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CHEMISTRY IN THE
SERVICE OF MAN
By the same Author
INTRODUCTION TO PHYSICAL CHEMISTRY
PRACTICAL PHYSICAL CHEMISTRY
CHEMISTRY IN THE
SERVICE OF MAN
BY
ALEXANDER FINDLAY
RIl US-PROFESSOR OF CHEMISTRY, UNIVERSITY OF ABERDEEN
WITH PORTRAITS, DIAGRAMS
AND ILLUSTRATIONS
"He that enlarges his curiosity after the works of Nature
demonstrably multiplies the inlets to happiness."
JOHNSON, Rambler, No. 5.
SEVENTH EDITION
LONGMANS, GREEN AND CO,
LONDON * NEW YORK + TORONTO
LONGMANS, GREEN AND CO. LTD.
6 & 7 CLIFFORD STREET, LONDON, W.I
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LONGMANS, GREEN AND CO.
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BIBLIOGRAPHICAL NOTE
i st Edition
2nd Edition
May 1916
July 1917
New Impressions;
December 1917 ; March 1919,
July 1920
yd Edition December 1924
4th Edition - September 1931
5<A Edition - November 1939
6th Edition - Januofwftj^s
7th Edition - September 1947
CODE NUMBER 16905
PRINTED IN GREAT BRITAIN BY J. AND J. GRAY, EDINBURGH
TO
MY WIFE
PREFACE TO THE SEVENTH EDITION
THIRTY-ONE years ago, when the preface to the first edition
of this book was written, the author regarded it as his duty to
emphasise how greatly we, as a nation, had thitherto 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. At the present time,
we have every right to look back with a feeling of satisfaction
but certainly not of complacency, for much still remains to
be done on the great advances which have been made in this
country during the past three decades in the encouragement
and promotion of scientific research and in the application of
science to the improvement of old and the development of
new industries. Moreover, although this book. is concerned
with the advance of chemical science not only in this country
but throughout the world, and with the service which
chemistry has rendered to mankind, we, in this country, can
feel proud of the part which British chemists have played in
the general advance of the science no less than of its appli-
cations to the advantage of our industries and the material
welfare of the people.
In times of war men are inclined to think of the work of
chemists as being directed solely to destructive ends, but the
discoveries of chemists are contributions to knowledge and,
in themselves, are neither beneficent nor maleficent. It is
in man's power and it is his responsibility, the responsibility
of each individual citizen, to use these discoveries aright.
The magnitude of the power which chemists have placed in
the hands of men is a challenge to their moral greatness ;
and the greater the power the greater is man's opportunity
for its right use and for high endeavour. The frightfulness of
vi
PREFACE Vll
the atomic bomb, by which all men were appalled, should be
a constant warning and should strengthen the admonition :
" Turn back, O Man, forswear thy foolish ways."
Great as have been the suffering and destruction of life
brought about by the misuse of the discoveries of chemists,
very much greater have been the relief from suffering and the
saving of life which their discoveries have made possible. Let
the reader turn to page 321 and let him try to compute the
sum of misery, suffering and loss of life from which mankind
has been saved by the anaesthetics, antiseptics, drugs and
insecticides which we owe to the ability, trained intellect,
scientific imagination and persistent endeavour of the
chemist. It is no exaggeration to say that the health and
well-being of the people are more fundamentally dependent
on the chemist than on the physician.
In the following pages, also, it has been sought to give
some account of the advances which have been made in
elucidating the constitution of the atom and in opening up
the prospect of the beneficent utilisation of atomic energy,
as well as of the recent achievements of chemists in other
fields of social and industrial importance : light alloys,
plastics, vitamins, hormones, etc.
While we should all be grateful for the many material
benefits which chemical science has provided and for the
service which it has rendered, and can in increasing measure
still render, to industry, one must not fait to encourage or be
niggardly in promoting the advance of science by investi-
gations which are " motivated solely by a desire to increase
knowledge " ; for the material benefits which derive from
science are, as Cuvier said, " applications of verities of a
superior order, not sought with a practical intent, verities
which their authors have pursued for their own sake, im-
pelled solely by an ardour for knowledge/' Moreover, in our
eagerness to achieve results of material value we must not
lose sight of the idealism of science and of the intellectual
satisfaction which its study can give. For the community as a
Vlll PREFACE
whole it is of importance not so much that its individual
members should acquire a knowledge of the practical appli-
cations of science as that they should become imbued with
the spirit of science, the passion for truth and the forming of
judgments on the basis of ascertainable facts, the spirit of
co-operation, of tolerance, of charity and of unselfishness,
which are the spirit of true scientific endeavour. The study
of science ministers to the satisfaction of the intellectual need
of the human mind to understand more fully the phenomena
of nature, which become not less but more wonderful the
more fully we learn their meaning. The interpretations of
science, moreover, do not destroy but give significance to
the beauty of nature.
A. F.
66 MANOR WAY,
BECKENHAM, KENT.
March 1947.
PREFACE TO THE FIRST EDITION
WHEN the writer was invited to deliver the Thomson Lectures
before the United Free Church College, Aberdeen, at the end
of 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 home
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 manufacturing 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 civilisation demanded to pro-
mote and encourage the development 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 super-
structure of successful industrial achievement must be raised,
British chemists have, according to the measure of their
numbers, contributed an honourable share ; but the people
as a whole, being ignorant of science, have mistrusted and
X PREFACE
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 need-
less 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 chem-
ist, 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 efficiency, has found a home elsewhere
amid more congenial surroundings.
But there are now welcome signs that the country is
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, some-
thing which is, perhaps, more difficult of achievement than
Governmental aid. The mental outlook 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
PREFACE XI
for efficiency in all the 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 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 a uni-
versal 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 indebted-
ness to the chemist, and may also stimulate the interest of,
at least, the younger students of chemical science by present-
ing 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. Longmans,
Green & Co., for permission to use Figures i, 2, 9, and 10,
xii PREFACE
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.
YGLYN,
LLANFARIAN,
NR. ABERYSTWYTH.
March 1916.
CONTENTS
CHAPTER I
INTRODUCTION
Definition and scope of chemistry. Constitution of matter. Views
of Aristotle. Alchemy. latrochemistry. Elements and com-
pounds. Composition of the earth. Atomic hypothesis.
Dalton's atomic theory. Molecules. Symbols and formulae.
Valency. Modern scientific method .....
CHAPTER II
RADIOACTIVITY AND ATOMIC STRUCTURE
Relations between the elements. Periodic law. Cathode rays and
electrons. Radioactivity. Disintegration theory. Atomic
structure. Atomic number. Isotopes. Planetary electrons.
Explanation of valency. Transmutation of the elements.
Sub-atomic energy. Atomic bomb .....
CHAPTER III
THE GASES OF THE ATMOSPHERE
Composition of the atmosphere. Nitrogen. Oxygen. Carbon di-
oxide. Argon. Identification of gases by spectroscopy.
Helium. Neon. Krypton. Xenon. Liquefaction of air . . 46
CHAPTER IV
COMBUSTION AND THE PRODUCTION OF FIRE
Explanation of combustion in air. Phlogiston theory. Lavoisier's
explanation. Ignition point. Safety lamp. Slow combustion^
Combustion in the living organism. Spontaneous combustion.
Combustion by means of combined oxygen. Thermit.
Ammonal. Matches. Petrol-lighters . . . .61
xiii
XIV CONTENTS
CHAPTER V
FUELS AND ILLUMINANTS
SOLID FUELS Calorific value. Wood. Peat. Coal. Smokeless fuel.
Air pollution. SOLID ILLUMINANTS. Candles. LIQUID FUELS
AND ILLUMINANTS. Petroleum. Saturated and unsaturated
hydrocarbons. Refining petroleum. Flash point. Cracking
of oil. Octane number. Oil shale. Hydrogenation of coal.
Synthetic production of oils. GASEOUS FUELS AND ILLU-
MINANTS. Natural Gas. Coal-gas. Luminosity of flame.
Water-gas. Therms. Carbon monoxide. Bunsen burner. Oxy-
coal-gas flame. Lime-light. Oxy-hydrogen flame. Production
of rubies and sapphires. Incandescent gas-mantle. Petrol-air
gas. Acetylene ........ 79
CHAPTER VI
MATTER, ENERGY AND EXPLOSIVES
Energy of chemical reactions. Exothermal and endothermal re-
actions. Ozone. Allotropic forms of carbon. Diamond.
Graphite. Crystalline structure. Charcoal. Carbon black.
Explosives . . . . . . . . .116
CHAPTER VII
CELLULOSE AND CELLULOSE PRODUCTS
Carbohydrates. Cellulose. Cotton. Wood pulp. Paper. Artificial
silk (rayon). Staple fibre. Rayolana. Cellophane. Mercerised
cotton. Celluloid. Cellon and non-inflammable celluloid.
Imitation leather. Collodion. Nitro-cellulose lacquers.
Glucose from cellulose. Xylose from cellulose . . 137
CHAPTER VIII
METALS AND THEIR ALLOYS
Properties of metals. Seven metals of antiquity. Gold, silver and
platinum. Iron and steel. Tungsten. Copper and non-
ferrous alloys. Nickel. Chromium. Mercury. Tin. Zinc.
Lead .......... 152
CHAPTER IX
VELOCITY OF REACTIONS AND CATALYSIS
Chemical affinity. Influence of concentration. Influence of tem-
perature. Reversible reactions. Catalysis. Enzymes. Manu-
CONTENTS XV
PAGE
facture of sulphuric acid. Sulphur. Cement. Recovery of
sulphur. Hydrogenation or hardening of oils. Margarine.
Syntheses from water-gas. Hydrogen from methane . .172
CHAPTER X
CHEMISTRY AND AGRICULTURE. POTASH, PHOSPHATE
AND NITROGENOUS FERTILISERS
Substances necessary for the growth of plants. Potassium salts.
Phosphates. Nitrogenous fertilisers. Fixation of atmospheric
nitrogen i . Direct combination of nitrogen and oxygen ;
2. Fixation of nitrogen by means of carbides ; 3. Synthetic
production of ammonia. Urea. Lime. Trace elements.
Catalytic oxidation of ammonia . . . . -195
CHAPTER XI
GLASS, SODA, SOAP, LIME AND CLAY
Discovery of glass. States of matter. Crystalline and amorphous
solids. Crystallisation of liquids. Super-cooled liquids.
Devitrification. Fused quartz or silica glass. Water-glass.
Glass. Annealing of glass. Toughened glass. Safety glass.
Pyrex. Crystal glass. Strass or paste. Coloured glass.
Silvering of glass. Manufacture of soda. Hydrochloric
acid. Chlorine. Bleaching powder. Saponification of fats.
Manufacture of soap. Soft soap. Hard soap. Cleansing
power of soap. Hard water. Softening of hard water. Per-
mutit. Removal of salts from sea- water. Limestone caves.
Stalactites and stalagmites. Quicklime. Slaked lime. Mortar.
Limestone, chalk, coral, marble, Iceland spar, pearls. Clay.
Porcelain, stoneware, earthenware. Portland cement. Con-
crete .......... 214
CHAPTER XII
ELECTRICITY AND CHEMISTRY
Voltaic cell. Sodium and potassium. Electro-plating. Conduction
of electricity by solutions. Electrolytes and non-electrolytes.
Electrolysis. Ions. Movement of ions. Leclanche" cell. Lead
accumulator. Nickel-iron cell. Nickel-cadmium cell. Re-
fining of copper. Manufacture of chlorine and of caustic
soda. | Hydrogen and oxygen. Aluminium. Alloys of
aluminium. Magnesium. Carborundum. Alundum. Artificial
graphite 249
XVI CONTENTS
PAGE
CHAPTER XIII
THE COLLOIDAL STATE
Analogy between solutions and gases. Diffusion. Colloids and
crystalloids. The colloidal state. Tyndall phenomenon. The
ultramicroscope. Ruby gold. Size of colloid particles. Ad-
sorption. Emulsoids and suspensoids. Electrophoresis.
Sedimentation in rivers. Process of dyeing. Mordants.
Colloids in agriculture. Purification of water and sewage.
Protective action of emulsoids. Peptisation. Mass of the
molecule. Brownian movement ..... 273
CHAPTER XIV
MOLECULAR ARCHITECTURE
Organic chemistry. Isomensm. Molecular constitution. Valency.
Formulae of Couper and 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. Production of optically active compounds . 290
CHAPTER XV
SYNTHETIC CHEMISTRY I
Chief constituents of coal-tar. The coal-tar dyes. Synthesis of
alizarin. Synthesis of indigotin. Anaesthetics, Antiseptics,
Drugs, Insecticides : Chloroform, novocaine, amethocaine,
adrenaline (suprarenine) ; chloral, veronal, luminal ; chlor-
amineT, penicillin; antifebrin, phenacetin, aspirin ; salvarsan,
plasmoquin (pamaquin), mepacrine (atebrin), paludrine,
sulpha-drugs ; pyrethrins, rotenone, D.D.T., gammexane . 310
CHAPTER XVI
SYNTHETIC CHEMISTRY II
Synthetic perfumes : coumarin, oil of wintergreen, oil of bitter
almonds, lily of the valley, hawthorn blossom, ambergris,
lonone (imitation violet). Imitation musk. Oil of mirbane.
Synthetic camphor. Plastics : bakelite, beetle ware, perspex
(Incite), diakon, polythene (alkathene), butvar, erinpid
(galalith), nylon, silicones. Rubber-like materials : vulcanite,
isoprene, butadiene, neoprene, chloroprene, alloprene . . 330
CONTENTS XV11
CHAPTER XVII
FERMENTATION AND THE ACTION OF ENZYMES
AND MICRO-ORGANISMS
Explanation of fermentation. Enzymes. Manufacture of alcohol.
Proof spirit. Methylated spirit. Saccharification of starch
(amylo-process). Alcoholic beverages. Whisky, gin, brandy,
rum. Wines. Beers. Fusel oils. Artificial fruit essences.
Plasticisers. Vinegar. Acetic acid. Acetone. Curdling of
milk. Cheese. Casein. Distempers. Lanital, aralac, ardil.
Production of glycerine. Yeast as food-stuff. Marmite.
" Mineral yeast "........ 343
CHAPTER XVIII
VITAMINS AND HORMONES
Nutrition. Vitamins. Vitamin A. Carotene. Vitamin Bj. Aneurine
(thiamine). Vitamin B a -complex. "Vitamin C. Ascorbic acid.
Vitamin D. Calciferol. Pyridoxm (B 6 ). Biotin (H). Toco-
pherol (E). Hormones. Adrenaline. Thyroxine. Insulin.
Sex hormones. Trace elements . . . . .361
INDEX 375
LIST OF ILLUSTRATIONS
PAGE
A sixteenth-century twin " pelican," or circulatory vessel . . 6
The Alchemist . 7
ROBERT BOYLE ......... 8
JOHN DALTON ... . . . . . . .14
Extinguishing an oil-fire by means of Foamite Firefoam . . 49
Neon Lighthouse ......... 56
ANTOINE LAURENT LAVOISIER ....... 63
Machine for making matches . . . . . . .76
Oil wells near Summerland, California ..... 88
A modern petroleum distillation unit ..... 93
A Peep at the Gaslights in Pall Mall 101
Cutting steel by oxy-acetylene flame . . . . . .114
Diamond crystal in blue ground . . . . . .120
Char coal- burning at Longhope, Forest of Dean. Making the
chimney . . . . . . . . . .124
Charcoal-burning at Longhope, Forest of Dean. The " pit *' .125
Charcoal- burning at Longhope, Forest of Dean. The pit in action . 126
Teasing cotton preparatory to nitration . . . . .129
Pans for nitrating cellulose . . . . . . .130
Breaking up a large cast-iron pot . . . . . 133
Beaters for disintegration of fibres . . . . . .141
Paper-making machine . . . . . . . .142
Passage from Hooke's Micrographia . . . . . -143
Season-cracking of brass . . . . . . .163
Eradication of weeds by spraying with dilute sulphuric acid . 185
Effect of potash salts on growth of mangolds . . . 197
Potash mine in Alsace * . . . . . . . -199
Crystallising vats for potassium chloride . . .199
Searles Lake, California ........ 200
Effect of nitrogenous fertilisers (ammonium sulphate) on plant
growth 203
XX ILLUSTRATIONS
PAGE
Sheet glass, produced by the Fourcault process, passing between
rollers .......... 221
Sheet glass, produced by the Fourcault process. Glass ready to be
cut 222
Cracking of ordinary plate glass ...... 225
Cracking of " Armourplate " glass ...... 226
Manufacture of soap. Saponification pans . . . -235
Soap cut into bars, piled for drying . . . . . .238
Manufacture of soap. Jacobi rapid cooling press . . -238
Limestone terraces, Mammoth Hot Springs, Yellowstone Park . 244
Iceland spar, showing double refraction ..... 245
Production of hydrogen and oxygen by electrolysis . . . 263
Knowles* cell for the electrolytic production of hydrogen and oxygen 264
Graphite furnace in action ....... 270
Louis PASTEUR ......... 298
Crushing the Leaves of woad in a rotating horse-mill . . -316
Tablets of atebrin packed in polythene envelopes -327
Fine mesh of Nylon stocking -338
CHEMISTRY IN THE SERVICE
OF MAN
/
CHAPTER I
INTRODUCTION
CHEMISTRY is a branch of science which deals with matter,
or 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 and specific pro-
perties of these substances, the methods of their preparation,
the changes which they undergo, and their behaviour, not
only in relation to what are called physical forces (heat,
light, electricity, etc.), but also in relation to other sub-
stances ; and it studies also how, from the materials already
known, new materials, whether useful or ornamental, may
be obtained. 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 materials 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 science ; f
of chemistry, in fact, more than on any other branch o|
organised knowledge, depend the material well-being and
comfort of man.
But the end and aim of chemistry is not merely material.
2 CHEMISTRY IN THE SERVICE OF MAN
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 beneath 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
modern 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 half-century there have been no more fruitful
regions of experimental and speculative activity than those
common territories where the sciences of chemistry and
physics and chemistry and biology overlap.
Chemistry, moreover, possesses a cultural value apart from
its applications. Its study is not only a means of cultivating
the mind and of training and strengthening the scientific
habit of thought, but it also brings us into closer relations
with and gives a fuller understanding of the physical universe
in which we live. In attempting, therefore, 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 to recount some of the achievements of chemists
and physicists who, during the present century, with amazing
insight and experimental skill, have been making known to
us the invisible texture of what Carlyle called " the Time-
vesture of the Eternal," the material universe.
INTRODUCTION 3
THE CONSTITUTION OF MATTER
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 ; and in the
philosophic epoch of the development of our knowledge
of the material universe, one cannot but recognise the pre-
eminence of ancient Greece. Men of other races and of
earlier civilisations had doubtless speculated on the problem
of the ultimate constitution of matter, but it was in Greece
that the streams of thought flowing from Chaldea, from
India and from Egypt, met and mingled, settled and became
clarified. It is in ancient Greek philosophy that we find
formulated most clearly many of the problems which face
the modern man of science, and it was by the Greek philoso-
phers that the first important attempts were made at their
solution. These philosophers, it is true, could not make
any very marked advance in their knowledge of the physical
universe, and their theories remained to a great extent
unfruitful, simply because their knowledge of facts was too
slight and there was no possibility of testing the validity of
their theories by experiment. Nevertheless, channels of
thought were cleared by them and lines of advance were
opened for others who through difference of temperament
and outlook, as well as by growth of knowledge, were
perhaps more fitted to travel along them.
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
4 CHEMISTRY IN THE SERVICE OF MAN
universe merely by the exercise of a vigorous imagination
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 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/*
In the philosophy of ARISTOTLE, based on that of EMPED-
OCLES, we find the conception of one primordial matter,
tether, which acted as the carrier of certain essential qualities
which were taken to be hotness, coldness, wetness, dryness ;
and the combination of these qualities in pairs was sup-
posed to give rise to the four elements or primary forms of
matter, fire (hot and dry), air (hot and wet), earth (cold and
dry), water (cold and wet). The elements were regarded not
as material things but rather as the combinations of the
essential qualities ; and by the union of these in different
proportions the different substances were considered to have
been 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.
During a period of many centuries before the beginning
of the Christian era, Egyptian craftsmen had acquired great
skill and expertness in the extraction and working of metals,
and had achieved much success in the surface-colouring of
metals and in the production of alloys which counterfeited
the appearance of gold and silver. In Alexandria, in the
early years of the Christian era, Egyptian technical know-
ledge became united with Greek philosophic speculation and
with the astrological and mystical views of the Chaldeans ;
and from Alexandria this body of knowledge, speculation
and mvsticism passed to Svria and Persia, and later, in the
INTRODUCTION 5
seventh century, to Arabia. To the Greek word, chemia*
applied to the art of making or counterfeiting gold~~and
silver, the Arabs prefixed the article al, and so gave us the
term alchemy.
Alchemy was, from the very beginning, not only an art
but a philosophy, and the philosophic basis of alchemy is
to be found in the Aristotelian doctrine of the essential unity
of matter, and the view that matter is merely the carrier or
embodiment of certain qualities which could be removed
from one form of matter and transferred to another form of
matter. The belief in the transmutability of matter, in the
transmutability, for example, of lead into gold, followed
naturally from the Aristotelian theory.
The alchemists also reasoned much by analogy and were
thereby often led woefully astray. Thus it was thought that
just as in the case of animals birth and growth occur, so
also in the mineral world metals were thought of as being
generated and growing in the earth ; and just as a chicken
grows from an egg, so
( The same we say of lead, and other metalls,
, Which would be gold, if they had time.
' for 'twere absurd
\ To think that nature, in the earth bred gold
Perfect i' the instant. Something went before. 2
How absurd these views would seem to be ; and yet,
although the alchemists were misled by a false analogy,
recent work on artificial transmutation (p. 41) shows that
the idea of " growth " in minerals is not so fantastic as at
one time it appeared to be.
The production of gold, the perfect and complete metal,
was regarded, then, as being the end and aim of Nature's
striving 3 ; and it was the aim of the alchemists to hasten
1 This word is probably derived from chemi (meaning black), the
ancient name given to Egypt on account of the dark colour of its soil.
2 Ben Jonson : The Alchemist.
8 The occurrence of gold and silver in association with base metals,
such as copper and lead, was held to support the view that base metals
grow into the metals silver and gold,
6 CHEMISTRY IN THE SERVICE OF MAN
the process of growth of imperfect or base metals into gold
by means of a medicine or transmuting agent called the
philosopher's stone, the elixir, the magisterium, etc. To
obtain this, all the kingdoms of nature animal, vegetable
and mineral were ransacked ; and materials of all kinds
were calcined, boiled, fused and distilled.
Alchemy, then, was a philosophy of nature, and to many
of the scholars of the Middle Ages, such as ALBERTUS
MAGNUS and ROGER BACON, it made chiefly an intellectual
appeal. There were many others, however, for whom
A sixteenth-century twin " pelican/* or circu-
latory vessel, for the prolonged heating of
liquids.
avarice and cupidity were the loadstars, and in the fifteenth
and sixteenth centuries, especially, alchemy passed into the
hands of visionaries and swindlers. Europe swarmed with
rogues and tricksters, and it is they who have caused alchemy
to be associated in men's minds only with deceit, quackery
and charlatanism.
f Although the alchemists failed in their endeavour to
transmute the base metals into gold, yet by their unceasing
labour they laid the foundations of present-day chemistry.
To the alchemists we owe the preparation of substances of
^upreme importance in chemical science, such as sulphuric
acid or oil of vitriol, hydrochloric acid or spirit of salt, nitric
INTRODUCTION 7
acid or aqua fortis, aqua regia the solvent of gold, and
many others. In the sixteenth century, moreover, alchemy
acquired a nobler aim and ideal under the influence of that
erratic genius and rebel against convention and tradition
Philippus Aureolus Bombastus von Hohenheim, generally
known as PARACELSUS, who was born at Einsiedeln in Switzer-
THE ALCHEMIST.
After a painting by A. van Ostade (1661). (National Gallery, London.)
On the sheet of paper lying on the floor, the artist, with ironic humour,
has painted the words, oleum et operam perdis thou labourest in vain.
land in 1493, and died at Salzburg in Austria in 1541.
Paracelsus taught that the true aim of alchemy should be,
as the handmaid of medicine, the curing of human illness
and disease, and that the preparation and study of the
properties of drugs should be the main object of the chemist.
A new era in chemistry was thereby inaugurated, known as
the period of iatrochemistry or medical chemistry.
8 CHEMISTRY IN THE SERVICE OF MAN
The teachings of Paracelsus not only turned men's minds
from the obsession of gold-making and " the deceitful and
mischievous art of alchemy," but led also to the preparation
and study of many new materials. latrochemistry acted as
ROBERT BOYLE.
From the painting after F. Kerseboom.
(National Portrait Gallery, London.)
the bridge between the alchemy of the fifteenth and the
beginnings of an exact science of chemistry in the seventeenth
century. The philosophy of Aristotle held sway in the minds
of men and as a dogma of the Church throughout the Middle
Ages, but from time to time protests were raised against
the doctrine of the four elements ; and the overthrow of
this philosophy was completed in the seventeenth century by
INTRODUCTION 9
the Hon. ROBERT BovLE, 1 of whom it has been said that
" he was the father of chemistry and brother of the Earl of
Cork."
Pure substances, as Boyle pointed out, can be divided 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 definition,
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 realised. 2
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 the red substance known
as red precipitate or oxide of mercury is heated in a glass
tube, 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. The red substance has
thus been decomposed into metallic mercury and a gaseous
substance, to which the name of oxygen has been given.
This red substance, therefore, is a compound of mercury
and oxygen.
In spite of most laborious and prolonged efforts, chemists
have hitherto not succeeded in reducing the number of the
elements to less than ninety. Of these ninety elements, a
list of which, for convenience of future reference, is given
below, all the substances in the known universe are built up.
1 Robert Boyle, the youngest son of the first Earl of Cork, was born
at Lismore, Ireland, in 1627, and died in 1691. He was the author of
The Sceptical Chymist, the publication of which marks the beginning of
chemistry as a science.
2 Although this definition may still serve for most purposes, the
phenomena of radioactivity and the existence of isotopes, to which
reference is made in the following chapter, show the need of a new
definition.
IO
CHEMISTRY IN THE SERVICE OF MAN
LIST OF THE ELEMENTS
Atomic
Atomic
Atomic
Atomic
number
Svmbol
weight
number
Symbol
weight
I.
Hydrogen
, *H
I -008
47-
Silver .
Ag
107-88
2.
Helium
. He
4*003
48.
Cadmium
Cd
112-41
3-
Lithium
. Li
6-94
49.
Indium .
In
114-76
4-
Beryllium
. Be
9'02
50.
Tin
Sn
118-70
5-
Boron
. B
10-82
SI-
Antimony
Sb
121-76
6.
Carbon
. C
12-01
52.
Tellurium
Te
127-61
7-
Nitrogen
. N
14-008
53-
Iodine
I
126-92
8.
Oxygen
.
16-00
'54-
Xenon .
Xe
I3I'3
9-
Fluorine
. F
19-00
55-
Caesium
Cs
132-91
IO.
Neon
. Ne
20-183
56.
Barium .
Ba
I37-36
ii.
Sodium
. Na
22-997
57-
Lanthanum
La
138-92
12.
Magnesium
. Mg
24-32
58.
Cerium .
Ce
140-13
13-
Aluminium
. Al
26-97
59-
Praseodymium
Pr
140-92
14.
Silicon .
. Si
28-06
60.
Neodymium .
Nd
144-27
I5
Phosphorus
. P
30-98
61.
Illinium 1
11
16.
Sulphur
. S
32-06
62.
Samarium
Sa
I50-43
17-
Chlorine
. CJ
35-457
63.
Europium
Eu
152-0
18.
Argon .
. A
39-94
64.
Gadolinium
Gd
156-9
19.
Potassium
. K
39-096
65-
Terbium
Tb
159-2
20.
Calcium
. Ca
40-08
66.
Dysprosium
Dy
162-46
21.
Scandium
. Sc
45-10
67-
Holmium
Ho
164-94
22.
Titanium
. Ti
47-90
68.
Erbium .
Er
167-2
23-
Vanadium
. V
50-95
69.
Thulium
Tm
169-4
24.
Chromium
. Cr
52-01
70.
Ytterbium
Yb
173-04
25-
Manganese
. Mn
54 % 93
7i.
Lutecium
Lu
174-99
26.
Iron
. Fe
55-85
72.
Hafnium
Hf
178-6
27-
Cobalt .
. Co
58-94
73-
Tantalum
Ta
180-88
28.
Nfckel .
. Ni
58-69
74-
Tungsten
W
183-92
29.
Copper .
. Cu
63-57
75-
Rhenium
Re
186-31
30.
Zinc
. Zn
65-38
76.
Osmium
Os
190-2
31.
Gallium .
. Ga
69-72
77-
Iridium
Ir
193-1
32.
Germanium
. Ge
72-60
78.
Platinum
Pt
I95-23
33-
Arsenic .
. As
74-91
79-
Gold .
Au
I97-2
34-
Selenium
. Se
78-96
80.
Mercury
Hg
20O-6i
35-
Bromine
. Br
79-92
81.
Thallium
Tl
204-39
36.
Krypton
. Kr
83-7
82.
Lead
Pb
207-21
37-
Rubidium
. Rb
85-48
83.
Bismuth
Bi
209-0
38.
Strontium
. Sr
87-63
84.
Polonium
Po
39-
Yttrium .
. Yt
88-92
85.
i
40.
Zirconium
. Zr
91-22
86.
Radon .
Rn
222
41.
Niobium
. Nb
92-91
87.
Francium
Fr
42.
Molybdenum
. Mo
95-95
88.
Radium .
Ra
226*05
43-
Masurium 1
. Ma
89.
Actinium
Ac
.
44.
Ruthenium
. Ru
101-7
90.
Thorium
Th
232-I2
45-
Rhodium
. Rh
102-91
91.
Protoactinium .
Pa
231
46.
Palladium
. Pd
106-7
92.
Uranium
U
238-07
1 The occurrence in nature of elements 4-? and 61 has not been con-
firmed. Isotopes (p. 36) of these elements and also of 85 have been
produced artificially. See also p. 45.
INTRODUCTION
II
Only about twenty of the elements occur free or uncom-
bined 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 TERRESTRIAL MATTER
(Earth, Air and Sea)
per cent.
50-02
Potassium
25'8o
Magnesium
7-30
4-18
Hydrogen
Titanium
3'22
Chlorine
2- 3 6
Carbon .
per cent.
2-28
2'08
Oxygen .
Silicon .
Aluminium
Iron . 4 1 8 Titanium 0-43
Calcium 3*22 Chlorine 0-20
Sodium 2-36 Carbon . 0-18
99'00
From the numbers in this table one learns that the two
elements, oxygen and silicon, in the free or in the combined
state, constitute together three-quarters of the whole of
terrestrial matter, by weight, so far as this is accessible to
direct investigation.
If one considers the composition merely of the earth's
crust accessible to investigation, the average values do not
differ greatly from those given above. There is, however,
evidence to show that the composition of the interior of the
earth is very different from that of the crust ; and, from in-
vestigations of different kinds, the conclusion has been drawn
that beneath the crust of the earth there occur zones dimin-
ishingly rich in silicates and increasingly rich in iron, and
that there is lastly a core consisting essentially of iron and
nickel.
THE ATOMIC THEORY
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
12 CHEMISTRY IN THE SERVICE OF MAN
hypothesis which had been put forward in the fifth and
fourth centuries B.C., by LEUCIPPUS, DEMOCRITUS, and
EPICURUS. According to the doctrine of these philosophers,
a doctrine which comes nearer to modern scientific views
than any other system of philosophy of the ancient world,
and which has been preserved and expounded for us by the
Roman poet LUCRETIUS, matter is made up of indivisible
particles, the " atoms " or the " first-beginnings of things,"
which are immutable and eternal. These " first-beginnings "
are in constant motion, travelling through void. " Of this
truth which I am telling," writes Lucretius, 1 " we have a
representation and picture always going on before our eyes
and present to us : observe whenever the rays are let in
and pour the sunlight through the dark chambers of houses,
you will see many minute bodies in many ways through the
apparent void mingle in the midst of the light of the rays,
and as in never-ending conflict skirmish and give battle,
combating in troops and never halting, driven about in
frequent meetings and partings, so that you may guess from
this what it is for first-beginnings of things to be ever tossing
about in the great void." 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 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."
These views must seem crude to the modern mind, and
even NEWTON, at the end of the seventeenth century, could
1 Lucretius : De rerunt naturci, translation by Munro,
INTRODUCTION 13
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, movable particles,
of such sizes and figures, and with such other properties,
and in such proportion to space, as most conduced to the
end for which He formed them ; and that those primitive
particles, being solids, are incomparably harder than any por-
ous 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 gave 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 ob-
served 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 become
of any real value in science, and nothing has influenced the
progress of chemistry so much as the achievement of this
by the Manchester schoolmaster, JOHN DALTON. 1
To the older philosophers, the atoms or indivisible par-
ticles 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 has already been given, the atoms were assumed
to be all exactly alike in their properties, including, of course,
their mass ; but they differed from the atoms of every other
element.
Further, according to Dalton, a compound is formed by
the combination of atoms of different kinds ; and since the
nature of the compound will necessarily depend on the
1 John Dalton, the son of a hand-loom weaver in Cumberland, was
born in 1766. After teaching for some years in a Manchester school
he became a private tutor. The atomic theory, on which his fame mainly
rests, was formulated in 1803 and published in 1807. He died in 1844.
14 CHEMISTRY IN THE SERVICE OF MAN
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 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
JOHN D ALTON.
if one particular element A combines with another element
B to form compounds containing different proportions of
A and B, these different proportions stand to one another
in the ratio of integral, or whole, numbers. That is
to say, we can have the compounds A + B, A + 26,
2A + B, 2A + 36, etc., where A and B represent atoms of
the elements A and B. Here, then, we have the explanation
INTRODUCTION 15
of the second fundamental law of chemistry, the law of
multiple proportions.
At first Dalton made no distinction between the smallest
particle of an element and the smallest particle of a com-
pound. 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 com-
pound must still be capable of being split up into smaller
particles, namely the atoms of the component elements. A
new name was therefore introduced in 1811 by the Italian
physicist, AVOGADRO, who called the smallest particle of a
compound a molecule. The molecule of a compound, there-
fore, 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 mole-
cule, 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.
It does not, however, follow that the atom and molecule
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.
The atomic theory of Dalton, modified by the conception
of molecules, served to co-ordinate or explain the funda-
mental laws of chemistry, the laws of definite and of multiple
proportions ; and on the basis of this theory the super-
structure of modern chemistry was largely built.
Symbols and Formula. In the table given on p. 10 it will
be seen that opposite each element is a letter or group of
1 6 CHEMISTRY IN THE SERVICE OF MAN
letters, by means of which one can represent shortly the
particular element. Each of these symbols, 1 as they are called,
represents an atom or one atomic proportion by weight of
the particular element ; and since a compound is regarded
as being formed by the combination of atoms, one 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 consists of one atom of sodium and one
atom of chlorine ; CO, similarly, represents a compound of
carbon and oxygen, and so on. Frequently, however, the
molecule of a compound is formed by the combination of
elements in more than one atomic proportion, and so one
writes, for example, H 2 O, which is the formula 2 for water ;
a formula which indicates that the molecule of water con-
sists of two atoms of hydrogen and one atom of oxygen.
The formula NH 3 , similarly, which is the formula for
ammonia, indicates that the molecule of this compound
consists of three atoms of hydrogen united with one atom
of nitrogen.
The use of these symbols and formulae is a great con-
venience and renders much assistance to the chemist in
understanding and in representing chemical changes ; and
they will be employed to some extent in the following pages.
They will, however, be used to assist the understanding,
not to burden the memory.
To one point more we must refer. According to the
1 These symbols were introduced early last century by the Swedish
chemist, Berzelius, who used 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 one can thus understand why, in certain cases, the
symbols are not obvious abbreviations of the English name of the element.
Thus, we have, Sb= antimony (stibium) ; Cu= copper (cuprum) ; Au=
gold (aurum) ; Fe=iron (ferrum) ; Pb=lead (plumbum) ; Hg= mer-
cury (hydrargyrum) ; K "potassium (kalium) ; Ag= silver (argentum) ;
Na=* sodium (natrium) ; Sn=tin (stannum).
1 One speaks of the symbol of an element and the formula of a compound
or of a molecule.
INTRODUCTION 17
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, on
the basis of various experimental investigations, the absolute
masses of atoms have been calculated (p. 26), it is clear that
one cannot handle these infinitesimally small particles of
which many millions are contained in the tiniest piece of
matter which can be seen even with the help of a microscope ;
one cannot place these atoms on the scale pan of a balance
and ascertain their weight. It is, however, comparatively
easy to 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, referred to
the value 16-00 as the atomic weight of oxygen, are given in
the table on p. 10. By the introduction of these atomic
weights, a new and extended meaning is given to chemical
symbols and formulae. The symbol, Na, for example, not
merely represents the element sodium, but stands for one
atomic proportion or 22-997 parts by weight of sodium ;
and the formula, NaCl, is not merely a convenient shorthand
symbol for the compound sodium chloride (which is the
chemical name for common salt), but it stands for one
molecular proportion by weight, or 22-997 + 35'457 = 5^*454
parts by weight of sodium chloride, the numbers 22-997
and 35*457 being the atomic weights of sodium and chlorine
respectively. It will be clear, also, that the molecular weight
of a compound, which is equal to the sum of the atomic
weights of the elements forming it, is the weight of a molecule
relatively to the weight of an atom of the standard element,
oxygen, taken as 16-00.
Valency. Although atoms can combine with one another
to form a compound or compounds, it has been established
that elementary atoms do not possess an unlimited power of
1 8 CHEMISTRY IN THE SERVICE OF MAN
combination. The atoms of two different elements may
combine in more than one proportion, but not in every pro-
portion. 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. On the other hand, an atom of the metal calcium
can combine with two atoms of chlorine to form the com-
pound calcium chloride (CaCl 2 ) ; an atom of aluminium can
combine with three atoms of chlorine to give A1C1 3 ; and
an atom of carbon can combine with four atoms of chlorine
to form carbon tetrachloride, CC1 4 . The atoms of different
elements, therefore, have a certain combining capacity, or
have a certain valence 1 or valency, as it is called ; and since
one atomic proportion of hydrogen is never known to com-
bine with more than one atomic proportion of any other
element, the combining capacity or valence of hydrogen is
taken as the standard and put equal to unity. Chlorine, an
atom of which can combine with only one atom of hydrogen,
is also said to have unit valence or to be univalent. Oxygen,
an atom of which can combine with two atoms of hydrogen
(as in water, H 2 O), is said to be bivalent ; nitrogen, an atom of
which can combine with three atoms of hydrogen (as in
ammonia, NH 3 ), is said to be trivalent ; carbon, an atom of
which can combine with four atoms of hydrogen, is said to
be quadrivalent ; and so on.
The doctrine of valency, first clearly stated by Sir EDWARD
FRANKLAND in 1852, was put forward as an empirical doc-
trine, and it is only in comparatively recent years that a
theoretical basis has been found for it in the conception of
the electronic constitution of matter which will be discussed
in the next chapter.
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 something of your
1 From the Latin valere, to be worth.
INTRODUCTION 19
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 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 modern physical science ; and it is by
the introduction of mathematics and by the quantitative treat-
ment of chemical phenomena that modern chemistry is mainly
distinguished from the chemistry of a hundred years ago.
MODERN SCIENTIFIC METHOD
In so far as philosophic views were founded, as many of
the Greek views regarding the constitution of matter were
founded, on observations of facts, even when the observa-
tions were faulty, one need not be surprised that the vigorous
imagination and keen intellect of the Greeks should formulate
views or theories regarding the constitution of matter which
find their counterpart in modern scientific theory. That,
notwithstanding their intellectual powers, the assertion
could be made, as it was made by Whewell, that " the
whole mass of the Greek philosophy shrinks into an almost
imperceptible compass when viewed with reference to the
progress of physical knowledge," is due to the fact that the
aims and methods of Greek philosophy were so different
from the aims and methods of modern science. The Greek
philosophers sought for a general philosophic doctrine or
formula which should throughout be consistent with itself
and should embrace not merely the phenomena of the
material universe, but should also include the activities of
thought, of life and of conduct. Starting from a postulate
or premiss based, it might be, on an observation of fact or on
an analogy (often false), a comprehensive philosophy was
developed by the exercise of a rigorous logic ; but not even
Aristotle, in spite of the principles he himself laid down,
principles which are at the foundation of the inductive and
2O CHEMISTRY IN THE SERVICE OF MAN
experimental methods of modern science, tested his con-
clusions on the touchstone of fact. In modern science,
which has developed from the time of FRANCIS BACON in
the early part of the seventeenth century, one has adopted a
less comprehensive aim and a more experimental method.
The first step in the building up of knowledge by the
scientific method is to ascertain the facts by observation and
experiment. Thus, in order to learn how the volume of a
gas is altered by pressure, a certain mass of the gas must be
subjected to a series of different pressures, and at each
pressure the volume of the gas must be measured. In this
way, Robert Boyle found that the volume of a gas is inversely
proportional to the pressure (Boyle's law). If the pressure is
doubled, the volume is halved. This generalised statement of
observed facts is called a scientific law, or law of nature.
Such a law, it should be emphasised, merely summarises, in
a general statement or formula, a relationship which has been
observed in a certain number of cases. A scientific law,
therefore, differs from a civil law in being merely descriptive,
not prescriptive ; and the enunciation of a scientific law by
the generalisation of experimentally determined facts the
arguing from particular cases to a general or universal
relation is called induction. It forms the second stage in
the building up of the scientific edifice.
The method and aim of science, however, does not
consist merely in the " ordering of nature " in descriptive
laws. It seeks also to correlate or " explain " the laws ; and
so, with the general laws as a starting point, scientific
imagination is called upon to frame an hypothesis or con-
ception regarding the fundamental nature of things. This
hypothesis must, of course, be in harmony with all the facts
already known and it must be such that the general laws,
obtained inductively from experiment, follow as necessary
consequences from the hypothesis. When the deductions
from the hypothesis are found to be in harmony with the
inductively derived laws, the hypothesis takes rank as a theory.
INTRODUCTION 21
An hypothesis or theory makes it possible not only to
co-ordinate or correlate the various known laws to explain
these laws, as one says but also to predict new and undreamt-
of laws. It not only gives satisfaction to the mind by pro-
ducing coherence and order among diverse phenomena, but
it opens up vistas of new knowledge, suggests new tests of its
own validity and spurs one on to fresh endeavour. Before
the new laws obtained deductively from an hypothesis or
theory are accepted, however, they must be subjected to
verification by experiment. With the continual necessity,
therefore, of experimental investigation and testing of
deductions from theory, it will readily be understood that
** Science moves, but slowly slowly, creeping on from point to point";
and the building up of the edifice of science is a slow and
laborious task.
CHAPTER II
RADIOACTIVITY AND ATOMIC STRUCTURE
ALTHOUGH the atomic theory, formulated by Dalton in 1803,
was generally accepted as a guiding principle in physical
science, it was regarded by some merely as a convenient
" working hypothesis," useful but not necessarily represent-
ihg actual fact. No direct, experimental proof of the objec-
tive reality of atoms existed. Investigations, however, belong-
ing mainly to the present century, have contributed, from
several different directions, towards establishing the atomic
theory in a position of unassailable strength, and have
furnished a proof of the objective reality of atoms or discrete
particles as constituting the fundamental basis of matter.
By the phenomena of diffusion, more especially diffusion of
gases (Chap, xm) ; by the Brownian movement observed in
the case of minute particles in suspension (Chap, xm) ; by
the phenomena of radioactivity, and even by the blue colour
of the sky, the discontinuous structure of matter is made
manifest and the existence of atoms or discrete particles
established with a probability amounting to a certainty.
To Dalton, as to Newton, the atoms were " solid, massy,
hard, impenetrable particles," incapable of sub-division ;
but during the greater part of the nineteenth century the
ground was being prepared for a revision of this view. To
this work of preparation attention may be given for a moment.
As the determinations of atomic weights increased in
number, it was observed that most of the values, when
referred to the atomic weight of hydrogen as unity, were
either whole numbers or very nearly whole numbers. This
remarkable fact gave rise to the view, first put forward in
1816 by WILLIAM PROUT, a physician and Lecturer on
Chemistry in London, that the atoms of different substances
22
RADIOACTIVITY AND ATOMIC STRUCTURE 23
are made up of various amounts of some primordial matter,
and that this primordial matter is hydrogen. This view,
however, did not meet with general acceptance, because it
was found that the deviation of the atomic weights of a
number of the elements from whole multiples of the atomic
weight of hydrogen could not be explained as due to experi-
mental error. Many chemists felt, however, that although
they could not accept Prout's view, it contained some
element of truth ; and this feeling was strengthened when,
in 1901, the Hon. R. J. STRUTT, now Lord RAYLEIGH,
by applying the law of probabilities, showed that " the
atomic weights tend to approximate to whole numbers far
more closely than can reasonably be accounted for by any
accidental coincidence." How nearly the hypothesis of Prout
agrees with present-day views regarding the constitution of
the atom will become clear in the sequel.
Periodic Law. Although Prout's hypothesis was not
accepted by chemists, the study of the atomic weights of the
elements brought to light a number of regularities and
relationships which pointed to the existence of some genetic
connection between the elements ; and of these regularities
the most important was that discovered by the Russian
chemist, MENDELI*EFF, and by the German chemist, LOTHAR
MEYER, in 1869 and 1870, the so-called periodic law. It was
observed by these chemists that when the elements are
arranged in the order of their atomic weights, there is a
periodic recurrence of properties. Thus, leaving hydrogen
and helium out of account for the present, and starting with
lithium, we have the series,
lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon,
and then the series,
sodium, magnesium, aluminium, silicon, phosphorus, sulphur, chlorine,
argon,
in which the properties of the elements are similar to those of
the corresponding members of the former series ; that is,
24 CHEMISTRY IN THE SERVICE OF MAN
sodium is similar to lithium, magnesium to beryllium, and
so on till we come to argon which has properties similar to
those of neon. After argon, which is similar to helium and
neon, there comes the element potassium, 1 and so a new series
is begun. Now, however, as the diagram (Fig. i) shows, new
types of elements occur and the period becomes longer ; so
2. He
FIG. i. PERIODIC CLASSIFICATION OF THE ELEMENTS.
that, from potassium, which corresponds to lithium and
sodium on the one hand, to krypton, which corresponds to
neon and argon on the other hand, there is a period not of
eight but of eighteen elements. This is followed by another
period of eighteen elements from rubidium to xenon, and
then there is a jump to a still longer period of thirty-two
elements (one of which is still not definitely characterised).
1 Argon is placed before potassium, although the latter has the smaller
atomic weight. This is one of the anomalies of the Mendele"eff periodic
Classification, and will receive its explanation later.
RADIOACTIVITY AND ATOMIC STRUCTURE 25
A fragmentary period of six elements completes the table.
Owing to the periodicity of properties, elements of similar
or analogous character fall into corresponding places in the
various periods, and, in the diagram, the members of these
" natural families " or groups of related elements are joined
together by full drawn lines. Dotted lines join elements
which are less closely related than are the members of the
" natural families."
The periodic law has proved a most valuable guide in
chemical investigation, and so uniform is the variation of
properties from element to element that Mendel 6eff was
FIG. 2. CROOKES TUBE.
able to predict the properties of several elements, then
unknown, with what was later found to be surprising accuracy.
Recognition of the essential validity of the periodic law
greatly stimulated speculation and investigation into the
nature and genesis of the elements, and during the nineteenth
century evidence was accumulating that the older views
regarding the nature of the atoms must be revised. Modern
investigation has now amply proved that the atom of the
chemist, the unit of chemical exchange, can no longer be
regarded as the unit of sub-division of matter. On the
contrary, the atom is now known to be a complex structure
built up of much smaller particles, the nature and arrange-
26 CHEMISTRY IN THE SERVICE OF MAN
ment of which have been, for a number of years, the subject
of experimental investigation.
Cathode Rays. The new light which, during the present
century, has been shed on the problem of the constitution of
matter came first from an unexpected direction, namely,
from a study of the discharge of electricity through highly
rarefied gases. In 1859, it was discovered by the German
physicist PLUCKER, that when an electric discharge is allowed
to take place in a highly evacuated glass tube, a peculiar
radiation is projected from the negative electrode or cathode,
as it is called ; and this radiation excites a phosphorescent
light in the glass of the tube opposite the cathode. This
radiation, moreover, known as the cathode rays, travels in
straight lines, and if a solid object is placed in the path of the
rays, a shadow is cast (Fig. 2). Moreover, by using a concave
cathode, whereby the rays can be brought to a focus, a metal
can be raised to incandescence, or even melted, under the
fury of the bombardment by the cathode rays. These
phenomena were studied more fully by Sir WILLIAM CROOKES
who, in 1879, surmised that the cathode rays were composed
of extremely small particles or corpuscles ; and in 1897, Sir
JOSEPH J. THOMSON, while Professor of Physics in the
University of Cambridge, proved that they consist of
negatively charged particles which travel with the enormous
velocity of from 10,000 to 100,000 miles per second, the
latter velocity being such that the particles would engirdle
the earth four times in the space of a second.
The mass of these negatively charged particles or electrons,
as they are called, is exceedingly small and equal only to one
eighteen-hundred-and-fortieth (y-gViO of the mass of the
hydrogen atom, the lightest atom or lightest particle of
matter hitherto known. 1 In this way, the existence of
1 The mass of a hydrogen atom has been calculated to be 1-67 X io~ 24
gram (i.e. 1-67 divided twenty-four times by 10), and the mass of an
electron is therefore o/n Xio~ 28 gram. In other words, it would take
about one million million million million atoms of hydrogen to make
up the weight of i gram (15*4 grains).
RADIOACTIVITY AND ATOMIC STRUCTURE 2J
particles very much smaller than the chemical atom was
discovered ; and since it was found that these electrons are
given off by substances under various conditions, as, for
example, when a body is raised to incandescence, 1 the con-
ception of the electronic constitution of matter, i.e. of the
atom, arose.
From another direction, also, further impressive evidence
was soon obtained that the atom is no longer to be thought
of as a single, indivisible, unchangeable particle, but as a
vibrant microcosm, a complex system possessing enormous
potential energy and capable, in certain cases at least, of
undergoing an amazing and spontaneous transformation into
atoms of a different kind.
Radioactivity. The property of radioactivity was dis-
covered in 1896 by the French physicist, HENRI BECQUEREL,
who found that the compounds of uranium continuously and
spontaneously emit " rays " or radiations which have the
power of passing through wood, paper and other opaque
materials, and of affecting a photographic plate in a manner
similar to the X-rays which had shortly before been dis-
covered by the German physicist, RONTGEN. Further
investigation of radioactive phenomena by Professor PIERRE
CURIE and his wife, MARIE SKLODOVSKA CURIE, in Paris, led
to the discovery, in 1898, of the much more highly radioactive
element radium, which occurs, to the extent of about one part
in 10,000,000, in the uranium-containing mineral, pitch-
blende. From this mineral, by a long and laborious process,
Mme. Curie later prepared the salt of radium, radium chloride,
a white substance similar in appearance to common salt.
Although the element radium has been isolated, and has
been found to resemble, in its chemical properties, the metals
calcium and barium, it is in the form of its chloride that it is
generally employed ; and when, in ordinary language, one
speaks of radium, it is to this salt, radium chloride, that one
generally refers.
1 As in the " valve " used in wireless telephony.
28 CHEMISTRY IN THE SERVICE OF MAN
Small amounts of radium are still obtained from its
original source, the pitchblende deposits at Joachimstal in
Bohemia, as well as from deposits of carnotite occurring
in the States of Colorado and Utah in America, but it
was the Katanga Mines in the Belgian Congo that, until
about 1930, furnished almost the whole of the world's
supply of radium. In that year, however, large deposits of
pitchblende were discovered on the shores of the Great
Bear Lake in Northern Canada, and, since 1933, ever-
increasing quantities of radium have been produced
there. The El Dorado Mine of Northern Canada has
become one of the richest radium-producing mines in the
world.
Radium is a substance which must be handled with care,
for, if kept for a short time near the body, it cauterises the
skin and produces a sore which is difficult to heal. It is used
extensively in the treatment of cancer and other malignant
growths.
The investigation of the radioactive elements, uranium,
thorium and radium, has shown that the atoms of these
elements are continuously giving out positively and nega-
tively charged particles, the so-called alpha and beta rays ;
and they are the source, also, of ethereal vibrations, the
gamma rays, which are similar in nature to the X-rays. The
beta rays, or negatively charged electrons, and, more especially,
the gamma rays, are highly penetrating, 1 but the alpha rays,
which are positively charged particles of atomic dimensions
(p. 31), are easily stopped by a sheet of note-paper, or even
by a few centimetres 2 of air. These alpha particles, however,
contain much more -energy than the electrons and are much
more effective in breaking up the molecules of the atmo-
spheric gases, whereby the air is rendered a conductor for
electricity. These alpha rays are, of course, all stopped by
1 It is these very penetrating rays that destroy the unhealthily growing
cells in cancer.
2 A centimetre is rather less than half an inch ; 3-54 centimetres
(cm.)=i inch.
RADIOACTIVITY AND ATOMIC STRUCTURE 29
the walls of the glass or metal tube in which, ordinarily, the
small quantities of radium salt are sealed up.
The three most important radio-elements are, as has been
mentioned, uranium, thorium and radium, but electrical
measurements have shown that these elements give rise to
a large number of other radio-elements which have a much
more transient existence. Thus, radium gives rise to a gas,
radon or radium emanation, which is itself radioactive and
can be observed, like radium, to glow in the dark ; and
thorium, also, gives rise to a radioactive gas, thorium emana-
tion. These gases, however, when removed from the original
material, gradually lose their radioactive property and
disappear ; but just as fast as the separated emanation dis-
appears, just so fast is fresh emanation produced by the
original radium or thorium, spontaneously and always at the
same rate, unaltered by anything that man can do. Nor is this
all. From the radium and thorium whole series of radioactive
substances are produced successively, e.g. radium, radon,
radium A, radium B, etc., down to radium G, which is identi-
cal with lead. These different members of a radioactive series,
which are obtained, for the most part, only in unweighable
amounts, are distinguished from one another and identified
by the rate at which the radioactive power diminishes or
" decays/' Thus, the radioactive power of radium falls to
half its value in a period of 1590 years, whereas the corre-
sponding time for radon is 3-825 days, and for raclium A,
3-05 minutes.
On account of its high radioactive power, an indication of
which is given by its short " life," radon is now very generally
employed in radio-therapy in place of, or in addition to,
radium (radium chloride).
One of the disintegration products of thorium, known as
mesothorium-i, is obtained in considerable quantities as
a by-product of the incandescent gas-mantle industry.
Mesothorium-i loses half its radioactivity in 5^ years, so
that its life is comparatively short ; but for that very reason
30 CHEMISTRY IN THE SERVICE OF MAN
highly active preparations can be obtained. The commercial
mesothorium is largely employed in the manufacture of
luminous paints, which can be applied, for example, to the
hands of watches and so make it possible for the time to
be read in the dark.
Although the fact of radioactivity is now familiar to all,
the phenomena of radioactivity were, in the closing years
of the nineteenth century, startling in their unexpectedness ;
and they were bewildering and inexplicable until, in 1902,
ERNEST RUTHERFORD (afterwards Lord Rutherford) and
FREDERICK SODDY put forward their now universally accepted
hypothesis of atomic disintegration. According to this
hypothesis, the atom of a radioactive element is a complex
system of particles which undergoes spontaneous change, or
explodes, as it were, with projection at a very high velocity of
negatively charged electrons (the so-called beta rays), and
of heavier, positively charged particles or alpha rays. Not all
the atoms, however, of a radioactive substance undergo disin-
tegration at one moment ; only a certain definite fraction of
the atoms reach the condition of instability at the same time,
and the fraction is different for each radioactive element.
In the case of radium, for example, only about one atom
out of every hundred thousand million breaks up each second.
In the case of uranium, the process of disintegration is a
very slow one, otherwise the element would have already dis-
appeared from the earth. Of the uranium existing at the
present time, half will have disappeared by transformation
into other elements, including radium, only at the end of
rather less than five thousand million years. On the other
hand, half the radium now existing will have disappeared
at the end of 1590 years, and half of what then remains will
have disappeared at the end of a further period of 1590 years.
Fresh amounts of radium, however, are being slowly pro-
duced by the parent element uranium. The radioactive gas,
radon, when separated from the parent radium, rather
rapidly disappears half of it goes in less than four days (see
RADIOACTIVITY AND ATOMIC STRUCTURE 3!
p. 29), and half of what is then left disappears in another
four days, and so on. Just as fast as the separated radon
disappears, however, fresh radon is produced by the original
radium, and so the supply is kept up.
Other radioactive elements similarly undergo disintegration
and become transformed into other elements, as we have
already seen (p. 29).
A striking confirmation of the correctness of the disinteg-
ration hypothesis of radioactivity and of the complexity of
atoms was obtained when Sir WILLIAM RAMSAY and Lord
RUTHERFORD showed, by direct experiment and in different
ways, that the positively charged alpha particle which is
expelled from radioactive substances is in fact a positively
charged helium atom, or a helium atom which has lost two
electrons. Not only did Rutherford isolate the alpha particles
and show that on losing their electrical charge by taking up
electrons they form ordinary helium, but he also succeeded
in counting the number of alpha particles emitted by a given
weight of radium, by allowing the particles to pass through
a small hole and impinge on a fluorescent screen. At each
impact of an alpha particle, a little flash of light was pro-
duced, 1 and by counting the number of flashes the number
of particles passing through the opening was obtained.
Since the number of alpha particles expelled from a given
weight of radium can be counted, and since each alpha
particle becomes a helium atom, it is possible, by measuring
the volume of helium produced by a given weight of radium
in a given time, to calculate the number of helium atoms
(or molecules) in a given volume of the gas. The number
obtained by Lord Rutherford, namely, twenty-seven trillion
five hundred thousand billion (2-75 X io 19 ), in i cubic centi-
metre at o C. (32 F.), is in good agreement with the value
deduced from measurements of an entirely different kind. 2
1 This fact was made use of by Cropkes in the construction of the
small instrument known as the spinthariscope.
z In the above statement, a billion is taken as a million million, and a
trillion as a million billion.
32 CHEMISTRY IN THE SERVICE OF MAN
According, moreover, to a well-known theorem of Avo-
gadro, equal volumes of all gases when under the same pressure
and at the same temperature, contain the same number of
molecules. It follows, therefore, that at o C. and under
standard atmospheric pressure (76 cm. of mercury), i cubic
:entimetre of any and every gas will contain 2-69 Xio 19
molecules, to use a more accurate number than that obtained
3y Lord Rutherford.
Atomic Structure. The striking proof of the complexity
)f the chemical atom which was afforded by electrical and
adioactive phenomena gave a great impetus to the formation
)f definite views regarding the inner structure or constitution
)f what was formerly thought of as indivisible. Since
icgatively charged electrons constitute part of the atom
p. 27), and since the atom as a whole is electrically neutral,
t follows that there must be an amount of positive electricity
within the atom equal to the total negative charge carried by
,he electrons. How, then, is the structure of the atom to be
conceived ?
Experiment showed that when alpha rays, from radium,
or example, were passed through a gas, most of the tracks
vere straight lines ; some showed a slight bending, while a
fery few showed a sharp deflection. A similar behaviour
vas also found when alpha rays were passed through thin
netal foil, e.g. gold leaf. In this case, some of the alpha rays
vere thrown back almost on their own tracks. From a study
>f these results, Lord Rutherford suggested that the positive
electricity in the atom is concentrated in a very minute
lucleus, in which, also, almost the whole mass of the atom
s supposed to be resident. Around this minute positively
charged nucleus the negative electrons are arranged in the
brm of concentric rings or orbits, like a sun 'ringed round
vith planets. This atomic model, the general correctness of
vhich has been confirmed by all later work, was a brilliant
nference from experimentally determined data.
And what is the nature of the positively charged nucleus ?
RADIOACTIVITY AND ATOMIC STRUCTURE 33
The atoms or nuclei of radioactive elements emit, on dis-
integrating, alpha particles or positively charged helium
nuclei, as well as beta rays or negatively charged electrons.
In the case of the heavy atoms of the radioactive elements,
therefore, we seem to have a proof that the positively charged
nucleus of the helium atom is one of the units of nuclear
structure ; but since the mass of the helium atom (or nucleus)
is nearly four times that of the hydrogen atom, the helium
nucleus must itself be regarded as complex. The conclusion,
therefore, is reached that the positively charged nucleus of the
hydrogen atom, the lightest atom, is the simplest, positively
charged unit of atomic structure. This unit is called a proton.
The proton was for long regarded as being the unit of
positive electricity, but in 1933 it was found that there can
be produced, under certain conditions, a particle which has
the same mass as the electron, but which has a positive
instead of a negative charge. This particle, therefore, to
which the name positron has been given, must be regarded
as the unit of positive electricity, just as the electron is the
unit of negative electricity. It exists as some sort of structural
unit in the nucleus of the atom.
Besides the positively charged protons and positrons and
the negatively charged electrons, the investigations of
physicists have revealed the presence in the atom of un-
charged particles or neutrons, produced by the firm com-
bination of a proton and an electron. Such particles have
been liberated, for example, by the bombardment of atoms
of beryllium and of boron by alpha rays (p. 42), and have
proved to be most valuable missiles in bringing about the
artificial disintegration of atomic nuclei.
Modern investigations of the structure of the atom, there-
fore,, have extended enormously the limit of sub-division of
matter ; and the atom now takes the form of a very open-
spaced system of particles, the diameters of which are very
small compared with that of the system as a whole, or of
the atomic domain as it has been called. The hydrogep
B
34 CHEMISTRY IN THE SERVICE OF MAN
atom, according to the modern view, consists of a positively
charged nucleus, a minute speck of positively charged
matter (the proton), round which, at a relatively very great
distance, there circles a negatively charged electron. The
structure of an atom of hydrogen, therefore, has been com-
pared with that of the solar system, and it has been pointed
out that since the diameter of the earth is one twenty-
thousandth of the diameter of its orbit round the sun, one
can think of a hydrogen atom as a system in which the earth
represents an electron circling round a nucleus (much
smaller than itself), at a distance equal to twice the distance
of the earth from the sun. The atom, therefore, is mainly
void, a thing of specks and spaces, mainly spaces ; and one
can readily understand how a positively charged alpha particle
can pursue a straight path through the atoms of matter and be
only occasionally deflected by a near approach to, or collision
with, the massive, positively charged nucleus (p. 32).
The atom of helium, the element of next higher atomic
weight to hydrogen, has a nucleus which carries two positive
charges, and round this nucleus there circle, therefore, two
electrons. This helium nucleus, since its mass is four times
that of the hydrogen atom, is to be regarded as being made
up of two neutrons and two protons, the resultant nucleus,
therefore, carrying two positive charges. The atoms of the
elements of higher atomic weight, similarly, are to be re-
garded as constituted of positively charged nuclei, built up
of protons and neutrons, encircled by rings of planetary
electrons ; and the important discovery has been made that
as one passes from element to element, the number of positive
charges on the nucleus and y therefore, the number of planetary
electrons surrounding the nucleus, increases by single units.
Atomic Number. The number of excess positive charges on
the nucleus, which determines the number of planetary elec-
trons, is of much importance, because it is on these planetary
electrons that the chief chemical and physical properties
nf the elements depend. One of the great advances made in
RADIOACTIVITY AND ATOMIC STRUCTURE 35
modern times has been the recognition of the fact that the
number of excess positive charges on the atomic nucleus is
the same as the serial number or atomic number, as it is called,
of the element in the periodic classification given on p. 24.
For the determination of the atomic number several methods
are now available. In the case, therefore, of uranium, the
element of highest atomic weight occurring in nature, 1 the
atomic number of which is 92, the atom consists, it is believed,
of a complex nucleus carrying an excess positive charge of
92 units, surrounded by rings or shells of 92 electrons.
The recognition of the fact that the properties of an
element depend on the atomic number, rather than on the
atomic weight of the element, enables one to take account
of the anomalies occurring in the Mendeleeff classification
(p. 23), namely, that argon must, on account of its chemical
properties, be placed before potassium, and similarly tel-
lurium before iodine, although the atomic weights are in the
reverse order. When the elements are arranged in the order
of their atomic numbers, instead of their atomic weights,
these anomalies disappear, and argon and tellurium fall
into their proper places (p. 24). Generally, it is true, the
atomic numbers and atomic weights follow the same order,
but not always ; and for the periodic recurrence of chemical
properties it is the atomic number which is of importance.
The periodic law (p. 23), therefore, must now be stated in
the form : The properties of the elements vary in a periodic
manner with the ATOMIC NUMBER.
The existence of a series of integral atomic numbers
throws important light on the number of elements still to
be discovered. On arranging the elements serially in order
of the atomic numbers, as in the table on p. 10, it is found
that only two gaps occur, indicating that between hydrogen
and uranium only two elements remain to be discovered.
Experimental evidence of the existence of these has been
1 Artificially produced elements of higher atomic weight are now known
(P. 45).
36 CHEMISTRY IN THE SERVICE OF MAN
obtained, although the elements have not been definitely
characterised (p. 10).
Although there appears to be justification for the view that
the ultimate structural units of the nuclei of all atoms are
protons and neutrons, the fact that in the explosive dis-
ruption of radioactive atoms, helium nuclei (alpha rays) are
ejected, suggests that the helium nucleus of two neutrons
and two protons is a particularly stable complex ; and the
helium nucleus, therefore, appears to be a very important
secondary structural unit of the more complex atoms.
Isotopes. Since 1913, great advances in our knowledge
of the constitution of matter have been made. By electrical
methods, introduced and developed by Sir J. J. THOMSON
and F. W, ASTON of the University of Cambridge, the mass
of the positive nuclei, and therefore the mass of the atoms, 1 of
different elements has been determined ; and it has been
shown that if the atomic weight of oxygen be represented by
the number 16, the atomic weights of all other atoms are to
be represented by whole numbers, 2 e.g. the atomic weight of
helium by 4, of carbon by 12, of nitrogen by 14, etc. These
numbers are identical with the atomic weights as determined
by chemical methods. In the case of those elements, how-
ever, which yield fractional atomic weights when determined
chemically, Aston showed that the element, as it exists in
nature, is not simple, but consists of a mixture of different
atoms, the masses of which are represented by whole num-
bers. Thus the atomic weight of 'chlorine, determined by
chemical methods, is 35-46 (the atomic weight of oxygen
being 16). By the method of positive ray analysis, as it is
called, Aston showed that ordinary chlorine is a mixture of
atoms having atomic weights 35 and 37 respectively, mixed
together in the proportion of about 3 to i. The two varieties
of atoms are chemically indistinguishable and are called
1 The mass of the electrons may be neglected.
2 Slight divergences may be found, the explanation of which, however,
cannot be discussed here.
RADIOACTIVITY AND ATOMIC STRUCTURE 37
isotopes. The existence of isotopes, first realised in the case
of radioactive elements, will readily be understood when one
remembers that the atomic weight depends on the mass of
the nucleus, whereas the chemical properties of the element
depend on the number of planetary electrons or the number of
excess positive charges on the nucleus. By adding one proton
and one electron, or one neutron, to the nucleus of a given
atom, the mass of the atom will be increased by one, but the
positive charge on the nucleus, and therefore the chemical
properties, will remain unchanged. In the case of the two
isotopes of chlorine, the atomic number of which is 17, the
nucleus of one consists of 18 neutrons and 17 protons, while
the nucleus of the other consists of 20 neutrons and 17 pro-
tons. Most of the elements have been found to exist in isotopic
forms, the separation of which is generally very difficult.
In 1932, the very interesting and rather startling discovery
was made by Professor H. C. UREY and his fellow-workers
in America that ordinary hydrogen is a mixture of two
isotopes, the lighter having the atomic weight i and the
heavier the atomic weight 2, the nucleus, in this case, con-
sisting of one neutron and one proton. For the lighter
isotope the name hydrogen has been retained, and the heavier
isotope has been christened deuterium (symbol D). Whereas
the isotopes of the elements of higher atomic weight differ
only slightly from one another in their properties, deuterium
differs quite markedly from hydrogen, as, indeed, one might
expect from the fact that its atomic weight is twice that
of hydrogen. Deuterium is chemically less reactive than
hydrogen, and the compounds which it forms are less reactive
than the corresponding hydrogen compounds. " Heavy
water " or deuterium oxide, D 2 O, the analogue of the
hydrogen compound H 2 O, has a density (i-n) which is
ii per cent, greater than that of the hydrogen oxide, and
it cannot replace the hydrogen compound in the animal
organism. Tadpoles, for example, will die if placed in
" heavy water." Ordinary water is not pure hydrogen oxide,
38 CHEMISTRY IN THE SERVICE OF MAN
H 2 O, but contains deuterium oxide, D 2 O, to the extent of
about i part in 6500.
The fact that elements exist in different isotopic forms
is not only of great interest in connection with the theory
of atomic structure, but is becoming increasingly important
for certain branches of chemical and medical research,
because of the use of such isotopes as so-called tracer
elements. The isotopes of an element, although chemically
identical, can be distinguished by physical methods ; and
this is more especially the case when the isotopes are
radioactive. They are thereby labelled. If, therefore, a
foodstuff, for example, or a compound containing, say,
carbon, nitrogen or phosphorus, is prepared from a naturally
rare or artificially prepared isotope of the ordinary element
and is introduced into the body, the track of that compound
through the body can be followed. By this means it has
been shown, for example, that phosphorus introduced into
the body in a meal, finds its way into the bones within a
few hours.
Some of the isotopes are stable, but many radioactive
isotopes, with a comparatively short life, are now being
produced in considerable quantities not only by means of
the cyclotron (p. 42), but, more especially, in the apparatus
used for the production of atomic bombs (p. 44). These
radioactive isotopes, of which the most important are C 14,
S 35, P 32, 1 131, where the numerals are the atomic weights,
promise to be of great value not only as tracer elements but
also, it may be, for the treatment of disease. An artificially
prepared radioactive isotope of phosphorus, for example,
has been used in the treatment of leukaemia.
Planetary Electrons. As one passes from element to
element, we have seen, the number of planetary electrons
increases, at each step, by unity, and as their number increases,
the planetary electrons are regarded as grouping themselves
on the surface of concentric spheres or shells. Except in the
case of helium, which has only two planetary electrons, the
RADIOACTIVITY AND ATOMIC STRUCTURE 39
maximum degree of stability is reached when the number of
electrons in the outermost shell reaches eight, forming what
is known as an octet. When more planetary electrons are
added, as when one passes from neon to sodium, a new ring
of electrons begins to be formed. This is built up by the
successive addition of one electron until one comes to argon
with its outermost ring of eight electrons.
It may be noted that although the number of electrons in
the outermost orbit never exceeds eight, the number in the
inner orbits may rise to thirty-two. Thus, in the case of the
element radon, which belongs to the helium family (Fig. i,
p. 24) and has the atomic number 86, the numbers of electrons
in successive orbits, from the nucleus outwards, are 2, 8, 18,
32,18,8.
According to present views, it is the electrons of the outer-
most shell which are involved in chemical combination, and
chemical combination may be regarded as an expression of
the tendency of an atom to lose or gain electrons so as to
form the most stable system with an outermost shell of eight
electrons, such as exists in the case of the rare gases, except
helium. As these elements have the most stable outermost
shell of eight electrons, they show no tendency either to gain
or to lose electrons ; they are chemically inactive and have
zero valency. The sodium atom has one electron in the outer-
most shell, and it readily gives up this electron so as to
form a system having the arrangement of the nearest inert
gas, neon (see p. 24). Chlorine, on the other hand, which
has an outermost shell of seven electrons, readily takes up
one electron to complete the octet, thereby forming a system
which has the arrangement of the inert gas argon. Com-
bination between sodium and chlorine, therefore, readily
occurs by the transfer of one electron from the sodium atom
to the chlorine atom ; and since the sodium atom thereby
becomes positively charged and the chlorine atom negatively
charged, the two atoms are held together by electrostatic
attraction. Sodium and chlorine are said to be univalent
40 CHEMISTRY IN THE SERVICE OF MAN
elements. Similarly, calcium can give up and oxygen can
take up two electrons, and are therefore said to be bivalent.
Valency thus appears as a measure of the number of planetary
electrons which an atom has in its outermost shell in excess
of or in defect of eight.
In many cases, however, combination between atoms
depends not on the giving and receiving of electrons, but on
the SHARING of one or more pairs of electrons, so that each
atom has eight electrons in its outermost shell.
From the preceding discussion it will be evident how very
nearly the hypothesis of Prout agrees with the now generally
accepted views regarding the constitution of the atoms of
different elements. Although the atoms of the elements are
not to be regarded as built up of hydrogen atoms but rather
of hydrogen nuclei (protons) and electrons, the idea under-
lying the two views is essentially the same ; and as a result
of recent investigations and deductions one is beginning
to see more clearly something of the order and unity which
run through the whole series of diverse elements known to
the chemist. One is also getting glimpses of that evolu-
tionary process through which the material universe has
passed since the time of which Ovid speaks in his well-known
lines :
Ere earth and sea and covering heavens were known,
The face of nature, o'er the world, was one ;
And men have called it Chaos ; formless, rude,
The mass ; dead matter's weight, inert and crude ;
Where in mix'd heap of ill-compounded mould,
The jarring seeds of things confusedly roll'd.
By the investigations of the twentieth century the atomic
or discontinuous constitution of matter has been established
beyond any reasonable doubt ; and in the process our views
regarding the ultimate units of matter have undergone a
change. To quote the words of the eminent French physicist,
JEAN PERRIN : " Atoms are no longer eternal, indivisible
entities, setting a limit to the possible by their irreducible
simplicity ; inconceivably minute though they be, we are
RADIOACTIVITY AND ATOMIC STRUCTURE 4!
beginning to see in them a vast host of new worlds. . . .
Nature reveals the same wide grandeur in the atom and the
nebula, and each new aid to knowledge shows her vaster and
more diverse, more fruitful and more unexpected, and,
above all, unfathomably immense."
Transmutation of Elements. The knowledge which has
been gained regarding the constitution of matter, and more
especially the discovery of the phenomena of radioactivity,
place in a new light the question of the transmutation of the
elements, the achievement of which was one of the great aims
of the mediaeval alchemist.
Whether the elements such as we know them at the present
day represent the halting points in a process of disintegration
of more complex elements, or of integration from simpler
units of matter, they appear to consist, for the most part, of
stable atomic systems. In the radioactive elements, however,
we have atomic systems which pass spontaneously into a con-
dition of instability and undergo a process of disintegration
into simpler atomic structures. In this way, a transmutation,
not of lead to gold but of radium or of thorium to lead, may
be said to take place. This process of transmutation, how-
ever, is quite uncontrollable by man.
It was in 1919 that the first artificial transmutation of one
element into another, by the disintegration of atomic nuclei,
was effected by Lord RUTHERFORD. Atoms, as we have seen,
are very open-spaced structures, and when atoms of nitrogen
were bombarded by alpha particles, liberated, for example,
by the radioactive disintegration of radium, most of the
particles passed in a straight line through the open structure
of the atom. Some, however, of the particles, which are
projectiles of great kinetic energy, registered direct " hits "
against the nucleus of the nitrogen atoms, and, in fact,
penetrated into the nucleus of the nitrogen atoms. An un-
stable structure was thereby produced which immediately
broke up with the emission of a proton and the production
of a stable oxygen isotope of atomic \veight 17. A number
4-5 CHEMISTRY IN THE SERVICE OF MAN
of other light elements could be similarly " transmuted.'*
The important discovery was also made by Sir JAMES
CHADWICK, working in Rutherford's laboratory, that by the
bombardment of the element beryllium with alpha particles,
carbon was formed with the emission, not of protons, but of
swift, penetrating, uncharged particles, or neutrons. These
neutrons are very efficient agents for the disintegration
and transmutation of atoms, for, owing to the absence of an
electric charge, they are not repelled by the nucleus and so
can more readily enter into it. The unstable structure pro-
duced then breaks up into atoms of a different kind. Such
transmutations may, in fact, be actually taking place in
many naturally occurring minerals. Rapidly moving
protons and deuterons (positively charged nuclei of
deuterium), their motions greatly accelerated by a powerful
electric field, as in the apparatus known as a cyclotron,
have also been used for the purpose of bringing about
artificial transmutations, some of which may in the future
prove to be of much value. By the bombardment of atoms
of the elements with these different missiles alpha particles,
neutrons, protons, deuterons many transformations have
been effected, and even new radioactive elements have been
obtained which may some day be used as a substitute for
radium in radio-therapy. The experiments of the old
alchemists, based on vague and ill-defined speculation, ended
in failure ; the experiments of the new alchemists, founded
on definite and experimentally verified views, have ended
in a brilliant success. Lead, it is true, has not been changed
to gold, but something of much greater importance has been
achieved. The modern alchemists, who have pursued their
investigations with the sole purpose of increasing knowledge
and have thereby revealed to us the nature and structure of
the atom, have, by their discoveries, opened up visions of
great storehouses of energy which may be used to transform
the whole material life of man.
Sab-atomic Energy. The particles forming the nucleus of
RADIOACTIVITY AND ATOMIC STRUCTURE 43
an atom are held together by very powerful forces, and when
the nucleus undergoes radioactive transformation great stores
of energy are set free. Each disintegration of an atomic
nucleus is accompanied by a decrease of mass, which is
partially converted into energy ; x and so great is the energy
produced by the decrease of mass that one ounce of matter
transformed entirely into heat energy would, it has been
calculated, be sufficient to convert nearly a million tons of
water into steam. The energy liberated, therefore, in atomic
nuclear reactions is enormous compared with that set free
by a corresponding number of atoms in even the most
intense chemical reactions, in which only the outer shells
of planetary electrons are engaged. The radioactive trans-
formations, however, are uncontrollable by man.
The discovery that the atoms of matter are vast storehouses
of potential energy stirred the imagination and gave rise to
the belief that in the complex systems of particles constituting
the atoms of matter, there must exist inconceivably great,
untapped and formerly unsuspected reservoirs of energy,
compared with which the energy of combustion of all our
fuel reserves is quite trifling. If one could only gain control
of sub-atomic energy, or could control the process of atomic
disintegration so as to bring it about at will, then, it was
thought, untold stores of energy would be available to carry on
the work of the world when the reserves of coal should be ex-
hausted ; or which, in the hands of the evilly disposed, would
suffice to shatter the globe. Until 1939, however, neither the
former hope nor the latter fear appeared to be well founded.
Although the disintegration of atomic nuclei had been
effected by Lord Rutherford in 1919, only one out of many
thousands of the bombarding particles brought about dis-
integration of atomic nuclei. From each successful collision,
it is true, energy was gained, but the total energy used up in
1 It was shown by Einstein, as long ago as igo'5, that, according to the
theory of relativity, there is no essential difference between mass and
energy. The continual emission by the sun of energy in the form of
heat is considered to be due to a loss of mass.
44 CHEMISTRY IN THE SERVICE OF MAN
producing the bombarding particles was far greater than the
energy released from the relatively few successful collisions.
Moreover, unlike the chemical process of combustion, for
example, the atomic disintegrations were not self-propagating,
for the energy released by one nuclear disintegration did not
suffice to bring about the disintegration of the neighbouring
nuclei. There seemed to be little hope, therefore, that one
would be able to gain useful energy from the atoms by
artificial processes of atomic transformations.
Early in 1939, the outlook was entirely altered. In that
year it was discovered that when the atoms of uranium, and
especially the isotope of atomic weight 235, were bombarded
by neutrons, 1 the uranium nuclei do not disintegrate like
those previously studied, but undergo " fission/ 5 or split
into two parts of nearly equal mass. Not only was this
process accompanied by the liberation of a large amount of
energy, but other neutrons were also released which could
then bring about the fission of neighbouring uranium nuclei.
For the first time, as the result of investigations carried out
by physicists in a number of different countries, there
seemed to be an experimental basis for the hope that the store
of atomic energy might be usefully released ; for, once
the fission of uranium nuclei had been initiated in a few
atoms, the neutrons produced would bring about the fission
of other atoms. A chain process would thus be established
which would propagate itself throughout the mass of uranium
with great velocity and with the liberation of a large amount
of energy. The energy required to start the chain is very
small compared with the total energy liberated.
It has been found, moreover, that when the uranium
isotope, U 238, is bombarded by neutrons which have a
velocity (and therefore an energy) intermediate between that
required to bring about the fission of U 238 and U 235, a
new nucleus is produced with a mass number of 239. This
loses two electrons in successive steps and gives rise to the
1 Produced, for examplt^ by mixing beryllium with radium (p. 42).
RADIOACTIVITY AND ATOMIC STRUCTURE 45
two elements not found in nature, neptunium (atomic number
93) and plutonium (atomic number 94) ; and the latter
element, when bombarded by neutrons of low velocity,
also undergoes fission with release of neutrons. 1
Everyone is now aware how through the ability and
co-operative labours of a large number of scientists, drawn
from different allied countries, and the expenditure of
500,000,000, there was accomplished in 1945 what is
probably the greatest achievement of scientific genius of all
time, the liberation of the great stores of energy locked up
in the atoms of matter. That this achievement should have
to announce itself to the world through the bursting of an
atomic bomb over Hiroshima on 6th August 1945, creating
destruction equal to that produced by 20,000 tons of high
explosive, is one of the tragedies of our time and of our
civilisation. We may well bear in mind the words contained
in the statement issued by Mr. Winston Churchill : " This
revelation of the secrets of nature, long mercifully withheld
from man, should arouse the most solemn reflections in the
mind and conscience of every human being capable of
comprehension. We must indeed pray that these awful
agencies will be made to conduce to peace among the
nations, and that instead of wreaking measureless havoc
upon the entire globe, they may become a perennial fountain
of world prosperity."
With the bursting of the first atomic bomb, a new epoch
in the world's history and in the history of human civilisation
began ; and one can only speculate, vaguely, perhaps, but
hopefully, on the possibilities for good opened up for the
world, when the stores of sub-atomic energy are liberated,
not with world-shattering violence, but as a steadily flowing
stream controlled and directed for the use and benefit of
mankind.
1 Elements with atomic numbers 95 (Americium, Am) and 96 (Curium,
Cm) have also been produced artificially.
CHAPTER III
THE GASES OF THE ATMOSPHERE
THE composite nature of atmospheric air, which from earliest
times had been regarded as an element, was first demon-
strated, in 1674, by the English physician, JOHN MAYOW,
who showed that when a substance is burned in air enclosed
in a vessel standing over water, the volume of the air is
diminished, and that in the residual gas combustion will no
longer take place. Subsequent investigations, belonging in
some cases to comparatively recent times, have shown that
atmospheric air is a mixture of a number of different gases
in proportions which remain remarkably constant. The
gases normally present in air are : nitrogen, oxygen, carbon
dioxide, water vapour, and a group of gases, known as the
rare gases, the most abundant of which is argon. Besides
these normal constituents, other gases and also solid particles,
derived from local sources, may be present as impurities.
As the result of analysis it has been found that the average
composition of purified air, free from carbon dioxide and
water vapour, is as follows :
Per cent, by volume. Per cent, by weight.
Nitrogen . . 78-06 75-5
Oxygen . . 21-00 23-2
Rare gases. . 0-94 1-3
Nearly four-fifths of the air, by volume, therefore, consists
of nitrogen, and one-fifth of oxygen. Normally, there are
about three parts of carbon dioxide in ten thousand parts
of air by volume.
Nitrogen was first obtained, in 1772, by a botanist, DANIEL
RUTHERFORD, who burned phosphorus in a vessel con-
taining air, an.& exa emove d> as * s now known, the oxygen
46
THE GASES OF THE ATMOSPHERE 47
which is present. At the present day, very large quantities
of nitrogen are obtained industrially by the distillation of
liquid air, the production of which will be described later
(p. 58). Although it plays a very important role in the
economy of nature, nitrogen is a very inert or chemically
inactive element at the ordinary temperature, and supports
neither combustion nor life. It was first called azote.
The discovery of oxygen, in 1773-1774, we owe to CARL
WILHELM SCHEELE, a Swedish apothecary who was recog-
nised as one of the foremost chemists of the time, and to
JOSEPH PRIESTLEY, an English Unitarian Minister and
amateur of science, and one of the most versatile and in-
tellectually active men of the eighteenth century. Both these
investigators obtained oxygen by decomposing, by heat, red
oxide of mercury, a compound of mercury and oxygen, but
the gas is now best prepared on a small scale by heating a
mixture of potassium chlorate and manganese dioxide. On
an industrial scale, the gas is produced mainly by the dis-
tillation of liquid air, but a certain amount is also obtained by
a process of electrolysis which will be discussed in Chap. xn.
The most conspicuous property of oxygen is the readiness
with which it combines with other substances, as shown, for
example, in the vigour with which it supports combustion.
A merely glowing strip of wood bursts into flame when
introduced into oxygen, and phosphorus burns in the gas
with dazzling brightness. At the present time, oxygen finds
extensive application not only in medicine, in cases of diffi-
cult respiration, but also in industry for the production of
high temperatures by means of the oxy-hydrogen blowpipe
(p. no) and the oxy-acetylene blowpipe (p. 114).
Carbon dioxide, which is normally present in air only in
very small amounts, may escape in considerable quantity
through fissures in the earth in volcanic regions, as in the
Poison Valley of Java. It occurs also dissolved in many
mineral waters, from which it may escape with effervescence.
Artificial aerated waters are produced by dissolving carbon
48 CHEMISTRY IN THE SERVICE OF MAN
dioxide in water under pressure. The gas is one and a half
times as heavy as air.
Carbon dioxide is formed in large quantity in many
natural and industrial processes, as when coal burns and
when limestone or chalk is heated for the production of
quicklime. It is also formed abundantly in the process of
fermentation for the production of alcohol, and also when
an acid is brought in contact with chalk, soda, or other
carbonate. Owing to the fact that carbon dioxide does not
support combustion, it is used to extinguish fires. Some
portable fire-extinguishers are filled with a solution of
sodium bicarbonate and contain also a quantity of acid in a
glass tube which can be broken by means of a plunger. By
the action of the acid on the bicarbonate of soda, carbon
dioxide is formed and partly dissolves in the water. On open-
ing the nozzle, the solution of carbon dioxide is ejected by the
pressure of the gas. The effectiveness of the arrangement
can be increased, as in the Foamite Firefoam apparatus, by
adding to the liquid in the extinguisher, glue, liquorice or
some other material which is capable of forming a foam or
froth. When the mixture is ejected from the apparatus, a
stiff foam, containing carbon dioxide, is produced, which
effectively " blankets " or smothers the fire. In the " Fire-
foam " apparatus the carbon dioxide is produced, not by
the action of an acid, but by the action of a solution of
aluminium sulphate on sodium bicarbonate.
When carbon dioxide is passed into lime water (a solution
of slaked lime or calcium hydroxide in water), a turbidity
is produced owing to the fact that the gas reacts with the
calcium hydroxide and forms insoluble calcium carbonate.
This is clearly represented by the chemical equation :
Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O
Calcium Carbon Calcium Water
hydroxide. dioxide. carbonate.
This reaction is used as a test for carbon dioxide.
Courtesy of Aberdeen Journals, Ltd.
Extinguishing an Oil-fire by means of Foamite Firefoam.
50 CHEMISTRY IN THE SERVICE OF MAN
Carbon dioxide can be liquefied, and the liquid is placed
on the market in steel cylinders. On allowing the liquid to
be discharged through the nozzle of the cylinder into a cloth
bag, rapid evaporation of the liquid takes place and the
temperature is thereby lowered to such an extent that the
liquid freezes to a snow-like solid. This solid passes into
gas without melting and gives a temperature of 79 C.
(110-2 F.). 1 It is therefore largely used as a refrigerant in
the manufacture, for example, of ice cream. Owing to the
fact that the solid carbon dioxide is surrounded by a layer of
gas, the solid may, notwithstanding its very low temperature,
be lightly placed in contact with the skin without any harm
resulting. If, however, the carbon dioxide snow is pressed
against the skin, painful " burns " will be produced and the
skin destroyed. Carbon dioxide snow is also used, instead
of ice, in railway refrigerator cars, blocks of compressed
solid carbon dioxide being placed on the floor of the car.
The cold heavy gas, which is formed by sublimation, gradu-
ally rises, filling the whole car and overflowing through vents
at the top. This carbon dioxide snow "drikold " or " dry
ice " as it is sometimes called is found to be as effective as
more than ten times its weight of ordinary ice. Cartons of
ice cream are also frequently packed in small quantities of
carbon dioxide snow and the cream can thus be kept frozen
for considerable periods of time.
Since oxygen is being removed from and carbon dioxide is
continually being poured into the air owing to the respiration
of animals, the combustion of coal and other fuels, processes
of fermentation and other industrial operations, the question
arises : How does Nature achieve the degree of constancy
1 In scientific work, temperature is always measured on the Centigrade
scale. On this scale, the melting-point of ice is represented by o, and
the boiling point of water by 100. On the Fahrenheit scale, the corre-
sponding temperatures are 32 and 212. For the conversion of tem-
perature on the Centigrade scale to temperature on the Fahrenheit scale,
one can make use of the formula :
THE GASES OF THE ATMOSPHERE 51
in the composition of the air which is so remarkable ? Large
quantities of carbon dioxide are, in the first place, removed
from the air by solution in rain and in the water of the rivers
and oceans. Further, as was shown by de Saussure early in
the nineteenth century, the green leaves of plants take up
carbon dioxide and water vapour from the air, and, through
the radiant energy of sunlight and in presence of the chloro-
phyll or green colouring matter in the leaves, these sub-
stances are used to build up, step by step, various complex
compounds, such as sugar, starch and cellulose. During this
process, moreover, there is set free and given up to the air
a quantity of oxygen equal in volume to the carbon dioxide
removed. The green vegetation on the earth's surface,
therefore, plays a very important part in maintaining the
constancy of composition of the air.
The Rare Gases of the atmosphere, under which name are
included helium, neon, argon, krypton and xenon, form a
group of related elements, the discovery of which is one of
the most romantic episodes in the history of chemistry.
In 1785, the Hon. HENRY CAVENDISH, a man noted for his
great ability no less than for his extreme shyness and hatred
of publicity, described before the Royal Society in London
experiments which are at the very root of the discovery of
the rare gases. Cavendish showed that when electric sparks
are passed through air, combination of nitrogen and oxygen
takes place ; and if a solution of potash is present in the
vessel of air, nitre or saltpetre is formed. By adding further
quantities of oxygen and continuing to pass the sparks, the
nitrogen could be removed, and any excess of oxygen could
be absorbed by a solution of liver of sulphur (potassium
sulphide). As a result of his experiments, however, Cavendish
found that no matter how long the passage of electric sparks
was continued, there always remained a small bubble of gas,
equal to about I per cent, of the r which did not
combine with the oxygen. Littl that in that
bubble of gas five hitherto unknow * contained,
52 CHEMISTRY IN THE SERVICE OF MAN
chemists assumed that the gas was only nitrogen ; and for
over a hundred years the importance of Cavendish's experi-
ment was overlooked, and the little bubble of gas, so big
with scientific interest, was ignored. Until 1893, therefore,
chemists everywhere believed that dry air, freed from inci-
dental impurities, consists solely of oxygen (21*0 per cent.),
and nitrogen (79-0 per cent.), together with a minute amount
of carbon dioxide (about 3 parts in 10,000 of air) ; and so
confident were chemists that they knew all about the com-
position of the atmosphere that the announcement of the
discovery of a new element in the air, made by the late Lord
RAYLEIGH and Sir WILLIAM RAMSAY at the Oxford meeting
of the British Association in 1894, was received with in-
credulity. The story of that discovery is the story of skilful
and accurate experiment, and of clear and logical reasoning.
The late Lord Rayleigh, Cavendish Professor of Physics in
the University of Cambridge, while engaged in the accurate
investigation of the density of different gases, found that
" atmospheric nitrogen/' or the gas left after removal of the
oxygen from the air, had a somewhat greater density than
nitrogen obtained from one of its compounds. The difference
was not great, being only about i part in 230, but it was
much greater than the possible errors of the determination.
Lord Rayleigh announced his results early in 1893, and
invited the help of chemists in explaining the discrepancy.
With the permission of Lord Rayleigh, the late Sir William
Ramsay 1 joined in the investigation and, making use of the
fact that magnesium combines with nitrogen to form a
nitride, Ramsay passed " atmospheric nitrogen " repeatedly
over a red-hot mixture of magnesium and quicklime, and
obtained a small quantity of residual gas which did not
combine with the metal. Lord Rayleigh, also, repeated the
experiment of Cavendish, but on a much larger scale, and
1 Perhaps the m r V ;r ' of British chemists since the time of Sir
Humphry Davy.' 'asgow in 1852, he became Professor of
Chemistry at Ur" , London (1887-1912) and was awarded
the Nobel Prizei 1904. He died in 1916.
THE GASES OF THE ATMOSPHERE 53
instead of a small bubble he obtained no less than two litres x
of gas which did not combine with oxygen. The density of
the residual gas obtained by Ramsay and by Lord Rayleigh
was found to be about 20, compared with the value of 14 for
nitrogen. The gas was subjected to chemical and physical
treatment of every imaginable kind, but it underwent no
change ; and attempts to cause it to combine with other
substances were entirely unsuccessful. It was a quite in-
active and inert element, the first such element to be dis-
covered, and it received, in consequence, the name argon
(Greek a=not, ergon=work). Since atoms of argon can
exist in the free state, the molecule of argon is the same as
the atom. Argon is said to be monatomic.
Argon, which forms rather less than one per cent, of air by
volume and which was, at first, of purely scientific interest,
is now obtained commercially in large quantities from
liquid air, and finds an important industrial application in
filling incandescent electric lamps of the " half- watt "
type. Owing to the presence of the gas, the tungsten filament
of the lamp can be heated to a much higher temperature, and
a brighter light can therefore be obtained, without dispersion
of the metal and blackening of the bulb taking place.
When an electric discharge is passed through a mixture
of argon and mercury vapour contained, under reduced
pressure, in a glass tube, a bright blue light is emitted. This
fact is made use of for the production of illuminated signs.
For the identification of the rare gases, all of which are
chemically quite inert, use is made of the spectroscope.
When white light from an incandescent solid body is allowed
to pass through a prism, it is found that the light is drawn
out into a rainbow band of colour, known as a spectrum. In
the case of the light emitted by an incandescent gas, how-
ever, the spectrum consists not of a continuous band of
colour, but of isolated lines of colour, each line occupying a
certain definite position and corresponding with light of a
1 A litre or 1000 cubic centimetres (c.c.) is equal to 1*76 imperial pints.
54 CHEMISTRY IN THE SERVICE OF MAN
certain definite wave-length. Since each gas gives its own
characteristic spectrum or arrangement of lines, it is easy,
by determining the position of the lines, with the aid of a
spectroscope, to identify a gas.
In 1868, the French astronomer, Professor JANSSEN, and
the English astronomer, Sir NORMAN LOCKYER, while
examining the spectrum of the sun's photosphere during an
eclipse, observed a yellow line which they could not find in
the spectrum of any known terrestrial substance. Lockyer,
therefore, concluded that it must be due to some extra-
terrestrial element to which he gave the name of helium
(from helios, the Greek word for sun). The element remained
unknown on the earth until the year 1895, the year after the
discovery of argon, when it was isolated by RAMSAY from the
uranium-containing mineral, cleveite. That a gas was given
off by this mineral on treatment with acid was already
known, but the gas was thought to be nitrogen. On examin-
ing the spectrum of the gas, however, Ramsay at once saw
that the gas was neither nitrogen nor argon ; and examination
of the spectrum of the gas by Sir WILLIAM CROOKES showed
that the gas was none other than the helium of Lockyer and
Janssen.
Investigation of this new gas showed that it is an element
with the atomic weight 4/00, and that, like argon, it is
chemically inert and incapable of forming any compounds.
As in the case of argon, also, the molecule consists of only
one atom. It is the most difficult of all gases to liquefy, and
it boils, under atmospheric pressure, at a temperature of
-2687* C. (-5157 F.).
Helium is now known as a disintegration product of
radioactive substances, and it is consequently found in most
radioactive minerals. It has also been found in certain
naturally occurring waters, e.g. in the mineral springs of
Bath, and it occurs in air to the extent of about i part in
200,000 by volume. The main source from which it is
obtained is the natural gas which escapes from the earth in
55
certain parts of the world, more especially in the State of
Texas, in North America, where many millions of cubic feet
of helium are produced annually.
The natural gas, which comes to the separation building
under a pressure of 650 Ibs. per square inch, is cooled and
allowed to expand. The lowering of temperature which is
thereby produced serves to liquefy most of the natural
gas, whereas the helium is collected in the gaseous form.
The liquid is again allowed to pass into gas and the cold
gas so obtained serves to cool down the incoming gas. The
natural gas, freed from helium, is used for heating and
illuminating purposes.
Helium is used for filling balloons, and for this purpose
it possesses the great advantage over hydrogen of not being
inflammable. Although the density of helium is twice that
of hydrogen, its lifting power is not much less, because the
lifting power depends only on the "difference between the
density of the air and that of the gas. Taking the densities
of hydrogen, helium and air as i, 2 and 14-4 respectively,
the lifting power of hydrogen and of helium will be as
13*4 is to 12*4. That is to say, the lifting power of helium
is 92*5 per cent, of the lifting power of hydrogen.
Helium also finds use in the treatment of respiratory
diseases and for the production of artificial breathing atmo-
spheres for caisson workers and divers working at great
depths. If, in these cases, divers are supplied with ordinary
air, nitrogen dissolves in considerable quantities in the blood
under the existing high pressure ; and if the diver were
brought rapidly to the surface, the dissolved nitrogen would
pass out of solution and cause death by a blocking of the
blood vessels with gas. To avoid this, a long period of
gradual decompression is necessary. If, however, the diver
is supplied with a mixture of oxygen and helium, the period
of decompression can be very greatly reduced, as the solu-
bility of helium is much less than that of nitrogen.
Under the influence of an electric discharge, the gas emits
5 CHEMISTRY IN THE SERVICE OF MAN
a pale yellow light, and is used in the construction of illu-
minated signs.
Owing to the discovery of the monatomic elements, argon
NEON LIGHTHOUSE.
[From The Approach towards a System of Imperial Air Communications ,
by permission of the Controller of H.M. Stationery Office.]
and helium, which are chemically inert and may therefore
be regarded as having zero valency, a new family of elements
had to be inserted in the periodic classification. Since,
moreover, helium preceded the metallic element lithium,
THE GASES OF THE ATMOSPHERE 57
and argon the element potassium, it seemed probable that
other similar elements should exist which would take their
places in front of the elements sodium, rubidium, and
caesium (Fig. i, p, 24). In 1896, therefore, a systematic
search for the missing elements was commenced by Sir
WILLIAM RAMSAY and Dr. MORRIS W. TRAVERS, and was
pursued with such energy and ability that in a short time
three new elements were obtained from the air, namely, neon,
krypton and xenon. The identity of these gases was estab-
lished by means of the characteristic spectra which they
give ; and the determination of their atomic weights showed
that they were the elements sought for. In the space of a
few years, therefore, no fewer than five new elements,
present in the air, were discovered ; and the series of the
rare gases was completed some years later by the discovery
of radon, the radioactive gas or " emanation " given off by
radium.
Besides helium and argon, neon, which occurs in the air
to the extent of only fifteen parts per million, has already
found practical application for filling " Osglim " lamps
(night lights and emergency lights), and neon tubes, used
for testing the sparking plugs of motor cars and in the
construction of illuminated signs. Under the influence of
the electric discharge, the gas glows with a brilliant rose
colour.
I Since the light emitted by neon lamps has a great power
[of penetrating mist and fog, such lamps are also used for
'lighthouses at air-ports.
Krypton and xenon, also, are now being used in place of
argon for filling electric lamp bulbs. Such lamps are said to
be one-third more efficient than those containing argon.
Krypton occurs to the extent of one part per million, and
xenon to the extent of one part per eleven million parts of air.
In modern times, owing to the great development of the
nitrogen industries, more especially the synthetic production
58 CHEMISTRY IN THE SERVICE OF MAN
of ammonia (p. 207), a cheap source of nitrogen, as well as of
hydrogen, has become essential. As we shall learn in the
sequel, various sources of industrial hydrogen are now
available.
For the purpose of obtaining nitrogen, the method which
is most frequently employed in industry is the distillation of
liquid air. Liquid air, of course, consists of a mixture of
liquid nitrogen (together with argon, etc.) and liquid oxygen,
which boil at 196 and 183* C. (319 and 296-5 F.)
respectively. Just as the different hydrocarbons in crude
petroleum can, as will be pointed out later, be separated by
fractional distillation, so also, in the case of liquid air, one
can separate the nitrogen from the oxygen. As nitrogen
boils at a lower temperature than oxygen, it distils off first,
and can, by suitable arrangements, be obtained free from
oxygen.
The production of liquid air is now a very simple matter,
and has developed into an industry of enormous propor-
tions, many millions of gallons of liquid air being produced
daily in the different factories of the world. 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 tem-
perature is lowered on expansion is all the greater the lower
the temperature of the compressed gas previous to the
expansion.
The industrial application of this principle is due mainly
to a German and to an English engineer, von Linde and
W. Hampson, and their process will be understood from
Fig. 3. Air under a pressure of about 150 atmospheres, and
free from moisture and carbon dioxide, enters the apparatus
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
FIG. 3. 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, pressure gauge to indicate pressure at which the
air enters the apparatus ; P, valve closing tube R, through which the
liquid air is withdrawn ; T, wheel for opening the valve R.
60 CHEMISTRY IN THE SERVICE OF MAN
temperature is thereby produced. The cool air now passes
upwards over the coils of copper tubing, and so cools down
the compressed air which is passing through them 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 G, from which it can be drawn off from time to
time through the tube R.
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 know-
ledge. By means of liquid air, one is enabled to
extend the scope of scientific investigation to
temperatures which otherwise would be in-
accessible ; and the increase of knowledge which
has accrued therefrom is of the highest scientific
interest and practical value. The utilisation of
this new aid to scientific research was greatly
facilitated by the introduction of the well-known
FlG Dewar " vacuum vessels." These " vacuum
DEWAR vessels," which are now so familiar under the
name of " thermos " flasks, consist of double-
walled glass vessels (Fig. 4), the air being re-
moved 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 Fahrenheit colder than
the surrounding 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.
The efficiency of the vacuum vessel may be considerably
increased by silvering the inner walls of the vessel. By this
means the passage of radiant heat can to a great extent be
prevented.
CHAPTER IV
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 will doubtless always remain
unknown. It may, perhaps, have had its origin in some
lightning flash, or in the sparks struck from the flints of
primitive man ; or it may have been produced by the self-
heating of combustible material, or by the rubbing together of
dried wood ; or it may be that, as in the Song of Hiawatha :
Gitche Manito, the mighty,
Breathed upon the neighbouring forest,
Made its great boughs chafe together,
Till in flame they burst and kindled.
But in whatever way fire was first produced, its importance
and value were early recognised, as one 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 well as from the later belief of the
followers of Zoroaster, that fire is the special abode of divinity.
And even in modern times, although the feeling of rever-
ence or of awe is no longer inspired by a process which can
be explained in terms of chemical action, and can be pro-
duced at will by the striking of a match, one is not likely to
underrate the importance of combustion when it is re-
membered that our present-day civilisation in all its manifold
forms of expression, in manufactures, in railway and steam-
ship transport, in artificial illumination, etc., is based on a
process of combustion.
61
62 CHEMISTRY IN THE SERVICE OF MAN
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 j 1 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 there-
fore regarded as being almost pure phlogiston. This was the
explanation of combustion given, more especially, by the
German chemist, STAHL, towards the end of the seventeenth
century ; and it was not till a hundred years later that the
" phlogiston theory " was finally overthrown by LAVOISIER, 2
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 combustible
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 one may be inclined to smile at such an explana-
tion, one ought to remember that the phlogiston theory
served usefully its day and generation, and satisfied even the
modern requirements of a theory, in that it gave an explana-
tion of combustion which satisfied men's minds at the time,
1 The word is derived from the Greek verb, phlogizein, meaning to
burn.
2 Antoine Laurent Lavoisier, the most brilliant of the French chemists
of the eighteenth century, was born in Paris in 1743, and made many
contributions of the greatest importance to chemistry. He became a
member of the Ferme G6n6rale t was denounced by Marat as acting
contrary to the commonweal, and was beheaded on 8th May 1794.
COMBUSTION AND THE PRODUCTION OF FIRE 63
and also inspired a large amount of fruitful investigation.
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 phlogiston
theory, however, long outlived its usefulness, and the
ANTOINE LAURENT LAVOISIER.
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
64 CHEMISTRY IN THE SERVICE OF MAN
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. "
The irresistible force of facts, however, 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.
It was known that air consists of two parts or constituents,
an " active " part which enables a substance to burn and an
" inactive " part (azote or nitrogen), in which combustion
does not take place. During a visit to Paris in 1774, Priestley,
while dining one day with Lavoisier, mentioned his discovery
of a gas, now known as oxygen (p. 47), in which a candle
burned much better than in common air. Lavoisier at once
conceived the idea that this new gas represents the portion
of the air which combines with a metal and gives rise to the
calx ; and the explanation of combustion was thus to be
found in the chemical combination of the burning substance
with the oxygen of the air. The correctness of this idea
was proved by quantitative experiment and the actual
weighing of the substances. 1
The calx of mercury (now known as oxide of mercury)
was first produced by heating a weighed amount of mercury
in a retort which communicated with a known volume of
1 It may, perhaps, 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 funda-
mental law of physical science, the law of the conservation of matter or
conservation of mass, 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 THE PRODUCTION OF FIRE 65
air contained in a bell-jar standing over mercury (Fig. 5).
The mercury in the retort was heated on a charcoal furnace
for twelve days at a temperature just below its boiling-point.
At the end of this time a quantity of the red calx of mercury,
45 grains in all, had formed on the surface of the metal, and
the volume of the air in the bell-jar had diminished by 7-8
cubic inches. The residual gas in the bell-jar did not sup-
port life or combustion.
FIG. 5. LAVOISIER'S EXPERIMENT OF HEATING MERCURY IN AIR.
The red calx of mercury was then heated to a higher
temperature, and Lavoisier found that from 45 grains of the
calx, 41 grains of metallic mercury were formed and 7-8
cubic inches of a gas (oxygen) were evolved.
It was thus shown by Lavoisier that when a metal or other
substance is burned in air, the oxygen of the air combines
with the metal or burning substance. In other words, the
process of combustion is a chemical reaction between the burning
substance and the oxygen of the air, the process being accom-
panied by emission of heat and, it may be, light. A flame,
however, 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.
66 CHEMISTRY IN THE SERVICE OF MAN
Since combustion in air is due to a chemical reaction
between the burning material and oxygen, a process which is
known as oxidation, the vigour of combustion can be increased
by increasing the rate at which oxygen is supplied to the
burning material ; and this is what one does when one
blows a fire with a bellows. Conversely, combustion can
be stopped by preventing access of oxygen to the burn-
ing material, as happens when one uses, for example, the
Foamite fire extinguisher (p. 48). Similarly, the Pyrene
fire extinguisher, largely used on motor cars, is filled with a
liquid, carbon tetrachloride, which when squirted on burning
material forms a heavy vapour. This vapour effectually
" blankets " the fire and prevents access of atmospheric
oxygen to the burning material.
If, however, the explanation of combustion which has just
been given is correct, the question arises : Why does a com-
bustible material not take fire when it is exposed to the air ?
Coal gas, for example, may be allowed to escape from the
burner, or a candle or piece of wood or coal may be left
exposed to 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. Combustion then goes on of itself. The
explanation of this fact is that the velocity or vigour of every
chemical change is increased by raising 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, and the temperature rises
progressively. When this reaches a certain point, the
COMBUSTION AND THE PRODUCTION OF FIRE 67
ignition-point, the reaction takes place with such rapidity
that the heat which is produced 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 ignition-
point, and so the combustion ceases. A simple experiment
which can be carried out by anyone will serve to demonstrate
FIG. 6. EXTINCTION OF FLAME BY WIRE GAUZE.
this important truth. If a piece of metal wire gauze is held
at a distance of half an inch or an inch above a burner from
which coal gas is issuing, and if a light is then applied to
the gas above the gauze, it will be found that the flame of
burning gas is arrested by the gauze and does not pass
through to the burner (Fig. 6) ; 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
the gauze has become quite hot does the gas below the gauze
become ignited. Similarly, 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
68
CHEMISTRY IN THE SERVICE OF MAN
lamp has undergone a striking change and marked improve-
ment since the time of its first invention, and the modern
safety lamp (Fig. 7) shows little sign of the means whereby
safety is secured. On careful examination, however, it is
seen that all the holes through which air can pass to the
flame, or the hot air and products of combustion can pass
out, are protected by fine wire gauze. Although, therefore,
A B
FIG. 7. 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,
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 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 temperatures
COMBUSTION AND THE PRODUCTION OF FIRE 69
below the ignition-point. Thus, when metallic iron is ex-
posed to moist air, it rusts. This rust is oxide of iron, a com-
pound of iron and oxygen ; and the process of rusting is
therefore a process of oxidation, a process of 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. The rusting of iron is said to be a process of
slow combustion, because the temperature does not rise to the
point of incandescence. Slow combustion can be demon-
strated more strikingly with the metal aluminium, which
combines with oxygen more vigorously than iron does. 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 protects the metal from further attack,
and therefore no change is apparent. By coating the surface
of the metal with mercury, however, a liquid amalgam or
alloy of mercury and aluminium is produced, and the for-
mation of a coherent film of aluminium oxide is thereby
prevented. The aluminium is consequently no longer pro-
tected from the continued action of the oxygen of the air.
In this case it is observed that the aluminium undergoes
oxidation quite rapidly, the oxide forming a moss-like
growth on the surface of the metal. The heat which is
produced by the oxidation, although quite marked, is dis-
sipated so quickly that the temperature does not rise to the
point of incandescence, 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 blood vessels,
70 CHEMISTRY IN THE SERVICE OF MAN
and combines with the haemoglobin present in the red blood
corpuscles. On the other hand, carbon dioxide passes from
the venous blood into the air-spaces of the lungs and is
expelled in the expired air. The oxygen, in the form of oxy-
haemoglobin, 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. Oxygen, then, is necessary for respiration
as well as for combustion in air, and, although prolonged
inhalation of pure oxygen would be harmful by producing
too rapid oxidation in the body, the gas is frequently ad-
ministered in cases of difficult breathing due to pneumonia
or other diseases of the lungs.
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 car-
bonate of lime, formed by the combination of carbon dioxide
with the slaked lime (p. 48).
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 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 combination
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, or chemical combination, increases. More and
more heat, therefore, is produced in a given time, the tem-
perature rises more and more rapidly until, finally, it reaches
the ignition-point of the combustible material. The slow
COMBUSTION AND THE PRODUCTION OF FIRE Jl
combustion passes into rapid combustion, and the com-
bustible material takes fire without the application of ex-
ternal heat ; in other words, it undergoes spontaneous com-
bustion. 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 readiness 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 disul-
phide, and if the solution is then poured on a sheet of filter
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 incan-
descent and emits light ; and such a process may occur
even when no air or oxygen is present. Thus, for example,
the gas hydrogen will burn not only in air, 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
72 CHEMISTRY IN THE SERVICE OF MAN
present in the gaseous form, but may be yielded up by
some compound containing it. Various well-known sub-
stances, such as chlorate of potash (potassium chlorate),
KC10 3 , and saltpetre (potassium nitrate), KNO 3 , can act
as suppliers of oxygen in this way, and the use of such sub-
stances for promoting combustion has long been known.
Touchpaper, for example, the slow-burning paper which is
so familiar in connection with fireworks, is prepared by
soaking paper in a solution of saltpetre 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 will be discussed at a later point, saltpetre is similarly
made use of as a reservoir of oxygen.
The process of combustion by means of combined oxygen
has also been turned to very good account for the pro-
duction of high temperatures and for the purpose of
obtaining certain metals from their oxides. The metal
aluminium, we have seen, reacts energetically with oxygen,
and it combines with great vigour not only with gaseous
oxygen but also with the oxygen contained in compounds.
If, then, oxide of iron is mixed with powdered aluminium
and the mass strongly heated at one point by means of a
special ignition mixture, the aluminium combines with the
oxygen of the iron oxide ; and so much heat is thereby
generated that a temperature of nearly 3000 C. (about
5400 F.) is produced. This reaction forms the basis of the
so-called thermit process, a process which has become
familiar through its application to the welding of tramway
rails and to the repair, in situ, of broken castings, shafting, etc.
The mixture of iron oxide and aluminium is ignited and the
molten iron which is produced in the process and raised
to a high temperature by the vigour of the reaction is run
into a mould formed round the ends of the rails or fractured
COMBUSTION AND THE PRODUCTION OF FIRE 73
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
of aluminium has led to the use of thermit mixture in
incendiary bombs designed to be dropped from aeroplanes or
airships, the bombs being furnished with a special mechanism
by means of which the mixture can be ignited automatically.
The intense heat produced by the oxidation of aluminium
has also been made use of in certain high explosives used
for military purposes. The best known of these is ammonal,
which consists of a mixture of aluminium powder with
ammonium nitrate and trinitrotoluene (or T.N.T.). When
this mixture explodes, the aluminium is oxidised by the
ammonium nitrate, and the temperature of the explosion is
thereby greatly raised (see also p. 135).
In order to bring about combustion, 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 modern 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 nineteenth
century that practical suggestions were made for the em-
ployment of such means of producing fire. One of the
earliest of these suggestions which had a certain measure of
success was made, about i&io, by a Frenchman named
CHANCEL, who tipped strips of wood with a mixture of
potassium chlorate and sugar, bound together by means of
74 CHEMISTRY IN THE SERVICE OF MAN
gum. When this composition was dipped into concentrated
sulphuric acid (oil of vitriol), the sugar took fire and burned
at the expense 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 the beginning of 1827, J H N
WALKER, an English apothecary, invented 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 " friction lights," and later 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 by heating to a high temperature in an electric furnace
a mixture of calcium phosphate, silica (sand), and coke.
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 near the end
of the nineteenth century. 1 The tips of these matches con-
sisted, 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. 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 found the price
1 Even as early as 1786, an Italian had brought out in Paris " le briquet
phosphorique," which consisted of a bottle coated internally with phos-
phorus, and matches tipped with sulphur. When one of the matches was
rubbed against the inside of the bottle so as to remove a little of the
phosphorus, and was then brought into the air, the phosphorus took fire.
Such a match was used by Faraday as late as 1827.
COMBUSTION AND THE PRODUCTION OF FIRE 75
too heavy. The accidental fires due to the ready inflam-
mability of the phosphorus, and the general danger of its
unrestricted use ; the number of deaths, accidental or in-
tentional, produced by phosphorus poisoning ; and the
terrible disease, known as " phossy 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 l
has, in all civilised countries, been forbidden by law.
The element phosphorus, however, occurs not only in
the readily inflammable and poisonous white variety, but
also in a totally distinct form, that of a dark red powder
known as red phosphorus. Such physically distinct forms of
an element are frequently spoken of as allotropic modifica-
tions.
Since red phosphorus, which is produced by heating white
phosphorus in closed vessels to a temperature of about
240 C. (464 F.), is much less readily inflammable than
white phosphorus and is also non-poisonous, attempts were
made to utilise it for the manufacture of matches. Diffi-
culties were at first encountered, but these were overcome
by a German chemist about the middle of last century ; and
his invention, first taken up in Sweden, led to the introduc-
tion 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 composition 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 dichromate ; and
sulphur and charcoal 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
1 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 in colour owing to its conversion into the so-called red phos-
phorus.
76 CHEMISTRY IN THE SERVICE OF MAN
of antimony and powdered glass. Moreover, in order to
diminish the risk of accidental fire through the glowing
wood of a used match, safety matches are soaked in a solu-
tion of alum, sodium phosphate, ammonium phosphate, or
some other salt. The charred wood of the match is thereby
Courtesy of Bryant & May Ltd.
MACHINE FOR MAKING MATCHES.
The splints of wood, fixed in holes in an endless metal band, are
carried through a bath of melted paraffin to impregnate the wood, and
then over the surface of the match composition contained in a trough
on the left. As the band travels on, the matches are given time to dry
before being pushed out of the holes in the band.
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
COMBUSTION AND THE PRODUCTION OF FIRE 77
old phosphorus match, of striking on any rough surface. In
the case of this " strike anywhere " match, the tipping com-
position 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 inflamma-
tion 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 Continental
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 sandalwood, is
added. This head is then tipped with a striking mixture
such as has already been described.
The making of matches, once a " dangerous occupation/*
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 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.
Although the ordinary match forms by far the most
usual means of obtaining fire and light, one must not fail
to mention the now familiar " petrol 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 the vapour of petrol, or similar volatile
liquid, the latter takes fire and a flame is obtained. In this
apparatus we have, in a refined form, the flint and steel
of olden days .
78 CHEMISTRY IN THE SERVICE OF MAN
Ceria, or oxide of cerium, is now produced in large
quantity as a by-product of the manufacture of incan-
descent gas-mantles (p. in), and is derived mainly from
monazite sand, valuable deposits of which are found in
Brazil and also in Travancore, India. It was while investi-
gating 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.
The pyrophoric cerium-iron alloy has also found use in
tracer shells and tracer bullets. The friction of the air, as
the shell or bullet speeds on its way, causes a small piece of
the alloy, attached to the shell or bullet, to take fire and so
trace out the path of flight.
CHAPTER V
FUELS AND ILLUMINANTS
SOLID FUELS
UNTIL comparatively recent times, down, say, to the seven-
teenth 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 un-
questioned 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 con-
verted, under the influence of high temperature and pressure,
into more highly carbonised compounds, the proportion of
hydrogen and oxygen becoming diminished owing to the forma-
tion of gaseous substances such as carbon dioxide and marsh
gas. From the figures given in the following table, one can
Carbon. Hydrogen. Oxygen Calorific value
B.Th U. per Ib.
Cellulose (C 6 H 10 O 5 ) . 44-5 6-2 49-3 7, 500
Wood (dry) . . 50*0 6*0 44-0 8,600
Peat (Irish) . . 60-0 5*9 34-1 9,900
Lignite . . . 67-0 5-2 27-8 11,700
Bituminous coal . 88-4 5*6 6-0 14,950
Welsh steam coal . 92-5 4-7 2-7 \
Anthracite . . . 94-1 3*4 2'5J
recognise the gradual carbonisation of cellulose, the materials
peat, lignite or brown coal, bituminous coal and anthracite
representing progressive stages in the natural process. 1
1 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
approximate values representing, as it were, the composition and calorific
79
80 CHEMISTRY IN THE SERVICE OF MAN
The process of carbonisation is accompanied by a diminu-
tion 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 ad-
vanced stage in the natural process of carbonisation of woody
fibre, is ignited only with difficulty, and burns with a very
small and not strongly luminous flame.
It is not, however, the cheerfulness with which the fuel
burns that concerns us here, but the all-important question
of how much heat is given out in the process of combustion.
It is the " calorific value " of the fuel that claims our atten-
tion just now.
When one examines the different solid fuels from this
point of view, it is found, as the figures in the last column
of the table on p. 79 show, that with the progressive car-
bonisation, the heat-producing power of the fuel increases,
so that among all the solid fuels, anthracite stands pre-
eminent. A British thermal unit x 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 dry wood will give out, on burning,
about 8,600 units, 2 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. On this fact depends
the great value of anthracite as a fuel.
Although wood is still used to some extent as a fuel, more
value of an average member of the different classes. Moreover, other
substances, more especially compounds of nitrogen and sulphur, are
present, besides carbon, hydrogen and oxygen ; but although, under certain
conditions, these substances may give rise to important and sometimes
undesirable by-products, their influence on the fuel-value of the combus-
tible materials is very small.
1 Heat energy is very frequently measured also in calories, a calorie
being the amount of heat required to raise i gram of water through i C.
A British thermal unit is equal to 252 calories.
1 Under ordinary conditions the calorific value is considerably less
than this owing to the presence of 15-20 per cent, of moisture.
FUELS AND ILLUMlNANtS 8 1
especially in domestic heating, it cannot, on account of its
price and low heat-producing power, find general adoption.
The value of wood, in fact, as a material for constructional
purposes and as a source of cellulose (for the manufacture of
paper, rayon or artificial silk, etc.) and other products is
much greater than its value as a fuel.
In the great peat deposits of the world, 1 also, there exists
an enormous potential supply of fuel, but although peat has
a local importance as a domestic fuel, the cost of removing
the large amount of water which it contains has hitherto
proved an effective barrier to its commercial exploitation as
an industrial fuel.
When one considers the very great variations in the
calorific value of different kinds of coal, it will at once be
clear that it is rather irrational to buy coal merely by 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. Clearly, then, the price paid should be related
to the heat-producing value of the coal, and this is the basis
on which, to an increasing extent, large consumers of coal
contract for their supplies.
The world's supply of coal, on which our present-day
industrial civilisation depends, is being used up incom-
parably more quickly than fresh coal is being formed ; and
the question, how most efficiently to utilise the irreplaceable
coal reserves is therefore exercising the minds of the scientific
leaders of industry in all countries. The problem of coal
economy and coal utilisation, moreover, must not be re-
1 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.
82 CHEMISTRY IN THE SERVICE OF MAN
garded merely from the point of view of the use of this
mineral as a fuel or as the source of other fuels (oil or gas),
for it must not be forgotten that coal, in the hands of the
chemist, is also the ultimate source of very valuable chemical
products dyes, drugs, plastics, explosives, etc. derived
from the product of its distillation, coal tar. From coke and
steam, moreover, a gas (water-gas) is produced which, as we
shall learn later, is not only an important fuel but also the
raw material from which substances of great industrial and
economic value are obtained.
Whereas, in industry, the necessity for the efficient utilisa-
tion of coal as a fuel is generally recognised, it must be con-
fessed that the use of raw coal in the open domestic fire-
place, so common in Great Britain, is a most wasteful method
of heating. When fresh coal is put on a fire, a process of
" dry distillation " takes place with production of gas and
tarry products, which, undergoing a partial decomposition
with separation of carbon (soot), give rise to clouds of smoke.
Thereby, it has been shown, as much as a third of the heat
value of the coal is lost. With the ordinary open fire-place
only about one-fifth of the heat of the burning coal becomes
effective in heating the room.
But if the open fire is wasteful, one will not willingly
consent to give it up, and against its wastefulness one
may place 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
a fuel which can be burned in the open fire and which avoids
the waste accompanying the production of smoke. By
carrying out the distillation 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, ammonia and tar which
FUELS AND ILLUMINANTS 83
are produced are collected, and the coke which is left behind
can be used as a smokeless fuel. Although the ordinary coke
of the gas works, obtained by distilling coal at a temperature
of about 1100 C. (2012 F.), is such that it cannot be burned
as readily as coal in the open fire although great advances
in this direction have recently been made it has been
found that by carrying out the distillation at a temperature
of about 500 C. (932 F.), the residual coke still contains
sufficient volatile matter to enable it to burn readily and
without smoke in the ordinary grate. Considerable quantities
of this low-temperature coke, having a calorific value of
13,500 B.Th.U., are now produced under various names
(coalite, fuelite, etc.), and the greatly increased production
and use of such a smokeless fuel calls for serious con-
sideration.
Not only does the use of raw coal as a fuel involve the loss
of by-products, but it is also accompanied by the production
of much smoke by which the atmosphere is polluted and the
health of the people prejudicially affected. What could be
more depressing to the spirits of the people in our large
towns than the want of sunlight and the appearance of " the
sombre houses hearsed with plumes of smoke " ? In some
industrial areas it has been shown that the available sunlight,
the great minister of health, is reduced by as much as 40
per cent., owing to the presence of smoke in the air ; and no
less than 400-500 tons of soot fall per square mile per
annum.
Moreover, besides the lowering of vitality and the pre-
disposition to disease, brought about by a smoky atmosphere
and absence of sunlight, great material damage is also done,
and great monetary loss is caused owing to the increased
cost of cleaning and larger laundry bills. Although the use
of raw coal in our industries can be dispensed with only
slowly, it is highly desirable that in the domestic fire-place,
which after all is mainly responsible, in Great Britain, for
the production of smoke and soot, raw coal will soon cease
84 CHEMISTRY IN THE SERVICE OF MAN
to be burned. The poet will then no longer be able to
exclaim :
Look ! where round the wide horizon
Many a million-peopled city
Vomits smoke in the bright air.
In recent years improvements have been introduced in
the design and use of appliances for burning solid fuel for
domestic heating, cooking, etc. These make it possible to
burn coal and other solid fuels with greater ease and efficiency,
and with the emission of less smoke.
Coal also contains small quantities of compounds of
sulphur, and when the coal is burned an acid oxide of
sulphur, sulphur dioxide, is formed. This has a harmful
action on vegetation, stone and metal work, etc. It is
therefore necessary, when coal is burned in very large quan-
tities in a restricted area, as in the large power stations at
Battersea and Fulham, London, to remove the sulphur
dioxide from the flue gases before their emission into the air.
This is done by spraying the flue gases with a slurry or fine
suspension of lime or chalk in water. The flue gases are then
discharged into the air practically free from smoke, grit and
sulphur dioxide.
SOLID ILLUMINANTS
At the present time when, by the mere touch of the
finger on a button, a flood of brilliant light can instantly be
obtained, it is difficult to realise what must have been the con-
ditions of life when man had to be content with the smoky
flame of the pine torch or of the rush dipped in olive oil.
When, also, one thinks of the old guttering candle, with
its constant need of " snuffing/' one can appreciate 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.
FUELS AND ILLUMINANTS 85
The production of light depends in all cases, with the
exception of electric light, on the process of combustion 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.
For the earliest candles a solid animal fat was employed,
such as ox-fat or tallow, and the candle was made by re-
peatedly dipping the wick into the melted tallow. At first,
the wick was made from the dried pith of the rush (whence
was derived the name rushlight), but later, wicks of cotton
fibre were employed. From the manner in which they were
made, these candles were called dips.
During the nineteenth century the manufacture of candles
was greatly improved owing to the elucidation of the chemical
nature of fats and oils by the French chemist, CHEVREUL.
Animal and vegetable fats and oils, it was shown, are all
compounds of the familiar substance glycerine, C 3 H 5 (OH) 3 ,
with various acids, such as palmitic acid (C 15 H 31 -COOH),
stearic acid (C 17 H 36 -COOH) and oleic acid (C 17 H 33 -COOH).
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.
In the making of the modern candle, the fat or tallow is
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, whereby the fat is de-
composed into glycerine and the acids with which it was
combined stearic, palmitic and oleic acids. After purifi-
cation, the mixture of acids is distilled, and the solid acids
separated from the liquid oleic acid by pressing. The solid
86 CHEMISTRY IN THE SERVICE OF MAN
thus obtained consists mainly of stearic acid or stearin, and
forms, generally with the addition of a small quantity of
solid paraffin or 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 reference has just been made,
is itself also largely used for making candles. It is a white
material which is obtained by distilling oil shale and brown
coal or lignite, and is also extracted from American, Galician
and especially from Burma or Rangoon petroleum. It con-
sists of a mixture of compounds which contain only hydrogen
and carbon, and are therefore called hydrocarbons, and belongs,
therefore, to an entirely different class of compounds from
the fats or the fatty acids, all of which contain oxygen.
The wax candles formerly so highly prized were made
of beeswax ; and spermaceti, a compound obtained from
the oil of the sperm whale, was also used in the manufacture
of candles. The hard China wax, produced by a coccus,
a small insect similar to the wood-louse, and various kinds
of vegetable wax are also used for candle-making in China
and Japan.
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 candle is lit, the heat of the flame melts 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.
In the old tallow candles, the wick required to be snuffed
from time to time ; that is, the unburnt end of the wick had
FUELS AND ILLUMINANTS 87
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, continues 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.
The necessity for snuffing, however, is now obviated by
the use of twisted or flat-plaited wicks. As the candle burns,
the end of the wick, as every one may see by looking at
a burning candle, curls or bends outwards to the edge
of the flame, and coming, in this way, into contact with
the oxygen of the air, it burns away, and so no snuffing is
required.
LIQUID FUELS AND ILLUMINANTS
The occurrence of a natural mineral oil has been known
from a very early period, and " slime " or bitumen (formed
from mineral oil or petroleum, 1 as it is now called, by the
loss of its more volatile constituents) was used as a mortar
by the builders of the Tower of Babel. Classical writers,
also, record the presence of oil in various regions and describe
its use both as an embrocation and as an illuminant. In the
region of Baku on the Caspian Sea, moreover, the " Holy
Fire " of the burning oil and of the gas which accompanies
it was, in ancient times, a place of pilgrimage of the Persian
Guebers or fire- worshippers. 2
1 The word petroleum means " rock oil."
2 In the hills near Kirkuk in Iraq lies a shallow depression where
inflammable gas, escaping from the crust of the earth, burns continuously,
night and day, with dancing, flickering flames. This spot, known
locally as the " Fiery Furnace," may have been the scene of the " trial
by fire " to which Shadrach, Meshach and Abednego were subjected by
Nebuchadnezzar .
88
CHEMISTRY IN THE SERVICE OF MAN
In America, exudations of mineral oil had long been
known and the oil had, by reason of its medicinal and curative
properties, been used both internally and externally. It was,
however, only in 1859 that the first oil-well was drilled in
Pennsylvania for the purpose of winning the oil for use as
an illuminant and lubricant. The increasing demand for
Courtesy of Southern Pacific Company
OIL WELLS NEAR SUMMERLAND, CALIFORNIA.
oil, for use more especially as a fuel, has, during the present
century, led to the development and exploitation of many
new oil-fields in different parts of the world. In 1938, the
world production of petroleum amounted to 270,000,000 tons,
nearly two-thirds of this being produced in the United States. *
1 During the past decade oil has been obtained in England, more
especially from|wells near Eakring in Nottinghamshire. The amount
produced down to 1945 was about 400,000 tons. The life of this oil-field
js put at from ten to twenty years.
FUELS AND ILLUMINANTS 89
Of the origin of petroleum, little can be asserted with
confidence, but it is generally considered that the oil has
been formed by the gradual decomposition, under bacterial
action, of deposits of marine animal and vegetable matter.
The oil occurs in pools between layers of impervious rock,
and is associated with a gas, the pressure of which is, in some
cases, sufficient to force the oil up through the bore-pipe so
as to form a mighty fountain.
Although the petroleum from different oil-fields may vary
greatly in composition, it consists, in all cases, essentially of
a mixture of hydrocarbons, or compounds which contain
carbon and hydrogen only. For the most part, the hydro-
carbons belong* to what is known as the methane or paraffin
series (see below), but other hydrocarbons, known as naph-
thenes, may also be present in varying amounts. These
compounds contain a lower proportion of hydrogen and are
more akin to the so-called aromatic hydrocarbons (benzene,
toluene, etc.), which are contained in coal-tar (Chap. xv).
Small amounts of these aromatic hydrocarbons are also
present in certain types of petroleum.
METHANE, or marsh gas, is the lowest member of a long
series of hydrocarbons, 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, one can
represent the molecule of methane thus :
H
H C H
H
or, more simply, by the formula CH 4 .
90 CHEMISTRY IN THE SERVICE OF MAN
Methane is the inflammable gas which rises in bubbles
when one stirs the mud of decaying vegetation at the bottom
of a stagnant pool hence the name marsh gas ; and it is
also the gas which, produced during the formation of coal, 1
escapes from the coal-beds during mining and which, mixed
with the air of the mine, constitutes the explosive mixture,
fire-datnp. Methane, moreover, is the main constituent of
the " natural gas " which escapes from the earth in various
oil-bearing regions (p. 99).
Large quantities of methane are produced by bacterial
action on the sludge formed in the processes of sewage
purification which are being introduced by an increasing
number of local authorities. In one installation, more than
a million cubic feet of gas, containing 70 per cent, of
methane, are produced daily. Since methane finds many
important uses not only as a fuel but also in chemical
industry, for the production of carbon black (p. 125),
hydrogen (p. 194), methanol, etc., waste of it should be
avoided and increased production and utilisation should be
encouraged.
The element carbon is remarkable among all the elements
in the property that its atoms can combine with one another
so as to form " chains v of carbon atoms, and give rise to a
series of compounds which may be represented by the
formulae :
CH 3 CH 3 (ethane), CH 3 CH 2 CH 3 (propane),
CH 3 CH 2 CH 2 CH 3 (butane), etc.
A large number of such compounds are known, and it
will be observed that the composition of each of them can
be represented by the formula C w H 2n _ h2 . Owing to their
1 The total quantity of methane which might be made available from
the coal mines in Great Britain alone is very large. One mine is stated
to produce as much as 10 million cubic feet of gas, containing 80-90 per
cent, of methane, per day. As a motor fuel, this is equivalent to about
60,000 gallons of petrol.
FUELS AND ILLUMINANTS 9 1
chemical inertness, the hydrocarbons belonging to this
series are spoken of as paraffins. 1
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 atoms in the molecule is greater than
sixteen, the compounds are solid at the ordinary temperature.
It may also be mentioned here that besides the saturated
hydrocarbons, other hydrocarbons are known which contain
a lower proportion of hydrogen, and are therefore said to
be unsaturated. Thus, if two hydrogen atoms are removed
from each of the compounds of the methane series, hydro-
carbons are obtained which can be represented by the
formulae :
H H
H II H | |
\C=C C H etc.
H W |
H
C 2 H 4 (Ethylene) C 3 H fl (Propylene)
These constitute another series of hydrocarbons, known by
the name of the first member ethylene. Some of these
hydrocarbons occur in natural gas and also in the gas pro-
duced in the " cracking " of oil (p. 95), and they are the
raw materials for the production of " polymer petrol "
(p. 98) and for the manufacture of solvents and other sub-
stances of great value.
Hydrocarbons are also known which contain a still lower
proportion of hydrogen, or higher proportion of carbon,
for example acetylene, C 2 H 2 or HC=CH, the first member
of a series having the general formula C n H 2n _ 2 .
Crude Petroleum is generally a thick yellow, brown, or
black liquid, which shows a green fluorescence. After the
gaseous hydrocarbons which may be dissolved in it have
1 From the Latin parum (little) and affimtas (affinity).
92 CHEMISTRY IN THE SERVICE OF MAN
been removed, the petroleum has to be refined or purified
and then submitted to fractional distillation, in order to
separate it into portions adapted for different purposes.
The crude petroleum is heated in a still and the vapour
led into a high tower fitted with perforated transverse plates,
at which condensation of the vapour takes place. The
constituents of higher boiling point condense at the lower,
hotter plates, and the vapour of the more volatile con-
stituents bubbles through the liquid and condenses at
successively higher levels. By tapping off the condensed
liquid at different heights of the tower, a series of " fractions "
of different boiling-points can be obtained. 1
The most volatile fraction, which distils over up to a
temperature of about 70 C. (158 F.), is called petroleum
ether and is largely used as a solvent and as a local anaesthetic
owing to the cold produced by its evaporation. The next
fraction, with a distilling temperature between 70 and 120 C.
(248 F.), is called gasoline or petrol, and is used as a motor
spirit and also for illuminating purposes (petrol-air gas). At
a higher temperature, from 120 to 150 C. (302 F.), there
is obtained a fraction called petroleum benzine 2 or benzoline,
which is used as a solvent and as a " dry-cleaning " agent for
the removal of oil and grease stains.
The fraction condensing between 150 and 300 C.
(300 and 570 F.) constitutes burning oil or kerosine, 3 or
paraffin oil ; that condensing between 250 and 340 C.
(482 and 644 F.) constitutes solar oil or gas oil, which is
used in Diesel engines. The distillation of the less volatile
residues is then carried out under reduced pressure and
oils of various grades are obtained and are used as lubricat-
ing oils and for burning under boilers. From the highest
fractions of all one obtains vaseline and, in some cases, solid
1 The temperatures at which the different fractions are collected may
vary in different refineries.
a Not to be confused with benzene obtained from coal-tar.
3 This spelling, with the termination -ine in place of -ene, has been
adopted by international agreement.
FUELS AND ILLUMINANTS
93
7 '-"v/' ;, v,v^
; '^vf>;'; f v
Courtesy Anglo-Iranian Oil Co. Ltd.
A MODERN PETROLEUM DISTILLATION UNIT.
The main fractionating tower (122 feet high) is on the right, with
the primary flash tower for the removal of the most volatile constituents
in the centre and the vacuum column on the left.
94 CHEMISTRY IN THE SERVICE OF MAN
paraffin, which is used for making candles, water-proofing
paper, and other purposes. 1 A final residue of pitch is
obtained.
Nearly all crude petroleum oils contain compounds of
sulphur, and compounds of nitrogen are also frequently
present. These pass over into the various " fractions "
obtained by distillation and have to be removed by suitable
chemical treatment before the finished products are placed
on the market.
Since paraffin oil, or kerosine, contains a relatively large
proportion of carbon, its vapour 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, there-
fore, the flame is surrounded by a chimney whereby a draught
of air is created, and oxygen is 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 conditions, and deter-
mining the temperature at which, on passing a light over
the mouth of the vessel containing the oil, a flash of flame is
1 It is of interest to note that in the Kettleman Hills, California, a well
was tapped which gave an, oil consisting almost entirely of volatile
hydrocarbons, and a natural gas consisting mainly of methane. Over
100,000 gallons of gasoline and 90,000,000 cubic feet of gas were obtained
daily.
FUELS AND ILLUMINANTS 95
seen. This is known as the flash-point of the oil, and in
Great Britain it has been enacted that the flash-point of
burning oil must not be below 73 F., when determined by
what is known as the " closed " test.
Until well into the present century, petroleum was of
importance chiefly as a source of illuminants and lubricants.
For some time now, however, owing to the development
of the internal combustion engine and the increasing use
of the oil-fired steam boiler, the value of petroleum depends
mainly on its being a source of fuel supply. Since i Ib. of
fuel oil, the higher boiling fractions of petroleum, has a
calorific value of about 19,500 B.Th.U. about one and a
quarter times greater than anthracite and since oil possesses
many advantages over coal in the matter of cleanliness,
control of consumption, stowage room, etc., its use as a
fuel, especially for ocean steamers, has greatly increased.
It is, however, in the use of gasoline or petrol as a fuel
for the internal combustion, motor car and aeroplane engine
that the greatest developments have taken place ; and as
the gasoline fraction obtained by the distillation of petroleum
is quite insufficient to meet the demand, large quantities of
motor spirit have to be produced by the " cracking " of gas
oil and even of kerosine, for which now there is a relatively
reduced demand. By heating these oils under pressure to a
temperature of 380 C. (716 F.), or more, the relatively
large molecules are broken down into the simpler molecules
of the hydrocarbons which constitute gasoline or petrol.
This process is facilitated by the presence of aluminium
chloride which acts as a catalyst (see Chap. ix). The spirit
obtained by cracking contains also unsaturated hydrocarbons
(p. 91), as well as iso-parafBns 1 and so-called aromatic hydro-
1 In the iso-paraffins the carbon atoms are joined together so as to
form not a straight but a branched chain, as is shown by the formula for
iso-octane ' cil. CH 3
CHa-C-CH,- CH-CH 8
CII 3
96 CHEMISTRY IN THE SERVICE OF MAN
carbons (benzene, toluene, etc.). These are of value because
they help to prevent the unpleasant phenomenon of
" knocking," which is due to the passing of the relatively
slow wave of combustion into the relatively very rapid wave
of explosion in the gasoline-air mixture in .the engine cylinder.
Detonation or explosion takes place when the compression of
the gasoline-air mixture exceeds a certain value for a given fuel.
Since the efficiency of the internal combustion engine
increases with the degree of compression of the fuel-air
mixture in the cylinder before firing, it is of advantage to
use a fuel which has little tendency to detonate on com-
pression, or which has, as it is said, a high anti-knock (or
high octane) value. 1 The tendency of a motor spirit to
knock varies with the composition and nature of the hydro-
carbons of which the spirit is made up, and great advances
have been made in recent years in the production of motoj;
fuels of high octane number by blending the gasoline ob-
tained by the distillation of petroleum with " cracked "
spirit, benzene (benzole) or lead ethyl, Pb(C 2 H 5 ) 4 , spoken
of popularly as " Ethyl. " By blending petrol with up to
40 per cent, of isopropyl ether (produced from propylene), a
motor fuel with an octane number of 100 can be obtained.
Through the introduction of these improved motor fuels,
the motor car engineer has been able, during the past decade,
to design his engine so as to increase the compression ratip
from about 4 : i to 6-5 : i. The efficiency has thereby been
very greatly increased.
The natural reserves of oil are not inexhaustible, and the
question arises whether any substitute can be obtained.
Fortunately, the outlook is full of hope.
1 The anti-knock value of a motor spirit is determined by comparison
with the anti-knock value of known mixtures by volume of the two
hydrocarbons, normal heptane (C 7 H 16 ) and iso-octane (C 8 Hi 8 ) having
the formula (CHaVCH-CHa'C^CHa^. A motor fuel which has the
same anti-knock properties as a mixture of 70 volumes of octane and
30 volumes of heptane is said to have an octane number of 70. " Ethyl
petrol " has an octane number of 80. The higher the octane number,
the smaller is the tendency to knock.
FUELS AND ILLUMINANTS 97
In Scotland, ever since 1860, mineral oil has been obtained
by heating a carbonaceous shale, called oil shale. From one
ton of this shale one can obtain about thirty gallons of oil
from which, by distillation, motor spirit, illuminating oil,
fuel oil, lubricating oil and solid paraffin can be obtained.
Since enormous deposits of oil shale occur in many different
countries, it will be possible to obtain abundant supplies of
oil fuel at a greater cost it may be than at present when
the oil wells shall have ceased to flow. 1
From coal, also, fuel oil may be obtained, and is being
obtained, by various processes. By the low temperature
carbonisation (distillation) of bituminous coal (p. 83) a tar
is produced from which one can obtain, % fractional dis-
tillation, motor spirit, fuel and lubricating oils, similar to those
obtained from petroleum ; whereas by the high temperature
distillation of coal (p. 104) a tar is produced from which
benzene (or benzole) 2 is obtained. Although benzene is not
used as a motor spirit by itself, mixtures of benzene with
petrol and also with alcohol are extensively employed. The
addition of benzene to petrol increases the anti-knock value.
Motor spirit can also be produced, and has been produced
in very large amounts, by the hydrogenation of coal, a
process developed originally tjy the German chemist,
F. BERGIUS. Ground coal, made into a paste with oil for
convenience of handling and treatment, is subjected to the
action of hydrogen at a temperature of 42O~5oo C. (788-
932 F.), and under a pressure of about 200 atmospheres.
The coal is thereby converted, by the action of heat and the
taking up of hydrogen, into gaseous hydrocarbons (methane,
ethane, propane, butane), 3 petrol, middle oils and heavy oil.
1 Since 1940, petrol has been produced commercially at Glen Davis in
Australia from oil shale, a yield of 100 gallons of oil being obtained per
ton of shale. It is planned to produce 30,000,000 gallons of oil per annum.
2 The term benzole is applied to various commercial mixtures of
benzene hydrocarbons (benzene, toluene, etc.).
3 The propane and butane are separated and compressed into cylinders
for use as a gaseous fuel (" Calor Gas ") in country districts, while the
other hydrocarbons can be used for the production of hydrogen (p. 194).
D
98 CHEMISTRY IN THE SERVICE OF MAN
The heavy oil is used for making the ground coal into a
paste and the middle oils, in the form of vapour, are passed
with hydrogen through heated tubes in the presence of
molybdenum sulphide as catalyst. The oils are thereby
" cracked " and partially hydrogenated, and the spirit so
obtained is added to the petrol to produce a motor fuel with
an octane number of 71-73. By the use of suitable catalysts,
whereby the various reactions can not only be accelerated
but also have their course directed, control is obtained of
the nature of the oils formed. With tin as catalyst, in presence
of hydrochloric acid gas, 180 gallons of motor spirit can be
obtained by the hydrogenation of one ton of bituminous coal.
Petrol is also produced by the hydrogenation of coal-tar
creosote (a process used in England) and of the tar produced
in the low temperature carbonisation of coal (p. 83). More-
over, increasingly large quantities of high-grade petrol are
now also being produced from natural gas (p. 99) and from
refinery gas, formed in the process of " cracking " oils. These
gases, which are available in enormous quantities, 1 consist
partly of saturated and partly of unsaturated hydrocarbons.
The saturated hydrocarbons can be decomposed by heat, with
formation of unsaturated hydrocarbons of the ethylene type.
These unsaturated hydrocarbons, when passed at a tempera-
ture of about 450 F. and under a pressure of about 14
atmospheres over a catalyst, pyrophosphoric acid, undergo
polymerisation, two or more simple molecules uniting together
to form more complex molecules. In this way motor spirit
(" polymer petrol ") of a high octane number, and even
iso-octane itself, can be obtained, suitable for blending with
and improving the anti-knock properties of ordinary petrol.
In 1935, F. FISCHER and H. TROPSCH, in Germany,
found that water-gas (p. 107), in presence of a suitable
catalyst (e.g. cobalt and thorium) and at a temperature of
about 400 F., is converted into a mixture of liquid and
1 In 1938, the annual production of cracked gas amounted to
3oo,ooo,oop,ooo cubic feet.
FUELS AND ILLUMINANTS 99
gaseous hydrocarbons. The low-boiling fraction of the liquid
has a low anti-knock value and must be improved by the
addition of lead ethyl, benzole, or the " polymer petrol "
just described ; but the higher-boiling fraction, on being
" cracked, " gives good yields of high anti-knock motor spirit.
From water-gas, also, high-grade, viscous lubricating oils
can be produced, with the help of aluminium chloride as
catalyst.
In various ways/ therefore, research chemists have suc-
ceeded in producing motor fuel and lubricating oils from
coal, directly or indirectly, and from natural and oil refinery
gases ; and they have so greatly improved the products
that a gallon of petrol will, to-day, do twice as much work
as a gallon did ten or fifteen years ago.
In addition to the mineral oils, alcohol or spirits of wine
(Chap, xvn) is also used to some extent as a fuel for motor-
car engines. Natalite, for example, is a mixture of alcohol
and ether and is produced as a motor fuel in Natal, South
Africa ; and mixtures of alcohol with benzene and with
petrol are also used as motor fuels. Although the calorific
value of alcohol is not so high as that of gasoline, higher
compressions can be used without detonation, or " knocking, "
taking place, and the increase of efficiency of an internal
combustion engine with compression is so great, that it may
compensate for the lower calorific value of the alcohol. The
possibility of a great extension in the use of alcohol as a
motor fuel in the future must not be overlooked.
Although petroleum is chiefly valuable as being a source
of supply of fuels and lubricants, it has now also gained a
position of major importance as a raw material for the
production of compounds of great value (see Chap. xv).
GASEOUS FUELS AND ILLUMINANTS
In various countries (the United States, Russia, Rumania,
Canada, and others) great reservoirs of " natural gas " are
100 CHEMISTRY IN THE SERVICE OF MAN
found, unassociated with oil, and this gas has been used for
many years, in the United States, not only for illuminating
purposes but also as a fuel for steel manufacture, for the
melting of glass, and for other industrial purposes. 1 Its use
for the production of motor spirit has just been discussed. As
a fuel, natural gas is of great importance on account of its
high calorific value of over 1000 B.Th.U. per cubic foot.
This is twice as great as the calorific value of the gas obtained
by the high temperature distillation of coal. In the United
States, many million cubic feet of gas are daily conveyed
many hundreds of miles through pipes to industrial
centres.
Although natural gas has a very great value in the countries
where it is found, the most important gases used at the
'present day for the production of heat and light are those
which are obtained, by one process or another, from coal,
and more especially the gas which is obtained by heating
coal in closed vessels or " retorts," out of contact with the
air. That a combustible gas can be produced in this way
was observed about 1688, by John Clayton, a Yorkshire
clergyman, who later became Dean of Kildare ; 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. 2 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 introduction of gas for street
lighting was due to a Moravian, Winzer or Winsor, and
through his efforts Pall Mall in London was lighted by gas
on 28th January 1807, and created quite a sensation. By 1816
1 It is estimated that the available world supply of natural gas (mainly
methane) is about ten million tons a year.
2 William Murdoch, who was born at Lugar in Ayrshire, in 1754,
was associated with the engineering firm of Messrs. Boulton & Watt,
Birmingham. In 1792 he lighted his house at Redruth, in Cornwall,
with coal-gas, and it was at the works of Boulton & Watt at Soho,
Birmingham, that coal-gas was first used (in 1798) on a large scale as an
illuminant.
FUELS AND ILLUMINANTS
101
IO2 CHEMISTRY IN TIIK SERVICE OF MAN
the greater part of London was lighted by gas. 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 1810 ; 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. "
Coal is not a definite chemical substance, but a com-
plex 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 nd heating purposes, but also considerable
quantities of ammonia and of tar, and there remains in the
retort a residue of coke. Down to the middle of last century
the ammonia and the tar were regarded as by-products of
little value, but, as we shall learn more fully later, they have
since then become materials of great importance; 1 while,
owing to the great developments of the iron and steel in-
dustry, 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. 2
Although the nature of the products as well as their
1 Owing to the great developments which have taken place in the
industrial production of synthetic ammonia (Chapter x), the importance
of gas-works ammonia has again greatly diminished.
2 During the period 1936-38, about forty million tons of coal were
carbonised annually in Great Britain, half for the production of
300,000,000,000 cubic feet of gas, and half for the production of
metallurgical coke.
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104 CHEMISTRY IN THE SERVICE OF MAN
relative amounts depend on the kind of coal distilled and
on the temperature at which the process is carried out, one
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
i Illuminating gas . . . 11,000 cubic feet.
2. Coal-tar . . . . 120 Ibs.
3. Ammonium sulphate . . 25 ,,
4. Coke .... 1,500 ,,
In the manufacture of illuminating gas, the coal is heated
in large fire-clay retorts, placed horizontally or vertically,
at a temperature of iooo-iioo C. (i832-2oi2 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. 8). 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 (hydrogen sulphide) 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), w r hich
exercises a destructive action on plants, metal work, etc. ;
and the presence of carbon dioxide is objectionable because
it lowers the heating and 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 con-
taining hydrated oxide of iron (e.g. bog iron ore), which
FUELS AND ILLUMINANTS
I0 5
removes the sulphuretted hydrogen, by forming with it the
compound, sulphide of iron. By introducing a small and
regulated amount of air into the gas at this stage, the sulphide
of iron is continuously oxidised to iron oxide and free sulphur.
When the amount of free sulphur reaches about 60 per cent,
of the iron oxide, the latter loses its efficacy, but this " spent
oxide " still has its uses, for it is sold to the manufacturer of
sulphuric acid, who utilises it in the manner we shall learn
later.
Besides hydrogen sulphide, other substances carbon
disulphide, naphthalene and hydrocyanic acid (prussic acid)
are also removed from coal-gas and form or give rise to
by-products of value. Among the by-products obtained is
ammonium thiocyanate, NH 4 CNS, which, on being heated,
forms the compound thiourea, CS(NH 2 ) 2 . This compound
is used in the production of synthetic plastics (p. 335).
After undergoing the various processes of purification, the
illuminating gas passes to the gas-holder, 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
I lydrogen
Methane
Unsaturated hydrocarboi
etc.)
Carbon monoxide
Carbon dioxide
Nitrogen
Oxygen
is (Ed
lylene
56 per
22-8 ,
2'5
10*9
i'3
6
0-5
cent, by
>
volume.
>
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.
106 CHEMISTRY IN THE SERVICE OF MAN
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 i 1 and methane, with a flame which has only a slight
illuminating power. Ethylene, however, burns with a
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 men-
tioned benzene (or benzole, 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 of petroleum ?
The answer is that which was given long ago by Sir HUMPHRY
DAVY : The luminosity is due to the decomposition 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, however, 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, one
sees in these flames three zones : an inner non-luminous
zone of unburnt 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
1 The lambent blue flame seen on the top of a clear-burning coal fire is
due to the combustion of carbon monoxide. It is an exceedingly poisonous
gas.
FUELS AND ILLUMINANTS
increased by increasing the proportion of carbon-yielding
substances in the burning gas ; and hydrocarbons, and more
especially unsaturated hydrocarbons, which contain a rela-
tively large proportion of carbon, will be the most effec-
tive 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 white-hot
coke, a gas is obtained which is a mixture of hydrogen and
carbon monoxide :
C + H 2 O = CO + H 2
Carbon (coke) and water give carbon monoxide and hydrogen.
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 hydro-
carbons, obtained by the decomposition or " cracking " of
oil at a high temperature, it is added (as carburetted water-
gas) to the gas obtained by the distillation of coal. Water-
gas is also frequently added without enrichment to coal-gas,
so as to give a cheaper gas of lower illuminating power.
Formerly when coal-gas was used almost entirely as an
illuminant, gas-producing companies had to supply gas of
a certain minimum illuminating power ; but at the present
time coal-gas is employed mainly as a domestic and industrial
fuel for the production of heat. The illuminating power
standard has therefore been abandoned in Great Britain, and
gas-producing companies may supply gas of varying quality,
but the charge to the consumer may be made only on the
basis of the heat- value of the gas. Greater freedom is thus
given to the producer, and the consumer pays for the amount
of heat energy or the number of therms he receives, i therm
being equal to 100,000 B.Th.U.
Coal-gas, produced by high temperature carbonisation,
has a calorific value of about 480-520 B.Th.U. per cubic
108 CHEMISTRY IN THE SERVICE OF MAN
foot ; while that produced by low temperature carbonisa-
tion has a value of 800-1000 B.Th.U. per cubic foot. The
calorific value of water-gas, which is largely used as an
industrial fuel, alone or mixed with coal-gas, is about 280
B.Th.U. per cubic foot.
The gas, carbon monoxide, which forms one of the con-
stituents of water-gas, differs from the other oxide of carbon,
carbon dioxide, to which reference has already been made
(p. 48), not only in being a combustible gas but also in
being intensely poisonous. This is due to the fact that the
gas combines with the haemoglobin, or oxygen-carrying
constituent of the blood, to form a very stable, bright-red
compound, carboxy-haemoglobin, which is no longer able
to take up oxygen from the air entering the lungs. The
presence of i volume of carbon monoxide in 5000-10,000
volumes of air will cause headache, while if i per cent, of
carbon monoxide is present, unconsciousness and death will
occur in a few minutes. Many cases of poisoning by carbon
monoxide have occurred owing to its presence in illu-
minating gas and in the products of imperfect combustion
in stoves or in the engines of motor cars, from which it passes
out in the exhaust. In cases of necessity, protection against
the gas can be obtained by wearing a mask containing a
mixture of the oxides of manganese, copper, cobalt and
silver a mixture known technically as hopcalite. In the
presence of this mixture, or even of a specially prepared
manganese dioxide alone, carbon monoxide is oxidised by
atmospheric oxygen to carbon dioxide.
When coal-gas is used as a fuel for heating purposes, it
is important that combustion takes place rapidly and com-
pletely without the separation of carbon particles, and this
result is secured if the coal-gas, before being burned, is
mixed with a suitable amount of air. The molecules of the
combustible gas then find oxygen with which they can com-
bine, ready at hand, so to say, and combustion takes place
rapidly and completely without the separation of carbon
FUELS AND ILLUMINANTS 109
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. 9 and 10). 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 thereby
becomes mixed with air, the amount
of which necessary to ensure complete
combustion can be regulated by enlarg-
ing or diminishing the size of the air
openings. If too much air is admitted
to the gas, the mixture becomes ex-
plosive, 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 com- A , air-hole by which air
bustion takes place and products of a can pass into the tube
i , r i and mix with the gas
very poisonous character are formed. which enters at the
These, fortunately, betray their presence small jet seen through
by a powerful and unpleasant odour.
FIG. 9. BUNSEN
BURNER.
a can be
In gas fires, burners of the same type regulated by means of
as the Bunsen burner are employed, the movable ring R '
and the long, hot gas flames which are formed raise to
a high temperature special " radiants " of fire-clay and
asbestos, which then radiate heat into the room. Such
gas fires have in recent years been improved in construction
so that their ventilating efficiency and their emission of
radiant heat have been greatly increased, and they have
now lost practically all their former unhygienic properties.
If the luminous coal-gas flame is supplied with oxygen
instead of with air, a higher temperature can be obtained ;
for the nitrogen of the air acts as a diluent and so cools down
110 CHEMISTRY IN THE SERVICE OF MAN
the flame. One cannot, however, in this case make use of
the ordinary burner, for the mixture of oxygen and coal-gas
is 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 gas as it
burns at the mouth of the burner, and one thus obtains what
is known as the oxy-coal-gas blowpipe flame (Fig. n). If
this flame is allowed to impinge on a highly refractory
material like quicklime, the latter is raised to a brilliant in-
candescence, producing the well-known lime-light. (Now-
adays the oxide of the rare
metal zirconium is largely used
in place of lime.)
If hydrogen is used in place
FIG. io. GAS COOKER, CON- of coal-gas, a still higher
STRUCTED ON THE PRINCIPLE OF temperature, up to about
THE BlINSEN BURNER. r o ~ , ' J . t
2000 C. (3632 K), can be
obtained, and the high temperature produced by means
of the oxy-hydrogen flame has found an interesting and
important application in the manufacture of artificial gems,
such as rubies and sapphires. These gems consist essentially
of oxide of aluminium (alumina), a substance which occurs
naturally as corundum, and, in an impure state, as emery.
It is a very refractory substance, but it can be melted in the
oxy-hydrogen blowpipe flame. When a mixture of 97-5 per
cent, of alumina and 2-5 per cent, of oxide of chromium is
heated in the blowpipe flame, it is fused, and, on cooling,
solidifies to a ruby-red solid. It is 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 described, artificial rubies weighing as much
as eighty carats, or over half an ounce avoirdupois, have
been obtained. These artificial rubies, on account of their
great hardness, are now manufactured in large quantities
for use in the bearings of watches and for other purposes.
FUELS AND ILLUMINANTS III
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 vigorously assailed by electricity, and
Gas
FIG. ii. BLOWPIPE.
When the gas is burning at the mouth
of the wider tube, air or oxygen is blown
into the flame through the inner tube.
it is very doubtful if the industry could have maintained
itself even as it has done but for the invention of the now
familiar incandescent mantle. This invention, it is important
to bear in mind, was not due to any conscious desire or well-
directed search for a means to improve the illuminating
efficiency of gas, but to a purely scientific investigation of the
oxides of the so-called rare metals which was carried out by
AUER VON WELSBACH in 1884. In the course of his investi-
gations, von Welsbach was struck by the fact that some of the
oxides of the rare metals emit an exceptionally brilliant light
when incandescent ; 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
112 CHEMISTRY IN THE SERVICE OF MAN
carried out before the incandescent mantle could be made a
commercial success and be brought to its present state of
perfection.
To make the discovery of practical utility, " mantles " or
" stockings " of woven cotton, artificial silk (p. 144), or
ramie fibre (fibre produced from a plant of the nettle class),
are soaked in a solution containing the nitrates of thorium
and cerium 1 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 preserving the shape
of the mantle. To protect the fragile mantle from injury
during transport, it is dipped in collodion. When the mantle
is suspended in the hot, non-luminous flame of a special
burner constructed on the principle of the Bunsen burner,
it is raised to incandescence and emits a brilliant white light.
From a careful investigation 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 accom-
panied 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 focused on
1 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 and at Travancore, India.
FUELS AND ILLUMINANTS 113
the small particles of ceria. As a consequence, the tem-
perature of these particles rises above the average tem-
perature of the mantle, and the brightness of the incan-
descence is thereby increased. This action of the ceria is
spoken of as a catalytic action, about which we shall have
more to say later. 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 industry. Not only could a very
bright light, rivalling that of the electric incandescent lamp,
be obtained, but the cost of production of the gas 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 illuminating power of
this gas when burned in a flat flame is lower than formerly,
the temperature produced in the Bunsen flame and there-
fore the incandescence of the mantle are not greatly affected.
Incandescent mantles are employed not only with coal-
gas but also with a combustible mixture of petrol vapour and
air ; and petrol-air gas is now largely installed in houses in
country districts remote from centres of coal-gas manufacture.
. One other illuminant must be mentioned, the use of which
depends on the process of combustion in air, namely, acety-
lene, a gas which is readily obtained by the action of water
on a compound of calcium and carbon, known as calcium
carbide. 1 This substance is obtained by heating to a high
1 Acetylene can also be produced by the pyrolysis, or decomposition
at high temperature, of methane ; and owing to the enormous supplies of
methane which are available from petroleum and natural gas, the pro-
duction of acetylene from this substance may, in the future, assume great
importance.
114 CHEMISTRY IN THE SERVICE OF MAN
temperature a mixture of quicklime (calcium oxide) and
carbon in the form of anthracite 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, 1 and owing to its use for the production of acetylene,
calcium cyanamide (Chap, x), and other substances, calcium
carbide is now manufactured in large quantities.
( omtcsy of British Oxygen Co. >
CUTTING STEEL BY OXY- ACETYLENE FLAME,
Acetylene is an unsaturated hydrocarbon having a rela-
tively large proportion (over 92 per cent.) of carbon, as is
shown by its formula C 2 H 2 . Under ordinary conditions the
gas burns with a luminous and very smoky flame, but by
using a special burner which 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 tem-
1 A temperature estimated at about 3000 C. (about 5400 F.) can,
in this way, be obtained.
FUELS AND ILLUMINANTS US
perature of about 3480 C. (6300 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 or steel, 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 steel rods,
shafts, or girders as easily as a knife will cut through cheese,
and with a cut almost as fine. One of the first applications
to be made of the oxy-acetylene blowpipe flame was to cut
through the dense tangle of iron girders formed by the
collapse of the buildings in the fire at the Brussels Exhibition
of 1910, and so to allow of their removal. Acetylene is also
very extensively used for the welding of metals.
Owing to the readiness with which compressed or liquid
acetylene may undergo explosive decomposition, the gas is
generally dissolved in a solvent, acetone, under pressure, and
the solution stored and transported in steel cylinders. These
cylinders contain a porous, absorbent material which acts as
a carrier 'for the solvent, acetone, and increases the storage
capacity of the cylinder. The danger of explosion is also
thereby diminished.
Besides being used in the manner described above, large
quantities of acetylene are also used for the production of
acetic acid (Chap, xvn), of ethyl alcohol, of butyl alcohol
(p. 354), synthetic rubber (p. 341), etc. Acetylene, in a
concentration of about i per cent., is also used to accelerate
the ripening of peaches, oranges and other fruits. The
manufacture of calcium carbide and the production there-
from of acetylene is, therefore, an industry of very great
importance.
CHAPTER VI
MATTER, ENERGY AND EXPLOSIVES
THE consideration of the process of combustion, controlled
and utilised for the production of heat and light, leads to a
realisation of the fact that in the chemical reactions and
transformations which take place, one is not dealing merely
with material things. In the case of the burning candle, oil,
or coal-gas, it is not the combustible substances (stearin,
paraffin, hydrogen, methane, etc.), nor the products of
combustion (carbon dioxide and water vapour), which
interest us primarily, but the immaterial light, the ethereal
vibrations to which the process of combustion gives rise.
So also, passing on to the consideration of combustible sub-
stances as fuels, and of the process of combustion as a
source of heat, we again recognise that our interest is focused
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 substances
together with the oxygen of the air represent so much
potential energy, and the process of combustion is 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 transformation of the
different forms of energy, we see* one of the greatest achieve-
ments 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
116
MATTER, ENERGY AND EXPLOSIVES 117
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 in his presi-
dential address to the British Association in 1911, " real gain,
real progress consists 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 trans-
forming energy, that the nineteenth and twentieth centuries are
so strongly marked off from the centuries which preceded 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, as has already been pointed out (p. 51), the
green plants, absorbing the radiant energy of sunlight,
transform and utilise the carbon dioxide for the purpose of
building up their own structures and producing compounds
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,
there is 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.
The synthetic or building up processes which thus take
place in the green plant were imitated by Professor E. C. C.
BALY in the Chemical Laboratories of the University of
Liverpool. It was found that carbon dioxide and water when
exposed to light, in presence of a suitable catalyst 1 (a material
1 For example, ferric oxide, to which a small amount of thorium oxide
has been added. See also Chapter ix.
Il8 CHEMISTRY IN THE SERVICE OF MAN
which accelerates a reaction without itself entering into the
products of change), combine to form compounds of a sugar-
like character, called generally carbohydrates (p, 137). The
" yield " or proportion of carbohydrate so far obtained is
very small ; but the artificial synthesis resembles in several
points the natural synthesis in the plant. The process is one
which is at present of no practical utility, but its purely
scientific interest and importance are very great.
Although the association of energy with chemical change
is very obvious in the process of combustion, it is also found
in 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 is observed, and which
constitutes what is called 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 reaction 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
accompanied by an evolution of heat. In some cases, the
initial substances possess less energy than the final products,
and the chemical change therefore takes place with absorption
of heat. Energy, that is to say, must be supplied to the
initial substances in order that they may pass into the final
products of change. One distinguishes, therefore, between
exothermal reactions or reactions accompanied by evolution
of heat, and endothermal reactions or reactions accompanied
by absorption or taking in of heat energy.
This way of regarding chemical change as being the out-
ward and visible sign' of energy change is very instructive ;
for it is clear that if we can make a substance 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
MATTER, ENERGY AND EXPLOSIVES
substance is the carrier, and so change its nature. This fact
is clearly illustrated by the behaviour of the familiar sub-
stance, oxygen.
The molecule of oxygen consists of two atoms, O 2 , but
when the gas is subjected to the action of an electric discharge
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 ozo y 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, O 3 . Since ozone contains more
energy than ordinary oxygen, it is a more active oxidising
agent, and for this reason it is used for the purification of
water and other bactericidal purposes, and for bleaching
wax, starch, flour, ivory and other substances.
At Niagara Falls, large quantities of ozone are used in
the production of vanillin, the sweet-smelling constituent
of vanilla pods, by the oxidation of oil of cloves (p. 330).
In white phosphorus and red phosphorus (p. 75), and in
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. That the three forms of carbon, which differ so
markedly in appearance and physical properties, are associ-
ated with different amounts of energy, is shown by the fact
that when equal weights are burned different amounts of
heat are evolved. The applications and uses of the different
forms of carbon, however, do not centre round their calorific
values, but round other properties of quite a different
character.
Diamond is a crystalline form of carbon which is now
found mainly in South Africa, the Congo and Gold Coast,
and is greatly valued as a gem. The crystals, generally in
the form of octahedra, may occur either embedded in a
120
CHEMISTRY IN THE SERVICE OF MAN
rocky matrix, known in South Africa as blue ground, from
which they are recovered by crushing and washing, or in
loose alluvial deposits. Diamond has a* high index of
refraction and, consequently, when suitably cut, scintillates
Courtesy of De Beers Consolidated Mines Ltd
DIAMOND CRYSTAL IN BLUE GROUND.
and flashes in varied colours. It is the hardest of all sub-
stances and therefore finds important use as a cutting, drilling
and polishing material. For this purpose the impure black
diamonds, known as carbonado or bort, are largely employed.
Graphite is also a crystalline form of carbon, deposits of
which are found especially in Ceylon and Madagascar. It
MATTER, ENERGY AND EXPLOSIVES
121
has a greasy or unctuous feel and is extensively used as a
lubricant. Unlike diamond, graphite is soft and has long
been used for the manufacture of lead pencils. For this
purpose, the graphite is ground to a fine powder and mixed
with various amounts of clay or powdered retort carbon in
order to produce pencils of different hardness. On account
of its resistance to heat, graphite is used for making crucibles.
It is also a moderately good conductor of electricity and is
FIG. 12. ARRANGEMENT OF THE CARBON ATOMS IN GRAPHITE.
employed in the construction of dry cells and of electrodes for
use in electro-chemical industry (Chap. xn). As we shall learn
later, graphite is now manufactured artificially in large amount.
The marked differences in the properties of diamond and
graphite are due to differences of crystalline structure, or
arrangement of the carbon atoms in the crystal. In graphite,
as is shown by examination with X-rays, the crystal consists
of layers of carbon atoms, the atoms in each layer being
arranged in the form of hexagons lying in one plane ; and
the different parallel layers are relatively far apart (Fig. 12).
The forces acting between adjacent layers are much less than
those between the atoms of the same layer, and the different
122 CHEMISTRY IN THE SERVICE OF MAN
layers can therefore move past one another relatively easily.
This explains the soft, unctuous feel of graphite and its use
as a lubricant.
In diamond there are also layers of carbon atoms arranged
in hexagons. The atoms in a given layer, however, are not
all in one plane, but have a zig-zag arrangement, so that the
layers have, as it were, a corrugated surface (Fig. 13). The
atoms in adjacent layers, moreover, are as near together as
FIG. 13. LAYER OF CARBON ATOMS IN DIAMOND.
FIG. 14. ARRANGEMENT OF CARBON ATOMS IN DIAMOND.
the atoms in a given layer (Fig. 14). The crystal is therefore
more compact than graphite, and the adjacent layers, being
near together and " corrugated/' do not readily move past
one another. Hence the hardness of diamond.
Charcoal, an amorphous or non-crystalline form of carbon,
is obtained by heating wood, bone, coco-nut shell and other
carbonaceous matter" in a closed vessel, or retort, out of
contact with the air ; and at the present day large quantities
of wood are " distilled " not only for the production of
charcoal but also for the sake of the other products formed.
MATTER, ENERGY AND EXPLOSIVES 123
When wood is heated in retorts, volatile products wood
tar, wood spirit or methyl alcohol, 1 acetic acid, acetone, and
various gases pass off and charcoal remains in the retort.
The gases are used for heating the retorts.
Charcoal is very porous and possesses in a very high
degree the property of condensing on its surface, or adsorbing,
different gases and vapours, and for this reason may be used
for removing foul or noxious gases from the air. It finds
important application in the construction of gas masks for
protection against poisonous gases, and it is also largely used
for removing gasoline vapour from the " natural gas " which
escapes from many oil wells. The adsorptive power of
charcoal is greatly increased by lowering the temperature ;
and this fact is made use of for the purpose of producing
high vacua. The vessel to be exhausted is connected with a
tube containing charcoal cooled in liquid air. At this low
temperature, the air is very completely condensed on the
surface of the charcoal.
Charcoal also finds a very wide use for the decolorising of
liquids, e.g. sugar molasses.
The " pyroligneous acid " or aqueous distillate from wood
was until 1925 the main source of methyl alcohol (or methanol
as it is now frequently called), acetic acid and acetone, all of
which are important substances in industry. Methyl alcohol,
however, is now produced in very large amounts from
water-gas (p. 193), acetic acid is produced from acetylene
(Chap, xvn), and acetone is produced by a fermentation
process (Chap, xvn), as well as from ethyl alcohol and from
acetic acid. As a result of these developments, which well
illustrate how in chemical science and industry there can
be no standing still, the wood distillation industry has been
dealt a serious blow.
From a very early time, charcoal has been used as a fuel
1 Crude wood-spirit, which contains a number of substances besides
methyl alcohol, is extensively used in Great Britain for the purpose of
denaturing spirits of wine (ethyl alcohol).
124 CHEMISTRY IN THE SERVICE OF MAN
as well as in metallurgy, and in all the forests of Europe
the " coallier " or charcoal-burner was a well-known and
picturesque figure. Although most of the charcoal is now
produced in retorts, a certain amount is still produced by the
primitive, centuries-old and very wasteful method of the
" pit," a certain preference being shown by some industries
for such forest-burned charcoal. In constructing a pit, logs
uounesy oj " me limes.'
CHARCOAL-BURNING AT LONGHOPE, FOREST OF DEAN.
Making the chimney before piling up the lengths of wood.
of wood are built up in tiers round a central chimney or flue,
covered with shavings or brushwood, and cemented down
with earth or turf, to prevent access of air. A fire is lighted
in the central chimney, and the burning carefully watched
and adjusted, so as to prevent excessive combustion and to
bring about even " coaling." After the smoke has ceased
to escape, all the air vents are closed to exclude air, and the
mass is left to cool down. By this method, the heat of
MATTER, ENERGY AND EXPLOSIVES 125
combustion of part of the wood serves to carbonise the
rest.
Carbon black, lampblack, or soot, another form of amor-
phous carbon, is produced by the combustion, in a limited
supply of air, of coal-tar residues and also by burning
natural gas and methane against a cold surface. It is used
in the manufacture of printer's ink, Chinese ink, and boot-
Courtesy of" The Times."
CHARCOAL-BURNING AT LONGHOPE, FOREST OF DEAN.
The " pit," built in three tiers of cordwood round the chimney, being
covered with shavings and earth.
blacking. It is most extensively employed, however, in the
manufacture of rubber tyres, because when mixed with the
rubber it gives increased toughness, elasticity and durability.
By this means, a fourfold increase in the mileage of a
motor car tyre can be obtained.
The idea that a spontaneously occurring chemical change
126
CHEMISTRY IN THE SERVICE OF MAN
represents the conversion of so much potential energy into
other forms of energy, can perhaps be most vividly realised
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
Courtesy of " The Times."
CHARCOAL-BURNING AT LONGHOPE, FOREST OF DEAN.
The pit in action.
a volume which, at the temperature of the explosion, is,
perhaps, 15,000 to 20,000 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, was used by the inhabitants
of Constantinople in their defence of the city against the
Moslems, and, even as late as the thirteenth century, rapidly
burning mixtures of sulphur, pitch, naphtha and other
substances which " came flying through the air like a winged
MATTER, ENERGY AND EXPLOSIVES 127
long-tailed dragon, about the thickness of a hogshead, with
the report of thunder and the velocity of lightning/' were
used by the Moslems in the crusades. When and by whom
the first real explosive, gunpowder, was invented is unknown,
although the invention has frequently, but erroneously, been
attributed to Roger Bacon in the thirteenth century. During
the nineteenth century, more especially, man strove to dis-
cover new explosives 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 Crcy in 1346, when the guns " threw little balls
of iron to frighten the horses/' with the modern 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 charcoal
at the expense of the oxygen contained in the saltpetre. The
composition varies in different countries and according to
the use to which the explosive is to be put, but generally gun-
powder consists of about 75 per cent, of saltpetre, 10 per cent,
of sulphur, and 15 per cent, of charcoal. Although in modern
times great improvements have been made in gunpowder,
these improvements have been of a physical or mechanical
and not of a chemical nature. In the manufacture of black
powder, the constituents are finely ground, mixed together
and the mixture passed through a fine-mesh sieve of copper
or brass wire. To secure thorough mixing or incorporation,
the mixture, kept in a moist state, is ground in a mill under
heavy edge-runners. The cake so produced is broken up
into pieces and then subjected to a pressure of, perhaps, 400
Ibs. per square inch whereby a hard mass is obtained. The
press-cake is then granulated by passage between rollers
128 CHEMISTRY IN THE SERVICE OF MAN
with pyramidal teeth of different sizes, and the grains
polished or glazed in rotating wooden drums. Finally, the
gunpowder is dried by air at a temperature of about 40 C.
(104 F.). The violence of the powder as a blasting explosive
can be varied by altering the density and size of the grains.
Increase of density and coarsening of the grains make the
powder slower.
While still largely used in connection with the beneficent
operations of mining and also for pyrotechnic displays, gun-
powder is no longer employed as a propellant for military or
naval purposes. 1 Its use has been given up not only on
account of the large volume of smoke produced in the ex-
plosion, which by speedily hiding everything from view
prevents the effective use of quickfiring guns, but also be-
cause 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 of gun-cotton, in 1846, by CHRISTIAN
FRIEDRICH SCHONBEIN, Professor of Chemistry in the
University of Basle. Cotton consists, essentially, of the
chemical substance cellulose, which is, as we have seen
(p. 79), a 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 are
formed, the composition and properties of which depend
on the strength of the acid mixture and the temperature and
duration of reaction. The compounds so formed, strictly
called cellulose nitrates, are more popularly called nitro-
cellulose*. Since not only cotton but also purified wood
fibre or wood pulp and other vegetable fibres consist essen-
tially of cellulose, such materials can also be used, and are
to a certain extent used in the production of nitro-cellulose,
as we shall learn more fully in the following chapter. For
the production of explosives cotton is almost exclusively
1 It is, however, still used for the bursting-charge of shrapnel, for
filling the rings of time-fuses for shells, etc.
MATTER, ENERGY AND EXPLOSIVES
129
employed, and in its preparation and treatment great care is
exercised.
Gun-cotton, which is defined as a nitro-cellulose with
more than 12-3 per cent, of nitrogen and not less than 85
per cent, insoluble in a mixture of ether and alcohol (two
Courtesy of Imperial Chemical Industries Ltd. (Nobel Section).
TEASING COTTON PREPARATORY TO NITRATION.
volumes of ether to one of alcohol), is prepared from cotton
linters, or the short fibres which are left after the cotton
used for textile purposes has been removed from the cotton
seed. The linters, after being freed from dust, are boiled
with a solution of caustic soda (sodium hydroxide or
NaOH), in order to remove natural oil and non-cellulosic
matter, and then bleached. The bleached linters are then
opened in a teasing machine and subjected for a period of
about two and a half hours to the action of a mixture of
130
CHEMISTRY IN THE SERVICE OF MAN
nitric and sulphuric acids, an operation frequently carried
out in shallow, earthenware pans. After nitration, the waste
acid is allowed to run off at the bottom of the pan while
water is run on to a perforated plate which rests on
the top of the cellulose. The nitrated cotton is then very
thoroughly washed and boiled, to render it more stable.
Courtesy of Imperial Chemical Industries Ltd. (Nobel Section).
PANS FOR NITRATING CELLULOSE.
When ignited, loose gun-cotton burns with great rapidity,
but not so rapidly as to constitute an explosion. The mole-
cule of gun-cotton, however, which, as one 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 or lead azide is caused to detonate near
it, it suddenly decomposes and gives rise to a large 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
production of smoke.
As an explosive, gun-cotton possesses the very important
property that it can be used wet. This wet gun-cotton will
MATTER, ENERGY AND EXPLOSIVES 131
not take fire when a light is applied to it, but when sub-
jected to the shock of a fulminate of mercury or lead azide
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 disruptive effect of gun-cotton is very great by reason
of the rapidity with which the decomposition of the substance
takes place. Thus, whereas a couple of pounds of gun-
powder 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. For effective propulsion, it is necessary to have a rapid
and increasing push behind the projectile, not an instan-
taneous increase of pressure.
' Although gun-cotton cannot be employed as a propellant,
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.
Although gun-cotton dissolves only to a slight extent in a
mixture of ether and alcohol, nitro-cotton with a lower per-
centage of nitrogen dissolves completely, 1 yielding a liquid
well known under the name of collodion. If, then, gun-
cotton be mixed with a soluble nitro-cotton and the mixture
kneaded with ether-alcohol to form a paste, and if the paste
be then granulated by passage through suitable dies, gelatin-
like grains are obtained after the ether and alcohol have been
1 The solubility of nitro-cellulose can be greatly altered by treatment,
and a nitro-cellulose with high solubility can be obtained from a nitro-
cellulose with low solubility by heating the latter with water under
pressure.
132 CHEMISTRY IN THE SERVICE OF MAN
removed by volatilisation. Such gelatinised nitro-cotton is
widely used as a smokeless powder for naval and military
purposes in Europe and in the United States of America.
It was the first smokeless powder to be used for military
purposes. To render the material less liable to undergo
decomposition with time, a small amount of a stabiliser,
e.g. diphenylamine, is incorporated in it.
A further advance in the chemistry of explosives was made
by the Swedish chemist, ALFRED NOBEL. When glycerine,
which, as we have seen (p. 85), is readily obtained 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 substance, discovered by
the Italian chemist, SOBRERO, in 1847, and first manufactured
on a commercial scale in 1862 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 kieselguhr,
a fine earth composed of the siliceous skeletons of marine
diatoms, the explosive could be transported and handled
with comparative freedom from danger. 1 In this form
nitro-glycerine has been extensively used under the name of
dynamite, its explosion being brought about by means of a
fulminate of mercury detonator.
When about 8 per cent, of nitro-cotton is mixed with 92
per cent, of 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 substance which is
itself an explosive. Some of the most commonly used blast-
ing agents are the gelignites, formed by adding varying pro-
1 Wood -flour or wood-meal, burnt cork, charcoal and other materials
are also used as absorbents in place of kieselguhr.
" Vl L " r r ' v ' ; ll ^;^t'"'' !l ^"^
Courtesy of Imperial Chemical Industries Ltd. (Nobel Section).
BREAKING UP A LARGE CAST- IRON POT.
A large cast-iron pot which was to be broken up was filled with water
and a charge of blasting gelatin, submerged in the water, was exploded.
The upper picture shows the fountain of water following on the ex-
plosion ; the lower, fragments of the pot.
134 CHEMISTRY IN THE SERVICE OF MAN
portions of such materials as potassium nitrate, ammonium
nitrate, wood-meal, chalk, to the blasting gelatin.
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.). 1 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 insen-
sitive to shock and safe to handle. The " 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 gun-cotton is extensively employed as a high
explosive, more especially in torpedoes, other explosives
derived from the products of distillation of coal are em-
ployed in shells. Of these explosives the two most important
and most used are picric acid and trinitrotoluene.
When carbolic acid or phenol, to give it its scientific name,
is treated with a mixture of nitric acid and sulphuric acid
there is formed trinitrophenol or picric acid. As ordinarily
obtained, it is a faintly yellow crystalline substance, which
was long used as a yellow dye .for silk. As an explosive it
goes by various names, such as melinite, lyddite, dunnite,
pertite, and shimosite.
Picric acid, however, has now been largely superseded by
another explosive which is derived from the hydrocarbon
toluene, and is called trinitrotoluene, or T.N.T., or trotyl.
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,
1 Vaseline lowers the temperature of the explosion and so reduces the
erosion of the gun-barrel, and it also increases the stability of the cordite
when stored.
MATTER, ENERGY AND EXPLOSIVES 135
however, trinitrotoluene explodes with a violence not much
inferior to picric acid, but as the oxidation of the carbon in
the compound is by no means complete, dense black clouds
of carbonaceous matter are produced. In order to secure
more perfect combustion and, at the same time, to reduce the
amount of T.N.T. required, ammonium nitrate, a substance
containing a large proportion of oxygen, is now generally
added. In this way the British service high explosive, amatol,
a mixture of eighty parts of ammonium nitrate with twenty
parts of T.N.T., is obtained. A mixture of T.N.T. and
aluminium powder, known as tritonal, was used during the
war for filling the bombs known as " block busters/'
The compound, cyclonite y referred to by the Research
Department at Woolwich as R.D.X., is an explosive which
in blasting power and brisance is greatly superior to any other
explosive hitherto used for bursting charges. Cyclonite is
not produced from coal tar but from methanol (p. 193), now
manufactured mainly from water-gas. By the oxidation of
methanol there is produced formaldehyde (H-CHO) sold in
solution as a disinfectant under the name of formalin which
reacts with ammonia to form a compound known as hexamine.
By the action of concentrated nitric acid on this compound,
cyclonite (CH 2 -N-NO 2 )3 is obtained ; a compound in which
the CH 2 and the N'NO 2 groups are arranged alternately in
the form of an hexagonal " ring." A mixture of T.N.T.,
R.D.X. and aluminium powder, known as torpex, was used
during the war as the most effective under-water explosive
for the destruction of U-boats.
It is, one must remember, not merely or even mainly for
the purpose of strengthening man's arm in war that explosives
have found an application ; they have also, through their
use in mining and by rendering possible such great engineer-
ing works as the Suez Canal and the Panama Canal, and the
removal, in 1885, of the reefs known as Hell Gate in the
channel of the East River, New York, played an important
part in the peaceful progress of civilisation. Through the
136 CHEMISTRY IN THE SERVICE OF MAN
labours of chemists a wide range of explosives has been
obtained to satisfy the very varied demands of industry and
engineering ; and even in the piping times of peace, hundreds
of thousands of tons of explosives are produced for mining,
blasting and sporting purposes.
CHAPTER VII
CELLULOSE AND CELLULOSE PRODUCTS
WE have seen in a 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,
ministering 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, erroneously, that cellulose and
the other compounds belonging to that group were com-
pounds of carbon with water, and so the name carbohydrate
was applied to them. The different sugars, such as glucose
and sucrose (cane and beet-root sugar), and also starch and
a number of other substances, belong to the class of
the carbohydrates ; and 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 6 H 10 6 ).
The molecule of cellulose is very large and may be regarded
as built up of several hundreds, of molecules of glucose,
138 CHEMISTRY IN THE SERVICE OF MAN
C 6 H 12 O 6 , 1 formed into a chain by a process of condensation;
that is, by the elimination of a molecule of water between
each pair of glucose molecules. Thus :
OH HO O
\/ \/ \ / \x
C + C -> C C + H 2 O
/ \ / \ / \ / \
H H H H
Cellulose is therefore represented by the formula (C 6 H 10 O 6 ) W
where n is more than 100.
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 manu-
facture 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 later. Its great value for the manu-
facture 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.
The cotton fibre is to be regarded as made up of a bundle
of long-chain molecules, arranged parallelwise, with forces of
1 Represented diagrammatically thus
OH H
TT Q Q OH
/ c \ y c \
HO O C H
CH 2 OH
CELLULOSE AND CELLULOSE PRODUCTS 139
attraction holding these bundles together. It is on the
existence of long-chain molecules, packed closely side by
side, that the strength of a fibre depends.
Less than a hundred years ago, when the production of
paper was hampered by a Government duty, and before
education had created the present demand for cheap news-
papers and cheap books, paper was manufactured entirely
from cotton and linen 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 plant structures. Large
quantities of more or less pure cellulose, therefore, are pro-
duced at the present day from straw, various grasses (especi-
ally esparto grass), and from wood, for use in the different
industries of which cellulose is the basis.
Of these different sources of cellulose, wood is by far
the most important. Wood fibre consists mainly of a com-
pound of cellulose with lignone, encrusted frequently 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 this substance
has now been very largely replaced by calcium bisulphite
(or acid sulphite of lime), 1 the wood being boiled with
the liquor under a pressure of several atmospheres. Not
only is the wood fibre thereby broken up chemically with
production 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 ").
For the treatment of resinous woods, more especially, a
mixed solution of caustic soda and sodium sulphate is used,
the pulp so obtained being known as " sulphate pulp."
1 This substance is formed by passing sulphur dioxide into milk of
lime (suspension of slaked lime or calcium hydroxide in water).
140 CHEMISTRY IN THE SERVICE OF MAN
This pulp is employed in the manufacture of a strong
wrapping paper (Kraft paper).
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 is not 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, for the production of a
cheap paper. Owing to the presence of non-cellulosic
matter in the ground wood, this paper turns yellow in a
comparatively short time (owing to oxidation), and undergoes
disintegration. It is suitable, therefore, only for ephemeral
literature.
Of the paper at present manufactured, by far the largest
proportion is made from wood pulp.
For the manufacture of paper, the cotton rags, grass,
or crude wood pulp (" half stuff ") are disintegrated in
" potchers " and bleached by means of chlorine or bleach-
ing powder. The disintegrated fibres are then placed with
water in " beaters " where they are cut and frayed into short
fibrillae by means of rotating blades, so that they may felt
together better in the later process of paper-making. Dyes,
also, are added at this stage if a coloured paper is desired.
When the fibres have been sufficiently broken down, they
are suspended in water and run in a uniform stream 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
fibres is now carried between rollers which press out the
excess of water, and then between heated rollers in order to
dry the paper.
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
CELLULOSE AND CELLULOSE PRODUCTS 141
through solutions of alum and of rosin soap (p. 237), 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. In the case of finer papers,
the paper may be sized by passage through a solution of
Courtesy of A . Pirie & Sons, Ltd.
BEATERS FOR DISINTEGRATION OF FIBRES.
gelatin. Sometimes, also, powdered gypsum, white clay,
titanium oxide, 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 highly glazed surface being
obtained by calendering, or rolling between 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
Courtesy of A. Pirie & Sons, Ltd.
PAPER-MAKING MACHINE.
Upper ; wet end : Lower ; dry end.
CELLULOSE AND CELLULOSE PRODUCTS 143
resembling parchment (prepared skin of the sheep or she-
goat). Such parchment paper can also be prepared by im-
mersing 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 long ago as the seventeenth century, threads " re-
sembling silk " were being sold in England, and Dr. ROBERT
HOOKE, in 1664, put forward in his Micrographia the
perhaps but a fraafl pait of the fubftance, yet being fo highly impregnated
with the colour, as to be almoft black with it, may leave an impreffion
ftrong enough to exhibite the defir'd colour. A pretty kindc of artifi-
cial Stuff I have feen, looking almoft liketranfparcnt Parchment, Horn,
or Ming-glafs, and peihaps fbme fuch thing it may be nude of, which be-
ing traniparent, and of a. glutinous nature, and eaGly mollified by keep-
ing in water, as I found upon trial, had irnbib'd, and did remain ting'd
with a great variety of very vivid colours, and to the naked eye, it look'd
very like the fubftance of the Silk. And J have often thought, that pro-
bably there might be away found out, to make nn artificial glutinous
compofition, much refemblbg, if not full as good, nay better, then that
ExcrementjOr whatever other fubftance it be out of which, the Silk-worm
wire-draws his clew* If fuch a compofition were found, it were certain-
ly an eafie matter to find very quick ways of drawing it out ioto (mall
wires for ufe. I need not mention the ufe of fuch an Invemion,not the be-
nefit that is likely to accrue to the find er,they being fumciently obvious.
This hint therefore, may, I hope, give fbmc Ingenious inquifitive Perfon
an occafion of making ionic trials, which if fucceisfull, I have my aim, and
1 fuppofc he will have no occafion to be difplea*\i
PASSAGE FROM HOOKE'S Micrographia
144 CHEMISTRY IN THE SERVICE OF MAN
suggestion that it might be possible to make an " artificial
glutinous composition " resembling silk. This suggestion
was realised in 1883 by Sir JOSEPH WILSON SWAN, who was
the first to produce filaments by squirting solutions of nitro-
cellulose and the first to de-nitrate the filaments produced.
The incentive which led Swan to his invention was the
demand for a continuous filament for use in the recently
introduced electric light bulbs ; but Swan also soon realised
the possible uses of these filaments for textile purposes, and
gave them the name of " artificial silk."
Swan's process was adapted commercially by the French
chemist, Count HILAIRE DE CHARDONNET, who, in 1889,
exhibited in Paris a material which, in its general appearance,
imitated in a remarkable manner the fibre spun from the
glands of the silkworm. 1
Nitro-cellulose (cellulose nitrate), as we have seen, can,
when suitably prepared, be dissolved in 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 formed. By treating these threads with certain
solutions, e.g. a solution of sulphide of ammonium, the
nitrate groups (NO 3 ), to the presence of which the nitro-
cellulose owes its ready inflammability, are removed, and
one obtains a regenerated cellulose, the natural structure
of which has, however, been destroyed by the treatment to
which it has been subjected. Threads or filaments 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 com-
mercially successful manner.
It was, however, not long before chemists discovered
other methods of transforming cellulose into filaments and
threads resembling silk. We have already seen that cellulose
1 True silk belongs to a class of substances known as proteins, and
contains nitrogen as well as carbon, hydrogen and oxygen.
CELLULOSE AND CELLULOSE PRODUCTS 145
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 also obtained.
The method by which most of the artificial silk, or rayon,
as it is now called, is made at the present day, the so-called
viscose process, was invented by the English chemists,
C. F. CROSS and E. J. BEVAN. As raw material for this
process, wood pulp, prepared by the maceration and chemical
treatment of wood, is used. This pulp is treated with a
solution of caustic soda and then with the liquid called
carbon disulphide, whereby a thick syrup-like mass (viscose)
is obtained. By forcing this viscous material through minute
jets, or spinnerets, into a bath containing sulphuric acid,
sodium sulphate, zinc sulphate and glucose, the viscose
filament is coagulated and reconverted into cellulose. Silky
filaments are thus produced which can be spun into threads
or yarn suitable for weaving. Although, originally, the
popularity of rayon depended mainly on its lustrous appear-
ance, in which it is superior to natural silk, de-lustred rayon,
or rayon with a dull lustre, was introduced in 1926 and
rapidly gained popularity. To produce a rayon with dull
lustre, the viscose is forced through spinnerets into a solution
containing a white pigment (e.g. titanium oxide).
Although costing very much less than silk, rayon 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. So great,
in fact, has this field of usefulness already become that the
production of rayon in 1938 amounted to no less than
1,900,000,000 Ibs., about ten times the production of silk.
Another type of artificial silk has also come into use under
the name of celanese or acetate rayon. Unlike the viscose
146 CHEMISTRY IN THE SERVICE OF MAN
rayon, celanese does not consist merely of transformed
cellulose, but is a compound of cellulose with acetic acid,
cellulose acetate. A viscous solution of cellulose acetate in
acetone is forced through spinnerets and the acetone is
removed from the issuing filaments by means of warm air.
Celanese forms from eight to ten per cent, of the total pro-
duction of rayon.
When celanese is treated with a dilute solution of alkali,
it undergoes hydrolysis (p. 150); the acetate groups are
removed and the celanese is reconverted into cellulose. If,
at the same time, the fibre is stretched, so as to bring about
a favourable arrangement of the long-chain molecules, its
strength is so greatly increased that, weight for weight, it
is stronger than the strongest steel. Ropes made of this
regenerated and stretched cellulose (known as " fortisan ")
were used, during the war, for towing gliders carrying air-
borne troops.
While, in the early days of the rayon industry, the fila-
ments from the spinnerets were spun into yarn, now, nearly
half of the total amount of rayon produced is made into
staple fibre by cutting the filaments into short lengths, like
the fibres of cotton or wool. The staple fibre is then spun,
either alone or mixed with other natural or artificial fibres,
on a cotton or woollen mill, and a yarn obtained with which
the textile manufacturer can obtain novel and interesting
effects. Staple fibre, also, produced from de-lustred rayon
and specially crimped or curled, is used as a wool substitute.
Fibres which may be used as wool substitutes and which
possess the dyeing properties of wool in varying degrees are
also produced, under the name of rayolana, by impregnating
the viscose filaments with synthetic resins (p. 333) ; and to
other synthetic materials with silk- or wool-like properties,
reference will be made later (p. 358). These synthetic fibres
are used mainly in admixture with natural fibres, such as
cotton and wool, and are to be regarded not as substitutes
for silk and wool but as supplementary to these natural
CELLULOSE AND CELLULOSE PRODUCTS 147
fibres for the production of cheaper fabrics and new
effects.
One should not fail to realise that the invention of rayon
has not only given rise to an industry of great magnitude and
economic importance, but has also brought about social
reactions of a very marked character. By making a material,
having much of the attractiveness of silk, readily available
for textiles of varied character and use, for stockings and other
articles of apparel, a profound change has been effected in
the taste, outlook and way of life of large sections of the
community.
Viscose is used for the production not only of rayon but
also of a transparent cellulose film under the registered name
of Cellophane. From a slit pouring machine a continuous
band of viscose is formed which is then passed through a
salt and acid solution in order to decompose the viscose.
The sheet of transparent cellulose is then bleached with
hydrogen peroxide, washed, and dried in warm air. Thin
sheets of Cellophane are now much used for wrapping
foodstuffs and other materials, and also by druggists for
capping the stoppers of bottles. Placed in position while
wet, it shrinks greatly on drying and so fits tightly to the
bottle.
Cellulose acetate, also, is used not only as a thermo-
plastic material (p. 149) but also, in the form of sheets
reinforced with wire netting, as a substitute for glass, under
the names vimlite and windolite.
The artificial silks described in preceding pages must not
be confused with the lustrous material known as mercerised
cotton, so called after JOHN MERCER, an English calico
printer who, in 1844, found that, when cotton is acted on
by a solution of caustic soda, the naturally flat, twisted fibres
swell to a cylindrical form and become shorter. Forty-five
years later, in 1889, H. A. LOWE discovered that when the
cotton fibres are tightly stretched during their treatment with
caustic soda solution, so that they cannot shrink, they exhibit,
148 CHEMISTRY IN THE SERVICE OF MAN
after washing and drying, a silky lustre, due to the reflection
of light from the smooth surface of the fibre.
In the middle of last century, the supply of billiard balls
was threatened owing to a shortage of elephant tusks ; and
an American newspaper offered a prize of $10,000 for the
most successful ivory substitute. Working under this
incentive, two brothers HYATT, of Albany, N.Y., in 1869,
made use of the fact, discovered in 1865 by ALEXANDER
PARKES of Birmingham, that if camphor is added to a mixture
of nitro-cellulose and alcohol, a hard, horn-like material is
obtained which can readily be fashioned, while hot, into
articles of various shapes and forms. To this material the
name celluloid was given. 1 Although naturally of a clear
gelatin-like appearance, celluloid can easily be dyed 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 amber,
tortoise-shell, marble and agate. Light in weight and not
readily breakable, celluloid is used for the manufacture of
photographic films, combs, knife-handles, soap-boxes, and
other articles of common use too numerous to mention. It
is, however, a material the use of which is not altogether
free from danger, since the basis of celluloid is the highly
inflammable nitro-cellulose. It has, indeed, 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 focusing
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, dextrine, and
1 Soon after the introduction of celluloid a similar material was pro-
duced in England under the name xylonite.
CELLULOSE AND CELLULOSE PRODUCTS 149
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, when, mixed with
suitable plasticisers, yields a material called cellon or
lumarith, which resembles, and is even superio r to, celluloid
in its general properties, and is not inflammable: It is more
elastic than celluloid, is used as a substitute for gutta-
percha, vulcanite, etc., and is also used for making the
bristles of hair-brushes, for the production of the invitation
horse-hair of which ladies' hats are frequently made\ and
for the manufacture of cinematograph films. In the ivorm
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.
But we have not yet exhausted the uses to which this 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 used very
extensively for the upholstering of furniture and for other
purposes. It is widely used for the upholstery of motor
cars, for which purpose the world's total supply of leather
would be quite inadequate.
At the present time, also, nitro-cellulose is very extensively
employed for the production of collodion (a solution of nitro-
cellulose in a mixture of ether and alcohol), for use in phar-
macy and as a dip for incandescent mantles (p. in). It is
also used for the preparation of aeroplane dopes and of
lacquers and enamels for wood, leather and metal. For the
production of these lacquers and enamels, which are widely
used for the finishing of motor-car bodies, etc., the nitro-
150 CHEMISTRY IN THE SERVICE OF MAN
cellulose is dissolved in a suitable solvent, and to the solution
there are added a diluent, a gum or resin (dammar, mastic,
shellac, etc.), 1 a plasticiser and a pigment. The resin is
added in order to give gloss, hardness and impermeability to
the film, and the plasticiser, in order to prevent the film from
becoming too brittle. After application, the lacquer rapidly
dries and the film obtained is characterised by its hardness,
toughness and resistance to scratching and rubbing. The
production of satisfactory lacquers is a work of great com-
plexity, and success has been obtained only as the result of
prolonged research, deep knowledge and rigid scientific
control.
The introduction of these nitro-cellulose lacquers has
created a demand for a large number of solvents of different
volatility, such as ethyl acetate, acetone, butyl acetate, amyl
acetate, ethyl lactate, butyl lactate, etc., and for plasticisers
such as triphenyl phosphate, tricresyl phosphate, diethyl
phthalate. As a result of this demand, substances which
formerly were laboratory products of purely scientific
interest are now produced on a large scale for industrial
application.
It has already been stated that the cellulose molecule may
be regarded as built up of glucose molecules, with elimination
of water. It is found, therefore, that when cellulose is heated
under pressure with dilute acid, it undergoes hydrolysis, or
is hydrolysed, as it is said ; that is, water is taken up and the
molecule of cellulose is decomposed into its constituent
glucose molecules. In recent years this process has found
successful industrial application in the production of alcohol
from sawdust 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 six
or seven atmospheres. The cellulose is rapidly hydrolysed,
1 Synthetic resins of the type of bakelite (Chap, xvi) are also largely
used.
CELLULOSE AND CELLULOSE PRODUCTS 151
and the glucose formed passes into solution. In Switzerland,
the hydrolysis of the cellulose is carried out with cold, con-
centrated hydrochloric acid in vessels constructed of a
highly resistant material known as prodorite (a pitch cement) ;
and hydrolysis also takes place to a certain extent in the
process of producing sulphite pulp (p. 139)^ The glucose
solution obtained in these processes, after removal of the
acid, is subjected to fermentation (Chap, xvn), and alcohol
is formed. In view of the economic value of alcohol, the
process promises to become of increasing importance in the
future. In Sweden the alcohol produced from the sulphite
pulp liquors is used, mixed with petrol (75 per cent.), as a
motor fuel.
By the acid hydrolysis of wood there are also formed
acetic acid and a sugar known as xylose, C 5 H 10 O 5> which'
is suitable as a foodstuff for diabetics. Great possibilities
are thereby opened up for the development and economic
utilisation of forests and forest products.
CHAPTER VIII
METALS AND THEIR ALLOYS
CHEMISTS are accustomed to classify the elements into
metals and non-metals, and this grouping of the elements,
although not always sharply defined, is at least convenient.
Ordinarily, one thinks of a metal as being opaque and as
showing, in the compact state, a lustre, the so-called metallic
lustre ; and one thinks also of a metal as being a good or
fairly good conductor of heat and electricity. These pro-
perties serve by no means satisfactorily to define a metal or
to distinguish it from a non-metal, but we need not at present
trouble ourselves too much about definitions. There are
certain familiar substances which are spoken of as metals,
such as gold, silver, iron, copper, aluminium, zinc, lead, etc.,
and it is these substances that will now be discussed.
Certain metals, more especially gold, occur native or in
the free state, and it may therefore be supposed that it was
with such metals that primitive man first became acquainted.
Gold, probably, was the first metal known, and its natural
beauty and the ease with which it can be worked must have
attracted primitive man, as it has attracted men throughout
all ages, and have led to its use, at an early period, for pur-
poses of personal adornment. The beautiful gold jewellery,
bracelets, rings, etc., to be seen in the Museum at Cairo
show that the use of gold for ornamental purposes was
already well known in Egypt as early as about 3500 B.C.
Almost all the other metals, however, occur only in the
form of compounds from which the metal must be isolated,
and before these metals could be put to use, a knowledge of
how they could be extracted from their ores had first to
be gained.
152
METALS AND THEIR ALLOYS 153
The history of the development of human civilisation has
frequently been divided into three ages or epochs : the
stone age, the bronze age and the iron age ; and it has been
thought that these three periods followed each other suc-
cessively. This view is in harmony with what is doubtless
the case, that copper and bronze were known and widely
used before man had become acquainted with iron or had
learned how to extract it in quantity from its ores. There
was, however, much overlapping of the different " ages,"
and, among certain races, iron was in common use *at a time
when, among other races, bronze was generally employed.
At the present day, one may perhaps say that we are Uill in
the iron (or steel) age, although other metals are, year by
year, finding an ever-extending application. '
In ancient times, seven metals were known, and as thes'e
metals were thought by the alchemists to be affected by
and to derive their properties from the planets (including
the sun), the names of the planets were applied to the metals
which were also represented by the astronomical signs of the
planets, as shown in the following list :
Metal Planet Sign Metal Planet Sign
Gold Sun O Lead Saturn h
Silver Moon ([ Tin Jupiter 2J.
Copper Venus $ Quick- Mercury $
Iron Mars <J silver
Traces of these old designations are still met with, e.g.
lunar caustic (silver nitrate), but of the old names only one
remains in use, namely, mercury.
GOLD, SILVER AND PLATINUM
These three precious metals are widely used for cur-
rency, jewellery and scientific purposes. All occur in the free
state, and silver and platinum also occur as compounds
associated with other metals.
154 CHEMISTRY IN THE SERVICE OF MAN
Gold is very widely distributed, but is produced mainly
in South Africa (Transvaal), Russia (U.S.S.R.), the United
States of America and Canada. Although, in the past, much
gold was obtained from sands and alluvial deposits, most of
the gold is now isolated from gold-bearing rock. This rock
is crushed by means of " stamps " or heavy steel pestles, and
ground in rotary mills. 1 The finely crushed material is
washed over large plates covered with corduroy cloth, which
retains the heavy gold particles. After these have been
washed from the cloth and separated on a rocking table from
particles of other material, they are shaken in closed vessels
with mercury, and the amalgam so obtained is distilled.
The mercury passes off and the gold is left behind. The
sands from which the gold has for the most part been
separated are treated with a solution of sodium cyanide
which dissolves the gold. The cyanide solution is then run
into large vats and ribbons of zinc are immersed in the
solution. The gold is thereby caused to separate out, while
the zinc goes into solution.
Gold is a very malleable metal which can be rolled or
beaten out into leaves one ten-thousandth of a millimetre
(one two-hundred-and-fifty-thousandth of an inch) in
thickness, and can also be drawn into wires of extreme
tenuity. The purity or fineness of gold is generally expressed
in carats, pure gold having a fineness of 24 carats. Since
pure gold is too soft for use, it is alloyed or mixed with
copper or silver. British currency gold has a fineness of
22 carats, and consists of a mixture of 22 parts of gold with
2 parts of silver and copper, or 91-67 per cent, of gold, 2 per
cent, of silver, and 6-33 per cent, of copper. In Australia,
silver is used in place of copper. In the United States
currency gold consists of 90 per cent, of gold and 10 per
cent, of other metals. The finest quality of jewellery gold
is 1 8 carat gold, or a mixture of 18 parts of gold with 6
1 The method of extraction described here is that used in the Trans-
vaal, whence nearly a third of the world's annual production is derived.
METALS AND THEIR ALLOYS 155
parts of copper ; but lower qualities, especially 15 and 9
carat gold, are also employed. " White gold," now much
used for jewellery in place of platinum, is produced by
alloying gold with palladium or with nickel.
The best solvent for gold is a mixture of nitric and hydro-
chloric acids a mixture called by the alchemists, aqua regia.
A yellow substance, so-called " gold chloride," crystallises
from the solution. It is used for toning photographic prints.
Stiver is a metal which also occurs native, more especially
in Ontario, Canada ; but it is generally found as a sulphide
associated with lead or copper, and is produced mainly in
Mexico, the United States, South America and Canada.
Various methods of a more or less complex kind are em-
ployed for the extraction or recovery of silver from its ores.
Silver has long been prized as a jewellery metal on account
of its appearance, and it was also used very widely as a
currency metal. 1 Formerly, British sterling silver was an
alloy containing 7-^ per cent, of copper, while the silver
coinage of the United States contained 10 per cent, of copper.
Now, however, sterling silver contains only 50 per cent, of
silver, and is alloyed with 40 per cent, of copper, 5 per cent,
of nickel, and 5 per cent, of zinc. 2
Silver does not combine with oxygen at the ordinary
or even at higher temperatures and does not, therefore,
tarnish when exposed to pure air. The tarnishing which
takes place when silver is exposed to the air, especially of
large towns, is due to the presence of sulphur compounds
in the air and the formation of silver sulphide. Similarly,
" oxidised silver " is not oxidised at all, but " sulphidised "
by treatment with a solution of an alkaline sulphide. A film
of dark silver sulphide is thereby formed on the surface of
the metal.
Silver is the best conductor of heat and of electricity.
1 Its use for this purpose is now being abandoned.
2 Owing to the increase in the price of silver, the amount of silver in a
half-crown (two shillings and sixpence) was worth three shillings and
fourpence in 1920. The present alloy was adopted in 1927.
156 CHEMISTRY IN THE SERVICE OF MAN
On account of the fact that they are acted on by light,
silver salts, especially the chloride and bromide, are ex-
tensively employed in photography. The amount of silver
so employed is second only to that used for currency.
Platinum is a metal rather more costly than gold. Formerly
most of the world's supply of platinum was obtained from
Russia, where the metal was found in the region of the
Ural Mountains. At the present time, however, more than
half of the total world's production of platinum and the
platinum metals (palladium, iridium, rhodium) comes from
Canada and less than a quarter from Russia. South Africa,
where there are extensive deposits of platiniferous ores, and
the Republic of Colombia, South America, also produce
notable amounts of these costly metals.
Platinum is a malleable and ductile metal, much valued as a
jewellery metal for the setting of diamonds and other gems ;
and it is largely used in chemical laboratories, on account
of its high melting-point and its resistance to attack by
chemicals. It finds, also, considerable application in industry
as a catalyst, as will be discussed in the following chapter.
Owing to the fact that platinum expands and contracts
with change of temperature at nearly the same rate as
glass, a wire of this metal can be melted into glass and the
latter does not crack on cooling. For this reason, platinum
wire used to be employed in making connection between
the filament of an electric incandescent lamp and the fittings
outside. Owing to its high price, however, it is no longer
used for this purpose, its place being taken by the nickel-
iron alloy, platinite (p. 161). The saving thereby effected
has been estimated at about 1,000,000 per annum.
IRON AND STEEL
Highly valued as gold and silver may be for their beauty
and for their use as jewellery and currency metals, and
important as the former may be regarded as a basis of values
METALS AND THEIR ALLOYS
IS7
in international exchange, these metals are of small import-
ance in our present-day civilisation compared with the metal
iron. In the words of Rudyard Kipling :
' Gold is for the mistress silver for the maid
Copper for the craftsman cunning at hu trade'
1 Good ! ' said the Baron, sitting in his hall,
' But Iron Cold Iron- is master of them all '
Yes, master both in peace and in war. We still live in the
" iron age," and iron constitutes more than 90 per cent, of
the world's total tonnage of metals.
Although the element iron forms about 5 per cent, of the
solid crust of the earth, so far as we know it, it occurs, with the
exception of small quantities of meteoric iron, only in the form
of compounds, more especially
with oxygen and with sulphur.
Of these, the most important are
haematite (Fe 2 O 3 ), limonite, a
hydrated oxide (2Fe 2 O 3 , 3H 2 O),
magnetic iron ore (Fe 3 O 4 ), and
the sulphide, iron pyrites (FeS 2 ),
the well-known brass-like mineral
sometimes called " fool's gold."
This mineral is never used for
the production of iron, but large
quantities are employed in the
manufacture of sulphuric acid.
Various red and brown pigments,
ochres, are prepared from purified
haematite and limonite.
The extraction of iron from its
ores (generally the oxide, Fe 2 O 3 ,
or the carbonate, FeCOo) is
. , ^ . ., L7 . ' FIG. 15. DIAGRAM OF BLAST
carried out in the blast furnace, FURNACE.
a tall structure with a roughly
egg-shaped interior (Fig. 15). After fires have been lit and
the furnace has been heated up, a mixture of ore, coke (or
158 CHEMISTRY IN THE SERVICE OF MAN
coal), and limestone (calcium carbonate) is introduced from
the top, and a blast of hot air is blown in through pipes or
" twyers " (French, tuyeres) at the bottom of the furnace.
In this way a high temperature is produced ; the coke
burns and gives rise to carbon dioxide, and this gas in
contact with the red-hot coke passes into carbon monoxide,
which ascends through the hot mass, combines with the
oxygen of the iron ore and so sets free the metal. At
the high temperature of the furnace, the metal melts and
flows down to the bottom, and at the same time the lime
formed by the decomposition of the limestone combines
with the silicates (clay) added to or present as impurities
in the iron ore, to form a glass-like material or slag. This
likewise flows in the molten state to the bottom of the furnace,
where it floats on the surface of the molten iron. From
time to time the slag is removed and the molten iron run
off into moulds, where it solidifies and forms pig iron.
The slag which is obtained from the blast furnace and which
has been formed by reaction between the limestone added to
the ore and the clay (a hydrated silicate of aluminium) with
which the ore is generally associated, is used in the manu-
facture of Portland cement, which consists of a mixture of
calcium silicate and calcium aluminate (p. 190). This cement
when mixed to a paste with water has the property of setting
to a hard mass even under water, and is therefore of great
value for the construction of piers or other engineering works
under or in contact with water. The carbon monoxide, also,
which escapes in large quantities from the top of the blast
furnace is made use of, partly for burning in furnaces to
heat the air of the blast, and partly for the production of
power in gas engines.
Pure iron is never used industrially, and all commercial
forms of iron are mixtures of iron with larger or smaller
amounts of other substances. The three main kinds of
commercial iron are cast iron, wrought iron, and steel, and
of these, the first is the least pure form of iron. Cast iron
METALS AND THEIR ALLOYS 159
is essentially the iron as it comes from the blast furnace,
and contains generally from 2 to 5 per cent, of carbon, much
of it in the form of graphite, together with other impurities,
such as silicon, sulphur and phosphorus, in amounts de-
pending on the ore employed. It is a hard but brittle form
of commercial iron.
Ordinary cast iron is readily attacked by dilute hydro-
chloric and sulphuric acids, but the rate of attack can be
reduced to a very remarkable extent by increasing the
proportion of silicon. Thus, ware made of a cast iron con-
taining from 12 to 19 per cent, of silicon (e.g. tantiron,
duriron, ironac, narki) is so acid-proof that it can be used
for the evaporation of sulphuric acid. Such cast iron, how-
ever, is extremely brittle.
Wrought iron is the purest form of iron used industrially,
and is obtained by strongly heating pig iron in a furnace
along with haematite. This oxide oxidises the carbon and
silicon, as well as any phosphorus and sulphur which may
be present. Wrought iron is soft and fibrous in structure,
and is also tough and malleable, so that it can readily be
worked, even at the ordinary temperature.
Steel, by far the most important form of commercial iron,
is not a definite substance ; there are many different kinds
of steel, all of which are alloys of iron with other substances.
Ordinary steels are essentially alloys of iron and carbon, the
amount of carbon varying from o-i to 2-0 per cent. The
carbon is present in the form of a compound with iron
known as cementite, Fe 3 C.
Steel is produced either by the Bessemer or, generally,
by the Siemens-Martin open-hearth process, the aim in
either case being to remove, by burning or oxidation, the
impurities present in pig iron, and more especially the
sulphur and phosphorus, the presence of which is very
detrimental to the steel. In the Bessemer process, the
oxidation is effected by blowing air through the molten
metal, and in the open-hearth process by the addition of
l6o CHEMISTRY IN THE SERVICE OF MAN
oxide of iron or haematite. When phosphorus is present in
the pig iron, the furnace is lined with magnesite (magnesium
carbonate) or with dolomite (double carbonate of calcium
and magnesium), with which the oxidised phosphorus com-
bines to form a phosphate known as basic slag. This is
largely employed as a phosphatic manure in agriculture.
Besides possessing a much greater tensile strength than
cast or wrought iron, steel is characterised by the fact that
it can be hardened by heating to a fairly high temperature
and then cooling in oil or in water. The process is known
as tempering, and the temper (hardness, elasticity, etc.)
produced in the steel depends not only on the composition
but also on the temperature to which it is heated and the
rate at which it is cooled down. According to the treatment
employed, the highly elastic steel of the watch-spring or the
hard steel of the cutting tool can be obtained.
The effect of adding other substances to steel has been
the subject of intensive investigation by metallurgical
chemists, and as a result many new steels possessing distinct
and valuable properties have been introduced into the
service of man. The addition of chromium, for example,
gives hardness to steel, and thus by the addition of about
2 per cent, of chromium one obtains chrome steel, which is
employed for steel tyres, ball bearings, files, rock-crushing
machinery and armour plate. By adding a small amount of
nickel to the chrome steel, greater elasticity is given. " Stain-
less steel," which does not rust or tarnish in contact with food
or fruit acids, is a steel containing from 12 to 15 per cent, of
chromium. It is extensively used for the manufacture of
table cutlery. " Staybrite " steel, containing about 18 per
cent, of chromium and about 8 per cent, of nickel, is highly
resistant to the corrosive action of sea- water, acids, etc., and
is finding increasing use in chemical industry and also for
many articles of domestic utility.
Addition of nickel to steel imparts hardness and elasticity,
and nickel steel is therefore used for armour plate, propeller
METALS AND THEIR ALLOYS l6l
shafts, etc. When the percentage of nickel is greatly in-
creased, steels having very valuable and special properties
are obtained. Thus, invar, a steel containing 36 per cent,
of nickel and only 0-2-0-5 per cent, of carbon, has a negligible
coefficient of expansion throughout the ordinary range of
temperature variation. It is therefore used for the manu-
facture of measuring rods, surveyors' tapes, instruments of
precision, and the pendulums of clocks. A similar alloy,
elinvar, is used for the balance spring of watches, because its
coefficient of elasticity and, therefore, the control which the
spring exerts, do not alter with the temperature. Platinite,
similarly, is a nickel steel containing 46 per cent, of nickel.
Its coefficient of expansion, which can be varied by slightly
varying its composition, is practically the same as that of
glass, and so wires of platinite may be sealed into glass.
The alloy consisting of 53-8 per cent, of iron, 29 per cent,
of nickel, 17 per cent, of cobalt, and 0-2 per cent, of man-
ganese has a coefficient of expansion (4Xio~ 6 ) almost
identical with that of hard glass. This alloy is therefore very
useful for sealing into glass for electrical purposes.
When the amount of manganese, which is normally present
in small amounts in all steels, is increased up to, say, 9-14 per
cent., a very hard, tough steel is obtained, which is exten-
sively used for rock-crushing machinery, switch-points on
railways, burglar-proof safes and steel helmets. As this
steel is also non-magnetic, it is used in the construction of those
parts of ships which are in the neighbourhood of the compass.
As a cutting tool, ordinary high-carbon steel is quite
satisfactory so long as the work is carried out at such a rate
that the temperature does not greatly rise ; but it is useless
for the high-speed cutting of metals, when the cutting tool
may become red-hot. Under these conditions, ordinary steel
speedily loses its hardness. It was, however, found that by
the addition of tungsten or of molybdenum to a chrome steel,
an alloy was obtained which retained its hardness even at a
red heat. Such high-speed tool steel, which contains, say, o6
1 62 CHEMISTRY IN THE SERVICE OF MAN
per cent, of carbon, 4 per cent, of chromium, 14-20 per cent,
of tungsten (or 5-6 per cent, of molybdenum), and sometimes
also about i per cent, of vanadium, is therefore a material
of the very highest value in modern engineering practice.
When exposed to moist air, iron readily undergoes oxida-
tion or rusts. When used, therefore, in constructional work,
protection of the metal by frequent painting is necessary.
In other cases the metal may be coated with zinc (galvanised
iron), or with tin (tinplate).
Tungsten, which is obtained from the mineral wolfram,
is a metal which fuses only at a very high temperature. It
finds a very widespread use in metal filament electric lamps.
Tungsten carbides (compounds of tungsten and carbon),
alloyed with small amounts of cobalt, known as carboloy, are,
on account of their diamond-like hardness, superior to
tungsten steels for the high-speed cutting of metals.
COPPER AND NON-FERROUS ALLOYS
Copper is one of the metals with which man earliest
became acquainted, and the copper mines of Sinai were
worked as early as 5000 B.C. Its name is derived from the
Latin, ces cyprium, later cuprum, so called because in Roman
times it was largely obtained from the island of Cyprus.
Although copper occurs native, more especially in the
region of Lake Superior, it is mainly from its compounds,
the sulphide and carbonate, that the metal is at present
extracted. It is produced in large quantities in the United
States, Chile, Northern Rhodesia and the Belgian Congo.
The chief industrial, use of copper is for the construction
of wire and cable for the conduction of electricity ; and
since the conductivity, which is inferior only to that of silver,
is greatly diminished even by small amounts of impurity,
the metal, as extracted from its ores, must be refined or
purified. This is now carried out by electrolysis, so-called
electrolytic copper being obtained (p. 262).
METALS AND THEIR ALLOYS l6j
In association with other metals, copper gives rise to a
number of alloys, some of which, the brasses, find a very
widespread use. Brass is an alloy of copper and zinc, and
brasses with different properties are obtained by varying the
Courtesy ofH. Moore and S. Beckinsale.
SEASON-CRACKING OF BRASS.
proportions of the two metals. Brasses containing about
30 per cent, of zinc are among the most important, and are
used for castings and for cartridge cases. A brass containing
40 per cent, of zinc and known as Muntz metal is used in
sheathing ships on account of its resistance to corrosion.
164 CHEMISTRY IN THE SERVICE OF MAN
Dutch metal is an alloy containing about 20 per cent, of
zinc.
Brass and certain other alloys which have been subjected
to mechanical stress by being hammered, drawn, or pressed,
are liable to undergo what is called " season-cracking."
Thus, hard-drawn tubes, cartridges cases, etc., may crack
some time after they have been made, more especially when
exposed to an atmosphere in which traces of ammonia are
present. This liability to crack may, however, be removed
by heating the metal to a temperature of 200 to 300 C.
(392 to 572 F.). At this temperature the internal stresses
are relieved but the hardness of the metal is not de-
stroyed.
Bronzes are alloys of copper and tin, but they sometimes
also contain zinc. Gun metal is a bronze containing from
8 to 12 per cent., and bell metal a bronze containing from
12 to 24 per cent, of tin. Bronze coinage contains 4 per
cent, of tin and i per cent, of zinc ; while phosphor-bronze,
which is widely used for taps, valves, etc., where corrosion
has to be avoided, contains varying proportions of copper,
tin, lead and phosphorus.
An alloy consisting of copper and nickel (68 per cent.),
known as monel metal, has proved of great value on account
of its general resistance to corrosion and to the action of
sea-water. It is extensively used for condenser tubes in
steamships. Losses due to corrosion have thereby been
greatly reduced. The alloy, consisting of 54 per cent, of
copper, 45 per cent, of nickel, and i per cent, of manganese,
is used for decorating and ornamental metal work under the
name silveroid.
When exposed to the action of moist air, copper becomes
coated with a green-coloured, basic copper carbonate,
called verdigris j 1 and the metal readily dissolves in nitric
acid with formation of copper nitrate. Copper sulphate, the
1 In the neighbourhood of towns, the patina which forms on copper
is mainly a basic copper sulphate.
METALS AND THEIR ALLOYS 165
best known salt of copper, crystallises from solution in deep-
blue coloured hydrated crystals, having the formula CuSO 4 ,
5H 2 O, and known popularly as bluestone. When added even
in small amount to water, it prevents the growth of algae.
A mixture of copper sulphate solution and milk of lime
(slaked lime or calcium hydroxide) is , largely used, under
the name of Bordeaux mixture, for spraying fruit trees and
bushes, especially vines, to protect them against insect and
fungoid pests. This is the main use to which copper sulphate
is put.
The metal Nickel, ores of which occur mainly at Sudbury
in Ontario, is purified by the Mond process. When carbon
monoxide is passed over nickel at a temperature below
100 C. (212 F.), combination takes place and a volatile
liquid known as nickel carbonyl is obtained. On heating the
vapour of this compound, decomposition takes place ; pure
nickel is deposited and carbon monoxide is regenerated, and
can be used for the purification of a further quantity of metal.
When in a coherent form, nickel is a hard, white, lustrous
metal, and is used for the electrodes of sparking plugs for
motor-car engines, etc. It is highly resistant to the action of
the atmosphere, and for this reason it is used for protecting
iron or steel from rust, the metal being deposited by electrolysis
[nickel plating). Before being plated with nickel, iron or steel
is generally plated with copper.
Nickel is extensively employed as a constituent of many
important alloys. Besides those to which reference has
already been made, one may mention white metal or German
silver, an alloy of copper, nickel and zinc, which is used as
a basis for silver-plated ware, and nichrome, an alloy of
nickel and chromium with about 23 per cent, of nickel.
This alloy, the life of which can be greatly increased by the
addition of cerium (up to 1-2 per cent.), is widely used as
resistance wire in electric heaters. Nickel currency alloy is
an alloy of nickel and copper containing about 25 per cent,
of nickel.
1 66 CHEMISTRY IN THE SERVICE OF MAN
Permalloy or Mumetal is a nickel-iron alloy containing
about 78 per cent, of nickel. It possesses a high value of
what is known as magnetic permeability, and if a sub-
marine cable is sheathed with permalloy, attenuation and
distortion of the signals are eliminated. By this means, it
has been possible to increase the rate of cable communication
from 300 to 1500 signals per minute.
Chromium, which, as has been mentioned, forms a con-
stituent of a number of valuable alloys and is now extensively
used for the plating of other metals, is obtained by reducing
its oxide with aluminium as in the thermit process (p. 72).
It is harder than nickel and more resistant to atmospheric
action.
Mercury, the heavy, liquid, lustrous metal, the well-
known properties of which lend to it a peculiar fascination,
is extracted from the naturally-occurring compound, mer-
curic sulphide (HgS) or cinnabar, a substance which, when
ground, yields a powder of a bright-red colour (vermilion).
When cinnabar is strongly heated in air, the sulphur combines
with the oxygen to form sulphur dioxide, and the mercury is
vaporised. By condensing the vapour in cold chambers, the
liquid metal is obtained. It is widely used in the construc-
tion of thermometers and barometers. Its alloys with other
metals are called amalgams.
Mercury gives rise to two classes of salts, known respec-
tively as mercurous and mercuric salts. Mercurous chloride
(Hg 2 Cl 2 ) or calomel is used in medicine and mercuric chloride
(HgCl 2 ) or corrosive sublimate, a corrosive poison, is used
as a germicide.
Tin is one of the metals which were known in ancient
times, its alloys with copper constituting one of the earliest
known alloys of which we have knowledge, namely, bronze.
At least as early as 1000 B.C. the great traders of antiquity,
the Phoenicians, obtained this metal from the tin mines
of Cornwall, where it was found in the form of its oxide,
known as tinstone or cassiterite. To this fact is due the old
METALS AND THEIR ALLOYS 167
name of Cassiterides or Tin Islands applied to Britain.
For a long time the whereabouts of the Cassiterides remained
known only to the Phoenicians, and provoked much anxious
curiosity on the part of the Romans. So highly, however,
was the secret prized that it is recounted that Phoenician
sailors, on being followed by a Roman ship, while on their
way to Cornwall, ran their ship ashore rather than betray
the position of the valuable tin mines.
Now the glory of the Cornish tin mines has departed.
More important deposits have in modern times been found
in other parts of the world, chief amongst these being those
at Perak and Selangor (Malay States), in Bolivia, Nigeria,
Siam, and in the islands of Banca and Billiton in the Dutch
East Indies. Little, if any, tin is now mined in Cornwall.
Tin is a metal of manifold uses. Its resistance to atmo-
spheric attack has led to its use for coating iron and steel as
a protection against rusting. Tinplate, used for making con-
tainers, " cans " or " tins," for biscuits, preserved foods, etc.,
is made by dipping steel sheets in molten tin. The malle-
ability of the metal, owing to which it may be rolled out into
thin leaves or foil, has also led to its use as a wrapping for
chocolate and other materials. So-called silver paper is not
silver at all, but the much less valuable metal tin.
In association with other metals tin forms part of a number
of alloys. Thus there are known bronze (copper and tin) ;
Britannia metal and the Babbitt metals (tin, antimony, and
copper) used for bearings of engines ; pewter and solder
(tin and lead).
Except during the warmer summer months, ordinary
lustrous tin, or white tin, is not in a really stable condition,
but at all temperatures below 13 C. (about 55 F.) is liable
to undergo change and pass into a less dense form known
as grey tin. At ordinary temperatures this change takes
place with extreme slowness, and may, indeed, not take
place for centuries ; and the change is retarded by the
presence even of traces of bismuth, lead, antimony, or
1 68 CHEMISTRY IN THE SERVICE OF MAN
cadmium. At very low temperatures, however, and even
during severe winters in European countries, the change
may occur with considerable rapidity, and is accelerated by
traces of aluminium, zinc, cobalt and manganese. Generally,
the conversion of white to grey tin takes place in spots or
patches, and owing to the lower density of grey tin, wart-
like powdery growths are formed, the appearance of which
on the surface of the bright metal has earned for the trans-
formation the name of tin plague. In Fig. 16, is shown a
picture of a medal, dated 1692, suffering from tin plague.
This " plague," moreover, is contagious, for the conversion
of white tin to grey tin is stimulated and accelerated by
contact with the latter. All articles of tin, organ pipes,
medals, pewter pots, etc., are liable to suffer from tin plague,
and the results may sometimes be disastrous.
Zinc occurs in many countries, mainly in the form of its
sulphide, known as zinc blende, some of the most important
deposits being found in the United States, in British Columbia
and at Broken Hill, Australia. The zinc is generally associated
with other metals in the ore, so that the latter has first to be
subjected to a process whereby the zinc ore is concentrated.
The zinc concentrate is then treated for the extraction of the
metal, which in the crude state is known as spelter.
Zinc is a bluish-white metal, the main uses of which are
for the production of brass and for galvanising iron. It is
also used in the construction of Leclanch and dry cells.
Oxide of zinc is used in surgical dusting powders and oint-
ments and as a pigment under the name of zinc white ; and
a mixture of zinc sulphide and barium sulphate is employed
as a pigment under the name of lithopone.
Lead is a heavy metal which has been known and used
from the earliest times and which also finds wide application
at the present day. Owing to its resistance to atmospheric
attack and to the action of acids, this metal is employed for
roofing purposes, for sulphuric acid plant, for lining vats
in which chemical processes are carried out, etc. Its most
METALS AND THEIR ALLOYS
169
Courtesy of Prof. E. Cohen.
FIG. 1 6. MEDAL SHQWJNQ TIN PLAGUE.
1 70 CHEMISTRY IN THE SERVICE OF MAN
extensive single use is in the manufacture of storage batteries.
Lead is so plastic that it can be squirted, under pressure,
through dies into the form of rods and pipes, and lead pipes
have been used from very early times for the conveyance of
water. Water containing carbon dioxide in solution attacks
lead fairly readily, but this action is checked by the presence
of carbonates or sulphates of calcium and magnesium. Since
these salts are present in what is called " hard " water
(Chap, xi), it follows that hard water attacks lead to a much
less extent than distilled or than a soft moorland water.
Owing to the fact that lead in solution is poisonous, the
resistance of this metal to the action of water is of great
importance in connection with the use of lead pipes for the
conveyance of drinking water. Where the water of a town's
supply is very soft, it is necessary to " harden " it somewhat
by the introduction of small quantities of lime.
Lead hardened by the addition of a small amount of
arsenic is used in the manufacture of shot, and lead haf dened
by the addition of antimony finds use as type metal. Alloys
of lead, tin and bismuth, or lead, tin, bismuth and cadmium,
are used as fusible metals, some of which melt considerably
below the boiling-point of water.
Lead combines with oxygen to form a number of oxides,
the most important of which are litharge (PbO), red lead
(Pb 3 O 4 ) and lead dioxide (Pb0 2 ). Red lead is extensively
used in the production of " crystal " glass (Chap xi), as a
plumber's cement, and as a pigment, minium. Lead dioxide
(or lead peroxide as it is sometimes called) forms the material
of the positive plate of the lead storage cell (Chap. xii).
Another very important compound of lead is white lead,
a so-called basic carbonate of lead having the composition,
2PbCO 3 , Pb(OH) 2 . In the production of this pigment, lead
plates are supported in earthenware pots, at the bottom of
which is a layer of acetic acid. The pots are placed close
together, hundreds of them, on a layer of spent and fer-
menting tanner's bark, spread on the floor of the building.
METALS AND THEIR ALLOYS 1 71
The first tier of pots is covered by wooden boards on which
a layer of tanner's bark and a second tier of pots are placed ;
and so on, tier above tier of pots, containing plates of lead
and acetic acid. As the bark ferments, heat is liberated and
carbon dioxide is evolved. The lead is acted on by the
vapour of the acetic acid and forms lead acetate, and this
then reacts with the carbon dioxide to form the basic lead
carbonate. In twelve or thirteen weeks the whole of the
metal is converted into white lead.
Although white lead is valuable as a pigment on account
of its covering power, it suffers from the disadvantage that
when exposed to air containing sulphuretted hydrogen, it
becomes dark owing to the formation of black lead sulphide.
The white pigment, titanium white (titanium oxide), which
has a high opacity, does not darken in sulphurous air and
has a lower density than white lead, is now largely used.
Certain other metals, e.g. magnesium and aluminium,
will be discussed at a later point (Chap. xn).
CHAPTER IX
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, marked the
beginning of a new era in chemical science. After that time,
the activities of chemists were directed in an increasing degree
to the preparation and to the 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 com-
pounds 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 pre-
paration of dyes, drugs, perfumes, and many 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 success, chemical
reactions were regarded entirely or mainly from the material
point of view, from the point of view of the substances
undergoing change and of the substances produced by the
172
VELOCITY OF REACTIONS AND CATALYSIS 173
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
products 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 questions 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 one 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 de-
velopment and success of which depend on dynamical
investigations.
When, in the thirteenth century, the great Dominican
monk and Bishop of Regensburg, ALBERTUS MAGNUS
magnus in magia naturali, maior in philosophia, maximus in
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 sub-
stances. 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, electrical in nature, 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 sub-
stances when thereby potential energy can be converted
into work. Chemical affinity, it should be noted, does not
174 CHEMISTRY IN THE SERVICE OF MAN
give an explanation of chemical change ; it is, rather, a
measure of the work done by a system when it undergoes
change.
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 are great differences in
the rates 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 important is the concentration
of the reacting substances, that is, the amount of the sub-
stances in a given volume. We shall be able to understand
this more readily if we fix 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 (p. 273), 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
molecules 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. Suppose that the number of B molecules 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
VELOCITY OF REACTIONS AND CATALYSIS 175
with it, and the rate of reaction will therefore be twice as
great as it was originally. Similarly, if the Concentration not
only of the B molecules, but also of the A molecules be
doubled, 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 con-
centrations 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.
The velocity of chemical change is also very greatly
influenced by the temperature, a fact to which we have
already alluded (p. 66). Although the speed of different
reactions is affected in a different degree by temperature,
it may be taken as a convenient approximation that the
speed of a reaction is doubled by raising the temperature
10 C. (18 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 melting-point
of ice, that is at o C. (32 F.). At 100 C. (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 200 C. (400 F.), 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 200 C., would
need, at o C., 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.
A further very important result which has followed from
the dynamical study of chemical reactions is the recognition
of the fact that chemical changes are reversible, and that the
176 CHEMISTRY IN THE SERVICE OF MAN
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
(Iron Iron oxide^i
i of hydrogen Hydrogen J
r
I Oxide <
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, and 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, one can cause reaction to take place in whichever
direction one pleases. Suppose, now, that the experiment is
arranged in such a way as to prevent the removal of the
hydrogen or of the steam, as can be done by heating all four
substances together in a closed vessel, then it will be found
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, in general, also be altered. By raising or lowering the
temperature the one or the other reaction can be caused to
VfcLUUllY U* KEAUllUJNS AJND UA1AJLYS1S IJJ
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. 1
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 has been 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 con-
sideration.
In the early decades of last century a number of pheno-
mena were observed, which, although isolated and apparently
unconnected, all possessed one common characteristic,
namely, that the rate at which a chemical change took place
was markedly increased by the addition of certain substances
in minute, sometimes in almost infinitely minute, amount.
Owing to such additions, it was found, substances which
seemed under the particular conditions to be without action
on each other, reacted with appreciable, sometimes even
with great, readiness. From the magnitude of the result
produced, it was evident that the foreign substance could not
enter into the reaction in the ordinary way ; but, as the
1 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 accompanied by an absorption
of heat. When the temperature is raised, the latter reaction, the reaction
accompanied by absorption of heat, is favoured, whereas lowering the tem-
perature favours the reaction which takes place with evolution of heat. Only
when no heat effect accompanies chemical change is the equilibrium
unaffected by change of temperature.
178 CHEMISTRY IN THE SERVICE OF MAN
Swedish chemist, BERZELIUS, pointed out, the substance
which was added appeared to act merely by 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, in 1838, 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 phenomenon of catalysis, of which the number
of cases observed rapidly increased during the nineteenth
century, was regarded by chemists, as Gulliver was regarded
by the learned men of Brobdingnag, as a lusus naturce ; it
was relegated to the realms 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 measuring
the rate of chemical change, that the phenomenon of catalysis
and the behaviour of catalysts began to form the subject of
systematic investigation. For a long time now, the energy
of many workers has been directed along this line of in-
vestigation, 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 has already been indicated, one of the most striking
features of catalysis is the magnitude of the effect produced,
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 oxygen, the two
gaseous substances by whose combination water is formed,
are heated together, they combine, and if the temperature is
sufficiently high, say about 600 C. (ni2F.), the com-
bination takes place with explosive violence. But this occurs
VELOCITY OF REACTIONS AND CATALYSIS 179
only when a trace of moisture is present in the gases. If the
last traces of moisture are removed from the gases by pro-
longed contact with the substance known as phosphorus
pentoxide (obtained by burning phosphorus in air), a sub-
stance which combines with the greatest avidity with water,
the mixture of hydrogen and oxygen can then be heated
even to a temperature of nearly 1000 C. (1832 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, have 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.
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 conception of them.
In order, however, 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 sodium sulphite or sulphite of soda
(Na 2 SO 3 ) in water, the oxygen of the air slowly oxidises the
sulphite of soda to sulphate of soda or sodium sulphate
(Na 2 SO 4 ). By the addition of certain 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 bluestone 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 ! Even water which has
remained in contact with metallic copper for three-quarters
l8o CHEMISTRY IN THE SERVICE OF MAN
of a minute, contains sufficient copper to show a notice-
able effect. One is, however, so accustomed to judge of the
importance of a 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 example 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.
Not only may catalysts increase the velocity of a chemical
change, they may also decrease it. That is, we may have
negative as well as positive catalysis. The oxidation of a
solution of sodium sulphite by oxygen is, as we have learned,
accelerated by copper salts, but it is retarded by tin salts ;
and it is retarded also by certain alkaloids, e.g. nicotine.
Even a puff of tobacco smoke (containing nicotine) through
the solution of sodium sulphite produces a detectable re-
tardation of the oxidation. The occurrence of negative
catalysis is frequently of great importance because it becomes
possible to retard processes of decomposition and so to
stabilise a substance by means of suitable catalysts. Thus,
certain explosives are stabilised by diphenylamine (p. 132) ;
and the oxidation process which causes rubber and silk to
" perish " can be greatly retarded by means of thiourea,
CS(NH 2 ) 2 > and other substances.
Catalysis may occur not only in homogeneous but also in
heterogeneous systems, as when solid substances act as
catalysts in gaseous and liquid systems. Thus, if the case
of hydrogen and oxygen be again considered, it is found that
although combination of the two gases takes place at high
temperatures with explosive velocity, at the ordinary tem-
perature no trace of combination can be detected. If, h6w-
ever, 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, and the
amount of heat evolved so large, that the platinum is heated
VELOCITY OF REACTIONS AND CATALYSIS l8l
to incandescence and ignites the mixture. 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 phenomenon, 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 applica-
tion. In 1823 it was observed by a German chemist,
DOBEREINER, that if a jet of hydrogen is allowed to impinge
on a piece of spongy platinum exposed to the air, the heat
of combination of hydrogen and oxygen raises the platinum
to incandescence and the hydrogen becomes ignited.
Dobereiner, therefore, 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
and impinged on a piece of spongy platinum. In this way
fire could be obtained, and, as a matter of fact, this Dobereiner
lamp was widely used for that purpose before the days of
matches.
Although platinum is by no means a 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 complete 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
1 82 CHEMISTRY IN fHE SERVICE OF MAN
importance, the recognition of which has been, as we shall
learn more fully presently, not only of scientific interest, but
also of the greatest industrial importance.
By chemists the importance of catalysis is now fully
recognised, and the systematic search for the most suitable
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
role which catalysts 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 neces-
sary ingredients were heated for some time in a vessel made
of iron. 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 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,
VELOCITY OF REACTIONS AND CATALYSIS I
as well as a number of other similar substances, to react
a particular manner, and in this way a new and importc
series of dyes was discovered. It all seems very simple ;
a matter of " happy accident/' But was it by a hap
accident that the cause of the trouble in the first instan
was discovered ? Or was it a happy accident that convert
a source of trouble in one process into a source of gain
another ? How would the matter have stood without t
trained intelligence of the chemist with his knowledge of t
importance of little things, with his trained faculty of obs
vation and his ability to make use of the facts which
observed ?
Important as are the phenomena of catalysis in pu
science and in industry, they are, literally, of much me
vital importance in the animal and vegetable organism.
The animal organism is like a laboratory in which mime
ous reactions and marvellous transformations take pla
unceasingly the transformation of the food consumed in
the bone and flesh and blood of the body, and the sk
combustion of the tissues to yield the energy and he
necessary for vital activity. And so it is also with the pla
organism in which there takes place the building up
synthesis, not only of the complex materials which serve
foodstuffs for the animal creation, but also of those swee
smelling essences and the compounds which give to flowe
their varied odours and colours. Many of these substances, tl
products of Nature's laboratory, can also be made in tl
laboratory of the chemist, and their synthesis from simp
inorganic materials constitutes the crowning achieveme
of chemical science. But how different are the methods
the chemist from those of Nature. In his laboratory tl
chemist makes use of high temperatures and the action
powerful and corrosive reagents ; but ia the laboratory <
Nature, the building up of even the most complex con
pounds takes place quietly and smoothly at the ordinal
184 CHEMISTRY IN THE SERVICE OF MAN
accomplishes by utilising appropriate catalysts, accelerators
of reactions, the so-called enzymes, which are themselves
produced within the living cell of a plant or animal. The
ptyalin of the saliva, the pepsin of the gastric juice, the
trypsin of the pancreas, the diastase of the sprouting barley-
corn, the zymase of the yeast, which has from time imme-
morial been u^ed 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. Not only
do enzymes play an indispensable role in the economy of
Nature, but they are also being made to play a part of ever-
increasing importance in industry, as we shall learn more
fully later (Chap. xvn).
In the manufacturing industries it may truly be said that
time is money ; and to produce an article of manufacture
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, there-
fore, not surprising that in almost all branches of chemical
industry the value of catalysts has become increasingly
recognised, and that, by their introduction, new industries
of the highest importance have been established, and older
industries have been revolutionised. It would, in fact, be
no exaggeration to speak of the present as the catalytic age
in chemical manufacture. Although reference has already
been made to the industrial application of catalysts (e.g. in
the hydrogenation of coal and production of oils, p. 97), a
little space may appropriately be devoted here to, the dis-
cussion of a few other important reactions in which catalysis
has found industrial application. In succeeding chapters,
other applications will be discussed.
MANUFACTURE OF SULPHURIC ACID
Sulphuric acid, or oil of vitriol (H 2 SO 4 ), the discovery of
which dates from the fifteenth century, is one of the most
VELOCITY OF REACTIONS AND CATALYSIS 185
important substances in our modern civilisation, for it finds
a use in almost every manufacturing industry, and in agri-
culture, for the eradication of weeds. 1 Although in a number
of industries, such as the manufacture of superphosphates,
hydrochloric acid and ammonium sulphate, changes have
taken and are taking place which make the use of sulphuric
Courtesy of Imperial Chemical Industries, Ltd.
ERADICATION OF WEEDS BY SPRAYING WITH DILUTE SULPHURIC ACID.
acid less necessary, the production of the acid has gone on
increasing, so that the annual production throughout the
world now amounts to about 11,000,000 tons.
The reaction on which the production of sulphuric acid
1 A complex organic compound, methoxone, which has been prepared
by the chemists of Imperial Chemical Industries, is a weed-killer with
marked selective action. It will destroy charlock, pennycress and corn
buttercup without damaging the cereal crop. It is put on the market
under the name agroxone> and may well supersede sulphuric acid as a
1 86 CHEMISTRY IN THE SERVICE OF MAN
depends is the oxidation of the gas sulphur dioxide (SO 2 ),
to form the compound sulphur trioxide (SO 3 ), which com-
bines readily with water to give the compound known as
sulphuric acid. The difficulty is met with, however, that
combination between sulphur dioxide and oxygen does not
take place appreciably at the ordinary temperature ; and
when one seeks to hasten 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 tem-
perature 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 by a process depend-
ing on the use of these oxides. This method of manufactur-
ing sulphuric acid consists, essentially, in passing sulphur
dioxide, together with air, oxides of nitrogen, and steam,
into a series of large lead 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 " lead chamber process,"
as it is called, contains about 65 per cent, of sulphuric acid
VELOCITY OF REACTIONS AND CATALYSIS 187
(H 2 SO 4 ), and must be subjected to processes of purification
and concentration before the pure acid is obtained.
At the beginning of the present century, however, another
process began to come into prominence. This was due
mainly to the successful development of the process of manu-
facture of synthetic indigotin (p. 317), 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 or " oleum."
As far back as the year 1817, it was suggested by Sir
HUMPHRY DAVY that platinum sponge might be employed
to accelerate the oxidation of sulphur dioxide by oxygen,
just as we have seen that this metal accelerates the com-
bination of hydrogen and oxygen; and in 1831, practical
application of this suggestion was made by a vinegar manu-
facturer of Bristol, PEREGRINE PHILLIPS by name. Great
hopes were aroused for the success of this method of manu-
facturing sulphuric acid, and 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 lead chambers and nitric acid. But the
unwisdom of prophecy is proverbial, 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 develop-
ing the discovery of Peregrine Phillips into a successful
industrial process. 1
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
1 On a restricted scale, Squire and Messel, in England, manufactured
oleum by the contact process, from 1875 onwards. They obtained the
sulphur dioxide by the combustion of sulphur or by the decomposition
of sulphuric acid on hot brick surfaces. The oleum so prepared was too
costly except for special purposes.
1 88 CHEMISTRY IN THE SERVICE OF MAN
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 con-
tained 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 lead chambers, with a capacity some-
times of 150,000 cubic feet, are replaced by comparatively
small, cylindrical vessels containing a suitable catalyst. For
this purpose, platinum deposited on asbestos (platinised
asbestos), or on a porous magnesium sulphate or on
silica gel (p. 279), has mainly been used in the past, but com-
pounds of vanadium are now coming into widespread use
as catalysts. They are much less costly than platinum
and they are not " poisoned " by arsenic or by hydrogen
chloride. Through the reaction vessels which are main-
tained at the proper temperature, about 450 C. (842 F.),
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 com-
pletely, and the sulphur trioxide issues from the apparatus
as a white mist, which is then passed into a solution of sul-
phuric acid containing about 98 per cent, of acid. In this
way a pure sulphuric acid, as well also as the powerful
fuming sulphuric acid (called " oleum "), 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
VELOCITY OF REACTIONS AND CATALYSIS 189
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. Most probably both processes
will continue to develop in varying degrees according to
circumstances.
The sulphur dioxide required for the production of sul-
phuric acid may be obtained by heating iron pyrites (sul-
phide of iron, FeS 2 ) or spent oxide of iron from the gas
works (p. 105) in a current of air, or by burning sulphur
in air. SULPHUR occurs free over an extensive area in Sicily,
and also forms great deposits, 30-40 yards in thickness and
situated at a depth of some 700 feet below the surface of
the earth, in the State of Texas, U.S.A. These deposits
constitute the main source of supply at the present day.
Large amounts of sulphur are now recovered from the
sulphur dioxide which is formed as a by-product in the
smelting of copper and zinc sulphide ores, and in the manu-
facture of cement (see below) from anhydrite (calcium
sulphate) ; but the sulphur dioxide produced in these pro-
cesses must first be concentrated by freeing it from the other
gases (flue gases and air) with which it is mixed. For this
purpose it is absorbed in a solution of basic aluminium
sulphate (aluminium sulphate with excess of aluminium
hydroxide). On warming the solution, the dissolved sulphur
dioxide, mixed with water vapour, is evolved, and the gas,
after condensation of the water vapour, is passed through
coke, at a temperature of about 1000 C. (1832 F.). The
coke reduces the sulphur dioxide to sulphur, with formation,
mainly, of carbon dioxide (SO 2 +C S+CO 2 ). The sulphur
can then be burned for the production of sulphur dioxide
in the sulphuric acid plant.
When anhydrite (calcium sulphate, CaSO 4 ) is heated in a
furnace with sand (silica), clay (p. 246) and coke, sulphur
dioxide is evolved. From this the sulphur can be recovered
as described above. The clinker which is left in the furnace
190 CHEMISTRY IN THE SERVICE OF MAN
consists of calcium silicate (CaSiO 3 ) and calcium aluminate
(3CaO,Al 2 O 3 ) and, when ground, forms cement.
Considerable quantities of sulphur are now also being
recovered from the hydrogen sulphide present in coke-
oven gas, formed by the distillation of coal for the pro-
duction of the coke required for use in blast furnaces and
for other metallurgical purposes. In this process, known
as the Thylox process, the gas is passed through a solution
which contains a substance known as ammonium thio-
arsenate. This compound exchanges an atom of oxygen for
the sulphur in the hydrogen sulphide, as represented by the
equation :
(NH 4 ) 3 As0 2 S 2 +H 2 S-(NH 4 ) 3 AsOS 3 +H 2 O.
Air (oxygen) is then passed through the solution, heated to
a temperature of about 45 C. (113 F.), whereby the original
thioarsenate (" thylox ") is regenerated and sulphur separates
out. The sulphur is purified by distillation, and is used not
only for the production of sulphur dioxide but also as an
insecticide, in the vulcanising of rubber, and for other
purposes in chemical industry.
HYDROGENATION OR HARDENING OF OILS
Another important industry which depends on the
application of catalysis is that of the conversion of liquid
oils into solid fats ; a process referred to as the hydrogenation
or hardening of oils.
It has already been pointed out (p. 85) 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. 85) 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
the chief constituent of olive oil ; and the other natural
VELOCITY OF REACTIONS AND CATALYSIS IQI
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 foodstuffs, to supply the body with the necessary
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 diet
became of increasing importance. The solution of the
problem we owe to French ingenuity, and the industrial
production of butter substitutes, e.g. margarine, which dates
from 1870, has now attained to very great dimensions. Beef-
fat or hog's lard, after being melted and clarified, is mixed
in churning machines with various vegetable oils, such as
cotton-seed oil, soya-bean oil, coco-nut oil, palm- kernel oil,
and also with milk. The milk is added in order to emulsify
the fats and also to confer flavour, the flavouring properties
being developed by the addition to the milk of bacteria
which bring about the production of lactic acid. Although
the margarine so obtained is an efficient substitute for butter
so far as the supply of energy is concerned, it is lacking in
certain important food accessories, to which the name of
vitamins (p. 363) has been given. This defect is now
remedied by the addition to the margarine of vitamins A and
D, obtained partly by synthesis and partly from fish liver
oils ; and vitaminised margarines are now put on the market
certified to contain these vitamins in as high a proportion
as they are contained in the best butter.
Since these butter substitutes are derived mainly from
animal fats, the supply of solid fats necessary for the
manufacture of soap was 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.
192 CHEMISTRY IN THE SERVICE OF MAN
Oleic acid, for example, differs from stearic acid only in the
fact that it contains less hydrogen. It is what has been called
an unsaturated compound, and if the oleic acid is combined
with the proper amount of hydrogen, it is converted into the
solid stearic acid ; or, on the other hand, if hydrogen is
combined with the liquid glycerine oleate, the solid fat,
glycerine stearate, is obtained. Similarly with the other un-
saturated 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 cata-
lyst. In the presence of this metal, the liquid oils, olive oil,
linseed oil, whale oil, etc., combine with gaseous hydrogen
and become converted into solid fats suitable for use in the
manufacture of soap and for the preparation of edible fats.
This important industrial application of catalysis is based
on the purely scientific investigations of the French chemists,
PAUL SABATIER and JEAN BAPTISTE SENDERENS, carried out
at the beginning of the present century.
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 employment 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
process mentioned, into a solid, odourless material suitable
for the making of soap.
This result has led to a great expansion of the whaling
industry. The introduction of the hydrogenation process,
moreover, will, by stimulating the cultivation of oil-produc-
ing plants, exercise a profound influence on the economic
development of those countries which are suitable for such
cultivation. In America, for example, seven million acres
are under soya bean cultivation, and in Great Britain the
cultivation of soya bean has also been introduced and
VELOCITY OF REACTIONS AND CATALYSIS 193
will, it is hoped, be rapidly extended. Soya beans contain
18-20 per cent, of oil, which is easily converted into edible
fat, and it contains proteins and other substances which
make it specially valuable as a feeding stuff for cattle. Of
the importance in the service of man of this modern in-
dustrial hydrogenation process, founded as so many in-
dustrial processes are on investigations of apparently purely
scientific interest, it is impossible to form an estimate.
SYNTHESES FROM WATER-GAS
Mention has been made of the fact that the action of
catalysts is largely specific, and it is found that by a proper
choice of catalyst and regulation of the conditions of reaction,
the same substances may be made to react in various ways.
No better illustration of these statements could be obtained
than what is offered by the numerous products which can
be obtained from the mixture of carbon monoxide and
hydrogen, known as water-gas (p. 107). This mixture, we
have seen (p. 98), is the basis of the Fischer- Tropsch
process, and from it hydrocarbons can be produced which
are not only of great value as fuels and lubricants, but which,
in the hands of chemists, have also been made to yield a
great array of materials which are of service to man.
Formerly, practically all the methyl alcohol or methanol,
which is used in large amount as a solvent and in the manu-
facture of formaldehyde, dyes, perfumes, etc., was produced
by the distillation of wood (p. 123) ; but since 1925, a large
and rapidly increasing proportion has been produced by a
catalytic process founded on researches carried out mainly
by French and German chemists. When a mixture of carbon
monoxide and hydrogen is passed over a suitable catalyst
(e.g. zinc oxide, or a mixture of zinc oxide and copper), under
regulated conditions of temperature and pressure, the two
gases combine to form methyl alcohol or methanol, CH 3 OH,
as shown by the equation, 2H 2 +CO==CH 3 OH.
194 CHEMISTRY IN THE SERVICE OF MAN
From the mixture of carbon monoxide and hydrogen,
also, by the use of different catalysts and by suitable
variation of the conditions of temperature and pressure,
butyl alcohol, C 4 H 9 OH, a valuable solvent for nitro-cellulose
lacquers, can be obtained.
Further, very large amounts of water-gas are used at the
present day as a source of industrial hydrogen. Although the
hydrogen may be separated from the carbon monoxide by a
process of liquefaction and distillation, similar to that used
in the case of liquid air (p. 58), a catalytic method is mainly
employed. Thus, when water-gas and steam, at a tem-
perature of about 500 C. (932 F.), are passed over a catalyst
consisting essentially of iron oxide, the carbon monoxide
reacts with the steam to form carbon dioxide and hydrogen.
The carbon dioxide is then easily removed by dissolving in
water under pressure.
A mixture of carbon monoxide and hydrogen is obtained
not only when steam is passed over red-hot coke but also
when methane and steam are passed over a catalyst of nickel
and aluminium at a temperature of about 900 C. (1652 F.) :
CH 4 +H 2 O CO+3H 2 . This reaction has become of great
importance as it can also be used as a means of obtaining
cheap hydrogen for the hydrogenation of coal methane
being one of the by-products of the process (p. 97).
CHAPTER X
CHEMISTRY AND AGRICULTURE. POTASH,
PHOSPHATE AND NITROGENOUS FERTILISERS
ALTHOUGH agriculture has been practised from time imme-
morial, it is only in comparatively recent years that a more
exact knowledge has been obtained of soil fertility and plant
growth. As early as 1563, the view was clearly stated by
the French potter, BERNARD PALISSY, that dung was applied
to the land in order to replace something which the growing
crop had removed, although, early in the following century,
the Belgian chemist, JEAN BAPTISTE VAN HELMONT, concluded
that water is the sole nutrient of plants. " I took an earthen
vessel/' records van Helmont, " in which I put 200 pounds
of soil dried in an oven, then I moistened with rain water
and pressed hard into it a shoot of willow weighing 5 pounds.
After exactly five years the tree that had grown up weighed
169 pounds and about 3 ounces. But the vessel had never
received anything but rain water or distilled water to moisten
the soil when this was necessary, and it remained full of soil,
which was still tightly packed, and, lest any dust from
outside should get into the soil, it was covered with a sheet
of iron coated with tin but perforated with many holes. I
did not take the weight of the leaves that fell in the autumn.
In the end I dried the soil once more and got the same
200 pounds that I started with, less about two ounces. There-
fore the 164 pounds of wood, bark and root arose from the
water alone."
The experiment was simple but the conclusion, although
it seemed to be convincing, was nevertheless incorrect, for
van Helmont had omitted to take account of two factors
the carbon dioxide and water vapour in the air and the
salts which had been removed from the soil ; for, as we
1 96 CHEMISTRY IN THE SERVICE OF MAN
have already learned, the green leaves of plants take in
carbon dioxide and water vapour and, absorbing the radiant
energy of sunlight, transmute these substances into sugar,
starch and cellulose. In the erroneous conclusion drawn by
van Helmont we have a warning of the care which must be
exercised in the performance of a scientific experiment and
in the interpretation of the results.
Although it had long been known that plants contain
inorganic constituents which appear in the ash when the
plant is burned, it was the German chemist, JUSTUS VON
LIEBIG, who first, in 1840, gained definite acceptance of the
view that plants do not subsist merely on the water and
carbon dioxide which they abstract from the air and the
soil, but that they have also to be fed with the elements
necessary for the building up of their structures. No fewer
than about thirteen elements are required by plants, and o,.
these, the most important, apart from carbon and hydrogen
are nitrogen, phosphorus and potassium ; and these mui' '
be present in the soil in the form of salts or soluble con
pounds which can be taken up by the plants. One ton c ,
wheat, it is stated, abstracts from the soil 47 pounds ot
nitrogen, 18 pounds of phosphoric acid and 12 pounds of
potash. So long as the population of the world was com-
paratively small, the great tracts of virgin soil contained an
ample supply of the necessary mineral salts to secure crops
adequate for the feeding of the people ; and although
the efficacy of dung in increasing the crop was well known,
and although such manure was applied, the farmer had
little to do but till the soil and sow the seed. Owing to
exhaustion of the soil, however, and to the great increase of
population which has taken place in modern times, it has
become necessary to increase the yield of the soil by the
addition in larger and larger amounts of the inorganic salts
necessary for the life and growth of food plants. Although
some of the fertilisers which are now indispensable for
intensive agriculture are found ready-formed in Nature, yet
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 197
in the economic exploitation of these natural deposits, in
rendering them suitable for absorption by the plant, and
in the artificial production of fertilisers in ample amount
and at lower cost, we may recognise one of the greatest
services which chemists have done for man. Since, moreover,
the nature and amount of the different fertilisers to be used
depend on the plant, soil and climatic conditions, chemical
y
Courtesy of Sir John Russell.
EFFECT OF POTASH SALTS ON GROWTH OF MANGOLDS.
The root on the left has been grown in soil to which a potash fertiliser
has been added ; that on the right, in a soil containing no potash.
knowledge and investigation are necessary for the production
of a properly balanced fertiliser.
While it is a matter of the highest importance that agri-
culturists should have at their command adequate supplies
of the essential fertilisers, it is also important to bear in
mind that a deterioration of the soil may occur if artificial,
inorganic fertilisers alone are used, and if attention is not
paid to the renewal of the store of organic humus in the
soil. This humus can be renewed by the addition to the
soil of leaves, vegetable waste, straw, farmyard manure, etc.,
198 CHEMISTRY IN THE SERVICE OF MAN
which have been allowed to rot or undergo change under
the action of bacteria. Seaweed, also, may profitably be
brought into service ; and the ploughing up and re-seeding
of old grasslands may also be used for the effective renewal
of humus. Through the loss of humus, brought about by
intensive cultivation and by the sole use of artificial fertilisers,
the soil structure is destroyed and soil fertility and quality
of the crops may be impaired. Serious erosion, also, may
take place owing to the soil becoming less permeable to and
being washed away by rain. Artificial fertilisers, therefore,
must be made use of with knowledge and understanding.
The addition of POTASSIUM SALTS to the soil is of great
importance because such salts give health and vigour to the
plant, and make the leaves more efficient in utilising the
energy of sunlight and more efficient producers, for example,
of sugar and starch. In root crops, therefore, there is a
greater storage of food material and the roots become
larger. Potassium salts are of importance for the cultivation,
more especially, of potatoes, beet and fruit crops, and the
banana plant responds in a most surprising fashion when
manured with salts of potassium.
When land vegetation is burned, the potassium which
the plants had taken from the soil is recovered in the ash
in the form of potassium carbonate (K 2 CO 3 ). This salt was
obtained by lixiviation of the ash with water, evaporation of
the solution and calcination of the residue in pots. Hence
the name pot-ash given to potassium carbonate. For long,
the potash so obtained constituted the main source of supply
of this salt, and in the middle of last century nearly three-
quarters of the world's supply came from the wood ashes
of the Canadian lumber camps.
At the present time, nearly all the potassium salts used
are of mineral origin, and are obtained mainly from the
great salt deposits which are found in the neighbourhood of
Stassfurt, in Germany, and in the neighbourhood of Mul-
house in Alsace. In the former deposits, which form the
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 199
Courtesy of Societt Commerciale de Potasses d' Alsace,
POTASH MINE IN ALSACE.
Courtesy of Socieit Commerciale de Potasses d" Alsace.
CRYSTALLISING VATS FOR POTASSIUM CHLORIDE.
zoo
CHEMISTRY IN THE SERVICE OF MAN
largest source of potassium compounds, the chief potassium
salts are sylvine (potassium chloride), kainite (a double
sulphate containing not only potassium but also magnesium)
and carnallite (a double chloride of potassium and mag-
1 ' wr r l {;'j|jU-t i't'' J t - iS r" n M' I' *-i t ,( n a
SEARLES LAKE, CALIFORNIA.
Below the crust of salts there lies a saturated brine from which
potassium chloride, borax and other salts are extracted.
nesium). The crude salts may themselves be used as potash
fertilisers, or the potassium salts may be extracted and
purified by crystallisation from water ; and to learn how
this can best be effected very long and laborious investi-
gations had to be carried out. The successful exploitation
of these deposits is due mainly to the work of the great
Dutch chemist, J. H. VAN'T HOFF,
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 2OI
Deposits of potassium salts are also being worked in
Russia, in Spain, and in the U.S.A., especially in Texas
and near Carlsbad in New Mexico. Very large amounts of
potassium salts are also being extracted from the brine of
Searles Lake in the Mojave Desert, California, from the water
of the Dead Sea, and from the flue-dust of cement works.
That PHOSPHATES are necessary for healthy plant growth
has been known since the end of the eighteenth century,
and their importance, more especially for cereals and pasture,
became more fully appreciated in later years. In countries
with a low rainfall, phosphates are of especial value in in-
creasing and strengthening the crop and also in accelerating
the processes of growth and ripening. They are of great
value also in improving the feeding value of crops, especially
of pastures, so that, by their application, grass land may be
greatly improved and may be made to carry more stock.
Before the year 1840, phosphorus was added to the soil
chiefly in the form of crushed bones, the phosphorus being
present as calcium phosphate, the calcium salt of phosphoric
acid. Between 1840 and 1850, however, JOHN BENNET
LAWES, founder of the Agricultural Experimental Station at
Rothamsted in Hertfordshire, showed that the phosphate
could be rendered more readily soluble in the soil and
therefore more readily available for the plant, by treating the
ground bones with sulphuric acid. The so-called normal
calcium phosphate, Ca 3 (PO 4 ) 2 , is thereby converted, into
acid calcium phosphate, CaH 4 (PO 4 ) 2 , with production at the
same time of hydrated calcium sulphate or gypsum. To the
mixture of acid calcium phosphate and gypsum the name
superphosphate was given. Soon thereafter, deposits of
mineral rock (phosphate rock) were discovered, and from
this nearly all superphosphate is now produced. About
60 per cent, of the world's supply of mineral phosphate
comes from the enormous deposits in French North Africa,
and about 30 per cent, from America.
Ground basic slag (p. 160) is also used, in large amount,
202 CHEMISTRY IN THE SERVICE OF MAN
as a phosphatic fertiliser, more especially for the treatment
of grazing land.
In various countries, the production of another phosphate
fertiliser is being developed which may perhaps largely
supersede superphosphate. When phosphorus is heated to
a high temperature with steam, phosphoric acid is formed
and hydrogen is liberated. The hydrogen is used, as we shall
learn presently, for the production of ammonia, and the
ammonia is then combined with the phosphoric acid to form
ammonium phosphate (" di-ammon-phos "), which may be
used both as a phosphatic and as a nitrogenous fertiliser.
Of the different fertilisers used in agriculture the most
important are those which feed the plant with nitrogen,
for it is on such fertilisers that increased crop production,
in those countries with a not too low rainfall, 1 mainly
depends. More especially is this the case with wheat and
other cereals. Although it has been found that leguminous
plants (peas, beans, lucerne, clover, etc.), through the
symbiotic action of colonies of bacteria occurring in nodules
on the roots, are able to take up and assimilate elementary
nitrogen from the air, most plants are unable to do so ; and
combined nitrogen must, therefore, be added to the soil in
a form which the plants can assimilate.
Owing to the apparent impossibility of coaxing the enor-
mous store of elementary nitrogen contained in the air into
suitable combination with other elements, mankind con-
tented 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
1 Where the annual rainfall is less than about 20 inches, nitrogenous
fertilisers do not produce large increases in crops. In such countries
phosphate fertilisers are specially important.
ilA-il$ AJND NITROGENOUS FERTILISERS 203
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 intensive cultivation, which in its turn
Courtesy of Sir John Russell.
EFFECT OF NITROGENOUS FERTILISERS (AMMONIUM SULPHATE) ON
PLANT GROWTH.
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.
Apart from waste animal and vegetable matter, which was
quite inadequate in amount and, in some cases, had only
204 CHEMISTRY IN THE SERVICE OF MAN
a local importance, agriculture depended for its supply of
nitrogenous fertilisers mainly on the ammonia produced
as a by-product in the distillation of coal, and on Chile
saltpetre or sodium nitrate. In 1898, nearly 300,000 tons of
nitrogen, in a combined state, were used for fertiliser pur-
poses, and of this amount about one-third was in the form of
by-product ammonium sulphate and two-thirds in the form
of Chile saltpetre. Coal, therefore, was a valuable source of
supply of combined nitrogen and it became more and more
important that as much coal as possible should be distilled
and that the ammonia should be recovered. It was, how-
ever, economically impracticable to produce by this means
an adequate supply of nitrogenous fertiliser. Moreover, al-
though it was possible greatly to increase the production of
Chile saltpetre, the nitrate deposits, although enormous, were
not inexhaustible. 1 It is clear, therefore, that the situation
in 1898 was one which might well cause grave concern to
men of foresight and scientific knowledge ; and Sir William
Crookes was 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 would be 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. Since about 1903, not one but several methods have
1 While it was at one time thought that the Chile saltpetre deposits
would be exhausted by 1923, it now seems probable that there will be
sufficient to supply world needs for one or two hundred years.
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 205
been discovered by means of which the atmospheric nitrogen
can, on a large scale and in a commercially successful man-
ner, be forced into useful combination 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, the possibility of which had been proved by
the experiments of Cavendish in 1785 (p. 51).
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, who commenced
the industrial production of nitric acid in 1903. For the
production of the high temperature required to bring about
the combination of nitrogen and oxygen, they made use of
the electric arc, the only means whereby a temperature of
from 2500 C. to 3000 C. (4532 F. to 5432 F.) can be
satisfactorily and economically obtained. By the com-
bustion of the nitrogen there was formed an oxide of nitrogen
called nitric oxide (NO), which, after being cooled, was
passed into chambers lined with acid-proof stone and mixed
with air. The nitric oxide combines at once with the oxygen
of the air to form a brown-coloured gas, nitrogen dioxide
(NO 2 ), which, when absorbed in water, gives nitric acid.
For convenience of transport, the nitric acid was neutralised
with limestone (carbonate of lime or calcium carbonate), and so
converted into nitrate of lime (calcium nitrate). This was then
used as a fertiliser under the name of Norwegian saltpetre.
The production of nitric acid and nitrates by the direct
combination of atmospheric nitrogen and oxygen was carried
out mainly in Southern Norway, where the abundant and
206 CHEMISTRY IN THE SERVICE OF MAN
very cheap water-power which is necessary for the industrial
success of the process was available. But science marches
unhaltingly forward, and the Birkeland-Eyde process, the
development of which aroused much interest and had im-
portant social-economic consequences in Southern Norway,
was, in 1928, after a life of twenty-five years, forced to sur-
render to a more efficient rival. Instead of the electrical
energy being used to bring about the combination of nitrogen
and oxygen, it is now applied to the electrolysis of water and
the production of hydrogen ; and this hydrogen is employed
for the production of synthetic ammonia in a manner to be
described presently.
(2) Fixation of Nitrogen by means of Carbides.
In 1906, another process was introduced for the fixation
of atmospheric nitrogen, which depended on the use of
calcium carbide, a compound manufactured in large amount
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 (CaCN 2 ), 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. The physical qualities of the commercial
nitrolim, however, its dustiness and dirtiness, were pre-
judicial 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,
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 2OJ
ammonia being readily obtained by passing superheated
steam over the cyanamide.
(3) Synthetic Production of Ammonia.
However important may be the processes to which refer-
ence has already been made, and however great their contri-
bution 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 announce-
ment, in 1912, that the direct combination of nitrogen and
hydrogen to form ammonia had been developed into a com-
mercially successful 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 had
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 is produced,
but only in very minute amount. It was, moreover, also
known that when electric sparks 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 equili-
brium ; but the concentration of ammonia present is ex-
ceedingly small, and all attempts to obtain an appreciable
amount of the compound by direct combination of nitrogen
and hydrogen ended in failure. New weapons, however, were
being forged, the weapons of chemical dynamics, and with
these the problem was again attacked. In 1912, as the
result of ably-directed and painstaking endeavour, the
problem was solved.
Experiment has shown that when nitrogen and hydrogen
208 CHEMISTRY IN THE SERVICE OF MAN
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, com-
bination of nitrogen and hydrogen takes place with evolution
of heat ; and therefore (p. 177, 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 amount of ammonia in the equilibrium
Temperature mixture when the pressure was
i atmosphere 100 atmospheres
800 C. (1472 F.) o-oii i-i
700 C. (1292 F.) 0-021 2-1
6ooC.(iii2 F.) 0-048 45
500 C.( 932 F) 0-13 10-8
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 500 C., 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
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 2OQ
destroyed, and it was only by laborious and careful investiga-
tion of the behaviour of different catalysts, and of the be-
haviour of other substances towards these catalysts, that
success was made possible. Nor indeed were the engineering
difficulties much less than the chemical, but they were all
overcome, and the synthetic production of ammonia was
added to the industries of the world. In the economic
utilisation of Nature's boundless store of nitrogen, therefore,
catalysts play an all-important part.
In the manufacturing process, first successfully achieved
by the German chemist, FRITZ HABER, and often spoken of
as the Haber process, a mixture of nitrogen and hydrogen,
under a pressure of 150-200 atmospheres, is circulated, by
means of a pump, over the catalyst 1 heated to a temperature
of about 500 C. (932 F.). After passing over the catalyst,
the gases, which now contain a certain proportion of am-
monia, are washed with water, so as to dissolve the ammonia,
while the unchanged nitrogen and hydrogen are made to
circulate again over the catalyst.
A number of modifications of the original Haber process
have been introduced, of which the two most important are
the Claude (French) and the Casale (Italian) processes.
These differ from the Haber process mainly in the fact
that they operate under very much higher pressures. As has
already been mentioned (p. 208), the production of ammonia
is favoured by high pressures, and in the Claude and the
Casale processes, pressures up to 800 or 1000 atmospheres
are employed. In these processes, the percentage of am-
monia in the gas after passage over the catalyst is much
higher than in the Haber process ; and under the high
pressures employed, also, the ammonia is readily liquefied
merely by cooling with water, and is thus easily separated
from the residual mixture of hydrogen and nitrogen.
1 While the exact nature of the catalyst is kept secret, it may be re-
garded as oxide of iron to which potassium oxide, molybdenum, aluminium
oxide or other substances are added to increase the efficiency.
210 CHEMISTRY IN THE SERVICE OF MAN
For use as a nitrogenous fertiliser, ammonia is converted
into ammonium sulphate. Formerly, this salt was obtained
by combining the ammonia with sulphuric acid, but now
use is very extensively made of calcium sulphate (CaSO 4 ). If
a suspension of finely ground calcium sulphate (anhydrite
or gypsum) in water is treated in a closed vessel with am-
monia and carbon dioxide, 1 ammonium sulphate and calcium
carbonate are formed, as indicated by the equation :
CaS0 4 +H 2 0+2NH 3 +C0 2 -CaC0 3 +(NH 4 ) 2 S0 4
The calcium carbonate can then be used for the production
of cement (p. 248), or as a liming agent in agriculture.
Mixed with ammonium nitrate it is used as a fertiliser under
the name of nitro-chalk.
As a consequence mainly of the development of the
synthetic ammonia process, the position of the nitrogen
industry has undergone a very remarkable change. Not
only has the total production of nitrogen compounds greatly
increased in recent years, but the amount produced by the
industrial fixation of atmospheric nitrogen (about 60 per
cent, of the total) now greatly exceeds the amount con-
tributed by Chile saltpetre and by the distillation of coal.
This fact, by itself, will give some indication of the success
which has attended the efforts made to utilise the stores of
atmospheric nitrogen ; and chemists surely may justifiably
feel some pride and satisfaction, and may even look for
some sign of appreciation from their fellow-men, by reason
of 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.
In recent years the substance, urea, CO(NH 2 ) 2 , first
1 This carbon dioxide is produced in the process used for obtaining
the hydrogen required for the synthesis of ammonia, namely, by passing
water-gas (p. 107) and steam over a catalyst. Hydrogen and carbon
dioxide are formed (p. 194).
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 211
known as a product of animal metabolism, has begun to
come into use as a fertiliser and for the production of plastic
materials (Chap. xvi). It is produced industrially by the
direct union of ammonia and carbon dioxide, under the
influence of a catalyst, at a temperature of about 150 C.
(302 F.), and under a pressure of about 70 atmospheres.
The reaction is represented by the equation, CO 2 +2NH 3
-CO(NH 2 ) 2 +H 2 0.
Besides potassium, phosphorus and nitrogen, a number
of other elements are required to act either as plant nutrients
or to improve the fertility of the soil. Of these, perhaps the
most important is calcium in the form chiefly of calcium
carbonate (limestone, chalk) or of slaked lime (calcium
hydroxide). The addition of lime to the soil is of importance,
in the first place, in order to prevent undue acidity ; but it
has also a specific action not possessed, say, by magnesium.
The fertility of a soil, also, depends in great measure on the
amount and nature of the colloidal material (p. 273) present ;
and the compounds of calcium are of great value in bringing
about such a degree of flocculation and deflocculation of the
colloids in the soil as to secure adequate aeration of the soil
and the retention of the soluble salts.
Magnesium, also, is an element which must be present in
the soil, for it is an essential constituent of chlorophyll, the
green colouring matter of leaves, etc. Usually there is an
adequate supply of magnesium salts in the soil, but, if not,
they must be added.
Whereas the elements already referred to are to be re-
garded as plant nutrients and must be present in the soil in
adequate amount in a form which the plant can assimilate,
recent investigation has shown that the health of a plant may
depend on the presence in the soil of other elements in
minute quantities. These trace elements, as they are called,
seem in their action to partake somewhat of the character
of catalysts, and to resemble the hormones (p. 369) in the
animal organism. Small quantities of iron, for example,
212 CHEMISTRY IN THE SERVICE OF MAN
seem to facilitate the formation of chlorophyll, although
chlorophyll itself contains no iron ; and other elements,
although they may be harmful when present in large amount,
may have a beneficial action on the health of the plant when
present in minute quantities.
During the present century it has come to be realised that
two elements especially, boron and manganese, are necessary
for the health of higher plants, although the amounts re-
quired may be very small. Manganese seems to be an
essential factor in plant metabolism and growth, and acts,
apparently, as a catalyst of the enzymic reactions of the
organism. Boron, also, has been found to be essential for
the normal growth of a number of plants, but the addition
of i part of boric acid in 12,500,000 parts of water has been
found sufficient to prevent signs of malnutrition. Various
plant diseases, also, such as internal cork of apples, heart
rot of sugar-beet and brown heart of swedes, have been
found to be due to a boron deficiency and may be prevented
by applications of borax (sodium borate) to the soil. Simi-
larly, the disease known as mottle-leaf of citrus has been
shown to be induced by a deficiency of available zinc in the
soil. The effect of even minute quantities of different
elements in the soil is now being energetically investigated.
Although the fixation of atmospheric nitrogen has been
considered only as a means of obtaining nitrogenous fer-
tilisers, a brief reference to the industrial importance of
nitrogen should not be omitted. Owing to the large amount
of heat which becomes latent, and the consequent lowering
of temperature which takes place, when liquid ammonia is
converted into vapour, this substance is widely used at the
present day in refrigeration. It is now also being used to an
increasing extent for the production of nitric acid, which, as
we have learned, is an essential reagent in the manufacture
of explosives and is also required in the dye industry, as
well as for the production of the oxides of nitrogen used in
POTASH, PHOSPHATE AND NITROGENOUS FERTILISERS 213
the manufacture of sulphuric acid by the lead chamber pro-
cess (p. 1 86). Previous to 1913, Chile saltpetre was the only
practicable source of nitric acid, 1 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, WILHELM OSTWALD,
in the early years of this century, addressed himself to the
successful development of a process of obtaining nitric acid
from ammonia. Just as platinum acts as a catalyst for the
combustion of hydrogen (p. 180), so also it acts as a catalyst
for the combustion of ammonia ; and when a mixture of
ammonia and air is passed over platinum, or platinum-
rhodium alloy, in the form of wire gauze heated to a tem-
perature of about 800 C. (1472 F.), the ammonia reacts
with the oxygen of the air to form oxides of nitrogen which,
dissolved in water, yield nitric acid. By suitably regulating
the process of oxidation, one can also obtain ammonium
nitrate, NH 4 NO 3 , which is used as a fertiliser (p. 210) and
as a constituent of high explosives (p. 135).
The social-economic consequences of these developments
in chemical industry have been stupendous. It was in 1913
(a noteworthy and ominous date) that Germany established
the synthetic production of ammonia on an industrial scale ;
and since the later years of the war of 1914-18 she has
obtained, through that process and through the catalytic
oxidation of ammonia, all the ammonium nitrate and nitric
acid which she has required for use in explosives and in the
manufacture of explosives and nitrogenous fertilisers.
1 Obtained by heating Chile saltpetre with sulphuric acid : NaNO 3
O 4 = NaHSO 4 4-HNO 3 (nitric acidV
CHAPTER XI
GLASS, SODA, SOAP, LIME AND CLAY
IN the previous chapter there was discussed one of the
younger of the chemical industries, the production of syn-
thetic ammonia, an industry which was 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 valu-
able 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. Although
it may be that it was by some such accident 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 that one must look for the first know-
ledge 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
214
GLASS, SODA, SOAP, LIME AND CLAY 215
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 enjoy-
ment of light, enlarging the avenues of science, and con-
ferring the highest and most lasting pleasures ; he was
enabling the student to contemplate nature and the beauty
to behold herself. " And in modern times glass has under-
gone a wonderful evolution through the work and labours
of chemists, who have shown how, by variation of the com-
position, the properties of glass may be altered in a most
marvellous degree. Through the production of different
kinds of glass there has been made possible the construction
of apparatus for the most diverse uses, prisms and lenses for
lighthouses, microscopes, telescopes and other instruments,
which have contributed to the service of man and a knowledge
of the universe.
Before considering more fully the nature and properties
of glass, however, there are one or two points of general
importance to which it is necessary to direct attention.
Everyone is familiar with the statement that matter can
exist in three states solid, liquid and gaseous ; and this
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 claims
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 and
give rise to a structure bounded by plane faces or surfaces,
2l6 CHEMISTRY IN THE SERVICE OF MAN
such as we see in the naturally occurring rock crystal,
amethyst, etc. ; whereas an amorphous solid does not natur-
ally 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, however, a liquid
is cooled down, it is found quite generally that the tempera-
ture can be lowered below the normal freezing-point, or
below the melting-point of the solid, without any of the solid
form being produced. One can, for example, with care, cool
water to a temperature much below o C. (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. 1 The process of crystal-
1 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.
GLASS, SODA, SOAP, LIME AND CLAY 2 17
lisation, 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 the
rate at which crystallisation proceeds depends also on the
degree of supercooling. The farther a liquid is cooled below
the normal freezing-point, the faster will solidification occur
once it has been started. This law, however, is subject to
modification through the operation of another factor. It has
already been pointed out 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 be-
coming 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
influence the speed of crystallisation. At first the effect of
supercooling is predominant, and so as the degree of super-
cooling is increased, the rate of crystallisation 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 increase as the temperature is
lowered, and in fact begins now to decrease. There is,
therefore, a certain temperature, a certain degree of super-
cooling, at which the velocity of crystallisation is a maximum,
and below which it becomes less and less ; and, ultimately,
it becomes practically equal to zero. The supercooled liquid
no longer crystallises even when brought into contact with
the crystalline solid.
We know, however, that as a liquid is cooled down, 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 amor-
phous solid is just such a supercooled liquid, a liquid cooled
so far below its crystallisation point that the rate of crystal-
lisation is infinitely slow. In this way are formed, for example,
the glassy lavas, or obsidians, by the rapid cooling of molten
lava, as well as ordinary glass with which we are so familiar.
21 8 CHEMISTRY IN THE SERVICE OF MAN
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.
SILICA AND GLASS
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 dis-
tinguished in granite ; coloured by certain impurities 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 crystallises in six-
sided prisms ending in six-sided pyramids. It is largely
employed for making spectacle glasses and optical instru-
ments.
When this crystalline quartz is heated in the oxyhydrogen
blowpipe flame, or in a specially constructed electric furnace,
to a temperature of about 1650 C. (3000 F.), it melts to a
colourless liquid ; and when this liquid is cooled fairly
rapidly, the quartz can be obtained as a clear, colourless,
glassy mass a supercooled liquid which looks just like
ordinary glass, but is much more transparent. It is, in fact,
the most transparent solid material known. This fused
quartz, or quartz glass, possesses the exceedingly valuable
property that it expands and contracts only very slightly
with alteration of the temperature (its coefficient of expansion
is less than 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 then plunged into cold water, or when cold it can
GLASS, SODA, SOAP, LIME AND CLAY 219
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 encountered.
Although readily attacked by alkalies, it is very resistant to
acids, except hydrofluoric acid. Apart from its scientific and
industrial uses, fused silica is now largely used in the manu-
facture of globes for incandescent gas burners and in electric
radiators.
When heated for some time to a temperature of about
H50C. (2102 F.), a temperature considerably below
the point at which it becomes fluid, the glassy quartz
passes into 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, is heated together with soda (sodium carbonate),
the silica, being an acid oxide, 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 known as water-glass, so called because of
its solubility in water. Commercial water-glass is an aqueous
solution of sodium silicate with excess of silica dissolved in
it, and is used as an adhesive for glass and porcelain, as a
preservative for eggs and for numerous other purposes. Its
use depends on the fact that it readily forms a gelatinous
film on objects. If, instead of heating sand or quartz with
soda (or potash) only, one also adds other metal oxides or
carbonates, such as lime, or alumina (oxide of aluminium),
or oxide of lead, mixtures of silicates are obtained which
220 CHEMISTRY IN THE SERVICE OF MAN
solidify to glasses that do not dissolve in water, and which
constitute what one ordinarily calls glass. Glass has, therefore,
no definite composition, and by varying not only the con-
stituents but also their relative amounts, glasses of various
kinds and possessing very different properties can be prepared.
All glasses, however, contain sodium or potassium silicate.
Glass for table-ware and for general use consists essen-
tially of a mixture of the silicates of sodium and of calcium,
but potassium and aluminium are also frequently present.
The quality and appearance of the glass depend largely on
the purity of the materials employed in its manufacture.
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. 1 Such sand,
mixed thoroughly with sodium carbonate and sulphate, 2
potassium carbonate, pure white chalk or limestone, and
felspar (to supply the aluminium), 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 carbon dioxide which
permeate it, but these bubbles gradually 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 articles of varied shape can, by
the expert skill of the glass blower, be obtained.
The blowing of electric light bulbs and of bottles, and'
the production of sheet glass for glazing, etc., are now carried
out in automatic or semi-automatic machines ; and the
introduction of these machines has made necessary various
1 An abundant deposit of sand at Lochaline on the Sound of Mull,
in Scotland, has now been developed for glass manufacture. Its purity ex-
ceeds that of the best continental quartz sand imported before 1 940 from
Belgium, Holland and France.
2 The addition of sodium sulphate has the effect of strengthening the
finished glass.
GLASS, SODA, SOAP, LIME AND CLAY 221
alterations in the composition of the glass mixture. For the
successful working of these machines the molten glass must
set or solidify more slowly than the glasses worked by hand.
This could be secured by reducing the amount of calcium
oxide and increasing the amount of soda, but the resulting
glass would then be too readily corroded by water. It was
found, however, that if a small amount of magnesia and
SHEET GLASS, PRODUCED BY THE FOURCAULT
PROCESS, PASSING BETWEEN ROLLERS.
(From Glastechnische Berichte, 1928.)
alumina was added to the glass mixture, a sufficiently slow
setting glass could be obtained which could be worked in
the machine without showing devitrification (p. 218) and
which was not corroded on exposure to the air. Such a
glass has the percentage composition : SiO 2 , 72-5 ; Na 2 O,
13-5 ; CaO, 10-5 ; MgO, 2-0 ; A1 2 O 3 , i-o.
By the process, developed more especially in Belgium
by EMILE FOURCAULT, and in America by J. W. COLBURN,
sheet glass is produced directly by lowering a metal bar into
222 CHEMISTRY IN THE SERVICE OF MAN
the molten glass which is caused to well-up through a slit
in a fire-clay plate. As the bar is raised, the glass adheres
to it and solidifies, and in this way a sheet of glass is formed.
This sheet is drawn slowly upwards between asbestos-
covered rollers enclosed in a tall metal box, and is thus
slowly cooled. As it passes out at the top of the box it can
be cut into lengths as desired. In the Libbey-Owens process
SHEET GLASS, PRODUCED BY THE FOURCAULT
PROCESS. GLASS AT TOP OF COOLING CHAMBER
READY TO BE CUT.
(From Glastechnische Berichte, 1928.)
which is now superseding the Fourcault process, the sheet
of glass, after rising out of the tank, passes over a roller and
is drawn along in a horizontal position (Fig. 17).
The surface of sheet glass is not quite plane, but is covered
with slight depressions and ridges, 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 ground
as in the case of plate glass, and in this way
GLASS, SODA, SOAP, LIME AND CLAY
223
one obtains what is known as " patent plate. " Such glass
is largely used for the framing of pictures.
Glass articles which have been formed by blowing or
moulding must be again heated to near the softening point
and then placed in an " annealing " chamber where they 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
Courtesy of Prof . A. Silverman.
FIG. 17. PRODUCTION OF SHEET GLASS BY THE LIBBEY-OWENS
PROCESS.
The sheet of glass which is drawn from the tank of molten glass at
point A, passes over the rollers at BC and then passes between moving
endless bands.
scratched. This can be illustrated by what are known as
Rupert's drops, 1 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 cooling
1 So called because introduced as a toy by Prince Rupert in the seven-
teenth century.
224 CHEMISTRY IN THE SERVICE OF MAN
the hot glass in oil, appears to have been known at least as
early as the first century A.D., as the following incident,
related by Petronius in that excellent satire, " Cena Tri-
malchionis," 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 commended, 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 anyone 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 esteem than dirt.* " In such fashion did Nero
encourage and foster science.
To obviate the danger of personal hurt by sharp splinters
of glass, it is required by law that the windscreens of motor
cars shall be made of safety glass. Such safety glass was first
produced, under the name of " Triplex Glass," by pressing
together, in a hydraulic press heated by hot water, two sheets
GLASS, SODA, SOAP, LIME AND CLAY
225
of plate glass with a sheet of transparent celluloid or cellu-
lose acetate between. In England, vtnal, a polyvinyl plastic
(Chap, xvi), is now used as interlayer. When such glass is
struck a blow sufficiently hard to shatter it, the broken pieces
of glass, often dangerously large and with sharp points or
edges^onotflyboit remain firmly adhering to the plastic inter-
CRACKING OF ORDINARY PLATE GLASS.
layer. Still more recently, " Armourplate " glass, or " Triplex
Toughened " glass, has been introduced, and, in Great
Britain, has largely displaced the laminated glass. This is
not, in spite of its name, a triplex glass at all, but a single
sheet of plate glass which is toughened or hardened, like
Rupert's drops, by being heated to the softening point and
then cooled rapidly, but in a carefully regulated manner, by
226 CHEMISTRY IN THE SERVICE OF MAN
blasts of cold air. By this treatment the glass acquires a
much greater strength and flexibility, and a greater resist-
ance not only to breakage by bending but also to fracture
by impact. Thus, while untreated plate glass, one quarter
of an inch in thickness, was fractured by a weight of 1-68 Ib.
CRACKING OF " ARMOURPLATE " GLASS.
falling from a height of 127 inches, the toughened " Armour-
plate " glass was broken only when the same weight was
dropped from a height of 122 inches. Moreover, when
this toughened glass is broken it does not splinter into
dangerously large and sharp pieces which may inflict severe
or even fatal wounds, as does ordinary plate glass, but
GLASS, SODA, SOAP, LIME AND CLAY 227
breaks up into a mass of small and comparatively harm-
less fragments. Since " Armourplate " glass cannot be cut
or chipped without falling to pieces, the plate glass must
be cut to shape before being subjected to the hardening
process.
In the U.S.A., toughened glass was never widely used,
and a laminated " triplex " glass has received official
approval. In the production of this " safety glass," a sheet
of butvar, a polyvinyl butyraldehyde plastic (p. 337), is
used as interlayer. The unusual strength and resistance to
shock of this glass is shown by the fact that, at the ordinary
temperature, it withstands the impact of a steel ball half a
pound in weight, dropped from a height of 100 feet.
A reinforced glass, much used for constructional pur-
poses (e.g. roofing), can be obtained by embedding in the
still molten glass a network of steel or nickel-steel wire.
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 special optical 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 ex-
pansibilities 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.
Heat-resisting glass with low coefficient of expansion is now
widely used for cooking utensils (e.g. pyrex ware). Such
glass is obtained by reducing the proportion of soda and
increasing the proportion of silica, and boric oxide, which
greatly reduces the coefficient of expansion of glass, is also
added. Thus, pyrex glass contains about 80 per cent, of
silica, 12 per cent, of boric oxide, with smaller amounts
228 CHEMISTRY IN THE SERVICE OF MAN
(3-4 per cent.) of soda and alumina (aluminium oxide).
The value of glass as compared with metal ware for cooking
purposes depends on the fact that glass reflects a com-
paratively very small proportion of the radiant heat which
reaches it, so that baking takes place more rapidly in glass
than in metal dishes.
To avoid distortion with change of temperature, a glass
of the pyrex type, with low coefficient of expansion, has
been adopted for the reflector of a large zoo-inch telescope
which is being constructed for the observatory at Pasadena,
California.
By fusing silica with a mixture of potash and red lead
(oxide of lead, Pb 3 O 4 ), 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 dishes of different
kinds. A still more lustrous glass can be obtained by re-
placing 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, 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 con-
GLASS, SODA, SOAP, LIME AND CLAY 229
fused with the artificially prepared sapphires and rubies to
which reference has already been made (p. no). 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 formation
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 gold in what is called the colloidal state (Chap,
xni). That is, the gold is present in particles so minute that
they are invisible even under a powerful microscope. If,
however, too much gold is added, the metal may separate
out in visible particles and so render the glass opaque. If
one adds selenium to a glass in which the place of lime has
been taken by zinc oxide, a highly transparent red glass,
much used for signal lamps, tail-lights of automobiles, etc.,
is obtained.
The transparency of glass, not only for the rays of visible
light but also for the invisible rays of longer wave length
(infra-red) and of shorter wave length (ultra-violet), can be
greatly increased by the use of very highly purified materials.
Thus, glass of the " Vita glass " type, which has a consider-
able degree of transparency to ultra-violet light, must be as
free as possible from iron. On the other hand, glass con-
taining a considerable proportion of iron, in what is known
as the ferrous state, 1 is used for making goggles to protect
the eyes from infra-red rays (heat rays) and ultra-violet
rays.
Glasses can also be obtained which are opaque to visible
radiations but transparent to ultra-violet rays (e.g. Wood's
glass, which contains nickel oxide), or to infra-red rays.
Glass is also used in large quantities for the production
of mirrors, which are greatly superior to the polished metal
mirrors of our forefathers. In order to avoid distortion,
* Iron forms two oxides, FeO and Fe 2 O 3) known respectively as ferrous
oxide and ferric oxide. From these oxides are derived two series of salts,
ferrous salts and ferric salts.
230 CHEMISTRY IN THE SERVICE OF MAN
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 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. Alu-
minium, deposited on glass, is now also being used in place
of silver for the production of mirrors.
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.
SODA
The use of carbonate of soda in the manufacture of glass
brings that industry into the closest relations with an im-*
portant series of chemical industries, namely, the manufacture
not only of soda itself but also of sulphuric acid, hydrochloric
acid, chlorine and bleaching powder.
Sodium carbonate or soda has been known from remotest
ages as forming a deposit on the floor and shores of the soda-
lakes of Egypt, and this was probably the chief source from
which the early Phoenician traders obtained the salt/ At the
present day, these natural deposits are again being worked
(e.g. at Lake Magadi in East Africa, and at Owens Lake,
GLASS, SODA, SOAP, LIME AND CLAY 231
California). Formerly, soda was called " nitre/' and by this
name it is referred to in the Bible. 1
Previous to the nineteenth century, the car&onate 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 the saltwort (Salsola kali L.). This
was grown on large areas reclaimed from the sea along the
coast of Spain, and more especially along the coast of Alicante,
and was reduced to ash by ignition. This ash, containing up
to 15-20 per cent, of sodium carbonate, was sold under the
name of barilla* The supply, however, was scanty, and
barely sufficient to meet the demand. There was, therefore,
great need for an abundant source of cheap soda, and the
Academy of Paris 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 carbonate
of sodium or soda. This problem was solved by the French
chemist, NICOLAS LEBLANC, and in 1791 a factory for the
manufacture of soda by the Leblanc process was established
at St. Denis. In 1793, however, this 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.
Important and successful as was the Leblanc process
during the first half and more of the nineteenth century, it
had by the end of the century practically succumbed before
an economically more successful rival, the so-called am-
monia-soda or Solvay process. The reaction underlying this
1 " 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 effervescence due to the production of carbonic acid gas.
2 The barilla industry was introduced into Spain by the Saracens,
who called the saltwort, or the ash of saltwort, al qali or al kali. From
this the term alkali is derived. On the salt steppes of the Argentine the
saltwort is still grown, and burned for the production of soda.
232 CHEMISTRY IN THE SERVICE OF MAN
process, a reaction between sodium chloride and ammonium
bicarbonate giving rise to sodium bicarbonate and ammonium
chloride, had been placed before the French Academy in
competition with the Leblanc process ; but the Academy,
fearing the loss of ammonia, rejected the process in favour
of that proposed by Leblanc. In 1838, DYAR and HEMMING,
in England, took out a patent for the working of the ammonia-
soda process, but production on an industrial scale was un-
successful. In 1863, however, after many others had failed,
the Belgian chemist, ERNEST SOLVAY, successfully developed
the process whereby soda can be produced more economi-
cally and in a purer form than by the method of Leblanc.
The process depends on the fact that when carbon dioxide is
passed into a solution of common salt saturated with am-
monia, bicarbonate of soda (baking soda) is deposited. By
heating the bicarbonate, NaHCO 3 , carbon dioxide and water
are driven off and the ordinary carbonate of soda, Na 2 CO 3 , is
obtained j 1 and when this is crystallised from water it forms
clear, colourless crystals, Na 2 CO 3 , ioH 2 O, known as washing
soda. Bath salts consist, as a rule, of sodium carbonate, mixed
with borax or other salts, tinted and perfumed. Baking powders
contain the bicarbonate and a solid organic acid, such as
citric or tartaric acid or cream of tartar (p. 352). So long
as this mixture is kept dry, no action occurs ; but when it
is brought in contact with water, as in the preparation of
dough, the acid reacts with the bicarbonate and carbon
dioxide is evolved. The dough is thereby caused to
rise.
Although the Leblanc process is no longer used for the
manufacture of soda, the first stage of the process, which
consists in heating sodium chloride (common salt) with
sulphuric acid, is still carried out for the production of
hydrochloric acid (muriatic acid or spirit of salt). In this
reaction, a knowledge of which goes back to before the
seventeenth century, the sodium chloride is converted into
1 According to the equation : 2NaHCO 8 =Na 2 CO 3 -f H a O-f-CO 2 .
GLASS, SODA, SOAP, LIME AND CLAY 233
sodium sulphate or " salt-cake/' which is used in the manu-
facture of glass, and at the same time large quantities of
hydrogen chloride or hydrochloric acid gas, HC1, are pro-
duced. When this gas is passed into water, in which it is
exceedingly soluble, the acid, hydrochloric acid, is obtained.
This is one of the most important of the so-called mineral
acids.
Hydrogen chloride, moreover, is a source of the very
important substance, chlorine ; for, when hydrogen chloride
mixed with air is passed over heated pumice, impregnated
with copper chloride, the copper chloride acts as a catalyst
and accelerates the oxidation of the hydrogen chloride by
the oxygen of the air, with formation of chlorine a process
known as Deacon's process. Chlorine is a gaseous element
and a most valuable bleaching and disinfecting agent (see
also p. 323). It is used in the manufacture of dyes, in-
secticides, etc. For convenience of transport and use, the
chlorine may be passed over slaked lime (p. 245), which
reacts with it and 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 require to be
bleached before use. It is still extensively employed at the
present day.
Owing to the development of the electrolytic production
of chlorine (p. 262), the Deacon process is becoming of less
importance.
SOAP
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 re-
sembling what is now known as 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
234 CHEMISTRY IN THE SERVICE OF MAN
considerably, 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 pro-
perties 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
steam. This process of hydrolysis, as it is called, or decom-
position by water, which is catalytically accelerated by acids,
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.
Caustic soda (NaOH) and caustic potash (KOH) are
obtained by boiling solutions of sodium carbonate or potas-
sium carbonate with slaked lime or calcium hydroxide,
Ca(OH) 2 . Mutual decomposition takes place with formation
of sodium or potassium hydroxide and calcium carbonate,
and the latter, being insoluble, separates out. Nowadays
an electrolytic process (p. 262) in which not only caustic
soda or caustic potash is formed, but also chlorine and
hydrogen, is assuming ever greater proportions, and may
one day 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
GLASS, SODA, SOAP, LIME AND CLAY
235
pointed out (p. 191), 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 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 (p. 190), for use in the manufacture of
Courtesy of Lever Brothers, Ltd.
MANUFACTURE OF SOAP.
Pans in which the saponification is carried out.
hard soap. By the admixture of different raw materials in
varying proportions, soaps of different kinds and qualities
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
236 CHEMISTRY IN THE SERVICE OF MAN
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. Additions
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 dis-
tillation in special vacuum stills in order to recover the
glycerine, for which there exists a large demand for the
manufacture of dynamite and other explosives. It is also
used in the manufacture of synthetic resins known as
" Glyptals " (e.g. glyceryl phthalate), as a humidifying agent
in rayon, cellophane and other industries, and as an " anti-
freeze " in the radiators of motor cars and in gas meters.
Although glycerine is obtained mainly by the hydrolysis
or saponification of fats and vegetable oils, its synthesis from
propylene, CH 2 : CH-CH 3 , one of the gases formed in the
cracking of mineral oils (p. 95), promises to become of
increasing importance. Under normal conditions, however,
it is too costly.
The soap curd, after being boiled up with water to remove
impurities, and again " salted out," is hardened by cooling,
dried, cut into flakes, mixed with colouring matter or per-
fumes, and formed into bars. The bars are then cut into
lengths 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. The soap is thereby hardened, and since the
GLASS, SODA, SOAP, LIME AND CLAY 237
added salts act as water softeners, its detergent power is
increased.
The familiar transparent soaps are obtained by dissolving
pure soap in alcohol and then evaporating off the alcohol.
In the case of the cheaper varieties of soap, such as com-
mon 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. This soap is generally cut into bars, as shown in
the illustration.
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 (" persil "), etc.
The cleansing power of soap depends on its physical as
well as on its chemical properties ; and in this connection
its most important property is that it lowers the surface
tension of water. What do we mean by this ? Everyone
knows that when water is brushed over a greasy 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. It is to the action of surface ten-
sion that is due the proverbial ease with which water runs off
a duck's back. If the surface tension is reduced sufficiently,
if, as it were, one reduces 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 soap
in the water. 1 This property of soap of lowering the surface
1 The effect described here will be familiar to everyone who has
interested himself in watei -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.
Courtesy of Lever Brothers, Ltd.
Soap cut into bars, piled for drying.
Courtesy oj Lever Brothers, Ltd.
MANUFACTURE OF SOAP.
Jacobi Rapid Cooling Press in which the liquid soap is cooled in frames
clamped between plates round which cold water circulates.
GLASS, SODA, SOAP, LIME AND CLAY 239
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 appearance 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, much
whiter than before), and they do not run together and form
a separate layer on standing. The oil is permanently emulsi-
fied. 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 emul-
sifying 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.
In the light of the explanation, just given, of the cleans-
ing power of soap, attempts have been made to produce
other detergents very different in chemical nature from an
ordinary soap or salt of a fat acid. Thus, by the action of
sulphuric acid on higher unsaturated hydrocarbons of the
ethylene type (p. 91), containing between ten and eighteen
carbon atoms, acids are formed ; and the sodium salts of
these, placed on the market under various names, such as
Lissapol, Teepoly etc., are found greatly to reduce the surface
240 CHEMISTRY IN THE SERVICE OF MAN
tension of water and to have valuable detergent properties.
Some of them, e.g. sodium lauryl sulphate, find use in shampoo
powders. Since these substances do not form insoluble
compounds with lime or magnesia, they readily form a
lather, and can therefore be advantageously used, even with
hard water. They are being increasingly used as substitutes
for soap.
Although the salts of the fat acids with sodium and
potassium, the ordinary soaps, are soluble in water, the salts
with calcium and magnesium are insoluble. Consequently,
when soap is brought into water containing salts of calcium
or magnesium in solution, 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,^ f Sodium bicarbonate (sulphate,
etc.) and LivJ etc ^ and
Calcium bicarbonate (sul- f * j Insoluble soap (calcium stear-
phate, etc.) J ^ ate, etc.).
From its " feel " in washing, water containing calcium or
magnesium salts is called " hard/' and, since the soap is de-
composed, no lather can be obtained until sufficient soap has
been added to combine with all the calcium and magnesium
salts present. Moreover, since the bicarbonate or other salt
of sodium which is formed 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 calcium and magnesium (the so-called " fur "),
which insulates the kettle or boiler and so causes a loss
of heat. Explosions, moreover, may be caused in boiler
tubes owing to the " scale " cracking and so allowing
water to come in contact with the overheated tubes. It
is of importance, therefore, to get rid of or to reduce the
hardness.
GLASS, SODA, SOAP, LIME AND CLAY 24!
The formation of " fur " or " scale " may be prevented
not only by softening the water, as explained in the following
paragraphs, but also by the addition to the water of a small
quantity of sodium hexametaphosphate (NaPO 3 ) 6 , obtained
by fusing the ordinary sodium phosphate, NaH 2 PO 4 . This
hexametaphosphate is produced commercially in the United
States under the trade name of " Calgon " and prevents the
formation of " fur " by forming with the calcium salts
soluble complex phosphates.
When the hardness of water is due to the presence of
calcium bicarbonate (formed by the action on limestone, or
calcium carbonate, of the carbonic acid gas dissolved in rain
water), 1 it can be got rid of by boiling, and is therefore
known as temporary hardness. On a large scale, the " soften-
ing " of the water can be effected by the addition of slaked
lime in proper amount (Clark's process). The soluble
bicarbonate is thereby converted into the carbonate which,
being insoluble, separates out and is removed by filtration :
Ca(HCO 3 ) 2 +Ca(OH) 2 -2CaCO 3 +2H 2 O.
Hardness which is due to the presence of sulphate of
calcium or magnesium 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
calcium or magnesium being thereby thrown out of solution
as insoluble carbonates. Hence the use of washing soda in
the laundry.
For industrial and domestic purposes, another process
for softening hard water has been introduced, known as the
permutit process. Permutit is an artificially prepared zeolite,
sodium aluminium silicate, formed by fusing together
quartz, alumina and sodium carbonate. When hard water is
filtered through a layer of this material, the calcium and
Calcium Calcium
carbonate . bicarbonate .
When calcium bicarbonate is heated, it decomposes into calcium car-
bonate, water and carbon dioxide.
242 CHEMISTRY IN THE SERVICE OF MAN
magnesium replace the sodium in the silicate, forming
calcium or magnesium aluminium silicate, and are thus
removed from the solution. The water is thereby rendered
soft. When all the sodium has been replaced, the permutit
ceases to be effective, but its activity can be restored by
flushing with a solution of common salt (sodium chloride).
By this means the sodium aluminium silicate is regenerated.
More recently, great advances in water purification have
been made owing to the discovery, in 1935, by chemists
working at the National Chemical Laboratory at Teddington,
that certain synthetic resins and other products (obtained by
treating coal with fuming sulphuric acid) can remove from
solution not only calcium and magnesium, but also sodium
and other metals (cations, p. 256), present in salts, while
synthetic resins of another type can remove the acid ions
(unions, p. 256), such as sulphate and chloride. Thus, by
passing water containing, say, calcium, magnesium and
sodium salts in solution through resins of the first type, the
metal ions are removed and replaced by hydrogen ions, and
the effluent contains only free acids. On passing this acid
water through resins of the second type, the acids present are
removed and replaced by carbonic acid. Water free from
dissolved salts is thereby obtained. By passing a current of
air through this water, the carbonic acid (CO 2 ) is removed
and the water then resembles distilled water in purity.
The activity of the resins can be restored by treatment with
dilute sulphuric acid, in the former case, and with a solution
of sodium carbonate, in the latter. By means of these ion-
exchange resins, as they are called, industries can now obtain,
much more cheaply than by distillation, water equal in purity
to distilled water, or, also, water containing any concentration
of salts that may be desired (e.g. for use as a potable
water).
The methods just described for removing dissolved salts
from water found, during the war, an application of the
highest importance in placing in ti?e hands of airmen,
GLASS, SODA, SOAP, LIME AND CLAY 243
compelled to " bale out " over the sea, a means of obtaining
a potable water from sea-water. For this purpose, a mixed
barium and silver zeolite (barium and silver aluminium
silicates), containing also a small amount of silver oxide,
was employed. When this was shaken up with sea water,
the salts were removed by conversion into insoluble barium
sulphate, silver chloride, magnesium hydroxide, sodium
zeolite, etc., and, by straining through a filtering cloth, a
water, almost like distilled water, was obtained. In order to
remove from the water any colour imparted to it, by the
zeolite, a quantity of charcoal (p. 123) was incorporated in the
mixture.
LIME
The solvent action on limestone of water containing
carbon dioxide in solution, to which reference has been
made, is of great economic and geological importance. Not
only is the process mainly responsible for the production of
hard water, which is met with in all limestone and chalk
districts, but it is the chief agent by which lime is transported
through the soil and rendered available for plants.
How great may be the effect of this solvent action of
carbonic acid, acting through the ages, is seen from the great
limestone caves, like the Mammoth Cave, Kentucky, which
have been gradually eaten out of the solid rock by water
containing carbonic acid in solution. No sooner, however,
are these caves formed than Nature begins to fill them up
again, for the rain water, bearing carbonic acid in solution,
percolates through the rock and dissolves it. On reaching the
roof of the cave the water evaporates and leaves behind a
minute grain of limestone ; and as drop follows drop through
endless years, grain is added to grain and an icicle-like
stalactite hangs pendent from the roof. As Shelley has so
beautifully written :
From the curved roof the mountain's frozen tears,
Like snow or silver or long diamond spires,
Hang downward, raining forth a doubtful light.
244 CHEMISTRY IN THE SERVICE OF MAN
If the drops of water come faster, some may fall to the
floor of the cave and, evaporating there, build up a mighty
column or stalagmite. Many and varied, graceful and
grotesque, delicate and massive, are the forms which may
thus be produced, and the sight presented by such a cave,
'* -
Courtesy of Union Pacific System. Copyright, J. E. JIaynes, St. Paul.
LIMESTONE TERRACES, MAMMOTH HOT SPRINGS, YELLOWSTONE PARK.
suitably illuminated, is one of the most impressive that can
be experienced.
Spring water carrying calcium bicarbonate in solution will
deposit calcium carbonate as the carbon dioxide escapes and
the water evaporates. In this way there have been and are
being formed the great terraced basins of limestone deposited,
for example, at Mammoth Hot Springs, Yellowstone Park,
U.S.A.
Limestone, or calcium carbonate, when strongly heated,
GLASS, SODA, SOAP, LIME AND CLAY
245
decomposes into quicklime (calcium oxide) and carbon
dioxide. This process, which is known as the burning of
lime, is carried out on a very large scale in rotary kilns as
a step, more especially, in the production of slaked lime
and mortar.
When water is poured on quicklime, combination takes
ICELAND SPAR, SHOWING DOUBLE REFRACTION.
place and the quicklime is converted into slaked lime (calcium
hydroxide). So great is the heat evolved in this process that
large volumes of steam are produced, and the water may
even be made to boil. In the making of mortar, the slaked
lime is mixed with a certain amount of sand, in order to
prevent too great a contraction taking place when the mortar
sets ; and the setting of mortar depends on the fact that on
exposure to the air the slaked lime reacts with the carbon
dioxide to form a coherent mass of interlocking crystals of
calcium carbonate (limestone).
Slaked lime or calcium hydroxide dissolves sparingly in
246 CHEMISTRY IN THE SERVICE OF MAN
water, the solution being known as lime water. It is used
medicinally as a mild alkali.
Calcium carbonate occurs in various forms. Chalk and
limestone have been formed from the shells or skeletons of
marine organisms, deposits of which have become com-
pacted under pressure ; and coral is built up by the minute
coral polyp. Marble represents a limestone which has been
transformed by heat and pressure into a mass of small
crystals. Large transparent crystals of calcium carbonate
are also found as calcite or Iceland spar. This material has
the property of double refraction, as it is called, so that an
object, printed matter for example, appears double when
viewed through a crystal of Iceland spar.
Pearls, also, consist essentially of calcium carbonate
deposited, layer on layer, by the oyster on a particle of sand,
or other foreign body. Since all carbonates are decomposed
by acids, with evolution of carbon dioxide, pearls will be
destroyed if allowed to come in contact with acid liquids,
e.g. vinegar. In this connection one may recall the story
told by Plutarch of how Cleopatra, wishing to impress
Antony with her wealth and magnificence, wagered that
she could spend the equivalent of 150,000 on a single
meal. The wager having been accepted, Cleopatra, who was
wearing two pearls each equal to half the sum, detached one
and dropped it into a cup of vinegar. The pearl quickly
disappeared and she then drank the liquid. She was pro-
ceeding to do likewise with the second pearl when she was
restrained, it being decided that the wager had already been
won.
CLAY
Among the most important of the naturally occurring
minerals are those double silicates of an alkali metal (sodium
or potassium) and aluminium which are known as felspars.
These compounds, present so abundantly in granites, while
insoluble in water, are attacked by the atmospheric carbonic
GLASS, SODA, SOAP, LIME AND CLAY 247
acid and undergo decomposition with formation of alkali
carbonate and aluminium silicate ; and this aluminium
silicate, in a hydrated state and known as kaolinite, is the
main constituent of kaolin or white china clay. To this
material also is mainly due the plastic properties of the
common clays in which the kaolinite is mixed with various
impurities.
Clay is, in our modern no less than in the ancient civilisa-
tions, a material of great importance, and is used for the
production not only of building materials but also of por-
celain, stoneware and earthenware. This importance it owes
mainly to the fact that it forms a plastic mass with water and
becomes hard and stone-like when heated to a high tem-
perature. Clay is also used in the manufacture of cement.
In the manufacture of porcelain or china, pure white clay
is mixed with the requisite amount of ground felspar and
quartz, known as " frit," and the soft, plastic mass is then
formed into the desired shape. On being heated in a kiln
to a temperature of about 1200 C. (2192 F.), the clay
loses water and passes into an anhydrous silicate, 3A1 2 O 3 ,
2SiO 2 , and the felspar fuses and dissolves the quartz. A
glass is thus formed which binds the mass together and
renders it non-porous and non-absorbent of water. The
mass also becomes translucent, in proportion to the amount
of glassy material present.
In the production of stoneware, the fusion of the " frit "
is not so complete, so that the body of the ware, although
non-porous, is not translucent.
In the manufacture of earthenware, the ware is fired at a
lower temperature and very little vitreous material is formed.
The body of the ware, therefore, is porous. This is known
as bisque or " biscuit " ware. When pure materials are
employed, such earthenware is largely used as table-ware.
After the ware has been fired, it is coated with ground
felspar, or other fusible silicate, and again heated. A glassy
film or glaze is thereby formed on the surface of the ware.
248 CHEMISTRY IN THE SERVICE OF MAN
Clay also finds a very important application at the present
day for the production of Portland cement, a material which
owes its name to its resemblance to Portland stone. Clay
and limestone (or other form of calcium carbonate) are mixed
together so as to give the proper proportions of lime, alumina
and silica, and the mixture is then ground to a fine powder
and heated in long, rotary kilns to the point of incipient fusion.
The partially fused mass, which consists essentially of a
mixture of calcium silicate and calcium aluminate (sCaO,
A1 2 O 3 ), is ground and constitutes the Portland cement of
commerce. This has the property of setting even under
water.
Concrete, now so largely employed for building purposes
and for road making, is a mixture of cement with sand or
gravel.
CHAPTER XII
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, electrical energy, the
utilisation of which is so notable a feature of modern times.
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 anatomist, LUIGI 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 science
which has revolutionised the world, which has made practic-
able the telegraph, telephone and " radio," 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-country-
man, ALESSANDRO VoLTA, 1 Professor of Physics in the
1 The intimate connection of Volta with electricity is held in remem-
brance by the use of the term volt as the unit of pressure (or voltage)
of an electric current.
24Q
250 CHEMISTRY IN THE SERVICE OF MAN
University of Pavia, that the science' owes its further develop-
ment. Rightly interpreting the muscular contraction 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
effects 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 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, sodium and potassium, which are doubt-
less unfamiliar to most people, are silvery-white in colour,
and very lustrous. When exposed to the air, however, they
tarnish immediately, owing to the readiness with which
they react with the water vapour in the air. They are soft
and of a cheese-like consistency, so that they can be readily
cut with a knife. 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
ELECTRICITY AND CHEMISTRY 251
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.
Sodium cyanide, NaCN, which is extensively used in the
extraction of gold (p. 154) is produced industrially by passing
ammonia over a heated mixture of sodium and carbon :
The hydrogen formed in the process can be used in the
synthesis of ammonia (p. 207) or for other purposes.
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 intro-
duction of the dynamo (made possible by the scientific
researches of Faraday), that the industrial application of
electricity became 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. The couronne
de tasses of Volta has been replaced by multitudes of hum-
ming dynamos ; 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 electroplating,
a process which has been widely 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
252 CHEMISTRY IN THE SERVICE OF MAN
and gold, but also with nickel and with chromium, metals
which are much used on account of their white colour and
power of resisting atmospheric conditions without tar-
nishing.
In principle the process is comparatively simple, and con-
sists 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
FIG. 1 8. CONDUCTIVITY OF SOLUTIONS FOR ELECTRICITY.
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 water
the ends of two wires which are connected with an electric-
lighting circuit and lamp (Fig. 18), 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 substances 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 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
ELECTRICITY AND CHEMISTRY 253
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 acids, which have a sour taste and the
property of turning red a blue solution of the vegetable
colouring matter called litmus, are electrolytes ; 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 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 to 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 por-
tions of the metallic conductor dipping into the solution
are called) immediately becomes coated with a bright rose-
floured deposit of copper. This is the process used in
electroplating. In the case of solutions of sodium chloride,
hydrogen is liberated at one of the electrodes and can be
seen rising in bubbles from the electrode. The solution also
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
254 CHEMISTRY IN THE SERVICE OF MAN
having bleaching properties, as is shown by the fact that it
discharges the colour of a litmus solution. Whenever, there-
fore, an electric current passes through a conducting solution,
there is a movement of electrically charged matter through
the liquid charged particles of copper, or hydrogen, 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 natural philosopher, MICHAEL FARADAY, who called
the electrically charged moving particles which thus con-
veyed the electricity 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, the conductivity of
electrolytes in solution was the subject of much discussion.
Faraday, and many others after him, assumed that the
molecules of an electrolyte are decomposed by the electric
current into positively and negatively charged particles the
ions which then move in opposite directions through the
solution. This view was later shown to be incorrect, and in
1886 the Swedish physicist, SVANTE ARRHENIUS, put forward
the very revolutionary view that some of the molecules of an
electrolyte, when dissolved in water, break up spontaneously
into ions, and that the fraction of the molecules which
undergoes this process of ionisation increases as the solution
is made more and more dilute. Thus, the molecules of
common salt, or sodium chloride, for example, were supposed
to break up in solution into positively charged sodium atoms
or sodium ions, Na + , and negatively charged chloride ions,
Cl~ ; and these ions were regarded as leading a free and
independent existence in the solution, each exhibiting its
own properties and showing its own chemical reactions.
This theory of electrolytic dissociation, as it was called, proved
to be, in many respects, exceedingly satisfactory, and was
very generally accepted.
In one important respect, however, the theory of Arrhenius,
ELECTRICITY AND CHEMISTRY 255
when applied to solutions of salts, was found to be defective.
It has already been pointed out (p. 39) that the molecule
of sodium chloride is formed by the electrostatic attraction
between a sodium atom which has acquired a positive charge
through the loss of an electron and a chlorine atom which
has become negatively charged through taking up this
electron. In the molecule of sodium chloride, therefore,
the sodium and chlorine are already present as electrically
charged particles, i.e. as tons. Solution of salt in water,
therefore, does not, as Arrhenius thought, bring about the
formation of ions ; solution merely brings about a diminution
of the force of attraction between the electrically charged
sodium and chlorine atoms (ions), and makes it possible for
them to move about freely in the solution. A similar freedom
of movement is made possible by melting the salt, and fused
sodium chloride or fused sodium hydroxide is also found
to conduct the electric current (p. 250), owing to the presence
of ions.
As in the case of sodium chloride, so also in the case of
other salts, the ions are pre-existent in the molecules, and
solution in water merely makes freedom of movement
possible.
The same explanation is valid also in the case of the metal
hydroxides, such as sodium or potassium hydroxide. These
all contain the hydroxide ion, OH", and solutions of these
hydroxides, therefore, all contain this ion. It is, in fact, to
the presence of these ions in solution that the general
properties of alkalies are due.
The theory of Arrhenius, however, applies to acids, such
As hydrochloric acid, which do not conduct the electric
current in the liquid state. Ion formation takes place only
on solution, and one may assume the occurrence of a reaction
such as HC1+H 2 O-=H 3 O + +C1-, the ion H 3 O+ being a
hydrated hydrogen ion H+.H 2 O. All acids in solution give
rise to this ion, and the so-called acid properties of a solu-
tion are really due to the presence of hydrogen ion.
256 CHEMISTRY IN THE SERVICE OF MAN
In the light of what has just been stated, the fact that the
solution of a salt, an acid or an alkali in water conducts the
electric current, becomes readily intelligible. These solu-
tions contain free, positively charged cations (hydrogen or
metal ion), and free, negatively charged anions (hydroxide
ion, OH", or acid ion, Cl~, NO 3 ~,
etc.). When, therefore, two elec-
trodes 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 posi-
tively charged ions, the cations.
These anions and cations move
in opposite directions through
the solution, and give up their
charges at the electrodes ; they
transport or convey the electricity
through the solution, and it is
this movement or procession of
electrically charged particles that
constitutes what is called the
electric current in the solution.
This explanation of the
passage of a current through a
B
FIG. I 9 .-MIGRATION OF IONS.
lation, not a mere phantasy, for
it is easy to demonstrate not only that there is a movement
of the ions through the solution, 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. 19) is poured a solution
of potassium chloride to which sufficient gelatin has been
ELECTRICITY AND CHEMISTRY 257
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 drop or two of alkali. (Phenolphthalein
is a colourless substance which yields a deep-red colour with
alkalies, or solutions containing hydroxide 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 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 platinum
wire connected with the positive pole of a battery in the
solution of hydrochloric acid and copper chloride ; and a
platinum 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 decolorised
the reddened phenolphthalein, and have produced, there-
fore, 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 pro-
duced by the hydrogen ions, and give a blue colour to the
gelatin (B). In the other limb of the tube, the hydroxide
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
258 CHEMISTRY IN THE SERVICE OF MAN
copper ions, but not so deep as the colourless, band produced
by the hydrogen ions, from which one concludes that the
hydrogen ions move faster than the hydroxide ions, and the
latter faster than the copper ions.
As has been pointed out, it is not only when in a state of
solution that a salt conducts the electric current ; it conducts
also when fused, or converted into the liquid state by heat.
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 ionisation afford an ex-
planation of the process of
-PorOUS e l ectr ly s * s > whereby elec-
trical energy is transformed
Graphite
/-Plate
FIG. 20. LECLANCHE CELL.
into chemical energy, or the
potential energy of chemi-
cally reactive substances, but
it helps us also to understand
the reverse process of the
transformation of chemical
energy into electrical energy,
as it occurs in the different voltaic cells.
One of the best known cells, widely used for work-
ing telephones and electric bells, is the Leclanche cell
(Fig. 20). This very simple cell consists of a jar con-
taining 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 dioxide), and a zinc rod. The
porous pot also contains a solution of sal-ammoniac. When
the cell is in use, zinc readily gives up electrons (negative
charges of electricity) and passes into solution as positively
charged zinc ions. The electrons given up by the zinc
atoms pass through the metallic conductor to the graphite
ELECTRICITY AND CHEMISTRY 259
plate where they neutralise the positive charge on the
ammonium ions (NH 4 " f ) formed by the ionisation of am-
monium chloride, and so give rise to the uncharged
group of atoms, ammonium (NH 4 ). This group cannot
exist as such and immediately reacts with the water (just
as sodium does), with production of ammonium hydroxide
(NH 4 OH) and hydrogen. * This hydrogen, however, is
oxidised to water by the oxide of manganese, and so is
prevented from forming a non-conducting layer on the
electrode, and thereby stopping the current. The elec-
trode is thereby " depolarised " as it is said. When the
cell becomes exhausted, its activity can be renewed by re-
placing the spent liquid by a fresh solution of ammonium
chloride. The Leclanche cell has an electro-motive force
of 1-5 volt.
The Leclanche type of cell has, in recent years, passed
into very widespread use owing to its modification to form
the common dry cell. In this cell there is a zinc container
which also acts as the negative pole of the cell, and inside
this is placed the graphite plate or rod with its depolarising
packing. The latter is separated from the zinc container by
a layer of paper which, like the whole contents of the cell, is
soaked with a solution of sal-ammoniac (Fig. 21). Such dry
cells are now in use for flash-light lamps, bells, telephones,
radio-batteries, etc.
Although, as has been said, the much more efficient
dynamo has superseded the voltaic cell as a source of elec-
tricity 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 dioxide
as it is called, immersed in a solution of sulphuric acid
of specific gravity about 1*30. On joining these two plates
by means of a conductor, a current of electricity flows
through the conductor from the lead dioxide plate to the lead
plate. The chemical reaction which yields the energy which
260
CHEMISTRY IN THE SERVICE OF MAN
Zinc
Paper
is transformed into electricity, is the conversion of the lead
and lead dioxide into lead sulphate : Pb+PbO 2 +2H 2 SO 4 =
2PbSO 4 +2H 2 O. 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 back to its former condition, can be
readily recharged, by sending a current of electricity ob-
tained, say, from a dynamo through the cell in the opposite
direction to that of the
current which the cell
itself gives. In the pro-
Graphite cess of charging, the lead
Depolariser sulphate is converted to
lead at the negative pole,
and to lead dioxide at the
positive pole. In this way,
electrical energy is con-
verted into potential,
chemical energy ; and in
this form the energy is
stored, and is available
for use just when and
where it is required.
The process of charge and discharge can be followed by
means of a hydrometer which enables the specific gravity
of the acid to be determined. When the cell is being dis-
charged, sulphuric acid is used up to form lead sulphate,
and the specific gravity of the solution falls ; but when the
cell is being charged, sulphuric acid is returned to the solu-
tion and the specific gravity increases. In the fully charged
cell the specific gravity should be about 1-30 ; when the
cell is discharged, the specific gravity falls to 1-15.
The 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 energising the self-starters of motor cars ; for
FIG. 21. DRY CELL.
ELECTRICITY AND CHEMISTRY 261
use in portable " wireless " sets ; and in many other cases
where a readily transported supply of energy is desired.
Another storage cell, possessing a number of advantages
over the ordinary lead accumulator, is the nickel-iron cell
which is sometimes known as the Edison cell. In this cell
the active mass of the positive plates consists essentially of
nickelic hydroxide, Ni(OH) 3 , or nickelic oxide, Ni 2 O 3 , in a
hydrated form, and this is mixed with powdered graphite to
give increased conductivity. The active mass of the negative
plates is finely divided iron. The electrolyte is a solution
of potassium hydroxide of specific gravity 1-190. The active
materials are contained in pockets in the nickelled steel
plates and are formed under a pressure of 200 tons.
When this cell is yielding current, the nickelic oxide on
the positive plate is reduced to the lower oxide, nickelous
oxide (NiO), in a hydrated form, or to nickelous hydroxide,
Ni(OH) 2 ; and the iron on the negative plate is oxidised to
the oxide (FeO), or hydroxide, Fe(OH) 2 . The chemical
change which takes place, therefore, may be represented by
the equation : Fe+2Ni(OH) 3 -Fe(OH) 2 +2Ni(OH) 2 . The
charged cell has a voltage of 1-35 volts.
When the cell has become discharged, it can be recharged
by passing a current through the cell in a direction opposite
to that of the current given by the cell. Thereby, the
nickelous hydroxide is oxidised to nickelic hydroxide, and
the iron hydroxide is reduced to metallic iron.
The nickel-iron accumulator has a lighter weight and
greater robustness than the lead accumulator, and it does
not undergo deterioration, as the lead accumulator does,
when left in a discharged state. It is, in fact, much less
liable to damage by careless treatment, and has a longer life.
The nickel-cadmium cell is similar to the one just de-
scribed. Its electromotive force is 1-25 volts.
The application of electricity to chemical manufactures
has produced an industrial revolution. Not only have electro-
262 CHEMISTRY IN THE SERVICE OF MAN
chemical processes more or less completely displaced 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 production of many new
substances of great value. One of the earliest applications
of electricity, we have seen, was to the electroplating of
metals by a process of electrolysis. By this process metals
can be obtained in a state of great 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
mainly for electrical purposes. The importance of pure
copper in this connection is due to the fact that the con-
ductivity of copper for electricity is greatly diminished even
by small amounts of impurity.
The electrolytic preparation of sodium hydroxide or
caustic soda and of chlorine, to which reference has already
been made (p. 234), depends on the electrolysis of a solution
ELECTRICITY AND CHEMISTRY 263
of sodium chloride or common salt. When a pure caustic
soda is desired, the electrolysis is carried out in a large
covered-in tank filled with a solution of sodium chloride
into which dip graphite electrodes. These serve as anodes.
At these electrodes, when the cell is in action, chlorine is
evolved and passes away through a pipe in the roof of the
Courtesy of The International Electrolytic Plant Co.
PRODUCTION OF HYDROGEN AND OXYGEN BY ELECTROLYSIS.
tank. Along the floor of the cell mercury is allowed to flow
in a slowly moving stream. This forms the cathode, and the
sodium which is here set free dissolves in the mercury. The
solution of sodium in mercury flows out at the end of the
tank and is treated with pure water. The sodium reacts with
the water, giving rise to hydrogen and a solution of caustic
soda, and the mercury is passed through the cell again.
When the electrolysis is carried out mainly for the pro-
duction of chlorine, other types of cell are frequently used.
Solid caustic soda is obtained from the solution by
264 CHEMISTRY IN THE SERVICE OF MAN
evaporating off the water. It forms a white very hygroscopic
solid which undergoes deliquescence or becomes moist
when exposed to the air. It is readily soluble in water, and
the solution has the soapy feeling characteristic of alkalies.
KSOWLES' CELL FOR THE ELECTROLYTIC PRODUCTION OF HYDROGEN
AND OXYGEN.
The electrodes, A, are separated by diaphragms of asbestos cloth,
L, and are surmounted by metal boxes, B, in which the gases collect.
From these boxes the gases pass by the pipes, J, to the off-take pipes, K.
Large quantities of caustic soda are used in the manufacture
of soap.
For the chlorine which is produced in the above electrolytic
process, there has developed an ever- widening range of
application, both for bleaching and as a reagent in chemical
ELECTRICITY AND CHEMISTRY 265
industry. Owing to its very powerful germicidal action,
chlorine is now very widely used for the sterilisation of the
water supply of towns, as well as for the sterilisation of the
water of public swimming pools, etc.
In the electrolysis of solutions of sodium chloride for the
production of sodium hydroxide, the hydrogen which is
produced must be considered as a by-product and is some-
times neglected. To an increasing extent, however, the
hydrogen and chlorine are now caused to combine together
hydrogen burns in chlorine so as to form hydrogen chloride.
On dissolving this gas in water, a pure hydrochloric acid is
obtained.
The electrolytic process is also extensively used for the
production, on a large scale, of pure hydrogen and oxygen.
In this case, a solution of caustic soda is generally employed
as the electrolyte. When the current is passed through the
solution, hydrogen is liberated at the cathode, and oxygen is
liberated at the anode.
It has already been pointed out that electrolysis may be
applied not only to substances dissolved in liquids but also
to substances in the fused state, as in the production of the
metals sodium and potassium. One of the most, important
examples of this is found in the electrolytic production of
the metal aluminium. This is the most abundant of all the
metallic elements in the world, but it occurs naturally only
in the form of compounds, in combination with other
elements. So difficult is it to isolate the metal from its com-
pounds 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 since 1886 that it has become possible, by the applica-
tion of an electrolytic method, to produce the metal at a
reasonable price. The isolation of the metal is effected by
the electrolysis of a solution of purified bauxite or oxide of
aluminium in molten cryolite (a naturally occurring com-
266 CHEMISTRY IN THE SERVICE OF MAN
pound 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 elec-
trolysis, an iron bath, lined with graphite, is used, and this
forms the cathode, while large graphite 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 com-
bines with the carbon electrode, producing the poisonous
gas carbon monoxide, which may either escape as such or
burn to form carbon dioxide.
Aluminium 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 where lightness
and portability are of importance, 1 but it is also used as a
conductor of electricity, and, as we have seen, for the pro-
duction, 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 removed to a large extent 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 ; and
when added to brass, aluminium greatly increases the ten-
acity of that alloy. With the metal magnesium, aluminium
forms a valuable alloy called magnalium (containing from
i to 2 per cent, of magnesium), which is even lighter than
aluminium itself and is equal to brass in strength ; and the
construction of aeroplanes has been revolutionised by the
discovery of the alloy duralumin, an alloy of aluminium with
copper (4 per cent.), magnesium (0-5 per cent.), and man-
ganese (o'5 per cent.). This alloy, while having a tensile
1 The specific gravity of aluminium is only 2-7, that of steel about 7*8.
ELECTRICITY AND CHEMISTRY 267
stress equal to or greater than steel, has only one-third of
its weight.
The metal magnesium, to which reference has just been
made, is a grey-coloured metal which burns with a very
bright and photographically active light. Hitherto, it had
been generally known through its use in the preparation of
" flash-light " powders, or in the form of ribbon for use in
photography. In recent years, however, magnesium has
come into rapidly expanding use as an industrial metal, the
lightest of all the industrial metals, with a specific gravity of
only 1 74. Its main use now is for the production of " ultra
light " alloys, containing 90 per cent, or more of magnesium,
as structural materials in aircraft and other vehicles and for
castings of various kinds. It is also used in the upper
structures of ships.
By alloying magnesium with other metals, especially
aluminium and zinc, together sometimes with small amounts
of manganese or other metals, increased mechanical strength
is obtained.
The metal occurs in nature only in the form of compounds.
Magnesium chloride, combined with potassium chloride to
form the mineral carnallite, occurs in the great salt deposits
near Stassfurt, and the metal is obtained by the electrolysis
of fused carnallite or of magnesium chloride to which
potassium chloride is added in order to lower the temperature
of fusion.
Magnesium occurs also as the carbonate, known as
magnetite, in various countries of the world ; and the double
carbonate of magnesium and calcium, known as dolomite,
is abundant and widespread. From these carbonates, the
oxide, magnesia, can be obtained by calcination ; and pro-
cesses have been devised for obtaining the metal by the
reduction of the oxide by means of various reducing agents,
such as calcium carbide, aluminium and silicon. Salts oi
magnesium occur in very dilute solution in sea-water, and
from this the hydroxide is being successfully produced both
268
CHEMISTRY IN THE SERVICE OF MAN
in Great Britain and in the United States, by precipitation
with slaked lime.
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
FIG. 22. 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 surrounding mixture, C, react with formation of carborundum.
seen, also, that by means of the electric arc, electrical energy
is transformed into heat energy, and that the very high
temperature of about 3000 C. (5432 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 know-
ledge 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
ELECTRICITY AND CHEMISTRY 269
oxygen, and in the manufacture of calcium carbide. Fused
quartz or silica glass, with the valuable properties of
which we have 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 from
a mixture of calcium phosphate, quartz sand (silica) and
coke (carbon).
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,
EDWARD G. ACHESON, in 1891. By heating a mixture of
coke (carbon) and sand (oxide of silicon) to a high tem-
perature in an electric furnace (Fig. 22), oxygen is removed
by the carbon from its 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 pro-
duced in large quantities and used as a grinding or abrasive
material, as well as for incorporating in the surface layer of
concrete pavements, stairs, etc. By reason of its very re-
fractory character (it will withstand a temperature of 2200 C.,
or 4000 F., without undergoing change), it is also used 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 alu-
minium 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,
by Dr. Acheson, of a method of making artificial graphite.
Until 1896, graphite, a crystalline form of carbon familiar
under the names of plumbago and black lead (although
270
CHEMISTRY IN THE SERVICE OF MAN
it contains no lead at all), was known only as a naturally
occurring mineral (p. 120). During the process of manufac-
ture of carborundum, however, 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
Courtesy of Acheson Graphite Corporation.
GRAPHITE FURNACE IN ACTION.
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 a great development in recent years.
For the production of Acheson graphite, amorphous
carbon (anthracite coal, coke, etc.), mixed with a small
ELECTRICITY AND CHEMISTRY 271
amount of oxide of iron, alumina, or silica, is heated to a
high temperature, about 3000 C., in an electric furnace of
the same type as the carborundum furnace. At this high
temperature the iron, alumina, or silica which was 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 amor-
phous carbon into crystalline graphite ; in their absence
the change takes place only with difficulty. The graphite so
obtained is superior to the natural mineral by reason of its
greater purity and uniformity.
To obtain graphite rods, plates, etc., finely-ground anthra-
cite, 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 con-
verted into graphite.
Someone has said, " Nature's storehouse is man's bene-
factor, and no gift from it renders greater service than the
waters of the earth " ; and in the recent developments 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 in the flowing waters
of the earth, the rendering available 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 impressed 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
272 CHEMISTRY IN THE SERVICE OF MAN
man, without the smoke and dirt and clatter of the ordinary
factory, are transforming the energy of the rushing river
into the energy of electricity which, in the adjacent fac-
tories, is then made to contribute to the material well-being
of man and the advance of civilisation.
CHAPTER XIII
/
THE COLLOIDAL STATE
WHEN one brings sugar, salt, washing-soda and many other
common and familiar 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
is called a solution. A solution, however, must not be re-
garded as a compound of the dissolved substance, or solute,
and the solvent, for the composition of a solution may be
varied, whereas the composition of a compound is definite
and constant. A solution, rather, is to be regarded merely
as a homogeneous mixture in which the molecules of the
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 a
solvent. It is a homogeneous mixture of variable com-
position.
Whatever the nature of the solution process may be, one
of the most remarkable facts established by the modern in-
vestigation of solutions is the very close analogy which exists
between a substance in solution and a gas, an analogy which
is illustrated by the property more especially 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 something
like a mile a second, colliding ever and anon, some eighteen
thousand million times a second, with other molecules, and
pursuing, therefore, 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 throughout
273
274 CHEMISTRY IN THE SERVICE OF MAN
a room, or can fill completely the space, however large that
space may be, which is offered to it. In the case of liquids
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. That diffusion
does take place can be easily demonstrated by gently pour-
ing a layer of pure water on to a solution of some strongly
coloured substance, such as bluestone (copper sulphate) or
dichromate of potash. After some time it will be found 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 mem-
brane (e.g. pig's bladder), diffusion takes place just the same,
as can be shown by enclosing the solution of copper sulphate
in a tube of parchment paper which is then immersed in
water. Very soon the presence of the copper sulphate in the
water outside the membrane will be detected.
During the sixties of last century this diffusion of dis-
solved substances through a parchment paper or animal
membrane was studied by THOMAS GRAHAM, a native of
Glasgow, who later became Professor of Chemistry in
University College, London, and Master of the Mint. As
a result of his investigations, Graham found that although
certain substances pass through a membrane of parchment
paper, other substances 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
THE COLLOIDAL STATE 275
would not pass through, e.g. starch, gelatin, glue, were
believed to be amorphous and non-crystallisable, Graham
divided substances into the two classes, crystalloids and
colloids (from the Greek kolla, glue) ; and this distinction
was one which was long maintained. 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 parchment 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 preparation of colloids free from crystalloids.
Appropriate as Graham's classification of substances
appeared at the time, investigation has shown that it cannot
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 it is
now recognised that the distinction between crystalloids and
colloids is to be found in the degree of dispersion or sub-
division. The term " colloidal state " of matter is now
applied to that grange of sub-division of matter which lies
between the limits of the microscopically visible and the
molecular state.
That this particular range of sub-division of matter
should be singled out for special study is justified by the
fact that matter in the colloidal state possesses properties
which are not exhibited, or are not exhibited so markedly,
either by molecular matter or by the grosser microscopic
particles. Matter in the colloidal state, moreover, plays a
very important part in almost every field of human activity
in agriculture and in the tanning of leather, in the working
of clay, in the production of rayon, in the dyeing of textile
fibres, etc. It is also responsible for the blue of the sky and
the blue of the eye, and matter in the colloidal state has
been chosen by Nature as the vehicle of life.
276 CHEMISTRY IN THE SERVICE OF MAN
Since the term colloidal refers only to a certain degree of
dispersion or sub-division, colloidally dispersed matter may
exist in the solid, the liquid or the gaseous state, and the
medium in which the particles are dispersed (the so-called
dispersion medium) may also be solid, liquid or gaseous. In
this way one obtains colloidal suspensions, emulsions,
smokes, mists, etc. In the present discussion we shall be
concerned mainly with those systems in which water is the
dispersion medium.
While it could be inferred from the experiments of
Graham that the apparently homogeneous colloidal solutions
or colloidal sols, as they are called in order to distinguish
them from true solutions, are in reality heterogeneous, the
question arises how this can be proved. The answer is that
even if one cannot see the particles themselves their presence
can be detected by what is known as the Tyndall Phenomenon.
When the air of a room is bathed in a uniform light no
particles are seen, but if the sunlight be allowed to pass
through a hole in the shutters of a darkened room one sees
a diffused light, the sunbeam made visible, in which the
larger dust particles are seen to
" Glitter like a swarm of fireflies, tangled in a silver braid."
The diffused light also is 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/' the presence
of particles in a colloidal sol can be detected. If a beam of
light is passed through pure water or through a solution of
salt, the path of the beam is invisible ; the liquid is " opti-
cally empty." 1 But if the beam is passed through a colloidal
sol the path of the beam is traced by a diffused light, like
the sunbeam in a darkened room.
1 Owing to the presence of floating particles even in filtered water,
the " Tyndall phenomenon " will be observed with ordinary pure water.
Special precautions must be adopted to free the water from all suspended
particles.
THE COLLOIDAL STATE 277
From this " Tyndall phenomenon/* then, one learns that
particles which may be too small to be seen in the ordinary
way, may be detected if only the light reflected or dispersed
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, one employs a microscope to
examine the scattered light, the range of vision will be ex-
tended, and it will be possible to detect, although not actually
FIG. 23. ULTRA-MICROSCOPE.
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. On the basis of this principle there has
been devised an arrangement known as the ultra-microscope,
by means of which not only the heterogeneity of colloid sols
can be detected, but also the number of particles in a given
volume of the sol can be determined. The arrangement is
shown diagrammatically in Fig. 23. 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. 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
278 CHEMISTRY IN THE SERVICE OF MAN
be reflected and dispersed, and the minute points of light
thus produced will stand out as bright specks against a dark
background, in the field of view of the microscope.
A very suitable liquid for examination with the ultra-
microscope is colloidal gold sol which formed the basis of
the " potable gold " of the alchemists, and was rediscovered
in 1856 by Faraday, who obtained it by the reduction of
gold chloride with phosphorus. The sol can readily be pre-
pared by adding to a very dilute solution of gold chloride,
freed from acid by the careful addition of sodium carbonate,
a dilute solution of tannin (tannic acid). In the cold, no
change occurs, but when the liquid is heated, a pink colour
soon begins to develop ; and by making further additions
of the gold and tannin solutions a clear, deep ruby-red
coloured liquid is obtained. This contains the gold in a
colloidal state, and is similar, in fact, to ruby glass (p. 229).
A similar colloidal sol can be obtained by passing hydrogen
sulphide (sulphuretted hydrogen, H 2 S) through a solution
of white arsenic (oxide of arsenic). A clear yellow liquid is
formed which passes unchanged through filter paper (a finely
porous, unglazed paper), and is a colloidal sol of arsenious
sulphide.
And how large are those particles which are thus 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 ten-thousandth part
of a millimetre or one two-hundred-and-fifty-thousandth
part of an inch ; but by means of the ultra-microscope,
particles about one-twentieth of this size, with a diameter of
about six-millionths of a millimetre (-nnroinnj- mm.) or one
four-millionth of an inch, can be detected. This, however,
is still about sixty 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
THE COLLOIDAL STATE 279
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.
Since matter in the colloidal state is very finely sub-
divided, the extent of surface exposed is very large relatively
to the total volume of the matter. Surface forces, therefore,
play an important part and bring about what is known as
adsorption, or changes of concentration at the surface.
Charcoal, a finely porous material with a large surface, has
the property (p. 123) of removing noxious gases (e.g. sul-
phuretted hydrogen) from the air and colouring matters
from solution. This is due to the fact that under the action
of surface forces, the noxious gases or colouring matters are
adsorbed or concentrated on the surface of the charcoal.
Similarly, gelatinous silicic acid obtained by adding hydro-
chloric acid to a solution of water-glass (p. 219) and separating
the silicic acid from the sodium chloride by dialysis when
partially dehydrated, forms a porous material, silica gel.
This also shows the property of adsorption in a very marked
degree, and is extensively employed in industry for the
recovery of volatile solvents, the removal of gasoline vapour
from natural gas, etc. Thus, when air containing the vapour
of a solvent such as acetone is passed through a layer of
silica gel, the acetone is condensed on the surface of the gel
and so removed from the air. The solvent can be recovered
by heating the gel.
Adsorption plays a very important part in the production
and character of colloids. By the adsorption of ions from the
dispersion medium or from electrolytes present in solution,
the colloid particles acquire an electric charge ; and adsorp-
tion of the medium as a whole may also take place. In the
280 CHEMISTRY IN THE SERVICE OF MAN
case of the so-called suspensoid colloids, e.g. colloidal gold
and colloidal arsenious sulphide, the dispersed particles
adsorb practically none of the dispersion medium, and their
stability is due to their motion (Brownian movement, p. 288),
and to the electric charge which they carry. The particles,
being charged, mutually repel one another and so agglo-
meration and precipitation are prevented. In the case of the
emulsoid colloids, however, e.g. gelatin, silicic acid, etc., the
dispersion medium itself is adsorbed to a greater or less
extent. The greater the adsorption of the medium, the more
will the stability and properties of the colloidal sol be de-
pendent on this adsorbed medium, and the less will they
depend on the electric charge. Owing to the adsorption of
the dispersion medium, emulsoid colloids show certain
marked differences in behaviour from that of suspensoid
colloids.
That the particles of a suspensoid colloid are electrically
charged can readily be demonstrated with a colloidal solution
of sulphide of arsenic. If this is placed in a U-shaped tube,
and if wires connected with the terminals of a high voltage
battery or dynamo 1 are inserted in the liquid, one in either
limb of the tube, it will be found that the sulphide of arsenic
migrates towards and collects around the positive terminal.
The particles of arsenic sulphide are thus shown to carry a
negative charge of electricity. Even with fine suspensions,
such as a suspension of fine clay or a slime of peat, the same
phenomenon is observed ; the clay particles 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 electrophoresis, or electric transport of suspended
particles, may be applied for the purpose of freeing a fine
suspension from water, and has, in fact, been applied to the
drying and purification of clay.
1 The ordinary electric-lighting circuit can conveniently be employed,
provided it supplies direct current.
THE COLLOIDAL STATE 281
The process of electrophoresis is also applied to the
manufacture of articles of rubber. The juice or latex of
the rubber plant consists of a liquid in which negatively
charged particles of rubber are suspended, and these
particles will therefore be carried to the positively charged
electrode or anode. Moulds of any desired form, or fabric
or wire, may thus be coated with a layer of rubber, and in
this way hot-water bottles, bathing caps, etc., may be
produced, or wire may be insulated.
Since the stability of the suspensoid colloids is mainly
due to the electric charge carried by the particles, pre-
cipitation of the colloid is brought about by neutralising
the electric charge. This can be effected by the addition of
an electrolyte (p. 254). Negatively charged colloid particles
will preferentially take up or adsorb positive ions, and posi-
tively charged colloids will adsorb negative ions, and the
charge on the colloid will thereby be neutralised. The colloid
particles will then no longer repel one another but will
agglomerate into larger particles and settle out of the liquid.
Thus, when a small quantity of hydrochloric acid (hydrogen
ion) or of calcium chloride (calcium ion) or of some other
electrolyte is added to a colloidal sol of arsenious sulphide
or of gold, precipitation of the colloid takes place.
A similar behaviour is found in the case of ordinary fine
suspensions (e.g. of clay in water), the particles of which
are also electrically charged ; and this fact 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, and takes 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 for-
mation of deltas, such as has taken place at the mouth of the
Nile and of the Mississippi.
The electrical charge on a colloid particle may be
282 CHEMISTRY IN THE SERVICE OF MAN
neutralised not only by the ion of an electrolyte but also by
another colloid carrying an electric charge of opposite sign.
Thus, 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 process of adsorption plays an important part in the
dyeing of textiles. In the case of what are called substantive
dyes, the dye itself is in a colloidal state, and may be pre-
cipitated and fixed on the fibre by the addition of salts, just
as arsenious sulphide is precipitated by electrolytes. In the
case of acid and basic dyes one is dealing with coloured ions.
Since, in an acid bath the textile fibre becomes positively
charged, owing to adsorption of hydrogen ion, the fibre will
attract and retain negatively charged or acid dyes ; but in
an alkaline bath the fibre becomes negatively charged and
so will attract and retain positive or basic dyes.
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. Accord-
ing 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. After the dye has been adsorbed, secondary
changes may take place which render the dye less easily
removed.
In agriculture, also, the colloidal state is of the greatest
importance. In the soil there exist various colloidal sub-
THE COLLOIDAL STATE 283
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 vegetation
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 a form which can be taken
up by the plants, as well as for the other bacteria always
present in the soil. The water-holding power of the soil
colloids may be considerably modified by the addition of
various substances, e.g. lime ; and the addition of lime may
have an effect on the fertility of the soil, not only by neu-
tralising excess of acid but also by altering the structure of
the soil colloids (p. 211).
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, nega-
tively 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, depends on the removal of impurities by adsorption
on the large filtering surface exposed and on the retention of
positively charged colloidal matter, bacteria, etc., by the
negatively charged sand or charcoal particles.
An important application of the behaviour just described
284 CHEMISTRY IN THE SERVICE OF MAN
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 as
well as phosphates and other salts are retained and afford
a rich nutriment for the growing crops, while the liquid
effluent which drains away is free from objectionable im-
purities. By such means can, in suitable surroundings, a
source of annoyance and loss be turned to profit.
In the case of emulsoid colloids, such as gelatin, albumin,
etc., the stability of the colloid is due not so much to the
electric charge on the particles as to the adsorbed water.
Such colloids, therefore, are not so sensitive to added elec-
trolytes, and actual precipitation does not take place until
the concentration of electrolyte is relatively large, although
changes may be brought about in the water-content of the
colloid. This comparatively great insensitiveness to electro-
lytes, further, may be transferred to suspensoids. Thus
when gelatin, for example, is added to a colloidal gold sol,
the gold is adsorbed by the gelatin and a much greater
concentration of electrolyte is required in order to precipitate
the gold than is necessary in the absence of the gelatin. The
gelatin is said to " protect " the gold, and owing to this
so-called protective action, a suspension or 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. A number of colloidal
sols find application as therapeutic agents. Thus, colloidal
silver is administered for influenza, colitis, and bacillary
dysentery ; injections of colloidal manganese are given in
cases of acne ; colloidal sulphur and colloidal iodine have
been recommended for rheumatism and neuritis.
In the manufacture of photographic plates, prepared by
coating plates with gelatin containing a fine suspension of
silver bromide, one finds an important industrial application
THE COLLOIDAL STATE 285
of the protective action of emulsoid colloids. If a 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 is also clearly
seen in the nature of the curd which is formed from milk,
and in the readiness with which it is formed on addition of
acid or of rennet. In cow's milk there is a relatively large
amount of casein and a relatively small amount of the pro-
tective colloid, lact-albumin. Cow's milk, therefore, readily
curdles. In human milk, there is a smaller proportion of
casein and a larger proportion of lact-albumin. The casein
is therefore more effectively " protected " and curdling
takes place less readily. Human milk is, therefore, more
readily digested than cow's milk. In ass's milk, the pro-
portion of protective colloid to casein is highest of all, and
curdling, therefore, takes place still less readily. The digesti-
bility of ass's milk is greatest of all. By increasing the pro-
portion of protective colloid in cow's milk by the addition,
for example, of gelatin, white of egg, or barley water (con-
taining starch), the formation of a curd in the stomach may
be more or less completely prevented ; and the curd, when
formed, is less compact. The digestibility of the milk is
thereby increased.
In the manufacture of ice cream, likewise, the addition of
protective colloids, like albumin (white of egg) and gelatin,
to the milk ensures a smoother product, because the casein is
prevented from coagulating and the ice particles are kept
very small.
The protective action of emulsoid colloids and the pre-
cipitating action of salts are excellently illustrated, also, on
286 CHEMISTRY IN THE SERVICE OF MAN
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,
owing to the presence of a large amount of colloidal organic
matter, which stabilises the fine suspension of clay and
soil ; and it is only when the rivers reach the salt waters of
the sea with its high concentration of salts, that the sus-
pended matter is precipitated with the production of river
bars and deltas.
Many colloidal sols, e.g. gelatin, starch, etc., when cooled
or coagulated, pass into a jelly, owing to the coalescence of
the hydrated colloid particles. The jelly so formed may be
regarded as constituted by a honeycomb or network of
hydrated colloid, the meshes or cells of which are filled with
a dilute solution of the colloid. The water-holding or liquid-
holding power of such jellies is sometimes very great, as is
seen from the fact that jellies have been obtained which
contain less than 0-5 per cent, of the colloid. " Solidified
alcohol, " used as a fuel for spirit lamps, is a jelly formed by
colloidal calcium acetate in alcohol.
Although electrolytes, as we have seen, may bring about
the precipitation of colloids, they may also, when present
in only very small amount, facilitate the dispersion of a
solid substance by giving to the particles, by adsorption,
the electric charge necessary for the stability of the colloidal
sol (p. 279). This process of deflocculation or breaking up of
large particles is spoken of as peptisation, on account of its
superficial resemblance to the process of conversion of in-
soluble protein into soluble or colloidally dispersed peptone.
Even when adsorbed substances may not, by themselves,
be able to peptise solids, they may, by acting as stabilisers
and as protective colloids, assist mechanical or other pro-
cesses in the production of the colloidal state. Thus, Dr.
E. G. Acheson, to whom we owe the discovery of carborun-
dum and the process of making artificial graphite, found
THE COLLOIDAL STATE - 287
that when graphite is ground with a solution of tannin
(tannic acid), a colloidal sol of graphite can be obtained.
This so-called deflocculated Acheson graphite (" Dag "), when
mixed with oil, is largely used as a lubricant.
The production of colloidally dispersed or deflocculated
materials by grinding in special mills in presence of pro-
tective colloids or " dispersators " is now a considerable
industry. Such very finely divided materials find application
in the paint industry and as " fillers " in paper, rubber, etc.
Although, in recent years, the importance of the colloidal
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 con-
densation 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 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 made it possible to calculate not
only the absolute mass of the molecule the hydrogen mole-
cule weighs about three quadrillionths (or three million
million million millionths) of a gram 1 but also its dimensions
1 This number is more conveniently represented by 3 X io~ 24 gram,
which is the same as dividing 3 by 10 twenty-four times in succession.
288 CHEMISTRY IN THE SERVICE OF MAN
(rather less than a three hundred millionth of a centimetre
in diameter), 1 and the speed of its flight (say, a mile per
second), there were not wanting some who refused to believe
in the objective reality of molecules and of the picture pre-
sented 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 manifest by the eifects
which they produced. In thai: 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 perpetually
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 manifestation 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 one sees in the Brownian
movement, but only the effect of the incessant bombard
ment 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 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 the period of time
is made sufficiently short, the number of impacts of the
liquid molecules will no longer be equal in different direc-
tions, 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,
1 The diameter of a hydrogen molecule is 2-68 X io~ 8 cm.
THE COLLOIDAL STATE 289
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 con-
stitutes the Brownian movement. With particles of ultra-
microscopic dimensions the phenomenon is exhibited with
extraordinary vividness, and it is an impressive sight to
observe the rapid darting motions of a colloid particle by
means of the ultra-microscope. As Zsigmondy, who first
observed it, wrote : " A swarm of dancing gnats in a sun-
beam will give one an idea of the motion of the gold particles
in the hydrosol of gold. They hop, dance, spring, dash
together and fly apart so rapidly that the eye can scarcely
make out their movements. . . . These motions show that
there is a continual mixing together of the interior parts of
every liquid going on unceasingly, year in year out." It is to
this Brownian movement that the stability of colloidal sols
is largely due. From the careful quantitative investigations
of this phenomenon, carried out during the present century,
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 one to expect, that one cannot any
longer hesitate to believe that in the rapid, darting motions
of the ultra-microscopic particles there is made manifest to
us something 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 XIV
MOLECULAR ARCHITECTURE
OF all the known elements, the element carbon, familiar to
all 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
250,000 that their study has developed into a special
branch of chemistry, organic chemistry. This name is a
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 compounds which
were formerly regarded as typical products of animal and
vegetable 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 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.
290
MOLECULAR ARCHITECTURE 291
But if I have referred here particularly to the com-
pounds of carbon, it is not for the purpose of describ-
ing 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 modern 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 pro-
portions. But while the law, " One compound, one com-
position/' has remained unshaken, the progress, more
especially of organic chemistry, soon showed that the con-
verse 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 compounds became multiplied, it began to be
more and more frequently observed that the same elements
may be united in the same proportions and yet yield com-
pounds with entirely different properties. More than a
hundred different compounds, for example, can be pro-
duced by combining together 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 molecular structures, or
different compounds. In other words, the discovery of
isomerism, so entirely unforeseen by Dalton and by the
292 CHEMISTRY IN THE SERVICE OF MAN
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. We must gain a knowledge of the molecular
architecture.
A knowledge of the molecular constitution is, moreover,
essential for the successful building up or synthesis of a
compound from simpler materials, which will be discussed
more fully in the following chapters. To elucidate the con-
stitution 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. As to how this problem is solved, only this much
can be said here. Through the laborious efforts of number-
less chemists, a knowledge has been gradually built up 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 determine the constitution of
an unknown compound, therefore, the properties and re-
actions of the substance are studied, and the compound is
also, by the action of various chemical reagents, decomposed
into simpler compounds. It is broken down into bits, as it
were, and one then seeks to identify the fragments, the
simpler substances, so obtained, with substances of which
the constitution is already known. From the knowledge
gained in this way, the chemist, with his imaginative insight
and wide knowledge of how substances react with one
another, 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 ARCHITECTURE 293
molecular constitution can be represented. It was, there-
fore, a great step in advance when the Scottish chemist,
ARCHIBALD SCOTT COUPER, and the German chemist,
FRIEDRICH AUGUST KEKUL, in 1858, showed how molecular
constitutions could be represented diagrammatically, using
as a guiding principle what is known as the doctrine of
valency (p. 17).
Although there is, of course, no material link or bond
between the atoms, one 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 marsh
H
gas by the diagrammatic formula H C H, and the higher
H
hydrocarbons of that series by such a chain of carbon and
H rf H
I I I
hydrogen atoms as H C C C H ; a formula which can
I I I
H H H
also be written in the simpler form, CH 3 - CH 2 CH 3 . 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 com-
pounds. Thus, for example, in the case of the compound
CH 3 -CH 2 'CH 3 (the bond between the carbon atoms being
now represented by a dot), it is clear that one atom of
hydrogen in this compound can be replaced by an atom, say,
of chlorine, in two ways, so as to form either the compound
CH 3 -CH 2 -CH 2 C1, or the compound CH 3 -CHC1-CH 3 , the
294 CHEMISTRY IN THE SERVICE OF MAN
chlorine being in the former case attached to a terminal
carbon atom and in the latter case to the intermediate carbon
atom. Accordingly, there should exist two and only two
different compounds having the composition C 3 H 7 C1 ; and
as a matter of fact two compounds and only two are
known.
The origin of this theory of chemical structure, as it
occurred to Kekule, 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 was staying at
Clapham. " One fine summer evening, " he relates, 1 " 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
putting on paper at least sketches of these dream-forms."
From these sketches were developed the constitutional
or structural formulae, of which examples have just been
given.
And 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 twisting in snake-
like motion. " But look ! What was that ? One of the snakes
had seized hold of its own tail, and the form whirled mock-
ingly before my eyes. As if by a flash of lightning I awoke " ;
1 F. R. Japp, " Kekul6 Memorial Lecture " (Transactions of the
Chemical Society, 1898).
MOLECULAR ARCHITECTURE 295
but the picture Kekul6 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 one hydrogen
atom is attached. Thus we obtain the structural formula 1
of the benzene molecule,
H
H.C. C.H
H
the " ring " of carbon atoms being written in the form
of a hexagon 2 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, " let us beware of
publishing our dreams before they have been put to the
proof by the waking understanding." The hexagonal form
of the benzene molecule has been confirmed by X-ray
examination.
By the introduction of the doctrine of valency and of
Couper's and Kekule's diagrammatic method of repre-
senting 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 inadequacy
of this theory of chemical structure became only too apparent,
1 Just as in the study of the architecture of buildings, plans and archi-
tectural drawings are necessary for the proper understanding of the
subject, so also structural formulae are required for the understanding of
molecular architecture.
2 The reason why six carbon atoms readily arrange themselves in the
form of a hexagon is that the four valencies of a carbon atom are directed
in space towards the four corners of a regular tetrahedron (p. 303). The
angle between the valencies is 109 28', and the angles of a hexagon are
120. The six carbon atoms can thus join up to form a hexagon with only
a small degree of " strain."
2Q6 CHEMISTRY IN THE SERVICE OF MAN
owing to the discovery that, in some cases, the number of
isomeric compounds is greater than can be represented by
the structural formulae of Couper and Kekule. A new
isomerism was discovered, an isomerism which manifested
itself in the property known as optical activity. Let me try
to explain this.
Early last century it was discovered that when 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 depolarised. When, now,
this polarised light is passed through
certain substances, quartz, turpentine,
a solution of cane sugar, etc., it is
found that the plane of polarisation,
the plane in which the ethereal vibra-
tions take place, is rotated or twisted,
this rotation or twisting taking place
sometimes to the right, sometimes to the
left ; an effect which one 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. 24.
Substances which possess this property of rotating the
plane of polarised light are said to be " optically active/'
This property of optical activity can also be demonstrated
by a modification of a very interesting experiment due to
the late Sir George Stokes. When a parallel beam of light
from a projection lantern (Fig. 25) 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. 276) ; and the beam of light appears
equally bright all round. But if the light from the lantern
MOLECULAR ARCHITECTURE 297
is first polarised by passage through a so-called Nicol prism
formed from Iceland spar or through a disc of polaroid, 1 and
then reflected downwards 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 Nicol prism or polarised disc, the band also
rotates and turns alternately its light and dark sides to the
eye. The effect produced is as if the beam of light on passing
through the Nicol prism or polaroid disc, were given a flat
form, like a book, from the two opposite edges of which
FIG. 25. DEMONSTRATION OF THE POLARISATION 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 suspen-
sion 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 .
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, also containing a suspension of
rosin, the band of light is twisted into a spiral form ; and
on rotating the polarising prism or disc, this spiral band of
1 Polaroid consists of a film of cellulose acetate mounted between two
plane glass plates. The film is a matrix for sub-microscopic dichroic
crystals accurately oriented in such a way that the entire film acts as a
single polarising crystal.
298 CHEMISTRY IN THE SERVICE OF MAN
light will appear to move with a screw-like motion. From
the fact that the different rays of coloured light which
together constitute white light are twisted or rotated to
Louis PASTEUR.
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 remarkable
property of substances, the study of which, starting with the
MOLECULAR ARCHITECTURE
299
brilliant discoveries of PASTEUR 1 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 (now called racemic acid).
The former, which is found occurring in grape juice, is
n
'1 e
\V
/
y
u'
u
Y7>
\ r
<~ai
FIG. 26, HEMIHEDRAL CRYSTALS OF d- AND /- SODIUM AMMONIUM
TARTRATE, AND HOLOHEDRAL CRYSTAL (RIGHT) OF SODIUM AMMONIUM
RACEMATE.
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 racemic acid and its salts were all fully developed,
and the crystals symmetrical (Fig. 26), the full development
of the crystalline faces of the active tartaric acid was inter-
rupted by the occurrence of so-called- hemihedral faces
(Fig. 26). 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 HERSCHEL
in the case of crystalline quartz, which is also optically active.
1 Louis Pasteur, the son of a tanner, was born in 1822. For a number
of years he was Professor of Chemistry at Strasbourg, Lille, and Paris,
and carried out a large number of important investigations in bio-
chemistry and bacteriology. On his work, antiseptic surgery was built
up and a cure for rabies or hydrophobia obtained. He died in 1895.
300 CHEMISTRY IN THE SERVICE OF MAN
But whereas quartz is optically active only in the crystalline
state, tartaric acid retains the property even when dissolved.
In the former case, the property depends on the crystalline
structure ; in the latter, it depends on the internal molecular
structure.
A further discovery was made by Pasteur. During his
investigation of one of the salts of tartaric and racemic acid
(namely, sodium ammonium tartrate and sodium ammonium
racemate), 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 in the different crystals. The crystals
obtained by crystallisation from a solution of the racemate,
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, some-
times to the right and sometimes to the left (Fig. 26). 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 the left. On dissolving together equal
amounts of the two sets of crystals, a solution was obtained
which was quite inactive.
Here, then, we have the discovery of that new kind of
isomerism to which reference has just been made, and
which showed the inadequacy of the structural formulae of
Kekute. The two salts into which the racemate 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 occurring 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 ;
MOLECULAR ARCHITECTURE 301
3ne having the power of rotating the plane of polarised light
:o the right and identical with the acid occurring in grape
uice, the other hitherto unknown, and having the power of
stating the plane of polarised light to the left. Moreover,
jn mixing together in solution equal quantities of these
;wo optically active acids, there separate from the solu-
tion crystals of the inactive racemic 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 one can well
understand the feeling of happiness and the nervous excite-
ment by which Pasteur was overcome on making the dis-
covery. Rushing from hfs laboratory and meeting the
breparateur in physics, 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 dextrotartrate. I am so
happy and overcome by such nervous excitement that I
am unable to place my eye again to the polarisation ap-
paratus/' The question, however, now arose as to how
the existence of the two optically active tartaric acids could
be explained.
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 can or can 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 one 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. A hand, therefore,
is an asymmetrical object, which can exist in two distinct,
302 CHEMISTRY IN THE SERVICE OF MAN
so-called enantiomorphic forms, similar in all respects, but
not superposable, not identical. And when one examines
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. 26),
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, one is 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 corners of an irregular tetrahedron, or are they
arranged in some other asymmetrical manner ? " And
he replied, " We are not as yet in a position to answer
these questions. But it cannot be a subject of 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, one cannot suppress a feeling of disappointment
that it was not vouchsafed to him, with the clear views he
possessed, 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 com-
pounds to make it possible to give an answer to Pasteur's
questions. Nevertheless, Pasteur introduced into chemistry
a conception of extraordinary importance and fruitfulness,
the conception of molecular asymmetry, and he recognised
that molecular structure is not a matter of two dimensions
only, but of three. The atoms are not arranged in a plane,
as the formulae of Couper and of Kekute represent them,
MOLECULAR ARCHITECTURE 303
but in three-dimensional space. In this way Pasteur in-
augurated a new chemistry, a " Chemistry in Space " or
" Stereochemistry."
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 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 mole-
cule, 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. 27, which represents such a tetrahedron
and its mirror image. The right-hand tetrahedron, obviously,
only requires to be turned through an angle of rather more
than 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 someric forms are therefore possible. This will be
304 CHEMISTRY IN THE SERVICE OF MAN
understood from Fig. 28. Viewing these tetrahedra from a
similar position, we see that the groups B C D, 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
the molecules of all compounds which are optically active
do contain at least one atom of carbon to which four different
B ~ D
FIG. 28.
atoms or groups are attached a so-called asymmetric carbon
atom or are, for some other reason, asymmetric, but also,
no compound has been obtained the possible existence of
which could not be predicted by means of the van't Hoff
and Le Bel theory. So fruitful has the conception of mole-
cular asymmetry and of the asymmetric carbon atom proved,
that it has been extended also to the atoms of elements other
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 for all other optically active substances
there exist, or can exist, not only the two optically active
isomers, but also an inactive isomer, produced by the com-
bination of the two oppositely active forms in equal amounts,
MOLECULAR ARCHITECTURE 305
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 para-
tartrate, as we have seen, this breaking up of the racemic
form (the paratartrate) takes place on crystallising from water
at the ordinary temperature. But this method is capable of
only a limited application. 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,
Penicillium glaucum, the fungus feeds on and destroys
the dextro-rotatory acid, which occurs naturally in grapes,
but leaves unchanged, or acts much more slowly on, the
laevo-acid, which is an artificial product of the laboratory.
The solution, therefore, becomes laevo-rotatory, and the
laevo-acid can be obtained by concentrating the solution
and allowing it to crystallise. In the process of fermenta-
tion, also, under the action of various enzymes, which
are themselves asymmetric agents, produced in living
animal and vegetable cells, we find a similar selective action.
Thus, whereas the dextro-rotating glucose, the well-known
grape sugar, undergoes fermentation, the laevo-rotating
glucose, a compound obtained only 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 fit only into a right-handed thread.
So long as the two optically active homers are brought into
relations with symmetrical agents, they behave identically ;
but when they react with an asymmetric agent, a different
behaviour is exhibited by the two forms.
This selective action is of great physiological importance,
since in all life processes, such as digestion and assimila-
tion, one is dealing with the action of the optically active,
306 CHEMISTRY IN THE SERVICE OF MAN
asymmetric materials contained in the cells and tissues. It
is found, 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 physiological kind, and it
intervenes in the role of a modifier of chemical affinity. . . .
Thus we find introduced into physiological principles the
idea of the influence of the 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 importance,
and the knowledge which has been gained has exercised an
important influence on the understanding and interpretation
of biological processes, opening to physiology, 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 stereochemistry ; the most funda-
mental 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 optically active compounds
introduced a new factor. As Professor F. R. JAPP, in his
MOLECULAR ARCHITECTURE 307
Presidential Address to the Chemical Section of the British
Association in 1898, so admirably emphasised, " the pheno-
mena of stereochemistry support the doctrine of vitalism
as revived by the younger physiologists, and point to the
existence of a directive force 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 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 laevo-rotatory. When, however, 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 optically 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 artificial synthesis, can be separated into
the two optically active forms, with the help of asymmetric,
optically active compounds ; or one 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 com-
pound. 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. How-
ever, as has been pointed out, Pasteur found that, in some
cases, the resolution of the racemic form can be effected
simply by crystallisation. By allowing a solution of the
308 CHEMISTRY IN THE SERVICE OF MAN
inactive racemic sodium ammonium paratartrate to crystal-
lise, crystals of the dextro- and of the laevo-rotatory sodium
ammonium tartrate were 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 sym-
metrically 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 resolving
itself simultaneously into a right-handed compound and its
opposite, is in no way comparable with the possibility of
transforming an inactive compound into a single active com-
pound. This is what no one has ever done ; it is, on the
other hand, what living nature is doing unceasingly 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 " requires the living operator,
whose intellect embraces the conception of opposite forms
of symmetry/* And, as 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.
MOLECULAR ARCHITECTURE 309
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 syn-
thesis might be removed ; for while he recognised the
necessity for the existence of asymmetric forces " at he
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." In 1894, also, van't
Hoff made the suggestion that the formation of optically
active compounds might take place under the directive action
of right or left circularly polarised light. Many attempts
were made to effect the synthesis of such compounds under
the action of circularly polarised light, but it was not till
1929 that success was attained. By the action of circularly
polarised light on a symmetrical compound, an optically
active compound was obtained, the rotatory power of which
varied in sign according as the light was dextro- or laevo-
circularly polarised. The possibility of an asymmetric
synthesis under the directive action of a purely physical
force was thereby demonstrated. Moreover, it has been
shown that dextro-circularly polarised light predominates
at the earth's surface in reflected sunlight, and it would
therefore appear that an unsymmetrical form of photo-
chemical energy exists in Nature under the directive action
of which an asymmetric synthesis could take place. The
possibility that the formation of the first asymmetric mole-
cule (from which other asymmetric molecules might later be
formed) took place under such directive influence has thus
been established. The proof that it did in fact so take place
cannot of course be given.
CHAPTER XV
SYNTHETIC CHEMISTRY I
IT may, perhaps, have seemed to some that however in-
teresting, as an intellectual speculation, the theories of mole-
cular structure discussed in the previous chapter might be,
however much they might satisfy a philosophical 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.
Nothing could be farther from the truth, for these theories
form the very basis and foundation of some of the greatest
industries of the present day ! Kekule'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, it must be remembered, the purpose of a
scientific theory is not only 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 Kekule,
van't Hoff, Le Bel and others, 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 that
crowning achievement of chemists, the artificial, synthetic
preparation of many of Nature's own products, and the
industrial production of those innumerable dyes, thera-
peutic agents, perfumes and other materials, which are
regarded as necessaries in our modern civilisation.
While, however, the theories of molecular structure and
constitution gave the guidance necessary for the altogether
phenomenal development of organic chemistry during the
310
SYNTHETIC CHEMISTRY 31 1
past hundred years, that development could actually take
place only through the genius, scientific insight, energy and
persistence of hundreds of zealous workers who devoted
themselves to the development of knowledge by experimental
investigation, and to the task of elucidating the constitution
of and synthesising thousands of organic compounds. And
it must not be forgotten that the industries dependent on
synthetic organic chemistry can flourish only if the import-
ance of intensive and unremitting experimental investigation
is whole-heartedly recognised and its prosecution generously
encouraged.
Not only has the chemist prepared 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 pro-
duction 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, com-
pete with the natural products, but they have even driven
these entirely out of the market. In this way great industries
have arisen, the social and economic effects of which have
been both profound and widespread.
In achieving the successful building up of molecular
structures, whether of naturally occurring substances or of
substances hitherto unknown, the chemist may start with
molecular structures which occur in nature (e.g. cellulose)
or which can be readily obtained from naturally occurring
materials (e.g. benzene) ; or he may start from the elements
or simple compounds (e.g. carbon from coal, oxygen and
nitrogen from the air, hydrogen from water, etc.), and from
these build up molecular structures of increasing diversity
and complexity. In the nineteenth century, important and
closely interdependent industries were established, which
found their raw materials mainly in coal tar ; but in more
recent years synthetic organic chemistry has drawn its raw
materials to an increasing extent from petroleum.
312 CHEMISTRY IN THE SERVICE OF MAN
By the distillation of coal there is obtained not only the
gaseous mixture so largely employed as a fuel and illuminant,
but also considerable amounts of ammonia and of 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 ; antiseptics and drugs ; the
sweet-smelling essences of flowers ; photographic chemicals ;
plastics and rubber-like materials, the manufacture of which
has developed into enormous and rapidly expanding in-
dustries. 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,
as is done in the refining of crude petroleum, various sub-
stances are obtained which distil over at different tem-
peratures. Of these the most important are the following :
LIQUIDS.
b.p.
Benzene 80-5 C. (176-9 F.)
Toluene 111 C. (231-8 F.)
SOLIDS.
m.p.
Phenol (carbolic acid) . . . 41 C, (105-8 F.)
Naphthalene .... 80 .(176 F.)
Anthracene .... 213 .(415 F.)
Benzene, C e H 6 , or benzole, as it is frequently called in
commerce, 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 NH 2 ) ; and
this, in turn, is the starting-point in the preparation of a
large number of dyes the aniline dyes. These aniline
SYNTHETIC CHEMISTRY 313
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.
Benzene is not only an important raw material in chemical
industry, but is also mixed with petrol for use as motor
fuel (p. 96). When the hydrogen atoms at two opposite
corners of the benzene hexagon are replaced by chlorine
atoms, one obtains paradichlorobenzene (Cl<^ /Cl), which
is a powerful moth insecticide.
Toluene, C 6 H 5 -CH 3 (commercially, toluole), 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.
As the formula indicates, the structure of toluene is that of
benzene in which one hydrogen atom is replaced by the
methyl group (CH 3 ). To satisfy the very large war demand
for toluene, this hydrocarbon had also to be produced from
petroleum.
Phenol or Carbolic Acid, C 6 H 5 -OH, is a well-known anti-
septic, 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 and of plastics.
Cresols, CH 3 -C 6 H 4 -OH, of which there are three isomeric
forms, also occur in coal-tar and are largely used in the
preparation of antiseptics (Lysol, Jeyes' Fluid, etc.) and for
the production of plastic materials (p. 335).
Naphthalene, C 10 H 8 , is a valuable constituent of coal-tar.
Its molecular structure is represented by two benzene
hexagons joined together. It is the raw material chiefly
employed in the manufacture of indigotin. When naph-
thalene is heated with hydrogen under pressure and in
presence of nickel as catalyst (cf. p. 190), hydrogenation takes
place and the important solvents tetralin, C 10 H 12 , and decalin 9
C 10 H 18 , are obtained. By the action of chlorine on naphtha-
lene, non-inflammable waxes (e.g. Seekay) are formed.
Anthracene, C H H 10 , is the raw material employed in the
314 CHEMISTRY IN THE SERVICE OF MAN
manufacture of a large number of important dyes, the most
familiar of which is the red dye, alizarin, or Turkey red. Its
molecular structure is represented by three benzene hexagons
joined together.
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 manufacture. By
the distillation of one ton of coal, therefore, we should obtain
the above constituents in the following quantities, roughly :
Benzene and Toluene . . . . 3} Ibs.
Phenol i| Ibs.
Naphthalene . . . . . 6 Ibs.
Anthracene . . . . . . 10 oz.
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 and
of safHower ; the animal dyes, kermes and 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
extensively cultivated in Southern Europe ; and the costliest
of all dyes, the most famous dye of the ancient world,
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.}
SYNTHETIC CHEMISTRY 315
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 W. H. PERKIN, by
the oxidation of crude aniline (C 6 H 5 NH 2 ), and since that
time colouring matters to the number of several thousands
have been synthesised by the chemist. The natural dyes are
mostly of a pronounced, even crude, colour, but the products
of the chemist are of an almost infinite variety ; and, far
outrivalling 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, con-
stituents of the dark-coloured liquid, coal-tar, which less
than a hundred years ago was a useless waste material and
a nuisance to the gas manufacturer, dyes and other organic
compounds are now prepared in large quantities.
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 compounds 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 haphazard process,
but one of which the conditions of success are clearly known.
Although thousands of different dyestuffs have been
prepared, it is in the artificial production of Nature's own
colouring matters, more especially of alizarin and indigotin,
that organic chemistry has achieved some of its most striking
successes. Through the labours of many chemists the com-
position of these natural products was determined and their
constitution or molecular structure unravelled ; and with
the knowledge thus obtained chemists have succeeded in
preparing these compounds artificially not merely sub-
stitutes for or imitations of the natural products, but the
actual products themselves and that more cheaply than
Nature herself can produce them.
316 CHEMISTRY IN THE SERVICE OF MAN
Until about 1870, over the whole of Southern Europe,
and eastwards to Asia Minor, great tracts of land, some
three or four hundred thousand acres, were devoted to the
growing of the madder plant ; in France 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
CRUSHING THE LEAVES OF Wo AD IN A ROTATING HORSE-MILL.
(Painting of a Lincolnshire Woad-mill by J. Doyle Penrose.)
root, was formed. This substance was capable of dyeing
cotton a bright red colour the so-called Turkey red
and was one of the oldest of dyes and 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 (C 14 H 10 ) to anthra-
SYNTHETIC CHEMISTRY 317
quinone (C 14 H 8 O 2 ), and from anthraquinone to dihydroxy-
anthraquinone or alizarin [C 14 H 6 O 2 (OH) 2 ]. More recently,
a new and more economical process has been introduced and
anthraquinone is now produced by allowing benzene and
phthalic anhydride (obtained from the more abundant
hydrocarbon naphthalene, p. 313) to react together in
presence of aluminium chloride as catalyst. The anthra-
quinone is then converted into alizarin. In this way the
madder dye can be manufactured much more cheaply than
Nature can produce it, and the madder fields of Southern
Europe exist no more.
Similar social-economic effects have been produced in
India, which was for long the chief home of the indigo-
bearing plants. Known for over three thousand years,
indigo was obtained from various species of Indigoferce,
cultivated more especially in India. The woad (Isatis
tinctorid), from which indigo is obtained, was cultivated in
Europe even as late as the seventeenth century, and its
cultivation lingered on in the Eastern Counties of England
until recent years. In the sixteenth century, with the opening
up of trade with the East, the superior Indian indigo began
to make its appearance in Europe, and although the use of
the " devilish drug " was at first prohibited by law, the ban
was removed in the eighteenth century. Down to near the
beginning of the present century the Indian indigo planta-
tions controlled the markets of the world. In 1896-7,
India produced over eight thousand tons of indigo, the value
of which was 4,000,000. It was a valuable prize, therefore,
which the German dye-manufacturers set themselves to win,
and after seventeen years of effort the genius and resourceful-
ness of their chemists won the day. In 1897, synthetic
indigotin 1 was placed on the market in competition with the
1 Indigo, the dye material obtained from the indigo plant, is not a
single substance but a mixture, the chief constituent of which is the
blue dye-stuff indigotin. It is on this difference between indigo and
synthetic indigotin that the difference between the dyeing power and
quality of (so-called natural) indigo and synthetic indigotin (wrongly
called synthetic indigo) depends*
318 CHEMISTRY IN THE SERVICE OF MAN
product from the Indian plantations, which it has almost
entirely replaced ; and more than a million acres of land,
formerly devoted to the production of indigo, are now given
over to the growing of food. The industrialist, however,
has not achieved a complete victory, for the production of
the natural indigo has, by the application of scientific know-
ledge, been improved and cheapened, and the natural dye is
still favoured by dyers for certain purposes. In 1938, some
55,000 acres were still under cultivation for indigo.
Since the industrial production of indigotin involves a con-
siderable 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 con-
stituent 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 indigotin is to
convert this naphthalene into a compound called phthalic
COOH\
acid (CeH4<TT ), and then into phthalic anhydride
CO
(C 6 H 4 <p~>O). 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 indigotin
unremunerative. But here a lucky 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
SYNTHETIC CHEMISTRY 319
to allow it to be carried out with commercial success. The
method is, however, no longer used, and naphthalene in the
state of vapour is now oxidised to phthalic anhydride by the
oxygen of the air with the help of a catalyst, vanadium
pentoxide.
A broken thermometer sealed the fate of the Indian indigo
plantations ! Yet, this fate might, perhaps, have been
averted if only a fraction of the money and energy and
scientific ability which were devoted to the industrial pro-
duction of the synthetic dye had been devoted to research
into the improvement of the production of the natural dye.
The successful industrial production of indigotin depended
also on improvements being effected in the manufacture of
the various chemicals employed. Thus the demand for
a very powerful sulphuric acid pyrosulphuric acid or
"oleum" and the fact that during the process of heating
it with naphthalene large quantities of sulphur dioxide are
formed, led to the development of a new method of making the
acid, namely, the " contact process " to which reference was
made in Chapter IX. 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
has been replaced by the electrolysis of a solution of common
salt, the chlorine being then obtained in a pure state by lique-
faction. The ammonia may be obtained, as we have seen,
as a product of the distillation of coal, but is mainly produced
by direct synthesis from nitrogen and hydrogen (p. 207) ;
and the acetic acid is obtained by the distillation of wood,
and from acetylene (p. 356).
Although it is not possible to enter into a detailed dis-
cussion 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 (see p. 282). 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
32O CHEMISTRY IN THE SERVICE OF MAN
to be dyed 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,
therefore, developed in the fibre after its removal from the
bath. The vat dyes, it is interesting to note, have now been
obtained in a soluble form and so have become available for
dyeing wool and silk which are destroyed by the strongly
alkaline solutions formerly required. Important as has been
the rSle played by indigo in the past, this dye, like other
dyes, is always under peril of being replaced by newer and
better synthetic dyes.
Closely related, chemically, to indigo, is that other ancient
dye, Tyrian purple, which is secreted by certain species of
marine snail, the Murex brandaris and Murex trunculus,
found, more especially, on the shores of the Mediterranean.
On investigation, it was ascertained that this " dye of dyes,
whereof one drop worked miracles/' is a compound of
indigotin 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 from
the glands of twelve thousand shell-fish by the German
chemist who investigated the dye, amounted only to about
twenty-three grains, and the estimated cost of the dye was
nearly 60 an ounce.
During the present century many synthetic dyes with very
valuable properties have been produced. Thus, the so-called
indanthrene dyes, prepared from anthraquinone, an oxide
of the hydrocarbon, anthracene, are distinguished by their
great fastness to light and are used for dyeing various
" fadeless " fabrics ; while another important series of dyes
finds application for the dyeing of celanese or acetate rayon
(p. 145). Anthracene occurs only in small amounts in coal-tar
but anthraquinone can now, as has been pointed out, be
prepared from phthalic acid, produced by the oxidation of
the relatively abundant naphthalene, and benzene (p. 317).
SYNTHETIC CHEMISTRY 321
AN/ESTHETICS, ANTISEPTICS, DRUGS AND INSECTICIDES
The sixteenth and seventeenth centuries are regarded as
marking a distinct era in chemistry, inaugurated by Para-
celsus. 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 or
medical 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 medicine are
greater beyond comparison than all the iatro-chemists were
ever able to perform, or even to imagine. 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 anaesthetics,
hypnotics, antipyretics, and drugs for the treatment of special
diseases, has developed into an industry of great importance.
Ancesthetics. The first of these synthetic products to
come into use was chloroform (CHC1 3 ), which had been pre-
pared by the German chemist LIEBIG in 1832, by the action
of bleaching powder on alcohol. 1 It was first used as an
anaesthetic by Sir JAMES SIMPSON in 1847, and has not only
facilitated the work of the surgeon but has freed mankind
from untold misery and suffering. The discovery of the
anaesthetic properties of chloroform led to a search for and
discovery of other anaesthetics, such as ether and ethyl
chloride, substances which are also produced from alcohol.
1 Chloroform is now prepared from acetone (p. 356).
L
322 CHEMISTRY IN THE SERVICE OF MAN
The introduction as a local anaesthetic of the alkaloid
cocaine, which occurs in the leaves of the coca plant, aroused,
in 1884, much interest among surgeons, and led chemists to
undertake a systematic investigation of substances related
structurally to cocaine, the molecular constitution of which
had been elucidated in 1898. As a result, it was found that
a particular physiological action is due, in many cases, to the
presence of certain groupings of atoms in the molecule of a
compound, and can be modified or even entirely altered by
the introduction of different atoms or groups into the parent
molecule, or by eliminating certain groups from it. Guided
by this discovery, chemists succeeded in synthesising a
number of compounds, all of which possess local anaesthetic
action. Of these, one may mention novocaine and ametho-
caine (known also by other names), the latter compound
being, it is stated, a perfect substitute for cocaine for all
purposes. It has, moreover, greater stability, and is not
habit-forming.
The introduction of the anaesthetic chloroform marked a
new era in surgery, and a further advance was made through
the introduction of the substance adrenaline, the active
principle of the suprarenal glands (p. 370). 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 suprarenal glands of sheep and oxen, close on 1000 Ibs.
of tissue (the glands from 20,000 oxen) being required to
yield i Ib. of adrenaline. It was not long, however, before
the molecular structure 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 polarised light to
SYNTHETIC CHEMISTRY 323
the left ; whereas the synthetic product is a racemic com-
pound of the two optically active forms, and is therefore
inactive (p. 305). With the help of dextro-tartaric acid,
however, this racemic form can be resolved into its two
optically active isomers, and the laevo-form isolated.
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 illustra-
tion of this property is afforded 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 .
Hypnotics. Following closely on the discovery of chloro-
form came the discovery of chloral (CC1 3 *CHO) and its
soluble crystalline hydrate, the first hypnotic to be produced
industrially. The dangers attending the use of chloral,
however, led to the search for and discovery of other hypnotics
which are free from its bad qualities ; and at the present day
quite a number of synthetic hypnotics are available. Two
of the most familiar are veronal and luminal, compounds
derived from barbituric acid and known as barbiturates.
Antiseptics. Since the discovery by Pasteur of the
bacterial origin of putrefaction and disease, and the intro-
duction by Lord Lister of aseptic surgery, chemists have
applied themselves to the synthesis or building up of com-
pounds which should be more and more effective as
germicides but should be non-toxic to the leucocytes or
white " warrior cells " of the blood, which are the natural
defence of the patient against the organisms producing sepsis.
Although the germicidal properties of chlorine have long been
known, and are widely applied for the destruction of bacteria
in water, this element is not suitable for use as an antiseptic
in the treatment of wounds. Various compounds, however,
of chlorine, such as chloramine T (CH 3 -C 6 H 4 -SO 2 -NC1 Na),
324 CHEMISTRY IN THE SERVICE OF MAN
the relation of which to toluene is clear from the formula, and
the chlorine derivatives of the cresols (p. 313), have powerful
antiseptic properties and are non-toxic and non-corrosive.
A number of dyes, e.g. acriflavine, prepared from the coal-tar
constituent, acridine, also act as powerful antiseptics without
interfering with the normal processes of healing.
In 1929, the important discovery was made by Sir
ALEXANDER FLEMING, of St. Mary's Hospital, London, that
the mould Penicillium notatum produces, during its growth,
a material which has powerful bacteriostatic properties.
He gave to it the name penicillin. In 1940, the method of
isolating and of producing it in quantity was developed by a
team of workers under Sir H. W. FLOREY at Oxford, and
there was thus put into the hands of the surgeon and physician
a unique antiseptic which, while non-toxic to the patient, is
extremely efficacious in rendering harmless the micro-
organisms responsible for pus formation, gas gangrene and
other wound infections which, in the past, have been the
cause of many deaths. Penicillin, it has been found, may also
be used beneficially in the treatment of diphtheria, tetanus,
carbuncles and impetigo.
As a result of an intensive co-operative effort directed
towards the elucidation of the chemical nature of this rather
unstable material, it has been found that there are several
different natural penicillins, the complex molecular structure
of which chemists have succeeded in unravelling. The
penicillins, it has been found, are acids with the general
formula C 9 H 11 O 4 SN 2 R, where R stands for C 5 H 9 -,
C 6 H 5 -CH 2 - or HOC 6 H 4 -CH 2 -. With the knowledge of the
chemical nature and molecular structure thus revealed it
may be hoped that great as have been the achievements
made possible with penicillin, new synthetic compounds
may be obtained possessing still greater efficacy and range
of application.
Drugs and Therapeutic Agents. During the last quarter
,of the nineteenth century, chemists, seeking to obtain drugs
SYNTHETIC CHEMISTRY 325
which might supplement or replace the specific anti-malarial
alkaloid quinine, prepared a number of compounds which
were found to possess valuable antipyretic and analgesic
(or pain alleviating) properties. One of the first
of these was antifebrin, known to chemists as acetanilide
(CH 3 -CO-NH-C 6 H 6 ), the physiological properties of which
were accidentally discovered in 1886 ; and this was followed,
in 1887, by t ' ie analgesic drug phenacetin, obtained by
introducing the ethoxy-group (C 2 H 5 O) into the molecule of
acetanilide. The toxic action of this compound is thereby
greatly diminished. Similarly, by a modification of the
OH
molecular structure of salicylic acid
there was prepared acetylsalicylic acid i C 6 H 4
\ \COOH
or aspirin, which does not produce the gastric disturbances
caused by the parent compound. As an anti-rheumatic and
anti-neuralgic drug, aspirin is by far the most popular and
widely used of all the synthetic drugs, over 130 tons of it
being sold annually in Great Britain alone.
Valuable, however, as these compounds were found to be
as therapeutic agents, their use merely alleviated the symp-
toms of disease ; and it was not until early in the present
century that the foundations of a true chemotherapy were
laid, by which the causes of disease were attacked by
means of chemical compounds of specially planned molecular
structure. 1
Guided by the observation that various living tissues and
organisms show selective absorption for different dyes, the
German physiologist and chemist, PAUL EHRLICH, con-
ceived the idea of combating diseases due to protozoal
parasites by the use of substances which are poisons for the
1 The natural alkaloid, quinine, had of course long been in use as a
specific against the organism causing malaria.
326 CHEMISTRY IN THE SERVICE OF MAN
parasites but which are not absorbed by and are therefore
not harmful to the cells of the host. After many trials and
many failures, Ehrlich was successful in finding, in 1912,
in the complex, arsenic-containing compound which he
called salvarsan, a cure for syphilis. Since that time, chemists
have prepared a number of other compounds which have
proved effective in treating many tropical and other diseases
(e.g. sleeping sickness, kala azar, etc.), of protozoal origin.
Even for the treatment of malaria, quinine 1 has met with
rivals in the synthetic drugs plasmoquin (or pamaquiri), a deri-
vative of quinoline, and mepacrine hydrochloride (or atebriri),
a derivative of acridine. These substances are specific
poisons for the malarial parasite at two different stages of its
life cycle and are widely used for the treatment of malaria.
Tablets of atebrin, packed between thin sheets of the plastic
polythene (p. 336), to protect them from moisture, were issued
to British and Allied troops in Burma and the Far East.
Valuable as mepacrine has proved itself to be as a sub-
stitute for quinine, a new drug, paludrine, prepared in 1945
by the chemists of Imperial Chemical Industries, has been
found to be more effective than quinine and mepacrine as a
protective against infection from the bite of mosquitoes and
more powerful in destroying the parasites and in controlling
the symptoms of malaria. 2
Since 1935, great advances have been made, and one of
the most remarkable discoveries in the domain of chemo-
therapy has been that of the therapeutic value of a number
of compounds belonging to what is called the sulphanilamide
(NH 2 -C 6 H 4 -SO 2 NH 2 ) group, and generally spoken of as
sulpha-drugs. Sulphanilamide itself arrests the action 3 of
1 Although the synthesis of quinine has been achieved in the laboratory,
it has not yet been developed industrially.
2 It has been announced that over 99 per cent, of malaria cases treated
in the State of Victoria, Australia, were cured by paludrine.
8 The sulpha-drugs are bacteriostatic, not bactericidal, in action ; that
is, they prevent the multiplication and arrest the action of the bacteria,
which are then destroyed by the leucocytes of the blood.
SYNTHETIC CHEMISTRY 327
the streptococci which are the cause of puerperal fever,
scarlet fever and erysipelas, and is also of value in preventing
sepsis in wounds. It was found, however, as the result of
chemical investigation by the research staff of Messrs. May
and Baker, that if one of the hydrogen atoms of the SO 2 NH 2
[Courtesy of Imperial Chemical Industries Ltd.
TABLETS OF ATEBRIN PACKED IN POLYTHENE ENVELOPES.
group is replaced by various molecular structures (pyridine,
thiazole, guanidine, etc.), the effectiveness and range of
usefulness of the sulpha-drugs could be extended. Thus,
sulphapyridine (M. and B. 693) and sulphathiazole (M. and B.
760) are effective in combating not only streptococci but also
pneumococci and meningococci, the organisms responsible
for pneumonia and meningitis. Sulpha-guanidine is especially
valuable in the treatment of dysentery.
Through the introduction of the sulpha-drugs, regarded,
popularly and not without reason, almost as miracle-working
328 CHEMISTRY IN THE SERVICE OF MAN
drugs, the treatment of bacterial diseases in man has, since
1935, been completely revolutionised ; and a very notable
reduction in the number of deaths due to puerperal fever,
pneumonia, pneumococcal meningitis and other diseases
has been effected. There even seems good reason for hope
that, through the genius of chemists, drugs may be obtained
by which also tuberculosis may be combated.
The important contribution which the chemist has made
to the alleviation of pain, the maintenance of health and the
conquest of disease, is one of the most notable features of the
history of medicine. By none has a greater service been
rendered to mankind.
Insecticides. Since it has been found that many protozoal
and bacterial diseases are transmitted from man to man by
insects, one may combat these diseases not only by means of
prophylactic drugs but also by the destruction of the insect
carriers. For many years one has used, for the destruction
of mosquitoes and other insects, an extract of pyrethrum
flowers (containing two active ingredients, the pyrethrins),
dissolved in kerosine (as in the familiar " flit "), or in the
liquid freon (dichlorodifluoromethane), as well as an extract
of Derris root, the chief active principle of which is rotenone.
The larvae of mosquitoes, on the other hand, have been
destroyed by spraying the breeding areas with kerosine or
with Paris green, an organic compound containing arsenic
and copper.
During the war of 1939-45, however, supplies of the above
insecticides were largely cut off, owing to the entrance of
Japan into the war, and it became necessary to obtain other
insecticides to cope not only with mosquitoes but also with
other insect carriers of disease. Of these, especially in times
of war, the louse, carrier of typhus, which in the past has
decimated armies and civilian communities, is one of the
most important. During the war, therefore, as the result
of research work by the chemists of this country and
also of America, there was developed the manufacture
SYNTHETIC CHEMISTRY 329
of an insecticide known to chemists by the somewhat
formidable name of diparadichlorodiphenyltrichloroethane
/C1-C.H 4X \
I ^>CH*CC1 3 I, disguised under the official con-
\C1-C 6 H/ /
traction D.D.T. This compound has been found to be an
insecticide of remarkable potency and persistence, although
it does not possess the rapid " knock-down " property of the
pyrethrins. It can be used for the destruction of the insect
carriers of malaria, yellow fever, sleeping sickness (tsetse fly),
dysentery (house fly), typhus (louse), plague (flea), etc. In
1942 it had one of its greatest triumphs in successfully com-
bating an epidemic of typhus which broke out in Naples.
The freedom of the men of the Allied forces from lice
infestation was due largely to the impregnation of their
clothing with D.D.T.
More recently, chemists of Imperial Chemical Industries
have produced a compound which is an even more powerful
insecticide than D.D.T. This substance, to which the name
gammexane has been given, is one of the four isomeric forms
of the compound, benzene hexachloride (C 6 H 6 C1 6 ). Like
D.D.T., gammexane is a solid and can be used either as a
dusting powder, mixed, say, with gypsum, or as a spray,
when dissolved in a suitable solvent. Like D.D.T., gam-
mexane has a persistent rather than an immediate knock-
down action, and is outstanding in its toxicity to locusts.
CHAPTER XVI
SYNTHETIC CHEMISTRY II
SYNTHETIC PERFUMES
FOR thousands of years the volatile substances to which the
different flowers and plants owe their odours have been ob-
tained by distillation or by extraction by means of solvents.
In the past sixty or seventy years, however, the secrets of
Nature have been largely unravelled, and the chemical
laboratory has become odorous as a garden and filled with
the perfumes of violet and rose, heliotrope, lilac, hyacinth
and orange blossom ; and from the stills of the chemist
there also flow liquids the flavours of which imitate those
of the apple, pear, pineapple and other fruits, and which,
in consequence, find application as artificial fruit essences
(p. 354). Although in a number of cases the synthetic per-
fumes and flavouring essences merely imitate the products of
Nature, in other cases the chemist has succeeded in prepar-
ing the identical substances 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 prepared
by the chemist was the substance coumarin, the odoriferous
principle of the sweet woodruff (Asperula odor at a), a fragrant
substance used in the preparation of the perfumes known as
Jockey Club and New-mown Hay. This synthetic prepara-
tion 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,
formed by the oxidation of eugenol, the chief constituent of
clove oil, 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
330
SYNTHETIC CHEMISTRY 33!
(met hylsalicy late), oil of bitter almonds (benzaldehyde), haw-
thorn blossom (anisic aldehyde), lily of the valley (terpineol),
ambergris (ambrein), and others, can now be prepared arti-
ficially. Other synthetic compounds, while not identical
with the natural perfumes, closely resemble them in odour,
and are employed in large quantities either as substitutes
for the natural perfumes or for blending with them. Of
these the most important are ionone, or imitation violet,
imitation musk, and imitation oil of bitter almonds, or " oil
of mirbane " (nttro-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.
It has been pointed out that the synthetic production of
the colouring matters alizarin and indigotin produced vast
social and economic changes by the more or less complete
supersession of natural by synthetic dyes. In the commercial
production of camphor one finds another 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, Formosa,
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 has for long been a highly valued substance on
account of its therapeutic, disinfecting and other properties,
and the demand for the compound has been very greatly
increased in the past fifty or sixty years owing, more especi-
ally, to its employment in the manufacture of celluloid for
332 CHEMISTRY IN THE SERVICE OF MAN
cinema and photographic films and plastics. Japan had,
therefore, a valuable source of revenue in her practical
monopoly of the production of camphor through her posses-
sion 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 the utmost.
The substance, however, 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.
The Japanese camphor plantations have hitherto 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 different species of pine,
and which is not only restricted in quantity, but is also
subject to increase in price. The synthetic camphor, there-
fore, has not been able to displace the natural, but it has
prevented an excessive rise in the price of the compound.
The remarkable achievements of the last half century in
the synthesis of dyes, drugs, perfumes, etc., give an almost
prophetic sound to the words of Lucretius : " I tell you,
barbaric robes and radiant Melibcean purple dipped in
Thessalian dye of shells (and the hues which are displayed)
by the golden brood of peacocks steeped in laughing beauty
would be thrown aside surpassed by some new colour of things ;
the smell of myrrh would be despised and the flavours of
honey . . . would in like sort be suppressed ... for some-
thing ever would arise more surpassing than the rest."
SYNTHETIC CHEMISTRY 333
PLASTICS
Among the most important of industrial synthetic pro-
ducts are those numerous materials which are known by
the general name of plastics. These materials, although
hard and rigid under ordinary conditions, exhibit the
property of plasticity, or the property of undergoing de-
formation under mechanical stress, during some stage of
their manufacture. In some cases, they are thermoplastic ;
in others, thermosetting. The former become plastic when
heated, and can be repeatedly moulded and remoulded by
the application of heat and pressure ; the latter also can be
moulded by heat and pressure, but undergo a chemical
change under the action of heat and pass into a hard mass
which cannot be softened and remoulded by the further
application of heat and pressure. To the former group
belongs celluloid (p. 148), one of the first plastics to be
introduced ; to the latter, bakelite.
To whichever group they belong, plastics are compounds
with large molecules, or compounds of high molecular weight.
In some cases, the large molecules have been built up by
nature and exist in the raw material (e.g. cellulose) used in
the manufacture of the plastic ; but in most cases, the large
molecules are formed during manufacture, either by the
combining together of a large number of small molecules,
that is, by polymerisation (p. 98), or by a chemical reaction
in which a molecule of water is eliminated between each
pair of simple molecules, that is, by condensation (p. 138).
The formation of polythene (p. 336) is an example of the
former process ; the formation of nylon (p. 337), an example
of the latter.
Although, no doubt, plastics were at first introduced as
substitutes for naturally occurring materials bone, ivory,
gums and resins they must no longer be so regarded ; and
certainly not as substitutes which are inferior to natural
products. Plastics are new materials made available to man,
334 CHEMISTRY IN THE SERVICE OF MAN
materials which have their own distinctive and valuable
properties. For many purposes, they are superior to and
have displaced wood, metal and stoneware, and they have
found very widespread and varied use as new constructional
materials. The foundation of what has now become a vast
and rapidly expanding industry was laid by the American
chemist, L. H. BAEKELAND, about the year 1908.
On warming together phenol (carbolic acid) and form-
aldehyde (p. 135), along with a little ammonia, which
hastens the reaction, a thick gummy mass is produced.
When freshly prepared this gummy material can be dissolved
in alcohol, acetone and other similar solvents, and used as a
lacquer or varnish ; but on being heated, under pressure,
to a temperature of over 100 C. or 212 F., it undergoes
polymerisation and changes into a hard, resin-like solid, to
which the commercial name of bake lite is given. Bakelite
is a thermosetting plastic, is infusible and insoluble in all
solvents, and is the most versatile and widely used of all the
synthetic resins. It is an excellent insulator for electricity,
and finds, in consequence, 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 and beads ; and for making buttons, knobs, knife-
handles, telephone instruments and many other articles
for which bone, celluloid, ebonite, or other material was
formerly employed. It is not so flexible as celluloid, but
it is more durable, is not inflammable, and is less expensive.
In some of their most important applications, the phenol-
formaldehyde resins are used along with various fibrous
" fillers " wood-meal, cotton fibre, asbestos, etc. whereby
the strength and resistance to shock are increased and the
moulding properties improved. Layers of textile fabric,
impregnated with a solution of phenol-formaldehyde resin in
volatile organic solvents, and moulded and hardened under
heat and pressure, are used not only as insulating materials,
but also for noiseless gears, bearings and decorative panelling.
SYNTHETIC CHEMISTRY 335
Wood, also, 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.
For the production of plastics, use may be made not only
of phenol but also of cresol, and besides formaldehyde other
aldehydes may be employed. Thus, when phenol is allowed
to react with an aldehyde known as furfuraldehyde (obtained
by heating bran, corn-cobs, etc., with acid), another series
of resins can be obtained, which, like bakelite, can also be
used as plastic material.
A notable advance in the production of synthetic resins
was made when it was discovered that a clear colourless solid
is formed by the reaction between urea (p. 210) and form-
aldehyde. Attempts, however, to produce in this way an
" organic glass/' as a substitute for ordinary glass, failed,
as it was not found possible to prevent the material from
cracking under the strains brought about by shrinkage.
Fortunately it was found by the English chemist, E. C.
ROSSITER, that when thiourea (p. 105) is substituted for urea,
colourless resins are also produced ; and by acting with
formaldehyde on a mixture of urea and thiourea, under
suitable conditions, a mixed thermosetting resin is obtained
which has properties superior to either of the single resins,
and which shows no tendency to crack. This mixed resin,
produced industrially under the name beetle ware, forms a
transparent, colourless material, of glass-like clearness. It
may also be tinted or coloured and used for domestic ware,
electrical switches and fittings, lacquers and many other
purposes.
Urea-formaldehyde resins are also made use of for the
production of non-creasing cotton goods. The fabric is
impregnated with a solution of urea and formaldehyde and
the resin formed, by heating, on the fibre.
Of still greater importance as a transparent " organic
336 CHEMISTRY IN THE SERVICE OF MAN
glass " is the synthetic resin introduced by Imperial Chemical
Industries under the name perspex, a material produced
from the compound known as methyl methacrylate
T \
^C-COOCH 3 ). This compound formed from
acetone, hydrocyanic acid and methyl alcohol is a liquid
which, in presence of oxygen or organic peroxides, undergoes
polymerisation and is gradually transformed into a colourless
glass.
Perspex (also called Incite in America) has a transparency
second only to that of quartz glass (p. 218) and is the most
successful organic substitute for glass so far obtained. It
is thermoplastic and can be moulded into spectacle lenses,
photographic lenses, and other optical apparatus. The cost
involved in grinding glass is thus avoided. As it is non-
splinterable, perspex is now also finding extensive use in
the construction of the cockpits, turrets, etc., of aeroplanes
and in the production of bullet-proof " glass. " Its specific
gravity is only about one-third that of glass, but a sheet of
perspex is about ten times as strong as glass of equal thick-
ness. It is largely used for dentures.
By allowing methyl methacrylate to undergo polymer-
isation in an emulsified condition, the resin is obtained in a
granular form. This is sold for moulding purposes under
the name diakon.
By means of a trace of oxygen, the unsaturated hydro-
carbon ethylene, when under a high pressure, undergoes
polymerisation and forms polyethylene or polythene, a long
chain hydrocarbon consisting of about 1000-2000 CH 2 -
groups joined together. In this way one obtains a very
remarkable plastic, the trade name of which is alkathene.
It is one of the lightest of all the plastics and will float on
water. It is characterised by its toughness and flexibility,
its resistance to water, its chemical inertness and its unique
electrical properties. Its tensile strength can be increased
by cold drawing. It is used as a flexible insulating covering
SYNTHETIC CHEMISTRY 337
for electric wires and cables, for making collapsible tubes
for creams, cosmetics, etc., and for the production of flexible
or rigid piping.
By allowing butyraldehyde, C 3 H 7 -CHO, to react with poly-
merised vinyl alcohol
(. . . -CH(OH)-CH 2 -CH(OH)-CH 2 - . . .),
a long chain molecule is formed, one link of which can be
represented by the formula
-CH 2 -CH-CH 2 -CH- CH 2 -
O CH 6
C 3 H 7
This forms a strong plastic material, polyvinyl butyral or
butvar, used in the U.S.A. as an interlayer for triplex safety
glass.
As in the case of celluloid, so also in the case of the plastic
erinoid or galalith, the raw material is a natural product of
high molecular weight, a protein known as casein (p. 357).
Ground casein, mixed with filler and pigment, if desired, is
heated and extruded by pressure in the form of a rod, or
formed into sheets by pressing between metal plates at a
suitable temperature. It is then " cured " or hardened and
rendered insoluble and horn-like by being soaked in a
solution of formaldehyde (formalin). By suitable working
it can be made to resemble bone, ivory, horn, coral, tortoise-
shell, amber, etc., and is used for a great variety of articles,
e.g. buttons, beads, umbrella handles, combs. It is non-
inflammable but cannot be. obtained in a form suitable for
photographic films.
In 1940, there was produced by the firm du Pont de
Nemours, in America, a compound to which the trade name
nylon was given. It is obtained by allowing the compound
hexamethylene diamine, NH 2 '(CH 2 ) 6 'NH 2 , to react with
adipic acid, COOH-(CH 2 ) 4 -COOH. By a process of con-
densation (p. 138), a highly complex molecule with the
338 CHEMISTRY IN THE SERVICE OF MAN
protein-like structure [-NH-(CH 2 ) 6 'NH-CO-(CH 2 ) 4 -CO-] rt
is built up, the molecular weight of the compound being
greater than 10,000. In the molten state it can be extruded
through perforated plates to form strong and elastic filaments
with a silky lustre. By drawing out these extruded filaments
to about four times their original length, the long chain
[Courtesy of Science Service, Inc.
FINE MESH OF NYLON STOCKINGS, CONTRASTED WITH A HUMAN HAIR
(FINE HORIZONTAL LINE) AND A PIECE OF No. 60 SEWING COTTON)
(HEAVY DIAGONAL LINE).
molecules are orientated and the tensile strength is greatly
increased. Transparency and a high degree of lustre are
also developed. On account of its great tensile strength,
fabric woven of nylon yarn has found extensive use for
parachutes ; and ropes of nylon were used during the war
for towing gliders. A nylon rope, half an inch in diameter,
will support a weight of three tons. Weight for weight, it
has a greater tensile strength than steel.
SYNTHETIC CHEMISTRY 339
Nylon can also be obtained in the form of sheets and of
bristles, for use in tooth brushes, for example. Bristles for
paint brushes, which have to have tapering ends, are also pro-
duced. Nylon is also extensively used in the manufacture
of ladies' stockings and of strong fabrics for upholstery.
In 1904, Professor F. S. KIPPING, of University College,
Nottingham, synthesised a number of compounds of the
types R-Si(OH) 3 , R 2 -Si(OH) 2 , where R stands for a hydro-
carbon radical such as CH 3 - , C 2 H 5 - , etc. These compounds,
which were called silicok> were found readily to undergo
condensation with loss of water and production of sub-
stances of high molecular weight known as silicones. These
compounds were for long of theoretical interest only, but
since 1945 their production on an industrial scale has been
developed. By allowing condensation of different silicols
or mixtures of silicols to take place, a great variety of
silicones, liquid, semi-liquid and solid, can be obtained
which have very remarkable properties. Possessing great
heat resistance and high electrical insulating properties, the
silicones have been coming into use as heat-resisting
varnishes, as insulating liquids in electrical transformers,
as lubricants, the viscosity of which varies very little with
the temperature, as a rubber-like material which is stable
to heat and is not hardened by cold. " Bouncing putty "
is a methyl silicone polymer which is extremely elastic to
sudden impact but is plastic under gradually imposed
pressure. The silicones are highly water-repelling and
may be used to impregnate cotton to give a waterproof
material. Cost of production still restricts the use of these
remarkable substances.
RUBBER-LIKE MATERIALS
One of the most important materials in our present-day
civilisation is rubber, obtained by the coagulation, by means
of acid, of the sap or latex of certain species of trees, more
340 CHEMISTRY IN THE SERVICE OF MAN
especially Hevea Brasiliensis. Although, formerly, rubber
was obtained mainly from the " wild " rubber trees, in-
digenous to the Amazon Valley, most of it is now derived
from the plantations of cultivated trees in Malaya, Ceylon and
Dutch East Indies. The production of plantation rubber has
been greatly improved and increased by scientific investigation.
The development of the rubber industry dates especially
from the discovery, made more than a hundred years ago
by Thomas Hancock in London, that when rubber is
" masticated " by being disintegrated and worked between
rollers, it forms a plastic mass, and from the later discovery
that rubber can be vulcanised by means of sulphur or by
treatment with certain compounds of sulphur. In this way
the stickiness of rubber on being heated is counteracted.
When the amount of sulphur taken up by the rubber amounts
to about 50 per cent., a hard rubber known as vulcanite or
ebonite is obtained. This is a material which had, at one
time, a great vogue for the production of moulded articles.
Most of the rubber used at the present day for motor-
car tyres and for rubber articles of all kinds is vulcanised,
but the properties of the finished article can be greatly
modified and the process of manufacture facilitated by the
addition of different substances. In 1915, it was found
that the addition of carbon black, for example, increases the
tensile strength of the rubber and confers a high degree of
resistance to abrasion. By the addition to rubber of about
28 per cent, of carbon black and of certain " anti-oxidants,"
whereby the tendency to crack on exposure to light and air
is counteracted, the life of a motor-car tyre has been trebled
or quadrupled.
For many years chemists have sought to produce artificially
rubber or a rubber-like material, and in recent times great
success has attended their efforts.
It has long been known that when natural rubber is
decomposed by heat, the most important product is a
hydrocarbon called isoprene (CH 2 :C(CH 3 )-CH:CH 2 ) ; and
SYNTHETIC CHEMISTRY 341
it was found that this compound, on being kept, very slowly
undergoes polymerisation to form a rubber-like material,
consisting of a large number of isoprene molecules combined
together to form a large complex molecule. The process of
polymerisation, however, took place so slowly that it was
industrially of no value. In 1910, the important discovery
was made, first in England and then in Germany, that the
polymerisation of isoprene is very greatly accelerated by
metallic sodium.
Although the polymerised isoprene was of no practical
significance, it was found that the simpler hydrocarbon
butadiene (CH 2 :CH>CH:CH 2 ) can also be caused to poly-
merise with the formation of a rubber-like material ; and it
is on the development of this process, more especially, that
the efforts of chemists, at first in Germany but, in recent
years, also in the U.S.A., Canada and Russia, have been
concentrated. The artificial rubber produced from bu-
tadiene is generally referred to as Buna. 1 The butadiene
required for this process can be synthesised from acetylene,
and it is also obtained by various processes from alcohol
and from the gases butane and butylene which are present in
or can be obtained from petroleum. To bring about the
polymerisation of butadiene, other catalysts than sodium,
e.g. benzoyl peroxide, are now used.
To improve the qualities of the butadiene rubber, the
butadiene is generally mixed with another polymerisable
substance, especially with styrene, C 6 H 5 -CH:CH 2 , or with
acrylic nitrile, CH 2 :CH*CN, and the two substances are
polymerised together. The products so obtained are known
is Buna S and Buna N. During the war, the U.S.A. estab-
lished a synthetic rubber industry, the production of which
in 1944 amounted to over 700,000 tons of Buna S (renamed
GR-S).
1 The name Buna is derived from bu (tadiene) and Na, the symbol for
lodium. The name has, however, lost its significance as sodium is no
onger used as catalyst to accelerate the polymerisation of butadiene.
342 CHEMISTRY IN THE SERVICE OF MAN
At an earlier date, the firm of du Pont de Nemours intro-
duced another synthetic rubber-like material, neoprene y
formed by the polymerisation of chlorinated butadiene or
chloroprene (CH 2 :CC1-CH:CH 2 ). Although more similar to
rubber in its molecular constitution than are other synthetic
products, neoprene should not be regarded merely as a
rubber substitute. It should rather be regarded as a new
material with its own special qualities which make it suit-
able for a great variety of purposes for which rubber is not
so well adapted. Neoprene, while it equals rubber in
elasticity, strength and resistance to abrasion, is greatly
superior to rubber in its resistance to petrol, oils, fats,
solvents, heat and ozone. It is also less pervious to gases.
While it can be destroyed by heat, it does not propagate
flame. For many purposes, therefore, neoprene should be
used in preference to rubber.
By treatment with chlorine, rubber can be chlorinated,
and chlorinated rubber is now produced under the name
alloprene. Mixed with a suitable solvent (e.g. xylene), with
addition of decalin (decahydronaphthalene) or solvent
naphtha, according to the rate of drying required, and with
a plasticiser (e.g. cerechlor or chlorinated paraffin wax), allo-
prene is used as a protective paint, highly resistant to acids,
alkalies and salts. In a fibrous or spongy form, alloprene is
also an excellent heat and sound insulator. It can readily
be moulded when hot.
CHAPTER XVII
FERMENTATION AND THE ACTION OF
ENZYMES AND MICRO-ORGANISMS
WE have already seen (p. 184) 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 contained
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, bac-
teria 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 develop-
ment 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 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-catalyst appropriate to
the process.
343
344 CHEMISTRY IN THE SERVICE OF MAN
This explanation of the fermentation process a term at
first applied to all changes which are accompanied by effer-
vescence 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 explana-
tions put forward by Berzelius and Liebig. The former, who
introduced the conception of " catalytic force " (p. 178),
likened fermentation to the decomposition of hydrogen
peroxide under the influence of platinum ; and the latter,
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, undergoes a decomposition. 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 are
associated with and produced by living organisms ; and
this vitalistic explanation, summed up by Pasteur in the
well-known phrase, " No fermentation without life," is
accepted, in the main, at the present day. The growth of
knowledge, however, has rendered necessary a certain modi-
fication of the views which were put forward in the middle of
last century. For a considerable time the view was held that
the fermentation processes are the result of the direct action
of the living organism on the fermentable material. Cases,
however, began to accumulate of changes brought about by
substances, e.g. 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>
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 345
produced by and contained in the cell of the yeast. 1 It is
now generally accepted, therefore, that fermentation changes
are produced by substances which although produced by
living organisms are not themselves living ; and to these
substances the name enzyme (eV, in ; fopy, yeast), intro-
duced in 1878, is applied. In proposing the adoption of this
term, the German physiologist, W. KUHNE, stated : " This is
not intended to imply any particular hypothesis, but it
merely states that eV ty^y (in yeast) something occurs that
exerts this or that activity, which is considered to belong to
the class called fermentative. The name is ... intended to
imply that more complex organisms, from which the en-
zymes, 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 role 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 greater
importance than that which has been carried on from the
earliest days of man's history, the fermentation of sugar
with production 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 hydroxyl group (OH) is present, the name when
used without qualification is applied to the best known and
most valuable of the alcohols, ethyl alcohol (C 2 H 6 'OH), or
as it is frequently called, spirits of wine. In the fermenta-
tion 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,
1 Zymase, it has been shown, consists of at least two substances, an
enzyme and a co-enzyme, one a colloid, the other a crystalloid (p. 275),
and the presence of both is necessary for fermentation.
346 CHEMISTRY IN THE SERVICE OF MAN
zymase, on certain sugars, the most important of which is
the sugar glucose which, along with the isomeric sugar,
fructose, 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
beetroot sugar (known chemically as sucrose), and malt sugar
or maltose, are not fermentable with zymase. If, however,
yeast is introduced into solutions of these sugars, fermenta-
tion does take place, owing to the fact that yeast secrete^
not only the enzyme zymase, but also the enzymes invertase
and maltase. The former of these converts cane and beetroot
sugar into the two simpler isomeric sugars, glucose and
fructose, by a process of hydrolysis (p. 150),
^C 6 H 12 O 6 -f-C 6 H 12 O 6
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 fermenta-
tion 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 beetroot
molasses), but also from starch, which constitutes, as a
matter of fact, by far the most important raw material for
the manufacture of alcohol. The starch is of varied
origin. In England it is derived mainly from maize, rice,
wheat and barley, and in the United States, also, maize
(corn) is largely used. In the future, cellulose, from wood-
waste, may perhaps play a role of still greater importance
(p. 150). In Germany, most of the starch is derived from
potatoes.
For the conversion of the starch into fermentable sugar,
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 347
use is chiefly made of the enzyme diastase, contained in
malt ; or, the starch can also be converted into glucose by
heating with dilute sulphuric acid. In the latter process,
the large starch molecule undergoes hydrolysis (p. 150) and
breaks up into the smaller molecules of glucose of which,
like the cellulose molecule, it is built up. It is of some
interest to note here, that the reverse process, the synthesis
or building up of the starch molecule by the condensation
of molecules of glucose, has also been effected under the
influence of enzymes.
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 allow access of air to
the grains, and sprinkled with water 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 con-
siderable 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 potafo 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 " mashing " 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. 1 By the
action of the enzyme maltase, which is contained in the yeast,
the maltose is converted into glucose ; and this, in turn, is
1 The necessity for using pure culture yeasts belonging to definite races is
now recognised . The result of the fermentation varies with different yeasts .
348 CHEMISTRY IN THE SERVICE OF MAN
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. 150), with dilute sulphuric acid, or
on cane sugar and beetroot 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
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 fermenta-
tion," and is the process which is mostly used in England.
On the other hand, when the temperature is kept low, say about
6 C. or 43 F., 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 proceed
indefinitely, and when the liquid contains from 10 to 18 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 (or furfuraldehyde) and fusel oil
a mixture of higher-boiling alcohols, such as butyl alcohol,
C 4 H 9 -QH, and amyl alcohol, C 5 H n -OH, and other sub-
stances. From these different substances the ethyl alcohol
is separated by distillation in special fractionating 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
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 349
stand over quicklime for some time and then distilling,
" absolute alcohol/' or pure ethyl alcohol, is obtained. 1
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,
when mixed with ether or with benzene. 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 ; 2 in the manufacture of ether, chloro-
form, acetic acid, celluloid, 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 (crude wood spirit or methyl
alcohol), and mineral naphtha, 3 the presence of which is
intended to render the liquid undrinkable. Such methylated
spirit is free from the excise duty ordinarily placed on
alcohol. For industrial purposes, special industrial methy-
lated spirit can also be obtained which consists of alcohol
denatured with wood-naphtha only or with other denaturants
suitable for particular industries.
1 For the purposes of taxation in Great Britain the strength or con-
centration of a spirit is generally expressed in terms of " proof " spirit.
Proof spirit is a mixture containing 49-24 per cent, by weight, or 57-1
per cent, by volume, of alcohol. Weaker spirits are said to be so much
" under proof " according to the percentage 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 diluted with
water to proof strength. If 100 volumes of an over-proof spirit would
yield 1 50 volumes of proof spirit, it is said to be 50 over proof.
2 For many technical purposes the place of ethyl alcohol is being taken
by the cheaper isopropyl alcohol (CHa'CH-OH-CHa), which is prepared
synthetically by passing acetone vapour and hydrogen over a heated
nickel catalyst, or by the action of dilute sulphuric acid, in presence of a
catalyst, on propylene obtained by the cracking of mineral oils (p. 95).
3 In the United States, alcotate, a mineral oil product, is used, and in
Germany, methyl alcohol and pyridine bases, derived from coal-tar.
350 CHEMISTRY IN THE SERVICE OF MAN
In the process already described, starch is converted into
fermentable sugars by means of diastase or by heating with
dilute sulphuric acid. About the beginning of this century,
however, another process, the so-called " amylo" process, was
introduced for the saccharification of starch, and this process
has now developed into an industry of considerable magnitude.
Many moulds produce the enzyme diastase and possess,
therefore, the power of converting starch into fermentable
sugar. This fact has been made use of in the East from very
early times, Chinese yeast, which has been largely used for
this purpose, containing the mould Mucor rouxii. Mixed
with various materials, it is sold under the name of " migen "
or " men." In the modern process, which has been carried
out chiefly in France, and to a less extent in Spain, Italy
and the United States, the moulds employed are Rhizopus
Delemar and Mucor Boulard.
Maize, rice, potatoes, or other starchy material is reduced
to a state of fine division and then steeped for a short time
in water ; after this, it is heated by means of steam so as
to render the starch gelatinous. The liquid (" mash ") is
transferred to the fermenting vessel and after it has cooled
down, spores of the mould are added. Growth takes place
rapidly, and in twelve or fifteen hours the mass is penetrated
by the mycelium of the mould. A few hours after the intro-
duction of the mould, when, therefore, a certain amount of
sugar has been formed, yeast is added ; the processes of
saccharification and of fermentation then go on side by side.
Less fusel oil is produced in this process and the yield of
alcohol is higher than when the fermentation is carried out
in the ordinary way.
Although ethyl alcohol is produced mainly by the fer-
mentation process, large quantities are also produced in
Switzerland from acetylene (p. 356), and it can readily be
manufactured, also, from the hydrocarbon ethylene, enor-
mous quantities of which are available in natural gas and
the gas from the cracking of mineral oils.
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 351
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 vary 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,
FIG. 29. APPARATUS USED FOR 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.
is employed, and the wash is distilled from a simple pot-still
similar to that shown in Fig. 29. The result, therefore, is not
merely a mixture of pure alcohol and water, 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 alde-
hydes become converted into acids which 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 re-
distilling with juniper berries, coriander, fennel, or other
352 CHEMISTRY IN THE SERVICE OF MAN
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 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, colour-
ing 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
press has not yet ceased to be practised. The juice ex-
tracted from the grape is called " must/' and by its fermen-
tation, alcohol is produced. After the first " active fer-
mentation " 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. 355). In
the casks, 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
hydrogen tartrate, 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
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 353
and allowed to ripen for perhaps two or three years. During
this process, the tannin and some other impurities are pre-
cipitated, 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. 1 This dextrin is retained in order to
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 sub-
stances 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 fer-
mented with yeast. When the active fermentation has sub-
sided, the new beer is run into casks and slow fermentation
allowed to continue, the froth which is formed being allowed
to pass out through the bung-hole. At the conclusion of the
process, the beer is drawn off into casks or bottles.
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
1 Dextrin is also produced industrially by heating starch with dilute
sulphuric acid. It is used as an adhesive on stamps, envelopes, etc. It
constitutes the so-called " British gum."
M
354 CHEMISTRY IN THE SERVICE OF MAN
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 (C 3 H 7 -OH), butyl and
iso-butyl alcohol (C 4 H 9 -OH), and amyl and iso-amyl alcohol
(C 5 H n 'OH). These alcohols find their use not 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 pineapples ; 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.
The introduction and increasing use of nitro-cellulose
lacquers (p. 149), and the need for special, solvents and
plasticisers, have led to a demand for butyl and amyl alcohols
which is greater than can be satisfied by fusel oil. Chemists,
therefore, have been called upon to develop processes for
the large-scale manufacture of these alcohols and of esters
derived from them. At the present day, butyl alcohol (or
butanol) is produced industrially from a mixture of carbon
monoxide and hydrogen (p. 194), from acetylene and by
the fermentation of starch (from maize, for example), by
means of special bacterial cultures introduced by Professor
FERNBACH, of the Pasteur Institute. In this process there are
produced butyl alcohol (about 60 per cent.), acetone (about
30 per cent.), and ethyl alcohol (about 10 per cent.), as well
as large quantities of carbon dioxide and hydrogen. The
carbon dioxide is liquefied and then converted into carbon
dioxide snow (p. 50), while the hydrogen is used for the
production of ammonia (p. 207). From butyl alcohol there
are produced various compounds, e.g. the solvent, butyl
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 355
acetate, and the plasticiser, butyl phthalate (from butyl
alcohol and phthalic acid). Acetone, also, is a valuable
solvent and is used in the manufacture of cordite, etc. Amyl
alcohol is now produced industrially from the hydrocarbon
pentane, C 5 H 12 , large quantities of which are present in
natural gas.
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 fungi 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 England, 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 10 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 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 off from the bottom of the vat and
passed repeatedly over the same shavings or basket work,
until conversion of the alcohol tp acid is nearly complete.
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
356 CHEMISTRY IN THE SERVICE OF MAN
acid in water, it receives its special flavour and quality from
the presence of small quantities of other substances 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, as we have seen, by the distillation of wood.
The pure acid forms ice-like crystals, which melt at 17 C.
(62-6 F.), and is spoken of as glacial acetic acid.
Since, owing to the synthetic production of methanol
from carbon monoxide and hydrogen, the wood distillation
industry has greatly diminished, other methods have come
into prominence for the production of acetic acid. When
acetylene is passed into a dilute sulphuric acid solution
containing mercuric sulphate, which acts as a catalyst,
the acetylene combines with water to form a compound
known as acetaldehyde (CH 3 -CHO). Acetaldehyde is also
produced industrially by passing the vapour of ethyl alcohol
over heated silver-gauze. Under the catalytic action of the
silver, hydrogen is removed from the ethyl alcohol and
acetaldehyde is formed. By passing air or oxygen into liquid
acetaldehyde to which solid manganese acetate has been
added, oxidation of the aldehyde to acetic acid (CH 3 -COOH)
readily takes place. By acting on acetaldehyde with hydrogen
in presence of nickel, as catalyst, the aldehyde is reduced to
ethyl alcohol, CH 3 -CH 2 -OH.
At a low temperature, in presence of acids, acetaldehyde
undergoes polymerisation and forms a white solid, known
as metaldehyde. This is used as a " solid fuel/' in place of
methylated spirit, under the name " Meta."
, The solvent acetone, to which repeated reference has been
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 357
made, is produced not only by the fermentation process
already described, but also by passing the vapour of acetic
acid, at a temperature of about 400 C. (752 F.), over a
catalyst, e.g. oxide of thorium or of manganese. It is also
produced by passing ethyl alcohol and steam over a suitable
catalyst ; by passing the vapour of isopropyl alcohol (p. 349,
footnote) over a copper catalyst at 500 C. ; or by passing a
mixture of acetylene and steam over a heated zinc oxide-iron
catalyst. These processes afford further illustration of the
importance of catalysis, on which emphasis has already been
laid.
When rennet is added to milk, the enzyme rennin, which
it contains, brings about a curdling of the milk by causing
a decomposition of the casein present in the milk into para-
casein, 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 production of
casein, but also as the first step in the manufacture of cheese.
In making cheese, a " starter," or culture of bacteria capable
of producing lactic acid from milk-sugar is added to milk
at a controlled temperature, and rennet is then added. By
careful control of the temperature and of the acidity, which
increases gradually owing to the production of lactic acid,
casein separates out as a curd, from which, later, whey is
expelled. After allowing the curd to remain for some time
in order to mature, it is ground, salted and pressed in a
cheese-niould. 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 decom-
position products gives the characteristic flavour to the
cheese. The different kinds of cheese vary considerably in
composition, but contain about 24 to 40 per cent, of water,
358 CHEMISTRY IN THE SERVICE OF MAN
23 to 39 per cent, of fat, 27 to 33 per cent, of casein and other
nitrogenous compounds, and 3 to 7 per cent, of salts.
In the industrial production -of casein, skimmed milk is
used, and the milk may be curdled by means of rennet, as
already described, or by the addition of hydrochloric acid
with careful control of the acidity. This acid-produced
casein has a different composition and different physical
properties from that obtained with rennet. It is largely 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 slaked lime, to which mineral
colouring matters are added).
Reference has already been made to the production of
rayon and to the use of de-lustred rayon as a textile fibre of
a wool-like appearance (p. 146). In 1935, another wool
substitute or wool-like fibre, the invention of an Italian
chemist, ANTONIO FERRETTI, of Milan, was placed on the
market by the firm Snia Viscosa. This material, known as
lanital, is made from casein and, in its molecular structure
that of a protein approaches much more closely to wool
than rayon does to silk.
Casein, made into a paste, is squirted through fine per-
forations in a steel disc, and the filaments so formed are
coagulated in sulphuric acid. After drying, the filaments
are treated with formaldehyde and a suitable plasticiser,
whereby they are hardened, rendered more elastic and more
resistant to water. By treatment with chlorine, the wool-
like appearance of the lanital is accentuated. In its strength,
lanital is somewhat inferior to wool, but great improvements
have recently taken place and a material, not greatly inferior
to wool in strength, has been obtained. Casein fibres of a
superior quality are produced in America and marketed
under the name aralac. Lanital and aralac are generally
used in admixture with wool or cotton. They are non-
creasing and do not shrink.
In 1945, the production in Great Britain of a wool-like
THE ACTION OF ENZYMES AND MICRO-ORGANISMS 359
synthetic fibre, the invention of the chemists of Imperial
Chemical Industries at Ardeer, was announced. It has been
given the name ardil and is produced from the protein of
ground-nuts or pea-nuts. An alkaline solution of the protein
is extruded through spinnerets into a bath of sodium sul-
phate and sulphuric acid, the filaments stretched in order to
increase their tensile strength and hardened in a solution
of sodium chloride to which a small quantity of hydro-
chloric acid and of formaldehyde has been added.
When the fermentation of sugar solutions is brought
about by means of yeast, ethyl alcohol, as we have learned,
is formed as chief product. As far back as 1858, however,
Pasteur had shown that appreciable amounts of glycerine
are also produced, about three parts of glycerine being
formed from one hundred parts of sugar. Since glycerine
is a valuable substance, attempts began to be made to increase
the proportion of glycerine by altering the conditions under
which the yeast acted, and it was found that by making the
fermenting liquid slightly alkaline by the addition of sodium
sulphite or of sodium carbonate, the yield of glycerine could
be increased up to nearly 40 per cent, of the sugar used.
During the Great War of 1914-1918, this fermentation
method for the production of glycerine was extensively
employed in Germany, where, owing to the scarcity of fats,
a dearth of glycerine, used for explosives, was threatened.
By the fermentation process as much as 1,000,000 kilograms
of glycerine a month are stated to have been produced. The
cost of production, however, is higher than by the saponifica-
tion of fats (p. 236).
During the past quarter of a century, the attention of
chemists has been turned to the utilisation of the many
thousands of tons of yeast which are produced annually in
excess of that required in the fermentation industries.
During the process of fermentation, the yeast grows and
multiplies with very great rapidity, and builds up its proto-
360 CHEMISTRY IN THE SERVICE OF MAN
plasmic cell contents from the organic and inorganic materials
present in the fermenting liquid. Since the yeast contains
large quantities of proteins and carbohydrates in addition
to small amounts of fat and mineral matter, dried yeast has
been used to a considerable extent as a food for cattle ; and
from it also has been prepared, for human consumption, an
extract (marmite), similar to extract of meat. This yeast
extract is, indeed, claimed to be superior in its nourishing
qualities to extract of meat by reason of the presence of the
accessory food substances, the so-called vitamins.
The rapid growth and synthesising power of other micro-
organisms have also been utilised, or their utilisation has
been suggested, for the production of feeding stuffs. Thus,
" mineral yeast/' a form of Torula, can produce both pro-
teins and fat when grown on a medium containing sugars
and ammonium salts ; and the organism, Endomyces vernalis,
can build up a material containing 18 per cent, of fat, 31 per
cent, of proteins, and 43 per cent, of carbohydrates. These
sources of proteins and fats may be of great importance in
tropical countries where carbohydrates are plentiful but
proteins are scarce.
CHAPTER XVIII
VITAMINS AND HORMONES
THE fundamental problem of organic chemistry, according
to the French chemist, MARCELIN BERTHELOT, was the
investigation of the compounds occurring in plants and
animals and the proof " beyond all question that com-
pounds identical with those produced by plants and animals
can be synthesised from inorganic or mineral matter." This,
no doubt, is somewhat too narrow a view to take of the aims
and objects of organic chemistry, but the interest of such
investigations made a powerful appeal to some of the fore-
most organic chemists in the second half of the nineteenth
century, and led to the elucidation of the constitution and, in
some cases, to the synthesis of sugars, essential oils, proteins
and other products of the animal or plant organism. During
the present century, interest in the compounds produced in
plants and animals has been revived, and through the in-
vestigations of such substances there has been built up the
important and rapidly growing branch of science known as
bio-chemistry. One of the most notable features of this
development has been the close co-operation which has been
established between the organic chemist and the physiologist
in the investigation of the processes of human nutrition and
of the factors involved in the maintenance of health. It is
possible to consider here only a few of the more important
discoveries which have resulted from this co-operation.
In these days when so much interest is being taken in the
health of the people and in the attainment of physical fitness,
it can be no matter for surprise it is, in fact, most desirable
that, especially in days of food scarcity, the subject of
nutrition should arouse the widespread interest not only of
those responsible for government and administration but also
361
362 CHEMISTRY IN THE SERVICE OF MAN
of the people as a whole ; for health depends on adequate
and proper nourishment, and without good health there can
be no physical fitness.
Until early in this century, the problem of nutrition
seemed to be a comparatively simple one and to find its
solution in the supply to each individual of a sufficient
amount of the proteins, fats and carbohydrates, together
with salts and water, necessary to build up the tissues of the
growing body, to repair waste, and to supply the energy
necessary for the maintenance of the body temperature and
the performance of mechanical work. It was the fear that
the supply of food might become inadequate in amount that
oppressed Sir William Crookes in 1898 (p. 202), and it was
the prospect of famine that stimulated the increased pro-
duction and use of fertilisers. That fear has, to a great
extent, been removed and the problem of producing an
ample supply of food to feed the world's starving millions has
been solved. At the present day, interest is centred not so
much in the quantity of food as in the quality ; not in the
amount but in the kind. A sufficiency of proteins, fats and
carbohydrates is, of course, still essential, but the danger to
health comes, except in times of special crisis, not so much
from under feeding, although that is not everywhere absent,
as from wrong feeding.
Before the recent discoveries in the science of nutrition
had been made, food was thought of mainly as a fuel, and
the adequacy of a diet was decided largely on the basis of its
fuel value, the amount of energy or the number of calories
(p. 80) to which it could give rise by its combustion in the
body. In the absence of fuller and more exact knowledge,
one had to be content, more or less, with this view, although
its inadequacy had been demonstrated by medical experience.
It had long been known, for example, that one of the most
distressing and fatal diseases to which sailors absent from
home on long voyages were subject, was scurvy, a disease
affecting not only the skin but the whole system, and which,
VITAMINS AND HORM6NES ' 363
if not checked, must end fatally. Even on land, thousands
have died of this disease and, during the Great War of
1914-1918, it attacked the Indian soldiers in Mesopotamia
(Iraq). And yet, early in the eighteenth century, it had been
shown that this disease could be cured by the administration
of lemon or orange juice. 1 No drugs, in the ordinary sense,
were necessary ; only a slight alteration of the diet. Many
found it difficult to believe that such a dreadful disease could
be cured by such easy means. In a similar manner it gradually
came to be realised that other diseases, e.g. beri-beri and
rickets, could be cured by dietary measures. In other words,
it came to be realised that these diseases are due not to the
presence of toxins or other harmful substances in the diet
or produced in the body, but to the absence of certain
essential substances from the diet.
It was, more especially, by the work of Sir F. GOWLAND
HOPKINS, at Cambridge, in 1906, and, later, of Professor
McCoLLUM and Miss MARGUERITE DAVIS, in America, that
definite proof was obtained that health cannot be maintained
on a diet of protein, fat, carbohydrate and salts only, but
that small quantities, sometimes very minute quantities, of
other substances, which were given the general name of
vitamins, are necessary. By the application of this new know-
ledge, results, sometimes of a spectacular character, have
been obtained in the prevention and cure of a number of
diseases, the cause of which had long been obscure. It has
also come to be realised that there may be a wide gap between
perfect health and obvious disease ; and that, even when
there is no obvious disease, improvement of health, vigour
and enjoyment of life may be brought about by an increase
of the vitamins in the diet. It is now realised that minor
ailments, carious teeth, slight rickets, gastric disturbances,
etc., may be the result of mistakes in feeding and lack of
vitamins. For this reason, greater attention is now also being
1 Even in the seventeenth century, lemons and oranges were used for
the cure of scurvy among the crews on the ships of the East India Compare*
\\
364 CHEMISTRY IN THE SERVICE OF MAN
given to improving the quality or vitamin content of foodstuffs,
a matter which is of especial importance in these days of a more
sophisticated civilisation, when so much of our food is " pro-
cessed " and thereby sometimes rendered deficient in vitamins.
The discovery of the existence and importance of vitamins
initiated a search for and an investigation into the sources
and nature of these " accessory food factors/' as they were
first called ; and this investigation has been and is being
carried out with great energy and success. Already some
fifteen vitamins have been distinguished, and their number
is continually being increased. Moreover, not only have the
physiological effects of these vitamins been investigated,
but their chemical composition and constitution have been
the subject of intensive study ; and so successful has this
been that a number of these vitamins can now be produced,
and are being produced, synthetically, on an industrial scale.
Through the extraction from natural sources and standard-
isation of the potency of vitamins, as well as through their
chemical synthesis in the laboratory or factory, it is now
possible to enrich foods, when so desired, with vitamins in
definite and controlled amount.
Ignorance of the nature and chemical individuality of the
vitamins, when first discovered, led to their being designated
by the letters of the alphabet, and this nomenclature is still
to some extent retained. Some of the vitamins, however,
originally thought to be single, have been shown to be
mixtures of several vitamins, which have to be distinguished
by numerals, e.g. vitamin B 1? vitamin B 2 , etc.
Vitamin A. This vitamin is of importance in promoting
growth in children. It also improves the health of the skin
and of the mucous membranes of the respiratory passages,
and for this reason it gives increased resistance to bacterial
infection. When this vitamin is absent from the diet for
prolonged periods, night blindness, or inability to see in a
dim light, and later, xerophthalmia, an infective condition of
the eyes, supervene.
VITAMINS AND HORMONES 365
Chemical investigation has shown that the forerunner
of vitamin A is a hydrocarbon, carotene, which has a large
and complex molecule and a composition represented by
the formula C 40 H 66 . This compound is found widely dis-
tributed in the vegetable kingdom : in tomatoes, apricots,
bananas ; in carrots, spinach, lettuce and grass, and in various
marine algae. Carotene, when taken into the animal organism,
is decomposed by water (hydrolysed) with production of
vitamin A, a compound which has been shown by chemists
to have its molecule built up as indicated by the formula :
CH 3 CH 8
\/
/\ CH 2 CH 8
H 8 C C-CH-CH-C-CH-CH-CH-C-CH-CH 2 OH.
I II
H 2 C C-CH 3
CH a
It is formed by the splitting of the carotene molecule into
two parts and the combination of each part with two atoms
of hydrogen and one atom of oxygen.
Man may obtain the necessary supply of vitamin A either
from the carotene present in various vegetable foodstuffs or,
ready formed, from foodstuffs, e.g. milk, butter, eggs, etc.,
derived from animals which have formed it from the carotene
in their food. Any excess of the vitamin above that needed
to satisfy immediate requirements is stored in the liver. A
well-nourished person, therefore, possesses a certain reserve
of vitamin A on which he can draw during periods (e.g.
winter months), when fresh supplies of carotene or of ready-
formed vitamin may not be so readily available. By far the
richest natural sources of vitamin A are fish-liver oils,
especially halibut-liver oil. This vitamin has been formed
from the carotene present in the green marine algae and has
been stored up in the liver of the fish. From these fish-liver
oils the vitamin is now extracted and placed on the market
in a standardised and highly concentrated form, so that it h
366 CHEMISTRY IN THE SERVICE OF MAN
now very easy to make good any deficiency of this vitamin
in the diet. In Great Britain it is now always added to
margarine. Although the chemical constitution of carotene
has been elucidated and its synthesis effected in the laboratory,
the compound has not so far been produced industrially.
Vitamin A is necessary to regenerate visual purple, the light
sensitive substance in the retina, and it has been found that
daily doses of carotene refieve eye-strain, reduce fatigue and
increase the efficiency of workers engaged in matching colours.
Vitamin B. Deficiency of this vitamin leads to the
dangerous neuritic disease known as beri-beri. This disease
was particularly prevalent among Eastern peoples whose
food consisted mainly of fish and rice. The vitamin is present
in the germ or embryo of the rice and so long as the natural
rice was used, beri-beri did not occur. When, however,
polished rice, from which the germ has been removed,
replaced the natural grain, the disease became rampant, and
in the eighties of last century sailors of the Japanese Navy
suffered greatly until the diet of meat and polished rice was
supplemented by whole barley, in which vitamin E l is
present. Foodstuffs which are rich in vitamin E l are yeast,
wheat germ, egg yolk, lentils and ox liver. Since the vitamin
is not stored in the body, adequate amounts of it must be
supplied in the daily diet.
The composition and molecular structure of vitamin E
have been ascertained by chemists ; and the compound,
C 12 H 17 C1N 4 OS.HC1, to which the name aneurine (in
America, thiamine) has been given, is now produced synthetic-
ally on an industrial scale. How complex is this structure
which chemists have succeeded in building up will be under-
stood from the formula :
= C-NH 2 -HC1 9 H 3
I
-C C -
CH 2 - N
II II // %H-
N CH Cl ^
VITAMINS AND HORMONES 367
Vitamin jB 2 , which is present in yeast, egg-white, tomatoes
and other foods, has been shown to be a complex of a number
of different vitamins. One of the'se is a growth-promoting
vitamin, and another is effective in preventing the disease
called pellagra. The former constituent has been shown
to be identical with the yellow pigment riboflavin, obtained
from whey, and has the composition represented by the
formula C 17 H 20 N 4 O 6 . The riboflavin content of milk is
rapidly reduced by exposure to sunlight. The latter con-
stituent was found to be identical with nicotinic acid, a
compound which had been known to chemists long before
its vitamin activity was recognised in the B 2 complex.
Vitamin C. This is the antiscorbutic vitamin ; the
vitamin which is effective in preventing scurvy. This vitamin,
which was known to be present in fresh green vegetables and
in citrus fruits, 1 was, in 1932, isolated in a pure crystalline
state and in relatively large amount from Hungarian red
pepper (paprika), and in the following year its constitution
was ascertained and its synthesis effected. This compound,
identical with vitamin C, is known as ascorbic acid, and has
the constitution
CH,OH - CH(OH) - CH CO
\ /
C = C
OH OH
Ascorbic acid (vitamin C) is now produced industrially
from glucose. It is optically active and rotates the plane of
polarised light to the right. The laevo-rotatory acid can also
be prepared, and this is found to have no anti-scorbutic
effect. This is a further example of the difference in be-
haviour of two optically active isomers towards the molecu-
larly asymmetric living tissues to which reference has already
been made (pp. 306, 323).
1 Zakatalsk nuts, grown in Russia, are said to have a vitamin C content
about forty times that of lemons or oranges.
368 CHEMISTRY IN THE SERVICE OF MAN
Ascorbic acid, now an article of manufacture and so
made readily available to all, may suitably be added to jams
and other preserves.
Vitamin D. Rickets, which is generally associated with
an imperfect calcification of the bones and teeth, is brought
about not only through the absence of the necessary calcium
salts and phosphates but also through absence or deficiency
of vitamin D, a term now used to denote a group of different
substances which have anti-rachitic properties. Even when
the necessary salts are present, this vitamin is required for
their proper utilisation. Although the obvious signs of
rickets curvature of bones, knock knees, etc. may be
absent, radiological examination may reveal the presence
of this disease in apparently healthy children. In adults,
also, deficiency of vitamin D may be the cause of the
imperfect utilisation of calcium and phosphorus salts which
may finally manifest itself in osteomalacia (a softening of
the bones).
The most effective natural source of vitamin D is cod-
liver oil or halibut-liver oil. The vitamin is present, also, in
milk, butter and eggs, but in winter the amount may be
small and may have to be supplemented by doses of cod-
or halibut-liver oil, or of the pure vitamin.
In 1919 it was discovered that rickets was associated with
absence of sunlight and could be cured, or alleviated, by
exposure to sunlight or to the light of short wave length
(ultraviolet light) emitted by a mercury vapour lamp. Later,
in 1924, it was found that foods could be rendered anti-
rachitically active by irradiation with ultraviolet light. The
explanation of this action of sunlight or of ultraviolet light,
whether emitted by the sun or by a mercury vapour lamp,
was obtained when, in 1927, it was found that a substance,
ergosterol, which is present in plants (e.g. ergot), yeast, etc.,
is converted by the light into a compound which is anti-
rachitically active. This compound was isolated in the
crystalline state in 1932 and was called calciferol. It was, at
VITAMINS AND HORMONES 369
first, thought to be identical with the vitamin D from cod-
liver oil, but this is not the case. Calciferol, sometimes
referred to as vitamin D 2 , is not so anti-rachitically potent
as the natural vitamin, referred to as D 3 , present in cod-liver
oil or formed by the action of the sun's rays or of ultraviolet
light on the cholesterol (dehydrocholesterol) present in the
fat glands of the skin of animals. This natural vitamin appears
to be formed on the surface of the skin and is then absorbed
by the body. This fact suggests that the anti-rachitic
benefits of sun-bathing may be destroyed by subsequent
bathing in water, unless sufficient time is given for the D 3 to
be absorbed by the body.
Pure calciferol is now an article of commerce and can be
used, when necessary, to supplement the natural supply of
vitamin D in the daily diet. Addition of calciferol is now
usually made to margarine.
Besides those just discussed, other vitamins are known
pyridoxin (B 6 ), biotin (H), tocopherol (E), etc. and the
synthetic production of some of them has already been
worked out.
HORMONES
Besides the vitamins which, as we have seen, are essential
for the proper nutrition of the body and the prevention of
certain diseases, other substances are required if health is
to be maintained and if the various metabolic changes in the
body are to take place in a normal and satisfactory manner.
These substances, unlike the vitamins, are produced by the
living animal cells in the ductless or endocrine glands, and
are passed directly into the blood stream. Deficiency or
excess of these substances brings about physiological abnor-
malities or disease. The purpose of these glandular secre-
tions is to excite or arouse certain responses or reactions and,
for this reason, they are called hormones. 1 They are,
however, not always stimulating or activating, they may
1 From the Greek hormad, to excite or to arouse.
370 CHEMISTRY IN THE SERVICE OF MAN
also be restraining. They are, in general, regulators of the
metabolic changes in the body.
Reference has already been made to adrenaline and its
use in bloodless surgery (p. 322). This hormone has the
composition and structure represented by the formula
(OH) 2 :C 6 H 3 -CH(OH)-CH 2 -NH'CH 3 , and is now produced
synthetically from catechol, C 6 H 4 (OH) 2 , a substance which
is formed in the dry distillation of catechu or cutch, a hard
gum secreted by certain Indian species of Acacia and used
in tanning and in calico-printing.
In the suprarenal glands, the adrenaline is probably stored
as a readily decomposable compound with a protein, and
during periods of emotional disturbance its production
increases. When adrenaline is introduced into the blood,
" it produces all the vascular and visceral reactions which
accompany the emotions of danger, excitement and fright.
The hair stands on end, the face becomes pale, the heart
thumps urgently on the chest wall, the arterial blood pressure
rises rapidly, the muscular coat of the bronchioles relaxes and
leaves the airway clear for vigorous breathing, and glucose,
the fuel of the muscular machine, is poured from the carbo-
hydrate depot of the liver into the blood stream." The
presence, however, of minute quantities of this hormone
in the blood is necessary for the maintenance of a healthy
tone.
Thyroxine. This is the active principle of the hormone,
thyroglobulin, formed in the thyroid gland. The hormone
.is needed in order to maintain the " basal metabolic rate,"
or the rate of heat production through oxidation in the body
at rest, at its most advantageous value. If the thyroid secre-
tion is absent or deficient in amount in infancy, cretinism,
or a halt in the mental and physical development, occurs ;
and in adults there is a slowing down of the life processes,
accumulation of fat, and a mental dullness and sluggishness.
These are the symptoms of the disease known as myxcedema.
VITAMINS AND HORMONES 371
tion of extract of the thyroid gland. If there is hypertrophy
of the thyroid gland, leading to an excessive production of
the hormone, the consumption of oxygen is unduly acceler-
ated, the life processes take place too rapidly, and the restless-
ness and nervous debility characteristic of Graves' disease,
supervene.
In 1915 the active principle of the thyroid gland hormone
was isolated in a crystalline form and called thyroxine ; and
in 1926 its constitution was determined and its synthesis
effected. Thyroxine was thus shown to be a compound
containing iodine and to have the formula,
CH a -CH (NH,)-COOH.
This compound is now synthesised industrially at a cost
lower than that of the substance extracted from the thyroid
gland, and can be used in place of the extract in the treat-
ment of cretinism and myxcedema. The naturally-occurring
thyroxine is laevo-rotatory, while the synthetic product is,
of course, inactive (racemic). This product, however, can
be resolved into two oppositely active isomers dextro-
rotatory and laevo-rotatory thyroxine. The laevo-rotatory
form is three times more active physiologically than the
artificially produced dextro-rotatory isomer, another ex-
ample of the difference in action of two optically active
isomers on natural tissues.
The characteristic feature of thyroxine is its content of
iodine, and this, element, in the form of iodides or other
compounds of iodine, must be taken into the body to furnish
the necessary iodine. Failure to satisfy this requirement
leads to goitre, or an enlargement of the thyroid, due to an
attempt to increase the production of thyroxine. Hence the
use of iodides in the treatment of goitre. Long ago, burnt
sponge was used, and the effectiveness of this remedy
372 CHEMISTRY IN THE SERVICE OF MAN
became intelligible when it was shown that sponges, sea-
weeds, etc., contain iodine in combination. Normally,
iodine is taken in with the food or drinking water ; and the
main sources of this element are fish, crabs, lobsters, oysters,
green peas, and beans.
Insulin. Another hormone which is essential for the
maintenance of health is insulin. This is produced in the
pancreas and its main purpose seems to be to control
the carbohydrate metabolism, or the changes which
carbohydrates (sugars and starches) undergo in the body.
A diminution in the production of insulin leads to a failure
of the body tissues to burn and to store sugar (in the form of
glycogen) in the liver. The content of sugar in the blood
increases above the normal and brings about the state
known as diabetes. Defective production of insulin by the
pancreas can be made good by the subcutaneous injection
of insulin, but excess must be avoided.
Insulin is a complex protein, the constitution of which is
not yet known. It has, however, been separated in crystalline
form, and one may therefore hope that its molecular con-
stitution will in due course be unravelled and its synthetic
production worked out. At present the active principle is
extracted from the pancreas of the ox, pig or sheep, and this
extract is used in the treatment of diabetes.
Besides the hormones just mentioned, there exist also a
number which are associated with and are indispensable
for normal and healthy sex activity, and the appearance of
the secondary sex characteristics. Chemists have been very
successful in elucidating the nature of the sex hormones,
which are related chemically to the compounds cholesterol
and ergosterol already mentioned. Not only have some of
these hormones been synthesised, but chemists have also
prepared substitutes, which are now produced industrially.
These synthetic compounds can be successfully used
clinically in place of the natural hormones to which, indeed,
for many purposes, they are to be preferred.
VITAMINS AND HORMONES 373
From the discussion of the phenomena of catalysis
(Chap, ix) one could not fail to realise the importance of
minute quantities of certain substances in influencing the rate
of chemical change ; and in the vitamins and hormones we
meet with substances which seem to exercise some sort of
catalytic effect in regulating the various chemical processes
which go on in the living plant or animal organism. The
presence of these substances, even though their amount
may be extremely small, is of vital importance for health.
The study of how even minute amounts of certain substances
may completely change the state of health of man or of the
animals is clearly one which exercises a peculiar fascination ;
and just as it became known, through the investigations of
chemists, that certain small amounts of iodine (in a com-
bined state) must be present in the food in order that the
secretion of the thyroid gland may be effective, so, in recent
years, it has been found that traces of a number of other
elements are essential for the health of man or of the animals.
Reference has already been made to the importance of trace
elements for the health of plants (p. 211).
That iron, which is a constituent of haemoglobin, is
essential for health has long been known, but it is only in
recent years that it has become known that the presence of
minute quantities of copper is necessary for the efficient
transference of the iron into the haemoglobin, and many
cases of pernicious anaemia are due to a deficiency of copper.
The daily intake of copper for an adult should be about
4-5 milligrams, and if this is not supplied in the food,
health is impaired. In many cases, severe wastage diseases
among animals have been cured by the addition of small
quantities of copper salts to the diet.
Small quantities of manganese salts are necessary for the
proper development of the foetus, and deficiency of cobalt
has been found to be the cause of "bush sickness " in sheep
and cattle. It may be cured by adding cobalt salts to the
soil (whence it passes into the pasture) or to the salt licks.
374 CHEMISTRY IN THE SERVICE OF MAN
As little as i milligram of cobalt per day is sufficient to
secure health. It may be noted, also, that trace elements,
especially zinc and manganese, are intimately connected with
the proper utilisation of vitamins by the body and are
generally associated with the natural vitamins. They are,
of course, not present in the synthetic vitamins.
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
Accumulator, lead, 259
nickel-cadmium, 261
nickel-iron, 261
Acetaldehyde, 356
Acetanilide, 325
Acetate, amyl, 354
butyl, 355
cellulose, 146
Acetone, 115, 123, 354, 35^
production of, 357
Acetylene, 91, 113
and ripening of fruit, 1 15
from methane, 113
ACHESON, 269, 286
Acid, acetic, 123, 355, 356
from acetylene, 356
glacial, 356
acetyl salicylic, 325
adipic, 337
ascorbic, 367
carbolic, 313
hydrochloric, 6, 233
hydrocyanic, 105
muriatic, 232
nicotinic, 367
nitric, 6, 205
from ammonia, 212
oleic, 85
palmitic, 85
paratartaric, 299
picric, 134
prussic, 105
pyroligneous, 123
pyrosulphuric, 319
racemic, 299
salicylic, 325
stearic, 85
sulphuric, 6, 184
contact process, 1 87
eradication of weeds by, 1 85
fuming, 187
manufacture of, 186
tartaric, 299
Acids, 253, 255
ionisation of, 255
Activity, optical, 296
Activity, optical and vitalism, 307
production of, 309
Adrenaline, 322, 370
Adsorption, 279
^Ether, 4
Affinity, chemical, 173
Agent, catalytic, 178
Agriculture, chemistry and, 195
colloids in, 282
Agroxone, 185
Air, composition of atmospheric, 46
constancy of, 51
liquefaction of, 58
liquid, 58
pollution of, 83
ALBERTUS MAGNUS, 6, 173
Alchemists, 5
Alchemy, 5
Alcohol, 345
absolute, 349
amyl, 348, 354, 355
butyl, 115, 194, 354
ethyl, 345, 356
from acetylene, 350, 356
from cellulose, 151
from ethylene, 350
iso-amyl, 354
iso-butyl, 354
iso-propyl, 349
manufacture of, 345
methyl, 123, 193
motor fuel, 99
production of, 345
Propyl, 354
solidified, 286
uses of, 349
vinyl, 337
Alcotate, 349
Alizarin, 316
synthesis of, 316
Alkali, 231
Alkalies, 253, 255
ionisation of, 255
Alkathene, 336
Alloprene, 342
Allotropic forms, 119
375
376 INDEX
Allotropic modifications, 75
Alloy, pyrophoric, 78
Alloys, 152
non-ferrous, 162
Almonds, oil of bitter, 331
imitation, 331
Alpha particle, nature of, 31
Aluminium, 265
alloys, 266
bronze, 266
combustion of, 69
silicate, 247
Alundum, 269
Amatol, 135
Ambergris, 331
Ambrein, 331
Americium, 45
Amethocaine, 322
Amethyst, 218
Ammonal, 73
Ammonia, catalytic oxidation of , 2 1 3
combustion of, 213
from coal, 102
oxidation of, 213
synthetic production of, 207
uses of, 212
Ammonia-soda process, 231
Ammonium nitrate, 73, 135, 213
phosphate, 202
sulphate, 210
as fertiliser, 204
thiocyanate, 105
Amylo-process, 350
Anaesthetics, 321
Analysis, positive ray, 36
Aneurine, 366
Anhydrite, 189
Anions, 256
Anisic aldehyde, 331
Anode, 256
mud, 262
Anthracene, 314, 316
Anthracite, calorific value of, 79
Anthraquinone, 316
synthesis of, 317
Antifebrin, 325
Antiseptics, 323
Anti-knock value, 96
Antipyretics, 325
Aqua fortis, 7
regia, 7, 155
Aralac, 358
Architecture, molecular, 290
Ardil, 359
Argol, 352
Argon, 53
discovery of, 52
ARISTOTLE, 4
ARRHENIUS, 254
Arsemous sulphide, colloidal, 278
Aspirin, 325
ASTON, 36
Asymmetry, molecular, 302
Atebrin, 326
Atmosphere, composition of the, 46
gases of the, 46
rare gases of the, 5 1
Atom, definition of, 15
electronic constitution of, 27
structure of, 32
Atomic number, 34
theory, 13
weights, 17
Atoms, early views regarding, n
AVOGADRO, 15
theorem of, 32
Azote, 47
Babbitt metals, 167
BACON, Francis, 20
BACON, Roger, 6, 127
BAEKELAND, 334
Bakelite, 334
Baking powders, 232
BALY, 117
Barilla, 231
Bath salts, 232
BECQUEREL, 27
Beers, 353
Beetle ware, 335
Bell metal, 164
Benzaldehyde, 331
Benzene (benzole), 97, 312
formula of, 295
hexachloride, 329
Benzine (benzolme), 92
BERGIUS, 97
BERZELIUS, 16, 178
Bessemer process, 159
BEVAN, 145
Beverages, alcoholic, 351
Bio-chemistry, 361
Biotin, 369
BlRKELAND, 205
Biscuit ware, 247
Bisque, 247
Black lead, 369
INDEX
377
Blast furnace, 157
Blasting gelatin, 132
Bleaching powder, 233
Blowpipe, no
oxy-acetylene, 115
oxy-coal-gas, no
oxy- hydrogen, no
Bluestone, 165
Boiler scale, 240
Bomb, atomic, 45
Bombs, incendiary, 73
Bordeaux mixture, 165
Boron and health of plants, 212
in soil, 212
Bort, 1 20
BOYLE, 4, 9
Brandy, 352
Brass, 163
season cracking of, 164
Briquet phosphonque, 74
Brisance, 131
Britannia metal, 167
Bronze, 167
coinage, 164
Bronzes, 164
BROWN, CRUM, 308
BROWN, Robert, 288
Brownian movement, 288
BUCHNER, 344
Buna, 341
- -N, 341
S, 341
BUNSEN, IOQ
Bunsen burner, 109
Butadiene, 341
Butane, 90, 97
Butanol, 354
Butter substitutes, 191
Butvar, 227
Butyrate, amyl, 354
ethyl, 354 '
Cairngorm, 218
Calciferol, 368
Calcite, 246
Calcium bicarbonate, 241
carbide, 113
carbonate, 244
cyanamide, 206
hydroxide, 245
nitrate, 205
oxide, 245
phosphate, 201
Calcium phosphate acid, 201
sulphate, 210
Calgon, 241
Calomel, 166
Calor gas, 97
Calorie, 80
Camphor, 331
Candles, 85
beeswax, 86
china wax, 86
paraffin, 86
snuffing of, 86
spermaceti, 86
stearin, 86
Carbides, fixation of nitrogen by,
206
Carbohydrates, 137
production of, 360
synthesis of, 117
Carboloy, 162
Carbon, allotropic forms of, 119
atom, asymmetric, 304
black, 125
chemistry of, 290
circulation of, 51, 117
dioxide, 47
and aerated water, 47
in fire extinguishers, 48
solid, 50
test for, 48
disulphide, 105
monoxide, 107, 108
flame of, 106
from methane, 194
oxidation of, 108
Carbonado, 120
Carborundum, 269
Car boxy-haemoglobin, 108
Carnallite, 200, 267
Carotene, 365
CAS ALE, 209
Casein, 357
Cassiterides, 167
Cassiterite, 166
Catalysis, 172, 178
in industry, 184
in nature, 183
negative, 180
positive, 1 80
Catalyst, 178
copper as, 179, 182
enzymes as, 184
moisture as, 179
nicotine as negative, 180
378 INDEX
Catalyst, platinum as, 180
poisoning of, 181, 188
tin as negative, 180
Catechol, 370
Catechu, 370
Cathode, 26, 256
Cation, 256
Caustic, lunar, 153
CAVENDISH, 51
Celanese, 145
Cell, dry, 259
Edison, 261
Leclanche*, 258
nickel-cadmium, 261
nickel-iron, 261
voltaic, 250
Cellon, 149
Cellophane, 147
Celluloid, 148
non-inflammable, 149
Cellulose, 137
acetate, 146
alcohol from, 151
calorific value of, 79
glucose from, 150
hydrolysis of, 150
lacquers, 149
nitrates, 128
products, 137
xylose from, 151
Cement, 190
Portland, 158, 248
Centigrade scale of temperature, 50
Cerechlor, 342
Ceria, 78, 112
catalytic action of, 113
Cerium, iron alloy, 78
oxide, 78, 112
CHADWICK, 42
Chalk, 246
CHANCEL, 73
Charcoal, 122
adsorbing power of, 123, 279
burning, 124
decolorising of liquids by, 123,
279 .
use in gas-masks, 123
de CHARDONNET, 144
Cheese, 357
Chemia, 5
Chemistry and agriculture, 195
and electricity, 249
cultural value of, 2
definition and scope of, i
Chemistry, medical, 7
organic, 290
synthetic, 310, 330
Chemotherapy, 325
CHEVREUL, 85
Chile saltpetre, 204
China, 247
Chloral, 323
Chloramine T, 323
Chlorine, 233
electrolytic production of, 262
isotopes of, 36
uses of, 264
Chloroform, 321
Chloroprene, 342
Cholesterol, 369
Chrome steel, 160
Chromium, 166
plating, 252
CHURCHILL, 45
Cinnabar, 166
CLAUDE, 209
Clay, 246
white china, 247
CLAYTON, 100
CLEMENT-DESORMES, 187
Coal, 79
calorific value of, 79
distillation of, 100, 102
hydrogenation of, 97
oil from, 97
products of distillation of, 104
utilisation of, 81
Coal-gas, 100, 104
calorific value of, 107, 108
composition of, 105
enriching of, 107
flame, luminosity of, 106
manufacture of, 104
purification of, 104
Coalite, 83
Coal-tar, 102
constituents of, 312
dyes, 314
hydrogenation of, 98
Cocaine, 322
Coffey still, 348
Coinage, bronze, 164
gold, 154
silver, 155
Coke, 83, 102
COLBURN, 221
Collodion, 131, 149
Colloidal sol, 276
INDEX
379
Colloidal state, 275
properties of, 275
Colloid particles, electrical charge
on, 280
size of, 278
gold, 278
iodine, 284
manganese, 284
silver, 284
sulphur, 284
Colloids, 275
as therapeutic agents, 284
emulsoid, 280
protective action of, 284
mutual precipitation of, 282
peptisation of, 286
precipitation of, by electrolytes,
281
suspensoid, 280
Combustion, 61
by means of combined oxygen,
72
explanation of, 62, 64, 65
in absence of oxygen, 71
in air, 68
slow, 69
in the living organism, 69
of aluminium, 69
of iron, 69
spontaneous, 71
Compounds, 9
Concentration, influence of, on
velocity of reaction, 174
Concrete, 248
Condensation, 138, 333
Conduction of electricity by
solutions, 253
Congreves, 74
Conservation of mass, law of, 64
of matter, law of, 64
Constant proportions, law of, 14
Constitution, atomic, 32
molecular, 292
Contact process, 187
Copper, 162
alloys, 163
electrolytic, 162, 262
refining of, 262
sulphate, 164
Coral, 246
Cordite, 134
Corundum, no
Cotton, 138
fibre, structure of, 138
Cotton, mercerised, 147
nitration of, 129
Coumarin, 330
COUPER, 293
Couronne de tasses, 250
Cracking of oil, 95, 98
Cream of tartar, 352
Cresols, 313
CROOKES, 26, 31, 54, 202, 204
tube, 25, 26
CROSS, 145
Crystal (glass), 228
Crystalline solid, 215
Crystallisation, velocity of, 217
Crystalloids, 275
Crystals, enantiomorphic, 302
hemihedral, 299
holohedral, 299
CURIE, Marie, 27
CURIE, Pierre, 27
Curium, 45
Current, electric, in solutions, 254
Cutch, 370
Cyclonite, 135
Cyclotron, 38, 42
DALTON, 13
DAVIS, 363
DAVY, 67, 187, 250
D.D.T., 329
Deacon's process, 233
Decalin, 313
Decolorising of liquids by charcoal
123
Deduction, 20
Deltas, formation of, 281
DEMOCRITUS, 12
Detergents, 239
Deuterium, 37
oxide, 37
Deuterons, 42
Devitrification, 218, 219
Dewar vacuum vessel, 60
Dextrin, 353
Diakon, 336
Dialysis, 275
Di-arnrnon-phos, 202
Diamond, 119
arrangement of atoms in, 1 22
crystalline structure, 122
Diastase, 347
Dips (candles), 85
Disintegration, atomic, 30
380 INDEX
Dissociation, electrolytic, theory of,
254
Distempers, 358
Distillation, fractional, 92
DOBEREINER, l8l
lamp, 181
Dolomite, 267
Drikold, 50
Drugs, synthetic, 324
Dry cleaning, 92
Dunnite, 134
Duralumin, 266
Dutch metal, 164
DYAR, 232
Dyeing, 282
Dyes, aniline, 312
coal-tar, 314
indanthrene, 320
vat, 319
Dynamics, chemical, 173
Dynamite, 132
Earth, composition of the, 1 1
Earthenware, 247
Ebonite, 340
EHRLICH, 325
EINSTEIN, 43
Electricity and chemistry, 249
conduction of, by solutions, 253
in chemical industry, 261
Electro-chemistry, 249
Electrodes, 253
Electrolysis, 253
of copper sulphate, 253
of sodium chloride, 263
mechanism of, 256
Electrolytes, 253
Electron, mass of, 26
Electrons, 26
planetary, 34, 38
arrangement of, 39
production of, 27
sharing of, 40
transfer of, 39
Electrophoresis, 280
Electroplating, 251
Element, definition of, 9
Elements, 9
list of, 10
number of, 35
of Aristotle, 4
^ periodic classification of, 24
production of, 42
Elements required by plants, 196
trace, 211
tracer, 38
transmutation of, 41
Elinvar, 161
Elixir, 6
Emery, no
EMPEDOCLES, 4
Emulsoid colloids, 280
protective action of, 284
Enamels, nitro-cellulose, 149
Energy, 116
and mass, 43
nuclear, 43
of chemical reactions, 1 18
potential, 116
sub-atomic, 42
Enzyme action, 345
Enzymes, 184
action of, 345
catalytic action of, 345
EPICURUS, 12
Equation, chemical, 48
Equilibrium, chemical, 176
influence of concentration on,
i 7 6
influence of temperature on,
177
Ergosterol, 368
Erinoid, 337
Esters, 354
Ethane, 90
Ether, 321
" Ethyl," 96
Ethyl chloride, 321
Ethylene, 91
alcohol from, 350
Explosives, 126
disruptive effect of, 131
high, 131
low, 131
stabilisation of, 132
taming of, 134
Extract, 353
EYDE, 205
Fabrics, non-creasing, 335
Fahrenheit scale of temperature,
50
FARADAY, 254
Fats, chemical nature of, 85
hydrolysis of, 234
production of, 360
INDEX
Felspars, 246
Fermentation, 344
bottom, 348
explanation of, 345
top, 348
FERNBACH, 354
FERRETTI, 358
Fertilisers, 195
nitrogenous, 195, 202
phosphate, 195, 201
potash, 195, 198
Fibre, compressed, 143
hard, 143
staple, 146
Fibres, synthetic, 144, 337, 358
Fire, extinguishing by carbon di-
oxide, 48
production, 61, 73
Fire-damp, 90
FISCHER, 98
Fission, nuclear, 44
Fixation of atmospheric nitrogen,
205
Flame, extinction of, by wire gauze,
67
luminosity of , 106
Flash lights, 267
point of oil, 95
FLEMING, 324
FLOREY, 324
Foamite fire foam, 48
Food factors, accessory, 364
Formaldehyde (formalin), 135
Formula, 15, 1 6
Formulae, constitutional, 293
graphic, 293
Fortisan, 146
FOURCAULT, 221
FRANKLAND, 18
Freon, 328
Friction lights, 74
Frit, 247
Fructose, 346
Fruit essences, imitation, 354
Fuelite, 83
Fuels, 79
calorific value of, 79
; gaseous, 99
r- liquid, 87
motor, 96
smokeless, 88
solid, 79
Fur, 240
Furfural (furfuraldehyde), 335
Fusel oil, 348, 353
Fusible metals, 170
Galalith, 337
GALVANI, 249
Gammexane, 329
Gas, from coal, 100
from cracked oil, 98
marsh, 90
natural, 99
calorific value of, 100
petrol-air, 92
water, 107
Gases, kinetic theory of, 273
rare, of the atmosphere, 5 1
Gasoline, 92, 95
Gelatin, blasting, 132
colloidal sol of, 280
Gelignite, 132
German silver, 165
Gin, 351
Glass, 214, 218, 219, 220
annealing of, 223
armourplate, 225
as supercooled liquid, 217
coloured, 228
composition of, 221
crystal, 228
devitrification of, 230
hardened (malleable), 223
invention of, 214
manufacture of, 220
patent plate, 223
pyrex, 227
quartz, 218
reinforced, 227
ruby, 229
safety, 224
sheet, 220
silica, 218
silvered, 230
toughened, 223
transparency of, 229
triplex, 224
triplex toughened, 225
window, 220
Wood's, 229
Glucose, 137, 346
from sulphite pulp liquors, 151
from wood, 150
Glycerine, 85, 236
production of, by fermentation,
359
382 INDEX
.Glycerine, synthesis of, 236
Glyptals, 236
" Gob " fires, 71
Gold, 154
chloride, 155
colloidal, 278
fool's, 157
isolation of, 154
potable, 278
white, 155
GRAHAM, 274
Graphite, 120
arrangement of atoms in, 121
artificial, 269
crystalline structure of, 121
deflocculated Acheson, 287
Greek fire, 126
GR-S, 341
GULDBERG, 175
Gurn, British, 353
Gun-cotton, 128, 129
Gun-metal, 164
Gunpowder, 127
Gypsum, 201
HABER, 209
Haematite, 157
HAMPSON, 58
Hardness of water, 240
permanent, 241
temporary, 241
Hawthorn blossom (perfume), 331
Helium, 31, 54
atoms, number in i c.c., 31
nuclei, 33
nucleus, 34
HEMMING, 232
HERSCHEL, 299
Hexamethylene diamine, 337
VON HOHENHEIM, 7
HOOKE, 143
Hopcalite, 108
HOPKINS, 363
Hormones, 369
Humus in soil, 197
HYATT, 148
Hydrocarbons, 86, 89
aromatic, 89
paraffin, 89
saturated, 89
unsaturated, 91
Hydrogen atom, mass of, 26
chloride, 233
Hydrogen from methane, 194
from water-gas, 194
industrial, 194
ion, 255
and acid properties, 255
hydra ted, 255
nucleus, 34
production of, 194, 202, 251
Hydrogenation of coal, 97
of oils, 192
Hydrolysis, 150, 234
Hydroxide ion, 255
and alkali properties, 255
Hydroxyl group, 345
Hypnotics, 323
Hypothesis, 20
latrochemistry, 7
Ice cream, protective colloids in, 285
Ice, dry, 50
Iceland spar, 246
Ignition point, 66
Illuminants, 79
gaseous, 99
liquid, 87
solid, 84
Incandescent mantles, 112
Indigo, 317
Indigotin, 317
synthesis of, 318
Induction, 20
Insecticides, 328
Insulin, 372
Invar, 161
Invertase, 346
Iodine, colloidal, 284
lonisation, 254
lonone, 331
Ions, 254
migration of, 256
Iron, 156
cast, 158
cerium alloy, 77
galvanised, 162
ore, magnetic, 157
ores, 157
Pig, 158
pyrites, 157
rusting of, 162
tinned, 162
wrought, 159
Isomerism, 291
Iso-octane, 95,
INDEX
383
Isoprene, 340
Iso-propyl ether, 96
Isotopes, 36
production of, 38
Iso-valerate, amyl, 354
JANSSEN, 54
JAPP, 306
Jellies, water-holding power of, 286
Jeyes' fluid, 313
JOHNSON, 215
JONSON, 5
Kainite, 200
Kaolin, 247
Kaolinite, 247
KEKULE", 293
theory, 293
KELVIN, 18
Kerosine, 92
Kieselguhr, 132
KIPPING, 339
Knocking, 96
Krypton, 57
KUHNE, 345
Lacquer, nitro-cellulose, 149
bakelite, 335
Lampblack, 125
Lanital, 358
LAVOISIER, 62
Law, Boyle's, 20
of conservation of mass, 64
of conservation of matter, 64
of constant proportions, 14
of mass action, 175
of multiple proportions, 15
of nature, 20
periodic, 23, 35
anomalies in, 23, 35
scientific, 20
LAWES, 201
Lead, 168
accumulator, 259
- action of water on, 170
dioxide, 170
ethyl, 96
oxides of, 170
red, 170
white, 170
Leather, imitation, 149
LE BEL, 303
LEBLANC, 231
Leclanch cell, 258
LEUCIPPUS, 12
Libbey-Owens process (glass), 223
LIEBIG, 63, 196, 321
Light, polarisation of, 296
Lignite, calorific value of, 79
Lily of the valley (perfume), 331
Lime, 243, 245
and fertility of soil, 21 1
burning, 245
chloride of, 233
in soil, 211
nitrogen, 206
slaked, 245
water, 246
Limelight, no
Limestone, 244, 246
caves, 243
terraces, 244
Limonite, 157
VON LINDE, 58
Liquids, supercooled, 216
crystallisation of, 216
Lissapol, 239
Litharge, 170
Lithopone, 168
LOCKYER, 54
LOWE, 147
Lucifers, 74
Lucite, 336
LUCRETIUS, 12
Lumarith, 149
Luminal, 323
Lunar caustic, 153
Lyddite, 134
Lysol, 313
M. and B. 693, 327
760, 327
McCOLLUM, 363
Magisterium, 6
Magnalium, 266
Magnesia, 267
Magnesite, 267
Magnesium, 267
from sea water, 267
in soil, 2ii
Malt, 347
sugar, 346
Maltase, 346
Maltose, 346
INDEX
Manganese, colloidal, 284
and health of plants, 212
steel, 161
Mantle, incandescent, 1 1 1
Marble, 246
Margarine, 191
Marmite, 360
Marsh gas, 89
Mashing, 347
Mass action, law of, 175
and energy, 43
atomic, 36
Matches, 73
manufacture of, 77
safety, 75
strike anywhere, 77
Swedish, 75
Matter, constitution of, 3, 27, 34
electronic constitution of, 27
states of, 215
terrestrial, composition of, 1 1
Mauve, 315
MAYOW, 46
Melinite, 134
Men, 350
MENDELEEF, 23
Mepacrine, 326
MERCER, 147
Mercuric chloride, 166
salts, 1 66
Mercurous chloride, 166
salts, 1 66
Mercury, 166
oxide of, 9
Mesothorium -I, i, 29
" Meta," 356
Metal, white, 165
Metaldehyde, 356
Metals, 152
and planets, 153
fusible, 170
Methane, 89
acetylene from, 113
carbon monoxide from, 194
formation from coal, 90
hydrogen from, 194
uses of, 90
Methanol, 123, 193
Method, scientific, 19
Methoxone, 185
Methyl alcohol, 123, 193
methacrylate, 336
salicylate, 331
MEYER, 23
Micro-organisms, action of, 343
Migen, 350
Milk, curdling of, 357
protective colloids in, 285
Minium, 170
Mirbane, oil of, 331
Mirrors, glass, 229
Moisture, catalytic action of, 178
Molecule, definition of, 15
Molecules, number of, in i c.c., 32
objective reality of, 288
Molybdenum, 161
Monazite, 112
Monel metal, 164
Mordant, 282
Mortar, 245
Moth insecticide, 313
Motor spirit from coal, 97
from water-gas, 98
Mumetal, 166
Muntz metal, 163
MURDOCH, 100
Musk, imitation, 331
Must, 352
Naphthalene, 105
catalytic oxidation of, 318
Naphthenes, 89
Natalite, 99
Neon, 57
Neoprene, 342
Neptunium, 45
Neutron, 33, 42
NEWTON, 12
Nichrome, 165
Nickel, 165
carbonyl, 165
catalytic action of, 192
plating, 165, 252
purification of, 165
Nicol prism, 297
Nitre, 231
Nitric oxide, 205
Nitro-benzene, 331
Nitro-cellulose, 128, 144
Nitro-chalk, 210
Nitro-cotton, gelatinisation of, 13;
Nitrogen, 46
and oxygen, direct combination
of, 205
assimilation of, 202
atmospheric, fixation of, 204,
206
INDEX
Nitrogen, compounds, sources of,
204
dioxide, 205
importance of, in nature, 202
liquid, 58
Nitro-glycerine, 132
Nitrolim, 206
NOBEL, 132
Non-electrolytes, 253
Novocaine, 322
Nuclei, disintegration of, 43
Nucleus, atomic, 32
constitution of, 33
mass of, 36
positive charge on, 32, 34
Number, atomic, 34
Nutrition, 361
Nylon, 337
Ochres, 157
Octane, 95
number (value), 96
Octet, 39
Oil, burning, 92
cracking of, 95
Diesel engine, 92
flash point of, 95
from coal, 97
from water-gas, 98
fuel, 92
calorific value of, 95
gas, 92
illuminating, 92, 94
lubricating, 92
mineral, 92
of bitter almonds, 331
of wmtergreen, 330
paraffin, 92
shale, 97
solar, 92
Oils, chemical nature of, 85
hardening of, 190
hydrogenation of, 190, 192
Oleum, 187, 319
Open-hearth process, 159
Osglim lamps, 57
OSTWALD, 213
Oxidation, 66
Oxy-acetylene flame, 115
Oxy-coal-gas flame, no
Oxy-hydrogen flame, no
Oxygen, 47
liquid, 58
N
Oxygen, preparation of, 47
production of, 58
Ozone, 119
PALISSY, 195
Paludrine, 326
Pamaquin, 326
Paper, 139
Kraft, 140
manufacture of, 140
parchment, 143
silver, 167
sizing of, 140
waterproof, 143
Willesden, 143
PARACELSUS, 7
Paradichlorobenzene, 313
Paraffin, 94
hydrocarbons, 91
oil, 92
solid, 86
wax, 86
Paraffins, 91
PARKES, 148
Particles, colloid, electric charge on,
280
size of, 278
Paste, 228
PASTEUR, 299
Pearls, 246
Peat, 8 1
calorific value of, 79
" Pelican," 6
Penicillin, 324
constitution of, 324
Peptase, 353
Peptisation, 286
Perfumes, synthetic, 330
PERKIN, 315
Permalloy, 166
Permutit, 241
PERRIN, 40
Persil, 237
Perspex, 336
Pertite, 134
Petrol, 92, 95
air gas, 92
from coal, 98
from coal-tar, 98
from natural gas, 98
from oil shale, 97
from refinery gas, 98
from water-gas, 98
3 86
Petrol lighters, 77
polymer, 98
Petroleum, 87
benzine, 92
crude, 91
ether, 92
fractions, 92
origin of, 89
Pewter, 167
Phenacetin, 325
Phenol, 313
PHILLIPS, 187
Philosophy, Greek, 19
Phlogiston, theory of, 62
Phosphate, calcium, 201
Phosphates, 201
Phosphor-bronze, 164
Phosphorus, 74
allotropic modifications of, 75
in matches, 74
production of, 269
red, 75
white, 75
Phossy jaw, 75
Photographic plates, 284
Phthalate, butyl, 355
Phthalic anhydride, 318
Pitch, 94
Plasmoquin, 326
Plasticisers, 355
Plastics, 333
thermoplastic, 333
thermosettmg, 333
Platinite, 161
Platinum, 156
catalytic action of, 180, 187
PLUCKER, 26
Plumbago, 269
Plutonium, 45
Poisoning of catalysts, 188
Polarisation of light, 296
Polaroid, 297
Polyethylene, 336
Polymerisation, 98, 333
Polymer petrol, 98
Polythene, 336
Porcelain, 247
Positron, 33
Potash, 198
caustic, 234
fertilisers, 198
Potassium, 250
carbonate, 198
hydroxide, 234
INDEX
Potassium salts, 198
Powder, smokeless, 132
Precipitate red, 9
PRIESTLEY, 47
Prodorite, 151
Propane, 90, 97
Propylene, 91, 236
Proteins, constitution of, 144, 338
production of, 360
Proton, 33
PROUT, 22
Prout's hypothesis, 23
Pulp, mechanical, 140
soda, 139
sulphate, 139
sulphite, 139
wood, 139
Purple, Tyrian, 314, 320
Pyrene fire extinguisher, 66
Pyrethrins, 328
Pyrex ware, 227
Pyridoxin, 369
Quartz, 218
glass, 218
Quicklime, 245
Quinine, 326
Racemates, 305
resolution of, 305
Radioactivity, 22, 27
decay of, 29
disintegration theory of, 30
Radium, 27
chloride, 27
disintegration of, 30
emanation, 29, 57
radioactive substances from, 29
radioactivity of, 28
Radon, 29, 57
Ramie fibre, 112
RAMSAY, 31, 52, 54, 57
RAYLEIGH, 52
RAYLEIGH (R. J. Strutt), 23
Rayolana, 146
Rayon, 145
acetate, 145
delustred, 145
viscose, 145
Rays, alpha, 28
nature of, 31
INDEX
387
Rays, beta, 28
cathode, 26
gamma, 28
R.D.X., 135
Reactions, endothermal, 118
energy of, 118
exothermal, 118
influence of concentration on
velocity of, 175
influence of temperature on
velocity of, 175
reversible, 175
velocity of, 172
Rennin, 357
Resins, synthetic, 333
Rexine, 149
Riboflavin, 367
Rock crystal, 218
RONTGEN, 27
ROSSITER, 335
Rotenone, 328
Rubber, 339
hard, 340
synthetic, 341
Rubies, artificial, no
imitation, 228
Rum, 352
Rupert's drops, 223
Rushlight, 85
RUtHERFORD, D., 46
RUTHERFORD, Lord, 30, 32, 41,
43
SABATIER, 192
Safety lamp, 67
Salt, spirit of, 6
Salt-cake, 233
Saltpetre, Chile, 204
Norwegian, 205
Salts, 253
Saltwort, 231
Salvarsan, 326
Saponification, 234
Sapphires, artificial, no
imitation, 228
Scale, boiler, 240
SCHEELE, 47
SCHONBEIN, 2l8
Science, method of, 19
Sea-sand, 219
Season-cracking, 164
Sedimentation in rivers, 286
Seekay wax, 313
SENDERENS, 192
Sewage farms, 284
purification of, 283
Shale oil, 97
Shampoo powders, 240
Shimosite, 134
Siemens-Martin process, 159
Silica, 218
gel, 279
glass, 218
Silk, 144
artificial, 144
Silver, 155
bromide, 156
chloride, 156
colloidal, 284
German, 165
oxidised, 155
paper, 167
Silveroid, 164
SIMPSON, 321
Slag, basic, 160, 201
blast furnace, 158
Soap, 233
cleansing power of, 237
emulsifying action of, 239
hard, 234
manufacture of, 235
soft, 234
substitute for, 239
transparent, 237
SOBRERO, 132
Soda, 230
baking, 232
bicarbonate of, 232
carbonate of, 232
caustic, 234
lakes, 230
washing, 232, 241
SODDY, 30
Sodium, 250
bicarbonate, 232
carbonate, 230
chloride, 17
electrolysis of, 262
cyanide, 251
hexametaphosphate, 241
hydroxide, 234
Solder, 167
Solid, amorphous, 217
crystalline, 215
Sols, colloidal, 276
Solute, 273
Solution, 273
388 INDEX
Solutions, conduction of electricity
by, 253
electrolytic, ponstitution of, 252
SOLVAY, 232
Soot, 125
Spectroscope, identification of gases
by, 53
Spectrum, 53
Spelter, 168
Spermaceti, 86
Spinthariscope, 31
Spirit, methylated, 349
of salt, 6
patent still, 348
proof, 349
silent, 348
STAHL, 62
Stalactite, 243
Stalagmite, 244
Staple fibre, 146
Starch, conversion into glucose,
346
saccharification of, 350
State, colloidal, 275
States of matter, 215
Stearin, 86
Steel, 159
chrome, 160
high speed tool, 161
manganese, 161
nickel, 160
stainless, 160
staybrite, 160
temper, 160
tool, 161
Stereo-chemistry, 303
and vitalism, 306
STOKES, 296
Stone, philosopher's, 6
Stoneware, 247
Storage cell, 259
Strass, 228
Structure, atomic, 22, 32
molecular, 293
STRUTT (Lord Rayleigh), 23
Sublimate corrosive, 166
Substances, pure, 9
Sucrose, 346
Sugar, beetroot, 346
cane, 346
malt, 346
Sulpha-drugs, 326
Sulphaguanidine, 327
Sulphanilamide, 326
Sulphapyridine, 327
Sulphathiazole, 327
Sulphur, 189
colloidal, 284
dioxide, 189
removal from flue gases, 84
from hydrogen sulphide, 190
from sulphur dioxide,. 189
recovery of, 189
tnoxide, 186
uses of, 190
Superphosphate, 201
Suprarenine, 322
Surface tension, 237
Surgery, bloodless, 322
Suspensoid colloids, 280
SWAN, 144
Sylvine, 200
Symbols, 15, 1 6
Teepol, 239
Tempering of steel, 160
Terpineol, 331
Tetralm, 313
Theory, 20
atomic, 11,13
disintegration of radioactivity,
30
electrolytic dissociation, 254
kinetic, of gases, 273
of molecular structure, 293
Therm, 107
Thermit, 72
Thermos flask, 60
Thiamine, 366
Thiourea, 105
THOMSON, 26, 36
Thoria, 112
Thorium oxide, 112
radioactivity of, 28
Thylox process, 190
Thyroxine, 370
Tin, 166
foil, 167
grey, 167
Islands, 167
plague, 1 68
plate, 167
white, 167
Tinstone, 166
Titanium oxide, 171
white, 171
T.N.T., 73, 134
INDEX
389
Tocopherol, 369
Toluene (toluole), 313
Torpex, 135
Touchpaper, 72
Trace elements, 211
Tracer elements, 38
bullets, 78
shells, 78
Transformations, radioactive, 30
Transmutation of elements, 41
TR AVERS, 57
Trinitrotoluene, 73, 134
Tntonal, 135
TROPSCH, 98
Trotyl, 134
Tungsten, 162
Twyers, 158
Tyndall phenomenon, 276
Type metal, 170
Tyrian purple, 314, 320
Ultramicroscope, 277
Unit, British thermal, 80
Uranium, 27
disintegration of, 30
radioactivity of, 28
Urea, 210, 335
as fertiliser, 211
UREY, 37
Vacuum vessel, Dewar, 60
Valence, 18
Valency, 17, 18, 40
explanation of, 40
Value, calorific, 79, 80
VAN HELMONT, 195
Vanillin, 330
VAN'T HOFF, 200, 303
Vaseline, 92
Velocity of reactions, 172
influence of concentration
on, 175
influence of temperature on,
Verdigris, 164
Vermilion, 166
Veronal, 323
Vesuvians, 77
Vimlite, 147
Vinal, 225
Vinegar, 355
. Violet, imitation (perfume), 331
Viscose, 145
Vita glass, 229
Vitamin A, 364
Bj, 366
B 2 , 367
complex, 367
C, 367
D, 368
E, 369
H, 369
Vitamins, 191, 361
Vitriol, oil of, 6
Volt, 249
VOLTA, 249
Vulcanite, 340
WAAGE, 175
WALKER, 74
Wash, 348
Water, hard, 240
heavy, 37
ordinary, 38
potable, from sea-water, 243
removal of salts from, 242
softening of, 241
Water-gas, 107
calorific value of, 108
carburetted, 107
hydrogen from, 194
oil from, 98
synthesis from, 193
Water-glass, 219
Weeds, eradication of, 185
Weight, atomic, 17
molecular, 1 7
WELSBACH, 78, in
Whisky, 351
White metal, 165
Windolite, 147
Wine, spirits of, 345
Wines, 352
diseases of, 353
Wintergreen, oil of, 330
Winzer (Winsor), 100
Wire-gauze, cooling action of,
67
Woad, 317
Wood, calorific value of, 79
distillation of, 122
glucose from, 150
39 INDEX
Wood, hydrolysis of, 150 Yeast, 346, 359
pulp, 139 as food-stuff, 360
spirit, 123 Chinese, 350
tar, 123 mineral, 360
xylose from, 151
Wool, substitute for, 358, 359
Wort, 347 Zakatalsk nuts, 367
.Zeolite, 241, 243
Zinc, 1 68
Xenon, 57 oxide, 168
X-rays, 27 white, 168
Xylonite, 148 Zirconium oxide, no
Xylose, 151 Zymase, 344