Full text of "The story of the five elements"

See other formats

Plate I

ROBERT BOYLE

THE STORY OF THE

FIVE ELEMENTS

E. W. EDMUNDS, M.A..B.SC.

AND

J. B. HOBLYN, A.R.C.S., A.I.C.

WITH EIGHT FULL-PAGE PLATES AND
OVER FORTY DIAGRAMS IN THE TEXT

GASSELL AND COMPANY, LTD.

London, New York, Toronto and Melbourne
1911

PREFATORY NOTE

THE aim of the authors in this volume has been to
produce neither a treatise on chemistry nor a dish
of popular tit-bits from that science. Both of these
tasks are at the present time unnecessary. But there
seemed to be room for a volume intermediate to them,
appealing, on the one hand, to the young student
who is beginning a serious study of chemistry; and,
on the other, to the intelligent general reader who,
having a genuine interest in science, is nevertheless
unable to follow up any one branch of it in close
detail. No science can be made altogether easy, even
in its elements ; and in their choice of material the
authors have not been concerned to evade the true
difficulties of the subject. They have rather sought
to expound, in suggestive outline, a few of the facts
and theories of modern chemistry ; to set the thought-
ful reader thinking about some of Nature's constructive
processes ; and to stimulate him in the scientific
spirit and method.

31O534

CONTENTS

CHAPTER I
SOME IDEAS ABOUT MATTER

PAGE

The Aims of Science — Practical and Theoretical Aspects —
The Nature of Matter — Ancient Chemistry — Discovery
of Metals — Greek Speculation — The Four Elements — The
Idea of Atoms — Alchemy, and its Failure — Clearer
Notions of Chemical Changes — Synthesis and Analysis —
Laws of Chemical Combination — The New Theory of
Atoms — Chemical Symbols — What are the Atoms ? . i

CHAPTER II
AIR

Early Views about Air — Weight of the Air — Pressure Exerted
by it — Evaporation — Production of a Vacuum — Air
Pumps — How Air Exerts Pressure — Boyle's Law — Effect
of Heat and Cold on Air — Liquid Air — Relation of Air to
Combustion — Composition of the Air — Experiments of
Priestley and Lavoisier — Cavendish's Analyses — The Rare
Elements of the Air — Oxygen — Action of Animals and
Plants on the Air — Nitrogen — " Fixation " of Nitrogen 37

CHAPTER III
OTHER AIRS

Fixed Air — Inflammable Air — Marine Acid Air — Dephlogis-

ticated Marine Acid— Alkaline Air — Vitriolic Acid Air . 87

CHAPTER IV
FIRE

Ancient Speculations— Production of Fire by Friction — Heat
a form of Motion — Heat and Combustion — Source of the
Heat in Burning — Production of Flame — Phosphorescence
— Structure of Flames — The Bunsen Burner and the Nature
of its Flame — Flames for Illumination : their Wasteful-
ness— What is Fire ? — The Internal Energy of the Atoms 112

™ CONTENTS

CHAPTER V
WATER

PAGE

Early Views about Water— The Action of Metals on Water
— The Gravimetric Composition of Water — The Volu-
metric Composition of Water — Natural Waters and their
Impurities — Solution and Crystallisation — The Freezing
and Boiling of Solutions — The Freezing of Alloys — The
Nature of Aqueous Solutions — The Formation of Water
in Chemical Changes — The Functions of Water in Pro-
moting Chemical Change . . . . . .139

CHAPTER VI
EARTH

How " Earth " becomes " Water " or " Air " — Sulphur One
of the Earth-elements — Its Purification — Its Various
Modifications — Crystals and their Formation — Amor-
phous Substances — Combinations of Sulphur with Metals
— Chalk — Its Occurrence and Transformations — Lime
and Limestone — Marble — Action of Water on Calcium
Carbonate — Formation of Calcium Carbide — Gypsum —
Plaster of Paris — Rocks from the Earth's Interior —
Granite — Forms of Silica — Glass — Natural Silicates and
their Decomposition — Clay — Earthenware — Alum — The
Chief Earth-elements . . . . . .182

CHAPTER VII
ETHER

Unity of the Elements — Is Hydrogen the Fundamental Stuff ?
— Family Groups among the Elements — The Periodic Law
— Evolution of the Elements Indicated in the Stars —
lonisation of Gases — Discharge of Electricity through
Rarefied Gases — Electrons — Atoms Reduced to Electrons
— Spontaneous Decomposition of the Radium Atom —
The Uranium Series — Evolution of Material Atoms from
Electrons — Real Mass of the Atoms — Is the Ether the
Foundation and Basis of all Things ? . . . . 228

APPENDIX — List of Elements, Symbols, and Atomic Weights 259
INDEX 261

LIST OF PLATES

1. ROBERT BOYLE . . . • . Frontispiece

PACING PAGE

2. JOHN DAI/TON ........ 24

3. JOSEPH PRIESTLEY ....... 62

4. GAS FLAME, SHOWING THE EFFECT OF INCREASING OR

DIMINISHING THE SUPPLY OF AIR . . . 134

5. APPARATUS FOR SHOWING THE COMPOSITION OF WATER

BY WEIGHT . . . . . .. .150

6. MICROSCOPIC APPEARANCE OF CHALK COMPARED WITH

GLOBIGERINA OOZE . . . . . .196

7. DMITRI IVANOVITCH MENDELEEFF , . . . 232

8. RADIO PHOTOGRAPHS . . . « . . . 244

LIST OF DIAGRAMS

FIGURE PAGE

1. Apparatus for Showing the Weight of Air . . . 39

2. An Experiment Showing the Pressure of Air . . 40

3. A Simple Experiment for Showing the Pressure of Air . 41

4. A Simple Barometer . . . . . ". .41

5. Apparatus Showing the Effect of Pressure on the Height

of Mercury . . . . . . -41

6. A Simple Air-pump . . . . . , . 47

7. A Filter-pump . . . , . . 48

8. Illustrating the Effect of Pressure on Air . . » 50

9. Boyle's Tube . . . . ,; * . . . 51
10. A Simple " Air Thermometer " . * . -52

viii LIST OF DIAGRAMS

FIGURE PAGE

11. (a) Faraday's Experiment for the Liquefaction of Gases ;

(6) Vacuum Vessel for Holding Liquid Gases . . 56

12. Priestley's Experiment ...;.. 62

13. Lavoisier's Experiment , . . . . .64

14. A Eudiometer « . i . , . . .67

15. The Preparation of Oxygen ..... 72

1 6. Burning Sulphur in Oxygen ..... 73

17. Apparatus for Preparing Finely Divided Iron . . 77

1 8. Inhaling and Exhaling ...... 79

19. The Preparation of Carbon Dioxide .... 89

20. Potassium Burning in Carbon Dioxide .... 90

21. Apparatus for Preparing Hydrogen . . . -93

22. Diagram Showing that Hydrogen will not Support the

Combustion of a Candle . . . . .95

23. The Preparation of Hydrogen Chloride . . -97

24. Diagram Illustrating the Solubility of Hydrogen Chloride

in Water ........ 98

25. Apparatus for Preparing Ammonia . . . .106

26. Illustrating the Combination of Hydrogen Chloride and

Ammonia . •'.."./. . . . . . 107

27. Air Burning in Coal-gas . . . . . .122

28. Candle Flame / . -. . . . . . 126

29. Conducting Gases from Dark Zone . . . . .126

30. Bunsen Burner and Flame . * .,\ . . . .130

31. The Two-coned Structure of Flames . . . .133

32. Decomposition of Steam by Red-hot Iron . . .145

33. Decomposition of Steam by Magnesium . . .145

34. Decomposition of Water by Sodium . . . .147

35. Decomposition of Water by Calcium . . . .148

36. Formation of a Cryohydrate . . . .164

37. The Eutectic Point of an Alloy . ... . .167

38. Curve of Alloy Forming a Compound at E . . . 167

39. An Iron Retort for the Refinement of Sulphur . .187

40. Rhombic Crystal . ' .-*• > - .. . . .188

41. Electric Furnace . • - i . . • •' -. . 208

42. Rock Crystal . v .... ,„ . 215

43. Discharge in a Vacuum Tube . . • . . . 238

44. Madame Curie's Experiment ... ... . . . 245

THE STORY OF THE FIVE
ELEMENTS

CHAPTER I

SOME IDEAS ABOUT MATTER

I. — THE AIMS OF SCIENCE

THE stimulus to all learning and all science is the
desire to know, which is one of the inherent properties
of the human brain. This desire, becoming more
eager and more insistent as mankind has advanced in
civilisation, has been the motive power of all arts and
all philosophies ; it has led to the building of the
noble temple of modern science, and it is guiding many
explorers across the dark ways into the unknown.

It seems to arise from two apparently distinct
needs of human nature. In the first place, man must
live — eat, dress, and house himself. The more he
knows about the things and laws of nature, the better
he can accomplish this ; and hence arises practical
science — farming, cookery, metal-working, quarrying,
engineering and the like. Man has desired to improve
upon his knowledge of such arts as glass-making or
dyeing, in order to satisfy his natural needs ; and
thus every branch of natural science has a great
stock of such practical and " useful " knowledge to
attend to.

But, over and above all this, there is, in the second
place, the desire to know per se — the pure desire of

TtiE STORY OF THE FIVE ELEMENTS

-the mind/ 'Man must think as well as live ; he must
fathom as far as may be the causes of things ; he must
soar to the beginning and to the end. Therefore
there arises speculative or theoretical science — cosmo-
gonies, atomic hypotheses, and so on.

These theories have done harm sometimes, but on
the whole much more good. It has been evil for
science when its two aspects have been held asunder.
Progress has been rapid when they have worked hand
in hand. Harness a theory to verifiable facts, and it
is well for both ; permit it to run amok, and invaluable
truth may be overshadowed. The raison d'etre of
theoretical science is to interpret and to arrange the
facts of practical science.

For these facts are many, varied and bewildering.
The untutored mind, observing nature for the first
time, is lost amid the labyrinth of the phenomena it
perceives. And when it begins to inquire into the
meaning and causes of what is seen, mystery is heaped
upon mystery at every step. The perception of this
mystery is the first step towards a real knowledge
of nature. The familiar and the obvious are no less
mysterious than the uncommon and out-of-the-way ;
we wonder over radium or a comet, but we accept,
unquestioning, water or the movements of the moon.

Once the mind has been perplexed by the aspect
of mystery, it must attempt to solve the riddle it has
aroused ; it begins to form a theory. If it does this
in a scientific manner, it will make sure first of its
observations ; thence will issue some formula, or form
of words, which will contain in itself a general expres-
sion of the whole of the facts. As thus : the movements
of the moon are recorded over months, and provide

THE SCIENTIFIC METHOD

a confused array of figures ; upon them we build the
theory that the moon moves round the earth in such
and such an orbit in a definite time ; from this we
infer the position of the moon at some future time.
Does this turn out correct ? If so, the theory is
serviceable ; it comprehends many facts in a simple
statement.

This indicates the method to be adopted in science
— the inductive method, from observation to inference,
from practice to theory, the theory acting as the
illuminator and interpreter and prophet of the real
fact. This book, we hope, will be a simple illustration
of the power and, at the same time, of the fascination
of the scientific method.

II. — THE PROBLEMS OF CHEMISTRY
THE fundamental mystery of the science nowadays
called chemistry is the nature of matter. By matter
we mean the actual substratum of sensible things, the
reality which is the ultimate basis of all the objects
of sense. When we speak of the material world, we
refer to that part of the universe of things that is
perceptible by the senses. There are philosophers who,
following out a strict logic, are sceptical concerning
the real existence of matter. We have a sensation of
hardness, of whiteness, of shape, and so on ; these
sensations blend in the mind into the image of a piece
of wood ; and we do not hesitate to say that there
is a real piece of wood, an actual something, which
exists apart from our sensations of colour, touch, etc.,
but which we cannot perceive without them. We may
be wrong in our simple supposition ; yet our belief
is apparently in accord with thousands of everyday

THE STORY OF THE FIVE ELEMENTS

experiences. The objects of our mind correspond with
real objects outside it ; and matter is the basis of all
of these. What the nature of matter is — that is the
question which philosophers have posed for them-
selves ; they have answered it to their satisfaction,
but not finally ; and the patient labour of a century
of chemists leaves the problem illumined, but still
unsolved. How near and how far we are from the
ultimate truth, we may be able to show ; at least, our
present theories have faced the riddling criticism of
an army of experimental facts, and have been tempered
accordingly.

What is the problem before us ? It is to investigate
the nature of wood, iron, water, air, granite, and the
many thousand different kinds of matter with which
we have become familiar. As we stand on the thres-
hold of our task, the manifold variety of the substances
with which we must deal might well appal us ; and
our difficulties are enlarged when we contemplate the
changes through which every form of matter may pass
under various circumstances. Wood can be charred ;
iron rusts ; water evaporates ; granite crumbles.
These changes, and the conditions under which they
occur, are all added to the burden of the student of
chemistry. And certainly the science would be over-
loaded with its facts, if its theories did not come to
the rescue. We shall see how they have educed from
the chaos some sort of order ; how diversity tends to
give place to unity, and complexity to simplicity.
The story of chemistry is, when fully told, a thrilling
history of man's growing practical knowledge of the
various kinds of matter — of metals, minerals, fluids,
foods, drugs ; it tells of a growing mastery over the

OBJECTS OF CHEMISTRY

processes of nature and the mutations of things ; and
it celebrates an ever-deepening insight into the funda-
mental laws and the ultimate constitution of the
material universe.

III. — ACHIEVEMENTS AND THEORIES OF THE
ANCIENTS

From immemorial antiquity men have extracted
metals from their ores ; but the necessary processes,
though chemical in their nature, were, of course, not
understood, and were carried out entirely by rule-of-
thumb methods. These must not, however, be hastily
despised : rather is it matter for wonder that metals
like iron, copper, or tin should ever have been made
at all. Moreover, the Egyptians at least had attained
real skill in the treatment of seven of the metals — gold,
silver, copper, iron, lead, tin, and mercury ; and there
is every reason to believe that they were acquainted
with the manufacture of glass. This implied a know-
ledge of soda, which had to be obtained from salt.
The use of soda and polash in soap-making was also
known to the ancients ; and among other manufac-
tured or extracted products very early known were
turpentine, sugar (from starch), blue vitriol, and alum,
the latter being employed in dyeing. Natural dyes
and pigments were also known.

All this represents many centuries of progress, and
is, in fact, a very remarkable body of achievements,
considering the circumstances. Yet, while the hand
had been industrious, the brain had not been idle.
No science was possible until thought was made to
operate upon the facts empirically known. But, unfor-
tunately, thought disdained common practical matters ;

THE STORY OF THE FIVE ELEMENTS

it turned its face at once to the highest and most
difficult problem of all : it sought to explain the con-
stitution of matter, but took no heed of the known
behaviour of matter in its most familiar forms. Thus
much of it has vanished into ghost-land ; it was from
the first intangible and inane, having no relation to real
things. Still, the intellectual activity implied in specu-
lation was not wholly vain ; it was a good thing in
itself, and produced many valuable results. To Egypt
came the Greeks ; imbibed there the spirit of inquiry
and the ambition to know ; returned, and for many
centuries were the scientific teachers of Europe.

Two^veryjyaluable idej&^injerge from the bold and
determined thinking of the Gr^fe pfrjflggnplwrg ) These
are the idea of elementa^nd the ajjpmic conceptions
Probably, the first of theslTcame

originally from Egypt : the word, or the idea it conveys,
is familiar in the thought of Thales, the earliest natural
philosopher of Greece. But it is to Arjsjtotle (384-322
B.C.) that WP. nwp^the^faci^that for a great many cen-
turies the Greek elements were accepted as the real
elements ; indeed, the word has scarcely died out of
figurative use at the present moment. Aristotle was a
great philosopher — one of the world's mighty thinkers ;
but he was not a great scientist ; and the best logic,
unsupported by observation, is not competent to
elucidate the constitution of matter. The influence of
Aristotle's name upon the science of succeeding cen-
turies was almost wholly bad ; authority took the
place of personal observation and thought, and the
result was stagnation.

The mind's desire in facing the manifold variety of
phenomena is simplification. Hence it was natural

THE FIVE ELEMENTS

that a mere thinker should conceive that the different
substances were compounded of a few simpler materials
in varying proportions ; these simpler materials would
be the elements out of which every kind of matter
could be formed. The Greek philosopher could have
known very little to support such a doctrine ; the con-
sequence is that his elements are not our elements, and
that whereas our elements are, approximately at all
events, the raw material of the universe, his turn out
to be mere abstractions. It seems to have been
Empedpcles (c. 450 B.C.) who first clearly taught the
"definite ~3octrine of the four elements — air, fire, water,
earth — as the origin of all things. Out of nothing,
nothing comes : in the beginning were the elements,
and out of them arose all the varied forms of matter.
Later, further simplification was attempted ; a fifth
element, the quinta essentia, or quintessence, was sup-
posed to unify the others, to be a more refined extract,
as it were, common to all four. It is small wonder
that such a doctrine captured the intellects of men
who were bent on describing the world in the simplest
and clearest terms. It was a most vital idea right
into the eighteenth century. " Does not our life
consist of the five elements ? " asks Sir Toby Belch
in Twelfth Night. It was the commonplace science of
Shakespeare's day.

This theory of the five elements was the first
chemical theory that had any force in it. We do not
acknowledge the elements as such now ; but we must
be careful not to scorn them ; our elements may quite
well become the joke of a future day. ' One Greek
philosopher, Anaxagoras (c. 550 B.C.), seems to have
vaguely perceived that the five elements were not

THE STORY OF THE FIVE ELEMENTS

sufficient ; he assumed a large number of " seeds " of
things, by whose interaction and combinations among
themselves the varied materials of the universe arose.
His speculations had, however, little or no influence ;
whereas those of Aristotle became a philosophical
tradition, accepted unthinkingly. We are to learn
from the Greek teachers, not that speculation is
dangerous or wrong, but the futility of not checking
them by an appeal to Nature and to experiment.

By Empedocles the four elements were, it appears,
conceived as real material things, unchanging and
unchangeable in themselves ; but caused to unite or
separate by " loves " and " hates," attractions and
repulsions, which corresponded very closely to what
modern chemistry calls chemical affinity. Some powder
of the metal antimony will take fire readily in chlorine
gas, but remains inert and unaltered in nitrogen gas :
in some sense antimony " loves " chlorine, but not
nitrogen ; and if we ascribe the " love " to an attrac-
tion which results from opposite electrical conditions
in the substances which " love " each other, we are still
far from appreciating the real nature of the attraction :
we have scarcely been able to conceive a theory of it
as yet. And the picture of the world, as apparently
conceived by Empedocles, is an acute and not con-
temptible one. He does not get lost among his
abstractions. He sees the four material elements, held
together by the play and interplay of non-material
and imperceptible forces ; whereas we see an uncertain
number of elements, charged possibly with electricity,
whose essence we know not, and endowed with non-
material energy, whose nature is almost as evanescent
in the mind as the " loves " and " hates " of Empe-

GREEK SPECULATIONS

docles. It is told of him that, despairing of the
possibility of penetrating to the ultimate essence of
knowledge, he ended his life in the crater of Etna.
We shall see that modern philosophers with their
fuller knowledge of the nature of matter would have
almost as good a reason as he to seek an untimely end.
The merit of Empedocles was that he was, in
chemical matters, a materialist ; he built his world
out of real things — not essences, nor properties, nor
any other abstraction. But he was not, and could
not be, equipped with the accumulated statistics of
science, which make the merest tyro in chemistry able
to derange his speculations. He had undoubtedly
watched such natural processes as came under his ken ;
and he had thought long and well about them. But
there were not enough of them within his range ; and
another century did nothing to increase their number.
So that when we come to Aristotle we find the four
elements conceived in less clear and less materialistic
forms. The Aristotelean elements were transformable
among themselves, and thus had no right to the term
element at all. In this later phase of Greek thought
the " element " air was conceived as a combination
of the properties of " hotness " and " moistness " ; in
fire, " hotness " and " dryness " — in water, " cold-
ness " and " moistness " — in earth, " coldness " and
" dryness " were united. Exchange moistness for dry-
ness and you turn air into fire, or water into earth !
Such a simple fact as the existence of a solid residue
after the evaporation of natural waters was held to
prove the transformation of water into earth. Thus,
indeed, the earth was formed from the sea. This is
evidently the reductio ad absurdum of speculation.

THE STORY OF THE FIVE ELEMENTS

Contact with the actual world is lost ; thought has
become phantasm ; and in the world of ghosts all
twists and leaps are possible. In certain branches of
natural knowledge — physics, astronomy, and natural
history — the Greeks had begun, and were to continue,
along the true path ; but in chemistry they produced
neither a Hipparchus nor an Archimedes.

The idea that there is, beneath the manifoldness
of things, an underlying unity is attractive and possibly
true. From this idea arose Aristotle's fifth element, the
ether, the immaterial essence from which all material
things originated, the Nirvana or nothingness of
Buddhism, into which all things are ultimately de-
veloped. The idea of one fundamental element is,
however, much older than Aristotle. Thales, in the
sixth century B.C., probably deriving from Egypt, saw
in water the primordial principle ; his successor,
Anaximenes, found in air the mainspring of all life
and the foundation of all matter. Up to the present
day the most scientific thinkers are fascinated by the
thought that the diversity of matter will probably be
reduced to simplicity, that one fundamental something
lies at the basis of all the forms of matter. Armed with
the unassailable suggestions of observed facts, we are
eager to reduce our modern elements into our modern
ether — as mysterious a quintessence as ever Aristotle's
was. What we make of the ether, we shall see in our last
chapter : what the other elements of the Greek specu-
lators have become we are to gain a little notion of
on the way thither. We at present convict the Greek
elements of a vagueness in their definition ; not until
the time of Robert Boyle (1627-91) do we come upon
a clear sense attributable to the word. His definition

ELEMENTS AND ATOMS

is qurs. An element must be regarded as a substance
which cannot be simplified or analysed into anything
other than itself. Iron cannot be reduced into any
form of matter simpler than itself ; out of iron nothing
but iron can yet be extracted ; so, iron, with some
eighty other substances, must at present be accounted
an element. Chalk, on the other hand, can readily be
reduced to simpler substances by the mere application
of heat : it is not an element, therefore. We are to
learn that some of the ancient elements will not stand
the test of this definition. We must not rashly take
general ideas in hand in science ; they cannot be
exactly expressed until the particular facts of which
they are properly made have been examined and
appraised.

The other theory of the Greeks, however, demands
our notice on account of its acuteness and fruit fulness.
It is unsatisfactory to be reducing matter — hard,
material things — to " principles/' quintessences, ethers
— mere ideas of the brain ! Let us follow Democritus,
the materialist " laughing philosopher " of Abdera.
He shivered matter into atoms. But the atom was still
matter — matter in its indivisible, fundamental form.
In the beginning was a concourse of falling atoms ;
somehow these atoms were formed into groups and
aggregations ; thus matter arose, sensible and gross.
Democritus, and Lucretius after him, could find nothing
in the universe but atoms and void and motion. Were
the atoms all alike? Has each atom the same pro-
perties as matter itself has ? Lucretius, expounding
the subject in the first century A.D. in his De Rerum
Natura, a true scientific poem, answers with full argu-
ments, No ! The differences between the varied forms

THE STORY OF THE FIVE ELEMENTS

of matter demand atoms of different shapes and sizes,
interposed by more or less void. A finite number of
different kinds, he is careful to insist upon ; so that
he recognized a finite number of elements, much as
we do, and, with splendid insight, developed a theory
of the evolution of worlds. His poem is a monument
of acute thought ; the atomic hypothesis which it
celebrates is perhaps the most profound scientific idea
that antiquity has bequeathed to us. The thought
slept for some eighteen centuries. The advance of
chemistry made it necessary to us, and now it is the
commonplace of science. In imagination we split
matter into its ultimate " uncuttable " or atomic parts ;
we have notions about the properties of these atoms,
and have even arrived at some tenable idea of their
weight ; we are even speculating further and reducing
them to the finer electrons — showing that the atom,
and consequently matter itself, is but a transient
phenomenon after all. (See Chapter VII.)

IV. — ALCHEMY

From the enlightened Greeks into the morass of
the Dark Ages is an unpalatable step : confused, and
largely unprofitable, were to be the workings of science
for many centuries. The spirit of inquiry, so bright
in Athens and Asia Minor, honourably kept aflame by
such as Lucretius and Pliny in the golden time of Rome,
did not so much as flicker in the waste of those ages.
Chemistry in particular fell under an evil spell.
Alchemy throve — among the ignorant largely by
imposture, among the initiated by means of a vast
lumber of incomprehensible jargon. Even when the
Renaissance awoke Europe, it did not expel alchemy.

THE ALCHEMISTS

Ben Jonson has exposed the alchemist of his day
in his vivid play of that title (1610), and certainly
does not exaggerate the absurdity of the alchemist's
formulae and beliefs.

Read the following catechism of Face by his
master Subtle, for an instance : —

Subtle : Sirrah, my varlet, stand you forth and preach to him

Like a philosopher : answer in the language.

Name the vexations, and the martyrizations

Of metals in the work.
Face: Sir, putrefaction,

Solution, ablution, sublimation,

Cohobation, calcination, ceration and

Fixation.
Subtle: This is heathen Greek to you, now ! —

And when comes vivification ?
Face: After mortification.
Subtle: What's cohobation ?
Face: 'Tis the pouring on

Your aqua regis, and then drawing him off,

To the trine circle of the seven spheres.
Subtle: What's the proper passion of metals ?
Face: Malleation.

Subtle: What's your ultimum supplicium auri ?
Face: Antimonium.
Subtle: . . . And what's your mercury ? . . .

How know you him ?
Face: By his viscosity,

His oleosity and his suscitability.
Subtle: How do you sublime him ?
Face: With the calce of egg-shells.

White marble, talc.

Subtle: Your magisterium now. What's that ?
Face: Shifting, sir, your elements,

Dry into cold, cold into moist, moist into hot,

Hot into dry.
Subtle: . . . Your lapis philosophicus ?

THE STORY OF THE FIVE ELEMENTS

Face: 'Tis a stone,

And not a stone ; a spirit, a soul and a body :
Which if you do dissolve, it is dissolved.
If you coagulate, it is coagulated ;
If you make it fly, it flieth.

All which is absurd — doubtless of malice afore-
thought— but hardly a caricature of the real thing.
Yet this was the only chemistry of the Middle Ages ;
and out of the dung a few grains of valuable facts can
be extracted.

Alexandria seems to have been the birthplace of
alchemy ; in Egypt the practical arts of the chemist
rubbed shoulders with the fantasies of the theorists.
The processes of metallurgy attracted the one : the
nature of the elements was the problem of the other.
It is not difficult to see how, from the idea that the
four elements could be transformed one into another,
the belief arose in the possibility of transforming the
metals into one another, and in particular the attractive
chance of changing the base metals into gold.

Facts seemed to be on the side of the transmuters,
too. For, is not a steel knife-blade covered with copper
when it is plunged into a solution of blue vitriol ? And
is not the mixing of a little zinc with copper effective
in changing at least the colour of the copper, so that
it becomes more nearly golden ? Steeped in the
Greek theory of the elements, the alchemists found it
easy enough to conceive their philosopher's stone, their
universal solvent or elixir of life^^Erferent forms of
the essence which could remove all the dross from
things. They sought a simple scheme whereby to
interpret all material phenomena ; they insisted that
simplicity was Nature's law, and developed their aim

ALCHEMY

in writings the most turbid and incomprehensible that
have ever come from the human mind. Of course,
they do not agree among themselves, and no one of
them ever attained to a coherent doctrine. The
Arabian, Geber, in the eighth century enjoyed as high
a repute as any ; and in our own country Roger
Bacon (c. 1214-94) was famous (or infamous) for his
knowledge of the magical arts. An acute, learned, and
in some respects scientific thinker was this same Friar
Bacon ; but Basil Valentine, an alchemist of the
seventeenth century, was a more creditable represen-
tative of his art. He made many valuable chemical
discoveries, though he held to the doctrines of the
earlier alchemists. From the confused mass of these,
we may perhaps endeavour to sublime the essence ;
but it must not be supposed that any one alchemist
ever had such a clear conception of his ideas.

There were, then, four elements, and a fifth essence
transcending them. These " elements," as we have
explained, were not material substances, but rather
properties ; too subtle, at all events, for man to be
able to isolate them. But why stop at the four pro-
perties of hotness, coldness, dryness, moistness ? Are
there no others ? There is colour, there is lustre :
gold is a union of lustrousness and yellow ! In order
to make gold these properties have merely to be
brought together ; and that is what the philosopher's
stone was to effect. The property of lustrousness exists
supremely in mercury, the yellow substance in its pure
condition is sulphur. Guessing vaguely upon the basis
of these ideas, three " principles " came to be added
to the four elements. These were mercury, sulphur,
and salt. All metals were supposed to contain these

THE STORY OF THE FIVE ELEMENTS

three " principles," not the three substances which we
associate with their names, but the " principles " of
lustre, colour, and solidity. The " salt " is a later
addition, and not universal ; the commoner view was
that metals differed among themselves only in the
proportion of mercury and sulphur that they con-
tained ; and if, by any process, the proportion of the
sulphur-principle could be diminished, a step nearer
to the noble metals was made. It was, therefore, the
alchemist's aim to study those processes by which
" sulphur " was driven out of the metals. They saw
that the metallic characters of some metals were lost
when sulphur was heated with them ; naturally they
inferred that sulphur was the evil spirit which thwarted
the refinement of the mercury-principle in the metals.

It must be understood that the alchemists did not
regard mercury or sulphur as identical with the sub-
stances thus named. They were conceived as compound
principles formed from the four elements. Mercury
was, according to their notions, produced when air
acted upon water ; sulphur when fire acted upon
air ; salt by the interaction of water and earth.
Thus the metals were composed of the four elements,
but only at second hand, as it were ; other sub-
stances, such as clay, chalk, the metallic ores, were
more impure and still more remote from the pure
nature of the elements.

Fantastic theories like these, worked out in elabo-
rate treatises and with a terrific apparatus of philoso-
phical terms, arouse little more than a scoff to-day ;
but they were not wholly useless ; they led to much
calcination, sublimation, distillation, cohobation, filtra-
tion and what not, and incidentally to a large accumu-

IDEAS OF THE ALCHEMISTS

lation of chemical facts and preparations. The meaning
of these experiments was often tortured to fit the
theories ; but the work done on acids and in the
preparation of metallic salts was valuable all the same.
The authority of the Greek conceptions hampered the
alchemists as students of Nature : they were not men
of science, because they did not face their facts with
unprejudiced minds.

The alchemists did not confine themselves to the
study of the metals in all cases. One of the most
famous of them was Paracelsus (c. 1493-1541), who did
much work on the connection between alchemy and
medicine. Paracelsus, in spite of a violent gift of
disputation, seems to have had the root of the matter
in him ; and to have spent his turbulent career in the
pursuit of knowledge. The human body was supposed
to be formed of the same elements an'd principles as
other matter : mercury, sulphur, and salt unite in its
composition ; any excess of either produces some kind
of illness ; and the object of medicine was to prescribe
drugs which re-establish the correct proportion.

Many preparations of mercury and sulphur, as well
as other drugs such as laudanum, we owe to the
medical experiments and theories of the alchemists.
But we cannot pursue the matter here. It is sufficient
to have indicated the point of view of those who, in
whatever obscure corners, kept alight the torch of
chemistry during the Middle Ages, and to have shown
how an unscientific method made their speculations
vain. As a result of the work of many learned seekers,
we have a collection of facts (which they did not value
much), but we are brought no nearer to their just
comprehension ; nor do we gain even a little light

Q I7

THE STORY OF THE FIVE ELEMENTS

upon the fundamental problem which they attacked —
the ultimate nature of matter. We do not complain
because their ideas were wrong : probably transmuta-
tion of the elements has already passed out of dream-
land into accomplished fact. They erred because they
did not proceed in the right direction — from experi-
ment to theory.

V. — CLEARER NOTIONS OF CHEMICAL ACTIONS

It was during the eighteenth century that the
alchemists gradually became chemists, and the
scientific examination of the nature of matter took a
more promising turn. We find much attention now
given to the " elements " air and fire — in modern
language to the properties of gases and the facts of
combustion. In our later chapters we shall explain
as much of this work as seems needful ; here let us
merely state that by the year 1810 the true nature of
air and water was known. Chemists had come to
look upon weight as the sure criterion of a material
substance ; attention was fixed upon the actual
matter, which was regarded as the unaltering reality
at the basis of things. Careful weighings of all the
substances used up in chemical operations and of all
those produced led to the law, so far uncontradicted
by a single reliable fact, that matter is indestructible ;
the total amount of matter — the total mass, as it
is called — of all the substances engaged in a series
of chemical changes can neither be increased nor
diminished, whatever the changes may be. Matter
may be transformed, but never obliterated. When
one substance is transformed into another it is not by
the loss or gain of certain non-material or evanescent

INDESTRUCTIBILITY OF MATTER

" principles " ; it is by the elimination or addition of
some other substances.

Let us follow a simple case. A piece of sulphur is
burned ; it disappears in the form of a choking fume.
According to ancient theory, sulphur consisted of air
and fire ; if you burn it, the fire-element or principle
escapes, leaving an impure air. No : we ask for some-
thing more tangible. We weigh, say, i oz. of sulphur ;
we can weigh the resulting fumes, and find them 2 oz.
The loss of the fire-element has made the sulphur
heavier then ? It is unthinkable now. Evidently the
sulphur must have had some matter, some substance,
added to it somehow, in order that it might become
sulphur-fumes. We now know that it is the air that
yields this additional substance — one ounce of it to
every ounce of sulphur. Cork a little sulphur in a glass
flask, and weigh it. Then gently warm the sulphur until
it takes fire. When the burning ceases, weigh again, and
you will find neither loss nor gain in weight. The
matter in the flask, sulphur and air, has been altered
and transfigured ; it is still there, every grain of it.
The greater the care taken, and the more refined the
experiment, the more striking is the confirmation of
the law that matter is not destroyed or created. This
is not, it will be seen, a mere speculation : it is science
Its credit is not derived from Aristotle or from Roger
Bacon, but from Nature and experiment.

It will be seen that it was the use of the balance
that gave the death-blow to the ancient theory of
elements. Air, water, and earth are material things
because they can be weighed. It was not yet recog-
nized that fire, i.e. heat, stands in a different category :
the true nature of heat was left to the nineteenth

THE STORY OF THE FIVE ELEMENTS

century to elucidate ; while the twentieth century is
concerned with the ether as the possible ultimate
quintessence of things. It is possible that matter can
be resolved under certain very special conditions into
something which is not matter, in the sense that it
is capable of being weighed. However this may be,
it is very important to realise that air is as truly a
material thing or substance as wood or water. A piece
of copper becomes heavier when it tarnishes, because
something heavy from the air has been added to it.
In reality the copper has been partly transformed into
a new substance, copper oxide, by the union of some
of it with the oxygen of the air. Such a change as
this, involving the formation of new substances, is
called a chemical change. It is by the careful study
of such changes that the science of chemistry has been
built up and our knowledge of the properties of matter
in its many forms greatly increased.

A chemical change may consist, as in the case of
the tarnishing copper above mentioned, in the for-
mation of a complex substance from two or more
simpler ones ; such a process is called a synthesis.
The process is not called chemical, it must be observed,
unless a new substance is formed, different from the
originals. The red copper and airy oxygen are very
different from the black tarnish which nevertheless
contains them both. Whatever the copper and oxygen
themselves may be, clearly the black tarnish is not
an entirely simple substance ; it is what is called a
chemical compound of copper and oxygen, to be very
carefully distinguished from a mixture of the two in
which neither is changed. Thus the results of the
processes of synthesis are compounds of continually

CHEMICAL CHANGES

growing complexity. Many of the beautiful aniline
dyes are compounds of a complex nature, formed by
synthesis from simpler compounds found in coal-tar.

The opposite process to synthesis is called analysis,
and is equally powerful as a weapon of investigation
and discovery. Any substance which, by the aid of
heat alone and in the absence of all other substances,
yields us two or more other substances must clearly
be a compound of these, although these in their turn
are not necessarily simple. Thus heat is able to
analyse chalk into two constituents, lime and carbonic
acid gas — revealing the fact that chalk is a compound
substance. Other processes, however, are needed to
show that both lime and carbonic acid gas are com-
pounds also. The methods of analysis are numerous
and varied ; their results, notwithstanding, can gener-
ally be confirmed by synthesis. It is as easy to form
the compound chalk by a union under suitable circum-
stances of its components, lime and carbonic acid gas,
as it is to decompose it into them.

Applied to all substances alike, the methods of
chemical analysis lead us to our modern conception
of elements. They are simply those substances which
cannot be analysed in any way into simpler substances.
There are some eighty or ninety of such undecom-
posable forms of matter known to us at present, and
additions are being made to the list from time to time,
chiefly in the form of very rare metals. Of the
original Greek " elements " none belongs to our
modern category. Water, for example, can easily be
shown, both by analysis and by synthesis, to be a
true chemical compound of two substances, hydrogen
and oxygen, which in their turn are, according to

THE STORY OF THE FIVE ELEMENTS

present knowledge, true elements. But, it must be
remembered that our modern elements are real
material substances, not indefinable " principles " ; and
our present state of knowledge forces us to suppose
that there are at least eighty or ninety different kinds
of matter contributing to the architecture of the
material universe. The nature of vthe forces which
regulate the combinations of the elements, whether we
name them chemical affinity or electrical attractions,
is still unknown to us — is as mysterious to us as the
" principles " which the Greeks associated with and
ascribed to their four elements.

Our problem in chemistry, however, is not primarily
this ; we are chiefly concerned with the nature of
matter, and the nature of matter means the ultimate
nature of our eighty or ninety elements. From these
arise the manifold compounds which in their thou-
sands are found in the earth or are manufactured
artificially ; from them we can in imagination form
the crystal, the living organism, the utmost stars.
But what are they ? The infinite is reduced to eighty :
the mind insists upon reducing the eighty still further.
Eighty different kinds of fundamental stuffs are too
many for our philosophical instinct ; we hanker for
the simple four, or for the quinta essentia, of the Greek
thinkers. In our last chapter we shall see what is
to be said scientifically in response to our natural
desire. This much we may say here : no substances
were more like elements in their behaviour, in their
possession of a unique property, than the alkalis
potash and soda, until Sir Humphry Davy decomposed
them by the then new process of electrolysis, and gave
us the extraordinarily active elements, potassium and

SIMPLIFICATION OF THE ELEMENTS

sodium ; so that it may well be that the metals will
be shown by some new-found and up-to-date philo-
sopher's stone to be not elements, but compounds.
It is, however, necessary for the present to regard our
eighty elements as the foundation-materials for our
study of matter.

VI. — THE NEW THEORY OF ATOMS

In the hands of Lavoisier, Cavendish, and the other
pioneers of scientific chemistry, the problems of
analysis and synthesis reduced themselves to a quan-
titative, and not merely a qualitative, determination
of the elements present in compounds. It is not
enough to know that water contains hydrogen and
oxygen ; we must go further, and know that the
weights of each are in the proportion i : 8. Now,
experiments tending towards the exact determination
of these proportional weights in a number of compounds
were carried out in the first instance by a Spaniard
named Proust ; and after him came John Dalton with
a series of classical researches which formed the basis
of the atomic theory of chemical changes with which
his name will be permanently associated. Proust's
experiments led him to the truth, which Dalton's work
clinched, that chemical compounds were of fixed and
unchanging composition. Wherever we find water,
for example, we shall find its composition to be that
stated above. In 9 oz. of water there will always
be i oz. of hydrogen and 8 oz. of oxygen. This con-
stancy and uniformity of composition has become, in
fact, the criterion of a pure chemical substance ; and
any chemist who came across a contradictory result
would at once suspect either the method of his experi-

THE STORY OF THE FIVE ELEMENTS

ment or the purity of his materials. This law of
" Definite Proportions " is indeed the bedrock of
exact chemical science.

Dalton's work was done with the crudest of
apparatus, but it led to still further results of great
consequence to the future of chemistry. It was known
to him that two gases, then known as carburetted
hydrogen and olefiant gas, now named respectively
methane and ethylene, were both reducible to the same
two elements, carbon and hydrogen. Each of these
two gases being a chemical compound has its own
constant composition : that of methane shows i part
by weight of hydrogen for every 3 parts of carbon ;
while in ethylene the proportions are i : 6. Dalton's
results were not exactly these ; but they were good
enough to enable him to deduce from them the laws
and the theory which will always go by his name.
For it will be seen that in ethylene there is twice
as much carbon, proportionally to the hydrogen, as
we find in methane. The same sort of result issued
from a study of other compounds ; in particular, we
ask our readers to note the following further case : —

In carbonic acid gas there are 3 parts of carbon to

8 parts of oxygen.
In carbonic oxide gas there are 6 parts of carbon to

8 parts of oxygen.

It will be observed that it is precisely 8 parts of
oxygen that unite with i part of hydrogen (by weight
in each case) to form water. These reciprocal connec-
tions between the three elements, carbon, hydrogen,
and oxygen, were made by Dalton the basis of his
laws of chemical combination.

Plate II

JOHN DALTON

The question now arises — in true scientific sequence
— how are these facts and laws, irrefragably based
upon experiment as they are, to be interpreted and
explained ? Can a theory be evolved from them,
wherewith the mind can form for itself a picture
of the whole process ? Dalton has it ready for us
in the guise of the old atomic theory of Democritus
and the Lucretius.

John Dalton (1766-1844), the founder of modern
theoretical chemistry, was an unobtrusive and humble
personality, who retained to the last the broad
Cumbrian accent of his early days. His early life was
hard, and he lived throughout with Quaker simplicity,
and on the frugal fare of the typical philosopher.
After a period of private tutorship in Cumberland,
he went to Manchester as teacher and lecturer in
physics and chemistry ; it was there that he wrote
the memoirs and made the experiments which led to
his new theory. His chemical work dealt mainly with
gases ; and, considering the rudeness of his appliances,
he obtained some remarkable results. His experiments
were naturally not very accurate ; but he had a
genius for generalization, and rarely failed to extract
some valuable teaching from his observations. The
laws of chemical combination explained above were
his most enduring, but not his only, contribution to
science. And his conception of the chemical atom was
the fitting crown to his work.

The atom was a familiar idea to others before
Dalton's time. Newton figured the atoms as hard
material particles surrounded by spheres of force ; and
others had felt that the facts of expansion and con-
traction made an atomic structure of matter necessary.

THE STORY OF THE FIVE ELEMENTS

It was the existence of diffusion among gases that first
threw Dalton on to the atoms. For how could a light
vapour like steam be thoroughly mixed with the
heavier gases of the air, unless the smallest particles
of both were free to move in and out among one
another ? If it were not for this thorough mixture of
the atoms, surely steam would rise to the upper surface
of the air, just as cork bodily rises to the surface of
water and floats there.

Having obtained a prejudice for the idea of atoms,
both from his reading and from his experimental work,
Dalton proceeded to apply it to his chemical results.
He supposed — and we now suppose with him — that
when chemical change takes place it is the ultimate
atoms of the acting substances that take part in it.
Thus, in a simple case : if we heat a little copper and
sulphur together, a black powder, known as copper
sulphide, results from the union of the two. This
union is not that of a mass of copper with a mass of
sulphur ; but every atom of copper takes part sepa-
rately, and combines with one or more sulphur atoms,
the result of the whole action being a number of
" atoms " of copper sulphide, each one containing both
copper atoms and sulphur atoms. We have only to
suppose that every " atom " of copper sulphide con-
tains a fixed number of atoms of its two constituents
to enable the atomic idea to explain the fixed consti-
tution of chemical compounds. But we must here
steer away from a possible source of confusion. The
atoms are literally the uncuttable things (Greek a, not ;
Tepvm, I cut) : the atom of sulphur means, therefore,
the smallest conceivable particle of sulphur. This
smallest particle of copper sulphide, however, cannot

ATOMS AND MOLECULES

be an uncuttable thing ; it must at least contain one
atom of copper and one atom of sulphur ; and con-
sequently it is only the elements whose fundamental
particles can be in the strict sense atoms. The term
molecule is applied to the collection of atoms that
forms the smallest thinkable particle of a compound
substance. The term is also applied to groups of
similar atoms, which form the smallest particles of
the elements that are capable of a separate existence ;
a jar of hydrogen gas consists of many molecules,
each of which we have good reasons for believing to
contain two hydrogen-atoms.

Now, suppose that all the atoms of any one element
have the same weight and the same properties ; we
shall then have no difficulty in showing how the
atomic theory, thus extended, comprises the laws of
combination, discovered by Dalton and verified by
many hundreds of later experiments. For, let us

suppose that the symbols f H Y ( O Y ( C Y stand for

the atoms of hydrogen, oxygen, and carbon, and that
the relative weights of these atoms are i, 8, and 3 units
respectively. Then clearly the simplest possible com-
bination of carbon and oxygen would be that in which
one atom of each is concerned, and we should obtain :

(carbonic
acid gas).
Relative weights : 8 + 3 = n

Now, if there be any other compound of these atoms,
the next simple of the many possible arrangements
would be that in which the molecule formed would
contain two atoms of the one element along with one
of the other : thus —

THE STORY OF THE FIVE ELEMENTS

Relative weights: 8 -f 3 + 3 =

s-v— (carbonic oxide

gas).

The atoms of carbon being indivisible and all of the
same weight, it is easy to see why the proportion of
carbon in the second compound must be exactly
doubled.

In the case of the other combinations mentioned,
our symbolical atomic representation of the composi-
tion of each would be —

Hl + f C 1 =

@-(H

The reader may easily check the weights involved
from the numbers previously given (p. 24). He will
also be able to understand how such atoms as Dalton
conceived are competent to explain the laws of
chemical action. He will also perceive the possibility
of affixing to each atom a definite atomic weight, which
shall tell, not indeed the actual weight of the atom,
but its weight in relation to that of some standard
atom. Taking the atom of hydrogen as a standard,

so that f H j weighs i unit, he would be inclined, like
Dalton, to write Co) = 8, and Cc j = 3, as the atomic

weights of oxygen and carbon respectively ; and those
numbers would serve his purpose, if we had none but

THE ATOMIC THEORY

the facts given to take into consideration. But Dalton
was like many another pioneer : he opened new
country, but could not occupy the whole of it. He
was conscious of difficulties, which only his successors
could overcome. One of these was the consideration
of the space occupied by the atoms. Is this the same
for all atoms ? We will express his difficulty in the
form of a simple experimental fact. If hydrogen gas
and oxygen gas are brought under suitable conditions,
it will be found that only when the hydrogen occupies
twice the space taken by the oxygen is the whole of
the mixture turned into water. Assuming all atoms
to occupy equal space, we should then have —

(water) .
Relative weights :i6+i +i = 18

„ volumes : i 4- 2 = 3

Thus, one atom of oxygen would unite with two
atoms of hydrogen and make one atom of steam ; but
experiment shows that the steam formed really occupies
the same space as the hydrogen did at first, i.e. the
same space as two atoms of hydrogen. Here is a dis-
crepancy that Dalton felt : the theory must give way,
and all atoms declared not necessarily to occupy an
equal space. The difficulty is got over by the assump-
tion that the molecules of all gases, under the same
physical conditions, occupy an equal space. The
molecule is defined as the smallest particle of any gas
that can exist free. If we have a jar of oxygen gas,
the gas consists of a vast number of molecules, all
alike and all occupying an equal space each. But

THE STORY OF THE FIVE ELEMENTS

each molecule can be imagined split into the smaller
atoms, which do not exist alone but (in the case of
oxygen) in pairs. [When the molecule has three
oxygen-atoms we obtain a rather different gas, ozone.]
The molecules of oxygen are split when it enters into
chemical combinations, wherein the atoms are the
all-important actors.

With this addition the atomic theory of Dalton has
been harmonized with all the facts known to chemical
science. Our symbols and atomic weights are not
those of Dalton ; but they spring from his idea. We
now represent each atom by a suitable letter or abbre-
viation of the name of the element ; thus H, 0, and C
stand for the atoms of hydrogen, oxygen, and carbon
respectively, each bearing its own atomic weight.
Various considerations have led to the choice of the
number 16 for oxygen and 12 for carbon, hydrogen
still being i. These numbers bear an obvious relation
to those given on p. 28. The crude and clumsy
symbols (or formulae) for compound substances are
replaced by a more expeditious shorthand ; as —

Methane - C + 4H - CHHHH, written CH4.

12 + 4 16

Ethylene = 2C + 4H = CCHHHH, „ C2H4.

24+4 28

Carbonic

acid gas = C + 2O = COO, „ CO2.

12 +.32 44

Water =2H+ O = HHO, „ H2O.

2 + 16 18

All compounds that can be analysed can be given
a formula of this kind, no matter how complex the

CHEMICAL FORMULA

substance may be. The mode of calculation can easily
be followed from the appended example. Formic
acid is the substance examined.

Result of Analysis Relative Simplest

^__ ^^ ^ Atomic number propor-

Element Percentage weight of atoms tion
Carbon .. .. 26'! -4- 12 .. 2'i5 . . i
Hydrogen . . 4*3 -f- i . . 4*3 . . 2

Oxygen . . . . 69*6 -f- 16 . . 4-3 . . 2
Simplest possible formula — CH2O2.

The full theory enables us very often to go further
and to decide whether CH2O2 or C2H4O4 or some
larger number of atoms in the same proportional
number constitutes the real molecule of the substance.
And even more : by the careful study of the actions
of a substance we can often gain an indispensable
insight into the arrangement of the atoms in respect
to one another in its molecule.

In the case of a compound substance the formula is
made to stand for the molecule of the substance. The
formula CO2 stands for one molecule of carbonic acid
gas, containing three atoms — one of carbon and two
of oxygen. Now, in any chemical change, what really
occurs is that all the atoms involved redistribute them-
selves in new combinations, form new molecules, but
are never destroyed. This fact enables us to construct
chemical equations to represent all the substances that
are in any way concerned in a chemical operation,
under the condition that not an atom is either destroyed
or created. We take a random example from many
thousands. When the gases methane and oxygen are
exploded together in the correct proportion, they are

THE STORY OF THE FIVE ELEMENTS

completely changed into a mixture of carbonic acid
gas and water. We know the formula of each of these
substances; we therefore construct our equation —

CH4 + O2 = CO2 + H2O

Relative weights : 16 32 44 18

Now, although this quite accurately represents the
actual nature of all the materials used or produced, it
is in error, because in the original molecules of methane
and oxygen we have altogether four atoms of hydrogen,
only two of which appear in the final molecules. Two
atoms of hydrogen have disappeared in the atomic
shuffling that has taken place ; and, it will be seen
also, one new atom of oxygen has come to light. There
is no evidence that two hydrogen atoms can be trans-
formed into one oxygen atom ; we, therefore, attempt
to reconstruct the equation thus : —

CH4 + 202 = CO2 + 2H2O
Relative weights : 16 + 64 44+36
„ volumes : i 2 i 2

This equation is correct, because in the first place
it represents no loss or gain of matter from the opera-
tion, and in the second it also represents the propor-
tion in which the gases must be mixed to give the
change complete. If more oxygen is taken than is
represented in the equation, it will be left unchanged
at the finish. This, and all that is implied in the
equation, can be completely tested and verified by
experiments. Equations of similar nature can be
built up from the facts of any and every chemical
change, all of which are found to verify the assump-
tion we make, that matter, as tested by weight, is
indestructible.

CHEMICAL EQUATIONS

We have thus arrived at this position. The material
universe contains a vast number of different kinds of
matter. Most of these are compound substances. We
can reduce these compound substances to a
certain number of undecomposable and, as far as we
can at present go, simple substances called elements.
The elements themselves are further conceived as
made up of the ultimate and indivisible atoms. There
is good reason for believing in the reality of these
atoms ; we assign to them certain definite properties,
and call upon them to interpret our chemical laws.

The fundamental question of speculative chemistry
is now — what is the nature of the atoms ? Are there
really eighty different kinds, or are they reducible to
few or one ? What is the nature of the forces that hold
them together, or drive them apart ? The various atoms
behave in a strangely fastidious manner in obedience
to the directions of these forces. The atoms of hydrogen
and oxygen hold together firmly in the molecule of
water (H20), but loosely in that of hydrogen peroxide
(H2O2), and will not hold together at all in any other
proportions. The atoms of nitrogen and hydrogen
combine stably in the proportion i : 3 and give us
ammonia gas (NH3) ; but in the opposite proportion
of 3:1, we obtain a violently explosive compound
known as azo-imide (N3H). And while all the metals
are ready enough to form compounds with oxygen gas;
almost all of them agree to refuse hydrogen. The
atoms show these preferences, and any theory of the
atom must account for them. And again : an atom
of oxygen will not exist with one atom of hydrogen
alone combined with it, and must needs have two
before it will settle down into a stable molecule of
D 33

,THE STORY OF THE FIVE ELEMENTS

water (H2O) ; whereas one atom of zinc suffices for
it in the formation of the molecule of zinc oxide (ZnO).
One atom of zinc, therefore, carries the same chemical
effect in combination as two atoms of hydrogen ; it has
a double chemical value, or valency, as we call it. Each
elementary atom has its own valency — hydrogen is
monovalent, zinc divalent, aluminium trivalent, and
so on — and thus another property of the atoms enters
to confuse us. A picture of the atom which is to rise
to the dignity of a scientific speculation must take all
these properties into account.

The determination of the atomic weight of an
element is the most important of the chemical processes
concerning it, and to this problem have been brought
together the highest manipulative skill and the best
thought of some of our best chemists. The first step
is the determination of the equivalent of the element,
which is defined as that quantity of it that will take
the place of one unit-weight of hydrogen in any com-
pound*. The weight of the element thus obtained is
clearly that which is chemically equivalent to the
unit-weight of the standard element. We shall see
later on that hydrogen is easily liberated from dilute
acids by many metals ; we find, for example, that
12 grams of magnesium are required to liberate one
gram of hydrogen from diluted sulphuric acid ; and
so, this number 12 is deemed the equivalent of mag-
nesium.

* In spite of much careful experimental work on the composition
of water, the equivalent of oxygen cannot be said to be settled with
absolute accuracy ; and, as it is generally easier to find equivalents
by means of combinations with oxygen, O = 8 is most commonly
adopted by chemists as the standard of equivalents. But this does
not affect our argument.

ATOMIC WEIGHTS

Many elements, however, do not act in this way
towards acids ; but they often combine easily with
elements whose equivalent is known. Thus, when a
piece of charcoal (or better, a diamond, which is pure
carbon) is heated in oxygen gas, we find 3 grams of
carbon always uniting with 8 grams of oxygen ; that
is to say, 3 grams of carbon are in the chemical sense
equivalent to i gram of hydrogen, because in the
formation of water, i gram of hydrogen is combined
with 8 grams of oxygen. Hence, the equivalent of
carbon will be 3. By similar methods we are able to
find the equivalents of most of the elements with great
accuracy.

The equivalent is not, however, the atomic weight.
It would be so if all elements had an equal combining
power or valency. In various indirect ways we are
able to arrive at an element's valency with a reason-
able certainty. Let us suppose that we have dis-
covered, as we can assuredly discover, that the atom
of magnesium is divalent ; each atom of magnesium
will therefore be able to do the work, or fill the place,
of two atoms of hydrogen. The weight of two atoms
of hydrogen is 2 : hence the weight of one atom of
magnesium will be 2 x 12 =24, since 12 is the equi-
valent of the metal. Similarly in the case of carbon :
the atom is found, only with great probability rather
than certainty, to be tetravalent (Gr. tetra = four).
Its atomic weight is therefore 4 x 3 = 12, as we have
mentioned previously. Of course, it is not necessary
to repeat that all these weights are merely relative to
that of the atom of hydrogen, taken as standard ; but
even so they are of indispensable value in the science
of chemistry, and for practical purposes a knowledge

THE STORY OF THE FIVE ELEMENTS

of the actual weights of the atoms would not add to
their usefulness.

The method most commonly adopted for the deter-
mination of atomic weights in the present day depends
upon a different, but no less interesting, principle from
that outlined above. Compounds of carbon, for
example, can be analysed and have their molecular
weights determined with considerable accuracy. Now,
the weight of carbon in any molecule can never be
less than that of one atom, though, of course, it may
be greater ; and among all the molecules of carbon
compounds that we have yet analysed, we have never
found one which contains less than 12 parts of carbon
by weight. We therefore adopt 12 as the atomic
weight of the element.

In this book the five elements of the Greeks are
taken as the text of five lessons in modern chemistry ;
wherein we show how we have reached the true con-
ception of those elements, and how our studies of
these have thrown light upon the great questions
which were working in the minds of Empedocles and
his like more than 2,000 years ago. On the way we
shall see how fruitful a scientific chemistry has been in
great discoveries and achievements of a practical
nature ; in pursuing our inquiries into the mysteries
of Nature, guided only by the determination to arrive
at truth, we have been rewarded at the same time with
a noble philosophy of matter and a long series of
invaluable new substances and processes.

CHAPTER II
AIR

I. — EARLY VIEWS ABOUT AIR

OF the four elements of the ancients, none surely was
more wonderful and mysterious than the air which
was so obviously necessary to human existence. Earth,
water, and fire — each cherished its mysteries, but at
least they could be seen. So the air — invisible, yet
ever present , peaceful, yet prone to violence ; cap-
able of irresistible motion — touched the imaginative
powers more nearly, and awakened a quicker specula-
tion.

The demand for a motive power behind the pheno-
mena of the air led a crude philosophy to people it
with gods ; and our word gas, which is our general
term for all air-like substances, originated in the
German Geist, ghost, and reminds us of such primitive
notions. To Anaximenes (c. 500 B.C.) came the
thought that air was the element. Did he not perceive
in his soul something akin to the air — something ever
moving, tending to uplift, yet ever invisible ? And,
just as the soul is the beginning of man, his permanent
and essential element, so must air be the beginning of
external things. Does not water come from the air,
earth from water, and fire from earth ? Looked at
with the science of Anaximenes, air is clearly the
parent of the other elements !

But Empedocles levelled air to the rank of fire,
water, and earth ; it was no longer prima materia,

THE STORY OF THE FIVE ELEMENTS

but became a spirit, a ghost, a gas, in which guise it
remained. Careful experiment, extending the field of
familiar observation, was wanted ; not for many cen-
turies was this, the method of science, to be applied.
We find, however, that in the days of the Roman
Empire the rise of water in pumps was attributed to
the weight of the air. Weight cannot be ascribed to
spirits, and it was something gained when air had
a material property attached to it. But through the
dark centuries, when alchemy was the only chemistry,
this fact was lost, and no real attempt was made to
elucidate the nature of air. On the contrary, darkness
became deeper as substances were endowed with
" air/' which had no claim to the name. Thus, sul-
phur, producing a sharp-smelling fume when burnt,
was therefore said to contain the element air, although
it must have been obvious that the choking fumes
were vastly different from atmospheric air. Indeed,
whatever we now define as a gas was in those days
described as an air ; but it was not until the eighteenth
century that it was clearly realised that all airs are
not alike, and that gases differ among themselves as
sharply as solids do. The actual truth about the
nature of air was held back almost to the end of that
century. But the Hon. Robert Boyle (1627-91), a
good experimenter and a shrewd reasoner, had first
established the important truth that air was matter
by demonstrating its weight and its " spring," or elas-
tic force, when compressed. What is true of air is
true of other gases : they can be weighed and com-
pressed.

In our study of air we shall follow broadly the
footsteps of history, and consider it first in its beha-

AIR A MATERIAL SUBSTANCE

viour as a substance in the gaseous form, without
inquiry about its inherent nature. We shall consider,
first, those physical changes which do not alter the
air intrinsically, leaving the more difficult chemical
changes, which do involve a change in its actual
material nature, to a later stage. Thus, an investiga-
tion of the weight of the air, a study of its expansion
under heat, a description of the principles by which
it has been brought into the liquid state — these are
physical inquiries, because they do not suppose any
change in the composition of the substance : the air
is air throughout. But if a piece of wood is burned
in the air, we shall see that the new air is now different
from the old air, though its physical properties are
the same.

II. — PRESSURE OF THE AIR

That air has weight and can exert pressure is
suggested by the force of the winds ; but it is advis-
able to weigh the air directly, and that
may be done by a very simple experi-
ment. A flask is fitted with a cork and
glass tube, as in Fig. i, and a long piece
of india-rubber tubing is fitted on the
glass. Place the whole on a balance,
and weigh it. Then suck as much air
out of the flask as possible ; pinch the Fig. i^

rubber and tie it in a knot, so as to for. sKhow;ng. the

weight ot atr.

prevent the re-entry of air. Weigh again,

and the flask will be found to be lighter now — of

course, by the weight of the air sucked out.

Possessed, therefore, of weight, the air must be
competent to exert pressure. Place a few pieces of

THE STORY OF THE FIVE ELEMENTS

any light substance upon a piece of paper which floats
on the surface of water in a tumbler about half-full
(Fig. 2). On bringing over the top of the paper an
inverted wine-glass, that can be comfortably accom-
modated in the tumbler, and gently pressing it down
into the water, the paper and its contents will appear
to sink beneath the surface, and may be pushed almost
to the bottom of the tumbler. What pushes the sub-
stance down ? Evidently something in the wine-glass ;

Fig. 2. — An experiment showing the pressure of air.

and evidently, also, that something is the air which by
its pressure prevents water from entering the glass. A
keen observer would notice that a small amount of
water does enter the wine-glass ; this shows that the
air inside is capable of compression. Neglecting this
for the present, we note that on carefully raising the
tumbler the substance on the paper has not been
wetted. Clearly the air is capable of exerting enough
pressure to push down the water.

This pressure is in all directions, upwards as well
as downwards. Place a cardboard slip over the
mouth of a tumbler full of water, and carefully invert
it, as in Fig. 3. The upward pressure of the air is

PRESSURE OF THE AIR

great enough to support the water in the tumbler,
and the card does not fall off or the water flow out.
If the air did not thus exert its pres-
sure in all directions the roofs of
buildings could not withstand the one-
sided pressure to which they would be
subjected. A tin can with its lid
sealed on is pressed perfectly flat by

,__ . , .j ., * .. Fig. 3.— A simple ex-

the air outside it, when the pressure periment for show-
is withdrawn from the interior. j*^ pressure

The actual pressure exerted by the
air is a valuable piece of information which can be
obtained with very considerable accuracy by means

of a barometer. The essential

part of a barometer is a straight

glass tube, about one yard long

and closed at one end. It is

filled with mercury and in-

verted in a basin of that liquid,

as shown in Fig. 4. A portion

of the mercury falls out of the

tube, but about 30 inches

always remain in it. How is

it supported, if not by the

pressure of the air ? That the

height of the column is de-
pendent upon the pressure
of the air on the mercury
Fig. 4. - A surface we can prove con-
y tne apparatus

Fig. 5 —
Apparatus

showing

the effect

of pressure

on the

height of

mercury.

bar°"

suggested by Fig. 5. Here the mercury
reservoir is a bottle which has a tight-fitting cork with
two holes. The barometer tube passes through one hole,

THE STORY OF THE FIVE ELEMENTS

and a tube by which air can be sucked out or blown
into the bottle passes through the other. When air
is sucked out, the mercury in the tube falls ; if more
air is blown in, the mercury rises. If the closed end of
the tube be cracked, all the mercury will fall out,
because the pressure of the outside air then becomes
operative inside the tube.

The space above the mercury in a barometer, of
course, contains no air, and would be a complete
vacuum were it not for a few molecules of mercury
which escape from the liquid in the form of gas or
vapour. If the tube be inclined a little, the mercury
will be seen to flow into the vacuum, meeting no impedi-
ment to its motion. This space, containing no matter
worth speaking of, was first recognised by Torricelli
in 1643.

By carefully measuring the height of the mercury
in the tube above the surface of the mercury in the
basin, we can, by a very simple calculation, express
the pressure of the air in pounds to the square inch.
A given volume of mercury weighs 13*6 times as
much as the same volume of water ; that is to say,
I cubic foot of mercury weighs 13*6 x 62*5 Ib. Thus,
30 inches of mercury standing on a base of a square

so
inch would weigh -^— g x 13-6 x 62-5, or about 15 Ib.

The air is therefore able to support, and so must
exert, a pressure of 15 Ib. per square inch, which is
a very remarkable amount when we try to realise it.

A barometer might be made by using water for the
liquid ; but it would, of course, have to be 13-6 times
as long as a mercury barometer need be. The air
will support 34 feet of water, but no more. Baro-

THE BAROMETER

meters are sometimes constructed with glycerine when
very delicate changes have to be recorded ; but they,
too, are absurdly cumbrous for ordinary purposes.
Many improvements have been made in order to
make the reading of the mercury barometer as accurate
as possible, and to make the instrument more con-
venient for practical use. Aneroid barometers are also
made, in which no mercury is used at all. They can,
however, only be graduated by reference to the
mercury barometer as standard.

However accurate the barometer, the record it
gives has the same meaning : namely, that the air is
really a material substance, exerting a very substantial
pressure, which varies from place to place, and from
hour to hour, but rarely falls below 28 inches of mercury
or rises beyond 31 inches. The variation of the pres-
sure may be caused by an alteration in the observer's
position or by a change in the air itself. If the observer
ascends a mountain with a barometer, he will find the
pressure diminishing ; and it is possible for him, from
the change of pressure indicated, to calculate how
high he has ascended. When the air is very moist,
or when it is tending to rise from the surface of the
ground, or when it is in rapid horizontal motion, it will
exert less pressure, and the mercury will fall. Con-
versely, a high barometer tells of a dry air, or of down-
ward currents, or of little wind ; hence its use as a
weather indicator. The changes in the pressure of
the air are, in fact, our best guides in forecasting the
weather.

III. — EVAPORATION

The disappearance of water into the air must have
attracted attention from the most cursory observers ;

THE STORY OF THE FIVE ELEMENTS

but the fact that the water is still there requires thought,
and it was very much more natural for the philosophic
mind, untutored by scientific processes, to postulate
that " water " is simply transformed into " air." But
the material, water, does exist in the air, thoroughly
mixed with it in the form of vapour ; the water has put
on the invisible garb of a gas, apparently of itself ; but
its molecules are no further changed. Let us consider
how modern science explains the loss of the liquid
" element/' i.e. the process of evaporation.

The molecules of matter have to be supposed to be
endowed with motion, and it is this motion which, as
we shall later see, confers upon them their heat. In a
liquid, apparently still, every molecule is moving, some
faster and some slower than a certain average which
gives the external temperature of the liquid. The more
rapid molecules, the hotter ones, may occasionally be
carried out of the surface of the liquid into the air-space
above. These molecules, therefore, will have left their
liquid condition ; the liquid thus partly evaporates,
and, as the slower molecules are left behind, the eva-
porating liquid will have become colder. We may
therefore describe evaporation as the process by which
a liquid becomes a vapour by the expenditure of its
own inherent energy.

We always find matter associated with energy in
some form, by virtue of which it is capable of doing
work. This energy may be due either to motion, as in
the case of the steam-hammer, or to position as in the
case of a wound-up watch-spring. Molecular energy
has as genuine an existence as these more obvious
forms, and if we utilise some of the molecular energy
of any body there will be less of it left. Now, when

EVAPORATION

evaporation takes place, some of the liquid's molecular
energy is expended in overcoming the cohesive forces
between its molecules and in doing work against the
atmospheric pressure ; and it is this loss of molecular
energy that is responsible for the cold which is always
produced during the process of evaporation. This
cold is always noticeable, and often very intense.

The vapour which results from evaporation enters
the air and adds to the pressure of the air its own
vapour-pressure. If the pressure exerted by the air
itself is diminished, evaporation will evidently be
easier ; the molecules of liquid have greater free-
dom, and so a greater chance of escape.

The behaviour of a gas or vapour shows us that
its molecules can move more freely than those of a
liquid. In the latter case the molecules must be held
together by some cohesive force which is inoperative
in the gaseous condition ; by artificially cooling a
vapour we cause its molecules to move more slowly,
and thus tend to re-form the liquid from which it arose.
The vapour is then said to condense, and when we
combine the vaporisation of a liquid with subse
quent condensation, the whole process is known as
distillation.

In many practical operations which involve dis-
tillation and the concentration of solutions, it is
necessary to convert the liquid into vapour quickly,
and we must then supply more heat, or molecular
energy, than it contains. The molecules can then
be made to move more rapidly and so pass more freely
into the air, until by continuing the addition of heat
we arrive at a point when the vapour-pressure of the
liquid is equal to the pressure of the air above it. At

THE STORY OF THE FIVE ELEMENTS

this point all the molecules of liquid will have acquired
enough energy to pass into the air, and the liquid is said
to boil. From what we have said, the boiling-point, or
temperature of boiling, will be seen to be dependent
upon the pressure of the air. Reduce the pressure
and we lower the boiling-point. This is a very im-
portant fact in a number of industrial operations.
Suppose liquids like benzene or chloroform to be neces-
sary for the solution of certain substances. Such
liquids are valuable, and must not be thrown away
like water, if the process in which they are used is to
be worked economically. The smallest expenditure
of energy upon fuel gives the soundest economy, since
the liquid then uses its own energy ; consequently
the liquids are placed in vacuum stills, so constructed
that the pressure of the air upon them can be reduced.
On slightly raising the temperature of the liquid by
passing steam through coils immersed in the stills,
boiling at once takes place, and the vapour pro-
duced is afterwards condensed. Thus the valuable
liquid is separated from the dissolved material, and
recovered for future use. The method is safe as well
as economical ; the low temperature of boiling very
greatly diminishes the danger from inflammable liquids
taking fire ; no vapour is lost by escape from the
condensers.

Many liquids also, such as glycerine or syrup,
begin to change when the attempt is made to concen-
trate them in the air at its ordinary pressure. The use
of vacuum stills in distilling glycerine, and of vacuum
pans in concentrating sugar solutions, has made it
possible to carry out such processes without loss by
the decomposition of the substance.

BOILING OF LIQUIDS

IV. — AlR-PUMPS

Since a reduced pressure is so useful, it will be
worth while taking a momentary glance at the pro-
cesses by which it may be obtained. The introduc-
tion of the air-pump is due to that pioneer of our
science of gases, Robert Boyle. A simple form is
sketched in Fig. 6.

A is the vessel to be exhausted, and p is the piston
which moves tightly in the brass cylinder c. At the

Fig. 6. — A simple air-pump

bottom of c, where it is in connection with A, there is
a valve, v, which can only open into c ; and in P there
is another valve, vlt which can only open outward.
Consider now what happens during one complete stroke
of P. Beginning at the bottom of the cylinder, p is
drawn up ; at once air, coming from A, lifts the valve
v and passes into the cylinder. Arrived at its limit,
p is then pressed down. The air in the cylinder, unable
to pass back into A by reason of v, will now lift vl and
escape into the atmosphere. Thus the to and fro
movement of p will have withdrawn from A a quantity

THE STORY OF THE FIVE ELEMENTS

of air enough to fill c. Every similar stroke of p will
reduce the pressure in A still further, although it will
never give us a perfect vacuum.

Various improvements in this simple pump have
been made, whereby its efficiency and convenience
have been increased. Large pumps, worked by elec-
trical or mechanical means, have superseded the hand-
worked instruments, and find
their uses in such industries as
we have previously mentioned,
and in other instances where
vacua are essential. A vacuum
is almost impervious to heat.
Glass bottles or tumblers, hav-
ing a double wall enclosing a
vacuum, as in the well-known
Thermos flask, are often used
to preserve hot liquids or very
cold liquids at temperatures
very different from that of the
air.

For the production of vacua,
or partial vacua, in small
vessels, a T-piece of glass
Fig. 7.-A fiiter-pump. tubing, fastened to a fairly
high-pressure water supply is remarkably efficient.
The pressure of the water along the main tube
causes bubbles of air from the side tip to be carried
along with it ; and consequently any vessel con-
nected with this tip suffers a partial exhaustion.
The laboratory filter-pump (Fig. 7) is based upon this
principle, and is particularly useful when distilling opera-
tions have to be performed with small quantities of

-— viiU,

To vzsszl bo be
exhausted

PRODUCTION OF VACUA

liquid. On the same principle also is based the very
efficient Sprengel pump, much used for evacuating
vessels like electric glow lamps. A long column of mer-
cury is allowed to fall past a narrow horizontal tube
on which the lamp is affixed. Each thread of mercury
carries away some air from the lamp, and the globe is
thus ultimately evacuated.

By reference to Fig. 6, the reader will notice that, if
the valves v and v} are arranged to open in the reverse
direction, air would be pumped into A when the piston
is worked. Hence, the air in A would be compressed,
and its high pressure could be utilised to do work if
such a pump could be constructed on a larger scale and
worked by other than hand-power. Compressed air
can be used, for example, to promote the efficient
stirring of liquids. A series of pipes is arranged along
the bottom of a vessel. Each pipe contains a large
number of fine orifices, and compressed air forced
through them causes gentle agitation and effective
contact of the substances to be mixed. Such a device
is used for making the intimate mixture of water and
milk of lime employed for softening hard water.

V.— How Am EXERTS PRESSURE : BOYLE'S LAW

Our experiments on air have so far taught us that
it exerts pressure upon surrounding objects. It is
obvious there must be a cause for such an effect ;
and we shall endeavour to find what the cause is. It
must be remembered that gases, along with liquids and
solids, are coarse-grained ; they have the molecular
structure. The gaseous molecules are, however, ani-
mated with much faster movements than those of
liquids and of solids, and in the course of their
E 49

THE STORY OF THE FIVE ELEMENTS

V/////////A

movements the molecules are continually bom-
barding the walls of the containing vessel. The
sum total of these molecular impacts constitutes
the pressure exerted by the gas. Suppose, now, we
confine a given amount of air in a cylinder in which
moves the familiar, yet purely hypothetical, friction-
less piston P (Fig. 8). By placing weights upon P we
diminish the volume of the air, but the
pressure of the confined air has increased,
since a balance is maintained between the
upward pressure of the air and the down-
ward pressure of the atmosphere and
added weights. Hence the pressure of
the gas has increased. In terms of our
molecular theory this must certainly
follow; for, on diminishing the striking
area of the molecules, we must increase
the number of impacts, thereby increas-
ing the pressure. It will be clear that, if
we reduce the striking area to one-half its
original value, the number of impacts
will be doubled ; or, by halving the volume,
we double the pressure. Explanations of the behaviour
of gases in terms of the motion of their molecules is
said to be a kinetic explanation, and the theory which
ascribes such motion to them is called the kinetic
theory of gases.

Let us see if an experiment may be devised whereby
we can test the truth of the statement that the in-
crease of pressure upon a gas by twice its former value
renders the volume of the gas half what it was. A long
tube, about J-in. internal bore, closed at one end, is
bent as shown in Fig. 9. The long limb should be

5°

Fig. 8. — I lus.
trating the
effect of pres-
sure on air.

PRESSURE OF GASES

about 40 inches, the short one about 12 inches, long. A
little mercury is poured in the open limb and adjusted
until the level in both tubes is identical. The pressure
of air in the closed limb then balances the pressure of
the air on the mercury in the open one.
We will suppose this value to be equal
to 30 inches of mercury. Note the length
of the closed column of air, and take this
as representing its volume, for the area
of cross section of the tube will be fairly
uniform. Now pour mercury into the
open limb until the difference in the
heights of mercury columns from the
bench top is 30 inches. The volume of
gas will then have been halved, and its
molecules are withstanding twice the
pressure to which they were originally
subjected. The apparatus may be varied
to ensure greater accuracy ; but there
is nowadays a prevalent desire to make
the apparatus rather than the experi-
menter responsible for accuracy — a desire
to be deplored in the case of beginners,
as a crude apparatus only necessitates
the concentration of the faculties essential
to successful operations ; those, namely, which lead to
accuracy by the elimination of as many sources of
error as can be found ; and to the evolution, in the
student's own mind, from the imperfect apparatus
to one of greater perfection. The law which the
experiment described illustrates was first given to
the world by Robert Boyle during the prosecution of
the researches to which we have previously referred ;

Fig. 9.— Boyle's
Tube.

THE STORY OF THE FIVE ELEMENTS

it is known as Boyle's Law, and has led to results of
far-reaching importance in the study of gases.

VI. — EFFECT OF HEAT AND COLD ON AIR

" The production of cold is a thing very worthy
of the inquisition, both for the use and disclosure of
causes. For heat and cold are Nature's two hands
whereby she chiefly worketh." jThus wrote
Francis Bacon, who met his death from a
cold caught while studying the process of
refrigeration. Evidently he realised justly
the importance of these great physical
agents, an importance until his time greatly
overlooked. The results of following up his
suggestions have very far surpassed the
imagination of the creator of the "New
Atlantis." As the air has played a great
part in the march of progress; it will be
profitable to follow in outline the effect of
heat and cold upon it. Galileo and Boyle
simple "air- were among the earliest students of the
thermometer.- phenomena. Galileo constructed an air-
thermometer, and Boyle found that air, subjected to the
freezing mixtures then at his disposal, had not its
spring weakened " anything near so considerable as
one would expect " — only, in fact, from 10 volumes to
9. A deeper range of cold has, as we shall see,
weakened the " spring " far beyond his conceptions.

The expansion of air may be shown by the con-
struction of a simple " air- thermometer," such as is
shown in Fig. 10. The air is confined between the
cork and the level of the coloured water which is con-
tained in the flask and the long straight tube. On

THE AIR-THERMOMETER

gently warming the flask by means of the heat of the
hands, sufficient expansion is obtained to be rendered
visible by the ascent of the liquid in the vertical
tube.

The consequences of this easy and quite consider-
able expansion are numerous. The fire in a grate, heat-
ing and expanding the air above it, causes the air to
rise on account of its lightness ; cooler and heavier
air must come in to fill its place ; and thus a draught
is established over and towards a fire. Fires were
formerly kindled at the base of the shaft in a coal-
mine, so that an upward draught of foul air was estab-
lished, and fresh air drawn into the mine from other
shafts. The rising of warm, expanded air sets the sur-
rounding air in motion as winds ; and ventilators are
constructed primarily with the same principle in view,
the inlet for fresh air being kept low down, and the
outlet discharging the hotter foul air being placed near
the roof.

Thermometers for common use are based upon the
principle of expansion by heat ; but the substances
used in them are liquids. Air expands much more
than either liquid or solid substances ; its expansion is
therefore easier to measure accurately ; and conse-
quently it should furnish a suitable expanding sub-
stance for accurate scientific thermometers. It has
been very largely so used in recent times, and our
liquid-in-glass thermometers are generally tested by
reference to air as a standard substance. Air-
thermometers can be used for very high and for low
temperatures ; the air expands very uniformly, as
well as largely. For these purposes it is therefore an
invaluable substance. For very accurate work, nitrogen

THE STORY OF THE FIVE ELEMENTS

gas (p. 80) is even more valuable, because its expan-
sion is more uniform.

In actual practice the air is not allowed to expand,
but is confined to a constant volume by an increase oi
pressure. For high temperatures the air is enclosed
in a porcelain vessel, which is placed in the substance
or bath to be tested. The tube connected with the
air has a mercury gauge similar to that in our Boyle's
tube described on p. 51. The tendency of the air
to expand is balanced by an increased supply of mer-
cury in the open limb ; it is easy to measure how much
mercury is required to keep the air at its original
volume ; and, since the law of increase of pressure
is the same as the law of expansion, it is easy to cal-
culate the temperature of the air in the vessel from
our measurements. No experiments have been con-
ducted more carefully than these on the expansion
and the increase of pressure of air when heated ; the
increase of pressure takes place always when the
expansion is prevented, and thus provides an exceed-
ingly accurate measure of temperature.

The level of the liquid in our simple air-thermometer
(Fig. 10) will gradually return to its former level when
the heat is withdrawn. If the air is still further cooled,
the level will fall ; air contracts on cooling at the same
rate as it expanded under heat. Very careful measure-
ments of this rate have been many times made by very
able and skilled experimenters, and the result is given in
the statement that a given volume of air at o° C. will
change by 2}g of itself for every rise or fall of a degree
Centigrade.* A little thought, however, will persuade

* On the Centigrade thermometric scale, always employed in
scientific work, there are 100 degrees between the freezing-point (o°)
and the boiling point (100°) of water.

THE COOLING OF GASES

us that, if this rate of contraction is continuously
maintained to any degree of cold, peculiar and in-
tensely interesting results will follow. As one volume
of air, when cooled from o° C. to — i° C. will contract
to |jf of this volume, it follows that, if cooled to
— 273° C., it should vanish altogether. At this tem-
perature we could cool it no further ; so we arrive at
an absolute zero of temperature, or the temperature
of the greatest degree of cold that could possibly be
applied. Many investigators had varied beliefs in
regard to this absolute zero temperature in the bygone
days. John Dalton, a man revered by chemists,
speculated —3,000° C., whilst Lavoisier essayed
—600° C., and not until the expansion and contrac-
tion of gases was studied quantitatively was the real
value found. We may here say that the temperature
of —273° C. as the absolute zero has been confirmed
by Lord Kelvin from theoretical considerations, and
no doubt at present exists about its accuracy.

Although this temperature of —273° C. has not
yet been in practice reached, we have experimental
evidence that, before it can be attained, a gas no
longer obeys gas laws, owing to the fact that it will
have assumed the liquid state. The contraction suf-
fered by a gas when cooled to a great extent is suffi-
cient to bring the molecules of the gas into such close
proximity that their attractive forces can come into
play, and this ultimately results in the gas becoming
liquid.

Experiments on the cooling of gases with a view
to liquefaction were commenced by Michael Faraday
in 1823. As early as 1805 chlorine and sulphur
dioxide had been liquefied by Northmore ; but Fara-

THE STORY OF THE FIVE ELEMENTS

day was the real pioneer of determined experimental
work on the subject. This investigator, who, beginning
life as a newsagent's boy, lived to lay the foundations
upon which many branches of physics are built, sub-
jected gases, such as ammonia, chlorine, cyanogen, to
a low temperature, and also to assist the reduction in
volume and bring the molecules closer together, to a
great pressure. The beautiful device he used for com-

Fig. 11.

a , Faraday's experiment for the liquefaction of gases.

b, Vacuum vessel for holding liquid gases.

bining the pressure and cold is shown in Fig. na. The
substance yielding the gas was placed in a stout tube
at A ; the narrow end of the tube was sealed; and
placed in a freezing mixture of ice and calcium chloride.
The gas, being generated by heat at A, accumulated,
and a great pressure was thus set up ; combined with
the cold, this caused the liquefaction of many gases.
Thus the real " airs," or some of them, became
" water." But a few gases resisted all Faraday's
attempts to change their " element," and these he
was led to describe as permanent gases. In 1835 a
step further was taken by a French physicist named
Thilorier, who succeeded in liquefying carbon dioxide

LIQUEFACTION OF GASES

gas (p. 87) in large quantities, by generating the gas
in a cast-iron cylinder and leading it under great
pressure into a second similar vessel. The great
pressure alone was sufficient for him. The liquid thus
produced Was a very great boon to investigators, as it
enabled them to obtain very much lower tempera-
tures than hitherto. By the rapid evaporation of the
new-found liquid, great cold is produced. Ever ready
to seize an opportunity, Faraday used this liquid and
succeeded in bringing other gases into the liquid state ;
but still air, hydrogen, and one or two other gases
refused to submit and remained permanent gases,
showing no sign of liquefaction.

In science there is always something new to learn,
and the clue to the mystery which baffled Faraday was
published in 1869. It was shown that cold, rather than
pressure, is the more important factor in the liquefac-
tion of gases. Dr. Andrews, of Belfast, experimenting
on carbon dioxide, discovered, to his astonishment,
that, above a temperature of 32° C., no amount of
pressure would cause that gas to liquefy, whereas it
could be easily liquefied at 31° or any temperature
below it. Between 31° and 32°, therefore, we have
a temperature which determines whether carbon
dioxide can exist as a gas or a liquid, a temperature
critical to the substance, and hence known as its
critical temperature. Above this temperature the sub-
stance cannot exist in the liquid form : it is a perfect
gas. Below, a suitable pressure will liquefy it. If,
then, we wish to make air liquid, we must reduce it
below the critical temperature ; otherwise it is useless
to employ the mightiest pressures obtainable. As the
critical temperature of air is about — 150° C., and that

THE STORY OF THE FIVE ELEMENTS

of hydrogen gas is about — 243° C., it is easy to see
that the problem to be solved is that of evolving some
process for obtaining the intense cold revealed by
these temperatures.

Oxygen was the first of the refractory gases to
yield to the apparatus of M. Raoul Pictet at Geneva
in 1877. The gas was submitted to a pressure of 500
atmospheres (about 3! tons per square inch) ; at the
same time it was cooled by the evaporation of liquid
carbon dioxide, which itself was surrounded and cooled
J}y liquid sulphur dioxide, made to boil rapidly. Air
soon yielded also, put off its aery nature, became liquid,
and was ultimately frozen ; but hydrogen remained
obtusely gaseous until a new principle was brought into
operation. Sir James Dewar then liquefied hydrogen
in 1897, and concluded the splendid work begun by
Faraday at the Royal Institution by liquefying helium.
In Dewar's experiments the highly cooled hydrogen —
still, however, above its critical temperature — was
kept under great pressure, and then allowed to
expand suddenly through a small orifice. The ex-
panding gas needs energy for its expansion ; this
it supplies for itself from its own store ; consequently
it becomes very cold, and a cloud of liquid (and
even solid) hydrogen is produced. The expanding
gas, made to circulate round the spiral containing
the compressed hydrogen, further cools the latter,
until it becomes liquid. It may be collected in a
vessel with a vacuum jacket (Fig. n b), kept, and
examined.

Experiments with these liquid gases have been
both difficult and dangerous ; and the reader will
doubtless have been struck by the fact that, while it

58 *

LIQUID AIR

is easy to heat a substance 273°, it has cost so much
skilful and expensive work to cool it a like amount.
Even now the absolute zero has not yet been reached.
At least six degrees, and perhaps more, remain un-
conquered. One thing has been satisfactorily estab-
lished, nevertheless ; all gases, reduced below their
critical temperature, become vapours, and can be
liquefied ; and even in the most " aery " substances,
like helium and hydrogen, the air-element does not
survive a suitable degree of cold.

Nor are these liquid gases of merely speculative
interest. The extension of the principle of free
expansion and consequent cooling has led to the in-
vention, by Herr Linde in Germany, and Dr. Hampson
in England, of apparatus by means of which liquid
air can be obtained in industrial quantities ; it is now
a useful article of commerce. Many curious scien-
tific results have been obtained by its use. The
effect of very low temperatures upon chemical changes
and upon such physical properties as elasticity and
magnetism can now be thoroughly studied ; so, too, it
has been observed that, while 120° above freezing-
point is destructive of all life, many seeds and bacteria
can survive — 240°.

If any of these liquid gases are contained in an
open tube, they are in much the same condition as a
drop of water in a red-hot fire. They boil away
with great rapidity. A little liquid hydrogen pro-
duces so much cold in this way that the air around it
is liquefied and frozen ; the manner in which this may
be employed to produce a perfect vacuum will occur
to the reader readily. It is the cold produced by the
boiling of hydrogen under reduced pressure, aided by

THE STORY OF THE FIVE ELEMENTS

the effect of free expansion, that has caused the lique-
faction of helium ; and we now await the discovery
of a new gas, more " permanent " than helium, in order
to reach that absolute zero of temperature at which
the substance contains no heat at all. Liquid helium
seems to boil about 6° above it.

VII. — THE RELATION OF Am TO COMBUSTION, AND
THE COMPOSITION OF THE AIR

We have hitherto been dealing with air merely as a
material gaseous substance. So important a part does
it play, however, in the life of man and beast ; so vital
is it to plant life , and so necessary to combustion, that
we must turn to a consideration of the part it plays in
these phenomena — a part which changes its characters
even more deeply. And seeing that its composition
has been ascertained primarily by studying its share
in combustion, and that its composition is necessary in
interpreting its many functions, we must see how
this has been arrived at.

The phenomena of fire must always have attracted
attention. So striking was this invaluable, but
mysterious, servant of mankind that it was con-
sidered of sufficient importance to be incorporated
among the four elements of the ancients. For many
years taken as a " property " of the particular burn-
ing substance, no attempts were made to explain its
cause, and not until about 1700 was any theory pre-
sented that was presumed to account for it. About
that time Stahl, a Swedish physician, put forth the
view that substances burnt because they burnt — a
theory surely simple, but which nevertheless attracted

COMBUSTION

numerous supporters and left its mark upon chemistry
as late as the dawn of the past century. Stahl attri-
buted two great principles to every burning substance,
one remaining when the substance was burnt, the
other disappearing. The latter was the burning
principle, or principle of inflammability, the phlogiston
contained by the substance ; the incombustible residue
was termed the calx. Substances which had the power
of burning brightly were supposed to be rich in phlo-
giston ; and varying degrees of inflammability were
ascribed to varying proportions of this immaterial
essence.

This theory, at its best but a mere refuge in words
when considered as an explanation of combustion, yet
attracted many scientists in its day ; and we shall
presently see how, contrary to all expectation, epoch-
making men clung to it with great tenacity. It is
surprising that the theory, born in Sweden, should
have found its chief adherents in France and England,
inasmuch as Boyle and Hooke in this country, and
Rey in France, had previously conducted experi-
ments which should have shown them clearly that
without air combustion cannot take place. Boyle
found, using his air pump, that a candle refused
to burn in an exhausted space ; and heating lead
in contact with air, he found that it increased in
weight. Hooke, at one time an assistant of Boyle's,
also stated that something in air, like the " fixed air "
in saltpetre, helps substances to burn. Mayow found
that air which had been used to support the burning
of a candle refused to allow another lighted candle to
burn in it, and Rey also confirmed Boyle's observa-
tion that lead increases in weight on being heated in the

THE STORY OF THE FIVE ELEMENTS

air. Rey also found that tin behaved similarly. In
the light of such evidence, culled from true inductive
methods, it is truly remarkable that room should ever
have been found in the scientific world for such a
theory as that of phlogiston. Like all theories which
are incapable of explaining facts, however, it was
destined to fall ; and it is somewhat significant that
its fall was completed by the introduction of a new
theory of combustion, which may be said to have
been also the dawn of a new chemistry.

The new ideas obtained and the truths
brought to light during this period have
had a far-reaching effect on subsequent
research and discovery. The experiments
of Boyle, Mayow, Hooke, and Rey were
conducted between 1660 and 1680. Stahl
was born in 1660 and died in 1734; and
the theory cf phlogiston still held sway
in the latter half of the eighteenth cen-
tury! During the latter period — in 1774
— Dr. Joseph Priestley submitted a preparation
known as " mercurius calcinatus " to the action
of heat. This substance, which had been made by
slowly roasting (or calcining) mercury in the open
air, he placed at the focus of a large lens and
concentrated the sun's rays upon it. To his astonish-
ment he found an " air " evolved which possessed
" vital " properties to an extent hitherto undreamt
of. The substance was contained in a small phial filled
with quicksilver and inverted in the latter (Fig. 12),
the pressure of the evolved " air " displacing the
quicksilver from the bottle to the basin. Having
collected about " three or four times as much "

Plate III

JOSEPH PRIESTLEY

1753-

VITAL AIR

as the bulk of his materials, Priestley examined the
gas with a view to finding its properties, and found it
to be a very active " air." To use his own words,
" what surprised me more than I can well express
was that a candle burned in this air with a remark-
ably vigorous flame/' a fact he was " utterly at a loss
to account for."

At the same time that Priestley made the above
experiment, he conducted a similar one, using " red
precipitate," a substance produced by the ignition of
a nitrate of mercury. He succeeded in isolating the
same " air," and surmised that it was possible for the
red precipitate to have yielded a substance which it
had obtained from the nitric acid used in its manu-
facture ; he also thought it possible that the mer-
curius calcinatus with which he was supplied had
not been made by calcining mercury, and that he had
really been supplied with red precipitate. Obtain-
ing, however, a pure sample of the mercurius cal-
cinatus, he again obtained the lively " air," and
mentioned the fact to Lavoisier during a visit to
Paris ; he subsequently obtained the same gas from
red lead. After the latter experiment he came to
the conclusion that the gas he obtained came first
from the air and was taken up from the air by the
mercury during its calcination. The comparison of
the properties of this new air with those of atmospheric
air convinced Priestley that air was not an element ;
such a view was only confirmatory of others which he
must previously have formed during experiments on
respiration and plant growth — experiments which we
shall consider a little more in detail later on.

But, although this was the case, and although it
63

THE STORY OF THE FIVE ELEMENTS

may be said that he held the key to the chemistry of the
air in his hands, Priestley came to altogether erroneous
conclusions about its composition, the result chiefly
ofjthe fact that he remained a firm adherent of the
phlogiston theory and tried to state the composition
of the air in terms of its impossible conceptions. The
communications that Priestley made to Lavoisier,

Fig. 13.— Lavoisier's experiment.

however, fell upon fertile soil. Lavoisier quickly
recognised that Priestley's gas was a constituent of
our atmosphere, and that it had been taken up by
the mercury during calcination. As it was so much
more active than ordinary air, he rightly inferred that
the air must contain some other constituent which
dilutes its action. He therefore promptly designed
an experiment which conclusively showed that the
air was not an element ; that as such its reign must
end, and that it contained at least two constituents.
The constituent which Priestley had found, and had
named vital air, Lavoisier called oxygen, and as such
we shall henceforth speak of it. The properties of

OXYGEN IN THE AIR

the gas were remarkably well demonstrated by Priest-
ley, who showed experimentally its great activity
as a supporter of combustion and of life. He studied
its effect upon mice and upon the human body, and
he also showed that it was not imbibed by water.

The classical experiment by which Lavoisier showed
for the first time that air was not an element was
conducted as follows :

Mercury in the retort (Fig. 13) was calcined in
the confined space indicated. As the oxygen of the
enclosed air was absorbed by the mercury — upon the
surface of which a red tarnish appeared — a loss in
volume naturally occurred, and this was shown by
the liquid rising in B. In the course of the experiment
a stage was reached when no further diminution in
the volume of the air took place. The gas remaining
was the second constituent of our atmosphere, and
obviously it will not support the calcination of mer-
cury. It was found to be an inactive gas, almost
incapable of chemical activity, and was for this reason
called azote. (We ought to mention that at high tem-
peratures it is more energetic.) It was subsequently
found to be of identical properties with a gas called
nitrogen that had previously been obtained from salt-
petre. The atmosphere was thus shown by Lavoisier
to be composed mainly of two gases — oxygen and
nitrogen.

The experiments of Lavoisier showed that the air
contained about four volumes of nitrogen to every one
volume of oxygen, and later experiments confirm the
general accuracy of this result. Henry Cavendish
(1731-1810) was the most careful of these early inves-
tigators, and his papers, when compared even with

THE STORY OF THE FIVE ELEMENTS

those of Priestley or Lavoisier, show a scrupulous
care and diligence in the prosecution of research, that
have very rarely been surpassed. He made more than
five hundred experiments in order to obtain an accu-
rate measure of the " goodness " of the air. The vessel
he used is called a eudiometer (Fig. 14), and his method
is in principle that which is at present used for the
same purpose. There is a gas, called nitric oxide,
which unites directly with half its volume of oxygen
and forms a new gas that is readily imbibed by water.
By carefully serving a measured volume of air with
this gas over water, the amount of oxygen consumed
can be obtained. The result of his analysis given by
Cavendish is, in the light of modern work, remarkable,
as will be seen from the numbers following : —

Cavendish (1781) obtained 20-833 vols. oxygen
per cent.

Lord Rayleigh (1894) obtained 20-61 vols. oxygen

per cent.

The close agreement of these numbers is a striking
testimony to the effect of personal care in the con-
duct of experiments. In modern analyses hydrogen
gas is preferred to nitric oxide, but it plays essen-
tially the same part. It is mixed with the air in known
proportions, and the mixture exploded by an electric
spark. Hydrogen and oxygen then unite in the pro-
portion of 2 : i, and a water-mist results which takes
up a negligible volume. There must therefore be con-
traction of volume as a result of this disappearance of
hydrogen and oxygen, and one-third of that contraction
will be due to the oxygen which has departed. For
the sake of simplicity, suppose 30 cubic centimetres
(c.c.) of dry air and 30 c.c. dry hydrogen are measured

ANALYSIS OF THE AIR

off carefully in some suitable vessel and exploded by
means of the electric spark. After explosion, the
volume is 42 c.c. It follows that 18 c.c. of gases have
gone to produce water. Of these, one-third, or 6 c.c.
is oxygen. Hence, of the 30 c.c. of air we have 6 c.c.
of oxygen, or 5 vols. of air contain i vol. oxygen. The
apparatus used is generally a stout glass tube of 100
c.c., closed at one end, into which two
platinum wires have been sealed (Fig.
14). The tube is carefully graduated to
admit of accurate measurement of the
gases. It is filled with mercury and in-
verted in mercury ; dry air is passed in,
followed by hydrogen, each volume being
carefully noted and corrections necessary
for temperature and pressure made. The
tube is then clamped securely upon a
piece of india-rubber, as during explosion
concussion occurs. A spark is passed,
union takes place, and on cooling and
releasing the tube the mercury enters
to take the place of the departed gases.
The final readings and corrections being Fig. 14.— A eudio-
made, the analysis is complete. meter'

Analyses have also been conducted with a view
to finding the composition of the atmosphere by
weight, the principle being to allow air to pass over
hot copper into a previously weighed and exhausted
globe. The hot copper has the power to unite with
the oxygen. The increase in weight of the globe
gives the nitrogen, and the increase in the copper
gives the weight of oxgyen in the same quantity of
air.

THE STORY OF THE FIVE ELEMENTS

VIII. — THE RARE ELEMENTS OF THE AIR
Many such experiments on the composition of
atmospheric air have been made since the days of
Cavendish and Lavoisier, all approximating more or
less closely, and none seeming in any way to vitiate the
accuracy of Lavoisier's conclusions in regard to the
elements present. Imagine, therefore, the consterna-
tion among grave men of science when Rayleigh and
Ramsay announced to the world in 1894 their dis-
covery of a new constituent of our atmosphere ! For
over 100 years the air had been treated as a mixture
of oxygen and nitrogen, and was then found to con-
tain a third element that had escaped so many
observers ! The story is too fascinating to leave
untold, and serves as an illustration of the scientific
truism that, accuracy being the first essential in scien-
tific work, fact will stand before authority or theory.
In order to obtain the density of nitrogen gas, Lord
Rayleigh had obtained nitrogen in a pure condition
from many sources, and naturally expected to obtain
uniform results in his determinations. The nitrogen
from the air, however, persisted in being heavier than
that derived from other sources. It is obvious that,
if one determination only had been made, and that
with nitrogen obtained from some chemical, this fact
would have been overlooked. The heaviness of the
nitrogen in the air, however, could only be caused by
the presence of some hitherto unknown gas, a sub-
stance itself heavier than nitrogen, or by some change
whereby the nitrogen molecules condensed to give
heavier ones. This latter idea had no support in
experimental fact, and the isolation of the unknown
gas settled the question.

DETECTION OF ARGON

This has been accomplished in two ways. If a mix-
ture of air with an excess of oxygen is exploded in
the eudiometer over water or alkalis, the nitrogen
and oxygen will enter into combination to form a gas
which is readily absorbed by the liquid. By using suf-
ficient oxygen, all the nitrogen can thus be with-
drawn from the air, and the excess of oxygen can
afterwards be absorbed by a small quantity of pyro-
gallic acid. When this was done several times it was
found that a small quantity of gas remained un-
changed and unabsorbed. It was, however, so small
that great difficulty was experienced in examining
it. Professor (now Sir William) Ramsay, there-
fore, sought a substance that would absorb nitrogen,
just as so many substances absorb oxygen. He found
it in the metal magnesium. When nitrogen is con-
tinually passed over hot magnesium turnings, it
combines with the metal to form magnesium nitride ;
this is the basis of the method finally adopted. Air,
freed from oxygen by being passed over hot copper, is
then freed from nitrogen by means of hot magnesium,
an arrangement being devised by which the gas could
be repeatedly brought into contact with the metal.
The resulting gas was sparked with oxygen to with-
draw the last traces of nitrogen ; then there remained
the new element, named argon because it would
not do any work. During the severe treatment to
which the air had been subjected it survived, indepen-
dent and uncombined. This is the cardinal charac-
teristic of the gas : it refuses to enter into chemical
combination with even the most active of other ele-
ments. For this reason it had so long escaped detec-
tion, although it forms about i per cent, of that

THE STORY OF THE FIVE ELEMENTS

part of the air which had been supposed to be
nitrogen.

It is interesting to note, however, that Cavendish,
during his experiments upon air, really made the
observation that might have led him to argon. After
repeated sparking he found that about jicth part
of the air used would not enter into union with oxygen.
This, doubtless, was argon; but the significance of
his observation did not strike anyone until argon was
definitely known. This is very singular when we
recollect that Cavendish had actually designed his
experiment to ascertain whether any part of the de-
phlogisticated air (nitrogen) was different from the
rest. And he concludes : "If there is any part of
the dephlogisticated air of our atmosphere which differs
from the rest, and cannot be reduced to nitrous acid,
we may safely conclude that it is not more than
rJ0th of the whole/' This ought to have been a
stimulating observation, but more than a century
elapsed before the nature of the inactive residue was
unfolded.

By the principles previously explained, argon,
subjected to a low temperature and a high pressure,
was liquefied. In boiling the liquid argon, however,
it was soon found that it was not a single substance.
The first vapours given off contained, besides argon,
appreciable quantities of two other elements, helium
and neon. The former element had been previously
found to exist in the sun and in certain rare minerals ;
it has received much attention from its connection
with radio-activity (Chapter VII.) ; and of all known
gases it is the last to become liquid. Neon occurs in
the air in very minute quantities. Like helium, it

THE RARE GASES IN THE AIR

does not condense when surrounded with boiling
liquid air ; but it yields to the intense cold of boiling
hydrogen, when helium does not. Two other gases,
krypton and xenon, heavier and less volatile than these,
have been extracted in very minute quantities from
the liquid argon. Their discovery and identification
indicate the possibilities of chemical research at very
low temperatures. Xenon exists in the air in the
proportion of one part in 20,000,000 ; krypton and
neon perhaps form one part out of every million. Yet
their atomic weights are known. We know also that
the five elements which remain untouched by the
process of Sir W. Ramsay are totally inert, and exist in
the universe apparently always in isolation.

We thus realise that air is not one element, as
ancient philosophers thought, but a mixture contain-
ing at least seven. It shares with many other sub-
stances the properties of a gas — its elasticity, com-
pressibility, power to mix or diffuse into other gases,
ready expansion under heat. But these properties
are general to all gases. Air is, however, a mixture
of two particular gases, nitrogen and oxygen, with
traces of five others. In the chemical sense its beha-
viour is that of oxygen, hampered and diluted by
the nitrogen which is mixed, and not chemically com-
bined, with it. It is important, therefore, to review
the salient qualities of these two gases.

IX. — OXYGEN

This gas, the most abundant element on the earth,
may now be prepared by methods other than that
adopted by Priestley to obtain it from the air. It is
a constituent of many substances, one of which, in

THE STORY OF THE FIVE ELEMENTS

particular, will readily yield the oxygen it contains.
This substance, potassium chlorate, white and crys-
talline, need only be cautiously heated in a test-tube
to teach one that it contains a large amount of oxygen
gas. After crackling and melting, the liquid begins
to effervesce, and on introducing a glowing splinter
into the mouth of the tube, it is at once rekindled,
and the rekindling will take place many times. Since
potassium chlorate is easy to obtain, and cheap, it

will suitably serve for
the preparation of the
gas in large quanti-
ties. To facilitate the
production of the gas,
it is usual to mix with
the chlorate a little
manganese dioxide,
which must be pure.
On gently heating the
mixture in the flask,
as shown in Fig. 15,
and neglecting the few
bubbles of air at first produced, oxygen may be col-
lected in jars, inverted and full of water, over the
beehive shelf placed in the pneumatic trough. This
shelf and trough, of the utmost service in the pre-
paration of gases, were invented by Priestley, the
trough being any suitable vessel containing water
and the shelf shaped like a cylindrical box, with a
hole in the side and in the top. The hole at the side
admits the end of the delivery tube ; the top one
allows the gas to pass into the inverted jar above,
thus displacing the water in the latter and ultimately

Fig. 15.— The preparation of oxygen.
(Inset is the beehive shelf.)

OXYGEN

filling it. In this way three or four jars full of oxygen
may be obtained.

The gas is without colour, taste, or smell, and
when breathed produces feelings of " life " ; it is, in
fact, the life-giving gas, and the conjecture of
Priestley that it would probably, in the future, be
used for patients suffering from shortage of breath,
has been realized. A few experiments will convince
us of its activity. A candle may be burnt
in the first jar. A piece of wire, bent
round the candle, and carrying the lid
of a canister, serves as an easy means
of introducing substances into the gas.
The candle is consumed very rapidly, and
a brilliant light results ; were the air com-
posed of oxygen only, wax candles would
not last long. The candle is finally ex-
tinguished, and refuses to burn in the same
gas jar again. It has, therefore, consumed
the oxygen, and a portion of the candle
has also disappeared, the candle and oxygen
evidently having produced something en-
tirely unlike oxygen in properties and evi-
dently unlike the candle also. The candle
and oxygen are said to have undergone a chemical
change. Such a change is evidently not a mere
mixing of the candle and oxygen, but brings them
into far closer contact, such contact resulting in
chemical combination. When such actions take
place, a mere change in appearance is not the
only change ; the products of the action are different
in themselves from the original substances. If the
oxygen used in the experiment is dry, water is, never-

Fig. 16.—
Burning

sulphur in
oxygen.

THE STORY OF THE FIVE ELEMENTS

theless, seen to be deposited upon the sides of the
jar in a mist, and if a little clear lime water be poured
into the jar after the burning it is turned milky.
Neither the candle nor the oxygen is like water ; nor
does either of them turn lime water milky. Hence a
wonderful change has occurred, a type of change met
only during the process of a chemical operation. The
gas turning the lime water milky is carbon-oxygen-
stuff, made by the oxygen combining with the carbon
which is a constituent of the wax of the candle. It
is generally spoken of as carbon dioxide. Water may
be chemically described as hydrogen-oxygen-stuff, and
can be made by the combination of those elements.
The hydrogen must also have been supplied, along
with the carbon, by the wax, as the only substance
present, in addition to the oxygen, was the burning
wax candle. We may express the whole change by
a statement, thus :

Wax Carbon-oxyjen Hydrogen-oxygen

s~— •*- ~x 4- Oxygen yields -stuff + -stuff

Carbon + Hydrogen (Carbon dioxide) (water)

As a second experiment, a little sulphur may be
ignited and gently lowered into a jar of the gas (Fig. 16).
The change will be quickly observed. Instantly the sul-
phur bursts into a beautiful blue flame ; evidently its
combustion is greatly helped by the oxygen. On
removing the spoon after the sulphur has been con-
sumed as far as possible, the jar will be observed to
be full of choking fumes, with the well-known pene-
trating smell of burning sulphur. On being shaken up
with a little water, these fumes will be seen to dis-
solve, and on adding a solution of the vegetable colour-
ing matter known as blue litmus, the latter is instantly
turned red, owing to the acid nature of the resulting

CHARACTERS OF OXYGEN

liquid, acids having this common property. Reason
tells us that the gas must contain sulphur and
oxygen, and that a mere mixture of sulphur and
oxygen would possess no such properties. It must,
therefore, be a compound of the two substances, and
may be called sulphur-oxygen-stuff. It is commonly
known as sulphur dioxide.

Sulphur -f- Oxygen = Sulphur-oxygen-stuff.
(Sulphur dioxide)

Lavoisier himself found that many products
formed by the combination of other substances with
oxygen, when dissolved in water, rendered the latter
acid ; and hence the name " oxygen " (or acid-pro-
ducer) was given to the gas which seemed to cause
the acidity. Lavoisier believed oxygen to be con-
tained in all acids, and this is true in the great majority
of cases ; an exception is the solution of hydrogen
chloride in water (commonly called hydrochloric acid).
In Lavoisier's day, however, this was thought to con-
tain oxygen (see page 100), and some chemists argue
even at the present time that this is by no means
improbable.

In a third jar of oxygen drop upon a piece of
thin aluminium foil a little charcoal which has been
made red hot. The aluminium at once burns bril-
liantly, and the inside of the jar is coated with a white
incrustation of aluminium-oxygen-stuff, or aluminium
oxide. This oxide, in distinction to the two previous
ones, is a white powder.

When oxygen combines with substances, a class of
bodies known as oxides is produced ; mercurius cal-
cinatus is evidently one of these, and the " red precipi-
tate " used by Priestley is really the same substance,

THE STORY OF THE FIVE ELEMENTS

mercuric oxide, which has obtained its oxygen from
nitric acid. This acid, like saltpetre, chlorate of
potash, and other solid or liquid substances, con-
tains much oxygen in its molecules ; and is often
commercially used for the quick preparation of metallic
oxides.

Just as oxygen supports life and combustion in its
free state, so it does in its diluted condition in our
atmosphere. Substances burn in the air because they
unite with oxygen, and when the oxygen in a confined
space is removed, the combustion ceases. Many other
changes may be likened to slow combustion — changes
all depending upon the oxygen in our air. The rusting
of iron, necessitating an enormous expenditure yearly
upon paints, is in its final state a union of iron with
oxygen, iron rust being chiefly a compound of iron and
oxygen, or iron oxide. The rusting is facilitated by
the presence of water and carbon dioxide, two sub-
stances always present in our air to some extent ;
these form intermediate compounds which end finally
in the iron oxide. Pure iron will not rust in pure
oxygen, and it may here be stated that no substance
in a pure, dry condition, even though it ordinarily
manifests a strong liking for oxygen, can be made to
unite with it ; it may be said, indeed, that no chemical
change can take place by the action of two pure sub-
stances upon each other. Some ihird substance is
necessary to help on the action. The conditions pre-
vailing in our atmosphere, however, always ensure
the presence of water-vapour and carbon dioxide, so
that iron can readily rust. In spite of third parties,
the rusting process is a slow oxidation, or a slow burn-
ing ; and heat is produced just the same as when the

RUSTING OF IRON

iron is burned rapidly. Iron in a finely divided state
may, in fact, rust so quickly as to take fire in the air,
and a piece of watch-spring will burn brilliantly in
oxygen. The " firing " of iron in the air may be
shown as follows :

A little jeweller's rouge (an oxide of iron) is placed
in a glass tube, and hydrogen gas (see Chapter III.),
generated in the flask, is robbed of any water by the Ll-
tube containing calcium chloride, and passes through

Fig. 17. — Apparatus for preparing finely divided iron.

the straight tube in a dry state. After passing for
some time, it may be ignited at the end of the appara-
tus. A may then be safely heated for fifteen minutes,
the hydrogen passing meanwhile. The lamp may then
be withdrawn and the tube allowed to cool in the
stream of hydrogen. We have then present in the
tube metallic iron, formed by the reduction of the iron
oxide by the hydrogen, the latter taking away the
oxygen which the oxide previously contained. On
opening ^the tube and throwing the filings into the
air, they immediately take fire, so quick is the union

THE STORY OF THE FIVE ELEMENTS

between them and the oxygen. Such quick union
with the oxygen in the air, whereby substances of
themselves ignite without the application of external
heat, is spoken of as spontaneous combustion. Stacks
of hay, oily rags, and heaps of coal have been known
to " fire " owing to the operation of a similar process.

X. — ACTION OF ANIMALS AND PLANTS ON THE AIR

Is there any difference in composition between
the air we inhale and that we exhale ? We know that
oxygen and nitrogen are inhaled. What gases do we
send back in place of them ? Procure a dry tumbler
and breathe into it ; a mist is quickly noted around
the sides, which on analysis can be shown to be water.
On pouring a little clear lime water into the tumbler,
it at once becomes turbid, teaching us that carbon
dioxide is also produced (p. 88). Hence we find
two products which can be detected quite easily, and
on submitting the exhaled air to analysis we find it
to contain about as much nitrogen as, but less oxygen
than, ordinary air, and, in addition, an appreciable
quantity of carbon dioxide and water. The action of
animals is, therefore, to use some of the oxygen, pro-
ducing thereby substances identical with those formed
when combustible substances such as wood and wool
burn in the air. The true nature of the changes
occurring during the vital process cannot be dis-
cussed here, but it may be stated that it is these
chemical changes that give us our animal heat ; the
energy of the body is as much dependent upon the
oxygen supply as is that of a railway locomotive.

That air once breathed is unfit to breathe again
may clearly be shown by the following experi-

EXHALED AIR

ment : A confined volume of air stands over water,
as shown in Fig. 18. The beil-jar is fitted with cork,
bent glass tube, and indiarubber tube. On taking the
amount of air into the lungs by suction at the end
of the rubber until the water almost reaches the cork,
and then returning the air, the bell-jar space becomes
occupied by breathed air. On introducing a lighted
candle, the latter refuses to burn, showing that the
exhaled air is incapable of
supporting the combustion of
a candle. It is equally injuri-
ous to human life.

Suppose, now, that into
the exhaled air thus produced
a sprig of mint be introduced,
and the rubber tied in order
to prevent the entrance of
the pure air outside. If the
apparatus is left in ordinary
sunlight for a few days, it
will be found that a candle

... , . . Fig. 18.— Inhaling and exhaling air.

will continue to burn in the

enclosed air, as if this were pure. So if the air
had originally been vitiated by the burning of a
candle, the healthy growth of green plants in
the sunlight would have restored its vital proper-
ties. The carbon dioxide is withdrawn and utilised
by the plants which return oxygen to the air by
way of compensation ; and the oxygen returned is
exactly that which was contained in the carbon
dioxide — that is to say, it is the equivalent in
amount of the oxygen originally consumed in breath-
ing or in burning. It is well to ponder over this

THE STORY OF THE FIVE ELEMENTS

very remarkable fact. Coal, wood, petrol, coal-gas
are continually undergoing combustion and producing
carbon dioxide and water ; * animals are continually
breathing and producing the same gases ; and, we must
remember, one ton of coal produces at least three tons
of carbon dioxide. This vast accumulation of carbon
dioxide is, by a process exactly the reverse of that of
combustion — a process demanding energy in the form
of sunlight instead of yielding it in the form of heat
— gradually taken from the air and used as one of the
raw materials in the architecture of plants. Other-
wise the air would soon become entirely " dephlogis-
ticated " — unable to yield fires or support life. The
fate of the water that also passes into the air in large
quantities, it is needless — in Great Britain — to describe
in detail. We pass, therefore, to a brief considera-
tion of the nitrogen of the air, which is always apt to
be kept in the background by its more active but
much less plentiful companion.

XL — NITROGEN

Many substances are fond of oxygen or, in more
dignified language, have a strong chemical affinity for
that element ; such can readily be used to abstract the
oxygen from the air and leave the nitrogen. Thus,
air passed over hot copper loses its oxygen owing to
the formation of copper oxide ; the rest of the air,
chiefly nitrogen, can be collected with the pneu-
matic trough. Phosphorus burnt in a confined space
of air has the same effect as hot copper ; if the air has
been confined over water, the oxide of phosphorus

* Soot and smoke only when the combustion is incomplete and
unscientific.

NITROGEN

formed — a cloud of snowy fumes — quickly dissolves,
and leaves the nitrogen in the confined space free.
But probably the easiest way to collect a few jars
of the gas is a more indirect one. Some strong solu-
tion of sal-ammoniac (ammonium chloride) should be
poured upon a little sodium nitrite in a flask, fitted
like that used for the preparation of oxygen (p. 72).
On gently heating this mixture several jars of nitro-
gen can be quickly obtained.

Apparently the most noteworthy characteristic of
this gas is its masterly inactivity. It seems to prefer
to exist alone, and does not readily enter into com-
bination with other elements. It will, under compul-
sion, as it were, form compounds with hydrogen,
oxygen, and other substances, but for the most part
such compounds are easily decomposed; so that the
nitrogen becomes free. Most familiar, and many un-
familiar, explosives contain nitrogen, whose atoms
seem to confer upon the molecules into which they
enter a certain instability. Even the molecules of
living substance possibly owe their unstable character
to the exceptional amount of the unsociable nitrogen
they contain.

At ordinary temperatures nitrogen will extinguish a
burning candle ; with some difficulty magnesium may
be burnt in the gas, but all other ordinary com-
bustibles refuse to burn. Yet nitrogen is not abso-
lutely inert, like argon and its companions. At higher
temperatures it becomes decidedly more active ; under
the influence of a strong electric spark, for example,
it will enter into union with both oxygen and hydro-
gen. Still, its comparative sluggishness is, for animal
life, its most valuable property ; if the air were entirely

G 8l

THE STORY OF THE FIVE ELEMENTS

composed ot oxygen, all combustion would be five
times as rapid as it is, and life would be livelier,
indeed.

It has been said that nitrogen enters into the living
substance of animals and plants as one of the essential
elements. It follows, therefore, that it must form one
constituent of their food-stuffs. Our nitrogenous
food-stuffs, mainly derived from the animal world,
are members of a class of exceedingly complex bodies
called proteins. The animal economy does not rise
to the manufacture of proteins from simpler sources,
all that our digestive processes enable us to accom-
plish is the transformation of proteins into more use-
ful or more available kinds. The animal world is
therefore dependent upon the vegetable world for its
ultimate supply of the all-necessary proteins. It is
the plant alone that can manufacture proteins from
simpler materials.

What are these simpler materials ? The element
nitrogen must be obtained somehow. If a plant is cut
off entirely from all sources of nitrogen, it does not
make proteins — it dies of starvation. But the nitro-
gen in the air, vast as its quantity is, cannot be used
by the plant as such ; and so we have the ironical
position of the plant, growing in a great sea of nitro-
gen, vitally needing this nitrogen, and yet unable
to avail itself of it. Chemistry is now helping
the plant along lines which it is not difficult to
follow.

Manures and other fertilisers of the soil exist
mainly for the purpose of supplying plants with nitro-
gen in a suitable form. By its decay all animal and
vegetable refuse passes through a series of changes,

NITROGEN AND LIFE

aided by the air and by certain bacteria in the soil,
the final stage of which, so far as nitrogen is con-
cerned, is a nitrate.

Now, a nitrate is a compound containing nitrogen
in combination with much oxygen and a metal ; the
best -known is saltpetre or potassium nitrate (KNO3),
and it is in this form of nitrate that plants seem to
prefer their nitrogen. The effect of adding a nitrate
to the soil around growing plants is always to stimu-
late vitality, to increase the weight, and enhance
the healthy appearance of the crop. Hence the
problem before chemists is that of finding some
source of nitrate which shall be cheap and perma-
nent as well as efficient.

Nitrate of soda (NaN03) occurs in fair quantity
native in Chili ; but the demand for this is in-
creasing annually, and the supply is limited. Sir
William Crookes drew attention to the matter in
1898, and made us realise that, if a new source of
nitrates cannot be found, a shortage of wheat would
inevitably arise. Nitrogen the air contains in
abundance ; it is natural that we should look to
this inexhaustible store of the essential element as
the possible source of the nitrates of the future.
Can the nitrogen of the atmosphere be " fixed " in
nitrates by any workable process ? That is our
problem.

We have previously explained (p. 69) that, when
the nitrogen and oxygen of the air are submitted to
the action of strong electric sparks over water, the
two gases do combine ; the fact was known to Caven-
dish, and has been utilised for the preparation of
argon. The water is then found to contain nitric

THE STORY OF THE FIVE ELEMENTS

acid, which is easily converted into a nitrate by an
alkali. We thus have : —

Nitrogen -f Oxygen

-> — - + Alkali give Nitrate

Under electric spark

Why should not this process be attempted on a
large scale ? After several unsuccessful attempts a
factory has been started at Notodden in Norway
(1905) to manufacture a nitrate by the electric method,
the particular nitrate produced being calcium nitrate,
in which the alkali is lime. There is every present
indication that this product can compete, commer*
daily and scientifically, with the nitrate of soda that
had been in universal use. The method is that of
Cavendish, conducted on a tremendous scale and with
the most up-to-date electrical installation. A powerful
electric arc-light is produced which, situate between
the poles of a powerful magnet, is caused to rotate, and
is known as a " rotary arc." This arc is enclosed in a
fire-brick furnace and air is gently blown through the
flame by a Roots blower at the rate of about 75,000
litres a minute. On leaving the chamber the air con-
tains about i per cent, of a simple compound of nitro-
gen and oxygen, called nitric oxide (NO), and is at a
temperature of about 700° C. This gas is cooled by
being passed through steam boilers and by other
means, and is then led into " oxidisers " — chambers
which contain oxygen. Here the nitric oxide becomes
nitrogen peroxide (NO2) by simple combination with
more oxygen ; this peroxide is absorbed by milk of
lime, and the resulting liquid converted into solid
nitrate of lime by evaporation. Thus, a fact dis-
covered first in the course of a purely scientific re-

FIXATION OF NITROGEN

search is now the basis of a commercial process fraught
with possibilities of enormous benefit to mankind.

Another method of " fixing " the nitrogen of the
atmosphere for the use of plants is due to observations
made by Drs. Traube and Caro. Calcium carbide, which
is largely made nowadays for the purpose of obtain-
ing acetylene, when heated in nitrogen gas, absorbs
some of it and is converted into an unstable com-
pound known as calcium cyanamide (CaCN2). This
compound, when added to the soil, is decomposed
by the water it meets there, forming ammonia and
calcium carbonate. Both these substances are ser-
viceable to the soil, the latter by preventing it from
becoming acid and the ammonia by supplying the
" nutrient " nitrogen necessary to plants. The ammo-
nia is a compound of nitrogen and hydrogen (NH3),
and is readily made available for use by the plant by
the action of the soil itself. So that in this process also
it is nitrogen from the air that ultimately finds its way
to the plants ; in fact, in commerce it is by the dis-
tillation of liquid air that the nitrogen is obtained.
The calcium cyanamide (known commercially as
" nitrolim ") is produced by heating the carbide in
fireproof retorts to 800° C. and passing the nitrogen
distilled from liquid air over it. Its action towards
water may be thus represented :

CaCN2 + 3 H2O = CaCO3 + 2 NH3

Calcium Ammonia.

Carbonate

We have said that plants cannot use nitrogen as
such ; and this is true of green plants. But certain
bacteria which grow on the roots of some members of
the pea family (Leguminosae) seem to have the power
of making direct use of the nitrogen, incorporating

THE STORY OF THE FIVE ELEMENTS

it into living material and passing it on to the plants
upon which they grow. This additional source of
nitrogen is of great advantage to vetches, clover,
lucerne, etc., which yield a much more handsome crop
when the soil is infected with the bacteria. How the
bacteria accomplish their unique work is a secret
hidden at present from the insight of the chemist ; but
it is sufficient to show us once again that the nitrogen
of the air is not the inert and uninteresting gas that
we were at first inclined to name it. It is gradually
being compelled to contribute its part to the develop-
ment of living Nature.

Here it is profitable to pause and survey our posi-
tion. We have seen how air has been gradually brought
from the vague realm of shadows into the clear light
of science ; how it is no " element," but a mixture
ol gases of different and individual characteristics ;
how it has been shown to be as truly a material sub-
stance as wood or water ; how our more exact know-
ledge has been self-productive of still more knowledge ;
and how all this has in many ways enlarged our intellec-
tual vision and served our practical ends. The story
of the air element is, indeed, a magnificent object-lesson
in the methods of science. Laborious experimental
inquiries have in little more than a century dissipated
the philosophical mists which obscured the path of
truth during so many generations.

CHAPTER III

OTHER AIRS

I. — FIXED Am (CARBON DIOXIDE)

HALES, Black, Cavendish and Priestley were the
four great English pneumatic chemists of the eighteenth
century. With the researches of Cavendish and
Priestley we have already become, to some extent,
familiar, but Hales and Black we have as yet had
no occasion to mention. The merit of the former
consists, not in the preparation of any new substance,
nor in the propounding of any new theory, but in
pointing out the fact that many substances not hitherto
investigated contained locked in them certain airs.
He, however, in common with other investigators of
his time, connoted them all as air, recognising funda-
mentally no difference between them and ordinary
atmospheric air. Any investigation into their indi-
vidual nature and their difference from atmospheric
air did not appeal to him.

Black, on the other hand, snowed that one sub-
stance, magnesia alba (carbonate of magnesium), con-
tained, locked in its solid consistency, a gas, or " air/'
entirely different from atmospheric air ; and in 1755
he published his " Essay on Magnesia Alba/' Herein
he showed that a gas existed, different in properties
from atmospheric air, the gas being obtained by the
action of heat upon the substance. It was subsequently
obtained in a similar manner from other solid sub-
stances, and became recognised as a gas fixed in these

THE STORY OF THE FIVE ELEMENTS

bodies. Therefore the name " Fixed Air " was applied
to it, and it was thus learnt that all " airs " were not
made of the same stuff. As time advanced, still other
" airs " were discovered, and each was distinguished
by a name signifying either its source or some par-
ticular striking property of the gas. We shall briefly
outline the preparation and properties of these new
" airs," and show in some instances how their true
composition may be obtained.

To study the gas discovered by Black, let us imi-
tate him by heating a few of these carbonates we
have spoken of. An interesting one is copper car-
bonate, a green substance in the powdered condition.
If a little be heated in a dry test-tube, a visible change
is immediately noticed, the substance darkening in
colour. This change is accompanied by a change in
the composition of the substance ; and if the original
substance and the final product be each weighed, a
marked diminution in weight would be noted. Thus
some gas has escaped from the carbonate. If, during
the experiment, we had gently tilted our tube so that
the gas could be poured downwards, and placed a
tube containing clear lime water underneath, the lime
water would have become turbid when the gas came
into contact with it. Now, we have previously
shown that the gas obtained by burning carbon
in oxygen (carbon dioxide) possessed the property
of turning lime water milky ; hence these two gases
have at least one property in common. Further
comparison would show that the gases are identical,
and hence we find that the gas fixed in copper car-
bonate is really carbon dioxide. The black substance
left in our test-tube used for heating the carbonate

FIXED AIR

is called copper oxide. Somewhat similar results
would be obtained by heating the carbonates of lead,
zinc, and (at a higher temperature) naturally occurring
forms of calcium carbonate, such as marble, chalk, or
limestone. The gas would be evolved, and the oxides
of the metals would remain behind, colour changes in
some cases accompanying the decomposition.

If, again, these carbonates are separately treated
with dilute hydrochloric acid, in each case a brisk
effervescence occurs, and the gas, when subjected to
experiment, is again found to be carbon dioxide.
That the gas comes from the carbonate, and not from
the acid, may be seen when the loss in weight suffered
by one gram of the particular carbonate (say, marble)
when strongly heated is compared with the loss in
weight suffered by treatment with acid. In each
case the loss will be found to be the same.

The gas has also been mentioned as a product of
decay ; and it is also formed during alcoholic fermen-
tation ; indeed, some of the properties of the gas were
investigated by Priestley, who obtained his supply
from a brewery.

To study the properties of
the gas, we must provide some
easy means of preparation in
bulk, and the easiest way is to
decompose some carbonate with
dilute hydrochloric acid. For this
purpose an apparatus is prepared
as shown in Fig. 19 ; the flask
contains marble chippings covered
with water and hydrochloric acid
is poured down the funnel. As

Fig. 19.— The preparation
of carbon dioxide.

THE STORY OF THE FIVE ELEMENTS

the gas is evolved, it streams down the delivery
tube, and may be collected in the gas jar indicated.
It is a heavy gas, and its ascent in the jar may
be followed by introducing a lighted candle on a
deflagrating spoon. As it will not easily support
combustion, the candle is extinguished. A few of
the properties of this most interesting gas may
be studied when a few jars have been thus filled.
By pouring the gas downwards into a jar filled
with air, it displaces the air, and the jar ultimately
fills with carbon dioxide, as may be noticed when
a lighted candle is introduced. Thus it is heavier
than ordinary air. If a large glass vessel similar to
those used for the storing of gold fish be filled with
the gas, and a soap-bubble carefully dropped into it,
the bubble floats ; being full of air, it is buoyed up
by the heavier, but invisible, " air " in the vessel.

We have said that carbon dioxide does not sup-
port combustion, yet if some substance which is very
fond of oxygen be heated in the gas, that substance
may have the power of consuming the oxygen in it
and liberating the carbon. Such substances are potas-
sium and magnesium ; and if either of these metals

be heated strongly in a
stream of the gas, they
unite with the oxygen it
: contains. Magnesium may
be set alight in the air and
then plunged into carbon
dioxide, when it continues
to burn with difficulty ; and
potassium may be placed in
a hard glass tube (Fig. 20)
90

Fig. 20. — Potassium burning in
.carbon dioxide.

CARBON DIOXIDE

and heated by means of a Bunsen burner while the gas
is being passed. When a sufficiently high tempera-
ture has been attained to start union, the metal burns
with a beautiful violet flame ; potassium oxide and
black carbon are liberated.

Carbon dioxide is soluble in water. If a small
quantity of distilled water be tinted with blue litmus
and carbon dioxide passed into it, the solution turns
red, owing to the formation of an acid named car-
bonic acid (H2CO3). Its formation may be thus ex-
pressed in symbols : —

C02 + HaO = H2C03

dioxide + Watcr = Carbonic acid.

If this solution be now boiled, we note with aston-
ishment that the blue colour reappears, the water
evidently losing its acidic properties. Thus, carbonic
acid is a most unstable acid. It is very interesting
to note that water has the power of dissolving its
own volume of carbon dioxide, no matter what the
pressure of the latter. It is evident, therefore, that by
having the gas under great pressure a considerable
amount of it may be taken into solution by the water ;
but when the pressure is released the gas will, to a
great extent, escape. This is the principle used in the
manufacture of effervescing drinks ; soda water is
merely water highly charged with carbon dioxide, and
the properties of " fixed air " can be quite well exa-
mined in the gas that escapes from a bottle of soda-
water. It is of interest to note that a paper on this
subject marked the first of Priestley's contributions
to pneumatic chemistry (1772).

This air, fixed in combination with the oxides of
metals in the wide range of solid substances called

THE STORY OF THE FIVE ELEMENTS

carbonates, is thus shcxwn to be identical with the
gas breathed into the air during the respiration of
animals, during the processes of decay, and in the
act of combustion of coal, wood, petrol, coal-gas, and
other combustible substances containing carbon. It
is itself a compound, with the atoms of the solid
carbon incorporated within its molecules so firmly that
these molecules are difficult to break up. But it is
an air which must be taken from the atmosphere as
fast as it is sent into it ; and this it is the special
work of green plants to do. Ordinary air contains
normally about 4 parts in every 10,000 of carbon
dioxide ; when this proportion rises to 9 in 10,000
the air is injurious to health. And this small quan-
tity is all-important to plants as their first article of
diet. Under the influence of sufficient sunlight, the
chlorophyll, or green stuff of leaves, has the power to
decompose carbon dioxide, retaining the carbon for
the use of the plant and returning the oxygen into the
atmosphere. The carbon can easily be recognised in
an active leaf, because it is at once compounded with
water to form starch (C6H1005). This action is the
beginning of the plant's vital processes ; it is the
indispensable first step for the existence of life on
the earth. We cannot, therefore, exaggerate the
importance of Black's " fixed air " in nature ; but it
was not until the nineteenth century was well on
its way that the point just referred to was elucidated.

II. — INFLAMMABLE AIR (HYDROGEN)

When metals, such as zinc and iron, are treated
with dilute hydrochloric or sulphuric acid, an " air "
is evolved which has the property of inflammability,

INFLAMMABLE AIR

unlike any " air " we have as yet considered. It
can scarcely be questioned that the alchemists, during
their random gropings, had met with this " air " ;
yet the real discovery of it seems wrapped in obscurity.
Certain it is that Boyle encountered it ; and equally
certain that Cavendish established its chief proper-
ties, showing it to be, along with " fixed air," a gas
entirely different in nature from atmospheric air.

Cavendish obtained the gas by the solution in
dilute sulphuric acid or muriatic acid (hydrochloric
acid) of the metals zinc, iron, and tin. Believing, how-
ever, that these metals contained phlogiston (the in-
flammable principle), he naturally thought that the
acid turned the inflammable air out of the metals.
These he supposed to contain the gas locked in them
in a similar manner to that in which carbonates
contain their gas. We now know that zinc, iron,
and tin contain no gas, and that the gas Cavendish
obtained arose from the killing of the acid, the latter
yielding the inflammable air they contain under such
conditions, and losing their acidic properties at the
same time. We now call inflammable air hydrogen,
and it is known to be a constituent of all the com-
monly occurring acids.
It also exists in water
(p. 142).

To prepare the gas,
the method we have
briefly outlined is fol-
lowed. Zinc in a
granulated condition
is placed in the flask

(Fig. 21), COVered H(|< 2l.-APpar.t». for Prep.ring hydrogen.

THE STORY OF THE FIVE ELEMENTS

with water, and sulphuric or hydrochloric acid poured
down the thistle funnel. The dilute acid sets up a brisk
effervescence, and the ensuing gas may be collected
over water in the pneumatic trough. The gas is colour-
less, and on bringing the first jar collected near a light,
an explosion follows. The second jar, however, will be
found to contain a gas that burns quietly at the mouth
of the jar. This difference is evidently due to the
fact that the gas in the first jar was mixed with air,
which was ultimately cleared out of the flask by the
stream of hydrogen. Thus admixture with air causes
the explosion. Like ordinary coal-gas, pure hydrogen
burns quietly at the mouth of a tube or jar. The
gas in the air that promotes combustion is, as we
know, oxygen ; and the question may arise, does
hydrogen explode more violently when mixed with
oxygen than when mixed with air ? In order to test
this point we fill a stout soda-water bottle approximately
two-thirds with hydrogen and the remaining one-third
with oxygen ; if this mixture be presented to a flame,
it explodes violently, owing to the rapid union of the
two elements. So violent is the explosion that a
duster should be wrapped round the bottle to diminish
the danger from its possible bursting.

As we shall see in our chapter on water, the union
of hydrogen with oxygen is most fascinating, in con-
sequence of the production of pure water by the
combination, a matter which we must abstain from
discussing until then. We simply note now that if
a jar of pure hydrogen be ignited in the air, it burns
quietly at the mouth of the jar, only being capable of
combustion when the air is present ; but when the
air and the hydrogen are well mixed, the molecules of

COMBUSTION OF HYDROGEN

the various gases are in such close proximity that
the hydrogen molecules can burn all at once, giving
suddenly so much heat and producing such a sudden
change of volume that explosion results. The pure
gas may easily be burnt at a jet just as coal-gas may ;
but before applying a light at any such jet leading from
a hydrogen generator, a sample of the issuing gas should
be tested by collecting a little in a small test-tube
and presenting it to a flame. If the gas burns quietly,
the light may be brought to the jet ; but if explosion
occurs, it is safer to wait a short time.

The flame of hydrogen, although commonly spoken
of as pale blue, is really invisible when the gas is pure.
It quickly attains a yellow tint, however, but emits
no luminosity. It is intensely hot. Seeing
that hydrogen is a combustible body, the
question may be asked : Will it support com-
bustion ? If we collect a jar of the gas,
invert it, and gently push into it a lighted
candle on the end of a glass rod (Fig. 22),
the gas will be ignited at the mouth of the
jar, but the candle at the same time will
be extinguished. Thus the hydrogen does
not support the combustion of a candle. It
is interesting to note, however, that hy-
drogen supports the combustion of oxygen ;

not support
the combus-
tion of a
candle.

Fig. 22.—
Diagram
. r showing that

for if a jet of oxygen be introduced into hydrogen win
a jar of burning hydrogen, the oxygen will
be ignited and continue to burn. The flame
produced by thus burning oxygen in hydro-
gen (or vice versa) is intensely hot ; and the oxy-hy-
drogen flame thus obtained is used to supply the great
heat necessary to obtain the glow of the limelight.

THE STORY OF THE FIVE ELEMENTS

The great use of hydrogen to the chemist arises
from the fact that it is extremely fond of oxygen ;
and when substances such as oxides of metals are
roasted in a stream of hydrogen, the latter is cap-
able of abstracting the oxygen by uniting with it,
and thus leaving the metal in its pure condition.
Such a withdrawal of oxygen from oxides is a simple
case of what is called reduction ; and in countless
instances hydrogen is of great service to the chemist
as a reducing agent. We may recall the reader's atten-
tion, for example, to the reduction of rouge to metallic
iron mentioned at p. 77.

In addition to the foregoing interesting properties
of hydrogen, its extreme lightness renders it an attrac-
tive gas. Thus it may be poured upwards from one
jar to another ; it may be poured into a tumbler that
has been counterpoised in an inverted position on a
balance, when at once the tumbler is found to be lighter,
because the hydrogen has taken the place of the air
that was inside it. It may be siphoned upwards from
one jar to another ; and soap-bubbles blown with it
rise rapidly. On account of its extreme lightness it
is used in filling balloons. It is more than fourteen
times lighter than air.

III. — MARINE ACID AIR (HYDROGEN CHLORIDE)

Although " spirits of salt " (hydrochloric acid)
had been used for many years, it had not, until Priest-
ley's time, been recognised as containing a specific
" air " in solution. Examining the action of copper
upon spirits of salts, Priestley found an acid air
evolved, and subsequently found that it could be
obtained by merely warming the liquid. This gas

MARINE ACID AIR

he called marine acid air, and it was subsequently
made by the process still adopted : that of the action
of sulphuric acid (oil of vitriol) upon salt. The gas
is so interesting that we intend briefly to study the
method of its preparation
and investigate its pro-
perties.

To prepare the gas, the
apparatus shown in Fig.
23 may be used. Common
salt is placed in the flask
and sulphuric acid (about
2 volumes of strong acid
to i of water) poured
down the funnel. A great
effervescence at once oc-
curs : this afterwards sub-
sides ; but the application
of gentle heat is suffi-

tO produce a Steady Fig. 23.— The preparation of hydrogen

stream of the gas. This can

best be collected over mercury ; but as mercury is
expensive, we generally collect it as indicated, by
allowing it to displace the air in an open gas jar. The
gas is colourless, but forms abundant fumes in the air,
and possesses a sharp, penetrating smell. On placing
a lighted candle in the gas, the candle is extinguished :
it will not support combustion.

One of its most interesting properties is its extreme
solubility in water. Thus, if a jar containing the gas
be inverted, mouth downwards, in water, the water
rises to the top of the jar, indicating that all the gas
in the jar has passed into the water. The liquid
H 97

THE STORY OF THE FIVE ELEMENTS

formed turns blue litmus solution red ; hence it
belongs to the class of bodies we call acids. It is, in
fact, a solution of hydrochloric acid, commonly known
as spirits of salts.

Its extreme solubility may be shown by filling a
round-bottomed flask with the gas, and corking up
the flask with a rubber bung through
which passes a glass tube with a jet
at one end (Fig. 24). The other end
dips into water. On causing the
gas in :the flask to contract by
pouring over it a little ether, which
rapidly evaporates and produces
cold, the water enters the flask.
As soon as a few drops enter they
absorb the whole of the gas, and
thus produce a vacuum. More water
then enters as a fountain, and ulti-
mately fills the flask.

During the solution of this
" marine acid air " in water, a con-
siderable evolution of heat occurs.
Thus, if an air-thermometer be wretted with water and
placed in a jar of the gas, so much heat is produced
by the absorption of the gas that the liquid in the
tube shows a considerable rise. And if the gas be
passed for a long time through water a tremendous
absorption takes place, considerable heat is produced,
and a strong solution of hydrochloric acid obtained.

It may be instructive if we endeavour to find, by
adopting the experimental method, what this " marine
acid air " contains. Is it an element ? And if a
compound, what are its constituent elements ? In

.Fig. 24.— -Diagram illus-
(rating the solubility of
hydrogen chloride in
water.

HYDROCHLORIC ACID

the first place we may note, as Priestley did, that
a strong solution in water attacks iron filings most
violently, and that a considerable amount of hydrogen
is at the same time evolved. As we know that iron
has no such power of rapidly evolving hydrogen from
water, we must conclude that the gas has been obtained
from the " marine acid air." Hence it contains
hydrogen. All its properties, however, tell us that it
is not merely hydrogen ; hence some other substance
must be combined with the hydrogen. The question
naturally follows : How may we discover what this
other substance is ? and the answer is as readily
given : Take the hydrogen away. To do this means
that we must bring the " marine acid air " into con-
tact with some substance capable of taking away the
hydrogen. Now it happens that there are certain
substances that contain in their molecules oxygen
which may be looked upon as loosely attached. Thus,
in hydrogen peroxide (H2O2) we have in the molecule
two atoms of oxygen combined with two atoms of
hydrogen, whereas in stable chemical combination
one atom of oxygen is the maximum amount that two
atoms are capable of holding. The additional oxygen
atom present in hydrogen peroxide can therefore be
given up to substances which are capable of taking
oxygen, and these are then said to be oxidised. Can
we, we may ask, oxidise the hydrogen in " marine
acid air " by such a process ? We will try by using
for this purpose a convenient solid substance of the
same class as the hydrogen peroxide — namely man-
ganese peroxide, which occurs native in the mineral
pyrolusite. If a little of this black substance is placed in
a glass tube open at both ends and " marine acid air "

THE STORY OF THE FIVE ELEMENTS

passed over it, on warming the manganese peroxide in
the tube, a gas with a greenish colour will be seen
coming from the remote end of the tube ; and, on plac-
ing there a piece of moistened blue litmus paper, we find
that the gas no longer turns the blue litmus red, but
bleaches it. Thus a second gas is obtained from
" marine acid air," a gas of a greenish yellow colour,
which possesses the power of bleaching, and is
also entirely different in chemical properties from
the original " air." Hence the latter contains at least
two distinct gases, chemically combined ; and further
experiments have shown that these are its only con-
stituents. The greenish-yellow gas is called chlorine,
and thus we see that the acid air is a compound
of hydrogen and chlorine. For this reason it is now
referred to as hydrogen chloride ; its solution in
water is still universally known as hydrochloric acid,
or (by metal workers) as spirits of salts.

IV. — DEPHLOGISTICATED " MARINE ACID Am "
(CHLORINE)

A study of the properties and uses of the second
constituent of " marine acid air " must now be con-
sidered. Probably no gas has so interesting a history.
Its exact nature was the subject of much contro-
versy among many scientists of repute at the time
of its discovery; and almost all had different ideas
regarding it. It was very commonly held to contain
oxygen, but the most far-sighted thinkers perceived
its elementary character. The gas owed its discovery
to Scheele, a great Swedish chemist, who in 1774 dis-
covered it by heating together a mixture of marine
acid and braunstein, a native variety of manganese

100

CHLORINE

peroxide. Even when left in the cold, this mixture
gave off a wonderful green gas, fraught with many
astonishing properties, and Scheele, a thorough-going
follower of Stahl, and hence an ardent phlogistonisi;;
regarded it as the substance remaining when the
phlogiston had departed from the marine acid. By
many of its properties, Scheele had come to regard
braunstein as a dephlogisticator (a substance capable
of removing phlogiston), and interpreted the part it
played in this change by supposing that the phlogiston
was removed by it. This, as we know, is in the
main, what really does occur ; but Scheele's inter-
pretation is now stated in a different chemical lan-
guage. The braunstein does not take phlogiston
away, but supplies oxygen. Acting up to his theory,
Scheele named the gas dephlogisticated marine acid.
Subsequently Lavoisier and his French contem-
poraries, arguing that when substances become de-
phlogisticated they really become oxidised, called it
oxymuriatic acid (muriatic acid being another name
for spirits of salts). It was left, however, for Humphry
Davy to show the true nature of the substance. After
exhaustively studying the gas experimentally, he
came to the conclusion that it contained no oxygen,
and that the name oxymuriatic acid was there-
fore unsuitable. Further, he convinced himself that
the gas was simple in nature ; that all experiments
made with a view to decomposing it were failures ;
that, in short, it was an element. In 1810 he sug-
gested the name chlorine for the gas — a name which
was only adopted after some controversy. It is
still retained ; and, though certain facts tempt us to
doubt its elementary character, those facts do not

IOI

.THE STORY OF THE FIVE ELEMENTS

include any sign of its decomposition into simpler
elements.

'*,; To prepare the gas, we still adopt the method of
Scheele — that of wanning manganese peroxide with
-Hydrochloric acid. A little of the former substance is
placed in a flask and hydrochloric acid poured on it,
the apparatus used being similar to that in which we
made hydrogen chloride. As the gas collects in the
jar, it is found to have a greenish^ellow appear-
ance, not easily perceptible by gaslight, but easily
seen in daylight or by the light of burning magnesium.
It possesses a characteristic smell, and if taken in
quantity is poisonous. Even in small quantities it is
very irritating to the throat and nose. Its general
properties are most interesting. It shows no fondness
for oxygen ; indeed, it resembles oxygen in its very
strong partiality for hydrogen and for metals.

In a jar of chlorine a lighted candle may be
placed, when it will be observed that it continues to
burn with a very smoky flame, emitting dense, sooty
fumes of carbon, and producing at the same time
fuming clouds of hydrogen chloride. As these are the
only products formed, we see that candle wax con-
sists of carbon and hydrogen ; and that the chlorine
acts towards it very much as oxygen did.

A little powdered antimony, sprinkled in a jar of the
chlorine, burns spontaneously, forming a white sub-
stance called chloride of antimony ; and a thin leaf of
Dutch metal (an alloy of copper and zinc) also ignites
spontaneously in the gas. Thus it is a very active gas,
uniting with many metals vigorously without any ex-
ternal application of heat, and yielding chlorides. A jet
of hydrogen may be burned in chlorine gas, when fumes

CHARACTERS OF CHLORINE

of hydrogen chloride are again synthesised. If a
mixture of these gases in equal volumes is sealed up in
a glass bulb and exposed to direct sunlight, a vigorous
explosion occurs as the two gases unite. Hence
hydrogen and chlorine are proved to have a strong
affinity for each other.

One of the most useful properties of chlorine is its
power to bleach natural colouring matters and to strip
away the colours from ordinary dyed articles. If a
dyed piece of calico be placed in moist chlorine, the
latter oxidises the colouring matter, and produces a
colourless compound. The colour of ordinary writing ink
may similarly be removed from paper, and numerous
other substances can be decolorised by the chlorine.
It is of interest to note, however, that chlorine in a dry
condition, with a dry fabric, has but little activity ;
and is thus robbed of its bleaching properties. The
water is an essential factor in the bleaching action;
and it is supposed that the hydrogen in it unites with
the chlorine and that oxygen is thus liberated from
the water. Set free in this manner, right in the midst
of matter they can attack, the oxygen atoms have
not the opportunity to combine together and so form
oxygen molecules, but at once attack the unoxidised
substance with which the fabric is dyed, and bleach
it. Oxygen, or any element in this condition, is said
to be nascent, or fresh ; it is much more active in this
condition, because the oxygen molecules have not to
be split up as a preliminary to the activity of the
element. Thus the bleaching activity of chlorine
depends upon its fondness for hydrogen, and the
actual bleaching work is done by the nascent atoms
of oxygen.

103

THE STORY OF THE FIVE ELEMENTS

Chlorine as a bleaching agent is not universally
employed, on account of its great tendency, not only
to bleach, but to impoverish the fibre of the material
used. When it is used, however, the portable form
in which it is supplied is bleaching powder, or " chloride
of lime," made by passing chlorine into slaked lime.
The latter substance has the power of absorbing
chlorine, as may be seen by shaking a little with
chlorine in a gas jar, when the colour of the gas dis-
appears. Quicklime, on the other hand, does not
absorb chlorine.

Bleaching powder, which smells of chlorine, is
generally used in dilute aqueous solution, though often
it is mixed with sodium carbonate solution and filtered
from the precipitate that forms. The clear solution
then contains sodium hypochlorite, and this is much
used as a laundry agent.

If the lime is well incorporated with the water, and
the chlorine passed through the milky fluid while it is
hot, we do not obtain bleaching powder, but a solution
containing calcium chlorate, which is afterwards used
for the production of the well-known chlorate of
potash, which has no bleaching powers.

We may conclude our remarks upon this gas by
mentioning that it is now made industrially by pass-
ing strong currents of electricity through brine or
fused salt. In each case chlorine is produced along
with other products, and the method is cheap and
economical in those places where electric energy is
easily obtained. In this country, owing chiefly to
lack of water power and the high initial cost of coal,
electric energy is expensive ; consequently the old
method used by Scheele is still in vogue. For a few

104

USES OF CHLORINE

other industrial preparations that have been used in
this country, the student is referred to some higher
text-book on industrial chemistry.

V. — ALKALINE Am (AMMONIA)

Our tale of Priestley's researches on " airs " is
not yet ended, and once more we have to chronicle a
discovery made by this indefatigable worker. Judg-
ing from the fact that sal-ammoniac was well known
to the alchemists, we might have expected them to
have recognised this alkaline air ; especially when,
by heating sal-ammoniac with slaked lime, they had
really obtained it and passed it into water, forming for
themselves a solution with alkaline properties, which
they called the volatile spirit of sal-ammoniac. It was
from this liquid that Priestley obtained his first sample
of " alkaline air." Arguing from analogy with the
case of " marine acid air," he heated a little of the
volatile spirit in a phial by the flame of a candle.
He found a torrent of vapour to be discharged from
it, and he collected it over mercury. He afterwards
collected some of the air by heating the mixture of sal-
ammoniac and slaked lime. He named the gas " alka-
line air," because of its most striking property : it
restores the blue colour to reddened litmus, and is
able to neutralise acids — that is, destroy their acid
properties — and convert them into salts. The gas is
now known as ammonia, and the salts made by it
with the various acids are called ammonium com-
pounds.

In order to make the gas most conveniently, we still
use a mixture similar to Priestley's — i part of sal-
ammoniac with 3 parts of slaked lime. Being lighter

105

THE STORY OF THE FIVE ELEMENTS

than air, the ammonia formed must be collected by
upward displacement (Fig. 25). It has a characteristic
and very pungent odour, and when a jar full of the gas

is placed, mouth
downwards, in water,
the water almost in-
stantly rises to the
top of the jar, show-
ing that the whole of
the gas has been dis-
solved. It is, in fact,
extremely soluble in
water : one pint of
water will hold some-

Fig. 25. — Ap-
paratus for
preparing am-
monia.

thing like 1,150 times
as much ammonia gas in solution. Its solubility can
be demonstrated by the same striking method as we
described for hydrogen chloride (Fig. 24). The liquor
ammonia of commerce is a very strong solution of the
gas, with a specific gravity of 0-880 ; it is known to
chemists as ammonium hydroxide, and enters into the
composition of many cleansing agents.

Ammonia gas will not burn in air ; but if it is liber-
ally supplied with oxygen combustion takes place,
and the products of such combustion are found to be
nitrogen and water. Hence ammonia is a compound
" air," containing at least nitrogen and hydrogen (the
latter of which, of course, gave the water). That it con-
tains nothing else we may prove by attempting to
synthesise it from nitrogen and hydrogen alone. Under
the influence of powerful electric sparks, a very small
quantity of ammonia is produced — enough, however, to
show that it can be made from the two elements. It is,

106

ALKALINE AIR

however, much easier to decompose ammonia than
to make it up again. In presence of chlorine gas, the
ammonia gives up its hydrogen very readily, and
nitrogen alone is left. It cannot be said that ammonia
is a very unstable gas ; still, the atoms of nitrogen in
its molecules are easily liberated when any element,
like oxygen or chlorine, which is fond of hydrogen is
given its opportunity. Fairly simple experiments only
are required further to settle the proportion of the
two constituents and to give to the
alkaline air the formula NH3.

If a jar of ammonia be brought
into contact with a jar of hydrogen
chloride (Fig. 26), immediate com-
bination takes place. Dense white
clouds are formed, which settle as a
fine powder on the sides of the
jars, and are found on examination
to consist of sal-ammoniac, or
ammonium chloride. Thus the
function of the slaked lime in the
preparation of ammonia was the
withdrawal of the acid from the sal-
ammoniac, leaving the ammonia ~~ .

Fig. 26.— Illustrating the

free. Ammonia is a volatile alkali, combination of hydrogen

i *i i i t -i chloride and ammonia.

and can easily be removed from its
salts by any of the " fixed " alkalis, like lime, soda, or
potash. If ammonia be introduced into sulphuric acid
a violent combination, with great evolution of heat, fol-
lows ; and there results the sulphate of ammonia now
largely used as a manure. From this sulphate any
alkali will liberate the ammonia if gently heated with
it, just as lime sets the gas free from sal-ammoniac.

107

- Ammonia

THE STORY OF THE FIVE ELEMENTS

Ammonia is produced when many organic sub-
stances, such as horn, glue, etc., are subjected to
destructive distillation — that is, heated away from
communication with the open air. It is a com-
mon product of the decay of vegetation, and slowly
forms in stagnant urine, which accounts for its
common presence in stables. Much of the liquor
ammonia of commerce is obtained as a by-product
in the manufacture of coal-gas. Coal is sub-
mitted to destructive distillation in large retorts,
and ammonia is one of the vapours given off. These
vapours, during the process of purification, are led
through water, when the very soluble ammonia is
retained, along with a few other compounds. This
liquid is the liquor ammonia, and if heated with
lime it yields a copious supply of ammonia gas. Led
into dilute sulphuric or hydrochloric acid, the gas gives
the sulphate or chloride of ammonia. The latter sub-
stance finds a commercial use in electrical work as an
ingredient of many dry cells and of the Leclanche cell.

VI. — VITRIOLIC ACID Am (SULPHUR DIOXIDE)

Oil of vitriol was a liquid Priestley also subjected
to the action of heat with the object of testing whether
it would yield an air when thus treated. Mixing it
with olive oil, and subsequently heating, he collected
an air over mercury in a manner similar to that
adopted when collecting " marine acid air." Priest-
ley concluded that olive oil, being, as he put it, rich
in phlogiston, gave the latter to the vitriol ; and he
determined to try other substances which were simi-
larly rich in the inflammable principle. He accord-
ingly heated the vitriol with charcoal, and again

108

VITRIOLIC ACID AIR

obtained a supply of the same gas ; and finally, when
trying to disengage the air by the mere application of
heat to the acid, the mercury in his collecting vessel
accidentally sucked back into the hot acid, and a
tremendous evolution of the gas took place. This at
once opened up the whole field of the action of metals
upon vitriol, and it was found that if such metals as
copper, mercury, and zinc are heated with oil of vitriol
a gas with a suffocating odour is evolved — the gas
called by Priestley vitriolic acid air.

Let us endeavour to study a few of the properties
of this air. For a supply of the gas we might con-
veniently use the apparatus of Fig. 23, copper being
placed in the flask and sulphuric acid (oil of vitriol)
poured down the funnel. On the gentle application of
heat, the contents of the flask darken in colour (owing
to the formation of a compound of copper and sulphur,
Cu2S), and presently a brisk effervescence occurs.
The heavy gas collects in the gas- jar and may be
subsequently examined.

The new air has a choking smell, and may at once
be recognised as similar in this respect to the gas
obtained by burning sulphur in oxygen, previously
referred to as sulphur-oxygen-stuff or sulphur di-
oxide. If a jar containing the gas be inverted in
water, the gas is found to be very soluble, and to
change a solution of blue litmus red, exactly as
our sulphur dioxide did. If further accurate com-
parisons were made, this vitriolic acid air would
be found identical in all respects with sulphur di-
oxide ; hence this name is given to it. We have,
then, a new method for its preparation ; but it may
be at once said that the method invariably used for

109

THE STORY OF THE FIVE ELEMENTS

making sulphur dioxide in large quantity is that of
burning sulphur (or some compound of sulphur in
which the element is present in a combustible con-
dition) in a stream of air.

A solution of this gas in water is known as sul-
phurous acid, and it has a large application as a bleach-
ing agent. If the gas be led into solutions of the
alkalis potash or soda, salts known as sulphites are
obtained, which are sold as " sulphite liquors " for
bleaching purposes. Chemically speaking, both sul-
phur dioxide and the sulphites are good reducing
agents (p. 96) ; the gas is also a useful disinfectant,
and its solution a fairly powerful antiseptic.

Sulphur dioxide itself can easily be liquefied ; it is
sufficient to pass some of it through a tube immersed
in a mixture of ice and salt. The liquid sulphur dioxide
is indeed an article of commerce, and serves as a con-
venient supply for the gas when a large quantity of
it is required for experimental work.

We have previously seen that hydrogen gas is con
tained in sulphuric acid, since zinc is capable of dis-
placing it from the diluted acid. We now see that it
must also contain sulphur and oxygen, inasmuch as the
sulphur dioxide, which we have made from it, contains
these two elements. Other experiments that we
might make with the acid would fail to reveal the pre-
sence of any other element in it ; and we may safely
conclude that oil of vitriol is made up of hydrogen,
sulphur, and oxygen as its fundamental elements.
It is natural for the scientific mind now to seek a pro-
cess for the synthesis of sulphuric acid from these
three elements. If sulphur dioxide is dissolved in
water, however, we do not obtain sulphuric, but sul-

IIO

SULPHUR DIOXIDE

phurous, acid ; the sulphurous acid smells strongly
of burning sulphur (sulphur dioxide), but if left in
contact with the air gradually loses this or any smell ;
the oxygen of the air slowly oxidises it, in fact, into
dilute sulphuric acid. This may be carefully concen-
trated by evaporation, and pure oil of vitriol obtained.
We may represent the two steps of this action in
symbols, thus : —

SO2 -f H2O = H2S03 (Sulphurous Acid)
H2SO3 + O = H2SO4 (Sulphuric Acid)

We thus arrive at the principle of the method for
the manufacture of the acid which, on account of its
immense utility, Liebig described as the " key to
chemistry." Its manufacture is one of the largest
and most important chemical industries ; the student
will find it a most instructive lesson in applied che-
mistry, if he will consult in a larger work the methods
by which the principle we have outlined has become
practically operative.

From the airs that we have briefly studied in this
chapter, it will be easy to gather that the air-element
is as varied in its appearances and characteristics as
its companion " elements/' water and earth. Some
of the airs here dealt with must literally have stunk
in the nostrils of the early workers in chemistry, but,
hampered by ill-founded speculations, they failed to
recognise their individual differences. All airs or gases
— and there are hundreds known to us — are now
material stuffs, and not spirits. When this step
had been gained the course of science was cleared of
a great obstacle ; and the rush of discovery during
the time of Priestley, Lavoisier, andlscheele was the
consequence.

CHAPTER IV

FIRE

I. — SOME EARLY THEORIES AND SIMPLE EXPERIMENTS

FIRE raised man from the savage state and placed him
on the upward road to civilisation. Its obvious powers
we need not dwell upon here, except to ask what
man would be now if he could not work in metals
or stone, cook his food, and provide himself with arti-
ficial warmth. Little wonder that the myths of the
nations have their Prometheus, the fire-stealer, for
their first benefactor, giver of arts, intelligence, and
learning. From heaven, from the sun, it came ; but
how, except through a demi-god, a Titan defying a
jealous Zeus ?

But the Greeks advanced early from the ruts of
superstition, and inoculated the world with the germ
of science. What is Fire ? Surely it is one of the
fundamental formative essences — one of the primor-
dial elements ? It can scarcely be otherwise, in the
infancy of science. And the philosophical mind,
eager to reduce these four elements to one, the primi-
tive principle or Urstoff, whence all the others arise,
names, first, water, then air, later fire, as the finest,
irreducible first cause. It was Heraclitus (c. 535-
475 B.C.) who gave the honour to fire, mainly because
he saw that fire — by which he meant heat — was the
main cause of motion or change — the cardinal pheno-
menon of the universe. Heat the cause of motion !
The step is not a long one into the great physical dis-

112

FIRE

covery of the nineteenth century. Yet fire was not
regarded, any more than air, as a stuff, but as a principle
combining the properties of hotness and dryness. Ver-
biage like this crossed the dark ages and the middle
ages without criticism, though the root of the matter
was near at hand all the time.

Heat does not imply flame, though flame is always
accompanied by heat. We may have a substance hot
without being able to perceive it with the eye ; when
we can so perceive it, the substance is described as
incandescent. Incandescence is the consequence of
exceptionally intense heating, and always means a very
high temperature or degree of heat. We do not get
incandescence or flame without heat, so that our first
real inquiry concerning the fire-element must be
directed to the heat which is its basis.

First, what can heat do ? It can flow from one
body to another like a fluid, always from bodies at
a high temperature to others at a lower, until the
two temperatures are the same. It can set up motion,
as when we boil water. It can cause expansion. It
can travel from the sun or stars across empty space.
These and many other characteristics have been known
very many centuries. And further : it is old know-
ledge that heat is produced, i.e. becomes perceptible
in an increased degree, when certain chemical changes,
such as combustion, take place ; and that it always
arises from somewhere whenever there is friction.
When a savage obtains fire by rubbing two sticks
together ; when a schoolboy makes a brass button
painfully hot by rubbing it briskly on his coat ; when
the red-hot spark flies off the wheel of a railway
carriage when the brakes are sharply applied ; when

i 113

THE STORY OF THE FIVE ELEMENTS

a match is rubbed along a rough surface — these, and
many similar cases, remind us of the connection
between heat and friction.

Now, the salient point about friction is that it
always leads to the destruction of motion : in modern
language, energy disappears. Energy is a something
which bodies in motion possess, and by virtue of
which they are able to do work — to overcome resist-
ances, exert force, and communicate motion to other
bodies. If the speed of a train is reduced, it has less
energy than it had before. Now, is the energy lost
in friction really destroyed, or is it merely trans-
formed ? In other words, does the heat which is pro-
duced when motion is destroyed by friction represent
the energy that has disappeared ? That is to say : is
it energy ? Is heat a kind of motion ?

Think of two other simple experiments. Strike an
iron nail a few times sharply with a hammer. Does
it not become hot ? Whence comes the heat ?
Assuredly it must be the equivalent of the energy
which you have expended ; for, the more you hammer
the hotter the nail becomes. And again, take the
case of the fire syringe. This is an accurately bored
glass cylinder in which an air-tight piston can move ;
if a piece of phosphorus be placed at the bottom of it
and the piston pushed down, the phosphorus will
ignite. Again we are struck by the coincidence
that energy expended develops heat ; again we are
driven to the thought that energy and heat are but
different forms of one thing.

What is the alternative ? Heat may be a substance,
like air — it may be a real element ; and this idea was
prevalent among men of science in the eighteenth cen-

THE NATURE OF HEAT

tury. A hot body was held to possess a certain highly
subtle and penetrating fluid called caloric ; this could
move freely through the densest matter, and out of it
through the air into space or elsewhere. This caloric
is not so obnoxious to modern science as phlogiston,
because it was exceedingly difficult to decide by
experiment whether heat per se made any difference
to the weight of a body. But in cases of friction the
apparently limitless reservoir of caloric that must be
presupposed is an insuperable difficulty. This was
present to the mind of Count Rumford when he made
his decisive experiments in 1798. He bored a hollow
gun-metal cylinder with a steel borer, and found
that 837 grains (troy) of filings were produced ; but
that, during the operation, the temperature of the
barrel had risen to 70° F. Enough heat had been pro-
duced to raise 5 Ib. of ice-cold water up to the boiling-
point. " Is it possible," he asked, " that such a
quantity of heat . . . could have been furnished by
so inconsiderable a quantity of metallic dust merely
in consequence of a change in its capacity for heat ? "
The believers in caloric would have explained the
appearance of the heat by the supposition that the
powdered metal could not hold so much caloric as
the original solid, so that the caloric was, as it were,
squeezed out in the process of powdering. But even
this explanation cannot be applied to the experiment
in which Sir Humphry Davy melted large quantities
of ice by merely rubbing two pieces together.

We are, then, left with the theory that heat is a
form of energy ; and careful measurements by Joule
(begun in 1840) established beyond doubt that the
heat produced is in all cases proportional to the work

115

THE STORY OF THE FIVE ELEMENTS

wasted in producing it. Joule measured also the con-
nection between the two, and found that the energy
spent when i Ib. falls 772 feet would, if all turned
into heat, raise the temperature of i Ib. of water by
i° Fahrenheit. The converse process of turning heat
into motion is, we need not remind our readers,
carried out — imperfectly, it is true — in the steam
engine.

If the molecules of a hot body are conceived to
be in motion, we can explain all the facts known
about heat as a physical agent. The molecules may
be actually moving or merely in vibration, or both.
The vibrations of the molecules will be communicated
to the ether (Chapter VII.) surrounding them, and
carried off as waves. The waves which produce heat
only are longer and less rapid than those which produce
light ; but they are of the same nature. As waves
through the ether comes then the energy of the sun to
us. The sun's heat is one form of motion ; the waves in
the ether are another form. When these waves fall upon
any substance on the earth they may be absorbed and
transformed into heat again. Thus does our theory
of heat link itself up with other branches of physics,
and thus do we find further cause to admire the
intuition of the Greeks in contemplating their opinion
that Fire is motion.

II. — HEAT AND COMBUSTION
Let us now briefly reconnoitre our position. We
know by experiment that energy and heat are closely
related : that when energy is wasted heat is produced,
and in many instances the heat produced is sufficient
to cause the ignition and consequent burning of some

116

HEAT AND MOTION

particular substance. Now from our chapter on air
we know that burning is a chemical change, and the
energy we waste in the production of heat thus gives
rise to chemical energy. Where, we may ask, has this
energy its origin ? To answer this question, we must
take the reader once again to those coarse grains of
which matter is supposed to be built : those ultimate
molecules which are accountable in modern belief for
many kinds of phenomena. We have evidence that,
in the solid, liquid, and gaseous conditions of matter,
these molecules are possessed of motion. If an iron
ball be heated in a fire to a dull red heat and then re-
moved, no visible external signs on the ball may mani-
fest themselves ; but a little above it we may see the
quivering of objects, showing that the air has been
disturbed : it is in motion, and obviously has received
its energy by communication from the ball. If the
ball be made hotter, its molecules vibrate at a still
greater rate ; and the greater rapidity of the waves
they generate in the ether is revealed by an effect
on the retina of the eye : we perceive the ball in a
red-hot and finally white-hot condition. That in the
dull red, red and white-hot states it starts waves of
different length may also be beautifully shown by means
of the spectroscope, an instrument by the help of
which the wave-lengths may be compared. It is then
seen that these undulations, started by the vibration
of the molecules, are of long length when the ball is dull
red, but that as a white heat is obtained they are pro-
duced more and more quickly, finally ^ssuing at an un-
imaginable rate — something like 500 billions per
second. So thoroughly does theory adjust itself to
facts that we may safely conclude, in the words of

117

THE STORY OF THE FIVE ELEMENTS

Davy, that " heat is a mode of motion," and that the
motions of the molecules of a body may be revealed
by their heat effect.

Continuing our consideration of the iron ball, we
may imagine that the ball is made white-hot and then
plunged in oxygen gas. The heat energy possessed
by the iron now renders it capable of quick union
with the oxygen ; this is impossible in the air owing to
the diluted condition of the oxygen, the molecules of
the iron and oxygen not being in close enough proxi-
mity. This quick union shows itself in combustion ; the
iron commences to burn. In burning, we have a che-
mical change, and such changes involve atomic con-
siderations. On the one hand, we have atoms of iron
and atoms of oxygen, each possessed of energy. This
energy is of a complex nature. Some of it is doubt-
less due to motion or to vibration, but some of it is
also due to the nature of the atom itself. The atoms
have affinities — loves or hates, as Empedocles styled
them ; the atom of iron has a chemical attraction
for the atoms of oxygen, and this attraction, possibly
of an electrical character in its essence, is responsible
for their union into molecules when they can get into
one another's sphere of action. When the union
takes place, a substance, black oxide of iron, is pro-
duced, which possesses far less intrinsic energy than
the atoms forming it possessed when free or un-
combined. Hence the production of oxide of iron is
accompanied by a change in the energy of the system,
and it is this change in energy which results in the
liberation of a large amount of heat, this heat being
sufficient to keep up the combustion of the iron. The
change here in the energies of the constituent atoms

1x8

THE HEAT OF COMBUSTION

results in combustion, and is really a transformation
of atomic energy into heat.

In a similar manner, we may consider the burning
of carbon in oxygen. Both the atoms of carbon and
oxygen possess intrinsic energy, and the intrinsic
energy of carbon dioxide is less than the total intrinsic
energy contained in the atoms of carbon and oxygen
producing it. This excess energy is transformed into
heat during combustion, and sufficient heat is pro-
duced by completely burning I Ib. of wood charcoal
to carbon dioxide to raise the temperature of 80 Ib.
of water from freezing-point to boiling-point.

The consideration of many problems of combustion
such as these leads us to state that mechanical work
transformed into heat may raise the temperature of
some bodies sufficiently to ignite them. Combustion
is produced by such ignition, and during combustion
some of the intrinsic energy of the constituent atoms
of the reacting substances is converted into heat.
Thus first mechanical energy, and secondly chemical
energy, are transformed into heat.

In our chapter on air we had many instances of
combustion, but we must pause a few moments in our
consideration of this phenomenon. Combustion is
really chemical change accompanied by heat and
light, and too often is it assumed that only in air and
in oxygen can combustion take place. We have, how-
ever, many other instances where the chemical union
between two substances is so violent as to liberate
enough energy in the form of heat to start spontane-
ously the combustion of one of them. Thus a piece of
phosphorus, held in chlorine on a deflagrating spoon,
first melts and then fires, the combustion continuing

119

THE STORY OF THE FIVE ELEMENTS

until one of the reacting substances is exhausted. A
piece of dry phosphorus, placed by the side of a few
flakes of iodine, also bursts into flame. Powdered
antimony thrown in chlorine instantly flashes and
burns, and copper is at once ignited if thrown into
sulphur vapour. These are instances of combustion
where clearly oxygen plays no part ; and there are
many others. In our subsequent work, however, un-
less stated to the contrary, we shall consider combus-
tion as referring to the burning of substances in air,
i.e. in oxygen.

In observing the combustion of various substances,
equally various phenomena are observed. Thus char-
coal burns slowly in air, or smoulders, generally with-
out the emission of any flame. But when coals burn
flame is produced, and this is due to the production
of vaporous compounds of carbon and hydrogen,
which continue to burn and emit the flame. When
the hydrocarbons, as these compounds are called, have
been driven from the coal, the carbonaceous matter
that remains burns without any further flame-forma-
tion. In short, if the combustible solid substance does
not in any way yield a vapour, we shall find that no
flame is produced ; but if vapours are found, the com-
bustion is attended by flame. In all cases of flame for-
mation the combustible substance is first converted into
a gas or yields some vapour which is inflammable.

It will also be evident that the temperature of the
combustible body is an important consideration.
Some substances will ignite at a low temperature ;
others need to be strongly heated before visible burning
begins. The heat energy given to the combustible sub-
stances in a match-head by friction is sufficient to cause

120

FORMATION OF FLAME

ignition. The vapour of carbon disulphide may be
ignited by introducing into it a warm glass rod ; yet
carbon requires a very high temperature before it
can ignite. This temperature at which ignition takes
place is generally referred to as the ignition tempera-
ture of the substance. Nothing can more impressively
illustrate the mysterious character of the process of
chemical combination than the fact that, whereas
carbon and sulphur have a comparatively high ignition
temperature, the flashing-point of their compound
(CS2) is so dangerously low. The same oxides are
produced whether the atoms are burned singly or in
the compound form.

III.— PRODUCTION AND NATURE OF FLAME
It will be interesting now to consider in greater
detail the production of flames, as these are, gener-
ally speaking, the most noticeable attendants of the
process of combustion. They are, as we have said,
produced by the combustion of gases ; and it at once
follows that the conditions of any system of reacting
gases should be capable of being reversed. Thus, if
coal-gas unites with oxygen in air, and the combustion
of the coal-gas is due to union between these bodies,
then air should be capable of being burnt in coal-gas.
Similarly, a jet of oxygen should burn in hydrogen,
and chlorine should also burn in hydrogen. By lead-
ing a little chlorine through a jet and introducing the
jet into a jar of hydrogen — which has been ignited
at the mouth of the jar — the chlorine will continue to
burn, showing that the positions of combustible body
and supporter of combustion can be reversed. A
similar experiment may be conducted, using oxygen

121

THE STORY OF THE FIVE ELEMENTS

in place of chlorine ; the oxygen burns in the hydrogen
with a very hot flame as freely as the hydrogen itself
burns in oxygen. The following experiment may also
be performed to show that air is capable of burning
in coal-gas.

A lamp-glass chimney is provided with a cork at
its base, two tubes passing through
the cork as shown in Fig. 27.
At the top the chimney has a
sheet of asbestos placed over,
through which passes a straight
glass tube. By leading in coal-
gas through the right-angled tube,
and closing A, coal-gas may be
ignited in a few seconds' time at
B. If now the finger be released
a* A> the flame ascends the tube
B c and sits on the tube at c. Air
is now being dragged up B c, and
continues to burn as shown.
The excess of coal-gas may be
ignited at the end of A.

It was at one time thought that combustion imme-
diately antecedent to flame-formation started suddenly
at the ignition temperature of the gas, and that this
temperature must be attained before combustion can
take place. This, however, seems to imply that the
transformation is sudden ; but careful experiments
have shown that the transition from hot gas to flame
is gradual, not sudden. And, although an ignition
temperature must first be reached before full combus-
tion can proceed, the actual process is a very gradual
one, the heat effect as it gradually increases being

Coaf-gd$

Fig. 27. -Air burning in

coal-gas.

122

SLOW COMBUSTION

attended by certain changes immediately before igni-
tion takes place.

In some cases the preliminary effects of heat may
be noticed. If a little ether, for instance, be dropped
on to a hot plate in a dark room, it is seen to emit a
light, although it is not ignited. In short, it phos-
phoresces ; and only if it is raised to a higher tem-
perature does it burst into flame. The phosphores-
cence of the ether vapour precedes the ignition. The
vapour of turpentine and that of carbon disulphide
have also been obtained in a phosphorescent condi-
tion before yielding a true flame. In the case of one
substance, yellow phosphorus to wit, this phosphores-
cence is manifested at ordinary temperatures, owing
to the extremely low ignition temperature of phos-
phorus (about 44° C.) ; and common experience, in
the case of this substance, tells us that the phosphores-
cence is an effect immediately preceding combustion.
It is, in fact, a slow combustion of the substance ; but
the substance is in such a condition that it is losing
heat to its environment by conduction, etc., more
quickly than it is generating heat ; and full combus-
tion cannot take place. Immediately the production
of heat by the phosphorus-oxygen system is greater
than that lost by conduction, etc., the ignition tem-
perature is reached and full combustion begins and
proceeds. In many other instances it can be shown
that phosphorescence is antecedent to full combus-
tion, and probably in all instances of flame produc-
tion the combustible substance first passes through
the phosphorescent state. Thus then, if, by some means
— mechanical, chemical, electrical, or by heat — we can
supply a combustible with energy, we ultimately get

123

THE STORY OF THE FIVE ELEMENTS

it at a temperature when full combustion can take place.
If vaporisation takes place, or if the combustible body
is itself a gas, such combustion is attended by flame
formation ; flame is the final stage of a series of gradual
changes.

On closely observing the flame of an ordinary gas-
burner, or of a burning candle, it at once becomes
evident that the flame has a definite structure. In the
study of such structure, it will obviously be the sim-
plest method to commence with some simple flame,
and gradually work up to the more complex. Now, if
a flame is produced by the combustion of some simple
substance which can yield only one possible product
of combustion, we should expect such a flame to be of
the simplest type. Such, indeed, is the case. The
flames of hydrogen and carbon monoxide, where only
one product of combustion can possibly be produced,
are beautiful shells of blue ; although pure hydrogen
has a colourless flame, the gas is generally admixed
with some slight impurity, which imparts the tint.
Carbon monoxide (C 0) is really carbon imperfectly
oxidised ; given the opportunity, it will readily pass
into carbon dioxide, with the blue flame often seen
flickering above a very red coal fire. Now, in each of
these instances the burning substance is oxidised
straight away, the hydrogen to water and the carbon
monoxide to carbon dioxide. If, however, a more
complex compound, say cyanogen (C2N2), be burnt,
a gas which may be oxidised in two separate stages,
the flame obtained shows two cones very distinctly.
The inner cone is of a roseate or purple hue ; the
outer cone pale blue. When cyanogen burns in this
way, the carbon it contains can be supposed to burn

124

SIMPLE FLAMES

first to the halfway stage of oxidation, to carbon
monoxide, the nitrogen being simply liberated un-
changed. This change is accomplished in the inner
cone of the flame, and the carbon monoxide and nitro-
gen then pass to the outer cone, the former then burn-
ing more completely to produce carbon dioxide. The
blue outer cone is thus due to the carbon monoxide
burning in air to produce carbon dioxide. We thus
learn from this case the very important truth that
the two-coned structure of the flame is dependent
upon the fact that the oxidation can take place in two
stages.

We will now extend our considerations to the
flames of still more complex substances. Compounds
are known which contain only the two combustible
elements, carbon and hydrogen, and are called hydro-
carbons. Many of these, such as petroleum, marsh-
gas, etc., occur naturally, whilst some are produced by
destructively distilling certain natural substances rich
in carbon and hydrogen. Thus when coal is heated
out of contact with the air, as in the retorts of the gas
manufacturers, many volatile products are obtained,
chiefly hydrocarbons and free hydrogen. Of the
hydrocarbons, we may mention marsh-gas (CH4),
ethylene (C2H4), benzene (C(5HG), toluene (C7H8), and
naphthalene (C10H8). Of these, the marsh-gas and
ethylene, along with hydrogen and a little benzene
vapour, escape condensation when the volatile pro-
ducts are cooled, and pass along to gasometers, from
which they are supplied as coal-gas. Our common illu-
minating gas, then, may be looked upon as a mixture
of hydrogen with light hydrocarbons. The major
portion of the benzene, along with the toluene, naph-

125

THE STORY OF THE FIVE ELEMENTS

thalene, and other hydrocarbons, is condensed and
afterwards obtained by distillation from the tar.
The benzene and toluene are liquids ; naphthalene is
a solid. The hydrocarbons as a class can easily be
converted into vapour, and burn with characteristic
luminously sooty flames, the carbon in them burning
finally to carbon dioxide and the hydrogen to water.
Composed of such a substance is the wax of which
ordinary candles are made, and the products of the

Faint luminous
mantle

Yellow zone

Dark zone
Blue zone
Molten wax

Fig. 28.— Candle flame.

Fig. 29.— Conducting gases from
dark zone.

combustion of a candle are carbon dioxide and
water. This combustion, however, is not so simple
as the mere expression implies, and the study of the
flames of hydrocarbons, commencing with that of a
candle, is brimful of interest.

A burning candle shows wonderfully well the change
from solid to vapour undergone by a substance burn-
ing to produce flame. The heat supplied by the match
melts and vaporises a little wax, and this burns. The
heat produced melts the wax at the immediate base
of the flame, which then rises in the wick by capillary

126

THE CANDLE FLAME

attraction, is vaporised by the heat of the flame,
and afterwards takes fire. Careful observation of a
burning candle shows that the flame formed by the
combustion of the wax may be divided into four
portions and reference to Fig. 28 may serve somewhat
to make these portions clear.

We have the wick surrounded by a blue portion,
which gradually merges into a darker region ; and this
region, at about one-third the height of the flame,
shades off fairly abruptly into a yellow portion, the
region of greatest luminosity. A close observation also
reveals a faintly luminous mantle surmounting the
whole flame, although this is often missed in a casual
glance. It is quite natural to suppose, therefore, that
these different appearances arise from definite causes,
and it is our desire to find these causes for the varying
effects. Let us introduce one end of an open straight
glass tube into the dark portion (Fig. 29). If care be
exercised, a light may be obtained at the other end of
the tube ; combustion proceeds, showing that gases
still capable of being burnt exist in this portion of the
flame. In all probability, this dark portion is a zone
where no true combustion is proceeding, the hollow
space being filled by vapours formed by the mere effect
of heat upon the wax — gases whose combustible por-
tions will be burnt on their ascent up the flame.

Let us now examine the yellow or luminous por-
tion of the flame. On introducing into the flame a
piece of white porcelain, it is at once coated with soot,
which is really carbon in very fine powder. Hence on
momentarily cooling the luminous area of the flame,
carbon is deposited. It is now generally supposed that
the luminosity is due to particles of this carbon, dis-

127

THE STORY OF THE FIVE ELEMENTS

seminated in a free and hot condition in the flame.
They shine because they are very hot — so hot as to be
incandescent. It was suggested, some years ago, that
the luminosity was due to the vapours of dense hydro-
carbons in an incandescent state ; but we may take it
now as more likely that the incandescence of free par-
ticles of solid carbon is the cause of the brightness.
The question of the origin of this carbon is one which
has, from time to time, aroused most interesting con-
troversies among investigators. The simplest sug-
gestion is that the hydrocarbons decompose under the
action of the heat into carbon and hydrogen ; and,
relying upon this suggestion, it has been supposed, and
believed for many years, that the hydrogen in the
hydrocarbon obtains preferential treatment over the
carbon, the oxygen uniting with the hydrogen first and
producing an intensely hot flame, in which the par-
ticles of liberated carbon become incandescent.

This theory is, however, hard to reconcile with many
known facts. The gas methane (CH4) burns with a blue
flame, with little luminosity. Admixture with chlorine
greatly increases the luminosity of the flame by virtue
of the fact that chlorine is very fond of hydrogen.
Thus preferential treatment, as it were, occurs, and the
liberated carbon becomes incandescent in the flame
produced. But admixture of the methane with oxygen
(which we might expect to behave similarly to the
chlorine) has the reverse effect, even diminishing the
luminosity. Again, the hydrocarbon ethylene (C2H4),
when served with its own volume of oxygen and
exploded, has all the hydrogen it contains set free,
whilst all the carbon it contains is found to be burnt
(incompletely) to carbon monoxide.

128

LUMINOSITY OF FLAMES

These facts, we say, have been urged against the
theory that the hydrogen is preferentially burnt at
the expense of the carbon. Within recent years
certain compounds, intermediate between the hydro-
carbon and its final products of combustion, have been
shown to be produced by certain gradual stages of
union of the carbon, hydrogen, and oxygen ; and it
is probable that these in some way interact among
themselves and with the hydrocarbons to produce the
liberation of carbon. Any idea of preferential treat-
ment, either for the carbon or the hydrogen, has
had to be abandoned.

The blue region at the base of the candle flame
is probably due to the burning of carbon monoxide
and hydrogen, and hence is a zone beneath which par-
tial oxidation is proceeding ; whilst the faint lumin-
ous mantle surmounting the whole flame is the place
where, air being in greatest abundance, the carbon
monoxide, and any hydrogen and hydrocarbons, pass-
ing from the blue region, undergo complete combus-
tion. That the complex structure of a candle flame
is due to the possibility of partial combustion is cer-
tain, but precisely how the various gases are distri-
buted throughout the flame it would be hazardous at
present to say.

IV. — THE BUNSEN FLAME

A stream of coal-gas, issuing from the open end of
a glass tube, presents a flame very similar to that of
a candle ; but if a supply of air is fed into the flame,
the luminosity begins to decrease, and the greater
the amount the less the luminosity and the more
complete the combustion. As gas names are in great

J 129

THE STORY OF THE FIVE ELEMENTS

demand for heating purposes, and as luminosity in
such cases is an undoubted disadvantage, it was long
ago felt that a burner producing a good hot non-
flickering flame would be an advantage. The first
really successful one was due to Bunsen, and the
burner which bears his name has been adopted uni-
versally. The burner, as generally met with, has an
( iron base (Fig. 30 a), upon

which screws a cylin-
drical chimney b, con-
taining at the base two
holes, which are capable
of being closed or shut
by a ring slipping round
the tube. The gas
escapes through a fine
orifice in the base ; it
comes out under pres-
sure, and is ignited at
the top of the chimney.

holesatthe

air is dragged up

Fig. 30.-1. Bunsen burner. 2.Bun8en flame.

base are open, a current
the tube, and the coal-gas and air are so far mixed
that the gas can undergo more rapid and complete
combustion than before. Under these circumstances
the flame is non-luminous. If, however, the holes in
the base be partially or completely closed, the air is
shut off, and once more a luminous flame is produced,
the luminosity depending on the extent to which the
air-holes are closed. The burner used with the
Welsbach mantle is one of this type.

If one observes the non-luminous flame, it is easy
to see that two distinct cones are present. Lower a

130

NON-LUMINOUS FLAMES

piece of paper over the flame and quickly pull it away.
It will be found to be scorched where the flattened
outer cone has come in contact with it, but to be un-
affected where it met the inner cone, This gives us, as
it were, a section across the flame. The inner cone
evidently contains cool and unburnt gas, which is
afterwards consumed in the outer cone. A match head
may be held in the inner cone for some considerable
time without ignition, on account of its hollow nature ;
and on drawing out a sample of the gas in the inner
cone, and burning it at the end of a straight glass
tube, it will be found to be combustible.

When the air-holes at the base are open, the flame
generally burns quietly, revealing markedly its two-
coned structure. If, however, the air comes in a little
too rapidly, the flame " roars," and the conal portions
are even more distinctly developed. There seems, under
these conditions, to be a tendency on the part of the
inner cone to move in a downward direction. If now
we could still further increase the supply of air, what
would happen ? We may answer this by allowing the
supply of coal-gas to diminish, the air supply remain-
ing somewhat the same. We then ultimately arrive at
a condition where the air and coal-gas are mixed in
such proportions that quick union can occur between
them. In other words, we have an explosive mixture,
and this ignites all at once, producing an explosion
which passes down the tube at a rate depending on the
proportions of the constituents in the mixture. The
gas is then said to " suck back," which often happens
in the Welsbach burner if the light is applied too
soon. This phenomenon may be more completely
studied by burning a mixture of coal-gas and air at

THE STORY OF THE FIVE ELEMENTS

the end of a long glass tube. With a particular admix-
ture of air we may have the coal-gas burning with a
non-luminous flame. If the air current be then in-
creased, we ultimately arrive at the condition when
the air and coal-gas are in proportions favourable
to explosion, with the result that the flame travels
down the tube, and with care it can be induced to travel
so slowly that its velocity can easily be measured.
Hence admixture with air has greatly affected the
flame, and the experiment may with truth be said to
bear out Sir Humphry Davy's remark that " flame is
a tethered explosion."

If, in the glass tube referred to, we get at any
point a condition of stability, with the flame at rest
and, as it were, balanced in the tube, what would be
the cause ? For even when the mixture is explosive
by reason of its composition, the flame need not travel
down the tube ; it all depends on the rate of influx
of the explosive mixture, as compared with the rate
at which the explosion would pass down the tube. If
now the velocity of the ascending' current of coal-gas
and air at a particular place in the tube just overcomes
the descending flame produced by explosion at the
top, the flame will stop ; easily able to go thus far, it
can go no farther. Hence we should see a flame at
that point, in addition to the flame at the top of the
tube. The lower flame would then correspond to the
inner cone of a Bunsen burner, the outer flame to the
outer cone, and the space between would furnish us
with the inter-conal gases.

This interesting state of things may be obtained
experimentally in several ways. We may have the glass
tube constricted at some point A (Fig. 31). The air

132

DECOMPOSITION OF FLAMES

and gas are supposed mixed in an explosive state. On
applying a light at the top of the tube; the flame travels
downward till it reaches the constriction at A, and
there it burns with a steady cone
of blue flame. The effect of the
constriction is to increase the
speed of the uprushing gas at
that point, this increase produc-
ing an opposing current to that
of the explosive mixture too great
to allow the latter to progress
any further downwards.

The method adopted by Pro-
fessor Smithells in his beautiful
experiment is also illustrated in
Fig. 31. The Bunsen burner is
fitted to the glass tube by means
of a perforated cork, and a wider
outer tube slides over it, acting
as a sheath. A little asbestos at s
keeps the tubes coaxial. Quoting
from the paper in the " Journal
of the Chemical Society " for
March, 1892, we find that " if
the apparatus be arranged so that
the mouth of the inner tube is about 10 c.m. below
that of the outer one, and the gas be lighted, an
ordinary Bunsen flame is obtained at the mouth of
the latter. If, now, the gas supply be gradually dimin-
ished, the flame becomes smaller and the two-coned
structure more evident until the inner cone, having
become very small and very green in colour, shows a
tendency to enter the tube. As the gas supply is

'33

Fig. 31.— The two-coned
structure of flames.

[THE STORY OF THE FIVE ELEMENTS

further cut off, the inner cone will probably descend
and reascend a few centimetres, until finally it descends
as far as the orifice of the inner tube at c, on which it
will then suddenly settle and remain. This point is
equivalent to a constriction in the tube, and the con-
sequent increase in the velocity of ascending gases
determines the sudden arrest of the receding flames.
While this is going on a feeble flame, consisting of a
single hollow cone of pale lilac colour, remains at the
orifice of the outer tube F. The two conical areas are
thus widely separated, and the gases coming from the
lower one can be easily aspirated by introducing one
limb of a bent tube at F."

This separating apparatus also gives us the means
of analysing the inter-conal gases. These are found
to consist of carbon-monoxide, hydrogen, carbon
dioxide and water, with excess of nitrogen. Hence
the main chemical change in the inner cone consists
in the imperfect combustion of the hydrocarbons to
form carbon monoxide and water, with smaller quan-
tities of carbon dioxide and unoxidised hydrogen.
In the outer cone the unburnt gases are burnt, and
the oxidation is complete. It will thus appear that,
in the inner cone, owing to the limited supply of air,
we have imperfect combustion, both of the carbon
and of the hydrogen proceeding at once. There is no
preferential treatment of the hydrogen ; imper-
fect combustion of hydrogen simply means that some
of it remains unburnt, while imperfect combustion of
the carbon gives us a different oxide — carbon mon-
oxide, instead of the dioxide produced when it is fully
burnt.

Plate IV., which we owe to the courtesy of Professor
134

HYDROCARBON FLAMES

Smithells, illustrates beautifully the effect of increas-
ing the supply of coal-gas or of air to an ordinary
gas-flame. From a to d, we see the effect of increas-
ing the supply of gas ; from d to g we have the influ-
ence of an increased air-supply to the same flame.
Of course, the blue portions of the flame appear too
bright in the photographs because of their exception-
ally strong effect upon the plates ; nevertheless the
connection between the luminous zone and the supply
of gas is clear. The appearance of the special lumin-
ous zone in c and its disappearance in / should be
especially noted.

V. — FLAMES FOR LIGHT

The Bunsen flame is used entirely as a source of
heat. For many years the candle and ordinary coal-
gas flames served for lighting man's darkness ; but in
the advance of time we have had a corresponding
advance in science, and the science of lighting has
added its quota in the forward march. For many years
it has been known that three great factors influence
the luminosity of a flame : first, the density of the
flame gases ; secondly, their temperature ; and,
thirdly, the presence in the flame of some infusible
substance which, being rendered incandescent, con-
tinued to glow as the carbon particles glow in the
candle flame. The denser hydrocarbons yield more
luminous flames than the lighter ones when burnt
under similar conditions, and increased pressure upon
a combustible gas increases its luminosity. If, also,
a stream of combustible gas be burnt at the end of a
platinum tube, and the tube be then made red hot as
the gas is passing through, the increased luminosity is

THE STORY OF THE FIVE ELEMENTS

clearly seen. It is in the third factor, however, that
the chief advances along industrial lines have been
made. Welsbach, in pursuing investigations on certain
rare earths, thoria and ceria, found that their infusible
nature rendered them incandescent when subjected to
a high flame temperature, and that the incandescence
contained a larger proportion of light-waves than is
usual. Adapting this knowledge in practice, he
prepared his well-known mantle to surround the
flame of a Bunsen burner. This mantle consists
merely of a framework of some fabric dipped in
" milk of thoria," to which is added a little " milk of
ceria." The framework is then dried, and a film of the
oxides is deposited all round. On placing in position
for use, the fabric is first burnt away, leaving the
thin film of oxide, which, being made incandescent by
suspension over the flame of the Bunsen burner,
emits the beautiful white light known as the incan-
descent light. It seems to be the small percentage of
ceria used that is responsible for the brilliant light
effect.

In incandescent lights a substance, white hot,
emits the light ; consequently the incandescent body
must be given a considerable amount of heat to main-
tain it at a glowing temperature. Hence, although
such lights may be used for illuminating purposes, they
nevertheless are not of maximum efficiency owing to
the large amount of heat given out along with the
light. For light production, therefore, it seems hardly
sound to do as we are doing at the present day with
gas ; namely, to waste a considerable amount of its
energy of combustion as heat. There are some lights,
however, that are produced without heat, although

136

THE INCANDESCENT LIGHT

such lights are not, unfortunately, producible in prac-
tice. Substances like calcium sulphide, for instance,
after exposure to the sun's rays, have the power of
absorbing a certain amount of solar energy, by virtue
of which they possess the property of glowing in the
dark and of emitting light without heat. Such glow-
ing bodies are said to be luminescent, as distinct from
incandescent ; and a light -producing body, giving
light by luminescence only, converting some form of
energy into light without heat, is badly wanted. The
mercury vapour lamp partly fulfils this purpose, con-
verting electrical energy into light, and we may hope
it is but the precursor of better things in the future.

VI. — ULTIMATE NATURE OF THE FIRE ELEMENT
In our brief glance at the properties of fire and
flame we thus leave many mysteries unsolved, enchant-
ing and tantalising. Have we not indicated that the
old fire-element does indeed open to us a thousand
avenues of knowledge and thought ? We have shown
some of the probes which have exposed the ignorance
of the past and revealed the truth of the present ;
yet much remains also for the future. We have not
penetrated quite to the root of the matter.

Heraclitus, we remember, claimed that fire was
the beginning of motion, and that this motion was
the cause of the endless metamorphoses which are
the chief acts in the great spectacle of the universe.
And when we remember what fire is, what a remark-
able intuition was this of the old philosopher ! We
see an electric tramcar speeding along the streets :
what is its motion but fire transformed ? It begins
with the combustion of coal ; the heat generated thus

THE STORY OF THE FIVE ELEMENTS

causes water to boil and expand into steam ; this ex-
pansion drives the machinery which in its turn drives
the dynamo, and this sets free the electrical energy
which, transformed again, appears in the motion of
the car. But the fire itself is not in existence ab initio.
It is not as such locked up in the coal. It is, > we
have previously explained, itself but a transLrma-
tion of the energy inherent in the atoms of the coal
and of the oxygen in which it is burned. So that we
have to consider fire and change to spring from what
is called the intra-atomic energy of the atoms of matter.
That the atoms of coal derived some at least of their
energy from the sun does not solve the difficulty
which confronts us now that we have reached the
ultimate roots of speculation on this question. For we
have still to ask for the origin of the stupendous amount
of atomic energy that exists in the sun. Fire, whether
we mean by it incandescence or flame, is but the evi-
dence of a transformation — its concomitant but not
its cause. Fire is a motion transmuted from ante-
cedent motion ; and when we inquire whence arose
this motion that is locked up in such inconceivable
quantities in the atoms we are groping among the
" first Causes," the prima philosophia which lies beyond
the ken of science.

'3*

CHAPTER V

WATER

I. — EARLY VIEWS ABOUT WATER

" WATER — water everywhere ! " might well be the
exclamation of the ancient mariner of Nature who
would explore the inner secrets of the composition of
the earth. We look around us and see it in river, lake
or sea ; look above and read it in the clouds, in mists
and in rain. We can watch it disappear and reappear ;
put on the invisible garb of vapour, and clothe itself
in the palpable form of mist ; evaporate, and condense
again according to circumstances. The countless
metamorphoses of the clouds are matched by the
subtle beauty of the snowflake and the grandeur of
the glacier ; and little more need be said to empha-
sise the value of water as a contributor to the varied
beauties of Nature. Without it our skies would be ail
intolerable glare of unbroken light, and the earth itself
a monotonous and lifeless desert.

Its universality must strike the least observant of
us. It is literally everywhere ; and even where it is
not now seen, there is evidence that it once spread as
a sea over our present continents, whose rocks bear
within them the unmistakable sign-manual of their
aqueous origin. The dry land rose from the bosom of
the deep, carrying with it the remains of the living
millions which once flourished there. Water is indeed
a necessity of life, and doubtless the earliest organisms
had their home in it. Thus in the present, as in the

139

THE STORY OF THE FIVE ELEMENTS

past, water is a substance which is essential to the
system of Nature as we see it — to its skies and storms
and seas, to its land and its life.

And the uses which man must make of it give it
still further claim to our attention. To enumerate them
would be impossible ; they enter every phase of our
daily life. It cleanses our homes, our cities, and our-
selves ; it is food for man, beast and plant ; even our
solid foods contain very much water. Through its
transformation into steam it drives our machinery ; in
falling streams it supplies energy to innumerable mill-
wheels ; while it bears across its ocean depths the
Dreadnoughts and Mauretanias which make the future
of the nations. To deal well with one aspect of this
fascinating element would require a large volume —
much larger than any man could write. It is not re-
markable that, from the very earliest times, the
thoughtful philosopher should have pondered over its
nature and wrought theories of its meaning.

In the dawning days of Greek philosophy, when
men first strove to interpret the universe in the light
of certain fundamental " causes," Thales, a pioneer of
the Ionian school in the sixth century B.C., found the
first Cause of all things in water. Wrapped, as it were,
like an envelope round the land, the latter peeping
through here and there, and breaking the unending
expanse, water was naturally regarded as the birth-
place and original source of the land. This notion
seemed to be supported by the fact that water was
found by digging in the earth ; and, as water came
from the clouds to fertilise the land and cause man's
food to spring therefrom, it is easy to understand how
the untrained, but still thoughtful, mind came to

140

THE LIQUID ELEMENT

regard water as ike element — the great Invariable out
of which sprang the many Variables met with in
Nature. Water became to Thales what air was sub-
sequently in the speculations of Anaximenes — the
First Cause, the life-giver, the ultimate basis of the
material universe.

But as philosophy expanded and knowledge grew,
this place of honour was seen to be unsuitable, and
water became the liquid element par excellence. It
was regarded as the chief property of those sub-
stances which existed or could exist in the liquid form.
Substances like sulphur, gold, or metals generally,
which became liquid under suitable treatment, were
held to contain water ; that is to say, in modern lan-
guage, they possessed the property which water was
held to have in its unmixed form. Water conferred the
liquid character upon earthy things, just as air con-
ferred the gaseous character. In this way water
came to be regarded as one of the four elements,
and took its place alongside air, fire and earth as one
of the four properties which by their interaction gave
birth to the many things of the universe.

For many centuries this view prevailed ; and even
after Boyle had given to the word " element " its true
meaning, water was considered to be still one of the
simple stuffs ; out of water, no one expected that any-
thing but water would ever be obtained. The fate,
however, that attended the similar views held about
air fell also upon the water. Its reign as an element
lasted only a little longer than that of air, and in fact
ended during the period that the air was receiving
systematic examination. While engaged in his re-
searches on the air, Cavendish was led to explode

141

THE STORY OF THE FIVE ELEMENTS

hydrogen gas with air in a specially constructed eudio-
meter, expecting that the hydrogen would phlogis-
ticate the air, i.e. rid it of the oxygen it contained.
Whenever he performed this experiment he found that
a dew was produced ; and although for a time he be-
lieved this dew to be nitric acid, he finally demon-
strated it to be water. Cavendish's own account of
the matter is brimful of interest ; it shows his observa-
tion of the dew and the inference he drew from it. His
mind was critical and scientific ; though hampered
by a fallacious theory of combustion, his observation
and his explanation were alike accurate and acute ;
and he pointed out the nature of the further experi-
mental work needed before the belief that the dew
was in reality water could be accepted.

" From the fourth experiment it appears that
433 measures of inflammable air are nearly sufficient
to phlogisticate completely 1,000 of common air ; and
that the bulk of air remaining after explosion is then
very little more than four-fifths of the common air
employed ; so that as common air cannot be reduced
to a much less bulk than that by any known method
of phlogistication, we may safely conclude that when
they are mixed in this proportion and exploded, almost
all the inflammable air, and about one-fifth part of
common air, lose their elasticity, and are converted
into the dew which lines the glass/'

Hence hydrogen and oxygen disappeared to form
the dew. But what was this dew ? Cavendish, as we
have stated, thought it at first to be nitric acid ; but
experiment dispossessed him of this belief. He obtained
more of the dew by burning " 500,000 grain measures
of inflammable air in 2| times that quantity of ordinary

142

EXPERIMENT OF CAVENDISH

air, and collected 135 grains of the dew." He found
that it had neither taste nor smell ; it yielded no
residue on evaporation ; nor did it give any offensive
or pungent smell during the process. In short, " it
seemed pure water."

It was thus that Cavendish, in 1781, gave to the
world the true composition of water. Its position
among the elements had to be abandoned ; and we
hope to show in the present chapter how a fuller
chemical knowledge has merely served to confirm the
views of the original investigator.

II.— THE EFFECT OF WATER ON METALS

The rusting of iron or steel objects is one of the
most familiar of everyday phenomena, and everyone
knows that the rusting process is facilitated by, if not
actually dependent upon, the presence of moisture.
Iron utensils, if they are to be preserved for any
length of time, must be kept in a dry condition and
in a dry place. Now iron-rust, in its final condi-
tion, is essentially an oxide of iron — that is to say,
a compound of iron and oxygen. A more thorough
examination shows that the oxide of iron exists
in rust in the form of a compound with water,
forming a hydrated oxide, to which the formula
Fe2O3.H2O is generally given. The rusting of iron,
therefore, takes place in two steps : first, the iron is
oxidised by combination with oxygen ; secondly, we
have the more complicated hydrated oxide formed.
Water is evidently essential to the second step ; it
may fairly become a subject of inquiry whether it
also enters into the first. And if water is what Caven-
dish supposed it — a compound of hydrogen and oxy-

143

THE STORY OF THE FIVE ELEMENTS

gen — it is clear that the necessary oxygen is present
in it and that iron may be completely rusted by it.
The possibility is the fact ; at ordinary temperatures
iron has the power of slowly abstracting oxygen from
water and becoming rusty. It is interesting, how-
ever, to notice that this statement is not in the strict-
est sense truthful, because in absolutely pure water
iron may be kept for a very long time without show-
ing the least tendency to rust. The commencement
of the rusting seems to be dependent on the
presence of a trace of carbon dioxide in the water, a
carbonate of iron being first formed. This is converted
into the hydrated oxide by the joint action of air
and water. Chemists are not unanimous about the
exact mechanism of the process ; but, whatever this
may be, the essential facts are the formation of the oxide
and that water yields some of the oxygen needed.

If, now, iron is found slowly to abstract oxygen
from water at ordinary temperatures, will it abstract
it more quickly if the temperature is raised ? In
numerous cases we have evidence to show that an
elevated temperature of the reacting bodies promotes
chemical change. Let us then raise water to its boil-
ing point and pass steam over red-hot iron. A suit-
able apparatus to use is shown in Fig. 32. The iron
(preferably iron tacks) is loosely packed in the iron tube
A, which is heated in a furnace or by several Bunsen
burners, and steam passed over from the boiling
water in the flask B. If the end of the delivery tube
be placed under the bee-hive shelf in the pneumatic
trough, bubbles of gas may be collected in the jar as
shown. On examining the gas it will be found to burn
easily, to be very light, and not to support the com-

144

EFFECT OF WATER ON IRON

bustion of a candle. In short, the gas has all the pro-
perties of hydrogen. It is evident, therefore, that
when oxygen is absorbed from steam by red-hot iron,

Fig. 32. — Decomposition of steam by red-hot iron.

hydrogen gas is formed. The oxide of iron produced
may be noticed on the surface of the tacks on their
removal from the furnace ;
but in this case the com-
pound formed varies slightly
in composition from the pre-
vious iron rust ; it is a dif-
ferent oxide of iron, with
rather less oxygen than the
latter contains. The action
of iron on water, therefore,
serves to show us the com-
pound nature of the water.

Iron is not the only me-
tal which has the power of
decomposing steam. Magne-
sium, a metal which burns with a brilliant flame when
heated in presence of oxygen, may also be used by
slightly varying the conditions of the experiment. The
metal is placed in the glass tube A (Fig. 33), and steam

K 145

Fig. 33.— Decomposition of steam
by magnesium.

THE STORY OF THE FIVE ELEMENTS

is blown over as the metal is being strongly heated.
So energetically does magnesium decompose the steam
that it burns brilliantly and the issuing gas may be
ignited. This is a beautiful experiment, as the com-
bustion of the magnesium in the steam is little less
bright than its combustion in the air.

Far more vigorous, however, in their actions on
water are the metals potassium, sodium, and calcium.
Even at ordinary temperatures these metals possess
the power of abstracting the oxygen and turning out
the hydrogen from water. If a small piece of the former
metal be thrown upon water a most vigorous reaction
ensues, the metal uniting with the oxygen so vio-
lently that sufficient heat is produced to ignite the
liberated hydrogen ; and the latter burns, the colour
of the flame being violet, owing to the vapour of
potassium disseminated through it. During the re-
action white fumes of oxide of potassium may be
observed rising from the water, but the greater por-
tion of these dissolves in the water and confers upon
it a soapy feel. If a little red litmus solution be added
to the water, the solution is turned blue, as the water
now possesses the properties of an alkali. It is a solu-
tion of potassium hydroxide, more commonly known
as caustic potash.

If a fragment of sodium be thrown upon water,
the reaction is less violent than in the case of potas-
sium ; and in this instance the liberated hydrogen
does not burn, because a temperature high enough to
ignite it is not produced. Hence, if due caution is mani-
fested, a little of the gas may be collected. For this
purpose a piece of stout wire should be bent in a large
loop at the lower end and a piece of wire gauze wrapped

146

EFFECT OF WATER ON METALS

Gauze brap

Sodium

Fig. 34.— Decomposition of water by
sodium.

round it, the gauze being a little larger than the loop
and the overlapping portion being bent underneath.
This is to serve as a " trap " for the sodium. If a frag-
ment of the latter be placed on the water and the
gauze gently lowered
over it, a growling noise
is heard, and the collect-
ed gas bubbles through
the meshes of the gauze
into the jar above (Fig.
34). The process may
be repeated with very
small pieces of sodium,
and the gas finally tested.

It is hydrogen. The liquid again has alkaline pro-
perties ; the sodium oxide produced by the union of
the sodium and oxygen dissolves in the water, form-
ing a solution of sodium hydroxide or caustic soda.
The indiscriminate use of these metals, however, is
attended with some danger, and numerous explosions
have followed their rash use. Hence they should
only be used by the reader if he is under the guidance
of a qualified teacher.

A safe metal to use is calcium, now cheap and
easily obtained. If a few small pieces be placed in
a flask containing a little water, hydrogen is gently
evolved, and in a few minutes a jar full of gas may be
collected (Fig. 35). This is probably the easiest method
of procuring hydrogen by the decomposition of water.
The water in the flask has once more alkaline pro-
perties, containing as it does a solution of calcium
hydroxide, which we shall later see to be merely an
accurate name for slaked lime. If, however, much

THE STORY OF THE FIVE ELEMENTS

calcium be used, a heavy white precipitate of calcium
hydroxide, i.e. slaked lime, begins to make its appear-
ance : the experiment furnishes a beautiful example of
chemical change, a shining metal and water produc-
ing an inflammable gas
and a copious deposit,
or precipitate, of a white
solid.

Five metals have thus
been separately used to
decompose water. But
no chemical change is so
simple as it seems at
first sight, and it is note-

D*=.

Fig. 35.— Decomposition of water by

worthy that whereas iron

and magnesium possess the power of completely de-
composing water, potassium, sodium and calcium can
only partially do so. Let us, therefore, push our
experimental work a little further.

If pieces of sodium be gradually added to water
in a small porcelain basin, we arrive at a point when
the action of the metal seems to be retarded, the
retardation being accompanied by the formation of
a thick syrupy liquid. Finally, the sodium refuses to
react, and we have then in the basin a semi-solid
mass of sodium hydroxide, which is strongly caustic.
If this be dissolved in some more water and a piece
of aluminium foil added, the whole being then
gently heated, a great effervescence occurs, and con-
siderable quantities of gas may be collected, which
gas is on examination found to be hydrogen. Now
water and aluminium do not yield hydrogen when
boiled ; hence the water used to dissolve the sodium

148

HYDROGEN FROM WATER

hydroxide has not yielded the hydrogen obtained
in our experiment. It must, therefore, have come
from the sodium hydroxide, showing that the latter
still retained hydrogen from the original water —
hydrogen which the sodium was incapable of turning
out. Thus the hydrogen in water is displaceable in
two steps, and accurate measurements would show
that the volume of gas first evolved by the action of
the sodium is equal to that evolved by the subsequent
action of the aluminium. At each step, therefore,
equal amounts of hydrogen are displaced. Assuming
now we could start with one molecule of water, we
could divide its hydrogen into two portions, but never
into more than two. We may, therefore, say that the
molecule yields two atoms of hydrogen, and thus
contains two. Similar changes would occur if we
used potassium or calcium, and it may be inferred
from our action of metals on water that the latter
contains hydrogen and oxygen, and that it contains
to its molecule two atoms of the former gas.

III. — THE COMPOSITION OF WATER BY WEIGHT

Seeing that we have found the nature of the sub-
stances which go to make up the compound water,
can we not now arrive at some method whereby the
water may be accurately synthesised and the quanti-
ties of the reacting substances weighed carefully ?
This would make the general knowledge that we have
obtained exact and accurate ; synthesis will clinch
the results of analysis.

To accomplish this, it is obvious that we must
have some substance capable of yielding us oxygen,
and must have our hydrogen in a very pure condi-

THE STORY OF THE FIVE ELEMENTS

tion. Now we have previously found that hydrogen
is a good reducing agent (i.e. it possesses the power
of abstracting oxygen from certain substances), and
we can suitably make use of this property. A con-
venient material for reduction is copper oxide, the
black substance formed by roasting copper in the air or
in oxygen. Some of this compound, in a dry con-
dition, is placed in a bulb tube A (Plate 5) and very
accurately weighed. Hydrogen gas, made by pour-
ing dilute sulphuric acid upon zinc, is generated in a
flask B, purified and dried by passing through tubes
containing lead nitrate and calcium chloride respec-
tively. At the farther end of A is a small flask, and
attached to it we have a calcium chloride tube. The
flask and calcium chloride tube we will call c. These
are also carefully weighed. The tubes are then joined
together and hydrogen allowed to sweep out all the air
until a sample collected at the end of the apparatus
burns quietly. The copper oxide is then heated, and as
the hydrogen continues to pass it abstracts oxygen from
the oxide to form water, most of which condenses in
the flask, the remainder being absorbed by the calcium
chloride tube. Meanwhile the copper oxide continues
to glow. After continuing the action for a few minutes,
the flame is removed and the apparatus allowed to
cool, while the current of hydrogen is still being passed
through. When cold, we detach and re-weigh A and
c. The loss in weight of A gives us the oxygen which
has departed ; the increase in weight in c gives the
water formed.

Hence the amount of hydrogen is got by sub-
tracting the weight of oxygen from the weight of
water produced. In this manner the percentage

150

COMPOSITION OF WATER

zoo parts of water contain {£

composition may be found ; and, in rough numbers,
accurate for our purpose, we find that —

« ^ of

Using much more elaborate apparatus, yet adopt-
ing the same principle, Dumas first found the gravi-
metric composition of water.

In our first chapter we briefly outlined the Atomic
Theory, according to which compounds are expressed
by formulae representing their composition, this sys-
tem being far better than constantly writing down
clumsy percentages.

Now as each molecule, or smallest indivisible par-
ticle, of water must contain oxygen and hydrogen
in the same proportions, it follows that the numbers
88-88 and ii-n respectively must represent in each
case the weights of exact numbers of atoms. The
weight of the atom of oxgyen is 16 ; that of the atom
of hydrogen is i ; and the atoms in the molecule of
water, of course, bear these weights. We can there-
fore find the relative numbers of each kind of atom in
the molecule of water thus : —

No. of Atoms of Oxygen 88-88 -r 16 5-55 i

NoTof Atoms of Hydrogen ~~ n-ii-j- i " ii-n = 2

Hence, in its simplest form the molecule of water
would contain two atoms of hydrogen and one atom of
oxygen, and its formula would be H2O. But, obvi-
ously, formulae like H4O2, HGO3, etc., maintain the
same proportional number of atoms, and we ought,
perhaps, to give a hint of the method of reasoning by
means of which the simpler formula, H20, is chosen.
In 1811 an Italian scientist, named Avogadro,
helped the atomic theory out of a real difficulty by

'51

THE STORY OF THE FIVE ELEMENTS

the hypothesis that, under similar conditions of tem-
perature and pressure, equal volumes of gases and
vapours contain an equal number of molecules ; in
other words, the molecules of all gases under the
same conditions take up the same space. Thus, if
we weigh equal volumes of hydrogen and steam, we
shall obtain the ratio of the molecular weights of the
two gases. This can be accomplished with a considerable
degree of accuracy, and we find that a given volume of
steam is nine times as heavy as the same volume of
hydrogen at the same temperature and pressure. Now,
the molecular weight of hydrogen is found to be 2, and
hence the molecular weight of steam is 18. This corre-
sponds to the formula H20, and not to H4O2, HGO3
etc. The formula of water — in the state of vapour,
at all events — is H20 ; and the sure establishment of
this truth was one of the earliest triumphs of the
atomic theory. But the assumption of Avogadro,
it must be remembered, was necessary to this ; and
it is, of course, by its very nature unproved, though
by no means unverified.

IV. — THE VOLUMETRIC COMPOSITION OF WATER

Chemical theory, supported by experiment, gives
us the information that both hydrogen and oxygen
contain two atoms to their molecules. As the mole-
cules of these gases occupy equal spaces, it follows
that their atoms do likewise ; and when hydrogen and
oxygen are united to form water, we should therefore
expect two volumes of hydrogen and one volume of
oxygen to disappear in such union if our formula for
water is correct*

The determination of the volumetric composition
152

COMPOSITION OF WATER

of water was first made by Cavendish ; and his method
is, except for improvements in the apparatus, that
which is in use at the present day. For the purpose we
use the eudiometer previously described, following
the method laid down there, and exploding oxygen
with excess of hydrogen. Suppose 30 c.c. of oxygen
were bubbled in, followed by 30 c.c. of hydrogen, and
that after explosion 15 c.c. of a gas, found to be wholly
oxygen, remained. This would clearly show that two
volumes of hydrogen and one volume of oxygen had
been used. Figures giving this information are ob-
tained by the use of the eudiometer, and the whole
of the experimental evidence at our command indi-
cates that the composition of water is accurately
expressed by the formula we have arrived at. Thus
it is known, not as an element in the sense that it was
known to the early philosophers, nor yet as it was
known to the chemists in more enlightened times,
but as a compound, compounded of two gases, each
differing markedly in properties, these characteristics
disappearing, however, when union occurs and the
glistening dew is formed.

V. — NATURAL WATERS

Naturally occurring waters are never pure. Rain-
water, caught in country places before reaching the
ground, approximates very closely to pure water ;
but even this contains air in solution, the air having
been collected during the passage of the water through
it. Any other gaseous impurities in the atmosphere
are also dissolved to some extent by the water, and
these are carried by the water wherever it goes. As
our drinking waters have all been rain water in the

'53

THE STORY OF THE FIVE ELEMENTS

first instance, these dissolved gases will still be pre-
sent in all waters. By boiling the water they are
expelled, and the loss of air leaves the water insipid.
The dissolved air is thus useful in imparting a taste to
the water, and also in supporting the lives of aquatic
animals.

As soon as rain water comes in contact with the
ground, it meets with impurities, some of which the
water can dissolve, while others resist its solvent
action. The former are spoken of as dissolved impuri-
ties, the latter are described as suspended, and the
nature of such impurities depends upon the path along
which the water passes. If it passes, say, through beds
of chalk, the water, charged with a little carbon dioxide,
has the power of dissolving the chalk, and hence chalk
becomes the dissolved impurity. Salt would likewise
be dissolved, while mud, sand, clay, etc., would remain
suspended in the water ; and, if their particles were
fine enough, might be carried off with it. The study of
these impurities is most interesting, and furnishes
useful information respecting the suitability of water
for drinking, domestic and other purposes.

The suspended impurities, as we have stated above,
chiefly consist of sand, mud and dirt, and to purify
the water containing only suspended matter it is neces-
sary to allow the water to stand, when, in course of
time, the solid matter sinks and the clear liquid can
be decanted off. As this settling process takes some
considerable time, it is more usual to pass the water
through some porous substance, the holes in which are
small enough to arrest the particles of solid matter,
while the clear water percolates through. The process
is referred to as filtration, and the porous substances

154

IMPURITIES IN WATER

in use are many and varied. Charcoal, sponge, very
fine gauze, and unglazed earthenware are each used in
domestic filters. In the Pasteur-Chamberland filters
the water is passed through fine unglazed porcelain ;
and this substance is so efficacious that it stops the
passage of micro-organisms, as well as the mechanically
suspended particles of mud. With domestic sup-
plies, however, it is rare to find any large quantity
of suspended matter, and when the water is heavily
charged with such, it should be first passed through
canvas, coke, or some such substance. It may after-
wards be deprived of the small amount these fail to
arrest by passing through the finer substances enu-
merated. The efficiency of filtration in removing sus-
pended impurities may be demonstrated by pouring
the impure water through unglazed paper. This
paper, similar to blotting paper, is generally met with
in circular pieces, which admit of such folding as to
fit easily in a funnel. On pouring the water through
such a paper the solid matter is removed. This is the
process used by the student for removing suspended
matter and, although simple, it is remarkably effi-
cacious.

On the very large scale where water must be filtered
for industrial uses, sand, charcoal, or coke is used, and
in some cases the porous ashes from the furnaces are
packed together and the water passed through. Barrels
filled with shavings are also much in use.

The dissolved impurities are by far the most im-
portant, however, and upon their presence depends,
to a great extent, the value of the water as an article
of food. Perfectly pure water would not possess the
value it would have if it contained dissolved matter

THE STORY OF THE FIVE ELEMENTS

helpful in building up the system, and a water con-
taining slight amounts of salt, Epsom salts, and lime
or chalk is of great value to the community. On the
other hand, dissolved matter may be of a poisonous
nature. As the dissolved impurities cannot be seen
in water it is evident that, by mere appearance, a
water may be judged quite wrongly, and many times
indeed water absolutely unfit to drink has been con-
sumed because it looked bright and pure. A few simple
experiments will give us a fund of information about
water, and we shall briefly mention a few to indicate
how the presence of the commoner soluble impurities
may be detected.

The presence of dissolved matter in general may
be ascertained by boiling a pint or two of water to
dryness in some clean vessel, when the impurity would
be left dry at the bottom. In some towns it is a
matter of common occurrence to find this kind of im-
purity around the sides of vessels, such as saucepans
and kettles, that are in constant use, and " furrs " are
due to this cause. Having ascertained that dissolved
matter is present, we may endeavour to ascertain
roughly its nature. Such impurities generally consist
of chlorides, sulphates, and carbonates of sodium,
magnesium and calcium. We may roughly say salt,
Epsom salts, and chalk or gypsum. To ascertain if
salt is present, we must fill a clean glass jar with a
sample of the water and add a little nitric acid and a
solution of nitrate of silver. The presence of salt is
indicated by an opalescence in the water. Epsom
salts may be detected by adding barium chloride solu-
tion and hydrochloric acid to a fresh sample, when a
white cloudiness comes over the liquid ; and to test

'56

IMPURE WATERS

for chalk or gypsum we add a solution of ammonium
oxalate. A white precipitate, faint or strong, indicates
the presence of chalk or gypsum.

These impurities, in moderate amounts, confer
upon the water useful properties ; but frequently it
happens that when a water contains none of these
impurities, it is very liable to dissolve lead from the
pipes through which it passes. Waters containing little
dissolved matter are said to be soft, since they easily
lather with soap ; those containing much dissolved
matter are said to be hard. Now, soft waters have
been found to have an appreciable action on lead,
since they form inside the pipe a compound called lead
hydroxide, which is soluble in water ; and further,
moorland waters, possessed of acidic properties, can dis-
solve lead by virtue of their acidity. In towns supplied,
therefore, with such waters, the standing of the water
in the leaden pipes throughout the night greatly facili-
tates the action, since the water remains a long time in
contact with the lead ; and the first runnings on a
morning contain an appreciable quantity of the metal
in solution. Continual drinking of such waters brings
about lead poisoning. In towns supplied by such
water it is imperative that a sufficient quantity be
first discarded to clear out the water which has been
standing in the pipes, as, during the day, owing to
constant service, it does not get the opportunity pro-
vided during the night. The presence of lead in water
may be detected by adding to the water a little solu-
tion of sulphuretted hydrogen, when a light brown
colour is produced if the metal be present. A water
containing chalk in solution does not exert an action
upon lead, as continual passage through the pipe causes

'57

THE STORY OF THE FIVE ELEMENTS

a slight deposition of chalk on the interior, which
serves as a protector to the lead.

Of all the impurities met with in water, those due
to the operation of micro-organisms are the most
injurious. The waters commonly referred to as polluted
waters owe their pollution to such causes, the micro-
organisms present being of a species which the human
body is incapable of easily rejecting. Such a state-
ment must not be construed as meaning that water
containing micro-organisms is necessarily injurious ;
all waters contain armies of them, and the majority
are friends, not foes, to mankind. But certain species
do exist, which, when present in water, produce cholera,
typhoid fever, etc., when the water is consumed ; and
water so polluted may poison a whole community,
so virile are these foes. Rarely does it happen, how-
ever, that a good source of supply ever suffers con-
tamination ; but frequently it happens that a water
badly chosen may be contaminated. The waters of
shallow wells may very easily become polluted by decay-
ing vegetable and animal refuse from above ; the drain-
age easily percolates through the soil and subsoil, and
finds a way to the water. In all cases the water from
shallow wells must be avoided, and in boring wells the
deep water, and not surface water, must be used. Very
often such waters smell, and when this is the case
they must on all accounts be rejected. In other cases
an odour is manifested when the water is warmed, and
again it should be avoided ; in fact, such a water may
be said to be unfit for drinking purposes. Filtration
has been known to remove a certain amount of bac-
teria from water ; but where a water is found to be
polluted it must be rejected and advice sought. A

158

POLLUTED WATERS

water may generally be said to be dangerous when it
possesses the power of destroying the purple colour of
a permanganate solution, although exceptions are met
with. Such exceptions are waters containing sulphur-
etted hydrogen at our health resorts ; but then people
do not .habitually resort to such, and they are taken
under medical guidance. Only a comparatively short
time ago polluted waters were responsible for epidemics
of disease, particularly for cholera ; but the onward
march of science has, happily, done much to alter
that state of things, and almost every town has now
a source of supply that is beyond suspicion.

VI. — SOLUTION AND CRYSTALLISATION

It is common knowledge that, when many sub-
stances are added to water, they mix with the liquid,
and some of their characteristics disappear. Thus a
piece of sugar when immersed in water gradually
loses the properties characterising it as a solid,
and disappears into the water to form a solution.
This act of solution is not confined to solids, as
we have previously seen that gases dissolve in water ;
nor is the property in any wise restricted to water.
In fact, many liquids are often used commercially
as solvents, particularly petrol, alcohol, carbon
tetrachloride, etc. ; and we have many instances on
record in which one metal dissolves in another
to form a solid solution. In the first instance,
however, we will confine our study to the solvent
properties of water and to the solution of solids in
the same.

If a little potassium nitrate (saltpetre) be finely
powdered and added to water in successive small

'59

THE STORY OF THE FIVE ELEMENTS

quantities, the saltpetre dissolves to the accompani-
ment of an absorption of heat. The liquid becomes
cooled, heat having been taken from it by the solid as
it dissolves. In some cases of solution, however, heat
is developed, and the liquid becomes warmer. Waiv-
ing for the present the difficulty thus created, and
returning to the saltpetre, we find that, as we con-
tinue slowly to add the solid, more and more is taken
into solution until a point is reached when the water
will dissolve no more ; this point is marked by the
presence of undissolved solid at the bottom of the
liquid. Under these circumstances we say the solu-
tion is saturated in regard to the given solute (the salt-
petre). The question now arises, since heat is evi-
dently used up in the act of solution, will the saltpetre
dissolve to a greater extent if we give heat to the
liquid ? On gently warming the liquid, we find that
this is so, the elevated temperature helping the water
to take more into solution ; and on boiling the solu-
tion, we may add a considerable excess quantity of the
solid. It is evident that, on allowing the solution to
stand and cool gradually, this excess, when the original
temperature is reached, will separate out. When such
separation occurs, however, we notice that the sepa-
rated solid conforms to a particular shape, and
fashions itself into needle-shaped crystals. Such a
process of separation is referred to as crystallisation.
The more slowly the cooling takes place the more beau-
tifully do the molecules build up these structures, and
by cooling such solutions of various substances in
water crystals of beautiful shapes can be made. Thus,
alum separates in diamond-shaped crystals ; salt in
cubes ; whilst the familiar crystal of sugar candy is

j6o

SOLUTION IN WATER

well known to all. The observation of the growth of
these crystals forms most interesting experiments, and
might well be commended to the attention of our
readers. In some instances it happens that the
cooling takes place so slowly that absolutely no move-
ment occurs and no solid separates. Such a solution
is said to be super-saturated, and rapid crystallisation
is at once produced by disturbing it with a crystal
of the solid which has been dissolved.

It frequently happens that crystals of various sub-
stances, when in a perfectly dry condition, yet con-
tain, locked up in them, a large amount of water. Such
water is referred to as water of crystallisation, and we
generally speak of the crystals as hydrated crystals.
Thus, ordinary washing soda consists of carbonate of
soda crystals, containing more than 60 per cent, of
water ; and when this hydrated carbonate is heated
the water is evolved in copious amounts, the white sub-
stance remaining being anhydrous sodium carbonate.
The loss of water takes place slowly in the open air in
this case, and everyone is familiar with the result of this
change. Similarly, crystals of alum contain a large
amount of water, also capable of expulsion by the
application of heat ; and it is significant that when
crystals containing water are heated to the boiling-
point of water, the water they contain is gradually
expelled and the crystals fall to pieces. The inference
is therefore drawn that such crystals owe their struc-
ture to the water they contain. In some cases, how-
ever, all the water is not expelled at 100° C., and that
remaining is referred to as water of constitution, since
the affinity of the remaining water with the parent
substance is evidently of a stronger nature than with

L 161

THE STORY OF THE FIVE ELEMENTS

the greater portion of the water the crystals previously
contained. A substance in which this can be well
shown is the familiar blue vitriol or sulphate of copper.
At the temperature of boiling water this salt loses
much water, and with its water it loses its clear blue
colour and its crystalline character. The pale green-
ish powder left behind, however, still has water in its
constitution ; this can be driven off at a higher tem-
perature, and a white powder, pure anhydrous sul-
phate of copper, is left behind. In this case, as in so
many others, both the crystalline condition and the
colour of the salt are absolutely dependent upon the
presence of the water of crystallisation.

VII. — PHYSICAL PROPERTIES OF SOLUTIONS

It is not easy to say offhand what happens to
salt or sugar when it disappears into water ; but
during the past thirty years a great deal of skilful
experiment and careful thought has been given to
the question, and we have arrived at a satisfactory,
if not absolutely final, theory which we shall endeavour
in a simple way to make clear. But we must first
draw attention to certain changes which may be
observed in the properties of the solvent itself.

It is common to find, and the fact is well known,
that the water of lakes and rivers has frozen, while
the sea remains liquid ; it is familiar knowledge also
that salt tends" T>ause ice to melt when added to it.
Evidently wate? ' containing salt must be reduced to
a much lower temperature than water itself needs
before it will freeze. The effect can be studied with
accuracy by surrounding a tube containing pure
water with a mixture of ice and salt, and inserting a

162

PROPERTIES OF SOLUTIONS

delicate thermometer in the water. As this water,
under the influence of the cold mixture around it,
becomes cooler, it eventually arrives at the tempera-
ture marked o° on the thermometer. If it is then
disturbed a little, ice begins to form, and the tem-
perature is described as the freezing-point. If the
liquid is, however, kept perfectly quiet, it may be
supercooled, i.e. taken to a temperature much below
its freezing-point without freezing ; but it will return
to this temperature and yield ice on the slightest dis-
turbance. Having noted the freezing-point of pure
water, add to it enough salt to make i per cent, of its
weight, and thus form a " i per cent, solution " of
salt. The liquid now freezes at a slightly lower tem-
perature, and the depression of the freezing-point can
be recorded. Increasing the amount of salt to two
per cent, we shall observe that the total depression thus
produced is twice as great as that produced by the one
per cent, of salt. And the law thus indicated is
general : the depression of the freezing-point is always
proportional to the amount of substance dissolved.

If a dilute solution of potassium permanganate
be frozen, the important and interesting fact may be
observed that the solid ice is colourless ; the ice
obtained from the freezing of dilute solutions is pure.
But, obviously, during the freezing of a dilute solu-
tion of salt, as more and more ice separates, the
residual liquid becomes a strong nd stronger solu-
tion, until it must become satur^.^d. At that point
both ice and salt would separate from the liquid ; the
temperature thus reached would be the lowest obtain-
able by the freezing of salt solution — it would be the
freezing-point of a saturated solution of the salt.

163

THE STORY OF THE FIVE ELEMENTS

This temperature is called the eutectic temperatiwe of
the solution, and the mixture separating is known as
a cryohydrate. This was at one time thought to be
a definite compound of ice and salt ; but it has no
special chemical characteristics of its own ; the two
constituents can be readily separated, and we now

prefer to regard it
merely as a mixture of
the solute and its sol-
vent in the solid state.
The changes in the
freezing-point obtained
by experiment can be
represented instruc-
tively on squared
paper. Just as a place
on the earth's surface
is exactly fixed by its
latitude and longitude,
so the freezing-point of

Temperature in degrees C.

BFig. 36.— Formation'of^a cryohydrate.

-i-ou -0-5° o° a solution of a definite

Hncrr^ooe. f «

strength can be com-
pletely indicated by a
point, as in Fig. 36. The curve joining the various
points shows at a glance the whole variation of the
freezing-point as the solution is strengthened. Such
a curve is A c, which was constructed from experi-
ments on a solution of potassium chlorate. On the
same diagram we can also place the curve B c, which
indicates the amount of the substance that can be
dissolved at the various temperatures. These two
curves intersect at c, and evidently c stands at the
eutectic temperature. For that point is on A c, and

164

FREEZING OF SOLUTIONS

therefore tells us that ice is forming ; it is also on
B c, which is the curve of the saturated solution. In
other words, c is the point at which the solution is
both saturated and freezing.

Study of the boiling-point of solutions has yielded
equally interesting results. It is easy to show that
the boiling-point of water is raised by the presence of
dissolved substances, and that the rise is proportional
to the amount of substance present. The line of thought
here opened up has been of great importance in the de-
velopment of chemistry, both in theory and in practice.

VIIL— THE FREEZING OF ALLOYS
One of the most interesting practical applications
of the freezing of solutions has thrown a great deal
of light upon the nature of alloys. These useful
substances are, as is well known, formed by the
fusion and subsequent cooling of two or more metals
together ; and the question to be determined is
whether the metals form a mere mixture or enter
into any kind of chemical combination. Inasmuch
as the behaviour of an alloy often depends upon
the state in which one of the metals may be present,
i.e. whether it is free or combined, it is interesting
to follow out briefly one of the methods upon which
a decision can be made. Several methods can be
applied ; but that of freezing the molten alloy and
following the changes attendant upon cooling has
been applied with very considerable success.

If a particular metal be taken, its freezing-point
carefully obtained, and afterwards the freezing-points
of the metal when successive additional quantities
of a second metal have been dissolved in it, we find

165

THE STORY OF THE FIVE ELEMENTS

that a depression curve, very similar to that obtained
from solutions of salt in water, is followed for a time.
In all such cases the solvent metal is the first to sepa-
rate, and the microscopic examination of thin slices
of the solid shows the crystals of the pure metal clearly
distinguishable. Evidence such as this shows that
dilute solutions of metals in metals behave in essen-
tially the same way as dilute solutions of salts in
water. Pushing the comparison a little further, we
find in many simple alloys that, at a definite percentage
composition, both metals separate out at the same
time ; they yield a mixture which is similar to a
cryohydrate, at a definite eutectic temperature. Micro-
scopic examination again confirms the reasoning pro-
cess ; a conglomerate mass is seen, the nature of
which seems to indicate the presence of the two
separate metals.

Representing this behaviour diagrammatically (Fig.
37), we will call the two metals A and B. The melting-
points of these two metals are indicated, one on each
vertical line. If now to pure A a little of B is added,
the proportion added may be set off horizontally,
as shown, and the corresponding freezing-point repre-
sented vertically. By making the observation with
various proportions of A and B we obtain the curve
A c. Supposing c to be the point where both the
metals separate together, it is clear that this, being
the eutectic point, will also be found on the curve
B c, obtained by starting with B and adding succes-
sive quantities of A. This case is a simple one, and
in all probability the alloy formed at the eutectic
point is a substance corresponding to a cryohydrate,
i.e. a mixture of solvent and solute.

166

FREEZING OF ALLOYS

Meltirrg'Pti
pure A.

Melt/ing" Pfc.
pureB.

Percentage B I0°

Fig. 37.-— The eutectic point of an alloy.

But the case is different when our alloy is in part
a definite chemical compound. Such compound metals
have been isolated, and their freezing-point curves are

Melting Pb
pure A.

Melbin&Pb.
pure B.

Percentages — +- 100

Fig. 38.— Curve of alloy forming a compound at E

THE STORY OF THE FIVE ELEMENTS

of somewhat different type. Fig. 38 shows a typical one.
Here A c is the curve of B dissolving in A, c being the
eutectic point ; and B D is similarly the curve of A
dissolving in B, with D for the eutectic point. At c
and D we get mixtures of the metals of different com-
position ; but what happens between these points ?
If we start at c or D and add more of B or A, as the case
demands, the curve takes the course c E D, at the
summit of which we have a composition represented
that, when isolated and examined, behaves very much
like a compound of the two metals ; the microscope
reveals in thin sections a perfectly homogeneous mass,
and other methods of analysis confirm the belief.
It will thus be seen how a study of the freezing-point
curves can throw a much-needed light upon the nature
of an alloy.

IX. — WHAT is A SOLUTION ?

We have wandered somewhat from our original
question ; but our vagaries have not been useless if
we have succeeded in showing that the properties of
solutions lead us into unexpected and interesting lines
of work and thought. We come back now to the first
difficulty. What is the cause of solution ? What
happens actually to salt and sugar when they dis-
solve in water ? The old confusion, still rife among
people who have not acquired the scientific habit of
an accurate use of words, between dissolving and
melting, suggests a possible explanation. Does salt
really melt, i.e. become liquid, when it dissolves in
water ? At first sight it might seem to do so. The
molecules of salt do seem to acquire the liquid con-
dition ; and in most cases heat has to be supplied for

168

NATURE OF SOLUTIONS

solution, as it always must be supplied for melting.
But several considerations cut out this explanation ;
the mere fact that gases can dissolve in liquids is
enough — in those cases, at all events ; and the changes
which occur both in the properties of the water and
in those of the dissolved substance, make a more deep-
seated explanation imperative.

The promotion of the solution of a solid in water
probably depends upon the operation of forces which
tend to disintegrate the solid, the resultant of which
determines the extent to which the substance will dis-
solve. On the one hand we have the solid, made up
of molecules held firmly by cohesion ; on the other,
the liquid, the molecules of which are free to move,
their movement being accelerated by increase of tem-
perature. Further, every evidence tends to show
that in a solid the individual molecules are tending of
themselves to move, but are prevented from so doing
by the cohesive forces between them. It is evident
that, during solution, these cohesive forces are broken
down ; and this breaking down must result somehow
from the contact of the solid with the liquid. It may
be assumed, then, that contact of the solid with the
moving molecules of the liquid causes molecules of
the solid to acquire sufficient energy to break down
their mutual attractive forces ; and these molecules
pass away from the main mass along with the liquid.
Thus some of the substance passes into solution ; and,
as increased temperature means an increased mole-
cular motion, we should expect it to accelerate the
process of solution, as indeed we find it to do in most
cases. This passage of the substance into solution
continues until saturation occurs ; and even then it is

169

THE STORY OF THE FIVE ELEMENTS

fair to assume that the solution of the solid still pro-
ceeds ; but the process of solution is now balanced
by the deposition of some solid upon the substance
which remains undissolved. This fact will be ren-
dered clear when we consider that the latter must
be continually meeting with molecules of the
solution, which must in their turn leave behind
small amounts of the solid, even though some
further amount is washed into solution. When solu-
tion is continuing, then, we must picture the liquid
taking away substance and at the same time deposit-
ing a little, the amount removed being greater than
that deposited. When these are equal — i.e. when as
much solid is being taken away as is being brought
back in a given time — it is evident that no further
solid will, on the whole, pass into solution ; in other
words, the solution is saturated.

Having dissolved then, the substance has assumed
the liquid condition. But how does it exist now it is
in solution ? Have we molecules of liquid salt, liquid
sugar, and so forth, or has the water produced some
manifest change in the substance ? Now it is of great
significance, and somewhat remarkable, that the par-
ticular nature of the dissolved substance determines
many physical characteristics of the solution ; particu-
larly so in regard to one great property of solutions,
to wit, their electrical conductivity. Pure water
conducts the electric current to so slight an extent
that it can, broadly speaking, be termed a non-con-
ductor. If, therefore, two pieces of platinum foil,
attached to wires leading from the poles of a cell
generating a current, be dipped side by side in pure
water, no current will pass through the latter. But

170

ELECTROLYTES— NON-ELECTROLYTES

if a dilute solution of salt in water be substituted for
the vessel containing water, the current at once passes,
and its passage is attended by decomposition of the
salt. If a solution of sulphate of copper be used,
decomposition again accompanies the passage of the
current, and metallic copper is deposited upon the
strip of platinum where the electric current leaves the
liquid. A solution of any salt (p. 176) in water
confers upon the water the property of conduction
of the current.

On using now a solution of sugar instead of a solu-
tion of a salt, the current is once more refused passage ;
if a solution of gum be taken, again the current can-
not pass. Many substances, indeed, form solutions
that are non-conductors, and thus we can have,
among aqueous solutions, two great classes : those
which conduct the current of electricity, and those
which do not. The former are called electrolytes, the
latter are non-electrolytes. To the former belong
saline solutions, to the latter a vast army of soluble
substances which are compounds of carbon and have
no saline properties.

This difference in the behaviour of the two types
of solution is, as we have said, remarkable : it com-
plicates the whole question ; and our theory of solu-
tion must provide some explanation for it. What is
the nature of the change which salt undergoes, and
sugar does not, when it is dissolved in water ? As
water itself is a non-conductor and salt refuses to con-
duct a current of small strength — salt will conduct a
strong current when in a fused condition — we must
assume that the water and salt help each other in
some way. We can conceive this help to be given either

THE STORY OF THE FIVE ELEMENTS

by the water and salt uniting to form complex bodies
which we may term hydrates, and which would have the
power of conducting the current ; or, alternatively, by
the water resolving the salt into simplexes of some
kind, such simplexes being the conductors. We turn
to experiment for the necessary light upon these pos-
sible theories, and there is reasonable hope that such
experiments will throw light also upon the nature of
solutions in general.

It has been previously stated that the depression
in freezing-point produced by a dissolved substance is
proportional to its amount. To this we may now add
the further statement that careful investigation has
shown that, if quantities proportional to the molecular
weights of many substances are contained in 100 parts of
solution, the depression of the freezing-point would be
the same for all. This depression is known as the mole-
cular depression of the liquid used as solvent, and its
value for water has been found. But electrolytes are
all found to behave irregularly. Salt gives almost twice
the molecular depression in water that sugar and other
non-electrolytes give. Hence, in the salt solution we
must have present either heavier molecules than those
of the salt itself, or more molecular quantities than
we bargained for. If the salt -molecules join with
water-molecules to form hydrates, these hydrates might
well behave on freezing as sugar does. On the other
hand, if the salt-molecules were each separated into
two simplexes, we should have twice as many mole-
cular units, and thus obtain twice the molecular de-
pression. We can explain the anomalous result,
therefore, either by the aid of the hydrates or by
means of the simplexes, one of which we needed

172

THEORIES OF SOLUTION

also to explain the conducting power of the solu-
tion.

We cannot here enter into a full discussion of
these theories ; but the second of the two is the more
generally accepted, and we may profitably explain
how it can be applied to a special case. Think, then,
of common salt dissolving in water. Now, common
salt is on analysis found to be sodium chloride, i.e.
it is a compound of the two elements sodium and
chlorine, represented by the formula NaCl. The sup-
posed simplexes formed by the influence of the water
would be the atoms Na and Cl. But if, by merely
dissolving the salt, we obtain atoms of sodium and
chlorine, we should expect also the properties peculiar
to these atoms ; we should expect the sodium atoms to
decompose the water (p. 146) and the chlorine to confer
bleaching properties upon it. Needless to say, salt
does not behave so ; the simplexes cannot, therefore,
be the atoms of sodium and chlorine, unless they are
in an unusual condition. Now, it is well known that
an electric charge endows substances with new pro-
perties and obscures or modifies their ordinary beha-
viour. Suppose, then, that the atoms, as they exist
in the solution, are each accompanied by a definite
charge of electricity. These charged atoms, or ions,
need not act as the uncharged atoms would ; but they
would account for the easy manner in which an elec-
tric current passes through the solution. On this
hypothesis, the simplexes into which salt decomposes
in water would be sodium ions and chlorine ions ;
the ions possess equal electrical charges ; that on the
sodium ion will be positive, and that on the chlorine
negative. We represent the ions symbolically as

THE STORY OF THE FIVE ELEMENTS

Na and Cl, and the effect of water on salt will be
shown in chemical language, thus —

NaCl = Na + Cl

When the terminals of the battery are fastened
to strips of platinum dipped into the salt solution,
we introduce, as it were, a storehouse of positive elec-
tricity on one strip and of negative electricity on the
other. The chlorine ions will then migrate towards
the positive strip or anode, and the sodium ions will
similarly be drawn towards the cathode or negative
strip. There the ions will give up their charges, and
become converted into atoms of sodium and chlorine,
which atoms will now exercise their normal activity.
The sodium will produce hydrogen at the cathode,
and the chlorine will issue as a gas from the anode.
Thus we realise the difference between the atoms and
the ions.

Sometimes the ions are not composed of single elec-
trified atoms as in the case of salt. What happens to
sulphate of copper (CuS04) when it dissolves in water ?
On passing the current, what we really obtain is a
deposit of copper on the cathode and oxygen gas at

the anode, This is explained by supposing the salt to

+ +

be decomposed into two ions, Cu and SO4. The posi-
tive ions give up their charge and are deposited with-
out more change ; but the negative ions, having given
up their charge, are unstable and readily decompose
water, thus —

S04 + H2O = H2S04 + O

The presence of sulphuric acid (H2S04) in the liquid

IONIC THEORY OF SOLUTION

can easily be proved, and the essential correctness
of the explanation thus guaranteed.

In many cases, again, three or more ions may be
produced. Analysis shows copper chloride to have
the formula CuCl2. Dissolved in water, this molecule
would produce one copper ion and two chlorine ions.
Since the electricity on the copper ion neutralises that
on the two negative ions, the copper ion must have
a double charge, as represented above. The pre-
sence of the three ions in the solution can be checked
by the effect on the freezing-point of the liquid ; the
depression produced in this and other similar cases
would be found to be almost three times that which
would have occurred if no dissociation had taken place.
A very great body of experimental support is thus
available for what is called the ionic theory of solution.
But, of course, it only applies to electrolytes ; sub-
stances like sugar or gum cannot be dissociated into
ions ; their solutions do not conduct the electric cur-
rent, and their molecules must mix intimately and
unchanged with those of the solvent. And even in
the case of electrolytes, the dissociation is not com-
plete unless the solution is very dilute ; in the ordinary
way a good proportion of the molecules must remain
unchanged.

X. — ACIDS AND BASES

The main support of the ionic theory is the fact
that all electrolytes can be dissociated into positive
and negative ions. Now, when hydrogen is the
positive ion, the resulting solution has what are called
acid properties, whatever the negative ion may be.
The easiest method of showing the presence of an

175

THE STORY OF THE FIVE ELEMENTS

acid is to take advantage of the action of the hydro-
gen ions on certain dyes or vegetable colours, such
as blue litmus, which is turned pink by them. All
the familiar acids are electrolytes and undergo the
ionic dissociation in water ; those which at various
places we have had occasion to mention in this book
are hydrochloric (HC1), nitric (HN03), and sulphuric
(H2S04) acids. We have not the space to describe
the particular properties and special importance of
these invaluable substances, but we must discuss
them for a few lines in general terms.

An acid can be " killed," i.e. have its acidic pro-
perties destroyed, in several ways, which all imply,
however, the removal of the hydrogen and its re-
placement by some other positive ion. The replacing
ion may be a metal or an equivalent single group of
atoms. In the first case, we find that the metal is
often able to perform the change directly, as when
zinc dissolves in dilute sulphuric acid (p. 93) ; hydro-
gen gas is then eliminated, and the acid is said to be
neutralised. But frequently we find that the metals
will not act directly on the acid ; nevertheless the acid
may be neutralised and the said metal indirectly intro-
duced.

Zinc and zinc oxide both neutralise the common
acids directly, and the final product is the same in
both cases, so far as the zinc is concerned ; but whereas
the zinc liberates the hydrogen from the acid free,
zinc oxide liberates it in the form of water. Zinc
oxide is therefore described as a base, a term often
vaguely used, but here defined to be a substance cap-
able of neutralising an acid, water being produced at
the same time. The neutral substance formed, which

176

NEUTRALISATION OF ACIDS

has neither acid nor basic properties, is called a salt.
The salt is named after the acid and base contained
in it ; the name suggests the method of making it ;
thus, copper nitrate from copper or copper oxide
and nitric acid ; magnesium sulphate from magnesium
or magnesium oxide and sulphuric acid, and so on.

A few of the oxides of the metals dissolve in water
easily, and communicate to the water alkaline pro-
perties. But before doing so they change chemic-
ally into what are known as hydroxides, compounds
containing both hydrogen and oxygen. The most
familiar of these are sodium and potassium hydroxides,
the common caustic soda (NaOH), and caustic potash
(KOH). These alkalis are white solids, readily sol-
uble in water with evolution of heat, giving solutions
with soapy touch, which turn red litmus blue. In

4- +

solution they change into metallic ions (Na or K) and

the compound negative ion (OH), called hydroxyl.
It is this dissociated condition which enables them to
neutralise any acid whatever with ease. We may
express the reactions which occur in two cases as fol-
lows : —

HC1 + NaOH = Nad + H2O I

Acid -f Alkali = Salt + Water )

HNO3 + KOH = KNO3 + H20 1

Acid + Alkali = Salt -J- Water /

Now, as we have explained in our first chapter,
the symbols above used stand for definite quantities —
the molecules — of the reacting substances. If, then,
we make experiments with quantities of the above
acids and alkalis which are proportional to their mole-
cular weights, we obtain the interesting results that
the neutralisation is complete, and that the heat dis-

M 177

THE STORY OF THE FIVE ELEMENTS

engaged by the process is the same in each case. That
is to say, when one molecule of hydrochloric acid is
added to one molecule of caustic soda, approximately
the same amount of energy is liberated as would be set
free by a molecule of nitric acid neutralising a molecule
of soda or of potash. And this is true in numerous
other instances also. Searching our equations for the
common factor that is responsible for this uniform
behaviour, we find it in the constant amount of water
produced ; and the reason why this also implies a
constant amount of energy is clear if we assume both
acid and alkali to be dissociated into ions, but can-
not be comprehended otherwise. The water is pro-
duced in each of the reactions by the combination of
a positive hydrogen ion and a negative hydroxyl ion ;
at the same time the equal and opposite charges are
neutralised, because water itself is practically un-
dissociated. The withdrawal of these ions and their
conversion into equal quantities of water may be
represented on the ionic idea in the equations : —

H + Q + Na + OH = Na +C1 + H2O

Thus the essential process in the neutralisation of
acids by alkalis is this production of water by the union

of H from the acid and OH from the alkali. The ions
which constitute the salt still remain dissociated, until
the solution is concentrated, when they also tend to
unite to form neutral molecules. When the water
is all driven away the molecules of salt remain, neutral
and undissociated.

FORMATION OF SALTS

This formation of salts from acids and bases is one
of the most far-reaching and important of chemical
processes, and it lends very strong support to the elec-
trical theory of solution. That a solution should con-
tain a vast number of electrified atoms moving rapidly
among the molecules of the solvent it is difficult to
realise. Yet such an explanation is demanded by
many phenomena such as we have explained ; it is
contradicted by none ; and it only leaves us still to
ask, what becomes of those substances, like sugar,
which cannot dissociate and do not conduct electricity
when they are dissolved in water ?

XL — WATER AS AN INFLUENCE IN CHEMICAL CHANGES

How and why water is able to accomplish the dis-
sociation of acids, alkalis, and salts into ions which
render them capable of electric conduction, we are in

a complete quandary to tell. The water molecules,

+
themselves capable of being resolved into the ions H

and OH, are not in any noticeable degree dissociated ;
but a small quantity of salt or of an acid is almost
entirely separated into two ions, by the influence of
the water present in comparatively large quantities.
Almost as mysterious is the influence of mere traces
of water in certain other changes.

We have referred to certain gases, like oxygen
and chlorine, which, in contrast with others, like
argon, are very active in the chemical sense, entering
easily into combination with other elements and re-
maining stably in the compounds formed. It is, never-
theless, the fact that these gases are by no means
active in a pure and dry condition. Thus, hydrogen

179

THE STORY OF THE FIVE ELEMENTS

and oxygen, mixed in explosive proportions and care-
fully dried in sealed tubes in contact with phosphoric
oxide, refuse to explode when a light is presented to
them. Perfectly dry phosphorus will not burn in dry
oxygen, nor will it ignite in dry chlorine. The latter
gas ceases also to act upon Dutch gold, and refuses to
bleach a coloured fabric, if everything concerned is
perfectly dry. Ammonia and hydrogen chloride gases,
when dry, remain side by side without union. In all
these instances — and there are many more — the usual
chemical action is at once set afoot when water, even
the slightest trace of it, is introduced into the mixture.
What the exact function of the water is can be stated
only in a few cases. Its presence in the mixture of
ammonia and hydrogen chloride gases, for example, no
doubt converts them into solutions, one of which is
alkaline and the other acid. The formation of a salt
follows by the withdrawal of the ions, which cannot
exist except in water. But we have no absolute know-
ledge of the part played by water in the explosion, let
us say, of carbon monoxide and oxygen. Many che-
mists, however, consider chemical changes in general to
be dependent upon the presence of a third substance
which acts as a means of connection between the two
reacting substances. We have sufficient data to show
that in many hundreds of chemical changes water
plays the part of this necessary adjunct to the action.
Thus we perceive that water is not less interesting
since it has been deposed from its place among the
elements and has been subjected to the scrutiny of
science. The beauty of Nature is magnified a thou-
sandfold when the intellect and the imagination yoke
themselves to the chariot of wisdom which they drive

180

WATER IN CHEMICAL CHANGES

along the pathways of experiment and speculation in
the pursuit of Truth. In a new sense through science,
water is the wrecker of rocks, the builder of contin-
ents, the architect of clouds, the beginning of life.
We have learnt much about the intimate nature and
the powers of water ; but no reader of these pages will
suppose that we have done more than break the ice
which covers a vast sea of mystery. The compound
of hydrogen and oxygen is, just because of our greater
knowledge, a more subtle and perplexing problem than
the prima materia of Thales.

iSi

CHAPTER VI

EARTH

I. — " EARTH " AND THE OTHER ELEMENTS
WHILE air and water are symbolic of all that is slip-
pery and elusive, the solid earth stands firm as the
emblem of stability. Terra firma is our natural sup-
port, relied upon as the unchanging and certain.
Once anchored there we feel safe. Yet nothing is
surer than that " earth " takes on itself as many be-
wildering forms as " air " or " water " ; its meta-
morphoses are of fascinating interest, and have been
turned by mankind to a thousand uses ; in contact
with the various airs and waters it crumbles, dissolves,
and changes beneath our feet, so that its romance is
no less thrilling than theirs.

The properties assigned to the " earth " element in
the Greek system were coldness and dryness. Nothing
could be cruder than this assignment to solid sub-
stances of these properties and no others ; yet it does
express a gleam of the truth. If the coldness is re-
placed by hotness, we were supposed to obtain the
fire-element : thus the fiery fluid lava became dead,
solid earth by an exchange of the principles of hot and
cold, the principle of dryness being the common
factor between the two. To us, after two thousand
years of science, the matter is read differently ; the
fluid lava consists of a certain material substance in-
fused with a large quantity of heat-energy ; if this
heat escapes in sufficient quantity, the lava loses its

182

SOLIDS AND LIQUIDS

fluid and fiery appearance, and becomes solid. The
fluid does differ from the solid in the possession of
more heat ; and indeed all solids, if they are supplied
with sufficient heat, will become liquid ; and, vice
versa, the liquid, when deprived of some of its heat,
becomes solid. There is thus an intimate connection
between " earth " and " water/' If we imagine the
whole earth possessed of enough heat, it would become
" water," i.e. liquid ; and when we recollect that the
earth is constantly cooling, it is evident that in the
distant past it was probably hot enough to be wholly
liquid, and that the " earth " element did not then
exist here.

Most " earths " have submitted to the high tem-
peratures that we are nowadays able to produce, and
yielded themselves to the liquid condition. A few solid
substances are still refractory ; and such substances
are, of Course, of great value. A cylinder of lime,
raised to an intense white heat by the flame of the
oxyhydrogen blow-pipe, shows no sign of melting ;
the small quantities of thoria and ceria used in the
construction of incandescent mantles glow white-hot,
but cannot be melted ; and the fire-clay used for
lining steel furnaces resists unchanged the tempera-
ture required to fuse steel. These are the substances
in which the solid properties — the " earth " element
— remain unimpaired. But there is no reason for
supposing that they too would not become liquid
if a sufficiently high temperature could be obtained.

Once become liquid, the originally solid substance
may even go further : it may continue to receive heat
until it boils, and is converted into " air/' i.e. into
the gaseous form. There is good reason for believing

183

THE STORY OF THE FIVE ELEMENTS

that iron on the surface of the sun is an air or gas,
and it may be boiled under terrestrial conditions in an
electric furnace. To us, under everyday circumstances,
it is an " earth," in which coldness and dryness are
apparently the paramount properties ; in our furnaces
it can be made liquid and cast into any and every
shape ; under the very much hotter conditions of the
sun it becomes a gas. These three conditions of the iron
are entirely dependent upon the heat-supply. The solid
earth, sufficiently heated, becomes liquid ; turn further
back into the earlier chapters of its history, and restore
to it the heat which it has lost during its aeons of cool-
ing : it has become a fiery gas. Thus, whatever the
substance may be, we may state : —

Solids 4- Heat become Liquids.
Liquids + More Heat become Gases.

The " earth/' " water " and " air " elements are linked
together by heat.

II. — SULPHUR

The changes that we have dwelt upon here can
be very readily studied with a little sulphur or brim-
stone. This very interesting substance is usually
found native in the neighbourhood of volcanoes, which
indicates its formation during volcanic eruptions, and
suggests the interior of the earth as its origin. Its
readiness to take fire, and the choking fumes that it
produces when it burns, have made " fire and brim-
stone " a well-known and appropriate byword. Its
association with metals, which we shall refer to again,
made it an interesting substance to the alchemists,
who regarded it as the dross to be purged from the

184

EFFECT OF HEAT ON SULPHUR

baser metals by the philosopher's stone. It was also
looked upon as the principle of combustibility in the
more confused heyday of alchemical speculation.

If a little of this yellow flowers of sulphur, such as
can be purchased from a druggist's, be gently heated
at the bottom of a test-tube, it can be seen to become
liquid (and at the same time change colour) and ulti-
mately to boil just as water would. These changes,
produced by heat, are accompanied by changes in the
appearance of the material which it is very interesting
to watch. But a little careful observation will con-
vince the experimenter that, in spite of all the changes
seen, the sulphur remains essentially the same stuff.
The liquid sulphur, on being allowed to cool, becomes
yellow solid sulphur again, and this, if re-heated, passes
through exactly the same series of changes as did the
original sulphur. So the gaseous sulphur condenses
on the cold upper parts of the tube into the pale yellow
powder which gave rise to it. Throughout the whole
process of melting and boiling the sulphur remains
— in itself unchanged. It is ready, on allowing the
heat given to it to escape, to go through anew the whole
cycle of changes, and to do so as often as we supply
or withdraw the heat.

The solid sulphur, apart from its ready inflamma-
bility, is not a particularly active substance. But,
by virtue of the increase of energy which it receives
when heated, it becomes much more active in the
gaseous condition. A few iron or copper filings flash
brightly when they are dropped into boiling sulphur,
and are completely changed into blackish solids, with
no lustre, while the sulphur disappears. Solid sulphur
would not affect iron or copper, if they were left in

185

THE STORY OF THE FIVE ELEMENTS

contact for years. The solid condition is far less help-
ful to chemical changes than the liquid or gaseous ; it
has far less energy bound up in it. It would be diffi-
cult to discover a case in which two solids, placed
side by side, affect each other in any appreciable
degree ; any apparent instance can be attributed to
vapours or liquids produced by one or both of the
solids. Whatever chemical property the solid may
have is enhanced when it becomes liquid, and still
more when it has become gaseous. Even in the com-
bustion of sulphur, a little heat is needed to start the
process ; this melts and vaporises a small amount of
the sulphur, and, thus making it more active, sets
afoot the combination with oxygen which has been
previously explained.

Much sulphur comes from Sicily, where, of course,
it is found mixed with other earthy matter. In order
to purify it from the useless earth the Sicilians heap
the crude stuff into a large, deep hole, say 10 yards
broad and 3 yards deep. Air-channels are left among
the masses of earth, and the sulphur is set alight.
The whole is covered with a layer of some refractory
solid like plaster-of-Paris in order to limit the supply
of air. When the heaps are carefully made, a slow
combustion, lasting for some weeks, is set up ; the
heat produced by this combustion is sufficient to
melt much of the sulphur without affecting its earthy
companions, and the liquid sulphur runs to the bottom
of the heap, from which it can be obtained when the
combustion is finished. The solid sulphur is easily
melted, and thus can be separated from the other
solids which accompany it.

Still we have by no means a pure sulphur. In
186

Fig. 39.— An iron retort for the refinement of sulphur.

PURIFICATION OF SULPHUR

order to obtain this the impure substance is heated
in an iron retort (b, Fig. 39) until the sulphur becomes
vapour. The vapour is conducted into a large brick
chamber (a), on whose cold walls it returns to the
solid state. At
the same time
it gives up
much heat —
much of the
heat, in fact,
that had been
needed to bring
it into the gase-
ous form. The
walls of a, there-
fore, soon become hot enough to melt the sulphur on
them ; the liquid sulphur thus formed trickles to the
floor of the chamber (s), whence it is drawn off (m) into
wooden moulds, where again the liquid solidifies. The
solid thus obtained is the hard sulphur sticks or brim-
stone of commerce ; the sulphur taken from the
walls before it is allowed to melt is the flowers of
sulphur familiar to everybody. Clearly the only im-
purities that the sulphur can now contain will be
such as boil at a lower temperature than itself, and
such earthy substances are at best rare and not found
in association with sulphur. The purification of
sulphur, therefore, depends upon the fact that its
" earthy " properties are more readily lost than are
those of its companion earths ; it easily becomes a
liquid and a gas, and thus shows us that the property
of solidity is not an essential characteristic of the sub-
stance, but depends entirely upon the amount of

187

THE STORY OF THE FIVE ELEMENTS

heat it contains. Heat causes sulphur to melt and
boil ; more heat is the only requisite to bring all
" earths " into the same conditions. And, we repeat,
the processes of melting and boiling do not involve
any change in the nature of the substance acted upon :
sulphur is sulphur, whether the earth-element, or the
fire-element, or the air-element is dominant in it.
It is a true element in our modern sense of the word,
not a compound of air and fire, nor playing the impor-
tant part in the economy of the earth which alche-
mists ascribed to their sulphur-principle, but still a
useful example of a real earth-element.

But although sulphur is a true element, it may be
made to assume several different dis-
guises, independent of its changes into
liquid or gaseous form. If a little roll
sulphur be powdered, it can easily be
* dissolved in the stinking liquid called
carbon disulphide ; and this liquid, being
very volatile, rapidly evaporates and
leaves the sulphur in the form of very
Fig. 4o.-Rhombic well-defined crystals. These crystals, how-
symSit[""«f ever much they may vary in size, do
not vary at all in their general shape.
They form figures similar to Fig. 40, which has for
its characteristic three unequal axes at right angles
(shown in dotted lines) that divide the figure sym-
metrically ; such a figure is said to belong to the
rhombic type of crystal.

Now, if these crystals be examined under a micro-
scope, or simply viewed by a lens, many of them will
be seen to be perfect, as if they had been artificially
cut according to a geometrical pattern ; and those

188

CRYSTALS OF SULPHUR

which are not perfect will be seen to have been endea-
vouring to reach the same form, and this is true whether
they be large or small. Let this process be atten-
tively considered and, if possible, watched by the
reader. The sulphur disappears in solution ; the
solvent evaporates, and the sulphur reappears, this
time in definite crystalline form. The ultimate atoms
of sulphur do not aggregate themselves together into
haphazard masses. They never form into round
balls or cubes, always into the rhombic figure ; and
the crystals are always found to be largest when they
are able to form most slowly. Prolong the evapora-
tion by making it take place in a cool spot, and the
crystals are both larger and more perfect. Thus it
is clear that, in the formation of solid sulphur, some
very interesting architectural force is at work, shaping
the atoms in this precise and definite way. The atoms
doubtless first group themselves into molecules ; these
molecules exercise their attracting force on one another
unequally in different directions, with the result that a
small crystal forms ; to this small crystal new mole-
cules adhere, guided by the same force, and the crystal
thus grows by successive invisible accretions of new
molecules.

But why crystals of sulphur are necessarily rhom-
bic, while those of sand, for example, are as consis-
tently hexagonal, is a mystery of the molecules them-
selves. The study of the many different crystal-forms
that " earth " can assume impresses us prof oundly with
the intricacy and variety of the " loves " and " hates "
of the atoms. Whenever a solid forms slowly from its
solution in a liquid, it takes its own special crystalline
form. The reader may easily watch the process for

189

THE STORY OF THE FIVE ELEMENTS

himself, if he will dissolve as much alum or saltpetre
as he can in hot water and then leave the liquid to
cool ; the different shapes of these and other crystals
that come across our common experience are well
worthy of observation (p. 160).

To return to sulphur : if some flowers of sulphur
are melted in a small earthen crucible and the liquid
allowed to cool, and if as soon as a solid film begins
to form on the surface the still liquid sulphur be
rapidly poured out from beneath it, the solid adhering
to the sides of the crucible will be found to have
crystallised in the form of long needles, which are
not of the rhombic form. Close examination shows
them to be monoclinic, i.e. to have one of their axes
of symmetry oblique to the other two. Under these
special circumstances the sulphur is made to assume
a new crystal form. But this form does not last ; it
is unstable, as we say ; and if it is kept for a day or
two will be found to change slowly into the rhombic
form. The method of crystal formation here indicated
is, it will be noticed, not the same as in the previous
case. The liquid sulphur crystallises, as it solidifies
or freezes ; the crystals are therefore formed at a
higher temperature, and, under the conditions of our
experiment, in a hurried manner. The molecules of
sulphur have not time to arrange themselves in their
normal style of architecture ; a compromise is hastily
effected, and the perfect, finished crystal-edifice is
completed slowly. The final result goes to show that
the rhombic form is the natural habit of the sulphur
molecules. When the monoclinic crystals pass into
the rhombic, a little heat is liberated ; this heat
represents some of the energy that is required to keep

190

DIFFERENT FORMS OF SULPHUR

the sulphur molecules in their unstable and unusual
form, just as energy is required to support any edifice
that is anxious to collapse.

Roll sulphur, having been formed by the solidifica-
tion of liquid sulphur, is a mass of crystals in the
rhombic form ; but the flowers of sulphur obtained
from the walls of the refining chamber is formed from
the vapour, and is amorphous. It is a powder whose
particles show no trace of the geometrical forms that
we see in roll sulphur. Moreover, it does not dissolve
in carbon disulphide, as roll sulphur does. Yet it is
sulphur, as truly as is roll sulphur ; it goes through
the same series of changes when it is heated, and,
after being melted, crystallises into the rhombic
crystals with which we have become familiar. The
milk of sulphur of medicine is similarly an amorphous
form of the element prepared by decomposing alkaline
sulphides with dilute acids.

In order to account for the differences between the
amorphous and crystalline forms of sulphur, it is neces-
sary to go down to the atoms, and to suppose that
these may group themselves in different numbers,
with different results to the properties of the mole-
cules formed. Suppose a certain number of atoms, say
eight, to come together, and that one molecule results
from their mutual attractions which has the power
to form crystals with other similar molecules. This
might then be the habit of sulphur when it is in a
condition to form the rhombic crystals, i.e. when it
is liquid. But we have evidence for the belief that
in sulphur-vapour these complex molecules are sim-
plified into smaller groups — into molecules which
contain, say, only two atoms each, As flowers of

191

THE STORY OF THE FIVE ELEMENTS

sulphur is formed straightway from these, its mole-
cules may well be supposed to contain fewer atoms
each than those of the rhombic crystals — to be, at
all events, different in some such way, and thus to
yield a variety of sulphur that is incapable of form-
ing crystals. The differences between the two kinds
of sulphur is not in their chemical actions : the atoms
are the same in the two cases, but are grouped in
different numbers and possibly in different ways. They
may hold together in twos, in fours, in eights, maybe in
larger numbers ; and of the varied molecules thus
formed, which are of course individually far beyond
the range of the best microscopes, some will appar-
ently group themselves anyhow in amorphous fashion,
while to others belongs the special power of organising
themselves into crystal-forms.

A further variety of sulphur may finally be men-
tioned. When molten sulphur is carefully heated, its
colour will be observed to change from a light amber-
yellow to a deeper red, and ultimately to become almost
black. At that point the liquid is more viscid than
treacle. If this thick liquid be allowed to drop into cold
water, it is found to set into a dark brown gummy
mass known as plastic sulphur. This mass is obviously
amorphous, but obviously also very different from the
powdery flowers of sulphur. Clearly it shows our
element in still another molecular condition. These
molecules are different from those which form ordinary
liquid sulphur and those which form sulphur-vapour,
doubtless in containing a different number of atoms.
They cannot move freely among themselves : hence
the liquid is viscid ; and, being suddenly cooled in this
condition, they have not the power to rearrange them-

192

FORMS OF SULPHUR

selves into those atomic groups which yield the
crystal-forming molecules. Hence arises the plastic
solid. But, as this comes from an abnormal set of
circumstances, we should expect it to be an un-
stable form ; and, on being allowed to stand for a
few days, it actually does become hard and yellow,
like ordinary roll sulphur. Yet even while plastic it is
still sulphur and sulphur only, in its atomic founda-
tion. It shows us again how atoms of the same kind
may be variously grouped into molecules which have
quite different physical properties.

These transformations of sulphur, known as they
were to the alchemists, may well have puzzled them
greatly ; and we need not wonder at the shifty dis-
guises under which their " sulphur-principle " appeared
in their speculations. But as further and even deeper
mysteries, this same sulphur disappears completely
into a smoky fume when it is burned, and destroys
the nature of most of the metals when it is heated with
them. We have already learned what the nature of
the smoky fume is : it is a gas — sulphur dioxide — not
an element, not an impure " fire/' but a compound in
which the sulphur still exists, though with its activi-
ties modified by the companionship of another ele-
ment. And in regard to the metals, the case is not
essentially different. The atoms of the metal unite
with the atoms of sulphur, and form new molecules
which contain both and are called sulphides. Thus,
symbolically :

Fe + S FeS

One iron atom One sulphur atom One molecule of iron sulphide.

These sulphides have no metallic properties, and
show no sign of the sulphur they contain. Yet it is

THE STORY OF THE FIVE ELEMENTS

quite easy to prove that both are there. Indeed,
many of them are to be found in the earth, and form
the commonest and most easily worked ores for the
metals contained in them. Thus there is galena, or lead
sulphide, which has only to be roasted in the open air
to yield bright beads of lead along with clouds of the
choking fumes characteristic of burning sulphur and
a film of the oxide of the metal. The mere roasting
has revealed the metal and the sulphur in this sul-
phide. By the alchemists, galena seems to have
been read as an impure metal. It has a dull grey
metallic lustre, something like that of black-lead.
The driving out of the sulphur only increased the
proportion of the mercury-principle ; and when, out
of some lead ores, a small amount of silver could
also be got, it is not difficult to account for the alche-
mists' belief. Silver is nearer to the pure metallic
essence than lead, and lead nearer than galena. Of
course really the silver is but an impurity in the
lead.

Other sulphides of interest are pyrites (FeS2) ;
copper pyrites, containing copper, iron, and sulphur ;
zinc blende (zinc sulphide) ; orpiment (arsenic sulphide) ;
and so on. They are found in various parts of the
world, generally in older rocks, and often beautifully
crystallised. Pyrites has a golden lustre, and its
crystals are found in the faults and cracks of the rocks,
as if they have been deposited there from infiltrating
waters. Like the other sulphides, it is also found in
mineral veins ; that is, in larger or smaller masses
intruded in other rock-masses. These mineral veins
tell us a tale of prolonged water-action on the solid
rocks, of the accumulation of this water in the

J94

SULPHIDES

gaps and cracks underground, and of its very slow
evaporation while the minerals have leisure to crys-
tallise in their perfect forms. Many other valuable
substances, besides the sulphides, are to be found
in them.

We have dealt with sulphur in this rather full
manner, because it is a substance in which the charac-
teristic earth-property of solidity is well and easily
exhibited. As an earth or " solid/' it is capable of
existence in the crystalline, amorphous, or plastic
form, according to conditions. We learn from it how
the mere action of heat alone is sufficient to destroy
its " earth " nature, and to endow it successfully with
the water and air " elements.'* We see how its atoms
are capable of arranging themselves in different
aggregations, and of forming thus its different appear-
ances. We note finally how those atoms have a dis-
tinct liking or affinity for certain metals, as well as
for oxygen and other elements ; and how from this
liking there arise many compounds in which sulphur
is one of the partners. It illustrates well the possi-
bilities of a solid element, an important contributor to
the minerals of the earth-crust.

We might, though not so well, have told similar
tales of other elements like carbon or phosphorus, or
many metals. The former, for example, is well known
in the various forms of charcoal, and can be proved
to exist in a pure crystalline condition in diamonds ;
it may well give us room to ponder over the wonder-
ful results of atomic rearrangings, when we recollect
that the very atoms which compose charcoal could
under changed conditions form a diamond. Charcoal
dissolves in molten iron, and the liquid, if cooled

'95

THE STORY OF THE FIVE ELEMENTS

slowly and under great pressures, deposits the carbon
in small crystals, which are in effect diamonds, though
how diamonds have been formed in Nature we can-
not yet tell. Diamond and charcoal are different
enough, yet fundamentally the same ; burnt in air,
they produce only one gas, the same for both ; their
atoms prefer seemingly to be amorphous, and are
refractory to deal with, yielding to the crystal-forming
forces only under strong coercion. They do not take
to the liquid state under any easily obtained terrestrial
temperature ; and only in the intensely hot electric arc
are they driven into the gaseous form. But, however
different among themselves the true solid elements
may be — whether highly active like phosphorus, easily
melted and changed like sulphur, inert and infusible
like carbon, metallic and readily changed like iron, or
metallic and unchanging like platinum — it must be
remembered that they are the true elements of the
earth, the true raw material of the old earth-element.
They do not occur in any large quantity free, and we
should not expect that they would. Moreover, it must
not be supposed that the solid elements alone are to
be found in the rocks of the earth. The elements of
the air, especially oxygen, would be exceptionally
active at the higher temperatures of the earth's earlier
ages ; elements like sulphur, phosphorus, and many
of the metals would certainly be converted into their
oxides ; and naturally, therefore, we should expect to
find many compounds containing oxygen even in the
solid earth. This proves to be so strongly the fact
that quite one half of the solid crust of the earth is
supposed to be oxygen, combined with one or more
of the other elements.

196

Plate VI

^•.•53F-:. - . ' •-.V£i'irf*>-»^av -^.4

. .^ ' -^ ' ?•:*?-*, ??*?''&£(

* •*'

MICROSCOPIC APPEARANCE OF (1) CHALK COMPARED
WITH (2) GLOBIGERINA OOZE

FORMS OF CARBON

III. — CHALK AND ITS RELATIVES

Sulphur, although an interesting and important
element, in spite of its deposition from the conspicu-
ous pedestal on which the alchemists placed it, is,
nevertheless, not of any large occurrence either alone
or even in compound form. Sulphides may form fairly
extensive mineral veins ; but they do not form any
of those great rock-masses which span great areas of
the earth's surface. It is obviously these — the clays,
sands, granites, limestones — wherein the earth-element
will be most characteristically present. We must learn
how some of these stand in regard to our modern
elements, and erect a finger-post to point out the road
leading to a knowledge of their exact nature.

Let us take, for our first rock-substance, chalk.
The first question which chemistry has to put to it is,
element or compound — which ? As a preliminary
step, we examine its personal appearance thoroughly.
This is familiar enough superficially ; it seems a soft,
amorphous white powder, and no more. But a micro-
scopic study of its structure reveals the fact that it
is almost entirely composed of the remains of the
very small shells belonging to the lowly family of
Foraminifera, the chief type present being one of
spherical form called Globigerina. Very similar shells,
although not quite the same, are found in some kinds
of the ooze dredged from the deep sea floor, at depths
from 1,500 to 2,000 fathoms. Chalk is, therefore, not
a crystalline nor an amorphous rock, but clearly of
organic origin ; and its materials must, in the first
instance, have been obtained from the sea in which

the foraminifera lived.

. -

197

THE STORY OF THE FIVE ELEMENTS

This, however interesting it may be, does not,
nevertheless, lead us much nearer our chemical goal.
We therefore proceed to inquire into the changes our
substance may undergo. Now, everyone who lives in
a chalk district will be familiar with the process of
lime-burning, in which the chalk is put into large kilns
and subjected to the heat of a steady fire for some
time, wherefrom it is withdrawn in a new guise : it
has been changed into lime. Is this a chemical
change ? Is lime a new substance, or merely the
chalk in slight disguise, as plastic sulphur is only
another form of roll sulphur ? In order to answer
this, let us contrast the behaviour of the two ; and we
need only appeal to familiar facts.

First we note but a slight change in the appearance
of the chalk, insufficient at all events to base any secure
deduction upon. But if a small piece of each is soaked
with water, the chalk becomes merely a slimy mass,
whereas the lime grows hot and presently falls into
a dry, white powder : lime can be slaked and chalk
cannot. Again, if both chalk and lime are separately
shaken up with some distilled water, the muddy
liquids filtered, and the clear liquids that filter through
evaporated to dryness, no solid residue will be left
in the case of the chalk, whereas the lime water will
be seen to leave a residue of lime. Hence lime does,
and chalk does not, dissolve in pure water. Are
these differences sufficient ? In order to clinch the
matter, we weigh out a quantity of chalk and heat
it in a crucible. The weight of lime left is found to
be less by more than 40 per cent, than that of the
chalk originally taken, and this result is obtained
whether the air be excluded or not. We are therefore

198

GHALK AND LIME

free to conclude that chalk is not a true element, and
that lime is one of its constituent parts. That the
other is a gaseous substance is rendered most likely
by the loss of weight ; simple experiments prove that
it is the carbon dioxide discussed on p. 88. Thus
chalk becomes a compound of lime and carbon di-
oxide.

The latter of these substances is itself a compound,
and the nature of lime is still a problem before us. No
simple process is available for its decomposition. No
amount of heat seems to have the least effect upon it,
except to make it glow intensely, without altering its
properties. The most definite of its chemical proper-
ties is its action towards water, with which it forms
a new compound called slaked lime, soluble in water
and giving an alkaline liquid. It is one of the most
stable of substances, and it is only by indirect means
that it can be shown to be the oxide of a metallic
element known as calcium. Like the other alkalis,
soda and potash, lime contains an exceedingly active
metal, which undergoes oxidation readily. On account
of its earthy nature, lime is called an alkaline earth ;
but, strictly speaking, only its solution in water is
really alkaline, and that is not necessarily the same
thing as lime itself.

We thus realise that chalk is a compound of two
substances, each of which is in its turn a compound
— lime and carbon dioxide ; or, in symbolic language :

CaCO3 = CaO + COg

[Chalk : One Molecule] [Lime : One Molecule] [Carbon Dioxide : One

Molecule]

A considerable temperature is needed before all the
carbon dioxide is driven away from the chalk ; but

199

THE STORY OF THE FIVE ELEMENTS

any diluted acid will effect this rapidly and is at the
same time neutralised. Any substance which behaves
in this manner — yielding carbon dioxide with a brisk
effervescence when acid is poured upon it — is known as
a carbonate. The pure substance which forms the basis
of chalk, and becomes lime when it is heated, is
therefore properly known as calcium carbonate ; and
many similar compounds are known in which other
metals play the part of the calcium in chalk. The
brown clay ironstone which is one of the most impor-
tant of iron ores is mainly iron carbonate (FeC03) ;
the familiar white-lead of the painters is a carbonate
of lead ; and the common washing-soda of every-
day use is a crystalline form of sodium carbonate
(Na2C03). All these substances agree in their ready
loss of carbon dioxide gas, with accompanying effer-
vescence, when a dilute acid is added to them.

Returning to calcium carbonate, our readers will
hardly need now to be told that limestone is another
form of it. It is well known that in many districts
limestone is used for the production of lime : in the
chemical sense limestone and chalk are identical.
Apart, however, from its occurrence in large shells,
limestone is much harder than chalk ; some forms of
it are, in fact, hard enough to be used for building-
stone, and a very casual inspection only is needed to
reveal to us its finely crystalline nature. Marble
also is calcium carbonate, still harder and more com-
pact than limestone. Microscopic examination reveals
the fact that marble is made of many almost equal
grains, each of which is composed of a little collection
of crystals. Marble shows, indeed, every sign of having
been subjected to very great pressures ; it is generally

200

CALCIUM CARBONATE

found in the earth in the close neighbourhood of
igneous rocks, i.e. of rocks that were once in the
molten condition ; and what seems to have happened
is that a fiery lava intruded itself into a mass of lime-
stone, subjecting the limestone near it to intense
heat, while the pressure of the overlying rocks
prevented the escape of carbon dioxide. The lime-
stone was therefore brought into a fluid or semi-fluid
condition, from which condition it solidified, as the
intruding lava cooled, in the crystalline form ; just
as we saw that liquid sulphur yielded us a crystalline
mass when it solidified into roll sulphur. The great
pressures prevented the formation of large crystals,
though the process of cooling was exceedingly slow ;
the pressure, too, was responsible for the granular
fracture of the changed rock.

We thus see that the compound calcium carbonate,
like the element sulphur, is capable of entering into
various molecular arrangements or groupings, which
result in the compound taking upon itself either a
crystalline or an amorphous habit, according to cir-
cumstances. The crystalline habit may be assumed
by large masses of rock, as in limestone or marble ;
but more conspicuous crystals are often found which
suggest a very slow formation from solution. These
crystals form the mineral called calcite, which can be
easily recognised, when the crystals are well formed,
by its fracture. When struck, a mass of calcite breaks
up easily into fragments, which may be of very dif-
ferent sizes, but are all alike rhombs, i.e. figures in
which every face is a parallelogram. The rhombs may
vary in shape within very wide limits ; but the angles
at corresponding corners of the crystals are always

201

THE STORY OF THE FIVE ELEMENTS

the same. The smallest crystals of calcite, formed by
the molecular habits peculiar to calcium carbonate,
fit themselves into larger crystals, very much as the
individual bricks in a piled stack are arranged when
they do not overlap : the whole stack will have the
same angles, but only in a general sense the same
shape, as the individual bricks ; and what happens
when a portion of the stack is broken away illustrates
very well what is meant by the regular fracture of
crystals. In a mass of calcite the crystals are fitted
together as compactly as is possible ; in ordinary lime-
stone the crystals are heaped together haphazard, not
without injury to their individuality.

Calcite, as ordinarily found, is opaque ; but in
Iceland the crystals are often transparent and give
us the beautiful mineral called Iceland spar. This
has the very unusual property of double refraction,
by which any object viewed through a piece of it is
seen double. The crystals of Iceland spar are, how-
ever, rhombs, like those of calcite. A different crys-
talline form altogether is found in aragonite, another
species of calcium carbonate, found in mineral veins,
near geysers, and under other conditions which sug-
gest that it has been formed by crystallisation from
hot water. It is said to be less stable than calcite ;
if so, it bears the same sort of relation to the rhombic
form as monoclinic sulphur does to its rhombic form.
However this may be, we find here abundant evidence
of the crystallisation of calcium carbonate from some
solvent, just as sulphur crystallised from carbon
disulphide.

That the solvent is in all probability water is ren-
dered reasonable to our minds by the familiar trouble

202

HARDNESS OF WATER

of hardness which so often affects our natural waters.
Everyone is familiar with the furr that lines kettles,
boilers, etc., in which such water has been boiled.
Everyone knows the simple fact that it is the waters
of limestone or chalk districts that are most affected
by hardness. Putting two and two together, everyone
has arrived at the conclusion that water dissolved the
calcium carbonate from the hills. Our chemical tests
would confirm the fact that the furr is calcium car-
bonate ; and it can all be dissolved out with a dilute
acid. And yet pure water does not in any measurable
degree dissolve chalk or any other form of calcium
carbonate.

But natural water is, of course, ultimately rain
water, and this is not necessarily pure. In passing
through the air, it has the chance to dissolve any of
the gases that occur in the air. Now, all the familiar
gases of the air dissolve in water to some extent ; and
if he will attend to the teaching of the following ex-
periment the student will learn that one of these gives
to the water the power to dissolve calcium carbonate.
When carbon dioxide is bubbled into lime-water a
milky deposit is gradually formed, which acts, in fact,
as a very ready test for the gas ; but, if the gas be
continued, we should notice the turbidity of the liquid
disappear gradually, leaving the liquid quite clear.
No further bubbling of the gas will restore the tur-
bidity or produce any other visible change. If now
the clear liquid be heated, bubbles of gas will be seen
to escape, in larger numbers as the liquid becomes
hotter ; and when it is boiled, the whole of the dis-
solved gas will escape and the turbidity will be found
to have returned.

203

THE STORY OF THE FIVE ELEMENTS

Let us contemplate these results carefully. First,
we attend to the turbid precipitate formed when the
gas is led first into the lime-water. What is it ? The
simplest suggestion would undoubtedly be the correct
one, namely, that it consists of calcium carbonate,
produced by a synthesis of the lime and carbon di-
oxide, and becomes visible as a white precipitate, because
of its insolubility in the water. It may be allowed to
settle or be filtered from the water, and shown assuredly
to be so. As long as there is any unchanged lime in
the liquid, the continued passage of the gas will increase
the turbidity by increasing the amount of calcium car-
bonate ; but at last all the lime will be converted into
the carbonate, and at that point the second phase of
the action will commence. The excess of carbon
dioxide now bubbled into the liquid evidently brings
about the solution of the calcium carbonate, which
just as evidently reappears when the gas is merely
boiled out of the water again. If the gas forms a new
compound when it is thus in excess, that compound
cannot resist the temperature of boiling water ; we
need not here inquire into that, but content ourselves
with the observation that calcium carbonate dissolves
to a considerable extent in water which also contains
carbon dioxide dissolved in it. Rain water which has
filtered through soil will most certainly contain carbon
dioxide, and will consequently have the power to dis-
solve some of the chalk or limestone through which
it may have to percolate. Thus the water becomes
hard, and is virtually a solution of calcium carbonate.
This hardness can be removed by boiling, and hence
is called temporary hardness, as distinguished from
the permanent hardness which boiling does not remove.

204

TEMPORARY HARDNESS

It can also be removed by the addition of more lime-
water, which throws down the excess of carbon dioxide
as calcium carbonate, and at the same time liberates
the original chalk or limestone from its solution.
Natural waters are thus partially softened for public
use.

The calcium carbonate precipitated by the boiling
process is a fine amorphous powder ; but when the
water in which it is dissolved is very slowly evaporated
crystals of calcite are usually formed. In Nature this
process is continually going on. Thus, for example, it
is -found that many fossils in very varied formations
are composed of calcite crystals ; the organic matter
of which they were composed has decayed and the
products of decay been removed by the infiltrating
waters ; but so slow has been the process that calcite
has been deposited in its place in perfect correspond-
ence with its original structure, and we have the
whole animal, as it were, petrified in calcium carbonate.
To the slow crystallisation of calcium carbonate is
also due the formation of the beautiful stalactites
which hang like rocky icicles from the roofs of many
caverns ; the flatter stalagmites which are formed
opposite to the stalactites on the cavern floors have
arisen from the water which dripped too soon from
the hanging stalactites.

Evidence of the rate of formation of these stalag-
mites has been obtained from Kent's Cavern at Tor-
quay, pointing to a growth of ^ inch in two cen-
turies. The increase is doubtless more rapid in the
Derbyshire caverns, where the spring waters will cover
any object like an open umbrella with such a deposit
of limestone that it seems to be completely petrified

205

THE STORY OF THE FIVE ELEMENTS

in a few weeks. But in that case there is a perfectly
free evaporation. Under natural conditions we have
to picture the solid masses of limestone or chalk being
very slowly pierced and riddled by the active water ;
we have then to follow this water into the interstices
of other rocks, into gaps, or spaces once occupied maybe
by dead organisms, and there quietly forming, accord-
ing to its own plans leisurely put into action, the .beau-
tiful crystals of calcite that are often found. Or
possibly, the water finds its way into springs, rivers,
and the sea ; and the common presence of calcium
carbonate in the shells of marine molluscs and other
lowly organisms of the sea reminds us of a possible
destination for the limestone dissolved from our
mountains. A limestone rock which has to endure
the rain is very clearly not terra firma when we think
of it through the centuries. Every particle of it was
once formed from water, and into water it will be
dissolved again — but only if the water contains carbon
dioxide !

i Dry quicklime does not take up carbon dioxide,
except under considerable pressures ; and we ought
not to part with it before noting that its action with
water is really a chemical change, and slaked lime
a different substance from quicklime. The latter, if
merely moistened with water, becomes in a few minutes
a dry, white powder, with evolution of heat ; it has
combined with the water and formed the new com-
pound, calcium hydroxide, as thus :

CaO + H2O = CaH2O2

Lime Water Slaked Lime

[= Calcium oxide] = Calcium Hydroxide]

It is this calcium hydroxide which dissolves in water

206

LIME

and forms lime-water, and the effect of carbon dioxide
upon it may thus be represented :

CaH2O2 + CO2 = CaCO3 + H2O

When it is mixed with sand for making the mortar
of the bricklayer, lime is first slaked ; and the first
stage in the setting process is the production of the
calcium carbonate with the carbon dioxide of the air
and the simultaneous production of water. As some
of the soluble slaked lime soaks into the porous bricks,
we can account for its action as a cement to the dif-
ferent layers ; and the water produced in its setting
shows us why a plaster remains so long damp. A fire
in the newly plastered room aids the setting process
both by its heat and by the carbon dioxide which it
affords.

Lime, we have said, is an exceedingly stable com-
pound in the sense that it is difficult to separate it
into its two constituents. In point of fact, this can-
not be directly done at all ; but indirectly it is done
in an interesting process which has become commer-
cially important. Electric currents have brought about
the decomposition of a number of compounds which
otherwise it is difficult to split up ; but in order that
electrolysis may be possible the substance must be
liquid. Lime, however, shows no sign of melting before
5,400° F., and it cannot be electrolysed directly even
then. If, however, it is mixed with finely divided
carbon and the mixture packed in the electric furnace
between two poles of carbon (Fig. 41), somewhat as in
an arc-lamp, the lime appears to be decomposed when
the high-tension electric current is passed through it ;
but both its constituents combine with the carbon imme-

207

THE STORY OF THE FIVE ELEMENTS

diately, and no true separation of them is obtained.
No decomposition at all occurs if the carbon is not
there ; consequently, the action is probably in part
one of reduction, the carbon by its affinity for oxygen

helping to draw the two ele-
ments asunder. However this
may be, the calcium does not
appear alone, but combined
with the carbon as calcium
carbide. This carbide is a
greyish solid with a disagree-
able odour ; when water is
allowed to fall upon it drop
by drop, it gives a gas called
Fig. 4i.-Eiectric furnace. acetylene, which takes fire

c, Crucible containing material to be ,., , , ..,

acted upon (m) ; /, positive eiec- readily and burns with a very

trode ; n, negative electrode of car- 1 _ j x O.T_

bon which can be raised or lowered. lummOUS llame \ anQ lOr the

The whole is surrounded by a hoi- .,, . . . ...

low metal jacket i, packed loosely illuminating properties of thlS
with non-conducting material a. .

gas calcium carbide is now

manufactured by the process above noted. The large
amount of energy that is required for that process is
an indication of the tenacious' nature of the combina-
tion of calcium and oxygen in lime.

Lime water, a solution of calcium hydroxide, is
highly alkaline ; the molecules of calcium hydroxide
are therefore supposed to be partly dissociated in
solution into ions, the calcium ion being separated
from the hydroxyl ions, as thus :

CaH2O2 (in solution) = Ca+ + (OH) + (OH).

Thus, in solution, the calcium is conceived as separated
from its oxygen. Now, if we can find some means of
keeping this ion away from the oxygen, we can at the

208

CALCIUM CARBIDE

same time decompose our lime. The electric current
is not sufficient, because as soon as the calcium ions
begin to combine into calcium molecules they proceed
to act on the water and produce lime and hydrogen
again. If an acid be mixed with the lime-water, how-
ever, its negative ion may so be chosen that it carries
off the calcium ion with it in the form of a new com-
pound. Like all acids, sulphuric acid has hydrogen for
its positive ions, and it so happens that its negative
ion forms almost insoluble molecules with the calcium
ion. In these new molecules, therefore, we have the
calcium, in an indirect way, parted from its original
oxygen. The new molecules are those of a substance
called calcium sulphate ; and it is perfectly easy to
produce it from lime, as well as from slaked lime, or
from lime-water, by addition of sulphuric acid. In
symbols, thus :

CaO + H2SO< = CaS04 + HaO

Lime Sulphuric Acid Calcium Sulphate Water

Ca.2(OH) + HH(SO4) = CaS04 + 2H2O

Slaked Lime in Water Sulphuric Acid in Water

All acids will form new substances in this way with
lime ; only in some cases the solution must be still
further concentrated before the new compound will
appear. Of these compounds, calcium phosphate, as
the chief mineral constituent of bones, is the most
important.

The compound called calcium sulphate (CaSOJ
occurs very widely as a natural mineral ; it is then
known as gypsum. Usually it forms large masses of
compact crystals, often fibrous in fracture, and very
frequently it is found in association with rock-salt.
It is soluble in water to a small extent, and is, next to
o 209

THE STORY OF THE FIVE ELEMENTS

salt, the most common dissolved impurity in the sea
and salt lakes. When the water in these latter begins
to become scanty, gypsum is always deposited in a
crystalline mass along their floor ; but the salt, being
more soluble, does not solidify until the lakes are
nearly dry. If then we find, as we do, alternating
strata of gypsum and salt embedded in the earth, we
have very strong circumstantial evidence of the exist-
ence and drying-up of ancient salt lakes on the site ;
and in the present epoch such alternate layers are
being formed by the drying up and refilling of the
Dead Sea.

Gypsum dissolves in ordinary water, and natur-
ally it will therefore be found scattered among any
rocks that water can percolate ; that is to say, it is
almost everywhere. Large, isolated crystals of the
compound, called selenite, also occur to give evidence
of the transportal of the mineral into the hidden
crannies of the rocks, where a very slow crystallisation
can take place. The water which contains it has the
property of permanent hardness, which can only be
removed by chemical actions, and not by boiling. All
kinds of hardness are caused by the presence of some
calcium-containing compound in the water. It is the
calcium which forms the scum, or precipitate, when
soap is added to the water ; all the calcium has to be
chemically removed in this scum before the soap will
give its lather ; and the scum thus represents a large
waste of soap, as well as an inconvenience. Soap softens
the water, but very expensively ; and for permanent
hardness it is best to precipitate the calcium with com-
mon washing-soda. The soda is a carbonate, and forms
insoluble calcium carbonate, thus :

2IO

GYPSUM

CaSO< + Na2CO3 = CaCO, + Na2SO4

Calcium Sulphate Soda Calcium Carbonate Sulphate of Soda

(Insoluble) (Harmless)

It is useless to add lime in this case, as there is no
carbon dioxide to destroy ; and lime-water is itself
permanently hard.

Very few springs are without gypsum in more or
less degree dissolved in their waters ; but, as show-
ing the manifold variety of chemical changes that
take place in our solid earth, we will mention one of
its possible transformations. Water that has passed
through a soil contains necessarily a considerable
amount of organic matter in a state of more or less
complete decomposition. Such matter makes the
water a reducing agent ; any substance in it that can
yield oxygen will be tempted to do so, in order to fur-
ther the decomposition, and will itself be reduced to
a less advanced stage of oxidation. Thus gypsum,
calcium sulphate (CaSO4) will, on yielding up its
oxygen, become calcium sulphide (CaS). But calcium
sulphide, in the presence of even the feeblest acid, is
unstable, giving a gas, known as sulphuretted hydro-
gen, with the fetid odour of rotten eggs. The smell
will be familiar to those who know the medicinal
waters of Harrogate and other sulphurous springs.
Water containing this gas, however, slowly deposits
sulphur itself when it comes into contact with the
air ; and thus some of the sulphur found in Nature can
be traced back to gypsum as its original source ; but
of course it existed in the compound molecules of
gypsum all along.

When the calcium sulphide gave up its sulphur as
sulphuretted hydrogen, an acid was required, and this
is to be sought in the carbon dioxide, which is always

THE STORY OF THE FIVE ELEMENTS

faintly acid when it is dissolved in water. We shall
not, therefore, be surprised to see the calcium from
the sulphide transformed into carbonate, in the sense
of the equation :

CaS + C02 + H2O = CaCOg + H2S

(Sulphuretted Hydrogen)

This gives us an indication of a possible method of
accounting for the production of calcium carbonate
by the animals of the sea in such vast amounts. There
is little carbonate present in sea-water in the ordinary
way ; there is much sulphate, and the transformation
has to be accounted for in some way. In all probability,
therefore, we are to look upon calcium sulphate as an
older terrestrial substance than the carbonate ; the
link between gypsum and limestone being forged by
the molluscs and other shell-organisms whose shells
are composed of calcium carbonate. As for the origin
of the gypsum itself, it is not possible to speculate
profitably upon that at present.

The changes which gypsum has been thus undergo-
ing over the long periods of time covered by the earth's
history prove to be of unexpected interest ; it does
not diminish this interest to find it filling a little niche
in the practical arts of civilised man. When it is
heated carefully a little beyond the boiling-point of
water, gypsum loses water and falls into a fine, heavy,
white powder. This water was absolutely necessary to
its assumption of the crystalline form, and shows con-
clusively that it was deposited from standing water,
and not merely through the liquid's complete evapora-
tion to dryness. The powder left is amorphous, and
is well known as plaster of Paris. The use of plaster
of Paris depends upon the fact that it will absorb

PLASTER OF PARIS

water and re-form gypsum. If the powder is thoroughly
moistened and then shaped by a mould into any
desired form, it will quickly harden, because every
fine grain of it combines chemically with water, form-
ing small crystals of gypsum in a very compact, fine-
grained mass.

A little water still remains combined in the dry
plaster of Paris, for if this is overheated the residual
water is driven off and a perfectly anhydrous calcium
sulphate is obtained. This is found to be quite use-
less for moulding ; it will re-form gypsum certainly,
but the resulting crystals are not consolidated into a
firm and compact mass. In Nature the anhydrous
substance is found where salt-lakes have been com-
pletely dried up. It is there harder and heavier than
gypsum, into which it is converted, with evolution of
heat, by the slow action of water. It is most interest-
ing, however, to notice that the successful action of
plaster of Paris is dependent upon so small a matter
as the retention of a little water. The crystals of gyp-
sum are supposed to contain two water-molecules,
associated in loose union with one of calcium sulphate ;
in plaster of Paris the proportion is reversed, thus :
Gypsum = CaSO4.2H2O

Plaster of Paris = 2CaSO4.H2O

Anhydrous Sulphate = CaSO4

In many another preparation in chemistry, inatten-
tion to an apparently insignificant detail like this is
fatal to the success of the operation.

We have thus in lime, limestone, chalk, and gypsum
dealt with a group of earth-substances of wide occur-
rence and consequently very many interests. The
element that binds them is the metal calcium, of which

213

THE STORY OF THE FIVE ELEMENTS

we have seen nothing in our descriptions, and it is by
no means easy to isolate. In fact, until quite recent
electrical improvements have facilitated its prepara-
tion, it was very little more than a chemical curiosity.
Is calcium, then, the earth-element ? It is, at any
rate, one of them ; but not more than oxygen, which
also enters into all these compounds, can it be re-
garded as the only and characteristic constituent
of " earth." All and any of the elements can
enter into the composition of the many varied earth-
materials. One special group is so important, and so
different from our calcium group, that we must now
just break the ground in preparation for a fuller study
at a more advanced stage.

IV. — SILICA AND SILICATES

The calcium minerals and rocks furnish us with
examples of earth-substances in the formation of which
the water element has played a conspicuous part. We
must spare a few pages in inquiring whether those solid
rocks, which are fire-formed in the earth's interior, and
anon issue from its surface in lava-streams, are of essen-
tially different nature.

Examine, then, a piece of granite, and read the tale
of its formation. When it is in the unpolished state its
story can be easily read in its physical structure with
the naked eye ; and a careful inspection reveals clearly
its threefold composition. We can see a blackish
mineral which readily peals off in small flakes with a
penknife ; along with it is a glassy, clear substance
which the knife will not scratch ; and the third con-
stituent is a dull white or pink mineral which readily
gives under the knife. Further, it would seem that

214

THE MINERALS IN GRANITE

these three minerals form together a crystalline mass,
but that each one exists quite separately and inde-
pendently of the other. Granite is therefore a mixture
of the dark mica, the glassy quartz, and the dull and
readily-scratched felspar ; a mixture in which the three
constituents are in no constant proportion, but where
each occurs in its own independent crystalline habit.

None of these minerals is affected by water or even
by acids in the ordinary way ; the crystals were prob-
ably not formed from solution, therefore, but from
fusion ; their size assures us of a very slow formation,
and the evidence thus converges on to the supposition
that granite was once a molten rock or lava, and solidi-
fied under slow-cooling conditions, probably deep down
in the earth-crust. In other
words, granite is a product
of earth's deeps ; its min-
erals have stood the great
temperatures of the earth's
interior ; its materials are of
those which form the basis
of the earth-crust ; and it is
as well to take a glance at
their characteristics.

Quartz turns out to be

the simplest of them. Like „., 42 Rock.cry!tal.

many other natural sub-
stances it is found in several forms : sometimes amor-
phous, as in flint and opal ; sometimes semi-crystal-
line only, as in chalcedony ; sometimes in large masses
of small crystals, as in sand and sandstone ; some-
times beautifully crystallised in large six-sided prisms
with pyramidal ends, forming then what is known as

215

THE STORY OF THE FIVE ELEMENTS

rock-crystal. Its crystals are often found in mineral
veins, and as intrusions in other rocks ; they are fre-
quent in fossils, and under such circumstances as show
that it has replaced other minerals, such as calcite.
Under various forms or other, therefore, it is an ex-
tremely widespread substance. The matter of which
these various forms are built up is known as silica;
and, as one would expect, it is an exceedingly stable
substance. It has, however, been shown to be a
compound — an oxide, in fact, of an element similar
to carbon when it is isolated — an element which, like
carbon, also returns easily to its combination with
oxygen ; it is known as silicon, and silica quartz
and its various forms are really silicon dioxide (Si02).

Silica is a very obtuse substance towards chemical
reagents ; none of the common solvents dissolves it ;
acids do not affect it, except hydrofluoric, which turns
it into a gaseous compound. Yet the circumstances
under which flint and quartz often occur make it clear
that some sort of solution of silica must be effected in
Nature. Flint almost certainly is of organic origin,
and if so its silica must have been obtained from
sea-water ; in the deep sea certain organisms are found
which have siliceous shells. It seems highly probable
that the other impurities of the water, especially when
they are alkaline, confer on it the power to dissolve
silica ; but the process cannot be directly imitated
with quartz or sand or other natural forms of silica.

If silica cannot, however, be directly dissolved or
decomposed, we might suppose that, like lime or carbon
dioxide, it would be able to enter into new combina-
tions. That this is the case is one of the oldest pieces
of chemical knowledge. When a clean white sand,

216

GLASS

which is nearly pure silica, is mixed with chalk and
soda, and the whole heated, the mass melts and solidi-
fies afterwards into glass. This process was in its
essentials known to the ancient Egyptians ; and we
are well aware that mediaeval church-builders had
discovered, not merely how to make a good glass, but
also how to colour it in several beautiful tints. A
harder and altogether better glass is obtained when
potash is used instead of soda ; this is the Bohemian
glass used for the construction of scientific apparatus.
Further, the chalk (or lime) is replaceable by lead
oxide (or white-lead), to give us the highly re-
fractive flint-glass used for the best optical instru-
ments. Whatever kind it is, the glass has the same
peculiarly glass-like characters : it is brittle, trans-
parent, amorphous ; it readily melts before the blow-
pipe into a pasty liquid that can be moulded, blown,
or worked into any shape that may be desired ; it
resists the action of nearly all chemical agents, except
hydrofluoric acid and the strong boiling alkalis, potash
and soda. It is the combination of these properties
that makes it so valuable a substance.

If soda is used alone in the fusion with sand, the
glass which we obtain is soluble in water ; and when
heated to dryness with an acid gives amorphous silica
and a salt. We are thus drawn to regard the glass
as a combination of soda with silica, as a kind of salt
in which the acid part is played by the silica. The
soluble glass will then be properly named silicate of
soda ; while ordinary glass is a mixture of the silicates
of soda (or potash) and lime (calcium). Nothing could
be less like our ordinary conception of an acid than
silica is. Yet its readiness to enter into combination

217

THE STORY OF THE FIVE ELEMENTS

with the molten alkalis, and its consequent produc-
tion of a whole series of silicates, is proof enough
that it acts the part. Besides, a curious gelatinous
compound can be prepared which is named silicic acid,
and yields when heated nothing but water and amor-
phous silica ; by indirect means the silica has thus
been compelled to combine with water and to produce
the very faintly acid substance, silicic acid.

If then we grasp this fact clearly, that silica can
with fused alkalis be coerced into combination as the
acid constituent of a group of silicates, we shall be
prepared to understand the part which it plays in
mineral formation. For, think of the condition of
the metallic elements in the early stages of the earth's
history. How could they, themselves vapours, resist
the strong affinity of the vast stores of oxygen by
which they were surrounded ? They would ultimately,
most of them, become oxides ; and in the hot, molten
condition these oxides would form silicates, by union
with silica, as in the process of glass manufacture. We
shall not be surprised at finding, therefore, large stores
of silicates among the fundamental, and especially the
volcanic, rock materials of the earth. Vast quanti-
ties of silica remained uncombined, as the presence of
free quartz shows ; but far vaster quantities were
taken up by the metallic oxides, and converted into
silicates.

We have mentioned the fact that glass is corroded
by boiling alkalis. This is a fact not difficult to inter-
pret when we recollect that the lime which forms an
essential constituent of glass is an alkali weaker than
soda or potash. The silica, therefore, when the choice
is presented under favourable conditions, will prefer

218

SILICA AND SILICATES

the stronger alkali ; the lime will be replaced by the
soda ; and the glass turned into silicate of soda
entirely. As this is soluble in water, it is not difficult
to explain why the glass is appreciably affected by the
alkali. Any natural silicate or mixture of silicates can
be completely changed into silicate of soda if it is melted
with the soda. Now this silicate of soda is decomposed
by the weakest acids ; the silica is so weak in its acid
affinity for the alkali that even carbonic acid, the
solution of carbon dioxide in water, is sufficient to
set it free ; the alkali becomes a carbonate, and the
silica is liberated.

We can thus perceive the principle of the process
by which silica can be released from the silicates. But
does this process operate in Nature ? In a slow and
modified degree we may answer yes. Fused alkalis
we do not meet ; but an alkaline water, even when it
is dilute, will, given sufficient time, attack the natural
silicates forming the soluble silicate of soda ; and it is
in this form that the silica is dissolved in water. Almost
certainly we may then assert that the silica itself
is precipitated through the action of carbonic acid, or
by the action of living organisms. Certain kinds of
ooze dredged from the deep sea consist almost entirely
of minute organisms called Radiolaria, with beauti-
fully marked siliceous shells ; and flint is often dark-
coloured, to remind us of the living creature that com-
menced the precipitation of the silica of which it is
composed. The exact conditions under which the
splendid crystals of quartz are formed cannot, how-
ever, be said to be fully known ; when thrown out of
silicate of soda by an acid, the silica is amorphous,
but possibly this uncrystalline silica can itself be

219

THE STORY OF THE FIVE ELEMENTS

somehow dissolved and re-deposited as quartz or rock
crystal.

The changes in the natural silicates which have
just been explained depend upon the presence of an
alkali, like soda or potash, in the water. What is the
source of this alkali ? In order to answer this, we
will turn briefly to consider one of the other constitu-
ents of granite. The mineral felspar is, like glass, a
double silicate : it contains two bases in union with
much silica, viz. potash and alumina. It is in vari-
ous forms one of the commonest of minerals, and, in
contact with the air, it very slowly undergoes a change
known as weathering. The change may be easily
observed in an exposed piece of rough granite. A
new piece of felspar, shown by a fresh fracture, is
lustrous and obviously crystalline ; an old piece
is rough, and, superficially at least, not crystalline.
Air and water, working persistently year by year, are
responsible for this change, which is not one of appear-
ance merely, but a true chemical change. The carbonic
acid has performed the same change as we have pre-
viously explained. It has decomposed the silicate of
potash into silica, which is set free, and potash, with
which it forms the alkaline carbonate of potash, which
is soluble in water ; the silicate of alumina is not
decomposed, but it becomes hydrated — that is, com-
bined with water — and carried away in suspension
as a very fine powder. Thus we see at once how a
natural water may become alkaline. The massive
silicates are slowly, very slowly, but quite surely,
corroded — simpler silicates, silica, and an alkali being
the result. We may represent it in tabular form,
thus :

220

WEATHERING OF SILICATES

Felspar \ SiHcate of Potash -t- Silicate of Alumina

Air, water
and C03

= Silica Carbonate Hydrated Silicate of Alumina

{Carried away of Potash {Carried away in suspension]

in suspension] {Dissolves in
water]

This decomposition of natural silicates by atmo-
spheric agencies is of great and necessary importance
in Nature. It is the condition precedent to the growth
of a soil and to making a home for incipient vegeta-
tion. In order that mineral substances may be utilised
by a plant they must first become soluble, and the
formation of carbonate of potash is the first step to-
wards this. Besides, no plant could grow on a firm,
unyielding rock like granite ; a superficial layer of
soil at least must be formed to give anchorage to
even the tiniest root-system. Once any form of vege-
tation has made a start, even if it be no more than
some lowly alga or lichen, the process of rock-change
will be speeded somewhat ; the decay of the first
plants will provide carbon dioxide and other soil acids,
which will render the water more active ; and new soil
will be added to the old. How slow the whole process
must have been in the first instance, when the solid
earth-crust consisted almost entirely of these highly
stable silicates, we can only vaguely realise. That
they did ultimately yield, the living forms of plant and
animal, with their age-long evolution behind them,
are here to show.

The insoluble materials formed by the decomposi-
tion of felspar, the pure silica and the silicate of alu-
mina, are either washed away or form a portion of the
soil in situ. In the former case they are carried off
by the water in suspension, and are forced to settle

221

THE STORY OF THE FIVE ELEMENTS

as soon as the water becomes stagnant. This hap-
pens, of course, as soon as it reaches a lake or the
sea ; and thus we find that deposits of sand and mud
are, and have been, in continual process of formation
in lakes and seas. Geologists have taught us how these
sands and muds have, in the course of ages, become
consolidated into the sandstones and clays of the solid
earth ; and we should therefore expect to find these
rocks containing our silica and silicate of alumina.
But felspar is only one of many silicates, such as
mica, hornblende, olivine, and many others ; and
these often contain other bases, such as iron, lime,
magnesia, and soda, instead of the potash and alumina
of felspar. We are therefore not unprepared to find
our sands and muds impure mixtures of many derived
materials. Sand is often enough red, for instance,
owing to the presence of iron oxide among the quartz
crystals ; clay, too, is often coloured more or less by
various compounds of iron, and in marl is plenti-
fully mixed with calcium carbonate. But there are
forms of clay in which almost the only mineral pre-
sent is silicate of alumina ; such is the pure white
clay known as kaolin. Such a clay is thus com-
posed exclusively of one of the substances set free
by the weathering of granites or other rocks contain-
ing felspar.

The particles of clay are amorphous and exceed-
ingly fine ; so fine that a mass of clay holds water
with stubborn tenacity. It is this water which makes
a clayey soil heavy ; it is that also which makes clay
a valuable substance for bricks, earthenware, and
porcelain. Clay in the moist state can be moulded
into almost any shape ; when it is baked its water is

323

GLAY

driven off, and a hard and fire-resistent material re-
sults. The latter property is exceptionally notable in
fireclay, to which some pure silica has been added ; it is
weakened very much if the strong alkalis are present,
because their silicates are fusible. For porcelain,
kaolin must be used ; for earthenware a less pure
clay will serve. In either case the result is porous,
and the material must be glazed. This is done, either
directly or indirectly, by forming a glassy silicate
on the surface : soda, or hme, or lead oxide is used for
this purpose ; and upon the skill with which this is
done depends the quality of the porcelain or pottery
obtained.

When clay is steeped in strong sulphuric acid and
warmed, it does not remain unaltered, as most sili-
cates do. The silica is liberated from it, and the
alumina dissolves. If the acid liquid be diluted, de-
canted from the silica, and some carbonate of potash
also added, there can be crystallised from the resulting
solution a familiar substance, much used for various
purposes — alum. This was known as a natural product
in very early times, and used as a mordant to fix the
colours in dyed cloths. We are mentioning it here, how-
ever, in order to draw attention to a rather remarkable
law. If soda had been used instead of potash in the
preparation of alum, we should still have obtained
what we should at once name alum ; because its
crystals are almost indistinguishable in shape from
those of the first alum. The interchange of soda and
potash produced very little change of property, and
none in the crystalline habit. Two different elements
can replace each other without making any real
change of molecular configuration. That this must

223

THE STORY OF THE FIVE ELEMENTS

be decidedly complex may be judged from the fol-
lowing formulae :

Potash Alum . . KAl(SO4)2.i2H2O
Soda Alum . . . NaAl(SO4)2.i2H2O
Chrome Alum . . KCr(S04)2.i2H2O

Alums are thus known which contain no aluminium,
but in which the aluminium is replaced by equivalent
elements. They are all isomorphous, and form their
crystals according to the same system. Let a crystal
of the dark purple chrome alum be placed in a strong
solution of ordinary potash alum, and it will grow by
the accretion of the molecules of the latter without
any alteration of shape. This fact of isomorphism
shows us then that, though there are many elements,
some of them have at least one common property to
group them in a sort of genus by themselves.

V. — GENERAL COMPOSITION OF EARTH

The base alumina of which we have spoken is the
oxide of the metal aluminium, which therefore exists
in vast quantities, wrapped up in the molecules of
its silicate, in the earth's crust. The metals are true
elements with whose properties we have not space
to deal here. As we have seen, they are found some-
times in the form of sulphides ; occasionally they are
found alone ; but more frequently they occur, like
aluminium, combined with oxygen, as oxides. These
oxides may occur, as the oxides of iron very largely
do, uncombined, or, more generally, formed into
silicates or carbonates. If, therefore, we wish to con-
ceive under a general view the nature of the earth-
element, we must commence with the earth in its hot,

224

THE SOLID EARTH

gaseous condition. As far as positive knowledge
now takes us, we must conceive some eighty different
fundamental stuffs or elements to have been exist-
ing then. Between the atoms of these elements
there were strong affinities, repulsions, and indiffer-
ences. For long, however, they were kept apart by
the high temperature ; then they began to combine
with one another, according to their affinities. Most
active oxygen evidently was : forming oxides with
metals like iron or aluminium, which were abundant ;
making oxides also with non-metals like sulphur,
silicon, and carbon. These oxides, too, have their
acid or basic affinities. Silicates result, as we have
shown, from the liquid earth ; carbonates, sulphates,
sulphides, come when all is cooler and solid crusts begin
to form.

The elements of water and the air now remain, to
set afoot those new changes in the solid earth which
we have endeavoured to adumbrate. The trans-
formations are still actively proceeding without cessa-
tion, but without hurry. Now and then overflows of
the original earth-rocks in volcanic activity remind
us of the conditions of bygone ages ; but on the new
rocks weathering begins to operate ; soils form, and
the vast, solid masses are slowly changed and carried
off, in suspension or in solution, to be subject to new
chemical changes, and transformed anew and again.
Earth is really more changeful than water or air, more
varied and more complex. We began with " dry-
ness " and " coldness " ; we end our chapter with a
vision of some eighty elements, organised into many
hundreds of compounds by the action of principles
far other than " dryness " or " coldness " ; and of
P 225

.THE STORY OF THE FIVE ELEMENTS

226

COMPOSITION OF THE EARTH

these compounds obeying, in fusion or solution, those
mysterious laws which build crystals of such constant
and characteristic shapes. In the earth these com-
pounds are solid, because their molecules are close
together, and hamper one another's free movement.
We raise the temperature, and the molecules are able
to move more freely : " earth " has become " water " !
We go on heating, and the molecules have a still greater
freedom : " earth " is then " air." There is no differ-
ence, essentially, between "earth," "water" and
" air " ; the elements of the one can enter into the
composition of the others, as oxygen does so largely
under present conditions. The study of the earth-
element shows us well how valuable it has been to leave
" principles " and come down to the " things." The
things have led us to a knowledge of just and sound
principles, such as a mere philosopher could not
have conceived, even in his wildest flights of meta-
physical imagination.

The table on the opposite page shows in a diagram-
matic form the resolution of earth into the chief
elements which go towards its formation.

227

CHAPTER VII

ETHER

I. — UNITY OF THE ELEMENTS

WE have seen in our previous pages how the idea of
the ancients concerning the constitution of matter
has been pulverised by a thorough examination of its
various forms. The four elements have been multiplied
into some eighty or more ; and it would seem that
we cannot think of the material universe without all
these. The atoms composing these eighty elements
represent the foundations of all matter. They are all
characterised by that basal property of matter known
as inertia, by virtue of which they demand a force of
some kind before their state of uniform motion in a
straight line can be changed. They differ in the amount
of this inertia, but not in the quality itself ; in other
properties they differ not only in degree, but also in
kind. Plainly said, all atoms have weight, but no other
necessary quality.

With their four elements only, the Greek philo-
sophers felt the need of further simplification. How
much more must we, who have so many more ? The
Greek mind had, however, nothing but " principles "
to reduce ; the fifth essence, which vitalised these, and
was as hazily fantastic as they, could easily be postu-
lated. But we are dealing with matter, recognised by
its property of inertia or reluctance to move, a pro-
perty measurable under our conditions by its weight.
And this matter of ours, as indicated by its inertia, is

228

UNITY OF THE ELEMENTS

indestructible ; so that we seem compelled to postu-
late matter ab initio ; and all that we can ask is by
way of a cross-examination of the facts of chemistry
concerning the necessity or otherwise of eighty dif-
ferent kinds. To reduce our eighty kinds of atoms into
one kind is a thinkable proposition ; but to reduce
these uniform atoms to something more elementary
— to some essence, ether, or other spirit-stuff : that
involves the annihilation of the whole sensible uni-
verse, the dissipation of all things into an immaterial
and insubstantial essence. What has been done in
both these respects we are briefly to consider ; but
we are here in the realm of speculation mainly, with
only a few dim gleams of experimental truth to guide
our intrepid imaginations.

Hydrogen is the lightest of the known elements —
its atom the smallest unit of matter, therefore, whereof
we have knowledge. It is a very simple suggestion,
made something like a century ago, that all other
atoms are but aggregations of the hydrogen-atom, and
that hydrogen is the aboriginal world-matter, of which
all other is the outcome. Simple and attractive, but
impossible. We may waive the difficulty of imagin-
ing how sixteen hydrogen-atoms could by any process
of mutual arrangement give an oxygen-atom with
quite opposite chemical properties ; but all the atomic
weights would have to be exact whole numbers, else
we should have to conceive the atoms as losing or
gaining weight by their aggregation. If the weight of
an atom of chlorine is 35-45, it is impossible for it to
be made of hydrogen atoms of weight i. And the
more refined the method of determination is, the more
sure are we that our atomic weights cannot be made

229

THE STORY OF THE FIVE ELEMENTS

to fit in with the supposition that hydrogen is the pri-
mordial stuff of the material world ; and obviously
no other of our eighty elements can be even considered
in the case. For a long time the question had to be
allowed to rest there, no more probable suggestion
or more illuminative evidence being forthcoming.

II. — RELATIONSHIPS OF THE ELEMENTS

Yet many facts irritate us into our determination
somehow to reduce the number of our primitive stuffs.
Think of the three elements, lithium, sodium, potas-
sium. Almost every property of the one exists in
some degree in the other. They are all soft metals
which take fire when thrown into water, liberating
hydrogen and giving strongly alkaline liquids. Their
compounds with other elements differ only in un-
essential ways. Their atoms are mutually replace-
able in crystals. In solution each gives electropositive
ions. Their atomic weights form a regular progression
with a constant difference of 16 : Li = 7, Na = 23,
K = 39. In short, they obviously form a family
of elements, wherein it is impossible to avoid seeking
some common strain or substratum of matter ; and
we have the right to do this, because the lithium family-
characters extend also to two rare elements, rubidium
and caesium ; and because also the other elements
group themselves into well-marked families, some of
them almost as strongly inter-related as the members
of the lithium family are. Only hydrogen seems at
present to stand quite solitary, and out of all relation-
ship with the other elements. We have oxygen
linked by many similar properties with sulphur, car-
bon with silicon, phosphorus with arsenic and anti-

230

RELATED ELEMENTS

mony, zinc with magnesium : we seek naturally for
some cause of these relationships, and find it in the
notion that the related elements, if they do not look
to a common ancestor, at least have a common material
factor running through them.

In 1864 an English chemist, named Newlands,
advanced this line of thought by the observation that,
when the elements were arranged in the order of their
atomic weights, like properties seemed to reappear
at intervals of eight. Thus between Li = 7 and
Na = 23, there were six elements included ; between
Na = 33 and K = 39 six also. There seemed to be
something in this, but there were too many irregulari-
ties, and it was left to the Russian chemist Men-
deleeff to establish on a firm basis the Periodic Law
which Newlands' " Law of Octaves " had dimly adum-
brated. Mendeleeff, boldly leaving gaps and drop-
ping out the elements which refused to adapt them-
selves to the scheme, produced his periodic table of
the elements, which at once groups the elements in
their natural families and provides for new elements
to be discovered. Additions and alterations of the
table have been necessary since the original list was
published, as a result, of course, of the additions to
the list of elements made since then ; but in principle
the table shows now, what it showed then, that any
particular chemical property seems to ebb and flow as
we proceed through the elements in the order of the
atomic weights.

Thus, to take one very characteristic chemical
property : most of the elements are capable of form-
ing oxides, and these oxides are some of them acid
in character, and some basic. Now, as we pass along

231

THE STORY OF THE FIVE ELEMENTS

•8 ••

III

"wo

rt
O

crv

232

Plate VII

DMITRI IVANOVITCH MENDILEEFF

THE PERIODIC LAW

the various rows or series from the elements of Group
I. to those of Group VII., we find the oxides at first
strongly basic and not at all acid ; the basic charac-
ter gradually weakens and the acid character increases,
until at last the acidity is the dominant property of
the element's most stable oxide. This happens in each
series. To emphasise the point still further, let us
suppose that we start with Li = 7, whose oxide is a
very active base. Adding 5 units, we arrive at C = 12,
whose oxide is a weak acid and not in the least basic.
But an addition of 16 units brings us to Na = 23,
wherein the characteristics of lithium reappear ; and
a further addition of 5 carries us to Si = 28, where
we find a repetition of many of the salient habits of
carbon and a weakly acid oxide. A close examination
of other properties than these purely chemical ones
bears out the broad truth of the table, that the pro-
perties of the elements vary periodically with their
atomic weight ; the addition of about (but not exactly,
or regularly) 16 units seems somehow to cause a recur-
rence of the same properties in the atoms of a new
element. It should, however, be clearly observed that
these properties do not return in the same degree.
There is a very distinct tendency for the heavier
elements in each group to be more metallic in them-
selves, and in their oxides more strongly basic, than
their lighter relatives. This process is well marked
in Group V. The oxides of nitrogen are strongly
acidic, but this feature is far weaker in the oxides of
antimony and bismuth. The latter element, indeed, is
quite a metal, and its oxide is quite a distinct base
in its action towards the stronger acids.

A most important property of the atoms, and one
233

THE STORY OF THE FIVE ELEMENTS

very difficult to explain, is their valency or combin-
ing power. All the elements in Group I. are mono-
valent, their atoms having the same combining power
as the atom of hydrogen ; those in Group II. are
divalent, and each atom can occupy the place, chemic-
ally speaking, of two hydrogen atoms ; those of Group
III. are trivalent ; those of Group IV. tetravalent ;
and thus we observe a regular increase in the valency
of the atoms as we pass across the series. But the
elements of the fifth, sixth, and seventh groups show
an alternative valency, and the property is by no
means so definite as in the earlier groups. Neverthe-
less, the elements of Group V. are either trivalent or
pentavalent ; those of Group VI. generally divalent
or hexa valent ; and those of Group VII. generally
monovalent or heptavalent, the change being gradual
and continuous in either case. Any explanation of the
formation of the elements must take into account
these very striking changes.

The periodic table is interesting especially because
it sets the problem of the relation between the elements
in a more definite light. But there are several diffi-
culties about accepting it exa'ctly as it stands. There
are the nine elements which form the eighth group
and about which no satisfactory explanation can be
given. The inert gases of the air, again, have had to
have a new " zero " group provided for them ; and,
still further, there is a group of several known elements
related to cerium, rare but quite well defined, for which
no suitable place seems to be available. The neces-
sary gaps, too, are numerous. Several of these have,
however, been filled since Mendeleef s time : but the
awkward lacunae in the first series remain. Hydrogen

234

VALUE OF THE PERIODIC TABLE

is still alone, and its companions are only known in
hypothesis. With all these limitations, nevertheless,
the periodic scheme does suggest some plan of evolu-
tion among the elements, and gives us more than a
hint for the reduction of the eighty to a few more truly
fundamental elements.

III.— EVIDENCES OF DECOMPOSITION OF THE ELEMENTS

By a careful analysis of the light of the stars it is
possible to obtain reliable evidence, both of their
physical condition and of their chemical constitution.
The industry of a number of astronomers has resulted
in the accumulation of a great body of valuable facts
of this kind ; and from them Sir Norman Lockyer has
suggested a classification of the stars, upon which we
may found a general idea of inorganic evolution. In
the sun a large number of our terrestrial elements have
been with certainty identified, so that even at the
high temperature there existent those elements retain
their individuality unimpaired. Some of the stars,
such as Arcturus and Betelgeuse, reveal a similar con-
dition of things ; but, though the sun's temperature
does not fall short of 15,000° F., it is, as celestial
temperatures go, a cold star. Examination of the
light of the bluer stars, such as Vega or Sirius, shows
unmistakably that they are hotter, probably very
much hotter, than the sun ; and at the same time the
number of the terrestrial elements present is very
much reduced. Between stars of the solar type and
stars of the Sirius type lie many other examples show-
ing the stages of transition which indicate the develop-
ment of the one kind from the cooling and condensa-
tion of the other ; and accompanying this develop-

235

THE STORY OF THE FIVE ELEMENTS

ment we find a gradual increase in the number of
recognisable elements. Thus we may reasonably sup-
pose that, at the very high temperature of Sirius, sub-
stances which are elements on the cooler sun are
decomposed into simpler substances, just as we are
able in laboratory experiments to decompose many
compounds into simpler compounds or into elements.
As water cannot exist as such above a certain tem-
perature, but must needs resolve itself into its con-
stituent elements, so silicon, which is not decomposed
on the sun, cannot resist the terrific temperature of
Sirius.

Proceeding still farther back, to the nebulae, from
which, in all probability, stars or suns are to be evolved,
we approach more nearly the aboriginal state of matter.
The light of these bodies teaches us conclusively that
they are gaseous, often of exceeding tenuity ; and not
necessarily at a high temperature. In those which
show no condensation, only three elements are to be
recognised — hydrogen and two others which are un-
known to terrestrial chemistry ; at a later stage helium
seems to make its appearance. In this primitive
condition of matter, therefore, we have the elements
reduced to four only ; the process of stellar formation
and development is accompanied by the appearance
of new elements as condensation, or cooling, or both,
goes on. The four simple elements of the nebulas give
rise to a few more, such as calcium, magnesium, iron,
and sodium, in the hotter stars, the others being
formed as the condensation and cooling of the stars
proceed.

What are the four elements of the nebulae ? The
universal presence of hydrogen in the nebulae and the

236

CHEMISTRY OF THE STARS

stars, in enormous quantities, marks it out as one of
earliest forms, even if it be not an absolutely original
form, of the primitive world-stuff. Helium we know
as a rare gas on the earth and as the head of the
indifferent or " zero " group of elements in the periodic
table. We can only guess at the other two, and
imagine them to be two of the missing elements of the
first series and the parents of the elements in the two
groups which they head. We do not pursue this point
at present, but content ourselves with repeating the
statement that the stars do give us the evidence we
desire, of a simplification of the elements under the
stress of a very high temperature, and at the same
time doubtless of greatly modified electrical condi-
tions.

IV. — FORMATION OF ELECTRONS

The intimate association of electricity with matter
makes it impossible entirely to separate the two, and
certain experiments upon the behaviour of gases under
electrical stress have opened up a new line of in-
sight into the nature of matter. When an insulated
metal body is electrified in the open air, it is well
known that the electrification tends to " leak " slowly
away until the body is discharged. This is usually a
process of some duration, but it can be considerably
hastened by directing towards the electrified body the
X-rays, or the radiation of the radio-active substances
described below. What the radiation seems to do is to
convert some of the atoms of the air into ions, either
positive or negative ; and these gaseous ions seem to
give up their charges to the electrified body, which
therefore becomes ultimately neutral, i.e. is dis-
charged.

337

THE STORY OF THE FIVE ELEMENTS

Now, how do the atoms become ions ? We are here
asking for the actual nature of the electric charge,
positive or negative, which attaches itself to the atom ;
the question ultimately involves the fundamental
structure of electricity itself. Now, let us suppose that
electricity is, like matter, atomic in its nature, com-
posed of indivisible particles or units — we will call them
electrons, positive or negative. The attachment of
these electrons, one or more, to an atom would ionise
it, and thus confer upon it electrical properties. But
the source of the necessary electrons is still a difficulty,
which we may most easily sorre by supposing them
to be within the atom itself. In this view, the atoms
must be considered to contain both positive and nega-
tive electrons which will ordinarily counteract one
another, leaving the atom electrically neutral. But
if by some agency, say the X-rays, a negative electron
could be detached from an atom, the atom would clearly
be positively ionised, and the said negative electron
might attach itself to another atom and ionise that
negatively. If this be a correct picture of the process
of ionisation, its consequences are far-reaching indeed.
The atoms, not of one element only, but of all, would
be shown to be themselves of complex constitution.
We must therefore indicate the nature of the evidence
which shows that the atoms contain the electrons
within themselves — contain possibly nothing else but
electrons.

When an electric discharge passes through a gas

at very
low pres-
sures, en-

Ffc. 43.— Discharge in a vacuum'tube ; a, anode; c, cathode; r!n<;pH in 3.
d. dark space round c; s, nickering strie.

238

ELECTRONS

vacuum tube, exceptional phenomena present them-
selves, especially around the cathode or negative pole
of the tube (Fig. 43). The appearances can be well
accounted for on the supposition that from the
cathode there is, during the discharge, a rush of
negatively electrified particles, travelling in straight
lines at very high velocity. These " cathode rays "
can pass through thin sheets of metal, but are
stopped by thicker pieces ; they cause the walls
of the tube to glow with a characteristic phos-
phorescent light ; and they can be bent out of their
straight-line course by a powerful magnet, just as we
should expect a stream of negatively electrified par-
ticles to be. They were at first thought to be merely
electrified atoms ; but their great penetrative power,
and the fact that the nature of the original gas in the
tube, or of the metal which made the cathode, caused
no essential difference to the rays, led Sir William
Crookes to make the pregnant suggestion that they
were the particles or corpuscles of a fourth state of
matter, an ultra-gaseous, ethereal state which he
called radiant matter. The particles of radiant matter
are now regarded as electrons, detached from the
atoms under the influence of the great electric stress
set up in the vacuum tube. Here, then, we appear to
have definite evidence of the rupture of the atoms,
with these negative electrons as the most readily recog-
nisable products.

An electron is a particle of electricity, and not of
matter ; but Sir J. J. Thomson has shown that an
electric charge in rapid motion would possess the
property which we regard as the test-property of
matter, viz. inertia. And even more ; he has expert-

239

THE STORY OF THE FIVE ELEMENTS

mentally determined that the mass of an electron
(which measures its inertia) is something like T^th
of the mass of a hydrogen-atom. He has thus bridged
the difficulty of our supposing the material atoms to be
ultimately resolvable into electrons, and matter itself
to be reducible to electricity in motion. The theory
harmonises many otherwise inexplainable facts, and is
at present contradicted by none. There are many
difficulties in its way, of course ; but it does enable us
to see, if only in a fitful glimpse, something of the
design of the material atoms.

There must be two kinds of electrons, positive and
negative ; but we have a direct knowledge only of the
negative ones. What is known of the positive elec-
trons seems to suggest that they are larger than the
negative, and that their mass is comparable with
that of the hydrogen-atoms. Either the positive elec-
tron is different in its nature from the negative, or it
has not been detached from its material basis. With-
out making any hypothesis on that point, we may
follow Sir J. J. Thomson's model atoms, at least with
interest.

He has considered the case of a sphere of uniform
positive electrification, and studied the possible arrange-
ments of varying numbers of the negative electrons
in this sphere. Thus, if there were six negative elec-
trons, they would arrange themselves with one at the
centre of the sphere and the other five in a ring whose
radius would depend upon their rate of rotation.
This is the only stable arrangement of six, and an atom
containing only six electrons would necessarily have
them arranged so. With larger numbers the problem
becomes too difficult unless they are confined to one

ELECTRONS IN THE ATOMS

plane ; under this limitation the stable arrangement of,
say, 50 electrons would be in five rings containing
respectively i, 5, n, 15, and 18 electrons. Such an
arrangement, though stable, does not preclude the
addition of another electron, inasmuch as the five
rings, i, 6, n, 15, 18, also form a stable arrangement.
Two such atoms as these arrangements represent might
well belong to elements of the same series, differing
only by a unit of valency ; but the matter is hardly
so simple, inasmuch as in the first place a single elec-
tron does not add enough to the atomic weight to
make the jump from one element to its neighbour in
the periodic series, and in the second place the arrange-
ment is probably not in one plane entirely. But the
comparison of an atom with the solar system, in which
the sun represents the positive centre of attraction
and the planets and their moons correspond to the
negative electrons, gives a fair idea of what physicists
now conceive the atom to be. This comparison, sug-
gested by Sir Oliver Lodge, is based upon the limits
of size and mass that must be assigned to the electrons
and the atoms respectively ; if, therefore, the electronic
theory of the atom be true, by far the greatest part of
the space occupied by the atom will be empty, as much
so at least as the space from the sun out to Neptune,
its most distant attendant : it contains only the un-
material and all-pervading ether which is the assumed
medium whereby light-waves are conveyed.

Atoms thus constituted might differ from one
another in very many ways — in the number of the
electrons, in their rates of rotation, in their varying
arrangements. Thus the eighty different kinds of
elementary atoms can be conceptually accounted for ;
Q 24^

THE STORY OF THE FIVE ELEMENTS

and, since there appears to be no frictional resistance
between the ether and the electrons, there is no reason
why these atoms, if left to themselves, should not be
permanent and eternal.

But is it possible that this condition should ever-
lastingly prevail ? We know that the atoms are cer-
tainly subject to very rapid motion and to continual
vibration : the first accounts for their heat, and the
latter for the light-waves in the ether by which matter
becomes visible.

In the first case, is it not likely that an atom,
brought near enough to a neighbouring atom, might
so disturb the equilibrium as to detach an electron or a
group of electrons, and thus reduce the original atom
to a simpler one ? Or, two different atoms might be
brought so close to each other that they form a system
in mutual revolution about one another, and thus
give us a molecule of a binary compound, just as we
often find two stellar systems " combined " in the
heavens into double stars. Or, again, just as a comet
or a meteorite may be drawn into or escape from our
solar system, so a negative electron might be drawn
into or escape from an atom, and thus transform it into
a negative or positive ion, as we see happen in the
electrolysis of liquids and the ionisation of gases. Or,
still again, some atoms, like those of helium or argon,
may be conceived to be quite neutral, the total effect
of their electric units externally being null, and show-
ing itself in the absence of all chemical affinity from
those elements, whereas other atoms might have the
influence of the positive electrons predominating, so
that they are as a whole electro-positive like those of
lithium or sodium ; and still others might have the

242

BREAK-UP OF THE ATOM

negative influence in excess, and thus be electronega-
tive like those of oxygen or chlorine.

The difficult problem of valency seems capable of
interpretation in terms of the possibilities of this
theory. For, if we suppose an atom, completely neu-
tral and of no valency, to have added to it one small
atom with a positive residue, it might become thereby
monovalent ; and if two such atoms came into its
system a divalent element would result ; and so on.
But while the positive affinity would thus be doubled,
it would not necessarily be doubled in its external
manifestation, inasmuch as a new balancing of the
electric forces would certainly come about ; and thus
the divalent atom of magnesium is not in the result
so strongly electro-positive as the monovalent atom
of sodium, from which it is only separated by one unit
of atomic weight ; and the tetravalent atom of silicon
is actually electro-negative. Of course, the negative
valency of atoms like those of oxygen or chlorine
might also be explained by the similar process of in-
corporation applied to negative atoms.

V. — RADIO-ACTIVITY

The development of this new atomic theory, in
which we only postulate the positive and negative
electrons, has been very largely stimulated by the
discovery of the strange element, radium, and its still
stranger properties. Following up the clue afforded
by the cathode-rays, Rontgen was led to his discovery
of the X-rays ; his revelation of these mysterious and
highly penetrating rays led to further search for
similar rays, and soon Becquerel announced his dis-
covery of the ray-giving property in the salts of the

243

THE STORY OF THE FIVE ELEMENTS

element uranium. These rays, even through a thin
sheet of metal, affected a photographic plate, and
slowly discharged an electrified body by ionising the
air. Minute though this action was, it was nevertheless
sufficient to show certain irregularities, which led
Madame Curie to investigate the uranium minerals
closely ; and, as the result of a very patient and
laborious series of separations, she succeeded in isolat-
ing the compounds of a new element, radium, in which
the properties of the uranium rays were enhanced a
million times.

The radium occurs in company with the uranium
in a number of rare minerals ; but in so small a quan-
tity that some 200 tons of the richest of them (pitch-
blende) were required to yield 300 grains of radium
bromide, and the value of this is something like £300
per grain. It is therefore clear that experiments with
radium can be made with only very small quantities of
the substance. In spite of this, Madame Curie has
examined several of its compounds, recognised it as a
divalent element of the second group, found its atomic
weight, and recently isolated the metal itself. In addi-
tion, its radiations have been thoroughly examined,
and applied to therapeutic uses ; we have a theory of
its atomic structure, and its behaviour has modified
our vista of geologic time. A slight and unsuspicious
phenomenon has thus fired a train of theoretical and
practical consequences, great enough to undermine the
very foundations of the science of matter.

Radio-activity, as this phenomenon is called,
means the discharge by the active substance of rays,
either in the form of projected particles or in the
form of waves in the ether. The X-rays are of the

244

Plate VIII

By kind permission of Prof, yean Becg^(erel

RADIO PHOTOGRAPHS

1. Deviable and Non-Deviable Rays of Radium [cf. Fig. 44].

2. Radiograph of Aluminium Medal produced by Rays of Uranium.

THE RAYS FROM RADIUM

latter type, the cathode rays of the former. The rays
from radium, however, belong to both kinds, and
afford us some very strong circumstantial proof of the
spontaneous transformation of its atoms.

Three kinds of rays have been recognised and
thoroughly examined by Rutherford and others ; they
are differentiated experimentally by their penetra-
tive powers, and by their different attitudes towards
magnetic forces. The a-rays are stopped by a very
thin sheet of aluminium, and behave like positively
electrified particles, of a mass something like that of
the hydrogen atom, and moving with a speed which
is about one-twelfth that of light. The £-rays are
able to penetrate 100 times the thickness of aluminium ;
they behave towards a magnet exactly like the cathode
rays, i.e. as negative electrons moving with a velocity
of the same order as that of light. Finally, the y-rays
are still more penetrating, are not affected by a magnet,
and behave generally like X-rays. The lower photo-
graph in Plate 8 shows the nature of the photo-
graphic effect produced. The whole radiation keeps
the radium salt itself phosphorescent, and produces
phosphorescence in many
other substances besides ;
each kind of ray ionises the
air, and affects the com-
pounds on a photographic
plate, just as light does.
The accompanying figure IS Ni

(Fig. 44) , based Upon an Fi*- ^—M***™* Curie'* experiment

experiment by Madame Curie, illustrates the varying
extent of the magnetic action on the different rays.
The projection of these particles with such high

245

THE STORY OF THE FIVE ELEMENTS

velocities is eloquent of a great liberation *of energy
during the process of radio-activity ; and careful
measurement has shown that radium salts produce
also enough heat by their activity to melt more than
their own weight of ice in one hour. This makes the
atomic disruptions which are the beginning of the
activity far more violent than the molecular collapse
which accompanies the explosion of nitro-glycerine,
and bewilders us when we attempt to contemplate the
enormous stores of energy that are locked up in the
atoms of matter. The heat given out by a quantity of
radium in one hour would be sufficient, if converted
into mechanical work, to lift it more than twenty
miles against the action of gravitation.

As if the evidence of degradation afforded by the
a- and /3-rays were not sufficient, it has also been proved
that radium compounds give rise to a small quantity
of a true gas. Very small quantities of this radium
emanation, as it is called, have been obtained ; but
modern methods have made it possible to work in
certain directions upon very small quantities of gases,
and radium emanation has been subjected to a rigor-
ous chemical examination, which shows it to be a com-
pletely inert substance, as loath to enter into any chem-
ical combination as helium or argon. It is in all prob-
ability, therefore, a gas of the same family as these.
But the interesting fact about this emanation is its
radio-activity and its rapid change. No change of tem-
perature that has yet been applied seems to modify
in any degree the rate of radio-activity, either in radium
or its emanation ; the whole process is plainly an in-
herent act of the atoms. But the emanation is found
to have lost half its activity in 37 days, and to have

246

RADIO-ACTIVITY

given rise during that time to an easily recognisable
quantity of helium. Meanwhile the walls of the tube
containing the emanation have themselves become
highly radio-active, and this induced activity itself
decays irregularly to half its value in about half an
hour, after having produced a-, /?-, and y-rays. Fur-
ther experiments by various scientists have revealed
the identity of the a-particles with atoms of helium
containing enough positive electricity to neutralise
two electrons. We thus obtain : —

Radium produces Radium ) Helium ) Electrons )
Emanation i (a-rays) 1 (/?-rays) \

Radium \ -D^AW** A Helium

Emanation! " Radmm A + (a-rays)

The substance here called Radium A has been
shown to decay and form new radio-active substances
down to Radium F, this latter being apparently iden-
tical with an element polonium, likewise discovered
by Madame Curie. Thus the original radium, by the
elimination of atoms of helium, has produced a series
of new elements. Some of these have had only a few
minutes of existence ; others last for years, but ulti-
mately decay, leaving at the end a totally inactive
product.

Radium itself differs from its products chiefly in its
life-duration, which goes into some thousands of years.
It loses half its activity in 1760 years. But there is
very strong reason for regarding it as itself a product
at three removes of the disintegration of uranium,
and so its presence in uranium-minerals is explained.
This element, whose atom is the heaviest known, is
radio-active in a slight degree ; it produces an element.
Uranium X, which decays with fair rapidity into a

247

THE STORY OF THE FIVE ELEMENTS

new element, ionium, that has been separated in inde-
pendent quantities, and is supposed to be the imme-
diate parent of radium itself. We have thus the fol-
lowing series of radio-active elements formed succes-
sively from uranium by the loss of a-rays, which con-
sist of atoms of helium of atomic weight 4, and of /5-
and y-rays, whose weight we may ignore.

THE URANIUM SERIES

Name of
Element

Rays Given
Off
(a-rays =He)

Atomic Weight
[He = 4]

Half-life Period*

Uranium

238-5

About 10' years

Uranium X

[230-5]

About 20 days

Ionium

[230-5]

About 1,500 years

Radium

a, 0, T

226-5

About 1,760 years

Radium Emana-

[222-5J

About 4 days

tion (Niton)

Radium A to Ra-

[218-5]

About 1 7 years

dium F ( = Polo-

(in unequal

nium) (in five

stages)

Polonium

a, /?, 7,

2IO-5

About 140 days

Final Inactive Ble-

None

206-5

—

ment (=L,ead ?)

* This means the time taken for the radio-activity of the substance to
diminish to half its value. It is independent of the amount taken, and must
not be read to mean half the life of the element.

The final product of the radio-active changes in
uranium is an inactive element, supposed, for two
reasons, to be lead. Small quantities of lead are found
in all uranium minerals, although lead ores do not
occur in the same strata ; and the atomic weight
obtained by subtracting eight atoms of helium from
the atom of uranium is very close to that of lead (206-9).

If this be the case, we have Nature slowly trans-
248

TRANSMUTATION OF URANIUM

forming the atoms of uranium, by a process lasting
millions of years, into atoms of lead — a spontaneous,
self-originated process unconditioned and unmodified
by external circumstances. Evidently the uranium
atom is over-bulky and unstable. Of the other
elements on the periodic table, thorium (232-5) appears
to go through a similar series of radio-active changes ;
that, too, is an element of high atomic weight, and so
unstable. But in a small degree the property belongs
to several other elements : notably potassium (39)
emits /2-rays with considerable freedom. Further,
there is good presumptive evidence that certain com-
pounds of copper give rise to lithium when subjected
to the action of radium emanation.

It is possible to measure the rate at which a given
radio-active substance produces helium by a direct
measurement. Now helium is not, of course, radio-
active ; hence, if a natural mineral is active, the
helium it produces will gradually accumulate in it.
Knowing the rate at which a mineral is producing
helium now, and knowing also how much helium it
contains, we can arrive at a reasonable estimate of its
age. In this way Strutt has examined the mineral
thorianite, and finds from the helium enclosed in it
that its age cannot be less than 250 million years.
Lord Kelvin, from considerations derived from the
earth's loss of heat, would only grant it 100 million
years of past history. It is easy to see how radium
has vitiated his calculations, which could not be
assailed by any physical facts then at his disposal.
For the radium also produces heat in such quantity
that, if we had about 120 Ib. of it distributed evenly
through a solid crust fifty miles thick all round the

249

THE STORY OF THE FIVE ELEMENTS

earth, it would be sufficient to compensate the earth
for its loss of heat by the processes of cooling. Thus
the unexpected discovery of this strange substance
has compelled us to lengthen the earth's past life to
an unknown but certainly very great extent.

All the transformations that we have mentioned,
supposing them to be verified by further research, are
in the nature of devolution from the larger atoms to
smaller and simpler ones. Nothing suggestive of the
opposite process has yet been observed ; but this is
hardly remarkable when we reflect upon the immense
concentration of energy in the atoms. The architecture
of an atom like that of radium is not merely a matter
of bringing a few simpler atoms together ; it involves
also the communication to them of a high velocity
comparable with that of light. Still, it is a pleasing
symptom of the rapid progress of true science that
we are able to picture in any way the atoms of the
elements, still more that our conceptions are prolific
of new lines of thought and research, as well as illu-
minative of present facts.

VI. — EVOLUTION OF THE ATOMS

The simplification of the larger atoms may now
be regarded as an established fact. Beyond this, the
scientific imagination has liberty to probe tentatively,
using our known laws as our weapons. How many
fundamental kinds of matter are there ? Arguing
from the periodic table, we might be inclined to say
eight ; but the hottest stars suggest four at most ;
and the bold theory that the electrons are the ulti-
mate units of the atoms seems to require two. In the
latter case we are dealing, not with matter as we

250

EVOLUTION OF THE ATOMS

understand the term, but with electricity ; and we
have still the electrons to inquire about.

What are these ? The attempt is made by Lodge
and others to reduce these to strains or twists in the
ether — the something which permeates all matter
and fills the relatively large spaces within the atoms
themselves. This ether has properties most difficult
to conceive : great elasticity, high density, perfect
fluidity, offering no friction to the movement of atoms
in it, yet able to be distorted — caught up into twists,
or vortices which are the electrons, or the beginnings
thereof. Thus, on this bold theory, matter is reduced
to electricity, and electricity to ether. This ether is
thus the progenitor of all material things ; and, though
not easy to comprehend, it is still far from the evanescent
quintessence of the Greeks ; its existence is as sure
^s any intellectual conception can be, and scientists
have been driven to define its properties from phenomena
of light and electricity which are incontrovertible.

Leaving this alluring speculation as something for
the future to elucidate further, it is possible and fair
to conceive the existence of three entities at a very
early period in the history of the universe — viz. the
ether, and the positive and negative electrons possibly

4- —

formed out of it. We will denote these E and E. By
condensation of these together in varying numbers,
we arrive at the systems of electrons which we call
atoms. Among the earliest of the known atoms to
appear were doubtless those of hydrogen and helium,
with possibly other atoms now no longer known in the

free condition, except perhaps in the hotter stars.

+ —

The simpler atoms, with more of E and E, produced

251

THE STORY OF THE FIVE ELEMENTS

the more complex by still further condensation. These
atoms, by virtue of their valency, can unite to form
the compounds which make up the many aspects of
matter that we have met in our previous chapters.
All these changes and rearrangements involve also the
transformation of energy, often in vast quantities.

The source of this energy, like the source of the
ether itself, is of course beyond the ken of science
entirely. It is unprofitable for science to venture
upon this ground ; but in attempting to picture the
processes by which the universe has become what it
is — in seeking to read the past in the light of the
present — we are not only using our intellects and
knowledge wisely, but forging helpful weapons for
the advancement of the powers of both. As soon,
however, as our speculations are found to be inhar-
monious with a single well-attested fact, they must,
and will, be abandoned.

VII. — REAL WEIGHT OF THE ATOMS

Twenty years ago it was open to a chemist to
deny the real existence of his atoms, and to regard
them merely as convenient mental conceptions for
the units involved in chemical actions. The atom of
hydrogen was the smallest quantity of hydrogen
known to enter into any chemical combination ; it
need not be the smallest conceivable piece of hydro-
gen. Such a chemist might, indeed, have denied the
necessity of assuming the existence of such an atom.
But it is difficult to take that attitude now. Radio-
activity has made the atom again a reality to us.
Several lines of thought also converge towards a
fairly consistent value for the actual weight and size

252

WEIGHT OF THE ATOMS

of the atoms. Some of the arguments depend upon
electrical or other physical questions which we can-
not discuss here ; but, results obtained from electrical
considerations, from the thickness of soap films and
from the optical theory of the blue sky, are of the
same order of magnitude as the following result given
by Professor Rutherford.

We have said that there is very good ground for
the belief that the a-particles given off by radio-
active elements are atoms of helium, positively ionised.
Now it is possible to count the rate at which these
a-particles are being given off by a weighed piece of
radium salt. Sir William Crookes has found that a
screen covered with sulphide of zinc becomes phos-
phorescent when the a-rays strike it ; each a-particle
produces a distinct momentary scintillation. By means
of a microscope a very small area of such a screen
may be examined and the number of bombardments
in a given time counted. Assuming that the rays are
discharged evenly in all directions, we may thence
calculate how many are emitted per second. The
counting may also be directly done by permitting the
a-rays to enter through a very small hole in a sheet
of lead into an electrometer which will indicate a
very delicate electrical charge. A helium ion, falling
upon the needle of such an instrument, indicates its
presence by a deflection of the needle ; and the num-
ber of such deflections in a given time reveals the
number of charged atoms that have entered the hole.

From these two methods of counting it is esti-
mated that one gram of radium discharges about
14 x io10 or 140 thousand million atoms of helium in
one second. But other experiments show that one

253

THE STORY OF THE FIVE ELEMENTS

gram of radium produces 5 x lO"9, or one two-hun-
dredth-millionth part of a cubic centimetre of helium
in one second. Hence one cubic centimetre (about
T^th of a cubic inch) of helium contains (14 x io10) -*-
(5 x io •*) = 2-8 x io19 atoms, i.e. about 30 million
million millions ! But this quantity of helium weighs
1-8 x io -4 grams. Hence 2-8 x io19 atoms of helium
weigh 1-8 x io~4 grams, and each atom weighs

- - = about 7 x io'2* grams ; or, reduced

3°o x IO

to English weights, each atom weighs something like
J x io'34 oz.

Of course, a number so small is quite meaningless
to our senses ; but it serves to convey, however
vaguely, to our minds some notion of the real atomic
weight of helium ; and it is extremely interesting
because a number of a similar order of smallness is
derived from other and quite different methods of
working.

In these experiments, it will be observed, we have
really been counting ions of helium, not the true atoms ;
where it is merely a matter of number, however, this
does not affect the result. It is the fact that the
helium atom is ionised that enables us to detect it.
An ion differs from the atom in the presence of an
electric charge of some kind ; and this charge confers
upon it new properties. Thus an ionised atom or
molecule causes the condensation of a droplet of water
from an air that is saturated with water vapour.
Each a- or /^-particle that moves through such an air
ionises one molecule, and this is rendered visible by
the drop of condensed water. The number of drops
gives us the number of ions. A few ions can therefore

254

IONS AND ATOMS

be rendered visible ; but the smallest quantity of un-
electrified gas that can be examined would contain
at least a million million atoms. This can easily be
worked out by finding the number of atoms in the
smallest workable quantity of gas ; neon can be
recognised in the air by suitable means when there is
only one half-millionth of a cubic centimetre of
it. It is the ionisation of the atoms, then, that
enables us to get so near seeing them individually.

Recalling the comparison of an atom to a solar
system, we may liken an a- or /^-particle to a comet
which bursts into the system. If it is retained, clearly
the atom would be ionised. But in most cases it would
not be retained ; in that case it might go through the
system, i.e. the atom, without injuring it, as most
comets do with us ; or, alternatively, it might draw one
of the external members of the system out of the range
of the central attraction, and this, by disturbing the
electrical equilibrium, would again ionise the atom. It
is an interesting thought that the atoms of matter
can be thus penetrated, and that even the densest
solids are mainly composed of holes. The number of
electrons in an atom is approximately known from
electrical experiments of Sir J. J. Thomson, which
show that the /3-particles (electrons) have a mass about
TTVoth that of a hydrogen atom.

Inconceivably small as the atoms are, the excessive
delicacy of radio-active methods enables chemists to
detect the presence of even a few in minerals which
contain radio-active substances. The presence of a
hundred atoms of radium in a gram of pitchblende
could be detected. No other method of detecting sub-
stances can vie with this in its wonderful delicacy.

255

THE STORY OF THE FIVE ELEMENTS

VIII. — ETHER, ELECTRONS, AND ATOMS

On the most recent hypotheses we have reduced
our atoms or material units down to electrons or
units of electricity moving in an infinite ocean of
ether. This ether is a pure creation of the scientific
imagination, made necessary by the facts of light
and electricity ; and, incidentally, we may remark
that it is an essentially English conception, a long
list of distinguished Englishmen, from Newton to
J. J. Thomson and Lodge, having been chiefly occu-
pied with its properties.

Now, concerning this ether, it is necessary to pos-
tulate many remarkable properties. It is similar to
an incompressible perfect fluid, able to rotate and to
vibrate, but not to move. It permeates all matter,
and allows matter to move through it without friction
or drag of any kind. It carries electric waves, and can
thus become the vehicle of energy. Sir Oliver Lodge
calculated that it has a density 10", or a million
million times that of water ; this high density is due
possibly to the enormous pressures it has to sustain ;
and perhaps it would only have the density of an
excessively rarefied gas, which Mendel£eff supposes it
to be, under such pressures as ordinarily prevail with
us. Its strength must be enormous in order to sus-
tain the gravitation of suns and planets. For instance,
the force between the earth and the sun is something
like 4 x iol8, or 4 trillion tons weight. How can the
ether be a fluid, and yet sustain such a stress as this ?
Its rigidity must be incomparably greater than that
of steel. This can only be conceived by supposing that
the minute parts of the ether are in rotation ; only

256

ETHER

thus can a fluid simulate the characters of a solid.
If this is so, the ether must have a boundless store of
e* ^y locked up in it ; and Sir Oliver Lodge has
expressed this in a striking comparison in the state-
ment that one cubic millimetre of free ether contains
enough energy to run " a million horse-power station,
working continuously, for forty million years."

Portions of the ether can be caught up and indi-
vidualised somehow as centres of electric force ; these
are the electrons, made of ether, yet different from it
and able to move freely through it. No figure can yet
be given to represent the manufacture of an electron,
or to suggest its nature. Nor are there any pheno-
mena which suggest the destruction of an electron ;
and possibly the electrons are discrete and different
entities from the ether. How they may form the
more complex atoms of matter we have already seen.
As compared with the whole volume of ether enclosed,
even by a dense solid substance like platinum, the
space filled by electrons is extremely small, something
akin to that occupied by gossamer floating in the air.
This must be the case, because even a piece of platinum
is enormously less dense as a whole than the ether of
which its component electrons and atoms are sup-
posed to be made.

These alluring and beautiful speculations, the
reader will no doubt have noticed, have in one sense
inverted the method and the results of our first chap-
ter. There we started with five elements which were
purely theoretical and metaphysical ; and we pro-
ceeded to urge upon the student of chemistry the
necessity of fixing his mind upon the actual, material
elements ; from metaphysics we drew him on to
R 257

THE STORY OF THE FIVE ELEMENTS

reality. And, we hope, the story of four of the ele-
ments of speculation has shown him the value of this
method of study. But here we draw him back to the
mists : matter vanishes, and we have only a most
extraordinary ether, animated by an equally mysteri-
ous energy, wherewith to construct the universe.
There is, nevertheless, a difference. In contemplat-
ing the vast reaches of the Unknown, we do not leave
entirely that territory which is surely our own. The
verge is clear, on which we stand ; the Science which
is content with that is assuredly perishing ; but the
Science which leaves that is no longer Science. The
method of inquiry, of patient questioning of Nature as
she is — the inductive process by which theories are
the servants of the observed facts — has made Che-
mistry what it is : a weapon with which man has
harvested a notable crop of invaluable practical
achievements, and a star which throws a ray into the
philosophic deeps wherein lies intricately hidden the
ultimate rationale of Nature.

258

APPENDIX

LIST OF ELEMENTS, SYMBOLS, AND ATOMIC WEIGHTS

Element

Symbol

Atomic
Weight

Valency

NON-METALS

Argon .....

39'9

Boron .....

Tri

Bromine ....

79-96

Mono

Carbon ....

12-00

Tetra

x* Chlorine ....

35'45

Mono

Fluorine ....

Mono

^^lelium ....
X^-Hydrogen ....

He
H

4
I '008

Mono

Iodine ....

126*85

Mono

Krypton

81-8

Neon .....

Nitrogen .

Tri and penta

Oxygen ....

^Phosphorus ....
Selenion ....

31-0
79-2

Tri and penta
Di and hexa

Silicon . . .

28-4

Tetra

^Sulphur ....
/ Tellurium ....

S
Te

32-06
127-6

Di and hexa
Di and hexa

Xenon ....

128

—

METALLOIDS (imperfect metals)

Antimony . . .

I2O

Tri and penta

Arsenic . , » . • '• » .

,75

Tri and penta

METALS

• .

Aluminium

27-1

Tri

Barium

I37-4

Bismuth

208-5

Tri and penta

Cadmium

112-4

Caesium

132-9

Mono

Calcium . .

40-1

Cerium . . »

140-25

Tri and tetra

Chromium

52-1

Tri

Cobalt

59-o

Di and tri

Columbium (Niobium) .

94'o

Penta

Copper
Erbium , . '. *,

Cu
Er

63-6
1 66

Mono and di
Di and tri

Gallium , . :' .

Tri

259

APPENDIX

Element

Symbol

Atomic
Weight

Valency

METALS

Germanium .

72'5

Tetra

Glucinum (Beryllium)

9-1

Gold .

IQ7-2

Mono and tri

Indium

114

Tri

Iridium

193

Di and tri

Iron

Di and tri

Lanthanum .

138-9

Tri

Lead .

206-9

Di and tetra

Lithium

7-03

Mono

Magnesium .

24-36

Manganese .

Di and tri

Mercury

200

Mono and di

Molybdenum

96-0

Tri and penta

Neodymium

i44'3

Pent a

Nickel

58-7

Osmium

191

Di and tri

Palladium

106-5

Di and tetra

Platinum

194-8

Di and tetra

Potassium .

39-15

Mono

Praseodymium

140-5

Penta

^-Radium

225

Rhodium

103

Di and tri

Rubidium

85-4

Mono

Ruthenium .

101-7

Di and tri

Samarium

150

Tri

Scandium

44-1

Tri

Silver .

107-93

Mono

Sodium

23-05

Mono

Strontium

87-6

Tantalum

183

Penta

Terbium

160

Tri

Thallium

204-1

Mono and tri

Thorium

232-5

Tetra

Tin .

119-0

Di and tetra

Titanium

48-1

Tri and tetra

Tungsten
Uranium

W
U

184
238-5

Tetra and hexa
Tetra and hexa

Vanadium .

51-2

Tri and penta

Ytterbium .

i73

Tri

Yttrium

Tri

Zinc .

65-4

Zirconium

90-6

Tetra

Other elements less definitely known and occurring in small quantities
only are: Europium (Eu=i52), Gadolinium (Gd=i57)» Dysprosium
(D = i62'5), Thulium (Tu=i68'5), Lutecium (Lu=i74)» and the elements
of the Uranium series (See p. 248).

260

INDEX

Absolute zero of temperature, 55,
60

Acetylene, 208

Acids, 175-9

Affinity, chemical, 8

Air : early views, 37 ; pressure
of, 39-43, 49 ; liquefaction of,
59 ; volumetric composition
of, 66-7 ; gravimetric composi-
tion of, 67 ; rare elements
of, 68

Air-pumps, 47-9

Air thermometer, 52

Alchemical " principles," 15

Alchemy, 12 et seq.

Alkaline air, 105-8

Alkalis, 105, 177, 199, 218, 220

Alloys, freezing of, 165-8

Aluminium, 75

Aluminium silicate, 220-1

Alums, 223-4

Ammonia, 56, 105-8

Ammonium hydroxide, 106 ;
chloride, 107 ; sulphate, 107

Analysis, 21

Anaxagoras, 7

Anaximenes, 37

Andrews, 57

Animals and the air, 78

Aragonite, 202

Argon, 69

Aristotle, 6, 19

Atoms, n, 23, 26 et seq., 229,
237, 240-3, 250-5

Atomic theory, n, 26-36

Atomic weight, 28, 34-6, 252-4

Azote, 65

Bacon, Francis, 52
Bacon, Roger, 15, 19
Barometer, 41-3
Bases, 175-9

Becquerel, 243

Black, 87

Bleaching, 103

Bleaching powder, 104

Blende, 194

Boyle, 10, 38, 47, 52, 61, 62,

Boyle's law, 49-52
Bunsen flame, 129-135
Burning, 76

Calcite, 201

Calcium: 147, 199, 213, 236;
carbide, 85, 208 ; carbonate,
85, 199-206, an, 212; cyan-
amide, 85 ; hydroxide, 148,
206, 2O#; phosphate, 209;
sulphate, 209-213; sulphide,
211

Caloric, 115

Calx, 61

Candle, burning of, 74 ; flame
of, 126-9

Carbon, 195-6

Carbon dioxide, 57, 80, 87-92,
199

Carbon monoxide, 124

Carbonates, 87-9, 200

Carbonic acid, 91, 220

Cathode Rays, 239

Cavendish, 23, 65, 87, 93, 141-3

Chalcedony, 215

Chalk, 197-200

Charcoal, 195

Chemical change, 20, 39, 73

Chemical combination, laws of,

23-4

Chlorates, 104
Chlorine, 56, 100-5
Chrome alum, 224
Clay, 221-3
Clay ironstone, 200

261

INDEX

Combustion, 60 ; true nature of,

119

Compound, 21

Compounds and mixtures, 20
Condensation, 45
Constitution, water of, 161
Critical temperature, 57, 58
Crookes, 83, 239, 253
Cryohydrate, 164
Crystallisation, 160 ; water of,

161

Crystals, 159-61, 188-90, 201
Curie, Mme., 244-5, 247
Cyanogen, 56, 124

Dalton, 23, 25, 55

Davy, 22, 101, 115, 132

Definite proportions, law of, 23

Democritus, 6, u

Dewar, 58

Diamond, 196

Diffusion, 26

Discharge oT electricity, 237

Distillation, 45

Egyptian science, 5

Electric furnace, 207-8

Electrolytes, 171

Electrons, 238, 239-42, 247, 257

Elements : Greek idea of, 6 et
seq. ; Boyle's definition of,
10 ; modern conception of,
21 ; relationships of the,
230-5 ; evolution of the, 235-
7, 250-2

Emanation, radium, 246

Empedocles, 7, 37

Energy, 44, 58, 114, 252; trans-
formations of, 137-8

Equations, chemical, 31-2

Equivalents, 34-6

Ether, 251, 256-7

Eudiometer, 66

Eutectic point, 164, 167

Evaporation, 43-6

Expansion of gases, 54

Faraday, 55
Felspar, 215, 220-1
Filter-pump, 48
Filtration, 154
Fireclay, 223

Fixed air, 87, 92

Flame, 121-37 » °f Bunsen burner,

130

Flint, 215, 216
Foraminifera, 197
Formula, determination of

chemical, 31
Friction, heat from, 113

Galena, 194

Galileo, 52

Gases : pressure of, 49 ; kinetic
theory of, 50 ; expansion of,
54; liquefaction of, 55-60;
permanent, 56

Geber, 15

Glass, 217

Globigerina, 197

Granite, 214-5

Gypsum, 209-13

Hales, 87

Hard water, 157, 203

Heat : expansion by, 52 ; nature

of, 115
Helium, 58, 60, 70, 236, 247,

249, 251, 253
Heraclitus, 112, 137
Hooke, 6 1, 62
Hydrocarbons, 125
Hydrochloric acid, 98
Hydrogen, 58, 59, 77, 92-6, 142,

145-9, 229, 236, 251
Hydrogen chloride, 96-100
Hypochlorites, 104

Iceland spar, 202
Igneous rocks, 201
Ignition temperature, 121
Incandescence, 113, 136
Inflammable air, 92-6
Intratomic energy, 118, 138
Ions, 173, 237, 254-5
Iron, 236 ; effect of water on,

147-5
Isomorphism, 224

Joule, 115

Kaolin, 222
Kelvin, 55, 249
Kinetic theory, 50
Krypton, 71

262

INDEX

Lavoisier, 23, 55, 63-5, 101

Lead, 248

Leguminosae, 85

Liebig, in

Lime, 199-200, 206-9

Limestone, 200

Lithium group of elements, 230

Lodge, 241, 251, 256, 257

Lucretius, 1 1

Luminescence, 137

Luminosity of flame, 128

Magnesia alba, 87

Magnesium, 236 ; effect of water

on, 145
Marble, 200-1
Marine acid air, 96-100
Mayow, 61, 62
Mendeleeff, 231-2, 256
Mercurius calcinatus, 62-3
Mercury, 16, 62
Mica, 215

Mixtures and compounds, 20
Molecular energy, 44
Molecular motion, 117
Molecule, 27, 29, 44
Mortar, 207

Nascent state, 103

Nebulae, 236

Neon, 70

Neutralisation, 177-8

Newlands, 231

Newton, 25, 256

Nitrates, 83 ; manufacture of, 84

Nitrogen, 65, 80-86; fixation of,

83-86
Northmore, 55

Opal, 215
Oxidation, 99
Oxides, 75

Oxygen, 58, 64, 65, 72-78, 142,
196, 214

Paracelsus, 17
Periodic law, 231
Periodic table, 232
Peroxides, 99
Petrification, 205
Philosopher's stone, 14
Phlogiston, 61
Phosphorescence, 123

Physical change, 39

Pictet, 58

Pitchblende, 244, 255

Plants and the air, 78

Plaster of Paris, 212-3

Polluted waters, 158

Polonium, 247, 248

Porcelain, 223

Potash, 22

Potassium, 146

Potassium hydroxide, 146, 177

Priestley, 62-5, 87, 91, 99, 105,

1 08

Proteins, 82
Proust, 23
Pyrites, 194

Quartz, 215, 219
Quinta essentta, 7,

Radiant matter, 239

Radio-activity, 243-250, 252, 255

Radiolaria, 219

Radium, 243-250, 253, 255

Ramsay, 68

Rayleigh, 66, 68

Red lead, 63

Red precipitate, 63

Reducing agents, 96, no

Reduction, 77, 96

Rey, 61, 62

Rock-crystal, 215

Rontgen, 243

Rumford, 115

Rusting, 76, 143-4

Rutherford, 245, 253

Salt, 16, 97, 171, 173, 177
Sand, 215
Sandstone, 215
Scheele, 100, 104
Silica, 214-221
Silicates, 216-223
Silicic acid, 218
Silicon, 216

Smithells, Prof. A., 133
Soda, 22, 200
Sodium, 146

Sodium hydroxide, 147, 177
Soft water, 157
Solute, 160

Solution, 159-175 ; freezing of,
l63-$» saturated, 160, 170;
263

INDEX

supersaturated, 161 ; hydrate
theory of, 172 ; ionic theory
of, 173-9

Spirits of salts, 98, 100

Spontaneous combustion, 78

Stahl, 60, 62, 1 01

Stalactites and Stalagmites, 205

Starch, 92

Stars, elements on the, 235-6

Strutt, 249

Sulphides, 193-4, *97

Sulphites, no

Sulphur, 16, 19, 184-193

Sulphur dioxide, 73-4, io8-iy 193

Sulphuretted hydrogen, 211

Sulphuric acid, in

Sulphurous acid, no

Symbolic notation, 27-32

Synthesis, 20

Thales, 6, 140
Thilorier, 56
Thomson, 239, 255, 256
Thorium, 249

Uranium, 243, 244, 247, 249
Uranium series, 248

Vacuum, 42
Vacuum stills, 46
Vacuum tube, discharge in, 239
Vacuum vessels, 56, 58
Valency, 34, 234, 243
Valentine, Basil, 15
Vapour pressure, 45
Ventilation, 53
Vital air, 63, 64
Vitriolic acid air, 108-111
Volatile spirit of sal ammoniac,
105

Water : in the air, 80 ; effect of,
on metals, 143-149 ; compo-
sition of, I49-I53J impurities
in, 153-9 ; molecular depres-
sion of, 172 ; influence in
chemical changes, 179

Welsbach burner, 131

White lead, 200

Winds, 53

Xenon, 71
X-rays, 237, 245

Zero group of elements, 237

PRINTED BY CASSELL & COMPANY, LIMITED, LA BELLE SAUVAGE, LONDON, E.G.

FOURTEEN DAY USE

RETURN TO DESK FROM WHICH BORROWED

This book is due on the last date stamped below, or

on the date to which renewed.
Renewed books are subject to immediate recall.

LD 21-100m-2,'55
(B139s22)476

16929

UNIVERSITY OF CALIFORNIA LIBRARY

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "The story of the five elements"

See other formats