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• - *■

INORGANIC CHEMISTRY

BY THE SAME AUTHOR.

CHEMICAL LECTURE EXPERIMENTS.

With 224 Diagrams. Crown 8vo, $2.00.

ELEMENTARY INORGANIC CHEMISTRY.

With 108 Illustrations, and 254 Experiments.
Crown 8vo, $0.90.

A MANUAL OF CHEMICAL ANALYSIS.

Qualitation and Qtiantitation.

Crown 8vo, $1.75.

LONGMANS, GREEN, & CO.
NEW YORK, LONDON, AND BOMBAY.

A TEXT-BOOK

Inorganic Chemistry

• 1

« • •»

• •

G. S. ^EWTH, F.I.C., F.C.S.

DEMONSTKATOR IN THE ROYAL COLLK(;B OK SCIENCE, LONDON

ASSISTANT-EXAMINER IN CHEMISTRY, BOARD OF

EUt'CATlON, SOUTH KENSINGTON

EIGHTH EDITION,

LONGMANS, GREEN, AND CO.

91 AND 93 FIFTH AVENUE, NEW YORK
LONDON AND BOMBAY

1900
A II rigk ti rtttrved

■ •

• •

115-1

\|559
1 900

PREFACE

In drawing up a systematic course of elementary chemical
instruction based upon the periodic classification of the ele*
ments, whether it be as a course of lectures, or as a text-book,
a number of serious difficulties are at once encountered
These possibly are sufficient to account for the fact, that
although twenty-five years have elapsed since Mendelejeflf
published this natural system of classification, the method has
not been generally adopted as the basis of English elementary
text-books.

I have endeavoured to obviate many of these difficulties,
while still making the periodic system the foundation upon
which this little book is based, by dividing the book into
three parts. Part I. contains a brief sketch of the funda-
mental principles and theories upon which the science of
modem chemistry is built. Into this portion of the book I
have introduced, necessarily in briefest outlines, some of the
more recent developments of the science in a physico-chemical
direction, of which it is desirable that the student should gain
some knowledge, even early in his career.

Part II. consists of the study of the four tjrpical elements,
hydrogen, oxygen, nitrogen, and carbon, and of their more
important compounds. By dissociating these four elements
from their position in the periodic system, and treating them
separately, the student is early brought into contact with many
of the simpler and more familiar portions of the science. Such

vi Preface

iubjects as water^ vhe atmosphere^ and combustion^ to which it
is desirable that he should be introduced at an early stage in
his studies, are thus brought much more forward than would
otherwise be the case.

In Part III. the elements are treated systematically, accord-
««ig to the periodic classification. In this manner, while
avoiding a sharp separation of the elements into the two arbi-
trary classes of metals and non-metals, it has been possible to
80 far conform to the prevailing methods of instruction, that
all those elements which are usually regarded as non-metals
(with the two exceptions of boron and silicon) are treated in
the earlier portion of the book.

The science of chemistry has of recent years developed and
become extended to such a degree, that the difficulty of giving
a fairly balanced treatment of the subject, within the limits of
a small text-book, is an ever-increasing one, and it necessarily
resolves itself into a question of the judicious selection of
matter. In making such a selection, I have endeavoured, as
far as possible, to keep in view the requirements of students
at the present time, without, however, following any examina-
tion syllabus.

Acting upon this principle, I have omitted all detailed
description of the rare elements and their compounds, con-
fining myself merely to a short mention of them in a few
general remarks at the commencement of the various chapters.

Although from a purely scientific standpoint, many of these
rare substances are of the greatest interest and importance,
it must be admitted that they stand quite outside the range
of all the customary courses of chemical instruction ; and so
for as the wants of the ordinary student are concerned, the
space which would be occupied by an account of these
elements, is more advantageously devoted to such matters

Frejace vii

as are discussed in ihe Introductory Outlines. Moreover, it
is a matter of common observation^ that text-books, even
upon the shelves of reference libraries, and which bear un-
mistakable evidence of much use, are frequently uncut in those
portions which treat of these elements.

Details of metallurgical processes, also, are out of place
in a text-book of chemistry, and must be sought in metal-
lurgical text-books. Only such condensed outlines therefore
have been given as are sufficient to explain the chemical
changes that are involved in these operations.

The great importance to the student, of himself performing
experiments illustrating the preparation and properties of
many of the substances treated of in his text-book, cannot
well be over-estimated. If he be in attendance upon a course
of chemical lectures, opportunity should be given to him for
repeating the simpler experiments he may see performed
upon the lecture table : if he be not attending lectures, the
necessity for this practical work on his part is greater stilL
Instead of burdening this text-book with specific directions
for carrying out such elementary experiments, frequent refer-
ences have been made to my "Chemical Lecture Experi-
ments," where minute directions are given for carrying out
a large number of experiments, many of which may be easily
performed, and with the very simplest of apparatus.

Several of the woodcuts have been borrowed from existing
modem works, such as Thorpe's "Dictionary of Applied
Chemistry," MendelejefTs "Principles of Chemistry," Ost-
wald's "Solutions," and others. Care has been taken, how-
ever, to exclude all antiquated cuts, and a large number of
the illustrations are from original drawings and photographs.

G. S. N.
South Kensington.

PREFACE

TO THE FIFTH EDITION

With the exception of a few additions of more modern
processes, as, for example, the electrolytic manufacture of
sodium and of caustic soda, the cyanide process for the ex-
traction of gold, the recent method of Linde and of Dewar
for the liquefaction of oxygen, and the still more recent
liquefaction of fluorine by Moissan and Dewar, no material
alterations have been made in the book. I take this oppor-
tunity for thanking the numerous friends who have kindly
pointed out the various misprints and errors in the book,
which during the issue of the four previous editions have
been gradually eliminated, so that I venture to hope that
the present edition will be found to be almost entirely free
from such blemishes.

G. S N

July 1897.

HINTS TO STUDENTS

For the help of students who may use this book at the
commencement of their chemical studies, and especially for
those who may not be working under the immediate guidance
of a teacher, the following hints are given.

Begin by carefully reading the first four chapters (pages
I to 2$). Then pass on to Part II. (page 150), and begin
the study of the four typical elements, hydrogen, oxygen,
nitrogen, and carbon, and their compounds, in the order in
which they are treated. Accompany your reading by per-
forming as many of the experiments referred to as possible,
in order that you may become practically familiar with the
substances you are studying.

During the time occupied in the study of these four
elements and their compounds, again read chapters i to 4,
and slowly and carefully continue reading Part I., so that
by the time Part III. is reached, you may have fairly mastered
at least the first thirteen chapters of the Introductory Out-
lines.

The order in which the elements are treated in Part III.
is based upon the Periodic classification, therefore read the
short introductory remarks at the commencement of the
various chapters, in the light of the table on page loa.

Throughout the book, temperatures are given in degrees
of the Centigrade thermometer, i* Centigrade equals 1.8*

Hints to Students

Fahrenheit, and as the zero of the latter scale is 3 a* below
that of the Centigrade, temperatures given in degrees of one
scale, are readily translated into degrees of the other, by
the simple formula —

(n'C X 1.8) + 32 - 'F.

The abbreviation mm., stands for millimetre ; the yitW P^
of a metre (i metre « 39.37079 inches; or roughly, 25
mm. B I inch). The abbreviation cc, signifies cubic centi-
metre; the Y7^ part of a cubic decimetre, or litre (i
litre ■= 1.76077 pints).

I gramme (the weight of i cc of distilled water, taken at
its point of maximum density) « 15*43235 English grains.

TABLE OF CONTENTS

PART I

INTRODUCTORY OUTLINES

CNAf. fACI

1. Chf mical Change— The G)nstitution of Matter — Molecnlet —

Atomt I

II. Elements and Compounds — Mixtures — Chemical Affinity —

Modes of Chemical Action 6

III. Chemical Nomenclature • •IS

rV. Chemical Symbols 20

V. The Atomic Theory — Laws of Chemical Action ... 24

VI. Atomic Weights — Modes of Determining Atomic Weights . 33

VII. Quantitative Chemical Notation $2

VIII. Valency of the Elements 58

IX. General Properties of Gases — Relation to Heat .ind Pressure —

Liquefaction — DifTusion— The Kinetic Theory . . 68

X. Dissociation 85

XI. Electrolysis 91

XII. Classification of the Elements —The Periodic System . . 97

XIII. General Properties of Liquids — Evaporation and Boiling —

The Passage of Liquids into Solids 1 10

XIV. Solution— Gases in Liquids — Liquids in Liquids — Solids in

Liquids— Osmotic Pressure — Cry&talline Forms . .12a
XV. Thermo-chemistry 142

PART II

THB STUDY OP POUR TYPICAL ELEMENTS

Hydrogen — Oxygen — Nitrogen — Carbon,

AND THBIR MORB IMPORTANT COMPOUNDS.

I. Hydrogen — Hydrogenium 150

II. Oxygen — AUotropy— Ozone 159

III. Compounds of Hydrogen with Oxvfran . 179

xiv Contents

CMAP. PAGB

IV. Nitrogen 205

V. Oxides and Oxyacids of Nitrogen 209

VI. The Atmosphere ' . 227

VII. Compounds of Nitrogen and Hydrogen — Hydroxyhimine--

Nitrogen Chloride 239

VIII. Carb<m 250

IX. Carbon'^onoxide — Carbon Dioxide — Carbonates . . 259

X. Compounds of Carbon with Hydrof^en — Methane — Ethene —

Ethine 276

XI. Combustion — Heat of Combustion — Ignition Point — Flame —
Structure of Flame — Cause of Luminosity of Flames — The

Bunsen Flame 283

PART III

TUE SYSTEMATIC STUDY OF THE ELEMENTS, BASED
UPON THE PERIODIC CLASSIFICATION

I. Elbmbnts op Group VII (Family B.)

Fluorine : Hydrofluoric Acid. Chlorine : Hydrochloric
Add — Oxides and Oxyacids of Chlorine. Bromine:
Hydrobromic Acid — Oxyacids of Bromine. Iodine:
Hydriodic Acid — Oxyacids of Iodine — Periodates . . 307

11. El.BMBNTS OF GrOUP VI. (FAMILY B.)

Sulphur: Compounds of Sulphur with Hydrogen — Com-
pounds with Chlorine — Oxides and Oxyacids of Sulphur
— Oxychloride»- -Carbon Disulphide. Selenium — Teilu
rium 358

III. Elbmbnts of Group V. (Family B.)

Phosphorus : Compounds with Hydrogen — Compounds with
the Halogens — Oxides and Oxyacids. Arsenic : Arsenu-
retted Hydrogen — Halogen Compounds — Oxides and
Oxyacids — Sulphides. Antimony: Antimony Hydride —
Halogen Compounds — Oxides and Adds — Sulphides.
^tjmitf/A ; Bismuth and Halogens — Oxides — Sulphides . 411

rv. Elbmbnts of Group L (Family A.)

Potassium — Sodium — Lithium — Rubidium — Ammonium
Salts 466

V. Elbmbnts of Group L (Family B.)

Copper — Silver — Gold • . 505

Contents xv

CHAf. PACK

VI. Elements of Group II. (Family A.)

BtrylHum — Magnesium — Calcium^Strontium — Barium . 526

VII. Elements of Group II. (Family B.)

Zinc — Cadmium — Mercury ...... 545

VIII. Elements of Group III.

Family A. : Scandium — Yttrium — Lanthanum — Ytter^

bium.
Family B. : Boron — Aluminium — Gallium — Indium —

Thallium ......... 561

IX. Elements of Group IV.

Family A. : Titanium — Zirconium — Cerium — Thorium,
Family B. : Silicon— Germanium— Tin — Lead .581

X. Elements of Group V. (Family A.)

Vanadium — Niobium — Tantalum ..... 607

XI. Elements of Group VI. (Family A.)

Chromium — Molybdenum — Tungsten — Uranium . 609

XII. Elements ok Group VI I. (Family A.)

Manganese ......... 618

XIII. Transitional Elements of thf. First Lung Period.

Iron^'Cobalt — Nickel 623

XIV. Transitional Elements of the Second and Fourth

Long Period.
Ruthenium — Rhodium — Palladium — Osmium ^Iridium —
Platinum — Argon — Helium ..... 642

Index 651

INORGANIC CHEMISTRY

PAET I
INTRODUOTORT OUTLINES

CHAPTER I

CONSTITUTION OP MATTER

The science of chemistry may be described as the study of a
certain class of changes which matter is capable of undergoing.
Matter is susceptible of a variety of changes, some of which are
regarded as physical and others as chemical. Thus, when a steel
knitting-needle is rubbed upon a magnet, the needle undergoes a
change, by virtue of which it becomes endowed with the power
of attracting to itself iron filings or nails : and when an ordinary
lucifer match is rubbed upon a match-box, the match undergoes a
change, resulting in the production of flame. In the first case the
change is said to be a physical one, while the ignition and com-
bustion of the match is a chemical change.

When a fragment of ice is gently warmed, it is changed from a
hard, brittle solid to a mobile, transparent liquid ; and when white
of ^%% is gently heated, it changes from a transparent, colourless
liquid to an opaque white solid. These changes, which appear at
first sight to be of a similar order, are in reality essentially different
in their nature : the transformation of solid ice into liquid water
is a physical change, the coagulation of albumen is a chemical
change.

Again, when certain substances (such as the materials which
constitute the so-called luminous painf) are exposed to a bright
light, they undergo a change whereby they become invested with

2 Introductory Outlines

the power to emit a feeble light when seen in the dark. A stick of
phosphorus also emits a very similar light when seen in the dark.
The glowing of these materials under these circumstances might
readily be regarded as the result of the same kind of change in
both cases, but in reality the luminosity of the phosphorus is due
to a chemical change taking place upon the sur&ce of that sub-
stance, while the emission of light from the luminous paint is a
purely physical phenomenon.

The two sciences, chemistry and physics, are so closely related
and interdependent upon each other, that no sharp distinction or
line of separation between them is possible. Every chemical
change that takes place is attended by some physical change, and
it often happens that this accompanying physical change forms
the only indication of the chemical change that has taken place.
In certain important points, however, a chemical change is very
different from one that is purely physical : in the latter case no
material alteration in the essential nature of the substance takes
place. This will be seen in the examples quoted. The steel
needle remains unaltered in its essence, although by magnetisation
it has acquired a new property, a property which it again loses,
and which can be again and again imparted to it. The match, on
the other hand, when ignited has undergone a material and per-
manent change : the combustible substance is now no longer
combustible, neither will it ever return to its original state. The
solid water, in being transformed to liquid water, has not under-
gone any vital change : in essence it is the same substance merely
endowed with a new property of liquidity, a property which it loses
again when cooled, and which can be again and again imparted to
it : on the other hand, the coagulated albumen has undergone a
complete and lasting change, and never returns to its original
condition.

In the same way, the luminous paint gradually ceases to emit
light, and returns to its original state ; it may be exposed to the
influence of light, when it once more acquires the property of
phosphorescence, and this change may be brought about indefi-
nitely, without altering the intrinsic nature of the substance. The
glowing phosphorus, on the other hand, is gradually changed into
a white substance, which escapes from it as a smoke or fume ; in
the act of glowing the phosphorus is undergoing a process of slow
burning, and if allowed to remain will continue glowing and burn-
ing until the whole of it has disappeared in the form of smoke.

Molecules 3

The Constltatloii of Hatter. Holeoules.— Matter is regarded
by the chemist and physicist as being composed of aggregations
of minute particles : every substance, whether it be solid, liquid,
or gaseous, presents the appearance to his mind of a vast number
of extremely minute particles. To these particles the name mole-
cules (*' little masses ") has been given. The particles or molecules
of any particular substance are all alike : thus in sulphur the
molecules are all of one kind, while in water they are all of another
kind ; the properties associated with sulphur are the properties of
the individual sulphur molecules, while those belonging to water
are the properties of the molecules of that substance. All matter,
therefore, is to be conceived as having what may be called a
gained structure. The actual sizes of molecules is a matter which
has not yet been determined with exactness ; they are orders of
magnitude which are as difficult for the mind to grasp on account
of their minuteness, as many astronomical measurements are by
reason of their vastness. It is certain that their size is less than
half a single wave-length of light,* and that therefore they are
beyond the visual limits of the microscope. Some general idea
of their order of magnitude may be gathered from Lord Kelvin's
calculation, that if a single drop of water were magnified to the size
of the earth, each molecule being proportionately enlarged, the
grained appearance which the mass would present would probably
be finer than that of a heap of cricket- balls, but coarser than a
heap of small shot.

It will be evident, therefore, that in the strictest sense matter is
not homogeneous : a fragment of ice or a drop of water consists of
an aggregation of a certain number of molecules, between which
there exist certain interspaces. When the fragment of ice is heated,
the spaces between the molecules are enlarged, and the solid passes
into the liquid state ; and when water is still further heated, and
converted into water vapour, or steam, the molecules are still more
thrust asunder, and the inter-molecular spaces are still further
increased.

The forces which similar molecules exert upon each other are
regarded as physicaly in contradistinction to chemical. These
forces are either attractive in their nature, or repellent. When
the attractive forces are in the ascendency, the molecules are

• The wave-length of the blue ray (G) = 0.000431X millimetre, or
0*0000169 inch.

4 Introductory Outlines

drawn more or less closely together, and the substance assumes
the solid state. If the repellent forces have the upper hand the
material takes the gaseous condition, while the liquid state may
be regarded as resulting from a certain balance of these opposite
forces. Changes which matter undergoes by the action of these
forces are physical changes, they do not affect the inherent nature
and properties of the substance, which properties, as already stated,
reside in the molecules themselves.

In each of the three states of matter, viz., solid, liquid, or gaseous,
the molecules are conceived as being in a state of motion ; they
are regarded as executing some vibratory movement within the
spaces that divide them. In the solid state this movement is the
most restricted for the reason that the intermolecular spaces are
in this case the smallest. In the gaseous condition the amplitude
of vibration of the molecules is very greatly increased ; for the
attractive forces being at a minimum, and the intermolecular
spaces being greatest, the molecules have a further distance to
travel before they strike one another.

Such changes in matter, which are merely the result of altera-
tions in the motions of the molecules, are likewise purely physical
changes.

Molecules may be defined as the smallest particles of mattei'
which can exist in the free state; or as the smallest weight of
matter in which the original properties of the matter are retained.

Atoms. — It is the belief of chemists that most molecules are
possessed of a structure. That is to say, they are not simple,
single, indivisible masses, but themselves consist of aggregations
of still smaller particles, which are held together by the opera-
tions of some other force. These particles of which molecules
are composed are termed atoms, and the force which holds them
together is called chemical affinity, or chemical attraction. To
the mind of the chemist, such molecules are little systems, con-
sisting of a number of atoms which are attracted to each other
by this particular force ; in the ordinary movements of the mole-
cule, the system moves about as a whole. In this respect it bears
some analogy, on an infinitely minute scale, to a solar system.
The atoms of a molecule are regarded as in a state of motion as
respects one another, possibly revolving about one another, while
the entire system, or molecule, at the same time performs its in-
dependent movements, just as in a solar system the various
members perform various movements towards each other, while

Molecules and Atoms 5

at the same time the whole system travels upon its prescribed
orbit In the case of the heavenly bodies the force which regulates
the movements of the individual members of the system amongst
themselves, is the same force that controls the motion of the united
system, namely, gravitation. What is the precise relation, or
difference, if any, between the forces which control the movements
of molecules, and those which operate between the atoms of the
molecule, is not known ; but as the effects produced are different
the latter force is distinguished by the name of chemical affinity.

Any change which matter undergoes, in which the integrity of
the molecules is not destroyed, is regarded as a physical change ;
while any change which arises from an alteration in the structure
of the molecule is a chemical change. For example, the molecules
of water consist- of three separate atoms, one of oxygen and two
of hydrogen ; any change which water can be made to undergo,
in which these three atoms still remain associated together as the
molecule, is a physical change. The water may be converted into
ice, or it may be changed into steam ; but these alterations still
leave the molecules intact, the three atoms still remain united as
an unbroken system, and so long as this is the case chemical
change has not taken place.

Suppose now the molecules of water are heated to a much
higher temperature than that which is necessary to convert the
water into steam, by passing electric sparks through the steam.
It will then be found that a very different kind of change has come
over the substance. The steam, after being so heated, no longer
condenses to water again when cooled ; it has been changed into
a gas which can be bubbled through water and collected in an
inverted vessel filled with water standing in a pneumatic trough,
and if a flame be applied to this gas a sharp explosion takes place.
The change in this case is a chemical change, for the integrity
of the molecules of water has been destroyed. The two atoms
of hydrogen have become detached from the oxygen atom, and
the original triune structure of the system is destroyed.

Atoms are therefore defined as the smallest particles of matter
which can take part in a chemical change.

CHAPTER II
ELEMENTS AND COMPOUNDS

There are certain molecules in which all the atoms present are
of the same kind, and there are other molecules which arc com-
posed of atoms which differ from one another. Thus, in the
substance sulphur, all the atoms composing the molecules are
alike ; while in water, as already mentioned, there are two distinct
kinds of atoms in the molecule. Matter, therefore, is divided into
two classes, according as to whether its molecules are composed of
similar or of dissimilar atoms. Molecules consisting of atoms of
the same kind are termed elementary molecules^ and substances
whose molecules are so constituted are known as elements ; mole-
cules, on the other hand, which contain dissimilar elements are
called compound molecules^ and substances whose molecules are
thus composed are distinguished as compounds.

Sulphur, therefore, is an element^ and water is a compound. It
will be evident that in the case of elementary molecules, whatever
processes they may be subjected to, only one kind of matter can
be obtained from them ; while in the case of compounds, the
molecules consisting of dissimilar atoms, as many different kinds
of matter can be obtained as there are different atoms present.
By appropriate means the atoms of hydrogen and oxygen in water
molecules can be separated, and two totally different kinds of
matter, namely, hydrogen and oxygen, can be obtained from this
compound.

At the present time there are about seventy substances known to
chemists which are believed to be elements. In the history of the
science it has frequently happened that substances which were
considered to be elements have proved, when subjected to new
methods of investigation, to be in reality compound bodies : thus,
prior to the year 1783, water was thought to be an elementary
substance, it was indeed regarded as the very type of an element,
until Cavendish and Lavoisier proved that it was composed of

Elevients and Compounds 7

two entirely different kinds of matter. In the year 1807, Sir
Humphrey Davy showed that the substances known as potash
and soda, which were believed to be elements, were in reality
compound bodies, and he succeeded in separating the constituent
atoms in the molecules of these substances, and in obtaining from
them two essentially different kinds of matter. It is therefore
quite possible, perhaps even probable, that some at least of the
forms of matter which are now held to be elements, may yet prove
to be compound bodies.

The number of compounds is practically infinite.

The elements are very unequally distributed in nature, and are
of very different degrees of importance to mankind. Some are
absolutely essential to life as it is constituted, while others might
be blotted out of creation without, so far as is known, their absence
being appreciated. The following thirty elements include all the
most important (for the complete list see page 21) : —

Aluminium.

Gold.

Oxygen.

Antimony.

Hydrogen.

Phosphorus

Arsenic.

Iodine.

Platinum.

Bismuth.

Iron.

Potassium.

Bromine.

Lead.

Silicon.

Calcium.

Magnesium.

Silver.

Carbon.

Manganese.

Sodium.

Chlorine.

Mercury.

Sulphur.

Copper.

Nickel.

Tin.

Fluorine.

Nitrogen.

Zinc

On account of certain properties common to a large number of
the elements, and more or less absent in others, properties which
are for the most part physical in character, the elements are
divided into two classes, known as metals and non-metals. The
metals generally are opaque, and their smoothed surfaces reflect
light to a high degree, thus giving them the appearance known as
metallic lustre. They also conduct heat and electricity. Gold,
silver, copper, iron, are metals ; sulphur, bromine, oxygen, phos-
phorus, are non-metals. These two classes, however, gradually
merge into one another, and certain elements are sometimes
placed in one division and sometimes in the other, depending
upon whether the distinction is based more upon their physical
or their chemical properties : thus, the element arsenic possesses

8 Introductory Outlines

many of the physical properties of a metal, but in its chemical
relations it is more allied to the non-metals : such elements as
these are often distinguished by the name metalloids. By general
consent the following fifteen elements are regarded as including
all the non-metals and metalloids : —

Arsenic

Fluorine.

Phosphorus

Boron.

Hydrogen.

Selenium.

Bromine.

Iodine.

Silicon.

Carbon.

Nitrogen.

Sulphur.

Chlorine.

Oxygen.

Tellurium.

The number of atoms which compose the various elementary
molecules is not the same in all cases : thus in the elements
sodium, potassium, cadmium, mercury, and zinc, the molecules
consist of only one atom. The molecules of these substances are
single particles of matter. The terms molecule and atom^ there-
fore, as applied to these elements, are synonymous. Such mole-
cules as these are called mono-atomic molecules. In many cases
elementary molecules consist of two atoms ; such is the case with
the elements hydrogen, bromine, chlorine, oxygen, nitrogen, and
others. Elementary molecules of this twin or dual nature are
known as di-atomic molecules. Only one instance is known in
which an elementary molecule consists of a trio of atoms, namely,
the molecule of ozone, which is an aggregation of three oxygen
atoms. This molecule is said to be tri-atomic. In two cases,
namely, arsenic and phosphorus, the molecules are composed of
a quartette of atoms, and these elements, therefore, are saia to
form tetr-atomic molecules. In a large number of instances the
atomic constitution of the molecule of the elements is not- known.
These terms, mono -atomic^ di-atomic^ &c, are applied exclu-
sively to molecules of elements^ and are not used in reference
to compounds, where the molecules are composed of dissimilar
atoms.

Mechanical Mixtores. — When molecules of different kinds of
matter are brought together, one of two results may follow : either
they will merely mingle together without losing their identity, that
is to say, the atoms composing the individual molecules will still
remain associated together as before, or the atoms in the molecules
of one kind will attach themselves to certain atoms present in
molecules of another kind to form still different molecules ; in other

Mechanical Mixtures g

words, there will be a redistribution of the atoms, whereby diffe-
rent systems or molecules are produced.

In the first case the result is said to be a simple or mechani-
cal mixture, in the second it is the formation of a chemical
compound.

In a simple mixture, the ingredients can be again separated by
purely mechanical methods ; and as the properties of a substance
are the properties of the molecules of that substance, it follows that
if the integrity of the molecules is not broken, the properties of a
mechanical mixture will be those of the ingredients. For example,
oxygen is a colourless gas without taste or smell ; hydrogen also is
a colourless gas without taste or smell : when these two gases are
mixed together, the mixture is gaseous, is colourless, and tasteless,
and, being only a mixture, the molecules of one gas can be readily
sifted away from the other.

Again, charcoal is a black solid, insoluble in water ; sulphur is a
yellow solid, also insoluble in water ; nitre is a white solid, readily
dissolved by water: when these three substances are finely
powdered and mixed together, the result is a mechanical mixture,
which is solid, and which is dark grey or nearly black in colour.
If this mixture be placed in water, the nitre is dissolved away and
the charcoal and sulphur are left.

When, however, the integrity of the molecules is disturbed,
when, by bringing together molecules of different substances, a
rearrangement of the atoms takes place, resulting in the formation
of new molecules, then it is said that chemical action has taken
place.

Chemical action, therefore, always results in the formation of
new molecules, — new molecules which are endowed with their
own special properties, differing often in the most remarkable and
quite inexplicable manner from those of the original molecules.
One or two examples may be quoted in order to illustrate this
extraordinary modifying effect of chemical action. The two
colourless gases, oxygen and hydrogen, when simply mixed to-
gether, give rise, as already mentioned, to a colourless, gaseous
mixture, in which the dual molecules of hydrogen and the simi-
larly constituted oxygen molecules move about freely amongst
each other. By suitable means chemical action may be made
to take place between these two elements, whereby a complete
rearrangement of the atoms takes place, resulting in the formation
of molecules of water— molecules in which, as has been already

ro Introductory Outlines

mentioned, one atom of oxygen is associated with two atoms of
hydrogen. The product of the chemical action is therefore water,
while both the forms of matter of which it is composed are
gaseous.

The air we breathe, and which is necessary to life, consists of
a simple mixture of two colourless gases, viz., oxygen and nitrogen :
when chemical action takes place between these substances, a
brown-coloured gas is produced in which no animal or vegetable
life could exist for many minutes, on account of its suffocating
nature.

Common salt, which is a white solid substance, and not only
harmless but even a necessary article of food, contains two atoms
in its molecules— one an atom of chlorine, which is a yellow gas,
intensely suffocating and poisonous ; and the other an atom of
sodium, a soft, silver-like metal, which takes fire in contact with
water.

Why it is that a molecule, consisting of an atom of chlorine and
an atom of sodium held together by chemical affinity, should be
endowed with properties so totally different from those of the
contained elements, is altogether unknown ; and, similarly, it is
quite impossible to predicate from the properties of any compound
what are the particular elements of which it is composed. Thus,
sugar is a white crystalline solid, soluble in water, and possessing
a sweet taste, but no one would have ventured to predict that the
molecules of this substance were composed of atoms of carbon
{i.e., charcoal), a black, tasteless, insoluble solid ; hydrogen, a
colourless, tasteless gas ; and oxygen, another colourless, tasteless
gas.

Chemieal Affinity.— When molecules, consisting of two atoms,
say A B, come in contact with molecules consisting of other two
atoms, C D, and a chemical change takes place resulting in the
formation of new molecules, A C and B D ; the question naturally
arises, Why does the atom A leave the atom B and attach itself to
C ? In other words, what determines the rearrangement of the
atoms into new molecules ?

At present no exact answer can be given to this question.
Chemists express the fact by saying that the chemical affinity
existing between A and C is greater than that exerted by B upon
A. This remarkable selective power possessed by the atoms of
different elements lies at the root of all chemical phenomena, and
it differs between the various elements to an extraordinary degree.

Chemical Affinity ii

For example, the atom of chlorine possesses a very powerful
chemical affinity for the atom of hydrogen : when hydrogen mole-
cules, which consist of two atoms, are mixed with chlorine mole-
cules, which are also aggregations of two atoms, at first a simple
mechanical mixture is obtained, the two different kinds of mole-
cules move amongst each other without undergoing change. Qn
very small provocation, however, the affinity of the hydrogen atoms
for the chlorine atoms can be caused to exert itself ; by merely
momentarily exposing the mixture to sunlight a complete redistri-
bution of the atoms suddenly takes place with explosive violence
and new molecules are formed, each containing one atom of
hydrogen and one atom of chlorine.

Again, an atom of nitrogen is capable of associating itself in
chemical union with three atoms of the element chlorine, forming
a compound whose molecules therefore contain four atoms. The
chemical affinity between the atoms of chlorine and nitrogen is
so feeble, the system is, so to speak, in a state of such unstable
equilibrium, that the very slightest causes are sufficient to instantly
separate the atoms in the most violently explosive manner, and
so break up the compound molectile into separate molecules of
chlorine and nitrogen. In this case the affinity between one
<:hlorine atom and another chlorine atom is greater than that
between chlorine and nitrogen, consequently the redistribution
that results is of the opposite order to that of the former
example.

As a rule, those elements which the more closely resemble each
other in their chemical habits have the least affinity for each other,
while the greatest affinity usually exists between those which are
most dissimilar.

Chemical Action. — The actual process of redistribution of the
atoms that takes place when molecules of different kinds of matter
are brought together, is called chemical action. In many cases
chemical action takes place when the substances are merely
brought together, while in others it is necessary to expose the
bodies to the influence of some external energy : thus chemical
action is brought about in a great number of instances by the
application of heat to the substances. In some cases the influence
of light has the effect of causing chemical action to take place :
for example, when the gases chlorine and hydrogen are mingled
together, no chemical action takes place ii> the dark, but on

12 Introductory Outlines

exposing the mixture to light the hydrogen and chlorine combine,
and form the compound hydrochloric acid. It is upon the effect
of light in causing chemical action to take place that the art
of photography depends.

Chemical action may sometimes be induced by the influence of
pressure : thus when the two gases, hydrochloric acid, and phos-
phoretted hydrogen, are subjected to increased pressure, they
combine together to form a crystalline solid compound known as
phosphonium chloride. In the same way, by very great mechanical
pressure, a mixture of powdered lead and sulphur can be caused
to combine together, when they form the compound, lead sulphide.
There are also a number of chemical actions that are only able
to proceed in the presence of small quantities (often extremely
small) of a third substance, which itself remains unchanged at the
conclusion of the action. These cases are generally included
under the name of catalytic actions : in some of them the f nodus
operandi of the third substance can be traced (see Oxygen, Modes
of Formation ; also Chlorine, Deacon's Process), while in others
it is not understood ; thus it is found that a number of chemical
actions are quite unable to take place if the materials are abso'
lutely dry : for example, the element chlorine has a powerful
affinity for the metal sodium, and when these substances are
brought together under ordinary conditions, chemical action in-
stantly takes place, and the compound known as sodium chloride
(common salt) is produced. If, however, every trace of moisture
be perfectly removed from both the sodium and the chlorine, no
action between these elements takes place when they are brought
together, and so long as they remain in this state of perfect dryness
no chemical change takes place. The admission into the mixture
of the minutest trace of the vapour of water, however, at once
induces chemical action between the chlorine and the sodium, but
the exact part that the trace of moisture plays in producing this
effect, is not known with certainty. (See also foot-note, page 86.)

A few interesting cases are known in which chemical action is
brought about by the vibration caused by a loud sound or note :
for example, the molecules of the gas acetylene consist of two
atoms of carbon associated with two of hydrogen ; when a quantity
of this gas is exposed to the report produced by the detonation of
mercury fulminate, the mere shock of the explosion causes a re-
distribution of the atoms whereby solid carbon is deposited and

Chemical Action 13

hydrogen set free. We may suppose that the particular vibration
produced by the detonation of the fulminate exercises a disturbing
effect upon the motions of the atoms constituting the molecules of
acetylene, and thereby causes them to swing beyond the sphere of
their mutual attractions, and thus the system undergoes disruption
and rearrangement.

All known instances of chemical action can be referred to one
of three modes, in which the rearrangement of the atoms can take
place.

(i.) By ike direct union of two molecules to form a more
complex molecule. Thus, if CO and CI CI represent two mole-
cules between which chemical action takes place according to
this mode, they unite to form a molecule containing the four
atoms CO CI CI.

(2.) By an exchange of atoms taking place between different
molecules. In its simplest form this is illustrated in the action
of one element upon another to form a compound. Thus, if H H
and CI CI stand for two elementary molecules between which
chemical action takes place, the result is the formation of the two
molecules HCl HCl. Such a process as this, in which a com-
pound substance is produced directly from the elements which
compose it, is termed synthesis.

The same mode of chemical action may also be exemplified by
the exact opposite to this process, namely, the resolution of a
compound into its constituent elements. Thus, if OHH OHH
represent two molecules of the same compound, when chemical
action takes place it will result in the formation of the three
elementary molecules (-)(), HH, and HH. Such a process as
this, in which a compound is resolved into its elements, is known
as analysis,

(3.) By a rearrangement of the atoms contained in a molecule.
There are a number of instances of chemical change, in which the
molecules of the substance do not undergo any alteration in their
composition — that is to say, no atoms leave the molecule, nor are
any added to it. The molecule still consists of the same atoms
after the change as it did before, but the chemical action has
caused them to assume new relative positions, or different relative
motions with respect to each other. For example, the substances
known to chemists as ammonium cyanaie and urea are two totally
different and distinct kinds of matter. These molecules, however,

Introductory Outlines

each contain the same atoms and in the same number ; they each
consist of aggregations of one atom of carbon, one atom of oxygen,
two atoms of nitrogen, and four atoms of hydrogen. When am-
monium cyanate is gently warmed, the eight atoms composmg
the molecules undergo this process of rearrangement, and the
substance is changed into urea.

CHAPTER III
CHEMICAL NOMENCLATURE

The names which have been given to the various elementary forms
of matter are not based upon any scientific system. The names o!
some have their origin in mythology. Others have received names
which are indicative of some characteristic property, while those of
several bear reference to some special circumstance connected with
their discovery. It has been the custom in modem times, to dis-
tinguish metals from non-metals by applying to the former names
ending in the letters um^ and consequently such metals as are o!
more recent discovery all have names with this termination. The
common metals, however, which have been known since earlier
times, such as gold silver, tin, and copper, keep their old names.
The two elements selenium and tellurium were at the time of their
discovery thought to be metals, and they consequently received
names with the terminal umy these substances strongly resemble
metals in many of their physical properties, but in their chemical
relations they are so closely similar to the non-metal sulphur, that
they are by general consent classed among the non-metals ; they are
examples of those elements which are distinguished as metalloids.
On this account selenium is by some chemists termed selenion.

In naming chemical compounds, the chemist endeavours that
the names employed shall not only serve to identify the sub-
stances, but shall as far as possible indicate their composition.
The simplest chemical compounds are those composed of only
two different elements ; such are spoken of as binary compounds,
and their names are made up of the names of the two elements
composing them, thus —

The compound formed by the chemical union of—

Hydrogen with sulphur is called
Sodium „ chlorine „

1 hydrogen sulphide,
sodium chloride.

Copper „ oxygen
Calcium „ fluorine

»>
»>

copper oxide,
calcium fluoride.

Potassium „ iodine

potassium iodide.

1 6 Introductory Outlines

It continually happens, however, that the same two elements
combine together in more than one proportion, giving rise to as
many different compounds, in which case it becomes necessary to
so modify the names that each of the compounds may be dis-
tinguished. This is accomplished by the use of certain terminal
letters, or of certain prefixes ; for example, the element phos-
phorus combines with chlorine in two proportions, forming two
different compounds — in one the molecules contain one atom of
phosphorus united to three atoms of chlorine, in the other the
molecules consist of one atom of phosphorus associated with five
of chlorine. These two compounds may be distinguished in the
following ways : —

I atom of phosphorus with 3 atoms of chlorine forms phosphorovj chloride.
I ,, ,, M 5 ,, M M phosphoric chloride.

or —

I atom of phosphorus with 3 atoms of chlorine forms phosphorus /n'chloride.
I M I, ,, 5 .. M „ phosphorus/tfTf/achloride.

The latter method of distinction is the more general, thus —

I atom of sulphur with 2 atoms of oxygen forms sulphur dioxide.
1 ., M .. 3 .. .. .. sulphur trioxide.

I atom of carbon with i atom of oxygen forms carbon monoxide.
I ,, ,, M 2 atoms ,, ,, carbon dioxide.

Occasionally the prefixes sub and proto are employed to denote
these differences of composition, but their use is more limited, and
is becoming out of vogue. When more than two compounds are
formed by the union of the same two elements, the additional
prefixes hypo^ under, and per^ over, are sometimes used.

In a considerable number of instances the systematic names of
familiar compounds give way to the vulgar or conunon names by
which they are known, thus —

(Ammonia . . . Hydrogen nitride "\

Hydrochloric acid . Hydrogen chloride

Sulphuretted hydrogen . Hydrogen sulphide

Water .... Hydrogen monoxide.

Systematic
names.

Binary compounds that are formed by the union of elements with
oxygen are called the oxides of those elements. Certain of these
oxides are capable of entering into combination with water, giving
rise to substances known as acids : such oxides are distinguished

Cktmicai Nomenclaturt 17

at odd-forming oxidts, or ad^c oxides. They are also tame-
limes termed attkydridts. All the Don-meiallic elements, except
hydrogen, fonn oxides of this order, and the acids derived from
them are known as the oxy-acids.

Certain other oxides also unite with water, but give rise to com
pounds known as kydroxidu. When such oxides, which are all
derived from the metallic elements, are brought into contact with
acids, chemical union takes place, and a compound termed a salt
is formed. Such oxides are distinguished as salt-forming, or
bade oxides. There are also oxides which are neither addic nor
banc. The names of oxy-adds are derived from the name of the
particular oxide from which they are formed, thus—

When the same element forms two acid-forming oxides, the
terminals ic and ous are applied to the acids to denote respectively
the one with the greater and the less proportion of oxygen, thus —

Sulphur fri'oxide gives sulphunV acid.
Sulphur lilfoxide gives sulphuriwf acid.
Nitrogen /«ff/oxide gives nitn'^ acid.
Nitrogen /n'oxide givu nitruMt acid.

When more than two such adds are known, the additional
prelixes hypo or per are made use of. Thus /^rsulphuric acid
denotes an acid containing the highest quantity of oxygen, while
/ypooAioxa acid stands for an acid containing less oxygen than is
present in nitrous acid.

There is a class of binary compounds formed by the combination
ofalargenimiberof the elements with sulphur; these are known as
tulphides. Certain of these sulphides are also capable of forming
acids which are analogous in their constitution to oxy-acids, but in
which the oxygen atoms are substituted by atoms of sulphur.
These adds^are known as iMo adds (sometimes sulpha adds),
and the same system of nomenclature is adopted to distinguish
these : thus we have thio-aiseniMU- add, thio-arseniV acid, denoting
respectively the acid with the smaller and the larger proportion of

It was at one time believed that aU addt contained oxygen, that
indeed this dement wa* essential to an add. The name oxygen

1 8 Introductory Outlines

indicates this belief, the word signifying "the acid-producer."
This view is now seen to have been incorrect, for many acids are
known in which oxygen is not one of the constituents. Thus the
elements fluorine, chlorine, bromine, and iodine, which constitute
the so-called Halogen group of elements, each combines with
hydrogen, giving rise respectively to hydrofluoric, hydrochloric,
hydriodic, and hydrobromic acids.

All known acids contain hydrogen as one of their constituents.

As already stated, when chemical action takes place between an
acid and a base, a salt is formed. Oxy-acids in this way give rise
to oxy-salts, thio-acids to thio-salts, and halogen acids to haloid
salts.

The latter salts being binary compounds, their names are given
according to the system already explained, such for example as
calcium fluoride, sodium chloride, potassium bromide, silver iodide.

In the case of the oxy-salts and thio-salts, the names are made
up from the names of the acid and of the metal contained in the
base, with the addition of certain distinctive sufiixes : thus if the
acid be one whose name carries the terminal ous its salts will be
distinguished by the suffix ite^ while the names of the salts derived
from acids whose names end in ic are terminated by the letters ate,

Nitr^i^ add and potassium oxide give potassium nitnV^.
Sulphur<?f/j acid „ „ „ sulph//^.

Nitr^acid „ „ „ vi\\xate,

Sulphur/V add „ „ „ sulpha/^.

The formation of a salt by the action of an acid upon a base, is
due to the redistribution of the atoms composing the molecules of
the two compounds, in such a manner that some or all of the
hydrogen atoms in the add molecules, exchange places with certain
metallic atoms from the molecules of the base. Acids which con-
tain only one atom of hydrogen so capable of becoming exchanged
for a metal, are termed mono-basic acids ; those with two, three, or
four such hydrogen atoms are distinguished respectively as di-basic^
tri-basiCy and tetra-basic acids.

If the whole of the displaceable hydrogen in an acid becomes
replaced by the base, the salt formed is known as a normal salt.
On the other hand, when only a portion of the hydrogen atoms
is displaced by the base, the salt is distinguished as an acid
salt. Thus sulphuric add contains two atoms of hydrogen in its
molecule (associated with one of sulphur and four of oxygen) : if

Chemical Nomenclature

both the hydrogen atoms are exchanged for potassium, the salt
obtained is normal potassium sulphate^ and when only one is so
replaced the salt is known as acid potassium suiphcUe, By the
term acid salt^ therefore, must be understood a salt in which one
or more of the hydrogen atoms of the original acid are still left in
the molecule.*

A third class of salts is formed by the association of one or
more molecules of normal salt, with one or more additional mole-
cules of the base : these are known as basic salts. Thus, carbonic
acid and the base lead oxide, fonn such a salt known as basic lead
carbonate,

* Some chemists prefer to regard the acids themselves as the hydrogen salts ;
accordingly they apply to nitric acid, sulphuric acid, nitrous acid, sulphurous
add, &C., the names hydrogen nitrate, hydrogen sulphate, hydrogen nitrite,
hydrogen sulphite, ftc. , respectively.

CHAPTER IV

CHEMICAL SYMBOLS

Chemists are agreed in adopting certain symbols to denote the
atoms of the various elementary forms of matter. The table
opposite contains the names of the elements at present recognised,
and in the second column are given the symbols which, are em-
ployed to represent their atoms. The names of the rare elements
are printed in italics.

In a number of instances the atomic symbol is the initial letter
of the ordinary name of the element : thus Boron, B ; Carbon, C ;
Fluorine, F; Hydrogen, H ; Oxygen, O ; Sulphur, S.

When more than one element has the same initial, either the
first two letters of the name, or the first and another that is pro-
minently heard in pronouncing the word are employed, as Bromine,
Br ; Cobalt, Co ; Chlorine, CI ; Platinum, Pt. In some cases
letters taken from the Latin names for the elements are used, such
as Antimony (S/ih'um), Sb ; Gold (Aurum), Au ; Silver {Argentum)y
Ag ; Lead {Plumbum)^ Pb ; and Iron (Ferrum\ Fe.

These symbols are not intended to be employed as mere short-
hand signs, to be substituted as abbreviations for the ftdl names
of the elements, but in every case they denote one atom of the
element The symbol H stands for one atom of hydrogen, the
symbol O stands for one atom of oxygen ; CI means one atom of
chlorine, and Ag represents one atom of silver. No other use of
these symbols is legitimate.

It has been already mentioned (page 8) that the molecules of
the different elements are composed of different numbers of atoms ;
for example, the molecule of hydrogen consists of two atoms, and
ordinary oxygen also forms diatomic molecules. These facts are
expressed in chemical notation by the use of small numerals placed
immediately after the symbol of the atom, thus H2 denotes a mole-
cule of hydrogen, O, a molecule of oxygen. The molecule of ozone
consists of an aggregation of three atoms of oxygen, tnd is

Chemical Symhols

Atomic Wcif hlL

Almle Wd(liu.

.„

III

«».

ill

Ahminlum. .

Al ST

»7 04

MaMdn^m .

Sb 1»

119:6

Nictel . .

A ?

M-T

Ai£cnic. . . .

As W

74-9

NilroEen .

14,01

Buium . , . .

Bs 111

136.86 Oimi^m. .

IBl

Bayllnm . . .

Be ■

'.°°:SE™ :

1«

,sf

Bismuth . . .

Bi tOT»

Boron . . . .

B 11

3096

BrDmine . . .

Br U

79.76 PUtmum .

C«dniiuiD . . .

Cd 1 111
Ci IIU

II1.7 IPGt<i«mm(Aa
139.7 i iti») . .

/-I

39.03

cSrf^ :

CI to

l99^\jfML .

104

Cuboo ....

C 1 It

rt.gj,/fuHdium .

B$.i

Ctnwm. . .

Ce 1 lai

... \/fHl*tM,um.

Kii

1011

Chlorine . . .

a «i

3S-37\Samarium .

tio

Chromituii. . .

Cr tt

S»4S' .SciHirfrKiH ,

43-97

CoWt ....

Co M

58.6 1 Selenium .

78.87

Copper (Cw/f»«).

Cu n

aB.3

ge--; : .

Di llU
Er |1«

... Silver Mvraft
... lsodium(.VaM

.-.«■".

107.66

Fluorine.

F 1 le

i^ofi' Slronthim .

.Is,

STS

GaUium. . .

Oa 70

69.S6,Su1:>hur. .

3i.'98

GtrmtHium .

Ge It

181

G<M(Am».m) .

All 1ST

IS*:*

Tellurium .

'le

lit

HrdfOge. . .

H 1 I

Tballium .

101 -T

Imdium. . . .

D lis

T*.mum .

111

lOdiM . . . .

Tin iS/an«u«

Iliditim . . , .

T ISl'S

iTtmtFtmm). .

Fe < H

SS-M Tungltfn .

1S4

LtntiLinum . .

L« , lies

... \Ur/mum .

IMS

LmdlPi-mium).

Pb SOT

SlI

UtUum. . . .

7-01 yiltriiam .

171

Mtgaaiam

Mg' 14

33. M Yitriam .

Mn| U

S4.8 Zinc . - .

&t!8e

"W™- ■ ■ f

Hg 100

8 Zirtmium. , . . Zr

00 '4

Rprescnted by the symbol Oj, while the tetr-atomic character of
the phosphorus inf].- ■..>;;. ■■-.! in the symbol P4. The
composition of compound molecules is expressed by placing ihe
symbols of the atoms nhn h <rompi>se such molecules in juxia-
position : thus a molecule consisting of one atom of sodium (symbol

s an given in thli cohimn, tbo« In the third column maf

22 Tntraductory Outlines

Na) and one atom of chlorine (symbol Q) is represented by the
united symbols of these two elements, NaCI ; a compound con-
sisting of one atom of carbon and one atom of oxygen by the
symbols of these two atoms, CO. Such arrangements of symbols
representing molecules arc termed molecular formulee^ or, simply,
formula.

When the molecule contains more than one atom of any parti-
cular element, this £act is indicated by the use of numerals placed/
Immediately after the symbol to be multiplied : thus, a molecule of
water consists of two atoms of hydrogen and one atom of oxygen^
xYit formula for water is therefore HjO. One molecule of ammonia,
consisting of an atom of nitrogen with three atoms of hydrogen, is
represented by the formula NHs; and a molecule of sulphuric
acid, which is an aggregation of two atoms of hydrogen, one
atom of sulphur, and four atoms of oxygen, has the formula
H3SO4.

It is sometimes necessary to represent the presence in a mole-
cule of certain groups of atoms, groups which seem to hold together,
and often to function as a single atom. This is accomplished by
the use of brackets : thus (NH4)2S04 is the formula for a molecule
containing one atom of sulphur, four atoms of oxygen, eight atoms
of hydrogen, and two atoms of nitrogen ; the nitrogen and hydrogen
atoms being present as two groups, in each of which one nitrogen
atom is associated with four hydrogen atoms. Such groups of
atoms are termed compound radicals.

When it is required to indicate more than one molecule of the
same substance, numerals are placed immediately in front of the
formula : thus SHjO signifies two molecules of water, and SNHj
expresses three molecules of ammonia.

By means of these symbols and formulae, chemists are enabled
to represent, in a concise manner, the various chemical changes
which it is the province of chemistry to examine. Such changes
are usually termed chemical reactions^ and they are represented
in the form of equations in which the symbols and formulae of
the reacting substances as they are before the change are placed
on the left, and those of the substances which result from the
change upon the right, thus —

H, + Clj = 2HC1
HgClj -I- 2KI = Hglj + 2KCI.

The sign -I- has a different significance as used on the left side

Ckemtcal Symbols 23

of the equation to that which it bears upon the right On the
left hand it implies that chemical action takes place between the
substances, while on the opposite side it has the simple algebraic
meaning. Thus, the second of the above equations is understood
to mean, that when the compounds, mercuric chloride and potassium
iodide, are brought together in such a way that chemical action
results, a redistribution of the atoms will take place, resulting in
the formation of mercury iodide and also potassium chloride.

As further illustrations of the use of chemical symbols, the
following three examples may be given as exemplifying the three
modes of chemical action mentioned on page 13 : —

(i) NHj + HCl = NH4CI.

Ammonia combines with hydrochloric acid, and gives ammonium
chloride.

(2) H,S04 + NajCO, = NajS04 + CO, + HjO.

Sulphuric acid combines with normal sodium carbonate, and gives
normal sodium sulphate, carbon dioxide, and water.

(3) (CN)0(NHJ-(NH,),CO.
Ammonium cyanate is converted into urea.

In all cases where the nature of the chemical change is under-
stood, it is capable of expression by such equations, and as matter
is indestructible, every atom present in the interacting molecules
upon the left of the expression, reappears on the right hand side
in some fresh association of atoms.*

* See alflo Chemical Notation, chapter vii.

CHAPTER V
THE ATOMIC THEORY

The atomic view as to the constitution of matter, briefly sketched
out in Chapter I., forms a part of what is to-day known as the
cUomic theory.

When chemical changes were carefully studied from a quantita-
iive standpoint, four laws were discovered in obedience to which
chemical action takes place. These laws are distinguished as
the laws of chemical combination. Three of these generalisations
refer to quantitative relations as respects weight; while one expresses
quantitative relations with regard to volume^ and only relates to
matter in the gaseous state.

I. Law of Constant Proportion.— Tift^ same compound always
contains the same elements combined together in the same proportion
by weight J or expressed in other words, The weights of the con-
stituent elements of every compound bear an unalterable ratio to
each other ^ and to the weight of the compound formed.

II. Law of Multiple Proportions.— ^-*^« the same two

elements combine together to form more than one compound^ the
different weights of one of the elements which unite with a constant
weight of the other^ bear a simple ratio to one another; or this law
may be stated thus : When one element unites with another in
two or more different proportions by weighty these proportions are
simple multiples of a common factor,

III. Law of Reciprocal Proportions, or Law of Equivalent

Proportions. — The weights of different elements which combine
separately with one and the same weight of another element^ are
either the same or, or are simple multiples of the weights of these
different elements which combine with each other; or in other
words. The relative proportions by weight in which the elements^
A^ By C, Dy &*c,y combine with a constant weight of another
element^ A', are the same for their combinations with any other
element^ V,

•4

The Atomic Theory 25

lY. Law of Gaaaoiu Volumes, or The Law of Gay-Lussae.

— When chemical action takes plau bttween gases^ either elements
or compounds^ the volume of the gaseous product bears a simple
relation to the volumes of the reacting gases.

These four laws are the foundations upon which the whole
superstructure of modem chemistry rests.

(i.) The Law of Constant Proportions.— When two sub-
stances are mingled together, and remain as a mere mechanical
mixture, they may obviously be present in any proportion, and it
was at one time thought that when two substances entered into
chemical combination with each another, they could do so also in
any proportion, and that the composition of the resulting com-
pound would vary from this cause. This belief was finally
disproved, and the law of constant proportions definitely estab-
lished by Proust in the year 1806. The same compound, therefore,
however made, and from whatever source obtained, is always
found to contain the same elements united together in the same
proportion by weight Thus, common salt, or, to adopt its
systematic name, sodium chloride, which is a compound of the
two elements sodium and chlorine, may be made by bringing the
metal sodium into contact with chlorine gas, when the two
elements unite and form this compound. It can also be made
by the action of hydrochloric acid upon the metal sodium, or by
adding hydrochloric acid to sodium carbonate, and by a variety
of other chemical reactions. When the sodium chloride obtained
by any or all of these processes is analysed, it is invariably found
to contain the elements chlorine and sodium in the proportion by
weight of I : a6479, or, expressed centesimally —

Sodium . 39.33

Chlorine . 60.68

100.00

and when this is compared with the sodium chloride as found in
nature, obtained either from the salt-mines of Cheshire, or the
celebrated mines in Galicia, or by evaporating sea- water, it is
fbund that the composition of the compound in all cases is exactly
the same. In the same way the compound water, consisting of
the two elements hydrogen and oxygen, whether it be prepared
synthetically by causing the two elements to unite directly, or
obtained from any nattural source, as rain, or spring, or river, is

26 Introductory Outlines

found to contain its constituent elements hydrogen and oxygen in
the ratio by weight of i : 8, or,

Hydrogen . ii.ia

Oxygen . . SSiSS

1 00.00

If in the formation of sodium chloride by the direct combination
of its constituent elements, an excess of either one or other be
present beyond the proportions 39.32 per cent, of sodium and 60.68
per cent, of chlorine, that excess will simply remain unacted upon.
If eight parts by weight of hydrogen and eight parts by weight
of oxygen be brought together under conditions that will cause
chemical action, the eight parts of oxygen will unite with one part
of hydrogen, and the other seven parts of hydrogen merely remain
unchanged. This fact, that elements are only capable of uniting
with each other in certain definite proportions, marks one of the
most characteristic differences between chemical affinity and those
other forces, such as gravitation, that are usually distinguished as
physical forces, for although there are many instances known in
which the extent to which a chemical action may proceed (that is,
the particular proportion of the reacting bodies which will undergo
the permutation that results in the formation of different mole-
cules) is influenced by the mass of the acting substances, it never
governs the proportion in which the elements combine in these
compounds.

It follows from the law of constant composition that the sum of
the weights of the products of a chemical action will be equal to
that of the interacting bodies ; and upon the validity of this law
depend all processes of quantitative analyses.

(2.) The Law of Multiple Proportions was first recognised
by Dalton, who investigated certain cases where the same two
elements combine together in different proportions, giving rise to
as many totally distinct compounds. These proportions, however,
were always found to be constant for each compound so produced,
so that this law formed no contradiction to the law of constant
composition. The simple numerical relation existing between the
numbers representing the composition of such compounds will be
evident from the following examples. The two* compounds of

* In Dalton's day these two substances were the only known compounds of
carbon with hydrogen.

Tfu Atomic Theory 27

carbon with hydrogen, known as marsh gas and ethylene^ are
found to contain these elements in the proportions —

Marsh gas . . x port by weight of hydrogen with 3 parts of carbon.
Ethylene . . i ,, ,, ,, 6

>• >>

The two compounds of carbon with oxygen contain these ele-
ments in the proportion —

Carbon monoxide . i part of carbon with 1.334 parts of oxygen by weight
Carbon dioxide . i „ ., 2.667 »• »» ••

The elements nitrogen and oxygen form as many as five different
compounds, in which the two elements are present in the propor-
tions—

Nitrous oxide . . i part of nitrogen with a 571 parts of oxygen by weight.

Nitric oxide. . . 1 ,, ,, 1.143

Nitrogen trioxide .1 ., ., 1.714

Nitrogen peroxide i ,, ,, a.286 ,, ,, ,,

Nitrogen pentoxide i ,, ,. a. 857 ,, ,, ,,

rhe relative proportions of carbon combining with a constant
weight of hydrogen in the two first compounds are as i : 2.

Those of oxygen uniting with a constant weight of carbon in the
second example are also as i : 2, while in the nitrogen series the
relative proportions of oxygen in combination with a constant
weight of nitrogen are as i 12:3:4:5.

(3.) Law of Reciprocal Proportions.— Known also as the law
of proportionality, or the law of equivalent proportions. When
the weights of various elements, which were capable of uniting
separately with a given mass of another element, were compared
together, it was seen that these weights bore a simple relation to
the proportions in which these elements combined amongst them-
selves. For example, the elements chlorine and hydrogen each
separately combine with the same weight of phosphorus, the pro-
portions being —

Phosphorus : chlorine = i : 3.43
Phosphorus : hydrogen = i : 0.097

The elements chlorine and hydrogen can combine together, and
they do so in the proportion —

Chlorine : hydrogen « 35.5 : i
but 3S : » " 3-43 : o-097

28 Introductory Outlines

Therefore the proportions by weight in which chlorine and
hydrogen separately combine with phosphorus, is a measure of the
proportion in which they will unite together.

Again, the two elements carbon and sulphur each separately
combine with the same weight of oxygen, the proportion being —

Oxygen : carbon = i* : a375
Oxygen : sulphur = i : i

But the elements carbon and sulphur themselves unite together,
and in the proportion —

Carbon : sulphur « a 187 5 : i
but a 1875 ; I = 0.375 • 2

Therefore the proportion by weight in which carbon and sulphur
separately unite with the same mass of oxygen, is a simple multiple
of that in which these two elements combine together. These
remarkable numerical relations will be rendered still more evident,
by comparing the proportions in which the members of a series of
elements combine with a constant weight of various other elements :
thus —

Hydn^en. Sodium. Potassiam. Silver. Mercary. Chlorine.

0.02817 0.6479 i-<>3 3*^ a. 816 unite separately with z part.

It will be seen that the proportion in which these numbers stand
to each other is as —

1 : 23 : 39 : X07 : TOO 35.5

Let us now compare these proportions with those in which the
same elements unite with a constant weight of the element
bromine —

Hydrogen. Sodium. Potassium. Silver. Mercury. Bromine.

0.0125 0.2875 0.4875 X.34 X.25 unite with X part

or as —

I 23 : 39 : Z07 100 80

Each of these five elements in like manner combines with
oxygen, and the weights which are found to unite with a constant
mass of oxygen are —

Hydrogen. Sodium. Potassium. Silver. Mercury. Oxygen.

0.135 3.875 4.875 13.38 13.5 unite wfth I part.

again as —

K : 83 : 39 : 107 : xoo 8

The Atomic Theory 29

The same relation will appear in the case of the combination of
these five elements with a constant weight of sulphur —

Hydrogen. Sodium. Potusium. Silver. Mercury. Sulphur.

ao6a5 1.4375 3.4375 6.69 6.25 unite with x part

or AS —

X ' 93 ' 39 : 107 ' 100 16

It is thus evident that the proportions in which the members of
such a series combine with a constant weight of one element, is the
same as that in which they unite with a constant mass of another
element One part by weight of hydrogen combines with 35.5
parts of chlorine, 80 parts of bromine, 8 parts of oxygen, and 16
parts of sulphur — that is to say, these proportions of these four
elements satisfy the chemical affinity of i part of hydrogen ; they
are therefore said to be equivalent Twenty-three parts of sodium
is likewise equivalent to 35.5 parts of chlorine, 80 parts of bromine,
8 parts of oxygen, and 16 parts of sulphur, and by the same
reasoning it is also equivalent to i part of hydrogen, 39 parts of
potassium, 107 parts of silver, and 100 parts of mercury. These
numbers, therefore, are known as the equivalent weights of the
elements, or their comHning proportions^ and the combining weight
of an element may therefore be defined as the smallest weight of
that element which will combine with i part by weight of hydrogen.

This law of proportionality, or reciprocal proportion, was dis-
covered by Richter, but it was left for Dalton to trace the connec-
tion between these three generalisations. Dalton adopted and
adapted an ancient theory concerning the ultimate constitution of
matter which was expounded by certain of the early Greek philo-
sophers. The exponents of this theory held that matter is built up
of vast numbers of minute indivisible particles, in opposition to the
antagonistic theory believed by others, namely, that matter was
absolutely homogeneous and capable of infinite subdivision.

Dalton embraced the ancient doctrine of atoms, and extended it
into the scientific theory which is to-day known as Dalton's atomic
theory, and is accepted as a fundamental creed by modem chemists.

According to this theory, matter consists of aggregations of
minute particles, or atoms, which are indivisible. Dalton con-
ceived that chemical combination takes place between atoms —
that is to say, when chemical action takes place between twa
elements, it is due to the union of their atoms ; the atoms coming
into juxtaposition with each other under the influence of chemical

30 Introductory Outlines

affinity, are held together by the operation of this force. He fiirthei
assumed that the atoms of the various elements possessed different
relative weights, and that the relations existing between these
weights, was the same as that between the weights in which experi-
ment had shown the elements to be capable of combining together.
In other words, he said that the numbers representing the combin-
ing proportion of the elements expressed also the relative weights
of the atoms.

Let us now see how this theory satisfies and explains the first
three laws of chemical combination.

(i.) The Law of Constant Composition.— It has already been
shown, p. 25, that the compound sodium chloride, wheresoever and
howsoever obtained, CQntains the elements chlorine and sodium
in the proportion —

Chlorine : sodium = i : 06479.

These numbers have been shown on p. 28 to represent the com-
bining proportions—

Chlorine : sodium = 35.5 : 23.

Now the atomic theory states, that sodium chloride is formed by
the union of atoms of chlorine with atoms of sodium, and that the
relative weights of these atoms is expressed by the combining
weights of the elements, namely, 35.5 and 23. If, therefore, sodium
is to combine with chlorine, since atoms are indivisible masses, it
follows that the compound produced by the union of one atom of
each of these two elements must always have the same composi-
tion.

(2.) The Law of Multiple Proportions.— The ratio in which
oxygen combines with hydrogen to form the compound water, is
seen on p. 27 to be as 8 : i. This number 8, therefore, we will
for the present argument regard as the relative weight of the atom
of oxygen.*

Oxygen combines with carbon as already mentioned, forming
two different compounds ; in the first, the elements are present in
the proportion —

Carbon : oxygen = i : 1.334 = 6 ; 8

That is to say, in the proportion of one atom of carbon to one atom

* For reasons which will be explained later, chemists now regard the number
16 as representing (in round numbers) the relative weight of the atom of
oxygen.

The Atomic Theory 31

of oxygen. According to the theory, if the atom of carbon unites
with more oxygen than one atom, it must at least be with two
atoms. It may be with three or with four, but as the compound
must be formed by the accretion of these indivisible atoms, the
increment of oxygen must take place by multiples of 8. When the
second compound is examined it is found to contain its constituent
elements in the proportion —

Carbon : oxygen — 1 : 2.667 = 6:16

That is to say, in the proportion of one atom of carbon to two
atoms of oxygen. This information respecting the composition of
these two compounds is conveyed both in their names and their
formulae. The first is termed carbon m^moxide, and its formula is
expressed by the symbol CO ; while the second is distinguished as
carbon ^bxide, and has the symbol COa.

The difference in the composition of the five compounds that
nitrogen forms by union with oxygen, will be made evident by the
aid of this theory. The proportion of nitrogen to oxygen in these
compounds is —

(i.) Nitrogen : oxygen = i : 0.571 — 14
(2.) Nitrogen : oxygen =1 : 1.143 — 14
(3.) Nitrogen : oxygen — i : 1.7 14 — 14
(4.) Nitrogen : oxygen = i : 2.268 =■ 14
(5.) Nitrogen : oxygen - i : 2.857 — 14

8
16

24
32

And it will be seen that the increase in the proportion of oxygen in
the compounds, takes place by the regular addition of a weight of
that element equal to 8, which at the present stage of the argument
we are regarding as representing the relative weight of the atom
of oxygen.

(3.) The Law of Reciprocal Proportions.— If the illustrations

given on p. 27 of the operation of this law be examined in the light
of the atomic theory, their explanation will be evident : thus, the
relative proportions in which hydrogen and chlorine separately
combine with phosphorus is 0.097 : 3.43, and the ratio between these
numbers is as i : 35.5, which is the proportion in which these two
elements are known to unite together to form hydrochloric acid.
These numbers, however, represent the relative weights of the
atoms of these elements, therefore hydrochloric acid may be sup-
posed to be formed by the union of one atom of hydrogen with
one atom of chlorine.

Intradtictory Outlines

Again, the relative weights of carbon and sulphur which sepa-
rately combine with a constant weight of oxygen, are — carbon a375,
sulphur I, and the ratio between these numbers is as 6 : 16.

Carbon and sulphur, however, unite together in the relative
proportion —

Carbon : sulphur «= a 1875 : i «- 6 : 32

Therefore the compound they produce, may be supposed to consist
of one atom of carbon, having the relative weight 6, and two atoms
of sulphur, each with the relative weight 16.

CHAPTER VI

ATOMIC WEIGHTS

In the third colamn of the table on page ar, the numbers are
given, which are at the present time generally accepted by chemists
as representing the approximate atomic weights of the elements.
These numbers depart, in many instances, from those arrived at
by Dalton's methods ; thus, the relative weights of carbon, oxygen,
nitrogen, and sulphur, which were found to be equivalent to one
part of hydrogen, are carbon = 6,* oxygen = 8, nitrogen « 4.66,
sulphur ■- 16 ; while the figures given as the approximate atomic
weights of these elements in the table, are carbon » 12, oxygen
— 16, nitrogen ■■14, sulphur « 32. We must now discuss some
of the chief reasons for these departures. In the two compounds
of carbon and hydrogen known to Dalton, namely, marsh gas and
ethylene, the proportions of carbon to hydrogen are —

In ethylene .
In marsh gas

Carbon : hydrogen = 6:1.
Carbon : hydrogen = 6:2.

Dalton therefore concluded that ethylene was a compound con-
taining I atom of carbon, united with i atom of hydrogen, and to
which, therefore, he gave the formula CH ; and that marsh gas
consisted of i atom of carbon combined with 2 atoms of hydrogen,
and which he accordingly represented by the formula ClI,.

There was, however, nothing to prove that the weight of carbon
was constant in the two compounds, for it will be obvious that the
same ratio between the weight of carbon and hydrogen will still
be maintained by assuming that the hydrogen is constant, and
that the carbon varies, thus —

In marsh gas
In ethylene

Hydrogen : carbon : : i : 3.
Hydrogen : carbon : : i : 3 x 2.

* These are the numbers which Dalton ought to have obuined had his
methods of determination been more exact. The figures he actually found for
the combining weights of thew four elements were respectively 5, 7, 5, i^

M C

34 Introductory Outlines

That is to say, the ratios are not disturbed by the assumption
that in marsh gas we have i atom of hydrogen combined with i
atom of carbon, having the relative combining weight of 3, and in
ethylene i atom of hydrogen united with 2 atoms of carbon.

It will be evident, however, that if we could gain any exact
information as to the actual number of atoms which are present
in these various molecules, this difficulty would no longer exist.

For example, suppose it were possible to ascertain that in the
molecule of marsh gas there were 4 atoms of hydrogen, then as
the relative weights of hydrogen and carbon in this compound are
as I : 3, the weight of the carbon atom would obviously have 10
be raised from 3 to 1 2 ; and if it could be determined that in the
ethylene molecule there were also 4 atoms of hydrogen, then
seeing that the r^tio of hydrogen to carbon in this substance is
as I : 6, we should conclude that it contained 2 atoms of carbon,
of the relative weight not less than 1 2, and the composition of the
two compounds would be expressed by the fonnulae, marsh gas
CH4, ethylene C2H4.

Again, the relative weights of hydrogen and oxygen in water
are as i : 8. If the molecule of water contains only i atom of
hydrogen, then we conclude that 8 represents the relative weight
of the oxygen atom, and the formula for water will be HO. But
suppose it to be discovered that there are 2 atoms of hydrogen in
a molecule of this compound, then it becomes necessary, in order
to retain the ratio between the weight of these constituents (a
ratio ascertained by analyses), to double the number assigned to
the oxygen atom, and to regard its weight as 16, as compared with
I atom of hydrogen, and the formula for water in this case would
be H2O.

The compound ammonia contains the elements hydrogen and
nitrogen in the ratio —

Hydrogen : nitrogen : : 1 : 4.66.

If the molecule of ammonia contains only i atom of hydrogen,
then 4.66 represents the relative weight of the nitrogen atom, and
the formula will be NH ; but if it should be found that there are
3 atoms of hydrogen in this molecule, then again the relative
weight assigned to the nitrogen must be trebled in order to pre-
serve the ratio, and it will have to be raised from 4.66 to 14 (in
round numbers), and the formula for ammonia will be NH^

From these considerations it will be evident, that it is of the

Atomic Weights 35

highest importance to gain accurate knowledge aj to the actual
number of atoms which are contained in the molecules of matter —
in other words, to learn the true atomic composition or structure
of molecules ; and it may be said that this problem has occupied
the minds of chemists from the time that Dalton published his
atomic weights, in the year 1808, down to the present time. There
is no single method of general application, by means of which
chemists are able to determine the atomic weight of an element,
but they are guided by a number of independent considerations,
some of which are chemical in their character, while others are of
a physical nature ; and that particular number which is in accord
with the most of these considerations, or with what are judged to
be the most important of them, is accepted as the true atomic
weight.

The chief methods employed for determining atomic weights
may be arranged under the following four heads : —

1. Purely chemical methods.

2. Methods based upon volumetric relations.

3. Method based upon the specific heats of the elements.

4. Method based upon the isomorphism of compounds.

I. As an illustration of the chemical processes from which
atomic weights may be deduced, the following examples may be
given, namely, the case of the two elements oxygen and carbon.

Oxygen combines, as already stated, with hydrogen in the

proportion- Hydrogen : oxygen =1:8.

When water is acted upon by the element sodium, the compound
is decomposed and hydrogen is evolved ; and it is found that if
18 grammes of water are so acted on, i gramme of hydrogen is
evolved, and 40 grammes of a compound are formed, which
contains sodium, together with all the oxygen originally in the
18 grammes of water, and some hydrogen. This compound, under
suitable conditions, can be acted upon by metallic zinc, and when
these 40 grammes are so acted on, i gramme of hydrogen is again
evolved, and 7I.5 grammes are obtained of a compound containing
no hydrogen, but sodium and zinc combined with all the oxygen
originally contained in the 18 grammes of water.

It will be evident, therefore, that the hydrogen contained in
water can be expelled in two equal moieties ; there must, therefore,
be two atoms of hydrogen in this compound. Dy no known

process ca
thus, if te

Inlroductofy Outlinfs

in ihe oxygen be withdrawn from n
grammes o

;r are acted upon by chlorine, under tl
cal action can lake place, ^j grammes of
\\y chlorine and hydrogen are found, and
i thrown out of combination, and evolved
included, that water contains in its mole-

n which i
a compound coniatning o
the whole of the oxygen i
as gas. It is therefore c<
cule, 2 atoms of hydrogen and i atom of oxygen, and as they arc
combined in the relative proportion of I ; 8, the atomic weight of
oxygen cannot be less than i6. -

No compounds have been found in which a smaller weight of
oxygen, relative to one atom of hydrogen, than is represented by
the number l6 (approximately), is known to lake part in a chemical

The compound tnarsh gas contains hydrogen and carbon in
the proportion by weight of 1:3. By acting on this compound
with chlorine, it is possible to remove the hydrogen from ii in
four separate portions.

By the first action of chlorine upon 16 grammes of marsh gas,
t gramme of hydrogen b removed in combination n-ilh 3S'5
grammes of chlorine, and a co-npound containing carbon, hydrogen,
and chlorine, in the ratio 13:3: J5.5, is formed.

By the successive action of chlorine, three other moieties of
hydrogen can be thus withdrawn, each being in combination with
its equivalent (35.5 parts) of chlorine. The second and third com-
pounds that are formed contain carbon, hydrogen, and chlorine in
the ratios 12:1: (35.5 x 2) and 12 : i : (35.5 x 3).

The compound produced by the fourth action of chlorine, which
withdraws the fourth portion of hydrogen, contains only carbon
and chlorine, in the ratio 12 : (35.5 x 4). From the fact that the
hydrogen contained in marsh gas can thus be removed in four
separate portions, the molecule must contain four hydrogen atoms,
and therefore the atomic weight of carbon must be al least 12. No
compounds of carbon are known in which a smaller weight of
carbon, relative to ore atom of hydrogen, than is represented by
the number I2, lakes part in a chemical change.

The detinilLon of atomic weight, furnished by considerations
of a chemical nature, may be thus stated : the atomic weight of an
element, is the number which represents how many times heavier
the smallest inass of that element capable of taking part in a
chemical change is, than the smallest weight of hydrogen which

O fUQCtioiL

AUnnic Weights 37

The choice of hjrdrogen as the unit of atomic weights is a purely arbitrary
selection ; but since atomic weight values can only be determined relatively, it
becomes necessary to select some one element and to assign to its atom some
particular number to serve as a standard. As hydrogen is the lightest of all
elements, Dalton originally adopted it, and arbitrarily fixed unity as the
number which should stand for its atomic weight. The disadvantages of this
particular unit are twofold : in the firtt place the number of elements that form
hydrogen compounds that are suitable for atomic weight determinations is very
small, whereas nearly all the elements form convenient oxygen compounds, or
compounds Mnth elements whose atomic weights with reference to oxygen are
accurately known, and in actual practice such compounds are almost always
made use of for such determinations. In the second place, the exact ratio of
the ^'eights of an atom of hydrogen and oxygen is not known with certainty, so
that in calculating atomic weights that are determined with reference to oxygen,
possible errors may arise. The ratio Hydrogen : Oxygen is not exactly i : i6.
Various values have been obtained by different experimenters, and at the present
time 1 : 15.96 is accepted as more nearly the truth.

On account of the extreme difficulty of exactly determining this ratio,
chemists are now generally agreed in adopting as the unit in all exact determi-
nations of atomic weights, a number which is ^^th the weight of the atom of
oxygen : that is to say, tlie atomic weight of oxygen is in reality the standard,
and is fixed as 16, and the unit, instead of being the weight of i atom of
hydrogen, is f^th of this number.

The effect of this change is only of importance in cases of chemical investiga-
tion where a high degree of exactitude is required ; for purposes of ordinary
analyses and chemical calculations the difference that it makes is practically nil.
Fixing the atomic weight of oxygen at 16 merely raises the atonfic weight of
hydrogen from i to 1.003. ^ ^^^ ^^ ^^ small decimal fractions introduces
unnecessary complications which tend to obsctu^ simple processes of reasoning,
the approximate atomic weights given in the third column of page ai, will be
employed for the most part in the following Introductory chapters.

2. Determination of Atomic Weights ft*om Considerations
based upon Volumetric Relations. The Law of Gaseous

Volumes.— In the year 1805 the fact was discovered by Gay
Lussac and Humboldt, that when i litre of oxygen combines with
2 litres of hydrogen, the vapour of water (or steam) which was
produced, occupied 2 litres, the volumes in all cases being measured
under the same conditions of temperature and pressure. ''^ This
fact led to the discovery of the simple relation existing between
the volimies of other reacting gases and the volume of the products :
thus it was found that —

I voL of hydrogen unites with i vol. of chlorine, and gives
2 vols, of hydrocliloric acid.

* For the relations of gaseous volumes to temperature and pressure the
student is refeired to chapter ix.. on the general properties of gases.

38 Introductory Outlines

1 vol. of hydrogen unites with i vol. of bromine vapour, and

gives 2 vols, of hydrobroniic acid.

2 vols, of hydrogen unite with i vol. of oxygen, and give

2 vols, of steam.
2 vols, of carbon monoxide unite with i vol. of oxygen, and
give 2 vols, of carbon dioxide.

1 vol. of carbon monoxide unites with i vol. of chlorine, and

gives I vol. of phosgene gas.

In the same way with compounds that cannot be obtained by
the direct union of their constituent elements, it is found that on
being subjected to processes of decomposition, similar simple
volumetric relations exist : thus by suitable methods of decom-
position—

2 vols, of ammonia gas yield i vol. of nitrogen and 3 vols, of

hydrogen.
2 vols, of nitrous oxide yield 2 vols, of nitrogen and i vol of

oxygen.
2 vols, of nitric oxide yield i vol. of nitrogen and i vol. of

oxygen.
I vol. of marsh gas yields 2 vols, of hydrogen and some solid

carbon, which cannot be evaporated, and therefore its

Vapour volume is unknown.
I vol. of ethylene yields 2 vols, of hydrogen and solid carbon

as in the preceding.

The observations of these and similar facts gave rise to the law
of Gay Lussac, and it will be seen that there is evidently a close
connection between the simple volumetric relations, and those
existing between the multiple proportions by weighty in which one
clement unites with another. For example, in the two oxides of
nitrogen the ratios of the two elements by weight are —

Nitrous oxide . . Nitrogen : oxygen = 28 : 16.
Nitric oxide . . Nitrogen : oxygen = 28 : (16 x 2),

while the volumetric relation in which the two constituents are
present is —

Nitrous oxide . . Nitrogen : oxygen = 2:1.
Nitric oxide . . . Nitrogen : oxygen = 2 : (i x 2).

In other words, there is twice as much oxygen by weight in the
one conipound as in the other, and there is twice as much oxygen

Atomic Whj^kts 39

by volume in the one as compared to the other. Moreover, if 14
and 16 respectively represent the relative weights of atoms of nitro-
gen and oxygen, then the numbers representing the relative
volunus in which these elements unite will also express the number
of atoms of each in the molecule.

The connection existing between the proportions in which
elements unite by weight, and by volume, was first explained by
the Italian physicist and chemist Avogadro, who in the year
181 1 advanced the theory now recognised as a fundamental prin-^
ciple, and known as Avogadro's hypothesis. This theory may be
thus stated : Equal volumes of all gases or vapours^ under the
same conditions of temperature and pressure^ contain an equal
number of molecules^ If this be true, if there are the same
number of molecules in equal volumes of all gases, it must follow
that the ratio between the weights of equal volumes of any two
gases, will be the same as that between the single molecules of the
particular gases. If a litre of oxygen be found to weigh sixteen
times as much as a litre of hydrogen (under like conditions of tem-
perature and pressure), inasmuch as there are the same number
of molecules in each, the oxygen molecule must be sixteen times
heavier than that of hydrogen ; and therefore, by the comparatively
simple method of weighing equal volumes of different gases, it
becomes possible to arrive at the relative weights of their molecules.

The relative weights of equal volumes of gases and vapours, in
terms of a given unit, are known as their densities or specific
gravities. Sometimes densities are referred to air as the unit, but
more often hydrogen, as being the lightest gas, is taken as the
standard. Taking hydrogen as the unit, the density or specific
gravity of a gas, is the weight of a given volume of it, as compared
with the weight of the same volume of hydrogen — or in other
words, the ratio between the weight of a molecule of that gas, and
a molecule of hydrogen. The ratio that exists between the weight
of a gaseous molecule and half the weight of a molecule of hydrogen^
chemists term the molecular weight of that gas ; hence it will be
obvious that the number which represents the molecular weight of
a gas, is double that of its density or specific gravity.

If I litre of hydrogen and i litre of chlorine be caused to combine,
2 litres of gaseous hydrochloric acid are formed. As equal volumes
of all gases (under like conditions) contain the same number of
molecules, in the 2 litres of hydrochloric acid there must be twice
as many molecules of that compound, as there were of hydrogen

Introductory Outlines

molecules in the i litre, or of chlorine molecules in the other.
But each molecule of hydrochloric acid is composed of chlorine
and hydrogen (from other considerations one atom of each element),
therefore there must have been at least twice as many atoms
of hydrogen, in the litre of that gas, as there were molecules ;
and by the same reasoning, twice as many chlorine atoms in the
litre of chlorine, as there were molecules : in other words, both
hydrogen and chlorine molecules consist of two atoms. The
molecular weight of hydrogen therefore is 2 ; that is, its molecule
is twice as heavy as its atom. The atom of hydrogen is the unit
to which molecular weights are referred* while the weight of the
molecule of hydrogen is taken as the standard of densities or
specific gravities.

In order, therefore, to find the molecular weight of any gas or
vapour, it is necessary to learn its density — that is, to ascertain
how many times a gi^en volume of it is heavier than the same
volume of hydrogen,* and to double the number so obtained.t

The following table gives the densities or specific gravities of all
the elements whose vapour densities have been determined. The
list includes all those elements which are gases at the ordinary
temperature, and those that can be vaporised under conditions
which render such determinations experimentally possible. (Hy-
drogen being taken as unity, the other numbers are the approxi-
mate values, which for purposes of discussion are more suitable
than figures that run to two or three decimal places.)

Hydrogen .

Iodine

. 127

Nitrogen

. 14

Sodium

. 11.5

Oxygen

. 16

Potassium

. 19.5

Fluorine

. 19

. Zinc .

. 32.5

Sulphur

. 32

Cadmium .

. 56

Chlorine

• 35.5

Mercury .

. 100

Selenium

. 79

Phosphorus

. 62

Bromine

. 80

Arsenic

. 150

* Certain exceptions to this rule are discussed under the subject of Dissocia-
tion, chap. X., p. 85.

t The specific gravity of hydrogen, as compared with air taken as unity,
is 0.0693. or air is 14.43 times heavier than hydrogen. If, therefore, it be
desired to find the molecular weight of a given gas, whose density as compared
with air is known, it is only necessary to multiply its density (air = i) by thr
number 14.43. wh'c^i gives its density as compared with hydrogen, and then to
double thr number so obtained.

Atomic Weights 41

Let as now consider how the knowledge of the relative weights
of gaseous molecules is utilised, in assigning a particular number
as the atomic weight of an element

The molecular weight of chlorine is 71. It has been shown that
the molecule certainly contains more than i atom, and probably 2,
in which case 35.5 would represent the relative weight of the atom.

The compound hydrochloric acid has the molecular weight 36.5.
It has been already proved that this compound contains i atom of
hydrogen, therefore 36.5 - i « 35.5.

The compound carbon tetrachloride gives a molecular weight
154. Analysis shows that this compound contains 12 parts of
carbon in 154 parts, therefore 154- I2»i42»35.5 X4.

In these three molecules the weights of chlorine relative to the
weight of 1 atom of hydrogen are 142, 35.5, and 71, the greatest
common divisor of which is 35.5. This number, therefore, is
selected as the atomic weight of chlorine.

Again, it has been shown that by the action of sodium upon
water, the hydrogen contained in the water could be expelled in two
separate portions, thus proving that there must be 2 atoms of
hydrogen in the molecule of that compound.

The molecular weight of water is found to be 18, deducting from
tliis the weight of the two hydrogen atoms we get 18 - 2 = 16.

The molecular weight of carbon monoxide is 28 ; 28 parts of
this compound contain 12 parts of carbon, therefore 28 - \2 ^ 16.

The molecular weight of carbon dioxide is 44 ; 44 parts of this
compound also contain 12 parts of carbon, therefore 44 - 12 = 32.

When I litre of oxygen combines with two litres of hydrogen,
2 litres of water vapour are formed ; there are therefore twice the
number of water molecules produced as there are oxygen mole-
cules (since by Avogadro*s hypothesis 2 litres contain twice as many
molecules as i litre). But each water molecule contains certainly
I atom of oxygen, therefore the original oxygen molecules must
have consisted of not less than 2 atoms. When the density of
oxygen is determined it is found to be 16, its molecular weight
therefore is 32.

In these four various molecules the weights of oxygen relative to
the weight of i atom of hydrogen are 16, 16, 32, 32, the greatest
conunon divisor of which is 16. This number, therefore, is selected
as the atomic weight of oxygen.

Again, it has already been shown that in the compound ammonia,
the hydrogrn can be removed in three separate moieties, proving

42 Introductory Outlines

that there must be three atoms of that element in the molecule.
The molecular weight of ammonia is found to be 17, therefore
17 - 3 = 14, which is the weight of the nitrogen.

The molecular weight of nitrous oxide is 44 ; 44 parts of this
compound are found to contain 16 parts of oxygen and 28 parts of
nitrogen.

The molecular weight of nitric oxide is 30 ; 30 parts of this
compound contain 16 parts of oxygen and 14 parts of nitrogen.

The molecular weight of nitrogen is found to be 28.

In these four different molecules the weights of nitrogen relative
to the weight of i atom of hydrogen are 14, 28, 14, 28, the
greatest common divisor of which is 14. The atomic weight of
nitrogen, therefore, is regarded as 14.

These three examples, namely, chlorine, oxygen, and nitrogen
are instances of elements which are gaseous at ordinary tempera-
tures ; but the same methods are applicable in the case of the non-
volatile elements, such as carbon, provided they furnish a number
of compounds that are readily volatile.

On comparing the numbers in the foregoing table (p. 40), repre-
senting the densities of various elements, with the atomic weights
of those elements as given on p. 21, it will be seen that in the
first nine cases the numbers given are approximately the same*
This agreement is merely because the molecules of these elements
consist of two atoms. The molecules of sodium, potassium, zinc,
cadmium, and mercury consist of only one atom j their atomic
weights, therefore^ will be the same as their molecular weights, that
is, twice their densities. The elements arsenic and phosphorus, on
the other hand, contain in their molecules four atoms — that is to
say, the number which represents the smallest weight of phosphorus,
and of arsenic, capable of taking part in a chemical change, is only
half the density, and therefore a fourth of the molecular weight

The definition of atomic weight that is furnished by the con-
sideration of volumetric relations may be thus stated. The atomic
weight is the smallest weight of an element that is ever found in a
volume of any gas or vapour equal to the volume occupied by one
molecule of hydrogen^ at the same temperature and pressure.

The volume o^xupied by one molecule of hydrogen is regarded
as the stahdard molecular volume, while that occupied by an atom
of hydrogen — or, in other words, the atomic volume of hydrogen — is
called the unit volume. The standard molecular volume therefore
is ^id to be two unit volumes; and as, from Avogadro's law. all

Atomic Weights 43

gaseous molecules have the same volume, it follows that the mole-
cules of all gases and vapours occupy two unit volumes. Atomic
weight may therefore be defined as ihs smallest weight of an
element ever found in two unit volumes of any gas or vapour.

The molecular volume of a gas is its molecular weight divided
by its relative density, a ratio which in all cases will obviously
equal 2, that is, two unit volumes.

The atomic volume of an element in the state of vapour, is its

atomic weight divided by its relative density. In the case of such

elements as chlorine, nitrogen, oxygen, &c., whose molecules are

diatomic, the quotient will be i — that is to say, the atomic volumes

of these elements is equal to i unit volume. In the case of mer-

, , atomic weight = 200

cury vapour, however, we have . — .— ^ ■■ 2.

' '^ density = 100

The atomic volume of mercury vapour, therefore, is equal to 2

unit volumes, and is identical with its molecular volume.

On the other hand, with the element phosphorus the atomic

volume is aU)jmc^weight « 31 ^ ^^ one-half the unit volume,

density =» 62

and therefore one-fourth the molecular volume ; consequently, four
atoms exist in this molecule.

The method of determining atomic weights based upon volu-
metric relations, when taken by itself, is not an absolutely certain
criterion, for although the atomic weight of an element cannot be
greater than the smallest mass that enters into the composition of
the molecules of any of its known compounds, it might be less than
this, as there is always the possibility of a new compound being
discovered, in which the relative weight of an element is such as to
make it necessary to halve the previously accepted atomic weight.

3. Determination of Atomic Weight from the Specific
Heat of Elements in the Solid State. -When equal weights of

dinferent substances are heated through the same range of tempera-
ture, it is found that they absorb very different quantities of heat,
and on again cooling to the original temperature, they consequently
give out different amounts of heat Thus, if i kilogramme of water,
and I kilogramme of mercury, be each heated to a temperature of
100°, and then each be poured into a separate kilogramme of water
at o^ in the first case the resultant mixture will have a temperature
of 50*, while in the second it will only reach the temperature of 3.2* ;
that is to say, while the water in cooling through 50** has raised the
temperature of an equal weight of water from o* to 50% the amount

44 Introductory Outlines

of heat in i kilogramme of mercury at loo* has only raised the
temperature of an equal weight of water from o° to 3.2°, and in so
doing has itself become lowered in temperature 100 - 3.2 = 96.8'.
The amount of heat contained, therefore, in equal weights pf water
and of mercury at the same temperature, as shown by these figures,
is as —

therefore it requires 30 times as much heat to raise a given weight
of water through a given number of degrees as to raise an equal
weight of mercury through the same interval of temperature, or
the tJurmal capacity of mercury is j^th that of water.

The specific heat of a substance is the ratio of its thermal
capacity to that of an equal weight of water ; or, the ratio between
the amount of heat necessary to raise a unit weight of the sub-
stance from 0° to I*", and that required to raise the same weight
of water from o* to i' ; thus, the specific heat of mercury is ^, or
0.033. Water is chosen as the standard of comparison because it
possesses the highest thermal capacity of all known substances ;
the numbers, therefore, which express the specific heats of other
substances are all less than unity.

Dulong and Petit were the first to draw attention (18 19) to a
remarkable relation which exists between the specific heats, and
the atomic weights, of various solid elements, whose specific heats
they themselves had determined. They found that the specific
heats of the solid elements were inversely as their atomic weights ;
that is to say, the capacity for heat of masses of the elements pro-
portional to their atomic weight, was equal. This law, known as
the law of Dulong and Petit, may be thus stated : The thermal
capacities of atoms of all elements in the solid state are equal.

The thermal capacity of an atom is termed its atomic heat;
hence the law may be more bnefly stated, all elements in the
solid state have the satne atomic heat. This important constant,
is the product of the atomic weight into the specific heat. From
the following table it will be seen that the number expressing
the atomic heat is not perfectly constant : the departures from the
mean 6.4 are, as a rule, only slight, and may be attributed to
the fact that the determinations are not always made upon the
elements imdcr conditions that are strictly comparable. At the
end of the table, however, there are certain elements which appear
to present marked exceptions to the law.

Atomic Weights

Specific
Heat

Atomic Atomic

Weight. HeaL

. 0.94

7 = 6.6

. 0.29

23 = 6.7

. 0.166

39 - 6.5

. 0.122

55 - 6.7

. aii2

56 = 6.3

. 0.057

108 » 6.1

. 0.032

196 - 6.2

) . 0.032

200 » 6.4

. 0.031

206.4 =6.5

. 0.41

9.1 = 37

. 0.25

u = 2.75

nd) . 0.147

12 = 1.76

. 0.177

28 = 4.95

Element.

Lithium .

Sodium

Potassium

Manganese

Iron .

Silver

Gold

Mercury (solid)

Lead

{Beryllium
Boron (cryst)
Carbon (diamond)
Silicon (cryst)

It will be seen that, relatively speaking, the four elements
which show a considerable departure from the law of Dulong are
elements with low atomic weights. Low atomic weight, however,
is not always accompanied by such deviation, as is shown in the
case of lithium and sodium.

When the different allotropes of carbon are experimented upon,
it is found that the departure is not the same for each modification
of the element, thus —

Elcmeiit.

Diamond

Graphite

Charcoal

Specific
Heat.

0.147
0.200
0.241

Atomic Atomic
Weight. Heat.

X 12 =» 1.76
X 12 » 2.40
X 12 = 2.90

It has been observed that, as a general rule, the specific heat of
an element is slightly higher at higher temperatures ; but in the
case of the four elements showing abnormal atomic heats, this
increase rises rapidly with increased temperature, until a certain
point is reached, when it remains practically constant, and repre-
sents an atomic heat which closely approximates to the normal
value ; thus in the case of diamond, the specific heat at increasing
temperatures '

Diamond at 10.7'' .

Specific Atomic Atomic
Heat. Weight. Heat.

. 0.1 128 X 12 = 1.35

45° •

. 0.1470 X 12 = 1.76

>»

2o6* .

. 0.2733 X 12 = 3.28

607- .

. a44o8 X 12 = 5.30

»)

8o6» .

0.4489 X 12 = 5.4

•1

9«5' .

. 0.4589 X 12 » 5.5

46 Introductory Outlines

The same result is seen in the case of graphite,.and it is also to
be remarked, that while at low temperatures there exists a wide
difference between the specific heats of these twn modifications of
carbon, this difference vanishes at a temperature of about 600*.

Specific
Heat.

Atomrc Atomic

Weight. Heat.

Graphite at 10.8* . •

. a 1604

X 12 = 1.93

„ 61.3** .

. ai99o

X 12 « 2.39

y, 642 • •

. 0.4454

X 12 = 5.3s

978* . .

. 0.4670

X 12 = 5.50

Both the elements boron and silicon are found to follow the
same rule, and at moderate temperatures their atomic heats nearly
approximate the normal constant

The case of the somewhat rare element beryllium is of special
interest from another point of view, which will be referred to when
treating of the natural classification of the elements : from the
following numbers * it will be seen that its atomic heat very rapidly
rises with moderate increase of temperature.

Specific Atomic
Heat. Weight.

Atomic
Heat.

Ilium ajt loo* .

•

. 0.4702 X 9.1 =

4.28

„ 200* .

•

. a542o X 9.1 =

4.93

„ 400"' .

•

. 0.6172 X 9.1 =

5.61

500'

•

. 0.6206 X 9.1 =

5.65

The relation between atomic weight and specific heat, established
by Dulong and Petit, is of service in the determination of atomic
weights, not as a method of ascertaining the exact value with any
degree of refinement, but rather as a means of deciding between
two numbers which are multiples of a common factor.
. If specific heat x atomic weight = atomic heat, it will be obvious
that, if we experimentally determine the specific heat, and divide
that value into the constant atomic heat, 6.4, we obtain the
approximate atomic weight.

The two following examples will serve to illustrate the applica-
tion of the method.

The clement indium combines with chlorine in the proportion-
Indium : chlorine = 37.8 : 35.5
• HumpidjfC.

Atomic Weights 47

If InCl is the fonnula, then 37.8 is the atomic weight of indium ;
but from the chemical similarity between indium and zinc (whose
chloride has the fonnula ZnCI]), it was believed that the formula
for indium chloride was InCl^ in which case, in order to preserve
the ratio between the two elements, the atomic weight would have
to be 37.8 X 2 «= 75.6.

When the specific heat of indium was determined/ it was found
to be ao57.

6.4

0.057

112.28

Therefore the atomic weight must be raised by one-half, from
75.6 to 113.4, and the formula for the chloride will be InClj.
The element thallium combines with chlorine in the proportion —

Thallium : chlorine = 203.6 : 35.$

In some of its compounds thallium exhibits a strong resemblance
to potassium, the chloride of which has the formula KCl. If the
formula for the thallium chloride is TlCl, the atomic weight of the
metal must be 203.6.

In many respects tliallium exhibits a striking analogy with lead,
the chloride of which has the formula PbCl^ If thallium chloride
has a corresponding formula, TlCl^ then the atomic weight of
thallium must be raised to 407.2.

When the specific heat of thallium was ascertained,t it was found

to be 0.0335.

6.4

0.0335.

191-3

This result shows that the number 203.6 and not 407.2 is the
atomic weight of thallium, and that the chloride has the formula
TlCl.

Moleeolar Heat of Compounds.— The capacity for heat of an

atom, undergoes no alteration when the atom enters into combina-
tion with different atoms — in other words, the atomic heat of an
element is the same in its compounds. The molecular heat of a
compound (that is, the product of the molecular weight into the
specific heat) will therefore be the simi of the atomic heats of its
constituent elements. Hence it is possible to calculate what will
be the atomic heat of an element, which does not exist as a solid

* Bunsen, 1870. t RegnaulL

48 Introductory Outlines

under ordinary conditions ; and therefore the atomic weight of
such an element, as deduced from other considerations, is capable
of verification, by determinations of the molecular heat of various
of its compounds : thus —

The specific heat of silver chloride, AgCl, is 0.089 : —

Specific

Molecular

Molecula

Heat.

Weight.

Heat

0.089

X 143-5 =

'■ 12.77.

The atomic heat of silver = 6.1, therefore, as deduced from this
compound, the atomic heat of chlorine is 12.77 — 6.1 = 6.6.
Again, the specific heat of stannous chloride, SnCl,, is 0.1016 : —

Specific

Molecular

Heat

Weight

Heat

aioi6

X 189 =

19.2.

The atomic heat of tin is 6.6, therefore the atomic heat of two
atoms of chlorine, as deduced from this compound, is 19.2-6.6=
12.6, giving 6.3 as the atomic heat of chlorine.

The differences that appear in the value, as deduced from
various compounds, are lessened, because the errors of the
method are more equally distributed, if we divide the molecular
heat by the number of atoms in the molecule. Thus, in the
two examples quoted, silver chloride consists of two atoms, while
the molecule of stannous chloride contains three ; if, therefore, the
molecular heats of these two compounds are divided respectively
by 2 and by 3 we get —

iHf = 6.38.and'f = 6.4,

as the value representing the atomic heat of chlorine.
The element calcium combines with chlorine in the proportion —

Calcium : chlorine = 20 : 35.5.

If the atomic weight of calcium is 20, the formula will be CaCl^
whereas if 40 is the atomic weight of the metal, the compound
must be represented by the formula CaCI).

The molecular weight of CaCl would be 55.5, that of CaClj 1 1 i.o.

When the specific heat of the compound was determined, it
was found to be 0.1642. In order, therefore, to decide between

Atomic Weights 49

the two values for the atomic weight of calcium, we calculate the
molecular heat from both of the molecular weights, and divide the
result by the number of atoms in the molecule in each case.

On the supposition that Ca •• 20, and that CaCl represents the
chloride : —

ca. . .?L'i4A.pJ.^55.

Or, if Ca—40^ and CaCl, is the formula for the cbloiide, theD^

,- ^1 0.1642 X iii.o ,
CaCli . . . — ^^ _ 6.07.

The number 6.07, which nearly agrees with the constant 6.4,
decides the value 40 as the atomic weight of calcium. The
element calcium is one of (hose metals which it is very difficult to
isolate and obtain in a state of purity, but when in recent years
the specific heat of this metal was experimentally determined,*
it was found to be o. 1 704 : —

0.1704 X 40 — 6.8.

Thus affording direct confirmation of the value 40 for the atomic
weight of calcium, which had been deduced from the molecular
heat of its compounds.

Deductions based upon molecular heats of compounds, are only
trustworthy in the case of the most simply constituted compounds.

4. Determination of Atomle Weight from Conalderatloiu
bsaed on Isomorphism. — It was early observed that certain rela-
tions existed between the crystalline forms of compounds, and their
chemical composition. Mitscherlich found that certain substances
having an analogous chemical composition, as for example, sodium
phosphate and sodium arsenate, crystallised in the same geometric
form. In theyeari82i he stated his /me (i/M0«(i»?)Ainn as fallows :
"The same number of atoms, combined in the same way, give rise
to the same crystalline form, which is independent of the chemical
nature of the atoms, being influenced only by their number and
mode of arrangemenL" Subsequent investigations, however, have
shown that this statement is too general.

In its broad sense, as signifying the same crystalline form,
isomorphism is found to exist —

1. Between compounds containing the same number of atoms

So rntroductory Outlines

similarly combined, and which bear close chemical analogies to
each other.

isomorphous P-^^*^ ^P*^^ .... ZaS04.7H,0.
( Magnesium sulphate . MgSOf.TH/).

Isomorphous \ "y^^gcn disodium phosphate . HNa,P04.12H/).
I Hydrogen disodium arsenate HNa3As04,l2HjO.

/Rubidium alum. . Rb,S04.Al,(S04),.24H,0.

I:.omorphous<P°*«5^^^^*^"»«*^"" • ' K^SO*. 0^804),. 24 H^O.
I Potassium aluminium selenium ) ,. « ^ *. ,„ ^ » «.,, ^
I alum .... } K;^04.Al,(Se04),.24II,0.

2. Between compounds containing a different number of atoms,
but which also bear dose chemical analogies to one another.

Isomorohous I Ammonium chloride . . NH4CL

I Potassium chloride . . KCL

Isomorphous I ^™"™°"*"™ '"^P***** • * (NH4),S04.

( Potassium sulphate . KJSO4.

3. Between compounds containing either the same or a different
number of atoms, and which exhibit little or no chemical analogies.

Isomorohous I ^^^""™ nitrate .... NaNOj.
I Calcium carbonate . CaCOj.

Isomorphous i ^^*"™ "^^^P*^^ ^^^y*^®"*' ' Na^4.
I Barium permanganate BaMn^Og.

Isomorphism of this order, where little or no chemical relations
exist between the compounds, is sometimes distinguished as
isogonism. It must not be supposed, that because two chemically
analogous compounds contain the same number of atoms, they will
necessarily crystallise in the same form : there are indeed a large
number of similarly constituted analogous compounds that do not
exhibit isomorphism.

No simple definition of isomorphism is possible, but the following
test is generally accepted as a criterion, namely, the power to form
either mixed crystals or layer crystals. Thus, when two substances
are mixed in a state of liquidity, and allowed to crystallise, if the
crystals are perfectly homogeneous, they are known as mixed
crystals^ and the substances are regarded as isomorphous.

Or when a crystal of one compound is placed in a solution of
another compoimd, and the crystal continues tq grow regularly
in the liquic^^th^ compounds ape isof1lqrp^oas. Thus, if a crystad

V*.: .•'• •••>•:: : ••:•": -"^^^

• • • •••. •• : -.J • ••• '"

• • • • • "

Atomic Weights

or potassium alum (white) be placed in a solution of manganese
alum, the crystal coniicues lo grow without cli.inge of fonn, and
a layer of aniethysi- coloured manganese alum is deposited upon it.

In making use of the law of isomorphism in the determination of
atomic weights, it is assumed that the weights of ditfereni atoms
that can mutually replace each other without altering the crystal-
line form, are proportional to their atomic weights.*

Thus, if we suppose (hat, in the case of the sulphates of zinc
and magnesium, the atomic weight of sine is known, vit., 65, and
that of magnesium is doubtful ; from the fact of the isomorphism
of the sulphates ii may be premised that the elements are present in
proportions relative to [heir atomic weights. Analysis shows that
ihe proportion is 24 of magnesium to 65 of line, therefore 34 is pre*
sumably the atomic weight of magnesium,

la this way Berzelius corrected many of the atomic weights
which in his day had been assigned to the elements.

* 'rhegroup(NH^iiiaf ba ragudnt u v

n. bavins llicrtUttv«w*i|{tilil.

CHAPTER VII

QUANTITATIVE CHEMICAL NOTATION

The use of chemical symbols and formulae, as a convenient means
of representing concisely the qualitative nature of chemical changes,
has been explained in chapter iv. We are now in a position to
read into these symbols a quantitative significance, which at that
stage it would have been premature to explain.

The symbol of an element stands for an atom ; but, as we have
now learnt, the atoms of the various elements have different relative
weights, hence these symbols represent relative weights of matter.
The symbol Na signifies 23 relative parts by weight of sodium, O
stands for 16 relative parts by weight of oxygen, H for i pait of
hydrogen ; in other words, the weight of sodium represented by
the symbol Na, is 23 times as heavy as that which is conveyed
by the symbol H. A chemical equation, therefore, is a strictly
quantitative expression, in which certain definite weights of matter
are present in the form of the reacting substances, and which
reappear without loss or gain in the compounds resulting from the
change. In this sense a chemical equation is a mathematical
expression. Thus, the equation —

Na + CI = NaCl,

not only means that an atom of sodium combines with an atom of
chlorine and forms i molecule of sodium chloride, but it also means

23 + 35.5 = 58.5
Na CI NaCl.

In other words, that sodium and chlorine unite in the relative pro-
portion of 23 parts of the former, and 35.5 parts of chlorine, and
produce 58.5 parts of sodium chloride.

In the same way, into the equation which expresses the action of
sulphuric acid upon sodium carbonate, we read the quantitative
meaning of the symbols —

Quantitative Notation $3

H,S04 + Na,CO, - Na2S04 + CO, + H,0.
2 46 46

32 12 32 12 a

64 48 64 32 16

98* + 106 - 142 +44+18

That is to say, 98 parts by weight of sulphuric acid act upon
106 parts of sodium carbonate, producing 142 parts of sodium
sulphate, 44 parts of carbon dioxide, and 18 parts of water. It will
be evident that it becomes a matter of the simplest arithmetic, to
calculate the weight of any product that can be obtained from a
given weight of the reacting substances ; or vice versd^ to find
the weight of any reacting substance which would be required to
produce a given weight of the product of the action.

Not only is information respecting the quantitative relations
by weight embodied in a chemical equation, but when gaseous
substances are reacting, the equation also represents the volu-
metric relation between the gases. In order that the volumetric
relations may be more manifest, the equations expressing the re-
actions are written in such a manner as to represent the molecules

of the substances.

H + CI - HCl

is an atomic equation, but as the molecule is the smallest particle
which can exist alone, a more exact statement of the chemical
change is made, by representing the action as taking place between
molecules, thus —

H, + CI, - 2HCL

From such an equation we see that i molecule of hydrogen, or

2 unit volumes, unites with i molecule or 2 unit volumes of chlorine,

and forms 2 molecules or 4 unit volumes of hydrochloric acid :

or again —

O, f 2H, - 2H,0.

One molecule, or 2 unit volumes of oxygen, unite with 2 mole-
cules, or 4 unit volumes of hydrogen, and produce 2 molecules of
water, which when vaporised, and measured under the same con-
ditions of temperature and pressure, occupy 4 unit volumes. In

* The number obtained by adding together the weights of the atoms in a
fonnula is known as a '* rormula weight," thus 98 is the formula weight of
sulphuric add.

54 Introductory Outlines

other words, the number of molecules, in all cases * where gases
and vapours are concerned, represent exactly the volumetric
relations. In the cases quoted, it will be observed, the same ratio
also subsists between the number of cUoms of the reacting gases
and the molecules of the compound, but this is not always the
case, for example —

Atomic equation, Hg + 2C1 = HgCl,.

In this equation 3 atoms unite to produce i molecule, but the
ratio between the volumes is not represented by the statement,

1 volume of mercury vapour and 2 volumes of chlorine produce

2 volumes of vapour of mercury chloride.

Molecular equation, Hg + CI, = HgClji-

By this we see that i molecule + (2 unit volumes) of mercury
vapour, and i molecule (2 unit volumes) of chlorine, give i mole-
cule (2 unit volumes) of vapour of mercury chloride.

Again, P + 3C1 = pci, is an atomic equation, showing that
I atom of phosphorus unites with 3 atoms of chlorine ; but it is not
true that the ratio between the volumes is represented by the state-
ment, I volume of phosphorus vapour combines with 3 volumes of
chlorine, and gives 2 volumes of the vapour of phosphorus trichlo-
ride, as will be seen by comparison with the molecular formulae —

P4 -H 6C1, = 4PC18.

This equation tells us that i molecule % (2 unit volumes) of phos-
phorus vapour combines with 6 molecules (12 unit volumes) of
chlorine, producing 4 molecules (8 unit volumes) of phosphorus
trichloride vapour.

Knowing the relative densities of gases compared with hydro-
gen, it is obviously possible, by ascertaining the actual weight in
grammes of some definite volume of hydrogen, to calculate the
actual weight of any given volume of any other gas.

Two units are in common use, namely —

(I.) The weight of i litre of hydrogen, measured at a temperature
of 0° C, and under a pressure of 760 mm. of mercury.§

* See Dissociation, ^^here apparent exceptions are explained,
t The atomic volume of mercury vapour being equal to 3 unit volumes (p. 43)
X The atomic volume of phosphorus is .5 of a unit volume (p. 43).
§ This temperature and pressure is chosen as the standard at which volumes
of KSisei are compared. See General Properties of Gases, chapter ix.

Quantitative Notation 5 $

(2.) The volume occupied by i gramme of hydrogen, measured
under the same conditions.

I. One litre of hydrogen, measured at the standard temperature
and pressure, weighs .0896 grammes.* This number is known as
the crith;\ and by means of it the weight of i litre, and therefore
any given volume, of any gas can be deduced : thus, the relative
densities of oxygen, nitrogen, and chlorine are 16, 14, and 35.5
respectively, therefore i litre of these gases (measured always at
the standard temperature and pressure) weighs 16 criths, 14 criths,
and 35.5 criths respectively, or —

I litre of oxygen weighs 16 x .0896 — 1.4336 grammes.
I „ nitrogen „ 14 x .0896 = 1.2544 „
I „ chlorine „ 35.5 x .0896 = 3.1808 „

So also with reference to compound gases, where in each case
the density is represented by the half of the molecular weight.
Thus, the relative densities of hydrochloric acid, ammonia, and
carbon dioxide are —

HCl L+JSJ . ,8 ,

2 "*

NH. 'A±3 = 8.S.

CO,"-+3J-23

and the weights of i litre of these gases are therefore —

I litre of hydrochloric acid » 18.25 ^ '0896 » 1.6352 gramme.
I „ ammonia » 8.5 x .0896 = a 76 10 ^

I „ carbon dioxide => 22.0 x .0896 » 1.97 12 „

II. The volume occupied by i gramme of hydrogen at the
standard temperature and pressure is 11.165 litres. As the rela-
tive density of oxygen is 16, it obviously follows that 16 grammes
of this gas will also occupy 11. 165 litres; in other words, this
number 11. 165 represents the volume in litres of any gas, which

* Fkom time to time slightly different values have been given for this
constant The most recent determinations give the number .08988.

t From the Greek, signifying a barley-corn, and used symbolically to denote
a littk weight

56 Introductory Outlines

will be occupied by the number of grammes corresponding to its
relative density, thus —

14 grammes of nitrogen . . occupy 11. 165 litres.
35.5 „ chlorine . „ 11.165 „

18.25 i> hydrochloric acid „ 11. 165 „
22.0 „ carbon dioxide . „ 11. 165 ^

The number of grammes of a substance, equal to the number
which represents its molecular weight, is spoken of as the gramme-
molecule. The molecular weight of hydrogen =« 2, therefore the
gramme-molecule of hydrogen (that is, 2 grammes of hydrogen)
will occupy 1 1. 165 X 2 = 22.33 litres. The molecular weight of
oxygen = 32, therefore 32 grammes of oxygen will occupy 22.33
litres ; in other words, 22.33 litres is the volume which will be
occupied by the gramme-molecule of any gas.

By means of this important constant, 22.33, the volume of any,
or all, of the gaseous products of a chemical change (when
measured at the standard temperature and pressure) can be de-
duced directly from the equation representing the change, thus —

Zn -H HjSO^ = ZnS04 -H H,

expresses the reaction taking place when zinc is dissolved in
sulphuric acid. Just as in the former illustrations it carries the
information that 65 grammes of zinc -H 98 grammes of sulphuric
acid produce 161 grammes of zinc sulphate and 2 grammes of
hydrogen. But 2 grammes of hydrogen occupy 22.33 litres, there-
fore by the solution of 65 grammes of zinc, the volume of hydrogen
obtained will be 22.33 litres.

So also in the following equation, which represents the formation
of carbon dioxide from chalk (calcium carbonate) by the action
upon it of hydrochloric acid —

CaCOg +

2HC1 -

CaClj + HjO -H

COj.

40+12-^48

2(1+35-5)

40-H7I 2 + 16

12 + 32

100 -H

III -H 18 -H

100 grammes of chalk, when acted upon by 73 grammes of hydro-
chloric acid, yield iii grammes of calcium chloride, and 18
grammes of water, and 4 4 grammes of carbon dioxide.

Carbon dioxide is gaseous, therefore 44 grammes (the gramme-
molecule) will occupy, at the standard temperature and pressure.

Quantttativi Notation 57

33.33 litres ; hence, by the decomposition of 100 grammes of
chalk, 22.33 litres of carbon dioxide are produced.

This chapter may be concluded with one illustration of the
methods employed in the exact determination of atomic weights,
which depends essentially upon the quantitative character of
chemical reactions. By the three following processes the atomic
weights of chlorine, potassium, and silver may be deduced.

1. By heating a known weight of potassium chlorate, the formula
weight of potassium chloride is found —

KClOi - KCl + 30.

50 grammes of p>otassium chlorate when heated, left a residue
of potassium chloride weighing 30.395 grammes. 50 - 30.395 «
19.605 «» grammes of oxygen evolved.

As potassium chlorate contains in its formula weight 3 atoms
of oxygen (16 x 3 = 48), we get the expression —

19.605 : 30.395 « 48 : 74.40Bformula weight of potassium chloride.

2. By dissolving a known weight of potassium chloride, and
adding to it excess of silver nitrate, silver chloride is precipitated,
which can be washed and dried and weighed, and from which
the formula weight of silver chloride is obtained —

KCl + AgNOj - AgCl + KNO5.

10 grammes of potassium chloride were found to yield 19.225
grammes of silver chloride ; therefore,

10 : 19.225 « 74.40 : 143.03 = formula weight of silver chloride.

3. By the direct combination of silver and chlorine, by heating
the metal in a stream of the gas, the ratio of chlorine to silver
in silver chloride is found :

10 grammes of silver so treated yielded 13.285 grammes of silver
chloride ; therefore,

13.285 : 10 =» 143.03 : 107.66 = atomic weight of silver.

Since the formula weight of silver chloride, AgCl = I4303>

therefore, 143.03 - 107.66 = 35.37 = atomic weight of chlorine.
And since the formula weight of potassium chloride, KCl «= 74.40^

therefore, 74.40 - 35.37 — 39.03 — atomic weight of potassium.

CHAPTER VIII

VALENCY OP THE ELEMENTS

When chlorine unites with hydrogen, the combination takes place
between one atom of chlorine (relative weight = 35- SX and one
atom of hydrogen (relative weight = i) ; but when oxygen com-
bines with hydrogen, one atom of oxygen unites with Iwo atoms
of hydrogen. The compound ammonia consists of one atom of
nitrogen, combined with /Aree atoms of hydrogen ; while one atom
of carbon, on the other hand, can unite with /our atoms of
hydrogen.

One atom of chlorine never combines with more than one atom
of hydrogen ; its affinity for that element is satisfied, or saturated^
by union with one atom.

The affinity of one atom of oxygen for hydrogen, however, is
not satisfied by one atom of that element, but requires two atoms
for its saturation ; while nitrogen requires three, and carbon four
hydrogen atoms, in order to satisfy their respective affinities for
this element

This varying power of combining with hydrogen is seen in a
number of other instances : thus, the elements fluorine, bromine,
and iodine, resemble chlorine in being only able to unite with one
atom of hydrogea Sulphur, like oxygen, has its affinity for
hydrogen saturated by two atoms of that element. Phosphorus
and arsenic require three atoms of hydrogen in order to saturate
their combining capacity, while silicon resembles carbon in com-
bining with four hydrogen atoms. This combining capacity of
an element is termed its valency. Elements like chlorine,
fluorine, bromine, and iodine, whose atoms are only capable
of uniting with one atom of hydrogen, are called monovalent
(or sometimes moncuT) elements ; while those whose atoms com-
bine with two, three, or four hydrogen atoms, are distinguished
as di-valent (or dyad), tri-valent (or triad), and tetra-valent (or
tetrad) elements. AD elements, however, are not capable of

Valency 59

entering into combination with hydrogen ; in which case, their
valency is measured by the number of atoms of some other
monovalent element which is capable of satisfying their com-
bining capacity. Thus : —

atom of sodium combines with i atom of chlorine, forming NaQ.
calcium ,. ,. 2 atoms .. .. CaCV

boron ., „ 3 „ „ „ BCV

II un ,, I, ^ ,, ,, ,, onv<i|,

phosphorus* „ 5 „ ,. „ PCla.

tungsten .. ., 6 ,, „ ,. WClf.

In the combinations of elements with hydrogen alone, no in-
stances are known in which a higher valency is exhibited than
that of four ; but with chlorine as here seen, cases are known in
which elements exhibit pentavalent and hexavalent characters.

Measured by their combining capacity for hydrogen and chlorine,
elements do not, however, always exhibit the same valency :
thus, the affinity of phosphorus for hydrogen is satisfied by three
hydrogen atoms, whereas one atom of this element can unite with
five atoms of chlorine.

As measured by hydrogen, the valency of sulphur is two, the
compound that it forms with hydrogen being expressed by the
formula SH|, while, as estimated by its capacity for chlorine, it
becomes tetravalent, as seen in the compound SCI4. As a general
rule, however, the highest number of monovalent atoms with which
one atom of an element is capable of combining, is accepted as
representing the valency of that element Thus, one atom of
phosphorus not only combines with five atoms of chlorine, but
also with five atoms of fluorine ; phosphorus is therefore a penta-
valent element

As measured by hydrogen alone, or by chlorine alone, nitrogen
is a trivalent element, for the largest number of these atoms with
which one atom of nitrogen can unite is three, as seen in the
compounds having the composition NH3 and NCI3 ; neverthe-
less, one atom of nitrogen is capable of combining with four
atoms of hydrogen and one of chlorine, forming the compound
NH4CI, ammonium chloride, in which the nitrogen atom is penta-
valent

This rule, however, is not always followed ; for example, one
atom of iodine will unite with three atoms of chlorine, forming the

* Phosphorus also combines with hydrogen.

6o Introductory Outlines

compound IC1|, but iodine is not generally regarded as a trivalent
element*

In symbolic notation, this power possessed by an atom, of uniting
to itself monovalent atoms, is often represented by lines, each line
signifying the power of combination with one monovalent atom.
Thus, in the symbol H — CI, the line is intended to give a concrete
expression to the fact that both hydrogen and chlorine are mono-
valent elements, and that the affinity of each element for the
other is satisfied, when one atom of the one, unites with one atom of
the other. The symbol H — O — H, in like manner, signifies that
the oxygen atom is divalent, that its affinity for hydrogen is satisfied
only, when it has united with two monad atoms. In the same way
we may express the facts that nitrogen and carbon, in their com-
binations with hydrogen, are respectively trivalent and tetravalent,

by the symbols H — N — H, and H — C — H. These lines are merely

H H

a convenient symbolic expression for the operation of the force of
chemical affinity ; their length and direction bear no meaning. "f
The power to combine with one monovalent atom is sometimes
spoken of simply as one affinity : thus it is said that in the com-
pound having the composition PH„ or H — P — H, three of the

H
affinities of the phosphorus atom are saturated, and that two
affinities still remain unsatisfied, phosphorus, as already stated,
being a pentavalent element.

* See Iodine, Compounds.

t Tb^ student cannot be too often warned against attaching any materialistic
significance to these lines. I'he use of this convention is always attended with
the danger that the beginner is liable to fall into the error of regarding these
lines as representing in some manner fixed points of attachment, or links,
between the atoms. It must be remembered, therefore, that these lines not only
have no materialistic signification, but they must not even be regarded as convey-
ing any statical meaning. The atoms are undergoing rapid movements with
respect to each other, which movements are in some way governed by the
chemically attractive force exerted by the individual atoms upon one another ;
and the molecule will be mo-e correctly considered, if we regard its atoms as
being held together in a manner resembling that by which the numbers of a
cosmical system are bound together. The lines simply denote that the atoms
\re held to each other by the attractive force which we call chemical affinity.

Valency 6i

Compounds of this order, in which one of the elements has still
unsatisfied affinities, are called unsaturated compounds.

In its power to satisfy the affinities of aii element, a divalent
atom is equal to two monovalent atoms : thus, when the affinities of
the tetravalent carbon atom are saturated with oxygen, the mole-
cule contains two atoms of oxygen, which may be symbolically
expressed thus, O «> C » O, in which the four affinities of the
carbon (represented by the four lines) are satisfied by the two
divalent atoms of oxygen. Carbon, however, combines with a
smaller proportion of oxygen, forming the compound carbon mon-
oxide, CO. The carbon atom in this case is divalent, as expressed
by the formula C ■> O, and this substance is also an imsaturated
compound.

The number of divalent atoms with which an element can unite,
cannot, however, be taken as a safe criterion or measure of the
valencji of that element in cases where that number is greater
than I ; for example, in such a compound as calcium oxide, CaO,
we regard the two affinities of the divalent atom of oxygen as being
satisfied by two affinities possessed by the calcium, and express this
belief in the formula Ca ■> O, and regard the calciimi as divalent
In the same way, in carbon monoxide, CO, the carbon being united
with one atom of the divalent element oxygen, is itself divalent in
this compound ; but in the case of carbon dioxide, where the carbon
atom is united with two atoms of divalent oxygen, we are not
justified in asserting that the atoms are united, as represented by
the formula O = C -» O, in which the four affinities of carbon
are represented as saturated with oxygen. There exists no posi-
tive proof that the carbon is not divalent in this compound, and
that the molecule does not consist of three divalent atoms united,

C
as shown in the formula /\. From the feet, however, that

O O

carbon forms a compound with four atoms of hydrogen, and
another with four atoms of chlorine, we know that this element
is tetravalent, and therefore we believe that in carbon dioxide it is
also tetravalent

Again, as measured by its compound with hydrogen, sulphur is
divalent ; while with chlorine it forms SCI4. But sulphur unites
with oxygen, forming the two compounds, sulphur dioxide SO, and
sulphur triozide SOy. If it be assumed that in these molecules the
whole of the oxygen affinities are satisfied ^nth sulphur, then the

62 Introductory Outlines

symbolic representation of these oxides will be O -^ S » O, and

O ~ S »" O, the sulphur being in one case tetravalent, and in the

II
O

other hexavalent. There is, however, no positive proof that the

affinities of one oxygen atom are not partially satisfied by union

with another oxygen atom, and that the valency of the sulphur is

higher than either two or four, as seen in the alternative formulas,

s 9\ s

so, /\;S0, ;S = 0; or / \

O — O 0/ 0—0—0

Although there are no known compounds in which an atom of
sulphur is united with six monovalent elements, sulphur is regarded
by many chemists as capable of fulfilling the functions of a hexa-
valent element.

It will be evident from these considerations, that in many
cases the valency of an element is a variable quantity, de-
pending partly upon the particular atoms with which it unites.
It is also found that it is dependent in many instances upon tem-
perature and upon pressure. Thus, between a certain limited range
of temperature, one atom of phosphorus combines with five atoms
of chlorine in the compound PCl^, but above that limit two atoms
of chlorine leave the molecule, and the phosphorus becomes trivalent.
Again, if phosphoretted hydrogen, PHj, be mixed with hydro-
chloric acid, HCl, and the mixed gases be subjected to increased
pressure, the gases combine and form a solid crystalline compound
known as phosphonium chloride, PH4CI, in which the phosphorus
atom, being united with five monovalent atoms, is pentavalent.
When the pressure is released, an atom of hydrogen and an atom
of chlorine leave the molecule, and the phosphorus returns to its
trivalent condition.

A compound, in whose molecules there is an atom which for the
time being is not functioning in its highest recognised valency,
often exhibits a readiness to unite with additional atoms to form
new compounds : thus, ammonia combines eagerly with hydro-
chloric acid, forming ammonium chloride —

NHj -H HCl = NH4CL

Carbon monoxide unites directly with chlorine to form carbonyl

chloride —

CO -I- CI, = COCI,

Valency

Carbon monoxide also combines with an additional atom of
oxygen, and gives carbon dioxide, thus—

SCO + Oi = 2C0»

In this last action it will be seen that the molecule of carbon
monoxide, in being converted into the dioxide, takes up one atom
of oxygen ; but as the molecule of oxygen is the smallest isolated
particle, it follows that the two atoms contained in such a molecule
must first separate, and each one then furnishes the requisite
additional oxygen for one molecule of carbon monoxide. In the
union of carbon monoxide with chlorine, and of anunonia with
hydrochloric add, are we to suppose that the same action takes
place? That is to say, do the two atoms in the molecule of
chlorine separate from each other and unite with carbon, thereby
satisfying its tetrad valency, in the manner here expressed ? —

CI —

— CI + CO = ;c

cix

And in the case of ammonia and hydrochloric acid, do the
hydrogen and chlorine atoms part, and each unite with the
nitrogen atom, thereby raising it from the trivalent to the penta-
valent condition ? thus —

CI H

U Cl+H — N — H- H— N — H.

I I

H H

H —

Or are we to suppose that the two molecules, without losing their
integrity, become held together as independent molecules, by
virtue of the unsatisfied affinities of the carbon, or the nitrogen,
as the case may be, in which case the compounds might be repre-
sented thus—

H — CI
H — N — H

This question would be settled by determining the vapour
density of the compound. If^ for instance, we were to find the
vapour-density of anunonium chloride to be 26.75, ^^^ ^^ c<*°^'

Introductory Outlines

pound having the composition NH,C1 would have the r
molecular volume, thai is, its molecule would occupy Iw
volumes,* and the conclusion would be that the vapour consisted
of single molecules of the composition represented by the formula
NH,C1. But ammonium chloride at ordinary temperatures is a
solid, and when heated to the temperature necessary to convert it
into vapour its molecules break up into separated molecules of the
two original gases— ammonia, NHj, and hydrochloric acid, HCl.t
So that we are unable to gain any information in this direction
as to the mode in which the atoms are disposed in the compound.
When the two gases are brought together imder ordinary condi-
tions, they combine with the evolution of considerable heat, owing
CO loss of energy ; this is taken as evidence that true chemical
action, in the sense of atomic rearrangement, has resulted, hence it
is behcvcd that in this compound the nitrogen is united with the
five monovalent atoms, and consequently is pentavalenl.

In the case of carbonyl chloride, COCI« the vapour-density can
be ascertained, this compound existing in the gaseous condition
at the ordinary temperature. Its vapour-density, determined by
experiment, is found to be 5a6, This number, divided into the
molecular weight of the compound having the composition
COCIj, gives practically the number 2 as the molecular volume
of the compound. Hence we conclude that these four atoms
constitute a single molecule.

There is a certain class of combinations, in which molecules
of different compounds unite, that do not so readily admit of
explanation, because in neither of the molecules is there any
atom Ainclioning in a lower state of valency tlian that which
it is known to be capable of. For example, the monovalent
elements, fluorine and hydrogen, form the compound hydrofluoric
acid, HF ; fluorine also combines with the monovalent element
potassium, fonning potassium fluoride, KF. Both of these com-
pounds come under the head of saturated compounds, in the sense
that neither of them contains an atom which is known to be
capable of exercising a higher valency than it exhibits in these
compounds. Nevertheless these two molecules unite together and
form a definite chemical compound, known as hydrogen-potassium
fluoride.

Again, the divalent element zinc combines with two atoms of

•S««p.*«.

t Sm Dilsodaiian, p. 86.

Valency 65

the monad dement chlorine, forming zinc chloride, ZnClj; the
two monovalent elements, sodium and chlorine, also combine,
giving the compound sodium chloride, NaCI. Both of these
substances must be regarded as saturated compounds, and yet
they unite with each other, forming a distinct chemical compound,
known as sodium zinc chloride. Such compounds as these are
known as double saltSy and examples might be multiplied almost
indefinitely. A similar union of molecules, where the recognised
valency of the atoms is all satisfied, is seen in a large number
of compounds containing water of crystallisation ; * for example,
the divalent element copper, in combination with two atoms of
chlorine, forms cupric chloride, CuCl^ The divalent element
oxygen, in combination with two hydrogen atoms, forms water,
H|0. When cupric chloride crystallises from aqueous solution,
each molecule of the chloride unites to itself two molecules of
water, which is therefore termed water of crystallisation.

In chemical notation, it is usual to represent compounds of this
order, by placing the formulae of the different molecules that have
entered into union, in juxtaposition, with a comma between ;
accordingly, the examples here quoted would be indicated thus —

Hydrogen potassium fluoride HF,KF.

Sodium zinc chloride .... ZnCl^NaCl.
Crystallised cupric chloride . CuC1^2HtO.

Combinations of this order are by no means confined to the
union of two kinds of molecules, as the following examples will
serve to show : —

Platinum sodium chloride . PtCl4,2NaCl,6H,0.

Mercuric potassium chloride SHgCl^KCIjSH^O.

At the present time our knowledge of the nature of the union
between these various molecules is too imperfect to admit of any
precise explanation ; such compounds are frequently distinguished
as molecular combinations.

It must be remembered that our ideas of valency are based mainly upon the
consideration of matter in the gaseous state ; at present we have little certain
knowledge as to the valency of elements in liquid and solid compounds. Most
of the compounds belonging to the rJass we are now discussing are solid, and

* See p. 19a.

Introductory Out/iiu

There i% also Ukotber coosiilerHlioii thai idusI nol be overlooked. The
onil of mcBSure ihat has beeo adopted for estimating valeDcy, nainely, i mono-
valent alom, is probably only an exlretnely rough and crude measuje, which
is incapable gf appreciating smaller differences of combining capacity that
may, bmA most probably do, exist. Its use may be compared to the adoption
of a single unit, say i gramroe. for (he eslimatioD of mass, or weight ; when.
If a given quantity of mallei' has a weight equal lo i gramme but less than
B grammes, iu weight would be i ; if gieater than a grammes but less
than 3. then its weight would be a— a method of estimating which lacllly
assumes that no inlermediale weights of malier beiurcen Ihe various multiples
of the selected imil are possible. 1'here ii no evidence to show thai Ihe com-
tHoing capacity of an demeni it ixaclly expressed by simple multiples of a

For example, in Ihe simplest form of combination, such as thai between
hydrogen and chlorine — where the molecule contains i alom of each element
— I hydrogen atom unites with i chlorine alom. thai is lu say, with a mass of
chlorine weighing 35 5 times its own weigh! ; and we say that Ihe mutual
affinities Of these atoms are satisfied. Bui for anyihing we know lo Ihe con-
iTBry, an atom of hydrogen may have an affinity for chlorine which would
enable it 10 unite with a mass of chlorine weighing 40 ot 45 or jo limes its own
(Keighl. bul <ir)(ajoass weighing 71 {^5.5 x a) limes its own. But since a mass
of cbloiine 35.5 times Ihe weight of a hydrogen alom is the smallest quantity
that is ever known to lake pan in a cbemical change, is the chemically indivisible
mass we call an atom, it follows thai as the hydrogen atom has not sufficient
combining capacity 10 imile with a atoms, il is compelled to be latislied with
I. It migbt still, however, retain a teiidual eomiining capoiily. Or the
nsidual combining capacity may he lodged in the chlorine atom, which may
be conceived as being able to unite with a gicatci weight of liydrogen than is
represented by i atom, bul not so much as that of a atoms.

Each of Ihe cleuients Buorine. chlorine, bromine, and iodine unites with
I aliHO of hydrogen, and we represent their compounds in a similar manner,

H-K; H-a; H-Br^ H-I;

but we make an enormous assumption If we suppose that in each ol these
compounds tbe mutual aflinilies of the atoms is equally satislied.

For example, the Huoiinc compound exhibits a tendency to unite itself tc
other compounds of fluorine (and lo a much more marked degree than is seeii
in Ibe case of hydrochloric add), resulting in the formation of such double
fluorides as the following :—

Hydrogen potassium fluoride .... KF.HF.

Hydrogen bismuth fluoride BiF,,3HF.

Hydrc^en silicon Suoride (Hydro-fluo-silicic aad) SiF,.2HF.

id there is reason for heUeving Ihal the molecules of hydrofluoric

VaUncy

are capable of uniting amongst themselves, fonning the double molecule

HF.IIF.*

Anuming the residual combining power to reside in the fluorine atom, and

representing this by means of dotted lines, we may express the composition of

these compounds thus—

F-. F-H

I
H - F-F - H. H - F- F - Bi - F-F - H ;

F. .F

H - F :' /^\ . ^ - "•

* See Hydrofluoric add.

CHAPTER IX

GENERAL PROPERTIES OP GASES

Under the head of the general properties of gases it will be oon-
vcnient to consider the following subjects : * —

1. The relation of gases to heat

2. The relation of gases to pressure.

3. The liquefaction of gases.

4. Diffusion of gases.

5. The kinetic theory of gases.

The Relation of Gases to Heat— The fact that substances
expand when heated, and again contract upon being cooled, was
observed in very early times. The fact also that all substances do
not undergo the same alterations in volume when subjected to the
same changes of temperature has been long known ; but it was not
until the beginning of the nineteenth century that it was proved by
Charles and Gay-Lussac that all gases expanded and contracted,
equally when exposed to the same alterations of temperature.
This law is generally known as the Law of Charles, and may be
thus stated : IV^n a gas is heatedy the pressure being constant^ it
increases in volume to the satne extent whatever the gas may be.

The increase in bulk suffered by i volume of a gas in being
heated from o** to i** is termed the coefficient of expansion, and if
the law of Charles is true all gases will have the same coefficient

Modem research has shown that the law of Charles is not cUfso-
lutely true, and the extent to which gases deviate from the strict
expression will be seen from the coefficients of expansion given in
the following table : —

* The study of these subjects belongs more especially to the sdence of

physics or chemico-physics. For fuller information on these points than can

be included within the scope of this book students are referred to special

treatises on physice.

Rtlatien of Gases to Heat 6g

Air 00366s)

Hydrogen .0036671

Carbon monoxide .... .003667 j

Nitrogen 003668/

Nitrous oxide 003676

Carbon dioxide .0036S8

Cyanogen 003819

Sulphur dioxide 00384S

It will be noticed that the first four gases have almost the same
coefficient of expansion : these gases are all very difficult of lique-
&ction, and it will be seen that the coefficient rapidly rises in the
case of the other gases, which are easily liquefied.

For purposes of ordinary calculation it is usual to adopt the
coefficient of expansion of air, as applicable to all gases. It will
be obvious that since the volume of a gas is aflected by alterations
of temperature, it becomes necessary, when measuring the volume
of a gas, to have regard to the particular temperature at which the
measurement is made, and in order to compare volumetric measures
they must be all referred to some standard temperature. This
standard temperature is by general consent 0° C

Taking the fraction .00366; therefore for the coefficient—

I volume of a gas at o* becomes 1 + .003665 volumes at t°

I „ „ o* „ I + .003665 X 3 „ 1*

or I „ „ o" „ I + .003665/ „ /=

Therefore the volume ai /° equals the volume at o* multiplied by
I -f .003665 /. Let V be the volume at /*, and v, the volume at o*,
then—

vv.(i +.003665/)

and conversely the volume at o* equals the volume at /° divided by
I + .003665/—

' I + .003665 /

The vulgar Araction equivalent to .003665 is j^tj. 373 volumes
at o* become 273 + / at /*.

What is known as the aiio/uU Umfiera/urt of a substance is the
number of degrees above - 373' C. Taking this point as the zero,
the absolute temperature of melting ice, for example, will be 273*.
Charle^ law, therefore, may be thus stated : TAt volumt of any

TO Introductory Outlines

gas, under constant preisure, ii proportional to the absolute t
pcrature.

The Belatlon of Oases to Pressure.— The effect of increase
of pressure upon a gas is to diminish its volume. The law which
connects the volume occupied by a gas, with the pressure to which it
is subjected was discovered by Robert Boyle (1661), and is known
as Boyle's Law. It may be thus stated ; The volume occupied by
a given weight of any gas is imiersely as the pressure. The
general truth of this law may readily be illustraled by subjecting a
gas to varying pressures, and it will be seen that when the pressure
is doub!ed the volume of gas is reduced to one-half, and so on.

Jusl as in the case of the law of Charles, modem investigations
have shown that the law of lloyle is not a mathematical truth. It
is found not to be absolutely true of any gas, for with the exception
of hydrogen, all gases are more compressible than is demanded by
the law. Hydrogen deviates from the law in an opposite sense, in
that it requires a higher pressure than the law would indicate, in
order to reduce a volume of it to a given point. These deviations
from Boyle's law are explained by the operation of two causes :
first, the attraction exerted by gaseous particles upon each other ;
second, the fact that increased pressure diminishes the space
between the molecules, and not the actual space occupied by the
molecules of a gas. When the former cause predominates, the
gas deviates from the law by being more compressible ; in the case
of hydrogen, the second cause operates mote powerfully. (See
Kinetic Theory of Gases.) P'or ordinary purposes of calculation
the law of Boyle may be regarded as true-
As the volume of a given weight of gas is so intimately related
to the pressure, and as the atmospheric pressure is variable, it
becomes necessary, in all quantitative manipulation with gases, to
Icnow the actual pressure under which the gas is at the time of
measurement, and to refer the volume (o a standard pressure.
The pressure that has been adopted as the standard is that of a
column of mercury 760 mm. in height. (See Atmosphere.)

If V equals the volume of gas measured at p pressure, and v,
the volume at the standard pressure, then

t usual !o make both

LiqutfacttoH of Gases

rature and pressun together; then v, being the volume
lUndard temperature and pressure, we get ^

L.<L

.00366s/ ■ 76S ^ ,t.4.V.k. J.*.^^
itions of tftn- ^

Th« Llqa«nwUon of Gases,— Under certain conditions
peraturc and pressure, the law of Cbatles and the law of Boyle
completely break down. According to
the law of Charles, 100 oc. of a gas al
0° C. should occupy 96.4 cc. if ihe tem-
perature were lowered to - 10*. If 100
cc. of the gas sulphur dioicide at o* C.
be confined in a glass tube standing in
mercury, and the gas be cooled to - 10*
by surrounding the tube with a freezing
mixture, it will be found that the volume
of gas, instead of occupying 96.4 c-C,
has been reduced to a few cubic centi-
metres only, and that the surface of the
mercury in the tube is wet owing to the
pressure of a minute layer of a colourless
liquid upon it. In this case the law of
Charles has broken down, and the sul-
phur dioxide has passed from the gaseous
to the liquid state.

Similarly, according to the law of
Boyle, 100 cc. of a gas measured at the '~

standard pressure should occupy 25 c.c. '''"' '■

when exposed to a pressure of four additional atmospheres. If
lOOCC of the gas sulphur dioxide be enclosed in one hmb of along
U-tnbe, as shown in Fig. i, the other limb being tilled with air,
and the two gases be simultaneously exposed to increased pressure
by raising the mercury reservoir, it will be seen that at first the
gases in both tubes are compressed equally. As the pressure
approaches three atmospheres, however, the mercury will be seen

* Tbe student sbould bnulioiiae hlmseir with the method of cakulaling the
dumges of volume suffered by gasta. by cbanges of (empenililre and pressure.
hf working out a number of eiamples such u the following :—

I. If 30 litres of gas aie cooled from aj* to o'. wbal Is tha diminution in
■nlnme, tbe pressure lieing fxuislanl? Ami, 3.51 litres.

a. ira litn of air u o* degrees weighs 1.193 grunmes wben the baronMter

iv-

72 Introductory OutUnei

to rise much more rapidly in the tube containing the sulpfai
dioxide, and when the mercury reservoir has been raised to such 4
height that the gases are subjected to four atmospheres, the sulphtn
dioxide will have completely broken down, and will be entirelj' c
verted into a few drops of liquid, which appear upon ihe surface O
the mercury. The air meantime, in the other limb, will be found tt
occupy 75 cc, as thai gas at thai pressure obeys Boylc'i
absolutely. We see, therefore, that at a certain temperature and a
a certain pressure the gas sulphur dioxide begins rapidly to dep
from the laws of Charles and Boyle, and ultimately passes into d
liquid condition.

All known gases, with the one exception of hydrogen,
exposed 10 certain conditions of temperature and pressure, c
lions which are special for each dilTereni gas, will pass from the
gaseous to the liquid slate : and as the point at which liquefacti
lakes place is approached, the departures Irom Boyle's law bei
more and more pronounced.

The first substance, recognised as being under ordinary o
lions a true gas, that was transformed into the liquid condiii
was chlorine, which was liquefied in Ihe year 1B06 by Northmore.
j,.^ The true nature of this liquid was

^^^S^ ■">• understood until Faraday inves-

/^ ^^^^ tigated the suhjeci.
/^r ^^^^ In his earlier experiments, Fara-

£iW ^Bl day's method consisted in sealing

M^ into a bent glass lube (Fig. 2) sub-

^■jr stances which, when heated, would

^^ yield the gas ; the substances being

^r contained in one limb of the tube,

and the empty limb being immersed
in ice. The pressure exerted by the gas thus generated in a con-
fined space, was sufficient to cause a piortion of ii to condense to

is Bl 760 mm., what will be the weiEhi of a litre of ail al 97°. It
standing at llie same height ? Am. 1.177 grammes,

5, Whai will be the weight of a litre of air at 43° when the larometer «
at 73 J mm. ? Am. 1.084 grammes.

4. Air 81 H temperalm-c of 15* is enclosed in a vessel and heated ti
Compare the piessm-e of ttie enclosed air with that of the aimosphcre.
As 6t : 48.

5, What will tie the volume, at the standard leroperature and pressu
joo cc of hydrogen, measured al 30*, and under a pressure of 800 mm.T9
Am, .490 e-t

Liquefaction of Gases 73

the liquid state, and the Hquid collected in the cooled limb. In
this way Faraday liquefied such gases as chlorine, sulphur dioxide,
ammonia, cyanogen. In his later experiments, Faraday compressed
the gas by means of a small compression pump, and at the same
time applied a low degree of cold, and by so doing he succeeded
in liquefying carbon dioxide, hydrochloric acid, nitrous oxide, and
other gases. There were a number of gases, however, which Fara-
day found it impossible to liquefy, such as hydrogen, oxygen, nitro-
gen, marsh gas, nitric oxide, carbon monoxide, &c It became the
custom to call these permanent gasesy and this term was applied to
them until the year 1877.

In that year it was proved by Pictet, and independently by Cail-
letet, that under sufficiently strong pressure, and a sufficiently low
degree of cold, the so called permanent gases could in the same
way be reduced to the liquid condition. Pictet's method was in
principle the same as that employed by Faraday, the difference
being, that with the machinery at his disposal, he was able to
employ enormously increased pressure, and a greater degree of
cold. For the liquefaction of oxygen, a quantity of potassium
chlorate was heated in a strong wrought iron retort, to which was
connected a long horizontal copper tube of great strength and small
bore. At the extreme end of this tube there was a pressure gauge
capable of indicating pressures up to 800 atmospheres, and a stop-
cock. The tube was cooled by being contained in a wider tube,
through which a constant stream of liquid carbon dioxide, at a tem-
perature of - 120' to - 140*, was caused to flow.

The machinery employed to maintain this flow of liquefied car-
bon dioxide was somewhat elaborate, consisting of condensing and
exhaust pumps for liquefying and rapidly evaporating sulphur
dioxide, and similar condensing and exhaust pumps for liquefying
and rapidly evaporating carbon dioxide : the sulphur dioxide being
merely the refrigerating agent used to assist the liquefaction of
the carbon dioxide. This machinery was driven by two eight-
borse-power engines. As the potassium chlorate was heated
and oxygen evolved, the internal pressure in the retort and
copper tube rapidly rose, and its amount was indicated by the
gauge.

When the stopcock upon the end of the tube was opened, liquid
oxygen was forcibly driven out in the form of a jet.

In the method employed by Cailletet, the pressure to which the
gas is subjected is obtained by purely mechanical means. The

Introdi4€t6ry Outlines

gas to be liquelied is introduced into a glass tube (Fig. 3), tl
narrow end of which consists of a strong capiliaty tube. The tuH
carries a metal collar, which enables it lo be secured in posirirarH
in the stnwg steel bottle (Fig. 4), by means of a nut, E' (Fig. S), I
which screws inlo the moulh. The bottle, which is partially lilted'
with mercury, is connected, by means of a flexible copper tube t
fine bore, with a small hydraulic pump, by means of which w
is forced into the steei bottle. The water so driven in, forces t

FiO. 3,

mercury op into the glass tube T, and thereby compresses
contained gas. In this way a pressure of several hundred
pheres may be applied to the gas. In his earlier experiments,
C^Uetel depended almost entirely for the refrigeration he required,
upon the fact, thai when a gas is allowed suddenly to expand, it
undergoes a great reduction in temperature. This method of
cooling may be termed inUraal refrigeration. In the case o(
cacygeo, the gas was Srst subjected to a pressure of 300

'-^

Liquefaction of doses

Ktmospheres, and was then allowed suddenly to expand by a rapid
release of the pressure. The result of the sudden expansion was
to momentarily lower the temperature of the gas to such a point
that the tube was filled with a fog, or mist, consisting of liquid
particles of oxygen.

This principle, namely, the self-cooling of a gas by its owtt
sudden' expansion, has recently been applied for the liquefaction
of oxygen in large quantities. When oxygen under considerable
pressure, say no atmospheres, is allowed to escape from a fine
orifice at the end of a long pipe, the issuing k^^ suddenly expands,
and thereby its temperature is greatly lowered. If this self-cooled
gas is made to

•vill

escapmg, it
cool the pipe, and
therefore lower the
temperature of the
remaining gas be-
fore it issues. In
this way the cooling
effect becomes cu-
mulative, (he initial
temperature of the
gas before it es-
capes being con-
tinually brought
lower and lower,
until M last the
point is reached at
which the oxygen
is liquefied.*

If the oxygen be
first cooled to about
-80* by means of
solid carbon di-
oxide, then in <i/nc
mittuUi, by the fur-
ther cooling due to

Pio.6.

expansion, the temfterature will fall
belowthe boiling-point of oxygen, and the liqu^edgas be obtained.
The apparatus for the purpose is shown in Fig. 6.t Oxygen
ider a pressure of 120 to 140 atmospheres is passed through a

Introductory Outlines

s of spirals of fine copper pipe contained in the chamber '
which is encased in a non conducting jacket ot cork-dust

-s by the pipe O (seen in the enlarged section), and pas
through the spiral S S, which is immersed in a mixture < '
and solid carbon dioxide {the liquid carbcn dioxide from the reserv
being admitted into the alcohol through the valve W, which is
laled by the screw B). The oxygen thus cooltd passes through tl
double spiral pipe D D, which ultimately extends through l"
bottom of the chamber, and terminates in a stirrup, U, the si
end of which is closed. In the bend of this stirrup thcr
hole, which can be closed or opened at will by the pointed e
of the rod V, connected to the screw A. On opening this vi
the oxygen, already cooled to about -80", escapes from the 1:
imder a pressure of 120 to 140 atmospheres. It instantly expai
and is thereby cooled still lower. This cold gas is prevented fi
the atmosphere by tht glass lube G, \
O rush upwards {as shown by the arrows), and, swee
ing past the double spiral, D D, cools this pip(
and therefore the succeeding portions ■ " '
oxygen. In a few minutes the temperature of ll
pipe is thereby brought so low, that the further
cooling of the gas by its expansion causes the
_.v liquefaction of a portion of it, and a tine spiay of
liquid is seen to spurt out from the hole. This spray
quickly increases in quantity, and rapidly collects
,0 as a clear hqmd in the glass tube G. This tube is
double- walled, the space between the walls being
perfectly vacuous. In such a vessel the liquid
,.N oxygen may be kept for a considerable time, eva-
porating only very slowly in spite of its extremely
tow boiling-point, as it has been found that such a
vacuous envelope forms the most perfect non-
conductor.

Oxygen can also be liquefied by the low tempera-
ture obtainable by the rapid evaporation of liquid
ethylene: and, similarly, by the rapid evaporation of
*'i(i- 7. liquid oxygen itself, such a low temperature can be

reached that almost all known gases have by this
means been reduced to the hquid state {see Hydrogen, p. 157).
Thus, if a quantity of liquid oxygen in the glass tube O (Fig, 7),
which is provided with a vacuous envelope, V, be caused to boil
rapidly by putting the pipe P in connection with an exhaust pump,
the temperature can be lowered to -300°, when air itself becomes
liquefied without the application of pressure, and drops of liquid

Critical Temperature of Gases

air quickly collect upon the walls of the inner empty tube, N, which
is freely open to the atmosphere. In this way considerable quan-
tities of liquefied air can be collected in a few minutes.

The Critical Point.— As far back as the year 1869, it was
shown by Andrews that when liquid carbon dioxide was heated
to a particular temperature, it passed from the liquid to the gaseous
state, and that no additional pressure was able to condense it again
so long as the temperature remained at or above that point This
particular temperature is called the critical pointy or the critical
tempetcUure of the gas. In the case of carbon dioxide this critical
temperature is 31.9*, and in order that this gas may be liquefied by
pressure, it is an essential condition that the temperature be below
that point ; above 32"* no pressure is capable of bringing about
liquefaction. All gases have a critical temperature, which is special
for each gas, and until the temperature of the gas be lowered to
that point, liquefaction is impossible. The critical temperatures
of the different gases vary through a very wide range, as will be
seen from the following examples : —

Nitrogen - 146.0*

Carbon monoxide . . - 140.0*

Oxygen -ii8.8*

Marsh gas .... - 8i.8*

Ethylene + io.i*

Carbon dioxide ... 31.9*

Nitrous oxide . . . 35.4'

Acetylene 37.0'

Hydrochloric acid . . 52.3'

Ammonia 13CX0'

Chlorine 141.0*

Sulphur dioxide . . . 155.4'

The gases in this list, from ethylene downwards, all have their
critical temperatures so high, that there is no difficulty in cooling
them below these points. These are the gases which were first
reduced to the liquid state. The first four upon the list have
very low critical temperatures ; these are the very gases which for
so long resisted all attempts to liquefy them, and which were on
that account called pennanent gases. We now know that the
failure to obtain them in the liquid state, was owing to the fact
that the relation between the critical temperature and the point
of liquefaction was not fully realised. Just as carbon dioxide
cannot be liquefied unless its temperature be brought down to
31.9*, so oxygen resists liquefaction under the highest possible
pressures, until its temperature be lowered to -ii8.8*, the critical
temperature of oxygen.

Introductory Outlines

The critical temperature of a gas is sometimes spuken uC as
absolute boiling point.

Critical Pressure. ^The pajticular pressure that is tequi
to liquefy a gas at its critical temperature, is called the critii
pressure. Thus the pressure necessary lo hquefy oxygen, whi
the temperature has been lowered to - 1 18.8°, is 50 atmospherea j
while that required to condense chlorine at its critical point, viz.,
+ 141*, isS4 atmospheres. Taken at their respective critical points,
therefare, chlorine is a more difficultly liquefiab]'; gas than oxygen,
although at 0° chlorine is condensed by a pressure of only 6
atmospheres; o*, however, is 141' below the critical point of
chlorine, and it is more than probable that if it were possible
to cool oxygen to a temperature 141'' below its critical point
that is, to — 1;9'8°, it, in like manner, would be capable of liquefi
lion by very slight pressure.

DlITUslon of Gases. —If a jar filled with hydrogen be pL
mouth to mouth with a jar of air, the hjdrogen being upperm<
it will be found that aller the lapse of a few minutes som
hydrogen will have passed into the bottom jar containing
some of the air will have made its way up into the hydrogen jar.
The light gas hydrogen does not, as might have been supposed,
remain floating upon the air, which is 14.44 times as heavy, but
gradually escapes into the lower jar ; and the heavier gas finds its
way, in opposition lo gravitation, info ihc upper jar. This process
goes on until there is a uniform mixture of air and hydrogen in both
jftTS, and the gases never separate again according to their densities.

This transmigration of gases will take place even through lubes
of considerable length : thus, if two soda-water bottles be filled one
with hydrogen, and the other with oxygen, and the two bottles be
connected by a piece of glass tube a metre in length, the system
being held in a vertical position with the light hydrogen upper-
most, it will be found after an hour or two that the two gases
have become mixed. Some of the hydrogen will have descended
through the long tube into the lower bottle, and in like manner
a portioD of the oxygen, although nearly sixteen times as heavy
as hydrogen, will have travelled up into the top bottle. That the
gases have so mixed may be readily shown by applying a lighted
taper to the mouth of each bottle, the detonation which then lakes
place proving that the bottles contained a mixture of oxygen and
hydrogen. This passage of one gas into another is called the
dtfiisiOH 0/ gluts. It was observed by Graham that when the

the I

Diffusion of Gases

two gases were separaied from each niher by a thin porout
•eptuin, such, for insiatice, u a piece of unglaicd porcelain (so-
Cftlled "biscuit"), or plaster of Paris, the pressure of the gas on
the two sides of the porous partition did not rcniain the same
during the process of difTusion : thai is to say, one gas made ii8
way through the partition (asier than the other, and it was noticed
that the lighter ihe gas, the more rapidly was it able to transpire
or dilTusc through the porous medium. This fad, vii., thai a light
gu dilTuses mote rapidly than a heavier one, rnay be observed
in & variety of ways.* The apparatus seen in Fig. S is a moditied

Pra. 9-

I form of Graham's diffusiometer. It consists of a long glass tube
with an cnlargcmenl or bulb near to one end. Into ihe short neck
of this bulb there is fastened a thin diaphragm of stucco, or other
porous maicrial. If the apparatus be filled with hydrogen by dis-
placement, the short neck being closed by a cork, and the long
limb be immersed in water, it will be seen, upon the withdrawal
of the cork, that the water rapidly rises in the long tube. The
hydrogen diffusing out through the diaphragm so much more
rapidly than air can make its way in, a diminution in pressure

• See ExperimenU No*. 350-359. Newlti* " Chcmtcal L««uie ExpcrimeDU,"

Introductory Outlines
whhin the apparatus results, and this causes the water b

ID the tube. The s

^ph,

strikingly by means of the appai-aius, Pig, 9, which consists of a
tall glass U-tube, upon the end of one limb of which there is
fastened, by means of a cork, a porous cylindrical pot, such as
is used in an ordioary Ounsen battery. The U-tube is half
filled with coloured water. Under ordinary circumstances air is
continually diffusing through the porous pot, but as it passes at
an equal rate in both directions, there is no disturbance of the
pressure, and consequently the coloured water remains level in
the two limbs. If now a beaker containing hydrogen be brought
over the apparatus, as seen in the figure, the hydrogen will stream
through the porous pot so much more rapidly than the air in the
pot can make its way out, that there will be an increase in the
loia! amount of gas insi<te (he apparatus, which will be instantly
rendered evident by the change of level of the liquid in the U-tube,
the water being forcibly driven down the tube which carries the
porous pot. Upon removing the beaker the reverse operation
will at once take place ; the hydrogen inside the apparatus now
rapidly diffuses out, and much more quickly than air can pass in,
consequently a reduction of pressure within the apparatus results,
which is indicated by a disturbance of the level of the water in the
tube, in the oppo'iile direction to that which occurred at Rrst.

The Law of Gaseous DiffuslOD. —Graham established the law
according to which the diffusion of gases is regulated, and it may
be thus staled ; T!ie relative velocities of diffusion of any two
gases are inversely as the square roots of their densities.

The density of hydrogen being i, that of air is 14.44, the velocity
of the diffusion of hydrogen therefore, as conipared "ith that ol
air, will be in the ratio of ^14. 44 to \j~i. Jn-Ai = 3.8, Ji = I.
Therefore hydrogen diffuses 3.S times faster than air ; or 3.8 volumes
of hydrogen will pass out through a porous septum, white only i
volume of air can enter.

If rf " the density of a gas. air being unity, and v = the volume
of the gas which diffuses in the same lime as i volume of a" ~

-S-

The following table gives in the last column, the results obtained
by Graham, which will be seen to accord very closely with the cal-
culated numbers demanded by the law of diffusion :~

'olume I

Diffusion of Gases

KiatalG-.

D«itr,<G»

1 VoluHofGu

-'. I—A-'

SS?S- :

Nitrogen ....
Sulphur dioxide

1.1911
i.Sa90

8.247

3-7794 1 3."3
'■337S 1 1.344
1,0165 1.0149
1,0147 1 1.0143
0.9510 ' 0.9487

0.6671 1 0.68

The property of diffuiioD is sometimes made use of it
sepante gases, having different densities, from gaseous r
This process of separation by diffusion is known at aimoiyiis.
The principle nuy readily be illustrated by causing a mixture of
oxygen and hydrogen, in proportion to form an explosive mixture,
to slowly traverse tubes made of porous material, such as ordinary
tobacco pipes. Two such pipes may be arranged as shown in
Fig. to^ and the gaseous mixture passed through in the direction
indicated by the arrow.
On coUecting the issuing
gas over water in a pneu-
matic trough, it will be
foimd to have so far lost
the hydrogen, by diffu-
sion through the tube,
that a glowing splint of
wood when introduced
into it, will be re-

From the rate of dif-
fusion of ozone, in a mix-
ture of oione and oxygen,
Soret was able to calcu-
late the density of this
allotropic form of oxy-
gen, and so confinn the
result he had previously obtained by other methods (see Oione).

Attempts have been made to utilise this principle in order to
obtain oxygen from the air. The relative densities of oxygen and

introductory Outlines

nitrogen are as l6 to 14* the rale of diRusion, therefoie, of aitrogen
is slightly greater than that of oxygen.

Effusion is the lenii applied by Graham to the passage of gases
through a fine opening in a very thin wall, and he found that it
Colloued the same law as difTusion, Bunsen utilised this principle
for determining the density, and therefore the molecular weights,
of certain gases. The method, in essence, is as follows : — A
straight glass eudiometer is so constructed, that a gas contained
in it can be put into communication with the outer air through a
minute pin-hole in a thin platinum plate. The gas is conlined in
the tube, which is placed In a cylindrical mercury trough, by
means of a stop-cock at [he top. When the tube is depressed
in the mercury, and the cock opened, the gas escapes through
the minute perforation in the platinum plate, and its rale of eflii-
sion is determined by the lime occupied by a glass floai, placed
in ihe lube, in rising a graduated distance within the eudiometer.

The flow of gases through capillary tubes is called transpiration
of giists. In this case ihc friclion between the gas and the tubes
becomes a factor in ihe movement, so that ihis phenomenon is
not governed by the same law as gaseous diffiision.

The Kinetic Theory of Gases.— The term kinetic signifies
motion, and as applied 10 this theory it expresses the modem
views of physicists concerning matter in the gaseous state, and
serves to harmonise and explain the physical laws relating to
the properties of gases. Maiter in the slate of gas or vapour,
is regarded as an aggregation of molecules in which the attractive
forces which tend to hold them together, are reduced to a minimum,
and in which the spaces thai separ^ile them are at a maximum.
These molecules are in a state of rapid motion, each one moving
in a straight hne until it strikes some other molecule, or rebounds
from the walls of the containing vessel, when it continues its move-
ment in another direction until it is once more diverted by another
encounter. As ihey constantly encounter and rebound from each
other, it will be evident that at any given instant some will be
moving with a greater speed than others ; the majority, however,
will have an average velocity. In these encounters no loss of
energy results so long as the temperature remains constant, but
any change of lemperalure results in a change in the velocity of
movement of the molecules, the speed being increased with
increased heat. The actual volume of the molecules is very small
as compared with the space occupied by the mass ; the space

The Kinetic Theory 83

between the molecules, therefore, in which they pass to and fro,
is relatively very great As the molecules are constantly colliding
and rebounding, the distances between them, as well as their speed,
will be sometimes greater and sometimes less ; but there will be
an average distance, which is known as the mean free path of the
molecule.

The pressure exerted by a gas, or its elastic force, is the combined
effect of the bombardment of its molecules against the containing
vessel ; in other words, the pressure of a gas is proportional to the
sum of the products obtained by multiplying the mass of each
molecule by half the square of its velocity. It will be obvious
that if the space within which a given mass of gas is confined be
reduced, the number of impacts of the molecules against the walls
of the containing vessel, in a given time, will be increased, and
therefore the pressure it exerts, or its elastic force, will also be
increased. If the space be reduced to one-half the original, the
number of these impacts will be doubled, or in other words, the
number of impacts in a given time is inversely as the volume.'
This statement is simply the law of Boyle stated in the language
of the kinetic theory.

When a given mass of gas contained in a confined space is
heated, the pressure it exerts, or its elastic force, is increased. But
as the number of molecules present has not been increased by
raising the temperature of the gas (provided no chemical decom-
position of the gas is brought about by the change of temperature),
the increased pressure can only have resulted from the greater
frequency, and greater energy, of the impacts of the molecules
against the walls of the vessel, owing to their greater velocity.

Two equal volumes of different gases imder the same conditions
of temperature and pressure, exert the same elastic force upon the
containing vessels, that is to say, the kinetic energy in each volume
is the same. According to Avogadro's hypothesis, equal volumes of
all gases under the same conditions of temperature and pressure,
contain an equal number of molecules, however much the weight
of these molecules may vary ; therefore the average kinetic energy
of each individual molecule will be the same. It follows from this
that the mean velocities of different molecules must vary, and the
calculated numbers representing the actual velocities of movement
of the molecules of different gases, show that these rates are pro-
portional to the inverse square roots of their respective densities.
But according to the law of gaseous diffusion (Graham's lawX the

84 Introductory Outlines

relative rapidity of diffusion of gases is inversely proportional to
the square roots of their densities, hence by purely mathematical
processes, based upon the kinetic theory of gases, the law of
gaseous diffusion is proved to be true.

The deviations from the laws of Boyle and Charles, already
referred to,* Are also explained by the dynamical theory of gases,
from considerLtions of the following order : —

1. That the molecules themselves are not mathematical points,
but occupy a space ; in other words, the space occupied by the
actual particles of matter is not infinitely small as compared with
the entire volume of the gas, <>., the bulk of the particle plus the
intermolecular spaces.

2. That the impact of the molecules against each other and
against the containing envelope occupies time ; or, in other words,
the time occupied by the impacts is not infinitely small compared
with the time elapsing between the impacts.

3. That the molecules themselves are not entirely without attrac-
tion for each other ; that is to say, although the attractive force
between the molecules which holds them together in the liquid
and solid states of matter, is at a minimum in the case of gases,
it is not entirely absent

* See pafeTa

CHAPTER X

DISSOCIATION

Dissociation is the term employed to denote a fpocukl dus ol
chemical decomposilion*. Wh^n potassium chlorate U bnted it
breaks up into potassium chloride and oxygen, thus—

SKCIOj - 2KC! + 80»

tmd when calcium carbonate (chalk) is heated it breaks up into
calcium oidde (lime) and caibon dioxide —

CaCOj = CaO +C0,

In the firai case the oxygen is incapable of reuniting with the
potassium chloride, but in the second, the carbon dioxide can
recombine with the lime and reproduce calcium caibonate ; there-
fore both the following expttsiions are possible —

CaCO, - CaO + CO^

CaO + CO, - CaCO^
Reactions of this order are known as rtrenti/e reactions, and the
breaking up of calcium carbonate by the action of heat is termed
dissociation, while that of the potassium chlorate under similar
circumstances is simple decomposilion.

When ammonia is passed through a tube healed to a dull red
heat, the gas is decompoitd mto nitrogen and hydrc^en —

2NH, = N, + 3H»

and the two gases pass out of the healed tube as separated gases,
and do not recombine again.*
But when steam is strongly heated it is dtssociiUtd into oxygen

* Nitrogen tnA ^jiiagKa can be caused to units tuukr niltablt cooditioQi,

86 Introductory Outlines

2nd hydtoECn, and as these separated gases pass away from the
heated retjion they reunite, fonning molecules of water vapour.
Such a reversible reaction may be thus expressed —

aH,o ;t 2Ha

O,.

Again, when the gases ammonia and hydrochloric acid are brought
together at the ordinary temperature, they unite to form solid
1 chloride, and when ammonium chloride is heated it
its two generators,* hence we have ihe expression —

NHj+ HCi::t NH.Cl.
The corresponding compound conlaining phosphorus in the place
of nitrogen, dissociates at a temperature as low as -30°, hence
when phosphoretied hydrogen and hydrochloric acid are mixed
al ordinary temperatures no combination lakes place, the separate
molecules are rn the same relation to one another as those o(
ammonia and hydrochloric acid at a higk temperature. When,
however, the mixture of gases is cooled below - 20, union lakes
place and crystals of phosphonium chloride are formed, which at
once begin lo dissociate into the original gases as the temperature
again rises. The change, as before, may be represented as a

^ibk o

PH, + HCI ;l PH.CL

In such cases of dissocialioD as thai of calcium carbonate, where
one of the products is gaseous and the other solid, no difficulty
exists in separating the simpler compounds that result from Ihe
decomposition ;bul where ihe products are entirely gaseous, special
meihods have lo be adopted lo withdraw the one from the other,
while ihey slili exist as separate molecules, and before ihey reunite
again. One such method, which is well adapted for the quali-
tative illustration of dissociation, is based on the law of gaseous
difTuiion. If when ammonium chloride is heated il is dissociated
into ammonia, NH,, and hydrochloric acid, HCI, these Iwo gases,
having the relative densities of 8.5 and 1S.3;, will diffuse through
a porous medium at very different rates. According 10 the law of
diDitsion, these rates will be inversely as the square roots of the
densities of the gases ; if therefore the conditions are so arranged

• Baker bai shown (May 1894) thai when aiinluulji dry, these gases do not
comlMQe ; and also, thai when aqueous vapour is tntirtly absent, a
Chloride daei not imdaeo this dixsociBtlon.

Dissociation

»7

that the heating of the anunonium chloride takes place in the
neighbourhood of a porous diaphragm, more of (he light ammonia
gas will diffuse through in a given time, than of the heavier hydro-
chloric acid, 10 that a partial separation of these gases will be
effected. Fig. 1 1 shows a convenient armngement fgr carrying out
the experiment A tragment of ammonium chloride is heated in a
short glass tube, through which passes the stem of an ordinary da.;;
tobacco pipe. As the dissociation takes place, both of the gaseous
products begirt to diffuse into the interior of the porous clay pipe,
but owing to their greater rate of diffusion, a larger number of am-
moDia molecules will pass in, than of hydrochloric acid, in the same
time ; consequently, when the gases pass nway from the heated
region and once more recombine, there will be a surplus of am-
monia molecules within the porous pipe, and for the same reason
an excess of hydrochloric acid molecules outside. If the gaseott*
conienls of the porous tube be driven out by means of a stream of

p^^^

air from an ordinary bellows, the presence of the free ammonia may
be recognised by allowing the air to impinge upon a piece of paper,
coloured yellow with turmeric, which is instantly turned brown by
ammonia. The excess of hydrochloric acid within the glass tube
may also be proved, by placing a piece of blue litmus paper in the
tube before heating the compound, and it will be reddened by the
free hydrochloric acid.

In all cases of dissociation, we may imagine two opposing forces
in operation, one being the external force supplying the energy
which tends to bring about the disruption of the molecules, and
me other being the force of the chemical affinity existing between
the disunited portions of the molecule, which tends to bring about
their reunion. When these forces are equally balanced, the same
number of molecules are dissociated as are recomhined in a given

88 Introductory Outlines

unii of time, and the system is said to be in a state of equilibrium.
If by any means the balance between the two opposing forces is
diEtiirbed, by augmenting or lessening either one or the other of
theni, the equilibrium of the system will also be disturbed and a
new condition of equilibrium will be set up, in which again an equal
number of molecules undergo dissociation and combination ii
given time, but in which the ratio of the number of united and dis- ]
united molecules is different from thai which obiained under the J
former condition of equilibrium. The relation between these ti
forces may be most readily disturbed, by either a change of
rature or pressure. Thus, in the case of nitrogen peroxide, N,0^1
when this gas is at a temperature of 26.7°, 10 per cent.
dissociated into molecules having the composition NO,;
long as this temperature is maintained this ratio of the weight a
the dissociated molecules to the total weif;ht of the system (knc
as the fraction of dissociation) slill subsists.

When the temperature of the gas is raised to 60.3*, the slali
equilibrium existing at the lower temperature is disturbed, and tl
system gradually assumes a new condition of equilibrium, whetS'^
once more the actual number of molecules undergoing dissociation
and recombination in a given unit of time is the same, but where
■be percentage of dissociated molecules in the gaseous mixture is

It might at first be supposed thai when such a gas is healed, and
a temperature is reached at which the molecules are dissociated,
that they would all dissociate, and that the process once begiin would
rapidly proceed until the decomposition was complete ; instead of
which, we Hnd a definite fraction of dissociation corresponding 10 a
particular temperature. This may be explained on the basis of the
kinetic molecular theory. Let us imagine the gas nitrogen per-
oxide to be at a temperature below that at which dissoci;ition
begins, when all the molecules will have the composition N,0,.
The molecules of the gas are in a state of rapid movement, and the
rapidity of their movement is increased by rise of temperature.
But the molecules in a given volume of the gas do not all move
at the same velocity, and therefore they have not all the same
temperature. On account of the infinite complications in their
movements caused by their impacts against one another, some will
be moving at a speed considerably greater than that of the average,
and will have a temperature proportionally higher, while others
agun will have a velocity and a temperature below the average.

Dissociaium 89

The observed temperature of the gas, therefore, is not that of the
molecules having the highest or the lowest velocity and tempera-
ture, but is the average or mean temperature between, possibly, a
very wide range.

On the application of heat to the gas, the observed or mean
temperature rises, but the velocity of some of the molecules, and
consequently their temperature, may have been thereby raised to
the point at which dissociation takes place, and they consequently
separate into the simpler molecules. Let us suppose that the
observed temperature of the nitrogen peroxide is 26.7*, and that it
is maintained at this point Although this temperature may be
below the dissociation temperature of the molecules, it must be
remembered that it only represents the mean temperature, and that
while some of the molecules have a lower, some also have a higher
temperature. As already mentioned, at the temperature of 26.7*,
20 per cent of the molecules are dissociated ; that is to say, at
any given instant one-fifth of the total number of molecules reach
a velocity which causes them to break down into the simpler NO,
molecules, which themselves then take up independent movements.
I( in the process of their movements, two of these disunited mole-
cules come mto contact with each other at a moment when their
velocities are lower than that at which they dissociated, they at
once reunite, so that at the same instant some are uniting and
others are dissociating, and, the two processes going on equally,
the percentage of disunited molecules at any moment is the same,
although the actual molecules which are dissociated at one point
of time may not be the identical ones that are in this state at
another time. Let us now suppose the gas to be heated until the
registered (1.^., the mean) temperature reaches 60.2*, and that it be
maintained at this point At this higher temperature a much
larger proportion of the molecules will acquire a velocity at which
they are unable to hold together, namely, 52.04 per cent ; but the
remainder, amounting to nearly one-half, still are at a temperature
below that at which dissociation takes place. Under these altered
conditions a greater number of disunions and reunions takes place
during a given interval of time, but the numbers are equal, and
therefore the equilibrium exists. If once more the gas be further
heated, until the indicated temperature is 140*, then it is found
that the whole of the N^Oi molecules have dissociated into NO,
molecules ; that is to say, when the mean temperature has reached
140^ then even those molecules that are moving with the slowest

ity lying

' is 3S.3 ■

:ase thp^^H

.ed. »^^l
constant ^^^

speed, hftvc reached the lemperature of dissocial ion. It will be
evident thai the rale at which the fraction of dissociation in-
creases, as the temperature of a gas is gradually raised, will be
greatest when the mean temperature approaches the real dissocia-
tion lemperatute of the gas, for the temperature of the greater
number of the molecules will be coincident with, or very closely
approximating to, that point.

The vapour density of nitrogen peroxide, if it could be ascertained
when all the gaseous molecules had the composition N,0,, would
be 4A ; while that of the gas, when entirely dissociated into NO^
molecules, is 23. At temperatures between these extremes, the gas,
consisting of mixtures of both molecules, will have a density lying
between these figures, thus al 27.6° and 6o.z* the density is 38.3
and 30.1 (see Nitrogen Peroxide, and also Phosphorus Penta-
chloride).

The eflect of increased pressure upon a gas being
(he mean free path of the molecules, and thereby increase
number of molecules in a given space, the number of imp;
between the molecules in a given time will be increased.
therefore, white the nitrogen peroxide is maintained
temperature, say 62.2°, the pressure be increased, the dissociated
molecules, having shorter distances to travel, and making more
frequent impacts in a given time, will unite more quickly than
others are being disunited, and a fresh condition of equilibrium
will be established for any particular pressure.

The case of phosphonium chloride already mentioned, may be
referred to as an illustration. This compound is completely dis-
sociated into molecules of phosplioretted hydrogen, 1*H„ and
hydrochloric acid, below a temperature of 0°. If, while at this

Ilempcrature, it be subjected to pressure, the dissociated molecules
are caused to unite, and at a pressure of thirteen atmospheres the
union is complete, the whole of the disunited molecules having
i:ombined to form molecules of phosphonium chloride, PH,C1.

aiecuies having
de, PH.Cl.

CHAPTER XI
ELECTROLYSIS

If a strip of pure zinc, and a strip of platinum, be together dipped
into a vessel containing dilute sulphuric acid, neither metal is
affected by the acid, so long as the metals do not touch each other.
If the ends of the strips outside the liquid be joined by means of a
metal wire, the zinc gradually dissolves in the acid, and bubbles
of hydrogen are disengaged fiom the liquid in contact with the
surface of the platinum plate (which itself is otherwise unaffected
by the acid), and at the same time an electric current passes
through the wire. So long as the chemical action of the sulphuric
acid upon the zinc proceeds, so long will the electric current con-
tinue to pass ; in other words, chemical energy will be transformed
into electrical energy. If the wire be severed, the electric current
can no longer pass, and the chemical action at once stops.

Such an arrangement constitutes a galvanic or voltaic element,
or cell, and a series of such cells forms a galvanic battery. The
zinc plate, or the end of a wire that may be connected to it, is
termed the negative pole of the battery, while the end of a wire
attached to the platinum plate is the positive pole. Other arrange-
ments can be employed for generating a galvanic current, but in
all cases the electrical energy is derived from chemical action.

If the two poles of a battery are connected together by placing
them both in contact with various different substances, it is seen
that in some cases the electric current passes, and in others not.
For instance, if the poles are joined by placing them both in contact
with a bar of sulphur, no current passes, whereas when connected
by a rod of graphite the current freely passes. Substances which
behave in this respect like the sulphur, are said to be non-con-
ductors of electricity, while those that allow the current to pass,
are distinguished as conductors. Substances capable of conducting
electricity are of two kinds, namely, those which are merely heated,
and those which undergo a chemical change, in consequence. All

92 Introductory Outlines

the meUls, and a lew of the noa-metals, belong to the first of these '
classes ; while Uie second Includes a large number of cotnpoimd I
substances, which are either in the liquid sta.te, or id solution in 1
some solvent. Thus, if the poles of a battery are immersed in pure
water, practically no current passes, because this liquid is a non-cod'
ductor; but if a quantity of hydrochloric acid (HCl) be dissolved ir
the water, the solution at once becomes a conductor, and it is seen \
■Jjal gus \% disengaged from the liquid upon the surface of each I
ivire. Upon examination it is found that the gas evolved at the 1
negative pole is hydrogen, while that from the positive pole
chlorine : the hydrochloric acid, therefore, is separated into i
elements by the passage of an electric current through its aqueous I
solution. Such a process of decomposition is termed eUctrolysisj
and the conducting liquid is known as an tlectrolyte.

Tlie poles that are introduced into the electrolyte ate called
tkcirodts, the negative electrode being sometimes termed the
eathodt, and the positive electrode the anedt.

In a great number of instances, the dectrolytic decomposition is
accompanied by certain secondary reactions, caused by the action
of the primary products of the decomposition upon either the
electrolyte or the solvent ; for example, when a solution of sodium
chloride (NaCl) is electrolysed, the primary products are sodium and
chlorine, the latter appearing at the anode and the sodium making
s appearance at the cathode. The metal sodium, however, in
jRiaci with the water in the neighbourhood of the cathode, at
ice exerts chemical action upon the liquid, with the liberation ol
its equivalent of hydrogen, according to the equation —

Na+ H,0 = NaHO + H. ■

In the same way, when an aqueous solution of copper sulphate A
(CuSO,) is submitted to electrolysis, the primary products are
copper, Cu, and the group SO,. Tlie copper is liberated at the
cathode, and is deposited as a metallic Aim upon the electrode.*

* Tbis is the essence of ihe process of eleclio-plaling Tlie melal to be de-
islled. whetbET it be gold, silver, oi nidcel, jtc, , in itie form of a suitable wll
(usually a double cyanide) in aqueous solution, forrns tbeelcctrolyle. Ilie object
;o Ik i^led is made Ihe cathode, that is. it is suspended in the Uquld and is
connected to Ihe negative electrode of a milable ballety. The aiicxle consists
of a ilripof Ihe metal to be deposiied. Thus in silver pbling, a strip of silver is
employed, and in ihis way the acidic radical that is Uberaled ai Ibe anode
dissolves the metal, and tbeieby prevenls Ihe weakening of Ibe solution, which
would otberwisa result from Ihe gradual deposition of silver upon the cathode.

Electrolysis 93

The group consisting of SO4 passes to the anode, where it under-
goes decomposition in the presence of the water, whereby ulti-
mately oxygen is evolved and sulphuric acid produced —

SO4 + H,0 - H^04 + O.

The primary products of electrolysis are termed the ions. Those
ions that appear at the anode (positive electrode) are those which
are negatively electrified, or which convey negative electricity ;
such as the elements fluorine, chlorine, bromine, iodine, and a
number of acidic groups, or radicals, such as the SO4 group already
mentioned. Inasmuch as the negative ions appear at the anode,
they are sometimes spoken of as anions.

Those ions, such as hydrogen and the metals, which travel to the
cathode (negative electrode) are those that are positively electri-
fied, or in other words, which convey positive electricity : positive
ions, therefore, are distinguished as ccUhions.

Fara4ay'S Law. — When the same quantity of electricity is
passed through different electrolytes, the ratio between the quan-
tities of the liberated products of the electrolysis, is the same as
that between their chemical equivalents.

Thus, if the two electrolytes, hydrochloric acid and dilute sul-
phuric acid, be introduced into the same electric circuit, hydrogen
and chlorine are evolved in the one case, and hydrogen and oxygen
in the other. If the gases be all collected in separate measuring
vessels, it will be seen (i) that the hydrogen and chlorine evolved
from the hydrochloric acid are equal in volume ; (2) that the
volume of hydrogen collected from the other electrolyte is the same,
while that of the oxygen is equal to only one-half this amount.
Knowing the relative weights of equal volumes of these three gases
to be hydrogen, oxygen, chlorine, as i, 16, 35.5, we see that they
must have been liberated in the proportions by weight of^

Hydrogen « i Oxygen - 8 Chlorine « 35.5.

Similarly, if the same quantity of electricity be passed through
aqueous solutions of hydrochloric acid (HCl), silver nitrate (AgNOg),
copper sulphate (CUSO4), and gold chloride (AuCl,), by the time
that 1 gramme of hydrogen has been liberated from the hydro-
chloric acid, there will be deposited upon the cathodes of the other
electrolytic cells, 108 grammes of silver, 31.7 grammes of copper,
and 65.6 grammes of gold. These numbers, which are the electro-

94 Introductory Outlines

chemical equivalents, arc identical with the chemical equivalents of ]
those elements, the chemical equivalent of an element being it
atomic weight divided by its valency.

Valency

Regarding the quantity of eleclricily required lo liberate I
gramme of hydrogen as the unit, we may say that i6 grammes of
oxygen require t units of electricity for its liberation, loS grammes
of silver i unit, 63.5 grammes of copper 1 units, and 197 grammes
of gold 3 units ; or, in other words, the number of units of electricity
required to liberate a gramme-atom, is identical with the number
tcprcsenling the valency of that atom in the particular electrolyte
employed.

Some metals, such as copper, mercury, tin, &c, nre capable of
functioning with different degrees of valency. Thus copper is
divalent in copper sulphate and in cupric chloride, but mono-
valent in cuprous chloride. If, therefore, i unit of electricity be
passed through aqueous solutions of each of these copper chlorides,
in the case of cupric chloride ^^ = 31.7 grammes of copper will

be deposited, while in the cuprous chloride

63.; grammes

are formed

The modem theory now generally held, to explain the pheno-
mena of electrolysis, is known as the theory oi electrolytic diiiocia-
lion. The passage of elearicity through conductors of the two
classes above mentioned, that is, through conductors such as metals,
and those which arc electrolytes, may be compared with the two
ways by which heat is transmitted, namely, by conduction and
convection. When a bar of metal is heated at one end, the heat
travels along the bar, the metal remaining stationary ; but when
water is contained in a tube which is healed at its lower end, the
heated particles of water travel along itie lube, conveying the heal
to the other extremity. In a similar manner, when electricity passes
through a metallic conductor, the electricity travels through, or
along, the metal, which itself does not move ; but when it Js passed
through an electrolyte, it is conveyed, or transported, through the
liquid by the moving ions. One set of ions charged with negative

Electrolysis 95

electricity travels towards the anode, while another set conveying
positive electricity moves towards the cathode. In the earlier stages
of the development of the present theory, it was supposed that the
electrolyte was only separated into its ions as the electric current
was passed into it, that the electricity was the prime cause of the
iissociation of the electrolyte, hence the expression electrolytic
dicampositiony still commonly used. If this were in truth the
case, it ought to be made manifest by the fact, that the electric
current would have to do work in effecting such decompositions ;
but exact experiment goes to show that electricity is conducted
with equal freedom by electrolytes as by metals. The theory
proposed by Arrhenius (1887) is that a certain proportion of the
molecules of the electrolyte are in a dissociated condition at all
times. When, for example, sodium chloride is dissolved in water,
some of the molecules, owing to their collisions, become separated
into the ions, sodium and chlorine, much in the same way as a
certain proportion of the molecules of a gaseous compound may
be dissociated, and that these convey the electricity as soon as
the electrodes are introduced into the solution.

From a number of other considerations, it is now believed that
in such a saline solution the greater proportion of the compound
is in the dissociated or disunited condition ; the proportion depend-
ing largely upon the state of dilution. The more dilute the solution,
and the more complete is the dissociation. At first it might appear
contrary to established ideas, that in the case, for example, of such
a compound as sodium chloride, the sodium and chlorine in the
free state should be capable of existence in the same liquid ; a
liquid, moreover, upon which one of the elements, namely sodium,
is under ordinary circumstances capable of exerting a chemical
(iction. According to the electrolytic dissociation theory, however,
the disunited constituents of the sodium chloride exist as separate
atoms, having enormous electrical charges, the sodium with positive
and the chlorine with negative electricity. Whenever the chlorine
atoms lose their electrical charge, they unite together, forming the
chlorine molecule Cl^ which then possesses the properties which
are usually associated with this element ; and in the same way
when the positively electrified sodium atoms give up their charge
they likewise unite, forming sodium molecules, which are endowed
with the ordinary properties belonging to that element When the
electrodes of a galvanic battery are pLiced into such a solution of
sodium chloride, the negatively charged chlorine atoms travel to

96 Introductory Outlines

the anode, and there dischai^ge their electricity, and in consequence,
the chlorine atoms at that point unite, and molecules of ordinary
chlorine escape as gas from the liquid. The sodium atoms with
their positive charge travel to the cathode, where in like manner
they are discharged, and at once unite to form sodium molecules,
having the ordinary properties of sodium, and consequently at
that point this element exerts its chemical action upon the water
and liberates hydrogen.

This theory, that electrolytes in dilute solution are dissociated
into their ions, is in harmony with, and derives support from, the
laws which regulate the influence of substances in solution, upon
osmotic pressure (page 1 36), upon the lowering of the vapour-pres-
sure (page 118), and upon the lowering of the solidifying point of
the solvent (page 121). Dilute solutions of electrolytes (strong
acids, bases, and salts) exhibit deviations from these laws, much
in the same way that gases which undergo dissociation, depart from
the ordinary gaseous laws. It is found that in the case of dilute
solutions of electrolytes, the osmotic pressure, the lowering of the
vapour pressure, and the lowering of the freezing-point of the
solvent, instead of being proportional to the number of molecules
of the dissolved substance, are proportional to the number of (US'
sociated ions; each ion behaving as a separate molecule.

CHAPTER XII

CLASSIFICATION OP THE ELEMENTS

It has already been mentioned (page 7), that the elements may
be classified under the two subdivisions, metals and non-meials.
Further classifications have from time to time been in use, based
upon other properties, such, for example, as the valency of the
elements.

Classified according to their valency, the elements foil into six
subdivisions, consisting of mono-, di-, tri-, tetra-, penta-, and hexa-
valent elements. This system of classification has now largely
fallen into disuse, owing partly to the difficulties arising out of the
variability of valency so often exhibited, but more especially to the
more recent development of another system, known as the natural
classification of the elements^ or the periodic system^ which practi-
cally absorbs and includes the older method.

Certain remarkable numerical relations have long been observed
to exist among the atomic weights of elements that closely re-
semble one another in their chemical habits. In such groups
or families it is frequently seen that the atomic weight of one
member, is approximately the arithmetic mean of the atomic
weights of those immediately before and after it, when they are
arranged in order of their atomic weights. This will be seen from
the following examples : —

Na.
23

7 + 39.33

Kb.

«5

133

39+133 ^ 85.8

2 ^

3»

Sb.
120

" \ ''° - 7S.5

Te.
125

3» + "5 . 78.5

Introductory Outlines

If the elements in. these various families are so arranged, as to
bring out the differences between their atomic weights, the striking
fact will be observed that the increase in the atomic weights in
each group takes place by practically the same increment. In
the following table the elements belonging to the same group
are placed in vertical columns, the differences between the various
atomic weights being placed between them : —

F= 19

N = i4

0 = 16

Na = a3

Mg = 24

Difference . 16.5

Diff. . 17

Diff. . 16

Diff . 16

Diff. . 16

CI = 35-5

P = 3i

S = 32

K = 39

Ca = 40

Difference . 44.5

Diff. . 44

Diff. . 47

Diff. . 46.2

Diff. . 47.3

Br = 80

As = 75

Sc = 79

Rb = 85.2

Sr = 87.3

Difference . 47

Diff. . 45

Diff . 46

Diff. . 47.8 1 Diff. . 49.7

I — 127

Sb=i20

Tc = 125

Cs = 133 Ba = 137

It will be seen that in each group the difference between the first
and second number is about 16, while between all the others the
increase in weight takes place by a number which approximates
to 16 X 3.

This numerical relation between the atomic weights of elements
of the same family, and between the various groups, is obviously
not a chance one, and chemists were led by it to believe that the
properties of the elements were in some way related to their atomic
weights. Newlands (1864) was the 6rst to point out, that if the
elements are tabulated in the order of increasing atomic weights,
the properties belonging to each of the first seven elements reap-
peared in the second seven, and he applied to this relation the
name of the law of octaves. A more elaborated and systematic
representation of Newlands* law of octaves was afterwards deve-
loped by^Mendelejeff (1869), and which is now generally known as
MendelejefTs periodic law.

If the fourteen elements with lowest atomic weights, after
liydrogen, be arranged in order of increasing atomic weights in
two horizontal rows of seven, some of these relations will be
recognised —

Li *=7 Be =9 B =ii
Na=23 Mg = 24 Al = 27

C-I2

N = i4 0=16 F=i9

Si « 28

P«3i S=32 Cl = 35t

Tfu Periodic Classification 99

in traveising (he upper row from lithium to fluorine, we meet with
certain characteristic properties belonging to each member, and
also a certain gradation in those properties that are common.
Coming to the second row, or octave, many of the characteristic
properties of the members of the first row again appear, and the
same tegular modulation is met with in passing along the series :
thus lithium resembles sodium, carbon corresponds to silicon,
fluorine to chlorine, and so on. These resemblances are seen
both in the physical as well as the chemical properties of the
elements, thus lithium and sodium are both soft white metals,
and are strongly electro-positive. Fluorine and chlorine are both
pungent corrosive gases, and are intensely electro -negative. Tak-
ing their power of combining with chlorine and with hydrogen as
indicative of their valency, we see that the change in this respect,
as the two series are traversed, is the same in each, thus —

LiCl BeCl, BCl, CCl, CH, NH, OH, FH
NaCl MgCI, (AICI^ SiCI, SiH, PH, SH, CIH

The gradation in properties exhibited by the elements in a series,
IS also seen in their power of combining with oxygen, which will
be more clearly brought out if the fonnulae of the compounds be
so written as to indicate the relative proportions of oxygen with
which two atoms of each element unites, thus—

Na,0* (Mg,0,) Al,0, (Si,0,) P.O. (S,0,) C/.O, +
MgO SiO, SO,

Regarding, then, the seven elements of the tirsi row as a ptriod, we
find that the various properties exhibited by the several members
are met with again in those of the second period.

Not only do the properties of the elements themselves reappear,
but also those possessed by the various compounds they form ; thus
lithium chloride (LiCI) and sodium chloride (NaCl) stibngly re-
semble one another. The oxides of beryllium and magnesium
(BeO and MgO) have similar properties. The compounds of fluo-
rine and chlorine with hydrogen (HF and HCl) closely resemble
each other, and so on.

This periodic reappearance of similar properties, exhibited by the

* See footnote on page 4S7.

t Percblodc oxide li Dot kouwo in ttie Itee uats.

lOO Introductory Outlines

elenienis and their compounds as the atomic weights of the former
gradually increase, is thus stated by Mendelejeff in his law of
periodicity. The properties of the elements^ as well as the proper-
ties of their compounds^ form a periodic function of the atomic
weights of ihe eietnents.

When the tabulation of the elements according to this system is
continued (after the completion of the second period with chlorine),
it will be seen, that beginning with potassium, seventeen elements
have to be arranged before we meet with the reappearance of those
properties that belong to the first ; that is to say, there are two
sets of seven each, and three elements over, which in the following
table are placed within brackets : —

K. Ca. Sc ri. V. Cr. Mn. (Fe. Ca NL)

39 40 44 48 51 52 55 (56 59 59)

Cu. Zn. Ga. Ge. As. S«. Br.

63.5 65 70 72 75 79 80

This constitutes what is known as a long period, in contradis-
tinction to the two first, which are distinguished as short periods.
In certain respects, however, the last seven elements in this long
period exhibit resemblances to the first seven ; that is to say, the
properties displayed by the members of the first period, which is
known as the typical period^ reappear twice over in the long period.
The three elements within the brackets are termed by Mendel ejeflf
transitional elements. Continuing the arrangement from bromine,
another long period occurs, again containing three transitional
elements : —

Rb. Sr. Y. Zr. Nb. Mo. — (Ru. Rh. Pd.)
85.2 87.3 89.6 90.4 93.7 96 ? (103.5 104 106)

Ag. Cd. In. So. Six Te. I.
108 112 113 118 120 125 127

It will be seen that a gap is left where the seventh member of
the first part of this period should be, an element which would
correspond, in this period, with manganese in the period above.
This element is at present unknown. The remaining elements
belong to three other long periods, in which, however, the number
of gaps is very considerable, thus—

Thi Periodic Classification loi

Ct.

Ba.

Ce. - -

- (-

—

»33

137

138.5

141

Yb.

- Ta. W.

- (O*.

Ir.

Pi.)

173

182 184

(191

192.5

195)

An.

Hg.

TL Pb.

RL -

—

197

200

203.7 207

207.5

—

Th. - Ur.
232 239.8

- (-

—

Those elements that fall in the first seven places of the long
periods, are termed the even series^ while the last seven are dis-
tinguished as the odd series; arranging them, therefore, in such a
manner as to bring the odd and even series into columns, we get
the table on page 102.

In this manner the elements are arranged in eight groups, the
eighth containing the transitional elements that come between the
even and odd series of the long periods.

In each of the remaining seven groups, the elements belonging
to the even series of their isspective long periods, are placed to the
left, while those belonging to the odd scries are arranged on the
right hand side of each vertical column. In this way the groups are
divided into the subdivisions, A and B, in which the resemblance
between the members is most pronounced Thus in Group II.,
although there are certain properties common to all the members,
there is a much closer similarity existing between the elements
calcium, strontium, and barium than between zinc and calcium, or
cadmium and barium.* The elements in the two short periods,
have been placed in that subdivision or family, with the members
of which they exhibit the closest resemblance. Thus, in Group I.
lithium and sodium are more allied to potassium, rubidium, and
caesium, than to copper, silver, and gold; while in Group VII.

* This, however, is by no means uniformly the case ; thus the element copper
(Group I. ) in many of its chemical attributes is much more closely allied to
mercury (Group II.) than to silver ; and silver again more strongly resembles
thallium (Group III.) than either copper or gold, with which it i^ associated in
this system of classification.

Introductory Outlin<s

1
1
1

a"
6

1
1
1

■

<
<

1
1

1
S

1
1

s
s

9 a-

1
s

i-i:

S
■"

1
a

1
1

S"|

i-i;

1
1

■1 :

h
1

5 ^

8 ■

1 =
N

1
J

i :

_
1

The Periodic Classification 103

fluorine and chlorine are placed in the same family with bromine
and iodine, with which they exhibit a dose similarity.

In the eighth group, containing the transitional elements, the
families consist of the horizontal and not the vertical rows ; that is
to say, the closest resemblance is between the three transitional
elements in each series, elements whose atomic weights, instead of
exhibiting a regular increase, as in the other famihes, have almost
the same value, such as Fe •■ 56 ; Co « 59 ; Ni « 59.

A glance at the table shows that in the last three long periods
there is a large number of gaps. It is possible that these gaps
may represent elements which yet await discovery. This supposi-
tion gains considerable support from the fact, that at the time
Mendelejeff first formulated the periodic law, there were three such
gaps in the first long period, which have since been filled up by the
subsequent discovery of three new elements ; these will be referred
to later. It is noteworthy, however, that all the elements belong-
ing to the last three periods, together make a total which is
almost exactly the number required for a single complete long
period, including three transitional elements ; and it is quite pos-
sible that future investigations may necessitate an alteration in
the accepted atomic weights of some of these elements, and con-
sequently a change in their positions in the system.

The periodic recurrence of some of the chemical properties,
is indicated in the lowest horizontal column, where the general
formulae of the oxygen compounds, and the hydrides, are given ; R
standing for one atom of any element in the group. As explained
on page 99, these formulae are so written as to show the relative
amount of oxygen to two atoms of element, in order to establish
the true relation between the different groups. For example, the
oxides of the elements of Group I. contain two atoms of the element
to one of oxygen, as LigO ; but those of the second group only con-
tain one atom of the element, as CaO : hence the general formula
is doubled, RgO^. It will be seen, therefore, that the proportion of
oxygen relative to two atoms of the element regularly increases
from the first group to the eighth. The oxides of the members of
the first group are strongly basic in character, and in general this
basic nature gradually diminishes as wc traverse the series, giving
place to acidic characteristics, which are strongly marked in the
seventh group.

The periodic reappearance of the physical properties of the
elements is seen in such points as their electrical characters, their

104

Introductory OutUnts

malleability, ductility, melting-points, &c., all of which are in
harmoDy with the periodic taw ; but in none is it more strikingly
seen than in their atomic volumes in the solid state. The atomic
volumes of the elements, aie the relative volumes occupied by
quantities proportional to their atomic weights, or by gramme-
atoms ; and they are obtained by dividing the atomic weights of
the elements by their specific gravities. In the case of gases, as
has been already explained on page 39, the specific gravity is
the density referred to hydrogen as the unit : the atomic volume,
therefore, of such a gas as oxygen is—

16 — atomic weight _
16 " density

The specific gravities of solids (and also liquids) arc referred to
water as the unit, and as i cubic centimetre of water weighs
I gramme, the specific gravity of a solid or liquid, expresses the
weight in grammes of 1 cubic centimetre of the substance. Dividing
the atomic weight, expressed in grammes, by the weight in grammes
of I cubic centimetre (i.e., the specific gravity), the atomic volume
will be represented in cubic centimetres. It must be remembered
that the atomic volumes do not express the relative volumes that
are actually occupied by the atoms, tbey represent in reality the
relative volume of the atoms plut the unknown volumes of the
spaces that separate them.

The following table gives the specific gravities, and the calculated
atomic volumes, of the first and the middle elements of the two
short and two long periods.

Orani)-

w^rghu.

VolZH

""-<»'{ tST: : : : ; :

andPenod ^J^™ ' ■ . ■ ■ ■

0.5s
3.0
0.97

38.3

11,9

4th Penod 1 (R„,|,pnmm- Rhodium) Palladium ,

Vzz

From the figures in the last .column it will be seen, that beginning

Tht Ptriodic Classification 105

with lithium, ti.9, the atomic volume fells as the middle clement ol
the period, namely carbon, is reached ; after which it again rises
and reaches a maximum with the first member of the second period,
namely sodium. In this period the same gradual fall in atomic
volume is again noticed until the middle element (silicon) is
reached, when the value of this function of the elements once more.
rises, and a second maximum is attained with the first member
(potassium) of the third period. The two next are long periods, and
the atomic volumes steadily decrease until the middle three (transi-
tional) elements, after which they gradually increase again to a
maximum in rubidium, the starting-point of the fourth period. In
the fourth period the same thing once more occurs, the minimum
atomic volumes being those of the middle or transition elements,
after which a maximum is again reached in caesium.

This periodicity of the atomic volumes may be graphically
represented by a curve, where the ordinates represent atomic
volumes, and the abscissfc atomic weights. This curve, which was
first constructed by Lothar Meyer, is known as Lothar Meyer's
curve (page 106), and a comparison of it with MendelejelTs table
is most instructive.

The divisions indicated by the Roman numerals correspiond to
the ditTerent periods : Groups 1. and 1 1, being the two short periods,
III. and IV. the two complete long periods, while V., VI., and VII,
correspond to the fragmentary portions of the last three periods.

The transitional elements of periods III,, IV., and VI. are all to
be found at the minima of the large hollows ; separating the even
series (situated on the descending portion of the curve), from the
odd series which lie on the ascending slope The elements belong-
ing to the difTcrent groups in MendelejefTs table, are seen 10 occupy
the same relative positions upon the dilTcrcnt portions of this curve.

Thus in Group I. the elements Li, Na, K, Rb, Cs, are all found
npon the ma-(ima of the curve, and Cu, Ag, and Au at those points
at the minima where the electro- negative properties reappear. The
halogen elements (chlorine, bromine, iodine) are seen in similar
positions upon the ascending, and the alkaline earths (beryllium,
magnesium, calcium, strontium, barium) on the descending
portions.

When the periodic law was first formulated by MendelejefT
(1869), there were a number of instances in which the system did
not harmonise with the then accepted atomic weights of the
elements. The discoverer boldly asserted that the atomic weights.

Introductory OuUina

aP^

^~*u

The Periodic Classification 107

and not the i7«ein, were at bult, and in every such case the care-
ful reinvestigation of the atomic weights by numerout chemittt,
hu proved (he conectneu of the assertion. One or two instances
may be quoted. The element indium had assigned to it the
atomic weight 76. Its combining proportion is 3S, and being
regarded as a divalent element, its oxide was believed- to have
the fonnula InO. Having an atomic weight — 76, indium would
occupy a place between As — 7; and Se — 79 ; but in the system
(see table on page \a2\ there is do room for an element with such
an atomic weight j and, moreover, if indium be a divalent element
having this atomic weight, it should come between Zn — 6; and
Sr ■> 87 in Group 11., where again there is no room. Mendelejefl'
made the assumption that the oxide of indium had the formula
ln,0^ believing the element to be an analogue of aluminium
(Group III.). If this be the true composition of the oxide, the
atomic weight of the element would be 3S x 3 — 1 14, and indium
would then take its place in Group III., between the elements
cadmium — iia and Sn — 118, in the odd series of the second long
period Bunsen afterwards determined the specific heat of indium
by means of his ice calorimeter, and found it to be 01057 :—

"^rhl""! .^- ."■3-..on,ic..i.h,(s«p«c4S>

Hence 114 and not 76 is the accepted (approximate) atomic weight
of indium.

Again, the element beryllium (formerly known as glucinum) hat
a combining proportion of 4.6. Its chloride was believed to have
the composition BeCIa, and its oxide to be a sesquioxide having
the fonnula BejO^ The atomic weight assigned to the element,
therefore, was 13.8.

With this atomic weight beryllium would take its place between
carbon M 12 and nitrogen— 14; but according to the periodic
classification there is no room for such an element, and moreover,
in such a position it would be among elements with which it has
w) properties in common. On the supposition that the oxide of
beryllium has the formula BeO, that is, that the element is divalent,
its atomic weight would have to be lowered from 13.S to 9.1 in
order to maintain the same ratio between the weights of metal and
oxygen in the compound. On this assumption, beryllium would
fall into the second place in the 6r3t series, between lithium = 7
and boron — 11, and in the same group as magnesium and tine

io8 Introductory Outlines

When the specific heat of beryllium was determined, it gave the
value 0.45, and this number divided into the atomic heat constant,
6.4, gave 14 as the atomic weight. In spite of this evidence in
favour of the higher value as the atomic weight of beryllium,
Mendelejeff still regarded the lower number as correct, and it
was suggested that possibly beryllium, like carbon and boron
(elements also of very low atomic weight), had an abnormally
low specific heat at ordinary temperatures. This was found to be
the case (see page 46), and at 500* the specific heat of beryllium
was found to be a62o6. This divided into 6.4 gives the value 10
as the atomic weight, which indicates that 9.1 and not 13.8 is in
reality the atomic weight of beryllium.

Not only has the periodic law been of service in bringing about
the correction of a number of doubtful atomic weights, but by
means of it, its originator was enabled to predict with considerable
certainty the existence of hitherto undiscovered elements, and
even to predicate many of the properties of these elements. As
already mentioned, at the time when the periodic law was first
formulated, there were three gaps in the system in the first long
period, namely, No. 3 in the even series (now occupied by scandium),
and Nos. 3 and 4 in the odd series (now filled by gallium and
germanium). To the unknown elements which were destined to
occupy these positions, Mendelejeff gave the names eka-boron^
eka'aluminium^ and eka-silicon (the prefix eka being the Sanscrit
numeral one\ and from the known properties of the neighbouring
elements of the scries (horizontal rows in the table, page 102), and
also of those situated nearest in the same family (vertical columns),
he predicted some of the prominent properties that would pro-
bably be possessed by these elements. Thus in the case of eka-
aluminium, from the known properties of aluminium and indium,
the neighbouring elements in the same family, and from zinc, the
contiguous element in the same series (the 5th place in the series
being unoccupied), Mendelejeff deduced the following properties
for the unknown element that he called eka-aluminium : —

Predicted Properties of Eka-Aluminium (1871).

(i.) Should have an atomic weight about 69.
(2 ) Will have a low melting-point.
(3.) Its specific gravity should be about 5.9.
(4.) Will not be acted upwn by the air.

The Periodic Classification 109

(5.) Will decompose water at a red heat.

(6.) Will give an oxide Ei 20^ a chloride El^CX^^ and sulphate

(7.) Will form a potassium alum, which will probably be more
soluble and less easily crystallisable than the corresponding alumi-
nium alum.

(8.) The oxide should be more easily reducible to the metal than
altunina. The metal will probably be more volatile than alumi-
nium, and therefore its discovery by means of the spectroscope
may be expected.

In the year 1875 I^coq de Boisbaudran discovered a new
element in a certain specimen of zinc blende (zinc sulphide), the
individuality of which he first recognised by the spectroscope,
the spectrum being characterised by a brilliant violet line. This
element he named gallium. The properties of this metal, as they
were subsequently observed, showed that it was, in fact, the pre-
dicted eka-aluminium of Mendclejeff, as will at once be seen by a
comparison of the following facts.

Properties of Gallium {discovered 1875).

(i.) Atomic weight =■ 69.9.
(2.) Melting-point, 30. 1 5*.
(3.) Specific gravity, 5.93.
(4.) Only slightly oxidised at a red heat.
(5.) Decomposes water at high temperatures.
(6.) Gallium oxide, Ga^Oj. Gallium chloride, Ga^Clf. Gallium
sulphate, Ga2(S04)3.
(7.) Forms a well-defined alum.
(8.) Is easily obtained by the electrolysis of alkaline solutions.

In a similar manner the properties of eka-boron and eka-silicon
were predicted, and the subsequent discovery oi scandium (Nilson,
1879), and germaniutn (Winkler, 1886), whose properties were
found to closely accord with these hypothetical elements, formed
an additional demonstration of the truth of the periodic law.

No satisfactory theory has yet been offered, to explain the law of
periodicity.

CHAPTER XHI
GENERAL PROPERTIES OF LIQUIDS
UNDEK this head the following subjects will be considered ;—

1. The passage nf liquids into vapours or gases.

2. The passage of liquids into solids.

3. Solution.

I. The Passage of Liquids Into Oases. Evaporation and
Bollin?-— Just as in the gaseous condition, so in the liquid state,
the molecules are in a stale of motion : in the liquid state, however,
the mean tdnetic energy of the molecules is unable lo overcome the
force of their mutual attraction. Some of the molecules have a
sirialler kinetic energy (that is, a lower temperature), and others
a greater kinetic energy, than the average ; and when in the course
of their movements the latter strike the surface of the liquid and
break through it, they continue their movements in the space
above, as gaseous molecules. If the space into which they wander
be unlimited, that is, if the liquid be freely exposed to the air, these
molecules escape away altogether, and consequently the liquid
diminishes in quantity. This process is known as evaporation^
and as the molecules which so leave the liquid aie those having
the highest temperature, it follows that the temperature of the
liquid, which is the average temperature of the molecules, will fall,
The more completely the molecules that so escape from the surface
of a liquid are prevented from falling back, that is, the more rapidly
they are swept away from the immediate neighbourhood of the
liquid, the more quickly will this escape of molecules take place,
and therefore the greater will be the fall of temperature that results
from evaporation. Thus, if a quantity of liquid, say water, be
exposed in a dish so that a current of air is blown across the sur-
face, the rate of evaporation is increased, and the temperature con-
sequently falls lower than if the water be merely placed in a still
aimospheic: similarly, if the water be placed in a vacuum the rate

;arx

Evaporation 1 1 1

of evaporation i* increased, because the molecules that escape from
the surface of the liquid are not impeded in their motions by
collisions with the molecules of air.

This fall of temperature resulting from evaporation, may be
readily seen by enveloping the bulb of a thermometer in a piece o(
thin muslin, and moistening it with water. If such a thermometer
be placed by the side of a naked thermometer, it will be seen that
the mercury will fall lower in the one that is moistened, and the
difterence will be still more marked If the instruments are placed
in a draught, whereby the
evaporation of the water
from the muslin is accele-
rated.

If the space above the
tiquidbelimited,moIecules
still continue to escape
from the surface ; but a
state of equilibrium is soon
established, when as many ip

are thrown back again by
rebounding from one an-
other and from the walls
of the containing vessel,
as leave the surface in a
given lime. Under these
conditions the enclosed
space is said to be salu-
rtUtd with the vapour of ^^

the liguid. The number '

of molecules which escape t .^^

from the surface, depends

upon the temperature, and i-'iu. is,

is independent of the pres-
sure, for if the volume of a saturated vapour be forcibly diminished,
it merely results in the condensation of a portion of the vapour ; and
if expanded, a corresponding vaporisation of an additional quantity
of the liquid, the pressure remaining always constant. The number
of molecules that re-enter the liquid, is determined by the number
and the velocity of those that exist as gaseous molecules in a
unit volume. But the pressure exerted by a gas is caused by the
sumber and velocity of the molecule* in a given volume, hence the

112 Introductory Outlines

condition of equilibrium is set up, when the vapour above the liquid
exerts a definite pressure, which pressure will be constant for any
given temperature. The pressure exerted by a vapour under these
conditions is termed the vapour tension of the liquid. The fact that
the vapour given off from a liquid exerts pressure, may readily be
experimentally illustrated by means of the apparatus seen in Fig.
12. Three glass tubes, A, B, and c, about one metre long, are com-
pletely filled with mercury and inverted in a trough of the same
liquid. The mercury will sink to the same level in each tube, the
length of the mercury column representing the atmospheric pres-
sure at the time. Into two of these barometer tubes, B and C,
a few drops of water are introduced, when it will be found that the
mercury is depressed, as indicated in B, below the level at which it
previously stood. This depression of the mercury column, repre-
sents the tension of the vapour of the water for the particular
temperature at which the experiment is made. If tube c be sur-
rounded by a wider glass tube, through which steam from a small
boiler is passed, it will be noticed that as the temperature of the
water in the tube rises, the mercury is more and more depressed,
thus showing that the tension of the vapour increases with rise
of temperature. As soon as the steam circulates freely and is
escaping at the bottom of the wide tube, in other words, as soon
as the temperature of the enclosed water in tube C reaches loo**,
/>., the temperature of the steam surrounding it, the mercury in
the tube will be depressed to the level of that in the trough. The
tension of the vapour within the tube, under these circumstances,
is therefore equal to the atmospheric pressure.

If, instead of introducing water into the barometer tube, ether
were employed, and a stream of vapour from boiling ether were
passed through the outer tube, it would be seen that when the ether
within the tube reached the temperature of the vapour from the
boiling ether, namely, 35*, the mercury would again be depressed
to the level of that in the trough ; that is, the tension of the ether
vapour would then be equal to the pressure of the atmosphere. We
see, therefore, that when water is heated to its boiling-point, viz.,
100", the tension of its vapour is equal to the atmospheric pressure;
and when ether is heated to its boiling-point, viz., 35", the pressure
exerted by its vapour is equal to the pressure of the atmosphere.
The boiling-point of a liquid may therefore be defined as the
temperature at which the vapour pressure is equal to the pressure
of the atmosffhere. As soon as this point is passed, the kinetic

Boiling-Points of Liquids 1 1 3

energy of the molecules has been so much augmented by the
supply of external heat, that it is able to overcome the force of
their mutual attractions, and, consequently, the molecules freely
pass away from the surface of the liquid.

As will be seen from the illustrations given, namely, water and
ether, the temperatures at which the vapours of different liquids
exert a pressure equal to that of the atmosphere are widely diffe-
rent This fact will be still more evident from the following table,
giving the temperatures at which the vapour pressure of various
liquids is equal to the standard atmospheric pressure : —

Liquid oxygen -181*

Liquid nitrous oxide .... - 92*

Liquid sulphur dioxide . - 10°

Ethyl chloride + ii*

Carbon disulphide .... 47*

Water loo*

Aniline 182*

Mercury 358*

Since the boiling-point of a liquid is that temperature at which
its vapour tension is equal to the atmospheric pressure, it will be
evident that, if the latter increases or decreases, the temperature
necessary to produce an equal vapour pressure must also rise or
fall ; in other words, the boiling-point of a liquid is dependent upon
the pressure. If a quantity of water, no warmer than the hand, be
placed beneath the receiver of an air-pump, which is then quickly
exhausted, the water will be seen to enter into violent ebullition.
It does this, when the pressure within the receiver is reduced to
the point at which it is equal to the tension of aqueous vapour at
the temperature taken.

For this reason water boils at a lower temperature in high
altitudes than at the sea-level ; and as the vapour tension of water
at various temperatures has been experimentally determined, we
can, by ascertaining the boiling-point of water at any particular
altitude, calculate the atmospheric pressure, and consequently the
height above the sea-level.

Many liquids when heated, especially in glass vessels that have
been carefully cleansed, may be raised several degrees above the
boiling-point without ebullition taking place. The liquid under
these circumstances assumes a pulsating movement, which con-
tinues for a short time, when a burst of vapour is suddenly evolved

114

Introductory Outlines

wiih violence, and the lemperaiure ai once drops tu ihe boiling-^
point The liquid ihen becomes quiescent, and again, as
temperature rises, liie pulsating movement begins, ending once
more in an explosive evolution of vapoui. This successive boiling,
or bumping, is sometimes sufficiently violent to cause the fracture of
the vessel. In order to experimentally ascertain the boiling-point
of a liquid, the thertnomeier, for this reason, Is not immersed in
the liquid, but is suspended in the vapour, ihe temperature of which
remains constant throughout these irregularities in the boiling.

Latent Heat of Vaporisation.— When a liquid Is heated, its
temperature rises, as indicated by the thermometer, until a certain
point is reached (the boiling-point of the liquid), when the con-
tinued application of heat causes no further rise of temperature.
Thermometers placed in the liquid, and in the vapour, indicate the
same temperature and remain constant, and all further applica-
tion of heat is unappreciated by these instruments, and disappears
in changing the liquid into vapour. The heat which in this way is
absorbed during the vaporisation of a liquid, is spoken of as the
lattnt keai of vaporisation ; and the same amount of heat which
thus disappears during the conversion of a liquid into a vapour,
is again rendered sensible when the vapour passes hack into the

The heat which is thus said to become latent, is in reality con-
verted into kinetic energy ; it is expended in imparting to the
molecules the kinetic energy necessary to overcome the attractive
forces operating between them while in the hquid state ; in other
words, it is doing the work of overcoming cohesion (internal work),
and also the external pressure on the vapour (externa! work).

In order that a liquid may pass into a
vapour it is necessary that heat be absorbed.
We have seen (page i lo) that a liquid under-
going spontaneous evaporation becomes colder
(that is, heal is absorbedby the molecules that
are converted into the gaseous slate), and also
that the more rapidly the liquid can be made
to pass into the vaporous condition, without
supplying external heat, the lower will its
temperature fall. Upon this fact depend a
number of methods for the artificial produc-
5 of cold. For example, ether boils at 35", but
■ 5 flask standing

tion of low degrc'

if a small quantity of ether be placed ii

Lattnt Heat of V^orisalioH

I'S

upon a wooden block, upon which a few drops of water have been
poured, and a current of air from a bellows be briskly blown
through the ether (Fig. 13), the temperature of the ether will
fall so rapidly that in a few moments the flask will be frozen to
the block. By the rapid evaporation of liquids with lower boiling'
points, the extreme degrees of cold necessary for the liquefiiction of
■nch gases as oxygen, carbon monoxide, air, &c., are obtained. Thus,
liquid methyl chloride boils at - 23° j by causing it to rapidly
vapotise, its tonperature can be reduced to — 70*. Liquid ethy-

lene in the same way falls to a temperature of - 120', and liquid
oxygen by rapid evaporation gives a temperature as low as -ico*.
The temperature of water, in like manner, may be so lowered by
its own rapid evaporation, as to cause it to freeie. We have already
seen that by reducing the pressure, the boiling-point of a liquid Js
lowered ; if, therefore, a quantity of water be placed in a vacuum,
and methods be adopted to remove the water vapour as rapidly
as it is formed, the water will eater into rapid ebullition. The

116

Introductory Outlinet

evaporalion will therefore proceed so rnpidly, and consequenl^
absoib heal so quickly, that the lemper.-iture of (he baiting liquia
will quickly fall to o* when it passes into the solid st.ile. The
instrument known as Carry's freezing machine depends upon this
principle. The water to be froien is placed in the glass bottle C
(Fig. 14), which is in connection with a metal reservoir R, half
filled with strong sulphuric acid. This in its turn is connected by
i with an air-pump P, worked by the lever M, to which is also
nitached a connecting rod /, so that a stirrer within the reservoir
is kept constantly in motion. As soon as
the apparatus is exhausted (o a pressure of
two or three millimetres, the water begins
rapidly to boil, and as the sulphuric acid
absorbs the water vapour as rapidly as it is
given off, the tempieraiure quickly falls and
the water freezes.

Fig. 15 illustrates another method by
which the same result may be obtained.
A lall glass vessel is exhausted by means of
an ordinary air-pump, and water is allowed
slowly 10 enter from a stoppered funnel,
upon the end of which is secured a short
Siring. At the same time strong sulphuric
acid is admitted by the second funnel, and
caused 10 flow down aglassrod, round which
is wound a spiral of asbestos thread. The
acid at once absorbs the aqueous vapour
from the evaporating water, the tempera-
lure of which, therefore, falls below the
freezing -point, and it solidifies as it Hows
3 over the string into the form of an icicle.

' Just as diminution in pressure lowers the

'''c- "S' boiling-point of a liquid, so increased pres-

sure raises the boihog-point. If water be
heated in a closed iron vessel, as in a high-pressure steam boiler,
the pressure caused by its own vapour raises the boiling-point
many degrees above loo". There is a definite temperature, how-
ever, for every hquid, beyond which the liquid state is impossible,
whatever may be the pressure : that is to say, the liquid when
heated beyond this fixed point passes into the gaseous state, how-
sver great the pressure may be. This temperature! is the critical _

Vapaur^Pressures of Solutions 117

Umperaturt (see page 77). If a liquid be heated in a sealed and
strong glass tube, as the critical temperature is approached, the
surfoce of the liquid gradually becomes ill -defined, and finally the
tube is completely occupied by transparent vapour. On again
cooling, as soon as the critical point is passed, the contents of
the tube again separate into two distinct layers consisting of liquid
and gas.

Vapoor-Pressupes of Solutions. —The boiling-point of a liquid
is modified by the presence in the liquid of dissolved substances.
If the substance in the solution be less volatile than the liquid, the
boiling-point is raised. Thus, while the boiling-point of pure
water (under the normal atmospheric pressure) is loo^ the tem-
perature at which saturated aqueous solutions of salts boil, is
considerably higher, thus : —

Containing Grammes of

Water Satormted with

Salt io 100 Grammes
of Water.

Boiling-point.

Sodium chloride .

41.3

io8.4*

Potassium nitrate .

• 33S.I

1 1 5.9'

Potassium carbonate

205.0

I33.0'

Calcium chloride .

• 325.0

179.5°

The temperature of the steam of these boiling solutions, as
ascertained by suspending a thermometer in the vapour, appears
to be the same as that from pure water, as the thermometer in
all cases indicates loo*'. In reality, however, the temperature is
higher, although not so high as that of the boiling liquid. The
reason that the thermometer indicates 100° in all cases is because
the water vapour continually condenses upon the bulb of the
instrument, covering it with a film of pure water, which boiling
off from the bulb indicates only the boiling-point of the pure
liquid. By special arrangements this condensation may be pre-
vented, when it has been shown (Magnus) that the temperature
of the vapour, from such boiling solutions, rises as the solutions
become more concentrated — that is, as the temperature of the
boiling liquids rise. It has been already explained that the boil-
ing-point of a liquid is that temperature at which the vapour
tension is equal to the atmospheric pressure ; since, then, the
presence of dissolved substances raises the boiling-point, it
therefore lowers the vapour-pressure, for (in the case of aqueous
solutions) when the temperature has reached too* the vapour-

Introductory Oullinei

tl8

prc&sare ii still below thai of the atmosphere, for the liquid does
not enter into ebullition at that temperatuie. By measuring
vapour' pressures of solutions al a constant temperature, instead
of measuring the temperature at a ronslaol pressure {i.t., the
boiling-point), the following general laws have been estab-
lished :~

I . The rtlatioH bttween the quantity of <i suhlnme in
solution and the diminution of the vapour -pressure beh-ai
that of the pun solvent., is the same at all temperatures.

1. The diminution of the vapour-pressure of a liquid, fy

a dissolved substance, is proportional to the amount of the

substance in solution {provided the substance itself exerts

HO appreciahle vapour^ressure at the temferatuie of the

, experiment).

3. The molecular loviering of vapour -ptessure by chemi-
cally similar substances is constant; that is to say, solu-
tions eontaining one molecular weight in grammes {one
gramme-molecule) of such substances in equal volumes of
Ike solvent, give rise to the same diminution of vapour
pressure,

4. The relative lowering of vapour-pressure is propor-
tional to the ratio 0/ the number of molecules of the dis-
solved substance, to the total number of molecules in the
solution, i.e., the sum of the number of molecules of the
dissolved substance and of the solvent.*

Upon these considerations it becomes possible, by means
of the lowering of the vapour- pressure, lo find the molecular
weigiil of a substance that is capable of being dissolved
in a volatile liquid.
The Passage of Liquids Into SoUds.— Most liquids,
yiG.t6. "*'*" cooled 10 some specific temperature, pass into the
solid state ; the lemperaiure at which this change takes
place is termed (he solidifying point. Generally speaking, the
icinpcralure at which a liquid solidifies is the same as that
at which the solid again melts ; but as the solidification of a
liquid is subject to disturbances from causes that do not affect
the melting-point, this is not always the case. Thus, water
may be cooled many degrees below 0° if it be previously freed
from dissolved air, and be kept perfectly still. This super-
cooling of water may readily be illuslraied by means of the

' GiDcpt in ihe cue ij decirolyles. Sec pa^ 96.

Solidifying Points of Liquids ii$

apparatus represented in Fig. t6. This consists of a thennomeier
whose bnlb is enclosed in a larger bulb containing water, which
before the bulb is sealed at a, is briskly boiled to expel all the air.
When the instrument is immersed in a freezing mixture the tem-
perature of the water may be lowered to - 15° without congeata-
tion taking place, but on the slightest agitation it ai once solidifies
and the temperature rise* to o'. (l is on account of this property
of water to suspend it) solidification, that in deteimining the lower
fixed point of a thermometer, the temperature of melting ice, and
not that of freezing water, is made use of.

Many other liquids exhibit suspended solidification to a very
high degree ; thus glycerine may be cooled to - 30* or - 40° with-
out solidifying, but if a crystal of solid glycerine be placed in the
liquid the entire mass freezes, and does not again melt until a
temperature of 15. s' is reached.

Chan^ of Toltune on Solldlfleatlon.— Most liquids, in the
act of solidifying, contract; that is to say, the solid occupies a smaller
volume than the liquid. Consequently the solid is specifically denser,
and sinks in the liquid. Thus 100 volumes of liquid phosphorus
at 44* (the melting-point) when solidified, occupy only 96.7 volumes.
Water expands upon solidification, hence ice is relatively lighter
than water, and floats upon ihe liquid. The reverse change of
volume accompanies the change of state in the opposite diieciion.

BfTeot of Pressure upon the Solidifying Point of Liquids.
— In the case of liquids that contract ujKin solidification, increased
pressure raises the point of solidification, and consequently raises
the melting-point of the solid. The effect, however, is extremely
small : thus the solidifying point (and melting-point) of spermaceti
under the standard atmospheric pressure is 47.7*, while under a
pressure of 156 atmospheres it is laised to 50,9°.

With liquids that expand on solidificaiian, increased pressure has
the opposite effect, and lowers the solidifying point. Thus, water
under great pressure may be cooled below o' and still re-nain liquid ;
and in the same way, ice may be liquefied by increased pressure
without altering its temperature. In the case of water it has been
found that an increased pressure of n atmospheres, lowers the soli-
difying point by o.ao74«° ; hence under a pressure of 135 atmos-
pheres, the freeiing-point of water (and the melting-point of ice)
is lowered 1*. This lowering of the melting-point of ice underpres-
sure may be illustrated by the experiment represented in Fig. 17,
Over a block of ice is slung a fine steet wire, to which are hung a

I20 Introductory Outlines

Qumbet of weights. The pressure thus exerted upon the ice, by
lowering the melting-point, causes the ice to liquefy immediately
beneath the wire, which therefore gradually cuts its way through
the block. But as the wire pa.sses through the mass, each layer of
water behind it, again resolidi6es, being no longer subject to the
increased pressure [ hence, although the wire cuts its way com-
pletely through the ice, the block still remains intact.

Latent Heat of Fusion.— \Vhen a liquid, at a temperature
above its solidifying point, is cooled,
•" a thermometer placed in the liquid

j indicates its loss of heal until solidi-
ficalion begins. At this point the
temperature remains constant until
solidification is complete, when the
thennometcr again begins to fall.
And again, when a solid, at a tem-
perature below its melting -point, is
heated, its temperature rises until
the melting begins, but no further
rise of temperature takes place by
the application of heat, until lique-
faction is complete. The sensible
heat that so disappears during
fusion is spoken of as the laUnt
heat of fusion. Just as in the pas-
sage of liquids into gases, this so-
called latent heat represents heal
that has ceased to be hsat, but which
Pic; i-j_ is converted into kinetic energy that

is taken up by the molecules : when
the liquid passes back into the solid state, this energy is again
Iransfomied into sensible heal.

The fact that heal is thus changed into energy, and so rendered
insensible to the Ihetmometer, may be seen by adding boiling water
to powdered ice, A thermometer placed in ice indicates the tem-
perature o°, and although boiling water is poured upon it, so long
as any ice remains unmelted no rise of temperature of the mixture
results, the heat contained in the boiling water being expended in
doing tlie work of liquefying the ice, and converting it into water at
o°. When such an eiperiment is made more exactly, it is found that
1 kilogramme of water at 80.15°, when mixed with 1 kiloKrammc of

Solidifying Points of Liquids I3i

ice at o*, gives i kilogrammes of water at o". That is to say, the
amount of heat contained in a kilogramme of water at 80.25*, '■
exactly capable of transfomiing an equal weight of ice at o* into
water at o*.

As the heat required to raise the temperature of i kilogramme of
water from o" to 1° is the unit of heat, or major calorie, we say that
the latent heat of fusion of ice is B0.15 thermal units, or calories.

During the so 1 id i Re at ion of a liquid, the latent heat of fusion is
attain given out The solidification, therefore, only takes place
gradually, for the heat evolved by the congelation of one portion,
is taken up by the neighbouring particles, whose solidification it
thereby retarded until this heat is dissipated. In the case of super-
cooled liquids and super- salt) rated saline solutions, the solidifica-
lion take*' place more suddenly, and the evolution of the latent heat
is therefore manifest by a rise of temperature.

Street of Substances In Solatfon upon the Solidifying: Point
of a liquid.— It has long been known, that a lower degree of cold
is necessary to freeze salt water than fresh ; and also that the water
obtained by remelting ice from froien sea water, is so little sail as
to be drinkable. Careful exfrerimeots have shown that when an
aqueous solution of a salt is frozen, pure ice alone separates out,
provided the solution is sufficiently dilute to prevent the dissolved
sail from crystallising out on account of the reduction in tempera-
ture. This also holds in the case of all other solvents that are
capable of being solidified, the pure solidified solvent alone sepa-
rating when the solution is frozen. The effect of dissolved sub-
stances in lowering the solidifying point of the solvent was first
discovered by Blagdeu (178S), who formulated the law that the
depression of the freezing-point of aqueous solutions of ihe same
substance, was proportional to the strength of the solution. By
referring the lowering of the solidifying point to quantities of the
dissolved substances that were in molecular proportions, instead of
10 equal weights, modem physicists have established Ihe following
genera] law; Solutions containing in equal volumes 0/ the solvent,
quantities of dissolved substances proportional to their molecular
weights, have the same point of solidification.*

The relations thus established between the molecular weight of
a compound and its influence in lowering the solidifying point of
a solvent, furnishes a method for the determination of the molecular
weight of a substance.

* EieeM in ibc cue of electrolyte*. See page 96.

CHAPTER XIV
SOLUTION

A SOLUTION may be defined as a homogeneous mixture of either a
gas, a liquid, or a solid, with a liquid, this liquid being termed the
solvent,*

Substances that are capable of forming such homogeneous mix-
tures with a solvent, are said to be soluble in that liquid. The
solution of matter in its three states will be treated separately.

I. Solution of Gases in Liquids.— When a gas is dissolved
by a liquid, the liquid is said to absorb the gas, and although it is
held that most liquids are capable of absorbing most gases to a
greater or less degree, most of the investigations in this direction
have been made with the two liquids, water and alcohol, by Bunsen.

The quantity of a gas which a liquid is capable of absorbing
depends upon four factors — (i) the specific nature of the liquid ;
(2) the nature of the gas ; (3) the temperature of the liquid ; (4)
the pressure.

(i.) The influence of the solvent may be seen by a comparison of
the quantities of the same gas which equal volumes of water and
of alcohol are capable of dissolving, thus —

Tcx> volumes of water at o* dissolve 179.6 volumes of carbon dioxide,
while ioo ,. alcohol ,, 432.9 m ••

(2.) The various quantities of different gases which the same
liquid viiW absorb are found to extend over a very wide range,
thus —

100 volumes of water at o" dissolve 4 114 volumes of oxygen,

while 100 ,. ,, ,. 1 14800.0 ,, ammonia.

* Mixtures of gases are sometimes regarded as solutions, one gas being said
to be dissolved in the other. Gases also are sometimes spoken of as dissolving
liquids and solids, when liquid and solid substances directly vaporise into
them.

Henrys Law

123

(j.) The volume or any gas which a liquid can absorb, diminishea
with rise of temperature. This will be seen from ihe ToDowing
tabic, where the volumes of different gases are given which loo
volumes of wa.(er will absorb at various temperatures.

Cuboo Dioiidc

Nitrou Olid*.

OMfKEa.

":«

'79-6

130. 5

4.11

'449

109.3

3.6a

'79

■0

..8.4

91-9

3.aS

1.60

90..

67.0

■-.,

1.40

It was at one time believed that the solvent power of water ibi
hydrogen was the same at all lempsTatures between o* and 25*.
Recent expetiments have shown, however, that there is no excep-
tion to the general law in this case ; thus it has been found that
100 volumes of water —

At o* dissolve 3.1 j volumes of hydrogen.

At 5* „ 2.06 „

At to* „ 1.98 „ „

At 20° „ 1.84

When a solution of a gas in water is heated, the gas being leu
■oloUe at the higher temperature is expelled, and in most cases
the whole of the ijas is driven off at the boiling leinperatuie.
Thit, however, is not invariably the case ; for example, the solution
of hydrochloric acid in water, when boiled, will distil, without further
evolution of gas, when a solution of defmite strength is reached
(see Hydrochloric Acid).

(4.) The influence of pressure upon the volume of a given gas
which a liquid can absorb, was discovered by Henry (1803), and is
known as Henry's law, namely, T/ie velum* of the ^as absorbed by
a liquid is directly proportional to the pressure of the gas. If the
pressure be doubled, the same volume of liquid will dissolve twice
the volume of (he gas, the volume in each case being measured
at o* and 760 mm. But since, according to Boyle's law, the
volume of a gas is inversely as the pressure, this law may be thus
stated : A given volume of a liquid will absorb the same volunu 0/
m gai at all pressures.

124 Introductory Outlines

Thus, i/ ic» volumes of waler at o* dissolve J.03 volumes of
nitrogen, under the standard atmospheiic pressure (ihe
the gas being measured at o* and 760 mm.), under iwice this
pressure, i'.^., two atmospheres, the same volume will absorb twice
the volume of nitrogen, vii., 4.06 volumes measured at o" and 760
mm. But 4.06 volumes of gas measured at o' and 760 mm. occupy
1.03 volumes under a pressure of two atmospheres, therefore the
liquid dissolves the same volume of compressed jjas as of gas
under ordinary pressure.

Henry's law is sometimes stated in a slightly altered form. If
the quantity of gas present in a unit volume of both ihe liquid and
the tpace above it, be called the canftntr»/ioii of the gas, iben the
law may be expressed by saying that uiuler aJi pressures, Ihe ratil
0/ Ihe concentrations oftheg<ts in the liguid,and in Ike space
it, remains comtanl. This ratio is termed the coefficient 0/
bility, or the " solubility " of the gas in the particular liquid.

The term coefficient of absorption, first introduced by Bunsen, 1:
the volume of the gas measured at 0° and 760 mm., which is
absorbed by 1 cubic centimetre of a liquid at the same tem-
perature and pressure ; and it is therefore simply Ihe volume
repieseniing the "solubility" of the gas, reduced to o'.

The solubility of gases in liquids is measured by agitating a
known volume of liquid with a measured volume of the gas, under
determinate conditions of lempeiature and pressure. The apparatus
employed by Bunsen, and known as Gtiiisen's absorptiometer, is
shown in Fig. 18. It consists of a graduated tube «, into which
known volumes of the gas and liquid are introduced. The lower
end of this lube is furnished with an iron screw, by means of
which il can be securely screwed down upon an indiarubber pad,
in order to completely close the tube (seen in the side figure).
The tube containing the gas and liquid under examination, is
lowered into a tall cylinder g g, in the bottom of which is a
quantity of mercury, The cylinder is then filled with water, and
the cap p screwed down. The thermometer k registers the tem-
perature. The apparatus is then briskly shaken, in order that the
liquid in the eudiometer may exert its full solvent action upon the
gas, and on slightly unscrewing the tube from the caoutchouc pad,
mercury enters 10 take the place of the dissolved gas. The tube
is again closed and the shaking repeated, and these operations are
continued until no further absorption results. Finally, the volume
of gas is measured, (he temperature noted, and the pressure

Introductory Oullims

1 2d

ucert^ined by reading the position of the mercury within the tube,
and deducting the heighi of ihe column from b to the surface of
the mercury a. from the barometric pressure at the time of making
Ihe experiment. The temperature of the water in the cylinder
may be varied, and (he coefficient of absorption at different tem-
peratures can thus be determined.

Fig. 19 represents a more modem absorptiometer, being a modi-
fied form of Heidenhaia and Meyer's apparatus. In this instni-
ment the measuring tube and the absorption vessel are separate, and
' it admits of the use of much larger volumes of liquid. By m^
of the three-way cock a, the ras to be experimented upon ii

troduced into A by first raising and .
ihen lowering B ; and the volume ii
' measured when the levels of the mer
cury in A and B are coincidenL By
means of the three-way cock 6, the
vessel C, of known capacity, and which
is connected with j4 by means of a flex-
ible metal capillary lube, is filled with
the desired liquid. The vessels A and C
are then put into communication, a,
by rising B and opening the tap c
deRnite volume of the liquid is run c
into a measuring vessel, which repre-
sents the volume of gas that enters.
The gas and liquid are then thoroughly
agitated, after which the gas is passed
b.ick into A by lowering S, and, when
A and C are in communication, opening
the tap c beneath mercury. By mea-
suring the diminution in volume suffered
by the gas, the volume absorbed by the known volume of liquid is
obtained. The measuring tube and absorption vessel are kept
constant at any desired temperature, by surrounding them by
water, or with vapours at known temperatures.

Solubility of Mixed Gases. — When two gases are mixed
together, the pressure exerted by each is the same as would be
exerted if the other were absent, and the entire space were
occupied by the same mass of the one. Tlius, if a mixture 0
two gases are in the proportion of two volumes of one and on
volume of the other, Ihe pressure exerted by th> one present n

The Law of Partial Pressures 1 27

(ar£^er proportion will be twice as great as that of the other ; this
pressure is termed the partial pressure of the gas under the
circiunstances, and obviously the total pressure of the mixture
will be the sum of the partial pressures of the constituents. As the
solubility of a gas in a liquid is proportional to the pressure, the
solubility of the gases in a gaseous mixture will be influenced by
the proportions in which they are present in the mixture. This
is known as Dalton's law of partial pressures, which may be thus
stated : The solubility of a gas in a gaseous mixture is proportional
to its partial pressure. For example, the atmosphere consists of
a mixture of oxygen and nitrogen, in the proportion of four volumes
of nitrogen to one volume of oxygen (in round numbers). The
partial pressure exerted by the oxygen is therefore only one- fifth of
the total atmospheric pressure, and consequently the amount of
oxygen which a given volume of a liquid is capable of dissolving
from the atmosphere, is only about one-fifth of that which it will
absorb from pure oxygen — in other words, will be one-fifth the
absorption coefficient of oxygen for that liquid.

The application of the law of partial pressures will be seen in
the solvent action of water upon the atmosphere. Taking the
coefficients of absorption of oxygen and nitrogen for water as
given by Bunsen —

Oxygen = .04114 ; Nitrogen = .02035,

and the proportion of oxygen to nitrogen in the air as one to four,
by volume, we get —

'— "^ « .00823, and -^°3iJi_4 ^ ,01628,

for the number of cubic centimetres of oxygen and nitrogen which
will be dissolved from the atmosphere, by i cubic centimetre of
water at o^

One hundred volumes of water, therefore, will dissolve 2.451
volumes of air, of which .823 volumes is oxygen and 1.628 volumes
is nitrogen ; and if this dissolved air be again expelled from the
water, by boiling, the air so obtained will contain oxygen and
nitrogen in the proportions —

Oxygen 33.6

Nitrogen 66.4

loao

128 Introductory Outlines

If a mixture of oxygen and nitrogen in this proportion be once
more dissolved in water, since the percentage of oxygen has risen
from 20 to 33.6, and the partial pressure proportionately increased,
the mixture of the two gases that will be dissolved, will be still
richer in oxygen ; and after solution in water for the third time the
boiled-out air will be found to contain as much as 75 per cent
of oxygen. It will be obvious that the partial pressure which de-
termines the extent to which the separate gases in a mixture are
dissolved, is not represented by the proportion in which the gases
are present before solution, but that in which they exist in the
gaseous mixture after the solvent has become saturated.

Henry's law does not hold good in the case of such very soluble
gases as ammonia, hydrochloric acid, &c These gases appear to
enter into a true chemical union with the water, and in most of
these cases, the act of solution is attended with considerable evolu-
tion of heat. In some of these instances the deviation from the
law diminishes with rise of temperature ; thus at temperatures
above 40** the absorption of sulphur dioxide obeys the law, while
in the case of ammonia conformity to the law is observed at 100°.

The gases dissolved by a liquid are not only expelled by boiling,
but are withdrawn by placing the solution in a vacuum. This, in-
deed, follows from Henry's law, for if the solubility is proportional
to the pressure, and the pressure is nil, the amount of gas dissolved
must also be nil.

The molecules of gas dissolved by a liquid, are regarded as being
held by some attractive forces exerted between them and the mole-
cules of the liquid ; in the course of their movements, gas molecules
are constantly leaving and entering the liquid, and equilibrium is
established when the same number enter and escape from the
surface of the liquid in the same time. When the pressure is in-
creased, more gas molecules strike the surface in a unit of time, and
consequently a greater volume is absorbed. When a solution of a
soluble gas is placed in an atmosphere of another gas, the dissolved
gas continues to leave the liquid, until equilibrium is established
between the pressure exerted by the gas so leaving, and the amount
remaining in solution. For this reason a solution of ammonia
when left exposed to the air, rapidly becomes weaker, owmg to
the escape of the dissolved gas into the atmosphere. This process
is accelerated if a stream of less soluble gas be caused to bubble
through the solution.

Solubility of Liquids in Liquids.— The solubility of liquids in

Solution 1 29

liquids may be divided into two orders. First, cases in which the
degree of solubility of one in the other is unlimited ; and, second,
cases where the extent of the solubility is limited. Two liquids
whose solubility in each other is unlimited, are said to be misdble
in all proportions ; thus alcohol and water are capable of forming a
homogeneous mixture when added together in any proportion.

In the second class, where the solubility of two liquids for each
other is limited, it is found that each liquid is capable of dissolving
some of the other. Thus, if equal volumes of ether and water are
shaken together, the liquids will afterwards separate out into two
distinct layers, one floating upon the other. The heavier layer at
the bottom is an aqueous solution of ether, containing about 10 per
cent, of ether ; while the upper liquid is an ethereal solution of water,
containing about 3 per cent of water. The presence of ether
dissolved in the water may be proved by separating the two layers
and gently heating the aqueous liquid in a small flask, when the
dissolved ether will be expelled and can be inflamed* The pre-
sence of the water, in the ether, is also readily proved, either by
introducing into the liquid a small quantity of dehydrated copper
sulphate, which will rehydrate itself at the expense of the water in
the ether, and be changed from white to blue ; or by placing in the
ethereal liquid a fragment of sodium, which decomposes the dis-
solved water with the liberation of hydrogen.

In most cases the solubility of liquids in liquids is increased by
rise of temperature, although in some it is decreased.* One notable
instance of the latter effect of rise of temperature is seen in the case
of a mixture of triethylamine and water. If equal volumes of these
liquids be mixed together, at a temperature below 20*, complete
solution takes place, and a single homogeneous liquid results. On
wanning the solution, it becomes turbid, owing to the separation of
the liquid into two portions, which ultimately settle out as two dis-
tinct layers. As the temperature of the solution approaches 20% the
liquid becomes very sensitive to a slight rise of temperature, the
heat of the hand being sufficient to cause turbidity in the solution.

Solution of Solids In Liquids.— When a solid is immersed in
a liquid, the forces which oppose the solution of the solid are the
attractive forces exerted by the molecules of the solid upon each
other, and those of the liquid upon themselves. The forces that
tend to effect solution are the attractive forces exerted by the

* See Experiments Nos. 195 to 130, "Chemical Lecture Experiments," new
ed. . by the author.

130 Introductory Otttlittes

molecules of ihe liquid upon Ihe molecules of ihe solid, and ll
kinetic energy of ihe molecules.

By [he action of the liquid, the attractive force between the mol
cules of the solid is diminished, and those molecules nearest
surface, by their owo energy and the attraction exerted by
liquid, pass into and through the liquid. In the c
movements, these sometimes return to Che solid, and a conditi
of equilibrium is finally established, when as many molecules 1(
the surface of the solid as return to it in a given time. Under thi
circumstances Ihe solution is said to be la/urii/eii vi\\h respect
the particular solid.

Saturated Solutions.— The amount of solid held in solutii
the liquid when the latter is saturated, depends upon the tempei
ture, for if the temperature be raised, the kinetic energy of tl
molecules is increased, and consequently an increased number '
become detached from the solid. As a general rule, therefore,
solubility of a solid in a liquid is increased by rise of temperatui
A saturated solution at a given temperature may be obtained
two ways, namely, by maintaining the liquid at that temperatui
and stirring into it an excess of the solid, until no more of it
solved ; or by dissolving a larger quantity of the sohd at a higher
temperature, and allowing the solution to stand in contact with an
excess of undissolved solid, until the temperature falls to the specified
point During the cooling, the amount of solid that the liquid had
taken up, over and above that which was necessary to saturation
at the lower temperature, is deposited.

Supersatiu-ated Solutions.— The condition of saturation can
only be determined when an excess of the undissolved solid is
present in the hquid ; for when a solution, which is not in contact
with any of the undissolved solid, is brought to the point of satura-
tion, either by cooling or by evaporation of the liquid, it frequently
happens that no separation of solid takes place. Solutions can in
this way be obtained, in which a larger amount of the solid remains
dissolved at a given temperature, than corresponds to the amount
required to form a saturated solution at that temperature : such
solutions are said to be supenaturaUd. If into such a supersatu-
rated solution, a fragment of the solid be introduced, molecules of
the dissolved solid at once deposit themselves upon it, and this
separation of the dissolved substance continues, until the solution
teaches a state of concentration corresponding to its normal satura-
tion at the particular temperature- The introduction into 3 super-

SoluticH

131

iatUTat«d solution of a particle of the solid, in respect to which thtt
solution i> supersaturated, is the only sure method of bringing
about the separation of the excess of the dissolved aubitance ; such
a solution, therefore, may be preserved for an indefinite time, if it be
kept in an beimetically sealed vesseL Minute particles of the solid.

■»

■'i

ijisi.

'^'

-rT^

''fi

iii

-i

o' JO' MO' to" *o" go' atf 70' 90' ao' ioo'
Tmihp emCurt .

towards which a solution is supersaturated, that might be present
in the dust of the air, bdling into such a solution, will detemune
the deposition of the dissolved solid.
The phenoKienon of supetsaturaiion is strictly analngoiu to that

132

Introductory Outlints

of supercooling, or the suspended solidification of fused solids, x
is exhibited most readily by sails containing water of cryslallis;
such as sodium acetate, NaCsH^Og.SHgO ; sodium Ihiosulphat
NajS,Oj,6HjO i and sodium sulphate, NajSO„10H,0. Thus, i
a smaJl quantity of water be poured into a flask nearly filled n' *'
crystallised sodium thiosulphaie (the so-called " Hypo '
phaiographer), and the mixture be warmed by immersio:
water, the whole of the salt will dissolve ; and if the solution \
then allowed to cool undisturbed, it will assume the ordinary W
peralure, and still remain fluid. If into this supetsaiu rated solutio^
a crystal of the sail be dropped, the excess of salt present in solutin
beyond the normal quantity for saturation al that temperature, w'
crystallise out, and so great is this excess thai the contei
flask will appear practically solid.

The different solubility of various solids in the same liquid, a:
ihe increased solubility by rise of temperature, is graphically shol
in Fiy. 20, where the solubility curves of five salts in wale
represented The abscissae indicate temperatures, and the
nates the number of parts of salt dissolved by too parts of wa:

Thus at 0°, 100 grammes of water will dissolve 35.7 parts «
sodium chloride, and as the lemperalure is raised, the quantity 0
salt which the water will dissolve very slowly increases, Lutil at
the amount is nearly 40 parts : sodium chloride is therefore n
equally soluble in water at all temperatures.

In the case of potassium nitrate, 100 grammes of water at o
only dissolve 13,3 grammes of the solid, but as the tempeiatut
rises the amount capable of being dissolved by this quantity d
water very rapidly increases, until at 75° 150 grammes are dissolve
Lead nitrate is more soluble than potassium nitrate between o'
JO*, but above this point it is not so soluble as the other, hence l]
two curves intersect al that lemperalure. The solubility of sodiuti
sulphate in water is anomalous. The solubility at first lapid^
increases with rise of temperature hasa 0°, and reaches a 1
at a point between 33° and 34°, when it gradually diminishes u
fiariher rise of temperature. This behaviour is in reality due t(
fact that we are not dealing with one and the same substanc
throughout the experiment. Sodium sulphate exists as a solid ii
at least three forms, namely, the dccahydrale, NaiSO,,10H^
(ordinary Glauber's salt); the hepiahydrate, Na^SOuTHjO; a
the anhydrous salt, Na^O(. The first portion of the curve (Fig. 1^
represents the solubility of Glauber's salt ; thus, at 20* such 1

SotufioH

"33

amoant of thit decahydnted salt is dissolved, that the solution
contain* 30 grammes of NOfSO, in loo grammes of water. The
solubility of this salt rapidly rises until 34° is reached, at which
temperature the salt melts, and is then miscible with water in all

I-

r—

>*!

„

-t~

Temperature-
Fio. 81.

proportions. The melted salt contains 78.8 parts of Na,SO, in
■00 parts of water, which is indicated as ihe highest point npon

14J

180

The decahydrated salt is unable to exist, as such, at temperatures
higher than 34*> and when ihe melted salt is heated above this
p(Hnt it is converted into the anhydrous salt, and water satu-
rated with the salt ; therefore above 34' it is not possible to have
a solution of sodium sulphate in contact with solid Glauber's
salt. It can, however, be in contact with ihe anhydrous salt, and
the second portion of Ihe curve expresses the solubility of this

134 Introductory Outlines

compound in water, which slowly diminishes a

ihe temperatm

Osmotic Pressure, —When a dilute solution of a substance
water is placed in a vessel dosed with an animal membrane,
as bladder (m, Fig. 22), and the who
immersed in water to such a depth
the level of the water outside is coincident
with that of the solution within, it is found
that the liquid in the inner vessel in-
creases in volume, as seen by the fact thai
il gradually rises rn the narrow stem of
the apparatus. Water, therefore, from the
outer vessel must have passed in through
the membrane, and inasmuch as some of
the dissolved substance is found in the
water of the outer vessel, some of the
I solution must at the same time have made

^^^Ar^ its escane through the membrane. After

^^9^1^ the liquid has risen to a cerlnin height in

IvvH "'^ narrow lube, it again begins to fall, as

B|FhH the contained solution continues to pene-

^B^^B^r~*' trate the membrane. This process is
^S^^^K/^^^^^ known as enrloimose, and the instrument
^H^J^^^B^Bp described is called an endosmomtifr,
^^^^^^^^^^ Many attempts were made to establish

Pio. 03. general relations between the height to

which the hquid rose in the narrow tube,
and the quantities of substance In the solution, but it was found
impossible 10 obtain accurate or comparable measurements, foi
not only were the results disturbed by the effect of the constantly
changing pressure upon the rale at which the dissolved substance
1 through the membrane, but different animal membranes
yielded different results.

Semipermeable Membranes.— It was first discovered by
Traubc (1867), and afterwards extended by PfefTer (1877), that
artificial membranes, or pellicles, could be obtained, which, while
allowing of the passage of water through them, Just as in the case
of animal membranes, unlike these materials, they offered a perfect
barrier to the passage of many substances in solution in the
Such pellicles are known as semipermeable membranes.
material ihftt has been found most suitable is precipitated copper

^Bdrtfi^

The
'PPer J

Osmotic Prtssure

'3S

fcmcjnnide. If a >oluiioD of copper ntphate (CuSOJ be brought
cautiously in contan with a solution of potassium ferrocyanide
(KfFcfCN^Xat the point when the two liquids meei,a film or pellicle
of precipitated copper ferro-

of this extremely fragile mem-
brane, PfefTer devised the plan
of precipitating it within the
walls of a vessel nude of un-
glazed porcelain. A small clay
cylindrical celt, after thorough
cleansing, wasfUledwithadiluie
solution of potassium ferro-
cyanide, and immersed in dilute
copper sulphate. As these solu-
tions entered (he pores of the
day, and there met, a mem-
brane, consisting of copper
ferrocyanide, was formed within
the walls, which, under these
circumstances, was sufficiently
strong to withstand a pressure
of 5 or 6 atmospheres.

If such a cell, furnished with
a semipermeable membrane, be
employed as an endosmometer,
and a dilute solution, say of
sugar, be placed within the
apparatus, which is then im-
mersed in water, it is found
that the liquid rises in the
narrow tube to a certain height .
above the level of the water in
the outside vessel, and remains
stationary. Water passes
through the membrane, but no
dissolved substance passe* out f ,g. ,3.

Ai first more water penetrates

inwards, than passes out, hence the increased volume of liquid in
the cell ; but when a certain pressure is reached, represented by

136

Introductory Outlines

the height to which the liquid rises in the narrow lube, equilibrium
is established, and water then passes in each direction at
rales. The pressure at which this equilibrium is established is
the osmotic presiuri of the solution.

Fig, 23 shows the apparatus employed by Pfcffer. >
porous cell, in ihe walls of which the semipermeable membrane S
predpitaied. Into this are cemenied the glass tubes v and i
latter being attached, in the manner indicated, lo a mercury tr
meter, m. When the cell containing a solution is immersed in n
the increased volume of the contained liquid thai results, cau
compression of Ihe air enclosed in Ihe upper pari of the apparatU
which consequently drives up the mercury in the lit
which Ihus afTords a means of measuring the osmotic pressure o:
the solution under examination.

The following laws in relation to osmotic pressure have been
established : —

1. Temperature and concentration being the same, difTen
substances when in solution exert different pressures.

2. For one and the same substance, al constant temperature, t
pressure exerted is proportional to the concentratio

3. The pressure for a solution of a given concentration is pro-
portional to the absolute lemperaiure,* the volume being kept
constant

4. Equimolecular quantities of different substances {i.t
ties in the ratio of their gramme .molecule weights), when dissolve
in the same volume of solvent, exert equal pressures a
temperalure.+

The analogy between these laws and those relating lo gasea
pressure is very close. Thus Ihe second statement correspond!
with Boyle's law, when we consider the term concettlralioH t
denote the quantity of gas, thai is, the niunber of molecules, in a
given space ; for if the number of molecules in a unit space be
doubled, the gaseous pressure is doubled, and if the number of
molecules of dissolved substance in a given volume of water be
doubted, the osmotic pressure is doubled.

-9^

g kept I

e san^^^l

t This is
Into <Jinplei
Sucbbodirs

<K lempoaMn

1 1 ibe number of degrees above — 373' C

Imion, I

«e96 I

Osmotic Pressure 1 37

The third statement corresponds with the law of Charles : the
volume of a gas is proportional to the absolute temperature ; or, if
the volume be maintained constant, the pressure exerted by a gas
is proportional to the absolute temperature.

Osmotic pressure, therefore, just as gaseous pressure, increases
with rise of temperature and diminishes with fall of temperature.

Again, in the last of these laws, we see the extension of Avogadro's
Hypothesis into the region of solution. Avogadro's hypothesis
states that equal volumes of all gases contain (under similar con-
ditions) an equal number of molecules ; that is to say, an equal
number of molecules at equal temperatures exert the same pressure ;
but an equal number of molecules of different gases represents an
amount of the gases in the ratio of their molecular weights, hence
Avogadro's hypothesis may be stated : equimolecular quantities of
gases at the same temperature exert equal pressures ; and this
statement, as we have seen, is only true of molecules which do
not dissociate when they pass into the gaseous state.

This close analogy between the gaseous laws and those regulat-
ing the behaviour of substances in dilute solution, is explained on
the assumption that the molecules of the dissolved body in a dilute
solution, are so far apart that their mutual attractive forces are
reduced to a minimum, just as they are in the case of gaseous
molecules ; and that only such properties are exhibited by them,
as depend upon their number in a unit space. Further, it has
been shown in the case of a dilute solution of sugar, that the
osmotic pressure (experimentally determined) is the same as the
gaseous pressure that would be exerted by the weight of sugar
present in the solution, if it were converted into gas, and made to
occupy the same volume as that occupied by the solution at the
same temperature ; hence the general statement that the pressure
exerted by a substance in dilute solution (its osmotic pressure) is the
same as would be exerted by the same amount of the substance if it
existed as gaSy and occupied the same volume at the same temperature,

Difftision Of Dissolved Substances.— If a quantity of a soluble
solid substance be placed at the bottom of a vessel, which is then
filled with water, the solid dissolves, and a layer of a strong solution
is formed at the bottom. In time, however, the dissolved substance
gradually diffuses throughout the liquid. This process of difRision
may be illustrated by means of the experiment represented in
Fig. 24. At the bottom of the tall cylinder is placed a layer of
a strong solution of ferric chloride, and upon this is carefully

I.l«

Introductory Out lit ts

poiireil a quantity of waier until the cylindci is nearly lull. Upon [I
top of the water is then floated a solution of potassium thiocy;
in alcohol, and the whole is allowed to remain undisturbed,
ferric chloride will gradually diffuse up into the water, and thi
solved ihiocyanate will diffuse down, and at the poiti! where
salts meet ihey will interact chemically upon each, giving i
a blood-red coloured solution, which will appear as a ring
midway down the cylinder.

This phenomenon of the diffusion of dissolved substances,
sinctly comparable with the diffijsion of gases, although in the
former case the operation proceeds with ex-
treme slowness. The force which impels the
molecules of dissolved substances to diffuse, is
the osmotic pressure of the substance in solu-
tion.

The extension of the gaseous laws into the
domain of solutions, necessitates the hypothesis
that in the case of some solutions the mole-
cules of the dissolved substance unite to farm
more complicated molecular associations ; while
in other cases (including those substances which
are electrolytes, such as the solutions of strong
acids, bases, and salts) the molecules of the sub
stances undergo dissociation into their ions {see
Electrolysis, page 93). For, just as in the case
of gases, where departures from the strict gas-
eous laws are seen to take place, on account of
the dissociation in some instances, and theiufc-
daiion in others, of the various molecules ; so
it is believed that the deviations from thi
continuity of the ideal gaseous laws into the realm of solution, are
due 10 the operation of similar causes.

Pic. «^

Crystalline Forms.

When a saturated solution of a solid in a liquid, is either cooled
or allowed to evaporate^ the dissolved solid begins to deposit,
and it does so in most cases in definite geometric shapes, termed
crystals. 'Solids which exhibit no cryslallii
be amorphous.)

The same arrangement of molecules into geometric forms often

iflen I

Crystalline Forms i ^9

takes place when substances in a state oi fusion (as distinguished
from solution) pass into the solid condition, as, for example, when
melted sulphur, or mercury, or water, are cooled to their respective
solidifying points ; and it also frequently takes place when vapours
condense to the solid state.

The more slowly the process of solidification takes place, and
the larger and more symmetrical are the crystals that are formed.

The variety of geometric forms that are met with in naturally
occurring, and artificially produced, crystals is practically infinite.
They are, however, susceptible of a classification, based upon their
development with respect to certain imaginary planes, called the
planes of symmetry. These are planes cut through the crystal in
such a manner, that the divided portions are the mirrored reflec-
tions the one of the other, the mirror being the plane itself. All
crystals may be referred to one or other of six great fiunilies,
according to their synmietry, known as crystallographic systems.

I. The Regular system. Crystals belonging to this system
have nine planes of symmetry, namely, three principal
planes at right angles to each other, and six others which
intersect one another at angles of 60°. Forms of this
system (such, for example, as the cube) possess the highest
possible order of symmetry.

II. The Hexagonal system. Crystals having seven planes of
symmetry, namely, one principal plane, nonnal to a
vertical axis in the crystal, and six other planes at right
angles to the principal plane, and intersecting each other
at angles of 30*.

III. The Quadratic system. Embracing crystals having five

planes of synmietry, namely, one principal plane, normal
to a vertical axis in the crystal, and four other planes at
right angles to the principal plane, and intersecting each
other at angles of 4$*.

IV. The Rhombic system. Including crystals having three

planes of symmetry at right angles to each other.

V. The Monosymmetric or Monoclinic system. Crystals with
only one plane of symmetry.

VI. The Asymmetric or Triclinic system. Including crystals
which have no plane of symmetry. The forms belonging to
this system, having symmetry with respect to a paint only.

140 Introductory Outlines

This system of classification brings the various crystalline forms
into direct relations with many of the physical properties possessed
by crystals, such, for example, as iheir optical characters : thus, in
the Regular system, the crystals in their normal condition are
singly refracting crystals — they are said to be isotropic. In the
Htxai-onal and Quadratic systems they are optically uniaxial ;
while in the Khombic, Monosymmtiric, and Asymmetric systems
they are all optically biaxial.

All crystals may be regarded as derivations from certain typical
forms belonging: to one of these six systems.* One of the simplest
forms of each system is the double pyramid, which in the hexagonal
system takes the shape of a double six-sided pyramid, and in tht
remaining systems that of a double four-sided pyramid, or octa-
hedron. Thus wc have the rtgular octahedron, the quadratii
octahedron, the rkombic ociahedion, and so on.

By the development ofceriain related faces, the octahedron passes
into the prism, hence we get the^uarfrd/zirprism, the rAnmiii: prism,
the hexagonal prism, &c. It will be obvious, therefore, that the
description of a crystal as bting prismatic, or octahedral, in form,
is incomplete unless the particular system to which it is referred be
also stated.

Crystals, whether naturally occurring or artificially obtained, very
seldom exhibit the perfect symmetry of the idea! form. By great
care, however, in regulating the formation of a crystal, by the
maintenance of a constant temperature, and controlling the rate of
evaporation of the solvent, it is possible to cause crystals to grow
in such a way, that they will approach very closely to the ideal
geometric form. Fig. 140+ represents crystals of alum, in the form
of regular octahedra, or double four-sided pyramids, whjcli were
obtained by careful crystallisation from aqueous solution ; and it
will be seen how near to the ideal they approach. In Fig, io6,t
also, are seen illustrations of crystals of sulphur, in the form of
rhombic octahedra. These crystals were produced by the carefully
controlled deposition of the sulphur, from a solution of the element
in carbon disulphide, and they illustrate the kind of variations in
the form that are introduced by the development of new faces.
Fig. 141 t shows a group of naturally occurring crystals, namely,

* The study of the relations t)i
types, forms ;l pari of the scienoe
Of a general cticmicftl liul-book.

t FroTTi a pbolograph of (he oi

[ crystallography, and blls 01

be scope

Crystalline Fortns

141

quartz, in the fonn of hexagofuU prisms, terminating in hexagonal
pyramids.

In order to determine the system to which a given crystal be-
longs, it is necessary to make a number of accurate measurements
of its angles, and since the inclinations of the faces to one another
bear geometric relations to the planes of symmetry, and the inclina-
tions of these planes towards each other, these latter may be calcu-
lated from the former values. The instnmients by means of which
such measures are made are termed goniometers.

Two or more substances which crystallise in the same form are
said to be isomarphous (see page 49), and, on the other hand, a
substance which is capable of crystallising in two forms which do
not belong to the same system, is termed a dimorphous substance.
Thus sulphur is dimorphous, as it is capable of crystallising in the
fonn of rhombic octahedra (Fig. 106), and in monosymmetric prisms
(Fig. 107).

Occasionally a dimoq;)hous substance is isomorphous with another
dimorphous body, in both its forms. To this double isomorphism
the term isodimarphism is applied.

CHAPTER XV

THBRMO-CHEMISTRY

ffE have seen thai by means of symbols and formuisc chemist*
express, in the Ibrm of equations, a certain amount of information
respecting chemical changes : thus by the equatioo C + O, = CO,
there are conveyed the facts, that carbon unites with oxygen lo
form carbon dioxide, that i:£ grammes of carbon combine with 32
giarnmes of oxygen, yielding 44 grammes of carbon dioxide, and
Ihat the volume of the gaseous carbon dioxide obtained is Ihe same
as thai of the oxygen taking part in its formation. All such
equations bear upon the face of them the truth, Ihai mailer can
neither be destroyed nor created. The total quantity of matter
taking pari in the action is unaltered by the process, although it
appears in altered form in the products of ihe reaction.

In a]l chemical changes, besides matter, ener^ also takes a
part; not only do the materials concerned undergo rearrangement,
or readjustment, but at the same time there is a rearrangement
readjustment of energy. This energy change is not expressed
the ordinary symbolic equation. Thus in the equation —

SO, + H,0 = H,SO,
ihe fact is embodied that 80 grammes of sulphur trioxide, combine
with 18 grammes of water, and form 98 grammes of sulphuric acid ;
bul the equation lakes no cognisance of the fact, thai when these
weights of these two substances unite to form 9E giaitmies of sul-
phuric acid, an amount of energy, in the form of heat, is disengaged
that would raise the temperature of 213 grammes of water from o*
to the boiling-point.

Similarly, in the equation 2NC1, = N^ + SCI, there is no recogni-
tion of the fact, that during Ihis change an enormous amount of
energy leaves the system in the form of external work,— (over-
coming the atmospheric pressure) ; in other words, that the con-
version of nitrogen trichloride into its constituent elements is
attended wilh the must violeni explosion.

Tkirmo-Chimistry 143

Energy, like matter, can neither be created nor destroyed, but as
a result of chemical action it reappears as energy in another form.
Thus it may appear as heat, as electrical energy, as kinetic
energy, or as chemical energy ; and jutt as the total amount of
mcUter taking part in a chemical change, reappears in altered form
in the products of the change, so the disappearance of energy in
any of its forms, gives rise to the reappearance of a proportionate
amount of energy in another form. This is the law of ihe conserva-
tion of energy y which may be thus stated ; * " The total energy of any
material system^ is a quantity which can neither be increased nor
diminished by any action between the parts of the system^ although
it may be transformed into any of the forms of which energy is
susceptible/*

Chemical energy, or that form of energy that is set fies during
chemical processes, cannot be measured by any direct method.
This energy, however, is generally transformed, during chemi*
cal change, into heat, and may therefore be measured by, and
expressed in, heat units. Thermo-chemistry may therefore be
defined as the science of the thermal changes which accompany
chemical changes.

All matter is regarded as containing a certain amount of energy
in some form, and the purpose of thermo-chemistry is, by measur-
ing the thermal disturbance that is conditioned by a chemical
change, to ascertain the difference between the amount of energy
contained in a system before and after such a change.

If all the energy of a system in its original state (/>., before the
chemical change takes place) that undergoes transformation into
other forms of energy, passes into heat ; if none of it leaves the
system as energy in some other form, and thereby escapes mea-
surement ; then the difference between the amount of energy
contained in the system in its original and its final state may be
ascertained. It by no means follows, however, that this represents
the chemical energy alone : it has already been explained that
chemical changes are always attended by physical changes, such
as change of volume, of physical state, and so on, and we have
also learned that such physical changes are likewise accompanied by
thermal changes ; the problem, therefore, is often a complicated one,
and it is not always possible to differentiate between the chemical
and the physical causes that may be operating simultaneously, and

* Clerk Maxwell, '* Matter and Motkm."

144 Introductory Out tines

to decide what share of the final result is due to the chemical phase
of the change, and what to the physical change that simultaneously
takes place.

As an illustration of the complex nature of chemical reactions
when considered from a thermal standpoint, and of the disturbing
effect of the accompanying physical changes, we may take the case
of the action of aqueous hydrochloric acid, upon crystallised sodium
sulphate, NajSO4,10H,O—

Na,SO4,10HjO + 2HC1 = 2NaCl + HjSO^ + 10H,O.

The chemical action here consists of (i) the decomposition of
sodium sulphate, (2) the decomposition of hydrochloric acid, (3)
the formation of sodium chloride, (4) the formation of sulphuric
acid Heat is absorbed by the first two portions of the action, and
heat is evolved by the other two. The physical changes include
the passage of ten molecules of water of crystallisation (/>., solid
water) into liquid water, and the solution of sodium chloride in
water. These changes are attended with absorption of heat, and
the net result of the entire change is the disappearance of a con-
siderable amount of heat, that is to say, the thermal value of the
reaction is a negative quantity.

The methods adopted in order to express thermo- chemical
reactions are quite simple. The ordinary chemical symbols and
formulae are used, and represent, in all cases, quantities in grammes
corresponding to the formula-weights of the substances. Thus CI
represents 35.5 grammes of chlorine ; H^O stands for 18 granmies
of water, and so on. The chemical equation is followed by a
number representing the quantity of heat, expressed in heat units,
which is either produced, or which disappears as a result of the
change. The unit of heat is the calorie^ or the quantity of heat
that is capable of raising the temperature of i gramme of water from
o* to 1°. Sometimes the unit employed is the quantity of heat
required to raise i gramme of water from o** to 100*, and this unit
(which is 100 times greater than the calorie) is indicated usually
by the letter K. When heat is produced by a chemical change,
the sign -f is placed in front of the number of units, and when
heat disappears, the fact is indicated by the sign — ,

Thus the equation —

H, -f CI, = 2HC1 + 44,000 cal.
or H, -f CI, - 2HC1 + 440 K,

Thermo-Ckemittry 145

meuu that when 3 gnunmes of hydrogen combine with 71
grammes of chlorine to form gaseous hydrochloric acid, heat is
disengaged to the amount of 44,000 calories, or 440 of the larger
units, K. Or, in other words, that when these quantities of these
substances combine, an amount of energy is lott to the system,
represented by 44,000 calories. Therefore the energy possessed
by 2 grammes of hydrogen and 71 granunes of chlorine is giieater
than that possessed by 73 grammes of hydrochloric add gas by an
amount which is represented by 44,000 gram-units of heat. Hence
the equation may be written —

SHCl - H, + Clt - 44,000 cal.

which signifies that when 73 grammes of gaseous hydrochloric acid
are decomposed into chlorine and hydn^en, it is necessary to
supply an amount of energy equal to 44,000 calories.

In order to indicate the state of aggregation of the different sub-
Stances, the method introduced by Ostwald consists in the use of
different type, thick type being employed to denote solids, ordinary
type indicating liquids, and italics signifying gases, thus—

0 + 0, - CO^ + 97/)oo cal.

means that the total energies of ti grammes of solid carbon and
33 grammes of gaseous oxygen is greater than the energy pos-
sessed by 44 grammes of gaseous carbon dioxide by ao amount
equivalent to 97,000 calories.
Or, again, the equation —

SO, + H,0 = H,SO, -I- 21,330 cat

signifies that 80 granunes of solid sulphur irioaide unites with 18
grammes of liquid water, and forms 98 grammes of liquid sulphuric
acid, with the liberation of 31,300 gram-units of heat.

Similarly the heal evolved by the passage of water into ice, and
the heat that disappears when water passes into steam, may be
expressed by the equations —

H,0 = n,0 + 1440 caL
H,0 = //,0 - 9670 caL

when water takes a direct part in the chemical change, as, for

146 Introductory Outlines

example, in the action of sulphur trioxide and water already quoted,
the formula represents a gram-molecule just as in all other cases ;
but where the presence of a large quantity of water affects the
thermal result of the chemical change, by exerting, for example, a
solvent action, the symbol Aq is employed to signify that the pre-
sence of the water is considered in the thermal expression.
Thus the expression —

HBr 4- Aq = HBrAq + 19,900 caL

signifies that when 81 grammes of gaseous hydrobromic acid are
dissolved in a large excess of water, 19,900 calories are evolved.
Again, the equation —

//, + Br^ + Aq = 2HBrAq + 64,000 cal.

means that when 160 grammes of gaseous bromine combine with
2 grammes of hydrogen, and the product is dissolved in an excess
of water (f>., such a quantity of water that no thermal change is
produced by the addition of any further quantity), 64,000 calories
are disengaged. Of this 64,000 calories, 19,900 x 2 = 39,800 are
due to the solution of the twice 81 grammes of hydrobromic acid,
and the difference, viz., 24,000 calories, represent the heat produced
by the combination of 2 grammes of hydrogen with 160 grammes
of bromine.

If water is formed as one of the products of the chemical reaction
taking place in the case of substances in aqueous solution, such as
when a solution of hydrochloric acid is added to a solution of
sodium hydroxide, HCl + NaHO = NaCl + HjO, as the. water so
produced simply mixes with the water in which the materials are
dissolved, without producing any thermal effects, it is usually
neglected in energy equations. Thus the above action may be
expressed —

HClAq + NaHOAq = NaOAq + 13,736 cal.

The heat that is produced, or that disappears, in a chemical
change which results in the formation of a particular compound,
is termed the heat of formation of that compound. Thus in the
equation —

H^ + C/, = 2^C/ + 44,000 cal.
the heat of formation of 73 grammes of hydrochloric acid is 44,000

Thermo- Chemistry 1 47

thennal units. This number, however, is in reality the algebraic sum
of three quantities. It does not express merely the heat developed
by the simple union of chlorine and hydrogen. The chemical
change expressed by the equation consists in reality of three
operations —

(i.)H,-H + H. (2.)C1,= C1 + C1. (3.)C1 + C1 + H + H-2HC1.

Each of these operations represents a distinct thermal effect ; in
Nos. (i) and (2) heat is absorbed, in No. (3) heat is evolved, and
calling these values k^ h^ and h^ we have as the net result
A, - (^ + A^ = 44»a» cal.

The number of heat-units, therefore, which expresses the heat of
formation of hydrochloric acid, is the heat produced by the union of
two atoms of hydrogen with two atoms of chlorine, minus the heat
absorbed in the decomposition of one hydrogen and one chlorine
molecule.

Compounds such as hydrochloric acid, in the formation of which
heat is developed, are termed exothermic compounds, the reaction
by which they are produced being an exothermic change ; com-
pounds, on the other hand, whose heats of formation are expressed
by a negative sign, that is, in whose formation heat disappears, are
distinguished as endothermic compounds^ and the reactions by which
they are formed are endothermic reaction.

Thus C + S, - CS, - 19,600 cal.,

signifies that in the formation of carbon disulphide, heat is absorbed,
and the compound is therefore an endothermic compound.

Thermo-chemical determinations are made by means of instru-
ments termed calorimeters. These are of great variety, although
the principle involved is the same. The chemical reaction is caused
to take place under such circumstances, that the whole of the heat
that is liberated shall be communicated to a known volume of water,
at a known temperature.*

Direct determinations of the thermal value of chemical changes,
have hitherto been made in only a limited number of comparatively
simple cases : it is possible, however, from a few known data, to cal-
culate the thermal values of a number of changes which cannot be
directly measured. This depends upon the fundamental principle

* For descriptions of the various calorimeters, see Treatises on Physics.

148

Introductory Outlines

of thermo-chemistry, which is itself the corollary of the law of ihe
conservation of ener^, and which was first cxperimcnlally proved
by Hess (1840). This principle, which issomeliines termed the lav/
0/ constant heal consummation, or the latv of cquii'itlence of heat
and chemical change, may be thus staled : The amouni of heal
that is liberated, or absorbed, during a chemical process, is de-
pendent solely upon the initial and final states of the system, and is
independent of the iniermediale stages. The following examples
will serve lo explain the application of the principle :—

I. Let us suppose it is desired 10 find the heat of formation of
carbon monoxide, the data at our disposal being (1) the heat pro-
duced when carbon unites with oxygen to form carbon dioxide ;
and (2) the heat formed by the combustion of carlion monoxide to
carbon dioxide. The thermal equations are —

(i) 0 + O, = CO, + 97,000 ca!,

(3) iCO + 0, = %COt + 136,000 cat

Halving the second equation, in order to get the heat produced
in the formation of 44 grammes of carbon dioxide (i>., the same
weight as in the first), we may represent the equation as —

CO^O=COy^ (&,<x

ical.»

TI1C difference between the two values 97,000 and 68,000 will be
the Ileal of fonnation of carton monoxide, therefore we get the
equation—

0 + O = CO + 29,000 cal.

3. The compound, methane (marsh gas), CH„ cannot be formed
by the direct union of its elements, but its heat of formation can
be calculated by the application of this principle. The data in
this case are the ascertained heats of formation of carbon dioxide

• [1 must ht rememlwreil that this equation does not express ihe whole
irulh : lu i( here slands it would implT thai 68,cx» calories represent Ihe heat
forniFd t>y the limple cliemical union of iS grBmmes of carbon monoxide with
16 gii^mmes of oxygen. In reaiiLy this number i$ half the sum of ibc iwo
mlues, namely. Ihe heal of coi, " .nation of 56 grammes uf carbon monoiidJ
with 3a erammes o( oiygcn. minus (he heal absorbed by tlie decomposition ol

atom doei not exist alone, and v> Uenever free oxygen lakes part ia a cberolcal
chuise, Ibe molecnlea ol ttie eleiueot are Htm separated into Uie*

Thermo-Chemistry

149

and of water, and the heat produced by the combustion of marsh
gas, the thermal equations being —

(i) 0 + (9, = CO, + 97,000 cal.

(2) %H^ + O, = 2//,0 + 136,800 cal.

(3) CH^ + 2(9, - C(9, + ^H^0 + 212,000 cal.

The difference between the thermal value of the last process, and
the sum of the first and second, represents the heat of formation of
marsh gas —

97,000 + 136,800 - 212,000 — 2I,8oO|

hence we get the expression —

0 + i//, - CH^ -t 21,800 cal.

PART II

THE STUDY OP POUR TYPICAL ELEMENTS

HYDR0GEN-0XTGEN-NITR06EN-CARB0N

AND THEIR MORE IMPORTANT COMPOUNDS

CHAPTER I

HYDROGEN
Symbol, H. Atomic weight = i. Molecular weight = 2. Density = 1.

History. — The existence of hydrogen as an individual sub-
stance was first established by Cavendish (1766), who applied to it
the name inflammable air. He obtained the gas by acting upon
certain metals, as iron, tin, and zinc, with either sulphuric or hydro-
chloric acid.

Occurrence. — In the free state hydrogen occurs only in small
quantities upon the earth. It is evolved with other volcanic gases,
and is present in the gases which escape from petroleimi wells.
It is evolved also during the fermentation and decomposition of
certain organic compounds, and is therefore present in the breath
and the intestinal gases of animals. Hydrogen has also been
found in many specimens of meteoric iron, where it is present as
occluded gas.

Hydrogen in the uncombined state exists in enormous masses
upon the sun, and is present in certain stars and nebulae. The
so-called prominences which are seen projecting from the sun's
disk to a distance of many thousands of miles, and which were
first observed during solar eclipses, consist of vast masses of in-
candescent hydrogen.

In combination with other elements hydrogen is extremely

ISO

l**t-

Hydrogen i 5 1

abundant : its commonest compnund is waiec, which consists of
one pan by weight of this element combined with eight piitts of
oxygen. In coinbinalon with chlorine, as hydrochloric acid, with
carbon as marsh g(Li, nnd wilb sulphur as siilphuielled hydrogen,
this elemenl also occurs in large quantities. All known acids
contain hydiogen ai one of their constituents, and il is present in
almost all oty.init compounds.
Hods* or FormaUon.— (1.) Hydrogen may be obUined from

^^K water by the action ol various metals upon ihat compnund under
^^P certain conditions. Tlie metals sodium and prtUssium will decom-
pose water at the ordinary temperatures ; when, therefore, B frag-
ment of either of these metals is thrown tipon water, the latter is
decomposed, and hydrogen set free :—

1H,0 + Na = NaHO + H.
The meials being lighter than water float upon its surface, and,
owing to the heal of the reaction, melt and roll about upon the
n<|uid as molten globules. With poias&ium, the heat deveK^ped a

152 Inorganic Chemistry

sufficiently great lo cause the hydrogen to inflame, and it b
with a flame coloured violet by the vapour of the metal,
hydroxide of the metal, which is the second prodticl of the ac
dissolves in the excess of water, rendering ihe liquid alk^lini
The alkalinity of the solution may be made evident by the addltiOE
of a reddened solution of litmus, which will be turned blue by tl
alkali.

In order lo collect the hydrogen evolved by the action of sodiiu
tipon water, the metal is placed in a short piece of lead lube don
at one end, which causes it lo sink in the liquid, and an inverted
glass cylinder tilled with water is placed over it, as shown in Fig. 9

The evolved hydrogen then rises as a stream of bubbles
cylinder and displaces the water.*

(2,) Water may be readily decomposed al the boiling-poinl
by means of linc, if ihe metal be previously coated with a
film of copper by immersion in a dilute solution of copper j:
phate. When this copper-coaled tine (known as zin
couple) is heated in a small flask filled with water, and provide
with a delivery lube, the oxygen of the water combines with tl
^inc forming zinc oxide, and hydrogen Is evolved, which may b
collecied over water al the pneumatic trough : * —
Zn + H,0 = ZnO + H^

* Foe detailed description of Ibese experinx

'Cbeml

Hydrogen

153

(3.) At a still higher temperature, water in the state of steam can
be readily decomposed by the metal magnesium, magnesium oxide
being formed and hydrogen liberated : —

Mg + H,0 = MgO + H^

For this purpose the magnesium is strongly heated in a glass
bulb (Fig. 26), while steam from a small boiler is passed over it.
As the temperature of the metal approaches a red heat it bursts
mto flame, and the issuing hydrogen may be ignited as it escapes
from the end of the tube.

(4.) If iron be heated to bright redness, and steam be passed
over it, the water is decomposed, the oxygen uniting with the iron

Fig. 27.

to form an oxide known as triferric tetroxide, or majrnetic oxide oj

iron^ thus —

3Fe + 4H,0 = FejO* + 4Hj.

This method is employed on a large scale for the preparation of
hydrogen for conunercial purposes. Iron borings or turnings are
packed into an iron tube, which is strongly heated in a furnace,
and steam from a boiler is passed through the tube.

(5.) For laboratory purposes hydrogen is most conveniently pre-
pared by the action of dilute sulphuric add upon zinc : —

Zn + H,S04 - ZnS04 + H,.

For this purpose granulated zinc (/.^., zinc which has been melted

Inorganic Chemistry

154

and poured inlo water) is placed in a two-necked WoulTs bottle
(Fig. vj\ and a quantity of sulphuric acid, previously diluted vrith
six times its volume of water, is introduced by means of the liinneL
A brisk action sets in, and hydrogen is rapidly disengaged. After
the lapse of a few minutes, the air within the apparatus will be
swept out by the hydrogen, when the gas may be collected over
water in the pneumatic trough.

The hydrogen bo obtained is never ^isolulely pure : It is liable ti
lisixs ofaiscnuielled hydiogCQ. sulphiireiied hydrogen, phosphoreited hydc^'l
gen, oiidca of nitrogen, and nitrogen. The nitrogen is derived from Ih
wtJcb finds iis way Ihrougb joinii in tbe upparaiiu. and also from ait diss
in the Hdd. There is no known process for removing this impurify.
other gases are due to impurities in the linc and ttie sulphurie acid, atu
be removed, if required, by passing the hydiogen thtougb a scnei o(
containing absoibenu (see p. 187).

Absolutely pure sulphuric acid, even when diluted with h
has no action upon perfectly pure zina

Scrap iron may be substituted for einc, but the hydrogen )
obtained is much less pure, and is accompanied by comjwunils o
carbon (derived from the carbon in the iron), which imparl v
gas an unpleasant smell ; the reaction in this case is the following ^'

Fe + H,SO, = KeSO, + H,

Hydrochloric acid can be employed in place of sulphuric ai:id1
with either ziac or iron, the reaction then being :—

Zn + 2HC1 = ZnCI, + H,

(6.) Hydrogen in a high degree of purity is conveniently prcparn
in small quantity by (he electrolysis of water acidulated with s
phuric acid (see p. 183).

(7.) Hydrogen is disengaged when certain metals, such a
iron, magnesium, and aluminium, are boiled with an aqueous solli>
Uon of potassium or sodium hydroxide. Thus, in the cas<
when this metal in the form of filings is boiled with a solution O
potas^um hydroxide, hydrogen is evolved, and a compound of n
potassium, and oxygen remains in solulioD, namely, potassium li
oxide, thus ; —

SKHO + Zn - H, + ZnK,0^

(8,) HydroKCn is also obtained by heating alluline oitalaies,

i, ot ^J

Hydrogen 1 5 5

formate^ with either poiasaium or sodium hydroxide, with thf
limultaneoo Tonnaiioii of an alkatiae carbonate i thus with sodium
oxalate :~

Na,C,0, + JNaHO = H, + aNa,CO,.

Properties. — Hydrogen is a colourless gas, and has nciihei
tasle nnr smelL It is ihe hghtest known substance, being 14.435
times lighter than air. Its specific giavjty is 0.0693 (ftii '* ■)'
One litre of the ){as at 0° C, and tinder a pressure of 760 nun. of
mercury {i.t.. the staniJard teniperature and pressure), weighs
0,0896 gramme \ at I gramme of hydrogen at the slaiid^id lein-
peramreaiid pressurr occupies 1 1.165 litres.

On account of its extreme h^hiness, hydru^i'n may be poured

up^ardi from one vessel to anoihci If a Urge Ijcaker be sus
pended mouth downward from the arm of .t balance, and counter-
poised, and the contents of a jar of hydrogen be poured upwards
into the beaker, the equilibrium of the system will be disttirbed,
and the arm carrying the beaker will lise.

The lightness of hydrogen can also be shown, by causing a
stream of the gas to issue from a tube placed in such a position
that its shadow is cast upon a white screen by means of a powerful
electric light. When the gas is streaming from the tube, its up-
ward rush will be visible upon the screen as a distinct shadow,
caused by ihe difTercnce between the refractive power of air and
hydrogen (Fig. iS).

1S6

Inorganic Cfumistry

Hydrogen is inflammable, and bums with a non-luminous flanu^.l
the icmperaturc of which is very high. The product of the com- J
buslion of hydrogen is water, and if a jet of the gas be burned 1
beneath the apparatus seen in Fig. ig, considerable quantitie;
water may be collected in the bulb. In the act of combustion, tbe i|
hydrogen combines with the oxygen of the air, forming the oxide oil
hydrogen, namely, water : * —

H, + O = H,0.

If hydrogen be mixed with the requisiie quantity of ai

and a light applied lo the i

The

the combination of the two gas
takes place instantly, with a violentl
explosion; hence the necessity of ci
fully expelling all the air from the 1
apparatus in which hydrogen is being- I
generated, before applying a flame ti
the issuing gas.

Hydrogen wiil not support the ci
bustion of ordinary combustibles ; tl
if a burning taper be thrust into a
of the gas, the hydrogen itself will bft \
ignited at the mouth of the jar, which I
must be held in an inverted position, but J
the taper will be extinguished ;
drawing the taper it may be re-iguitec
by the burning hydrogen.

Although hydrngen is not
ous, it is incapable of supporting a
mal life owing simply to the exclu
of oxygen. When mixed with air
inhaled, it raises the pilch of the v
effect may be seen by sounding

almost to

a pitch-pipe, or organ-pipe, by means of a stream of hydrogen
instead of ordinary air, when it will be noticed that the note given
out is greatly raised in pitch.

Hydrogen is very slightly soluble in water. It was formerly
believed that (his gas formed an exception lo the rule thai the
solubility of gases in water diminishes with rise of temperature,
and it was supposed that the solubility of hydrogen was constant
between the temperatures o° and 35°. More recent experiments
* From this (act ttie nante Hydrogen (sigaifyuig tlu

Hydro^nium 157

have shown that this is not the case. The solubility of this gas, as
delenniDed by W. Timofejeff ( 1 890), is seen in the table on p. 113.

Hydrogen was first liquefied on May 10, 1898, by Dcwar. Prior
to this time it had never been obtained as a coherent or static
liquid— that is, a liquid with a meniscus— although momentary
indications of its liquefaction had been obtained by Olszewski as
fiir back as 1895. The critical temperature of hydrogen ( - 334*,
Olsiewski) being below the lowest point obtainable by the rapid
ebullition of liquid oxygen 01 air, no external refrigerating agent
is available which is capable of cooling the gas below its critical
point, and therefore of causing its liquefaction. By an extension
of the principle of self-cooling explained on p. 7 J, however, namely,
by causing a jet of the gas previously cooled to -10;* to continu-
ously escape Arorn a fine orifice under a pressure of iSo atmos-
pheres, Professor Dewar has succeeded in collecting considerable
quantities of liquid hydrogen in specially constructed vacuum-
jacketed vessels.

Liquid hydrogen is deai and colourless as water, thus disposing
of the theory once advocated that if obtained in the liquid state
hydrogen would be found to exhibit metallic properties. The
boiling-point of the liquid is -253° (Dewar), at which temperature
air is immediately solidified. Thus, if a tube sealed at one end,
but freely open to the air at the other, be immersed in liquid
hydrogen, the cooled end of the tube quickly becomes filled with
solidified air. Similarly oxygen is frozen to a pale-blue solid.

The specific gravity of liquid hydrogen is about 0,07 ; that is to
say, it is only about ^tii the density of water, or about 14 cc. of the
liquid weigh only I gram. By means of liquid hydrogen as a
refrigerating agent, the newiy discovered gas Helium has also been
liquefied (see p. 649), hence alt the known gases have now been
condensed to the liquid slate.

Hydrogenlutn. — Certain metals, such as iron, platinum, and
notably palladium, possess the property when heated of absorbing
a large quantity of hydrogen, and of retaining it when cold.
Graham found that at a red heat palladium absorbed, or occluded,
about 900 times its own volume of hydrogen, while even at ordi-
nary temperatures it was able to absorb as much as 376 times its
volume.* Graham concluded that the hydrogen so occluded
assumed the solid form, and was alloyed with the palladium, and

■ AecordiDg lo Nnimann ud StricDU {ZtHickri/t fUr Anafytiickt Ch*mU,

■

TS8

Inorganic Cfutnistry

to denote the metallic nature of the gas he g'ave to il the n
hydrogenium. From recent experiments of Troost and Haute- I
fcuille, il seems probable that a definite compound of hydrogen I
and palladium wists, of the composition of PdH,

The absorption of hydrogen by palladium is readily seen, by 1
making a strip of palladium foil the negative electrode in
electrolytic cell containing acidulated water, the positive polel
being of platinum. Oxygen will be evolved from the latter*
electrode, while for some time no gas will be disengaged from ■
the surface of the palladium, the hydrogen being completely I
absorbed by the metal. During the absorption of hydrogen the
palladium undetgoes an increase in volume : Graham observed the I
increase in length of a palladium wire to be equal to 1.6 per cenL 1
This change in volume suffered by the meial may be strikingly I
demonstrated by employing two strips of palladium foil, protected I
on one side by a varnish, as the electrodes in the electrolytic celL I
On passing the current the negative electrode immediately beginv ■
to bend over towards the varnished side ; when the curren
reversed it again uncurls ; and the other, being now the negative J
pole, at once begins to perform the same curling movements.

Hydrogcnium is capable of bringing about a number of chen
changes which ordinary hydrogen is unable to effect : thus, «
a strip of hydrogenised palladium is immersed in a solution 1
ferric salt, a portion of ihe iron is reduced to the ferrous slate.'

vol, 3a), one "olmne of various metaU in » fine stal

abiorbing the fotlouang anioiinls of hydioeen ;—

Palladium, black . 509.35 vols. I Nickel

. _ 49-3 ■• Copper

Gold . . , , 46.3 ,. AluminiUJ

Iran , . , 19, 17 .. I Lead,

ofdivi

capable i

See ■■ ChemicaJ Lecii

■ Ejperiri!

CHAPTER 11

Srmbol, Oi Atum<c weight = is^s. Mrilt^tilnr weight = jr 91

History.— Oxygen was discovered by Priestley (1774). He ob-
uined ii by hcatinjj tbe i^d oxide of mercury (known in those days
ti nurcurius calcinalut, per it) hy concentrating the sun's rays
upon it by means of a powerful lens. Priestley applied to the gai
the name litphlogiUigaltd air. Oxygen was independently dis-
covered by Scheele. Scheele's discovery of oxygen was published
in 1775, but recent research among his original papers, has brought
to light the fad that the discovery was actually made in r773, prior
therefore to I'riesllcy's discovery. Scheele called the gas einpyttat
air, on account of its property of supporting combusiion, Lavoisier
subsequently applied to this gas the name " rxygene " (from ofiit,
sour J and ytnaia, I produce), to denote the fact that In many
instances, the products obtained by the combusiion of substances
in the gas were endowed with acid properties. Oxygen, indeed,
came to be regarded as an essential constituent of acids, and was
looked upon as the " acidifying principle.'' The subsequent deve'
lopment of the science has shown that this idea is erroneous, and
that oxygen is not a necessary constituent of -ill acids.

Ocourrenoe.— In the free stale oxygen occurs in the atmos-
phere, mechanically mixed with about four limes its volume of
nitrogen. In combination niili ether elements il is found in
enormous quantities. Thus it constitutes eight-ninths by weight
of water, and nearly one-half by weight of the rocks of which the
earth's crust is mainly composed.

The following table (Bunsen) gives the avernge composition of
the earth's solid crust, so far as it has been penetrated by man.
It must be remembered, however, that the greatest depth to which
man has examined, when compared with the diameter of the earth,
is after all only, as it were, a mere scratch.

i6o

Inorganic Chemistry

. 44.0 to

48.7

22,8 „

36.2

• 9.9 ,,

6.1

. 9-9 »

2.4

6.6 „

0.9

. 2.7 „

. 2.4 „

2.5

. 1.7 »»

Average Composition of the Earths Crust,

Oxygen .
Silicon .
Aluminium
Iron

Calcium .
Magnesium
Sodium .
Potassium

100.00 100.00

Modes of Formation. ^ I.) Oxygen may readily be obtained
by a slight modification of Priestley's original method, namely, by
heating mercuric oxide in a glass tube, by means of a Bunsen
flame. The red oxide of mercury first darkens in colour, and is
decomposed by the action of the heat into mercury and oxygen,
thus—

2HgO = 2Hg + Ojj.

The evolved oxygen^nay be collected over water in the pneumatic
trough, while the mercury condenses in the form of metallic
globules upon the cooler parts of the tube. This method of
obtaining oxygen is never employed when any quantity of the
gas is required — it is chiefly of historic interest.

(2.) For experimental purposes, oxygen is best prepared from
potassium chlorate. When this salt is heated it melts, and at
about 400* decomposes with brisk eflfervescence due to the evolution
of oxygen, while potassium chloride remains ; * —

KClOj = KCl + 30.

I f the potassium chlorate be previously mixed with about one-
fourth of its weight of manganese dioxide, it gives up the whole of
its oxygen at a temperature considerably below the melting-point
of the salt, and at a greatly accelerated rate. When, therefore, the
oxygen is not required to be perfectly pure, a mixture of these two

• The mechanism of this reaction is more complex than is represented by
this equation. It has been shown that during the decomposition, potassium
pcrchlorate. KCIO4, is continuously being formed, and again resolved into
KQO, and O.

Oxygtn l6l

lubstancei ii ostully employed. The mixtnre miy be conveniently
heated in a "Florence" flask, supported in ihe position shown in
the figure, and gently heated with a. Bunsen flame. The gas is
washed by being passed through water, and then cottecled either
at the pneumatic trough or in a gas-holder.

The manganese dioxide is found at the end of the reaction to be
unchanged : the part it plays in the decomposition belongs to a
class of phenomena to which the name calalyui is applied ; the
manganese dioxide, in this instance, being the catalytic agent. It
was at one time supposed that by its mere presence, itself under-
going no change, the manganese dioxide enabled tlie potassium
chlorate to give up its oxygen more readily and at a lower tempera-
ture ; but the accumulated evidence which has been collected by
the study of an increasing number of similar cases of catalytic
action, leads to the conclusion that the manganese dioxide is here

Fio, 90.

playing a more distinctly chemical part in the reaction. So far as
is known, in all phenomena of this order, the catalytic agent is a
substance which p>osseisei a certain degree of chemical affinity for
one of the constituents of the body to be decomposed, and the
influence of this attraction is a necessary factor in determining the
splitting up of the compound. Owing, however, to certain condi-
tions which are present, such, for example, as the particular
temperature at which the reaction is conducted, the catalytic agent
is unable to actually combine with the constituent for which it has
this affinity, or if it combines, the combination it forms is unable to
exist, and is instantly resolved again; hence the catalytic agent comes
out of Ihe action in the same state as it was at the commencement.
In the case before us, it is believed that a cycle of changes takes
place,* in which the power possessed by manganese to enter into
• M-LMd.

Inorganic Ckunistry

162

higher stales of oxidation, results first in the formation of potassium' I
permanganate, KMnO, ; with ihe simultaneous production \
chlorine and oxygen, thus —

(1) 2MnO, + BKCIO, - 2KMnO, -
The potassium permanganate then passes into potassium man-
ganaie, K,MnO^, with evolution of oxygen, and partial reformation
of manganese dioxide, thus^

(a) SKMnO, - KjMnOi + MnO, + O,
i is decomposed, by the chlorine evolved by the first re-
ito potassium chloride, manganese dioxide, and oxygen,

(3) KjMnO, + CI, = 2KCI + MnO, + 0»
(3.) When manganese dioitide itself is heated to bright redness, it
parts with one-third of its oxygen, and is convened into trimanganic

3MnO,= MnjO( + 0,
(4.) Other peroxides, when heated, similarly yield a portion of the
oxygen they contain. One of these, namely, barium peroxide, '
now largely employed for the preparation of oxygen upon a mant^'l
facttiring scale This method, known as Brin^ process, from tl
name of the inventor, is based upon the fact, that when barium I
oxide (BaO) is heated in contact with air, it unites with an additional J
atom of oxygen, fanning barium peroxide, thus-
BaO + O = BaOj.

And thi
thus—

still further heated, it again parti'i
reconverted into the monoxide— •■

And that when this substance
with the additional oxygen anc

BaO, - BaO + O.

The process, therefore, is only an indirect method of oblaiainj
oxygen from the air, ihe same quantity of barium monoxide bein]
emplojed over and over again. In practice it was found,
instead of effecting the two reactions by altering the lemperatura
which involved loss of time and considerable expense, tlie s
result could be obtained by altering Ihe pressure and keeping lh(
temperature constant. If the monoxide be heated to the lower '
temperature, at which the first reaction takes place, and air be
passed over it at the ordinary atmospheric pressure, atmospheric
oxygen is taken up and barium peroxide is formed. If the pressure

bite

Oxygen l6j

be ihcQ slightly reduced by suiiable exhaust pump*, the peroxide
immediaiely gives up one atom of oxygen without any funliei
application of heat, and is retransfarmed into the monoxide. In

wm.

1 iS

—

this way, by alternately sending air through the heated retorts
containing the oxide, and then exhausting the retorts, a continuous
process is obtained without change of temperature.

The mo.fut ofierattdi ol the process will be seen from Fig, J1,

1(34

Inorganic Cf until try

which icprcsenis the generaJ arrangement of ihc apparatus
number of retorts, R, consisting of long narrow iron pipes, j
arranged vertically in rows in the furnace, where they are healed^
bymeaiisor"producer-gas"(/.f. carbon monoxide with atmosplierii
nitrogen, obtained by the regulated combustion of coke).

Dy nteans of the pump P, air is drawn in at the " air intake," i
forced through purifiers in order to withdraw atmospheric carboal
dioxide ; the complete removal of this impurity being essential tofl
the successful carrying otit of the operation. The purifier
so arranged, that any of them can be Ihrown_oul of ti!
will.

liy means of automatic gear the purified air is sent through pip
J to the distributing valve X, from which il passes by the pipe Y intS
thcretoEts, being made to passdown throughonerow,aiid up through
the other. The oxygen is then absorbed, and the acciimulatii
nitrogen escapes by the relief valve W. When the absorplio
oxygen by the barium monoxide .in the retorts has continued ft
ten or fifteen minutes, the autoitiatic reversing gear comes intd
operation. The relief valve W is thereby closed, ci
with the purifiers is cut olT, and the action of the pumps at once
causes a reduction of pressure within the retorts. When the pres-
sure falls to about 660 mm. {26 inches, or about 13 lbs. on the
square inch), the peroxide gives up oxygen, and is reduced to the
monoxide. The oxygen is drawn away by the pipe J and is passed
on to a gas-holder. The first portions of gas that are drawn out
of the retorts, will obviously be mixed with the atmospheric nitrogen
which was there present ; in order that this shall be got rid of, the
automatic gear is so arranged, that communication with the pipe
leading to the gas-holder is not opened until a few seconds after
the reversing gear is in operation, and the first portions of gas that
arc pumped out, are made to escapie into the air by a snifting valve
S, which is automatically opened and closed.

(5.) Oxygen may be obtained by healing manganese dioxide with
sulphuric acid, the dioxide parting with the half of its oxyger
a sulphate of the lower oxide being formed —

MnO, + H,SO, = MnSOi + H,0 + O.

(a salt coniainiog chromium

(6.) Similarly, potassium dichi
trioxide, CrOg), when heated with sulphuric acid, yields oxygen
chromium at the same time being reduced to a lower

with I

T» j

Oxygen 16$

dation, viz., CriOn in which condition it unites with sulphuric .icid,
fonning chromium sulphate —

KjCrA + 4H^04 - K,S04 + Cr^SO^), + 4H,0 + 30.

During the reaction, the red colour of the dichromate changes to
the deep olive-green colour possessed by chromium sulphate.

(7.) Many other highly oxidised salts yield oxygen when acted
upon by sulphuric acid ; thus, with potassium permanganate, the
following action takes place : —

K,Mn,Os + 3H^04 - K^O^ + 2MnS04 + 3H,0 + 60.

(8.) If hydrogen peroxide be added to dilute sulphuric acid, and
the mixture dropped upon a solution of potassium permanganate
contained in a suitable generating flask, a rapid evolution of oxygen
takes place at the ordinary temperature, thus —

K,Mn,Os+3H,S04 + 6H,0,- K,S04+2MnS04+8H,0 + 60,.

(9.) When strong sulphuric acid is dropped upon fragments of
brick or pumice-stone, contained in an earthenware or platinum
retort, and maintained at a bright red heat, the acid is decomposed
into water, sulphur dioxide, and oxygen —

HjSO^ - H,0 + SO, + O.

The products of the decomposition are passed through water, which
absorbs the sulphur dioxide, and also arrests any undecomposed
sulphuric acid, and the oxygen is collected over water. When this
process is used on a large scale, the sulphur dioxide is absorbed by
being passed through a tower filled with coke, and down which a
stream of water is allowed to trickle, and the solution so obtained
can be utilised in the manufacture of sulphuric acid.

(la) Oxygen can be obtained from bleach ing-powder by methods
which afford interesting instances of catalytic action.* The
composition of bleaching- powder is expressed by the formula
Ca(OCl)Cl. If this substance be mixed with water, and a small
quantity of precipitated cobalt oxide added, and the mixture gently
warmed, oxygen is rapidly evolved. The cobalt oxide, CoO, is the
catalytic agent; it is able to combine with more oxygen to form

* Experiments 3^1 36, 37* iS^i "Chemical Lecture Experiments," new ed.

i66 Inorganic Oumislry

CojO^ but this compound is reduced as fast as it is formcf).
the oxy^n is evolved as gas—

(I.) Ca(OCI)CI +2CoO - CojO, + CaCl,

(i.) Co,Oj = 2CoO + O.

A solution of calcium hypochlorile, which. may be obtained from
bleaching- powder (see Bleach ing-powder), behaves in the same
way i and, as in the above reaciion, nickel oxide may be substi-
tuted for cobalt —

Ca(OCl), = CaCl, + O,

(II.) A similar instance of catalysis, by which oxygen mayba^
obtained, is seen when a stream of chlorine gas is passed through ]
boiling milk of lime, lo which a sma!! quantity of the oxide of J
cobalt or nickel has been added —

1A reaction of the same order takes place, when the milk of li
replaced by either potassium or sodium hydroxide —

CaH,0, + CI, = CaCI, + H,0 -f

2NaH0 -t- CI, = 2NaCl + H,0 + O.

(izO When a mixture of steam and chlorine gas is healed to brightl

ledness, the steam is decomposed, the hydrogen combining v
the chlorine to form hydrogen chloride (hydrochloric acid), ,
the oxygen is set Iree —

H,0 -I- CI, - 2HCI + O.

In order to prepare oxygen by this reaction, chlorine gas is caused
bubble through water which is briskly boiling in a glass llaski
F(Fig. 33). The mixture of chlorine and steam is then passed
through a porcelain lube filled with fragnients of porcelain, and
maintained at a bright red heat in a furnace. The issuing gases
ied through a Woulfs boiile, containing a solution of
sodium hydroxide, in order to absorb the hydrochloric acid, and
the oxygen is collected at the pneumatic trough.

(13.) Oxygen is formed on a large scale in nature by the decom-
position of atmospheric carbon dioxide by the green, leaves of
plants, under the influence of liRht. The carbon dioxide is decom-

Oxygm

tby

posed into oubon, which is assimiUlcd by the plant, and into
oxygen which ii throvm into the atmosphere. It has been esti-
mated that 1 square metre of green leaf is able, under the influ-
ence of sunlight, to decompose more than i litre of carbon dioxide
peT hour.

(14.) Of the many other methods by which it has been proposed,
from time to time, to manufacture oxygen on a large scale, may be
mentioned one, known as the Tessi^ du Motay process, from the
name of the inventor. This method consists in the alternate for-
mation and decomposition of sodium manganaie. The process
consists of two operations, which are carried out at different tem-
peratures. When a current of air is passed over a moderately

heated mixture of manganese dioxide and sodium hydroxide,
sodium manganaie is formed —

8MnO, + 4NaH0 + O, - SH,0 + SNajMnO^.

And if this sodium manganate be healed W bright redness, and a
current of steam at the same lime passed over it, the manganate is
reduced to dimanganic trioxide, sodium hydroxide is reformed, and
oxygen evolved, thus —

ZNa,MnO, + 2H,0 - Mn,0, + 4NaHO ■»■ 30.

On again passing air over the residue, after allowing the tempcia-

l68 Inorganic Chemistry

van. of the mass to fall lo that at which the 1
conducted, sodium manganate is once more refor

MnjOj + 4NaHO + »0 = 2H,0 + 2Na,MnO,.

Properties. — Oxygen is a colourless gas, having no taste or
smell. It is slightly heavier Ihan air, its specific gravity being
t.1056 (air = i), One litre of the gas, at the standard temperature
and pressure, weifihs j. 43028 grammes. Oxygen is slightly soluble
in water. 1 e.c of water at 0° C. dissolves 0.0489 c.c of oxygen ,
measured at o* C. and 760 mm, pressure. The solubility of oxygen _
in water, diminishes as the temperature rises in accordance with J
the interpolation formula (Winkler) : —

-ao489 -. 0013413/ -t-.o

m83/»-

9534^-

Fish are dependent upon the dissolved oxygen in water
supply of this gas for respiration. Oxygen is also soluble in moltM
silver, which is capable of absorbing about twenty times ii
volume of this gas (see Silver).

Oxygen is endowed with very powerful chemical affinities.
at the ordinary temperature it is able lo combine with such elements
as phosphorus, sodium, potassium, and iron. All the chemica
phenomena exhibited by the atmosphere, are due to the presenccfl
in it of free uxygen, the atmosphere being practically oxygen diluted
with four times its volume of nitrogen. Thus, when a piece 0
btighi metallic sodium is exposed to the air, the surface becomefl
instantly tarnished, and coated over with a tilm of oxide ; whe
iron rusts, it in the same way is being acted upon by the oxygc
of the air, forming oxide of iron : in these cases the metals a:
to become oxiiiised. If the metal be obtained in a sufhciently:]
finely divided condition before being exposed lo the air, o
oxygen, this process of oxidation may proceed so rapidly, thai tl
heat developed by the combination will cause the metal to bur^l
When the process of oxidation is accompanied by light and heatJ^
the phenomenon is known as combustion, the oxygen being spoke
of as i\\K siipporUr 0/ combustion : bodies which bum in
therefore, are simply undergoing rapid combination with oxyge
II will obviously follow, that bodies which are capable of bumingn
in ihe air, will bum with greatly increased rapidity and brilliancy,
when their combustion is carried on in pure or undiluted oxygen.
A glowing chip of wood, or a taper with a spark still upon the

Oxygen

169

wick, when plunged into pure oxygen, will be instantly rekindled.
Such substances as sulphur, charcoal, phosphorus, which readily
bum in air, when burnt in pure oxygen, carry on their combustion
with greatly increased brilliancy. Many substances which are not
usually regarded as combustible bodies will bum in oxygen, if their
temperature be raised sufficiently high to initiate the combustion ;
thus a steel watch-spring, or a bundle of steel wires, if strongly
heated at one end, will bum in oxygen, throwing out brilliant
scintillations. This experiment is most readily shown by project-
mg a spirit-lamp flame upon the ends of a bundle of steel wire, by
means of a stream of oxygen, as shown in Fig. 33. As soon as the
ends of the wire arc sufficiently heated, and begin to burn, the
lamp may be withdrawn and the wire held in the issuing stream

Kio. 33.

of oxygen, in which it will continue its combustion with great
brilliancy.*

It is a remarkable fact, and one which has not yet received any
satisfactory explanation, that these instances of combustion in
oxygen will not take place if both the gas and the material be
absolutely dry. It has been shown that phosphorus, sealed up in a
tube with oxygen which has been absolutely freed from aqueouj
vapour, may even be distilled in the gas without any combination
taking place. The presence of the minutest trace of moisture,
however, is sufficient to allow the action to proceed, but the exact
way in which this operates in causing the effect is at present not
known with certainty. See also p. 12.

Oxygen is the only gas which is cnpable of supporting respira-
tion : an animal placed in any gas or gaseous mixture containing
no free oxygen rapidly dies. Undiluted oxygen may be breathed

also Experiments 48 to 5a, " Chemical lecture Kxperiments."

\70 Jnorgaiiu Chemmry

«nth impunity for a short lime, but its continued inhalalio
produces febrile symptoms. The inhalation of oxyg^en is
sionally had recourse to in cases of asphyxiation, or
drcumstances of great bodily prostration, where the nec
oxygenation of the blood cannot take place on account
enfeebled action of the lungs.

Compressed oxygen acts upon the animal economy as a p
an animal placed in oxygen gas under a pressure of only a few^
atmospheres quickly dies.

During the respiration of man, air is drawn into the lungs, a
is there deprived of 4 to 5 per cent, of its oxygen, and gains 3 t<
per cent, of carbon dioxide. The oxygen that is withdrawn fro
the inhaled air by means of the lungs, is absorbed by the bloc
The power to absorb this oxygen is believed to reside in a ct
line substance, contained in the corpuscles of the blood, 1
hamoglobin, with which it enters into feeble chemical union,
ing the substance known as oxyhemoglobin. Tliis substance ii
red, and imparts to arterial blood its well-known colour. Ourin|
its circulation in the system, the oxyhemoglobin parts \
oxygen, and is reconverted into the purple- col on red hxmogloln
Under normal conditions, the whole of the oxyhajmoglobin
so reduced, for venous blood is found still to contain it to
extent. The amount of carbon dioxide exhaled is diminisht
during sleep, and to a still greater extent during bibetnation.

Oxygen can be liquefied at very low temperatures by the appli-';
cation of moderate pressure [see Liquefaction of Gases).
first liquefied in 1877 by CaiUelct, and independently by PicieC
Its cmiial Lemperalure is -II8.8', al which point a pressure a
;o atmospheres is required to bring about its liquefaciior

Liquid oxygen is a pale steel-blue, mobile liquid, which boils |
-181°. Us specific gravityat -iSi° is 1. 114. The liquid e
when warmed, much more rapidly than gases do for the s
mcremenl of temperature, and its density diminishes in proporti

At ~

i8r-

' density =

:.i24.

„ -

■19"

„ =

.877-

„ -

1^4*

.806.

Allotropy 171

Isomerism— Polvmerism—Allotropy.

Iiomarliai.— It is frequently found that two different compounds have the
same composition ; that is, thoir molecules are composed of the same number
of tlie same atoms, and jrct ihe substances have difTcrent properties. Such
compounds are said to be iwmeric^ the one is an isowur of the ot) er. and the
phenomenon is called isowurism. Cases of isomerism are so numerous among
the compounds of carbon (i.«., in the realm of organic chemistry, see Carbon,
p. 259), that it has been found convenient to classify them. The term
isomerism, therefore, is frequently restricted to cases in which the compounds
ha\*e the same percentage composition, the same molecular weight, and belong
to the same chemical type or class of substances. Thus, the two compotmds,
dimethyl benxene and ethyl benzene, are both expressed by the formula
Cgl l|^ The molecules in each case contain 8 atoms of carbon and lo atoms
of hydrogen, they therefore have the same molecular weight and the same
percentage composition ; and as they both belong to the same t)rpe, or family,
they are said to be isomeric with each other. The difference in the properties
of these compounds is due to a difference in the arrangement of the atoms
within the molecules, and this diflference is expressed in their formulae in the
following manner : —

Dimethyl benzene, Q^^{C)\^ Ethyl beniene. C^H^CCaHg).

Different compotmds having the same molecular weight and tlie same per-
centage composition, but which do not belong to tlte same family of compounds,
are distinguished as wntamers. Thus, the two compounds, acetone and allyl
alcohol, are each expressed by the formula CgllgO. They have the same
molecular weight and the same percentage composition, but belong to two
widely different types of compotmds ; they are therefoie called metanuric
compounds. Tlie difference between them is again due to a difference in
molecular structure, and they are distinguished by formulv which convey this
difference, thtis : —

Acetone, CO(CH,),. Allyl alcohol, C,I Ift(HO).

Polymerltm.— This term is employed to denote those cases in which dif-
ferent compounds belonging to the same family have the same percentage
composition, but differ in molecular weight : that is to say, their molecules are
composed of the same elements, which are pr sent in K\\it^Mv\t proportion ; but
tliey do not contain the same actual numlx-rs of the various atoms, and therefore
liave different weights. Thus, the compounds, ethylene, C2H4; propylene,
CsH«: butylene, ^x^\^^ belong to the same family, and have each the same
percentage composition, but they differ in molecular weight These sub-
stances are said to he polymers of one another.

Allotropy may be regarded as a special case of polymerism. In its widest
sense the term is sometimes used to denote pf>Iymerism in general, but it is
usttally restricted to those instances of polynierism which are exhibited by
elementary bodies only. Many of the elenoents are capable, under sporisO

Inorganic Chemistry

172

conditions, or assuming snch loully difF««m botai) vul propertlei, ihu 1
appear to be entirely different substancei. Tbus. tbe elcmenl sul|hur,
usually seen, Is a pricniDse-Tcllow, opaque, soli
and readily dissolved by carbon dlsiilpbjde. Under

may be made to appear a lolally diffcrent thing ; ii is then a iranslucenl amber'
coloured subslancc, soft and elastic like indiarubber, and insoluble in carbon
disulphide \ it is still sulphur, and nilplim only. Pbofpharus, again, as usually
known, is a nearly colourless, translucent, wax-lihe salid, which melts at a
temperature only slightly above that of the hand, and which Ukes fire a few
degrees bigber ; it is abo eilremely poisonous. Under Especial influences
phosphorus can be made to assume the foltowing properties : — A dark reddish-
broun powder, resembling chocolate, which may be hiated to 150* without
taking Bre. and which i> non-poisonous. The substance is itlU phosphorus,
and phosphonis only. This property possessed by certain of the elemeats ol
appearing in more than one form, of assiiniing. as il were, an aliai. Ii called
allolnfy; [he more uncommon form being spoken of as the a'/of/u/iV modifica-
Hen, or the alhlivp* ot the other.

From a study of the best known instances of this phenomenon, it is beliowd
that flllotropy, in nil cases, ii due to a diHerence in the number of atoms of the
element that are contained in the niolrcule. In the ease of oione. which is
the allottope of oiygen. this is known to lie the case. Ordinary oiygei
molecules consist of two atoms, while the molecule of oiOnc is an nggngalion
of three OTyger

Molecular symbol. O,. Molecular weight, 47.B8, Density. 13.94.

History.— When nn electrical machine is in tipernlion, a peculi
and cha tact eristic smell is noticed in its vicinity. The same smell
is Eomeliines observed in and about buildings, or other objects, when
struck by lightning. In 1785 it was observed by Van Marum that
when clearic sparks were passed in o.tygen, the oxygen acquired
this peculiar smell. Schonbein (1840) showed that the oxygen
obtained by the electrolysis of water, also contained tliis substance
having a smell, and he gave to it the name ozone, signifying ii mull.
SchSnbein made a careful study of the substance, and foimd thai it
might be obtained by various other methods. TTic more recent
work of Andrews, Sorel, and Brodic has brought our knowledge of
the constitution of oione to its present state.

Occurronce.— 0/one is present in the atmo5phere in
small quantities (see Atmospheric Oione).

Modes of Formation.— (i.) Mixed with an excess of oxyj
o«one is best obtained by exposing pure dry oxygen to the influi
of the silent electric discharge. This m.ay be effected by
It shown in Fig, 34, known as " Siemens' oin

onsi5lso(two<:onceniricg1aEstubcs, Aand B. Tube A is cimicd
Dpon its iiiiur surrace willi linfoil, which i* brouglii inio meUllic
contact with ihc binding anew D, as shown in tlie figure. Tube B
is conied upon the m/fr surface, also wlih tinfoil, which i» in
metallic conneclion with binding screw C. Tliese two surfaces of
tinfoil arc connected by nieaos of their respective binding screw*

adniiiied at E, and whitli [lu^^cs ^bn^ ihu anuulai space

between the (wo lubes, is there exposed to the action of the silent

electric discharge. A small portion of the oxygen so passing,

j^Htecomes converted into the alloiropic modification, and the mixture

> ^

*''G 3S-

s from the n

V cube a

■ "pposilc

of oxygen and ojone
end of the appuraius.

For general purposes oJ illusiralion, a very simple arrangement

■nay be subsiiiuicd for the alMive. It consists, as shuwn in Fig. 3;,

of a straight length of narrow glass tube having a piece of plftiinum

ivire down the inside, which passes out through the walls of the

, tube near to one end, and is there sealed to the glass, A second

plaiinum wire is coiled round the outside of the tube, and these luo
wires are connected to the induction coil. On passing a slow
stream of oxygen through the lube, the issuing gas will be found h
be highly charged with ozone.

(2.) Ozone is also formed when an electric cune
through water acidulated with sulphuric acid. Thus, in the ordinary
electfolysisof water, the oxygen evolved from the positive eleclrodel
is found to contnin ozone in sulltcicnt quantity 10 be readily detectecl)
both by its odour, and by oiher tests.

(3.) During many processes of slow oxidation at ordinary le
tures, oionc is formed in varying quantities. Thus, when phoS
phorus is exposed to the air, an appreciable amount of o
formed. One or two short sticks of freshly scraped phosphorll
are for this purpose put into a stoppered bottle containing a
allowed to remain for a short lime, when the air will be found 11

(4.) Ozone is also found during the combustion of ether upon the
surface of red-hol platinum. When a spiral of platinum wire is
wanned in a gas-flame, and while hoi is suspended over a small
quantity of clher contained in a beaker, the mixture of ether vapour
and air undergoes combustion upon the surrace of the platinum,
which continues in an incandescent state so long as any ether
remains. During this process of combustion, a considerable quantity
of ozone is formed. (See also Peroxide of Hydrogen.)

(5.) Ozone is formed during the liberation of oxygen in a number
of the reactions by which that gas is obtained ; thus from manga-
nese dioxide and sulphuric acid the oxygen that is evolved contains
sufficient oione to answer to the ordinary test. In the same way,
by the action of sulphuric acid upon barium peroxide or potassium
permanganate, this allotrope is present with the ordinary oxygen
thai is evolved.

Properties.— As prepared by any of the methods described,
oiooe is always mixed with a large excess of unaltered oxygen,
probably never less than about Bo per cent, of the latter gas being
present Even in this state of dilution it has a strong and rather
impleasanl smcli, which rapidly induces he.idache. When inhaled
it irritates the mucous membranes, and is rather suggestive of
dilute chlorine.

Ozone is a most powerful oxidising substance ; it attacks and
rapidly destroys organic matter : on this account ozonised oxygen
cannot be passed through the ordinary caoutchouc tubes, as these

heae 1

Osom 1 7 S

are immediately destroyed by it. It bleaches vegetable colours,
and most metals are at once acted upon by it Even metals like
mercury, which are entirely unaltered by ordinary oxygen, are
attack^ by ozone. Its action upon mercury is so marked in its
result, that the presence of exceedingly small traces of ozone can be
detected by it ; the mercury is seen to lose its condition of perfect
liquidity, and adheres to the surface of the glass vessel containing
it, leaving ** tails ^ upon the glass. Ozone converts lead sulphide
(PbS) into lead sulphate (PbSOJ, and liberates iodine from potas-
sium iodide —

2KI + H,0 + Oa - Oj + Ij + 2KH0.

This property is generally made use of for detecting the presence
of oxone, advantage being taken of the fact, that iodine, when set
free from combination in the presence of starch, gives rise to a
deep blue-coloured compound, the reaction being one of extreme
delicacy. In order to apply this test for ozone, strips of paper are
dipped in an emulsion of starch to which a small quantity of potas-
sium iodide has been added. These papers may be dried and
preserved, and are usually spoken of as ozone test papers. When
one of these papers is moistened with water, and placed in air
containing ozone, the iodine is liberated from the potassium iodide,
and being in the presence of starch, the paper instantly becomes
blue by the formation of the coloured compound of starch. It will
be obvious that this method of testing for ozone can only be relied
upon, when there is no other substance present which is able to
decompose potassium iodide ; for example, when testing for ozone
in the atmosphere, the presence of oxides of nitrogen or peroxide
of hydrogen (both of which are capable of liberating iodine, and
are liable to be present in the air), would materially vitiate the
result (see also Atmospheric Ozone). The above decomposition
of potassium iodide by ozone, may be made use of as a test for
ozone in another way, which, although less delicate, is also less
likely to be vitiated by the presence of other substances. Blue
litmus papers are dipped into water which has been rendered very
feebly acid, and to which a small quantity of potassium iodide has
been added. The papers may be dried and preserved. On
moistening one of these papers with water and exposing it to
ozone, the iodide is decomposed as in the former case, and the
potassium hydroxide which is formed, being a powerfully alkaline
substance, converts the colour of the litmus from red to blue.

176

Inorganic Ckitnistry

When beaicil lo a temperature of about 250', 01
formed into ordinary oxygen ; if, therefore, (he oionised gaa
obia'mcU by means uf tlie Siemens' ozone tube, be fiasscd through
a glass lube healed by means of a Uunsen flanie, the whole of the
ozone will be decomposed, and the issuing gas will therefore be
found to be withoui action upon the ozone test papers.

Ozone is also decomposed by certain metallic oxides, such as
those of manganese, copper, and silver. The action appears to be
one of alternate reduction and oxidation, [he metallic oxide
ing unaitered at the conclusion, thus —

gjO + O, =

Ag, + 20t
Ag,0 + O,

]

The oxidising power of ozone is due to the insl.ibilily of th
cule, and the readiness wilfa which il loses an atom of oxygi
leaving a molecule of ordinary oxygen, thus —

Oj = 0 + O,

The oxygen molecule is to mpara lively inert, but the liberated atom
in its nascent stale, is endowed with great chemical activity. No
change of volume accompanies these processes of oxidation by
oione, as the volume of the oxygen molecule (Oj) is the same as
that of the ozone molecule (O3), the third atom of oxygen being that
which enters into new combination with the o\idi5ed substance.

Ozone is soluble to a slight extent in water, imparting to Ihe
solution its own peculiar smell, looo cc, of water dissolve about
4.5CC of ozone.

Under the influence ol extreme cold, oione condenses to hquid
having an intense blue colour. So deep is the colour, that a layer
of it I mm. in thickness is opaque. This liquid is obtained by
passing oionised oxygen through a tube which is cooled by being

immersed in boiling liquid oxygen,

-l8i". At this temperature the oz
with whicli it was mixed passes on.

It is described by Olsiweskl and Dc

ConstltUllOD of Ozone.— The fundamental difference between
ordinary oxygen and its allotrope ozone, lies in [he fact that the
molecule of the latter contains three atoms, while that of ordini

which has a temperature of

one liquelies, bui the oxygen

Liquid ozone boils at - 106.

wer as an extremely explosive

M*M«

mftTj^^

Oaant

*77

oiygen ctmiisti of only iwo, Oione, therefore, is a polymer of
ox^en ; its molecule is more condensed, three atoms occupying
two unit volumes. This conclusion as to the constitution of oione
has been arrived at from the consideration of a number of experi-
mental facts.

(i.) When oxygen is subjected to the action of the electric dis-
charge, it is found to undergo a diminution in volume.* This was
shown by Andrews and Tait, by means of the tube seen in Fig. 36.
The tube was filled with dry oxygen, which was prevented from
escaping by means of the sulphuric acid contained in the bent por-
tion of the narrow tube, which served as a manometer. When the
«lent discharge was passed through the oxygen, a
contraction in the voltmie took place, indicated by
a disturbance of the level of the acid in the syphon.
When the tube was afterwards heated to about
300* C. and allowed to cool, the gas was found to
have returned to its original volume, and to be
devoid of Dione. This could be repealed inde-
finitely, the gas contracting when ozonised, and re-
expanding when the oione was converted by he.1l
into ordinary oxygen. As only a very small propor-
tion of the oxygen was converted into oione, this
experiment alone afforded no clue as to the rela-
tion between the change of volume and the extent
to which this conversion took place.

(a.) A small sealed glass bulb, containing a solu-
tion of potassium iodide, was placed in the tube
before the experiment. The oxygen was oionised, ^^^ Y

and the usual contraction noticed. The bulb was
then broken, and on coming in contact with Che ozone* present, the
potassium iodide was decomposed, iodine being liberated. No
fiirther contraction, however, followed ; and, further, when the
tube was subsequently heated to 300* and cooled, the gas suffered
no increase in volume. By carefully estimating the amount of
iodine that was liberated by the o»nc, the actual amount of oxygen
which had caused this liberation could be dciermincd, according
10 the equation —

2K1 -I- H,0 -t- O - I, + SKHO,

• "Chemical LeeWrc l".i;ieiimcnii," i;.-w ed., Nos. 63, 6

178 Inorganic Chemistry

and it was found, that the volume of oxygen so used up, was exactly
equal to ihe contraction which first resulted on the oionisalioD of
the oxygen.

These facts proved that when potassiuni iodide was oxidised by
ozone, a certain volume of ordinary oxygen was liberated, which
was equal 10 the volume of oione ; and a certain volume was used
up, which was equal to the original contraction.

These facts were explained by ihe supposition, thai ozone was
represented by the molecular symbol O, ; and its action upon
potassium iodide may be expressed as follows —

2K1 + H,0 + O, - O, + I, + SKHO.

(3,) To prove the correctness of this supposition, however, it
necessary to learn the exnct relation between these two volumes.
This Soret did, by making use of Ihe projwriy possessed by turpen-
tine (and other essential oils) of absorbing ozone without decom-
posing it ; and he found, that the diminution in volume which took
place, by absorbing o(one from ozonised oxygen, was exactly twice
as great as the increase in volume that resulted when the same
volume of ozonised oxygen was healed.

(4.) If the molecule of ozone be correctly represented by O3, its
density will be 24, as against 16 for oxygen ; and its rate of dilTu-
sion will be proportionately slower in accordance with the law ol
gaseous diffusion (sec Diffusion of Gases, p. Si)- Soret found that
this was actually the case, and from his experiments the number 34
for the density of ozone receives conclusive confirniation.

as"

CHAPTER III

COMPOUNDS OP HYDROGEN WITH OXYGEN

rHBKB are two oxides of hydrogea known, vii. :—

Hydrogen monoxide, or water .... Kfi
Hydrogen dioxide H|0,

Formuh, H^. Mcdecular wdgbt = 17.9&

Until the time of Carendish, water was considered to be an
elementary substance. Priestley had noticed that when hydrogen
and oxygen were mixed and inflamed, mcnsture was produced,
and he had also observed that
the water so obtained was some-
limea acid Cavendish showed,
that the water was actually the
prodoct of the chemical union of
hydrogen with oxygen, and he
also discovered that the acidity
which this water sometimes pos-
sessed, was due to the presence
of small quantities of nitric acid ;
and he traced the formation of
this add to the accidental pre-
sence of nitrogen (from the at-
mosphere) with which the gases
were sometimes coniaminated.

Cavendish filled a graduated
bell-Jar with a mixture of hydro- Fig. 37.

gen and oxygen, in the propor-
tion of two volumes of the former to one of oxygen, and he attached
to the bell-jar a stout glass vessel, resembling the pear-shaped
ai^Mratus shown in Fig. 37, which was perfectly dry, and rendered

,-*-,.

hwrgaiiic Chemistry

vacuous. On opening the stop-cocks, gas erilcicd Ihe e\lijiistril
tube, which is furnished ai ihc top with two platinum wires. 1 l.«
cocks were agiiin closed and an electric sp.irk passed through the
mixed gases, thereby causing their explosion, when the interior
surface of the previously dry glass vessel was found to be dimmed
with a film of moisture. On again opening ihe slop-cocks, more
gas was drawn into the upper vessel, the same volume passing in
as originally entered the evacuated apparatus. This showed that
the two gases in their combination with each other had entirely
disappeared. By repeatedly filling the vessel with the mixed gases,
and causing them to imite m this way, Cavendish succeeded in
collecting sufficient of the water to identify the liquid, and prove
that it was in reality pure water.

The more exact volumetric proportion in which oxygen and
hydrogen combine to form water, has been determined by modem
eudiometric methods, which have been developed from Cavendish's
experiment. Accurately measured volumes of the two gases are
introduced into a long graduated glass tube, standing in the mer-
curial trough, and provided vnlh two platinum wires, by means o(
which an electric spark can be passed. The gases are caused to
unite by means of the spark, and the contraction in volume is
carefully observed. Fig. 38 shows the apparatus for this purpose.
The long glass tube A having a millimetre scale graduated upon it,
and having two platinum wires sealed into the glass near the uppei
and closed end, is completely filled with mercury, and inverted in
the trough of the same liquid : this tube is known as a eudiometer.
A quantity of pure oxygen is then introduced into the lube, and
the volume occupied by the gas carefully read off upon the gradua-
tions. Seeing that the volume occupied by a (jiven mass of gas is
dependent both upon the temperature and the pressure, each of
these factors has to be taken into account in the process of ihjs
experiment. The temperature is ascertained by the attached
thermometer T. The pressure under which the gas is. will be the
atmospheric pressure at the lime (ascertained by the barometer H
placed near the appanttus) minus the pressure of a column o(
mercury, equal to the height of the mercury within the eudiometer
above the level of that in the trough. This height is obtained in
millimetres, by carefully reading upon the graduated scale the level
of ihc mercury in the trough, and the lop of the column in the
lube, and the number of millimetres so obtained is deducted from
the barometric reading. These observations are made by means

IK of I

IVattr

l3l

scope placed ai such ji cunvcniLDi dist.incc, thai ihe heat ol
C body may nol intrMluce disturbances.

e data obtnined, give the volume of gas at a p.irticular leni-
rature, and under a pressure less than thai of tlie atmnsphere.
Ily the process of c.-ilculntion e>iplained under the general pro-
perties of gases (p. 69), this is reduced to the standard temperature
,ind pressure, vii., o' and 7(10 mnv
A qunntiiy of hydrogen is then introduced ioto Ibc eudjonieier,
msiderably in excess of that required for complete combination

F.O, 38.

wiih the oxygen, and [he volume .igain ascertnined with the above
precautions and corrections.

The difference between the first and second reading will give the
volume of hydrogen which hns been added.

The eudiometer is then firmly held down against 3 pad of cnoui-
chouc upon the bottom of the trough, nnd the gases fired by an
electric spark from a Rubmkorff coil. A bright flash of light
passes down the tube, and on releasing it from the indianibbtf hed,
mercury enters to fill the space previously occupied by Ibe gasea
^hJch have combined.

i82 Fnotganic Chemistry

On allowing ihe insirumeni lo once more acquire the icmpcra-
turc of the surrounding atmosphere, the residual volume is read off,
and corrected for temperature and pressure.

The following data have now been obtained : —

(i.) The volume of oxygen, corrected for temperature and

(a.) The volume of mixed oxygen and hydrogen, corrected foi

temperature and pressure.
(3.) The volume of residual hydrogen, corrected for tempera-
ture and pressure.

1 how Ihe resuk is deduced from

Corrected voliimf! of oxygen used 45-35 ^^|

Correcied volurae liter the addition of hydrogan . aj&.oj ^^|

Corrected volume of residua] hydrogen .... iicto ^^|

056.05 - 45.35 = aiaTO = total volume of hydrogen employed.

aiATO - IJO.10 = 90.60= volume o( hydrogen which has combined wilb

45,33 volumes of oiygen.

■■■ .15-35 - « ;:9o.6o: 1.997.
. '. One volume of oxygen lias combined with 1.997 volumes ol hydrogen

lo form water.*

TI1C volume composition of water may be shown by analytical
processes, as well as the synthetical
inelliod described above. This decom-
position of water is most conveniently
effeaed by means of an electric cur-
rent. If the two terminals from a gal-
vanic battery are connected to two
pieces of plaiinum wire or foil, and
these are dipped into acidulated water,
bubbles of gas make their appearance
upon each of the wires. If these two
strips of plaiinum be so arranged in a
Flo. 39. bottle, that alt the gas evolved escapes

by a delivery-tube (Fig, 39), it will
be found that the gas explodes violently on the application lo it

IlVafff

of .1 lighted taper, showing ii to be a mtiii
drogen. By modifying the apparatus in
wch a way that Ihe gas from each
platinum pkie shall be collected in sepa-
rate tubes, so arranged that the volumes
of the gases can be measuied, it is found
that twice as much hydrogen is evolved,
in a given time, as oxygen. A conve-
nient form of voltameter is seen in Pig.
40, where the two measuring tubes art
suspended over the platinum plates con-
tained in a glass basin. The electrode,
which is connected with the ncgiilive
teiminal of the battery, is the one from
which the larger volume of gas, vii.,
the hydrogen, is evolved, while the oxy-
gen is hberated at the positive plate-
When the volumes of the gases nic
carefully measured, it is found that they
are not exactly in the proportion of two
of hydrogen to one of oxygen, but that
the oxygen is in deficit of this propor-
tion. This is due, in the first place,
to the greater solubility of oxygen in
water than of hydrogen ; and, secondly,
to the formation of a certain quantity of
otonc during the electrolysis, whereby
there is a shrinking of volume in the proper

>r three to l\

Tbe "clecUQljriii of micr." u ihis proceu ii usually callEd. ij not I]i<
simple phenomFnon thai at lirsi tight it iiil|;hl appear to lir, la the Bnl
place, pure walrt L> nol an elnclrolyif, and it Is necetsaiy either to acidulate
it. or to rendei ii alkaline by the addition of sodium or potassium hydroiidH.
The fiisl action of tbe electric current is (to the case of water acidulated with
tulphurie acid) to decompose the sulphuric acid into H|, which appears at tbe
negative elecuiide, and SO,, which is liberated at Ihe anode. SO,, bowevcf ,
hnaks down into SO, -t-0. the oiygen being liberated, and ttiesulpbur Irioiide
at onoe uniting with a molecule ot water presenl. Iq regcnersile sulphuric acid.
The changes may be thus repre»nlt:d ' —

^^^M Indirecllv. Ihi-tefore. 1

= H, -1- (SO, + O).
= H^O.,
r is decomposed. As alreac

hiorgmiic Chemistry

[he nascpnt oxyg<-n is convertrd inlo oione, some also oniies vriih >™ier it
fomi hyclrof;en peroxide, M,0], and prDbnbljr a still ISirgcr quantily is employed
Id OKidising the sulphuric acid [o per^phuric, which is always fonued in
solution at the anode. Denhelol considers thai the varialion of llie proponion
of hydrog'-ji and oxygen c^vo1ved dtiring the electrolysis of dilute sulphuric add,
from the proportitm of two volumes of hydrogen to one volume of oiygen, la
mainly, if not entirely, diK lo the formfllion of persulphuric add.

The Volumetric Composition of St«a.m.— When a mixture ot
oxygen and hydrogen is exploded in a eudiometer, we have seen
ihat a certain contraction of volume follows, due lo the formalion
of water by the uniting gases. The oxygen and hydrogen thai
have entered into conibination have disappeared as gases, the
volume of the resultant water being practically negligible. It is
important to know what relation exists between the volume of
the uniting gases, and the volume of the product of their combina-
tion when in a state of vapour ; that is to say, what volume of
steam is produced by the union of one volume of oxygen with
two volumes of hydrogen ; in other words, whether there is any
molecular contraction in the formation of steam.

To ascertain this, the mixed gases, in the exact proportions to
form water, must be made to combine under such circumstances
that the product shall remain in a stale of gas or vapour, so thai
its volume, and that of the mixed gases, tnay be measured under
comparable conditions. For this purpose a mixture of oxygen and
hydrogen, obtained by the electrolysis of acidulated water, is in-
troduced into the closed limb of the U-shaped eudiometer shown
in Fig, 41, • This tube is graduated into three equal divisions,
indicated by ilie broad black bands, and is furnished with two
pLntinum wires at the closed end, U is also surrounded by an
outer lube, so that a stream of vapour from some liquid, boiling
above the boiling-pioinl of water, can be made to circulate. The
most convenient liquid for ihi: purpose is amyl alcohol, which
boils at 130* In this way the eudiometer, and the contained gases,
will be maintained at a constant temperature, high enough to keep
the water formed by their combination, in the state of vapour.

The amyl alcohol is briskly boiled in the flask, and its vapour is
led into the lube sunounding the eudiometer. The temperature of
the mixed gases is thereby raised to 130°, nnd they occupy the
three divisions of the tube when the mercury in the open limb is
at the same level, that is, when the gases are under attnospheric

• See Eiperiroenti Noi. 74 and 7s. "Chemical Lecture Experiments,"

Wottr

I8S

preuure. The amy! alcohol vapour leaves the apparatus by the
glass tube at the bottom, and is conveyed away and condensed.
An electric spark is then passed through the gases by means of the
induction aril. (In order to prevent the mercury from being
forcibly ejected from the open limb of the U-tube at the moment ol
explosion, an additional quantity of mercury is poured in, and the
open end is closed by the thumb when the spark is passed.) On
bringing the enclosed gas again to the atmospheric pressure, by
.idjusting the level of the mercury unlit it is once more at the same

Fio. 41.

height in each limb, ii will be found that the mercury in the eudio-
meter is now standing at the second band ; that is to say, the three
volumes of gas originally present have now become two volumes of
steam. This condensation is expressed in the molecular equation—

O, + SH, - 8H1O.

The Onvlmetrio Composition of Water.— Having learned
the composition of water by volume, and knowing also that the

Inorganic Cfumistry

relative weighis of equal volumes of oxygen and hydroger
15.96 : (, the composition by weight can readily be calculated, thm

t volume of oxygen = iS.0
1 volumes of hydrogen = 2.00

17,96 parts by weight of water are composed of i.oa parts by
weight of hydrogen, and 15.96 parts of oxygen, or, expressed ceotesi-
mally, we hai-e^

Oxygen .... 88.80
Hydrogen . . . II. 14

The composition of *
determined with greal c;

ter by weight has been experimenta)
5 by a number of chemists.

^^^ The apparatus shown in Fig. 42 represents the method employed

^^H by Dumas (1843). When copper oxide is healed in a stream of

^^1 hydrngen, the copper oxide is deprived of its oxygen, which unites

^^V with the hydrogen to form water —

■ of,

CuO + H, - Cu + H,0.

Uumas' method is based upon this reaction. A weiglicd quantity
if perfectly dry copper oxide was heated in the bulb A, in a current
of hydrogen genei^ted from iinc and sulphuric acid in the bottle H,
;ndered absolutely pure and dry by its passage through a

Water 187

series of tubes containing absorbents. The water formed by the
union of the hydrogen with the oxygen of the copper oxide, was
collected in the second bulb, B, previously weighed ; and the un-
condensed aqueous vapour which was carried forward in the stream
of hydrogen, was arrested in the weighed tubes which follow. The
increase in weight of the bulb B and the weighed tubes, gave the
total weight of water produced ; while the loss of weight suffered
by the copper oxide, gave the weight of oxygen contained in that
water. The difference between these two weights is the weight
of the hydrogen that entered into combination with the oxygen.

As a mean of many experiments it was found that in the forma-
tion of 236.36 grammes of water, the oxygen given up by the
copper oxide was 2iao4 grammes.

236.36 - 210.04 = 26.32,

therefore 236.36 granmics of water were made up of

Hydrogen =« 26.32
Oxygen « 210.04

236.36

The ratio of hydrogen to oxygen is therefore as 2 : 15.96.

Hydrogen prepared from zinc and sulphuric acid is liable to contain traces of
(i.) Sulphuretted hydrogen. This is absorbed in the first tube containing

broken glass moistened with a solution of lead nitrate,
(a.) Arsenuretted hydrogen ( absorbed in the second tube, filled with glass
(3.) Phospboretted hydrogen ( moistened with silver sulphate.

(absorbed in the third tube, containing in one limb
pumice moistened with a solution of potassium
hydroxide, and in the other fragments of solid
potassium hydroxide.
Tubes 4, 5. 6, and 7, containing solid potassium hydroxide and phosphorus
pentoxide (the two latter being placed in a freezing mixture), are for the pur-
pose of withdrawing every trace of aqueous vapour. Tube 8 was weighed before
and after the experiment, in order to test the absolute dryness of the hydrogen
that entered the bulb. In order to get rid of dissolved air, the dilute sulphuric
acid used was previously boiled. Tubes 9, xo, xx were weighed both before and
after the experiment ; while tube la, which was not weighed, was placed at the
end to prevent any absorption of atmospheric moisture by the weighed tubes.

Since the time of Dumas this subject has been reinvestigated by other
experimenters, who have introduced various modifications into the process ;
thus, with a view to finding the weight of hydrogen directly, and of eliminating
many of th«' possible sources of error arising from the \irrf^x\cr of impurities in

hioigaiui. Uiematr}

(S.S

llie liydroycQ, Ihe liyiltogen has brcn abscrrbed irf palladiuiu, Tht nieul so. |
<diarged uUb byUrogvn. c.in be wciybed belorc and nltpr ilic cipcrinenl, n
ihc .iciiLil wiighl oj liydrogen used, ditecily ascertained.

Most ncxDllj [be mailer baa been Invenigaled by Stall uid RHyleigh, a
ihe resulls obiained show only the tUghtesi drpanure froni ibe niiiriti

Properties of Water.— Pure water is a tasteless and odourless

liquid When seen in moderate quantities it appears ID be colour-
less, bill when viewed ilirouf;h a stratuni of considerable thickness

it presents a beautiful greenish-blue colour. This colour nia,y be
seen by filling a boriiontal tube about 15 feet long with the purest
water, and passing a strong beam of liglit through it It may also
be perceived by directing a ray of light through a tall cylinder ol
waterin the manner shown in the figure, and causing it toberefiected
lip through the waler from the surface of a layer of mercury at the
ballom ; Ibe immerging ray, being then rclccled upon a screen,
shows the rhararlenslir rnloui "f 'he water. By intrrrepting the

Water i S9

rny by a hand mirror at A, the white hght can be thrown upon the
screen, as a contrast to the greenish-blue tint

Aitkin has recently shown, that the presence of extremely finely
divided stispended matters in water will give to the liquid the appear-
ance of a blue colour. 7*hus, in tanks where water is being soAened
by the addition of milk of lime, after the bulk of the precipitated chalk
has settled, and only the finest particles still remain suspended in
the liquid, it is often noticed that the water appears to have a rich
blue colour. The wonderful blue colour of the waters of many of
the Swiss lakes is probably due in part to this optical phenomenon,
as well as to the intrinsic colour of the water. When a mass of
pure snow, such as falls in high mountainous regions, is broken
open in such a way that the light is reflected from side to side of
the small crevice, the true greenish-blue colour of the water is very
manifest

Water is compressible to only a very slight extent ; thus, under
an additional pressure of one atmosphere, 1000 voliunes of water
become 999.93 volumes.

Small as this compressibility is, it exerts an important influence upon thr
distribution of land and water upon the earth. It has been calculated, that
owing to thb compression, where the ocean has a depth of six miles, its surface
is lower by 6ao feet than it would be if water were absolutely non-compressible;
and calculated from the average depth of the sea, its average level is depressed
116 feet. The effect of this depression of the sea-level is that a,ooo,ooo square
miles of land are now uncovered, which would otherwise be submerged beneath
the ocean.

Water is an extremely bad conductor of heat A quantity of water
contained in a tube held obliquely, may be boiled by the application
of heat to the upper layers, without appreciably affecting the
temperature of the water at the bottom ; a fragment of weighted
ice sunk to the bottom will remain for a long time unmelted, while
the water a few inches above it is vigorously boiling. This low
conductivity for heat is shared in common by all liquids that are
not metallic Indeed, Guthrie has shown, that water conducts heat
better than any other substance which is liquid at the ordinary
temperature, with the exception of mercury.

Steam. — Under a pressure of 760 nun., water boils at 100*
(see p. 112), and is converted into a colourless and invisible gas,
or vapour. 7*he visible effect that is observed when steam is
allowed to issue into the atmosphere, is due to the condensation of
the steam in the form of minute drops of water. What is poptilarty

190

Inorganic Chemistry

called sleam is in reality, therefore, not steam, but &n aggre

tion of small particles of liquid water. The invisibility of s

is readily demonst rated by bailing a small quantity of «

capacious flask ; as the sleam issues from the neck it condense

in contact with the cool air and presents the famllia:

ance, but within the flask it will be perfectly transparent an^l

invisible.

lee. — At a temperature of o° water solidifies to a transpare
crystalline mass. In the act of solidification, the water expaodi^
by nearly ^th of its volume, lo volumes of water become 10.908
volumes of ice ; solid water, therefore, is specifically lighter than
liquid water, and floats upon its surface. Water in this respect is
anomalous, for in the case of most other substances, the solid form
is denser than the liquid. The disruptive force exerted by water at
the moment of freezing, is the cause of the bursting of pipes and
other vessels containing water during winter ; and It is also an
important factor in the economy of nature, in the disintegration ot
rocks and of soil Under certain conditions, water may be cooled
many degrees below 0° without solidification taking place. Thus,
if a small quantity of water contained in a vacuous tube be care-
fully cooled without being subjected to vibration, its temperature
may be lowered lo -15° without it solidifying; a slight shock,
however, at rnce causes it to pass into the solid state, when its
temperature Instantly rises to o' (see p. 1 18). Although the exact
vater freezes is liable to uncertainly from
t which ice melts is, under ordinary cir-
Under increased pressure ice
" ; thus Mousson found that,
e melted at -18'. The

temperature at which v

s cause, Ibe point a

nstances, constant, i
will melt at temperatures belov
under a pressure of 13,000 atmospher

melting-point of ice is lowered by about 0,0074° by each additional
atmosphere of pressure (see p. 119).

Between the temperatures of +4° and 100°, water follows the
ordinary laws that govern the expansion and contraction of liquids
D change of temperature ; if water be cooled from loo*, it
gradually contracts until the temperature reaches 4°. Between
this point and o* it forms a remarkable exception to the general
law, for, when cooled below 4', it slowly expands instead of con-
tracting, and continues expanding until 0° is reached, when it
solidifies. At 4°, therefore, water expands whether it be healed
r cooled ; consequently, at this point it is denser than at any
other temperature- This temperalure is known as its point of

Water 191

maxiinam density. (The most accurate observations fix the exact

point at 3.945*-)

The following table shows the change of volume suffered by
water on being heated from o* to 8" . —

1. 000000 volumes at 0° becomes

0.999915

))

+ 2*

0.999870

»)

0*999900

1. 000000

>»

One cubic centimetre of water, measured at its point of maxi-
mum density and at 760 nmi., is the unit of weight of the metrical
system, and is called a gramme.

It is also at this temperature, that water is taken as the unit
for comparison of the densities of other liquids and of solids ;
thus, when it is stated that the density, or specific gravity, of
diamond is 3.5, it is meant that diamond is 3.5 times as heavy
as an equal bulk of water measured at its point of maximum
density.

The fact that water has a point of maximum density remote from
its freezing-point, is one of far-reaching consequences in the opera-
tions of nature.

When a mass of water, such as a lake, is exposed to the influence
of a cold wind, the superficial layer of water is cooled, and thereby
becoming specifically denser, it sinks to the bottom and exposes a
fresh surface. This in its turn has its temperature lowered, and in
like manner falls to the bottom. A circulation of the water in this
way is set up, until the entire mass reaches a temperature of 4°.
At this point the further cooling of the surface-layer causes expan-
sion instead of contraction, and the colder water becoming speci-
fically lighter now floats upon the top, where it remains until it
congeals. If water continued to contract as its temperature was
reduced below 4*, the circulatory motion would continue until the
whole body of the water was cooled to 0°, when solidification of the
entire mass would take place. The reason that certain very deep
waters seldom or never freeze, is because the duration of the cold
is not long enough to bring the temperature of the entire mass
of the water down to 4^ and until that is effected, no ice can form
upon the surface.

The Solvent Power of Water.— Water is possessed of more

Inorganic Chemistry

general solvtnl powers tban any other liquid ; ihal is \a say, a large)
nmnber of substances ate dissolved by water than by any other
liquid. The solvent action of water upon gases, liquids, and solids,
in so far as it is shared by other liquids, has been dealt with under
liie General Properties of Liquids (Part I., chap, xiii.}.

Water of Crystalllsatfon.— When solid substances are dis-
solved in water, and the water afterwards evaporated, ihe dissolved
substance is frequently deposited in definite crystalline shapes.
Many salts owe their crystalline nature to the fact, that a certain
number of molecules of water have solidified along with molecules
of the salt, each molecule of the salt being associated with a defi-
nite number of molecules of solid water. The water molecules
must be regarded as having entered into a feeble chemical union
with the salt molecule, but a union which is of a somewhat difTe-
rent order from that which holds together the atoms of oxygen and
hydrogen in the water molecules, or the atoms composing the salt
in the salt molecule (:ee p. 65). Thus, copper sulphate crj-stallises
associated with five molecules of water, CuS0„5H,0 ; magnesium
sulphate with seven, MgS0„7H,0. Water so associated with
crystals is known as ivater of cryslallisalhn, and the compound
is called a hydratt.

Many sails are capable of crystallising with more than one defi-
nite number of molecules of water, depending upon the temperature
at which the crystallisation takes place ; thus sodium carbonate,
crystallised at the ordinary temperature, has the composition,
NajCOj.lOHjO ; while at temperatures between 30° and 50° the salt
that is deposited contains 7 molecules of water, NajCOj,7H,0.
Sodium chloride, ctj-stallised from solution at -7°, has the compo-
sition, NaC1,SH,0 ; while the crystals that are deposited at -13'
contain 10 molecules of water, NaCl,i0H,O.

In such cases as these, the paiticular crystalline form of the salt
differs with the different degrees of hydration. Salts containing
water of crystallisation, which are deposited from solution at
temperatures below o', are sometimes termed cryohydrates.

Many crystalline salts, when exposed to the air, lose either some
or all of their water of crystallisation, and in so doing, lose their
particular geometric form. Thus, the salt, NajCOj,10H]O (ordinary
washing soda), when freely exposed, gradually loses its crystalline
form and falls down to a soft white powder, which consists of small
crystals of another form, having the composition Na^CO^HiO.
This process is known as fjffi>resctiict, the crystals being said to

Wa/fr 193

effloresce. Other crystals undergo exactly the reverse change ; they
combine with moisture from the air, and pass into other crystalline
forms containing more water of crystallisation, or in some cases
they absorb sufficient moisture to cause them to liquefy. Such
substances are said to deliquesce. This property of certain salts, is
made use of for withdrawing traces of water from either liquids or
gases. Thus, such a liquid as ether may be freed from dissolved
water, by adding to it copper sulphate containing one molecule of
water of crystallisation, CuSOi^HjO ; this compound takes up water
and passes into CuS04,5H,0, and thereby has the effect of drying
the ether. Gases in the same way are frequently dried by being
passed through tubes containing calcium chloride from which the
water of crystallisation has been removed. This substance absorbs
water with avidity, passing into the hydrated salt CaClijOHjO.

The characteristic colours of certain salts are in many cases
dependent upon the amount of water of crystallisation they contain.
Thus cobalt chloride, CoCI^ytiH^O, is a pink salt If it be gently
heated to 1 20* it loses its water, and becomes CoCl^, which has a
rich blue colour. Solutions of this salt have been employed for
the so-called sympathetic inks. The faint colour of the pink salt
renders words written upon paper with its dilute solution prac-
tically invisible ; but on warming the paper, and thereby expelling
the water from the salt, the written characters appear in a blue
colour, which again disappears as the salt is allowed to rehydrate
itself by exposure to the air.

One of the most striking examples of this change of colour
resulting from varying proportions of water of crystallisation, is seen
in the salt magnesium platino-cyanide, which crystallises under
ordinary circumstances as a bright scarlet salt with seven molecules
of water, MgPt(CN)4,7H,0. When this salt is heated to about 50"
it loses two molecules of water, and is converted into a canary-
yellow salt, MgPt(CN)4,5H,0. If the temperature be raised to
100** the yellow salt becomes white by the loss of three more mole-
cules, the composition of the white salt being MgPt(CN)4,2H,0.
When a solution of the salt is carefully evaporated to dryness in
a dish and gently warmed, these colour changes will be rendered
evident ; and upon exposing the dried and white residue to the air,
or by gently breathing into the dish, the salt rehydrates itself, and
is converted into the crimson compound having seven molecules
of water.

Many salts can have their combined water withdrawn by power-

Inorganic Cfufntstry

ful drhydrating agents ; thus, if a cryslal of copper sulphate (" I
vitriol," CuS0„5H,0} be immeised in strong sulphuric acid, tl
acid abstracts four out of the five molecules from the satl, leavin(^
the nearly white sail CuS04,H,0 ; or when alcohol is added to H
solution of cobalt chloride, or to crystals of the salt, CoCl^C
the alcohol abstracts water, and the solution becomes blue.

When salts containing water of crystal li sal ion are heated, I
frequently happens that a portion of the water is more easily par
with than ihe remainder. Thus copper sulphate, CuSO^.GH^
when healed to 100°, parts with four molecules of waier, leaving tliff
salt CuSOi,H,0; and in order to drive off this one remaining mole-
cule, the temperature must be raised above 200°. Zinc sulphate
(or while vitriol), ZnS0„7H,0, in like manner loses six molecules of
waier at 100°, but retains the seventh until a temperature of 140* is
reached. In order, therefore, to distinguish between the water that
is more firmly held and thai which is readily parted with, the t<
■water oj Cinstitulion is frequently applied lo ihe former, and tbe.i,
:s expressed in notation in the following ni

CuSO.H,0,'*H,0 ;

ZnSO,H,0,flH,0.

NatUfal Waters.— On account of the great solvent powers
water, tliis compound is never found upon the earth in a state
absolute purity ; even rain, as it falls in regions far removed froo)
the dirty atmosphere of towns, not only dissolves the gases of the
atmosphere, but also small quantities of those suspended mailers
which are always present in the air. As soon as Ihe rain reaches
the earth, the water at once exerls its solvent action upon the
mineral matter constituting the portion of Ihe earth's crust over
which it flows, and through which it percolates, and the liquid is
rapidly rendered less and less pure as it travels on ils course to
lake or ocean.

Natural waters may lie broadly divided into two classes, based
upon the amount of dissolved impurities they contain. If the sub-
stances in solution are present in excessive quantities, or to such, aa
extent as to be perceptible lo the taste, the water is s
mintral VL'atcr : while, on the other hand, walcrs that
rich in dissolved impurities are knoim z.i fresh waters.

Hlneral Waters.— The most exaggerated examples of mineral
waters ate 10 be found in sea water, and in tl
lakes, which, havmg do outlet, are fulfilling ihe purpose of enormous

lb-

Natural Waters 195

evaporating basins, in which the waters that flow into them are
undergoing evaporation and therefore concentration ; such, for
example, as the salt lakes of Egypt, the Elton lake in Russia, and
the Dead Sea. In waters of this description the total quantity of
dissolved solid matter is very considerable, and, as in the case of the
Dead Sea, is often deposited in crystalline masses round the shores
of the lake. The following table gives the total amount of dissolved
saline matter contained in 1000 grammes of certain of these waters : —

Irish Sea . . 33-^

Mediterranean Sea 40.0

Dead Sea 228.:;

Elton Lake 271.43

As a typical example of a sea water, the composition of the water
of the British Channel may be quoted ; 1000 grammes of this water
contain —

Sodium chloride 27.059

Magnesium chloride .... 3.666

Magnesium sulphate .... 2.296

Calcium sulphate 1.406

Potassium diloride 0.766

Calcium carbonate 0.033

Magnesium bromide .... 0.029

35.255

Water 964-745

1000.000

Passing from these highly concentrated mineral waters, we find
a large number of spring waters which are classed as mineral^ not
because the total quantity of foreign matter in solution is excessive,
but rather because they contain an abnormally large proportion of
a few special substances. Thus, large quantities of magnesium
sulphate, and chloride, are found in such springs as those at
Epsom and Friedrichshall. Others are found to contain consider-
able quantities of sodium sulphate and sodium carbonate ; while
those known as chalybeate waters, contain ferrous carbonate in solu-
tion. Spring waters that are charged with unusual quantities of
soluble gases, are likewise placed in the category of mineral waters,
such as the waters of Apollinaris and Seltzer, containing large
quantities of carbon dioxide ; and the sulphur springs at Harrogate

196 Inorganic Chemistry

and Aachen, which hold in solution sulphuretted hydrogen as well
as alkaline sulphides.

Fresh Waters. — The purest form of natural water is rain water.
The average weight of solid matter dissolved in rain water, collected
in the country and in perfectly clean vessels upon which it exerts
no solvent action, is found to be 0.0295 P^rts in 1000 parts of water.
Collected in or near towns, rain water always contains a larger
amount of dissolved impurities, such as nitrates, sulphates, anmio-
niacal salts, and often considerable quantities of sulphuric acid : it
is the acid nature of the rain that causes so much damage to stone
buildings.

The nature and extent of the contamination that rain water
suffers after it has fallen, must obviously depend very largely upon
geographical and geological circiunstances, and therefore there
are no special features that are distinctly characteristic of waters
from rivers, lakes, or springs.

Thus, the total solid impurity in 1000 parts of water from the
river Dee at Aberdeen is 0.057, while that contained in the Thames
is 0.30 parts.

The water of Loch Katrine only contains 0.032 parts of solid
matter dissolved in 1000 parts, while that of Elton lake contains as
much as 271.43.

The same wide differences are also seen in spring waters from
different geological strata. Spring waters from granite and gneiss
rocks, contain on an average 0.059 parts of dissolved solid matter
in 1000 parts, while those from magnesian limestone average as
much as 0.665 parts. As a broad general rule, river waters are
found to contain less solid matter in solution than spring waters,
and these in their turn less than deep well waters. Thus, com-
paring waters from different sources, and selecting only such
samples as are known to be free from pollution from either sewage
matter or other abnormal impurities, it will be seen that, with
regard to the dissolved solid matter they contain, they fall in the
following order —

Total Solid Impurity Dissolved in 1000 Parts of
Unpolluted Waters.

Rain water (average of 39 samples) . .0295

Rivers and lakes (average of 195 samples) . .0967

Spring waters (average of 198 samples) . . .2820

Deep well waters (average of 1 57 samples) . .4378

Natural Waters 197

Hardness of Water. — Certain of the salts that are very fre-
quently present as impurities in natural waters, give to these
waters the property that is known as hardness. The chief com-
pounds that produce this effect, are the salts of lime and magnesia.
The term hardness is applied to such waters, on account of the
difficulty of obtaining a lather, with soap, in the ordinary process
of washing. Pure soap may be regarded as a mixture of the
sodium salts of certain fatty acids (oleic, stearic, palmitic, &c),
which are soluble in pure water. In the presence of salts of lime
and magnesium the soap is decomposed ; and an insoluble curdy
precipitate is formed, by the union of the fatty acid of the soap
with the lime and magnesium of the salts. Until the whole of the
hardening salts have in this way been thrown out of solution, no
lather can be obtained, and the soap is useless as a cleansing agent ;
but as soon as this point is reached, the addition of any further
quantity of soap at once raises a lather on the water, and the soap
is capable of acting as a detergent. This process of precipitating
the salts of lime and magnesium is known as softenings and in this
instance the water is softened at the expense of the soap.

Hard waters often become less hard after being boiled for a
short time, and this hardness which is so removed is termed the
temporary hardness. The degree of hardness which the water still
possesses after prolonged boiling, is distinguished by the term
permanent hardness. The diminution of the total hardness of a
water by boiling, is due to the fact that the soluble acid carbonates
of lime and magnesium are decomposed during this process, into
Mrater, carbon dioxide (which escapes as gas), and the practically
insoluble normal carbonates of these metals ; thus, in the case of the
lime salt —

CaH^COa), = HJO + CO, + CaCO,.

When such a water is boiled, the calcium carbonate is thrown down
as a white precipitate, which gradually collects upon the bottom
of the containing vessel The " furring " of kettles, and the forma-
tion of calcareous deposits in boilers, is largely due to this cause.

In the case of waters that are highly charged with calcium car-
bonate, held in solution by dissolved carbonic acid, this deposition
of calcium carbonate may even take place at the ordinary tempe-
rature, owing to the diffusion of the dissolved carbon dioxide into
the air. It is in this way that those remarkable, and often beauti-
fully fantastic, formations, known as staltutites^ have been produced

19!

Inorganic Chemistry

in certain subterranean caves. Water charged with the aolubt
calcium carbonate, in slowly dropping from the roof of such a cavi
loses a portion of its dissolved carbon dioxide, and, in consequence
deposits a certain amount of the calcium carbonate which h
solution. Each drop, as it slowly forms, adds its little share n
calcium carbonate to the deposit, which thereby gradually grotn
much as an icicle grows, as a dependent mass called a stalacti
Wlielher the water that drops from the stalactite has deposits
the whole of its calcium carbonate, will depend largely upon t'
time occupied by each drop in g^athering and dropping ; if, a
happens, the whole has not been precipitated, the remainder i|
deposited upon the floor of the cave, and a growing column t
calcium t:arbonale, called a stalagmite, gradually rises from I
ground until il ultimately meets the stalactite.

Clark's Process Tor Softening Water.— Waters whose har
ness is due to the presence of the carbonates of lime and magnwi
sitim, can be deprived of their hardtiess by the addition to them O
lime. The amount of hardness is first estimated, and such i
amount of milk of lime is then added as is demanded by the follow^J
ing equation : —

CaH^CO,), + CaO = H,0 + QCaCO^

la this way, the soluble lime salt is converted into the insoluU
normal carbonate, which settles to the bottom of the tank.

The sails, which are mainly instrumental in causing the [
manent hardness, are the sulphates of lime and magnesium.
degree of hardness and its particular order, thai is, whether ter
rary or permane.it, will obviously be determined entirely by i
particular geological formation from which the water is derived.

Potable Waters.— Undoubtedly the most important i
which water is put, is its employment as an article of food Ii
and since il has been proved beyond dispute thai many virulef
diseases, such as cholera, typhoid fever, and others are propagated
through the medium of drinking-water, it becomes a matter o' " '
greatest sanitary importance that the waters supplied for this pur
pose should be as pure as possible. Excepting in very rai
stances, where poisonous mineral matters accidentally gain a
lo drinking-water {as for example, in the case of certain w
which are capable of attacking, and to a slight extent dissolvi
the lead of the pipes through which they may be passed), the si

Natural WaUrs

»99

matters that are usually found in waters are not injurious to health.
The living germs or bacilli, through whose agency zymotic diseases
are caused, cannot be detected in a sample of water by any Mr€Ct
chemical or microscopical analysis. A specimen of pure dislilled
water might be artificially contaminated with such organisms so as
to constitute it a most virulent poison, and still chemical analysis
would fail to detect the danger, and the water would be pronounced
pure. Chemical analysis can, however, reveal the presence of
excrementitious matter, and also of the characteristic products re*
suiting from its decomposiiioo : it can with certainty detect in the
water the evidence of recent contamination with sewage matters,
and it can also, with considerable precision, trace the evidences
of its having been so contaminated at an earlier stage of its history.
It cannot, however, distinguish between pollution with healthy, and
with infected excreta, and therefore it is necessary to regard with
the greatest stispicion any water to which sewage has at any time
gained access. Waters that are made use of for dnnking purposes
may be classified in the following order ;—

/ I. Spring water.
Safe . . < a. Deep well water.

( 3. Mountain rivers and lakes,
o 54. Stored rain water.

i 5. Surface water from cultivated land.

Dangerous |

HTOBOOBH PEBOXIOS.
Formnlfc H«Or

OeeomtlM.— This compound is occasionally found In anall
quantities in the atmosphere, and also in dew and rain.

■odes of FormatlOD.— <i.) Hydrogen peroxide is produced io
small quantities during the burning of hydrogen in the air. If a
jet of burning hydrogen be caused to impinge upon the surface of
water, the temperature of which is not allowed to rise above 30°,
the water will be found, aAer a short time, to contain hydrogen
peroxide.*

■ See " Chenial Lsetun Eipvimmts," new ed., p> 74.

200 Inorganic Chemistry

(2.) This compound is also produced by the decomposition of
barium peroxide by carbonic acid. For this purpose a stream of
carbon dioxide is passed through ice cold water, into which from
time to time small quantities of barium peroxide are stirred.
Barium carbonate is precipitated, and a dilute aqueous solution of
hydrogen peroxide is obtained —

BaOg + HjCOj = BaCO, + H,0,.

(3.) Barium peroxide may be decomposed by either hydrochloric,
sulphuric, silicofluoric, or phosphoric acid. Whichever acid be
employed, the barium peroxide, previously mixed with a small
quantity of water, is added gradually to the acid ; which, in the case
of either hydrochloric or sulphuric acid, should be diluted with from
five to ten times its volume of water. The temperature of the
mixture i^ not allowed to rise above 20*. Thus, in the case of
hydrochloric acid —

BaOs + 2HC1 - BaClj + HjO,,

the soluble barium chloride is removed by the addition of sulphuric
acid, whereby barium sulphate is precipitated, and hydrochloric
acid formed —

BaClj + H^04 = BaS04 + 2HC1.

The hydrochloric acid may be removed by adding a solution of
silver sulphate, which precipitates silver chloride, leaving sulphuric
acid in solution—

2HC1 + Ag,S04 = 2AgCl + H8SO4.

And, lastly, the free sulphuric acid is withdrawn by the addition of
barium carbonate —

H2SO4 4- BaCOa = BaS04 + H2O + COj.

When sulphuric is employed for the decomposition of barium
peroxide, the crystallised, or hydrated peroxide (Ba02,8H20), is
most advantageous for the purpose. This salt, made into a paste
with water, is gradually added to the diluted and cooled acid, until
the acid is nearly but not quite neutralised. The slight excess of
acid is removed by the addition of the exact quantity of barium

Hydrogen Peroxide 20 1

hydroxide (baryta-water) necessary to neutralise it, and the insoluble
barium sulphate is removed by filtration. On a large scale silico-
fluoric acid, or phosphoric acid, is usually employed, preferably the
latter, as it is found that small quantities of free phosphoric acid
in hydrogen peroxide greatly retard its decomposition.

(4.) Hydrogen peroxide is also readily obtained by decomposing
potassium peroxide by means of tartaric acid. The potassium
peroxide is added to a cooled strong aqueous solution of tartaric
acid, when potassiiun tartrate separates out, and an aqueous solu-
tion of hydrogen peroxide is obtained.

(5.) When small quantities of hydrogen peroxide are required
for the purpose of illustrating its properties, it is most conveniently
obtained by adding sodium peroxide to dilute and well-cooled
hydrochloric acid, whereby sodium chloride and hydrogen per-
oxide are formed, both of which remain in solution —

NajOg -I- 2HC1 - 2NaCl -I- HjO,.

(6.) Hydrogen peroxide is formed in considerable quantity when
ozone is passed through ether floating upon water. Probably a
peroxidised compound of ether is first produced, which is then
decomposed by the water. This production of hydrogen peroxide
may readily be demonstrated by placing a small quantity of water
and ether in a beaker, and suspending into the vapour a spiral of
platinum wire which has been gently heated. The combustion of
the ether vapour upon the wire, whereby the latter is maintained
at a red heat, is attended with the formation of ozone, and this
acting upon the ether, as already described, results in the pro-
duction of hydrogen peroxide, which may be detected in solution
in the water.

(7.) In small quantities, hydrogen peroxide is produced when
moist ether is exposed to the action of oxygen, under the prolonged
influence of sunlight

Properties. — The dilute aqueous solution of hydrogen peroxide,
obtained by the foregoing methods, is concentrated by evaporation
over sulphuric acid in vacuo. In the pure condition it is a colour-
less and odourless, syrupy liquid, having an extremely bitter and
metallic taste. The specific gravity of the liquid is 1.4532. The
substance is extremely unstable, giving up some of its oxygen even
at temperatures as low as - 20*, and decomposing with explosive
violence when heated to too*. Hydrogen peroxide bleaches

Inorganic Chemistry

203

organic colours, bul less rapidly ihaji chlorine. When plac
upon the skJn it destroys the colour, and gives ni>e to an it[itat1l)|
blister. When diluted with water, and especially if rendered ack|
the compound is far more stable, and in this condition may b
preserved at the ordinary temperature for a considerable length t
time. When such an .iqucous solution is strongly cooled, i'
ice, and in this way, by the renioval of the frozen water,
tion may be concentrated ; hydrogen peroxide itself r»
at ~ 3a^ When heated the solution is decomposed i]
and oxygen—

H,0, = H,0 + O,

Owing to the readiness with which hydrogen peroxide gives tio]
the half of its oxygen, and is converted into water, its properlie
are generally those of a powerful oxidising agent It liberati
iodine from potassium iodide ; it converts sulphurous acid J
sulphuric acid, and oxidises lead sulphide into lead sulphai
action upon lead sulphide is made use of, in restoring som
of the original brilliancy to oil paintings that have become d
coloured. The " white-lead " used in oil paints is gradually ci
verted into lead sulphide when such paintings are exposed t
especially the air of towns, which is liable to contain
quantities of sulphuretted hydrngen. Lead sulphide being h
die picture slowly assumes a uniformly dark colour, until 1
finally quite black. \Vhen such a discoloured picture is

r with dilute hydrogen peroxide, the black sulphide is o

o tbe white lead sulphate—

PbS + 4H,Oj = *HjO + PbSO^

This c

npound is employed for bleaching articles that would I
r injury by the use of other bleaching agents, such as ivoiT,l
feathers, and even tbe teeth.

Hydrogen peroxide is also capable of oxidising hydrogen, wl
that clement in the nascent condition is brought in contact n
this compound. Thus, if a dilute acidulated solution of hydrogen
peroxide be subjected to electrolysis, oxygen will be evolw
from the positive electrode, but no gas will be disengaged a
negative pole. The hydrogen, in the presence of the hydr
peroxide, is oxidised into water —

H,Oj-

H, = 2H,0

Hydrogen Peroxide 203

Hydrogen peroxide, in many of its reactions, appears to act as a
deoxidising agent ; thus, manganese dioxide in contact with this
substance is reduced to manganous oxide —

MnO, + H,0, = MnO + O, + H,0.

Similarly silver oxide is reduced to metallic silver with the
evolution of oxygen —

Ag,0 + H,0, «= Ag, + O, + H,0.

In like manner, when ozone is acted upon by hydrogen per-
oxide, a reaction takes place exactly analogous to that with silver
oxide, which will be the more obvious if the formula for ozone be
written 0|0 instead of O3, thus —

0,0 + HjO, = O, + O, + H,0.

Although, in a sense, these reactions m.iy be regarded as reduc-
ing^ or deoxidising^ actions, in essence they are not different from
those which have been given as illustrative of the oxidising power
of hydrogen peroxide. It will be seen that they all depend upon
the readiness with which the compound parts with an atom of
oxygen, but that in these latter cases the oxygen that is so given
up is engaged in oxidising another atom ofoxygen^ contained in the
other compound. Thus, in the case of silver oxide, its atom of
oxygen is oxidised by the liberated oxygen from the hydrogen
peroxide, and converted into the complete molecule of oxygen.
By these reactions Brodie first demonstrated the dual, or di-
atomic, character of the molecule of oxygen.

When hydrogen peroxide is added to a dilute acidulated solution
of potassium dichromate, a deep azure-blue solution is obtained
(see ChromiumX which affords a delicate test for this com-
pound. To apply the test, the dilute hydrogen peroxide iS^'sHaken
up with ether, and being soluble in this liquid, the ethereal layer
which rises to the surface will contain nearly the whole of the
peroxide ; a few drops of acidulated potassium dichromate are
then added, and the mixture again shaken, when the ethereal
liquid will separate as a blue laye«. In this way, the presence of
aooo25 grammes of hydrogen peroxide in 20 cc of water can
be detected.

Hydrogen peroxide is decomposed by contact with many sub-
stances which themselves do not combine with the oxygen ; thus

204 Inorganic Chemistry

charcoal, finely divided palladium, platinum, mercury, and notably
silver, when brought into hydrogen peroxide, determine its decom-
position into water and oxygen, the rapidity of the action being
increased if the liquid be made alkaline. The action is doubtless
catalytic, although in all cases the exact modus operandi is not
clearly understood. In the case of silver it is believed that silver
oxide (perhaps peroxide) is first formed, and then decomposed,
thus —

Ag, + H,0, = HjO + AgjjO
Ag,0 + H,0, = H,0 + O, + Agj.

When hydrogen peroxide is added to solutions of the hydroxides
of barium, strontium, or calcium, the peroxide of the metal is
precipitated —

Ba(HO), + H,0, = 2H,0 + 13aO^

The compound is deposited in crystals having the composition
BaOjjSHjO.

With the hydroxides of the alkali metals, the peroxide (which is
soluble in water) may be precipitated by the addition of alcohol ;
when in the case of sodium peroxide, crystals are obtained ol
NaaOj^8H,0.

Hydrogen peroxide is a useful antiseptic : it possesses the ad-
vantages of being free from smell, without poisonous or injurious
action upon the system, and of leaving as a residue, after having
furnished its available oxygen, only water.

CHAPTER IV

NITROGEN

Symbol, N. Atomic weight = 14.01. Molecular weight = 98.0%

History. — Nitrogen was discovered by Rutherford in 1772. He
showed that when an animal is placed in a confined volume of air
for some time, .ind the air aften^'ards treated with caustic potash,
to absorb from it the carbon dioxide ("fixed air"), there still
remained a gas which was incapable of supporting either respira-
tion or combustion. He called the gas mephitic air, Scheele was
the first to recognise that this gas was a constituent of the air.
Lavoisier applied the name azote to the gas, to denote its inability
to support life. The name nitrogftty signifying the nitre-producer,
was suggested by Chaptal, from the fact that the gas was a con-
stituent of nitre.

Occurrenee. — In the free state nitrogen is present in the atmos-
phere, of which it forms about four-fifths. Certain nebulae have
been shown, by spectroscopic observation, to contain nitrogen in
the uncombined condition. In combination, nitrogen is found in
ammonia, in nitre (potassium nitrate), and in a great number of
animal and vegetable compounds.

Modes of FoPmation.— (i.) Nitrogen is very readily obtained
from the atmosphere, by the abstraction of the oxygen with which
it is there mixed.* This is conveniently done by burning a piece
of phosphorus in air, confined over water. The phosphorus in
burning combines with the oxygen, forming dense white fumes of
phosphorous pentoxide, which gradually dissolve in the water, and
nitrogen remains in the vessel The nitrogen obtained in this way
is never quite pure, for the phosphorus becomes extinguished
before the oxygen is entirely repioved ; and also the gas will
contain atmospheric carbon dioxide.

(2.) Nitrogen in a purer state can be prepared from the atmos-

* Experiments 354, 355, " Chemical Lecture Experiments," new ed.

206

Inorganic Cfumiitry

phere, by passing a stream of puie air over metallic coppei 1

contained in a combustion tube, and heated to redness in a fuma
The air is contained in a gas-holder, and is passed through I
U-tubes, the first containing potassium hydroxide (caustic potash), ]
in order to absorb the carbon dioxide ; and the second filled with |
fragments a{ pumice moistened with sulphuric add, in order to ]
arrest the aqueous vapour. The purified air, on passing ov«
heated copper, is deprived of the whole of its oxygen, cupric oxide,
CuO, being formed, while the nitrogen passes on and may be J
collecied. This gas contains small quantities of argoo (p. 64S).

(3,] Oxygen is rapidly absorbed by a solution of cuprous chloride i
in hydrochloric acid ; a ready method, therefore, of obtaining 1
nitrogen from the air, is to place a quantity of this solution i)
stoppered bottle, and shake it up with the contained air. The '
colouriess cuprous chloride solution quickly absorbs the oxygen,
becoming dark in colour, and being converted into cupric chlorid^
the nitrogen of the air remaining in the bottle —

CujCl, + 2Ha + O - H,0 + 2CuCI»

{4,) Nitrogen is obtained by heating a strong solution of ammo-
niimi nitrite in a flask, the salt splilimg up into water and nitrogen —

NH,NO, = 3H,0 + N,

t to employ a mixture ol

NH,C1 + NaNO, = NaCl + 2H,0 + N^

(j.) By heating a mixture of ammonium nitrate and ammoniinn. \
chloride, a mixture of nitrogen and chlorine is evolved ; the latter 1
gas may be absorbed, by passing the mixture through either milk \
of lime, or a solution of sodium hydroxide —

SNH.NO, + NH.CI - SN + CI + 6H,0.

(6.) Nitrogen is also evolved when ammonium chromate, o
mixture of potassium dichromate and ammoniimi chloride, it, J

(NH,),Cr,OT = CrjO, + 4H,0 + N,
K,Cr,0, + SNH^Cl = Cr,0, + SKCl + 4H,0 + N,

Nitrogen 207

(7.) VVhen ammonia is acted upon by chlorine, it is decomposed,
the chlorine combining with the hydrogen to form hydrochloric
arid, and the nitrogen being liberated —

2NH, + 3CI, = 6HCI + N^

If the chlorine be passed into a strong solution of ammonia, the
hydrochloric add which is produced combines with the excess of
ammonia, forming ammonium chloiide ; thiu—

8NH, + 3a, - BNH.CI + N»

The chlorine, after being washed by passing through water, is
bubbled through strong aqueous ammonia contained in a Woulf's
bottle. As »ach bubble of chlorine enters into the ammonia, the

Fio.44-

combination is attended by a focble yellowish flash of light, and a
rapid stream of nitrogen is evolved. The nitrogen, which carries
with it dense white fumes of anunonium chloride, should be scrubbed
by being passed through a second bottle, filled with fragments of
broken glass moistened with water, and it can then be collected
over water in the oixlinary way, as shown in Fig. 44.* In prepar-
ing nitrogen by this reaction, it is very necessary that the ammonia
should be in considerable excess, otherwise there is liable to be
formed the dangerously explosive compound of nitrogen and chlo-
rine. See Nitrogen Trichloride.

Inorganic Chemistry

208

PropePtiflS. — Nitrogen is a colourless gas without taste 01
smell. It is slightly lighter than air, its specific gravity being
0.972 (air = i). One litre of the gas at 0° C. and 760 mm. weighs
14 criths, or i.2j6.grainmes.

Nitrogen is only very slightly soluble in water, its coefficient of
absorption at 0° C, being 0.020346.
Nitrogen will not bum, nwther will it support the combustion of
ordinary combustibles. It is not
poisonous, but is incapable of sup-
porting respiration.

Nitrogen is one of the most chemi-
cally inert substances known, com-
bining directly, and with difficulty,
with onlya very few elements. Under
I the influence of the high temperature
ll, of the electric spark it can be made
to unite directly with oxygen (see
p. 210}. Certain metals also com-
bine directly with it, forming nitrides
Thus, when lithium or magnesium
are heated in nitrogen, tlity form
respectively NLi, and N,Mg]. This
rc.iction may be conveniently shown
by means of the apparatus seen in
Fig.4;. Asmallquantityofpowdered
magnesium is placed in a hard glass
tube, which is connected to a long
narrow tube dipping into water, and a
stream of nitrogen is passed through.
When the air is all displaced, the
stopped, and the magnesium strongly
At a red heat the nitrogen will be rapidly absorbed, and
the water will be seen to rise in the long tube.

The critical temperature of nitrogen is - 146', and when cooled
to this point, a pressure of 35 atmospheres causes its liquefaction.
Under ordinary atmospheric pressure, the liquid boils at - 193°;
the gas, therefore, can be liquefied by the cold obtained by the
rapid evaporation of liquid oxygen (see p. 76).

Fig. 45.

CHAPTER V

OXIDES AND OXY-ACIDS OP NITROGEN

Nitrogen combines with oxygen, forming five oxides :—

( I.) Nitrous oxide (hyponitrous anhydride) . NjO. /^>'^»

(2.) Nitric oxide. NO.

(3.) Nitrogen trioxide (nitrous anhydride) . N^Os. ^ '^^^a^

(4.) Nitrogen peroxide NOsandN|0«.

(5.) Nitrogen pentoxide (nitric anhydride) . N1O5. u--^ ^^

Three oxy-acids of nitrogen are known, corresponding to the

three oxides, Nos. i, 3i 5 : —

Hyponitrous acid . HNO.

Nitrous acid HNO,.

Nitric acid HNOj.

The relation in which these three acids stand to their corre-
sponding oxides may be seen by the following formulae : —

N ) . N ?

Hyponitrous anhydride «^ / O. Hyponitrous acid u r O.

Nitrous anhydride . jjq ( ^' Nitrous acid . h l ^'
Nitric anhydride . no'[^- Nitric acid . ^^lo.

The most important of all these compounds, and the one from
which all the others are directly or indirectly obtained, is nitric
acid.

NITRIC ACID.

Formula, HNO^. Molecular wdght = 6a. 88.

History. — Nitric acid, or aquafortis^ was a well-known and
valued liquid to the alchemists. Down to the time of Lavoiaier

•09 Q

210 Inorganic Ckemislry

(1776) its true nature was not known ; he showed that oxygen
one of its constituents, but as to its other components he was
certain. Its exact composition was determined by Cavendish.

Modes of Formation. — (1-) When an electric spark is pas:
throug:h a detonating mixture of oxygen and hydrogen with
a certain quantity of air, or nitrogen, is mixed, the water that
produced by the union of the oxygen and hydrogen is found
contain nitric acid. This fact was first observed by Cavendish
the course of his invesligalions on the composition of
owing lo the accidental admixture of air with the mixed gi
oxygen and hydrogen, he found that the water resulting IVo

The direct union of nitrogen and oxygen may be brought
by allowing a series of electric sparks to pass between plati
wires, in a confined volume of air, contained in a
shown in Fig. 46. In a short time the air in the globe will bei
distinctly reddish in colour, owing to the forrnaiion of
peroxide. The rapidity of the formation of the red fu
be gready increased, by compressing the air within the
means of a small compression pump, as indicated in the f

If a small quantity of water be introduced, and the contents
the globe shaken up, the red gas will be seen to dissolve
water, which will then acquire an acid reaction, owing lo the foi
tion of nitric add-
Similarly, when a jet of hydrogen is allowed 10 bum in air to
which additional oxygen has been added, considerable quantities
of nitrogen peroxide are formed. The hydrogen may be burnt
from a jet, surrounded by a glass tube, as shown in Fig, 47, into
which oxygen can be passed by means of the small bcni tube at
the bottom. On holding a clean dry cylinder over the flame,
sufficient of the products of combustion will collect in a few seconds
to show the presence of nitrogen peroxide.

(2.) Nitric acid is formed when nitrogenous animal matter under-
goes slow oxidation in the air, in the presence of water and an
alkali, the nitric acid combining with the alkali lo form a nitrate.
In this way nitrates are found in the soil, and from the soil often
find iheir way inlo shallow well waters of towns. In hot and rain-
less countries these nitrates are sometimes foimd as crystalline
deposits on the surface of the soil, as in Chili and India. (See
Potassium Nitrate.)
(3.) Nitric add is prepared by acting upon potassium nitrate

litrate |

Nitric Acid

211

{nitri'Saltpitn) with sulphuric add. The nitre is placed in a glass
retort, together with an equal weight of sulphuric acid, and the
mixture gently heated. The nitric acid readily distils over, and
may be collected in a cooled receiver. The residue in the retort
consists of hydrogen potassium sulphate—

KNO, + H^04 = KHSO4 + HNO,.

The acid so obtained is not entirely free from water, and contains
nitrogen peroxide in solution, which imparts to it a yellowish-red

Pio. 46.

Fig. 47.

colour. To purify it, it is again distilled with an equal volume of
sulphuric acid ; and the redistilled acid is deprived of the last traces
of dissolved peroxide of nitrogen, by causing a stream of dry air to
bubble through it while slightly warm. Nitric acid 'so prepared
may contain as much as 99.8 per cent, of anhydrous acid, HNO3.

(4.) Nitric acid is an article of commercial manufacture. In this
process potassium nitrate is replaced by the sodium salt, as being
the cheaper material, and the proportion of acid to sodium nitrate
employed is arranged in accordance with the equation—

2NaN0, + H^O* - Na^O^ -I- 2HNO^

And then,

sulphate

NaNO,

The lemperature necessaiy to effect this second stage, howi
causes (he decomposition of a certain quantity of the c'
itself, thus—

8HNO, = H,0 + 8N0, + O.

The retorts usually employed for the manufaaure of this acid are
large cast-iron cylinders, which are sometimes lined, either entirely
or in part, with liicclay, and whidi are built into a furnace in such
a manner as to allow of their being heated as uniformly as possible.
The ends of the cylinders are closed by slabs of Yorkshire fiag,
securely cemented to the iron. The charge of sodium nilraie
(Chili saltpetre) and sulphuric acid is introduced through a hole in
one end, which is afterwards plugged up, and the vapours are
carried off through an earthenware pipe {.:, Fig. 48), cemented
through a hole in the other end, and connected to a series ot
earthenware pots, b, in the manner shown in the figure. The last
of these jars is connected with a tower, filled with coke, down which
water is caused lo percolate, and any peroxide of nitrogen which
escapes condensation with the acid in the jats is thereby absorbed.

Properties. — Nitric acid is a colourless liquid having a specific
gravity of i.;3. It fumes strongly in the air, and has a peculiar
and choking smell. It is extremely hygroscopic, absorbing moisture
from the air with great readiness. Nitric acid is an intensely
corrosive liquid : the strongest acid, when brought in contact with
the skin, causes painful wounds, while in more dilute conditions
it stains the skin, and other organic materials, a bright yellow
colour. A quantity of strong nitric acid thrown upon sawdust
causes it 10 burst into flame. When nitric acid is distilled it first
begins to boil at 86°, a< the same lime it is partially decomposed
into water, nitrogen peroxide, and oxygen ; the distillate, therefore.

radually becomes weaker, and the boitios- point gradually rises.

5 continues until a certain poini is reached, when both the

mperature of the boiling liquid and the slrenglh of ihe dislillaie

P Rirain conaiani. If, on rhc u[hi::i imi), a -r.ik add be dijiilled.
e distillate gradually mcrcascb m ,u cii^ih. iiniil wben the same
r point is reached, the boiling liquid has aijain the same temperature.

214 Inorganic Chemistry

This constant boiliDg-point is iza;*, and the distillate
conies over ai that temperature contains 68 fier cent, of 1
Wliatever the strength oi the acid, therefore, on being boiled it
loses either nitric acid or water until the strength reaches 68 per
cent., and this liquid boils at 120° C. The specific gravity of this
acid at i;° is 1.414. It was formerly supposed that the acid of this
strength constituted a definite hydrate, but Roscoe has shown that
the strength of the acid is purely a function of the pressure, for by
varying the pressure under which the distillation is conducted,
acids of various compositions can be caused to distil at a constant
temperature.

When nitric acid is mixed with water there is a rise in tempera-
ture and a contraction in volume, the maximum effect being pro-
duced when the mixture is made in the proportion of three molecules
of water with one molecule of acid.

Nitric acid is a powerful oxidising agent, on account of the readi-
ness with which it parts with oxygen. Elements such as sulphur
and phosphorus are oxidised into sulphuric and phosphoric acids ;
arsenious oxide into arsenic acid ; and many protosajts are con-
verted into persalts. It attacks a large number of metals, forming
in many cases the nitrate. Its action upon metals is often of
a complicated nature, and depends not only upon the paniculai
metal, but also upon the strength of the acid, the temperature,
and the presence of the saline products of the reaction ;
when nitric acid acts upon copper, the following reaction
place-

3Cu -I- 8HN0, = 3Cu(N0i), + 4HjO + 2N0.
It is found, however, that as the amount of coppt
mulates, the nitric oxide which is evolved is mixed more
largely with nitrous oxide, NjO, and even with nitrogen.

Again, when dilute nitric acid acts upon linc, nilrou.
produced, according to the following equation —

4Zn + IOHNO3 = 4Zn(N0,)j + SH^O + N,0.
When, however, strong nitric acid is employed,
which combines with the excess of add—

4Zn 4- 9HN0j = 4Zn(N0j), + SHjO
In some cases, as with copper and silver, the presence of ni/rvui
acid (either as an impurity in the nitric acid, or as a first produa
of its attack upon the metal) is believed to be a necessary condition
or the action.

Nitric Acid 215

Owing to the strong oxidising properties of nitric acid, hydro-
gen is rarely isolated by the action of metals upon this acid, the
hydrogen which is displaced from the acid being converted into
water. With magnesium, however, free hydrogen is evolved.

The chief reactions of nitric acid may be broadly divided into
three classes : —

(i.) With metallic oxides its behaviour is in common with other
acids. It exchanges its hydrogen for an equivalent quantity of the
metal, forming a nitrate, with the elimination of water, e,g. —

Ag,0 + 2HN0, - 2AgNO, + H,0.

(2.) Reactions in which it acts as an oxidising agent ; as an
example, its action upon iodine, which is converted into iodic acid,
may be cited —

l+SHNOj^HIOj + HaO + NO + SNO,.

(3.) Actions in which hydrogen in an organic compound is
replaced by the elements NOs, with the elimination of H|0, 00
gas being evolved. The conversion of cotton-wool, or cellulose,
CuH|oO|o, into gun-cotton, or nitro-cellulose) CuH|40io(NO|)ai is
an illustration of this class of reactions —

Ci,H„Om + 6HN0, = 6H,0 + Cy^xfi^l^O^^

Nitric add is without action upon the so-called nobU metals,
gold and platinum.

Commercial nitric acid, which is of a reddish colour, is liable
to contain many impurities : chlorine and iodic acid, derived from
the Chili saltpetre ; iron, sulphuric add, and sodium sulphate,
carried mechanically over from the retorts ; and nitrogen peroxide,
from the decomposition of the acid. From these it is purified by
redistillation.

Nitric add is a monobasic add ; the salts of which, known as
the nitrates, are for the most part readily soluble in water, and
crystallise in well-defined forms. They are all decomposed at a
high temperature, evolving oxygen and nitrogen peroxide, or oxy-
gen and nitrogen, leaving an oxide of the metal

The presence of a nitrate in solution is easily recognised by the
following characteristic test A solution of ferrous sulphate is first
added to the solution containing the nitrate, and concentrated ml-

2l0 Inorganic Chemistry

phuric acid is then cautiously poured down the side of the I
tube, held in a sloping position, so as to fail to the boliom withoV
mixing with the solution. The sulphuric acid acting upon t"'
nitrate, liberates nitric acid ; this is reduced by the ferrous sulphi
to nitric oxide, which, dissolving in the ferrous sulphate, formsV
brown-coloured solution a[ the point where the two layers of Uqini
meet (See Nitric Oxide.)

When nitric acid is added to hydrochloric acid, a mini
obtained which is known by the name of aqua regia, TTiis ;
was applied to it by the alchemists on account of its power o;
solving gold. Aqua regia is used in the laboratory for disso
gold, platinum, and certain ores, Us solvent power depends upC
the free chlorine which is evolved from the mixture —

HNOj + 3HC1 = SHjO + NOCl + CI,

NITEOQEN PENTOXIDE (A'iKrt Ankydridt).
Formula, NjOj. Molecular weigbt - 107.8.
Modes of Formation.— (l.) By withdrawing from nilric acS
the elements of water, by means of phosphorus pentoxide — -

2HNO, + P.Oj = 2HP0j + NjOj.

For this purpose the strongest nilric acid is cautiously added i
phosphorus pentoxide in a cooled retort, in the proportion ("
manded by the equation ; the mixture being made as far as possib^
without rise of temperature. The pasty mass is then gently heato'
when the nitrogen penloxide distils over, and, if collected it
cooled receiver, at once crystallises.

(z.) Yht method adopted by Deville, who discovered this o
pound (1849), was by passing dry chlorine over dry silver n
contained in a U-tube, which was kept at the desired tempieratilj
by being immersed in a water-bath. The following equation a
presses the final result of the action—

2AgN0, + CI, - 3AgCT + N,0» + O.

Properties. — Nitrogen penloxide is a white solid substancj
ciystallising in brilliant prismatic crystals, which melt ;
with partial decomposition. Between 4;° and s°* it undergc
rapid decomposition, evolving brown fumes. It is a very unsta.'

Nitrogen Peroxide 217

compound ; when suddenly heated it decomposes with explosive
violence, and even at ordinary temperatures decomposition slowly
takes place. It absorbs moisture rapidly, and when thrown into
water it dissolves with the evolution of great heat —

N,Oj + H,0 - 2HNO,.

When nitrogen pentoxide is gradually mixed with nitric acid, a
compound is formed having the composition 2N20(,H,0 ; which
separates, on cooling, as a definite crystalline hydrate.

NITROOEN PEROXIDE.

ForaiuU. NO, and N,04. Molecular weight = 45.99 and 91.84*

Density = 93.96 and 45.9a.

Modes of Formation.— { I.) This compound may be prepared
by mixing one volume of oxygen with two volumes ot nitric oxide,
and passing the red gas so obtained through a tube surrounded
by a freezing mixture —

2NO + O, - 2NO^

(2.) The nitrates of certain metals, when heated, are decomposed
into nitrogen peroxide, oxygen, and an oxide of the metal ; thus,
if dry lead nitrate be heated in a retort, and the gaseous products
of decomposition are conducted into a U-tube placed in a freezing
mixture, the nitrogen peroxide collects in the tube —

Pb(NOs), =. PbO + N,04 + O.

(5.) When arsenious oxide is gently warmed with nitric acid, a
mixture of nitric oxide, NO, and peroxide, NO,, is evolved, and if
this gaseous mixture be passed through a cooled tube, it condenses
to a blue liquid. On passing a stream of oxygen through this
liquid it loses its blue colour, and is converted into a yellowish
liquid, which consists of nitrogen peroxide.

Properties. — At low temperatures nitrogen peroxide is a colour-
less crystalline compound. It melts at ~ 9*, but requires a tem-
perature as low as - 30* to solidify it At a temperature slightly
above its melting-point the liquid begins to acquire a pale yellowish
tint, which rapidly deepens, until at the ordinary temperature it is
a full orange colour. The liquid boils at 22*, and gives a vapour

Inorganic Chemistry

218

having a reddish brown colour. The colour of the vapour ■
becomes dcqier as its temperature is raised, i "
dark chocolate brown, and almost opaque. On allowing; 1
vapour 10 cool the reverse changes take place. This change (
colour, as the tempieralure rises, is accompanied by a e
change in the density of the gas, as will be seen from the table :-~l

53.04
89.23
98.69

140.0

The density required by the fonnula NjO, is 45.92, while tbi
demanded by the formula NO, is 33.96 ; hence as the tempera
rises a process of dissociation goes on, in which N,0, moleculcj)
are broken down into molecules of the simpler composition "
At 140° this process is complete, and the gas is entirely 1
solved into NO, It is believed that at low temperatures, nilrog*
peroxide has the composition represented by the formula N,OJ
but that dissociation begins to take place even during the si
liquidity, as indicated by the gradual change of colour ; and there
fore at temperatures between the boiling-point of the liquid, vi
23\and 140', the gas consists of mixtures of molecules of NO, !
N|0,. The calculated percentage of NO^ molecules, which Uiq
gas contains at the temperatures at which the above densities a
taken, are given in the third column.

Nitrogen peroxide is decomposed by water. At low
tures, and with small quantities of water, nitric and niti
are the products of the action, thus —

N.O, -

H.O = HNO, + HNOj

At the ordinary temperature, and with an excess
following reaction takes place —

3N0, + H,0 = BHNOj + NO.

Gaseous nitrogen peroxide is incapable of supporting the com-
bustion of a taper. Phosphorus, when strongly burning and
plunged into the gas, continues it» combustion with brilliancy,

ncy, j

Nitrous Acid 219

the temperature of the burning phosphorus bemg sufficiently high
to effect the decomposition of the gas. Nitrogen peroxide is a
suffocating and highly poisonous gas, and even when largely
diluted with air rapidly produces headache and sickness.

Nitrogen peroxide unites directly with certain metals, giving rise to a re-
markable series of compounds, to which the name nitro-metals, or metallic
nitroxyls, may be given (Sabatier and Senderens).* Thus, when the vapour
of nitrogen peroxide is passed over metallic copper (obtained by the reduction
of copper oxide in a stream of h]rdrogen), the gas is rapidly absorbed by the
metal with considerable rise of temperature, and a solid brown compound is
formed. This substance is the copper-nitroxyl, and its compositioo is ex-
pressed by the formula Cu^NOj.

Copper-nitroxyl is a fiedrly stable compound, and is unacted upon by dry air.
It is decomposed by water and by nitric acid, hence in its preparation care
must be taken to free the nitrogen peroxide from these substances.

At a temperature of about 90* copper-nitroxyl is decomposed into copper
and nitrogen peroxide. If, therefore, a quantity of the compound be scaled
up in a bent glass tube, and the empty limb of the tube be immersed in a
freezing mixture while the compound is gently warmed, the nitrogen peroxide
which is evolved will be condensed in the cold portion of the tube.

Similar compounds are formed with the metails cobalt, nickel, and iron.

Nitrous Aeid, HNO^. — This substance is not known in the pure
state. Even in dilute aqueous solution it rapidly decomposes into
nitric acid, nitric oxide, and water —

3HNO, =- HNO, + 2N0 + H,0.

The solution of this acid sometimes acts as a reducing agent,
taking up oxygen from such highly oxidised compoimds as per-
manganates, or chromates, and passing into nitric add —

HNO, + O - HNO,.

Under other conditions it exerts an oxidising action, as when it
bleaches indigo, or liberates iodine from potassium iodide, being
itself reduced to nitric oxide and water, with the elimination of
oxygen —

2HNO,-2NO + H,0 + 0.

The salts of nitrous add, viz., the nitriitSy are stable compoimds.
The nitrites of the alkalies are best prepared by careftilly heating

* BulUHm 4» U S^cUii CAimtftu, SepCembo: ZS93.

220 Inorganic Chemistry

the nitrates ; thus, when potassium nitrate is fused, it parts with
oxygen, and is transformed into potassium nitrite —

KNO3 = KNO, + O.

At a higher temperature the nitrite is also decomposed.

Nitrites are decomposed by dilute acids, evolving brown vapours,
and in this way are at once distinguished from nitrates.

Nitrogen Trlozide. — There is considerable doubt as to the existence of this
compound. It has been usually stated that it is formed by the action of nitric
add upon arsenious oxide, according to the equation —

AsPe + 4HNO, = 2Asj08 + 2H,0 + 2NaOs.
It has, however, been shown by the determination of the vapour density, that
in the gaseous state the compound N^Qs <lo^ "O^ exist, but that the gas is a
mixture of molecules of NO and NO]. It will be seen that a mixture contain-
ing equal volumes of these two gases will have a composition represented by
the formula N^Oj, therefore the above reaction may be regarded as taking
place thus —

As fit + 4HNOj = 2Asa05 + 2H3O +2NO + 2NO,.

Simultaneously with this reaction the following decomposition also goes
forward —

As40e + 8HNOj = 2Asa05 + 4H3O -f 8NO3.

The result, therefore, of the action of nitric acid upon arsenious oxide is a
mixture of nitric oxide and peroxide in varying proportions.

When this mixture is strongly cooled, it condenses to a blue liquid, believed
by some to be the true compound NjOg. Others regard it as merely a solu-
tion of the difficultly liquefiable gas, NO, in liquid nitrogen peroxide, NOg. If
the two oxides are in a state of combination, it would appear to be at best a
feeble union, for it has been shown that at temperatures as low as —90** the
liquid slowly evolves NO, while at this temperature no nitrogen peroxide is
given off.

The most recent work on the subject, however, based upon minute changes
of volume which result when NO and NOg are mixed (Dixon and Peterkin,
Proc. Chem. Soc.y June 1899), points to the conclusion that the reaction which may
be expressed N.jOj = NO + NOj is to a slight extent a reversible one ; and
that therefore a mixture of the two gases NO and NO2 at ordinary tempera-
tures actually does contain a small percentage oli NjO;^ molecules.

NITRIC OXIDE.

Formula, NO. Molecular weight = 29.96. Density = 14.96.

History. — Nitric oxide was first obtained by Van Helmont.
Priestley, however, was the first to investigate this gas, which he
termed nitrous air, and which was employed by him in his analysis
of air.

Modes of Formation. — (i.) This gas is obtained by the action
of nitric acid of specific gravity 1.2 upon copper or mercury. In

Nitric Oxidi 231

practice, copper is always employed* The action may be repre-
sented thus —

3Cu + 8HNO, - 3Cu(NO0,-» 4H,0 + 2NO.

The gas obtained by this method is always liable to contain
nitrous oxide, and even free nitrogen ; the amount of these im-
purities rapidly increasing if the temperature be allowed to rise,
and still more so as the amount of copper nitrate in solution
increases.

(2.) Pure nitric oxide is readily obtained by the action of nitric
acid upon ferrous sulphate. The reaction is best applied by gene-
rating the nitric add from potassium nitrate and sulphuric acid in
the presence of ferrous sulphate. A mixture of the two salts, in
the proportion of about one part of nitre to four of ferrous sulphate,
is introduced into a flask, with a small quantity of water. Strong
sulphuric acid is dropped upon the mixture by means of a drop-
ping funnel, and the mixture gently warmed, when a steady stream
of pure nitric oxide is evolved —

2ICNO, + 6H4SO4 + 6FeS04 = 2HKSO4 -H 3Fe,(S04), + iH^O + 2NO.

A precisely similar result may be obtained by the reduction of
potassium nitrate by means of ferrous chloride in the presence of
hydrochloric acid, thus —

KNO, -I- SFeClj -I- 4HC1 - 3FeCl, -I- KCl -h 2H,0 + NO.

Properties. — Nitric oxide is a colourless gas, having a specific
gravity of 1.039. When bit>ught into the air, it combines with the
atmospheric oxygen, forming red brown vapours, consisting of
nitrogen per-oxide, the combination being attended with a rise
of temperature. The formation of these red fumes in contact
with oxygen, is characteristic of this gas, thereby distinguishing
it from all other gases. This property of nitric oxide renders
it impossible to ascertain whether this gas has any smell, or
is possessed of any toxicological action. Nitric oxide is only
very sparingly soluble in water. It is the most stable of all the
oxides of nitrogen, being able to stand a dull red heat without
decomposition. It is not a supporter of combustion. A lighted
taper, or a burning piece of sulphur, when introduced into the gas,

* ExperiiDent 314, "Chemical Lecture Experiments," new ed.

222 Inorganic Chemistry

are extinguished If the temperature of the burning subitance It ]

sufficiently high to decompose the gas, combustion then continue
31 the expense of the liberated oxygen : thus, if a piece of phos
phonis, which is freely burning in the air, be plunged into this gas,
it continues its combustion with greal brilliancy ; if, however, the
phosphorus be only feebly burning when thrust inl
is HI once extinguished. A mixture of carbon disulphide vapour I
and nitric oxide, obtained by allowing a few drops of the liquid t

fall into a cylinder of the gas, bums, when J
inflamed, with an intensely vivid bluish I
flame, which is especially rich in the violet '
or aclinic rays, and has on this account
been sometimes employed by phot
graphers to ^(illuminate dark
Nitric oxide is soluble in a sc
ferrous sulphate, forming a dark brown
solution, containing an unstable compound
of ferrous sulphate and
2FeS0„N0. This compound is readily 1
decomposed by heat, nitric oxide being i
evolved. By means of this reaction, nitric
oxide may be separated from other gases.
Nitric oxide is a difficultly liquefiable gas, I
its critical temperature being - 93.5 : at ihii
temperature a pressure of 71.2 atmospheres is required to liquefy it

The composition of nitric oxide may be proved, by heating a \
spiral of iron wire by means of an electric current, in a measured I
volume of the gas (as shown in Fig. 49).* As ihe metal become« ]
red hot Ihe gas is gradually decomposed, and the oxygen combine
with the iron to form ferric oxide. The residual nitrogen «ill 1
be found to occupy one-half the original volume.

F:g. 49-

Therefore we learn that twi
one volume of nitrogen and o
condensation.

iS.<)f>=fm^t et I voL of oxygen.

volumes of nitric oxide consist (
! volume of oxygen united without \

Nitrous Oxide 235

mTBOOT OXIDB {Hyponitrous anhydridi^ Laughing gas).
Formula, N^. Molecular weight = 43.96. Density = ai.98.

History. — This gas was discovered by Priestley, and called by
him dephlogisticaUd nitrous air.

Modes of FormatiOlL — (i.) Nitrous oxide is formed by the
reduction of nitric acid by certain metals, as zinc or copper, imder
special conditions (see Nitric Acid). These reactions, however,
are never made use of for the preparation of the gas for experi-
mental purposes.

(3.) The most convenient method for obtaining this compoimd
is by the decomposition of ammoniimi nitrate. A quantity of the
dry salt is gently heated in a flask fitted with a cork and delivery-
tube. The salt rapidly melts and splits up into nitrous oxide and

water—*

NH4NO, - 2H,0 + N,0.

The heat should be carefully regulated, or the decomposition is
liable to become violent, in which case nitric oxide is also evolved
Nitrous oxide being rather soluble in cold water, the gas should
be cAlected either over mercury, or over hot water.

When the gas is to be used for ansBSthetic purposes, it should be purified
by being passed first through a solution of ferrous sulphate to absorb any nitric
oxide, and afterwards through caustic soda, to remove any chlorine which may
have been derived from the presence of ammonium chloride in the nitrate.

Properties. — Nitrous oxide is a. colourless gas, having a faint
and not unpleasant smell, and a peculiar sweetish taste. Its
specific gravity is 1.53. The gas is somewhat soluble in water, its
coefficient of absorption at o** being 1.3052. The solubility rapidly
decreases as the temperatiure rises, as will be seen by the follow-
ing table (Carius) : —

XC.C. Water at ccNgOato'C

760 mm. Diatolw and 760 mm.

At o* 1.3052

„ 10* 0.9196

„ 20* 0.6700

•I 25* a5963

The loss of gas during its collection over water in the pneumatic
trough, arising from its solubility in that liquid, is therefore greatly

224

Inorganu: Chemistry

lessened by using warm water. Nitrous oxide is much
readily decomposed than nitric oxide, a red liot splint of wi
instantly rekindled, and bursts into flatne when plunged into the
gas. Phosphorus burns in it with a brilliancy, scarcely perceptibly
less daiiling ihan in pure oxygea If a piece of sulphur, which is
only feebly burning, be thrust into a jar of this gas, the sulphur is
extinguished, the temperature of the flame not being sufficiently
high to decompose the gas. When, however, the sulphur is
allowed to get into active combustion before being placed in the
gas, the combustion continues with greatly increased brilliancy.
In all cases of combustion in nitrous oxide, the combustion is
simply the union of the burning body with oxygen, the nitrogen
being eliminated. From its behaviour towards combustibles,
nitrous oxide might readily be mistaken for oxygen
e»er, be easily distinguished from that gas by the fact that when
added to nitric oxide it does not produce red vapours, whereas
when oxygen is mixed with Dilric oxide these coloured gases are
instantly formed.

When equal volumes of nitrous oxide and hydrogen are n
in a eudiometer, and an electric spark passed through the
lure, the gases combine with explosion, water being produced and
nitrogen set free ; the volume of nitrogen so resulting being equal
to that of the nitrous oxide employed. This compound, therefore,
cotitains its own volume of nitrogen, and half ils own volume ol
oxygen. Nitrous oxide, when inhaled, exerts a remarkable aclion
upon the animal organism. This fact was first observed by Davy,
If breathed for a short time, the gas induces a condition of hysterical
excitement, often accompanied by boisterous laughter, hence the
name laughing gas. If the inhalation be continued, this is followed
by a condition of complete insensibility, and ultimately by death.
On account of the ease with which the state of insensibility can be
brought about, this gas is extensively employed as an anicsihetic,
especially in dentistry.

Nitrous oxide is a gas which is moderately easily liqueRed ; at
0° C. a pressure of thirty atmospheres is required to effect its
liquefaction.

Liquid nitrous oxide is colourless and mobile ; it boils at -92*1
and when dropped upon the skin produces painful blislen.
When thrown upon water, a quantity of the water i*
verted into ice : mercury poured into a tube containing a snudl'
quantity of the liquid is instantly frozen. An ignited fragment of <

Nitrous Oxidi 225

charcoal thrown upon the liquid floats upon the surface, at the
■ame time burning with brillianC]r. If the liquid be mixed with
carbon disulphidc, and placed in vacuo, the temperature USi,%
to - 140, By strongly cooling the liquid, contained in a sealed
tube, Faraday succeeded in solidifying it ; this may also be
effected by the rapid evaporation of the liquid. The solid melts
at —99*, and if placed upon the hand causes a panful blister ; in
this respect it dilfen from solid carbon dioxide, which gasifies
without previous liquefaction.

Brponltrona Aoid, NHO.— This subsunce bat noi yet been iioUted. bdng
(■nly known in its lalts and in ugueous lolulioa.

When a loliilion of pouussium nitrate, or nitrite, is acted upon by KxUnn
amalgain (ui Llloy ol sodiutn and tnercuty), the salt is reduced by the nascent
hydrogen, evolved bytbe Action of the amalgam upon water, and Ibe potassium
•alt of hypooitrous add is left in wlution—

KNO, + 2Hi = 2H,0 + XNO.

The MluliOD, which is alkaline, owing to the presence oT sodium hydroxide,
li then nude neutral by the addition of acetic add, and silver nitrate added.
A yellow preclpilale is thrown down, conustlng of lilver hyponitrile, AgNO.

When a solution of potaasiuni hyponitrile is addified and llien heated, tlie
hyponitrous add, which may be regarded as lilicrated by the add, is troken up
into nllroui oxide and water—

2HN0 = N,0 + Hp.

aNO + CI, = aNOCi

n is also formed by the action of phosphorus pentachlonde upon potai^um
nitrite, thus —

PCI, + KNO,- NOCl + POCl, + KCL

HNOs + IHO = NOCl + CI, + SHA

in of nitrosyl hydrogen

(NOjHSO, + Naa = NOCl >r NaHSOj.

* TlUen ba* ibown Ihal (his is the only oxy-chlorlde of nitrogen that ei

226

Inorganic Chemistry

orange-yellow liquid, which boils at about - 8". it is decomposed by water
into nitrous add and hydrochloric acid —

NOCl + Hj,0 = HNO, + HCL

In a similar manner it is decomposed by metallic oxides and hydroxides,
thus —

NOa + 2KHO = KNO, + KQ + HjO.

Nitrosyl chloride has no action upon gold and platinum, but it attacks
mercury with the formation of mercurous chloride and the liberation of nitrio
oxide —

2NOa + Hg, = HgjCl, + 2NO.

CHAPTER VI

THB ATMOSPHERE

The atmosphere is the name applied to the gaseous mixture
which envelops the earth, and which is commonly called the air.
The older chemists used the word atr much as in modem times
the word gas is employed ; thus they spoke of inflammable air,
dephlogisticated air, alkaline air, and so on.

The air consists of a mixture of gases, the two chief ingredients
being nitrogen and oxygen. Lavoisier was the first to clearly
prove that oxygen was a constituent of the air, although Robert
Boyle and others before him had shown, that air was absorbed by
metals in the process of forming a calx, and that the metal gained
weight as the calx formed. When the fact that the air was com-
posed of oxygen and nitrogen became established, various devices
were adopted to determine the proportion of oxygen in it.
Priestle/s method was by means of nitric oxide. It depended
upon the fact that when nitric oxide is mixed with air, it combines
with the oxygen, forming brown fumes which dissolve in the water.
A contraction in volume therefore takes place, from which the
volume of oxygen may be calculated. This method yielded results
which seemed to show that there was considerable variation in the
proportion of oxygen present in different samples of air, and the
idea arose that the wholesomeness, or goodness, of the air was
dependent upon the quantity of oxygen which it contained. Hence
arose the term eudiomeiry, signifying io measure the goodness.
Cavendish, on the other hand, as the result of a large number of
experiments made by him, came to the conclusion that there was
no difference in the samples of air that he experimented upon.

Since the time of Cavendish, eudiometric analysis has been
brought to a state of great perfection and accuracy by Bunsen,
Regnault, Frankland, and others. The conclusion to be drawn
from the extended researches of these chemists is, that although
the atmosphere certainly shows a remarkable uniformity of com-
position, there do exist perceptible, though very slight, variations

««7

^[_^l

^ft 328 Inorgan

k Chimislry

^H in the amount of oxygen present at different places an<
^H times. Samples of air collected from all parts kA the

at differea^H
globe, frn^H

1 bli few

S ^

■Vj

§3

llrl

■

a;'

t' ^f

r ^

■C: ..

^^^^ t-j.-. .

^^^^^L t^' E

1 1-\

^^M

^H w

'I'

^^H '^1;)

i''

^V mid ocean, from high moun
^H crowded cities, show a varialio
^^^ tag front 30.99 (0 I0.36. Ang^

tain peak, American prairie, and
n in the proportion of oxygen rang-

^^^^^^^■f

■^IM^^

■

^a^^^^M

Tkg Atmospfun 339

#eather the oxygen in the air in towns, sometimes falls as low as
2a82. Samples of air taken from crowded theatres, have been
found to contain as little as 2a 28, while in many mines the amount
averages as low as 20.26.

The mean proportions of oxygen and nitrogen in the atmosphere
may be given

Oxygen 20.96 parts by volume.

Nitrogen .... 79.04 „ „

loaoo

The composition of the atmosphere by weight was determined
by Dumas and Boussingault (1841). In their method, air which was
freed from carbon dioxide and moisture, was slowly drawn through
a glass tube containing a known weight of metallic copper, heated
to redness. The oxygen combined with the copper, forming copper
oxide, which was aAerwards weighed, and the nitrogen passed into
a vacuous flask, and was also weighed. The apparatus as em-
ployed by Dumas is seen in Fig. 5a B is a glass flask having a
capacity of 10 to 15 litres, which was exhausted and then weighed.
It was then attached, as fthown, to the tube T, containing a known
weight of metallic copper, and which was also exhausted. The
bulbs L contained a solution of potassium hydroxide, and the tubes
/I solid potash, for the removal of atmospheric carbon dioxide.
The bulbs O contained strong sulphuric acid, and the tubes / were
fllled with pumice moistened with the same acid, by means of
which the moisture was withdrawn from the air. When the copper
was heated and the cocks partially opened, air, free from carbon
dioxide and moisture, was slowly drawn over the heated metal,
which was thereby converted into the oxide. At the conclusion
of the experiment the globe and the tube T were reweighed. The
nitrogen remaining in tube T was then pumped out and the tube
once more weighed. The difference between the two last weigh-
ings of the tube, added to the gain in weight suffered by the globe,
gave the nitrogen ; while the difference between the original and
flnal weights of the tube gave the increase of weight suffered by
the copper, that is, the amount of oxygen. The result of numerouf
experiments gave the mean composition —

Oxygen 23 parts by weight

Nitrogen Jl ^ ••

100

Inorganic Cktmistry

: modern inetliod for estimaling ihe amounts of oxygen
and nitrogen in the air, based upon (he same principle, namely, Ihe '
absorption of ilie oxygen by healed metallic copper, is illustraled
in Fig. 51 (known as Jolly's apparatus). Tlic sample of air to be
examined is allowed 10 enter the glass globe A {whose cap.icity is
about 100 cc, and which has been previously e>Jiausted) by means
of the three'way cock b. (The air is firsi dried, by beiny drawn
through tubes filled with pumice moistened with sulphuric acid, on

lis way into the apparatus.) The bulb is then surrounded
metal jacket B, which is filled with broken ice, and when the t«n-
peraiure has fallen to o' the bulb is put into communication with
the lube d by means of the three-way cock. The tube g is then
raised or lowered, so as to bring the mercury in rf 10 a fixed point
in the tube at m, and the tension of the enclosed air is ascenained
by the graduated scale behind tube g. The ice-jacket is then
removed, and the spiral of copper wire wiihb the bulb is heated

Bated ^1

The Atmosphere

231

to redness by the passage through it of an electric current. The
copper combines under these conditions with the oxygen, form«
ing copper oxide, thereby reducing the volume of the contained
gas. The globe is again cooled, and the tube g lowered to. such
a position, that when communication is once more made between
the globe and tube d^ the mercury shall stand at the same point m.
From the observed tension of the gas before and after the
experiment, the volume relations of the two constituents can be
calculated. Thus, suppose the tension of the enclosed air to be
720.25 mm., and that of the residual nitrogen 569.28 mm., then for
I volume of air the reduction would be—

569.28 ,

i-:;^ -;..'" -7904 vols.

720.25

Therefore in 100 volumes the composition would be—

Nitrogen * — 79.04
Oxygen = 20.96

100.00

Besides oxygen and nitrogen, the air contains variable quantities
of the following gases : carbon dioxide, aqueous vapour, ammonia,
ozone, nitric acid. With the exception of aqueous vapour, these
substances are present only in relatively small proportions, and
with all of them the amount is liable to considerable variation.
Especially is this the case with the aqueous vapour, as the amount
of this constituent present at any time is largely influenced by the
temperature. The average composition of normal air may be

•

taken as follows : —

Vols, per looa

Nitrogen*

, 779.0600

Oxygen .

, 206.5940

Aqueous vapour

> - • <

14.0000

Carbon dioxide

0.3360

Ammonia

0.0080

Ozone .

0.0015

Nitric acid

. •

aooo5
1000.0000

Aqueous Vapour. — For any given temperature there is a
maximum amount of aqueous vapour, which a given volume of air

* The smmll percentmfe of trgoo present is here included with the nitrogen.

23* Inorganic Chtmistry

is capable of taking up : under ihese condiiions the air is said ta
be saturaltd •milH moisture at ihe particular temperatuie. Thus t
cubic metre of ait is saturated with moisture at the various tempera-^
tures stated, when it has taken up the following weights oiV

At o*

When air, saturated with moisture at say lo", is cooled t
the excess of water beyond 9.363 (the maxiinum for 10*) is deposited
cither as riiisi or rain. Tho temperature at which air thus begins
to deposit moisture is called the dew-point. The deposition of
moisture from the air caused by the lowering of ilie temperature
is a matter of everyday observation. A glass vessel containing
iced water, becomes bedewed with moisture upon the outside, as
the air in its immediate vicinity is cooled. When a season oF
severe frost is suddenly followed by a warm wind, highly charged
with aqueous vapour, it is not unusual to see condensed moisture
collecting upon, and streaming down, the cold surface of walls.
For the same reason, after the sun has set, and the heat from the
ground has radiated, leaving the ground colder than the atmos-
phere, the temperature of the air is lowered, and it begins to
deposit its aqueous vapour in the fonn of tiew.

The amount of aqueous vapour in the air, or the humidity of tha <
air, is estimated by meteorologists by means of an instrumenl 1
called the wet and dry bulb thermometer.

Carbon Dioxide,— The proportion of this gas present x
air is also liable to considerable variation, although not through^
such a wide range as the aqueous v.-ipour. The processes offl
respiration, combustion, and putrefaction are attended by thSa
evolution of carbon dioxide, hence the amount of this gas presentM
in dosed inhabited places, is greater than that in the open a
badly ventilated and crowded rooms, the proportion sometimeail
rises to three parts in 1000 vols. Frankland has found that at higlK
elevations the amount of carbon dioxide in the air is often, althou^'l
not invariably, considerably above the normal.

At CtiBDiounix (3000 feci) tbc aiaount of carbon dioxide was 0.63 pel loeo *<
„ Grands Mulfis (ii.Qoo feel) .. „ ,. t.ii

., Modi Blaoc (15,733 (eel) ,, .. ., o di ,, ,

This fact is probably due to the absence, in these high regioi

The Atmosphere 233

of the vegetation which is one of the chief natural causes operating
to remove atmospheric carbonic dioxide (see Oxygen, page 166).

The amount of carbon dioxide is slightly higher during the
night, and often rises considerably during foggy weather. Thorpe
has shown that near the surface of the sea, the amount of carbon
dioxide in the air is slightly less, being on an average ajoo vols,
per 1000.

Ammonia in the atmosphere is derived from the decomposition
of nitrogenous organic nuitter. Although present in relatively
very small quantities, it varies in amount very considerably. From
the experiments of Angus Smith, 1000 grams of air from varioui
sources were found to contain the following amounts of anunonia :-~

London . . 0.05 granunes.

Glasgow 0.06 „

Manchester. . aio „

The proportion of ammonia appears to be higher during the
night than in the daytime, and immediately after heavy rain the
amount is perceptibly diminished.

Rain water always contains ammonia, although the amount
varies greatly with changing atmospheric and climatic conditions.
Lawes and Gilbert, Angus Smith, and others, have made a large
number of estimations of the amount of ammonia in rain water at
various places and seasons, and under many different conditions.

Nitric Acid, present in the form of nitrates and nitrites, is
produced in the atmosphere by the direct union of oxygen and
nitrogen whenever a lightning flash passes through the air (see
Nitric Acid). Rain which falls during or immediately after a
thunderstorm is found to contain nitrates and nitrites.

These two nitrogenous compounds, anunonia and nitric acid,
although present only in such small proportion in the atmosphere,
fulfil a most important function in the economy of nature. From
the experiments of Lawes and Gilbert and others, it has been shown,
that most plants are unable to draw upon the free nitrogen of the
atmosphere, for the supply of that element which they require for
the development of their structure and fruit* Although they are
surrounded by, and bathed in, nitrogen, they cannot assimilate it.
Plants that are growing in unmanured soil, therefore, derive their

* Leguminous plants, such as cloven, vetc<.«*s. bean«. p^as. which develop
root-nodnW or tnb^rel^. are escepCioDt.

234

Inorganic Chemistry

nitrogen from ihc ammonia and nitric acid which are present in
tbe air, and which are washed inlo the g^round by the rain. It has
been found that a plant grown tinder such experimental conditions
as to exclude the possibility of its obtaining supplies of these nitro-
genous compounds, will yield upon analysis exactly the same
amouni of nitrogen as was originally contained in the seed from
which it grew.

Ozone. — The causes which operate in the formation of this sub-
stance in the air arc ai present imperfectly known : it is supposed
that its occurrence is related to the development of electricity in
the atmosphere. On account of the powerful oxidising character
of OEone, its presence can never be detected in the air, where much
organic matter of an oxidisable nature is present, as is the case in
tbe air of such place? as malarial svi'.imps, dwelling-houses, and
large towns.

The amount of oione in pure country air has been found to vary
with the lime of year, reaching a maximum in the spring-time, and
gradtially falling towards winter. Thorpe has found that in sea
air the amount of otone is practically constant during all seasons.

The usual method «hich is available for the deteaion and
estimation of ozone in the air is extremely crude. It consists in
exposing oione test-papers (sec Oione) to the air for a certain lime,
and comparing the colour that is produced with a standard scale
of tints : moreover, other substances than oionc, which may be
present in tbe atmosphere, will also liberate iodine from potassium
iodide, and these are therefore measured as ozone. Besides the
higher oxides of nitrogen, which, as we have seen, are formed in the
atmosphere, and which liberate iodine from potassium iodide, it has
been shown that peroxide of hydrogen is also present The state of
our knowledge at present, therefore, respecting the exact amount of
atmospheric ozone, and its variation, is far from satisfactory ; it is,
indeed, quite possible that many of the effects which have been attri-
buted to oione, are in reality due to peroxide of hydrogen. Thus it
has been shown by Schiinbein that this compound is farmed during
the evaporation of water, and this statement probably derives con-
Rrmaiion from the fact that its presence may be detected in rati)
water. The salubrity of the air of the sea-shore, where large areas
of wet sand and stones offer the most perfect conditions for the
rapid evaporation of water, and, consequently, for the formation of
peroxide of hydrogen, may therefore be attributable as much to th«
presence of this substance as to the provertual 0H>n&

The Atmospfurt 235

The various gases of which the air is composed, are not com-
bined, but are merely mingled together. The remarkable con-
stancy of its composition, as regards the oxygen and nitrogen, led
chemists at one time to suppose, that these gases were in chemical
union with each other in the atmosphere ; but a number of facts
which have since been learnt respecting these gases, prove with-
out doubt that this is not the case, and that the air is simply a
mechanical mixture. This evidence may be briefly summed up
as follows : —

(i.) When oxygen and nitrogen are mixed together in the pro-
portion in which they occur in air, the resulting mixture behaves
in all respects like ordinary air, and the mixing of the gases is not
attended by any volumetric or thermal disturbance, such as would
be expected to accompany the chemical union of two elements.

(2.) The degree to which air is capable of refracting light, is
found to be the mean of the refractive power of oxygen and
nitrogen. Were these gases chemically combined, the compound
should behave in this respect as other compound gases, where it
is found that the refractive index is always either greater or less
than the mean of that of the constituents.

(3.) According to a fundamental law of chemical science, the
composition of a chemical compound is constant Such a thing as
variability in the composition of a compound is unknown. The
proportion of oxygen and nitrogen, as we have seen, does vary in
the air, although through only small limits, hence they cannot be
united to form a compound.

(4.) The proportion by weight in which oxygen and nitrogen are
present in air, bears no simple relation to the atomic weights of
these elements.

(5.) When air is dissolved in water, the oxygen and nitrogen
dissolve as from a simple mixture of these gases, in accordance to
the law of partial pressures (see page 127).

(6.) The oxygen and nitrogen can be partially separated, by
taking advantage of the different rates of diffusion of these two
gases (see Diffusion of Gases, page 80).

The various gases of the atmosphere are maintained in a state
of uniform admixture, in spite of their widely different densities,
by the operation of two causes : first, air currents, which effect the
rapid removal of large masses of air from place to place ; and,
second, their own molecular movements, which bring about the
phenomena of gaseoos difiusion.

236 Inorganic Chemistry

Suspended Impurities in the Atmosphere. — Uesidu ihe j
gaseous coostituenis of the air, there is alwa)s present a
quantity of suspended matter, boih liquid and solid. The emi- I
cnce of this suspended matter in the air, cati be rendered evident 1
from Ihe fact, ihal ihese minute panicles are capable of refJecting I
light; if, therefore, a strong beam of light be passed through I
darkened room, the track of the beam is distinctly visible, t
account of its being reflected from mnumeiable particles floatill|
about in the air, many of ihem appearing quite large. Pasleur bai I
shown, that this suspended matter can be removed by filtration 1
through cotton wool.' Tyndall also has shown, that in uodift- j
turbed air (be suspended matter settles in Ihe course of a few 1
hours, leaving the air almost entirely free from this impurity. .
For '.his purpose the floor of a large oblong glass box 1

smeared over with glycerine. The box, after being hermeiicalir J
dosed, was (hen allowed 10 stand for twenty-four hours, duriiq
which time the suspended matter subsided, and adhered t
glycerine. When a beam of light is allowed lo pass through a
that has been thus freed from suspended matter, there bein|
nothing present to reflect the tight, the beam cannot be s
its track will be evident in the air of the room as it enters
leaves the box, but within the box it will be invisible (as repre"!
sentcd in Fig. 52). To air in which a beam of light is in ll
invisible, Tyndall has applied the term " optically pure."

1 he suspended matters are partly mineral and partly organic
or ibe mineral matters, sodium chloride and certain sulphatetl
ate present in greatest quantity. These are thrown into
in ilie sea-spray, and as the small globules of ivater evaporatq^l

* See F.ipcniDCnli 334 [□ 341, "Cbemlcal I.eeturc Eiperimenli,"

TA^ Atmospfun 237

they leave minute residua} particles of saline matter, which,
being driven by the wind, remain floating in the atmosphere. It
is only very rarely, even at fiar inland places in Europe, that spec-
troscopic examination fails to detect the presence of sodium com-
pounds in the air. In the air of islands, such as England, it is
never absent. Sulphates are also produced by the oxidation and
combustion of sulphuretted compounds ; the amount of these, there-
fore, is greatly increased in the neighbourhood of towns.

The organic suspended matter of the air has of late years been
made the subject of extended research. Pasteur has shown that
amongst these organic substances are the germs and organisms
which produce fermentation, putrefaction, and disease. Putrescible
substances, such as milk, urine, flesh, &c, if themselves carefully
freed from all such germs, may be preserved unchanged, for ap-
parently any length of time, in air that has been deprived of sill
suspended matter. It is highly probable that the salubrity or
otherwise of different places, is associated with the nature and
amount of the organic matter in the air, and it is certain that
these organisms play a most important part in relation to the life
and health of man. The feelings of lassitude and headache, which
result from the prolonged breathing of the air of rooms containing
numy people, are brought about more by the poisonous effects of
the organic emanations evolved during respiration, than by any
diminution in the supply of oxygen, or increase in the proportion
of carbon dioxide in the air. The well-known and unpleasant
smell that is perceived on first entering a crowded room, is also
due to the same cause, and it has been shown that the moisture
which condenses from such an atmosphere upon a cold object, if
preserved for a short time, rapidly becomes putrescent, owing to
the decomposition of this organic matter.

Tlie presence of suspended matter in the air, appears to exert a
remarkable influence upon the formation and character of fogs.
Aitkin has shown that Uiose conditions which result in the forma-
tion of a fog in ordinary air, are incapable of producing that effect
in air that has been freed from suspended matter. It would appear
that the suspended particles act as innumerable points, or nuclei,
which facilitate the deposition of moisture, much in the same way
as the crystallisation of a salt, from its solution, is known to start
from any minute particles of foreign matter that may be floating in
the liquid.

The height to which the atmosphere extends has been variously

238

Inorganic Chemistry

estimated. From observations of the flight of meteorites, it ap-
pears that even at a height of seventy to seventy-five miles the
air still has a sensible degree of density. The air being elastic,
and subject to the law of gravitation, its density, which is greatest
at the earth's surface, rapidly diminishes as the altitude increases ;
thus, at about three and a half miles the density is only one-half,
and at seven miles one-third, of that which obtains at the sea-level.
From a consideration of the physical properties of gases, there is
every reason to believe, that in an extremely attenuated condition
the atmosphere extends far into space, and it has been calculated,
that the pressure exerted by our atmosphere upon the surface of
the moon, is equal to about i mm. of mercury.

The density of the atmosphere varies at different points of the
earth's surface, and at the same point at different times. The
pressure exerted by the atmosphere is measured by the height
of a column of mercury which it is capable of supporting, the
instrument employed for the purpose being called the barometer.
At the sea-level in the latitude of London, the average weight of
the atmosphere is equal to that of a column of mercury 760 nrni.
at 0°, and this is taken as the standard pressure of the cdtnos-
phere

CHAPTER VII

COMPOUNDS OF NITROGEN AND HYDROGEN

Three compounds of nitrogen with hydrogen have been pre-
pared, namely : —

Ammonia NH9.

Hydraxinc N.H^ or (NH^^

Hydrazoic acid .... N^H or H N,.

AMMONIA.

Formula, NH3. Molecular weight = 17. Density = 8.5.

History. — Salts of ammonia, and also the aqueous solution, were
known to the alchemists. It was termed by Glauber, spin /us vola-
tilts salts armaniacii being obtained by the action of an alkali upon
sal-armoniacum. Subsequently, when ammonia was obtained by
the destructive distillation of such refuse as hoofs and horns of
animals, the name spirits of hartshorn was applied to it The
actual discovery of gaseous anunonia was made by Priestley
(1774), when he collected the gas, evolved by the action of lime
upon sal-ammoniac, by means of his mercurial pneumatic trough.
Priestley named the gas alkaline air,

Occurrenee. — In combination as carbonate of ammonia it is pre-
sent in small quantities in the air, derived by the decay of nitro-
genous animal and vegetable matter. As nitrate and nitrite it is
found in rain water. It is evolved, along with boric acid, from the
fumaroles of Tuscany (see Boric Acid), and is found as chloride
and sulphate in the vicinity of active volcanoes.

Modes of FoFmation.---<i.) Ammonia can be synthetically pro-
duced, by submitting a mixture of nitrogen and hydrogen to the
influence of the silent electric discharge (Donkm). The amount
of ammonia so obtained, however, is extremely small, and can best
be shown by passing the gases, as they issue from the ''ozone
tube," through a cylinder containing a small quantity of Nessler^s

•39

240 Inorganic Cfumisiry

Kolulioo.* In a short time the solution will b«gln to show a
yellotvish brown colour, indicating the presence of traces of

(z.) Ammonia may be prepared by gently heating any of Its
salts, with either of (he caustic alkalies, potash or soda, or with
slaked lime. The salt most commonly employed is the chloride.
When this is mixed with an excess of slaked lime, and the mixture
gently healed in a flask, ammonia is evolved, and calcium chloride
and water are formed —

SNH^Cl + CaH,0, = CaCI, + SH.O + 2NH,.

;rby ^

The gas may be dried by being passed through a cylinder
taining lumps of quicklime,^ and may then be collected either
upward displacement, or in the mercurial trough. On account of
its extreme solubility it cannot be collected over wati

{3.) Ammonia is formed by the action of nascent hydrogen upon
salts of nitrous and nitric acid, thus —

NaNO, + 4H, = NaHO + SH,0 + NH^

This method is often made use of, in the quantitative e
of niiraies in drinking water.

(4.) When Ditrogenous organic matter is subjected to destm
live disiillaiion, that is, strongly heated out of contact with a!||
ammonia is formed : hence when coal, which usually contains abo
3 per cent, of nitrogen, is distilled in the process of the
facture of ordinary illuminating gas, one of the products
decomposition is ammonia- The "ammoniacal liquor"
gas works, is the source of all ammonia salts at the present d
The liquor is boiled with milk of lime, and the e
expelled is absorbed by sulphuric acid. The ammonium sulphati
obtained is evapomtcd to dryness, and purified by recrystallisatioru

Properties. — Ammonia is a colourless gas, having a powerfully
pungent smell, and a strong caustic taste. It is lighter than air,
its density being 0.589 (air = i). Ammonia possesses the property
of alkalinity in a very high degree ; it turns red litmus blue, and
yellow turmeric brown. The g.-is is unable to support combustion,

* A lotulion of meicuiic iodide in poia^siura iodide, nndeied alkaline 1
potassium hydioiiilc.

t Tht wual desiccaling agenti. namel]', aulphuric acid, or phospbi
pcntoiide. are inadmiislbk: in Ihe cue of amiDonia. oi Ihii ga* at once ur

Ammonia

24 »

and is irrespirable. Under ordinary conditions ammonia is not
combustible, but if the air be heated, or if the amount of oxygen be
increased, the gas will then bum with a flame of a characteristic
yellow-ochre colour. This behaviour of ammonia as regards com-
bustibility, is most conveniently
illustrated by means of the ap-
paratus shown in Fig. 53. A
stream of the gas, obtained by
gently heating a quantity of the
strong aqueous solution in a
small flask, is delivered through
a tube which is surrounded by
a wider glass tube. Through
the cork which carries this tube
a second tube passes, through
which a supply of oxygen can
be passed. On applying a
lighted taper to the jet of am-
monia as it issues from the tube,
it will be noticed that the gas
bums in the heated air round
the flame of the taper, but is
unable to continue buming when
the taper is withdrawn. If now
a gentle stream of oxygen be
admitted into the annular space
between the two tubes, the am-
monia readily ignites, and continues to burn with its character-
istic flame. On cutting ofl* the supply of oxygen, the flame of the
buming ammonia languishes and dies out

Ammonia is extremely soluble in water ; i c.c of water at o* C,
and at the standard pressure, dissolves 11 48 cc of anmionia,
measured at o* C. and 760 nun. The solubility rapidly decreases
as the temperature rises, as will be seen by the following table : —

X cc of Water at
760 mm. Dittolves

At O* .

8* .

Fig. 53.

»»
»»

i6* .

50- .

Cnunmet, NHj.

. a875 .

cc at 0* C and
760 mm.

. 1 148

. 0.713 .
. 0.582 .

764

• 0.403 .
. a229 .

529
306

Inorganic Chmistry

Is healed, the gas is rapidly evol*
and at ihe boiling temperature the whole of ii is given up.

The great solubility of this gas in water may be shown by filling
a large bolt-head flask with ammonia by displacement, the fiask
being dosed by means of a cort through uhicli a. long tube passes,
as shown in Fig. 54. On removing the cork from the end of the
tube, water slowly rises until it reaches the top, and as soon as the
first drops enter the globe the absorption
proceeds with great rapidity, the water being
forced up the tube in the form of a fountain,
which continues until the flask is 5lled.

Commercial lii/iior ammonia is prepared
by passing ammonia gas into watery the
strongest solution has a specific gravity o(
0,883 at 15', and contains 35 per cent oi
ammonia. During the process of solution
heat is liberated, and when the gas is again
expelled, the same amount of heat is reab-
sorbed. If a rapid stream of air be driven
through a quantity of strong ammonia solu-
tion, contained in a glass flask, the am-
monia gas is quickly expelled ; and if the
flask be placed upon a wooden block, as
seen in Fig. 5;, upon which a few drops of
water have been poured, it will be found
that after a few moments the flask will have
become firmly froten to the block. By Ihe rapid evaporation of
ammonia in this way, It is possible lo lower the temperature to
- 40° C.

Ammonia is an easily tiquefiable gas ; thus at 13.5° it requires a
pressure of 6.9 atmospheres, and ato'only4.2 atmospheres, in order
lo liquefy it. The gas was first liquefied by Faraday (182J). by heat-
ing in one limb of a closed and bent glass tube (see Fig. 3), a quantity
of a compound of ammonia with silver chloride, the other limb of
llie tube being immersed in a freeiing mixture- The experiment
may be made in a lube eonstnicted as seen in Fig, ;6. The wide
limb is nearly filled with dry precipitated silver chloridr, which lias
been saturated with ammonia gas. This compound melts at
about 38', and at a somenliai higher temperature it gives up
its ammonia. If the narrow limb of Ihe tube be immersed in a
fteeiinR mixture while the compound is being heated, ihi

FiO. S4-

Ammonia

243

bined influence of the cold, and the pressure exerted by the
evolved ammonia, will cause the gas to liquefy and collect in the
cold portion of the tube. On removing the tube from the freexing
mixtuxe, and allowing the other end to cool, the liquid ammonia
will boil off, and be reabsorbed by the silver chloride, reforming
the original compound.

Liquid aounonia is easily obtained in larger quantity, by passing
the gas through a glass tube inunersed in a bath of solid carbonic
add and ether. Liquid ammonia is a colourless, mobile, and
highly refracting liquid, boiling at -33.7*, and having a specific
gravity at o* of a6234. When cooled below - 75* it solidifies to a
mass of white crystals.

Liquid aounonia dissolves the metals sodium and potassium, the
solution in each case being of an intense blue colour. On the
evaporation of the liquid, the metal is deposited unchanged.

Pia 55.

Fia 56.

During the evaporation of liquid ammonia, boiling as it does at
so low a temperature as - 33.7*1 a rapid absorption of heat takes
place, and as this substance is so easily obtained it was one of the
earliest liquids employed for the artificial production of ice. Various
ice-making machines have been invented by M. Carr^ in which
the reduction of temperature required is obtained by the evapora-
tion of liquid anunonia.

Ammonia is decomposed into its elements at a temperature
below a red heat In this decomposition, two volumes of ammonia
give one volume of nitrogen, and three volumes of hydrogen. The
gaseous products, therefore, obtained by passing anunonia through
a red hot tube, are inflanmiable. In the same way, when electric
sparks are passed through ammonia, the gas is resolved into its
constituents. Bf performing this experiment upon a measured
volume of ammonia, confined in a eudiometer over mercury, it will

244

Inorganic Chemistry

be found, ihal after the passage of the sparks for a short time, a
the readjustment of the levels of mercury, the original volume 6
Uie gas has been doubled.

The fad that llie hydrogen and nitrogen are present in ammonia
in the proportion of three volumes of hydrogen lo one of nitrogen,
can be shown by uking advantage of the fact thai ammonia is
decomposed by chlorine, the latter combining with the hydrogen
lo form hydrochloric acid, and the nitrogen being set free. This is
effected by means of the apparatus shown
in Fig. 57. The long glass Itjbe, divided
into three equal divisions, is filled with
chlorine and closed by a cork carrying a
small dropping funnel. A few cubic cen-
timetres of strong aqueous ammonia are
potired into ihe funnel and allowed (o
enter the tube drop by drop. As ihe first
two or three drops fal) inlo ihe clilorine,
it will be seen that the combination is
attended with a feeble flash of light, and
fumes of ammonium chloride arc foimed.
When the reaction is complete, the whole
of the chlopne will have combined with
hydrogen, derived from the ammonia, to
form hydrochloric acid, and this in its turn
will combine with Ihe excess of ammonia
added, forming anrnionium chloride. This
substance dissolves in the water. A small
quantity of dilute sulphuric acid is next
introduced by means of the dropping funnel
in order to absorb the remaining excess of
Fig. 57. ammonia. The atmospheric pressure is

then once more restored by attaching to
the funnel a bent tube, dipping into a beaker of water as shown
in the figure, and when Ihe water is allowed lo enter, it will be
found 10 flow into the tube until it reaches the second gradua-
tion. The gas which is lefl, and which occupies one of the
divisions of the tube, is found on examination to be nitrogen.
This one measure of nitrogen, therefore, has been eliminated from
that amouni of ammonia which has been decomposed by ihe
chlorine, with which ihe lube was originally filled. Now chlorine
combines with its own volume of hydrogen, therefore the volumis

Hydrazint 245

of hydrogen which was in combination with the one measure of
nitrogen, is equal to the volume of chlorine contained in the tube,
that is to say, it was three measures. We have, therefore, one
measure of nitrogen and three measures of hydrogen, or, in other
words, ammonia is a combination of nitrogen and hydrogen in the
proportion of one volume of nitrogen to three volumes of hydrogen.
Ammonia combines directly with acids forming salts, known
as ammonium salts, in which the nitrogen functions as a pentad
element ; thus with hydrochloric and sulphuric acids it forms respec-
tively ammonium chloride and ammonium sulphate —

NH, + HC1-(NH4)C1.
2NHj + H,SO| - (NHJjSO^.

(The ammonium salts will be described with the compounds of
the alkali metals.)

Hydrasine, NHs'NHj or N]H4.— This compound was first prepared by
Curtius (1887). -It is obtained by heating together in a sealed tube, to 9
temperature of 170*, hydrazine hydrate, N]H4,H^, and barium monoxide.
Under these circumstances the barium oxide takes up the water from the
hydrazine hydrate, according to the equation —

BaO + NjH^HjO = Ba{HO), + NaH4.

When the tube is opened, the gaseous hydrazine, which is under considerable
pressure, rushes out of the tube, forming dense fumes in contact with the
atmospheric moisture, with which it combines with great readiness.

Hydraslne Hydrate, N,H4H,0.— The compound formed by the combina-
tion of hydrazine with water is obtained by distilling hydrazine sulphate,
NsH4H)S04, with an aqueous solution of potassium hydroxide (caustic potash)
in a vessel of silver. It is a colourless, fuming, powerfully corrosive liquid,
which boils at 118. 5*. It atucks glass, corks, and indiarubber, and can only
be prepared in vessels of silver or platinum which are screwed together at their
junctions. With the halogen acids it forms two series of salts, in which either
one or two molecules of the halogen acid are present ; thus with hydrochloric
acid we have^

Hydrazine monohydrochloride . . N3H4,HC1.

Hydrazine dihydrochloride .... N|H4,2HCL
Hydrmsoio Add, HN,.— Discovered by Curtius (1890). The sodium salt is
prepared by boiling benzoylazo-imide with sodium hydroxide, when sodiuiu
t)enzoate and sodium hydrazoate are formed, thus —

C,H,CO- N II + 2NaHO=C,HaCOONa + Na - N || + H,0.
\N XN

It is also produced when sodamide (obtained by heating sodium in dry
ammonia gas) is heated to aoo* in a stream of nitrous oxide *—

2NH,Na + NaO=NaN3 + NaHO+NH5.
• See Experiment 298. " Chj?mical Leciurt ExpenmtivV^r Tvn^ ^^

PropmUM. — This compound is a coU
It and poverfulty penctralinE odoi

s metnbnme.
As iu name denolei il is on acid substance, and in many of ill properlics il
itronglr resembles the halogen acids. The gas is eitnmely soluble in waler.
and forms a strongly add liqtud wbtcb smells of the gai. This solution when
boiled, finally assumes a definite strength, and yields on dislilUIion an aqueoui
add of consiani composition, in ibis respect resembling aqueous hydrochloric

In its constitution this acid may be compared with hydrocyanic acid, and
with Ibe halogen acids —

H(N,); H(CN); H(C1); H(BrJ.

ir the halogen elements. CI ai

in which the radical cyanogen (CN).
repEaced by the group consisting of II

When a lolulion of hydrsiolc add is added lo s solution of silver nliralc,
white predpllate of silver hydraioale is formed, strongly resembling silver
cyanide and silver chloride This sllvei salt, however, is not acted upon by
ligbl in the way the chloride is. and it diHen also in being eitremely explosive.
A minute (Juantily of the compound, when touched with a hoi wire, detonates
violently.

When gaseous hydiaioic acid is mlied with gaseous ammonia, dense white
fumes ate fomied, consisting of ammonium bydrazoate. These two hydrides
of nilrogen, apparenlly so similar, but in reality so widely di
form Ibe ammonium salt, just as gaseous hydrochloric acid and amr
comtnne lo fonn ammonium chtorii
NH,-

The alkalinthydridr: of nitrogen, ammonia, combines with the otitf hydrictodj
nitrogen, hydrsiolc acid, and forms the Salt ammonium hydrasoate NH, ~
or N.H,.

BTDSOZSLAUINB.

Formula, NH.iOH).

Discovered by Lossen in 1S65.

Hocles of Formation. — (1.) By the action of nascent hydro

upon nitric oxide, nitric acid, or certain niiraies —

2N0 + 3H, = 2NH,(0H).

HNO, + 3H, = 2H,0 + NH,(OH).

The nascent hydrogen is evolved from tin and hydrochloric ai

and J streair of nitric oxide passed through the r

Hydroxylatnim 247

hydrochloride of hydroxylamine is thus obtained. This is purified
by first passing a stream of sulphuretted hydrogen through the
solution. The tin is thus precipitated as sulphide, and is removed
by filtration. The filtered solution is then evaporated to dryness, and
the hydrochloride of hydroxylamine is dissolved out of the residue
by means of absolute alcohol, in which solvent ammonium chloride
is only very slightly soluble. The alcohol is then distilled off, and
the residue is converted into the sulphate by being treated with the
requisite quantity of sulphuric acid. Hydroxylamine itself, in
aqueous solution, is obtained from the sulphate by the addition of
baryta-water.

(2.) By boiling potassium hydroxylamine-disulphonate with water
for several hours —

2N(0HXS0jK), + 4H,0 - (NH30H),S0| + 2K,S04 + H,S04.

The potassium sulphate is removed by crystallisation.

Properties. — Hydroxylamine is known only in aqueous solution.
The solution is colourless, and has an alkaline character. When
the solution is distilled the substance is partially decomposed. The
solution is a powerful reducing agent : it precipitates gold and
mercury from their solutions, and reduces cupric salts, throwing
down the red cuprous oxide on being boiled.

Hydroxylamine is a base, and may be regarded as ammonia, in
which one of the hydrogen atoms has been replaced by the monad
group hydroxy! (OH). Its salts, like those of ammonia, are formed
by direct union with an acid, without the elimination of water.

NHjOH + HCl - NH3OHCI (or NH,0H,HC1).
2NH,0H + H^0| = (NH30H)2S04 (or 2NHaOH,H,S04).

The salts of hydroxylamine all decompose on the application of
heat, with a more or less sudden and violent evolution of gas ; thus
the nitrate breaks up with almost explosive violence into nitric
oxide and water —

NHjOH-HNOs - 2N0 + 2H2O.

AHMON-SULPHONATES.

These compounds may be regarded as derived from ammonia, by the
gradual replacement of the hydrogen by the group SO^Ii or SOsOH.

Ammon-sulphonic acid Niif(SOsH).

Ammon-disulphonic acid . NH(SO|H),.

Ammon-trisulpbonic add . N(SO^H\^

Polassium ammon-lrisulphonate is precipitated as * crystalliDC salt «
excess or a solution of potussiuni sulphite is added ic

3KiS0i + KNO, + 2H,0 = 4KH0 + N(SO,K),.
Prolonged boiling with water converts il first into the ammon-disulphon

N(SO,K},+ H,0 = NH(SO,K),+ HKSO..
and finally into ammon-sulphonale —

NH(SO,K), + H,0 = NHgiSOjK) + HKSO^
Amraoti-sulphonic acid is a stable crjiialline body : the olhet I
only known in their salts.

When an Ice-cotd solution of sodium nitriLe is addfd to hydrogen sodiwi
fulphite, a comjxnind ii oblaincd which may be regarded
■mmon-trisulpbonic acid by (he replacement of one of tbc groups. SOiH, t
hydroxy 1, OH—

NnNO, + 2NaHS0, = N(OH)(SOjNa), + NaHO.

On Ihe addition ofa saturated solution of potassium chloride, in the cold, (
sodium Kdl is converted into Ihe polassiuni salt, which slowly crystallise!
the solution, with two molecules of water. N(0H)(S0,K),.2H,0.

This potassium hydroxylamine disulphonate is an unstable com
on boiling with water the two SO,K groups are replaced by hydrogen, fan
first potassium bydroiylamine monosuiphonate. NH(OK)SO,1C: and Sna
hydroiylamine, NHjOH.

Compounds of Nitrogen with the Halogen Elemi

Sitrogen Trichloride. NCI,.— This c.
(leii). Its true composiljoti was proved by l^attermann (i8S8),

Hods Of Fonnatloa.— Nitrogen tiicliloiide is obtajned by Ihe a
chlorine upon ammonium chloride—

NH,a + 3CI, = NCT, + *Ha
When a solution of Bmmonium chloride is electrolysed, the cblorine, w
evolved at ihe positive electrode, acts upon (he amraoniuin chloride. Fonn
trichloride or nitrogen. *

PropertlM.— Nitrogen tKchlatiile is a thin oily liquid, of a pale f
colour, and hanng a specific graviiy of 1.65. It is very volatile, and b
unpleasant pungent smell, the vapour I: '

il Ihe most d.ingerously explosive compound known, and when suddenly
healed, or brought Inio contact with grease, lurpenline. or phospiioius it at once
explodes. It also explodes on exposure to iimlight, At a tempefitute t/t 71*
it may be distilled, but the operation is one of Ihe utmost danger. Nitrogen
Iriehloride is decomposed by ammonia, forming ammonium chluridc and Iree

* Sn "Cbcmicsl Leclure Eiperii

Nitrogen Iodide 249

nitrogen ; hence in the preparation of nitrogen by the action of chlorine upon
ammonia, the presence of an excess of ammonia prevents the formation of iliis
dangerous compound.

Kitrosren Trlbromlde, NBr,. — When potassium bromide is added to nitro-
gen trichloride beneath water, a red, oily, highly explosive substance is
obtained, believed to be ihe tribromide of nitrogen.

Nitrogen Iodide, NjHsI,. — When strong aqueous ammonia is added to
powdered iodine, a brown-coloured powder is formed which has violently
explosive properties. Also when alcoholic solutions of iodine and of ammonia
are mixed, a brown and highly explosive compound is produced.

Curtois, who first prepared the substance, believed it to have the composi-
tion NI3, and this view was held by Gay-Lussac and others. Gladstone and
others considered that the substance contained one atom of hydrogen, and that
the formula NHI2 expressed the composition. The investigations of Szuhay
(1893) also led him to believe that the compound obtained by the addition
of an excess of aqueous ammonia to a concentrated solution of iodine in
potassium odide, has the composition NHI^.

The subject has recently been reinvestigated by Chattaway {Proc, Chtm, Soc, ,
1899), who for the first time appears to have obtained the compound in a state
of purity by the addition of ammonia to a solution of potassium hypoiodite.
Under these circumstances the substance separates out in the form of well-
defined crystals having a composition expressed by the formula NgHjIj, which
may be regarded either as NIj.NHj or NHIg.NH,!. The equations represent-
ing the formation of the compound may be thus expressed—

KIO + NH4HO = NH4 10 + KHO

3NHJ0 == NaH^Ij + NH, + 3H,0.

The reaction which takes place when the compound is obtained by the
action of iodine upon strong ammonia, appears also to involve the first forma-
tion of the unstable ammonium hypoiodite, thus—

I2 + 2NH4HO = NH4IO + NH^I + HjO,

which then breaks up as shown above.

Properties.— Nitrogen iodide is a copper-coloured glittering crystalline com-
pound, appearing red by transmitted light. In the amorphous state, as obtained
by the action of iodine upon strong ammonia, it presents the appearance of
a dark chocolate-brown powder. When moist it may be handled without much
risk of explosion, although it has been known to explode even under water.
When dry, the substance is extremely explosive, the shock caused by the tread
of a fly upon it is more than suflicient to explode it ; even falling dust particles
will sometimes cause it to explode.

When nitrogen iodide is placed in dilute aqueous ammonia, and exposed to
bright light, it is decomposed, and bubbles of nitrogen are seen escaping from
the compound —

N2H3T3=Na-|-3HI.

the hydriodic acid being neutralised by the ammonia present. At the same
time a jwa// quantity of the compound is converted into ammonium hypoiodite,
which being unstable slowly passes into the iodate, thus —

N,H,I, + SHjO + NH, = 3NH4IO

3NH4IO = NH4IO, + 2NH4I.

CHAPTER VIII

Symbol. C.

"■97.

Occnrrence.— This element is capable of assuming three allw
tropic fomis, and it occurs free in nature in each of these modifid
tions, viL, diatnond, graphite, and charcoal

In combination with oxygen, carbon occurs in ca.rl)on dioxide, ■
gas which is present in the air, being a constant product of
busiion and respiration. In combination with hydrogen it c
as marsh gas. Carbon is a constituent of all the natural c
bonates, such as limestone, dolomite, &c, which fonn an import)
fraction of the earth's crust, and it is also an essentia! cc
of all organic substances.

Diamond.

OedUTence.—This substance has been known and prized fro
the remotest antiquity. It is found in various parts of Indii
mostly in river gravels and superficial deposits, in Draiil, Soiit
Africa, Australia, and various parts of the United Slates.
diamond has also recently been obtained from extra-terrei
sources. In a meteorite which fell in Russia on September I
1886, carbon was found, partly as amorphous, and partly as
man tine carbon.

The diamond form of carbon is found of various colours ; s
limes it is dark grey, or even black, siones of these colours beini
known as carbonado and bort. The former of these is extremd^
hard, and is of great value for use in rock-boring and drilling
instruments. Bort is used in the crushed condition by lapidati<
for grinding and polishing.

Occasionally the diamond is found coloured blue, or red, C
green, by traces of foreign material!. Some of these colours

Carbon 2$?

stones are of great value as gems: the «rell- known "Hope**
diamond, a stone weighing 44} carats, has a fine sapphire colour.

The origin of the diamond is unknown, although many theories
have been put forward to explain its formation. Newton's famous
suggestion that diamond was *' an unctuous substance coagulated,"
was based upon its remarkably high refractive index. The cellular
structure which is sometimes to be seen in the ash that is left when
the diamond is burnt, seems to indicate that it is of vegetable
origin.

Modes of Formation.— Innumerable attempts have been made
to effect the crystallisation of carbon in the adamantine form ; but
while it is readily possible to convert this variety of carbon into its
aDotropes graphite and charcoal, the transformation of these back
again to the diamond, is a problem that is beset with the greatest
difficulties. Moissan has recently shown * that the carbon which
is capable of being dissolved in molten iron, and which is usually
deposited in the graphitic form on cooling, can, under certain
conditions, be caused to take up the adamantine form.

Dy raising the temperature of the iron to about 3000* by means
of an electric furnace, and then suddenly cooling the molten mass
by plunging the crucible into water or molten lead, until the cooled
and solidified surface is at a dull red heat, an enormous pressure is
brought to bear upon the interior and still liquid portion. Under
these circumstances, a part of the carbon which is deposited by the
slowly cooling mass, was found by Moissan to be in the adamantine
form. On dissolving the iron in hydrochloric acid, amongst the
carbonaceous residue were found fragments having a specific
gravity between 3.0 and 3.5, and sufficiently hard to scratch ruby.
Some of the fragments were the black or carbonado variety, while
others were transparent. On combustion in oxygen, Moissan
proved that these were really carbon in the diamond form.

Properties* — The diamond in its purest condition is a colourless
crystalline substance. Its cr)'stalline forms belong to the cubic
system, and appear to some extent to be characteristic of the
locality in which the element occurs. It is extremely hard, and
moderately brittle. When struck with a hammer, the diamond not
only splits along its cleavage-planes, but also in other directions,
with a conch oidal fracture. It does not conduct electricity. The
specific gravity of diamond varies slightly in different specimens,

* CompUs Rgmdus dt TAcaddwtii da Scumcu, toL anri. p. aiS.

2S2

Inorganic Chemistry

ihe mean being about 3.5. lis refraciive index is higher than lhUi{
of any other substance, and it is this properly which gives it*
peculiar beauty and brilliancy to the cut slone.

The value of diamond as a gem, depends largely upon its colour-,
lessness, except in the case of those rare insiances where the
colour is quite definite and also pleasing, such as distinct red, blti^r
or green.

When diamond is strongly heated it becomes black, and ii>«
creases in bulk, being converted into a substance having th«.
properties of graphiie. Lavoisier (1772) was the first lo show'
tbal the diamond was a combustible body, and tliai it yielded
carbon dioxide. Davy (1814) showed that carbon dioxide was thft'
only product of its combustion, and proved
that diamond was pure carbon.

The combustion of diamond in oxygen
may readily be accomplished by means of
the apparatus shown in Fig. 58. A fragment
of diamond is supported upon a small gutter"
of platinum foil, which bridges across two
stout copper wires, A. These wires pass
through a cork in a pwrforaled glass plate,
and are lowered into a cylinder of oxygen.
By the passage of an electric current, the
little platinum boat can be strongly heated,
when the diamond will become ignited, and
3 bum brilliantly in the oxygen, with the formation of
carbon dioxide. The ash, which is always left after a diamond
has been burnt, varies from 0.2 to 0.05 per cent, of the stone.
It is found usually lo contain ferric oude and silica.

Fig. jB.

Graphite.

Occurrence. — This second alloirope of carbon is much mors 1
plentiful in nature than the first. It is found in large quanti^n
in Siberia, Ceylon, and various parts of India. In England t]
chief source of graphite has been the mines at Ilorrowdale, i:
Cumberland; this supply is now practically exhausted. Enor^
mous quantities of very pure graphite arc now obtained from l]
Eureka iStack-Lead Mines, in Catifomia. Graphite also
in many specimens of meteoric iron.

node of Formation.— Molten iron, especially when it o

Carbon 253

silicon, is capable of dissolving a considerable amount of carbon,
which, on cooling, is deposited in the form of black shining crystals
of graphite. Occasionally considerable quantities of graphite are
found deposited in this way in iron-smelting furnaces, to which the
name " kish '' has been applied.

Properties. — Graphite is a soft, shiny, greyish-black substance,
which is smooth and soapy to the touch. It is usually found in
compact laminated masses, but sometimes crystallised in sbc-sided
plates. Its specific gravity varies in different specimens, aver-
aging about 2.5. Graphite is a good conductor of both heat and
electricity.

When strongly heated in oxygen, graphite takes fire and bums,
forming carbon dioxide, and leaving an ash consisting of silica,
alumina, and oxide of iron. Graphite has been found by Regnault
to contain, usually, traces of hydrogen. Graphite is employed for
the manufacture of ordinary lead pencils ; for, on account of its soft-
ness, it leaves a black mark upon paper when drawn across it.
For the purposes of the pencil manufacture the natural graphite is
ground to powder, and carefully washed free from gritty matter.
It is then mixed with the finest washed clay, and the pasty mass is
forced by hydraulic pressure through perforated plates. The name
" graphite,** from the Greek to writer is given to this substance on
account of its use for this purpose. It was formerly supposed
that this material contained lead, hence the names black-lead and
plumbago.

Graphite is largely employed, on account of its refractoriness,
for the manufacture of the so-called plumbago crucibles, which
consist of fireclay, mixed with finely-ground graphite:

Other uses to which graphite is put, are for glazing or polishing
gunpowder, especially the larger grained varieties ; as a lubricant
for machinery, where oil is inadmissible on account of high tem-
perature ; for electrotyping processes, and also as a coating for
ironwork, to prevent rusting.

Amorphous Carbon.

This non-crystalline form of carbon, may be obtained by the
decomposition of a great variety of carbon compounds, by the
process known as destructive distillation. The carbon so obtained
differs very much as regards its purity, according to the particular
organic compound used for its preparation. The commonest forms

of amorphous carbon to be met with, are lampbUck, or soot ; gu
carbon ; coke ; charcoal ; animal charcoal, or bone-black. None
of these substances is pure carbon ; animal charcoal, for exampln,
usually containing only about lo per cenL of carbon.

Lampblack. ^T his substance is manufaclured by burning sub-
stances rich in carbon, and which bum with a smoky flame, (as
turpentine, petroleum, or tar.) with a limited supply of air. The
smoke is passed into chambers in which are suspended coarse
blankets, upon which the soot collects. This lampblack always
contains hydrogen, in the form of hydrocarbons. If the soot be
heated to redness in a stream of chlorine, this hydrogen can be
removed, and pure amorphous carbon will be left.

Lampblack is used for printers' Ink, and for black paint.

Qas Carbon. — This form of carbon is obtained by the destruc-
tive distillation of coal, in the manufacture of illuminating gas.
It remains in the retorts as an extremely hard deposit, lining the
roof and sides. It is a very pure carbon, coming second to puri-
fied lampblack. Its specific gravity is about 3.3;. Gas carbon is
a good conductor of electricity, and is extensively used lor the
manufacture of carbon rods for the arc light.

Coke. — This substance ditfers from gas carbon, although it also
is obtained in the process of coal distilling. It contains all the
inorganic matter which constitutes the ash of the coal, and also
small quantities of hydrogen, nitrogen, and oxygen. The average
amount of carbon in coke is about 9t per cent.

ChaPCOal.— The purest form of charcoal is obtained by the
carbonisation of pure white sugar, and the subsequent ignition ol
the charcoal in a stream of chlorine gas. Charcoal so obtained
has a specific gravity of 1.57. Charcoal in a much less pure con-
dition is manufactured from wood. The methods by which the
carbonisation of wood is carried out are, broadly, of two kinds :
Gnt, those in which access of air is permitted 10 the burning
material ; and, second, those In which air is excluded-

lost ancient, is generally carried on
s wood is plentiful The wood is
which are built with some care.
■, by means of a lighted bundle
of brushwood, which is introduced through a vertical open!
chimney, left for this purpose in the centre of the mound during ti
construclion. The outside of the heap is covered with brushwoodi
and finally with turi^ in order to regulate the acce:

The first of these, and the n
in more priinitive parts, wher
piled into mounds or stacks.
They are si

wood, ^^H
lo Om^H

Charcoal 2$$

biterior, and therefore to control the i;^te of combustion of the wood.
The object of the charcoal-burner is to carbonise the wood as
slowly as possible. In this process there is great liability to loss,
by the too rapid combustion of the wood ; and, in addition, it pos-
sesses the disadvantage that the secondary products, such as the
pyroligneous acid, tar, &c, are entirely lost

Various modifications have been introduced into the method of
coaling wood, as the process is termed, with a view to collect these
products.

In the second general process of carbonising wood, the material
is heated in ovens or retorts from the outside, no air being admitted
to the wood. The operation is very similar to that employed in
the destructive distillation of coal, in the manufacture of coal gas.
In these methods all the volatile and condensable products are
collected ; among these are water, pyroligneous acid, wood spirit,
acetone, and fatty oils. The non-condensable products consist
mainly of such gases as hydrogen, carbon monoxide, carbon di-
oxide, marsh gas, and acetylene.

Animal CharooaL — Bone-black is obtained by the carbonisa-
tion of bones in iron retorts. This variety of charcoal is the least
pure of all the ordinary forms of amorphous carbon.

Bone contains only about 30 per cent, of organic matter, the
other 70 per cent consisting chiefly of calcium phosphate, asso-
ciated with small quantities of magnesium phosphate and calcium
carbonate. It will be obvious, therefore, that as the carbon is
derived from the organic matter, the amount of it in carbonised
bones must be small. The average composition of animal char-
coal is found to be —

Carbon ...•••• lo.o

Calcium phosphate 88.0

Other saline substances . . . .2.0

loao

Although containing relatively so small an amount of carbon,
animal charcoal possesses many of the valuable properties of
charcoal in a highly marked degree, owing to the fact that it con-
tains its carbon disseminated throughout an extremely porous mass
of calcium phosphate.

Properties of Charcoal. — Charcoal varies very considerably in
its properties, depending upon the particular wood from which it

25C

Inorganic Ckttnutry

is obtained, and the method by which it i& prepared. Thus, c
coal obtained al 300° is a soft, brownish -black, very friable materii
having an igniting poini as low as 380°, On the other
charcoal prepared al very high tempera lures is black and c
paratively dense, and requires 10 be strongly healed i
ignite iL

Under ordinary circumstances, cliarcoal burns in air witlioot the
formation of a fiame, or the production of smoife. Al high tem-
peratures, however, llie combuslion of charcoal is seen to be
attended by a flame. This is probably accounted for by the fact,
that as the temperature al which the combustion of carbon lakes
place is raised above 700^, [he amount of carbon monoxide which
is formed increases, and the carbon dioxide decreases.*

When charcoal is thrown upon water it floats, c
ait which is enclosed within its poies. The specific gravity a
charcoal when thus filled with air, varies from 0-I06 (charcoal n
from the ash) to 0.203 (charcoal from the birch). If the a"
withdrawn from charcoal it sinks in water, Ihe average %
gravity of diarcoal itselfbeing \.%.

Ordinary charcoal is a bad conductor of electricity, but il
ductivity is greatly increased by strongly heating the charcoal i]
dosed vessels.

Charcoal has the power of absorbing gases and vapours ti
remarkable extent : this power, which is exhibited to a dilTere
degree by the various kinds of charcoal, is due to the porosity q
the material, whereby it exposes a very large surface ; and |
bdongs to a dass of phenomena known as surface action.

If a fragment of charcoal, recently strongly heated to expel ti
air from its potes, be passed up into a cylinder of a
standing in a trough of mercury, the ammonia will be gradua
absorbed by the charcoal, and the mercury will ascend i
cylinder. Saussure found, that recently heated beech-wood char-
coal was capable of absorbing ninety limes its ou-n volume of
ammonia gas; while Hunter, by employing charcoal made from
cocoa-nut shell, found Ihal 171,7 volumcsof ammonia were absorbed
by one volume of charcoal. The results of both of these experi-
ments show, that those gases are absorbed in the largest quantities
which ate the most readily liquefiable. The gas so held by the
charcoal, is in a highly condensed condition apon the surface ol

* Ernst {CktmiiiUi Hiftnenum. vot. %

Coal 257

the porous mass. Probably in the case of easily liquefied gases
such as ammonia, sulphur dioxide, and others, the gases are par-
tially liquefied upon the sur&ce of the charcoal In this condensed
state, the gas is more chemically active than under ordinary condi-
tions, and charcoal is therefore able to induce many striking com-
binations to take place. Thus, if charcoal be allowed to absorb
chlorine, and dry hydrogen be then passed over it, the chlorine is
capable of combining with the hydrogen even in the dark, with the
formation of hydrochloric add. This chemical activity of gases,
when absorbed by charcoal, is strikingly exemplified in the case
of sulphuretted hydrogen. If a quantity of powdered charcoal,
which has been saturated with sulphuretted hydrogen, be brought
into oxygen, the rapid combination of the two gases is attended
with the development of so much heat, that the charcoal bursts
into active combustion. In the same way a mixture of air, with
10 or 15 per cent of sulphuretted hydrogen, may be passed
rapidly through a tube, about a metre in length, filled with char-
coal, without a trace of sulphuretted hydrogen escaping at the
end* Owing to this property, charcoal is largely employed
to absorb noxious gases, the atmospheric oxygen which is con-
densed in the pores of the charcoal, oxidising these offensive and
injurious compounds : thus sewer ventilators are often trapped
with a layer of charcoal, which effectually arrests all bad-smelling
gases.

Charcoal also has the power of absorbing colouring-matters from
solution : thus, if water which has been tinted with an organic
colouring-matter, be shaken up with powdered charcoal, and filtered,
the solution will be found to be entirely decolourised The variety
of charcoal which possesses this property in the highest degree, is
animal charcoal, or bone-black, and this substance is largely em-
ployed in many manu£&cturing processes, such as sugar refining,
in order to remove all colouring-matter from the liquid.

Charcoal under ordinary conditions is unacted upon by the air
but when the temperature is raised, it enters into active combus-
tion, forming carbon dioxide. In an extremely divided condition,
however, carbon is capable of combining spontaneously with the
oxygen of the air, and with so much energy as to take fire.

CoaL — The carbonaceous minerals that are included under the
name coal^ are an impure form of carbon, containing compoimds

* " Chemical Lecture Ezperimeats," 394-396, new ed

»s»

Inorganic Chtmiitry

of carbon with hydrogen and oxygen- Coal is ihe Anal lesult of
series of decotnposilion changes, which have been undergone by
vegetable maiter of ihe remote past, the process having extended
over long geological periods. During this prolonged process,
lion of the carbon and h)'drogen is eliminated as marsh gas, and
large quantities of this gas are found associated with, aad occluded

liioadly speaking, the numerous varieties of coal may be divii
into soft or bituminous, and hard <3t anthracilic.

The former are employed for Ihe manufacture of coal gas,
for ordinary domestic purposes ; they bum with a smoky Hame,
evolve large quantities of gases and volatile vapours, on i
lion or distillation. Anthracite coal is much harder, igni
more difficulty, and bums with the formation of very liiile flame
smoke. It contains a higher percentage of carbon, and
gleal heal on combustion, and is employed largely as
coal.

The following table shows the average composition of coals ft
various sources, and the general difference between coals of
two main classes —

LocliW.

8,.4J

S-Bj

7.90

a.os

0.74

a. 07

1.3S

t&TO

Wales

83.78

4-79

4.>5

0.9S

>-43

4.91

7a.6o

Isuflonbliice

7fl.S7

S.99

11. B8

».84

0.39

1.03

11.89

S7-«

i^-

S, Wmlei ,

90-45 1 "-13

"■45

4-6

■■

...

ided

witH

CHAPTER IX
CARBON COMPOUNDS

The compounds of the element carbon are so numerous, that it
has been found convenient to constitute the study of these sub-
stances a separate branch of chemistry. In the early history of
the science, it was believed that there were a large number of
substances which could only be obtained as the product of living
organisms. They were known to be elaborated by the action of
life, or, as it was termed, the vital force^ and it was believed, that
owing to some inherent specific quality belonging to this vital force,
the substances produced by its action were distinct from such
substances as could be prepared by any laboratory processes. To
denote this distinction, the term organic was applied to those things
which were known to be the products of living organisms, and
other compounds were distinguished as inorganic substances. This
distinction received its deathblow in 1828, when Wohler produced,
by purely laboratory processes, one of the most typical of all organic
compounds, namely, urea. The names '^ organic " and " inorganic "
chemistry are still retained, but their old significance is entirely
gone, as no distinction is to-day recognised between products elabo-
rated by the action of life, and those which can be synthetically
produced.

Speaking broadly, organic chemistry may be defined as the
chemistry of the carbon compounds. This definition,' however,
includes such compounds as the oxides of carbon and all the
carbonates, such as chalk, limestone, dolomite, &c, compounds
which are more conveniently classed as inorganic A more exact
definition is the following: — The chemistry of those compounds of
carbon which contain in thi molecule an atom of carbon^ directly
associated with either hydrogen^ nitrogen^ or another carbon atom.
This definition excludes all the carbon compounds which are by
general consent regarded as belonging to the inorganic division of
the science.

a6o Inorganic Chemistry

Three organic compounds will be briefly studied in the foUowing
chapters, namely, methane {marsh gas), CHj ; ethene (ethylene), j
C,H, ; and acetylene, C,H^ These three compounds play t
important part in our ordinary illuminating flames, and in coal ga

COMPOtJNDS or Carbon with Oxygen.
Two oxides of carbon are known, both of which are

CABBOH MONOXIDE.

Formula, CO. Moleculai wcigbi = a7-96- Densily = 13.9I

Modes of Formation.— (i.) Carbon monoxide is fonned when
carbon dioxide is passed over charcoal heated to bright redness-

CO, + C - SCO.

The same result is obtained, when a slow stream of air
is passed over red-hot charcoal contained in a tube. The f
action of the air, on coming in contact with the carbon, J:
carbon dioxide, which, passing over the remainder of the heaM
material, is deprived of a portion of its oxygen, according t<
above eqtiation. This operation goes on in an ordinary fire-graU^
the air, on first gaining access to the burning coal or coke, cam
thecomplete oxidation of a portion of the carbon, 10 carbon dioxidsfl
and as this gas passes through the mass of red-hot carbon, it it
reduced to the lower oxide, which either escapes with the
products of combustion, or becomes ignited and bums with |
lambent bluish flame, such as may frequently be noticed upon tl ^
lop of a " clear " fire.

(i.) When steam is passed over strongly heated carbon, a 1
of carbon monoxide and hydrogen is pioduced. This n
known as water gas, is employed in many manufaauring pro

fuel-

H^ + C - CO + H,

Carbon Monoxide 261

(3.) Carbon monoxide is also formed by the action of carbon
dioxide npon red-hot iron —

4C0, + 3Fe - Fe,04 + *CO.

(4.) Or by strongly heating either carbon or iron with a car-
bonate, such as calcium carbonate, which is capable of yielding
carbon dioxide, thus —

CaCOj + C - CaO + 2C0.
4CaCOs + Sf'c =" F«i04 + 4CaO + 4C0.

($.) Carbon monoxide is most conveniently prepared, by the
decomposition of certain organic compounds by means of sulphuric
add. Thus, when formic acid, or a formate, is acted upon by sul-
phuric add, the sulphuric add withdraws the elements of water
from the molecule of formic acid, and leaves carbon monoxide —

HCOOH - H,0 - CO.

(6.) By a similar decomposition, oxalic add yields a mixture of
carbon monoxide and carbon dioxide in equal volumes —

CfHA - H,0 - CO, + CO.

The carbon dioxide is readily removed from the mixture, by passing
the gases through a solution of sodium hydroxide (caustic soda),
in which carbon dioxide is absorbed with the formation of sodium
carbonate.

(7.) The method usually employed when carbon monoxide is
required for experimental purposes, consists in heating a mixture
of I part by weight of crystallised potassium ferrocyanide (yellow
prussiate of potash) with ten parts of strong sulphuric acid in a
capacious flask, when the following reaction takes place —

K^FcCgN, + 6H,S04 + 6H,0 = 2K,S04 + FeSO|
+ 3(NH4),S04 + 6C0.

The six molecules of water required by the reaction, are derived
partly from the add employed, and partly from the salt, which
contains three molecules of water of crystallisation.*
PropeFties. — Carbon monoxide is a colourless, tasteless gas,

* " Chemical Lecture Experimenti," new ed., 435-439.

Inorganic Chtmittry

having a feint smell. It is only slightly soliiblt '\

efficient of absorption at o* being 0.03187. It bums in the airw

a characteristic pale blue ftanie, forming carbon dioxide^

SCO + O, - 2CO^

When mixed with half its own volume of ojiypen, and ii
[he mixture explodes with some violence.* If the t
confined in a eudiometer standing over mercury, and be n
absolutely free from aqueous vapour by powerful desiccating agents,
no explosion will take place upon the passage of an electric spark
through the mixture. And in the same way if carbon monoxide,
which has been deprived of all aqueous vapour, be burned from a
jet in the air, and the jet be lowered into a cylinder containing air
which has been similarly dried, the flame will be extinguished.

Carbon monoxide is an extremely poisonous gas : very small
quantities present in the air, rapidly give rise to headache and
giddiness, and if inhaled for a length of time, or if taken into the
lungs in a less dilute condition, insensibility and death quickly
follow. The deaths that have resuUed from the use of unvenii-
lated fires — either of charcoal or coke, or in some cases of coal gas
— in dwelling' rooms, have been due to the escape of this poisonous
gas into the air. The extremely deadly nature of the a/lrr-damf
resulting from a colliery explosion, is due to the presence of carbon
monoxide in the carbon dioxide which is formed as a product of
the combustion.

The poimraus nctlon of this gas is due to its absarplion bf (he blood, with
ih« fonrmlion of & bright red compound, to which Ihe name sftrhtJKy-h^iniy
gltbin a applied, Utood so charged appears 10 be oaable to fulfil its function
of abdorbing and diiUnbuliag oiygen throughout the syitem. This cartnij-
haemoglobin gives a chuiacleristic abiorplion spednim, which himishes • _
i^aAj meihod of dnieclion, in cases of poisoriing from Iheinhatalionor cartM
mrmoxide.

Carbon monoxide is one of the most difficultly liqueliahlc g
its critical temperature being — tjo'.

At high temperatures this gas is a powerful reducing ;
uniting with another atom of oxygen to form carbon dio
This fact is made use of in many metallurgical processes, for r
ducing the oxides of the metals to the metallic state.

• Thei

tXf at which the combuslion is propagaled Ihrougbout a fniatur
onoiide and oiygen. is much slower Ibao Ihnnigh hrdrosen
Bunseu has estirnalcd H at less than ■ metre per second.

Carbon Manoxidi 263

Carbon monoxide is absorbed at ordinary temperatures by a
solution of cuprous chloride, forming the compound COCU|Clf.

At a temperature of boiling water, carbon monoxide is slowly
absorbed by solid potassium hydroxide, with the formation of
potassium formate —

KHO + CO - H • COOK.

Carbon monoxide unites directly with chlorine, under the in-
fluence of sunlight, forming the compound known 2^ phosgene gas^
or carbonyl chloride —

CO + CI, - COClf

If the two gases are mixed in equal volumes, and kept in the
dark, no action takes place, but on exposure to sunlight they com-
bine, and the yellowish colour due to the chlorine will disappear.
On opening the vessel in moist air, clouds of hydrochloric acid
ire formed, owmg to the decomposition of carbonyl chloride by
the moisture, according to the equation —

COCl, + H,0 - CO, + 2HCL

Carbonyl chloride may be readily condensed to a liquid, its
boiling-point being ^ 8^

Carbon monoxide unites directly with certain metals, giving rise
to compounds which possess some very remarkable properties,
and to which the name metallic carbonyls has been applied by
their discoverer.*

When carbon monoxide is allowed to stream slowly over metallic
nickel (obtained by the reduction of nickel oxide in a stream of
hydrogen), the gas is absorbed by the finely-divided metal, forming
a compound having the composition Ni(C0)4. If the issuing gas
be passed through a cooled tube, the nickel carbonyl condenses
to a colourless, mobile, highly refracting liquid, having a specific
gravity at o* of 1.356, and boiling at 43° under a pressure of
751 mm.t

Nickel carbonyl vapour bums with a luminous flame, which
produces a black deposit of metallic nickel when a cold porcelain
dish is depressed upon the fiame. The gas is decomposed into
nkJcel and carbon monoxide if passed through a hot glass tube,

* Mood, 189a t Se« "Chemical Lecture Ezperiroents," Dew ed., 446-448.

264

Inorganic Chemistry

a bright metallic

the nickel being deposited
glass-

Ni(CO)j = 4CO + Ni.

A limilai compound of carbon monotide and iron bai >1bo been otH
bavjng the composition Fc(CO)^ Iron carbonrl ii a pile-bellow. i
liquid, Imlling ai ioa,S° nndcr b pressure of 7^ mm. its specific gravity %
i8* is 1.4664. Wben liesled to iBq" ihe vapour is dwomposed. i
deposited and carbon nionoiide tieing' evolved. This compound hiu b
in iron crlinders in which Ilie so-called imlcrgas (a mixiure of H and CO) b
been sloned under pressure (or a length of lime ; it is also said to be present 11
minute quantities in coal gas.

OABBOir DIOXIDS.

Fomiula, CCV Molecular weight = 43.91. DensIlT = ai.9<L

HlstO^. -Van Helmont, in the seventeenth century, was the firal
to distinguish between this gas and ordinary ait ; he observed that it
was formed during the processes of combustion and fermentatioD,
and he applied to it the name gas lyh'estre. Black showed that
this gas was a consliluent of what in his day were known as the
mild alkalis (alkaline carbonates), and on account of its being so
COtnbined, 01 fixed, in these substances, he named the gas Jlxed
air. Lavoisier lirst proved its true chemical composition to be
that of an oxide of carbon.

Oceurrenoe. — Carbon dioxide is a constant constituent of the
atmosphere, being present to the extent of about 3 volumes in
10,000 volumes of air, li is also found in solution in all spring-
water, which is sometimes so highly charged with this gas under
pressure, that the water is effervescent, or "sparkling," from thBa
escape of the gas. Carbon dioxide is evolved in large quantitie*a
from vents and fissures in the earth in voicanic districts. Thsf
wcll'known Poison Valley in Java, which is an old volcanic ci
and the Grotto del Cane near Naples, owe their peculiar pro-l
parties to the discharge into them of targe quantities of carboa J
dioxide from such subterranean sources.

Modes of Fopmatlon.— (1,) Carbon dioxid«* is produced whw
carbon is burnt with a free supply of air or oxygen —

C t O, = CO,

n cartion dioxide, Not. 400-4J4, "Chemical Lecture 8vfl

Carbon Dioxidi

265

If an insufficient supply of oxygen be employed, carbon mon-
oxide is produced at the same time.

(3.) When limestone, or chalk, is strongly heated, as in the
process of burning lime, carbon dioxide is evolved in large
quantities—

CaCO, - CaO + CO,.

(3.) In the ordinary processes of fermentation, and during the
decay of many organic substances, carbon dioxide is also formed.
Thus, wh':n sugar undergoes alcoholic fermentation by means of
yeast, the sugar is converted into alcohol and carbon dioxide —

CuHaOu + H,0 - 4C,HeO + 4CO»

(4.) Carbon dioxide is formed during the process of respiration ;

Fio. 59b

also by the combustion of all ordinary fuels, and of any compound
containing carbon, such as candles, oils, gas, &c

(5.) For experimental purposes, carbon dioxide is most readily
obtained by the decomposition of a carbonate by means of a
stronger acid The effervescence that results from the action of
tartaric acid upon sodium carbonate, in an ordinary Seidlitz powder,
is due to the disengagement of this gas. The most convenient
carbonate for the preparation of this gas is calcium carbonate, in
one of its many naturally occurring forms, such as marble, lime-
stone, or chalk. Fragments of marble are for this purpose placed
in a two-necked bottle (Fig. S9)i with a quantity of water, and

srrong hydrochloric acid is added by means of the funncl-tab(

A rapid efTervescence takes place owing to the elin

gas, and a solution of calcium chloride remains in the boiile-

CaCO, + SHCl = CaCI, + H,0

If stilphoric acid be substituted for hydrochloric acid, the frag-
ments of marble rapidly become coated with a cnisl of insoluble
calcium sulphate, which soon prevents the further action of the
acid, and therefore puts an end to the reaction : by employing
finely powdered chalk, however, instead of lumps of calcium car-

bonate, this difficulty is obviated. This gas is largely mnnufei
lured from these materials.

Properties.— Carbon dioxide is a colourless gas, having a feehk
add laste, and a faint and pleasantly pungent smell. It is incap-
able of supporting either combustion or respiration : a burning
taper is instantly extinguished, and an animal speedily dies when
introduced into this gas. Although carbon dioxide is not such a
poisonous compound as the monoxide, it nevertheless does

Carbon DioxicU 367

ft direct poisonous effect upon the system, and death caused by
this %aA is not merely due to the absence of oxygen. The pro-
longed inhalation of air containing only a very slightly increased
amount of carbon dioxide, has a distinctly lowering effect upon
the vitality.

Carbon dioxide is a heavy gas, being about one and a half
times heavier than air. On this account it may readily be col-
lected by displacement By virtue of its great density it may be
poured from one vessel to another, much in the same way as an
ordinary liquid : thus, if a large bell jar be filled with the gas by
displacement, a beaker- full may be drawn up, as water from a
well (Fig. 60). If the gas so drawn up be poured into a similar
beaker, suspended from the arm of a balance, and counterpoised,
the weight of the gas will be evident by the disturbance of the
equilibrium of the system.

If a soap bubble be allowed to fall into a larp^e jar filled with
carbon dioxide, it will be seen to float upon the surface of the
dense gas (Fig. 61). The power of carbon dioxide to extinguish
flame is so great, that a taper will not bum in air in which this gas
is present to the extent of 2.5 per cent., and in which the oxygen
is reduced to 18.5 per cent. For this reason a comparatively small
quantity of carbon dioxide, brought into the air surrounding a bum
ing body, is capable of extinguishing the flame. This property has
been put to valuable service in the construction of numerous con-
trivances for extinguishing fire, such as the " extincteur." This is
a metal vessel containing carbon dioxide under pressure, the gas
having been generated within the closed apparatus by the action
of dilute sulphuric acid upon sodium carbonate. A stream of the
gas, projected judiciously upon a moderate conflagration in a
dwelling, readily extinguishes the fire. This property may be
illustrated by inflaming a quantity of turpentine in a dish, and
pouring upon the flames a quantity of carbon dioxide contained
in a large bell jar (Fig. 62), when it will instantly extinguish the
conflagration.

Although carbon dioxide is incapable of supporting combus-
tion in the ordinary sense, certain metals are capable of hum-
ing in this gas. Thus, a fragment of potassium when heated
in this gas, bums brightly, forming potassium carbonate with
the deposition of carbon —

2K, -I- 3C0, - «K,CO, -I- C.

When carbon dioxide is passed into a solution of <
hydroxide (lime water) a turbidity at once results, owing 1

precipitaiinD of insoluble calcium carbonaie, or chalk—

CaH,0,

This reaction furnishes the readiest means for the detection of
carbon dioxide. Thus, if the gas obiained by any of (he modes of
formation described, be passed into clear lime water, the formation
of this while precipitate of chalk, is proof that the gas is carbon
dioxide. By this test it may readily be shown that carbon dioxida I
is a product of respiration, by merely causing the exhaled brestli J

r, which will quickly be 1

to bubble through a quantity of lime «
rendered turbid.

Carbon dioxide is moderately soluble in water. At the ordinary
temperature, water dissolves about its own volume of this gas.

The coefficient of absorption at o' is 1-7967, the solubility de-
creasing with rise of lemperatuie in accordance with the i
polation formula —

e— 1.7967 - 0,07761/+ 0.0016424/*.

Carbon dioxide shows a slight departure from Henrys Inw
(see page 1J3), when the pressures art greater than that of tl
atmosphera; Thiu, when the pressure is doubled, the amount d

Carbon Dioxide 369

solved is slightly more than doubled. The solubility of carbon
dioxide in water, and its increased solubility under pressure, is
illustrated in the ordinary aerated waters. Water under a pres-
sure of several atmospheres is saturated with the gas, and upon
the release of this pressure by the withdrawal of the cork, the
excess of gas, over and above that which the water can dissolve at
the ordinary pressure, escapes with the familiar effervescence. In
a similar manner the natural aerated waters have thus become
charged with carbon dioxide, under subterranean pressure, and
when such waters come to the surface, the dissolved gas begins
to make its escape.

The solution of carbon dioxide in water is feebly add, turning
blue litmus to a port-wine red colour, characteristically different
from the scariet red given by stronger adds. This add may be
regarded as the true carbonic add —

CO, + H,0 - HjCO,.

A recently-made sample of aerated water is seen to effervesce
more briskly, and give off the dissolved gas more rapidly, than
specimens that have been long preserved. In process of time the
dissolved carbon dioxide gradually combines with the water, with
the formation of carbonic add, an unstable compound which slowly
decomposes into carbon dioxide and water, espedally at a slight
elevation of temperature. Many of the naturally occurring aerated
waters, such as Apollinaris, when opened, exhibit scarcely any
effervescence, but give off carbon dioxide gradually. Such waters
have in all probability been exposed to pressure for a great length
of time, and their dissolved carbon dioxide has almost entirely
combined to form carbonic add. When such a water is gently
warmed, a rapid stream of gas is evolved.

When carbon dioxide is strongly heated, as by the passage of
electric sparks, it is partially dissodated into carbon monoxide
and oxygen. This decomposition is never complete; for when
the amount of these two gases in the mixture reaches a certain
proportion, they reunite to form carbon dioxide, and a point of
equilibrium is reached, when as many molecules are united as are
dissociated in the same time.

liquid Carbon Dioxide. — Carbon dioxide is easily liquefied.
At - 5* it requires a pressure of 3a8 atmospheres ; at + 5*, 4a4
atmospheres; while at + 15^ a pressure of 52.1 atmospheres is
required.

2/0 Inorganic Chemistry

Faraday first liquefied this gas, by introducing into a strong bent *
glass tube a quantity of sulphuric acid, and a few lumps of ammo-
nium carbonate, which were prevented from touching the acid by
means of a plug of platinum foil The tube was then hermetically
sealed, and the acid allowed gently to come in contact with the
carbonate, which was at once decomposed with tlie formation of
ammonium sulphate and carbon dioxide. By the internal pres-
sure exerted by the evolved gas, aided by the application of cold
to one end of the bent tube, the gas condensed to a colourless
liquid.

Large quantities of this liquefied gas were obtained by Thilorier
by a precisely similar method, the experiment being performed io
strong wrought-iron vessels.

Liquid carbon dioxide is to-day manufactured on a large scale,
by pumping the gas into steel cylinders by means of powerful
compression pumps. The enormous volumes of carbon dioxide
evolved in the process of brewing, and which until quite recently
were allowed to escape into the atmosphere, are now utilised foi
this purpose. The gas, as it is evolved from the fermenting vats,
is washed and purified, and pumped into steel bottles for the
market. In this form the gas is largely employed by manufac-
turers of aerated waters.

Liquid carbon dioxide is a colourless and extremely mobile
liquid, which floats upon water without mixing. It boils at - 78*.2
under atmospheric pressure.

When heated, liquid carbon dioxide expands at a more rapid
rate than a gas, its coefficient of expansion being greater than that
of any known substance. Its rapid change of volume is seen by
the following figures : —

volumes at

-10°

become

lOO

•>

©•

io6

+ !©•

•1

114

»i

+ 20*»

The critical temperature of carbon dioxide is 31.9^ If the liquid
be heated to this point, it passes into the gaseous state without any
change of volume. The line of demarcation, between the liquid
and gas in the tube, gradually &des away, and the tube appears
filled with gas. Above this temperature no additional pressure is
able to liquefy the gas. On once more cooling the tube, when the

Cardan Diaxuie

171

critiaJ point is passed the liquid again appears, and the dividing
line between it and the gas ii once more shaiply defined.

Solid Carbon Dioxide.— When liquid caibon dioxide is allowed
to escape into the air, the absorption of heat due to its rapid eva-
poration causes a portion of the liquid to solidify. This solid is
most conveniently collected, by allowing the jet of liquid to stream
into a round metal box (Fig. 63), in which it is caused to revolve by
being made to impinge upon the curved tongue of metal. The box
is furnished with hollow wooden handles, through which the gai
makes its escape. Large quantities of the frozen carbon dioxide
can in this way be collected io a few minutes.

Solid carbon dioxide is a soft, white, snow-like substance. When
exposed to the air it quickly passes into gas, without going through
the intermediate state of liquidity.

«^D*

Fig. 63.

F10.64-

Solid carbon dioxide is readily soluble in ether, and this solution
constitutes one of the most convenient sources of cold. A large
number of gases can readily be liquefied by being passed through
tubes immersed in this freezing mixture. When this ethereal
solution is rapidly evaporated, its temperature can be lowered to

"Carbonic acid snow," as this substance is sometimes temied, is
now an article of commerce, the compound being sent into the
market in this form, to avoid the cost of the carriage of the
necessarily heavy steel bottles containing the liquid.

CompoilUon of Carbon DiozU*.— When carbon bunu in

vr*

Inorganic Chemistry

oxygen, the oxygen undergoes no change in volume in being
formed into carbon dioxide. The volume of carbon dioxide prodi
is the same a5 thai of the oxygen which is required for its
tioiL This may be shown by means of the apparatus, Fig.
Tbe bulb of the U-tube is filled wilh oxygen, and the
which carries a small bonC'ash crucible, upon which a fragment'
of charcoal is placed, is lowered into position. The charcoal is
ignited by means of a thin loop of platinum wire, as shown in (he
figure, which can be healed by an electric current. As the carbon
bums, the heat causes a temporary expansion of the included gas ;
but after the combustion Is complete, and the apparatus has
cooled, the level of mercury will be found to be undisturbed.
Carbon dioxide, therefore, contains its own volume of oxygen.
From this experiment the composition of carbon dioxide by weight
can be deduced. One litre of carbon dioxide weighs 21.96 criths ;
deducting from this the weight of i litre of oxygen, viz., 15.96
criths, we get 6 as a remainder. Six parts by weight of carbon,
therefore, combine with 1 5.96 parts by weight of oxygen to form
11.96 parts of carbon dioxide : expressing this proportion atomic-
ally, the proportion of carbon to oxygen is 12 to 31.92.

The gravimetric composition of carbon dioxide may be directly
determined, by the combustion of a known weight of pure carbon
in a stream of oxygen gas, and absorbing and weighing the carbon
dioxide that is formed. This was done with great care and
accuracy by Dimias and Stas, in the experiments by which they
determined the atomic weight of carbon. Fig. 6; represents the
apparatus employed for this purpose. A weighed quantity of
diamond, contained in a small platinum boat, was introduced into
a porcelain tube, which could be strongly healed in a liimace. The
oxygen for its combustion was contained in a glass bottle, from
which it could be expelled by allowing water to enter through the
(iumd. As it was necessary that the oxygen should be absolutely
free from any carbon dioxide, the water used in the little gas-
holder contained potassium hydroxide in solution. The ojcygen
was then passed through the tubes A, B, C in order to deprive it
of carbon dioxide and moisture, and lastly through a small desic-
cating tube, d, which was weighed before and after the experiment.
The pure dry oxygen then entered the strongly heated tube, and
the carbon there burnt away to carbon dioxide, leaving a minute
quaniiiy of ash, which was carefully weighed at tbe conclusion of
the experiment A small layer of copper oxide was placed '

Ml ID tue I

Cardon Dioxide

273

tube, in the position indicated in the figure, in order to oxidise any
traces of carbon monoxide,
which were liable to be formed,
into the dioxide. The pro-
duct of the combustion was
carried forward by the stream
of oxygen, through a series of
tubes ; <r is a small weighed
desiccating tube, the weight of
which, if the diamond used
contained no hydrogen, should
remain unchanged. It then
passes through the bulbs F
and G, where the carbon di-
oxide is entirely absorbed. To
arrest aqueous vapour which
would be carried away from
the solution in these bulbs by
the escaping oxygen, the gas
is passed through H, contain-
ing fragments of solid potas-
sium hydroxide ; this tube is
weighed along with the potash
bulbs. K is a guard tube,
containing fragments of solid
potassium hydroxide, in order
to prevent atmospheric carbon
dioxide, and moisture, from
gaining access to the weighed
portions of the apparatus.

The weight of the diamond,
minus the weight of the ash
which was left, gave the actual
weight of the carbon burnt ;
the increase in weight of the
tubes gave the weight of the
carbon dioxide which was pro-
duced, and this weight, minus
the weight of carbon used,
gave the weight of oxygen that
was constuned. As a mean of

2?4

Inorganic Chemistry

a namb«r of experiinents, Dumas and Stas found ihat 80 pans of
oxygen by weight, combined with J9.99 parts of carbon.

Frotn a knowledge of the density of carbon dioxide,
volume of oxygen it contains, we know that ihe molecule of tl
□ atoms ; therefore, by the simple equalio

: 31-92 :: J9-99

11.97 P*fis of carbon combine with 31.93 parts of oxygen, and ti

number 11.97 is therefore the atomic weight of carbon as determined
by these chemists.

The Carbonates. ^Although carbonic acid, HjCOj, is a very
unstable compound, the sails it fortns are stable. Being a dibasic
acid, it is capable of forming salts in which either one or both of
the hydrogen atoms have been replaced by an equivalent of a
metal ; thus in the case of sodium we have —

Similarly, with the divalent metal calcium, it is possible

(b) Hydrogen caldiini carbotiaie {hicarbonalf of lime) . CaH,(CO,)»

The formation of ca.rbon3tes, by the action of carbon dioxidi
Ibe hydroxides, may be illustrated by the following equations

8KH0 + CO, = K,CO, + HjO.
CaH,0, + CO, = CaCOj + H,0.

The first of these changes is the one that takes place, »
carbon dioxide is absorbed by the potassium hydroxide employed
by Dumas and Stas in the course of their experiments, already
described. The second equation represt^nts the reaction whidi
results, when carbon dioxide is passed into lime water, with the
precipitation of chalk. In this latter case, if the gas be passed
through the turbid solution for some time, the turbidity will gradu-
ally disappear, and the solution once more become clear. The
normal calcium carbonate (CaCO,) which is first formed, and
which is insoluble, is converted into the soluble bicarbonate,
CaH,(CO|)r If thii (olution be boiled, this unstable salt is decani>

Carbofiates

275

posed with the evolution of carbon dioxide and water, and the
reprecipitation of the normal calcium carbonate of lime —

CaH^COg), = CaCO, + H,0 + C0»

The presence of this compound in natural waters is associated
with the property known as the hardness of water (see Natural
Waters, p. 197).

When one volume of dry carbon dioxide is mixed with two volumes of dry
ammonia, the two gases mite, forming a compound known as ammonium
carbamate —

CX>, + 2NH, = CX>|,2NH. or ^^q \ CO,
which is the ammonium salt of the unknown carbamic add, ^q* > CXX

CHAPTER X

COMPOUNDS OP CARBON WITH HYDROGEN

These two elements unite together in various proportions, form-
ing an enormous number of compounds, known generally under
the name of the hydrocarbons. The reason for the existence of so
great a number of compounds of these two elements, is to be found
in the fact, that the atoms of carbon possess, in a very high degree,
the property of tmiting amongst themselves. This property of
carbon gives rise to the formation of a number of groups or series
of compounds, the members of which are related to each other,
and to the simplest member of the series. Thus, the compound
methane, CH4, is the simplest member, or the " foundation-stone,"
of a series of hydrocarbons of which the following are the first
four : —

Methane . . . CH4
Kthane .... Cf H^

Propane . . C^Hg
Butane . . . C4H10

It will at once be seen that each compound differs in composi-
tion from its predecessor, by an increment of CH^ and that each
may be expressed by the general formula, CnHsn + 2.

In the following chapter the three hydrocarbons, methane,
ethene, and acetylene, will be briefly studied. Each of these is a
** foundation-stone," or starting-point, of a series similar to the one
already mentioned ; thus

Methane, CH4, first member of the CnHsn ^ 3 series of hydrocarbons.
Ethene, CjH^, ,, ,, CnHan >> ••

Acetylene, C^Ha, ,, ,, CnHsn-s «i .,

METHANE {Marsh Gas— Fire- Damp).
Formula, CH4. Molectilar weight = 16. Density = 8.

Oecurrenee. — Methane is found in the free state in large quan-
tities in nature. It is one of the products of the decompositions

t76

Metha^u

277

which has resulted in the formation of the coal-measures. It ii
therefore found in enormous quantities in coal-mines, where it
not only occurs in vast pent-up volumes, under great pressure,
which escape with a rushing sound when the coal is being hewn ;
but it is also occluded within the pores of the coal. Methane is
also evolved from petroleum springs.

The name marsh gas has been given to this compound, on
account of its occurrence in marshy places, by the decomposition of
vegetable matter. The bubbles of gas which rise to the surface
when the mud at the bottom of a pond is gently disturbed, consist
largely of marsh gas.

Modes of FonxiatioiL — (i.) When a mixture of sodium acetate
and sodium hydroxide is strongly heated
in a copper retort, sodium carbonate is
produced and marsh gas is evolved —

CH.-COONa + NaHO - Na,CO, + CH^.

The gas obtained by this reaction always
contains more or less hydrogen.

(2.) Pure methame may be obtained by
the decomposition of zinc methyl, by means
of water —

Zn(CH^ + JHjO - ZnH.O, -h 2C H^.

(3.} The most convenient method for
preparing methane, is by the action of zinc- fig. 66.

copper couple upon methyl iodide.**^ For

this purpose the zinc-copper couple is placed in a small flask, and a
mixture of equal volumes of methyl iodide and methyl alcohol is
introduced by means of the stoppered funnel (Fig. 66). The gas
is caused to pass through a tube filled with the zinc-copper couple,
whereby it is deprived of any vapour of the volatile methyl iodide,
and is collected over water in the pneumatic trough.

Marsh g«s is fonned during the process of the distillation of coal, and is
therefore a large constituent of coal gas, the amount varying from 35 to 40
per cent

* " Chemical Lecture Experiments," new ed.. No. 449,

378 Inorganic Cfumislry

PropflrtlflS. — Methane is a colourless ga.s, having n
smelL It bums with a pate, feebly luminous Hame. Wheo s
with air or oxygen and ignited, the mixture explodes with violence
The products of its combustion are water and carbon dioxide-

CHj + 20, = CO, + 2H,0.

Methane is only about one-half as heavy as air, its :
t;ravily being 0.55 (air = i), The fire-damp of coal-mines n
pure methane ; its average composition being —

Meltaane 96.0

Carbon dioxide 0,5

Nitrogen 3.5

BTHTLEME {OUfinnl Ga.).
Fonnula, C,Hj, Molecolar weigbt = »8. Denailf = i<

Modes of Formation.— (I.) This compound is obtained, what
elbyl iodide is acted upon by an alcoholic solution of potassui
hydroxide —

CjHil -1- KHO = Kl + H,0 -H C,H(.

(1.) It is also formed, when ethylene dibromide is brought ir
(act with zinc-copper couple, the ethylene dibromide being diluted!
with its own volume of alcohol—

CjH.Br, -h Zn = ZnBr, -h C,H4.

(3.) The method usually employed for preparing ethylene i
quantity, consists in abstraaing the elements of water from alcolK
by means of strong dehydrating agents, such as phosphorus p
oxide, or sulphuric acid^

CHjO - H,0 = C,H,.

The mixture of alcohol and sulphuric acid is heated in a flask
10 about 165* \ and the ethylene, after being washed by bubbling. ,
through water, may be colteaed at the pneumatic trough.*

Proper lies.— Ethylene is a colourless gas, havmg a somewhi

• ■■ Ubemical L«lure Eiperiaienls." nc" Hi. Nov 455 ID 4S8.

Acetylene 279

pieMMit ethereal smell ; it bums with a highly luminous flame,
fonning carbon dioxide and water, one volume of the gas requiring
three volimies of oxygen for its complete combustion —

CJ1H4 + 30, - 2COj| + 2H,0.

If mixed with oxygen in this proportion and inflamed, the mix-
ture explodes with great violence.

When mixed with twice its voltmie of chlorine and ignited, the
mixture bums rapidly with a lurid flame, with the formation of
hydrochloric acid and deposition of carbon —

CjH^ + 2C1, - 4HC1 + 2C

Ethylene ii reduced to the liquid state, at a temperature of o^,
by a pressure of 41 atmospheres ; the critical temperature of
the gas is + lai*, at which point a pressure of 51 atmospheres is
required to liquefy it Liquefled ethylene boils at - 103*, and by
increasing its rate of evaporation, temperatures as low as - 140° can
readily be obtained ; this substance, therefore, furnishes an ex-
tremely useful refrigerating agent when very low temperatures are
required, as, for example, in the liquefaction of oxygen, nitrogen,
and other gases having low critical points. Ethylene (together with
higher members of the same series) constitutes the chief illumi-
nating constituent of ordinary coal gas, of which it forms from
4 to 10 per cent.

A0BT7LENE.

Formula, CsH,. Molecular weight =a6. Density=:Z3.

Modes of Formation.— ( I.) Acetylene is capable of being syn-
thetically formed by the direct union of its elements. For this
purpose a stream of hydrogen is passed through a three-way globe,
in which an electric arc is burning between two carbon rods,
arranged as seen in Fig. 67 (a quantity of sand being placed in
the globe, to prevent fracture from falling fragments of red-hot
carbon). Under these circumstances, a small quantity of the
carbon and hydrogen unites to form acetylene, which is swept out
of the globe by the current of hydrogen.*

(2.) Acetylene is more conveniently prepared by the action of
alcoholic potash upon ethylene dibromide. Alcoholic potash is

* The formation of acetylene appears to be a secondary result, due to the
nigh temperature decomposition of methane which is first produced. (Bone,
/. C. HiK,, i8g7.)

2gO

Inorganic Chemistry

heated in a flask, and ethylene dibromlde dropped upon it fioiii a
stoppered funnel, when the following reaction takes place —

CjH^Br, + 2KH0 = 2KBr + 2H,0 + CjH,.

(3.) Acetylene is formed when marsh gas, or coal gas, is burned
with an insufficient supply of air for complete combustion ; thus,
when a Bunsen lamp becomes accidentally ignited at the base of

Fig. 67.

the chimney, the peculiar and unpleasant smell that is perceived is
due to the formation of acetylene.

(4.) For experimental purposes acetylene is most readily obtained
by the action of water upon calcium carbide. The carbide is placed
in a dry flask provided with a dropping funnel and delivery tube ;
and on gradually admitting water, a rapid evolution of nearly pure
acetylene at once takes place. Thus—

CaC, + 2H,0 = Ca(HO)j| + C,H,.

Acetylene is present in small quantities in ordinary coal gas.

Properties. — Acetylene is a colourless gas having an extremely
offensive smell, which rapidly induces headache ; when inhaled in
an undiluted state it is poisonous. The gas bums iRth a highly
luminous and smoky flame. It is more soluble in water than
either echylene or marsh gas ; water at the ordinary temperature
dissolving about its own volume of this gas. At a temperature of
+ 10°, and under a pressure of 63 atmospheres, acetylene con-
denses to a colourless liquid.

When acetylene is passed into an ammoniacal solution of cuprous
chloride, a deep-red coloured compound is produced, known as
cuprous acetylide —

Cu2Clj,2NH3 + H2O + CjH, = 2NH4CI + CjHjCuaO.*

* Keiser has shown that when (perfectly dry, the com}X>sition of this compound
is represented by the formula QCus, and not CsHjCujO (or CsCu9,H]0).

Acetylene

281

This reaction fiirnishes not only a ready and delicate test for the
presence of this gas, but also a means of removing acetylene from
admixture with other gases, and obtaining it in a form of combina-
tion from which it can easily be disengaged again in a state of
purity.

Large quantities of this compound may readily be obtained, by
aspirating the products of the imperfect combustion of coal gas,
through ammoniacal cuprous chloride. For this purpose, a flame
of air burning in an atmosphere of coal gaS' (see Combustion,
page 286) is arranged as seen in Fig. 68, and the products of
combustion are drawn through the copper solution contained in
the cylinder, by means of a suitable aspirator. The cuprous

Fiu 68.

acetylide rapidly forms as a red precipitate, which can' be sepa
rated from the solution by filtration.

From this substance, pure acetylene is readily obtained by the
addition to it of hydrochloric acid —

C,Hj|Cuj|0 + 2HC1 - CujCl, + HjO + C,H,.

Coal Gas. — When coal is distilled, the volatile products obtained
are : (i) coal tar ; (2) an aqueous liquid containing ammonia and
other products, and known as ammoniacal liquor ; (3) coal gas.

Coal gas, after being subjected to ordinary purification, is a
mixture of gases which may be divided into three classes, namely :
illuminants^ diluents^ and impurities. The most important of
these substances

383

Inorganic Chemistry

IEthytene, CsH4 ; propfkne, CgHf ; butylene, \
C4Ha (CnHte) ( About 6.S
Acciylene, C,H, ; aUylene. C,H4 . (CnHm -«)(?«■ cent.

Diluents. — Hydrogen, marsh gas, carbon monoxide . About 90 per cent.
Impurities. — Nitrogen, carbon dioxide, sulphuretted

hydrogen ...... About 3.5 per cent.

The composition of the gas is largely determined by the nature
of the coal employed, as may be seen from the following analyses
of gas from bituminous and from cannel coal : —

Frvm Bituminous CoaL

Prom Cannel Coal,

LfOndon
(FnnklaodX

Manchcaier

(Bunsen aad

RoMoeX

Hydrogen .

• 50.05

SX.»4

35-94

45.58

Marsh gas .

. 32.87

35- »8

4x99

Carbon monoxide

. Z2.89

7.40

laoy

Illuminants .

. 3.87

3.56

laSz

6.46

Nitrogen

• • ••

2.24

• ••

•.46

Carbon dioxide .

0.30

a28

1.19

3-67

Sulphuretted hydrogen

• • • «

• • •

• ••

a29

loaoo

zoaoo

loaoo

zoaoo

CHAPTER XI
COMBUSTION

When chemical action is accompanied by light and heat, the
phenomenon is called combustion. All exhibitions of light and
heat are not necessarily instances of combustion ; thus, when am
electric current is passed through a spiral of platinum wire, or
through a carbon thread in a vacuous bulb (as in the familiar
**glow" lamps), these substances become hot, and emit a bright
light Neither the platinum nor the carbon, however, is under-
going any chemical change, and therefore the phenomenon is not
one of combustion. The materials are simply being heated to a
state of incandescence by external causes, and as soon as these
cease to operate, the glowing substances return to their original
condition unchanged.

Combustion may be defined as the chemical union of two sub-
sianceSy taking place with sufficient energy to develop light and
heat. When the amount of light and heat are feeble, the combus-
tion is described as slow or incipient; while, on the other hand,
when they are considerable, the combustion is said to be rapid ox
active. The true nature of combustion was not understood until
after the discovery of oxygen in 1775. From about the year 1650
until after that important discovery, the phlogistic theory was
universally adopted. According to this view, a combustible body
was one which contained, as one of its constituents, a substance or
principle to which the mxat phlogiston was applied. Easily com-
bustible substances were considered to be rich in phlogiston, while
those that were less inflammable were held to contain but little of
this ingredient The act of combustion, was regarded as the
escape of this principle from the burning substance. Thus, when
a metal was burnt in the air, it was considered to be giving off its
phlogiston, and the material that was left after the combustion
(which we now know to be the oxide of the metal) was regarded as
the other constituent of the metal, and was called the calx. The

tl3

284 Inorganic Chemistry

metal, therefore, was supposed to be a compound of a calx with
phlogiston. By heating a calx along with some substance rich in
phlogiston, the former again combined with this principle and the
metal was once more produced. Thus, when the calx of lead was
heated with charcoal (a substance pre-eminently rich in phlo-
giston), the charcoal supplied the calx with the necessary amount of
phlogiston, to produce the compound of calx of lead and phlogiston,
which was metallic lead. This theory of combustion, after sustain-
ing many severe shocks (from such experiments as those of Boyle
and others, who showed that the calx of a metal was kearuUr than
the metal used in its formation), received its death-blow on the
discovery of the compound nature of water, and that this substance
was produced by the combustion of hydrogen in oxygen.

In all processes of combustion, it is customary to regard one of
substances taking part in the chemical change as the combustible^
and the other as the supporter of combustion. Usually that sub-
stance which surrounds or envelops the other, is called the sup-
porter of combustion. Thus, when a jet of burning hydrogen is
introduced into a jar of chlorine, or when a fragment of charcoal
bums in oxygen, the chlorine and the oxygen are spoken of as the
supporters of combustion^ while the hydrogen and carbon are termed
the combustibles.

In all the more familiar processes of combustion, the atmosphere
itself is the enveloping medium, and the air is therefore, par excel-
lence^ the supporter of combustion ; and in ordinary language the
terms combustible and incombustible are applied to denote sub-
stances which bum, or do not bum, in the air. By a similar
process ol limitation, it has become customary to speak of other
gases as supporters or non-supporters of combustion, if they behave
towards ordinary combustibles as air does. Thus we say of hydro-
gen, or marsh gas, or coal gas, that they are combustible, but do
not support combustion ; and of oxygen, or chlorine, or nitrous
oxide, that they do not bum, but will support combustion ; and,
lastly, of such gases as anunonia, or carbon dioxide, or sulphur
dioxide, that they neither bum nor support combustion.

This distinction, however, is a purely conventional one, and has
little or no scientific significance ; for, by a slight modification of the
conditions, either hydrogen, marsh gas, or coal gas may become
■Qpporters of combustion, and oxygen, chlorine, or nitrous oxide
combustible substances. Thus, when a jet of hydrogen bums

oxygoii we say that the hydrogen is the combustible, and the

Combustion

a85

oxygen the supporter of combustion (Fig. 69, a) ; but if a jet of
oxygen be thrust up into ajar of hydrogen (Fig. 69, b), it ignites as it
passes the burning hydrogen, and continues to bum in the hydrogen.
By means of the apparatus shown in Fig. 70, this may be still
more strikingly shown.* A stream of hydrogen is passed into the
lamp chimney by the tube H, and the issuing gas inflamed as it
escapes at the top. Oxygen is admitted through the tube o, and
the jet of gas ignited by pushing the long tube up into the burning
hydrogen at the top, and then drawing it down to the position

Fig. 69.

Pia 7a

shown in the figure, where the jet of oxygen continues to bum in
the atmosphere of hydrogen.

By means of the same apparatus, oxygen, or chlorine, or nitrous
oxide, may be caused to bum in either hydrogen, marsh gas, or
coal gas. Ammonia, which, as already mentioned, is usually
described as being neither combustible nor a supporter of com-
bustion, when surrounded by an atmosphere of oxygen is readily
inflammable, and will as readily support the combustion of oxygen.

The atmosphere itself becomes the combustible body when the
usual conditions of combustion are reversed. Thus, if a stream of

* " Chemical Lecture Ezperiinents," new ed., Na 367.

coal gas be passed through a similar lamp glass, through the coric
of which a short straight glass tube passes (Fig. 71), air will be
drawn up through this tube, and may be inflamed by passing up a,
lighted taper. The jei of aii will then coniinue to bum
luminous flame. The air is here the combustible, and the coal gas"
the supporter of combustion. If the excess of coal gas be inflamed
as it escapes from the top, the opposite conditions wiil be fulfilled,
the air being the supporter of combustion, and the coal gas the
combustible. ''

This interchangeableness of the terms combustible and stip-
porter of combustion, applies also to substances that are liquid
or even solid, at the ordinary
temperature. If a small quan-
tity of some inllamniable liquid,
as ether, carbon disulphide, tur-
pentine, &c, be boiled in a
flask, and the issuing vapour
inflamed, a jet of oxygen gas
when lowered into the flask
will ignite as it passes the flame,
and continue to bum ,n the
vapour of the liquid. In the
same way, sulphur, which is a
combustible solid, and whose
vapour is inflammable in the
air, is capable in the state of
vapour of supporting the com-
bustion of oxygen. Since eom-
is the result of energetic

nical u

e also

i. ,,, . , it is a mere condition of experi'

ment which of the two acting
substances shall (unction as the environment of the other, it will
be seen that the terms combustible and supporter of combustion,
as applied to a chemical substance, do not express any definite
or characteristic property of that body.

It was demonstrated by Boyle, that when a metal is burnt in
the air, the calx (or oxide) that is obtained, weighs mort than the
metal employed, instead of less, as the phlogistic theory seemed to
demand. This fact, which the upholders of phlogiston found it so
difficult to reconcile, is seen to be a necessary consequence of

m^M

Camfustum

?i7

combustion, considered from the modem point of view. In all
instances of combustion, the weight of the products of the action
is equa^ to the total weight of each of the two substances taking
part in the chemical combination. When, for example, the metal
magnesium bums in the air, the weight of the product of the com-
bustion is equal to the weight of the metal, p/us the weight of a
certain amount of oxygen with which it united in the act of bum-
ing. This gain in weight during combustion may be demonstrated
in a number c^ ways. Thus, if a small heap of finely divided iron,
obtained by the reduction of the oxide, be counterpoised upon the
pan of a balance, and then
ignited, the iron will be seen
to bum, and as it bums the
balance will show that the
smouldering mass is increasing
in weight In this case the
sole product of the combustion
is a solid substance, namely,
iron oxide, which remains upon
the pan of the balance ; but
the same result follows when
the product of the action is
gaseous. Thus, for instance,
when a fragment of sulphur is
bumt, although it disappears
from sight, it, like the iron,
combines with oxygen to form
an oxide. This oxide, however,
being a gas, escapes into the
atmosphere. If the sulphur be
bumt in such a manner that

the sulphur dioxide is collected and weighed, it also will be found
to be heavier than the original sulphur. In the process of bum-
ing, I gramme of sulphur unites with about i granune of oxygen,
and the product therefore weighs 2 grammes. By causing an
ordinary candle to bum in the apparatus shown in Fig. 72, where
the invisible products of its combustion are arrested, the increase
ui weight may easily be seen. The candle being essentially a
compound of carbon and hydrogen, the products of its buming
will be carbon dioxide and water, both of which will be absorbed
by the sodium hydroxide in the upper part of the tube. Conse-

T ..

Fig. 7a.

388 Inorganic Chemistry

quently, as the randle bums away, ihe arTAiigemcnt graJudlly
gains in weight ; ihe incre^^c being the weight of the almospheric-
oxygen which has combined with the carbon and the hydtogen,
form the compounds carbon dioxide and water.

Heat of CombosUon.— During the proce^is of combustion,
certain amount ot heat is evolved, and a ctttain temperature
attained — (WO results which are quite distinc. The Itmptralure
measured by thermometers, or pyrometers, while the amount oj
heal is measured in terms of the calorie, or beat unit.*

The amount of heat produced by the combustion of any sub<
stance, Is the same, whether it bums rapidly or slowly, provided
always that the same tinal products are formed in each ca^e.
Thus, when i gramme of phosphorus bums in the air to fbnn
phosphorus penioiide, it evolves 5747 calories ; and when the
same weight of phosphorus is buml in oxygen although the com-
bustion is much more rapid and energetic, and the ttntperature
consequently rises higher, the nrfioufi/ (^/'Aeii/ evolved is precisely
the same.

Ag^n, when iron is heated in oxygen it bums with great bril-
liancy, and with evolution of much heat ; if, however, the same
weight of iron be allowed slowly to combine with oxygen, even
without any manifestation of combustion, but simply by the pro-
cess of spontanenus oxidation, or rusting, it is found that the
amount of keal produced, in forming the same oxide, is absolutely
I he same.

So far, therefore, as the quantity of heat produced is concerned,
there is no difference between active combustion and ilow com-
bustion, or (confining ourselves to the case of combinations with
oxygen) between active combustion and the ordinary process of
spontaneous oxidation at ordinary temperatures. In the latter
case Ihe heat is given out slowly ; so slowly that it is conveyed
away by conduction and radiation as fast as it is produced, and
consequently the temperature of Ihe material undergoes no per-
ceptible change. In the case of active combustion, the action is
crowded into a few minutes or seconds, and, as all the heal de-
veloped is evolved in this short space of time, the temperature of
the substances rapidly rises to the pomi at which light is emitted.

That heal is developed during the process of spontaneous oxida-
Don is readily shown. Thus, if a small heap of fragments of

* The major caloric sometimes used is equal lo looo calories. Sec Tbimto-
P^n I. chap, n.

Heat of Combustion

phosphorus be exposed to the air, it will be evident from the
rormation of fumes of oxide, that it is underj{oing oxidation. As
the action proceeds, and as the heal produced by the oxidation is
developed more rapidly than it is radiated away (especially from
the interior portions of the heap), it will be seen that the phos-
phorus quickly begins to mell, and finally the temperature will
rise to the point at which actrvt combustion begins, when thi
will burst into flame.

It has been shown, that many destructive lires have arisen from
masses of combustible material, such as heaps of oily cotton waste,
undergoing this process of spontaneous oxidation, until the heat
developed within the mass has risen sufficiently high to inflame
the material. To the operation of the same causes, is to be
referred the spontaneous firing of hay -stacks which have been
built with damp hay ; and also the spontaneous inflammation of
coal in the holds of ships.

As the temperature produced by combustion is augmented by
increasing the rapidity with which the chemical action takes place,
it will be at once obvious why substances which bum in the a,ir,
bum with increased brilliancy and with higher temperature in pure
oxygen. In the air, every molecule of oxygen is surrounded by
four molecules of nitrogen, therefore for every one molecule o(
oxygen that comes in contact with the burning substance, four
molecules of this inert element strike it ; and by so doing they noi
only prevent the contact of so much oxygen in a given interval of
time, bui they themselves have their temperature raised at the
expense of the heal of the burning material. The number of
oxygen molecules coming in contact with a substance burning in
the nir, in a given time, may be increased by artificially setting the
air in rapid motion : hence the increased rapidity of combtjstion
(and consequent rise of lemperalure] that is efl'ectcd by the U9e of
bellows, or by increasing the draught by means of chimneys and
dam piers.

The augmentation of temperature obtained by the substitution
of pure oxygen for air, is well illustrated in the case of burning
hydrogen. The temperature of the flame of hydrogen burning
in oxygen, Icnown as the oxy-hydrogen flame, is extremely high,
and when allowed to impinge upon a fragment of lime, it quickly
raises Ibe lemperaturc of that substance to an intense white
heat, when it emits a powerful light— the so-called eiyhydrogtn
" eli£k(.

Inorganic Chemistry

290

The following results obtained by Bunsen. show the tempcratum;
reached by ihe combustion of hydrogen, and of carbon monoxid^^
in air and in oxygen : —

The Dame of hydrogen burning in air , . . 2024'

.. „ „ oxygen . . 2844°

„ carbon monoxide burning in air . 1997'

i> II .1 oxygen 3003'

Fig. 73.

of (he carbon monoiide flainc ii higher thin that of bjpdrogen. This li due
to Ibc partial dissociation of the wB.Ler, which results from the combqslioa ol
the latter. ]< has been shown thai when a mixture of bydrogen and oiygen. In
the proporiiDn to form water, is ignited, the temperature produced by Ihe
union of a portion of ibe raiiture, rises above ihe point ai which water du-
sodates : and consequent!)' for a certain small in

which ai

as are formed : during this stare the (en
tion once more proceeds. l( will be se
temperature which can lie reached by
point a( which Ihe products of oombus(io[

iperatuie falls, when rapid

.mbus- I

to [he

t>y the J

Ignition Point

291 J

Ijrnltlon Point— The lemperature 10 which a lubstance must \
be raised, in order that combustion may take place, is called i'
ignition point. Every cotnbustible subsiajice has its own ignilioD
lettiperature. If this point be below the ordinary temperature,
the substance will obviously take fire when brought into the air,
without the application of heal : such substances nre said to be
spontaneously inflammablt, and must necessarily be preserved out

ofc.

ivith a

Passing from cases of spontaneous inflammability, we find a
very wide range existing between the igniting points of differeni
substances. Thus, a jei of gaseous phosphorciied hydrogen m&y
be ignited, by causing It to impinge upon a lesi-iube containing
boiling water : carbon disulphide vapour is inflamed by a glass
rod heated to I30*, while the diamond requires lo l>e raised nearly
to a while heat before combustion begins.

The difference between (he temperatures of ignition of hydrogen,
and marsh gas, may be
well seen by means of the
old ttttl mill of the miner
(Fig. 73)- By causing ihe
sieel disk to revolve at a
high speed, while a frag-
ment of film is lightly
pressed against its edge, a
shower of sparks is thrown
out; andondirectingajel Fig. 7*

of hydrogen upon these

sparks, the gas is instantly ignited, while they may be projected
into a stream of marsh-gas without causing its inflammation.
The same fact is also made strikingly apparent by depressing a
piece of fine wire gauze upon ftames of marsh gas (or coal gas),
and hydrogen, (n the former case, the flame will not p)ass through
the gauie, although it may be shown that marsh gas is making its
way through, by applying a lighted taper immediately above the
wire. If the game be held over the issuing jet of gas, the latter
may be ignited by a taper upon the upper side of the gauie, but
the combustion will not be communicated to the inflamniable gai
beneath (Fig. 74). The gauze conducts the heat away from ihe
flame so rapidly, that the temperature of the melal does not rise
to the ignition point of the marsh gas on the other side, and
therefore the combustion cannot be propagated tbroush the gauM.

292 Inorganic Cktmistry

In the case of hydrogen, however, it will he found Ihai ihe i
the gas upon the upper side of the gauie is inflamed, the
passes through, and ignties the hydrogen beneath.*

Ii is upon ihis principle ihai the safely of the "Davy lanip" dej
TTiia consists of on ordinary oil lamp, the flame of which is surrounded
a cylinder of wire gnuie (usually made double at Ihe top), Ihiougb which
to supply the flame freely passes in, and the products of combustion pass out.
When such a lamp is taken Into an atmosphere in which marsh gas is pre-
sent, this gas, entering through the gauie, becomes ignited within the chimney,
producing a very characteristic effect upon the lamp fljtne. According to the
amount of marsh gas present, the flame is seen to become more and more
extended, at Ihe same lime becoming less luminous, until the whole interior
of the gaiuc cylinder is filled with the burning gas, emitting a faint bluish
light, known among Ihe miners as Ihe lorfst-lighl. The burning maish gas
is unable to communicate its comtnistion to the .inflammable mixture ouiude,
for the same reason that ihe Hame, in ibe eiperimenl already referred to, was
unable to pass through the wire gauie. If from any cause, the flame should
heat any spot of Ihe gnuie chimney lo a temperature above Ihe ignition point
of marsh gas, the outside combustible miilure will become ignited. It has
been shown, thai l>y exposing llie lamp to a strong air draught, the flame may
be so driven against the game as to unduly heat the meiaL It has also been
proved, that the same result frequently follows from the eiplosive wave ibat
is produced in a mine, when, from some accidental cause, Ihe operation ol
blasting (or ilwt-/riitg] results, not in Ibe splitting of the rock, but in merely
blowing out the " lamping." The violent concussion to the air. wbijh follows
such a fiiowv-ou/ ihof. has been known lo blow ihc flames of the Davy lamps,
even in remole pans of ihe workings, bodily through ihe game ; and if such
lamps arc liurning bI the time in an inflammable minlure, it would thereby be
fired.

I(; Ihe behaviour of the llame of a Davy lamp, when pl.iced into an almos-
pbere mntaining mnrsh gas, it b possible to estimate, with n rough degree ol
accuracy, the percentage amount of that gas which is present,
pose the flame is turned down as low as possible, and the height
burning maish gas extends (ihe so-called .;f«^a(«/ caf) is measui
scale graduated in lenlhs of inches. Fig. 75 {two-thirds the aclual site) shows
Ibe " caps" obtained by the presence of 4. 5, and 6 per cent, of marsh gas.t

WhcD the ignition point ol a substance is lower than the tein*
peralure produced by its combustion, such a substance, when

* Recent experiments of Victor Meyer {Bericilt. No, 16, 1893), upon the

ignition temperature of explosive gaseous mixtures, give the following results

A mixlure of onygen and hydrogen (electrolytic gas} explodes at 6t9°

Explosive miiture of oxygen and marsh gas . , , . 656°

coal gas ... . 647"

t In a recent development of this method of testing, a small bydrog

Qame is sulistiiutcd for the oil lamp flame, wbecetiy it is possible lo deieci 1

Fnstnce of 0.95 per cent, of marsh gai (Gowest.

^pendS^I
ded br ^^

Ignition Point

293

I ignited, will continue to burn without further application of ex-
ternal heal, the intlammation being^ propagated from particle to
panicle by the beat developed by their own combustion. All the
ordinary processes of combustion are actions of this order, and
belong to the class of chemical reactions known as exofkermie,
that is to say, reactions which are accompanied by an evolulJon
of heal (page 147).

If, on the other hand, the ignition point be hi)jhcr than the heal
L produced by chemical union, combustion cannot proceed without
I the continuous application of ciiemal heat. The igniting point of

nitrogen in oxygen, for eitample, is higlier ih.tn the temperature
produced by the union of these elements ; therefore, although the
nitrogen may be ignited by the heal of the electric spark, it is
unable 10 communicate its combustion to contiguous particles, and
the inflammaiion does not spread. If the ignition point of nitro-
gen in oxygen had been lower instead of higher than the heal ol
the chemical union of these elements, the first flash of lightning that
discharged into the air would have initiated a conttagration, which
would have extended through the whole atmosphere, and resulted
in the removal of the oxygen, and iti replacemrjit by oxide* of

Inorganic Chemistry

The production of acaylene bj the combinaiion of eacboo with hydcoKOt I
undET the inOuence of high lemperalure ; and ihe forrnalion of cyinogco, mod
carbon disulphidc, by the imion of the same elemenl *ilh nitrogen and with
(ulpbur respcclirely, arc illuslrations of Ibe same class o( action : phenomena

attended with tui absorption of heal (page 147).

Flame. — When both the substances taking part in ctimbustioD
ate gases or vapours, the sphere of the chemical action assumes
the character of Dame ; while, on the other hand, if one of the
materials is a solid which is not volatile at the temperature of its
combustion, no flame accompanies its burning. Sucli solids as
sulphur, phosphorus, camphor, wax, &c, during combustion in air,
undergo vaporisation, and consequently bum with the formation of
flame ; while such substances as iron, copper, carbon,* Sto., which
do not pass into vapour at the temperature produced by iheir com-
bustion in oxygen, bum in this gas without giving rise to a flame.

Flames difler very widely in their general appearance, and in
the majority of cases are distinctly characteristic ; thus, hydrogen
bums in air with a flame that is almost absolutely colourless, and
is scarcely visible in bright dayhght ; sulphur burning in air pro-
duces a pale blue flame ; ammonia in oxygen a flame having a
yellow-ochre colour ; carbon monoxide a rich blue flame, while
cyanogen burns with a flame having the delicate colour of the
peach blossom. Other flames are characterised by their luminosity.
Thus, phosphorus burning in oxygen emits a dazzling yellow light,
that is almost blinding to the eyes ; magnesium bums in the air
with an intense bluisb-white light ; the flame produced by the
combustion of the vapour of nickel carbonyl in air emits a bright
white light ; and the flames that are produced by most hydro-
carbons during their combustion, give a characteristic yellowish-
while light

The General Strutiture of Flame.— The simplest form of
flame, is one that is obtained by the combustion of a substance
which itself undergoes no decomposition, and in which the product
of combustion is arrived at in a single stage. Such fiamcs, for
example, as that of hydrogen burning in chlorine or in air ; or of
carbon monoxide burning in air. lo the case of hydrogen burning
in air, the materials taking part in Ihe process being elementary

□ndilioi

■mbustioo of carbon in

htbi* I

Flame

295

bodies, no com plications arising from decomposilion are possible ;
and although carbon monoxide is a compound, it unites with
oxygen without itself undergoing any decomposition, and passes
directly into carbon dioxide. Such tiames as these, when burning
from the end of a tube, consist of a single hallow conical sheath
of actively burning gas. Fig, 76 represents a tiame of burning
hydrogen : the darker region d is the hollow space within the flame,
consisting of unbumt hydrogen ; while the flame proper, the actual
burning portion, is the sheath b, which appears practically unifonn
throughout. That the flame-cone is hollow may be proved by a
variety of experiments. Thus, if a sheet of white paper be quickly
depressed into a flame, a charred impression of the section of the
cone will be obtained, as shown in Fig-, 77, from which it will be

Fig, 76. Fig. 77.

seen that no combustion is taking place within the cone. In the
game way, an ordinary lucifer match may be suspended within the
flame, where it will remain without ignition so long as the burning
walls of the flame do not touch it The shape of a flame is due to
the fact, that as (he gas issues, the layer nearest to the walls of the
lube bum round the orifice of the tube as a ring, consequently (he
next layer has to reach up above this ring before it can meet with
air for its combustion, and each successive layer has to pass up
higher and higher in order to find its supply of air, and in this way
(he burning area is built up into the form of a cone. To show that
the hollow space consists of unbumt gas, it is only necessary (<
insert a tube into the interior of the flame in lucb a way as b

Inorganic Chemistry ^^|

in or the gas, when it will be found Iha! the gai wi^^H

this simplest type, to substances that undcrgl^^^^
Itiring combustion, or which yield the Tina! produq^^^^
successive stages, it is Tound that the flames th^^^^|
less simple in siruciure. ^^^H

ns of various degrees of complexity, the fo1lowiit^^^|
le mentioned : — ^^^B

draw ofTa poition or the gas, when
withdrawn will bum.

Passing from this simplest type, to substances that
decomposition during combustion, or which yield the fina! prodi
of oxidation by successive stages, it is Tound that the flames
give rise to are less simpli

As illustrations of various degrees of complexity, the folic
examples may be mentioned

(i.) Ammonia burning in oxygen. This flame (Fig, 78) is very

characteiislic, and on inspection it is al once obvious that it has a

less simple structure than the hydrogen flame. In this case the

inner hollow portion d is surrounded by a double flame-cone, the

inner cone a having a yellow-ochre colour, and

Bihe outer portion b possessing a much p.oler
colour, and tending to green. During the
combustion of ammonia, the compound under-
goes decomposition into nitrogen and hydro-
gen. This decomposition, which begins in (he
hollow region d, takes place mainly in the inner
cone a, and the hydrogen which escapes com-
bustion in this region, passes to the outside,
and there bums, forming the outer cone. Pro-
bably there is also a partial combustion of the
nitrogen.
(2.) Carban disuiphide burning in air. Thwl
flame, like the ammonia flame, constats of a '
double flame-cone, consisting of an inner lilac-
coloured cone, surrounded by an outer region
having a deeper blue colour. During combustion, carbon disui-
phide, like ammonia, is decomposed, but in this case not only are
both of the constituents readily combustible, but the carbon passes
into its final state of oxidation in two stages, forming first carbon
monoxide and afterwards carbon dioAide.

(3.) Hydrocarbons burning in air. The flames produced by the
combustion of these compounds, include those which are commonly
employed for illuminating purposes, such as candle, gas, and oil
Barnes, and in all essential points of construction they are practi-
cally identical. This may be seen to be the case by a comparison
of the flames of a candle and of coal gas (Figs. 79 and So). la
these flames, as in the former cases, there is the dark hollow space
dt coDsistincc of heated unbumi gas (in the candle flame this ga*i

FiO. 78,

Flame

39;

■1 generated by the vaporisalion of the materials of Uie caudle,
which in the melted condition arc drawn up the wick by capillary
action), Above this there is a region, a, which, in comparison
with the rest of the flame, appears almost opaque, and which
emits a bright yellow light. This luminous area constittites rela-
tively the largest part of the flame, and in flames that are used for
light-giving purposes, it is mtentionally made as large as possible
by means of various devices. At (he base of the flame, there is
I small region, <, whicli appears briKhi blue in colour, and is non

Fic 79.

Fig. to.

t pans,

:d surrounding the entire flame there will be seen a
faintly luminous mantle, b.

The flame proper, therefore, consists of three dist
namely : (1) the blue region c, at the base ; (z) the faintly lur
mantle b \ and (3) Ihe yellow, brightly luminous region a. These
three parts constitute the flame-cone, the actual area of combustion,
which envelops the dark region d; this, as already staled, consists
of unburot gas, and therefore is not, strictly speaking, a pari of the

U the supply of gas 10 a flame, burning as represented in Fig. 80,

Inorganic Cfumtslry

293

be diminished, or if air be slowly admitted 10 the inleriar, the flamfl
will shrink down, and the luminous area become less and less,
until it finally disappears altogether. The flame-cone will then be
found lo consist of two pans, resembling in structure the double
cone of Ihe ammonia flame, Fig. 78. The blue region e. Fig. 80,
which is only fragmentary in the flame as Iherc represented, will
have become continuous, and now constitutes the inner cone ;
while the mantle b forms the outer cone, the flame presenting the
appearance seen in Fig. 81. The region d, as before, consists of
unbumt gas.

Il has been shown, in the case of coal gas flames burning in this
manner, thai in the inner cone c, the changes going on result
mainly in the formation of carbon monoxide and water, together
with smaJl quantities of carbon dioxide and
hydrogen ; and that in (he outer cone, or
mantle, the carbon monoxide and hydrogen
are burning to carbon dioxide and water.
In the inner cone, therefore, the carbon is
burnt lo its first stage of oxidation, and ft
portion of the hydrogen is oxidised lo water ;
in the outer cone^ the second stage of oxi-
Flg, Sl dation of the carbon takes place by the com-

bustion of the carbon monoxide to carbon
dioxide, and the hydrogen which escapes combustion in the inner
cone is also bumL

It has been known since the time of Dalton, that when certain
hydrocarbons are bumi with an insuflicieni amount of oxygen for
the complete oxidation of both the hydrogen and carbon, carbon
monoxide, water, and hydrogen are produced. This result is pro-
bably due to a secondary reaction ; the first stage being the com-
bustion of hydrogen to form water, which at Ihe high temperature
is then decomposed, either by the carbon, or the hydrocarbon!,
according to the following equations —

CH, -fO, -aH,o + C
C,H, -I- O, = 8H,0

8C-

Thev;

.rious parts of an ordinary gas or candle flame, therefor^ ]
are due to the different chemical reactions that are taking plac
these areas ; these changes are not of such a nature that they can ]
1 all cases be perfectly traced, neither is one set of reactionsj

Flame 299

exdosively confined to each area, but rather is it the case that
certain chemical actions predominate in each particular part of the
flame.

In the blue region ^ Figs. 79 and 80, the main reactions going
forward are those already indicated, by which carbon monoxide,
water, and hydrogen are produced In the £untly luminous
Doantle ^, carbon monoxide and hydrogen are burning, together
with small quantities of hydrocarbons which may have escaped
combustion and decomposition in the luminous region. The non-
luminous character of this mantle, is due to the cooling effect of the
air which is drawn into the flame, and which even extinguishes
combustion upon the outer limits of the flame before every trace of
combustible material is burnt ; for it has been shown that small
quantities of carbon monoxide, marsh gas, and even hydrogen
escape unbumt from a gas flame.

The chemical decompositions which go on in the luminous area
cannot be said to have been thoroughly established. It has been
shown that very early in its passage up the flame, a certain amount
of the marsh gas and ethylene present is converted into acetylene,
the change taking place as the result of heat alone. The gases
ascending the dark region </are surrounded on all sides by a wall
of burning material, and are thereby raised in temperature to the
point at which the marsh gas and ethylene sufler decomposition
into acetylene and hydrogen —

8CH4 - C,H, + 8H,.

The following table (Lewes) shows the gradual development of
acetylene in such a flame : —

ilo«tylen«

PcrCmt.

0.035

0.340

a56o
I.4I0

0.045

aoo

Therefore, by the time the gases have reached the tip of the dark
region, the efiect of heat upon them has been to nuse the amount
of acetylene to over 70 per cent of the total unsaturated hydro-
carbons present As the acetylene and other hydrocarbons pass

Gas in burner

Toul Uiuaturatod
Hydrocarbons.
PcrCcDK.

• 4.38

\ inch above rim of burner .

. 4-00

i^ inches above rim .
Tip of dark region
Centre of luminous area

. 1-53
. 1.98

. . 045

Tip of luminous area .

. aoo

on through the Hame, along with stesun, carbon dioxide, and
carbon monoxide, other and more complex changes go on, whereby
denser hydrocarbons are formed, and carbon Itself is precipitated.

The formation of acetylene in that region of the flame where the
coal gas is in excess, is well exemplified in the case of air burning
in an atmosphere of coa! gas (see Fig. 71). In this (tame, the air
is in the inside and the coal gas upon the outside ; it is, in effeci, an
ordinary coal gas flame turned inside oul. The formation of acety-
lene, instead of taking place ■within the flame (in which case it has
to pass through the heated area, and is thereby decomposed),
takes place upon the outer surface or periphery of the flame, ant)
therefore largely escapes combustion and decomposition, and passes
away into the coal gas atmosphere. (See Acetylene, where this
method is described for the preparation of this compound.)

TbeCiAiueOtLuinlnOtitrlllFlunM.— The light-giving propt-nyol a. Haine
is not due 10 the operation of uny one simpk caiue. It wns al one liine sip-
posed, that the luniitioiily of a flame di-pended sok-Iy upon the presence in it
of suspcDded solid matter, resulting from ibe chemical dnnmpositions going
Ml di^HB combration. II hai b«n ihosm, howevrr. ilial this general slale-
menl does not satisfy all cases, as there are a Dumber of blghly luminous
flames in which, [rom the linown propenles of the products of comliustion,
there cannor possibly be any solid matter preseni. Thus, foi example,
phosphorus burning in air gives a flame of a high degree of iuniioosily : bat
ttK phosphorus pentoiide which is the product of combusiion, although si
at ordinary temperatures, is volatile al a temperature far below that of tlM •
tlame. The same may lie said oF the luminous flame of arsenic burning h) I
oxygen, where the still more volatile arscnious oxide is the product

When carbon disulpbide burns in oxygen or In nitric oxide, a wcll-kn
intensely luminous flame is obiaioed. in which only gaseous products
busiion can be present ; and. lastly, the tlame of hydrogen burning in oxygeo, J
can be made under certain circumstances to emit a tiright light : Ihi
mixture of these gases is ignited in 3 closed eudiometer. Ibeir combustion i» I
attended with a brilliant Bash of light, ihe only product b-ing water.

There are three causes which may operate, either sepualely 01 togelber, in 1
Imparting luminotily to a Barae, or in increasing ils light-giving power
are— I. The temperaluie of Ihe flame, a. The density of Ihe flame gases, ai
3, Tba introduction into Ihe flame of solid mailer. These three a
\x treated separately, and lllusualions given, which, so fnr as our kuowled
extends, can be directly traced to Ihe independent operation of eacfa

I. The effect of temperature.

(a.) Upon flames in which solid matter is knuwn lo be absent

When phosphorus is introduced into chlorine, it spontaneously inflames and
bonu wiUi a flame of such eitremelj' feeble luminosity that il may be regarded
as QOD-lumlnou) ; If, tiawever, Ihe chlorine tie previously strongly heated by
being pused Ihrough a nd hot tube, aod the phas[dionB be boillnE when il

itad with Ifae gM,
plUform of leaiperature is accomparlcd b; i

Ttw flame of carbon disulphldc bumini; in «lr emits bul a feeble light ; but
when this substance burns in pure oiygen. its tempFniture of combnnlon Is
grcBll)' raised, and the luminosily of the tlnme ii enormousli' incteased.

rtiosphoiEtted hydrogen burning In air gives a flume of cnnsidernble luml-
Dostly: bul when this flame ii fed with pure oiygen. and Its lempcralutc
thereby raised, it becomes inlmiely luminous.

(/9,) Upon flanies in which solid matter is known to be present.

Tbe flames produced by the combustion of line or miignejliini In the air.
and in which the solid oiides are present, have their luminosity greatly in-
creased when pure oxygen is substituted for air, and the temperaluie of eom-
Imstioo thereby augmcnled.

The same result is seen in the case of flames In which the solid mailer Is
anificially introduced, as in the familiar Welsbach burner, where a totld gaiue
mantle, composed of an alkaline earth, ii placed in the Same-cone of a non-
luminous gas flame, thereby rendering it luminous, tf the lempecnture of
this flame Ik augmented by feeding it with oaygen, the light emitted by tlie
incandescent solid is greatly increased.

{■),) Upon flames in which solid matter is believed to be present, nicb as
candle, gdx. and other hydrocarbon flames.

When a candle or gas flame is introduced Into oiygen. although it shrltiks
In tise. Its luminosity is increased. It bas also been shown that when a coaJ
gas flame is chilled, by causing it to spread against scald surfaee, its luminosity
Is diminished or destroyed altogether ; and, conversely, if (he gu and the air
supplying the flame be strongly healed before combustion, the luminoslly is
greatly increased. In this case, however, the direct effect of change of tem-
perature Is complicated by tbe decompositions going on In the flame; for. as
alieady mentioned, the convenion of the non- illuminating marsh gas Into the
highly illumlnaling gas acetylene, is a function of the temperature.

The increase of light obtained from a gas flame by previously beating the
gas and air. is the pnndple underlying all tbe so-called ruuftraHvi burners.

It Is evident, therefore, thai most flames gain luminosity by having their
temperature raised. There are, however, cases in which inirease of tempera-
ture ahiit appears to eicrt no influence upon the luminosily. The Same ol
hydrogen. For example, which is practically noU'luminous when burning in
air, does not liecome more luminous when burnt in oiygen. although lu
temperature is greatly increased.

a. The influence of the density of the flame gases.

It has been shown by Fnuiklend * that the luminosily of flame is Inlimalely
associated with the piessure to which it is subjected, or with the density of the
flame gases. Thus, it is found that a gas or candle flame, when burnt either
at high altitudes, or in aniScially rarefied atmospheres, has Its luminosily
greatly reduced : and. ftr conlra, when caused to bum under increased pres-
ihe luminosity is increased. In tbe case of hydrocarbons, complicuion
I ftomthe fact, that the temperature of the flame is changed by alieratloni

i. p. Gb9; Ptoc. Royal Sodety. KoL ivi. p. 419.

d preasim the temperalure Mil. and sltboil|b 3
(ben Is less loss of heat by ndislion !□ rareliGd air. than in afr al Ibe oi "
preMure, tt ii possible ihal the general lowering of the lempcralun! o
flame, may iDOdify tbe chemical decompositions in the dttcoion a"

Flames otbet than those of hydiocarbons, however, and tn which i
IS when the densiijr of ll
fias is increased by pressure. Thus, the Rame of carbon raonoiide In oiyjeBi ■
at ordinary pressures, emits B moderate light ; bill wh
of two atmospheres Ihe luminosity is greatly increased. Even '±e nt
fhune of hydrogen burning in o»ygen, becomes luminous under a pressiin
two atmospbetcs. and when examined by (br spedroscope is found to give ftfl

Fia. 8a. Kii, ?;

coDtinnotis spectrum. It has been found, as a general rule, iliat denK gues
and vapours, when healed, become incandescent, or luminous, at much lower
temperatures than those of low specific gravity : thus, if different gases be
raised to incandescence by the passage through them of electric sparks, under
limilv oondilions, it is seen that the light emlKed by the glowing vapour,
vanes with the density of Ihe gas. The luminosity of glowing oxygen {density.
15.96) is eteally superior to that of hydrogen (density, i), while the light emitted

advance of eiiher. And it

und that

of (be spark increases as the density is

le and the sa

egas.

increased by anificis

le liuninasily

Other things being equal, it may be said that the denser tb
b Tbe IntmdDction of nlid a

Tke Bunien Flatits

303

Non-luinlncHU lUma may Ix rendered luTninoui by the Inlentlooal Introdoc-
Ikn iolo tbem of solid muiEr. mrhlch, bjr being raised to 11 lufficientlir hlgb
teinpenlure, irlU become nronglr incandeiceni. Thui, tbe ordinary lime-
light Dwei \a laitattovxj to Ihe incuidescenoe of ihe fragment oF lime, whicb
ii nuied Id ■ bright white heat by ihe high temperaiure of the non-luminous
oxy-hydniKen flune. Tbe Hme ii not vapociied at the lempentture of the
Bune, ibe light being enlitely due to tbe glowing solid matter.

The " Welibacb" burner, alreadf referred to. is another example of the same
order, the luininoiity in Ibis case being due to Ihe Introduetioa into »n
ordinary non-himinoui Bunsen fl&me. of n fine game manlle made of aluminA
or other metallic oiide (Fig. 8a). When lucb B mantle ii raised to iocandee-
oenix by Ibe heat of the gai flame, ii emits a bright wtilte light, nrongly
resembling that of an ordinary Argond giu tiame. A fUinie may kIso tie
rendered luminous by Ibe inlenlional precipitation within it of carbon, which,
by IIS ignitioD and III combuilloo, praducei a high degree of luminoiily : thus.
if a small quantity of alcohol be boiled In a flask, and a jet from which cbloiine
Is issuing be then lowered through the burning vapour Into the flask, as ihown
in Fig. I3. the chlorine will bum in Ihe alcohol vapour with a luminous flame ;
and the piecipltaled carbon (wbicb is thrown out c4 combination by tbe action
of the chlorine upon Ihe alcohol) iscendixg Into the previously non-lumlnoua
alcohol flame will render it brightly luminous.

From these conilderallous it will be evident thai the lununoiity of a Same
may he due, 6rst. to Ihe presence of vapours luflidently dense to become
incandescent ai the temperature of tbe 9ame ; or, second, to the presence of
•oUds rendered incandescent, either by tbe heat of the Same gases atone, or
in con)unction with their own combuslioo; or. third, from tbe simultaneous
operation of all these causes. Ordinary gas and candle flames come under
the last of ihete beads. The decomposillans that go forward in these flames,
nol only give rise to denie vapours which become incandescent, but also to
the precipitation of solid carbon, which by its Ignition and combustion adds
10 the luminosity of the flame.

TiM BnBMn Flamt.— The conilruciion of the Bunsen tamp Is too Well
known 10 need descriplion. Tbe gas, issuing from a smalt Jet situated at Ihe
base of a meial lube, and mixing with air which Is drawn in through openings in
the lube, bums at the lop of the chimney with Ihe familiar non-luminous tinme.
The eiislence of this flame in its ordinary condition depends upon two main
causes; lim, upon Ihe fact that in tbe immediate neighbourhood of a jet of
gas Issuing from a small orllice. ilure is a reduction of pressure ; and, second,
upon the relation between tbe velocity at which tbe gases pass up Ibe lube,
and the rale of propagation of combustion in tbe niitiire of air and coal gns.
Upon Ihe lirsi of these causes depends the entiance of air into tbe "air-bolci"
of the lamp, and upon Ihe second depends Ihe continuance of Ihe flame in iu
position upon ibe lop of tbe lube.

As the coal gas issues ^m tbe small jet at the base of tlie chimney, instead
gas escaping through the side-holes, air ii drawn into the lube by virtue
reduced pressure produced immediately round the jeL That Ibisareaol
<d pressure actually exists In the neighbourhood of Ibe jet of a Bunsen,
le proved by attaching a delicate manometer to tbe air-hole of sucb a
Iftmp. as itaiwn In Fig. 84. As Ibe gas li lunwd on, Ibe liquid in

304

Inorganic Chemistry

tube will be sucked lowardi tbe Ismp. sbowlng llui itie Issuing gas cauxs ■
partial vacuum In 111 Immediate Belghbourhood. *

In ordei thai the flame shall remain at Ibe lop of Ibe lubi!, ihcre must be a
certain nlAtion between Ibe velocity of tbe issuing gases, and the rate of pro-
pagBtioC of combustion in the mimure; for if the tallei be greater than the
fonaei, the flam- will travel down the lube and ignite Ihe gas at ihe jet below.
By gradually reducing the supply of gas lo tbe flame, and so altering the pro-
portion of gas and air ascending the tube, the mixture becomes more and
more explosive, until a point is reached when the velocity of inflammaiion <i
grealerlhanlheiateof efflux of the gases, and the flame travels down the lube,
and the lamiliar efl'ect of the Bame "striking down" is obtained,

Tbe same result may be brought about, and the effect more closely observed,
by eitending [he chimney of the lamp by means of a wide glass lube. As lh(
supply of gas is reduced, or the quantity ot air iniroduced it 'ocreased, ihe
flame will be seen to shrink in siie and finally descend Ibe lube. By adjust-
ment it may be caused eiiher to ex-
plode rapidly down the tube, or to
travel quite slowly, or evm 10 remain
stationary at some point in the tibe
which is slighily constricted, and where,
therefore, the flow of tbe Issuing gas li
Slightly accelerated, t

The non-luminosity of a Dunsen
flame is due lo the combined opemiion
of ibree causes, namely, oxidation,
dilution, and coaling. It was formerly
supposed that the deslniclion of Ihe
luminosity of a gas flame, by the
of air with the gas before

irely owi

t oxygen

. . .._ ...,„-. -1 bringing

i'lG- 84. aboui a more rapid and complete state

of oxidation, that the hytlrocarbons

.e additional supply of oxygen so pro-

lal not only is this efl'ect brought about

by air, but aHo by the use of such inert gases as nitrogen, carbon dioxide, and

even steam. The following table (Lewes) shows Ihe relative volumes of vari

gases that are required to destroy Ihe luminosity of a gas flame :—

1 volume of coal gas requires a 5 volumes of oxygen.

1. 96 .. carbon dioxide,

I. „ ,. a. 30 ., nitrogen.

Thai the atmospheric oxygen eflecls ibe result by a direct oxidising »
and is not acting merely as oilrogen does, is proved by the fact, Ihol mlitom
of oxygen and nitrogen containing a higher proportion of oxygen that! Il

* See "Cbemical Lecture Eiperimenu," new ed., 498-509. i

Tkt BunstH Flame

30s

pment in air, dtmojr the himinnrity more rapidly tbmn is cfliDCted by air
Tboi, when mixtures containing nitrogen and oxygen in the proportion of 3 to
I, 9 to X, X to X by vohmie are employed, the volumes of the mixtures required
to destroy the luminosity of one volume of ooal gas, are respectively 9.09, x.49,
and x.oa

It has been shown that when coal gas is diluted with nitrogen, a higher
temperature is neceswry to efiiect its decomposition ; hence the action of the
atmospheric nitrogen in causing the loss of luminosity of a gas flame, is in part
due to the higher temperature that is required for the formation of acetylene,
wliich, as already mentioned, is the first step in the decomposition and con-
densation of the hydrocarbomi in the gas.

As already mentioned, the luminosity of a flame b very much influenced by
alterations of temperature ; and |ust as the non-luminosity of the outer mantle
of an ordinary flame, is partly due to the cooling action of the air which is
dragged into the flame Amn the outside, so the want of luminosity of the
Bunsen flame, is in part due to the cooling influence of the large volume of air
that is drawn up into the interior of the flame. That the gases which are
drawn into a flame reduce the luminosity by virtue of their cooling action, is
borne out by the fisct, that the higher the specific heat of the diluent (and
therefore the greater its power to abstract heat from the flame) the lets of
it is required to effect the destruction of the luminosity ; thus, as already men-
tioned, less carbon dioxide than nitrogen b necessary to render a flame non-
luminous : the specific heat of nitrogen is a 9370, wlUle that of carbon dioxide
^0.3307.

The specific heat of oxygen Is also slightly greater than that of nitrogen,
being a9405 ; but the cooling efiiect of dihitioo with this gas, is enormously
overpoweied by the increased temperature due to its oxidising action upon
the combustible materiab of the flame.

Experiments made upon the actual temperatures of various regions of a
Bunsen flame, rendered non-huninous by admixture with different gases, the
results of which are seen in the following table (Lewes), show the cooling efiiect
of these diluents upon the flame : —

Ttmperatmn tf FUwufrom Butum Burmr, kuming 6 euhicfati of Coal

Gasftr Hour.

Ragioii in FboM.

T^ffl{fl5^i«

flame rendered Non-
huninous hy

Air.

Nitrogen.

Carbon
Dioxide.

FlaoM.

\ inch above burner ....
x| inch above burner ....
lip of inner cone ....
Centre of outer cone ....
Tip of outer cone ....
Side of outer cone, level with tip of)
inneroooe . . • . |

Degrees.

«35

491

913
1398

798
X936

Degrees.
54

«75
X090

1533
"75

X333

Degrees.
30

XXX

444

999

"51

1*36

Dcgreea

393
770

951
970

306

Inorganic Clumislry

Id ibe casevf air, it will b
bin in Uic upper region, whf
lemperature rapidly rises to
the lip of the inner and outc
by Ihe (wo inert gases, the 1:

seen IhU the finl effect ii to cool the flu»a;

B Ihe oxidising action of the oiygen is fell, Uw
maximum al a paint aboul half way lieiweeB
cones. Iq Ihe flames rendered non-liuninoiil

ghcst lemperaiiu^ is only leschcd al the outer
limil. where Ihe full amount of oiygen for combustion is obtained from [he

On account of the vide range of lemperalure exhibited by the various
regions of a Bunsen flame, it constitutes a mosl valuable analytical instiu-
menl. for by the judicious use of the difleteDl parts of the flame, it is oflsi
possible to delect Ihe presence of several iiame-colouring substances in ■
miilure. Thin, i( a mimure of sodium and potassium salts be introduced
Upon platinum wire into the cooler region of Ihe flame near its base, the more
volatile potassium compound will impart its characteristic violet lint to the
flame, before the sodium sail is volatilised sulEcieDtly to mask the colour, by
Ibe Rrotig yellow ii iiself gives to the flame. In this way many mintures may
readily be dilTerenlialed.

If a

II be seen that Ihe wire in conuci with [he edges
of Ibe flame becomes coated wilh copper onide, while the portion in the centre
remains bright. On moving Ihe vrire so as to bring Ihe oxidised portion into
the inner region, ihe oxide will be reduced, the metal once more becoming
;re oxygen is in excess, is called the
in which healed and unburnl hydro-
is the ridnciHg flame. These regions
ising action of Ihe outer flame of a
n Ihe behaviour of the wick. So long as
le flame it ii not bumi ; and in the

bright. The outer area of a
oxidiiing flanu : while the inr
gen or hydrocarbons exist, is s;
eiin in all ordinary flames,
candle, for example, is illustrated ii
Ihe wick n

arljt days al candles, as the tallow gradually consumed, the w
standing straight up, and by degrees extended into the luminous area of Ihe
flame, where, owing to the deposition of soot upon il, ii frequently developed
a eeuliflower-like acoelion. which greatly impaired the luminosity of the
flame, end which neces^laled Ihe use of snuflers. In the modem candle,
owing to a method of plaiting the wick, it is caused to bend over |as shown
in Fig. 79), and so Ihnisis its point into the oxidising region, where it is
continually burnt away.

PART III

THB SYSTBMATIO STUDY OF THE BLBMBNT8,
BASBD UPON THB PERIODIC OLASSIFIOA-
TION.

CHAPTER I

THB BLBMBNTS OP GROUP VIL (PAMILY B.)

Fluorine, F 19.06 I Bromine, Br . 79*76

Chlorine, CI . . 35.37 I Iodine, I . . . 126.54

The first to be discovered, and the most important element of the
group, is chlorine, which is a constituent of sea salt (sodium
chloride). The term halogen^ signifying sea salt producer, has
been applied to this family of elements, on account of the close
resemblance between their sodium salts and sea salt This family
exhibits, in a marked manner, many of the features which are
found to exist in most chemical families of elements.

In their general behaviour they strongly resemble one another,
and readily displace each other in combinations without producing
any very marked change upon the character of the compounds.
They each unite with hydrogen, giving rise respectively to hydro-
fluoric acid, HF ; hydrochloric acid, HCl ; hydrobromic acid,
HBr ; hydriodic acid, HI.

These hydrogen compounds are all colourless gases, which fume
strongly in the air ; they are extremely soluble in water, and are
strongly acid in character. In combination with potassium and
with sodium, the halogens form a series of compounds, which are
similarly constituted, and which closely resemble each other in their
habits. Their similarity of composition is expressed in the follow-
ing formulae —

Compounds with potassium, KF, KCl, KBr, KI.

Compounds with sodium, NaF, NaCl, NaBr, Nal.

307

308 Inorganic Chemistry

The physical properties orihc elemenls, exhibit a regular grada-
tion with JncreasidB atomic weight ; thus, fluorine and chlorine
gases, bromine is liquid, while iodine is solid, at ordinary
tures. In Iheir chemical activity they also show the same gradl
change 1 thus, in the case of their combination with hydroget^'
when fluorine and hydrogen are brought together, combination
instantly takes place with explosion, even in the dark. Chlorine
and hydrogen do not combine in the dark, but in diffused daylight
Ihey unite slowly, and in direct sunlight their combination takes
place suddenly with explosion.

Bromine vapour and hydrogen do not combine even in
sunhght, but a mixture of the two gases ignites in contact
Rame, yielding hydrobromic acid, while iodine vapour and hyt
gen require to be strongly heated in contact with spongy plalinimii]
to etTect Iheir combination. TTiis difference in the activity of
halogens towards hydrogen, is seen by a comparison of the heats
fonnation of their hydrogen compounds, thus —

adti^H
lation "^^

H + CI = Hcn

H + Br= HBr^

H + I

: HI

o cal. (Thomscn).

The heat of fonnation of hydrofluoric acid has not
determined, but there can be no doubt that it is consideraU
greater than that of hydrochloric acid.

Although a strong resemblance exists between all the membc
of the halogen family, the element fluorine, which is the tyfiim
member (see p. loo), stands marked off from the others in many q
its attributes. Thus Huorine exhibits a great tendency to forii
double salts which have no counterpart among the compounds i
the other elements of the family, and at temperatures below 3)^
the molecule of hydrofluoric acid consists of two atoms of hydrog*
and two of fluorine, having the composition H,Ft,

FLDOftnTE.

Symtoi. F. Atomi: weigtil ^ 19.06.

History.— This element, the first of the halogen series, was tl

most recent (o be discovered, it having baffled all attempti t|

Pluartne 309

isolate it until the year 1886^ when Moissan succeeded in solving
the problem.

Oceurrenee. — Fluorine occurs in considerable quantities in com-
bination with calcium in the mineral JUior spar (CaF^ which is
found in cubical crystals. On account of the occurrence of this
mineral in large quantities in Derbyshire it is frequently termed
Derbyshire spar. It is a constituent also oi cryolite^ NafAlF^^^k^^r-
apatite^ 3P|OgCa3|CaF^ and many others. In small quantities
fluorine is found in bones, in the enamel of teeth, and also in
certain mineral waters.

Mode of Formation. — When an electric current is passed into
an aqueous solution of hydrochloric acid, the acid is decomposed
into its elements, chlorine being liberated at the positive electrode,
while hydrogen is evolved at the negative. When aqueous hydro-
fluoric acid is treated in the same way, the water only is decom-
posed, oxygen and hydrogen being liberated. Davy found that the
more nearly the acid approached the anhydrous condition, the less
easily did it conduct electricity ; and that in the perfectly pure
state, that is, entirely free from water, hydrofluoric acid was a non-
conductor. Moissan's recent success in the isolation of fluorine,
depends upon the discovery that a solution of the acid potassium
fluoride, HF,KF, in anhydrous hydrofluoric acid is an electrolyte,
and that by the passage of an electric current through this solution,
fluorine is disengaged at the anode, or positive electrode, and
hydrogen is evolved at the cathode.

The primary decomposition taking place is the breaking up of
the acid potassium fluoride —

HF,KF - F, + H + K.

The atom of potassium, in contact with the free hydrofluoric acid
present, is then converted into potassium fluoride with the elimina-
tion of an equivalent of hydrogen —

K + HF - KF + H.

And the normal potassium fluoride then unites with a molecule
of the acid, to regenerate the acid salt —

KF + HF - HF,KF.

The reaction is performed in a U-tube made of an alloy of
platinum and iridium, a material which is less acted upon by the

liberated fluorine than platinum alone. The apparatus has t

aide-tubes (Fig. 85), which can be either dosed wii

or connected to platinum delivery tubes by meaos of the

The two limbs of the tube are closed by means of stoppers n

of fluor spar, shown in section at S, and which can be securdjr '

screwed into the tube. These serve to insulate the electrodes,

which are constructed of the same platinum -iridium alloy. The

anhydrous hydrofluoric acid is introduced into the apparatus, and

about 25 per cent, of its weight of the acid potassium fluoride ii

added, which really dissolves in the liquid. The tube is immerseclia

in a balh of methyl chloride (m, Fig. 86), which boils ai

supply being continuously replenished from the reservoir B, while

the vapour is drawn away by the pipe C. On passing a current

from zo 10 25 Grove's cells through the apparatus, fluorine is

evolved at the positive electrode, and hydrogen is liberated at the

negative.'

Properties.— Fluorine is, of all known elements, the most
chemically active. It is on account of its intense chemical affinities

* Fluorine hw recently besn obtained by Braunet (June 1894) by heating
tauium fluorplumbalF, 3K.F.HP,PbF,. At wo" this sail give) off hydro-
oric add. HF, and when healed to a3o*-aso* fluorine Is evolved.

■ng

Ira-

Fluorine

Ihal it so long resisted all attempis to isolate it, as when libe-
rated from combination it instantly combined with the maleriftls
of the vessels in which the reactions were made. It is impossible
to collect this gas by any of the usual methods. Tor it decomposes
water, and instantly combines wiib mercury. It also attacks glass,
so that it can only be collected by displacement of air, in vessels of
platinum. Fluorine appears to be a colourless gas, judged by the
small volume of it that can be viewed at once. The smell of the
gas is very characierisiic, ii is irritating to the mucous membranes,
and is not unlike the odour of the mixture of chlorine and chlorine

(Kroxide, evolved from potassium chlorate and hydrochloric acid.
Whether the smell actually perceived is the true smell of fluorine
is doubtful, for when fluorine comes into contact with the moisture
in the nostrils, water is decomposed, with the formation of ojonised
oxygen and hydrofluoric acid.

Fluorine not only decomposes potassium iodide, with liberation
of iodine, but also displaces chlorine from sodium chloride.

It combines directly with a large number of elements with in-
tense enerjry ; in contact with hydroprn it insianlly explode*.

312 Inorganic Chemistry

Iodine, sulphur, and phosphorus first melt, and then take Rre
fluorine. Crystals of silicon when brought into the gas, sponian^ '
ously inflame, and bum with brilliancy. All of the metals are acted
upon by fluorine ; some, when finely divided, undergoing spontane-
ous inflammation when thrown into the gas. Even gold and plati-
num are attacked by fluorine, especially if gently warmed ;
upon the latter metal being seen by the corrosion of the apparatus, |
and espeaally the positive electrode employed in its preparation.

Organic compounds are attacked by fluorine with violence, and 1
often inflamed.

When fluorine is cooled in a temperature about - iS; {i^., a. few I
degrees below the temperature of boiling oxygen, obtained bjr *
boiling the oxygen under slightly reduced pressure) it condenses
to the liquid state.* Liquid fluorine is a mobile yellow liquid,
resembling liquid chlorine. It is without action upon silicon,
phosphorus, sulphur, or glass ; it can therefore be produced and
contained in glass vessels. Even at this tow temperature, how-
ever, fluorine attacks hydrogen and hydrocarbor

HTIIBOFLDOBIC ACID.

Formula, H^, and HF. Molecular welgbt. 40 and 30. Deouty, so and ux |

Modes of Formation.— ( I.) Hydrofluoric add is produced when |
powdered calcium fluoride (fluor spar) is acted upon by strong I
sulphuric acid—

CaF, + H,SO, = CaSO, + 2HF.

This method is employed for the commercial preparation of'l
aqueous solutions of hydrofluoric acid. The mixture of fluor spar
and sulphuric acid is gently warmed in a leaden retort, and the
gaseous acid passed into water contained in leaden bottles. This
aqueous acid is sent into the market in gutta-percha bottles.

(I.) The anhydrous acid is prepared by heating hydrogen potas<

sium fluoride (acid potassium fluoride) in a platinum retort The |

double fluoride of potassium and hydrogen splits i>p into normal I

potassium fluoride, and hydrofluoric acid —

HF,KF = KF + HF.

For this purpose the perfectly dry double fluoride is placed L
a platinum retort, which is screwed to a platinum condensing J
arrangement, as seen in Fig. 87. The wooden trough through 1
which the long lube passes is filled with a freezing mixture, a
the platinum bottle is also surrounded by a similar n
• Moiiaan, May 1897.

Hydrofluoric Acid

313

Properties. — Anhydrous hydrofluoric acid is a colourless,
limpid, strongly fuming liquid, which boils at rg.j". It has a
powerful affinity for water, and can only be preserved in perfectly
stoppered platinum vessels, which are kept in a cool place. The
acid at once attacks gulta-percha. Gore found that the anhydrous
acid was without action upon glass.

Pure hydrofluoric acid is an extremely dangerous substance to
manipulate ; its vapour, even when diluted with air, has a most
irritating and injurious effect upon the respiratory organs, and i(
inhaled in the pure state causes death.

A singledropof the liquid upon the skin causes the most pajnfiil
ulcerated sores, accompanied by distressing aching pains through'

out the whole body. The metals potassium and sodium dissolve in
pure hydrofluoric acid, with the formation of fluorides and evolution
of hydrogen.

The vapour density of hydrofluoric acid at a temperature of 31*,
corresponds to the formula HjFj. As the temperaiutc is raised,
the density of the vapour falls steadily, until at 88* it is io,adensity
which is normal for the formula H F. The composition of this com-
pound, therefore, as ordinarily seen, is probably rcprescnled by ihe
formula H,F^ the molecules of which undergo dissociation when
the temperature rises, until at 88' the substance consists entirely of
the simpler molecules HF.

Gaseous hydrofluoric acid rapidly attacks glass, and ii is largely
employed for etching purposes, both for obtaining designs upon

314 Inorganic Chemistry

glass, and for ihe purpose of etching graduations upon glass mea-
suring instruments. The object to be etched is first coaled with
wax, and the design or other marks cut upon the wax by means of
a poinied sieel tool. In this way the surface of the glass is laid
bare in parts, and on exposing 'he object to the action of the acid,
either as gas or aqueous solution, the glass is rapidly eaten into,
where the surface has been exposed. Its action upon glass is
due to the readiness with which it attacks silicates, the fluorine
combining with the silicon to form silicon tetrafluoride —
SiO, + 4HF = 2H,0 + SiF,.

Crystallised silicon, when gently heated, takes fire in gaseouil
hydrofluoric acid, giving silicon fluoride and hydrogen,

Hydrofluoric acid is extremely soluble in water, fonning si
strongly acid corrosive liquid, which readily dissolves many of ■
the melals with evolution of hydrogen^

Fe + 2HF = FcF, -t- H»

Silver and copper are also dissolved by this acid.

CBLORIKB.

SjTnboL, CL Aloniic weighl, 35.37. MolrculBf weight, 70.;

History. — Chlorine was discovered by Scheele (1774), but was
regarded by him as a compound substance. He applied to it the
name of dephlo^sticattd murine acid air, having obtained it by
the action of hydrochloric acid upon ores of manganese. The
belief that chlorine was a compound of oxygen and hydrochloric
acid, was generally held until Davy's time, and gave rise lo the
name of oxymuriatic acid.

The elementary nature of chlorine was proved by Davy (1810),
who gave to it the name Morim, in allusion to the greenish -ye How
colour of the gas.

Occurrence.— In the uncombined condition chlorine does nol
occur in nature. In combination with metals, as chlorides, chlorine
is very abundant, the commonest chloride being sodium chloride
(common salt).

Many of the salts found in the Stassfurc deposits, consist largely
of chlorides (sec Alkali Melals). Chlorides of the alkali metals
are also found in animal secretions and in certain pi;
occurs in combination with hydrogen, as hydrochloric acid,
volcanic gases, and also in the gastric juice.

Modes of Formation.— ( I.) When hydrochloric acid is poured,
upon manganese dioxide, and t\it mixlvncVep^ «»\,s.4MWtT

3ured^^H

Chiorint

315

aolulion \% obtained, wbidi rapidly decompOMs M a slight Hm of
temperature with the evolution of chlorine.

It has not yet been dearly establiihed whether this brown solu-
tion consists of the compound MnCl, or Mn|CI« (brmed according
to one of the equations—

MnO, + 4HC1 - MnCl, + SH,0.

SMnO. + ana - Mn,CI, + CI, + 4H/).

When this dajic-brawn solution is gently wanned, the higher

chloride break* up into manganous chloride (MnCl^ and chlorine ;

the complete reaction being expressed by the equation—

MnO, + 4Ha - IH/) -h MnCI, + CI,.

The experiment is conveniently carried oat in the apparatus seen
in Kig. 88. The mixture of manganese dioxide and hydrochloric

as\

add is gendy heated in a large flask, and the gas, after being
passed through water in the Woulf s bottle, may be collected by
downward displacement, as shown in the figure.*

(3.) Instead of employing hydrochloric acid, the materials from
wbidi this componnd is prepared, namely, sodium chloride and
sulphuric acid, may be used. Thus, if a mixture of sodium

* S«e fi^eriaem 154, "Chemical Lecture ExfecVnmaar t

(3.) Many other highly oiygenised compounds, when acted u;
by hydrochloric acid, evolve chlorine ; thus, when crystals of potas* I
I bichromale are drenched with hydrochloric acid, and tbc ■
mixture healed, a rapid stream of chlorine takes place, thus —

(4<) When crystals of potassium chlorate are similarly treated, »M

■e of chlorine and chlorine peroxide is evolved, even without I

the application of heat—

4KCIOj + 12HC1 = 4KC1 + eH,0 + 3CIO, + 90,

(5.) Red lead CPb,0,), when treated with hydrochloric aa^;l
r similar to manganese dioxide and many olhc
pecoirides. In the case of lead, however, there is no intermedistV:!

chloride formed —

PhjOj + 8HC1 = SPbCI, + 4H,0 + CI,

(6.) Manufacturing Processes — Deacon's Process,— ThwJ

method for the preparation of chlorine, is by the oxidation of thva
hydrogen in hydrochloric acid by ainwspheric oxygen. It will h
n the foregoing methods the oxidation of Ibis hydrogei)
is carried on at the expense of the oxygen c
metallic peroxide, or the highly oxygenated salt used ; i
Deacon process atmospheric oxygen is made use of. When a
mixture of gaseous hydrochloric acid and oxygen is healed, a
slight decomposition takes place ; but if these gases be healed in
the presence of a third substance, which acts as a catalytic agent,
the decomposition of the hydrochloric acid is much more readily
effected. The catalytic agent employed in the Deacon process is
IS chloride (CtigCy. This substance is capable of taking up

ui additional qnuititjr of chlorine, and of bnng convened into
cupric chloride (CuCl^ thus—

Ca^]t + CI, - KuCV

If, therefore, a miKlure of hydrochloric add and oxygen be
passed over fraginenti of pumice impregnated with cuprous
chloride, contained in a tube which is heated to dull redness, the
hydrochloric add will be decomposed. We may suppose that the
affinity of oxygen for the hydrogen in hydrochloric acid, is un-
able to overcome the affinity existing between the hydrogen and
chlorine, but that the additional pull exerted upon the molecules
of hydrochloric add by the cuprous chloride, is suffident to dis-
turb the equilibrium and rupture the molecule —

0-"

*Cu,Clr

The result of the actkm bong H,0 + SCnCV

Fia B9.

At the temperature at which the reaction ii carried on, however,
the compound CuCl, cannot exist ; two molecules of it are con-
verted into one of Cu,Cl|, and a molecule of chlorine is evolved.
The 6nal result, therefore, of the reaction may be thus expressed —

O +■ 2Ha + CaJZlt - H,0 + CI, + Cu,Cl,.

3 1 8 Inorganic Chemistry

oiycbloilde of copper tbeu acu upon Iha hrdrochloric acid ai mm
foUawliig equBiiaos : —

(I) Cu,Clj + O = Ci^OCI^

(a) Ci^OCl, + 2HC1 = 2Cua, + HA

(3) 2CuCl, = Cu,a, + Cl*

This reaction may be made on a small scaJe by means of tlie^
apparatus shown in Fig. 89. Hydrochloric acid is generated f
salt and sulphuric acid in the flask, and a stream of the gas passed \
through the WoulPs bottle, into which also enters a stri
oxygen. The mixed gases are then passed through the bulb-tub^ \
containing fragments of pumice which have previously been soaked 1

5 solution of cupric chloride, and dried. On heating the bulb by^
means of a Bunsen flame, chlorine will issue (com the end of the-l
tube. When chlorine is manufactured on an industrial scale by J
the Deacon process, the mixture of hydrochloric acid and air fia
the proportion of four volumes of the latter to one volume of hydro
chloric acid) is drawn by means of a Root's blower first througl
iron pipes, which are heated to a temperature of about 500°,
then the hot gases pass on through the decomposer. This con!
of a cylinder of cast iron, containing masses of broken brick, o|
burnt clay, impregnated with cupric chloride, and so arran
the gases are drawn through the mnss.

Chlorine 319

The gas leaving the decomposer, consists of a mixture of chlorine,
undecomposed hydrochloric acid, and atmospheric nitrogen and
oxygen. By passing them through water, the hydrochloric acid is
removed, and the chlorine is usually converted at once into bleach-
ing-powder.

The process by which chlorine is usually nuule on a manufactur-
ing scale, is by the action of hydrochloric acid upon manganese
dioxide. The best ore for the purpose is pyrolusite. The process
is conducted in stills made of thick slabs of stone, usually '* York-
shire flag," which are fitted and luted together, and securely bound
by cast-iron clamps. Fig. 90 shows such a chlorine still, repre-
sented as cut across the centre.

The charge of manganese is placed upon the false bottom a, and
the acid is run in through the funnel tube ^, which, dipping into a
small pot, does not allow the gas to escape. As the action begins
to slacken, steam is cautiously blown in from time to time. The
chlorine escapes by the pipe g^ and passes from thence into the
main h.

The reaction that goes on in the still, is the same as that given
Above in the first mode of formation, except that as pyrolusite is
not pure MnO|, small quantities of other compounds are formed.
The following analysis, by Black, of sHll-liquor from stone stills,
shows the general composition of this substance : —

MnCl| ia57oo

Al|Cle .... 0.6200

Fe,Cl« a455i

HCl (undecomposed) . 6.6220

H|0 ... . , 81.7329

loaoooo

(7.) The Weldon Proeess, although indirectly a method for
making chlorine, is in reality a process for recovering the man-
ganese contained in the still-liquors as manganous chloride, and of
reconverting it into available numganese dioxide. The manganese
so recovered, however, is again utilised for the preparation of
chlorine by the decomposition of a further quantity of hydrochloric
acid. The essence of the process is the following : — The still-
liquor is mixed with ground chalk, or limestone dust, in large tanks
or wells, and the mixture thoroughly stirred by agitators. One of
thew wells, A, is shown in the diagrammatic figure. By this npera-

Inorganic Cfumutry

Uoo the free acid is neutralised, and the iron precipitated I
hydrated oxide. The neutral liquor, consisting of nianganoui^
chloride and calcium chloride, is then pumped into large tanks,
where it is allowed to selUe ; one of these " settlers," B, is shown
in the figTire. By means of a pipe upon a swivel-joint,/, the clear
liquid from the settler can be drawn olT wilhoul disturbing the
sediment, and run Into the oxidiser C. The oxidizer is merely a
flat-bottomed iron cylinder, open at the lop. Milk of lime trom

Fra.91,

the tank E, where lime and water are stirred logetlier, i:

into the oxidiser as required.

The milk of lime is added i:
precipitate the manganese i
Into this mixture, which c
1 hydroxide (milk of li

1 quantity more than sufficient to
i manganous hydroxide, MnH,0^
s of manganous hydroxide and
1 suspension, and to a smaller
extent in solution in the calcium chloride which is present, a
stream of compressed air is forced by means of the pipe A, whicll._

Chlorine 321

passes 10 Uic bottom of the oxidiser, where it ends in perforated
branches. During this process the manganese becomes oxidised,
and is converted mainly into calcitmi manganite, a compound of
manganese dioxide with calcitmi oxide, CaO,MnOs, or CaMnO,.
By a further addition of the neutral liquor from tank B, and by
raising the temperature within the oxidiser by injecting steam, a
portion of the calcium manganite is converted into a compound
having the composition CaO,2MnO^

When the operation is complete, the contents of the oxidiser arc
run out into a series of tanks called mud settUrs^ of which one
is shown at D in the figure. The product here settles as a thin
black mud, known as the Weldon mud; and this is ultimately
drawn from the settlers, and run direct into chlorine stills, where
it is at once treated with hydrochloric acid for the preparation
of chlorine. The Weldon stills are similar to the ordinary chlorine
stills, but are much larger, and usually octagonal in shape.

Properties. — ^^Chlorine is a greenish-yellow coloured gas, with a
strong suffocating smell. It is quite irrespirable, and if inhaled in
the pure state causes death. Even when largely diluted with air
it is extremely disagreeable and injurious, as it acts rapidly upon
the mucous membranes of the nose and throat, causing irritation
and inflanmiation, which usually result in severe catarrh. A few
bubbles of chlorine allowed to escape and diffuse into the air of a
room, give to the air a distinct and rather pleasant smell. Chlorine

is an extremely heavy gas, being ^JilZ a 2.45 times heavier than

14.44

air. One litre of the gas, measured under the standard conditions
of temperature and pressure, weighs 3.168 grammes. The density
of chlorine, taken at all temperatures, does not exactly agree with
that which is required for the molecular formula Cl|. At tempe-
ratures above 1200* the density is markedly less than theory
demands, showing that partial dissociation of the chlorine mole-
cules into single atoms has taken place. (Compare Bromine and
Iodine.)

On account of its heaviness, chlorine is readily collected by dis-
placement ; it cannot be collected over mercury, as it attacks that
metal, and in water it is considerably soluble. It may, however,
be collected over a strong brine, as it is much less soluble in this
solution than in water.

Chlorine is not inflanmiable, but it supports the combustion of
many biuming bodies. It is possessed of such extremely powerful

322 Inorganic Chemistry

chemical affinities that it acts upon a targe number of substance
at ordinary temperatures, and in many cases the combination i
sufficienlly energetic lo result in the inflammation of the bodies.
Phosphorus, when introduced into chlorine, tirst melts and then
spontaneous!/ inJIames, burning with a somewhat feeble light to
form phosphorus trichloride (PClj) and phosphorus pentachloride
(PCl^ The elements arsenic and antimony, when finely powdered
and dusted into a vessel of chlorine, at once take fire and bum,
forming their respective chlorides. Many metals, when finely
divided, or in the form of thin leaf, such as ordinary Dutch metal,
instantly lake fire when brought into chlorine. If a quantity of
sodium be heated in a deflagrating spoon until it begins to bum in
the air, and be then plunged into chlorine, the sodium continues to
bum in the gas with dazzling brilliancy, forming sodium chlotide.

Although under ordinary circimis lances chlorine unites with
metals with great readiness, it has been shown that this action will
not take place if the chlorine be absolutely dry. Thus, if chlorine
which has been completely freed from aqueous vapour be passed
into a tube containing bright metallic sodium, and the tube sealed,
the sodium not only remains bright and unaffected by the gas, but
may even be melted in the atmosphere of chlorine without any
action taking place. Similarly, dry chlorine, when allowed to enter
a flask filled with Dutch metal, has no action upon it ; but upon the
introduction of the smallest trace of moisture, the metal at once
lakes fire.* These facts are of the same order as those mentioned
in connection with oxygen, and have not yet received any satis-
factory explanation.

Chlorine is not capable of direct combination with carbon ; ordi-
nary combustibles, therefore, which consist of hydrocarbons, bum
in chlorine by virtue of the combination of their hydrogen with the
yas, and they bum with a lurid smoky flame, owing to the elimina-
nation of their carbon in the form of soot. A burning taper or
ordinary gas fiame, when introduced into chlorine, burns in this
manner, emitting a dense smoke and forming fumes of hydro-
chloric acid.

Chlorine has a most powerfiil affinity for hydrogen ; a jet of
hydrogen bums freely in chlorine, with the formation of hydro-
chloric acid. A mixture of hydrogen and chlorine unites with
explosion on the application of a flame. This combination takes
place also under the influence of light (see Hydrochloric Add),

* See Eiperiments 17^ 17;, "ClieniiciU Lecture Eiperimcnti," nei* «!■

Chlorini 323

The affinity shown by chlorine for hydrogen is seen in its action
upon many of the compounds of hydrogen and carbon. If one
volume of ethylene (CsHJ be mixed with two volumes of chlorine,
and the mixture ignited, the carbon is instantly thrown out of com-
bination as a black smoke, while the hydrogen unites with the
chlorine, forming a cloud of hydrochloric acid. Similarly, if a
liquid hydrocarbon, such as turpentine (CioHi^), be poured upon a
piece of filter paper and the paper be thrust into a jar of chlorine,
instant inflanmiation takes place, with deposition of a large quantity
of carbon.

Chlorine possesses strong bleaching properties, which depend
upon its power of combining with hydrogen, for it is an essential
condition that water shall be present. The chlorine unites with
the hydrogen of the water, and the liberated oxygen oxidises the
colouring matter. If chlorine be bubbled into liquids coloured
with any vegetable colouring matter, or if a dyed rag be dipped into
chlorine water, the colour will be rapidly discharged. Ordinary
writing-ink (which usually consists of a compound of iron with
tannic and gallic acids) is readily bleached by chlorine ; while
printer's ink, which consists mainly of carbon, in the form of lamp-
black, is not acted upon by this gas. If, therefore, a piece of printed
paper be brushed over with writing-ink so as to completely obli-
terate the print, and the blackened paper be immersed in chlorine
water, the writing-ink will be rapidly bleached away, leaving the
print unchanged.

The bleaching power of chlorine constitutes its most valuable
property from an industrial point of view ; the chlorine for this
purpose is combined with lime to form the substance known as
bleaching-powder. (See Calcium Compounds.)

Chlorine is soluble in water to a considerable extent. One
volume of water at 10* absorbs 3.0361 volumes of chlorine
measured at o* and under 760 nmi. pressure. This solution,
known as chlorine water, has the same colour as the gas, and
smells strongly of chlorine. If exposed to the air, the chlorine
rapidly diffuses out of the solution. Chlorine water cannot l)e
preserved for any length of time, as it slowly undergoes de-
composition, the chlorine combining with the hydrogen of the
water, fonning hydrochloric acid, which remains in solution, and
the oxygen being liberated, thus —

H,0 + CI, - iHCl + O,

324 Inorganic Oumistry

This action, which proceeds slowly under ordinary conditions,
is greatly accelerated by the influence of light, and if exposed
to direct sunlight the decomposition is very rapid.

If chlorine water be cooled to within one or two degrees of the
freezing-point of water, or if chlorine be passed into ice-cold water,
a solid crystalline compound of chlorine with water is deposited.
This substance is termed chlorine hydrate^ and has a composition
expressed by the formula Cl2,10HsO. The compound is very un-
stable, and when exposed to the air it melts and rapidly gives off
chlorine. If the crystals are quickly freed from adhering water,
and are then sealed up in a glass tube, they may be heated to
a temperature of 38° before being decomposed. Faraday made
use of this compound in order to obtain liquefied chlorine. A
quantity of the hydrate was sealed up in one limb of a bent
tube and was gently warmed, the compound dissociated into
water and chlorine, and the internal pressure caused the condensa-
tion of the chlorine to the liquid condition.

Liquid Chlorine. — Under the ordinary atmospheric pressure,
chlorine may be liquefied by lowering its temperature to - 34*.

At a temperature of 0° the pressure required to effect its lique-
faction is equal to six atmospheres. When, therefore, the liquid
is obtained by heating the crystalline hydrate, as in Faraday's
method, one limb of the tube should be cooled by being placed
in ice.

The critical temperature of chlorine is 141°, and the pressure
required to effect its liquefaction at that point, or its critical
pressure, is 84 atmospheres. (See Liquefaction of Gases.)

Liquid chlorine has a bright golden yellow colour, entirely free
from the greenish tint possessed by the gas. Its specific gravity
is 1.33, and it boils at -33.6*. When cooled to a temperature
of -102, it freezes to a yellow crystalline mass. Liquid chlori ne
is now an article of commerce. It is contained in iron bottles
lined with lead, and is largely exported in this form, for use in the
extraction of gold, to parts of the world where the carriage of the
plant and materials necessary for generating large quantities of
chlorine, would be attended with great difficulties.

ffydrocklaric Acid

HTDBOOHLOBIO ACID {/fydn>tin CUtruU).
Formula. HCL Molecular wright = 36.37. Deniit]' = iS-iBs.

History.— In solution in water, this compound was known to
the early alchemists, and the mixture ot this solution with nitric
acid constituted the valued liquid known as agua rtgia. The
preparation of hydrochloric acid from common salt is associated
with the name of Glauber (i6so), who obtained it by the action
of sulphuric add upon sodium chloride (common salt). Gaseous
hydrochloric acid was first collected and examined by Priestley,

who collected it over mercury, in the mercurial pneumatic trough
invented by him. He named the gas mariiu add air.

Oecurrenee.— Caseous hydrochloric acid is evolved in consider-
able quantities from volcanoes during active eruption.

Modes of Formation. — (t.) Hydrochloric acid may be syn-
thetically produced directly from its elements ; thus, this compound
is formed when a jet of hydrogen is caused to bum in an atmos-
phere of chlorine. If a mixture of chlorine and hydrogen be
ignited, the union takes place instantaneously with explosion, and
hydrochloric acid is produced. The union of hydrogen with
chlorine will also take place under the inQuence of light ; thus, if a

320

Inorganic Chemistry

"e of these two gases be eiposed to even diffused daylight
a few hours, the greenish colour imparted to the mixture by
chlorine will gradually disappear, and on examination it is fc
that the tube contains hydrochloric acid. This combination, w
is only gradual when the mixture is exposed 10 diffused dayli
becomes eiplosively sudden if the mixed gases are exposed
direct sunlight, or any artilicial light which is ridi in rays of hi
refrangibiliiy — the so-called actinic rays. If, therefore, a
vessel be filled with a mixture of these gases in
I volumes, and the mixture be placed in bright suoshii
^ a violent explosion will result, and hydrochloric acid
P be producei This phenomenon is best illustrated
I filling small thin glass bulbs with a mixture ofihe '
< gases obtained by the electrolysis of aqueous hydrochli
acid. The bulbs when filled can be hermetically s
before the blowpipe without causing the combinati
the gases,'* and if kepi in the dark may be pieservi
indefinitely.

On exposing one of these bulbs to the light of bum!
magnesium, the combination of the two gases insla
takes place, with a sharp explosion, which shatters
bulb to powder. The bulb should therefore be screei
as shown in Fig. 92.

The rays of light which are capable of causing
combination are those which compose the blue and vi
end of the spectrum ; if these particular rays are absorl
from the light by means of ruby glass,
gases may be exposed to the red light so obtained wil
out any action taking place-t

The combination of chlorine with hydrogen
attended by any alteration in volume \ one voltune
Fig. 93. chlorine combines with one volume of hydrogen, and
the resultant hydrochloric acid occupies two volumes.
This may be readily proved by filling a stout glass lube, provided
with a stop-cock at each end, with a mixture of the two gases
in exactly equal volumes, and causing them to combine either by
the influence of light, or by the passage of an electric spark by
means of the platinum wires sealed into the tube (Fig. 93). On
opening one of the slop-cocks under mercury, it will be seen

■' Chemical Lecture Experiments," new ed.

)■ On I

Hydroddorie Acid 327

no mercury is dntmi in, ndUier does any gu pass out from the
tube, thus showing that the union has taken place without any
alieralion in the volume. If one of the cocks be now opened
beneath water, the hydrochloric acid which has resulted from the
union of the hydrogen and chlorine, being extremely soluble in
water, the liquid will rush up into the tube and completely fill it,
showiug that no free hydrogen or chlorine remains in the tube.

(3.] For all ordinary purposes, hydrochloric acid is always obtained
by the action of sulphuric acid upon sodium chloride. For labo-
ratory uset the apparatus seen in Fig. 94 may be couveoiently

Fio. 94.

employed. Sulphuric acid, previously diluted with rather less than
its own volume of water, is placed in the flask, and a quantity of '
common salt is added. On the application of a gentle heat a
steady stream of gas is evolved, which may be dried by being
passed through the tubulated bottle, containing pumice moistened
with strong sulphuric acid. The gas is then collected either over
mercury, or by displacement The reaciion which takes place
is expressed by the equation —

NaCI + H^O, - NaHSO, + HCL
If strong sulphuric add be employed along with an excess
of salt, both of the atoms of hydrogen can be displaced from
the acid; and instead of the hydrogen sodium sulphate, iher*
is formed the normal sodium sulphate —

9Naa -I- H^O, - Na^Ot + SHCL

J28

Inorganic Chemistry

htr icinperature is necessary in ordcf to coi
the reaction indicated by this equalioo.

Properties,— Hydrochloric acid is a colourless gas '
choking, pungent odour. In contact wllh the moist air il
dense fumes, consisting of minute globules of a solution
gas in the atmospheric aqueous vapour. Hydrochloric acii
not bum, neither does il support ordioary combustion.

Il is heavier than .lir, its specific gravity being—

■ .=5 (.»

■).

Hence llic gas is readily collected by djsph
ilie gas weighs 18.1 E5 criths.

Hydrochloric acid is extremely soluble i
water at o* and under a pressure of 760 r
solving 503 volumes of gaseous hydrochio
o' and 760 mm. As the temperature rises the solubility di
as seen by llie following table : —

water ; i volume e
II. is capable of dis^l

z acid, measured a

503

364

The solubility of hydrochloric acid may be illustrated by c
plelely filling a large globular flask with the gas, by displacem
Ihc flask being provided «nth a long tube passing through the ci
as seen in Fig. 95. On opening this tube beneath water, the
begins to dissolve, and the liquid rises slowly in the lube until %
reaches ihe top. As soon as the first few drops enter ihe globf
Ihey rapidly absorb the gas, thereby causing a partial vai
._4!jt vessel, so that the water is driven up the lube with consider
""*e force, forming a. fountain, which continues until the globe h
iriy filled with liquid. If the water in the dish is reridcrcd bllM
^the addition of litmus solution, the acid nature of the solutioB
of Ihe gas will be evident by the reddening of the liquid a
enters the globe.

When a weak aqueous solution of hydrochloric acid is boiloc^J
it loses water and becomes stronger [ while, on the other haad,9
if a strong solution be healed, it loses gas and becomes weaker|V
until in both cases an acid containing 20.24 P^r cent, of HCl u
produced which boils at 1 10°. This sireng^th of acid correspond

HydrocUoric Acid 339

to a composition expiejsed by the fonnula HCI + 6H,0, and it
was at one time supposed to represent a definite compound.
Roscoe and Dittmar have shown, however, that, as with nitric
acid, the composition of the liquid which boils at a constant
temperature is simply a function of the pressure.

The strongest aqueous solution of hydrochloric acid at ij* C.
has a specific gravity of i.iri, and contains
41.9 per cenL of HCI.

Hydrochloric acid gas is readily lique-
fied by pressure. At a lemperalure of 10°
a pressure of 40 atmospheres will effect
its liquefaction. If the temperature be
lowered to -16*, the same result is ob-
tained by a pressure of 10 atmospheres.
The critical temperature of hydrochloric
acid is 51,3'.

Condensed hydrochloric acid is .1 colour*
less liquid. Gore has shown that this
liquefied add is without action on most
of the metals which are readily dissolved
by the aqueous acid.

The composition of hydrochloric Acid
may be experimentally proved by a num-
ber of methods. It may be shown synthetically by the volumetric
experiment referred to above (page 336).

Thevolumetric proportion of hydrogen contained in the gas may
be shown by means of sodium amalgam. The sodium in the
amalgam, acts upon the hydrochloric acid, combining with the
chlorine, and liberating the hydrogen —

Na + HCI - NaCl -I- H.

For this purpose gaseous hydrochloric acid is introduced into one
limb of [he U-shaped eudiometer (Fig. 96), and its volume indicated
by means of a ring upon the tube, the mercury being level in both
limbs. A second ring marks exactly half the volume. A quantity
of liquid sodium amalgam is then poured into the open limb until
it is completely filled, and on being dosed by the thumb the tube
can be inverted so as to decant the gas into this limb.* Afler being
bubbled once or twice through the amalgam, the gas is again
returned to its fbimer place ; and by drawing mercury from the

Flags-

branch tube, the levels in each limb c&a be again adjusted, when it

will be found that the gas remaining in the lube occupies t1
rtactly down lo the upper ring, that is lo say. two volumes o
hydrochloric acid contain one volume of hydrogen. That the
is hydrogen can be shown by again filling up the open limb w
mercury, and driving the gas out of the stop-cock, where it can b
inflamed as it escapes.

FK3. 96.

P1C.9S.

The faa that hydrochloric acid contains the same volume ot
chlorine as of hydrogen, may also be demonstrated by collecting
the mixed ^ases, evolved by the electrolysis of the aqueous add, JD
a long tube provided with a stoppered funnel, as shown In Fig. 97.
The gases may be collected over a saturated solution of salt in
wat er, and the lube filled to the tower ring. On allowing a solution
of p otassium iodide to enter by means of the fiinnel, the chlorine it

Hydrochloric Acid 331

absorbed with the liberation of iodine, which partially dissolves
and partly separates as a solid. When the absorption of the
chlorine is complete, the water will have risen to the second band
placed half way up the tube, showing that one-half of the gaseous
mixture consists of chlorine. The former experiment proved that
hydrochloric acid contained half its volume of hydrogen, therefore
the two elements, in uniting to form this compound, do so in equal
volumes and without any contraction in volume.

When aqueous hydrochloric acid is subjected to electrolysis, the
hydrochloric acid is decomposed, hydrogen being evolved at the
negative electrode and chlorine at the positive. At first the
liberated chlorine is dissolved in the solution ; but after the liquid
has become saturated with the gas, the whole of the chlorine is
liberated. By conducting this decomposition in the apparatus
seen in Fig. 98, and continuing the passage of the electric current
until the liquid in one limb is saturated with chlorine before closing
the stop-cocks, it will be seen, when the gases are collected in the
tubes, that they are evolved in equal volumes.

The Hanufaetare of Hydpoehlorie Aeid. — The aqueous
solution of hydrochloric acid is an object of commercial manu-
facture, which is carried out on an enormous scale. It is obtained
by the decomposition of conunon salt by means of sulphuric acid,
according to the reaction —

SNaCl + H,S04 = Na,S04 + 2HC1.

Formerly hydrochloric acid was a waste product obtained in the* manufacture
of sodium carbonate by the method known as the Lehlanc process ; the first
stage in this process being the conversion of sodium chloride into sodium
sulphate, by the action upon it of sulphuric add. The hydrochloric add
evolved as gas in this reaction was idlowed to escape into the atmosphere.
The nuisance caused by this acid gas being thrown into the air, ultimatdy
resulted in the "Alkali Act," which compelled manufacturers to absorb this
waste add. Since that time, the Leblanc process for the manufacture of sodium
carbonate has had a formidable rival in another method, known as the
ammonia-soda process (see Sodium Compotmds), which would probably have
completely driven the older method out of the field, but for the commerdal
value of the hydrochloric add which is obtained as a secondary product in
the Leblanc process. The hydrochloric acid, therefore, which formerly was
thrown away as a waste product, is now the salvation of the process, and the
utmost care is taken to prevent any of it from escaping, not now by com-
pulsion of the Alkali Act, so mudi as from purdy economic reasons.

The charge of salt and sulphuric add is heated in an enormous
hemispherical cast-iron pan, built into a brickwork chamber, so

332

f'lorganic Ckrmistry

tliat II can be healed by 3 lire bcncalli, and so that the evolved
gas can be conveyed aivay by brick or earthenware flues. The g
evolved by the reaction, is led into (oweis which are filled with coke'l
or bricks, and down which water is made to percolate ; thi
being caused to flow cquaJly over the mass, by means of specMl J
distributing contrivances. As the gaseous hydrochloric acid p
up the towers and meets the descending stream of water,
entirely dissolved, and tbe aqueous acid becomes nearly saturatedl
as it reaches the bottom of the lower.

In works where the condensers, or towers, are not of great'1
height, it is usual either to cool the gas before admiiting it int

Fia. 99.

Ihc towers, or 10 pnss it through a
gigantic Woulfs bottles (Fig. 99).

The water in these bottles is m.ide to flow steadily from one to
the other by tbe side pipes c, c (in the direction from left to right),
while the gas passes through the system in the opposite direction.
In this way a constantly changing surface of water is exposed lu
the gas, and a very strong solution is obtained.

Commercial hydrochloric acid is generally yellow in colout^ |
owing 10 the presence of iron as an impurity ; and it is always^
liiible to contain sulphuric acid, free chlorine, arsenic, and s
times sulphur dioxide. This aqueous solution of hydrochloriofl
acid is also known under the names of "spirits of salt," ■

Chlorint Monoxide 333

OXIDES AND OXY ACIDS OF CHLORINE.

The elements oxygen and chlorine have never been made to
unite together directly : two compounds, however, of these elements
can be obtained by indirect methods ; these are —

Chlorine monoxide (hypochlorous anhydride) Cl^O.

Chlorine peroxide CIO,.

Three oxyacids are known, viz. : —

Hypochlorous add HCIO.

Chloric acid HClOj.

Perchloric acid HCIO4.

CHLORINE MONOXIDE {Hyf^hhrous anhydride^
Formula, C1|0. Molecular weight = 86.7a Density = 43.35.

Mode of FormatiGll. — This compound is obtained by passing
dry chlorine over dry precipitated mercuric oxide contained in a
glass tube, the temperature of which is not allowed to rise. The
chlorine combines with the mercuric oxide, forming mercuric oxy-
chloride, and chlorine monoxide is liberated —

2HgO + 2C1, - HgO,HgCl, + C\fi.

Properties. — At ordinary temperatures chlorine monoxide is a
pale yellow gas, without the greenish tint possessed by chlorine.
Its smell strongly suggests chlorine, but is readily distinguishable
from it It is a very unstable compound, decomposing with more
or less violence with moderate rise of temperature. When strongly
cooled it is condensed to an orange-yellow coloured liquid, which
boils at about - 20*. This liquid is extremely unstable, exploding
with great violence on the gentlest application of heat, and some-
times on merely being poured from one vessel to another. When
exposed to direct sunlight it also explodes with violence.

Gaseous chlorine monoxide is considerably soluble in water, one
volume dissolving about 100 volumes of the gas, forming hypo-
chlorous acid —

CUO + H,0 - 2HC10.

InorgMtit Chemiitry

OHLOBINE FEBOZmE.

Formula. CIO, Molecular weight = 67.99. Ucnsilf = 33.^S

Modes of Formation.— (1.) By the action of sulphuric acid U|
potassium chloraie —

3KC10, + 2H,S0, = KCIO, + 8HKS0, + H,0 + SCIO^

Finely powdered potassium chlorate is added little by little n
concentrated sulphuric acid in a small retort The salt dissolve
wilh the formation of a reddish liquid, and if the temperature il
not allowed to rise, no gas is evolved. On very cautiously wann*^
ing the reion by means of warm water, taking care not to bcat.l
the glass above the level of the liquid in the retort, the chlorioe I
peroxide is evolved.

(j.) A mixture of chlorine peroxide and carbon dioxide, in equal fl
volumes, is obtained by heating a mixture of powdered potassiiual
cliloraie and oxalic acid to a temperature of 70° in a waicr-bath—

2KC10, + 2H,C,Oi - K,C,0, + aH,0 + 2C0j + SCIO^

(3.) Chlorine peroxide, mixed with chlorine, is evolved by ti
action of hydrochloric add upon potassium chlorate—

4KC10, + 12HCI = 4KC1 + 6H,0 + 9CI + 300,.

This mixture ol gases was formerly supposed to be a definiitj
compound of oxygen and chlorioe, and received the i
tuchlorine.

Properties,— Chlorine peroxide is a heavy gas, with a dec
yellow colour. It h". an intensely unpleasant smell, and if u
baled, even when largely diluted with air, produces headactM
The gas attacks itiercuiy, and is soluble in water, so that il
only be collected by displacement. Chlorine peroxide is an exill
tremely unstable cojupound, it is gradually resolved into its ele*J
ments by the influence of light ; the passage of an electric sparl^fl
or ihe introduction into il of a hot wire, causes it to decompc
with violent explosion. It is a powerful oxidising compound ;
piece of phosphorus introduced into the gas takes fire sponti
ously. If a jet of sulphuretted hydrogen be lowered into a jar flj

Hypochlarous Acid 335

chlorine peroxide, the sulphuretted hydrogen ignites spontaneously,
and continues burning in the gas.

Its oxidising action upon organic matter, may be shown by
liberating the gas in the presence of such a substance as sugar,
by adding a drop of sulphuric acid to a mixture of powdered sugar
and potassium chlorate. The chlorine peroxide, liberated by the
action of the acid upon the chlorate, ignites the mixture, and the
entire mass then bursts into flame.

When chlorine peroxide is strongly cooled, it condenses to a
dark red liquid, which is even more explosive than the gas.

HTPOCHLOBOUS ACID.

Formula. HC-O.

Modes of Formation. — (i.) As already mentioned, this acid is
formed when chlorine monoxide is dissolved in water.

(2.) It may readily be obtained in dilute solution, by passing an
excess of chlorine through water in which precipitated mercuric
oxide is suspended —

HgO + HgO + 2C1, = HgCl, + 2HC10.

On distilling the liquid, the dilute acid passes over as a colourless
distillate.

(3.) In dilute solution, hypochlorous acid may be obtained by the
decomposition of a hypochlorite by a very dilute mineral acid, and
subsequent distillation of the mixture ; thus, if to a solution of
calcium hypochlorite (obtained by treating bleaching-powder with
water and filtering the solution) very dilute nitric acid be added
and the solution distilled, a dilute colourless acid is obtained —

Ca(C10), + 2HNO3 = Ca(NO,), + 2HC10.

(4.) This compound is also fonned, when a stream of chlorine is
passed through water containing precipitated calcium carbonate in
suspension —

CaCOs + H,0 + 2C1, « CaCl, + CO, + 2HC10.

Properties.— Pure hypochlorous acid, free from water, has
never been obtained. The add produced by the solution in water
of chlorine monoxide, has a pale straw-yellow colour, and a very

336 Inorganic Chemistry

characteristic chlorous smelL Dilute solutions of this acid are
moderately stable, while more concentrated solutions readily
undergo spontaneous decomposition.

Hypochlorous acid is a powerful oxidising and bleaching agent,
as it readily gives up its oxygen, and is resolved into hydrochloric
acid— -

HCIO = HCl + O.

As an oxidising agent it is twice as effective as an equivalent
quantity of chlorine in chlorine water, for two atoms of chlorine are
liere necessary for the liberation of one atom of oxygen —

CI, + H,0 = 2HC1 + O.

Hypochlorous acid is decomposed by hydrochloric acid, with
the evolution of chlorine —

HCIO + HCl =. HjO + CV

It is also decomposed by silver oxide, oxygen being liberated —

Ag,0 + 2HC10 = 2AgCl + H^O + O,.

The salts of hypochlorous acid may be obtained by the action of
the acid upon the hydroxides of the metals ; thus —

HCIO + KHO = KCIO + H,0.

The most important salt of this acid is bleachirt^r. powder (sec
Calcium Salts).

CHLORIC ACID.

Formula, HClOj.

Mode of Formation.— This compound is best obtained, by
decomposing barium chlorate with an exact equivalent of sulphuric
acid, previously diluted with water —

BaCClO,), + H2SO4 = BaSO* + 2HCIO3.

The clear liquid is decanted from the precipitated barium sul-
phate, and is then concentrated by evaporation in vacuo.
The strongest acid that can be obtained still contains 80 pei

Perchloric Acid 337

cent of water. Attempts to concentrate it further, result in its
decomposition into free chlorine and oxygen, with the formation of
perchloric acid and water.

Properties. — The strong aqueous acid has powerful oxidising
properties ; many organic substances, as wood or paper, are so
rapidly oxidised by it that when the acid is dropped upon them
they are frequently inflamed.

The acid even in dilute solution has strong bleaching powers.

The salts of chloric acid are far more stable than the acid, and
some of them are of considerable technical importance. The
chlorates are all soluble in water, and all yield oxygen on being
heated. Chloric acid is a monobasic acid ; the chlorates, there-
fore, have the general formula M'ClOj and M'(C105)^ where* M'
and M' stand for monovalent and divalent metals respectively.

Of all the chlorates, potassiiun chlorate, KClOs, ^^ by far the
most important (See Potassium Compounds.)

PERCHLORIC ACID.

Formula, HQO4.

Mode of Formation. — Perchloric acid is best prepared, by the
action of strong sulphuric acid upon potassium perchlorate—

2KCIO4 + H,S04 - K,S04 + 2HCIO4.

Pure and dry potassium perchlorate is mixed with four times its
weight of concentrated sulphuric acid, and the mixture gently dis-
tilled in a small retort The distillate at first consists of perchloric
acid ; but as the operation proceeds, a portion of the perchloric acid
is decomposed into lower oxides of chlorine, and water, and the
latter, combining with the first portions of the distillate, forms a
white crystalline compound, having the composition HClOfyH^O.
This body, when gently heated, gives ofT perchloric acid ; it may,
therefore, be employed for the preparation of the acid in a state of
purity.

Properties. — Perchloric acid is a colourless, volatile, and strongly
fuming liquid, having a specific gravity of 1.782 at 15*. It is an
extremely powerful oxidising substance ; a drop of the liquid
allowed to fall upon paper, wood, or charcoal is instantly decom-
posed, sometimes with a violent explosion. In contact with the

338

Inorganic Cfumistry

skin it produces most painful wounds ; when allowed to drop xnXp
water it produces a hissing sound, owing to the energy of the
combination.

Perchloric acid cannot be preserved, as it slowly decomposes
even in the dark, and often explodes spontaneously.

The salts of this acid are the pcrchloratcs, of which the most
important is potassium perchlorate ; they are all soluble in water.

Constitution of the OxideB and Ozyacidi of Chlorine.— On the assump-
tion that chlorine is a monovalent element, the constitution of these compounds
may be thus represented : —

Chlorine monoxide, CI - O - CL I Hypochlorous acid, CI -O - H.
Chlorine peroxide, CI- 0-0-. I Chloric acid, a-O-O-O-li.

Perchloric acid, Cl-O-O-O-O-^H.

It is possible, however, that in some of these compounds the chk>rioe
functions as a trivalent element, and that these compounds have a constitutioo
similar to the oxides and oxyacids of nitrogen, thus —

Chlorine monoxide, CI - O - CL
Chlorine peroxide,

[ide, — Cl^ I .

' — — '-'» — - "^ ^

tide, -n/| .

Hypochlorous acid, CI - O - H.

Chloricacid. II-O-Cl^ |.

Nitrogen monoxide, N -O - N.
Nitrogen peroxide,
Ilyponitrous acid, N - O - 1 1.
Niuic acid, H - O - n/^ | .

Perchloric acid. H - O - CI

I'hcrc are several facts which point to the belief that not only chlorine, but
also bromine and iodine, are capable of fulfilling the functions of a trivalent
element. The existence, foi example, of such a compound as trichloride of
iodine, ICls, is difficult to explain on any other assumption than that iodine is
here a trivalent element.

Indeed, from a consideration o( the salts of periodic acid, some chemists are
in favour of assigning to iodine even a still higher valency, and of regarding it
as a bcptad element in these compounds (see Periodates, page 356). The
constitution of such molecules as those of hydrofluoric acid at low temperatures,
namely, H,F,, and of the acid fluoride of potassium. HF,KF, is readily
understood if we regard the fluorine as fimctioning ii: these compounds as a
trivalent element, thus —

H-F = F-H. andH-F=F-K.

Bromine 339

BROMINE.

Symtiol, Br. Atomic weight = 79.76. Molecular weight = 159.5a.

Vapour density = 79.76.

History. — This element was discovered by Balard (1826), in the
mother-liquor obtained after the crystallisation of salt from con-
centrated sea-water. He applied the name bromine (si^^ifying a
stench) to the element, in allusion to its unpleasant smell.

Occurrence. — Bromine is never found in the uncombined state
in nature. In combination chiefly with the metals potassium,
sodiiun, and magnesium, it occurs in small quantities in all sea-
water, and more abundantly in many mineral waters and salt
springs. The saline deposits of Stassfurt contain notable quantities
of bromides, and the main supply of bromine for the market is
manufactured from this source.

Modes of Formation.— { I.) Bromine may be obtained from a
bromide by displacement with chlorine. If to a solution of mag-
nesium bromide, chlorine water is added, the chlorine combines
with the magnesium and the bromine is liberated —

MgBr, + CI, - MgCl, + Br,.

On distilling the liquid the bromine is driven off, and can be
collected in a well-cooled receiver. The addition of any excess of
chlorine results in the formation of bromide of chlorine, and is
therefore to be avoided.

(2.) Bromine is readily obtained from potassium bromide by the
action of manganese dioxide and sulphuric acid, a reaction exactly
analogous to that by which chlorine is obtained from sodium
chloride —

2KBr + MnO, + 2H,S04 - MnSO^ -h K,S04 -h 2H,0 -h Br,.

The mixture is gently distilled from a retort into a receiver kept
cold by means of ice.

(3.) Manufacturing Methods. — Practically all the bromine
that is required at the present day, is manufactured from crude
camallite obtained at Stassfurt (see Alkali Metals). This salt
contains bromine combined with magnesium, the magnesium
bromide forming about i per cent of the magnesium chloride in
the crude substance. The final mother liauors from the manuiac-

340

Inorganic Chemistry

ture of potassium chloride, and which were formeriy nin to waste,
are found to contain about .25 per c^t of bromine as magnesium
bromide, and these liquors are now utilised for the manufacture of
bromine.

The bromine is liberated from its combination with magnesium,
by means of chlorine. In some processes, the mother liquor is
mixed with manganese dioxide and sulphuric acid in a stone vessel

^^M^

BBSOOOO0

■ ■III

J — C

«v

(!=

=~ Stmm

:— CI

=•;

Fig. 100.

resembling an ordinary chlorine still. The magnesium chloride in
the liquor, is acted upon by the manganese dioxide and sulphuric
acid with the evolution of chlorine, and this decomposes the
bromide present, displacing the bromine —

MgCl, + MnO, + 2H,S04 = MnS04 + MgS04 + 2H,0 + CI,.

MgBr, + CI, = MgCl, + Br,.

The bromine that is driven out, is condensed by means of a worm
condenser.

Bromifu

341

Injteail of the chlorine being generated within the mother liquor,
it is now more usually produced in a separate chlorine still, and
passed into the liquor. Fig. too shows in diagranimatic form the
method employed The hot mother liquor is admitted by the pipe
A ioto the lower T, which is Riled with earthenware balls, between
which the liquid percolates. It leaves the tower by the pipe B,
and flows into the tank W, which is provided with shelves in such
a way that the liquid must circulate through it in the direction
indicated by the arrows. The exit-pipe from this tank, empties
into a waste, placed at such a height that the tank is always nearly
fiilL The liquid in the tank is kept at, or near, the boiling-point, by
means of a current of steam blown in through S. Chlorine from a

still is admitted by the pipe L, and passing into the tower by the
pipe B, travels in an opposite direction to the current of liquid.
As the chlorine passes up the tower, it meets the descending mother
liquor, and decomposes the magnesium bromide contuned in it
with the liberation of bromine. The bromine vapour leaves the
tower by the pipe C, and is conveyed to a worm (Fig. loi), where it
is condensed. Any bromine which dissolves in the water in the
lower, is i^ain expelled from solution by the steam as the liquid tra-
verses the tank W, and is swept up into the tower by the currentof
chlorine. Thecondensedbromine,asit leaves the worm, is collected
in a tubulated bottle, and any vapour which escapes condensation

342 Inorganic Chemistry

is arrested by the vessel F, Fig. loi. This tube is filled with iron
borings, kept moist by the constant dropping of water upon them,
and any bromine, or bromide of chlorine, is there converted into
iron compounds, which are dissolved by the water, and flow away
into the receiver. The bromine is purified by redistillation.

Properties. — Bromine is a heavy but mobile liquid, of a deep
reddish-brown colour. Except in extremely thin layers it is opaque.
It is the only non-metallic element which is liquid at the ordinary
temperature. Bromine boils at 59*, but being a very volatile liquid
it gives off vapour rapidly at the ordinary temperature. A drop of
bromine allowed to fall into a flask, inunediately evaporates and
fills the vessel with a dark red-brown vapour. The specific gravity
of the liquid at o^ is 3.188. At - 7* bromine solidifies to a crystal-
line mass. Bromine has a powerful and disagreeable smell. When
the vapour, largely diluted with air, is inhaled, it suggests chlorine
by its smell and by its action upon the mucous membrane of the
throat and nose ; it has in addition, however, a most irritating
action upon the eyes. It is very poisonous, and the liquid exerts a
corrosive action upon the skin ; it produces a yellow colour when
brought in contact with starch.

The vapour density of bromine, taken at moderately high tem-
peratures, gradually becomes less than is demanded by the formula
Br^ showing that dissociation takes place. In the case of bromine
this is more marked than with chlorine.

Bromine is soluble in water, imparting its own colour to the
solution which is known as bromine water, 100 granunes of water
at o* dissolve 3.60 grammes of bromine. The solubility steadily
diminishes as the temperature rises : at 20* it is 3.208, and at 30*
it is 3.126.

When bromine water is cooled to o* it deposits a crystalline
hydrate similar in composition to the hydrate of chlorine, Br2,10H,O.

Bromine resembles chlorine in its chemical attributes ; it com-
bines directly with metals and many other elements, although with
less energy than is exhibited by chlorine. A fragment of arsenic,
for example, when dropped upon bromine, ignites and bums upon
the surface of the liquid.

Like chlorine, it has bleaching properties, due to its power of
combining with hydrogen.

Hydrobromic Acid 343

HTDROBROMIC ACID.

Formula, HRr. Molecular weight s 80.76. Density = 40.38.

Modes of FormatiOlL — (i.) Hydrobromic acid can be obtained
by the direct union of its elements. Bromine vapour and hydrogen,
when mixed, do not combine under the influence of light ; neither
does such a mixture explode when a light is applied to it. The
mixture, however, may be caused to bum, when hydrobromic acid
is formed ; or, if the mixed gases be passed through a red-hot tube,
the same result follows. A simple method of preparing hydro-
bromic acid synthetically, consists in passing a mixture of hydrogen
and bromine vapour over a spiral of platinum wire, maintained at a
red heat by means of an electric current*

(2.) The best method for the preparation of gaseous hydrobromic
acid) consists in dropping bromine upon red phosphorus which has
been moistened with a small quantity of water, when tribasic
phosphoric acid is formed, and hydrobromic acid is liberated —

P + 4H,0 + 5Br = H5PO4 + 6HBr.

We may suppose that in this reaction the bromides of phosphorus
are formed and simultaneously decomposed, the action of water
upon these compounds being thus expressed —

PBrj + 3HP - H3PO3 + 3HBr.
PBrj + 4H,0 = H3PO4 + 5HBr.

(3.) Hydrobromic acid may be obtained by the action of phos-
phoric acid upon potassium bromide —

3KBr + H3PO4 - K3PO4 + 3HBr.

(4.) If sulphuric acid be employed (as in the formation of hydro-
chloric acid from a chloride), free bromine is simultaneously pro-
duced, owing to the reduction of a portion of the sulphuric acid
by the hydrobromic acid which is first evolved, thus —

H,S04 + 2HBr = SO, + %\\fi + Br^^.
(5.) A dilute aqueous solution of hydrobromic acid may also be

* See "Chemical Lecture Experiments," new ed., Na 225.

nic ChtmUtry

■\ of sulphuretted hydrogen thronj

SH, + Br, = S + 2HBr.

(6.) Hydrobromic acid is readily obtained, by the
bromine upon certain hydrocarbons, such as turpentine
paratlin. The action is one of substitution, one atom of bromi^
replacing one alom of hydrogen in the compound, and the hydro
so displaced combining with a second bromine alom to form h
bromic acid Thus, if the hydrocarbon be represented by t
general formula, CnHso + !, the action of bromine will be r
sen led thus —

CoHan +

= CnHan + iBr+ HBr.

Properties.— Hydrobromic acid is a colourless, pungent-smel-
ling gas, which fumes strongly in the air. It is extremely soluble
in water, forming an acid liquid strongly resembling aqui
hydrochloric acid.

When boiled, this solution loses either acid or water, until
reaches a degree of concentration al which it contains 48 per
of hydrobromic acid. The acid of this strength then
boil unchanged at 126°. As with hydrochloric acid, the
of the liquid which boils at a constant temperature, depend'
the pressure.

Hydrobromic acid is decomposed by chlorine, with the liberatii
of bromine —

2HBr + CI, = 2HCI + Bi

In its chemical behaviour, hydrobromic acid closely resembles
hydrochloric acid, and this resemblance is extended to the bromides.
All bromides are soluble in water, except mercurous bromide
silver bromide, and lead bromide, the latter being slightly soiubl

ng aqueoi^^^H

until j^^l
per <:b^^^H

hTsr.^rg^H

:pend5 upi^^^H

le liberati^^^^l

OXYAC!D& OF BROMINE.

No oxides of bromine corresponding with the oxides of c
have as yet been obtained ; two onyacids, however, are knom

Hxpobramous Aeid 345

HTPOBBOMOUB ACID.

Formula, HBrO.

Mode of FomiatioiL — An aqueous solution of hypobromous
acid may be obtained, by shaking together a mixture of bromine
water and precipitated mercuric oxide, the reaction being ana-
logous to that by which hypochlorous acid is prepared —

HgO + H,0 + 2Br, - HgBrj + 2HBrO.

Properties. — Hypobromous acid is an unstable compound ; it
breaks up on distillation into oxygen and bromine. By heating to
40* in vacuo, however, it can be distilled without decomposition.
The aqueous liquid so obtained has a pale yellow colour. It
readily gives up its oxygen, and is a strong bleaching agent ;
when heated to about 60* it decomposes.

BBOMIO ACID.

Formula, HBrO|.

Modes of Formatioil. — (i.) This acid is only known in aqueous
solution ; in this form it may be obtained by the action of bromine
upon silver bromate in the presence of water —

6AgBrO, + 3Br, + 3H,0 - 5AgBr + 6HBrO,.

The insoluble silver bromide separates out, and the aqueous
acid can be decanted from the precipitate.

(2.) A solution of this acid, mixed with hydrochloric acid, is also
formed when chlorine is passed through bromine water—

Br, + 5C1, + 6H,0 = lOHCl + 2HBrOs.

(3.) The decomposition of barium bromate by the requisite
weight of sulphuric acid, affords the best method for the preparation
of a pure aqueous solution of bromic acid —

Ba(BrOg), + HjSO* = BaSO^ + 2HBrO,.

Properties. — Bromic add is an unstable, strongly acid sub-
stance, closely resembling chloric acid. The aqueous solution
may be concentrated in vacuo until it contains about 50 per cent

346 Ifiorganic Chemistry

o( bromic acid, representing a composition of i molecule of the
acid to 7 of water. Beyond this degree of concentration, or il
heated to loo*, the acid decomposes into bromine, oxygen, and
water.

The bromates are formed by reactions similar to those by which
the chlorates are produced ; thus, by adding bromine to a solution
of potassium hydroxide, a mixture of potassium bromide and
bromate is obtained —

6KH0 + 3Br, =- 6KBr + KBrO, + 3H,0.

And the two salts can be separated by crystallisation, owing to the
greater solubility of the bromide.

The bromates decompose on being heated, some with the
liberation of oxygen and formation of bromide —

KBrO, = KBr + 30,

but without the intermediate production of a perbromate. Others
give off their bromine as well as a part of the oxygen they contain,
leaving the metal in combination with oxygen —

Mg(BrOs), = MgO + Brj + 60.

lODINB.

Symbol, I. Atomic weight = 126.54. Molecular weight = 253.08.

Vapour density =126.54.

HlstOfy. — Iodine was discovered by Courtois (181 2), who ob-
served that a beautiful violet vapour was evolved, during his
endeavours to prepare nitre from liquors obtained by lixiviating
the ashes of burnt seaweed. The substance was subsequently
investigated by Gay-Lussac.

Occurrence.— Like all the other members of this group of
elements, iodine is never found in nature in the uncombined con-
dition. In combination it occurs associated principally with
potassium, sodium, magnesium, and calcium, as iodides and
iodates.

Iodine is a widely distributed element, although not occurring
in more than small quantities in any particular source. Thus it is
found in small quantities in sea- water and in both marine plants
and animals. The amount of iodine in seaweed, varies with difTe-

Iodine 347

rent plants ; generally speaking, those from greater depths, contain
more than weeds which grow in comparatively shallow waters.

n«» \v«^«^ P*' Cent, of

*^ ^^^^ Iodine.

Drift weed \ Laminaria digitata (stem) . 0.4535

( Laminaria stenophylla . 0.4777

Cut weed i Fucus serratus . . . . 0.0856

i Ascophyllum nodosum . 0.0572

Iodine is also found in small quantities in many mineral waters
and medicinal springs.

In small quantities iodine is present in the natural sodium nitrate
of Chili and Peru, known as Chili saltpetre, and at the present day
this constitutes the most abundant source of this element.

Mode of Formation.— Iodine may be readily obtained by a
precisely similar reaction to that by which both bromine and
chlorine ore produced ; thus, if potassium iodide be mixed with
manganese dioxide and sulphuric acid, and the mixture gently
heated in a retort, iodine distils over and condenses in the form of
greyish black crystals —

2KI + MnO, + 2H,S04 - K,SO^ + MnSO^ + 2H,0 + I,.

Manufacturingr Processes.— On an industrial scale iodine is
obtained from two sources, namely, from seaweed and from caliche
(Chili saltpetre).

(i.) From seaweed. The weeds chiefly employed, are the Lami-
naria digitata and Laminaria stenophylla. The weed is burnt in
shallow pits, care being taken to avoid too high a temperature ; the
maximum yield of iodine being obtained if the ash is not allowed
to fuse. This ash is technically known as keip^ and if the weed is
properly burnt, it should yield a kelp containing from 25 to 30 lbs.
of iodine per ton. The kelpers, however, usually lose about half
the iodine on account of burning the weed at too high a tempera-
ture, thereby fusing the ash into a hard slag, instead of obtaining
a porous residue.

An improved process of carbonising the weed, was introduced by
Stanford (1863), in which it was heated in large retorts, whereby
the volatile products of the distillation, consisting largely of tar
and ammoniacal liquor, could be collected. The kelp obtained
by this method is in a very porous condition, and contains the
whole of the iodine originally present in the weed.

Inorganic Chemistry

A still more recent process for extracting the iodine from si
weed, and at the same lime obtaining other useful materials, t
since been discovered by Stanford. The weed is boiled with
sodium carbonate and filiered : the residue consists of a substance
called alguhse. Hydrochloric acid is added to the filtered liquid,
which precipitates a compound known as aigimc aciii, and this
is again separated by filtration. The liquor is neutralised with
sodium hydrate, evaporated to dryness and carbonised. The
residue, which is known as "kelp substitute," contains all the
iodine, as well as the potash salts, and should yield about 30 lbs.
of iodine per ton.

[The ilginlc acid obtained in this process. Is purified Rnd convened fnio the
sodium sail, which eonsiiiuies die commerciai '- tigin." b malcrial of a Kclatio-
0113 or olbiiniinoiis nalure which has latelj' been put to & number or useful
applications.]

The kelp obtained by either of these methods, is lixiviated with
water in lar^e iron vats, whereby all the soluble salts are extracted.
This aqueous liquid is concentrated in lai^e open boiling paiu^
and the less soluble salts, viz., the alkaline sulphates, carbonate^
and chlorides, are allowed to crystallise. The mother liquor ia
then mixed with sulphuric acid and allowed to stand. The sul-
phuric acid decomposes any sulphides and sulphites which may
be present, with the separation of sulphur ; it also converts the
bromides and iodides into the corresponding sulphates, with the
liberation of hydrobromic and hydriodic acids which remain in
solution, while the alkaline sulphates are deposited from the liquid,
and art technically known as plate sulphate. The liquor is then
transferred to the iodine still, which is an iron pot furnished with
a leaden cover into which two exit-pipes are fixed (Fig. loa].
These are connected to a series (usually ten in each tow) of large
earthenware jars or aluHels. A gentle heal is applied, and
manganese dioxide is introduced from lime to time through
the opening. The iodine is evolved according to the following
equation —

2H1 + MnO, + H,SO, = MnSO. + 2HjO + I,

and condenses in the jars. These vessels are also furnished with ^
tubulus upon their under side, so that the water which is evolveiffl
during the distillation can drain out, and run off down the trough if
which the jars are resting-

(z.) J^rom Ckili sallpttre. The crude sodium nitraie of Chili
Uid Peru, known as caliche, contains small quantities of iodine,
chiefly as sodium iodate. Although the amount of iodine in
caliche is only very small, avcr^t^'ing about o.z per cent., in view
of Ihe enormous quantity of nitrate that is lumed out, the aggre-
gate amount of iodine is very great. This iodine is now extracted,
and the supply of ihis element thai is now manufactured from this
source, is more than (he total consumption of iodine in the whole
world. The process is based upon the fact, thai when a solution

fof hydrogen soditm) sulphite (soditun bisulphite) is added lo a
solution of an iodate, iodine is precipitated, ihus—

2NaI0, ■► ONaHSO, = SNaHSO, + 2Na^0, + H,0 + 1,

The final mother liquor from the sodium nitrate, or caliche, in
which all the iodaie has concentrated, contains as much as «
per ceni. of Ihis sail. This liquor is mixed with the requisite
proportion of the hydrogen sodium sulphite solution, in lai^e lead-
lined vats, and the precipitated iodine allowed to scitle. It is
then washed and pressed into blacks, and is found to contain
from 80 to 85 per ccnL of iodine. This impure product is llien
distilled at a gentle heal from iron retorts, the vapour being con-
densed in a series of earthenware receivers much as in the aider
method.

Properties.— Iodine is a bluish-black shining solid, somewhat
resembling graphite in lustre and general outward appearance. Il

350

Inorganic Chemistry

crystallises in lar^e brilliant plates, which have a specific ^ravitpl
of 4.95. When heated 10 107* iodine rnelts, and gives offvapfl
having a beautiful violet colour. Us boUing-poinl is about 175*,

Iodine vaporises slowly at ordinary temperatures, and sublimM
from one part to anoiUer of a bottle in which a small quantity of
it is contained. The smell of iodine vapour is somewhat irritating
and unpleasant, recalling the smell of moderately diluted chlorine.
When iodine vapour is heated, it passes from a violet colour to .1
deep indigo blue." This change in the colour is accompanied
by a diminution of the vapour density. Up 10 a temperature ol
700'' the density of iodine corresponds to the formula I, : as ilie
temperature is rnised the density gradually diminishes, until ai
1468 it is reduced to less than Iwo-thirds. Al this point, 73.1 pci
cent, of the iodine molecules have become dissociated into single

Iodine is slightly solubie in water, i gramme of iodine being
dissolved hy 3.524 litres of water at ro°. This dilute solution,
however, has a perceptible brown colour. Iodine is ficely soluble
in aqueous potassium iodide solution, in alcohol, elher, and aqueous
hydriodic acid ; in all these solvents it dissolves to a dark reddish
brown solution. In chloroform, carbon disutphide, and many
liquid hydrocarbons, iodine is also soluble, but in these solvents

it dissolves K

a deep violi
vapour.

When iodine is brought
intense blue colour. This
it is capable of revealing the
nature of this blue compound

solut

1, resembling the colour of the

ilact with starch, it forms i

extremely delicate, thitfl
e of iodine. The exsct.ff

known. The colour disappeatSH

when the liquid is heated to about So', but returns on cooling i:l
continued boiling destroys ii permanently.

In its chemical relations iodine resembles chlorine and bromii
but with a lesser degree of energy. lioili these elements
capable of displacing iodine from its combinations with elect!
positive elemenis, thus —

Kl + I!r- KBr + I.

KI -'■ CI - KCl + I.

Iodine combines with many elements, both metals and noaj

metals forming iodides. Phosphorus, when brought in conta

with iodine, at once melts and inflames ; antimony ponder droppc

wcd..No.!i3t.

Uydriodie A cid 3 % I

into iodine vapour also spontaneously inflames. Wlien mercury
and iodine are gently healed, energetic combinaiion takes place,
'c iodide is formed.

HTDKIODIC AGIO.
FormuU, III. Molecular wcighi = i37.5t. DGntiiy= 355.08.

Hades of Formation. ~( I.) Hydriodic acid cin be obtained
synilieiically, by passing a mixture of hydrogen and iodine vapour
over strongly heated, finely divided platinum.

(1.) It is also obtained by the action of phosphoric acid upon
sodium or potassium iodide. (See Hydrobromic Acid.)

As in the case of the corresponding bromine compound, sul-
phuric acid cannot be employed, as by its action upon the iodide,
iodine and sulphur dioxide are liberated, thus —

SKI + 311^0, -SHKSOj + 2H,0 + SO, + I^

(3.) Hydriodic acid is produced by (he action of sulphuretted
hydrogen upon iodine (p. 371). At Ihe ordinary lenipcraiure,
and in the absence
of water, tliesc two
substances do not
react , hydriod ic acid
bcin); an endollier-
mic compound (p.
147) ; but if (he
iodine be suspended

phu retted hydrogen
passed through, the
heat of solution of
the hydriodic acid
supplies the neces-
sary energy to en-
able the action to
proceed. When,
hon-ever, the solu- _ - -- ■

V FlC. 103.

tion reaches a sp. g.

of 1.56 the action ceases, bec.iuse, as N.iumann h.is shown, the
he.-ii produced by the solution of the product is insulTicieni to carry
on the process beyond (his degree of concentration.

(4.) Hydriodic acid is most readily prepared, by the action of
phosphorus upon iodine in the presencr of water —
P +61 +4H,0- H.rO, + 6HI.

Inorganic Chtmiitry

lite red phosphorus and iodine for this reaction may be placed
in a dry flask, and water gradually dropped upon the mixture, when
hydriodic acid is rapidly evolved. The gas is allowed lo pass
through El U-lube containing red phosphorus, in order lo arresi any
iodine vapour which may accompany it. Hydriodic acid may be
collected over mercury or by displacement, as shown in Fig. 103.

Properties.— Hydriodic acid is a colourless, pungent -smelling
gas, which (umes strongly on coming into the air. The gas is
readily decomposed by heal into hydrogen and iodine. Thus, if a
healed wire be thrust into the gas, or if a spiral of platinum wire
be healed in the gas by means of an eleciric current, the violet
vapour of iodine at once makes its appearance.

When mixed with chlorine, hydriodic acid is at once decomposed,
with the liberation of iodine, thus—

SHI + CI, = 2HCI + I,

Hydriodic a

le of Ihe most readily liquefied ga;
0°, and under a pressure of four atmos-
pheres, il condenses lo a colourless
liquid.

The gas is extremely soluble in waler.
An aqueous solution of it is readily pro-
duced, by allowing the gas, obtained
by the method of preparation above de-
scribed, to pass into water. In order to
prevent the waler from being drawn back
into the generating flask, it is convenient
to pass the gas through a retort arranged
in the position seen in Fig. 104, Should
there be any back rush of water, owing
to the iniennission of the evolution of
gas in the apparatus, the liquid in the
beaker will be drawn up into the retort
and there lodge, leaving the end of the neck open to the atr.

A saturated aqueous solution of hydriodic acid at o* has a
specific gravity of 2. At Ihe ordinary pressure the strongest add
that can be obtained by dislillalion has a specific gravity of 1.67,
and contains 57.7 per cent, of hydriodic acid. This solution boila
at I V}'. As in the case of the corresponding bromine and chlorine
compounds, the particular strength of acid which bas a constant
boiling-poinl, is a fimction of the pressure.

FlQ. 104-

Iodic Acid 353

Aqueous hydriodic acid, when freshly prepared, is colourless ; bul
it rapidly turns brown, owing to the oxidation of the compound;
and the solution of the liberated iodine in the acid —

4HI + 0, -2H,0 + 21^

OXIDE AND OXY ACIDS OF IODINE.

One compound of iodine with oxygen b known, and three oxy-
acids, viz. : —

Iodine pentoxide .... 1,05.

Iodic acid HIO3.

Periodic acid . . . HIO4.

Hypoiodous acid • . . HIO.

lODIHB PENTOXIDS {/odu AnkydHJi),
Komiula, I^O^

Mode of Formation.— When iodic acid is heated to 170*, it
loses water and is converted into the pentoxide —

2HI0,- HjO + IjOft.

Properties. — Iodine pentoxide is a white crystalline solid body.
It is soluble in water, combining with a molecule of the water to
form iodic acid Iodine pentoxide is more stable than any of the
oxides of the other halogens ; but, when heated to a temperature of
300*, it decomposes into its elements.

IODIC ACID.

Formula. HlOf.

Modes of FormatioiL— (i.) Iodic acid can be prepared by
adding to a solution of baritun iodate the requisite amount ul
sulphuric acid demanded by the equation —

Ba(IO,), + H,S04 - BaS04 + 2HI0^

The aqueous solution of iodic acid is decanted from the preci-
pitated bariimi sulphate, and may be concentrated at 100* without
being decomposed.

(2.) When chlorine is passed through water in which powdered

ioUine is suspended, a n
is produced —

3H,0 H

Inorganic Chemistry

« of iodic add and hydrochloric aci^j

I + 5C1 = BHC1 + lllOj.

The hydrochloric acid may be removed by the addition of preci-
pitated silver oxide to the solution, and separating the precipitated
silver chloride by filtration.

(3.) Iodic acid is most conveniently prepared by healing iodine
with nitric acid, whereby the iodine is oxidised, and a
oxides of nitrogen is evolved as dense red vapours—

:d I

3HNO, + 1 - HIO,

H,0 ^ N,Oj + NOf

crystalline solid, soluble ll

Properties.— Iodic acid is a v
water. The aqueous solution shows an acid reaction with liln
but the colour is ultimately discharged by the bleaching actioi
the compound. Iodic acid does not form any blue colour »
starch ; being, however, an oxidising substance, it readily give;
oxygen to such reducing agents as sulphur dioxide, sulphuretted
hydrogen, or hydriodic acid, with the liberation of iodine, thus —

SHlOj

, + 4H,0 + 6SO,

-6HjS0,

SHIO,

+ 6H,S

= 6S +

6H,0 i- 1,

HlOj

+ 5HI-

3H,0 +

If. therefore, a small quantity of sulphutous acid be added to a
dilute solution of iodic acid, previously mixed with starch, the blue
iodide of starch will be formed. This reaction affords aa excellent
illustration of the time required for certain chemical changes to go
forward. It is readily possible to obtain an interval of 30 to 60
seconds between the addition of the sulphurous acid ajid appear-
ance of any visible result, when at the expiration of that time the I
whole mass of the liquid suddenly turns blue.*

—When iodine is dissolved in potassium hydroxide, a

-e of potassium iodide and iodate is produced, by an analogOlM

.0 that which takes place with either bromine or chlorine-

6KH0 + 31, - OKI + KIOj + 8H,0.

With the exception of the iodates of the alkali metals, the iodatS
ire for the most part insoluble in water. On being heated tl

" Sre Eitperiment 146, " Clieoiica! l.ecmre Eipcrimenls," nt

Periodic Acid 355

behave in a similar manner to the bromates, some being decom-
posed into an iodide and oxygen, while others leave a metallic
oxide and evolve iodine as well as oxygen. The alkaline iodates
are capable of uniting with iodic acid, forming salts which are
termed ctcid and di-acid iodates, thus —

Normal potassium iodate . . KIO^.

Acid potassium iodate KIOjyHIOs.

Di-acid potassium iodate . KI0|,21110,.

PERIODIC ACID.

Formula, 1 1 104.211,0 or IlftlO,.

Modes of Formation.— (i.) The compound represented by the
formula H104has never been obtained; when aqueous solutions
of periodic acid are evaporated, the compound which crystallises
out has the composition ill04,2H,0, or H^IO^

It may be obtained by boiling silver periodate with water, when
an insoluble basic silver salt is produced —

2Agl04 + 4H,0 = AgjHjIO. + HI04,2H,0.

The silver periodate is prepared by passing chlorine Into an aqueous solu-
tion of sodium iodate and sodium hydroxide, when the sparingly soluble
disodium periodate separates out—

NalOa + SNaHO + CI, = SNaQ + NaaHalO«.

This sodium salt is then dissolved in nitric add, and silver nitrate added,
whereby AgI04 ^ formed, which crystallises out on concentration—

( 2Na,H,IO« + 2HN0, = 2NaN0, + 4H,0 + 2Nal04.
\ 2Nal04 + 2AgN0, = 2NaNOa + 2AgI04.

(2.) Periodic acid is also formed by the addition of iodine to
an aqueous solution of perchloric acid —

2HCIO4 + 2H,0 + I, - CI, + 2HI04,2H,0.

Properties.— The add having the composition HI04,2H,0
is a colourless, crystalline, deliquescent substance. It melts at
133*, and at 150** is decomposed into iodine pentoxide, water, and
oxygen —

2HftI0« - 1 ,0ft + ftH,0 + O^

The acid cannot be converted into HIO4 by heat, for oxygen is
evolved as soon as water begins to be given ofL

JS6

Inorganic Chemistry

On lbea<

of sails, man)' ol ihnn being d^
ption ihal iodine is nionovaleML|
is somewhal difficult, and ihey m
represented as aasociaiions of raoleeulfs of saUi of (he unknown monc
periodic *dd, HlOf, with metallic oiide and water in various proporiion*— ■
(bus, ibe silver periodale in the rorcgoing equation, Ag,H,IO(, would be
cipiessed by the formula, 2AglOj.AB,0,2HjO,

The classiScation of these compounds is much simplified, if «e regard iodine
as here functioning ais a beptavalent element. On this assumption the perio-
dates may be considered as the salts of various hypothetical adds, which are
■11 derived from the compound IfHO); (itself hypothetical) by Ibe wiltidrawol \
of varying quajitilies of water, Thus, by the successive removal of
cule of water the following three acids woul J be formed —

l(HO), -H,0 = 10(H0), .
lO(MO), - n,0 = 10,(HO), .
10,(1I0), - H,0= IO.(HOl
n these three acids the rullowing «

HjlO,.
H,IO^
HIOj.

('.)

(t.) Ka,H,IO,, AeJIjIO,: Ag.lO,: iJa^(io,t
(a.) AgjlO,: l'b,(IO.V
(3-1 KIO.; Agio,.

-action of c

me mob

cule of water from ilw r

nolecutrs of

e complo. 1

icids would he derived, ibus-

lOlHO).

lEllSI;-

- li,0 =

h or H,l^u.

lO(HO).

IO,( HO),

(4-)

'«!:

-H^^

: O or H,1,0^
iO^HO),

(s.)

eselwoaei.

is the fol

lowing periodales may be

regarded ms '

(4-)

ZnJJX

,; Ba^I^,.

(5-) Ag.I,0,

; CajlA: BijIsO,

H7F0I0D0DS ACID AHD HTPOIODITBa

joryia-ii-aier, a colourless soluiio

liquid is a dilute lolulica

onger soluljoni

When an nqueous solution of iodi
or soJium hydroiidei. lime-watei or baryta-
obtained which possesses bleaqjiing properties,
of the iiypoioditc and iodide i>[

luoed by adding s
2KHO+I, + Aq

all quaoliiies ol powdered ii
. K10+ KI + HjO+Aq.

Iodine Trichloride 357

A dilute solution of the acid itself is obtained by shaking mercuric oxide
with iodine and water. (See Hypochlorous Acid, p. 335.)

Neither the acid nor any of its salts has been isolated, being known only in
dilute solution. The compounds are all extremely unstable, decomposing at
the ordinary temperature in a few hours, and in a few minutes when the
solutions are boiled ; the salts passing into iodides and iodatcs,

3KI0 = 2K1 + KIO3,

while the acid decomposes first into hydriodic and iodic acids, which then
react upon each other with elimination of free iodine.

Compounds of the Halogens with each Other.

Chlorine unites both with bromine and with iodine, and the two kitter
elements combine with each other.

(i.) Chlorine and Bromine. — Bromine monochloride. This substance is
obtained as a rcddish-ycUow liquid, when chlorine gas is passed into bromine.
The compound is believed to have the composition BrCL

(2.) CUorine and Iodine. — lodme monochloride ^ ICl. When dry chlorine
is passed over iodine, the latter rapidly melts, forming a dark reddish-brown
liquid, strongly resembling bromine in appearance. The liquid solidifies to a
mass of red prismatic crystals, which melt at 25^ It is decomposed by water
into iodic and hydrochloric acids, and iodine is liberated—

6IC1 + 3H,0 = HIO, + 6HC1 + 21,.

Iodine trichloride, IClg. This compound is formed by passing an excess of
chlorine over iodine, or by passing chlorine through iodine monochloride. It
is also formed when hydriodic acid is acted upon by an excess of chlorine —

HI + 2Cla = HCl + ICl,.

Iodine trichloride is a yellow solid substance, crystallising in long brilliant
needle-shaped crystals, which sublime at the ordinary temperature. When
gently warmed it melts, at the same lime dissociating into chlorine and the
monochloride ; on cooling, re-union takes place with the reformation of ICl,.

(3.) Bromine and Iodine. — Two compoimds of these elements are believed
to exist, viz. , a crystalline solid, and a deep-coloured liquid. Their compositioo
is probably expressed by the formulae, I Br and IBr^

CHAPTER II

THE ELEMENTS OF GROUP VL {FAMILY D.)

Oxygen. O . . 15.96 I Selenium, Se . 78.87

Sulphur, S .31.98 I Tellurium, Tc . 125

The relation in which oxygen, the typical element, stands to the
remaining members of the family is very similar to that between
fluorine and the other halogens.

All the elements of this family unite with hydrogen, forming
compounds of the type RHj —

OH.., SH^ SeH^ TeH,;

but the hydride of oxygen stands apart from the others in many of
iis attributes. Thus at ordinary temperatures it is a colourless and
odourless liquid, while the remaining compounds are all foetid-
smelling and poisonous gases.

Sulphur, selenium, and tellurium each combine with oxygen,
forming respectively SO3, SeOj, and TeOj, while none of^ these
elements in a divalent capacity forms a similar compound ; that is
to say, no such combinations are known as OS3, or OSe^, although
amongst themselves they unite, forming SeS^ and TcSg.

Sulphur, selenium, and tellurium also unite with oxygen, forming
dioxides, SO^ SeO,, and TeO^ in which these elements are pos-
sibly tetravalent, in which case the constitution of the compounds
will be represented thus, 0 = S = 0; 0 = Se = 0.

We may, however, consider them as functioning in a divalent

yO /O

>, < I ; Se< I ,

NO NO

capacity, and regard the oxides as constituted thus,

ID which case we may look upon ozone as being the corresponding

oxygen compound, OOf,

o< |.

Sulphur 359

All the elements of this family combine with chlorine, producing
compounds having the following composition —

Oxygen.

Sulphur.

Selenium.

Tellurium.

0,C1

• t t

t ••

• • •

S,C1,

ScjCl,

• • •

OCI,

SCI,

• • •

TeCl,

t • •

SC14

SCCI4

TeCl4

Oxygen again differs from the other members, by alone forming
a compound of the t>'pe, RgCL This element also shows no ten-
dency to function with a higher atomicity than that of a divalent ;
while the others unite with four atoms of the halogen, thereby
exhibiting their tetravalent nature.

The members of this family pass by a regular gradation from
the strongly electro-negative, gaseous, non-metal oxygen, to the
feebly negative and slightly basic clement tellurium, which possesses
many of the properties of a true metal. Selenium and tellurium
are both elements which lie very close to that ill-defmed bound.iry
between the metals and non-metals, and are on this account some-
times termed metalloids. In tellurous oxide, TeO^, we have a
compound which is both an acid-forming and a salt-forming oxide,
its acidic and basic properties being nearly equally balanced. Thus,
it replaces hydrogen in sulphuric acid, forming tellurium sulphate,
Te(S04)2 ; and it also unites with water, forming tellurous acid,
HgTeO,, corresponding to sulphurous acid, H2SO3.

Of the four elements of this family, oxygen is by far the most
abundant, both in combination and in the free state ; sulphur is
more plentiful than the other two, and tellurium occurs in the
smallest quantity.

The element oxygen has already been treated in Part II., p 159.

SULPHUB.
Symbol, S. Atomic weight = 31.98. Molecular vreight s 65.96.

Occurx*ence. — In the free state this element occurs chiefly in
volcanic districts. In Italy and Sicily large quantities of native
sulphur are found, which have long been the most important
European sources of this substance. Large deposits are to be met
\rith in Transylvania and in Iceland, and it also occurs in beds,
often of great thickness, in j;>arts of China, India, California, and

360

InorganU Chemiilry

Ihc Yellowstone disirici of the Rocky Mouniairs, These n
deposits are sometimes found stratified niih beds of day o
but they often occur as wbnl arc knomi as "living" beds, in
the sulphur is continuously being formed as the result of diemicB
decompositions which are at present ax. work. Such a "
sulphur bed is known as a so!/aluiu, and, as in the case of the Ice
land deposits, they are usually found associated with geysers,
fumaroles, and other signs of volcanic action.

In combination with hydrogen, sulphur occurs as sul)^hureited
hydrogen, Enonnous quantities of sulphur are found combined
with various metals, constituting the important class of substances
known as sulphides ; as, for example, galena, or lead sulphide,
FbS ; Mine bltide, or line sulphide, ZnS ; pyrites, or iron sulphide,
FeS, ; cofyprr pyrites, or copper iron sulphide, CujFcjS, ; stiiHiU,.m
or antimony sulphide, SbjSs ; dnnaiar, or mercury sulphide, Hgi J

In combination with metals and oxygen, sulphur occurs in
sulphates, such as gypsum, CaSO^.aHjO ; heavy spar, liaSO,;
iieseriU, MgSOj.HjO.

Modes or Formation.— (i.) Sulphur i^ formed "hen sulphu-
retted hydrogen is brought in contact with sulphur dioxide ; ihe
two gases mutually decompose one another, with the formatior
water and the precipitation of sulphur —

21!,S + S0,= 2H,0 + 3S,

(a.) It is also produced when sulphuretted hydrogen is buml J
with an insuftideDt supply □fair-'

H,S + O - H,0 + S.

This reaction probably takes place in two stages, a portionfl
of the sulphuretted hydrogen burning to sulphur dioxide, and thia ■
then reacting upon a further quantity of sulphuretted hydrog«n,. J
thus—

(<i) H,S + 30 = H,0 + SO,.

(*) 2H,S + SO, = 2H,0 + 3S.

It is supposed that some of the free sulphur found in volcanic
regions, has been produced by this action of these two gases upon
one another.

Extraction of Sulphur from Native Sulphur.— Nat uisM
■ulphur is always more or less mixed with eanhy or mioen^J

Sulphur 361

matters, from which it is necessary to free it. This is usually
effected by melting the sulphur and allowing it to flow away from
the accompanying impurities. The crude sulphur rock is stacked
in brick kilns having a sloping floor, and the mass ignited by
introducing through openings in the heap, burning faggots of
brushwood. The heat produced by the combustion of a part of the
sulphur, causes the remainder to melt and collect upon the sloping
floor of the kiln, from which it can be drawn off into rough moulds.
The loss of sulphur by this method is very considerable, usually
not more than two- thirds of the total amount contained in the rock
being obtained.

(3.) Sulphur may be obtained by heating certain metallic sul-
phides ; thus when iron pyrites is heated it yields one-third of its
sulphur —

3FeS, = FejSi + S,.

If the pyrites be roasted in kilns, the whole of the sulphur is
obtained, partly as free sulphur, and partly as sulphur dioxide,
thus —

3FeS, + 50j - FejOi + 3S0, + 3S.

This method was at one time rather extensively employed for
the preparation of sulphur on a manufacturing scale, but has now
practically gone out of use, the pyrites being usually roasted with
excess of air, whereby the whole of the sulphur is converted into
sulphur dioxide for use in the manufacture of sulphuric acid

By a similar process, sulphur is obtained as a bye-product during
the roasting of copper pyrites, in the first stage of the operation of
copper-smelling,

(4.) Large quantities of sulphur are now extracted from the vat-
waste^ or alkali'waste^ obtained in the manufacture of sodium
carbonate by the Leblanc process. This material consists largely
of an insoluble oxy- sulphide of lime, a compound containing calcium
sulphide (CaS) and calcium oxide (CaO) in varying proportions.
Either in the lixiviating tanks themselves, or in special vats, a
current of air is blown through the compound, whereby the caldimi
sulphide it contains is ultimately converted into a mixture of calcium
hydrosulphide (CaHjSt), thiosulphaie (CaS^Os), and polysulphide
(CaS^), according to the following equations —

(I.) «CaS + «H,0 - CaHjS, + CaH.O,.

362 Inorganic Chemistry

This reaction goes forward in several stages, in the course ol
which a quantity of sulphur is set free ; this is then acted upon by
the calcium hydroxide, with the formation of calcium polysulphide
and calcium thiosulphate, thus—

(2.) 3CaH,0, + 12s = 2CaS4 + CaS,0, + 3H,0.

The materials are alternately oxidised and lixiviated several
times, and the liquor is then treated with excess of hydrochloric
acid, at a temperature of about 60**, which decomposes the various
sulphur compounds according to the following equation!

(<!.> CaHjS, + 2HC1 = CaCl, + SH^S.

(b,) CaSft + 2HC1 = CaCl, + H,S + 4S.

(c.) CaSjO, + 2HC1 - CaCl, + SO, + S + H,0

The best results are obtained, when the sulphur compounds are
present in such proportions that the SO, evolved by reaction c is
sufficient to decompose the whole of the SH, produced by the
other two reactions, so that neither gas escapes —

SO, + 2H,S = 2H,0 + 3S.

(5.) Sulphur is also obtained from the spent oxide of iron which
has been used in the " purifiers " employed upon gas-works. Coal
gas contains considerable quantities of sulphuretted hydrogen,
which are removed from the gas by passing it through hydrated
ferric oxide (Fe^H^O^), which absorbs the whole of the sulphuretted
hydrogen, thus —

Fe^H^Oa + 3H,S = 2FeS + S + 6H,0.

When the compound has lost its power to absorb sulphuretted
hydrogen, the material is thrown out of the purifiers and exposed
to air and moisture, when the iron becomes reconverted into the
hydrated oxide, and the sulphur is set free—

2FeS + 30 + 3H,0 = Fe,H«0« + 2S.

This revivified material is then employed for the purification of
a further quantity of gas. It is found that after a certain number
of revivifying operations, the substance begins to lose its power of
absorbing any additional sulphuretted hydrogen, and as it then

Silfhui

S«3

ins nearly half iti weight of sulphur, ii becomes a va'uable
e of this elemeni. The sulphur is obiained from it by distil-
Lttion, or the ni,iierial may be masted in specinl kilns, whereby ihe
sulphur is convened into sulphur dioxide, and employed for Ihe
manufacture of sulphuric acid.

Purification.— The crude sulphur obtained by ihc foregoing
mclhods is purified by distillation, the process being carried out in

bieans of the pipe F into ihe retort B, The sulphur is there
boiled by means of the lire, and the vapour allowed to issue into Ihe
large brickwork chamber C. As the vapour enters the chamber, i(
condenses upon ilie walls and floor in Ihe form of a light, powdery
deposit, consisting of minute crystals, and constituting the fioven
of sulphur of commerce. As the process continues, and the brick-
work becomes hot, this soft powder melis and collects upon llie
floor as an amber- coloured liquid, which is run out from time lo

Inorganic Ckemistry

time from the opening al H, and cast either into large blocks ot
into cylindrical tods, by means of woatlen moultls. In the latin
form il is known as roll sulphur.

When the sulphur vapour first enters the chamber and
with the air, the mixture frequenily ignites with a feeble expli
the chamber, therefore, is furnished with a valve, S, at th
whereby the pressure developed at Ihe
be relieied

Properties —Sulphur -IS ordinarily si
crystalhne solid It is msoluble in wat
carbon disulphide and to a greater or \

beniene chloroform sulphur chloride, and many other solvents.
It IS a non conductor of electricity, and an extremely b
ductor of heat A piece of sulphur on being very gently »

cksot
laiiB^I

of combustion may

m, is a pnle-yellow brittle
r, but readily dissolves In
s degree in turpentine,

even by being grasped in the hand, may be heard to crack by (he
unequal heating, and will uhimalely fa!l to pieces. At a tem-
perature of 114.5 sulphur melts to a clear amber-coloured and
moderately mobile liquid ; on raising the temperature of this
liquid its colour rapidly darkens, and at the same time il loses its
mobility, until at a temperature of about 230' the mass appears
almost black, and is so viscous that it can no longer be poured
from the vessel. As ihe temperature is still further raised, the
substance, while retaining its dark colour, again becomes liquid,
although it does not regain its original limpidity. At 448' the
liquid boils, and is converted into a pale yellowish -brown coloured
vapour. On allowing the boiling sulphur to cool, it passes through
the same changes in reverse order until it solidifies.

When the vapour of sulphur is heated to looo', it is converted

^^^^DiH ~

■

Sulphur 36s

ioto a tnie gas, and has a density of 33, one litre of ihe gas weigh-
iDg 33 crilhs.

Su!pliut it known to exist in four allotropic modilications, two ol

(o) Rhombic Sulphur.— 0{ the two crystalline varieties (his is
Ihe more stable. Sulphur, therefore, that occurs native is found
crystallised in this form, [t may be obtained by allowing a solu-
tion of sulphur in carbon disulphide to slowly evaporate. Fig. 106
represents two large rhombic octahedral crystals of sulphur
obtained in this way.

Octahedral crystals of sulphur can also be obtained under certais
conditions, when melted sulphur is allowed to crystallise. Sulphur

Kic, .07.

in (be fiquid condition exhibits the phenomenon of suspended
solidification to a very high degree, and if (he liquid be carefiilly
cooled out of contact with air, the temperature may fall to 90'

before solidification lakes place. If into the liquid in this state a
crystal of the rhombic variety be dropped, the sulphur begins to
solidify in crystals of that form. If the superfused sulphur be con-
tained in a hermetically dosed flask, the liquid frequently deposits
octahedral crystals, and by allowing (he mass lo partially solidify,

bottom of the vessel

The specific gravity of this form of sulphur is 1.05.

09) "Prismatic" 5i.*A»i-. ~ When melted sulphur is allowed

1
1

366 Inorganic Chemistry

to cool under ordinaiy conditions, such as in a crucible, oi
beaker, it crystallises in the form of prismatic needles, belong-
ing to the monoclinic, or monosymmetric system. By allowing
the mass to partially solidify, and pouring off the still liquid por-
tion, these crystals will be seen lining the inside of the beaker
as long translucent prisms. Fig. 107 shows such a mass cf
crystals. Prismatic crystals of sulphur are also obtained, when
this element is crystallised from a hot solution in oil of tur-
pentine.

The specific gravity of this form of sulphur is less than that of
the octahedral variety, being 1.98.

At ordinary temperatures this modification is unstable, and in
the course of a day or two the crystals lose their translucent
appearance, owing to their becoming broken down into a number
of smaller crystals of the rhombic variety, and present the opaque
yellow appearance of ordinar)* loll sulphur. This change from
the prismatic to the octahedral variety, which takes place mure
quickly when the crystals are scratched, or subjected 10 vibration,
is attended with evolution of heat. When monoclinic sulphur is
thrown into carbon disulphide, its transformation into the stable
modification takes place rapidly, and in this way, by means of a
thermopile, the heat evolved by the change may be rendered
evident As carbon disulphide, however, at once exerts its solvent
action upon the rhombic sulphur the moment it is formed, the
reduction of temperature resulting from this cause, would com-
pletely over-balance and mask the more feeble heat effect produced
by the pxissage of the sulphur from the unstable to the stable form.
In order, therefore, to render evident the heat resulting from the
change of crystalline form, the carbon disulphide must be pre-
viously allowed to dissolve as much sulphur as it can take up. If
a small quantity of carbon disulphide, so saturated with sulphur,
be placed in a corked flask, and stood upon the face of a thermo-
electric pile* in connection with a galvanometer, and a quantity
of prismatic crystals of sulphur be quickly thrown into the liquid,
a sensible deflection of the galvanometer needle will be seen in the
direction caused by heat

Although under ordinary conditions, monoclinic sulphur is un-
stable and passes into rhombic form, at temperatures between

* The thermo-electric pile is a delicate physical instniment employed for
registering slight changes of temperature: for descriptions of the apparatus
the student ntu»i cuiouli tcJti-buuks on physio*.

Sulphur

367

100* and 114*, it appear! to be the more stable variety, for at ihii
temperature rhombic sulphur passes bto the monoclinic variety.

(r) Plailic Jw^Awr.— When sulphur which has been heated
tintil it reaches the viscous condition, is suddenly plunged into
water, or when boiling sulphur is poured in a Ihin stream into
water, the substance solidities to a tough elastic material some-
what resembling indianibber. The sulphur in this form is known
as piatlic sulphur. This variety is best obtained by distilling a
quantity of ordinary sulphur from a glass retort (Fig. 108), and
allowing the distilled liquid 10 flow in a fine stream into cold
water placed for its reception. As the liquid sulphur falls into
the water, it congeals to the plastic conditio
thread, which winds itself in
a regular manner into beauti-
ful coils of a delicate trans-
lucent amber colour. The
specific gravity of plastic sul-
phur is 1.95, and it is not
soluble in carbon disulphide.
At ordinary temperatures this
allotrope of sulphur is gra-
dually transformed into the
stable rhombic variety ; in
the course of a few days it
loses its transparency and
elasticity, and becomes con-
verted into the ordinary lemon yellow brittle condition of common
sulphur. This change takes-place more quickly if the plastic
material be stretched and worked between the fingers, and still
mon readily by heating it for a few moments to 100°, and allowing
it again to cool.

(Jl) White Amorphous Su/pAur.—\Vhe.D sulphur is heated, and
the vapour condensed upon a cool surface, as in the formation of
ordinary flowers of sulphur, although the greater portion of the
sulphur is sublimed in the rhombic octahednJ form, the sublimate
contains a small amount of sulphur in the form of an amoiphous
powder, which is almost milk-white in colour.

This modificatioa is best obtained by treating flowers of sulphur,
which usually contains as much as 5 or 6 per cent, of amorphous
sulphur, with carbon disulphide, whereby the rhombic variety is
dissolved, and the white amorphous substance, which is insoluCla^

in ihat liquid, is left behind, liy Gltenng the liquid and washing
the residue with carbon disulphidc uniil the whole of the soluble
sulphur is removed, the amorphous powder may be obtained in a
state of purity.

This amorphous svibslance is also produced in small quantity, by
the action of light upon a solution of sulphur in carbon disulphide.
Thus, if n perfectly clear solution of sulphur in this liquid be placed
for even a few minutes in the path of a beam of electric light, the
solution will be seen to become rapidly turbid, owing to the forma-
tion of (his insoluble modification.

This milk-white amorphous modilication is stable at the ordinary
temperature, and therefore does not pass spontaneously into the
rhombic variety. When heated lo a temperature of 100°, it quickly
becomes yellow in colour, and is then readily soluble in carbon
disulphide, having been Iransfurmed at that temperature into the
ordinary stable form.

Hilk of Stllphur.— This substance is a medicinal preparation,
obtained by precipitating sulphur from a polysulphide of lime by
meatis of hydrochloric acid. Flowers of sulphur and milk of lime
are boiled together for some time, and after settling, the cleat
reddish liquid containing the calcium polysulphides is decanted oRI
and hydrochloric acid added lo il ; calcium chloride is formed ~
and sulphur in a fine slate of subdivision is precipitated—

CaS^ + 2HC1 - CaCl, + HjS + (j— 1)S.

The product so obtained is pale yellow in colour, and C
ordinary sulphur often contaminated with considerable quantitu
of calcium sulphate, derived from sulphuric acid present i
hydrochloric acid employed in the precipitation.

When sulphur in any of its modifications is heated in the air, HM
lakes fire and bums with a pale blue tlame, giving rise to sulphur
dioxide ; when burnt in oxygen a small quantity of sulphur Ui-
oiide is at the same time produced.

Finely divided sulphur, when exposed to air and moisture, under-
goes slow oxidation even at ordinary temperattires, with the forma'
tion of sulphuric acid. Thus, if flowers of sulphur be moistenedj
with water and freely exposed to the air, in a short time the watO.
will be distinctly acid. On this account, sulphur that is used liO.
pyrotechnic purposes, is thoroughly washed and dried, and p
ecutJ in warm dry places.

Hydrogen Sulphide 369

Sulphur combines directly with many metals under the influence
of beat, forming sulphides ; the union in many cases being accom-
panied by vivid combustion. Thus, a strip of copper, when intro-
duced into sulphur vapour, bums brilliantly with' the formation of
copper sulphide ; and a red-hot bar of iron, when pressed against
a roll of sulphur, bums in the vapour which is generated, and the
molten sidphide fidls in scintillating masses through the air —

Fc + S = FeS.

Heated with sodiiun or potassium, the alkaline sulphides arc
formed with deflagration—

1^1 *r o ^ r^^o.

COMPOUNDS OP SULPHUR WITH HYDROGEN.

Two compounds of these elements are known, namely —

Hydrogen sulphide or sulphuretted hydrogen . H^S.
Hydrogen persulphide H^Sj.

HTDROOEH &ULPHIDE.
Formula, HjS. Molecular weight = 34. Density = 17.

OccuPrenee. — This gas is evolved in volcanic regions, and is
met with in solution in sulphur mineral waters.

Modes of FormatlOlL— -(i.) Sulphuretted hydrogen may be
formed by the direct union of its elements, by passing a mixture of
hydrogen and the vapour of sulphur through a strongly heated
tube. In small quantity it is produced when hydrogen is passed
into boiling sulphur, or over certain heated metallic sulphides.

(2.) Sulphuretted hydrogen is most readily obtained by the
action of either hydrochloric or sulphuric acid upon ferrous sul-
phide, thus —

FeS + SHQ « FeCl, + H,S.

FeS + H,S04 - FeSOi + H,S.

The ferrous sulphide in broken fragments is placed in a two-
necked bottle, similar to the apparatus. Fig. 27, employed for
the preparation of hydrogen, and the dilute add poured upon it
The gas is rapidly evolved without the application of heat The
gas obtained by this method always contsuns free hydrogen,
owing to the presence of uncombined iron in the ferrous sulphide.

370 Tnorganie Chemistry

(3.) Pure sulphureiied hydrogen may be obtained by heating

antimony trisulphide (grey antimony ore) with strong hydrochloric

acid, when antimony trichloride is produced and hydrogen sulphide

evolved —

SbjSa + 6HC1 = aSbClj + 3H,S.

(4.) Sulphuretted hydrogen is produced during the putrefaction
of organic substances containing sulphur, the offensive smell of a
decomposing ^%% being due to the presence of this gas. It is also
produced during the destructive distillation of coal, by the direct
union of hydrogen with the sulphur contained in the pyrites, hence
coal gas always contains sulphuretted hydrogen amongst its
impurities.

Properties. — Sulphuretted hydrogen is a colourless gas having a
somewhat sickly sweetish taste, and an extremely offensive odour.
It acts as a powerful poison when inhaled in the pure state, and
even when very largely diluted with air it gives rise to dizziness
and headache. Its poisonous effects are more marked upon some
animals than others : thus, a bird was found to die in an atmosphere
containing only rrnr of sulphuretted hydrogen, while it required an
amount equal to vH to poison a hare ; and again, cold-blooded
animals are in no way affected by inhaling these proportions of
the gas. Sulphuretted hydrogen is moderately soluble in water ;
at ordinary temperatures water dissolves about three times its own
volume of the gas. In collecting it over water, therefore, consider-
able loss results unless the water be warm. The coefficient of
absorption by water at o' is 4.3706.

The aqueous solution gives an acid reaction with litmus, and
possesses the taste and smell of the gas. It quickly decomposes
on exposure to air, the hydrogen of the sulphuretted hydrogen
combines with oxygen, and the liquid becomes turbid by the preci-
pitation of sulphur. Hydrogen sulphide is an inflammable gas,
burning with a bluish flame, and producing sulphur dioxide and

water —

2H,S 4- 30, = 2S0, 4- 2H,0.

If mixed with oxygen in the proportion demanded by this equa-
tion, viz., two volumes of sulphuretted hydrogen and three volumes
of oxygen, and ignited, the mixture explodes with violence. When
the gas is burned with an insufficient supply of air or oxygen for
its complete combustion, the sulphur is deposited.

Sulphuretted hydrogen is decomposed by the halogens, with the

Hydrogen Sulphide 371

deposition of sulphur, and the formation of the hydrogen compound
of the halogen element, thus —

H,S 4- CI, - ?.HC1 f S.

Fluorine, chlorine, and bromine are capable of bringing about
this decomposition at ordinary temperatures ; in the case of iodine,
the reaction is attended with absorption of heat, which may be
supplied by passing the mixture of iodine vapour and sulphuretted
hydrogen through a hot tube, or by causing the action to take
place in the presence of water. In the latter case the heat of solu-
tion of the hydriodic acid, determines the reaction.

When passed into sulphuric acid, reduction of the acid takes
place with the precipitation of sulphur —

H,S04 + H,S = SO, + 2H,0 + S.

Sulphuretted hydrogen, therefore, cannot be dried by means of
sulphuric acid.

The gas acts upon many metals with the formation of sulphides ;
thus, when potassium is heated in a stream of hydrogen sulphide
it readily bums and produces potassium hydro-sulphide, H,S + K
» KHS + H. Such metals as tin, lead, silver, &c, are rapidly
tarnished in contact with this gas. On this account articles of
silver, when exposed to the air of towns, quickly become covered
with a film of sulphide, which first appears yellowish-brown, and
gradually becomes black. The discoloration of a silver spoon,
when introduced into an tig% which is partially decomposed, is due
to the same cause.

Sulphuretted hydrogen also acts upon metallic salts, combining
with the metal to form a sulphide. The *' white-lead" employed
in ordinary paint is gr^ually blackened on prolonged exposure
to the air by the formation of lead sulphide.

Hydrogen sulphide is rapidly absorbed by lime, with the forma-
tion of calcium hydrosulphide —

CaH,0, + SH,S - CaH,S, + SH,0.

It is also absorbed by calcium sulphide, yielding the same
compound. This reaction is employed in the method known as
Chances process^ for utilising the sulphur of the vat waste of the
alkali manu£ftctare. This consists in passing lime-ldln gases
through a series of vessels containing the waste mixed with water.
In the first vessels the carbon dioxide is absorbed, and sulphuretted

hydrogen evalved. This, passing inio ihe later vessels, is absoit
by ihe vat waste, forming calcium hydiosulpliide, which i
turn is decomposed by carbon dioxide, with the cvoluiioi
ihe volume of sulphuretted hydrogen for a given volume of carb
dioxide, as in the first reaction —

{[) CaS + CO, + H,0 = CaCOa + H,S.

(3) CaS + H(S = Can,S,

(3) CaH,S, + CO, + H,0 = CaCO, + 2H,S.

The sulphuretted hydrogen, mixed with atnioipheric
and a small quantity of carbon dioxide, is sufTicicnlly rich to buM
yielding sulphur dioxide, which can then be employed for I"
manufacture of sulphuric acid.

Sulphuretted hydrogen is also decomposed by ferric hydro
with the formation of ferrous sulphide and water, and the deposi-
tion of sulphur, as described on page 362. This action lake^
plice with the evolution of considerable heat, the temperature
rising high enough 10 ignite a mixture of sulphuretted hydrogen
and oxygen.*

Sulphuretted hydrogen is a valuable laborator)- reagent, on

account of the generaJ behaviour of certain classes of sulphides.

Thus, (he sulphides of certain metaU, being insoluble in dilute

acids, are precipitated from acid solutions ; for example —

CuSOj + H,S = CuS + HjSO,.

CdCl, + H,S = CdS + 2HC1.

Others are soluble in acids, but insoluble in alkaline liquids, a
are therefore precipitated by sulpliuretied hydrogen in the presenci
of ammonia, or by the addition of ammonium sulphide, thus>-
ZnSO, + (NH,),S = ZnS + (NH,)2S0,.

A third group of metals yield sulphides that are soluble ii
and therefore are not separated either in acid or alkaline soluiioi

Many of Ihe metallic sulphides are also possessed of chat
teristic colours, which readily serve lor their identificalio:
atsenious sulphide is fiale yellow, and cadmium sulphide gold*
yellow. Anlimonious sulphide has a bright red colour,
sulphide is while.

This behaviour of metals towards sulphuretted hydrogen I
the basis upon which certain methods of qualitative analyses ■:

I Lnture Eip

," new ed. Xoi, 577. sr*

Hydrogen Persulphide 373

H7DB00EH PBBSULPHIDB.

Ponnula, H^

Modes of Formation. — (i.) This substance, which stands in the
same relation to hydrogen sulphide, as hydrogen peroxide does to
water, may be obtained by slowly pouring a solution of calcium
disulphide into hydrochloric acid, in the cold ; the liquids being
rapidly stirred during the process of mixing, and the acid bein^;
kept in considerable excess —

CaS, + 2nCl= CaCl^ + II, S^

The hydrogen persulphide separates out as a heavy, pale yellow,
oily compound, which settles to the bottom of the liquid. The
calcium dfsulphide is prepared by boiling together one part of
lime with about twenty parts of water, and one part of flowers of
sulphur. Tlie yellow liquid that is obtained u-ill contain more or
less of the higher sulphides of lime, and in proportion as these are
present there will be a precipitation of sulphur with the hydrogen
persulphide, thus —

CaSft + 21iCl - CaCl, *■ H,S, + 3S.

(2.) Hydrogen persulphide may also be obtained from a com-
pound that is produced by the action of sulphuretted hydrogen
upon strychnine, in the presence of oxygen —

SCjiIfaNjO, + 6SH, + 30 - 3H,0 + 2C,iH„N3,0„3H,S,.

This substance, on treatment with an acid, yields the persulphide.

Properties. — Hydrogen persulphide is an oily liquid having a
specific gravity of 1.73. It has a pungent smell, accompanied by
the odour of sulphuretted hydrogen, due probably to the partial
decomposition of the compound, and its vapour is irritating to the
eyes. It is an unstable substance, decomposing at ordinary tem-
peratures into sulphur and sulphuretted hydrogen : when heated,
this decomposition takes place rapidly. It readily dissolves sul-
phur, and on this account, and the readiness with which the
compound decomposes, it is extremely difficult to obtain it in a
state of purity, and so to determine its exact composition. It i»
msoluble in water, but dissolves readily in carbon disulphide «a|ft

374 Inorganic Chemistry

ether: its solution in the former liquid is more stable than the
liquid substance itself.

Hydrogen persulphide bums with a blue flame, yielding sulphur
dioxide and water.

Hydrogen persulphide possesses feeble bleaching properties,
and like its oxygen analogue it is decomposed by certain metallic
oxides, with the evolution of sulphuretted hydrogen.

COMPOUNDS OF SULPHUR WITH CHLORINE.

Two of these compounds exist at ordinary temperatures, while a
third is only known at temperatures below ~ 22*.

1. Disulphur dichloride or sulphothionyl chloride S^Cl^

2. Sulphur dichloride SCI,.

3. Sulphur tetrachloride SCI4.

Disulphur Dichloride, S^Cl,.— This substance is obtained by
passing dry chlorine over the surface of heated sulphur, con-
tained in a retort ; the compound, which distils away as fast as
it is formed, condenses in the receiver as a yellow liquid —

Sj + CI, = SjCl,.

Properties. — The redistilled liquid is an amber-coloured fuming
substance with a disagreeable penetrating odour, the vapour of
which irritates the eyes. Its specific gravity is 1.709, and it boils
at 1 38. I*. In contact with water it gradually decomposes into
hydrochloric acid and sulphur dioxide, with the precipitation of
sulphur. The action takes place in two stages, thiosulphunc acid
being formed as an intermediate product, thus —

(a.) 2S,Cl2 4- SHjO = 4HC1 + S, 4- HjSp,.
09.) H2S2O3 = HjSOa + S.

Disulphur dichloride dissolves sulphur with great retidiness, and
the solution so obtained is largely employed in the process of
vulcanising indiarubber.

This compound is the most stable of the three chlorides of
lulphur. From the fact that it contains chlorine and sulphur in

Oxides and Oxyacitls of Sulphu r 375

the proportion of one atom of each element, it is sometimes called

sulphur monochloride ; but as its vapour density (67.4) shows that

it contains two atoms of each element in the molecule, the use of

the word monochloride is calculated to mislead. The name sul-

phothionyl chloride indicates its analogy to thionyl chloride, sOCl^,

from which it may be regarded as being derived, by the rcplace-

yr\\ pi

ment of the oxygen by an atom of sulphur, 0 = 5^.; ^"^^vpi

Snlphnr Dlehlorlde, SCl^ — This compound is obtained by passing a stream
of dry chlorioe into disulpbur dichloride at a temperature not above o*. Wlien
the maximam amount of chlorine is absorlxKl, tlie liquid assumes a dark
reddish -broM'n colour. Excess of chlorine is removed by passing a stream of
carbon dioxide through the liquid.

Sulphur dichloride rapidly dissociates with ri^e of temperature into free
chlorine and disulpbur dichloride; at +ao* this decomposition amounts to
6.5 per cent., at 50* 24.59 P^ cent., and at 100* 80.85 P*^'' <^cnt. On boiling
the compound, therefore, chlorine is evolved, and the disulpbur dichloride
remains behind.

In contact with water it is decomposed in the same manner as the mon*
stable compound.

Sulphur Tetnichloxlde, SQ4.— This compound only exists at temperatures
below - aa*. and is produced by saturating sulphur dichloride with chlorine at
that temperature. It dissociates very rapidly as the temperature rises ; thus,
at 7* above the temperature at which it is formed, viz., at - 15*, this decom*
position amounts to 58.05 per cent. At -a* 88.07 per cent of the compound
dissociates, while at +6. a the percentage rises to 97.57.

The compound is decomposed by water with violence into sulphur dioxide
and hydrochloric acid —

SCI4 + 2H,0 = SOj + 4HCL

Compounds of Stilphar with Bromine and Iodine have licen obtained,
corresponding to SjClf S,Br] as a red-coloiu^d liquid, boiling with partial
decomposition at aoo* ; and S,!] as a dark-grey crystalline solid, which meltf
at a temperat'.ire about 6o*.

OXIDES AND OXYACIDS OP SULPHUR.
Four oxides of sulphur are known, namely —

(1.) Sulphur dioxide (sulphurous anhydride) . SOf.

(2.) Sulphur trioxide (sulphuric anhydride) SO3.

(3.) Sulphur sesquioxide .... SjOj.

(4.) Persulphuric anhydride .... S^Oj,

Three of these oxides, namely, Nos. i, 2, 4, give rise respectively

376 Inorganic Chemistry

to the three acids, sulphurous, sulphuric, and persulpburic, besides
which several others are known —

Hyposulphurous acid . . . H|SO| 52 \ S.

Sulphurous acid .... H^SO, HO [ ^^"

Sulphuric acid HjSO* HO [ ^^«'

Persulphuric acid .... HSO4* ^o | ^^«'

Thiosulphuric acid 1 . . . . H,S,03 HS [ ^^*

Pyrosulphuric acid (Nordhausen ) u o rk HO. SO, ) ri
sulphuric acid) . . . .J"«^«"t hO.SO,/"-

Besides these acids, there is a series known under the general
name of the polythionic acids. They may be regarded as being
derived from dithionic acid, which is the first of the series, by the
absorption into the molecule of various quantities of sulphur.
Four of these acids are believed to exist, viz. : —

Dithionic acid (sometimes called ) t t c n HO. 80^ )
hyposulphuric acid) . . .J "a^a^e hO.SO, J

Trithionic acid H^SjO, HO SO* I S-

Tetrathionic acid .... HjS^Oj hq SO* I ^»
Pentathionic acid .... H^O^ hOSO*[^»-

SULPHTJE DIOXIDE.
Foimula, SO3. Molecular weight = 63.92. Density = 31.96.

Occurrence. — This compound is met with in the gaseous
emanations from volcanoes, and in solution in certain volcanic
springs. It is also present in the air of towns, being derived from
the combustion of the sulphur compounds present in coaL

Modes of Formation. — (i.) Sulphur dioxide is formed when
sulphur burns in air or oxygen —

S + O, = SO2.

• By some chemists- H,S,08, {}q ^^^ } Oj.

t This acid is sometimes incorrectly called hyposulphurous acid, its sodium sak
beinj; known as sodium hyposulphiU: the so-called ' ' hypo " of the photogra|>heGp.

Stdphur Dioxide 377

At the same time small quantities of sulphur trioxide are formed,
which render the gas obtained by this combustion more or less

foggy-

(2.) Sulphur dioxide may also be obtained by heating sulphur
with a metallic peroxide, such as manganese dioxide, thus —

S, + MnO, - SO, + MnS.

(3.) It is obtained when such metallic sulphides as copper pyrites
or iron pyrites are roasted in a current of air, the metal being con-
verted into oxide, thus —

2FeS, + no = FcjiOs + 4S0,.

(4.) The most convenient laboratory process for preparing sul-
phur dioxide consists in heating sulphuric acid with copper, the
final products of the reaction being copper sulphate, water, and
sulphur dioxide —

Cu + 2H,S04 - CUSO4 + SO, + 2H,0.

The metals mercury or silver may be substituted for copper, but
in practice the latter metal is usually employed.

($.} Sulphur dioxide is also formed when sulphuric acid is heated
with sulphur, the oxidation of the sulphur and the reduction of the
sulphuric acid going on simultaneously —

S + 2H,S04 - 2H,0 + 3S0,.

(6.) The reduction of sulphuric acid may be brought about by
means of carbon ; thus, if sulphuric acid be heated with carbon, the
latter is oxidised to carbon dioxide, and the acid is reduced to
sulphur dioxide —

C + 2H,S04 - 2H,0 + 2S0, + CO,.

This method is employed on a large scale for the preparation of
alkaline sulphites. The carbon dioxide which accompanies the sul-
phur dioxide, not being soluble to any extent in water containing
sulphurous acid, is not in any way detrimental

(7.) Sulphur dioxide is formed by the decomposition of a sulphite
by dilute sulphuric acid, thus —

Na.SO, f 11.50, - Na,S04 + H,0 + SO^

378 Inorganic Chemistry

Properties. — Sulphur dioxide is a colourless gas, ha^nng the
well-known suffocating smell usually associated with burning
sulphur. The gas will not bum in the air, nor will it support the
combustion of ordinary combustibles : a taper introduced into the
gas is instantly extinguished. Sulphur dioxide is more than twice
as heavy as air, its specific gravity being 2.21 1 (airsi). On this
account it is readily collected by displacement : it cannot be
collected over water on account of its solubility in that liquid, but
may be collected over mercury. The solubility of sulphur dioxide
in water at various temperatures is seen by the following figures —

I vol. of water at o" dissolves 79789 vols. SCj.

»*

f»

20'

39.374

»»

t»

»f

40"

•1

18.766

t»

The solution is strongly acid, and is regarded as sulphurous
acid, the gas having entered into chemical union with the water—

SO, + H,0 = HjSOj.

On cooling a saturated solution of sulphur dioxide to o", a solid
crystalline hydrate is deposited, having the composition H^SOj,

BH^O.*
When the solution is boiled, the whole of the sulphur dioxide is

expelled.

Sulphur dioxide is an easily liquefied gas. At o* a pi assure of
1.53 atmospheres is sufficient to condense it, while at ordinary
pressures it may be liquefied by a cold of - 10'. Its criticsd
temperature is 155.4'-

To obtain liquid sulphur dioxide, the gas, as evolved from the
action of sulphuric acid upon copper, is dried by being passed
through a bottle containing sulphuric acid, and is then passed
through a gas-condensing tube. Fig. 109, immersed in a freez-
ing mixture. The gas at once condenses in the bulb of the
apparatus, as a colourless, transparent, mobile liquid, which boils
at -8*. When the liquid is cooled to -76* it solidifies to a trans-
parent, ice-like mass.

Liquid sulphur dioxide is largely employed as a refrigerating
agent, low temperatures being obtained by its rapid evaporation

• Several cryohydraies of sulphurous acid h.ive been obtained. H^O,,6II,0
HaSO,.10n,O; H,S0^14H,0.

Sulphur Dioxidt

379

onder reduced pressure. The liquid dissolt-es phosphonu, iodine,
sulphur, and many resins. When thrown upon water, a portion of
the liquid dissolves, and, owing to the reduction of temperature
caused by the rapid evaporation of the remainder, a quantity of
the water is froieo. The ice so produced contains a large pro-
portion of the solid hydrate H,S0„8H,0.

Although sulphur dioxide is incapable of supporting the com-
bustion of ordinary combustibles, many metals will take fire and

burn when heated in the gas. Thus, «hcn finely divided iron is
heated in a stream of sulphur dioxide it bums, forming sulphide
and oxide of the mclal.

It also unites with many m
much energy as to give rise to
over peroxide of lead, the ma
and lead sulphate is produced-

Elnllic peroxides, and often with so
light and heat. Tlius, when passed
ss glows spontaneously in the gas.

PbO, + SO, - rbSO,.
Sulphur dioude is decomposed by the influence of strong light

If a conccniraied beam of elRctric light be passed through avessel
iilled with gaseous sulphur dioxide, the gas at first will appear
perfectly tratispareni and clear ; but in the course of a few minutes
the track of the beam will become more and more visible as tl
traverses the gas, owing lo the formation of thin ckiuds of sulphur
trioxide and sulphur, until the atmosphere of the vessel appeara j
10 be filled with fog (Fig. i lo)—

3SO, = 2S0, + S-

AJter the lapse of a short time, if the vessel be removed hato

the strong light, the atmosphere will once more become clea
owing to the reformation of sulphur dioxide.

Sulphur dioxide possesses powerful bleaching properties, whdl
in the presence of water, lis bleaching actio
absorption of oxygen from water, and consequent liberation of
hydrogen, ihus^

SO, + 2H50 = H,SO, + 11,.

The hydrogen so set free reduces the colouring-mailer, with the
formation of colourless compounds : the action in this case being
the reverse to that which lakes place with chlorine. In some
instances, the bleaching is due to the formation of a colourless
compound, by the direct combination of sulphur dioxide with llie
colouring-mailer, as the origirial colour may often be restored by
ticalmcnl with dilute sulphuric acid, or by weak alkaline solutions.
Thus, by passing sulphur dioxide into an itifu^ion of rose leaves,
(he ted colour of the liquid is quickly discharged, but (

Sulphur Dioxide 38 1

addition of a small quantity of sulphuric acid the colour is
restored.

Sulphur dioxide is employed in bleaching materials that would
be injured by exposure to chlorine, such as straw, silk, wool,
sponge, &c, and the familiar yellow colour which gradually comes
over a sponge or a piece of bleached flannel when it is washed
^nth soap, is an illustration of the power of alkalies to restore the
original colour to materials that have been bleached by this
substance.

In the presence of water, sulphur dioxide converts chlorine into
hydrochloric acid, and on this account is employed as an "anti-
chlor "—

SO, + 2H,0 + CI, = 2HC1 + H,S04.

In the same way it acts upon iodine, with the formation of
hydriodic acid —

SO, + 2H,0 + I, - 2H1 + H^SO^.

In the case of iodine, however, this reaction only takes place
when a certain degree of dilution is maintained, for in a more
concentrated condition sulphuric acid is reduced by hydriodic acid,
into sulphur dioxide, according to the reverse equation, thus—

H,S04 + 2HI - I, + 2H,0 + SO,.

It has been shown ^ that aqueous sulphurous acid can only be
completely oxidised by iodine, as indicated in the former equation,
when the proportion of sulphur dioxide does not exceed 0.05 per
cent. : when the amoimt exceeds this proportion the second reaction
comes into operation.

Sulphur dioxide brought into contact with iodic acid, or an
iodate, is oxidised into sulphuric acid and liberates iodine, thus —

2HI0, + 4H,0 + 6S0, - 6H,S04 + la-

This reaction is made use of^ as a method for the detection of
the presence of sulphur dioxide. Paper which has been moistened
with a solution of potassium iodate and starch, on exposure to
sulphur dioxide is at once turned blue, owing to the liberated
iodine combining with the starch.

Inorganic Clumistry

The composiiion of sulphur dioxide may be delermined by die
combustion of sulphur in a measured volume of o^gen, in ihe
apparatus employed for showing [he volume composition of carbon
dioxide (Fig. 64). After the fragment of sulphur has burnt, and
ihe apparatus has been allowed to cool, it will be seen that there
is no alteration in the volume of the contained gas ; the sulphur
dioxide produced, occupying the s.ime volume as the oxygen used
Id its foimaiion. Sulphur dioxide, in other nords, contains its
own volume ol oxygen. One molecule, therefore, of sulphur
dioxide contains one molecule of oxygen, weighing 31.91. But
the molecular weight of sulphur dioxide is 63.92 \ therefore
63.92 - 31.91 = 32 " the weight of sulphur contained in the
molecule of the gas. Sulphur dioxide, therefore, contains in ihe
molecule one atom of sulphur, combined with two atoms of oxj'gen,
hence its composition is expressed by the formula SO^

Sulphurous Acid and Sulphites. — Sulphurous add is only
known in solution and in its cryohydrates. The solution smells
of sulphur dioxide, and gradually undergoes decomposition by
absorption of oxygen. The acid is dibasic, having two atoms of
hydrogen replaceable by metals : it is therefore capable of form-
ing two series of sails, according to whether one or both of the
hydrogen atoms are replaced. Thus, by its action upon potassium
hydroxide, when the acid is in excess the so-called acid potassium
sulphite, or hydrogen potassium sulphite, is obtained —

KHO + H,SO, = HjO -h HKSOi-

Whereas, il the metallic hydroxide be in excess, the noi
potassium sulphite is formed—

2KH0 -<- H,SO, = 2H,0 ■^ K,SO^

The alkaline sulphites are readily soluble in water, all c
normal sulphites being either difficult of solution or insoluble.

SULFEUB TRIOZmR

Formula, SO^ Molecular weighl = 79.88. Vapour

modes of Formation. — (1.) This compound is produced, when
a mixture of sulphur dioxide and oxygen is passed over heated
spongy platinum or platinised asbesios —

SO, -t- o - so*

mal J

sed over heated 1

Sulphur Trioxidi 383

On leading the product through a well-cooled receiver, the sulphur
trioxidc condenses in white silky needles. This method has been
successfully employed on a commercial scale. The mixture of
sulphur dioxide and oxygen, is obtained by allowing ordinary strong
sulphuric acid to drop into earthenware retorts heated to bright
redness, whereby it is almost entirely broken up into these two
gases and water, thus —

H,S04 = SOj + O + HjO.

The gases are then deprived of the water, by passage first through
a condenser, and then through a leaden tower containing coke
moistened with sulphuric acid, and are finally passed over heated
platinised asbestos contained in glazed earthenware pipes.

(2.) Sulphur trioxide is most conveniently obtained by gently
heating pyrosulphuric acid in a glass retort The trioxide distils
over and may be collected in a well-cooled receiver —

HgSjO; - H,S04 + SO,.

(3.) It may also be obtained by heating sodium pyrosulphate to
bright redness —

Na,S,Or « Na,S04 + SO,.

The sodium pyrosulphate is produced when hydrogen sodium
sulphate (so-called bisulphaie 0/ soda) is heated to about 300^
thus —

8HNaS04 - HgO + ^z^Sfiv

And on account of this origin it is sometimes termed anhydrous
sodium bisu^haU,

(4.) Sulphur trioxide can also be produced by the action of
phosphorus pentoxide upon sulphuric acid. This most powerful
dehydrating substance withdraws from the sulphuric acid the
elements of water, when gently heated, thus —

H,S04 -I- P,Og - 2HP0, + SOr

The trioxide is distilled from the mixture, and the metaphosphoric
acid remains in the retort

Properties. — Sulphur trioxide is a white, silky-looking, crystal-
line substance, which melts at 14.8* and boils at 46*. It is very
volatile, and gives oflT dense white fumes in contact with air, owing

j84

to the combination of its vapour with atmospheric ir
sulphuric acid. It combines with water with great energy li
sulphuric acid ; a fragment of the compound dropped into
dissolves with a hissing sound resembling the quenching of red-li

When brought in contact with the skin, or other organic
containing hydrogen and oxygen, it abstracts these elements a
produces a burnt or charred effect upon the substance.

Eclly with barium OJtide, DaO, and if the bary
be dry, the mass becomes incandescent owing to the heal of (I
union, and barium sulphate is fonned —

When the vapour of sulphui trioxide is passed through a red-h
lube, it is broken down into sulphur dioxide and oxygen.

When the trioxide is heated, it melts to a colourless liquid, which
exhibits a remarkably high rate of expansion by heal ; between
ij°and4S*its mean coefficient of expansion is 0.0027, nearly three-
fourths of the expansion coefficient of a gas.

SulphuF Sesquloxlde, S,0^— A solution of this compound in
fuming sulphuric acid was obtained early in the century by healing
flowers of sulphur with Nordhausen sulphuric acid, whereby a blue
solution was obtained. The substance may be prepared by tiie
gradual addition of dry flowers of sulphur 10 melted sulphur
trioxide, at a temperature just above its melting-point, when a
malachite-green cryilallinc solid separates out.

The compound is unstable at ordinary temperatures, being
resolved into sulphur dioxide and sulphur, the decomposition taking
place rapidly upon gently wanning —

8S,0, = S + 3S0,

If the sesquioxide be sealed up in a bent glass lube and gently

warmed, the sulphur dioxide may be obttiined liquid in one limb a

Ibe tube. '

PEESULFHUBIC AHETDKIDE.

Fonnula, S^

This compound is lormed when a mixture of dry sulphur dio:

and oxygen is subjected to the silent electric discharxc ii

Persulphuric Acid 385

tube, or by treating sulphur trioxide and oxygen in the same
manner. At the end of some hours a small quantity of a viscous
liquid collects upon the walls of the glass vessel, which when
cooled, solidifies in the form of long transparent needle-shaped
crystals, resembling sulphur trioxide in appearance. It is a very
unstable substance, and can only be preserved a short time even at
low temperatures. It is soluble in water, with the formation of
persulphuric acid, but the solution rapidly undergoes decomposition
into oxygen and sulphuric acid —

SjOt + H,0 = 2HSO4.
2HSO4 + H,0 = 2H,S04 -^ O.

When very gently warmed, persulphuric anhydride rapidly
breaks up into sulphur trioxide and oxygen —

SjO: = 2S08 + O.

The readiness with which it gives up oxygen, constitutes this com-
pound a powerful oxidising agent, and affords the clue to most of
its reactions.

Pennlplrarlo Add and Pennlphatef.— When dilute stilphuric acid is sub-
jected to electrolysis (as in the process commonly spoken of as the eUctrolysu
oftoaUr), appreciable quantities of persulphuric acid are found in solution at
the positive electrode, or anode.

The add itself has never been obtained in a state of purity, its aqueous
solution rapidly undergoing decomposition, as already mentioned.

In solution this compound displays all the oxidising properties of the oxide.

The potassium salt may be obtained by the electrolysis of a saturated solu-
tion of hydrogen potassium sulphate in a divided cell, the action being due to
the oxidation of the hydrogen potassium sulphate by the nascent oxygen
developed at the anode, thus —

2HKSO4 + O = H,0 + 2KSO4.

The potassium persulphate, being a sparingly soluble salt, crystallises out.
and may be freed from the acid sulphate by recrystallisation.

The ammonium salt, NH4SO4, and the barium salt, Ba(S04)3.4H30, have
also been obtained. Barium persulphate is soluble in water, being much more
readily dissolved than the potassium salt ; thus, xoo parts of water at o* dissolve
1.77 parts of potassium persulphate and 53.2 parts of the barium salt. On
this account solutions of persulphates give no precipitate with barium chloride,
whereby they are distinguished from sulphates : if the mixtive be warmed,
however, the persulphate is decomposed into a sulphate, with evolution of
chlorine, thus —

3iCS04 -k- Bad, s Ba(S04), -I- 2Ka = BaS04 -»- K,S04 + Of.

384

Inorga$dc C

to the combination of its vapour wif
sulphuric acid It combines with v
sulphuric add ; a fragment of the
dissolves with a hissing sound reseii
iron —

SO, + H,0

When brought in contact with th
containing hydrogen and oxygen,
produces a burnt or charred effec
trioxide unites directly with bariun
be dry, the mass becomes incand
union, and barium sulphate is fom

BaO + SO;

\Vhen the vapour of sulphui tri
tube, it is broken down into snip;

WHicn the trioxide is heated, it
exhibits a remarkably high rat
25* and 45* its mean coefficient 1
fourths of the expansion coeffici*

Sulphur Sesquioxlde, SjOg.
fuming sulphuric acid was obtai'
flowers of sulphur with Nordha-
solulion was obtained. The s
gradual addition of dry ilow<
trioxide, at a temperature ju^
malachite-grccn crystalline sol:

The compound is unstabl*.
resolved into sulphur dioxide a
place rapidly upon gently war:

If the scsquioxide be seale
warmed, the sulphur dioxide 1
the tube.

PER8ULFB'

This compound is formed ■
and oxygen is subjected to tl:

: 1

i:=S

Sulphuric Acid 387

Tbe sodium udt po&sesses the same bleaching and reducing powrrs as the
acid ; and when wet, or in solution, it rapidly absorbs oxygen from the air and
is converted into hydrogen sodium sulphite —

HNaSOa + O = HNaSO^

SULPHURIC ACID.
Formula. H^SOi.

Modes of Formation. — (i.) This acid is formed when sulphur
trioxide is dissolved in water —

SO, + H,0 = H,S04.

(2.) It is «ilso formed by the direct union of sulphur dioxide with
hydrogen peroxide —

SO, + H,0, - H,S04.

(3.) An aqueous solution of sulphur dioxide gradually absorbs
oxygen, and is converted into sulphuric acid —

H,SO, + O - HjSO^.

(4.) Manufaeture of Sulphurie Acid.— Sulphur dioxide is un-
able to absorb an additional atom of oxygen, and so pass into
sulphur trioxide, without the aid of some third substance, which
can act as a catalytic agent, or a carrier of oxygen. The material
which is employed for this purpose, in the process by which sul-
phuric acid is manufactured, is one of the oxides of nitrogen, which
is capable of giving up oxygen to the sulphur dioxide, and of again
taking up oxygen from the air. Thus, nitrogen peroxide (NOj),
by the loss of one atom of oxygen, is reduced to nitric oxide, NO ;
which in its turn combines with atmospheric oxygen, and is re-
converted into nitrogen peroxide. Therefore, when sulphur dioxide
and oxygen are mixed with nitrogen peroxide in the presence of
steam, a series of reactions takes place, the final result of which
is that the oxygen is caused to combine with the sulphur dioxide
and water, with the formation of sulphuric acid —

SO, -h O + H,0 - H,S04.

The nitrogen peroxide at the end of the reaction is unchanged,
and is able to react in the same series of changes over and over

388

Inorganic Cktmistry

again, thus trans fo mi in g, theotctically, an unlimited, and, I
practice, a relatively large quantity of sulphur dioxide into s
phuric acid.

Tlie aeries of changes that gives rise lo the ultimate product is
the following ;^The sulphur dioxide, nitrogen peroxide, and water
give rise, in the lirsi place, lo the formaiion of niiro-sulphonic
acid and a molecule of nitric oxide—

(j.) 2S0, + 3N0, + H,0 = SH(NO)SO, + NO.

Nitro-sulphonic acid (somelimes called nitro-iulphuri( acid, and
mtrosyl sulphate) may be regarded as sulphuric acid in which one
of the hydrogen atoms is replaced by the group (NO), thus,

'\o

in which case the nitrogen is linked to the sulphur

by Ihe inien-ention of oxygen ; or it may be considered as derived
from sulphuric acid by the replacement of one of the groups (HO)

when the nitrogen is directly

by the group NO^ S0,<

NO,

ind the former
ic OKygen, is at

attached to the sulphur. The substance is a white crystalline
compound, which in the presence of water is instantly decomposed
into sulphuric acid and a mixture of nitric oxide and lutrogen
peroxide, thus —

(a.) SSO^HOXNO,) + H,0 = 2H,S0, + NO 4 NO^

The nitric oxide in this
contact with the atmospht
nitrogen peroxide —

(3.) NO + O - NO,.

In the process of the manufacture, the crj-stalllne compound
SO,(HOXNO,) (known as eAamifr crystals) is not actually isolated,
unless from accidenial causes the supply of water is in deficit, the
production of these crystals being regarded as an indication that
the process is not being well carried out.

The formation of sulphuric acid by these reactions, with the
inlcrmedi.ite production of the chamber crystals, may be carried
out on a small scale by means of the apparatus shown in Fig. iii,
A large flask, F, is fitted with a cork, through which pass five
lubes : three of these are connected to separate two-necked boliles
containing sulphuric acid, through which can be delivered lespec-

Sulphuric Acid

]S«

tively, nitric oxidr^ sulphur dioxide, and oxygen. Tb« fbunh tube
is attached to a flask in which water may be boiled, and through
which oxygen can be passed, and the fifth tube (not shown in
the figure) serves as an exit. A quantity of oxygen is first passed
into the large flask through the drying-bottle D, and sufficient
nitric oxide is then allowed to enter, to form deep red vapours ; at
the same time sulphur dioxide is passed in through the bottle S.
Id order to introduce a small quantity of moisture, oxygen is
allowed (o enter through the flask of boiling water, and in a few
moments large white crystals begin to form all over the interior

of the flask, and rapidly spread until the whole surface it

In order to show the second reaction in the cycle, the gaseous
contents of the flask may be swept out by means of a rapid stream
of oxygen, passed in through the drying-bottle D ; and when the
atmosphere within the apparatus is colourless, a quantity of steajn
is driven in from the small flask. The chamber crystals will be
seen to dissolve with effervescence, and the flask once more
becomes filled with brown fumes. The nitric oxide evolved by
the decomposition of the nitrosyl sulphate, coming in contact with
the oxygen within the flask, at once regenerates nitrogen peroxide,
in accordance with equation No. 3.

The solution formed in tbe flaik will be found to yield a pre-

390 Inorganic Chewislry

cipitaie of barium sulphate, oo the addition to it of a soluble
bariiuii salt.

On a man u fact u ring scale, the combination of the reacting gases
and vapours whidi gives rise to the sulphuric acid, lakes place in
large leaden chambers, usually about loo feet long, 25 feel wide,
and 20 feet high, having therefore a capacity of 50,000 cubic feet ;
several of such chambers being placed in scries. (nto these
chambers there is delivered sulpliur dioxide, nir, oxides of nitrogen,

The plan', employed for the manufacture of sulphuric acid con-
sists broadly of four parts, i. Apparatus for generating sulphur
dioxide. 2. Apparatus for producing oxides of nitrogen. 3. Appa-
ratus for absorbing oxides of nitrogen from the gases leaving the
chambers. 4. The chambers in which the reactions are made.

(1.) Pyrites Burners.— The sulphur dioxide is obtained either by
burning native sulphur, or roasting the "spent oxide" of the gas
works (see Sulphur), or by roasting pyrites, the latter being the
most general method. The pyrites burner, Fig, 1 ii, B, is essen-
tially a small furnace or kiln in which the ore is heated, and in
which the admission of air can be duly regulated ; as not only is it
necessary to admit sufficient air to completely bum the whole of
the sulphur, and so prevent any volatilisation of it in an unbumt
condition, but also to supply the requisite volume of oxygen for the
requirements of the reactions whicli are to go on within the chani'
ber. Too large a volume of air must be avoided, in order not to
unduly dilute the chamber gases.

(2.} If no loss of nitrogen peroxide took place during the cycle
of changes, the same quantity of this gas would convert an infinite
amount of sulphur dioxide and water into sulphuric acid ; but in
practice, owing to leakage, defective absorption, and the reduction
of a certain percentage of this compound into nitrous oxide, it is
necessary to constantly replenish the supply. This is usually done
by generating a small quantity of nitric acid (by the action o<
sulphuric acid upon nitre) in earthenware pots, which are usually
placed in an enlarged part of the flue of the pyrites burner, known
as the " nitre oven," and which is provided with a door for the
introduction of the pots. Fig. 112, N, The heated gases playing
upon these pots, promotes the evolution of the nitric acid, which in
contact with sulphur dio^tide is ai once decomposed aecordinfr 10
the equation —

suno, + SO, = H^o, t awOp

Sulphuric Acid 39 1

It is found that to make up for the loss of nitrogen peroxide,
about three to four parts of nitre are required for every loo parts
of sulphur, burnt as pyrites.

(3.) The apparatus for the absorption of the nitrogen peroxide
from the gases that are drawn from the chamber at the end of the
series, is known as the "Gay-Lussac Tower," Fig. 112, T. This
consists of a square leaden tower filled with fragments of coke,
and down which there is caused to slowly percolate, a stream of
cold strong sulphuric acid, the acid being evenly spread over the
mass of coke by a special distributing arrangement. The nitrogen
peroxide is absorbed by the acid, with the formation of nitro-
sul phonic acid, SO,(HO)(NO,). In order to make use of the
absorbed nitroxygen compound, the acid which flows from the
Gay-Lussac tower is pumped to the top of another very similar
tower, situated between the '* burners " and the first of the cham-
bers, and known as the " Glover Tower," G. The hot gases from
the burners, consisting of sulphur dioxide, nitrogen, and oxygen,
together with the small quantities of nitrogen peroxide from the
nitre pots, are made to pass up this tower on their way to the first
chamber, and meeting with the descending stream of nitro-sul-
phonic add as it percolates through the mass of coke with which
the tower is filled, denitrification of the latter takes place, thus —

2SO,{HOXNO,) + SO,+2H,0-2NO + 3SO,(HOXHO),

or 3H,S04.

The nitric oxide thus evolved, in presence of the atmospheric
oxygen, is converted into nitrogen peroxide, and swept along with
the other gases into the chambers.

In practice, it is usual to deliver down the Glover tower, besides
the nitro-sulphonic acid, a quantity of ''chamber acid" from a
separate tank. The effect of the heated gases upon this dilute
acid, is to remove a portion of the water from it, thereby effecting
its partial concentration, and furnishing the water demanded by
the above equation. It will be seen, therefore, that there is a
scrubber tower at each end of the series of chambers, the
*' Gay-Lussac " at the exit, where nitrogen peroxide is absorbed ;
and the ''Glover" at the commencement, where the dissolved
nitrogen compound is again liberated and returned to the
chambers.

(4.) The chambers are made of sheet lead, conneaed togethei

ig2 Inorganic Chemistry

by bsing the edges by means of an oxyhydrogen flama, wi
the intervemion of solder, as the presence of another metal
rise to the rapid corrosion of the lead on account of gal'
action being set up ; this method of joining the lead is known
autogenous soldering. The enormous leaden chamber is suppoj
in a framework of wood, to which the lead is secured by bands
the same metal, and the whole is usually supported on iton or
brick pillars.

Tlie genera] arrangement of a modem sulphuric acid works is
seen in Fig. 112. The gases from the double row of pyrites
burners B, are led througb the Glover towet G, where they
efTect the denitrification of the nitro-sul phonic acid, as already
explained. From this tower they are delivered into the scries ol
chambers, where they meet with the necessary supply of steam.
The acid collects upon the floor of the chambers, and samples are
constantly drawn off by means of an arrangement known as a
dfip pipe, which, acting in a manner similar to a rain gauge, indi-
cates the progress of the processes going on within. The gases
after being drawn through the entire scries of chambers, by means
of the draught caused by the tall chimney, are finaily passed up
the Gay-Lussac tower T, whete all the nittogen peroxide is
absorbed, and returned to the chambers through tbe intervention
of the Glover tower G, as above described.

The acid which collects in the chambers, is usually not permitted
to reach a higher specific gravity than about 1.6, when il
about 6g per cent, of sulphuric acid ; for if the strength be allowed
to exceed this, the acid not only begins to dissolve the nitrogen
peroxide in the chamber, but exerts a corrosive action upon
lead of which the chamber is constructed. It is therefore witl
drawn, and the first stage in the further concentration is elTect
either by the action of the Glover lower, or by evaporation
shallow leaden p.tns.

In order to bring up the strength of tbe acid to that of "oil of
vitriol," that is, to about 98 per cent., the acid from the Glover
tower, or the leaden pans, is heated in either glass or platinum

stills.

Sulphuric acid, unless specially purified, is hable to contain a
number of impurities, such as lead sulphate, derived from the
action of the acid upon the chamber ; arsenic, from the pyrites
employed ; oxides of nitrogen, and sulphur dioxide. From most
of the Impurities, except the anenic, the acid may be purified

tbe^H

:ted^H

difa

Sulfifturic Aciii

iibsequeni redi»- ^^H

(NH,),SO, * 8SO,(HOKNO,) - 3H,SO, + SH ,0 + iN,

B - DwUe mw of

ne Oicwn u vperu

flf) with iwD timksmt IM

? altn>-iulpharii: wdd A

C. — LciuJcn cbunibvi) af wbkh rbtt u

P —Pipe (aniTyina the nset hum it
iUkI chumlKi IS iht Gay-Um

T.-CyLuiutTowtr. Tbeui

Arsenic may be removed by boiling the acid with hydrochloric

acid or sodium chloride, when it passes away as arsenious chloride.

PFOpertlss. —Sulphuric acid is a perfectly colourless, heavyi

394

Inorganic Chtmistry

oily liquid. The acid obtained by disiitlaiion, always cODtSUM

about I per cent, of water ; stronger than this it cannot be prepare

by evaporation or distillation. When, however, acid of this strengtlO

is cooled to o°, colourless crystals of pure sulphuric acid, cc

too per cent. H,SO„ are deposited The crystals melt al ia;^

and remain liquid at temperatures much below this point.

specific gravity of the pure acid is 1.854 al oV When boiled,!

gives off sulphur trioxide until the amount of water in i'

1.5 per cent., when it distils unchanged at a temperature of 338".

hiulphuric actd has a powerful affinity for water, and absorb
moisture from the atmosphere with great readiness. On thif
account it constitutes one or the most valuable desiccating agcnttt
and is constantly made use of for depriving gast'S, upon which il
exerts no chemical action, of aqueous vapour. Owing to its strong
afGnity for water, it decomposes many organic substances contain-
ing hydrogen and oxygen, withdrawing from the compounds these
elements in the proportion to yield water : its action upon formic
acid, oxalic acid (see Carbon Monoxide), and alcohol (see Ethy-
lene) are examples of this action.

When the acid is poured upon such substances as wood or sugar,
the elements composing water are withdrawn, and the carbon is
liberated, with the result that the compounds are blackened or
charred.

When sulphuric acid is tnixed with water, considerable heat is
disengaged, the temperature ofLen rising to the boiling-poini of
water, and al the same lime a diminution in volume takes place.
The maximum contraction is obtained upon mixing the materials
in the proportion of one molecule of acid to two molecules of water.
The diminution in volume in this case amounts to 8 per ccnL, and
the composition of the acid produced, corresponds to the formula
H,S0„2H,0.

Sulphuric acid combines with water in various proportions, form-
ing a number of hydrates, and cryohydraies, of a more or less
definile character. The best known hydrates are those represented
bythe formula H,S0.,H50 and H,SO„2H,0. These compounds
may be regarded as respectively leirabasic and hesabasic sulphuric
acid, and their relation to the ordinary dibasic acid may be
expressed by the following formula —

H,SO, ... or SO^HO)^
H.SOi or H,SO..H,0 „ SO(HCj,.
H,SO, „ H,bOt,aH,0„ S(KO),

Pyrosulpkuric Acid 395

Salts of each of these acids are known —

Hydrogen potassium sulphate . . HKSO^'v

Normal potassium sulphate . . K1SO4 }- Derived from H1SO4.

Barium sulphate BaS04 J

Tetrabosic lead sulphate . . . Pb^fSOi .. •> H^SO^

Hexabasic mercuric sulphate ) u- cr^ xx sir\

(Turpclh mmeral) j o. • •- w

Most sulphates are soluble in water : those of lead, calcium, and
strontium are only very sparingly soluble, whilst barium sulphate is
insoluble both in water and acids. The presence of sulphuric acid
or a sulphate, may therefore be readily detected by the addition of
a soluble barium salt, which causes the immediate precipitation 0/
white barium sulphate, insoluble in hydrochloric acid.

PTSOSULPHUBIC ACID {NorJhausm Acid; Fuming Sulphuric Add),

Formula, HAO7 or {Jg:|gj}0.

Modes of Formation.— ( I.) This acid may be obtained by dis-
solving sulphur trioxide in ordinary sulphuric acid —

H,S04 + SO, = HjSjOy.

On cooling the solution to o*, the pyrosulphuric acid separates out
in the form of large colourless crystals.

(2.) Pyrosulphuric acid is manufactured by the distillation of
ferrous sulphate in day retorts, mounted in series in a large
'* K^llcy " furnace. The first action of heat upon crystallised ferrous
sulphate (green vitriol) is to expel six molecules of water of crystal-
lisation, leaving the salt of the composition FeS04,H20. When
this substance is further heated it is decomposed finally into ferric
oxide, with the formation of sulphur trioxide, water, and sulphur
dioxide, thus —

2FeS04,H,0 = Fe,0, + SO, + SO, + 2H,0.

The decomposition takes place in two stages, the sulphur dioxide
and water being evolved in the first part of the process with the
formation of ferric sulphate, which is afterwards broken up in the
manner shown in the following equation —

(I.) 6FeS04,H,0 - Fe,(S04), + 2Fe,0, f 3SO, + 6I1,0.
(2.) Fc,(SO/, - Fe,0, + 3S0»

J96

Inorganic Chemistry

The sulphur trioxide is condensed in receivers, containing eiUl<|
a small quanlily of water, or a charge of sulphuric acid.

(3.) Pyrosulphuric acid may also be obtained by decoinpoaia|
sodium pyrosulphate (NajSiOj), either by heating it to
temperature (see Sulphur Trioxide, page 383), or by acting upon^
with sulphuric add, thus—

Na,S,0, + H^O« - SHNaSO,

SO,.

.cid,as«

The sulphur trioxide obtained, is dissolved in sulphur
the former methods ; and the hydrogen sodium sulphal
gently heated to about 300°, is reconverted into pyrosulphalc t
the loss of a molecule of water (page 383).

Propei^es. — Pyrosulphuric acid is a colourless, strongly fiimiD
hquid, having a specific gravity of 1.88. When cooled, it solidifi(
(o a crystalline mass, which melts at 35°. The compound may haM
regarded as consisting of one molecule of sulphuric acid plus t
molecule of sulphur irloxide, H,SO^SO] ; or, as being derive
from two molecules of sulphuric acid, by the withdrawal of a
molecule of water, thus—

/OH
=<0-H '

HOS
H-O/'

'SO. = H,0 + SO,

/O-H H-0\

Pyrosulphuric acid forms a stable series of salts, of which t
sodium compound already mentioned is a typical eitample.
salts are sometimes spoken of as the dhulphates, and are analogov
to ihe dichromates \,q.v.').

Two olbei deHnite compounds of sulpbur (riaxide and solpburic
known to exist, t»tti of which are fuming acids. The cotnposillor
lubslances is expressed by the formulK —

H^Oi,3SO„ or H^,Oi, ; and 3H^0.,SO,. or HjS.Oi^

TmOSULPHITBIO ACID.

Formula. H^O,.

This acid has never beeji obtained in the free state, as it decom
poses almost as soon as liberated from its salts, Into sulphur dioxii
and water, with precipitation of sulphur —

H,S,0| = SO, 4- H,0 + S.

Thiosulphufic Acid 397

The thiosulphates, however, are stable and important salts, the
sodium salt being largely used in photography under the name of
hyposulphite of soda^ or " hypo."

Modes of Formation of Thiosulphates.— (i.) These salts

may be obtained by digesting flowers of sulphur with solutions of
the sulphites, thus —

Na,SO, + S « NajSjOf

(2.) Sodium thiosulphate is also formed, when sulphur dioxide is
passed into a solution of sodium sulphide. The reaction may be
regarded as taking place in three steps, in which sodiiun sulphite
and sulphuretted hydrogen are the flrst products. The latter com-
pound is then acted upon by sulphur dioxide with the precipitation
of sulphur, thus —

SOj + HjO + Na,S = Na,SO, + H,S.
SO, + 2H,S = 2H,0 + 3S.

And the sulphur reacts with the already formed sulphite, as indi-
cated in the equation given above.

(3.) When sulphur is boiled with sodiiun hydroxide, or with milk
of lime, mixtures of sulphides and thiosulphates are obtained in
both cases—

6NaHO + 4S - Na,S,0, -f 2Na,S -f 8H,0.
3Ca(HO), -I- 12s = CaSjO, -f SCaS^ -f 3H,0.

The sodiiun sulphide can be converted into thiosulphate by the
reactions given above. Calcium pentasulphide, on exposure to air,
absorbs oxygen and forms a further quantity of thiosulphate with
precipitation of sulphur —

CaSft + 30 = 3S + CaSjO,.

The thiosulphates are decomposed by most acids, with the libera-
tion of sulphur dioxide, and precipitation of sulphur. They show a
great tendency to form double salts, many of which are soluble in
water ; thus sodium thiosulphate, in contact with either silver
chloride, bromide, or iodide, forms the soluble double sodium-silver
thiosulphate, NaAgSfOg —

Na,S,0, -I- AgCl - NaCl « NaAgS^O,.

398 Inorganic Chemistry

The employment of sodium thiosulphate in photography, for
*' fixing'' negatives or silver prints, depends upon this property.

Thiosulphuric acid may be regarded as being derived from sul-
phuric acid by the replacement of one of the (HO) or hydroxy!
groups, by an equivalent of (HS) or hydrosulphyl —

HO)so HS?so

XMUdonle Aeld, H|S|0« or p^n-S^ [.—This compound is preparrd. by

passing a stream of sulphur dioxide through wrater in which manganese
dioxide is suspended, whereby manganese dithionate is formed ; while at the
same time a portion of the salt is acted upon by manganese dioxide, and^con-
▼erted into manganous sulphate, thus —

2SO| + MnO, = MnS,0«.
MnS^c + MnO, = 2MnS04.

On the addition of barium hydroxide to the solution, txuium dithionate,
barium sulphate, and manganous hydrate are formed —

MnSjO, + Ha(HO), = BaSjO, + Mn(HO)»

Barium dithionate, being soluble, is separated by filtration, and up>on
evaporation separates out in crystals of the composition BaSaOc,2H30.

Upon the addition of dilute sulphuric acid in amount demanded by the
equation

BaSjO, + H,S04 = BaS04 + H AO«.

the acid itself is obtained. The solution may be concentrated in vacuo until
it reaches a specific gravity of x.347. Further concentration results in its de-
composition into sulphuric acid and sulphur dioxide —

H^O, = SOa + HJSO4.

Dithionic acid forms well-defined crystalline salts, which on heating, decom-
pose into sulphates with evolution of sulphur dioxide.

Dithionic acid was formerly called hyposulphuric acid, and its salts are stiU

sometimes referred to as hy^sulpkates,

H O "SO )
Trlthionlc Add, HjSgO,, or uq-so" ( S-'"'^*'*^ potassium salt of this acid

may be obtained, by passing sulphur dioxide through a strong solution of
potassium thiosulphate —

3SO2 + 2KJS2O, - S + 2KjS,0,.

It is also formed when a solution of potassium silver thiosulphate is boiled -

AgS ion ~ ^^ KOSO, S

}so.

Pentathionic Acid 399

The fodium salt may be obtained, by tbe addition of iodine to a mixture of
sodium sulphite and tbiosulpbate —

NaO

NaS

}sO,+ Na^, + I. = 2NaH-N-0|0,|g^

The add itself is obtained by the addition of fluosilicic acid to a solution of
the potassium salt, when insoluble potassiiun fluosilicate is precipitated.

Both the acid itself, and its salts, are readily decomposed into sulphur dioxide,
sulphur, and either sulphuric acid or a sulphate, thus —

When acted upon by sodium amalgam, sodium trithionate is converted
bock again into its generators, sodium sulphite and thiosulphate, thus—

Tttntthlonio Add, H^^Of or hoI^} ^'^^ sodium salt is obtained
by the action of iodine upon sodium thiosulphate —

2NaSNaO-SO, + I, = XNal + JJ^Q'S^ } ^

The barium salt, from which the add itself is most remdily obtained, is pre-
oared by the gradual addition of iodine to barium thiosulphate in water —

2UaS«0, + I, = Bal, + BaS40«.

The barium tetrathionate is separated by the addition of alcohol, which dis-
solves the iodide and excess of iodine, leaving the tetrathionate. By the
addition of dihite sulphuric add to an aqueous solution of this salt, in
amount demanded by the equation —

BaS40c + H,S04 = HaS^Of + BaS04.

a dilute aqueous solution of the acid may be obtained. The dilute acid may
be boiled without decomposition; but when concentrated, it readily passes into
sulphuric add, sulphur dioxide, and sulphur.

Sodium anudgam decomposes the sodium salt into two molecules of thio-
sulphate, reversing the reaction by which it is produced.

PraUthlonle Add, HaS»0« or ho-S^}Si.— This add is prepared by

passing sulphuretted hydrogen into a strong aqueous solution of sulphur
dioxide —

fiSO, + 6HaS s HjS^c + 6S + 4H,0.

5H,SO, + 6H,S sr H^Of + &S + 9H^.

The solution contains, however, more or less of the other thionic acids, but
as the passage of sulphuretted hydrogen is oootinurd. these are gradually

Inorganu^ Cfumistry

H^,0, + 6H^ = 6HjO

Tlic solulion oblained by Ihe firsl aciion, maji be conccniraicd by cj
evaporalion in vacuo, iinlil a specific gravilyor 1,46 isoblaineil, wben qd
inluralion with polaralum hydroxide and (iliiaiion, a solulion isobiainedwhidi
on spoDlaneousevaporalion duposilscryjlals of pol.nsium pcnialhionale, having
Ibe ccmposilion K^0,,3H,0. On healing, [he sail spUis up ioio polassium
flilpbate. sulphur dioxide, and sulphur.

OXYCni ORtDES OP SULPHUR.

Four of these compounds are known, all of which may b« r
garded as being derived from the oxyaclds by the replacement Q
hydroKyl (HO) by its equivalent of chlorine.

I. Thionyl chlonde.

Sulfhur^i (hhridt Cl/'
a. Sulphuryl chloride, or CI 1 (J-..

Sulphurit chloride CIJ^ '" l"°ls(V '

3. Su1phuricchlorhydniie.0ra(j.n fHO/""*

Chlon

ulfhonu

,. Disiilphuryl chloridf.

110 J"

rClSClo

cisoj ■

SO(NaO), + aPOt = SOCl, + 2P0CI, + 2NaCL

It i* alio obtained when dry sulphur dioxiite b passed over phospbo
penlachloride —

SO, + PCI, = SOCl, + PCtCl,.

PropartlH, — Thionyl chloride Is a. coleurleas and highly refractive liqd
which fumes in moisi air, and has a pungent unpleasant snielL II t "
and is at once decomposed by water, inio its corresponding ojyadd wiih ill
maiion of hydrochloric Ficid—

SOCl, + 2H,0 = HjSO^ + HU.

gulphiurl Chloride, SOgCI, ; mol
(sometiroes known as chloiviulfhur
union of chlorine and sulphur dioxidi

kf weight = 134.7a. This compound
id) can be obtained by Ihe dir««
der the prolonged in

SO, 4 Cl, = SO,Cl»
1 by Ihe aetloo of beat npoo sulobunc chli

Disulphuryl Chloride 401

This substance, on being simply healed to 180* in sealed tubes for a few hours,
breaks up into sulphuryl chloride and sulphuric add^

PropertiM.— Sulphuryl chloride is a colourless liquid, which fiinies in moist
air, and has a specific gravity of 1.66. It boils at 70*, and is decomposed by
water with formation of sulphuric add and hydrochloric add~>

g I SO, + 2H/> = 2Ha + HO } ^^

Sulphiirlo Chlorliydrate, SOsCl(HO). This compound is the first pro-
duct of the replacement of the (HO) groups in sulphuric add by chlorine,
and is formed by the direct combination of sulphur trioxide and hydrochloric
add~>

SQ, + HQ a: HCISO, or SO,a(HO).

It may be obtained by distilling sulphuric add with phosphorus oxychloride

2 Ho}^"*"^^^» = * Q^}sO,+ Ha + HPO>.

Or by passing dry gaseous hydrochloric add into melted pyrosulphuric acid —

H AO7 + 2Ha = H^ + 2HClS0i.

PropertiM. — Sulphuric chlorhydrate is a colourless fuming liquid, having a
spedfic gravity of 1.76, and boiling at i49*-i5x*, with partial dissociation into
its generators, sulphur trioxide and hydrochloric add. In contact with water
it is decomposed with considerable violence, with formation of sulphuric and
hydrochloric adds —

gO|sO,+ H,0 = HCl + {Jg}sO^

Vllnljiivxfl^Stilx^^ This

substance is obtained by the action of sulphur trioxide, or sulphuric chlor-
hydrate, upon phosphorus pentachloride —

2SO, + PCI, = POO, + SjOgCV
2SO,a(HO) + PCI, = POCl, + 2Ha + SjOjCl,.

It is also produced by the action of sulphur trioxide upon sulphur
dichloride —

6SO, + SiCl, = S^,C1, + 6SO,.

Or by the action of sulphur trioxide upon sulphuric chloride—

g}so. + so.«g|g;}o.

a C

Inorganic Chemistry

FropertlM. — Pjrosulpbi

bling pjnosulpburic add
boils Bl 146*. When TDixed villi
and hydrochlocic acids, allowing
mlphuric chIorh;drale —

ic chloride ii a heavy, oily, flimuig Uiiaid. r
.ppearaDce. It has a specific gravity of 1.B19. a

lowtx dEComposei into sulphuric
difference in ihii nspcct Irom

S^,CI, + 3H,0 = SH^. + 3Ha

OARBOH DIBULPBIDB.

Formula, CS^ Molecular weight = 76. Vapour denslijr = 3B.

History.— This compound was accidentally produced by I
padius (1796) when heating a mixture of charcoal and pyrites.

Mode of Formation.— Carbon dlsulphlde is prepared by passing
the vapour of sulphur over red-hot charcoal, when the two elements
unite and form the volatile product, which is condensed ii
■urrounded with cold water —

C + S, - CS,

The product is always contaminated with free sulphur, which

Iphuric \

issing

siderable quantitie

>n of sulphur upon the

volatilises, and is also accompanied by ci
sulphuretted hydrogen, formed by the ac
hydrogen contained in the charcoal.

When carbon disulphide is prepared on a manufacturing scale,
the charcoal is heated in a vertical cast-iron or earthenware retort,
C, Fig. 113, having an elliptical section, and provided with three
openings. The retort is built into a suitable fiimace, whereby it
can be uniformly heated to redness. A quantity of sulphur, con-
tained in the pot S, kept liquid by the heat of the furnace, is
allowed to enter at intervals through the pipe B. As the vapour
conies in contact with the red-hot charcoal, combination ensues,
and the carbon disulphide escapes through the pipe D, which is
inclined to the retort so as to allow condensed sulphur to run back.
Sulphur which escapes condensation in this pipe, collects, for the
aiost part, in the vessel E, which is dosed by water seals as seen
in the figure. The volatile compounds are then passed through a
Licbig's condenser about 30 ft. long, and the crude disulphide so
condensed is collected in a receiver. Any vapour of carbon disulphide
which is carried on by the sulphuretted hydrogen, is absorbed by
passing the gas through a scnibbet containing oil : and (inallv the

Carbon Disulphtde

40J

sulphuretted hydrogen is absorbed in a lime purifier, similar to
those employed for the purification of coal gas. The ashes are
withdrawn from the retort through the wide tube B ; and the
fresh charcoal is introduced through the opening A. In order to
prevent the escape of the unpleasant and injurious vapours from
A, during the addition of fresh charcoal, the opening A' is put into
communication with the chimney of the furnace. The sulphur
which flows back into the retort from D, is conveyed by means
of the pipe /, neariy to the bottom of the mass of heated char-
coal, so that its vapour shall once
more be made to pass over the
carbon.

The crude product is purified
by distillation, and subsequent
agitation with mercury.

Properties. — Carbon disul-
phide is a colourless, mobile, and
highly refracting liquid When
perfectly pure it possesses a sweet-
ish, and not unpleasant, ethereal
smell, but as usually met with the
odour is decidedly fcctid

Its specific gravity at o* is 1.292,
and it boils at 46*. The vapour
of carbon disulphide has a very

low igniting-point (see page 291). It bums with a blue flame,
which, when fed with oxygen, emits a dazzling blue light. When
carbon disulphide vapour is mixed with three times its volume
of oxygen, and a light applied, the mixture explodes with
violence ; the products of the combustion being carbon dioxide
and sulphur dioxidt

Fig. 113.

CS, + 30, - CO, + 2SOr

The vapour of carbon disulphide, when constantly inhaled in
small quantities, has an injurious effect upon the health, and if
breathed in large quantities is a powerful poison.

When heated to a bright red heat, carbon disulphide vapour is
decomposed into its constituent elements : on this account, in the
manufacture of this compound, care is taken that the temperature
does not rise too high.

The vapour of carbon disulphide is decomposed by potassium,

which, when healed, bums In

sulphide, ajid hberating^ carbon —

When passed over heated slaked lime, carbon disulphidc v,

IS converted into carbon dioxide and sulphuretted hydrogen—

+ 2CaH,0,

This reaction is made use of for converting the carbon disul-
phide, which is always present in coal gas, Into the two easily
removed substances, carbon dioxide and sulphuretted hydrogen.

When a mixture of carbon disulphide vapour and sulphurett
hydrogen, is passed over heated copper, marsh gas is formed-

4Cu + CS, + 2H,S = CH, + 4CuS.

a~ I

Carbon disulphidc is soluble to a minute extent in water
volume of water dissolves .001 volume of this liquid, and the
solution possesses the tasle and the smell of the disulphidc II
mixes in all proportions with alcohol, ether, the hydrocarbons of
the benzene family, and most essential oils. It also dissolves
sulphur, phosphorus, iodine, bromine, caoutchouc, and most fats ;
and is largely used in the arts, both as a solvent for caoutchouc,
and in extracting essential oils, spices, and perfumes.

ThlocarbonlC Acid.— Carbon disulphide is the sulphur ana-
logue of carbon dioxide, CSj ; CO^ Like the oxygen compound,
it foims a feeble acid, which has received the name thiocarbonic
acid, H,CS, ; carbonic acid, HjCO,.

The thiocarbonatcs are produced by reactions analogous 10
those by which carbonates are formed. Thus, when carbon disul-
phide is brought into contact with potassium sulphide, poti
thiocarbonate a obtained—

which may be c<
potassium oxide-

CS, + K^ = K,CS^
npared with the action of carbon dioxide a
CO, + K,0 = KjCOf

Thiocarbonaies are likewise formed by the action of c

disulphide upon metallic hydroxides —

aCS, + 6KHO - 2K,CS, + K,CO, + 3H,0.

Selenium 405

The acid itself is obtained as a yellow oil, having an unpleasant
odour, by the decomposition of a thiocarbonate by dilute hydro-
chloric acid

A large number of compounds are known, in which divalent
sulphur replaces oxygen, and which therefore stand in the same
relation to the oxygen compounds, as thiocarbonic acid stands to
carbonic acid ; for example —

Thiocarbamic acid, CS„NH„ or ?J^« i CS ;

HS )

Carbamic acid, CO^NH,, or JJ^« | CO.

Ottier Oomponndi of OariMm and Sulphur.— When carbon disutphide it
rxposed to the influence of light, there is gradually formed upon the glasi
vessel containing it, a brown deposit, which is believed to be carbon mono-
sulphide. CS; the sulphur analogue of carbon monoxide. When electric
sparks from carbon poles are passed through the vapour of carbon disulphide,
or when the electric arc is produced in the vapour, an offensive-smelling liquid
is obtained, which exerts a most irritating and tear-producing efTect upon the
eyes. This liquid has been shown to have the composition C^^*

SBLBHIVM.

Symbol, Se. Atomic weight a 78.87. Molecular weight = 157.74.

History.— This element was discovered by Berselhis (1817), who gave it
the name selenium (signifying the moon) on account of its close analogy with
the previously discovered element tellurium (signifying the earth).

Occorrenoe. — Selenium is occasionally met with associated with native
sulphur, probably as a selenide of sulphur. In a few minerals of considerable
rarity, selenium is met with in the form of selenides of such meuls as mercury,
lead, silver. It occurs In very small quantities in a large number of meullic
sulphides.

Modt of Formation — (i.) When pyrites containing selenium is employed
in the manufocture of sulphuric add, the selenium is oxidised by the atmos-
pheric oxygen into selenium dioxide, which is carried forward with the sulphur
dioxide. Selenium dioxide, being a solid substance, is partly deposited in the
flues, and in the Qlover tower, and partly carried forviard into the chambers,
where it foi ms a red-coloured deposit To obtain the selenium, either the flue
dust or the chamber deposit, is first boiled with dilute sulphuric acid, and either
nitric acid or potassium chlorate added, in order to oxidise it completely into
selenic add, H|Se04. The solution is then boiled with strong hydrochloric
acid, whereby it is reduced to selenious add, HtSeO^, when a stream of sulphur
dioxide is passed through it which predpitates the selenium as a red powder^

H,SeO, + 2SO, + H,0 = Se + 2H^«.
• Von Lengyel. 1894.

depMil. consists in digesiing
]( is convened Into soluble
addition of bydrochloric ncid

Inorganic Chemistry

e preparation of Klenlum rrom the i
e substance with potassium cyanide,
olassium lelenocyanide. SeK{CN). On the

5eK(CN) + HCl = Se + KCl

1 potBUium chloride go \t
r H(CN).

FroiwrtlM.— Selenium ta known in various ailotropic modifications.

I. SalvbU in carbm disvlfkidt. — a. Brick-red amorphous powder, olxajned
by precipiation with acids, or reduction of selenious add, in the cold, bj"
sulphur dioiide.

{9. Black crystalline powder, obtained by rednclion of hoi selenious acid by
sulphur dioxide.

y. Dark f«d lianslucent monoclinlc crystals, specific gravity 4.5, deposTled
from solution In carbon disulpbide.

JL Black, shining, brittle amorphous mass, having a conchwdal Iraciiire,
and a specific gravity or 4.3, obtained by rapidly cooling melted selenium.

a. /nsBluiU in caiim dii^lfhidi. —Black, metallic-lDoking crystalline mass,
having a grantilar rrsciure. Obtained by quickly cooling melted selenium to
3to' and keeping it for some time at that temperature, when the mass solidities
with rise of temperature to 317*. This insoluble variety, sometimes called
metallic selenium, ii also formed as a deposit of minute black cryslab. when

rated 5(

if sodiui

!lenide 1

:o the I

This modification has a spedBc gravity of

Selenium boils at 6S0', forming a dark red vapour which condenses in (he
form oljltnven of ulenium, having a scarlet -red colour.

Al high temperatures the vapour of selenium, like that of sulphur, becomes
a true gas; thus at 1430*. the vapour density is found to be Si.j. approaching
very closely to the normal density demanded by the molecule Se^

"Metallic" selenium conducts electriiniy, and the element eihibils the
remarkable property of having its conductivity increased by light; the coti-
ductivily of selenium when exposed to diffused daylight being about twice as
great as when In the dark. This alteration in the electrical resistance wllb
varying intensities of light, is a property of selenium that was made use of, in
Ihe construction of an instrument known as the photophone, but it has not a*
yet been put lo any practical use. When selenium is heated in the air, it
bumswithablueftame, with Ihe formaiion of seleniuin dioxide, and at Ihe same
lime emits a powerful and characteristic smell resembling rotten hotse-radish.

When selenium is heated in a tube, filled with an indi(T<;rcnl gas, it sublimei
in the form of a red deposit ; but when heated in hydrogen, the sublimate is in
Ihe form of black shining crystals. The formation of these crystals is due 10
Ihe fact, thai selenium combines with the hydrogen, and the hydrugen selenide
is again decomposed by the heal.

Hydrogsn Eelmlde (irlmurtlltd hydrogen), H,Se; molecular w^ghl
Hydrogen selenide is formed when selenium is healed in hydrogen.

This compound is also obtained, by the action of dilute hydrochloric or!
phuric Bcid, upon eilber potasiitun selenide or (errooi selenidi
PeSe + H^O, = FoSO, -f H^

SiUnium Dioxids 407

PiulMl Um.— Hydrogen Mlenide b a colourless gas, strongly resembling
sulphuretted hydrogen, both in its smeU, and in its chemical behaviour. It is
readily soluble in water, and when passed through metallic solutions, precipi-
tates insoluble selenides of most of the heavy metals. Hydrogen selenide
bums with a blue flame, with the production of water and selenium dioxide.
Its smell, although resembling that of its sulphur analogue, is more implcisant,
and its effects upon the system are more persistent and injurious. A single small
bubble inhaled through the nostril, produces temporary paralysis of the olfac-
tory nerves, accompanied by inflammation of the mucous membrane.

No compound of selenium corresponding to hydrogen disulphide is knovm.

Compounds with Halogsns.

DlMlaiiliiiii Dlohlorlda, SejCI,, is obtained by passing chlorine over
selenium, or by passing gaseous hydrochloric acid through a solution of
selenium in nitric acid. ,

Properttai. — Selenium chloride is a brown oily liquid, in which selenium
itself is readily soluble, and from which the element is deposited in the form
which is insoluble in carbon disulphide. It is slowly decomposed by water,
thus —

2Se^l, + SH3O = H,SeO, + 8Se + 4HCI

Corresponding bromine and iodine compounds are known, ScjiBrs, and

Selenium Tetraoblorlde, SeCl4, is prepared either by the action of chlorine
upon selenium chloride —

Se,Cl, + 3C1, s 2SeCl4,

or by heating a mixture of selenixun dioxide and phosphorus pentachloride —

SSeOi + 8PC1, = 3SeCl4 + P,0, + PCKH,.

PropartlM.— Selenium tetrachloride is a white, crystalline, volatile com-
pound ; which may be sublimed without decomposition and without fusion.
When the vapour is heated above aoo*. it begins to dissociate into selenium
and chlorine. It dissolves in water, with decomposition into hydrochloric and
selenious acids —

SeCU -I- 3H,0 = 4HC1 -I- H,SeO,.

Corresponding bromine and iodine compounds are known. SeBr4 and Sel^.

Oxides and Oxyacidb of SsLENiini.

Only one oxide of selenium is known, namely, selenium dioxide, SeOj,
although a second oxide of unknown composition is believed to exist, and to
constitute the peculiar smelling substance which is alvrays formed when
selenium is burnt in the air.

Belenlnin Dlozldt is prepared by burning selenium in a stream of oxygen
in a glass tube ; the element bums In the gas with a blue flame, and the oxide
condenses upon the distant portions of the tube, as a white crystalline deposit.

408 Inorganic Chemistry

ProptrtliM.— Sdenhmi dioxide crystallises in lonfi^ white prisms, which when
heated, readily sublime without pas.rr.g through the state of liquidity. It dis-
solves in water and gives rise ti. selenious acid.

The following oxyadds of selenium are known —

Selenious add, H,SeQ|, corresponding to sulphurous add, H|SO}.
Selenic add, H]Se04, corresponding to sulphuric acid, H,S04.
Selenosulphuric HO ) q^^ corresponding) thiosulphuric HO ) q^
add, HSef^'* to t add, HS 1^*

Selenloas Add, HsSeQi, is obtained as a white crystalline compound, when
the dioxide is dissolved in hot water, and the solution allowed to cool. The
add is dibasic, and forms both add and normal selenites, corresponding to
the sulphites : it also forms a series of so-called niptracid salts, containing a
molecule of the add salt, combined with a molecule of acid, thus —

H ivSeO|, HgSeO^

Selanle Add, H,Se04.— This acid is best prepared, by the addition of
bromine to silver selenite suspended in water, when insoluble silver bromide is
formed and selenic add is left in solution —

AgfSeO, + H^ + Br, = 2AgBr + H,Se04.

The solution may be evaporated by heating, until it contains 94 per cent of
selenic add, and still further evaporated in vacuo, until it reaches 97.4 per cent.,
when its specific gravity is 2.627. When heated to 280° it decomposes into
selenium dioxide, water, and selenium.

PropertleB. — Selenic add in its most concentrated condition, is a colourless,
strongly add liquid, which mixes with water with the development of con-
siderable heat It dissolves iron and zinc with evolution of hydrogen ; and when
heated, dissolves copper with formation of selenious add.

The selenates closely resemble the sulphates. Barium selenate, like the
sulphate, is quite insoluble in water, but cUfTers from that compound in being
converted by boiling hydrochloric add into barium selenite, which is soluble.

Selenium also forms a compound with oxygen and chlorine, selenium oxy-
chloride, or selenyl chloride, SeOClj, corresponding with thionyl chloride,
SOCl^

TELLURIUIL

Symbol, Te. Atomic weight,* 125 (?).

Oconrrenoe. — In the free state, small quantities of this element have been
found as crystals, consisting of almost pure tellurium. In combination it is

• Various numbers have been obtained, by different observers, for the
atomic weight of tellurium. Some of these numbers are higher than the atomic
weij;^ht of iodine, which would make it impossible to gi\'e to tellurium a posi-
tion between antimony (atomic wdght = lao) and iodine (atomic weight =
126.54) as demanded by the periodic law. Brauner. who has spent many
years investigating this point, considers that hitherto /vrv tellurium has nevet
been obtained.

Telluraus Acid 409

met with in a few rmre minerab, such as ttUmrite (TeO|), and. more commonly,
tetrmdfmiit (B^Tei). Some specimens of pyrites contain small quantities of
this element, hence it is found in the deposit from the vitriol chambers, from
which selenium is obtained.

Mode of Formation.— TeUurimn is j;»btained from bismuth telluride, Bi,Te^
by fusion with an intimate mixture of sodium carbonate and carbon. The
mass on treatment with water, yields a solution oootaining a mixture of sodium
telluride and sodium sulphide, which on exposure to the air deposits tellurium
as a grey powder. The element is purified by distillation in a stream of
hydrogen.

Propsrttof. ^Tellurium is a bluish-white, silver-like solid, possessing metallic
lustre. It conducts heat and electricity, although badly, and is very brittle.
Its specific gravity is 6.36, and it melts at 452*. When melted tellurium is
slowly cooled, it forms rhombohedral crystals. When heated in the air, it bums
with a blue flame, and forms tellurium dioxide, TeO). When heated in a
sealed tube with hjrdrogen, tellurium sublimes in the form of brilliani prismatic
crystals.

Hydrogen Tellnrld* {Tellureited Hydrogen), H,Te.— When tellurium
is heated in hydrogen, the elements combine, forming hjrdrogen telluride,
which exhibits the same phenomenon as is shown by selcnuretted hydrogen,
of being decomposed by heat, and depositing the element as a crystalline
sublimate.

Hydrogen telluride is obtained by the action of hydrochloric add upon dnc
telluride —

ZnTe + 2Ha = ZnCl, + H,Te.

Proptrfclfll. — Hydrogen telluride is a most offensive smelling, and highly
poisonous gas. It behaves like sulphuretted hydrogen in precipitating metals
from solutions. It is soluble in water, and the solution gradually absorbs
oxygen and deposits tellurium.

Compounds with the Halogsn&

Two chlorides of tellurium are known, namely, tellurium dichloride, TeClf ,
and tellurium tetrachloride, TeCl4. It will be noticed that the composition of
the dichloride is not analogous with the lower chloride of either selenium
(Se,Cy or sulphur (S,C1,).

Two bromides, TeBr^ and TeBr4, and corresponding iodides are known.

Oxides and Oxtacids of Tellurium.

Two oxides of tellurium are known with certainty, namely, tellurium dioxide,
TeO], and tellurium trioxide. TeOj, which give rise respectively to the two
adds, tellurous add, HtTeO,, and telluric add, H,Te04.

Tellnroni Add is obtained, by pouring a solution of tellurium in nitric acid
into an excess of water. The acid is predpitated as a white amorphous
powder. When strongly heated, it is converted into the dioxide and water.

Tellurous add, like sulphurous add, is dibasic, and gives rise to both add
and normal salts : thus, with potassium it forms hydrogen potassium tellurite.

410

Inorganic Ctumistry

HKTeQi, and dipocanhim tdhirite, KfTeCV
such

It also fbniis niper-acid salt*

Quadradd potassium tellurite . HKTeQg. H^TeOt.

Potassium tetratellurite .... K^TeO^. STeOf.

TWlnrlo Aeid is prepared by fusing other teUurinm, or tellurium dioxide,
with a mixture of potassium nitrate and carbonate^

Te, + KtCOi + 2KN0k = 2IC,Te04 + N, + CO.

The fused mass, after solution in water, is mixed with a solution of barinm
diloride, which precipitates barium tellurate ; this b then decomposed by the
addition of the exact amount of sulphuric acid, and after filtration, the clear
solution deposits crystals of telluric acid, HfTe04,2H30. When these crystals
are heated to zdo**. the water is expelled, and the anhydrous add in the form of
a white powder is left On strongly heating, telluric add decomposes into
water and tellurium triozide, which at a higher temperature splits up into the
dioxide and oxygen.

Like tellurous add, telluric add forms not only normal and add salts, but a
number of more complex superadd salts —

Normal potassium tellurate
Hydrogen potassium tellurate
Quadracid potassium tellurate
Potassium tetratellurate

K,Te04,5H,0.

HKTe04.

K,Te04, H,Te04,3H,0.

K,Te04.8H,Te04. H^O.

CHAPTER III
THB ELEMENTS OP GROUP V. (PAMILY B.)

Nitrogen, N

. 14.OX

Antimony, Sb

119.6

Phosphonis, P .

. 30-96

Bismuth, Bi

. ao7.S

Arsenic, As.

. 74-9

In this family of elements we have a gradual transition from the
non-metals to the metals. Nitrogen and phosphorus may be con-
sidered as typical non-metallic elements, both as regards their
physical and chemical properties. The third member, arsenic,
begins to exhibit metalline properties ; its specific gravity is more
than three times as high as that of phosphorus, and it possesses
considerable metallic lustre : arsenic is called a nutallaid on this
account. Antimony is still more metallic in its character, possess-
ing most of the physical attributes of a true metal, while in bismuth
all non-metallic properties cease altogether to exist

All these elements form more than one compound with oxygen,
of which the following may be compared —

N,0, ; (P.Os), ; {^sfi^ ; Sb,0, ; Bi.O,.
NjO*; PjO*; — SbjO*; Bi,04.
NjO^; PA; AsjOj; SbjO^ ; BiA-

The oxides (which in the case of nitrogen and phosphorus are
strongly acidic in their nature, combining with water to form adds)
gradually become less and less acidic and more basic as the series
is traversed.

Thus, nitrogen pentoxide, NA* unites violently with water to
form nitnc acid, which with bases yields nitrates. Antimony pent-
oxide is insoluble in water, and no antimonic acid has been isolated,
although its salts, the antimonates, are known. The oxides of
antimony, on the other hand, begin to exhibit basic properties, and
unite with adds, forming salts in which the antimony ftmctions as
the base.

411

4t3 Inorganic Chemistry

In the case of the lost element, [he acidic nnture of the oxides II
entirely lost ; no bismuth coinpoirnds bciriR known, coirespondm
to anlimonates or arsenates, while these oxides unite wit]
the capacity of bases, giving rise to bismuth salts.

Four of the elements of this group unite with hydrogen, faimiill
similarly constituted compounds, NHj, PHj, AsHj, SbH,.

The stability of these compounds gradually decreases as
from nitrogen to antimony. Antimony hydride has never been oM
tained free from other gases, while no similar bismuth compound if
known. Ammonia is alkaline and strongly basic, and unites readifj
with acids to form ammonium salts. Phosphorus hydride has
alkaline character, and is only feebly b.isic. It combines, howev
with the halogen acids to form phosphonium chloride, bromtdl
and iodide, PH.CI, PH.Br, PH,1, analogous lo ai
chloride, bromide, and iodide. The hydrides of arsenic am!
antimony exhibit no basic character. All the elements of thiC
group unite with chlorine, giving rise to the compounds
NCl^ PCIj, AsClj, SbClj, BiClfc

which also exhibit a gradation in their properties ; thus, nitrogellM
trichloride is an exitemety unstable liquid, exploding with e
ordinary violence upon very slight causes, while the analogoo
bismuth compotind is a perfectly stable solid.

The boiling-points of these compounds show a gradual
with the increasing atomic weight of the element : thus,
chloride boils at 71°, phosphorus trichloride at 78°, arsenic t
chloride at 130.1°, and antimony trichloride at 200°.

The elements arsenic, antimony, and bismuth are isomorphov
and their corresponding compounds are also isomorphou

The first member of this family, namely, nitrogen, has 1:
already treated in Part II., as one of the four typical elemeBlf
studied in that section of the book. It occupies a position iaj
relation to the other members of the family, very similar to that a
oxygen towards sulphur, selenium, and tellurium,

PH08PH0BU8.

History. — Phosphorus was first discovered by the alchen
Brand, of Hamburg (1669), who obtained it by distillinK a m*

Phosphorus 413

of sand with urine which had been evaporated to a thick syrup.
The process, however, was kept secret Robert Boyle (1680) dis-
covered tlie process of obtaining this element, but the method was
not published till after his death. Until the year 1771, when
Scheele published a method by which phosphorus could be ob-
tained from bone ash, this element was looked upon as a rare
chemical curiosity. The name phosphorus was not first coined for
this element : it had been in previous use to denote various sub-
stances known at that time, which had the property of glowing in
the dark. To distinguish the element it was called BraruPs phos-
phorus^ or English phosphorus,

Occurrenee. — Phosphorus has never been found in nature
in the free state. In combination with oxygen and metals, as
phosphates, it is very widely distributed, especially as calcium
phosphate. The following are some of the conunonest natural
phosphates —

Sombrerite, or estramadurite . Ca^POi)].

Apatite 3Ca,(P04)„CaCla.

WaveUite 2Alt(P04)„Al/HO)„9H,0.

Calcium phosphate is present in all fertile soils, being derived
from the disintegration of rocks : the presence of phosphates in
soil has been shown to be essential to the growth of plants. From
the vegetable it passes into the animal kingdom, where it is chiefly
present in the urine, brain, and bones. Bones contain about 60
per cent, of calciimi phosphate, to which they entirely owe their
rigidity.

Mode of Formation. — Manu/iufure, The chief source of
phosphorus is bone ash, a material obtained by burning bones,
and which consists of nearly pure calcium phosphate, Ca3(P04)y
Other varieties of calcium phosphate, such as sombrerite and
apatite, are also egiployed, as well as phosphates of other metals,
such as the Redonda phosphates, which consist of phosphates oif
iron and alumina The bone ash, in fine powder, is first decom-
posed by means of sulphuric acid, specific gravity 1.5 to 1.6. This
operation is performed in large circular wooden vessels, resem-
bling a brewei^s "mash tim," provided with an agitator, and into
which high pressure steam can be driven. Finely-ground bone ash
and sulphuric acid, in charges of a few cwts. at a time, are alter-
nately stirred into the decomposer, imtil from four to five tons of

dull red heat. During this process, the tribasic phosphor

(or arthophosphoric acid), H,PO^ is converted by loss of wM

into metaphosphoric acid, HPO, —

H.PO, = H,0 + HPO,.

The charred mixture is ihen distilled in bottle-shaped ri
Stourbridge day, about 3 feet long, and having an internal dtameler
of 8 inches. A number of these retorts, usuaily twenty-four, are
arranged in two tiers, in a galley fiirnace, as seen in section in Fig
1 14. The empty retorts are Arst gradually raised to a bright red
heat, and a charge uf the mixture is then quickly introduced. Bent

Phosphorus

4t5

pieces of 2-inch malleable iron pipe are then luted into the
mouths of the retorts, connecting diem with the pipes, D D'.
These pipes dip into troughs of water, £ £', which run along the
entire length of the furnace, and in which the phosphorus con-
denses. The temperature of the furnace is then raised to a white
heat, when decomposition of the metaphosphoric acid commences,
and phosphorus begins to distil over. The process is continued
for about sixteen hours. The change that goes on is mainly
represented by the following equation —

4HP0, + 12C - 12C0 + 2H, + 4P.

The crude product, which is usually dark red or black in appear-
ance, is first melted under hot water, and thoroughly stirred, in
order to allow the greater part of the rougher suspended matters to

..>0-- • ■^-"?'*i'^"' :"■■■••■ -.
■ ■■■■!■ fn — I —

, ■■.■■I';

^■^M

Fig. 115.

rise to the surface. The mass is then allowed to resolidify. The
exact processes by which phosphorus is further purified on a manu-
facturing scale are guarded as trade secrets : one method that has
been in use, consists in treating the phosphorus while melted under
water, with a mixture of potassium dichromate and sulphuric acid,
whereby some of the impurities are oxidised, and others are caused
to rise to the surfiEure as a scum, leaving the phosphorus as a dear
liquid beneath.

Phosphorus usually comes into commerce either in the form of
wedges, or as sticks. The operation of casting the phosphorus into
sticks is performed beneath water. A quantity of phosphorus
beneath a shallow layer of water is placed in the vessel C, Fig. 1 1 5,
which is contained in a tank of water through which a steam-coil
passes. Connected to the phosphorus reservoir is a glass tube, G,
which passes into a second shallow tank of cold water. On open-
ing the cock D, the liquid phosphorus flows into the cold glass tube,
where it congeals, and it may then be drawn through as a continuous
rod of phosphorus, if care be taken not to draw it out faster than it

4)6

Inorganic ChtmiUry

tbick-

•olidifies. It is the custom to adopt a uniform length and tbick-
ness of stick, namdy, ^\ inches long and j inch di
such Slicks weigh I lb.

Properties.— When freshly prepared and kept
phosphorus is a translucent, almost colourless, v
Even in the dark it soon loses its transparency, and bccomeif
coated with an opaque white film ; while if exposed to ihe lighl,
the film that forms becomes first yellow, then brown, and in time
the phosphorus assumes a red and even a black colour throughout
its entire mass, lis specific gravity at 16° is 1.B3. Al o* phos-
phorus becomes moderately brittle, and a stick of it may be readily
snapped, when its crystalline character will be seen. Al 15* it
becomes soft, and may be cut with a knife, like wax. Phosphorus
mells under water at 43.3", and the liquid exhibits ilie property o(
suspended solidification. If the melted material, which has been
cooled below its solidifying point, be touched with a Iragmenl of
phosphorus upon the end of a capillary glass lube, the mass
instandy congeals with rise of temperature.*

Phosphorus contained in a closed vessel, without water, melts
at as low a temperature as 3o°,t and when heated in air to 34' it
lakes fire. Al a temperature of 369* phosphorus boils, and fonns
a colourless vapour.

Phosphorus is volatile at ordinary temperatures : if a small
quantity of phosphorus be sealed in a vacuous tube, and ihe lube
be placed in the dark, the phosphorus will slowly vaporise ; and il
one end of the tube be kept slightly cooler than the rest, the phos-
phorus will sublime upon that part, in the form of brilliant, colour-
less, and highly refracting rhombic crystals, which retain their
beauty so long as they are kept in the dark. The density of
the vapour of phosphorus is 61.92, giving a molecular weight of
123.S4, which is four times the atomic weight, showing thai the
molecule of phosphorus contains four atoms. Even at lemperaluies
as high as 1040 these letraiomic molecules are stable, but it has
been shown that at higher temperatures, dissociation begins to take

On account of its ready inflammability, phosphorus is always
preserved under water, which exerts practically
upon it. It is extremely soluble in carbon disulphide, 1 pan of 1

• S« "CheiDicsJ t-etiui

Era

Phosphorus 417

liquid dissolving 9.26 parts of phosphorus. On evaporation, the
element is deposited in the form of colourless crystals. Phosphorus
is also soluble, but to a less extent, in chloroform, benzene, turpen-
tine, alcohol, olive oil, and many other solvents. A solution of
phosphorus in carbon di sulphide, when allowed to evaporate upon
a piece of blotting-paper, leaves the element in so finely divided a
condition, that its rapid oxidation almost immediately raises the
temperature to the ignition point of the phosphorus, when it
takes fire.

On exposure to moist air in the dark, phosphorus appears faintly
luminous, emitting a pale greenish-white light, and at the same
time evolving white fumes which possess an unpleasant, garlic-like
smell, and are poisonous. These fumes consist mainly of phos-
phorous oxide, P4O41 and the glowing of the phosphorus is the
result of its oxidation ; phosphorus does not glow when placed
in an inert gas which is perfectly free from admixed oxygen,
although the presence of very small traces of free oxygen in such a
gas, is sufficient to cause the phosphorescence. At a few de-
grees below o*, phosphorus ceases to glow in the air. Although
the glowing is due to oxidation, phosphorus does not appear
luminous in pure oxygen at temperatures below about 15*. If,
therefore, a stick of phosphorus which is glowing in the air,
be immersed in a jar of oxygen, its phosphorescence is at once
stopped. If, however, the oxygen be slightly rarefied, the phos-
phorus again becomes luminous. Similarly, the phosphorescence
that is exhibited in air, is stopped if the air be compressed. ''^ The
glow of phosphorus is believed to be associated with the formation
of ozone, for the presence in the air of traces of such gases and
vapours as ethylene, turpentine, or ether, which are known to
possess the power of destroying ozone, at once stops the glowing
of a stick of phosphorus.

Phosphorus is incapable of uniting with oxygen if the gas be
perfectly pure and free from aqueous vapour. It has been shown
that in oxygen which has been dried by prolonged exposure to the
desiccating action of phosphorus pentoxide, phosphorus may not
oniy be melted, but even distilled, without any combination with
the oxygen taking place.

I f water, beneath which is a small quantity of melted phosphorus,
be boiled, the phosphorus vaporises with the steam, and renders

* '* Chemical Lecture Experiments." new ed., Nos. 530 to 534.

2 D

418

Inorganic Chemistry

ilie steam luminous : use is made of ihis property, as
delecting free phosphorus, in toxicological analysis.

Phosphorus is a powerfully poisonous substance ; in large dosea
it causes death in a few hours, in smaller quantities it produces
itomachjc pains and sickness, usually ending in convulsion.
I'ersons constantly exposed to the vapours arising from the hand-
hng of phosphoi-us, either in its manufacture or in the manufacture
of matches, are very liable to suffer from caries of the bones of (he
jaw and nose ; it is believed that this injurious effect is caused \if

Fig. ii6.

the white fumes which are the product of oxidation, and nal

the actual vapour of phosphorus.

Red Phosphorus.— V.^l en phosphorus is heated to a tempera-
ture between 240' and 150', out of contact with air, it passes mto
an allolropic modification. The same transformation takes place
when phosphorus is heated to 300* with an extremely small pro-
portion of iodine.

Red phofphorus is manuiaclurcd by heating ordinary phospbonu
in a cast-iron pot, provided with a cover, through which passa

Rid Phosphorus 419

short open pipe, D (Fig. 1 16). The pot is carefully and uniformly
heated to between 240* and 250*, as incUcated by the thermometers
C C, which are encased in metal tubes, to prevent the phosphorus
from attacking the glass. A small quantity of the phosphorus
becomes oxidised by the air within the vessel, but after this atmos-
pheric oxygen is used up, no further oxidation takes place. If the
temperature be allowed to rise above 260^ the red phosphorus is
reconverted into the ordinary modification, and with the evolution
of so much heat, that unless the open tube be provided, as a safety-
valve, the iron vessel is liable to burst The material that is
obtained at the end of the operation, is in the form of hard, solid
lumps, which still contain a certain amount of the unchanged
phosphorus mixed with them. It is first ground to powder beneath
water, and then boiled with a solution of sodium hydroxide (caustic
soda), to remove the ordinary phosphorus, and finally washed and
dried.

Properties. — Red phosphorus, as usually sent into commerce,
is a chocolate-red powder, having a specific gravity of 2.25. It
is not luminous in the dark, and has no taste or smell It is
not poisonous, and when taken into the system is excreted un-
changed. It is not soluble in carbon disulphide, or in any of the
solvents which dissolve ordinary phosphorus. Red phosphorus is
unaffected by exposure to dry air or oxygen, but in the presence
of moisture it is very slowly oxidised. If red phosphorus which
has been perfectly freed from ordinary phosphorus, and carefully
washed and dried, be exposed to air and moisture, it is found after
the lapse of some time to have become acid, owing to slight oxida-
tion into phosphoric acid. When heated in contact with air, red
phosphorus does not ignite below a temperature of 240*, Red
phosphorus may be obtained in the form of rhombohedral crystals
by heating the substance under pressure to a temperature of 580*.

The chief use of phosphorus is in the manufacture of matches.
When ordinary phosphorus is employed, the bundles of wooden
splints are first tipped with melted paraffin wax, and afterwards
dipped into a paste, made of an emulsion of phosphorus, chlorate
of potash, and glue. Matches so made, ignite when nibbed upon
any rough surface ; the paraffin (which is sometimes replaced by
sulphur) serving to transmit the combustion from the phosphorus
to the wood. Since the discovery of red phosphorus, and its non-
injurious properties, the old phosphorus match has been largely
superseded by the so-called ca/ity matches. In these matches the

420 Inorganic Chemistry

splints are tipped with a mixture of potassium chlorate, potassium
dichromate, red lead, and antimony sulphide, and they are ignited
by being nibbed upon a prepared sur&ce, consisting of a mixture
of antimony sulphide and red phosphorus. Although these matches
will not ignite by ordinary friction upon any but the specially
prepared surface, they may be inflamed by being swiftly drawn
along a sheet of ground glass, or strip of linoleunL

COMPOUNDS OF PHOSPHORUS WITH HYDROGEN.

Three compounds of phosphorus and hydrogen are known,
namely—

PHj (gaseous) ; PjH^ (liquid) ; and P4H/?) (solid).

GASEOUS PHOSPHOBETTED HTDBOOEN {Hydrogen phosphide :

Phosphine),

Formula. PH|. Molecular weight = 33.96. Density = 16.98.

Modes of Fopmation.— (i.) This substance is formed when red
phosphorus is gently heated in a stream of hydrogen.

(2.) It may be prepared by boiling phosphorus with a solution of
potassium or sodium hydroxide —

3NaH0 + 4P + 3H,0 = 3NaH,POj + PHj.

In this reaction a small quantity of the liquid hydride (PjHJ is
simultaneously formed, which imparts to the gas the property of
spontaneous inflammability. It also contains a certain quantity
of free hydrogen, produced by the action of the caustic alkali upon
the sodium hypophosphite, thus —

NaHjPOj + 2NaH0 = SHj + Na3P04.

To obtain the gas by this method, a quantity of a strong solution
of caustic soda, and a few fragments of phosphorus, are placed in
a flask, fitted as shown in Fig. 117. A stream of coal gas is passed
through the apparatus, in order to displace the air, and the solution
is gently heated. Phosphoretted hydrogen is readily disengaged,
and as each bubble escapes into the air, it bursts into flame, and
forms a vortex ring of white smoke of phosphoric acid.

If alcoholic potash be substituted for the aqueous solution in
this reaction, the liquid phosphoretted hydrogen is dissolved in

Phosphoretted Hydrogen

421

the alcohol, and the gas which is evolved is therefore not spon-
taneously infianunable.*

(3.) Phosphoretted hydrogen is also produced by the action ol
water upon calcium phosphid<

3P,Ca, + 12H,0 - 6Ca(HO)8 + 4PH, + 2P.

A secondary reaction, by which liquid phosphoretted hydrogec
is formed, goes on simultaneously —

PjCa, + 4H,0 - 2Ca(H0), + P,H4.
The gas, therefore, that is evolved is spontaneously inflammable.

Fig. 117.

(4.) Pure gaseors phosphoretted hydrogen may be prepared by
the action of potassium hydroxide upon phosphonium iodide —

PH4I + KHO - KI + H,0 + PH,.

Properties. — Gaseous phosphoretted hydrogen, or phosphine,
is a colourless gas, having an offensive smell resembling rotting
fish. It is not spontaneously inflammable, but its ignition tem-
perature is below too* C. (see page 291). The gas bums with a
brightly luminous flame, producing water and metaphosphoric
acid —

PH, + 20, - HPO, + H,0.

When burnt in oxygen the flame is extremely dazzling.

The gas is not acted upon by oxygen at ordinary temperatures
and pressures, but if a mixture of these gases be suddenly rarefied,

* See " Cbemkal Lecture Expenmenu." new ed., No. 545.

Inorganic Ckemhtry

combination ai once lakes place with explosion. Pliosplifireited
hydrogen is decomposed by chlorine or bromine, a jet of the
spontaneously igniting when introduced into chlorine,

PH.

4C], '

3HCI + PCIf.

The gas is also decomposed by iodine, bui
action is less energetic, and a portion of the hydriodic acid which
is produced, unites with the phosphinc and forms phosphonium
iodide, thus —

(I.) PH, + 81, = PI, + 3H1.

(1.) PHj + HI = PH.I,

Phosphine is a highly poisonous gas, and the inhalation
small quantities of it is attended with injurious effects,
slightly soluble in water, and imparls its own smell and
pleasant taste to the liquid. The solution decomposes aftw
short lime, especially in the light, and deposits red phosphorus.

t'hosphoretted hydrogen has no action upon either litmus
turmeric paper, but it resembles its nitrogen analogue, anunoi
in combining with hydrochloric, hydrobromic, and hydriodic
forming respectively phosphonium chloride, bromide, and iodidt

Phosphonium Chloride, PH,C1.— When a mixture of pht
phine and gaseous hydrochloric acid is passed through a
immersed in a freezing mixture, the gases unite and form a white
crystalline incrustation upon the tube. U the ;ube be afterwards
sealed up, the compound may be sublimed from one part of the
lube to another, when it crystallises in large, brilliant, transparent
cubes. If the tube be opened, the compound rapidly dissociates
into its two generators. This compound may also be obtained by
subjecting a mixture of the two gases to pressure. Under a pres-
sure of about eighteen atmospheres at the ordinary temperature,
crystals of phosphonium chloride are deposited ; and as the pres-
sure is released the crystals gradually dissociate again.

Phosphonium Bromide, PH(Br. — Phosphoreiied hydrogen
combines with hydrobromic acid at ordinary lemperatuios and pres-
sures, but as the compound begins to dissociate at the ordinary
temperature, the combination is only completely brought about by
cooling the gases Phosphonium bromide may be readily pre-
pared by passing the two gases into a flask immersed
tale freezing mixture The sail may be obtained in t

I gM I

. thr I

Liquid Phosphorttttd Hydrogen 423

large transparent cubical crystals by sublimation in a sealed
vessel.

Phosphonlum Iodide, PH4I. — This compound may be obtained
by a method similar to that given for the preparation of the bro-
mide. It is also produced when phosphoretted hydrogen is passed
over iodine, as already mentioned. It is most readily prepared by
the action of water upon a mixture of phosphorus and iodine. For
this purpose ten parts of phosphorus are dissolved in carbon disul-
phide in a tubulated retort, to which seventeen parts of iodine are
gradually added, the retort being kept cold. The carbon disul-
phide is then distilled off from a water-bath, a stream of carbon
dioxide being passed through the apparatus towards the end of
the distillation, to assist in expelling the last traces of the disul-
phide.

Six parts of water are then gradually introduced from a dropping
funnel, when a brisk action takes place, and the phosphonium
iodide produced is volatilised, and may be condensed in a long
wide glass tube connected to the retort. Hydriodic acid is at the
same time formed —

21 + 2P + 4H,0 = PH4I + HI + H3PO4.

The phosphonium iodide condenses in the form of brilliant
quadratic prisms.

Liquid Phosphoretted Hydrogen, P,H4.— This compound is
obtained in small quantities, when phosphorus is boiled with a
solution of caustic soda. It is obtained in large quantities, by the
decomposition of calciiun phosphide with wattr, by the reaction
already mentioned. In order to collect the compound, a quantity
of calcium phosphide is introduced into a flask provided with a
dropping funnel and exit tube. After displacing the air from the
apparatus by an inert gas, water is gradually introduced from the
fiixmel, and the products of the reaction, after passing through a
small empty tube, where water is arrested, are passed through a
U-tube immersed in a freezing mixture, where the liquid phos-
phoretted hydrogen condenses.

Properties* — Liquid phosphoretted hydrogen is a colourless,
highly refracting, and spontaneously infianmiable liquid. On ex-
posure to light it is quickly decomposed into the gaseous and the
solid hydrides of phosphorus —

ftPjH^ - P4H, + 6PH»

Inorganic Chemistry "

The rormation of a sponianeously inflammable gas by the action
of water upon calcium phosphide, has (bund a practical application
in the marine appliance known as " Holmes' signal." This con-
sists of a tin canister filled with lumps of calcium phosphide- A
metal lube, closed ai ihe bottom with a piece of block tin, enters the
canister from below, and a short cone of the same soft metal is
soldered upon the top. When the signal is to be used, it is securely
fixed into a wooden float. Fig. Il8, The cone is cut off, and a
hole punctured through the bottom of the tube below, and the
apparatus thrown into the sea. The phosphoretled hydrogi
spontaneously ignites and bums with a large brilliant flame
the top of the tin, illuminating a coasiderable area.

Solid Phosphoretled Hydrogen, P,H,(?)— TTie composition
of this compound is not known willi certainty, ll is a yellow
powder, obtained, as already mentioned, by the spontaneous decom-
position of the liquid compound.

COMPOUNDS OF PHOSPHORUS WITH THE HALOGENS.
Phosphorus combines with all the halogen elements, fontung Ibt
following compounds —

PF, PCI, PBr, Pl»

PF, PCI, PBr, P,l,.

Phosphorus Trlfluoride, PF^ is obtained by the action of
arsenic trifluoride upon phosphorus trichloride —
AsF, + PCI, = PF, + AsCV
II ia more conveniently prepared by gently heating a
<inc fluoride and phosphorus tnbromide —

37.0F, + SPBr, - IPF, + SZnBi.

Phosphorus Trichloride 425

Propartiet. — Phosphorus trifluoride is a colourless, pungent-
smelling gas. It has no action upon glass in the cold, but when
heated it forms silicon fluoride and phosphorus. It is moderately
soluble in water. Phosphorus trifluoride unites directly with
bromine, forming the compound PFsBri.

Phosphorus Pentafluoride, PFf.— This compound is formed
when phosphorus bums in fluorine. It is best prepared by the
action of arsenic trifluoride upon phosphorus pentachloride —

6AsF, + 3PCI4 - 8PF, + SAsCl,.

Properties. — Phosphorus pentafluoride is a heavy, colourless
gas, which fumes strongly in moist air, being decomposed by water
into hydrofluoric and phosphoric adds —

PF, + 4H,0 - 6HF + H,P04.

Owing to this decomposition it has a pungent and irritating
effect upon the mucous membrane.

It is not acted upon by oxygen, but unites directly with dry
gaseous anmionia, forming a white solid compound having the
composition 2PF5,6NH,.

Phosphorus pentafluoride is an extremely stable compound, being
capable of withstanding a very high temperature without dissocia-
tion. On this account it is of special interest, as affording an
example of a compound in which phosphorus is united to five
monovalent atoms to fonn a stable substance. The corresponding
chlorine and bromine compounds readily dissociate, when heated,
into compounds containing trivalent phosphorus and the free
halogen.

Phosphorus Trichloride, PCls.— This compound is prepared
by passing dry chlorine over red phosphorus, gently heated in a
tubulated retort. The two elements readily combine, and the
volatile trichloride, mixed with more or less of the pentachloride,
distils off, and is collected in a well-cooled receiver. The product
is freed from the higher chloride by redistillation over ordinary
phosphorus.

Properties. — Phosphorus trichloride is a colourless, mobile
liquid, which boils at 75*95*. It has a pungent smell, and fumes
strongly in moist air. Water at once decomposes if into hydro-
chloric and phosphorous acidsr-

PCI, -I- 3H,0 - HgPO, + 3HCL

426

Inorganic: CkeinUtry

Phosphorus Pentxchlorlde, PCli.— This compound is formed
when ph 05 phonis bums in excess of chlorine. It is prepared by
the action of chlotine upon the trichloride. Dry chlorine is passed
on to the surface of a quantify of the tridiloride, contained in a
flask which is kept cool, llie absorption of the chlorine is attended
with considerable rise of temperature, and the contents of the flask
rapidly become converted into a dry, pale yellow solid.

Phosphorus pentachloride is convenieniiy obtained by passing'
chlorine through a solution of phosphorus in carbon disulphide,
the solution being kepi cold.

Properties.— Phosphorus penUchloride is a yellowish • white,

crystalline solid, having a pungent and irritating odour. It fimies

strongly in contact with moist air, being decomposed by moisliuift ■

into hydiochloric acid and phosphorus oxychloride —

PC1» + H,0 - 2HC1 + POClj.

With excess of water, both phosphorus oxychloride and phoi
phorus pentachloride dissolve with evolution of heat,
hydrochloric and phosphoric acids—

POCl, + 3H,0 = HjPO, + 3HCL

PCIs + 4H,0 = HjPO, + 5HCL

Phosphorus pentachloride readily sublimes, without melting, i
a lemperature below that of boiling water. It can only be meltC
by being heated under pressure, to a temperamre of 148*.

As the vapour of phosphorus pentachloride is heated, the c
pound dissociates into phosphorus trichloride and free chloiii
At 300^ ibis dissociation is complete, and the vapour c
equal molecules of the trichloride and chlorine. The graduatV
breaking down of the molecules of pentachloride, is seen from th«y
following table, which gives the densities of the gas at differe
temperatures —

Temperatures
Density . .

182'

250

300'

At 300* it consists of molecules of PClj (molecular weights
137.07), and molecules of chloiine (molecular weight = 7a74), il
equal numbers, which theoretically gives the molecular weight—

=S"-9S.

Phosphorus Pintachloridi 427

Phosphoros pentachloride is an important chemical reagent, in-
asmuch as by its action upon oxyacids, both inorganic and organic,
the (HO) group in the add can be replaced by chlorine. Thus
with sulphuric acid, chlorosulphuric add is formed —

}{° } so, + PCI, - ^Q } so, + POO. + Ha

With acetic add it yields acetyl chloride —

HO
CH

^ I CO + PCI, - ^^ I CO + POCl, + HCL

It also effects the replacement of (HO) by chlorine, in alcohols
Thus, with ethyl alcohol (spirits of wine) it forms ethyl chloride —

HO
CH

' X CH, + PCI4 «= ^^ \ CH, + POCl, + HCL

Photphoroi Trlliromide, PBr,, is best prepared by dropping bromine upon
an excess of red pbosphoms. It forms a colourless pungent-smelling liquid,
whicb boils at 172.9*.

PhOfphoms Pentatoomide, PBts, is prepared by adding bromine to tbe
tribromide. It is a yellow solid, whicb melts to a reddish liquid. It is very
unstable, being dtssociatsd below 100* into its generators, the tribromide and
bromine.

Diphotphoms Tetrlodidt {phosphorus di-iodidt), P,l4.— This substance is
prepared by the gradual addition of 8. a parts of iodine to i part of phosphorus
dissolved in carbon disulphide. On gently distilling off the carbon disulphide.
the iodide is left as a 3rellow crystalline solid. Tbe compound melts at no*.

Phoaplionis Tri-lodidt, PI,, is obtained by employing a larger proportion of
iodine in the above reaction. It is a solid substance, crystallising in red six-
sided prisms, which are decomposed by water into h]rdriodic and phosphorous
adds.

OXY AND THIO COMPOUNDS OP PHOSPHORUS

AND THE HALOGENS.

The following compounds are known, containing phosphorus
combined witl) the halogens, and either oxygen or sulphur —

POF, ; POCl, ; P,0,Cl4 ; POBrCl, ; POBr,.
PSF,; PSCl,; — — PSBr,.

These compounds may be regarded as derived from the haloid
compounds, by tbe replacement of two atoms of the halogen by an

438 fnorganu Chemistry

equivalent of oxygen, or of divalent sulphur ; or they may be viewed
as derivatives of phosphoric add, by the substitution of halogen
elements in the place of (HO) groups. The tribasic phosphoric
acid, P0(H0)3, may be regarded as giving rise to the compounds
POFs, POCls, &c ; while the compound, PiOjCl^ may be viewed as
a derivative of pyrophosphoric add, P|0|(HO)^

Phosphoryl Flnoxldt {phosph<frus axyjhufridt)^ POF,, may be obtained by
the action of phosphoryl chloride (POClf) upon sine fluoride —

8ZnF, + 2POa, = 2POF, + SZnCH,.

It may also be prepared by gently heating a mixture of finely powdered
cryolite and phosphorus pentoxide —

2(AIF,.8NaF) + 2P,0, = 4POF, + Al^, + 3Na/).

Phosphoryl fluoride is a coloiu-less gas. which fumes in the air. and is de-
composed by water. The gas in a dry condition does not attack glass.

Thiophosplioryl Fluorldt, PSFg, is most readily prepared by gently heat-
ing in a leaden tube, a mixture of dry lead fluoride and phosphorus penta-
sulphide —

8PbF, + PA = SPbS + 2PSF,.

The gas may be collected over mercury.

Thiophosphoryl fluoride is a colourless gas, which spontaneously inflames
when a jet of it is allowed to escape into the air. It bums with a pale greenish
non-luminous flame. In pure oxygen the gas bums with a yellow and mcMV
luminous flame. The gas is decomposed by heat, into phosphorus fluoride,
phosphorus, and sulphur. When heated in a glass vessel, sulphur and phoa-
phorus are deposited, and silicon tetrafluoride is formed—

4PSF, -I- 8Si = 8SiF4 + 4P -I- 4S.

Phosphoryl Chloride {phosphorus oxychlaride\ POCI3.— This
compound is formed, by the first action of water upon phosphorus
pentachloride {g,v^. It is also obtained when phosphorus penta-
chloride and pentoxide are heated together in a sealed tube —

8PCI5 + PA = BPOCls.

It is most readily prepared by heating phosphorus pentachloride
with either oxalic acid, or boric acid, thus —

PCI4 + HjCA = POClj + 2HC1 + CO, + CO.
3PC1» + 2H8BO, = aPOClj + 6HC1 + B,0,.

Oxtdes and Oxyactds of Phosphorus 429

Properties. — Phosphoryl chloride is a colourless fuming liquid,
which boils at 107.23^ When cooled to about - 10* it solidifies to
a white crystalline mass, which melts at 0.8*. It is decomposed by
water with formation of tribasic phosphoric acid and hydrochloric
acid —

POClj + 8HjO = P0(H0)3 + 3HG1.

PyropliMpboiTl Oblorlde, PtOsCl4, is obtained by passing nitrogen peroxide
through phosphorus trichloride, and subsequently distilling the liquid. The
reaction is complicated, and cannot be expressed by a single equation ; nitro-
gen is evolved, and phosphorus pentoxide, nitrosyl chloride, and phosphoryl
chloride are simuUanecusly formed. Pyrophosphoryl chloride is a colourless
fuming liquid, boiling between aio* and ai5*. It is decomposed by water,
and forms hydrochloric acid and orthophospboric acid {not fyropkosphoric
acid)—

PjO,a4 + 5H,0 = 2H,P04 + 4HCL

It is converted by phosphorus pentachloride into phosphoryl chloride—

PjO^a* + PCI9 = 3POC1,.

Thlophotphoryl CnUorldt, PSQ„ is prepared by beating a mixture cf
phosphorus pentasulphide and pentachloride-^

3Pa, + PA = BPSCl^

It is a colourless liquid, boiling at las*. It fumes in moist air, being de-
composed by water into sulphuretted hydrogen, phosphoric and hydrochloric
acids—

PSa, + 4H,0 = H^ + H,P04 + SHQ.

OXIDES AND OXY ACIDS OF PHOSPHORUS,

Four compounds of phosphorus and oxygen are known, all of
which are formed when phosphorus is burned in a limited supply
of air—

Phosphorus Monoxide F^O f

Phosphorous oxide (phosphorus trioxide) ^S^i^

Phosphorus tetroxide ^/\-

Phosphorus pentoxide l^O-,.

The two compounds, phosphorus trioxide and pentoxide, are tlie
best known of these oxides, and they give rise respectively to
phosphorous and phosphoric acids. The following oxyacids of
phosphorus are known —

Inorganic Cfieitiistry

Hypo phosphorous acid H3PO, —

Phosphorous acid. . H^POj or P{HO),

Onhophosphoric acid . HaPO, „ PO(HO)i

Pyrophosphoric acid . H,P,0, „ P,0,(HO),

Metaphosphoric acid . HPO, „ POj(HO)

p,o,
p,o.

Wben ph(Mphorus is dissolved in a lolulion of aqueous alooholio potash, fl
dilute hydrochloric acid is added, a yellow or reddisb precipitate '
which was believed (o have [lie composition Pfi. Recent invBtigalioiis,
ever, seem to prove that the substance so obtained is identical wi
phorus. {Chem. Soc. Journal. Nov. 1899.)

Phosphorous Oxtde [phospkerous anhydridt), PjO, ; molec
weight = 221. $2.— This oxide is obtained, mixed with a large ei
of the pentoxide, when phosphorus is burned in a tube thro

Fio. 119.

•rhicTi a regulated stream oT air is passed. In order to obtain Hw
coiiipound in a state of purity, ihe following method is employed.

A quantity of phosphorus is introduced into a glass lube, bent in the
manner indicated in Fig. 119, and fitted into one end of a long,
wide, Liebig's condenser. Into the end of the condenser neatest to
the U-tube, there is introduced a loose plug of glass wool, which
serves to arrest the penioxide. The phosphorus is ignited at the
open end of the glass tube, and a stream of air drawrn through
the apparatus by means of an aspirator. A stream of water, at
60*, is circulated through the condenser, when the easily fusible
phosphorous oxide is carried over, and condenses in the U
which is immersed in a freering mixture.

Phosphorus Pentoxide

43*

Properties. — Phosphorous oxide, as it collects in the cooled
tube, is a snow-white crystalline solid, which melts at 22.5* to a
colourless liquid The liquid solidifies at 2 1* to a white, waxy-looking
mass, consisting of monoclinic prismatic crystals. The liquid boils
at 173. i^ It possesses an unpleasant garlic smell, and is highly
poisonous. Phosphorous oxide is only very slowly acted upon by
cold water, which gradually dissolves it, forming phosphorous
acid —

PA + 6H,0 - 4HsP03.

In contact with hot water a violent action takes place, in which
spontaneously inflammable phosphoretted hy-
drogen is evolved, and a red deposit, consisting
of red phosphorus and phosphorus monoxide,
is formed.

When heated in a sealed tube to a tem-
perature of 440*, phosphorous oxide is de-
composed into phosphorus tetroxide, and red
phosphorus —

aPiOe = 3P,04 + 2P.

Fig. 120.

When exposed to air or oxygen, phosphorous
oxide is gradually oxidised into phosphorus
pentoxide, but when placed in warm oxygen
it bursts into flame. When brought into chlorine it also spon-
taneously inflames.

Pliosphoms Tttroxidt, P^4.— This stibsunce is obtained when phos-
phorous oxide is heated in a sealed tube to a temperature of 440*. It forms
brilliant transparent crystals, which appear as a sublimate in the tube. This
oxide is highly deliquescent, and dissolves in water with evolution of heat.

Phosphorus Pentoxide, PjOj ; molecular weight = 141.82.—
This oxide is the main product of the combustion of phosphorus in
air or oxygen. It may readily be obtained, by burning a quantity
of phosphorus in a small capsule, and covering the whole with a
large bell-jar, Fig. 120. The white clouds of phosphorus pent-
oxide collect as a soft snow-like substance.

Properties. — Phosphorus pentoxide is a white, amorphous, and
very voluminous powder. It is without smell, although as usually
prepared it frequently possesses a slight garlic odour, owio^ to the
presence of phosphorous oxide.

432 Inorganic Chemistry

Phosphorus pentoxide is extremely hygroscopic, absorbing mois-
ture firom the air with great rapidity. It must therefore be pre-
served either in well-fitting stopper bottles, or in hermetically
sealed vessels. Its affinity for water, constitutes it the most use-
ful desiccating agent known to chemists : prolonged exposure to
phosphoric pentoxide, removes the last traces of aqueous vapour
from gases.

When thrown into water, phosphorus pentoxide is dissolved with
a hissing souiid, resembling the quenching of hot iron, and forms
metaphosphoric acid —

PA + H,0 = 2HP0,
which gradually passes into orthophosphoric acid —

HPO, + H,0 = HjPO^.

Phosphorus pentoxide is capable of abstracting the elements ol
water ^om a number of substances, both inorganic and organic ;
thus, it converts nitric acid into nitrogen pentoxide —

2HNOs - HjO = NjOft-

In the same way it withdraws the elements of water from alcohol,
with the evolution of ethylene —

CgHfO — HgO ^ Cgxii.

Hypophosphorous Acid, HjPOj. — This acid is prepared by the
action of sulphuric acid upon the barium salt —

BaCHjPO^j + HjS04 = ^^^O^ + 2HsP0,.

The solution, after the removal of the barium sulphate by filtra-
tion, is gently heated until its temperature rises to 130°, when it
will be sufficiently concentrated to deposit crystals, when cooled
too\

The barium hypophosphite is obtained by boiling phosphorus
with a solution of barium hydroxide —

3Ba(HO)2 + 8P + GHjO = 2PH3 + SBaCHsPO,),.

Properties. — Hypophosphorous acid is a white crystalline com-
pound, which melts at 1 7.4". When strongly heated, it is converted

Phosp/iorous Acid 433

into orthophosphoric acid with the evolution of gaseous phos-
phoretted hydrogen —

2H,PO, - H3PO4 + PH,.

Hypophosphorous acid acts as a powerful reducing agent, on
account of the readiness with which it absorbs oxygen and is con-
verted into orthophosphoric add —

H 1 HO^ H 1 HO^

H IpO + O, - ho VPO ; or HO Ip + O, = HO IPO.
HOj HOj HOj HOj

Hypophosphorous acid is a feeble monobasic acid ; its salts with
monovalent metals being represented by the formula MH|PO|.

It is customary to express the basicity of oxyacids by the number of (HO)
groups that are contained in the molecule, and as this acid is monobasic its
constitution would be expressed by the formula POHs(HO). Many of the
oxyacids of phosphorus, however, show a tendency to exhibit a lower degree
of basicity than is represented by the number of (HO) groups they contain ;
thus, orthophosphoric acid, PO(HO)s. which is tribasic, and forms the salt
trisoditmi phosphate, PO(NaO)f , holds the third atom of the metal so loosely,
that even such a feeble acid as carbonic acid is capable of expelling it —

PO(NaO), + CO, + H^ = PO(HO)(NaO), + HNaCOj.

" NagPO* + CO, + H,0 = HNa,P04 + HNaCQj.

The weaker acid, phosphorous add, is also tribasic, P(HO)s, and forms
trisodium phosphite, P(NaO),. or NagPOg. But this salt is even decomposed
by water, into the disodium phosphite, P(HO)(NaO)„ or HNa,PO|.

Hypophosphorous add being a still weaker acid, its addic power is destroyed
stf soon as one atom of hydrogen is replaced by a base, and its constitution may,

in harmony with these facts, be expressed by the formula PH(HO)], or HO > P.

HOj

Phosphorous Acid, H3PO3, or P(H0)3.— As already mentioned,
this acid is formed when phosphorous oxide is dissolved in cold
water.

It is most readily prepared by the action of water upon phos-
phorus trichloride —

PCla + 3H,0 - 3HC1 + P(HO),.

The production and decomposition of the phosphorus trichloride

a £

434 Inorganic Chemistry

may be carried on simultaneously, by passing a stream of chlorine
through phosphorus which is melted beneath water. The solution
is evaporated until its temperature rises to i8o*, when the liquid
will have become so concentrated that on cooling it solidifies to a
crystalline solid.

Properties. — Phosphorous acid is a white crystalline substance
which melts at 70.1*. When heated, it decomposes into ortho-
phosphoric acid, with evolution of phosphoretted hydrogen —

4H,P03 = 3H8P04 + PH,.

Like hypophosphorous acid this compound absorbs oxygen, and
therefore is a powerful reducing agent ; silver salts are reduced
to metallic silver, and mercuric saUs are reduced to mercurous
salts. By the absorption of oxygen it is converted into ortho-
phosphoric acid —

H3PO, + O « H3PO4.

Although a tribasic acid, its tribasic salts are unstable ; the
sodium compound, NajPOj, which is the most stable inorganic
salt, is decomposed by water into the dibasic salt —

NasPOj + HjO = HNajPOj + NaHO.
NaO^ HO \

or NaO
NaO

P + HgO = NaO [ P + NaHO.
NaoJ

Orthophosphorie Acid, HSPO4, or P0(H0)3.— This acid is
formed when phosphorus pentoxide is dissolved in boiling water,
or when the solution of the oxide in cold water is boiled —

PA + 3H,0 = 2HsP04.

Orthophosphorie acid is readily obtained by the oxidation of red
phosphorus with nitric acid. Copious red fumes are evolved, and
phospkoric acid remains in solution.

Phosphoric acid is prepared on a large scale by the action of
sulphuric acid upon bone ash, as in the process for the manu-
facture of phosphorus —

Cag(P04), + 3H,S04 = 3CaS04 + 2H,P04.
The calcium sulphate is removed by filtration, and tlie soiutioD

Pyraphosphoric Acid 435

evaporated to a syrup. Prepared in this way the acid usually
contains arsenic This is lemoved by first reducing it to arsenious
oxide, by means of sulphur dioxide, and after boiling off the excess
of sulphur dioxide, precipitating the arsenic as sulphide by means
of sulphuretted hydrogen.

Properties. — The solution obtained by these methods is either
concentrated in vacuo, or heated to a temperature of 140", and
allowed to cool, when the acid is obtained in the form of trans-
parent six-sided prisnuitic crystals, belonging to the rhombic
system. The substance is deliquescent, and melts at 38.6*.

Phosphoric acid is tribasic, and forms three series of salts,
according as one, two, or three of its hydrogen atoms are replaced
by an equivalent of metal. Thus, with the metal sodium the three
salts arc known —

Trisodium phosphate (normal sodium phosphate) Na,P04.
Hydrogen disodium phosphate .... HNa^POf.
Dihydrogen sodium phosphate .... HiNaPOi.

The hydrogen may be replaced by its equivalent of more than
one base. Thus, the well-known compound, microcosmic sedt^ is
hydrogen sodium ammonium phosphate, HNa(NH4)P04. The
salt which is precipitated when magnesium sulphate (in the pre-
sence of ammonium chloride and ammonia) is added to a solution
of a phosphate, consists of the compound ammoniimi magnesium
phosphate (NH4)MgP04.

The heavy metals usually only form normal phosphates. Thus,
on the addition of silver nitrate to a solution of either of the three
sodium salts, the same silver salt is precipitated, namely, tri-
argentic phosphate.

Na3P04 + 3AgN0, - Ag8P04 + SNaNO,.
* HNa^P04 + 3AgN0, = Ag,P04 + 2NaN03 + HNO,.
H,NaP04 + 3AgN08 = Ag,P04 + NaNO, + 2HNO,.

PyrophosphoriC Acid, H4P,Oy, or P,Oj(H 0)4.— This acid i&

* Hydrogen disodiam phosphate, although belonging to that class of com-
pounds commonly called acid salts, on account of the fact that it still retains
a portion of the replaceable hjrdrogen of the add, is strongly alkaline in its
action upon litmus : iflver nitrale is a neutral compound, hence in this reaction,
by mixing an alkaline and a neutral liqukl, an acid liquid is obtained, oo
armnnt nf the molccolc a# nitric ackl thai tf set fret.

43^ Inorganic ChtmUtry

derived froni onhophosphoric acid, by the withdrawal of t
Diolecule of water from two molecules of the acid. This change tjj
effected by heating the ortho acid to 213'—

SHjPO, - H,0 = H.PjO,"

The formation of this add from two molecules of orthophc
plioric acid will be made clear by the following fonnulK —

HO HO HO HO HO HO HO HO J

0 = P- |o-M HJ-O-VsO a H,0 + O = i'-0-V=0

Pyrophosphates are formed when monohydrogen orthopboi
phales are heated. Thus, by healing hydrogen disodium <
phosphate, sodium pyrophosphate is formed —

2HNa,PO, - H,0 = NajP.O,.

When ammonium magnesium phosphate (see above) is heated
in the same way, it loses water and ammonia, and is transformed
into magnesium pyrophosphate, thus —

2(NH0MgPO, - Mg,P,0, + H,0 + SNHj.

Properties.— Pyro phosphoric acid is an opaque white crystal-
line solid, readily soluble in water. Its aqueous solution passes
slowly into ortliophosphoric acid, the change taking place rapidly
on boiling ; a solution of this acid therefore cannot be concen-
traied by boiling.

The pyrophosphates arc stable salts, and their solutions may be
boiled without change ; by boiling with acids, however, they are
converted into ortho phosphates.

MetaphosphOPic Add, H POj or POj(HO).— This acid is formed
when phosphorus pentoxide is allowed to deliquesce. It may be
obtained by the abstraction of one molecule of water from one
molecule of orthophosphoric acid, which is brought about by beat-
ing the tribasic acid to redness —

HjPO, - H,0= HPOr

It is also obtained by strongly heating pyrophosphoric add —

H,P,0,- H,0-SHPO^

Metaphosphoric Acid

437

The sodium salt is obtained by strongly igniting either dihydrogen
sodium phosphate, H|NaPO|, or hydrogen sodium ammonium
phosphate (microcosmic scUt)^ HNa(NH4)P04; or dihydrogen
sodium pyrophosphate, HiNa^PiOr.

Properties. — Metaphosphoric acid is a transparent vitreous
solid (frequently termed glacial phosphoric acid). It is readily
fusible, and is usually cast into sticks. At a high temperature it
may be volatilised. Metaphosphoric add is easily soluble in
water, and its solution is slowly transformed into orthophosphoric
acid : this change takes place rapidly on boiling, and the acid
passes directly into the tribasic acid without the intermediate
formation of pyrophosphoric add —

HPO, + H,0 - H,P04.

Metaphosphoric acid is monobasic, but it possesses the remark-
able property of forming a number of salts, which may be regarded
as derived from several hypothetical polymeric varieties of the
acid.

Monometaphospboric acid, HPO|, fonns
Dimetaphosphoric add, (HPOj)].
Trimeta phosphoric add, (HPOt)t*
Tetrametaphosphoric add. (HPO|)4, ,.
Hexametaphosphoric add, (HPOt)c, ••

•I

monometapbosphates, NaPOj.
dimetaphosphates, K^PjO^.
trimetaphosphates, Na^PtO}.
tetrametaphosphates, Pb|P40is.
hexametaphosphates, Na^P^Oi^

The three compounds, ortho-, pyro-, and metaphosphoric adds,
are readily distinguished from each other by means of silver nitrate,
and their action upon albumen : —

Reagent

Orthophosphoric

Pyrophosphoric

Metaphosphoric
Add.

White gelatinous
precipitate of
AgP6,

Coagulates

Silver nitrate .
Albumen . .

Canary yellow
precipitate of
AfoPO*

No action

White crystalline
precipitate of
Ag^Ppy

No action

Orthophosphoric add is also distinguished by giving a yellow
precipitate of ammonium phospho-molybdate, upon the addition of
excess of a solution of ammoniimi molybdate in nitric add (see
Molybdenum).

invrganit Ckimistry

Oompoimda of Pboapbonu oonulnlnc nitrogen. —By ihr ai

monla upon phosphnrus ponlachloride. and upon phospboryl cliloriile (POCIf),

li pa.s$ed ova- phospbonu pmacblondr, and Ibe solid rasis so obtained U
bcaled in a stream of an ineil gas, until the Binmoniuni ebloride is driveo
ofl, a while insoluble powder remBins, having the composriion represented hf-

lheforTnulaPN(NH|, to which the n«me;iADip*o»i has been give

PClj

7NH, = eNHjQ + PN(NH|,

obtained bj llie a

POCi, + 6NH, = PO(NHJ, + aNHjCL
>ut of conlact with air, pbospboryl triamide yields a

PO(NHa), = aNH, + PON,

Fyroplioiplumle Addi.— Three of ibe«e compounds are knowi
may Ik re|;Hjded as pyrophosphoric add. in which 1. 1, and 3 of i
groups have been replaced respectively by Xhc group (NH^), thuA—

Pyraphospboric ncid
Pyrophoiphamic add
Pyrophosphodiamtc acit

P,0.(HO),.
P,0,(HOWNHJ.
PA{HOWNHJ,
P,0,|H01(NHJ,.

CampoundB of Phospbonut with Sulphur.— a numher of compounded
phospliorus and sulpbui hsve been obtained by healing together varying
portions of sulpbur and red phosphorus. The following compounds I

P.S,

Phosphonis Irisulphide

■ P.O,

Phosphorus tettasolphide (?)

. PrSi

. P^,

Phoaphonis pentasulphide .

. P,0>

Fhoiphonu Fantaiiilphlda, P^— This compound is ibe besi-k

member of the series, li is prepared by gently beating red phosphonH aj
fragments of sulphur, in the proportion required by the formula
The elements combine wilb energy, and on cooling, a solid mass
This solid material is then distdled in a current of carbon diotide, when ij|
pentasulphide is obtained in the form of yellow crystals. The compound ■
also be obtained by dissolving ordinary iTbo^phorus and sulphur in t)<e p
proportions in carbon disulphide, and healing the solution in sealed ti
)io' On allowing the solution to cool, yellow crystals of the pentasulplj
tit deposited. Phosphorus pentasulphide is decomposed by wa
lormallon of onhophospboric acid and the evolution oriulphutctled hydroga
P^,+ RH/3 = )H.rO, *SH,S.

Arsenic 439

Symbol. At. Atomic wngbi •=- 7^.9. Molecular weight = 299.6.

Vapour density = 149.8.

Oeeurrenee. — Arsenic is found in the free state in nature,
usually in the form of small nodules, more rarely as distinct crystals.
In combination with sulphur it constitutes the minerals realgar^ or
ruby sulphur^ A.s^| ; and orpiment^ AsiS,. In combination with
metals, as arsenides, it occurs widdy distributed, the commonest
ores being arsenical iran^ FeAs^ and FeiAs, ; kupfemickel^ NiAs
and NiAS) ; and tin white cobalt, CoAs^ With metals and sulphur,
it is met with in such minerals as arsenical pyrites^ mispickel,
or white mundtc, FeS^FeAsj ; cobalt glance, CoS^CoAsj ; nickel
glance, NiS,, NiAs^. Arsenic is present in small quantities in most
samples of iron pyrites, hence it finds its way into sulphuric acid
manufactured from pyrites. It also occurs in coal smoke, being
derived from the pyrites contained in coal, and hence is present in
the atmosphere : during the prevalence of yellow fogs the amount
of arsenic present is very appreciable

Modes of Formation. — On the small scale, arsenic is obtained
by heating a mixture of arsenious oxide, ASfO^ with powdered
charcoal —

AsiOe + 6C = 6C0 + 4 As.

On a larger scale it is usually obtained either from native arsenic
or from arsenical pyrites ; the latter substance, when heated, gives
up arsenic, and ferrous sulphide is left behind —

FeS„FeAs, - 2As f 2FeS.

The mineral is heated in long narrow horizontal earthenware
retorts, into whose mouths are fitted earthenware receivers. The
arsenic volatilises, and condenses in these receivers as a compact
crystalline solid. It is purified by redistillation.

Properties.— Arsenic which has been rcsublimed, is a brilliant
steel-grey metallic-looking substance, forming hexagonal rhombo-
hedral crystals, having a specific gravity of 5.62 to 5.96. It is very
brittle, and is a good conductor of heat and electricity. Arsenic
begins to volatilise at 100*, and rapidly vaporises at a dark-
red heat, passing from the solid to the vaporous states without

Inorganic Chemistry

liquefying. The vapour has a yellow colour and an unpli
garlic smell. When heated under ptessuie, arsenic melts at
and on cooling, solidifies to a compact crystalline mass. When
arsenic is vaporised in a glass lube, in a current of hydrogen, it
condenses along the tube in three distinct conditions : thai which
is deposited nearest to the heated portion of the lube is in the form
of rhombohedral crystals ; that which sublimes a little farther
along, and condenses at a point where the temperature is about
2io-iio', consists of a black shining amorphous deposit, while at a
still more distant and cooler portion of the tube, a grey crystalline
sublimate is formed. These are regarded as allotropic modifica-
tions of arsenic The amorphous variety is also formed, when
arsenuretted hydrogen is decomposed by being passed through a
heated tube {.g.v.). Amorphous arsenic is unacted upon by air ai
ordinary temperatures, and only slightly oxidised at So". The grey
crystalline variety is readily oxidised on exposure to air at ordinary
temperatures.

Amorphous arsenic, when healed out of contact with air to jf.
is convened into the rhombohedral variety.

Arsenic, like phosphorus, forms tctralomicmolecules.itsmoleculi
weight as deduced from its vapour density being 74.9 x 4. = 299.6.

When healed in oxygen, arsenic burns with a bright bluish-wbite
flame, forming arsenious oxide, As,Oj. It is oxidised by sulphuric
acid, nitric acid, and other oxidising agents. Il combines readily
with chlorine, and when thrown into this gas in the condition of
powder it spontaneously inflames, forming arsenic trichloride.

ITlirown into bromine, a fragment of arsenic spontaneously in-
flames, and bums as it floats about upon the surface of the liquid
Arsenic, in many of its charade ristics, resembles the true metals ;
it is one of those elements lying on the borderiand between true
metals and non-metals, to which the name metalMii \a applied. It
is capable of forming alloys with metals, and an alloy of this
element with lead, is employed for the manufacture of shot II is
found that by the addition of a small proportion of arsenic lo lead,
the melted meial is more fluid, and therefore more readily assumes
Che spheroidal form when projected from the skol la^tr, and od
solidification the alloy is considerably harder than pure lead.

sary^l
|6c^H

A rsenuretud Hydrogen 44 1

ABSEHUBSnED ETDBOOEH {Arsenu trihydrUU, Arsine),

Formula, AsHy. Molecular weight = 77-9* Density = 38.95.

Modes of FormatlOIL— (i.) Arsenuretted hydrogen is formed
when soluble arsenic compounds are exposed to the action of
nascent hydrogen : thus, when a solution of arsenious oxide is
introduced into a mixture from which hydrogen is being generated,
such as zinc or iron and dilute hydrochloric or sulphuric acid,
arsenic trihydride is obtained, mixed with free hydrogen —

Pisfi% + 12H, « 4AsH, + 6H,0.

(2.) By the same action of nascent hydrogen, arsenic trihydride
is formed when a solution of either arsenious oxide, AS4O0, or
arsenic oxide, As^Of, is subjected to electrolysis.

(3.) Arsenic trihydride is also formed, when arsenical compounds
are in contact with organic matter which is undergoing decom-
position. During the growth of certain moulds and fungi a small
quantity of hydrogen is evolved, which by its action upon the
arsenic compound, gives rise to the formation of arsenic trihydride.
By this action arsenic trihydride is sometimes formed in dwelling-
houses where arsenical wall-papers are employed, and where, from
dampness or other causes, mould develops.

(4.) Pure arsenic trihydride is prepared by the action of dilute
hydrochloric or sulphuric acid upon an alloy of arsenic and zinc —

As^n, + 8H,S04 =■ SAsH, 4- 8ZnS04,

or by the action of either water or dilute acid upon an alloy of
arsenic and sodium, prepared by heating sodium in the impure
arsenic trihydride obtained by method No. i.

Properties. — Arsenic trihydride is a colourless, offensive- smell-
ing, and highly poisonous gas. Under pressure it condenses to a
colourless liquid, which boils at -$4-^* ^^^d solidifies at -113.5*.
The gas bums with a lilac-coloured fiame, forming water and white
%nes of arsenious oxide —

4AsH, + 60, - hsfi^ + 6H,0.

When the supply of air to the flame is limited, as when a cold

surface is depressed upoi
as a shining black amorphi

4AsHj

As, + 6H,0.

may he carried oul by n
Hydrogen is generated ir

Arsenurctled hydrogen is readily decomposed by heat h
elements: Ihus, whenthegas is passed ih rough a glass tube, whicb
is heated at one point by a Ilimsen flame, arsenic in the amoi^
phous condition is deposited upon the lube immediately beyond
the healed spot. Even wiien greatly diluted with hydtxjgen this
reaction takes place, and it therefore affords a delicate lest for the
presence of exceedingly small qnanlilies of arsenic This method
for the delectifin of arsenical compounds is known as Marsks (est.
% of the apparatus seen in Fig,
two-necked bottle from zinc and
dilute sulphuric acid(whicb
are themselves free from
arsenic), and the arsenic in
[he form of an oxygen or a
haloid compound is intro-
duced. On igniting the
issuing gas, and depres-
sing a white porcelain cap-
FiG. rai. sule into the flame, black

Slain s o f amorphous arseji i c
arc produced : ajid if the tube be healed as shown in the figure,
the arsenic is deposited as a black film. The corresponding anti-
mony comptound, SbK, (g.v.\ givfss rise to a similar deposit of
metallic antimony, when treated in the same way ; but the arsenic
deposit is readily distinguished by being easily soluble in a solu-
tion of calcium hypochlorite. Many metals, such as sodium, or
potassium, when healed in arsenuretted hydrogen, form alloys
with the arsenic, and hydrogen is set at liberty; while metallic
onides when similarly treated form metallic arsenides and water.

Arsenurelled hydrogen is slightly soluble in water, but the solu-
tion on exposure to air deposits arsenic

When passed into a solution of silver nitrate, metallic silver
pi^cipitaled, and a solution of arsenious oxide (the hypolhet

id, HjAsO,) is obtained, ihus-
AsH, + 6AgNO, + 3H,0 ■= 3A^, \- GHNO. ^- H^O,

Mk^^

. Arsenic Chloride 443

When the gas is passed into copper sulphate solution, cuprous
arsenide is precipitated —

2AsH, + 3CUSO4 - 3H,S04 + As^Cu,.

Arsenuretted hydrogen is decomposed by the halogens with
energy, forming the haloid compound of arsenic, and the halogen
acid —

AsH, + 3C1, = AsClj + 3HC1.

Solid Ars«iiir«tt«d Bydxogen.— When arsenide of potassium or sodium is
acted upon by water, a soft brown solid substance separates, which contains
equal atomic proportions of arsenic and hydrogen. Its molecular weight is
unknown, its composition is therefore expressed by the formula, (AsH)b.

COMPOUNDS OP ARSENIC WITH THE HALOGENS.
The following compounds are known —

AsF| ; AsClg ; AsBr| ; Asl^.

Two other compounds with iodine have been described, contain-
ing the elements in the proportion represented by the formula',
AsT, and As^l^, the molecular weights of which are unknown.

Arsenic Fluoride, AsFs ; molecular weight — 131.9, is formed
when sodiimi fluoride is heated with arsenic chloride —

3NaF + AsClj - 3NaCl + AsF,.

It is best obtained by distilling a mixture of arsenious oxide,
powdered Huor spar, and sulphuric acid in a leaden retort. The
hydrofluoric acid generated by the action of the acid upon the
calcium fluoride, reacts upon the arsenious oxide, thus —

As^Oe + 12HF = 4ASF3 + 6H,0.

Properties. — Arsenic fluoride is a colourless fuming liquid,
boiling at 60.4*. It is rapidly decomposed by water into arsenious
oxide and hydrofluoric acid. On this account it forms painful
wounds when brought into contact with the skin.

Arsenic Chloride, AsClj; molecular weight « 181.11, is ob-
tained when arsenic bums in chlorine, or when chlorine is passed
over fragments of arsenic in a ttibe.

444 Inorganic Chemistry

It is also produced when either arsenic or arsenioos sulphide is
distilled with mercuric chloride —

2A8 + 6HgCl, - 3Hg,Cl, + SAsQ,.
As^S, + 3HgCl, - 3HgS + SAsCl,.

It is readily prepared by the action of hydrochloric acid upon
arsenious oxide; for which purpose sodium chloride, arsenious
oxide, and sulphuric add are gently heated together in a retort
connected with a well-cooled receiver—

ASfOf + 12HC1 - 4AsCl, + 6H,0.

Properties. — Arsenic chloride is a colourless, fuming, and some-
what oily liquid, which boils at 130.2°, and is extremely poisonous.
In the presence of excess of water, or when added to warm water,
it is decomposed into arsenious oxide and hydrochloric acid.
With a small quantity of water a solid crystalline arsenic chlor-
hydroxide is formed, As(HO)2Cl —

AsCl, + 2H2O = 2HC1 + As(HO),Cl.

ArsenlOTUi Bromide, AsBrs. — This compound is formed by the direct union
of arsenic with bromine, and is prepared by adding powdered arsenic to a
solution of bromine in carbon disulphide. On evaporation, the compound is
deposited in the form of colourless deliquescent crystals, which melt at ao"* to
25° to a straw-coloured liquid.

Arsenious Iodide, Asis, is obtained by heating a mixture of arsenic and
iodine. It is most conveniently prepared by digesting a saturated ethereal
solution of iodine, with powdered arsenic, in a flask with a reflux condenser.
On Altering and cooling, the iodide deposits in the form of lustrous red hexa-
gonal crystals

OXIDES AND OXYACIDS OP ARSENIC.

Two oxides of arsenic are known, both of which act as anhy-
drides—

Arsenious oxide AS4O9.

Arsenic oxide (arsenic pentoxide) . . As^Oji.

No acid corresponding to arsenious oxide is known in the free
state, although the arsenites constitute a class of stable salts.

Arienious Oxidt

Three usenic acids, derived from arseoic; pentoxide, are known,
an^ogous in constitution to the three phosphoric acids, namely—

Ortho-arsenic add
Pyro-arsenic acid .
Metarsenic acid .

H,As04 0rAsO(HOV
H^AsjOiOr As,0,(H0)4.
HAsO, or AsOiCHO).

ARBSmODS OZHPE.
Formula, hifi* Molecular wdgbl = 395.3&

Mode of Formation.— Arsenious oxide is farmed when arsenic
air or in oxygen, or when arsenic minerals are roasted in
a current of air. On a small scale it may be produced by burning
arsenic in a hard glaas tube in a stream of oxygen, and allowing
the while fumes of areenious oxide to pass into a glass cylinder (as

bums

shown in Fig. ill), where the greater part condenses, while the rest
is led into a draught flue.

Arsenious oxide la obtained as a secondary product, in the
metallurgical process of roasting arsenical ores of nickel, cobalt,
tin, silver, and others, for the extraction of these metals. It
is also obtained as a principal product by roasting arsenical
pyrites. The ore is heated either upon the hearth of a rever-
berator/ furnace, where it is raked over from time to time, or
it is introduced by means of a hopper, into one end of a long clay-
lined iron cylinder, placed at an incline of about I in i8, and caused
■lowly to revolve about its longitudinal axis, Fig. 133. The lower
end of this cylinder eaten a fiinuce, the upper end is coooected to

of brickwork Hues.

Ifu>rganic Cfumistry

The ore ia delivered into the upper
end of the revolving cylinder,
and as it gradually gravitates
down the incline, it is com-
pletely roasted by the fiimace
Sames which pass over it, and
Bnally falls out into a chamber

^ beneath The fiimes of arseni-
ous oxide pass through a series
of chambers or flues, so ar-
ranged as to present an exten-
sive condensing surface to the
gases, and the crude product,
known as arsenical soot, is from
time to time collected This
IS known as Oxland and Hock-
ing's revolving calciner.

Properties.— Arsenious
oxide, known familiarly as inhitt

Lnown in three modifications —

O ] Amorphous.

(i) Octahedral crystals of the

regular system.
(3.) Prismatic crystals of the

tri metric system.

Amorpkeui Arunious Oxide
is a colourless, transparent, vit-
reous substance, which is ob-
tained when the vapour of the
□xide is condensed at a tem-
perature only slighily below its
vaporising poini. On exposure,
it gradually becomes opaque,
being iranslbrmed into the regu-
lar octahedral variety. This
change takes place from the
outside, and lumps of opaque
" white arsenic." *heo broken,

Ar sent Us 447

often show a nucleus of the vitreous modification. Amorphous
arsenious oxide may be preserved unchanged in sealed tubes.
The change from the vitreous to the crystalline form is attended
with evolution of beat, and a diminution of specific gravity from
3.738 to 3.689.

Amorphous arsenious oxide, when heated to about 200*, melts,
and at a higher temperature vaporises. It is soluble in 108 parts
of cold water.

Octahedral Arsenious Oxide, — The vitreous form passes spon-
taneously into this variety. It is obtained directly, by quickly
cooling the vapour of arsenious oxide, or by crystallisation from
the aqueous solution of either form of the oxide. Arsenious oxide
is also deposited in this form from solution in hydrochloric acid.

Octahedral arsenious oxide is less soluble in water than the amor-
phous variety, i part requiring 355 parts of water for its solution.
When heated, the crystals vaporise without fusion, but when heated
under pressure they melt, and are converted into the vitreous form.

Prismaiic Arsenious Oxide is obtained by crystallisation from a
hot saturated solution of arsenious oxide in potassium hydroxide.

Aqueous solutions of arsenious oxide possess a feeble acid re-
action, probably due to the formation of unstable arsenious acid.
HgAsOs. '^c ^<^id h^ ^o( httn isolated, and on concentration
the solution deposits crystals of arsenious oxide.

Arsenious oxide is a powerful poison : from 2 to 4 grains usually
prove fatal. It is possible, however, by the habitual use of it, to
so accustom the system to this poison, that doses sufficiently large
to cause certain death to one unused to it, may be taken with
apparent impunity. The use of arsenic is said to beautify the
complexion, and to improve the wind The men who are em-
ployed upon arsenic works, are constantly liable to swallow doses
of arsenious oxide which would cause death to one unaccustomed
to the occupation.

Arsenltes. — Three classes of arsenites are known, which may
be regarded as being derived from the three hypothetical acids —

(Silver ortho-arsenite, AgiAsOf
"i!^te(Scrj^lHCuAsO,.
green), J

(Calcium psrro-arsenite.CatAs^i.

448 Inorganic Chemistry

(Potassium metanenite. KAaCV
A-^^^PJ^^J^ } KAsO»HAiO»
Lead metanenite, Pb(AsO|)»

The pigment known as Schweinfurt green^ is a double metar-
senite and acetate of copper —

3Cu(AsOa}8,Cu(C,H,Os),.

All arsenites, except those of the alkali metals, are insoluble in
water. When heated, most arsenites are converted into arsenai^
and arsenic ; and when heated with charcoal the whole of the
arsenic is reduced.

Arsenic Pentoxide, As^O^ — This oxide is not formed when
arsenic bums in oxygen. It is obtained by the oxidation of arseni-
ous oxide by nitric acid, and subsequently heating the arsenic add
so produced, to a dark-red heat —

2H3ASO4 = 3H,0 + AsjOft.

Properties. — Arsenic pentoxide is a white deliquescent solid,

completely soluble in water, with the formation of arsenic acid

When strongly heated it breaks up into arsenious oxide and

oxygen —

SAs,Oft - Pksfi^ + 20^

ARSENIC ACIDS AND ARSENATES.

When arsenic pentoxide is dissolved in water, crystals are ob-
tained having the composition 2AsO(HO)3,H20« At 100° these
melt and lose water, leaving ortho-arsenic acid, H3ASO4. By the
withdrawal of water from this acid, both pyro- and metarsenic acids
are obtained.

Heated between 140' and i8o', two molecules of the "ortho"
acid lose one of water —

2H8ASO4 = H4AS20y + H,0.

And by beating the pyro-arsenic acid so obtained to 200*, another
molecule of water is expelled, with the formation of metarsenic acid
{compare corresponding acids 0/ phosphorus) —

H4ASSO7 = 2H AsO, + HjO.

Pyro- and metarsenic acids are both crystalline solids, which

Arsenic Disulpkide 449

diss<^e in water with the evolution of heat and formation of ortho-
arsenic acid ; aqueous solutions of these two acids, therefore,
cannot exist In this respect they differ from the corresponding
phosphorus acids, both of which can be obtained in aqueous
solution.

Each of the three arsenic acids fonns salts, of which the following
are examples : —

Trisodium ortho-arsenate . Na3As04.

Hydrogen disodium ortho-arsenate HNa9As04.

Dihydrogen sodium ortho-arsenate H|NaAs04.

Ammonium magnesium ortho-arsenate . (N H4)MgAs04.

Sodium pyro-arsenate .... Na^ASfOy.

Sodium metarsenate .... NaAsOf^

The salts of pyro- and metarsenic acids, like the adds them-
selves, only exist in the solid state ; when dissolved in water they
pass into the ortho-compounds.

The arsenates are isomoiphous with the corresponding phos-
phates.

COMPOUNDS OP ARSENIC WITH SULPHUR.

Three sulphides of arsenic are known, namely —

Arsenic disulphide (Jound native as Realgar) As^Sf.

Arsenic trisulphide {found native as Orpimeni) . As,Ss.
Arsenic pentasulphide AsyS^.

Arsenic Disulphide, AsfSi, is formed when sulphur and arsenic,
or arsenic trisulphide and arsenic, are heated together; or by
heating arsenious oxide and sulphur —

AS4OC + 7S - 2AssS, + 3S0,.

It is prepared on a large scale by distilling a mixture of iron
pyrites and arsenical pyrites —

FeS^FeAs, + 2FeS, = As,S, + 4FeS.

Properties. — Arsenic disulphide is a red, vitreous, brittle solid,
having a specific gravity of 3.5. It is readily fusible, and sublimes
unchanged. Heated in air or oxygen, it bums with a blue flame,
forming arsenious oxide and sulphur dioxide —

8As,S, + 70, - 4S0, + AS4O9.

a r

450 Inorganic Chemistry

Arsenic disuJphidc is employed in pyrotechny. So-called Btng^
fire consists of a mixture of realgar, sulphur, and nilre.

Arsenic Trlsutphlde, As,S„ is obtained by heating sulphur
and arsenic in the proportion required by the forniiila, and sublim-
ing the comfiound.

It may readily be produced by piassing sulphuretted hydiQ
through a solution of arsenious oxide in hydrochloric add—

As.Oj -I- 6H,S = 3As,S, + 6HjO.

Properties. — The compound, as obtained by precipitation with
sulphuretted hydrogen, is a pure canary-yellow solid, which easily
melts, and on again cooling forms a brittle crystalline mass. It
volatilises and sublimes unchanged, but when heated in air or
oxygen it bums with fomialion of arsenious oxide and sulphur
dioxide.

Anenlc trimlphjde may be regiided as a thlo-onhyilrldF, u ii gives rise lo

Irisulphide is brought into a solution of a causlic alkali,
hydroxide, the sulpbide readily dissolves with Ihe formatioi
thioarsenile, Ihus—

ASgS, -)- 4KHO = HKgAsDj,

Upon Ibe addition of an acid, the salts
sulphide reprecipilaied —

HK^O, + HKjAsS, + 4HC1 =

HK,AsS, + Hfi.

4KC1 + 8H^ + As^

Oriho-thlo-aisenious acid , H,AsSr
Pyro-lhio-arsenious acid, H^As^^

Thio-arsenitcs of the alkali melaU. the metals of the alkaline earths, aod of
magnesium, are soluble in walei, liul di-compose on boiling. Their solutic
are decomposed by adds, with evolution of lulphuieiicd hydrogen a
cipilalion of aisenic trisulphide, ihus—

3it,AsS, -I- 6HC1 = 6KCI + 3H,S + AsA-
Arsenic Pentasulphtde, AsjSj,— This compound is prepa
adding an acid to a solution of a thio- arsenate, thus—

SNa^S. -(- 6HCI - 6NaCl + 3H,S -I- As,S*

Afitimany 451

Arsenic pentasulphide is a yellow, easily fusible solid. It is
readily soluble in caustic alkalies, forming an arsenate and a thio-
arsenate —

4AsjS5 + 16KH0 = 3HK,As04 + OHK^S^ + 4H,0.

Arsenic pentasulphide, like the trisiilphide, gives rite to a series of salts,
known as thio-arsenates. These may be regarded as being derived firom the
three hypothetical thio-arsenic adds —

{Tripotassium ortho-thio-arsenate, K^AsS^
Hydrogen disodium ortho-thio- arsenate,
HNaaAsS^.
Pyro-thio-arsenicacid,H4ASfSy. Magnesium pyro-thio-arsenate. Mg^ASfST.
Meta-Chio-arsenic acid, HAsS|. Ammonium meta-thio-arsenate,(NH4)AsS^

ANTIMOtfT.

Symbol, Sb. Atomic weight = 119.&

Oeenrrenee. — Antimony in the uncombined state is found in
small quantities in various parts of the world, and notably in
Bomea In combination with oxygen, as SbiOg, it constitutes
the mineral anHmany bloom^ or white antimony; and as Sb|04 it
occurs in antimony ochre. In combination with sulphur, as SbtSg,
it occurs as the mineral stibnite^ or grey antimony ore^ which is the
most important source of the metal ; and with both oxygen and
sulphur, as SbtOi^SSbtSs, it constitutes the mineral antimony blende^
or red antimony.

It also occurs in combination with sulphur and with metals, in
the form of thto-antimonites.

Modes of Formatloil.— (i.) Antimony is obtained from the
native sulphide by one of the two following methods. The
broken-up ore is heated in plumbago crucibles, along with scrap
iron. As the mass melts, the sulphur combines with the iron,
forming a slag of iron sulphide, and the libe];ated antimony settles
out beneath —

Sb,S, + 8Fe - 2Sb + 3FeS

(2.) The crude sulphide is first liquated^ or melted in such a
manner as to separate the sulphide from the rocky matter associated
with it. The liquated sulphide is then mixed with about half its
weight of charcmil, in order to prevent the mass from caking* and

4112 J norgaitic Chemistry ^|

carefully roasted. During this process, ihe antimony sulphide It?

pariially converted into antimony trioxide (Sb,0^^ which passes
intu flues, and is there condensed, leaving a mixture containing
antimony letroxide (Sb,0,), and unchanged sulphide. Most of
Ihe arsenic present is also oxidised, and volatilises with the anti-
mony trioxide, while sulphur dioxide escapes. The residue, con-
sisting of ihe letroxide and sulphide (known as antimony ash), is
mixed with an additional quantity of charcoal and with sodium
carbonate, and heated to redness in a crucible, when the changes
represented by (he following equations take ptace^
(I.) Sb,0, + 4C = 4CO + asb.
By the action of the carbon upon the sodium carbonate, sodium
is liberated, which combines with the sulphur of the trisulphide,
forming sodium sulphide and metallic antimony —

(a.) NajCOj + 2C = 3C0 + 2Na.
(3.) Sb,S, + 3Na, " 3Na,S + 2Sb.

TTic sodium sulphide in its turn unites with a further quantity
antimony sulphide, forming a double sulphide of sodium and anti-
mony, which, mixed with the sodium carbonate and charcoal,
constitutes the slag. The metal obtained hy either process is
subsequently rtfinid.

PPOpei^les.— Antimony is a bright, highly crystalline, and very
brittle meial, possessing a bluish-white colour, and having a specific
gravity of 6.7 to 6.8, It is unacted upon by air or oxygen at the
ordinary lemperalure, but when heated it bums brilliantly, forming
antimony trioxide. The metal melts at 450° ; and when allowed to
solidify, its crystalline character is seen by the fem-like appearance
of its surface- If a quantity of the molten metal be allowed slowly
to cool, and when partially solidified the remaining liquid portion
be poured olT, the interior of the mass is found to be lined with
well-foniied rliombohedral crystals, isomorphous with arsenic In
the act of solidification antimony expands, a property which it
imparts to its alloys, thus giving to them Ihe valuable quality of
taking very fine and sharp castings. The most imporianl of these
alloys are type metal (lead 75, antimony zo, tin 5) ; stereotype tnetai
(lead 1 12, antimony iS, tin 3) ; Britannia metal (tin 140, copper 3,
antimony 9). Regarded as a metal, antimony is a bad conductor
of heat and electricity.

Dilute sulphuric and hydrochloric acids are without action upoj^

ti- I

pa»^y

Antimony Hydride 453

antimony. The concentrated acids convert it into sulphate and
chloride respectively —

asb + eH,S04 - 3S0, + eH,o + ^y^i^o^

Antimony is oxidised by nitric acid, dilute acid converting it into
antimony trioxide, or a compound of the oxide with nitrogen pent-
oxide, Sb|0|,3NsOf, while strong acid oxidises it chiefly into anti-
mony tetroxide and pentoxide.

Powdered antimony, when thrown into chlorine, takes fire
spontaneously, and forms antimony trichloride.

Amorphous Antimony.— Antimony is obtained in an amor-
phous form, by the electrolysis of a solution of tartar emetic in
antimony trichloride.

Properties. — Amorphous antimony presents the appearance of
a smooth polished rod of graphite, and has a specific gravity of
5.78. It always contains a certain quantity of antimony trichloride
(from 4 to 12 per cent); but whether this is in chemical union, or
merely mechanically retained by the metal, is not known. Amor-
phous antimony is very unstable, and readily .passes into the
crystalline modification : a slight blow, even a scratch with a
needle, causes it instantly to transfonn itself into the stable form,
with explosive violence; the temperature at the same moment
rising to 250*, and clouds of the vapour of antimony trichloride
being evolved.

ANTIMOtfT HTDRIDB {AntimcninrttUd HydrogtH\,

Symbol, SbH,.

Modes of Formation. — (i.) This compound has never been
obtained in the pure state, as usually prepared it is always mixed
with hydrogen. It is formed when a solution of antimony tri-
chlonde in hydrochloric acid is introduced into a mixture generating
hydrogen, such as zinc and sulphuric acid.

(2.) It is also found by the action of dilute sulphuric acid upon
alloys of antimony and zinc —

Sb|Zn, + 3H,S04 - SZnSOf + SSbH,.

Properties. — Antimony hydride is a colourless, offensive-smell-
ing, and poisonous gas, closely resembling the corresponding

454 Inorganic Chemistry

arsenic compound in its general behaviour. It bums with a
tinted flame, forming water and antimony trioxide —

4SbH, + 60j = 6H,0 + Sb.O^

When the supply of air is limiled, water is formed and antimony
is deposited ; when, therefore, a cold obje« is depressed upon the
flame, black stains of metallic antimony are obtained. The gas is
easily decomposed by heat, and if passed through a glass tube
heated at one point, a black deposit of antimony is formed upon
the glass. The antimony so deposited is insoluble in a solution of
bleaching powder {see Arsenic Hydride). Antimony hydride is
decomposed by the halogen elements, with the formation of tl
halogen hydride, and the haloyen rompound of antimony—

SbH, + 3Cl, = 3HC1 +SbCl,.

Sulphuretted hydrogen, under the influence of sunsliine, conven
intimony hydride into antimony tri sulphide^

asbH, + 3H,S - Sb^, + eH,

When passed into silver nitrate solution, the antimony is pte
pitated in combination with silver, in this way differing from £
arsenic analogue —

SbHj + 3AgNO, = BHNO, + SbAft

COMPOUNDS OP ANTIMONY WITH THE HALOGENS.

The compounds represented by the following formulae i

SbF.i SbCI,; SbBr,: Sbl»
SbFj; SbCla-

AntiinoQ7 Trllluorlde, SbF,, is prrparrd by dissolving Ibe I
aqueous hydrofluoric acid. From the concentrated soluiion It is deposited fl
the form of while deliquescent crystals. It dissolves in water, and is er>dua

AnOmooy PentaHiiorlde, SbF,, is olnained when hydialed uilimoi
Oidde Is dissolved in aqueous hydrofluoiic acid. When ihe solution is
nled the compound remains as an amorphous gum-like residue.

A ntimony PentachloriJe 45s

BoCb of Umm flooridet exhibit a groii tendency to unite witli alkaline
flooridefl, forming doable lahs, lucfa as SbF,,2KF; SbP^H4F, in the case
of the trifliioride ; and SbPf^KF ; SbF|.2KF, with the pentafluoride.

Antimony Trichloride, SbCli, is formed when chlorine is
passed over metallic antimony, or antimony trisulphide —

8Sb + 8C1, - 2SbCl,.
8Sb,S, + 9C1, - 4SbCl, + 8S,C1,.

It may also be obtained by the action of boiling hydrochloric
acid, containing a small quantity of nitric acid, upon either metallic
antimony, antimony trioxide, or trisulphide —

Sb,S, + 6HC1 - aSbCl, + 3H,S.

Properties. — Antimony trichloride is a colourless, deliquescent,
crystalline substance, melting at 73.3* to an oily liquid, which
again solidifies to a soft translucent mass. It is soluble in alcohol
and in carbon disulphide, and from the latter may be crystallised.
It may be dissolved in a small quantity of water unchanged. Thus,
if allowed to deliquesce it liquefies in the water it absorbs, forming
a colourless solution, which, upon evaporation over sulphuric acid,
again deposits crystals of the trichloride. The addition of larger
quantities of water results in the formation of ox)'chlorides * —

(I.) SbCl, + H,0 - 2HC1 + SbOCL
(2.) 4SbCl, + 6H,0 - lOHCl + Sb^OjCl,.

Continued boiling with water removes the whole of the chlorine,
forming the trioxide —

Sb404Cl, + H,0 - 2HC1 + Sb^O..

Antimony chloride unites with alkaline chlorides, forming double salts (see
Antimony fluoride), such as SbCl„2NH4a; SbCl,.8KCL With potassium
bromide it forms the compound SbQ,.3KBr, which, strangely enough, appears
to be identical with the doable compound of antimony tribromide with
potassium chloride, SbBr,,8Ka.

Antimony Pentaehloride» SbCl^ is obtained by passing excess
of dry chlorine over metallic antimony, or antimony trichloride, in

* The mixed product obtained by the action of water upon antimony tri-
chloride is known 9M forndtr tf AlgoroUu

4 $6 Inorganic Chemistry

a retort, when antimony pentachloride distils over in the excess of
chlorine—

SbClj + CI, = SbCV

Properties. — Antimony pentachloride is a nearly colourless,
strongly -fuming liquid. It solidifies, when cooled, to a mass d
colourless crystals, which remelt at - 6^ Under the ordinary
atmospheric pressure the pentachloride dissociates, when heated,
into the trichloride and chlorine, but under reduced pressure it
may be boiled and distilled. Thus, under a pressure of 22 nun. it
boils at 79*.

By the regulated action of ice cold water, oxychlorides are
formed —

(I.) SbClg + H,0 = SbOCl, + 2HCL
(2.) SbOCl, + H,0 = SbOjCl + 2HCL

Antimony pentachloride, and also the oxychlorides, are con-
verted by hot water into pyro-antimonic acid (analogous to pyro-
arsenic and pyro-phosphoric acids) —

2SbCl5 + 7HjO = H4Sb,0y + lOHCl.
2SbO,Cl + 3HjO * H^SbjOy + 2HCL

Sulphuretted hydrogen (the sulphur analogue of water) acts
upon antimony pentachloride, forming antimony sulphotrichloride,
corresponding to the oxytrichloride —

SbClfi + HjS = SbSClj + 2HC1.

Antimony tribromide, SbBr^, and antimony tri-iodide, Sbl,, are obtained by
adding powdered antimony to solutions of the halogens in carbon disulphlde,
from which liquid the compounds are crystallised : the bromide as colourless
deliquescent crystals, and the iodide as hexagonal ruby-red crystals. Both of
these compounds are similarly acted upon by water, forming the oxybromides
SbOBr ; Sb40BBr3. and the oxyiodides SbOI ; Sb^OsI,.

OXIDES AND OXY ACIDS OF ANTIMONY.

Three oxides of antimony are known —

Antimony trioxide (antimonious oxide) . (SbsO,), or Sb40^
Antimony tetroxide .... Sb204.
Antimony pentoxide .... Sb^Os.

Aniifmmy Teiroxidi 4$ 7

No adds are known oorresponding to the trkudde, ahbough a aodhiin lalt
of the hypothetical metantimonious acid, HSbOti has been described, having
the composition NaSbOi. 3H^.

Three adds are known derived from antimony pentoxide, which
are analagous to the three arsenic and phosphoric acids —

Orthoantimonic add .... HsSbO^.

Pyroantimonic acid H^SbsOy.

Metantimonic acid ..... HSbOs.

Antimony Trioxlde» Sb4O0| nuiy be prepared by the addition of
hot water to a solution of either antimony trichloride or antimony
sulphate, and washing the predpitated oxide with a solution of
sodium carbonate to remove the free acid —

iSbClj + 6H,0- Sb40e + 12HCL

Properties. — Antimonious oxide is a white powder, which,
when volatilised, condenses in two distinct forms, namely, pris-
matic crystals of the trimetric system, and regular octahedra. The
former are deposited nearest to the heated material, the latter in
more remote and cooler regions. (See Arsenious Oxide^ with
which antimonious oxide is isodimorfihous.) Antimonious oxide
is only very slightly soluble in water, and the solution is without
action upon litmus. It is insoluble in nitric or sulphuric acid, but
is dissolved by hydrochloric add with formation of the trichloride.
It is readily soluble in tartaric add, and in a boiling solution
of hydrogen potassium tartrate {cream of tartar\ giving rise to
potassium antimony tartrate, or tartar emttic —

4HK(C4H40e) + Sb40. - 4(SbO)K(C4H40e) + 2H,0.

Antimonious oxide bums in the air, forming the tetroxide —

(SbjO,), + O, - 2Sb,04.

Antimony Tetroxide, Sb|04, is formed when the trioxide bums
in air. It may be prepared by strongly heating antimony pent-
oxide —

SSbjOj - 2Sbj04 + O,

Properties.-~Antimony tetroxide is a white non-volatile powder,
which is insoluble in water. It is decomposed by boiling hydrogen

Inorganic Che^nistry

isium lartrate, formiD^' tartar emetic and

HK{C,H,0,) + Sb,0, - (SbO)K(C,H40,) + HSbO»

Antimony Pentoxlde. 5b,0„ is obtained by oxidising metallic

antimony with nitric acid, and healing the antimonic acid sc
obtained to a temperature not exceeding 575*.

Properties, — Aniimony penloxide is a straw-coloured powder,
insoluble in water. When heated to 300°, it gives up oxygen and
is converted into the tetroxide. Its feeble acidic character is seen
by its formation of an alkaline metaniimonaie, when fused with an
alkaline carbonate —

SbjOs + NajCOj = CO, + 2NaSbOa.

AnUmonte Acids uid AuUmonatea. — None o[ ibe tbrce

can be obiained by ihe action ot n-alef upon Ihe oxide. Pyic

is rormed when aniimony punlachloride is treated wub hoi

precipLiate dried al log' —

2SbCI, + 7Hrf) = HjSbiO, + lOHCL

taHiC ^^

H.Sb,0, - h!,0 = 2HSbO,

Metuillrnonic at

2St> + 4HNO,=

iSHSbO

i + NO, -i- 8N0 + H,0.

ofniuicudd-

KSbO,+

HNOjz

: KNO, + HSbO^

imonale by meU

On allowing the precipiiale
in contact wiih waiet. il is coni

1 melui'
/etled in

limonic add to remain for > long tia

HSbO, + H,0 = H^bO,.

thirerore, belong la the two acids, pyro-antimonic acid and m

monaie. K,Sb,0,.
Hydrogen polassiiun pym
anlimona,e. H,K^Sh,0,

M»>mim«i

L*ate. KSbO,.
nale, Ba(SbOJ,

Anttnumy Pintasulphtde 459

COMPOUNDS OF ANTIMONY WITH SULPHUR.
Two sulphides of antimony are knou-n, namely —

Antimony trisulphide .... SbjSi.
Antimony pentasulphide Sb^S^

Antimony Trisnlphlde* SbsS,. — This compound occurs native
as the mineral stibmU^ or grey antimony or$. It is prepared by
heating a mixture of powdered antimony and sulphur (in propor-
tion required by the formula) beneath a layer of fused sodium
chloride in a crucible. It is also formed when sulphuretted hydro-
gen is passed through a solution of antimony trichloride, or a
solution of tartar emetic —

aSbCl, + 8H,S - Sb,S, + 6HC1.

Properties. — Antimony trisulphide as it occurs native, and as
obtained by the direct union of antimony and sulphur, is a grey-
black crystalline substance; as prepared by precipitation with
sulphuretted hydrogen, and subsequently drying at 300*, it is a
brick-red amorphous powder, which when melted and slowly
cooled, solidifies in the crystalline form. Antimony sulphide sub-
limes tmchanged when heated in an inert gas, but when heated in
air, sulphur dioxide is evolved, and antimonious oxide and tetroxide
are formed. Heated with hydrochloric acid, it evolves sulphuretted
hydrogen, and forms antimony trichloride —

Sb,S, + 6HC1 - 2SbCl, + 8H^

Antimony Pentasulphide, Sb,S|, is obtained when antimony
pentachloride is mixed with water, and sulphuretted hydrogen
passed through the liquid —

aSbClft + 6H,S - Sb^Sft + lOHCl,
or —

2SbO,Cl + 6H,S - Sb,S4 + 4H,0 + 2HCL

them, and the term miiantimaHates was given to the salu belonging to the
other class. It is better, however, to adopt the same system of nomenclature
for the antimony compounds, as that which is in use for the similarly constituted
arsenic and phosphorus compounds —

AiMiutca.

Ortbo

. M,P04.

M,As04

• ••

Pyro

. M4PA

M^As^

M«SbA

Meta

MPOb

MAaO,

MSbO,

460

Inorganic Chemistry

Both of then: Bi
illhougli no ibio*ai

Properties. — Antimonv pentasulphide is a dark, oraii]
powder, which on being healed, is decomposed into the trisulphi<to
and free sulphur.

ly sulphides mar he regarded as thio-anhrdrida, foi
trived from them are known, salts have been produced
3 dErivalives of hypotheiical Ibio-acids, When ibe
I witb causiic potash, or boiled In an aqueous solulion.
e Is foraied —

2Sli^, + 4KH0 = SKSbS, + KSbO, + 2H^.

Similarly, when aniiniony pentasulphide is dissolved >n polasslum hyi
a m-ilure of anliraonate and ihio-aniimonaie is obia.nert-

4Sb,S, + 24KKO = 6K^bS, ■»- SK^bO, -H lSH,a

The rollowing %tc illuitrallons of [be Ihio-salu of antimony—

f(Ortho) H^bS,
\ (Mela) HSbS^

^rmbol, Bi. Atomic

Potassliun Ihto-anlknonili-. KjSl

Sllverltii>anti

Lead thio-anti
( Polassium Ihit
I Sodium Ihio-ai
I (Scbllppe's salt)
^ Barium thio-i

right = 107.5

most comrnonly in

in combination with oxygen, i
I combination with sulphur, :

Oecorrenoe Bismuth occurs

biDcd condition. It is met with
Bi,0,, in bUmulk ochre; and i.
BijSj, in bismuth glani:e.

Mode of FormatloQ.— Bismuth is principally obtained from
the native mcia!, and from ores with which metallic bismuth is
associated. The broken-up ore is liquated by being heated in
inclined iron pipes, when the bismuth readily melts and drains

Pure bismuth can be prepared from the crude meial thus ob-
tained, by first dissolving; it in nitric acid, forming bismuth nitrate

Bisfftutk Trichloride 461

Bi(NO,)i, and then precipitating the basic nitrate by the addition
of water —

Bi(NOj)3 + 2H,0 - (BiO)NO„H,0 + 2HNO,.

The basic nitrate is next dried, and heated in a crucible with
charcoal ; the salt is first converted into the trioxide by the action
of heat, and the oxide is reduced then by the carbon —

2(BiO)N03,H,0 - BijO, + NjO* + O + 2H,0.
Bi,0, + 8C - SCO + 2Bi.

Properties. — Bismuth is a lustrous white metal with a faint
reddish tinge. It melts at 268.3*. If the molten metal be allowed
to cool until partially solidified, and the remaining liquid be then
poured off, obtuse rhombohedral crystals, closely approaching to
the cube, are obtained.

The specific gravity of bismuth is 9.823 ; it is extremely brittle,
and a poor conductor of electricity. Bismuth is unacted upon by
dry air at ordinary temperatures ; moist air tarnishes its surface.
Heated in air, or oxygen, it bums, forming the trioxide. It is only
slightly attacked by hydrochloric add, but is converted by hot
sulphuric acid into a basic sulphate.

Bismuth readily forms alloys with other metals, and imparts to
them the useful properties of ready fusibility and hardness. The
alloys known by the general name oiJusibU metal contain bismuth ;
thus, WooiPs fusible metal^ which melts at 65*, consists of 4 parts
of bismuth, 2 of lead, i of tin, and i of cadmium.

COMPOUNDS OF BISMUTH WITH THE HALOGENS.

Compounds represented by the following formuls are known—

BiF, BiCl, BiBr, Bil,.

— (BiCl,), (BiBrO,? —

Bismuth Triehloride» BiCl,, may be prepared, by passing dry
chlorine over powdered bismuth gently heated in a retort. A
yellow liquid is first formed, after which the stream of chlorine is
stopped and the liquid distilled, when the trichloride sublimes in
the form of crystals. It may also be obtained by distilling a mix-
ture of powdered bismuth and mercuric chloride —

2Bi + 6HgCl| - 8Hg,Cl, + SBiCV

Inorganic Ckemislry

ProperUes.— Bismuth irichloride is a white, extremely d<
quescent, crystalline compound. Healed in an atmosphere
chlorine, it melts to a yeilow liquid. It is decomposed by water
with the precipitation of bismuth oxychloride —

! of ^^

BiClj

h H,0 = 2HC1 -(

JiOCl.

Bismuth DIchloride, (BiCy. is obtained by ihe prol<
heating of mercurous chloride and finely powdered bismuth ti
in a sealed tube. The mixture meils, and mercury collects at
the bottom, and on cooling, the dichloHde solidifies as a black,
extreinely deliquescent solid upon the surface of the mercuiy.
When heated above 300*, the dichloride is resolved into the
chloride and metallic bismuth. The molecular weight of
compound is unknown.

'B«rB

rpared by gradually adding tirorafna
den yellow, ddiquesceot crystals, ■

BluButH Tribromlda, BiBr,, is

powdeml bismuiti. and slightly w
bromide sublimes in the form of )
ju« decomposed by vraler, forming

BUmntb Trl-iodldB, Bit,, is prepared by subliming it mixiure of iodine ■)
bismuth. The sublimate is afterwards finely powdered tmd again sutdlioi
and the product finally di^liUed in a stream of carlxin dioxid
dark grey crystals, with a bright metallic tu^ue. Boiling ■
Ihe compound, with formatioa of bismutb oxyiodide. BiOI.

COMPOUNDS OF BISMUTH WITH OXYGEN.

Four oxides of bismuth are known, namely —

Bismuth dioxide {Hypobitmuikous oxide) . Bi^O,

„ trioxide {Bismulhous oxide) BigO^

letroxide {Hypobiimuthtc oxide) . . Bi,0,.

„ pcTiMiddc (Biimu/iic oxidt) BijOj.

None of these compounds is an actd-forming oxide, althougkj
with the exception of the first, they all form hydrated oxidei
These hydrated oxides have no acidic properties, and n
have been obtained in which the acidic portion of the molecule '
consists of bismuth and oxygen. All [he four oxides, when acted
upon by acids, yield the same series of salts, in which the bismuth
fiilfils the functions of a trivaleni element, replacing three atomi of

Bismuth Trioxide 463

hydrogen. Tn the case of the dioxide, metallic bismuth is de-
posited, thus —

8Bi,0, + 6H,S04 = SBi^SO*), + 2Bi + 6H,0.

While with the higher oxides oxygen is evolved —

Bi,0| + 6HN0, - 8Bi(NOs)| + 20 + 3H,0.

Bismuth trioxide is the most stable and the most important of
the oxides ; when heated in air, the remaining three compounds
are converted into the trioxide ; the dioxide by oxidation, and the
tetroxide and pentoxide by loss of oxygen. The trioxide alone is
unchanged on being heated in air or oxygen.

Btsmath Dioxide, B%0|.— This oxide is prepared by adding a mixed solu-
tion of bismuth trichloride and stannous chloride to an excess of a 10 per cent
solution of caustic potash, air being excluded : potassium stannate is formed,
and bismuth dioxide is precipitated —

SnCl, + 2BiCl, + lOKHO ^ Bi^, + SKQ + K^nO, + 5H,0.

ProperttflS. — The precipitated compound, after Ixing washed in dilute
caustic potash, and dried in vacuo, is obtained as a black crystalline powder.
When heated in air it smoulders, uniting with oxygen to form the trioxide.
When moist it oxidises spontaneously —

Bi^, + O = Bi,0,.

Bismuth Trioxide, Bi|0|, is formed when the metal is burnt in
air or oxygen. It may also be obtained by heating the hydrated
oxides, the carbonate, or basic nitrate, thus—

Bi,0„H,0 -» BijO, + H,0.

Bi,0„CO, - BijO, + CO,.

2(BiO)NO„H,0 - Bi,0, + NjO* + O + 2H,0.

Properties. — Bismuth trioxide is a cream-coloured powder,
insoluble in and unacted upon by water, and is the only oxide of
bismuth which is imchanged when heated in the air or in oxygen.
It dissolves in adds, forming salts of bismuth —

Bi,0, + 6HN0, - 8H,0 + 2Bi(NO,),.
Bi,0, + 8H,S04 = 8H,0 + Bi^CSO*),.

With small qtiantities of hydrochloric add it first forms bismuth

Inorganic Chemistry

I additional add, yielt

Bi,0, + SHCl = H,0 + 2BiOCL
BiOCl + 2HCI = H,0 + BiClj.

None of these compounds is soluble in water wiihoui the presence
of excess of the acid. Water alone converts them into insoluble
basic salts, and free acid, which in the state of extreme dilation
is unable to exert any solvent action. Thus, in the case of tbt
nitrate, when water is added, this compound is decomposed
basic nitrate and free nitric acid —

Bi(NO,), + 2H,0 = (BiO)NO^H,0 + 2HN0,

Bi,0„H,O Bi,0„2H,0 Bi,0ft3H,0

These hydrates have no add properties, and arc incapabli

combining with bases to form salts, but themselves play the pan
of a base, uniting with acids to form bismuth salts.

The trihydrale is obtained, by pouring an acid solution of bis-
muth nitrate into an excess of strong aqueous

Heated

SBi(NO,), + eNHjHjO - 6NH,(N0,) 4 Bi,0,3H,a

it is converted by loss of water into the moil
,0).3H,0 - Ci,0„H,0 + 2H,0.

Bismuth Tetrozide, Bi,0„ is formed by the action of potastini
hypochlorite upon the trioxide, the product being dried at i8o*— .

Bi,0, + KCIO = Bi,04 + KCI.

Properties. — Bismuth tetroxide is a brownlsb-yellow powder,
which readily parts with an atom of oxygen, and passes into the

Bismuth Pentoxide, 01,0^ is prepared by passing chlorine
into a nearly boiling solution of caustic potash, in which la sus-
pended a quantity of bismuth trioxide —

Bi,0, -I- 4KHO + 2C1, = 4KCI + H,0 + Bi,0»,H,0.

Bismuth TrisulpfUde 465

Properties. — Bismuth pentoxide is a red powder, which is
readily deoxidised into the tetroxide and trioxide by heat It com-
bines with water, forming the hydrate Bi|05,H|0, but with excess
of water it is gradually deoxidised into hydrates of the tetroxide or
trioxide.

Bismuth pentoxide is reduced, with evolution of oxygen, by both
nitric and sulphuric acids —

BijOj + 3H,S04 - Bi,(S04), + 3H,0 + O^

With hydrochloric add it behaves in the usual manner of
peroxides, causing the evolution of chlorine —

BijOj + lOHCl - 8BiCl, + 6H,0 + CI,.

Bismuth TrlSUlphide» 'BiaS,.— This compound is the only com-
pound of bismuth with sulphur that is known with certainty. It
occurs native as the mineral bismuth glance.

It is precipitated when sulphuretted hydrogen is passed into a
solution of a bismuth salt —

8Bi(NO,)3 -^ 3H,S - Bi^S, + 6HNO,.

It is also obtained by heating together the requisite proportions
of bismuth and sulphur.

Properties. — As obtained by precipitation, bismuth sulphide is
a dark brown, almost black powder; the native sulphide forms
steel-grey lustrous crystals.

It is decomposed, when strongly heated, into its constituent
elements. Bismuth sulphide differs from the corresponding anti-
mony and arsenic compound, in not being dissoWed by alkaline
hydrates or sulphides.

CHAPTER IV

THE ELEMENTS OP GROUP I. {FAMILY A.)

THrs family comprises
a/iali mttah—

Liihium(U) ,

the following five elemenls, known a
. 7.01 . . i8o-

Sodium (N.) .

RtMdium (Rb)
C«,iu^ (Cs) .

. aB.99 .... 9S.f
. . 39^03 . ■ . . Sa-S"
. .85.= . . . . -^.t

. 1317 .... ats"

The

are potassium and sodium, which also were the lirsi to be dis-
covered, having been isolated by Davy in ihe year 1807, TTie
element lithium, although widely distributed in nature, is tor the
nio5i part found only in minute quantities : ihe element was first
isolated by Bunsen in the year 1855. The two remaining elemenls
are still rarer substances, usually met with in very minute quantities
accompanying sodium and pntassium. Both of these elemenls
were discovered by Bunsen by means of the spectroscope — caesium
in i860, and rubidium in the following year.

All these elements are soft, silvery-white metals, which may be,
readily cut with a knife, and which rapidly tarnish in the air.
They all decompose water al the ordinary temperature. The
members of this family exhibit that gradation in properties which
is met with in all similar families. Thus, iheir meUiug- points
gradually decrease as their atomic weights rise, as will be seen
from the figures given above. Their chemical activity also steadily
increases as we pass from lithium to caesium. Thus, in the case
of their behaviour in contact with water ; potassium, when thrown
upon cold water, decomposes that liquid with sufficient energy to
cause the ignition of the hydrogen which is evolved : sodium under
the same conditions melts and Boats about upon the surface, but
the action is not sufficiently energetic to effect the inflammation of
the gas, unless the water be previously heated ; while with lichiiun,
even with boiling water, the temperature produced by the reaction.

mion^^J

The Alkali Metals 467

does not rise to the ignition-point of hydrogen. The same is also
seen in the spontaneous oxidation of these elements when they are
exposed to the air. Thus, lithium when cut with a knife, although
it is soon covered with a film of oxide, nevertheless retains its
bright metallic surfiice for some seconds : sodium tarnishes so
much more quickly, that the film of oxide appears almost to follow
the knife. When potassium is cut, the bright surface can scarcely
be seen, so rapid is the oxidation, and if left exposed, a fragment of
the metal soon begins to melt by the heat of its own oxidation, and
frequently spontaneously ignites. With rubidium and caesium the
oxidation is even more rapid, and a fragment of these metals freely
exposed to the air very rapidly takes fire spontaneously.

The electro-positive character of these elements gradually in-
creases from lithium to caesium, which is the most electro-positive
of all the known elements.

The term alkali^ applied to metals of this family, was originally
used (before any distinction was made between potash and soda) to
denote the salt obtained by treating the ashes of plants with water.
Later on, in order to distinguish between this substance and what
became known as the volcUiU alkali (i.#., ammonium carbonate),
it was termed the Jixed alkali. The first distinction between
potash and soda, was based upon the erroneous belief that the
former was entirely of vegetable origin, while the latter was only
to be found in the mineral kingdom : hence the names vegetable
alkali and mineral alkali were used to denote these two sub-
stances, both of which were regarded as elementary bodies until
1807, when Davy showed that they contained the two metals,
potassium and sodium.

The resemblance between the different members of this family,
and between their compounds, is very close ,' so much so, that in the
case of sodium, potassium, rubidium, and caesium, there are scarcely
any ordinary chemical reactions by which they can be distinguished.
They are all readily identified, however, by means of the spectro-
scope. When a minute quantity of a lithium salt is introduced
upon a loop of platinum wire, into the non-luminous Bunsen flame,
the latter is tinged a brilliant crimson red colour : a potassium salt
similarly treated, colours the flame a delicate lilac, while a sodiiun
compound gives a brilliant daffodil -yellow colour. The colour
imparted to a flame by rubidium and caesium salts, is indistinguish-
able by the eye from that given by potassium compounds ; and,
moreover, when any of these are mixed with a sodium salt, the

468

Inorganic Chemistry

iDlense yellow emitted by the latter, completely masks ihe coloun I
given by the others. By means of the spectroscope, not only art
the apparently similar colours given by potassium, rubidium, and
caesium readily distinguished, but the presence of any or all of
them is easily detected, even when admixed with sodium salts.
Spectrum analysis is based upon the fact, that light of different
colours has different degrees of refrangibility, and therefore when
passed through a prism, the different coloured rays are bent out _
of their straight course at different angles. Ordinary while ligl

is composed of rays of all degrees of refrangibility, i.e., rays of i
colours : hence, when a beam of such light is passed through a
prism, Ihe various coloured rays are separated, and become spread
out in the order of their refrangibility, from Ihe least refrangible red
ai the one extreme, to the deep violet at the other. This familiar
" rainbow " coloured hand of light is lenned the conlinuous spectrum.
A simple form of spectroscope is seen in Fig. ii4- The hght is
caused to pass through a narrow slit at the end of the fixed lele-
icope B If the prism P be lemoved, and the telescope A be

Tiu Alkali Metals

moved round so as to be in x continuous line with B, a ntagnified
image of the slit is seen by the observer. When the prism is
replaced, and A is moved into such a position that the bent ray^
fall upon its lens, the continuous spectrum is seen, which is an
infinite number of strips of light (corresponding to the image of the
slil) of all colours, arranged side by side. If the light to be
examined, instead of being ordinary while light, were composed of
rays all of one degree of infrangibility {i.e., monochromatic light),
there would be produced only a single image of the slit, which
would fall in ihai position corresponding to the particular degree
of refrangtbility of the light. Such a monochromatic light is pro-
duced when a sodium salt is heated in a Bunsen flame ; if, there-
fore, a salt of this metal be introduced upon a loop of platinum
wire mto the non-luminous flame G, and the light, after passing
through the prism, be observed through A, instead of a continuous
speclium, there will be seen a single image of the slit, falling in
the brightest yellow pari of the spectrum. When the sodium salt
is replaced by a lithium salt, it is seen that two images of the slit
are obtained, one in the red and the other in the yellow regions of
the spectrum. Tlie light emitted from this element consists of rays
of two degrees of refrangibility. We say, therefore, that the
spectrum of soitium is one yellow lint,* and that of lithium consists
of one red and one yellow line. In order to distinguish the posi-
tions of, for example, the yellow lithium line and thai given by
sodium, an image of a graduated scale, illuminated by the candle
flame F, is also thrown into the telescope A,

If sails of sodium and lithium mixed [ofielher be introduced irio
the flame G, then three images of the slit are seen, namely, the
yellow line given by the sodium, the yellow line of the lithium,
situated slightly nearer ihe red, and the lithium red line.

Potassium, like lithium, gives a light of two degrees of refrangi-
bility, forming consequently two images of the slit, one in the
deep red and the other in the deep violet ; if, therefore, lithium,
sodium, and potassium salts are mixed, and examined by the
spectroscope, five lines are seen (Fig. 125), namely, two red (one
belonging to lithium and <
belonging to lithium and one to sodiu:
potassium.

by t, tilftici diipetiiire power, the sodium lioe

470 Inorganic Oumistry ■

Wben analysed in this manner, the lights emilted by rutncUniti^
and caesium compounds, are seen lo be totally diffeieni from each
oiher, and from potassium. The spectrum of rubidium consists of
■wo prominent lines in the violet (nearer the blue region than that
belonging to potassium), two brilliant red lines (very near the
potassium red line), and a number of less brilliant lines in the
orange, yellow, and green. Thai of caesium consists of two bril-
liant blue lines, two bright red lines (near the lithium red line), and
a number of less prominent lines in the yellow and green. It will
be seen, iherefore, that the three elements potassium, rubidium,
and caesium may be at once sharply distinguished by this optical
method of analysis, although ihey so closely resemble one anothei
in theii chemical behaviour, as to render it highly probable tl
the separate existence of the two latter would never have been d
covered by chemical methods alone.

FlO. IS5.

Indeed, before the discovery of caesium by bunsen,
mineral known as Pollux (now known to contain caesium), a
mistaken for a potassium mineral.*

The element hthium, the member of the family ihat belongs
the Typical series, exhibits certain characteristic differences fr
the other members. This is seen particularly in the case of the
carbonate and phosphate of this element. Lithium carbonate is so
little soluble in water, that it is precipitated by the addition of
carbonate of either sodium or potassium to a solution of a lithium
compound. The phosphates of all the other members are readily
soluble in water, while lithium phosphate is almost insoluble, and
is precipitated tram solutions of a lithium salt by the phosphates of
either sodium or potassium. In these two compoundi
bonatc and phosphate,lithium behaves more like one of the melall
of the alkaline earths.

il should CDOsull special iirorki on tpeclrum uwlnU.

lelali

Potassium 471

AU the metals of this £Eunily tire monovalent, and replace each
other, atom for atom, in chemical compounds.

poTABsnnf.

Symbol K. Atomic weight = 39.03.

Oeenmnee. — In combination this element is widely distributed
in nature. It forms an essential constituent of many of the com-
mon silicates, and rocks, which form the earth's crust. From
these rocks, by processes of disintegration, the potassium com-
pounds find their way into the soil, from whence they are absorbed
by plants, which can only flourish in a soil that contains com-
pounds of potassium. Most of the potassium found in plants is
present in combination with organic acids.

From the vegetable kingdom, potash passes directly into the
bodies of animals. The material known as suint^ which is the
oily perspiration of the sheep, that accumulates in, and is extracted
from, the wool, consists of the potassium salt of an organic acid
(sudoric acid). In the form of chloride and sulphate, potassium
is present in sea water and many mineral springs. As nitrate it is
found as a crystallised efflorescence upon the soil, notably in Pem
and Chili, where it is associated with sodium nitrate. The largest
supplies of potassium compounds are met with in the great saline
deposits of Stassfurt, where the element is found as chloride (KCl)
in sylviney as a double chloride of potassium and magnesium
(KClyMgCl^GH^O) in camallite^ and as a mixed sulphate in kcUnite
(K,S04,MgS04,MgCl»6H,0).

Modes of FormatioiL— (i.) The method by which Davy first
effected the isolation of potassium was by the electrolysis of
potassium hydroxide : the method may be illustrated by the ex-
periment represented in Fig. I26w A snudl quantity of potassium
hydroxide is gently heated in a platinum capsule, whidi is con-
nected to the positive terminal of a powerfiil battery. A stout
platinum wire, flattened out at one end, is made the negative pole.
When this is introduced into the fused potash, a brisk evolution
of gas takes place, and minute beads of metallic potassium make
their appearance in the liquid, and upon the negative electrode,
some of which ignite upon the surfiice. The decomposition takes
place according to the equation —

SKHO - H, + O, + K^

472 Inorganic Chemistry

(2,) Potassium may also be nbtaineil by allowing melted potassint
hydroxide to pass over iron turnings heated to whiteness, when tl
magnetic oxide of iron is formed —

4KH0 + 3Fe = FcjO, + 2H, + 2K,

This is known a.s Cay-Lussac and Thdnard's method.

(3.) The nieihod devised by Brunner, and modified by WohlerJ
Deville, and others, consisted in heating to whiteness an ~ ~

mixture of potassium carbonate and carbon. This mixture *
obtained by first igniting in a covered iron pot, crude tattaj
gen potassium tartrate, or cream of tartar), which was
decomposed as indicated by the cquatioa^ —

2HKC,H,0, = K,CO, + 3C + 5H,0 + 4CO.

-- b

The charred mass was Ihen introduced into ad iron rclon (P,
Fig. ij?), and siiongly healed in ihe furnace, when the potassium
carbonate was reduced by the carbon as follows —

Ascertairted by the green appearance of the vapour, seen on looking
in at the open mouih of the retort, Ihe condenser was attached.
This consisted ofa flat, shallow iron tray, d (Fig. 128}, upon which
was fitted the cover a, the two portions being clamped together.
The object of this special form of
condenser is to cool the potassium
as rapidly as possible, for it is
found that unless the metal is
quickly cooled, it com Lines with
the carbon monoxide, forming n
highly explosive compound (be-
lieved to have the composition
K,(CO),). By the use of this
form of coniiensinij apparatus the
formation of this compound is

entirely prevcr

(4.) A more recent method by
which potassium (and sodium)
is prepared on a manufaciurini; scale, «

I devised by Castnei

474 Inorganic Chemistry

(1B86). In this process potassium hydroxide is strongly heal
with a carbide of iron, having approicimalely the compositian CFi
(This compound is obtained by heating a mixture of pitch
finely divided iron.)

The potassium hydroxide, with the powdered carbide of Ire
introduced into latf e egg-shaped retorts, one of which is repre-
senled in Fig. 129. These retorts are placed upon hydraulic lifts,
so that they can be lowered away from their covers, to the ground-

level, in order to be discharged al the end of the disiillatioij
The letorts are heated by gaseous luel, and the metal, i
is passed into long narrow cast-iron condensers, from which |
drops into iron pots, and is protected from oxidation by r
cmI. The reaction which takes place may be represented by ti

6KHO -H SC = SKjCOj + 3H, + K^

By avoiding any excess of carbon, no carbon monoxide is p
duced, and hence there is no formation of the explowve compc
of this gas with potassium.

Potassium Peroxide 475

PropertlM. — Potassium is a lustrous, white metal, which at
ordinary temperatures is sufficiently soft to be moulded between
the fingers ; at o* it is brittle, and shows a crystalline fracture.
The metal is readily crystallised by melting a quantity of it in a
vacuous tube, and when it has partially solidified, pouring the still
liquid portion to the other end of the tube. Potassium melts at
62.5*, and when boiled gives an emerald-green vapour. The
metal is rapidly acted on by ordinary air, its freshly cut surfrtce
becoming instantly covered with a film of oxide, which, by absorp-
tion of atmospheric moisture and carbon dioxide, passes first into
the hydroxide and finally into the carbonate. Potassium is there-
fore usually preserved beneath naphtha, or some other liquid
devoid of oxygen.

When potassium is volatilised in a vacuous tube, the thin film of
metal which condenses upon the cool portion of the tube, is seen to
possess a rich violet-blue colour, when viewed by transmitted light
The density of potassium vapour is about 20 (Dewar and Scott),
showing that in the vaporous pondition the molecules are mon-
atomic

Potassium dissolves in liquefied ammonia, forming a deep indigo
solution (p. 243). When potassium is thrown upon water, that
liquid is decomposed with sufficient energy to cause the ignition
of the liberated hydrogen (p. 151). When heated in carbon
dioxide, potassium takes fire, forming potassium carbonate, and
carbon (p. 267). Heated in carbon monoxide, it forms the explosive
compound already mentioned. Potassium takes fire spontaneously
in contact with the halogens, forming the haloid compounds of
the metaL When heated in hydrogen, it absorbs the gas, forming
a brittle lustrous substance, which inflames spontaneously in the
air. This compound has the composition KfHi^

When heated in nitric oxide, potassium bums, forming a mixture
of potassium nitrate and nitrite (Holt and Sims).

Oxides of Potassimn. — When potassium is heated in ordinary
air, it takes fire and bums, giving rise to a mixture of the oxides
of the metal. Perfectly dry air or oxygen is without action upon
potassium.

Potassium Peroxide, K3O4, may be obtained by melting potas-
sium in an atmosphere of nitrogen, and gradually displadng the
nitrogen by moderately dry oxygen. It is also produced by hf^ting
potassium in nitrous oxide.

Potassium peroxide is a yellow powder, which, when strongly

Inorganic Chemistry

heated, is converted into the dioxide K,0, and 0]cygen. Wbeag
thrown into water, oxygen is evolved, potassium hydioxide a
hydrogen peroxide being fonned —

, + 2H,0= 2KHO

It oxidation into K,0,.

Potassium Hydroxide {caustic potask), KHO, is prepared by
adding lime to a dilute boiling solution of potassium carbonate, in
iron vessels, when calcium carbonate is precipitated and potassiuia
hydroxide remains in solution —

K,CO, + Ca(HO), = CaCO, + 2KH0,

ihe reaction being complete, when the addition of an add to

small lest sample of the clear Itquor, produces no effervescent
This reaction is a reversible one, and if the concentration is beyowtj
a certain limit, the poiassium hydroxide reacts upon the calcium'
carbonate, reforming potassium carbonate. The liquid is therefore
constantly maintained al a certain stale of dilution during the
reaction, at the completion of which the mixture is allowed to
settle, and the clear solution is then partially concentrated in
iron vessels, and finally in silver, until on cooling, the substance
solidifies. It is then usually cast into sticks.

Caustic potash is a white brittle solid ; it is extremely deliques-
cent, and dissolves in water with evolution of heal, forming a
highly caustic liquid. The solid, as well as the solution, readily
absorbs carbon dioxide, and is employed in the laboratory for this
purpose when it is desired to deprive a gas of the last traces of any
admixed carbon dioxide. A hot saturated solution of potassium
hydroxide, when cooled, deposits crystals of a hydrate having the
composition KHO.SHjO.

Potassium Fluoride, KFV— This salt is prepared by netitralising
aqueous hydrofluoric acid with potassium carbonate, and evaporat-
ing the solution in a platinum vessel, when the salt is obtained in
the form of deliquesecni cubical crystals. Poiassium fluoride dis-
solves in aqueous hydrofluoric acid with evolution of heat, forming
the acid fluoride of potassium, HF.KF, which is obtained as an
(uhydrous salt when the solution is evaporated to dryness and
heated to i lo*. This salt is not deliquescent When heated to a

ore ^^

Potassium ChloraU 477

dull red heat it decomposes into the nonnal salt and hydrofluoric
acid (see p. 312).

Potassiom Chloride, KCL— This salt is found in sea water, and
was at one time obtained as a secondary product in the manufocture
of bromine from sea salt, and of iodine from seaweed, as well as in
various other industrial processes. Ai the present day it is almost
exclusively obtained from the enormous deposits of camallite at
Stassfiirt. The method by which potassium chloride is obtained
from this double salt, KCl,MgC1^6H|0, is based upon the fact,
that when dissolved in water, the salt dissociates into its two
constituents ; and when the solution is concentrated, the more
insoluble potassium chloride first separates out, leaving the mag-
nesium chloride in solution.

In practice, the crushed crude camallite is treated with boiling
mother liquors from previous operations, in large tanks into which
steam can be driven. These mother liquors tu« practically a
strong solution of magnesium chloride, and it is found that while
potassium chloride is readily soluble in this liquid, the sodium
chloride and magnesium sulphate which tu« present in the crude
camallite are only slightly dissolved by it, and are therefore left
behind in the residue.

The -muddy liquid is allowed to settle for about an hour, when it
is drawn off into large iron crystallising tanks. The salt which is
then deposited, contains from So to 90 per cent of potassium
chloride, the remainder being mainly sodium and magnesium
chlorides.

The mother liquor from these crystallising tanks, is either used
again for treating a fresh charge of mineral, or is further evaporated,
when crystals of carnalliie separate out ; for it is found that when
the amount of magnesium chloride present, is greater than three
times the proportion of potassium chloride in the solution, the liquid
on crystallising, deposits the double chloride of the two metals. The
impure potassium chloride from the crystallising tanks is purified by
washing with cold water, in which the salt is only slightly soluble,
and by subsequent recrystallisation. Potassium chloride crystal-
lises, like the dilorides of sodimn, rubidium, and caesium, in cubes.

Potassium Clllorate, KCIO,.— When chlorine is passed into a
solution of potassium hydroxide, a mixture of potassium chlorate
and chloride is obtained, thus —

6KH0 -f 3C1, - KCIO, + SKQ + aH^O.

478

InorganU Chemistry

The two salts in solution may be separated by crystallisaticrt
the chlorale being much less soluble in cold water than tfa^
chloride.

On the manufacrurjng scale, potassium chlorate is obtained by
passing chlorine into milk of lime, when a mixture of calcium
chlorate and chloride is fomied —

6Ca(H0), + eCl, = Ca(C10,), + BCaCI, + eH,0.

The operation is conducted in cast-iron cylinders connected
in series, one of which is shown in section in Fig. 130, furnished

with mechanical stirring gear, a, b, b. The shaft, and the pipi
conveying the chlorine into, and from the vessel, are connected lO
it by means of the water-sealed joints e, e, e. The manhole/is a
short wide leaden pipe, dipping a few inches into the liquid, which
allows of the periodic withdrawal of samples for examinalion.
SeveraJ reactions are involved in the final formation of the calcium
chlorate; in the lirst case calcium hypochlorite is produced,
thus—

2Ca(H0), + SCI, - Ca(OCI}, + CaCI, + 2H,0.

hypochlorite then passes into i
accordance with the equation—

3Ca(0CI), = Ca(C10^ + 2CaCV

I brought about by the opcratii

The second change

Potassium ChlaraU 479

causes, namely, rise of temperature, and the presence of excess of
chlorine. Heat alone is incapable of converting more than a
small proportion of the hypochlorite into chlorate, for the former
compound is at the same time decomposed into calcium chloride
and free oxygen. The excess of chlorine is believed to act, through
the intervention of hypochlorous add, HOCl, merely as a carrier
of oxygen, reducing two molecules of calcium hypochlorite to
chloride, and oxidising the third to chlorate, thus —

8Ca(OCl), + 2C1, + 2H,0 - CaCl, + 4H0C1 + 2Ca(0Cl)| -
2CaCl, + Ca(C10j), + «a, + 2H,0.

The absorption of chlorine by the milk of lime is attended with
evolution of heat ; care is taken to prevent the temperature from
rising above about 70*, otherwise loss results by the decomposition
of hypochlorite with evolution of oxygen, thus —

Ca(OCl), - CaCl, + O,.

When the formation of calcium chlorate is complete, the liquid
is allowed to settle, and is then run into concentrating pans, where
the requisite amount of potassium chloride in solution demanded
by the following equation, is added —

Ca(C10,), + 2KC1 - CaCl, + 2KaO»

The liquid is then concentrated in iron pans and allowed to
crystallise, when the moderately soluble potassitun chlorate sepa-
rates out, leaving the very soluble calcium chloride in solution.
The chlorate is afterwards purified by recrystallisation.

Potasshun chlorate, although only moderately loluble in water, is modi
more iolubte in a strong lohitioo of calcium chloride, hence there is always a
\on (usually about 10 per cent) of chlorate in this process. Ptehme/s pro-
cess for obviating this, consists in concentrating the liquid, obtained by the
chlorination of the lime, to a definite specific gravity, and then cooling it to
la*, when about 78 per cent, of the calcium chloride crystallises out. The
mother liquor, containing all the cak?ium chlorate, and only the comparatively
small proportion of calciMm chloride, is then treated with potassium chloride
as usual

Potassium chlorate crystallises in white tables, belonging to the
monosynunetric system, which when of large sise often exhibit fine

Inorganic Ckemistry

3 parts of

480

iridesceni colours.

the salt ; while ^ 100', 59 parts arc dissolved.

Potassium chlorate is used largely in the manufaciure of tnatchei, 1
□n account of the ease with which it gives up its oxygen : thus, if s J
small quantity of ihe finely powdered salt be carefully mixed with '
an equally small amount of red phosphorus, the friction caused by
lightly rubbing it with a spatula, is sufficient t<
10 detonate violently. Similarly, when powdered potassium chlo-
rate and sulphur are rubbed together in a mortar, the minture
explodes with violence. Potassium chlorate is also largely em-
ployed in pyrotechny, especially in the production of coloured J
effects, where a fiercely burning mixture is required

Potassium chlorate melts between 360* and 370°, and at a tem- I
perature about 380' begins to evolve oxygen.

Pota£sliim Perchlorate, KCIO,.— When the chlorate is heated,!
it first melts and begins to give ofT oxygen ; but it Boon begins ta \
partially solidify, owing to the formalion of potassium perchlorate, I
and the evolution of oxygen stops unless a stronger heat be 1
applied. The reaction at this stage is expressed by the equ&- J
tion—

SKCIOj = KCIO, + KCl + O,

The perchlorate is separated, by first treating the residue w
cold water, which dissolves the greater part of the chloride, I
afterwards with warm hydrochloric acid, which decomposes aojt I
remaining chlorate. The salt is then purified by crystallisation.

Potassium perchlorate is very slightly soluble in cold water, lOc
parts of water at 0° dissolving only 0.7 parts of the salt ; while «
[00°, 20 parts are dissolved.

Potassium Bromide, KBr, and Iodide, KI.— These two salia^
are obtained by similar methods. When bromine or iodine iif
added to a solution of potassium hydroxide, the reaction whidil
takes place is exactly analogous to that in the case of cfalorincl
(see Potassium Chlorate, above) —

6KH0 + 3Br, - KBrOj + BKBr ^ 3HjO.

If the solution so obtained be evaporated by dryness, and dl#fl
dry residue ignited, the bromate (or iodate) is decomposed, just ■
potassium chlorate is decomposed by heat, giving off its oxyge^ 1
and being converted into bromide (or iodide) —
KBrO, = KBr + 30.

Potassium Carbonate 481

Tlie residue, on being dissolved in water and recrystallised,
yields pure potassium bromide (or iodide).

These salts are manufactured by decomposing ferrous bromide,
FejBrg (or iodide, Feslg), with potassium carbonate, thus —

FejBrg + 4K,C0, - Fe,04 + 8KBr + 4C0,.

The ferrous bromide is obtained by adding bromine to moistened
iron borings (see Manufacture of Bromine).

Potassium iodide and bromide both crystallise in cubes, and are
both readily soluble in water. These salts are chiefly used for
medicinal and photographic purposes.

Potassium Sulphate, K,S04.— This salt is present in the Stass-
furt deposits principally as kainitty K,S04,MgS04,MgC1^6HsO,
and as polyhalite, K,S04,MgS04,2CaS04,2H30. When kainite
is treated with small quantities of water, or mother liquors from
other processes, the extremely soluble magnesium chloride is
removed, leaving the potassium magnesium sulphate; and on
adding to this the requisite amount of potassium chloride, the
following change takes plac

K,S04,MgS04 + 3KC1 - 2K,S04 + KCl,MgCl,.

From this solution the potassium sulphate crystallises out

Potassium sulphate is also obtained by the action of sulphuric
acid upon the chloride, by a process corresponding exactly to the
first stage in the Leblanc soda process {g^v^ —

2KC1 + H,S04 - K,S04 + 2HCL

Potassium sulphate forms colourless rhombic crystals, contain-
ing no water of crystallisation, therein differing from sodium
sulphate, which crystallises with ten molecules of water.

Potassium sulphate is largely used for agricultural purposes.

Potassium Carbonate, K^COs.— This salt was formeriy obtained
exclusively from the ashes of wood and other land plants, and was
known under the name of pot-ashes. The process is still carried
on in parts of Canada and the United States. The wood is burned
in pits, and the ashes are collected and lixiviated with water
(with the addition of a small quantity of lime) in wooden tubs
with perforated £Edse bottoms. The liquid which is drawn off is
evaporated to dryness, and usually calcined to bum away the
organic matter. This material, known as American pot-ashes,

% H

482 Inorganic Chtmistry

contains vatying quanlilics of caustic potash, on a<
previously added lime. The so-called American pearl-ash is
purer product, oblaincd by concentrating the liquor from the
lixiviating tubs until the less soluble impurities crystallise out,
and finally evaporating the mother liquor, containing the potassium
carbonate, lo dryness, and calcining ihe residue.

Potassium carbonate is also obtained from beet-root molajses,
an uncrystalli sable residue obtained in the manufndure of beet
sugar, carried on chiefly in France. The synip is fermented with
yeast, whereby the sugar it contains is convened into alcohol, and
then distilled. The residual liquid, known as vinasse, is evaporated
10 dryness ; and from the black residue, termed "vinasse cinder,"
the potassium carbonate is extracted.

Potassium carbonate is obtained also from siiiiit, which, as
already staled, contains considerable quantities of poiassium in
the form of potassium sudorate. The sheep's wool is lixiviated
with water, and the solution evaporated to dryness. The residue
is heated in iron tetorts, whereby the organic potassium salts are
converted into carbonate, while at the same lime ammonia, and
sn illuminating gas, are evolved. Tlie carbonaceous residue is
extracted with water, and the poiassium carbonate separated by
crystallisation.

Since the development of the Stassfurt potash supplies, these
sources of potassium carbonate ate rapidly sinking into the back-
ground, and the bulk of this compound is now manufactured from
poiassium sulphate by a process exactly similar to the Lcblanc
soda process (q.v.).

Potassium carbonate is not manufactured by a method analogous
to the ammonia-soda process (Solvay), on account of the loo great
solubility of potassium bicarbonate (hydrogen potassium carbonate).

Pure poiassium carbonate may be obiained by igniting cream
of tartar (see page 472), and extracting with water ; or by healing
hydrogen p>otassium carbonate, which gives up water and carbon
dioxide, thus —

SHKCOj = K,CO, -I- H,0 + CO,.

Potassium carbonate forms long prismatic crystals belonging |
the monosymmetric system, and containing three molecules 1
water, KjCOjiSHjO. The anhydrous sail is highly deliqucso
and very soluble in water.

Hydrogen Potassium Carbonate {bicarbenatt cj p^tan

IS a I

Potassium NitraU 483

HKCO3, is produced by passing carbon dioxide into an aqueous
solution of the normal carbonate, thus —

KjCOj + CO, + H,0 - 2HKC0,,

This salt is much less soluble in water than the normal salt, and is
readily purified by crystallisation.

Potassium Nitrate {jiitrty saltpetre), KNO,.— This salt has
been known since very early times. It occurs as an efflorescence
upon the earth, as a result of the oxidation of organic nitrogenous
matter in the 'presence of the potash in the soil, and is found in
the neighbourhood of villages, more especially in hot climates,
where urine and other readily decomposable organic matters rich
in nitrogen find their way into the surface soil. It has been shown
that the process of nitrification which results in the formation of
nitre under these circumstances, is due to the action of specific
organisms, or microbes, and never takes place in their absence.
At various times this natural process has been artificially carried
on, by mixing manure and other decomposing refuse, with porous
soil, lime, and wood ashes, and exposing the mixture in heaps
which were moistened from time to time with drainage from
manure. The saltpetre earth, collected from the natural sources,
or from the artificial nitre plantations, on lixiviation with water, and
subsequent evaporation, yielded crystals of potassium nitrate.

At the present time, potassium nitrate is almost exclusively ob-
tained from sodium nitrate {Chili saltpetre), by treatment with
potassium chloride derived from the Stassfurt supplies. The requi-
site quantities of the two solutions are run into a tank, and heated
by means of steam, when the following double decomposition takes
place —

NaNO, + KCl - NaCl + KNO,.

The greater part of the sodium chloride is at once precipitated,
and is removed by canvas filters. The clear liquid is then allowed
to crystallise in tanks furnished with stirring gear, in order to
cause the formation of small crystals, and the nitre-meal so ob-
tained is purified by recrystallisation.

Potassium nitrate crystallises usually in rhombic prisms, but it
can also be obtained in the form of small rhombohedral crystals,
isomorphous with sodium nitrate.

The solubility of potassium nitrate rapidly increases with rise of

484

Inorganic Chemistry

tempetalure (see Solubilily Curve, p. 131). 100 p.iits of water tt
o* dissolve 13.3 parts ; at ;o°, S6 parts ; and a[ 100*, 147 parts.

Nitre mells al 339*, and at a higher tempcralure loses oxygen
and is converted inlo potassium nilrile ; on this account it readily
OKidiscs many of the elements when heated in contact with Ihem.
Thus, a fragment of charcoal or sulphur thrown upon melted nitre,
takes fire and bums with great energy ; in the one case with forma-
tion of potassium carbonate and carbon dioxide, and in the olhet
of potassium sulphate and sulphur dioxide —

4KN0, + 5C = 2K,COj + SCO, + SN»
2KN0j +■ 2S - K,SO, + SO, ■(- N^

Nitre is chiefly used in the manufacture of gunpowder and
pyrotechny.

Gunpowder

e of nilre. charcoal, and sulphur. The proporti
e ingredieciLs arc present varies, wiiliia ^niaJl limlis, accordin|_
to the tpcdal kind of powder, Oi will bo been from Ibe following table (Alxl
and Notwl), giving analyies of various powders manufactured al Waltbaro
Abbey,

n«-p>U

RlBs
ilnt-cruiL

Km.

L»ri«^«ln.

PebWi

Sulphur , , . ,
Charcoal ....

iao»
14.59

7S.04

74-9S
0.IS
tea?

13. s«

74.67
0.09
10.07

0-9S

Tbese proportions are very close to ibose which would be demamled by U|
Equation —

2KN0, + S 4 3C = K^ + SCO, + N„

which was al one lime su^^xised lo represent the change which i.iliei idacfij
^hen gunpowder is exploded. In lealily the decomposition ii much more
complex, and il has been shown that the solid producn consist of m
the following subelances in varying proportions, depending upon tbc particular
powder, and Ihe conditions oF Hring —

latk^^l

Compounds of Potassium with Sulphur 48$

While the gases that are evolved consist of—

Carbon dioiide.
Nitrogen.
Carbon monoxide.
Sulphuretted hjdrogen.

Marsh gas.

Oxygen.

Hydrogen.

From the combustion of one gramme of powder, the total weight of solids
ranges from 0.55 to a 58 gramme, and the total weight of the gaseous products
from a 45 to a 4a gramme.

COMPOUNDS OP POTASSIUM WITH SULPHUR.

Four sulphides of potassium have been obtained, namely —

Potassium monosulphide K..S

Potassium trisulphide K;tS;i

Potassium tetrasulphide ...... I<^4

Potassium pentasulphide K^S^

Just as potassium decomposes water with evolution of hydrogen

and formation of potassium hydroxide, so also, when heated in

sulphuretted hydrogen (the sulphur analogue of water) it forms

potassiimi hydrosulphide (the analogue of potassiimi hydroxide)

^ and liberates hydrogen, thus —

H,S -H K - KHS + H,

when potassium hydroxide and hydrosulphide are mixed in equi-
molecular proportions, potassium monosulphide and water are
formed —

KHO + KHS - K^ + H,0.

The liquid, on evaporation in vacuo, deposits reddish prismatic
deliquescent crystals having the composition K^SySHjO.

When potassitmi carbonate and sulphtir are heated together, a
mixture of the higher sulphides of potassiiun with pota^ium thio-
sulphate is obtained, thus —

3K,COs + 8S - 2K^ + K,S,Os + SCO,.
3K,COs + l^S - SK^Sf + K,S,Os + 3C0,.

The reddish-Drown solid product was named by the early
chemists A/par su/pAuris, or " liver of sulphur."

!HorganU ChtmUtry

Occurrence.— The mosi abundant natural compound of sodiuiii'
is ihe chloride, which is present in sea^water, and in many
lakes and springs. Enormous deposits of sodium chloride, or
rock-salt, ate found in Cheshire, Lancashire, and other parts of
llie world. As nitraic, this element occurs in large quantities in
Chili and Peru ; and in combination with silicic acid it is a con-
stituent of many rocks.

Modes or Formation.— Sodium was fitst isolated by Davy, by
ilie elcclrolysis of sodium hydronide. On a manufacturing scale w
either by the "Castncr" process, as' described for the
preparation of potassium, or by ihe siill more recent method (also
due 10 Castncr) of decomposing fused sodium hydroxide by means
of a powerful electric current. The caustic soda is melted in a
lat^e iron vessel, through the bottom of which passes vertically the
negative electiode. Above this electrode an inverted iron pot is
suspended, its moutb dipping into the liquid. The sodium and
hydrogen, liberated at the cathode, together rise to the surface
under the inverted iron pot. The gas escapes by bubbling beneath
Ihe edges of the vessel, while the metal remains floating upon tli^

Properties. — Sodium closely resembles potassium in its general
properties, li is a soft, white metal which can be readily moulded
by the fingers, and is easily pressed into wire. At - zo' it is hard.
The colour of sodium vapour is violet, while the colour exhibited
by a thin film of the metal, obtained by sublimation in vacuo, is
greenish-blue. The vapour density of sodium is about 1 1 (Dewar and
Scott), showing that this metal in the vaporous state is monatomic.

Like potassium, sodium dissolves in liquid ammonia, yielding a
blue solution. When heated in the air, sodium bums, forming the
peroxide, Na,0,. Perfectly dry air or oxygen is without action
upon the metal.

When heated in hydrogen, sodium forms the hydride, NafH^
analogous to the potassium compound, but not spontaneously in-
flammable in air. When this is heated to about 300* in vacuo, the
whole of ihc hydrogen is evolved.

Alloy of Sodium and Potassium. —When these two metals are
melted together beneath petroleum, an alloy is obtained which is

iuitti^^
salt I

Sodium Hydroxide 487

liquid at ordinary temperatures. When prepared and preserved
out of contact with air, the alloy resembles mercury in appearance.
This alloy is employed in the construction of thermometers for regis-
tering high temperatures, where mercury would be inadmissible.

Oxides of Sodium.—Two oxides are ssdd to exist, viz., sodium
monoxide, Na^O, and sodium dioxide, or peroxide, Na^O^.

Sodium Monoxide, Na^O,* is said to be obtained by burning
sodium in nitrous oxide, at a temperature not higher than x8o*.

Sodium Peroxide, Na^O^ is obtained by allowing sodium to
bum briskly in oxygen. It is a yellowish-white solid, which de-
composes in contact with water, with considerable rise of tem-
perature and evolution of oxygen —

NajO, + H,0 « 2NaH0 + O.

The oxygen which is evolved contains appreciable quantities of
ozone. When sodium peroxide is slowly added to water, or to dilute
hydrochloric acid in the cold, hydrogen peroxide is formed —

Na A + 21 1,0 - 2NaH0 + H,0^

Sodium peroxide forms a crystalline hydrate of the composition,
Na,0^8H,0 (p. 204). When heated in either nitrous or nitric
oxides, it yields sodium nitrite ; in the former case, with the elimina-
tion of nitrogen —

Na^O, + 2N,0 - 2NaN0, + Nf
Na,0, + 2N0 -2NaN0,.

Sodium YLj^iTO:M» {caustic soda\ NaHO.— This compound ib
produced when sodium is brought into contact with water, and also
when either sodium monoxide, or peroxide, is dissolved in water.
On the large scale, caustic soda is prepared by the action of lime
upon a boiling solution of sodium carbonate (see Caustic Potash).

The so-called tank liquors {ohXa^ntd. in the manufacture of sodium
carbonate by the Leblanc process, q,v,) are heated to the boiling-
point, and an excess of lime is stirred into the mixture. The
sodium sulphide present in the tank liquor, is oxidised into sul-
phate by the combined action of air injected into the mixture,

* Doubt has recently been throvm upon the existence of this oxide. Erdmann
»nd Kttthner (AnnaUn der CJUmu, Nov. 1896), have shown that rubidium and
potassium do not Torm oiddes of the type R^O. And although lithium, the fint
member of the series, undoutHedly jrields the oxide Li^, it appears doubtful
» bether sodium i« capable of forming a similar compound.

488 Inorganic Chemistry

and of sodiuin nitrate, which is added for this purpose. The
liquor, aRcr being causiicised, is decanted, or tillered, {rom the
precipiiaied calcium carbonate, and is concentrated in large casc-
iron hemispherical pans. The decomposiiion suffered by the
sodium nitrate depends upon the temperature and concentration
of [he liquid: at 300° to j6o* the change may be expressed t
the equation —

NaNOj + 2H,0 = NaHO + NHj + 40.

The liberated oxygen oxidises the sulphides lo sulphates.

Caustic soda is now being manufactured by the electrolysil ■
brine. Mercury is employed as the cathode, with which the 1J~
rated sodiuin forms an amalgam ; and on treating this with watd
hydrogen is liberated and a solution of caustic soda is obtained. ]

Sodium hydroxide is a white, strongly caustic, and highly d
liquescent sohd. It is soluble in water, with considerable
temperature, and a concentrated aqueous solution when coc
to - 8*, deposits a crystalline hydrate, having the composilil
2NaHO,7H,0.

Sodium Chloride, NaCI.— Of the compounds of sodium »
the halogens, the chloride is the most important.
climates, as upon the shores of the Mediterranean, sodium chloride
is obtained by the evaporation of sea water in large shallow basins,
or pools, constructed upon the sea-shore, and exposed to the sun's
heat. As the brine concentrates in these saKnits, the crystals
of salt are raked off the liquid, and allowed to drain in heaps at
the side of the pools. The mother liquors, known as bilttra,
were formerly utilised for the extraction of the bromine which

Salt is obtained from salt-beds, where it is found in enormous
deposits, either by direct mining operations, when the salt is
sufficiently pure, or by first dissolving the material m water,
whereby insoluble admixed impurities are removed, and afterwards
evaporating the brine so obtained. The latter method is carried
out by sinking borings through the upper strata of rock, and
sending waier down to the salt-beds beneath. The brine is then
pumped up, and the salt obtained by evaporation. The first stage
of the concentrating process, especially where the brine is not very
strong, is in some parts carried on by exposing the liquid to the
wind. This is effected by causing the solution 10 trickle over
s of brushwood known as grailualori (Fig, 131), whifl

Sodium Chloride

489

built so ihai ihe prevailing winds blow Across them. The brine is
pumped up into ihe wooden troughs running along the lop, from
which it escapes by a number of openings, a, a, a, and flows over
Ihe pile of brushwood down into the reservoir upon which the
's constructed. In this way the solution is made to ex-

t quickly reaches a
;. of salt in the solution. The
evaporated in shallow iron pans by n
5 the salt crystallises it is lifted out by n;

perforated iron skimmers. Salt obtained in
contains small quantities of other salts, such

sodium sulphate,

49°

Inorganic Cfufttistry

calcium sulphate, call
of chlorides of magne"

magnesiuinchlonaes. Iheprei
■ calcium, causes Ihe sail to becomi,
moisi, especially in Aaatf^

Pure sodium chloriih
may be prepared by a
ing hydrochloric acid t
slrong aqueous solution d
sail ; the sodium chloride is '
thereby precipitated, while
the other salts remain in
solution.

Sodium chloride forms
colourless, cubical crystals,
which are anhydrous. If
deposited at - io° it crys-
tallises in monosymmetric
prisms, with two molecules
of water of crystallisation,
which at the ordinary lem
peraturelosetheirw aler,and
break up into minute cubes.
Sodium chloride is a

^^^ ^^^^nrnHB necessary article of food, for

^ I ^^H ^^^H^HB> "^^^ ^"'^ other animals

^^^^ ^^■^^^^^BB- -|j estimated that about ao

lbs. of salt per head of

population is annually used,

directly or indirectly, for

this purpose. The hydro-

^^^^ ^^^^^1^^^^—, chloric add present in the

£^ '■ ^^^S^^^^^I^^^H gastric and other acid fluids

^^~"^ ^^■■^^^^^■^^^K of the stomach, is derived

from the decomposition of

sodium chloride which is

L3k«ii into the organism.

Enormous quanlilics of sodium chloride are employed in the

alkali industry, and all the chlorine that is manufactured is derived

primarily from this compouttd.

Sodium Bromide, NaBr, and Sodliun Iodide, Nal, are pre-
pared by methods similar to those for obtaining the potaisiung

Sodium CarbonaU 491

compounds. They are both isomorphous with sodium chloride,
and when deposited at low temperatures they form monosymmetric
crystals containing two molecules of water.

Sodium Carbonate* Na^COi.— The preparation of this com-
pound is carried on by two methods, and constitutes that important
industry, the alkali manufacture. The two processes are known
by the names of their respective discoverers, namely, the Leblanc
process, and the Solvay process, the latter being also known as
the ammonia-soda process.

1. The Leblanc method of manufacture consists essentially of
three processes, namely —

(i.) The conversion of sodium chloride into sodium sulphate
by the action of sulphuric acid, known as the salt-cake
process. Two chemical reactions are involved in the
process —

NaCl + H,S04 = NaHS04 + HCl.
NaCl -H NaHSO^ = Na^SOi + HCL

(2.) The decomposition of sodium sulphate, salt-cake^ by means
of calcium carbonate (limestone) and coal, at a high
temperature, whereby a crude mixture of sodium car-
bonate and calcium sulphide is obtained, known as
black-ash. This black-ash process takes place in accord-
ance with the following equation —

NajSO^ + CaCOs -H 2C = Na^CO, + CaS + 2C0^

The change may be conveniently regarded as taking place in two
stages, which proceed simultaneously, according to the equations —

NajSO^ + 2C - Na^S + 2C0,.
Na,S + CaCO, - CaS + Na^CO,.

(3.) 7*he process of extracting and purifying the sodium car-
bonate contained in the black-ash,

(i.) The Salt-cake Process, — The first stage of this process is
usually carried on in a large cast-iron pan (ZP, Fig. 132), built into
a furnace in such a manner that it shall be heated as uniformly as
possible. The charge of common salt is placed in the covered pan,
and the requisite quantity of sulphuric add is then run in. Hydro-
chloric acid is given ofT in torrents, according to the first of the
above equations, and the gas is led away by the pipe K in the
arched roof, to the condensing-towers, where it is absorbed by water
(see Hydrochloric Acid, page 331). The mia^ture is heated until it

^^^^HH

H 493

tnorganie Cheinistry ^^H

^H begins to siifTen into a solid mass, when the damper h is raiied^^l

and the mass is raked out of

the pan on to the heanh of
the roaster, or leverberatory

f^^i^^

K "^

)W|

furnace, b. Here it is exposed

lo the hoi gases from Ihe coke

^^B

■

fire .1, which sweep over it, and

■

ullimalcly raise its tempera-

■

lure neatly 10 a red heat,

^^1

■

whereby Ihe second of the

■

above reactions is completed.

^^L

■

The acid gas, together with ilic

^^H

fire gases, leave the roaster by

■

the chimneys, and are also led

^^^^^^1

■

to condensing - towers, wheie

^^^^^1

■

the hydrochloric acid is ab-

^^^^^^1

■

sorbed. The mass is from

^^^^^^H

time to lime raked, or worked.

^^^^^B

'■

^^^^™

^ or "working doors," in the

■P

? roaster, and as soon as the

■ 1 lii^

d operation Is completed the

■

^ salt-cake is withdrawn. The

w ^

sah-cake so obtained, usually

■ B

contains from 95 lo 96 per cent.

■ ^

of normal sodium sulphate,

^^K

per cent, consisting of hydrogen

^^1

sodium sulphate, NaHSO„ un-

■

decom posed sodium chloride,
and such impurities as were

originally present in the salt.

^^H

(2.) The Black-ash Proctii.

^^H

—The salt-cake is mixed with

■

■—

limestone (or chalk) and coal
dust (ilaci), and healed in a
reverberatory furnace, known

■

1^ '

■ 1

as the black-ash, or balling,
furnace. As the mixture softens
with the heat, it requires to

I
I
I

Sodium Carbonate 493

whidi, in ihe older forms of furnace (still used in many pUccs), n

RCcomptished by manual labour. Fig. ij] shows such a furnace in
section. The malerials are introduced
by the hopper k on 10 the hearth 1,
where ihey arc exposed to the hot gases
from Ihe Rre a ; and as Ihe decom-
position proceeds, they are raked along
to the more strongly- heated front por-
tion of the hearth A. During this pro-
cess, carbon dioiidc is freely evolved,
the escaping bubbles of gas giving the
5emi-f1uid mass the appearance of boil-
ing. As the temperature rises, and the
process approaches completion, the
mass thickens, when it is worked up
into large balls by means of rakes or
PadiiUs. At this stage, carbon mon-
oxide begins to be evolved, the bubbles
of which, bursting from the doughy
material, become ignited and burn upon
its surface as small jets of flame,
coloured yellow by Ihe soda. As soon
as these appear, Ihe ball is quickly
withdrawn from the furnace. The for-
mation of carbon monoxide, al the high ''
temperature reached at this point in the
process, is due to the action of carbon
upon the limestone, according to the
equation —

CaCO, -I- C = CaO -)■ 2C0,

excess of these malerials being inien-
tionally present in the mixture. The
effect of the escaping carbon mononide
at this point in the process, in rendering
the black*ash light and porous (an impor-
tant consideration in view of ihe next operation),
of baking-powder when used for cooking purposes. The heated
gases from the furnace are made to pass over large evaporating
pans, P, where liouors from a subsequent process arc cob-
ccDtrUed.

494

Inorganic Chemistry

In the more modern forms of black-ash furnace, the mixing and
workmg up of the materials is accomplished mechanically, by
means of a revolving hearth. Fig. 134 shows the general arrange-
ment of a revolving black-ash furnace. The mixture is placed in
the cylinder /, which is made to slowly revolve upon its horizontal
axis. The heated gases from the fire a pass through this revolv-
ing hearth ; they are then conveyed through a dust-chamber, m, and
finally over concentrating-pans. Limestone and two-thirds of the
coal are first thrown into the furnace, and heated until the blue
fiame of burning carbon monoxide makes its appearance, when
the salt-cake, along with the rest of the coal, is added, and the
process continued until the yellow flames appear upon the surface
of the mass. The contents of the cylinder are then thrown out
into iron trucks beneath.

DIack-ash is a mixture of variable composition, containing—

Sodiimi carbonate, Na-jCOj
Calciimi sulphide, CaS .
Calcium carbonate, CaCO^
Coke ....
Calcium oxide, CaO

from

40 to 45 per

cent

»i

30 1,

»»

6.1

4 i>

2 „

And smaller quantities of sodium chloride, sodium sulphate, sodiimi
sulphite, sodium sulphide, sodium thiosulphate, oxides of iron,
alumina.

(3.) Ldxiviaiion of Black-ash. — The lixiviation of black-ash is
carried on in a series of tanks, so arranged that the liquid can be
made to pass from one to the other. The action of water upon
the black-ash is more than a simple process of dissolving the
sodium carbonate from the mixture, for in the presence of water,
chemical action takes place between some of the ingredients.
Thus, the lime reacts upon sodium carbonate, forming sodium
hydroxide, hence the iank liquor always contains caustic soda in
varying quantities. Under certain conditions of temperature and
dilution, the calcium sulphide also reacts upon the sodium car-
bonate, forming sodium sulphide <ind calcium carbonate, thus —

CaS -I- Na^COj •= CaCO, -I- Na^S.

Also by the oxidising influence of atmospheric oxygen, calcium
sulphide, CaS, is converted into calcium sulphate, CaSO^ which,

Sodium Carbonate 495

in its turn, is acted upon by the sodium carbonate, involving loss
of this product —

CaSO^ + NajCO, = CaCOj + NaaS04.

The process of lixiviation is carried on as rapidly as possible,
and at temperatures ranging from about 30° (for the dilute liquors)
to about 60° (for those more concentrated) ; for the formation of
sodium sulphide diminishes as the concentration of the liquid
increases. The tank liquor, after settling, is then either at once
concentrated by evaporation, when the soda crystallises out, leav-
ing the caustic soda in the mother liquor, or it is submitted to the
action of carbon dioxide, whereby both the caustic soda and the
sodium sulphide are converted into sodium carbonate, thus —

2NaH0 + COa = NajCOj + H^
Na,S + CO, + 11^0 = NaXOj + H,S.

The concentration of the tank liquor is accomplished in the
shallow pans above-mentioned, by means of the waste heat from
the black -ash furnace ; and the product obtained by evaporating the
liquid, is usually calcined at a red heat in an ordinary reverberatory
furnace. This substance is known as soda-ash^ and when dissolved
in water, and the solution allowed to crystallise, the so-called soda
crystals are obtained, having the composition Na3COs,10H,O.

1 1. The Ammonia-Soda Process. — This process is based upon the
fact, that hydrogen ammonium carbonate {bicarbonate of ammonia)
is decomposed by a strong solution of sodium chloride, according
to the equation —

H(NH,)C03 + NaCl = HNaCOj + NH^Cl.

In practice, the brine is first saturated with ammonia gas, and
I he cooled ammoniacal liquid is then charged with carbon dioxide,
under moderate pressure, in carbonating towers.

The hydrogen sodium carbonate {bicarboncUe of soda\ being
much less soluble, separates out, leaving the more soluble am-
monium chloride in solution, from which the ammonia is recovered
by subsequent treatment with lime.

The hydrogen sodium carbonate is converted into normal sodium
carbonate by calcination, and the carbon dioxide evolved is again
utilised in carbonating a further quantity of ammoniacal brine -

iHNarr), « Na,COj -»■ CO, ■»- H,0.

496

Inorganic Chemistry

Sodium carbonate crystallises in large, transpareni. mono
metric crystals, commonly known as " soda," or " washing-si
having the composition Na,COj,10H|O. On exposure to tb
the crystals give up tvatet, and become effloresced upon tbe sur&cj
and finally fait to powder, having the composition Na)COj,H,C
When crystallised from hot solutions, it forms rhombic crystals,
containing 7H;0, The solubility of sodium carbonate in water
increases with rise of temperature, reaching a maximum of 32.5°,
when 100 parts of water dissolve 59 parts of the salt. Above thi* •■
temperature the solubility lalls, and at 100° the amount dissolve
is 45.4 parts.

Hydrogen Sodium Carboaate {bicarbonate of soda), HNaCQ
niay be obtained by the action of carbon dioxide upon the
carbonate, either in solution, or as crystals —

Na,CO„10H,O + CO, = 2HNaCO, + 9H,0.

The greater part of the bicarbonate of soda of commerce j
obtained in the ammonia-soda process above described.

This salt is less soluble in water than the nornial c
Thus, 100 parts of water at different temperatures dissolves tl
following quantities of these compounds—

HNaCO, . . 8.8 9,8 10.8 r

When a solution of hydrogen sodium carbonate is healed, the st
gives ofT a portion of its carbon dioxide, and on cooling, the solution
deposits crystals having the composition Na,COj,8HNaCOj,2H,0,
known as sodium sesqui carbonate. On continued boiling, the sail
is completely converted into the normal carbonate. Sodium
sesqui carbon ale occurs as a namral deposit in Egypt, Africa,
South America, and elsewliere, known as Ironity from which the

Sodium Sulphate {Glauber's salt), Na,SO„ occurs native in the
anhydrous condition as the mineral thenardite, and as a double
sulphate of sodium and calcium, NajSO,,CaSO,, in the mineral
Glauberile.

It is manufactured in immense quantities in the first (salt-c*
process in the alkali manufacture, by the Leblanc method.

It is also obtained in targe supplies from the Slassfurt depoHH

Sodium Nitrate 497

by double decomposition between magnesium sulphate (from
kieseriie) and sodium chloride.

The solution of the mixed salts, when cooled a few degrees
below o"*, deposits sodium sulphate, and the soluble magnesium
chloride remains in solution —

2NaCl + MgS04 = Na^SO^ + MgCl^

Sodium sulphate is also manufactured by the action of sulphur
dioxide and oxygen upon sodium chloride. This is known as
Hargreav^s process. The reaction is expressed by the equation —

2NaCl + SO, + O + H,0 = Na^SO^ + 2HC1.

This process is, in essence, the production of sodium sulphate
from sodium chloride, and the constituents of sulphuric acid^ with-
out the intermediate manufacture of the acid. The gases from
pyrites burners, similar to those used by the " vitriol " manufacturer,
together with steam, are passed through a series of cast-iron
cylinders containing sodium chloride, and maintained at a tem-
perature of 500* to 550*. Many days are required for the com-
plete conversion of the chloride into sulphate by this process.

Sodium sulphate crystallises in colourless prisms belonging to
the monosymmetric system, containing ten molecules of water:
wHen exposed to the air the crystals effloresce, and when heated
to 33°, they melt in their own water of crystallisation (see page 132).

When sodium sulphate is heated with sulphuric acid, in the pro-
portions required by the following equation, hydrogen sodium
sulphate is formed —

Na,S04 + HjSOi - SHNaSO^.

Sodium Nitrate, NaNOs, occurs associated with other salts, in
Bolivia and Peru, as cubical nitre^ or Chili saltpetre. The crude
salt is purified by solution in water, and crystallisation. It forms
rhombohedral cr>'stals, isomorphous with calcspar.

Sodium nitrate is very soluble in water, loo parts of water dis-
solve at o', 68.8 parts ; at 40*, 102 parts ; and at loo*, 180 parts, of
the salt. When exposed to the air, the salt absorbs moisture, and
on this account cannot be employed as a substitute for potassium
nitrate in the manufacture of gunpowder, or in pyrotechny. Its
chief uses are for the manufacture of nitric acid ; for the manufacture

a I

Inorganic Chemistry

of potassium nitiale by double decomposition with potasai
chloride ; and as an ingredient in artificial manures.

Sodium Phosphates. — The most important of these compounds
is the hydrogen disodium orlhophosphate, or cammon fi/iospkalt
of soda, HNa,PO,. TTiis salt is prepared on a large scale, by
adding sodium carbonate to phosphoric acid until the solution is
alkaline, and then (illering and evaporating the solution, when
large transparent prisms, belonging to the monosymmetric system,
are deposited, having the composition HNajP0,,12H,0. Exposed
to the air the crystals effloresce, and when healed become an-
hydrous. The salt melts at 35°.

One hundred parts of ivaier at 10° dissolve 4. 1 parts ; at 50°, 43.3
parts ; and at too", lo8,2 parts, of the anhydrous salt

Normal Sodium Orthophosphate, Na^PO,, is obtained from
hydrogen disodium phosphate, by evaporating a solution of the
latter salt with sodium hydroxide, until the liquid crystalli

This salt
six-sided prisms.
absorbs atmosphci
sodium carbonate

HNa,PO, + NaHO = NajPO, + H,0.

'elve molecules of water, and forms thin
Its aqueous solution is strongly alkalin
: carbon dioxide, with the formation of hydrogen
nd hydrogen disodium phosphate, thus—

NajPO, -I- CO, + H,0 = HNajPO, -I- HNaCO,.

and

oeen 1

Dlhydrogen Sodium Orlhophosphate, HgNaPO^ is obtained

when phosphoric acid is added to ordinary phosphate of soda, until
the liquid gives no precipitate with barium chloride. On evapo-
rating the solution, the salt crystallises.

HNajPOj + H,PO, = 2H,NaPO,

The aqueous solution of this salt is acid.

Hydt^gen Sodium Ammonium Phosphate {microeasmitM

HNaCNHJPO,, is obtained by adding a strong solutlo
mon sodium phosphate to ammonium chloride —

HNa,PO, + NH.Cl = NaCI + HNa(NH,)PO,.

The orthophosphaies are readily converted ii
phosphates (see page 436).

Lithium 499

UTHIUM.

Symbol, Li. Atomic weight = 7.0Z. '

Oeeurrence. — Lithium is only found in combination with other
elements. It is a constituent of a few somewhat rare minerals, as
peialite, 30SiOt»4Al,O„Na,O,2Li,O ; spodumene, 16SiOt»4A],Oa,
3Li,0 ; lepidoliU, or lithium mica, 9SiO„3Al,0„K,0,4LiF.

By means of the spectroscope, lithium compounck have been
detected in sea water, and in most spring and river waters. In a
few cases spring waters are met with which contain considerable
quantities of lithium salts. Thus, W. A. Miller found as much as
0.372 gramme of lithium chloride in i litre of the water of a spring
near Redruth in Cornwall

Mode of Formation. — Lithium is obtained by the electrolytic
decomposition of the fused chloride. For this purpose the dry
salt is heated in a porcelain crucible, when it melts at a low red
heat to a mobile liquid. A rod <AgcLS carbon is made the positive
electrode ; and a stout iron wire, one end of which is flattened out,
is used for the negative pole, upon which the lithium is collected.
On passing an electric current through the molten chloride, the
metal forms as a bright globule upon the negative electrode. The
wire is withdrawn and quickly dipped beneath petroleum, and the
solidified globule of lithium is then cut off with a knife. The
reduced metal, in its passage from the crucible to the petroleiun,
is protected from oxidation by the film of fused chloride which
coats it.

Properties. — Lithium is a soft, silver-white metal, which soon
tarnishes on exposure to the air. It is easily cut with a knife,
being softer than lead, but harder than sodium. It may be pressed
into wire, and two pieces of the metal may be made to adhere,
or welded together, at the ordinary temperature. Lithium is the
lightest known solid, its specific gravity being a 59. Its extreme
lightness is illustrated by the fact that the metal floats upon
petroleum, a liquid which itself floats upon water. Lithium melts
at 180**, and at a higher temperature it takes fire and bums with
a bright white light Lithium decomposes water at the ordinar>
temperature, liberating hydrogen and forming lithium hydroxide,
LiHO ; but when a fragment of the metal is thrown upon cold
water it does not melt, and even with boiling water the action is
not attended by inflammation of the hydrogen.

When strongly heated in nilrogcn the Iv
feeble combustion, forming lithium nitride, NLij.

Lithium Oxide, Lip, is (omicd when the metal bums in the
air. It is also obiatned by heating the nitrate, li dissolves in
water, forming lithium hydroxide, LiHO.

Lithium Hydroxide is produced by the prolonged boiling of
lithium carbonate with milk of lime, the carbonate of this metal,
unlike potassium and sodium carbonates, being only very slightly
soluble in water.

Uthlum Carbonate, Li^COj, is obtained as a while precipitate
when a solution of either potassium, sodium, or ammonium car-
bonate is added to a solution of either chloride or nitrate of
lithium. The compound is only slightly soluble in cold water, too
parts of water at 13° dissoUing 0.77 parts of Ihe carbonate.

Litlllum Phosphate, LijPO,, is precipitated as a ctyslaliine
powder, by the addition of hydrogen disodiura phosphate to a
solution of a lithium salt. In the presence of sodium hydroxide the
precipitation is complete, and the formation of this compoimd is
employed as a quantitative method for estimating lithium. The
crystals contain 2H,0, which they lose when heated. Lithium
phosphate is soluble in nitric, hydrochloric, and phosphoric acids,
and from the latter solution, on evaporation, the dihydrogeo
phosphate i9deposLted(H]Li?04), as deliquescent, and very soluble
crystals. The chloride, nitrate, and sulphate of lithium are obtained
by dissolving the carbonate in the respective acids. The salts
are readily soluble in water.

Satildloin and CaeBltun.*— These two rare elemenu. which vcre firai dU-
eorcred by Bunsen in Ibe waters of DUrkbeim, in llie years 1860-61, arc met

lepidoliles (lithium mica), porphyriies, and in camallile. They are also found
in many mineral wnten, in Ihe mother liquors trom Ibe eiapotillon ot sea
water, and in the ashes of planls. Althougti widely dislritnited, the quanlilics
present are eilremely minute, one of tbe ricbeal lepidoliles in wbidi these
melals occur, containing only 0,34 per ceni. of rubidium oiide.

The tare raineial feltux, a silicate of aluminium and caesium, containing
also iron calcium and sodium, is [be only known mineral in which either ot
these two dements occurs as an essential constituent. The analpli of PiMtii
(1S64) gives 34.07 per cent, or caesium oitde in this subsiance.

Rubidium is cit>iained by beating the carbonate with carbon (the charred
in the older method for tbe preparation of sodium and polas^um.

. Ammonium Chloride 501

Caesium cannot be isolated by this reaction, but is obtained by the electro-
lysis of the fused cyanide, Cs(CN) (mixed with barium cyanide in order to
render it more readily fusible). Rubidium melts at 38.5, caesium at 26.5.

Rubidium gives a green vapour, and when sublimed in a vacuous tube yields
a thin film of metal, which appears deep blue by transmitted light : when
slowly sublimed in this way the metal forms small needle-shaped crystals.
The compounds of these metals closely resemble those of potassium, from
which they can only be distinguished by the different spectra they give.

AMMONIUM SALTS.

The monovalent group or radical (NH4) is capable of replacing
one atom of hydrogen in acids, thereby giving rise to a series of
salts which are closely analogous to, and are isomorphous with,
those of potassium. The radical (NH4), to which the name
ammonium is given, has never been isolated. W^en an amalgam
of sodium and mercury is thrown into a solution of ammonium
chloride, the mercury swells up into a honeycombed or sponge-
like mass, which floats upon the surface of the liquid This so-
called ammonium amalgam was at one time thought to be a true
amalgam of mercury with the metallic radical ammonium. It is
now generally believed to consist of mercury which is simply
inflated by the evolution of hydrogen and ammonia gas. When
this sponge-like substance is subjected to changes of pressure, it
is found to contract and expand in conformity to Boyle's law : its
formation may be represented by the equation —

HgxNay + yNH^Cl - yNaCl + xHg + yNHj + yH.

In the course of a few minutes the inflated mass shrinks down,
and ordinary mercury remains at the bottom of the solution,
hydrogen and ammonia having been rapidly evolved.

The ammonium salts are obtained for the most part from the
ammofiiacal liquor of the gasworks. This material is treated with
lime, and distilled ; and the anunonia so driven off is absorbed in
sulphuric or hydrochloric acid, giving rise to ammonium sulphate
or chloride.

Ammonium Chloride {sal ammoniac\ NH4CI.— The product
obtained by absorbing ammonia from gas liquor in hydrochloric
acid, is purified by sublimation. The crude material is heated
in large iron pots, covered with iron dome-shaped vessels, into
which the substance sublimes. Ammonium chloride crystallises in

Itorgami Chemistry

arborescent or fem-like cr^'Sta.ls (Fig. 135), consisting of groups a
small octahedra belonging to the regular system.

too parts of water at 10° dissolve 31.8 parts, and at 100°, 77 partt
of the salt- On boiling the aqueous solution, dissociation to i
small extent takes place, and a portion of the ammonia escapei
with the steam ; the solution at the same time becoming slight]]
add.

FlO. IJ5.

Ammonlam Sulphate (NHjj^O,.— The product obtained by the
absorption of ammonia obtained from gas liquors, by sulphuric
acid, is purified by recrystallisation, when it forms colourless
rhombic crystals, isomorphous with potassium sulphate. loo pans
of water at the ordinary temperature dissolve 50 parts of the salt-
The chief use of ammoriium sulphate is for agricultural purposes,
as a manure ; and for this use the crude salt, as first obtained,,
which is usually more or less coloured with tarry matters, is em-
ployed. Anunonium sulphate is also used for the preparation of]

Ammonium CarbonaU 503

ammonia alum, and other ammonium compounds, as well as in
the ammonia-soda process.

Ammonium Carbonates.— Commercial anmionium carbonate
{sal volatile) is obtained, by heating a mixture of ammonium
sulphate and ground chalk to redness in horizontal iron retorts or
cylinders, and conducting the vapours into leaden receivers or
chambers, where the carbonate condenses as a solid crust It is
afterwards purified by resublimation, when it is obtained as a
white fibrous mass. This substance is a mixture of hydrogen
ammonium carbonate, H(NH4)C08, and ammonium carbamate
(NH4)C0](NHs), and smells strongly anunoniacal When treated
with alcohol the ammonium carbamate is dissolved, leaving the
carbonate behind.

Normal Ammonium Carbonate, (NH4)tC0a, is obtained from
the commercial compound, by passing ammonia gas into a strong
aqueous solution, or by digesting the compound in strong aqueous
ammonia. The carbamate present is converted into normal car-
bonate by the action of the water, thus —

(NHJCOjCNHJ + H,0 - (NH4)C08(NH4) - (NH4),C0a ;

and the ammonia converts the bicarbonate into the normal salt,
thus—

H(NH4)C0| + NHg - (NH4),C0r

Normal ammonium carbonate on exposure to the air gives off
ammonia, and passes back into hydrogen anmioniimi carbonate.
When heated to 60* the salt breaks up into carbon dioxide,
anmionia, and water.

Hydrogen Ammonium Carbonate, H(NH4)C0„ may also be
obtained by passing carbon dioxide into a solution of the nonnal
salt—

(NH4),C0| + CO, + H,0 - 2H(NH4)COr

It forms large lustrous crystals belonging to the rhombic system,
which, when dry, do not smell of ammonia. 100 parts of water at
15* dissolve 12.5 parts of this salt. At ordinary temperatures this
solution on exposure to the air slowly gives off carbon dioxide, and
becomes alkaline ; and when heated above 36* the liquid begins to
effervesce, owing to the rapid evolution of carbon dioxide. This
salt forms with the normal carbonate a double salt, analofifous tg

504 Inorganic Ctumistry

sodium sesquicarbonate, and having the composition (NH4)sCOs,
2H(NH4)C08, H,0.

Ammonium Thlocyanate, NHfSCCN), is prepared by adding
aqueous ammonia to an alcoholic solution of carbon disulphide,
and allowing the mixture to stand, when ammonium thiocarbonate
is formed, thus —

6NH, + 3H,0 + 3CS, - 2(NH4),CSi, + (NHJ,CO^

On heating this solution, the anmionium thiocarbonate is de-
composed with evolution of sulphuretted hydrogen —

(NH4)sCS, = 2H,S + NH^SCCN).

Ammonium thiocyanate (known also as ammonium sulpko-
cyanaie) forms colourless crystals, which are extremely soluble
both in water and alcohol. The solution in water is attended with
considerable absorption of heat : thus, if 20 grammes of the saU
be dissolved in 25 cubic centimetres of water at 18°, the temperature
of the liquid falls to - 13*.

CHAPTER V

THB BLBhfENTS OP GROUP L {FAMILY B.)

Copper, Cu 65.18

Silver, Ag 107.66

Gold, All 196.8

The elements of this family present many striking contrasts to

those of the other family belonging to the first group. These

three metals are not acted upon by oxygen, or by water, at

ordinary temperatures ; they are all found native in the un-

combined state, and on this account are amongst the earliest

metals known to man. The alkali metals, on the other hand, are

instantly oxidised on exposure to air, they decompose water at

the ordinary temperature, are never found native, and are amongst

the most recently discovered metals. With the exception of

sodium and potassium, which are used in a few manufacturing

processes, the alkali metals, as such, are of little practical service

to mankind, whilst the metals of this family are amongst the most

useful of all the metals, and are the three universally adopted for

coinage. Many of the compounds of the elements of this family,

are similarly constituted to those of the alkali metals : thus, with

oxygen and with sulphur we have Cu^^O, Ag^O, AujO, and Cu,S,

AgjS, AujS, corresponding to Li^O and KjS.

With the halogens they all form compounds of the type

RX. Although the three elements, copper, silver, and gold, fall

into the same family, upon the basis of the periodic classification

of the elements, they are in many respects widely dissimilar.

Thus, silver is consistently monovalent, while copper is divalent,

forming compounds of the type CuX^, and gold is trivalent, giving

compounds AuXj. The chlorides, AgCl and Cu^^Clj, on the other

hand, are both insoluble in water, are both soluble in ammonia,

and both absorb ammonia.

In many of their physical attributes, these metals show a regular

505

5o6

Inorganic Chemistry

gradation in their properties. Thus, as regards malleability an
ductility, silver is intermediate between copper and gold, tl
latter possessing these properties in the highest degree. Wil
respect to their tenacity, silver is again intermediate, copper bein
the most, and gold the least tenacious of the three.

GOPPEB.

Sjmbol, Cu* Atomic weight = ^z8L

Oceurrence. — Copper is found in the elementary condition i
various parts of the world, notably in the neighbourhood of Lali
Superior, where native copper occurs in enormous masses. I
combination, copper is a very abundant element, and is wide!
distributed, the most important of these natural compounds bein
the following —

Ruby ore
Copper glance
Copper pjrrites

Cu,0.

CuaS.
CuaS.FeaS,.

Purple copper ore SCuyS.Fe^Ss.
Malachite . . CuC03,Cu(H0)»
Axurite . . 2CuCO,.Cu(HO)

Modes of FormatioiL — The methods by which copper i
obtained from its ores, vary with the nature of the ore. Froi
ores containing no sulphur, such as the carbonates and oxid<
the metal may be obtained by a method known as the reducin
process^ which consists in smelting down the ore in a blast-fumac
with coal or coke, when the metal is reduced according to th
equation —

CujO + C = CO + 2Cu.

In the case of mixed ores, containing sulphides, the proces
(known as the English method) consists of six distinct siaj^es —

(i.) The ores, which contain on an average 30 per cent, of iro
and 13 of copper (the remainder being chiefly sulphur and silica
are first calcined ; usually in a reverberatory furnace, whereby
portion of the sulphur is burnt to sulphur dioxide, and the metal
are partially oxidised

(2.) The second step consists in fusing the calcined ore ; whe
the copper oxides, formed during calcination, react upon a portio:
of the ferrous sulphide with the formation of cuprous sulphid
and ferrous oxide, thus —

Cu,0 + FeS = Cu^S + FeO.
2CuO + 2FcS « Cu,S + 2FeO + S,

Copper 507

The oxide of iron combines with the silica already present (or
Mrhich is added in the form of meted slag obtained from the fourth
process) to form a fusible silicate of iron, or slag, which contains
little or no copper. This is run off, and a fused regulus remains,
consisting of cuprous and ferrous sulphides, known as coarse-metal^
and containing from 30 to 35 per cent, of copper. This molten
regulus, which has a composition very similar to copper pyrites,
is usually allowed to flow into water, whereby it is obtained in a
granulated condition ^Eivourable for the next operation.

(3.) The third step consists in calcining the granulated coarse-
metal ; the result, as in the first calcination, being the removal of
a part of the sulphur as sulphur dioxide, and the partial oxidation
of the metals.

(4.) The calcined mass is next fused along with refinery-stag^
which results in the production of a regulus consisting of nearly
pure cuprous sulphide, the greater part of the iron having passed
into the slag (known as metal-stag). This regulus, ciXX^d fine-
metal ^ or white-metal^ contains from 60 to 75 per cent of copper.

(5.) The fifUi operation consists in roasting the " white-metal "
in a reverberatory furnace. A portion of the cuprous sulphide is
here oxidised into cuprous oxide, which, as the temperature rises,
reacts upon another portion of cuprous sulphide, thus —

2Cu,0 + Cu^ - 6Cu + SO,.

At the same time any remaining ferrous sulphide is converted into
oxide, thus —

aCujjO -I- FeS « 6Cu + FeO -I- SO,.

The metallic copper so obtained, presents a blistered appearance,
and on this account is known as blister-copper,

(6.) This impure copper is lastly subjected to a refining process.
For this purpose it is melted down upon the hearth of a reverbera-
tory furnace, in an oxidising atmosphere. The impurities present
in the metal, such as iron, lead, and arsenic, are the first to oxidise ;
and the oxides either volatilise, or combine with the siliceous matter
of which the furnace bed is composed, forming a slag, which is
removed. The oxidation is continued until the copper itself begins
to oxidise, when the oxide so formed reacts upon any remaining
cuprous sulphide with the reduction of copper and the evolution of
sulphur dioxide, according to the above equation. The metal at
this stage is termed dry copper; and in order to reduce the copper

5o8 Inorganic Chemistry

oxide which it still contains, the molten mass is stirred with poles
of wood, and a quantity of anthracite is thrown upon the surface to
complete the reducing process.

Wet Process. — Copper is extracted from the burnt pyrites,
obtained in enormous quantities in the manufacture of sulphuric
acid, which contains about 3 per cent, of copper. Although too
poor in copper to be submitted to the smelting process, it is
found that when calcined with 12 to 15 per cent, of common salt,
the copper is all converted into cupric chloride. On lixiviating the
calcined mass with water, the cupric chloride goes into solution, and
metallic copper can be precipitated from it by means of scrap-iron.

Properties. — Copper is a lustrous metal, having a characteristic
reddish-brown colour. The peculiar copper-red colour of the metal
is best seen, by causing the light to be several times reflected from
the surface before reaching the eye.

Native copper is occasionally found crystallised in regular octa*
hedra, and small crystals of the same form may be artificially
obtained, by the slow deposition of the metal from solutions of its
salts by processes of reduction.

Copper is an extremely tough metal, and admits of being drawn
into fine wire, and hammered out into thin leaf. Its ductility and
malleability are greatly diminished by admixture with even minute
quantities of impurities. WTien heated nearly to its melting-point,
copper becomes sufficiently brittle to be powdered. The specific
gravity of pure copper, electrolytically deposited, is 8.945, which
by hammering is increased lo 8.95.

Copper is only slowly acted upon by exposure to dry air
at ordinary temperatures ; but in the presence of atmospheric
moisture and carbon dioxide, it becomes coated with a greenish
basic carbonate. When healed in air or oxygen, it is converted
into black cupric oxide, which flakes off the surface in the form of
scales. When volatilised in the electric arc, copper gives a vapour
having a rich emerald green colour.

Copper is readily attacked by nitric acid, either dilute or con-
centrated, with the formation of copper nitrate and oxides of
nitrogen (page 221).

Dilute hydrochloric and sulphuric acids are without action upon
copper when air is excluded, but slowly attack it in the presence
of air, or in contact with platinum. Cold concentrated sulphuric
acid does not act upon copper ; but, when heated, copper sulphate
and sulphur dioxide are formed (page 377).

Cuprous Oxide 509

Finely divided copper is slowly dissolved by boiling concen-
trated hydrochloric acid, with evolution of hydrogen and formation
of cuprous chloride : —

2Cu + 2HC1 - CujCl, + Hj^

In the presence of air, copper is acted upon by a solution of
ammonia, the oxide dissolving in the ammonia forming a deep
blue solution.

Copper is an extremely good electric conductor, being only
second to silver in this respect ; it is therefore extensively em-
ployed for cables, or leads, for purposes of telegraphy and electric
lighting. -

Copper possesses the property, in a high degree, of being de-
posited in a coherent form by the electrolysis of solutions of its
salts. On this account it is extensively used in processes of
electrotyping.

Alloys of Copper. — The most extensive use of copper is in
the formation of certain alloys, many of which are of great technical
value. The following are among the most important : —

English brass .

Copper 2 parts

Zinc I pa

Dutch brass {Totnbac)

II 5 »i

>i ' II

Muntz metal .

11 3 ft

It ' II

Gun metal

II 9 n

Tin I „

Aluminium bronze .

11 9 It

Aluminium i „

Oxides of Copper. — Two oxides of copper are well known,
namely, cuprous oxide {copper 5ub-oxide\ CugO, and cupric oxide
(copper monoxide\ CuO.

Cuprous Oxide, Cu^O, occurs native as red copper ore. It is
formed when finely divided copper is gently heated in a current
of air or when a mixture of cuprous chloride and sodiimi carbonate
is gently heated in a covered crucible.

CujCl, -I- NajCO, = 2NaCl -H CO, -I- Cu,0.

Cuprous oxide is also obtained when an alkaline solution of a
copper salt is reduced by grape sugar.

Cuprous oxide is insoluble in water ; it is converted into cuprous
chloride by strong hydrochloric acid. Nitric acid converts it into

510 Inorganic Cktmhtry

cupric nitrate with the evolution of oxides of nitrogcD. When
acted upon by dilute sulphuric acid, it is partly reduced to metallic i
copper, and partly oxidised into copper sulphate, thus—

Cu,0 + H,SO, = CuSO, + Cu + H,0.

When heated with the strong acid it is entirely oxidised, ihu!

Cu,0 + 3H,S0, - aCuSO, + SOj + 3H,0.

Cuprous oxide fuses at a red heat, and when melted ii
imparts to the latter a rich ruby-red colour.

CuprIc Oxide, CuO, occurs as the rather rare mineral, ftnorilt.
It is formed when cqpper is strongly heated in the air or ie oxygen,
or by gently igniting either the nitrate, carbonate, or hydroxide.
Il is a black powder, which rapidly absorbs moisture from the
air. When heated, it first cakes together and finally fuses,
giving up a pari of its oxygen, and leaving a residue consisting
of CuO,2CujO.

When heated in a stream of carbon monoxide, marsh gas, or
hydrogen, it is reduced to the metallic state. Similarly, when
mixed with organic compounds containing carbon and hydrogen,
it oxidises these elements lo carbon dioxide and water, itself being
reduced : on this property depends its use in ihe ultimate analysis
of organic compounds.

Cupric Hydroxide, Cii(HO]i, is the pale blue precipitate pro-
duced when sodium or potassium hydroxide is added in excess to a
solution of a copper salt. The compound, when washed, may be
dried at ioo° without parting with water ; but if the liquid in which
it is precipitated be boiled, the compound blackens, and is con-
verted into a hydrate having the composition Cu(HO)^2CuO.
Cupnc hydrate dissolves in ammonia, forming a deep blue liquid,
which possesses the property of dissolving cellulose (cotton wool,
filter paper, &c)

Salts of Copper.— Copper forms two series of salts, namely,
(uproiis and cupric salts. The fonner, which are colourless,
readily pass by oxidation into cupric salts, and serve therefore
as powerful reducing agents, and are mostly insoluble in water.
The cupric salts in the hydrated condition, are either blue oi
green in colour ; the anhydrous aipric salts ate colourless or
yellow. The normal salts are mostly soluble in water. Copper
salts impart lo a non-luminous flame a blue or green colour, and

Cupric Chloride 5 1 1

on this account are employed in pyrotechny. The soluble salts
are poisonous.

Cuprous Chloride, Cu,Cl^ may be obtained by dissolving
cuprous oxide in hydrochloric acid. It is more readily prepared
by boiling a solution of cupric chloride in hydrochloric acid,
with copper turnings or foil. The nascent hydrogen, liberated by
the action of the hydrochloric acid upon the copper, reduces the
cupric chloride to cuprous chloride. The liquid is then poured
into water, which causes the precipitation of the cuprous chloride
as a white crystalline powder.

A mixture of zinc dust and copper oxide added to strong hydro-
chloric acid, also yields cuprous chloride, the nascent hydrogen in
this case being derived from the action of the acid upon the zinc,
and this causes the reduction of cupric chloride formed by the
action of the acid upon the cupric oxide.

Cuprous chloride melts when heated, and volatilises without
decomposition. It is insoluble in water, but dissolves in hydro-
chloric acid, anunonia, and alkaline chlorides. These solutions, on
exposure to the air, absorb oxygen, turning first brown, and finally
depositing a greenish-blue precipitate of copper oxychloride,
CuC1^3CuO,4H]0. This compound occurs native as the mineral
atacamiU, Solutions of cuprous chloride also absorb carbon mon-
oxide, forming a crystalline compound, believed to have the com-
position, C0CusC1^2H]0. They also absorb acetylene (see page
280).

Cuprous bromide, Cu^Br] ; iodide, Cu^I] ; and fluoride, Cu^Fj,
are also known.

Cupric Chloride, CuG^ — This compound is formed when
copper is dissolved in nitro-hydrochloric acid, or when cupric
oxide, carbonate, or hydroxide, are dissolved in hydrochloric acid.
It is also produced when copper is burnt in chlorine.

Cupric chloride is readily soluble in water, forming a deep green
solution, which, on being largely diluted, turns blue. The salt
crystallises in green rhombic prisms, with SH^O. When heated,
it loses its water, and at a dull red heat is converted into cuprous
chloride, with evolution of chlorine (see page 317).

Cupric chloride forms three compounds with ammonia. The
anhydrous salt absorbs ammonia gas, forming a blue compound,
CuCl2,6NH3. When ammonia is passed into aqueous cupric
chloride, the solution deposits deep blue quadratic octahedral
crystals of the compound, CoC1^4NHsiH,0. Both these sub

5 1 2 Inorganic Chemistry

stances, when moderately heated, yield the green compoand
CuQ2,2NH3, which at a higher temperature is decomposed,
thus —

6(CuCl8,2NHs) = 3Cu,Cl, + 6NH4CI + 4NH, + N,.

Cupric bromide, CuBrj, and fluoride, CuF^, are known, but the
iodide is unknown.

Cupric Nitrate, Cu(N0s)s,3H,0, may be obtained by the
action of nitric acid upon cupric oxide, hydroxide, carbonate, or
the metal itself. It is deposited from the solution in deep blue
deliquescent crystals, soluble in alcohol When heated to about
65", the crystals lose nitric acid and vv*ater, and are converted into
the basic nitrate, Cu(NOs)2,3Cu(HO)s. The normal salt, there-
fore, cannot be obtained anhydrous. Cupric nitrate is a caustic,
powerfully oxidising substance. If the moist salt be rubbed in a
mortar with a quantity of tinfoil, the tin is quickly converted into
oxide, with considerable rise of temperature. Wlien a solution
containing copper nitrate and ammonium nitrate is evaporated, the
mixture suddenly deflagrates when a certain degree of concentra-
tion is reached.

Cupric Sulphate (blue vitriol)^ CuSO^jSHjO, is the most
important of all the copper salts. It is formed when either the
metal or the oxide is dissolved in sulphuric acid. On a com-
mercial scale, it is obtained from waste copper by first converting
the metal into sulphide, by heating it in a furnace, and throwing
sulphur upon the red-hot metal. Air is then admitted, and the
sulphide is thereby oxidised into sulphate, which is dissolved in
water, and crystallised.

It is also manufactured from the sulphur ores of copper, by
roasting them under such conditions that the iron is for the most
part converted into oxide, while the copper is oxidised to sulphate.
On lixiviating the roasted mass, the copper sulphate, with a certain
amount of ferrous sulphate, is dissolved out The ores may
also be roasted so as to convert both the metals into oxides ;
the mass is then treated nith "chamber acid," which dissolves
copper oxide, leaving the iron oxide for the most part unacted
upon.

Cupric and ferrous sulphates cannot be entirely separated by
crystallisation, as a solution of these salts deposits a double
sulphate of the two metals. If, however, the amount of iron pre-
sent is comparatively small, the first crop of crystals obtained, is

Copper Sulphides 513

moderately pnre copper sulphate. The copper is remoTcd from
the mother liquors by precipitation upon plates of iron, and the
copper so obtained is converted into sulphide, as above described.

Copper sulphate forms large blue asymmetric {triclinic) crystals,
with 6H2O. At 100* it is converted into a bluish-white salt,
CuSOffHjO, and at 220* to 240* it becomes anhydrous. The
anhydrous salt is white, and extremely hygroscopic, and is used
both for the detection and removal of small quantities of water
in organic liquids.

One hundred parts of water at 10* dissolve 36.6 parts, and at
100*, 203.3 parts, of the crystallised salt

Several basic sulphates of copper are known : thus, when the
normal salt is submitted to prolonged heating, it is converted into
an amorphous yellow powder, consisting of CuSOfjCuO, which,
when thrown into cold water, forms an insoluble green compound,
CuS04,3Cu(HO)s, and on treatment with boiling water yields
CuS04,2Cu(HO)^ Copper sulphate forms several compounds
with ammonia. Thus, the anhydrous salt readily absorbs ammonia
gas, forming the compound, CuS04,5NH3. When excess of
ammonia is added to a solution of copper sulphate, the deep blue
solution deposits blue crystals of CuS04,H,0,4NHj. At 150*
this compound is converted into CuS04,2NHs, and at 200* it
loses one more molecule of ammonia, leaving CuS04,NH,.

Cuprie Carbonates.— The normal carbonate has not been
obtained. The two most important basic carbonates are (i)
CuCOs,Cu(HO)2, occurring native as malcichite^ and obtained when
sodium carbonate is added to a solution of copper sulphate (the
green deposit which appears upon copper, when exposed to atmos-
pheric moisture and carbon dioxide {verdt£ris\ is the same com-
pound) ; and (2) 2CuCOs,Cu(HO)j, occurring as the mineral azuriie.

Sulphides of Copper. — Two sulphides are known, correspond-
ing to the two oxides.

Cuprous sulphide^ Cu^S, occurs in nature as capf^er glance^
in the form of grey metallic-looking rhombic crystals. It is
produced when copper bums in sulphur vapour, or when an
excess of copper filings is heated with sulphur.

Cuprie Sulphide^ CuS, is met with in nature as the mineral indigo-
copper. It is obtained when either copper or cuprous sulphide is
heated with sulphur to a temperature not beyond 1 14* ; so obtained,
the compound is blue. As a black precipitate, it is formed when
sulphuretted hydrogen is passed into solutions of cuprie salts.

2 K

514 Inorganic Chemistry

SILVER.

Symbol. Ag. Atomic weight = 107.66.

Occurrenee. — Silver is found uncombined, occasionally in
masses weighing several cwts. Such native silver usually contains
copper, gold, and other metals.

Amongst the more important natural compounds of silver are
the following : —

Argentite, or silver glance . Ag^S.

Pyrargyrite, or ruby silver ore . SAgjSySbjSs, or AgsSbS|.

Proustite, or light-red silver ore 3Ag2S,AssS, „ AgjAsSj.

Stephanite SAg^SjSbjSs „ Ag5SbS4.

Polybasite 9(Ag2S,Cu2S),SbsSa,AS)Ss.

Stromeyerite AgsSjCu^S.

Horn silver AgCl.

Silver is present also in most ores of lead, notably with galena
(lead sulphide) ; argentiferous lead ores constituting one of the
main supplies of silver.

Modes of Formation. — This element may be obtained from
its salts by the electrolysis of their aqueous solutions. The metal
is so readily reduced from its compounds, that many organic
substances, such as grape sugar, aldehyde, certain tartrates, &c.,
are capable of effecting its deposition. When a strip of zinc is
introduced into silver nitrate solution, the silver is at once de-
posited upon the zinc as a crystalline mass.

Pure silver for analytical purposes may be prepared by pre-
cipitating silver chloride, by the addition of hydrochloric acid to
a solution of the nitrate, and reducing the chloride by boiling with
sodium hydroxide and sugar, or by means of metallic zinc In
this way the metal is obtained as a fine grey powder. The
chloride may also be reduced by fusion with sodium carbonate,
when the silver is obtained as a button at the bottom of the
crucible. The methods by which silver is obtained from its ores
are very varied ; they may, however, be classed under th ree heads,
namely —

I. Processes involving the use of mercury. (Amalgamation
processes.)

^. Processes by means of lead.

Silver 515

3. Wet processes.

(i.) Amalgitmation Proeoases.— These depend upon the fact
that certain compounds of silver are reduced by mercury. The
reduced silver then dissolves in the mercury, forming an amalgam,
from which the silver is obtained, and the mercury recovered by
distillation. The process, as still carried on in Mexico and South
America, is the following. The ore is first crushed and then
ground to a fine powder with water, and the mud so obtained is
mixed with 3 to 5 per cent of common salt, and spread upon the
floor of a circular paved space, the nuxing being effected by the
treading of mules. Af^er the lapse of a day, mercury is added,
together with a quantity of roasted pyrites (known as magistral^
and consisting of a crude mixture of cupric and ferric sulphates
and oxides), and the materials thoroughly incorporated. Fresh
mercury is added from time to time, during the several days
required for the completion of the chemical decompositions that
take place. The exact nature of these changes is not thoroughly
understood, but it is probable that they involve first the formation
of copper chlorides, by double deconlposition between the copper
sulphate and sodium chloride, and the subsequent action of these
upon the silver sulphide present in the ore, thus —

aCuCl, + Ag,S - 2AgCl + CujCl, -•• S.
CujCl, + Ag,S - 2AgCl + CujS.

The silver chloride dissolves in the sodium chloride present, and
is reduced by the mercury, with the production of mercurous
chloride {calomel)^ which is ultimately lost in the washing —

2AgCl + 2Hg = HgjCl, + 2Ag.

The amalgam is first washed, and freed from adhering particles
of mineral, and is then filtered through canvas bags, whereby the
excess of mercury is removed. The solid residue, containing the
silver, is then submitted to distillation.

In other amalgamation processes the ore is first roasted with
salt, in order to convert the silver into chloride. The roasted
ore is reduced to fine powder with water, and introduced into
revolving casks along with scrap iron, when the chloride is reduced
according to the equation —

2AgCl + Fe - 2Ag + FeCl„

5 1 6 Inorganic Chemistry

and the reduced silver is then extracted by the addition of mercury,
with which it amalgamates.

In the modem amalgamation process, the finely crushed ore, with
water, is placed in iron pans provided with revolving machinery,
which serves the purpose of further grinding, and also of mixing.
When the ore is reduced to an almost impalpable powder, mercury
is added, and the machinery is kept in operation for a few hours,
when the amalgamation is complete ; sometimes common salt and
copper sulphate are added, either together or singly. Their pre-
sence does not appear to be necessary to the process, except in so
far as they aid in keeping the surface of the mercury clean, or
" quick ; " for in the extremely finely divided condition to which the
ore is reduced in this "pan** amalgamation process, the silver
sulphide is readily acted upon by mercury, with the formation of
mercuric sulphide —

Ag,S + Hg - HgS + 2Ag,

and the silver so reduced, dissolves in the excess of mercury, from
which it is finally separated by distillation.

(2.) Processes by Means of Lead.— When silver ores are
smelted with lead, or with materials which yield metallic lead ; in
other words, when silver ores are smelted with lead ores, an alloy ol
silver and lead is obtained, from which the silver can be separated
When the argentiferous lead is rich in silver, the alloy is submitted
to cupellation^ which consists in heating the metal in a reverbera-
tory furnace, the hearth of which consists of a movable, oval-shaped,
shallow dish, made of bone ash, known as a cupei^ or test The
alloy is fed into this cupel from a melting-pot, and a blast of air is
projected upon the surface of the molten metal. The lead is thus
converted into litharge, and the melted oxide, by the force of the
blast, is made to overflow into iron pots. As the oxidation of the
lead reaches completion, the thin film of litharge begins to exhibit
iridescent interference colours, which presently disappear, leaving
the brilliant surface of the melted silver. The sudden appearance
of the bright metallic surface is known as \\\t flashing of silver.

In the case of argentiferous lead too poor in silver to be directly
cupellea, '.he alloy is submitted to one of two processes of con-
centration, namely, the Pattinson process^ or the Parkes^s process.

The Pattinson process for desilverising lead, depends upon the
fact that alloys of silver and lead have a lower melting-point than

Silver 517

pure lead, and therefore when argentiferous lead is melted and
allowed to cool, the crystals which first form, consist of lead which
is nearly or quite pure, and the greater part of the silver is io
the still liquid portion. The operation is carried out in a row of
iron pots. A quantity of the metal is melted in one pot, and as
it cools, the crystals which begin to form are removed by means
of a perforated iron ladle, and transferred to the next pot on
one side. This operation is continued until a definite proportion
(either two-thirds or seven-eighths, depending upon the propor-
tion of silver) has been removed. The residue is then transferred
to the neighbouring pot on the opposite side, and a second charge
melted up in the first pot. As the neighbouring pots fill up, they
are similarly treated, and in this way an alloy, gradually becoming
richer and richer in silver, is passed along in one direction, and
purer and purer lead is sent in the opposite way. The rich alloy
is then cupelled.

The Parkers process depends upon the fact that when zinc is
added to a melted alloy of lead and silver, the zinc deprives the
lead of the silver, and itself forms an alloy with it The alloy of
zinc and silver rises to the surface, and is the first portion to solidify,
and can be removed. The operation is carried out in iron pots.
The argentiferous lead is melted, and a quantity of zinc is
thoroughly stirred into the molten mass, the amount of zinc
depending upon the richness of the lead. As the mixture cools,
the first portions to solidify are skimmed off with a ladle, and
transferred to another pot. These skimmings, consisting of zinc,
silver, and lead, are first liquated ; that is, carefully heated to such
a temperature that the adhering lead melts, and flows away from
the less fusible zinc silver alloy. The solid alloy is then distilled,
and the residue, consisting of silver and lead, is submitted to
cupellation.

(3 ) Wet Processes {Ziervogel Process). — When argentiferous
pyrites, or an artificially formed regulus containing sulphides of
silver, copper, and iron, is roasted, the sulphides are first converted
into sulphates ; and, as the roasting continues, first the iron, then
the copper, and lastly, the silver sulphate is converted into oxide.
By careful regulation, the process is continued until the whole
of the iron and a part of the copper sulphates are decomposed.
On lixiviating the roasted mass with water, the silver sulphate,
together with the remaining copper sulphate, dissolves. From
this solution the silver is precipitated by scrap copper.

5.8

The copper

fnorganic Ckemistty
s recovered from ihe solution by precipitation I

TAe Ptrcy-Pattra Pr<ices!.—\n this method the ore is I
vith sail, and the silver chloride so formed is then e
neans of sodium tbiosulphate —

Na,S,0, + A^l - NaCI + NaAgS,0,'

r calcium sulphide U

To the solution so obtained, sodiuir
which precipitates silver sulphide—

aNaAgS,0, + Na,S = AgjS + aNa,S,0^

The silvei sulphide is then reduced by being roasted in a n
beralnry furnace.

Properties.— Silver is a lustrous white metal, which ap]
yellow when the light is reflecled many times from its sati
before reaching the eye.
unacted upon by atmospheric it
gen, but quickly becomes tamisIiaS
by traces of sulphutetled hydrogen
in the air. Silver has (he highest
conductivity for heat and electricity
of all the inelals. It is extremely
mallcableand ductile, being second
only 10 gold. Thin films of silver
appear blue by transmilled light.
Silver melts at 954°, and, when
heated by the oxyhydrogen tiame, may be readily made to boil, and
distil. The pure metal employed by Stas for the detennination of
the atomic weight, was obtained by distillation in this way. When
volatilised in the electric arc, the vapour of silver has a brilliant
green colour. Molten silver absorbs as much as twenty-two times
its volume of oxygen, which it gives up again (with the exception
of 0.7 volume) on solidification. As the mass cools, the oxygen
evolved often bursts through the outer crust of solidified metal
with considerable violence, ejecting portions of the still liquid
silver as irregular excrescences, as seen in Fig. 136. This pheno-
known as the "spitting" of silver. Small quantities of
admixed metals prevent the absorption of oxygen.
Silvei is readily soluble in nitric acid, forming argentic i

Fi<i.i3&

mtic nitrate J

Silver Oxides 519

with liberation of oxides of nitrogen. Hot concentrated sulphuric
acid converts it into argentic sulphate, with formation of sulphur
dioxide (the reactions in both cases being the same as with copper).
Silver Alloys.— Silver, alloyed with copper, is largely employed
for coinage, and for ornamental purposes. English standard
silver contains 925 parts of silver per 1000. It is said, therefore,
to have a fineness of 925. In France three standards are used.
That for coinage contains 900 parts per looa For medals and
plate the silver has a fineness of 950, while for jewellery it con-
tains only 800 parts per looa

8ilTer-plati]i|f. —For purposes of electro-plating, a solution of silver cyanide
in potassium cyanide is used. When a feeble electric current is passed
through this solution (the article to be silvered toeing the negative electrode,
and a plate of silver the positive), silver in a coherent form is precipitated
upon the negative electrode, thereby coating the object ; and cyanogen is dis-
engaged at the positive pole, where it dissolves the electrode, reforming silver
cyanide.

Silver is reduced from solutions, and deposited as a coherent film, by a
variety of organic compounds ; and various methods, based upon this property,
are in use for obtaining mirrors, and silvered glass specula for optical pur-
poses. One such method is the following. Two solutions are prepared,
thus—

(z.) Ten grammes of silver nitrate are dissolved in a small quantity of
water, and ammonia added until the precipitate dissolves. The liquid is then
filtered, and diluted up to one litre.

(2.) Two grammes of silver nitrate are dissolved in a litre of boiling water,
and X.66 grammes of Rochelle salt (sodium potassium tartrate, NaKC4H40e)
are added, and the liquid filtered. Equal volumes of these two solutions are
poured into a shallow dish, and the glass to be sihered (after being perfectly
cleaned) is laid in the solution. In about twenty minutes the silver will have
formed a brilliant mirror upon the glass.*

Oxides of Silver. — Three oxides are believed to exist, namely —

Silver monoxide .... Ag^O.
Silver peroxide .... AggOi?
Silver suboxide .... Ag40 ?

Silver Monoxide (argentic oxide\ Ag,0, is obtained by adding

* By the reduction of silver solutions in the presence of certain organic
compounds, Carey L«a has obtained the metal in the form of a dark bronze
powder, which, when dry, resembles burnished gold. He has also obtained
it exhibiting bluish-green and ruby-red colours. The material differs in
many of its properties from ordinary silver, and is regarded by its discoverer
as an allotropic form of sihrv {Jmerican /ournal (f Science , iSqx)*

520

Inorganic Chemistry

sodium or potassium hydroxide to a solution of silver nitrate.
brown precipitate, consisting of hydrated oxide, is obtained, v
when bcaied, is convened inio the anhydrous compound,
also formed when silver cliloride is boiled with a strong soluti
potassium hydroxide —

2AgCl + 2KHO-2KCH- H,0 + Ag,0.

Silver oxide is a black amorphous powder, which when heaiod
10 260*, begins 10 give off oxygen, and become reduced to metallic
silver. U is a powerful oxidising substance, and when rubbed
with sulphur, red phosphorus, sulphides of antimony or arsenic, or
other readily oxidised substances, it causes them to ignite.

Silver oxide, although only very slightly soluble in water (1 paitW
about 3000), imparts to the solution a distinct metallic tasi
alkaline reaction.

It is reduced by hydrogen at loo^ with formation of w
metallic silver; and when brought into contact with peroxide4|
hydrogen, oxygen is evolved and metallic silver formed (see p. 1

Silver oxide is soluble in strong ammonia, and, on standing, \
solution deposits black shining crystals of the so-called/M/'nino/fju
sihtr. When dry, this compound is extremely explosive, and Q
often explodes when wet. Fulminating silver is believed Ii
nitride, with the composition NAg,.

Silver Peroxide, Ag,0, (?).— When a solulion at silver nitrate is sub
cleclrolysis, a black powder. consistiDg or small octahedral ctjsIbIs, isi
upon ibc positive electrode. Tbe same tximpaund is obtained when i
silver ij made Ilie positive electrode in the electrolysis of acidulated M
uid also when silver i] acted upon by otone. Tbe exact compc
compound \sai not been placed beyond doubt ; it is lielievcd 10 be a dioxl^

It readily parts with oxygen, and is a still more powerful oxidising aj
than the monoxide, ll dissolves in aqueous ammonia, with the evolutic
nitrogeD —

8Ae,0, + UNH, = 3Ag^ + :iH^ + N^

SUrar Bubozlde, Ag.Ot?).— Tbe black powder, obtained when n
reiluced in a curreril □( hydrogen ai too°, and potassium hydroxide i< add*
Ibe aqueous sQliiiion of itie residue, is tielieved to have the composltloo A

Silver Chloride, AgCl, is obtained as a while, bulky, 1
precipitate when a soluble chloride is added to silver nitrate. It
melts at 451° to a yellowish liquid, which on cooling, congeals to a
tough homy mass [hence the name Aom silvtr, as applied to the

Silver Fluoride 521

native silver chloride). The precipitated chloride is soluble to a
slight extent in strong hydrochloric acid, but readily soluble in
alkaline chlorides, in ammonia, and in sodium thiosulphate. Potas-
sium cyanide converts silver chloride into silver cyanide, which
dissolves in the excess of alkaline cyanide, forming the double
cyanide KCN,AgCN. When exposed to the light, silver chloride
darkens in colour, assuming first a violet tint, and finally becoming
dark brown or black (see Photo-salts, p. 522).

Silver chloride absorbs large volumes of ammonia, forming the
compound 2AgCl,3NH, (see p. 242).

Silver Bromide, AgBr, is prepared similarly to the chloride,
the precipitated compound having a pale yellow colour. It is less
soluble in ammonia than silver chloride ; in dilute anmionia it is
nearly insoluble. Silver bromide is decomposed by chlorine, and
at a temperature of 100* by hydrochloric acid. At ordinary
temperatures this reaction is reversed, hydrobromic acid convert-
ing silver chloride into the bromide.

Dry silver bromide does not absorb gaseous ammonia. Silver
bromide is extremely sensitive to the action of light, and is tl)e
chief silver compound used in dry-plate photography.

Silver Iodide, Agl, may be obtained by precipitation from silver
nitrate, with a soluble iodide ; or by dissolving silver in strong
hydriodic acid. As obtained by precipitation it is an amorphous
yellow substance, less soluble in ammonia than either the bromide
or chloride. It dissolves in hot hydriodic acid, which on cooling
deposits colourless crystals of AgI,HI ; the addition of water to
the solution precipitates the normal iodide, Agl. Silver iodide
absorbs gaseous ammonia, forming a white compound, 2AgI,NH„
which, on free exposure to the air, evolves ammonia, and is recon-
verted into the yellow iodide.

Silver iodide is the most stable of the three halogen compounds.
When either the chloride or bromide is treated with hydriodic acid
or potassium iodide, iodine replaces the other halogens, forming
silver iodide.

Silver Fluoride, AgF.—This compound is markedly different
in many respects from the other halogen silver salts. It is obtained
by dissolving silver oxide or carbonate in hydrofluoric acid, and
it deposited from the solution in colourless, quadratic pyramids,
AgF,H,0, or in prisms, AgF,2H,0. The salt is extremely deli-
quescent, and very soluble in water. When dried in vacuo, the
salt AgF,H,0 undergoes partial decomposition, leaving a browmsb

residue When heated, it is partiftUy decomposed, a
tilt equation —

SAgF.HjO - 2Ag + SHF 4 H,0 + O.

The dry salt ab-iorbs gaseous anunonia Id lai^e quantities, n
tb:tn 3oo times its own volume being laken up by the powi
subs I a nee.

Sliver Nitrate, AgNO,, is obtained by dissolving ;
nitric acid. It forms large colourless rhombic tables, which n
at Ii8', aod resolidify to a white, Rbrous, crystalline mass, known
as lunar caus/ic. Below a red heal it gives off oxygen, and form*
silver nitrite ; and at higher temperatures it is decomposed into
metallic silver, and oJiides of nitrogen, too parts of water at o'
dissolve T3I.9 parts, and at lOo*, ttio parts of the crystallised
salt \ the solution is neutral. In contact with organic matter,
silver nitrate is biaclcened on exposure to light. Thus, when the
tkin is touched with a solution of this sijt, a few seconds' exposure
to light causes a brown or black slain. Owing to this property,
silver nitrate is employed for marking -inks. Silver nitrate absorbs
gaseous ammonia, forming the compound AgN03,3NHj, the ab-
sorption being accompanied with considerable rise of tempera ttj re
The compound AgNOj,2N Hj is deposited as rhombic prisms when
aqueous silver nitrate is saturated with ammonia.

SllveP Sulphate, Ag^S'ij, is formed when silver, silver carbo-
nate, or silver o^ide is dissolved in sulphuric acid. It crystallises
in rhombic prisms, isomorphous with sodiiun sulphate. With
aluminium sulphate it forms an alum, Id which the monovalent
element silver, tnkes the place of potassium in common alum,
Ag,SO„AI^SO,)„34 H ,0.

PbOtA-aalta.— Tbis name bos Ixxn a.pplied b; Carey Lea, to the coloured
compounds formetl by ihe aciion o( light upon silver cbloride, bromide, and
todide Tbe exact composiiion or tbe cocupounds thai are formed wben these
silvET salts are eipDied Id lighi is not deiinilely known. The change which they
3 Ihe partial reduciion to metallic silvers
luch OS Ag,CI, Ag,Br, wiib elitnination ol
onnatiar. of oiycbloride or oiybromide ;
smpouads oF variable comroallMi, of tbc

undergo has bee

n allribtited

(i>

(al lo [be

fonDflllon of sub-

alls

chlorine

r broi

ine : (3) lo

Ihe

(4) 10 lb

lion of double

lub-»It w

Ihlhe

nomulMlt

Gold $23

GOLD.

Symbol, Aa. Atomic weight s 1(^.8.

Ooeurrenee. — This element occurs in nature almost exclusively
in the uncombined condition, chiefly in quartz veins and in alluvial
deposits formed by the disintegration of auriferous rocks. It is
present in small quantities in many specimens of iron pyrites,
copper pyrites, and many lead ores, from which it is often
profitably extracted.

Gold is also met with in the form of an amalgam with mercury,
and in combination with the element tellurium in the minerals
petzite (AgAu)|Te, and sylvamte (AgAu)Te^

Extraetion. — Gold is extracted from auriferous quartz by caus-
ing the finely-crushed substance to flow, by means of a stream
of water, over amalgamated copper plates. The gold particles
adhere to the merctiry, with which they amalgamate, and the
amalgam so obtained is carefully removed and distilled.

From alluvial deposits, the native gold is separated by me-
chanical washing.

Gold is extracted from auriferous pyrites by means of chlorine.
The ore is first carefully roasted, and, after being wetted, is exposed
to the action of chlorine gas. The gold is thereby converted into
the soluble auric chloride, AuClj, which is extracted by lixiviation,
and precipitated by the addition of ferrous sulphate —

2AuCl, + 6FeS04 - 2Au + Fe^Clg + 2Fe,(S04),.

Native gold usually contains silver, from which it may be sepa-
rated by passing chlorine over the molten metal, in crucibles glazed
with borax. The fused chloride of silver rises to the surface, and
is prevented from volatilising by a covering of melted borax.
When the operation is complete, the crucible is allowed to cool,
when the gold solidifies, and the still liquid silver chloride is
poured off.

The Cyanide Process. — Increasing quantities of gold are at
the present time extracted by solution in potassium cyanide. The
method is specially advantageous in cases where the gold is present
in the ore in a very finely divided condition, and it also possesses
the advantage over the " chlori nation process," that the preliminary
operation of roasting is obviated. The crushed ore is treated with

fnorganic Chemistry

a dilute solution of potassium cyanide {conuining (ram o.i
J per ceol. of poiassimn cyanide), wiih free exposure to the am
phere, since it has been shown that atmosphenc oxygen takes |j
necessary pan in the action. The gold is dissolved in the form fl
a double cyanide, according to tbe equation^

JAti + bKCy + 2H,0 + O, = 4KH0 + 4KAuCy^

Fiom this solution the gold is precipitated either by m
metallic linc (usually in the form of fine turnings) or by electn
lytic dcftosition. The precipitation by means of linc takes placi
according to the equation—

2KAuCy, 4- Zn = K^oCy, + 2Au.

The deposit, after being freed as far as possible from i
melted don-n with a suitable flux, and yields ao alloy cont,
70 to 80 per cent, of gold.

When the gold is precipitated eleclrolytically, llie anodes «
ployed arc of lead foil. These are finally melted down and cupellti^
yielding gold of a high degree of purity.

Properties.— Gold is a soft yellow metal, which, when seen fa
light many limes reflected from its surface, appears red.
acted upon by air or oxygen at any temperature, and does n
decompose steam. No single acid is capable of attacking I
(except selenic acid) ; but it is dissolved by aqua-regia, with li
mation of auric chloride. Cold is the most malleable and 1
of all the metals, and n'hen beaten into very ihin teal^ it a
green by transmitted light.

Gold is moat easily reduced from its combinations.
metals, when placed in a solution of a gold salt, precipitate I
gold, and the most feeble reducing agents bring about the s:
result. On this account a solution of auric chloride ii
lotting photographs. All the compounds of gold, when ignited I|
the air, are reduced to metallic gold. Gold is readily deposit
opon other metals, by the process of electro-gilding, the i
suitable solution being that of the double cyanide of gold 1
potassium, Au(CN)„KCN.

Gold Alloys. — Alloys of gold with copper and with !
are used for coinage, and for ornamental purposes, pure g
being loo soft for these purposes. Silver gives the alloy a
colour than thai of pure gold, while copper imparts lo it a t
tinge- The alloy used for English gold coin consists of g

Gold Sulphides 525

parts ; copper, i part. The proportion of gold in alloys is usually
expressed in parts per 24 (instead of in percentages), these parts
being termed carats. Thus pure gold, is said to be 24-carat gold ;
i8-carat gold contains, therefore, 18 parts of gold, and 6 parts of
copper, or silver. Most countries have their own legal standards.
In England the legal standard for gold coinage is 22-carats.

Oompoandi of Qold. — Gold forms two series of compounds, namely,
aurous^ in which the metal is monovalent, and auric^ in whidi it is trivalent

The composition of aurqiis compounds corresponds to that of the silver
compounds. They are very readily decomposed. Thus, aurous chloride
cannot exist in the presence of water, being decompoised into auric chloride
and metallic gold. For this reason, when aurous oxide. Au^O. is acted upon
by aqueous hydrodiloric acid, it forms auric, and not aurous chloride, thus—

SAujO + 6Ha = 2AuCl, + 3HjO + 4Au.

With iodine, gold forms only aurous iodide, Aul ; therefore, when auric oxide
is acted upon by hydriodic add, aurous iodide and free iodine are formed,
thus —

Au^, + 6HI = 2AuI + 21, + 8H,0.

Anrio Chloride, AuClg, is obtained by dissolving gold in aqua-regia, and
evaporating the solution to dryness. When the residue is dissolv^ in water, the
concentrated solution deposits reddish crystals of the composition AuCl32HsO.
1 hese lose their water when carefully heated, leaving a brown mass of deliques-
cent crystals. Auric chloride forms double chlorides with the alkaline chlorides,
and with hydrochloric acid, which may be obtained as crystalline compounds.
Thus, the compound AuOs,HCl,3HfO is deposited from a strong solution ol
gold in aqua-regia. This substance is sometimes termed cklorxhaurU acid,
and the double compounds with metallic chlorides, such as AuCls,NaQ,2H^
and (AuClj,KCl)iH,0, are known as cAlonhaurates,

Aurlo Oxide, AugO), is obtained as a brown powder, when the h]rdrated
oxide, AugOstSHsO (or Au(HO)t), is gently warmed. At loo* it begins to de
compose, and at higher temperatures is completely converted into oxygen and
metallic gold.

Auric oxide is feebly basic, forming a few unstable salts, in which gold
replaces the hydrogen in acids. It is also a feeble acid-forming oxide, and
forms salts called aurates, such as potassium aurate, KAuOf,3H20, which may
be regarded as being derived from an acid of the composition HAuOj.

Auric oxide forms a compound with ammonia, known as fulminating i^old,
the exact composition of which is not known. It explodes with violence when
dry, if struck, or gently warmed.

Gold Sulphides. — Two sulphides of gold have been obtained, aurous
sulp)iide. Au^S, and auro-auric sulphide, AU|S,Au^ (or AuS). The latter is
formed when sulphuretted hydrogen is passed into a cold solution of auric
chloride—

OAuCl, + 9HaS \ 4H,0 = 2(AU|S,AuaS.) H 24Ha + ^lsSO«.

CHAPTER VI
BLBMBNTS OP GROUP II. (PAMILY A.)

Atomic

■

Atomic

Weights.

Weights

BerylliuMt Be

9.08

Strontium, Sr

87.3

Magnesium, Mg .

. 23.94

Barium, Ba

. X36.86

Caldmn, Ca

. 39-91

With the exception of the rare element beryllium, these metals
were first obtained (although not in the pure state) by Davy, who,
soon alter his discovery of the metals potassium and sodium,
showed that the so-called earths were not elementary bodies as
had been supposed, but were compounds of diflferent metals with
oxygen.

The element beryllium is of later discovery, for although as
early as 1798 it had been shown by Vanquelin that the particular
" earth " in the mineral beryl was different from any other known
earth, it was not until 1827 that the metal it contained was iso-
lated by Wohler. In a state approaching to purity, beryllium was
first prepared by Humpidge, 1885.

None of the elements of this family occurs in nature in the un-
combined condition ; and, with the exception of magnesium, the
metals themselves, in their isolated condition, are at present little
more than chemical curiosities. In the case of beryllium this is
due to the comparative rarity of its compounds ; but with calcium,
strontium, and barium, whose compounds are extremely abundant,
it is owing partly to the difficulty of isolating the metals in a pure
state, and also to the fact that hitherto they have received no
useful application. Beryllium and magnesium are white metals,
which retain their lustre in the air. Calcium, strontium, and
barium have a yellow colour, and on exposure to air become
converted into oxide.

All these metals form an oxide of the type RO. Beryllium oxide
is insoluble in water ; magnesium oxide is very slightly soluble
(i part in 55,000 or 100,000 parts of water), but the solution

Metals of ttu Alkaiim Earths 527

shows a feeble alkaline reaction. The calcium, strontium, and
barium oxides show increasing solubility, and stronger alkalinity
and causticity. On this account these elements are known as the
metals of the alkaline earths. These three elements also form
peroxides of the type R0|.

All the monoxides are basic, and combine with acids to form
salts of the types RC1„ RSO4, R(NO,),.

The element beryllium (the typical element) stands apart from
the others of this family in many of itd chemical relations. Thus,
the oxide BeO, unlike the corresponding compounds of the other
elements, does not combine with water to form the hydroxide.
The hydroxide Be(HO)) is soluble in sodium and potassium
hydroxide. In this respect beryllium exhibits its resemblance to
zinc The chloride also differs from the other chlorides in being
volatile.

In its permanence in air, its colour, its high melting-point, the
solubility of its sulphate, and the readiness with which its hydroxide
is converted by heat into the oxide, beryllium exhibits a close
similarity to magnesium. In the solubility of its hydroxide in
potassium hydroxide, and in its inability to decompose water,
beryllium also shows a marked resemblance to zinc

The three elements, calcium, strontium, and barium, exhibit
a closer resemblance to each other in most of the physical and
chemical relations, than to either magnesium or beryllium.

They are readily distinguished by their different spectra.
Barium salts, when heated in a non-luminous flame, impart to
it a green colour. Calcium and strontium, under the same cir-
cumstances, each give a red colour ; but the red imparted by
strontium compounds is more brilliant, and less orange, than that
of calcium salts. When the flames are examined by the spectro-
scope, the most characteristic lines given by barium, are two in the
bright green (Baa and Ba^). These are accompanied by a number
of less brilliant lines. The spectrum of strontium consists of four
specially prominent lines, one in the bright blue (Srd), one in the
orange (Sra), and two in the red (Sr/9 and Sry), with others less
pronounced ; while that of calcium contains one brilliant green
line (Ca^X and one equally brilliant orange line (Caa), t>esidrs a
large number of less prominent lines.

$28 Inorganic Chemistry

BEBTLUUM.

Sjmbol, Be. Atomic weight s 9.08.

Ooeomnoe. — This element occurs princifAlly in the mineral heryit a dodUfe
silicate of the composition 3BeO,Al30^.6SiO|. The transparent nurieties are
used as gems, the transparent green beryl being the precious twuraU,

PktnaciU is beryllium silicate, Be|Si04, while ckrysoUryl has the compo-
sition BeO.Al^Os.

Formatloii.~The element b obtained by heating sodium in the vapour of
beryllitun chloride, all air having been prevtously replaced by hjrdrogen. The
product is afterwards melted beneath fused sodium chloride, when it is
obtained as a coherent of solid metal.

PropertieB. — Beryllium is a white metal resembling magnesium. It has a
specific gravity of a.x, and is moderately malleable. It does not readily
tarnish in the air at ordinary temperatures, but, when strongly heated,
becomes coated with a protecting film of oxide. The powdered metal, when
heated, takes fire, and bums with a bright light It has no action upon
water, even at the boiling temperature.

Beryllium is easily dissolved by dilute hydrochloric acid, with evolution of
hydrogen. Cold dilute sulphuric add is without action, but, when heated,
slowly dissolves it. Nitric acid slowly attacks it when concentrated and hot.
It readily dissolves in potassium hydroxide, with evolution of hydrogen.

Beryllium Compounds.— The best known are the oxide {berylla), BeO, a
white infusible powder, insoluble in water, soluble in acids; the chloride,
BeCI^, obtained by heating the oxide with charcoal in a stream of chlorine, a
white OTstallinc solid, readily fused and volatilised.

Beryllium compounds do not impart any colour to a Bunsen flnme. The>
are characterised by possessing a sweet taste, tience the name o( glucinum
originally given to this element.

MAGNESIUM.

Symbol, Mg. Atomic weight =93.94.

OcCUFFence. — Magnesium is not found in the uncombined state
In combination it is widely distributed, and is extremely abundant.
In the mineral dolomite^ associated with lime as carbonate, it
occurs in mountainous masses.

MagTiesite^ MgCOj ; kieserite, MgS04.H20 ; carnailite^ MgClt,
KCljGHjO, are amongst the commoner naturally occurring magne-
sium compounds. It is also a constituent of <isbestos^ meerschaum^
serpentine^ taiCy and a large number of other silicates. As sulphate
and chloride it is met with in sea water and many saline springs.

Modes of Formation. — Magnesium can be obtained by the

Magnesium Oxide 529

electrolysis of the (used chloride, or a mixture ol magnesium and
potassium chlorides.

On a larger scale magnesium is prepared by reducing the chloride
with sodium. A mixture of anhydrous magnesium chloride (or
fused mixed chlorides of magnesium and sodium, or potassium),
powdered cryolite, and sodium is thrown into a red-hot crucible,
which is quickly closed. A violent reaction takes place, at the
conclusion of which the melted mixture is stirred with an iron rod
to cause the globules of magnesium to run together.

The crude metal is afterwards purified by distillation.

Properties. — Magnesium is a silvery-white metal, which does
not tarnish in dry air, but becomes coated with a film of oxide
when exposed to air and moisture. At a red heat it melts, and at
higher temperatures may be distilled. When heated in the air it
takes fire, and bums with a dazzling white light, which is extremely
rich in the chemically active rays. The flash of light, obtained by
projecting a small quantity of magnesium filings into a spirit flame,
is used for photographic purposes. Magnesium is only moderately
malleable, and is only ductile at high temperatures ; it is readily
pressed into the form of wire at a temperature slightly below its
melting-point Magnesium only slightly decomposes water even at
the boiling-point ; but M^ien strongly heated in a current of steam, the
metal takes fire (p. 152). Magnesium is rapidly dissolved by dilute
acids, with brisk evolution of hydrogen, but solutions of caustic
alkahes are unacted upon by it (compare Zinc). When heated with
aqueous solutions of ammonium salts, hydrogen is evolved, and a
double salt of magnesium and ammonium is found in the solution.

Magnesium combines directly with nitrogen, when strongly
heated in that gas, forming magnesium nitride, N^Mgj (p. 208).

On account of the brilliant light emitted by burning magnesium,
it is employed for signalling purposes, and also in pyrotechny.

Magnesium Oxide {magnesia)^ MgO, is found native as the
nixTktxdX periclase. It is formed when magnesium bums in the air,
or when magnesium carbonate is submitted to prolonged gentle
calcination, when it is obtained as a white, bulky powder, known in
commerce as calcined maf^nesia or fna^;nesia usta.

Magnesia is extensively manufactured from the magnesiiun
chloride occurring in the Stassfurt deposits, by first converting the
chloride into carbonate, and subjecting this to calcination. Mag-
nesia has been obtained in the crystalline form, identical with that
of peridase, by heating the amorphous compound in a stream of

2 L

530 Inorganic Chemistry

gaseous hydrochloric acid. It may be fused in the ozyhydrogen
flame, and on cooling, it solidifies to a vitreous mass which is suffi-
ciently hard to cut glass. On account of its extreme refnu:toruiess«
magnesia is used for a variety of metallurgical purposes, such as
the manufacture of crucibles, cupels, &c

Magnesium Hydroxide, Mg(HO)s, is found in nature as the
mineral bruciie. It is prepared by precipitating a magnesium salt
by sodium or potassium hydroxide. At a dull red heat it loses
water, and is converted into the oxide, and the magnesia so
obtained has the property of rehydrating itself in contact with
water, with evolution of heat.

Magnesium hydroxide slowly absorbs carbon dioxide, fomriing
the carbonate ; owing to this fact, and to the property it possesses
of rehydration, magnesia that has been prepared by calcination at
a low temperature can be employed as a cement. Thus, if calcined
magnesite be made into a paste with water, the mixture is found to
harden in about twelve hours, and ultimately to acquire a hardness
equal to that of Portland cement.

Magnesium Chloride, MgClj.— This salt is formed when mag-
nesia, or magnesium carbonate, or the metal itself, is dissolved in
hydrochloric acid. From this solution monosymmetric crystals of
the composition MgCl2,6H,0 are deposited. When this salt is
heated it loses water, and at the same time is partially decomposed
into hydrochloric acid and magnesia ; in order, therefore, to pre-
pare the pure anhydrous compound, the double magnesium ammo-
nium chloride is first formed, by adding ammonium chloride to a
solution of magnesium chloride. On evaporation, the double salt
separates out, MgC]2,NH4Cl,6HsO. This salt allows itself to be
dehydrated by heating, without any decomposition of the magne-
sium chloride. When the dried salt is more strongly heated,
ammonium chloride volatilises and leaves the anhydrous magnesium
chloride as a fused mass, which congeals to a white crystalline
solid. Magnesium chloride is deliquescent, and dissolves in water
with evolution of heat With alkaline chlorides it forms double
salts, as the ammonium salt above mentioned. The potassium
salt, MgCl2,KCl,6HsO, occurs in large quantities as the mineral
camallite ; and the calcium salt, 2MgCl2CaCl2,12HgO, as tachydrite^
in the Siassflirt deposits. When a strong solution of magnesium
chloride is made into a thick paste with calcined magnesia, the
mass quickly sets and hardens, like plaster of Paris, and is found
to contain an oxychloride having the composition MgCl^fiMgO,

Afagnesium Sulphate 531

associated with varying quantities of water. The white deposit
which forms in bottles containing the solution known as magnesia
mixture^ consists of MgClj,BMgO,13H|0.

When magnesium oxychloride is heated to redness in a current
of air, the magnesium is converted into oxide, and a mixture of
chlorine and hydrochloric acid is evolved. The reaction may be
represented as taking place as follows —

2MgCl, + H,0 -f O - 2MgO + 2HC1 + CI3,

The Weldon-Pechiney process for manufacturing chlorine is
based upon this reaction.

Magnesium Sulphate, MgSOf {Epsom salts\ is met with in
many mineral springs, and in large quantities as the mineral
kieserite^ MgS04,HjO.

Magnesium sulphate nuiy be obtained by decomposing dolomite^
(CaiMg)COti with sulphuric add, the nearly insoluble calcium
sulphate being readily removed from the soluble magnesium salt
Magnesium sulphate is now very largely manufactured from
kieserite^ which in contact with water is converted from the slightly
soluble monohydrated salt, into MgSOfjTHgO, which is readily
soluble, and is purified by recrystallisation. As usually obtained,
crystallised magnesium sulphate, MgS04,7H|0, forms colourless
rhombic prisms ; but when deposited from a cold supersaturated
solution, it sometimes forms prisms belonging to the monosymmetric
(monoclinic) system, having the same degree of hydration. Above
50^ monosynunetric prisms of the composition MgS04,6H20 are
deposited.

When the ordinary salt, MgSOijTHgO, is placed over sulphuric
acid, it loses two molecules of water : when heated to iso"" it loses
six molecules, and at 200* it becomes anhydrous. At the ordinary
temperature, 100 parts of water dissolve 126 parts of crystallised
magnesium sulphate ; the solution has a bitter taste, and acts as a
purgative. With alkaline sulphates, magnesium sulphate forms a
series of double salts, having the general formula MgS04,R2S04,
6H)0. They are isomorphous with each other, crystallising in
monosymmetric prisms. The potassitun salt occurs in the Stassfurt
deposits as schonite.

When anhydrous magnesium sulphate is dissolved in hot sul-
phuric acid, two acid sulphates are obtained. One, having the com-
position MgS04,HaS0«, is deposited from the hot solution : whila

Inorganic Chemistry

from the cold liquid ihe salt that crystallises has ihe compositl
Mj;SO„3H.SO,. They are at once decomposed by water

Magnesium Carbonate, MgCOj, occurs as the mineral ntagnt-
site, which is sometimes found as rhomboliedral crystals, isomor-
phous with crystals of calciU (CaCO,). Magnesium exhibits ■
great tendency to form basic and hydraled carbonates ; the normal
carbonate, MgCO,, is therefore not obtained by precipitating a
magnesium sail with an alkaline carbonate ; the white predpitaie
formed under these circumstances is a basic carbonate, whose
composition varies with the conditions of precipitation. \l, how-
ever, this precipitate be suspended in water, and the liquid saturated
with carbon dioxide, the compound dissolves (more readily under
increased pressure), and when the solution is healed to 300° under
pressure, in such a manner that the evolved carbon dioxide caji
escape, the normal anhydrous carbonate is deposited in rhombo-
hedral crystals isomorphous with calcite. If the solution be
evaporated to dryness, the normal carbonate is deposited in
rhombic crystals isomorphous with arragomU (CaCOj). Mag-
nesium and calcium carbonates are therefore isodimorphous.

Basic Carbonates.— The mineral hydrotnagnesite is a basic
carbonate of the composition 3MgCOj,Mg(HO),,3HjO. A numbei
of basic carbonates are formed by the precipitation of a magnesium
salt with sodium carbonate. Thus, under ordinary conditions a
white bulky precipitate is obtained, known in pharmacy as »io^wy»a
alba levis. Its composition, although liable to vary through the
presence of other basic carbonates, is in the main the same as that
of hydromagnesile.

If the predpilalion be made with boiling solutions, and the pre^
cipitate so obtained be dried at 100°, a denser carbonate is ob-
tained, termed magnesia alba pondtroia, 4MgCOj,Mg(HO)„4H,0.

When an excess of sodium carbonate is employed, and tl»_
mixture is subjected to prolonged boiling, a carbonate is obtains;'
having the composition 2MgC03,Mg(HO)„ZH,0.

CALCmu

Symbol, Ca. Atomic weigbt — 39.91.

Occurrence.— Calcium is only met with in nature in combini^

tion. It occurs in enormous quantities as the carbonate, in a

variety of different minerals, such as iiiarblt^ timtstone., calcspar

and also a* coral; and with carbonate of magnesia as dolomiit, s

Calcium Oxidg 533

wtagmsian limestone. In combination with sulphoric acid, calcium
occurs as gypsutn and selenite^ CaS04,2H|0, and as anhydrite^
CaS04. The fluoride CaF, occurs as fluorspar; and ihc various
siltcious rocks contain compound silicates of calcium and other
metals. The carbonate and sulphate are present in most spring
and river waters. Calcium compounds are also present in all
vegetable and animal organisms. Thus, bones consist largely of
calcium phosphate.

Modes of Formation. — Although calcium compounds are so
extremely abundant, the element itself is a rare substance. The
element was first isolated in an impure state by Davy (1808). It
may be obtained by the electrolysis of the fused chloride, or by
fusing together calcium chloride, sodium, and zinc, when an alloy
of zinc and calcium is obtained, from which the zinc is removed by
distillation.

Properties. — Calcium is a yellow metal, somewhat the colour
of pale brass. It is sufficiently hard to be worked with a file, and
may be hammered out into leaf. In moist air it is soon converted
into the hydroxide, but in dry air it remains untarnished for a con-
siderable time. It decomposes water at the ordinary temperature,
with rapid evolution of hydrogen. When heated in the air, it takes
fire and bums.

Oxides of Calcium. — Two oxides are known, namely, calcium
monoxide, CaO, and calcium dioxide, CaO].

Calcium Oxide {lime^ quicklime)^ CaO, is obtained by heating
calcium carbonate to redness —

CaCO, - CO, + CaO.

0*1 a large scale, lime is manufactured by burning limestone or
chalk in kilns with coal. If much clay be present with the lime-
stone, care is required to prevent the mass from fusing, when it is
said to be dead burnt. Lime is a white amorphous substance^
which is infusible by the oxyhydrogen flame ; but which, when so
heated, emits a bright light, known as the oxyhydrogen lime-light
It absorbs moisture and carbon dioxide from the air. On account
of its power of absorbing moisture, lime is frequendy employed as
a dehydrating agent Thus, gases which cannot be dried by means
of sulphuric acid {e,g,^ ammonia) may be deprived of moisture by
being passed over calcium oxide. It is also used for withdrawing
water from alcohol, in the preparation of absolute alcohol When

534 Inorganic Chemistry

a small quantity of water is poured upon liuie, the mass rapidly
becomes hot, and volumes of steam are given off; the lime at the
same time swelling up and crumbling to a soft, dry powder. This
process is known as the slaking of lime, and the product is termed
slaked lime^ in contradistinction to quick lime. The lime enters
into chemical union with water, forming calcium hydroxide, thus —

CaO + H,0 - Ca(HO),.

Calcium Hydroxide, Ca(H0)3, is a white amorphous powder,
sparingly soluble in water ; and, unlike the majority of solids, it is
less soluble in hot than in cold water. One hundred parts of water
at the ordinary temperature dissolve a 14 parts of calcium hydroxide,
while at 100" the same voltmie of water dissolves about half that
amount. This solution, known as lime waUr^ has an alkaline
reaction, and absorbs carbon dioxide, with the precipitation of
calcium carbonate.

Milk of Lime is the name given to a mixture of lime with less
water than will dissolve it, whereby an emulsion of lime is obtained.
\^'llen a thick paste of lime and water is exposed to the atmos-
phere, in a few days it sets, and continues gradually to harden.
On this account lime is used for mortars and cements. Mortar
consists of a mixture of lime and sand with water. The sand
serves the double purpose of preventing shrinkage on drying, and
also of rendering the mass more permeable to atmospheric carbon
dioxide. The setting of mortar is due to the combined action of
evaporation and absorption of carbon dioxide.

Calcium Dioxide, CaOs, is obtained by adding lime-water to
hydrogen peroxide, or to sodiimi peroxide acidulated with dilute
nitric acid : sparingly soluble crystals of CaOjjSHjO separate out,
which at 130" lose their water. When more strongly heated, the
monoxide is formed, with evolution of oxygen.

Calcium Chloride, CaClj, occurs in sea and river waters, and is
present in carnal iiU and tacky drite^ of the Stassfurt deposits. It
is obtained in large quantities as a bye-product in many manu-
facturing processes, such as that of potassium chlorate, ammonia
from ammonium chloride, &c It may be obtained by the action
of hydrochloric acid upon calcium carbonate, and is deposited on
concentration, in large colourless, deliquescent, hexagonal prisms,
CaCljjjCHjO, which melt at 29* in their water of crystallisation.
When heated below 200*, the crystals part with four molecules of

BUaching-PoiMHier 535

water, and above 200^ become anhydrous. As thus obtained, the
anhydrous salt is a porous mass, which is extremely hygroscopic,
and on this account is used as a desiccating agent, both for gases
and liquids. At a red heat it fuses, and on cooling, solidifies to a
crystalline, deliquescent mass. Calcium chloride combines with
ammonia, forming the compound CaCl^dNH,. Calcium chloride,
therefore, cannot be employed for drying gaseous ammonia.

Crystallised calcium chloride is extremely soluble in water ;
100 parts of water at 16* dissolve 400 parts of the salt, the solu-
tion being attended with considerable absorption of heat When
mixed with powdered ice, or snow, liquefaction of both the solids
rapidly takes place (owing to the formation of a cryohydrate), and
the consequent absorption of heat, lowers the temperature of the
mixture to - 40*.

Bleachlnff-Powder {chlaridg of lime\ Ca(OCl)CL— This im-
portant compound is manufactured on a large scale by the action
of chlorine upon slaked lime. The hydrated lime is spread upon
the floor of the bleaching-powder chambers to a depth of three or
four inches, and raked into ridges or furrows with a special wooden
rake. Chlorine is then led into the chambers, which are provided
with glass windows to enable the operator to examine the colour
of the atmosphere within. At first the absorption of the chlorine is
rapid, but as the reaction proceeds it becomes slower, and the lime
is from time to time raked over to expose a fresh surface. The
lime is left in contact with the gas for twelve to twenty-four hours.
The excess of chlorine is absorbed by projecting into the chamber
a shower of fine lime-dust, by means of a mechanical fan-distributor.
This, in settling, rapidly absorbs all the chlorine, and the chambers
can then be opened without any unpleasant smell of chlorine being
perceptible.

The reaction which takes place is expressed by the equation—

Ca(HO), + CI, - Ca(OCl)Cl -H H,0.

It was formerly believed that bleaching-powder was a mechani-
cal mixture of calcium chloride, CaCl„ and calcium hypochlorite,
Ca(OCl)„ but it has been conclusively shown that the substance
does not contain any free calcium chloride. It may, however, be
regarded as a compound consisting of equivalent proportions of
these two salts, and its composition may be expressed by the for-
mula Ca(OCl)„CaCl„ which corresponds to 2Ca(0Cl)CL

S36 Inorganic Chemistry

The relation in which bleaching-powder stands to calcium chlo-
ride on the one hand, and calcium hypochlorite on the other. wiU
be seen by the following formulae —

Cddum Chloride. C*Id«m Hypochlorif. CiagS;fSff<JSS:^^

CI— Ca— CI CIO— Ca—OCl CI— Ca— OCL

In practice, the absorption of chlorine by the lime is never as
complete as is represented by the above equation, and the com-
mercial value of the product depends upon the amount of availadU
chlorine it contains, f>., chlorine which is evolved on treating the
compound with hydrochloric l>r sulphuric acid. This ranges from
30 to 38 per cent

When treated with water, bleaching-powder is converted into
calcium chloride and hypochlorite, thus —

2Ca(OCl)Cl - CaCl, + Ca(OCl)^

Bleaching-powder decomposes slowly even in stoppered bottles,
and more rapidly on exposure to atmospheric moisture and carbon
dioxide.

When acted upon by acids, chlorine is evolved, thus —

Ca(OCl)Cl + 2HC1 = CaCl, + HjO + CI,
Ca(OCl)Cl -f H,S04 = CaS04 + H,0 + CI,.

When a solution of bleaching-powder is treated with very dilute
acids, hypochlorous acid is first liberated, which in contact with
hydrochloric acid yields chlorine —

(i) Ca(0Cl)2.Aq + 2HCl.Aq = CaCl, + 2HC10.Aq.
(2) HCIO + HCl - H,0 + CI,.

In the process of bleaching, the material is first steeped in a
dilute solution of bleaching-powder, and then in dilute acid. The
hypochlorous acid first formed is decomposed in the presence of
excess of hydrochloric acid, generating chlorine within the fibres
of the wet cloth.

Calcium Sulphate, CaS04, occurs as the mineral anhydrite^
and in the hydrated condition as gyPsum, CaS04,2H,0, of which
satinspar (or fibrous gypsum\ alabaster^ and selenite are different
varieties. It is obtained in the hydrated condition by precipita-

Ccdcium Carbonate 537

tion from a solution of calcium chloride, on the addition of sul-
phuric acid or a soluble sulphate. When dried at no* to 120* it
loses a portion of its water, leaving the hydrate, (CaS04)j,H,0 ; at
200"" it becomes anhydrous. Calcium sulphate, in the hydrated
condition, is slightly soluble in water, the solubility reaching a
maximiun at 35*, when i part of the compound requires 432 parts
of water for its solution ; above this temperature the solubility
again diminishes. Its solubility is increased by the presence of
alkaline chlorides and free hydrochloric acid.

When boiled in strong sulphuric acid, calcitun sulphate partially
dissolves, and on cooling, an acid sulphate crystallises out, having
the composition CaS04,H|S04.

Plaster of Paris is calcium sulphate which has been partially
deprived of its water of hydration by heat, and converted into the
hydrate, (CaS04)sH|0. It is manufactured by burning gypsum in
a kiln, or oven, in such a way that the carbonaceous fuel does
not come in contact with the sulphate, which would result in its
reduction to sulphide ; the temperature is not allowed to exceed
about 130^ If heated more strongly (above 200'') the sulphate
becomes anhydrous, and is said to be decui burnt; in this con-
dition its property of setting when mixed with water is greatly
impaired. When plaster of Paris is made into a paste with water,
it rapidly sets to a hard mass : this setting is due to its rehydra-
tion, whereby gypsum is reformed, thus —

(CaS04)„H80 -H 3H,0 = 2CaS04,2H80.

Calcium Carbonate: CaCO,.~This compound is extensively
met with in nature, as limestone^ chalky marble^ and innmnerable
varieties of calcspar. It is formed when lime is exposed to atmos-
pheric carbon dioxide. It is obtained when an alkaline carbonate
is added to a soluble calcium salt

Calcium carbonate is dimorphous ; it occurs as arragoniti in
crystals belonging to the rhombic system, and as calcspar in
crystals belonging to the hexagonal system. Both these crystal-
line varieties can be artificially obtained : when deposited from
solutions at the ordinary temperature, the crystals are identical
with calcite ; but when crystallised from hot solutions, they form
rhombic crystals corresponding to arragonite.

Calcium carbonate is nearly msoluble in water ; 1000 grammes
of water dissolve .0018 grammes of the compound. It is more

538 Inorganic Chemistry

soluble in water charged with carbon dioxide, forming the add
carbonate of lime, CaCO^HiCO,, or H,Ca(CO,},.

looo grammes of water saturated with carbon dioxide will dis-
solve, at o^ o.y grammes of calcium carbonate. By increasing the
pressure (thereby increasing the amount of dissolved gas) as much
as 3 grammes of caldum carbonate may be dissolved. When this
solution is boiled, the acid carbonate is decomposed (p. 197).

Calcium Phosphate [friccUcium orthophospkaie\ C9lJ^VO^ is
the most important of the phosphates of calcium. It is foimd as
the mineral ostedite^ Ca3(P04^2H|0, and also as sombrerite^
estramadurite^ and coprolitis, Ap<UiU consists of phosphate and
fluoride, 3Cas(P04)s,CaFs ; and the mineral constituents of bones
consist chiefly of calcium phosphate.

It is obtained in a pure state by the addition of ordinary sodium
phosphate to a solution of calcium chloride, in the presence of
ammonia. The precipitate is decomposed on boiling, into an
insoluble basic salt, and a soluble acid salt Although nearly
insoluble in pure water, calcium phosphate dissolves in water con-
taining salts in solution, such as sodium chloride or nitrate, or
even dissolved carbon dioxide. On this fact depends the readi-
ness with which this substance is absorbed by the roots of
plants.

Calcium phosphate is readily soluble in both nitric and hydro-
chloric acids. It is decomposed by sulphuric acid, with the forma-
tion of monocalcium onhophosphaie and calcium sulphate, thus —

Ca8(P04)j -H 2H,S04 = 2CaS04 + H4Ca(P04)j.

This mixture of calcium sulphate and monocalcium phosphate
is known as superphosphate of lime^ and is largely used as an arti-
ficial manure.

With a larger quantity of sulphuric acid, the phosphate is con-
verted into tribasic phosphoric acid. (See Phosphorus, p. 414.)

Calcium Sulphide, CaS, is formed when sulphuretted hydrogen
is passed over heated lime —

Ca(H0)2 -I- H^S - CaS -H 2H,0

Or by heating calcium sulphate with carbon —

CaSO^ -f 4C - CaS + 4CO.

Strontium 539

Calcium sulphide is decomposed on boiling with water, forming
calcium hydroxide and hydrosulphide, thus —

2CaS -»- 2H,0 = Ca(HO), + Ca(HS),.

Calcium sulphide (in conunon with barium and strontium sul-
phides), as usually obtained^ possesses the property of emitting a
feeble light (or phosphorescence) in the dark, after being previously
exposed to a bright light The light emitted gradually diminishes
in intensity, but on re-exposing the compound to the light, its
luminosity is again restored. This property has *ieen long known,
and calcium sulphide was formerly termed Cahloris phosphorus.
The material formerly known as Bononian (or Bologniaii) phos-
phorus is the corresponding barium compound.

These varioos sulphides ar6 now manufactured for the preparation of
so-called luminous paint. The pbosphoresoenoe of these compounds appears
to be due to the presence of small quantities of foreign substances ; thus, not
only is the particular colour of the light emitted changed by the intentional
introduction of minute traces of bismuth, cadmium, manganese, dnc, and
many other metals, but it has been shown, in the case of calcium sulphide,
that the perfectly pure substance does not exhibit phosphorescence.

STBONTnTH.
Formula, Sr. Atomic weight =87.3.

Occurrence. — The chief natural compounds of this element are
strontianite^ SrCOs, and celesHne^ SrS04.

Modes of Formation.— The metal was first obtained in snuUl
quantity by Davy, by the electrolysis of the hydroxide, or chloride,
moistened with water.

It is more advantageously obtained by electrolysing the fused
chloride. An amalgam of mercury and strontium (from which the
strontium may be separated by volatilising the mercury in a stream
of hydrogen) has been obtained by heating a saturated solution of
strontium chloride with sodium amalgam.

Properties. — Strontium is a yellowish metal resembling calciimi.
It is readily oxidised by air, and decomposes water at ordinary
temperatures ; when heated in the air it bums brilliantly.

Oxides of Strontium. —Two oxides, corresponding to those of
calcium, are known, namely, strontium monoxide, SrO, and dioxide,
SrO,.

Strontium Monoxide {strontia), SrO, is obtained by heating the

540

Inorganic Chemistry

nitrate or carbonale, It is prepared on a Urge si^alc by decompos-
ing 5ironlium carbonalc by superheaied steam ; carbon dioxide ia
evolved, and strontium hydroxide remains, which on ignition forms
the monoxide, Slrontia strongly resembles lime. When treated
with water ii slakes with evolution of heal, formin
hydroxide, Sr(HO)». The hydroxide is more soluble it
the lime compound, and the solution on cooling deposits quadratic
crystals, Sr(HO)„8HjO. The solution is strongly alkaline.

Strontium hydroxide combines with sugar, forming a saccharate
of slrontia, which is readily decomposed by carbon dioxide. On
this account it is prepared on a large scale for use in the manu-
facture of beet-sugar. One process by which it is obtained on a
commercial scaJe, consists in first forming strontium sulphide^ by
reducing the natural sulphate with carbon, and treating the solution
of the sulphide with sodium hydroxide, thus^

SrS -1- NaHO -^ H,0 - Sr(HO}j + NaHS.

Strontlam Dioxide, SrO,,— When hydrogen peroxide is added
to a solution of strontium hydrnxide, a hydrate of the peroxide
•eparales out in the form of pearly crystals, SrO^SHjO. On gently
healing this compound, it is converted into the anhydrous peroxide.
On heating to redness it evolves oxygen, and is convened into the
monoxide.

Strontium Chloride, SrCI^ is obtained from strontianite by the -
action of hydrochloric acid. The salt deposits from the solution in
deliquescent hexafjonal prisms, SrClj.6H,0, isomorphous with the
corresponding calcium compound.

Strontium Sulphate, SrSOj.— The native compound ctUstint
occurs in amorphous fibrous masses, and also in rhombic crystals
The name of the mitier:il is derived from the fact that it usually
has a light-blue colour. It ts produced by precipitation from a
strontium salt by sulphuric acid. It is only slightly soluble in cold
water, and still less in hot. When boiled with solutions of alkali
carbonates, strontium sulphate is completely converted into Stron*
tium carbonate —

SrSO, -1- Na,CO, = SrCOj + NajSO,.

In this respect strontium sulph.ile diifecs from barium sulphalct'
which under these conditions remains unchanged. On iieatmcnt
with strong sulphuric acid, strontium sii'phale forms SrSOj.HiSO,,

Barium 541

which, like the corresponding calcium compound, is converted by
water into sulphuric acid and the normal sulphate.

Strontium Nitrate, Sr(NOs)» is obtained by dissolving the
natural carbonate in dilute nitric acid. On concentration, the
anhydrous salt separates out in regular octahedrons. From dilute
solution, on cooling, it forms monosymmetric prisms, Sr(N03)j,
4H,0, which effloresce on exposure to the air. When heated with
carbon, or other readily combustible substances, the mixture in-
flames, and bums with the red colour characteristic of strontium
compounds ; strontium nitrate is therefore largely used in pyro-
techny for the production of red fire. This property is most
readily illustrated by mixing dry powdered strontium nitrate with
ammonium picrate, and igniting the mixture, which bums with a
brilliant red light

RARIUK.

Symbol, Ba. Atomic weight — 136.86.

Occurrence. — The most abundant natural compounds of barium
are heavy spar^ BaSOi, and witherite^ BaCOs- It occurs also,
associated with calciimi, in the mineral barytocalcitiy BaC03,CaCOf

Modes of Formation. — ^The element barium is more difficult to isolate than
either strontium qk caldum. and it is doubtful whether pure barium has ever
txren obtained. Davy electrolysed various barium salts, made into a thick
paste with water, using mercury as the negative electrode: in this way an
amalgam of barium was formed, from which, on distilling away the mercury,
a dark porous mass was obtained. Amalgams of tiarium and mercury have
been prepared in other ways, but it has been shown that the product obtained
after distilling the mercury from these, is not pure barium, but is a solid alloy
or compound of barium with mercury.

By the electrolysis of the fused chloride, Matthiessen obtained small globules
of metal, which on exposure to the air rapidly oxidised. More recent experi-
menters fail to obtain the metal by this process (Limb., compt, rtnd^^ iia).

Oxides of Barium. — Two oxides are known, namely, barium
monoxide, BaO, and dioxide, BaOj.

Barium Monoxide {baryta\ BaO, is usually prepared by heat-
ing the nitrate. The mass fuses and evolves oxygen and oxides of
nitrogen, leaving a greyish white friable residue of the oxide. It
may also be obtained by heating the carbonate ; but as the tem-
perature necessary to expel the carbon dioxide is very high, it is
usual to mix the carbonate with lampblack, lar, or other sub-

542 Inorganic Chemistry

stances which on heating will yield carbon, when the converaiop
takes place more readily, carbon monoxide being evolved, thus —

BaCO, + C = BaO + 2CO.

Small quantities may readily be obtained by heating barium
iodate in a porcelain crucible, when the iodate is decomposed as
follows —

Ba(IO,), -= BaO + I, + 60.

Barium oxide is a strongly caustic and alkaline compound ; in
contact with water it slakes with evolution of so much heat, that
the mass may become visibly red hot if too much water be not
added.

When heated to a dull red heat in oxygen, or air, it takes up an
additional atom of oxygen and forms the dioxide (see p. 162).

Barium Hydroxide, Ba(H0)2, ^s obtained when the monoxide
is slaked with water. It is manufactured by first heating the
powdered native sulphate with coal, when a crude barium sulphide
is formed. This is then heated in a stream of moist carbon
dioxide, whereby it is converted into the carbonate, and super-
heated steam is then passed over the heated carbonate —

BaS + H,0 + CO, = BaCOa + H,S
BaCOj + H2O « Ba(H0)8 + COj,

Barium hydroxide is soluble in water : the solution, known as
baryta-water^ absorbs carbon dioxide with the precipitation of
barium carbonate.

The aqueous solution deposits crystals of hydrated barium
hydroxide, Ba(HO)2,8H,0, in the form of colourless quadratic
prisms, which on exposure to the air lose seven molecules of water.

Barium hydroxide, when heated in a current of air, yields barium
dioxide.

Barium hydroxide was formerly employed in sugar-refining, but
owing 10 its poisonous nature it has been superseded by strontium
hydroxide (^.v.).

Barium Dioxide {barium peroxide), BaOjj. — This oxide is
obtained by heating the monoxide to a low red heat in a stream of
oxygen, or of air which has been deprived of atmospheric carbon
dioxide.

The pure compound may be obtained by adding an excess of

Barium Chloride 543

baryt;i-water to hydrogen peroxide, when hydrated barium per-
oxide separates out in crystalline scales —

Ba(HO), + HjOa + 6H,0 = naO„8H,0.

On drying in vacuo at 130* this compound loses water and is
converted into the anhydrous peroxide.

The commercial peroxide may be purified by treatment with
dilute hydrochloric acid, whereby barium chloride and hydrogen
peroxide are formed. After the removal of insoluble impurities by
filtration, baryta-water is cautiously added, which causes the pre-
cipitation of ferric oxide and silica. The liquid is then filtered,
and to the clear liquid, consisting of a solution of barium chloride
and hydrogen peroxide, an excess of strong baryta-water is added,
when the hydrated barium peroxide is precipitated, as already
explained.

Barium peroxide is a grey powder, which on being heated to a
bright red heat gives up oxygen and forms the monoxide (p. 162).

Dilute acids decompose barium peroxide, with formation of
hydrogen peroxide and a barium salt. Concentrated sulphuric
acid forms barium sulphate and ozonised oxygen. When gently
warmed in a stream of sulphur dioxide, the mass becomes incan-
descent and forms barium sulphate —

BaO, + SO, = BaSO|.

Barium Chloride, BaCl,, may be obtained by dissolving the
natural carbonate in hydrochloric acid. It may be obtained from
the natural sulphate, either by first co/iverting it into the sulphide,
and decomposing that with hydrochloric acid, or by roasting the
mineral with powdered coal, limestone, and calcium chloride, when
the following reactions take place —

BaS04 + 4C = BaS + 4C0
BaS + CaCI, « BaCl, + CaS.

The barium chloride is dissolved in water, and an insoluble oxy-
sulphide of calcium remains.

Barium chloride forms colourless rhombic tables, BaCl,,2H,0,
which at i^.t)" are soluble to the extent of 43.5 parts in 100 parts
of water. The salt is nearly insoluble in hydrochloric acid, and
may therefore be precipitated from an aqueous solution by the
addition of this acid.

544 Inorganic Chemistry

Barium chloride, in common with all the soluble salts of thk
element, is highly poisonous.

Barium Sulphate, BaS04, is the most abundant naturally
occurring barium compound. It is frequently met with as lax^e
rhombic crystals. The specific gravity of the mineral is 4.3 to
4.7 ; and on account of its high specific gravity, it received the
name of barytes^ or Heavy spar.

It is formed as a heavy white precipitate, when sulphuric add,
or a soluble sulphate, is added to a solution of a barium salt It is
insoluble in water, and only very slightly soluble in dilute adds.
It is soluble in hot concentrated sulphuric add, espedally when
freshly predpitated ; and the solution deposits, on cooling, an add
sulphate, BaS04,HsS04. On exposure to moisture the solutioD
deposits crystals of BaS04,H,S04,2H,0. Both of these com-
pounds, in contact with water, yield insoluble normal barium
sulphate and sulphuric add.

Precipitated barium sulphate is largely used as a pigment,
known as permanent white.

Barium Nitrate, Ba(NO,)^ is obtained by dissolving the native
carbonate, or the sulphide, in dilute nitric acid. It is also formed
by double decomposition, when hot saturated solutions of sodium
nitrate and barium chloride are mixed. The salt crystallises in
large colourless octahedra belonging to the regular system. 100
parts of water at the ordinary temperature dissolve 9 parts, and at
100", 32.2 parts of barium nitrate. When strongly heated, it is
converted into barium oxide, with the evolution of nitrogen per-
oxide, oxygen, and nitrogen.

Barium nitrate is used in pyrotechny, in the preparation of
mixtures for green fire.

Barium Sulphide, BaS, is obtained by methods analogous to
those for preparing calcium sulphide (page 538), which it dosely
resembles in its properties.

CHAPTER VII

ELEMENTS OP GROUP IL (PAMILY B.)

Zinc, Zn 65

Cadmium, Cd X11.7

Mercury, Hg i99*^

The three elements composing this family do not exhibit such
a close resemblance to each other as exists between barium,
strontium, and calcium ; for although zinc and cadmium are very
closely related, mercury in many respects differs widely from these,
and from all the other elements in the same group.

Cadmium and zinc are almost invariably found associated
together in nature, they are both fairiy permanent in the air,
and both readily take fire and bum, when strongly heated,
forming the oxides. Both are acted upon by dilute hydrochloric
and sulphuric acids, with evolution of hydrogen, and most of their
salts are isomorphous.

Mercury is peculiar in being liquid at ordinary temperatures.
Zinc and cadmium melt at 420* and 320* respectively, while
mercury melts at - 38*.8. It is quite unacted upon by oxygen at
ordinary temperatures, and combines with extreme slowness when
heated. Its oxide, also, is readily decomposed by heat into its
elements.

Dilute hydrochloric and sulphuric adds are entirely without
action upon it, and it forms no hydroxide.

The hydroxide of zinc, Zn(HO)^ differs from the corresponding
cadmium compound, in being soluble in alkaline hydroxides.

These three elements resemble each other, and differ from
those of £Eunily A of this group, in that they can be volatilised,
mercury at a temperature about 357*, cadmium and zinc at
temperatures approaching 1000*.

These three elements are also alike, in that their vapours con-
sist of mono-atomic molecules.

546

Tnorganic Chemistry

zuic.

Symbol, Zn. Alomlc weigbl =65.

Oceurrence.— Zinc is stated to have been found in Austialiftl

the uncombined condition ; with this exception, it is always ni«
with in combination, chiefly as carbonate in calamint or xinc-spar,
ZnCO,, and as sulphide in sine-blende or blaci-jack, ZnS. Other
ores are red line ore, ZnO ; xaA frankUmU, (ZnFe)0,Fe,0^

Gahnite, or einc-spinnelU, has the composition ZnO,Al,0].

Modes of Formation.— The ores chiefly employed for Cbe pre-
paration of zinc are the carbonate and sulphide, although in New
Jersey the red oxide and franklinite are used. The process con-
sists of two operations, namely, first, the conversion of the ore into
oxide of zinc, by calcination ; and, second, the reduction of [he oxide
by means of coal ai a high temperature- The calcination of ttae
natural carbonate is readily accomplished, this compound n
giving up its carbon dioxide at the high temperature —

ZnCOj = ZnO + C0»

In the case of zinc blende, the opei^tion consists in the o
tion of both the sulphur and the tine by atmospheric oxygen, tl

ZnS + 30 = ZnO + SO^

Considerable care has to be exercised in order to prevent the
formation of tine sulphate, which, in the subsequent operation,
would be reconverted into sulphide, and so lost The finely-
crushed calcined ore is mixed with coke or coal, and healed to
bright redness in earthenware retorts, when the oxide is reduced
with the formation of carbon monoxide, and the metal distils and
is collected in iron receivers. Zinc ores frequently contain small
quantities of cadmium, and as this metal is more readily volatilised
than zinc, it passes over in the first portions of the distilled
product

The two processes now almost exclusively in use for the reduc-
tion of zinc, known as the SUesian and the Belgian process,*
dilTer only in metallurgical details, &c.

■ The cJd c

1 fnais. or dislHUHom
Uls and all other niel»lli
metalluif^. such u Poor,

Zm S47

CoiniTiercial linc usually contains carbon, iron, and lead, and
occasionally arsenic and cadmium. It may be obtained in a higher
degree oi purity by careful distillation, but pure line is best ob-
tained by first preparing the pure carbonate by precipitation, and
then calcining and finally reducing with charcoal obtained from
HJgar.

Properties.^ Zinc is a bluish -while, highly crystalline, and
brittle metal. At a temperature of 300' it can be readily powdered
in a mortar, while between too' and 150° it admits of being drawn
into wire or rolled into thin sheet. The presence of a small
quantity of lead greatly enhances this property, but is detrimental
when the zinc is required for making brass. Zinc which has been
either rolled or drawn, no longer becomes brittle when cold, but
retains its malleability.

Zinc melts at 420*, and when heated in air much beyond this
point, the metal takes fire and burns with a bluish-white flame, the
brilliancy of which becomes dazzling if a stieam of oxygen be pro-
jected upon the burning mass. The product of its combustion is
rinc oxide, ZnO, which forms a soft, white, (locculeni substance re-
sembling wool, and (brmerly known a& phtlosopktt's wool.

Zinc is permanent in dry air at ordinary temperatures, but when
exposed to moist air it tarnishes superficially ; it is also imaltacked
by water at the boiling temperature. It is soluble in a hot solution
of sodium or potassium hydroxide, with evolution of hydrogen
(p. '54)-

Pure line is scarcely acted upon by pure sulphuric or hydrochloric
acid, either dilate or strong. The presence of small quantities of
impurities, however, determines the solution of the metal with (he
rapid evolution of hydrogen, hence ordinary commercial linc is
readily attacked by these acids, and also decomposes water at the
boiling-point with the evolution of hydrogen,*

• The difference between the tieha
nie)d4l fine, wu fonnetly eiplaiaed 01
formed vilh itie linc a voltaic couple.

i> of ftcids towards pure azict oom-
B ground Itial tlie impuriiies present
:rebj local elpctric currenH were lel
up, while In the csh of pure linc no such unioo took place. The reOBTii
obsfrvaiioiu of PuUinger (Chem. Sex.. 57) and Weeien (Berichle, a^) ibsw ihai
Ihii is not a complete expUualiOD. Weereo conclude! ttiat ibe insolubility ol
pure line in dilute HCids, is due la the fonnalion of ■ lilni of condensed liydrogen
upon l!ie nirface of ihe meial. wbicb slops all funher action. Tbe addition of
oiidising agents, sucb as hydrogen peroude. 01 dilute sulphuric acid wbicb bai
lieen electrolysed, and ibeiaforv coniuni peinilphuric acid, leodi to destroy
lliit 61ro ttj oiidliinK ihp hydrOfen, and thenriore promntn ibe toliiilon of itM

S48
Zinc i'

Inorganic Chemistry
:ly used in the process of gaive

extensivdlj
and (MmH

•s, the mos^^

oivaHising iroa, which
consists in coating iron with a film of tine, not by electrical deposi'
tion, as would be implied by the name, but by dipping the iron
into a bath of molten linc. The layer of line preserves the iron
from rusting. GalvaHiitd iron is better able lo withstand the
action of air and moisture than tinned iron, hence
used for wire netting, corrugated roofing, water tanks, and
purposes where the metal is exposed lo the oxidising influen<

Alloys of Z1dc.~— Zinc forms a number of useful alloys, the
important of which are the various fonns of brass {see Copper).
With certain metals, such as tin, copper, and antimony, tine wiil
mix la all proportions i while with otheis, such as lead and bismuth,
it is only possible to obtain solid alloys of detinile composition.
When, therefore, lead and zinc are melted together, although in
the molten condition the mixture is homogeneous, on cooling, the
metals separate into two layers, the lighter line rising to the surface.
The separation of the metals, however, \% not perfect, for the tine
will have dissolved a certain quantity of the lead (1.2 per cent),
and the tower layer of lead is found to have dissolved a small
proportion of line {1.6 per cent), just as water and ether, when
shaken together, separate into two layers, the uppermost being an
ethereal solution of water, and the lower an aqueous solution ol
ether.

This property is made use of ii
(see p. 517).

The so-called German silver,
alloy of copper, nickel, and zinc

Bronie coinage consists of 95 parts of copper, 4 of tin, and 1 of
zinc, the small proportion of tine giving to the alloy an increased
hardness and durability.

Zinc Oxide. ZnO, the only oxide of zinc, occurs native as r^
line art, the colour being due lo the presence of inanganese. It is
formed as a soft white substance, when zinc is burnt in the air. It
is manufactured under the name of xinc white by the combustion

(inc. He also fiuds, that by meohKnically removing ihii layer of hydrogen,
eiihcT by conslanlly brushing the melallic suiface 01 placing tbe materiab
Odder reduced preuure, tbe solution of t^ie sine by tbe acid is promoted. ]| ti
also found that the ehaiaeier of the surface of the nirtaJ, whether smoolh or
rough. alTecls ihe result; line <hal is unncled upon when its surface is perfectly
tmuotb. \i more readily iiucked lay (he dilute acid uhrn its turficr isfouEh.

of silver from lead

r nicktl silver, is a nearly white

Zinc Chlondt 549

of sine, the fumes being led into condensing-chambers, where the
oxide collects.

Zinc oxide is a pure-white substance, which when heated becomes
yellow, but again becomes white on cooling. When strongly heated
in oxygen, it may be obtained in the form of hexagonal crystals ;
such crystals are occasionally found in the cooler parts of zinc
furnaces. The oxide does not fuse in the oxyhydrogen flame, but,
like lime, under these circumstances it becomes intensely incan-
descent ; for some time after being so heated it appears phos-
phorescent in the dark. It is insoluble in water, and does not
combine directly with water to form the hydroxide. It dissolves
in acids, giving rise to the different zinc salts. Zinc oxide is largely
used in the place of " white lead" as a pigment : although it does
not equal white lead in covering power, or hody^ it possesses the
advantage of not being blackened by exposure to atmospheric
sulphuretted hydrogen.

Zine Hydroxide, Zn(HO)|, is formed as a white flocculent pre-
cipitate, when either sodium or potassium hydroxide, or a solution
of ammonia, is added to a solution of zinc sulphate. The compound
is soluble in an excess of either alkali, and is deposited from a
strong solution in regular octahedra of the hydrated hydroxide,
Zn(HO)s,H|0. Both of these compounds on heating, readily lose
water, and are converted into the oxide.

Zlne Chloride, ZnCl^, is formed by the direct combination of zinc
with chlorine, or by the action of hydrochloric acid upon the metal
It is also obtained in the anhydrous state by distilling a mixture of
mercuric chloride and zinc, or a mixture of anhydrous zinc sulphate
and calcium chloride.

It is usually prepared on a large scale by dissolving zinc in
hydrochloric acid, and after precipitating any manganese and ironi
the liquid is boiled down in enamelled iron vessels, until on cooling
it solidifies ; it is usually cast into sticks.

Zinc chloride is a soft, white, easily fusible solid, which volatilises
and distils without decomposition. It is extremely deliquescent,
and readily soluble in water and in alcohol, its solution being
powerfully caustic From a strong aqueous solution, deliquescent
crystals are deposited, having the composition ZnCls,H|0.

When the aqueous solution is evaporated, partial decomposition
takes place, hydrochloric add being evolved, and basic compounds
being precipitated, consisting of combinations of the chloride and
oxide. Hence, during the concentration of the liquid in the pre-

Inorganic Ckemistry

paration ol linc chloride, hydrochl<
this compound.

A paste made by moislening tine oxide with linc chloride, mpidly
sets to a hard mass ; this mixture, under the name of oicychloHde
of line, is employed in dentistry as a filling or stopping for teeth.

Zinc chloride unites with alkaline chlorides, forming a series of
crystaUine double salts having the general formula ZnCl^SRCl.

Zlne Sulphate, ZnSO,, is formed when tine is dissolved in
sulphuric acid. It is obtained on a targe scale by roasting the
natural sulphide, whereby it is partially converted into the sulphate,
which is then extracted with water,

The salt crystallises from its aqueous solution at ordinary tem-
peratures in colourless rhombic prisms, ZnS0(,7H,0, isomorphous
with MgSO,7HiO. It is extremely soluble in water ; loo parts of
water at the ordinary temperature dissolve i6o parts, and at ioo°,
653.6 parts, of the crystalline salts. When exposed to the air, the
crystals slowly effloresce, and if placed in vacuo over sulphuric
acid, or if heated to too', they lose six molecules of water, leaving
the monohydrated salt ZnSO(,H,0. At a temperature about 300'
this is converted into the anhydrous compound, and at a wbiir.,
heat it gives off sulphur dioxide and oxygen, leaving the oxide.

The hydrated salt, ZnSO„6HjO, is obtained in the form of
symmetric crystals, when the salt is deposited ai temperati
above 40°. This compound is isomorphous with MgS0^6H,0.

Zinc sulphate combines with alkaline sulphates, forming
of double salts, having the general formula ZnS0,,R,SO(,6H|
which are also isomorphous with the corresponding magnesil
compounds (page 531),

Zinc sulphate, in common with all the soluble salts of zinc,
an astringent taste, and is poisonous.

Zinc Sulphide, ZnS.— The natural compound, ii>u-blendt,
usually dark-brown or black, and exhibits crystalline forms belong-
ing to the regular system. The mineral ■wurUilc is a less common
variety of zinc sulphide, crystallising in hexagonal prisms. Zinc
sulphide is obtained as a while amorphous precipitate, when
alkalme sulphide is added to a solution of a zinc salt,
sulphuretted hydrogen 15 passed through an alkaline solution of
zmc salt.

Precipitated zinc sulphide is insoluble in acetic acid, but readily
dissolves in dilute mineral acids, with evolution o( sulphuretted
hydrogen ; hence the compound is not formed when sulphuretted

idily I

Cadmium 551

hydrogen is passed through a solution of a sine salt containing a
free mineral acid.

Zine Carbonate, ZnCOi, is obtained as a white powder, when
hydrogen sodium carbonate is added to a solution of zinc sulphate.

If normal sodium carbonate be employed, the precipitated zinc
compound consists of a basic carbonate, whose composition varies
with the conditions of temperature and concentration of the liquids.

A basic carbonate, having the composition ZnC03,2Zn(HO)|,H|0,
is employed as a pharmaceutical preparation, under the name limt
carlwfias.

GADmUM.

Symbol, Cd. Atomic weight = 111.7.

Oeearrence. — Cadmium is never found in the uncombined state.
The only natural compound of which cadmium is the chief con-
stituent, is the extremely rare mineral greenockiUy which is the
sulphide, CdS. Cadmium occurs in small quantities in many zinc
ores, such as the sulphide and carbonate ; and in the process of
extracting zinc from these ores, the cadmium is obtained in the
first portions of the product of the distillation, partly as metal,
and partly as oxide.

Mode of Formation.— The crude product of distillation is dis-
solved in dilute sulphuric or hydrochloric acid, and the cadmium
precipitated as sulphide by means of sulphuretted hydrogen. The
cadmium sulphide is then dissolved in strong hydrochloric acid,
and precipitated as carbonate by means of ammonium carbonate.
The washed and dried carbonate is first converted into oxide by
calcination, and finally mixed with charcoal and distilled.

Properties. — Cadmium is a bluish-white metal resembling zinc
in appearance, but much more malleable and ductile. It tarnishes
superficially on exposure to the air, and, when strongly heated,
bums with the formation of a brown smoke of cadmium oxide,
CdO. The metal is attacked by dilute hydrochloric and sulphuric
acids, with the evolution of hydrogen. It readily dissolves in nitric
acid, yielding the nitrate, with the formation of oxides of nitrogen.
Cadmium is less electro-positive than zinc, and is precipitated in
the metallic condition from its solutions by that metal.

Cadmium melts at 320*, and when volatilised in an atmosphere
of hydrogen, it forms crystals belonging to the regular system.

Cadmium Oxide, CdO, is formed as a brown ftime or smoke

when cadmium bums in the air. It may be obtained by
the carbonate or nitrate. Thai obtained by ihe ignition of tbe
laller salt, is in the form of minute crystals, having a bluish-black
appearance. Cadmium oxide is insoluble in water, but dissolveis
in acids yielding cadmium salts. It is icfusible In the ox)-hydrogen
flame, but is readily reduced when heated on charcoal before the
blowpipe : and the reduced metal, as it volatilises and bums, lorms
a characteristic brown incrustation of oxide upon the charcoal.

Cadmium Chloride, CdClf, is obtained by the action of hydro-
chloric acid upon the metal or the oxide. The salt is deposited
from the solution in white silky crystals, having the composition,
CdCl„2H,0. On exposure to the air the crystals effloresce, and
when heated become anhydrous.

Cadmitim Sulphide, CdS, is obtained as a bright yellow preci-
pitate, when sulphuretted hydrogen is passed through a solution of
a cadmium salt. The precipitate is soluble in concentrated hydro-
chloric and nitric acids, and in warm dilute sulphuric acid. Cad-
mium sulphide is insoluble in ammonium sulphide ; this property
readily distinguishes it from arsenious sulphide, which in colour
it closely resembles.

Cadmium sulphide is used as a pigment, both in oil and wato^''

colours.

Symbid, Hg. Atomic weight = 199,8.

Oeeurrenoe,— In the uncombined state mercury is met with
small globules, disseminated through its ores, especially the sul-
phide. It is also occasionally found as an amalgam with silver
and gold The principal ore is cinnabar, HgS, and the chief
mines of this ore arc those of Almaden (Spain), Idria (Camiola),
California, and the Bavarian Palatinate,

Modes of Formation. — Mercury may be obtained from
natural sulphides, by either roasting the ore, whereby the sulj
is oxidised to sulphur dioxide, and the metal liberated, or by
tillation in dosed retorts with lime, when calcium sulphide
sulphate are formed, and the mercury set free. The first m
IS almost exclusively employed.

At Idria the crude ore, consisting of cinnabar mixed with
and earthy mattery is roasted in a furnace, upon perforated ai
". "' ; A fi\ t'lR- 1 37- The action of the fire and heated

Afirctiry

5S3

oiidise the sulphur, and volatilise the mercury, and Ihe gases and
vapours together pass through a seriei of Ituei or chambers, C, C,
where the mercury condenses.

By the use of a rcvcrberaiory furnace (the Alberti furnace) the
process can be made continuous. The ore is fed into the furnace
through a hopper, and the calcined residue is raked out through
an opening at the opposite end of the hearth. The gases ate
passed first through iron pipes, kept coot by water, and then

ining mclal ii c

I Ihrougfa a series of chambers where the

The method adopted at Aimaden is esseoiially the same a« the
Idrian process, except that the condensation lakes place in a series
of pear-shaped earthenware vessels, called aludtls, which are con-
nected together as shown in Fig.
138. Usually six rows of forty-
seven such aludels, are connected
with six openings in a chamber Fio. 13S,

immediately above the furnace.

The impure mercury is freed from mechanically mixed impurities
by straining or filtering through chamois leather, but from metals
in solution, such as linc, tin, lead, and others, it is purified by
distillation, For laboratory purposes, pure mercury is best obtained
by distillation in vacuo, by means of the apparatus shown in Fig.
139 (Clarke). In this arrangement the mercury is distilled in a
Sprtngtl vacuum. The mercury (previously cleaned by being
thoroughly agiuiied with mercuric nitrate) is placed in the reser-

554

Inorganic Che misery

\oit R, which is then placed upon the upper shelf S, and by means
of the damp, mercury is allowed lo pa^s inio the 'ong wide tub* T,
and up into the bulb. The air in the tube and bulb escapes down
ihe narrow inner tube, which reaches nearly lo the lop of the bulb,
as seen in the enlarged detail, /. The mercury is allowed to rise
in the bulb and fall down the long inner tube, after the n
the Sprengel pump. The reservoir is then placed upon the 1<

adjustable stand, and its heiylil so arranged that the m
the bulb falls lo the position shown in the figure. This space il
Torricellian vacuum. The mercury is then healed by a i
burner, B, and the whole is protected from draught by the h
As the mercury distils, it passes down the inner tube, and b
fall continues to preserve the Sprengel vacuum wnhtn the bulb.
Properties. ^Al ordinary temperatures mercury is a brighl,silvfl

Mercury 555

white liquid metal (hence its old name qutcknlvtr). When cooled
to - 38.8* it solidifies to a highly crystalline solid, which is ductile
and malleable, and softer than lead When the liquid is cooled, it
contracts uniformly until the solidifying point is reached, when
considerable contraction takes place. Solid mercury, therefore, is
denser than the liquid metal, and sinks in it. The specific gravity
of liquid mercury at 0° is 13.596, while that of the solid at its
melting-point is 14- 193. Mercury in extremely thin films appears
a violet colour by transmitted light

Under a pressure of 760 nun. mercury boils at 357.25*, giving
a colourless vapour. The density of mercury vapour referred to
hydrogen is 100.93 ; hence this element, like its associates in the
family to which it belongs, consists of mono- atomic molecules when
in a state of vapour. Mercury gives off vapour even at ordinary
temperatures, and a g^ld leaf stispended over mercury in a stop-
pered bottle, gradually becomes white upon the surface, owing to
its amalgamation with the mercurial vapour.

The vapour of mercury is poisonous, giving rise to salivation.

Mercury does not tarnish on exposure to the air, and is unacted
upon by a large number of gases : hence this liquid is invaluable
to the chemist, affording a means of collecting and measuring
gases which are soluble in water.

When submitted to prolonged heating in the air, it is slowly
converted into the red oxide, which at a higher temperature is
again decomposed into its elements.

Mercury is obtained in the form of a dull-grey powder, when it
is shaken up with oil, or triturated with sugar, chalk, or lard. This
operation is known as diodifdng^ and is made use of in the pre-
paration of mercurial ointment The grey powder consists simply
of very finely-divided mercury, in the form of minute globules.

Mercury is not attacked by hydrochloric acid. Strong sulphuric
acid is without action upon it in the cold, but when heated the
metal dissolves, with evolution of sulphur dioxide. Strong nitric
acid rapidly attacks it, with formation of mercuric nitrate and
oxides of nitrogen. Cold dilute nitric acid slowly dissolves it,
forming mercurous nitrate.

Alloys of Mereary. — When mercury is one of the constituents
of an alloy, the mixture is called an amalgam. Most metals will
form an amalgam with mercury. In some cases, as with the
alkali metals, the union is attended with great rise of temperature.
In other cases, as with tin, an absorption of heat takes place.

556

Inorg/tnic Chemistry

Sodium and potassium amalgajns arc oblained b^ dissolving
various amounts of the metals in mercury. In contact with water
[hey are decomposed, hydrogen being evolved, and tbe alkaline

hydroxide formed. On (his account sodium amalgam is frequently
used in the laboratory as a reducing agent. When heated
440', these amalgams leave behind crystalline compounds, K^Hg
and NasHg, which spontaneously inflame in contact with tbe
Zinc amalgams are only very slowly acted upon by dilute
phuric acid ; therefore, by the superficial amalfiamation of
line plates used for galvanic batteries, the same result
tained, as though the line were perfectly pure (see page 547),
no solution of zinc takes place until the electric circuit is closed-
Tin amalgams are employed for the construction of ordinary

Amalgams of gold, and also copper and iiiic. are used i
dentistry as a Ailing or stopping for teeth.

Oxides of Mercury.— Two oxides are known, namely, t
roua oxide, Hg,0, and mercuric oxide, HgO.

Hercurous Oxide, Hg^O, is obtained as an unstable dark-bro
or black powder, when sodium hydroxide is added to mercuro
chloride. When exposed to the light, or when gently heated, itS
converted into mercuric oxide and mercury.

Hercuric Oxide, HgO, is produced in small quantity by the pi
longed heating of mercury in contact with air, or by igniting tl
nitrate. It is prepared on a large scale by heating ai
mixture of mercuric nitrate and mercury. Obtained by I
methods, it is a brick-red crystalline powder ; but when sodiia
hydroxide is added to a solution of a mercuric salt, the ox
cipitated as an orange-yellow amorphous powder. When heats
mercuric oxide first darkens in colour, and gradually becoin
almost black, but returns to its original bright red colour o
ing. At a red heat it is completely decomposed into its elemenoil

Salts of Mercury.— Two series of salts, corresponding to t
two oxides, are known— (a) mercuroui salts, in which tw(
the hydrogen of the acids are replaced by the divalent radid
or double atom (Hg,); and Ifi) mercun'i: sails, in which I"
same amount of hydrogen is replaced by the single divolcs
atom (Kg). All the mercury salts are poisonoua.

d to

Meraitaus Sulpha U 557

(•} HEBCUBOUS SALTS.

Mereurous Chloride, Hg^Cl, (.calomel), is met with in small
quantities as the mineral horn mercury. It may be obtained by
the addition of sodium chloride, or hydrochloric acid, to a solution
of mereurous nitrate. On a large scale it is usually prepared by
heating a mixture of mercuric chloride and mercury, when the
mereurous chloride sublimes as a white or translucent fibrous
cake.

When a mixture of mercuric sulphate, common salt, and mercury
is heated, mereurous chloride is also obtained, thus —

HgSO^ + 2NaCl + Hg - Na,S04 + Hg,CV

Calomel is perfectly tasteless, and is insoluble in water. When
heated, it vaporises without fusing. The density of the vapour
that is formed by heating mereurous chloride is 117.59, which is
half that demanded by the formula Hg|Cl|. It has been shown,
however, that the compound dissociates when vaporised, into
mercuric chloride and mercury.* Boiling hydrochloric acid de-
composes mereurous chloride into mercury, which separates out,
and mercuric chloride, which dissolves.

MercuFonB Nitrate, Hg,(NO,)^ is deposited in the form of
colourless monosynmietric crystals containing 2H,0, from a solu-
tion of mercury in cold dilute nitric acid. The salt is soluble in
water acidulated with nitric acid, but an excess of water causes
the precipitation of a basic nitrate having the composition —

Hg,(NO,)„HgAH,0 (or 2Hg,(N0,)(H0)X

which, on boiling, is converted into mercuric nitrate and mercury.
If either this or the normal salt, be boiled in the presence of an
excess of mercury, a basic nitrate of the composition —

3Hg^NO,)„2HgA2H,0 (or Hg^N0,)„4Hg,(N0,XH0)),

is obtained.

Mereurous Sulphate, Hg,S04, is obtained as a white crystalline
precipitate, when dilute sulphuric acid is added to a solution of
mereurous nitrate. It is very slightly soluble in water.

* Harris and Meyer. Bcrichte, June 1894.

Inorganic Ckemislry

SS8

(^) HEBCDBIC SALTS.

Hereuric Chloride, HgCl, (corrosive sublimate), is foimed wbtf
chlorine is passed over heated mercury. It is prepared o
scale, fay heating a mixture of mercuric sulphate and c
a small quantity of manganese dioxide being added, to prevent
as far as possible, the formation of mercurous chloride. The
mercuric chloride sublimes as a white translucent mass. It dis-
solves in water to the extent of 6,57 parts in 100 parts of water at
10*, and 54 parts In the same volume of water at 100°, formiiig aji
acid solution from which the salt is deposited in long white silky
needles. It readily melts, and volatihses unchanged- It dissolvf
without decomposition in nitric acid, and in sulphuric add, ;
volatilises unchanged from its solution in the latter acid on boilin]

Mercuric chloride is a violent poison ; (he bes
men, with which it forms an insoluble compound. It has alaaV
strong antiseptic properties, and on this account is largely used byV
taxidermists.

With hydrochloric acid, mercuric chloride forms two crystalliiwfl
double chlorides, HgCI^HCl and SHgCI^HCl ; and with tfatti
alkaline chlorides it forms a number of similar double sails, oil
which the ammonium compound, HgClc3NH,CI,H,0, was knowi
to ihc early chemists under the name sal alembroth.

Mercuric Iodide, Hgl,— When mercury and iodine a
together in a mortar, and moistened with a small quantity ofj
alcohol, the red mercuric iodide is formed. It is also obtained byj
precipitation from a solution of mercuric chloride, upon the additionT
of potassium iodide. The precipitate first appears yellow, but in ■
few seconds becomes scarlet.

MerCTiric iodide is insoluble in water, but readily dissolves il
either mercuric chloride or potassium iodide, and also in alcoho|
and in nitric acid. From its solutions it is deposited i:
quadratic octahedra.

Mercuric iodide is dimorphous ; when heated to about Ijo*, t
scarlet quadratic crystals are changed into bright yellow rhombi
prisms. At ordinary temperatures this yellow rhombic form \
unstable, and on being lightly touched it is ai once retransforri
into the red quadratic form. At very low temperatures, how<
the yellowvariety is the more stable : thus, when th^ red e

Ammoniacal Mercurous Compounds 559

are exposed to the temperature of evaporating liquid oxygen, they
pass into the yellow variety.

Mercuric Nitrate, Hg(NOt)|, is prepared by boiling nitric acid
with mercury, until sodium chloride produces no precipitate with a
sample of the liquid If this solution be evaporated over sulphuric
acid, deliquescent crystals are obtained of 2Hg(N03)2,H20, while
the mother liquor has the composition Hg(N0s)],2H)0.

Mercuric nitrate exhibits a great tendency to form basic salts :
thus, when this mother liquor is boiled, the compound Hg(NO,)^
HgO,2HsO is precipitated. When this compound, or the normal
nitrate, is treated with an excess of cold water, there is formed the
still more basic salt Hg(NO,)„2HgO,H,0.

Mercuric Sulphide, HgS {(cinnabar),—\^\itxi mercury and
sulphur are triturated together in a mortar, or when excess of
sulphuretted hydrogen is passed into a solution of a mercuric salt,
mercuric sulphide is obtained as a black amorphous powder. If
this be sublimed, it is obtained as a red crystalline substance

Mercuric sulphide in the red condition, is also obtained by
digesting the black amorphous product for some hours in alkaline
sulphides. A soluble double sulphide is first formed, which when
heated, is decomposed, with the deposition of red mercuric sulphide.
This compound is manu^Etctured on a large scale for use as the
pigment vermilion.

Mercuric sulphide is insoluble in either nitric, hydrochloric, or
sulphuric acid In the presence of an alkali it is soluble in sodium
or potassium sulphide, and deposits crystals from these solutions
having the composition HgS,NasS,8H|0, and HgS,K|S,6H,0
respectively.

Ammoniacal Mercury Compounds.— These may be regarded
as anunonium salts, in which two atoms of hydrogen in ammonium
(NH4) have been replaced by either (Hg^) in the mercurous^ or by
(Hg) in the mercuric compounds ; the two atoms so replaced, being
either drawn from one and the same anunonium group, or from two.

(•) MEBCUaOUS GOHPOXnsrDB.

Mercurous Ammonium Chloride, (NH,Hg|)Cl, is the black
powder produced by the action of aqueous ammonia upon calomel,
thus- -

Hg,Cl, -»- «NH,aq - (NH^Hg^Cl + NH^Claq.

S6o Inorganic Chemistry

MereorouB Ammonium Nitrate, (NHtHg|)NQ3 is formed, to-
gether with other compounds, when aqueous ammonia is added to
mercurous nitrate.

Merearoas Diammonlum Chloride, ^!?*^! I Hg, or (NHJ,

N£l|Cl )
HgiCl), is obtained when calomel absorbs dry gaseous ammonia.
On exposure to the air, it gives up its ammonia, and is reconverted
into mercurous chloride

08) MBBOUSIO OOMFOUHDB.

Mereurle Ammonium Chloride, (NH|Hg)Cl {infussbie wkiu

pr€cifiHate\ is formed when ammonia is added to a solution of
mercuric chlorid<

HgCl, + 2NH, = (NH,Hg)Cl + NH4CL

Dlmereuric Ammonium Chloride, (NHga)Cl, is obtained by
the action of water on the preceding compound

Mercuric Diammonlum Chloride, ^JJ'^j | Hg,or(NH3),HgCl

(fusible white precipitate\ is obtained by adding mercuric chloride
to a boiling aqueous solution of ammonium chloride and ammonia,
until the precipitate which first forms, no longer dissolves. On
cooling, the solution deposits small crystals belonging to the
regular system.

Oxy-dimercurie Ammonium Iodide, (NH2Hg)l,HgO, is pro-
duced by the action of aqueous ammonia upon mercuric iodide,
thus —

4NH, + 2HgI, + H,0 - (NH,Hg)I,HgO + SNHJ.

It is readily produced as a brown precipitate, by adding ammonia
to a solution of mercuric iodide in potassium iodide containing an
excess of potassium hydroxide.

The alkaline solution of potassium mercuric iodide is known as
Nessler's solution^ and constitutes a delicate reagent for detecting
the presence of ammonia. Minute traces of free anunonia in solu-
tion produce a yellow or brown coloration with this test.

CHAFFER VIII
THE ELEMENTS OF GROUP III

Family A.

Family a

Scandium, Sc

. 43.97

Boron, B . . .

xa9

Yttrium, Y .

89.6

Aluminium, Al .

97.04

Lanthanum, La .

• 138. S

Gallium, Ga

69.86

Ytterbium, Yb .

. 173

Jndium, In

"3-4

Thallium, Tl

203.7

With the e.xception of boron, aluminium, and thallium, the mem-
bers of this group are amongst the rarest of the elements.**^ Some
of these occur only in minute traces in certain ores of other metals :
such is the case with the elements gallium and indium, which are
met with in certain specimens of zinc blende, the ore being con-
sidered ricM in gallium if it contains as much as 0.002 per cent, of
this element. Both gallium and indium were discovered by means
of the spectroscope ; the latter by Reich and Richter (1863), ^^^
named indium on account of two characteristic lines in the indigo-
blue part of the spectrum ; gallium by Lecocq de Boisbaudran
(1875), ^^^ named after his own country. The spectrum of this
metal is characterised by two violet lines. One of the most
remarkable properties of gallium is its extremely low fusing-point,
the metal melting at 3a 1 5". (For a comparison of the properties
of gallium with MendelejefTs eka-aluminium^ see p 109.)

Others of these elements are met with in certain rare minerals,
thus, lanthanum occurs in the mineral orthiU (from Greenland) ;
and both yttrium and lanthanum (associated also with the rare
elements cerium and erbium) are found in gadolinitey or ytterbUe
(from Ytterby).

Boron (the typical element of the group) is the only non-metal :
all the others exhibit well-marked metallic properties. They all
yield sesquioxides of the type R^Os ; in the case of boron this
oxide, B^Osi is acidic

* For detailed descriptions of the rare elements, the student is referred to
larjfer treatises, or to chirniical dictionari'^.

562 Inorganic Chemistry

Thallium in many respects is peculiar. It forms two series of
compounds ; in one class it functions as a monovalent, and in the
other as a trivalent element In some of its properties it exhibits a
close analogy to the alkali metals ; thus, it forms a soluble strongly
alkaline hydroxide, TIHO, corresponding to KHO. And many of
its salts, such as the sulphate, TISSO4 ; perchlorate, TICIO4, and
the phosphates, are isomorphous with the corresponding potassium
compounds.

Thallium also shows many properties in common with lead,
which in the periodic system is the next element in the series
(the fourth long series). Thus, the chloride, like lead chloride,
is thrown down as a white curdy precipitate on the addition of
hydrochloric acid to a soluble salt of the metal, and like lead
chloride, thallous chloride is soluble in hot water. Thallous
iodide also closely resembles lead iodide, being formed as a yellow
crystalline precipitate when potassium iodide is added to a soluble
thallous salt

Metallic thallium also bears the closest resemblance to metallic
lead.

In the thcUlic compounds this element is more closely related to
the other members of this family : thus thallic oxide, Tl^Oj ; thallic
chloride, TICls ; and thallic sulphide, Tl^Sj, are analogous to the
corresponding boron compounds, BgO,, BCl), UtS,.

BOBON.

STmbol, B. Atomic weight = la?.

Ocourrence. — The element boron has never been found in the
free state. In combination it occurs principally as boric acid in
volcanic steam, and as metallic borates, of which the commonest
are tincal^ a crude sodium borate, or borax, Na^B^Oj ; boraci/e
and colemanitey or borate spar^ CagBgOu ; and borofuUrocalcite^ or
ulexife, CajB60ii,Na2B40T,16H,0.

Modes of Formation. — (i.) Boron maybe prepared by heating
boron trioxide with either sodium or potassium in a covered
crucible —

B,Os + 3K2 = 3K,0 + 2B.

The fused mass is boiled with dilute hydrochloric acid, and the

Boron Trioxidi 563

boron, which is in the form of a dark-brown powder, is separated
by filtration.

(2.) The element may also be obtained by heatmg potassium
borofiuoride with potassium —

BF5,KF + 3K - 4KF + B.

(3.) Boron is also formed .when potassium is heated in the
vapour of boron trichloride —

BCl, + 8K - 8KC1 + B.

Properties. — Boron, as obtained by these methods, is a dark
greenish-brown powder. When strongly heated in air it bums,
uniting both with oxygen and nitrogen, forming a mixture of boron
trioxide, B^Os, and boron nitride, BN. It is unacted upon by air
at ordinary temperatures.

Boron has no action upon boiling water, but cold nitric acid
converts it into boric acid —

B + 3HN0, - H5BO5 + 3NO^

When heated with sulphuric acid it is similarly oxidised—

2B + 3H,S04 - B,0, -f 3S0, + 3HaO.

When fused with alkaline carbonates, nitrates, sulphates, and
hydroxides it forms borates of the alkali metals, thus—

2B + 3Na,COa " SNajBO, + SCO.
2B + 6KH0 - 2K,B0, + 3H^

Boron dissolves in molten aluminium, which on cooling deposits
crystals of a compound of aluminium and boron.**^

Boron Trioxide, B^Oi, is formed when boron bums in the air,
or in oxygen. The readiest method for its preparation consists in
heating boric acid to redness, when it fuses and gives up water —

2B(H0), - 3H,0 -H BjO,.

Properties. — The fused mass solidifies to a transparent, colour-

* This compound was at one time mistaken for an allotropic modification
of boron.

Inorganic Chemistry

less, vitreous solid, which gradually absorbs aimosphetic moisture,
and becomes opaque. Ii is not volatile below a white heat, and
on this account, although only a feeble acid, it is capable ai high
lemperalures of displacing strong acids which are volatile, from
their combinations ; thus, when boron Irioxide is fused with potas-
sium sulphate, potassium borate is formed, and sulphur ui<

B,0, + 3K,S0, = 2B(K0)j + 3S0»

icnid^

Boron triojtide at a high temperature is capable of dissoli
many metallic oxides, some of which impart to Ihe fused ma&s a
characteristic colour.

Boron forms three oxyacids, namely —

Onhoboric acid, B(HO)„ or HjBO,

Metaboric acid, U.OjCHO)^ or li,B,0„ or B,0„H,O.

Pyroboric acid, BjO((HO;^ or H,B,0„ or 2^0„H,0.

Orthoborlc Acid, or Boric Acid, B(HO)„ occurs naturally,
both in the waters and in the jets ol steam which issue from the
ground in many volcanic districts, notably in Tuscany.

The aaual amount of boric add in these natural jets of steam,
or soffioni, is very small ; but as the steam becomes condensed in
the pools of water, or lagoons, which often surround the jets, the
amount of boric acid with which the water becomes charged, is suffi-
cient to constitute this a profitable source of supply. To obtain the
acid, large brick-work basins are buill round Ihe steam jets, in such
a manner that the liquid can be caused to flow from one to another.
Water is placed in the highest basin, and, after the steam from the
fumaroles beneath it has blown through for twenty-four hours, the
liquid is passed on to the second basin, and a fresh supply of water
is run into the first. In this way the water passes on through a
series of four or five such basins, receiving the steam of the soffioni
for twenty-four hours in each. The muddy liquor, after passing
through a settling reservoir, is concentrated by evaporation, the
heat from the natural steam being utilised. The concentrated
liquor, having a specilic gravity about 1.07, is allowed to cool in
lead-lined tanks ; and the crystals, after being drained, are dried
upon the floor of a chamber, also heated by the natural steam.
Ihe crude boric acid thus obtained, is purified by tecrystallisa-

by tecrystallisa- I

Borax $6$

Boric acid may be prepared by the action of sulphuric acid, or
hydrochloric acid, upon a strong solution of borax —

NajB^Or + 6H,0 + 2HCI - 2NaCl + 4H,B0>

Properties. — Boric acid crystallises in lustrous white laminae,
which are soft and soapy to the touch. loo parts of water at i8*
dissolve 3.9 parts of the acid The aqueous solution turns blue
litmus to a port wine red, similar to the colour produced by car-
bonic acid. In contact with turmeric paper, it gives a brown
stain, resembling that caused by alkalies, but readily distinguished
by not being destroyed by acids, and by being turned black in
contact with a solution of sodium hydroxide. Boric add is more
soluble in alcohol than in water ; and when this solution is boiled,
a portion of the boric acid volatilises with the alcohol, and imparts
a green colour to the flame of the burning vapour.

The orthoborates are mostly unstable salts.

Hetaborie Aeld, H|B|0|, is obtained when boric acid is heated
to loo*—

2H,BO, - 2H,0 + H,B,04.

The metaborates are more stable salts than the orthoborates.
The acid is dibasic, and forms normal and acid salts, as well as
super-acid salts, thus —

Normal potassium metaborate . KtB,0|.

Acid potassium metaborate . HKB^Oi*

Super-acid potassium metaborate HKB,04,H|B,0|.

Pyroborle Acid, H^BfOr, ^s obtained by heating either meta-
boric acid, or orthoboric acid, to 140* for some time —

2H,B,04 - H,0 -I- HjB^Oy.
4HgBO, - 5H,0 + H,B40y.

Borax. — The most important salt of pyroboric acid is the sodium
salt, ordinary borax, NasBfO^. This compound occurs naturally
as the mineral tinad. It is manu&ctured from boric acid by
double decomposition with sodium carbonate —

4H5BO, -I- Na,CO, - Na,B40r + 6H,0 -I- CO,.
Anhydrous sodium carbonate is added to a boiling solution of

566 Inorganic Chemistry

boric acid, and the liquid is then aUowed to crystallise, when it
forms large transparent prisms belonging to the mono-symmetric
system, of the composition NafB4O7,10HsO.

Borax is also obtained from the natural calcium borate, which
-has the composition CagBfOu. The powdered mineral is boiled
with water, and soda ash is added to the mixture, when calcium
carbonate is precipitated, and a mixture of borax and sodium
metaborate is formed —

Ca,BeO,i + 2NasC0, - 2CaCO, + NasBfO, + NasB^Of.

On crystallisation, the borax deposits, and the more soluble
metaborate remains in the mother liquor. On concentrating
these mother liquors, and blowing carbon dioxide through the
solution, the metaborate is converted into borax, which is pre-
cipitated as a fine meal, leaving sodium carbonate in solution —

2Na,B,04 + CO, = Na^gCOj + NasBfO,.

When heated, borax loses its water of crystallisation, and swells
up, forming a white porous mass, which finally melts to a clear
glass.

One hundred parts of water at lo** dissolve 4.6 parts of crystal-
lised borax, and at 100% 201.4 parts ; the solution possesses a feeble
alkaline reaction.

When deposited slowly from warm solutions, borax crystallises
in octahedra belonging to the regular system, and having the
composition Na^BfOriSH^O.

Boron Trifluoride, BF,. is formed when boron is brought into
fluorine : the boron takes fire spontaneously in the gas, forming
the trifluoride.

It is also produced when a mixture of dry powdered fluorspar
and boron trioxide is heated to redness in an iron vessel, calcium
borate being at the same time produced—

2B20a + 3CaF, - CasBjOe + 2BF,.

It is more conveniently prepared by heating together fluorspar,
boron trioxide, and sulphuric acid. The reaction may be regarded
as taking place in two stages, thus —

(I.) CaF, + H,S04 = CaS04 + 2HF.
(2.) B,0, + 6HF = 3H,0 + 2BF,.

Boron Trichloride 567

Properties. — Boron trifluoride is a colourless, pungent-smelling
gas, which fumes strongly in moist air on account of its powerful
afhnity for water. So great is this affinity, that a strip of paper
introduced into the gas is charred, by the abstraction of the
elements of water.

Boron fluoride neither bums, nor supports the combustion of
ordinary combustibles. When potassium is heated in the gas, it
bums brilliantly, forming the borofluoride.

At 0° one volume of water dissolves about 1000 volumes of the
gas, the absorption being attended with rise of temperature.

When the gas is passed into water until the solution is distinctly add, a
mixture of metaboric add and hydrofluoboric add is obtained ; the fonner
separates out, while the latter remains in solution —

8BF, + 4H,0 = H,B,04 + 6HBF4.

When the gas is passed into water until the latter is saturated, a synip-like
liquid is obtained whidi chars organic matter and is strongly corrosive. This
liquid is sometimes called fluoboric add, and contains boron trifluoride and
water in the proportions represented by the formula 2BF|,4H|0 ; or it may
t)e regarded as consisting of metaboric add and hydrofluoric add, as ex-
pressed by the formula H|B|04,6HF.* In presence of an excess of water,
this substance is decomposed into metaboric acid and hydrofluoboric add.

When mixed with its own volume of dry ammonia gas, boron fluoride forms a
white crystalline compound, having the composition represented by the formula
BFt,NH|. This substance may be sublimed without change. Two other
compounds with ammonia are knovm, namely BF|,2N(f9, <^d BFt,.3NH|.
These are both colourless liquids, which on being heated give off ammonia,
leaving the solid BF,.NHa.

The salts of hydrofluoboric add, HBF4, are known as boro/itioridts, and are
formed by the action of the acid upon metallic hydroxides —

HBF4 + KHO a H,0 + KBF4.

In many instances, their aqueous solutions redden litmus ; this is the case
with ammonium borofluoride, NH4BF4, and caldum borofluoride, Ca(BF4)|.

Boron Triehloride, BC1|, is produced when boron is heated in
a stream of dry chlorine.

It is most readily prepared by passing dry chlorine over an
intimate mucture of boron trioxide and charcoal, heated to redness
in a porcelain tube. The volatile product is condensed in a tube
immersed in a freezing mixture —

B,0, + 8C1, -f 3C = 3C0 -I- 2BC1,.

* It is considered very doubtful whether this substance can be regarded
as a definite compound.

568 Inorganic Chemistry

Properties. — Boron trichloride is a mobile, oolouriess liquid,
boiling at 18.23*. It fiimes in moist air, bdng decomposed in
contact with water, with formation of boric and hydrochloric
acids —

BCl, + 8H,0 - B(HO), + 8HCL

Boron trichloride unites directly with dry gaseous ammonia,
with evolution of considerable heat, forming a white crystalline
compound, having the composition 2BCls,8NH9.

Boron Hydride, BH9.~This compound has never been obtained in a state
of purity. When magnesium boride (an impure substance obtained by fusing
boron triozide and magnesium in a covered crucible) is acted opoD by
hydrochloric add, a gas is evolved which has a characteristic and unpleasant
smell, and which produces headache and sickness when inhaled. The gas
is largely hydrogen, containing, however, a certain quantity of boron hydride,
which imparts to the flame a green colour, and produces boron triozide.
When passed through a heated tube, boron is deposited as a brown film.
When burnt with a limited supply of air, or when a cold porcelain dhdi is
depressed into the flame of Uie burning gas, a brown stain of boron is
deposited.

Boron Nitride, BN, is formed when boron is strongly heated in nitrogen
or in ammonia. It is best obtained by heating, in a covered platinum
crucible, a mixture of one part of dehydrated borax, and two parts ol
ammonium chloride —

NaaB407 + 2NH4CI = 2BN + B,0| + 2Naa + 4H,0.

Boron nitride is a white amorphous powder. It is insoluble in water, but
is slowly acted upon by boiling caustic alkalies, with evolution of ammonia —

BN + 3KHO = K,BO, + NH,.

Heated in a current of steam it forms boron trioxide and ammonia —

2BN + 3HjO = BjO, + 2NH,.

Boron Sulphide, B^Ss. is prepared by beating a mixture of boron trioxide
and carbon (made by mixing tx>ron trioxide and soot with oil, and heating
the pellets out of contact with air) to bright redness in a stream of vapour
of carbon disulphide —

2BaO, + 8C + 3CS, = 6CO + 2BA.

Boron sulphide is a yellowish solid, consisting of small crystals. It has
a strong unpleasant smell, and its vapotu- attacks the eyes. It is immediately
decomposed by water, being converted into boric acid and mlphnrett*^
bydio);ea —

«,S, + 6HiO = 2B<HO), + 3H^S.

Aluminium 569

ALUmNIUM.

Sjrmbol, Al. Atomic weight = 27.04.

Oecorrence. — Aliuninium is one of the most abundant of all
the elements, although it has never been found in the uncombined
state. In combination with oxygen as Al^Os, it constitutes such
minerals as corundum, ^^fyi sapphire. As the hydrated oxide,
Al,Os,H|0, it occurs associated with iron oxide in the mineral
bauxite^ which constitutes the chief source from which the metal
itself is obtained As a double fluoride of aluminium and sodium,
Al,F0,6NaF, it occurs in the mineral cryolite, and as a hydrated
phosphate in the various forms of turquoise. Aluminium is met
with in enormous quantities in the form of silicate, constituting
the various clays ; and as compound silicates in the felspars, and
other conunon minerals constituting a large proportion of the
solid crust of the earth.

Mode of Formation. — Aluminitmi is prepared on a large scale
from the mineral bauxite, the process being conducted in four
stages : — (i.) and (2.) The preparation of pure aluminium oxide,
free from iron. (3.) The preparation of a double chloride of
aliuninium and sodium. (4.) The reduction of the double chloride
by means of sodium.

(i.) The powdered bauxite (usually containing about 50 per
cent, of alumina) is mixed with sodium carbonate and heated for
Bve or six hours in a reverberatory furnace, when carbon dioxide
is evolved and sodium altuninate is formed —

AljOj + SNa^CO, = Al,0s,3Na,0 + 3CO,.

(2.) The sodium aluminate is extracted with water, leaving the
iron in the form of insoluble oxide. Through the Altered liquid a
stream of carbon dioxide is then passed, which decomposes the
sodium aluminate, regenerating sodium carbonate, and precipitat-
ing hydrated aliuninium oxid<

Al,0„3Na,0 + 8H,0 + 3C0, - SNa^CO, -f Al,0s,3H,0.

(3.) The purified alumina, after being washed and dried, is mixed
with sodium chloride and powdered wood charcoal, and sufficient
water added to enable the mixture to be worked up into balls.
These are dried at i V^ and then packed into a vertical flrerlay

570 Inorganic Chemistry

qflinder, where they are strongly heated in a stream of chlorine^

AljO, + 3C + 8C1, - 3C0 + AljClt.
The aluminium chloride combines with the sodium chloride present
in the mixture, forming the double chloride, Al|C1^2NaCl, which
volatilises from the retort, and is condensed in an earthenware
receiver as a nearly white crystalline salt, which is almost entirely
free from iron.

(4.) In order to reduce the double chloride, three char^ges (each
consisting of a mixture of 25 kilos of the salt, 1 1 kilos of powdered
cryolite (as a flux), and 12 Idlos of metallic sodium in small pieces)
are thrown into a strongly heated reverberatory furnace, and are
immediately followed by a fourth charge, containing the same
quantity of the double chloride and of cryolite, but without sodUum.
A violent reaction at first takes place, and after a short time the
entire mass is in a state of fusion, the metal separating out beneath

the slag —

Al,CIe,2NaCl + 6Na - 2A1 + 8NaCl.

At the present time aluminium is almost exclusively obtained
by means of the electric furnace. A solution of alumina in fused
cryolite is electrolysed by a powerfid current, in a carbon-lined
crucible ; the crucible being the cathode, and a bundle of carbon
rods the anode. The alumina alone is decomposed, the pure metal
collecting at the bottom of the crucible.

Properties. — Aluminium is a tin-white metal, possessing great
tensile strength. It is very ductile and malleable, but requires
frequent annealing during the process of drawing or hanunering.
Its specific gravity is 2.58 ; by hammering and rolling it may be
raised to 2.68. Its power of conducting heat and electricity is
about one-third that of silver. Aluminium is an extremely sonor-
ous metal, and when struck it emits a clear and sustained note.
It is not tarnished by air under ordinary circumstances, but when
strongly heated it becomes oxidised ; and in the condition of thin
foil it readily bums in oxygen, forming alumina, Al^Og. The metal
melts at a temperature about 700*. Aluminium is scarcely acted
upon by nitric acid of any strength, but readily dissolves in hydro-
chloric acid, and in solutions of sodium or potassium hydroxide
with elimination of hydrogen. When heated with strong sulphiuic
acid, aluminium sulphate is formed, and sulphur dioxide is evolved.

Organic acids are almost without action upon aluminium, but in
the presence of sodium chloride they are capable of dissolving it to
a slight extent Pure aluminium is scarcely acted upon by water or

Alumina 571

steam, but ine presence of impurities such as usually occur in the
commercial metal, renders it much more readily oxidised.

Aluminium is a highly electro-positive element, and is capable
of reducing a number of other metals from their combinations with
oxygen or sulphur. Thus, when finely divided aluminium is heated
with the oxides of such metals as manganese, chromium, tungsten,
uranium, along with lime to form a slag, an energetic action takes
place, in which the aluminium combines with the oxygen, and the
metals are thrown out of combination, and are obtained as a
coherent mass. Similarly, iron pyrites is reduced to the condition
of metallic iron, with the formation of aluminium sulphide.

AUoys of Aluminium. — The most important of these is an
alloy with copper, containing 10 per cent, of aluminium, and
known as aluminium dranse. This alloy has a yellow colour,
resembling that of gold ; it is scarcely tarnished by exposure to
air, and is susceptible of a high polish. Its specific gravity is 7.69,
and it possesses a tenacity equal to that of steel, and more than
twice that of the best gun-metaL The alloy is malleable, and
yields good castings, and on account of its many valuable pro-
perties it is employed for a variety of purposes.

Aluminium Oxide {alumina)^ AI^O,, occurs native in a colour-
less crystalline condition as corundum, and coloured by traces of
various metallic oxides in such precious stones as rudy, sapphire,
and amethyst. In a less pure condition, it occurs in large quantities
as emery. These naturally occurring crystalline forms of alumina
are extremely hard, ranking second only to diamond. Alumina is
obtained in an amorphous condition, by igniting either the pre-
cipitated hydroxide, or ammonia alum, thus —

Al,(H0)e-3H,0 + AljOj.
Al,(S04)j,(NH4),S04 - 2NH, + H,0 + 4SO, + AljO,.

It is also obtained by the action of carbon dioxide upon sodium

aluminate (p. 569). In the crystalline form it is obtained by

strongly heating a mixture of aluminium fluoride and boron tri-

oxide —

AljFe + B,0, - AljO, -I- SBFg.

The boron trifluoride volatilises, leaving aliunina in the form of
rhombohedral crystals. Artificial rubies have been obtained by
heating bariimi fluoride with alumina, and adding a trace of
potassiiun dichromate.

!7»

inorganic Chetnistry

Amorphous alumina is a soft white pon-der, insoluble ii
but dissolved by acids with the formatian of aluminium salts ; a
being stronglj- healed, however, alumina is attacked only t
slowness by hydrochloric or sulphuric acid.

Aluminium Hydroxides. —Three hydroxides, or hydraM
oxides, are known. Thus, when ammonia is added lo a solutial
of an aluminium salt, a white gelatinous precipitate is obtained
which when dried at 100° consists of Che trihydrate, Al,0j,3HiC
or AI,(HO),. If this be healed lo 300° it loses aH,0, and is ci
verted into the mono-hydrate, Alj03,H,0, or AI,Oj(HO)^ By ll
addition of ammonia lo a boiling solution of an aluminiu
and drying the precipitate at 100*, the dihydrate Is obtained*!
Al,0„8HjO, or AI,0(HO)i.

These compounds are soluble in acids, and all yield the s.
aluminium salts.

Aluminium liydroxide unites with many soluble organic c
ing-mailers, and precipitates them from solution as lakes.
this properly depends the use of aluminium salts as mordants i^
dyeing and calico printing : the colouring -ma tier being held in tl
fibres of the material by the aluminium hydroxide, which is
usiy precipitated upon the fabric.

Alumlnates. — Alumina is capable of acting as a feeble s
oxide : thus, the hydroxides are dissolved by sodium or polassitn
hydroxide, yielding salts known as aluminales. Certaii

r native, such as spiiulU (magnesium alumin
Al,0„MgO, and chrysoberyl {beryllium aluminate), AI}0„Bi
Sodium aluminate is now manufactured on a large scale, ft
preparation of the metal (p. 569) and also of aluminium salts.

It is readily decomposed even by carbonic acid (p. 569], and fa
aluminium chloride^

AI,0„3Na,0 + AljCI, = BNaCI -H aAI,Oj.

On ihe manufacturing scale powdered cryolite is employed t
effect this decomposition, the aluminium hydroxide being f
cipitated, and the sodium fluoride going into solution —

AI,0,.3Na,0 -I- AI,F„flNaF = 12NaF + SAljO..

Alumlntom Sulphate, A1,[S0,)„I6H,0, is found native as tbi
«y sail and alumiaite, the latter being a basic s
having the composition AI,0,S0v9H,0 The normal sulphxl

Tk: Alums

573

Is obtainrrl by dissolving the hydratcd oxide in sulphuric acid.
Large quantities of commercial aluminium sulphate are made, by
directl)' dissolving bauxite in sulphuric acid. The product, how-
ever, contains iron, which is detrimental to the technical uses to
which the sulphate ii applied, and from which therefore it must
be carefully purified. Pure aluminium sulphate is prepared from''
either bauxiie, or cryolite, by first forming sodium aluminate ; in
the former case by healing the mineral with sodium carbonate
(p. 569), and in the case of cryolite by boiling with milk of lime—
AI,F,.GNaF + 0Ca{HO>, = GCaF, + 8H,0 + AI,0j.3Na,0.
The sodium aluminate, free from iron, is then decomposed by
carbon dioxide, as already described, and the precipitated liydraied
oxide dissolved in sulphuric acid. On concern ration, the mass
solidifies to a white, difficultly crystal li sable solid.

The Alums.— Aluminium sulpliaie unites with cert.iin other
julphalcs, forming double salts, which belong to a class of com-
pounds known as the alums. The most important of these
compounds is the double sulphate of aluminium and potaisiuin,
AI,(S0,),,K,SO4,S4H,O, known as potaitium alum, or simpljr

The alums have the general formula R^SO,)„M,SO„24HtO,
in which R may be either aluminium, iron, chromium, manganese
(indium or gallium), and M a monovalent element or gmup. such
as sodium, potassiitm. or ammonium.

Inorganic Clumisiry

These compounds ace all isomoiphous, crystallising in tlie
regular system (usually in cubes or oclahedra) with twenty-foin
molecules of waler. Fig, 140 represents a crystal of potassium
alum (A) and potassium chromium alum (B). In naming the
alums* it is usual, when the salt contains aluminium, only to
* introduce the name of the monovalent element or f;ioup : thus,
ammonium aium, or potassium aium, sigiiifies the double sulphate
of ammonium, or potassium, and aluminium. If, on the other hand,
the compound contains no aluminiuni, the names of both meialc
are used, Ihu*, ficiassium chromium alum, ammonium iron aluiH.

A second class of double snlphalei is known, which resemble the alun
aUhough they are not isomorphom with Ihcni, These are Icrmed /in>db-~1
aluits. They may be regnrded 05 Blums, in which the Iwo aloms of (he
nionovalenL element are replaceil by one atom of a divntent element, ihm~

AySO J,MnS0,.a4 H^,
Al,{S0,lsFeSO„24H,O.

Fei,iS0i),CuS0,.31H,0.
Fi!,(50,),ZoSO„WI[,O.
Kn,iS0i),MgS,0t.3iHfi.

Magnesium manganese, pseudo-alum

The alums are all soluble in water, and their solutions have an
acid reaction and posiesb an astringent taste. When heated,
they gradually part with water, and at higher temperatures are
broken up into oxides and alkaline sulphates; in the case of
ammonium alums, leaving only the metallic oxide.

Potassium Alura. Alj(SO,)j,K,SO„24H,0. is prepared by
the addition of the requisite quantity of potassium sulphate to
aluminium sulphate. A considerable quantity of alum is also
obtained from a naturally occurring basic potassium alum, known
as a/um stone, or alunite, which has the composition AI,(SO,)b
K,SO„2AJ)Oj,8HjO. At Tolfa this is first calcined, and after-
wards lixiviated with waler, which dissolves the potassium alum, _
leaving alumina undissolved. The alum so obtained is known u f
Roman alum; and although it has a reddish colour, due to thf-]

• Sdenic ncid (Ihe selenium analogue of sulphuric add) fc
consiituied leiies of double selenaie«, cry^ialhsing in itie same form, 1
with the tame number of molecules of waler. The system of n
adopted for these compounds is the same : thus, ammenium

Alum 575

presence of iron, this iron is present only as the insoluble oxide,
which is readily removed, and the salt is in reality extremely
pure.

Alunite is also converted into alum, by treating the calcined
mineral with sulphuric acid, and adding the requisite quantity of
potassium sulphate. A large quantity of alum is manufactured
from alum shale^ which is a bituminous mineral, consisting chiefly
of alimiinium silicate, with finely-divided iron pyrites dissemi-
nated throughout the mass. Fhe shale is usually first roasted,
and is then exposed to the aaion of air and moisttu^ whereby
the oxidation of the pyrites is completed. The result of this
oxidation is the formation of sulphuric acid, which, acting upon
the aluminium silicate, forms aluminium sulphate, while the iron
is converted into ferrous and ferric sulphates, and ferric oxide. The
oxidised mass is then lixiviated with water, and, after concentra-
tion, the requisite quantity of potassium chloride or sulphate is
added to the hot liquor. (The use of potassium chloride is pre-
ferable, as by double decomposition the ferrous and ferric sulphates
are converted into the very soluble chlorides, and an equivalent
amount of potassium sulphate is formed.) The liquor is stirred
mechanically during its cooling, whereby the alum is deposited in
small crystals known as alum meal^ which permit of its more
ready purification by recrystallisation.

Alum crystallises in fine colourless regular octahedra. which, on
exposure to the air, become coated with a white efflorescene, due
not to loss of water, but to absorption of atmospheric ammonia, and
the fonnation of a basic salt.

The solubility of alum in water increases rapidly with rise of
temperature. Thus, loo parts of water at o* dissolve 3.9 parts of
alum; at 50*, 44.1 parts; and at 100*, 357.5 parts. Alimi is in-
soluble in alcohol.

When heated to 42*^, alum loses 11 molecules of water; and
when heated to 61° in a closed vessel over sulphuric acid, it parts
with 18 molecules.

On the application of heat, alum first melts in its own water of
crystallisation, which is gradually expelled, until at a dull red heat
the salt is converted into a white porous mass, known as burnt
alum. At a still higher temperature it is broken up into potassium
sulphate, alumina, and sulphur trioxide. Burnt alum is only very
slowly dissolved by water. The chief use of alum is as a mordant
in dyeing, alum being a salt which is much more easily obtained
in a state of purity than aluminium sulphate. By the addition of

576 Inorganic Ckemiitry

sodium hydroxide or carbonate to a solution of alum, until the pre-
cipitate first thrown down is just redissolved, a basic alum is prO'
duced known as neutral alum —

2Al^SO,),,K,SO, + 0NaHO = Al,(SO,}),AVHO)a,K,SO,+
3NajS0,+ K,S0,.
This solution gives up its alumina to the lahnc with great ease, and
on this account is used toy dyers and calico printers as a mordant.
When this solution is heated to 40', ordinary alum is re-formed,
and a precipitate is obtained consisting of another basic salt, hav-
ing the same composition as alunile, thus —

2A!,(SO,)j,Al,(HO)„K,SO,=Ala{SO,)3KiSO„ +
Al,(SO,)s,aAI,0„K,SO, + 6HjO.

Almnllllnm Tlnorlill, AI,F|. — This compound may tie prepared by passing
ga^ooiu hydroctilorir acid over a mixture of fluorspar and oiumi
whilcnes; in a grapliile lulw, vrlien aluminiuiD fluoride volatilises, leaving
calcium chloride-

SCflF, + AljO, + 6HC1 = 3H.jO + 3CaCl, + A1,F,

obtained by dissolving kIi

A1,0, + 6HF + H,0 = AI^,.7H,0.

Aluminium fluoride forms colourless rbombohedral crystals,
soluble in water. Ii tomljincs with alkali (luoiides, forming insoluble
fluorides, of wbich llie sodium compound is Ihe most imponant. " ~
This compound occurs native as the mineral cryolilt.

Aluminium Chloride, AljCig.— This compound is produced
when powdered aluminium is strongly healed In chlorine, or with
certain metallic chlorides, such as zinc chloride. It is best obtained
by passing chlorine over a strongly -heated mixture of alumina
and charcoal.

An aqueous solution of aluminiiun chloride may be obtained by
dissolving alumina in hydrochloric acid. On evaporation, the
solution deposits rrystals of a hydrate, Ai^CI^ISHjO.

Aluminium chloride forms white hexagonal crystals, which fume
strongly in moist air. When gently heated it vaporises, and sub-
limes without fusion. When heated under pressure of its own
vapour, the compound melts. It dissolves in water with the
evolution of heat, and the solution, on evaporation, deposit!
hydrated chloride, which, on being healed, breaks up i:
chloric acid, water, and altunina —

A1,C1*12H,0 - 6HC1 -t- 9H,0 + AI,0,

I into hydr»^^

Thallium $77

Aluminium chloride unites with other metallic chlorides, forming
double salts, of which the sodium compound Al^Cl^fiNaCI (page
570) is the most important It also combines with ammonia,
forming the compounds AljCleidNH, and AljCl0,2NH^

Alaminiam Sulphide, AlsS).— When finely divided aluminium
is heated with iron pyrites, an energetic reaction takes place;
metallic iron being reduced, and aluminium sulphide being fonned.
The same compound is produced when sulphur is thrown upon
strongly heated aluminium. As obtained by these methods,
aluminium sulphide is a greyish black solid, which, when thrown
into water, is converted into the oxide with evolution of sul-
phuretted hydrogen —

AljS, + 3H,0 - AljO, + 3H^.

The compound is decomposed in the same manner by atmos-
pheric moisture, when exposed to the air.

THALUUM.

Fonnula, TL Atomic weight = 903.7.

History. — Thallium was discovered by Crookes (1861) in the
seleniferous deposit from a sulphuric add manufsictory. In the
spectroscopic examination of certain residues obtained in the ex-
traction of selenium from this deposit, the presence of an unknown
element vras manifested, by the appearance of one bright green
line. From its characteristic spectrum, the name thtxilium (signi-
fying a green twig) was given to the element

Occorrenee. — Thallium is found in small quantities in many
varieties of iron pyrites, and when these are employed in the
manu£Eicture of sulphuric acid, oxide of thallium collects in the
flue dust of the pyrites burners. Thallium also occurs associated
with copper, selenium, and silver, in the rare mineral crookesiU,

Mode of FormatloiL — The metal is obtained by reducing the
sulphate, by immersing strips of zinc into the solution. The thal-
lium is deposited upon the rinc, as a spongy or crystalline mass,
which is then pressed together, and fused beneath potassium
cyanide in a crucible.

Properties. — Thallium is a soft heavy metal, resembling lead.
It is readily cut with a knife, and leaves a streak when drawn
across paper. When preserved out of contact with air, it is a tin-

a o

S78

Inorganic Chemistry

I
I

white lustrous metal ; but on exposure to the air, it tarnishes
upon its surface, with the formation of black ihalloua oxide.
specific gravity is 1 1.8, and it metis at 290°.

When exposed to air and moismre, or when placed in wa
which is free to absorb atmospheric oxygen, the metal is slo'
converted into thallous hydroxide, which is soluble in water, ;
imparts 10 the liquid a strong alkaline reaction. The soluiio
absorbs carbon dioxide, with the formation of thallous carbonate^
When heated in the air thallium melts, and rapidly oxidisi
thallium trioxide, TIjOj ; healed in oxygen it burns, forming the'1
same oxide. It rcadil/ bums when heated in chlorine, producing' J
thallous chloride, TlCl. The metal is soluble in dilute acids.

Oxides of ThalUum.— Two oxides are known, namely, thallous
oxide, TI,0, and thaiUc oxide, Tl,Oy

Thallous Oxldo, Tl,0, forms as a dark grey film apon the
surface of the metal, on exposure to the air. It may also be
obtained by heating the hydroxide to 100*. It dissolves in water,
forming the hydroxide.

Thallous Hydroxide is obtained by the addition of barium
hydroxide 10 a solution of thallous sulphate, the precipitated barium
sulphate being removed by filtration —

T1,S04 + Ba(HO), = BaSO, + 2T1H0.

The solution, on coDcentration, deposits yellow needle-shaped I
crystals of TIHO,H,0. Thallous hydroxide is soluble
yielding an alkaline* solution, which gives a brown stain upon ,
turmeric paper. This stain soon disappears, owing to the de- !
struction of the colouring -matter, and is thereby distinguished ,
from the similar stains produced by sodium and potassium ]
hydroxides.

ThalllO Oxide, TL,0^ is obtained when thallium bum
air, or when thallium oxyhydroxide, TIO(HO), is heated
It forms a dark reddish powder, insoluble in water. I
dilute sulphuric acid it dissolves, forming thallic sulphate-

but with hot concentrated
sulphate formed—

TljOa + 3H,SO, - TI^SO,), + 3H,0,
id oxygen

evolved, and thsUonil

T1,0, + H,S04 - TI,SO, + O, + H,a

Tkallic Oxysalts 579

At a red heat thallic oxide it converted into thallous oxide with
loss of oxygen.

Thalliom Ozyhydroxlde, TIO(HO), is formed by the action of
potassium hydroxide upon thallium tridiloride —

TlCl, + 3KH0 - 3KC1 + H,0 + TIO(HO).

Thallous Chloride, TlCl, is obtained as a white curdy precipi-
tate, when hydrochloric acid is added to a solution of a thallous
salt It is considerably more soluble in hot than in cold water :
loo parts of water at i6* dissolve a265 parts ; and at loo*, 1.427
parts of thallous chloride.

Thallle Chloride, TlCl^ is formed by passing chlorine through
water, in which thallous chloride is suspended. The solution so
obtained, on evaporation in vacuo, deposits colourless transparent
crystals of T1C1„2H,0.

When either thallium or thallous chloride is gently heated in a
stream of chlorine, a compound is obtained, having the composi-
tion TlCls,TlCl, or Tl^Cl^. If this be further heated, it loses
chlorine, and is converted into a yellow crystalline compound of
the composition TlCljjSTlCl, or Tl4Cl^ thus—

2Tl,Cl4 = CI, + TI4CV

Thallous Oxysalts.— The sulphate TI^SOa, and niiraU TlNOai
are best obtained by dissolving the metal in the respective acids.
Both salts are soluble in water.

Thallous Carbonate, Tl^COs, is prepared by saturating a solu-
tion of thallous hydroxide with carbon dioxide. The salt forms
long white prismatic (monosynunetric) crystals, which are mode-
rately soluble in water, giving an alkaline solution.

Thallous Phosphate, T1,P04, is obtained by precipitation from
a thallous solution, by the corresponding potassium phosphate.
The monohydrogen phosphate, HTIJPO4, on being heated to 200*,
is converted into pyrophosphate —

2HT1,P04 - H,0 + Tl^PjOr,

and the dihydrogen salt, on being ignited, yields the metaphos-
phate —

H,T1P04 - H,0 + TlPOr

Thallic Oxysalts.- The chief of these are thallic sulphate,

58o

Inorganic Chtmistty

TVSOf), ; and thallic nitrate, Tl(NOs),. They are obtained fay tbc
acUon of sulphuric acid and nitric add respectively upon thallic
oxide, TI,Oa. Thallic sulphate forms colourless crystals of the
composition TI^ 804)3,7 H^O. It is decomposed by excess of water,
with precipitation of the hydrated oxide ; and when heatedi pelds
thallous sulphate, sulphur trioxide, and oxygen —

TliCSOJj - T1,S04 + «S0, + Of

Thallic nitrate isdeposited in colourless crystalsof Tl(N0|)|i8H^,
which are decomposed in the presence of much water.

CHAPTER IX
THE ELEMENTS OF GROUP IV

Family

Family B.

Titanium, Ti

•

. 48

Carbon, C .

11.97

Zirconium t Zr

•

• 90-4

Silicon, Si .

a8.3

Cerium t Ce .

•

141.9

Germanium, Ge.

Thorium, Tb

. 932

Tin. Sn . . .
I.ead, Pb .

"7.3s
906.39

Family A consists of four rare elements.* Titanium, as the
oxide TiOs, occurs in the three rare minerals — rutiie^ brookite^ and
anaiase. The metal is extremely difficult to isolate in a pure
state, owing to the fact that it unites directly with nitrogen, form-
ing a nitride.

Zirconium is met with as the silicate ZrSi04 (or ZrO^iSiOs) in
the mineral uircon. Like silicon, it has been obtained in two
forms, crystalline and amorphous. The latter variety, when gently
heated, bums in the sur, while the crystalline variety requires the
high temperature of the oxyhydrogen flame for its ignition.

Cerium occurs associated with lanthanum, in the rare minerals
ceriie and orthiie^ and with yttrium and ytterbium in gadoliniU and
wbhUrite,

Thorium is found in the extremely rare minerals, thorite and
orangeiie^ met with in Norway.

Family B. — In this family the rare element germanium forms
a link between carbon and silicon on the one hand, and tin and
lead on the other.

Carbon (the typical element) is essentially non-metallic, and
forms an acidic oxide. Silicon approaches more nearly to the
metals in its physical properties, but its oxide is still acidic, and
no compounds are known in which silicon functions as a b.isic
element Germanium is both metaUic and non-metaUic ; its oxide

* For descripttoos of tbete nuv dements, tbt student b referred to krger
treatiaes.

5ti

rnorganic Chemistry

unites with acids ; and it also combines with alkaline hydroxides,
forming germanates corresponding to silicates. Tin is a still more
basic element, forming well-marked salts with acids ; but it is also
acidic, and with alkalies fonns stannales.

Carbon and silicon exhibit a close relationship. They both
form allotropes, which correspond in many respeas. They both
unite with hydrogen, forming the analogous compounds CH, and
SiH, ; and with hydrogen and chlorine they (onn the similarly con-
stituted compounds, chloroform, CHCI, ; and silicon chloroform,
SiHClj.

Tin and lead approach r
their physical properties, than ti
They both form compounds,

as divalent and tetravalent elements. Although ti
lead (as often happens with the heaviest metals of a family), the I
element eidiibits much greater readiness to act in the loi
of atomicity. Until quite recently (1893), no compound was known
in which an atom of lead is united with four monovalent atoms,
although lead ethide, P^CjHjjj, had been obtained. Now, how-
ever, the compound PbCI, has been produced, corresponding to
SnCI(, which it resembles in many respects ; and slill t
recently (1894)1 ihe tetrafluoride has been obtained.

Carbon, as ustial with the typical elements, stands apart from '
the other members of the family in many of its attribules. Thus, '
its oJtides ate both gaseous ; it also forms a vast number o( c
pounds with hydrogen, oxygen, and nitrogen, the study of which I
constitutes the science of organic chemistry. This element hai j
already been treated in Part II. (page zjo).

i nearly to each other, especially in
■> the other members of the lamily.
1 which the meials function botb j

Symtid, Si. Atomic weight = 38,3.

Occurrence.— Silicon is not known to occur in the uncombined \
stale, although in combination it is the most abundant and widely \
distributed of all the elements, with the exception of oxygen. ]
combination with oxygen, as silicon dioxide or siUcay -SiO,
Jtint, sand, guartz, rock crystal, and chalcedony; whi

combination with oxygen and such metals as calcium, magnesitun, .1
and aluminium, it occurs in clay and soil, and constitutes a large J
number of the rocks which make up the earth's crust Silicon, id J

Silicon 583

combination with oxygen, is also met with in the vegetable kingdom,
being absorbed by plants from the soil

Modes of Formation.— ( I.) Silicon may be obtained by strongly
heating a mixture of potassium silico-fluoride and potassium —

K^iF« + SKs - Si + 6KF.

The mass, after cooling, it treated with water, which dissolves
the potassium fluoride, leaving the liberated silicon.

(2.) This element may also be prepared by heating sodium in a
stream of the vapour of silicon tetrachloride —

SiCl4 + 2Na, - Si + 4NaCL

As obtained by either of these methods the silicon is in the form
of an amorphous, dark brown powder.

(3.) Silicon is obtained in a crystalline condition, by passing a
slow stream of the vapour of silicon tetrachloride over aluminium,
previously melted in a current of hydrogen ; the volatile aluminium
chloride passes on in the stream of gas, and the liberated silicon
dissolves in the excess of aluminium —

3SiCl4 + 4A1 - 3Si + 8A1,C1«.

As the mass cools, silicon is deposited in the form of long, lustrous,
needle-shaped crystals.

(4.) The most convenient method for the preparation of crystal-
lised silicon, consists in heating in a crucible a mixture of 3 parts
of potassium silico-fluoride, i part of sodium, and 4 parts of granu-
lated zinc The regulus so obtained contains crystallised silicon.
It is gently heated, and the excess of zinc drained away, the
remainder being removed by treatment with acids.

Properties.— Amorphous Silicon, as obtained by the reactions
Nos. I and 2, is a dark brown amorphous powder, having a specific
gravity of 2.15. When heated in the air it bums with the forma-
tion of silicon dioxide, which, being non-volatile, coats the particles
of the element, and protects it from complete oxidation. It bums
when heated in a stream of chlorine, with formation of silicon
tetrachloride. It is insoluble in water, and in all adds except
hydrofluoric acid, in which it dissolves, with the formation of silico-
fluoric acid and evolution of hydrogen —

Si -f 6HF - H,SiFfl + 8H^

584

Inorganic Ckemistty

On boilmg with potauiu
and hydrogen —

L hydroxide, it fonns potassium silicato

t- BKHO + H,0 - K^iO, + 2H,

Crystallised SUleon.— As obtained by reactions Nos. 3 and 4,
silicon is a brilliant, steely-grey substance, crystallised in needles
derived horn the rhombic octahedron. The specific gravity of the
crystals is 2.34 to 2.49. Crystallised silicon does not burn in
oxygen, even when strongly heated : it bums when heated in
chlorine, and takes lire spontaneously when brought into Ruorine.
It is not soluble in any acid except a mixture of nitric and hydro-
fluoric acids. Crystallised silicon is very hard, being capable of
scratching glass. When silicon is eiposed to a high temperature,
out of contact with air, it becomes denser and harder, and has I
been obtained in the form of small, steel-grey nodules, showing a 1
crystalline slruclure, and having a specific gravity as high as 3.1

Silicon Hydride, Si H,.— This compound is evolved at the
negative electrode (along with hydrogen), when dilute sulphuric
acid is electrolysed, the electrodes consisting of aluminium con-
taining silicon.

[n an impure condition, also mixed with hydrogen, this gas may
be obtained by the action of hydrochloric acid upon magnesium
•Uicide—

SiMg, + 4HCI = SMgCI, + SiH,.

* Allboogb silicon in combiaation is sue
u tt does, about one-rourib of llie tolal weight of the solid cnul of tbe eanh,
ID tbe fr«e nale il must >Iill be nifBrded as somewhat qI a raiitj, and coa>
■equently a good deal of uncertainty eiists as to its properties. Prom differs
ences Ibot have been olserved in tbe substaace, as obutined by diHerenl
methods, and fiom the close analogy that oisis belwecD silicon and carbon,
It was at one time believed that three allotropes of Ibis etemcnl exisled, cone-
spending to lliose of carbon. Amorphous silicon was considered 10 represent
ehannol A crystalline substance obiained by Wohlei. bx hiating potassium
lilico-Buonde with aluminium, has been legarded as corresponding to grspfaite,
and called grafkiHc ^Ucon ; while Ibe oclabedral crystals of silicon prepared
by reactioni 3 and 4 given above (Deville). were thought to be tbe analogue at
diamond ; and this substance has. iberefore, been called iiammd, or ailamaii-
biids^ooa. There is considerable doubt as to whether the silicon obtained
l>y all these various methods was sulBcicnlly pure to
and (his doubt is not diminished by tbe recently discovered fad, that nlicoo -
unites with cartwo. forming a bard crystaUine sulHiance, which has recdvad ]

Silicon Fluoride 585

(Magnesium silidde for this reaction may be prepared by fusing
together, in a covered cmdble, a miztiue of dry magnesium chloride
40 parts, dry sodium chloride 10 parts, sodium silico-fluoride 35
parts, and metaUic sodium 20 parts.)

Pure silicon hydride is prepared by acting upon triethyl silico-
formate with metallic sodium. The mode of action of the sodium
is not known, the ethyl silico-formate breaks up into silicon hydride
and ethyl silicate —

4SiH(OC,H4), - SiH^ + SSiCOCjH^)^

Properties. — Silicon hydride is a colourless gas. As obtained
by the first two methods it inflames spontaneously. The pure
gas does not possess this property. Its ignition point, however,
is very low, and if the gas be slightly warmed, or if a jet of it be
caused to impinge upon an object a few degrees above the ordinary
temperature, the gas at once takes fire and bums with a brightly
luminous flame : it is also rendered spontaneously inflammable
by reduction of pressure, or by admixture with hydrogen. When
brought into chlorine the gas takes fire, with formation of silicon
chloride and hydrochloric add

Silicon Fluoride, SiF4. — This compound is formed when silicon
is brought into fluorine, the silicon taking fire spontaneously in
the gas.

It is prepared by the action of sulphuric add upon a mixture
of powdered fluorspar and sand —

2CaF, + 2H,S04 + SiO, - 2CaS04 + 2H,0 + SiF4.

Properties. — Silicon fluoride is a colourless, fiuning gas. It is
not inflammable, and does not support combustion. It is de-
composed by water into hydrofluosilidc add, and silidc add,
hence the gas cannot be collected over water —

8SiF4 + 3H,0 - SHjSiFg + H,SiO,.

The silicic add is predpitated as a gelatinous mass. Each
bubble of gas as it comes in contact with the water is at once
decomposed, and a little sack-like envelope of silidc add is
formed round it On filtering the liquid, a solution of hydrofluo-
silidc acid is obtained. When silicon fluoride is passed over
strongly heated silicon, a white powder is obtained, having the
composition Si^F^

586

Inorganic Chtmislry

SIUCOQ Chloride, SiC1„ is formed when
itream of chlorine. Under these

It is obtuned by heating an intimate mixture of silica and
carbon in a stream of chlorine, and passing ibe products through
a cooled tube —

SiO, + 2C + 2C1, = 2CO + SiCl,.

Properties. — Silicon chloride is a colourless liquid, which
ilrongly in moist air, and bolls at 58.3°.
water into silidc and hydrochloric acids —

SiCl, + 4H,0 - Si{HO), + 4HCI,

id, which fiuna^^^H
decomposed Ii^^^|

Si(H0)4 - SiO(HO), + H,0.

8SC1, + Si = asi,ci^

Si,I, + SHgCl, = Si,Cl, + 3HgI^

pTopaitiM. — Dliiticon beiachloride is a mobile, colourleu, fuming liquid. |
which boils at 147° and crysiallises ai - 1°. When Ihc liquid is boiled. 1
tbe bol vapoui allowed 10 escape into the air, it spontaoeously ignites.

Silicon fonns two compounds with bromine and with iodine, c
to Ibe chlorides, naraely—

SiBrj : Si,Dr, : Sil, : Si,!,.

SiUcon Dioxide, SiO„ occurs in nature in a more or less pum J
form in a large number of minerals, some of which have already.}
been alluded to, as natural compounds of silicon. Silicon J
dioxide in an amorphous form, is met wilh in ihe different varielwi ij
aiopal, and in enormous quantities in the deposit known as li'iiueA J
gukr. This substance consists of the remains of extinct
maces, and is met with in various pans of Germany.
crystalline condition silica occurs as guartt at rod erystal, i
alto in a rarer form as iriifymiu.

Silicon Diaxidt

S87

Modsa of FOmiaUoiL — (i.) Silicon dioxide ii formed when
amorphous lilicon it barnt in air oi oxygen.

(3.) It may be prepared by heating silicic acid, which readily parts
with water, and leaves pore silicon dioxide as a light white amor-
phous powder —

Si(HO), - SiO, + 2H,0 ; or
SiO(HO), - SiO, + H,0.

s obtained by strongly

' ) a seated glass tube,

(3.) In minnie crystals, silicon dion
heating a solution of an alkaline silicate ii
whereby a portion of the
silica of the glass is dissolved.
When this solution is cooled,
silicon dioxide is deposited
If the crystallisation takes
place above a temperature of
180°, crystals of quarti are
obtained ; if below this point,
it deposits crystals of Eridy-
miie, while at ordinary tem-
peratures the silica is depo-
sited in the amorphous con-
dition. Much larger quartz
crystals have been obtained,
by the prolonged heating to
350*, of a 10 per cent, aque-
ous solution of silicic acid
(obtained by dialysis), in
stout sealed glass flasks.

Properties,— In the crys-
talline condition as quartt,
silicon dioxide forms pris-
matic crystals belonging to
the hexagonal system, terminating in hexagonal pyramids. Fig.
141 represents a mass of quarti or rock crystal

Tie purest forms of rock crystal are p^ectly colourless, having
a specific gravity of 3.69, and are suffidently hard to cut glass.
When cut and polished, it exhitnts a brilliancy not &r inferior
to that of the diamond, and is occasionally substituted for this
gem.

Quarts is often found coloured by the presence of email quan(i>

Fio. 141-

588

Inorganic Chemistry

ties of impurities, ai in the varieties known as amethyst guar/t a
smoky quarli, and in great quanlilies as ntilky quartw.

The variety of silicon dioxide known as tridymite, is found as
minute crystals in cavities in certain specimens of trachytic rocks
The crystalline form of tridymite, although belonging to the hexa-
gonal system, is distinct from that of quarti, and the crystals are
frequently met with grown together in the manner known as tvnH-
crystals.

Amorphous silicon dioxide, as ii occurs in nature, is a translu-
cent substance, having a conchoids! or vitreous fracture ; its specific
gravity is 2.3. As artiScially prepared, it is a soft white powder,
whose specific gravity is z.2. At the temperature of the oxy>
hydrogen flame, silicon dioxide melts to a transparent glass-like
substance, which is capable of being drawn out ialo fine threads
resembling spun glass- These fibres possess cany valuable pro-
perties, and are employed by physicists in delic

, and in all acids with (he
exception of hydrofluoric acid. It dissolves in alkalies, and the
amorphous powder can be dissolved in a boiling solution of sodium
carbonate. Many natural hot springs contain silica held in solu-
tion as an alkaline silicate, and on exposure to atmospheric carbon
dioxide, the silicate is decomposed with the deposition of silica and
the reformation of an alkaline carbonate. The enormous quantities
of siliceous sinter deposited by geysera at Rotomahama, New Zea-
land, were formed in this way. When fused with sodium carbo-
nate, silicon dioxide is converted into soluble sodium silicate —
SiO, + SNajCO. - SCO, -•- Si(NaO),.

SiUcIe Acids. — Silicon dioxide is capable of forming weak
polybasic acids, but from the readiness with which they give up
is probable that none have ever been obtained in a state
of purity. The compound represented by the formula Si(HO}, is
known as orthosilicic acid, and is tetrabasic. By the loss of one
molecule of water, it forms metasilicic acid, SiO(HO)). When
hydrochloric acid is added to a solution of an alkaline silicate, a
gelatinous precipitate is obtained, which consists of the dibasic
add SiO(HO)„ or H.SiO,—

SiO(NaO), -♦- 2HC1 = SiO(HO), + SNaCl.

If^ on the other hand, the solution of alkaline silicate be added

Silicic Acid 589

cautiously to an excess of hydrochlorir acid, the silicic acid remains
in solution, and is probably present as orthosilicic acid, Si(HO)„ or
H4SiO,—

SiO{NaO), + SHCI + H,0 - Si(HO). + SNaCL

The sodium chloride in the solution may be removed by a pro-
cess of sepaTatioQ known as dialysis. This process, discovered by
Graham, is based upon a property belonging to certain classes of
substances, of passing when in solution through certain mem-
branes. The mixture is placed in an apparatus resembling a
small tambourine (Fig. 143) (made by stretching eitbei parch*

ment, or parchment paper, over a wooden hoop), which is then
floated upon water, llie sodium chloride passes through the
membrane, while the silicic add remains behind in the dialyser,
as a dilute aqueous solution. Substances in solution which are
capable of readily diffusing through such a membrane, were termed
by Graham crystalloidtj- while others, such as the silicic acid,
which either do not pass through, or only do so with difficulty, are
known as colloids.

This aqueous solution of silicic acid may be concentrated by
boiling, and further by evaporation in vacuo over sulphuric acid,
until it contains about 3t per cent, of tetrabasic silicic add, or 14
per cent of nlicon dioxide. In this condition it is a tasteless
liquid, having a feeble add reaction. It cannot be preserved, as
on standing it solidifies to a transparent gelatinous mass, which
has approximately the composition H,SiO,.

590

Iitorganic Cfuintstry

oT these siUcalei are derived fiom the dibulc and ipinbailc kddi alieulj
described, while others nuy be legsrded as Ihe talis of a number of bn>o-
Ihelical polyba^c sitidc acldj, derived liom melasillcic scid by Ihe gradiul
eliminatLon of water. Thus, by the withdrawal of one molecule of waler from
iwo molecules of melaslUcic add, an add kacwo ai disilidu acid Is obtained.
having the composition Si,0,tHO),, or 2SiO„H,0. or H|Si,0,—

25iO(HO), = H,0 + Si50,{H0)^

Si(H0l4 = "lO + Si,0(HO),, or 2SiO,.3H,0. or H^^.
watei from three molectiles of silidi
icids majr be derived, such as—

)r H.Si,Oa; 3SiO„6H,0 or H,^i,Ou ;

3SiO„7H,0 or Hi^i^i^

SilicBtei deriiid from >ui acid conli

monositicstes : those from adds witb

tLvely, disillcales and Irisilicales.
Thus, Ihe miiiernl/i!ririi>/f is a monosilicale, MgjSil
Strftitlint is a ditilicale. MgiSiiOj, and
Fthfar, or mihiclast, is a irJaihnle, Al,K^Si^^

Ihrce atoms of silicon tecpeo-

Symbol, So.

Occurrence.— TiD iJoes n

with chiefly a

nic weigh! = 1.7.35.

ccur in nature in the tincombined
s Ihe oxide SnOi in Ihe mineral
jsiieriie,\ which is found in immense deposits,
although in comparatively few localities. It is usually associated
with arsenical ores, copper pyrites, wolfram (a tungstaie of iron
and manganese), and other minerals. Occasionally it is met with
in nodules of nearly pure oxide, known as stream-tin.

Mode of Fomifitlon. — Tin is obtained exclusively from tin-
stone: and the process with ordinary ore consists of three opera-
tions, namely— (i) calcining, (3) washing, (3) reducing or smelting.
If the ore be nearly pure tin-stone it may be at once smelted.
The finely crushed ore, after being washed from earthy matters,

• MeiaUic tin has been found in Bolivia, but iu origin, whether natural 01
arllGcial, is doubtfiiL

t Cassilerides. the andeni name for the British tiles, is derived from the
fact that lin-slone was found in LuRe auanlitid in Devooihire and Cornwall.

Tin 591

is caldned in a reverberatory fomace. The sulphur and arsenic
pass away as sulphur dioxide and arsenious oxide, and are led into
condensing flues, where the arsenic deposits and is collected. The
iron and copper are oxidised to oxide and sulphate. This calcina-
tion is sometimes conducted in the revolving caldner, shown on
page 446. The calcined ore is next washed, whereby copper
sulphate is dissolved, and the iron oxide and other light matters
are removed. The purified ore is then mixed with powdered
anthracite, and smelted in a reverberatory furnace —

SnO, + 8C - SCO + Sn.

The metal so obtained, is purified by first heating it upon the
hearth of a similar furnace, until the more readily fusible tin melts
and flows away from the associated alloys ; and afterwards by
stirring into the molten tin so separated, billets of green wood,
which results in the separation of a sctun or dross carrying with it
the impurities.

Properties, — Tin is a bright white metal, which retains its
lustre unimpaired in the air. It is sufficiently soft to be cut with a
knife, but is harder than lead, although less hard than zinc At
ordinary temperatures it is readily beaten out into leaf (known as
tin-foil), and may be drawn into wire ; but at temperatures a little
below its melting-point (228^ it becomes brittle and may be
powdered. Tin may be obtained in the form of crystals, by melt-
ing a quantity of the metal in a crucible, and when partially
solidified, pouring out the remaining liquid portion. Its crystalline
character is also seen by pouring over the surface of a block of
cast tin, or a sheet of ordinary tinned iron, a quantity of warm
dilute aqua-regia, when the surface of the metal will immediately
exhibit a beautiful crystallme appearance.

When a bar of tin is bent, it emits a fiunt crackling sound, and
if quickly bent backwards and forwards two or three times, the
metal becomes perceptibly hot at the point of flexure. These
phenomena are due to the friction of the crystalline particles.
When strongly heated, tin takes fire and bums, forming stannic
oxide, SnOf. It is oxidised by both sulphuric and nitric acids ;
thus, when heated with strong sulphuric add, stannous sulphate
and sulphur dioxide are produced —

Sn -H 8H,S04 - SnSO« -H SO, -H 8H,0.

59* Inorganic Chemistry

The Btrongeai nitric acid (specific gravity, i.j) is without a
upon tin. Ordinary concentrated nitric acid (specific gravity, t.4
attacks it with violence, forming metastannic acid (p. 593), white in
cold dilute acid, it slowly dissolves with the production of stannous

4Sn + 9HNO, = 4Sn{N0j), + 3H,0 + NHj.

The ammonia unites with another portion of nitric acid, forming
■ale. Strong hydrochloric acid converts it into
s chloride, with evolution of hydrogen.

Tin is extensively employed in the process of tinning, which
consists in coating other metals with a thin fi\m of tin, by dipping
into a bath of the molten metal. Ordinary tin-plate (or in common
parlance, " tin," the material of which articles generally called
"tins" are made) is thin sheet-iron which has been thus super-
ficially coated with tin.

Alloys of Tin. — Tin enters into the composition of a large
number of useful alloys. With lead, tin will mix in all proportions,
and many alloys are in use consisting of these two metals. They
are all white, and melt at temperatures lower than that of either

Pewter cont^ns 3 parts of tin to I part of lead. Common
solder consists of i part tin and 1 part lead, while coarse and fine
solder contain half, and twice this proportion of tin respectively.
With copper, the most important alloys are the various brasses
and bronzes- Britannia metal contains tin 84 pans, antimony 10
parts, cofiper 4 parts, and bismuth 2 parts. Tin is a constituent
also of the so-called /«j/A/f alloys (see Bismuth, page 461).

Oxides of Tin.— Two oxides are definitely known, namely,
stannous oxide, SnO, and stannic oxide, SnO,. The monoxide is
a base, yielding the stannous sails; the dioxide is both a basic and
an acidic oxide.

Stannotis Oxide, SnO, is obtained by heating stannous oxalate
out of contact with air, thus—

SnCjO, = SnO -I- CO, + CO.

When sodium carbonate and stannous chloride are mixed, carbon
dioxide is evolved, and the white hydraied oxide is precipit
thus—

SSnCl, + 2Na,C0j + H,0 = 4NaCl + SCO, + aSnO,H/)L-

arbon J
tato^^

Metastannic Acid 593

When this hydrated oxide is boiled with insufficient caustic
alkali to dissolve it, the undissolved portion is dehydrated and
converted into the black monoxide.

When heated in the air, stannous oxide becomes incandescent,
burning to the dioxide. It is soluble in acids, forming stannous
salts. The solution of stannous oxide in sodium hydroxide is
used by the calico printer, and is known conmiercially as sodium
stannite.

Stannic Oxide, SnO, {tin dioxide\ is the chief ore of tin. It is
formed where the metal is burnt in the air, but is most readily pre-
pared by igniting metastannic acid.

It is a white amorphous powder, which changes to yellow and
brown on heating, but returns to its original condition on cooling.
When strongly heated in a stream of gaseous hydrochloric acid, it
may be obtained in small crystals, identical with the natural com-
pound. Stannic oxide is unacted upon by acids or alkalies, but
in contact with fused potassium hydroxide it is converted into
potassium stannate.

Stannic Acid, H^nO„ or SnO„H,0, is obtained in a hydrated
condition, as a white gelatinous precipitate, when calcium car-
bonate is added to stannic chloride in insufficient quantity for
complete precipitation. When the precipitate is dried in vacuo,
it has the composition H,SnO). The equation representing its
formation may be expressed thus —

SCaCO, + SnCU + H,0 - 2CaCl, + 2C0, + H,SnO,.

Stannic acid forms a number of salts, of which sodium and
potassium stannates are the most important ; the former being
extensively employed as a mordant in dyeing, under the name of
preparing salt The salts have the composition Na|Sn03,3H|0,
and K|Sn03,3H|0 respectively, and are both soluble in water.

Metastannic Acid, HioSn^Ois, is obtained as a white amorphous
powder, when tin is acted upon by strong nitric acid ; the reaction
may be represented thus —

5Sn + 20HNO, - HioSn^O^ + fiH,0 + aONO,.

The composition of the compound depends upon the particular
temperature at which it is dried. This acid is sometimes regarded
as a polymer of stannic acid, which may be expressed by the
formula 6(H|SnOt) ! metastannic add, however, appears to be

2 P

Inorganic ChtmUtry

dibasic, forming salts in which two only of the hydrogeii atom*
are replaced ; its composition may Iherefbre be convenientlr ex-
pressed thus —

HjSnO,4SnOB4H,0, or H,Sn(0u,4H,0.

Potassium and sodium metasiannates are the best known salts,
iheir formulse beings

K,SnOj,4Sn064H,0, and Na,SnO^4Sn0^4H,O.

Stannous Chloride, SnClj, is obtained by dissolving tin in
hydrochloric acid, and evaporating the solution, when monosyni-
metric prisms separate out, having the composition SnCI^aHgO.
Wlien dried in vacuo they become anhydrous. The anbydrons
chloride is directly obtained when tin filings and mercuric chloride
are heated together —

HgCl, + Sn - SnCI, + Hg.

The reduced mercury volatilises and leaves the chloride, which
at a higher temperature may be distilled

Staiinous chloride dissolves in a small quantity of water, but
with an excess of water, or on eiposure to the air, an oxychloride
(or basic chloride) Is precipitated with simultaneous elimination of
hydrochloric acid, thus —

SSnCI, + SH,0 = Sna„SnO,H,0 + 2HCL

The composition of this oxychloride may also be
either of the following formula; —

Sn,OCI,H,0, or 2Sn(0H)Cl, or 8(SnO,HCI).
Stannous chloride is a powerfiit reducing agent, as it readily
combines with either oxygen or chlorine ; thus, when added to a
solution of mercuric chloride, the latter is first reduced to met-
curous chloride, which, on being gently warmed, is reduced to
metallic mercury —

2HgCI, + SnCI, = Hg,CI, + SnCI,
Hg,Cl, -H SnCI, = SHg + SnCI,
By the absorption of oxygen, the above oxychloride and stannic
chloride are formed, thus —

3SnCI, -f O + H,0 ~ SnC)rSnO,H,0 -f S0CI4.

Stannic Sulphide 595

Stannous chloride boils at a temperature about 606*. The
density of the vapour only agrees with the formula SnClj at tem-
peratures above 900^, at lower temperatures its vapour density
approaches more nearly to that required by the formula Sn|Cl4.

Stannic Chloride, SnClf, is obtained by passing a stream of
dry chlorine over melted tin in a glass retort ; or by heating a
mixture of i>owdered tin with an excess of mercuric chloride, when
the anhydrous chloride distils over as a colourless, mobile, fuming
liquid, which boils at 113.9*. It unites with water with evolution
of heat, fonning hydrated compounds of the composition SnCl^,
3H,0 ; SnCl4,6H,0, and SnCl4,8H|0. The compound containing
5H|0 is employed as a mordant, and is commercially known as
oxy muriate of tin.

Stannic chloride combines with alkaline chlorides forming
double chlorides (sometimes called chloro-stanfuUes)^ such as
SnCl4,2NH4Cl, and SnCl4,2KCL

Stannous Slllphide» SnS. — When tinfoil is introduced into
sulphur vapour the metal takes fire, and yields a leaden-coloured
mass of stannous sulphide.

In the hydrated condition, stannous sulphide is precipitated as
a brown powder, when sulphuretted hydrogen is passed through
stannous chloride ; on drying, this becomes black and anhydrous.

Stannous sulphide dissolves in hot concentrated hydrochloric
acid. It is also soluble in alkaline polysulphides, forming sulpho-
stannates, thus —

(i) 4SnS + K,St - K,SnS, ■¥ 3SnS,.
(2) SnS, + K,S = K^SnS^

On the addition of hydrochloric add to the solution, stannic
sulphide is precipitated —

K,SnSs + 8HC1 - 8KC1 + H,S + SnS,.

Stannic Sulphide, SnS,. — This compound cannot be formed
by heating tin and sulphur alone, as the heat of the reaction is
greater than that at which stannic sulphide is resolved into
stannous sulphide and sulphur. It is obtained by heating tin
amalgam, sulphur and anunonium chloride, in a retort The action
that takes place is a complicated one, various products being
volatilised, and stannic sulphide remaining in the retort as a mass
of golden yellow scales. Amongst the products expelled during
the process are ammonium chloride, sulphur, mercuric chloride.

59^ Inorganic Chetnistry

Ws9«

^V mercuric sulphide, and sulphuretted hydrogen. The ammoniain
^^ chloride present, probably acts by the formation of ammoniutn
stannous chloride, as an intermediate product, which is then de-
composed with the production of stannic sulphide and amnnoniuin
stannic chloride, thus —

■ 2SnC1^3NH,Cl H SS = SnS, + NH.Cl + SnCl4,SNH,CL

Stannic sulphide is a golden yellow crystalline substance, which
I when heated, partially sublimes as such, but is for the mast pari

decomposed into the monosulphide and free sulphur. It is largiJy
used as a pigment known as mosaic gold.

OQeiHTOnce.^-l'ead has been found in small quantities in the
uncombined state, probably reduced from its nrcs by volcanic

In combination with sulphur it occurs in enormous quantities Jn
the minera! galena, PbS, which is [he ore from which the metal
is chiefly obtained. Large quantities are also met with as carbonate
in the mineral ctrussiU, PbCOj. Other natural compounds
anglesite, PbSO, ; lanarkite, PbSO„PbO j matiockUe, PbClj,PbO \
fiyromorpAiU, SPbaPjOi.PbCl,

Modes of Formation.— Lead is very readily reduced from it*
compounds, and on this account was ore of the earliest known
metals. It was termed by the Romans ^/uMJum nigrum.

Two general processes are made use of for the reduction of lead
from its ores : —

In the lirst method (known as the reduction process), the lead I
sulphide is reduced by double decomposiiioo with lead oxide and
sulphate, which are formed by roasting the ore.

In the second (called the prtcipilatton process), the sulphide is
reduced by metallic iron.

(i.) The galena is introduced into a reverberatory furnace, where
it is partially roasted, whereby a portion of the sulphide Is oxidised
to sulphate and oxide —

PbS + 20, - PbSO,.

SPbS + 30, - apbo + «S0»

' The temperature is then raised, when the oxide and sulphate
react upon a Turther pnition of the sulphide, with the formaiion oi

metallic lead and the evolution of sulphur dioxide—

pbso, + Pbs " 2Pb + aso,

SPbO + PbS - 3Pb + SO,

This method of lead smelting is followed when the oie is fairly
ftee fiom other metallic sulphides. The reverberatory furnace
usually employed (known as the FUntshirt furnan] has a con-
siderable depression, or well, in the heaith, where the metallic

Kia. .43-

lead collects during the process, and from which it is drawn olf
into a metal pot.

The same process is carried out in the North of England, and
in Scotland, where a very pure lead ore is employed, upon open
shallow hearths (known as the ore hearth, or Scotch hearth), built
under a brickwork hood or chimney in such a manner that the
fumes of lead which escape are caused to pass into condensing
chambers. Fig, 143 shows such a hearth in section. The fire of
peal and coai is urged by a small blast admitted from behind, and
the ore is added in small quantities at a time. The reduced metal
sinking to the bottom, runs under the fire-bar, and overflows
^ from the shallow hearth down a chaAQet upon an inclined stone

Inorganic Chemistry

surfaces (called the ■work-slont) into an iron pot P, which is gentlr
healed by a small fire to enable the ape»lot to ladle the metal out
into moulds.

(i.) This method of lead smelling depends upon the fact, that at
a high temperature metallic iron, in contact with lead sulphide, ii
converted into ferrous sulphide, with separation of lead —

PbS + Fe - FeS + Pb.

The ores (either in the raw state, or after previous calcioalion)
are smelted in a blastfurnace with coke and either metallic iron,
or such materials as wiU yield iron under the furnace conditions.
The sulphide of iron, along with other metallic sulphides, rises to
the top of the molten lead as a matt or regulus, while above this a
fusible slag collects, consisting chiefly of silicate of iron.

The lead Grst obtained by any of these processes usually con-
tains antimony, tin, copper, and other metals. These impurities
are removed by healing the metal in a shallow, flal-bottomed
reverberalory furnace. Most of Ihe admixed metals oxidise before
the lead, and collect in the dross which forms upon the surface
This process is known as the softening of ieail. The silver, how-
ever, which is always present, is not removed by this operation,
but is extracted by one of the methods for desilverising lead
desctibcd under silver, page 516.

Properties. —Lead is a soft, bluish-white metal, which whea
freshly cut exhibits a bright metallic lustre. On exposure to the
air its bright surface becomes quickly covered with a film of oxide.
Lead is sufficiently soft to be scratched with the finger nail, and
it leaves a black streak when drawn across paper, it cannot be
hammered into foil, or drawn into wire, but may readily be obtained
in these forms by rolling and pressing. When a quantity of
melted lead is allowed partially to resolidify, and the still liquid
portion poured off, the metal is obtained in the form of octahedral
crystals belonging to the regular system. Its crystalline nature is
also readily seen by submitting a solution of a lead salt to electro-
lysis, when the metal is deposited upon the negative electrode in
beautiful arborescent crystals with a brilliant metallic lustre (Fig.
144). It is deposited in a similar form, known as the Uad trie, by
suspending a strip of zinc in such a solution. The specific gravity
of lead is 11.3 ; it melts ai 330° to 335", and becomes covered with
a black film of the suboxide, PbiO : when tnore strongly heated
it is oxidised to the monoxide. PbO.

Ltad S99

Lead is i^udly diuolved \>j nitric add, bot hydroditoTic and
■olphotic adds are almost withoat action upon it in the cold. Hot
concentrated hydrochloric add, however, slowly convert) it into
lead chloride.

Lead is unacted upon by pure water, in the absence of air ; but
in contact with air, lead bydrozide ii formed, which ia slightly
soluble in water. By the action of atmospheric carbon dioside upon
this solution, a basic carbonate is predpitated, having the com-
pontion SPbCO^PbCHOV The solTent action of water upon lead
is greatly influenced by the preseoce of various dissolved tut>

Pin. i4«.

stances in the water ; thus, water containing small quantities of
ammoniacal salts, notably the nitrate, dissolves lead mudi more
rapidly, and the same is the case with water charged with carbon
dioxide under pressure. In the latter case the action is probably
due to the formation of a soluUe add carbonate.

Water, on the other hand, containing small quantities of phos-
phates and carbonates, espedally the add caldum carbonate, are
almoat entirely without action upon lead. Certain drinking waten
(such as the Loch Katrine water), which on accoimt of thor purity

Ittorgank Chemistry

exert a solvent action upon the lead pipes through which ttiey aie
conveyed, are rendered incapable of acting upon the lead by being
first filtered through chalk or animal charcoal, which enables them
10 take up sufficient calcium carbonate or phosphate lo prevent
this action.

On account of the exhaustive melhods of desilverisation to which
the lead is subjected, commercial lead possesses a degree of purity
not found in any other metal as commonly met with -, the total
amount of foreign metals present in ordinary commercial lead,
ranges from 0.1 to 0,006 per cent.

Lead is put to a large number of uses in the arts, on account ot
the ease with which it can be worked, and its power of resisting
the action of water and many acids. In the manufacture of lead
pipes advantage is taken of the extreme softness of the metal, and
the readiness with which it can be pressed into shape ; the lead,
in a pasty or semi-molten condition, being merely squeezed,
squirted, through a steel die, by hydraulic pressure.

Lead bullets are also made by squeezing the metal into moulds
for as lead contracts on solidification, bullets made by castii
always contain a small cavity, which (unless it happens to foi
exactly at the point of centre of gravity) renders the flight of
bullet untrue.

Oxides of Lead. — Five oxides of lead are known, having
composition PbjO, I'bO, Pb,Oj, PhjO^ PbO^

Lead Suboxide {plumbous oxide), Pb,0, is the black compound
i\hich is formed when lead is heated to its melting- point. It is
obtained by heating plumbic oxalate to about 300° in a glass tube

2PbC,0( = CO + SCO, + PbjO.

When healed in the air it bums, forming plumbic oxide ; in the
absence of air it is decomposed into the same oxide and metallic
lead, the reactions being —

Pb,0 + O - SPbO.
PhjO - Pb + PbO.

In contact with acids it decomposes in the same manner, lead
being deposited, and the plumbic oxide dissolving in the acid to
form a plumbic salt.

Plumble Oxide {Uad monoxide, litharge, massieof), PbO, is
formed when lead is strongly heated in the air, and is obtained in

;ad.

Rid Lead 6oi

large quantities in the cupellation of argentiferous lead. It may
be obtained by heating lead nitrate or carbonate, and it is produced
when any of the other oxides are heated.

Plumbic oxide is a yellowish powder, known conunercially as
massicot^ which, when melted and resolidified, is obtained as a
crystalline mass, known as litharge. Plumbic oxide is very slightly
soluble in water, i part dissolving in 7000 parts of water : this
solution is alkaline, and on exposure to the air absorbs carbon
dioxide, forming an insoluble basic carbonate. Plumbic oxide is
dissolved by acids, with formation of the salts of lead ; it also
dissolves in warm potassium, or sodium hydroxide.

This oxide forms two hydrated compounds, having the com-
position 2PbO,H,0 and 3PbO,H,0. The former is obtained as a
white precipitate when ammonia is added to a solution of lead
acetate ; the second, by the action of anunonia on basic lead
acetate at 25*.

Lead Sesquioxide, PhjOs, is obtained as an orange-coloured
precipitate by adding sodium hypochlorite to a solution of plumbic
oxide in potassium hydroxide. Heat decomposes it into oxygen
and plumbic oxide. Acids convert it into the monoxide and
dioxide, the former dissolving and yielding a salt of lead. This
oxide may be regarded as a compound of two oxides, PbO,PbOf.

Trlplumbic Tetroxide {red lead^ mimum\ Vhfi^ is obtained
when lead carbonate, or monoxide, is subjected to prolonged
heating in contact with air, at a temperature not above 450*. At
higher temperatures it again gives up oxygen. It is a scarlet
crystalline powder, varying somewhat in colour, according to its
mode of preparation. Dilute acids convert it into PbO] and
2PbO, the latter oxide dissolving to yield lead salts. With strong
hydrochloric acid and sulphuric add, the molecule of lead dioxide
is acted upon with evolution of chlorine and oxygen respectively —

PbjOi + 8HC1 - 4H,0 + 3PbCl, + CI,.
Pb,04 + 3H,S04 - 3H,0 + 3PbS04 + O.

Red lead* is employed as a pigment, and also in the manu-
facture of flint glass.

* Commercial red lead varies oonsiderablj in composition, and although it
has been shown that a definite compound exists, of the composition Pb|04
(which may also be expressed by the formula 2PbO,PbOs), it is still uncer-
tain whether there are not other compounds consisting of these two oxides
united in different proportions.

602 Inorganic Chemistry

Plumbic Peroxide (Itad dioxide), PbO„ may be obuined by
the action of dilute nitric acid upon red lead —

Pb,0, (or PbOfcSPbO) + 4HNO» - PbO, + 8Pb(NO,), + aH,a

Or it may be prepared by the action of oxidising af^ents upon

the monoxide. Thus, when chlorine is passed through an alkaline
solution, in which the monoxide is suspended, or when bleaching-
powder is added to a solution of lead acetate, the dioxide i>
produced.

The dark brown deprosit which forms upon the positive electrode
when a soluiion of a lead salt is electrolysed, also consists of tbe
dioxide.

Plumbic peroxide is a brown or puce-coloured powder.
powerful oxidising substance, and when gently rubbed with floi
of sulphur in a wnrm mortar the mass suddenly infiames.
a stream of sulphur dioxide is passed over the peroxide in a tube,'
the two compounds unite to form lead sulphate, the mass becom-
ing incandescent. Nitric acid is without action upon it, but
hydrochloric and sulphuric acids act upon it in the same manner
as upon red lead. When strongly heated, tbe peroxide gives up
oicygen, and is converted into the monoxide.

When plumbic peroxide is boiled with strong aqueous potassium
hydroxide it dissolves, and the solution deposits crystals of pocaa-
sium plumbaie, K,Pb03,3H,0. This compound corresponds with
potassium stannatc, K,SnOs,3H,0, and its existence shows that
lead possesses, although to a very feeble extent, the acidic properties
exhibited by the other members of the same family of dements.

Plumbic Chloride [lead dichloride), PbCl^ is obtained as ■
while curdy precipitate, when hydrochloric acid, or a soIuUs
chloride, is added to a solution of a lead salt. It is also produced
by the action of boiling hydrochloric acid upon lead in the pi^
sence of air. It is best prepared by dissolving lead oxide
carbonate in hot hydrochloric acid, when the lead chloride se]

cooling, in long white, lustrous, needle-shaped crysiali

1 the rhombic system. Lead chloride is soluble ill

r to the extent of about 4 parts in loo parts of water.

On cooling the solution, the greater part of the salt separates

~ the liquid contains 0.8 parts in solutioa Tbe prcsentMT
of hydrochloric acid and soluble chlorides diminishes ifai
bility of lead chloride..

irooe
f the

belonging
boiling wa
^^ On coolinf
^^ and at t
^^1 of bydrod
^^K bility

Lead NitraU 603

When heated in contact with air, it is converted into an ozy-
chloride, of the composition Pb,OClt, or PbCli,PbO, corresponding
with the natural compound mailockite. This compound, in the
hydrated condition, Pb,OCli,H|0, is prepared on a large scale by
the addition of lime-water to a solution of lead chloride, and is
employed as a white pigment, known as Pattinsotis white lead.

Cosset yettow is an oxychloride of lead of the composition
PbClt,7PbO, obtained by heating lead oxide and anmionium
chloride.

Lead Tetrachloride (tecut perchtoride\ PbCl4.— When plumbic
peroxide is dissolved in cold concentrated hydrochloric acid, a
yellow liquid is obtained, which, on warming, yields chlorine,
with precipitation of lead dichloride. This liquid contains the
tetrachloride of lead in solution.

When lead dichloride is suspended in hydrochloric acid, and
chlorine is passed through the mixture, a solution of lead tetra-
chloride is obtained ; and on the addition of ammonium chloride,
ammonium plumbic chloride, PbCl4,2NH4Cl (corresponding to
ammonium stannic chloride), separates out When this compound
is acted upon with strong sulphuric acid, in the cold, lead tetra-
chloride separates out as a yellow oily liquid.

Lead tetrachloride is a yellow, highly-refracting, fuming liquid,
which decomposes in contact with moisture into lead dichloride
and chlorine. It may be preserved beneath concentrated sul-
phuric acid. With small quantities of water, it forms a hydrated
compound, but excess of water decomposes it into hydrochloric
acid and lead peroxide —

PbCl4 + 2H,0 « PbO, + 4HCL

When heated with strong sulphuric add to about 105*, it suddenly
decomposes with explosion.

Lead Nitrate, Pb(N0s)2, is obtained by dissolving litharge in
nitric acid. The salt is deposited from the solution in the form of
regular octahedral crystals. It is soluble in water to the extent of
50 parts in 100 parts of water, at the ordinary temperature. When
heated, it evolves nitrogen peroxide and oxygen, leaving plumbic
oxide (page 217).

On boiling an aqueous solution of lead nitrate with lead oxide,
the latter dissolves, and the solution on cooling, deposits crystals
of a basic nitrate, Pb(NOt)HO or Pb(NOg)a,PbO,H,0. By the
addition of ammonia to a solution of lead nitrate, other basic

Inorganic Cfumutry

; are obtaioed, which may be regarded as consisting of
compounds of Pb(NO,)HO with PbO, or of P^NOj), wilh PbO
and H,0 in varying proportions.

Lead Carbonate, PbCO„ is obtained as a white crysialliae
powder, by the addition of ammonium sesqui carbonate to a solu-
n of lead nitrate. It occurs in the form of transparent rhombic
crystals in ihcmineral etrussiU, isomorphous with arragonitc Lead
carbonate is almost insoluble in water, but is appreciably dissolved
r charged with carbon dioxide. When sodium or potassium
carbonate is added 10 a solution of lead nitrate, basic carbonates
of lead are precipitated, varying in composition with the conditioo>
of tempeniiur& The most important of the basic carbonates ii
■white lead, aPbCOj,Pb(HO)a. This compound is mantifactured
a large scale by several processes, for use as a pigment. The
oldest process, and that which
yields the best produtS, b
known as the Dutch milhod.
It depends upon the action
of acetic acid upon metallic
lead, in the presence of moist
air and carbon dioxide. The
lead, cast into rough gratings
in order to expose a large
surface, is placed in earthen-
ware pots, as shown in Fig.
145. Asmallquaniityofdilute
acetic acid (in the old Dutch
1 the pots, and the gratings of lead,
which rest upon the shoulder of the pot, ate piled one upon the
other. These pots are then placed upon a thick bed of spent tan-
bark (in the original method, dung), upon the floor of a shed, and
covered with planks. Upon these another layer of tan-bark is
spread, and a second row of pots similarly chained. In this
yihe layers of pots are built up to the roof of the shed, and
the whole allowed to remain for about three months. Such a stack
will coninin many tons of lead, and about 65 gallons of dilute acetic
ncid to the Ion of metal. The acid is gradually vaporised by the
heat developed by the fermenting tan-bark, which results 6rst u
the formation of a basic lead acetate —

icale by several process

Fig. 145.

process, viiugar) is placed i

SH(C,H,0^ + SPb -f O,- Pb(C,H,O0»Pb(HOV

results Drst m 1

Lead Sulphate 605

This btisic acetate is then acted upon by the carbon dioxide
evolved during the fermentation, with the production of a mixture
of normal lead acetate, and basic lead carbonate, thus —

3{Pb(C,H,0,)j.Pb(H0)J +2CO,=3Pb(C,H,0,), +2PbCO,.Pb(HO), + 2HiO.

/Vnd the lead acetate, in the presence of air and moisture, reacts
upon a further portion of the metal, regenerating the basic acetate,
which is once more decomposed by carbon dioxide —

Pb(C,H,0^, + Pb + O + H,0 - {Pb(C,H,O^Pb(HOW.

In this cycle of reactions, therefore, the acetic acid acts as a
carrier, a comparatively small quantity being able to convert an
indefinite amount of lead into white lead.

White lead is also prepared by passing carbon dioxide into a
solution of the basic acetate, obtained by boiling plumbic oxide
(litharge) with lead acetate. The product, however, is not so
opaque as that obtained by the former method, and is therefore
not so valuable as a pigment (This method is known as the
Clichy^ or Th^nard's process.)

Milnet^s process consists in grinding together litharge, sodium
chloride, and water, whereby a mixture of an oxychloride of lead
and sodium hydroxide is formed —

4PbO + 2NaCl + 6H,0 = PbCl„3PbO,4H,0 + 2NaHO,

and then passing carbon dioxide into the mixture, which converts
it into white lecut and sodium chloride, thus —

3[PbCl„3PbO,4H,0] + 6NaH0 + SCO, - 6NaCl +
4[2PbCO„Pb(HO)J + 11H,0.

White lead is a heavy, amorphous powder, whose value as a
pigment, or body colour, depends upon its opacity and density.
Although this compound labours under the disadvantages^bf being
extremely poisonous, and of becoming blackened by sulphuretted
hydrogen, no substitute for it has yet been found which possesses
the same " body " or covering power.

Lead Sulphate, PbSOi. — The mineral anglesite^ PbSOf, occurs
in the form of rhombic crystals, isomorphous with strontium and
barium sulphates. Lead sulphate is obtained as a white powder,
by precipitating a lead salt with sulphuric acid, or a soluble

606 Inorganic Chemiitry

sulphate. It is soluble in water only to an extremely slight esieju,

and still less in dilute sulphuric acid, but strong sulphuric acid
dissolves it readily. It also dissolves in potassium hydrtixide, and
in many ammoniacal salts, notably the acetate, and in sodiuni
tbiosulphace.

An acid sulphate, of the composition PbSO„H,SO^,H,0 is
obtained by boiling the normal sujptiaie wilh sulphuric acid ; and
a basic sulphate, PbSO,,PbO, is formed by the action of a.nunonia
upon the normal salt.

Lead Sulphide, PbS. — The natural sulphide, galena, is found
in the form of cubical crj-stals, possessing very much the colour
and the metallic lustre of freshly cut lead. It is arliticially formed
when lead is healed in sulphur vapour, or when sulphuretted
hydrogen is passed through a solution of a lead salt.

When healed in vacuo, or in a stream of an inert gas, lead
sulphide melts, and sublimes in the form of small cubes.* When
heated with free access of air it is converted into lead sulphate.

Boiling dilute nitric acid converts lead sulphide into the nitrate,
with separation of sulphur ; but strong eitric acid oxidises it into
fead sulphate. Il is decomposed by hoi concentrated hydrochloric
acid, with evolution of sulphuretted hydrogen.

When sulphuretted hydrogen is passed into a solution of lead
chloride, the precipitate which fonns is first yellow, then reddish-
brown, and finally black ; the yellow and red precipitates a
pounds of lead chloride and lead sulphide, termed sulphochtorido, j
having the composition, PbS,PbClj, and SPbS.PbC^

The compounds of lead are powerful poisons, and when con- {
linuously taken into the system in small quantities, they act X^m
cumulative poisons. Painters and others who constantly hand!
white lead, are liable to suffer from chronic lead poisoning.

• Fiom the readiness wilh wliich lead sulpiride volatilises when bealetl %

B strEam of sulphur dioxide, Hannay eondudes {Prae. Chcm, inc.. May 1894

tbal the two subalances unite to form a volatile compound. PbS.SO> A

PbS^t, wbich when its temper.ituiE fails, again tireaju up into lead SulphidI

and sulphur dioxide. He sulcd thai when sulphur dioxide \\ geiiaaled Ii.

inlimale contact wilh galena, as when a Hream of air is passed llirough the

roollen substance, one halfof tlie lead is reduced, and one half vo Utilises with ibe

■•nglo the equauon 2PbS+ 0,= Pb + PbS.bOj. Bui llie nceot

ol Smltli and Jenkins \Pr(K. Clum. Soc.. June iBy?] &ho>v (bat

ratio between the volatilised and reduced lead does not olitKia;;

nodlbey find no evidence of Ilie existence of the compound Pt>S^

CHAPTER X

ELEMENTS OP GROUP V. {JPAHILY A.)

Vanadium^ V = 51.x ; NioHum, Nb = 93.7 ; Tantalum^ Ta s 183.

Thr three rare metals comprising this family are closely related to each
other, and also to the elements of fiunUy B oif the same group, namely, the
nitrogen and phosphorus series.

Vanaditmi occurs in a few rare minerals, as vanadite^ 8Pb,(V04)),PbClf
(the vanadium analogue of pyromorphite) ; fucheriU^ BiVOfj mottramiie,
(PbCu),(V04)s.2(PbCu)(HO),. Small quantities also occur in certain iron
ores, the vanadium ultimately finding its way into the Bessemer slag, in
which it has been found concentrated to the extent of 1.5 per cent.

Metallic vanadium was first isolated by Roscoe (1867), although its existence

was previously discovered by Del Rio (x8oi). The metal is extremely difficult

to obtain, as at a red heat it combines %irith oxygen with great readiness,

fielding the pentoxide VgOf, and also with nitrogen, forming the nitride VN.

The element is prepared by heating the dichloride in a stream of perfectly

pure hydrogen —

VCl,+ Ht = 2Ha + V.

Vanadium is unacted upon by air at ordinary temperatures, but when
heated bums brilliantly to the pentoxide.

Niobium and tantalum are found associated together in the rare mineral
tanialitt or columHU. The first to be discovered was tantalum (Hatchett,
i8ox), and was originally named columHum ; and the name niobium (from
Niobe, the daughter of Tantalus) was given to the allied element, by Rose
(1846). Niobium is obtained by beating the trichloride, NbO,, in a stream
of hydrogen.

Vanadium forms five oxides, corresponding to the oxides of nitrogen,
while three oxides of niobium and two of tantalum are known :^

ViO ; VA(or VO)
- : NbO

V,0, : V A(or VO^ ; V^^

— ; NbO, ; NbgO^

— ; TaO, ; Ta^O^

The pentoxides are obtained when the metals are burned in air or oxygen,
lliey give rise respectively to vanadates, niobates, and tantalates, correspond
Ing to nitrates and metaphosphates, thus —

Sodium nitrate, NaNO,. Sodium metaniobate, NaNbOt.

Soditmi metaphosphate, NalXV Sodium metatantalate, NaTaCV
Sodium metavanadate, NaVO^

607

6o8 Inorganic Chemistry

The doaer relation of these eleroentt to phoephorai thsn to nltrocen. Is warn
in the formation of salts derived from ortbo- and pyR>«cids» correspotiding
to orthopbosphates and pyrophospl^iues. The naturally oocwiiiig ▼arnuthm
compounds above mentioned are vanadates derived fr6m the hypotbeiical
orthovanadic add, H8VO4. Both meUvanadlo add, H VO^, and pjrnyvanadie
add, H4V^, have been obtained. Unlike the phosphorus compounds, the
metavanadates are the most stable of the three classes of salts, and the
orthovanadates the least stable. The most important of these aalu is the
ammonium metavanadate. NH4V0^ whidi is prepared by dissolving the
pentozide in ammonia. This salt is insoluble in ammonium chloride, and
use is made of this property in the prepaiation of vanadium compounds
from the mineral moUramiU, When ammonium metavanadate is Ignited,
vanadium pentozide is obtained —

2NH4VO^ s VA + 2NH| + H A

Vanadium acts also as a feeble basei Thus, when the tetroxide, or hypo-
vanadic oxide, is dissolved in sulphui;ic add, hypovanadic sulphate. V^OafSQJ^
is fr)rmed. The solution of this salt possesses a rich blue colour.

Vanadium forms three chlorides, having the composition^

VCI, (or VjCy ; VCI, (or V^CIJ ; VCI4.

Niobium gives a trichloride, NbClg, and pentachloride, NbCls, while only
the pentachloride of tantalum is Icnown, TaQf.

Vanadium forms a number of compotmds with oxygen and chlorine. Thus,
when vanadium tetrachloride is acted upon by water, it yields h3rpovanadic
chloride, V^^CIq, which dissolves in the water, giving a blue solution.

Vanadium oxychloride, or vanadyl trichloride, VOCl^, corresponds to phos-
phorus oxychloride, POClt. From vanadyl trichloride, by treatment with
zinc, vanadyl dichloride is obtained, VCXZlt, and by the action of hydrogen at
a high temperature upon this, both vanadyl monochloride. VOCl, and divanadyl-
monochloride, V^Cl. are formed.

CHAPTER XI

ELEMENTS OP GROUP VI. {PAMILY A,)

Chromium, Cr . . 53 I Tumgtttn, W . . - i<f

Alolybdtnum, Mo . . . 95.9 | Uramittm, U . . . a3».a

GHBOJUUM.

Symbol, Cr. Atomic weight = 5a.

Oocorrence. — Chromium does not occur in nature m the on*
combined state. In combination with oxygen and associated
with iron, it is met with in considerable quantities in the mineral
chrome iron ore^ or ckromiity Qxfi^¥tO, This ore is the chiel
source of chromium compounds. Other natural compounds axe
crocoisite^ PbCrOi, and chrome-ochn^ Qxfi^ Traces of chromium
are present in various minerals, such as the emerald and green
serpentine, and impart to them their green colour.

Modes of Formation. — Although chromium compounds are
manufactured for industrial purposes, the element itself has re-
ceived no technical application.

It was obtained by W5hler, by the reduction of fused chromium
chloride with metallic zinc, beneath a layer of fused sodium and
potassium chlorides. The regulus, or alloy of zinc and chromium,
was then treated with dilute nitric acid, whereby the zinc was
dissolved, and the chromium was obtained in the form of a
powder. ' Chromium may also be obtained as bright metallic
scales, by the electrolysis of a solution of chromous chloride
containing chromic oxide. The metal may be prepared by the
reduction of the oxide, CriOn by means of carbon, at a high
temperature ; or by heating the oxide with metallic aluminium.

Properties. — Chromium is a hard, steel-grey metal, which is
not oxidised in dry air. When heated in the oxyhydrogen flame
it bums brilliantly. It dissolves in hydrochloric acid with evolu-
tion of hydrogen. The metal is not magnetic The presence of

fa9 2 Q

6 10 Inorganic Chemistry

minute quantities of chromium in steel, imparts to the latter great
hardness and tenacity.
Oxides of Chromium.—Two oxides of chromiam are definitely

known, namely —

Chromium sesquioxide {chromic oxide) Qtfi^

Chromium trioxide {chromium ofikydruU) . CrO^.

The first is a basic, and the second an acidic oxide. Besides
these two compounds, a hydrated oxide, derived from the unknown
chromous oxide, also exists, having the composition CrO,HtO, or
Cr(H 0)t. It is obtained as a yellowish precipitate by adding potas-
sium hydroxide to a solution of chromium dichloride (cfaromoas
chloride), with the exclusion of air. It rapidly absorbs oxygen,
turning dark brown. When heated out of contact with ur it is
converted into the sesquioxide, with evolution of hydrogen —

2CrO,H,0 - Cr,0, + H,0 + H,.

Cther compounds of chromium and oxygen are described, whose composi-
tion, however, is not definitely established ; thus, the product obtained as a
brown powder, either by the partial reduction of the trioxide, or the oxidation
of the sesquioxide, is regarded by some chemists as chromium dioxide. CrOf,
and by others as chromium chromate, CrtOt,CrOj. It is readily obtained by
passing nitric oxide into a solution of potassium dichromate.

Chromium Sesquioxide, CriO^, is obtained as a grey-green

powder, when either the hydroxide, or the trioxide, or ammonium
dichromate is ignited (see page 206).

When the vapour of diromyl dichloride, CrOfCl^ is passed
through a red-liot tube, chromic oxide is deposited in the form of
dark-green hexagonal crystals. Chromic oxide which has been
strongly ignited, is nearly soluble in acids. It is used imder the
name oi chrome green as a pigment, and for giving a green colour
to glass.

Chromic Hydroxides. — Chromic oxide yields a niunber of
hydrated compounds. When ammonia is added to a solution of
chromic chloride, or other chromic salt, free from alkali, a light-
blue compound is precipitated, which, when dried over sulphuric
acid, has the composition Crj(H0)»4H,0 (or Ctfi^lHfi). When
this is dried in vacuo, it loses 3H,0, and becomes Cr^HO)^HsO
(or Cr203,4H,0) ; and on being heated at 200°, it afrain parts with
3 11,0, and has the composition Cr,Os,H,0.

Chromium Trioxide 6ii

When potassium dichromate and boric acid are heated to doll
redness, and the mass treated with water, a rich green residue is
obtained, having the composition Cr|OaiSH|0. This compound,
known as Guignefs greeny is employed as a pigment

The first two of these compounds, which may be looked upon as
consisting of the hydroxide Cr|(HO)e in a hydrated condition,
namely, Cr2(HO)^4H,0 and Cr^HO)»HsO, are readily soluble in
acids, yielding the chromic salts.

Chromium Trioxide {chromic anhydride)^ CrOj. — When strong
sulphuric acid is added to a cold saturated solution of potassium
dichromate, the trioxide separates out in long, red, needle-shaped
crystals —

K,Cr,Or + HgSOi = K,S04 + HgO + 2CrO,.

The liquid is decanted from the crystals, which are drained
upon porous tiles, and the adhering sulphuric acid and potassium
sulphate washed away by strong nitric acid. The crystals are
finally heated upon a sand-bath, whereby the nitric acid is
evaporated.

Chromium trioxide dissolves in water to the extent of 63 parts
in 100 parts of water at 26*. It melts at a temperature about 19a*.
At 250* it begins to give off oxygen, and is ultimately converted
into the sesquioxide —

JCrOs - CrjO, + 80.

Chromium trioxide is a powerfiil oxidising agent, and in contact
with most organic substances it is reduced. In the preparation
of the compound, therefore, the liquid cannot be filtered through
paper in the usual way. Warm alcohol dropped upon the trioxide
at once takes fire, while in a more diluted condition it is oxidised
to acetic acid ; and the reduction of the chromium trioxide is made
evident by the change of colour of the liquid, from red or yellow,
to olive green.

Gaseous ammonia reduces the trioxide to the sesquioxide, with
formation of water and nitrogen —

2NH, + 2CrO, - Cr,0, + N, + 3HA

the reaction being accompanied with the evolution of so much heat
that the chromic oxide pioduced becomes incandescent
When hydrogen peroxide is added to a dilute solution of

6l2 Inorganic Chemistry

chromium trioxide, or to a dilute solution of potassium dichromate,
acidified with sulphuric acid, a deep indigo-blue solution is ob-
tained. This blue compound is believed to be perchromic acid^
but its composition has not been definitely established. It may be
regarded as a compound of chromium tnoxide, CrOs, with hydrogen
peroxide, H^Oj, in undetermined proportions.

In aqueous solution, the blue colour quickly disappears, oxygen
being eliminated. The compound is soluble in ether ; and, there-
fore, when the aqueous solution is shaken up with that liquid, a
deep blue ethereal solution rises to the top. In this solution the
compound is more stable, but when evaporated it evolves oxygen,
leaving chromium trioxide. It is decomposed by alkalies, forming
alkaline chromates, with evolution of oxygen. The formation of
this compound constitutes a delicate test for either chromium
trioxide or hydrogen peroxide (see Hydrogen Peroxide, page 203).

Chromons Compounds.— These correspond to chromous hydrate, Cr(HO)^
in which the chromium functions as a divalent element. Comparatively few
of these salts are known.

ChromouB Chloride, CrCl^, is formed when the metal dissolves in hydro-
chloric add. It is prepared in the anhydrous state by gently heating chromic
chloride in a current of pure hydrogen. It is a white crystalline compound,
soluble in water to a blue solution, which rapidly absorbs oxygen.

Chromoufl Sulphate. CrS04.7H20. is obtained by dissolving chromous
acetate in dilute sulphuric acid. It is deposited from the solution in blue
crystals, isomorphous with ferrous sulphate, FeS04,7H20.

Chromic Compounds. — These are derived from chromic oxide,
the oxide acting as a base.

Chromic Chloride, CrCl,, or CrjCle, is prepared by strongly
heating a mixture of chromic oxide, CrjOj, and carbon, in a stream
of ory chlorine. The chromic chloride sublimes in the form of
scales, having a reddish-pink colour. The molecular weight of
chromic chloride is 158.6, showing that in the vaporous state its
molecules have the formula CrCls.

It is nearly insoluble in water, but readily dissolves in water
containing minute traces of chromous chloride, forming a green
solution. The same solution is obtained by dissolving hydrated
chromic hydroxide, Cr,(H0)(„4H,0, in hydrochloric acid, and if
this solution be slowly evaporated, very soluble green crystals
separate out having the composition CrsC1^12H20. If strongly
heated in the air, this compound gives off water and hydrochloric
acid, leaving chromic oxide, CrjOf ; but when heated to 250*, in

Ckronu Abim 6 1 3

either gaseous hydrochloric add or chlorine, it is converted into
the pink anhydrous chromic chloride, which redissolves in water
to the green solution. If heated strongly and sublimed, the com-
pound obtained is nearly insoluble in water.

Chromic Sulphate, CriCSOf),, is obtained by dissolving chro-
mium hydroxide in concentrated sulphuric acid, when a green
solution is formed, which on standing changes to blue, and slowly
deposits violet-blue crystals. The salt may be purified by dis-
solving in cold water and precipitating with alcohol. If insufficient
alcohol be added to cause inmiediate precipitation, the salt slowly
deposits from the dilute spirit in blue octahedrons, belonging to
the regular system.

A cold aqueous solution, which has a violet colour, becomes
green when boiled.

Chromic sulphate forms double salts with the sulphates of the
alkalies, which belong to the alums.

Potassium Chromium Alum {chrome alum\ K2S04,Cr,(S04)3,
24H]0. — This double sulphate is formed when solutions of potas<
sium and chromium sulphates are mixed together in molecular
proportions. It is most conveniently prepared, by the addition of
the requisite amount of sulphuric acid to an aqueous solution of
potassium dichromate, and reducing the chromic oxide by passing
sulphur dioxide through the liquid —

(i) KjCrjOr + HjSO^ = SCrOj + H,0 + KjSOi.
(2) SCrOj + 3S0, - CrjCSO^V

The resulting solution, containing the two sulphates in mole-
cular proportions, deposits crystals of the double sulphate, in the
form of dark plum-coloured octahedrons (Fig. 140, B, p. 573),
which appear red by transmitted light

Chrome alum dissolves in water, yielding a plum-coloured solu-
tion, which on boiling turns green, but on long standing returns to
its original colour.

Sodium chromium alum is more soluble, and anunonium chro-
miimi alum is less soluble, than the potassium salt.

Cliromltes. — Chroniic oxide acts also as a weak acid, and combines with
other oxides, forming compounds resembling the aluminates. When potas-
sium hydroxide is added to a solution of a chromic salt, the green bydrated
oxide which is precipitated contains alkali wh'ch cannot be removed by hot
water ; this is present in the form of potassiua chromite. The best known

6 14 Inorganic Chemistry

chromites are dnc cfaromite, Cr^g^ZnO ; mmnganoni chromlte. CriP^MnO,
and feiTous chromite, CrfOs,FeO; the latter oocun natinally as chronic
iron ore.

Chromates. — When chromium trioxide is dissolved in water,
the solution is believed to contain chromic add, HsCr04 ; when
the solution is evaporated, however, the trioxide alone is left. (Red
crystals have been obtained, by cooling a hot saturated solution of
the trioxide, which have been regarded as the acid.)

Potassium Chromate, YijZxO^ is prepared by addin^r potas-
sium hydroxide to a solution of the dichromate —

KjCrA + 2KHO = 2K,Cr04 + H,0.

On evaporation, the yellow chromate of potash separates out, iD
rhombic crystals, isomorphous with potassium sulphate. It is
soluble in water at the ordinary temperature to the extent of 6o
parts in loo parts of water, forming a yellow solution having an
alkaline reaction.

Potassium Dichromate, K^CrjOf, is manufactured from chrome
iron ore by roasting the finely crushed ore with potassium car-
bonate and lime in a reverberatory furnace ; the mass being
frequently raked over to expose fresh portions to the oxidising
action of the flames. In this way a mixture of calcium and potas-
sium chromates is produced —

2Cr,Oa,FeO + 3K,CO,+CaO+70 = CaCr04+8KjCr04+FejOt+8CX>,.

The yellow mass, when cold, is broken up and lixiviated with a
hot solution of potassium sulphate, which by double decomposition
with the calcium chromate, forms potassium chromate and precipi-
tates calcium sulphate. The solution after settling, is treated with
the requisite quantity of sulphuric acid to convert the chromate
into the dichromate, thus —

2K,Cr04 + HjSOi - K,S04 + H,0 + K,Cr,Or.

The dichromate being much less soluble than the normal chro-
mate, a large proportion of it at once deposits as the solution cools ;
and the mother liquor containing potassium sulphate is used again
to lixiviate a fresh quantity of the roasted mixture.

Potassium dichromate forms large red prisms or tables, belong-
ing to the asymmetric (tridinic) system. It is soluble in water ai

Chromyl Chloride 615

the oidinary icmpcrature to the extent of 10 parts in 100 parts of
water, yielding an acid solution, which is extremely poisonous.
When a film of gelatine is impregnated with potassium dichromate
and exposed to light, a reduction of the chromium to chromic
oxide takes place, and at the same time the gelatine is rendered
insoluble. This property is utilised in photographic processes.*

Potassium dichromate is also known under the misnomer bichromate of
fotash, which would suggest that the salt was in reality hydrogen potassium
chromate, corresponding to bisulphate of potash, HKSO4. Such a chromium
compound does not exist The dichromates correspond to the disulphates (or
pyrosulphates), see page 396.

Potasaiuin TrichrozrUe, K/>,Oxe (or KtCr04,2CrO|), and Potassium
Tetracbromata, K,Cr40is (or K,Cr04,8CrOs), are also known.

Lead Chromate, PbCr04, is found as the mineral crocoisiU,
It is produced by precipitation from a lead salt, with either
potassium chromate or dichromate. It forms a bright yellow
powder, known as chrome-yellawy and is employed as a pigment.
It melts without decomposition, and resolidifies on cooling to a
brown crystalline solid. At higher temperatures it gives off
oxygen, and is converted into chromic oxide and a basic lead
chromate. When heated with organic compounds, the latter are
completely oxidised ; lead chromate is therefore employed in
organic analyses.

When lead chromate is digested with sodiiun hydroxide, or with
normal potassium chromate, a basic lead chromate is obtained
as a rich red powder —

2PbCr04 + 2NaHO = Na^CrO^ + H,0 + VhJZxOy

This compoimd is known as chronu-red,

Chromyl Chloride, CrO,Cls.— This compound is prepared by
distilling a mixture of potassium dichromate and sodium chloride
with strong sulphuric acid. Chromyl chloride is a deep red, mobile,
strongly fuming liquid. It is decomposed by water into hydro-
chloric acid and chromium trioxide, and acts as a powerful
oxidising substance. When dropped upon phosphorus it explodes.
When heated in sealed tubes it is converted into trichromyl
chloride with loss of chlorine, (JZxO^^l^

Chromyl chloride may be regarded as being derived from
chromic acid, CrO^HO)^ {unknawn\ by the complete substitution

* Aboey, ** Treatise on Photography."

6i6 Inorganic Chimistry

of (HO) by CL The intennediate cxxmpoaiid, diloro-Ghromic add
CrO,(HO)Cl is also unknown, although iu salu have been pfe-
pared ; thus, by the gentle action of hydrochloric add upon
potassium dichromate, potassium chloro-chromate is obtained as
a red crystalline salt —

K,Cr,Ox + 2HC1 = 2CrO,(KO)Cl + HA
Molybdenum, Mo = 95.9 ; Tungsten, W s 184 ; Uranium, U » i99>S.

These three somewhat rare elements are closely related to chromhwn.

Molybdenum occurs in the mineral uutfykUnitt, MoSf, (which aCrongly re-
sembles graphite in appearance), and more rarely as mofybdmmm acMrw^ MoO^
and wulftnitet PbMoOi.

Tungsten is found chiefly in wolfram, 2FeW04,SMnW04 (occurriog io
the Cornish tin mines); more rarely as scAeelimU, PbW04. and woffhum
o€hre, WOfi

Uranium occurs as an oxide, U03,2UOs, in ^IcAUendi (a ooDsiderable
quantity of which, associated with other uranium compounds, has recentiy
been discovered at St. Stephens, Cornwall).

MolyMenum is obtained by the action of hydrogen upon the heated ojdde
or chloride ; uranium, by the action of sodium upon the chloride ; while
tungsten has been obtained by both methods. In their specific gravities,
tungsten and uranium exhibit a marked difference from chromium and
molybdenum ; thus. Cr, sp. gr. = 6 ; Mo, sp. gr. = 8.6 ; while W, sp. gr. s
19. 1 ; U, sp. gr. = 18.7.

Molybdenum and uranium form a large number of oxides, some of which
are regarded as definite oxides, while others are looked upon as combinations
of two oxides. Only two oxides of tungsten are known. The composition of
these compounds is as follows —

MoO — -

MoaO, — —

MoO, WO, UO,

MoO, WO, UO^ u,U5- uu,.uu^

- - UO4. UiOs = UO,.2UO,.

The trioxide of each metal is an acid oxide ; uranium trioxide, however, is
both acidic and basic. They are insoluble in water, but by the action of
alkalies they yield molybdates, tungstates, and uranates. Molybdates amd
tungstates, derived from the adds H,Mo04,2H,0, and H,W04,2H,0 (corre-
sponding to chromic acid), are known. And all three oxides yield salts
corresponding to potassium dichromate, thus —

Sodium DimolyUlate. Sodium Ditnngsute. Sodium Diunmate.

Na,Mo,07 Na,W^ Na,U,07.

Molybdic and ttmgstic acids also form numerous pol3rmolybdates and poly*
tungstates, by the absorption of varying quantities of the trioxide into the

Molybdenum^ Tungsten^ Uranium

617

molecule of the normal salt (see Cbromates, page 615). And in the case of
tungsten, the compound, metatungstic acid, H^'^^Oig.iliJ^, Is known.

Uranium dioxide and triozide are both basic oxides, the former yielding the
unstable uranous salts, such as uranous sulphate, U(S04)s; and the Litter
producing the uranyl salts, of which the sulphate (U0s)S04 and (UO|)(NOs)s,
are well known.

Uranium p>eroxide. UO4, is an add oxide, which yields per-uranates.

Both molybdic and tungstic acids form compka compounds with phos-
phoric add, known as phospho-molybdic and phospbo-tungstic adds : thus,
Hben a nitric add solution of ammonium molybdate (NH4),Mo04, is added
in excess to a solution of orthophosphoric add, or an (Mthophosphate. a
canary yellow crystalline predpitate of ammonium phospho-molybdate
2(NH,),P04,22MoO„12H20 b obtained (see page 437). It is soluble in
alkalies and in excess of phosphoric acid, but insoluble in dilute mineral acids.
When this compound is dissolved in aqua-ngia, the solution deposits yellow
crystals of phospho-molybdic add, 2HsP04,22MoO}.

Compounds with chlorine having the following composition are known —

MoCl,

WCl,

—

MoCl| or MojClf

—

M0Q4

WCI4

UC14.

MoQi

WCl,

ucv

—

wo.

—

CHAPTER XII

GROUP VII. (FAMILY A.)

Symbol, Mn. Atomic weight s 54.&

Oeeurrenee.— This element is never found in nature in the free
state. It is widely distributed in combination with oxygen, as
pyrolusiie^ MnOg ; braunite^ MngOs » ^"^^ hausmannite^ MujO^.
Also as a hydrated oxide in mangamie^ yinfi^Hfi, It is met
with also as carbonate in manganese spar^ MnCO^ ; and as sul-
phide in numganese blende^ MnS.

Modes of Formation. — Manganese may be obtained by the
reduction of the oxide by means of carbon, at a very high
temperature. The product, however, contains carbon. In a
purer state it may be prepared by the reduction of fused an-
hydrous manganous chloride, by means of metallic magnesium,
or by reducing the oxide with aluminium at a high temperature.

Properties. — Manganese is a hard, steel-grey, brittle metaL
It rapidly oxidises on exposure to moist air, and is readily dis-
solved by dilute sulphuric or hydrochloric acid, with evolution of
hydrogen.

Oxides of Manganese. — The four most important of these
are—

Manganous oxide {manganese monoxide . MnO.

Red manganese oxide {hnusmannite) . MnjO^.

Manganic oxide {manganese sesquioxide) . Mn^O^i

Manganese dioxide {fiyrolusiie) .... MnOf.

The monoxide and sesquioxide are basic, giving rise to man-
ganous and manganic salts respectively. The oxide, MnjOf, is
also basic, but yields with acids both manganous and manganic
salts. Manganese dioxide, or peroxide, MnO^, gives manganous

Manganese Dioxide 619

salts with eliminatiOD of available oxygen. It also combines with
certain more basic oxides, forming unstable compounds known as
manganiUs,

Manganese trioxide, MnOn and hept-oxide, MnjO^, have also
been obtained. They are both acid oxides, giving rise respec-
tively to the manganaies and permanganates,

Manganoos Oxide, MnO, is obtained by heating any of the
higher oxides in a stream of hydrogen ; or by igniting a mixture of
manganous chloride, sodium carbonate, and ammonium chloride.
It is a light green powder, which, if prepared at a low tempera-
ture, oxidises in the air. When perfectly air-free solutions of
potassium hydroxide and a manganous salt are mixed, with exclu-
sion of air, hydrated manganous oxide, or manganous hydroxide,
Mn(H0)2. ^s obtained as a white precipitate, which rapidly oxidises
on exposure to air.

Red Manganese Oxide {mangano-manganic oxide\ Mn^Of, is
the most stable of the oxides of manganese, being formed when
both the higher or lower oxides are strongly heated. Thus, in the
preparation of oxygen by heating the dioxide, this compound
remains (page 162). With cold sulphuric acid, it yields a mix-
ture of manganous and manganic sulphates ; but when heated with
dilute acid, manganous sulphate and dioxide are formed—

MujO* -h 2H,S04 - 2MnS04 + MnO, -k- 2H,0.

Manganie Oxide {manganese sesquioxide\ Mn,0„ occurs native
as h^aunite^SLnd in the hydrated condition as ptangant'/e^ MngO^H^O.
The hydrated oxide is formed by the spontaneous oxidation of
manganous hydroxide, and when gently heated it yields the oxide.
Both the oxide and the hydrate, on treatment with warm nitric
acid, yield manganous nitrate and manganese dioxide.

Manganese Dioxide, MnO,, is the most important of the man-
ganese ores. It may be obtained by the cautious ignition of
manganous nitrate —

Mn(NOJg = N,04 -H MnOj.

Manganese dioxide is a hard black solid, which conducts electri-
city, and is strongly electro-negative to metals. On this account
it is employed in certain forms of voltaic battery. When heated
it loses oxygen, and forms first the sesquioxide, and finally MugOi.
Mant^anese dioxide dissolves in cold concentrated hydrochloric

Inorganic Chtmiury

620

acid, forming r dark brown solution, which is believed to cont^
the compound Mn,Cl(. On wanning, it evolves chlorine, t
leaves manganous chloride, MaCi,

Hanganites, — Manganese dioxide combmes with c
tallic oxides, formiDg unstable compound oxides. Thus with lin
it forms CaO.MnO, ; CaO,2MnO^ and CaO,6MnO, These o
pounds are produced in the Weldon recovery procea (page 331).

HJUIQANOHS SALTS.

Hancr&DOIlS Chloride, MnCl^ is the only chloride of this
that has been isolated. It is obtained by dissolvinj; any of tlu
oxides, or the carbonate, in hydrochloric acid ; and on evapoiatioi
is deposited as pink crystals of MnCI„4H,0. The anhydra '
sail is prepared by heating the crystals in a stream of hydl
chloric acid. Manganese chloride forms double salts, with chtj
rides of the alkalies, the ammonium salt MnCI„aNH,CI.H,0 beiii|
the best known.

Manganous Sulphate, MnSO,, is prepared byslrongly heatu
a pasty mixture of the dioiiide and strong sulphuric aci
iron present is thereby converted into ferric oxide, and a
ing the calcined mass with water, manganous sulphaie dissolve
The solution on evaporaiion, deposits, at ordinary leinperature^
large pink crystals of MnS04,6H,0 (isomorphous with copper
sulphate). Below 6° rhombic crystals are formed (also pink) of the
composition MnSO„7HjO (isomorphous with ferrous sulphate).

When these salts are heated to 200", or when iheir solutions are
boiled, the anhydrous sail is formed. Wilh sulphalcs of ihe
alkalies, manganous sulphate forms double salts, as potassium
manganous sulphate, K,SO„MiiSO„6H]0 ; and wiih aluminium^
sulphate it yields % puudo-ahm (see page 574). MniiOj,'^»(SOJ]
S4H,0.

MAKaAHIC SALTS.

HanganlC Chloride is oblained as a dark brown soluliQ
when the dioxide is dissolved in cold hydrochloric acid,
never been isolated, and is believed to have the compositi
Mn,CV

Manganic Sulphate, Mn^SO,),, is obtained as a green d<
quesccni powder, by the action of sulphuric acid upon thi

Permanganates 621

cipitated peroxide. On exposure to the air, the deliquesced mass
becomes muddy, by the precipitation of hydrated manganic oxide,
thus —

Mn,(S04)s + 4HjO - SH^Oi + Mn,0„H,0.

On the addition of potassium sulphate to a solution of manganic
sulphate in dilute sulphuric add, potassium manganese alum is
obtained, K|S04,Mn,(S04)t,S4H|0, which deposits in violet regular
octahedra. In the presence of much water the salt is decomposed,
and deposits the hydrated manganic oxide.

KANGANATES.

These salts are derived from the hypothetical manganic acid,
IIiMnOf. The oxide corresponding to this acid is known, viz.,
MnOs. It is an unstable compound, obtained as a reddish amor-
phous mass, by adding a solution of potassium permanganate in
sulphuric acid to dry sodium carbonate.

The manganates of the alkalies are obtained by fusing manganese
dioxide with potassium or sodium hydroxide. If air be excluded,
the following reaction takes place —

8MnO, + 2KH0 - K^MnOi + Mn,0, + H,0.

In the presence of air or oxygen, or by the addition of potassium
nitrate or chlorate, more of the manganese is converted into man-
ganate. The fused mass has a dark green colour, and dissolves in
a small quantity of cold water to a deep green solution, which is
only stable in the presence of free alkali.

When a solution of potassium manganate is largely diluted, or
gently warmed, it changes from green to pink, owing to the con-
version of the manganate into permanganate, thus —

SKjMnOi + 2H,0 - 2KMn04 + MnO, + 4KHO.

The same change takes place when carbon dioxide is passed
through the solution.

PEBMAHGANATES.

These siJts are derived from permanganic acid, HMnOi. When
potassium ptrmanganate is cautiously added to cold strong sul-
phuric addi green oily drops of the unstable manganese heptoxide

623 Inorganic Chemistry

(or permanganic a$ihydrid£) are obtained, Mn^Of. This compoond
dissolves in a small quantity of water to a purple solution, which
contains the unstable acid Mn|07,H|0, or H|Mn|Os » SHMnO^.
The solution evolves oxygen and deposits manganese dioxide.

Potassium Permanganate, KMnOi^ is the most important salt
of this class. It is prepared by fusing the dioxide with potassium
hydroxide and potassium chlorite, dissolving the manganate so
obtained in water, and passing carbon dioxide through the solu-
tion. The filtered solution, on evaporation, deposits dark purple
rhombic prisms, which appear deep red by transmitted light
Potassium permanganate is isomorphous with potassium per-
chlorate, KCIO4: it dissolves in water, forming a rich purple
solution. When boiled with strong caustic alkalies it loses oxygen
and forms the green potassium manganate —

SKMn04 + SKHO - SK^MnOi + H^O -¥ O.

It readily gives up oxygen to oxidisable and organic compounds,
and on this account is used both as a laboratory oxidising agent,
and as a disinfectant The crude sodium salt is largely employed,
under the name of Condys Disinfecting Fluids for this purpose.
When solid potassium permanganate is heated to 240* it evolves
oxygen, and forms potassium manganate and manganese dioxide-=^

2KMn04 = KjMnOi + MnO, + O^

CHAPTER XIII

THB TRANSITIONAL ELEMENTS OF THE FIRST

LONG PERIOD

Iron, Pe s 55.88. Cobalt, Co s 58.6. Nickel, Ni = 58.6.

These three elements belonging to Group VIII. (see classifica-
tion, page 102) stand in a different relation to each other than the
members of the other seven groups.

Iron, cobalt, and nickel belong to the same period^ being the
transitional elements falling between the first and second series of
the first long period. They are related, on the one hand, through
iron, to the preceding metals manganese and chromium (^see such
compounds cu ferrates^ manganates^ ckromates) : while, on the other
hand, through nickel, they approach the metal copper, which is
the next following in the period.

Iron, cobalt, and nickel are closely related elements ; in nature
they are usually associated together. They are all attracted by
the magnet, and are nearly white, hard, and difficultly fusible
metals. In their chemical habits, however, they exhibit a gradual
transition in their properties. Thus, iron forms two basic oxides,
yielding two series of stable salts, svi,^ ferrous zxA ferric. Cobalt
also has two basic oxides, but the basicity of the sesquioxide is
very feeble, and cobalt/V salts (except double salts) are unstable,
and are only known in solution. Nickel only forms one basic
oxide, and yields only one series of salts corresponding to the
ferrous salts : the sesquioxide of nickel behaving with acids as a
peroxide.

ntoN.

Symbol, Fe. Atomic weight =55.88.

Occurrenee. — Iron is one of the most abundant and widely
distributed elements. It occurs in the uncombined state in small
particles disseminated through certain basalts, and also in meteoric

6«)

624 Inorganic Chemistry

iron, where it is usually associated with nickel, cobalt, and c:oppeT.
Masses of iroD have also been found, which have been formed by
the reduction of iron ores, owing to the lirJng of coal pits : sucb
iron is known as natural steel.

The chief ores of iron are rtil kamatite and specular iron ore,
FcjO, ; Brown liatnati/e, 2FeiOj,3H,0 ; magnetic iron ore (load-
stone), FcjO, ; spathic iron ore, FeCO, ; clay iron stone consists
of spaihose iron mixed with day ; and blackbaud is clay iron
stone containing from ;o lo 15 per cent of coal.

Iron is also found in combination with sulphur, as iron pyrites,
FeSj, and with iron and copper in copper pyrites, Cu,S,Fe^j, but
these compounds are not employed in the metallurgy of iron.

Modes of Formation. — Iron is readily reduced from its com-
pounds. Thus, if ferric oxide, or oxalate, be gently heated in a
stream of hydrogen, the metal is obtained as a black powder,
which spontaneously oxidises with incandescence when brought
into the air. On the industrial scale the reduction is elTected by
means of coke and limestone. The ore is first calcined, whereby
water and carbon dioxide are expelled, and any sulphides present
are oxidised, with the expulsion of sulphur dioxide. By this pro-
cess also, the ore is rendered more porous. The calcined ore is
then smelted in a blast-furnace, with limestone and coke. Fig. 146
shows in section a modern blast-furnace. The charge is adiiutted
ai the lop by means of the cup and cone arrangement, which closes
the furnace, and a powerful hot-blast is forced through tuyeres,
placed round the base of the furnace. The furnace gases are led off
by the side pipe at the top, and are utilised for heating the blasL

The chemical reactions which take place in a blast-furnace are
many and complex, and differ in different p:ir[a of the furnace.
In the main, the following are the changes which occur. The
atmospheric oxygen of the hot-blast, on coming in contact with
the carbon, forms carbon monoxide (at the high temperature
carbon dioxide is probably not first formed). As the charges of
ore gradually work their way down the furnace, Ihey soon arrive
at a point where the ferric oxide bej^ins to be reduced by the
heated carbon monoxide, first to ferrous oxide, and then to a
spongy or porous mass of metallic iron. The region where ibis
lakes place is termed the aone 0/ reduction —

f 3CO - 3C0, + 2Fe.

ts descent through the furnace, the

Iron 625

stone ii converted into carbon dioxide and lime. The reduced
spcmgy metal, as it passes down through the hotter icgions of the
furnace, begins to take up carbon. It is probable that carbon

monoxide first combines wHfa the reduced i
carbonyl (see page 346), which at a higher temperature is decom-
posed, with the preci|Htatiaa of finely divided carbon within the
pores of the mass. More and more carbon is taken up by the iron

626 Inorganic Chemistry

as it descends, until it passes from a pasty condition to a state of
complete fusion, when it collects upon the bottom, or hearth, of the
furnace. In passing through the hottest regions, the lime combines
with the siliceous materials originally present in the ore^ to form a
fusible slag, beneath which the molten iron collects. Other re-
actions which go on in various r^ons of the furnace, are the reduc-
tion of sulphur compounds, and of phosphates and silicates, with
the absorption into the iron of a certain amount of sulphur, phos-
phorus, and silicon. The precise nature of the changes suffered
by the gases in the various regions of the furnace, is still obscure.
The cyanogen formed by the direct union of atmospheric nitrogen
with carbon, and also the hydrocarbons present, doubtless undergo
a chemical change in contact with the heated iron, and probably
aid in its carburisation. The molten iron is drawn off at intervals
from a tap-hole into moulds, and is known as cast iron or pig iron.
The slag as it accumulates, overflows in a regular stream through
an opening known as the slag hole. When such a furnace is in full
blast, fresh charges of materials are introduced at regular intervals,
and the process continues uninterruptedly for years. The metal
obtained from the blast-furnace is far from pure iron, but contains
varying quantities of carbon, silicon, phosphorus, sulphur, and
manganese.

The carbon may be present either in combination with iron as
a carbide, or distributed throughout the metal as fine particles of
graphite, or in both of these forms. White cast iron contains its
carbon in the combined form, while grey cast iron owes it grey
colour to the presence of minute crystals of graphite disseminated
throughout the metal. When grey cast iron is dissolved in hydro-
chloric acid, the graphite remains behind as a black powder ; but
on similarly treating iron containing combined carbon^ the carbon
unites with the hydrogen, forming various hydrocarbons, which
impart to the escaping gas a characteristic and unpleasant smell.
Average cast iron contains from 90 to 95 per cent, of iron, and 3 to
5 per cent, of carbon. Spiegel is a variety of white cast iron con-
taining 5.5 to 6 per cent, of carbon, and from 5 to 20 per cent of
manganese. With more than 20 per cent, of manganese, the
metal is X.^vvcitdL ferro-fnanganese,

PurificatiolL — The properties of iron are greatly modified by
the presence of various impurities, especially carbon, and for
different purposes for which iron is used, metal of different degrees
of purity is required. The purest form of ordinary commercial

Iron 627

iron is known as wrought iron^ while sUel is intermediate between
this and ctist iron.

The process by which cast iron is converted into wrought iron,
is termed puddling; and the method is called either dry puddling
or pig-boilings depending upon whether the cast iron is subjected
to a preliminary refining or not The chemical reactions in both
cases are the same, and consist in the oxidation of the impurities ;
the carbon being expelled as carbon dioxide, while the oxides of
silicon, phosphorus, and manganese pass into the slag. The
method oi pig-boiling is almost exclusively adopted

The cast iron is melted in a reverberatory furnace, the working
bottom of which, as well as the lining (or ffttling\ consists of a
layer of ferric oxide. The decarburisation of the iron is mainly
effected by means of the oxide of iron derived from the fettling ;
and for some time the molten mass appears to boil, owing to the
escape of carbon monoxide. As the impurities are oxidised and
removed, the mass becomes pasty (owing to the fact that the
melting-point of pure iron is much higher than that of cast iron),
and is then worked up into lumps, or blooms^ which are ultimately
removed and placed under a steam hammer, whereby admixed slag
!s squeezed out, and the metal is welded into a solid mass.

Wrought iron contains from ao6 to a 1 5 per cent of carbon.

Steel may be produced either from wrought iron, by adding
carbon, or from cast iron by removing that impurity. Formerly
steel was exclusively obtained by the first method, by what is
known as the cementation process. This simply consists in heating
the bars of iron, buried in broken charcoal, for several days to a red
heat The precise nature of the chemical change which results in
the carburisation of the iron, is not definitely established. In all
probability, the carbon is conveyed into the body of the metal
(which is not even heated to the softening point) by the intervention
of iron carbonyl ; the carbon monoxide being formed by the union
of the carbon with the air retained within the layer of charcoal
At the conclusion of the operation, the iron presents a blistered
appearance, and on this account is termed blister-sUel,

At the present time, steel is mostly produced by the Bessemer
process^ which consists in oxidising the impurities present in cast
iron, by blowing through the molten metal a blast of air. This
operation is performed in a large pear-shaped vessel, known as a
convertsr^ which is mounted on trunnions, and through the bottom
of which a powerful air blast can be admitted. The converter is

628

fnorganic Chemistry

tilted into a horizontal position, and a quantity of molten cast iron
is run in. The air blast is then started and the converter immedi-
ately swung back into a vertical position. In the course of a very
short time the whole of the impurities are burnt away, and the
stage at which the operation is complete is sharply marked, by the
sudden disappearance of the flame from the open mouth of the
converter, llie converter is once more swung into a horizontal
position, and the blast is stopped. The exact quantity of molten
Spiegel is then added, to supply the carbon required to convert the
entire charge into steel, and the blast is turned on for a few
moments in order to thoroughly mix the materials, after which the
contents are poured out into the casting ladle.

The comparative purity of the three forms of iron will be seen
from the three following typical examples : —

Gut Iron.

StaeL

Wrought Iron.

Carbon .

. 3-8i

a65

aio

Silicon .

. 1.68

ao7

O.OS

Phosphorus

. 0.70

0.03

ai5

Sulphur .

. 0.60

0.02

0.05

Manganese

0.41

0.40

0.07

Iron

• 7.20
92.80

loaoo

- 1.17
98.83

100.00

- a42
99.58

100.00

Properties. — Pure iron is a white lustrous metal, capable of
taking a high polish. Its specific gravity is 7.84 to «^.I39. It is
more difllicultly fusible and more malleable than wrought iron, but
at a red heat it becomes soft and can be welded. The physical
properties usually associated with iron, are in reality those of
iron containing varying amounts of impurities : thus, pure iron
when rendered magnetic, quickly loses this property, whereas
steel retains its magnetism at ordinary temperatures, losing it,
however, when heated. Pure iron, when heated and suddenly
cooled, does not take a temper, while steel when so treated be-
comes extremely hard and brittle.

Iron is unacted upon by dry air, at ordinary temperatures,
but in moist air, especially in the presence of carbon dioxide, it
becomes coated with rust, and the process which is slow to begin,
proceeds rapidly when a film of oxide has been once formed. Iron
decomposes water readily at a red heat ; in the finely divided

Oxides of Iron 629

state, the metal decomposes water at 100*. Dilute hydrochloric and
sulphuric acids rapidly dissolve iron with evolution of hydrogen.
Dilute nitric acid dissolves it, forming ferrous nitrate and am-
monium nitrate ; with stronger nitric acid, ferric nitrate and oxides
of nitrogen are formed.

Concentrated nitric add (specific gravity 1.45) is without solvent
action upon iron. A strip of iron which has been immersed in
such strong acid, is unacted upon when afterwards dipped into
the more dilute acid, and is also incapable of precipitating metallic
copper from a solution of copper sulphate. Iron in this condition
is said to be passive. Other oxidising agents, as chromic acid, or
hydrogen peroxide, are capable of bringing about the same result
It is believed that this condition is due to the formation of a film
of the oxide Fe,04 upon the surfi^ce.

Finely divided iron takes fire spontaneously in chlorine ; and
when gently warmed in sulphur dioxide it combines with that gas
with incandescence. It absorbs carbon monoxide with formation
of iron carbonyl, Fe(CO)^ When heated in anmionia it forms a
nitride, FcgNj.

Oxides of Iron. — Three oxides of iron are known, namely : —

Ferrous oxide {iron monoxide) . . FeO.
Ferric oxide (iron sesquioxide) . Fe^Oj.

Ferroso-ferric oxide {magnetic oxide) . FcjO^, or FejOjjFeO.

The two first are basic oxides, giving rise respectively to ferrous
and ferric salts : the third yields both ferrous and ferric salts.

Ferric oxide combines with certain more basic oxides, form-
ing compounds analogous to FeaOs^FeO ; such as Fe^OsjCaO,
FejOjZnO. These are known z&ferrites.

Ferrous Oxide {protoxide ofiron\ FeO, is formed as an inter-
mediate product during the reduction of ferric oxide by hydrogen,
or carbon monoxide ; but it is difRcult to obtain it free from either
the higher oxide, or the metal. It is also formed when ferrous
oxalate is heated out of contact with air. It is a black powder,
which oxidises in the air, and which dissolves in acids yielding
ferrous salts.

Ferrous Hydroxide, Fe(HO)» or FeO,H,0, is obtained as a
white precipitate, when potassium hydroxide is added to a solution
of a ferrous salt with entire exclusion of air. In the presence of
air it is green. It readily absorbs oxygen and passes into ferric
oxide-

630 Inorganic Chimistry

Ferrte Ozlde {sesguioxide 0/ iroH)y ¥tfi^ occurs in brilliani
black crystals belonging to the hexagonal s]rstem, in ip§cul4v
iron ore. It is obtained as a red amorphous powder by heating
hydrated ferric oxide, ferrous sulphate, or ferrous carbonate. In
a crystalline condition it may be produced by carefully heating a
mixture of ferrous sulphate and conmion salt, or by heating the
amorphous oxide in gaseous hydrochloric add. The natural com-
pound, and also the artificial substance after strong ignition, is
only slowly dissolved by adds. Ferric oxide is extremely hygro*
scopic When strongly heated it is partially converted into FegOi.
The amorphous substance, obtained by distilling ferrous sulphate
for the manufacture of Nordhausen sulphuric add, is employed
as a red pigment, and a polishing powder, under the name of
rouge.

Ferric Hydroxide* or Hydrated Ferrle Oxide, Fe,(HO)s, or
Fes08,3H|0. — When an excess of anunonia is added to a solution
of ferric chloride, and the voluminous brown predpitate is dried
at a moderate temperature, it has the composition FesOsi3H,0.
On exposure to various temperatures, or by precipitation under
various conditions, hydrated oxides of the composition Fe^Os,
2H2O ; Fe^OsjHsO, and others, have been obtained ; and several
of these compounds occur in nature. Ordinary rust of iron has the
composition 2Fe,08,3H,0, or FeaOs,Fea(HO)e.

The monohydrate FesOjiHiG has been obtained as a soluble modification,
by lieating an acetic acid solution of precipitated ferric hydroxide to 100* in
scaled vessels. On the addition of sulphuric add, a brown precipitate is
obtained, having the composition FesOs.H^O, which is insoluble in adds,
but soluble in water. The solution gives no reaction with potassium ferro-
cyanide. Another soluble hydroxide is produced by dissolving the ordinary
precipitated hydroxide in ferric chloride, and subjecting the solution to
dialysis. This solution is employed in medicine under the name of diafysed
iron,

Ferroso-ferric Oxide, FejOi, occurs native as magnetite and
magnetic oxide of iron; the magnetic variety being known also
as loadstone. When iron is heated in the air, the black film
which forms (the so-called iron-scale^ or hammer-scale) consists of
the oxide Fe304, with more or less ferric oxide, Y^fi^ upon the
outer surface. It is also produced when steam or carbon dioxide
is passed over heated iron, with evolution of hydrogen and carbon
monoxide respectively, these reactions beinjj the reverse of those

Ferrous SulphaU 631

by which oxides of iron are reduced by hydrogen or carbon
monoxide.

Ferrates. — These compounds correspond to the manganates,
but neither the add FeHgOi nor the oxide FeOj are known.
Potassium ferrate, KiFeOi, is formed when chlorine is passed
through a solution of potassium hydroxide in which ferric hydroxide
is suspended.

FBBSOUS SALTS.

Perrons Chloride, FeCl). — The anhydrous compound is ob-
tained by heating iron wire in gaseous hydrochloric acid, when the
salt sublimes in the form of white deliquescent crystals. In aqueous
solution, it is obtained when iron is dissolved in hydrochloric acid,
and is deposited in pale blue-green crystals of FeClx,4H,0.

When heated in the air it is converted into ferric oxide and
chloride, the latter volatilising —

6FeCl, -I- 80 - Fe,0, -»- 2FeCl,.

When volatilised in an atmosphere of hydrochloric acid, its
vapour density at high temperatures corresponds to the formula
FeCI| ; at lower temperatures it lies between the values required
for FeCl| and Fe,Cl4.

When strongly heated in a current of steam it is decomposed as
follows —

3FcCl, + 4H,0 - Fe,04 -»■ H, + 6HC1.

Ferrous Sulphate {green viiriol\ FeS04,7H,0, is obtained
when iron is dissolved in sulphuric acid. It is prepared on a
large scale by exposing heaps of iron pyrites, FeS^, to the action
of air and moisture. The liquor which drains away contains
ferrous sulphate and sulphuric acid, and the latter is converted
into ferrous sulphate by the introduction of scrap iron.

Ferrous sulphate forms pale green monosymmetric crystals,
which effloresce on exposure to the air. They are soluble in water
to the extent of 70 parts in 100 parts of water at 1 5*, and 370 parts
in 100 parts at 90*. At 100* the crystals lose 6H,0, being con-
verted into FeSO|,H|0.

If a crystal of rinc sulphate be thrown into a supersaturated
solution of ferrous sulphate, the iron salt is deposited in rhombic
prisms (isomorphous with zinc sulphate). On the other hand, if a
crystal of copper sulphate be added, asymmetric (triclinic) crystals
of FeSO^i&HtO (isomorphous with copper sulphate) are formed.

632 fnorganic Chtmisiry

Ferrous sulphate forms double salts with the sulphates of the
alkalies. Thus, when mixed with ammonium sulphate in the re-
quisite proportions, ammonium ferrous sulphate, FeS04,(NH4)sSQ|,
6H2O, is obtained. This salt is less readily oxidised on exposure
to air than ferrous sulphate itselfl

Ferrous salts give, with potassium ferroqranide (K4Fe(CN)g|
or 4KCN,Fe(CN)|), a white precipitate of potassium ferrous ferro-
cyanide (FeK,Fe(CN)«, or 2KCN,2Fe(CN)0. The precipitate is
quickly oxidised, and becomes blue. With potassium ferricyanide
(K,Fe(CN)a, or 3KCN,Fe(CN),), ferrous salts yield a blue pre
dpitate of ferrous ferricyanide {TumMPs blue) (Fej^FeCCN),}^ or
8Fe(CN)^2Fe(CN)a), thus-

8FeS04 + 2K,Fe(CN)e - Fe,{Fe(CNW, + SK^O^.

FEBBIC 8ALT8.

Ferric Chloride, FeCls, is prepared in the anhydrous state by
passing dry chlorine over heated iron wire. In solution it may
be obtained by dissolving iron in aqua regia ; or ferric oxide in
hydrochloric acid. The anhydrous salt forms nearly black crystals,
appearing deep red by transmitted light It readily volatilises, and
at temperatures above 700* the density of its vapour corresponds to
the formula FeClj, while at lower temperatures its density agrees
more nearly with the formula Fe^CIe.

Ferric chloride is extremely deliquescent, and readily dissolves in
water. When the solution is slowly evaporated, yellow crystals are
deposited, having the composition Fe,Clfl,12H,0 (or FeCl8,6HgO).
When a* dilute solution of ferric chloride is boiled, it decomposes,
forming either an insoluble oxychloride, or a soluble hydroxide and
free hydrochloric acid (depending upon the strength of the solution).

Ferric Sulphate, Y^J^^SO^ is prepared by the addition of sul-
phuric and nitric acids to a solution of ferrous sulphate —

GFeSOi + 3H2SO4 + 2HNOs = 2N0 + 4HjO + '6YtJiS0;)y

The brown solution, on evaporation, leaves the anhydrous salt
as a white mass. When the requisite quantity of potassium sul-
phate is dissolved in a strong solution of ferric sulphate at o%
the double potassium iron sulphate (iron alum), KjS04,Fej(S04)8,
24H.^O, separates out in the form of violet octahedrons.

Ferric salts jjive, with potassium ferrocyanide (K4Fe(CN)g, or

Sulphides of Iron 633

4KCN,Fe(CN)|X a dark blue precipitate of ferric ferrocyanidc
(Prussian bltu) (4Fe(CN)a,3Fe(CN)0 or Fe4{Fe(CN)e}3-

4FcCI, + 3K4Fe(CN)e - Fc^lFcCCN),}, + 12KCL

With potassium ferricyanide ferric salts give no precipitate.

8ULPHIDB8 OF IBON.

Perrons Sulphide, FeS.— When a white-hot bar of wrought
iron is dipped into melted sulphur, the elements unite ; and the
readily fusible monosulphide of iron falls to the bottom. It may
be prepared by throwing into a red hot crucible a mixture of iron
filings and sulphur. So obtained, it is a dark, yellowish -grey,
metallic-looking mass. When heated out of contact with air, it
does not part with sulphur, but in the presence of air is converted
into ferric oxide and sulphur dioxide. Ferrous sulphide is pre-
cipitated from either ferrous or ferric solutions, by alkaline sul-
phides, as a black amorphous powder, which in the moist state is
quickly oxidised by the air. Dilute sulphuric acid, or hydrochloric
acid, decomposes ferrous sulphide, with evolution of sulphuretted
hydrogen.

Iron Sesqnisnlphide, Fe^S^ is formed when equal weights of
iron and sulphur are heated to a moderate temperature. It can-
not be obtained by precipitation from a ferric salt, as the product
so formed consists of ferrous sulphide and sulphur —

Fe,Cl« + 3{NH4),S - 6NH4CI -»- 2FeS + S.

It is a yellow, metallic-looking solid, which is decomposed by
dilute hydrochloric acid, yielding sulphuretted hydrogen.

Ferric Disuiphide, FeS^ occurs in nature in large quantities as
iron Pyrites^ sometimes in the massive condition, and at others in
the form of brass-yellow cubical crystals. In many cases the
native compound bears the impression, or assumes the shape,
of various organised forms, such as wood, ammonites, &c., the
mineral having been formed by the reducing action of the organic
matter, upon ferrous sulphate in solution. Ferric disulphide is
also found in the form of brass-like, rhombic crystals, in raatated
pyrites.

The compound may be prepared by heating to a low red heat
a mixture of ferrous sulphide and sulphur.

Ferric disnlphide is unacted upon by dilute acids : hot con

634 Inorganic Chemistry

centrated hydrochloric add decomposes it, with liberation of sul-
phur and sulphuretted hydrogen. When heated in hjrdrogen,
sulphur is evolved (which partly combines with the hydrogen^
and ferrous sulphide remains. When heated in the air, ferric
oxide and sulphur dioxide are formed.

Ferroso-ferric Sulphide {magnetic pyrites)^ FesSf, occurs in
the fonn of hexagonal crystals. Like the corresponding oxide^
this compound is attracted by the magnet, and is itself sometimes
magnetic

OOBALT.

Symbol, Ca Atomic weight » 58.6.

Oeenrrence. — With the exception of small quantities present in
meteoric iron, cobalt is not found uncombined in nature. Its
chief natural compounds, which are only sparsely distributed, are
speiss-cobalt^ or snudtiney CoAs^ ; cobalt glance^ CoAsS, in both of
which the cobalt is partially replaced by nickel and iron ; and
cobalt-bloofn, Co,(As04)„8H20.

Modes of Formation.— Cobalt is obtained by reducing the
oxide, or the chloride, in a stream of hydrogen, or by strongly
heating cobalt oxalate in a closed crucible.

Properties.— Cobalt is an almost white, hard metal, which,
when polished, resembles nickel, but is slightly bluer. It is
malleable, and when heated is very ductile. Like both iron and
nickel, it is attracted by the magnet ; but unlike these, it retains
this property, even at a red heat. In the massive form, cobalt is
unacted upon by the air ; but the finely-powdered metal, obtained
by the reduction of the oxide in hydrogen, rapidly oxidises on
exposure to the air, sometimes with incandescence. When heated
in the air, it forms the oxide C03O4. Cobalt decomposes steam at
a red heat, yielding cobaltous oxide, CoO.

Oxides of Cobalt. — Three oxides of cobalt are recognised,
namely, cobaltous oxide, CoO ; cobaltic oxide, C02O3 ; and cobalto-
cobaltic oxide, C03O4.

Four other oxides are known, which are regarded as compounds of the two
first, having the composition 2CoO,Co302 ; ^CoO.CosOg ; 4CoO,CoyOs ;
6CoO,CoaO,.

The monoxide, CoO, is basic, and yields the cobaltous salts.
The sesquioxide, C0|0|, is feebly basic, forming only unstable

Cohaltous Chhridi 635

salts. Stab!e double salts, however, corresponding to this oxide
are known.

ColMdtOllS Oxide {coMi monoxide\ CoO, is formed when the
sesquiozide is heated to redness in a stream of carbon dioxide, or
gently heated in hydrogen. It is also obtained when the carbo-
nate or hydroxide is heated in the absence of air. It forms a drab-
coloured powder, which is unacted upon by the air, but when heated,
forms CogO^. When heated in either hydrogen or carbon mon-
oxide, it is reduced to metallic cobalt

Cobaltous Hydrozlde» Co(HO)t.— When potassium hydroxide
is added to a solution of a cobaltous salt, a blue basic hydrate is
precipitated, which, on boiling, is converted into the pink hydroxide
Co(HO)«. It turns brown on exposure to the air, by the absorp-
tion of oxygen. Both the oxide and hydroxide are really soluble
in adds, giving cobaltous salts.

Cobaltie Oxide {cobalt sesquioxid€\ C0|0|, is obtained by care-
fully heating cobaltous nitrate until red fumes cease to be evolved.
It is a dark grey powder, which, when strongly heated, is con-
verted into the intermediate black oxide, CojO^. Cobaltie oxide
dissolves in cold acids, forming brown solutions, which contain
unstable cobaltie salts. When warmed, these are converted into
cobaltous salts, with evolution of oxygen in the case of oxy-salts,
and of the halogen from haloid salts. This sesquioxide, therefore,
behaves as a peroxide.

Cobaltie Hydroxide, Co,(HO)fl, or Co,0,,3H,0, is obtained as a
nearly black precipitate, by the addition of an alkaline hypochlorite
to a cobaltous salt With acids it behaves as the oxide.

Ck)baltO-Cobaltic Oxide, €0,04, is formed as a black powder,
when the sesquioxide is strongly heated in air.

COBALTOUS 8ALT8.

Cobaltous Chloride, CoCl,. — When the carbonate, or any of
the oxides, are dissolved in hydrochloric acid, the concentrated
solution deposits dark red prisms (monosymmetric), having the
composition CoCl|,6H|0. When exposed over sulphuric acid, they
lose 4H2O, and are converted into a rose- red salt, CoCl|,2H|0,
which reabsorbs moisture from the air to form the hexa-hydrate.
When the di-hydrate is heated to about 100% it is converted into
violet-blue crystals of CoCl«H|0 ; and at 120* it becomes an-

636 Inorganic Chemistry

hydrous, and is blue. The blue salts, on exposure to the aii^
rapidly rehydrate themselves, and become pink.

Cobaltous chloride dissolves in alcohol, giving a deep blue solu-
tion, which, on the addition of water, also becomes pink. This
property of forming pink hydrated salts, which become blue or
green when nearly 01; quite anhydrous, is common to most cobal-
tous salts. Thus, the iodide CoIs,6H,0 forms rose-coloored
crystals. When gently heated, it changes to a moss-green salt,
CoI|,2H|0, which, when dehydrated, becomes nearly black.

GobaltOUS Sulphate, CoS04,7H|0, is obtained by dissolving
the carbonate or oxides in sulphuric acid, and is deposited from
the solution in dark red crystals, isomorphous with ferrous sul-
phate. Cobalt sulphate, like the sulphates of iron and nickel,
forms double salts with alkaline sulphates, of which cobalt potas-
sium sulphate, CoS04,KtS04,6H|0, is the best known.

Cobaltle Salts. — Single salts corresponding to cobalt sesqui*
oxide are unstable, and exist only in solution. More stable double
salts are known. Thus, when potassium nitrite is added to an
acetic acid solution of cobalt chloride, a yellow crystalline precipi-
tate is obtained, consisting of the double nitrite of cobalt and
potassium —

2CoClt + lOKNO, + 4HN0, = Co,(NOa)o,6KNO, +

2N0 + 4KC1 + 2HaO.

The formation of this compound is made use of for separating cobalt from
nickel, the latter element yielding no corresponding double nitrite. In the
presence, however, of salts of barium, strontium, or calcium, nickel forms,
with potassium nitrite, triple salts, such as Ni(X02)2tBa(NOs)2.2KN02, which
are precipitated as yellow crystalline powders. Hence, in the presence of
metals of the alkaline earths, nickel and cobalt cannot be separated by this
method.

SULPHIDES OF COBALT.

Cobaltous Sulphide, CoS, is obtained by heating cobaltous
oxide with sulphur, or by fusing a mixture of cobalt sulphate,
barium sulphide, and common salt. It forms bronze- coloured
cr>'stals, which are soluble in strong hydrochloric acid. Cobalt
sulphide is precipitated as a black amorphous powder, when
ammonium sulphide is added to a cobalt solution. The precipi-
tate slowly dissolves in dilute mineral acids, but is insoluble in

Cobaltamims 637

acetic acid. When heated in a stream of sulphuretted hydrogen,
it yields the sesquisulphide CO|S| ; and if mixed with sulphur, and
heated in a current of hydrogen, it forms the disulphide CoS|.

Cobaltamlnes {flmnummcal cobalt compounds *). Cobalt forms
a large number of complex ammoniacal salts. A few of these
contain the metal in the divalent conditio^, and are known as
afnmonio'cobaltous salts; but by far the larger number contain
the hexavalent double atom CO|, and are tenned ammomo-cobaltic
compounds. These compounds are classified as follows t : —

Ammonlo-Cobaltons Balta are formed by the absorption of gaseous am-
monia by anhydrous cobaltous salts, or b^ dissolving the salts in strong
aqueous ammonia, with exclusion of air. In this Mray the following salts have
been obtained —

Ammonio^baltous chloride, CoCl»6NH, \ ''*?*''*"• ^li^l'^J*'*''*^*^

^ ■ ( into CoCl,,2NH^

Ammonio-cobaltotts sulphate, CoS04,6NH^
Ammonio-cobaltous nitrate, Co(NOs)f,6NH|,2H]0.

Ammonio-Cotwltio Balti.— These may be arranged under the following
classes and subdivisions : —

I. Hexammcnio Salts. — General formula, CO|(NH,)g'R^, where R equals
A monacid radical, or its equivalent of di or tri add radicals.

{Hexammonio-oobaltic chloride (dicArthcobattic chloride),
Co,-(NH,),Clg.2H,0.
Hexammonio-cobaltic sulphate, Co,'(NH|)c'(S04)t,6H30.

II. Ociammonio Salts —

(a.) PrastoX 5a/lj.— Oeaeral formula, Co,'(NH,)8'R^

fPraseo-cobaltic chloride, Co,(NH,)8'Cl«,2H,0.
Examples \ Praseo-cobalticchloro-nitrate,Co,(NH,),'a4'(NO,),.
[ 2H^.

(/S.) Fujco Salts.^GenenA formula, Co,(NH,)g(HO),'R4.

fFusco-cobalUc chloride. Co,(NH,)g(HO),'Cl4.2H|0.
Examples ^ Fusco - cobaltic sulphate, Co,(NH,)8(HO)s'(S04)a.
[ 2H,0.

(7.) CfO£<o 5a//i.— General formula, Co,(NH,),(NO,)4'R9.

Rxamti>Ut i Croceo-cobaltic chloride, Coj(NH,)8(N 02)4-0,.
nxamytej ^ Crooeo-oobaltic sulphate, Co8(NH,)8(N08)4-S04.

* For details respecting the preparation and properties of these salts, the
student is referred to larger works.

t On the constitution of metallamroonium compounds generally, see Werner,
Zeitschrift ftir Anorganiscke Chemit, 1893, voL iii.

X These names denote the characteristic colours of the salts ; thus, prasimus,
\f^\-f^titx\ ; futcuSf iwarthv: rmntrf, fellow. &«.

BxampUs'

638 Inorganic Cfumistry

III. Decammonio SaUs'-

(a.) Rosta 5a/^i.— General formula, C(%(NHa)it(H^)tR^

r Roseo-cobaUic chloride, Co|(NH,}|«(H^),at.
BxampUs \ Roseo-cobftUic sulphate, 0)^NH^it(H^)i-(SQJ»

ifi.) Puffuno Salii— General formula, Coa(NHa),«XsR4

(where X and R are either the same, or different add radicab).

'Chloro-purporeo-eobaltic chloride, Coa(NH,)igClj-CI«.
Chloro-purpureo-cobaltic sulphate, Co^NHs)2fClfl'

Bromo - purpureo - cobaltic nitrate, COs(NHg)]0Brf *
. (NOJ,.

(7.) XamtMo ^oAi.— General formula, Co,(NH,)m(NO^*R4.

rXanth(H»balUc chloride, Co|(NH,},o(NOa)i-a4.
Rxaw^Us J Xantho-cobaltic bromo-nitrate, Coa(NH3)io(NO|)t'
\ Br,(NO,)»

IV. Oxy^icammonio 5a/(f.— General formula, Cos(NHa)i0R4*XO(HO)

(where X is either (HO) or an add radical either the same as,

or different from. R).

(Oxy-decammonio cobaltic chloride, Cos(NH|)i9Cl4*
(HO)-O(HO).
Anhydro - ozy - decammonio cobalt chloride,
Co,(NH,)ipCl4-Cl,-0(HO).

V. Dodecammonio Salts (luteo-cobalticsalts). — General formula.Co^N Hjli^R^

Rxamtlei i Luteo-cobaltic chloride, Co^NHa)uCl«i
axamptes ^ Luteo-cobaliic sulphate, Co^NH,)i^S04)„5HjO.

When cobalt compounds are fused with borax, a clear blue
vitreous mass is obtained, which contains a borate of cobalt A
similar blue colour is imparted to ordinary potash glass, when a
small quantity of a cobalt salt is added to the molten material,
owing to the formation of a silicate of cobalt Under the name
ofsfnal/f this substance has been manufactured for use as a pig-
ment, by fusing the roasted cobalt ore with quartz sand and pearl-
ash. The fused mass of deep blue glass is then finely ground
beneath water.

Nickel AUays 639

nOKBL.

Symbol, Nt. Atomic weight = 58.6.

Oecurrenoe. — Nickel occurs chiefly in combination with arsenic
AS kupfer nickel f Ni^Asj; whiU nickel^ NiAs, ; nickel glance^
Ni|(AsS)s, also as nickel blende^ NiS. Nickel ore almost invari-
ably contains cobalt, and frequently antimony and bismuth.

Modes of Formation. — Nickel is obtained by reducing the
oxide with carbon at a high temperature. It may be obtained as a
black powder by reducing nickelous oxide in a stream of hydrogen,
or by heating nickelous oxalate out of contact with air. It is also
obtained as a lustrous coherent deposit by the electrolysis of an
ammoniacal solution of the double sulphate of nickel and anunonia.

Properties. — Nickel is a lustrous white metal, with a faint
fellow tinge when compared with silver. It is ductile and malle-
able, and at the same time very hard and tenaceous. It is sus-
ceptible of a very high polish. Nickel is attracted by the magnet,
but loses this property when moderately heated. When obtained
by reduction with charcoal, the metal contains a certaii\ amount of
carbon (like cast iron), which renders it less malleable ; and when
produced by reduction of the oxalate at a low temperature the
powder is pyrophonc

In the massive fonn, nickel is unacted upon by moderately dry
air, but in moist air it tarnishes, and becomes covered with a film
of nickelous oxide. It decomposes steam only slowly at a red
heat, and is slowly attacked by dilute hydrochloric or sulphuric
acid (contrast iron).

In a finely divided state, nickel absorbs carbon monoxide (see
page 263).

Nickel is largely used for electro-plating iron and steel articles.

Nickel Alloys. — With copper, and with copper and zinc, nickel
furnishes several important alloys. The small coinage in use in
Belgium, Germany, and the United States, consists of i part of

* Kupfer nickel signifies the false copper ^ and was applied by the Germans
in the middle ages to this ore, which resembled a copper ore, because they
tried in vain to extract copper from it. It is probable that this ore had beea
smelted along with copper ores, under the belief that it contained copper, bf
the early ancients. Thus, a coin, 335 B.C. , has been found to contain 90 per
cent, ofnickd.

640 Inorganic Chemistry

nickel and 3 parts of copper ; while the so-called German sOver^
or nickel-silvery contains in addition about 1.5 parts of zinc.

Oxides of Nickel— Three oxides of nickel have been obtained,
namely, nickelous oxide, NiO ; nickelic oxide, Ni^Oi ; and nickelo-
nickelic oxide, NisOf. The first alone is basic

Nickelous Oxide {nickel monoxide\ NiO, is obtained as a
greenish powder by heating nickel carbonate, or hydroxide, out of
contact with air. It is dissolved by acids yielding nickel salts.
When heated in hydrogen, or carbon monoxide, it is readily re-
duced to the metallic state.

Nickelous Hydroxide, Ni(H0)2, is obtained as a pale green
precipitate when potassium hydroxide is added to a solution of a
nickel salt : the precipitate has the composition 4Ni(HO)^H^.
When strongly heated it is converted into nickelous oxide and
water. It is readily soluble in acids, forming the nickel salts ; and
it also dissolves in ammonia and in solutions of ammonium salts.

Nickel Sesquioxide, NigO,, is obtained as a black powder
when the nitrate is decomposed by heat at the lowest temperature.
With hydrochloric acid and sulphuric acid it behaves like a per-
oxide ; yielding nickel salts, with the elimination of chlorine and
oxygen respectively —

NijOs + 6HC1 = 2NiCl, + 3H,0 + Cl^
NigOs + 2H2SO4 = 2NiS04 + 2H2O + O.

It is soluble in ammonia, with evolution of nitrogen —
2Ni203 + 2NHs = 6Ni(H0), + 3H,0 + N^

Hydrated Sesquioxide of Nickel, Nij(HO)a, or Nij08,3H,0.

When chlorine is passed through water, or sodium hydroxide, in
which nickelous hydroxide, Ni(H0)2, is suspended, a black powder
is obtained having the composition NijOsjSHgO. The same com-
pound is obtained when a nickel salt is added to a solution of
bleaching-powder. In contact with acids and ammonia it behaves
like the oxide.

Nickelo-nickelic Oxide, Ni304, is obtained as a grey metallic-
looking mass, when nickel chloride is heated to about 400* in a
stream of oxygen.

Nickel Salts. — Nickel forms only one series of salts, corre
sponding to the monoxide. In the anhydrous state these arc
usually yellowish, while in the hvdrated condition they are green.

Nickelaus Sulphide 641

Nickel Chloride, NiCl2, is obtained as a yellow amorphous
mass, by dissolving the oxide or carbonate in hydrochloric acid,
and evaporating the solution to dryness. When heated in a
current of chlorine it sublimes in the form of lustrous golden
.yellow scales, which dissolve in water forming a green solution.
From the aqueous solution, green crystals of the composition
NiCl^BHjO are deposited.

Anhydrous nickel chloride absorbs gaseous ammonia forming the
compoimd NiCljjGNH,, which when deposited from an aqueous
solution, forms blue octahedrons.

Nickel Sulphate, NiS04,7H20, is produced when the metal,
the carbonate, or the oxide is dissolved in dilute sulphuric acid,
and the concentrated solution is allowed to cr>'stallise at the ordi-
nary temperature. It forms green crystals, isomorphous with
magnesium sulphate. When heated to 100* the crystals lose
GHjO, and above 300* the salt becomes anhydrous. The anhy-
drous salt absorbs gaseous ammonia, being converted into a pale
violet powder having the composition NiS04,6NH3. When nickel
sulphate is dissolved in strong aqueous ammonia, the solution
deposits dark blue quadratic crystals of NiS04,4NH3,2H20.

With sulphates of the alkalies, nickel sulphate fonns double
salts, of which the anunonium salt is the most important, NiSOf,
(NH4)2b04,6H30. It is obtained by mixing concentrated solu-
tions of the two sulphates in the requisite proportions. This salt
is employed in the process of nickel-plating.

Nlckelous Sulphide (nickel monosulphide\ NiS, occurs as the
mineral capillary Pyrites, It is obtained as a bronze-like mass,
insoluble in hydrochloric acid, by heating sulphur and nickel
together. In the hydrated condition, nickel sulphide is precipitated
as an amorphous black powder, on the addition of ammonium
sulphide to a nickel salt. The precipitate is scarcely soluble in
hydrochloric acid, but partially dissolves in excess of ammonium
sulphide forming a brown solution. Three other sulphides have
been obtained, having the composition Ni|S, NiS2, and NisSf.

2 s

CHAPTER XIV

THE TRANSITIONAL ELEMENTS OP THE SECOND
AND FOURTH LONG PERIOD

If u/Aenium, Ru = 103. s- If Aodium, Rh = 10^.1. Palladium, 106. a.
Osmium, Os = igi. Iridium, Ir = 19a. 5. Platinum, 194.3.

These elements, although constituting two transitional groups, are very closely
related to each other. In nature they all occur associated together in what is
commonly known 9S platinum ore, and they are on this account usually spoken
of as the platinum metals.

Platinum Ore, or native platinum, contains all these elements in the metallic
state. It is found in small grains, sometimes in nuggets, in alluvial deposits and
river sand, principally in Brazil, Borneo, California, Australia, and the Urals.
Native platinum contains from 60 to 86 per cent, of platinum, the remaindej"
consisting of the other five metals of the group, together with varying quan-
tities of gold, copper, and iron. Amongst the grains of platinum ore, there
are also found grains which consist essentially of an alloy of platinum and
iridium (containing from 30 to 75 per cent, of iridium) known as plaHn-
iridium : and also particles of an alloy of osmium and iridium (called oswiiri-
dium), which contain from 30 to 40 per cent, of osmium, as well as small
quantities of rhodium and ruthenium.

They are all white lustrous metals, having high melting-points. They are
unacted upon by air or oxygen at ordinary temperatures ; and, with the excep-
tion of osmium (which bums when strongly heated, forming the tetroxide).
they are scarcely oxidised by oxygen at any temperature.

With the exception of palladium, which readily dissolves in hot nitric acid,
these metals are unacted upon by ordinary acids. Aqua regia converts
osmium into the tetroxide ; it dissolves platinum with formation of the tetra-
chloride, and slowly acts upon ruthenium, but is without action upon
rhodium and iridium.

The specific gravities of the metals of the first group, although very close to
one another, are widely different from those of the second group ; and it will
be seen that the sf)ecific gravities fall, with increasing atomic weights, thus —

Ru, sp. gr. = 12.26. Rh, sp. gr. = 12. i. Pd, sp. gr. = 11.4.

Os, ,, =22.47. Jr. .. =22.38. Pt, ,, =21.5.

The element osmium is the heaviest known substance.

The most easily fusible of these metals is palladium, which melts about the

temperature of >*Toughl iron. The melting-point of platinum is somewhat

higher, but it may be boiled by the oxyhydrogen flame. Rhodium 9nd

643

Platinum 643

iridium come next in order of fusibility, the latter metal being just fusible by
the oxyhydrogen flame, while ruthenium has a still higher melting-point
Osmium has not been melted. Wlien heated to the melting-point of iridium,
osmium volatilises ; and if air be present, it bums.
The following oxides of these metals are known —

—

Pd-^O

—

RuO

OsO

RhO

—

PdO

PtO

RUgOj

OsjO,

RhaOa

Ir,0,

—

RuOa

OsO,

RhOa

IrOa

PdOj

PtOa

RUO4

OSO4

—

Ruthenium, osmium, rhodium, and iridium form salts corresponding to the
lesquioxide, such as ruthenious chloride, Ru2Cl« ; rhodium sulphate, Rha(S04)3 ;
iridious chloride, IraCl^.

With the exception of rhodium, they all form chlorides, corresponding to
the dioxides, thus — ruthenic chloride, RUCI4 ; iridic chloride, IrCl4 1 platinic
chloride, PtCl4, while palladium and platinum yield palIad£^uJ and palatim^iM
compounds, corresponding to their monoxides.

The tetroxides of ruthenium and osmium are remarkable in melting at
an extremely low temperature (about 40**), and boiling about 100'. They
yield intensely irritating vap>ours, which, in the case of osmium tctroxidc,
exerts a most injurious effect upon the eyes, and is extremely p>oisonous.
(Osmium tetroxide is commonly known as osmic acid.) Osmium and ruthenium
also exhibit a non-metallic cliaractcr in forming compounds derived from the
unknown ruthenic and osmic trioxides, such as potassium ruthenate. K2RUO4,
and potassium osmate, KaOs04 (the corresponding ruthenic and osmic acids
are unknown). Ruthenium also forms potassium pcr-ruthenate, KRUO4
(analagous to permanganate), although the corresponding acid and peroxide,
RUjO?, are unknown. The most important of these elements is platinum.

PLATINUK.

Symbol, Pt. Atomic weight = 194. 1.

In order to separate platinum from the other metals with which
the native platinum (see page 642) is mixed, the ore is digested in
dilute aqua regia, under slightly increased pressure. The solution
so obt«'iined contains the higher chlorides of platinum, palladium,
rhodium and indium (for although in the pure state the last two
named metals are scarcely attacked by aqua regia, when alloyed with
much platinum they dissolve). The solution is evaporated to dry-
ness, and heated to 125*, whereby the palladium and rhodium are
obtained in the form of their lower chlorides, PdCl, and Rh)Cl«
(the latter of which, in the anhydrous condition, is insoluble in
water). The residue is extracted with water, and to the clear sola

644 Inorganic Chemistry

tion, acidified with hydrochloric add, ammonium chloride is added
The double chloride of platinum and ammonium (PtCl^^fiNHiClX
separates out as yellow crystals, while the corresponding- iridium
salt, being more soluble, remains for the most part in solution,
and may be obtained by concentrating the mother liquor. The
ammonium platinic chloride, on being ignited, loses amxnonimn
chloride and chlorine, leaving the metal in the form of a black
spongy mass known as spongy platinum^ which is then melted by
means of the oxyhydrogen flame in a lime crucible. The platinum
so obtained, usually contains small quantities of iridium, and traces
of associated metals.

Pure platinum is obtained by alloying conunercial platinum
with pure lead, and treating the alloy first with nitric acid, which
dissolves any copper and iron, a part of the palladium and rhodium,
and most of the lead ; and then with dilute aqua regia, which dis-
solves the whole of the platinum and the remaining lead, with
traces of rhodium. From this solution the lead is precipitated as
sulphate, and the platinum is then precipitated as the double
chloride, by ammonium chloride. To remove traces of rhodium
which are present, the dried double chloride is ignited with
hydrogen potassium sulphate, whereby the rhodium is converted
into a soluble double sulphate of rhodium and potassium, while
the platinum is reduced to the condition of the spongy metal.

Properties. — Platinum is a lustrous, greyish-white, malleable,
and ductile metal. At a red heat it may be welded with great
ease. It is melted by the oxyhydrogen flame, and vessels of
platinum are readily made by fusing the metal together in this
way. Heated platinum absorbs large quantities of hydrogen
(see page 157) ; and when the metal is melted in the oxyhydrogen
flame, it exhibits the phenomenon of "spitting," when it again
solidifies (see Silver, page 518). Platinum does not combine with
oxygen at any temperature, neither does the heated metal absorb
this gas ; but it has the property, when cold, of condensing oxygen
upon its surface. A piece of clean platinum foil or wire, when
introduced into a mixture of oxygen, and a readily inflammable
gas or vapour (such as hydrogen, ether, alcohol, &c), causes their
combination ; and occasionally the metal becomes red hot, and
ignites the mixture. This action is more rapid in the case of
platinum sponge, when a larger surface is brought into play, and
a fragment of this material introduced into a detonating mixture
of oxygen and hydrogen at once determines its explosion.

Platinum Bichloride 645

Platinum is not acted upon by either nitric or hydrochloric acid.
It is oxidised when fused with caustic alkalies, or with potassium
nitrate, and is also attacked by fused alkaline cyanides. In the
form of sponge, it is dissolved by boiling potassium cyanide with
the evolution of hydrogen, and formation of a double cyanide.

Platinum readily combines with phosphorus, silicon, and carbon.
The carbide of platinum is formed when the metal is continuously
heated by a smoky flame, or one in which combustion is incom-
plete, hence care is necessary in the use of platinum vessels.

Platinum Black is the name given to the finely-divided metal
obtained by precipitating platinum from its solutions by reducing
agents, or by metals. It is a soft, black powder, which is capable
of absorbing, or condensing upon its surface, large quantities of
oxygen. It therefore acts as a powerful oxidising agent

Platinum Alloys.— Platinum readily alloys with many metals ;
hence compounds of easily reducible metals should not be heated
in vessels of platinum. The most important alloys are those with
iridium. The addition of 2 per cent of iridium is found greatly to
increase the hardness, and raise the melting-point of platinum.
An alloy containing 10 per cent of iridium resists the corrosive
action of chemical reagents to a greater extent than pure platinum
(see Fluorine, page 310).

Oxides of Platinum. — Platinous oxide, PtO, and platinic oxide,
PtO], are obtained in the form of dark grey or black powders, by
gently heating the corresponding hydroxides. When strongly
heated they are converted into the metal.

Platinous Hydroxide, Pt(H0)2, is obtained by the action of
potassium hydroxide upon platinum dichloride. It is a black
powder, which dissolves in the halogen acids, yielding platin^wj
compounds.

Platinic Hydroxido, PtCHO)^, is prepared by adding boiling
potassium hydroxide to a solution of platinum tetrachloride, and
treating the precipitate with acetic acid to remove the potash.
When dried it forms a yellowish powder, which is soluble in acids
to form platinic salts. Platinic hydioxide behaves both as a weak
base, and a feeble acid With stronger bases it forms compounds
known as platinatts^ which are yellow crystalline salts. The
sodium salt has the composition Na20,3PtOj,6H,0.

Platinum Dichloride {platinous chloride)^ PtCl,, is produced
when platinum tetrachloride is heated to about 250*. It fonhs a
greenish powder, insoluble in water. It dissolves in hydrochloric

646 Inorganic Chemistry

acid, giving a reddish-brown solution which is believed to contain
the double compound PtCI^tSHCl, or HsPtCli, to which the name
Morthplatinous acid has been given : the compound has never
been isolated, but a number of double salts of platinous chloride
with other chlorides are known, which may be regarded as
derivatives of this acid, and which are therefore termed chloro-
platinites ; thus, potassium platinous chloride, 2KCI,PtCls» or
potassium chloro-platinite, K2PtCl4, is obtained as fine red crystals,
by adding potassium chloride to a solution of platinous chloride
in hydrochloric acid. This salt is used in the platinoiype photo-
graphic process.

Platinum Tetrachloride {plcuinic chloride), PtCl4, is obtained
by dissolving the metal in aqua regia, and removing the excess
of the acids by evaporating to dryness and gently heating the
residue. From its aqueous solution, the salt deposits in large
red crystals having the composition PtCl4,5H20, which are not
deliquescent. When the salt is crystallised from a hydrochloric
acid solution, or when the aqua regia solution is evaporated to
expel the nitric acid, with frequent addition of hydrochloric add,
the double compound of platinic chloride a^id hydrochloric acid is
formed, PtCl^jSHCl, which is deposited as reddish-brown deli-
quescent crystals, with 6H0O. To this substance (which is
commonly called platinic chloride), the name chloro-platinic acid
has been given, and the double salts of platinic chloride and
various chlorides are regarded as salts of this acid The most
important of these chloro-platinates are those of the alkali metals,
their different solubilities being made the basis for the separation
of these metals.

Potassium Chloro-platinate (or potassium platinic chloride),
2KCl,IHCl4 or KaPtClg, is obtained as a yellow cr>'stalline pre-
cipitate, by adding potassium chloride to platinic chloride. It is
soluble in 100 parts of water at the ordinary temperature to the
extent of 1. 1 parts, and at 100°, 5. 1 8 parts. It is insoluble in alcohol.

The rubidium and caesium compounds are ver>' similar, but are
still less soluble in water, 100 parts of water at 20° dissolving 0.141
of the rubidium and 0.07 of the caesium salt.

Ammonium Chloro-platinate, ZNH^CljPtCl^jcloselyresembles
the potassium salt, being slightly less soluble, but more so than
the rubidium compound.

Sodium Chloro-platinate, 2NaCl,PtCl4,GH20, is a reddish-
yellow salt, readily soluble in both water and alcohol.

Platinamines 647

Platino-cyanldes. — Just as platinous chloride combines with
metallic chlorides to fonn chloro-platinites, so platinous cyanide,
Pt(CN)2) unites with other cyanides, forming similarly constituted
double compounds, known as platino-cyanides.*

Potassium platino-cyanide, K,Pt(CN)4, or 2KCN,Pt(CN)j|, is
formed when spongy platinum is dissolved in boiling potassium
cyanide. The platino-cyanides may be regarded as the salts of
platino-cyanic acid, H|Pt(CN)4. Both the acid and the salts are
characterised by the wonderful play of colours they exhibit, when
viewed in different lights ; and by forming different coloured
crystals with varying quantities of water of crystallisation (see
page 193).

Sulphiides of Platinum.— Platinous sulphide, PtS, and platinic
sulphide, PtS^ are obtained as amorphous black powders by the
action of sulphuretted hydrogen upon the respective chlorides.

Os^ysalts of Platinum.— Few well defined single salts of
platinum with oxyacids are known. This element, however,
exhibits a great tendency to form complex double salts. One such
series of compounds is seen in the piatino-nitrites^ which may
be regarded as the salts of platino-nitrous acid, H2Pt(N02)4.

These salts are remarkable, in that the platinum they contain
cannot be detected by the ordinary tests for that metal ; just as
the iron present in ferro-cyanides is not detected by the ordinary
reagents used in testing for that metal.

Ammonlacal Platinum Ba«M, or Platinaminet.

Like cobalt, platinum forms a large number of basic compounds with
ammonia, many of which are of extremely complex composition. The first
of these to be discovered was a bright green salt, obtained by the action
of ammonia upon platinous chloride, having the composition PtCl3,2NH3, or
PtlNHjIsCl), and known as tht ^een salt of Afagnus, Many of the platina-
mines exhibit isomerism ; thus, a compound known as the chloride of Reiafs
second dose is a yellow crystalline salt having the same composition as
Magnus's green salt. Twelve distinct series of ammoniacal platinum com-
potmds are known, four of whjch are derived from platini^j and the remainder
from platintV salts ; the former are termed platoso ammonia compounds,
while the latter are distinguished as ihtpiatino compounds, f

* llie name Cyano-platinites might with advantage be applied to these
compounds.

t For detailed descriptions of these compounds, the student is referred to
larger works on chemistry : and on the constitution of these, and metallam-
monium compounds generally, the article by Werne^. in the Zeitsckrift fUp
Anorgamuhi Chemiet 1893, vol tii. p. 967. may be conmilted.

648 Inorganic Chemistry

ABGOV.

Symbol, A. Density, 19.9. Atomic weight, undetermined.

History. — More than a hundred years ago Cavendish observed that when a
mixture of nitrogen (pkhgisticated air) and oxygen {dephlqgisHcated air) was
confined in a glass tube over mercury along with a solution of caustic potash,
and the gases exposed to the continued action of electric sparks, there was a
small residue of gas (amounting to about t^ of the volume of the nitrogen)
which was not absorbed; and he raised the question as to whether the
" phlogisticated air'* of our atmosphere is entirely of one kind.*

This observation and speculation of Cavendish's remained buried until 1894,
when Lord Rayleigh and Professor Ramsay announced to the world the dis-
covery of a new gaseous constituent of the atmosphere.

In making exact determinations of the densities of gases, Lord Rayleigh
found that nitrogen obtained from atmospheric sources always gax-e a slightly
higher number than that obtained for nitrogen which was prepared from
chemical compounds. On careful investigation, in conjunction with Professor
Ramsay, it was fotmd that this higher density of " atmospheric nitrogen" was
due to the presence in the air of a hitherto unknown gas. which they succeeded
in isolating, and to which they gave the name Argons (1894)

Occurrence. — Argon occurs in the atmosphere, where it is present to the
extent of about .80 per cent.t or i per cent, of " atmospheric nitrogen " is
argon. It is also present in the occluded gases in certain specimens of meteoric
iron. Argon has not been met with in a state of combination, and no com-
pounds containing it are known.

Modes of Formation.— ( I.) Argon may be obtained from the atmosphere
by sparking a mixture of air and oxygen. The nitrogen combines with the
oxygen, and the oxidised product is absorbed by potash. When no further
contraction of volume is obtained, the excess of oxygen is removed by alkaline
pyroKallate, and the residual gas is the argon. Unless a high-tension alternat-
ing electric discharge is employed the process is extremely slow.

(2. ) Ar|^on may also be separated from the other atmospheric gases by first
withdrawing the oxygen by means of red hot copper, and after removing the
carbon dioxide and aqueous vapour, passing the remaining gas over strongly
heated magnesium turnings, llie magnesium combines with the nitrogen
(p. 208), and leaves the argon. In order to effect the complete absorption of
every trace of nitrogen, the gas is passed backwards and forwards over the
heated magnesium for many hours.

Properties. — Argon is remarkable for its extraordinary inertness; and it has
hitherto baffled all attempts to get it to combine with any other element. No
compounds of argon therefore are known. The density of the gas is 19.9. and
therefore its molecular weight is 39.8. Whether its atomic weight is 19.9 or
39.8 depends upon whether the molecules are diatomic, like hydrogen and
oxygen, or monatomic. like mercury. This point is not yet settled (1897).

Argon is about 2^ times as soluble in water as nitrogen, 100 volumes of water
at 12 dissolvit^ about 4 volumes of argon. Owing to this higher solubility
the gases which are expelled from solution in rain water are richer in argon
than ordinary air. Argon is more difficult to liquefy than oxygen. Its critical
temperature is — 121°, at which point a pressure of 50.6 atmospheres causes its
liquefaction. Liquid argon boils at - xSy", and solidifies at - 189.6"* (Olszewski).

The most characteristic lines in the spectrum of argon are two in the red (less
refrangible than those of either hydrogen or lithium), a bright yellow line (more
refrangible than that of sodium), and a group of five green lines.

• Experiments on Air: Phil. Trans., 75, 37a, 1785.

Helium 649

HELiniL

During the year 1895 Professor Ramsay discovered that the gas which is
found occluded in certain minerals, and which was supposed to be nitrogen,
contains a gas whose spectrum is different from that of any other known
substance.

Tts spectrum is characterised b^r a brilliant yellow line, coincident with the line
D3 of the solar spectrum, which is the characteristic line of a hitherto unknovm
solar element discovered many years ago by Professors Lockyer and FrankLind,
and by them called " helium."

The minerals from which terrestrial helium has been obtained in largest
quantity are cUveite and broggeriie, although traces of the gas have been dis*
covered in many other minerals containing uranium.

The gas is obtained from these minerals by strongly heating them in vacuo.

The density of helium, determined by Ramsay, is 2. 18 ; by Cl&ve, a.02.

Like argon, this ^^ is also believed to consist of monatomic molecule, in
which case its atomic weight will be the same as the molecular weight, namely,
4.36.

By employing liquid hydrogen as a refrigerating agent. Dewar has succeeded
in liquefying helium (May 1898), and he concludes that the boiling-point of the
new gas is only slightly different from that of hydrogen. No combinations of
helium have as yet been discovered.

OTHEB OASES IN THE ATMOSPHERE.

During the present year, 1898, Prof. Ramsay has obtained indications of the
presence in the atmosphere, in extremely minute quantities, of other hitheno
unknown gases. Considerable quantities of liquid air are allowed to evaporate
in such a manner that the gas derived from the residual and least volatile
portions is collected in separate fractions; in other words, the liquid air is
submitted to a process of fractional evaporation. In this way it has been
found that these residual gaj>es exhibit spectra which in some cases appear to
be different from those given by any other known gases, and this fact has led
to the belief that at least three new gases are present, which have been named
in the meantime by their discoverer. Krypton (hidden), Neon (new), and
Metargon. Investigations into the nature of these gases are now being pro-
secuted, and until more facts have been brought to light nothing definite can
be said as to their elemental or compound character.

INDEX

(•

•I

Absoluts boiling-point, 78

„ temperature, 69
Absorptiometer (Bunsen), 125
Absorption of gases by charcoal, 256
Acetylene, 279
Acetylide of copper, 280
Acid, antimonic, 458
,, arsenic, 448

arsenious, 447

boric, 564

bromic. 345

carbamic. 275, 405

carbonic, 274

chloric, 336

chloro-auric, 524

chlorochromic. 616

chloroplatinic, 646

chloroplatinous, 646

chlorosulphuric, 400

chlorosulphonic, 400

chromic, 614

dithionic. 398

hydrazoic, 245

bydriodic, 351

bydrobromic, 343

hydrochloric, 325

hydrofluoboric. 567

hydrofluoric, 3x2

hydrofluosilicic, 585

hydrosulphurous, 386

hypobromous, 345

bypochlorous, 335

hyponitrous, 225

hypophosphorous, 432

byposulphuric, 398

hyposulphurous, 386

iodic, 353

manganic, 621

metaboric, 564

»i

•»

•t

Acid,

• I
> I

I >
II

• I
•I

• I

I I
II
II

I •

I I
•I
II
•I
•I
II
II

• I
1 1
II
II
1 1
•I

• I
II
1 1
•I
•I
II
II
II

• I
1 1

• I

metantimonic, 458
metaphosphoric, 436
metarscnic, 448
metasilicic, 588
metastannic, 593
metatungstic, 617
metavanadic, 608
molybdic, 617
muriatic, 33a
nitric, 210
nitrosulphuric, 388
nitrous, 2x9

Nordhausen sulphuric, 395
ortho-antimonic, 458
ortho-arsenic, 448
ortho-arsenious, 447
orthoboric, 564
orthophosphoric, 434
orthosilicic, 588
osmic, 643
oxymuriatic, 3x4
pentathionic, 399
perchloric, 337
perchromic, 6xa
periodic, 355
permanganic, 631
persulphuric, 385
phosphomolybdic, 617
phosphoric, 434
phosphoric (glacial), 437
phosphorous, 433
P3rro-antimonic, 458
pyro-arscnic, 448
pyro-arsenious, 447
pyroboric, 565
pyrophosphamic, 438
pyrophosphodiamic, 438
pyrophosphoric, 435
pyropbospbotriamic. 438

esi

652

Index

It
It
t(
••
(I
((
It
II
II
•I
II
II
II
II
••

Add, pyrosulphuric, 395

pyrovanadic, 608

sdenic, 408

aelenious, 408

silicic, 588

stannic, 593

sulphuric, 387 '

sulphurous, 38a

telluric, 4x0

tdlurous, 409

letrathionic, 399

thiocarbamic, 405

thiocarbonic, 404

thiosulphuric, 396

trithionlc, 398
„ tungstic, 617
Acid-forming oxides, 17
Acids, dibasic, z8

„ mono-, tetra-, and tribasic, 18
Affinities, 60

Affinity, chemical, 10, 60
After-damp, 26a
Alabaster, 536
Algjn, 348
Alkali manufacture, 490

,, metals, 466
Alkali-w-aste, 361
Alkaline earths, 537
Allotropy, 171
Aludels, 348, S53
Alum, 573

„ burnt, S75
,, meal, 575
,, shale, ^jt^
„ stone, 574
Alumina, 571
Aluminates, 57a
Aluminite, 572
Aluminium, 569

alloys, 571

bronre, 509, 571

chloride, 576

fluoride, 576

hydroxides, 57a

sodium chloride, 577

sulphate, 573

sulphide, 571, 577
Alums, 573
Aliiaite, 574
Amalgamation process (silver), 515

1 1

• I

1 1

•I

II
II
II
II
II
ti
II

Amalgams, 555
American pot-ashes, 48a
Amethyst, 571
Ammonia, 939

„ solubility of, in water, 241
Ammonia-soda process, 495
Ammoniacal cobalt compounds, 637

liquor, s8i, 501

mercury compounds, 559

platinum compounds, 647
Anunoniom, 501

alum, 574

amalgam, 501

borotluoridc, 567

carbamate, 375, 503

carbonate, 503

chloride, 501

chloroplatinate, 646

chromate, 906

cyanate, 14, 23

dissociation of, 86

ferrous sulphate, 632

hydrazoate, 246

iron alum, 574

magnesium arsenate, 449

magnesium phosphate, 435

manganous chloride, 6ao

meta-thio- arsenate, 451

mctavanadat;, 608

molybdate, 617

nitrate, 323

nitrite, 307

phosphomolybdate, 437. 617

plumbic chloride, 603

pyro-arsenite, 447
,, pyro-thio-arsenite, 450
,, salts, SOI
,, sesquicarbonate, 504
,, sodium phosphate, 435
, , stannic chloride, 596
,. sulphate, 502
,, thiocyanate, 504
Ammon-sulphonates, 247
Amorphous silicon, 583
Analysis, 13
Anastase, 581
Anglesite, 596
Anhydrides, 17
Anhydrite, 536
Animal charcoal, 355

Index

653

Anions, 93

Arsine, 441

Anodes, 9a

Asbestos, 528

Anthracite, 258

Asymmetric system, 139

Antimonates, 458

Aucamite, 511

Antimonious oxide, 457

Atmolyses, 81

Antimoniuretted hydrogen, 453

Atmosphere, 227

Antimony, 451

,, composition of, 229

„ amorphous, 453

„ height of, 237

„ blende, 451

,, suspended impurities in, 236

„ bloom, 451

Atmospheric ammonia, 233

„ compounds with halogens.

„ aqueous vapour, 231

454

,, carbon dioxide, 232

„ chlorides, 455

, , gases mechanically mixed, 235

,. hydride, 453

,, nitric acid, 233

„ ochre, 451

„ ozone. 234

„ oxides and oxyacids, 456

Atomic heat, 44

„ oxychlorides, 456

„ theory, 24

„ sulphides, 457

„ volumes, 43, 104

„ sulpho-trichloride, 456

„ weight, definitions of, 36, 42

„ tetroxide. 457

„ weight, determination of, by

,, trioxide, 457

chemical methods, 35, 57

Apatite, 309, 538

,, weight, determination of, by

Apollinaris water, 195

means of isomorphism, 49

Aquafortis, 909

,, weight, determination of, by

Aqua regia, 216

means of specific heat, 43

Aqueous vapour (atmospheric), 231

„ weight, determination of.

Argentic compounds (set Silver), 514

from volumetric relations

Argentiferous lead, 516

Argentite, 514

Atomic weights, list of, 21

Argon, 648

Atoms, 4

Arragonite, 537

Aurates, 535

Arsenates, 449

Auric chloride, 524

(Arsenic, 439

„ oxide, 525

, , allotropic modifications of, 4 40

Auro-auric sulphide, 525

M chlorhydroxide, 444

Aurous iodide, 524

,. chloride, 443

Autogenous soldering, 399

M compounds with halogens,

Avogadro's hypothesis, 39

443

Azote, 205

„ fluoride, 443

Axurite, 506

„ oxides and oxyacids, 444

„ pentoxide, 448

,, sulphides, 449

Balling furnace, 492

„ trihydride, 441

Barium, 541

Arsenical iron, 439

„ amalgam, 541

„ pyntes, 439

„ bromate, 345

Arsenious bromide, 444

M carbonate, 541

„ iodide, 444

„ chlorate, 336

„ oxide, 445

„ chloride, 543

Arsenites, 447

,, dioxide, 162, 543

Ar3enur«^t<Hl hydrogen, 441

,, dithionate, 398

654

Index

Barium hydroxide, 54a

hjrpophosphite, 433
iodate, 542
monoxide, 541
nitrate, 544
oxides, 541
peroxide, 54a
sulphate, 544
,, sulphide, 544
tetrathionate, 399
thiosulphate, 399

Baryte, 541

„ water, 54a
Barytocalcite, 541
Basic oxides, 17

„ salts, 19
Basicity of adds, the, 18, 433
Battery, galvanic, 91
Bauxite, 569
Beryl, 528
Bcrylla, 528
Beryllum, 528

,, aluminate, 57a

., compounds, 528

,, specific heat of, 46
Bessemer process (steel), 627
Biaxial crystals, optically, 140
Binary compounds, 15
Bismuth, 460

,. alloys, 461

,, carbonate, 463

,, compounds with halogens,
461

,, dichloride, 46a
dioxide, 463

,, glance, 460
nitrate, 463

,, nitrate, basic. 463

,, ochre, 460

,, oxides, 462

., oxychloride, 464
pentoxide, 464

,, tetroxide, 464
tribromide, 462
trichloride, 461

,, tri-iodide, 46a
trioxide, 463

,, trisulphide, 465
Bismuthic oxide, 462
Bismuthous oxide. 462

Bisulphate of soda, 383
Bittern, 488
Bituminous coal, 258
Black ash, composition of, 494

fixmaoe, 49a

revolving furnace, 493
Black-band, 624
Black-jack, 546
Blacklead, a53
Blast-ftunace, 6a5
Bleaching-powder, 165, 335, 535
Blister copper, 507

„ steel, 6a7
Blue vitriol, 51a »

Boiling-point, definition of, iza

,, absolute, 78
Boiling-points, 113

of saturated saline solutions,
H7

effect of pressure upon, Z13
,, effect of dissolved substances
upon, 118
Bolognian phosphorus, 539
Bone ash, 4x3

,, black, 255
Bones, composition of, 255
Boracite, 562
Borate spar, 562
Borates, 565
Borax, 565
Dorofluorides, 567
Boron, 562

hydride, 568

nitride, 568

sulphide, 568

trichloride, 567

trifiuoride, 566

trioxide, 563
Boronatrocalcite, 562
Bort, 250
Boyle, law of, 70
Brass, 509
Braunite, 618

Brin's process (oxygen), 162
Britannia metal, 452. 592
British Channel, composition of, 195
Bromates, 346
Bromides, 344
Bromine, 339

hydrate, 34a

Index

655

Rromine monochloride, 356
,, oxyadds. 344
„ water. 34a
Bronze, 59a
Brookite, 581
Brown haematite, 634
Brown iron ore, 624
Brudte, 530
Bunsen flame, the, 303

,, non-luminosity of, 304
,, temperature of, 305
Burnt alum, 575
Cadmium, 551

chloride, 553
„ oxide, SSI
„ sulphide, 55a
Caesium, 466, 500

,, spectrum of. 470
CaiUetet's apparatus, 74
Calamine, 546
Calcined magnesia, 5^9
Caldte, S3a
Caldum, SS^

bicarbonate, 197, 274, 533

borate, 566

borofluoride, 567

carbide, 380

carbonate, S37

chlorate, 478

chloride, S34

chloro-hjrpochlorite, S36

dioxide, 534

fluoride, 31a

hydroxide, 534

hypochlorite, 478, 536

manganite, 331, 630

oxides. 533

phosphate, 413, 538

phosphide, 431

sulphate, 536

sulphide, 361, 373, 538
Calc-spar, S3a
Caliche, 349
Calomel. 557
Calorie, 144, 388
Calx, 337, 383
Candle flame, 398
Canton's phosphorus, 539
Capillary pyrites. 641
Carat, definition of, 534

Carbide of barium, 380

„ of iron, 474
Carbon, 3So, 581

,, compounds, 359

., dioxide, 364

,, .atmospheric, 333

,, ,, composition of, 373

solid, 371

,, disulphide, 403

,, hydrogen, compounds of, 376

,, monoxide, a6o

.. oxides of, a6o

,. spedflc heat of, 4S
Carbonado, aso
Carbonates. 374
Carbonyl chloride, 363
Carbonyls, metallic, 363
Carborundum, 584
Carboxy-hsemoglobin, a69
Camallite, 471, sa8
Carre's freezing machine, 116
Cossiterite, S90
Cast iron, 636
Catalysis, x6i
Catalytic action, 13, 161
Cathions, 93
Cathodes, 9a
Caustic potash, 476

,, soda, 487
Celestine, S39
Cellulose, ais

Cementation process (steel), 637
Cerite, s8x
Cerium, s8i
Cerussite, S96
Chalcedony, 583
Chalk, 357

Chalybeate waters, 19s
Chamber acid, 391
Chamber crystals, 388
Chance's process, 371
Change of volume on solidification,

119
Charcoal, 354

,, absorption of gases by, 356

,, animal, 356

., specific heat of. 45
Charles' law, 68
Chemical action, 11
I Chemical action, modes of, 13

656

Index

Chemical action, affinity, lo

combinaticm, laws of, 24
equations, aa
formuke, aa
nomenclature, 15
notation, quantitative, 53
reactions, aa
symbols, ao
ChiU saltpetre, 497
Chlorates, 337
Chloride of lune, 535
Chlorine, 3x4

hydrate, 334
liquefaction of, 7a
liquid, 324
monoxide, 333
oxides and oxyacids, 333
peroxide, 334
water, 323
Chloro-aurates, 535
Chloro-chromates, 6x6
Chloro-btannates, 595
Chromates, 614
Chrome alum, 613
,, green, 610
,, iron ore, 609
,, ochre, 609
red, 615
yellow, 615
Chromic anhydride, 61 1
,, chloride, 6ia
,, hydroxides, 610
,, sulphate, 613
Chroraite, 609
Chromites, 613
Chromium, 609

,, anhydride, 610
,, chromate, 610
,, dioxide, 610
,, oxides of, 610
,, sesquioxide, 610
,, trioxide, 611
Chromous chloride, 6x3
,, hydratcd oxide, 610
,, sulphate, 613
Chromyl chloride, 615
Chrysoberyl, 538, 572
Cinnabar, 553

Clark's process for softening water,
zq8

i»

Clarification of elements, 97
Clay, 569

Clay, ironstone, 634
Coal, 357

„ gas, a8i
Coarse metal (copper), 507
Cobalt, 634

bloom, 634
glance, 439, 634
oxides of, 634
Cobaltamines, 637
Cobaltic hydroxide, 635

„ oxide, 63s
Cobalto-cobaltic oxide, 63c
Cobaltous chloride, 635
,. hydroxide. 635
„ oxide, 63s
,, sulphate, 636
,, sulphide, 636
Coefficient of absorption, 124

solubility, 124
Coefficients of expansion of gases, h
Coke, 354
Colemanite, 562
Colloids, 589
Columbite, 607
Combining proportions, 29
Combustibles, 384
Combustion, 383

,, gain in weight by, ©87
,, heat of, 288
,, supporters of, 284
Common salt, 488
Compound radicals, 2s
Compounds, 7
Condy's fluid, 622
Constant composition, law of, 3c
Constitution of matter, 3
Copper, 506

acetylide, 280
alloys, 509
arsenite, 447
bromide, 512
carbonates, 513
chlorides, 511
ferrocyanide, 135
fluoride, 512
glance, 506
hydroxide, 510
nitrate, qia

^^^^J"^

^^f li*dix 6S7 ^1

^Heppo-nllmtTl. *I9

Dlamund, ijo ^^^|

H .. <»l<lei,sa9

specllic htal (if. 45 ^^^^1

■ .. pjTiua. so6

DJflusiomElet. 79 ^^^|

DiffiuiOQ of teasel, 78 ^^H

;; sdphidci. S.J

u«or. So ^^1

or diuol'ed uibsuucet, 137 _^^H

Ctiml. W»

DimotpbUm. 141 ^^H

^Cofp«Ugh..,,>

Dissocial ioo, Bj ^^^H

KCoTTOiiin: snbUmue. 55*

Disulphut dichloride. 374 ^^H

Disulphorvl chloride. 401 ^^^H

^Cre«m of iinar, 457. 47a

Di IhioriRtes. 396 ^^H

^ Crilh. ss

L>in!ent elemenu, 58 ^^^H

Crillol presnuc, 78.

Uototnite. 59B ^^H

„ Kinperalure, 77. i'7

Dry capper. 507 ^^H

Croceo-Mbatlii; lalls, 637

Dulong and Pelil, law □!. 44 ^^^H

^ Crocotoile. 609

Dutch brass. 509 ^^^|

|_&00tedl<!. S77

,. •neial.3^ ^H

UindelemeDU, 58 ^^1

Kryollte. 309. S69

^Qy,Wlinefomi.. .38

RbuUition, IK ^^H

.. waller of, 193

Lf9oresccoce.'i93 ^^H

Crjii-lloidi. 589

Effusion of ^KS, Bi ^^^H

Cubical nitM, 497

Cupel. S'6

Eka-boroti, 108 ^^H

Cupellaiioo progesi(iilYcr). ;.6

Eka-iillcoa, loS ^^H

.. chloride. SI-

l£1cclro-giIdi[>g. 534 ^^H

EleclrDl;il9, 91 ^^H

^1 nitnw, 5"

Eleclrolyiet, 91 ^^H

H .. <»ide.s«>

■ .. »lpb«l«.st)

^ .. TOlphid«.s.3

Elemenli and compouads, t, ^^H

Cuprous ucrjUdi^ ■B<i.

,. chloride,;"

ibi » ^^H

,. oride. 509

non-metal lie, ^^^H

.. wUphlde. i.3

Ellon LjOie, water of. 195 ^^H

Cyanide process, gold. 513

Emeraid, 598 ^^H

Dalton. Biomlc ibeory, 39

S7> ^H

Da-rr lamp, B91

Deauon'i process. 316

Dead S«, solid mailer in, 195

Deep well mteii. 196

Endothermic compounds, >]} ^^^^H

EogUsh brass, 509 ^^H

l^piom salts, 531 ^^^H

DewpoiDl, tyi

Eqiulloni. dirmlcal, » ^^H

Dialomie molecule., <

Equivalence \m Valency. jB) ^^H

Diolyied Iron. 610

Dimlwis. 5^1

elenRO-chcDiiul, 93 ^^^1

^^^H

6$8

Indix

Estramadurite, 413, 538
Ethenc, 278
Ethine, 279
Ethyl silicate, 585
Ethylene, 278

M dibromide, 278
Euchlorine, 334
Eudiometry, 237
Evaporation, iii

,, cold produced by, 76, 114,

243
Exothermic compounds. 147, 293

Expansion by heat of liquid carbon

(Uoxide, 270
Expansion by heat of liquid oxygen,

170
Extincteur, 267

Faraday's law, 93
Felspar, 569, 590
Ferrates, 631
Ferric chloride, 632

,, ferrocyanide, 633

,. hydroxide, 630

., soluble, 630

,, oxide, 630

,, sulphate, 632
sulphide, 633
Ferrites, 629
Ferro-manganese, 626
Ferroso-fcrric oxide, 630

,, sulphide, 634
Ferrous bromide, 481

,, chloride, 631

,, chromite, 614

,, ferricyanide, 632

,, ferrocyanide, 632

,, hydroxide, 629

„ oxide, 629

,, sulphate, 631
sulphide, 633
Fettling, 627
Fine metal (copper), 507
Fire-damp, 277
Fire-damp caps, 294
Fixed air, 264
Fixed alkali, 467
Flame, 294

,, candle, 297

the Bunsen. 3fol^

FluMi ttmctore of* 99^

Flames, cause of lumiiiadtj of, 3^1

Flint, 58a

Flintshire liimaoe, 597

Fluoiapadte, 309

Fluorides, 3x5

Fluorine, 308

Fluoivphmibates, 3x0

Fluor-spar, 309, 533

Forces, chemioU and physical, 3

Formida weight, 53

Formulae, 99

Fraction of dissociation, the, 88

Franklinite, 546

Fulminating gold, 505

„ silver. 590
Fusco-cobaltic salts, 637
Fusible metal, 461
Fusion, latent heat of, tso

Gadolinitb, 561
Gahnite, 546
Galena, Si4i596
Gallium, 109, 561
Galvanised iron, 548
Gas carbon, 254

Gases, absorption by charcoal, 256
coefficients of expansion ol

critical pressure, 78
critical temperature of, 77
diffusion of, 78
effusion of, 82
kinetic theory of, 82
liquefaction of, 71
occlusion of. 257
relation to heat, 68
relation to pressure, 70
solubility of, in liquids, zaii
transpiration of, 82

Gastric juice, 490

Gay-Lussac, law of. 25, 37

General properties of gases. 68
„ liquids, no

German silver, 548

Germanium, X09, 581

Gilding, 524

Glauberite, 496

Glauber's salt. 496

Glucinum, 528

•t

•I

• I

Index

6S9

Gold, 523

„ alloys, 594

,, compounds of, 534

,, fineness of, 534
fulminating, 525
Graduators. 488
Graham's law, 80
Gramme-molecule, 56
Graphite, 352

„ specific heat of, 45
Oreenockite, 551
" Green salt of Magnus," 647
Green vitriol, 395, 631
Grey antimony ore, 451

„ cast iron, 6a6
Guignet's green, 611
Gun-cotton, 315
Gun-metal, 509
Gunpowder, 484

„ products of comtMistionof,484

Gypsum, 536

„ fibrous, 536

HiBMATITE, 624

Haemoglobin, 170
Hair salt, 579
Halogens, 18, 307
Haloid salts, x8
Hardness (water), 197
Hargreave's process, 497
Hausmannite, 618
Heat, atomic, 44

;, molecular, 47

,, of combustion, 388
of formation, 146
specific, 44
specific, table of, 45

„ units, Z44
Heavy spar, 541
Helium, 649
Henry's law, 133
Htpar sulphuris, 485
Hexagonal system, 139
Holmes's signal, 434
Horn mercury, 557
Horn silver, 514
Hydrazine, 345

,, hydrochloride, 245

„ hydrate. 345

„ sulphate. 345

»i

Hydrocarbons, 376
Hydrogen, 150

chloride, 325

., compounds with oxygen, 179

,, dioxide, 179

,, disodium phosphate, 435

,, displaceable, z8

., monoxide, 179

,, nitrate, 19

,, occlusion, of, 150, 157

,, peroxide, 199
persulphide, 373

,, phosphide, 420

,, potassium fluoride, 309

,, potassium sulphate, 395

,, sodium ammonium phos-
phate, 435

,, sulphate, 19

,, sulphide, 369
Hydrogenium, 157
Hydromagnesite, 539
Hydroxides, 17
Hydroxyl, 247
Hydroxylamine, 346

„ disulphonate, 248

,, hydrochloride, 247

,, mono-sulphonate, 248
Hypobismuthic oxide, 462
Hypobismuthous oxide, 462
Hypochlorites, 336
Hypochlorous anhydride. 333
Hypoiodous acid, 356
Hyponitrous anhydride, 223
Hypophosphites, 433
Hypovanadic chloride, 608

,, oxide. 608

„ sulphate, 608
Ice, 190 ^

„ effect of pressure upon, ^

,. the melting-point of, iso
Icicle, 116
Ignition-point, 391
Indifferent substances, 136
Indigo-copper, 513
Indium, 107, 561
Inflammable air, 150
Intestinal gases, hydrogen in, 150
lodates, 354
Iodic anhydride, 353
Iodine, 34^

66o

Index

Iodine, bromides, 357

Law of constant heat consummatioz

M chlorides, 346

148

„ pcntoxide, 353

•»

constant proportion, 24

Ions. 93

Dulong and Petit, 44

Iridium, 64a

gaseous diffusion, 80

„ chlorides, 643

Gay-Lussac, 25, 37

„ oxides, 643

»i

multiple proportions, 26

Irish Sea, solid impurity in, 195

•1

octaves, 98

Iron, 623

partial pressures, 127

», alum, 639

•I

penodic, 100

„ carbide, 474, 626

reciprocal proportions, 07

M carbonyl, 064

Layer

crystals, 50

„ magnetic oxide of, 630

Lead,

596

„ monoxide, 629

acetate, 605

„ oxides of, 699

action of water upon, 599

„ passive, 699

carbonate, 604

„ pyrites, 360, 624

chromate, 615

M sesquioxide, 630

•1

composition of commerda]

,, sesquisulphidc, 633

600

„ sulphides of, 633

desilverisation of, 516

Isodimorphism. 141

dichloride, 602

Isogonism, 50

1 1

dioxide, 602

Isomerism, 171

IjcaA ethide, 582

Isomorphism, 49, 141

nitrate, 603

„ law of, 49

oxides of, 600

Isotropic crystals, 140

• 1

oxychloride, 603

sesquioxide, 601

Jolly's apparatus, 230

;•

softening of, 598

squirted, 600

Kainitb, 471

• •

suboxide, 600

Kelp, 347

sulphate, 605

Kelp substitute, 345

sulphide, 606

Kiesel-guhr, 586

sulphochlorides, 606

Kicscrilc, 528, 531

1 >

tetrachloride, 603

Kinetic theory. 83

tree, 598

Kish, 253

• 1

white, 604

Kupfemickel, 439, 639

Leblanc process, 490

L^OONS (boric acid), 564

Leguminous plants, 233

Lepidolite, 499

Lakes, 572

Light red silver ore, 514

Laminaria digiuta, 347

Lime,

533

„ sleuophylla, 347

chloride of, 535

I^mp-black, 254

dead burnt, 533

Lanarkite, 596

milk of, 534

Lanthanum, 561

quick, 534

Intent heat of fusion, 120

1 •

slaked, 534

,, „ vaporisation, 1x4

superphosphate of, 538

Laughing-gas, 223

Limestone, 532

Law of Boyle, 70

Liquefaction of air, 76

„ Charles, 68

of gases, 71

Uquidi, general propertlei of. i

Litharge, 6oa
Lilbium, 499

hydroxide, 500
m(ca.499
nftrlde, 90S
oiide, 500

iOJ

spectnun of, 469
Uver of sulphur, 485
Load-slone, 624, 630
Lottiar Meyer's curve
Litdfer matches, 419
Luminous paint, 539
Lunar caustic, 51a
Luleo-Coboltic salts, Gjl

Magistkai^ 515
Magnesia, 519
MagTUiia alia Iniii, 531
„ pondtniia, 533

Magnesia minure. S3'
Magnesian limestone, 196, 533
Magnesile, 518
Mamiesiura, 518

alumitinte, 571

ammonium chloride, 530

ammDniuin phosphate, 435

boride, 568

bromale, 346

calcium chloride, 53a

carbooalea, S39

chloride, 530

hydioiide, 530
nitride, aoS. 539
oiide, 529
oxychloride, 530
phosphate, 435
platinocyanide, 193
potassium chloridr;, 530
I>yrophosphale, 436
filicide. 584
julpbale, 531
Magnetic iron ore, 624

oiide of iron, 630
PTTiles, 634

Manganese, 618

biende, 61B

dioxide, 619

, monoiide, 61S

, oddes of, 618

, sesquioiide, 619

Manganic chloride, 610

cbromiu, 614

, taydioiide. 619

„ sulphate, 610
Marble, S37
Marine acid air, 333
Marsh gas, 976

„ synthesis of, 404
Maiih'i test. 44a
Massicot, 600
Matches, 419
Mallockite, 596
Mechanical miiluies, 8
Meditenanean Sea, 195
Meosehaum, 51a
MendelejelTs periodic law, loo
Mephitic air. 305

rcurie ammonium chloride. SS'

„ chloride. S58

„ iodide, 558
oxide, ss6
potassium chloride, 6Sm

Mercuroua chloride, 557
„ nitrate, SS7

oxide, ss6

sulphate, 557
Mercury, 553

alloys of (amalgams), 55J

deadening of, 555

distiilation of. 554

oxides of, 556
Metal slag (copper), 597
MeUllic nitroxyks. 919

662

Index

MeUlloids, 8

Metals and non-metab, 7

Metamcric compounds, 171

Mctantimonates, 458

Metaphosphates, 437, 459

Metarsenates, 449, 459

Metarsenites, 448

Metastannates, 594

Metavanadates, 607

Meteoric iron, 150

Methane, 376

Meyer, Lotbar, ctirve of atomic

volumes, xo6
Microcosniic salt, 498
Milk of lime. 534

„ sulphur, 368
Milky quartz. 588
Mineral alkali. 467 .
Mineral chameleon, 621
Minium, 6ox
Mispickel, 439
Mixed crystals, 50
Modes of chemical action, 13
Molecular combinations, 65

,, equations, 54

,, formulae. 32

,, heats, 47

lowering of vapour pressure,
118

,, volume, 43

„ weight, 39

,, weight, determination of, by
the depression of freezing-
point, 121
Molecules, 3

,, compound, 6

,, definition of, 4
elementary, 6
mean free path of, 83
size of, 3
Molybdates, 616
Molybdenite, 616
Molybdenum, 616

chlorides, 617
ochre. 616

,, oxides, 616
Monad elements, 58
Mono-atomic moleail(;s. 8
Monoclinic system, 139
Monosymmctric system. 139

•I

•»

Monovalent dements, 58
Mordants, 57a
Mortar, 534

„ the setting of, 534
Mosaic gold, 596
Mottramite, 607
Mundic, 439
Muntx metal, 509
Multiple proportions, law o(. f6

Natural waters. 194
Natural steel, 624
Nessler's solution, 941, 560
Neutral alum, 576
Nickel, 639

alloys of, 639
blende, 639
carbonyl, 363
chloride, 641
glance, 439, 639
monosulphide, 641
monoxide, 640
oxides of, 640
sesquioxide, 640
silver, 548
sulphate, 641
Nickelo-nickelic oxide, 640
Nickelous oxide, 640
,, sulphide, 641
Niobates, 607
Niobium, 607

,, oxides of, 607
Nitrates, 3x5

,, detection of, 315
Nitre, 483

,, plantations, 483
Nitric anhydride, 3x6

„ oxide, 330
Nitrification, 483
Nitrites, 3x9
Nitro-cellulose, 315
Nitrogen, 305
., iodide, 349
, , oxides and acids of, 309
,, pcntoxide, 3x6
,, peroxide, 2x7
,, tribromide, 249
,, trichloride, 348
Niiro-mctals, 319
Nitro-sulphuric acid, 368

Index

663

Nitrotyl chloride, 225

,, hydrogen sulphate, 235

„ sulphate, 388
Nitrous anhydride, 909
Nomenclature, 15
Non-metals, 7
" Nordhauaen " suad, 395
Notation, chemical, ai, 59

OCCLUDKD hydrogen, 151

Oodusioo of gases, 157

Olefiant gas, 978

Opal, 586

Ore hearth, 597

Orangeite, 581

Organic chemistry, definition of, 259

Orpiment, 439

Orthite, 561

Orthodase, 590

Osmiridium, 64s

Osmium, 64a

„ oxides of, 643

„ tetroxide, 643
Osmotic pressure, 134
Osteolite, $3^
Oxides, 16
Oxygen, 159

,, allotropic, 179
Brin's process, 162
Tessi^ du Motay process, 167
Oxyhsemoglobin, 170
Oxyhydrogen flame. 291
Ozone, 179

„ atmospheric, 934

,, constitution of, 176

,, tube, Siemens', 173
„ Andrews', 177

Palladium, 649

,, absorption of hydrogen by,

157

,, chlorides, 643

„ hydride, 157

„ oxides, 643
Parkes's process, 516
Partial pressures, law of, 197
Passive iron, 699
Pattinson's process, 5x6

„ white lead, 603
Pearl-ash, 489

Perchlorates, 338
Percy-Patera process, 518
Periclase, 599
Peridote, 590
Periodates, 356
Periodic classification, loa
Permanent white, 544

„ hardness, 197
Permanganates, 621
Permanganic anhydride, 622
Persulphates, 385
Persulpburic anhydride, 384
Petalite, 499
PeUite, 523
Pewter, 592
Phenacite, 528
Phlogiston, 283
Phosgene gas, 963
Pbospham, 438
Phosphates, 435
Phosphine, 490
Phosphites, 434
Phosphonium bromide, 490

,, chloride, 499

„ iodide, 493
Phosphoretted hydrogen, gaseous, 4ac
liquid, 423
solid, 494
Phosphorous oxide, 430
Phosphorus, 419

,, allotropic, 4x8

,, compounds with sulphur, 438
oxides and oxyacids, 429

,, oxychloride, 428

,, oxyfluoride, 428

, , pentabromide, . 427

,, pentachloride, 426

,, pentafluoride, 425

,, pentasulphide, 438

,, pentoxide, 431

,, red, 4x8

,, tetriodide, 497
tribromide, 497

,, trichloride, 495

,. trifluoride, 494

,, triodide, 427
Pbosphoryl chloride, 498

,, fluoride, 498
nitride, 438
triamide, 438

•I

«i

664

A rWV^^'

Photo-salU, 533

Potassium carixmate, 481

Pig-boiling, 607

chlorate, 477

Pig iron, 626

chloride, 477

Pitchblende, 616

cfalorocfaroniate, 616

Planes of symmetry, 139

diloroplatinate, 646

Plaster of Paris, 537

dilon^datinite, 64is

Plastic sulphur, 367

chromate, 614

Plate sulphate, 348

chromium alum, 574, 613

Platinamines, 647

dichromate, 614

Platinates, 645

ferrate, 631

Platinic hydroxide, 645

t»

ferricyanidfi, ^

„ chloride, 646

ferrocyanide, 961, 63a

Platinlridium, 642

•f

fluoride, 476

Platino-chlorides, 646

floor-plmnbate, 310

„ cyanides, 647

hydride, 475

„ nitrites, 647

hydroxide, 476

Platinotype process, 646

hyponitrite, 225

Platinous chloride, 645

iodate, 355

„ hydroxide, 645

iodide, 480

Platinum, 643

manganate, 621

„ alloys, 645

metaborate, 565

„ black, 645

metantimonate, 458

„ oxides of, 645

• 1

metarsenite, 448

„ oxysalts, 647

metastannate, 594

„ sodium chloride, 65

1 •

meta-thio-arsenite, 450

„ spongy, 644

nitrate, 483

„ sulphides of, 647

nitrite, 220

,, tetrachloride, 646

osmate, 643

Platoso-ammonia compounds, 647

oxides of, 475

Plumbago, 253

ortho-thio-antimonate, 46c

Plumbic chloride, 602

• 1

ortho-thto-anttmonite, 460

,, oxalate, 600

• 1

ortho-thio-arsenate, 451

,, oxide, 600

ortho-thio-arsentte, 450

,, peroxide, 60a

• 1

pentasulphide, 485

Plumbous oxide, 600

pentathionate, 400

Plumbum nigrum^ 596

perchlorate, 480

Pollux, 470

pcriodatc, 356

Polybasite, 514

1 1

permanganate, 622

Polyhalite, 481

peroxide, 475

Polymerism, 171

I •

platinic chloride, 646

Pot-ashes, 481

• I

platino-cyanide, 647

Potash, caustic, 476

1 1

platinous chloride, 646

Potassium. 471

• •

plumbate, 602

„ alum, 574

1 >

pyro-antimonate, 458

,, aluminate, 572

1 >

ruthenate, 643

,, aluminium chloride, 576

1 •

silico-fluoridc, 583

,, antimonate, 458

• •

silver thiosulphate, 398

borofluoride, 563, 567

■ fl

stannate, 593

,, bromate, 346, 480

sulphate, 481

bromide, 480

1 ••

sulphite. 362

Index

665

Pocassium, lulphides of, 485

tetrachromate, 615

trichromate, 615

zinc oxide, 154
Powder of Algaroth. 455
Praseo-cobaltic salts, 637
Preparing salt, 593
Producer gas, 164
Proustite, 514
Prussian blue, 633
Pseudo^lms, 574
Pucherite, 607
Puddling, 6a7
Purple copper ore, 506
Purpureo-coboltic salts, 638
Pjrrargyriie, 5x4
Pyrites burners, 390
Pyrolusite, 6x8
Pyromorpbite, 596
Pyrophosphates, 436
Pyrosulphuric chloride, 401

Quadratic system, 139
Quantitative notation, 53
Quartz, 586
Quicklime, 533

Radiated pyrites, 633

Radicals, compound, 2a

Rain water, solid impurity in, 196

Realgar, 439

Red antimony, 451

., copper ore, 509

,, haematite, 694

,. lead, 60Z

manganese oxide, 6t8

,. phosphorus, 418

, , zinc ore, 546
Refinery slag (copper), 507
Regular system, 139
Reiset's second base, chloride of, 647
Relation of gases to heat, 68

,, ,, ,, pressure, 70

Reversible reactions, 85
Rhodium, 64a
Rhombic system, 139
Rochelle salt, 5x9
Rock crystal, 586
Rock salt, 486
Rodonda phosphates, 4x3

Roll iulphar, 364
Roman alum, 574
Roseo-cobaltic salts, 638
Rouge, 630
Rubidium, 500
Rubies, artificial, 571
Ruby, 569
Ruby ore, 506

„ silver ore, 514

.. sulphur, 439
Rust. 388
Ruthenium, 649

,, chlorides of, 643

., oxides, 643
Rutile, 581

Sal alembroth, 558

,, ammonia, 501
Salt-cake process, 491
Salt-forming oxides, 17
Salterns, 488
Saltpetre. 483
Salts, acid, 19

basic. 2^
haloid, x8
normal, 18

,. oxy-, 18

,. thio-, 18
Sand, 583
Sapphire, 569
Satinspar, 536
Saturated solutions, 130

,. vapours, 111
Scandium, 561
Scheele's green, 447
Scheelinite, 616
Schlippe's salt, 460
Schdnite, 531
Schweinfurt green, 448
Scotch hearth, 597
Seaweed, iodine in, 347
Selenite, 536
Selenium, 405

„ alums, 574

,. dichloride, 407

„ dioxide, 407
Selenuretted hydrogen, 406
Seltzer water, 195
Semipermeable membranes, 134
Serpentine, 538, S9a

•I

••

666

Index

»•

•I

(■

• •

Siemens' ozone tube, 173
Saica,586
Silicates, 589

Siliduretted hydrogen, 584
Silicon, 58a

chloride, 586
(dilorofonn, 5^
dioxide, 586
fluoride, 585
hezachloride, 586
hezafluoride, 585
„ hydride, 584
Silver, 514

„ allotrc^c, 519
alloys, 519
alum, 522
„ bromide, 531
chloride, 520
flashing of, 516
fluoride, 521
fulminating, 520
glance, 514
iodide, 531
nitrate, 53a
oxides, 5x9
oxylM'omide, 529
oxychloride. 533
periodate, 355
phosphates, 435, 437
plating, 519
spitting of, 518
standards, 59
suboxide, 520
sulphate, 523
,, sulphide, 514
Singly refracting crystals, 140
Slaked lime, 534
Smalt, 638 .
Smaltine, 634
Smoky quartz, 588
Soda, 496
Soda-ash, 495
,, caustic, 487
„ crystals, 495
Sodium, 486

,, acetate, 377

,, alloy with potassium, 486

,, aluminate, 569

„ aluminium chloride, 570

„ amalgam, 555

•I

Sodium antfanoiiale, 458

antimonite, 457

anenate, 449

benioate, 845

bkarbonate, 496

bromide, 490

carbonate, 490

chloride, 488

chloro-platinate, 646

hydrazoate, 945

h3rdride, 486

hydroxide, 487

hypophosphite, 490

hyposulphite, 386

iodide, 490

metaniobate, 607

metaphosphate, 437

metastannate, 594

metatantalate, 607

metavanadate, 607

nitrate, 497

oxalate, 155

oxides, 486

permanganate, 622

phosphates, 498

pyro-arsenate, 449

pyrophosphate, 436

sesquicarbonate, 496

silicate, 588

silver thiosulphate, 518

stannite, 593

sulphate, 496

,, solubility curve, 152

sulphide, 491

thio*antimonate, 460

thiosulphate, 397

tungstate, 616

uranate, 616

zinc chloride, 65
Soflioni, 564
Solar prominences, 150
Solder, 59a
Solfatara, 360

Solidification, suspended, xx8, 365, 416
Solidifying points of liquids, 1x9
, , points of liquids, efifect of dis-
solved substances upon, xai
,, points of liquids, eflF^n ot
pressure on, 119
Solubilities, diagram of, 131

Index

667

• (

■ t

Solubility of gases in liquids, laa

of liquids in liquids, ia8

of mixed gases, za6

of solids in liquids, 199
Solution, 139
Solutions, saturated, 130

,, supersaturated, 130
Sombrerite, 413, 538
Spathic iron ore, 634
Specific gravity of gases, 39

,, liquids and solids,

Z04

heat, 44

heats, tables, 45
Spectra of alkali metals, 469
Spectroscope, 468
Sp>ecular iron ore, 634
Speiss-cobalt, 634
Spiegel, 696
Spinelle, 57a
Spirits of hartshorn, 939
Spitting of silver, the, 518
Spodumene, 499
Spring water, 196-19-9
Stalactites, 197
Stalagmites, 198
Standard temperature and pressure,

69,70
Stannates, 594
Stannic chloride, 595
„ sulphide, 595
Stannous chloride, 594

hydrated oxide, 599

nitrate, 593

oxide, 599

oxychloride, 594

sulphate, 591

sulphide, 595
Stassfurt deposits, 471, 481, 530
Steam, 189

,, volume composition of, 184
Steel, 697
Steel mill, 991
Stepbanite, 5x4
Stereotype metal, 459
Stibnite, 451

StiU-liquor, composition of, 319
Stream-tin, 590
Strome3rerite, 5x4
Sirontia, 539

(•

•t

Strontianite, 539
Strontium, 539

chloride, 540

dioxide. 540

hydroxide, 540

nitrate, 541

oxides, 539

sulphate, 540
Substitution, 344
Suint, 471
Sulphates, 395
Sulphides, 371
Sulphites. 389
Sulpho4icids, 17
Sulpho-thionyl chloride, 374
Sulphur, 359

allotropic modifications, 365

chlorides of, 374

dioxide, 376

flowjers of, 363

milk of, 368

oxides and oxyadds of, 375

oxychlorides of, 400

plastic, 367

prismatic, 365

recovery of, from alkali waste,

recovery of (Chance's process),

37X

rhombic, 365

sesquioxide, 384

tetrachloride, 375

trioxide, 389
Sulphuretted hydrogen, 369
Sulphuric anhydride, 375
,, chlorh3rdrate, 40X
Sulphurous anhydride, 375
Sulphuryl chloride, 400
Supercooling of water, 118
Superphosphate of lime, 538
Supersaturated solutions, 130
Suspended solidification, 119, 365, 41^
Sylvanite, 593
Sylvine, 47X
Symbols, 91
Sympathetic inks, 193
Synthesis, X3

Tacuydritk, 530
Talc, 598

668

Index

Tank liquor, 494
Tantalite, 607
Tantalum, 607

„ oxides of, 607
Tartar emetic, 457
TeUurates, 410
TeUuretted hydrogen, 409
Tellurites, 410
Tellurium, 408
Temporary hardness, 197
Tenorite, 510

Tessi^ du Motay process, 167
Tetradymite, 409
Tetratomic molecules, 8
Tetravalent elements, 58
Thallic chloride, 579
nitrate, 580
oxide, 562, 578
sulphate, 580
sulphide, 562 .
Thallium, 577

,, oxides of, 578
,, oxyhydroxide, 579

perchlorate, 562
,, sulphate, 562
Thallous carbonate, 579
,, chloride, 579
hydroxide, 578
iodide, 562
oxide, 578
phosphate, 579
Thdnardite, 496
Thermochemistry, 142
Thio-acids, 17
Thio-antiraonates, 460
Thio-antimonites, 460
Thio-arsenates, 451
Thio-arsenites, 450
Thiocarbonates, 404
Thionyl chloride, 400
Thiophosphoryl chloride, 429
Thiophosphoryl fluoride, 428
Iliorite, 581
Thorium, 581
Tin, 590

alloys of, 592
dioxide, 593
,, oxides of, 592
,, oxymuriate, 595
Tin-plate, 592

Tln-<tone, 590
Tin-white cotelt, 439
Tincal, 56a
Tinning, 59a
Titanium, 581
Tombac, 509

Tiransitional elements, 100, 693
Transpiration of gases, 8a
Triad elements, 58
Triclim'c system, 139
Tridymite, 586
Triethylamine, 129
Triethyl silico-formate, 585
Trivalent elements, 58
Trona, 496
Tungsutes, 6x6
Tungsten, 6x6

„ chlorides, 617

„ oxides, 6x6
Tumbull's blue, 632
Turpetb mineral, 395
I'urquoise, 569
Tjrpe metal, 452
Typical elements, 100
Twin crystals, 588

Ulexite, 562

Uniaxial crystals, optically, i^

Unit of heat, 144, 289

,, volume, 42
Unsaturated compounds, 61
Uranatcs, 616
Uranium, 616

,, chlorides, 617

,, oxides, 6x6
Uranous salts, 6x7

,, sulphate, 617
Uranyl salts, 617
Urea, X3, 23, 257

' Valency, 58

Vanadates, 608

Vanadite, 607

Vanadium, 607

,, chlorides of, 608

,, oxides of, 607

,, oxychlorides of, 608

Vaporisation, latent heat of, 1 14

Vapour densities of elements, 40
pressures of solutions. 117

Index

669

Vapour tension, iii

Welsbach burner, 303

Verdigris, 5x3

White arsenic, 446

Vermilion, 559

cast iron, 636

Vinasse, 483

lead, 604

„ cinder, 482

1 1

metal (copper), 507

Vital force, 359

nickel. 639

Vitriol chambers, 393

• 1

vitriol, 194

Volatile alkali. 467

Witherite, 541
Wahlerite. s8x

Water, 180

Wolfram, 6x6

,, Clark's process for softening,

ochre, 616

198

Wood-

s fusible metal, 461

„ colour of, 188

Wrought iron, 637

„ compressibility of, 189

Wulfenite, 616

„ electrolysis of, 183

Wurtzite, 550

„ freezing of, 115

„ gas, 260

Xantho-cobaltic salts. 6

„ gravimetric composition

Of.

185

Ytterbite, 56X

„ hardness of, 197

Ytterbium, 561

„ maximum density of, 191

Yttrium, 561

„ of constitution, 194

„ of crystaUisation, 193

ZiBRVOGEL process, 517

„ ram, 196

Zinc, 546

M solubility of gases in, 137

alloys of, 548

M >* salts in, 131

•1

aluminate, 546

M solvent power of, 191

amalgam, 556

M supercooling of, xx8

f I

blende, 546

„ volumetric composition

Of,

• I

carbonate, 551

181

chloride, 549

Waters, chalybeate, 195

•I

chromite, 6x4

M dangerous, 199.

• I

granulated, 153

M derp well, 196

hydroxide, 549

If fresh, X96

1 1

methyl, 377

„ hard, X97

nitrate, 3x5

„ mineral, 194

oxide, 548

1, natural, 194

spar, 546

„ potable, 198

1 1

spinnelle, 546

„ river. 196

f I

sulphate, 550

„ safe, X99

• 1

sulphide, 550

„ sea, 196

white, 548

.. spring, 196

Zirui cardonas, 55 x

,, suspiciotis, 199

Zinc-copper couple, xsa, a/

Wavellite, 4x3

Zircon,

.581

Weldoo's process, 319

Zirconium, 58 x

Printed by BaLLANTI

I'Nu, Hanson ir Co.

Edinburgh

&> London

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