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CHEMISTRY IN THE SERVICE
OF MAN
BY THE SAME AUTHOR.
PRACTICAL PHYSICAL CHEMISTRY.
With 104 Illustrations. Crown Svo, 4^. bd.
net.
PHYSICAL CHEMISTRY AND ITS AP-
PLICATIONS IN MEDICAL AND
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TIONS. With 134 Figures in the Text.
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iPhoto : Emery Walkery Ltd.
ROBERT BOYLE, 1626-1691.
{^From the painting afttr F. Kcrseboom in the National Portrait Gallery.)
Frontispiece.
CHEMISTRY IN THE
SERVICE OF MAN
ALEXANDER FINDLAY
M.A.. D.Sc., F.I.C.
PROFESSOR or CHKMISTRY IN THE UNIVBRSITV OF WALBS
AMD UISKCSOR OF THE KDWARO DAVISS CHEMICAL LABORATORIES
UNIVBKSITV COLLKCK OF WALBS, ABERYSTWrTH
WITH 3 PORTRAITS AND 33 DIAGRAMS IN THE TEXT
SECOND EDITION
LONGMANS, GREEN AND CO.
39 PATERNOSTER ROW, LONDON
FOURTH AVENUE 4 30TH STREET, NEW YORK
EO^BAY, CALCUTTA, AND MADRAS
I917
All right t rturved
TO
MY WIFE
PREFACE TO THE SECOND
EDITION
In the year which has passed since this book was first
published, signs have not been wanting that interest in
physical science, and more particularly in chemical science,
has become more deep and widespread, and that the
country has awakened to a fuller consciousness of the
need of promoting and encouraging the study of chemistry
and its advancement by research. Most clearly, perhaps,
is this increase of interest shown in the sphere of education.
Throughout all sections of the community, the demand is
being made with increasing insistence, that the study of
science shall form an integral part in all our schemes for a
liberal education, both in School and University ; and this
demand is based, and rightly based, not so much on the
utilitarian as on the cultural value of science. For the
majority of our people, who will not be actively engaged
in chemical pursuits, it is, as the author believes, not so
much a knowledge of a wide range of facts that is required
— although some of the facts are so important that they
should be known by all — but rather the gaining of the
scientific spirit, and of an understanding of the theoretic
basis of science. As the late Professor Meldola once
wrote : " If the progress of a nation is dependent — as we
are now beginning to realise — upon its general appreciation
of Science, that appreciation must be of the highest and
broadest character — it is Science in the abstract, and not
purely utilitarian concrete knowledge, which must be raised
to the level of one of the most exalted branches of human
viii PREFACE TO THE SECOND EDITION
culture." And it was in this belief that the author
attempted, in writing the present book, to blend the more
philosophic with the more practical side of chemical science,
hoping thereby not only to arouse the interest of the
general reader, but also to appeal to his imagination and
his intellect. That this aim has only been very partially
achieved, the author is very conscious, but he offers the
work, such as it is, as a small contribution towards repair-
ing the failure, to which the President of the Board of
Education (Mr. H. A. L. Fisher) has recently alluded, " to
find a form of scientific instruction which might appeal to
the imagination and interest of the general mass of the
population in the schools who are not destined for a
specifically scientific career,"
In the industrial applications of chemistry, also, progress
is undoubtedly being made, and in one most important
industry, the utilisation of atmospheric nitrogen for the
production of fertilisers and nitric acid, the author is glad
to think that active steps are already being taken to remove
the stigma of neglect which rested for so long on this
country.
The faith in science which the people of this country
have begun to gain during the years of war must be con-
firmed and stablished in the equally testing times of
peace ; and it can be kept alive only if it is based on a
knowledge and understanding of the aims of science, and
of what has been achieved in the past.
In the present edition the book remains essentially
unchanged, but a certain amount of new matter, more
especially a chapter on " Fermentation and Enzyme
Action," has been added.
A. F.
Y Glyn,
Llanfarian,
Cardigansbirca
May^ 1917.
PREFACE
When the writer was invited to deliver the Thomson
Lectures before the United Free Church College, Aber-
deen, at the end ot the year 1915, he felt that, as a
teacher of chemistry, he could attempt no higher task than
that of giving to his hearers, who made no claim to
chemical knowledge, some account of what the science of
chemistry, both in its general principles and in its industrial
applications, has accomplished for the material well-being
and uplifting of mankind ; and the lectures which were
then delivered form the basis of the present work.
The reasons which prompted the choice of subject are,
of course, not far to seek. The crisis through which this
and other European countries are now passing, has brought
heme to us how greatly we, as a nation, have hitherto failed
to recognise the intimate and vital dependence of our social
and national prosperity on a knowledge and appreciation
of the facts and principles of 'science, and not least of
chemistry, and on their application in industry. All the
industries of the country on which not only the comfort
but even the life of the people depend — the great manu-
facturing industries and agriculture, the greatest industry
of all — claim tribute of chemistry. And yet we, as a nation,
have done much less than the responsibilities of our civilisa-
tion demanded, to promote and encourage the development
X PREFACE
of chemical knowledge ; we have even, indeed, largely
failed to avail ourselves of that tribute which science is so
willing to pay. To the work of laying the foundation of
pure science, on which the superstructure of successful
industrial achievement must be raised, British chemists
have, according to the measure of their numbers, con-
tributed an honourable share ; but the people as a whole,
being ignorant of science, have mistrusted and looked
askance at those who alone could enlarge the scope of
their industries and increase the efficiency of their labours.
And so we have witnessed in the past an appalling and
needless waste of our national resources, and in too many
cases industries have languished and succumbed, or, even
when born under conditions of great promise, have remained
dwarfed and stunted in growth. In 1862, the German
chemist, Hofmann, at that time a Professor of Chemistry in
London, could utter the prophecy : " England will, beyond
question, at no distant day, become herself the greatest
colour-producing country in the world, nay, by the strangest
of revolutions, she may, ere long, send her coal-derived
blues to indigo-growing India, her tar-distilled crimsons
to cochineal-producing Mexico, and her fossil substitutes
for quercitron and safflower to China, Japan, and the
other countries whence these articles are now derived."
But, alas ! that prophecy has not yet been fulfilled, and
the industry of synthetic dyes, an industry which above
all others depends on the fostering and encouragement
of chemical research and on the highest scientific effici-
ency, has found a home elsewhere amid more congenial
surroundings.
But there are now welcome signs that the country is
PREFACE xi
awakening to a sense of past deficiencies, and already the
Government has taken a first short step in the direction
of encouraging and assisting scientific and industrial
research. But if the national effort is really to become
effective and to exert a lasting influence, something more
is necessary, something which is, perhaps, more difficult
of achievement than Governmental aid. The mental out-
look and the attitude of the people as a whole towards
science must be changed, and the scientific habit, and a
spirit of trust in science must be cultivated ; and we must
also attract in much larger numbers into the ranks of
scientific workers, men of equal mental calibre to, and
capable of taking the same wide outlook as those who
are at present attracted into the higher ranks of the legal
profession or into the Civil Services. Science stands for
efficiency in all tlie activities of life, and the neglect of
science spells waste and industrial decay. It is for the
country to choose the path which it will follow, but in
making their choice let the people bear in mind the words
spoken by the King when Prince of Wales : " Does not
experience warn us that the rule of thumb is dead, and
the rule of science has taken its place ; that to-day we
cannot be satisfied with the crude methods which were
sufficient for our forefathers, and that those great industries
which do not keep abreast of the advance of science must
surely and rapidly decline } "
But we must learn to appreciate science not merely on
account of its utilitarian value as a means of increasing
wealth and material prosperity. From the material point
of view, doubtless, " science is the knowledge most worth,"
and in the case of most people, perhaps, interest in science
xii PREFACE
centres round its industrial or economic utility. Nisi utile
est quod facias, stulta est gloria {" All useless science is an
empty boast ") is a sentiment which will find a wide if not
an universal acceptance, but we must beware of interpreting
the usefulness of science in too narrow a spirit. The
study of science possesses a cultural value which is quite
independent of the utility of its applications ; and as an
instrument of culture, as a means of coming into closer
relations with Nature and the Infinite, science claims a
fuller and more widespread recognition.
At a time of awakening interest in science, the author
hopes that the present attempt to give a readily intelligible
account of some of the more important general principles
and theories of chemical science and of their applications,
may afford to the general reader some idea of the world's
indebtedness to the chemist, and may also stimulate the
interest of, at least, the younger students of chemical
science by presenting to them a picture of that land into
a fuller possession of which they one day hope to enter.
My thanks are due to the publishers, Messrs. Long-
mans, Green & Co., for permission to use Figures i, 2, 9,
and 10, taken from works published by them ; and I
desire, also, to express my indebtedness to my wife for
her assistance not only in preparing the manuscript for
publication, but also in reading the proof-sheets.
A. F.
Y Glyn,
Llanfarian,
Nr. Aberystwythi
AfartAf 1916.
CONTENTS
CHAPTER I
INTRODUCTION
tAQM
Definition and scope of chemistry. Constitution of matter. Views of
Aristotle. The alchemists. Elements and compounds. Compo-
sition of the earth. Atomic hypothesis. Dalton's atomic theory.
Symbols and formulae . I
CHAPTER II
COMBUSTION, AND THE PRODUCTION OF FIRE
Explanation of combustion in air. Phlogiston theory. Laroisier's
explanation. Ignition point. Safety lamp. Slow combustion.
Combustion in the living organism. Spontaneous combustion.
Combustion by means of combined oxygen. Production of
chromium. Thermit. Matches 1 5
CHAPTER III
THE CHEMISTRY OF ILLUMINANTS
Candles. Snuffing of candles rendered unnecessary. Shale oil.
Saturated and unsaturated hydrocarbons. Petroleum. Flash
point. Coal-gas. Luminosity of flames. Water-gas. Bunsen
burner. Oxy-coal-gas flame. Lime light. Production of rubies
and sapphires. Incandescent gas mantle. Acetylene .... 3a
CHAPTER IV
ENERGY, FUEL, AND EXPLOSIVES
Energy of chemical reactions. Production of coal. Calorific value
of coal. Conservation of the coal reserves. Producer gas.
Mond ga& Exothermic and endothermic reactions. Ozone.
Explosives 57
XIV
CONTENTS
CHAPTER V
CELLULOSE AND CELLULOSE PRODUCTS
PASS
Carbohydrates. Cotton. Wood pulp. Paper. Artificial silk.
Mercerised cotton. Xylonite or celluloid. Cellon and non-
inflammable celluloid. Glucose from cellulose 78
CHAPTER VI
VELOCITY OF REACTIONS AND CATALYSIS
Chemical affinity. Influence of concentration. Influence of tempera*
tare. Reversible reactions. Catalysis. Surface combustion.
Enzymes. Manufacture of sulphuric acid. Hardening of fats.
Margarine . . . t 88
CHAPTER VII
FIXATION OF ATMOSPHERIC NITROGEN
Importance of nitrogen in the economy of nature. Sources of supply
of combined nitrogen. Fixation of atmospheric nitrogen. Direct
combination of nitrogen and oxygen. Fixation of nitrogen by
means of carbides. Catalytic oxidation of ammonia. Synthetic
production of ammonia. Combination of nitrogen with metals.
Liquefaction of air. Thermos flasks
CHAPTER VIII
GLASS, SODA, SOAP
Discovery of glass. States of matter. Crystalline and amorphous
solids. Crystallisation of liquids. Supercooled liquids. Devitri-
fication. Fused quartz or silica glass. Water glass. Window
glass. "Patent plate." Annealing of glass. Hardened glass.
Crystal glass. Strass or paste. Coloured glass. Silvering of
glass. Manufacture of soda by tlie Leblanc process. Hydrochloric
acid. Chlorine. Bleaching powder. Manufacture of soda by the
Solvay process. Saponification of fats. Manufacture of soap.
Soft soap. Hard soap. Cleansing power of soap. Hard water.
Softening of bard water. Permutit
136
CONTENTS XV
CHAPTER IX
ELECTRICITY AND CHEMISTRY
rAGK
GalvanL Volta. Voltaic cell. Sodium and potassium. Electro-
plating. Conduction of electricity by solutions. Electrolytes and
non-electrolvtes. Electrolysis. Ions. Movement of Ions.
Daniell cell. Leclanche cell. Lead accumulator. Edison cell.
Refining of copper. Manufacture of chlorine and of caustic soda.
Aluminium. Alloys of aluminium. Magnesium. Carborundum.
Alundum. Artificial graphite l6i
CHAPTER X
THE COLLOIDAL STATE
Analogy between solutions and gases. Diffusion. Colloids and
crystalloids. The colloidal state. Tyndall phenomenon. The
ultramicroscope. Size of colloid particles. Emulsoids and
suspensoids. Protective action of emulsoids. Photographic plates.
Sedimentation in rivers. Plasticity of clay. " Egyptianised clay."
Aquadag. Oildag. Adsorption. Decolorising of liquids by
charcoal. Cataphoresis. Drying of peat. Process of dyeing.
Mordants. Colloids in agriculture. Purification of water and
sewage. Brownian movement 185
CHAPTER XI
MOLECULAR STRUCTURE
Organic chemistry. Isomerism. Molecular constitution. Valency.
Formulae of Kekule. Optical activity. Stereo-chemistry. Theory
of van't Hoff and Le Bel. Resolution of the racemic into the
optically active forms. Stereo-chemistry and vitalism 206
CHAPTER XII
SYNTHETIC CHEMISTRY
Chief constituents of coal-tar. The coal-tar dyes. Synthesis of
alizarin. Synthesis of indigo. Synthetic drugs : chloroform,
iodoform, chloral, veronal, sulphonal, trional, tetronal, suprarenine,
antifebrin, phenacetin, aspirin. Synthetic perfumes : couraarin,
oil of wintergreen, oil of bitter almonds, lily of the valley, haw-
thorn blossom, ambergris. lonone {artificial violet). Artificial
musk. Oil of mirbane. Synthetic camphor. Bakelite .... 229
CHAPTER XIII
FERMENTATION AND ENZYME ACTION
Explanation of fermentation. Enzymes. Manufacture of alcohol.
Proof spirit. Methylated spirit. Fusel oils. Artificial fruit essences.
Alcoholic beverages. Whisky, gin, brandy, rum. Wines. Beers.
Vinegar. Acetic acid. Acetone. Curdling of milk. Cheese.
Casein. Distempers. Plasmon. Sanatogen. Erinoid .... 249
Index 265
PORTRAITS
ROBEkT Boyle, i 626-1 691 Frontispiece
From the painting after P. Kerseboom in the National
Portrait Gallery. (Photo: Emery Walker, Ltd.)
John Dalton, 1766-1844 To face p. \o
Louis Pasteur, i 822-1 895 „ 215
From a Photograph by Pierre Petit.
CHAPTER I
INTRODUCTION
Chemistry is a branch of science which deals with
matter ; with the material universe which is revealed to us
by our senses. It studies the different kinds of substances
found in the world, whether in the living animal and
vegetable organisms, or in the non-living mineral matter of
the universe. Chemistry investigates the composition of
these substances, the methods of their preparation and
their behaviour not only in relation to what are called
physical forces but also in relation to other substances ; and
it endeavours to " manipulate " the different substances so
as to obtain from them new materials, either useful or
ornamental. Through a knowledge of chemistry one may
learn how to prepare, artificially, substances which are
normally the products of the vital activity of animal and
vegetable organisms, or how to prepare substitutes for
these naturally occurring substances. Chemistry, further,
occupies itself with the question of how things already
manufactured, can be manufactured more economically, or
be replaced by more suitable materials ; and it helps us to
understand how the natural and, it may be, irreplaceable
resources of the world, can be economised. on the
B
2 CHEMISTRY IN THE SERVICE OF MAN
science of chemistry, indeed, more than on any other
branch of organised knowledge, depend the material well-
being and comfort of man.
But the end and aim of chemistry is not merely
material. Chemistry offers its contribution also to the
deeper interests of the human mind. Occupied as he is
with the study of material substances and of the marvellous
transformations which he is able to bring about in them,
the thinking chemist is forced to look below the surface
of things and to seek an answer to the fundamental
questions relating to the ultimate constitution and structure
of matter, and to the forces which govern the changes and
transformations which he observes in his laboratory, or
which are wrought out in the larger laboratory of Nature,
The study, not merely of the products but also of the
principles and laws underlying the processes of chemical
change, forms the work of the modem chemist In its
wider sweep, chemistry ignores the conventional and
artificial frontiers which mark it off from the other
branches of science, more especially physics ; and in the
last quarter of a century there has been no more fruitful
region of experimental and speculative activity than that
common territory where the sciences of chemistry and
physics overlap.
In attempting a brief and necessarily incomplete survey
of chemistry in the service of man, I shall endeavour not
merely to recount some of the manifold ways in which
chemistry has revolutionised life and has contributed, on the
material side, to a civilised existence ; but I shall try, also,
to indicate, if I cannot do more, some of the principles
which underlie chemical change, and some part of the
INTRODUCTION 3
contribution which chemistry has made to our knowledge
of the constitution of matter.
I say here constitution, not nature, of matter. The
question of what matter, in its ultimate analysis, may be,
whether it consists, as some suggest, of " empty cracks in a
stagnant sea of ether," or whether it is, as others suppose,
" a persistent strain-form flitting through an universal sea
of ether," cannot be discussed here. The explanation of
matter, that is, the description of matter in terms of some-
thing simpler, something more fundamental, lies outside the
domain of the chemist. We must be content to accept
matter as itself a fundamental reality, as itself an ultimate,
beyond which chemistry, at least, does not go.
The question of the constitution of matter is one which
has occupied the minds of thinking and reasoning men from
the earliest beginnings of philosophic enquiry, more
especially as developed among the ancient Greeks. Many
and varied were the views which were held, and although
the study of these will always prove interesting, it must be
borne in mind that the considerations which governed the
speculations of many of the ancient philosophers were quite
different from those by which the modern scientist feels
himself bound. To many of the Greek philosophers, the
fact that our eyes make things manifest to us, was no
proof that those things exist. By them, intuition, a very
valuable gift indeed, and reason were made the all-
sufficient grounds of knowledge ; and they sought to explain
the universe merely by the exercise of a vigorous imagina-
tion and a rigorous logic. one cannot therefore wonder
that they sometimes lost touch with reality. As has been
said: "The intellectual vigour of the philosophers of
4 CHEMISTRY IN THE SERVICE OF MAN
antiquity, indeed, was capable of the grandest and most
comprehensive views of nature, and often conducted them
to the most sublime truths, but in attempting perpetually
to soar above the vulgar paths of observation and
experience, they speedily became confounded in the
mists of error and conceit."
To two only of those ancient views special reference
need be made on account of the important part which they
played in the evolution of the science of chemistry.
In the philosophy of Aristotle, based on that of Empe-
docles, we find the conception of one primordial matter
which acted as the carrier of certain essential qualities
which were taken to be hotness, coldness, wetness, dryness.
The elements were regarded not as material things but
rather as the combinations of these qualities ; and by the
union of these in different proportions the different sub-
stances were formed.
This conception of the constitution of matter dominated
science until the time of Robert Boyle in the seventeenth
century ; and the idea of the existence of four " elements "
(fire, air, earth, water) lingers on, in popular thought, even
to the present day. Moreover, so long as the view was
held that matter has no reality in itself, but is merely the
carrier or embodiment of certain qualities, it is clear that
the conversion of one form of matter into another by
altering the proportions of the elemental qualities, would
appear to be quite feasible ; and the aim of the ancient and
mediaeval alchemists to effect such a transmutation (to wit,
a transmutation of the base metals into gold), would seem
to be neither hopeless nor absurd.
Fruitless as their efforts in this direction proved, the
INTRODUCTION 5
alchemists, like the Arabian Geber, the Spaniard Raymund
Lully, the German Albertus Magnus, and the English
Roger Bacon, added much of the highest value to our
knowledge of substances ; and some of the materials which
they were the first to obtain, like aqua fortis or nitric acid,
and oil of vitriol or sulphuric acid, are among the most
important in the whole of modern chemistry. Wrapping
itself up in a cloak of mystery and making pretence of a
knowledge which it did not possess, alchemy, doubtless, in
many cases, exercised a baneful influence by its appeal to
the cupidity and baser passions of men, but it acquired
at last a nobler aim and ideal under the influence of
Paracelsus, in the sixteenth century. Not the curing of
" diseased " metals, as the Arabians called the base metalsi
but, as the handmaid of medicine, the curing of diseased
men, was the true avocation of alchemy ; and the study
and preparation of drugs became the main object of the
chemist. And it is of interest, in this connection, to note
that in our older Universities, the predecessors of the
present professors of chemistry were professors of medi-
cine ; and the makers and sellers of drugs, our pharmacists
and apothecaries, are those to whom in the common and
legal language of the present day we apply the name of
chemist.
Powerful as was the influence exerted by the philosophy
of Aristotle, there arose, in time, men who refused to accept
the doctrine of the four elements ; and the overthrow of
this philosophy was completed in the seventeenth century
by Robert Boyle, of whom it has been said that " he was
the father of chemistry and the uncle of the Earl of Cork."
Pure substances, as Boyle pointed out, can be divided
6 CHEMISTRY IN THE SERVICE OF MAN
into two classes. In the one class are those which have, so
far, resisted all attempts to decompose them, or to break
them down into substances simpler than themselves. These
substances, according to Boyle, are the true elements, and
this definition of an element is still retained. The defini-
tion, it should be noted, does not postulate the impossibility
of decomposition, but insists merely on the fact that the
possibility, if it exists, has not so far been realized.
In the second class of pure substances are placed
those which, by one means or another, can be resolved
into simpler substances. These more complex substances
are called compounds. Thus, for example, if we heat in a
glass tube the red substance known as red precipitate or
oxide of mercury, we find that a gas is given off which has
the property that it will cause a glowing splint of wood
to re-ignite ; and, at the same time, metallic mercury is
deposited in shining droplets on the cooler portions of the
tube. We have thus decomposed the red substance into
metallic mercury and a gaseous substance, to which the
name of oxygen has been given. This red substance, there-
fore, is a compound, a compound of mercury and oxygen.
In spite of most laborious and prolonged efforts,
chemists have not succeeded in reducing the number of
the elements to less than about eighty. Of these eighty
odd elements, a list of which for convenience of future
reference we give below, all the substances in the known
universe are built up.
INTRODUCTION
List of the Elements.
Aluminium AI 27*1
ADtimony Sb 120*2
Argon A 39'^^
Arsenic... .As 74*96
Barium Ba 137*37
Bismuth Bi 3oS*o
Boron B iro
Bromine Br 79'92
Cadmium... Cd 112*40
Caesium Cs 132*81
Calcium Ca 40*07
Carbon C l2*oo
Cerium Ce 140*25
Chlorine CI 35*46
Chromium Cr 52*0
Cobalt Co 58*97
Columbium Cb 93*5
Copper Cu 63*57
Dysprosium Dy 162*5
Erbium Er 167*7
Europium Eu 152*0
Fluorine F 19*0
Gadolinium Gd 157*3
Gallium Ga 69*9
Germanium Ge 72*5
Glucinum Gl 9*1
Gold Au 197*2
Helium He 3*99
Holmium Ho 163*5
Hydrogen H 1008
Indium In 114*8
Iodine I 126*92
Iridium Ir I93'i
Iron Fe 5584
Krypton Kr 82*92
Lanthanum La 139*0
Lead Pb 207*10
Lithium Li 6*94
Lutecium Lu 174*0
Magnesium Mg 24*33
Manganese Mn 54*93
Mercury Hg 200*6
Molybdenum Mo 96*0
Neodymium Nd 144*3
Neon Ne 20-3
Nickel Nl 5868
Niton (radium emanation) Nt 222*4
Nitrogen N 14*01
Osmium Os 190*9
Oxygen O i6'oo
Palladium Pd 106*7
Phosphorus P 31*04
Platinum Pt 195*3
Potassium K 39*10
Praseodymium Pr 140*6
Radium Ra 226*4
Rhodium Rh 102*9
Rubidium Rb 8545
Ruthenium Ru lor?
Samarium Sa 150*4
Scandium Sc 44*1
Selenium Se 79*3
Silicon Si 28*3
Silver Ag 107*88
Sodium Na 23*00
Strontium Sr 87*63
Sulphur S 32*07
Tantalum Ta 181*5
Tellurium Te 127*5
Terbium Tb 159*3
Thallium Tl 204*0
Thorium Th 233*4
Thulium Tm 168*5
Tin Sn 119*0
Titanium Ti 48*1
Tungsten W 184*0
Uranium U 238*5
Vanadium V 51*0
Xenon.... Xe 130*2
Ytterbium (Neoytterbium)Yb 172*0
Yttrium Yt 89*0
Zinc Zn 65*37
Zirconiam Zi 90*6
8 CHEMISTRY IN THE SERVICE OF MAN
only about twenty of the elements occur free or un-
combined in nature ; and the amounts in which the
different elements exist vary very greatly. Of all the
elements found in the earth, the seas, and the air, oxygen
and silicon are by far the most abundant, as the following
analysis shows : —
Chemical Composition of the Earth.
Per cent.
Oxygen 4985
Silicon 26*03
Aluminium 7*28
Iron 4*12
Calcium 3*18
Per cent.
Sodium 2*33
Potassium 2'33
Magnesium 2*11
Hydrogen 0*97
Other elements i'8o
In other words, the two elements, oxygen and silicon,
constitute together three-quarters of the whole of terrestrial
matter.
Underlying the philosophy of Aristotle was the idea
that matter is continuous, that it is capable of infinite
sub-division ; but with the overthrow of the doctrine of
the four elements of Aristotle there was revived another
ancient hypothesis which had been put forward by the
Greek philosophers Leucippus and Democritus, an hypo-
thesis which has been preserved and expounded for us,
with a wealth of poetic imagery, by the Roman poet
Lucretius. According to this hypothesis, the ultimate con-
stituents of matter are indivisible particles — the "atoms"
or " first beginnings of things " — eternal and immutable,
in which, as explained by Aristotle, " the common primitive
matter, differing in size and form of its parts, is the principle
of them all." By the coming together of these atoms the
substances constituting the material world were regarded
as being formed ; and the diversity of substances was held
INTRODUCTION 9
to be due to differences in the size and shape of the atoms
composing the substances. " Now mark and next in order
apprehend of what kind and how widely differing in their
forms are the beginnings of things, how varied by manifold
diversities of shape, . . . The things which are able to
affect the senses pleasantly, consist of smooth and round
elements ; while all those, on the other hand, which are
found to be bitter and harsh, are held in connection by
particles that are more hooked, and for this reason are
wont to tear open passages into our senses." (Lucretius.)
These views must seem crude to the modern mind, and
even Newton, at the end of the seventeenth century, could
not greatly refine them. Thus he expressed the view : " It
seems probable to me that God, in the beginning, formed
matter in solid, massy, hard, impenetrable, moveable
particles, of such sizes and figures, and with such other
properties, and in such proportion to space, as most con-
duced to the end for which He formed them ; and that
those primitive particles, being solids, are incomparably
harder than any porous bodies compounded of them ; even
so very hard as never to wear or break in pieces ; no
ordinary power being able to divide what God himself
made one in the first creation."
The great authority of Newton was a powerful support
to the atomic conception of matter, but it was not till the
beginning of the nineteenth century that this fundamental
hypothesis was developed into a theory by which the
observed phenomena and the laws of chemical combination
could be quantitatively explained or co-ordinated. It was
only after this had been done, however, that the general
hypothesis of the atomic constitution of matter could
10 CHEMISTRY IN THE SERVICE OF MAN
become of any real value in science, and nothing has in-
fluenced the progress of chemistry so much as the achieve-
ment of this by the Manchester schoolmaster, John Dalton.
To the older philosophers, the atoms or indivisible
particles into which matter could be divided, all consisted
of the same primordial material, although differing in size
and shape. The atoms of Dalton, however, differed in
their nature. In the case of any particular element, the
definition of which we have already learned, the atoms
were assumed to be all exactly alike in their properties,
including, of course, their mass ; but they differed from the
atoms of any other element.
Further, according to Dalton, a compound is formed
by the coming together or combination of atoms of different
kinds ; and since the nature of the compound will neces-
sarily depend on the number and kind of the atoms
present, the composition of the compound must be definite.
This is the first fundamental law of chemistry, the law of
constant or definite proportions.
And still further. Since the fundamental assumption
of the atomic theory is that atoms are indivisible, that they
cannot be broken up into anything smaller, it follows that
if one particular element A combines with another element
B to form compounds containing different proportions of A
and B, the higher proportions of the elements must be
whole multiples of the lowest proportion. That is to say,
we can have the compounds A 4- B, A + 2B, 2A + B,
2 A + 3B, etc., where A and B represent atoms of the
elements A and B. Here, then, we have the explanation
of the second fundamental law of chemistry, the law of
multiple proportions.
JOHN DALTON, 1766-1844.
To face p. lo.
INTRODUCTION ii
At first Dalton made no distinction between the
smallest particle of an element and the smallest particle
of a compound. Both were called atoms. But it is
clear that this must cause difficulty, because although the
atom of an element may be regarded as indivisible, the
atom of a compound must still be capable of being split
up into smaller particles, namely the atoms of the com-
ponent elements. A new name was therefore introduced
by the Italian chemist, Avogadro, who called the smallest
particle of a compound a molecule ; and a molecule of a
compound, therefore, consists of a number of elementary
atoms. We have, then, the definition that an atom is the
smallest particle of an element which can enter into the
composition of a molecule, or which can take part in
chemical exchange. It is, so to speak, the smallest coin
in chemical currency. A molecule, on the other hand,
is the smallest particle of a substance which can exist in
the free state.
But it does not follow that the atoms and molecules of
an element mean the same thing. In some cases they do,
and the atoms of such elements as argon and helium, for
example, can exist in the free state, by reason of the fact
that they possess no power of combination. But in very
many cases the free atoms of an element combine together
to form aggregates of like atoms, so that the molecule of
an element, or the smallest particle of the element capable
of free existence, may consist of two or three or even of
four atoms combined together.
In the table given on p. 7, we see that opposite each
element is a letter or group of letters, by means of which
we can represent shortly the particular element. Each of
12 CHEMISTRY IN THE SERVICE OF MAN
those symbols^ as they are called, represents an atom or
one atomic proportion of the particular element ; and since
a compound is regarded as being formed by the combina-
tion of atoms, we can conveniently represent the molecule
of a compound by writing the symbols of the constituent
atoms side by side. Thus, NaCl represents a compound
of sodium and chlorine, the molecule of which contains one
atom of sodium and one atom of chlorine ; CO, similarly,
represents a compound of carbon and oxygen ; and so on.
But, frequently, the molecule of a compound is formed by
the combination of elements in more than one atomic pro-
portion, and so we write, for example, H3O, which is the
formula (as it is called) for water ; a formula which
indicates that the molecule of water contains two atoms
of hydrogen and one atom of oxygen. The formula NH3,
similarly, which is the formula for ammonia, indicates
that the molecule of this compound contains three atoms
of hydrogen united with one atom of nitrogen.
The use of these symbols and formulae is a great
convenience and renders much assistance to the chemist
in understanding chemical changes ; and we shall make
use of them to some extent in our future discussions.
To one point more we must refer. According to the
' These symbols were introduced early last century by the Swedish
chemist Berzelius, who ased the initial letter of the Latin name to represent
the element. Where the name of more than one element began with the
same letter, a second letter was added as a distinguishing mark. By using
the Latin names of the elements, the symbols were rendered international ;
and we can thus understand why, in certain cases, the symbols are not
obvious abbreviations of the English name of the element. Thus, we have,
Sb a antimony (stibium) ; Cu « copper (cuprum) ; Au ■■ gold (aurum) ;
Fe «■ iron (ferrum) ; Pb ■■ lead (plumbum) ; Hg =■ mercury (hydrargyrum) j
' K ■> potassium (kalium) ; Ag — silver (argentum) ; Na «■ sodium (natiium) ;
ba =a tin (st:>anum).
INTRODUCTION 13
atomic theory of Dalton, the atoms of a particular element
are all exactly alike, and different from the atoms of other
elements. If the atoms have definite properties, however,
they must also have a definite mass or weight. Although
shrewd estimates of the absolute weights of atoms have
been made, it is clear that we cannot handle these infini-
tesimally small particles of which many millions are con-
tained in the tiniest piece of matter which can be seen by
the eye ; we cannot place these atoms on the scale pan
of our balance and ascertain their weight. But we can
determine the relative weights of the atoms, and such
determinations constitute one of the greatest achievements
of science which followed in the train of Dalton's atomic
theory. These relative weights are what are called the
atomic weights of the elements, and their values are given
in the table on p. 7. By the introduction of these
atomic weights, a new and extended meaning is given
to our formulae. NaCl then becomes not merely a con-
venient shorthand symbol for the compound sodium
chloride (rvhich is the chemical name for common salt),
but it tells us that this compound consists of one atomic
proportion or 23 parts by weight of sodium, and one
atomic proportion or 3 5 "46 parts by weight of chlorine,
the numbers 23 and 35*46 being the relative weights of
the sodium and the chlorine atom respectively.
one of the greatest of scientists. Lord Kelvin, said :
•' I often say that if you can measure that of which you
speak, and can express it by a number, you know some-
thing of your subject ; but if you cannot measure it,
your knowledge is meagre and unsatisfactory." And it
is because Dalton's theory is a quantitative theory, or
14 CHEMISTRY IN THE SERVICE OF MAN
capable of quantitative ｅxpression, that it was possible for
the hypothesis of the discontinuous or atomic constitution
of matter to become the foundation stone of all modem
physical science ; and it is by the introduction of mathe-
matics and by the quantitative treatment of chemical
phenomena, that modern chemistry is mainly distinguished
from the chemistry of fifty years ago.
CFI AFTER II
COMBUSTION AND THE PRODUCTION OF FIRE
one of the most typical, most familiar, and most important
cases of chemical action is that which is observed in the
process of combustion or the burning of substances in air.
The manner in which the first visible combustion, or fire,
was brought about on the earth, whether by some lightning
flash, or by the sparks struck from the flints of primitive
man ; by the rubbing together of dried wood, or by the
self-heating of combustible material, will doubtless always
remain unknown. But in whatever way fire was first
produced, its importance and value were early recognised,
as we can understand from the sanctity with which all
primitive peoples have endowed the hearth ; from the
Promethean legend of a boon stolen from, not granted
by the gods ; as ivell as from the later belief of the
followers of Zoroaster, that fire is the special abode of
divinity.
And even in modem times, although the feeling of
reverence or of awe is no longer inspired by a process
which can be explained in terms of chemical action, and
can be produced at will by the striking of a match, we
are not likely to underrate the importance of combustion
when we remember that our present-day civilisation, in
all its manifold forms of ｅxpression, in manufactures,
i6 CHEMISTRY IN THE SERVICE OF MAN
in railway and steamship transport, in artificial illumina-
tion, etc., is based on a process of combustion.
What then is the explanation of this process of com-
bustion } Not so very long ago, the view was held that the
property of combustibility was due to the presence in the
combustible substance, of a fiery principle, phlogiston ; and
that when a substance burns, the phlogiston escapes,
leaving behind the ash, or calx, as it was called in the case
of a metal. Charcoal, which burns leaving practically no
ash, was therefore regarded as being almost pure phlo-
giston. This was the explanation of combustion given,
more especially, by Stahl, towards the end of the seven-
teenth century ; and it was not till a hundred years later
that the "phlogiston theory" was finally overthrown by
the French chemist Lavoisier, who died in 1794, a victim
of the guillotine, in the troublous times of the French
Revolution.
The long life of such an erroneous theory as that due to
Stahl may be attributed to the fact that chemistry was, at
that time, still largely a qualitative or descriptive science,
and it was considered that form rather than weight was the
characteristic property of substances. The balance, of
course, was known and used, but its importance was not
fully appreciated ; so that when it was found that the
products of a combustion weigh more than the original com-
bustible substance, the upholders of the phlogiston theory
sought to defend their position by identifying phlogiston
with the principle of levity. The escape of the principle of
levity from the body, left the body heavier.
Much as we may be inclined to smile at such an expla-
nation, we must remember that the phlogiston theory served
COMBUSTION AND PRODUCTION OF FIRE 17
usefully its day and generation, and satisfied even the
modern requirements of a theory, in that it gave an expla-
nation of combustion which satisfied men's minds at the
time, and also inspired a large amount of fruitful investi-
gation. Who can say that even some of our most cherished
theories may not be considered by the unthinking a hundred
years hence, to be equally worthy of derision ? The phlo-
giston theory, however, long outlived its usefulness, and the
tenacity with which it maintained itself is an instructive
illustration of the difficulty which most minds have of
freeing themselves from the authority of a long-held
theory ; and it conveys a lesson, which is not unnecessary
even at the present day, that a theory from being a helpful
guide may readily become an oppressive tyrant. As
Liebig wrote many years ago, after having himself been a
victim of the misfortune to which he refers : " No greater
misfortune could befall a chemist than that of being unable
to shake himself free from the power of preconceived ideas,
and, yielding to the bias of his mind, of seeking to account
for all phenomena which do not fit in with these ideas by
explanations which have no basis in experiment."
But the irresistible force of facts was gradually
increasing, and after the discovery of the gas oxygen by
Priestley and by Scheele, in the year 1774, Lavoisier was
able to put forward a new interpretation of the process of
combustion of substances in air; and with that interpre-
tation, modern chemistry was born.
Air is, essentially, a mixture (not a compound), of the
two invisible gases, oxygen and nitrogen.* The former of
1 Air contains also, quite norraally, small quantities of carbon dioxide
(carbonic acid gas) and water rapour, both of which play an important part
c
i8 CHEMISTRY IN THE SERVICE OF MAN
these, constituting about one-fifth of the air by volume, not
only allows combustion to take place, but promotes it to such
an extent that a glowing splint of wood, when immersed
in the gas, bursts into flame, and the substance phosphorus
burns with dazzling brilliancy. Oxygen is very " active,"
and combines with practically every other element, the
process of combination being known as oxidation. Nitro-
gen is, however, an inert gas, and even the most brightly
burning phosphorus is extinguished when introduced into
it The explanation of combustion is thus not far to seek,
and is to be found, as Lavoisier proved by the actual
weighing of the substances, in the chemical combination of
the burning substance with the oxygen of the air.^ The
process of combustion, in other words, is a chemical re-
action, a process of oxidation of the combustible substance
by the oxygen of the air, which is accompanied by the
emission of heat and light ; but a flame is formed only
when the burning substance is a gas at the temperature
of the combustion. The nitrogen of the air takes no
part in the process, but acts merely as a diluent which
moderates the vigour of the combustion.
But if combustion in air is a chemical reaction between
in the economy of nature ; as well also as the rare gases argon, helium, neon,
krypton, and xenon.
' It may, perhaps, also be remarked in passing, that it was Lavoisier, who,
owing to the constant use which he made of the balance and the importance
which he attached to its indications, established the fundamental law of
miaterial science, the law of the conservation of matter, which states that in no
chemical action is matter either created or destroyed ; the sum of the masses of
the reacting substances is equal to the sum of the masses of the products
formed. The matter can be changed in form ; it cannot be altered in quantity.
All later experimental investigation, even the most recent, carried out with all
the care and refinement of accuracy of which the modern balance is capable,
has served only to confirm this law discovered by Lavoisier.
COMBUSTION AND PRODUCTION OF FIRE 19
the combustible substance and the oxygen of the air, why
does the former not take fire when exposed to the air ?
We may allow the coal gas to escape from the burner, or
a candle or piece of wood or coal may be left exposed lo
the air, or even to pure oxygen, without any apparent
change taking place ; and in order that they shall exhibit
the phenomenon of combustion, that is, in order that they
shall undergo the process of oxidation, or combination with
oxygen, with production of heat and light, it is necessary to
heat the materials up to a certain temperature, called the
ignition point of the substance. Combustion then goes on
of itself. The explanation of this fact is that the velocity
or vigour of every chemical change is increased by eleva-
tion of the temperature. At the ordinary temperature, the
oxidation of the candle or the coal takes place so slowly
that no change is apparent even over long periods of time.
If, however, the temperature of the combustible material is
raised, the rate at which it reacts with the oxygen of the
air rapidly increases, and consequently the production of
heat which accompanies the reaction also rapidly increases,
until, at a certain point, the ignition point, the reaction
takes place with such rapidity that the heat which is pro-
duced by the process of oxidation is sufficient to raise
the substances to incandescence and also to maintain the
burning substance at a temperature above the ignition
point. The process of combustion is thus enabled to
proceed continuously.
on the other hand, if the burning substance is cooled
sufficiently, the temperature is lowered to below the igni-
tion point, and so the combustion ceases. A simple
experiment which can be carried out by any one will
20 CHEMISTRY IN THE SERVICE OF MAN
serve to demonstrate this important truth. If we hold a
piece of metal wire gauze at a distance of half an inch or
an inch above a burner from which coal gas is issuing, and
if we then apply a light to the gas above tJte gauze, we shall
find that the flame of burning gas is arrested by the gauze
and does not pass through to the burner (Fig. i) ; for the
wire gauze conducts the heat of the flame away so rapidly
that the temperature is lowered to below the ignition point
of the gas. only after tlie gauze has become quite hot
does the gas below the gauze become ignited. Similarly,
Fig. I.
if the gauze is brought down on a flame of burning gas,
the flame is extinguished at the gauze. The gas itself,
however, passes through, as can be shown by bringing a
light to the upper surface of the gauze, when the gas will
take fire.
The cooling power of wire gauze received, early last
century, an application of the highest importance in the
miner's safety lamp invented by Sir Humphry Davy.
This lamp has undergone a striking change and marked
improvement since the time of its first invention, and the
modern safety lamp (Fig. 2) shows little sign of the means
whereby safety is secured. But on careful examination it
is seen that all the holes through which air can pass to the
COMBUSTION AND PRODUCTION OF FIRE 21
fiame, or the hot air and products of combustion can pass
out, are protected by fine wire gauze. Although, therefore,
the combustible gas, the " fire-damp," can pass through this
gauze and can burn inside the lamp, the flame cannot pass
through the gauze and be communicated to the explosive
mixture of fire-damp and air in the mine.
Warning of the presence of the dangerous fire-damp is
given to the miner through the luminous flame of the lamp
lYirt SMoza.
-Miner's Safety Lamp.
In the old form of lamp, the flame was surrounded by a closed cylinder
of wire gauze which considerably diminished the light emitted by the lamp ;
but in the modern type, a cylinder of glass is inserted, whereby the efficiency
of the lamp is greatly increased.
becoming crowned by a "cap" of pale blue flame. The
greater the amount of fire-damp the larger is the cap.
The process of combination with oxygen which, as we
have seen, is the essential feature of the combustion process
in air, may, however, go on appreciably even at tempera-
tures below the ignition point. Thus, when metallic iron
is exposed to moist air, it rusts. This rust is oxide of iron,
a compound of iron and oxygen ; and the process of
rusting is therefore a process of oxidation, a process of
22 CHEMISTRY IN THE SERVICE OF MAN
combustion, against which it is necessary to protect, by
paint or other means, all iron structures exposed to the
air, if we would have them last. This slow combustion, as
it is termed, can be demonstrated more strikingly with the
metal aluminium, which has a greater affinity for oxygen
than iron has. When finely divided aluminium is heated
in the air, as, for example, when aluminium powder is
blown through a flame, it burns with a very bright light ;
but when exposed to the air at the ordinary temperature,
the metal remains apparently unchanged. As a matter of
fact it rapidly combines with the oxygen of the air, but the
coherent film of oxide which is formed on the surface, pro-
tects the metal from further attack, and therefore no change
is apparent. But let us now coat the surface of the metal
with mercury. By this means a liquid amalgam or alloy of
mercury and aluminium is produced, and the formation of
a coherent film of aluminium oxide is thereby prevented.
The aluminium is consequently no longer protected from
the continued action of the oxygen of the air. In this case
we observe that the aluminium undergoes oxidation quite
rapidly, the oxide forming a moss-like growth on the sur-
face of the metal. The heat which is produced by the
oxidation, although quite marked, is dissipated so quickly
that the temperature does not rise to the point of incan-
descence, and so no light is seen.
Processes of slow combustion, or combustion unaccom-
panied by the emission of light, are going on continually
within our bodies, and are the source of the heat by means
of which the temperature of the body necessary for health,
is maintained. When air is drawn into the lungs, the
oxygen passes or diffuses through the thin walls of the
COMBUSTION AND PRODUCTION OF FIRE 23
blood vessels, and is absorbed by the blood, whereas carbon
dioxide passes from the blood into the air-spaces of the
lungs and is expelled in the expired air. The oxygen is
carried by the blood to all parts of the body, and oxidises
or burns the tissues and assimilated food materials with
production of carbon dioxide and water, the former being
then conveyed by the blood back to the lungs and so
got rid of.
The presence of carbon dioxide in expired air is readily
shown by blowing through a tube into clear lime water
(a solution of slaked lime in water). The liquid very
speedily becomes turbid owing to the separation of
insoluble carbonate of lime, formed by the combination
of carbon dioxide with the slaked lime. The production
of a turbidity with lime water is used as a test for, or
method of, detecting the presence of carbon dioxide.
In the processes of putrefaction and decay, also, we
have examples of slow combustion, in which animal and
vegetable material is oxidised by the oxygen of the air,
with the co-operation of various micro-organisms ; and
efficient aeration, as in a rushing and tumbling stream, is
an excellent means of purifying water from all kinds of
organic and bacterial contamination.
Under favourable conditions, the process of slow com-
bustion may pass into rapid combustion with production of
light. For, if the heat which is produced by the com-
bination of the oxygen with the combustible material is
prevented from being dissipated, the temperature will go
on rising gradually, and as the temperature rises, the
vigour of the combustion increases. More and more heat,
therefore, is produced in a given time, the temperature
24 CHEMISTRY IN THE SERVICE OF MAN
rises more and more rapidly until, finally, it reaches the
point at which light is emitted. The slow combustion
passes into rapid combustion, and the combustible material
takes fire without the application of external heat ; in
other words, it undergoes spontaneous combustion. In this
way arise, for example, the so-called " gob " fires, in spaces
from which coal has been removed, and where coal-dust
and fine coal remain behind ; so also may fire break
out in coal bunkers and in other confined spaces in
which combustible matter, like oily cotton waste, is
stored without proper ventilation. Such spontaneous
combustion will, of course, take place with special readi-
ness in the case of readily inflammable substances, or
substances which have a low ignition point, such as
phosphorus. Thus if this substance is dissolved in the
liquid known as carbon disulphide, and if the solution is
then poured on a sheet of filtering paper, or thin blotting-
paper, the carbon disulphide soon evaporates and leaves
the phosphorus on the paper in a finely divided state. The
oxygen of the air rapidly unites with the phosphorus, and
the heat which is thereby developed soon raises the
temperature to the ignition point of the phosphorus, and
rapid combustion sets in.
Although the most familiar examples of combustion
are those which take place in air, the term combustion
must not be restricted only to such cases. Combustion,
in its widest meaning, is a process of chemical action in
which so much heat is generated that the burning substance
becomes incandescent and emits light ; and such a process
may occur even when no air or oxygen is present. Thus,
for example, the gas hydrogen will bum not only in air,
COMBUSTION AND PRODUCTION OF FIRE 25
with production of the substance water, but it will also
burn in the gas chlorine with formation of the compound
known as hydrogen chloride or hydrochloric acid gas. And
similarly, other cases of combustion are known which do
not depend on the presence of oxygen, and are not
processes of oxidation.
Even when the combustion is due to the combination
of the combustible material with oxygen, to a process of
oxidation as we have called it, the oxygen need not be
present in the gaseous form, but may be yielded up by some
compound containing it. Various well-known substances,
such as chlorate of potash and saltpetre (potassium
nitrate), can act as suppliers of oxygen in this way, and
the use of such substances for promoting combustion has
long been known. Touchpaper^ for example, the slowly
burning paper which is so familiar in connection with fire-
works, is prepared by soaking paper in a solution of salt-
petre, and allowing it to dry. The saltpetre is in this way
deposited in the fibres of the paper, and renders the latter
more readily combustible. Such paper does not require
the presence of gaseous oxygen for its combustion, but
will burn in an atmosphere of nitrogen or other inert gas.
In the case of gunpowder, also, which we shall discuss at
a later point (p. 70), saltpetre is similarly made use of as
a reservoir of oxygen.
In recent years, the process of combustion by means
of combined oxygen has been turned to very good account
for the purpose of obtaining economically and with ease,
the metals chromium, manganese and titanium, which
could formerly be obtained only with considerable difficulty.
The metal aluminium, we have seen, has a great affinity
26 CHEMISTRY IN THE SERVICE OF MAN
for oxygen, and it combines with great vigour not only with
gaseous oxygen but also with the oxygen contained in
compounds. If, then, we mix the oxide of chromium with
aluminium powder, and strongly heat the mass at one
point by means of a special ignition mixture, the aluminium
combines with the oxygen of the chromium oxide, and so
much heat is thereby generated that the combustion rapidly
spreads throughout the whole mass. Oxide of aluminium
is formed, and the metallic chromium, which is set free, is
fused and collects at the bottom of the vessel. In this way
large quantities of chromium are now produced for use,
more especially, in the manufacture of a " stainless steel "
which does not tarnish in contact with food or acids ; and
also of a very hard steel known as chrome steel. By the
introduction of this process, known as the Goldschmidt pro-
cess, chromium, which twenty years ago cost as much as
;^25 a pound, can now be obtained for I2s. 6d. a pound.
A modification of the above process has become familiar
in recent years through its application to the welding of
tramway rails, and to the repair, in situ, of broken castings,
shafting, etc., by the so-called thermit process. For this
process, oxide of iron is employed instead of oxide of
chromium, and the molten iron which is produced, and
which has been raised to a temperature of about 5400"* F.,
by the vigour of the reaction, is run into a mould formed
round the ends of the rails or fractured metal. The rails
are thus raised to such a high temperature that they can
be readily welded by pressure, or the fracture is filled with
fresh iron and a solid joint effected
The very high temperature produced by the combustion
has also led to the use of thermit mi.xture in incendiary
COMBUSTION AND PRODUCTION OF FIRE 27
bombs designed to be dropped from airships, the bombs
being furnished with a special mechanism by means of
which the thermit mixture can be ignited automatically.
In order to bring about the various cases of combustion
which we have been discussing, it is necessary, as we have
seen, to raise the temperature to a certain point, the ignition
point. Nowadays this causes no difficulty ; and it may be
regarded as not the least of the services which chemistry
has rendered to man, that it has put it within his power to
obtain fire at will, with a minimum both of trouble and
expense. From the primitive method of rubbing two dried
sticks together to the use of the flint and steel ; and from
the latter to the modern safety match, is indeed an advance
the importance of which for our modem civilisation it
would be difficult to estimate and impossible to over-
estimate.
one of the characteristics of chemical action, as we
have seen it exemplified in the process of combustion, is
the production of heat, but it was not till early in the nine-
teenth century that practical suggestions were made for the
employment of such a means of producing fire. one of the
earliest of these suggestions which had a certain measure of
success was made by a Frenchman named Chancel, who
tipped strips of wood with a mixture of potassium chlorate
and sugar, bound together by means of gum. When this
composition was dipped into concentrated sulphuric acid
(oil of vitriol), the sugar took fire and burned at the ex-
pense of the oxygen contained in the potassium chlorate ;
and this combustion was then communicated to the wood
splint. These matches were sold as late as the middle of
last century. About 1827, John Walker, an Englishman,
28 CHEMISTRY IN THE SERVICE OF MAN
patented a match the tip of which consisted of a mixture
of potassium chlorate and sulphide of antimony, and this
mixture could be ignited by being drawn between folds of
glass paper. These matches, known as lucifers, were the
first friction matches used.
But there is a substance the use of which for matches is
at once suggested both by its name and by its properties,
the readily inflammable substance phosphorus, which was
discovered as long ago as 1669, and is prepared at the
present day from calcium phosphate. From the readiness
with which this substance ignites, it was only natural that
attempts should be made to utilise it as a convenient fire-
producer. Such attempts were at last successful, and
phosphorus-tipped matches, known as Congreves, were in
almost universal use until a comparatively recent time.
The tips of these matches consisted, essentially, of a
mixture of phosphorus and some substance rich in oxygen,
such as potassium chlorate, or red lead (oxide of lead),
bound together with gum or glue, and coloured with
various pigments. We can all recollect these matches,
which had such a fascination for us in our younger days
through the glow of phosphorescent light which they
emitted when slightly warmed by rubbing on the hand.
As fire-producers these matches were a great advance on
those which had gone before. But for every advance a
certain price has to be paid, and for the phosphorus match
mankind has found the price too heavy. The accidental
fires due to the ready inflammability of the phosphorus, and
the general danger of its unrestricted use ; the number of
deaths, accidental or intentional, produced by phosphorus
poisoning ; and the terrible disease, known its " phossy
COMBUSTION AND PRODUCTION OF FIRE 29
jaw," or necrosis of the jaw-bone, which attacked the
workers in the match factories, led to a ban being placed
on what had been hailed as a boon ; and the use of
ordinary white or yellow phosphorus ^ has, in most civilised
countries, been forbidden by law.
But the element phosphorus occurs not only in the
readily inflammable and poisonous white variety, but also
in a totally distinct form, that of a dark red powder which
is much less readily inflammable and is non-poisonous.
It is produced by heating ordinary phosphorus in closed
vessels to a temperature of about 480" F. Attempts were
therefore made to utilise this form of phosphorus, and the
difficulties which were at first encountered, were ultimately
overcome by a German chemist about the middle of last
century ; and his invention, first taken up in Sweden, led
to the introduction of the so-called Swedish or safety
match. In these matches the red phosphorus is not
incorporated in the match head, but is used in the com-
position with which the rubbing surface is coated. The
match tip consists of a mixture of sulphide of antimony
and an oxidising substance such as potassium chlorate,
red lead, or potassium bichromate ; and sulphur and char-
coal are sometimes added. This mixture will not take
fire when rubbed on a rough surface, but only when rubbed
on the specially prepared surface coated with a paste of
red phosphorus mixed, sometimes, with sulphide of anti-
mony and powdered glass. Moreover, in order to diminish
the risk of accidental fire through the glowing wood of a
' Pure phosphorus is a white, translucent, wax-like substance which can be
cut with a knife. When exposed to sunlight it becomes yellow or even red io
colour owing to its conversion into the so-called red phosphorus.
30 CHEMISTRY IN THE SERVICE OF MAN
used match, safety matches are soaked in a solution of
alum, sodium phosphate, ammonium phosphate, or some
other salt. The charred wood of the match is thereby
strengthened, and the match ceases to glow almost imme-
diately after being blown out.
When the use of white phosphorus was forbidden, the
attention of chemists was directed to the discovery of other
materials which might be used instead, and a non-poisonous
match was produced which possessed the advantage of the
old phosphorus match, of striking on any rough surface.
In the case of this "strike anywhere" match, the tipping
composition consists of a mixture of sulphide of phosphorus
and potassium chlorate, or other oxidising material, bound
together with glue, and powdered glass is also sometimes
added to increase the friction and so facilitate the inflam-
mation of the match head.
To render the wood of the match more readily inflam-
mable and so allow of the combustion passing on from
the tip to the wood, the latter is impregnated with paraffin
wax, although, sometimes, as in the case of some Con-
tinental matches, sulphur is employed instead.
In the case of vesuvians, the match head consists of
a mixture of 'powdered charcoal and nitre, to which some
scenting material, such as gum benzoin or sandal wood,
is added. This head is then tipped with a striking mixture
such as has already been described.
The making of matches, once a " dangerous occupa-
tion," has now passed from the handworker to the machine,
which not only cuts the blocks of wood into splints of
proper size and shape, but tips them with the inflammable
mixture and packs them into boxes, which it also makes
COMBUSTION AND PRODUCTION OF FIRE 31
and labels. A single machine can thus turn out over
5,000,000 matches in a day. only by such means could the
almost incredible number of matches be produced which are
turned out annually by the match factories of the world.
The firm of Bryant and May, the largest British manu-
facturers, can alone produce, in the course of a year, as
many as 90,000,000,000 matches, not to mention wax
vestas and tapers, and it has been estimated that the
annual consumption of matches in Great Britain amounts
to about nine matches per head of population per day.
Although the ordinary match forms by far the most
usual means of obtaining fire and light, one must not fail
to mention the recently introduced briqiiets, or " cigar
lighters." When an alloy of iron and the metal cerium
is rubbed against a piece of steel, small particles of the
alloy are rubbed off and take fire in the air. If the
sparks so produced are allowed to come into contact with
a piece of tinder or with the vapour of petrol, or similar
volatile liquid, the latter takes fire and we thus obtain a
flame. In this apparatus we have, in a refined form, the
old flint and steel of our fathers.
Ceria, or oxide of cerium, is now produced in large
quantity as a by-product of the manufacture of incandescent
gas mantles {p. 53), and is derived mainly from monazite
sand, valuable deposits of which are found in Brazil and
also in Travancore, India. It was while investigating how
the accumulations of ceria might be utilised that Auer
von Welsbach discovered, early in the present century, the
peculiar property of the iron-cerium alloy which led to the
above application.
CHAPTER III
THE CHEMISTRY OF ILLUMINANTS
At the present time when, by the mere touch of the
finger on a button, we can instantly obtain a flood of
brilliant light, it is difficult to realise what must have been
the conditions of life when man had to be content with
the smoky flame of the pine torch or of the rush dipped in
olive oil which burned with but a feeble light even in its
vase of finest workmanship. Think also of the old gutter-
ing candle, with its constant need of "snuffing," and you
will understand how great has been the advance in the
direction of artificial illumination ; and practically the
whole of this advance has taken place since the beginning
of the nineteenth century.
The production of light depends in all cases, with
the exception of electric light, on the process of com-
bustion in air, and it is therefore only what one would
expect, that man first made use of those naturally occurring
substances and materials which can be burned without
requiring previous special treatment. Thus, the vegetable
oils, such as olive oil and rape-seed oil, furnished, from a
very early period, the main light-giving material ; and at
a later date, the need of a vessel to contain the oil was
done away with by using the solid animal fats, in the
form of candles.
THE CHEMISTRY OF ILLUMINANTS 33
For the earliest candles a solid animal fat was em-
ployed, such as ox-fat or tallow, and the candle was
made by repeatedly dipping the wick, which was first made
from the pith of the rush and later of cotton fibres, into
the melted tallow. From the manner in which they were
made, these candles were called dips.
But early in the nineteenth century, the advance of
chemical knowledge enabled man to improve upon nature ;
the natural was superseded by the artificial, and the task
of the careful housewife, who used to save the superfluous
kitchen lard for the purpose of candle making, became
the business of the manufacturer. This development of
the modern candle- making industry we owe to the eluci-
dation by a French chemist, Chevreul, of the chemical
nature of fats and oils.
The animal and vegetable fats and oils, so different
in outward appearance, are all of the same chemical
nature ; all are compounds of the familiar substance glyce-
rine (CsHgOs), with various acids, such as palmitic acid
(C16H32O2), stearic acid (CigHggOa), and oleic acid
{CigH3402). The first two acids are solids and give rise
to solid fats ; but oleic acid is a liquid, and the glycerine
compound derived from it is also a liquid, and the main
constituent of olive oil. When, therefore, animal fat or
tallow was used in making the old-fashioned dip, the soft
material, the glycerine compound of oleic acid, present
in varying amounts in the different fats, ran from the
burning candle and so caused a wasteful guttering ; while
the glycerine present in the fat also gave rise, on burning,
to an unpleasantly smelling product.
In the making of the modern candle, the fat or tallow is
D
34 CHEMISTRY IN THE SERVICE OF MAN
first boiled with acidified water in order to separate the
fibrous matter from the fat, and the latter is then subjected
to the action of superheated steam in presence of a little
slaked lime, whereby the fat is decomposed into glycerine
and the acids with which it was combined — stearic, palmitic
and oleic acids. After purification, the mixture of acids is
distilled, and the solid acids separated from the liquid oleic
acid by pressing. The solid thus obtained consists mainly
of stearic acid or stearin, and forms, generally with the
addition of a small quantity of paraffin wax, the material of
the ordinary stearin candle of the present day. This
candle has the advantage over the old tallow dip, in being
harder and cleaner to handle, in having a better appearance
— white and opaque — in showing no tendency to bend or
to gutter, and in burning with a bright and smokeless
flame.
The paraffin wax, to which we have just referred, is
itself also largely used for making candles. It is a white
material which was formerly chiefly obtained by heating in
retorts, or distilling, the oil shale found in the Lothians,
Scotland. It is now also produced in large quantities
in Germany by distilling brown coal or lignite, and is
obtained from American and Galician petroleum. It
consists of a mixture of compounds which contain only
hydrogen and carbon, and are therefore called hydrocarbons ;
it thus belongs to an entirely different class of compounds
from the fats or the fatty acids, all of which contain
oxygen. Before being employed for the making of
candles, the crude paraffin is subjected to a refining process
for the purpose of obtaining a wax of higher melting point
and free from coloured impurities. The material so
J
THE CHEMISTRY OF ILLUMINANTS 35
obtained is valued for its slightly translucent appearance,
but it has the disadvantage, as compared with stearic acid
or stearin, that when exposed to a warm atmosphere, it is
h'able to bend under its own weight.
The wax candles formerly so highly prized, were made
of beeswax, a substance related in its composition to the
fats and oils, and consisting mainly of a compound of
palmitic acid with an alcohol known as melissyl alcohol.
Lastly, spermaceti, a similar compound obtained from the
oil of the sperm whale {physeter -macrocephalus), is another
excellent but expensive material used in the manufacture
of candles. Candles made of this material have long
been used as a standard measure of artificial light, on
account of the large and regular flame with which they
bum.
Although the materials of which candles are made are,
of course, combustible, it should be remembered that they
do not burn unless the temperature is raised to a point
sufficiently high to cause them to pass into vapour ; and it
is the vapour which burns and so gives rise to the flame.
When a match is applied to the wick of a candle, the small
amount of stearin or paraffin which remains in the wick
from previous use, is vaporised and ignited, and a bright
flame is at once produced. But as the amount of combus-
tible material in the wick is very small, the flame quickly
subsides, and it increases again to its normal size only when
the heat of the flame has melted a quantity of the solid
candle. This liquid then rises up the wick by what is
known as capillary action — just as one can mop up water
with a piece of blotting paper — and is then vaporised and
ignited by the heat of the flame. Moreover, the upward
36 CHEMISTRY IN THE SERVICE OF MAN
current of air produced by the flame, cools the surface of
the candle so that the upper edge remains solid and so
forms a cup in which the liquid produced by the heat of
the flame, collects. If the candle is placed in a draught, or
if for any other reason the flame does not burn symmetri-
cally, the rim of the cup gets melted away, and the candle
" gutters." This is the reason why the ornamental candles
with fluted or otherwise moulded surface, however
beautiful, while unburnt, they may appear to the eye, do
not fulfil the proper function of a candle so well as the
plain and unadorned variety.
In the old tallow candles, the wick required to be
snuffed from time to time ; that is, the unburnt end of the
wick had to be removed with a pair of special scissors.
The reason for this is as follows. Immediately surrounding
the wick of the candle there is the unburnt vapour of the
candle material, and this vapour cuts the wick off" from
contact with the atmospheric oxygen. Consequently,
although the wick becomes charred by the heat of the flame,
it is not consumed, because the oxygen of the air is not
allowed access to it. The charred wick, therefore, con-
tinues to increase in length and there is conducted up into
the flame more of the liquid fuel than can properly be
consumed. The flame then burns dim and emits a large
amount of smoke. one can readily understand how all the
trouble and inconvenience of the constant snuffing could
lead a Goethe to declare, in words which may be rendered
thus —
There could be no greater discovery made,
Than of candles to burn without snuffers' aid.
And this discovery was made by the Frenchman <^
'i
THE CHEMISTRY OF ILLUMINANTS 37
Cambac^res in 1825, the necessity for snuffing being
obviated by the use of twisted or flat plaited wicks. As
the candle burns, the end of the wick, as everyone may see
by looking at a burning candle, curls or bends outwards to
the edge of the flame, and coming, in this way, into con-
tact with the oxygen of the air, it burns away, and so no
snuffing is required. But if the best results are to be
obtained, the manufacturer must pay great attention
to the proper selection of the wick as regards its size and
texture in relation to the material of the candle ; and care
also must be given to the proper treatment or " pickling "
of the wick with saltpetre or other chemicals, in order
to prevent smoking and the formation of an ash.
In its fight with other illuminants, the candle dies hard ;
indeed, it does not die at all, for the consumption of
candles goes on increasing. Convenience in use, especially
in mines ; poetic sentiment and an age-long tradition which
have made the candle the type of all light-bearers ; as well
also as aesthetic and economic considerations, all conspire
in favour of the candle. In Great Britain alone, between
40,000 and 50,000 tons of candles are consumed annually,
by far the greatest proportion of these being paraffin candles.
In the southern districts of Scotland there occur deposits
of shale which, when heated in retorts out of contact with
the air, yields the white paraffin wax to which we have
already referred. But besides this, large quantities of
h'quid oil are also produced which, in the early days of the
industry, was a by-product of comparatively little value.
But the oil was bought, bought indeed at a low price, and
shipped to Germany; and when its use there was investigated,
38 CHEMISTRY IN THE SERVICE OF MAN
it was found that a special lamp had been invented in
which the oil was used as an illuminant. So commenced
the use of mineral oil for the production of light. Soon,
however, this Scottish industry was seriously threatened
by the discovery and exploitation of oil deposits in
America, Russia and other parts of the world; but it
fought for its life, fought with the only weapons which were
of any avail, the weapons of science, and it prevailed.
And we have in Scotland, in the life of the oil shale
industry, a striking testimony to the power of science in its
practical applications.
When one stirs the mud of decaying vegetation at the
bottom of a stagnant pool, bubbles of a gas rise up, and
on holding a light near the surface of the water the gas
takes fire. This inflammable gas, from its occurrence in
marshy districts, has long been known as marsh gas. It
is this gas, also, which, escaping from the coal beds
during mining, mixes witli the air of the colliery and
constitutes the explosive mixture fire-damp. Marsh gas,
or methane as it is called in chemistry, is also the main
constituent of the combustible gas which escapes from the
earth in various oil-bearing regions in America, and in the
region of Baku on the Caspian Sea, where the Holy Fire
of the burning gas was for long a place of pilgrimage of
the Persian Guebers, or fire-worshippers. To-day all this
is changed. "The worship of the Eternal Fire in the
Surakhani temple is dead ; the priest has left behind no
followers ; but the oil that dimly lit a shrine now illumi-
nates an empire, and bids, ere long, to give light and
heat to an entire hemisphere." ^
» Matvin, •• The Region of the Eternal Fire." 1884,
THE CHEMISTRY OF ILLUMINANTS 39
Methane, or marsh gas, is the lowest member of a
long series of hydrocarbons (the name given to compounds
composed entirely of hydrogen and carbon), all of which
have similar chemical properties and composition. The
molecule of methane consists of one atom of carbon to
which four atoms of hydrogen are united ; and since an
atom of carbon is never found to combine with more than
four atoms of hydrogen, the carbon is said to be saturated,
and methane is spoken of as a saturated hydrocarbon.
Diagrammatically, we can represent the molecule of
methane thus :
H
H— C— H
I
H
But the element carbon is remarkable among all the
elements in its property of combining also with other atoms
of carbon, and so forming " chains " of carbon atoms, so
that a series of compounds is obtained which may be
represented by the diagrams :
H H H H H
II III
H— C— C— H ; H— C-C— C— H ; etc
II III
H H H H H
C,H, (Ethane). C,H, (Propane).
A large number of such compounds are known, and
it will be observed that we can represent the composition
of each of them by the formula Q^^^n + 2.
It may also be mentioned here that other hydrocarbons
are known which contain a lower proportion of hydrogen,
40 CHEMISTRY IN THE SERVICE OF MAN
aiid are therefore said to be unsaturated. Thus, if we
take away two hydrogen atoms from each of the com-
pounds of the methane series, we obtain hydrocarbons
which we can represent by the formulae :
H H
n. /H H. I I
>C=C<: ; >C=C— C~H; etc.
H/ \H IV I
H
CjH^ (Ethylene). C,TI, (Propylene).
These constitute another series of hydrocarbons, known
by the name of the first member ethylene. As we shall
see, this gas plays an important part in coal gas.
Hydrocarbons are also known which contain a still
lower proportion of hydrogen, or higher proportion of
carbon, for example acetylene, C2HJ or HC^CH, the
first of a series having the general formula C^Hj^ _ 2-
American petroleum consists mainly of a number of
hydrocarbons belonging to the methane series, from CH4
up to C30 He2 ; but the petroleum obtained in Southern
Russia contains also a number of hydrocarbons belonging
to a different series with a lower proportion of hydrogen,
and more akin to the substance benzene. These naturally
occurring mineral oils, then, formed by the gradual de-
composition of marine animal and vegetable matter under
the age-long action of heat and pressure, are not single
substances but mixtures of a large number of different
compounds, the lowest members of which are gases which
escape from the earth as " natural gas." As the proportion
of carbon in the compounds increases, the hydrocarbons
become less and less volatile, and boil, therefore, at higher
and higher temperatures ; and when the number of carbon
THE CHEMISTRY OF ILLUMINANTS 41
atoms in the molecule is greater than sixteen, the com-
pounds are solid at the ordinary temperature.
When the crude petroleum is distilled (Fig. 3), the lower
and more volatile hydrocarbons pass over first ; and by
collecting the liquid which distils over at different tem-
peratures, a series of " fractions," as they are called, is
obtained. The liquid which distils over between the
temperatures of 120** and 140" F., is called petroleum ether,
and is largely used as a solvent ; the fraction distilling
over between 160* and 190" F., is called gasoline or petrol.
Fig. 3. — Apparatus used fob Distilling Liquids.
A, a vessel in which the liquid is boiled and so converted into vapour
which passes through the long neck, B, to a spiral " worm," or condenser, C,
kept cold by means of flowing water. The condensed vapour issues at D and
can be collected. E, tube through which cold water enters ; F, exit for warm
condenser water ; T, thermometer to indicate the temperature of the vapour.
and finds extensive use in the engines of motor cars, and
also for illuminating purposes (petrol-air gas) ; while the
fraction distilling between 250° and 300° F. is called
benzine (not benzene) or benzoline, and is used as a " dry
cleaning " agent, for the removal of oil and grease stains
from leather, cloth, etc.
As the temperature of distillation rises, the hydro-
carbons of higher boiling-point distil over. The fraction
distilling between 300** and 570** F., constitutes burning oil
42 CHEMISTRY IN THE SERVICE OF MAN
or kerosene, while from the higher fractions one obtains
lubricating oils, vaseline, and in some cases, solid paraffin,
which is used for making candles, waterproofing paper,
and other purposes.
Since paraffin oil, or kerosene, contains a relatively
large proportion of carbon, it burns with a smoky flame,
owing to incomplete combustion, unless there is a liberal
supply of air. When this oil is used as an illuminant,
therefore, the flame is surrounded by a chimney whereby
a draught of air is created and oxygen thus brought in
larger amount to the flame ; and in the case of lamps
with a circular wick, a tube must also be provided through
which air can pass to the inner surface of the flame.
In the early days after the introduction of mineral oil
as an illuminant, explosions and fires were not infrequent,
and these led to the introduction of special legislation to
regulate the use of such oil. The accidents which occurred
were due mainly to the insufficient removal of the more
volatile constituents of the petroleum, and these, mixing
with the air in the oil reservoir of the lamp, formed an
explosive mixture which became ignited by the flame.
To obviate such risks, it has been enacted that only such
oil shall be used as does not give off an inflammable
vapour below a certain temperature. This is tested by
heating the oil in a special apparatus under specified con-
ditions, and determining the temperature at which, on
passing a light over the mouth of the vessel containing
the oil, a flash of flame is seen. This is known as the
flash-point of the oil, and in Great Britain it has been
enacted that the flash-point must not be below 73° F.,
when determined by what is known as the "closed" test
THE CHEMISTRY OF ILLUMINANTS 43
By far the most important illuminant at the present
day is the gas obtained by heating coal in a closed vessel
or "retort," out of contact with the air. That a com-
bustible gas can be produced in this way has long
been known, but it is to a Scotsman, William Murdoch,
that belongs the credit of having developed the process
for the production of an illuminating gas for general
use.* That was towards the end of the eighteenth century,
but it was only after the lapse of ten or twelve years
that the gas began to be publicly and generally used.
The great change which was thereby effected in the
appearance of the towns and in the comfort of the people,
is described by a writer in the early nineteenth century:
"We all remember the dismal appearance of our most
public streets previous to the year 18 10; before that time,
the light afforded by the street lamps hardly enabled the
passenger to distinguish a watchman from a thief, or the
pavement from the gutter. The case is now different,
for the gas-lamps afford a light little inferior to daylight
and the streets are consequently divested of many terrors
and disagreeables, formerly borne with because they were
inevitable."
When we recall what street illumination was like in
our own times, before the introduction of the incandescent
mantle and electric light, the fact that the writer just
quoted could regard the light afforded by the gas-lamps
of the early nineteenth century as being little inferior to
daylight, must certainly convince us that " the appear-
ance of our most public streets previous to the year 1810"
* William Murdoch was associated with the engineering firm of Messrs.
Boulton and Watt, Birmingham, and it was in their works at Sobo that coal
gas was first used (in 179S) on a large scale as an illuminant.
44 CHEMISTRY IN THE SERVICE OF MAN
must have been very dismal indeed. And yet the cry is
for light and still more light
Coal is not a definite chemical substance, but a complex
mixture of substances, the nature of which is not yet
definitely known. The essential elementary constituents of
coal are carbon, hydrogen, and oxygen, but the elements
nitrogen and sulphur also occur in small amounts ; and
when coal is heated in closed retorts, or " distilled " as one
says, there is obtained not only the gas which is used for
illuminating purposes, but also considerable quantities of
ammonia and of tar, and there remains in the retort a
residue of coke. Half a century ago, the ammonia and the
tar were regarded as by-products of little value, but, as we
shall learn more fully later, they have more recently
acquired an importance but little inferior to the illuminating
gas itself;^ while, owing to the great developments of the
iron and steel industry, the demand for coke has, in recent
times, become so great, that many millions of tons of coal
are now distilled annually for the production, primarily, not
of gas but of coke.
Although the nature of the products as well as their
relative amounts depend on the kind of coal distilled and
on the temperature at which the process is carried out, we
may say that, under the general conditions met with in
gas works, the main products obtained and their relative
amounts are as follows : —
Approximate quantity formed
from I ton of coal.
1. Illuminating gas 1 1 ,000 cubic feet.
2. Coal tar 120 lbs.
3. Ammonium sulphate 25 „
4. Coke 1500 „
I In some cases the value of the ammonium sulphate recovered as a by>
prodnct may equal or even exceed the cost of the coal distilled.
THE CHEMISTRY OF ILLUMINANTS 45
In the manufacture of illuminating gas, the coal is
heated in large fire-clay retorts at a temperature of about
1800° F., and the products of decomposition are led away by
a pipe the mouth of which dips under the surface of water
contained in what is known as the hydraulic main (Fig. 4).
Here, part of the water and of the coal tar condense, while
the gaseous products pass away to a series of cooling pipes,
exposed to the air, in which a further condensation of
water vapour and of tar takes place. The ammonia present
in the gas dissolves for the most part in the water
produced, and the remainder is removed by passing the gas
through "scrubbers." The gas still contains a number of
substances the presence of which would be deleterious, the
more important of these being sulphuretted hydrogen and
carbon dioxide. The sulphuretted hydrogen is harmful
because it gives rise, in the burning gas, to sulphur
dioxide (the pungent gas formed when sulphur burns in
air), which exercises a destructive action on plants,
furniture, etc. ; and the presence of carbon dioxide is
objectionable because it lowers the illuminating power
of the gas. To free the gas from these impurities,
therefore, it is passed, first of all, through a series of boxes
containing trays covered with slaked lime which combines
with and so removes the carbon dioxide ; and then through
another series of boxes containing oxide of iron, which
removes the sulphuretted hydrogen, by forming with it the
compound sulphide of iron. When conversion of the oxide
into sulphide is complete, the material is incapable of
removing any more sulphuretted hydrogen, but it can be
revivified by exposure to the air. Through this exposure,
the oxygen of the air reconverts the sulphide of iron into
46 CHEMISTRY IN THE SERVICE OF MAN
THE CHEMISTRY OF ILLUMINANTS 47
oxide of iron, and the sulphur is set free. In this way the
oxide of iron may be used repeatedly, until at length
the accumulation of sulphur renders it inefficient The
material, however, still has its uses, for it is sold to the
manufacturer of sulphuric acid who utilises it in the
manner we shall learn later.
After undergoing the various processes of purification,
the illuminating gas passes to the gasometer, and is then
ready for distribution to the consumers. Although the
composition of the gas supplied by different works is by no
means the same, nor invariable even in the case of the
same works, the following numbers may be taken as
representing an average composition of illuminating gas.
Composition of Coal-Gas
Hydrogen 49 pcr cent, by volume
Methane 35
Unsaturated hydrocarbons (Ethylene, etc.) 4
Carbon monoxide 5
Carbon dioxide * . 0*5
Nitrogen 6
Oxygen O'S
Coal-gas, then, as we see, is a mixture of a number of
gases, and of these carbon dioxide, nitrogen, and oxygen
represent what we may call impurities ; they act merely as
diluents and lower the illuminating power of the gas.
Of the combustible gases present in coal-gas, hydrogen
burns with a non-luminous, scarcely visible flame ; carbon
monoxide, with a non-luminous flame of a bright blue
colour ; ^ and methane, with a flame which has only a slight
illuminating power. Ethylene, however, burns with a
' The lambent blue flame seen on the top of a clear-burning fire, is due to
the combustion of carbon monoxide.
48 CHEMISTRY IN THE SERVICE OF MAN
strongly luminous flame, and it is to this gas, and to the
other unsaturated hydrocarbons present in small amounts,
that the luminosity of a coal-gas flame is mainly due.
Among the unsaturated hydrocarbons present, there may
be mentioned benzene (or benzol, to give it the name by
which it is known in commerce), the vapour of which
burns with a luminous flame and with the production of
a large amount of soot.
What, then, is the explanation of the luminosity of the
flame of burning coal-gas, or of a candle, or petroleum ?
The answer is that which was given long ago by Sir
Humphry Davy : The luminosity depends on the de-
composition of the hydrocarbons with liberation of particles
of carbon which are then raised to incandescence by the
heat of the burning gases. The presence of this finely
divided carbon can, indeed, be readily shown by bringing
a cold object into the luminous part of the flame ; it
becomes coated with soot These carbon particles, how-
ever, do not escape into the air, but on reaching the edge
of the flame where they come into contact with the oxygen
of the air, they are completely burned to the invisible gas
carbon dioxide. And so, on examination, we see in these
flames three zones : an inner non-luminous zone of un-
burnt gas or vapour ; a luminous zone in which the carbon
particles are raised to incandescence ; and a very faint outer
zone surrounding the flame, in which complete combustion
of the carbon particles takes place.
From the explanation which has just been given, it will
readily be understood that the luminosity of a flame will
be increased by increasing the proportion of carbon-yield-
ing substances in the burning gas ; and hydrocarbons, and
THE CHEMISTRY OF ILLUMINANTS 49
more especially unsaturated hydrocarbons, which contain
a relatively large proportion of carbon, will be the most
effective substances to use. By such additions it is possible
to " enrich " a poorly luminous gas, a fact which is made
use of at the present day in many of the larger gas works.
Not only can a combustible gas be manufactured by
the distillation of coal, but when steam is passed over red-
hot coke, a gas is obtained which is a mixture of hydrogen
and carbon monoxide :
C + H2O = CO + H2
Carbon (coke) and water give carbon monoxide and hydrogen, v
Although this gas mixture, known as water gas, has no
illuminating power, it can be manufactured at a small cost,
and after being enriched by the addition of unsaturated
hydrocarbons, obtained by the decomposition or "crack-
ing " of oil at a high temperature, it is added (as carburetted
water gas) to the gas obtained by the distillation of coal.
If the coal-gas, before being burned, is mixed with a
suitable amount of air, the molecules of the combustible
gas find oxygen with which they can combine, ready at
hand, so to say, and combustion takes place rapidly and
completely without the separation of carbon particles ; the
flame is therefore non-luminous, but much hotter than the
ordinary luminous flame. This principle was made use of
by the German chemist Bunsen in the burner which goes
by his name, and is applied in gas fires, gas cookers, etc
(Figs. 5 and 6). In the Bunsen burner, the gas issues
from a jet which is surrounded by a wider tube, near
the foot of which holes are pierced through which air is
drawn into the burner by the uprush of gas. The gas
B
50 CHEMISTRY IN THE SERVICE OF MAN
thereby becomes mixed with air, the amount of which
necessary to ensure complete combustion can be regu-
lated by enlarging or diminishing the size of the air
openings. If too much air is admitted to the gas, the
mixture becomes explosive, and the flame strikes back
to the jet where the gas enters the
burner. If this occurs, the gas must
be at once turned out, as incomplete
combustion takes place and products
of a very poisonous character are
formed. These, fortunately, betray
their presence by a powerful and
unpleasant odour.
If, instead of supplying the lumi-
nous coal-gas flame with air, we
Fig. 5.— Bunskn Burner.
A, air-hole by which air
can pass into the tube and
mix with the gas which
enters at the small jet seen
through the opening. The
supply of air can be regu-
lated by means of the
movable ring R.
Oi»
Fig. 6. — Gas Cooker, constructed
on the principle of the bunsen
Burner.
supply it with oxygen, a still better result, that is, a
greater production of heat, and therefore a higher tempera-
ture, can be obtained ; for the nitrogen of the air acts
merely as a diluent and so cools down the flame. We
cannot, however, in this case make use of the ordinary
burner, for the mixture of oxygen and coal-gas would be
explosive, and the flame would at once " strike back." A
burner of special construction is therefore employed which
allows of a jet of oxygen being blown into the geis as it
burns at the mouth of the burner, and we thus obtain what
THE CHEMISTRY OF ILLUMINANTS $1
is known as the oxy-coal-gas blowpipe flame (Fig. 7). If
this flame is allowed to impinge on a highly refractory
material like quicklime, the latter is raised to a brilliant
incandescence, producing the well-known lime-light (Now-
adays, the oxide of the rare metal zirconium is largely
used in place of lime.)
The high tempera-
ture produced by
means of the oxy-coal-
gas flame ^ has recently
found an interesting
and important applica-
tion in the manufacture
of artificial gems, such
as rubies and sapphires.
These gems consist Air
.' 11 r -J r Fig. 7. — Blowpipb.
essentially of oxide of . , . ,
When the gas is burning at the mouth of
aluminium (alumina), the wider tube, air or oxygen is blown into the
, , . , flame through the inner tube.
a substance which oc-
curs naturally as corundum, and, in an impure state, as
emery. It is a very refractory substance, but it can be
melted in the oxy-coal-gas blowpipe flame. When a
mixture of 975 per cent, of alumina and 25 per cent, of
oxide of chromium is heated in the blowpipe flame, it is
fused, and, on cooling, solidifies in the crystalline form of
the ruby. It ts a ruby, identical in physical and chemical
properties with the natural gem ; and it differs from the
latter solely in minute irregularities of internal structure
detectable only by the eye of the expert. In the manner
' If hydrogen is used in place of coal-gas, a still higher temperature, up to
about 3600° F., can be obtained.
52 CHEMISTRY IN THE SERVICE OF MAN
described, artificial rubies weighing as much as eighty
carats, or over half an ounce avoirdupois, have been
obtained ; and they can be purchased uncut at about 8d.
per carat, and at 5j. per carat cut as a gem. These artificial
rubies, on account of their great hardness, are now manu-
factured in large quantities for use in the bearings of
watches and for other purposes.
Sapphires can be obtained in a similar manner by fusing
a mixture consisting of alumina and small quantities of the
oxides of titanium and iron.
For a number of years the position of coal-gas as an
illuminant has been persistently assailed by electricity ; and
it is very doubtful if the industry could have maintained
itself but for the invention of the now familiar incandescent
mantle.
It is a proverbial saying that necessity is the mother of
invention, but we should miss the real lesson which the
incandescent mantle should convey to us, if we allowed
ourselves to think that it was invented under the pressure
or the stimulus of necessity or out of the conscious desire
to improve the illuminating efficiency of gas. Some, indeed,
had laboured with that end in view, but they laboured in
vain, and we owe the incandescent mantle, with all its
enormous economic and industrial consequences, to a
purely scientific investigation of the oxides of the rare
metals which was carried out by Auer von Welsbach in the
laboratory of Bunscn at Heidelberg, in 1884.
In the course of his investigations, von Welsbach was
struck by the fact that some of the oxides of the rare metals
emitted an exceptionally brilliant light when incandescent ;
THE CHEMISTRY OF ILLUMINANTS 53
and at once his mind grasped the potentialities of
the fact A scientific discovery, however, is one thing ; to
make that discovery of practical utility is quite another ;
and in the present case, as in all cases, a large amount of
patient and careful investigation had to be carried out
before the incandescent mantle could be made a com-
mercial success and be brought to its present state of
perfection. How great has been its success, into what
an enormous industry a single observation may develop,
although made in the course of an investigation having
apparently no practical importance, is clearly seen from
the fact that the world's annual consumption of incan-
descent mantles has been placed at about 300,000,000.
Let us take the lesson of that discovery and of its
application to heart.
To make the discovery of practical utility, " mantles ** or
" stockings " of woven cotton or, as is now generally used,
ramie fibre (fibre produced from a plant of the nettle class),
are soaked in a solution containing the nitrates of thorium
and cerium * in the proper proportions. These mantles are
then dried and incinerated, whereby the fibre is burned
away and the nitrates are converted into a mixture of
the oxides of the metals, which form a skeleton work pre-
serving the shape of the mantle. on suspending this in
the hot, non-luminous flame of a special burner constructed
on the principle of the Bunsen burner, the mantle is raised
to incandescence and emits a brilliant white light, about four
times brighter than is given by the old flat flame consum-
ing the same amount of gas. From a careful investigation
' The chief source of these elements is a mineral known as monazite,
which is found in various parts of the world, but more especially in Brazil.
54 CHEMISTRY IN THE SERVICE OF MAN
it was found that the best results are obtained when
the oxides are present in the proportion of 99 per cent,
of thoria (thorium oxide) to i per cent, of ceria (cerium
oxide). Neither thoria itself nor ceria itself has much
light-giving power ; and any variation in the proportions
of the two oxides from those given, is accompanied by a
diminution in the light-giving power of the mantle. The
part played by the small quantity of ceria in the mantle
is, therefore, a very important one, for which, however,
no completely satisfactory explanation has yet been
found.
The most plausible explanation so far advanced is that
the particles of ceria are embedded in a badly conducting
mass of thoria, which allows of the ceria being heated up to
a point of brilliant incandescence ; and further, the ceria
possesses the property of accelerating the combustion of
the gas, so that the combustion is concentrated or focussed
on the small particles of ceria. As a consequence, the
temperature of these particles rises above the average
temperature of the mantle, and the brightness of the in-
candescence is thereby increased. This action of the ceria
is spoken of as a catalytic action, about which we shall have
more to say later on. Ceria, however, is a substance which
radiates heat rapidly, and if present in the mantle in larger
amounts, the loss of heat by radiation is so great that the
catalytic action is more than counterbalanced, and the
illuminating power of the mantle is diminished.
The invention of the incandescent mantle completely
revolutionised the gas industr>'. Not only could a very
bright light, rivalling that of the electric incandescent
lamp, be obtained, but the cost of production of the gas
THE CHEMISTRY OF ILLUMINANTS 55
was lowered because it was found that equally good results
could be obtained with a gas of poorer quality, that is, of
lower illuminating power. Gas manufacturers, therefore,
were able to use cheaper coal, and, by carrying out the
distillation at a higher temperature, were able to obtain a
larger volume of gas from the coal. Although the illumi-
nating power of this gas when burned in a flat flame is
lower than formerly, the temperature produced in the flame,
and therefore the incandescence of the mantle, are not
greatly affected.
one other illuminant must be mentioned, th6 use of
which depends on the process of combustion in air, namely,
acetylene, a gas which is readily obtained by the action
of water on a compound of calcium and carbon, known as
calcium carbide. This substance is obtained by heating to
a high temperature a mixture of quicklime (calcium oxide)
and carbon in the form of anthracite coal or coke. The
preparation is carried out in a special type of furnace
in which the high temperature necessary is obtained by
means of the electric arc,^ and owing to its use for the
production of acetylene and for other purposes, carbide
is now manufactured in large quantities in most civilised
countries.
Acetylene is an unsaturated hydrocarbon, having a
relatively large proportion (over 92 per cent.) of carbon,
as is shown by its formula C2H2 (cf. p. 13). Under
ordinary conditions the gas burns with a luminous and
very smoky flame, but by using a special burner which
* A temperature estimated at between 5000° and 6000° F. can in this way
be obtained.
56 CHEMISTRY IN THE SERVICE OF MAN
ensures the admixture with the gas of a small amount of
air, a white, intensely luminous flame is obtained.
By injecting oxygen into a flame of acetylene, a
temperature of over 5000° F. can be obtained, and this
fact has received important applications. If, for example,
the oxy-acetylene flame is allowed to impinge on a piece of
iron, the metal is heated locally to redness, and if a fine
jet of oxygen is then directed against the red-hot metal,
the iron is oxidised to oxide of iron which melts in the
intensely hot blowpipe flame, and flows away like water.
By this means one can cut through even large rods, shafts,
or girders as easily as a knife will cut through cheese, and
with a cut almost as fine. The oxy-acetylene blowpipe
flame was, in fact, used in this way with great effect to
cut through the dense tangle of iron girders formed by
the collapse of the buildings in the fire at the Brussels
Exhibition of 19 10.
CHAPTER IV
ENERGY, FUEL, AND EXPLOSIVES
The consideration of the process of combustion, con-
trolled and utilised for the production of light, leads
us to the realisation of the fact that in the chemical
reactions and transformations which take place, we are
not dealing merely with material things. In the case of
the burning candle, oil, or coal-gas, it is not the material
substances — the stearin, paraffin, hydrogen, methane,
etc. — which interest us primarily, nor the products of
combustion, the carbon dioxide and the water vapour,
but the immaterial light, the ethereal vibrations to which
the process of combustion gives rise. So also, passing on
to the consideration of combustible substances as fuels,
and of the process of combustion as a source of heat, we
again recognise that our interest is focussed not on the
material nature of the combustibles, but on their efficiency
as heat-producers. Heat, however, is a form of energy,
and can be converted into other forms of energy, such
as mechanical energy, and can perform what we call work ;
and so it is really in their power of doing work that we
see the value of combustibles. The combustible sub-
stances together with the oxygen of the air, represent so
much potential energy, and the process of combustion is
58 CHEMISTRY IN THE SERVICE OF MAN
like the downward rush of the waterfall in being a process
by which potential energy becomes available for doing
work. In the recognition of the supreme importance of
energy, in the establishment of the law of the conservation
of energy and of the laws governing the mutual transfor-
mation of the different forms of energy, we see the crowning
achievement of nineteenth century physical science ; and
if one would grasp the spirit of modern chemistry, one
must learn to regard a chemical change or reaction not
merely as involving some material transformation but as
representing a flow of energy out of or into the substances
undergoing the change. " Real gain," as Sir William
Ramsay said some years ago in his presidential address
to the British Association, "real gain, real progress con-
sists in learning how better to employ energy — how better
to effect its transformation " ; and it is by the utilisation
of energy and by the methods of applying and transform-
ing energy, that the nineteenth and twentieth centuries
are so strongly marked off from the centuries which pre-
ceded them.
At the present day by far the greatest part of the
energy necessary for the continuance of vital activity, as
well as for carrying on the industrial life of the world,
is derived from the energy of combustion of carbon, and
of its compounds. Through the oxidation of carbonaceous
food by means of the oxygen taken in through the lungs,
the vital activity of the animal organism is maintained,
and the inert carbon dioxide produced in the process is
sent into the atmosphere in the expired air. But the
carbon does not thereby cease to be available, for the
green plants, absorbing the radiant energy of sunlight,
ENERGY, FUEL, AND EXPLOSIVES 59
transform and utilise the carbon dioxide for the purpose
of building up their own structures and producing com-
pounds like starch and sugar, which again become the
food and the source of energy of animals. In the case,
therefore, of the element carbon which constitutes the
basic element of all life, we find a continual circulation
in nature, whereby the mutual preservation of the animal
and vegetable worlds is secured. The green plants act
as transformers of the radiant energy of sunlight into the
potential energy of combustible substances.
Until comparatively recent times, down, say, to the
thirteenth century, wood was the almost universal fuel ; but
since coal first began to be mined, it has become, in an
ever-increasing degree, the immediate source of the energy
on the utilisation and transformation of which our present-
day civilisation depends, and it now occupies a position
of unquestioned pre-eminence.
Coal consists of the fossil remains of early, luxuriant
vegetations. Through an age-long process the cellulose
of which the woody fibre essentially consists, has become
converted into more highly carbonised compounds, the
proportion of hydrogen and oxygen becoming diminished
owing to the formation of gaseous substances such as
carbon dioxide and marsh gas. From the figures given
in the following table, we can recognise the gradual
carbonisation of cellulose, the materials peat, lignite or
brown coal, bituminous coal, and anthracite representing
progressive stages in the natural process.*
' It must be noted that wood, peat, and coal are not definite chemical
compounds, and that the composition of the different kinds of coal may vary
considerably. The numbers given in the table, therefore, are only approxi-
mate values representing, as it were, the composition and calorific value of
6o CHEMISTRY IN THE SERVICE OF MAN
Carbon. Hydrogen. Oxygen. Calorific value
B. Th. U. per lb.
Cellulose (C,H„0») . 44*5 62 49*3 7500
Wood 50*0 6*o 44*o 7400
Peat (Irish). . . . 600 $'9 34' » 99«>
Lignite .
Bituminous coal
Welsh steam coal
Anthracite .
670 5-2 278 11,700
884 5-6 6-0 14,950
92s 47 27j
IS.720
. 94- » 3'4 2*5^
The process of carbonisation is accompanied by a
diminution of the amount of gaseous and volatile matter
which the fuel can yield on being heated, and this
markedly affects the manner in which the different
materials burn. Dry wood, we know, burns readily and
with a bright and cheerful flame, whereas anthracite, which
represents the most advanced stage in the natural process
of carbonisation of woody fibre, is ignited only with diffi-
culty, and burns with a very small and not strongly lumi-
nous flame.
But it is not with the cheerfulness with which the
fuel burns that we are concerned here, but with the all-
important question of how much heat, how much energy
is given out in the process of combustion. It is the
" calorific value " of the fuel that claims our attention
just now.
When we examine the different solid fuels from this
point of view we find, as the figures in the last column of
the table given above show, that with the progressive
carbonisation, the heat-producing power of the fuel in-
creases, so that among all the solid fuels, anthracite stands
an average member of the different classes. Moreover, other substances,
more especially nitrogen, are present, besides carbon, hydrogen, and oxygen,
and although, under certain conditions, these substances may give rise to
important by-products, their influence on the fuel value of the combustible
materials is very small.
ENERGY, FUEL, AND EXPLOSIVES 6i
pre-eminent. A British thermal unit represents the amount
of heat required to raise the temperature of one pound of
water through i° F., and the numbers in the table show
that whereas one pound of wood will give out, on burning,
about 7400 units, an equal weight of bituminous or house-
hold coal will yield about 14,900, while Welsh steam coal
and anthracite will give 15,700, units. Hence the im-
portance which we attach to our supplies of Welsh steam
coal and anthracite.
A consideration of these calorific values will, perhaps,
also help to convince us how unscientific, how irrational it
is to buy coal, as we do, merely by the weight without
regard to the amount of heat which the coal can give out.
It is true that the existence of different kinds of coal having
varying quality or calorific value, is recognised to some
extent by a variation in the price charged ; but what is,
perhaps, not sufficiently recognised is that there may be
considerable variation in the heat value of even the same
kind of coal, or of coal drawn at different times from the
same mine. If we could only realise more thoroughly
that when we buy coal we do so not for the sake of the
material itself, but for the energy which can be obtained
from it, we should soon, I hope, everywhere adopt the
practice, which is common in the United States and
on the Continent, of purchasing our coal not merely by
weight, but with some consideration of its heat-producing
value, a certificate of which the sellers of the fuel might
be made to provide.
During the past fifty years there has taken place thiough-
out the world an enormous increase in industrial production,
and the great river of energy which has thus flowed through
62 CHEMISTRY IN THE SERVICE OF MAN
the channel of industry, has had its source mainly in coal.
The control and direction of such a flow of energy is a
matter on which man may legitimately congratulate him-
self. But is there not also some cause for anxiety ? What
of the future ? The world's supply of coal, this " bottled-up
sunshine," on which the whole of our boasted civilisation
depends, is being used up with an almost appalling rapidity ;
and although, no doubt, the storing up of the sun's energy
is going on now as in the past, the rate at which coal is
being formed is so incomparably slower than that at
which it is being consumed, that it can only be a question
of time when the coal supply will become exhausted.
In this country the natural stock of coal is being
depleted at the rate of nearly 290,000,000 tons per annum,
and the rate increases rather than diminishes. How long
can this go on ? With regard to this point, there must in-
evitably be some uncertainty, and authorities are divided
in their opinion. But even if we double the estimate of 175
years, the period — 350 years — is not a very long one in the
history of the nation. At the end of that time our reserves
of coal will be exhausted and the industries on which our
national life and civilisation so largely depend, will be
imperilled or destroyed. It is therefore of the highest
national importance that everything possible should be
done to avoid waste of our irreplaceable supplies of coal,
and to seek for and develop all other available sources
of energy.
How then can we delay the exhaustion of our coal
supply, and so preserve this life-blood of our industries ?
Can we, by altering the manner in which we burn our coal,
procure a better utilisation of the energy and thereby effect
ENERGY, FUEL, AND EXPLOSIVES 63
a saving of the fuel ? The problem is a very complex one
and a detailed consideration of it would carry us far
beyond the limits of our present discussion. Anything in
the nature of a violent revolution is scarcely possible, and
perhaps not advisable ; but that the public mind should
become alive to the call for a reform, is imperative in the
interests of the country as a whole. That a check should be
placed on the wasteful use of the irreplaceable reserves of
energy, of which we are the stewards, is a matter which
should appeal, if not to the moral sense of the nation, then
surely to that scientific conscience which the stress of the
times is slowly awakening into life.
When we consider merely the case of domestic heating,
in which about forty million tons of coal are consumed
annually in Great Britain, we have to confess that the
British open fire is a most wasteful method of heating.
When fresh coal is put on a fire, a process of distillation
takes place with production of gas and tarry products
which, undergoing a partial decomposition with separation
of carbon, give rise to clouds of smoke. Thereby, it has
been shown, as much as a third of the heating value of the
coal is lost.
But if the open fire is wasteful we shall not willingly
consent to give it up, and we may place against its waste-
fulness, its efficiency in promoting ventilation and the
hygienically advantageous manner of heating by radiation.
Moreover, its comfortable appearance, " the wee bit ingle
blinkin' bonnily," is something which has a value of its
own, not recognised perhaps by science, but which doubt-
less reacts powerfully on the temperament and character of
the people. Attempts therefore have been made to produce
64 CHEMISTRY IN THE SERVICE OF MAN
a fuel which can be burned in the open fire and which, by
avoiding the waste accompanying the production of smoke,
would not only effect an economy but would also do much
to abate the " smoke nuisance." By carrying out the dis-
tillation of coal in retorts one can avoid the most wasteful
part of the process of burning coal in the open fire, for the
illuminating gas and the very valuable ammonia and tar
are collected, and the coke which is left behind can be used
as a smokeless fuel. Although the ordinary coke of the
gas-works is such that it cannot be burned readily in the
open fire, it has been found that by carrying out the distil-
lation of the coal at a lower temperature, the residual coke
still contains sufficient volatile matter to enable it to burn
readily and without smoke in the ordinary grate. Coalite,
for example, of which much was recently heard, and of
which, or of similar material, much will doubtless be heard
in the future, is a smokeless fuel of this description.
But another way in which economy can be effected,
especially in towns, is by the use of gas for heating and
cooking purposes, and recent years have, indeed, seen a
very great development in this direction. Many improve-
ments, also, have been effected in the construction of gas
fires so that their ventilating efficiency and their emission
of radiant heat have been greatly improved, and they have
now lost practically all their former unhygienic properties.
Moreover, owing to the introduction to a greater extent
of the chemist into gas-works, improvements have been
brought about not only in the actual methods of gas
manufacture, but also in the recovery and use of the by-
products, so that gas can in some cases effectually compete
with coal even when used for continuous heating. The
ENERGY, FUEL, AND EXPLOSIVES 65
more general use of gaseous fuel would doubtless be
greatly encouraged by an alteration of the municipal
regulations. In most cases these prescribe a certain
standard of illuminating power, but at the present time,
when incandescent mantles are in almost universal use
for gas lighting, and when gas is so much employed for
heating and cooking purposes, it is not the illuminating
power but the heating power of the gas that is of import-
ance. And since the cost of producing a gas of high
illuminating power is greater than that of manufacturing
a gas of almost equal heat value but lower illuminating
power, the present regulations, by increasing the cost of
production, exercise a certain restraint on the increased
use of gas for heating purposes.
In the industrial use of coal, also, there is room for
very considerable improvement. Great economies can be
and have been effected by the installation of more efficient
furnaces, and by the more careful control of the air supply ;
and a still greater saving can in many cases be effected by
replacing the very inefficient steam engine by the far more
efficient gas engine. For driving such engines one can
employ not only the ordinary illuminating gas obtained by
the distillation of coal, but also other combustible gases
which can be produced more cheaply. Thus water gas,
obtained by passing steam over red-hot coke, and consisting
essentially of carbon monoxide and hydrogen ; producer
gaSt obtained by passing air over red-hot coke, and consist-
ing of carbon monoxide and nitrogen ; Mond gas, obtained
by passing both air and steam over heated coal, and con-
sisting of a mixture of carbon monoxide, hydrogen and
nitrogen ; as well as the waste gases formed in many
F
66 CHEMISTRY IN THE SERVICE OF MAN
industrial processes, are now largely used for the production
of power. By adopting such methods of fuel economy to
a greater and greater extent, and by recovering in all cases
the by-products (ammonia and tar), produced from the
twenty million tons of coal annually distilled in Great
Britain for the production of the coke required in metal-
lurgical processes, savings would be effected which could
be estimated only in millions of pounds sterling.
But we can also make use of other combustible
materials, other fuels, and so reduce the rate at which our
stock of coal is being depleted. Of these fuels, oil ranks
first in importance. Not only does petrol, the more
volatile portion of crude petroleum, constitute a fuel for
which the demand threatens to exceed the supply, but the
higher boiling portions of petroleum, which distil over after
the kerosene or illuminating oil, form a fuel which can be
burned in boilers, and used for raising steam. At present,
the world's production of crude petroleum amounts to
between fifty million and sixty million tons, and this
therefore constitutes a very valuable supplementary source
of energy. In recent years the use of oil has greatly
increased, and so great is its heat-producing power — it is
one and a half times greater even than anthracite — that it
would almost seem as if oil were marked out to take the
place of coal, and to become the fuel of the future. But
alas ! even at the present rate of consumption, it is esti-
mated that the world's reserves of oil would last only a
hundred years ; and there seems, therefore, no hope that
the dream of an age of oil succeeding an age of coal, will
ever be realised.
In some of the great timber-producing countries, wood
ENERGY, FUEL, AND EXPLOSIVES 67
is still used to some extent as a fuel, but on account of its
price and low heat-producing power (about half that of
ordinary coal), it cannot find general adoption. Moreover,
owing to the great demand for timber not only for con-
structional purposes, but also for use in many manufactures,
of which the manufacture of paper may be taken as an
example, the world's reserves of timber are becoming
greatly depleted ; and the need for the preservation of our
timber supplies and for the extension of afforestation, is
more urgent even than the saving of coal which would be
effected by the greater use of wood as fuel.
But there is one other source of heat energy whith, we
may hope, will prove capable of more abundant use and so
postpone for centuries a world-bankruptcy in fuel. Peat
occurs in great abundance and widely distributed, and it
has been estimated that the amount of combustible matter
in the peat deposits already existing, is greater than in all
the known coal-fields.^ But the removal of the large
amount of water which peat contains, is a difficulty which
lies in the way of the utilisation of this material as a fuel ;
and when peat is dried in what was formerly the only
economically successful way, namely, by natural drying in
air, a bulky fuel with only a low calorific value is obtained.
The invention, however, of what is called the " \yet carbpn-
isatiop " process, inspires the hope that a way out of the
difficulty has already been found. In this process, the wet
peat is heated under pressure to a temperature of about
400° F., and the resulting material, which can be dehydrated
' The area of peat moors in Europe has been estimated at 140,000,000
acres ; and in Ireland alone the available peat has been estimated as equal to
2,500,000,000 tons of coal.
6S CHEMISTRY IN THE SERVICE OF MAN
by pressure, is formed into hard briquettes of " peat coal."
This material bums readily and has a calorific value not
greatly inferior to that of bituminous coal. Or the de-
hydrated peat can be employed for the manufacture of
producer gas which can be used for power purposes, while
the valuable by-products ammonia, tar, and acetic acid, can
be recovered.
The utilisation of water-power is, as we shall see later
(Chap. IX), a matter in which the chemist can play an
important part, and we may be sure that future years and
future ages will witness the utilisation, to an ever greater
extent, of the energy of flowing and falling water in which,
at the present time, such enormous amounts of energy
are running to waste.
Although the association of energy with chemical change
has been made very obvious to us in con nection with the
process of combustion, it is also found in connection with all
chemical changes. Every chemical system, every collection
of substances which can spontaneously undergo chemical
change, represents a certain amount of potential energy,
and the material change which we observe, and which
constitutes what we call a chemical reaction, is merely
the outward sign of the conversion of so much potential
energy into active energy — heat energy, or some other form
of energy. Moreover, whenever a chemical change or re-
action occurs, the heat which is given out, the so-called heat
of reaction, is, for a given weight of the reacting materials
and under specified conditions, constant and definite in
amount.
But it must not be thought that all chemical change is
ENERGY, FUEL, AND EXPLOSIVES 69
accompanied by an evolution of heat. In some cases, the
initial substances possess less energy than the final pro-
ducts, and the chemical change therefore takes place with
absorption of heat. Energy, that is to say, must be sup-
plied to the initial substances in order that they may pass
into the final products of change. We distinguish, there-
fore, between exothermal reactions or reactions accompanied
by evolution of heat, and endo thermal reactions or re-
actions accompanied by absorption or taking in of heat
energy.
This way of regarding chemical change as being the
outward and visible sign of energy change is a very in-
structive one ; for it is clear that if we can make a sub-
stance take up energy — if we can, as it were, pump
energy into a substance — we can thereby alter the amount
of energy of which that substance is the carrier, and so
change its nature. This fact is clearly illustrated by the
behaviour of the familiar substance, oxygen.
The molecule of oxygen consists of two atoms, but
when the gas is subjected to the action of an electric dis-
charge under particular conditions, it takes up or absorbs
some of the energy of the discharge and passes into a gas
which, on account of its powerful and characteristic smell
received the name of ozone (Greek o^tu, I smell). The
material change, the chemical change, which accompanies
the absorption of energy, is the addition of a third atom of
oxygen to the molecule of that gas, so that the molecule
of ozone consists of three atoms of oxygen. Since ozone
contains more energy than ordinary oxygen, it is a more
active oxidising agent, and for this reason it is sometimes
used for the sterilization of drinking water, the ozone
70 CHEMISTRY IN THE SERVICE OF MAN
oxidizing and so destroying the bacterial impurities
present. Ozone is also used for the purification of air in
confined spaces and in underground " tubes," but opinion
is divided with regard to the desirability and efiicacy of
such treatment.
At Niagara Falls, large quantities of ozone are used in
the production of vanillin, the sweet-smelling constituent
of the vanilla bean pod, by the oxidation of oil of cloves.
In the case of white phosphorus and red phosphorus,
and in the case of the three forms of carbon — charcoal,
graphite, and diamond — we have further examples of
elements existing in different, so-called allotropic^ forms
containing different amounts of energy.
Perhaps the most vivid idea of the large amount of
potential energy stored up in substances can be gained
from a consideration of the materials known as explosives.
In the case of the explosives actually in use, the chemical
process which occurs is essentially one of very rapid com-
bustion, with production of gaseous substances occupying
a volume which, at the temperature of the explosion, is
much greater, perhaps io,ocx) to i5,cxx> times as great as
that of the explosive itself.
As early as the seventh century, we read, a rapidly burning
mixture, known as Greek Fire, which " came flying through
the air like a winged long-tailed dragon, about the thickness
of an hogshead, with the report of thunder and the velocity
of lightning," was used by the inhabitants of Constanti-
nople in their defence of the city against the Saracens.
The discovery of the first real explosive, ^««/t7Wdfer, is, how-
ever, attributed to Roger Bacon in the thirteenth century ;
ENERGY, FUEL, AND EXPLOSIVES 71
and since that time man has striven to discover new ex-
plosives of greater and greater power, to learn how better
to utilise and control the transformation of the enormous
stores of potential energy contained in explosives, and to
make them work for him both in peace and in war. Some
idea of the advance which has been made is gained when
we compare the artillery used by the English at the battle
of Crecy in 1346, when the guns "threw little balls of iron
to frighten the horses," with the modem large gun which
can hurl a projectile of nearly a ton in weight to a distance
of thirty miles.
Gunpowder is a mixture of potassium nitrate or salt-
petre, charcoal, and sulphur, and its action as an explosive
depends on the rapid combustion of the sulphur and char-
coal at the expense of the oxygen contained in the salt-
petre ; and although great improvements have been made
in gunpowder in recent times, these improvements have
been of a physical or mechanical and not of a chemical
nature. While still largely used in connection with the
beneficent operations of mining and also for pyrotechnic
displays, gunpowder is no longer employed as a propellant
for military or naval purposes. Its use has been given up
not only on account of the large volume of smoke produced
in the explosion, which, by speedily hiding everything from
view prevents the effective use of quickfiring guns, but also
because explosives of very much greater power and
efficiency have been discovered.
The first great advance in the chemistry of explosives
took place with the discovery in 1846 of gun-cotton or
" nitro-cotton." Cotton consists, essentially, of the chemical
substance cellulose, which is, as we have seen (p. 60), a
72 CHEMISTRY IN THE SERVICE OF MAN
compound of carbon, hydrogen and oxygen. When this
is acted on by a mixture of nitric and sulphuric acids,
various compounds of cellulose with nitric acid (nitrates)
are formed which are generally known as " nitro-cellulose."
Since not only cotton, but also purified wood fibre or wood
pulp (p. 80), and other vegetable fibres consist essentially
of cellulose, it might be thought that such materials could
also be used for the manufacture of "nitro-cellulose."
And this indeed can be done. But in none of these cases
are we really dealing with a chemical substance possessing
entirely uniform properties, and the explosive qualities of
the " nitro-cellulose " prepared from the cellulose derived
from different sources are not identical. Consequently,
although the " nitro-cellulose " from wood pulp could be
used as the basis of propulsive ammunition, guns which
had been designed for use with a *' nitro-cotton " propellant
would have to be re-adjusted as regards size of explosion
chamber and sighting before they could be used with the
different ammunition. Hitherto cotton waste has always
been employed for the preparation of gun-cotton, and in
order to obtain a reliable explosive with uniform properties,
great care must be exercised in the preparation and sub-
sequent purification of the gun-cotton as well as in the
selection and treatment of the material used.
When ignited, loose gun-cotton burns with great
rapidity, but not so rapidly as to constitute an explosion.
The molecule of gun-cotton, however, which, as we might
say, is almost bursting with energy, is in a very unstable
condition, and when subjected to a shock, as, for example,
when a little fulminate of mercury is caused to detonate
near it, it suddenly decomposes and gives rise to a large
ENERGY, FUEL, AND EXPLOSVES 73
volume of gaseous substances, nitrogen, oxides of carbon,
and water vapour. Since these gases are all colourless,
and as no solid materials are formed, gun-cotton explodes
without smoke.
As an explosive, gun-cotton possesses the very im-
portant property that it can be used wet This wet gun-
cotton will not take fire when a light is applied to it, but
when subjected to the shock of a fulminate of mercury
detonator, it explodes just as readily as when it is dry.
Thus, torpedoes and sea- mines are charged with rolls of
moist gun-cotton which have been subjected to a high
pressure (six tons per square inch) and so compressed into
hard blocks.
The explosive or disruptive effect of gun-cotton is very
great by reason of the rapidity with which the decomposi-
tion of the substance takes place. Thus, whereas a couple
of pounds of gunpowder require about a hundredth of a
second for complete combustion, the same weight of gun-
cotton undergoes decomposition in about one fifty-thousandth
part of a second. It is on this fact that the shattering or
disruptive effect, the " brisance," depends. It is this fact
also, which makes gun-cotton, which is very valuable as a
" high " or " disruptive " explosive, unsuitable for use as
a " low " or " propulsive " explosive in guns. It would
simply burst the gun.
The difference in the action of a " low " and of a " high "
explosive can be illustrated by a well-known experiment.
A piece of thin sewing cotton is attached to a fairly heavy
weight suspended so that it can swing freely. If the thread
be now pulled very gently, the weight can be caused to
assume a vigorous motion. This corresponds with the
74 CHEMISTRY IN THE SERVICE OF MAN
action of a " low " explosive, in which the explosion takes
place relatively slowly. If, on the other hand, a sharp
sudden pull be given, the thread snaps. This corresponds
with the action of a " high " explosive.
Although gun-cotton cannot be employed as a pro-
pellant, the advantages attaching to a smokeless explosive
are so obvious, that attempts were made to overcome the
difficulties due to the rapid rate of explosion. These
attempts to "tame" the gun-cotton, have been entirely
successful. Nitro-cotton dissolves in various liquids, such
as acetone or a mixture of alcohol and ether, and when
these solvents are evaporated off, the nitro-cotton is obtained
as a gelatin-like material, which is familiar to everyone
under the name of collodion. In this gelatinised material
the disruptive properties of the gun-cotton are greatly
modified. Such gelatinised gun-cotton was the first
smokeless powder to be used.
A further advance in the chemistry of explosives was
made by the Swedish chemist, Alfred Nobel. When
glycerine, which, as we have seen (p. 34), is readily ob-
tained from animal or vegetable fats and oils, is treated
with a mixture of nitric and sulphuric acids, it behaves
similarly to cotton and yields a substance " nitro-glycerine,"
which is a liquid and very powerful explosive. This sub-
stance, discovered by Nobel, was difficult to handle on
account of its great sensitiveness to shock, and was the
cause of many fatal accidents ; but it was found that
if the liquid nitro-glycerine was mixed with kiesel-
guhr, a fine earth composed of the siliceous skeletons
of marine diatoms, the explosive could be trans-
ported and handled with comparative freedom from
ENERGY, FUEL, AND EXPLOSIVES 75
danger.* In this form nitro-glycerine has been largely used
under the name oi dynamite, its explosion being brought
about by means of a fulminate of mercury detonator.
When nitro-cotton is added to nitro-glycerine a tough
jelly-like mass is formed known as blasting gelatin. That
this explosive is more powerful than dynamite, that it is,
indeed, one of the most powerful blasting explosives known,
will cause no wonder, since the nitro-glycerine is not mixed
with an inactive material like kieselguhr, but with a sub-
stance which is itself an explosive.
The British service powder, cordite, is prepared by
mixing a " paste " of gun-cotton (65 per cent.) and nitro-
glycerine (30 per cent), with acetone, and adding a quantity
of vaseline (5 per cent.). The mixture is then forced by
hydraulic pressure through a die into the form of a thread
or cord. Hence the name cordite. After evaporating off
the acetone, the cordite forms a horn-like material which is
very insensitive to shock and safe to handle. This
" taming " action of gelatinisation on two of the most
powerful explosives, is one of the most important and
remarkable discoveries in this branch of science ; and nitro-
cotton, gelatinised in one way or another, is now the basis
of all propulsive ammunition.
Although nitro-cotton or gun-cotton is extensively em-
ployed as a high explosive, more especially in torpedoes,
for use in shells other explosives derived from the products
of distillation of coal are employed. Of these explosives
the two most important and most used are picric acid and
trinitrotoluene.
' Wood-flour or wood-meal, burnt cork, charcoal aad other materials are
also used as absorbents in place of kieselguhr.
76 CHEMISTRY IN THE SERVICE OF MAN'
When carbolic acid or phenol, to give it its scientific
name, is treated with a mixture of nitric and sulphuric acids,
there is formed trinitrophenol or picric acid. As ordinarily
obtained, it is a faintly yellow crystalline substance, which
has long been used as a yellow dye for silk. It melts to a
liquid at a temperature of 252° F., and in this state it is
run into the shell. on account of the honey-yellow colour
of the molten picric acid, this substance received from the
French the name of melinite ; while in this country it is
called lyddite, on account of the fact that it was at Lydd, in
Kent, that its use as a high explosive was first tested. In
other countries it receives still other names, such as pertite,
ecrasite, and shimose. Although picric acid can be handled
with perfect safety, its destructive power, when exploded by
means of a suitable detonator, exceeds that of gun-cotton
or dynamite. Some idea of the enormous amount of
potential energy contained in picric, acid can be gained from
the fact that when a pound of the substance is exploded, it
liberates an amount of energy equal to that required to
raise a weight of over a ton more than one hundred yards
into the air. Unfortunately picric acid has the property of
forming with metals compounds which are much more
sensitive than itself, and so may give rise to untoward
accidents. Another explosive, therefore, has come into
favour in recent years, a substance derived from the hydro-
carbon toluene, and called trinitrotoluene, or T.N.T. This
substance also is a solid, and can be subjected with impunity
to very rough usage ; a bullet, even, may be fired into the
mass without producing any effect. When detonated,
however, trinitrotoluene explodes with a violence not much
inferior to picric acid, but as the oxidation of the carbon in
ENERGY, FUEL, AND EXPLOSIVES -jy
the compound is by no means complete, dense black clouds
of carbonaceous matter are produced, and this has led to
the nicknames of " Coal boxes " and " Jack Johnsons "
being applied to the shells filled with this explosive. For
use as a high explosive, trinitrotoluene is also frequently
mixed with ammonium nitrate.
But it is not merely for the purpose of strengthening
man's arm in war that explosives have found an appli-
cation ; they have also, by rendering possible such great
engineering works as the Suez Canal and the Panama
Canal and the boring of tunnels through the mountains
of the earth, through their use in mining, and in many
other ways, played an important part in the peaceful
progress of civilisation. Even in the piping times of
peace, high explosives are produced, in the United
Kingdom alone, and chiefly at Nobel's factory at Ardeer
in Ayrshire, the largest explosives factory in the world, to
the amount of 17,000 to 18,000 tons per annum. Enormous
as is now the power wielded by man by means of these
explosives, it may confidently be anticipated that chemistry
will yet give him control of still more concentrated forms
of energy, and will put into his hands still more powerful
weapons for the advance of civilisation — or, if he will, for
its destruction.
CHAPTER V
CELLULOSE AND CELLULOSE PRODUCTS
We have seen in the previous chapter how the woody
material of plants has, by the age-long action of natural
forces, become converted into the most valuable of all
fuels, coal ; and we have also seen how cotton can, by
the action of nitric acid, be transformed into one of the
most powerful of explosives. We must now consider
very briefly how the chemist has, in other ways, succeeded
in changing the aspect and nature of the cellulose, of which
cotton and wood fibre essentially consist, so as to produce
other materials which can be fashioned into articles of
utility and of beauty, which minister to the wants, the
comfort, and even the luxury of man.
The chemical substance cellulose belongs to a group
of compounds consisting of carbon, hydrogen, and oxygen,
in which the hydrogen and oxygen are present in the
proportion of two atoms of the former to one of the latter.
Since this is the proportion in which these two elements
combine to form water, it was thought that cellulose and
the other compounds belonging to that group, were
compounds of carbon with water, and so the name
carbohydrate was applied to them. The different sugars,
such as grape sugar, fruit sugar, cane sugar, and also
starch and a number of other substances, belong to the
CELLULOSE AND CELLULOSE PRODUCTS 79
class of the carbohydrates. In cellulose the carbon,
hydrogen and oxygen are united in the proportions of
six atoms of carbon, ten atoms of hydrogen, and five
atoms of oxygen (C^HjoOs), although we do not know
how many atoms of carbon, hydrogen and oxygen are
really contained in the molecule. We therefore repre-
sent cellulose by the formula (CoHiQOf^n where « is an
unknown whole number.
The purest naturally occurring form of cellulose is
cotton, the hairy material which covers the seeds of various
species of the cotton plant {Gossypium). When this has
been chemically treated with alkalies and bleaching
agents, and with acids, in order to remove various
organic and mineral impurities, the product constitutes
what is called cellulose. This is one of the most important
and valuable substances in present-day civilisation, being
employed in the manufacture not only of cotton and linen
textile materials, but also of explosives, of paper, and of
other substances to some of which we shall refer below.
Its great value for the manufacture of paper depends
mainly on the fibrous character of naturally occurring
cellulose, and also on the fact that it is a very stable
substance and is not acted on by the atmosphere nor by
most of the other substances with which it ordinarily comes
into contact
Less than a hundred years ago, when the production
of paper was hampered by a Government duty, and before
a penny postage had stimulated the growth of private
and business correspondence, or education had created
the present demand for cheap newspapers and cheap books,
paper was manufactured entirely from cotton and linen
8o CHEMISTRY IN THE SERVICE OF MAN
rags. But nowadays the supply of these is quite inadequate
to meet the demand, and recourse is had to the less pure
forms of cellulose which constitute the skeletal frame-work
of all vegetable structures ; and large quantities of more
or less pure cellulose are produced at the present day,
from straw, various grasses (especially esparto grass), and
from wood, for use in the different industries of which
cellulose is the basis.
Of these different sources of cellulose, wood constitutes
by far the most important. Wood fibre consists mainly
of a compound of cellulose with lignone, encrusted fre-
quently with resinous matter, and in order to isolate
the cellulose, this compound must be decomposed.
Formerly this was done by boiling the wood, in the
form of shavings or chips, with caustic soda (giving rise
to "soda pulp"), but the latter substance has now been
very largely replaced by calcium bisulphite (or acid
sulphite of lime),^ the wood being boiled with the liquor
under a pressure of several atmospheres. Not only is
the wood fibre thereby chemically broken up with produc-
tion of cellulose, but the latter is also bleached to some
extent by the sulphite. The cellulose is now separated
from the sulphite liquor, washed and beaten with water
so as to break down the fibres into small shreds, in which
form it constitutes wood pulp (" sulphite pulp "). A
solution of sulphate of soda is also employed to a certain
extent for the disintegration of the wood-fibre and the
production of cellulose, the pulp so obtained being known
as " sulphate pulp."
' This substance is formed by the action of sulphurous acid (solution of
sulphur dioxide in water) on limestone.
CELLULOSE AND CELLULOSE PRODUCTS 8i
Pulp is produced, however, not only by chemical but
also by mechanical means, the wood being ground to
powder on rapidly revolving, wet grindstones. In this
"mechanical pulp," however, the cellulose has not been
separated from the lignone and the resins in the wood ;
it is not of a strictly fibrous nature and does not felt
together readily. It is suitable, however, for mixing
with other paper-making, fibrous material, especially
cotton.
Of the paper manufactured in Great Britain, by far
the largest proportion is made from wood pulp.
For the manufacture of paper, the fine cellulose fibres
obtained from the disintegrated cotton rags, grass, or
wood pulp, are bleached, washed, and mixed with colouring
matters if desired. They are then suspended in water
and run over an endless band of wire gauze, through
which the water drains away, and the fibres are caused
to felt together by giving a vibratory motion to the band
of gauze. The web of felted pulp is now carried between
heated rollers whereby the paper is dried.
The paper so obtained is loose in texture and of the
nature of blotting paper ; and to make it suitable for
writing or printing it must be sized. For this purpose it
is passed through solutions of alum and of rosin soap (p. 1 56),
whereby a compound of rosin and aluminium is formed
which binds the fibres together and prevents the ink from
running. The addition of the sizing materials may also be
made to the pulp before making into paper. Sometimes,
also, powdered gypsum, white clay, or similar substances
are added to the paper pulp in order to " load " or give
body to the paper, fill up its pores, and allow of a more
G
82 CHEMISTRY IN THE SERVICE OF MAN
highly glazed surface being obtained by calendering, or
rolling with hot rollers.
By immersing paper for a short time in a fairly concen-
trated solution of sulphuric acid, the cellulose is converted
into a gelatinous mass which fills up the pores of the paper,
and on being thoroughly washed, the paper is found to be
parchmentised, or converted into a non-porous material
resembling parchment (prepared skin of the sheep or she-
goat). Such parchment paper can also be prepared by
immersing paper in a solution of zinc chloride ; and by
compressing together a number of sheets of such parch-
ment paper, the compressed fibre, or " hard fibre," so largely
used in the manufacture of travelling cases and trunks and
as an insulating material for electricity, is obtained.
When one adds ammonia to a solution of bluestone or
copper sulphate, a pale blue solid, copper hydroxide, is
formed ; and if this solid is dissolved in ammonia, a clear
deep blue coloured liquid (a solution of cuprammonium
hydroxide) is produced. This liquid has the important
property that it can dissolve cellulose, and by coating
paper with the solution obtained and then immersing it in
acid, the cellulose is thrown out of solution as a gelatinous
mass which coats the paper and renders it waterproof. In
this way Willesden paper is prepared.
As far back as 1889, there was exhibited in Paris a
material which, in its general appearance, imitated in a
remarkable manner the fibre spun from the glands of the
silkworm. This material, however, invented by the French
chemist Count Hilaire de Chardonnet, was not silk, nor
was it derived from any animal source whatever, but from
CELLULOSE AND CELLULOSE PRODUCTS 83
the vegetable material cellulose.* Nitro-cellulose, or nitro-
cotton, as we have seen, can be dissolved in certain liquids,
such as a mixture of alcohol and ether, and when the
somewhat viscous liquid which is thus obtained is squirted
through fine openings, and the jet of liquid allowed to pass
through water, thin threads or filaments are obtained. By
treating these threads with certain solutions, e.g. a solution
of sulphide of ammonium, the "nitro-groups," (NO2), to
the presence of which the gun-cotton owes its explosive
properties, are removed, and there is again obtained what
is practically cellulose, the natural structure of which has,
however, been destroyed by the treatment to which it has
been subjected. The threads and fibres so produced have
all the superficial appearance and lustre of silk, and it was
by this process that the fibre produced by the silkworm was
first imitated and counterfeited in a commercially success-
ful manner.
But it was not long before other and better methods of
transforming cellulose into fibres and threads resembling
silk were invented. We have already seen that cellulose
dissolves in a solution of blue cuprammonium hydroxide,
and when the viscous mass which is thus obtained is
squirted into a suitable hardening liquid, threads of a silk-
like lustre are obtained.
The method, however, by which most of the artificial
or imitation silk is made at the present day, the so-called
viscose process, was invented by two English chemists,
C. F. Cross and E. J. Bevan. As the basis of this process
there is used wood pulp, prepared by the maceration and
* True silk belongs to a class of substances known as proteins, and
contains nitrogen as well as carbon, hydrogen and oxygen.
84 CHEMISTRY IN THE SERVICE OF MAN
chemical treatment of wood. This pulp is treated with a
solution of caustic soda and then with the liquid called
carbon disulphide, whereby a thick syrup-like mass
is obtained. By forcing this viscous material through
minute apertures into a suitable liquid, silky filaments are
produced which can be spun into threads suitable for
knitting or weaving. The artificial silk, the transformed
and transfigured wood fibre, obtained by this process is
superior in lustre, in strength, and in the uniformity with
which it can be dyed, to that obtained by the processes
previously described. Although more lustrous than silk
and costing only half the price, artificial silk has not been
found to enter into direct competition with the natural
product ; but for use in the production of articles of
apparel, whether woven or knitted, of embroideries and
laces, imitation furs and tapestries, it has developed for
itself and by reason of its own distinctive properties, a field
of usefulness already great and rapidly expanding. At
the present day the world's production of artificial silk is
estimated at about 7000 tons. And when we admire the
beauty of this material, do not let us altogether withhold
our appreciation of the work of the chemists by whose
ability the woody fibre of the tree has been increased in
value not merely a hundred but almost even a thousand-
fold.
When the syrup-like viscose is kept for some days it
undergoes spontaneous decomposition with production of a
hard horn-like material which may for many purposes
replace the material celluloid. Transparent and non-
inflammable films can also be obtained by spreading
viscose on glass at a temperature of about 175° F.
CELLULOSE AND CELLULOSE PRODUCTS 85
The artificial silk to which we have just referred, must
not be confused with the lustrous material known as
mercerised cotton, so called after the discoverer of the
process, John Mercer. Cotton, in its natural state, consists
of flat, twisted fibres, but when these fibres, tightly
stretched, are immersed in a solution of caustic soda or
soda lye, the fibres swell up, become untwisted, and assume
a nearly straight, rod-like form. The surface of these
fibres is covered with a number of smooth ridges which,
reflecting the light falling on them at different angles, give
rise to a lustrous appearance or sheen.
To one more application of cellulose, familiar to all, a
brief reference must be made. In 1869 it was found that
if camphor is added to a mixture of nitro-cotton and
alcohol, a hard, horn-like material is obtained, which can
readily be fashioned, while hot, into articles of various
shapes and form. This material has received the name of
xylonite or celluloid, the trade-mark name by which it is
registered in the United States, the country in which it
is chiefly manufactured. Although naturally of a clear
gelatin-like appearance, celluloid can easily be dyed of
various colours, can be rendered opaque by the addition of
different substances, and can, by special treatment, be
made to imitate not only such materials as bone and ivory,
but also tortoise-shell, marble, and agate. Light in
weight and not readily breakable, celluloid is used in
imitating amber, and for the manufacture of photographic
films, combs, knife-handles, soap-boxes, and other articles
of common use too numerous to mention. But it is a
material the use of which is not altogether free from danger.
86 CHEMISTRY IN THE SERVICE OF MAN
The basis of celluloid, we must remember, is a form of gun-
cotton, and although the more violent activities of the
latter are considerably subdued by the camphor and other
substances with which it is mixed, the material is, never-
theless, very readily inflammable and has, in consequence,
given rise to many disastrous conflagrations. To start the
combustion of the celluloid, it is not necessary to bring it
into contact with a naked flame. Contact for a short time
with an incandescent electric light bulb may be sufficient to
start the combustion, and fires have even been caused by
the accidental focussing of the sun's rays on articles of
celluloid exhibited in shop windows.
Although the dangerous inflammability of celluloid can
be reduced by the addition of various salts, dextrin, and
similar substances, the discovery of a material having the
many good qualities of celluloid, but free from the dangers
attending its ready inflammability, is clearly one of great
importance. The acetate of cellulose, known commercially
as cellite, when mixed with camphor or suitable substitutes,
yields a material called cellon or sicoid (as it is called in
France), which resembles, and is even superior to, celluloid
in its general properties, and is not inflammable. It is
more elastic than celluloid and is used as a substitute for
guttapercha, vulcanite, etc. It is used for making the
bristles of hair brushes, for the production of the imitation
horse-hair of which ladies' hats are frequently made, and for
the manufacture of cinematograph films. In the form
of a thick viscous solution it is employed as a flexible
varnish for wood, paper, and metal, for enamelling
aeroplanes, and as an insulating covering for electrical
conductors.
CELLULOSE AND CELLULOSE PRODUCTS Zj
But we have not yet exhausted the uses to which the
most valuable substance cellulose can be put through the
ingenuity of the chemist. If instead of mixing the nitro-
cellulose with camphor so as to produce celluloid, it is
mixed with a drying oil, like linseed oil, and with colouring
matters, and is then spread on a fabric, a sort of
" oil-cloth " is obtained ; and on passing this between
suitably cut rollers, the material is grained and a very
good imitation leather is produced. Such imitation
leathers, like Rexine for example, are now very largely
used for the upholstering of furniture and for other
purposes.
When cellulose is heated under pressure with dilute
acid, it is decomposed by the water, or hydrolysed as it is
said, with production of the sugar, glucose ; and in recent
years this process has found successful industrial application
in the production of alcohol from saw-dust and other wood-
waste. The wood-waste, moistened with dilute sulphuric
acid, is placed in a closed digester, and steam is passed in
until the pressure rises to 6 or 7 atmospheres. The cellulose
is rapidly hydrolysed, and the glucose formed passes into
solution. The sugar solution so obtained, after removal of
the acid, is subjected to fermentation (see Chap. XIIL),
and alcohol is formed. The production of alcohol from
wood is already being carried out, on a limited scale, in
America, where enormous quantities of wood-waste are
available ; and in view of the vast economic value of
alcohol, the process promises to become of increasing
importance in the future.
CHAPTER VI
VELOCITY OF REACTIONS AND CATALYSIS
The overthrow of the phlogiston theory by Lavoisier
towards the end of the eighteenth, and the enunciation of
the atomic theory by Dalton early in the nineteenth century,
mark the beginning of a new era in chemical science, when
the activities of chemists were directed in an increasing
degree to the preparation and quantitative determination of
the composition of new substances and naturally occurring
materials, as well also as to the determination of the atomic
weights of the elements. Moreover, the study of the
compounds of carbon, a branch of science to which the name
of Organic Chemistry is applied, began to be developed
with an ever-increasing energy ; and in this domain, the
problems connected with the constitution of the molecule,
that is, with the arrangement of the atoms within the
molecule, were so important for the proper understanding of
the enormous array of substances which chemists were able
to prepare, that such questions exercised, and very properly
exercised, a powerful fascination over the workers in that
branch of chemistry. The quite wonderful results which
were thereby obtained had their value, also, not merely in
the domain of theoretical chemistry, but led to some of the
most brilliant achievements of practical chemical science —
to the preparation of dyes, drugs, perfumes, and many
VELOCITY OF REACTIONS AND CATALYSIS 89
other materials of the greatest industrial and, one may say,
human value — so that one need not hesitate to regard such
work as amongst the most important in the whole history
of the science. By the workers who achieved such splendid
successes, chemical reactions were regarded entirely or
mainly from the materialistic point of view, from the point
of view of the substances undergoing change and of the
substances produced by the change. But there is clearly
another aspect of the subject which demands attention.
Just as we have already recognised that substances are
carriers of energy, and that a chemical reaction or chemical
change is a mode of transforming chemical energy into
other forms of energy, so also in modern chemistry, one is
concerned not merely with the material /r^^«f/j of chemical
change, but also with the process of chemical change itself.
Why does a chemical reaction take place, and what are
the laws governing the rate at which and the extent to
which a chemical reaction proceeds .'' These are the ques-
tions which chemical dynamics, one of the most important
branches of modern chemistry, seeks to answer.
Although it is not possible to discuss the subject fully
here, the attempt must be made to give some indication of
the more general principles in order that we may gain a
better appreciation of present-day chemistry and a more
intelligent understanding of some of the most recent
and economically most important industrial processes, the
development and success of which depend on dynamical
investigations.
When, in the thirteenth century, the great Dominican
monk and Bishop of Regensburg, Albertus Magnus —
viagnus in magia naturally malor in phllosophla, viaximus in
90 CHEMISTRY IN THE SERVICE OF MAN
theologia — used the word " affinitas," he merely summed up
the views current at that time, that chemical reaction is due
to a similarity or kinship between the reacting substances.
But although this term affinity or chemical affinity is still in
use, it must now be regarded not as signifying any natural
resemblance or family relationship, but rather as a force, of
the nature of which we have as yet no certain knowledge,
which acts between different kinds of matter and which,
under certain conditions, brings about a chemical action
between them. The existence of this force is postulated in
order to account for the fact that chemical change or
reaction will take place between substances when thereby
potential energy can be converted into work.
one of the most important factors in the process of
chemical change is the speed with which it takes place,
the velocity of the reaction. That there is a great varia-
tion in the rate at which chemical change takes place is
so obvious as almost to render its emphasis unnecessary.
The rusting of iron, the oxidation of aluminium, the
burning of wood, the explosion of gun-cotton, are chemical
changes which take place with markedly different
velocities. This great difference in the rate of reaction we
shall be inclined to attribute to differences in the chemical
affinity, and in so doing we shall be right, but only partly
right ; for when one studies the process of chemical change
more fully, it is found that the rate of a reaction does not
depend merely on chemical affinity, but also on a number
of other factors. Of these factors, one of the most im-
portant is the concentration of the reacting substances, that
is, the amount of the substances in a given volume. We
shall be able to understand this more readily, if we fix
VELOCITY OF REACTIONS AND CATALYSIS 91
our attention, for the present, on reactions between gaseous
substances. When a substance is in the state of a gas, its
molecules are supposed, according to the kinetic theory of
matter, to be moving about with great velocity in all
directions, and combination or reaction between two
substances, A and B, can take place only when molecules
of A and B collide or come within each other's sphere of
influence. If, then, we have a certain number of mole-
cules of the substance A and a certain number of molecules
of B moving about in a given space, an A molecule will
collide with a B molecule a certain number of times per
second, and the rate of reaction, therefore, will have a
certain value. But suppose that the number of B mole-
cules is now doubled. It is clear that in the same unit of
time, an A molecule will now have double the number of
chances of colliding with a B molecule and of entering into
reaction with it, and the rate of reaction will therefore be
doubled. Similarly, if we double not only the concen-
tration of the B molecules, but also that of the A mole-
cules, then it is clear that the rate of reaction will again be
doubled ; that is, the reaction now takes place four times
as fast as it would have done with the original concen-
trations of the two substances. The speed of a reaction, in
fact, is proportional to the product of concentrations of the
reacting substances. This law of the dependence of
the speed of a chemical change on the concentrations of
the reacting substances, was discovered by two Norwegian
scientists, Guldberg and Waage, and is generally known as
the law of mass action.
But the velocity of chemical change is also very greatly
influenced by the temperature, a fact to which we have
92 CHEMISTRY IN THE SERVICE OF MAN
already alluded in Chapter II. Although the speed of
different reactions is affected in a different degree by
temperature, we can take it as a convenient approxima-
tion that the speed of a reaction is doubled by raising the
temperature i8° F. A simple calculation will show what
the magnitude of this effect may be. Suppose that a reaction
requires one second for its completion at the freezing-point
of water, that is .at 32° F. At 212" F., the boiling-point
of water, the same change would take place in about one-
thousandth of a second ; and if we raise the temperature
but a little more, say to 400**, the time required for the
change will now be only about one-millionth of a second.
on the other hand, a change which would require one
second to take place at 400", would need, at 32°, a period
of a million seconds, that is, about eleven and a half days.
This influence of temperature is of the greatest importance,
and on its recognition may depend the success of an
industrial process.
But there is another important result which has followed
from the dynamical study of chemical reactions, the re-
cognition, namely, of the fact that chemical changes are
reversible, and that the direction in which reaction between
different substances takes place depends not merely on
chemical affinity but on the relative concentrations of the
different substances. When steam (oxide of hydrogen) is
passed over heated iron, oxide of iron and hydrogen are
produced. on the other hand, when hydrogen is passed
over heated oxide of iron, steam (oxide of hydrogen) and
metallic iron are formed.
Iron Iron oxide
Oxide of hydrogen Hydrogen
VELOCITY OF REACTIONS AND CATALYSIS 93
In the former case, the steam is present in large abundance
whereas the hydrogen which is formed is swept away and
cannot, therefore, react with the oxide of iron. In the
latter case, the hydrogen is present in abundance, while
the water vapour is carried away in the stream of gas and
so is prevented from reacting with the metallic iron. By
altering the relative concentrations of the steam and the
hydrogen, therefore, we can cause reaction to take place in
whichever direction we please. But let us now arrange
matters so as to prevent the removal of the hydrogen or of
the steam, by heating the substances together in a closed
vessel, then we shall find that both reactions will take
place ; steam will react with iron, and hydrogen will react
with oxide of iron, so that finally a state of balance or
equilibrium will be produced, at which there will be a
certain definite relationship between the concentration
of the steam and the concentration of the hydrogen.
So long as the temperature is kept constant, the same
state of balance or equilibrium will be reached, no matter
what may be the initial amounts of hydrogen and of steam,
but if the temperature is altered, the state of equilibrium
will also be altered. By raising or lowering the temperature
the one or the other reaction can be caused to take place
to a greater and greater extent, and the direction in which
the equilibrium is thereby altered is found to be intimately
associated with the heat effects which accompany the
chemical change.*
' The law which is found to obtain here can be stated in a simple form. It
will be clear that if one reaction is accompanied by an evolution of heat, then
the reverse reaction must be accom-panied by an absorption of heat. IVhen
the temperature is raised, the latter reaction, the reaction accompanied by absorp^
ttJH of heat, u favoured, whereas lowering the temperature favours the reaction
94 CHEMISTRY IN THE SERVICE OF MAN
The discovery of the laws of chemical change, and the
recognition that, theoretically at least, all reactions are
reversible, mark one of the most important advances in our
knowledge of chemical processes and of the action of
chemical affinity. Some of the consequences which flow
from this will be discussed in the sequel.
Although, as we have said, the progress of a chemical
reaction and the rate at which a chemical change proceeds,
are influenced both by the concentration of the substances
and by the temperature, it is found that the velocity of a
chemical reaction may also be profoundly affected in
another way which, on account of its very great importance
both in the laboratory and in the factory, demands a fuller
consideration.
In the early decades of last century, a number of
phenomena were observed which, although isolated and
apparently unconnected, all possessed one common
characteristic, namely that of a reaction the speed of which
was markedly increased by the addition of certain sub-
stances in minute, sometimes in almost infinitely minute
amount. Owing to such additions, it was found, substances
which seemed, under the particular conditions, to be with-
out action on each other, reacted with appreciable, some-
times even with great readiness. From the magnitude of
the result produced, it was evident that the foreign sub-
stance could not enter into the reaction in the ordinary
way ; but, as the Swedish chemist, Berzelius, pointed out,
the substance which was added appeared to act merely by
which takts plact with tvolution of heat. Ooly when no beat effect accompanies
chemical change is the equilibrium unaffected by change of temperature.
VELOCITY OF REACTIONS AND CATALYSIS 95
its presence and by " arousing the slumbering affinities of
the substances," and so allowing them to react. How
these slumbering affinities were aroused, Berzelius did
not hazard a guess, but in order to give a name under
which such phenomena could be classed, he introduced the
term " catalysis " (a word which signifies a loosening) ; and
a substance which brings about catalysis is called a
" catalytic agent " or a " catalyst." For long the pheno-
menon of catalysis, of which the number of cases observed
rapidly increased during the nineteenth century, was re-
garded by chemists as Gulliver was regarded by the learned
men of Brobdingnag, as a lusus natures ; it was relegated
to the realm of the mysterious, and chemists became only
too prone to think that the label of catalysis was at the
same time an explanation of the phenomenon. It was,
indeed, only towards the end of last century and owing
to the development of the experimental methods of measur-
ing the rate of chemical change, that the phenomenon of
catalysis and the behaviour of catalysts began to form the
subject of systematic investigation. During the past thirty
years, the energy of many workers has been directed along
this line of investigation, and much valuable information
has been accumulated regarding the main characteristics of
catalysis and the behaviour of different catalysts. With
some of these we must now become acquainted.
As we have already indicated, one of the most striking
features of catalysis is the magnitude of the effect pro-
duced, compared with the small amount of the substance
producing it. An excellent illustration of this is seen
in the influence which moisture exercises on the rate of
combination of gaseous substances. When hydrogen and
96 CHEMISTRY IN THE SERVICE OF MAN
oxygen, the two gaseous substances by whose combina-
tion water is formed, are heated together, they combine,
and if the temperature is sufficiently high, say about
1 1 00° F., the combination takes place with explosive
violence. But this occurs only when a trace of moisture
is present in the gases. If the last traces of moisture
are removed from the gases by allowing them to remain
for more than a week in contact with the substance
known as phosphorus pentoxide (obtained by burning
phosphorus in air), which combines with the greatest
avidity with water, the mixture of hydrogen and oxygen
can then be heated even to a temperature of nearly
1800° F. without explosion occurring. Not only in the
case of hydrogen and oxygen, but in the case also
of many other gases, combination is found to depend on
the presence of moisture, of which, however, the merest
trace suffices.
This action of moisture, and, indeed, the action of
catalysts generally, has been likened to the action of
oil in the bearings of a machine ; a catalyst diminishes, as
it were, the hindrances to change of whatever nature these
may be without itself being used up in the process.
No less interesting or important is the extraordinary
influence exerted by many solid substances on the rate
at which combination between gases takes place. Thus,
if we again consider the case of hydrogen and oxygen, it
is found that although combination of the two gases takes
place at high temperatures with great and explosive
velocity, at the ordinary temperature no trace of com-
bination can be detected. In fact, from the influence
which temperature has been found to exercise on the
VELOCITY OF REACTIONS AND CATALYSIS 97
rate of combination, it has been estimated that no appre-
ciable amount of combination would occur at the ordinary
temperature even in a period of a billion years. But if
a little metallic platinum be brought into contact with
the mixture of the two gases, combination proceeds with
appreciable velocity ; indeed, if the platinum is used in a
finely divided form, known as platinum sponge or platinum
black, the rate of combination may be so great that an
explosion results. This action of platinum, one of the
first cases of catalytic action to be observed, brings out
very clearly two of the main characteristics of the pheno-
menon, namely, the great change produced in the speed
of the reaction, and the fact that the catalyst remains
unchanged in amount. The same piece of platinum can
be used to bring about the combination of unlimited
quantities of hydrogen and oxygen.
This remarkable behaviour of finely divided platinum
which greatly impressed, as well it might, the minds of
the early observers, was not long in receiving a practical
application. In 1823 it was observed by Dobereiner that
if a jet of hydrogen was allowed to impinge on a piece
of spongy platinum exposed to the air, the heat of com-
bustion of the hydrogen raised the platinum to incan-
descence, and the hydrogen became ignited. Dobereiner
constructed an apparatus in which hydrogen was produced
by the action of sulphuric acid on zinc ; and when a tap
was opened the gas escaped in a fine jet which impinged
on a piece of spongy platinum. In this way fire could
be obtained, and, as a matter of fact, this Dobereiner
lamp was largely used for that purpose before the days
of matches.
H
98 CHEMISTRY IN THE SERVICE OF MAN
Although platinum is by no means an universal catalyst
for all reactions — no such universal catalyst is known — it
has nevertheless been found that platinum acts very
generally as a catalytic accelerator of oxidation reactions,
or reactions in which gaseous oxygen takes part. Oxide
of cerium, which forms a small part of the Welsbach
incandescent gas mantle, also acts as a catalyst and
accelerates the combustion of the coal-gas.
The attempt made in recent years to apply spongy
platinum for the purpose of automatically lighting a jet
of coal-gas did not meet with success, by reason of the
fact that after a time the platinum was found to lose its
effectiveness. This destruction of the catalytic activity,
this "poisoning" of the catalyst, as it has been called,
is a phenomenon of the greatest importance, the recog-
nition of which has been, as we shall learn more fully
presently, not only of purely scientific interest, but also of
the greatest industrial importance.
The acceleration of the combustion of hydrogen by
platinum can be regarded as a particular case of " surface
action," the reacting gases, hydrogen and oxygen, being
"condensed" on the surface of the platinum and so brought
into more intimate contact. But all solids, and not merely
platinum, exhibit this surface action and accelerate the
combustion of gases at temperatures below their ignition
point, although with an efficiency which varies greatly with
the nature of the substance and the fineness of its sub-
division. The difference between the catalytic activity of
the different substances tends, however, to disappear as the
temperature is raised, and when the solid substances are
raised to incandescence they are all found to possess the
VELOCITY OF REACTIONS AND CATALYSIS 99
property of accelerating gaseous combustion in about
the same degree. This fact has recently received, in
this country and in America, important applications in
the process known as " surface combustion."
If a mixture of, say, coal-gas and air is forced through
the walls of a porous tube of fire-resisting material, and
the issuing gas is ignited, combustion takes place, without
flame, in the surface layers of the tube which is soon raised
to incandescence and becomes a
powerful radiator of heat ; or, one
may pass the gas mixture through a
mass of small granules of refractory
material — fireclay, alundum (oxide of
aluminium), etc. — forming for ex-
ample the hearth of the furnace, and
so obtain "surface combustion" on
each granule (Fig. 8), By these
means the efficiency of gaseous
heating, either for industrial or for
domestic purposes, can be greatly
increased.
We have already seen (p. 19) that when a burning
gas is cooled to below its ignition temperature, it is
extinguished. And so, when using a gas flame to heat
a cold object, the flame in contact with the object to be
heated is extinguished, and heating takes place only by
radiation from the hot gas. By means of " surface com-
bustion," however, the whole of the combustible gas can be
burned and its heat value therefore completely utilised,
while the radiation from the incandescent solid surface is
greatly superior to that from the gas. With the increased
Fig. 8.— Surface Com-
bustion Gas Cookbr
The gas, passing op
through the narrow chan-
nels in the body of the
cooker, burns on the sur-
face of the granules of
refractory material, which
are thereby raised to in-
candescence and radiate
heat.
100 CHEMISTRY IN THE SERVICE OF MAN
use of gas for heating purposes, the surface combustion
process promises, therefore, to be of the highest importance
in increasing the efficiency and diminishing the cost of
heating.
By chemists the importance of catalysis is now fully
recognised, and the systematic search for the most suit-
able and effective catalyst for a given reaction, is a well-
established part of chemical investigation. But it is part of
the romance of science that discoveries of value are made
not only as the result of consciously directed effort, but
also by the aid of "that power which erring men call
Chance." And in this connection the following tale may
be re-told, for it illustrates not only the special action of a
catalyst, but also the important rdle which catalysis may
play in industry.
For the preparation of a certain dye — it was a dye
called sky-blue alizarin, but the name does not matter —
the necessary ingredients were heated for some time in a
vessel made of iron. But in the course of time fresh
apparatus had to be installed ; and with this apparatus no
sky-blue alizarin was obtained, but something entirely
different. What could be the reason of the failure ? The
process was carried out in the same way as before, and the
workmen were the same, or were under the same direction.
The apparatus, certainly, was new, but it was exactly the
same as the old apparatus. And yet, no ; it was not
exactly the same. The new apparatus, instead of being
entirely of iron, had a copper lid. But surely that could
not be the cause of the different behaviour. Yet so it was,
for the small trace of copper derived from the lid exerted,
it was found, a powerful catalytic influence on the course of
VELOCITY OF REACTIONS AND CATALYSIS loi
the reaction, and instead of the substances reacting so as to
form sky-blue alizarin, a further reaction took place which
gave rise to a totally different substance.
It might perhaps seem as if the tracing of the trouble
to its source would finish the story, but this is by no
means the case. Accident had thrown a catalyst for a
new reaction in the way of the chemist, who, by careful
investigation, found that a trace of copper enabled the
ingredients used, as well as a number of other similar
substances, to react in a particular manner, and in this
way a nezv and important series of dyes was discovered. It
all seems very simple ; all a matter of " happy accident."
But was it by a happy accident that the cause of the
trouble in the first instance was discovered ? Or was it a
happy accident that converted a source of trouble in one
process into a source of gain in another ? How would the
matter have stood without the trained intelligence of the
chemist with his knowledge of the importance of little
things, with his trained faculty of observation and his
ability to make use of the facts which he observed }
In astronomy one deals with magnitudes so vast as to
be beyond the grasp of our minds ; in the domain of
catalysis the magnitudes are, in some cases, so small that
it becomes almost equally impossible to form a true con-
ception of them. But in order that the reader may have
some knowledge of the very minute amounts of substance
which will yet suffice to affect appreciably the speed of a
reaction, let me give one example out of the many which
might be chosen. When one dissolves sulphite of soda in
water, the oxygen of the air slowly oxidises the sulphite
of soda to sulphate of soda. By the addition of certain
102 CHEMISTRY IN THE SERVICE OF MAN
catalysts, the speed with which this process takes place can
be greatly increased, and in this connection copper has
been found to be very efficient. In fact, if only one grain
of blue-stone or copper sulphate is dissolved in 1,400,000
gallons of water, or one grain in about 250,000 cubic feet
of water, the presence of the copper can be detected by its
action in accelerating the oxidation of the sulphite of soda !
But we are so accustomed to judge of the importance of d
thing by the amount of space it occupies, that in asking
the reader to recognise the infinite importance of the
infinitely small, and to accept the illustration I have
given, sober fact of science as it is, I am almost afraid
that I shall be considered as putting too great a strain
on his credulity.
But, indeed, we need not go far in order to have im-
pressed upon us the importance of these catalytic actions.
The human organism itself is like a laboratory in which
numerous reactions and marvellous transformations take
place unceasingly ; the transformation of the food con-
sumed into the bone, and flesh, and blood of the body,
and the slow combustion of the tissues to yield the energy
and heat necessary for vital activity. And so it is also
with the vegetable organism in which we have the building
up or synthesis^ not only of the complex materials which
serve as foodstuffs for the animal creation, but also of those
sweet-smelling essences and the compounds which give to
flowers their varied odours and colours. Many of these
substances, the products of Nature's laboratory, can also be
made in the laboratory of the chemist, and their synthesis
from simple inorganic materials constitutes the crowning
achievement of chemical science. But how different are
VELOCITY OF REACTIONS AND CATALYSIS 103
the methods of the chemist from those of Nature. In his
laboratory the chemist makes use of high temperatures and
the action of powerful and corrosive reagents ; but in the
laboratory of Nature, the building up of even the most
complex compounds takes place quietly and smoothly at
the ordinary temperature. All this the animal or vegetable
organism accomplishes by utilising appropriate catalysts,
accelerators of reactions, the so-called enzymes, which are
themselves produced within the living cell of the plant or
animal. The ptyalin of the saliva, the pepsin of the gastric
juice, the trypsin of the pancreas, the diastase of the sprout-
ing barley-corn, the zymase of the yeast, which has from
time immemorial been used by man for the conversion
of sugars into alcohol — these are some of the numerous
catalytic agents which Nature produces and of which she
makes use in her marvellous achievements in chemical
synthesis.
But substances exist which can destroy the efficiency
of these catalysts, and thereby retard the life processes in
the plant or animal. These substances we call poisons.
And it is a noteworthy fact that this behaviour, so
familiar in the case of living organisms, has its analogy,
as has been pointed out, in the case of non-living
catalysts. The recognition of this fact has proved to be
of the greatest importance in the application of catalysis
to industrial processes.
In the manufacturing industries it may truly be said
that time is money ; and to produce an article of manu-
facture at a more rapid rate is the same as saving time.
And this is just exactly what a catalyst enables one to do.
It is, therefore, not surprising that in almost all branches
104 CHEMISTRY IN THE SERVICE OF MAN
of chemical industry the value of catalysts has become
increasingly recognised. By their introduction, new
industries of the highest importance have been established,
and older industries have been revolutionised ; and at
the conclusion of this chapter we may appropriately
devote a little space to the discussion of some of the
more important cases in which catalysis has found an
application in industrial chemistry. In succeeding chapters
other applications of catalysis will be met with.
Manufacture of Sulphuric Acid.
Sulphuric acid, or oil of vitriol, the discovery of which
dates from the fifteenth century, is one of the most
important substances in our modern civilisation. Not
only is it used in the older process of manufacture of
soda and of hydrochloric acid, but also in the production
of nitric acid and of explosives, in the manufacture of dyes,
fertilisers, glucose, and alum, and in most chemical and
metallurgical industries. Owing to the great development
last century of the soap and cotton industries, with their
great demand for soda and bleaching powder, England
became the chief producer of sulphuric acid, and supplied
most of the world with this indispensable chemical. But
this has now been changed. Owing to the march of
science and the development of chemical industries in other
countries, the position has completely altered, and Great
Britain now ranks only third in the list of producers of
sulphuric acid, the total annual consumption of which
throughout the world amounts to about 5,000,000 tons.
The reaction on which the production of sulphuric acid
VELOCITY OF REACTIONS AND CATALYSIS 105
depends is the oxidation of the gas sulphur dioxide to
form the compound sulphur trioxide, which combines
readily with water to give the compound known as
sulphuric acid. The difficulty is, however, met with that
combination between sulphur dioxide and oxygen does
not take place appreciably at the ordinary temperature ;
and when one seeks to hasten on the combination by
raising the temperature, another difficulty is encountered.
As the temperature is raised the rate at which the sulphur
dioxide and the oxygen combine certainly increases, as we
have already learned to be universally the case, but as the
temperature rises the extent to which combination takes
place becomes less and less, by reason of the fact that at
high temperatures the sulphur trioxide decomposes again
into sulphur dioxide and oxygen. The result, therefore, is
that at a temperature at which the combination of sulphur
dioxide and oxygen would take place sufficiently rapidly,
the amount of sulphur trioxide formed is too small to
allow of the process being commercially successful. We
now know, however, the direction in which to look for a way
out of the difficulty. We must find a catalyst which will
so accelerate the rate of oxidation of the sulphur dioxide
that the process may be carried out with sufficient rapidity
at a temperature so low that the decomposition of the
sulphur trioxide is negligible. Such a catalyst was found
at an early date in the oxides of nitrogen, and since the
year 1746 the manufacture of sulphuric acid has been
carried on in this country by a process depending on the
use of these oxides. This method of manufacturing
sulphuric acid consists, essentially, in passing sulphur
dioxide, obtained by burning sulphur, or by heating iron
io6 CHEMISTRY IN THE SERVICE OF MAN
pyrites (sulphide of iron) or the spent oxide of iron from
gas-works, etc., together with air, oxides of nitrogen, and
steam, into a series of large leaden chambers. Here the
sulphur dioxide combines with the oxygen of the air
under the catalytic influence of the oxides of nitrogen,
and the sulphur trioxide formed combines with the steam
to form sulphuric acid. The acid produced in this " leaden
chamber process," as it is called, is a rather impure aqueous
solution of sulphuric acid (known as brown oil of vitriol),
and must be subjected to processes of purification and
concentration before the pure acid is obtained.
At the beginning of the present century, however, a
revolution began to take place in the process of manu-
facture. This was due mainly to the successful develop-
ment of the process of manufacture of synthetic indigo,
which necessitated the use of the very powerful reagent
obtained by the addition of sulphur trioxide to pure
sulphuric acid, and known as fuming sulphuric acid.
It had been observed as far back as the year 183 1 by
a vinegar manufacturer of Bristol, Peregrine Phillips by
name, that the oxidation of sulphur dioxide by oxygen is
greatly accelerated by the presence of platinum, just as
we have seen that this metal also accelerates the combina-
tion of hydrogen and oxygen ; and this observation gave
rise to many hopes of an improved method of manu-
facturing sulphuric acid. Even in 1835 a well-known
French chemist, Clement-Desormes, gave ｅxpression to
the conviction that in ten years at most it would be
possible to manufacture sulphuric acid directly from its
constituents, without the use of leaden chambers and
nitric acid. But the unwisdom of prophecy is proverbial,
VELOCITY OF REACTIONS AND CATALYSIS 107
and the period of ten years lengthened out to one of
nearly seventy, before the ability and persistence of the
technical chemists in one of Germany's greatest chemical
works succeeded in developing the discovery of Peregrine
Phillips into a successful industrial process.
When the attempt was made to utilise the "contact
process," as it is called, for the commercial production of
sulphuric acid, a difficulty was met with which delayed
success and threatened complete failure. The production
of sulphur trioxide which at first took place with great
readiness soon began to diminish, and after some time
ceased altogether. The platinum lost its catalytic activity.
on investigation, this loss of activity was found to be due
to a "poisoning" of the platinum— a phenomenon to
which we have already referred — and the substance which
was found to be chiefly responsible for this was arsenic.
This arsenic was derived from a small amount of impurity
contained in the iron pyrites, a naturally occurring sulphide
of iron used as the source of the sulphur dioxide, and it
was only after much labour that a means was found of
ridding the gas of all traces of this poison. When this had
been done, the contact process could be carried out with
success.
For the production of sulphuric acid by the contact
process, the enormous leaden chambers, with a capacity
sometimes of i5o,cxxD cubic feet, are replaced by com-
paratively small, cylindrical vessels containing a number of
tubes filled with platinised asbestos * ; that is, asbestos
on which finely divided platinum has been deposited.
Through these tubes, which are maintained at the proper
^ Oxide of iron can also be used as a catalyst.
lo8 CHEMISTRY IN THE SERVICE OF MAN
temperature by the heat given out in the reaction, the
mixture of sulphur dioxide and oxygen (or air) is passed.
The oxidation of the sulphur dioxide takes place rapidly
and practically completely, and the sulphur trioxide issues
from the apparatus as a white mist, which is then passed
into a solution of sulphuric acid containing about 98 per
cent, of acid. In this way a pure sulphuric acid, as well
also as the powerful fuming sulphuric acid to which we
have referred, can readily be obtained.
Whether the contact process will eventually succeed in
entirely superseding the older leaden-chamber process, it is
impossible to say ; for, under the stimulus of competition,
improvements have been effected in the latter process
which will in any case retard, if they do not altogether
prevent, its complete disappearance.
Hardening of Fats.
Another industry of recent but rapidly increasing
growth, which depends on the application of catalysis, is
that of the conversion of liquid oils into solid fats ; a
process generally, if erroneously, referred to as the harden-
ing of fats.
It has already been pointed out (p. 33), that the animal
and vegetable fats and oils are, essentially, compounds of
glycerine with acids, such as palmitic, stearic, and oleic
acids. The glycerine compounds of the saturated palmitic
and stearic acids (p. 33), are solid, and constitute the main
portion of the hard fat, beef suet The glycerine compound
of the unsaturated oleic acid is, however, a liquid, and is
VELOCITY OF REACTIONS AND CATALYSIS 109
the chief constituent of olive oil ; and the other natural
animal and vegetable oils are also mainly compounds of
glycerine with unsaturated acids. For these different fats
and oils there are, at the present day, two main uses ;
namely, as foodstufifs, to supply the body with the neces-
sary amounts of carbonaceous matter, and for the purpose
of making soap. So far as foodstuffs are concerned,
butter, or the fat of milk, constitutes a large part of the
fatty material consumed. Owing, however, to the increase
of population and to the rising price of butter, the problem
of obtaining some substitute for this very important
article of food became of increasing importance. The
solution of the problem we owe to French ingenuity, and
the industrial production of butter substitutes, e.g. marga-
rine, which dates from 1870, has now attained to very great
dimensions, Beef-fat or hog's lard, after being melted and
clarified, is separated from the oil which it contains, and
mixed in churning machines with various vegetable oils,
such as cotton-seed oil, soya-bean oil, cocoa-nut oil, palm-
kernel oil, and also with milk, and in this way a material
is obtained which can be used as an efficient substitute for
butter. But since these butter substitutes are derived
mainly from animal fats, the supply of solid fats necessary
for the manufacture of soap has been seriously diminished ;
and it became, therefore, a matter of great importance to
discover a method by means of which liquid oils could be
converted into solid fats. Theoretically, the process is a
simple one. Oleic acid, for example, differs from stearic
acid only in the fact that it contains less hydrogen. It is
what we have called an unsaturated compound, and if we
add the proper amount of hydrogen to the oleic acid, we
no CHEMISTRY IN THE SERVICE OF MAN
shall convert it into the solid stearic acid ; or, on the other
hand, if we add the hydrogen to the liquid glycerine oleate
we shall convert it into the solid fat glycerine stearate ; and
similarly with the other unsaturated compounds present in
other oils. Although it was not difficult to carry out such
a conversion in the laboratory, no commercially successful
process was discovered until it was found that finely
divided nickel acts as an efficient catalyst In the presence
of this metal, the liquid oils, olive oil, linseed oil, fish oil,
etc., combine readily with gaseous hydrogen and become
converted into solid fats suitable for use in the manufacture
of soap.
Not only does the introduction of this process offer to
the soap boiler a fresh source of the material which he
requires, but it also permits of the profitable employ-
ment of substances for which formerly comparatively
little use could be found. Thus, for example, whale
oil, which on account of its unprepossessing taste
and smell found formerly but little application, is now
converted in large amount, by the above process, into
a solid, odourless material suitable for the making of
soap.
This recent discovery of chemical science, which is
chiefly worked in England by the firm of Messrs. Crosfield
and Son, promises to be one of far-reaching importance.
Not only does it secure a fresh source of raw material for
the manufacture of an article of such importance in our
modern civilisation as is soap, and thereby prevent a rapid
rise in the cost of its production, but by stimulating the
cultivation of oil-producing plants, it will exercise a pro-
found influence on the economic development of those
VELOCITY OF REACTIONS AND CATALYSIS 1 1 1
countries which are suitable for such cultivation. Of the
importance in the service of man of this modern industrial
process, founded as so many industrial processes are on
investigations of apparently purely scientific interest, it is
impossible to form an estimate.
CHAPTER VII
FIXATION OF ATMOSPHERIC NITROGEN
Of all the chemical elements of which our text-books
describe the properties, none, perhaps, was, until a few
years ago, so uninteresting as nitrogen. From the time
of its discovery by the botanist Rutherford in 1772, down
almost to the present day, scarcely a property or character
of a positive nature was ascribed to the element Its
properties were negative properties, and were described
in negative terms. Useless when alone, it stubbornly
resisted almost all attempts to make it associate with its
fellow-elements ; and it played, at best, the rdle — again
negative in character — of acting as a drag on the too
vigorous activity of the atmospheric oxygen.
That an important part in the economy of nature had,
nevertheless, been assigned to this element, was abundantly
clear from the fact that it is an essential constituent of the
most important animal and vegetable materials, a con-
stituent without which life itself is impossible. With few
exceptions, however, plants are unable to absorb and
utilise elementary nitrogen, which exists abundantly in
the air ; and they must therefore be supplied with com-
bined nitrogen in such forms as they can assimilate.
Animals are equally incapable of assimilating elementary
FIXATION OF ATMOSPHERIC NITROGEN 113
nitrogen, and are dependent on plant food for their supply
of nitrogen compounds.
Owing to the apparent impossibility of coaxing the
enormous store of elementary nitrogen contained in the
air into suitable combination with other elements, mankind
contented itself, resignedly if not complacently, with the
natural sources of supply of useful nitrogen compounds ;
and this position was all the easier to adopt as the natural
supply was sufficient for the needs of the day. In 1898,
however, Sir William Crookes, as President of the British
Association, delivered the solemn warning that the years
of plenty were quickly passing. The supply of wheat, the
staple foodstuff of Western peoples, from all the land
available for cultivation, would soon be insufficient to
provide for the needs of the growing population unless
the yield of the soil could be greatly increased by inten-
sive cultivation, which in its turn would, in a few years,
exhaust all the known sources of combined nitrogen.
Famine, therefore, stared them in the face, and there
would be no Egypt from whose granaries supplies could
be obtained.
It is unnecessary to discuss whether the warning given
by Sir William Crookes was too alarmist or not ; there
was undoubtedly need for the warning to be given. If
the produce of the wheat-bearing Idnds was to keep pace
with the increase in the population, more intensive cultiva-
tion must be resorted to, and ever-increasing quantities of
nitrogen compounds must therefore be applied to the soil.
But the world's demands for compounds of nitrogen were
rapidly increasing, not only for purposes of agriculture,
but in other directions also. For the manufacture of
I
114 CHEMISTRY IN THE SERVICE OF MAN
dynamite, gun-cotton, and other explosives, as well as for
the production of dyes, the demand for nitric acid goes on
increasing ; for the manufacture of sodium carbonate or
soda there is an ever-growing demand for ammonia ; and
so it is also with regard to the cyanides, used in con-
nection with the extraction of gold from its ores, and the
plating of metals.
But while the demand for nitrogen compounds was
increasing rapidly, the sources of supply showed no
such elasticity. The main sources of supply were the
following : —
(i) Matter of vegetable origin : Vegetable refuse,
nitrogen compounds in the humus of the soil, etc.
(2) Matter of animal origin : Animal manures, fish
meal, guano, coprolites, etc.
(3) Ammonium compounds from coal, lignite, peat,
silt.
(4) Mineral deposits : Saltpetre (from the Indian nitre
plantations), Chile saltpetre.
(5) Combined nitrogen in rocks.
(6) Absorption of free nitrogen by nodules on the roots
of leguminous plants, through the agency of bacteria.
Of the above sources of supply it may be said that
the waste animal and vegetable materials, although of
great local importance, do very little to relieve the general
situation ; the supply of fish meal is strictly limited, and
the guano deposits are nearing the point of exhaustion.
Of very considerable importance is the supply of
ammonium compounds from coal, peat, etc. The following
table gives the total amount of ammonium sulphate
obtained annually from the distillation of coal : —
FIXATION OF ATMOSPHERIC NITROGEN 115
World's Production of Ammonium Sulphate.
Tons.
1902 S43.000
igo8 852,000
1909 978,000
1910 i,iii,8oo
1911 1,181,000
The maximnm amount obtainable if all the coal mined were distilled or
coked would be 11,800,000 tons.
In coal, therefore, we have a very valuable source of
supply of combined nitrogen, a fact which adds weight
to the arguments put forward on the ground of economy
in a previous chapter, in favour of the preliminary carbo-
nisation or coking of coal, with recovery of the ammonia
as by-product. But, on the other hand, it must be
remembered that the coal supply itself is not inexhaustible,
and the recovery of ammonia from coal, therefore, while
it might postpone could not avert the danger of which
Sir William Crookes gave warning.
on the other hand, there are two very valuable sources
of ammonia which have not yet been exploited as they
might be. When peat is carbonised, the nitrogen present
can be recovered to a large extent as ammonia, and in
view of the enormous peat moors which exist in the world
(in Russia there are no fewer than 95,000,000 acres, and
in Finland, 18,500,000 acres), the reserve stock of nitrogen
is very great. It seems certain, therefore, that the process
of carbonisation of peat, with production of a power gas
and recovery of the nitrogen present, as ammonia, might
be developed in many regions as it has already been
developed in some, into a profitable industry. All attempts
made in this direction should certainly be welcomed and
encouraged.
ii6 CHEMISTRY IN THE SERVICE OF MAN
Another important source of ammonia is the blast
furnace. At the present time, over 12,000 tons of ammo-
nium sulphate are obtained from blast furnaces in Great
Britain alone ; and it seems that this amount might be
largely increased.
But by far the most important natural source of com-
bined nitrogen at the present time is found in the deposits
of sodium nitrate or Chile saltpetre, which occur in the
rainless districts of South America. These deposits have
not only been the main source of supply of the nitrogen
compounds used in agriculture, but they have also furnished
practically the whole of the material used for the manu-
facture of nitric acid and of potassium nitrate. As a con-
sequence, the demands made on these deposits have gone
on increasing, as is evident from the following table : —
Export of Chile Saltpetre.
Tons.
1830 ..... 1000
1850 25.000
1890 i,ooo,coo
1900 1,454,000
1902 1,379,000
1904 i,497,cxx)
1906 1,732,000
1908 2,052,000
1910 2,324,000
191 1 2,449,000
The valae of the annual production now amounts to over jf 24,000,000.
But the nitrate beds although enormous are not in-
exhaustible, and whether the time of exhaustion lies
distant fifty years, as some have estimated, or a hundred
and fifty years, it is obvious that the situation in 1898 was
one which might well cause grave concern. Sir William
FIXATION OF ATMOSPHERIC NITROGEN 117
Crookes, therefore, was surely only doing his duty in
calling the attention of his countrymen and of the world
to the inevitable disaster which threatened unless some
fresh means were found of obtaining combined nitrogen.
As the discovery of any considerable new supplies of
naturally occurring nitrogen compounds was scarcely to be
relied on, there was an imperative demand laid on chemists
to discover some means of forcing the inexhaustible store
of elementary nitrogen into such a state of combination
that its assimilation by plants is rendered possible. As
Sir William Crookes said : " The fixation of atmospheric
nitrogen is one of the greatest discoveries awaiting the
ingenuity of chemists." And the ingenuity of chemists,
assisted by the engineers, has proved itself equal to the
task. During the past eight or nine years not one but
several methods have been discovered by means of which
the atmospheric nitrogen can, on a large scale and in a
commercially successful manner, be forced into useful com-
bination with other elements. Indeed, so far as nitrogenous
fertilisers are concerned, the prospect of a wheat famine
has now been removed to an indefinitely remote future.
i» Direct Combination of Nitrogen and Oxygen.
Since the atmosphere consists essentially of a mixture
of nitrogen and oxygen, it is obviously most natural that
attempts should be made to bring about the combination
of these two gases. That this combination does actually
occur under suitable conditions, was shown as long ago as
1784 by Cavendish and by Priestley. Cavendish, for
example, had shown that when electric sparks are passed
ii8 CHEMISTRY IN THE SERVICE OF MAN
through air, oxides of nitrogen are formed ; and by absorb-
ing these oxides in water or in alkalies, nitric acid or
nitrates could be obtained. The possibility of obtaining
nitric acid from the air was therefore proved, and the
difficulty which faced the chemist and engineer was that
of applying the scientific fact and of developing it into a
commercially successful process. Into the history of the
attempts to overcome this difficulty, it is not possible to
enter here, and I must restrict myself to a very brief
description of the processes which are in successful
operation at the present day.
Before we enter on a discussion of these processes,
however, a few words are necessary on the theory of the
chemical reactions involved, on the recognition of which the
success of the processes depends.
In the first place one must note an important respect in
which the combustion of nitrogen, or the combination of
nitrogen with oxygen, differs from the combustion, say,
of hydrogen. When hydrogen bums, a large amount of
heat is given out, and consequently, when a mixture of
hydrogen and oxygen is ignited at any point, the tempera-
ture of the surrounding gas is raised to the ignition point
and the flame spreads throughout the whole mixture.
But in the case of nitrogen and oxygen, combination takes
place with absorption of heat — the reaction is an endo-
thermic one — and heat must therefore be continually
added to the mixture in order to allow the process of
combustion or combination to proceed. Indeed, if it were
not so, a flash of lightning would set the whole atmosphere
ablaze, and "deluge the world in a sea of nitric and
nitrous acids."
FIXATION OF ATMOSPHERIC NITROGEN 119
Further, the reaction between nitrogen and oxygen
whereby the compound nitric oxide is formed, is a re-
versible reaction (p, 92), represented by the ｅxpression —
N + O ^ NO
and at a given temperature, therefore, only a certain pro-
portion of the gases combines. But it is a general rule that
in such a case, the reaction which takes place with absorp-
tion of heat is favoured by raising the temperature ; and it
is therefore to be expected that as the temperature is raised,
the proportion of nitric oxide produced will become greater
and greater. This prediction from theory was confirmed
by experiment, as the following numbers show : —
Volumes of nitric oxide to
Temperature. loo volumes of gas.
2800° F. 0-37
2919° F. 0*42
3200° F. 0*64
4185° F. 2-05
4356° F. 223
5301" F. 5
It is clear, therefore, that in order to obtain as large a
proportion of nitric oxide as possible, it is necessary to con-
duct the reaction at as high a temperature as possible.
And this carries with it another advantage, for the higher
the temperature, the more rapidly does the combination of
oxygen and nitrogen occur ; the sooner, therefore, is the
equilibrium concentration of nitric oxide reached. This is
seen from the following figures : —
Time
required for the pro*
Temperature,
duction of equilibrium.
1832° F.
82 days
2732° F.
125 „
3812° F.
5 seconds
4533" F.
o'oi second
120 CHEMISTRY IN THE SERVICE OF MAN
But there is one important point to bear in mind.
Since the reaction is a reversible one, decomposition of
the nitric oxide will take place as the temperature is
lowered ; and just as high temperature increases the
velocity of combination, so also it will increase the
velocity of decomposition. It is, therefore, of the greatest
importance that the mixture of gases, after equilibrium
has been established at a high temperature, shall be
cooled down as rapidly as possible to a temperature at
which the velocity of decomposition is comparatively slow,
to a temperature, say, of about 2000° F.
Let us now see how these different requirements which
theory and laboratory experiments show to be necessary,
are realised in industrial practice.
The first successfully to solve the problem of the com-
bination of nitrogen and oxygen on a commercial scale,
were two Norwegians, Birkeland and Eyde. For the
production of the high temperature required, they made
use of the electric arc, the only means whereby a temper-
ature of from 5000® to 6000" F. can be satisfactorily and
economically obtained ; and the arc, produced by an
alternating current, was caused to expand out into a
circular sheet of flame by the action of a powerful electro-
magnet. The arc, expanded in this way into a sheet of
flame about two yards in diameter, is formed in a furnace
of circular shape, a section through which is shown in
Fig. 9. The flame chamber is of fire-brick, pierced by
channels through which air can be fed into the flame, and
the fire-clay is cased in iron. From the flame-chamber,
the temperature of which may rise from 5000° to 6000** F.,
the hot gases are led away through channels in the
FIXATION OF ATMOSPHERIC NITROGEN i2t
periphery of the furnace, and are cooled rapidly to a
temperature of about 1800° to 1900** F., the heat which
is given up by the gases being used in boilers for the
production of steam. When sufficiently cooled, the gases
Fig. 9.— Birkeland and Eyde Furnace.
Air, entering at I, passes as shown by the arrows to the centre of the
furnace in which the electric arc, formed at A, is spread out into a disc of
flame by means of the electro-magnet M M. The gas then passes out at E.
C C are the coils of wire through which the electric current passes in order to
actuate the electro-magnet.
are passed into chambers lined with acid-proof stone,
where time is given to the nitric oxide to combine with
the free oxygen present in the mixture of gases and
so to form a higher oxide called nitrogen peroxide, NOj.
122 CHEMISTRY IN THE SERVICE OF MAN
From the oxidation chambers, the gases pass on through
a series of absorption towers, the first of which contains
broken quartz over which a fine stream of water is allowed
to trickle. The greater portion of the nitrogen peroxide
is absorbed by the water and gives rise to nitric acid.
For the purpose of removing the last traces of the oxides
of nitrogen, the gases are caused to pass through a
second series of absorption towers, down which trickles
a solution of sodium hydroxide (caustic soda), and in
these towers sodium nitrite is produced. The nitric acid
obtained from the first series of towers is neutralised by
means of limestone (carbonate of lime), and the solution
of nitrate of lime (calcium nitrate) is concentrated by
evaporation under reduced pressure. When sufficiently
concentrated, it is pumped on to cold revolving cylinders
on which the liquid rapidly solidifies, and from which it
can then be scraped ofif in flakes. This nitrate of lime is
known as Norwegian saltpetre, or air saltpetre, and it can
be used directly, like Chile saltpetre, as a fertiliser. A
certain amount of the nitric acid is also used for making
nitrate of ammonia (ammonium nitrate), the richest of
all nitrogen fertilisers. For this purpose the ammonia,
in solution, is imported from England, converted into
ammonium nitrate by the addition of nitric acid, and
exported again in this form to England.
The sodium nitrite obtained from the second series of
absorption towers is used in large quantities, more especi-
ally in Germany, in the manufacture of dyes.
Besides the one invented by Birkeland and Eyde,
other types of furnace have also been introduced, such as
the Schonherr furnace in which a long cylindrical flame
FIXATION OF ATMOSPHERIC NITROGEN 123
is produced in a tubular furnace, and the Pauling furnace,
in which a flame of burning gas is obtained by blowing
a stream of air through an electric arc formed between
AZ_-shaped terminals.
The production of nitric acid and nitrates by the
direct combination of atmospheric nitrogen and oxygen,
is carried out mainly, though not entirely, at Notodden
and other parts of the Telemark district in Southern
Norway, where an abundant and very cheap water-power
is available. At Notodden there are two power stations
capable of supplying 60,000 h.p., but at Vemork, near the
Rjukan waterfall, some distance away, two other power-
stations, capable of supplying 250,000 h.p., have recently
beerv constructed. To ensure a constant water supply for
these two power-stations, a dam was constructed a short
distance below Lake Mos, whereby a reservoir was created
with a storage capacity of about 190 thousand million
gallons, an amount nearly equal to that retained by the
great barrage at Assouan.
With the advantages which Southern Norway pos-
sesses, it is possible to produce synthetic nitrates at a
cost considerably lower than that of Chile saltpetre. At
present the annual output is about 160,000 tons ; a large
amount, certainly, although only a small proportion of
the world's annual consumption.
2. Fixation of Nitrogen by means of Carbides.
The process of direct combination of nitrogen and
oxygen demands for its success a very cheap electric
power, and it can therefore be carried out only at a few
124 CHEMISTRY IN THE SERVICE OF MAN
places where an abundant water-power can be made avail-
able at a low cost. But other processes for the fixation
of atmospheric nitrogen have been discovered since the
beginning of the present century in which the cost of
electricity is not such an important factor, and which can
therefore be carried out with commercial success even
when the electrical power is somewhat expensive.
In one of these processes, the starting-point is the
compound calcium carbide which, as we have seen, is now
manufactured in large quantities for the production of
acetylene. When nitrogen is passed over this carbide,
suitably heated in retorts, a reaction takes place with
formation of a compound known as calcium cyanamide,
and the production at the same time of a quantity of
carbon. The dark grey coloured mixture which is thus
obtained, and which contains about 60 per cent, of calcium
cyanamide, is put on the market under the name of
nitrolim^ or lime nitrogen^ as it is called in America.
For this compound, calcium cyanamide, quite a number
of uses have been developed, but the most important is
that as a source of nitrogen in agriculture. When properly
applied to the soil, calcium cyanamide has been found to
have a fertilising value for cereals nearly equal to that of
ammonium salts. But the physical qualities of the com-
mercial nitrolim, its dustiness and dirtiness, were prejudicial
to its use, and although the former defect has been largely
removed, much of the cyanamide is used, not directly as
a fertiliser but for conversion into ammonium salts,
ammonia being readily obtained by passing superheated
steam over the cyanamide.
FIXATION OF ATMOSPHERIC NITROGEN 125
In the previous chapter I endeavoured to emphasise
how man had learnt to avail himself of the catalytic
activity of certain substances and to make them work
for him at no expense, and here, in connection with the
economic utilisation of Nature's boundless stores of
nitrogen, catalysts have again been made to play an
important part.
Just as we have seen (p. 97) that hydrogen burns
to water with great vigour, even at the ordinary tempera-
ture, in the presence of platinum, so also it was found
that when a mixture of ammonia and air (or oxygen)
is passed over platinum, the ammonia burns and forms
nitric acid. By a proper regulation of the process, it is
possible to effect the combustion of only half of the
ammonia, the other half then combining with the nitric
acid produced to form nitrate of ammonia. It is in this
direction that the manufacturers of cyanamide are
apparently now turning their attention.
It is perhaps worth while to emphasise here the
importance of this application of catalysis. Not only can
it be used as a convenient method of obtaining the
valuable fertiliser nitrate of ammonia, but it can be used
also for the purpose of obtaining nitric acid. For the
most part this acid, the indispensable necessity of which
in the manufacture of explosives has already been pointed
out, is prepared from Chile saltpetre, and it is therefore
clear that a country whose supplies of this salt might be
cut off, would, in time of war, be rendered powerless. It
was, indeed, under the stimulus of the apprehension that
such might be the fate of his country, that the German
chemist, Professor Ostwald, addressed himself to the
126 CHEMISTRY IN THE SERVICE OF MAN
successful development of the process of burning ammonia
to nitric acid, to which we have just referred. The
necessary ammonia can be obtained by the distillation
of coal, by the decomposition of calcium cyanamide, and
also, as we shall see, by the direct combination of nitrogen
and hydrogen. This synthesis of ammonia, indeed, is
perhaps the most valuable method of utilising the
atmospheric nitrogen, and to its consideration we must
now turn our attention.
3. Synthetic Production of Ammonia.
However important the processes to which we have
referred may be, and however great the contribution which
they have made towards a solution of the "nitrogen
problem," they could scarcely, on account of their greater
or less dependence on cheap electric power, furnish a
complete solution of the problem. Something more was
needed, and the announcement some years ago that the
direct combination of nitrogen and hydrogen to form
ammonia had been developed into a commercially suc-
cessful process, was recognised as of the highest significance
and importance.
The problem of successfully bringing about the direct
combination of nitrogen and hydrogen is one which has
taxed the ingenuity of chemists for many years. Inert
as the two gases are towards each other at the ordinary
temperature, it was well known that by the passage of
electric sparks through a mixture of the two gases,
ammonia was produced, but only in very minute amount.
It was, moreover, also known that when electric sparks
FIXATION OF ATMOSPHERIC NITROGEN 127
are passed through gaseous ammonia, decomposition,
almost but not quite complete, into nitrogen and hydrogen
takes place. In other words, it was known that the
reaction between nitrogen and hydrogen is a reversible
one, and leads therefore to a state of equilibrium ; but the
concentration of ammonia present was exceedingly small
and all attempts to obtain an appreciable amount of the
compound by direct combination of nitrogen and hydrogen
ended in failure. But new weapons were being forged,
the weapons of chemical dynamics, and with these the
problem was again attacked, and only within the past
few years, as the result of ably-directed and painstaking
endeavour, the problem has been solved.
Experiment has shown that when nitrogen and
hydrogen combine, the volume of the ammonia produced
is less than that of the mixed hydrogen and nitrogen ; and
therefore, according to the laws of chemical dynamics, the
relative amount of ammonia produced will be increased
by bringing the gases together under a high pressure.
Moreover, contrary to what was found to be the case in
the combination of nitrogen and oxygen (p. 118), com-
bination of nitrogen and hydrogen takes place with
evolution of heat ; and therefore (p. 93, footnote), the
formation of ammonia will be favoured by keeping the
temperature low. The following table will show how
the predictions of theory were borne out by experiment : —
Percentage amonnt ot ammonia in the equilibrium
mixture when the pressure was
I atmosphere lOQ atmospheres
O'OII I 'I
o'02i a*i
0-048 4'5
0*13 io*8
Temperattire.
1472°
F.
1292°
F,
1112°
F.
932*
F.
128 CHEMISTRY IN THE SERVICE OF MAN
In order, therefore, to attain success in the industrial
synthesis of ammonia from its elements, the rule must be
borne in mind: Maintain the gases under as high a
pressure and at as low a temperature as possible.
But here again we meet with that factor which so
sharply distinguishes success in the scientific laboratory
from success in the factory, the factor of time. At about
900*, it is true, quite an appreciable amount of ammonia
is formed by the direct combination of hydrogen and
nitrogen, but the rate at which this amount is produced
is so slow that the process would be industrially useless.
Again, therefore, the first immediate requirement is the
discovery of a suitable catalyst, and such a catalyst was
found in osmium, in uranium, in iron, and in certain other
substances, some of which previous investigators had also
employed, but without achieving success. And here
again, as in other cases to which reference has been made,
failure was due to a non-recognition of the fact that
catalysts can be "poisoned." Through the presence of
minute traces of different impurities in the nitrogen or
hydrogen, the efficiency of the catalyst can be destroyed,
and it was only by laborious and careful investigation
of the behaviour of different catalysts and of the behaviour
of other substances towards these catalysts, that success
was made possible. Nor indeed were the engineering
difficulties much less than the chemical, but they have
been overcome, and the synthetic production of ammonia
has now been added to the industries of the world.
In the manufacturing process, a mixture of nitrogen,
and hydrogen, under a pressure of 1 50-200 atmospheres, is
circulated, by means of a pump, over the catalyst contained
FIXATION OF ATMOSPHERIC NITROGEN 129
in a tube heated electrically to a temperature of about
930° F. After passing over the catalyst, the gases, which
now contain a certain proportion of ammonia, are passed
through a tube immersed in a freezing mixture, so as to
liquefy the ammonia, while the unchanged nitrogen and
hydrogen are made to circulate again over the catalyst.
The importance of this synthetic process for preparing
ammonia lies in the fact that its success is not dependent
on a cheap supply of electrical power, and that it can
therefore be carried out in countries which are unfavour-
ably situated for the production of the electricity required
in the previous methods of " fixing " the atmospheric
nitrogen. By this process one is enabled not only to
produce the nitrogenous fertiliser, sulphate of ammonia,
which is so valuable in agriculture, but, by the catalytic
oxidation of the ammonia, one can obtain nitric acid, and
the nitrates, which are so esserttial for the manufacture of
explosives. From the last mentioned compounds, also, is
prepared the nitrite of soda, of which enormous quantities
are consumed in the manufacture of dyes.
4. Combination of Nitrogen with Metals.
But there is one other process for the fixation of
atmospheric nitrogen which promises to have much success,
especially in France, where the process is already being
worked, and in the other countries where the necessary
ores of aluminium exist. According to what is known as
the Serpek process, nitrogen is passed over a heated
mixture of bauxite (naturally occurring aluminium oxide),
and coal. Combination takes place between the nitrogen
K
130 CHEMISTRY IN THE SERVICE OF MAN
and the aluminium with formation of a compound known
as aluminium nitride, and when this is boiled with water,
almost the whole of the nitrogen present is liberated as
ammonia, while the aluminium is obtained in the form
of pure oxide, suitable for use in the production of the
metal. Although by this process sulphate of ammonia
can be produced at a low cost, the successful development
of the process is intimately bound up with the demand for
pure oxide of aluminium ; and this, in turn, depends on
the demand for the metal.
From what has now been said, it may be agreed that
the outlook with regard to the supply of nitrogen com-
pounds for agricultural and industrial operations is full of
hope ; and although the atmospheric nitrogen has, as yet,
only been made to satisfy a small part of the world's
demands, no difficulties stand in the way of a greatly
increased supply by one or all of the processes which I have
attempted to describe. And chemists surely may justifi-
ably feel some pride and satisfaction, and may even
reasonably look for some sign of appreciation on the part
of their fellow men, in the fact that in the solution of the
great problem of the fixation of atmospheric nitrogen,
their ingenuity has not altogether been found wanting.
To make two ears of corn to grow where only one grew
before, is an achievement which should surely win for
science some larger measure of popular recognition and
esteem.
But when we contemplate the position which our own
country occupies in this matter, we must confess to a
feeling of great disappointment. Norway, Germany,
Austria, Italy, France, the United States, Canada, India,
FIXATION OF ATMOSPHERIC NITROGEN 131
Japan, in fact, practically every civilised country but our
own, is actively engaged in developing the nitrogen
industries. It is true that we produce a considerable
quantity of ammonia in our gas-works, and other works,
and we are also, on a very small scale, producing ammonia
from peat. But we are thereby merely using up resources
which cannot be replaced, and we are doing nothing to
create further supplies of the vitally necessary compounds
of nitrogen. We export our coal to Odda and buy it back
again, at an enhanced price, as calcium cyanamide ; we
export our ammonia to Notodden, and buy it back as
ammonium nitrate. It is often stated that we are at a
disadvantage in this country in not having at our disposal
the cheap water-power which is available in some other
countries at least. But it has also been pointed out by
competent authorities that electrical power could be
developed in this country at a price which would allow of
the successful working more especially of the cyanamide
process. Moreover, we must bear in mind that the
synthetic production of ammonia which has only within
the past few years been developed in Germany, is not
dependent on specially cheap power at all. Surely the
time is more than come for some effort to be made to
produce within our own borders those substances which are
of such vital importance in the life of our people.
Even the simplest process of chemical manufacture
involves, as a rule, the working together of several
processes, each of which forms a detail in the complete
series of operations ; and the success of the process as a
whole depends on the efficiency with which the preliminary
132 CHEMISTRY IN THE SERVICE OF MAN
and detail processes can be carried out. Thus, in the
nitrogen industries, for example, it is essential for success
that a cheap source of pure nitrogen and also, in the case
of the synthetic production of ammonia, a cheap source
of hydrogen should be available.
For the purpose of obtaining nitrogen the method
which is most frequently employed on the manufacturing
scale is the distillation of liquid air. Liquid air, of course,
consists of a mixture of liquid nitrogen and liquid oxygen,
which boil at —319° and — 296*5° F. respectively. Just as
we saw that the different hydrocarbons in crude petroleum
can be separated by fractional distillation, so also in the
case of liquid air, we can separate the nitrogen from
the oxygen. As the nitrogen has the lower boiling-point,
it distils off first, and by suitable arrangements can
be obtained free from oxygen.
The production of liquid air is now a very simple
matter, and has already developed into an industry of
very considerable proportions. At Niagara Falls, for
example, two million cubic feet of nitrogen are prepared
from the air daily, by the distillation of liquid air ; and
the scale on which the liquefaction of air is carried out
may be gathered from the fact that this liquid is thrown
to waste at the rate of thirty gallons an hour, merely
to keep the apparatus flushed out and in good order. The
principle on which the process of liquefaction depends
is that when highly compressed air is allowed to expand
rapidly its temperature falls ; and the amount by which
the temperature is lowered on expansion is all the greater
the lower the temperature of the compressed gas previous
to the expansion.
FIXATION OF ATMOSPHERIC NITROGEN 133
The industrial application of this principle is due
mainly to a German and
an English engineer,
Linde and Hampson,
and their method will
be understood from Fig.
10. Air under a pres-
sure of about 1 50 atmo-
spheres, and free from
moisture and carbon
dioxide, enters the ap-
paratus at A, and passes,
as shown by the arrows,
to the central tube, where
it sub-divides into a
series of three or four
tubes, B, of thin copper
wound spirally round
the central rod D. At
the lower end, these
tubes pass together into
a valve C, at which the
compressed air rapidly
expands. A lowering
of temperature is thereby
produced. The cool air
now passes upwards over
Fig. 10. — Hampson Apparatus for Liquefying Air.
A, tube by which air enters ; B, section through spirals of copper tubing ;
C, expansion valve ; D, central spindle ; E, wheel for opening and closing
expansion valve ; G, tank in which liquid air collects ; H, gauge to indicate
amount of liquid air in G ; J, tube connecting tank with gauge ; O, prc'^sure
gauge to indicate pressure at which the air enters the apparatus ; P, valve
closing tube R, through which the liquid air is withdrawn ; T, wlieel for
opening the valve P.
134 CHEMISTRY IN THE SERVICE OF MAN
the layers of copper tubing, and so cools down the com-
pressed air \yhich is passing through these towards the
expansion valve. In this way the air expanding at the
valve gets progressively colder and colder, until at last a
point is reached when the lowering of temperature on
expansion is so great that the air liquefies. It collects in
the tank E, from which it can be drawn off from time to
time through the tube R.
This apparatus can also be made use of for the cheap
production of hydrogen on a commercial scale, use being
made of water gas (a mixture of carbon monoxide and
hydrogen), as the source of the hydrogen. By liquefying
this mixture of gases in the Linde apparatus, a practically
complete separation of the two gases can be effected by
distillation, as in the case of nitrogen and oxygen, and
the last traces of carbon monoxide can be readily removed
by suitable chemical absorbents.
A large amount of hydrogen is also prepared by
passing a current of electricity through a solution of
caustic potash or of potassium carbonate. In this process
oxygen is also produced, and the process can be economi-
cally carried out at places where there is a demand for
the two gases.
The ease with which liquid air can now be produced
is not only of great industrial importance, but is also of
much value in the furtherance of scientific knowledge.
By means of liquid air, one is enabled to extend the scope
of scientific investigation to temperatures which other-
wise would be inaccessible ; and the increase of knowledge
which has accrued therefrom is of the highest scientific
interest and practical value. The utilisation of this new
FIXATION OF ATMOSPHERIC NITROGEN 135
^=5:1
aid to scientific research was greatly facilitated by the
introduction of the well-known Dewar " vacuum vessels."
These " vacuum vessels," which are now so familiar under
the name of " thermos " flasks, consist of
double-walled glass vessels (Fig. 11), the air
being removed as completely as possible from
the space between the two walls. The " vacuum "
by which the vessel containing the liquid air is
thus surrounded, acts as a very efficient heat
insulator, so that although the liquid air is
several hundred degrees colder than the sur-
rounding atmosphere, the heat from the latter
is conducted only very slowly to the liquid air,
which may thus be preserved for hours without any
considerable loss.
\^
Fig, II.—
Dewar
Vacuum
Vessel.
CHAPTER VIII
GLASS, SODA, SOAP
In the previous chapter we discussed one of the youngest
of the chemical industries, an industry which has been
developed at the call of necessity to contribute to the
well-being of man and the advance of civilisation. In
the present chapter we shall turn our attention, in the
first place, to one of the oldest industries, which by reason
of the unique and valuable properties of the product, is
still one of the foremost industries of civilised countries,
the industry of glass making.
Many, doubtless, are familiar with the legend reported
by the Roman writer Pliny in the first century of our
era, which ascribed the discovery of glass to a party
of Phoenician sailors who were forced by stress of weather
to land on the sandy shore under Mount Carmel. Here,
standing their cooking-pots on lumps of soda, with which
their ship was laden, they observed the soda and the
sand to fuse together under the heat of the fire, and so
to form a glass. But we can be sure that it was not
thus that glass was discovered, and although the Phoenician
towns of Tyre and Sidon were, at an early period, almost
as celebrated for their glass as for the famous purple
dye which coloured the robes of kings, it is to Egypt
GLASS, SODA, SOAP 137
that we must lcx)k for the first knowledge of glass or
glass-like material ; to that country which, as Herodotus
wrote, " contains more wonders than any other land, and
is pre-eminent above all countries of the world for works
which almost baffle description." The representation of
the art of glass-blowing on the walls of the tomb of Tih
(about 3800 B.C.), with which every visitor to Egypt is
familiar, and the discovery of glass beads and ornaments
among the ruins of the ancient city of Memphis, bear
testimony to a knowledge of this material at a very early
period in Egyptian civilisation. What mankind owes to
the first discoverer of the process of making glass, it is
scarcely possible to describe. That first artificer in glass,
as Dr. Johnson wrote, "was facilitating and prolonging
the enjoyment of light, enlarging the avenues of science,
and conferring the highest and most lasting pleasures ;
he was enabling the student to contemplate nature and
the beauty to behold herself" And in recent years glass
has undergone a wonderful evolution through the work
and labours of chemists, who have shown how, by variation
of the composition, the properties of glass may be altered
in a most marvellous degree ; and they have thereby
made possible the construction of apparatus for the most
diverse uses, prisms and lenses for lighthouses, microscopes,
telescopes and other instruments, and so have contributed
to the service of man and a knowledge of the universe.
But before we consider more fully the nature and
properties of glass, there are one or two points of general
importance to which it is necessary to direct attention.
We are all familiar with the statement that matter can
exist in three states — the solid, liquid, and gaseous ; and this
138 CHEMISTRY IN THE SERVICE OF MAN
statement is familiarly illustrated by the substance water,
which is well known in the three forms of ice, water, and
steam. By elevation of the temperature, solid is made to
pass into liquid, and liquid into gas, whereas by lowering
the temperature the reverse series of changes is brought
about.
At the present moment it is the change from solid to
liquid, and more especially from liquid to solid, that de-
mands our interest ; and in using the term solid, I mean
crystalline solid, and not amorphous solid. In a crystalline
solid the particles are arranged in a definite geometrical
form bounded by plane faces or surfaces, such as we see
in the naturally occurring rock crystal, amethyst, etc. ;
whereas an amorphous solid does not naturally assume any
definite shape, although it may, of course, be cut into
definite forms in imitation of crystals. When a crystalline
solid is heated it is found that it passes, at a definite
temperature, known as its melting-point, from the solid to
the liquid state, whereas an amorphous solid, like sealing
wax for example, gradually loses its rigidity and possesses,
therefore, no definite melting-point.
When a crystalline solid substance is heated, it is found
that melting or liquefaction occurs as soon as the melting
point is reached, and it has never yet been found possible
to heat a crystalline solid to a temperature above its
melting-point without such a change occurring. If, how-
ever, a liquid is cooled down, it is found quite generally
that the temperature can be lowered below the normal
freezing-point, or below the melting-point of the solid
without any of the solid form being produced. We can,
for example, with care, cool water to a temperature much
GLASS, SODA, SOAP 139
below 32° F. without any ice being formed, and liquids
which are in this way cooled to below the normal freezing-
point, are said to be supercooled. Such supercooled liquids
appear to be quite stable — they can, apparently, be kept
for any length of time unchanged — provided that all traces
of the solid form are rigidly excluded. If, however, even
a minute trace, even the ten thousand millionth part of a
grain, of the solid substance — a particle which might dance
as a mote in the sunbeam — is brought into contact with the
supercooled liquid, the state of apparent equilibrium is
upset, separation of the crystalline solid form begins, and
the process goes on until all the liquid has passed into
solid.* The process of crystallisation, however, does not
take place at once throughout the whole mass of the liquid,
but only those portions of liquid which are in contact with
the solid crystallise out, and so we find the process of
crystallisation gradually extending throughout the whole
of the supercooled liquid. Moreover, the rate at which
crystallisation takes place in a supercooled liquid depends
on several factors ; it depends on the nature of the sub-
stance itself, for it is found that different substances crystal-
lise at different rates, and also on the purity of the substance,
the rate of crystallisation being lowered by the presence of
foreign substances. The velocity of crystallisation depends
also on the degree of supercooling, and that is the factor
on which I desire to lay most stress at present. The more
a liquid is cooled below the normal freezing-point, the
• When the cooling is carried out slowly, it is found that substances differ
greatly in the readiness with which they remain supercooled, but, in general,
when a substance has been supercooled to a certain extent, crystallisation or
separation of the solid in the crystalline form, takes place spontaneously, that
is, without the previous addition of the solid form.
140 CHEMISTRY IN THE SERVICE OF MAN
faster will solidification occur once it has been started.
But this law, which is a perfectly general one, is subject to
modification through the operation of another factor. We
have already seen that the speed with which a chemical
change takes place, depends on the temperature, the speed
being all the greater the higher the temperature, and
becoming less as the temperature is lowered. Similarly
with the process of crystallisation. When crystallisation is
started in a supercooled liquid, two opposing factors
operate to affect the speed of crystallisation. At first
the effect of supercooling is predominant, and so as the
degree of supercooling is increased the rate of crystal-
lisation also increases. But after a point, the effect of
the lowering of temperature counterbalances the effect of
the supercooling, the rate of crystallisation ceases to in-
crease as the temperature is lowered, and in fact begins
now to decrease. There is, therefore, a certain tempera-
ture, a certain degree of supercooling, at which the velocity
of crystallisation is a maximum, and below which it
becomes less and less ; and, ultimately, it becomes practi-
cally equal to zero. The supercooled liquid no longer
crystallises even when brought into contact with the
crystalline solid.
But we know that as we cool down a liquid, it becomes
more and more viscous, and at last it becomes so viscous
that it does not " run " at all so far as ordinary observation
can detect, and so we call it a solid. An amorphous solid
is just such a supercooled liquid, a liquid cooled so far
below its crystallising point that the rate of crystallisation
is infinitely slow. In this way are formed, for example,
the glassy lavas, or obsidians, by the rapid cooling of
GLASS, SODA, SOAP 141
molten lava, as well as ordinary glass with which we are so
familiar.
When a supercooled liquid or " glass " is maintained at
a temperature in the neighbourhood of the softening point,
spontaneous crystallisation may set in, and thereby cause
the glass to lose its transparent, vitreous character ; the
glass, it is said, devitrifies. Under certain circumstances,
this may prove a source of much annoyance.
A substance which affords an excellent illustration of
the behaviour which has just been discussed, is quartz or
silica (an oxide of the element silicon), a substance which
is very familiar to everyone. It occurs as the clear, glassy
particles which form sea-sand, and which can also be
readily distinguished in granite ; coloured by certain im-
purities it forms the well-known ornamental stones, the
Cairngorm and the amethyst, while in the pure colourless
form it is known as rock crystal, which ordinarily crystal-
lises in six-sided prisms ending in six-sided pyramids.
It is largely employed for making spectacle glasses and
optical instruments.
When this crystalline quartz is heated in the oxy-
hydrogen blowpipe flame, or in a specially constructed
electric furnace, to a temperature of about 3000" F., it
melts to a colourless liquid ; and when this liquid is cooled
fairly rapidly, the quartz can be obtained as a clear, colour-
less, glassy mass — a supercooled liquid — which looks just
like ordinary glass. This fused quartz, or quartz glass,
possesses the exceedingly valuable property that it ex-
pands and contracts only very slightly with alteration of
the temperature (its coefficient of expansion is less than
142 CHEMISTRY IN THE SERVICE OF MAN
one-tenth that of glass), and for this reason it can, unlike
ordinary glass, be rapidly heated or rapidly cooled without
cracking. It can, for example, be heated red hot and
ithen plunged into cold water, or when cold, it can be
suddenly introduced into the blowpipe flame, or a wire
enclosed within a tube of quartz glass may be heated to
a bright red heat by means of an electric current while the
tube is immersed in cold water, and the quartz glass
remains in all cases uncracked. By reason of this property,
quartz glass, formed into apparatus of various kinds, has
come increasingly into use in recent years, more especially
in cases where rapid changes of temperature are en-
countered. Although readily attacked by alkalies, it is
very resistant to acids, except hydrofluoric acid.
When heated for some time to a temperature of about
2280** F., a temperature considerably below the melting-
point of quartz, the glassy quartz passes into the crystalline
form, it " devitrifies," and can then no longer withstand,
as before, sudden changes of temperature.
Unlike fused quartz or silica glass, ordinary glass is not a
single substance but a homogeneous mixture of substances.
When quartz or silica, which occurs in great abundance
as sea-sand — the grains of this consist of almost pure
silica — is heated together with soda (sodium carbonate),
the silica displaces the carbonic acid from the carbonate
and a compound is obtained known as sodium silicate.
When this is allowed to cool, it solidifies to a glassy
material familiar to every one as water-glass, so called
because of its solubility in water. A similar substance is
obtained by fusing quartz with potash. If, instead of
GLASS, SODA, SOAP 143
heating sand or quartz with soda (or potash), only, one also
adds other metallic oxides or carbonates, such as lime,
or alumina, or oxide of lead, mixtures of silicates are
obtained which solidify to glasses that do not dissolve
in water, and constitute what we ordinarily call glass.
Glass has, therefore, no definite composition, and by
varying not only the constituents but also their relative
amounts, glasses of various kinds and possessing very
different properties can be prepared. All glasses, however,
contain soda or potash.
Ordinary window glass, glass for table-ware and for
general use, consists essentially of a mixture of the silicates
of soda and of lime, although aluminium is also very
frequently present in very small amount The quality
and appearance of the glass depend largely on the purity
of the materials employed in its manufacture, and the
principal source of the silica is a fine white sand found
in various parts of England, but the purer sands of France
and of Belgium are also laid under contribution. Such
sand, mixed thoroughly with sodium carbonate ^ and pure
white chalk or limestone, is melted in large fire-clay pots,
placed in furnaces which are now generally heated by
means of gas. At first the molten mass is almost opaque
owing to the multitude of bubbles of carbonic acid gas
which permeate it, but after a time these bubbles gradu-
ally escape, and a clear liquid is obtained. The desired
articles can then be formed either by pouring the molten
glass into moulds or by blowing. In the latter case,
a quantity of molten glass is taken up on the end of a
long metal tube, and by blowing through the tube, hollow
' Sulphate of soda is also largely employed in place of the carbonate.
144 CHEMISTRY IN THE SERVICE OF MAN
articles of varied shape can, by the expert skill of the
glass blower, be obtained. For the production of " sheet
glass," used for windows, the molten glass is first blown
into the form of a hollow cylinder, the ends of which
are then cut off. By means of a diamond, this cylinder
is then cut along its entire length and placed in a furnace
heated to the softening point of the glass. The cylinder
begins to unroll, and it is then flattened out into a sheet
by means of a special instrument.
The surface of this glass is not quite plane, but is
covered with slight depressions and bulgings, and in
consequence of this, objects viewed through such glass
are more or less distorted. To get rid of this defect, the
sheet glass is sometimes ground and polished, as in the
case of plate glass, and in this way one obtains what is
known as "patent plate." Such glass is largely used
for the framing of pictures.
After the sheet of glass or other article has been
formed, it must be again heated to near its softening point
and then placed in an " annealing " chamber where it can
cool very slowly. The purpose of this is to get rid of
the stresses which are set up in the rapidly cooled glass
and which render the glass very liable to fall to pieces
when scratched. This can be illustrated by what are
known as Rupert's drops, obtained by dropping molten
glass into hot oil, so that the glass is suddenly cooled.
This glass is very hard, and can withstand even heavy
blows with a hammer, but if the " tail " attached to the
drop is broken, or if the glass be scratched with a file,
the whole drop falls to a powder. Such hardened or
toughened glass, produced by annealing glass in oil,
GLASS, SODA, SOAP 1^5
appears to have been known at least as early as the
first century A.D., as the following incident, related by
Fetronius in that excellent satire, "Cena Trimalchionis,"
shows : " There was an artist who made glass vessels so
tough and hard that they were no more to be broken
than gold and silver ones : It so happen'd that the same
person having made a very fine glass mug, fit for no
man, as he thought, less than Caesar himself, he went
with his present to the Emperor, and had admittance ;
both the gift and the hand of the workman were com-
mended, and the design of the giver accepted. This
artist, that he might turn the admiration of the beholders
into astonishment, and work himself the more into the
Emperor's favour, begged the glass out of Caesar's hand ;
and having received it, threw it with such a force against
a paved floor, that the most solid and most firmest metal
could not but have received some hurt thereby. Caesar
also was equally amazed and troubled at the action ; but
the other took up the mug from the ground, not broken
but only a little bulg'd, as if the substance of metal had
put on the likeness of glass ; and therewith taking a
hammer out of his pocket he hammer'd it as if it had
been a brass kettle, and beat out the bruise : and now
the fellow thought himself in heaven, in having, as he
fancied, gotten the acquaintance of Caesar, and the
admiration of all mankind ; but it fell out quite contrary
to his expectation : Caesar asking him if any one knew
how to make this malleable glass but himself, and
he answering in the negative, the emperor commanded
his head to be struck off; 'For,' said he, 'if this art
were once known, gold and silver will be of no more
L
146 CHEMISTRY IN THE SERVICE OF MAN
esteem than dirt' " In such fashion did Nero encourage
and foster science.
By a systematic study of the influence of a large
number of substances on the properties of glass, hundreds
of different glasses have been produced and their physical
and optical properties examined. Some of these glasses
have proved themselves to be of the highest value and
have made possible the construction of apparatus by
which scientific knowledge and material well-being have
been greatly promoted. Moreover, glasses possessing
very different expansibilities with heat have also been
produced, and by welding together combinations of these,
glasses have been obtained which undergo little change
of volume on heating and can withstand even considerable
and sudden alterations of temperature without cracking.
The green colour so well known in the case of cheap
bottle glass, and seen in practically all old window glass,
is due to the presence of small amounts of iron derived
from the impure materials, especially the sand, used in
the manufacture of the glass. This green colour can be
" corrected " by the addition of black oxide of manganese.
The amethyst colour which is thereby produced neutralises
the green due to the iron, and a white glass is obtained.
The amethyst or purple colour due to the manganese
becomes evident when such glass is exposed for a
lengthened period to bright sunlight.
By fusing silica with a mixture of potash and red
lead (oxide of lead), a lustrous glass with a high refrac-
tivity is obtained, and is known as "crystal." When
cast in suitable moulds or, preferably, cut with a wheel
and polished, it is much prized for vases and ornamental
GLASS, SODA. SOAP 147
dishes of different kinds. A still more lustrous glass
can be obtained by replacing part of the silica in the
crystal glass mixture by boric acid, and so giving rise
to what is called generally a boro-silicate glass. By
reason of its brilliant lustre and high refractive power,
such a glass, when suitably cut, sparkles and flashes in
a myriad colours. It is, therefore, largely employed under
the name of "strass," or "paste," for counterfeiting
diamonds, and, when suitably coloured, other gems as
well.
The production of coloured or stained glass is easily
effected by adding small quantities of suitable substances
to the molten mixture of silicates. Thus, as we have
already mentioned, addition of iron imparts a green
colour to the glass, whereas the addition of manganese
oxide colours the glass of an amethyst or purple shade.
Salts of the metal uranium give to glass a yellowish-
green fluorescence, and are much used in the production
of fancy glass. With cobalt oxide the colour is deep
blue, while with gold, a ruby red is obtained. Paste
coloured blue with cobalt, or red with gold, is used to
counterfeit the sapphire and the ruby. These counterfeit
gems must not be confused with the artificially prepared
sapphires and rubies to which reference was made pre-
viously (p. 51). They can readily be distinguished from
the latter or from the naturally occurring gems by their
much greater softness.
In most cases the colour in glass is due to the forma-
tion of coloured silicates, silicate of manganese, silicate
of cobalt, etc. ; but in the case of ruby glass, the colour
is due to the presence of excessively minute particles of
148 CHEMISTRY IN THE SERVICE OF MAN
metallic gold. When a small quantity of gold is added
to molten glass it dissolves, much as sugar dissolves in
water, and if the glass is rapidly cooled it is found to
be white or to have only a very faint yellow tinge. If,
however, this glass is re-heated, or if the molten glass is
allowed to cool slowly, metallic gold begins to separate
out in very minute particles. As the particles increase
in size, the colour deepens more and more to a dark
ruby red, and different shades can be obtained by careful
regulation of the heating and cooling. The particles, how-
ever, are so minute that they are quite invisible not only
to the naked eye, but even under a powerful microscope,
and the gold is said to be in the colloidal state (Chap. X).
If, however, too much gold is added, the metal may
separate out in visible particles and so render the glass
opaque.
Glass is also used in large quantities for the pro-
duction of mirrors, which constitute a great advance on
the polished metal mirrors of our forefathers. In order
to avoid distortion, plate glass, the surface of which has
been polished quite plane and smooth, must be used, and
one side of this is " silvered." Formerly, this was effected
by coating the glass with an amalgam of tin and mercury,
but mercury is a very expensive metal and its use also
involves the danger to the workman of mercurial poisoning.
For the production of mirrors, therefore, this metal has
been superseded by silver, the use of which is not only
free from danger but allows also of a whiter reflecting
surface being obtained. By adding caustic soda and
ammonia to the solution of a silver salt, e.g. silver nitrate,
a solution is obtained from which metallic silver can
GLASS, SODA, SOAP 149
readily be caused to separate out by the addition of certain
substances, such as glucose. The surface of the mirror
glass, previously well cleaned, is laid on the silver solution,
and if the conditions are properly arranged, the silver
separates out very slowly and forms a coherent and highly
reflecting coating on the surface of the glass. Although
silver is a fairly expensive metal, the amount used is so
small that the silver required to coat even a large mirror
would not cost more than a few pence. The silvering of
the well-known " thermos " flasks is carried out in a similar
manner.
When glass is heated for some time to a temperature
just below the softening point, it devitrifies and becomes
opaque owing to the crystallisation of the silicates present
in the glass.
The use of carbonate of soda in the manufacture of
glass brings that industry into the closest relations with
a series of chemical industries in which this country was
for long predominant, namely, the manufacture not only
of soda itself but also of sulphuric acid, hydrochloric acid,
chlorine, and bleaching powder.
Previous to the nineteenth century, the carbonate of
soda required, more especially, for the manufacture of
glass and of soap, to which we shall refer presently, was
obtained mainly from the ash of marine plants which was
prepared chiefly in Spain and sold under the name of
barilla} But the supply was scanty, and barely sufl[icient
' Sodium carboiute or soda has been known from remotest ages as
forming a deposit on the shores of the soda-lakes of Eg)'pt, and is obtained
from that source at the present day. Formerly it was called "nitre," and
ISO CHEMISTRY IN THE SERVICE OF MAN
to meet the demand. There was, therefore, great need for
an abundant source of cheap soda, and the Academy of
Paris in 1775 offered a prize for a process of converting
common salt, or chloride of sodium, of which there are
such abundant supplies occurring naturally, into the car-
bonate of sodium or soda. This problem was solved by
the French chemist Leblanc, in 179 1. A factory for the
manufacture of soda by the Leblanc process was started
in 1793, but was confiscated by the Committee of Public
Safety, and in 1806, filled with despair, the inventor of
a process which has contributed so much to the comfort
and well-being of the people by giving to them cheap
glass and cheap soap, ended his days by his own hand.
It was an inauspicious start for a great industry, but one,
perhaps, not altogether out of keeping with the many
vicissitudes through which it had afterwards to pass.
The process invented by Leblanc consists of several
stages. Salt, first of all, is heated with sulphuric acid,
whereby the chloride of sodium is converted into sulphate
of sodium or "salt-cake," as it is called commercially.
At the same time there are produced large quantities of
hydrochloric acid gas. The salt-cake is then heated with
a mixture of limestone (calcium carbonate), and coal,
whereby the sulphate of soda is converted into carbonate
of soda, which can then be extracted by means of water.
A residue, consisting mainly of sulphide of lime, and
known as alkali waste or soda waste, is left For long,
by this name it is referred to in the Bible : " As he that taketh away a
garment in cold weather, and as vinegar upon nitre, so is he that singeth
songs to an heavy heart " (Proverbs xxv. 20). Soda, when acted on by
vinegar (acetic acid), is decomposed with brisk eflervescence due to the
production of carbonic acid gas.
GLASS, SODA, SOAP 151
the accumulations of this soda waste were a source of
much annoyance to the community (by reason of the
evil-smelling gas, sulphuretted hydrogen, which they
evolved), as well as a loss to the manufacturers. After
many failures, however, a process was discovered whereby
the sulphur present in the waste could be recovered, and
the economy which was thereby effected enabled the
Leblanc process to maintain itself, at least for a time,
against the formidable rival by which, as we shall learn,
it was assailed during the latter half of the century.
It was in England that the Leblanc process was
chiefly worked, and there, together with the manufacture
of sulphuric acid, the industry assumed very large pro-
portions. But its history has been a checkered one.
At first the hydrochloric acid gas which was evolved in
the process was discharged into the air and became an
intolerable nuisance, by reason of the fact that it destroyed
all the vegetation in the neighbourhood of the works and
rapidly corroded all ironwork. To still the outcry which
was raised, more or less successful attempts were made
to absorb the gas in water, in which it dissolves with
great readiness. But if one trouble was thereby removed,
a fresh one arose, and the soda manufacturers found
themselves with large quantities of hydrochloric acid, for
which there was scarcely any use, and which could not
be run into the rivers as it would kill the fish. A way
out of the difficulty, however, was at length discovered,
and the hydrochloric acid which had been a source of
annoyance to the community and of worry to the manu-
facturers, became a source of considerable profit. By
heating the hydrochloric acid with black oxide of
152 CHEMISTRY IN THE SERVICE OF MAN
manganese, and in other ways, chlorine is obtained, and
this chlorine is a valuable bleaching and disinfecting agent.
For convenience of transport and use, the chlorine is
generally passed over slaked lime, which absorbs it and
so gives rise to bleaching powder, or chloride of lime as
it is popularly called. For this bleaching powder a great
demand sprang up in the middle of last century, due to
the development not only of the cotton but also of the
paper industry, the raw materials for which required to
be bleached before use. The production of hydrochloric
acid played henceforward an important part in the success
of the Leblanc process.
During the past fifty years, however, the Leblanc soda
process has been faced with a competition before which
it has almost entirely succumbed. In 1863 the Belgian
chemist, Ernest Solvay, developed a process, the Solvay or
ammonia-soda process, based on a reaction discovered by
two English chemists, whereby soda can be produced more
economically and in a purer form than by the Leblanc pro-
cess. The process depends on the fact that when carbon
dioxide is passed into a solution of common salt saturated
with ammonia, bicarbonate of soda (used in the prepara-
tion of baking powder), is deposited. By heating the
bicarbonate, carbon dioxide is driven off and the ordinary
carbonate of soda is obtained. For a time the older pro-
cess was able to maintain itself against its new rival, but
although a quantity of soda is still manufactured by the
Leblanc process, it is chiefly for the sake of the hydro-
chloric acid and the chlorine obtainable from it, that the
manufacture is continued. The continuation of the process
is also made more easy from the fact that the sulphate of
GLASS, SODA, SOAP 153
soda formed can be used, instead of the carbonate, for glass
making. But yet " the old order changeth giving place to
new," and the introduction of the electrolytic methods of
making chlorine (owing, more especially, to the require-
ments of the dye industry), and caustic soda, which was
formerly prepared entirely from the carbonate, seems
seriously to menace the existence of the Leblanc process.
But whatever may be the final result, the introduction of
the Solvay process for the manufacture of soda, and of the
" contact process" for the manufacture of sulphuric acid, has
deprived this country of the predominance which she once
possessed in the manufacture of these chemicals, and has
enabled the other countries to become independent of us
for their supplies. Of the 2,I50,CXX) tons of soda produced
in 19 10, only 820,CXX3 tons were produced in this country.
Another very large industry which is dependent on the
use of soda is that of soap-making. Even at an early
period, about the beginning of the Christian era, a material
resembling our soft soap, and used largely as an ointment,
was prepared by boiling fat with potashes ; and although
in later times the manufacture of soap developed consider-
ably, it was not till early last century that it passed from
being a handicraft carried on by rule of thumb, to an
industry controlled by an exact knowledge of the proper-
ties of the materials used.
It has already been pointed out that the animal and
vegetable fats and oils were shown by the French chemist,
Chevreul, to be compounds of glycerine with different acids'
which could be obtained by boiling the fats and oils with
dilute sulphuric acid, or by treating them with superheated
154 CHEMISTRY IN THE SERVICE OF MAN
steam. This process of hydrolysis^ as it is called, or
decomposition by water, can also be facilitated by caustic
soda (sodium hydroxide), or caustic potash (potassium
hydroxide), and the acid of the fat or oil then combines
with the soda or the potash to form a sodium or potassium
salt of the acid. This sodium or potassium salt of the fat
or oil acid constitutes soap ; and hence the process of
decomposing a fat or oil by means of alkali is known as
saponification.
For the manufacture of soap one cannot employ the
carbonate of soda or of potash, but must first convert these
into caustic soda or caustic potash. on adding slaked lime
(calcium hydroxide), to the solution of the carbonate of
soda or potash, a mutual decomposition takes place with
formation of sodium or potassium hydroxide and calcium
carbonate, and the latter, being insoluble, separates out.
In this way the caustic lye of the soap-maker is
generally prepared. The electrolytic preparation of caustic
alkali is, however, assuming ever greater proportions, and
may soon largely supersede the method which has just
been described.
Although soap can be obtained by using either caustic
soda or caustic potash, the nature of the product obtained
in the two cases is different, the potash soaps being soft,
the soda soaps hard.
The fats and oils used in soap-making are very varied
in character. Formerly, animal tallow and olive oil were
the chief raw materials employed, but, as has already
been pointed out, the increased demand for margarine and
other butter substitutes has driven the soap-maker to seek
other sources of supply, and a number of different animal
GLASS, SODA, SOAP 155
and vegetable oils have now been forced into his service ;
these are either used as such, for the manufacture of soft
soap, or are first " hardened " by the catalytic process
referred to previously, for use in the manufacture of hard
soap. By the admixture of different raw materials in
varying proportions, soaps of different kinds and quality
can be obtained ; and in the proper blending of the raw
materials lies the art of the soap-maker, an art which is
now guided by careful scientific investigation.
In the manufacture of soft soap or potash soap, different
animal or vegetable oils, e.g. linseed oil, cotton seed oil,
soya-bean oil, are boiled with caustic potash. The oils are
thereby decomposed with formation of glycerine and the oil
acid, which combines with the potash to form soap. A
thick paste is thus obtained which, owing to the presence
of glycerine derived from the oil, does not dry up. Addi-
tions of water-glass and other "loading" materials are
frequently made.
In the manufacture of hard soaps or soda soaps, caustic
soda is gradually added to the fat or hardened oil, which is
melted and kept stirred by means of steam. After the fat
has become saponified, common salt is added, and this
causes the paste of soap to separate out as a curdy mass
on the surface of the liquid which contains not only the
added salt and excess of alkali and various impurities, but
also the glycerine of the fat Although, at one time, this
liquid used to be run to waste, it is now subjected to a
process of distillation in special vacuum stills in order to
recover the glycerine, for which there now exists a large
demand for the manufacture of dynamite and other ex-
plosives. So valuable, indeed, is the glycerine that it
156 CHEMISTRY IN THE SERVICE OF MAN
has been stated that the profit from the recovery of the
glycerine is sometimes greater than that from the soap
itself.
With the soap curd, after it has been suitably freed
from the impurities present, there is incorporated any
colouring matter or perfume which it may be desired to
add. The soap is then placed in frames, allowed to dry
and harden, cut into bars, and moulded into tablets.
Not infrequently this "genuine soap" is "filled" by
the addition of other substances, such as carbonate of
soda and water-glass. It is asserted that the soap is
thereby hardened and its detergent power increased.
The familiar transparent soaps are obtained by dis-
solving pure soap in alcohol and then evaporating off the
alcohol.
In the case of the cheaper varieties of soap, such as
common yellow soap, the fat used is mixed with a quantity
of rosin, which also undergoes a process of saponification
to form a soap ; and in this way a mixed fat and rosin soap
is obtained.
Almost endless is the list of modern commercial soaps
now offered for sale for special purposes, in which, with the
genuine soap, there are incorporated disinfectants, medica-
ments of various kinds, scouring materials such as infusorial
earth, bleaching materials such as perborates, etc.
The cleansing power of soap depends on its physical
as well as on its chemical properties ; and in this connec-
tion, its most important property is that it lowers the
surface tension of water. What do we mean by this ?
Every one knows that when water is brushed over a greasy
GLASS, SODA, SOAP 157
surface, it does not form a continuous film wetting the
surface, but breaks up into a number of separate drops, for
all the world as if each little drop were surrounded by a
thin elastic skin ; and the force which keeps the water in
the form of a drop is called the surface tension. If we
reduce the surface tension sufficiently, if we reduce the
strength of the imaginary elastic skin surrounding the drop,
then the water will spread out over the greasy surface and
wet it ; and this lowering of the surface tension can be
effected by dissolving a little soap in the water.^ This
property of soap of lowering the surface tension of water,
is an important factor in its cleansing power, because it
enables the water to wet and so to come into close contact
with even a greasy surface. But there is another property
of soap solutions which plays perhaps the most important
part of all in the cleansing process. This is the property of
emulsifying oils and fats. on shaking up any oil, pure
olive oil, paraffin oil, etc., vigorously with water, it is found
that a milky liquid is obtained owing to the oil being broken
up into a large number of droplets. But this milky appear-
ance is not permanent ; in the course of a few minutes the
droplets of oil run together to form larger drops, which
then collect as a separate layer on the surface of the water.
The milkiness thus disappears. If, however, the oil is
shaken not with pure water but with water containing a
little soap, the droplets into which the oil breaks up are
much smaller (the emulsion appearing, in consequence,
* The efiect described here will be familiar to every one who has interested
himself in water-colour painting. To make the water-colour '* take," a little
ox-gall is added, when necessary, in order to reduce the surface tension of the
water.
158 CHEMISTRY IN THE SERVICE OF MAN
much whiter than before), and they do not run together
and form a separate layer on standing. The oil is per-
manently emulsified. And this is what happens when
soap is used in cleansing a greasy surface to which
dust and other dirt so readily adhere ; the film of grease
is broken up owing to the emulsifying action of the
soap solution, and the grease and dirt are then readily
washed away. The removal of dirt is also facilitated in
a purely mechanical way by the lather or foam which the
soap-water forms, the production of lather being another
result of the lowering of the surface tension of water.
Although the salts of the fat acids with soda and
potash, the ordinary soaps, are soluble in water, the salts
with lime and magnesia are insoluble. Consequently, when
soap is brought into water containing salts of lime or
magnesia, the soap is decomposed with production of the
insoluble calcium or magnesium salt of the fat acid, which
separates out as a scum. Thus —
Soluble soap (sodium stearate, etc.), and calcium
bicarbonate (sulphate, etc.)
give
Sodium bicarbonate (sulphate, etc.), and insoluble soap
(calcium stearate, etc.).
From its " feel " in washing such water is called " hard,"
and as the soap is decomposed, no lather can be obtained
until sufficient soap has been added to combine with all
the calcium and magnesium salts present. Since the
bicarbonate or other salt of sodium which is formed,
GLASS, SODA, SOAP 159
does not lower the surface tension of water and has no
power of emulsifying oils, the soap cannot exercise its
proper cleansing function until after the removal of the
calcium and magnesium salts.
Not only is hard water most wasteful of soap, but it
may also be a source of annoyance, both domestic and
industrial, owing to the separation out, in hot-water and
steam boilers, of the salts of lime and magnesia. It is
of importance, therefore, to get rid of or reduce the
hardness.
When the hardness of water is due to the presence of
bicarbonate of lime (formed by the action, on limestone or
carbonate of lime, of the carbonic acid gas dissolved in rain
water), it can be got rid of by boiling, and is therefore
known as temporary hardness. on a large scale, the
" softening " of the water can be effected by the addition
of slaked lime in proper amount. The soluble bicarbonate
is thereby converted into the carbonate which, being
insoluble, separates out and is removed by filtration.
Hardness which is due to the presence of sulphate of
lime or magnesia, cannot be removed by boiling, and is
known as permanent hardness. It can be got rid of by
the addition of carbonate of soda, or " washing soda,"
the lime or magnesia being thereby thrown out of
solution as insoluble carbonates. Hence the use of
washing soda in the laundry.
For industrial purposes, another process for softening
hard water has recently been introduced, known as the
permutit process. Permutit is an artificially prepared
material formed by fusing together quartz, alumina and
carbonate of soda. When hard water is filtered through
i6o CHEMISTRY IN THE SERVICE OF MAN
a layer of this material, the lime and magnesia are removed
and the water is thereby rendered soft. When the per-
mutit ceases to be efifective, its activity can be restored
by allowing it to remain in contact for some time with a
solution of common salt
CHAPTER IX
ELECTRICITY AND CHEMISTRY
In a previous chapter it was sought to point out and to
emphasise that a chemical reaction must no longer be con-
sidered as involving merely a transformation of material,
but also a flow of energy ; and it was also claimed that
one of the chief characteristics of the scientific advance
during the past hundred years has been the manner in
which and the extent to which the different forms of
energy have been transformed and utilised. In our
study of the subject of combustion we had a glimpse into
that branch of science, thermo-chemistry, which deals with
the relations which exist between chemical energy and heat
energy ; and from the present chapter, it is hoped, the
reader will gain some insight into the relationships which
obtain between chemical energy and that other form of
energy, the utilisation of which is so notable a feature of
the past fifty years, electrical energy.
The birth of electro-chemistry, as this twin branch of
science which deals with the relations between electricity
and chemistry is called, may be dated from the time when,
in 1791, the Italian physiologist, Galvani, observed the
convulsive twitching of the muscle of a freshly dissected
frog, each time the muscle and nerve were connected by
two different metals. It was a humble birth, surely, for a
M
i62 CHEMISTRY IN THE SERVICE OF MAN
science which has revolutionised the world, which has made
practicable the telegraph and telephone, and has supplied
mankind with many materials both of ornament and
of use.
If it is to Galvani that we owe the observation in
which electro-chemistry found its birth, it is to his fellow-
countryman, Alessandro Volta,* Professor of Physics in the
University of Pavia, that the science owes its further
development. Rightly interpreting the muscular con-
traction of the frog's leg as being due to the current of
electricity which is produced whenever contact is made
between two different metals separated from each other
by a liquid conductor, Volta constructed an apparatus
whereby a continuous current of electricity could be
obtained through the transformation of chemical energy
into electrical energy. When a strip of copper and a strip
of zinc are partially immersed in a solution of sulphuric
acid, Volta found that on connecting the free ends of the
metals by means of a conducting wire, a current of
electricity is obtained. By connecting a number of such
cells together, so that the copper plate of one was joined
to the zinc plate of the next, Volta built up a battery —
the famous couronne de tasses, or crown of cups — with
which eflfects of the most notable character were obtained ;
and the voltaic cell, as it was called, was the scientific
sensation and curiosity of the end of the eighteenth and
the beginning of the nineteenth century. Cells of a
similar but more efficient character were constructed by
' The intimate connection of Volta with electricity is held in remembrance
by the use of the term volt as the unit of pressure (or voltage) of an electric
curientt
ELECTRICITY AND CHEMISTRY 163
others, and the effect of the electric current was tried on
a great variety of substances, with the result that, under
the guiding genius of Sir Humphry Davy, the alkali
metals, sodium and potassium, were isolated for the first
time in 1807, by passing a current of electricity through
molten caustic soda and molten caustic potash.
These two metals, which are doubtless unfamiliar to
most people, are silvery-white in colour, and very lustrous.
When exposed to the air, however, they tarnish immedi-
ately, owing to the readiness with which they combine with
the oxygen of the air. They are soft and of a cheese-like
consistency, so that they can be readily cut with a knife.
So great is their affinity for oxygen, that when brought
into contact with water, they decompose it with great
vigour, with production of hydrogen and formation of
caustic soda and caustic potash. Such, in fact, is the
vigour of the reaction that the hydrogen which is liberated,
may become ignited and burn, with a yellow flame in
the case of sodium, and a violet flame in the case of
potassium. These metals find no application in ordinary
life, but are used in considerable quantities in chemical
manufactures.
Such was the beginning of man's triumphant success
in transforming chemical into electrical, and electrical
into chemical energy. Important as were the results
obtained by the use of the voltaic cells, when regarded
from the purely scientific point of view, the cost of
working the cells was very considerable, and it was
not, therefore, until the introduction of the dynamo
(made possible by the scientific researches of Faraday),
that the industrial application of electricity became
i64 CHEMISTRY IN THE SERVICE OF MAN
practicable. With the aid of the engineer and by means
of the dynamo it has now become possible to obtain a
cheap supply of electrical energy, more especially by
harnessing the great waterfalls of the world and by the
use of gas engines. The couronne de iasses of Volta has
been replaced by the rows of humming dynamos which
one sees, in our own country, for example, at the works
of 'the British Aluminium Company at Kinlochleven in
Argyllshire, at Niagara Falls, and in many other parts
of the world ; and in place of the few globules of metallic
sodium which Sir Humphry Davy succeeded, with much
difficulty, in isolating, that and many other substances
are now produced by hundreds and thousands of tons in
the electro-chemical factories of the world.
one of the earliest industrial uses to which electricity
was put, was to the coating of cheaper with more
expensive or more resistant metals, by a process known
as electro-platings a process which has been largely used
from before the middle of last century. At the present
day the process is largely applied to the plating of metals
not only with silver and gold, but also with nickel, a metal
much used on account of its white colour and its power
of resisting atmospheric conditions without tarnishing.
In practice the process is comparatively simple, and
consists in passing a current of electricity through a
solution of a salt of the metal with which the article is
to be plated ; but in order that we may understand the
process better, I would ask the reader to consider with
me for a short time what is the nature of the liquids
which conduct the electric current
When one places in a vessel containing pure distilled
ELECTRICITY AND CHEMISTRY
165
water, the ends of two wires which are connected with
an electric h'ghting circuit and lamp (Fig. 12), the lamp
remains dark. The electrical circuit is broken by the
water which is a non-conductor of electricity. If to the
water one adds cane sugar, glycerine, or alcohol, the lamp
still gives forth no light, for the solutions of these sub-
stances do not conduct the electric current. But if one
dissolves in the water even a very little common salt, or
washing-soda, or hydrochloric acid (spirit of salt as it is
frequently called), the lamp at once lights up, showing that
Fig. 12.
the flow of electricity is no longer interrupted by the liquid.
In the same way other substances soluble in water may be
tested, and it will be found that all substances can be
divided into two classes, those that yield solutions which
conduct electricity, and those that yield solutions which do
not conduct electricity. Substances belonging to the former
class are called electrolytes^ substances belonging to the
latter class, non-electrolytes. Sugar is a non-electrolyte ;
salt is an electrolyte. Similarly, all the substances known
as acidsy which have a sour taste and the property of
turning red a blue solution of the vegetable colouring
i66 CHEMISTRY IN THE SERVICE OF MAN
matter called litmus ; all the substances, also, known as
alkalies, which have the opposite property of restoring
the blue colour to solutions of litmus which have been
reddened by acids ; and lastly, all the substances known
as salts, which are formed by the combination of acids
and alkalies ; all these substances, acids, alkalies, and
salts, are electrolytes, and yield solutions which conduct
the electric current.
When an electric current passes through the solution
of an electrolyte, even the most superficial observation
will teach us that a liquid conductor differs from a
metallic one. In the latter case, no apparent change
may take place, but in the former there is a very
obvious decomposition of the conducting solution. This
process of decomposition by an electric current is known
as electrolysis. If one dips into a solution of copper
sulphate, for example, two bright wires or plates of
platinum which are connected with the poles of a battery,
the solution of copper sulphate is decomposed and one
sees that the surface of one of the electrodes (as the
portions of the metallic conductor dipping into the solu-
tion are called), immediately becomes coated with a
bright rose-coloured deposit of copper. This is the
process used in electro-plating. In the case of solu-
tions of sodium chloride, the sodium liberated at one
of the electrodes decomposes the water with production
of hydrogen gas, which can be seen rising in bubbles
from the electrode, and the solution acquires an alkaline
reaction, as is shown by the fact that it turns reddened
litmus blue. At the other electrode, chlorine is set free
and, dissolving in the water, yields a solution having
ELECTRICITY AND CHEMISTRY 167
bleaching properties, as is shown by the fact that it
discharges the colour of a litmus solution. Whenever,
therefore, an electric current passes through a conducting
solution, there is a movement of electrically charged
matter through the liquid — charged particles of copper,
or sodium, or chlorine, for example — and some of these
particles move towards the one electrode, others towards
the other electrode.
This conclusion was reached early last century by that
great chemist, Michael Faraday, who called the electrically
charged moving particles which thus conveyed the elec-
tricity through the solution, by the happily chosen Greek
term ions {i.e. wanderers) ; and this term is still retained.
During a great part of last century there was much
discussion as to the way in which the electric current was
conveyed through a solution, and it was only in 1886 that
a satisfactory explanation of the constitution of electrolytic
solutions and of the mechanism of electrolysis was given
by the Swedish physicist, Svante Arrhenius. Instead of
assuming, as Faraday did, that the molecules of an
electrolyte are broken up by the electric current — a view
which has since been shown to be incorrect — Arrhenius
assumed that the molecules of an electrolyte when dis-
solved in water, break tip or ionise of their own accord^
and the part-molecules which are formed are the electri-
cally charged ions, some of these ions being charged
positively, the others being charged negatively. These
ions lead an independent existence in the solution and
exhibit their own properties. Thus, sodium chloride,
for example, when dissolved in water, ionises, not into
ordinary sodium and chlorine, but into positively charged
i68 CHEMISTRY IN THE SERVICE OF MAN
sodium ions and negatively charged chlorine ions; and
these ions lead an independent existence in the solu-
tion. Similarly, other salts, as well as acids and alkalies,
undergo this process of ionisation or dissociation into ions,
the metal part of the salt forming the positively charged
ion, or cation as it is called, and the acid part forming the
negatively charged ion, or anion. In the case of acids,
hydrogen forms the cation, so that hydrochloric acid (HCl),
for example, ionises into positively charged hydrogen
ions, and negatively charged chlorine ions. It is, in fact,
to the presence of hydrogen ions that the so-called acid
properties are to be ascribed. In the case of alkalies,
e.g. caustic soda or sodium hydroxide (NaOH), the anion
is formed by the group of atoms OH, known as the
hydroxyl group, so that sodium hydroxide ionises into
positively charged sodium ions and negatively charged
hydroxyl ions. It is to the presence of these hydroxyl
ions that the general properties of alkalies are due.
In the light of the hypothesis of Arrhenius, the fact
that addition of sodium chloride, or of any other salt, acid,
or alkali to water, yields a solution which conducts the
electric current, becomes readily intelligible. These solu-
tions, according to the hypothesis, contain free, positively
charged cations, and free, negatively charged anions.
When, therefore, two electrodes are placed in the solution
of an electrolyte and connected with an electric battery,
the positively charged electrode (the anode) attracts the
negatively charged ions, the anions ; and the negatively
charged electrode (the cathode) attracts the positively
charged ions, the cations. These anions and cations move
in opposite directions through the solution, and give up
ELECTRICITY AND CHEMISTRY
169
their charges at the electrodes ; they transport or convey
the electricity through the solution, and it is this move-
ment or procession of electrically charged particles that
constitutes what we call the electric current in the solution.
This explanation of the passage of a current through
a solution is not a mere specu-
lation, not a mere phantasy, for
it is easy to demonstrate not
only that there is a movement
of the ions through the solu-
tion, but also that the ions move
with different velocities. There
is a pretty experiment by which
one can make this clear. Into
the bend of a tube bent into
the form of the letter U (Fig. 13),
is placed a solution of potassium
chloride to which sufficient
gelatin has been added to make
the liquid set to a jelly ; and
the solution is also coloured red
by the addition of a substance
called phenolphthalein and a
little alkali. (Phenolphthalein
is a colourless substance which
yields a deep-red colour with
alkalies, or solutions containing hydroxyl ions ; and the
red colour is again destroyed by addition of acids, or
solutions containing hydrogen ions.) After the solution
in the bend of the tube has set, a further quantity of the
same coloured solution is poured into one limb of the
v_y
D
Fig. 13.— Migration of
Ions.
170 CHEMISTRY IN THE SERVICE OF MAN
tube (D), while into the other limb (E) is poured the same
solution after it has been decolorised by the addition of
the requisite amount of acid.
Above this colourless layer of gelatin is placed a
quantity of a mixed solution of caustic potash (potassium
hydroxide), and potassium chloride (G), while in the other
limb of the tube is placed a mixed solution of hydrochloric
acid and copper chloride (A). An electric current is now
passed through the solutions in the tube, by placing a
wire connected with the positive pole of a battery in the
solution of hydrochloric acid and copper chloride ; and a
wire connected with the negative pole of the battery in the
solution of caustic potash and potassium chloride. After
the current has passed for some time it is found that the
hydrogen ions (from the hydrochloric acid), moving from
the positive towards the negative electrode, have decolor-
ised the reddened phenolphthalein, and have produced,
therefore, a colourless band (C) of a certain depth. The
blue-coloured copper ions (from the copper chloride), which
move in the same direction as the hydrogen ions but with
a slower speed, follow on into the colourless band produced
by the hydrogen ions, and give a blue colour to the
gelatin (B). In the other limb of the tube, the hydroxyl
ions (from the caustic potash), moving from the negative
to the positive electrode, pass into the colourless gelatin
and produce with the phenolphthalein there a band of
red (F). This band is deeper than the blue band produced
by the copper ions, but not so deep as that produced by
the hydrogen ions, from which we conclude that the
hydrogen ions move faster than the hydroxyl ions, and
the latter faster than the copper ions.
ELECTRICITY AND CHEMISTRY
171
But it IS not only when in a state of solution that an
electrolyte conducts the electric current ; it conducts also
when fused, or converted into the liquid state by heat.
We conclude, therefore, that when fused an electrolyte
dissociates into ions, and that the mechanism of electro-
lysis is essentially the same in the case of a fused
electrolyte as in the case of an electrolyte in solution.
This fact, as we shall see presently, is of the greatest im-
portance for the practical applications of electricity to
preparative chemistry.
Not only does the theory of Arrhenius afford an
explanation of the process of electrolysis whereby electrical
energy is transformed into
chemical energy, or the poten-
tial energy of chemically reac-
tive substances, but it helps us
also to understand the reverse
process of the transformation
of chemical energy into elec-
trical energy, as we see it
occurring in the different voltaic
cells.
one of the simplest of the
voltaic cells is that known
the Daniell cell, which
as
Coppc
'Sulphatm
Fig. 14.— Daniell Cell.
consists of an electrode of
copper immersed in a solution of copper sulphate, and an
electrode of zinc immersed in a solution of zinc sulphate.
The latter solution is contained in a porous pot which
prevents the mixing of the two solutions (Fig. 14).
172 CHEMISTRY IN THE SERVICE OF MAN
When the copper electrode and the zinc electrode are
connected by means of a conductor, an electric current
flows through this conductor from the copper to the zinc.
If an electric motor, for example, is inserted in the circuit,
it will be caused to rotate, and so mechanical work can
be done. What, then, is the source of this supply of
energy which, either in the form of electrical energy, or
in the form of the mechanical energy into which it is
transformed, is given out by the Daniell cell ?
When a strip of zinc is immersed in a solution of
copper sulphate, copper is deposited on the zinc, and at
the same time a corresponding amount of zinc passes
into solution. The chemical change which takes place
is therefore represented by the equation :
Zinc -f- copper sulphate = zinc sulphate + copper.
This is a reaction which takes place spontaneously ;
zinc and copper sulphate represent a system with a certain
amount of potential energy, and it is capable, therefore,
of doing work, of yielding energy. When the zinc is im-
mersed in the solution of copper sulphate, the chemical
energy is transformed into heat energy. How, then, can
we obtain the transformation of the chemical energy into
electrical energy .? The answer is : by so arranging
matters that the change represented by the above equation
takes place by means of the electrically charged particles,
the ions, which are formed when a salt is dissolved in
water. In the Daniell cell, the solution of copper sulphate
contains copper ions and sulphate ions, whereas the zinc
sulphate solution contains zinc ions and sulphate ions.
When the poles of the Daniell cell are connected by means
ELECTRICITY AND CHEMISTRY 173
of a conductor, a movement of the ions in the solution
takes place. The copper ions move towards the copper
electrode, and the sulphate ions move in the opposite
direction towards the zinc electrode. This movement of
ions constitutes, as we have seen, the electric current in the
cell. When the copper ions reach the copper electrode,
they lose their positive charge, and are deposited as
metallic copper on the electrode, while the positive elec-
tricity, to put it somewhat crudely, flows along the metallic
conductor towards the zinc electrode. on the other hand,
the negatively charged sulphate ions move towards the
zinc electrode, where they give up their charge of negative
electricity which neutralises the positive electricity flowing
from the copper electrode. At the same time the zinc
combines with the discharged sulphate ions to form zinc
sulphate, which dissolves and again ionises into zinc ions
and sulphate ions. The total result, therefore, is that
copper ions pass into metallic copper at one electrode,
while metallic zinc passes into zinc ions at the other
electrode. In other words, instead of the reaction between
zinc and copper sulphate taking place at one point by
direct contact, whereby the chemical energy is converted
into heat, the reaction in the Daniell cell takes place in
two parts, at the two electrodes, and the chemical energy
now appears in the form of electrical energy.
A better-known cell, widely employed for working tele-
phones and electric bells, is the Leclanche cell. This very
simple cell consists of a pot containing a solution of sal-
ammoniac (ammonium chloride), in which are immersed
a plate of graphite, packed in a porous pot with granules
of graphite and black oxide of manganese (manganese
174 CHEMISTRY IN THE SERVICE OF MAN
dioxide), and a zinc rod. The porous pot also contains a
solution of sal-ammoniac When the cell is in use, zinc
passes into solution, while the hydrogen which is produced
at the graphite plate is oxidised to water by the oxide of
manganese, and so is prevented from forming a non-con-
ducting layer on the electrode, and thereby stopping the
current.^ When the cell becomes exhausted, its activity
can be renewed by replacing the spent liquid by a fresh
solution of sal-ammoniac.
Although, as has been said, the much more efficient
dynamo has superseded the voltaic cell as a source of
electricity for industrial purposes, there is one cell which
occupies an important place as an auxiliary to the dynamo.
This is the lead accumulator, or storage cell. This cell
consists of plates of lead and of brown oxide of lead,
lead peroxide as it is called, immersed in a solution of
sulphuric acid. on joining these two plates by means of
a conductor, a current of electricity flows through the con-
ductor from the lead peroxide plate to the lead plate.
The chemical reaction which, in this case, yields the energy
which is transformed into electricity, is the conversion of
the lead and lead peroxide into lead sulphate ; and when
this change has taken place, no more electricity is given
out ; the cell is " run down " or " discharged." But this
cell has the great advantage that it can be readily brought
* The ammonium chloride in solution gives rise to ammoninm ions (con*
sisting of the positively charged group of atoms NH^), and to chloride ions
or negatively charged chlorine atoms. When the cell is in action, the chloride
ions move to the zinc pole and, on discharge, combine with the zinc to form
zinc chloride which passes into solution ; and the ammonium ions move to
the graphite pole and there give up their positive charge. The discharged
ammonium ions then react with the water with production of hydrogen.
ELECTRICITY AND CHEMISTRY 175
back to its former condition, can be readily re-charged,
by sending a current of electricity — obtained, say, from a
dynamo — through the cell in the opposite direction to that
of the current which the cell itself gives. In this way we
convert electrical energy into potential, chemical energy ;
and in this form the energy is stored, and is available for
use just when and where it is required. This lead storage
cell is one which has now a multitude of uses, such as
giving current for electric lighting on a large scale (as an
auxiliary to the dynamo), or in portable hand-lamps ; for
driving motor cars or motor-boats ; and in many other
cases where a readily transported supply of energy is
desired. As a competitor with the lead storage cell, much
has, in recent years, been heard of what is generally known
as the Edison cell. This cell consists of plates of iron and
nickel hydroxide immersed in a solution of caustic potash,
and has the advantage over the lead cell of less weight,
and of being less harmed by careless or rough handling.
The application of electricity to chemical manufactures
has produced an industrial revolution. Not only have
electro-chemical processes more or less completely dis-
placed the older chemical methods employed for the
manufacture of such substances as caustic soda and of
chlorine, or for the isolation of such metals as sodium,
potassium, calcium, magnesium, and aluminium, but they
have made possible also the discovery and economic pro-
duction of many new substances of great value. one of the
earliest applications of electricity we have seen was to the
electro-plating of metals by a process of electrolysis. By
this process metals can be obtained in a state of great
176 CHEMISTRY IN THE SERVICE OF MAN
purity, and the method is now used for the refining of
certain metals, more especially of copper. The crude
copper, obtained by smelting its ores, contains a number
of impurities, among which are silver and gold, sometimes
in not inconsiderable quantities. This crude copper, cast
into plates, is made the anode in a bath of copper sulphate
solution, while a thin plate of pure copper is made the
cathode. When the electric current is passed, copper is
deposited in a pure state on the cathode, from which it
can afterwards be readily stripped, whereas the copper of
the anode passes into solution by combining with the
sulphate ions which are discharged at the anode. Some
of the impurities present in the copper may also dissolve
and accumulate in the solution ; other impurities, however,
such as silver and gold, do not dissolve, but fall to the
bottom of the bath as a slime or mud, known as the
" anode mud," from which the valuable metals are extracted
by suitable methods.
By this simple process, the purest commercial copper,
so-called "electrolytic copper," is obtained, and is used
largely for electrical purposes. The importance of pure
copper in this connection is due to the fact that the
conductivity of copper for electricity is greatly diminished
even by small traces of impurity.
The electrolytic preparation of caustic soda and of
chlorine, to which reference has already been made (p. 153),
depends on the electrolysis of a solution of sodium chloride
or common salt. As we have seen, chlorine is evolved at
the positive electrode or anode, while the sodium ions, dis-
charged at the cathode, decompose the water and yield
hydrogen and a solution of caustic soda. By this process,
ELECTRICITY AND CHEMISTRY 177
not only caustic soda but also chlorine and hydrogen can
be economically produced on a large scale, and it might
seem as if this electro-chemical process would speedily
prove an irresistible competitor with the purely chemical
method of manufacturing caustic soda (p. 1 54). And so it
doubtless would, if it were not for the fact that the demand
for chlorine and for hydrogen is at present rather limited.
It is true that this electrolytic chlorine, generally liquefied
and transported in iron cylinders, is used, in Germany
alone, to the extent of some thousands of tons annually
for the production of bromine as well as in connection
with the manufacture of synthetic indigo ; and for hydrogen,
also, various uses can be found (e.g. in connection with the
production of synthetic ammonia), but before any great
development and extension of this electro-chemical process
can take place, new fields of usefulness must be found for
the chlorine and the hydrogen which are formed at the
same time as the caustic soda.
Of the different substances produced with the aid of
electricity, the best known is probably the metal aluminium.
This is the most abundant of all the metallic elements in
the world, but it occurs only in the form of compounds, in
combination with other elements. So difficult is it to
isolate the metal from its compounds by purely chemical
methods, that it was not till 1845 that the metal was
obtained in the compact form. And it was then merely a
chemical curiosity ; for any general or industrial application,
its cost was prohibitive. It is, in fact, only during the
past thirty years, that it has become possible, by the
application of an electrolytic method, to produce the metal
at a reasonable price. The isolation of the metal is
N
178 CHEMISTRY IN THE SERVICE OF MAN
effected by the electrolysis of a solution of purified bauxite
or oxide of aluminium in molten cryolite (a naturally
occurring compound of aluminium with fluorine and sodium,
mainly obtained from Greenland), and the entire world's
production of the metal is now obtained by this means
For the electrolysis, an iron bath, lined with carbon, is used,
and forms the cathode, while large carbon rods dipping into
the molten mixture form the anode. As the current of
electricity passes through the molten mass, aluminium
separates out at the cathode and collects in the liquid
form at the bottom of the bath, whence it can be run off
from time to time. At the anode, the oxygen which is
liberated combines with the carbon electrode, producing
the poisonous gas carbon monoxide, which may either
escape as such or burn to form carbon dioxide.
The production of aluminium is now carried on in a
number of countries, more especially in those where an
abundant water-power is available. In this country the
isolation of the metal is carried out by the British
Aluminium Company at Kinlochleven, in the north of
Argyllshire. To obtain the power necessary to drive the
dynamos for the generation of the electricity required, a
great storage reservoir has been created, high up among
the mountains, by building a great barrage across the
valley of the River Leven.^ From this reservoir the water
is led through an aqueduct, three and a half miles in
length, to a penstock, situated on a shoulder of the
mountain, 900 feet above the factory and more than a
* The dam is over 1000 yards in length, with a maximum height of about
86 feet, and is capable of impounding twenty thousand million gallons of
water.
ELECTRICITY AND CHEMISTRY 179
mile distant from it ; and from this point the water rushes
down to the turbines, through pipes of more than a yard
in diameter.
Although the great expectations which were at one
time entertained with regard to this metal have not been
entirely fulfilled, aluminium, nevertheless, now occupies a
permanent and ever-growing place in our modern life.
Not only is it largely employed for articles of ornament
and of domestic use, and where lightness and portability
are of importance, but it is being increasingly used as a
conductor of electricity and, as we have seen, for the
production, by the " thermit " process, of high temperatures
and for the isolation of certain metals. Moreover, some of
the defects which militated against a more widespread use
of the metal, its low tensile strength and softness for
example, can be partly removed by admixture with other
metals, some of the alloys formed possessing properties of
great value. With copper, aluminium yields a bronze,
aluminium bronze^ of great hardness and high tensile
strength, which is practically not corrodible by sea-water ;
and when added to brass, aluminium greatly increases the
tenacity of that alloy. With the metal magnesium,
aluminium forms a valuable alloy called magnalium (con-
taining from 1-2 per cent of magnesium), which is even
lighter than aluminium itself and is equal to brass in
strength. The metal magnesium, used in the production of
this alloy, is a grey-coloured metal, which burns with a
very bright and photographically active light, and is
consequently used in the preparation of "flash-lights."
It is obtained by the electrolysis of fused chloride of
magnesiunL
i8o CHEMISTRY IN THE SERVICE OF MAN
But it is not only of the decomposing action of elec-
tricity, in the process of electrolysis, that use is made.
From the everyday use of electricity for heating and
lighting purposes, all are familiar with the fact that heat
is produced by the passage of electricity through a
conductor which offers a certain amount of resistance to
the current ; and by increasing the strength of the
current, the temperature may be raised to any point we
please, limited only by the melting or vaporising of the
conducting material. We have already seen, also, that
by means of the electric arc, electrical energy is trans-
formed into heat energy, and that the very high tempera-
ture of 50O0°-6ooo° F. can in that way be obtained. A
most powerful instrument has, therefore, been put into the
hands of the chemist, and by its means he has been
enabled not only to advance to a fuller knowledge of
substances and materials already known, but also to
prepare others which were hitherto unknown.
Of the utility of electricity applied to the production of
high temperatures, we have already had some examples
in the direct combination of atmospheric nitrogen and
oxygen, and in the manufacture of calcium carbide and
calcium cyanamide. Fused quartz or silica glass, with the
valuable properties of which we have also become
acquainted, is also produced by the fusion of quartz sand
in specially constructed, electrically heated furnaces ; and
the high temperatures which can now be produced
economically by means of electricity, are made use of in
the preparation of the substance phosphorus, which is so
largely used in connection, for example, with the manu-
facture of matches.
ELECTRICITY AND CHEMISTRY i8i
As a direct result of the successful application of
electricity to the production of high temperatures, we owe
the very valuable material known as carborundum, a
compound of carbon and silicon, discovered by the
American chemist, Dr. Edward G. Acheson, in 1891.
By heating a mixture of coke (carbon) and sand (oxide
of silicon) to a high temperature in an electric furnace
(Fig- I5)> oxygen is removed by the carbon from its
T — r
Fig. 15. — Carborundum Furnace.
A core of granular graphite is raised to a white heat by a powerful current
of electricity which passes between the graphite terminals A and B. At the
high temperature which is thereby produced, the carbon and sand of the
f uriounding mixture, C, react with formation of carborundum.
combination with silicon, and the latter then combines
with the excess carbon to form the crystalline substance,
carborundum, the hardness of which approaches that of
the diamond. This material is now produced in large
quantities and used as a grinding or abrasive material,
as well as for incorporating in the surface flayer of
concrete pavements, stairs, etc. By reason of its very
refractory character (it will withstand a temperature of
4000° F. without undergoing change), it is also used
i82 CHEMISTRY IN THE SERVICE OF MAN
for the protection of furnace walls, and for other heat-
resisting purposes.
Another very valuable abrasive and refractory material
of which mention may be made, is alundum (alumina or
aluminium oxide), obtained by fusing purified bauxite in
an electric furnace.
From the manufacture of carborundum there resulted
still another discovery of much importance, the discovery
of a method of making artificial graphite. Until about
twenty years ago, graphite, a crystalline form of carbon
familiar under the names of plumbago and black lead
(although it contains no lead at all), was known only as
a naturally occurring mineral. But during the process of
manufacture of carborundum it was found that the ends
of the rods of gas carbon (a very dense amorphous variety
of carbon formed in gas retorts), by which the electric
current was carried into the furnace, were converted, by
the high temperature to which they were exposed, into
graphite ; and, moreover, carborundum itself, when heated
to a sufficiently high temperature, decomposes with pro-
duction of graphite. In this way there was initiated a new
industry, the manufacture of artificial graphite, which has
undergone so great a development that artificial graphite
is now produced at Niagara Falls at the rate of 15,000,000
lbs. annually.
For the production of Acheson graphite, amorphous
carbon (anthracite coal, coke, etc.), mixed with a small
amount of oxide of iron, alumina, or silica, is heated to
a high temperature (5ooo°-6ooo° F.) in an electric furnace
of the same type as the carborundum furnace. At this
high temperature the iron, alumina, or silica which was
ELECTRICITY AND CHEMISTRY 183
added, is converted into vapour, and the amorphous carbon
passes into graphite. The silica and metal oxides added
to the coke act as catalysts and accelerate the conversion
of amorphous carbon into crystalline graphite ; in their
absence the change takes place only with difficulty.
To obtain graphite rods, plates, etc., finely-ground coke>
to which a small quantity of oxide of iron is added, is
mixed into a thick paste with pitch or tar. After this
paste has been moulded under high pressure it is heated in
the electric furnace, and the amorphous carbon thereby
converted into graphite.
This artificial graphite, which is superior to the natural
mineral by reason of its greater purity and uniformity, is
employed in a variety of ways. For electrical purposes,
whether for use in the construction of dry cells or as
electrodes in electro-chemical processes, it is greatly
superior to the dense gas carbon formerly employed, on
account of its greater electrical conductivity and its
mechanical properties ; and to another very important
use to which artificial graphite is put, reference will be
made in the following chapter.
Some one has said, "Nature's storehouse is man's
benefactor, and no gift from it renders greater service
than the waters of the earth " ; and in the recent develop-
ments of electro-chemistry we have seen how Nature's gift
has proved of service to man. Although the harnessing
of the great rivers and waterfalls of the world is due to
the engineer, and was made possible only by the advances
in mechanical and electrical engineering of last century,
the utilisation of the enormous amounts of energy contained
i84 CHEMISTRY IN THE SERVICE OF MAN
in the flowing waters of the earth, the rendering avail-
able of which represents so much real gain, so much real
progress for the benefit of mankind, is due chiefly to
the labours of the chemist. The combined achievement
is one that may well fill the mind with wonder ; and even
the most careless tourist cannot but be profoundly im-
pressed if, after gazing, shall we say, on the majestic,
down-leaping of the mighty waters of Niagara, he passes
into the power stations near by, where the turbines and
humming dynamos, working in obedience to the will of
man, without the smoke and dirt and clatter of the ordi-
nary factory, are transforming the energy of the rushing
river into the energy of electricity which, in the adjacent
factories, is then made to contribute to the material well-
being of man and the advance of civilisatioo.
CHAPTER X
THE COLLOIDAL STATE
When one brings sugar, salt, washing-soda, and many
other common and famiUar substances into contact with
water, the solid substance, if present in not too large
amount, disappears ; it dissolves, and a clear liquid is
obtained which we call a solution. For long chemists
and physicists have puzzled over this process, and they
puzzle even yet ; for while some consider the production
of a solution to be due to the chemical combination of
the dissolved substance, or solute, with the solvent, others
see in the process nothing more than the mechanical
intermingling of the molecules of the constituents of the
solution. Doubtless there is truth in both these views,
but even if combination does take place we must not
regard the solution as a whole as being a compound of
water with the sugar, salt, or whichever other substance
is taken. A compound is characterised, as we have already
seen, by the fact that its composition is perfectly definite
and constant, and cannot be altered by adding more or
less of one of the constituents. The composition of a
solution, however, can be altered as we please ; the pro-
portions in which the solid and the liquid are present in
the solution may be varied, in some cases varied very
i86 CHEMISTRY IN THE SERVICE OF MAN
greatly, so that we obtain solutions of different strength
or concentration. Even if chemical combination does
take place, it appears to do so only to a limited
extent, and is accompanied by a mechanical intermingling
of the molecules. We may, therefore, regard a solution as
being merely a homogeneous mixture in which the mole-
cules of the dissolved substance or solute, combined, it
may be, with a limited number of solvent molecules, are
uniformly distributed throughout and among the molecules
of the water, or other liquid which acts as the solvent It
is a homogeneous mixture of variable composition.
If, however, we leave on one side the question of the
nature of the solution process, and consider merely the pro-
perties of the solution produced, one of the most remark-
able facts established by the modern investigation of solu-
tions is the very close analogy which exists between a
substance in solution and a gas. For our present purpose
it is sufficient to refer to only one feature of the analogy,
the property of diffusion.
To account for the properties of gases there was
developed, about the middle of last century, a theory
known as the kinetic theory of gases, which was based
on the hypothesis that the molecules of a gas are in
perpetual and rapid motion, darting about in straight
lines with the speed of sometliing like a mile a second,
colliding ever and anon, some eighteen tliousand million
times a second, with other molecules, and pursuing, there-
fore, as the result of these collisions, a very zigzag course.
It is by virtue of this motion inherent in the molecules
that a gas can distribute itself or diffuse rapidly throughout
a room, or can fill completely the space, howso large that
THE COLLOIDAL STATE 187
space may be, which is offered to it. In the case of h'quids
the same inherent motion of the molecules, and therefore
the same power of diffusion, exists ; but the process now
takes place more slowly, for the molecules of the liquid
are packed more closely together, and the mutual collisions
are therefore more frequent. The forward progress of a
molecule is therefore very slow, like that of a man who
might try to pass through a dense and jostling crowd.
But still diffusion does take place, as we can easily satisfy
ourselves by gently pouring a layer of pure water on to a
solution of some strongly coloured substance, such as blue-
stone (copper sulphate) or bichromate of potash. After
some time we shall find that the coloured substance has
diffused upwards some distance into the water. The
experiment may be made more easily by dissolving in
the water sufficient gelatin to make a firm jelly, and then
placing a piece of this jelly in the coloured solution. After
a few hours it will be found that the coloured substance
has penetrated some distance into the jelly.
Even when the solution is separated from the pure
water by a membrane of parchment paper or by an animal
membrane {e.g. pig's bladder), diffusion takes place just the
same, as we can show by enclosing the solution of copper
sulphate in a tube of parchment paper which we then
immerse in water. Very soon we shall be able to detect
the presence of the copper sulphate in the water outside
the membrane.
During the sixties of last century this diffusion of dis-
solved substances through a parchment or animal membrane
was studied more fully by Thomas Graham, a native of
Glasgow, who later became a Professor of Chemistry in
i88 CHEMISTRY IN THE SERVICE OF MAN
London, and Master of the Mint. As a result of his in-
vestigation, Graham found that although certain substances
pass through a membrane of parchment paper, other sub-
stances do not do so. Since the substances, e.g. sugar or
salt, which could pass through this membrane, were such
as generally crystallise well, whereas those which would
not pass through, e.g. starch, gelatin, glue, were amorphous
and non-crystallisable, Graham divided substances into the
two classes, crystalloids and colloids (from the Greek KoXXa,
glue), and this distinction was one which was long main-
tained. From a practical point of view, in any case, this
distinction was of importance, for, as Graham showed, if a
mixture of crystalloids and colloids is placed in a parch-
ment cell and immersed in water, the crystalloids, but not
the colloids, diffuse out into the water. In this way a
separation of crystalloid from colloid can be effected by
a process to which Graham gave the name of dialysis^ a
process used universally at the present day for the prepara-
tion of colloids free from crystalloids.
Appropriate as Graham's classification of substances
appeared at the time, recent investigation has shown that
it cannot any longer be retained. The terms colloid and
crystalloid can now no longer be employed to connote
definite and different kinds of substances, but only different
states of matter ; for not only have substances such as
albumin and gelatin, which Graham regarded as dis-
tinctively colloid, been obtained in the crystalline form,
but even such definitely crystalloid substances as common
salt have been obtained in the colloidal state. But
language changes slowly, and although, through the
advance of knowledge, a term may acquire a different
THE COLLOIDAL STATE 189
signification, the term itself persists. And so one still
speaks of colloid substances, but means thereby substances
in the colloidal state, which may be defined as a state in
which one substance forms with another mixtures which
although they may appear homogeneous to the eye, even
when aided by the microscope, are nevertheless hetero-
geneous, the diverse colloid particles having a magnitude
greater than molecular. These apparently homogeneous,
but in reality heterogeneous mixtures, are called colloidal
solutions, or simply colloidal sols.
But it may be asked, how can we assert that these
colloidal sols are heterogeneous mixtures when we cannot
detect any want of uniformity even with the aid of the
microscope ? The answer is, that even if we cannot see
the particles themselves we can detect their presence,
and the manner in which this can be done was shown
long ago by Tyndall. Regard the air of a room bathed
in a uniform light. Can you see any particles there ? No.
But darken the room and let a ray of sunlight pass
through a hole or chink in the shutters, and what do you
see ? A diffused light, the sunbeam made visible, in which
the larger dust particles are seen to dance and swirl ; the
diffused light also being due to particles which are large
enough to reflect and scatter the waves of light, although
too small to be seen as separate individuals by the eye.
So also, by means of this " Tyndall phenomenon," as it is
called, the presence of particles in a colloidal sol can be
detected. Pass a beam of light through pure water or
through a solution of salt, the path of the beam is in-
visible ; the liquid is " optically empty." ' But pass the
• Owing to the presence of floating particles even in filtered water, the
I90 CHEMISTRY IN THE SERVICE OF MAN
beam through a colloidal sol, and the path of the beam
is traced by a diffused light, like the sunbeam in a
darkened room.
From this " Tyndall phenomenon," then, we learn that
particles which may be too small to be seen in the ordinary
way, may be detected if only the light reflected or dis-
persed by the particles, and not the direct rays from the
source of light, are allowed to enter the eye. And it is
clear that if, instead of the unaided eye, we employ a
microscope to examine the scattered light, we shall still
further extend our range of vision, and be able to detect,
although not actually to see in their own shape and colour,
particles which are much smaller than can be seen when
the microscope is used in the ordinary way. Through the
recognition of this principle there has been devised, in
recent years, an arrangement known as the ultra-
mkroscopey by means of which not only the heterogeneity
can be detected, but also the number of particles in a given
volume of the sol determined. A powerful beam of light,
instead of being directed into the microscope through the
liquid to be examined, is sent horizontally into the liquid,
at right angles to the line of vision through the microscope
(Fig. 1 6). If the liquid under examination is optically
empty, the field of view in the microscope will appear quite
dark ; but if particles are present in the liquid, the light
will be reflected and dispersed, and the minute points of
light thus produced will stand out, against a dark back-
ground, in the field of view of the microscope.
And how large are those particles which are thus
" Tyndall phenomenon " will be observed with ordinary pure water. Special
precautions most be adopted to free the water from all suspended particles.
THE COLLOIDAL STATE
191
detected in the apparently homogeneous colloidal sols ?
With the aid of even the most powerful microscope, the
smallest particle that can be seen by the ordinary method,
must have a diameter of not less than about one sixty-
thousandth part of an inch ; but by means of the ultra-
microscope, particles one-eightieth of this size, with a
diameter of about one five-millionth of an inch, can be
Fig. 16. — Ultra-microscope.
detected. This, however, is still about thirty times greater
than the diameter of the hydrogen molecule.
From the investigations carried out by means of the
ultra-microscope, it is found that colloidal sols may contain
particles of very different size, even in the case of the
same substance, and there is every reason to believe that
there exist in some at least of the sols particles which
are smaller than can be detected by the ultra-microscope,
although they are of greater than molecular dimensions.
In short, there appears to be no sharp division between
colloidal sols and true solutions, and it is possible to pass
gradually and without break from one to the other.
192 CHEMISTRY IN THE SERVICE OF MAN
And now let us see what are the main properties of
this colloidal state.
If we dissolve, say, two or three parts of gelatin in
a hundred parts of water,* we obtain a rather viscous
liquid which, on being cooled down, "sets" to a firm
jelly ; and this jelly, on being heated, melts again to a
viscous liquid. In this case, therefore, which is familiar
to every one, a reversible change from the liquid or sol
state to the state of a more or less rigid jelly, known
as a geU can be effected. If we add small quantities of
salts to this gelatin sol, there will be no apparent change,
but it will be found that the temperature at which gelation,
or the change from the liquid sol to the rigid gel takes
place, is altered ; it is raised or lowered according to the
salt taken.
But a very different behaviour is found in the case,
say, of the colloidal sol of sulphide of arsenic (arsenious
sulphide), obtained by passing sulphuretted hydrogen into
a solution of white arsenic (oxide of arsenic). This is a
clear, yellow-coloured liquid which can be passed un-
changed through filtering paper (a finely porous, unglazed
paper) ; it is as mobile as water itself, not viscous like
the gelatin sol ; and it does not set to a gel when
cooled down. The water, indeed, may be frozen to ice,
but, on thawing the ice, the sol of arsenic sulphide is
obtained as before. The arsenic sulphide sol, also, differs
very markedly from the gelatin sol in its behaviour
towards salts. By the addition even of small amounts
* The gelatin is first allowed to remain in contact with cold water until
it has swelled up and become soft. It is then warmed up with water, or
is placed in hot water.
THE COLLOIDAL STATE 193
of different salts, the sulphide of arsenic is caused to
separate out as an insoluble yellow solid.
This marked difference in the behaviour of colloidal
solutions of gelatin and of sulphide of arsenic, which may
be taken as typical of two classes of colloids, is traceable
to a distinct difference in the nature of the two sols. In
the case of the gelatin sol, we have a mixture of two
liquids ; it is comparable, therefore, with an emulsion, say,
of oil and water, and is, for that reason, called an
emulsoid. When jelly formation takes place, a honey-
comb structure is produced due to the separation of the
sol into two parts. one part, forming the walls of the
"honey-comb," consists chiefly of the colloid (gelatin)
with a little water ; the other part, filling the cells of the
"honey-comb," consists chiefly of water with a little of
the colloid. When such an emulsoid colloid is examined
by means of the ultra-microscope, no definite particles are
seen, but only a general diffused light.
In the case of the colloidal solution of sulphide of
arsenic, however, we have a mixture, not of two liquids,
but of a solid (arsenic sulphide) and a liquid (water) ;
and examination with the ultra-microscope shows that the
arsenic sulphide is present in the form of minute particles,
too small to be seen by the eye. Such a colloidal sol
is therefore comparable with an ordinary suspension, such
as muddy water, and is therefore called a suspensoid
colloid.
one of the most marked characteristics of suspensoid
colloids, and one which we have already seen demonstrated
in the case of sulphide of arsenic, is found in the fact
that addition of salts, or, speaking generally, of electrolytes,
o
194 CHEMISTRY IN THE SERVICE OF MAN
brings about, with varying degrees of effectiveness, the
separation or precipitation of the colloid in an insoluble
form. A similar behaviour is found in the case of ordi-
nary fine suspensions, e.g. of clay in water, and this
is sometimes of considerable geological or geographical
importance. Thus, the sedimentation of finely divided,
water-borne clay is markedly influenced by the purity of
the water transporting it, taking place more rapidly when
salts are present than when they are absent. This, indeed,
is one reason for the rapid deposition of river mud on
mixing with sea-water, and for the consequent silting up
of river mouths and the formation of deltas, such as has
taken place at the mouth of the Nile.
But this precipitation of suspensoid colloids and the
sedimentation of fine suspensions by electrolytes, is counter-
acted more or less effectively by the presence of emulsoid
colloids, e.g. gelatin or albumin, so that, in their presence,
a much larger amount of electrolyte is necessary to pro-
duce precipitation or sedimentation. The emulsoid colloids
exert a "protective" action, and the suspension or the
suspensoid colloid is rendered much more stable. Indeed,
so stable may the colloid become that the colloidal sol
may even be evaporated to dryness without destroying
the colloidal state ; on treating the dried solid with water,
it passes back again into the state of a colloidal sol.
Such colloid sols, e.g. colloid silver or collargol, now find
important uses in medical practice as powerful bactericides.
In the manufacture of photographic plates, prepared by
coating plates with gelatin containing a fine suspension
of silver bromide, we have an important industrial appli-
cation of the. protective action of emulsoid colloids. If a
THE COLLOIDAL STATE 195
solution of potassium bromide is added to a solution of
silver nitrate, silver bromide is formed and separates out
as an insoluble curd, quite unsuitable, on account of its
coarseness, for photographic purposes. But if gelatin is
first dissolved in the solutions of potassium bromide and
of silver nitrate, no curdy precipitate but only a uniform
colloidal suspension of very fine particles of silver bromide
is obtained on mixing the solutions.
The protective action of emulsoid colloids and the
precipitating action of salts, are excellently illustrated, also,
on a large scale in nature. Some of the great rivers of the
world, like the Mississippi and the storied Nile, whose
turbid waters have from time immemorial carried in their
bosom the promise of bountiful harvests, are always
muddy, whereas other rivers which are even more swiftly
flowing, like the Ohio, are, except in times of flood,
perfectly clear. In the case of the first two rivers there is
much colloidal organic matter washed into them by which
the clay and soil are retained in a state of fine suspension ;
and it is only when the rivers reach the salt waters
of the sea that the suspended matter is precipitated with
the production of river bars and deltas. In the case of
the River Ohio, however, the water remains clear owing
to the absence of colloidal organic matter and the presence
of lime and other salts.
Even when a colloid has separated out from solution
in the solid form, it can, in many cases, be brought back
into colloidal solution again, or be " peptised," as it is
said, by small quantities of various substances. A
very interesting illustration of this behaviour, and one
which is of the greatest importance in our everyday
196 CHEMISTRY IN THE SERVICE OF MAN
life, is seen in the plastic properties of clay. Clay is a
hydrated silicate of alumina which possesses the property,
in its normal condition, of forming, more or less readily,
with water, a fine suspension or suspensoid colloid. on this
property depends what is called the plasticity of clay, and
just as the presence of certain substances renders the clay
suspension more stable, so also certain substances facilitate
the passage of the precipitated clay into the state of
colloidal suspension ; they render the clay more plastic.
Everyone is familiar with the story of how Pharaoh
commanded his taskmasters to increase the burdens laid on
the Israelites by withholding from them straw wherewith to
make bricks ; and doubtless many have wondered wherein
the hardship lay. By most people, probably, the view has
been held that the straw was added as a binding material,
much as hair is used in mortar ; but such an explanation is
scarcely satisfying when it is remembered that the straw
fibre is a very weak one, and when we read, moreover, that
when straw could not be obtained, stubble was used.
Another explanation may therefore be offered.
About fourteen years ago it was found by Dr. E. G.
Acheson, to whom we owe the discovery of carborundum
and the process of making artificial graphite, that when
clay is mixed with a dilute solution of tannin, it becomes
much more plastic, and the strength of the dried brick is,
moreover, greatly increased. Although straw does not
contain tannin, it was found that when straw is treated
with water, the extract obtained has the same action on
clay as tannin has, the plasticity of the clay and the
hardness of the brick being greatly increased. It seems
therefore a plausible view that the straw was used, not for
THE COLLOIDAL STATE 197
the purpose of binding the clay, but for the purpose of
rendering the clay more plastic ; and the particular burden
imposed on the Israelites would therefore consist in their
having to make bricks with a less plastic and, consequently,
more difficultly worked material. In allusion to this Dr.
Acheson gave to the clay which had been rendered more
plastic by the addition of tannin, the name of " Egyptian-
ised clay."
The property of tannin of facilitating the production of
an ultra-microscopic or colloidal suspension, has also been
applied to the production of a colloidal suspension of
graphite for use as a lubricant. By means of the very
high temperature which can be obtained in the electric
furnace. Dr. Acheson was able to prepare from anthracite
coal a form of graphite which could be ground to a fine
powder. Such graphite, however, when shaken with
water or oil, yields a suspension from which the graphite
soon settles out ; but if the graphite is first treated with a
solution of tannin, it becomes " deflocculated," as it was
said, and forms a colloidal suspension which can be kept
indefinitely without showing any tendency to separate out.
The colloidal suspension of " Deflocculated Acheson
Graphite " in water is known as aquadag} or water-dag^
and is used as a lubricant for metal-cutting tools. By
filtering the aquadag under pressure through thin films of
rubber, the colloidal graphite can be obtained as a paste.
When this is mixed with oil, a colloidal suspension known
as oildag is obtained which is much more efficient as a
lubricant than oil alone.
1 The termiDation dag is derived from the initial letters of Deflocculated
Acheson Giapbite.
198 CHEMISTRY IN THE SERVICE OF MAN
These colloidal suspensions of graphite are so fine that
the graphite particles will pass through the finest filter
paper. on adding salts, however, the graphite is floccu-
lated, as we have seen is the case witl> colloidal suspensions
of sulphide of arsenic and of clay, and the graphite is now
retained by filter paper, and separates as a sediment on
standing.
Although we have seen that various differences exist
in the nature and behaviour of the two classes of colloidal
solutions, the emulsoid and the suspensoid, there is one
respect in which the two classes resemble each other,
namely, in the relatively large extent of surface exposed
by a given amount of colloid. This large development of
surface is due, in the one case, to the honey-comb or
sponge-like structure of the colloid sol ; and, in the other
case, to the minute size of the particles, for the more a
given mass of matter is subdivided, the greater becomes
the extent of surface exposed. To the existence of this
highly developed surface, one of the most characteristic
and important actions of colloids, namely, the removal of
substances from solution, is due. When, for example, a
colloidal solution of ferric hydroxide, the so-called dialysed
iron of the pharmacist, is shaken with a dilute solution of
white arsenic, a large proportion, it may be practically
the whole, of the arsenic is removed from solution and
collected or adsorbed on the surface of the colloid, and it
is to this property of colloids that the use of dialysed iron
as an antidote in arsenical poisoning is due.
This adsorbing action of a large surface depends on
the fact that the concentration of a dissolved substance in
THE COLLOIDAL STATE 199
the surface layer of a solution is different from, and
frequently greater than, what it is in the body of the
solution. When the concentration of the dissolved sub-
stance in the boundary layer is greater than in the body of
the solution, the dissolved substance becomes concentrated
in the layer of solution in contact with the solid, and this
film of concentrated solution remains adhering to the
surface of the solid when the rest of the liquid is poured
off. Herein we find, also, the explanation of the action
of the very porous material, charcoal, in removing dissolved
colouring matter from solution, a property which finds a
very important application for the removal of the colour
from molasses in sugar refining.
But the special and peculiar behaviour of colloids
depends not only on their power of surface adsorption,
but also on the fact that the colloid particles are electri-
cally charged. In some cases, e.g. ferric hydroxide and
aluminium hydroxide, the colloid is positively charged,
but in most cases, it is negatively charged.
The existence of such an electric charge can readily
be demonstrated with a colloidal solution of sulphide of
arsenic. If this is placed in a U-shaped tube, and if we
then insert in the liquid wires connected with the terminals
of a high voltage battery or dynamo (the ordinary electric
lighting circuit can conveniently be employed), one in
either limb of the tube, we shall find that the sulphide of
arsenic migrates towards and collects around the positive
terminal. The particles of arsenic sulphide, therefore, carry
a negative charge of electricity. Even with fine sus-
pensions, such as a suspension of fine clay or a slime of
peat, the same phenomenon is observed ; the clay particles
200 CHEMISTRY IN THE SERVICE OF MAN
or the peat fibres collect around the positive terminal in a
firm mass. Since the effect depends primarily on the
voltage of the current, while only an insignificant amount
of electricity is used, this process of cataphoresis, or
electric transport of suspended particles, constitutes a very
economical means of freeing a fine suspension of slime from
water; and it has, in fact, found industrial application in
Germany to the partial drying of very wet peat or peat
slime. The high cost of fuel required to evaporate off the
water from such very wet peat is thereby saved, so that it
becomes possible to utilise peat-bogs which are so wet
that they could not otherwise be worked with commercial
success.
When a positively charged and a negatively charged
colloid, such as ferric hydroxide and arsenic sulphide, are
brought together, the oppositely charged particles attract
one another, and this leads to a mutual flocculation and
precipitation of the colloids.
The property of adsorbing and removing substances
from solution which colloids possess in virtue of the large
surface which they expose, together with the fact that the
colloids are electrically charged, plays an important part
in the processes of dyeing, in agriculture, in the purification
of water and of sewage, in the life processes of animals and
plants, and in many other domains.
The process of dyeing is by no means a simple one,
and no single explanation can be given of the way in
which dyes are, in all cases, fixed on the fibre of the
material dyed. But in recent years the general advance
in our knowledge of the peculiar behaviour of the
THE COLLOIDAL STATE aoi
substances in the colloidal state, has led to the recognition
of the important role which colloids may play in the
dyeing process. Not only are the fibres of silk, wool,
and cotton similar, in many respects, to colloids, more
especially in possessing a structure exhibiting a largely
developed surface, but many of the dye-stuffs are also
colloids. In some cases the dye may be fixed on the
fibre by the addition of salts, the colloidal dye being
thereby precipitated in the fibre just as addition of salts
produces a precipitation of colloidal sulphide of arsenic.
But in other cases the process of dyeing is probably one
which depends largely on a mutual precipitation of colloids
having opposite electric charges, the negatively charged
fibres attracting and fixing on themselves positively
charged dye-stuffs.
Whilst it is found that, in very many cases, silk and
wool have the power of taking up and fixing the dye-stuff
directly, it is frequently found that in the case of cotton
the fixation of the dye has to be assisted by a mordant,
which is either a colloid itself or can give rise to a colloid.
The colloid so formed is deposited on and within the fibre
to be dyed, and attracts and fixes oppositely charged
colloidal dyes. According to the nature of the dye, so
must be the nature of the mordant employed, salts of
aluminium, chromium, etc., which give rise to the
hydroxides of the metals, being used when the dye has a
negative charge or has acid properties {e.g. alizarin) ;
while tannic acid and similar substances are employed for
dyes with a positive charge or with basic properties.
Chemical actions, however, also play an important part in
the dyeing processes.
202 CHEMISTRY IN THE SERVICE OF MAN
In agriculture, also, the colloidal state is of the greatest
importance. In the soil there exist various colloidal sub-
stances, such as the humus, colloidal ferric hydroxide and
aluminium hydroxide, clay, etc. Owing to the presence of
these, soluble substances, such as the salts of potassium,
phosphates, and other substances necessary for the life of
the plant, are adsorbed and retained in the soil, and so
kept available for the support and nourishment of vegeta-
tion instead of being washed away into the rivers and sea.
The humus, moreover, being a colloid similar to albumin
and gelatin, has the property of imbibing water and so
helps to maintain the soil in a moist condition, while it
also acts as a substrate for the bacteria concerned in the
conversion of nitrogenous organic matter into such a form
as can be taken up by the plants, as well as for the other
bacteria always present in the soil.
Owing to the presence of such colloids as ferric
hydroxide and aluminium hydroxide, filtration through
soil acts as a very efficient means of purifying sewage
and other waste water, from organic impurities. These
impurities in sewage, for example, have been found to
be, to a large extent, negatively charged colloids which
are therefore precipitated and retained by the positively
charged colloids, ferric hydroxide and aluminium hydroxide.
By such filtration through the soil, therefore, even the highly
impure water which drains from cultivated and manured
land is rendered comparatively sweet and harmless. In
the same way, the purification of drinking-water by
filtration through beds of sand or through charcoal, de-
pends on the removal of impurities by adsorption on the
large filtering surface exposed, and on the retention of
THE COLLOIDAL STATE 203
positively charged colloidal matter, bacteria, etc., by the
negatively charged sand or charcoal particles.
An important application of the behaviour just described,
is found in sewage farms, where the drainage of towns is
pumped on to the land and the liquid allowed to drain
through the porous soil. Here, the waste organic matter
is retained and affords a rich nutriment for the growing
crops, while the liquid effluent which drains away is such
that it might be drunk with safety. By such means can, in
suitable surroundings, a source of annoyance and loss be
turned to profit.
Although, in recent years, the importance of the col-
loidal state in its bearing on many of the activities of
daily life, has become more clearly recognised and more
fully appreciated, it is in connection with our conceptions
of the constitution of matter that the investigations of
microscopic and ultra-microscopic suspensions have gained
some of their most brilliant triumphs. For more than two
thousand years there has existed in men's minds the idea
of matter as made up of separate, discrete particles ; and
in the nineteenth century, as we have seen, this idea was
given a more definite form at the hands of Dalton and
of Avogadro. But the particles, the molecules, which
make up matter as our eyes reveal it to us, are not in a
state of rest. In the case of a gas, these molecules are
in a state of almost inconceivable tumult and commotion,
which even the restraint imposed by the condensation and
the congealing of the gas to the liquid and the solid state,
is not able wholly to subdue. Such, at least, is the picture
of matter which the genius of a Clerk Maxwell and a
204 CHEMISTRY IN THE SERVICE OF MAN
Clausius revealed to us in what is known as the kinetic
theory of matter. But although this theory has been found
to give a satisfactory explanation of the behaviour, more
especially of gases, and has enabled one to calculate not
only the size of the molecules (roughly, one hundred
millionth of an inch in diameter), but also the speed of
their flight, there were not wanting some who refused to
believe in the objective reality of molecules and of the
picture presented by the kinetic theory. And yet, 'even
as early as 1827, these molecules, although by their minute
size removed far beyond the range of human vision, had,
all unknown to their observers, made their presence mani-
fest by their actions. In that year, the botanist Robert
Brown, while examining suspensions of pollen grains under
the microscope, observed that the particles were never at
rest, but were in rapid motion, vibrating, rotating, moving
irregularly along a zigzag path, sinking, rising, — perpetu-
ally in motion. In this Brownian movement, as it is
called, the full significance of which has only recently
been grasped — it had, indeed, been observed long ago by
the French naturalist, Buffon, who saw in it a manifesta-
tion of life — we have an actual picture of that tumult and
commotion of the molecules which were revealed to the
mental vision of mathematical physicists. But it is not,
of course, the motions of the molecules themselves that
we see in the Brownian movement, but only the effect of
the incessant bombardment of the coarser, visible particles
of the suspension, by the molecules of the liquid.
Over a lengthened period of time, the number of blows
which a suspended particle of sufficient size, say such as
is visible to the naked eye, would receive from the
tHE COLLOIDAL STATE 205
molecules of the liquid in which it is suspended, would
be the same in the different directions. The suspended
particle, therefore, would show no sign of motion. But if
we imagine the period of time made sufficiently short, the
number of impacts of the liquid molecules will no longer
be equal in different directions, the impacts will no longer
balance one another, and if the suspended particle is small
enough it will, at each blow, be caused to move, first in
one direction and then in another, and all the faster the
smaller the particle ; and it is this motion of a particle of
a suspension under the blows which are rained upon it by
the molecules of the liquid, that constitutes the Brownian
movement. With particles of ultra-microscopic dimensions
the phenomenon is exhibited with extraordinary vividness,
and it is to this Brownian movement that the stability of
colloidal suspensions is largely due. From the careful
quantitative investigations of this phenomenon which have
been carried out in recent years, the various molecular
magnitudes — the kinetic energy of the particles and their
velocity of diffusion, for example — have been computed ;
and such is the closeness of agreement between the results
so obtained and the values which the kinetic theory would
lead us to expect, that we cannot any longer hesitate to
believe that in the rapid, darting motions of the ultra-
microscopic particles we have made manifest to us some-
thing of the turbulent stir and bustle which is going on
unceasingly in that under-world of molecules which lies
beyond the reach of our senses.
CHAPTER XI
MOLECULAR STRUCTURE
Of all the known elements, the element carbon, familiar
to us in the three physically distinct forms, charcoal,
graphite, diamond, stands out pre-eminent in its power
of forming compounds with other elements. So numerous,
indeed, are its compounds — their number at the present day
exceeding 150,000 — that their study has developed into a
special branch of chemistry, organic chemistry. This name
is but the survival from an older period when chemists drew
a distinction between the compounds occurring in the non-
living, mineral world, and those occurring in the living animal
and vegetable organisms, and which were thought to be
producible only with the help of a special form of energy,
the so-called vital force, inherent in the living cell. That
any essential difference exists between the two classes of
compounds, that the chemical laws which obtain within the
domain of living nature are different from those which are
found in inanimate nature, can no longer be held. For not
only can many, very many, of the compxjunds which were
formerly regarded as typical products of animal and vege-
table metabolism, typical organic compounds in the older
sense, be prepared in the laboratory from purely mineral
materials, but the synthetic production of not a few of these
compounds has even developed into industries of enormous
MOLECULAR STRUCTURE 207
magnitude. The term, " organic chemistry," is still retained,
not with its old signification, but merely as denoting the
chemistry of carbon and its compounds ; for, indeed, the
vast majority of these " organic " compounds are found in
no animal or vegetable organism, but have been prepared
by the intelligent combining together of substances by the
chemist
But if I have referred particularly to the compounds of
carbon, it is not for the purpose of describing either the
methods of preparation or the specific properties of any of
these substances, but rather for the purpose of discussing
very briefly a phenomenon which, although met with in
the case of the compounds of other elements, is found with
extraordinary frequency in the case of the compounds of
carbon. This is the phenomenon to which the name of
isomerism has been given.
When Dalton introduced his atomic theory, the basis on
which all modem chemistry has been built, he showed, as
we have seen, that a compound could be regarded as being
formed by the combination or uniting of the atoms of the
constituent elements in certain constant and definite propor-
tions. But whilst the law, " one compound, one composition,"
has remained unshaken, the progress, more especially of
organic chemistry, soon showed that the converse statement,
" one composition, one compound," which, to the earlier
chemists, was equally an article of faith with the former, is
very far removed from the truth. As the number of com-
pounds became multiplied, it began to be more and more fre-
quently observed, that the same elements might be united
in the same proportions and yet yield compounds with
entirely different properties. More than a hundred different
208 CHEMISTRY IN THE SERVICE OF MAN
compounds, for example, can be produced by the combining
together of nine atoms of carbon, ten atoms of hydrogen,
and three atoms of oxygen. To this phenomenon, that
different compounds may have the same composition, the
term isomerism has been applied. Just as the same set of
bricks can, by varying their arrangement, be formed into
structures of totally different kinds, so also the same atoms
can, by varying their arrangement within the molecule, give
rise to different atomic structures, or different compounds.
In other words, the discovery of isomerism, so entirely
unforeseen by Dalton and by the earlier organic chemists,
led to the recognition of the fact that the properties of a
compound depend not merely on its composition, but also
on its internal structure or the arrangement of the atoms
within the molecule ; and our knowledge of a substance is
not complete until we know what is this internal structure
or constitution of the molecule.
A knowledge of the constitution is essential for the
successful building up or synthesis of a compound from
simpler materials, which we shall discuss more fully in the
following chapter. To elucidate the constitution of the
different compounds, is one of the main aims of the organic
chemist, and in the case of the more complex compounds,
the problem becomes one of the greatest difficulty. only
this much can be said here. Through the laborious efforts
of numberless chemists, a knowledge has been gradually
accumulated of the internal structure or constitution of a
very large number of substances, and also of the relations
between these different structures and the physical and
chemical properties of the compound. In order to deter-
mine the constitution of an unknown compound, therefore.
MOLECULAR STRUCTURE 209
the substance is, by various chemical actions, broken down
into bits, as it were, and one then seeks to identify the
fragments, the simpler substances, so obtained, with sub-
stances of which the constitution is already known. From
the knowledge gained in this way, one then attempts to
piece the fragments together again, and so to build up or
synthesise the original substance.
But the task of elucidating the constitution of organic
compounds would be a hopeless one without the aid of
some guiding principle and some method by which the
molecular constitution can be represented. It was, there-
fore, a great step in advance when Kekule, in 1858, showed
how molecular constitutions could be represented diagram-
matically, using as a guiding principle what is known as
the doctrine of valency.
This doctrine of valency, the introduction of which we
owe mainly to the late Sir Edward Frankland, is merely a
recognition of the fact that the elementary atoms do not
possess an unlimited power of combination. Hydrogen
and chlorine, for example, can combine together only atom
for atom ; an atom of hydrogen cannot combine with more
than one atom of chlorine, and an atom of chlorine cannot
combine with more than one atom of hydrogen. No
element is known having a lower combining power than
hydrogen, and this is therefore taken as the standard of
reference. Chlorine, an atom of which can combine with
only one atom of hydrogen is said to have unit com-
bining power, or unit valency ; it is univalent. Oxygen,
an atom of which can combine with two atoms of hydrogen
(as in water, HjO), is said to be bivalent ; nitrogen, an
atom of which can combine with three atoms of hydrogen,
P
210 CHEMISTRY IN THE SERVICE OF MAN
is said to be tervalent; carbon, an atom of which can
combine with four atoms of hydrogen, is said to be quadri-
valent ; and so on.
Although there is, of course, no material link or bond
between the atoms, we can nevertheless represent union
between atoms as if it were material, by means of a line,
or lines, according to the valency of the atom. Thus, as
we have already seen, we can represent the compound
H
I
marsh-gas by the diagrammatic formula H — C — H, and
I
H
the higher hydrocarbons of that series by such a chain
H H H
I I I
of carbon and hydrogen atoms as H — C — C — C — H ;
I I i
H H H
a formula which we can also write in the simpler form,
CH3 — CHj — CH3. By the extension of this idea, it became
possible not only to represent the molecular constitution
of known compounds, but also to foresee the possible
existence of isomeric compounds. Thus, for example, if
we have the compound CH3 . CH2. CH3, (the bond between
the carbon atoms being now represented by a dot), it is
clear that we can replace one atom of hydrogen in this
compound by an atom, say, of chlorine, in two ways, so that
we should obtain either the compound CH3. CHj. CH^Cl,
or the compound CH3.CHCl.CH3, the chlorine being
in the former case attached to a terminal carbon atom
and in the latter case to the intermediate carbon atom.
According to this, there should exist two and only two
MOLECULAR STRUCTURE 211
different compounds having the composition C3H7CI ; and
as a matter of fact two compounds and only two are
known.
The origin of this theory of chemical structure has been
recounted by Kekul6 himself. During a period of residence
in London he was returning from a visit paid at Islington
to where he stayed at Clapham. " one fine summer
evening," he relates/ " I was returning by the last omnibus,
* outside ' as usual, through the deserted streets of the
metropolis, which are at other times so full of life. I fell
into a reverie, and lo ! the atoms were gambolling before
my eyes! Whenever, hitherto, these diminutive beings
had appeared to me, they had always been in motion ; but
up to that time, I had never been able to discern the
nature of their motion. Now, however, I saw how,
frequently, two smaller atoms united to form a pair ; how
a larger one embraced two smaller ones ; how still larger
ones kept hold of three or even four of the smaller ; whilst
the whole kept whirling in a giddy dance. I saw how the
larger ones formed a chain," . . . And then he adds : " I
spent part of the night in putting on paper at least sketches
of these dream-forms." From these sketches were de-
veloped the constitutional or structural formulae, of which
examples have just been given.
But again he had a dream. Now he was at Ghent,
and dozed before his fire. Again he saw the atoms
gambolling before his eyes, the chains twining and twist-
ing in snake-like motion. "But look! What was that?
one of the snakes had seized hold of its own tail, and the
» F. R, Japp, " Kekule Memorial Lecture" (Transactions of the Chemical
Society, 1898).
212 CHEMISTRY IN THE SERVICE OF MAN
form whirled mockingly before my eyes. As if by a flash
of lightning I awoke ; " • . . but the picture Kekule had
seen of the snake which had seized its own tail gave him
the clue to one of the most puzzling molecular structures,
the structure of the benzene molecule, a ring of six carbon
atoms to each of which a hydrogen atom is attached.
Thus we obtain the structural formula of the benzene
molecule,
H
/\
U.C^ X.H
I I!
H.C C.H
H
the " ring " of carbon atoms being written in the form
of a hexagon instead of in the form of a circle. " Let
us learn to dream," said Kekule, "then perhaps we
shall find the truth." But he wisely added : " But let us
beware of publishing our dreams before they have been
put to the proof by the waking understanding."
By the introduction of the doctrine of valency and of
Kekule's diagrammatic method of representing molecular
constitution, a satisfactory basis seemed to have been
obtained for the future development of organic chemistry.
And yet, it was not long before the insufficiency of thife
theory of chemical structure became only too apparent,
owing to the discovery that, in some cases, the number of
isomeric compounds is greater than can be represented
by the structural formulae of Kekul^. A new isomerism
MOLECULAR STRUCTURE 213
was discovered, an isomerism which manifested itself in
the property known as optical activity.
Early last century it was discovered that whe« a ray
of light is passed through a crystal of Iceland spar, the
ethereal vibrations, which propagate the light, and which,
ordinarily, take place in all directions at right angles to
the path of the ray, are all brought into one plane. The
light is said to be polarised. When, now, this polarised
light is passed through certain substances, quartz, turpen-
tine, a solution of cane sugar, etc., it is found that the plane
of polarisation, the plane in which the
ethereal vibrations take place, is rotated
or twisted, this rotation or twisting
taking place sometimes to the right,
sometimes to the left ; an effect which
we can illustrate by the twisting of a
strip of stout paper into a right-
handed or left-handed spiral, such as
is represented in Fig. 17. Substances
which possess this property of rotating
the plane of polarised light, are said Fig. 17.
to be " optically active."
This property ot optical activity can also be de-
monstrated by a modification of a very interesting ex-
periment due to the late Sir George Stokes. When a
beam of light from a projection lantern (Fig. 1 8), is reflected
vertically downwards by means of a mirror, through a
column of water rendered slightly turbid by the addition
of a few drops of an alcoholic solution of rosin, the path
of the beam is rendered visible by the fine suspension of
rosin particles (Tyndall phenomenon, p. 189) j and the
214 CHEMISTRY IN THE SERVICE OF MAN
beam of light appears equally bright all round. But if
the light from the lantern is first polarised by passage
through a prism of Iceland spar, and then reflected down-
wards through the column of water, the appearance obtained
is that of a band which is light only on two opposed sides,
and dark on the other two opposed sides. on rotating
the prism of Iceland spar, the band also rotates and turns
alternately its light and dark sides to the eye. The effect
Fig. i8.— Demonstration of thji Pouuiisation of Light.
Light from a lantern is polarised by passage through the polarising prism P,
and the beam of light is then directed by the lens L on to a mirror M, by which
the light is directed vertically downwards through water contained in the cylinder
C, and rendered turbid by a fine suspension of rosin. A vertical, polarised
band of light is obtained. If the cylinder C is replaced by D, which contains
a concentrated solution of cane sugar, the band of light is twisted into the
form of a spiral.
produced is as if the beam of light on passing through the
prism of Iceland spar, were given a flat form, like a book,
from the two opposite edges of which light is emitted,
while the sides remain dark. Thus we have illustrated
the phenomenon of polarisation of light. If, now, the
cylinder of water is replaced by a cylinder containing a
solution of cane sugar, the band of light is twisted into a
spiral form, and on rotating the prism of Iceland-spar,
this spiral band of light will appear to move with a
LOUIS PASTEUR, 1822-1895.
(From a Photograph by Pierre Pdil.)
To /ace p. 215.
MOLECULAR STRUCTURE 215
screw-like motion. From the fact that the different rays of
coloured h'ght which together constitute white light, are
twisted or rotated to different extents (the blue rays being
rotated more than the red), the spiral band of light shows
the colours of the rainbow.
What then is the explanation to be given of this re-
markable property of substances, the study of which, start-
ing with the brilliant discoveries of Pasteur in 1848, has
occupied the attention of many of our foremost chemists
down to the present day ?
When Pasteur commenced the investigations which were
to initiate a revolution in the current ideas regarding the
molecular structure of organic compounds, two isomeric acids
were known having the same composition, namely, tartaric
acid and paratartaric acid. The former, which is found
occurring in grape juice, is optically active ; the latter is
inactive. on examining the crystals of these two acids, and
of a number of their salts, Pasteur found that whereas the
crystalline faces of the inactive paratartaric acid and its
salts, were all fully developed, and the crystals symmetrical
(Fig. 19) ; in the case of the active tartaric acid, the full
development of the crystalline faces was interrupted by the
occurrence of so-called hemihedral faces (Fig. 20). The
occurrence of these hemihedral faces was regarded by
Pasteur as the outward and visible manifestation of the
property of optical activity, in accordance with a view which
had been suggested by Sir John Herschell in the case of
crystalline quartz, which is also optically active. But
whereas quartz is optically active only in the crystalline
state, tartaric acid retains the property even when dis-
solved. In the former case, the property depends on the
2i6 CHEMISTRY IN THE SERVICE OF MAN
crystalline structure, in the latter, it depends on the internal
molecular structure.
But a further discovery was made by Pasteur.
During his investigation of one of the salts of tartaric
and paratartaric acid (namely, sodium ammonium tartrate
and sodium ammonium paratartrate), Pasteur found, as
was to be expected, that the crystals of the tartrate
resembled those of the other tartrates he had examined
in possessing hemihedral faces, arranged in a similar
manner. The crystals obtained from the solution of the
Fig. 19. — HoLOHEDRAL Crystal
OF Paratartaric Acid.
Fig. 20, — Crystal showing
Hemihedral Facks.
paratartrate, however, instead of being holohedral, with
the crystalline faces fully developed, were found also to
have hemihedral faces ; but these hemihedral faces, instead
of, as in the tartrates, all being turned the same way,
were inclined, sometimes to the right and sometimes to
the left (Fig. 21). This result was quite unexpected;
and Pasteur, on carefully separating the two sets of
crystals and examining their solutions, discovered, with
no less surprise than pleasure, that one set of crystals
rotated the plane of polarised light to the right, while
the other set rotated the plane by an equal amount to
MOLECULAR STRUCTURE
2lf
the left. on dissolving together equal amounts of the
two sets of crystals, a solution was obtained which was
quite inactive.
Here, thea* we have the discovery of that new kind
of isomerism to which reference has just been made, and
which showed the insufficiency of the structural formulae
of Kekule. The two salts into which the paratartrate
had been separated were identical in all their chemical
and physical properties, save only in the disposition, to the
right or to the left, of the small hemihedral faces occur-
fl^
Pi
Fig. 21.— Enantiomorphic Crystals of Optically Activb
Tartrates.
ring on their crystals, and in the property of rotating the
plane of polarised light to an equal extent but in opposite
directions. From these two salts, Pasteur obtained two
different tartaric acids ; one having the power of rotating
the plane of polarised light to the right and identical with
the acid occurring in grape juice, the other, hitherto
unknown, and having the power of rotating the plane of
polarised light to the left. Moreover, on mixing together
in solution equal quantities of these two optically active
acids, there separate from the solution crystals of the
2i8 CHEMISTRY IN THE SERVICE OF MAN
inactive paratartaric acid, which is thus shown to be a
compound of the two active acids in equal proportion.
The discovery of the two optically active tartaric acids
was a momentous one, effecting a revolution in the views
of chemists regarding molecular structure ; and we can
well understand the feeling of happiness and the nervous
excitement by which Pasteur was overcome on making
the discovery. Rushing from his laboratory and meeting
a curator, he embraced him, exclaiming : " I have just
made a great discovery! I have separated the sodium
ammonium paratartrate into two salts of opposite action
on the plane of polarisation of light The dextro-salt is
in all respects identical with the dextro-tartrate. I am
so happy and overcome by such nervous excitement that
I am unable to place my eye again to the polarisation
apparatus." But the question now arose as to how the
existence of the two optically active tartaric acids could
be accounted for.
All material things belong to one or other of two
classes, according as the image which is formed of the
object in a mirror, is such that it could or could not be
superposed on the object. In the case of a cube, for
example, the image formed in a mirror is identical with
the object, and we can imagine the image superposed on
the original cube. A cube is a symmetrical object. But
if a right hand is held in front of a mirror, the image
which is obtained represents a left hand, and this cannot
be superposed on the right hand ; a right hand will not
fit into a left-hand glove. In the case oi a hand, there-
fore, we have an asymmetrical object, which can exist in
two distinct, so-called enantiomorphic forms, similar in all
MOLECULAR STRUCTURE 219
respects, but not superposable, not identical. And when
we examine the crystals of the two optically active
tartaric acids (or of their salts), it is seen that they also
are related to each other as the right hand is to the
left hand; each represents the non-superposable mirror
image of the other (Fig. 21), and the two crystals,
although in all points similar, are not identical. If,
however, the crystalline form is to be regarded, as Pasteur
regarded it, as a visible manifestation of the internal
structure, we are led to the conclusion that the molecular
structures of the two active tartaric acids are asymmetric
and enantiomorphously related to each other as object
to non-superposable mirror image. "Are the atoms,"
Pasteur asked, " are the atoms of the dextro-acid grouped
in the form of a right-handed helix, or do they stand
at the comers of an irregular tetrahedron, or are they
arranged in some other asymmetrical manner?" And
he replied, "We are not yet in a position to answer
these questions. But it cannot be a subject ot doubt
that there exists an arrangement of the atoms in an
asymmetric order, having a non-superposable image."
Looking back on the experimental investigations of
Pasteur, we cannot suppress a feeling of disappointment
that it was not vouchsafed to him, with the clear views
he possessed regarding chemical structure, to take but
a little step forward and to develop these views into a
theory of chemical structure. But the time was not yet
ripe, and it was not until after more than twenty years
that the study of organic chemistry furnished a sufficient
number of examples of optically active compounds, to
make it possible to give an answer to Pasteur's questions.
220 CHEMISTRY IN THE SERVICE OF MAN
Nevertheless, Pasteur introduced into chemistry a con-
ception of extraordinary importance and fruitfulness, the
conception of molecular asymmetry, and he recognised
that molecular structure is not a matter of two dimen-
sions only, but of three. The atoms are not arranged
in a plane, as the formulae of Kekule represent them,
but in three-dimensional space. In this way Pasteur
inaugurated a new chemistry, a "Chemistry in Space"
or " Stereo-Chemistry."
The conception of molecular asymmetry and the idea
of the grouping of the atoms at the corners of an
irregular tetrahedron were developed, in 1874, into a
A A
consistent theory of molecular structure, embracing the
optically active isomeric compounds, by a Dutch and a
French chemist independently, van't Hoff and Le Bel.
If we imagine a carbon atom at the centre of a
tetrahedron, and if the four atoms or groups, with which,
as we have seen, a carbon atom can be united, are
situated at the four corners of the tetrahedron, it will
be found that so long as two, at least, of the atoms
or groups are the same, the molecule, represented as a
tetrahedron, will be symmetrical and its mirror image
will be superposable on and therefore identical with the
original. This will be clear from an inspection of Fig. 22,
MOLECULAR STRUCTURE
221
which represents such a tetrahedron and its mirror image.
The right-hand tetrahedron, obviously, only requires to
be turned through an angle of 90°, on the corner B as
a pivot, to become identical in disposition with the left-
hand tetrahedron;
If, however, the four atoms or groups attached to the
carbon atom are all different, the molecule, as represented
by the tetrahedron, becomes asymmetric, and gives a
mirror image which is no longer superposable on the
original. Two isomeric forms are therefore possible. This
will be understood from Fig. 23. Viewing these tetrahedra
A A
Fig. 23.
from a similar position, we see that the groups BCD,
in the one case, are arranged from left to right ; in the
other case, from right to left. If one of these represents
a molecule which rotates the plane of polarised light to
the right, the other will represent a molecule which rotates
the plane of polarised light to the left.
The views of van't Hoff and Le Bel have received the
amplest confirmation. Not only has it been found that
all compounds which are optically active do contain at
least one atom of carbon to which four different atoms
or groups are attached — a so-called asymmetric carbon
222 CHEMISTRY IN THE SERVICE OF MAN
atom — but also, no compound has been obtained the pos-
sible existence of which could not be predicted by means
of the van't Hoff and Le Bel theory. So fruitful has the
conception of molecular asymmetry and of the asymmetric
carbon atom proved, that it has been extended also to the
atoms of other elements than carbon, of which optically
active isomers have been prepared.
We have already seen that in the case of tartaric acid
— and the same holds in all other cases of optically active
substances — there exist, or can exist, not only the two
optically active isomers, but also an inactive isomer, pro-
duced by the combination of the two oppositely active
forms in equal amounts, and separable again, by suitable
means, into the active forms. This inactive form is known
as the racemic form. In the case of one particular salt,
sodium ammonium paratartrate, as we have seen, this
breaking up of the racemic form (the paratartrate) takes
place on crystallising from water at the ordinary tempera-
ture. But this method is capable of only a limited appli-
cation. Pasteur, however, introduced two other methods
for effecting the resolution of the racemic into the active
forms or for obtaining one of the active forms separate
from the other, namely, by making use of some living
organism or of some other asymmetric, optically active
material. When, for example, the solution of the racemic
paratartaric acid is acted on by blue mould, Peniallium
glaucum, the fungus feeds on and destroys the dextro-
rotatory acid, which occurs naturally in grapes, but leaves
unchanged the laevo-acid, which is an artificial product
of the laboratory. The solution, therefore, becomes
MOLECULAR STRUCTURE 223,
laevorotatory, and the laevo-acid can be obtained by concen-
trating the solution and allowing it to crystallise. In the
process of fermentation, also, under the action of various
enzymes, which are themselves asymmetric agents, pro-
duced in the living animal and vegetable cells, we find a
similar selective action. Thus, whereas the dextro-rotating
glucose, the well-known grape sugar, undergoes fermenta-
tion, the laevo-rotating glucose, a compound only obtained
artificially, remains unchanged in the presence of yeast.
An asymmetric agent acts only on materials of similar
asymmetry to itself, just as a right-handed screw will only
fit into a right-handed thread. So long as the two optically
active isomers are brought into relations with symmetrical
agents^ they behave identically ; but wJten they recu:t with
an asymmetric agent, a different behaviour is exhibited by
the two forms.
This selective action is ot great physiological import-
ance, since in all the life processes, such as digestion and
assimilation, we are dealing with the action of the opti-
cally active, asymmetric materials contained in the cells and
tissues. We find, therefore, that although the naturally
occurring albumins and sugars, for example, are capable
of being digested, the isomeric compounds of opposite
activity pass through the body without being absorbed.
And a similar differentiation of action is met with in the
case of many of the optically active alkaloids. " Here,
then," said Pasteur, "the molecular asymmetry proper to
organic substances intervenes in a phenomenon of a physio-
logical kind, and it intervenes in the rdle of a modifier
of chemical affinity. . . . Thus we find introduced into
physiological principles the idea of the influence of the
224 CHEMISTRY IN THE SERVICE OF MAN
molecular asymmetry of natural organic products, of this
great character which establishes, perhaps, the only well-
marked line of demarcation that can at present be drawn
between the chemistry of dead matter and the chemistry of
living matter."
In the investigation of molecular structure, the study
of optically active substances has been of supreme im-
portance, and the knowledge which has been gained has
exercised an important influence on the understanding and
interpretation of biological processes, opening to physio-
logy, as Pasteur said, new horizons, distant but sure. But
it is not merely the domain of the material sciences which
has been enriched by the investigations of stereo-chemistry ;
the most fundamental problems of life, our very ideas with
regard to life itself, and the phenomena of life, receive
illumination.
Until 1828, as we have seen, the production of the
organic substances occurring in the animal and vegetable
organisms was considered to be the prerogative of life ;
but the synthetic production in the laboratory of many of
the compounds which are typical products of the animal
and vegetable organism, led to the abandonment of that
belief, and science began to look upon the phenomena of
life as completely explicable in terms of physics and of
chemistry. But the discovery and investigation of the
optically active compounds introduced a new factor. As
Professor F. R. Japp, in his Presidential Address to the
Chemical Section of the British Association in 1898, so
admirably emphasised, " the phenomena of stereo-chemistry
support the doctrine of vitalism as revived by the younger
physiologists, and point to the existence of a directive force
I
MOLECULAR STRUCTURE 225
which enters upon the scene with life itself, and which,
whilst in no way violating the laws of the kinetics of
atoms, determines the course of their operation within the
living organism."
In Nature, most asymmetric compounds are found
occurring in one of the optically active forms only.
Dextro-rotatory tartaric acid, for example, occurs in grape
juice, but the laevo-rotatory tartaric acid is not found in
Nature, and is known only as a laboratory product ; grape
sugar likewise occurs naturally only as the dextro-rotatory
form ; while the albumins are Isevo-rotatory. When, how-
ever, it is attempted to prepare an asymmetric compound
in the laboratory from symmetric substances only, from
substances, that is to say, which are not themselves opti-
cally active, it is always found that the product obtained
is inactive. As Pasteur said: "Artificial products have
no molecular asymmetry ; and I could not point out the
existence of any more profound distinction between the
products formed under the influence of life and all others."
It is true that the inactive, racemic form, which is
obtained as the result of the artificial synthesis, can be
separated into the two optically active forms, with the
help of asymmetric, optically active compounds ; or we
can even, by the process of fermentation or the action of
organisms, destroy one of the active forms and so obtain
a single optically active compound. But these processes
involve the use either of living organisms or of materials
which have been produced by living organisms, and the
production of the active form is, therefore, due directly or
indirectly to living matter. But, as we have seen, Pasteur
also found that, in some cases, the resolution of the racemic
Q
226 CHEMISTRY IN THE SERVICE OF MAN
form can be effected simply by crystallisation. By allowing
a solution of the inactive racemic sodium ammonium
paratartrate to crystallise, crystals of the dextro- and of the
laevo-rotatory sodium ammonium tartrate were, as we have
already seen, deposited separately, and could, owing to the
difference in their crystalline forms, be distinguished from
one another and be separated by hand. Since the original
racemic paratartrate could be prepared synthetically from
symmetrical materials by the action of only symmetrically
acting reagents, and since this racemic form could be
resolved into the active forms by the symmetrically acting
process of crystallisation, it was thought that " the barrier
which M. Pasteur had placed between natural and artificial
products " had been thereby broken down. And this was
undoubtedly the view held by the majority of chemists.
But was this view — a view still held by many — correct ?
Pasteur certainly did not think so, and he pointed out very
pertinently, that " to transform one inactive compound into
another inactive compound which has the power of resolv-
ing itself simultaneously into a right-handed compound
and its opposite, is in no way comparable with the possi-
bility of transforming an inactive compound into a single
active compound. This is what no one has ever done ; it
is, on the other hand, what living nature is doing unceas-
ingly before our eyes." The artificial, racemic compound
certainly, had been resolved into the two active forms by
the symmetrical process of crystallisation, but these two
forms had not been separated from each other ; both active
forms were present side by side. Their separation "re-
quires the living operator, whose intellect embraces the
conception of opposite forms of symmetry." But, as
MOLECULAR STRUCTURE 227
Professor Crum Brown asked long ago : " Is not the
observation and deliberate choice by which a human
being picks out the two kinds of crystals and places each
in a vessel by itself, the specific act of a living organism
of a kind not altogether dissimilar to the selection made
by Penicillium glaucum ? ", a mould which, as we saw,
destroys one optically active form but not the other.
While Pasteur certainly believed that all the attempts
which had been made to synthesise a single optically active
form, without the intervention, direct or indirect, of life,
had been unsuccessful, he appears to have held the view
that as science advanced, the inability to effect such a
synthesis might be removed, for while he recognised the
necessity for the existence of asymmetric forces "at the
moment of the elaboration of natural organic products,"
he conceived the possibility that such asymmetric forces
might lie outside the living organism and " reside in light,
in electricity, in magnetism, or in heat." This view,
certainly, is one that cannot be dismissed off-hand, and
some see in circularly polarised light an asymmetric agent
which might account for the production in nature of single
optically active forms. But the suggestions and experi-
mental evidence which have been offered in support of this
view cannot certainly be regarded as convincing. What-
ever of fuller knowledge and more successful achievement
the future may hold, one thing, at least, may be said now —
that all attempts to synthesise a single optically active
compound under the influence of circularly polarised light
or of magnetic or other purely physical forces, have met
with failure. And if the evidence of stereo-chemistry is to
be accepted, it points to the conclusion, to quote the words
228 CHEMISTRY IN THE SERVICE OF MAN
of Professor Japp, that "at the moment when life first
arose, a directive force came into play — a force of precisely
the same character as that which enables the intelligent
operator, by the exercise of his will, to select one crystal-
lised enantiomorph and reject its asymmetric opposite."
CHAPTER XII
SYNTHETIC CHEMISTRY
It may, perhaps, have seemed to some that however
interesting, as an intellectual speculation, the theories of
molecular structure discussed in the previous chapter
might be ; however much they might satisfy a philo-
sophical curiosity regarding the mystery which lies at
the heart of things, they could be of very little practical
importance and could scarcely come at all into direct
touch with the daily life of mankind. And yet, these
theories form the very basis and foundation of some of
the greatest industries of the present day ! Kekul^'s
dreams, perhaps, were an interesting psychological
phenomenon, but the stuff that his dreams were made
of, the theories of molecular structure, were as important
for the advance and development of organic chemistry,
as a chart and compass are for a mariner. For, the purpose
of a scientific theory is not merely to explain or co-ordinate
knowledge already acquired, but also to be a guide to the
exploration of the unknown ; and without the theories
of molecular structure or constitution put forward by
Kekul6, van't Hoff and Le Bel, there could not have been
built up that vast structure of organic chemistry such as we
know it at the present day, nor could we have witnessed
230 CHEMISTRY IN THE SERVICE OF MAN
that crowning achievement of organic chemistry, the
artificial, synthetic preparation of many of Nature's own
products, from which has developed the industrial pro-
duction of those innumerable dyes, therapeutic agents,
perfumes, and other materials, which are regarded as
necessaries in our modern civilisation.
But while the theories of molecular structure and con-
stitution gave the guidance necessary for the altogether
phenomenal development of organic chemistry during the
past sixty years, that development could actually take place
only through the genius, the energy and the persistence
of hundreds of zealous workers who devoted themselves
to the task of synthesising and elucidating the constitution
of thousands of organic compounds, and it is therefore
only natural that it is in that country — Germany — which
amongst all other countries has been conspicuous for its
recognition of the importance of such investigations, and
for the encouragement which it has given to them, that
we find the industries dependent on synthetic organic
chemistry chiefly flourishing.
Not only has the chemist discovered numberless com-
pounds hitherto unknown, but he has even entered into
competition with Nature herself, and has successfully broken
the monopoly which heretofore she had enjoyed in the
production of many compounds both of ornament and
of utility. In fact, so successful has the chemist been,
that not only can the artificial products, in a number
of cases, compete with the natural products, but they have
even driven these entirely out of the market. In this way
great industries have arisen, of which the most important
are those closely interdependent industries which find their
SYNTHETIC CHEMISTRY 231
raw materials mainly in coal tar, and it is to these that we
shall first turn our attention.
By the distillation of coal there is obtained not only
the gaseous mixture so largely employed as an illuminant,
but also considerable amounts of ammonia and a thick,
dark-coloured, evil-smelling liquid, coal tar— one of the
most valuable and important materials obtained by man.
It is not an attractive-looking material, and yet there have
been evolved from it, by the painstaking labours of a
multitude of chemists, substances innumerable — dyes by
the thousand, which rival in range and beauty of tone the
finest products of Nature's imagining ; explosives which
the strongest works of man are powerless to resist ; anti-
septics and drugs ; the sweet-smelling essences of flowers ;
and developers of the latent photographic image. This
coal tar is, indeed, an almost inexhaustible storehouse of
raw materials for the manufacture of products of manifold
variety.
By subjecting the crude coal tar to a process of
distillation, such as is done in the refining of crude
petroleum, various substances are obtained which distil
over at different temperatures. Of these the most im-
portant are the following ; —
Liquids.
b.p.
Benzene 176° F.
Toluene 230° F.
Solids.
m.p.
Phenol (carbolic acid) 106° F.
Naphthalene 174'' F.
Aolbiacene 415° F.
232 CHEMISTRY IN THE SERVICE OF MAN
Benzene^ or as it is frequently called in commerce,
benzol, forms the starting-point in the manufacture of
aniline (which can be regarded as benzene in which one of
the atoms of hydrogen is replaced by the group NH2) ; and
this, in turn, is the starting-point in the preparation of
a large number of dyes — the aniline dyes. These aniline
dyes, which were the first synthetic dyes to be prepared,
constitute, however, only a part of the total number of dye-
stuffs which are now manufactured from coal-tar products.
Toluene (commercially, toluol) is used as a raw
material in the manufacture not only of dyes, but also
of the powerful high explosive, trinitrotoluene, or T.N.T.
Phenol or Carbolic Acid, is a well-known antiseptic, and
is also the starting-point in the preparation of the explosive
picric acid, lyddite or melinite. It is also used in the
manufacture of dyes.
Naphthalene is a valuable constituent of coal tar. It is
the raw material chiefly employed in the manufacture of
indigo.
Anthracene is the raw material employed in the manu-
facture of a large number of important dyes, the most
familiar of which is the red dye, alizarin, or Turkey red.
Important as these different substances are, they con-
stitute only a small part of coal tar, the amounts in which
they occur being, moreover, dependent not only on the
nature of the coal used but also on the temperature at
which the coal is distilled. Thus, the benzene and toluene
together constitute about 3 per cent, phenol about i per
cent., naphthalene about 5 per cent, and anthracene
about 0"5 per cent of the coal tar formed in gas manu-
facture. By the distillation of one ton of coal, therefore,
SYNTHETIC CHEMISTRY 233
we should obtain the above constituents in the following
quantities, roughly : —
Benzene and Toluene 3i lbs.
Phenol . . l| lbs.
Naphthalene 6 lbs.
Anthracene lo ozs.
The Coal-Tar Dyes.
Until the middle of last century, men were dependent
for all the dyes with which they coloured their bodies or
their garments, on colouring matters which were chiefly
of animal and vegetable origin : the colouring matter of
logwood ; the animal dye, cochineal ; the blue dye, indigo
or woad, with which our ancestors in these islands are
said to have stained their bodies ; the red dye, alizarin,
obtained from the root of the madder plant, once exten-
sively cultivated in Southern Europe ; and the costliest
of all dyes, the most famous dye of the ancient world, the
Tyrian purple, obtained from a shell- fish {Murex brandaris)
found on the eastern shores of the Mediterranean.
*• Who has not heard how Tyrian shells
Enclosed the blue, that dye of dyes
Whereof one drop worked miracles,
And coloured like Astarte's eyes
Raw silk the merchant sells ? "
(Browning : Popularity.)
These dyes, and a few others, were all that were available
until the year 1856. In that year the first synthetic dye,
the once favourite mauve, was prepared by the late Sir
W. H. Perkin, by the oxidation of crude aniline, and since
that time colouring matters to the number ot several
thousands have been discovered by the chemist. The
natural dyes are mostly of a pronounced, even crude
234 CHEMISTRY IN THE SERVICE OF MAN
colour, but the products of the chemist are of an almost
infinite variety ; and, far out-rivalling the natural dyes in
range of colour and delicacy of tone, they have ousted
these dyes from the dye-works. Starting from benzene,
naphthalene, and anthracene, constituents of the dirty-
looking liquid, coal tar, which less than a hundred years
ago was a useless waste material and a nuisance to the
gas manufacturer, synthetic dyes to the value of over
;^20,ooo,ooo, are manufactured annually, more than three-
quarters of this amount being produced in Germany.
It is quite impossible here to enter into a discussion
of the composition and constitution of the coal-tar dyes,
some of which are among the most complex of the com-
pounds of carbon ; but it may be said that the technique
of dye manufacture has become so perfected, and our
knowledge of the variation of colour with the constitution
of the compound has become so well established, that the
synthetic production of new shades is no longer a hap-
hazard process, but one of which the conditions of success
are clearly known.
But it is, perhaps, in the artificial production of
Nature's own colouring matters, more especially of alizarin
and indigo, that organic chemistry has achieved its most
striking successes. Through the labours of many chemists
the composition of these natural products was determined
and their constitution or molecular structure unravelled,
and with the knowledge thus obtained chemists have suc-
ceeded in preparing these compounds artificially — not
merely substitutes for or imitations of the natural products,
but the actual products themselves — and that more cheaply
than Nature herself can produce them.
SYNTHETIC CHEMISTRY 235
Forty or fifty years ago, over the whole of Southern
Europe, and eastwards to Asia Minor, great tracts of land
were devoted to the growing of the madder plant ; in
PVance alone, 50,000 acres were devoted to its culture.
When the roots of this plant were allowed to ferment, a
substance alizarin, so called from the name given by the
Arabs to the madder root, was formed, which was capable
of dyeing cotton of a bright red colour — the so-called
Turkey red, one of the oldest of dyes and most largely
used in the dyeing of cotton goods. But these madder
fields have now all disappeared ; for when the composition
and nature of this dye-stuff had once been ascertained,
it was not long before chemists discovered a method by
which the dye could be manufactured from what was then
practically a waste material, anthracene, one of the
constituents of coal tar. By a series of comparatively
simple reactions one could pass from the hydrocarbon
anthracene (C14H10) to anthraquinone (CnHg02), and
from anthraquinone to dihydroxy-anthraquinone or ali-
zarin [Ci4H802(OH)2]. In this way the madder dye
can be manufactured much more cheaply than Nature
can produce it, and instead of the 750 tons of alizarin
extracted from madder roots in 1870, over 2000 tons are
now manufactured annually in chemical works.
The fate of the madder threatens also to be the fate
of another dye-producing plant {isatis tinctoria) from
which the much prized dye-stuff, indigo, has for thousands
of years been obtained. Even as late as the seventeenth
century, the woad was cultivated in Europe, but with the
opening up of trade with the East, the European dye could
not hold its own with the cheaper indigo obtained from the
236 CHEMISTRY IN THE SERVICE OF MAN
Indian plantations ; and these, until recently, controlled
the markets of the world. But even they have not been
able to stand against the march of science, and, in the
production of synthetic indigo, the conquest of Nature by
the chemist and manufacturer constitutes one of the most
striking features of the nineteenth century. The fight
was a long one, and I know of no other case in which
the genius and resourcefulness of the chemist and the
persistence and enterprise of the directors of German
chemical industry, themselves expert chemists^ have been
so conspicuously shown, as in the successful industrial
production of this dye. Let me try to recount, in the
briefest possible outline, the achievement which has already
become historic
As far back as 1880, the artificial production of indigo
was first achieved by the German chemist, Adolf von
Baeyer, using as raw material the substance toluene, which,
as we have seen, is one of the constituents of coal tar.
But although this laboratory production of indigo consti-
tuted an achievement of the highest scientific importance,
the chemical manufacturer strove in vain to use this
discovery in his struggle to oust the natural product.
Indigo certainly could be manufactured, and manufactured
in quantity, but — and this is the whole essence of the
matter — the artificial indigo cost more than the natural,
and the raw material, toluene, was not procurable in
sufficient amount to make the displacement of the natural
indigo possible. For seventeen years the struggle went
on, the chemist assisting with his brains and experience,
the manufacturer assisting with his money, until at last,
in October, 1897, after many attempts and many failures,
SYNTHETIC CHEMISTRY 237
and the expenditure of close on ;^ 1,000,000, synthetic
indigo (indigo, that is, prepared by the skill of man from
simpler substances), was placed on the market in compe-
tition with the natural product from the Indian plantations.
And what, to-day, is the result of this competition ? Hear
how eloquently the following figures speak. In 1896
India exported indigo to the annual value of over
;^3»500.ooo; in 191 3 her exports of this dye were worth
about ;^6o,ooo, while the German export was valued at
about ;^2,ooo,ooo. Moreover, in the above period, the
price of indigo fell from about 8s. to about p. 6d. per lb.
Since the production of indigo involves a considerable
number of different processes, and requires the use of a
number of different substances, of which sulphuric acid,
ammonia, chlorine, and acetic acid are the chief, the
success of the synthesis as a whole, depends on the success
with which each step of the process can be carried out,
and on the cost of the substances employed. The starting-
point in the manufacture is the hydrocarbon naphthalene,
a constituent of the invaluable coal tar, and familiar to all
on account of its use in preserving furs against the attack
of moths ; and the first step in the synthesis of indigo
is to convert this naphthalene into a compound called
phthalic acid. This, it was known, could be done by
heating the naphthalene with strong sulphuric acid ; but
when the manufacturer attempted to make use of this
fact, he found that although the desired conversion did
indeed take place, it did not proceed sufficiently readily,
and the cost of carrying out this first step in the process
was so great that it would have rendered the industrial
production of indigo unremunerative. But here a lucky
238 CHEMISTRY IN THE SERVICE OF MAN
accident came to the assistance of the manufacturer, for,
through the accidental breaking of a thermometer, it was
discovered that mercury acts as an efficient catalyst in the
conversion of naphthalene to phthalic acid, facilitating the
process to such a degree as to allow it to be carried out
with commercial success.
But the commercial success of the production of indigo
depended also on improvements being effected in the
manufacture of the various chemicals employed. Thus
the demand for a very concentrated sulphuric acid and
the fact that during the process of heating with naphtha-
lene, large quantities of sulphur dioxide are formed, led to
the development of a new method of making the acid,
namely, by the " contact process " to which we referred in
Chapter VI. For the production of chlorine, also, of
which enormous quantities are required, the old method
of obtaining the gas from hydrochloric acid was useless,
and a new method had to be introduced, namely, by
passing a current of electricity through a solution of
common salt, the chlorine being then obtained in a pure
state by liquefaction. The ammonia is obtained, as we
have seen, as a product of the distillation of coal and can
now also be prepared synthetically ; and the acetic acid,
of which 3000 tons are used annually in the manufacture
of indigo, is obtained by the distillation of 150,000 cubic
yards of wood.
The industrial production of synthetic indigo, albeit
benefiting mankind as a whole, has not only dealt a
mortal blow at the prosperity of the Indian plantations,
but it has revolutionised two other industries, the manu-
facture of sulphuric acid, a staple chemical industry of
SYNTHETIC CHEMISTRY 239
England, and of chlorine, together with that of the
bleaching material prepared from it, bleaching powder.
Although it is not possible to enter into a detailed
discussion of the practical process of dyeing, it is of interest
to note that the process is different in the case of indigo
and other so-called vat dyes, from what it is in the case of
other dye-stuffs. on account of its insolubility, the indigo
is first converted into a colourless compound, called indigo-
white, which is soluble in alkalies. After the material
to be dyed, which may be cotton, wool, or silk, has been
immersed in this solution, it is removed and exposed to
the air, whereby the oxygen of the air oxidises the
colourless indigo-white to indigo-blue. The dye is, there-
fore, developed in the fibre after its removal from the
bath.
Closely related, chemically, with indigo, is that other
ancient dye, Tyrian purple. Some years ago the nature
of this dye was investigated by a German chemist who
extracted it from the glands of two species of marine
snail, the Murex brandaris and Murex truncidus, and
ascertained that this " dye of dyes, whereof one drop
worked miracles," was a compound of indigo with bromine,
a compound which can be prepared synthetically with
comparative ease. The costliness of this natural dye was
almost proverbial, and the reason for this is not far to
seek ; for the colouring matter obtained by the German
chemist from the glands of I2,0(X) shell-fish, amounted to
only about 23 grains, and the estimated cost of the dye was
nearly £60 an ounce.
240 CHEMISTRY IN THE SERVICE OF MAN
Synthetic Drugs.
The sixteenth and seventeenth centuries are regarded
as marking a distinct era in chemistry, inaugurated by
Paracelsus. During that period chemistry was looked upon
as the handmaid of medicine, and the study of the action
of substances on the human organism and the preparation
of drugs, were held to be the true functions of the chemist.
That was the period of what was called iatro-chemistry.
While the modern chemist would resent the restriction
of his functions within such narrow limits, the services
which chemistry has, in modern times, rendered to medi-
cine are greater beyond comparison than all the iatro-
chemists were ever able to perform. Not only have
" Nature's remedies," the juices and extracts of plants,
the valuable alkaloids like quinine and morphia, been
exhaustively studied and the methods of their extraction
improved, but they have been supplemented, in some cases
even displaced, by a large array of new drugs and
medicinal preparations which owe their origin to the
genius and painstaking labours of chemists. The herbalist,
in fact, has given place to the scientific chemist, and the
manufacture of synthetic drugs, anaesthetics, hypnotics,
antipyretics, and drugs for the treatment of special diseases,
has developed, in the past thirty years, into an industry of
great importance.
The earliest of these synthetic products dates from 1832,
when Liebig prepared the anaesthetic chloroform, by the
action of bleaching powder on alcohol.^ Who will dare
' Chloroform is now prepared from acetone, a product of the distillation of
wood.
SYNTHETIC CHEMISTRY 241
to compute the sum of misery and suffering from which
this one discovery has freed mankind, or place a money
value on the service it has rendered ? But the discovery
of chloroform has been followed by the discovery of other
anaesthetics ; general anaesthetics like ether and ethyl
chloride (also, like chloroform, produced from alcohol) ;
and local anaesthetics like novocaine (a derivative of coal-
tar benzene), used as a substitute for the vegetable alkaloid
cocaine.
Side by side with chloroform we may place the closely
related compound, iodoform, a yellow crystalline com-
pound largely used as an antiseptic.
Following closely on the discovery of chloroform came
the discovery of chloral, the first hypnotic to be produced
commercially. But the dangers attending the use of
chloral led to the search for and discovery of other
hypnotics which are free from the bad qualities of chloral ;
and at the present day quite a number of synthetic
hypnotics are known, of which perhaps the most familiar
are veronal, and the inter-related compounds, sulphonal,
trional, and tetronal.
If the introduction of the anaesthetic chloroform
marked a new era in surgery, a similar claim may perhaps
also be made in connection with the substance adrenaline,
the active principle of the supra-renal glands. This
substance when injected subcutaneously even in excessively
minute amount, produces so violent a contraction of the
arteries that the blood is driven away from the injected
tissues and " bloodless " surgery becomes a possibility.
Adrenaline was isolated for the first time in 1901,
from the supra-renal glands of sheep and oxen, close on
R
242 CHEMISTRY IN THE SERVICE OF MAN
looo lbs. of tissue (the glands from 20,000 oxen) being
required to yield i lb. of adrenaline. It was not long,
however, before the nature of the substance had been
determined, and a process for preparing it synthetically
on an industrial scale had been devised. It is now placed
on the market under the name suprarenine.
The compound adrenaline formed in the glands of
animals is optically active and rotates the plane of polar-
ised light to the left. It will, however, be understood
from the previous chapter that the synthetic product is
inactive and a compound of the two optically active
forms. This racemic form, as it is called, is only half
as active physiologically as the naturally occurring laevo-
rotatory form, and it is therefore important to resolve
the synthetic compound into its two optically active forms
and to isolate the laevo-form. This can be done with
the help of dextro-tartaric acid.
The difference in the behaviour of an optically active
substance towards the asymmetric living tissues was em-
phasised in the previous chapter, and an excellent illus-
tration of this property is afiforded by adrenaline ; for it
is found that the physiological action (the increase of the
blood pressure) is twelve to fifteen times greater in the
case of the naturally occurring laevo-adrenaline than in
the case of the synthetic dextro-adrenaline and about
twice as great as in the case of the inactive racemic form.
The great development which has taken place in recent
times in the industrial production of synthetic drugs is due
mainly to the discovery in 1 887 of antifebrin, the first of a
series of synthetic antipyretics which have entered into
competition with the natural alkaloid quinine. Strangely
SYNTHETIC CHEMISTRY 243
enough, the discovery of the antipyretic properties of anti-
febrin, a compound derived from acetic acid and aniline
and known in chemistry as acetanih'de, was due to a mis-
take on the part of a laboratory boy who supplied this
substance in mistake for naphthalene. During a pharma-
cological investigation of the substance, its strongly anti-
febrile action was detected, and from a chemical analysis,
it was learned what the substance really was. The success
of this first synthetic antipyretic soon led to the prepara-
tion and systematic study of the physiological action of a
large number of other substances, but although hundreds,
indeed thousands, of these have been found to have a
certain medicinal value, only a few have, by their special
properties or effectiveness, obtained a place in actual
practice. Among synthetic drugs, however, there exists a
ceaseless competition, and antifebrin has been largely super-
seded by newer and better drugs. Antifebrin, as we have
seen, is derived from aniline, and is liable to undergo
decomposition in the body, giving rise again to aniline
which exerts a toxic action ; and the continued use of the
drug is therefore dangerous. By slightly modifying the
composition of antifebrin, however, another compound,
the well-known phenacetin, is obtained, a substance which
possesses the valuable antipyretic properties of antifebrin,
but is much less toxic.
one other synthetic drug of which special mention
may be made is the anti-rheumatic, aspirin, a derivative
of salicylic acid, which is itself a therapeutic agent of
value, and is prepared from the coal-tar product, phenol
or carbolic acid. Owing, however, to the large amounts
of phenol used in different departments of synthetic
244 CHEMISTRY IN THE SERVICE OF MAN
chemistry, the amount obtained from coal tar is quite
insufficient to supply the demand, so that phenol itself is
now largely manufactured from coal-tar benzene.
Synthetic Perfumes.
If the synthesis of colouring matters and of drugs
constitutes an achievement of the greatest importance, the
significance of which is all too little realised, scarcely less
notable are the successes of the chemist in the synthesis
of those natural spices and perfumes, which have been
valued by man from the earliest days. For thousands of
years the volatile substances to which the different flowers
and plants owe their odours have been prepared by dis-
tillation or by extraction by means of solvents. But in
the past thirty or forty years the secrets of nature have
been largely unravelled, and the chemical laboratory has
become odorous as a garden and filled with the per-
fumes of violet and rose, heliotrope, lilac, hyacinth, and
orange blossom ; and from the stills of the chemist there
also flow liquids whose flavours imitate those of the apple,
pear, pineapple, and other fruits, and which, in consequence,
find application as artificial fruit essences. Although in a
number of cases these perfumes and flavouring essences
merely imitate the products of nature, in other cases the
chemist has succeeded in preparing the identical sub-
stances to which the flavour of the natural fruit or the
perfume of the growing flower is due.
one of the first of these natural substances to be pre-
pared by the chemist was the substance coumarin, the
odoriferous principle of the sweet woodruff {Asperula
SYNTHETIC CHEMISTRY 245
odorata)^ a fragrant substance used in the preparation of
the perfumes known as Jockey Club and New-mown
Hay. This synthetic preparation of a natural odoriferous
principle was speedily followed by the preparation of the
flavouring material, vanillin, the active principle occurring
in the vanilla bean. This substance is now manufactured
from toluene, as raw material, and is of great commercial
importance. To these earliest synthetic products numerous
others have since been added, so that the main odoriferous
principles of oil of wintergreen {methyl salicylate)^ oil of
bitter almonds {benzaldehyde), hawthorn blossom {anisic
aldehyde), lily of the valley [terpineol], ambergris {ambrein)^
and others, can now be prepared artificially. In the case
of other synthetic compounds we have substances which,
while not identical with the natural perfumes, closely
resemble them, and are employed in large quantities
either as substitutes for the natural perfumes or for blend-
ing with them. Of these the most important are ionone,
or imitation violet, imitation musk, and imitation oil of
bitter almonds, or " oil of mirbane " {nitro- benzene).
The synthetic production of sweet-smelling substances,
often at only a fraction of the cost of the natural product,
has led to a great extension in the use of such substances,
more especially for the perfuming of soaps, creams, and
other toilet materials.
We have already seen how the synthetic production
of the colouring matters alizarin and indigo have pro-
duced vast economic changes by the more or less com-
plete supersession of the natural by the synthetic dyes
In the commercial production of camphor we have another
246 CHEMISTRY IN THE SERVICE OF MAN
illustration of the successful synthesis of an important,
natural product, without, however, the same disastrous
consequences to the latter.
Camphor, one of the most familiar of substances, has
been produced for many centuries in Japan, Borneo, For-
mosa, and other regions of the Far East It is found
chiefly in the leaves of a species of the laurel tree, the
Laurus camphora^ from which it is obtained by distilling
the leaves or other parts of the tree, in a current of steam.
The camphor, being volatile, passes over with the steam
and can be condensed in cooled vessels.
Camphor his for long been a highly valued substance
on account of its therapeutic, disinfecting, and other proper-
ties, but the demand for the compound has been very
greatly increased in the past forty years owing to its
employment in the manufacture of celluloid or xylonite,
and of explosives. Japan had, therefore, a valuable source
of revenue in her practical monopoly of the production
of camphor through her possession of the plantations of
the camphor-tree in Formosa, the extent of which, in the
years following the Russo-Japanese War, she very greatly
increased ; and the monopoly she possessed she sought
to exploit to its utmost
But the substance had long attracted the attention of
chemists, and in spite of the difficulty of the problem, its
molecular constitution was at length unravelled and the
compound prepared synthetically in 1903. Two years
later, synthetic camphor, identical in all respects with the
substance produced in the camphor-tree, was placed on
the market in competition with the natural product.
But the Japanese camphor plantations have hitherto
SYNTHETIC CHEMISTRY 247
escaped the fate which befell the plantations of madder,
and, so far as can be foreseen, they are not likely to
suffer great disaster. The reason for this, however, lies
outside the control of the chemist, and is to be found in
the scarcity and cost of the raw material used in the
manufacture. The source of the raw material is oil of
turpentine, an essential oil which is produced in trees
belonging to the different species of pine, and which is
not only restricted in quantity, but is also subject to
increase in price. The synthetic camphor, therefore, has
not been able to displace the natural, but it has prevented
an excessive rise in the price of the compound.
Very different from the dyes, drugs, and other synthetic
products just described, is a remarkable material which we
owe to the American chemist, L. H. Baekeland, and which
has, in recent years, acquired a very great industrial value.
on warming together phenol (carbolic acid) and formalde-
hyde — obtained by the oxidation of methyl alcohol or
" wood spirit," and sold, in solution, as a disinfectant under
the name of formalin — along with a little ammonia, which
hastens the reaction, a thick gummy mass is produced.
When freshly prepared this gummy material can be dis-
solved in alcohol, acetone, and other similar solvents, but
on being heated to a temperature of over 100° C. or 212° F.,
it changes into a hard, resin-like solid, to which the com-
mercial name of bakelite is given. Bakelite is an infusible
material and insoluble in all solvents; it is not affected
by alkalies or acids, and may even be boiled with dilute
sulphuric acid without undergoing change. It is an excellent
insulator for electricity, and finds, in consequence, perhaps
248 CHEMISTRY IN THE SERVICE OF MAN
its most important applications in the electrical industries.
Bakelite may be employed for a great variety of purposes
— as a substitute for amber in pipe-stems ; for making
billiard balls, the elasticity of bakelite being nearly equal
to that of ivory ; and for making buttons, knobs, knife-
handles, and many other articles for which bone, celluloid,
ebonite, or other material is at present employed. It is
not so flexible as celluloid, but it is more durable, is not
inflammable, 'and is less expensive. Wood, impregnated
with the initial liquid material, and then heated, becomes
coated with a hard enamel-like layer, equal to the best
Japanese lacquer ; and metal articles, similarly, can be
covered with a hard and resistant coating.
CHAPTER XIII
FERMENTATION AND ENZYME ACTION
We have already seen (p. 103) how Nature, in carrying
out her wonderful syntheses and decompositions within the
animal and vegetable organism, makes use of a number of
catalysts, the so-called enzymes, produced within the cells
of the living plant or animal. Even in the lowliest forms
of life, when as yet differentiation of structure and function
has not appeared, when life with all its mystery is con-
tained in the microcosm of a single cell, even there also
these complex catalysts, without whose presence the great
life-processes would slow down to the sluggishness of death,
are produced, and exercise their quickening power. Borne
on the breeze, carried in water, the earth teeming with
their countless myriads, these micro-organisms — the yeasts,
bacteria, and moulds — through the enzymes which they
produce, carry out, unseen, the never-ceasing changes of an
ever-changing Nature. Putrefaction and decay, by means
of which Nature resolves the body of a life outlived into
the elements from which new living structures can be built ;
the souring and curdling of milk ; the production of the
dye-stuff indigo from the compound indican contained in
the woad ; the " puering " of hides and the curing of
tobacco ; the development of the pungent flavour of
mustard and the production of benzaldehyde or oil of bitter
almonds from the amygdalin contained in the almond
seed ; all these and many other processes — so-called
250 CHEMISTRY IN THE SERVICE OF MAN
fermentation processes — by which complex organic material
is broken down into simpler substances, are brought about
by the action of living organisms which secrete the enzyme
appropriate to the process.
This explanation of the fermentation process — a term
at first applied to all changes which are accompanied by
effervescence due to the escape of gas — is one which has
been accepted by science only in comparatively recent
years. Prior to 1857, chemists and biologists were divided
in their views. Some favoured the physical and chemical
explanations put forward by Berzelius, — who introduced
the conception of "catalytic force" (p. 95), and likened
fermentation to the decomposition of hydrogen peroxide
under the influence of platinum, — and by Liebig, who, with
greater apparent definiteness, regarded a ferment as being
an unstable substance which, formed by the action of
oxygen on the nitrogenous materials of the fermentable
liquid, underwent a decomposition ; and the internal motion
which thereby took place was regarded as being communi-
cated to the fermentable medium. With these mechanical
explanations, however, dissatisfaction became more and
more widely expressed, and in 1857 it was shown con-
clusively by Pasteur, to whose genius the advance of
science in many directions is due, that all fermentative
changes were associated with and produced by living
organisms ; and this vitalistic explanation, summed up by
Pasteur in the well-known phrase, " No fermentation with-
out life," is accepted at the present day. But the growth
of knowledge has rendered necessary a certain modification
of the views which were put forward sixty years ago. For
a considerable time the view was held that the fermentation
FERMENTATION AND ENZYME ACTION 251
processes are the result of Ihe direct action of the living
organism on the fermentable material. Cases, however,
began to accumulate of changes brought about by sub-
stances, for example, diastase and pepsin, which are the
product, certainly, of life, but are not themselves living ;
and the matter was put beyond dispute in 1897 when
E. Buchner showed that in the production of alcohol from
sugar, the fermentation is brought about not by the direct
action of the living organism, but by a substance, which he
called zymase^ produced by and contained in the cell of the
yeast.^ It is now generally accepted, therefore, that fer-
mentation changes are produced by substances which
although produced by living organisms are not themselves
living ; and to these substances the name enzyme {iv, in ;
X,\j\n\^ yeast), introduced in 1878, is applied. In proposing
the adoption of this term, the German physiologist, W.
Kiihne, stated: "This is not intended to imply any par-
ticular hypothesis, but it merely states that iv Z,\}fxt\ (in
yeast) something occurs that exerts this or that activity,
which is considered to belong to the class called fermenta-
tive. The name is . . . intended to imply that more com-
plex organisms, from which the enzymes pepsin, trypsin, etc.,
can be obtained, are not so fundamentally different from the
unicellular organisms as some people would have us believe."
Not only do the enzymes play an indispensable rdle in
the economy of Nature, but they play also an essential part
in many of the most important industrial processes. Of
the processes which depend on fermentation, none is of
* Zymase, it has been showa, consists of at least two substances, one a
colloid, the other a crystalloid (p. i88), and the presence of both is necessary
for fermentation.
252 CHEMISTRY IN THE SERVICE OF MAN
greater importance than that which has been carried on
from the earh'est days of man's history, the fermentation of
sugar with production of alcohol.
Manufacture of Alcohol
Although in chemistry the term " alcohol " is a generic
one, and is applied to a whole series of compounds in
which the so-called hydroxy I group (OH) is present, the
name when used without qualification is applied to the
best known and most valuable of the alcohols, ethyl alcohol
(C2H5.OH), or as it is frequently called, j/^W/i- of wine.
In the fermentation industry, it is sometimes also called
grain spirit or grain alcohol, or potato spirit, according as
the raw material of its manufacture is derived from grain
or from potatoes.
Alcohol is produced by the action of a particular
enzyme, zymase, on certain sugars, the most important
of which is the sugar glucose or dextrose which, along with
the isomeric sugar, fructose or laevulose, is found in sweet
fruits and in honey. Zymase is secreted by the micro-
organisms known as yeasts {Saccharomycetes), and when
yeast is introduced into a solution of glucose, decomposition
of the latter with production of alcohol and of carbon
dioxide, is brought about through the agency of the
zymase. Not all sugars, however, can be fermented by
zymase. Thus, cane or beet-root sugar (known chemically
as sucrose), and iftalt-sugar or maltose, are not fermentable
with zymase. If, however, yeast is introduced into solutions
of these sugars, fermentation does take place, owing to the
fact that yeast secretes not only the enzyme zymase, but
also the enzymes invertase and maltase. The former of
FERMENTATION AND ENZYME ACTION 253
these converts cane and beet-root sugar into the two
simpler isomeric sugars, glucose and fructose, by a process
of hydrolysis (p. 1 54),
C12H22O11 -f H2O -> CeHijOg -f CqUizOq
Sucrose Glucose Fructose
and maltase, similarly, converts maltose into glucose. The
production of alcohol from sugars by means of yeast is,
therefore, to be referred, in the last instance, to a fermentation
of glucose (sometimes also of fructose) by zymase.
Fermentable sugars can be obtained not only from
sucrose (which is largely employed in France in the form
of beet-root molasses), but also from starch, which con-
stitutes, as a matter of fact, by far the most important raw
material for the manufacture of alcohol. The starch is of
varied origin. In this country it is derived mainly from
maize, rice, wheat, and barley, and in the United States, also,
maize is largely used. In the future, cellulose, from wood-
waste, may perhaps play a role of great importance (p. 87).
In Germany, most of the starch is derived from potatoes.
For the conversion of the starch into fermentable sugar,
use is chiefly made of the enzyme diastase^ contained in
malt ; or, the starch is converted into glucose by heating
with dilute sulphuric acid.
For the production of malt, barley grains are steeped for
some days in water and then spread out, or " couched " to a
depth of two or three feet on the floor of the malt-house.
Soon the moist grain begins to sprout and to become hot.
As the temperature must not be allowed to rise above
15** C. or 60° F., the "couch" is broken down and the
germinating barley spread out in a thin layer, only a few
inches in depth, turned over from time to time so as to
254 CHEMISTRY IN THE SERVICE OF MAN
allow access of air to the grains, and sprinkled with watei
when necessary. During the germination of the barley,
diastase and other enzymes are produced, and when growth
has proceeded sufficiently far, it is stopped by allowing the
rootlets to wither, and then drying the malt in a kiln. The
malt, which contains a considerable amount of starch and
a small amount of sugar, together with the enzyme diastase,
is crushed and mixed with hot water, and a quantity of raw
grain or potato starch is added. By the action of the
diastase, which is best carried out at a temperature between
40" and 60° C. or 104° and 140° F., the starch is converted
into maltose or malt-sugar. When this process of " mash-
ing " is complete, the liquid is boiled to destroy the diastase,
and the sweet liquor or " wort " is run into the fermenting
vats and yeast is added.^ By the action of the enzyme
maltase, which is contained in the yeast, the maltose is
converted into glucose ; and this, in turn, is converted by
the yeast-enzyme zymase, mainly into alcohol and carbon
dioxide, although small quantities of other substances —
higher alcohols, succinic acid, etc. — are also produced.
Alcohol may also be produced by the action of yeast on
commercial glucose, obtained by heating starch {e.g. potato
starch), or cellulose (p. Z"])^ with dilute sulphuric acid, or on
cane-sugar and beet-root sugar molasses (sucrose). In the
latter case, conversion of the sucrose to the fermentable
sugars, glucose and fructose, is effected by the yeast-
enzyme, invertase.
When fermentation is allowed to take place at a tem-
perature of about 15° C. or 60° F., a turbulent effervescence
* The necessity for using pure culture yeasts belonging to definite races, is
now recognised. The result of the fermentation varies with different yeasts.
FERMENTATION AND ENZYME ACTION 255
is produced, and the evolution of carbon dioxide is so rapid
that the yeast cells are carried to the surface of the liquid
and there form a thick froth. This is known as "top
fermentation," and is mostly used in this country. on the
other hand, when the temperature is kept low, say about 6° C.
or 43° R, the evolution of carbon dioxide is too slow to buoy
up the yeast cells, which therefore remain at the bottom of
the vat. This is known as " bottom fermentation," and is
made use of in Germany in the production of certain beers.
The fermentation of the sugar solutions does not pro-
ceed indefinitely, and when the liquid contains from 10 to
1 8 per cent, of ethyl alcohol, the fermentation stops. The
liquid, or " wash," as it is now called, contains not only
ethyl alcohol, but also furfural and fusel oil — a mixture of
higher-boiling alcohols, such as butyl alcohol, C4H9 . OH,
and amyl alcohol, CgHu . OH, and other substances. From
these different substances the ethyl alcohol is separated by
distillation in special stills {e.g. the Coffey still), from which
a mixture of alcohol and water containing about 96 or
98 per cent, of alcohol by volume, is directly obtained.
Alcohol so obtained, is spoken of as "silent spirit," or
*' patent still spirit." By allowing this alcohol to stand over
quicklime for some time and then distilling, "absolute
alcohol," or pure ethyl alcohol, is obtained.*
' For the purposes of taxation, the strength or concentration of a spirit is
generally expressed in terms of "proof" spirit. Proof spirit is a mixture
containing 49*24 per cent, by weight, or 57' I per cent, by volume of alcohol.
"Weaker spirits are said to be so much "under proof" according to the per-
centage of water and proof spirit which they contain. Thus, a spirit 10° under
proof means a liquid which contains, at 60° F., 10 volumes of water and 90
volumes of proof spirit. " Over-proof" spirits are defined by the number of
volumes of proof spirit which 100 volumes of the spirit would give when
dilated with water to proof strength. If 100 volumes of an over-proof spirit
would yield 150 volumes of proof spirit, it is said to be 50"^ over proof.
256 CHEMISTRY IN THE SERVICE OF MAN
For industrial and other purposes, alcohol finds abundant
and varied use. Not only is it employed as a heating
agent, in spirit lamps, but it is also used, to some extent,
as an illuminant (with incandescent mantles), and as a
motor fuel. Its relatively high cost, however, militates
against any immediate and extensive development in this
direction. Alcohol is also used very extensively as a
solvent in the preparation of varnishes, lacquers, and
enamels ; in the manufacture of ether, chloroform, acetic
acid, celluloid and xylonite, collodion, dyes, cordite and
similar explosives, and many other substances. Ordinary
methylated spirit, so largely used in spirit lamps and for
other purposes, consists of ethyl alcohol "denatured" by
the addition of wood-naphtha and mineral naphtha,^ the
presence of which renders the liquid undrinkable. Such
methylated spirit is free from the excise duty ordinarily
placed on alcohol. For industrial purposes, special in-
dustrial methylated spirit can also be obtained which con-
sists of alcohol denatured with wood-naphtha only or with
other denaturants suitable for particular industries.
The fusel oils obtained as by-products in the manu-
facture of ethyl alcohol, and formerly regarded as waste
material, are now subjected to special distillation in order
to obtain the higher alcohols present. Although the com-
position of the fusel oil depends on the process in which it
is formed, one can obtain from the different fusel oils the
alcohols known as propyl alcohol (CsHy. OH), butyl and
isobutyl alcohol (C4H9.OH), and amy! and iso-amyl
alcohol (CsHii.OH). These alcohols find their use not
' In the United States, methyl alcohol and benzine are used, and ia
Germany, methyl alcohol and pyridine bases, derived from coal tar.
FERMENTATION AND ENZYME ACTION 257
only in the scientific laboratory, but also in industry, for
the purpose of preparing artificial fruit essences, and as
solvents. These artificial fruit essences and flavouring
materials are pleasant-smelling compounds of alcohols with
acids, known as esters. Thus amyl acetate (from amyl
alcohol and acetic acid) forms the main constituent of
artificial essence of pears ; ethyl butyrate (from ethyl
alcohol and butyric acid) is used in making artificial
essence of pine-apples ; amyl butyrate is used in making
apricot essence ; and amyl iso-valerate (from amyl alcohol
and iso-valeric acid) is used as a constituent of apple
essence. In recent years, Professor Fernbach, of the
Pasteur Institute, has obtained fusel oil and acetone, the
former consisting mainly of butyl alcohol, by the direct
fermentation of starch by means of a special culture. This
fact is of importance as butyl alcohol forms the starting
point in a suggested process for the s)mthesis of rubber.
In the case of alcoholic beverages, although ethyl alcohol
is the most important ingredient, the taste, aroma, and
special character of each depend on the presence of small
quantities of other substances, which differ both in amount
and in kind with the materials from which the beverage is
prepared, and with the method of its preparation. These
beverages may be classed into distilled liquors (spirits),
wines, and beers.
In the case of whisky, the process of fermentation is
carried out essentially as already described ; malted barley,
mainly, is employed, and the wash is distilled from a simple
pot-still similar to that shown on p. 41. The result, there-
fore, is not merely a mixture of pure alcohol and water,
s
258 CHEMISTRY IN THE SERVICE OF MAN
but one which also contains small quantities of various
other substances — fusel oil, aldehydes, esters, etc. This
raw whisky is then placed in casks to mature, and during
this process the aldehydes become converted into acids
which then unite with the alcohols present, to form esters,
which give a special flavour and aroma to the whisky.
In the case of gin, the distilled spirit is flavoured by
redistilling with juniper berries, coriander, fennel, or other
substances ; brandy is obtained by distilling wine, and owes
its particular flavour to the various esters contained in the
wine from which it is prepared ; and rum, prepared from
fermented molasses, owes its flavour chiefly to the esters,
ethyl acetate and ethyl butyrate. Sometimes it is also
flavoured by placing the leaves of the sugar-cane in the still.
These distilled liquors all contain a high percentage,
40 to 50 per cent, or more, of alcohol.
Wines are prepared by the fermentation of fruit juices
— chiefly the juice of the grape — in which the two sugars,
glucose and fructose, are present. The juice also contains
various acids, especially tartaric acid ; and the skins of the
grape contain tannin, various essential oils, and, it may be,
colouring matter. These all pass into the juice when the
grapes are pressed, and according to their nature and relative
amounts, give wines of different flavours and qualities.
Owing to the presence of a species of Saccharomyces on
the grape itself, fermentation of grape juice must have been
observed in warm, grape-growing countries at a very early
period in man's history ; and the manufacture of wine must
have been developed at a very remote time. Although
the grapes are now crushed mainly by wooden rollers, the
method of treading with the bare feet — treading the wine
FERMENTATION AND ENZYME ACTION 259
press — has not yet ceased to be practised. The juice
extracted from the grape is called "must," and by its
fermentation, alcohol is produced. After the first "active
fermentation " is over, the " new wine " is drawn into casks
which are filled full and loosely closed in order to prevent
the conversion of the alcohol into acetic acid (p. 260). In
the Ccisks, a " still fermentation " proceeds for several
months, during which time the yeast settles down, and
the tartaric acid, along with various salts and colouring
matters, separates out as argoL This consists chiefly of
potassium bitartrate, and is the main source of this salt,
known familiarly as cream of tartar.
After the wine has become clear, it is drawn off into
casks and allowed to ripen for perhaps two or three years.
During this process, the tannin and some other impurities
are precipitated, and at the same time the alcohol and fusel
oil combine with the small quantities of acids present to form
esters, which give the peculiar and characteristic flavour and
" bouquet " to the wine. After ripening, the wine is bottled.
Since the quality of the grape juice varies with the soil,
and also with the climate, some vintages give better wines
than others. Wines, also, are subject to " diseases," due to
the presence of enzymes, which bring about an alteration of
the wine, e.g. conversion of alcohol into acetic acid.
For the production of beers^ malted grain is employed,
but in the mashing process the complete conversion of the
starch into maltose is not allowed to take place, a portion
being converted only into the intermediate product of
hydrolysis, dextrin.^ This dextrin is retained in order to
' Dextrin is also produced industrially by heating starch with dilate
sulphuric acid. It is used as an adhesive, on stamps, envelopes, etCt It
constitutes the so-called '* British gum."
26o CHEMISTRY IN THE SERVICE OF MAN
give " body " to the beer. Further, the nitrogenous com-
pounds, the albuminoids and proteins, in the grain, are
converted by the malt-enzyme, peptase, into peptones and
other substances, which also add *' body " to and increase
the nutritive properties of the beer. All these various
substances are classed together under the name *' extract."
When mashing is complete, the wort is drawn off and
boiled with hops, and, after settling, the clear liquid is
fermented with yeast. When the active fermentation has
subsided, the new beer is run into casks and slow fermenta-
tion allowed to continue, the froth which is formed being
allowed to pass out through the bung-hole. At the con-
clusion of the process, the beer is drawn off into casks
or bottles.
Many weak alcoholic beverages, such as light wines,
become sour when exposed for some time to the air. This
souring is due to the conversion (oxidation) of the alcohol
to acetic acid by the oxygen of the air, under the influence
of certain moulds and bacteria {e.g. Mycoderma aceti and
Bacterium aceti) ; and the process is carried out on a large
scale for the production of vinegar.
In Britain vinegar is manufactured mainly from malt,
which is mashed and fermented with yeast as in the pre-
paration of alcohol. After fermentation, the alcoholic liquor
(in which not more than lo per cent, of alcohol should be
present), containing the nitrogenous matter and salts neces-
sary for the growth of the bacteria, is sprinkled over beech-
wood shavings or basket work inoculated with the acetic
acid bacteria, and contained in a large vat to which air can
be admitted. In this way the alcoholic liquor is spread
J
FERMENTATION AND ENZYME ACTION 261
over a large surface while exposed to the action of the air,
and oxidation of the alcohol to acetic acid rapidly takes
place. The liquid is drawn ofif from the bottom of the vat
and passed repeatedly over the same shavings or basket
work, until conversion of the alcohol to acid is nearly com-
plete. A very small amount of alcohol, however, is left in
the vinegar because, otherwise, oxidation and destruction of
the acetic acid would take place.
Vinegar thus obtained contains about 6 per cent, of
acetic acid, but commercial vinegars are frequently weaker.
Vinegar is also frequently made, especially in France, from
wines, the process being carried out, as a rule, in large casks.
Although vinegar is, essentially, a dilute solution of
acetic acid in water, it receives its special flavour and
quality from the presence of small quantities of other sub-
stances derived from the materials of its preparation, malt,
wine, etc. More especially does it contain esters, like ethyl
acetate, which impart their aroma to the vinegar.
Sometimes "vinegars" are prepared artificially by
adding to a solution of acetic acid in water, caramel or
burnt sugar, and various aromatic substances and esters.
The production of acetic acid on an industrial scale is
not carried out by the method just described, since only a
dilute solution (up to 10 per cent.) can be obtained in this
way, but by the distillation of wood ; and at the present
day large quantities of wood are distilled for the production
of this acid (cf. p. 238), and of "wood spirit" or methyl
alcohol. By distilling acetate of soda with sulphuric acid,
pure acetic acid can be obtained. Since, at the ordinary tem-
perature, this acid crystallises in ice-like crystals (which melt
at 17° C. or 626° F.), it is spoken of as glacial acetic acid.
262 CHEMISTRY IN THE SERVICE OF MAN
By heating acetate of lime or acetate of barium, the
very important solvent, acetone^ is obtained.
When rennet is added to milk, the enzyme rmnin
which it contains brings about a curdling of the milk by
causing a decomposition of the casein present in the milk
into paracasein, which forms the curd, and whey albumin.
This process of enzyme action is one of great importance,
because it is employed not only for the industrial pro-
duction of casein, but also as the first step in the manu-
facture of cheese. In making clieese, the curd, after being
separated from the whey, is allowed to stand some time,
when various changes take place, accompanied by the pro-
duction of acid. The curd is then ground, salted, and
pressed in a cheese-mould. The cheese is then allowed
to "ripen," when a complicated series of changes takes
place under the influence of various enzymes, part of the
casein undergoing a decomposition with production of a
number of different substances, the nature and amount of
which vary greatly in the different kinds of cheese. The
presence of these decomposition products gives the charac-
teristic flavour to the cheese. The different kinds of cheese
vary considerably in composition, and contain about 24 to
40 per cent, of water, 23 to 39 per cent, of fat, 27 to 33 per
cent, of casein and nitrogenous compounds, and 3 to 7 per
cent, of salts.
Milk can also be curdled by means of acids, and this
method is generally employed in the industrial preparation
of casein. The curd which separates out, and which has a
different composition from the curd obtained with rennet,
is washed and purified by dissolving it in ammonia, and
FERMENTATION AND ENZYME ACTION 263
precipitating the casein with acetic acid. It is then washed
and dried, and is thus obtained as a white amorphous
material, which finds very wide-spread application in the
arts, and also as a constituent in food-preparations. Made
into a paste with water containing a small quantity of
bicarbonate of soda, casein forms an excellent glue or
cement, which possesses the great advantage that it can
be applied cold. If desired, it can be rendered insoluble
by treatment with formalin (formaldehyde). Casein also
is widely used as a sizing material for paper and cotton ;
in calico printing ; and in the manufacture of casein water-
paints or distempers (casein mixed with alkali and quick-
lime, to which mineral colouring matters are added). The
food-preparation plasmon consists chiefly of a soda com-
pound of casein, together with a small quantity of fat and
milk-sugar ; and sanatogen consists of about 95 per cent, of
casein and 5 per cent, of sodium glycero-phosphate. A
number of other casein preparations, including bread substi-
tutes for diabetic patients, have also been put on the market
In recent years casein has been largely used in the
preparation of a horn and bone substitute, manufactured in
England under the name of erinoid. In the manufacture
of this material, casein is dissolved in a solution of sodium
carbonate, or of ammonia, and, after the solution has been
clarified, the casein is precipitated by acid, and the curd
subjected to pressure. When this compressed casein is
soaked for some time in formaldehyde solutions (formalin),
the casein is rendered insoluble and horn-like in appear-
ance. It can be mixed with pigments or coloured with
dyes, and can by such treatment be made to resemble
bone, ivory, horn, coral, tortoise-shell, amber, ebonite, etc.
264 CHEMISTRY IN THE SERVICE OF MAN
It is, in consequence, used for a great variety of articles —
buttons, beads, umbrella handles, combs, cigar and cigarette
holders, dominoes, electrical fittings, etc., and has the
advantage over celluloid of being non-inflammable. When
warmed with water, it can be moulded as desired. In
comparison with celluloid, it suffers from the drawback
that it cannot be obtained perfectly transparent or in
sheets less than 2 millimetres (^g inch) thick, and cannot,
therefore, be used for photographic films. It has, however,
its own special characteristics which make it, along with
celluloid and bakelite, one of the most important plastic
materials.
And now we must conclude. Giving a backward
look, we see how out of the mysticism and obscurantism
of the earlier alchemistic period there has grown the
science of chemistry, which offers to the mind a clear and
well-ordered account of the constitution of matter and of
the laws of chemical combination. We have seen also, how,
during the past hundred years, much has been added not
only to our philosophic conceptions regarding the universe
of matter, but also to the great array of substances which,
in various ways, have proved of benefit to mankind. But
great as have been the services rendered by chemistry
hitherto, its power to contribute to man's comfort and
well-being and to the general advancement of civilisation
and of culture, is not yet exhausted ; nay, rather, the
achievements of the past are but an earnest, we may
confidently believe, of what will still be accomplished in
the future.
INDEX
Acetic acid, 261
Acetone, 262
Acetylene, 40, 55
„ flame, 55
Acheson, Edward G., 181, 196
Acids, 165
Activity, optical, 213
Adrenaline, 241
Adsorption, 198
Affinity, chemical, 90
Agriculture, colloids in, 202
Air, composition of, 1 7
„ liquefaction of, 132
Albertus Magnus, 5, 89
Alchemists, 5
Alcohol, 252
,, absolute, 255
„ amyl, 255
butyl, 255, 257
„ ethyl, 252
„ manufacture of, 252
„ methyl, 247
,, uses of, 256
Alizarin, synthesis of, 234
Alkalies, 166
Alkali waste, 150
Allotropic forms, 70
Aluminium, 177
,, bronze, 179
„ nitride, 130
Alundum, 182
Ambergris, 245
Ambrein, 245
Amethyst, 141
Ammonia, catalytic oxidation of, 1 25
,, from blast furnaces, 1 16
,, from coal, 44
„ from peat, 115
„ synthetic production of,
126
Ammonium sulphate, world's produc-
tion of, 115
Amorphous solid, 138, 140
Anaesthetics, 241
Anions, 168
Anisic aldehyde, 245
Anode, 168
,, mud, 176
Anthracene, 232, 235
Anthracite, calorific value of^ 60
Antifebrin, 242
Antipyretics, 242
Aquadag, 197
Argol, 259
Aristotle, 4
Arrhenius, Svante, 167
Arsenic sulphide, colloidal, 192
Aspirin, 243
Asymmetric carbon atom, 221
Asymmetry, molecular, 220
Atomic theory of Dalton, 10
„ weights, 13
Atoms, definition of, 1 1
„ early views regarding, 8
Avogadro, 11
B
Bacon, Roger, S, 70
Baekeland, L. H., 247
Baeyer, Adolf von, 236
Bakelite, 247
Barilla, 149
Beers, 259
Beeswax, 35
Benzaldehyde, 245
Benzene (benzol), 232
„ formula of, 212
Benzine (benzoline), 41
Berzelius, 12, 94, 250
Bevan, E. J., 83
Beverages, alcoholic, 257
Birkeland, 120
Bitter almonds, oil of, 245
Black lead, 182
Blasting gelatin, 75
Bleaching powder, 152
266
INDEX
Blowpipe, oxy-acetylene, 56
„ oxy-coal-gas, 51
Boyle, Robert, 4, 5
Brandy, 258
Brick-making, use of straw in, 196
Brown, Crum, 227
Brown, Robert, 204
Brownian movement, 2C4
Buchner, E., 251
Bunsen, 49
„ burner, 49
Cairngorm, 141
Calcium carbide, 55
,, cyanamide, 124
,, nitrate, 122
Cambaceres, 37
Camphor, synthesis of, 245
Candles, 33
,, annual consumption of, 37
,, beeswax, 35
„ paraffin, 34
,, snuffing of, 36
,, spermaceti, 35
,, stearin, 34
Carbohydrates, 78
Carbolic acid, 232
Carbon atom, asymmetric, 221
,, chemistry of, 206
,, circulation of, 58
„ dioxide, test for, 23
Carborundum, 181
Casein, 262
Catalysis, 95
,, industrial applications of,
104, 128
Catalysts, 95
,, in Nature, 103
,, poisoning of, 98, 107, 128
Catalytic agent, 95
Cataphoresis, 200
Cathode, 168
Cations, i68
Caustic soda, preparation of, 154, 176
Cavendish, 117
Cellite, 86
Cellon, 86
Celluloid, 85
,, non-inflammable, 86
Cellulose, 60, 78
„ glucose from, 87
,, products, 78
Cerium iron alloy, 31
„ oxide, 31, 53
Cerium oxide, catalytic action of, 98
Chancel, 27
Charcoal, 70
„ decolonrising of L'qoids by,
199
Chardonnet, Count Hilaire de, 82
Cheese, 262
Chemical reactions, energy of, 57, 68
Chemistry and electricity, 161
,, definition and scope of, i
,, organic, 206
,, synthetic, 229
Chevreul, 33, 153
Chile saltpetre, 1 16
Chloral, 241
Chlorine, 152
„ electrolytic preparation of,
176
Chloroform, 240
Chromium, production of, 25
Cigar lighters, 31
Clausius, 204
Clay, •' Egyptianised," 197
,, plasticity of, 196
Clement-Desormes, 106
Coal, calorific value of, 60
„ conservation of, 62
,, distillation of, 44
,, production of, 59
,, products of distillation of, 44
Coal-gas, 44
,, composition of, 47
,, enriching of, 49
,, luminosity of, 48
,, manufacture of, 45
Coalite, 64
Coal-tar, 44, 231
„ dyes, 233
Coffijy still, 25s
Coke, 44
Collargol, 194
Collodion, 74
Colloidal sol, 189
,, state, 188
,, ,, properties of, 192
, , suspensions, stability of, 205
Colloid particles, electrical charge on,
199
,, „ size of, 191
„ silver, 194
Colloids, 188
,, emulsoid, protective action
of, 194
,, peptisation of, 195, 197
„ precipitation of, 194
Combustion by means of combined
oxygen, 25
„ expUmation of, 17
INDEX
267
Combustion in absence of oxygen, 24
„ in air, 15
„ slow, 22
,, „ of aluminium, 22
,, . ,, of iron, 21
,, „ in the living organ-
ism, 22
,, spontaneous, 24
Compounds, 6
Concentration, influence of, on velo-
city of reactions, 90
Conduction of electricity by solutions,
165
Conservation of matter, law of, 18
Constant proportions, law of, 10
Constitution, molecular, 208
Contact process, 107, 238
Copper, electrolytic, 176
,, refining of, 1 76
Cordite, 75
Corundum, 51
Cotton, 79
,, mercerised, 85
Coumarin, 244
Crookes, Sir William, 113
Cross, C. F., 83
Crystal (glass), 146
Crystalline solid, 138
Crystallisation, velocity of, 139
Crystalloids, 188
Crystals, hemihedral, 216
„ holohedral, 216
Dalton, John, 10
Daniellcell, 171
Davy, Sir Ilumphry, 20, 48, 163
Decolourising of liquids by charcoal,
199
Democritus, 8
Devitrification, 141, 142, 149
Dewar vacuum vessel, 135
Dextrin, 259
Dialysis, 188
Diamond, 70
Diastase, 253
Diffusion, 186
Dips (candles), 33
Distempers, 262
Dobereiner lamp, 97
Drugs, synthetic, 240
Dry cleaning, 41
Dyeing, 200
Dyes, coal-tar, 233
Dynamics, chemical, 89
Dynamite, 75
Earth, chemical composition of the, 8
Ecrasite, 76
Edison cell, 1 75
Egyptianised clay, 197
Electric current, production of, 162
Electricity and chemistry, 161
,, conduction of, by solu-
tions, 165
,, in chemical industry, 175
Electro-chemistry, 161
Electrodes, 166
Electrolysis, 166
„ of copper sulphate, 166
,, of sodmm chloride, 166
,, mechanism of, 167
Electrolytes, 165
Electro-plating, 164, 166
Elements of Aristotle, 4
„ list of, 7
Emery, 51
Empedocles, 4
Emulsoid colloids, 193, 194
Enantiomorphic crystals, 217
Endothermal reactions, 69
Energy, 57
„ of chemical reactions, 57, 68
Enzyme action, 249
Enzymes, 103, 249, 251
,, catalytic action of, 249
Equilibrium, chemical, 93
„ „ influence of
temperature
on, 93
Ethane, 39
Ethylene, 40
Exothermal reactions, 69
Explosives, 70
disruptive efifect of, 73
"high," 73
"low," 73
output of, 77
taming of, 75
Eyde,
Faraday, Michael, 163, 167
Fats, chemical nature of, 33
,, hardening of, 108
Fermentation, 249
„ bottom, 255
„ explanation of, 2^0
„ top, 255
26S
INDEX
Fibre, compressed, 82
Filtration through soil, 202
Fire-damp, 21, 38
„ production ot, 15
Fixation of atmospheric nitrogen, 112
Flash-lights, 179
Flashpoint of oil, 42
Formaldehyde, 247, 263
Formalin, 247, 263
Formulae, 12
,, constitutional, 210
Frankland, Sir Edward, 209
Fructose, 253
Fruit essences, artificial, 257
Fuel, smokeless, 64
Fuels, calorific value of, 60
Fusel oils, 255, 256
Galvani, 161
Gas, for heating and cooking, 64
„ from coal, 44
„ marsh, 38
,, Mond, 65
,, natural, 40
„ petrol-air, 41
,, producer, 65
„ water, 65
Gases, kinetic theory of, 1 86
Gasoline, 41
Gel, 192
Gelatin, blasting, 75
„ colloidal solution of, 192
Gelation, 192
Gin, 258
Glass, annealing of, 144
„ coloured, 147
,, crystal, 1 46
„ hardened, 144
,, invention of, 137
,, manufacture of, 143
,, patent plate, 144
,, plate, 144
„ quartz, 141
,, sheet, 144
,, silvering of, 148
,, window, 143
Glucose, 87, 252, 253, 254
Glycerine, 33
"Gob" fires, 24
Goethe, 36
Graham, Thomas, 187
Graphite, 70
„ artificial, 182
„ deflocculated, 197
Greek fire, 70
Guldberg, 91
Gum, British, 259
Guncotton, 71
Gunpowder, 70
11
Hampson, 133
Hardening of fats, ro8
Hard fibre, 82
Hardness of water, 159
Hawthorn blossom, artificial, 245
Herodotus, 137
Herschell, Sir John, 215
Holy Fire of Baku, 38
Hydro-carbons, 34
,, saturated, 39
,, unsaturated, 40
Hydrochloric acid, 151
Hydrogen, commercial production of,
134
Hydrolysis, 154
Hypnotics, 241
latro-chemistry, 240
Ignition point, 19
lUuminants, chemistry of, 32
Incandescent mantles, 52
Indigo, synthesis of, 235
Invertase, 252
Iodoform, 241
lonisation, 167
lonone, 245
Ions, 167
„ movement of, 169
Iron-cerium alloy, 31
Isomerism, 207, 208
Japp, F. R., 224, 227
Johnson, Dr., 137
K
Kekule, 209, 211
Kelvin, Lord, 13
Kerosene, 42
Kieselguhr, 74
Kinetic theory of gases, 186
Kiihne, W., 251
INDEX
269
Lavoisier, 16
Lead accumulator, 174
Leather, imitation, 87
Le Bel, 220
Leblanc, 150
Leclanchecell, 173
Leucippus, 8
Liebig, 17, 240, 250
Lignite, calorific value of, 60
Lily of the valley, artificial, 245
Limelight, 51
Lime nitrogen, 124
Linde, 133
Liquid air, 133
Liquids, supercooled, 1 39
Lucretius, 8
Lyddite, 76
M
Magnalium, 179
Magnesium, 1 79
Malt, 253
Maltase, 252
Maltose, 252
Manganese, 25
Mantles, incandescent, 52
Margarine, 109
Marsh gas, 38
Mass action, law of, 9 1
Matches, 27
Matter, constitution of, 3
„ states of, 137
Maxwell, Clerk, 203
Mechanical pulp, 8 1
Melinite, 76
Mercer, John, 85
Methane, 38
Methyl salicylate, 245
Mirbane, oil of, 245
Mirrors, 148
Moisture, catalytic action of, 95
Molecular asymmetry, 220
,, constitution, determination
of, 208
,, structure, 206
Molecules, definition of, 1 1
,, objective reality of, 204
Monazite, 31, 53
Mond gas, 65
Mordant, 201
Multiple proportions, law of, 10
Murdoch, William, 43
Musk, artificial, 245
Must, 259
N
Naphthalene, 232, 237
Natural gas, 40
Newton, 9
Nickel, catalytic action of, 1 10
Nitric acid, direct production of, 123
Nitrobenzene, 245
Nitro-cellulose, 72
Nitro-cotton, 71
Nitrogen and oxygen, direct combina-
tion of, 117
,, atmospheric, fixation of, 1 12
„ compounds, sources of sup-
ply of, 114
„ importance of, in nature,
112
„ liquid, 132
Nitro-glycerine, 74
Nitrolim, 124
Nobel, Alfred, 74
Non-electrolytes, 165
Novocaine, 241
Oildag, 197
Oil fuel, 66
Oils, chemical nature of, 33
,, lubricating, 42
Oleic acid, 33
Optical activity, 213
Organic chemistry, 206
Ostwald, 125
Oxidation, 18
Oxy-acetylene blowpipe, 56
Oxygen, liquid, 132
Ozone, 69
Palmitic acid, 33
Paper, manufacture of, 8i
„ parchment, 82
,, waterproof, 42, 82
,, Willesden, 82
Paracelsus, 5
Paraffin, 34, 42
Paratartaric acid, 215
Parchment paper, 82
Paste, 147
Pasteur, 215, 223, 250
270
INDEX
Fauling, 123
Peat, 67
„ calorific valae of, 60
„ carbonisation of, 1 1 5
„ coal, 68
,, drying of, 200
Peptase, 260
Perfumes, synthetic, 244
Perkin, W. H., 233
Permutit process, 159
Fertile, 76
Petrol, 41, 66
Petrol-air gas, 41
Petroleum, American, 40
„ distillation of, 4 1
„ ether, 41
,, Russian, 40
Petronius, 145
Phenacetin, 243
Phenol, 232
Phillips, Peregrine, 106
Phlogiston theory, 16
Phosphorus, in matches, 28
„ red, 29, 70
„ white 29, 70
Phossyjaw, 28
Photographic plates, 194
Picric acid, 75
Plane of polarised light, 213
„ », „ rotation of,
213
Plasmon, 263
Platinum, catalytic action of, 97
Pliny, 136
Plumbago, 182
Poisoning of catalysts, 98
Polarisation of light, 213
,, „ demonstration
of, 213
Potash, caustic, 154
Potassium, 163
Priestley, 17, 117
Producer gas, 65
Propane, 39
Propylene, 40
Pulp, mechanical, 81
„ soda, 80
„ sulphate, 80
,, sulphite, 80
,, wood, 80
Quartz, 141
„ glass, 141
R
Racemic forms, resolution of, 222
Ramie fibre, 53
Ramsay, Sir William, 58
Reactions, endothermal, 69
,, exothermal, 69
„ influence of concentration
on velocity of, 90
,, influence of temperature
on velocity of, 91
„ reversible, 92
Rennin, 262
Rexine, 87
Rock crystal, 141
Rubies, artificial, 51
Rum, 258
Rupert's drops, 144
Rutherford, 112
Safety lamp, 20
Saltcake, 150
Saltpetre, air, 122
„ Chile, 116
,, Norwegian, 123
Salts, 166
Sanatogen, 263
Saponification, 154
Sapphires, artificial, 52
Scheele, 17
Schonherr, 122
Sea-mines, 73
Sedimentation in rivers, 194
Serpek process, 129
Sewage farms, 203
,, purification of, 203
Shale oil, 37
Shimose, 76
Sicoid, 86
Silica, 141
Silk, artificial, 82
Soap making, materials used in, 1 54
„ solution, emulsifying action of,
157
Soaps, cleansing power of, 156
„ hard, 154, 155
„ soft, 154, 155
„ transparent, 156
Soda, bicarbonate of, 152
,, carbonate of, 149
,, caustic, 154, 176
„ pulp, 80
„ washing, 159
INDEX
271
Soda waste, 150
Sodium, 163
„ carbonate of, 149
„ nitrite, 122
Solid, amorphous, 140
„ crystalline, 138
Solutions, 185
,, and gases, analogy be-
tween, 186
,t conduction of electricity
by, 165
Solvay, Ernest, 152
Smokeless powder, 74
Snuffing of candles, 36
Spermaceti, 35
Spirit, methylated, 256
,, patent still, 255
„ proof, 255
„ silent, 255
Spirits of wine, 252
Stahl, 16
Stearic acid, 33
Stearin, 34
Steel, chrome, 26
,, stainless, 26
Stereo-chemistry, 220
,, ,, and vitalism, 224
Stokes, Sir George, 213
Storage cell, 174
Strass, 147
Sucrose, 252
Sugar, beet-root, 252
„ caiie, 252
„ malt, 252
Sulphate pulp, 80
Sulphite ,, 80
Sulphonal, 241
Sulphuric acid, manufacture of, 104,
los, 107
Supercooled liquids, 139
Suprarenine, 242
Surface combustion, 99
Surfaces, catalytic action of hot, 98
Suspensoid, 193
Symbols, 12
Synthetic chemistry, 229
Tartar, cream of, 259
Tartaric acid, 215, 259
Temperature, influence of, on chemical
equilibrium, 93
Temperature, influence of, on velocity
of reactions, gi
Terpineol, 245
Tetronal, 241
Thermit, 26
Thermos flasks, 135
Thorium oxide (Thoria), 53
Titanium, 25
Toluene (Toluol), 232
Torpedoes, 73
Touchpaper, 25 x
Trinitrotoluene, 75, 76, 232
Trional, 241
Tyndall phenomenon, 189
Tyrian purple, 239
Ultra-microscope, 190
Vacuum vessels, 135
Valency, 209
Vanillin, 70, 24$
van 't Hoff, 220
Vaseline, 42
Velocity of reactions, 88
„ „ influence of con-
centration on,
90
,, „ influence of
temperature on, 91
Veronal, 241
Vinegar, 260
Violet, artificial, 245
Viscose, 83
„ films, 84
Vitalism and stereo-chemistry, 224
Vitriol, oil of, 104
Volta, Alessandro, 162
Voltaic cell, 162
W
Waage, 91
Walker, John, 27
Wash, 255
Water-dag, 197
Water gas, 49, 65
„ ,, carburetted, 49
,, hard, 1 58
,, „ softening of, 159
,, power, utilisation of, 184
,, purification of, 202
„ „ by aeration, 23
Water-glass, 142
272
INDEX
Welsbach, Auer von, 52
" Wet carbonisation " process, 67
Whisky, 257
Willesden paper, 82
Wines, 258
Wintergreen, oil of, 245
Wire gauze, cooling action of, 20
Wood, calorific value of, 60
„ pulp, 80
Wood spirit, 247
Wort, 254
Xylonite, 85
Zoroaster, 15
THE END
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