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By the same Author 







"He that enlarges his curiosity after the works of Nature 
demonstrably multiplies the inlets to happiness." 

JOHNSON, Rambler, No. 5. 












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 






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 



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 


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. 

March 1947. 


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 


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 


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, 


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. 



March 1916. 




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 ..... 



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 ..... 


Composition of the atmosphere. Nitrogen. Oxygen. Carbon di- 
oxide. Argon. Identification of gases by spectroscopy. 
Helium. Neon. Krypton. Xenon. Liquefaction of air . . 46 



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 





SOLID FUELS Calorific value. Wood. Peat. Coal. Smokeless fuel. 
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 



Energy of chemical reactions. Exothermal and endothermal re- 
actions. Ozone. Allotropic forms of carbon. Diamond. 
Graphite. Crystalline structure. Charcoal. Carbon black. 
Explosives . . . . . . . . .116 



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 


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 



Chemical affinity. Influence of concentration. Influence of tem- 
perature. Reversible reactions. Catalysis. Enzymes. Manu- 



facture of sulphuric acid. Sulphur. Cement. Recovery of 
sulphur. Hydrogenation or hardening of oils. Margarine. 
Syntheses from water-gas. Hydrogen from methane . .172 



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 



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 


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 




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 



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 



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 



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 




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 



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 



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 


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 



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 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. 


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. 



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 


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 


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, 


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 

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 


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- 

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. 


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 


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 


the Hon. ROBERT BovLE, 1 of whom it has been said that 
" he was the father of chemistry and brother of the Earl of 

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 















, *H 

I -008 


Silver . 





. He 








. Li 



Indium . 





. Be 








. B 








. C 








. N 











Xenon . 





. F 








. Ne 



Barium . 





. Na 








. Mg 



Cerium . 





. Al 







Silicon . 

. Si 



Neodymium . 





. P 



Illinium 1 




. S 








. CJ 







Argon . 

. A 








. K 








. Ca 








. Sc 








. Ti 



Erbium . 





. V 








. Cr 








. Mn 

54 % 93 







. Fe 







Cobalt . 

. Co 







Nfckel . 

. Ni 







Copper . 

. Cu 








. Zn 







Gallium . 

. Ga 








. Ge 







Arsenic . 

. As 



Gold . 





. Se 








. Br 








. Kr 








. Rb 








. Sr 






Yttrium . 

. Yt 






. Zr 



Radon . 





. Nb 







. Mo 



Radium . 




Masurium 1 

. Ma 







. Ru 








. Rh 



Protoactinium . 





. Pd 






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. 



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 : 

(Earth, Air and Sea) 

per cent. 










2- 3 6 

Carbon . 

per cent. 

Oxygen . 

Silicon . 


Iron . 4 1 8 Titanium 0-43 

Calcium 3*22 Chlorine 0-20 

Sodium 2-36 Carbon . 0-18 


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 


Underlying the philosophy of Aristotle was the idea that 
matter is continuous, that it is capable of infinite sub- 
division ; but with the overthrow of the doctrine of the four 
elements of Aristotle there was revived another ancient 


hypothesis which had been put forward 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, 


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 

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. 


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 


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 


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 


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. 


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 


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. 


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. 


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 


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. 


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. 


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 



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, 


in which the properties of the elements are similar to those of 
the corresponding members of the former series ; that is, 


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 

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. 


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 


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- 


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). 


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. 


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 

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 

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. 


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 


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 


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. 


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 ? 


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 


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 


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). 


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. 


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, 


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 


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, 

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 


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 


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 


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 


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. 


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). 


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 

1 Elements with atomic numbers 95 (Americium, Am) and 96 (Curium, 
Cm) have also been produced artificially. 


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 



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 


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. 


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 : 


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, 


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. 


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. 


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 

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 


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 


a pale yellow light, and is used in the construction of illu- 
minated signs. 
Owing to the discovery of the monatomic elements, argon 


[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, 


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 
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 

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 

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 


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 

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 

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 

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 


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. 


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 



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. 



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 

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. 


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 


tenacity with which it maintained itself is an instructive 
illustration of the difficulty which most minds have of 
freeing themselves from the authority of a long-held theory ; 
and it conveys a lesson, which is not unnecessary even at 
the present day, that a theory from being a helpful guide 
may readily become an oppressive tyrant. As LIEBIG wrote 
many years ago, after having himself been a victim of the 
misfortune to which he refers : " No greater misfortune 


could befall a chemist than that of being unable to shake 
himself free from the power of preconceived ideas, and, 
yielding to the bias of his mind, of seeking to account for 
all phenomena which do not fit in with these ideas by 
explanations which have no basis in experiment. " 

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. 


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. 


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. 


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 


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 


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 



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 


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 

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 


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, 


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 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 


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 


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 


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. 


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- 

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- 


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. 


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 


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 . 


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. 



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 



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. 


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. 


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 


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- 

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 

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 


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. 


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 


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 


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 


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 


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 . 



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, 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. 


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 C H 


or, more simply, by the formula CH 4 . 


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 

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. 


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 | 


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). 


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. 



7 '-"v/' ;, v,v^ 

; '^vf>;'; f v 

Courtesy Anglo-Iranian Oil Co. Ltd. 


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. 


paraffin, which is used for making candles, water-proofing 
paper, and other purposes. 1 A final residue of pitch is 

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 


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 


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. 


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). 



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. 


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 

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). 


In various countries (the United States, Russia, Rumania, 
Canada, and others) great reservoirs of " natural gas " are 


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 

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 




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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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 


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 

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. 


I lydrogen 
Unsaturated hydrocarboi 
Carbon monoxide 
Carbon dioxide 

is (Ed 


56 per 
22-8 , 





cent, by 



Coal-gas, then, as we see, is a mixture of a number of 
gases, and of these carbon dioxide, nitrogen and oxygen 
represent what we may call impurities ; they act merely as 
diluents and lower the illuminating power of the gas. 


Of the combustible gases present in coal-gas, hydrogen 
burns with a non-luminous, scarcely visible flame ; carbon 
monoxide, with a non-luminous flame of a bright blue 
colour 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 


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 


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 


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. 


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 


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. 


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 


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 


carried out before the incandescent mantle could be made a 
commercial success and be brought to its present state of 

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. 


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 


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. > 


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. 


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 


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 



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. 


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 


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 

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 



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 

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 



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 


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 


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 



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. 


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). 


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.' 

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 


combustion of part of the wood serves to carbonise the 

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." 

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 



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." 

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 


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 


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. 



employed, and in its preparation and treatment great care is 

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). 


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 



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). 

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 


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 


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). 


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. 


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 

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. 


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 


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. 



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, 


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 : 


\/ \/ \ / \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 



/ c \ y c \ 


CH 2 OH 


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). 


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 

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 


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. 


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. 

Upper ; wet end : Lower ; dry end. 


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 



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. 


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 


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 


fibres for the production of cheaper fabrics and new 

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 

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 

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, 


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 

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. 


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- 


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 

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 

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 


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. 



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. 



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. 


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. 


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. 


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. 


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. 


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 



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 


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 


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 


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 


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 


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 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). 


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. 


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. 


Dutch metal is an alloy containing about 20 per cent, of 

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- 

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. 


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. 


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 

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 


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 


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 



Courtesy of Prof. E. Cohen. 



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. 


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). 


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 



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 

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 


give an explanation of chemical change ; it is, rather, a 
measure of the work done by a system when it undergoes 

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 


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 


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 


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 

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 


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- 

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. 


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 


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 


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 


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 

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 


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, 


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 


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. 


Sulphuric acid, or oil of vitriol (H 2 SO 4 ), the discovery of 
which dates from the fifteenth century, is one of the most 


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. 


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 


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 


(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. 


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 


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 

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 


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. 


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 


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. 


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, 
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 


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. 


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. 


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). 



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 


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 


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 


Courtesy of Sir John Russell. 


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., 


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 


Courtesy of Societt Commerciale de Potasses d' Alsace, 


Courtesy of Socieit Commerciale de Potasses d" Alsace. 




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 


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, 


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, 


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. 


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. 


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 


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. 


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 


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, 


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 


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 


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. 


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). 


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, 


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 


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 


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- 

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 



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 

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, 


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. 


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. 


When a supercooled liquid or " glass " is maintained at a 
temperature in the neighbourhood of the softening point, 
spontaneous crystallisation may set in, and thereby cause 
the glass to lose its transparent, vitreous character ; the 
glass, it is said, devitrifies. Under certain circumstances, 
this may prove a source of much annoyance. 


A substance which affords an excellent illustration of the 
behaviour which has just been discussed is quartz or silica 
(an oxide of the element silicon), a substance which is very 
familiar to everyone. It occurs as the clear, glassy particles 
which form sea-sand, and which can also be readily 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- 

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 


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 

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 

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 


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. 


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 


(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 


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 



(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 



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. 


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. 


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 



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- 


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 


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. 


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 


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 

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 


(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, 

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- 


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 

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. 


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 


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, 


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 

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. 


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 

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 . 


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 

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 


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 


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 

Although soap can be obtained by using either caustic 
soda or caustic potash, the nature of the product obtained 
in the two cases is different, the potash soaps being soft, 
the soda soaps hard. 

The fats and oils used in soap-making are very varied in 
character. Formerly, animal tallow and olive oil were the 
chief raw materials employed, but, as has already been 



pointed out (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. 

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 


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 

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 


added salts act as water softeners, its detergent power is 

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. 


Jacobi Rapid Cooling Press in which the liquid soap is cooled in frames 
clamped between plates round which cold water circulates. 


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 

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 


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 


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. 


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 

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, 


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 


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. 


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. 


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, 

Limestone, or calcium carbonate, when strongly heated, 



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 


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 


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 


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 


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 

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. 


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 

Concrete, now so largely employed for building purposes 
and for road making, is a mixture of cement with sand or 


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. 



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 


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 


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- 

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 


would ask the reader to consider with me for a short time 
what is the nature of the liquids which conduct the electric 

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 


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 


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, 


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 

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. 


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 



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 


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 


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 



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 


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 





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 



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- 


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 

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 


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. 


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 


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. 


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 


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 

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- 


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. 


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 



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 


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 


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 

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 



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. 


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 


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 


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. 


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- 

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 



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 


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. 


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 


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 


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 


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 

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 


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 


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 

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 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 


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 

In agriculture, also, the colloidal state is of the greatest 
importance. In the soil there exist various colloidal sub- 


stances, such as the humus, colloidal ferric hydroxide and 
aluminium hydroxide, clay, etc. Owing to the presence of 
these, soluble substances, such as the salts of potassium, 
phosphates and other substances necessary for the life of 
the plant, are adsorbed and retained in the soil, and so 
kept available for the support and nourishment of 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 


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 


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 


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 


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. 


(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. 


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. 


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. 



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 

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 


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 

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 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 


gas by the diagrammatic formula H C H, and the higher 


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 


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 

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 

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). 


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.C. C.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 

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." 


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 


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 


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. 


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 


different extents (the blue rays being rotated more than the 
red), the spiral band of light shows the colours of the 

What then is the explanation to be given of this remarkable 
property of substances, the study of which, starting with the 



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 


'1 e 







\ r 




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. 


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 

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 ; 


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 

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, 


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, 


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 


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 

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, 


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, 


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 


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 


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. 


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. 



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 



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 

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. 


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 : 



Benzene 80-5 C. (176-9 F.) 

Toluene 111 C. (231-8 F.) 



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 


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 

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 


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. 


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.} 


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. 


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 

(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- 


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* 


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 

acid (CeH4<TT ), and then into phthalic anhydride 

(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 


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 

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 


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). 



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). 


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 

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 


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), 


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 


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 


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. 


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. 


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. 

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 


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 


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. 



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 



(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 


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." 



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, 


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. 


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 

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 

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 


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 

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 


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 

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 


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. 


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. 


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. 


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 


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 


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 

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. 


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. 



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. 



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> 


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 
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. 


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 

For the conversion of the starch into fermentable sugar, 


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 . 


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 

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, 

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 

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 


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. 


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. 


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, 


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 


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 


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." 



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 


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 


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 


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 

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, 


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 


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- 


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. 


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 



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, 


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* 



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. 


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 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 


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 

-C C - 

CH 2 - N 

II II // %H- 

N CH Cl ^ 


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 


\ / 

C = C 


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. 


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 


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. 


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. 


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 

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. 


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, 

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 


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. 


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. 


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. 


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 
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 


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 

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 

theorem of, 32 
Azote, 47 

Babbitt metals, 167 
BACON, Francis, 20 
BACON, Roger, 6, 127 
Bakelite, 334 
Baking powders, 232 
BALY, 117 
Barilla, 231 
Bath salts, 232 
Beers, 353 
Beetle ware, 335 
Bell metal, 164 
Benzaldehyde, 331 
Benzene (benzole), 97, 312 

formula of, 295 

hexachloride, 329 
Benzine (benzolme), 92 
BERZELIUS, 16, 178 
Bessemer process, 159 
BEVAN, 145 

Beverages, alcoholic, 351 
Bio-chemistry, 361 
Biotin, 369 


Biscuit ware, 247 
Bisque, 247 
Black lead, 369 



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, Robert, 288 
Brownian movement, 288 

Buna, 341 
- -N, 341 
S, 341 


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, 

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 
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 
Chalk, 246 
Charcoal, 122 

adsorbing power of, 123, 279 

burning, 124 

decolorising of liquids by, 123, 

279 . 

use in gas-masks, 123 
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 

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 
Cinnabar, 166 
CLAUDE, 209 
Clay, 246 

white china, 247 
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 


Collodion, 131, 149 
Colloidal sol, 276 



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, 

suspensoid, 280 
Combustion, 61 

by means of combined oxygen, 

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 


DAVIS, 363 

DAVY, 67, 187, 250 

D.D.T., 329 

Deacon's process, 233 

Decalin, 313 

Decolorising of liquids by charcoal 


Deduction, 20 
Deltas, formation of, 281 
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, 


Distempers, 358 
Distillation, fractional, 92 


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 



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 
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 
Equation, chemical, 48 
Equilibrium, chemical, 176 
influence of concentration on, 

i 7 6 

influence of temperature on, 


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, 


Fats, chemical nature of, 85 

hydrolysis of, 234 

production of, 360 


Felspars, 246 
Fermentation, 344 

bottom, 348 

explanation of, 345 

top, 348 
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 
Fission, nuclear, 44 

Fixation of atmospheric nitrogen, 

Flame, extinction of, by wire gauze, 


luminosity of , 106 
Flash lights, 267 

point of oil, 95 
FLOREY, 324 
Foamite fire foam, 48 
Food factors, accessory, 364 
Formaldehyde (formalin), 135 
Formula, 15, 1 6 
Formulae, constitutional, 293 

graphic, 293 
Fortisan, 146 
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 
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, 

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 


Gurn, British, 353 
Gun-cotton, 128, 129 
Gun-metal, 164 
Gunpowder, 127 
Gypsum, 201 

HABER, 209 
Haematite, 157 
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 
Hexamethylene diamine, 337 

HOOKE, 143 

Hopcalite, 108 
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, 



Isoprene, 340 
Iso-propyl ether, 96 
Isotopes, 36 
production of, 38 
Iso-valerate, amyl, 354 


JAPP, 306 

Jellies, water-holding power of, 286 

Jeyes' fluid, 313 



Kainite, 200 
Kaolin, 247 
Kaolinite, 247 
KEKULE", 293 
theory, 293 
Kerosine, 92 
Kieselguhr, 132 
Knocking, 96 
Krypton, 57 
KUHNE, 345 

Lacquer, nitro-cellulose, 149 

bakelite, 335 
Lampblack, 125 
Lanital, 358 
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 


Leclanch cell, 258 


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 
Liquids, supercooled, 216 

crystallisation of, 216 

Lissapol, 239 

Litharge, 170 
Lithopone, 168 
LOWE, 147 
Lucifers, 74 
Lucite, 336 
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 


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 
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 
Musk, imitation, 331 
Must, 352 

Naphthalene, 105 

catalytic oxidation of, 318 
Naphthenes, 89 

Natalite, 99 
Neon, 57 
Neoprene, 342 
Neptunium, 45 
Neutron, 33, 42 
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, 


Nitrogen, compounds, sources of, 

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 

Oxidation, 66 
Oxy-acetylene flame, 115 
Oxy-coal-gas flame, no 
Oxy-hydrogen flame, no 
Oxygen, 47 

liquid, 58 

Oxygen, preparation of, 47 

production of, 58 
Ozone, 119 

Paludrine, 326 
Pamaquin, 326 
Paper, 139 

Kraft, 140 

manufacture of, 140 

parchment, 143 

silver, 167 

sizing of, 140 

waterproof, 143 

Willesden, 143 
Paradichlorobenzene, 313 
Paraffin, 94 

hydrocarbons, 91 

oil, 92 

solid, 86 

wax, 86 
Paraffins, 91 
PARKES, 148 

Particles, colloid, electric charge on, 

size of, 278 

Paste, 228 
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 

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 
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 

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 


Potassium salts, 198 

Powder, smokeless, 132 

Precipitate red, 9 


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 (R. J. Strutt), 23 
Rayolana, 146 

Rayon, 145 

acetate, 145 

delustred, 145 

viscose, 145 
Rays, alpha, 28 
nature of, 31 



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 
Rotenone, 328 
Rubber, 339 

hard, 340 

synthetic, 341 
Rubies, artificial, no 

imitation, 228 
Rum, 352 

Rupert's drops, 223 
Rushlight, 85 


RUTHERFORD, Lord, 30, 32, 41, 

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 


Science, method of, 19 
Sea-sand, 219 
Season-cracking, 164 
Sedimentation in rivers, 286 
Seekay wax, 313 

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 
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 
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, 

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, 

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 



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 
Trinitrotoluene, 73, 134 
Tntonal, 135 


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 


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 
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, 


Woad, 317 
Wood, calorific value of, 79 

distillation of, 122 

glucose from, 150 


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