confirms the statement already made that two volumes of hydrogen com-
bine with one volume of oxygen to form two volumes of water-gas. (See

= H2 O or H2+O = H2O.

145. Specific Gravity of Hydrogen. — In Fig. 39 is repre-
sented the weight or gravity of hydrogen as compared
with the gravity of some other substances. Platinum is the
heaviest of all substances ; hydrogen, on the other hand, is
the lightest substance known. In the figure are represented

THE CHEMISTRY OF WATER. — HYDROGEN.

117

Hydrogen.

Platinum.

equal quantities, by
weight, of these two
substances, as well as
of water and air. Air
is about fourteen and
a half times as heavy
as hydrogen, water
more than eleven
thousand times, and
platinum nearly a
quarter of a million
times. Here is a tab-
ular statement of the relative gravities of these substances:

Fig. 39.

Air

14.4

Water

11163

773

239921

16626

21.5

In the first column, taking hydrogen as 1, the proportionate
weights of the other substances are given. In the second
column we call air 1, and in the third water.

146. Hydrogen and Carbonic Anhydride Contrasted. — Car-
bonic anhydride'is twenty-two times as heavy as hydrogen.
It is so much heavier than air that you can set a jar of it
down with its mouth open, and the gas will remain in it for
some time. Its weight tends to keep it in the jar, and it
will only gradually escape by its disposition to mingle with
other gases, as noticed in § 120. But if you set down a jar
of hydrogen in this way, it rises out of the jar at once,
precisely as oil would rise out of a jar plunged into wa-
ter with its mouth upward. In order to keep the hydro-
gen in the jar it must be held with its mouth downward.
We can follow the contrast farther. Carbonic anhydride

118 CHEMISTRY.

is so much heavier than air that it can be poured down-
ward from one vessel into another. But if you wish to
transfer hydrogen from one vessel to another, you must, as
we may say, pour it upward, as repre-
sented in Fig. 40. Here the lower ves-
sel contains the hydrogen. This be-
ing only one fourteenth of the weight
of air, goes quickly upward into the
upper vessel, forcing the air that is in
it downward. You can not see the
gas pass, because it is invisible ; but
a similar phenomenon can be made visible by emptying a
vessel of oil into another under water. Here the lighter oil
passes upward into the upper vessel, forcing the water down
out of it, just as the hydrogen does to the air.

147. Ballooning. — Hydrogen gas has been much used in
balloons. Montgolfier, a Frenchman, who was the first to
make an ascent with a balloon, inflated it with heated air.
This was in 1783, thirteen years after the discovery of hy-
drogen by Cavendish. Hydrogen is much better than heat-
ed air for inflation on two accounts — first, because it is so
much lighter ; and, secondly, because it retains its lightness,
while the heated air becomes heavy by being cooled as the
balloon is on its passage. Hydrogen was used in ballooning
the same year that Montgolfier made his ascent, and yet
Montgolfier balloons continued to be used to some extent
even as late as 1812. Even so late as 1847, strange as it
may seem, an ascent was made with one of these balloons
by a Frenchman, Godard, who fell into the Seine, but was
saved from drowning. At the present time gas balloons
alone are used, and illuminating gas, a mixture of hydro-
carbons, is employed for inflation, as this, though heavier
than pure hydrogen, is sufficiently light, and can always be
readily obtained from neighboring gas-pipes. Ascending

THE CHEMISTRY OF WATER. — HYDROGEN.

119

in balloons is exceedingly dangerous. We have seen a list of
the most famous aeronauts, and of the whole forty-one there
were fourteen killed, and various injuries were received by
many of the others. Plainly, then, an ascent ought never
to be made for mere show, and the only useful purpose that
ballooning has yet subserved is for observation in time of
war. During the war of 1871 between France and Prussia,
both armies made use of balloons to a considerable extent.
The people shut up in Paris sent out balloons nearly every
day.

148. Combustibility of Hydrogen. — While oxygen is the
grand supporter of combustion, hydrogen

itself burns. The flame is very pale, and .
attended with so little light as to be al-
most invisible on a bright day. In Fig.
41 you have represented hydrogen burn-
ing from what has been called the "phi-
losopher's candle." The materials for
the production of hydrogen gas, noticed in
§ 143, are placed in the bottle, which has
a tube fastened into the cork. Here, too,
carelessness may occasion an explosion.
The air must be expelled from the bottle
before the "candle" is lighted.

149. Hydrogen Bubbles. — The lightness

and combustibility of hydrogen may both be very prettily

exhibited by having a tobacco-pipe, b, Fig.

42, attached to the stop-cock, a, of an India-

rubber gas-bag filled with hydrogen. If

the pipe be introduced into soap-suds while

the stop -cock is opened and the bag is

pressed upon, soap-bubbles will rise in the

air, which, on being touched with a light, quickly burn with

a slight explosion, occasioning a popping sound.

Fig. 41.

120

CHEMISTRY.

Fig. 43.

150. Hydrogen not a Supporter of Combustion. — Though

hydrogen burns, it does not support combustion.
This may be shown by the following experiment :
Let there be introduced into the bell-jar, a, Fig. 43,
filled with hydrogen, a lighted taper. It will set
the hydrogen on fire at the mouth of the bell-jar,
but will itself go out as soon as it is immersed in
the gas. If you take it immediately out, it will be
relighted as it passes through the burning hydrogen at the
mouth of the glass jar, and the putting out and relighting
may be repeated several times in succession.

151. Production of Musical Sounds. — If you let a "philo-
sophical candle " burn in a tube, as seen in Fig. 44, mu-
sical sounds will be
heard, which will
be varied in their
note by the size of
the tube, and by
raising or lowering
it. The sound is ow-
ing to the vibra-
tion of the air con-
fined in the tube,
caused by the burn-
ing of the hydrogen.
This experiment is
not peculiar to hy-
drogen, but may be
made with a small jet
of coal gas. In the
first -named form it
is sometimes called

" Ha rmonica che-

Fig.44. mica"

THE CHEMISTEY OF WATEE. — IIYDEOGEX.

121

152. Breathing Hydrogen. — This gas can not be breathed
alone for any time, simply because life can not be con-
tinued without oxygen. But oxygen and hydrogen can
be breathed together with impunity, showing that hy-
drogen does not act as a poison when introduced into
the lungs. It is in this respect like nitrogen, and un-
like carbonic anhydride. Of course it can be breathed
with air, though not in so large proportion as with pure
oxygen.

153. Sounds in Hydrogen. — If a bell be rung in a jar
of hydrogen gas the sound can be

scarcely heard, because the gas is so
very rare a medium. It is for the
same reason that sounds are so faint
in the attenuated air on the tops of
very high mountains. So, also, if one
speaks immediately after breathing in
a mixture of hydrogen with oxygen
or air, his voice has a small, squeaking
sound. If the common speaking toy
be made to utter its voice in a jar
of hydrogen, as represented in Fig. 45,
the sound is very laughable.

154. Illuminating Gas. — In the common gas that we burn
we have a mixture of hydrocarbons, or compounds of hy-
drogen with carbon. There are two forms of this combi-
nation, or rather two distinct compounds. They are marsh
gas and olefiant gas, sometimes called the light and the
heavy carburetted hydrogen. There is exactly twice as
much carbon in the latter as in the former — one being CH4,
and the latter C2H4. The light carburetted hydrogen is the
fire-damp of coal-mines, which by its explosions destroyed
so many lives before Sir Humphrey Davy invented his
safety-lamp (Part I). It is also one of the products when

Fig. 45.

J22

CHEMISTRY.

vegetable matter decays under water, and hence its name,
marsh gas. You can very easily secure some of this gas
from the mud of a pond in the way shown in Fig. 46.

A bottle filled with wa-
ter is held inverted in
the pond with a funnel
in its mouth, and the
mud is disturbed under-
neath with a stick. When
the bottle becomes filled
with gas, close it with a
cork before removing it
from the water. There
are two gases together in
the bottle — carburetted
hydrogen and carbonic
anhydride. In order to get rid of the latter you must intro-
duce something which will combine with it, and not with the
carburetted hydrogen. It is done in this way : Pour a little
water into the bottle, and then introduce a piece of quick-
lime or of potassium hydrate,
and,quickly returning the cork,
shake the bottle a few minutes.
The carbonic anhydride is thus
made to unite with the calcium
or potassium, forming a carbon-
ate. Remove now the cork from
the bottle, with its mouth under
water. Some of the water will
go up into the bottle, to take the
place of the carbonic anhydride
Fig. 4T. which has disappeared. If now

you apply a lighted match to the mouth of the bottle, the gas
will take fire and burn with a blue flame. By pouring water,

THE CHEMISTRY OP WATEE. — HYDROGEN. 123

Fig. 47, at the same time into the bottle you expel the gas,
and thus keep up a brisk burning till the gas is all consumed.
In the common illuminating gas we have a mixture of olefi-
ant and marsh gas. The brightness of the flame is owing
to the greater quantity of carbon which is in the former, as
will be noticed more particularly 'in the next chapter.

155. Hydrogen Peroxide, H2O2. — Water was for a long time sup-
posed to be the only compound of oxygen and hydrogen. It is really the only
compound existing in nature ; but another can be produced by a chemical
process that has exactly twice as much oxygen in it as water. It is called
hydrogen peroxide, water being considered as an oxide. This substance
has very peculiar qualities, differing greatly from those of water. It is a sir-
upy, colorless, transparent liquid, having a slight odor, and a very nau-
seous and astringent taste. The quality in which it differs most from
water is that no degree of cold can freeze it. The contact of carbon will
decompose it instantly, often with an explosion and a flash of light.
Heat also decomposes it, producing an effervescence. This singular com-
pound seems to have no tendency to combine with any other substance,
and as yet has not been found to be of any value, but a mere chemical
curiosity.

156. Nature of Hydrogen. — It is a common supposition
among chemists that hydrogen is a metal having two ox-
ides, water and hydrogen peroxide. At first thought it
seems impossible that this is true of the lightest substance
in the world. Metals we are accustomed to think of as be-
ing heavy and solid. But, as you will see in a future chap-
ter, there are some metals sufficiently light to float on wa-
ter. Besides, we have one metal, mercury, that is a liquid,
and why should there not as well be a gaseous metal ? And,
farther, the metal mercury is in a state of invisible vapor in
the space over the metal in every thermometer and barome-
ter. If a metal, then, can thus be gaseous under certain
circumstances, what difficulty is there in conceiving one to
be so under all ordinary circumstances ? Moreover, a com-
pound of the very rare metal palladium with hydrogen has

124 CHEMISTEY.

been made, which acts much like a true alloy, and confirms
the view that hydrogen is a metal.

157. How Compounds and Mixtures Differ. — We have al-
ready stated the proofs that air is a mixture. Having now
become acquainted with the composition of water, you readi-
ly see, in regard to air and water, the two grand distinctions
between compounds and mixtures. 1. A chemical compound
differs wholly in its character from either of its constituents,
while a mixture does not. Water is entirely unlike either
the oxygen or the hydrogen that compose it ; but air is in
many respects like the oxygen and nitrogen, which are its
chief ingredients, having a mixture, as we may say, of the
qualities of the two gases. So, also, is the difference strik-
ingly illustrated by contrasting air with nitric oxide, as has
been shown in § 85. 2. A compound always contains pre-
cisely the same proportions of its elements ; but in a mixt-
ure the proportions may be made to vary more or less.
Thus water always contains the same proportions of oxy-
gen and hydrogen ; but you can take away a part of the
oxygen of the air and increase its carbonic anhydride
(§ 126), and it will be air still, though not good and health-
ful.

158. Water as a Chemical Agent.— Though water is a
very mild substance, and not powerful like the acids, it has
a great deal to do with the chemical operations every where
going on, as you will see as we proceed with the investiga-
tion of other subjects. It is the common solvent of the
world, dissolving, as you have already seen, gases, as well as
liquids and solids. It unites, as you will learn in § 159, chem-
ically with many substances, being incorporated intimately
with them as water. Some solids can not exist in a crystal-
line form without having a certain amount of water in them,
and this is said to be their water of crystallization. Then
in the vegetable kingdom water is .decomposed to a consid-

TUE CUEMISTRY OF WATEK. HYDROGEN. 125

erable extent, and its elements arc used in the formation of
almost every variety of vegetable substance.

159. "Water of Crystallization. — In the crystals of many substan-
ces there is considerable water. This is the case with crystals of sulphate
of lime, commonly called plaster of Paris. A little over one fifth by weight
of these crystals is water. They are perfectly dry, because the water is com-
bined with the substance making a part of the solid. The water is in this
case really solidified without freezing. Not only is it a part of the crystals,
but they could not be formed without it. Drive out the water by heat, and
the crystals fall to pieces, and you have the plaster of Paris in powder. This
water, thus essential to the existence of the crystals of this substance, is
called its water of crystallization. Burned alum is alum deprived of this
water by heat, and therefore its crystalline arrangement is lost. The
amount of water required for crystallization varies in different substances.
The crystals of Epsom salts, so familiar to you, are fully half water. You
may perhaps have noticed that sometimes some of the crystals of this salt
have changed into a white powder. This is 'because some of the water of
crystallization has escaped into the air. Any crystalline substance which
is apt to have this occur is said to effloresce. "When a substance has a tend-
ency to absorb water from the air and run to liquid, it is said to deliquesce.
Do not confound these terms.

Water of crystallization is usually written separately in formulae, because
it seems to be less closely connected with the body than are the atoms com-
posing it. Thus crystallized gypsum is CaSO4+2H2O, and anhydrous
gypsum is simply CaSO4. Epsom salts is MgSO4+7H2O.

ICO. Ammonia. — Hydrogen and nitrogen united in the
proportion of three atoms of the former to one of the latter
form a colorless, alkaline, pungent gas called ammonia. Its
formula is therefore NH3. It is one of the products of the
decomposition of both animal and vegetable substances.
You therefore perceive its pungent smell in the stable ; and
it is also emitted from guano, the bird-manure which has for
many years been imported into this country from certain
islands. Ammonia is obtained for the purposes of commerce
as a secondary product in the distillation of coal. The ni-
trogen of the coal unites with the hydrogen to form ammo-

126 CHEMISTRY.

nia, which distills over and condenses in the water used to
wash the coal gas. It can also be obtained by distilling
animal substances, especially bones. It received the name
hartshorn from having been formerly obtained by the dis-
tillation of the horns of harts and deer. The name ammo-
nia comes from sal ammoniac ; and this was so called be-
cause it was first manufactured near the temple of Jupiter
Ammon by the distillation of camels' manure.

161. The Production of Ammonia Explained. — If you intro-
duce into a vessel the two gases of which ammonia is com-
posed, you can not in any way make them unite to form
this substance. You may heat them to any degree, and
they will not unite chemically, but will only be mixed to-
gether. But if you let these gases be together at the mo-
ment that they are produced, they will unite and form am-
monia. We will give you an illustration. If you heat some
potassium hydrate and iron filings together in a flask, hy-
drogen will be produced ; and if you heat iron filings and
potassium nitrate in another flask, nitrogen will be produced
there. Now if you conduct these two gases from these
flasks by tubes into another vessel, you will have only a
mixture of them ; but if you put all the materials into one
flask, nitrogen is liberated from the potassium nitrate, and
hydrogen from the potassium hydrate just as before, and
the two gases, being in each other's company at the mo-
ment they are produced, unite and form ammonia. The
chemist, therefore, says that they must be in their nascent
state in order to unite, as explained in § 42. Ammonia is
formed in the decomposition of animal and vegetable sub-
stances, because the two gases nitrogen and hydrogen are
evolved simultaneously, and are present in their nascent
state.

162. Preparation of Ammonia. — Ammonia is never actu-
ally prepared by heating the substances named above,

THE CHEMISTRY OF WATEK. — HYDEOGEX. 127

but is obtained for
the chemist's use by
heating sal ammo-
niac (or ammonium
chloride) with lime.
The materials may
be mixed in a glass
flask, and a gentle
heat suffices. The
gas is lighter than
air, and may be col-
lected by upward dis-
placement, as repre-
sented in Fig. 48.
The reaction is as fol-
lows :

Fig. 43.

2(H4NC1) + CaO = CaCl2 + HaO 4- 2(H,N)
Ammonium salts will be studied farther on.
163. Water of Ammonia. — Water eagerly absorbs ammo-
nia, and can dissolve nearly five hundred times its bulk of
this gas. The gas, in thus uniting with the water, becomes
greatly condensed, for it occupies a space nearly five hun-
dred times as small as it did before it was dissolved. We say
nearly, for the water is somewhat increased in bulk by dis-
solving the ammonia, the specific gravity of the solution be-
ing .870 compared with water reckoned as 1. This solution
is prepared in the apparatus represented in Fig. 49 (p. 128).
The ammonia is generated in the first flask, and enters
the water contained in the three -necked bottles (called
Woulfe -bottles), saturating them successively. The pun-
gent odor of this water of ammonia when in its full strength
is exceedingly strong. If it be applied to the skin, its irri-

128

ClIEMISTKY.

Fig. 49.

tation will even blister. When given as a medicine it re-
quires to be considerably diluted. If an overdose be taken
by accident, the best antidote is one which is always at
hand — viz., vinegar, which forms with the ammonia a salt
that is harmless. The water of ammonia with sweet-oil
forms a soapy liniment — the volatile liniment so much used
as an external application. The disposition of this solution
to form soapy compounds with fatty substances makes it
very effectual in removing grease spots from woolen clothes.

Both the gas ammonia and the solution react strongly
alkaline, turning reddened litmus paper blue.

164. Cyanogen, CN". — Carbon and nitrogen unite to form
a colorless gas of a penetrating odor much like that of hy-
drocyanic acid, its compound with hydrogen. It forms cy-
anides with the metals, as chlorine, iodine, etc., form chlo-
rides, iodides, etc. Because of this and its formation of an
acid with hydrogen it is classed with these elements. Yet
it is not an element, but a compound, the constituents of
which are carbon and nitrogen. A body which is compound,
and yet acts in some respects like an element, is called a rad-

THE CHEMISTRY OF WATER. — HYDROGEN. 129

ical; you will see that radicals play a very important part
in organic chemistry.

165. How Cyanogen is Obtained. — Though you can make carbon
and oxygen unite, forming carbonic anhydride, and oxygen and hydrogen,
forming water, you can not make carbon and nitrogen unite to form cyan-
ogen. This substance can be obtained only in an indirect manner. A
cyanide of some metal is first formed, and then the cyanogen is obtained
from this. We will state the process by which one of the cyanides, the cya-
nide of potassium, is formed. Potassium carbonate is strongly heated with
some refuse animal matter, as leather, horn, or dried blood. The animal
matter furnishes the elements of cyanogen, carbon and nitrogen, which in
their nascent state unite to form cyanogen, and this, seizing the potassium
of the potassium carbonate, forms cyanide of potassium. But the carbonic
acid and oxygen of the potassium carbonate are not yet accounted for. How
are they disposed of? They, together with a portion of the carbon evolved
from the animal matter, form carbonic oxide gas, which passes off. The
cyanide is left mingled with some refuse, from which it is separated by alco-
hol, which dissolves only the cyanide.

1G6. Prussia or Hydrocyanic Acid. — This acid is composed of
two gases, hydrogen and cyanogen, and hence its proper chemical name is
hydrocyanic acid. In its pure, undiluted state it is the most deadly of poi-
sons : a drop or two put upon the tongue of a dog causes instant death.
It is a colorless, limpid fluid, having a peculiar and powerful odor, like that
of peach blossoms and bitter almonds. The odor from these is caused, in-
deed, by a very minute quantity of this acid. And so, also, the flavor of
distilled waters of the cherry, laurel, and bitter almonds, etc., comes from
this acid very largely diluted. Indeed, this is an organic acid, produced in
certain vegetables by means of the processes alluded to in the second divis-
ion of this work. The chemist does not obtain this acid by extracting it
from the vegetable substances in which it exists in so diluted a state ; but
he heats certain cyanides with sulphuric acid in a distilling apparatus, and
collects the acid in a cool receiver. This is a dangerous experiment, and
we will not describe it further.

QUESTIONS.

140. What are the constituents of water ? What proportion of each by
weight and by volume ? — 141. Describe a physical method of decomposing

130 CHEMISTRY.

water. What is electrolysis ? — 142. Explain the process of obtaining hydro-
gen by decomposing water by means of red-hot iron. What reaction takes
place? How does this experiment illustrate decomposition and composition ?
— 143. Give in full the best method of preparing hydrogen gas. Give the ex-
planation of the chemical reaction. — 144. Under what circumstances will
oxygen and hydrogen unite ? How is a eudiometer used ? — 145. How does
the specific gravity of hydrogen compare with that of other substances ? Ex-
plain the table. — 146. Give the contrast between hydrogen and carbonic an-
hydride. How is hydrogen transferred from one jar to another? — 147.
What is said of ballooning ? When should balloons be used ? — 148. What
is hydrogen in relation to combustion ? Explain the ' ' philosopher's candle. "
What caution is needed to prevent explosion ? — 149. Describe the experi-
ment represented in Fig. 42. — 150. How may it be shown that hydrogen is
not a supporter of combustion ? — 151. Describe and explain the effects pro-
duced by burning hydrogen in glass tubes. — 152. What is said of breathing
hydrogen? — 153. What of sounds produced in this gas? — 154. What is the
composition of illuminating gas ? What is the fire-damp of coal-mines ?
What is marsh gas ? Describe the mode of collecting it represented in
Fig. 46. How is it freed from the carbonic anhydride that is mingled with
if? Describe the experiment represented in Fig. 47. To what is the
brightness of illuminating gas owing ? — 155. What is said of hydrogen per-
oxide ? — 156. State in full what is said of the nature of hydrogen ? — 157.
State and illustrate the differences between compounds and mixtures. —
158. What is said of the extent of the chemical agency of water ? Mention
some of the ways in which this agency is exerted. — 159. What is meant by
water of crystallization ? Give examples. What is efflorescence ? What
deliquescence ? How is water of crystallization usually expressed in form-
ulae ? — 160. \Vhat is ammonia ? Where does it occur ? Whence its name ?
— 161. Explain its production. — 162. Describe the preparation of ammonia.
Write the equation. — 163. What is said of the solution of ammonia in wa-
ter?— 164. What is cyanogen ? What is meant by a radical ? — 165. How
is cyanogen obtained? — 166. What are the properties of hydrocyanic
acid?

COMBUSTION. 131

CHAPTER X.

COMBUSTION.

167. Importance of the Subject— The interest attending
the subject of combustion is very great, because the chem-
ical processes involved in it produce such varied and ex-
tensive effects in the world. We are dependent upon com-
bustion in many ways for our comfort and enjoyment, and
even for the continuance of life. The preparation of our
food is effected in part by combustion. We guard by it
against the influence of cold. Nay more, it is by a real
combustion, though without flame, that the heat of our bod-
ies is maintained, as we shall show you in a part of this
chapter. Combustion gives us our light in the darkness
of night. It is very busy in many of the arts, especially in
preparing the metals for the various uses to which we ap-
propriate them. In these latter days it has been put ex-
tensively to a new use, in propelling steamers on the water,
and locomotives on the iron roads that thread the land. It
is by combustion, also, that the missiles of war are hurled.
The grandest scenes of destruction witnessed in the earth
come from combustion — conflagrations of towns and cities,
and forests and prairies ; explosions of masses of combusti-
ble material, and, above all, the bursting forth of the im-
mense and lofty volcanoes. Combustion, then, is one of the
principal things with which man has to do, and therefore a
thorough knowledge of it is not only interesting, but of
practical importance. As the old proverb has it, fire is a
good servant, but a bad master; and we trust that you will

132 CHEMISTRY.

see as we proceed that an acquaintance with the chemical
processes which it involves helps us to keep it in our serv-
ice, and to prevent it from gaining the mastery. We have
had considerable to say incidentally about combustion in
the previous chapters, but the subject demands a full and
systematic consideration.

168. Early Ideas of Combustion. — Fire was regarded by
the ancients as an element; this view prevailed largely
during the Middle Ages also, but gave way about the year
1700 to the idea that all combustible substances contain a
certain principle called Phlogiston, which escapes when they
burn. This theory, promulgated by Stahl, a celebrated Ger-
man physician, was accepted for nearly a century, but was
eventually abandoned when the discoveries of Priestley, of
Lavoisier, and others made chemistry a rational science.

169. Chemistry of Common Combustion. — In the combus-
tion which we commonly witness there occurs a chemical
union between oxygen, on the one hand, and carbon and
hydrogen on the other. The oxygen, in uniting with the
carbon, forms carbonic anhydride, which is diffused as gas
in the air. In uniting with the hydrogen it forms water
in the shape of vapor, which passes upward in company
with the carbonic anhydride. That this is the chemistry
of ordinary combustion you will see as we proceed to con-
sider its different modes and circumstances.

170. Burning Gas. — In the burning of hydrogen gas we
have only the union of this gas with oxygen, forming water.
That this is the product can be proved by holding a glass
bell-jar over a burning jet of hydrogen gas, Fig. 50 (p. 133).
It will soon become bedewed all over the inside with moist-
ure, and if the experiment be continued drops of liquid
will at length trickle down, which, if caught in a vessel and
examined, can be proved to be water. The metal sodium,
as you will hereafter learn, burns on touching water; so

COMBUSTION.

133

Fig. 50.

a little piece of this metal may be thrown into the bell-jar
to show that water has formed on its sides. In the flame
of burning coal gas we have both the unions mentioned in
§ 169, producing water and carbonic anhydride. The coal
gas consists of a mixture of several hydrocarbons, or bod-
ies consisting of hydrogen and carbon chemically combined.
Both of these in burning unite with the oxygen of the air.
In doing this, however, the carbon and hydrogen become
separated from each other. The hydrogen, being more com-
bustible than the carbon — that is, more ready to unite with
oxygen — burns first, and the little separated particles of
carbon burn in the flame of the hydrogen, giving to it its
brightness. The little bright flashes that you see continu-
ally shooting up in a gas-light are occasioned by the burn-
ing of these minute particles of carbon.

171. Chemistry of a Candle. — The same thing substan-
tially occurs in the combustion of a common candle. The
flame here is burning gas, and consists of nearly the same
gases as those which issue from a gas-burner. The tallow
is composed of carbon and hydrogen. The process, or rath-
er series of processes, by which this solid compound is con-

134

CHEMISTRY.

verted into a gas and burned, is, interesting to examine in
detail. First it is melted by the burning wick, and there is
all the while a lake of the melted tallow around it. This is
hemmed in by the outer part of the tallow, which is pre-
served in the shape of a raised edge, partly because it is so
far from the wick, and partly because the cool air, which
rises continually to feed the candle's flame, keeps this outer
part of the tallow comparatively cool. Sometimes this edge
is melted on one side because the wick is bent over so as to
be quite near it, and then the tallow runs down from the
lake which is about the wick. The next step in the process
is the raising of the melted tallow in the wick. This is
done by capillary attraction, which is explained in Part I.,
Chapter VI. Then the tallow is vaporized by the heat, and
lastly it is burned — that is, it unites with the oxygen of the
air, forming carbonic anhydride and water, precisely as is
done in the burning of illuminating gas. That water is
formed you can prove in the same way that it was proved
of the burning of hydrogen gas in the experiment present-
ed in Fig. 50. That carbonic anhydride is formed can be

proved by an experi-
ment shown in Fig.
51. A small funnel
is suspended over a
candle, and is con-
nected by a tube
with a bottle con-
taining lime-water.
Another tube pass-
mm es frorn this Bottle
to the mouth of the
experimenter. You
see that the tubes are so arranged that by the suction of
the mouth the gas from the candle can be made to pass

COMBUSTION.

135

into the lime-water. There it will form a milky cloud,
wjiich on settling is found to be calcium carbonate or chalk,
proving that the gas produced by the burning of the can-
dle is carbonic anhydride. It is just as we prove carbonic
anhydride to be discharged from the lungs, as described in
§ 125.

172. Structure of the Candle's Flame. — The flame of a can-
dle is quite a complex affair. You can see that it is not sim-
ply one thing, for some of it is dark,
and that which is bright is not all
equally so. It is really a shell of burn-
ing gas, containing within it a body of
gas that is not on fire. The shell itself
is not one thing, as you will see when
we describe Fig. 52, which is a sort of
map of the whole. At 3 we have the
gas that is not yet on fire. This is the
melted tallow which has come up the
wick, and is now vaporized by the heat.
Around this interior dark cone is a
very bright envelope, at 2 in the figure,
formed by active combustion of the
hydrocarbons, and containing the lit-
tle red-hot particles of carbon which,
sparkling brightly, give to this part of
the flame its strong light. Then at 1,
the outer part of the shell, the fine car-
bon is finishing its burning by uniting
thoroughly with the oxygen of the air
to form carbonic anhydride. This out-
side portion of the shell is called the
mantle, and this is the hottest part of the flame. Observe
why the gas at 3 is not on fire. It is shut in by the shell
of flame around it from the oxygen of the air, and there can

Fier. 52.

136

CHEMISTRY.

be no burning without oxygen. But as the gas is contin-
ually forming, and pressing upward and outward, some of
it passes all the time into 2, where it mingles with the oxy-
gen and takes fire. While the form of each of the parts of
the flame remains the same, the matter in them is continual-
ly changing.

173. Experiments. — What we have said of the flame of a

0 candle can be verified by many

very interesting experiments. If
we place one end of a small tube
in the dark part of the flame, Fig.
53, some of the unburned gas will
pass through the tube, and may be
lighted at the other end. This ex-
periment may be tried in another
Fig. 53. form, as represented in Fig. 54.

Here the gas passes into a flask. After considerable has
passed in we can take out
the tube, and with a match
set fire to the gas which we
have thus collected. We
do the same thing essential-
ly if we throw a piece of
candle into the flask, and
then vaporize it by a strong
heat. The same gas that
we have in the dark part
of the flame of a candle is
collected there, and we can
set fire to it. If you put a
small slip of wood directly
across the flame of a candle, Fi£- 54<

just above the wick, so that the middle of it will be in the
dark part, and hold it there a few seconds, on taking it out

COMBUSTION.

137

you will find that the middle is not burned at all, while
it is charred where the outer portions of the flame
touched it. So, also, it is possible to thrust a match so
quickly into the dark part of the flame that the phos-
phorus on its end will not take fire, while the wood that
is in the outer part of the flame burns readily. For the
same reason a piece of white paper
pressed down on the flame, nearly to
the wick, for an instant, Fig. 55, will
have a black ring marked on it. These
experiments prove that flame is really
hollow. If you blow out a candle, and
present a lighted taper to the smoke
at the distance of two or three inches, Fig. 56, you can see
a train of fire go along the smoke
till it reaches the candle and
lights it. This train of fire is
the burning of the gas that you
blow from the inside of the shell
of flame as you put out the can-
dle. To succeed in this experi-
ment you must do it very quiet-
ly, and at the same time quickly.
174. Experiment with Metals.
— If you take a slip of some
metal, as copper, which is tar-
nished— that is, oxidized on its K& 8ft>
surface — and hold it across the flame, the tarnish will be
removed from its middle portion, while it will be increased
each side of this where the metal is in contact with the very
outer part of the flame. The explanation is this : In this
outer faint blue part of the flame there is plenty of oxy-
gen from the surrounding air, and some of this unites with
the metal, increasing the oxide or tarnish. But in the inner

138 CHEMISTRY.

part, where the iminflamed gas is, there is no oxygen, and
the heated hydrogen and carbon are ready to unite with
oxygen, and so take it from the surface of the metal. Then,
too, in the bright part of the flame there is not a free access
of oxygen, and therefore the oxygen combined with the
metal is taken and used in the burning. The portions of
the flame, then, marked 2 and 3 in Fig. 52, are deoxidizing ;
that is, they take oxygen, de, from metallic oxides, while the
outer portion of the flame is oxidizing. The above experi-
ment is more satisfactory with a spirit-lamp than with a
candle, because in that there can be no trouble from soot.
A tarnished copper cent will answer for this experiment if
held with a pair of pincers horizontally in the flame.

175. Combustion of Wood. — The flame of burning wood
is essentially the same as that of the candle. It is not really
the wood that burns. As the tallow is turned into gas by
the heat before combustion occurs, so a part of the wood is
changed into gas, and this, burning, makes the flame. You
often see this illustrated in the kindling of wood. As it
lies with the bright coals beneath it, at first its under sur-
face smokes, but there is no flame. What is this smoke?
It is gas made visible by panicles of carbon, and perhaps
also by vapor from the water in the wood. Soon this smoke
takes fire, not from contact with the coals, but from their
heat radiated upward against it. We often see the same
thing in conflagrations. A wooden building, perhaps across
the street from the one that is on fire, begins to scorch and
smoke, and soon bursts into a flame. In these instances you
have clear illustrations of the fact that the formation of
gas and its combustion are two distinct processes. As an-
other example, we often see jets of gas blowing out from
some crevice in the wood, and set on fire by the heat. The
gas is generated in the wood by the heat, and comes out of
the crevice as from a gas-burner. If you hear the sound of

COMBUSTION.

139

such a blowing forth of gas, and sec no flame, you can at
once produce a flame by applying a burning match to the
crevice, just as you do by applying it to the opened orifice
of a common gas-burner.

176. Nature of Flame. — To understand the cause of flame
we must remember that it is produced by burning gases
only ; solid bodies, heated ever so intensely, emit light and
may burn, but they can not make flame if they are incapable
of being converted into vapor. Thus a piece of iron or sil-
ver may be heated hot enough to give out light, but can not
burn with a flame. So with carbon, which burns without
flame when alone.

In the examples mentioned the flame is caused by the
combustion of the gaseous hydrocarbons.

177. Combustion of Coal. — In the combustion of anthracite
coal when fully ignited there is no flame, for it contains no
hydrogen, but is nearly pure carbon. Its combustion is
like that of wood-coals, or charcoal. The reason that an-
thracite contains no hydrogen is that in its formation all
volatile matters were driven off by heat. There is a blue
flame given off by anthracite coal when it is kindling, and
especially wrhen a hot fire is freshly fed with coal, arising
from the generation of carbonic oxide, noticed in § 112 ; but
when the coal is fairly ignited it

burns without flame. Bituminous
coal, on the other hand, burns with
a flame because it contains hydro-
gen as well as carbon.

178. Manufacture of Gas. — If you
place some shavings in a test-tube,
Fig. 57, with a cork in its mouth
having a tube fixed into it, and ap-
ply heat, illuminating gas will pass

out through the tube, and you can Fig. si.

140 CHEMISTRY.

light it. The same effect will be produced if you use bitu-
minous coal, or oil, or tallow. The explanation is this : The
heat sets free the hydrogen and the carbon in the form of
carburetted hydrogen, just as it does in the case of the can-
dle. The gas that we bum in our houses is made from coal
substantially in the way indicated in the above experiment.
It is made in large iron retorts. It has many impurities
mingled with it, which are removed by certain chemical
processes before the gas is distributed in the pipes. Gas
which is made from oil is purer, and gives a stronger light,
than that which is made from coal.

179. Results of Combustion. — The results of combustion
are of two kinds — those which pass off in the form of gas or
vapor, and those which are deposited in a solid form. When
a gas burns, the results are all aeriform. The vapor, how-
ever, that is formed by the burning of hydrogen may be
condensed into a liquid form, or even be made solid in the
form of snow, hail, or ice. The results of the combustion
of some solids are wholly aeriform, as, for example, in the
case of the candle, whether it be tallow, wax, or stearine.
The results in the case of some solids, on the other hand,
are wholly solid. When a metal, as iron, burns, not a par-
ticle of it passes off as gas, but it all falls as a solid oxide.
When wood or coal burns, the results are both aeriform and
solid, the latter being in the form of ashes. The ashes of
different substances vary much both in character and in
quantity. When wood is burned, out of every 100 pounds
about 2 are ashes, while 98 pounds fly off into the air by
uniting with oxygen to form carbonic anhydride and water.
Of what ashes are composed we shall speak particularly in
another place.

180. Expedients for Increasing Combustion. — When any
thing is burning, the greater the supply of oxygen the
more brisk and perfect will be the combustion. If we blow

COMBUSTION". 141

a fire, we bring more air, and therefore more oxygen, to it.
The coals therefore brighten, the combustion being made
more active, and this increasing the heat, the wood burns
more briskly, or, if not burning at all, soon bursts into a
flame. It is chiefly for the same reason that when a build-
ing takes fire there is great danger that the fire will extend
to other buildings. So, also, whatever increases the draught
of a chimney makes the fire more brisk. On this account
the chimneys of foundries and other factories, in which
a very hot fire is needed, are made very tall. For the same
reason the tall chimneys of lamps cause them to give a very
bright light. If you should take the chimney from a lamp
that is burning brightly, leaving the wick at the same height,
there would be a great smoke, because the oxygen would
not come to the wick with sufficient rapidity to unite with
all the carbon and hydrogen that go up from it. A flat
wick gives a brighter light than a round one, because it
presents a larger surface to the oxygen of the air. Still
more light is given if a flat wick have a circular arrange-
ment, the air being admitted inside as well as outside of
the circle. This is the construction of the well-known Ar-
gand burner.

181. Bunsen's Burner. — By increasing the supply of oxy-
gen to a flame we increase its luminosity ; but if we mix
the combustible gases with oxygen before igniting them,
the resulting flame gives scarcely any light at all. This
will not seem so strange if you understand that the par-
ticles of carbon are completely burned np in the mixed
gases. Such a flame is not only smokeless, but deposits no
soot on cold surfaces placed in it, and consequently is a very
clean flame to cook or heat with. Many forms of stoves
and lamps have been contrived which produce this color-
less and very hot flame ; the one commonly used in chem-
ical laboratories is called Bunsen's Burner, after the great

142

CHEMISTRY.

Fig. 68.

German chemist who invented it. Coal
gas enters at «, Fig. 58, and air enters at
#/ they mix in the tube before they issue
at c, and on applying a light at this orifice
we have a very clean hot flame. By stop-
ping up the hole, £, with your fingers you
can cut off the supply of air, and conse-
quently of oxygen, and the flame will in-
stantly change its appearance, burning
with the usual partially smoky yellow
light of ordinary coal gas. Removing
your fingers, oxygen enters, a perfect com-
bustion of the carbon particles takes place, and the flame is
colorless again.

In all chemical laboratories where gas is to be had, these
burners, and stoves constructed on the same principle, are
in constant use, being clean, cheap, and needing no attention.
After a Bunsen burner has been long in use it sometimes
burns badly, the gas igniting at the base of the tube, c, and
burning within it with an illuminating flame. This is be-
cause there is too much air in proportion to the gas, and by
cleaning the little hole in the jet at the base of the tube, <?,
more gas may be admitted and the evil reme-
died.

182. Blowpipe. — The oxidizing and deoxidiz-
ing flames referred to in § 174 are obtained with
greater distinctness by using the little instru-
ment called a blow-pipe. This consists of a short
tube, generally of metal, either curved at one end
or made of two pieces, one fitting into the other
at right angles. By applying to a flame the
end which terminates in a jet with a very small
hole, and then blowing through the other end
with the mouth, the flame is materially altered

COMBUSTION. 143

in appearance. Its size is diminished, while its length is
increased, and its brightness almost entirely destroyed, ow-
ing to the more perfect combustion of the carbon within it.
The three cones named in § 172 are still seen, the inner one
is of a blue color, the middle one is partly luminous, and
the outer one is again paler. The middle cone is called the
deoxidizing or reducing flame, and has the effect of reduc-
in<^ metallic oxides brought under its influence. This is

O O

owin<* to the fact that it contains an excess of combustible

matter, and is ready to take oxygen from the metals. The
outermost cone, called the oxidizing flame, has the opposite
effect, for the supply of oxygen is here abundant, and any
substance eager to take it up is oxidized. The hottest part
of the flame is a little beyond the end of the middle cone.

In skillful hands either the reducing or the oxidizing
flame may be made to predominate, and advantage is taken
of this by the operator according as he may desire to reduce
or oxidize any substance. This little instrument is of great
service to the chemist and mineralogist to assist them in as-
certaining the nature of mineral substances. The material
to be examined is supported on charcoal, or in platinum-
pointed pincers, and heated in the blow-pipe flame ; by the
changes which take place in its appearance the chemist is
able to determine its constituents with considerable accu-
racy.

183. Improper Management at Fires. — The principles
above indicated are often disregarded in attempts to put
out fires. The more we can keep the air from having free
access to a fire, the more readily shall we put it out. If a
fire, then, be on the inside of a building, there should be no
more openings made into it than are absolutely necessary
to enable us to throw water upon the fire. Especially
should we avoid making any openings which will allow a
current of air to pass through the part that is burning. If,

144 CHEMISTRY.

at the same time that doors and windows are opened below,
windows are opened or broken in above, as is often the case,
the air sweeps up and through with great force, feeding
rapidly the fire with oxygen.

184. Blowing out a Candle. — The fact that a puff of breath
or a gust of wind puts out a candle seems at first thought
inconsistent with what we have stated, for really more oxy-
gen is thus carried to the candle than it gets when the air
is still. It is easy to see, however, that there is no inconsist-
ency. There is a certain amount of heat required to keep
up the combustion, and the air, therefore, may be made to
come so rapidly to the light as to take away sufficient heat
to stop the combustion. The more rapidly the air comes
to the light, the more oxygen, it is true, is brought to it ;
but this is not adequate to compensate for the loss of heat.
You have undoubtedly noticed that it is easier to avoid
having a lamp or candle go out in carrying it up stairs
than in carrying it down. The reason is that the flame is
blown in the first case, if you hold the candle inclined a
little forward, directly down upon the wick, increasing
therefore the fire and the heat, while in the other case the
flame is blown away from the wick. For the same reason,
in carrying a lighted taper or stick, you point it forward.
You see now what is the chemistry of a lantern, as we may
express it. The air is admitted freely that the light may
have a good supply of oxygen, but the orifices are so small
that no gusts of wind can reach the light and reduce its
heat below the burning point.

185. Putting out Fires. — Water is the common means of
putting out fires, and this acts in two ways. First, it shuts
out the oxygen of the air from the combustible substance,
acting as a covering to it, thin indeed, but yet effectual ;
and, secondly, it takes away some of the heat, and therefore
lessens the combustion. Of course, the colder the water is,

COMBUSTION. 145

the more serviceable it is in this respect. But even hot
water is of some service in this way; for it is not as hot as
the fire is. The fire converts it into steam, and thus parts
with a great deal of heat, which is rendered latent as the
steam forms, as noticed in Part L, Chapter XIIL And then,
for the purpose of shutting out the oxygen, hot water an-
swers as well as cold. Some other means are often resorted
to for extinguishing fires, all of them acting by excluding
the air. For example, we put an extinguisher over a candle
to put it out. So, also, if a person's clothes take fire, and no
water be at hand, we wrap some clothing or other article
quickly and closely around him. Such expedients, in com-
mon language, are said to smother the fire, but in scientific
language to prevent the oxygen of the air from coming in
contact with the combustible substance.

186. Fire Under Water. — If we put a very combustible
substance under water, we can make it burn

there by giving it a good supply of oxygen.

In Fig. 60 we have an experiment of this

kind represented. A bit of phosphorus, #,

is put in a glass of hot water, and a stream

of oxygen gas is directed upon it through

the tube, a. A brilliant combustion occurs.

It is necessary that the water should be hot Fis- «<>.

to make the phosphorus burn, or, in other words, unite with

the oxygen.

187. Fire Extinguishers. — Since carbonic anhydride is not
a supporter of combustion, it may be used for extinguishing
fires. It is usually employed in solution in water under
pressure, and various contrivances have been made for gen-
erating the gas quickly when needed, and throwing a stream
of it mixed with water in any direction desired. The " plain
soda-water" sold in apothecary shops would serve just as
well, for it is really the same thing. The pure dry gas has

146

CHEMISTRY.

also been used as a fire extinguisher. For example, a Mr.
Gurney, in the case of a fire which nad been burning for a
long time in a coal-mine in Scotland, contrived to generate
a large quantity of carbonic anhydride, so that it should
flow to the spot where the fire was raging, and thus extin-
guished it. Here water could not be made to reach the

fire, but the gas went to it without any difficulty.

188. Oxyhydrogen Blow-pipe. — When a jet of hydrogen
gas is lighted, and a jet of oxygen is made to mingle with
it, the union of the two gases produces the greatest heat
known, with the exception of that which is produced by the
galvanic battery. The sole product of this energetic com-
bustion is water, the grand extinguisher of combustion. In
Fig. 61 is represented an extemporaneous contrivance for

Fig. 61.

burning these gases. The oxygen is contained in the bag,
which has a weight upon it to press the gas out through the
pipe. At the same time hydrogen gas is coming up from
the bottle below through another pipe. Here you have the
essentials of the blow-pipe invented by Dr. Hare, of Phila-

COMBUSTION. 147

delphia. The common arrangement
of this instrument is, however, repre-
sented in Fig. 62. In one reservoir
is the oxygen, and in the other the
hydrogen ; flexible tubes lead to a
common jet, where the gases issue
and are set on fire. The flame, not-
withstanding its heat, has very little
brightness. It melts almost all sub-
stances, even the most refractory,
dissipating many of them in vapor.
Platinum, which can not be melted
in the hottest furnace, readily melts Fig. 62.

here. Most of the metals are oxidized as they bum in this
flame. Though the flame itself is so nearly colorless and
destitute of light, a dazzling light, variously colored, is pro-
duced as it burns the metals. Copper gives a beautiful
green light, and platinum a delicate white. The scintilla-
tions of iron are of a more dazzling brightness than when it
is burned in a jar of oxygen, as noticed in § 59.

189. Drummond Light. — There are some of the earths, as
lime and magnesia, that resist the heat of the oxyhydrogen
blow-pipe, and one of these, lime, placed in the flame, gives
a light which rivals in brightness the noonday sun. An
arrangement having a burning jet of the two gases thrown
upon a ball of lime is called the Drummond Light, because
Lieutenant Druramond, of the English navy, if he did not
first discover the fact that such an intense light could be
thus produced, was at least the first to discover and recom-
mend its use for most of the purposes to which it is now
applied. The light can be seen at such great distances that
it is exceedingly useful for signaling. In one case the light
was seen at the distance of 70 miles. That a flame which
gives so little light of itself should be made so intensely

148 CHEMISTRY.

luminous by merely striking against a solid substance, with-
out in the least altering it, confirms what we have before
learned, that the light-giving power of flame is dependent
chiefly on the presence of incandescent solids.

Instead of using pure oxygen and pure hydrogen, an ex-
cellent light for all practical purposes is obtained by em-
ploying oxygen and coal gas. Strong metallic cylinders
(see Fig. 62, p. 147) containing these gases under pressure
are now sold in the large cities to any one wanting a bright
light or intense heat. This light, also called the oxycalcium
light, is very frequently seen in theatres, torchlight proces-
sions, and even as a' means of advertising. The stereopti-
con used in illustrating public lectures is simply a magic-
lantern provided with a calcium light.

190. Cause of Explosions. — So long as the two gases hy-
drogen and oxygen are kept separate before burning them
no explosion takes place ; but if oxygen and hydrogen be
mingled together and then fire be applied there is a violent
action, and a report proportioned to the amount of the gases.
The combustion is alike in both cases, oxygen and hydro-
gen uniting to form water, and the explosion is due to the
sudden expansion of the gases caused by the intense heat
generated by their chemical union. The noise is pro-
duced by the sudden collision of the instantaneously ex-
panded vapor with the air surrounding the vessel contain-
ing it.

191. Experiments. — Some interesting experiments can be
tried illustrative of the explosive combustion of gases. If

into a strong brass vessel, a, Fig. 63, we in-
troduce a mixture of oxygen and hydrogen,
and, having pushed the cork, c, in tightly,
pass electricity by the ball and wire at b, an
explosion will occur. The cork will be violently driven out
by the expansive force of the heated vapor produced. Such

COMBUSTION. 149

an apparatus is called a " hydrogen pistol," but it ought
really to be called an " oxyhydrogen pistol," for only a
mixture of these gases explodes. The two gases can be
mingled in a bag, and by the aid of a common tobacco-pipe,
as seen in Fig. 64, soap-bubbles can be
formed, which on flying upward can be ex-
ploded by touching them with a light. To
obtain good soap-bubbles mix a little glyc-
erine with the soap-water before using. In
such experiments we use in bulk twice as
much hydrogen as oxygen, for it is in this proportion that
these gases unite to form water (§ 140). Common air is
often used in place of oxygen, and answers the purpose be-
cause it contains this gas. When this is used we introduce
about equal bulks of the air and the gas. In all such ex-
periments great care should be exercised. For example, in
the bubble experiment we should be careful not to bring
the light near the pipe of the gas-bag, else the whole might-
be exploded at once.

192. Spontaneous Combustion. — We mean by spontane-
ous combustion the taking fire of any substances without
the application of heat to them. We will give you some ex-
amples, and explain them. If you place a bit of phosphor-
us of the size of a pea upon blotting-paper, and sprinkle
over it some soot or powdered charcoal, it after a while
melts and bursts into a flame. This is owing to the large
absorption of oxygen gas by the carbon, as noticed in § 96.
Much oxygen is thus introduced to the phosphorus, for
which it has a strong affinity ; and a union is therefore
readily effected between them, which union is combustion.
Heat is generated by the absorption of the gas ; and as car-
bon is a non-conductor, the heat is retained, and is sufficient
to start the combustion of the phosphorus. Indeed, where
there is a large amount of powdered charcoal heaped to-

150 CHEMISTRY.

getlier,the heat thus developed and retained may be suffi-
cient to set fire to it. Gunpowder factories have sometimes
exploded from this cause. For the same reason spontane-
ous combustion may occur in a mixture of lamp-black and
linseed-oil, if the lamp-black be in excess, or if a portion of
it be dry. Any substances in which chemical action is apt
to take place, if heaped together so as to shut in the heat
which this action produces, may take fire spontaneously.
This is the case with oiled cotton and rags if there be in
them any drying oil, or even with damp goods packed to-
gether. Damp hay may take fire for the same reason. More
often, in this case, the combustion is imperfect, and the hay
is turned black — that is, charred or changed into charcoal,
just as wood is in the coal-pit. Spontaneous combustion of
the human body, often referred to by ignorant people, is a
fiction.

193. Combustion without Oxygen. — We have seen that
ordinary combustion is the union of a substance with oxy-
gen, accompanied by the development of light and heat.
The presence of oxygen, however, is not indispensable to
combustion, for we have many examples of chemical com-
bination taking place, with such intensity as to generate
light and heat, where oxygen is absent. Thus carbon will
burn when heated in the vapor of sulphur, and a yellowish
green gas called chlorine supports the combustion of metals
and even of a candle. But of this we will learn more far-
ther on.

194. Requisites for Combustion. — The variations in the
readiness with which ordinary combustion goes on depend
chiefly on three things: 1. The comparative affinity of the
substance for oxygen. 2. The amount of oxygen supplied.
3. The temperature to which the combustible body is raised.
Thus in the case of phosphorus, the slight heat caused by
friction is sufficient to make it take fire. Wood, on the oth-

COMBUSTION. 151

er hand, requires a much higher temperature to ignite it.
Friction will do it, but it must be brisk and long continued.
By increasing the quantity of oxygen present combustion
will take place with less heat than is ordinarily required.
This is the cause of spontaneous combustion in many cases,
as noticed in § 192. In the brisk and continued burning of
iron or steel in oxygen gas, § 59, we see the influence of an
abundance of oxygen about the iron, in contrast with the
mere spark that flies off in striking fire in the air, which is
only one-fifth part oxygen.

195. Ordinary Oxidation a Slow Combustion. — As carbon
and hydrogen in burning unite with oxygen, forming car-
bonic anhydride and water, so do the metals, forming ox-
ides. It is indeed this union which is the combustion. It
follows, then, that the gradual oxidation of the metals, the
rusting of iron, copper, zinc, etc., is a combustion — a slow
fire. And it undoubtedly produces as much heat in the ag-
gregate as rapid oxidation does, though the process is so
very slow that the heat at any one moment is so little as
to be imperceptible.

196. Sun-Bleaching is Combustion. — The old mode of
bleaching by exposure to the sun, grass-bleaching as it is
termed, is an example of oxidation — that is, combustion.
By the influence of the sun's light the oxygen of the air is
made to unite with the coloring matter of the cloth, and so
this is burned up, the product passing off in the air, just as
the products of ordinary combustion do. If the cloth be
exposed too long, some of the substance itself is burned up,
lessening the strength of the cloth, or rotting it, as it is
commonly expressed. The reason that the coloring matter
is affected before the substance is that it is more combusti-
ble, or, in other words, more readily oxidized.

197. Animal Heat. — The heat of the body is maintained
by a real combustion, though without light. To produce

152 CHEMISTRY.

this heat the same chemical unions take place as in the burn-
ing of a common candle. We have told you something al-
ready about the introduction of oxygen into the body in
breathing. It enters the blood in the lungs, and courses
about in search of carbon and hydrogen. It finds these
every where, and unites with them, forming with the car-
bon carbonic anhydride, and with the hydrogen water, as
in the case of the candle. In effecting this union heat is
produced, and thus the body is kept warm.

198. The Lungs not the Body's Furnace.— It was for a
long time supposed that the chemical combinations produc-
ing the heat occurred in the lungs, and that the heat gener-
ated there was carried with the blood all over the body.
But there were some facts observed that were inconsistent
with this doctrine. If it were the true doctrine, the lungs
should be hotter than any other organ in the body, just as
a furnace is always hotter than the apartments to which the
heat from it is carried. But it was found that the lungs
were no warmer than other organs, and that therefore they
were not the furnace of the body. Then, again, it was ob-
served that the heat of different parts of the body is often
temporarily increased. Thus when an inflammation occurs
there is more heat than usual. So, also, blushing will make
the face to burn. In such cases the increased heat is of
course produced where it manifests itself, and not in the
lungs. It was therefore found, on further investigation, that
the animal heat is produced in all parts of the body, every
little vessel being a chemical laboratory for this as well as
other purposes.

199. Temperature of the Body. — The heat of the body is
maintained quite uniformly at 98°.* You observe that this

* The temperatures named in this section are given in Fahrenheit de-
grees. See Appendix.

COMBUSTION. 153

is much above the ordinary temperature of the atmosphere,
so that our bodies are almost always giving out consider-
able heat to the air around us. This is very obvious where
there are many persons gathered together. A room that is
just comfortably warm with but few in it, becomes uncom-
fortably so very soon when it is crowded full of company. It
is very seldom that the air around us is as hot as our bodies,
and therefore very seldom that we are not giving off heat.
We are most comfortable when the air around us is at about
70° (Fahrenheit), and as this is 28° below the heat of our
bodies, we may say that we are comfortable only when we
are giving off considerable heat to the air. As this heat is
given off from the surface, the outer parts of the body are
not as warm as the inner. And as heat is constantly lost,
so it is constantly made. The myriads of furnaces are at
work all the time, night and day. The fires within us never
go out while life continues.

200. Sources of the Fuel. — The fuel used in producing
animal heat is carbon and hydrogen, as already intimated.
There are two sources from which these come : 1. The waste
of the body. In the wear and tear of the animal machine
there are particles every where that have ceased to-be use-
ful. They must be got rid of to make way for other par-
ticles to be deposited in their place. How is this done?
The oxygen that enters the lungs in breathing does it. This
goes in the blood to these useless particles, and burns up,
that is, unites with their carbon and hydrogen. This makes
heat just where the particles are, and the products of the
combustion, the carbonic anhydride and water, are carried
off in the blood that sweeps along in the veins. What be-
comes of them we will soon tell you. 2. A part of our food
furnishes fuel to feed the fires within us, the starchy, sug-
ary, and fatty articles. We shall speak particularly of this
subject in another part of this book, and so will not dwell

154 CHEMISTRY.

upon it here. Occasionally the fat which is deposited in
various parts of the body is used as fuel, the oxygen in the
blood seeking it out, and uniting with its constituents, car-
bon and hydrogen. This is done in sickness, when the ac-
cumulated fat disappears, and also in the hibernation of
many animals, as will be noticed farther on.

201. Amount of Fuel Consumed. — Some calculations have
been made in regard to the amount of fuel consumed in
keeping up animal heat. This is more easily done in regard
to carbon than hydrogen. A full-grown man requires
about 100 kilogrammes of charcoal to keep him warm
through the year. A horse needs about five times as
much — 500 kilogrammes.

202. The Windpipe the Smoke-pipe of the Body. — We have
told you that in the combustion that is every where going
on in the body carbonic anhydride and water are formed,
and pass into the blood in the veins. Observe how they
are disposed of. They are for the most part carried in the
blood to the lungs,* where they are discharged through the
windpipe into the air. The water comes out in the form of
vapor mingled with the carbonic anhydride, just as the two
rise together from the flame of a candle. As these products
of combustion are discharged from the body by the wind-
pipe, this may be termed the body's smoke-pipe. It acts
thus as we breathe out, but when we breathe in it serves to
introduce to all the little heat-laboratories of the body oxy-
gen, the supporter of their combustion.

203. Influence of Exercise on Animal Heat. — When the
body is in a state of activity the heat is increased, or, in
other words, the fires within us burn more briskly. This is

* For a particular description of the manner in which this is done we
refer to either Hooker's "Human Physiology" or his "First Book in
Physiology. "

COMBUSTION. 155

because the circulation is quickened, and with it the breath-
ing, and so more of the oxygen is introduced into the blood,
and thus to the carbon and hydrogen- The same effect is
produced in this way upon the combustion of the body as
upon an ordinary fire by blowing it. It is simply increasing
one of the three requisites for combustion mentioned in § 194.

204. Cold-blooded Animals. — Reptiles and fishes are cold-blooded
animals — that is, they have nearly the same temperature with the medium
in which they live. The fires in them are not at all brisk, and they use
little oxygen in comparison with warm-blooded animals. They have need
of but little, for they live a comparatively sluggish life, as you may fully
realize in relation to reptiles if you observe the difference in activity be-
tween a bird and a frog or toad. It may appear to you that this is not
true of fishes, as their motions are often very quick. But it must be re-
membered that it requires but little exertion really for them to move with
rapidity, because they live in a medium of a specific gravity so near their
own. For further illustration of this point we refer you to Chapter XX. of
Hooker's " Natural History."

205. Hibernation. — Animals are said to hibernate who go into a
torpid state in the winter. The degree of torpidity varies much in differ-
ent animals. In cold-blooded animals respiration and circulation may
cease altogether, and the operations of life may be as thoroughly suspend-
ed as in a seed that is kept from heat and moisture. They may be pre-
served in this state for a long time. Frogs and serpents have been kept in
ice for years without any signs of life, and then have been revived by ex-
posure to a warm atmosphere. While animals are in such a state, the ma-
chinery of life being stopped, there is no wear and tear, and therefore no
waste to be got rid of. As there is nothing to bum, no oxygen is needed.
In hibernating warm-blooded animals the torpidity is not so thorough, and
in proportion to the movements of life there is waste, and therefore need of
oxygen to burn it. Hence there is occasional respiration. In such cases
of imperfect torpidity the fat which has been acquired in summer is burned
up for the purpose of maintaining the requisite warmth, and such animals
therefore come out in the spring from their hiding-places in quite a lean
condition.

206. The Chief Elements. — The four elements with which
you have become so familiar in the previous chapters—

156 CHEMISTRY.

viz., oxygen, nitrogen, carbon, and hydrogen — are the chief
elements concerned in the formation of the earth. Especial-
ly is this true of orgianic substances, both vegetable and ani-
mal. In some of these, it is true, there are lime, phosphorus,
sulphur, iron, etc. ; but these are generally in small quan-
tities, while the great bulk of them is made up of combina-
tions of the four grand elements which we have mentioned.
Then of substances not living, the earth's envelope of air,
fifty miles thick, is a mixture mostly of two of these ele-
ments, oxygen and nitrogen, and all the water is composed
of oxygen and hydrogen. And to come to the solid crust
of the earth, carbon is seen in the enormous quantities of
coal treasured up in the bowels of the earth for the use of
man; carbon and oxygen united with a metal form the
limestone rocks and ranges of mountains ; oxygen is a large
constituent of the granite and other hard rocks ; and of the
compound mixture under our feet which we call earth the
four grand elements form a very large proportion.

207. Chemical Changes in Air and "Water. — These elements
are continually the subjects of chemical changes. You have
already seen how that mixture of gases, the air, is constantly
changing by means of the chemical operations going on in
the lungs of animals, in the leaves of vegetables, in combus-
tion, in the various arts of man, and in the decay of animal
and vegetable substances. Though, therefore, the atmos-
phere which envelops the earth is to-day composed of oxy-
gen, nitrogen, and carbonic anhydride, in precisely the same
proportions as that which enveloped it when our first parents
were in the Garden of Eden, yet it is not the same air, but
its elements have from that time to this been going through
many changes, entering into the composition now of liquids,
now of solids, and now of gaseous substances. The ele-
ments of water are also continually changing, though per-
haps not to such an extent as those of air. In § 9, Part L,

COMBUSTION. 157

we spoke of the exceeding movability of water. As it courses
about much of it becomes resolved into its elementary gases,
oxygen and hydrogen, to engage in the formation of other
substances, gaseous, liquid, and solid; and just as constantly
new water is forming to take the place of that which is
thus resolved. Especially do such changes in water take
place when it enters living substances. The constituents
of water form a part of all vegetable and animal substances,
and it is, therefore, decomposed continually to furnish these
in the growth that is every where going on.

QUESTIONS.

167. Mention some of the various effects of combustion. — 1G8. What was
Stahl's theory of phlogiston ? How long did his theory prevail ? — 169. What
takes place in ordinaiy combustion? — 170. Explain the experiment repre-
sented in Fig. 50. State what takes place in the burning of illuminating gas.
— 171. State the processes involved in the burning of a common candle.
How can you prove that water is formed in the burning of u candle ? How
that carbonic anhydride is formed ? — 172. Describe the structure of a can-
dle's flame as mapped in Fig. 52, and the processes involved in the burning.
— 173. State the experiments shown in Figs. 53 and 54. Give the experi-
ment with the slip of wood. That with the match. State the experiment
represented in Fig. 55. — 174. That represented in Fig. 56. State and ex-
plain the experiment with a slip of copper. — 175. Illustrate the fact that in
the combustion of wood the formation of gas and its combustion are two
distinct processes. — 176. What is the cause of flame ? — 177. What is said of
the burning of anthracite ? What of the difference between anthracite and
bituminous coal? — 178. What of the making of gas? — 179. Mention cases
of combustion in which the results are aeriform ; cases in which they are
solid ; and cases in which they are partly solid and partly aeriform. What
proportion is there of solid when wood is burned? — 180. How may combus-
tion be increased ? What is said of the chimneys and wicks of lamps ? —
181. Describe the gas-lamp known as Bunsen's Burner. What are its ad-
vantages ? — 182. Describe a blow-pipe. What is said about oxidizing and
reducing flames? How is a blow-pipe useful to chemists? — 183. What is
said of improper management at fires ? — 184. What of blowing out a can-
dle ? Explain the expedients resorted to for preventing lights from going

158 CHEMISTRY.

out as we carry them about. — 1 85. In what two ways does water act in put-
ting out fires ? Explain other means of putting out fires. — 186. How can
a fire be made under water? — 187. What is said about fire extinguishers?
Explain the extinguishing of a fire in a Scotch coal-mine. — 188. What is the
oxyhydrogen blow-pipe? \Vhat is its use? — 189. What is the Drummond
Light? What the oxycalcium light? When are they used? — 190. Ex-
plain the cause of explosions. What causes the noise? — 191. Describe the
hydrogen pistol, and the experiment with soap-bubbles? — 192. What is
spontaneous combustion? State and explain the experiment with phos-
phorus and charcoal. Give various examples of spontaneous combustion.
—193. Is oxygen indispensable to combustion ?— 194. What are the requi-
sites for ordinary combustion ? Give examples illustrating the variation of
these in different cases. — 195. What is said of ordinary oxidation ? — 196.
What of sun-bleaching ? — 197. How is animal heat the result of combus-
tion?— 198. What facts show that animal heat is not made in the lungs?
Where is it made?— 199. What is the temperature of the body? What is
said about the body's giving out heat ? — 200. What is the fuel of the fire in
the body ? What is said of the sources of the fuel ? What of the uses
sometimes made of the fat of the body? — 201. What of the amount of the
fuel used ?— 202. How is the windpipe the smoke-pipe of the body ?— 203.
Show how exercise influences animal heat. — 204. What is said of cold-
blooded animals ? — 205. What is said of hibernating cold-blooded animals ?
What of hibernating warm-blooded animals ?— 206. What is said of the
four chief elements ? — 207. What is the nature of the changes in air and
water? -

CHAPTER XL

CHLORINE, BROMINE, IODINE, AND FLUORINE.

208. A Natural Group. — Having now studied somewhat
at length the most important and widely distributed ele-
mentary bodies — oxygen, nitrogen, carbon, and hydrogen —
together with many of the compounds which they form, we
will now take up the remaining elements one by one, and, for
convenience' sake, will begin with the non-metals not yet
described. Four of these non-metals — chlorine, bromine, io-
dine, and fluorine — resemble each other, chemically speak-

CHLORINE, BROMINE, IODINE, AND FLUORINE. 159

ing, to a remarkable degree, and are said to form a natural
group; the most important member of this group is chlo-
rine.

209. Occurrence of Chlorine. — All common salt is made
up of this element and a metal called sodium. Afterward,
when you have learned the remarkable properties of the
constituents of salt, how one is a suffocating yellow gas, and
the other a very light, soft metal which burns on water, it
will seem rather strange that a union of these two bodies,
both of them so corrosive and dangerous, should produce
such a mild, healthful substance as common salt. And yet
this is only another example of the marvelous change which
elements experience when united, each one losing its iden-
tity, and the compound having the properties of neither of
them. Chlorine forms more than one half of common salt ;
so that, as salt is abundant in sea-water and in salt-mines,
and is also present to some extent in the soil and in animals
and vegetables, chlorine

is one of the elements
that exists in large quan-
tities in the earth.

210. Preparation of
Chlorine. — Chlorine is
never found free in nat-
ure ; we can make it
from common salt. Mix
some common salt, or
chloride of sodium, with
manganese dioxide, put
the mixture into a flask
fitted with a tube, as in ^
Fig. 65, and then add
some sulphuric acid

somewhat diluted. K"ow Fig. G&.

160

CHEMISTRY.

heat the contents of the flask, and yellowish-green vapors
of chlorine will arise and pass over into the jar arranged to
collect it.

The reaction which takes place is somewhat complex, but
you will understand it by studying this equation:

Sodi™ Sulphuric ^anpi. Hydro-sodium w Chlo-

dioxide. chlorlde' acl(L sulphate. sulphate. 'ter- rine.

MnOa + 2NaCl + 3H2SO4 = MnSO4 + 2(NaIISOJ + 2HaO + C12

The manganese dioxide is necessary to furnish oxygen to
unite with the hydrogen of the sulphuric acid, forming wa-
ter. What happens when we omit the addition of manga-
nese dioxide you will see very soon.

211. Another "Way of Obtaining Chlorine. — Chlorine gas
may also be obtained by heating hydrochloric acid with
manganese dioxide. The heat required is not high — plac-
ing the flask in a bowl of hot water is sufficient. If the
gas stops coming over, add more hydrochloric acid, for this
is the source of the chlorine.

As the gas is about two and a half times as heavy as air,

it can be collect-
ed in ajar, as rep-
resented in Fig.
66, the lighter
air being driven
out to give place
to it. The ex-
planation of the
chemical change
in the flask is
this: There is a
large amount of
oxygen in the ox-
ide of manganese,
which is therefore loosely attached to the metal, and ready

Fig. CO.

CHLORINE, BKOMINE, IODINE, AND FLUORINE. 161

to leave it at the slightest invitation. The hydrogen of
the hydrochloric acid, therefore, at once strikes up a union
with this oxygen, and the chlorine of the acid being there-
fore forsaken by the hydrogen, a part of it unites with the
manganese to form a chloride of that metal, and a part of
it escapes and passes out through the tube.

Manganese Hydrochloric Manganese w CM rf

dioxide. acid. chloride.

MnO3 + 4HC1 = MnCl2 + 2H2O + Cla

212. Breathing Chlorine. — This gas can not be breathed
with safety unless very largely diluted with air. If breathed
when'but little diluted, it occasions violent coughing and a
suffocating effect. Great care, therefore, is requisite in pre-
paring it and in experimenting with it. The very small
quantity that is in the air where bleaching is carried on, or
where it is disengaged from chloride of lime for disinfecting
purposes, though decidedly appreciable to the sense of smell,
occasions no embarrassment in the respiration.

213. Chlorine "Water. — Water will dissolve twice its bulk
of chlorine. This solution, called chlorine water, may be
used in a variety of interesting experiments. You can
make it very readily by passing the gas generated by either
method described into a bottle containing water. The gas
will be absorbed, and will communicate a yellow color to
the water. Chlorine water keeps best in the dark, so some
black paper may be pasted around the bottle.

214. Action of Chlorine on Metals. — This gas has a strong
disposition to combine with the metals, forjning chlorides.
If you put some pure gold-leaf into chlorine water it will
soon disappear, because the chlorine forms with the gold a
chloride, which is dissolved in the water as fast as it forms.
In some cases so eager are the chlorine and the metal to
unite that the violence of the action occasions the phenom-
enon of combustion. Thus if antimony in fine powder be

162

CHEMISTEY.

Fig. 6T.

dropped into a vessel of chlorine gas, it will fall in a show-
er of fire, and the vessel will
be filled with a white smoke
which is made up of small par-
ticles of chloride of antimony.
(Fig. 67.) If a fine brass wire,
with a little bit of tinsel fast-
ened to its end, be introduced
into a vessel of chlorine gas, the
wire will burn briskly, the tin-
sel of course taking fire first and
kindling the wire, as shavings
do wood. In this combustion
the zinc and copper, of which

brass is composed, unite with chlorine to form chlorides of

zinc and copper.

215. Attraction for Hydrogen. — Fill a jar with chlorine
water, and invert it in a vessel of water. If this be kept in
the dark no change will occur ; but if it be exposed to the
sun for a few days there will collect a colorless gas in the
upper part of the jar, and the water will be found to have
lost its chlorine and to have become sour. This is because
the chlorine in the solution has decomposed some of the
water by taking to itself its hydrogen to form hydrochloric
acid, while the other constituent of the water, oxygen, has
collected in the upper part of the jar. That this gas is oxy-
gen can be readily proved by setting the jar upright and
introducing into it a taper which is merely in a glow, and
not in a flame. It will burst into a bright flame at once.

Water. Chlorine. Hydrochloric acid. Oxygen.

H2O + C12 2HC1 + O

216. Bleaching. — The powerful attraction between chlo-
rine and hydrogen, and the consequent decomposition of
water, furnish us the explanation of chlorine bleaching. The

CHLORINE, BROMINE, IODINE, AND FLUORINE. 163

first step in the process is the decomposition of water, and
hence the necessity for having the substance to be bleached
moist. If a colored rag be introduced into chlorine gas dry,
the chlorine will have no effect upon it; but if it be moist-
ened, it will lose its color. The explanation of bleaching is
this : The chlorine, taking the hydrogen of the water, sets
free oxygen, and this in its nascent state (§ 42) has special
chemical power, and attacks the coloring matter, destroy-
ing it, or burning it up, as we may say, for the union of
oxygen with other elements is, as you have seen, essential-
ly a combustion. It is oxygen, then, that really does the
bleaching here, just as in the case of sun-bleaching (§ 196).
But the question arises, Why does the oxygen burn up the
coloring matter, and not the cloth itself? This is from a
principle which is well established in chemistry, viz., that
the more ingredients there are in a compound the more
easily it is decomposed. While the vegetable tissue or sub-
stance is composed of three elements, carbon, oxygen, and
hydrogen, the coloring matter is composed of these with ni-
trogen in addition, and therefore is more readily demolished
by the oxygen than the cloth is.

217. Carrying the Bleaching too Far. — But sometimes
the cloth is somewhat burned in the process — that is, some
of the tissue is destroyed by the released oxygen, and the
cloth consequently weakened. This is done whenever, after
the chlorine has released sufficient oxygen to destroy the
coloring matter, it continues to release more. The point,
then, to be aimed at by the bleacher is to set free only just
enough oxygen by means of the chlorine to oxidize the col-
oring matter, and not the substance. There is the same
danger that the process may be carried too far in the com-
mon sun -bleaching, or grass -bleaching, as it is usually
called.

218. Comparison with Grass-Bleaching. — The old mode

164 CHEMISTRY.

of bleaching was very tedious and uncertain, but chlorine
bleaching is both an expeditious and certain process. Pro-
fessor Pepper, an English author, thus remarks on the bene-
fits which the discovery of this process has conferred upon
English manufacturers : " All our linen used formerly to be
sent to Holland, where they had acquired great dexterity
in the ancient mode of bleaching, viz., by exposure of the
fabric to atmospheric air, or the action of the damps and
dews, assisted greatly by the agency of light. Some idea
may be formed of the present value of chlorine when it is
stated that the linen goods were retained by the Dutch
bleachers for nine months ; and if the spring and summer
happened to be favorable, the operation was well conduct-
ed ; on the other hand, if cold and wet, the goods might
be more or less injured by continual exposure to unfavor-
able atmospheric changes. At the present time as much
bleaching can be done in nine weeks as might formerly have
been conducted in the same number of months ; and the
whole of the process of chlorine bleaching is carried on inde-
pendent of external atmospheric caprices; while the money
paid for the process no longer passes to Holland, but re-
mains in the hands of our own diligent bleachers and man-
ufacturers." Quite as great is the usefulness of chlorine
bleaching in the art of paper-making in the preparation of
its material. A most valuable present, then, did the Swed-
ish chemist Scheele make to the arts when he discovered
chlorine and its application in bleaching.

219. Difference between Chlorine Bleaching and Sulphur
Bleaching. — In chlorine bleaching the coloring matter is actually de-
stroyed— burned up — that is, its elements are dispersed in new combinations.
But in sulphur bleaching, as you will learn, the coloring matter remains.
It is only changed, not dispersed, and therefore it can be restored as before
by certain chemical actions. Chlorine bleaching is inapplicable to straw,
because for some reason it imparts a brown tinge to the material. There-
fore for straw goods sulphur bleaching continues to be used.

CHLORINE, BEOMINE, IODINE, AND FLUORINE. 165

220. Chlorine a Disinfectant. — Chlorine not only decom-
poses colors, but also, and probably for the same reason, the
volatile compounds which are formed in decay, and which
are so disagreeable to the smell and injurious to the health.
It may be used, therefore, for purifying all morbid matters
and infected atmospheres, and even for arresting decay.
Musty casks may be cleansed by washing them first with
chlorine water, and then with milk of lime. Mouldy cellars,
in which milk readily turns sour, can be purified by fumi-
gating them with chlorine gas, or washing them with chlo-
rine water or a solution of chloride of lime.

221. Combustion in Chlorine. — It was formerly supposed
that oxygen is the sole supporter of combustion, but we
have an example to the contrary in chlorine. You

have already seen in § 214 that certain metals
spontaneously burn in this gas. In the burning of
ordinary substances in chlorine the flame comes
from the union of chlorine and hydrogen, no union
with the carbon, so commonly attending combus-
tion, taking place in this case. Thus, if a candle
be let down into a jar of this gas, Fig. 68, it burns
as it enters with a dull red flame, but a dense cloud of
smoke arises, and the light is soon extinguished. The ex-
planation is this : The hydrogen of the tallow unites with
the chlorine, giving aflame; and the carbon, being separated
from the hydrogen, flies off in minute particles, and soon ex-
tinguishes the flame. The results of the combustion are
hydrochloric acid and lamp-black, the former com-
ing from the union of the hydrogen of the candle
and the chlorine, and the latter from the carbon
of the caudle, which can find nothing in the jar
to unite with, and so takes this form, some of it
being deposited in a dark film upon the sides of
the jar. If you moisten a slip of paper with oil Fig. ca.

166 CHEMISTRY.

of turpentine, which is composed of carbon and hydrogen,
and put it into a jar of chlorine, it will burn spontaneously
(Fig. 69, p. 165), the hydrogen making the flame, and the re-
leased carbon producing a cloud of heavy smoke.

222. Hydrochloric Acid, HC1. — We have already had so
much to do with this acid that you know its composition
and nature. We have hitherto always used a solution of
gaseous hydrochloric acid in water without further expla-
nation. Hydrochloric acid, then, is a colorless gas, with acid
properties, pungent odor, and very soluble in water ; in fact,
water is capable of taking up 500 times its bulk of this gas.
Commercially this solution is called muriatic acid — a name
a hundred years old. Hydrochloric acid dissolves many
metals, forming chlorides. It is of great value in the arts.

223. Production of Hydrochloric Acid. — It can be pro-
duced synthetically, i. e.y by the direct combination of its
elements, and it is curious that light is the agent that makes
them combine. If equal quantities in bulk be mixed by
candle-light, and be kept in the dark, no combination will
take place, but the two gases will remain simply mixed to-
gether. If now the jar containing the gases be exposed to
the direct rays of the sun, the union will be so sudden as to
cause an explosion. Sometimes this result occurs by expos-
ure to the diffuse light of the sun, but commonly the di-
rect rays are required. Of course in this very dangerous
experiment the jar should be inclosed in a wire screen to
guard against injury.

224. Common Mode of Preparation. — Hydrochloric acid is
commonly prepared by mixing together common salt and
dilute sulphuric acid, and applying heat to the mixture.
The chemical reaction is as follows :

Sodium Sulphuric Hydro-sodium Hydrochloric

chloride. acid. sulphate. acid gas.

NaCl + H2S04 = NaHS04 + HC1

CHLORINE, BBOillNE, IODINE, AND FLUOBINE. 167

Fig. 70.

You see the chlorine of the sodium chloride unites with
part of the hydrogen of the sulphuric acid, forming hy-
drochloric acid ; and the sodium takes the place of the hy-
drogen which left the acid, forming an acid salt — hydro-
sodium sulphate. Now you see what would have taken
place had we omitted the manganese dioxide in the prepara-
tion of chlorine in § 211. Compare the two equations.

225. Aqua Regia. — This is a mixture of nitric and hydro-
chloric acids in the proportion of one part of the former to
three of the latter. Neither of these acids alone will dis-
solve gold or platinum, but this mixture of them will do it ;
and as gold is considered the king of metals, the liquid that
can dissolve it has been styled aqua regia, or royal water.
But we do not have in this case, in reality, a mere physical
solution of gold. It is something more. A chemical change
takes place by which a union is effected between the gold
and the chlorine of the hydrochloric acid, making chloride of
gold, and it is this salt of gold which is dissolved, and not gold
itself. The explanation is this : While gold put into hydro-
chloric acid can not take its chlorine, the nitric acid which

168 CHEMISTRY.

is added in making aqua regia forces the hydrochloric acid
to give up its chlorine, which at once unites with the gold.

226. Compounds of Chlorine with Oxygen. — Chlorine unites
with oxygen in several properties, forming anhydrides.
These form with water four acids : hypochlorous, IIC1O ;
chlorous, HC1O2 ; chloric, HC1O3 ; and perchloric, HC1O4, as
shown in the table on p. 35.

Two of these acids are formed on passing chlorine gas
into a solution of potassium hydrate; thus:

^i , . Potassium Potassium Potassium Potassium w
ine' hydrate. chloride. hypochlorite. chlorate.

C18 + 8KHO = 6KC1 + KC10 + KC1O3 + 4H2O
You see that part of the oxygen of the potassium hydrate
oxidizes the chlorine and combines with the potassium. Ac-
cording to the strength of the potassium solution you ob-
tain more of the hypochlorite or of the chlorate, the weaker
solution giving more of the former. Hypochlorous acid is a
powerful bleaching agent ; combined with calcium it makes
the so-called chloride of lime, of which you will learn more
later. Potassium chlorate, you remember, was used in the
preparation of oxygen gas. It is also used in medicine to
a limited extent. The anhydrides corresponding to the
first three acids named are unstable gases ; all have a red or
yellow color and a pungent odor. We will not describe them
further, but will notice the preparation of one of them — hy-
pochlorous anhydride. It is best prepared by the action of
chlorine upon dry mercuric oxide:

Mercuric oxide. Chlorine. 2° dride"8 Mercuric chloride.

2HgO + C14 = C120 + HgCl2

227. Other Compounds of Chlorine.— Chlorine also forms com-
pounds with carbon and with nitrogen, but they are far too rare and unin-
teresting to describe here. Chloride of nitrogen is one of the most danger-
ously explosive substances known, and must never be prepared by students
11 for fun." So we will not tell you how to make it.

CHLORINE, BROMINE, IODINE, AND FLUORINE. 169

228. Iodine. — While chlorine is a constituent of the salt
of the sea, iodine is found in many of the sea's products, as
sea- weed, sponge, etc., in combination with sodium and other
metals. It is commonly obtained by making a lye from the
ashes of sea-weeds, called kelp, and separating the iodine
from this lye by a chemical process. The lye is evaporated
till all the sodium carbonate and other salts in it are crys-
tallized, and the remaining liquor, after being treated with
sulphuric acid, is heated gently with manganese dioxide in
a leaden retort, a b c,Fig. 71, the iodine passing out in va-

Fig. 71.

por, and being condensed in the successive receivers, d. The
action of the manganese dioxide is the same as in the cor-
responding method of preparing chlorine. After the dis-
covery of iodine, in 1811, by M. Courtois, of Paris, the prep-
aration of kelp became quite a large business on the coast
of Scotland. Iodine is chiefly used in the arts in the proc-
ess of dyeing and in the making of photographic pictures.
It is also used in medicine.

170 CHEMISTEY.

229. Properties. — Iodine is a solid substance of a deep-
blue color, with a somewhat metallic lustre. By the ap-
plication of heat it may be made to rise in a beautiful vio-
let vapor or gas. This gives it its name, which comes from
a Greek word meaning violet-colored. The vapor of iodine
is nearly nine times as heavy as air, and is one of the heav-
iest of the gases. Iodine is not very soluble in water, but
is quite soluble in alcohol, and forms with it a tincture
much used in medicine.

230. Iodine a Supporter of Combustion. — Combustion in

iodine is much the same as in chlorine. For
purposes of experiment in this respect you can
prepare the gas by placing a few grains of the
solid iodine in a jar, «, Fig. 72, and heating the
jar by a sand-bath, b, and spirit-lamp, c. The
jar will become gradually filled with the violet-
colored gas, the air in the jar being pushed up
before it. If a lighted taper or candle be let
down into the jar it burns, but dimly, however. A piece
of phosphorus introduced into it takes fire spontaneously.

231. Bromine. — Bromine is contained in sea-water, where
it exists in small quantity, combined with magnesium. It
is the only elementary substance, save mercury, which is
liquid at ordinary temperatures. It is of a dark brown-red
color, and very heavy ; it has a powerful, irritating odor,
whence it receives its name, bromos being the Greek word
for bad odor. It is a corrosive and deadly poison. It is
used in medicine and in photography, chiefly as sodium bro-
mide. Iodine and bromine form hydrogen compounds and
oxygen compounds almost exactly the same as chlorine.
These three elements are always found associated, and seem
to be members of the same family.

232. Fluorine. — This element has never been prepared in
a free state, and is known to chemists only in combination.

CHLORINE, BROMINE, IODINE, AND FLUORINE. 171

It occurs rather abundantly in nature, combined with cal-
cium chiefly. The beautiful mineral fluor-spar is calcium
fluoride. The hydrogen compound of fluorine is of great
importance to the chemist and in the arts, owing to its val-
uable property of dissolving silica and attacking glass.
This hydrofluoric acid, as it is called, HF1, is a colorless,
acid gas, soluble in water. You can make a pretty experi-
ment with it, but be careful not to breathe the fumes.
Take a small leaden dish, and put into it some powdered
fluor-spar, calcium fluoride. Next take a watch-glass, warm
it gently, and make beeswax to flow evenly over the convex
surface. Now write a word, or scratch any thing you please
with a pin on this wax-covered glass, removing the wax
only where you wish lines to be eaten into the glass. Pour
some strong sulphuric acid into the leaden dish containing
the calcium fluoride, heat gently, and, as soon as you see
white fumes, cover the dish with the wax-covered glass.
The gaseous hydrofluoric acid will eat away the glass
where not covered by the wax. Remove the glass after
some minutes, scrape off the wax, wash the rest off with
benzol, and you will have an etched surface exposed. Par-
affin may be used instead of wax.

QUESTIONS.

208. What four bodies form a natural group ?— 209. Where and how
does chlorine occur in nature? Is it abundant? — 210. Describe and ex-
plain a method of obtaining chlorine from common salt. — 211. From hy-
drochloric acid. — 212. What is said about breathing chlorine ? — 213. What
about chlorine water? — 214. State what action chlorine has on some met-
als.— 215. Show its attraction for hydrogen by describing the experiment
named. — 216. How is advantage taken of this attraction in bleaching?
What really does the work? — 217. What happens if the chlorine be in too
great excess? — 218. What advantages has this method over grass-bleach-
ing? Who discovered chlorine? — 219. Explain the difference between
chlorine bleaching and sulphur bleaching. — 220. How is chlorine used as a

172 CHEMISTRY.

disinfectant? — 221. Describe a case of combustion in chlorine. Why does
a candle smoke so badly in chlorine ? How does oil of turpentine act in
chlorine gas? — 222. What is hydrochloric acid, and what are its properties?
What is its commercial name ? — 223. Show how this acid can be obtained
synthetically. — 224. Describe the common mode of preparing hydrochloric
acid. What will be formed if you add manganese dioxide to the materials
employed ? — 225. What is aqua regia ? Whence comes its name ? — 22G.
What is said of the oxygen compounds of chlorine ? What bodies form
when chlorine gas is passed into a solution of potassium hydrate ? — 228.
What is said of iodine ?— 229. What of its properties ?— 230. How does it
support combustion? — 231. What is noticeable about bromine ?— 232. Of
what use is fluorine itself? Explain a method of etching glass.

CHAPTER XII.

SULPHUR.

233. Occurrence of Sulphur. — Sulphur is a very abundant
substance in nature. In the combinations of sulphur with
copper, lead, silver, and many other metals, forming sul-
phides, we have their most important ores. Much of the sul-
phur which is used is obtained from a sulphide of iron, or
iron pyrites. Large beds of native sulphur are often found,
especially in volcanic localities. Combined with oxygen as
sulphuric acid, it exists in great amount in the sulphates, the
most abundant of which is the sulphate of lime, called gyp-
sum or plaster of Paris. It enters also in small proportion
into the composition of both vegetable and animal substan-
ces, being in considerable quantity in some of them, as in
beans, pease, horseradish, onions, etc., in the vegetable world,
and in eggs, hair, horns, hoofs, etc., in the animal.

234. Forms of Sulphur. — Sulphur is disposed to take a
crystalline arrangement, and always does to a greater or
less degree. Even when cast in roll there is some crystal-
lization, imperfect and irregular, so that when it is held in

SULPHUR.

173

the warm band the expansion occasioned by the heat causes
a separation and friction of the crystals, and consequently
a crackling sound. So, also, when the roll is broken the sur-
face presents a glistening appearance, because of the multi-
tude of surfaces of crystals. Even in the flowers of sulphur,
though apparently a fine powder, there is really the crystal-
line state, as may be seen by examining the pow-
der with a microscope. When a fair opportunity is
given to the particles of sulphur to arrange them-
selves without disturbance, crystals are formed of
considerable size and of great beauty. In the fis-
sures and cavities of the beds of sulphur in vol-
canic countries there are collections of crystals of Fig> T3*
the shape seen in Fig. 73. It is curious that the crystals
are of a different shape if they are formed artifi-
cially. Melt some sulphur in a crucible, then, let-
ting it stand till a crust forms over the surface,
quickly break the crust, and pour out all the sul-
phur that is yet liquid. On breaking the cruci-
ble afterward you will find the cavity of the
sulphur covered with fine crystals in the form
of lengthened pillars, as represented in Fig. 74.
Sulphur is said, therefore, on account of its taking
these two crystalline forms, to be dimorphous,
from the Greek dis9 twice, and morphe, form.
Amorphous Sulphur. — Twist a wire
the mouth of a test-tube, Fig. 75,
so that you can conveniently hold it, and,
filling the tube with flowers of sulphur, hold
it over a Bunsen burner. The sulphur as it
melts but half fills the tube. At first it is
thin like water, but on heating it more it
becomes brown and thick. If now you heat
it a little farther it becomes fluid again, Fig. 75.

Fig. T4.

235.
around

174

CHEMISTEY.

and then on being poured into water it becomes a soft
waxy mass, which slowly hardens. This sulphur, not being
at all crystalline, is said to be amorphous, from the Greek a,
without, and morphe, form. When in its waxy state it is
used for copying coins and medals, the copy becoming hard
in a few hours.

236. Flowers of Sulphur. — The two common forms of sul-
phur in commerce
are the roll sulphur
and the flowers of
sulphur. The roll
sulphur is obtained
by distillation in the
manner shown in
Fig. 76, or by sim-
ply melting tho
crude sulphur, and
as the impurities
sink in the liquid the
sulphur is poured
into moulds, where
it is left to cool. The
apparatus for making the flowers of sulphur is represented
in Fig. 77 (p. 175). The crude sulphur is melted in the iron
pot, a, whence it flows into the retort, c / here it is heated
to boiling by the fire, d, and the vapors pass into the large
chamber, e e e. After a while the sulphur vapor cools and
condenses on the sides of the chamber in the form of very
small crystals, so minute as to appear like a powder. When
a sufficient quantity of the flowers is thus formed they are
removed by the door at p. Some melted sulphur accumu-
lates at the bottom, and is drawn off into moulds and cooled.
This constitutes roll sulphur. If the mixture of sulphur
vapor and air should inflame, the consequent explosion will

Fig. 70.

SULPHUR.

175

Fig. 77.

do no harm, for it opens at once the valve, s, and the gases
escape. This process of raising a solid in vapor, and then
condensing it in the form of a powder, is called sublimation.
237. Properties of Sulphur. — Sulphur is familiar to you as
a brittle yellow solid. It is insoluble in water and alcohol.
It takes fire readily, or, in other words, its attraction for
oxygen is such that it requires but little heat comparatively
to render its union with oxygen sufficiently rapid to occa-
sion the phenomena of combustion. For this reason it has
been much used for kindling purposes. By means of it
other substances that unite less readily with oxygen may
be heated to the degree of temperature requisite to set them
on fire. The kindling of a coal fire in the times of the old-
fashioned tinder-box illustrates well the different degrees
of combustibility in various substances. The iron spark
cast off by the blow of the flint sets fire to the finely divided
charcoal of the tinder ; this kindles the sulphur on the match,

176 CHEMISTRY.

by means of which the paper, the wood, and the coal are
successively brought to the degree of heat requisite for
combustion. The following, then, is the order of these arti-
cles in relation to the degree of heat necessary to produce
their combustion — tinder, sulphur, paper, wood, coal. If the
phosphorus so much used at the present day in the lucifer-
matches be put in this list, its place will be at the head of it.

238. Sulphurous Anhydride, SO2. — This gas is produced
whenever sulphur is burned. You are familiar with its
smell and its suffocating power. The gas un-

mixed with air can not be breathed at all. It
extinguishes at once a lighted taper, as may be
seen when it is introduced into a jar of it, as
represented in Fig. 7& For this reason, when
a chimney takes fire, it may be extinguished by
sprinkling some sulphur upon the coals. The
sulphurous anhydride, rising, drives out all the
air, and, thus preventing the burning soot from being sup-
plied with oxygen, puts out the fire. The fact that the gas
is very heavy helps to produce this result, for while it fills
the chimney it is not disposed to pass rapidly upward.

239. Preparation of Sulphurous Anhydride. — This gas, though
easily obtained on a large scale by burning sulphur, is usually prepared in
the chemist's laboratory by heating copper with concentrated sulphuric acid.
The reaction is as follows :

Su,phuricacid. Copper.

2H2S04 + Cu = CuS04 + S02 + 2H2O
The sulphuric acid is decomposed, some of it furnishing S0a and 02 to
form water with H4, while some of it forms copper sulphate with the metal.
Charcoal can be used in place of copper, the reaction being different :

Pfli-hnn Sulphuric Sulphurous Carbonic WntPr

acid. anhydride. anhydride.

C + 2H2S04 = 2S02 + C02 + 2HSO
You see that more sulphurous anhydride is obtained by this method from

SULPHUB.

the same amount of sulphuric acid, but it is mixed with carbonic anhydride,
which is not wanted in many experiments.

Sulphurous anhydride is very eagerly absorbed by water,
which takes up 40 volumes. This solution is an unstable
acid, like carbonic acid :

Sulphurous anhydride. Water. Sulphurous acid.
S03 + H30 = H3SO3

Yet many salts are formed by replacement of the hydrogen
in this acid; such salts are called sulphites, " ous " acids
making "ites," as you learned in § 79.

240. Bleaching Properties of Sulphurous Anhydride. — It is
the sulphurous anhydride which is the bleaching agent when
straw goods are placed in a chamber in which sulphur is
burned. The gas unites chemically with the oxygen of the
coloring matter, and turns it white. The bleaching power
of this acid may be very prettily illustrated by holding a
red rose or peony over a burning stick of sulphur. The
coloring matter is not destroyed in bleaching, but there is a
chemical union between it and the acid ; and it is a union
that can be broken up either gradually by the action of light
and air, as is manifested in the return of color after a time
to the bleached articles, or quickly by the action of some
powerful agent, as sulphuric acid. We will give a single
illustration of the latter. If you pour a solution of sulphur-
ous anhydride in water into an infusion of logwood shav-
ings, the infusion loses its dark color ; but if you pour into
it a little sulphuric acid, the color will be at once restored.

241. Sulphuric Anhydride, SO3. — This body, which may
be considered as sulphuric acid less the elements of water,
is a glistening white solid. It can not be kept unless it be
shut in from the air in glass tubes hermetically sealed. On
exposure to the air it fumes violently, and soon becomes
fluid by attracting the moisture of the air. If it be thrown

II 2

178 CHEMISTRY.

into water it hisses like red-hot iron, and forms sulphuric
acid :

Sulphuric anhydride. Water. Sulphuric acid.
SO, + HaO = H3SO4

This anhydride dissolved in common sulphuric acid forms
the so-called Nordhausen or fuming sulphuric acid, gen-
erally obtained by distilling ferrous sulphate (sulphate of
iron) :

Ferrous sulphate. Ferric oxide. Sulphuric Sulphurous

anhydride. anhydride.

2(FeSOJ Fe303 + SO3 + SO3

When water is present, and this is generally the case, some
of the sulphuric anhydride dissolves in it, forming sulphuric
acid (as above), and some of this anhydride dissolves in the
acid thus formed. This acid is called Nordhausen acid, after
the town in Saxony where it has been made for many years.
This was one of the earliest ways of making sulphuric acid,
but common oil of vitriol is manufactured differently.

242. Manufacture of Sulphuric Acid. — This acid has one
more atom of oxygen in it than sulphurous acid, and there-
fore can be made from the latter by adding this amount of
oxygen to it. When sulphur burns it forms sulphurous an-
hydride, and will not take up any more oxygen from the
air; hence this oxygen must be added in an indirect manner,
as shown in the following sentences : Sulphurous anhydride
produced by burning sulphur, or by roasting iron or copper
pyrites, is conducted together with steam into an apartment
lined with lead, on the floor of which is some water. But
there is sent in with this some nitric acid; this acid on
meeting the sulphurous anhydride gives up to it a part of
its oxygen, and the sulphuric anhydride thus formed dis-
solves in the watery vapor present, making sulphuric acid.
Meanwhile the nitric acid, having parted with some of its

SULPHUR. 179

oxygen, is no longer nitric acid, but nitric oxide ; this imme-
diately absorbs oxygen from the air in the leaden chamber,
becoming nitric peroxide. Then this nitric peroxide, meet-
ing sulphurous anhydride, again gives up its oxygen; and
this process is repeated over and over. Thus you see the
nitric peroxide answers simply as a medium for delivering
over to the sulphurous anhydride the oxygen from the air.

Fig. 79.

The sulphuric acid that is formed becomes dissolved as
fast as it is made in the water in the lead chamber. In order
to facilitate this solution steam is constantly admitted into
the chamber, so that each particle of the acid may be dis-
solved as soon as it is formed. The water is in this way
sent in search of the acid.

243. Explanation in Formulae.— There are three stages :

!S±r »«*««. water. SU'P!TC ***«

annjduue. acid. oxide.

(1) 3(S03) + 2(HN03) + 2(H30) = 3(H3SOJ + 2(NO)

Nitric oxide. Oxygen. Nitric peroxide.

(2) NO + O N03

Nitric Sulphurous w Sulphuric Nitric

peroxide. anhydride. acid. oxide.

(3) N03 + SOa -f H3O = H3S04 + NO
then (2) is repeated, (3) follows, and so on.

244. Properties. — Sulphuric acid is the most powerful of
all the acids, and is therefore one of the most important

180 CHEMISTEY.

agents of the chemist in his operations. " What iron is to
the machinist," says Stockhardt, "sulphuric acid is to the
chemist. It stands, as it were, the Hercules among the acids,
and by it we are able to overpower all others, and expel
them from their combinations." It chars most vegetable

and animal substances. If a bit of wood be introduced
into it, it becomes black, and in fact is reduced to coal, as
if it had been burned ; for, being composed of carbon, oxy-
gen, and hydrogen, the sulphuric acid takes away the two
latter, combining them to form water, and leaves the car-
bon untouched. It does the same thing to sugar, as that is
composed of the same ingredients as wood.

245. Development of Heat. — If water and sulphuric acid
be mixed together, considerable heat is evolved by the
chemical union which takes place between them. This may
be shown very prettily by the following experiment : Put
some tow or cotton around a wine-glass, with some little
bits of phosphorus placed in it in such a way as to be in
contact with the glass. If now you pour into it some sul-
phuric acid, and then some water, the heat produced will
burn up the combustible material around the glass. It is
supposed that the heat is caused by a condensation which
takes place in the union of the acid and the water. If 50
measures of the acid are mixed with 50 of water, we do not
have as the result 100 measures of the mixture, but only 97,
showing a contraction or condensation which is considered
adequate to the production of the heat.

246. A Practical Direction. — The heat caused by the union
of water and sulphuric acid explains the reason of a practi-
cal direction that may be given in regard to an accident
which sometimes happens with sulphuric acid. If some of
the acid be spilled upon the skin, just wipe off as much of it
as you can with a piece of dry cloth or paper, and then use
a large quantity of water in washing off the rest, so that

SULPHUR 181

the acid may be well diluted. If you should apply water
at first, the heat produced by its union with so much acid
would cause an immediate corrosive action upon the skin.
That the acid itself acts rather slowly, and its action may
be greatly hastened by putting some water with it, may be
seen in the following experiment. Drop a little of the acid
upon paper, and you will see that the decomposition takes
place slowly ; but add a few drops of water, and the decom-
position or corrosive action will be instantaneous from the
influence of the heat produced.

247. Uses of Sulphuric Acid. — The sulphuric acid that we
commonly use is, when it is the strongest, nearly one fifth
water by weight, and its tendency to absorb water makes
it very difficult to keep it of this strength. Exposed to air
it will continually absorb its moisture, and of course increase
in bulk. In air that seems to us perfectly dry this acid
will find some moisture to drink. The chemist sometimes
wishes to obtain some gas in an entirely dry state, and for
this purpose lets it pass through sulphuric acid. The work
is thoroughly done. As the gas bubbles up through the
acid it loses every particle of water, and comes out perfectly
dry.

As sulphuric acid has such strong and varied chemical
powers, it is largely used in the arts. It is used, for exam-
ple, in bleaching, in dissolving indigo for use in dyeing and
calico printing, in manufacturing sodium carbonate and ni-
tric and hydrochloric acids, in the refining of gold and sil-
ver, in the purification of oils, in the manufacture of super-
phosphate of lime, so much used now in agriculture, etc.

Sulphuric acid having two atoms of hydrogen which can be replaced by a
metal, forms two classes of salts, neutral and acid. Thus we have sodium sul-
phate, Na2S04, which reacts neutral, and hydro-sodium sulphate, NaHSO4,
which reacts acid. The second forms when excess of acid is present ; on
heating the acid salt to redness, sulphuric acid is expelled and the neutral
salt remains.

182 CHEMISTRY.

Hydro-sodium sulphate. Sodium sulphate. Sulphuric acid.

2NaHS04 = NaaSO4 + HaSO4

A large number of the sulphates are very soluble ; the
sulphates of the alkaline earths are notable exceptions.
Sulphates are often formed in nature from the sulphides by
the latter taking up oxygen from the air.

248. Sulphuretted Hydrogen, H2S. — This may best be pre-
pared by acting on ferrous sulphide with hydrochloric or
sulphuric acids ; heating is not necessary.

Ferrous sulphide. Sulphuric acid. Ferrous sulphate.

FeS + HaS04 FeS04 + HaS

The apparatus used is shown in Fig. 80. The gas which
comes over is colorless, and has a very strong odor of rotten
eggs. It is produced in the decomposition not only of eggs,
but of other animal substances, and also of such vegetable

substances as contain
s u 1 p h u r, as pease,
beans, onions, etc.
When at all concen-
trated this gas has a
very decided effect
upon various metals
and their salts. Thus
it blackens white paint
because it attacks the

_ white-lead in it, form-

Fig. so. ing a sulphide of lead.

Silver or copper vessels exposed to it become dark from the
formation of sulphurets of these metals. There is some lit-
tle of this gas very generally in the atmosphere, and hence
silver articles become slowly tarnished. When much con-
centrated it is a very deadly gas, and it is this which oc-
casionally destroys the lives of men engaged in cleaning

SULPHUB. 183

out vaults and sewers. Sulphuretted hydrogen burns with
a pale blue flame, producing sulphurous anhydride and
water, H2S+O3=H2O-f SO2. It dissolves in water freely,
and the solution is of great service to the analytical
chemist as a reagent, for it forms colored sulphides with
solutions of many of the metals. This solution does not
keep perfectly, sulphur precipitating, and hydrogen escap-
ing or uniting with oxygen.

QUESTIONS.

233. How does sulphur occur in nature in the mineral kingdom ? How
in the vegetable ? How in the animal ? — 234. What is said about the forms
of sulphur ? What is the meaning of dimorphous ? — 235. How can soft sul-
phur be made ? Why is it called amorphous ?— 236. How are flowers of
sulphur made ?— 237. What are the properties of sulphur ?— 238. What does
burning sulphur produce ? — 239. How is sulphurous anhydride prepared ?
How are sulphites formed ? — 240. Explain the bleaching power of sulphur-
ous anhydride. — 241. What are the properties of sulphuric anhydride?
How is it prepared ? What is Nordhausen oil of vitriol ? — 242. State in
full the process of manufacturing sulphuric acid. — 243. Explain the reac-
tions by equations. — 244. What are the properties of sulphuric acid? — 245.
What happens when you mix concentrated sulphuric acid with water? —
246. What remedy should be employed to prevent the corrosive action of
sulphuric acid on the skin ? — 247. Name some of the uses of sulphuric acid.
What is the distinction between neutral and acid salts ? — 248. How is sul-
phuretted hydrogen best prepared ? What is the equation ? What are its
properties ? What is said of its burning ? What of its solution ?

184 CHEMISTRY.

CHAPTER

PHOSPHORUS.

249. Properties of Phosphorus. — This substance, discov-
ered more than two hundred years ago, and obtained now
extensively from bones, has very remarkable properties,
with which you have already become somewhat acquainted.
It is a nearly colorless substance, having a waxy appear-
ance. Exposed to the air it smokes, and in the dark emits
light, from which it gets its name, derived from two Greek
words signifying together to bear light. It is, you remem-
ber, inflammable at ordinary temperatures, and therefore in
order to preserve it we must keep it in water. From the
readiness with which it takes fire, and the violence with
which it burns, it is necessary to be careful in handling it.
It should be cut under water, and when taken from the
water it should be held by a forceps or on the point of a
knife, as even the warmth of the hand may set it on fire.
We should use small quantities in experimenting, and have
a vessel of water at hand to quench it in case it should
take fire accidentally \vhen we do not wish it. Phosphorus
is a violent poison, and is therefore used in getting rid of
rats and mice. The common rat electuary is made of a
dram of phosphorus and eight ounces each of hot water and
flour. Phosphorus is insoluble in water, but is soluble in
ether, alcohol, and oils.

250. Experiments. — Observing the cautions given, you
can try many interesting experiments with phosphorus,
some of which we will notice.

PHOSPHORUS. 185

Put into a phial half an ounce (a tablespoon ful) of ether,
and then a piece of phosphorus twice the size of a pea.
Cork the phial, and put it aside for several days, occasionally
shaking it. Pour the clear liquid now into another phial,
and it is ready for use. If you moisten your hands with
some of this solution, the ether will speedily evaporate,
leaving the phosphorus in small quantities all over the skin,
which of course combines with the oxygen of the air, and in
doing so-gives out a light which in the dark is very bright.
By rubbing the hands you make the light more vivid, be-
cause you quicken this union of the phosphorus and oxygen.
The quantity of phosphorus used in this case is so small
that little heat is evolved, and we have a slow combustion,
producing phosphorous anhydride.

Moisten a lump of sugar with this solution, and throw it
into hot water. The ether and phosphorus rise together to
the surface, and the moment they reach the air they take
fire. The combustion is here rapid and perfect, and there-
fore phosphoric anhydride, which has more oxygen in it
than the phosphorous anhydride, is formed.

Pour some of the solution upon fine blotting-paper, and
it will burst into flame as soon as the ether is evaporated.

If you boil water in a flask with some phosphorus in it,
the escaping steam will be luminous.

251. Amorphous Phosphorus. — When ordinary waxy phos-
phorus is heated for many hours in tightly closed vessels in
such a manner that it can not burn, a great change in its
properties takes place, and we obtain what is known as
amorphous phosphorus. This is dark-red in color, is opaque
instead of transparent, its specific gravity is higher, it is
insoluble in the liquids which dissolve ordinary phosphorus,
and, most remarkable of all, it no longer takes fire in the
open air at low temperatures. It may be heated quite hot,
beyond 200° C., without inflaming. This red phosphorus

180 CHEMISTRY.

is another case of allotropism, which, you remember, in the
case of ozone and carbon was attributed to a difference in
the arrangement of the atoms.

252. Lucifer-Matches. — As phosphorus can be ignited by
friction, it is used in the manufacture of hicifer-matches.
The substance on the ends of the matches is a mixture of
phosphorus with other substances that contain considerable
oxygen, the composition being done up in mucilage of gum
arabic. The object is to supply oxygen in the immediate
neighborhood of the phosphorus, that the friction may read-
ily produce combustion. The particles of the phosphorus
are so much shut in from the air in the dried mass that the
oxygen of the air can get admission to comparatively a
small portion of them. The substances containing oxygen
that are commonly used are red-lead (oxide of lead), potas-
sium nitrate, and potassium chlorate. A formula given by
Stockhardt is this: If parts of phosphorus, 4 each of gum-
arabic and water, 2 of nitre, and 2 of red -lead. Safety
matches are made with amorphous phosphorus, which is
less liable to be set on fire by accidental friction. Some-
times the phosphorus composition is applied only to the
surface of the box, and then the matches ignite only when
rubbed on this surface.

253. Mode of Obtaining Phosphorus. — As already stated,
phosphorus is obtained from bones. These are composed
mostly of an animal substance, gelatine, and a mineral sub-
stance, phosphate of lime. The gelatine is first burned out,
and the phosphate of lime which is left is reduced to pow-
der. This powder is digested with dilute sulphuric acid,
and in consequence a sulphate of lime is formed, which is
an insoluble substance. As, therefore, phosphate of lime is
composed of phosphoric acid and lime, the lime being re-
moved, we have the phosphoric acid dissolved in the dilute
sulphuric acid. This solution, after being strained, is mixed

PHOSPHOEUS.

187

Fig. 81.

with powdered charcoal, and when the mixture is dry it is
put into a stone-ware retort, a,
Fig. 81, to the neck of which is
attached a copper tube, £, the
mouth of which dips under wa-
ter in a vessel. The retort be-
ing subjected to a white heat,
the charcoal unites with the
oxygen of the phosphoric acid
to form carbonic oxide, and the
disengaged phosphorus be-
comes vaporized. The vapor
and the gas pass over together
through the tube, b, the phos-
phorus becoming condensed
and dropping into the water, and the gas passing out
through the small tube in the vessel. Phosphorus is com-
monly in the form of small round sticks, this form being
given to it by melting it in glass tubes in warm water.

254. Diffusion of Phosphorus in Nature. — Phosphorus is
quite widely diffused, not as phosphorus, for it is never
found as an element, but in combination with other sub-
stances. There is in the body of an adult man from 500 to
800 grammes of phosphorus. It is not all in the bones, but
there is some in the blood and the flesh, and especially in
the brain. Now the phosphorus that is in animals must
come from vegetables, and these must get it from the min-
eral world. The phosphate salts appear in all kinds of
grain, and in leguminous and many other plants, especially
in their seeds. If there were no such salts in the soil these
seeds could not be produced, and hence in part the great
usefulness of bones, in many cases, as a manure, supplying
the deficiency of these salts in the soil. From all this
you see that phosphorus has a wide and constant circula-

188

CHEMISTRY.

tion in the chemical and vital operations going on in the
world.

255. Phosphoretted Hydrogen, H3P. — This is a colorless
gas having the odor of garlic. A beautiful phenomenon
attends its production if it be allowed to escape into the air.
Let about 30 grammes of potassium hydrate be put into a
small retort, Fig. 82, and pour in upon it half a tumbler of

Fig. 82.

water ; then add a bit of phosphorus-stick half an inch long
and a teaspoonful of ether, and apply the heat, the beak of
the retort being under the surface of the water in the bowl.
The ether has nothing to do with making the gas, but this
is made by the action of the phosphorus and potassium hy-
drate and water together. The object of the ether is to
prevent an explosion, which would be liable to occur if the
gas escaped directly into the air in the retort. The ether
does this very effectually, for, being vaporized by the heat,
it rises, driving the air out before it, and then the gas, which
is generated as the heat increases, passes out behind the
ether, which acts thus as a sort of advance-guard. The gas,
as it comes up out of the water in the bowl, takes fire spon-

PHOSPHOBUS. 1 89

taneously, emitting a bright yellow light ; and the smoke
rises in rings, which enlarge as they go up, exhibiting at
the same time a singular rotary movement. The reaction
is complicated :

,,, . Potassium Phosphoretted Potassium

Phosphorus. Water. hydrate> hydrogen, hypophosphite.

P4 + 3H20 + 3KHO = H3P + 3KPH3O3

It is this gas, forming with hydrogen and nitrogen in the
decomposition in the mud of marshes, which causes the light
called " will-o'-the-wisp."

256. Another "Way of Making Phosphoretted Hydrogen, —
Phosphide of calcium thrown into water acidulated with
hydrochloric acid gives off phosphoretted hydrogen, which
ignites spontaneously. This experiment can be made in a
wine-glass without danger.

257. Compounds of Phosphorus -with Oxygen. — These are
two in number. First we have phosphorous anhydride,
formed by slow combustion, as exemplified in the first ex-
periment in § 250. Then we have phosphoric anhydride,
the result of perfect combustion, as in the second experi-
ment, and in the burning of phosphorus in oxygen gas, no-
ticed in § 58. Both of these anhydrides dissolve in water,
forming corresponding acids. Phosphoric acid is made in
another way, however, as this is inconvenient. Phosphorus
is heated with moderately strong nitric acid, the phosphor-
us is oxidized by the acid, and on concentrating the solu-
tion the excess of nitric acid is expelled and a sirupy liquid
remains. Phosphoric acid, H3PO4, containing three atoms
of hydrogen, is a tri-basic acid, and forms a great variety
of salts.

A third acid is known, hypophosphorous acid, the compounds of which
are used in medicine. Its anhydride has not as yet been prepared.

1 90 CHEMISTRY.

QUESTIONS.

249. How long has phosphorus been known ? What are its properties ?
How does it act physiologically? In what is it soluble? — 250. Describe
some experiments with a solution of phosphorus. — 251. How is amorphous
phosphorus obtained ? What is allotropism ?— 252. What is the chief use
of phosphorus? — 253. Detail the method of obtaining phosphorus. — 254.
Where and in what state does phosphorus occur in animals ? How do an-
imals get it ? — 255. What is the composition of phosphoretted hydrogen ?
What is its nature ? Explain a method of obtaining it. What name is
given to it when occurring in marshes ? — 256. Mention another way of
making this gas. — 257. What compounds does phosphorus form with oxy-
gen ? What is said of the acids ?

CHAPTER XIV.

SILICON AND BORON.

258. Silicon. — This element never occurs in nature in a
free state, but its compound with oxygen — silicic anhydride,
SiO2 — is most important and abundant. Silicon itself is ca-
pable of existing in three allotropic forms, like carbon ; the
form corresponding to lampblack is a dark-brown powder,
destitute of lustre ; the diamond form is crystalline, and so
hard as to scratch glass. These substances are mere chem-
ical curiosities, and their preparation does not interest us.
United with oxygen it forms silicic anhydride, commonly
called silica ; this unites with the elements of water, form-
ing a true acid, which, when freshly prepared, appears like a
transparent jelly. On igniting, water is driven off and sil-
ica remains. Compounds of silicic acid and metallic oxides
are called silicates.

259. Abundance of Silica. — It is estimated that silica con-
stitutes about one sixth of the bulk of the earth. It ap-
pears in various forms and combinations. It is nearly pure

SILICON AND BORON. 191

in quartz and flint. Various precious stones, carnelian, am-
ethyst, opal, jasper, etc., are silica, their different colors be-
ing caused by the presence of metallic oxides. Common
sand is silica, generally rendered yellow by the hydrated
oxides of iron or iron rust. Then silica is present in many
salts called silicates, constituting part of an abundant class
of rocks. In the granite rocks we have mingled with the
quartz, which is silica, two silicates — feldspar and mica.
There are silicates in many other rocks also. In clays there
are variable quantities of various silicates ; but the silicate
of alumina is largely predominant, and is the essential basis
of all clays. The best porcelain clay, which is perfectly
white, is nearly pure silicate of alumina. As earthenware
is made of clay, it is composed of silicates. The same thing
is true of the various kinds of glass.

260. Silica in "Water and in Plants. — Through the agency
of potash silica is rendered soluble to some extent, and
therefore is found in water and in plants. If spring-water
be evaporated, what remains in solid form is in part silica ;
and so if we burn plants, it is found in their ashes. There
is considerable silica in grasses and the various kinds of
grain, and they have therefore been called silicious plants.
Absorbed by the root, it goes up in the plant dissolved in
the sap, and is deposited chiefly in the stalks, giving to them
their requisite firmness. It is to them what the mineral
matter, the phosphate of lime, in our bones is to us. Silica
is also present to a considerable extent, especially in the
frame- work of those minute animals, which can be seen only
by means of the microscope, called infusoria.

261. Silicified Wood. — A singular result occurs when
wood decays in water that has considerable silica dissolved
in it. The water, of course, soaks into every part of the
wood, taking the silica along with it. Now, as the parti-
cles of wood are loosened one after another and carried

192 CHEMISTRY.

away, a particle of silica takes the place of every removed
particle of wood, so that at length all the wood is gone, and
is wholly replaced by silica. Because the shape and all the
lines of the wood are preserved, the common idea is that the
wood is turned to stone ; but, as you see, stone has merely
taken the place of wood. Silicified wood is found in great
quantity in certain parts of California and Oregon. Large
trunks of trees are found completely silicified. Such speci-
mens are erroneously called petrifactions, as if they were
the result of turning into stone.

262. Glass. — In making glass, the silica or silicic anhydride
is made, by an intense and long-coatinued heat, to unite
with various bases, according to the kind of glass required.
Window-glass is made by uniting silica with soda and lime ;
plate-glass, crown-glass, and the beautiful Bohemian glass,
by uniting silica with lime and potash ; and green-bottle
glass is commonly a silicate of lime and alumina, combined
with oxides of iron and manganese, and sodium and potas-
sium, its green color being produced by the oxide of iron.
Glass is in reality a very complex mixture of true salts.
What is called enamel is an opaque glass, made so by some
substance which, though it be thoroughly mixed with the
glass in melting, does not melt with it. Stannic oxide is
commonly used for this purpose. The silica used in mak-
ing glass is in the forms of sand, quartz, flint, and old broken
glass. The materials are subjected to intense heat in clay
pots for about forty-eight hours, in order to bring the mass
into a proper state to be worked. The manner in which
the melted glass is made into various articles we will not
detail. The common mode of making window-glass is de-
scribed in Part I, § 216.

263. Coloring Glass. — The various colors are given to glass
mostly by metals. We have already mentioned the bottle-
green color imparted by the ferrous oxide. Ferric oxide gives

SILICON AND BORON. 193

a yellowish-red color, oxide of cobalt blue, oxide of manga-
nese purplo and violet, oxide of copper a ruby red, etc.

264. Annealing. — Glass, like steel, must be annealed to de-
prive it of its brittleness. For this purpose the articles that
are made are placed in the annealing furnace, which is a very
long gallery containing iron trays that are moved very slowly
through it by means of an endless chain. The heat at the
end where the articles are put in is very great, and gradually
lessens toward the other end. Every article is from twenty-
four to forty-eight hours in passing through the gallery, and
the particles of the glass have time, in this slow cooling, to
assume such an arrangement as to give them

their highest degree of firmness. We see the
opposite result in what are called "Prince
Rupert's Drops," which are prepared by
taking up on an iron rod some melted glass
and allowing the drops of it to fall into cold
water. They assume the shape given in Fig.
83. The particles in this case, solidifying
hastily, have an exceedingly unstable ar-
rangement, which can be wholly destroyed
by a very slight disturbance. If, therefore,
you scratch the surface or break off the lit-
tle end, the whole flies into powder so quick-
ly as to cause a considerable report.

265. Slag. — The slag which is so often seen in reducing
metallic ores is composed of silicates, and is a kind of glass.
In the process of reducing iron ore, described in Chapter
XVIIL, the lime is used, because it makes, with the silica
that is mixed with the ore, a glass that is very fusible, and
is therefore easily removed. It is for this reason that oys-
ter-shells, introduced among the anthracite coal in a stove,
remove the clinker. The lime unites with the silica, and
the silicate formed, melting easily, runs down and min-

194 CHEMISTKY.

gles with the ashes. So, also, if there be much lime in
the clay that is used for making bricks, they will be apt
to be spoiled in burning, from the too great fusibility of
the silicate that is thus formed.

266. Soluble Glass. — Glass, as commonly made, is wholly
insoluble; but soluble glass can be produced by using a
very large proportion of alkali ; and a solution of it was
known a long time ago as the liquor of flints. Such a solu-
tion is sometimes employed as a fire-proof varnish for wood,
canvas, etc.

267. Earthenware. — All earthenware is made of clay,
which has as its essential ingredient silicate of aluminium.
There are mingled with this in different clays silicates of po-
tassium, sodium, calcium, etc. The coarsest clay employed
is used in making bricks and common flower-pots, and the
finest in making porcelain. The plastic nature of clay, and
its hardening by heat, are the causes of its peculiar adapta-
tion to the manufacture of earthenware. The moistened
clay, after being well kneaded, is shaped, either by pressure
in moulds, as in brick-making, or by the hand of the potter
as he makes it revolve with his lathe, thus pressing into
his service centrifugal force, as indicated in Part I., § 213.
The articles are first dried in the sun, and then are baked
in furnaces, both of which processes cause considerable
shrinking, especially the baking. The reddish-brown color
of bricks and flower-pots is owing to the presence of ferric
oxide. The bricks of the Egyptians, in the making of which
straw was used as one of the constituents, were merely sun-
dried. The bits of straw mingled with the clay were of
the same use as hair is in mortar which is used in plaster-
ing.

268. Glazing. — Although earthenware by baking becomes
hard and firm, it is quite porous, so that water can exude
through it. This is not objectionable in the case of flower-

SILICON AND BOEON. 195

pots, but would be decidedly so for most of the purposes to
which earthenware is applied. To remedy this defect the
ware is covered with a coat of glass. This glazing, as it is
called, is done in various ways. Common earthenware is
often glazed with oxide of lead. This is very dangerous if
the vessels are to be used in cooking or in preserving any
eatables, for the lead may be dislodged by some chemical
action of the contents, and act as a poison. Common salt
is also used. Being thrown into the kiln, it is raised in va-
por by the heat, and is decomposed on coining in contact
with the surface of the ware. The chlorine leaves the salt,
and its sodium becoming soda by attracting oxygen, the
soda unites with the silica of the ware and forms a glass.
For finer articles another mode is followed : A paste is made
of such materials as will, under the influence of powerful
heat, form a glass. These materials are reduced to an ex-
ceedingly fine powder, and this being diffused in water, the
article to be glazed is dipped into it. By this means it
gets a very thin coating of the glaze, for the clay absorbs
at once the moisture, and the fine powder remains uniformly
diffused over the surface. By intense heat this is converted
into a smooth coating of glass. The paste used is often
composed of feldspar, quartz, and borax. Glazing is not
necessary in the case of porcelain and some kinds of stone-
ware, for certain materials which form glass are mingled
with the clay, so that the heat of the baking fills up all the
minute spaces in the clay with glass. Still, the glazing is
usually done for the sake of adding to the beauty of the
ware.

2C9. Boron. — The element called boron is a gray amor-
phous powder. It is never found in nature, but the acid
which it forms, boracic acid, is sometimes exhaled from vol-
canic openings in the earth. The hot vapors of the lagoons
of Tuscany contain it in large quantity. In collecting it,

196 CHEMISTRY.

Fig. 84.— Lagoons of Tuscany

these vapors are made to pass into water, which condenses
them, and then the water is evaporated, which leaves the
boracic acid in large crystalline flakes, having the feeling
somewhat of spermaceti. Boracic acid is not volatile when
it is by itself. If heat be applied to it, it will melt, and be-
come a vitreous mass, but no degree of heat will make it fly
off in vapor. But it is volatile when it is in volatile com-
pany, as we may say ; which is often true of other substan-
ces, and, we may add, persons also. Thus, if we mix some
of it with alcohol in a mortar, and then set fire to the alco-
hol, it will burn with a green flame, because some of the
boracic acid rises in vapor with it. Boracic acid forms
with sodium a bi-borate, commonly called borax, which
we shall notice hereafter.

QUESTIONS.

258. In what does silicon resemble carbon ? What are silicates ?— 259.
What is said of the occurrence and abundance of silica ? What is quartz ?
What is granite ? What is clay ? — 2GO. What is said of the presence of sil-
ica in plants ? What animals contain silica ?— 261. What is silicified wood ?
Explain the error of common opinions regarding it. — 2G2. How is glass

METALS. 197

made ?— 263. What materials are used to color glass ?— 264. How is
ing done, and with what object ? Describe the experiment with Prince Bu-
pert's Drops.— 265. What is slag ? Why do oyster-shells remove clinker in
a furnace ?— 266. What is said of soluble glass ?— 267. Of what is earthen-
ware made ? Whence comes the reddish color of bricks ? Why did the
Egyptians use straw in making bricks ?— 268. How is glazing done ? How
are finer articles glazed ?— 269. What is said of the occurrence of boracic
acid? What is borax?

CHAPTER XV.

METALS.

270. Characteristics of the Metals. — Metals as a class of
substances have certain general characteristics. 1. In masses
they are opaque bodies. It has been thought by some that
gold is an exception, for they assert that light is transmitted
through it when made into lea£.even when the leaf is not
so thin as to permit transmission through multitudes of lit-
tle openings. 2. Metals are not soluble. It is commonly
stated that they are not soluble in water. But it may be
said with truth that they are not soluble in any liquid ;* for,
as you will see farther on in this book, in those cases in
which metals are spoken of as being dissolved, it is not
really the metal which dissolves, but a chemical compound
is formed with the metal by the liquid, and then this com-
pound is dissolved. 3. Metals have more or less of a certain
brilliancy, which is termed, whenever it is found in other
substances, the metallic lustre. 4. Metals are better con-
ductors of heat and electricity than the non- metals, -and
most of them have a higher specific gravity.

Some of the properties of metals require a closer examina-

Certain TymaA^Kte rnqgs excepted.

198

CHEMISTRY.

tion, especially malleability, ductility, fusibility, density or
specific gravity, and tenacity.

271. Density. — Most of the metals are dense, and there-
fore heavy substances. The idea of most people is that a
metal is of course heavy, and this was the idea also of phi-
losophers until Sir Humphrey Davy, in 1807, made his dis-
covery that potash and soda are oxides of metals. This is
illustrated in an anecdote of Dr. Wollaston, a celebrated
English chemist. Davy, just after he had succeeded in ob-
taining by a chemical process the metal potassium, of which
potash is the oxide, put a bit of it into the hands of Dr.
Wollaston, who spoke of it as being quite heavy, and was
surprised to learn that it was lighter than water. There is
a wide range in the specific gravities of the metals, as may
be seen from the following table, which contains a portion
of them :

SPECIFIC GRAVITIES OP METALS.

Sp. Gr. at
15.5° C.

Platinum 21.50

Gold 19.50

Uranium 18.40

Mercury 13.59

Thallium 11.90

Palladium 11.80

Lead 11.45

Silver 10.50

Bismuth 9.90

Copper 8.96

Nickel 8.80

Cadmium 8.70

Cobalt 8.54

Sp. Gr. at
15.5° C.

Manganese 8.00

Iron 7.79

Tin 7.29

Zinc 7.10

Antimony 6.80

Arsenic 5. 88

Aluminium 2.67

Magnesium 1.75

Calcium 1.58

Rubidium 1.52

Sodium 972

Potassium 865

Lithium.. 593

The comparison in this table is made with water, that being
considered 1. There is, you observe, a gradual diminution
in specific gravity in the list till we come to the last seven.
These are very light, three of them are even lighter than

METALS.

199

water, and one of them, lithium, being lighter than any
known liquid.

272. Color. — The colors of almost all the metals are vari-
ous shades between the pure white of silver and the bluish
gray of lead. Bismuth has a reddish-white color. There
are only two metals that have very decided colors — gold,
which is yellow ; and copper, which is red.

273. Tenacity.-— There is great variety in different metals
in their tenacity or power of holding together, iron being
the strongest and lead the weakest. This quality is tested
by using wires of the different metals of the same size and
appending weights to them, observing how much each wire
can possibly hold without breaking. In the following table
the experiments were made on wires one millimetre in di-
ameter:

Metals.

Breaking weight :

wires one millimetre

in diameter.

Lead 3.1 Ibs

Tin 6.9

Cadmium 9.5

Aluminium 18.0

Zinc 23.5

Gold 27.0

Silver 29.0

Copper 37.0

Platinum 44.0

(Brass 56.0

Iron 56.5

(Steel 96.0

Relative
tenacity.

1.00

2.20

3.06

5.80

7.58

8.71

9.35

11.90

14.20

18.00)

18.20

30.00)

274. Malleability.— Malleability, derived from the Latin
word for hammer, is the capability of being beaten into
leaves. Laminability, from the Latin for leaf, lamina, is
sometimes used for the same quality, as exhibited when the
leaves are made by pressure rather than by blows, as when
iron and other metals are flattened by passing between
heavy rollers of steel. More properly it should be used as

200 CHEMISTRY.

including both this and malleability, for in either case la*
minse or leaves are formed. Gold is the most malleable of
all the metals. It has been beaten so thin as to require
nearly 300,000 leaves to make an inch in thickness if they
could be pressed into a solid mass. A leaf of this book equals
forty or more of such leaves in thickness. Some metals are
perfectly malleable when cold, as gold, silver, lead, and tin ;
while others, as iron and platinum, are only slightly malle-
able when cold, but very much so when heated.

275. Ductility. — This quality, named from the Latin word
duco, to lead or draw, is the capability of being drawn out
in the form of wire. It is very nearly allied to malleability.
Wires are made small by being drawn successively through
smooth conical holes in a steel plate, each hole being a little
smaller than the one through which the wire was previously
drawn. Dr. Wollaston made a gold wire so fine that one
hundred and sixty-one metres (five hundred and thirty
feet) of it weighed but sixty-four milligrammes (one grain),
and he succeeded in making a wire of platinum six times
as fine as this. This, then, is more ductile than gold, while
it is not by any means as malleable.

276. Relations of the Metals to Heat. — The melting points
of the metals, or the degrees of temperature at which they
melt, are very different. Thus it requires a much less de-
gree of heat to melt lead than it does iron ; and platinum
resists the heat of the hottest furnace, and can only be
melted in the flame of the oxyhydrogen blow-pipe or the
current of a galvanic battery. This metal stands at one
extreme in regard to fusibility, while mercury stands at the
other. So low is the degree of temperature at which this
latter melts, or, in other words, so little heat is required to
melt it, that it is in the solid state in no weather except
that of winter in the arctic regions. Many metals are quite
volatile — that is, capable of being made to fly off in vapor

METALS.

201

by the application of heat ; some of them at quite a moder-
ate temperature. Thus mercury, arsenic, and zinc are vol-
atile below a red heat. Indeed, at ordinary temperatures
mercury is somewhat volatile, and there is always a thin
vapor of this metal in the vacuum of the thermometer, so
that it is not strictly a vacuum.

TABLE SHOWING THE FUSING POINTS OP METALS.

Mercury. —39° —39.4°

Rubidium 101.3 38.5

Potassium 144.5 62.5

Sodium 207.7 97.6

Lithium 356 180

Fusible Tin 442 235

below a - Bismuth 497 258

red heat. Thallium 561 294

Cadmium 599 315

Lead 626 330

Arsenic. Unknown.

Zinc 773 412

Antimony 842 450

fSilver. 1873 1023

Copper 1996 1091

Infusible Gold 2016 1102

22T*"; •*2786 153°

red heat.

Manganese, f Hi£hest heat
.Palladium, J
Chromium,
Titanium,

Osmium, [• Infusible in ordinary blast-furnaces.
Iridium,
Platinum,

277. Welding. — Some of the metals, as they approach to
the melting point, become semi-fluid or pasty. This is the
case with iron. In this state it can be welded — that is, two
pieces of it can be made to unite by hammering them to-

202 CHEMISTRY.

gether. Lead, potassium, and sodium can be welded without
being heated, and mercury can be welded when it is frozen.

278. Alloys and Amalgams. — Metals unite together to
form alloys. Some of the most common of these we will
mention. Brass is an alloy composed of copper and zinc,
the copper making from two thirds to three fourths of the
whole. The color of the mixture is intermediate between
the deep color of the copper and the light color of the zinc.
What is called pinchbeck is a kind of brass, with a larger
proportion of zinc than ordinary brass. What is called
German silver is a sort of brass with the addition of another
metal, nickel, the whiteness of which gives this alloy its re-
semblance to silver. Bronze is an alloy of copper and tin,
the latter being commonly one tenth of the whole. Bell-
metal is the same, with a larger proportion of tin. Common
type-metal is an alloy of lead with different proportions of
zinc, tin, bismuth, and antimony. Solders are commonly al-
loys of lead and tin. Pewter is tin alloyed with lead or
antimony. What is called Britannia ware is a kind of pew-
ter. The alloys which various metals form with mercury
are called amalgams. A familiar example you have in the
silvering of mirrors. The amalgam is formed in this case
by pouring mercury upon tin-foil laid over the glass.

279. Nature of Alloys. — An alloy is generally considered
as a mixture, and not a compound, for two reasons: 1. In
making alloys there are no fixed proportions in which the
metals must be combined. 2, The qualities of alloys are in-
termediate, for the most part, to those of their constituents.
Thus the color of brass is intermediate to the colors of the
copper and the zinc, and the hardness of type-metal to that
of the copper and that of the lead. But there are some
marked exceptions to this second characteristic of mixtures,
which seem to indicate the existence of some degree of
chemical affinity, sufficient to produce decidedly new quali-

METALS. 203

ties. For example, an alloy of copper and tin, in the pro-
portions of 90 of the former and 10 of the latter, called
speculum metal, is as brittle as glass and almost white.
Now if it were merely a mixture, its color should be that
of copper lightened by the small proportion of tin, as zinc
lightens the copper-color in brass, and the tin should give
to it but a slight degree of brittleness. A single example
more will suffice. There is an alloy which is sometimes
used as a source of amusement, for teaspoons made of it
will melt in a cup of very hot tea. It is composed of 8
parts of lead, 15 of bismuth, 4 of tin, and 3 of cadmium. If
it were only a mixture, the melting point of the alloy would
be somewhere between the melting points of its constituents.
But in fact it is far below them. Lead must be heated to
330° to melt it, bismuth to 258°, tin to 235°, and cadmium
to 315°; but this alloy melts at about 70° — that is, 30° be-
low the boiling point of water.

280. Ores. — The ores of metals are certain compounds
from which the metals are usually obtained. These com-
pounds are commonly oxides or sulphides. When any
metal is found in its uncombined state it is said to be
native. Some metals, as gold and platinum, are always
found in this state, and therefore, strictly speaking, have no
ores, though this word is sometimes loosely applied to them.
Such metals are often found alloyed with other metals.
Thus gold is usually alloyed with silver, copper, etc. Silver
is found in the three conditions, native, alloyed, and com-
bined. The word ore is not applied to all combinations of
metals, but only to those which are used in obtaining the
metals. Thus the carbonate of iron is an ore ; but the car-
bonate of calcium, occurring in the different forms of chalk,
limestone, marble, etc., is not an ore. So while an oxide
of iron is an ore, limestone, the carbonate of calcium, is
not.

204 CHEMISTRY.

281. Classification of Metals. — Metals may bo divided
for the sake of convenience into nine groups, according
to their attraction for oxygen and their chemical relations
generally :

GROUP I. — The Metals of the Alkalies: Potassium, Sodium [and the
very rare metals Lithium, Caesium, and Rubidium].

GKOUP II. — Metals of the Alkaline Earths: Barium, Strontium, and Cal-
cium.

GROUP III. — Metals of the Earths : Aluminium [and the very rare met-
als Glucinum, Yttrium, Erbium, Cerium, Lanthanium,
Didymium].

GROUP IV. — Magnesian Metals. Magnesium, Zinc [Cadmium, and In-
dium].

GROUP V. — Iron Group. Manganese, Iron, Cobalt, Nickel, Chromium
[and Uranium].

GROUP VI. — Tin Group. Tin [and the exceedingly rare metals Titanium,
Zirconium, Thorinum, Columbium, Tantalum, Molyb-
denum, and Tungsten].

GROUP VII. — Arsenic Group. Arsenic, Antimony, Bismuth [and Vana-
dium].

GROUP VIII. — Three Metals not closely related. Copper, Lead [and
Thallium].

GROUP IX. — Noble Metals. Mercury, Silver, Gold, Platinum [and the
accompanying metals Palladium, Rhodium, Ruthenium,
Iridium, and Osmium].

Of these forty-nine elementary substances we shall study
only twenty-three, the remainder (inclosed in brackets in
the above paragraphs) are far too rare and of too little im-
portance and interest to engage our attention. Sometimes
arsenic and antimony are placed for chemical reasons among
the non-metallic bodies alongside of phosphorus, but this is
only a matter of taste. The line drawn between the non-
metals and the metals is not absolute, but merely a con-
venient way of distinguishing them.

There is another way of grouping metals often followed, viz., with refer-
ence to their atomicity ; but this separates metals which seem to belong nat-

METALS. 205

urally in one class, as you see in the following list, where all the metals are
thus arranged, the rare ones being in brackets :

MONADS. DYADS. TEIAD8. TETRADS. PENTADS. IIEXADB.

K Ba [Tl] Ft As Cr

Na Sr [In] [PI] Sb [U]

[Li] Ca Au [Ir] Bi [W]

[Cs] Mg [Bo] [Vd] [Mo]

[Kb] Zn [Ru] [Ta]

Ag Cd [Os] [Cb]

Hg Sn

Cu [Ti]

[Gl] Pb

[Yt] [Zr]

[Er] [Th]

[La] Al

[Dd] Fe

Mu
Co
Ni
[Ce]

QUESTIONS.

270. What are the chief characteristics of metals? — 271. Illustrate the fact
that metals are not necessarily dense. Name the heaviest metal and the
second heaviest. Name the lightest metal. — 272. What three metals have
distinct colors? — 273. What is meant by tenacity? Which is the least
tenacious metal ? Which the strongest? — 274. What is meant by mallea-
bility ? Which is the most malleable of metals ?— 275. What is ductility ?
How fine a platinum wire did an English chemist make ? — 276. How does
a difference of temperature affect metals? Which metals are volatile?
Which is the most fusible metal ? Which the most infusible ?— 277. What
is welding ? — 278. What is said of alloys and amalgams ? Of what is solder
made? Of what German silver? — 279. Is an alloy a true chemical com-
pound ? Why not ? What are the ingredients of fusible metal ? At what
temperature does it melt? — 280. Give in full what is said of ores. — 281.
Into how many groups may the metals be divided ? What two bodies are
sometimes placed among the non-metals ?

206 CHEMISTRY.

CHAPTER XVI.

GROUP I. — POTASSIUM AND SODIUM.

282. Potassium and Sodium. — These metals have so great
an attraction for oxygen that they are never found native.
They occur only in combination, usually as salts. They de-
compose water at ordinary temperatures, setting hydrogen
free ; this is of itself a sufficient reason for their not existing
native. Their oxides and hydrates are exceedingly soluble
in water, forming intensely alkaline caustic solutions. They
form important compounds with the non-metals and with
the principal acids.

283. How Potassium is Obtained. — Potassium was origi-
nally obtained by Davy by decomposing the hydrate, by
means of a galvanic battery. But it is now commonly ob-
tained by decomposing potassium carbonate by a process
which we will describe. The carbonate and some charcoal

.finely pulverized and well mixed are exposed to a white
heat in an iron retort, a, Fig. 85 (p. 207). Observe now what
the chemical changes are. Potassium carbonate is composed
of K2CO3. This is decomposed, the oxygen uniting with
the carbon to form carbonic oxide. We have then formed
two things, carbonic oxide and the metal potassium :
Potassium carbonate. Carbon. Potassium. Carbonic oxide.

K2CO3 + 2C K2 + SCO

Now the heat is so great that the metal is in the state of
vapor, and this vapor and the carbonic oxide gas pass out
together through the tube, », into the copper receiver, h.
The upper part of this receiver is surrounded by a wire

POTASSIUM AND SODIUM. 207

Fig. 85.

basket, b x c c?, which is filled with ice. The object of this
is to condense the vapor of the metal, while the gas, the car-
bonic oxide, is allowed to escape through an opening. The
condensed metal falls to the bottom of the reservoir into
some mineral naphtha. This is a liquid which contains no
oxygen, its ingredients being only carbon and hydrogen,
and therefore it will not have any effect upon the potassium.
There are some minute details in this process wThich we have
omitted in order that the main points may be clear to you.
The process is expensive and difficult, and the metal is
obtained in small quantities, and therefore it bears a high
price.

284. Properties of Potassium. — Potassium is so light that
it floats on water. It is a white metal with a cast of blue,
and is very brilliant in its lustre if a piece be cut so as to
expose a fresh surface. But so great is its attraction for
oxygen that the cut surface immediately tarnishes from
uniting with the oxygen of the air, and if left exposed to

208 CHEMISTRY.

the air the oxide absorbs moisture, and very shortly becomes
potassium hydrate. It can not be kept in the air at all, and
is ordinarily kept in naphtha for the same reason that it is
received into that liquid when it is made. It is so soft that
it can be worked by the fingers like wax.

285. Potassium Set on Fire by Water. — When a little
piece of this metal is thrown upon water it instantly decom-
poses the water, taking the oxygen to itself to form an ox-
ide. Hydrogen, the other ingredient of water, being set

free, immediately takes fire, Fig. 86, from the
heat which is produced by this sudden union
of the oxygen and potassium. The flame of
the burning gas is of a beautiful violet color.
Fig. so. rpjjjg js Because the heat changes some of the
metal into vapor, and this rises with the burning hydrogen.
As the metal burns it runs about on the surface rapidly.
This is owing to the hydrogen gas which is constantly devel-
oped from the water, the steam produced from the water by
the heat, and the vapor of the metal. These act on the lit-
tle bit of potassium as the gases of burning powder do on
a rock. The motion is irregular, because the production of
the gas and steam and vapor is going on upon all sides of
the piece of metal. The results of this energetic action are
potassium hydrate and free hydrogen ; the latter, however,
immediately burns, i. €., unites with oxygen, forming water.
K+H2O=:KHO+H and H2+O=H2O. The same phenom-
ena and results occur if potassium be thrown upon ice. So
strong is its attraction for oxygen that the coldness of the
ice makes no difference.

286. Caustic Potash. — What is commonly termed caustic
potash is a hydrate of potassium, KHO. So strong is the
disposition of the oxide of potassium to become hydrated,
that the anhydrous oxide can be obtained only by exposing
the metal potassium to air or oxygen that is perfectly dry.

POTASSIUM AND SODIUM. 209

This is of course an expensive process, as potassium is a
costly metal. And, besides, this anhydrous oxide rapidly
becomes hydrated on exposure to common air by attracting
its moisture. The hydrate is a white solid. It has a soapy
feeling, owing to its dissolving the cuticle, forming with it a
kind of soap. It is a strong caustic, decomposing and dissolv-
ing the flesh, and making with it a soapy jelly. It eagerly
absorbs water from the air, and becomes dissolved in it. It
can therefore be kept in its solid state only by keeping it
shut in from the air. It can be dissolved in half its weight
of water. It has strong purifying powers, and hence is used
in making soap, which will be spoken of particularly in an-
other part of this book, when we show what the chemical
union is that it forms with fatty substances. This and the
other alkalies turn reddened litmus solution blue, as stated
in § 80.

287. How Potash is Obtained. — Neither potassium nor po-
tassium hydrate occur native, but are always found com-
bined with acids forming salts, as potassium chloride, car-
bonate, nitrate, etc. Thus combined it is a very abundant
substance in nature. Potassium carbonate abounds in veg-
etables, and the name potash comes from the pots in which
the vegetables from which it was obtained used formerly to
be burned, the alkaline carbonate remaining with the ashes
at the bottom of the pots. It is from this carbonate that
the caustic potash is ordinarily obtained. The carbonic
acid can not be driven off by heat, but it can be taken away
by some substance which has a stronger affinity for it than
the potash has. Such a substance is lime. This added to
a solution of potassium carbonate in proper quantity takes
the carbonic acid, forming calcium carbonate, and leaves
the potassium hydrate free in solution. On evaporating
this solution, by heating it in a basin of iron, we obtain
caustic potash :

210 CHEMISTRY.

Potassium ^ i • v j t Calcium Potassium

carbonate. Calcmm W™ie' carbonate. hydrate.

K8CO3 + CaII2O3 CaC03 + 2(KHO)

The same thing is done in part in the common leach-tubs.
Lime is put into the lower part of the tub, so that as the
dissolved carbonate of potash comes down a part of it is
deprived of its carbonic acid, and therefore becomes caustic
potash. The lye thus produced is then a solution of the
caustic potash and the carbonate together.

288. Potassium Carbonate, K2CO3. — If a lye be obtained
from wood-ashes, and be evaporated to dryness, we .have in
the mass which is left the common crude potash of com-
merce. There are in this many impurities mingled with the
potassium carbonate, for there are other soluble salts in the
ashes which appear in the lye. Pearlash is this common
potash partially purified from these impurities. Potassium
carbonate is decidedly alkaline, having an alkaline taste,
and turning red litmus paper blue. It has to some little
extent the cleansing power of caustic potash. Though quite
insoluble in alcohol, it is very soluble in water, though not
so much so as potassium hydrate. It dissolves in twice its
weight of water, while potassium hydrate requires only half
its weight of water to dissolve it. It is a very deliquescent
salt, and therefore to preserve it dry it must be kept in well-
stopped bottles.

289. Experiment. — You learned in § 287 that although no
degree of heat can drive away carbonic anhydride from po-
tassium carbonate, it can be taken away by a substance
which has a stronger affinity for it than potassium has, as,
for example, lime. It can also be driven off by any acid
stronger than carbonic acid. Such an acid we have in
acetic acid, the acid of vinegar, as may be shown by the
simple experiment represented in Fig. 87 (p. 211). Put a
teaspoonf ul or more of pearlash into a tumbler containing

POTASSIUM AND SODIUM:.

211

vinegar. There will be an effervescence,
because the acetic acid expels the car-
bonic anhydride and forms potassium ace-
tate. As the gas fills the tumbler it will
extinguish a burning taper introduced
into it.

290. Saleratus. — This is the bicarbonate
of potash, or, strictly speaking, hydro-
potassium carbonate, KHCO2, containing

precisely twice as much carbonic acid as the common car-
bonate. It is formed by passing carbonic anhydride through
a cold solution of potassium carbonate, and then evapo-
rating the solution. On heating the hydro-potassium car-
bonate, the extra amount of carbonic acid may be driven
off. It therefore loses some of its carbonic acid if it be dis-
solved in hot" water ; or, rather, some of it is converted into
the carbonate, and you have in the solution a mixture of
the two salts. The amount of carbonic anhydride in this
salt makes it useful in raising bread and cake. The acid
which is employed with it takes the potash to itself, and
sets free the gas, which by its expansive force puffs out the
dough, forming in it innumerable air-cells, and thus makes
it " light." The acid which is in sour milk is as good as
any other for this purpose.

291. Potassium Nitrate, or Saltpetre. — This salt, also called
nitre, is of special interest to us as being one of the ingre-
dients of gunpowder. It is a natural product in some soils
in hot climates, as in India and South America. The man-
ufacture of potassium nitrate is a curious chemical process.
First a calcium nitrate is produced in the following manner:
Animal substances, flesh, hides, etc., are mixed with lime
and earth, and this mixture is moistened and left to putrefy.
Ammonia results, the elements of which, nitrogen and hy-
drogen, unite with the oxygen of the air to form two things

212 CHEMISTBY.

— water and nitric acid. You see how this is. The oxy-
gen unites with the hydrogen of the ammonia to form
water, and with its nitrogen to form nitric acid. Then as
lime is ready on the spot, the acid at once unites with it,
forming calcium nitrate. This is obtained in solution from
the mass, and converted into potassium nitrate by treating
with potassium carbonate. Insoluble calcium carbonate
is precipitated, and potassium nitrate goes into the solu-
tion.

292. Gunpowder. — Gunpowder is composed of potassium
nitrate, charcoal, and sulphur, each carefully ground, and the
three well mixed in proper proportions. The effectiveness
of saltpetre as a constituent of gunpowder depends on the
fact that it quite readily parts with its oxygen gas, which
constitutes nearly one half of the salt. Bloxam thus ex-
plains the chemistry of the explosion of gunpowder: "The
oxygen of the saltpetre converts the carbon of the charcoal
chiefly into carbonic anhydride, part of which assumes the
gaseous state, while the remainder combines with the po-
tassium of the nitre to form potassium carbonate. The
greater part of the sulphur is converted into sulphuric acid,
which forms sulphate of potassium. The chief part of the
nitrogen contained in the potassium nitrate is evolved in
the uncombined state." Several other substances are form-
ed in small quantity besides those named, among which are
carbonic oxide, marsh gas, potassium sulphide, and sulphu-
retted hydrogen. The disagreeable odor of burned gun-
powder comes from the formation of sulphuretted hydrogen
by the action of the moisture of the air upon the sulphide
of potassium. The blackening of the surface of the gun-
barrel comes from the formation of sulphide of iron. There
is no water of crystallization in nitre. If there were any,
it would unfit it for being an ingredient in gunpowder ; for
this water, being released by the heat, would tend to put

POTASSIUM AND SODIUM. 213

out the fire which the oxygen and carbon are disposed to
get up together.

293. The Explosion Explained. — If the gases thus evolved by the
burning of gunpowder could remain condensed, occupying the same space
that they do in the powder, there would be no explosion. But the moment
they are evolved they immediately expand so as to occupy a space sev-
eral thousand times greater than before. And it is this expansive force
which causes the sound of the explosion, and which constitutes the power
of the burning powder in propelling balls, rending rocks, etc. It is the con-
cussion or blow which the suddenly expanding body of gas gives to the sur-
rounding air that causes the detonation. Observe the difference between
this explosion and that which occurs when gases unite suddenly to form a
liquid, as in the formation of water by the explosion of oxygen and hydro-
gen (§ 144). In the latter case there is condensation, while there is none
in the former. Now if the condensation were the sole cause of the detona-
tion, the explanation would be this : A vacuum is created by the condensa-
tion, and the air rushing into it from all quarters, and therefore coming to-
gether, produces a sound very much as clapping two hands together does.
But this explanation will not hold, for there is not only no evidence of col-
lapse at the moment of explosion, but, on the other hand, decisive evidence
of expansion. For example, when the gases are discharged in the gun, in
the experiment in § 191, the cork is driven out, showing that there must be
expansion at the first, although eventually there is condensation. But how
is this expansion produced ? It must come from the fact that the water is
formed in the midst of the great heat which always attends the combustion
of oxygen and hydrogen together, and is therefore steam largely expanded,
to be condensed, however, at the next instant. Whether this condensation
has any agency in the production of the sound is uncertain.

294. Sodium. — This is a soft, light metal, somewhat re-
sembling potassium, and, like it, never occurs in a free state
in nature owing to its powerful attraction for oxygen. This
attraction is not quite so strong as in the case of potassium ;
so when sodium is thrown upon cold water it runs about
with a hissing sound, but does not usually set fire to the
hydrogen evolved. By using hot water, the sodium will
set the hydrogen on fire, which then burns with a bright

214 CHEMISTRY.

yellow flame. Compounds of sodium are most abundant in
nature.

295. Experiment. — A very neat experiment can be tried
showing the decomposition of water by sodium. Boil some
water for about fifteen minutes in order to expel the air from
it, and after it is cool fill a bowl and a test-tube with it.

Close the test-tube with the finger, and invert
it under the water in the bowl, as seen in
Fig. 88. Throw a bit of sodium on the wa-
ter, catch it witli a spoon of wire gauze, and
thrust it quickly to the opening of the test-
tube, and disengage it from the spoon by
turning it over. As it is lighter than water,
it will rise at once to the top of the tube, and there will
busy itself in decomposing the water. By taking the oxy-
gen of the water and half the hydrogen the sodium becomes
sodium hydrate, and the rest of the hydrogen, being thus
set free, accumulates in the tube, forcing down the water
that is in it. When the sodium has all disappeared, close
the tube with the finger, and remove it from the vessel. If
now, holding the tube with its, opening upward, you apply
a light to it, the hydrogen will burst into a flame.

296. Common Salt. — The chloride of sodium, NaCl, is the
most abundant and important of the compounds of this
metal. This salt is composed of two elements that are en-
tirely different from the compound which they form. One
of them is a gas, which is so suffocating that no one can
breathe it undiluted and live. The other is a metal, which
has such an affinity for oxygen that if it were introduced
into your mouth it would set the moisture there on fire in
seizing its oxygen. And yet the compound which these two
elements make is a very mild substance, which we take into
our mouths every day in our food. It is most widely dif-
fused in the animal and vegetable as well as the mineral

POTASSIUM AND SODIUM. 215

world. It all originally comes from the mineral world, and
being absorbed from the soil by plants, through them it
gets into the blood of animals by their food. What its
special uses are in animals, beyond the fact that no food can
be digested without it, we know not; but that it is essen-
tial its constant presence in the blood shows. Salt is suffi-
ciently soluble for all practical purposes. It does not deli-
quesce easily, troubling us in this respect only when the air
happens to be very damp. Unlike most other salts, it dis-
solves almost equally well in cold and hot water. It is
scarcely soluble at all in alcohol. It crystallizes in the,form
of cubes. Sometimes the crystals have
an arrangement which is hopper-shaped,
as represented in Fig. 89. This is be-
cause that which is first formed on the
surface sinks a little in the solution, and
then there is an addition upon its outer Fis-

edge all around; and this goes on continually, the outer edge
all the time enlarging, and the solid salt all the time sink-
ing as it increases. The upper edge is during the whole
process just at the surface, evaporation adding continually
to it.

297. Decomposition of Salt. — Salt is decomposed in many
chemical operations, but its elements are so firmly united
that it is by no means easily decomposed. Heat, for ex-
ample, can not drive off the chlorine, as it does carbonic
anhydride, from limestone. Most of the substances with
which salt is apt to come in contact can not decompose it.
Strong as is the attraction of oxygen for sodium, it can not
take it away from chlorine. If now, on the other hand, salt
were easily decomposed, as it circulates by means of water
constantly among a great variety of substances — in the sea,
in the soil, and in the fluids of vegetables and animals — it
would be a source of continual danger. The evolution of

216 CHEMISTRY.

the suffocating chlorine, which would take place here and
there, would produce the most disastrous results.

298. Localities of Salt. — While salt is so widely diffused,
there are some localities where it is found in great abund-
ance. There are extensive beds of it in Spain, in some cases
rising in hills three or four hundred feet high. The same is
true of the north part of Africa. Then there are extensive
beds in various parts of the continent of Europe, in Cheshire,
England, in Persia, China, India, and South America. The
most remarkable salt-mines are in Prussia, Poland, and Hun-
gary. Some deposits have been found in this country, in
Virginia and Louisiana. There are extensive salt lakes in
Africa and South America. In this country there is the
famous Great Salt Lake, on a height among the Rocky
Mountains, 4200 feet above the level of the sea. There are
in this country some salt springs which are very productive.
The most celebrated are those at Salina and Syracuse, the
latter producing annually five millions of bushels of salt.

299. Modes of Obtaining Salt. — The rock-salt is sometimes
nearly pure, as at Norwich, in Cheshire, England, where
large masses from five to eight feet in diameter are found,
and it is prepared for use by crushing between rollers.
Commonly, however, it is impure, and to purify it the salt
is dissolved in water; and when the impurities have settled,
the solution is drawn off and evaporated, that the solid salt
may be obtained. In this country the salt is gathered by
evaporating the brine which is flowing continually in. For
this purpose wells are made from 50 to 150 feet deep, and
the brine, as it is pumped up, is conducted by troughs to
large boilers. Sometimes the evaporation is left to occur
without the application of heat, by exposing the brine to
the sun in large shallow vats. This process is often made
use of in hot climates for obtaining salt from sea-water. A
number of extensive shallow basins having a smooth bot-

POTASSIUM AND SODIUM. 217

torn of clay are made near the sea, all communicating with
each other. The water is let into the one adjoining the sea
at high tide, and when they are all filled it is shut off. The
sea-water affords a bushel of salt to every 300 or 350 gallons,
while the brine from the best springs gives a bushel to every
40 gallons.

300. Amount of Salt in the Sea. — About one thirty-sixth
part of sea-water is common salt. The proportion in the
best of our salt springs is one seventh ; in the water of the
Great Salt Lake it is over one fifth ; and in the Dead Sea it
is even more than that. The whole amount of salt in all
the seas and oceans of the earth is estimated to be at least
five times the mass of the Alps. It is enough to cover an
area of seven millions of square miles with a layer a mile in
thickness.

301. Sodium Carbonate, Na2CO3. — This salt is contained
in the ashes of sea-plants, as the carbonate of potassium is in
those of land-plants ; and originally it was obtained almost
wholly from that source by lixiviation — that is, by making
a lye. But it is now obtained entirely, because more easi-
ly, from common salt by certain chemical reactions, which
are somewhat complicated ; briefly, however, the process is
as follows: (1) Sodium chloride is heated with sulphuric
acid, forming sodium sulphate, or, as it is technically called,
"salt cake;" (2) this is mixed with coal and limestone,
heated in a furnace of peculiar form, and thereby converted
into very crude sodium carbonate ("black ash"); (3) this
is then purified by solution in water and crystallization
(" soda ash "). During the first step, the manufacture of
salt cake, immense quantities of hydrochloric acid gas are
given off, which are condensed in water. During the sec-
ond step abundance of calcium sulphide is formed as a waste
product.

The importance of this manufacture will be faintly ap-

2 1 8 CHEMISTRY.

predated by learning that 200,000 tons of "soda ash" (crude
sodium carbonate), worth ten million dollars, are made an-
nually in Great Britain alone. Carbonate of soda, when
crystallized, has a remarkably large amount of water com-
bined with it— 63 parts in every 100. When it is wholly
anhydrous — that is, when it has lost all its water of crystal-
lization— it is of more than twice the strength of the crys-
talline salt. If the crystals be heated, they fuse in their own
water of crystallization. Many mineral waters contain con-
siderable of this salt.

302. Sodium Bicarbonate. — This salt is, strictly speak-
ing, hydro-sodium carbonate, NaHCO3. It is much used in
making soda-powders. The powder in the blue paper is
the bicarbonate of sodium, while that in the white paper is
tartaric acid. When these are dissolved in water in separate
tumblers, and the two solutions are poured together, the
tartaric acid at once seizes the soda, forming tartratc of
sodium, and the carbonic anhydride, set free, effervesces
strongly. The same effect is produced if you mingle the
two powders intimately, and then throw the mixture into
the water.

303. Sodium Sulphate, or Glauber's-Salt, Na2SO4-f 10lI2O.
— This salt received the name of Glauber's-salt because it
was first obtained by means of a chemical process by a Ger-
man chemist of that name. It occurs in nature, but not
abundantly, except in a few localities, one of which is a cave
in the island of Hawaii, from which the natives gather it
for medical use. Ordinarily it is obtained by the action of
sulphuric acid upon common salt. More than half of this
salt in its crystalline state is water, and exposed to the air
the crystals effloresce, and fall to powder.

There is another sodium sulphate containing less sodium,
NaHSO4 ; this is formed when the sulphuric acid is used in
excess. It has a very acid reaction.

POTASSIUM AND SODIUM. 219

304. Borax. — Chemically this substance is sodium bibo-
rate. It is found native in some of the lakes of Asia and of
California, and is also prepared by neutralizing with sodi-
um carbonate boracic acid obtained from hot springs in
Italy. It contains half its weight of water of crystalliza-
tion, having the composition Na2B4O7-f 10H2O. Borax is
much used in the trades for soldering. If you hold with
pincers over a spirit-lamp a piece of copper on which are
placed a bit of tin and of iron wire, the tin will melt, but
will not adhere to either metal. But if you smear the
three metals over with a paste made of moistened borax,
and repeat the experiment, you will find that the wire is
firmly soldered to the copper. The explanation is this :
Metals will adhere to each other only wrhen they have a
pure surface ; but heating them always produces at once
a film of oxide, and so prevents their adhering. Now the
borax serves to keep the surfaces bright by forming with
this oxide a sort of melted glass, which is easily pushed
aside by the melted solder. There are various substances
used in soldering, and they all act by removing in some
way the oxides produced by the heat.

305. Soda Saltpetre. — This salt, sodium nitrate, NaNO3,
resembles common saltpetre. It is found in large quanti-
ties in South America, where extensive plains are covered
with it, and it is exported to other countries under the
name of Chili saltpetre. It has the same amount of oxy-
gen in it that nitre has, and parts with it as readily, as is
shown by its brisk deflagration on glowing coals. But it
will not answer in place of nitre in gunpowder, simply be-
cause it is strongly disposed to attract water from the air.
Keeping the powder dry would be difficult if one of its
ingredients be deliquescent.

306. Ammonium. — With the group of metals we are study-
ing, the salts of ammonium may be conveniently ranged.

220 CHEMISTBY.

The alkaline gas ammonia is composed, you remember, of
hydrogen and nitrogen, or is NH3. Now a solution of this
gas in water acts like the hydrate of an alkaline metal,
combining with acids to form crystallizable salts. This
analogy has caused chemists to conjecture that, since NH3-f
H2O is the same as NH4HO, there is a metal NH4, of which
NH4HO is the true hydrate, just as KHO is the hydrate of
potassium. This compound metal reminds us of cyanogen,
which, you remember, was a compound also, and was called
a radical.

Note that if there be an ammoniacal metal, it is not an element, as all
other metals are, but a compound. It is composed of nitrogen and hydro-
gen, just as is the ammoniacal gas, and it differs in composition from this
gas only in having one third more hydrogen in it. Though no one has
ever succeeded in obtaining this metal, all chemists seem to believe in its
existence. The evidence on which this belief is based is twofold. First,
the salts of ammonia are so much like other salts that have a metallic base
that it would be a very strange thing if they did not also have such a base.
Thus in sal ammoniac we have a salt so similar to other salts that we
should expect to find, as we do in them, that one of the constituents is a metal.
But it is composed of three gases— chlorine, nitrogen, and hydrogen. It is
supposed, therefore, that as common salt is composed of chlorine and the
metal sodium, so this salt is composed of chlorine and a metal ammonium,
the nitrogen and hydrogen being so combined as to act in this latter capac-
ity. But by whatever method the chemist separates the chlorine from this
combination, the metal eludes his grasp, and he gets only nitrogen and hy-
drogen, each by itself. The evidence, therefore, that there is a metal here
is incomplete. But there is, secondly, another proof of a more decided
character. If sal ammoniac — that is, chloride of ammonium — be mixed with
an amalgam of mercury and sodium, a change takes place resulting in the
formation of common salt, or chloride of sodium, and an amalgam different
from that which was put into the mixture. How is this ? The sodium has
left the mercury to unite with the chlorine of the sal ammoniac. What has
taken its place in the amalgam? Something from the sal ammoniac, and
that something must be a metal, for nothing but a metal has ever been
known to form an amalgam with mercury. The proof, therefore, is quite
decided that sal ammoniac is a chloride of a metal, and therefore its proper
name is chloride of ammonium.

POTASSIUM AND SODIUM. 221

307. Ammonium Salts. — This hypothetical metal forms a
whole series of important salts. Thus we have ammonium
sulphate, ammonium nitrate, which was used in the prepa-
ration of laughing-gas, ammonium phosphate, ammonium
carbonate, etc. This last-named salt is the common sal vol-
atile of the pharmaceutist, used as smelling-salts. It is so
volatile that it slowly passes away in the air in the form of
vapor. It is evolved in the decay of all animal and vegeta-
ble substances that contain nitrogen, and gives the peculiar
pungent odor to the stable and the manure heap. As pro-
duced in manures and brought down from the air in the
rain, it is a valuable agent in vegetation, and will be consid-
ered in this light in another part of this book.

QUESTIONS.

282. Why does potassium never occur native ? — 283. How is potassium
obtained ? Write the equation showing the reaction. — 281. What are the
properties of potassium ? Under what liquid is it kept ? — 285. What hap-
pens when potassium is thrown into water ? Explain. — 286. What is the
composition of caustic potash ? — 287. How is it obtained ? — 288. How is
potassium carbonate made ? What are its properties ? — 289. How does
acetic acid act on potassium carbonate ? — 290. What is saleratus ? What
raises bread and cake? — 291. Where does saltpetre occur? How is it
made ? — 292. Of what is gunpowder made ? Explain the chemistry of the
explosion. — 293. Whence comes the power when gunpowder is burned?
Whence the noise ? — 291. Mention the properties of sodium. — 295. De-
scribe the decomposition of water by sodium. — 29G. What is the most abun-
dant and useful compound of sodium ? What is said of it ? — 297. What
would happen if salt were easily decomposed ? — 298. Mention the principal
localities of salt deposits. — 299. Describe the modes of obtaining salt. — 300.
What is said of the amount of salt in different kinds of salt water? — 301.
Name the three steps in the manufacture of carbonate of sodium. How
much water of crystallization does it contain ? — 302. What is hydro-sodium
carbonate?— 303. What is Glauder's-salt ?— 301. What is borax, and whence
comes it ? What is the philosophy of its use by blacksmiths ? — 305. What
is said of sodium nitrate ? — 30G. Explain what is said of the ammonium
theory. — 307. Name some ammonium salts.

222

CHEMISTRY.

CHAPTER XVII.

GROUP II. — BAKIUM, STRONTIUM, AND CALCIUM.

308. Barium and Strontium. — These metals do not occur
native, their properties being in this respect much like
those of Group I. Barium salts are widely distributed,
but not in very great quantity. Strontium compounds
are comparatively rare. Both occur as sulphates and car-
bonates. Barium sulphate or larytes is used to adulter-
ate white-lead paint. Barium salts are poisonous. Bari-
um nitrate is used in making the green fire of fireworks,
and strontium nitrate for the red fire. AVe will give you a
receipt for a red fire if you will be
careful in making it : Take 80 parts
of dry strontium nitrate, 22 of sul-
phur, and 5 of lampblack ; mix these
intimately in fine powder ; then add
20 parts of potassium chlorate cau-
tiously and without rubbing. Mix
well on paper. This burns with a
brilliant crimson flame. Make no
more than you want to burn, for
it is dangerous to keep it.

309. Fire Under Water. — If this
mixture be put into a paper case, A,
well stopped with varnish at the end,
and then, after being set on fire, be
introduced into a jar of water, CC, it
Fig. so. will continue to burn under water,

BARIUM, STRONTIUM, AND CALCIUM. 223

the red flames making a brilliant display. B is a piece of
lead pipe fastened with copper wire to the case to hold it,
with its orifice downward. The oxygen in this mixture is
contained in the potassium chlorate and the strontium ni-
trate, while the sulphur and carbon are the combustible
substances. The red color is given to the flame by the
strontium nitrate.

310. Calcium. — This metal has no interest for us, but its
oxide and its hydrate, as well as many other of its com-
pounds, are of the greatest importance. Quicklime is cal-
cium oxide, CaO ; slaked lime is calcium hydrate, CaIT2O2.
We often use the word lime when we ought strictly to say
calcium. Lime is never found in nature, but abounds in
combination with acids. In this way it forms more than
half of chalk, limestone, and marble, is the base of plaster
of Paris and alabaster, and constitutes the greater part of
the mineral portion of the bones of animals. Lime is con-
sidered as occupying a middle place between the alkalies
and the earths. It is, therefore, called an alkaline earth.
The earths are insoluble, the alkalies are very soluble, but
the alkaline earths are but sparingly soluble. The alkaline
earths are also midway between the earths and the alkalies
as to being caustic, for they are somewhat caustic, while
the alkalies are very much so, and the earths not at all, but
perfectly inert. That lime is somewhat caustic you can
perceive by the feeling occasioned when you rub a little
of it, made into paste, between your fingers. It is from
this caustic quality that the milk of lime — that is, lime dif-
fused in water — is used to remove the hair from hides. So,
also, lime is often mixed with weeds to quicken their de-
composition.

311. Manufacture of Lime. — Quicklime is obtained from
the carbonate in its various forms — chalk, limestone, marble,
oyster-shells, etc. — simply by the application of strong heat,

224

CHEMISTRY.

the carbonic acid being driven off. The operation is car-
ried out on a large scale in a kind of furnace called a
lime-kiln, shown in Fig. 91. The decomposition takes places
at a lower temperature in a current of air than otherwise,
and this is effected by building a tall kiln.

Fig. 91.

How simply heating their bodies effects their decom-
position we will explain : Heat expands all bodies, or, in
other words, puts the particles in them farther apart. But,
as you have already learned, it is necessary that particles
of different substances should be in immediate contact, or
exceedingly near to each other, in order that the attractive
force may come into action. Now it is supposed that in
the case of the carbonate of lime the heat, in expanding it,
puts the particles of the carbonic anhydride at such a dis-

BARIUM, STRONTIUM, AND CALCIUM. 225

tance from the particles of the lime that they are out of
the range of their attraction, and so they escape. The ef-
fect of heat is, you see, just opposite to that of solution,
the latter bringing particles more nearly together. The
carbonate of lime is quite in contrast with the carbonate
of potassium in this respect, for no heat, however great,
can drive the carbonic acid away from the potassium hy-
drate, as you learned in § 287. And yet, strange as it may
seem, lime, as you also there learned, can take away the
carbonic acid from the potassium carbonate.

312. Attraction of Lime for Water and Carbonic Anhydride.
— The eagerness with which lime unites chemically with
water is shown in its slaking. So great is the heat pro-
duced by the rapid union that takes place that even gun-
powder has been ignited by it. It very readily ignites
phosphorus. Put a little quicklime in a heap upon a
board, and place on the top of it a bit of phosphorus. To
avoid wetting the phosphorus moisten the heap at the
bottom, and as the moisture spreads through the lime it
will very soon produce heat enough to set the phosphorus
on fire. Another experiment, showing the amount of heat
produced, may be tried as follows : Put some lime in a
bowl, and, moistening it, place a glass bell-
jar over it, Fig. 92. At first the steam
which rises from the slaking lime will be
condensed upon the inside of the glass.
But soon the heat will be so great that the -
steam in the bell-jar will form a transparent
atmosphere in it. If now you raise the Fig. 92.

glass, the steam as it escapes loses its transparency, and
becomes a thick cloud, because it is changed into a kind of
fog by the condensing influence of the cold air. By the
union of lime with water there is formed a hydrate of lime,
there being in every 100 grammes of dry slaked lime about

226 CHEMISTRY.

25 grammes of water. Lime has also a considerable affinity
for carbonic acid. When, therefore, it is exposed for some
time to the air, it unites with the carbonic anhydride of
the air as well as its moisture, and air-slaked lime is there-
fore a mixture of hydrate and carbonate of lime.

313. Solubility of Lime. — While lime has so great an af-
finity for water, the dry substance which results after its
thirst is slaked is very sparingly soluble. It is in strong
contrast in this respect with the alkalies. While potas-
sium hydrate is soluble in half its weight of water, the
hydrate of lime requires one thousand times its weight of
water to dissolve it. It is very remarkable that cold
water will dissolve more of it than warm. Lime-water, as
the solution of lime and water is called, is sometimes used
as a medicine. With sweet-oil it makes a soapy mixture
which is often used as an application to burns.

314. Mortar. — The most important use of lime is in mak-
ing mortar. As glue holds pieces of wood together, so does
mortar bricks and stones. In the making of mortar wre stir
sand, lime, and water together, and the sand becomes in-
timately mixed with the hydrate of lime while it is form-
ing. As the mortar becomes dry by the evaporation of
all the water that is not used up in the formation of the
hydrate, there occurs also another chemical change — car-
bonic anhydride is attracted from the air, and unites with
a portion of the lirne ; so that we have in the mortar a
mixture of carbonate and hydrate of lime, which has more
firmness than either of these substances separately. Then,
again, mortar becomes hard gradually, from a chemical
action between the sand and lime, whereby silicate of lime
is formed. The sand serves to give both body and firm-
ness to the mortar. When mortar is used as plastering,
hair is added, the fibres serving to hold the mortar more
thoroughly together.

BAEIUM, STRONTIUM, AND CALCIUM. 227

315. Carbonate of Calcium, CaCO3. — This salt presents it-
self in various forms — chalk, common limestone, and the
beautiful granular marble. The mineral calcite, which
sometimes appears in large, magnificent crystals of various
colors, is one of the forms of this salt. The variety of
form which this salt presents is analogous to the variety
that we so commonly see in sugar, which is perfectly crys-
talline in rock -candy, like calcite, imperfectly so in the
granular loaf-sugar, like marble, and without any trace of
crystallization when pulverized finely, like common chalk.
Carbonate of lime is very abundant, and is in fact one of
the chief constituents of our earth. There are hills and
ridges of mountains built up with limestone. In a pul-
verized state it exists extensively in the soil, in some dis-
tricts being very prominent, making what is called a cal-
careous soil. Oyster- shells, and the shells of shell-fish
generally, are composed almost entirely of carbonate of
lime. So are the shells or frame-work of many very
small animals, some of them exceedingly minute, and yet,
by their numbers, occupying much space in the earth.
The skeletons of the coral animals, of which so much of
some portions of the earth has been built up, are made
chiefly of this salt.

316. Depositions of Carbonate of Calcium. — If you breathe
into lime-water there will be precipitated carbonate of cal-
cium, or chalk, as you learned in § 125. If, after this pre-
cipitate is formed, however, you continue to breathe into
the lime-water, some of the precipitate will disappear, a part
of it being dissolved again. How is this, when carbonate
of calcium is insoluble in water ? It is because you have
now something more than water in the vessel ; it is water
considerably charged with carbonic anhydride. Now,
while pure, simple water can not dissolve carbonate of
calcium, water charged with this gas can do it. Hence the

228 CHEMISTRY.

disappearance of a part of the precipitate. If now you let
the liquid stand for a time exposed to the air, it becomes
turbid again, because the carbonic anhydride escapes,
which takes from the water its power of keeping the car-
bonate in solution, and this salt is therefore again pre-
cipitated. And here we have a key to the explanation
of some very interesting phenomena. Water, as it makes
its way among the particles of the soil, finds carbonic acid
as one of the results of decay, and dissolves it ; and there-
fore, as it issues from the earth in springs, it contains not
only carbonic acid, but also carbonate of lime, which it
has found in the soil and dissolved by the aid of the acid.
But as soon as the water is fairly exposed to the air the
carbonic anhydride begins to escape from it, and ac-
cordingly the carbonate of lime begins to be deposited.
Hence comes the grand difference between the hard water
of springs and wells, and the soft water that runs in brooks
and rivers. The water as it runs along exposed to the air
has discharged much of its carbonic acid upward, and
therefore precipitated much of its carbonate of lime down-
ward. Water can be more thoroughly freed of its car-
bonic acid, and therefore of its carbonate of lime, by boil-
ing it than by 'mere exposure to the air, which explains
the considerable deposition of this salt in large steam-boil-
ers when hard water is used, collecting gradually as a hard
crust. Such incrustations are of course particularly apt
to occur in limestone districts.

317. Stalactites and Stalagmites.— The roofs of caverns
in limestone regions often have stalactites of carbonate of
lime suspended from them like icicles in shape. The rea-
son is obvious. The water, as it percolates through the
soil above the cavern, becomes charged with carbonic acid
from decaying vegetable matter, and therefore dissolves
some of the limestone ; and then., as it is exposed to the air

BAKIUM, STRONTIUM, AND CALCIUM.

229

in dripping, losing in part its carbonic acid, and therefore
its solvent power, deposits some of its carbonate, which ac-
cumulates gradually in the stalactite form. But as the
solvent power of the water is not all lost, some of the car-
bonic acid still remaining, the water, as it falls upon the
floor of the cavern, loses another portion of the acid, and
so deposits more of the lime in eminences called stalag-
mites. These are of course less slender and pointed than
the stalactites. You see the same difference in form be-
tween icicles and the accumulations below them. There
are splendid displays of these formations in many of the
caves of the earth. Some of the most celebrated are,
Weyer's Cave, in Virginia ; the Cave of Thor, in Derby-
shire, England ; and the Grotto of Antiparos, on an island
of the same name in the Grecian Archipelago. A part
of this grotto is represented in Fig. 93. You can get an

Fig. 93.— The Grotto of Antipnros.

230 CHEMISTRY.

idea of the size of these formations, the accumulations of
constant dripping for ages, by the human figure at the foot
of one of them.

318. Carbonate of Calcium in the Sea. — Though rain-water
may be free from carbonate of lime, water which has per-
colated through the earth is never wholly free from it.
Though it may deposit it as it comes out of the springs
and runs along brooks and rivers to the ocean, yet even
when, it arrives there it retains some of it in solution, for
it has still dissolved in it some of the carbonic acid which
it derived from the soil. If it were not so, the shell-fish
would have no material for the formation of their external
skeletons, or houses, as they may more properly be called.

319. Sulphate of Calcium, CaSO4. — The common name of
this salt is gypsum. It has also the name of plaster of Paris,
which it received from the fact that it was first used in the
form of plaster in Paris, there being immense quantities of
it in the neighborhood of that city. It is a white and quite
soft mineral, occurring in various forms, some of them very
beautiful. One of its forms, alabaster, which is snowy
white, is cut into vases and ornaments of various kinds.
Sometimes it is crystallized in exceedingly thin leaves, laid
together so nicely that a multitude of them make a white
crystal clearer than the clearest glass. Then there is the
satin-spar, so called from the splendid lustre of its fibrous
arrangement. Gypsum is about one fifth water. This wa-
ter can be driven off by heat, and then this powdered an-
hydrous gypsum has the property of "setting" with wa-
ter; or, in other words, becoming with water a firm, coher-
ent, and dry mass. For this purpose it is moistened with
water to about the consistency of cream. In this state it
can be poured into moulds, or it can be put upon walls as
hard finish, the water disappearing as it hardens, partly by
evaporation, and partly by becoming a part of the solid,

BARIUM, STRONTIUM, AND CALCIUM. 231

dry substance. The hardening takes place quite rapidly.
The moistened plaster can also be moulded into casts, plas-
ter heads, ornamental work for walls, called stucco-work,
etc. It is remarkable that, in making the gypsum anhy-
drous, if the heat be carried above a certain point, its affin-
ity for water will be destroyed, and there will be no " set-
ting" of the plaster.

320. Casts of Coins. — Copies of coins and medals can be
taken very readily with the moistened plaster. For this
purpose put the coin into a paper box, or, if you have not
one of the proper size, fasten a slip of paper around the
coin, securing the loose end by a little sealing-wax, and
pour the plaster in upon the coin. After a few minutes it
will become so*hard that both the paper and the coin can
be removed. A reversed impression will be formed on the
under surface of the plaster. To get from this a real copy
of the coin, smear the impression with a very little of a
strong solution of soap, having a few drops of oil mixed
with it, and then pour upon it some of the plaster.

The use of gypsum in agriculture will be spoken of in
another part of this book.

321 . A Singular Case.— If sulphate of calcium (gypsum) and carbon-
ate of ammonium be mingled together in solution, there will result car-
bonate of calcium, or chalk, and sulphate of ammonium. Now if we take
these two substances thus resulting, and, powdering them finely, mix them
together, and expose the mixture to a red heat in a close vessel, we shall
have the original sulphate of calcium and carbonate of ammonium pro-
duced again. Here we have heat occasioning a chemical process exactly
the reverse of that caused in a solution at an ordinary temperature.

322. Chloride of Lime. — The salt which sometimes goes
by this name, and sometimes by the name of bleaching
powder, is a white powder, having the odor of chlorine gas,
because this gas escapes from it continually in a small
amount. The reason of its escape is that the carbonic an-

232 CHEMISTRY.

hydride of the air unites with the lime gradually, thus lib-
erating the chlorine. In using this salt for bleaching the
gas is liberated by some acid which is applied. The arti-
cle to be bleached is first soaked in a solution of the chlo-
ride, and then in a dilute sulphuric acid. Here you have
chloride of lime and sulphuric acid brought together, and
the result is that the acid takes the lime and releases the
chlorine. What does the released chlorine do ? Being set
free in immediate contact with the cloth, it acts at once
upon the coloring matter. The operation is not all done
at once; but as strong solutions are apt to injure the cloth,
the solutions are made weak, and the articles are moved
back and forth from one solution to the other several times.
White figures are sometimes made on colored cloth by this
bleaching process. The figures are first stamped upon the
cloth with a mixture of tartaric acid and gum-water, and
then the cloth is soaked in the solution of the chloride.
You see what the result is. The chloride is decomposed
by the acid, and therefore the chlorine whitens only where
the figures are stamped. This bleaching powder is very
valuable because we have the bleaching gas condensed in
it, a form convenient for transportation, which would not
be true of either chlorine gas or chlorine water.

323. Composition of Chloride of Lime. — The name which
is so universally given to this preparation is a very incor-
rect one. It is impossible to have a real chloride of lime,
for the chlorine can not be made to unite with an oxide of
a metal, but will unite only with the metal itself. If there-
fore this salt be a chloride, it must be chloride of calcium,
the metal of which lime is the oxide. But it has been
found that it is composed only in part of this chloride. It
is a mixture of chloride of calcium, calcium hydrate, and a
salt called hypochlorite of calcium. This latter salt is a
compound of calcium with hypochlorous acid, an acid com-

BARIUM, STRONTIUM, AND CALCIUM, 233

posed of chlorine and oxygen. Perhaps the reason that
the old name chloride of lime is retained is that it is diffi-
cult to fix upon a proper name for this mixture of two
salts.

Chloride of lime is made by exposing slaked lime, slightly
moistened, to chlorine gas ; this is eagerly absorbed by the
lime, forming calcium hypochlorite and calcium chloride,
while some of the calcium hydrate remains unchanged.
The bleaching powder thus prepared is very uncertain as
to the amount of its bleaching properties, and these are
very liable to be impaired by exposure to air and other
circumstances. As offered in the market it varies much in
its value according to its age, care in keeping it, and also
care in its original preparation.

324. Calcium Phosphate, Ca3(PO4)2. — While carbonate of
lime is the mineral out of which all shells are made, the
phosphate of calcium, mixed with very small quantities of
the carbonate and sulphate and fluoride, forms the mineral
portion of bones. It is estimated that the amount of phos-
phorus contained in this salt in the bones of a full-grown
man is from 500 to 800 grammes. Phosphorus is obtained
from bones, and the process is described in § 253. As phos-
phate of lime exists so largely in animals, it is necessary
that it be provided for them in the food that they eat.
Accordingly it is present in all cereal grains, in leguminous
plants, and many other vegetables, the soil of course fur-
nishing it to them. It is not only, then, the animal sub-
stance in bones, the gelatine, that makes them a good ma-
nure ; but the mineral part is of essential service, to some
crops especially, if the soil be at all deficient in phosphate
of lime.

Calcium phosphate occurs abundantly also in the min-
eral kingdom, as you will learn more particularly in the
study of Mineralogy, Part III.

234 CHEMISTEY.

GEOUP III. ALUMINIUM (ETC.). — GEOUP IV. MAGNESIUM
AND ZINC.

325. Aluminium. — This metal, the base of the oxide alu-
mina, though it was unknown until a few years ago, is al-
ready used for a variety of purposes. It is a white metal,
resembling silver in color and hardness, as well as in its
power of resisting the action of air and water, but differ-
ing from it greatly in weight, silver being four times as
heavy. It is admirably fitted for ornamental purposes, and
has already been so employed to a considerable extent. It
is very sonorous, and therefore will make good bells. The
French government at one time used it for helmets and
cuirasses, for which it is well fitted, as it is both light and
strong. Formerly this metal was very costly, but in the
year 1854 M. Deville, who had charge of the private lab-
oratory of the Emperor of France, discovered a process by
which it can be obtained in large quantities, and at com-
paratively low price. And as silver is four times as heavy,
articles can be made of this beautiful metal for less than
the cost of silver.

326. Aluminium Oxide, or Alumina, A12O3. — This earth is
the essential ingredient of all clays, and is present more or
less in all fertile soils and in many of the slaty rocks. The
metal of which this is an oxide is therefore quite abun-
dant, and widely diffused in the earth, though it is never
found in its metallic state, but is always in combination
with other substances. Alumina appears in some beauti-
ful forms. The sapphire, which in some of its varieties is,
next to the diamond, the most costly of gems, is pure alu-
mina crystallized. Blue is the true sapphire color. * When
this gem has other colors it receives other names : when
red, Oriental niby ; when yellow, Oriental topaz ; when vio-
let, Oriental amethyst; and when green, Oriental emerald.

ALUMINIUM. — MAGNESIUM AND ZINC. 235

The largest Oriental ruby yet found came from China, and
is now a jewel in the imperial crown of Russia. Emery
is nearly pure alumina. This, besides being used by the
ladies in their "emery-bags," is extensively employed in
polishing metals and precious stones.

327. Common Alum. — In this salt we have sulphuric acid
united with two bases, potassium and aluminium, forming
a sulphate. It is therefore said to be a double salt, and
has the composition Al2K2(SO4)4-f-24H2O. It is not a mere
mixture of the two salts, but a chemical compound always
precisely the same in the proportions of its constituents.
The water of crystallization in this salt constitutes nearly
one half of it. If it be heated, the escape of this water
causes it to foam and melt, and swell up into a large porous
mass. This is what is called burnt alum. This salt, like
all the salts of aluminium, has an astringent taste. Warm
water will dissolve much more of it than cold. It is much
used in dyeing and calico-printing for the purpose of fasten-
ing the colors, or, in other words, making the colors unite
thoroughly with the fibre of the cloth. It is not, however,
the alum that does this, but the alumina which is in it.
The alum is decomposed in preparing the lakes, or fast col-
ors. Thus an infusion of Brazil-wood, with alum dissolved
in it, presents a brilliant red color. If now there be added
a solution of carbonate of potassium or sodium, a precipitate
is produced, which is the alumina of the alum united with
the red coloring matter. This dried is the Brazil-wood lake
of commerce. In like manner other lakes are prepared
from other vegetable coloring substances. The alumina is
said to act in these lakes as a mordant, a word which is de-
rived from the Latin verb meaning to bite. It is because
the compound which it forms with the coloring -matter
takes such strong hold of the cloth. Alumina is also em-
ployed in the production of those beautiful blue pigments
called stnalts and ultramarine.

236 CHEMISTRY.

328. Other Alums. — Although there is but one substance
which is commonly called alum, the chemist recognizes sev-
eral different salts as alums. The common alum he calls
potassium alum. Then there is a sodium alum, in which
sodium has taken the place of potassium, and the salt is
therefore sulphate of aluminium and sodium, Al2Na2(SO4)4
-f 24II2O. We have also an ammonium alum, in which am-
monium takes the place of the potassium, making a sulphate
of aluminium and ammonium. There are others which we
will not mention. Now in all these different alums the
water of crystallization is exactly the same. And what is
more remarkable still, the crystals are alike in all these salts.
They are therefore termed isomorphous salts, this name com-
ing from two Greek words, isos, equal, and morphe, form.

329. Magnesium. — This is a white malleable and ductile
metal, somewhat resembling aluminium, but far lighter and
more readily oxidizable. A wire or tape of this metal
burns with a magnificent white light, which is sometimes
used for lighting up the interior of buildings for the pur-
pose of photographing.

Magnesium oxide, hydrate, carbonate, sulphate, chloride,
and iodide are all used in the arts. Magnesium oxide, ob-
tained by heating the carbonate to redness, is often called
calcined magnesia. This carbonate occurs native, but is
generally prepared artificially. Mixed with magnesium hy-
drate, it forms the magnesia alba of pharmacy. The sul-
phate of magnesia was originally called Epsom-salt, be-
cause the waters of Epsom Spa, in England, contained so
much of it. In its crystalline state, MgSO4-fVH2O, more
than one half of it is water, and it is efflorescent.

330. Other Earths.— There are several other earths, but they are all
rare, some exceedingly so. One of them, glucina, is one of the constitu-
ents of the precious stones called emerald, beryl, and chrysoberyl. Crys-
tals of another, zirconia, are in common use in jewelry.

ALUMINIUM. — MAGNESIUM AND ZINC. 237

331. Zinc. — The principal ores of this metal are the sul-
phide, the silicate called calamine, the oxide, and the car-
bonate. In obtaining the metal, if the sulphide

and carbonate are used, they are first roasted, the
heat driving off the carbonic acid from the car-
bonate, and the sulphur from the sulphide, in the
form of sulphurous anhydride. This leaves the
ore in the state of oxide. The ore is now mixed
with charcoal, and introduced into an iron cruci-
ble, a vertical section of which is given in Fig. Fis- 94
94. The crucible is closed at the top, and has an iron tube
passing through a hole in the bottom, and also down
through the floor of the furnace in which the crucible is
placed. The upper opening of this tube is above the sur-
face of the mixed ore and charcoal, and the lower opening
is very near to the surface of water in a reservoir. When
the heat is applied the carbon, uniting with the oxygen of
the oxide, forms carbonic oxide and anhydride, which pass
out through the tube and escape. Now as the zinc is vola-
tile, it passes out also with them in the form of vapor, but,
condensing as it gets in the tube below the fire of the fur-
nace, it drops as a liquid into the reservoir of water, where
it becomes solid. Zinc is a bluish-white metal. It has but
a single oxide, ZnO. It takes fire when heated to a bright
red heat, and burns with a brilliant white flame, with a tinge
of green. As it burns the oxide formed flies off in flakes,
which the alchemists fancifully called lana philosophica,
philosopher's wool, and nihil album, white nothing.

332. Carbonate of Zinc, ZnCO3. — The thin whitish film
which forms over the surface of zinc by exposure to air is
a carbonate of zinc, the water and the carbonic anhydride
of the air both entering into its composition. The carbon-
ate of zinc, under the name of smithsonite, is an important
ore of this metal.

238 CHEMISTRY.

. 333. Chloride of Zinc, ZnCI2. — This is a white substance
which is quite soft, and melts, if heated, a little above the
boiling point of water. "When the old names in chemistry
were in vogue, this substance, on account of its softness
and fusibility, had the name of butter of zinc. It has a
great attraction for water, and therefore is active as a caus-
tic, a use to which it is appropriated. While it thus de-
stroys when concentrated, if diluted it acts as a preserva-
tive against putrefaction, and is employed by the anatomist
for preserving bodies for dissection.

Sulphate of zinc — ZnSO4 — sometimes called white vitriol,
is a powerful emetic. It crystallizes in long, white needles,
and is very soluble in water. It is often obtained in the
laboratory as a residue in making hydrogen gas. Zinc,
sulphuric acid, and water yielding zinc sulphate and hy-
drogen, thus :

Zn + H2S04 = ZnS04 + Ha
334. Uses of Zinc. — Though zinc is quite an abundant
metal, it was formerly used but for little else than making
brass and pinchbeck. The variety of uses to which it is
now applied comes from a discovery which was made in
regard to its malleability. When cold it is very brittle;
but when heated to within a certain range of temperature
(100° to 150° C.), it becomes quite malleable, and may be
rolled into thin sheets. It retains the malleability thus
acquired after it becomes cold. It is a curious fact that if
this metal be carried beyond the range of temperature al-
luded to, it becomes brittle again. When in this range it
becomes ductile as well as malleable. The discovery of
these facts has introduced this metal to very numerous
valuable uses. It is now used in the manufacture of many
articles which were formerly made of lead, copper, and iron
— as nails, gasometers, gas-pipes, gutters, roofing, lining for
refrigerators and sinks, etc. It is harder and yet lighter

ALUMINIUM. — MAGNESIUM AND ZINC. 239

than lead. It is cheaper than copper. It is not affected
by air and water as readily as iron. Zinc melts at 412°,
and boils at 1040°. At a still higher heat it may be dis-
tilled. So-called galvanized iron is merely sheet iron coated
with zinc.

QUESTIONS.

308. What is said of barium and strontium compounds ? — 309. Describe
an experiment in which strontium nitrate is used. — 310. Where and how
does calcium occur in nature? What is quicklime? What is said of al-
kaline earths? What of the caustic power of lime? — 311. Explain the
manufacture of quicklime. How does heat effect this decomposition ? —
312. Illustrate the attraction of lime for water, and for carbonic anhy-
dride.— 313. What is stated as to the solubility of lime? To what uses is
lime-water applied?— 314. What are the ingredients of mortar? What
chemical changes occur in mortar as it hardens and dries ? — 315. Under
what forms is carbonate of calcium found ? Mention some animals which
furnish it.-*-316. Explain the deposition of carbonate of calcium from
natural waters. — 317. What are stalactites? What stalagmites? Where
found? How formed?— 318. What is said of calcium carbonate in the
sea? — 319. What is gypsum? How is plaster made? Explain the "set-
ting" of plaster. — 320. How may casts of medals be made? — 321. De-
scribe the mutual reactions of sulphate of calcium and carbonate of am-
monium under different circumstances. — 322. How is chloride of lime used
in bleaching ? — 323. Of what is it composed ? How made ? — 324. How
does calcium phosphate occur in nature ? — 325. What are the properties of
aluminium ? — 326. What is clay ? Name some precious stones containing
alumina. — 327. Of what is common alum composed? How is it used in
dyeing? What is a mordant ? — 328. Name some other alums. — 329. What
are the properties of magnesium ? What is Epsom-salt ? — 330. Name
some of the rare earths occurring in precious stones. — 331. How is zinc
obtained? What is "philosopher's wool?"— 332 and 333. What is said
of the salts of zinc ?— 334. What of its uses ?

240 CHEMISTRY.

CHAPTER XVIII.

GROUP V. — MANGANESE, IRON, COBALT, NICKEL, CHROMIUM.

335. Manganese. — This metal is never found in nature, and
it is rather difficult to obtain it from its ores on account
of the great stability of its oxides and its high melting-
point. It is remarkable for the number of the compounds
which it forms with oxygen. There are six of them. Here
follow their names and formulae :

1. Manganous oxide MnO.

2. Manganese sesquioxide Mn2O3.

3. Manganous manganic oxide Mrt^O4.

4. Manganese dioxide MnO2.

5. Manganous anhydride MnO.,.

6. Permanganic anhydride Mn3O7.

The first two form numerous compounds. Number 4 we
have already used for preparing oxygen. Numbers 5 and
6 are not known in the free state, but their compounds are
important; they combine with bases forming manganates
and permanganates respectively. Potassium permanganate
is used in dilute solution as a tooth- wash. Its solution
has a magnificent purple color. It is a powerful oxidizing
agent.

336. Iron. — Iron when pure is almost white, and is rather
soft, but very tenacious. It is quite malleable. It can be
made into leaves so thin that it would take over three hun-
dred of them to make half an inch in thickness. But even
the best of iron found in the market is far from being pure.
It contains small amounts of carbon and other substances.
Perfectly pure iron is never obtained except in small quan-

MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 241

titles, and by the chemist in his laboratory. The most
striking property of iron is its magnetic power.

337. Importance and Abundance of Iron. — As iron can be
applied to a greater variety of uses than any other metal,
it is very abundant. Stockhardt says of it, " If gold is
called the king of metals, iron must be deemed by far the
most important and useful subject in the metallic realm. It
is not only converted into swords and cannons, but into
plowshares and chisels, and into a thousand other imple-
ments and machines, from the simple coffee-mill to the won-
derful steam-engine. It is the ladder upon which the arts
and trades have mounted to such an extraordinary height.
It is the bridge upon which we now glide over mountains
and valleys with the rapidity almost of magic." Besides
all this, it is present in all soils and in almost all plants, and
is an ingredient of the blood in a large portion of the ani-
mal world. Although we understand but little in regard
to its influence upon plants and animals, we have sufficient
facts to show that, small as its amount is, it is as essential
in the chemical operations of the living world as are com-
mon salt, lime, and some other substances.

338. Oxides of Iron. — There are three oxides of iron : the
monoxide, FeO ; the sesquioxide, Fe2O3 ; and the so-called
magnetic oxide, Fe3O4. The first named has not been pre-
pared in a pure state owing to the rapidity with which it
takes up oxygen and passes to the sesquioxide. It occurs
in nature in combination with acids, forming important
minerals. Ferrous sulphate, or green vitriol ; ferrous car-
bonate, or spathic iron ore ; ferrous sulphide, FeS2, also
called iron pyrites, are the most abundant. On adding am-
monium hydrate to a solution of a ferrous salt, a white pre-
cipitate forms consisting of ferrous hydrate, but this imme-
diately begins to change in color, passing through green
to brownish red by absorption of oxygen from the air, and

242 CHEMISTRY.

becoming ferric hydrate. The second oxide, called sesqui-
oxide, forms one of the abundant ores of iron. It is some-
times crystallized, as in iron-glance; or compact, as in red
iron-stone ; or radiated, as in red hematite ; or earthy, as in
red ochre. When mixed with clay it is the clay iron-stone.
It is that which gives the red color to so many stones and
bodies of earth. The red chalk, so called, used in making:
red pencils, is one form of this oxide. This sesquioxide
may be prepared artificially by heating ferrous sulphate to
redness, or by igniting ferric hydrate, obtained by precip-
itating a ferric solution with an alkaline hydrate.

Ferric hydrate — Fe2O3.3H2O — also occurs in nature; in
large masses it is the brown iron ore, or limonite, from
which the metal can be profitably obtained. Mixed with
clay it forms the yellow day iron-stone, yellow ochre, etc.
The yellow or brown color of soils and of stones which
have been long exposed to the air is owing to ferric hy-
drate. The ochrey deposit which is seen always about the
edges of chalybeate springs is ferric hydrate, made in this
case chiefly from the carbonate, the carbonic acid passing
off and leaving the oxide to become a hydrated sesquioxide.
Observe the difference in color between the hydrated ses-
quioxide and that which is not hydrated ; the former is yel-
low, the latter red. The reason that bricks become red by
burning is that the water is expelled from the iron rust
which is in the clay, and it therefore becomes anhydrous.
This term, which is much used in chemistry, means dry, or
without water, the prefix an meaning without. Iron rust
is the ferric hydrate, 2Fe2O3.3H2O. This water is a part of
the dry solid, being combined intimately with its ingredi-
ents. It is really, therefore, water solidified without freez-
ing. In every hundred grammes of it there are about
fourteen and a half grammes of water, and nearly forty
grammes of oxygen. Both are condensed in uniting with

MANGANESE, IKON, COBALT, NICKEL, CHROMIUM. 243

the iron, the oxygen very much so. As about twenty-seven
gallons of this gas are used up in forming a pound of rust,
it must be vastly condensed to occupy so little space. This
remarkable condensation of oxygen takes place in the for-
mation of all the solid oxides.

The third oxide, Fe3O4, is sometimes considered as a
combination of the first and the second oxides, FeO.Fe2O3,
and hence is also called ferroso-ferric oxide. This oxide
forms no salts, but it occurs in nature very largely, forming
an important ore. This is endowed with magnetic proper-
ties. The common loadstone is ferroso-ferric oxide. Its
color is black, and many dark and green stones owe their
color to it. The celebrated Swedish iron is mostly made
from it. The scales thrown off from heated iron by the
hammer of the blacksmith are formed of this black oxide.

339. Meteorites. — Abundant as iron is, it is never found
in metallic form except in meteorites, and then it is alloyed
with nickel and some other metals. In the large meteorite
in the cabinet of Yale College, brought from Texas, and
weighing nearly two tons, there is from eight to ten per
cent, of nickel, the mixture of the two metals not being
uniform throughout.

340. Production of Iron from its Ores. — In order to obtain
iron from its ores they must be deprived of their oxygen,
and of the impurities that are mingled with them. The
oxygen is removed by subjecting the ores to intense heat
in a furnace with charcoal. This causes the oxygen to
leave the iron, and unite with the carbon of the charcoal to
form carbonic oxide and anhydride, which fly off. But an-
other thing is necessary to remove the impurities, silica,
clay, etc. For this purpose limestone is introduced into the
furnace, which forms with the impurities a slag or glassy
substance, which, as the iron is permitted to run out, floats
on the surface of the melted metal, and is raked off. The

244

CHEMISTRY.

stream of iron runs off into channels made in sand, and
when it becomes cool it forms what is called pig-iron.
Fig. 95 represents a common form of the blast-furnace

Fig. 95.— Blast-furnace.

MANGANESE, IKON, COBALT, NICKEL, CHROMIU3I. 245

used. Ore and fuel are dumped in at the top, the material
gets hotter and hotter as it descends, reduction of the ore
takes place, and the melted iron settles down into the lower
part of the tall furnace, whence it is run off from time to
time on the inclined plane to the left. The arrangement
for the blast of air, by means of which the combustion is
accelerated, is seen at the right hand in the lower portion
of the picture.

341. Cast Iron. — This pig-iron is used for making castings.
It is fit for this purpose from having had combined with it
in the process above described about five per cent, of car-
bon. It is from this addition that the metal runs so readily
into the moulds. If it were pure iron, or if it contained
much less carbon, it would not do this. Besides, this com-
bination of carbon and iron, as it passes from the liquid to
the solid state in cooling, increases a little in bulk, and so
fills out the mould in every line. This is owing to the crys-
tallization which takes place every where in it. Cast iron
is very brittle, and is not in the least malleable or ductile.
Its hardness and its capability of being cast in moulds fit it
for a great variety of uses, while its brittleness unfits it for
many uses to which other modifications of this metal are
especially adapted.

342. 'Wrought Iron. — This is obtained from cast iron by
taking advantage of the fact that carbon is more combusti-
ble than iron. The carbon is mostly burned out of the cast
iron. It is done by exposing the iron to a current of air
when it is strongly heated in what is called a reverberatory
furnace. The result is that the oxygen of the air unites
with the carbon of the cast iron, and passes off as carbonic
oxide. Fig. 96 (p. 246) will give you an idea of the con-
struction of the furnace. The upper figure is a vertical, and
the lower a horizontal section. At a is the fire, and b is the
ash-pit ; at c is a wall called the bridge, which serves to direct

246

CHEMISTRY.

the body of flame and heated air strongly against the arched
ceiling of the furnace, whence it rebounds, or is reverberated
down upon the iron which lies on the floor or hearth, d.
The openings, g and i, are for the introduction of the iron,
and at p is a damper by which the draught is regulated.
"When the "puddling" is finished the metal is taken out in

the shape of a ball, and aft-
er being subjected to great
pressure by machinery, to
squeeze out the slag, it is
passed through a succes-
sion of rollers, each pair
having a smaller space be-
tween them than the pre-
ceding. The conclusion of
all this is the formation of
the soft bar-iron of com-
merce. Its qualities are the
Flg-96- very opposite of those of

cast iron. It is soft, flexible, ductile, and malleable, while
cast iron is hard and brittle. When strongly heated it be-
comes only semifluid, and therefore can not be made to run
into moulds like cast iron. It is also different in its text-
ure. "While cast iron is granular, as you can see by ex-
amining a broken edge, the structure of wrought iron is
fibrous. It is a curious fact that long-continued jarring
will sometimes change the fibrous texture of wrought iron
into the granular arrangement peculiar to cast iron, show-
ing that it is not the mere absence of carbon that makes
wrought iron what it is. This has sometimes taken place
in the axles and wheels of railway cars, and the brittleness
induced has caused serious accidents. It is on account of
the peculiar structure of wrought iron that it can be
welded, which can not be done with cast iron. In welding

MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 247

the fibres of the iron intermingle. For this reason welding
adds to the strength of the material, and accordingly arti-
cles which require to be very strong, such as anchors, are
made not in a single piece, but by welding together a
bundle of bars of iron.

343. Steel. — Steel is a form of iron midway between
wrought and cast iron as to the quantity of carbon it con-
tains, which is from one to two per cent., while that of cast
iron is five per cent. It may be made from cast iron by
burning out half of its carbon, or from wrought iron by re-
storing half of the carbon of which it was deprived in its
preparation. The latter is the usual process, and consists
in heating the wrought iron in close iron boxes containing
charcoal for several days. Steel can be made to have dif-
ferent properties according to the uses to whicli we wish
to put it. If it be heated to redness, and then be quickly
quenched, it is rendered hard and brittle ; if cooled rather
gradually it becomes elastic ; and if cooled very slowly it
becomes soft, ductile, and malleable, like bar-iron. When
it is cooled slowly it is said to be annealed.

344. Bessemer Process. — This is a new and very rapid
method of preparing cast steel, of the greatest industrial
importance. It consists in burning out all the carbon and
silicon in cast iron by passing a blast of atmospheric air
through the molten metal, and then in adding such a quan-
tity of a pure cast iron as is necessary to give carbon
enough to convert the wrought iron into steel ; the melted
steel is then at once cast into ingots. In this way six tons
of cast iron can be converted into steel in one operation
lasting twenty minutes. This process has in large measure
revolutionized the old iron industry.

345. Tempering. — Steel when hardened, as mentioned
above, is not fit for use till it is tempered, as it is termed,
to the particular use for which it is designed. This tern-

248 CHEMISTRY.

pering process consists in reheating the steel and then let-
ting it cool slowly. The character of the effect depends
upon the degree of heat to which it is carried, and this is
measured by the workmen by the color caused by the heat.
You can see the various colors by experimenting with a
common knitting-needle. First heat it to redness in the
flame of a spirit-lamp, and quench it in cold water. Now
hold it again in the flame, and observe the changes of
color. It first becomes a pale yellow, then orange, crim-
son, violet, blue, and finally dark gray. The explanation
is this : A film of oxide forms, which, being at first exceed-
ingly thin, is pale yellow, and deepens in its tint as the in-
creased heat thickens it. The final dark-gray coating is
scales of the oxide of iron. Now there is a definite degree
of hardness on the one hand, and of elasticity on the other,
corresponding to each one of these colors, the yellow giv-
ing the most brittleness and hardness, and the blue the
most softness and elasticity, the other colors giving inter-
mediate results. Accordingly, tools for cutting metal,
which require to be very hard, are heated till they become
a pale yellow ; knives and planes to an orange ; chisels,
hatchets, etc., to a crimson ; and springs to a violet or blue
tint.

346. Sulphides of Iron. — There are three sulphides of
iron. One of them, the disulphide FeS2, is what is usually
called iron pyrites. It received this name among the an-
cients because it strikes fire, pur being the Greek for fire.
The idea which they had of it may be gathered from what
Pliny says, who states that " there was much fire in it."
It crystallizes, and has a brilliant yellowish brassy color.
It has sometimes been supposed by the ignorant to be gold,
and so has received the name of fool's gold. It is of great
value in the arts in obtaining several important substances,
as sulphur, ferrous sulphate, and sulphuric acid. As more

MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 249

than half of this salt is sulphur, heat will drive off a large
portion of it. It is therefore usually heated in clay retorts,
and the sulphur which passes off in vapor is collected.
The residue is taken out and thrown into heaps, and is
simply left exposed to the air. By the absorption of oxy-
gen from the air this sulphide gradually becomes a ferrous
sulphate, the oxygen converting the sulphur into sulphuric
acid, and the iron into oxide of iron, which unite to form
the sulphate.

347. Other Salts of Iron. — Metallic iron dissolves readily
in nitric and hydrochloric acid, forming nitrate and chloride
of iron. Two of each can be obtained, one in the ferrous
and the other in the ferric state. Ferric chloride is much
used in medicine and in the arts ; it is a valuable disinfect-
ant. Ferric solutions are usually yellowish red in color,
and ferrous solutions pale green.

348. Cobalt. — This is a brittle metal of a reddish-white
color. It exists in nature in combination with arsenic and
sulphur. There are two oxides, one of which, the monox-
ide, gives a beautiful blue color to glass. It is this colored
glass ground to a fine powder that constitutes the smalt
which is used to give. to writing-paper and linen a delicate
shade of blue. The blue colors on porcelain are also pro-
duced by cobalt, and the zaffer used to give a blue color
to common earthenware is an impure oxide of this metal.
The fly-poison, so commonly called cobalt by apothecaries,
is arsenic, and has not a particle of cobalt in it. The name
which this metal bears was given to it in a singular way.
When the superstitious miners of the Middle Ages found
the ores of cobalt, they expected, from their brilliancy, that
they should obtain something very valuable from them;
but they were disappointed in finding them crumble in
their smelting-furnaces into gray ashes, emitting at the
same time a disagreeable odor of garlic. They imagined,

250 CHEMISTRY.

therefore, that they were mocked in these results by the
earth-spirits of the mines, the Kobolds, as they were called,
and so named the ore after them. The name which the
metal now bears is a corruption of that which was orig-
inally bestowed by the miners upon the ore.

349. Chloride of Cobalt. — The solution of this salt makes
a beautiful sympathetic ink. It being of a pink color, what
is written upon pink paper will be invisible. If the paper
be warmed, the letters will become of a bright blue color,
and then they will fade again as the paper becomes cool.

This is owing to the difference of color between the hy-
drated and the anhydrous salt.

350. Nickel. — This is a white metal, and takes a good
polish. One of its chief uses is in making the alloy called
German silver. It is an ingredient in the meteorites, as
already noticed. Both cobalt and nickel are commonly
found in company with iron, and these three metals are the
only ones which are magnetic. The beautiful stone called
chrysoprase is quartz colored an apple-green by oxide of
nickel.

Nickel almost deserves to be classed among the noble
metals, it is so little prone to oxidize. Since nickel-plating
has been perfected we see nickel -covered objects in com-
mon use. The one-cent and five-cent coins are alloys of
copper and nickel. Nickel forms two oxides, only one,
NiO, being of importance.

351. Salts of Nickel. — The most abundant ore of nickel
is niccolite, an arsenide of nickel. Nickel dissolves in ni-
tric acid, forming a beautiful green nitrate of nickel. The
carbonate, sulphate, chloride, hydrate, etc., are well-known
salts, which have not obtained any extensive use in the
arts. A double salt, sulphate of nickel and ammonium, is
used in nickel-plating.

352. Chromium. — This is not very abundant in the earth.

TIX. 251

It occurs near Baltimore combined with iron, forming so-
called chromic iron.

Chromium forms a great many oxides, like manganese.
That having most oxygen plays the part of an acid. Some
of the salts of chromic acid are valuable. Chrome yellow,
a well-known pigment, is a chromate of lead. Chrome or-
\anye is made by digesting chrome yellow with potassium
carbonate, the effect of which is to remove a part of the
chromic acid from the salt.

The most important of the chromates, however, is the
potassium dichroniate, K2Cr2O7, a beautiful yellowish-red
crystalline substance. All the compounds of chromium
are strongly colored, and many of them are very beautiful.
The green color of our "greenbacks" is due to the sesqui-
oxide of chromium, Cr2O3, which is a very fast color, and
not easily attacked by acids or alkalies.

GROUP vi. — TIN.

353. Tin. — Tin is one of the most extensively useful of
the metals, for it is soft and malleable, and does not easily
tarnish. The tin-foil which you so often see shows how
malleable it is. Tin is used in making many of the alloys.
Our common tin-ware is not tin alone, but thin sheet-iron
covered with tin, the sheets having been dipped into the
melted metal. The object of the covering of tin is to pre-
sent a surface to the air and to liquids that is not easily
oxidized. For the same reason iron chains are often cov-
ered with tin. Pins are made of brass, and are coated with
an exceedingly thin covering of tin by a chemical process
which has been described in Part L Tin is a brilliant
white metal. It is quite disposed to crystallize, as may be
seen by a single experiment. Sponge a perfectly clean
piece of tin which has been slightly heated quickly over
with nitre-muriatic acid. After washing it in clean water

252 CHEMISTRY.

and drying it, the crystalline arrangement can be very
plainly seen. Ware which has been treated in this way is
called moire metallique. If a bar of tin be bent it gives a
peculiar sound, which is owing to the friction of the mi-
nute crystals of the metal against each other. This sound
has been fancifully called "the cry of tin." There are
three oxides of tin, one of Avhich, the dioxide, SnO2, is its
common one. The most famous and most abundant tin-
mines are those of Cornwall, in England. It is supposed
that they were worked long before the Christian era.

354. "Tin Salts." — By dissolving tin in hydrochloric acid,
stannotis chloride, SnCl2, separates from the solution in
needle-shaped crystals containing water. This forms the
"tin salts" so largely used by the calico-printer and dyer
as a mordant. Stannic chloride, SnCl4, is a fuming, color-
less, heavy liquid.

355. Sulphides of Tin. — There are two sulphides of tin, a mono- and
a di-sulphide. Stockhardt tells us how to obtain them. To obtain the
first inclose 2 grammes of flowers of sulphur in a piece of tin-foil weigh-
ing 4 grammes, and introduce the package into a test-tube. On heating
the tube, half of the sulphur will burn up, and the other half will unite with
the tin with a lively glowing, forming a brownish-black mass, which is the
monosulphide. If you sprinkle the glass, while still hot, with water, it is
rendered friable, and is easily separated from the fused salt, which will be
found to weigh about 5 grammes. Pulverize this, and mix intimately with
the powder 1 gramme of sulphur and 2 of sal ammoniac. Put this into a
thin flask, and let it be heated in a sand-bath for an hour and a half. The
disulphide will be found in the bottom of the flask in a mass having a gold-
en lustre, and the sal ammoniac will appear in the upper part of the flask,
deposited there by sublimation. The latter is not altered at all in compo-
sition, but it in some way serves to give the disulphide its golden color.
The beautiful substance thus obtained has been called aurum musivum, or
mosaic gold, and it may be used for giving a gold-like coating to wood,
plaster of Paris, etc.

ARSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 253

QUESTIONS.

335. Give the names and formulae of the oxides of manganese. Which
ones form salts?— 336. What are the properties of pure iron? — 337. What
is said of the abundance and importance of iron ? — 338. What oxides does
iron form ? What is said of ferrous hydrate ? Mention some of the ores
of the monoxide of iron. Of the sesquioxide. Of ferric hydrate. How
many grammes of water are there in 100 grammes of ferric hydrate ? How
many grammes of oxygen ? How many gallons of oxygen in one pound
of rust ? What is the composition of the so-called magnetic oxide of iron ?
What are its properties ?— 339. What are meteorites ?— 340. Describe the
process of making pig-iron. Why is limestone added ? — 341. What is said
of cast iron ?— 342. What is the process of converting cast iron into wrought
iron? Describe the change in properties thus produced. Why can
wrought iron be welded ? — 343. In what does steel differ from iron ?
What are its properties ? What is annealing ? — 344. In what does the
Bessemer process consist? — 345. What is said of tempering steel? What
colors does it assume? — 346. Name and describe the principal sulphide of
iron. Of what use is it ? — 347. Name some other salts of iron.— 348.
What is the nature of cobalt ? Whence its name ?— 349. What is said of
sympathetic ink? — 3.">0. What are the properties of nickel? — 351. Name
some of its salts. — 352. What are the most important oxides of chromium ?
What is said of the chromates? — 353. What are the uses of tin ? How are
pins made ? What is moirt metalllgue * What peculiar property has a
bar of tin ?— 354. What is known as " tin-salts ?" How used ?— 355. What
is mosaic gold ? How made ? How is the monosulphide obtained ?

CHAPTER XIX.

GROUP VII. ARSENIC, ANTIMONY, AND BISMUTU. GROUP VIII.

COPPER AND LEAD.

356. Arsenic. — What is known as arsenic in common lan-
guage is a compound of this metal with oxygen, called by
the chemist arsenious anhydride, As2O3. This arseniotis
anhydride is a deadly poison, so that " poisonous as arsenic"
is a common expression. It is used for the destruction of

254 CHEMISTRY.

life more often than any other poison. It is much used for
killing rats, moles, and other troublesome animals, and
hence the name ratsbane which is often given to it. It
looks much like sugar and flour, and its taste is rather sweet.
The metal arsenic is crystalline, of a bright steel-gray color.
It is not poisonous when free from oxide. It very soon
tarnishes when exposed to the air, and at length becomes a
coarse gray powder, which is a mixture of the metal and
its oxide. It is sometimes sold by druggists under the
names of " fly -powder," "cobalt," and "mercury." This
is wrong, for people who buy it are not as cautious in its
use as they would be if they knew that it wras arsenic.

357. Antidotes to Arsenic. — Every one ought to know
what to do if he chance to be with any person who has
taken arsenious anhydride — white arsenic, as it is called.
He should administer at once in considerable quantities
the whites of eggs, or milk, or flour and water, or soap-
suds. These, however, are but partial antidotes, doing
little, if any thing, more than sheathing the membranes of
the stomach from the arsenic. There is only one true
chemical antidote to this poison — ferric hydrate ; but it is
good for nothing unless it has been freshly prepared. Its
efficacy results from its forming with the arsenic a com-
pound which is insoluble, and therefore inactive.

There are some sure chemical tests of the presence or ab-
sence of arsenic in the bodies of those who are supposed to
have been killed by this poison ; but such investigations
belong properly only to the professional chemist, and there-
fore are not suited to this work.

358. Antiseptic Powers of Arsenic. — When arsenious an-
hydride is taken as a poison and destroys life, it has a
marked effect in preserving the body from putrefaction.
This is shown in various ways. Sometimes the whole
body is remarkably preserved for a long time after death.

ARSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 255

Iii this case the person lives so long after taking the poison
that it goes every where in the circulation, and pervades
the whole body. But sometimes, on the other hand, the
stomach and intestines alone have been found preserved
even after the rest of the body was far gone in decompo-
sition. Here the person died soon after taking the ar-
senic, and therefore its antiseptic influence was exerted
locally. It is on account of this preservative power that
skins intended for shipping have arsenic rubbed on the
flesh side.

359. Arsenic-Eating. — There is a strange habit of eating
arsenic prevalent among the inhabitants of Styria, a mount-
ainous district in Austria. The effects which are ascribed
to it are hardly credible, but the statements seem to be
well authenticated. It is said that the arsenic-eaters con-
tract the habit for the purpose of improving their personal
appearance. Another effect is that the respiration is im-
proved, so that mountains can be climbed with much less
embarrassment of the breathing than is usual. But the
habit is attended with great dangers. The arsenic-eater
begins with small doses, and gradually increases them.
Great caution is required, and very often too much is
taken ; aitd then symptoms of poisoning appear, perhaps
resulting in death. Then, again, when the habit is once
formed, any intermission in the regular taking of the ar-
senic is dangerous, bringing on at once the common symp-
toms of arsenic-poisoning. It is said that the same results
are produced on brute animals, and that in the city of Vi-
enna men sometimes throw a pinch of arsenic into the food
of horses. It makes them fat, sleek, and of good wind ; but
the practice once begun must be kept up. Notwithstand-
ing all this, thorough investigation would undoubtedly
show that arsenic-eating very considerably shortens life,
although cases are cited in which persons who for a long

256 CHEMISTRY.

time Lave been slaves to the habit are in good health even
at the age of sixty years or more.

360. Arsenetted Hydrogen. — Arsenic, like nitrogen and
phosphorus, combines with hydrogen in the proportion of
one atom to three. This body, arsenetted hydrogen, AsH3,
or hydrogen arsenide, as it is sometimes called, is a gas,
neither acid nor alkaline, and very poisonous. A German
chemist, named Gehlen, was fatally poisoned by it in 1815,
while investigating its properties. It is easily obtained
by throwing a little arsenious anhydride into an apparatus

for generating hy-
drogen by means
of zinc and sul-
phuric acid. The
arsenious oxide
is deprived of its
oxygen, and part
of the metal com-
bines with the hy-
drogen, forming ar-
senetted hydrogen.
This gas is inflam-

Fis-97- mable, and burns

with a lambent flame ; if a cold porcelain plate be held in
the flame a moment, the gas being decomposed by the
combustion, metallic arsenic will be deposited on the por-
celain, forming gray-black spots. This formation of ar-
senetted hydrogen and of a metallic deposit by the flame
is made use of in testing for arsenic. The delicacy of the
test is remarkable : -^^-QQ of a gramme can be detected in
this manner, using suitable precautions not necessary to
describe here. Antimony forms a similar compound with
hydrogen, SbH3, and the flame of this gas deposits a black
metallic coating on a cold porcelain surface just like ar-

AKSENIC, ANTIMONY, BISMUTH. — COPPER AND LEAD. 257

senic, but somewhat deeper black in color. The methods
of distinguishing between arsenic and antimony, however,
belong to works on analytical chemistry. You can easily
see, however, that when a chemist is called upon to deter-
mine whether a person has been poisoned by arsenic or
not, the chemist must be very careful not to mistake anti-
mony for arsenic, for antimony, as you will learn in § 363,
is a component of tartar emetic, which is sometimes given
to produce vomiting when poisoning is suspected.

361. Arsenical Pigments. — Arsenious acid in combina-
tion with copper makes several splendid green pigments.
Scheelds Green is an arsenite of copper formed by adding
an alkaline solution of arsenious acid to a hot solution of
copper sulphate. Paris Green is nearly the same, but con-
tains acetate of copper also. This brilliant color is exten-
sively used as a pigment. It is a very poisonous substance,
and its use is dangerous. "It may even prove danger-
ous," Stockhardt says, " as a green paint for rooms, since,
under some circumstances, volatile combinations of arsenic
are formed from it and mix with the air."

Brunswick Green is another arsenical pigment, prepared
like Scheele's Green, only some cream of tartar is added to
the copper sulphate, and some slaked lime to the arsenious
solution. The facility with which compounds of arsenic
can be obtained by the common people, and their cheap-
ness, is much to be deplored.

362. Antimony. — This metal is not so well known as one
of its salts called tartar emetic ; and yet in some of the arts
it is largely used. It is one of the constituents of type-
metal. The alloy of lead and antimony which we have in
type-metal at the moment that it becomes solid in casting
expands, so that the mould is well filled out, and the type
is therefore complete, with well-marked lines and angles.
But neither of these metals when alone makes a good cast-

258 CHEMISTRY.

ing, because they shrink in becoming solid, instead of swell-
ing as they do when mixed in alloy. The metal plates on
which music is sometimes engraved is an alloy of tin and
antimony. The Britannia Metal, which has taken the place
of the old-fashioned pewter, is composed of one hundred
parts of best block-tin, eight of the metal antimony, and
either two and a half parts each of copper and brass, or
two of copper and bismuth. Antimony is obtained chiefly
from its sulphide, which is quite an abundant ore. It is
associated commonly with ores of silver, copper, lead,
zinc, etc.

363. Compounds of Antimony. — Antimony forms two
chlorides, one of them, SbCl3, has long been known under
the name of butter of antimony. It forms also two oxides,
Sb2O3 and Sb2O5, and two sulphides of corresponding com-
position. Tartar emetic is a double tartrate of antimony
and potassium, K(SbO)C4H4O6. It is obtained by boiling
antimonious oxide with cream of tartar (hydro-potassium
tartrate), and evaporating the solution. Nearly all the
salts of antimonious oxide are decomposed on adding wa-
ter to their acid solutions. Antimonetted hydrogen has
been mentioned in § 360.

364. Bismuth. — This metal is found in but few localities,
and mostly in the metallic state. By far the largest part
of it comes from one locality, Schneeberg, in Saxony. It is
obtained from the rocks in which it is present by reducing
them to a coarse powder, which is burned in a sort of kiln.
The bismuth, which is quite fusible, is thus melted out, and
is collected in a trough at the bottom of the kiln. It is a
white metal with a peculiar reddish tint, and a remarkable
crystalline structure. It is used chiefly in forming certain
alloys, as one kind of type-metal, and the metal for stereo-
type plates.

365. Nitrate of Bismuth.— If a solution of this salt be

ARSENIC, ANTIMONY, BISMUTH. — COPPEE AND LEAD. 259

turned into a large quantity of water, the salt loses a part
of its nitric acid, and so becomes basic, and is called a sub-
nitrate. This appears in the form of a white precipitate.
This has been sometimes used as a cosmetic. It would be
dangerous for a lady who had used it for this purpose to
attend a chemical lecture at which any sulphuretted hydro-
gen should escape, for this gas blackens at once this salt.

366. Copper. — This metal is next to iron in strength. It
is one of the very few metals which have a decided color.
It is very malleable and ductile, and is therefore much used
in the forms of sheet and wire. It is largely used in sheath-
ing ships. It is a constituent of many alloys, as brass,
bronze, German silver, etc. Gold and silver, both in coins
and articles for use, are alloyed with copper, to give them
the requisite hardness. Native copper is found in abun-
dance in the neighborhood of Lake Superior. A mass of it
has been taken thence to Washington which weighed 3704
pounds, and a mass has been uncovered in one of the mines
which has been estimated to weigh 200 tons. The metal is
also largely obtained from copper pyrites, a double sul-
phide of iron and copper — that is, an ore in which the sul-
phur is chemically combined with both of these metals, the
particles of the .two sulphides being most intimately min-
gled together. There are also other ores of copper — the
pure sulphide, red oxide, carbonate, etc. There are two
oxides of copper — the monoxide, which is black, and the
suboxide, which is red. The latter is used in the manu-
facture of glass, giving it a splendid ruby-red color.

We have already named many of the salts of copper;
the sulphate sometimes called blue vitriol forms beautiful
blue crystals containing water. It is used in calico-print-
ing and in the manufacture of green pigments, some of
them containing arsenic, as you have just learned. Ace-
tate of copper, sometimes called verdigris, is another green

260 CHEMISTRY.

pigment. It is a very poisonous substance. It is formed
whenever acetic acid is brought in contact with copper.
No article of food, then, in which there is vinegar should
be cooked or kept in a copper vessel.

367. Experiment -with Sulphate of Copper. — If you hold a
knife -blade for a few minutes in a strong solution of sul-
phate of copper, it will be covered with a coating of metal-
lic copper.

The copper is precipitated upon the iron, while the iron
goes into the solution. This is shown as follows :

Sulphate of copper. Iron. Ferrous sulphate. Copper.
CuSO4 + Fe = FeSO4 + Cu

This experiment was tried on a large scale some years ago
in Ireland. In some pits at a mine in Wicklow there was
a large amount of the solution of sulphate of copper. In
order to get the metallic copper from this, 500 tons of iron
were placed in the pits and left there for a year. The re-
sult was that the iron was all united to the sulphuric acid,
forming ferrous sulphate, which was dissolved in the water,
and the metallic copper lay in the form of a reddish mud
at the bottom of the pits. This was taken out, and, after
being freed from its impurities, was melted and cast in bars.
The same expedient has been adopted in other mines.

368. Test for Copper. — Polished steel, as shown by the
experiment with the knife-blade, is a good test of the pres-
ence of salts of copper. If pickled cucumbers or preserved
fruit have been prepared in copper vessels, we can ascer-
tain whether copper be present in them by introducing a
slip of polished steel, or, what is the same thing, a bright
knife-blade. If there be any salt of copper, the metal it-
self will be deposited upon the steel. Of course, as the
quantity, if there be any, must be small, the steel must re-
main in the liquid for some little time, and the deposit must
necessarily be small. If the salt be acetate of copper, as it

ARSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 261

is very likely to be, the copper is set free by the formation
of an acetate of iron.

369. Lead. — Next to iron, lead is one of the most abun-
dant metals. Its softness and low melting-point are its
chief characteristics. It is used for a great variety of pur-
poses. It is the chief ingredient in type-metal. Bullets
and shot are made from it. The mode of manufacturing
shot is given in § 60, Part I. It is also largely used for
pipes for conducting water and other liquids. In the form
of sheet-lead it is applied to various uses. This metal is
obtained principally from its sulphide, called galena. One
mode of obtaining it is to mix the ore with iron, and then
apply heat. The sulphur, having a greater attraction for
iron than for lead, leaves the lead to unite with the iron.
The action of water upon lead we shall speak of in another
place.

370. Oxides of Lead. — The monoxide of lead, PbO, is a
yellow substance called massicot. If this be melted with
a strong heat it solidifies, on cooling, into a reddish-yellow
mass composed of brilliant scales, and is called litharge.
It is used extensively in the arts, in the manufacture of
glass, in making the lead plaster of the apothecary, in form-
ing a varnish with linseed-oil for the cabinet-maker, in the
manufacture of wliite-lead, red-lead, etc. The red oxide is
prepared by exposing for some time to a faint red heat the
monoxide which has not been fused. A brilliant red and
very heavy powder results called minium, which is used
as a cheap substitute for vermilion in painting.

The composition of the red oxide is 2PbO.PbO2, being a
compound of the monoxide and of a chocolate-colored ox-
ide, PbO2, not previously mentioned.

371. "White-Lead, or Carbonate of Lead, PbCO3. — This may
be prepared by mixing a solution of lead acetate or nitrate
with one of sodium carbonate, a white precipitate settling.

262 CHEMISTEY.

The commercial white-lead is prepared differently, usually
by exposing sheet-lead to the influence of the oxygen of
the air in the presence of acetic acid or vinegar. The
agency of the acetic acid of the vinegar is interesting. It
dissolves successive portions of the oxide of lead, forming
with it an acetate, and the moment that it does this the
carbonic acid takes away the oxide from it; so that the
office of the acetic acid is simply to take the oxide and
deliver it over to the carbonic acid. It is very much as
the nitric acid in the formation of sulphuric acid (§ 242)
continually takes oxygen from the air and delivers it over
to the sulphurous acid.

372. Lead-Poisoning. — The carbonate of lead is a poison,
producing, when introduced into the system, lead colic,
paralysis, and many other bad affections. Many persons
have been subjected to protracted suffering, and many lives
have been lost from this poison. Painters are liable to be
poisoned by it, but the liability has been much diminished
by precautions in the use of the article in their business.
The poisonous influence more often comes from drinking
water brought in lead pipes, and in that case is commonly
slow and insidious. And, as a general rule, the purer the
water, the more apt is it to be rendered poisonous by the
lead. The reason of this is obvious. You will remember
that we told you that there is always some carbonic anhy-
dride in water. Now this acts upon the metallic lead in
connection w7ith the water, and, forming carbonate of lead,
makes it poisonous. It will do so unless there be some-
thing to prevent it. If the water be quite pure, there is
nothing in it to prevent the carbonic anhydride from thus
acting ; but if there be certain impurities, as, for example,
sulphate of lime, there will be formed a thin coating over
the surface of the metal, which effectually shields it. Lead
pipes ought never to be used unless the water to be brought

ARSENIC, ANTIMONY, BISMUTH. — COPPER AND LEAD. 263

through them has been ascertained by a skillful chemist to
have the protective ingredients alluded to in it. There has
been great carelessness in this matter. Because in the
majority of cases there is no hazard, people have presumed
on safety without any examination, foolishly running the
risk of having the exception occur in their case.

Tin-lined pipes are said to be safer than ordinary lead
pipes.

373. Sugar of Lead, or Lead Acetate, Pb(C2H3O2)2.— Ace-
tate of lead is commonly called sugar of lead, on account
of its sweet taste. A very pretty experiment may be tried
with a solution of this salt. Dissolve 15 grammes of sugar
of lead in ISO cubic centimeters of water, making the liq-
uid clear by adding a few drops of acetic acid. If this
be poured into a phial, and a slip of zinc be fastened to the
cork, as seen in Fig. 98, brilliant metallic branches will
grow upon the zinc, filling the phial
in a day or two. These are crystals
of lead which have arranged them-
selves in this arborescent form. This
is because the zinc replaces the lead
in the lead acetate, forming zinc ace-
tate, which takes the place of the
lead acetate in the liquid. This
leaves the lead uncombined, and its
particles, as fast as they are released,
gather in crystals, the process taking its start from the
zinc where the chemical change occurs. Acetic acid is
H.C2H3O2, being an organic acid composed of carbon, hy-
drogen, and oxygen, in the proportions named. Lead ace-
tate is Pb(C2H3O2)2, therefore the reaction above described
may be expressed in an equation thus :

Lead acetate. Zinc. Zinc acetate. Lead.

rb(CaII,Oa)a + Zn = Zn(C3H303)2 + Pb

264 CHEMISTRY.

QUESTIONS.

356. What is said of the metal arsenic ? What is the composition of
ratsbane ? — 357. What are the antidotes to arsenic poisoning ? — 358. What
is said of the antiseptic properties of arsenic ? — 359. What of arsenic eat-
ing ? — 3GO. What is the composition of arsenetted hydrogen ? How is it
made ? What are its properties ? How delicate is this as a test for ar-
senic ? What is said of the danger of mistaking antimony for arsenic ?
— 361. Name some pigments containing arsenic. Of what are they com-
posed ? — 362. What is said of the uses of antimony ? — 363. Describe some
salts of antimony. What is tartar emetic ? — 364. What is said of bismuth ?
365. What of its nitrate ?— 366. What are the properties of copper ? What
its uses ? What is said of native copper ? What other ores of copper are
mentioned? What is said of the salts of copper ? — 367. Describe an experi-
ment with sulphate of copper. Where and why was this done on a large
scale ?— 368. What is a good test for copper ? — 369. How is lead obtained ?
For what is it used ? — 370. What is said of the oxides of lead ? What is
minium? — 371. What is white-lead? How made? — 372. Why is poison-
ing by lead so insidious? What danger is there in using lead pipes for
conveying drinking-water? What pipes are safer? — 373. What is the sci-
entific name of sugar of lead ? What is its composition ? How can a lead
tree be made ? What is the theory of its formation ?

CHAPTER XX.

GROUP IX. MERCURY, SILVER, GOLD, AND PLATINUM.

374. Mercury. — This metal was thus named from its
quickness of movement, because Mercury was considered
by the ancients the most active of the gods. The alche-
mists called it quicksilver, because they thought it to be
an enchanted kind of silver, and they endeavored by vari-
ous processes to obtain from it solid silver. Mercury is the
only metal which is liquid at ordinary temperatures. It
freezes or solidifies at about 39-j- degrees below zero, and
then it is malleable like lead. It evaporates like water,

MERCURY, SILVER, GOLD, AND PLATINUM. 205

though not as rapidly, at ordinary temperatures. This you
can prove by a simple experiment. Put some mercury in
a phial, and fasten to the cork a little bit of wood having
some gold-leaf attached to it. The gold, after a few days,
will have a white color, because the mercury has risen in
vapor and united with the gold, forming an amalgam.
There are two oxides of mercury, one of which, called red
precipitate, is with its bright red color a striking example
of the great difference which is so often seen between the
properties of a compound and those of its constituents.
Mercury is sometimes found native. It is said that the
mines of Mexico were discovered by a hunter, who, as he
took hold of a shrub in climbing a mountain, tore it up by
the roots, and a stream of what he supposed to be liquid
silver burst forth. But the metal is commonly obtained
from the ore called cinnabar, a sulphide.

So readily does the mercury in cinnabar part with the
sulphur that merely roasting it in a current of heated air
answers to reduce it. Sulphurous anhydride is formed by
the union of the sulphur with the oxygen of the air, and
this gas passes together with the vapor of the mercury into
a cool chamber, where the liquid mercury collects by the
condensation of the vapor.

375. Vermilion. — Cinnabar is of a beautiful red color, but
precipitated mercuric sulphide is black. If this artificial
sulphide is sublimed, then, without any chemical change, it
becomes a brilliant red, and is the so-called vermilion. This
substance is sometimes adulterated with minium or red-
lead, but the fraud can be easily detected. If a little of
pure vermilion be thrown upon a live coal, it is entirely
volatilized or sublimed with a blue sulphurous flame ; but
if it be adulterated with minium it will not all volatilize,
and beads of metallic lead will remain on the coal.

376. Chlorides of Mercury. — Mercurous chloride, Hg2Cl2,

266 CHEMISTRY.

is also called calomel. Mercuric chloride is commonly call-
ed corrosive sublimate ; it contains twice as much chlorine
as the first-named chloride, and is written HgCl2.

Calomel is an insoluble and mild substance ; but corro-
sive sublimate, merely by having this additional quantity
of chlorine, is soluble, and acts as a corrosive poison, burn-
ing and eating wherever it goes. It is much used for the
destruction of vermin. It has sometimes been swallowed
by mistake. It produces most distressing symptoms, end-
ing very commonly in death. The accident happens usu-
ally in one or the other of two ways : either a bottle which
has had a solution of corrosive sublimate in it is carelessly
put aside, and is afterward used for some other purpose,
perhaps for bottling cider ; or the bottle containing the so-
lution is put among other bottles without being properly
labeled, and, if the solution is made with alcohol, some of
it may be swallowed on the supposition that it is some kind
of liquor. It is in this latter case that such intense suffer-
ing is produced, because the poison is so concentrated.
But little is swallowed, for the individual is affected at
once by an intense burning in the throat, extending down
into the stomach. Every one ought to know the effectual
antidote which they have to this poison, for the earlier it is
used the better, and every moment's delay adds to the dan-
ger of the case. Fortunately the antidote is generally at
hand. It is the whites of eggs, which should be swallowed
freely. The albumen in this substance acts chemically
upon the corrosive sublimate, producing a compound that
is not poisonous. If there be no eggs at hand, give milk,
or flour stirred up in water, for there is some albumen in
these.

377. Amalgamation. — You have already learned (§ 278)
that mercury forms with some of the metals alloys called
amalgams. This fact is made use of in freeing certain

MEECUEY, SILVEE, GOLD, AND PLATINUM. 267

metals from substances with which they happen to be min-
gled. Silver and gold are often obtained by this process,
which is called amalgamation. Suppose, for example, that
we have some quartz with gold finely scattered through it.
The quartz is first powdered, and then the powder is agi-
tated with mercury, which seeks out, as we may say, all
the gold, and unites with it to form an amalgam. Suf-
ficient mercury is used to have the amalgam liquid, so that
it may be readily separated from the powder. This liquid
amalgam, which is really a solution of gold in mercury, is
poured upon buckskin or a closely woven cloth, which al-
lows most of the mercury to run through, leaving the gold
alloyed with a small part of the mercury. The remaining
mercury is driven off by heat, and the gold is obtained
pure. The dust of jeweler-shops is often treated in this
way to save the gold which has been scattered by filing
and other processes.

378. Silver. — This metal stands in regard to hardness be-
tween gold and copper, and requires to be alloyed with
copper to make it wear well In the coinage of the United
States the proportion of copper is one tenth. Silver is very
ductile and malleable. Its polished surface reflects both
light and heat better than any other metal, and accordingly
it is used for reflectors. The tarnishing which gradually
occurs is not from oxidation, but from the formation of a
sulphide of silver by the sulphuretted hydrogen which is
generally in the air in small quantity. When this gas is
present in the air in considerable amount, as in the neigh-
borhood of some sulphur springs, silver tarnishes rapidly.
It is the sulphur in the egg that discolors the spoon with
which you eat it, forming a sulphide. Silver is sometimes
found native, but is usually obtained from ores. The most
common of its ores is the sulphide called argentite. This
occurs abundantly in Nevada. It is sometimes combined

268 CHEMISTRY.

with antimony and arsenic. There is always some silver
in the common ore of lead, galena, and sometimes there is
so much of it that it is profitable to submit the lead ob-
tained from this ore to certain chemical processes for ex-
tracting the silver alloyed with it.

379. Extraction of Silver from Galena. — We have already
told you, in § 369, how the galena is freed from the sul-
phur. This gives you an alloy of lead and silver. This
is melted in a large basin and allowed to cool slowly. As
it cools a crust continually forms over the surface, which
is composed of crystallized lead without any of the silver,
this settling down in the liquid below simply because it
does not crystallize as readily as lead does. This crust is
taken off with an iron colander as fast as it forms, until
there is left only a small amount of the melted metal.
You see what the result is. You have an alloy containing
much more silver in proportion than the mass which you
melted. This alloy, after cooling, is submitted to a proc-
ess called cupellation. The cupel is a shallow dish made
of bone ashes, and is very porous. In this is placed the
alloy, and it is submitted to a strong heat. When it is at
a full red-heat a powerful current of air is thrown across
it by bellows in order to blow away the litharge or oxide
of lead which forms on the surface. What is not thus
blown away is absorbed by the pores of the cupel. When
the lead is all disposed of, and the silver is left alone, the
surface suddenly becomes brilliant, and the workman, see-
ing this flashing or lightening, as it is technically termed,
knows that the process is completed, and withdraws the
cupel from the fire.

380. Salts of Silver. — Silver forms many useful salts.
Silver nitrate is often called by physicians lunar caustic,
being used as a caustic by the surgeon. As it grows
black rapidly when exposed to the light in contact with

MERCURY, SILVER, GOLD, AND PLATINUM. 269

vegetable fibre, it is much used in solution as an indelible
ink for marking linen and cotton. Mercury introduced
into a weak solution of it precipitates the metallic silver
in beautiful tree-like forms called arbor Diance.

There have been cases in which nitrate of silver (lunar
caustic) has been swallowed in considerable quantity by
mistake. The sure antidote is common salt, producing two
harmless articles, chloride of silver and nitrate of sodium.

381. The Silver Assay. — The process by which the amount of al-
loy in silver is ascertained is called the silver assay. A sample of the sil-
ver to be examined is first dissolved in nitric acid. The assayer then in-
troduces salt (chloride of sodium) into this solution, and a curdlike sub-
stance is precipitated. This substance is chloride of silver, formed by the
union of the chlorine of the salt with the silver. He adds the salt slowly
till there ceases to be any precipitation, and then Stops, because he knows
that there is no more silver for the chlorine to unite with. Now observe
how he tests by this process the amount of silver in the specimen. Of
course, the more silver there is and the less alloy, the more salt is required
to precipitate all the silver. The assayer, therefore, judges of the purity
of the specimen by the amount of salt which he is obliged to use to com-
plete the process, and in order to ascertain this accurately he employs a so-
lution of a certain strength, which he pours from a graduated glass. He
knows beforehand just how much of this is required to precipitate a cer-
tain amount of pure silver— for example, a gramme. If now he is obliged
to use only half as much for a gramme of any sample, he infers that it
is only half silver ; if three fourths, it is three fourths silver, etc. The
explanation of the process is this : The solution of the silver in nitric acid
is a solution, not of silver, but of the salt called nitrate of silver. This is
decomposed, as is also the chloride of sodium when the two solutions min-
gle, producing chloride of silver and nitrate of sodium, as indicated in the
equation :

AgXO, + NaCl = AgCl + NaNO3.

382. Gold. — Gold is nearly always found in its metallic
state. It is usually, however, alloyed with silver. Some-
times it occurs in masses, but commonly in small round or
flattened grains. It is also found in veins in various rocks.

270 CHEMISTRY.

Its properties are, a splendid yellow color, brilliancy, high
specific gravity, softness, great malleability and ductility,
and indisposition to combine chemically with other sub-
stances, especially oxygen. Gilding is usually performed
by means of gold-leaf, except in case of the metals, on which
it is commonly done by amalgamation, a process just ex-
plained. Gold is so soft a metal that it is not fit for use
in its pure state, and is therefore always alloyed with sil-
ver and copper to give it the requisite hardness. The
gold coin of this country is one-tenth part an alloy of silver
arid copper. The word carat, used so much in express-
ing the degree of purity in specimens of gold, signifies one
twenty-fourth. If, therefore, it is said of any specimen of
gold that it is 18 carats fine, it means that the pure gold
in it is 18 parts out of the 24, or that it is three fourths
gold. Perfectly pure gold is, of course, 24 carats fine.
The word is of Eastern origin, and comes from a word
meaning bean.

Gold is not soluble in nitric acid, nor in hydrochloric,
but in a mixture of the two it dissolves readily, as ex-
plained in § 225.

383. Chloride of Gold. — This salt can be made in two
ways. If gold-leaf be put into chlorine water, the chlorine
will unite with it, and chloride of gold will be found in the
solution. But it is most commonly made by treating gold
with aqua regia. The chemical action is described in § 225.
If the solution thus obtained be evaporated, a brownish-red
salt will appear, which is the chloride of gold. It is very
easily decomposed, as can be shown by the following exper-
iment : Dip a test-tube which has been wiped dry into a
dilute solution of chloride of gold, and then heat it over a
spirit-lamp. It will become gilded, showing that heat suf-
fices to disengage the chlorine from the gold. The chloride
of gold is quite in contrast with the chloride of sodium in

MERCURY, SILVER, GOLD, AND* PLATINUM. 271

this respect, for no heat can decompose the latter. The
compound, then, of gold with chlorine can be called an un-
stable compound, as are its compounds with oxygen.

Chloride of gold is used to a limited extent in the arts,
chiefly in photography.

384. Platinum. — The color of this metal is between tin
and steel. It is the heaviest of all substances ; it has great
ductility and tenacity ; it is very malleable, especially when
heated, and it may then be welded, though not as perfectly
as iron. In fusibility this metal stands at one end of the
scale of metals, mercury being at the other. Mercury may
be said to melt at about 40° below zero ; while, on the other
hand, platinum withstands the heat of the hottest furnace,
and requires the intense heat of the oxyhydrogen blowpipe
to melt it. Hence the crucibles of the chemist are often
made of this metal. It is used, also, somewhat in the arts
— in the manufacture of apparatus for the distillation of
sulphuric acid, and in enameling glass and porcelain. If it
were an abundant metal, it might be put to many common
uses, and be a great convenience, for the utensils made of
it would never rust, and would not be in any danger of
melting, and when they became dirty they could be cleaned
and made bright again by heating them red-hot.

Platinum, like gold, dissolves in aqua regia only ; the so-
lution on evaporation gives a deliquescent brown-red mass
consisting of platinic chloride, PtCl4. This is used in chem-
ical laboratories as a test solution, and in photography to a
limited extent.

385. " Dobereiner's Lamp." — By a certain chemical process
platinum may be obtained in a finely divided state, furnish-
ing a soot-like substance called " spongy platinum." This
produces remarkable effects upon certain gases. If a little
of it be introduced into a mixture of oxygen and hydrogen
gases, an explosion is produced as quickly as if a lighted

272

CHEMISTRY.

taper had been introduced. So, also, if a piece be held in
a current of hydrogen it becomes red-hot, and then sets
fire to the gas. This is what takes place in Dobereiner's
Lamp, so called after the inventor. By turning a stop-cock
in this lamp you let a current of hydrogen strike upon a
bit of spongy platinum, and you have the result just men-
tioned. In Fig. 99 you have a plan of this lamp, a being a
glass jar covered by a brass lid, e, which has
a stop-cock, c, with its opening opposite to
a brass cylinder, d, which contains the
spongy platinum. There is a small bell-jar,
/, communicating at the top with the stop-
cock, and having suspended in it a cylinder
of zinc, z. "When the lamp is to be used the
jar, a, is two thirds filled with a mixture of
one part sulphuric acid and four parts wa-
ter, as indicated by the circular line. As
the bell-jar is open at the bottom, the acid
and water attack the zinc in it, producing hydrogen gas,
just as it is produced in the apparatus described in § 143.
If the cock be opened the hydrogen gas will escape, and be
directed against the spongy platinum in c7, and will make
it red-hot, and then this will set fire to the gas.

386. Other Illustrations. — This curious property is not
confined to spongy platinum, but the
metal in its ordinary condition shows it
to some extent. For example, if some
ether be poured into a glass jar, Fig. 100,
and a coil of platinum wire recently ig-
nited be put into it, the metal will glow
so long as there is any ether present.
Ozone is formed at the same time. In
Fig. 101 (p. 273) you have essentially
Fig. 100. the same experiment in a prettier form.

Fig. 99.

MERCURY, SILVER, GOLD, AND PLATINUM. 273

Take a common alcohol lamp, and, cutting the wick rather
short, surround it with a coil of small platinum wire about
half an inch high. Light the lamp, and when the wire be-
comes red-hot blow it out. The wire, in-
stead of cooling at once, as any common
wire would, will continue to glow till all
the alcohol is consumed. These curious
phenomena depend upon the power pos-
sessed by platinum of condensing gases
upon its surface.

387. Iridium and Osmium. — There are sev-
eral very rare metals found associated with platinum,

and having similar properties. Two of these, iridium and osmium, form
the hardest alloy known, a mineral called by the mineralogist iridosmine, a
name compounded of the names of the two metals. One use has been
found for this mineral : it is used to point gold pens, its great hardness
fitting it admirably for that purpose.

QUESTIONS.

374. Whence the name mercury ? How can the evaporation of mercury
be shown? What is cinnabar? How is mercury obtained from it? — 375.
What is vermilion ? When is it black ? W^hen red ? — 376. What is the com-
position of calomel ? What of corrosive sublimate ? What are their prop-
erties ? What antidote is recommended ? How does it act ? — 377. What
is amalgamation ? How carried on ?— 378. What is said of the properties
of silver ? Its uses ? Explain the tarnishing of silver. — 379. In what min-
eral does silver occur ? How is it extracted ? What is cupellation ? — 380.
What is the composition and nature of lunar caustic, so called? — 381. De-
scribe the silver assay. — 382. How is gold found in nature ? With what is
it alloyed ? What are its properties ? Explain the term carat.— 383. How
is gold chloride made? For what used? — 384. Give in full what is said of
the properties and uses of platinum. In what acids does it dissolve ? —
385. Describe and explain Dobereiner's Lamp. — 386. Describe the experi-
ment with ether and a coil of platinum wire. Explain this briefly. — 387.
What other metals belong to the platinum group ?

M 2

274 CHEMISTRY.

CHAPTER XXL

CHEMICAL INFLUENCE OP LIGHT.

388. Chemical Influence of Light. — You have already had
some illustrations of the fact that the rays of the sun not
only give light and heat to the earth, but also stimulate
many chemical operations. For example, you saw in § 223
that chlorine and hydrogen are very ready to unite under
the stimulus of light, when, if light be shut out, no such
union takes place. So strong is this disposition to unite
under this stimulus, that if a mixture of the two gases be
exposed to the direct rays of the sun, the union is so sud-
den as to occasion an explosion. A solution of ferrous
sulphate may be kept a long time in the dark without any
change ; but expose it to sunshine, and a precipitation of
ferric oxide at once begins. Indeed, it is ascertained that
precipitation in many cases may be quickened by the rays
of the sun. You have a familiar example of the chemical
influence of solar light in the blackening of common mark-
ing-ink when the marked articles are exposed to the light.
In sun-bleaching, also, the sun's rays stimulate the chemical
changes which take place.

389. Universality of this Influence. — Wherever light goes
it acts chemically. It was said by Niepce, who was asso-
ciated with Daguerre in the investigations which led to
his great discovery, that " no substance can be exposed to
the sun's rays without undergoing a chemical change."
Though, with the common notion which was prevalent that
the sun, the great source of light and heat, had little to do

CHEMICAL INFLUENCE OF LIGHT. 275

with chemical results in nature, the remark of this philos-
opher when it was made was considered extravagant, and
his light-pictures were looked upon by his friends as mere
pleasant curiosities, there is at the present time every day
more and more realization among chemists of the great
truth which he uttered. The solar ray is now regarded as
one of the grand chemical powers of our earth.

390. Chemical Influence of Light on Vegetables. — Light
produces chemical results in all of the three kingdoms of
nature, but they are perhaps the most observable in the
vegetable world. The green coloring substance called
chlorophyll, which, appearing in the leaves and other parts
of plants, makes the general face of nature so pleasant to
the eye, is entirely dependent upon the stimulus of light,
as may be seen in many common facts. The sprouts of
vegetables in our cellars, for example, are destitute of this
coloring substance exactly in proportion to the exclusion
of light. This explains the deep green of leaves in trop-
ical countries, where " the sun shines forever unchangeably
bright." Light has the same influence upon other colors,
and hence the rich deep colors of tropical fruits and flowers,
and the subdued tints of those of colder regions. But the
stimulus of light not only acts thus upon the colors of veg-
etables, but it is absolutely essential to the formation of
their substance. That chemistry of the leaves which, as
you learned in § 128, furnishes to plants from the air so
large a part of their carbon, can not go on without the in-
fluence of light. Indeed, as stated in § 129, the leaves rest
from this chemical work, this laying in of carbon, when the
light is withdrawn at night.

391. Light and Locomotives. — It was in relation to the in-
fluence of light upon vegetable growth that George Ste-
phenson, the great inventor of locomotives, said that light
was the power that moved them. The conversation in

276 CHEMISTRY.

which he said this is thus related : Mr. Stephenson asked
the late Dean Buckland, " Can you tell me what is the
power that is driving that train ?" alluding to a train which
happened to be passing at the moment. The learned dean
answered, "I suppose it is one of your big engines." — "But
what drives the engine?" — "Oh, very likely a canny New-
castle driver." — "What do you say to the light of the
sun ?" — " How can that be ?" asked Buckland.—" It is noth-
ing else," said Stephenson. " It is light bottled up for tens
of thousands of years ; light absorbed by plants and veg-
etables, being necessary for the condensation of carbon dur-
ing the process of their growth, if it be not carbon in an-
other form ; and now, after being buried in the earth for
long ages in fields of coal, that latent light is again brought
forth and liberated, made to work — as in that locomotive —
for great human purposes."

392. Chemical Influence of Light on Animals. — The influ-
ence of light upon color is very much the same in animals
as in vegetables. Accordingly, the plumage of birds in
tropical climates presents the richest hues, while the pre-
vailing color in the colder regions is a russet brown. So,
also, those fishes that swim near the surface have various
and rich colors, while those that live in deep water are
gray or brown or black. Those that live at so great a
depth that very little light reaches them are nearly color-
less. It is pretty well ascertained that at depths where no
light can penetrate there are no fishes or other animals of
a high order, showing how dependent animal life is upon
light. The influence of light upon life and health has at-
tracted considerable attention of late ; and, although some
extravagant things have been said about it by superficial
enthusiasts, there is no doubt that it is an influence which
should be seriously taken into the account in the arrange-
ment of our houses and workshops, and in the formation
of our habits of living.

CHEMICAL INFLUENCE OF LIGHT. 277

393. Light Dissected. — Light that does all this is not
one thing ; but in every ray, besides the seven colors which,
blended together, make the white light, there are two dis-
tinct powers — heat and chemical power. The dissection
of light effected by the prism is depicted in Fig. 102. We

Proportionate width of th« ^^^ .... Greatest Chemical Action.

of Colors*

Yellow 40 | I ....Greatest Light.

— Greatest Heat
Fig. 102.

have in Part I. described the manner in which this spec-
trum, so called, is made, and commented upon the colors
that compose white light, and we need to say no more hero
on these points. The chemical power is what concerns us
now. This is greatest at the violet end of the spectrum,
diminishing as you go from there toward the other end.
The greatest heat, on the other hand, is at the red end.
We have, then, bound up in every ray of light that comes
from the sun three powers — viz., light, heat, and chemical
power. This last has been called actinism, or the actinic
power. The reason that these three powers can be par-
tially separated in the spectrum, as well as the different
colors, is that different parts of the ray are differently re-
frangible— the calorific part the least, the actinic part the
most, and the illuminating part between the two. Then
of the colors, the least refrangible is the red, the most so
the violet. You observe that we speak of the separation of

278 CHEMISTRY.

the three forces or powers in the spectrum as being par-
tial. We will explain this. As the ray of light is bent out
of its course by the prism, and the spectrum is formed on
the screen, each of the three powers has a point in the spec-
trum where its influence is most concentrated. On each
side of this it lessens till you come to a point where it is
comparatively feeble. "The result of the action of any
ray depends, however, greatly on the physical state of the
surface upon which it falls and in the chemical constitution
of the body ; indeed, for every kind of ray a substance may
be found which under particular circumstances will be af-
fected by it; and thus it appears that the chemical func-
tions are by no means confined to any set of rays to the
exclusion of the rest " (Fownes).

394. Experiments. — Many interesting experiments can be
tried with the spectrum, some of which we will detail :

Brush over some paper with a solution of nitrate of sil-
ver, and then expose strips of it to different parts of the
spectrum. A strip applied at the lower part where the red
color or ray is will be scarcely affected, for the chemical
rays there have little or no power to affect this substance.
A strip at the violet end, on the other hand, will be dark-
ened quite rapidly, because there is the centre of the influ-
ence of this power. So, also, a strip in the green ray will
not be affected so much as one in the blue, because the lat-
ter is nearer to that centre.

Paper charged with chloride of silver is still more sensi-
tive to light than that charged with the nitrate, and there-
fore gives more decisive results. It may be charged in the
following manner: The paper is first wet in a solution of
common salt or chloride of sodium. Then it is brushed
over with a solution of nitrate of silver. This decomposes
the salt, leaving on the paper chloride of silver in place of
the chloride of sodium :

CHEMICAL INFLUENCE OF LIGHT. 279

Chloride of Nitrate of Chloride of Nitrate of

sodium. silver. silver. sodium.

NaCl + AgN03 = AgCl + NaNO3

Strips of paper thus prepared, placed in parts of the spec-
trum where the chemical power resides, will be darkened,
because the chloride of silver is decomposed, the chlorine
passing off and leaving the silver attached to the fibres of
the paper. It is to be remembered in preparing these pa-
pers that exposure to the light has the same effect upon
them that placing them in the chemical limits of the spec-
trum does, for every ray of white light has the chemical
power bound up in it. For this reason the papers must
be prepared in a dark room, and, after being dried by blot-
ting-paper, must be put between the leaves of a book to
prevent the light from coming to them.

Some other experiments akin to these may be tried with
colored glasses. Glass stained dark blue with oxide of co-
balt lets scarcely any light pass through, but offers no hin-
derance to the passage of actinism, as may be seen by using
the papers charged with chloride of silver. Yellow glass,
on the other hand, will let the light and heat pass, but not
the actinism. You remember that a mixture of hydrogen
and chlorine exposed to the direct light of the sun explodes,
so rapid is their union, while they do not unite at all if the
mixture be kept in the dark. Now when the mixture of
the two gases is exposed to the sun in a vessel or tube of
red glass scarcely any effect is produced ; but if it be ex-
posed in a tube of violet-colored glass the gases combine
rapidly with an explosion, just as they do when the glass
is without color.

395. Light-Pictures. — If lace be spread over paper charged
with chloride of silver, on exposure to light for a few min-
utes its whole shape, to the minutest thread, will be traced
in white lines. The explanation is this: The chemical

280

CHEMISTRY.

Fig. 103.

power of the sunlight acts upon the chloride of silver, dark-
ening it, except where
the threads of the lace
prevent it from doing
so. The tracings of the
lace consist, then, of the
chloride of silver un-
changed ; while in the
dark parts there is me-
tallic silver minutely di-
vided. In the same way
skeletons of leaves, or
even the leaves them-
selves, may be copied.
So, also, we may copy
engravings, if we oil
them so that the light may shine through the unprinted
portions. The dark parts of the engraving will of course
be light, and the light
parts dark in the copy.
This constitutes what is
called a " negative ;" and
a "positive" or true
copy can be obtained by
dealing with the " nega-
tive" as you do at first
with the engraving it-
self. In Fig. 103 you
have represented a "neg-
ative" of a leaf, the dark-
est parts of the picture
corresponding to the
thinnest parts of the
leaf, as the light coming through them decomposes the

Fig. 104.

CHEMICAL INFLUENCE OP LIGHT. 281

chloride of silver. In Fig. 104 (p. 280) you have the " posi-
tive " of the same leaf.

396. Fixing the Picture. — The figures of which we have
spoken can not be permanent, for exposure to light will
destroy them by making the whole surface equally dark.
To verify this, take a copy of lace and hold it up to a win-
dow. The white lines of the tracery will disappear quick-
ly, the whole surface being subjected to the chemical power
of the light, and becoming therefore covered with the dark
silver. This effect, however, will not occur if the window
be covered with a heavy yellow curtain, for this will not
allow the chemical power to pass through. Now if after
a picture is made we could by means of any substance re-
move from it all the chloride of silver, and at the same time
leave the metallic silver untouched, we should have a pict-
ure which the light can not affect. Such a substance we
have in sodium hyposulphite. This dissolves out the un-
decomposed chloride of silver, but produces little or no
effect upon the metallic silver which constitutes the parts
of a " positive " picture.

397. Photography. — We have given you a brief outline of
the principles on which the beautiful art of photography
is based. To pursue this interesting subject any farther
will lead us too deeply into this important branch of Ap-
plied Chemistry.

QUESTIONS.

388. Give some examples of the chemical influence of light. — 389. What
is said of the universality of its influence ? — 390. State in full what is said
of its influence on vegetables. — 391. Give the anecdote of George Stephen-
son. — 392. State in full what is said of the influence of light on animals. —
393. What three powers are there in the sun's rays ? Show how these are
arranged in the spectrum. Why can they be thus partially separated ?
What is actinism ? Where in the spectrum is the point of greatest light ?

282 CHEMISTRY.

Where the centre of actinic power ? Where the point of greatest heat ? —
394. State the experiments with paper charged with nitrate of silver. How
can you charge paper with chloride of silver ? What is said of the effect
of light upon it ? What experiments can be tried with variously colored
glasses? — 395. State in full what is represented in Figs. 103 and 104. —
396. What is said of "fixing" the picture obtained with the chloride of
silver ?

CHAPTER XXII.

SPECTEUM ANALYSIS.

398. Continuous Spectra. — You have learned in Part I.
that when light from the sun passes through a prism it is
separated into its different colors, because rays of differ-
ent colors are unequally refracted. The first band in the
figure on p. 287 represents roughly the spectrum thus ob-
tained.

Suppose light from other sources than the sun is thus
analyzed by a prism, what are the results ? Briefly, the
results vary according to the nature of the light emitted ;
how this is we will now explain to you. In the first place,
the emission of light is a question of temperature ; any solid
body heated high enough emits light. Now it is found
that all solid bodies heated to incandescence — that is, until
they glow with light — produce spectra resembling in the
main that of the sun, at least so far as the nature and order
of the colors are concerned. For example, a glowing plat-
inum wire, a candle, and a gas flame give the same sort
of spectrum, uninterrupted in the shading of its colors and
containing them all. Such spectra are termed continuous.

399. Discontinuous Spectra. — There is another kind of
spectrum called discontinuous or broken. These are pro-
duced by glowing gases. You have already learned that

SPECTRUM ANALYSIS. 283

some chemical substances burn with colored flames ; po-
tassium with a violet flame, and sodium with a yellow
flame, as seen when burning on water, or when common
salt is thrown into a fire. Then, again, strontium com-
pounds burn with a beautiful red flame, and barium with
a green flame, so that they are used in making fireworks.

Now in all these cases the flames are colored by the
bodies named in the state of gases.

If you examine the light from burning sodium by means
of a prism — -that is, allow the light from incandescent sodi-
um vapor to pass through a prism — you will obtain a dis-
continuous or broken spectrum: only one color will be
seen, viz., yellow, and this yellow color will fall at the
same point in the spectrum that the yellow rays of the
sun spectrum would strike. It appears, then, that sodium
vapor heated red-hot gives out rays of a particular re-
frangibility ; now this illustrates a well-defined law : That
every chemical element in the state of gas, when heated
until it becomes luminous, gives off a peculiar light. In
the example taken, light of all one color was given out by
the substance heated ; this is not the rule, however, but
rather exceptional, for most bodies emit light of various
kinds, possessing different degrees of refrangibility ; thus
the light from glowing strontium vapor analyzed by a
prism gives a spectrum made up of several yellow and red
rays, together with one blue one.

400. Use of the Slit. — The appearance of a continu-
ous spectrum, obtained from light of any source, depends
much upon the size and shape of the opening through
which the light passes before passing through the prism.
If a round opening be used, a series of disks will be seen
overlapping each other, as shown in Fig. 105 (p. 284).
If an opening having parallel sides be employed, the dif-
ferent colors will shade off into each other imperceptibly,

284

CHEMISTRY.

Fig. 105.

the brightest light appearing in the centre of the yellow

portion. By making
an opening of this
shape very narrow,
there is less overlap-
ping of the different
colors, and a purer
spectrum is obtained.
A very narrow open-
ing with parallel sides,
called a slit, is gener-
ally employed in ex-
amining the spectra of different bodies ; and in the case of
discontinuous or broken spectra, the colored image of the
slit is what produces the banded appearance of such spec-
tra. A narrow ray of yellow light produces a yellow
band of light in the spectrum, a red or a blue bundle of
rays produce a red or a blue line or band in the spectrum.
This is shown in Fig. 105.

401. The Spectroscope. — This is the name of the instru-
ment employed for thus analyzing the light emitted from
different sources. A brief description of Fig. 106 (p. 285)
will suffice. A spectroscope consists essentially of a prism,
a telescope, and a slit. In the figure before you the prism,
A, is placed on a plate of metal supported by a tripod, the
telescope is at B, and the slit is attached to the tube C,
which contains also a lens at the end next to the prism.
The substance to be examined, held on a platinum wire sup-
ported by the stand /*, is heated in the non- illuminating
flame of a Bunsen burner, I — the cone, w, at the top of the
burner serving simply to steady the flame. The light
passes from the flame, /, through the slit at the end of the
tube C into this tube ; the rays are made parallel by the
lens in this tube before they fall upon the prism, A. The

SPECTRUM ANALYSIS.

285

Fig. 106.— The Spectroscope.

rays are then refracted, and the image of the refracted rays
is observed through the telescope, B. In the instrument
here pictured, a third tube, D, contains a scale engraved on
a glass plate, and this being illuminated by the candle flame,
<7, can be seen at the same time with the spectrum ; one
face of the prism reflecting this scale through the telescope,
B, to the observer.

402. Spectrum Analysis. — The spectroscope, invented in
1859 by two distinguished Germans, a chemist (Bunsen)
and a physicist (Kirchhoff ), is of great importance to the
chemist, for it places in his hands a means for detecting
certain substances with great accuracy and extraordinary

286 CHEMISTEY.

delicacy. It follows from what we have told you in the
preceding sections that any chemical substance capable
of being converted into an incandescent vapor by the heat
of a Bunsen burner must give out light of a particular
degree of ref rangibility ; and consequently any one look-
ing through the telescope, B, will see a pictorial image in
brilliant colors characteristic of that particular substance.
Practically this is done as follows : Dip a small platinum
wire into the material you wish to examine, insert the sub-
stance into the flame (which, being non-luminous, gives no
spectrum), and place your eye at B. Now it is found that
only a certain number of chemical substances are capable
of being volatilized in the heat of a Bunsen burner or of
an alcohol lamp ; these are the salts of the alkalies, many
of the salts of the alkaline earths, besides some other bodies
not classifiable ; or, stating it differently, spectrum analysis,
under the circumstances described, enables the chemist to
detect sodium potassium (lithium, caesium, rubidium), calci-
um, strontium, barium, copper, boracic acid, and some other
bodies. The spectra seen are shown in Fig. 107 (p. 287),
and in the frontispiece to this work.

The first band represents the spectrum of the sun, the
vertical black lines in which you may for the present dis-
regard.

Sodium gives a single yellow line or band, occurring
at a on the scale ; potassium gives a red line at the right
end of the spectrum, a blue one at the extreme left, and
a long luminous band between. Barium gives a large
number of lines and bands, several red, orange, yellow, and
four very bright green ones. These lines and bands al-
ways occur at the same point on the scale of the same
spectroscope ; the scales of various instruments vary, but
the positions of lines can be compared by preparing maps
of the various spectra referred to a constant scale. Thus

XJf

SPECTRUM ANALYSIS.
0 P' IE

287

C JJ a A

Fig. 107.

you see the accuracy of the analysis is all that can be
desired.

We have referred to the delicacy of this method of anal-
ysis. This delicacy varies with different substances ; of so-
dium, the one three-millionth of a milligramme (3>ow>(!w>OUu
gramme) can easily be detected. Sodium in some shape,
combined with chlorine chiefly, is always present in the

288 CHEMISTRY.

air in sufficient quantity to be seen very readily in the
spectroscope by agitating the air ; clapping the hands to-
gether or dusting a book will make the yellow line flash
out brilliantly, the particles of dust always containing
salt.

Of strontium, the -^-^ of a milligramme is capable of
detection ; of calcium the same ; of lithium, the ^-^ of a
milligramme.

403. Discovery of New Elements. — So great is the deli-
cacy of spectrum analysis that many known elements have
been found more widely distributed than was previously
supposed, and four new elementary substances have been
discovered which existed in such minute quantities as to
be overlooked by the ordinary methods of examination.
Bunsen and Kirchhoff, the discoverers of spectrum analy-
sis, almost immediately after their invention discovered
two elements, ca3sium and rubidium, which belong to the
class of alkaline metals. Caesium was recognized by two
blue lines in its spectrum, which did not correspond in
position to the blue line of strontium, and rubidium by
two red lines. The material examined was the residue
from the evaporation of certain mineral waters.

Since then thallium has been discovered by Prof. Crookes,
of London, and indium by Profs. Reich and Richter, of Sax-
ony. These bodies are mere chemical curiosities, occur-
ring in far too small quantities to become of commercial
value unless some unexpected and rich source is awaiting
discovery. In the chapters on metals we have barely al-
luded to them by name.

404. Spectra of the Heavy Metals. — The heavy metals
and their salts as a rule do not give spectra when heated
in the non-illuminating flame of a Bunsen burner, but this
is only because the temperature is not high enough to vol-
atilize them. To obtain spectra of these substances, there-

SrECTEUM ANALYSIS. 289

fore, a strong current of electricity is used, excited by a
powerful galvanic battery, and the material heated in the
electric arc is converted into incandescent vapor, and thus
yields a spectrum. Maps have been made showing the
thousands of lines which are seen in the spectra of nearly
all the elements. The apparatus is difficult to manage and
very expensive, so for ordinary work the chemist depends
upon the Bunsen burner or alcohol lamp, and confines his
research to the lighter metals.

405. Celestial Spectroscopy. — "We have not previously re-
ferred to certain peculiarities in the sun's spectrum, be-
cause we did not want to tell you too many things at once.
If you examine the sun's spectrum with a good spectro-
scope having a narrow slit, you will see fine black lines
crossing the spectrum. These were observed many years
ago by Fraunhofer, a German optician, but no attempt was
made to explain them until after the perfection of the
spectroscope by Kirchhoff. For good and sufficient rea-
sons, which we can not explain to you in this book, it is be-
lieved that those black lines give us indications of the ele-
mentary bodies burning in the sun. A careful study of
these lines by many eminent men has led to a remarkably
accurate knowledge of the constitution of the sun. Thus,
wonderful as it may appear, we have good reason for be-
lieving that the sun contains sodium, calcium, magnesium,
iron, copper, zinc, hydrogen, and many other metals; and
that the sun does not contain gold, silver, mercury, po-
tassium, lead, arsenic, or platinum. More perfect instru-
ments may eventually remove some element from this last
list and place it among the bodies known to exist in the
sun. Not only have astronomers, thus aided by the chem-
ist, examined the light of the sun, but they have studied
the fixed stars, the nebula?, and comets, thus developing a
special branch of spectrum analysis called celestial spectro-

290 CHEMISTRY.

scopy. A description of the methods employed, the instru-
ments used, and the results obtained would be interesting,
but must be passed by in the present work.

QUESTIONS.

398. Do lights from other sources than the sun yield spectra ? Upon
what does the emission of light depend ? Give examples. What are
continuous spectra ? — 399. What produces discontinuous spectra ? What
bodies color flames ? What kind of a spectrum does sodium give ? What
strontium ? — 400. Explain the use of a narrow opening for the passage of
light. What produces the banded appearance of discontinuous spectra ? —
401. Describe and explain the spectroscope. How does the light pass ?
— 402. Who invented this instrument ? When ? How is it made prac-
tical ? What can be detected by it at the temperature of a Bunsen burn-
er ? What kind of a spectrum does barium yield ? What is said of the
delicacy of this instrument ?— 403. What elements were discovered by
Bunsen and Eirchhoff? How? From what source? What other ele-
ments have been discovered by this means ? — 404. How can spectra of
heavy metals be obtained ? — 405. State in full what is said of celestial
spectroscopy.

CHAPTER XXIII.

ORGANIC CHEMISTRY.

406. Introduction. — Formerly the term Organic Chemistry
was applied to that branch of chemistry treating of sub-
stances which derived their existence from the operations
of either vegetable or animal life ; it was erroneously sup-
posed that the production of these substances was due to a
mysterious power, called vital force, residing in the organs
of plants and animals, and that this class of substances could
not be artificially formed. Under this view organic chem-
istry was considered as the Chemistry of Life.

Within from twenty to thirty years, however, many sub-

ORGANIC CHEMISTRY. 291

stances Lave been made in the chemist's laboratory which
were formerly regarded as solely the products of the agency
of life, and consequently the theory of a special vital force
governing the attractions of matter in plants and animals
has been gradually abandoned. Urea (a constituent of
urine), alcohol, acetic acid, alizarine (a beautiful dye-stuff),
and indigo, are some of these organic bodies which have
been synthetically prepared — that is, by a putting together
of so-called inorganic materials.

The branch of chemistry you have been studying is some-
times called Inorganic, because opposed to Organic Chem-
istry; another and very suitable name is Mineral Chem-
istry, since it concerns chiefly mineral substances. This
division into Mineral and Organic Chemistry is, however,
a mere matter of convenience, and not countenanced by
Nature. The same elements compose the bodies and sub-
stances existing in the three kingdoms — mineral, vegetable,
and animal; and the same laws of attraction hold these
elements together, and govern their combinations.

Certain organic substances do, indeed, differ radically in
their nature and formation from mineral bodies, exhibiting

a fibrous and cellular structure, and forming parts of organs
peculiarly the product of life ; these are termed organized
bodies, and must not be confounded with organic bodies.
As an example of this difference take the case of a fruit ;
the fibrous, cellular, pulpy matter forming the woody frame-
work of the fruit is an organized body ; but the acids, the
sugar, the gum, the starch, the coloring matter, etc., con-
tained in these living organs are organic bodies. Whether
the chemist will ever be able to imitate organized struct-
ure is exceedingly problematical. The distinguishing pow-
er between organic and organized bodies lies in the micro-
scope.

407. Constituents of Organic Substances. — "We have stated

292 CHEMISTRY.

that organic bodies are composed of the same elements as
mineral bodies, and while this is perfectly true, the state-
ment must be qualified. The number of elements which
enter into the composition of organic bodies is compara-
tively small. You remember there are sixty-three element-
ary substances at present known to the chemist : now of
these four build up nearly the whole of the innumerable
organic bodies ; these four are carbon, hydrogen, oxygen,
and nitrogen.

Some of the other elements occur, it is true, but to a
comparatively limited extent. Thus we have calcium and
phosphorus in the bones, iron in the blood, silicon in tho
stalks of grains and grasses, and various other elements
in very small quantities for various purposes. The four
grand elements — C, H, O, and N — we have learned about in
studying mineral chemistry; one of them, you observe, is
a solid, while the other three are gases. They are all with-
out taste or smell, and the solid element is in its ordinary
form of a dark color ; and yet from these few materials
what an endless variety in taste, smell, color, and other
properties is produced in the vegetable and animal world !

Let us not be understood to say that other elements be-
sides the four — C, II, O, and N — are of little importance.
They are not only of use in their place, but they are essen-
tial, some of them as much so within a certain range as the
grand elements.

408. Sources of the Elements in Organized Substances.
— The elements of which vegetable and animal substances
are composed come from three sources — earth, air, and
water. In the case of the plant they enter by the root and
the leaves. By the root, with its millions of little mouths,
they are drunk up dissolved in water, and in the sap
they flow upward to the leaves, where carbon is added
from the air. It is in the leaves that the sap, the build-

OEGANIC CHEMISTRY. 293

ing material of the plant, is completed, so as to be fit for
use in constructing all the various parts — the wood, the
bark, the flowers, the fruit, etc. Animals, also, receive their
elements in part from the earth, but not in a direct man-
ner. They receive them from the plants which they eat.
The plant, then, gathers up, as we may say, the elements
from the earth for the use of the animal. They are com-
bined together in the blood, which is to the animal what
the sap is to the plant — the common building material of
the body. But as in the case of the plant, so with the an-
imal, all is not derived from the earth. A part of the ox-
ygen needed comes from the air, being admitted by the
pores of the lungs, as part of the carbon of the plant goes
into it by the pores of the leaves. It is believed that the
leaves of plants decompose the carbonic acid that comes to
them from the lungs of animals, separating it into its ele-
ments, carbon and oxygen, and that the carbon is absorbed
to make a part of the plant, while the oxygen thus set free
again returns to the lungs of animals. Every leaf, there-
fore, is a laboratory to purify the air, and maintain its prop-
er supply of oxygen for the use of the animal kingdom.

409. Subservience of Plants to Animals. — You see, then,
that the subservience of plants to animals is twofold.
First, they supply to animals the elements of their growth
by gathering them from earth, air, and water into their
own substance. This subservience is direct in the case of
herbivorous animals. It is no less real, though indirect, in
the case of the carnivorous, for they eat the flesh of the
herbivorous. Secondly, plants, by their chemical action
upon the air, keep up that supply of oxygen which is need-
ed by animals.

410. Difference of Vegetable and Animal Structures in
Composition. — In this subservience of plants to animals
there is one very interesting fact to be noted in regard to

294 CHEMISTRY.

the difference in their composition. All the four grand
elements — carbon, hydrogen, oxygen, and nitrogen — enter
into the structure of animals, but only the first three are
found in the structure of vegetables. The inquiry then
arises in what way the nitrogen is supplied to animals.
Nitrogen constitutes four fifths of the air which is so con-
stantly entering their lungs, and yet not a particle of it is
supplied to their bodies in this way. The blood in the
lungs receives oxygen from the air, but no nitrogen, as you
learned in § 132. The nitrogen which is needed is supplied
through the agency of plants. For this purpose, though
there is none of this element in their structure, many of
them have it in their juices and fruits. It is especially
present in Indian corn, the grains, pease, beans, etc., so ex-
tensively used for food. In such cases the plant may be
said to gather up this element, and deposit it, not in its
own structure, for it is not wanted there, but in repositories,
where man and other animals can take it and appropriate
it to their use. There is no case in which the design of
the Creator is manifested in a more marked manner than
it is here.

411. Definition of Organic Chemistry. — Of the four ele-
ments— C, H, O, and N" — playing such a wonderful part in
the vegetable and animal kingdoms, the first of these, carbon,
is by far the most important, its presence being character-
istic of organic substances. Hence organic chemistry is
often defined as the Chemistry of Carbon Compounds. This
definition includes the simple carbon compounds, carbonic
oxide, carbonic anhydride, and others which we have just
studied under the head of mineral chemistry ; but it is im-
possible to draw any precise line of distinction, especially
since the same elements and laws of union are common to
the two divisions. Organic bodies are characterized by
great complexity and instability of the molecules.

ORGANIC CHEMISTRY. 295

412. Molecules In Organic Bodies. — Organic substances
arc generally more complex in their constitution than min-
eral substances, their molecules containing a far larger
number of atoms. For example, while carbonic anhydride
has in each molecule one atom of carbon and two of oxy-
gen, CO2, and sulphuric acid two of hydrogen, one of sul-
phur, and four of oxygen, H2SO4, making 7 atoms in the
molecule, each molecule of tartaric acid contains 16 atoms,
as indicated in the formula H2C4H4O6 ; while a molecule of
starch is believed to contain 63 atoms (starch = C18H30O15),
and of stearin 173 atoms.

One of the most complex of organic bodies is albumen,
which is supposed to contain several hundred atoms in a
molecule ; but this number will probably be reduced when,
its composition is better understood.

413. Instability. — Organic substances are unstable com-
pounds, that is, very easy to decompose, because they are
so complex. It is with them as it is with machinery. The
greater the complication, the greater is the liability to
derangement. The more atoms there are in a molecule,
therefore, the more easily can it be broken up, and the
more kinds of atoms there are in it the greater is the lia-
bility to this result. Not only do organic substances differ
from the inorganic in this respect, but they differ among
themselves. We have a good example of this in bleach-
ing. The coloring matter of the cloth is broken up and
dissipated, while the cloth itself remains, for the simple rea-
son that the molecule of the coloring matter is composed
of four elements — carbon, hydrogen, oxygen, and nitrogen —
M'hile that of the vegetable tissue, the substance of the
cloth, is composed of only three — carbon, hydrogen, and ox-
ygen. The more complex substance is decomposed first ;
but if the process be continued after the cloth has become
white — that is, after the coloring substance is all destroyed

CIIEMISTEY.

— the vegetable tissue will be attacked, and the cloth will
become more or less rotten from the destruction of some
of its molecules.

414. Difference in Properties with Similarity of Composi-
tion.— There is often found in organic chemistry great sim-
ilarity of composition with wide difference in properties.
We will give a few examples. Alcohol, cotton, sugar, and
acetic acid are four substances certainly not much alike in
their properties, and yet these widely dissimilar bodies are
made of the same elements — carbon, hydrogen, and oxygen.
By examining the formulae of these bodies, here given,

Alcohol C2H6O I Grape sugar .C6H12O6

Cotton C6H10O5 Acetic acid C2H4O2

you will see that these three elements are combined in very
different proportions ; and this illustrates as well the com-
plexity of the molecules referred to in § 412, for each of the
formulae above represents one molecule. We have select-
ed only four bodies made of these three elements, but act-
ually there are many thousands of bodies composed of
these three elements only.

415. Isomerism. — Strange and mysterious as these facts
appear, a much more apparently inexplicable feature re-
mains to be shown. Examine closely the formulae of the
last two bodies named, grape sugar and acetic acid ; you
see that if we should multiply by three the little figures,
or co-efficients, of the atoms of C, H, and O in acetic acid,
we will get the formula of grape sugar ; thus :

Acetic acid = C2H4O3
. 3

Grape sugar = C6H12O6

Here, then, we have two bodies made up of the same
elements in the same proportion, and differing only in their
molecular weights, and yet how different in their proper-

ORGANIC CHEMISTRY. 297

ties! One is sweet, crystalline, capable of fermenting,
neutral to litmus paper, being neither an acid, a base, nor
a salt ; the other is sour, liquid at ordinary temperatures,
and capable of combining with bases to form a large series
of salts.

We have said these bodies differ in their molecular
weights ; we will explain why this is. You learned in § 30
that the molecular weight of a body is equal to the sum of
its atomic weights; hence we calculate thus:

Acetic acid. Grape Sugar. '

C - 12; C3 = 2± C6 = 72

H = 1; II4 = 4 H18 - 12

O = 16; O3 = 32 O« = 9G

Molecular weight = CO Molecular weight = 180

Substances which thus have the same chemical constitu-
tion, and yet are dissimilar in their qualities, are called iso-
meric substances, this term coming from two Greek words,
tsos, equal, and meros, part.

Isomeric substances may even have the same molecular weight ; they
are then said to be metamerlc.

Thus the molecular formula C3H6O3 represents three different bodies
possessing different properties and different constitutions ; how this can be
is shown in the following formulas :

C3H6O2 may be arranged thus: C3H5O. HO— which is Propionic Acid.

" C2H3O.CH30 " Methyl Acetate.

" " CHO.CaH3O " Ethyl Formate.

It is not necessary to know the nature of these bodies— their names
show you that they are essentially distinct. One, you observe, is an acid,
the other two are compound ethers belonging to the class described in
§ 423.

416. Explanation of Isomerism. — The explanation which
the atomic theory affords of this isomeric state is illustrated
by Stockhardt by the various grouping of white and black
squares which can be made on a chess-board, as seen in

N 2

Fig. 108.

Fig. 108. Here each figure is composed of eight white and
eight black squares; but though the number is the same
in all, the grouping is different. In a one and one; in b two
and two, in c and d four and four squares are so joined to-
gether as to make the figures look very different from
each other. If we imagine these squares to be atoms we
obtain an idea of isomeric substances, and can see how
there may be bodies of the same constitution and form, yet
presenting an entirely different appearance, and having
very different properties.

Isomeric bodies are far more numerous in organic than
in mineral chemistry, because the molecules of organic sub-
stances are more complex than those of inorganic ; for the
difference in properties can not be owing to any thing else
than a difference in arrangement of the atoms, and the more
atoms there are in a molecule obviously the greater is the
range afforded for differences in arrangement. This may
be illustrated by reference to Fig. 108. Each of the squares
contains eight small black squares, and eight white ones,
sixteen in all. It is obvious that more and greater changes
in arrangement can be made here than there could be if the
number of small squares were less — four, for example; and
so, also, more differences in arrangement can be had in a
molecule if it be composed of sixteen atoms than there can
be if there be only four atoms in it.

417. Graphic Formulae. — Another method of explaining isomerism
makes use of so-called graphic formula. You learned in § 44 that the
elements differ in atom-fixing power, and that they are divided into groups,
monads, dyads, triad?, tetrads, etc., according to this power. The four

ORGANIC CHEMISTRY. 299

grand elements of which most of the organic world is constituted are rep-
resentatives or types of these four classes, hydrogen being a monad, H' ;
oxygen a dyad, 0" ; nitrogen a triad, N'" ; and carbon a tetrad, Civ. By
taking advantage of these points of attraction, a peculiar kind of pictorial
formulae may be constructed, called "graphic formulae." Thus the ordi-
nary formula for water is H2O; but if we represent the dyad oxygen by
— O— , and the monad hydrogen by H — , we have by combining them
H — O — II, a graphic formula for water. Take a more complex example,
from organic chemistry. Alcohol has the formula CaH5.HO, graphically

represented thus :

H-C-H

H-C-O-H
I
H

!— being a tetrad, — O— a dyad, and the rest monad hydrogen, each

bond of affinity is satisfied by arranging the atoms in this manner. Now
you will see how graphic formulae help to explain metamerism, the highest
kind of isomerism. Take the three bodies which have already served us
as examples. On the following page you have the ordinary formulae, the
constitutional formulae, and the graphic formulae side by side, showing how
differently the atoms are arranged in the molecules of each body. We can
not explain to you how chemists are able to arrive at any probable knowl-
edge of the arrangement of atoms in the interior of a molecule, for the sub-
ject belongs to the highest branch of chemical philosophy. Of late years
the most wonderful progress has been made in precisely this field, and
indeed the whole aim of modern investigators is directed to this study
of internal atomic structure.

300

CHEMISTRY.

GRAPHIC EXPLANATION OF ISOMERISM.

0 !._.„ Constitutional
Substances. Formula;.

Graphic Formulae.

Propionic ^ f C3H5O. HO,

Acid

CH3

H-C-H

pj* 2

CH2

H-C-H

*•§ *S

'o -i

COOH

O=C-O-H

S "^
Methyl 1 8 O |
Acetate I ^ *

C2II3O.CH3O,

II
1
H-C-H II

" fe»

CII3

1 1

•2 ^

0=C-O-C-H

® •§

CO(OCHs)

« S

•^ ^

Ethyl

Formate .

iCHO.C2H5O,

II II II

1 1 1

O=C-O-C-C-H

1 I

CO(OC2H5)

II II

QUESTIONS.

406. Explain the change of views which has taken place with reference
to organic substances. What examples of synthesis are given ? What is
said of the division into mineral and organic chemistry ? What are or-
ganized bodies? How do they differ from organic bodies? Give exam-
ples.— 407. What are the four chief constituents of organic bodies ? What
others occur also ? — 408. What is said of the sources of the elements in or-
ganized bodies? Show how leaves purify the air for animal life. — 409.
Show that the subservience of plants to animals is twofold. — 410. How is
nitrogen furnished to animals ? — 411. Give a definition of organic chem-
istry. Explain it. — 412. Show that the molecules of organic bodies are
complex in constitution. How many atoms in a molecule of tartaric acid ?
Of starch ? Of stearine?— 413. What is said as to the instability of or-
ganic substances? Give an example from bleaching. — 414. Of what three

CLASSIFICATION OF OKGAXIC SUBSTANCES. 301

elements are cotton, alcohol, sugar, and acetic acid composed ? How do
you account for the difference in their properties? — 4 Jo. Show what is
meant by isomerism. Take acetic acid and grape sugar as examples.
When are substances metameric ? Give examples. — 41 6. Explain isomer-
ism by reference to a chess-board. Why is isomerism more common in
organic than in mineral chemistry?— 417. What are graphic formulae?
Illustrate by the graphic formula of water. Explain it. What is said of
the arrangement of atoms in the molecule ? Explain the table on page 300.

CHAPTER XXIV.

CLASSIFICATION OF OEGANIC SUBSTANCES.

418. Scientific Classification. — Two methods of classify-
ing organic bodies for the convenience of study may be
followed ; in one an empirical arrangement connects sub-
stances which are closely related in nature, and treats in
groups bodies possessing similarity of origin or properties ;
the other is a strictly scientific classification based on the
atomicity of the tetrad carbon. In this work we will fol-
low the former arrangement, prefixing it, however, with a
brief synopsis of the scientific method, in order to introduce
to you a number of bodies which would otherwise find no
place in the so-called natural system. Scientifically con-
sidered, organic bodies may be classified as follows :

I. Hydrocarbons.
II. Alcohols.

III. Ethers.

IV. Aldehydes (and Ketones).
V. Acids (and Anhydrides).

VI. Amines (including Alkaloids).
VII. Organo-metallic Compounds.

This is a greatly abbreviated scheme, and does not include
many bodies produced in the living organism, the chemical

302 CHEMISTEY.

relations of which are not yet well enough understood to
bring them within a scientific system: such are gelatin,
albumen, vegetable resins, and other compounds formed in
the bodies of plants and animals. .

We will now review briefly the chemical relations of the
above-named groups, reserving details until we meet with
them again farther on.

419. Hydrocarbons. — You have already become somewhat
familiar with two important hydrocarbons in the first part
of this work — marsh gas, CH4, and defiant gas, C2H4.
But besides these there is an immense number of other
bodies, solid and liquid as well as gaseous, made up solely
of C and H in various proportions. No two elements are
capable of combining in so many different forms as carbon
and hydrogen. On page 324 you will find a table giving
the names and formula of a large number of hydrocarbons
of the so-called Marsh Gas Series, occurring in American
petroleum. On examining the formula you will notice
that in each of the two series the hydrocarbons differ by
exactly CH2 ; that is, each successive formula may be ob-
tained by adding CH2 to the preceding one ; this is another
and striking example of isomerism.

Besides the long series of hydrocarbons given on page
324, there are several other series differing from each other
by H2, and the members in each differing by CH2. Thus
olefiant gas, C2H4, belongs to a series which takes its name
from this its important member. In the following table
you have this series with the formula?, and the correspond-
ing alcohol and acid, to which we will have occasion to re-
fer a little later. In this table olefiant gas is called Ethy-
lene.

CLASSIFICATION OF ORGANIC SUBSTANCES.

303

THE OLEFINES, OR ETHYLEXE SERIES OF HYDROCARBONS.

NAME.

FORMULA.

BOIT.TNQ
POINT.

COEBE8PONBIXQ
A1X3O110L.

CORRESPOND-
ING AOID.

Methylene.

CH2

Gas

Wood-Naphtha

Formic.

Ethylene

C«H.

Gas

Alcohol

Acetic.

Propylene. .

C3H6

— 17.7°

Propvlic

Propvlic.

Butvlene. . .

C4H8

Butylic

Butyric.

Amylene. . .

C5H10

Amylic (Fusel-Oil). .

Valerianic.

Hexvlene

C H

Caproic. .

Caproic

Heptvlene

C H

9 >

CEnanthic

Octvlene. . .

(TH1fi

115.5

Caprylic

Xonylene . .

C9H18

140

Pelargonic.

Decatylene.

C10H20

160

Cetvlene. . .

clfiu,.

275

Ethal.

Palmitic

Cerotene. .

r H

Solid

Cerotene.

•Cerotic

Melissene. .

C,0HSO

Solid

Melissene.

Melissic

420. Homologues and Isologues. — The members of a group
of hydrocarbons which differ regularly by CH2, as in this
table, are said to be homologues, or to form a homologous
series. Two or more series, on the other hand, differing
from each other by H2, are said to be isologites, or to form
an isologous series. Thus the members of the Ethylene or
Olefiant Gas Series are homologous among themselves, but
isologous with respect to the Marsh Gas Series on page
324. Many of the hydrocarbons of such isologous series
are rare bodies, mere chemical curiosities; but we will
give you a table showing some of these, that you may the
better understand the terms homologous and isologous, and
that you may see at a glance the enormous number of com-
pounds of hydrogen and carbon which are capable of ex-

304

CHEMISTRY.
•HOMOLOGUES-

«*-.

i ;

«*- p

K |

•^ p

^* !3

5:I1

TEREBENE8.
CnH2n-4

«•- s"

M K

Sn g.

S 1

ta I

r * «S

S c
r-% y.

a* «.
K i

oTc5

^ «5

o s

« j

S -r —

S3 .2 o1

S ^ c3

S3 "£,.5

sT £

£ M*

r1 ^* *"* r-^

" >^» *^

r ^ C "^

y3 *- s

(O J/

« d

" T!

^ .

° o ^

•3 ^

0 £

<J o

•c s

> 0

2 *«

W S

iJ O

o *•

CH2

Methylene,
or Methene.

C2H4

Ethylene,
or Ethene.

rf!

.gi"

C5H10

Amylene,
or Quintene.

C6H12
Caproylene,
or Sextene.

ARAFFIN8.
CnH2n+2

ell

.1 §

ss ^..3

S-|l

,ij

B2|-|

"?,(§

•r S

o"?J

^ s

•S o

».«

CLASSIFICATION OF ORGANIC SUBSTANCES. 305

isting. The bodies marked ? are not as yet known to
chemists.

At the head of each column is placed an algebraic for-
mula expressing the formula of the series in general terms.
By making n=l, n=2, n = 3, etc., each member of the ho-
mologous series can be obtained. Two sets of names are
given : the first are in general use among chemists, and the
second is a very ingenious plan proposed by Dr. A. W.
Hofmann, where the vowels a, e, i, o, and u are successively
used in the final syllable to indicate the position of any
member of the isologous series. The Marsh Gas Series, or
Paraffin Series, as it is called, and the Olefin Series, are of
first importance, next comes the Benzol Series ; of benzol
itself you will learn more farther on.

421. Substitution. — Marsh gas, you know, is CH4, but it
may be considered as CHHHH, which is really the same
thing. Each H represents one atom of hydrogen. Now
certain bodies, as chlorine, bromine, cyanogen, etc. (provided
they are monatomic ; see § 44), may take the place of these
atoms of H ; or, as we say, may be substituted, by means of
appropriate processes, for each atom of H in the compound
CHHHH; this substitution may take place all at once or
gradually, as shown below :

CHHHH or CH4 (1)

CHHHC1 or CH3C1 (2)

CHHC1C1 or CH2Cla (3)

CHC1C1C1 or CHC13 (4)

CC1C1C1C1 or CC14 (5)

thus giving rise to a large number of so-called substitution
compounds. The bodies numbered (1), (2), (3), (4), and (5)
really exist, one of them, (4), being the well-known and
valuable substance chloroform. Thus you see how the
theory of substitution is made use of to explain the forma-
tion of organic bodies. One more example, however, will
be given.

306 CHEMISTRY.

Ammonium, (NH4)', and cyanogen, (CN)', you have learn-
ed, are called radicals, because they act like simple elements
in certain cases. Now water is H— O— H; if you remove
one H, you have left — O— H, or (OH)', which acts also like
a radical, taking an important part in the building up of or-
ganic bodies. This radical, called hydroxyl, is monatomic,
or has one bond of affinity, as indicated above, and hence
may take the place of one atom of hydrogen in any com-
pound. Suppose, then, we substitute one atom of hydroxyl,
(HO)', for one atom of H in the hydrocarbon we have been
studying, CHHHH, what kind of a body will result?

This question can of course be answered by experience
only, and experience has taught the chemist that a body
very closely resembling common alcohol is formed. Act-
ually the substance is methylic alcohol, or CH3(OH). This
leads us to the next subdivision of the scientific classifica-
tion, which is that of alcohols.

422. Alcohols. — You are now prepared to understand the
relation between alcohols and hydrocarbons; for common
alcohol has become the type of a vast number of bodies,
some of which resemble it in its physical properties, but
many of which are crystalline solids, and have no apparent
connection with it. This relation is not founded on resem-
blance in properties, but on similarity of constitution, which,
indeed, is the key to this scheme of classification.

Alcohols, then, are substances derived from hydrocar-
bons by the substitution of one or more groups of hy-
droxyl, (OH)', for hydrogen. Take the case of common
alcohol : the formula of this body determined by analysis
is C2H6O ; certain facts show its relations to ethane, which
is C2H6. Now follow carefully the following formulae,
and you will see how common alcohol is a derivative of
ethane :

CCHHHHHH = ethane ; remove one H and substitute

CLASSIFICATION OF ORGANIC SUBSTANCES. 307

one (OH), and you have CCHHHHH(OH), which is the
same as C2H5(OH) or C2H6O, the formula for common
alcohol. This way of writing formulae has a great disad-
vantage : it does not bring out the idea of atomicity, so
we will repeat this explanation with graphic formulae.
(See §41 7.)

II H

I I

H-C-H H-C-H

I I

H-C-H II-C-O-H

I I

II H

Ethane. Common alcohol.

Of course it makes no difference which atom of H in the
formula is replaced. This is a matter of theory solely, and
is apt when thus briefly treated to leave rather crude no-
tions, of which we must beg you to beware.

423. Ethers. — From what has been said it is evident that
if we regard (C2H5) as a compound radical, alcohol may be
regarded as a hydrate; this similarity to the hydrates of
mineral chemistry is shown thus :

Radical K Na (NH4) (CaH5)

Hydrate KHO NaHO (NHJHO (CaH5)HO

Alcohols may therefore be looked at in another light,
viz., as hydrates of organic radicals.

Now if alcohols are hydrates, ethers are oxides. Here
again we must ask you to bear in mind that the term ethers
is a general one, applied to a great number of bodies sim-
ilar in constitution to common ether, though not at all
alike in other respects. You have probably been in the
habit of considering ether as a very mobile, volatile, odor-
ous, inflammable liquid used in medicine and photography ;
it will therefore be difficult to conceive of ethers which

308 CHEMISTRY.

are crystalline solids, some of them with a texture resem-
bling organized bodies. And yet this is the case, the word
ether having acquired a general meaning, just like oxide.
Common ether, then, is oxide of ethyl, the name of the radi-
cal C2H5 just mentioned, and its formula is (C2H5)2O, just
like K20, or (NH4)2O.

424. Acids. — We will pass over aldehydes and ketones,
as they are of no great importance to you. The number
of organic acids is enormous. To print their names alone
would require many pages* of this book. But it is important
to learn their general relations to the preceding bodies.
Take the simple example, acetic acid ; analysis shows it to
be composed of C2H4O2 ; now alcohol is C2IT5(OH) ; com-
pare these two formulae, and you will find one more atom
of oxygen in the acid than in the alcohol, and two atoms
less of hydrogen. This is the result of substitution, for one
O atom, being a dyad, may replace two II atoms, being mo-
nads. This is indeed the way acids are regarded; they
are derived from their corresponding alcohols by one atom
of oxygen replacing two atoms of hydrogen. Let us have
recourse once more to graphic formula? :

H-C-H

II-C-H

H-C-H

H-C-O-H

0-C-O-H

or C2H6

or C.,H6O

or C2IT4O2

Ethane.

Alcohol.

Acetic acid.

Observe that the two atoms of H in the lower left-hand
corner of the formula of alcohol disappear in the formula of
acetic acid, one atom of O taking their place, and held fast
to the carbon by two strokes, signifying its diatomic power.

CLASSIFICATION OF ORGANIC SUBSTANCES.

309

Now we have said that alcohols and ethers are names
given to classes of bodies ; this is also the case with acids.
Acetic acid may be regarded as the type of one class of
acids. We can not here go deeper into this abstruse sub-
ject ; if you wish to learn about mono- and di-basic, mon-
atornic and diatomic acids, we refer you to larger works,
especially to Fowne's Manual of Chemistry. All the acids
with which you will become familiar — citric (from lemons),
tartaric (from grapes), malic (from apples), formic (from
ants), and a host of others — belong to this division, and
are regarded as similarly constituted, their basicity, etc.,
excepted. Examine also the table, page 303, giving acids
and alcohols corresponding to the hydrocarbons of the
Ethylene Series.

TABLE

Showing the Chemical Relations of Hydrocarbons, Alcohols, Acids, and
Ethers in the First Three Members of the Marsh Gas Series:

HYDROCARBONS.

ALCOHOLS.

ACIDS.

ETIIEliS.

1 (or CHJ
CII3
Marsh gas,
or methane.

CH2(OH)
Wood-spirit,
or methylic
alcohol.

1
CO(OH)
Formic acid.

1
CHa(OCH3)
Methylic ether.

CH3

1 (or C2H6)
CH3
Ethane.

CH3

CH2(OH)
Common,
or ethylic
alcohol.

CH.

CO(OH)
Acetic acid.

CH3

CH2(OC2II5)
Common ether.

CH3
CH3 (or C3HB)

CH,

Propane.

CH.

CH./OH)
Propylic
alcohol.

CH3

co(OH;

Propionic acid.

CH3

CH2(OC3H7y

Propionic ether.

310 CHEMISTRY.

425. Amines. — These are bodies containing nitrogen, and
patterned after ammonia. Up to this point carbon, a tet-
rad, has been the foundation on which the organic bodies
are built up, but now we will assume that nitrogen takes

this position. Ammonia is NH3, NHHH, or N < H ; it mat-

ters not how it is written. Now the hydrogen atoms in
ammonia are capable of being replaced by organic groups,
which we have called radicals, either successively or all at
once. Suppose we take, for example, the same radical C2IT5
which is supposed to exist in alcohol, ether, etc. Now if

fH
we substitute C2H5 for one of the IT atoms in N i H, we

fH [H

get N j H , and this is called an amine / actually it is

[C2H6

ethylamine, for the radical C2U5 is called ethyl. Now what
do you suppose are the properties of ethylamine ? They re-
semble those of ammonia very closely ; it is a gas, with a
pungent, not disagreeable odor, very soluble in water, unites
with acids to form crystalline salts, etc., just like ammonia;
so that the substitution of the group C2H5 for H has made
but little change in the properties. Do you ask how
this exchange is actually performed in a laboratory ? We
will tell you. A liquid called ethyl iodide, C2H5T, is put
into a strong glass tube with a solution of ammonia ; the
tube is then sealed, and heated by immersion in boiling
water. In a short time a new body is formed, having a
very long name. The tube is then opened, and its contents
heated in a retort with potassium hydrate, when the ethyl-
amine distills over and dissolves out in the water, which
condenses at the same time. We have explained roughly
this operation in order to give you some idea how a chem-

CLASSIFICATION OF ORGANIC SUBSTANCES. 311

ical reaction of this nature is practically carried out, and
to enable you to understand that the " substitution " is not
merely a new arrangement of letters on paper, but an act-
ual rearrangement of the atoms of tangible matter.

Now as a matter of fact, when the above operation is
carried out the liquid which distills over, on heating with
potassium hydrate, contains other bodies besides ethyl-
amine. For not only is one atom of H replaced by C2H5,
but two, and all three atoms are likewise replaced, yielding
bodies having the composition shown in the formulaB fol-
lowing :

(H (H (C3H5

N •< H N < CaH5 N -j C2H5

(C2U5 (C2H5 (C3H5

Ethylamine. Diethylamine. Triethylamine.

These bodies are chemical curiosities; but we have explain-
ed their formation and constitution in order that you may
have some idea of the group of Amines, for to this class of
bodies it is believed that the Alkaloids belong; and the al-
kaloids you will learn are of immense importance, includ-
ing as they do the valuable and interesting bodies quinine,
strychnine, morphine, etc., occurring in plants. When the
replacing radical contains oxygen, the new body formed is
called an amide, but these are of less importance.

426. Organo-metallic Compounds. — These are compounds
of hydrocarbon radicals with monad, dyad, and tetrad met-
als, but, being mere chemical rarities for the most part, do not
interest us. One of them, called zinc-ethyl — Zn(C2H5)2 —
is a volatile liquid with a disagreeable odor, and possesses
the property of igniting spontaneously in contact with the
air, like phosphoretted hydrogen. "We will not return to
this class of bodies.

427. Organic Analysis. — Analytical chemistry does not
come within the scope of this work, but we will tell you

312 CHEMISTRY.

briefly how chemists determine the constitution of organic
bodies. There are two kinds of organic analysis : first, proxi-
mate analysis separates the several definite compounds or
proximate elements of which a complex substance is com-
posed ; second, ultimate analysis determines the number of
atoms of the elementary bodies in the molecule of & proxi-
mate constituent. For example, starch, cellulose, gluten,
sugar, coloring matters, alkaloids, etc., are proximate prin-
ciples of plants, while carbon, oxygen, and hydrogen in cer-
tain ratios are the ultimate elements of starch, sugar, and
other proximate principles.

The methods in use for separating proximate principles
of vegetables and animals vary with nearly every sub-
stance examined; no scientific scheme has been yet de-
vised, nor can be until our knowledge of this branch of or-
ganic chemistry is vastly increased.

On the other hand, ultimate organic analysis has been
brought to great perfection. The principles on which the
process is based are as follows : Organic bodies may be
considered as mainly made up of carbon, hydrogen, and
oxygen ; now when such a body is completely burned, or
oxidized (which is the same thing), the carbon, as you know,
burns to form carbonic anhydride, the hydrogen burns to
form water, and the oxygen escapes as such, or assists in
the oxidation. By taking a weighed amount, therefore, of
an organic substance, and oxidizing it carefully (by heating
with an oxidizing agent, or in a current of pure dry oxygen)
in a gas-tight apparatus, so arranged that all the carbonic
anhydride and water formed can be collected and weighed,
it is not difficult to calculate from the amounts of these
products the actual amount of carbon and of hydrogen in
the substance taken. How the operation is conducted, and
how the calculation is made, is a matter foreign to the
character of this work.

313

QUESTIONS.

418. "What two methods of classifying organic bodies may be pursued?
Give the scientific classification in seven groups. — 419. What is said of the
compounds of hydrogen and carbon as to number and variety ? How do
these isomeric bodies differ in constitution ? Name some of the hydro-
carbons of the Ethylene Series. — 420. Explain the terms homologous and
isologous. — 121. Show how bodies are formed by substitution. What is
CHC13? What is hydroxyl? — 422. Show the relation between alcohols
and hydrocarbons. Explain, taking common alcohol as an illustration. —
423. What are ethers ? — 424. What are the relations of acids to alcohols ?
Illustrate with acetic acid. — 425. Whence are amines derived ? How ?
How is ethylamine practically prepared? How theoretically derived?
What important constituents of plants belong to this class of bodies ? —
426. What is said of zinc-ethyl? — 427. What are the divisions of organic
analysis ? Illustrate. Explain briefly the method of ultimate analysis.

CHAPTER XXV.

CONSTITUENTS OP PLANTS, ETC.

428. Variety of Vegetable Substances. — There is a great
variety in the substances which are produced in plants.
They are wood, starch, gums, gluten, fatty substances, vola-
tile oils, coloring matters, alkaloids, etc. Then from many
of these are developed other compounds. A very wide
field is thus opened ; and, numerous as are the valuable
combinations already discovered, we know probably but
little as yet of the extent of the discoveries which are to
be made in this field. Stockhardt says on this point:
" Thousands of such new combinations have been discovered
within the last twenty years ; our posterity will probably
count them by millions."

Of the products of vegetation, there are some which are

314 CHEMISTRY.

so widely diffused that they can be considered essential
constituents of plants every where ; while others appear
only in particular plants, and though essential, are not uni-
versally so. It is the former class, which may properly be
called the constituents of plants, that we shall speak of now,
reserving the consideration of the latter class for another
chapter. In treating of them, we shall speak of the changes
effected in them by the operations both of nature and of
art.

429. "Wood. — What is termed wood in chemistry is the
vegetable tissue which makes the framework of all vegeta-
ble growths in all their parts, giving to them their shape
and firmness. It is the solid part of all vegetable organs.
It is to plants what bones, muscles, tendons, skin, etc., are
to animals. Woody fibre is present even in the most deli-
cate and tender fruits, holding in its interstices the juices.
It is sometimes so exceedingly delicate that in crushing the
fruit there seems to be almost nothing but juice. In some
fruits, as the orange, the woody tissue is beautifully ar-
ranged in long and slender sacs or bottles containing the
fluid for our use, the sacs being packed into several differ-
ent compartments, and each compartment being made of
woody tissue. This same tissue, which is so soft and finely
divided in the pulp of fruits, in leaves, and flowers, is con-
densed and hard in what is ordinarily called wood, in bark,
in straw, and the husks of grain, and especially in the shells
of nuts and the stones of cherries, peaches, etc. The so-
called vegetable ivory is chiefly condensed wood. In cork
we have wood in a very light, porous, and elastic form.

430. Cellulose. — The essential part of woody fibre is called
cellulose; this has the composition C6H10O5; it is nearly
pure in cotton, paper, and wood pulp, provided they are
not colored with any thing and are not starched.

Pure cellulose may be obtained by washing white cotton,

CONSTITUENTS OF PLANTS, ETC. 315

unsized paper or old linen with a warm solution of po-
tassium hydrate, then with cold dilute hydrochloric acid,
then with ammonia water and alcohol, repeating the process
several times. Thus purified it is white, translucent, and
unalterable in the air; it is insoluble in water, alcohol,
ether, and oils, but is decomposed by strong acids. Nitric
acid converts it into gun-cotton, as explained in § 433 ; sul-
phuric acid diluted with about one half its volume of water
acts upon cellulose in a peculiar manner, converting it with-
out change of composition into a tough substance resem-
bling animal parchment and applicable to the same pur-
poses. This so-called "vegetable parchment" is manu-
factured on a large scale.

431. Linen and Cotton. — These are composed of fibres of
wood, long and pliant. Hemp is also another form of a
similar kind. Linen is the inner bark of the flax plant. It
is separated from the outer bark by rotting and breaking.
In rotting there is long exposure to moisture and air, which
rots the outer bark, and in the breaking this is beaten and
rubbed off. Then follows the hatcheling, by which the fine
fibres are separated from each other but left parallel, and
the tangled ones are taken out, making what is called the
tow. The flax thus obtained has a gray color, which is re-
moved by bleaching and boiling with lye. Cotton is in the
form of fine hollow hairs, which are beautifully arranged in
the cotton-plant around the seeds. All cotton, except the
Nankin cotton, which is yellow, is so white that it would
need no bleaching were it not that in spinning and weaving
it oil and dirt are necessarily gathered upon it.

432. Uses of "Wood. — We put woody fibre to a great va-
riety of uses. We build houses with it, and fill them with
wooden furniture. Out of this fibre we make thread, twine,
cordage, and fabrics of every variety. We clothe ourselves
with it ; we write and print upon it ; we even eat it as a

316 CHEMISTKY.

part of much of our food. We burn it to keep ourselves
warm and to do our cooking. We spread it out in huge
sheets to the wind in our boats and ships.

433. Gun-Cotton. — If any form of cellulose in a divided
state, as cotton, linen, saw-dust, etc., be submitted for a
short time to the action of strong nitric acid, it becomes a
more explosive substance than even gunpowder. When
the discovery was first made it was proposed to use it in
place of powder, but this was found impracticable on two
accounts. First, it ignites so readily that it is very apt to
explode when we do not wish it. Secondly, its explosion
is too forcible and rapid, or, in other words, the gases pro-
duced expand too rapidly — four or five times more so than
they do in the case of gunpowder. The consequence of
this quick expansion is that there is danger that the gases
will not have time to escape, as in the case of gunpowder,
at the outlet of the gun-barrel, and therefore the barrel is
very apt to burst. Gun-cotton can be prepared by immers-
ing cotton for about five minutes in strong nitric acid, and
then washing it thoroughly, and drying it. Care must be
taken to use but a moderate heat in drying it, lest it should
explode. The explanation of its explosiveness is that the
cotton loses a portion of its hydrogen and takes in its place
nitric peroxide, thereby increasing the number of atoms in
the molecule and its consequent instability. § 413. The
reaction is shown in the following equation :

Cellulose. Nitric acid. Gun-cotton. Water.

C6H1005 + 3(HN03) = C6H7(NO3)305 + 3H3O

Gun-cotton is often called trinitro-cellulose on account of
its composition, as shown in the formula just given. It
contains much more both of oxygen and nitrogen than
common cotton does. It is, then, like potassium chlorate,
a substance highly charged with oxygen, and on that ac-
count explosive. It is the oxygen that produces the com-

CONSTITUENTS OP PLANTS, ETC. 317

bastion when the heat is applied; and the nitrogen, being
set free, expands with the other gases, and helps to give
force to the explosion. Sulphuric acid is commonly used
with the nitric acid in preparing gun-cotton. It is of use
only in taking the water from the cotton, by virtue of its
strong attraction for water (§ 244), thus making more room
for nitric acid, and securing a larger combination of this
acid with the cotton than it could otherwise obtain.

Collodion is a solution of gun-cotton in ether, making a
sirupy liquid. It is often used for court-plaster, and also*
for making small air-balloons. If it be put upon any thing
the exposure to the air causes an evaporation of the ether
at once, and the cotton is left in the form of a transparent
coating.

434. Products from Wood by Heat — When wood is con-
sumed with free access of air, it is decomposed, as you have
already learned, into its elements — carbon, oxygen, and hy-
drogen ; and these, together with some oxygen from the air,
form carbonic anhydride and water in the condition of va-
por. When, however, there is imperfect combustion from
a restricted access of air, the products are different. They
are four in number: 1. Charcoal ; 2. Illuminating gas, which
is a mixture of several hydrocarbons with some carbonic ox-
ide and carbonic anhydride ; 3. Pyroligneous acid, or wood-
vinegar ; 4. Wood-tar. In the common burning of wood the
combustion is not perfect, and we have three of these prod-
ucts deposited in the form of soot, for this substance is
composed of particles of carbon which have passed off un-
burned in the current of smoke, having united with them
some of the pyroligneous acid and the wood-tar. In the
case of the air-tight stoves, so called, soot forms which con-
tains a much larger proportion of the acid and the tar than
the soot of an open fire, because the current up the chimney
is too sluggish to carry up much of the carbon.

318 CHEMISTRY.

435. Dry Distillation of "Wood. — These products can be
obtained separate from each other by a process called dry

distillation, repre-
sented in Fig. 109.
Some pieces of
wood are heated
in a retort, and the
volatile matters
pass over through
the tube into a
receiver. The il-
luminating gas passes on through the bent tube, and is col-
lected in the usual manner. One of these, the wood-tar, is
very thick ; and the other, the wood-vinegar, is a thin, wa-
tery substance. Charcoal, not being at all volatile, is left
behind in the retort. Wood is composed of the three ele-
ments, carbon, oxygen, and hydrogen ; and it is out of these
that the products above mentioned are formed by the in-
complete combustion produced by the heat. They did not
exist in the wood, and therefore may be properly called
products. Even the carbon left in the retort may be called
a product, for in the wood it does not exist as carbon, but
is in combination with the other elements forming the com-
pound, wood; just as oxygen does not exist in water as
oxygen, but is in combination with hydrogen, forming the
compound, water.

Two of the above products — charcoal and illuminating
gas — have already been sufficiently described in other parts
of this book, and therefore we will now notice only the other
two.

436. Pyroligneous Acid. — The name of this acid is de-
rived from a Greek word, pur, fire, and a Latin word, lig-
num, wood. Its acidity comes from acetic acid, and hence
the propriety of calling this liquid wood-vinegar, Its pe-

CONSTITUENTS OP PLA.NTS, ETC. 319

culiar strong smell comes from creosote, wood-naphtha, and
other bodies. The same smell we have in smoke, and from
the presence of the same substances. It is the creosote
which makes smoke so irritating to the eyes. It is this
substance which, both in smoke and in pyroligneous acid,
acts upon meat as an antiseptic. Creosote is a liquid of an
oily consistency, and colorless when freshly prepared, but it
gradually becomes brown by age. It is a very powerful
substance when obtained pure, and is an irritating poison.
If taken into the mouth it has a very burning taste, and de-
stroys the tender membrane which lines the tongue and
mouth. Great care, therefore, should be exercised when it
is employed, as it often is, as a remedy for the toothache.

437. Wood-Naphtha. — The liquid portion of the products
of the distillation of wood contains, besides acetic acid and
creosote, eight or ten other substances; one of these, wood-
naphtha, is of considerable importance. It is a volatile,
odorous, mobile liquid, resembling alcohol, and yet having
a different composition. If it be purified by treatment
with lime to remove acetic acid, etc., and then by distilla-
tion, a pure substance is obtained, known as methylic alco-
hol. This is the first of a series of bodies called alcohols,
with one member of which you are familiar, viz., common
alcohol. Its composition is CH3HO, while common or
ethylic alcohol is C2H5HO. Methylic alcohol burns with
a flame much like that of common alcohol, is a good solvent
of resinous substances, and, being cheaper than ethylic alco-
hol, is of great nse in the arts.

438. Wood-Tar. — This is a resinous substance, and is
therefore soluble in alcohol, but not in water. If it be dis-
tilled, a volatile oil passes over, called oil of tar, and there
is left behind a black pitch. This separation takes place
gradually when wood is besmeared with tar, the volatile
oil flying off into the air, and the pitch becoming, there-

820 CHEMISTRY.

fore, solid on the wood and in its pores. There is always
some creosote in the tar, and this preserves the wood from
decay or putrefaction. You see, then, the object of apply-
ing tar in the calking of ships.

439. Coals found in the Earth. — These are conveniently
divided into three classes: lignites, bituminous coals, and
anthracites. The first named has more nearly the compo-
sition of wood ; the second is an intermediate state ; and
the last, anthracite, is nearly pure carbon, having under the
combined influence of heat and pressure lost most of its
hydrogen and nearly all of its oxygen.

Lignite is of a browner color than the others, and retains
in some degree its woody structure. Bituminous or soft
coal burns with a smoky flame containing some hydrocar-
bons, and hard coal burns with scarcely any flame at all.

All three were made from woody substance, and were
brought into their present state by an imperfect combus-
tion. We see the same process essentially going on at the
present time, to a certain extent, in the formation of peat.
This substance is formed from marsh plants. There is a
growth of these every year, which, rotting in the water,
sink to the bottom. There occurs, therefore, in the course
of time, a large accumulation of vegetable substance, most-
ly woody fibre, in the form of a brown net-work, in which
the separate parts of the plants are discoverable. By
the partial decay — that is, incomplete combustion — of this
mass it is converted into peat, which is a half-formed coal,
being mostly carbon, having some oxygen and hydrogen
combined with it.

The formation of coal in the earth will be particularly
noticed in Part III.

440. Imperfect Combustion of Bituminous Coal. — When
bituminous coal is heated with the air excluded, products
are obtained very similar to those which result from wood

CONSTITUENTS OF PLANTS, ETC. 321

when subjected to this process. They are these: 1. Coke,
which is nearly pure carbon ; 2. Illuminating gas ; 3. Tar-
water, a watery empyreumatic liquid containing some am-
monia ; 4. Coal-tar, a dark, viscid liquid. This process of
dry distillation of bituminous coal is employed for the pro-
duction of the gas so much used for illumination. The
coke which is left in the retorts of the gas-works is a valu-
able article of fuel. The ammonia in the tar-water is the
chief source of the commercial article ; it is derived from
the nitrogen, which is always present in coal in small quan-
tities, uniting with the hydrogen during the distillation.

Coal-tar is used for covering roofs, to protect them from
moisture, and, mixed with chalk and other substances, it is
employed as a cement. A great variety of products can
be obtained from it. By distilling it we can obtain two
oils, one of them a light oil, called benzol, which can be-
used for many purposes in place of spirits of turpentine ;
the other a heavy oil, used in the arts for lubrication and
for dissolving India rubber, and also sometimes for illumi-
nation.

Benzol is one of the large class of bodies called hydro-
carbons, so many of which are found in petroleum. Its for-
mula is C6H6. It is a colorless, volatile liquid, having a
low boiling-point. By treating it with nitric acid it is con-
verted into nitro-benzol — C6H5(NO2) — commonly called ar-
tificial oil of almonds, from its odor, which resembles bitter
almonds. It is much used in perfumery. Aniline is made
from benzol, and is the basis of many of the beautiful dye-
stuffs which have been introduced of late years. These
dyes are called aniline colors, or simply coal-tar colors;
their manufacture is interesting, but too complicated to
give here. Aniline is also a constituent of the heavy oil
mentioned above. This heavy oil also contains naphtha-
line, a solid hydrocarbon also yielding dye-stuffs, and car-

322 CHEMISTRY.

bolic acid (phenol), a substance of great value as a disin-
fectant. By acting on phenol with nitric acid, a beautiful
yellow dye is obtained called picric acid. The pitch which
is left after distilling off these oils is much used in Europe
as a cement for refuse coal-dust. The mixture thus made
is cut up into cakes for fuel.

441. Nature's Products from Bituminous Coal. — The re-
sults of the dry distillation of bituminous coal by art have
their counterpart in nature. Volcanic heat is the agent.
The anthracite coal is very much like the coke formed in
the retorts of the gas-works, except that immense pressure
has condensed and hardened it during the action of the
heat. Then we have inflammable gases issuing from crev-
ices of rocks, answering to the illuminating gas produced
by art. The oil of coal-tar has its representatives in nat-
ure in the naphtha that oozes out of the ground in Persia,
and in the mineral tar found in France as well as in Persia.
Then, to compare with the pitch, the artificial asphaltum
obtained from the coal-tar, we have the natural asphal-
tum of the Dead Sea of Judea, found also in other seas in
Asia.

442. Petroleum. — Petroleum has been known from a very
early period in the history of the earth, but it was reserved
for American enterprise to discover the inexhaustible sup-
ply beneath the surface. Evidences of the use of petro-
leum are found near the ruins of Nineveh and Babylon ;
the springs of Rangoon, in India, have been worked for
ages ; and in our own country the Indians collected petro-
leum for various purposes, chiefly medicinal. In 1854 a
company was formed for collecting "rock oil" at Oil
Creek, Pennsylvania ; but the process of gathering it from
ditches in blankets and squeezing it into tubs was too ex-
pensive. In 1858 Colonel Drake began to bore an artesian
well for oil, believing that that which oozed out of the

CONSTITUENTS OP PLANTS, ETC.

323

Fig. 110.— A View on Oil Creek, Penu., showing Oil- Wells, Derricks, etc.

ground and ran along the surface might be obtained in
great quantity by digging down to its source. His expec-
tations were more than realized ; and a well which yielded
400 gallons of oil a day, worth at the time 55 cents per
gallon, rewarded his exertions, and successfully answered
the ridicule of his neighbors. The eleven years succeeding
this discovery produced more than thirty-five million bar-
rels of this useful article.

443. Composition of Petroleum. — Petroleum is a mixture
of a great number of hydrocarbons, differing from each
other in volatility and density. These hydrocarbons be-
long to two series, one called the Marsh Gas Series and
the other the Olefiant Gas Series, because these bodies are
the first members of their respective series. The table

324

CHEMISTRY.

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CONSTITUENTS OP PLANTS, ETC.

325

on page 324 gives the names, formulae, and boiling points of
the chief hydrocarbons occurring in American petroleum.

444. Refining Petroleum. — Petroleum as it issues from the
earth is dark colored and ill-smelling ; some of its constitu-
ent hydrocarbons are too volatile for burning in lamps,
others are too heavy, consequently the petroleum is sub-
jected to a process of refining. The chief point in the re-
fining process is called fractional distillation, whereby the
bodies having different boiling points are separated; the
lighter portions boiling the lowest distill over first, and the
successive portions are denser and less volatile. This proc-
ess furnishes various products, which are still mixtures of
hydrocarbons, and which have no definite composition, but
they have received names for commercial uses ; the follow-
ing table shows these bodies and their uses :

PRODUCTS OF THE DISTILLATION OF CRUDE PETROLEUM.*

NAME.

PERCENTAGE
YIELDED.

SPECIFIC
GRAVITY.

CHIEF USES.

Cymogene

Rhigolene.
Gasolene

.625

665

0°C.

18.3

48 8

( Generally uncondensed — used
( in ice-machines,
f Condensed by ice and salt —
I used as an anaesthetic.

C Naphtha
B Naphtha
A Naphtha

Benzine .

}»

.706
.724
.742

82.2
104.4

148.8

iUsed for oil-cloths, cleaning,
adulterating kerosene, etc.
For paints and varnishes.
( Used to adulterate kerosene

Kerosene oil. . .
Mineral sperm.
Lubricating oil.
Paraffin

.804
.847
.833
Solid

176.6
218.3
301.6

i oil.
Ordinary oil for lamps.

Lubricating machinery.

• Rearranged from Dr. C. F. Chandler's Report on Petroleum, presented to the
Board of Health of the City of New York, 18TO.

326 CHEMISTEY.

445. Unsafe Kerosene. — The cheapness of kerosene oil, the
brilliancy of its light, the freedom of its flame from smoke
when burned in suitable lamps, makes it universally used
for illuminating purposes. Unfortunately many accidents
occur by explosion of lamps, but this is only because the
kerosene oil contains too much of the lighter oils, benzine
and naphtha. This makes the oil too readily inflammable,
for the vapors of the lighter oils are driven out by heating
(as when a lamp is burning), and these mixed with the oxy-
gen of the air form a dangerous explosive mixture. There
is a law requiring manufacturers to keep kerosene oil free
from these lighter oils ; but since the latter are not worth
so much, the wicked avarice of some manufacturers causes
them to break the law and run the risk of detection.
Hence so many fatal accidents.

446. White Rotten Wood. — There is a decay of wood in
the hollow trunks of trees which produces a singular sub-
stance when there is no opening in the trunk to permit the
access of air. This substance differs from that which or-
dinarily results from the decay of wood, very much as a
hydrate does from an anhydrous oxide. For example, it is
as iron rust differs from common oxide of iron. This rotten
wood can be prepared artificially. If you put some moist-
ened saw-dust into a closed vessel in summer, and let it
stand for some months, you will find it converted into a
white friable substance, which is perfectly dry because the
water has chemically united with it. White rotten wood
is sometimes luminous from some chemical change which is
going on in it.

447. Chlorophyll. — This substance, leaf-green, giving the
green color to leaves and twigs and stalks, is one of the
most widely diffused of vegetable substances. It is not one
single substance, but is a mixture of several coloring sub-
stances, the character of. which- has not been fully ascer-

CONSTITUENTS OF PLANTS, ETC. 327

tained ; it is known, however, that the green color is due to
the mixture of a blue with a yellow substance. Chloro-
phyll is not soluble in water, but is easily soluble in alcohol
and ether, which are used to extract it from green leaves.
Light is necessary for its formation, as we know by the
white color of plants that grow in darkness.

QUESTIONS.

428. What is said of the variety of vegetable substances ? — 129. What is
wood, chemically speaking ? — 430. What is the essential part of woody
fibre? — 431. What is said of linen and cotton ? — 132. What of the uses of
wood ? — 433. How is gun-cotton made ? Why is it explosive ? What is
its chemical constitution? What is collodion? For what is it used? —
434. What are the chief products of the distillation of wood ? — 435. De-
scribe them. — 436. Of what is pyroligneous acid composed? What are the
properties of creosote?— 437. What is said of wood-naphtha ? — 438. What
of wood-tar and its uses ? — 439. What coals are found in the earth ?
Wherein do they differ? How are they formed? — 440. What are the
chief products of the imperfect combustion of coal ? For what is coal-tar
used ? What is benzol ? What is nitro-benzol ? What is aniline ? — U I .
What is said of nature's products from bituminous coal ? What is asphal-
tum? Whence comes it? — 442. Give the history of petroleum. — 443.
What is its composition ? Name some of the hydrocarbons occurring in
petroleum. — 444. What is said of refining petroleum? Name some of the
products of distillation of petroleum ? — 445. What makes kerosene unsafe ?
—446. What is said of white rotten wood ? — 447. What is chlorophyll ?
What is necessary to its formation ?

CHAPTER XXVI.

CONSTITUENTS OF PLANTS (CONTINUED).

448. Starch. — This vegetable constituent, while it is pres-
ent to some extent in all plants, is especially abundant in
particular parts of some of them. It is one of the principal

328

CHEMISTRY.

ingredients in all cereal grains and other seeds, and in the
tubers and roots of various plants. It is also in the bark
and pith of many trees. It is abundant in all unripe fruits,
and some of it changes into sugar as they ripen. All vege-
table substances which are used as food contain more or
less of starch. Thus in bread, so prominent an article of
food as to be called the staff of life, about four fifths of the
substance (that is, exclusive of the water) is starch. Arrow-
root is a starchy meal which is prepared in the West and
East Indies from the roots of marshy plants. Sago is pre-
pared by heat and water from starch extracted from the
pith of palm-trees.

449. How Starch is Obtained. — Make some dough by

moistening flour,
and work it with
the hand on a sieve
or on muslin (Fig.
Ill), pouring some
water continually
upon it, until it
ceases to pass
through milky.
There will be a
substance left on
the muslin which
we will speak of
soon. That which
is in the water be-
low, giving it a
milky appearance,
is starch, which will settle in a little while as a white pow-
der. In a similar way it can be obtained from rasped po-
tato, and from other substances that contain it.

450. The Grains of Starch. — Starch appears to the naked

Fig. 111.

CONSTITUENTS OF PLANTS, ETC.

329

Fig. 112.

eye as if composed of par-
ticles of a mealy sub-
stance. But if we exam-
ine it with a powerful
microscope we find that
it is made up of grains
which are generally regu-
lar in their form. They
are of different forms and
sizes in different plants.
In Fig. 112 you see a rep-
resentation of the granules
of potato starch as seen
through the microscope. They are egg-shaped, and have
a covering consisting of many scales overlapping each
other, or perhaps consist altogether of such scales. They
glisten in the sun and are hard to the touch. The granules
of wheat starch are very
different; they are shown
in Fig. 113. They are
flattened and dull. The
granules of rice starch
are not rounded at all, as
those of wheat and pota-
to, but are angular, and
are only about one
twelfth of the size of
those of potato starch.

We have in starch

grains an example of a Fis- 113-

body with an organized structure. The exact composition
of starch is not known, but is C6H10O5 or some multiple of
these numbers. Probably the multiple is 3 ; if so, starch
is C18H30O15.

330 CHEMISTRY.

451. Properties of Starch. — Starch is not soluble in cold
water. But while cold water produces no effect at all upon
it, a very peculiar effect is produced upon it by boiling water.
The hot water is absorbed by the granules, swelling them up
and uniting them together, so that the mixture becomes at
first mucilaginous, and at length is as thick as jelly. If this
jelly be boiled with water for some time the starch is ren-
dered soluble. It is this swollen starch that is so much used
in giving stiffness and smoothness to linen and cotton cloth-
ing, and in thickening the colors used in printing cloth. The
swelling of beans, pease, rice, etc., when they are cooked,
is owing to this absorption of the hot water by the starch
granules, which compose so large a part of these vegetables.

452. Iodide of Starch. — You remember that in § 64 we
told you how to test for ozone by means of iodide of potas-
sium and starch paper. Ozone, however, is not necessary to
the production of the blue color ; any thing will do which
can set the iodine free — nitric acid, for example. Instead
of taking potassium iodide to get the blue iodide of starch,
you may take an alcoholic solution of free iodine. A very
weak solution of starch will give you a beautiful blue color.
Warm this solution and the color will disappear, let it cool
and it will return; this is because the iodine separates
from the starch while hot and returns on cooling.

453. Gums. — Gum is a generic term for various substan-
ces which are alike in both constitution and in properties.
They exist in certain plants, and sometimes so abundantly
that they exude from the bark as a thick liquid, and harden
on exposure to the air. We have familiar examples of this
in our peach and cherry trees. The most widely known of
the gums is gum-arabic, which exudes from several of the
species of acacia in Africa. Most of the gums dissolve
readily in water, forming a mucilage. The mucilage of
gum-arabic is quite adhesive, and therefore is much used

331

instead of paste and glue; and, as it can be made of a thick
consistency, it is used in calico-printing to thicken colors
and mordants. Some of the gums, as gum-tragacanth, do
not dissolve in water, but only swell up, forming a jelly.
The juices of many fruits and roots — as currants, cherries,
apples, carrots, etc. — contain a peculiar kind of gum, which
gives to the juices the property of hardening into a gelati-
nous mass on cooling, especially when they have been boiled
with sugar. This is called pectin.

454. Dextrin. — Starch, by certain processes, may be con-
verted into a gum called dextrin, C6H10O5. The change
can be produced simply by the action of heat. If starch
be roasted, being kept in motion all the while to prevent
its burning, it becomes at length of a brownish-yellow color,
and then has the property of being soluble in either cold or
hot water. This dextrin, or starch -gum, as it is common-
ly called, is much used in calico-printing for thickening
colors and mordants, and is prepared for this purpose in
large quantities by roasting it in the same way that coffee
is roasted. This gum is also used in making " fig-paste "
and other kinds of confectionery.

Dextrin can be made with a less degree of heat by the
agency of either sulphuric or nitric acid. Let a paste of
potato starch be made, and while it is yet hot drop a few
drops of sulphuric acid upon it in a saucer, and stir it in
well. You will find that the swollen starch soon becomes
liquid. Now place the saucer upon a jar in which water
is simmering, and let it remain over the steam until the
liquid is nearly transparent. You have now a solution of
dextrin, with the sulphuric acid in it unaltered. To rid
it of the acid you add prepared chalk until effervescence
ceases. There is gypsum now in the solution in place of
the sulphuric acid, for the acid has united with the lime of
the chalk, setting free its carbonic acid, which, decomposing

332 CHEMISTRY.

into water and carbonic anhydride, occasioned the efferves-
cence. The gypsum, being insoluble, is easily got rid of by
filtering, and then by evaporating the solution you obtain
the dextrin in solid form.

455. Explanation. — In this conversion of starch into dex-
trin the acid employed does not itself change in the least,
but acts only by its presence in some manner not compre-
hended. Starch has the composition C18H30O,5, and it takes
to itself one molecule of water, and then breaks up into
dextrin and glucose, a sugar about which you will learn
very soon. The reaction is then probably as follows :

Starch. Water. Glucose. Dextrin.

C19H30015 + H30 = C6H1306 -f 2C6H10O5

456. Sugar.— This substance is widely diffused in the
vegetable kingdom, though not as widely as starch. It is
abundant in all sweet fruits and vegetables. The Creator
has ordained certain plants to be great sugar-makers for
man, so that annually large stores of this article are laid up
in them for his use. The principal of these are the sugar-
cane, the sugar-beet, and the sugar-maple. In many fruits
we have an agreeable mixture of sugar with acids, the
chemistry of nature being competent to produce these two
results at the same time and in the same locality — a thing
impossible to the chemist in his laboratory, who can only
obtain sugar by one process and an acid by another, and
then bring them together in mixture, as we so often do in
making lemonade.

457. Different Kinds of Sugar. — Sugar is not, like starch,
always one thing. There are different kinds of sugar, all
agreeing in being composed of the same elements — carbon,
oxygen, and hydrogen — but differing in the proportions of
these elements. The four most prominent kinds are as fol-
lows: 1. Cane-sugar, or sucrose — C12H22On — found chiefly
in the juice of the cane, maple, and sugar-beet; 2. Milk-

CONSTITUENTS OF PLANTS, ETC. 333

sugar, or lactose, an important constituent of milk, having
the composition Ci2H22On.H2O, which differs from cane-
sugar only by one molecule of water; 3. Grape-sugar, or
glucose — C6H12O6 — which is especially abundant in fruits,
as grapes, prunes, figs, etc., and occurs solid and crystal-
lized in dried fruits — raisins, for instance ; 4. Fruit-sugar,
or cellulose, which occurs in honey and many fruits, togeth-
er with glucose, and possesses the same composition, but
differs in its optical properties. The last kind can not be
crystallized.

458. Cane-Sugar. — This kind of sugar is obtained more
largely from the sugar-cane than from other plants, and
hence comes its name. The amount of sugar extracted an-
nually from the sugar-cane in all parts of the world is many
millions of pounds, the largest portion coming from the
East and West Indies. Cane-sugar is obtained largely
from the sugar-beet on the continent of Europe, and from
the sugar-maple in the northern parts of this country. In
obtaining sugar from the cane the juice is first pressed out
by passing the cane between large iron rollers. The juice
is then clarified, and boiled down to such a point that it
will crystallize as it cools. The raw sugar is thus formed,
and the drainings which come from this make the common
molasses. The sugar thus obtained is refined by various
means and processes, by which it is pre-
pared in different forms for the market.

The crystals which sugar is disposed to

form are of the shape seen in Fig. 114, an

oblique six-sided prism, as you may ob- Fig. 114.

serve in what is called rock-candy.

459. Milk-Sugar. — The sweetness of milk depends upon
a peculiar kind of sugar. When the curd is separated from
milk in the making of cheese, the sugar remains dissolved
in the whey. It can be obtained from this by boiling it

334 CHEMISTEY.

down considerably, and then cooling it. This sugar is so
hard as to appear gritty when crushed between the teeth,
and is both less soluble and less sweet than cane-sugar. In
Switzerland and some other countries, where great quanti-
ties of cheese are made, there is some trade in this sugar ;
but very little of it is sold in the markets of the world in
comparison with other kinds of sugar. Milk-sugar is used
in pharmacy.

460. Grape-Sugar. — This is by no means as sweet as cane-
sugar, as you can readily see by comparing the taste of a
candied raisin with that of common sugar. A gramme of
common sugar has as much sweetening power as two and
a half grammes of grape-sugar. Cane-sugar is also twice
as soluble in water as grape-sugar, consequently the sirup
made with cane-sugar has a more tenacious consistency.
Their difference in composition may be shown thus:

Two molecules of One molecule of One molecule of

glucose. sucrose. water.

2(C6H1206) =' Ci2H22Ou + HaO

461. Sugar made from Starch and Wood. — Grape-sugar
can be made from either starch or wood by the agency of
heat and sulphuric acid. You saw in § 454 that sulphuric
acid with a certain degree of heat converts starch into the
gum called dextrin. Now with a higher degree of heat
you can make it convert the starch into sugar. Bring to
brisk boiling five tablespoonfuls of water, in which are
twenty drops of sulphuric acid, and add gradually thirty
grammes of starch made into a paste, keeping the water all
the while boiling. Let the boiling continue about half an
hour, and the requisite change is effected — you have a
sirup, that is, sugar dissolved in water. But the sulphuric
acid, which is not at all changed in the operation, is in the
sirup. This you can get rid of in the way described in
§ 454, and then on evaporating the sirup you have the

CONSTITUENTS OF PLANTS, ETC. 335

sugar. An infusion of brewer's malt can be used in this
process in place of the dilute sulphuric acid.

The process by which wood or cellulose is converted into
sugar is a little different. The wood must be in the form
of saw-dust. This is moistened with a little over its own
weight of sulphuric acid, and is left to stand for twelve
hours. The mass becomes very nearly dry in that time,
but on being pounded in a mortar it becomes liquid. "Wa-
ter is added to it, and boiling completes the transformation,
giving you a sirup which is to be treated in the same way
as that obtained from starch. Some kinds of wood yield
more sugar than others. Poplar wood is found to be the
best, every five pounds of the wood yielding four of sugar.
As the fibre of cotton and of linen is really cellulose, sugar
can be made by the above process from cotton and linen
rags.

The explanation of this reaction has been anticipated in
§ 455, in explaining the formation of dextrin. We need
hardly say that no way has yet been discovered of convert-
ing cellulose or starch into cane-sugar. If such a discovery
could be made it would be a vast mine of wealth to the
discoverer.-

462. Cheating in Sugar. — Cane-sugar is often adulterated
in England and on the continent of Europe with this grape-
sugar made from starch and wood. Stockhardt states that
the white sugar sold in Germany " is frequently found to be
composed partly or entirely of starch-sugar." In England
the manufacture of it has been prohibited by law. The
profit on such adulteration must be very great, for the ma-
terials used are all cheap, especially if an infusion of malt
be used instead of sulphuric acid in effecting the conver-
sion. Grape-sugar is used extensively by brewers, being
cheap and easily undergoing fermentation.

463. Starch and Wood changed into Sugar in Plants. — We

336 CHEMISTRY.

have beautiful examples of the change of starch and even
of wood into sugar in different plants. Fruits that become
sweet as they ripen have their starch converted into sug-
ar. This can be proved by the application of the iodine
test (§ 452). If tincture of iodine be applied to the fruit
when green, you will have the characteristic blue color of
iodide of starch; but if it be applied when the fruit is fully
ripe, no such color appears. When sugar -forms so abun-
dantly in the sugar-maple in the early spring it comes
partly from the conversion of the starch in the tree, and
probably some of its wood, into sugar.

464. Wood and Starch made from Sugar. — Wonderful as
are the changes effected by art, as described in § 461, still
more wonderful are those which are effected by nature.
The chemist can only produce one of the sugars from wood
and starch, and that of a poorer kind, while nature can not
only produce all kinds, but can change them back as occa-
sion requires into starch and wood. For example, the sap
of the maple loses its abundant sweetness as the leaves put
forth, the sugar in it being converted into wood in the an-
nual growth of the tree. So, also, in the case of the sugar-
beet, if left too long in the ground much of the sugar
changes into wood, making the beet tough and fibrous. If
grass be not cut soon enough, the hay is deficient in sweet-
ness, and is too coarse and strong, because much of the
sugar in its juice has been turned into wood. In cutting
the sugar-cane the tops are rejected, because they have
so little sugar in them. The reason of this is, that as
the plant grows upward the sugar is used up in making
the woody structure, but as soon as any of the struct-
ure is completed the cells in it are filled with the sugary
juice. The lower part, therefore, being complete, is fully
charged, while the upper part, which is growing, is not.

465. Honey. — The bee gathers sugar in the form of honey

CONSTITUENTS OF PLANTS, ETC. 337

from the nectaries of flowers and deposits it in its honey-
bag, which is really a crop connected with the gullet. Dur-
ing the time that it remains there it is probably acted upon
by the secretions of the mouth and the crop ; so that when
the bee, on its return, disgorges it into some honey-cell in
the hive, it is probably not exactly of the same chemical
composition as when it was first collected from the flowers.
Honey varies much in its qualities, from the coloring and
odoriferous substances of different plants, which become in-
timately combined with the honey as the bee gathers it.
Some honeys are for this reason much more highly valued
than others.

466. Manna. — There are various trees from which sub-
stances called manna are obtained. In these substances
there is a peculiar sugar called mannite — C6H14O6 — which
is less sweet than even the grape-sugar. There is also in
them some sugar which appears to be like grape-sugar, and
also some other matters. The composition of the ordinary
manna of commerce may be stated thus :

Per Cent

Mannite 40

Grape-sugar 10

Gum and other matters. 40

Water 10

100

The large proportion of gum and other matters in the
manna lessens, of course, its sweetening capacity. When
freshly gathered it is very agreeable to the taste, and is a
valuable article of food. But after it has been kept for
some time it has a laxative quality which unfits it for use
as food. This medicinal quality is not owing to the sugar,
but to some chemical change in the other substances. A
manna obtained from a tree in the neighborhood of Mount
Sinai is supposed by some learned men to be the same as

338 CHEMISTRY.

that on which the Israelites were fed in passing through
the wilderness. But this opinion is obviously incorrect,
and is not generally received. Besides the want of cor-
respondence in taste, general appearance, etc., there is
a chemical difference indicated in the following passage
from Exodus : " And Moses said, Let no man leave of it
till the morning. Notwithstanding they harkened not
unto Moses; but some of them left of it till the morn-
ing, and it bred worms and stank: and Moses was wroth
with them." No such change as this occurs in the man-
na now obtained near Mount Sinai, and it shows, therefore,
that the manna which was furnished miraculously to the
millions of Israelites was of a different chemical compo-
sition.

467. Gluten. — The constituents of plants thus far noticed
are composed of carbon, oxygen, and hydrogen. But these
alone could not sustain and nourish animals, for there is no
nitrogen in them. There are other constituents, therefore,
which contain this element, in addition to the three of
which sugar and starch are composed. The principal of
these is gluten, so called because it is a glutinous or sticky
substance like glue. You will recollect that in the process
of obtaining starch from wheat flour a substance was left
on the cloth. This was gluten. It is this in the flour
which gives cohesion to bread. Without this the bread
would crumble to pieces, for the cells in it, if made of
starch alone, would be easily broken down. Though glu-
ten is so important a part of grains as food for man and
animals, it bears but a small proportion to the starch. In
the bread that we commonly eat — wheat bread — there is
about eight times as much starch as gluten. Gluten is
analogous to a substance largely existing in animals called
fibrin, and for this reason it is often denominated vegetable
fibrin.

CONSTITUENTS OF PLANTS, ETC. 339

468. Albumen. — If in the process for obtaining starch de-
tailed in § 449, after the starch is settled you decant the
water from the vessel and boil it, it will become turbid, and
on standing will deposit a flocculent precipitate. This is
vegetable albumen, which has properties similar to those
of animal albumen, a common specimen of which we have
in white of egg. The precipitate above spoken of is essen-
tially the same as the white of egg coagulated by heat.
This albumen, which is thus found to be present in a small
amount in the grain of wheat, is very widely diffused in
the vegetable world. It is this substance in the sap of
wood which renders it so liable to decay.

469. Casein. — Vegetable casein is so called from its re-
semblance to the cheese contained in milk. It is found
chiefly in the seeds of leguminous plants, and therefore is
sometimes called legumin. Like gluten and albumen, it
contains nitrogen. It differs from albumen in not being
coagulated by heat ; but it is coagulated by acids, as is the
case with the cheesy matter or casein in milk. It may be
obtained from pease by the following process : Put a hand-
ful of pease into a vessel containing considerable water, and
let it stand for several days in a warm place. A great part
of the water will be absorbed by the pease, so that they will
become large and soft. Mash them, and add sufficient wa-
ter to make a thin paste. By treating this as the paste of
flour was treated in § 449, you obtain the same substances,
viz., the gluten on the cloth, the starch deposited from the
liquid, and the albumen coagulated in the boiling of the
decanted liquid. If now, after separating the albumen from
the liquid by filtering, you add to the liquid a little acid
of some kind, a flaky white substance will be precipitated,
which is casein.

470. Protein Substances. — The three nitrogenous sub-
stances which we have thus briefly noticed — albumen, fibrin,

340 CHEMISTEY.

and casein— have nearly the same chemical composition,
and are convertible into each other. The name, protein
compounds, has been given to them because they were sup-
posed to have a common base, which, from its importance
in the chemistry of life, was called protein, from the Greek
word protos, first. This supposition has been abandoned,
but the name has been retained, and these substances are
often spoken of still as the protein compounds. They are
often also spoken of as the albuminoids, especially in rela-
tion to the nutrition of animals. Then, again, they are
styled the plastic elements or constituents, because they are
used in building up structure in animals, this word being
derived from a Greek word meaning to form. Another
term still is often applied to them — azotized — because they
contain, unlike starch, gum, sugar, etc., nitrogen, or azote.
There is always in these substances a small amount of both
sulphur and phosphorus. It varies much, however, in dif-
ferent cases.

QUESTIONS.

448. What is starch? What proportion of bread is starch? What is
arrow-root? What is sago? — 449. How can starch be obtained ?— 450.
Describe the grains of various kinds of starch. What is the composition
of starch? — 451. What are the properties of starch? What causes the
swelling of rice when boiled ? — 452. What curious property has iodide of
starch ? — 453. What are gums ? What is a mucilage ? What is pectine ?
— 454. How is dextrin made from starch ? To what uses is dextrin ap-
plied ? Describe another way of making dextrin. — 455. Explain the
chemistry of this change. — 456. What is said of the production of sugar in
nature? What of the mingling of sugar and acids in fruits? — 457. What
are the different kinds of sugar ? — 458. What is the source of cane-sugar ?
How is it obtained from the cane ? What is rock-candy ? — 459. What is
said of milk-sugar ? — 460. How does grape-sugar differ from cane-sugar in
properties? How in composition? — 461. How can sugar be made from
starch and wood? Explain the change. — 462. What is said of the adul-
teration of cane-sugar ? — 463. What of the conversion of starch and wood

VEGETATION. 341

into sugar in plants? — 464. What is the difference between the artificial
and the natural production of sugar ? — 465. How does the bee form honey ?
— 466. What is manna ? What are its ingredients ? Its properties ? What
is said of the manna of the Israelites? — 467. What is the use of gluten in
plants ? How may gluten be obtained from wheat flour ? Why is gluten
called vegetable fibrin ? — 468. What is said of vegetable albumen ?— 469.
What of casein ? How may it be obtained ? — 470. What is said of protein
substances ? Why are they called plastic elements ? What is the mean-
ing of the term azotized ?

CHAPTER XXVIL

VEGETATION.

471. The Seed. — The beginning of the formation or build-
ing up of a plant is in certain operations in the seed. The
chemical forces remain dormant in the seed until awakened
to action by heat and light. These, in the presence of
moisture and air, operate upon the seed when it is put into
the ground. "With these stimuli wholly shut out seeds
may be kept a very long time in their dormant state, their
living power being preserved in the sleep. Thus seeds
which were found buried in the ruins of Herculaneum were
proved to be alive by growing when they were planted,
like the fresh seeds of the previous year.

On the whole our knowledge of the chemical operations
taking place in the plant is very slight; only here and
there have we glimpses of wonderful processes which pro-
duce such an immense variety of vegetable bodies.

472. Growth from the Seed. — A seed is composed chiefly
of starch, with some gluten. Both of these are insoluble
in water, and therefore can not be used in growth until
they are so changed as to be rendered soluble. Accord-
ingly the first thing which is done by the forces men-

342 CHEMISTRY.

tioned is the production of a substance which so acts upon
these materials as to make them soluble. This substance
is formed by the union of the oxygen of the air with some
of the gluten, and is therefore oxidized gluten. This union
will not take place unless there be moisture, just as iron
will not rust or oxidize in perfectly dry air. The substance
thus produced is called diastase. It has the power of con-
verting the starch into dextrin, and also into sugar, and
both of these substances are soluble. It also in some way
renders the gluten soluble. But little diastase is required
to produce these changes, and therefore but little of the
gluten is converted into diastase. There are some very
familiar examples of these changes. The malt of the
brewer is sweet and mucilaginous to the taste, because in
the germination of the barley the diastase converted some
of the starch into sugar and dextrin, the latter giving the
malt its mucilaginous character. For the same reason
when potatoes sprout they become soft, mucilaginous, and
sweet.

473. Root and Germ. — From the materials contained in
the seed, thus rendered soluble, the root is formed down-
ward and the germ upward. These are solid formations.
Observe how they are made. It is not by chemical power,
as particles are arranged in various crystalline forms. The
branching germ and root are not formed as the lead-tree
is, noticed in § 373. In this latter case particles are de-
posited on each crystal in regular layers, each layer outside
of that deposited before it. But in the formation of the
germ and root life is ever pushing along, making chan-
nels for the materials of the seed to flow in. By the time
that these materials are used up in the formation of the
plant it becomes fitted to go on in its growth by absorb-
ing materials from the earth and from the air, for the
same living power which constructs the channels for it

VEGETATION. 343

forms in the minute roots absorbent mouths to take ma-
terials from the earth, and other mouths in all the leaves
to absorb material from the air. This absorption from
earth and air begins indeed as soon as the root and germ
are at all formed, but it is not established in full until all
the nutriment of the seed is taken into the plant.

474. Source of Carbon in Plants. — You have already seen,
in § 408, the source of a large part of the carbon in plants.
Then there is some carbon introduced by the root, for there
is always carbonic anhydride in the soil, as the product
of decompositions going on there, and this is absorbed
with other materials by the innumerable mouths in the
minute fibres of the root. What proportion of the car-
bon comes from the air is not known, but it is probably by
no means always the same. It is supposed that generally
more is taken in by the leaves than by the roots.

475. Sources of the Oxygen and Hydrogen. — With the car-
bon there must be united oxygen and hydrogen to form
the various structures of the plant — the wood, bark, leaves,
etc., and also the substances contained in the plant — the
starch, sugar, gum, etc. From whence, then, does it get
the oxygen and hydrogen ? Probably mostly, and some-
times wholly, from water. As this fluid, absorbed by the
root, carries up in the channels which life has constituted
various materials gathered from the earth, some of it is de-
composed in order to furnish oxygen and hydrogen to unite
with carbon in forming the various compounds alluded to.
It is not a union, you observe, of water and carbon, but of
the elements of water and carbon, and to effect this the
water must be decomposed into its elements. This is done
by the vital force which alone can build up organized
structures. Man can not effect this decomposition except
by applying strong heat, and at the same time presenting
some substance to the water which has a decided affinity

344 CHEMISTRY.

for the oxygen, as you saw in § 142. But in the plant the
decomposition is effected in the most quiet manner, and the
two elements thus separated are united with carbon in the
production of a great variety of substances.

476. Plants Growing Without Earth. — You can now under-
stand how it is that plants often grow in water only. It
is because the air furnishes the carbon, while the water
furnishes the oxygen and hydrogen, and these are all the
elements which are absolutely necessary for the structure
of the plant. We have familiar examples in the hyacinths
raised in bulb glasses, in oats growing from seeds on cot-
ton floating in water, and in canary-seed throwing up del-
icate shoots from all parts of a pine-cone which stands im-
mersed in water in a glass. There is, it is true, in all these
cases some nitrogenous matter in the seeds, and also in the
water, unless it be freed from its impurities by distillation.
But this is too small in amount to satisfy the natural de-
mands of the plant, and therefore, though there be growth,
there is by no means that vigorous and productive growth
that there would be if all the materials naturally belonging
to the plant were at hand. The oats and canary-seed, there-
fore, produce no seeds, or very defective ones, and the hya-
cinth produces no additional bulb. And, farther than this,
in the case of the oats and canary-seed the growth is very
manifestly deficient, because the plants are naturally rich in
nitrogen, and therefore especially require that article of diet,
as we may express it, which is not true of the hyacinth.

477. Sources of the Nitrogen in Plants. — Although nitro-
gen is not needed, so far as the structure of plants is con-
cerned, it is generally present in some amount ; and it is
essential to the formation of the fruits of many plants, as
the grains, beans, pease, etc. From whence does it come ?
There is an abundance of it in the air, for four fifths of the
atmosphere is nitrogen. And it is not combined with any

VEGETATION. 345

other element, but is free ; and as it bathes the leaves it
would seem that it might be absorbed as the carbonic an-
hydride is. But not a particle of the nitrogen, so far as we
know, is absorbed by them. How, then, the question re-
turns, does the plant get its nitrogen ? It comes from the
soil. But how ? There is no free nitrogen in the soil, so
that the mouths of the roots may drink it up as they do
carbonic anhydride. But there are substances in the soil
which contain nitrogen in combination, and furnish it to
the plant. The principal of these is ammonia, which, as
you learned in § 160, is composed of nitrogen and hydro-
gen. In the process of decay always going on in the soil
there are produced ammonia, by the union of nitrogen and
hydrogen, and carbonic anhydride by the union of carbon
and oxygen. Then the ammonia and carbonic anhydride
unite with the elements of water to form carbonate of am-
monium. As this salt is volatile, much of it escapes into
the air ; but it is brought down to the earth again by the
dew and the rain. The existence of ammonia in rain-water
has been proved by Liebig. The amount is indeed very
small in any one quantity of water subjected to examina-
tion ; but the aggregate for the year is so large an amount
that we may say that the land receives great quantities
of one of its most valuable fertilizers from the rains of
heaven. This is but returning, however, to the ground
what is first generated there by decay. The value of ma-
nures containing ammonia will be spoken of hereafter.

478. Summary. — You see, then, that from carbonic anhy-
dride, water, and ammonia all the constituents of plants
can be furnished, for we have in these all the elements
which compose these constituents. We may state it thus :

Carbonic anhydride gives carbon, oxygen, )- . . , (wood, starch,
Water « hydrogen, oxygen, I JJ23 \ gum, gluten,

Ammonia " nitrogen, hydrogen, ) ai >a ( sugar, etc.

346 CHEMISTRY.

The materials of growth, then, are produced by decay,
which is really not destruction, but a set of chemical
changes for the purpose of a recombination of the elements
in new forms of life and beauty. It is thus that life con-
tinually springs out of what we call death.

479. Nitrogen from Nitric Acid. — Considerable nitrogen
is furnished to plants from the nitric acid, which we have
stated is formed in the air and brought down in the rain.
As long ago as 1785, Cavendish, an English chemist, dis-
covered that by passing a succession of electric sparks
through a mixture of nitrogen and oxygen in presence of
aqueous vapor in a glass tube, a little nitric acid is formed.
This is a small representation of what takes place on a
large scale in the atmosphere, for traces of nitric acid have
been found in samples of rain collected during and after
thunder-storms. As one of the elements of nitric acid is
nitrogen, its decomposition furnishes this element to plants
to be used in their growth.

480. Green Manuring. — Land which has been impover-
ished is often rendered fertile by raising some crop upon
it, as buckwheat, barley, rye, etc., and plowing it in while
green. The manner in which this process, called green
manuring, enriches the soil will be clear to you by referring
to what we have said of the sources of the materials for
growth. In the first place, all the ammonia and nitric acid
which are washed down by the rain are used by the plants,
and as these are plowed in there is really a store of nitro-
gen laid up in the ground for the next crop. Then, again,
every leaf of the plants is gathering in, by its multitude
of open mouths, carbon from the air ; and this carbon is
plowed in, therefore, with the nitrogen. But, besides all
this, the roots as they are pushed down by the living pow-
er of the plant break up the mass, and then thoroughly
mix with it in their decay. We have, therefore, a loosen-

VEGETATION. 347

ing and rearrangement of the soil which are favorable to
fertility.

481. Inorganic Food of Plants. — The materials of which we
have spoken as ministering to the growth of plants are said
to be their organic food. They are composed of the four
grand elements — carbon, oxygen, hydrogen, and nitrogen.
But there are other substances which are absorbed in va-
rious quantities in different plants, as silica, potash, lime,
phosphorus, etc. These are said to be their inorganic
food. Although the inorganic are not as essential to the
growth of plants as the organic substances, still the fact
that the most important of them are present to some ex-
tent in all plants shows that every plant requires some
amount of them for its full development. If a plant fails
to find them its growth is feeble, and it withers before at-
taining maturity.

482. Ashes of Plants. — If a plant be burned, we obtain in
the ashes the inorganic portion of it. The organic part
has flown off in the form of gas, the carbon having formed
carbonic anhydride with oxygen, the hydrogen water with
oxygen, and ammonia with nitrogen. The ashes show how
small a proportion of the substance of plants is inorganic.
Ordinarily every hundred grammes of wood affords but
two of ashes, the other ninety-eight grammes having been
dissipated in the air.

483. Mineral Classification of Plants. — The ashes of differ-
ent plants differ very much in their inorganic constituents.
A knowledge, therefore, of their composition in this respect,
derived from a chemical examination of their ashes, is very
important for an intelligent application of manures in rais-
ing different crops. The inorganic substances which are
found to predominate in the ashes of a plant must be con-
sidered as indispensable to its nourishment ; and if the soil
be deficient in them they must be supplied by the culti-

348 CHEMISTRY.

vator. If the soil be destitute of potash, neither turnips
nor grape-vines will grow well in it. If it be destitute of
lime, it will not answer for clover or pease. Liebig divides
all cultivated plants into three classes, according to the
chemical character of their ashes: I. Potash plants, the
ashes of which contain more than half their weight of salts,
having alkaline bases (potassium and sodium), soluble in
cold water. The beet, mangel-wurzel, and turnip belong
to this class. 2. Lime plants, the ingredients of which are
salts of lime and magnesia, soluble in acids. In this class
we have clover, beans, pease, tobacco, etc. 3. Silica plants,
in which silica predominates in the ashes. Wheat, barley,
rye, and oats are in this class.

484. Water in Plants. — In the processes of vegetation
water not only furnishes some of the material, but it is the
common carrier, as we may say, of all the other materials.
What is taken in by the roots and the leaves is carried to
all parts of the plant by the water. In doing this work
the water courses through the plant in larger quantity than
is commonly supposed. We can get some idea of this by
looking at the amount which is exhaled from the leaves of
plants into the air. Some investigations have been made
on this point. It was found that from the leaves of a sin-
gle cabbage there passed into the air nearly a quart of wa-
ter in twenty-four hours. With this great exhalation from
plants there must be a large amount of water passing up
from the earth through them in a rapid but quiet circula-
tion.

485. Annual Changes in Plants. — When annual plants
have stored up in their seeds a sufficient quantity of starch
and albuminous substance for the germs of a new race of
plants their work is done, and they fall to decay. But in
perennial plants, such as shrubs, fruit and forest trees, after
their fruit or seed has ripened, the woody fibre which has

VEGETATION. 349

been formed in the spring becomes harder by continued
woody deposit. At length, however, there ceases to be any
formation of wood, and in its stead starch is made, and dif-
fused through every part of the plant by the autumnal sap,
the buds of the next year being formed at the same time.
In the following spring this starch thus stored up is con-
verted into dextrine and sugar, from which the leaves and
tender branches are constructed, and the whole plant in-
creased in bulk.

QUESTIONS.

471. What is said of the dormant seed, and of its stimuli? What are
the constituents of the seed ? What changes do the stimuli effect in these ?
—472. What familiar examples have we of such changes? — 473. State the
contrast between the formation of the lead-tree and that of the root and
germ of the plant. From whence are the materials for their growth de-
rived?— 474. What is said of the supply of carbon to plants? — 475. What
of the sources of their oxygen and hydrogen ? What is said of the decom-
position of water in plants and in the laboratory of the chemist ? — 476.
Explain how plants can grow without earth. In what respects is their
growth defective, and why ? — 477. What is said of the nitrogen in the air
in relation to the supply of plants with it ? From what source is it sup-
plied, and how ? What is said of the presence of carbonate of ammonium
in the air? — 478. Give the summary in regard to growth and decay. — 479.
What is said of nitric acid as supplying nitrogen to plants ? — 480. What is
green manuring? How does it fertilize land?— 481. What is said of the
inorganic food of plants ? — 482. What of the ashes of plants ? — £83. Of
what use is the chemical examination of the ashes of plants to the culti-
vator? What are Liebig's three classes of plants ?— 484. What are the
offices of water in plants ? What is said of the quantity of water that
circulates in them ? — 485. WTiat provision is made by annual plants for
the following year ? What is the provision in perennial plants ?

350 CHEMISTRY.

CHAPTER XXVIII.

SOILS AND MANURES.

486. Soil the Food of Plants. — There is a striking analogy
between the root of a plant and the stomach of an animal.
In both there are minute absorbents which take up the
material for growth. As the food put into the stomach is
not all nutritious, and the absorbents take from it that
which is so, so also the soil, the food of plants, as it is min-
gled with the fine branches of the roots, has its nutritious
portion absorbed by the little mouths which are there ever
open to receive it. The root, therefore, may be regarded
as the stomach of the plant. The proportion of nutritious
substance is much greater in the food of the animal than in
that of the plant, and therefore the stomach of the latter is
a much more extensive organ than that of the animal.

487. Loosening the Soil. — As food put into the stomach
of an animal more readily furnishes its nutritious part to
the absorbents if it be well masticated, so it is with the
food of the plant. Hence the necessity of preparing the
ground for plants by plowing, digging, etc. ; and hencey
also, the usefulness of loosening the ground about plants
so well known to the gardener. One of the evils of an
abundance of clay in a soil is the close, compact character
which the clay gives to it. The cold of winter has much
influence in preparing the soil for the coming growth of
spring, for, as the ground freezes, the expansion of the wa-
ter, which is mingled up with its particles as it changes
into ice, separates these particles from each other, and thus

SOILS AXD MANURES. 351

loosens the compact soil. It is thought that earth-worms
are more beneficial than injurious, because the benefit which
they confer by loosening the soil is greater than the dam-
age which they do by extracting nutriment from it.

488. "Water in the Soil. — Food for either plant or animal
needs to be dissolved to be available, and the great solvent
is water. If a drought prevail plants languish, not because
there is a deficiency of nourishment in the soil, but because
there is not sufficient water to present the nutritious mat-
ter in good quantity to the absorbents, and to carry it up
in the tubes of the plants. You saw in § 484 that a large
amount of water is required for this. The solid matter of
nutrition must be carried along on a full tide in the chan-
nels made for it.

489. Soil as Generally Constituted. — Soil is commonly
made up of many substances mingled together, but derived
from two sources. The first is the rocks. The great bulk
of the soil conies from this source. This is very manifest
in gravelly and sandy soils, for in them a mere glance
shows you the broken pieces and grains which carrie from
the rocks. But it is true even of fine rich earth that the
most of it is mineral, and therefore that the rocks furnished
it. You can see this to be so if you take some earth in
your hand and examine it after it is dry. You will find
that the grains of stone predominate over the other ma-
terials. An analysis of the earth will develop the fact
more thoroughly, for two reasons. First, some of the in-
gredients from the rocks are dissolved in the water of the
earth ; and, secondly, some of them are very finely divided,
and therefore their mineral character is not manifest to the
naked eye. The second source of soil is the decay of veg-
etable and animal matters. All wood, leaves, bones, flesh,
etc., as they decay form a part of the soil.

490. Humus. — This second part of the soil is called hu-

352 CHEMISTRY.

mus. It is of a dark color, and hence fertile earth has a
darker color than sand. The substances forming humus
are chiefly those that are composed of carbon, oxygen,
and hydrogen, vegetable fibre as contained in wood, bark,
leaves, etc., being the principal. There is some nitrogen,
of course, in humus, from the juices of plants and the seeds,
and also from the decomposition of animal substances.
The immediate products of the decomposition of humus
are humic acid, so called, humic acid salts, carbonic acid,
water, ammonia, etc. The decomposition produces a good
effect mechanically upon the whole body of the soil, loosen-
ing it, and so making it mellow, as it is commonly termed.
Humus is also a great absorbent of water, swelling up as a
sponge, and this helps the mechanical effect produced by
the generation of gases by decay. Heat also is developed
by the chemical changes, which is often of very material
benefit when the soil is naturally a cold one.

491. How Soil was Originally Made.— All the soil, with
the exception of that portion of the carbon which has been
supplied from the air, and also the water which is diffused
in it, came originally from the rocks. There was a time
when there was nothing but rocks and water and air.
Some of the rocks became at length broken and ground up
by processes which the geologist describes, and thus was
furnished the soil on which the plants first grew. Soil be-
ing thus prepared, seeds were supplied by the Creator, the
plants from which, sending down their roots into the pow-
dered rock, took up there the soluble matters, and sending
up branches and leaves into the air, collected carbon there
with their outspread nets. And now the plants, decaying,
added humus to the soil, which, increasing year after year,
at length made the soil a fertile one. Besides those agita-
tions which break up and scatter fragments of rocks and
grind them to powder, there is another process, called

SOILS AND MANURES. 353

weathering, which is necessary in preparing the soil for
vegetation. This consists in the action of chemical forces,
in connection with heat and moisture, which not only aid
in the pulverization, but also render some of the materials
soluble, and therefore available for vegetation.

492. The Process Seen in Volcanic Countries. — The forma-
tion of soil is continually going on in all parts of the earth
in the manner indicated. It can be best seen in the neigh-
borhood of volcanoes. The lava that has issued from a
volcano lies barren for years; but the varying tempera-
ture, the water, and the oxygen of the air at length pro-
duce sufficient disintegration and chemical change to make
a soil for lichens. These succeed each other year after year
for generations, from which there is a gradual accumula-
tion of humus. This by its decay assists the other agencies
of disintegration, and so there is a yearly addition to the
soil on the rocky lava. Thus is preparation made for other
plants, and so the accumulation goes on till at length, per-
haps-in the lapse of centuries, the soil becomes deep enough
for shrubs and afterward trees. The various steps of this
process, thus briefly described, may often be observed in
deposits of lava of different ages in the neighborhood of
volcanoes.

493. Different Kinds of Soil. — In the agitations by which
rocks were broken up there was so wide a scattering of
the broken materials that the varied mineral ingredients
of soil are well mixed up in all parts of the earth. Still
there are peculiarities in soils here and there, owing to the
predominance sometimes of one and sometimes of another
mineral ingredient. For example, in the regions of lime-
stone formations there is apt to be a predominance of lime
in the soil. The three chief mineral ingredients of soil are
these: 1, Silica, in the shape of sand; 2, Alumina, mixed
or combined with sand, as clay ; and 3, Lime, in the form

354 CHEMISTRY.

of carbonate, as limestone, chalk, etc. Soils are named ac-
cording to the proportions of these ingredients. Thus if
an ordinary soil, dried, is found to contain but 10 per cent,
of clay, it is a sandy soil; if from 10 to 40 per cent, a
sandy loam ; if from 40 to 70, a loamy soil; if from 70
to 85, a clay loam; and if from 85 to 95, a strong clay,
fitted for making bricks. If a soil contains from 5 to 20
per cent, of carbonate of lime it is called a marl, and if
more than 20 per cent., a calcareous soil. Sometimes the
only difference in the character of two soils may be me-
chanical, while the one is barren and the other fertile.
Thus there are sandy soils in Ohio which for fifty years
have yielded, without manuring, eighty bushels of corn
to the acre, and yet they do not differ in chemical char-
acter, so far as inorganic matters are concerned, from sandy
soils in the Eastern States which are nearly barren. The
only difference discovered between the two soils is that
the barren consists mostly of coarse grains, while the other
is a very fine powder. Commonly, however, when there
is a marked difference in fertility, there is a considerable
difference in chemical composition.

494. Rotation in Crops. — The differences in soil are af-
fected by the crops which we raise. If, for example, a crop
be raised year after year upon a soil which contains in due
quantity a chemical ingredient particularly adapted to that
crop, the ingredient will be at length exhausted. Hence
comes the good policy of rotation of crops. Potassium
compounds are particularly needed in the raising of tur-
nips, but if turnips be cultivated on the same field year
after year, the potassium salts will finally become deficient,
and you will have poor crops of turnips. So, also, if pease
be raised successively on the same land, the soluble lime in
the soil will be at length exhausted. But change these
two crops on the two fields, and there will be no difficulty.

SOILS AND MANURES. 355

The turnips will flourish in the pea-field, because there is
plenty of potash there; and the pease will flourish in
the turnip-field, because the turnips have not used up the
lime.

495. Manures. — You have seen in § 486 what analogy
there is between the stomach of the animal and the root
of the plant. Let us follow out this analogy a little far-
ther. If we give an abundance of proper food to the ani-
mal it grows well, but with scanty and improper food it
becomes lean and languishing. So it is with the plant.
If its root be supplied in the soil with a proper amount of
those substances which are fitted for its nutrition, it grows
vigorously, and its leaves, flowers, and fruit are abundant.
The object of manures is to supply to the soil whatever of
these substances are deficient. In doing this we must have
regard to the kinds of food which different kinds of plants
need. There are certain substances the presence of which
in the soil is required by all plants in order to secure vig-
orous growth. But then in regard to many substances the
wants of plants are very different. A potash-plant, for ex-
ample, must have a soil that has considerable potash in it ;
while a lime-plant must have one that contains considera-
ble lime. If lime or potash be deficient where it is wanted,
it must be supplied in the form of manure. And the same
can be said of other substances.

The term manure is applied to any substance which acts
as a fertilizer. Sometimes such substances act indirectly
by producing some mechanical effect upon the soil, or by
modifying the action of other substances, instead of afford-
ing a direct supply of nutriment, as is generally done by
manures.

496. Chemical Knowledge Requisite. — In order to apply
manures appropriately we must know something of the
chemical characters of the soils, of the plants, and of the

356 CHEMISTRY. ,

manures. From a deficiency of this knowledge mistakes
are made continually by farmers. For example, lime has
been often applied where there was already enough of it,
as might be shown by a chemical analysis of the soil, and
so has proved, not merely a waste, but a positive injury to
the land. A very simple test will often give valuable in-
formation. Suppose, for instance, we take a pound of earth,
and after boiling it for some time in about a pint of water,
so that the lumps may be all destroyed, and the earth uni-
formly diffused in the water, introduce into the mass a strip
of blue litmus paper. If this after a little time turns red
it shows that the soil is sour, and that the humic acid in it
requires the application of lime to neutralize it. Chem-
istry may be made use of often by the farmer in discover-
ing rich materials for fertilizing his land. Beds of marl
have been found here and there which have proved of
great value as furnishing a fertilizer for certain soils. We
will quote here some remarks of Stockhardt on these dis-
coveries : " Probably such treasure still lies hidden in the
ground in many other places ; it appears only to require
the divining-rod to indicate where it lies, and the touch-
stone by which it can be ascertained whether it really is
what it appears to be. Yet both are close at hand : the
divining-rod is called 'look for it,' and a wine-glass of
'hydrochloric acid' serves as a touch-stone. How many
accidental opportunities the farmer has of penetrating a
little deeper than usual into the earth ! Here a well is
dug, or a ditch ; there a hill is leveled or cut through in
road-making ; in other spots a stone-quarry, a sand or loam
pit, is opened. These are all excellent opportunities — and
even deep -plowing' and ordinary work with the subsoil
plow not unfrequently furnish others — to make acquaint-
ance with the kind of earth lying beneath the cultivated
Boil. If an earth of different character is met with under

SOILS AND MANUKES. 357

the surface soil, a few drops of hydrochloric acid should be
poured upon a specimen of it; if this produces an efferves-
cence, it is a sure sign of the presence of carbonate of
lime, and the earth probably belongs to the useful kinds
of marl, which may then readily be ascertained more ex-
actly by a chemical examination."

497. Volatile Substances in Manures. — There are some
valuable substances in some manures which are volatile,
and the skill of the farmer is called in requisition to pre-
vent their flying off, or to fix them, as it is expressed. If
he carelessly leave his manure heaps to putrefaction, he
will lose a large part of some of their most valuable mate-
rial. He will lose, for example, much of the ammonia. It
will pass off into the air, and so will be lost to him, though
it will not be lost to the earth, for it will be brought down
by the rain. By losing it he will unwittingly benefit oth-
er farmers over a wide extent of territory, for the volatile
matter will be largely diffused. There are means of fixing
the ammonia, which are applied sometimes in the manure
heap, and sometimes in the field with the manure as it is
scattered. These means will be noticed hereafter.

498. Animal Manures. — These are of two kinds — the sub-
stances composing the body of the animal, and the excre-
tions. They are generally the most valuable manures that
we have, for they contain, besides other ingredients, a con-
siderable amount of that very important element, nitrogen.
The excretions of different animals vary much according
to the kinds of food upon which they live. This is of
course to be taken into consideration by the farmer in the
application of these manures, and in the mixture of other
manures with them.

499. Guano. — This is the manure of sea-birds, which has
been accumulated during a long period of time in deep
layers upon uninhabited islands and rocks. There are im-

358 CHEMISTRY.

raense quantities of it in different parts of the earth. It is
calculated that the deposits of it in South and Middle Peru
amount to more than twenty millions of tons. The value
of this manure, when it is good, is very great. Its good-
ness depends upon the amount of nitrogen it contains lock-
ed up in its ammonia. Next to nitrogen, phosphoric acid,
contained in phosphate of lime, must be considered as the
most valuable constituent of guano ; but of so much more
value is the nitrogen than this, that we may lay it down as
a rule that the more of ammoniacal salts and the less of
phosphate of lime guano contains, the higher is its value.
Peruvian guano is better on this account than the guano
of Patagonia and that of Africa. The reason that these
latter have so small a proportion of ammoniacal salts in
them is that by exposure to the action of air and water
these salts have been to a great extent washed out. Guano
is deficient in potash, and therefore in its application wood-
ashes make a useful addition.

500. Tests of Guano. — Guano varies much in its char-
acter, and on account of its pecuniary value is often adul-
terated, hence it is well that certain plain tests of its chem-
ical composition should be known, that they may be applied
by buyers of the article. We will mention some of them.
1. Test by Combustion. — Put fifteen grammes of the guano
to be examined in an iron spoon, and hold it over some red-
hot coals until a white or grayish ash is left. The weight
of the ash, subtracted from that of the guano, gives you
the proportion of nitrogenous substance, for this has been
burned tip and volatilized, while the phosphate of lime
makes the ash. In this application of heat the odor differs
according to the character of the guano. That from a good
specimen is pungent, like the vapor from spirits of harts-
horn, while the odor from a poor specimen is like that of
singed hair. 2. Lime Test. — Put a teaspoonful of guano

SOILS AND MANURES. 359

into a wine-glass, and upon this a teaspoonful of slaked
lime, and, adding a few teaspoonfuls of water, shake the
mixture briskly. The stronger the smell of ammonia the
better is the guano, for the lime, by taking away the acids
that are united with the ammonia, sets that pungent sub-
stance free. 3. Vinegar Test. — If on pouring vinegar upon
guano a strong effervescence ensues, we infer that there
has been an intentional adulteration with carbonate of
lime. 4. Test with Hot Water. — Make a filter of blot-
ting-paper, folded together in the form of a cone, and put
it into a common funnel. Put into this fifteen grammes
of guano well dried, and pour upon it hot water as long as
it passes through of a yellow color. Now dry the filter,
and, weighing the dried powder which is upon it, you find
what proportion of the guano is dissolved, or, in other
words, what proportion of ammoniacal salts it contains, for
it is this part of the guano alone that is soluble.

501. Ammoniacal Salts. — The salts of ammonium, some
of which, as you have seen, are the principal source of the
fertilizing power of guano, are chiefly the chloride, or sal
ammoniac, the sulphate, the nitrate, the humate (formed
with the acid of humus), and the carbonate or salt of harts-
horn. These salts are present in stable manure, and in oth-
er fertilizing substances which furnish nitrogen to plants.
There is considerable ammonia in the gas-liquor which is
formed in the process of cooling and purifying the gas.
This liquor is very valuable for manure. There also is con-
siderable ammonia in soot, and hence this substance is a
good fertilizer.

502. Bone-Dust. — The powder of bones is an exceedingly
valuable manure, as you can readily see it would be from
observing the composition of bone. A bone is composed
of an animal part, gelatin, and a mineral part, nine tenths
of which is phosphate of lime, and one tenth the carbonate.

360 CHEMISTRY.

These two parts can be obtained separate from each other
by processes which are described in the first chapter of
Hooker's "First Book in Physiology." The gelatin is of
great value as a fertilizer for any crop because of the nitro-
gen which it contains ; and the phosphate of lime is espe-
cially favorable to the development of seeds, and therefore
bone-dust is peculiarly appropriate as a manure for grain-
fields. It is on account of this phosphate of lime that bone-
dust is so beneficial to dairy lands. Milk and cheese both
contain this substance. There is about half a pound of it
in ten gallons of milk. Bone-dust is also an excellent ma-
nure for wheat; for though this is a silica plant (§ 483),
the presence of phosphates in the soil is essential to the
formation of the seeds. If the soil be rich in silicates but
deficient in phosphates, excellent straw will be obtained,
but the grain will be small in amount : it will be a crop
better calculated to make bonnets than bread. It is calcu-
lated that 1 cwt. of bone-dust is equal to 25 or 30 cwt. of
stable-manure. Although bones contain such fertilizing
materials, they must be well pulverized in order that they
may be immediately available for the nutrition of plants.
It often takes even twenty or more years for the soil to
disintegrate fragments of bone of the size of a hazel-nut
or a pea, and yet such fragments arc frequently seen in the
bone-dust of commerce.

503. Lime. — While guano, bone-dust, stable-manure, etc.,
act as direct nutrients, giving actual substance to the plant,
the action of lime is for the most part indirect. It acts in
many ways. In some cases its chief effect upon the soil is
mechanical, rendering it loose and porous. In other cases,
as stated in § 496, it neutralizes the acidity of the soil, and
thus makes it fertile. In still other cases it excites a more
rapid decay of the humus, and thus provides more nutri-
tious matter in the soil for the plants. And still again it

SOILS AND MANURES. 361

does good service often in aiding the weathering (§491) of
the mineral substances in the soil, and thus acts as a sol-
vent for matters which the plants need but can not get un-
less they are dissolved. The direct manures, you observe,
act with their own power, and furnish some of their own
material to plants ; but lime, on the other hand, does not
work with its own material, but at the expense of other
matters in the soil. Lime, therefore, tends eventually to
make the soil poorer unless other manures are applied at
the same time, and hence the maxim current among the
Belgian farmers :

"Much lime and no manure
Makes both farm and farmer poor."

504. Marl. — "VYe have alluded to this manure in § 493.
Marl is a lime mud which was deposited in the last over-
flowings of the surface of the earth in its preparation for
man. It is sometimes tolerably pure, but is commonly
mingled with clay, stones, shells, etc. The lime in it is in
the form of carbonate. Its effects upon soils are very
similar to those of quick-lime, just described. There are,
however, other substances mingled with the carbonate of
lime, which modify its effects, and render the marl more
valuable as a fertilizer than it otherwise would be. Yet
these are so small in amount that the Belgian proverb is
nearly as true of marl as it is of lime.

505. Gypsum. — The fertilizing properties of sulphate of
lime were known in Europe long before they were in this
country. Franklin, when abroad, was struck with the rich-
ness of the crops raised in fields manured with gypsum, and
endeavored to persuade American farmers to use it, but in
vain. To convince them of the truth of his statements he
resorted to the following expedient : He strewed gypsum
on a sloping field in such a way as to form in enormous
letters the words Effects of Gypsum. The abundant growth

362 CHEMISTRY.

on the part so prepared, making the letters legible to every
passer-by, brought the new manure at once into popular
favor. There has been much dispute as to the manner in
which gypsum acts as a fertilizer. One thing is quite set-
tled about it — it answers a good purpose infixing the am-
monia in the soil. This is effected by a double decompo-
sition between the sulphate of lime and the carbonate of
ammonium, the result being carbonate of lime and sulphate
of ammonium. In this connection we will mention that sul-
phuric acid is often used for fixing ammonia in manures,
forming with it a sulphate, which is not volatile like the
carbonate.

506. Vegetable Refuse. — In every garden and on every
farm all vegetable matter which is useless should, so far as
it can be done, be made to add to the stock of humus by
its decay. It is convenient to have in a garden a pit into
which all weeds, small trimmings, etc., can be thrown,
where, covered up, they may be left to decay, forming rich
humus. The decay may be hastened by the occasional ad-
dition of some lime. On most farms there is a large quan-
tity of vegetable matter left to decay on the surface of the
ground, and thus waste by volatilization a part of its fer-
tilizing material. This refuse might be of great value if
gathered up and mingled in a compost heap with other
materials.

507. Sewer- Water. — This always contains a great variety
of fertilizing substances, and therefore is one of our most
valuable manures. Yet it is very generally wasted. Vast
quantities of it in our towns and cities run off into the wa-
ter, where it is not only lost, but sometimes does much
harm. The water of the River Thames is becoming more
impure every year from this cause. It is calculated that
the London sewers pour into it fertilizing materials of the
annual value of over half a million pounds sterling. Great

SOILS AND MANURES. 363

attention has been attracted to this subject, and plans have
been broached for avoiding this enormous waste.

QUESTIONS.

486. State the analogy between the stomach of an animal and the root
of a plant. What is said of the difference in the proportion of nutritious
substance ? — 487. State the analogy in regard to loosening the soil. What
influence has clay upon soil ? What effect has the cold of winter upon it ?
What is said of earth-worms ? — 488. What of water in the soil ? — 489.
From what source comes the principal part of the soil ? In what two ways
can you see what its chief source is ?— 490. What is the second source of
the soil ? What name is given to the product from this source ? What
is said of its chemical character ? What are the products of its decompo-
sition ? What mechanical effect does this decomposition produce ? What
other effect is mentioned ? — 491. State in full how soil was originally made.
What is weathering ? — 492. Describe the process of making soil as seen in
volcanic countries. — 493. How are peculiarities in soil produced? What
are the three chief mineral ingredients in soil ? What are some of the dif-
ferent soils made by different proportions of these ingredients ? What is
said of the mechanical differences of soils ? — 494. What is said of the rota-
tion of crops ? — 495. Follow out the analogy between stomachs and roots
in regard to amount of food. WThat is the object of manures ? What cir-
cumstances should govern the selection of the kind of manure ? What is
said of the term manure, and of the modes in which manures act ? — 496.
Illustrate the truth that a knowledge of chemistry is necessary to a suita-
ble application of manures. What opportunities often offer for ascertain-
ing the chemical character of subsoils ? What is said of hydrochloric acid
as a test of the character of soils ? — 497. What of the management of vola-
tile substances in manures ? — 498. What of animal manures ?— 499. What
is guano ? What is said of its abundance ? What are the chemical in-
gredients that give it its value ? Why is the guano of Peru better than
that of Africa and Patagonia ? Why are wood-ashes a good addition to
guano when used ? — 500. State the test of guano by combustion. State
the lime test. The vinegar test. The test with hot water. — 501. What
are the ammoniacal salts present in various manures? What is said of
gas-liquor?— 502. What is the composition of bone? What is said of the
fertilizing powers of the ingredients ? What of their use in regard to dif-
ferent crops ? What of the value of bone-dust ? What of its degree of

364 CHEMISTRY.

pulverization ? — 503. How does lime differ from most other manures in its
action? Give the maxim in regard to lime, and the ground for it. — 504.
What is marl ? What is said of its effects on soils ? — 505. Give the anec-
dote of Franklin in regard to gypsum. What is said of the manner in
which gypsum acts as a fertilizer ? — 506. What is said of vegetable refuse ?
—507. What of sewer-water?

CHAPTER XXIX.

OILS AND FATS.

508. Acids. — The common idea that acids are sour bodies
must now be given up, for under this head are included
many oily and fatty substances which do not react acid
at all. The sources of organic acids are exceedingly vari-
ous; thus formic acids can be extracted both from red
ants and from nettles ; acetic acid is a product of fermen-
tation, as you will learn in the next chapter ; butyric acid
is contained in rancid butter, palmitic acid in palm-oil,
stearic acid in tallow, and melissic acid in beeswax. These
form part of a series called the Fatty Acid Series.* The
first one is a liquid, with a low boiling-point ; the rest in-
crease in density, becoming oily and finally solid. The
first acids of this series mix with water, but the last acids
are quite insoluble in water; thus a gradual transition of
properties is noticeable, and their formulae become heavier
and more complex as you ascend the series. Formic acid
is CH2O2, acetic acid C2H4O2, etc., while the last named,
melissic acid, has the formula C30H60O2.

There are many other acids which do not belong in this
series, also derived from various sources ; thus tartaric acid

* See last column in Table on page 303.

OILS AND FATS. 365

is found in grapes, citric acid in lemons and some other
fruits, malic acid in apples, lactic acid in sour milk, etc.

These organic acids form salts by replacement of hydro-
gen with a base just like the mineral acids. In fact the
acids mentioned as found in fruits do not exist as such,
but combined with potassium, sodium, or possibly calcium.
Thus in the case of tartaric acid it is combined with potas-
sium in the plant. Acid potassium tartrate, or so-called
cream of tartar, is gradually deposited in wine-casks from
the wine, and this is one cause of the improvement of wine
by age. Rochelle salt is a double salt — a tartrate of potas-
sium and sodium. So tartar emetic is a tartrate of potas-
sium and antimony. Then there is a double tartrate of
potassium and iron, which is a valuable medicine.

Many of the organic acids char on heating, owing to the
imperfect combustion of the carbon. If they are heated
more strongly complete decomposition ensues, just as in
the case of wood, sugar, etc. This distinguishes them in
their reactions from the mineral acids.

509. Tannic Acid. — This body is not a true acid, and
strictly belongs to another group of bodies called gluco-
sides, but it is of so much importance in many ways in the
arts that it should not be passed by. It exists extensively
in the bark of many trees, as the oak, horse-chestnut, hem-
lock, birch, etc., and is also found in some roots, and in the
leaves of roses and pomegranates. It exists most abun-
dantly in the gall-nut of the oak. Here we have a valuable
vegetable product as the result of disease, for the gall-nut is
a morbid growth which comes from the wound of an insect
made in the oak for the purpose of depositing its eggs.*
Tannin, as this body is commonly called, is a very astringent
substance. By the decomposition of tannic acid another

* See Hooker's "Natural History," page 270, for further particulars.

366 CHEMISTRY.

acid called gallic acid is obtained, and then by the decompo-
sition of this latter several other acids can be produced.

510. How Obtained. — The mode of obtaining tannin is as

follows: Into a globular funnel, 5, Fig. 115,
which can be closed at the top by a stopper,
is introduced a quantity of powdered nut-galls
after the tube of the funnel, c, has been stopped
with a little cotton. The funnel is then placed
in the bottle, a, and is filled up with the ether
of the shops, which is about one tenth water.
The apparatus being allowed to stand several
days, there appear two layers of liquid. The
lower one, which is as thick as sirup, is a con-
centrated solution of the tannin in water, with
very little ether in it, while the upper is ether containing
a mere trace of tannic and gallic acids. The theory of
this process is that the tannin has such a greedy affinity
for water that, as the liquid passes through the powder,
the tannin in it seizes the water, withdrawing it from the
ether. The tannin is obtained from this sirup-like solution
by evaporation.

511. Tanning. — In the common process of tanning the
tannic acid in the bark is the effective agent. It is a chem-
ical union of this acid with the gelatin of the skin that
converts the skin into leather. This combination prevents
the decay or putrefaction which would otherwise take place
in the skin, just as the chemical union of corrosive subli-
mate with the albumen of the wood in kyanizing prevents
the decay of the wood. A black color is given to the leath-
er by washing it with a solution of iron, the tannin of the
leather imiting w^ith the iron to form a tannate of iron.
The reason that drops of tea upon a knife-blade become of
a dark color is that the tannic acid in the tea forms a tan-
nate with the iron.

OILS AND FATS. 367

512. "Writing-Ink. — Common writing-ink is prepared from
nut-galls and ferrous sulphate. A solution of the tannic
acid is obtained by boiling the galls in water, and this is
mixed with a solution of ferrous sulphate. A feriws tan-
nate results, which makes a very pale solution ; but by ex-
posure to the air the tannate becomes more highly oxidized,
and thus changes to a feme tannate, which is of a very
dark color. It is desirable, for the permanency of the writ-
ing, that this change should take place in part in the fibres
of the paper, and not wholly in the ink before it is used.
The ink is, therefore, bottled, and thus shut in from the air
before the change is completed, so that when used in writ-
ing it may be rather pale, and become gradually dark on the
paper. To keep the tannate from settling gum is added to
the ink, and to prevent moulding oil of cloves or creosote is
introduced in small quantity. Corrosive sublimate is a very
effective preventive of moulding, but it is obviously danger-
ous to employ it with the ordinary careless habits of people
in using ink. It is from the action of tannin on ferrous sul-
phate and other salts of iron that it is used in dyeing.

513. Oils and Pats. — These substances are found widely
distributed in both the vegetable and the animal kingdoms,
and are constituted very much alike in both. In plants
they are generally contained in the investing membranes
of seeds or in the cellular substance of fruits. There is sel-
dom any fatty matter in leaves or in roots. The principal
vegetable oils and fats are as follows : Linseed-oil, which is
pressed out from flax-seed ; Olive-oil, from the pulp of the
fruit of the olive-tree; Palm-oil, a yellow fat, similar to
butter, from the fruit of a species of palm-tree; Castor-oil,
from the seeds of the castor-oil plant ; Butter of Cacao,
the tallow-like fat of the cacoa-nut, the cause of the fat
particles which rise on boiled chocolate; Hemp-oil, from
hemp-seed, etc. Oils can also be obtained from pumpkin-

368 CHEMISTEY.

seeds, walnuts, sunflower-seeds, hazel-nuts, even apple-seeds,
plum and cherry stones, etc.

514. Composition. — The oils and fats are composed most-
ly of three ingredients, called stearin, palmitin, and olein.
The stearin, when separated from the others, is a solid at
all ordinary temperatures, while the olein is a liquid ; the
palmitin is midway between the other two. In very cold
weather, when a portion of lamp-oil becomes solidified, we
have a partial separation between the stearin and the
olein. The consistency of fatty substances depends upon
the proportions of olein and stearin in them, the former
predominating in the liquid, and the latter in the more
solid bodies. But these constituents of fats are far from
being simple substances. They are compounds formed by
the union of acids with a certain b.ase or radical called
glyceryl. Thus stearin is a combination of stearic acid
with this base, a glyceryl stearate, just as pearlash is
potassium carbonate. Likewise olein is glyceryl oleate.
Bodies formed after this pattern are called salts in organic
chemistry just as in mineral chemistry, the only real differ-
ence being that the radicals and the acids in one instance
are far more complex than in the other. This the formula)
for stearin, palmitin, and olein show :

Glyceryl, a hydrocarbon radical, (C3H5)'"

Stearin, or glyceryl stearate, (C3H5)"'(C18H3502)3

Palmitin, or glyceryl palmitate, (C3H5)"'(C16H31O2)3

Olein, or glyceryl oleate, (C3H6)'"(C18H33O2)3

515. Glycerin. — This is a colorless, sirupy liquid, of a
sweet taste ; this latter quality gives it its name, which is de-
rived from a Greek word — glukus^ sweet. It belongs to the
class of bodies called alcohols, but is described in this con-
nection because it is a product of the decomposition of oils
and fats. It is a hydrate of glyceryl, and has the formula
C3H5(IIO)3.

OILS AND FATS. 369

Glycerin is soluble both in water and alcohol. It can
be obtained by boiling stearin and olein with a solution
of potassium hydrate. The fat (or stearin) is decomposed
by the substitution of potassium for glyceryl, and the re-
sulting products are potassium stearate and glyceryl hy-
drate or glycerin. We will explain this further in the
section on soaps. Glycerin has remarkable solvent powers,
dissolving readily the greatest variety of substances, min-
eral and organic. Nitrogtycerin is a powerfully explosive
oily liquid, made by the action of nitric acid on glycerin,
much as in the case of gun-cotton. It is very dangerous to
manufacture and to handle, and at the same time very use-
ful for blasting rocks. Mixed with porous silica and some
other substances it is called Dynamite.

510. Candles made of Stearin and Stearic Acid. — Stearin
may be obtained from lard and tallow by a simple process.
If the fat be melted, as it cools it hardens, forming a mass
from which the fluid olein can be pressed out, leaving the
stearin alone by itself. The stearin is used for making can-
dles, while the expressed olein is the well-known lard-oil.
But a better material for candles can be obtained by de-
composing the stearin with lime, thus forming a stearate of
lime, and then decomposing this with sulphuric acid. In
this way we obtain stearic acid, for the sulphuric acid takes
the lime away from the stearate of lime, and thus sets the
stearic acid free. This acid is a white, crystalline, translu-
cent substance with a brilliant lustre. It is a better ma-
terial for candles than stearin, because it is not so readily
softened by heat, its melting point being about ten degrees
higher than that of stearin.

517. Soaps. — In the preparation of glycerin, described
in § 5 15, we did not tell you any thing about the potassium
stearate which was produced along with the glycerin ; this
substance is soap. Soap, then, as well as oils and fats, is a

370 CHEMISTKY.

true chemical salt. In the manufacture of soap, lime, so-
dium hydrate, or potassium hydrate may be used ; calcium,
sodium, or potassium stearate being formed. Natural fats,
however, are composed of stearin, palmitin, and olein, con-
sequently the soaps are mixtures of stearates, palmitates,
and oleates of the bases named, and not pure stearates.
If we consider the formation of only one of these bodies,
it can be expressed in a rather complex equation, thus :

Caustic soda or Olive-oil or Gn^- , i i rn

Sodium hydrate. Glyceryl oleate. Sodmm oleate' Glycerin.

3(NaHO) + (C,H.)"/(C18H,,01), = 3(NaC19H33O2) + (C3H5)"'(HO)3

518. Hard and Soft Soap. — Hard soaps are formed by
soda, and soft by potash. A potash soap can be converted
into a soda soap by means of common salt. This is often
done by soap-makers on a large scale. The soft soap is
dissolved in boiling water, and salt is thrown into it.
There is a collection of soda soap on the surface of the wa-
ter, which on cooling becomes hard. The chemical change
is this : The chlorine of the salt goes to the potassium of
the soap, forming potassium chloride, while its sodium goes
to the stearic and oleic acids to form stearate and oleate
of sodium.

The cleansing power of soap in washing depends chiefly
upon the fact that the water used with them sets free some
of the alkali from its combination with the fatty acids, so
that we have a mixture of caustic alkali and fat-salts, the
alkali by its union with the greasy matters in the cloth
cleansing it, and the salts — the stearate and oleate — by their
lubrication, keeping the cloth pliant, and thus making the
operation easy. The alkali would not answer alone, be-
cause it would by shrinking the fibre of the cloth render it
rigid, and thus prevent its perfect cleansing, and at the
same time would injure it .by its too great causticity.

Alcohol dissolves soaps, and the common soap liniment

OILS AND FATS. 371

is a solution of soap in alcohol. Camphor added to this
makes the liquid opodeldoc. Volatile liniment is a sort of
soapy mixture made of oil and the volatile alkali ammonia.
Equal parts of lime-water and sweet-oil make a soapy mixt-
ure which is one of our best applications for a burn. A
solution of ammonia in alcohol is very effective in remov-
ing grease spots from woolen clothes, because it unites with
the grease to form a soap, which readily washes out with
the application of a little \vater.

519. Properties of Fats. — Fatty or oily substances have
some peculiar properties which fit them for many valuable
uses. They spread readily in the pores of substances, and
as they are not volatile they answer a valuable purpose in
keeping leathern and other articles soft and pliable for a
long time. As the fats float upon water, they can be used
for excluding air from various substances, thus preserving
them from chemical change. Thus a layer of oil is some-
times poured over preserved fruits. As the fats are not
only insoluble in water, but have a sort of repulsion for it,
they are extensively used for preserving substances from
being penetrated by water. Shoe-leather is rendered im-
pervious to water by greasing. Iron is oiled to protect it
from the damp air, and thus keep it from rusting. Tim-
bers saturated writh oil will be preserved a long time from
rotting in the damp earth.

520. Varnish Oils.— All fatty substances on exposure to the air grad-
ually absorb oxygen and evolve carbonic acid; and as there is always a cer-
tain amount of nitrogenous substance in them, a sort of fermentation occurs,
producing acids, and thus making the fats rancid. There are some oils,
however, that instead of changing thus gradually in the air, absorb oxygen
rapidly and become dry and hard. These drying oils are called varnish
oils, because they are so much used in mixing varnish. Linseed-oil is one
of the most important of them. It is prepared for varnishing by freeing it
from all mucilaginous matter by heating -it with litharge or oxide of lead
in it, and mixing it, after this clarifying, with some coloring substance.

372 CHEMISTRY.

Oil-cloth is cotton cloth covered with colored varnish, and oil-silk is var-
nished silk. Drying oils are used in painting, and mixed with lampblack
they constitute printers' ink.

521. Spontaneous Combustion. — It is because of the rapid
absorption of oxygen from the air that the drying oils are
sometimes the cause of spontaneous combustion. This com-
monly occurs in waste thrown together in a heap. The
heat produced by the absorption of the oxygen sets fire to
the combustible substance — cotton or linen or woolen — that
is impregnated with the oil, and the oil, being itself com-
bustible, burns also. The reason that the heat is adequate
to produce this effect is that it is so shut in among the
parts of the heap where it is generated that it accumulates,
reaching at length the point of combustion. The oil in
drying always produces heat; for condensation of a gas, as
it combines with a fluid or solid substance, can not take
place without this effect ; but the heat in all ordinary cir-
cumstances quietly escapes into the air as fast as it is pro-
duced. In the drying of paint upon any surface heat is
formed at every point of it, but it produces no combustion
because it escapes instead of accumulating.

522. Combustion of Fats. — As both the fat acids and their
base, glyceryl, are compounds of carbon, oxygen, and hy-
drogen, we have in them the same elements as in wood
and coal, and therefore their combustion is attended with
the same phenomena and the same results. The facts stated
in Chapter X. fully illustrate this, and we need not dwell
upon the point here.

523. Wax. — This substance has so decided a resemblance
in some respects to the fats that it may be classed with
them. It is a mixture of two substances — cerin and myri-
cin. A soap can be formed with cerin by boiling it in a
solution of potassium hydrate. Wax occurs in small quan-
tity in all plants. It gives a shining appearance to leaves,

OILS AND FATS. 373

stalks, and fruits, which in some cases is very decided.
Some plants in South America and China contain so much
wax that it is obtained from them by boiling and pressure,
and is sold under the name of vegetable or Chinese wax.
But most of the wax in use in the world is made by bees.
It has been supposed that the bees simply gathered the
wax from flowers as it exists in the pollen; but this is
certainly not true in regard to all of it, for it has been sat-
isfactorily proved that the bees actually convert the sug-
ary substance into wax in their abdominal sacs.

524. Volatile Oils. — The oils which we have already no-
ticed are called faced oils, because they have no tendency
to pass off into the air. The volatile oils, of which oil of
turpentine, oil of peppermint, and oil of lemons are familiar
examples, nearly all possess the same chemical composition
— C10H16 ; they differ from the fixed oils in three important
respects : 1. As their name imports, they are readily dissi-
pated in the air. Some of them are exceedingly volatile.
Sometimes a volatile oil is adulterated with some fixed oil;
but this can be readily detected by dropping some of the
specimen on paper, for if it be adulterated it will leave a
grease spot upon it. 2. Volatile oils dissolve in alcohol.
Such solutions form the bases of essences and cordials and
perfumed waters, such as the Eau de Cologne. 3. They are
hydrocarbons, and not salts of fatty acids like the fixed oils.
The volatile oils are very numerous, as you -may readily
see from the fact that all the varied odors of plants are
due to their presence. They are most frequently pro-
duced in flowers and seeds, sometimes in the stalks and
leaves, and in some plants in the roots. Sometimes there
are several sorts of oil in the same plant. Thus there are
three different kinds of oil in the orange-tree — one in the
leaves, another in the blossom, and still another in the peel
of the fruit.

374 CHEMISTRY.

525. Composition. — The volatile oils are divided into
three classes, according to their composition: 1. Oxygen-
ated oils. These, which are by far the most numerous class,
are composed of carbon, hydrogen, and oxygen. 2. Non-
oxygenated oils, which are composed only of carbon and
hydrogen, and are therefore called hydrocarbons. The
principal of these are the oils of turpentine, savin, juniper,
lemons, etc. 3. Sulphuretted oils, which are composed of
carbon, hydrogen, and sulphur. Nitrogen is a component
of some of them. These oils exist in mustard, horseradish,
garlic, onions, hops, etc. They have a very pungent smell,
causing lachrymation, and are so acrid that they raise blis-
ters when applied to the skin.

526. Camphor. — Camphor is obtained by distilling with
water the wood of the laurus camphora. This forms when
pure a white, crystalline, translucent solid, having a pecul-
iar odor which is familiar to every one. It gradually sub-
limes at ordinary temperatures, and often forms beautiful
crystals on the sides of the bottles in which it is kept.

527. Resins. — Where an essential or volatile oil is ex-
posed to the air, a part of it evaporates, diffusing an odor,
but a part combines with the oxygen of the air, forming a
resin. The pure rosin, or colophony, is thus produced from
the oil of turpentine. It is really a mixture of two acids.
This oxidation is, however, only partial, so that the turpen-
tine when gathered is a mixture of the oil and the resin.
Some of the resins are called balsams. The resins are very
indestructible, and have also the power of preserving other
substances from decay. The mummies found in the pyra-
mids of Egypt are bodies which were embalmed with res-
ins. Amber furnishes the most striking illustration of this
indestructibility. This resin was formed in the early ages
of the world, it having survived the destruction of the trees
from which it exuded. Insects are often seen inclosed in

OILS AND FATS. 375

pieces of it, embalmed, as we may say, centuries upon cent-
uries before the Egyptians lived whose mummies are found
in the pyramids.

528. Uses of the Resins. — The resins are chiefly used for
making varnishes. In spirit varnishes the solvent is alco-
hol ; in oil varnishes it is some drying oil. As the resins
are soluble in fat oils, they enter into the composition of
many ointments and plasters. Sealing-wax is mostly the
resin called shellac, with a little turpentine to make it melt
and burn more readily, and some cinnabar, lampblack, or
other substance to color it.

529. Caoutchouc and Gutta-Percha. — These are mixtures
of several hydrocarbons, and are in their composition very
much like turpentine oil. The caoutchouc is the milky
juice which exudes from incisions made in several kinds
of large trees in South America. This, when left to dry in
the air, becomes a white elastic mass. The drying is more
rapid when the exuded substance is spread upon moulds
of clay and suspended over a fire, as is commonly done.
The soot, which thus becomes incorporated with it, gives
it a dark color. Gutta-percha is obtained from certain trees
in the East Indies. Like the caoutchouc, it exudes as a
milky juice. It differs from caoutchouc in three respects
— it is very tough, has little elasticity, and becomes soft
and plastic with a moderate heat, hardening again as it
grows cool. This difference in properties fits these two
substances for different uses in the arts.

530. Vulcanized India-Rubber. — This substance is a com-
pound of sulphur and caoutchouc, which has received pecul-
iar qualities from being subjected to a certain degree of
heat. Unless this be done it is too soft for use. Shoes
and other articles of this material are therefore, after being
made, brought up to the required temperature, and on cool-
ing they have the two qualities of firmness and pliability.

376 CHEMISTRY.

The discovery of this effect of heat, so important in the
manufacture of India-rubber goods, is said to have been
made by our countryman, Goodyear, in consequence of an
accidental circumstance. As he was talking earnestly with
a friend, in making a gesture he threw into the tire a bit of
the compound of sulphur and caoutchouc. On taking it out
of the fire he observed that its properties were essentially
altered, and this observation led to experiments which re-
sulted in the discovery alluded to, and to its wide applica-
tion in the India-rubber manufacture.

531. Vegetable Alkaloids. — There are certain organic
bases, that is, bases which are extracted from the seeds,
bark, roots, and other parts of plants. They are called al-
kaloids, because, like the alkalies, they produce a basic re-
action on red litmus paper. We will mention a few of the
most prominent of them. There is morphine, which we
get from opium, and quinine, which we get from the cin-
chona bark. Caffeine, or theme, is the alkaloid found both
in the leaves of the tea-plant and the berries of the coffee-
plant. Strychnine, which is so exceedingly poisonous, is
obtained from the seeds of the strychnos mix vomica.
Nicotine is found in tobacco. It is an oily, colorless sub-
stance, which is so poisonous that a fourth part of a drop
will kill a rabbit. Most of these bases are crystalline, and
the crystals of some of them are beautifully delicate. Thus
the crystals of caffeine are fine white prisms of a silky lus-
tre ; and those of piperine, the active principle alike of
white, black, and long pepper, are white and needle-shaped.
Most of the organic bases, like the inorganic, unite with
acids to form salts. Thus morphine and quinine unite with
sulphuric acid to form sulphates.

The formula of these bodies are very complex. They all
contain nitrogen, however, besides C, H, and O, and belong
to the class of bodies called Amines, as mentioned in § 425.

OILS AND FATS. 377

What the organic radicals are of which these alkaloids are
composed is not definitely known. "When the exact con-
stitution of quinine, for instance, is discovered, it will be pos-
sible to prepare it artificially, instead of extracting it from
cinchona bark. This discovery will be of immense impor-
tance, and will doubtless prove a fortune to the happy dis-
coverer.

532. Coloring Matters. — There is a great variety of these
in the vegetable world. A portion of them are composed
of C, H, O, and N, but some of them contain no N. The
former are called nitrogenous because they contain nitro-
gen, and the latter non-nitrogenous. The principal of the
latter class are madder, hematoxyline, which is the color-
ing principle in logwood, Brazil-wood, and camwood, gam-
boge, etc. Indigo is the most important of the nitrogenous
class. This is derived from the juice of several species of
the plants called indigofera. The indigo is not, however,
of a blue color in the plants, but is almost colorless. It ac-
quires the brilliant blue color that we see it have by a fer-
mentation, to which the leaves of the plants are subjected
in the extraction of the indigo. Blue indigo is, therefore,
oxidized indigo, and by depriving it of its oxygen we can
restore it to its colorless state. When thus deoxidized it
is soluble, as it is in its natural state in the plant; but by
exposure to the air it absorbs oxygen rapidly, and so be-
comes blue and insoluble. The blue litmus, so much used
by the chemist in testing acids and bases, is a nitrogenous
coloring matter which is derived from certain lichens. Al-
most the only coloring matter of animal origin is cochineal
— an insect. The color from this insect is called carmine.

533. Mordants. — Some coloring matters have such an
affinity for the substance of cloth that they will unite inti-
mately and firmly with the fibres, and so make fast colors.
But some have not this power. In order to fix the colors

378 CIIEMISTKY.

in such cases, some substance must be employed which has
a strong attraction for both the coloring matter and the
substance of the cloth, and can therefore unite the two firm-
ly together. Such a substance is called a mordant, for rea-
sons already given. The cloth to be dyed is first charged
with the mordant, and then is immersed in the dye.

534. Colors Modified by Mordants. — The mordant not
only fixes the color, but modifies it, so that with different
mordants different colors can be produced with the same
dye. Thus, by using with madder the acetate of aluminium,
produced by mixing common alum with acetate of lead, a
red color is obtained ; but if ferrous sulphate be mixed with
the acetate of lead instead of the alum, a deep black color
is the result. Then, again, if some arsenious acid be added,
together with the ferrous sulphate, the madder gives a rich
purple color. Now all of these madder colors can be pro-
duced upon the same piece of calico by printing the different
figures with different mordants before introducing it into the
dye. The printing is done by rollers, between which the
calico is passed. These rollers are engraved with the fig-
ures, and the pastes containing the mordants are each put
upon its appropriate set of rollers. The calico is passed
through the several sets successively. After all the mor-
dants are thus printed upon the cloth it is immersed in the
dye. The process is not finished yet, for the common color
of the madder is in all those parts of the cloth not touched
by the mordants. But the color is not fast, and is easily
washed out, leaving a white ground, the washing out not
affecting at all the colors fastened by the mordants.

QUESTIONS.

508. Why must the common idea that acids are sour be abandoned ?
Name some of the sources of organic acids. What is said of the proper-
ties of the members of the fatty acid series ? In what conditions do the

OILS AXD FATS. 379

acids of fruits, etc., exist in the plant? How may some organic acids be
distinguished from mineral acids ? — 509. From what sources is tannic acid
obtained ? What is its character? What is said of the products of its de-
composition ? — 510. Describe the mode of obtaining it. — 511. What is tan-
nin ? To what is it compared ? Give the chemical explanation of the
black color of leather. Why do drops of tea on a knife-blade become
dark? — 512. Explain the common mode of making writing-ink. What is
said of securing permanency in writing ? What substances are added to
ink, and for what purposes ? — 513. In what parts of plants are oils and fats
formed ? Name some of the principal ones, with their sources. — 5U. What
is said of their composition ? What is stearin ? Olein ?— 515. What are the
properties of glycerin ? To what class of bodies does it belong ? What is
nitroglycerin ? What is dynamite? — 516. How can stearic acid be ob-
tained ? Of what are candles best made ? — 517. What is soap, chemically
considered ? Explain the action of caustic soda on olive-oil. Of what are
natural fats composed ?— 518. What is the difference between hard and soft
soaps ? Upon what does the cleansing power of soap depend ? Mention
some of the uses of soap. What is the best application for burns? — 519.
What is said of the properties of fats, and of the uses to which they are ac-
cordingly applied ? — 520. How do fats become rancid ? What are varnish
oils? How is linseed-oil prepared for varnishing? What are oil-cloth and
oil-silk? — 521. State in full what is said of spontaneous combustion. —
522. What is said of the combustion of fats ? — 523. What are the nature
and composition of wax ? What is said of its occurrence in plants ? What
of its preparation by bees ? — 524. How do volatile oils differ from fixed ?
How can adulteration of a volatile with a fixed oil be detected? In what
parts of plants are the volatile oils found ? — 525. Give the three classes of
volatile oils, and what is said of them. — 526. What is said of camphor? —
f>27. What are resins ? What is said of their indestructibility ? — 528. What
of their uses ? — 529. What is said of caoutchouc ? What of gutta-percha ? —
530. What of vulcanized India-rubber. — 531. What are vegetable alkaloids?
Mention some of them, and the sources from which they are obtained.
What is said of their crystals? What of their composition? — 532. What
are the two classes of coloring matters ? What is said of indigo ? — 533.
What is said of mordants? — 534. What is said of modifying color by mor-
dants ? In what way can different colors be put upon the same piece of
calico ?

380 CHEMISTRY.

CHAPTER XXX.

FERMENTATION.

535. Different Kinds of Fermentation. — The word fermen-
tation is applied to various decompositions and changes
which occur in organic substances. We have the alcohol-
ic fermentation, producing alcohol; the acetous, producing
vinegar, etc. It is of these two kinds that we shall speak
in this chapter. By the alcoholic fermentation sugar is
converted into alcohol, and by the acetous alcohol is con-
verted into acetic acid, the sour principle of vinegar ; or,
strictly speaking, alcohol is made from sugar, and acetic
acid from alcohol.

Putrefaction and fermentation are really the same thing,
only the former name is given to the decomposition when
accompanied by an offensive odor. Some fermentations
give rise to evolution of gases, derived from the constitu-
ents of the decomposing substance ; when these gases have
a disagreeable odor, as sulphuretted hydrogen, certain hy-
drocarbons, and ammonia, for example, produced in the
decomposition of animal matter, the term putrefaction is
used. Nitrogenous bodies are the most disposed to this
kind of decomposition. Substances which arrest fermen-
tation already begun, or deprive bodies of the power of
fermenting, are called antiseptics. Such are ferric chlo-
ride, arsenious anhydride, carbolic acid, etc.

536. Ferments. — There must always be a fermenting
agent to produce the change. Neither sugar nor alcohol
has any tendency to ferment of itself, but they very readily

FERMENTATION. 381

do so on the application of a small amount of some fer-
ment. This ferment may be either of the albuminous sub-
stances gluten, albumen, or casein.

The manner in which these bodies act in exciting fer-
mentation is very imperfectly understood; "they neither
add any thing to the fermenting body nor take any thing
away from it, but the motion or disturbance of their par-
ticles, while undergoing putrefaction, is supposed to be
communicated to the particles of the fermenting body with
which they are in contact, and thus induce decomposition."
Fermentation is always accompanied by the growth of
organized bodies — called fungi when vegetable, and infu-
soria when animal. In fact, their development is regarded
as the exciting cause of fermentation and putrefaction.

537. The Chemical Change in Alcoholic Fermentation. —
Alcohol is composed of the same elements as sugar, but
in different proportions. The production of alcohol by the
fermentation of sugar is not really a conversion of sugar
into this substance, but a splitting up of the sugar into al-
cohol and carbonic anhydride. Cane-sugar does not thus
break up, but is converted first into glucose, or grape-sug-
ar, and this is decomposed in the following manner:

Grape-sugar. Alcohol. Carbonic anhydride.
C6HlaO6 = 2C2H6O + 2CO3"

Some other substances are formed at the same time, but
only in small quantity ; and their production has been dis-
regarded in the equation.

538. Yeast. — What is commonly called yeast is really a
growth, for yeast is a collection of very minute plants ; so
minute that it is estimated that a cubic inch contains twelve
hundred millions of them. This plant, revealed to us by
the microscope, multiplies itself with exceedingly great
rapidity, and will continue to do so as long as there is ni-
trogenized matter to supply it with the means of growth.

382 CHEMISTRY.

Thus in a brewery the quantity of yeast continually in-
creases, and it is sold largely for the raising of bread, a fer-
menting process to be noticed soon. There is a difference
of opinion as to the mode in which yeast causes fermenta-
tion. Some suppose that it is the yeast-plants that produce
this effect, while others suppose it is their decomposition.

539. Wines, Cider, etc. — In making these no addition of
yeast is required, for there is nitrogenous matter in the
juices from which they are made, which by exposure to
the air becomes a ferment. In making Champagne and
other sparkling wines, the wine is bottled before the fer-
mentation is finished. Of course the process goes on in
the bottle, and the carbonic acid produced is pent up in
the liquid, ready to expand and escape the moment the
way is opened. Sweet wines are those in which there is
some sugar that has not been decomposed in the fermen-
tation. Wines are called dry when they contain very little
sugar. Wines are made from other fruits as well as the
grape, as, for example, the currant, the gooseberry, the
elderberry, etc. Cider is essentially a wine made from
apples. Much of the so-called Champagne wine is really
cider, to which a peculiar flavor is given. Other wines are
counterfeited, and there is probably no class of men more
often cheated than wine-drinkers.

540. Flavor of Wines. — The flavor which distinguishes grape wines
as a class from other spirituous drinks is produced by a very small amount
of an ethereal substance called cenanthic ether. When obtained in a sep-
arate state it is a very fluid liquid, having a sharp, disagreeable taste, and a
vinous odor so powerful as to be almost intoxicating. It does not exist in
the grape, but is one of the products of the fermentation, and increases with
the age of the wine. You can have some idea of the power of this sub-
stance from the fact that in few wines does it constitute more than the one
four-thousandth part of their bulk. It is often obtained by manufacturers
of wines from grain spirit and cheap wines, and is used by them for produc-
ing imitations of wines of higher prices with such cheap articles as potato

FERMENTATION. 383

whisky. Besides the general wine flavor given by the oenanthic ether,
there are other flavors imparted by other substances giving to the various
wines individual characteristics.

541. Acidity of "Wines. — The acidity of grape wines is owing to the
presence of tartaric acid in combination with potassium, forming the acid
tartrate of potassium, or cream of tartar. As this gradually separates from
the wine, and collects as a crust on the sides of the casks and bottles, the
longer wines are kept the less acid they become, and hence in part the val-
ue which age gives to them. The acid which is present in small amount
in malt beer is acetic acid, the acid of vinegar ; and that which we have in
cider is lactic acid, the acid which is present in soiir milk ; so that wine,
malt beer, and cider each has a different acid. When, however, the fer-
mentation goes in either of these beyond the production of alcohol, acetic
acid results, for then we have the acetous fermentation.

542. Amount of Alcohol in Wines. — The proportion of alcohol
varies very much in different wines. Even in the strongest wines more
than three fourths of the liquid is water. The proportion, by measure, of
alcohol in the most prominent wines is as follows :

Per Cent.

Port 21 to 23

Sherry 15 to 25

Madeira 18 to 22

Marsala 14 to 21

Malmsey 16

Per Cent .

Tokay 9

Khenish 8 to 13

Moselle 8 to 9

Champagne 5 to 15

Burgundy 7 to 13

Claret 9 to 15

543. Production of Alcohol from Starchy Substances. — In
the production of alcoholic liquors from barley, rye, pota-
toes, etc., in which starch is the chief ingredient, and sugar
is only present in very small amount, a preliminary process
is necessary in order to change the starch into sugar. In
making beer from barley this is done in the following man-
ner : The grain is first moistened in heaps, and spread upon
a floor in a dark room. It sprouts, and in doing this some
of the starch in it is turned into sugar by the action of the
diastase (§ 472), so that the barley has quite a sweet taste.
The process is arrested by drying in the kiln just as the
germs are about to burst from the seed, for if it be left to

384 CHEMISTRY.

go on beyond this some of the sugar will be lost by being
converted into vegetable fibre. The malt — for so this sug-
ared barley is called — after being dried, is bruised and put
into the mash-tun with water in the requisite quantity,
which is gently warmed. Here the sugar and diastase
are dissolved, the latter at the same time converting the
remaining starch of the seeds into grape-sugar. The liquor,
or wort, as it is called, is now put into the boiler, and
boiled with the hops, which not only give to the liquor its
bitter taste, but also help to clarify it. The boiled liquor
is run off into shallow vats, where it is cooled, and then it
is poured into the fermenting tun, where, with the addition
of yeast, the requisite fermentation is produced. In like
manner in making whisky from the potato the starch must
first be converted into sugar to prepare for the alcoholic
fermentation.

544. Distillation. — In the operations of which we have
spoken alcohol is obtained mingled with a large amount
of water. By the process of distillation this amount of
water can be much diminished, giving us the stronger spir-
ituous liquors called by the common names of distilled
liquors and ardent spirits. Brandy, for example, is distill-
ed from wine, and has from 50 to 54 per cent, of alcohol,
while the strongest wine has but 25 per cent. In rum, dis-
tilled from fermented molasses, there is from 72 to 77 per
cent, of alcohol. A common form of apparatus for distill-
ing brandy and spirits of wine is represented in Fig. 116
(p. 385). It consists of a copper still, A, having a dome-
shaped head, B, which by a tube, C, communicates with
the worm, D. Heat being applied to the still by the
Bunsen burner, the alcohol passes over to the worm more
freely than the water because it is more volatile. For the
purpose of condensing the vapor as it passes into the worm,
the worm is inclosed in a cylindrical vessel, E, which is full

FERMENTATION. 385

Fig. 116.

of water. To prevent the water from becoming hot a con-
stant supply of cold water flows in by the tube H to the
bottom of the vessel, the heated water rising and flowing
out by the tube G. The condensed liquor, passing out at
F, drops into the receiver.

545. Fusel-Oil. — This oily substance, which is very poisonous, was
first discovered in the distillation of liquor made from potatoes, and hence
has sometimes been called potato-oil. In reality it is amylic alcohol, one
of the large class of alcohols mentioned in the fourth column of the table
on page 303. Amylic alcohol is produced in the distillation of liquors
made from the grains, and occasionally at least in other distillations also.
It may be separated from the spirit by filtration through charcoal, this
substance absorbing the poison into its pores. But not only is this process
often omitted, thus leaving this poison to aggravate the deleterious effects
of the alcohol itself, but the fusel-oil is made use of to a large extent by
unprincipled manufacturers, of whom there are a great number, in getting
up factitious liquors, wines, and cordials. The enormous cheating and
destructive poisoning to which the drinkers of spirituous liquors are thus
subjected, though extensively known, seem to be little heeded.

546. Fermentation in Bread. — The "raising" is ordinarily
accomplished by alcoholic fermentation. The yeast first

386 CHEMISTRY.

converts some of the starch of the dough into sugar, and
then makes from this sugar alcohol and carbonic anhydride.
It is the expansion of the gas thus produced in every part
of the mass that makes the numberless cells in it, and thus
causes the "raising;" the volatile alcohol escapes at the
same time. In the baking of bread part of the starch of
the flour is converted by the heat into dextrin. A shining
coat is given to the loaf by dissolving some of this gum on
the surface by moistening the loaf after it is baked, and
then subjecting it for a few minutes to heat again, which
quickly dries and hardens the gum. Bread is often raised
by other means than fermentation. Tartaric acid and hy-
dro-sodium carbonate are used for this purpose. If the bi-
carbonate, as it is commonly called, be thoroughly mixed
with the dough, and the tartaric acid be then added, it will
seize the soda, and the released carbonic anhydride, as it ex-
pands into its gaseous state, raises the bread, as it does
when generated by yeast. Bakers sometimes use ammonium
carbonate to raise their light, spongy cakes. There is no
need of any acid in this case, for the heat volatilizes the
carbonate, and as it escapes it makes the cakes porous.
Hum and alcohol have sometimes been employed, the vapor
produced by the heat answering the purpose. There is
considerable water in bread. In every 100 pounds of flour
there are 16 of water. Then in the making of the flour into
bread there are added 50 pounds more of water, so that
there are 66 pounds of water in 150 pounds of bread. When
bread becomes "stale," its dryness is not owing to an es-
cape of water, but to a more thorough incorporation of the
water with the bread.

547. Ether. — This singular fluid, so different from alcohol
in its properties, is prepared from alcohol, and differs from
it but little in its composition — having the same ingredi-
ents, though not in the same proportions. Alcohol being

FERMENTATION. 387

C2H5(HO), ether is (C2H5)2O. As stated in § 423, if we re-
gard alcohol as a hydrate of the radical ethyl C2H5, ether
may be regarded as the oxide of this radical. Ether is a
very light liquid. If exposed to a heat of 35.6°, two de-
grees less than blood heat, it boils, and it has never yet
been frozen. It is exceedingly volatile. On account of its
volatility and the effect of heat upon it, it must be kept in
a cool place and in tightly closed bottles. If the hand be
moistened with it, there ensues a sensation of great cold,
owing to the rapid evaporation. It is very combustible, and
its vapor mingled with the air forms an explosive mixture.
The inhalation of it in considerable amount produces in-
sensibility, and it is therefore much used in surgery to pre-
vent the patient from suffering while undergoing an oper-
ation, and also to some extent in medicine to relieve the
pain of disease. It is also used to dissolve gun-cotton, or
pyroxyline ; the solution is largely employed by photog-
raphers to form the collodion films of the glass plates on
which the negative pictures are produced.

548. Compound Ethers. — As ether is an oxide it unites
with acids to form compounds which may properly be
termed salts. That very common medicine, the sweet
spirits of nitre, is one of these salts diluted with alcohol.
The essences used in flavoring wines, cordials, and in cook-
ing food, are really compound ethers, artificially prepared
on a large scale. In the following table (p. 388) you have
a list of some of these perfume ethers, their formulaa, and
the flavors they imitate. By mixing these ethers with each
other, and with essential oils in various proportions, the
odor and flavor of nearly every fruit may be imitated.
Dilution with alcohol best develops the flavor.

Salicylol is not an ether, but finds a place in this table
for obvious reasons.

549. How Ether is Obtained. — It is by the action of sul-

388 CHEMISTRY.

PERFUME ETHERS; FRUIT ESSENCES.

NAME.

FORMULA.

FLAVOB.

Ethyl butyrate.

Pine-apple

Ethyl cenanthylate. .

C2H5.C7H13O2

Greengage.

Ethyl pelargonate . .

GjHs.Ogllj^Oa

Quince.

Ethyl suberate. . .

C,H5.CSH12O,

Mulberry

Aroyl acetate. . .

P FT f1 TT O

Pear

.Amyl valerate

C-Hn C5H9O2

Salicylol

H.C7H4O.HO

Meadow-sweet

Methyl salicylate . . .

C7H4O.CH3.H.O2

Winter-green.

phuric acid upon alcohol that ether is generally obtained.
The process is represented in Fig. 117. Equal quantities by

Fig. 117.

weight of alcohol and the acid are introduced into a retort,
A, to which heat is applied by a ring-burner, or, better, by
means of a sand-bath. The retort is connected with an ap-
paratus for condensing the vapor of the ether, known as
Liebig's Condenser, and consisting essentially of two glass
tubes, C and D, one fitted into the other by means of corks ;
water entering the space between these tubes through the

FERMENTATION. 389

funnel, E, cools the vapor of the ether, and passes off through
the outlet, F. The ether condensing in the inner tube flows
into the two-necked receiver, G, and thence into a flask, H.
The Liebig condenser is supported by a stand, B ; the outer
tube of the condenser is often made of metal. The stopper
in the tubulure of the retort, A, may be removed, and more
alcohol added as may be needed for the continuance of the
formation of the ether to any considerable amount. The
chemical process here is this: Sulphuric acid takes away
the elements of water from the alcohol and leaves ether,
thus: 2(C2H6O) - H2O = (C2H5)2O. At least this is the
simplest explanation which we can give you. Ether is very
commonly called sulphuric ether, but the name is improper,
as it contains neither sulphuric acid nor sulphur. By man-
aging the alcohol and sulphuric acid differently a gas may
be produced which is a very different substance from ether.
The amount of sulphuric acid used for this purpose is five
times that of the alcohol. This gas is olefiant gas, one of
the hydrocarbons obtained by distillation of wood and coal.
The reaction in this case is a dehydration or abstraction of
water from the alcohol :

Alcohol. Olefiant gas. Water.

CaH60 = C3II4 + H2O

550. Chloroform. — This valuable substance can be ob-
tained in various ways. It is commonly produced by
distilling alcohol with water and chloride of lime. Its
molecule contains one atom of carbon, one of hydrogen,
and three of chlorine, and its composition is therefore ex-
pressed thus : CHC13. We have seen in § 421 how it may
be regarded as a substitution product of marsh gas. It is,
like ether, a colorless and very volatile liquid, having a
peculiar sweetish smell. Its inhalation produces insensi-
bility more readily than ether.

551. Vinegar.— This is a mixture of acetic acid with wa-

390 CHEMISTEY.

ter, there being diffused through the water also more or less
of some other matters. But a small percentage of the
whole is acetic acid. Common table vinegar contains but
from two to five per cent. As acetic acid is little if any
more volatile than water, it can not be obtained pure from
vinegar by distillation. The only way in which the chem-
ist can obtain it is to decompose some of the acetates, as
acetate of lead — the common sugar of lead — by an acid
which is strong enough to seize the base, and thus release
the acetic acid.

552. The Acetous Fermentation. — Vinegar is commonly
made by the exposure of some spirituous liquor, as cider or
wine, to the air. This occasions what is called the acetous
fermentation. This, like the alcoholic fermentation, can not
take place without the presence of a ferment. For this
reason, if a solution of alcohol in perfectly pure water be
exposed to the air, there will not be the least fermentation.
In the case of cider, wine, etc., there is no need of adding
any ferment, for there is one already present in the liquid,
the same which acted in its alcoholic fermentation. It is
the decomposition of this which produces that gelatinous
mass called the mother. As one of the results of this de-
composition we have the generation of infusoria, or vinegar
eels, as they are commonly called, which can often be seen
by the naked eye when a glass of vinegar is held up to the
light of the sun. When the acetous fermentation takes
place in liquids containing starch and sugar, it is always
really preceded by the alcoholic fermentation. For exam-
ple, when preserved fruits become acid there is first an al-
coholic fermentation, which passes into the acetous, pro-
ducing vinegar. The effervescence which occurs, causing
bubbles on the surface, is occasioned by the carbonic anhy-
dride generated by the preliminary alcoholic fermentation.
The more thoroughly the air is shut out from preserves the

FERMENTATION. 391

less apt will they be to ferment. Exposure to heat favors
fermentation, and hence preserves should be kept in a cool
place. A high degree of heat will, however, destroy the
power of the ferment, and hence preserves are scalded when
there is a suspicion that fermentation is commencing in
them. For the same reason vinegar is boiled to arrest the
formation of the mother in it.

553. Sour Bread. — When bread is sour it is because the
vinous fermentation has been followed by the acetous.
This may arise from two causes. Either the fermentation
has been allowed to go on too long before the bread was
baked, or the ferment used has been kept so long as to
enter into that state which makes it capable of producing
the acetous fermentation. If a flour paste stand in a ves-
sel covered with a board for six or eight days, it acquires
a pleasant smell in the change which has taken place in it,
and is now fit to act as an alcoholic ferment. Bread raised
by it will be sweet. But if this paste or dough be left to
stand a little longer, it acquires an acid taste, and will now,
indeed, excite an alcoholic fermentation in sugared water
or in bread, but this will at once pass on to the acetous fer-
mentation.

554. Explanation of Acetous Fermentation. — The change
which alcohol undergoes on conversion into acetic acid is
not strictly a result of fermentation, because this conversion
may be effected in various ways which exclude the idea
of any vegetable or animal growth. It is rather a case of
oxidation, for alcohol contains more oxygen and less hydro-
gen than acetic acid, as shown in the following equation :

Alcohol. Oxygen. Acetic acid. Water.
CaH60 + Oa = CaH4Oa + H0a

Since, however, pure alcohol may be exposed to the air>
either alone or mixed with water, for any period without
suffering oxidation, and the change is induced by the pres*

392

CHEMISTRY.

ence of unstable organic substances, the conversion may be
regarded as a sort of fermentation.

Actually the change is not so simple as represented in the equation just
given. It has two stages. As when starch is converted into sugar there
is an intermediate substance — dextrin — into which it is changed prepara-
tory to its conversion into sugar, so also, in the formation of acetic acid,
the alcohol is first changed into an intermediate substance called aldehyde.
The two changes may be expressed thus :

Alcohol. Oxygen. Aldehyde. Water.

C3H6O + O = C2H4O + H2O

Aldehyde.

Oxygen.
*0

Acetic acid.
CaH402

Compare the equations in § 537 explaining alcoholic fermentation.

555. Quick Mode of Making Vinegar. — Alcohol can be
converted into acetic acid in a very short time by provid-
ing for a very free exposure of it to the air, so that the ox-
ygen may act upon every
drop of it at once. This is
done in the manner repre-
sented in Fig. 118. A bar-
rel is filled with shavings
which have been steeped in
vinegar. Near the top of
the barrel is a shelf, perfo-
rated with holes, in which
there are fastened either
bits of string or straw, that
the liquid poured in, which

is alcohol and water with a little yeast, may trickle down
upon the shavings. A free access of air is secured to the
whole surface of the shavings by holes made in the side
of the barrel, and some holes in the perforated shelf large
enough to admit glass tubes of considerable size. Now
as the fermentation creates heat, the cold air admitted in

FERMENTATION. 393

the holes becomes expanded by the heat, and so rises to
pass out through the glass tubes ; and in this way quite
a brisk circulation of air is kept up, bringing, therefore,
oxygen to the whole surface of the shavings with con-
siderable rapidity. The fluid as it runs out below passes
into the receiver. Of course the barrel is whole as used ;
in the figure a portion of it is represented as cut away,
merely that you may see the interior arrangement.

556. Adulteration of Vinegar. — Even vinegar is some-
times adulterated. When a manufacturer desires to sell
poor vinegar as good he gives the requisite sharpness to it
by adding some substance, as, for example, sulphuric acid.
Adulteration with this article can be very easily detected.
Fill a jar or mug half full of water, and set upon it a cup
containing some of the vinegar with grape-sugar in it. If
you set the mug upon a hot stove the vinegar in a little
time will be all evaporated. If now what is left in the
cup be of a black color, there is proof of the presence
of free sulphuric acid. The explanation is this : As the
vinegar evaporates, the sulphuric acid, not being volatile,
remains in the cup, and at length, when all the water is
gone, is so concentrated that it carbonizes the non-volatile
organic matter. (See § 244.)

Great care must be taken not to heat the contents of
the mug too hot, or the organic matter may be charred
by the heat alone.

QUESTIONS.

535. What is said of different kinds of fermentation ? What is the dif-
ference between fermentation and putrefaction ? What are antiseptics ?
—536. Explain the nature and action of ferments. What is said of the
growth of organized bodies? — 537. Explain the chemical change in alco-
holic fermentation. Give the equation. — 538. What is yeast ? — 539. What
is said of the fermentation of wines ? When are wines dry ?— 540. What

394 CHEMISTBY.

gives peculiar flavor to grape wines ? How much of this ether do wines
contain? — 511. To what is the acidity of grape wines due? — 542. What is
said of the amount of alcohol in wines ? — 543. What is the first step in
making alcohol of starchy substances ? What is malt ? How is it made ?
— 544. Describe the process of distillation. — 545. What is fusel-oil ? How
produced? — 546. Explain the raising of bread by yeast. What other
means are employed to raise bread ? How much water is there in bread ?
What makes bread stale ?— 547. What is ether ? What are its properties ?
For what is it used ? — 548. How may compound ethers be regarded ? Give
the names and flavors of some of the so-called fruit essences. — 549. De-
scribe the process of making ether. Explain the chemical reaction which
ensues. What is obtained by managing the alcohol and sulphuric acid dif-
ferently?— 550. How is chloroform made? Of what composed? — 551.
What is vinegar ? Why can not acetic acid be obtained from it by distil-
lation? How is it obtained by the chemist? — 552. What is said of the
common mode of making vinegar ? What is the mother of vinegar ? What
are vinegar eels, and how are they produced ? State in full what is said
of the acetous fermentation in preserves. — 553. Explain the chemistry of
sour bread. — 554. Explain in full the chemical changes of the acetous fer-
mentation. In what two stages does this change take place? — 555. De-
scribe and explain the quick mode of making vinegar. — 556. How is
vinegar commonly adulterated, and how can the adulteration be detected ?

CHAPTER XXXI.

ANIMAL CHEMISTRY.

557. Materials. — The elements which enter into the com-
position of the various substances found in animals are the
same with those which compose vegetable substances. Wo
have first the four grand elements — carbon, oxygen, hydro-
gen, and nitrogen. There are also chlorine, sulphur, and
phosphorus, and also the metals calcium, potassium, so-
dium, and iron. As in vegetables, so in animals, these ele-
ments never appear as elements, but always in combina-
tion. Thus we never have chlorine alone, but it exists in

ANIMAL CHEMISTRY. 395

combination chiefly with sodium, forming the chloride or
common salt, which, as you will soon see, plays quite a
part in the animal economy. So phosphorus is mostly
united with oxygen and calcium, so as to form a phosphate
of calcium, and is never found as phosphorus. The com-
binations of the four grand elements are very various in
their character, for out of them are built animal structures
of every kind. It is not commonly the elements them-
selves, but the combinations of the elements, derived from
various sources — vegetable, animal, and mineral — that an-
imal chemistry works upon as materials in evolving ani-
mal substances, both liquid and solid. Thus phosphorus
and oxygen and calcium are not introduced into the an-
imal system separately, and there united to form phos-
phate of calcium; but this salt is introduced as such in
both vegetable and animal food. So the carbon, oxygen,
hydrogen, nitrogen, and sulphur which compose albumen
do not unite in the animal to produce this substance, but
it is formed in the vegetable for use in the animal.

558. How Animal and Vegetable Chemistry are Alike. —
They are alike, as you have just seen, in the elements which
are employed. They are also alike in many of the com-
binations of these elements. The chloride of sodium and
the phosphate of lime found in animals are also present in
vegetables. One of the principal constituents in animals
is like vegetable gluten. Then there are albumen and
casein, corresponding with substances of the same name in
vegetables. This resemblance between animal and vege-
table chemistry comes in consequence of the fact that the
vegetable world is so largely engaged in preparing for the
animal world what it gathers up from the mineral world.
It not only transfers, but prepares, and many of its prepa-
rations are combinations which enter with little or no al-
teration into the composition of animal substances.

396 CHEMISTEY.

559. How they Differ. — Animal and vegetable chemistry
differ in several important particulars. The former is much
more complex and mysterious than- the latter. Certain
substances, as starch and sugar, found in such abundance
in some vegetables, are not present in animals in their
normal state. When taken into the animal they are
changed into fat and other substances. Then there is
not only difference but opposition between the chemical
action of leaves and that of lungs, carbon being given
out by lungs and taken in by leaves, and oxygen being
given out by leaves and taken in by lungs, as stated in
§ 128. Besides all this, the plant lives upon unorganized
materials, while the animal lives upon organized materials
built up by the plant.

560. The Blood. — This universal building material of
the animal contains all the constituents needed for the
construction and repair of every part. There is fibrin,
out of which chiefly the various textures of the body are
formed. This is the firm part of the coagulum or clot
that separates when blood is left standing, there being in-
corporated with it the coloring matter of the blood. The
clot swims in a watery fluid called serum, which contains
albumen in solution. Besides these there is a variety of
materials in small amounts in the blood. There is iron,
which is contained in the matter which gives the blood its
red color. Then there are mineral materials for the manu-
facture of bones, teeth, etc., and various other substances.
Water constitutes about four fifths of the blood. Without
this the materials which we have mentioned could not be
carried to all parts of the body. In this they are sent to
their destination through innumerable tubes by the heart,
the great central pump of the circulation.

561. How the Blood is Made. — The blood is made mostly
from our food. We say mostly, because that important sub-

ANIMAL CHEMISTRY. 397

stance, oxygen, is partly furnished from, the air that enters
the lungs. The process of digestion, by which the blood
is made from the food, we shall not particularly describe
here, but will refer you to Hooker's two works on Physi-
ology. It is sufficient to speak of it here very briefly and
generally. The food on being ground up by the teeth is
at the same time mixed with the saliva, which is poured
into the mouth by several glands, or saliva factories, as
they may be called. In the stomach the ground and moist-
ened mass is acted upon by the gastric juice, a fluid which
oozes out from myriads of minute glands set into the inner
surface of the organ. This is a chemical operation, and it
is promoted by a constant motion which is kept up in the
stomach, thus stirring up the food so that the gastric juice
may be well mixed with it. After the proper chemical
change is effected the nutritious part of the mass is ab-
sorbed and poured into the blood, and becomes a part
of it.

562. Albumen. — The protein compounds, or albuminoids,
are very nearly identical in composition, as you have al-
ready learned, and they are convertible into each other.
In the animal the various tissues or structures, as we have
stated in § 560, are made chiefly of fibrin. Exactly how
fibrin is formed in the animal economy is an unsettled ques-
tion. It was formerly supposed that albumen was trans-
formed into fibrin, and that all other protein bodies were
first converted into albumen in the stomach, but this lacks
demonstration. Albumen is held in solution in the blood
by means of chloride of sodium associated with it. It does
not occur in the animal in the free state, jbut as an alkaline
albuminate. It forms about seven per cent, of blood, and
occurs in the brain, in the juice of the flesh, and in a greater
or smaller quantity in all the liquids effused from the blood-
vessels into different parts of the system.

398 CHEMISTRY.

563. Formation of the Bird in the Egg. — In the formation
of the bird in the egg we have a marked illustration of the
prominent part which albumen plays in nutrition. Both
the yolk and the white are composed chiefly of albumen
dissolved in water. The white is seven eighths water, and
only one eighth albumen. In the yolk we have the same
solution of albumen holding yellow globules of oily matter
suspended in it. There are in both the yolk and the white
minute amounts of various mineral substances, as common
salt, phosphate of lime, carbonate of soda, etc. These form
the ash of the egg when it is burned. It is the albumen
of the egg from which all the varied structures of the bird
are formed — the muscles, the skin, the feathers, etc. The
oily matter of the yolk, it is true, is diffused in the inter-
stices of many of the tissues, but it does not really form a
part of them, unless it be in the case of the brain. The
phosphate of lime also is deposited in the texture of the
bones, but it is the albumen that first forms that texture.
As we look at the white of an egg, so simple is it that we
can hardly believe that such a variety of tissues can be
evolved from it by the chemistry of life. And yet the ev-
idence is clear that it is so ; for shut up in the shell noth-
ing can gain admission to it but the oxygen of the air,
which acts upon it through the pores of the shell, and
thus materially aids in the process, as may be proved by
the interruption of it by a coat of varnish shutting up the
pores.

5G4. Gelatin. — There is considerable doubt as to the nat-
ure of this substance, which enters largely into the struct-
ure of some portions of animals. It is supposed that it is
formed from albumen and fibrin, as the gelatinous struct-
ures are well developed in animals which are fed upon these
substances alone. Its composition is nearly the same as
theirs, although its properties are very different. It forms

ANIMAL CHEMISTRY. 399

about one third of the substance of the bones, phosphate
of lime being almost all of the remaining two thirds. It
is the gelatin in the skin that tannin so firmly unites with,
converting it into leather. What is commonly called glue
is gelatin. This substance dissolves readily in water. The
various jellies that we use prepared from animal substances
are gelatin. The gelatin is first separated from them and
dissolved by hot water, and then the solution on cooling
leaves a jelly. Isinglass, so called, is chiefly gelatin pre-
pared from the sounds or air-bladders of certain fresh-wa-
ter fishes, particularly one of the sturgeon class found in
the rivers of Russia,

565. Two Kinds of Food. — All the varieties of food are
divided into two classes according to the purpose which
they serve, the one class serving to build up the tissues,
and the other to maintain the animal heat. To the former
class belong those substances that contain nitrogen, as the
gluten of bread, the fibrin of meat, the casein of milk, etc.
The other class comprises those substances that have no ni-
trogen in them, as starch, sugar, and oily substances. These
all serve to maintain the warmth of the body, and it is sup-
posed have little or nothing to do with building its struct-
ures. They are burned up, as we may express it, in creat-
ing heat, which is just as essential to the maintenance of
life as nutrition is. This food is called respiratory food,
because it is supposed that the oxygen introduced by the
respiration is employed in consuming or burning it. The
products of this flameless combustion are the same with
those of ordinary combustion with flame, water, and car-
bonic anhydride. The heat-making food is often called
carbonaceous from the predominance of carbon in it, while
the building food is called nitrogenous because it is dis-
tinguished from the other by containing nitrogen.

While the view thus presented is generally true, there

400 CHEMISTRY.

is ground for doubt whether the distinction can be as
strictly carried out as is attempted by Liebig and others.
The reasons for this doubt will be noticed soon.

566. Climate and Food. — If the view above presented be
substantially correct, climate must have a great influence
upon the choice of food, the necessities of the case influ-
encing that choice to a considerable extent through the
instincts. Accordingly we find that oily and fatty food
is largely used by the inhabitants of the arctic regions,
from the great demand of the system for heat -making
food amid the surrounding cold. And provision is made
by the Creator for this want ; for the animals from which
the Esquimaux, the Greenlanders, etc., obtain their chief
nutriment — as bears, seals, and whales — are loaded with
fat, while there is but little of this substance in those
animals which furnish meat to the inhabitants of hot
climates.

567. Warmth in Hibernation. — It is observed that the
woodchuck and other warm-blooded animals that are in a
torpid state in the winter mouths are lean when they come
out of this state in the' spring, though they were very fat
when they went into it. This is because the fat is burned
up during the winter in maintaining the warmth requisite
for the continuance of life in this torpid state. So, also, in
disease, the fat previously accumulated in the system is
often used in the production of animal heat, the other
sources being in part cut off by the impaired ability to ap-
propriate food.

568. Corpulency. — In this state of body there is an ac-
cumulation to a larger degree than usual of fatty matters
in all quarters of the system. This is supposed to arise
from the fact that the heat-making food is provided in so
great amount that the oxygen introduced into the system
is far from being sufficient to burn it up. In this case the

ANIMAL CHEMISTEY. 401

accumulation of fat does not corne from oily food alone, for
starch and sugar can be converted into fat by the chem-
istry of life. It is on account of this conversion that pota-
toes increase the butter or fatty part of the milk in the
cow. For the same reason the butter in milk is greater in
amount in the morning milk than in that of the evening,
when in cold weather the cow is kept in a warm stall
through the night, there being more starchy and sugary
matters converted into fat when there is less necessity for
their consumption in the production of heat. For the
same reason, also, in the fattening of animals in cold weath-
er, the more comfortably they are housed the less food will
it take to fatten them.

569. Heat in Carnivorous and Herbivorous Animals. — It is

obvious that carnivorous animals do not eat as much heat-making food as
herbivorous animals do, while they eat more of building-food; and yet
they have as much heat as the herbivorous animals, and do not have any
greater development of structure. This seems to be in contradiction to
the views presented of the purposes of food ; but the apparent discrepancy,
for it is only apparent, can be easily explained. There are two sources of
the fuel used in maintaining animal heat, viz., the food and the waste of
the tissues of the body. Now the heat in carnivorous animals is derived
almost wholly from the latter source, for they are so active in their habits
that there is much greater wear and tear of the tissues than in herbivorous
animals. You can realize this difference in activity if you observe the
constant restlessness which lions, tigers, hyenas, etc., manifest in their
cages in a menagerie. Herbivorous animals are so inactive that when
they are left to their natural habits they can live on food which contains
but very little nitrogenous substance, as common grass, potatoes, etc. But
when they are worked by man, if they are not fed in part on some of the
grains, they will lose flesh for want of building-food. But there is another
difference between carnivorous and herbivorous animals, which accounts
for the absence of that overheating that we might reasonably expect from
such an amount of heat-food as is commonly eaten by herbivorous animals.
They perspire freely, much more so than carnivorous animals, and a large
part of the heat made by their food passes off therefore as latent heat in
the vaporization of the perspired matter.

402 CHEMISTRY.

570. Relation of Food to Labor. — This topic, incidentally touched
upon in § 569, merits a more particular notice. If a horse is not worked
he will retain his good condition on such food as hay and potatoes. If oats
or corn be added he will gain in flesh ; that is, the tissues will be more
fully developed by this addition of plastic food, and at the same time the
fat will be increased, as his heat-making food is not used up freely in pro-
ducing heat. If now with this mixed diet he is put to work, he will retain
from day to day his usual bulk both in respect to fat and muscular fibre.
Laboring men require a larger proportion of nitrogenous food than those
who are inactive. It is for this reason that when men live almost wholly
on such articles as potatoes or rice or plantains there is the same failure
both in bulk and power as in the working horse that is fed on hay alone.
The Israelites could not have endured their journey if their manna had
been like the article now called by that name. They needed food which
was in part nitrogenous, and such was the manna miraculously furnished
to them, as the change in it when it was kept for any length of time clearly
showed (§ 4G6). It is calculated by Liebig that the proportion of nitrog-
enous to non-nitrogenous food most suitable to the wants of a laboring
man is about as one to four. If he eat too much of the former, like the sav-
age hunter who lives almost wholly on meat, there is deficiency of heat-
making food, and he is obliged to eat a larger amount of nitrogenous food
than is needed for nutrition, in order to get a sufficiency of that non-nitrog-
enous food which is combined with it, unless he pursue, like carnivorous
animals (§ 569), so active a life that the waste of the tissues shall supply
the requisite amount of fuel. The use of so large a quantity of animal food
by no means proportionally develops the tissues, for it burdens the digest-
ive and other organs with too much labor, and therefore produces disease
in spite of the invigorating influences of an outdoor life.

571. Mingling of Heat -Pood and Building -Food. — Gen-
erally in articles which are eaten the two kinds of food are
mingled together. Thus even in the lean part of meat
there is always some fat in addition to that which is de-
posited in masses in the neighborhood of the muscles ; and
gluten and starch are mingled in the grains. That mixture
of nitrogenous and non-nitrogenous food which we have in
bread is so especially suited to man that this article of diet
has from remote antiquity been styled " the staff of life."
The instincts of men seem to lead them to mingle the two

ANIMAL CHEMISTRY. 403

kinds of food together. Thus the Irishman eats with his
potatoes buttermilk for the casein it contains, or cabbage,
which is one of the vegetables that is rich in nitrogen. The
Italian for the same reason adds cheese to his macaroni, and
the wayfaring Spaniard eats with his bread an onion or two,
this vegetable containing much nitrogen, like the cabbage
of the Irishman.* So pork, which is only heat-food, is eaten
with cabbage or beans, butter with bread, and oil with salad.
Experiments which have been tried show decidedly that
life can be sustained only on mixtures of food. Animals
have been fed on various single substances extracted from
articles of food, and the results have always been bad, even
to the destruction of life. This is true of the nitrogenous
constituents as well as the carbonaceous. The fibrin ex-
tracted from meat is far from answering the same purpose
as the meat itself. The juices of the meat are needed
in combination with the fibrin to accomplish the full pur-
poses of nutrition. It may be laid down as a general truth
that no separated principles of food answer the same end
as the mixtures which are produced in nature. The gluten
of wheat does better than any other one thing, but this
alone is by no means as good food as its mixture in the
grain with starch and albumen.

572. Milk. — It is worthy of remark here that milk, the
only mixture of food which nature has provided as the sole
means of nutrition for some animals — the mammalia — in
their infancy, has the two kinds of food combined, the

* The dish so common in Ireland called Kol-cannon is prepared by beat-
ing potatoes and boiled cabbage together, putting in a little pork-fat, salt,
and pepper. Johnston says of this, " Take a pot-bellied potato-eater and
feed him on this dish, and he will become not only stronger and more act-
ive, but he will cease to carry before him an advertisement of the kind of
food he lives upon, and his stomach will fall to the dimensions of the same
organ in other men."

404 CHEMISTEY.

cheesy matter or casein being the nitrogenous part, and
the oily matter or butter the non-nitrogenous part. And
the proportions of the two, being as one of the former to
four of the latter, furnish a clear indication of what they
should be in food generally, making allowances, of course,
for varying circumstances. Milk must contain, besides the
casein and the oily matter, all the other materials required
in both the solids and fluids of the body, else there would
be some defect in the nutrition of an animal that lives en-
tirely upon milk. We have therefore in this liquid iron
for the blood, salt for this and various other fluids in the
body, phosphate and carbonate of lime for the bones, etc.
The milk, though of a white color, contains in fact all the
elements that are present in the red blood of the animal,
and in the same proportions, with the exception of that
portion of the oxygen which is added to the blood in the
lungs. A great error is often committed in confining a
child too exclusively to starchy articles of food, such as
arrow-root, thus depriving it not only of the albuminous
substances, but also of the iron, the phosphate of lime, etc.,
which are all contained in the complex food furnished it
by nature.

573. Proportions of Heat-Food and Building-Food in Dif-
ferent Articles. — In the following articles to every 10 parts
of nitrogenous substance there are the parts named of non-
nitrogenous substance: Cow's milk, 30; pease, 23; beef,
17; veal, 1; eggs, 15; wheat flour, 46; oatmeal, 50; rye
flour, 57; potatoes, 86; rice, 123; buckwheat flour, 130.
There are some variations according to circumstances, but
these are the average proportions. The percentage of
nitrogenous and non-nitrogenous substance, in three forms
of food used largely in three different quarters of the world,
may be thus stated :

ANIMAL CHEMISTBY. 405

Rice. Potato. Plantain.

Gluten 7^ 8 5|

Starch,etc 92^ _92 94|

100 100 100~

The percentage is reckoned here upon the dry food, that
is, the substance freed from the water which is naturally
in it. The albuminous material in cabbage is much great-
er than in these articles, being from 30 to 35 per cent., and
in cauliflower it is still greater. In the onion it is from
25 to 30 per cent. In tea-leaves it is 25 per cent., so that
if they were eaten they would prove good building-food.
Figs as imported, that is, partially dried, are thus com-
pared with wheat bread :

Figs. Wheat bread.

Waters 21 48

Gluten 6 5|

Starch, sugar, etc 73 46J

100 100.

Figs, therefore, have less water than the bread, a little
more gluten, and 27 per cent, more of starch and sugar.
There is a larger proportion of gluten in the covering or
husk of the wheat than in the grain itself, and therefore
the separation of the bran from the flour by bolting im-
pairs the nutritive power of the bread, that is, so far as
the building of structure is concerned.

574. Is the Division of Food into Two Kinds Correct? —

The classification of food given in § 565, which is that of Liebig, though
generally received, is considered by some as without foundation. One of
the chief objections to it is that the large proportion of heat-food which is
used in warm climates in the form of starch, in such articles as rice and
the plantain, is in opposition to it. But the objector forgets that man is
always throwing off heat freely into the air even in hot climates ; for when
in such climates the atmosphere is at a higher degree of temperature than
36.6° C., the animal heat passes off in the abundant perspiration, both sen-
sible and insensible. If it were not for this, disastrous consequences would
result from exposure to excessive heat, either in a hot climate or in the

406 CHEMISTEY.

heated apartments in which some manufactures are carried on. There
are other objections to Liebig's classification, but we will not dwell on
them. The division is probably in the main correct, and yet there are
some facts that seem to show that plastic food is sometimes used for
the production of heat, and that fuel -food is sometimes used for build-
ing. If so, it is an exception to a general rule, and indicates that the
chemistiy of life is not bound by such strict lines as is inorganic chem-
istry.

575. Amount of Animal Heat. — At first thought it seems
strange that so much of the food, ordinarily four fifths,
should be expended as fuel in producing heat, because we
are in the habit of thinking of food as doing good only in
building up and repairing the system. This is the com-
mon popular view of nourishment, and it is only the in-
vestigations of the chemical physiologist that make us
realize of what importance heat is in the maintenance of
living action. It is calculated that the amount of heat
produced in the body of an adult man in one year would
suffice to raise from twenty to twenty-five thousand pounds
of water from the freezing to the boiling point. The heat,
then, required to run the animal machine, as we may ex-
press it, is very great, and therefore there must be a large
provision of fuel.

576. Uses of Pat in the System.— There is one form of
heat-food — fatty matter — which is used quite extensively
in building up the structures of the system, though in the
wear and tear of these structures it may eventually serve
as fuel. But it is Liebig's idea that the fat which is so
largely present in many tissues is not really a part of them,
but is contained in them very much as water is contained
in the interstices of a sponge. The combination, however,
is certainly more intimate than this; perhaps it may be
considered like that of phosphate of lime with gelatin in
bone. And in the case of the brain there seerns to be even
a chemical combination of fatty matter with phosphoric

ANIMAL CHEMISTRY. 407

acid. More than one fifth of the solid matter of the brain
is fat, and this substance constitutes more than a sixth
part of the solid matter of muscle. It is present in con-
siderable quantity, also, in other structures. It must, then,
have other uses besides heat-making. Besides its useful-
ness in the textures of organs, it is of some local benefit as
deposited in masses. Thus the eyeball rests in its socket
upon a cushion of fat.

577. Phosphorus and Sulphur. — Phosphorus does not ex-
ist as such in animals, but is in combination with soda and
lime. The phosphate of lime is present in large quantity
in the bones. In the body of an adult man there is in the
bones from 2 to 3 kilogrammes of this salt, and the phos-
phorus in it amounts to from 500 to 800 grammes. Phos-
phorus forms one of the most important constituents of cer-
tain complex fatty bodies in the brain. It is extensively
provided for animals in their articles of food, mostly in
the form of phosphate of lime. Phosphorus exists in eggs,
and in all animal food. It is one of the components of
milk, the universal and sole food of the mammalia in their
infancy. It is also present in many seeds. So abundant is
it in oats that the horse is liable to an earthy concretion
in the bowels, of which phosphorus is a chief ingredient.
Sulphur also occurs in combination in animals, chiefly in
the albuminous or protein substances, and in some of the
tissues. It comes from both animal and vegetable sources.
Like phosphorus, it exists in flesh, eggs, and milk. It is also
in the nitrogenous compounds of plants, gluten, albumen,
and casein ; and, combined with lime in the form of a sul-
phate, it is in most of the water that we drink.

578. Lime. — This is one of the most widely diffused min-
eral substances both in the animal and vegetable kingdoms.
It exists largely in the seeds of most grasses, especially in
the grains of wheat. Beans and pease have more nitroge-

408 CHEMISTRY.

nous matter than wheat, and therefore would be more nutri-
tious were they not deficient in a salt of lime, the phosphate.
There is considerable lime supplied to plants and animals
from water in the forms of the carbonate and the sulphate,
these salts being present in all hard water. The thickness
of the shells of aquatic mollusks depends very much upon
the amount of carbonate of lime in the water. Those which
live in the sea have as much as they need, and their shells
have considerable thickness ; but those which are found in
fresh-water lakes, where there is but little lime, have thin
shells. There are some lakes, however, where, from local
causes, the water is greatly impregnated with calcareous
matter, and the mollusks that inhabit them have shells of
uncommon thickness. Hens require more lime than usual
when they are laying eggs, and they therefore instinctive-
ly at such times eat chalk, mortar, or any substance they
can find which contains carbonate of lime. If they are
shut up where they can not obtain this they lay eggs
without shells, and if they obtain it sparingly the shells
are thin.

579. Iron. — This metal is absolutely essential to the
blood, and is present in all the pigments of the body, in
the bile, and in various tissues, especially the hair. The
quantity of iron in the blood is very small, it being only
about the one four-hundredth part of its solid matter. It
varies in different persons, being greater in the sanguineous
than the lymphatic, in the well-fed than those who live on
a poor diet. It is found more or less in most articles of
food. It is in the yolk of eggs and in milk, as well as
in animal flesh. It is present in most of the vegetable
substances used as food by man, such as potatoes, cabbage,
pease, mustard, etc. We have said that iron is essential to
the blood. It is there not so much to be supplied to the
tissues as to execute certain offices in the blood itself.

ANIMAL CHEMISTRY. 409

These offices we will indicate so fur as they are ascer-
tained. The blood, examined by the microscope, is seen
to consist of two parts, an almost colorless liquid called
liquor sanguinis, or liquor of the blood, and floating in this
are multitudes of rounded particles called globules of the
blood, or blood-disks. These are little sacs or vesicles con-
taining a fluid, and the iron forms one of the constituents
of certain crystalline principles suspended in this fluid.
These globules convey the oxygen received in the lungs
to all parts of the body, and the liquor sanguinis probably
brings back to the lungs the carbonic acid which is to be
discharged there. The crystalline bodies containing iron
act as common carriers for oxygen. When iron is deficient
in the blood some form of iron medicine is administered by
the physician.

580. Salt. — The amount of salt in the blood is about
three times that of iron. Though it is nowhere present as
a part of any tissue, it is of much service in the formative
processes, both as salt and by its elements, it being to some
extent decomposed in the body. There is no salt found in
the juices of muscles, but one of its elements, chlorine, is
found there combined with potassium, and this element is
undoubtedly derived from the salt in the blood. In the
bile of land animals there is soda, derived from the same
source. Then there is hydrochloric acid, an efficient part
of the gastric juice in the process of digestion, which is
furnished in some way from the decomposition of salt. We
use salt instinctively with our food with some articles, as
potatoes, more than with others. As it is not as abundant
in plants as it is in animal food, considerable pains are taken
to supply our domestic herbivorous animals with a suf-
ficiency of this important article of diet. And, to meet the
instinctive desire of the wild animals for it, there are places
where it exists in the soil, to which they can resort for it.

410 CHEMISTRY.

Such are the " buffalo-licks " of this country. The results
of some experiments which have been tried with cattle in
relation to salt as an article of food are interesting and
instructive. The salt had no influence on the flesh or on
the amount of milk obtained ; but the set which had salt
mixed with their fodder had a much better coat, and were
much more lively than the set from which salt was with-
held.

581. Water. — This is the largest ingredient in animal
bodies. It constitutes nearly 80 per cent, of the blood, and
the same of the brain, and nearly 75 per cent, of the muscles.
The body of a human being is about three fourths water.
One great use of this abundant substance in the animal is
to furnish a proper vehicle for the solid substances in their
circulation. The materials for growth are carried every
where in it, and the worn-out particles are conveyed to their
natural outlets. It also serves various purposes in the tis-
sues, giving transparency to some, as the cornea, the beau-
tiful clear front-covering of the eye, and giving to the mus-
cles and the membranes their softness, flexibility, and elas-
ticity. Water is in these respects as essential to life as any
other substance. Being thus needed in the animal, it is
largely present in all the vegetable substances which are
used as food ; and as in vegetables it furnishes in its
decomposition its elements for the formation of the com-
pounds which they contain, so it may do to some extent
in animals.

582. Endosmose and Exosmose.— In connection with water, it is
proper to notice an agency which has a wide influence on the circulation of
matter, both in vegetable and animal substances. This agency is exhib-
ited in the following experiment: B C (Fig. 119, p. 411) is a glass tube
expanded at its lower end, which has a piece of moist membrane, as fresh
bladder, tied over it. If we pour some water into the vessel, and also so
much into the tube as will make it at the same level with that in the vessel,
there will be no change in the levels, however long the apparatus mny be left

ANIMAL CHEMISTRY.

411

Fig. 119.

to stand. But if we add salt to the water in the tube, the solution thus made
will in a few minutes rise in the tube, while the water in the vessel will
fall. This is because some of the water, attracted by the
solution of salt, passes through the pores of the bladder.
The salt has given the water in the tube something like a
power of suction. We can vary this experiment in several
ways. If the salt be put into the vessel, the contrary effect
will be produced — the water in the tube will fall below the
level of the fluid in the vessel. If salt be put into both ves-
sel and tube in equal proportions, no change will follow ;
but if in unequal proportions, the suction will be toward the
strongest solution. Suppose now that instead of salt you
put a solution of gum or sugar into the tube, holding it so
that the level shall be the same with that of the water in
the vessel. Here the fluid in the tube will rise, because the
water from without presses in through the bladder. This
passing inward is called by Dutrochet, who first developed
this subject, endosmose, from two Greek words — endon, inward, and osmos,
impulsion, or pressure. But some of the gum or sugar is found, after a
time, in the water outside. There is, therefore, also a transmission from
within outward, though less than that from without inward, and this he
called exosmose, ex meaning from or outward. The membrane used in
such experiments is called the septum. Similar phenomena are seen with
other substances ; as, for example, albumen, a substance which is largely
present in animals. You can readily see, then, that the agency which we
have described must have a very wide influence on the circulation of fluids
in both the animal and vegetable world, for salt, gum, sugar, albumen, etc.,
are common substances in these fluids, and there are soft and porous mem-
branes every where ready for this endosmotic and exosmotic action. And
we may remark, in passing, that the influence of this agency is very consid-
erable, also, in the mineral world, for gases as well as liquids are affected
by it, and it may act through almost any porous substance.

583. Circulation of Matter. — You have seen in this book
that in the ministration of nature to the wants of man and
other animals there is a constant circulation and inter-
change of matter between the three kingdoms of nature.
First there is a circulation in the strict sense of that word,
for there is a movement in a circle. As the vegetable re-

412 CHEMISTRY.

ceives its materials from the mineral world, and the ani-
mal from the vegetable, there is a continual return in de-
cay from the animal to the mineral world. Death is thus
constantly ministering to life, and life to death ; and life
may be considered as being maintained by a constant suc-
cession of resurrections, not a particle of matter being lost
in all the changes that take place, even in those where there
is apparent destruction. As that which is made of dust
returns to dust, a new life rises up out of that dust, exhib-
iting a reality more wonderful than that of the fabled
Phoenix which shadows it forth. But there is interchange
as well as circulation. The animal kingdom does not re-
ceive all its material through the vegetable, but some of
it comes directly from the mineral kingdom. And then
the vegetable, standing as it does between the animal and
mineral kingdoms, receives from both, and gives to them
in return. It yields back to the mineral world in decay
what it receives from it ;• and while it receives from the
lungs of animals carbonic acid, it gives back to them the
oxygen which they need every moment for the maintenance
of life. It is thus that the earth, with all its stability, has
vast changes going on continually and every where upon
its surface, in which air and water and heat and light and
electricity and chemical and vital agencies are ever busy ;
and yet, extensive as these changes are, and accompanied
with disturbance, conflict, and decay, the Creator, who
seeth the end from the beginning, preserves amid it all a
wonderful balancing and harmony, so that from age to age
we see the impress which he put upon creation at the first,
and bear witness that it is all " very good."

ANIMAL CHEMISTRY. 413

QUESTIONS.

557. What is said of the elements which come into play in animal chem-
istry ? Give examples of the combinations of elements that are introduced
into animals. — 558. Indicate some of the points in which animal and veg-
etable chemistry are alike. — 559. Indicate some in which they differ. —
SCO. Give in full- what is said of the composition of the blood. — 561. De-
scribe in full the way in which the blood is made. — 562. What is said of
the occurrence of albumen in animals ? — 563. What are the constituents
of the contents of an egg ? What is said of the formation of the bird
in the egg ? — 564. What of gelatin ?— 565. Into what two classes are the
various kinds of food divided? State what is said of the heat -making
class. — 566. What relation has climate to food? — 567. How is the warmth
of some hibernating animals maintained in their torpid state ? What is
said of the fat of the body in disease ? — 568. What of corpulency ? What
of the butter in milk ? What of fattening animals ? — 569. What apparent
discrepancy is there in regard to the food and the animal heat of carnivo-
rous and herbivorous animals ? State in full what is said to clear up this
discrepancy. — 570. What is said of the relation of food to labor? What
is said of the manna of the Israelites ? What of the proportion of nitrog-
enous to heat-making food ? What of the use of an excess of animal food ?
—571. What of the mingling of the two kinds of food ? What is said of
feeding animals on some single substance alone ? — 572. What of the com-
bination in milk? What error is frequently committed in the diet of chil-
dren ? — 573. State in full what is said of the proportions of the two classes
of food in different articles. — 574. What is said of the chief objection to
Liebig's classification? — 575. What is said of the amount of animal heat?
— 576. What of the uses of fat in the system ? — 577. What is said of phos-
phorus in animals and in their food? What of sulphur?— 578. What of
the diffusion of lime in nature ? What is said of the thickness of the shells
of mollusks ? What of the shells of hens' eggs ? — 579. What of the pres-
ence of iron in animals? WThat of its presence in food? What of its of-
fices in the blood ? — 580. What is said of the presence of salt in animals ?
What of its use as an accompaniment of food? — 581. State in full what is
said of water as an ingredient of animal and vegetable substances ? — 582.
Explain in full endosmose and exosmose. — 583. Give in full what is said
of the circulation of matter ? Also what is said of its interchange. And
what is said of the harmony of creation in the midst'-of all its change.

APPENDIX.

METRIC SYSTEM OF WEIGHTS AXD MEASURES.

(FROM: MILLER'S "INORGANIC CHEMISTRY.")

THE weights and measures used in this work are those
of the metric system, which, on account of their simplicity
and convenience, are now commonly employed by men of
science throughout the world.

The unit of length in this system is the meter, which is
equal to 3.937 English inches. From this integer all meas-
ures of surface capacity and weight are derived. The sub-
divisions of the meter are marked by the Latin prefixes
deci, ten, centi, a hundred, and mitti, a thousand ; so that the
tenth of a meter is called a decimeter, the hundredth of a
meter a centimeter, and the thousandth of a meter a mil-
limeter. The higher multiples are indicated by the Greek
prefixes deca, ten, hecto, one hundred, kilo, one thousand ;
but the prefix kilo, or multiple by one thousand, is almost
the only one used in practice. For instance, the higher
multiple, or 1000 meters, is called a kilometer. It is used
as a measure of distance by road, and represents about
1094 yards, 16 kilometers being equal to nearly 10 English
miles.

416 METEIC SYSTEM OF WEIGHTS AND MEASURES.

Each side of this square measures

1 Decimeter, or
10 Centimeters, or
100 Millimeters, or
3.937 English inches.

A liter is a cubic measure of 1 decimeter in the side, or a cube
each side of which has the dimensions of this figure.

When full of water at 4° C. a liter weighs exactly 1 kilogramme,
or 1000 grammes, and is equivalent to 1000 cubic centimeters, or
to 61.024 cubic inches, English.

A gramme is the weight of a centimeter cube of distilled water ;
at 4° C. it weighs 15.432 grains.

100.

Centim-
eter.

-1

-5

-in

- 4 inches. •

The measures of capacity are connected with those of
length by making the unit of capacity in this series a cube
of one decimeter, or 3.937 English inches, in the side; this,
which is termed a liter, is equal to 1.7637 imperial pints, or
to 61.024 cubic inches.

Finally, the system of weights is connected with both the
preceding systems by taking as its unit the weight of a
cubic centimeter of distilled water at 4° C.: it weighs 15.432
English grains. The gramme^ as this quantity is called, is

APPENDIX.

417

further subdivided into tenths or decigrammes, hundredths
or centigrammes, and thousandths or milligrammes, the mil-
ligramme being equal to about ^ of a grain.

The higher multiple of 1000 grammes constitutes the
kilogramme. It is the commercial unit of weight, and
represents 15,432 English grains, or rather less than 2^
Ibs. avoirdupois.

The weight of 1000 kilogrammes, or a cubic meter, of
water, is 0.9842 of a ton, which is sufficiently near to a ton
weight to allow of its being reckoned as one ton in rough
calculations.

Various plans have been devised for converting the
French weights and measures into their English equiva-
lents. The following tables will be found useful for this

purpose :

MEASURES OF LENGTH.

Millimeter

English inches.
= .03937

DccaniGtcr. ...

English inches.
= 393.70790

Centimeter ....

= .39371

Hectometer. . .

= 3,937.07900

Decimeter

= 3.93708

Kilometer ....

= 39,370.79000

Meter . .

. - 39.37079

Mvriameter. . .

= 393,707.90000

MEASURES OF VOLUME.

Milliliter, or 1 cubic centimeter

Centiliter, or 10 cubic centimeters

Deciliter, or 100 cubic centimeters

Liter, or 1 cubic decimeter, or 1000 cubic centimeters.

Decaliter

Hectoliter

Kiloliter

Myrialiter

Milligramme

Centigramme

Decigramme = 1.54323

Gramme... . = 15.43235

MEASURES OF WEIGHT.

English grains.
= .01543
= .15432

Decagramme..
Hectogramme.
Kilogramme . .
Myriagramme.

Cubic inches.

.06103

.61027

6.10271

61.02705

610.27052

6,102.70515

61,027.05152

010,270.51519

English grains.
154.32349
1,543.23488
15,432.34880
154,323.4880

418 METEIC SYSTEM OF WEIGHTS AND MEASUEES.

The temperatures given in this book are expressed
throughout in degrees of the Centigrade thermometer, un-
less otherwise specified. The following is a short compara-
tive table of the two scales, Centigrade and Fahrenheit.

—20°

-4°

15°

59°

45°

113°

75°

107°

— J5

122

176

-10

131

185

— 5

140

194

149

203

104

158

100

212

The formula for converting degrees on Fahrenheit's
scale to corresponding degrees on the Centigrade scale is
£ (F.° —32) = C.°; and for converting Centigrade to Fah-
renheit, | C.° +32 = F.°. For further data with regard to
thermometer scales, see Part L

INDEX.

[The numbers refer to the sections.]

Absorbent power of charcoal, 96.

Acetates, 508.

Acetous fermentation, 552.

Acetous fermentation explained, 554.

Acid, boracic, 269.

Acid, carbonic (foot-note on page 84),

102, 110.

Acid, hydrochloric, 222.
Acid, hydrochloric, preparation of,

224.

Acid, hydrocyanic, 166.
Acid, muriatic, 222.
Acid, nitric, 71.
Acid, phosphoric, 257.
Acid, picric, 440.
Acid, prussic, 166.
Acid, pyroligneous, 436.
Acid salts, 80.
Acid, stearic, 514.
Acid, sulphuric, fuming, 241.
Acid, sulphuric, manufacture of, 242.
Acid, sulphuric, Nordhausen, 241.
Acid, sulphuric, properties of, 244.
Acid, sulphuric, uses of, 247.
Acid, tannic, 509.
Acidity of wines, 541.
Acids, nomenclature of, 79.
Acids, organic, 508.
Acids, organic, how derived, 424.
Acids, tests for, 78.
Actinism, 393.
Adhesion, 37.

Affinity, bonds of, 44.
Affinity, chemical, 38.
Affinity, Providence seen in, 39.
Air, a mixture proved, 139.
Air, analysis of, 118.
Air and nitric oxide contrasted, 85.
Air, composition of, 45.
Air, impurities in the, 138.
Air in water, composition of, 134.
Air, water in the, 137.
Albumen, 562.
Albumen, vegetable, 468.
Albuminoids, 470.
Alcohol, amount of, in wines, 542.
Alcohol, amylic, 545.
Alcohol made from starchy substan-
ces, 543.

Alcohol, methylic, 437.
Alcoholic fermentation, 537.
Alcohols, how derived, 422.
Alkaline earths, 310.
Alkaloids related to amines, 425.
Alkaloids, vegetable, 531.
Allotropism, 65, 101.
Alloys, nature of, 279.
Alum, common, 327.
Alumina, 326.
Aluminium, 325.
Amalgamation, 377.
Amalgams, 278.
Amber, 527.
Amines defined, 425.
Ammonia in guanos, 501.
Ammonia in rain-water, 477.

420

INDEX.

Ammonia, preparation of, 162.

Ammonia, production of, 160.

Ammonium salts, 307.

Ammonium, the metal, 306.

Amorphous sulphur, 235.

Amylic alcohol, 545.

Analysis, 16.

Analysis, organic, described, 427.

Animal and vegetable structures
compared, 410.

Animal heat, 197.

Animal heat, amount of, 575.

Animal heat, exercise and, 203.

Animal substances, carbon in, 94.

Animals and vegetables compared,
558.

Animals, carnivorous and herbivo-
rous, 569.

Animals, cold-blooded, 204.

Animals, influence of light on, 392.

Animals, materials used in structure
of, 557.

Animals, subservience of plants to,
409.

Anthracite, 439.

Antimony, 362.

Antiseptics, 535.

Aqua regia, 225.

Arbor Dianas, 380.

Arsenetted hydrogen, 360.

Arsenic, 356.

Arsenic, antidotes to, 357.

Arsenic, antiseptic properties of, 358.

Arsenic-eating, 359.

Arsenical pigments, 361.

Artiads, 44.

Asphaltum, 441.

Assay of silver, 381.

Atmosphere, carbonic anhydride in
the, 116.

Atmosphere, ingredients of the, 115.

Atmosphere, nitric acid in the, 77.

Atmosphere, nitrogen in the, 117.

Atmosphere, sources of carbonic an-
hydride in the, 127.

Atomicity, table of, 44.

Atomic philosophy, 20.

Atoms, 22.

Atoms, properties of, 25.

Atoms, weight of, 26.

Attraction, chemical, 37.

Attraction, chemical, action of heat

on, 41.
Attraction, chemical, modifiers of, 40.

Ballooning, 147.

Barium, 308.

Barytes, 308.

Bases and salts, 80.

Benzol, 440.

Bessemer process for steel, 344.

Bismuth, 364.

Bismuth nitrate, 365.

Bituminous coal, distilled, 440.

Black ash, 301.

Blast-furnace, 340.

Bleaching, 196, 216.

Bleaching powder, 322.

Blood, 560.

Blood disks, 579.

Blood, how made, 561.

Blowpipe, use of, 182.

Blowpipe, oxy hydrogen, -188.

Blue vitriol, 366.

Body, temperature of the, 199.

Bonds of affinity, 44.

Bone-black, 93.

Bone-dust, 502.

Boracic acid, 269.

Borax, 304.

Boron, 269.

Bread, raising of, 546.

Bread, sour, 553.

Britannia ware, 278.

Bromine, 231.

Bronze, 278.

Brunswick green, 361 .

Bunsen and Kirchhoff, 402.

Bun sen's burner, 181.

INDEX.

421

Burner, Argand, 180.

Burner, Bunsen's, 181.

Butter of zinc, see Zinc chloride, 333.

Cadmium, 281.

Caffeine, 531.

Calamine,331.

Calcium, 310.

Calcium carbonate, 315.

Calcium, phosphate of, 324.

Calcium, phosphide of, 256.

Calcium, sulphate of, 319.

Calculations, mathematical, 3G.

Calico-printing, 534.

Calomel, 376.

Camphor, 526.

Candle, chemistry of a, 171.

Candle, experiments with a, 173.

Candle, extinguishing a, 184.

Candles made from stearin, 516.

Cane-sugar, 458.

Caoutchouc, 529.

Carat, 382.

Carbon, 89.

Carbon, abundance of, 89.

Carbon, sources of, in plants, 474.

Carbonate of lead, 371.

Carbonic anhydride, 102.

Carbonic anhydride, absorption of,

109.
Carbonic anhydride and combustion,

106.
Carbonic anhydride and digestion,

108.
Carbonic anhydride and respiration,

107.
Carbonic anhydride, preparation of,

103.
Carbonic anhydride, properties of,

104.
Carbonic anhydride, solidification of,

105.

Carbonic oxide, 112.
Carbonic oxide, preparation of, 113.

Carburetted hydrogen, 154.

asein, vegetable, 469.

ast iron, 341.
Casts of coins, 320.

atalysis, 43.
Caustic potash, 286.
Cavendish, 147, 479.

elestial spectroscopy, 405.
Cellulose, 430.

Centigrade thermometer compared
with Fahrenheit, see Appendix, p.
418.

Chalk, 316.
Champagne, 539.
Charcoal, absorbent power of, 96.
Charcoal burned in oxygen, 57.
Charcoal, fumes of, 124.
Charcoal, manufacture of, 90.
Charcoal, properties of, 95.
Chemical action, characteristics of,

15.

Chemical action, nature of, 10.
Chemical action, variety of, 12.
Chemical affinity, 38.
Chemical attraction, modifiers of, 40.
Chemical combination, laws of, 32.
Chemistry and Physics, difference

between, 23.

Chloride of lime, composition of, 323.
Chloride of sodium, 296.
Chlorine, 208.

Chlorine a disinfectant, 220.
Chlorine and respiration, 212.
Chlorine, attraction of, for hydrogen,

215.

Chlorine bleaching, 216.
Chlorine, combustion in, 221.
Chlorine, occurrence of, 209.
Chlorine, oxides of, 226.
Chlorine, preparation of, 210, 211.
Chlorine water, 213.
Chloroform, 550.
Chlorophyll, 447.
Chromium, 352.
Chrome yellow, 352.

422

INDEX.

Cinnabar, 374.
Clay, constituents of, 259.
Clays, ingredients of, 326.
Climate and food, 566.
Coal, 98.

Coal, combustion of, 177.
Coals, varieties of, 439.
Cobalt, 348.
Cohesion, 37.
Collodion, 433.
Coloring matters, 532.
Combustion by nitric acid, 76.
Combustion, chemistry of, 169.
Combustion, early ideas of, 168.
Combustion, general remarks on, 167.
Combustion in chlorine, 221.
Combustion, means of hastening, 180.
Combustion of hydrogen, 170.
Combustion, requisites for, 194.
Combustion, results of, 179.
Combustion, spontaneous, 192, 521.
Combustion without oxygen, 193.
Compound ethers (page 388), 548.
Compounds and mixtures, difference

between, 157.
Compounds, chemical, composition

of, 27.

Compounds, naming of, 18.
Copper, 366.
Copper, nitrate of, 73.
Copper, sulphate of, 367.
Copper, test for, 368.
Coral, 315.
Corpulency, 568.
Courtois, M., 228.
Cream of tartar, 508.
Creosote, 436.
Crops, rotation in, 494.
"Cry "of tin, 353.
Cyanogen, 164.
Cyanogen, preparation of, 165.

Daguerre, 389.

Davy, Sir Humphrey, 4, 154.

Definite proportions, law of, 27.
Deliquescence, 159.
Dephlogisticated air, 48.
Deville,M.,325.
Dextrin, 454.
Dextrin from starch, 455.
Diamond, 100.
Diastase, 472.
Diffusion of gases, 120.
Dimorphism, 234.
Displacement, 104.
Dissociation, 43.
Distillation of liquors, 544.
Dobereiner's lamp, 385.
Drummond light, 189.
Dyads, 44.
Dynamite, 515.

Eau de Cologne, 524.

Efflorescence, 159.

Egg, formation of the bird in the,

563.

Electrolysis, 141.
Element, definition of, 2.
Elements, ancient view of, 3.
Elements as found in nature, 6.
Elements, atomicity of, 44.
Elements, atomic weights of, 4, 26.
Elements, classification of, 5.
Elements, forms of, 5.
Elements in organized bodies, sources

of, 408.

Elements, principal, 4.
Elements, table of, 4.
Emerald, 330.
Emery, 326.
Endosmose, 582.
Epsom salt, 329.
Equations explained, 33, 35.
Etching on glass, 232.
Ether, preparation of, 549.
Ether, properties of, 547.
Ethers, compound (page 388), 548.
Ethers, how derived, 423.

INDEX.

423

Ethylamine, 425.
Ethylene, 419.
Eudiometer, 144.
Exosraose, 582.

Explosions of oxygen and hydrogen,
190.

Fahrenheit scale compared with the

Centigrade, see Appendix, p. 418.
Fat, uses of, in the system, 576.
Fats, combustion of, 522.
Fats, properties of, 519.
Fatty acid series (see table on page

303), 508.

Fermentation, acetous, 552.
Fermentation, alcoholic, 537.
Fermentation, varieties of, 535.
Ferments, 536.
Ferric hydrate, 338.
Fertilizers, 496.
Fibrin, vegetable, 467.
Fire extinguishers, 187.
Fire under water, 186.
Fires, bad management at, 183.
Fires, extinguishing, 185.
Fishes and water-plants, 136.
Flame, nature of, 176.
Flame shown to be hollow, 173.
Flame, structure of candle's, 172.
Flames, oxidizing and deoxidizing,

174.

Flints, liquor of, see Soluble glass.
Fluorine, 232.
Food and labor, 570.
Food, classification of, by Liebig,

565.

Food, heat, and building, 571.
Food, two kinds of, 565.
Fool's gold, 346.

Forces, physical and chemical, 37.
Forms of substances, how affected by

heat, 9.

Formula explained, 29.
Formulae, graphic, 417.

Franklin, anecdote of, 505.
Fuel, sources of, in animals, 200.
Fumes of burning charcoal, 124.
Fuming sulphuric acid, 241.
Fusel-oil, 545.
Fusible metal, 279.

Galena, extraction of silver from,
379.

Galvanized iron, 334.

Gas, illuminating, 154.

Gas, manufacture of, 178.

Gases and gravitation, 119.

Gases and vapors, difference between,
50.

Gases, diffusion of, 1 20.

Gelatin, 564.

Glass, annealing of, 264.

Glass, coloring of, 263.

Glass, etching on, 232.

Glass, general remarks on, 262.

Glass, soluble, 266.

Glauber's salt, 303.

Glazing, 268.

Gluten, 467.

Glycerin, 575.

Glyceryl, 514.

Gold, 382.

Gold chloride, 383.

Goodyear, anecdote of, 530.

Gramme, value of, see Appendix, p.
415.

Grape-sugar, 460.

Graphite, 99.

Grass-bleaching compared with chlo-
rine-bleaching, 218.

Grass-bleaching explained, 196.

Green fire, 308.

Grotto del Cane, 122.

Guano, 499.

Guano, tests of, 500.

Gums, 453.

Gun-cotton, 433.

Gunpowder, 292.

424

INDEX.

Gunpowder, explosion of, explained,

293.

Gutta-percha, 529.
Gypsum, 319.
Gypsum in agriculture, 505.

II.

Hard soap, 518.

Hare's blowpipe, 188.

Harmonica chemica, 151.

Hatcheling, 431.

Heat, relations of, to forms of sub-
stances, 9.

Hematite, 338.

Hibernation, 205.

Hibernation, warmth in, 567.

Homologues and isologues, 420.

Honey, 465.

Humus, 490.

Hydrates, 80.

Hydrocarbons, ethylene series of,
419.

Hydrocarbons in petroleum, 443.

Hydrocarbons of illuminating gas,
154.

Hydrochloric acid, production of,
223.

Hydrogen and respiration, 152.

Hydrogen, arsenetted, 360.

Hydrogen, combustibility of, 148.

Hydrogen compared with carbonic
anhydride, 146.

Hydrogen, metallic nature of, 156.

Hydrogen not a supporter of com-
bustion, 150.

Hydrogen peroxide, 155.

Hydrogen, phosphoretted, 255.

Hydrogen, preparation of, by iron
and steam, 142.

Hydrogen, preparation of, by zinc
and sulphuric acid, 143.

Hydrogen, sounds in, 153.

Hydrogen, specific gravity of, 145.

Hydrogen, sulphuretted, 248.

Hydroxyl, 421.

India rubber, 529.

Indigo, 532.

Ink, sympathetic, 349.

Ink, writing, how made, 512.

Instability of organic bodies, 413.

Iodine a supporter of combustion,

230.

Iodine, preparation of, 229.
Iodine, production of, 228.
Iridium, 387.
Iron, abundance of, 337.
Iron, galvanized, 334.
Iron in the animal kingdom, 579.
Iron, oxides of, 338.
Iron, production of, from ores, 340.
Iron, pure, 336.
Iron, sulphides of, 346.
Isologues and homologues, 420.
Isomerism defined, 415.
Isomerism explained, 416.
Isomorphism, 328.

Kelp, 228.

Kerosene, unsafe, 445.

Kirchhoff, 402.

Kol-cannon, foot-note on p. 403.

Lagoons of Tuscany, 269.

Lakes, 327.

Lamp, Dobereiner's, 385.

Lampblack, 92.

Lana philosophica, 331.

Laughing-gas, 81.

Lavoisier, 17, 48.

Laws of chemical combination, 27,

30, 31.
Lead, 369.
Lead acetate, 373.
Lead, oxides of, 370.
Lead-pencils, 99.
Lead-poisoning, 372.

INDEX.

425

Lead-tree, 373.

Leaves, chemistry of, 128, 130.

Liebig's classification of food, 574.

Light and locomotives, 391.

Light, chemical influence of, 388.

Light dissected, 393.

Light, Drummond, 189.

Light-pictures, 395.

Lignite, 439.

Lime, carbonate of, 315.

Lime, chloride of, 322.

Lime in the animal kingdom, 578.

Lime-kiln, 311.

Lime, phosphate of, 253.

Lime, solubility of, 313.

Limestone, 315.

Lime-water, 125.

Linen and cotton, 431.

Liquor sanguinis, 579.

Liter, value of, see Appendix, p. 415.

Litharge, 370.

Lunar caustic, 380.

Lungs, carbonic anhydride from the,

125.
Lungs not the body's furnace, 198.

Madder, 532.
Magnesia alba, 329.
Magnesium, 329.
Manganese, oxides of, 335.
Manna, 46G.
Manures, 495.
Manures, animal, 498.
Manures, volatile bodies in, 497.
Manuring, green, 480.
Marl, 493, 504.
Marsh gas, 154.
Marsh gas series, 420.
Massicot, 370.

Matches, manufacture of, 252.
Mathematical calculations, 36.
Matter, circulation of, in the three

kingdoms, 583.
Matter, constitution of, 19.

Matter, expansion of, explained, 21.

Matter, forms of, 11.

Mercuric chloride, 376.

Mercury, 374.

Metal, fusible, 279.

Metals, action of chlorine on, 214.

Metals, action of nitric acid on, 73.

Metals, atomicity of, 281.

Metals, characteristics of, 270.

Metals, classification of, 281.

Metals, color of, 272.

Metals, density of, 271.

Metals, ductility of, 275.

Metals, fusibility of, 276.

Metals, malleability of, 274.

Metals, specific gravity of, 271.

Metals, tenacity of, 273.

Metals, welding of, 277.

Metamerism, 415.

Meteorites, 339.

Meter, value of, see Appendix, p. 415.

Methylic alcohol, 437.

Milk, 572.

Milk-sugar, 459.

Minerals, peculiarity of, 8.

Minium, 370.

Moire' metallique, 353.

Molecular weights, law of, 30.

Molecules, 20.

Molecules and state of aggregation,

21.

Molecules, compound and simple, 24.
Mordants, 327, 533.
Mordants, colors modified by, 534.
Morphine, 531.
Mortar, 314.
Mother of vinegar, 552.
Multiple proportions, law of, 31.
Musical sounds of burning hydrogen,

151.

Nascent state, 42.

Nascent state illustrated by forma-
tion of ammonia, 1G1.

426

INDEX.

Neutral salts, 80.

New elements, discovery of, 403.

Nickel, 350.

Nicotine, 531.

Nihil album, 331.

Nitrates, 75.

Nitre, 291.

Nitric acid, preparation of, 71.

Nitric acid, properties of, 72.

Nitric anhydride, 70.

Nitric oxide, 83.

Nitric peroxide, 88.

Nitrogen, abundance of, G6.

Nitrogen, chloride of, 227.

Nitrogen in respiration, 68.

Nitrogen in the air, 132.

Nitrogen, oxides of, 69.

Nitrogen, preparation of, 66.

Nitrogen, properties of, 67.

Nitrogen, sources of, in plants, 477.

Nitroglycerin, 515.

Nitrous anhydride, 86.

Nitrous anhydride in nitric acid, 87.

Nitrous oxide, 81.

Nitrous oxide, properties of, 82.

Nomenclature, 17, 79.

Nordhausen sulphuric acid, 241.

Oils and fats, 513.

Oils, composition of, 514.

Oils, varnish, 520.

Oils, volatile, 524.

Olefins, 419.

Ores, 280.

Organic bodies, molecules in, 412.

Organic chemistry, definition of, 411.

Organic chemistry, remarks on, 406.

Organic substances, classification of,
418.

Organic substances, constituents of,
407.

Organic substances similarly com-
posed, 41 4.

Organized bodies, 406.

Organo-metallic compounds, 426.

Osmium, 387.

Oxalic acid, decomposition of, 113.

Oxidation a slow combustion, 195.

Oxidation, degrees of, 62.

Oxides, 61.

Oxygen, abundance of, 46.

Oxygen a supporter of combustion,
56.

Oxygen, discovery of, 48.

Oxygen essential to life, 60.

Oxygen, experiments with, 57, 58,
59.

Oxygen, preparation of, by various
methods, 54.

Oxygen, preparation of, from man-
ganese dioxide, 51.

Oxygen, preparation of, from mercu-
ric oxide, 47, 49.

Oxygen, preparation of, from potas-
sium chlorate, 52.

Oxygen, properties of, 55.

Oxygen, source of, in plants, 475.

Ozone, 63.

Ozone, nature of, 65.

Ozone, test for, 64.

Paraffin series of hydrocarbons, 420.
Paris green, 361.
Pectin, 453.

Perfume ethers (page 388), 548.
Perissads, 44.
Peroxide, 62.

Petrified wood, see Silicified wood.
Petroleum, composition of, 443.
Petroleum, discovery of, 442.
Petroleum, hydrocarbons in, 443.
Petroleum, refining of, 444.
Phlogiston, 48".
Phosphoretted hydrogen, 255.
Phosphorus, amorphous, 251.
Phosphorus burned in oxygen, 58.
Phosphorus, experiments with, 250.
Phosphorus in animals, 577.

INDEX.

427

Phosphorus in nature, 254.

Phosphorus, oxides of, 257.

Phosphorus, preparation of, from
bones, 2u3.

Phosphorus, properties of, 249.

Photography, principles of, 395.

Physics, or Natural Philosophy, 1.

Plants, action of lime in cultivation
of, 503.

Plants, annual changes in, 485.

Plants, ashes of, 482.

Plants, food of, 481.

Plants growing without earth, 476.

Plants, mineral classification of, 483.

Plants, silica in, 2GO.

Plants, soil the food of, 486.

Plants, source of carbon in, 474.

Plants, water in, 484.

Plaster casts, 320.

Platinum, 384.

Plumbago, 99.

Potash, preparation of, 287.

Potassium, 282.

Potassium and water, action of, 285.

Potassium carbonate, 288.

Potassium hydrate, 286.

Potassium hydrate, action of chlorine
on, 226.

Potassium hydro-carbonate, 290.

Potassium nitrate, 291.

Potassium permanganate, 335.

Potassium, preparation of, 283.

Potassium, properties of, 284.

Pottery, 267.

Priestley's discovery of oxygen, 48.

"Prince Rupert's drops," 264.

Protein substances, 470.

Providence balancing the atmos-
phere, 131.

Proximate analysis, 427.

Puddling iron, 342.

Quartz, composition of, 259.
Quicklime, 311.

Quicklime and water, 312.
Quinine, 531.

Radical, definition of, 164.

Rat-poison, 249.

Reciprocal proportions, law of, 31.

Red fire, 308.

Resins, 527.

Resins, uses of, 528.

Rochelle salt, 508.

Rocks; changes in, 13.

Rotten wood, 446.

Ruby, Oriental, 326.

Sal volatile, 307.

Saleratus, 290.

Salt cake, 301.

Salt, common, 296.

Salt, decomposition of, 297.

Salt in the animal economy, 580.

Salt, localities of common, 298.

Saltpetre, 291.

Salts, 80.

Salt-works, 299.

Scheele, 17.

Scheele's green, 361.

Sea, salt in the, 300.

Sea- water, lime in, 318.

Seed, growth of, 471.

Sesquioxide, 62.

Sewer-water, value of, 507.

Silica, abundance of, 259.

Silicified wood, 261.

Silicon, 258.

Silver, 378.

Silver, nitrate of, 380.

Silver, salts of, 380.

Size of molecules, 20.

Slag, 265.

Slaked lime, 3 10, 3 12.

Slit of spectroscope, use of, 400.

Smalt, 348.

Snow, experiment with, 135.

428

INDEX.

Soap-bubbles of hydrogen with oxy-
gen, 191.

Soaps, 517.

Soda ash, 301.

Soda saltpetre, 305.

Sodium, 294.

Sodium bi-borate, 269.

Sodium carbonate, 301.

Sodium chloride, 296.

Sodium hydrocarbonate, 302.

Sodium sulphate, 303.

Soft soap, 518.

Soil, constitution-of, 489.

Soil, origin of, 491.

Soil, treatment of, 487.

Soil, varieties of, 493.

Soil, water in, 488.

Solder, 278.

Soot, 91.

Specific gravity of metals, 271.

Spectra, continuous, 398.

Spectra, discontinuous, 399.

Spectra of alkaline metals, 402.

Spectra of heavy metals, 404.

Spectroscope explained, 401.

Spectrum analysis, 402.

Spectrum, experiments with the, 394.

Spectrum of white light, 393.

Spongy platinum, 386.

Spontaneous combustion, 192, 521.

Stalactites, 317.

Stalagmites, 317.

Starch converted into sugar, 463.

Starch, grains of, under the micro-
scope, 450.

Starch, iodide of, 452.

Starch, occurrence of, 448.

Starch, preparation of, 449.

Starch, properties of, 451.

Steel, Bessemer process for, 344.

Steel burned in oxygen, 59.

Steel, nature of, 343.

Steel, tempering of, 345.

Stephenson, anecdote of, 391.

Stereopticon, 189.

Stoichiometry, 36.

Strychnine, 531.

Suboxide, 62.

Substitution in organic bodies, 421.

Sucrose, 457.

Sugar, cane, 458.

Sugar, cheating in, 462.

Sugar, grape, 460.

Sugar, milk, 459.

Sugar of lead, 373.

Sugars in general, 456.

Sugars, varieties of, 457.

Sulphate of magnesium, 329.

Sulphur, amorphous, 235.

Sulphur, flowers of, 236.

Sulphur, forms of, 234.

Sulphur, occurrence in animals, 577.

Sulphur, occurrence of, 233.

Sulphur, properties of, 237.

Sulphuretted hydrogen, 248.

Sulphuretted oils, 525.

Sulphuric acid, manufacture of, 242.

Sulphuric acid, properties of, 244.

Sulphuric acid, remedy for burns by,

246.

Sulphuric acid, uses of, 247.
Sulphuric anhydride, 241.
Sulphurous anhydride, bleaching by,

240.

Sulphurous anhydride, nature of, 238.
Sulphurous anhydride, preparation of,

239.

Sun, agency of the, 14, 129.
Sun-bleaching explained, 196.
Symbols, chemical, 4, 28.
Symbols explained, 30.
Sympathetic ink, 349.
Synthesis, 16.

Table of atomicity, p. 48.

Table of classification of the metals

based on atomicity, p. 205.
Table of elementary bodies, their

symbols and atomic weights, p. 13.

INDEX.

429

Table of fusing points of metals, p.
201.

Table of hydrocarbons, homologues
and isologues, p. 301.

Table of hydrocarbons, showing their
relations to alcohols, acids, and
ethers, p. 309.

Table of hydrocarbons in petroleum,
p. 324.

Table of the olefin series of hydrocar-
bons, p. 303.

Table of perfume ethers, p. 388.

Table of petroleum products, p. 325.

Table of specific gravity of the met-
als, p. 198.

Table of tenacity of the metals, p.
199.

Table of thermometers, Centigrade
and Fahrenheit, see Appendix, p.
418.

Table of weights and measures, see
Appendix, p. 417.

Tannic acid, 510.

Tanning, 511.

Tartar emetic, 363, 508.

Tessie' du Motay, 54.

Tetrads, 44.

Thermometer, Centigrade and Fah-
renheit compared, see Appendix, p.
418.

Tin, 353.

Tin, "cry of," 353.

Tin salts, 354.

Tin, sulphides of, 355.

Triads, 44.

Tri-nitro-cellulose, 433.

Tuscany, lagoons of, 2G9.

Ultimate analysis, 427.
Ultramarine, 327.

Varnish oils, 520.
Vegetable parchment, 430.

Vegetable refuse, 506.

Vegetables, influence of light on, 390.

Ventilation, 126.

Verdigris, 366.

Vermilion, 375.

Vinegar, 551.

Vinegar, adulteration of, 556.

Vinegar, quick method of making,

555.

Volatile oils, 524.
Volume, combination by, 34.
Vulcanized India rubber, 530.

Water, air in, 133.
Water as a chemical agent, 158.
Water, chlorine, 213.
Water, constituents of, 140.
Water, decomposition of, 141.
Water, formation of, from elements,

144.

Water, hard and soft, 316.
Water in the animal economy, 581.
Water of ammonia, 163.
Water of crystallization, 159.
Water, silica in, 260.
Wax, 523.

Wells, carbonic anhydride in, 123.
White-lead, 371.
Will-o'-the wisp, 255.
Windpipe, the, the smoke-pipe of the

body, 202.

Wines, acidity of, 541.
Wines, amount of alcohol in, 542.
Wines, cider, etc., 539.
Wines, flavor of, 540.
Wood, combustion of, 175.
Wood, distillation of, 435.
Wood made from sugar, 464.
Wood-naphtha, 437.
Wood, products from, on heating,

434.

Wood, silicified, 261.
Wood, sugar made from, 461.
Wood-tar, 438.

430

Wood, uses of, 432.
Woody fibre, 429.
Wrought iron, 342.

Yeast, 538.

INDEX.

Zaffre, 348.
Zinc chloride, 333.
Zinc, production of, 331,
Zinc, uses of, 334.

THE END.

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