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T H E . P A G E A N T ® F P R O G R E S S

PHOT®GRAPHY TQ-BAY By D. A. SPENCER, PH.D., F.I.C., ( H O N . ) F . R . P . S .

FLIGHT T®-©AY By J. L. NAYLER, M.A., F.R.AE.S. andE. OWER, B.A., A.C.G.I., F.R.AE.S.

WIRELESS T®-DAY By E. H. CHAPMAN, M.A., D.SC.

ENGINES T®-E)AY Bj" JOHN HARRISON, A.M.I.MECH.E., A.M.I.A.E.

y C H E M I S T R Y T®-DAY \/By ARNOLD A1.LCOTT, B.SC, A.I.C. ^ and H. S, BOLTON, A. i . e . , A.T.I.

WARSHIPS TO-BAY By M. W. BURGESS, A.M.I.MECH.E., A.M.I.N.A.

ASTRONOMY By W. M. SMART, M.A., D.SC.

CIVIL ENGINEERING T®-n)AY By EDWARD CRESSY

RAILWAYS TO-DAY By J. W. WILLIAMSON, B.SC.

MOTOR-CARS TO-DAY By JOHN HARRlSOl^, A.M.IJ.IECK.E., A.M.I.A.E.

ELECTRICITY TO-DAY By T. B. VINYCOMB, M.A.

THE MERCHANT SERVICE TO-DAY By LESLIE HOWE

O X F O R D U N I V E R S I T Y P R E S S

PLATE 1

The Alchemist From the picture by David Teniers

Stills, re tor ts , and o ther ancient apparatus From an old print

CHEMISTRY TO-DAY

THE PAGEANT OF PROGRESS General Editor: j . w. BISPHAM, O.B.E., M.A., B.SC

HEMIISTRY TO=DAY

BY

ARNOLD ALLCOTT, B.Sc, A.I.C. AND

H. S. BOLTON, A.I.C, A.T.I.

THE SCIENTIFIC BOOK CLUB 121 Charing Cross Road, Lotidon, W.C. 2

OXFORD UNIVERSITY PRESS AMEK IIO(;SE, E.G. 4

London Edinburgh Glasgow New York Toronto Melbourne Capetown Bombay

Calcutta Madras

HUMPHREY MILFORD rUBLISlIER TO THE tJNlVERSIXy

THIS EDITION 1941

23255

imPniNTED I941 IN CREAT BRITAIN AT TUR UNIVERSITV PRESS. OXFORD, DV ,OMN JOHNSON

'^v<.

CONTENTS I. ALCHEMY—THE CHEMISTRY OF THE MIDDLE

AGES . . . .

II. THE BIRTH OF CHEMISTRY

III . CHEMISTRY AND NATURE

IV. CHEMISTRY AND THE SOIL

V. CHEMISTRY AND THE HOUSEWIFE. I

VI. „ » „ II

VII. CHEMISTRY AND THE BOUDOIR

VIII. CHEMISTRY AND THE BUILDER

IX. CHEMISTRY AND THE DETECTIVE

X. ATOMS AND MOLECULES

INDEX . ' .

13

24

41

57

75

91

109

118

136

147

161

L I S T OF PLATES 1. The Alchemist

Stills, retorts, and other ancient apparatus I Frontispiece

2. The Fathers of Chemistry: Paracelsus; Francis Bacon; Robert Boyle; Henry Cavendish; Joseph Priestley; Antoine Lavoisier . . . Tofacep. 14

3. Dalton collecting marsh-fire gas (from the painting by Ford Madox Bro^vn in the Town Hail, Manchester) . . . . .

4. Stalactites: The Frozen Waterfall, Kent's\ Cavehi, Torquay \

The Peal of Bells, Cheddar i

5. Limestone Cliffs, Cheddar Gorge |

The 'Dropping Well', Knaresborough /

6. Bottles being filled, sealed, and labelled by a single machine in a modem mineral-water factory

Chemical fire extinguishers at work on-a blazing motor-car

IS

48

49

52

7. Making solid carbon dioxide

Blocks of solid carbon dioxide

8. Broadbalk permanent wheatfield—the oldest in' the world

Photograph showing the effect of nitrate of soda on the potato crop

9. Broadbalk wheat sheaves grown with and without nitrogenous manures

Granular 'Aero' Cyanamid '

53

60

61

10 LIST OF PLATES

ID. The Nitrate Industry in Chile: Nitrate stored in> piles for final drying

Granulated nitrate ready for shipment Loading railway trucks

To face p. 64

11. Fixation of Nitrogen: Interior of Sulphate of Ammonia silo at Billingham-on-Tees .

12. Basic Slag: Tapping a steel furnace '1

Basic Slag being weighed and put into bags j

65

So

13. Match Making: Splint-cutting or chopping machine

One of the Bryant & May Match Halls 8i

14. In a Soap Works: One of the steel pans in which\ the fats and oils are boiled '

Soap ready to be cut up into slabs and bars i 96

15. Mercerizing Machine

Apparatus for chlorinating water 97

16. Rayon Manufacture: Extracting sheets of wood-s pulp from a bath of caustic soda

A cake of Rayon Rayon thread wound into hanks

100

17. Bakelite Products: Removing a laminated sheet^j of Bakelite from the press

Dining-table and sideboard made from Bakelite laminated sheet material

l O I

18. Two hanks of yarn immersed in water, showing the effect of shower-proofing

19. Sorting rough Diamonds . 109

LIST OF PLATES

20. Lime Burning: Broken stone being conveyed\ from the quarry to the kilns

Three of the gas-fired kilns Drawing Lime out of the kilns

I I

To face p. 116

21. A Cement MLxer 117

22. In a Cement Works: Rotatory kiln in which the^ raw material is burnt

Cooling drum into which the hot clinker passes from the kiln

Chemists testing the raw material

23. A paint-grinding laboratory at the Borough Polytechnic, London

Varnish running

124

125

CHAPTER I

ALCHEMY—THE CHEMISTRY OF T H E M I D D L E AGES

T H E story of any science is a record of man's attempts to understand the mysteries of Nature. The processes of Nature to-day are no different from those of long ago; the change lies only in man's comprehension and in his application of these processes.

The sun and other heavenly bodies obeyed the same laws and performed the same movements in bygone times as to-day, but only since man has understood these laws and movements has he been able to use them to find his way over the oceans of the world by day or night. The force of gravity and the forces producing electric energy have always existed, but only since man's imderstanding of these things has he been able to harness the water-power of our upland lakes to produce electricity for his own use.

Astronomer, physicist, biologist, and chemist, each working in his own sphere, lifts the^ veil a little higher and reveals more of the working of Nature's laws. The knowledge thus gained may be used to serve the ends of mankind. The many amenities of modern civilization result largely from the progress of science.

The chemist is concerned with the composition of things. He wants to know what things are made of and how Nature makes them. Then he tries to make these things himself. Sometimes he succeeds and sometimes he fails. But his knowledge grows; he learns alike from failure and success. With the knowledge thus gained he is able to make new substances or produce old ones in a new way.

14 ALCHEMY—CHEMISTRY OF THE MIDDLE AGES

In this book v e hope to show the intimate relation of the science of chemistry to almost every phase of modern life. There is scarcely an industrial process that does not owe its efficiency, if not its initiation, to the work of the chemist. The dyer of fabrics is no longer dependent on the few colours that may be extracted from plants, but, with the help of synthetic dyestuffs, produces bright colours and delicate shades in a never-ending variety. Saucepans of aluminium and knives of stainless steel are available only as the result of chemical research.

Medical science is daily indebted to the chemist, who produces and perfects the drugs and medicines used by doctors to alleviate pain. The achievements of chemistry are evident in the purity of our water supply, the increased yield of crops from our fields, and the variety and safety of our food supply.

Submarine cables and motor-cars, artificial lighting and broadcasting, photography and deiital mechanics, all owe much of their present state of perfection to the work of the chemist.

Chemistry as practised to-day is a comparatively modern science. I^ess than a hundred years ago it was possible for any serious student to become acquainted with all the then known facts of chemistry. To-day no man can master all the various branches of the science. The student must confine himself to obtaining a general all-round knowledge of the fundamentals, and then possibly a fuller knowledge of one or more branches, such as metallurgy, electro-chemistry, biochemistry, dyeing, fuel, oils, or resins.

But although chemistry as an exact science belongs to modern times, yet its origin, like that of other sciences, must be sought a long way back. The early Egyptians

PLATE 2

Francis Bacon

Paracelsus

Robert Boyle

Henry Cavendish

Antoine Lavoisier

THE FATHERS OF CHEMISTRY

PLATE 3

ALCHEIMY—CHEIMISTRY OF THE MIDDLE AGES 15 had some knowledge of the making of enamels, of refining gold, and of the use of natural dyes. The fact that they were able to embalm the bodies of their rulers with such success that the mummies have resisted decay for thousands of years would suggest that they also understood the use of antiseptics.

Whether this knowledge was the result of chance or of true scientific research is hard to say, for their secrets and recipes appear to have died with them.

We know, however, that from early times, probably from before the beginning of the Christian Era, there have been men who sought to unravel the secret of the constitution of matter. Some were actuated by a genuine desire for knowledge and others simply by a desire for gain. These men became known as Alchemists, or adepts in alchemy.

Whatever were the intentions and aspirations of the first alchemists, their successors for centuries appear to have been obsessed with three main objects of discovery. These were the Transmutation of Metals, the Elixir of Life, and the Universal Solvent. Needless to say, none of these discoveries was made.

It is not easy for the historian to find out exactly what the early alchemists thought, how they worked, or what they accomplished. Alchemy was essentially a secret art, and for long was practised only in priestly circles or under the patronage and control of ruling families. Few written records have been left, and most of these are couched in language so mysterious as to be almost unintelligible to modern minds.

It is doubtful even if the writings of one alchemist were understood by others of his brethren of the craft. Perhaps they were not intended to be understood, but were made purposely obscure, either an account of

16 ALCHEMY—CHEMISTRY OF THE MIDDLE AGES professional jealousy or to conceal the writer's failure to achieve anything of note. What, for example, are we to judge from the following seventeenth-century quotation:

•If we would elicit our medicine from the precious metals we must destroy the particular metallic form, without impairing its specific properties. The specific properties of the metal have their abode in its spiritual part, which resides in homogeneous water. Thus we must destroy the particular form of gold, and change it with its generic homogeneous water, in which the spirit of gold is preserved; this spirit afterivards'restores the consistency of its water and brings forth a new form (after the necessary putrefaction) a thousand times more perfect than the form of gold which it lost by being reincrudated.'

The belief of the alchemists in the possibility of transmutmg a base metal such as lead into gold seems to have been due to a series of strange misconceptions. They thought that the difference between one kind of matter and another was simply a question of purity If lead, for example could be sufficiently purified it would become gold They also appeared to draw no sharp distinction between animate and inanimate matter To them all kinds of matter were forms of the one thin^ and If a plant or an animal could slowly grow or be cultivated towards perfection, they saw no L s o n why a^base metal.should not be made to evolve into a nrble

In alchemical writings we meet with frequent refer ences to the Philosopher's Stone—a mvtbi.ni ? • that would enable t'he alchemi:t t o T ^ ^ f S f H " ^ gold. Whether they thought of it as aTa^ual /o^e s a liqmd, or simply as a recipe, is hard to sav n l T I some clauned to have seen it and touched j ' ' V l V^h a seventeenth-century alchemist, describes in hisTook

ALCHEMY—CHEMISTRY OF THE MIDDLE AGES 17 The Golde?i Calf, how he received a visit from a mysterious individual who showed him three large pieces of a substance resembling glass. Here, said the visitor, was sufficient of the Philosopher's Stone to produce twenty tons of gold. To repeated requests for a proof of his powers the visitor gave evasive answers, but at length was prevailed upon to leave with Helvetius a small piece of the stone, no larger than a grain of rape-seed. With the help of his wife, Helvetius enveloped the stone in wax and cast it into a crucible containing six drachms of molten lead. He states that there was a hissing sound, and that after a quarter of an hour he found that the whole mass of lead had turned into the finest gold, which passed all the tests applied to it by a neighbouring goldsmith. No more was heard of the mysterious visitor, and Helvetius was left in ignorance of the constitution of the magic substance.

The quest for the Philosopher's Stone appears to have continued right through the Middle Ages, generation after generation of alchemists passing their lives in the vain search.

In every case the hope with which each worker started his quest must eventually have given way to discouragement and despair, yet always there were others to take up the problem.

We may wonder why the hopeless nature of the task did not sooner become apparent, but we must remember that the alchemists of one generation probably knew little of the work of their predecessors, or even of their contemporaries. Many of them, like Helvetius, no doubt thought that the problem had really been solved by earlier workers and the secret lost or concealed.

Although alchemy failed in its main objects, yet the

i8 ALCHEMY—CHEMISTRY OF THE MIDDLE AGES alchemists made many notable contributions to learning. Fire was their chief ally, for by its aid they imagined it to be possible to 'draw out the soul of a metal'. They heated all manner of substances, noting the changes produced, and here and there stumbled on methods of producing new substances. They invented and used many kinds of apparatus which in a modified form are still used in modern laboratories. The water-baths, distilling vessels, condensing worms and receivers of the modern chemist had their counterpart in the cruder implements made by the alchemists.

The library of Leyden contains manuscripts purporting to be the writings of one Geber, an Arabian alchemist of the eighth century. They contain instructions for the preparation of many metals, acids, and salts, also details for distillation and the preparation of oils and essences.

From the twelfth century onwards alchemy flourished amid the ignorance and superstition of the general mass of mankind, and not unnaturally became associated in the popular mind with magic and the black art.

The chances for deception and fraud were many, and numbers of self-styled alchemists were no better than charlatans and swmdlers. They boasted of powers they did not possess and waxed fat on the credulity of mankind.

When one thinks how, even in these more enlightened days, people are willing to believe in quack remedies and widely advertised nostrums, it is not hard to understand that the spurious alchemist of the Dark Ages was able to foist upon his clients all manner of useless concoctions. The ailing man could buy from him medicines reputed to cure all ills, and to the amorous but bashful swain he would sell a love philtre guaranteed

ALCHEMY—CHEMISTRY OF THE MIDDLE AGES 19 to touch the heart of the coldest and most disdainful maiden.

Many a member of the nobility, in his greed for power, would take an alchemist into his service, in the hope of profiting by the adept's assumed power to manufacture unlimited gold. Failure on the part of the alchemist to fulfil his obligations resulted sometimes in death or imprisonment; and no doubt the attempt to retain the confidence of a patron who impatiently awaited results imposed a severe strain on the inventive powers of many an alchemist.

Here and there, among the numbers of dishonest and mercenary practitioners, we find records of a worker who was either wholly or partly a true seeker of knowledge. It is to these men that we owe the discoveries that have laid the foundations of modern chemistry. Near Ilchester was born, in 1214, Roger Bacon, whose name is commonly associated with the invention of gunpowder. Bacon became a friar and was one of the most learned men of his time. He was a firm believer in the transmutation of metals, is said to have invented the magnifying glass, and certainly knew something of the properties of many chemical compounds. In one of his books he describes how he made thunder and lightning by mixing together saltpetre, charcoal, and sulphur. These are, of course, the ingredients of gunpowder, which was first used by an English army in 1327. It is probable that he was not, in fact, the first inventor of gunpowder, but had heard of it during his travels in the East.

In later life he was imprisoned as a magician, and only saved his life by recanting his opinions with regard to the transmutation of metals.

His friend and pupil, Raymond Lully, is said to have

20 ALCHEMY—CHEMISTRY OF THE MIDDLE AGES taken up the study of alchemy in the hope of finding a cure for cancer, he having fallen in love with a lady who was suffering from cancer of the breast. Many writings on alchemy are attributed to LuUy, and he is reputed to have been provided by Edward I with a room in the Tower of London, where he made sufficient gold to fill the depleted coffers of the king.

An analysis of gold coins of the time of Edward I shows them to be of pure and not spurious gold, and it is suggested that the royal revenues owed more to Lully's advice on taxation than to his alchemy.

During the next few hundred years there were many rumours of the finding of the Philosopher's Stone, and alchemy, though looked upon with suspicion as being linked with the powers of darkness, had many followers. The English government of the fifteenth century, fearful of the effects of successful transmutation, passed a law making it a penal offence to manufacture gold from other metals. The chief effect of this was to make the practice of alchemy a still more secret art, and it is possible that on this account the progress of science was delayed, accidental discoveries of scientific value being concealed instead of being brought to light.

Early in the sbcteenth century a remarkable personage appeared in the ranks of the alchemists of Europe. This was Philippus Aureolus Theophrastus Paracelsus Bom-bastes von Hohenhcim, more generally known as Paracelsus, Born in 1493, the son of a Swiss physician, Paracelsus studied for a time at the University of Basle, but becoming embroiled with the authorities, left the university and wandered about Europe, picking up fragments of science and supporting himself by quack doctoring, fortune telling, and the like. Vain, blatant, self-opinionated, and of coarse and dissipated habits, he

ALCHEMY—CHEMISTRY OF THE MIDDLE AGES 21 appears to have got into trouble wherever he went. Yet in some extraordinary way he achieved a reputation as a worker of miraculous cures. Such an ascendancy did he gain over the minds of his contemporaries that in 1526 he returned to Basle and was appointed Professor of Medicine.

Here his overbearing manner and bombastic utterances disgusted his students, for he ruthlessly declared that existing medical practice was all wrong and that only he, Paracelsus, could teach the truth.

Working on the kill-or-cure principle, he boldly used dangerous medicines made from opium, lead, antimony, and mercury, and was sufficient of a showman to make sure that his cures were noised abroad and his failures concealed. He was undoubtedly a genius, but a drunken and vainglorious one.

The one debt we owe to Paracelsus is that he loudly and effectively rebuked the alchemists for seeldng to make gold when they should be spending their time in the preparation of drugs and medicines. We have no proof that he himself made any useful discoveries; more probably he collected and exploited the discoveries of others. He thought, like others before him, that all things were made of three elements—mercury, sulphur, and salt. The alkahest, or universal solvent, he considered to be a sovereign remedy for a sluggish liver. Unfortunately he has left us no directions for making this wonderful solvent.

Paracelsus was acquainted with many chemical preparations. He knew, for example, that when oil of vitriol was poured upon iron filings an inflammable gas was given off. The chemist of to-day prepares the same' gas and calls it hydrogen. He divided the substances he knew into two classes—^metals, which were ductile and

22 ALCHEMY—CHEMISTRY OF THE MIDDLE AGES malleable, and non-metals, which were not. Many of the medicines he used were compounds of metals, although he used a number of vegetable extracts as well.

Whatever we may think of the character and morals of Paracelsus, there is no doubt that he started a new era, both in chemistry and medicine. From now on, these two sciences walked hand in hand, chemistry as the handmaiden of medicine.

The reign of Paracelsus at Basle was short. His intemperance, his truculent nature, and his greed with regard to fees, embroiled him with the magistrates, and caused him to leave the town and commence once more his wandering habits. In later life he claimed to have discovered the Elixir of Life, but in spite of this he died of a fever at the early age of forty-eight.

Although alchemy had now received an impetus in a new direction, yet charlatanry was rife, and many were the impostors who professed to have discovered the secret of making gold. They imposed on a credulous public with such crude devices as gilded lead and poUshed brass. The more cunning used bars of lead with a small block of gold mside. On the metal being melted in a crucible the gold separated and gave the impression of a complete transmutation. In other cases gold-was concealed in hollowed-out sticks of charcoal and the charcoal burned in suitable receptacles.

The beUef in transmutation was not confined to the Middle Ages. Late in the eighteenth century, Dr. James Price, of Guildford, a Fellow of the Royal Society, published a statement that he had effected the change, and even exhibited gold said to have been made by his method. The Royal Society, jealous of its great reputation, msisted on Dr. Price giving proof of his powers

ALCHEMY—CHEiMISTRY OF THE MIDDLE AGES 23 to a committee of members. After vain attempts to extricate himself from his dilemma. Price agreed to receive the members at his house, where, after confessing his inability to make gold, he dramatically committed suicide in their presence.

CHAPTER II

THE BIRTH OF CHEMISTRY

IN the previous chapter we saw how the very beginnings of chemistry were an outgromh from the study of medicine, but from the early seventeenth century chemistry began to be studied for its own sake and during that century became definitely a distinct science. It will not be possible in a book of this size to trace all the history of its growth, for further information on which subject the reader should consult one of the numerous books on the history of chemistiy. It must suffice to show something of the influence exerted by a few of the better known early scientists, such as ^acon, Boyle, Priestley, Cavendish, Lavoisier, and Ualton These are but a few of the famous names that might be mentioned, the difficulty being to know what names to leave out, for, at any rate since the eighteenth century, the spread of the science has been so rapid Aat It would be difficult to follow it in strictly chrono-ogical order, much less to mention all who contributed

their quota.

vlr^^^^ ^ ' u ? ' , ^^'^°^^^ St. Albans, who in the InL ^ P^bi .shed his Novtm Orgamim, first laid down a plan which is what we might call the modern

^ n t r l"" ' '^?^- ^ ^ ' ° ^ ^^^ ^ ° t ' o "^^ch an experi-TonlH^ ' f f f ^ " ^ ^^^° ^o^ld see what others r ^ r . ^ ° ' u"^:. ^" '^^^cnh^d himself as an architect ra her than a builder, and, as he said, he 'rang a bell to call other wits together'. He insisted that a scientific investigation to have any hope of success must follow certain Imes which he laid down. We cannot do better than note, briefly, what those lines were:

THE BIRTH OF CHEMISTRY 25

1. The collection of all knoAvn facts relevant to the matter.

2. Imagining the underlying 'causes' and framing a statement covering the known facts.

3. Considering what additional facts are implicit in the statement.

4. Experimenting to see whether these facts can be confirmed.

5. Any statement which passes the test of 3 and 4 can be regarded as helpful—at least temporarily.

These steps are precisely those taken by scientists of to-day; the second is called theorizing, or making a hypothesis, and when a hypothesis, theory, or supposition has been sufficiently tested it is accepted as proven. The method represents the new spirit introduced into science by Francis Bacon, sometime Lord Chancellor of England, more widely known for his famous Essays. In the book already mentioned, he points out how, hitherto, knowledge had been sought by adding uncertain experience to fogged reasoning, and adding them, moreover, in the wrong order. The new method he proposed was an alternation of experiment with induction (or, as we might say, 'controlled guessing').

One of the earliest scientists to follow the Baconian method was Robert Boyle, born in 1627, a younger son of the Earl of Cork. He was a member of that band of scientists who called themselves the 'philosophical college', which, as it had no regular meeting-place in its earliest days, some of the wits of the time called the 'invisible college'. Whether visible or invisible, it was probably as important a band of men as any who ever gathered together either in this or any other country, for out of their meetings grew 'The Royal Society for the Improvement of Natural Knowledge',

26 THE BIRTH OF CHEMISTRY

which Society was incorporated by Royal Charter on the 15th July 1662. Thus Boyle was one of its foimders, along with such famous men as Hooke, Christopher Wren, Petty, Lord Brouncker, and Sir Robert Moray. Lord Brouncker was the first President, and the motto of the Society Nullius in Verba was chosen by John Evelyn. Samuel Pepys became a Fellow shortly after the incorporation, and describes in his diary his admission to membership.

'To Gresham College, where I had been by Mr. Povey the last week proposed to be a member, and was this day admitted, by signing a book and being taken by the hand of the President, my Lord Brouncker, and some words of admittance said to me. . . . Above all, Mr. Boyle was at the meeting and above him Mr. Hooke, who is the most, and promises the least, of any man in the world that ever I saw. Here excellent discourse till ten at night and then home.'

There are many references to the Royal Society in the famous diary, Pepys deriving great pleasure and instruction from the meetings, especially when he was one of the Council. Thus we read (22nd June 1668):

'Thence to my Lord Brouncker's, where a Council of the Royal Society; and there heard Mr. Harry Howard's noble offers about ground for our College, and his intentions of building his own house there most nobly. My business was to meet Mr. Boyle, which I did, and discoursed about my eyes; and he did give me the best advice he could.'

Boyle's most famous book, TJie Sceptical Chyjnist, appeared in 1661, and did much to clear the ground by disproving many of the current ideas, in particular, those relating to what constituted an element. He was able, also, to distinguish clearly between such things as chemical compounds and mechanical mixtures. On the whole, however, his work was destructive rather

THE BIRTH OF CHEAHSTRY 27

than constructive, but this was necessary at the tirne, as so many strange ideas, having no foimdation in fact, were current. He is probably best remembered for his famous experiments on 'The spring of air', for any one who has ever studied elementary science has heard of Boyle's Law. Boyle, then, was one of the first scientists to apply the principles laid down by Bacon to the study of chemistry, and he is, indeed, often called the 'Father of Chemistry'. He and his contemporary Fellows of the Royal Society began the search for knowledge by the new methods, establishing chemistry as an experimental science. A large number of the discoveries of this time were duly reported at meetings of the Royal Society, and detailed accounts were printed in the journal Imovra as the Philosophical Journal. This journal was at first printed privately by the secretary and sold to the Fellows, and contained also scientific news collected from all quarters. It filled much the same place as does Nature to-day.

Chemistry, as the result of the work of the early Fellows of the Royal Society, following the Baconian method, became firmly established as an experimental science, as something worthy of study for its own sake and no longer as a branch of medicine. There followed a period of about one hundred years during which loiowledge of the composition and behaviour of many substances was accumulating, awaiting the advent of some scientist able to summarize the facts learnt and draw general conclusions from them. It is worth while to look at some of the work accomplished during this period even though it may appear somewhat disconnected.

The branch of chemistry which received the most attention dealt with the nature of fire and combustion,


and here progress was for a time delayed by the wide credence given to a theory put forward on insufficient evidence by Johann Joachim Becher, the son of a German Lutheran minister. Becher had such a reputation that his theory, especially when ardently supported by his follower, Stahl, who had made rather a name for himself, was able to command respect. Briefly, to explain all kinds of combustion he assumed that all combustibles contained a proportion of some kind of 'fatty earth', for which the name 'phlogiston' was proposed, and that when they burnt they parted with phlogiston into the surrounding air. Thus, any kind of 'air' which encouraged burning was regarded as deficient in phlogiston, or 'dephlogisticated', while a gas which tended to prevent burning did so because it was already 'phlogisticated'. This was a very ingenious theory, and those who believed in it seem to have been so certain of its truth that they scorned all idea of testing it by experiment; indeed, when experiment appeared to show its impossibility they fell back on the most ingenious explanations rather than admit it to be false. As an example may be quoted the experiments conducted on the calcination of metals, chiefly by Jean Rey in France, van Helmont in Holland, and Mayow in England. They showed that air was necessary to combustion, and that the products of combustion (at least in the case of metals) weighed more than the material burnt, the only reasonable explanation of which was that something was absorbed from the air during burning; whereas the phlogistonists maintained that the air absorbed phlogiston which the material lost. The phlogistonists either denied the evidence of the balance, or tried to explain it away by asserting that phlogiston was 'the principle of levity'.


The phlogistic theory is an excellent example of the danger of forming a theory on insufficient evidence, and it also shows the value of theories in general, for this theory, though quite wrong and misleading, nevertheless so stimulated research as to do as much good as harm. We should also learn from it the necessity for abandoning, or at least modifymg, a theory when experiment shows it to be a mistaken explanation.

Joseph Priestley was bom in the West Riding of Yorkshire in 1733, and his family intended him to be a Calvinistic minister. This he became, but some of his views on the subjects of original sin and eternal punishment proving unorthodox, he found it difficult to remain long in one place, and, indeed, suffered great hardship in his early life because he could obtain no well-paid pastorate. At one time he had to eke out a stipend °f £3^ per annum by teaching in school from seven till four, and giving private tuition from four till seven in the evening. At this time he was a master of six foreign languages, though little over twenty years old. How he must have worked! In spite of this, he set himself, in his spare time, to write a history of the subject of electricity, as to which he said: *I was led, in the course of my writing this history, to endeavour to ascertain several facts which were disputed, and this led me by degrees into a larger field of original experiments in which I spared no expense that I could possibly furnish.' He made very many experiments with 'airs' (we should eall them gases), and discovered that carbonic acid gas can be dissolved in water. As he related, he made a glass of exceedingly pleasant sparkling water which

could hardly be distinguished from Seltzer water'. The Royal Society was very interested, and he was asked to repeat his experiments before the members of the


College of Physicians, who were so impressed that they recommended the discovery to the Lords of the Admiralty as a possible cure for scurvy in the Navy. Priestley was awarded the gold medal of the Royal Society for his discovery.

He became very expert in preparing and handling gases, and made use whenever possible of the pneumatic trough which then was but newly invented. To him belongs the credit of varying the usual method of using this apparatus by substituting quicksilver for water, whereby he successfully collected some new gases which had previously escaped notice because they dissolved in the water generally used in the trough. These included sulphur dioxide, ammonia, nitric oxide, and hydrochloric acid gas.

In his later days Priestley was in better case financially, and in the year 1775 he was acting as librarian and literary companion to Lord Shelburne, with whom he travelled much. The previous year he had been presented by some admirers with a large lens one foot in diameter, and with this 'burning glass' he had heated many substances under conditions that would otherwise have made heating difficult, even if possible. Among them was the red calx of mercuiy, from which he obtained a gas that so encouraged the burning of a candle that Priestley called it 'dephlogisticated air'. Priestley himself was astonished at this, and when he began the experiment had no idea at all as to what might happen. He himself said that it was quite by accident that a lighted candle stood by him, and that it was then the idea came into his head to see what effect the gas had on the candle flame. He was a phlogistonist, and therefore so befuddled that he quite failed to realize the importance of his discovery. In the

THE BIRTH OF CHEMISTRY 31 next year, when in Paris, he visited Lavoisier and told him of his experiment. Lavoisier immediately appreciated the importance of this chance discovery; indeed, it was the last bit of evidence he needed to disprove the phlogistic theory. The new gas was oxygen, the presence of which is necessary for combustion. Priestley, the discoverer of the gas, still failed to appreciate it, and remained a believer in phlogiston! We must, indeed, say that Priestley, though a prodigious and enthusiastic worker, 'muddled along'.

At this time, too, there were not wanting many who thought it wicked for a minister of religion to dabble in science and politics. Priestley was interested in politics too, and was so unwise as to make public utterance of sentiments favouring the revolutionaries in France. For these offences a mob broke into his house, smashed his apparatus and set fire to the wreckage, Priestley escaping with his life. He emigrated to America in April 1794, 3nd lived out his remaining years there honoured by all and doing much further good work till he died in 1804. He dictated his last notes from his death-bed, and only ceased within a half-hour of his death.

Henry Cavendish, who was born in 1731, was the most eccentric and, at the same time, the most brilliant scientist of his time. Coming of a wealthy and powerful family, he was expected to take his place in public life, but preferred instead the life of a recluse, mixing only with fellow scientists, and apparently taking pleasure in their society only in so far as was necessary for discussion of scientific progress. It is related that at one time he had over a million pounds on deposit at the Bank of England, but was so little interested in his wealth that he never was known to possess more than one suit of clothes at a time; and when the bankers tried


to persuade him to invest his money he became so annoyed at the way his work was .interrupted that he threatened to withdraw all of it if they did not leave him in peace! This must surely be a case without parallel.

Cavendish was extremely methodical in all he did. He seldom varied his daily routine, and never even took down a book from his own library shelves without solemnly entering his name in the loan-book which he kept.

He made many experiments with the gas he obtained by dissolving metals in acids—the gas we know as hydrogen—as a result of which he was able to show that water, so far from being an element, as was commonly believed, was a compound substance formed by the combination of hydrogen with oxygen (in the language of the period, 'dephlogisticated air united with phlogiston'). With wonderful accuracy he demonstrated the proportions in which the two gases would combine. He mixed 500,000-grain measures of hydrogen and 1,250,000-grain measures of common air, and after burning slowly, collected and condensed 'upwards of 135 grains of water'. Cavendish went farther, and, appreciating the fact that only a part of the common air (the oxygen) combined with the hydrogen, calculated how much of the air (the nitrogen) must remain unused. He was able to demonstrate that this amount of gas did remain unchanged; and then be repeated the whole experiment using pure hydrogen and pure oxygen. This time he burnt the gases in a glass globe (still preserved in the University of Manchester), and proved conclusively that two measures of hydrogen combined with one measure of oxygen to form pure water, which was equal in weight to the combined gases.


As an experimenter Cavendish was superb. To him science was measurement. He developed a method of analysing air, and examined hundreds of samples obtained from all possible sources. In the course of his analyses, in which he measured the amoimt of oxygen by adding pure hydrogen and exploding the mixture, he noted, as had also Priestley, Lavoisier, and others, that a small amount of an acid substance always appeared. Cavendish was not the man to pass over such an observation without attempting to find the reason. He found it in the fact that the electric spark caused small amounts of the nitrogen of the air to combine with the oxygen. He went very fully into this, and modem methods of fixing atmospheric nitrogen for use as artificial manures are developments from his experiments. Another fact that he noted was that there was present in the air something, amounting to about one per cent, of it, which resembled nitrogen but could not be induced to combine with oxygen. This observation was the starting-point of the brilliant work accomplished over a century later by Lord Rayleigh and Sir William Ramsay, as a result of which the so-called Noble Gases were isolated from the air. These gases include argon, helium, and neon, all of which are now articles of commerce.

Cavendish never married—he was too shy even to look at a woman and never willingly put himself into a position where he would be obliged to notice one. His housekeeper -communicated with him always in writing, and his other female servants were careful to keep out of his way, well knowing they risked dismissal if he caught sight of them. Although such a misanthrope. Cavendish was no niggard. It is said that once, when his librarian had fallen ill and he was asked for


financial help, he at once gave ten thousand pounds and asked if it would do! Since one hundred would have been ample, no doubt the recipient was very gratified.

Cavendish lived to be nearly eighty, when he returned one evening from a meeting of the Royal Society feeling ill. He called a manservant to him and gave detailed instructions of what must be done when he was dead, but cautioned the man to do nothing till his death occurred. This took place the same evening, and thus passed peacefully one of the world's greatest scientists. His name is commemorated in the Cavendish Research Laboratory at Cambridge.

In 1794 there perished at the guillotine in Paris Antoine Lavoisier, then at the comparatively early age of fifty-three. At the time of his arrest Lavoisier was engaged on a series of experiments on respiration and perspiration, his young wife, Marie Anne, acting as secretary. He had married when he was twenty-six, his wife being but fourteen years old, but it seems to have been a very happy marriage, for Madame Lavoisier never exhibited towards her first husband any of those violent tempers with which her second husband. Count Rumford, had to contend. Madame Lavoisier learnt English and Latin in order to help her husband, and as she had a talent for drawing, she made all the diagrams and sketches needed for his memoirs on scientific subjects.

Lavoisier appears to have been a very precocious youth, and his family having considerable means, he had the best education possible, his mind developing so rapidly that he was elected to the Academic at the early age of twenty-five. From this time his services were continually being requested by the government, and he occupied many important positions, such as secretary

THE BIRTH OF CHEMISTRY 35 to the Board of Agriculture, as well as being engaged with such schemes as the founding of savings-banks, workhouses, and insurance societies. He was also a *Fermier-g6nerar, and as such had been concerned with the imposition and collection of taxes; and this it was that led to his arrest, he being charged, among other things, with having added water to the soldiers' tobacco, and appropriating revenue which belonged to the State. He was tried before Coffinhal, President of the Tribunal, who sentenced him to be beheaded, remarking: 'The Republic has no need for savants.' The comment of the great mathematician Lagrange, then living in Paris, was: 'It took but a moment to cut off that head, though a hundred years will be required to produce another like it.'

Lavoisier it was who finally upset the phlogistic theory of combustion, for he was able to show that the *de-phlogisticated air', of which Priestley had told him, was that portion of the atmosphere that played a part in all processes of combustion and respiration. He also noted the formation of acidic oxides from sulphur, carbon, and phosphorus, and hence concluded, wrongly as we now know, that 'dephlogisticated air' was the acidifying principle. To indicate this he suggested it be called oxygen (a word derived from the Greek and signifying 'acid producer'). This was in the year 1778, four years after Priestley, visiting him, had told him of the remarkable gas he had made. Lavoisier's explanation of combustion was not readily accepted, and until he produced evidence of the composition of water some four or five years later there were many who looked scornfully at his theory. He heard from Blagden, who had been Cavendish's secretary, of the latter's experiments on water, and so was able to repeat some of them before they had


been announced to the Royal Society. Cavendish was never one to rush to pubUcation when he made a discovery, and in this instance he delayed communication of his experiments till he had inquired further into the question of what caused the presence of traces of acid when hydrogen was exploded with air. Thus Lavoisier was thought by many to have discovered the facts about water, and, anxious to have the credit for the discovery, he refrained from giving any hint of Blagden's communication, while Cavendish on his part cared little who had the credit so long as the facts were established.

Lavoisier was one of the first to try to put chemical language on a reasonable basis, to make it generally understandable, and to clear away the fog of mystery in which all scientific writing was wrapped. In collaboration with de Morveau, Berthollet, and Fourcroy, a new system of simplified nomenclature was worked out and eventually adopted, though, like most new ideas, not without opposition. De Morveau was a lawyer who found it impossible to understand scientific writings, and he so impressed Lavoisier that he invited him to join in working out the new system. Berthollet was personal instructor in chemistry to Napoleon; Fourcroy was another contemporary chemist. This new system was laid before the French Academy in April 1787, and t vo years later appeared Lavoisier's Traite eUmmtaire de chtfnie~the herald to the world of the new, antiphlogistic doctrine, and of the new nomenclature.

In his last days Lavoisier was engaged in analysing substances of animal and vegetable origin, noting that when burnt they all yielded carbonic acid gas and water; from which he inferred, quite correctly, that carbon and hydrogen were invariably constituents of such

THE BIRTH OF CHEMISTRY 37 substances. He began to work out a method of finding the composition of such substances by weighing the gases which were formed during combustion, but it remained for Liebig, the famous German chemist, to develop this process of analysis. Liebig's method is still used with very little change in the apparatus he devised.

At the close of the eighteenth century chemistry had reached a critical point. There had been collected a mass of new facts, out of which certain of Nature's laws began to emerge. For instance, owing very largely to the quantitative work of Berthollet and Lavoisier, it was increasingly clear that chemical changes were only changes, and that no new matter was formed—everything resulting from the experiments was there at the begiiming. This is now summed up as the Law of the Conservation of Matter. Another tiling beginning to be clear was that the composition of a pure substance never varied; but this was not readily accepted by all, owing to the difficulties of analysis and the doubts as to the purity of the substances analysed. Nowadays it is accepted as almost self-evident and summarized in the Law of Constant Composition. Still another thing which had been established was that those substances formerly thought of as elements (e.g. air and water) were not really simple substances, and that the number of elements was far greater than was believed, say, in Boyle's time.

The time was ripe for the next step—some theory which should explain the estabhshed facts and lead to new investigations. In 1766 there had been born in Cumberland John Dalton, the son of a weaver who had five other children. John Dalton, then, came of a poor family, and received most of his early education from his father and at the Quaker school near his home. At

38 THE BIRTH OF CHEMISTRY the age of twelve he began to teach to supplement the family income, and continued teaching till, when twenty-seven years old, he moved to Manchester to be the teacher of mathematics and philosophy at the new college.

Dalton appears to have read widely, and he was familiar with Lavoisier's Traite elenientaire de chimie. His own great study was the atmosphere, and he kept records of atmospheric conditions day by day for nearly fifty years. He knew that the air contained a number of gases, while those qualified to analyse it assured him that its composition varied only very slightly from place to place. Even samples taken in balloons at heights of 20,000 feet were found to contain almost the same small amount of the heavy carbonic acid gas as samples taken at the ground level. Dalton was very puzzled, and knowing himself to be but an indifferent experimenter, he realized that no experiment he could perform would be likely to help him to explain these facts. He therefore tried to imagine what the structure of gases must be, in order to explain this universal diffusion. Now throughout history philosophers had pictured matter, somewhat vaguely, as bcmg made up of atoms, a word which signifies something so small that it cannot be subdivided. Dalton believed that atoms did exist, and, in fact, if that were so, he could picture them having properties which would explain some of the facts. He developed the idea and produced what is known as Dalton's Atomic Theory, which he first mentioned, though only in outline, in lectures at the Royal Institution in 1803. Further details appeared (in 1808) in the System of Chemistry written by his friend Thomson, who may be said to have drawn attention to the theory.


The atomic theory may be summarized as follows: The elements consist of atoms, which for a given element are all alike, especially in weight. Atoms of different elements have different weights. Compounds are formed by the joining of atoms in definite proportions, as for example,

One atom of A with one atom of B or ,, „ „ two atoms of C or ,, B ,, ,, C, &c.

Dumas once said that theories are 'the crutches of science, to be tlirown away at the proper time'. Dalton's theory has proved so useful that it has never been necessary to 'throw it away'; indeed it has been sufficient merely to modify it in detail. With the optical instruments available in Dalton's time, it was quite impossible to see anything so small as an atom, but he may have hoped that in the future some one would be able to produce visible evidence of the atom's existence. We know now that even with our much improved instruments this will never be possible, for atoms are too small to have any visible action on those light rays that the human eye can perceive. There is a limit to the size of particle that can be seen, and this limit is imposed by the wavelength of the light, and has nothing to do with the degree of magnification of the microscope. Nevertheless, all the accumulated evidence goes to prove that atoms are real units; their size and actual weight have been measured indirectly, but with a fair degree of accuracy, as well as the relative weights of the various kinds of atoms. The importance of the atomic theory in chemistry is that by its aid we are able to picture what goes on in chemical changes, whether in changes leading to the production of simpler substances from compounds, or

40 THE BIRTH OF CHEMISTRY . the reverse. It enables us, in fact, to see just what we have to do to form any given molecule; how much of each substance will be required; how much of the required substance can be formed under perfect conditions, and so on. It does for chemistry what accountancy does for business.

We owe this to John Dalton, who, it is pleasant to record, Hved long enough to see his theory generally accepted and used. He lived till 1844, and like Priestley and Cavendish, died very peacefully and quickly, being able to continue his work in Manchester till within a very few hours of his death.

To commemorate his work a public subscription raised money to provide a research scholarship at Owens College, and one of the first holders of the scholarship was Joseph John Thomson, who afterwards moved to Cambridge, where he succeeded Lord Rayleigh as head of the Cavendish Laboratory. J. J. Thomson, more than any other man, has shown the way to the study of the individual atom, most of our present knowledge of which we owe to him or to his former assistants.

CHAPTER III

CHEMISTRY AND NATURE

T H E supreme importance of air and water to all living things was recognized by the thinkers of ancient times, who vaguely spoke of these, substances as two of the primal elements.

Although to us they are no longer elements, air being a mixture of gases and water a simple compound, their importance in the scheme of nature is more evident than ever. Both are intimately associated with vital processes and with the slow changes that are taking place in the contours of the earth's surface.

The principal constituents of the atmosphere are nitrogen, which forms nearly four-fifths of the bulk of dry air, and oxygen, which forms about one-fifth. Nitrogen as an element has few remarkable properties, and shows little desire to combine with other elements, and on this account its role in the atmosphere may appear to be a passive one. To a large extent this is so, for the nitrogen of the air plays no direct part in such processes as burning, breathing, and decay. But although nitrogen as an element has no very striking properties, yet compounds of nitrogen are in many cases of supreme importance.

The element is an essential constituent of all animal and vegetable bodies and of all fertile soils. Many dyes, scents, explosives, poisons, drugs, and foodstuffs are compounds of nitrogen. As will be seen in the next chapter, even the nitrogen of the air cannot be regarded as completely inactive, for under the influence of certain soil bacteria a small proportion combines with other elements to form compounds of value to plants.

42 CHEMISTRY AND NATURE

There are, however, small amounts of other gases in the atmosphere which are chemically inert and form no compounds whatsoever. The first of these is argon, which forms more than one per cent, of air. This gas finds its chief industrial use in the manufacture of gas-filled electric lamps, the inert gas showing no tendency

- Other Qascs. FIG. I. The composition of the air

to shorten the life of the white-hot filament by combining with it.

Helium, the non-inflammable gas used in America for filling airships, is another of the inert gases of the atmosphere, although existing in very small quantities. Its name (Gr. helios = sun) is a constant reminder of the romantic nature of its discovery. In 1868 the spectroscope revealed the presence in the sun of an element unknown on the earth. Only after the discovery of argon by Rayleigh and Ramsay in 1894 was i* found that the element helium existed on the earth, associated with a rare mineral known as cleveite. Shortly afterwards Ramsay found that small quantities of helium were also present in air. Since in this country the atmosphere is

CHEMISTRY AND NATURE 43 the only source of helium, it is not possible to obtain it in quantities sufficient for the filling of balloons and airships, but in Canada and the United States the gas is obtained in moderate quantities from certain hot springs. Helium has not the lifting power of hydrogen as it is twice as dense, but the fact that it does not leak so easily through balloon fabric, and above all, its non-inflammable property, make it a very desirable substitute.

One other inert gas is worthy of consideration. This is neo7i, which forms about one hundred-thousandth part of air, and is used in the manufacture of the well-known neon light tubes.

Ordinarily, a dry gas offers a great resistance to the passage of an electric discharge, and an extremely high voltage is necessary before there is any passage of electricity between two electrodes even if these are only a few inches apart, the discharge being then in the form of sparks similar to lightning flashes. If, however, the electrodes are enclosed in a sealed glass tube from which most of the air or other gas has been pumped, the passage of electricity tends to become continuous, the whole of the tube being filled with a glow of light, the colour of which depends partly on the nature of the small amount of gas left in the tube. Neon has proved to be a suitable gas for use in such a tube when certain types of illumination are desired, and its orange-red glow is now a familiar sight in street signs and aerodrome landing-lights. Other colours are produced by the use of other gases than neon or by using coloured glass for the tube. An argon-filled tube gives a pale violet light, helium ivory white, and mercury vapour blue. This type of lighting is usually spoken of as neon lighting whether neon is used or not.

The atmosphere contains, in addition to argon,


helium, and neon, two other inert gases, krypton and xenon, but in such minute quantities as to be useless for any industrial application.

A more active gaseous constituent of the atmosphere is oxygen, which forms about one-fifth of the bulk of dry air. The outstanding property of oxygen is its readiness to combine with other substances to form oxides. Burning is an example of rapid oxidation, the substances formed by the combustion of coal, wood, oil, and gas being, in general, oxides of the elements present in the fuel.

The rusting of iron is another form of oxidation, the red or brown rust being chiefly, though not entirely, composed of oxides of iron.

Oxygen plays an important part in the breathing of men and animals. Like nearly all other important machines, the animal machine obtains its energy by the burning of fuel, the fuel in this particular case being the food eaten.

The food first of all goes to build up various kinds of body tissue, and some of this tissue undergoes combustion. Hydrogen and carbon are two of the elements of which flesh is made, and the oxides of these elements, namely, water and carbon dioxide, are products of the combustion, and are exhaled from the lungs.

Of chief interest to us here is the carbon *;'dioxide delivered to the air as a result of breathing. Some account of the manner of its formation and its many functions in the atmosphere may be of interest.

In the breathing process the oxygen necessary for combustion is taken into the lungs with each inspiration and is carried by the blood to all parts of the body. Similarly, the carbon dioxide formed by the union of this oxygen with the carbon of the body tissues is

ANIMALS BREATHE OXYGEN

OXYGEN COMBINES WITH CARBON OF ANIMAL BODY ->• CARBON DIOXIDE

BREATHED OUT

OXYGEN GIVEN OFF,

FIG. 2. The oxygen cycle (from The Young Observers)

46 CHEMISTRY AND NATURE carried back by the blood to the lungs and eventually breathed out with the air.

The amount of oxygen required by a man varies with the call he makes on his muscles for the supply of energy. Thus a man engaged in manual work may need

WI/XD PIPE OR TRACMEA

R INGS OF BRONCHUS ^ CARTILAQE

AIR P I P E S

is %' A I R S A C S

FIG. 3

about a gallon of oxygen a minute, while at rest less than half this quantity would suffice.

In ordinary breathing the limgs are neither filled to their greatest capacity nor completely emptied with each breath. During easy natural respiration the lungs, of a normal man contain about five pints of air. With each breath rather less than a pint of air is taken in, mixes with the air already in the lungs, and then rather less than a pint of the mixture is exhaled. It is, however, possible, by breathing deeply, to take in an extra three pints of air, so that the lungs may contain nearly nine pints. Then, by breathing out to the fullest extent, about seven pints of this air can be expired, leaving only two pints in the almost deflated lungs.

The amount of carbon dioxide in exhaled air is

CHEMISTRY AND NATURE 47

normally about four or five per cent., although this proportion naturally varies both with the amount of carbon dioxide being delivered by the blood to the lungs, and with the rate and depth of breathing.

Continual deep breathing at a time when most of the

TMO

TRACHEA o« W I N D P I P E

THORAX

FIG. 4. Chest contracted Chest expanded

muscles are at rest and not producing much carbon dioxide will lower the carbon dioxide content of the air in the lungs and consequently of the expired air if deep breathing is continued. The natural result, however, of deep breathing while at rest is that the muscles concerned with involuntary respiration temporarily cease work, and so it becomes possible to hold the breath for some time. This explains why long-distance plungers and others who require to hold the breath for a long time preface their efforts by deep-breathing exercises.

The air receives a steady supply of carbon dioxide from sources other than the respiration of animals. All fuels in common use contain carbon, and on combustion add their quota of carbon dioxide to the atmosphere.

48 CHEMISTRY AND NATURE The gas is also a product of the decay of animal and vegetable remains, and on this account is present in all fertile soils. In certain areas it issues from cracks and fissures in the ground, and in some of these places the heavy gas, accumulating in hollows, forms a suffocating atmosphere, for carbon dioxide, although not particularly poisonous, is unable to support combustion and so is useless for respiration. In the Grotto del Cane, near Naples, where the gas lies in a layer two to three feet thick, dogs and other small animals are quicldy overcome, although there is no danger for a man unless he lies down.

Ordinary air contains about three parts of carbon dioxide in ten thousand, not a very large proportion, considering the constant supply produced by such processes as burning, breathing, and decay. The surprising thing is that the proportion shows very little variation so far as the open air is concerned.

All gases possess the power of rapid diffusion, and the excess carbon dioxide produced in centres of industry and habitation rapidly disseminates and mixes with the remoter parts of the atmosphere.

That the carbon dioxide content of air shows no increase is due to the manner in which green plants satisfy their carbon dioxide requirements. Plants are largely composed of carbohydrates, that is to say, of substances composed of carbon, hydrogen, and oxygen, the two latter components being present in the same proportion as in water. The carbohydrates may be present in the form of cellulose, starch, or sugar, and although the exact way in which these substances are synthesized by the plant is not known, it is thought that water taken in by the roots reacts with carbon dioxide absorbed by the leaves to form, first of all, formalde-

«r 'j B ? ^ ^•^vi=

i - v i - r -

The Frozen Waterfall, Kent's Cavern, Torquay The Peal of Bells, Cheddar

STALACTITES

Photos: Photochrome Co., Ltd.

PLATE 5


hyde and oxygen, the oxygen being liberated to the atmosphere and the formaldehyde undergoing a process known as polymerization to form carbohydrates i^-Wtiat-ever may be the intervening processes, it is known that during sunlight starch is formed in the green leaves with the Hberation of oxygen.

During the hours of darkn^s there is no starch formation, no absorption of carbon dioxide, and no liberation of oxygen.

The erroneous idea that plants at night give out a poisonous gas is due to a misconception. It is true that plants, in addition to assimilating carbon, also breathe,. that is to say, they take in oxygen and give out carbon dioxide.

This process is very slight, however, and in the daytime is well overbalanced by the reverse process. Even at night the demand made by a plant on the atmosphere is almost negligible, and there is no need on this account for the over-zealous nurse to remove a plant or vase of flowers from a sick-room. In fact, a person entering the room and remaining for a few minutes' conversation with the patient, would probably take in more oxygen and exhale more carbon dioxide than a bowl of roses left in for the night.

In spite of its small amount, atmospheric carbon dioxide plays a great part in the erosion of rocks.

Water at the ordinary pressure and temperature is capable of dissolving about its own volume of the gas. Some gas is dissolved by the rain as it descends through the atmosphere, but much more comes into solution as the water drains through the surface soil, where the decay of plant and animal remains results in the production of quantities of carbon dioxide. Thus, by the time the rain-water has found its way into rivers and


underground sources it is usually well charged with carbon dioxide.

But this is not all, for the slightly acid solution of carbon dioxide exerts a remarkable solvent power on certam types of rock, especially limestone and chalk, which are chiefly composed of calcium carbonate.

Carbonates, apart from sodium and potassium carbonates, are insoluble in water but soluble in solutions of carbon dioxide, bemg converted into soluble bicar-bonates. The solvent action of water containing carbon dioxide has far-reaching effects.

In the first place, such water trickling over hmestone rocks gradually dissolves the surface and, entering through cracks and fissures, may be responsible for the erosion of underground caverns.

Much of the dissolved calcium carbonate finds its K^J-T° * ^ ^^^' ^^^^^ ^ ^ extracted by various soft-1? • ^ k"^^^"^^ creatures and used in the building of

their shells. The calcareous coverings of bygone shell dwellers forms a thick ooze on the sea-floor and may, m some future geological era, be left uncovered by the sea to form chalk lands or hills once more.

II lie stalactites and stalagmites formed in many lime

stone caves are the direct result of the solvent power of carbonic acid. Water carrying calcium bicarbonate in solution trickles slowly through cracks in the roof of a cave. Each drop, as it hangs, loses water by evapora-

I tion and leaves on the cave ceiling a small deposit of tl solid calcium carbonate. The remainder of the drop , f talis to the floor and there produces a similar deposit. s Subsequent drops add their quota to the deposit until j at last a small icicle-shaped pimple hangs from the ^ roof, while directly under it grows another similar ; formation. -. / "


As the years go by the stalactite, descending from the roof, and the stalagmite, rising from the floor, increase in length and girth, and may eventually meet and form a pillar which seems to support the roof. Stalagmitic growths composed solely of the carbonates of calcium or magnesium, are white, but in some instances traces of compounds of other metals such as iron, copper, or chromium, tint or colour the deposit.

In England the Cheddar Caves, and in Belgium the Grottoes of Han, contain many beautiful examples of stalagmites and stalactites. The rate of growth naturally varies with the quantity and strength of the incoming calcareous solution and the speed of evaporation. Measurements of the present rate of growth cannot safely be used to determine the age of a deposit. It is reported that a party of investigators, after careful measurements extending over some years, came to the conclusion that the floor of a certain cave was receiving a calcareous layer at the rate of one inch in ten years. The correctness of the theory was, however, left in some doubt when, after digging down to a depth equivalent to two thousand years, a bottle was found bearing the label of a well-known firm of brewers.

The so-called petrifying wells provide another example of the solvent power of carbonic acid. These are usually situated in limestone country, and are fed by dripping water containing calcium bicarbonate in solution. Objects placed, not in the well, but in such a position that the dripping solution flows over them, become coated with calcium carbonate, and eventually present the appearance of having been turned to stone.

Boiler scale and fur in kettles are produced in a similar way, only in this case the chalky deposit is produced, not by evaporation, but by the loss of carbon dioxide

52 CHEMISTRY AND NATURE from the water. When water is heated to near its boiling-point any dissolved carbon dioxide is driven off, and the water thus loses its solvent power for calcium carbonate, which is deposited on the inside of boiler tubes

\ or kettles. The formation of scale in boilers is a serious drawback to efficient steam raising, for not only does the deposit reduce the effective bore of boiler pipes, but being a poor conductor of heat, the scale is respon-

: ^sible for an increased fuel consumption. ' Occasionally a burst may result from the total or

( partial blocking of a pipe; or a pipe may be ruptured by the expansion on heating of the mass of scale inside.

We can look upon carbon dioxide as the original cause of boiler scale, and incidentally as the cause of the enormous waste of soap resulting from water containing temporary hardness, that is to say, hardness which can be removed by boiling the water. For the permanent hardness, which may remain even in water that has been boiled, carbon dioxide has no direct responsibility, for permanent hardness is due to the presence of metallic sulphates or chlorides which dissolve in water without the aid of carbon dioxide.

To avoid misconception, it is necessary to point out here that boilers fed with water containing no dissolved bicarbonates do not necessarily escape scale deposits, as calcium sulphate, a frequent impurity in many natural waters, is less soluble in hot water than in cold, and may be precipitated in the tubes when the water is heated.

The solubility of carbon dioxide increases considerably when the gas is under pressure. In the manufacture of aerated waters the compressed gas is forced into water which is bottled and stoppered while still under pressure. The effervescence of a newly opened bottle

PLATE 6

Bottles being filled, sealed, and labelled by a single machine in a modern mineral-water factory Photo: Schweppes, Ltd.

Chemical fire extinguishers at work on a blazing motor-car Photo; Planet News, Ltd.

I I

^ •

Making solid carbon dioxide Gaseous carbon dioxide anTc°oole7a''n°d"lfnMPflV' ^T^'^^ l" '"^^ *°^<=^ (A). It is then compressed in the compressor (B) and cooled and liquefied in the condensers (C\. The linuiH rnrh^n AL^.A. :. .rr,r.A in strone steel cylinders (D), from which ensers (C). The liquid carbon dioxide is stored in strong^ hydraulic Dre« (P\ ^hi^u ""^^ be dr^^n off as required and expanded into the cylinder of the hydraulic press (E), which is operated by high-pressure oil from the accumulator (J), this being kepc

mjection of the liquid carbon dioxide results in the formation o ca^bo'ndioxid'j.^'fnnw^whi^k^' '^^u " ' 1 ' ' " ' ° " ° ' tne liqu,u >..„ oon aioxioe results in u.<= . , . , bock may be cut in7o Tnv H . " ' ' ^ ^ ' ' t ' ° " ' r " " " = ^ ' " ' ° => '°^'"^ ^lock. After removal from the press ths insulatTcontahers ( H r ' ' ' ' ^ ' P ' ^^ ^ ^"•^"'="- °' ^^"^ ''^ «=)• P^^X' d (G), and distributed m

Blocks of solid carbon dioxide Photos: I.C.I-

CHEMISTRY AND NATURE 53 of soda-water is due to the escape of bubbles of carbon dioxide as the pressure is released.

Soda-water, as a rule, contains no soda, as the name would appear to suggest, but is just plain water super-saturated with carbon dioxide. In the case of soda-water made in the old-fashioned seltzogene, very popular towards the end of the last century, the carbon dioxide was produced by a chemical reaction inside the container. The seltzogene was a bottle consisting of two strong bulbs united by a narrow neck, with a screw-on cap carrying a lever tap and a long glass tube reaching to the bottom of the lower bulb. To charge the bottle, the lower bulb was filled with water, and measured quantities of bicarbonate of soda and tartaric acid were introduced dry into the upper bulb. On inverting the bottle and shaking, the reagents dissolved and reacted to produce quantities of carbon dioxide, some of which dissolved, the rest remaining in a state of compression in the upper bulb. On pressing the lever the compressed gas forced the liquid up the glass tube and out of the spout.

The modern seidlitz powder produces its effervescence in the same way, the white packet containing tartaric acid and the blue sodiiun bicarbonate.

Champagne, home-made ginger beer, and other liquids which are allowed to ferment in closed bottles, all contain carbon dioxide dissolved imder pressure, the gas being one of the products of fermentation. The popping of a champagne cork is due to the pressure of the gaseous carbon dioxide which accumulates in the neck of the bottle.

FIG. 5. Seltzogene

Expansioi CKambcr

Discliargc Tube


Mineral waters and fire extinguishers would appear to have little in common, yet one type of chemical fire extinguisher is, in effect, a kind of large seltzogene. Reference to the diagram will make this clear. The

metal container is filled with a solution of sodium carbonate (washing soda) and the sealed glass tube contains sulphuric acid.

The apparatus is thus a potential source of carbon dioxide. A blow on the knob drives down the plunger, which shatters the glass tube and allows the acid to react with the carbonate. Large volumes of carbon dioxide are produced, and a fine spray of mingled gas and liquid is projected from the nozzle. An apparatus of this kind is effective in extinguishing a small conflagration,

especially an oil or petrol fire, where water would only spread the blazing liquid.

In one variation of this appliance, the liquid in the contamer is treated with soap or other emulsifier, with the result that the spray settles over the fire as a foam of carbon-dioxide charged bubbles, and the smothering power of the gas is considerably enhanced.

When cooled down to a temperature of —78° C , carbon dioxide condenses to a colourless liquid. By pressure alone it is possible to liquefy the gas at ordinary atmospheric temperatures. Thus at 15° C. (59° F.) a pressure of rather more than 52 atmospheres converts

unqer

FIG. 6. Chemical fire extinguisher shown in section

(Courtesy of Minimax, Ltd.)

CHEMISTRY AND NATURE 55 the gas into a liquid. The higher the temperature, the greater is the pressure required to liquefy the gas, and at temperatures above 32° C. no amount of pressure will liquefy it. 32° C. is known as the critical temperature of carbon dioxide.

Every gas has its own critical temperature, that is to say, a temperature below which it can be liquefied by pressure and above which no amount of pressure will cause it to liquefy. Oxygen and nitrogen, for example, have critical temperatures respectively of —119° C. and —146° C , and so must be cooled by artificial means before they can be liquefied by pressure. The difficulty of liquefying a gas like helium lies in the fact that its critical temperature is —268° C , a temperature difficult of attainment.

Gases such as carbon dioxide, ammonia, and sulphur dioxide with high critical temperatures can be usefully employed as refrigerating agents. Of the three gases mentioned, carbon dioxide, on account of its low toxicity and absence of smell, is particularly useful for use in refrigerators in places where a leak of noxious gas might have serious consequences.

When liquid carbon dioxide is made to evaporate rapidly the absorption of heat causes part of the liquid to freeze to a snow-like solid. The ordinary steel cylinder of compressed carbon dioxide contains most of the compound in a liquid condition. Solid carbon dioxide can readily be obtained from this by inverting the cylinder and allowing the liquid to escape from the nozzle through a canvas bag. The bag quickly becomes filled with a snow-like solid, which can be compressed into a solid block.

Blocks of solid carbon dioxide, sometimes known as 'dry ice', are produced commercially and sold as cooling

56 CHEMISTRY AND NATURE agents. The ices hawked about our streets in box tricycles are usually kept cool and in good condition by the presence of a block of 'dry ice' in the top of the box.

The advantage of these blocks over ordinary ice is that they leave no pools of water, for they evaporate in air without melting. The blocks can be handled safely provided no pressure is apphed, the film of non-con-ductmg gas protecting the skin from the intense cold. The effect of pressure is to break this film, and painful blisters, resembling burns, may result.

CHAPTER IV

CHEMISTRY AND T H E SOIL

AGRICULTURE is probably the oldest of the useful arts. Long before the dawn of alchemy man was a tiller of the soil, seeking in his crude way to assist and control those processes of nature which provided him with food. Almost down to modem times the farmer received little or no assistance from science, yet the cumulative experience of centuries resulted in methods of crop production that sufficed, except in times of climatic disaster, to feed the increasing populations of civilized countries.

The farmer became, and still is, possessed of that peculiar instinct for soil management which seems to come only to those brought up in association with the soil. Yet there came a time when the limit of the soil's productiveness appeared to have been reached, and increased demands for food meant the search for new areas to cultivate.

The chemist is now able to help the agriculturist, and although the skill and experience of the farmer are still of paramount importance, chemistry has become the handmaiden of agriculture.

The beginning of the association was beset with difficulties, for, apart from the natural suspicion of the practical farmer for the theorist, it was not easy to trace out the scientific principles underlying many of the empirical methods practised by the successful cultivator.

The first half of the nineteenth century saw the beginning of these attempts. Boussingault in France, Liebig in Germany, and Lawes and Gilbert in England, were the chief contributors.

58 CHEMISTRY AND THE SOIL It is worthy of note that the scientific partnership

between Lawes and Gilbert lasted for fifty-seven years and is- one of the longest on record. The partnership started in 1843 when the Rothamsted Experimental Station was founded by J. B. Lawes with J. H. Gilbert as his co-worker. This station has steadily increased in

Sir John Lawes Sir Henry Gilbert

importance, and is now concerned with the investigation of every aspect of agriculture. The work done there has been one of the. chief means of promoting a pleasant and useful liaison between the scientist and the practical farmer. During his lifetime Lawes met all the expenses of the institution, and shortly befbre his death created the Lawes Agricultural Trust, which he endowed to the extent of ;^ioo,ooo.

He was made a baronet in 1882 and Gilbert was' Icnighted in 1893. Lawes died in 1900 and Gilbert in 1901. From 1902 to 1912 the Institute was under the direction of Sir A. D. Hall, who was succeeded by the present director, Sir E. J. Russell.

The early scientific investigations were concerned with the fertility of the soil. It had long been realized

CHEMISTRY AND THE SOIL 59 that crops took a certain amount of nourishment from the ground,, which in due course became exhausted and gave diminished yields. It was also a matter of common experience that the fertility of exhausted land could be restored by the application of farm-yard manure.

The starting-point, therefore, of the investigations was an inquiry into the chemical constitution of farmyard manure.

Lawes and Gilbert came to the conclusion that the fertilizing power of farm-yard manure was due mainly to the presence of the three elements nitrogen, potassium, and phosphorus. It occurred to them that compounds of these elements could be introduced into the soil without the use of farm-yard manure. Farm-yard manure was less scarce than it is to-day, but was even then not always available in the quantities required by farmers. A mixture of ammonium sulphate (a compound of nitrogen), potassium compounds from the ashes of wood or seaweed, and phosphorus compounds in the form of ground bones or rock phosphates, appeared likely to prove an efficient substitute. There was the further advantage that such a fertilizer was much more concentrated than farm-yard manure, giving an enormous saving in cartage.

Lawes started a factory in Deptford for the manufacture of artificial manures, and from this began an industry that has-since grown to tremendous proportions, the world's annual output of artificial manures now being reckoned in millions of tons.

The original conclusion arrived at by Lawes and Gilbert, although correct so far as it went, was not the whole truth. The purely chemical view of the relationship between the plant and the soil does not explain everything.

6o CHEMISTRY AND THE SOIL It is true that nitrogen, potassium, and phosphorus

are essential to the healthy life of a plant, and that greatly increased crops can be produced by the use of artificial fertilizers containing these elements. The three elements alone, however, do not appear tcprovide everything the plant requires from the soil. Experienced farmers still look upon farm-yard manure as the fertilizer par excellence, and it is a fact that soil treated regularly with farm-yard manure shows no sign of deterioration, while that treated with 'artificials' does deteriorate after a time. A fertile soil is more than a simple mixture of mineral substances. It contains varying amounts of organic matter produced by the decay of dead animals and plants. This organic matter is known as humus. It is the part that burns away when soil is strongly ignited. Then there is the teeming life of the soil, not merely the worms and other large creatures that we can see, but micro-organisms invisible to the naked eye but existing in millions in each thimbleful of soil.

What part these various constituents play in promoting the growth of plants is not yet clearly understood, but they abnost certainly have some influence. The special value of farm-yard manure may lie in the fact that it increases the supply of humus and modifies the micro-organic life of the soil. Perhaps, also, it contains small amounts of constituents of use to the plant that are not provided by chemical fertilizers. In other directions the chemist has learnt to realize the importance of traces, and it is possible that in such a nicely balanced organism as the plant, even minute traces of certain substances may exert a great influence.

The sldlful farmer, therefore, uses all the farm-yard manure he can obtain and reinforces this with dressings of artificials. He is able to adjust the composition of

PLATE 8

Broadbalk Permanent Wheatfield. This is the oldest permanent wheatfield in the wor ld, having been cropped with wheat every year without exception since 1843 Photo: Lawes Agricultural Trust

•M

i >

Showing the effect of nitrate of soda on the potato crop Photo: Nitrate Corporation of Chile, Ltd.

PLATE 9

Broadbalk wheat sheaves grown with and withonr nitr^™„ r i u^rp of ammonia increases, so does the yield u ^ o a c e r S o n i " " " ' " " ' ' " „ ^' "-^^ ' ' ' " " " ' " ^ ? ^ ' " C

/ . up to a certain point Photo: Lowes kgricultural Trust

Granular ' A e r o ' cyanamid^ containing 22 per cent, nitr gen and 70 per cent. hydra^= lime, is a fine black powder

- ;W Co.

CHEMISTRY AND THE SOIL 6i

these latter according to the type of crop and the condition of his soil, for much is known of the particular effect of each type of fertilizer on the plant.

Nitrogenous manures, in general, promote rapid growth and a greater development of the green parts of plants. Potassium assists in the production of starch and other forms of carbohydrate. Phosphorus encourages root development and assists in the ripening processes.

So far as the plant's needs are concerned, the nitrogen compounds have received more attention than have the compounds of potassium and phosphorus. The two latter are largely of mineral origin, and, except for the demands made on them by the plant, are not readily lost from the soil.

It is otherwise with nitrogen compounds, for these are almost wholly derived from the decay of organic materials and are liable to be lost from the soil in a variety of ways.

Only liquid nourishment can enter the plant by the roots, and so only soluble soHds in the soil are directly available as plant food.

All forms of nitrogen compounds undergo changes in the soil, and eventually turn into soluble nitrates which become the food of plants. Unfortunately, nitrates are so soluble that they are easily washed out of the soil. For this reason nitrates as such do not stay long in the soil. What the plant does not take probably steals away in the drainage water.

Farm-yard manure and decaying dead plants both contain complex nitrogen compoimds. The chemical changes which these compounds midergo to become nitrates are brought about by soil bacteria. This was first shown to be the case by Schloesing and Miintz in ^

62 CHEMISTRY AND THE SOIL

1877. In order to study the action of sand-filters on sewage they caused a stream of Hquid sewage to trickle slowly through a column of mixed sand and chalk. For twenty days the ammonia in the sewage came through

unchanged. Then the ammonia began to come through in diminished quantity but mixed with nitrates. Finally the effluent contained only nitrates and no ammonia.

Up to then the transformation of ammonia into nitrates by sand-filters was thought to be a purely chemical process, due to the oxidizing action of the air in the porous filter. To Schloesing and Miintz the delay of twenty days in the starting of the action pointed to a bacterial rather than a chemical process. A simple oxidation process would have started at once, but it was conceivable that a bacterial process would start only after the necessary organisms had developed and multiplied sufficiently to fill the filter.

It was easy to test this theory. They added a little chloroform vapour to the filter with the idea of killing any organisms present. At once the change into nitrates stopped. The filter was then washed free from chloroform and a little soil from another filter added to supply fresh organisms. Very soon the action restarted.

Subsequent expermients by other investigators confirmed their conclusion that the formation of nitrates m the soil from other nitrogen compounds is due to action of bacteria. , ^ge

It has been the aim of the chemist to study ^ ^^^ changes with a view to suggesting methods . j-g economical use of both natural and artificial e ^^^^ containing nitrogen. Nitrogenous manures ^^^ .j ese expensive of all, and so it is desirable that ^^^ gj^le manures are applied, as little of the nitrogen as F should be washed out by the drainage water.

CHEMISTRY AND THE SOIL 63 Nitrate of soda from the Chile nitrate beds has for

many years been used in large quantities. It has the advantage of being, so to speak, ready for use by the plant.

For this reason, however, it must be applied very circumspectly. To begin with, if nitrate of spda is applied before sowmg, or before the roots of plants are sufficiently developed to absorb it, practically the whole of it is lost by drainage, without benefit to the land. Moreover, a plant is able to absorb by its roots very weak solutions only; a lavish application of such a soluble salt as nitrate of soda is likely to form a strong solution in the soil water which, instead of entering the roots, may actually draw moisture from the interior of the plant and cause shrivelling of the leaves and perhaps the death of the plant.

Small repeated doses of nitrate which can readily be absorbed by plants are likely to be much more satisfactory and less likely to result in loss, v / ^

This course of procedure, possible for the gardener or cultivator of a small plot, is in many cases out of the question for the farmer. He must apply his fertilizer either before sowing, or before the plants are high enough to be injured by trampling. For this reason something less soluble than a nitrate is generally preferred.

Until the end of the nineteenth century the only two forms of chemical nitrogen in general use were nitrate of soda and sulphate of ammonia. Then a note of warning was sounded by Sir William Crookes, who, speaking before the British Association at Bristol in 1898, showed the possibility of a world famine in the not very distant future. The factors likely to lead to this situation were as follows. First, the population of

64 CHEMISTRY AND THE SOIL the world was rapidly increasing, and the earth was being asked to produce more and more wheat to feed it. More and more nitrogen compounds were required to keep up the fertility of the land to the high level required. Farm-yard manure alone was insufRcient to do this; the nitrate beds of Chile would be worked out in a period of about sixty years, and the available sulphate of ammonia from gas-works was similarly limited in amounts. The time was thus not far distant when the earth would begin to decrease in fertility, and many mouths would go imfilled. There would be the strange anomaly of wheat plants suffering from nitrogen starvation while surrounded by all the nitrogen of the atmosphere, this nitrogen being useless to the plant because it is not in the form of a compoimd.

The forecast was a gloomy one, but coming from the lips of one of the foremost chemists of the day it could not be entirely ignored, although The Times subsequently printed a reassuring letter from Sir J. B. Lawes and Sir J. H. Gilbert in which they stated their opinion that Sir William Crookes had taken a too despondent view of the position.

However, Sir William Crookes made it clear that the future of the nitrates lay with the chemists. If only they could find a way of inducing the nitrogen of the ^^"^°' sphere to combine with other substances the^ worl would have an almost inexhaustible store of nitrogen compounds.

This was no easy task, for nitrogen is an element tna shows little tendency to combination. Two ways were already known in which nature brought about a combination, the first being biological, and the secon chemical.

With regard to the first method, it had been known

PLATE 10

Nitrate stored in piles for final drying

The finished product— granulated nitrate ready for shipment

•.- ''J

" ^

I Loading railway trucks

ft' If' j

Photos: Nitrate Corporation of Cliik. Ltd.

-^li^mi

9m'^: I THE NITRATE INDUSTRY IN CHILE

CHEMISTRY AND THE SOIL 65

for thousands of years that plants of the pod-bearing class, such as peas, beans, clover, and the like, appeared to improve the soil in which they grew. Ground on which clover, for example, had been grown was actually richer in nitrogen compounds than before.

T h i s remarkable state of affairs was not understood at all until the year 1886, when the mystery was solved by two German investigators.

They found that leguminous plants developed tiny nodules on their roots, and that in these nodules dwelt a class of bacteria that was capable of using the nitrogen of the atmosphere to form compounds useful to itself and also to the plant on whose roots it lived, A sort of mutual help association thus exists between leguminous or pod-bearing plants and the bacteria, the plant providing a home for the bacteria and the bacteria manufacturing nitrogen compounds for the use of the plant. These bacteria, incidentally, are not the same as those which are responsible for breaking down complex nitrogen compounds in the soil to nitrates.

FIG. 7. (a) Nodule on root of liSpin caused by bacteria which are able to assimilate atmospheric nitrogen; (6) section of nodule. The black specks in (c) show the bacteria highly magnified, (d), (e), and (/) show

various shapes of these bacteria (From The Kingdom of Man, by permission

of Messrs. Watts & Co.)

PLATE II

FIXATION OF NITROGEN

Interior of sulphate of ammonia silo at Billingham-on-Tees

Photo : I.C.I-

66 CHEMISTRY AND THE SOIL

discove 'e^d ?, '^^ ^ " " ^ ' ^ '^''''' °f '-'^^ bacteria were oimblnatfnn T ' ' ""^^'^^^ ^^ bringing about the from the oT^' ° ^ - ^ ^ f ^«' of nitrogen. T h l e differed

bacterid ^ c ^ • 1, , ^ ^ ^ ^ ' oê question of soil c o m T ; f V . r ; - ' " y ' ^ ' nitrogen-fixing bacteria, has be-T h a s n . V " ' ' ' ? ' ' ^ ^ ^ being extensively studied.

thesep 'ce tsT^^^^^^ P°"^^^^ ' ^ « — ' ^« ^^^^^^ to trv TînlT u * ^ laboratory, and so it was necessary wav7of m n n ^ ""-""^ "^"'^°^« in order to discover

R e s e a r T n ""'J^^ ^^*^°g^^ compounds in bulk.

thougntls p^gt's t:T'' '• ^ • ^°" ' ^'' '-m a position to sav tlt!^ T ^.'^^PPO"^ting, we are now the situation chemistry has once more saved

point S e Z ' o w n ' S T h i ' ^ ^ . ^^^ ' '°°^^ "^ ^ ''^''^û amounts of oxides f - " " ^ ^ thunderstorm small ^/mosphere the hi' h ^^^°S^^ are produced in the of a lightning d i s c W r ^ " " ' ' . * " " ^ ^"^ ^^ the passage nitroge?^ and oxygen ''^''^'''^ ^^^ ^^^^^t union of

By making use of the pf. i Nor^vay, Birkeland and F T I ' ' ' P"^''^^ available in , Nature to some extent Th f ^^^ ^^^^ ^^^^ to imitate arc between two copper e]l f" ^ a powerful electric

made of thick copper tubi "" u ' ^ ^ ^^^^^°^^^ ^^^"^ streams of water pass. "^ through which cooling

A powerful electro-magnet i . out the flame of the arc hito a d° f "^"g^d as to spread across. The whole is enclos d • ^^^^^ ^hree metres chamber shaped something li^g ^^ ^ firebrick-lined passed through the chamber, and ' P^'^'ôx. Air is hot arc some nitrogen is oxidized t^^ .^°ntact with the oxide is subsequently converted tc^ '^.n^tric oxide. This

nitric acid, which in

CHEMISTRY AND TPIE SOIL 67

u Poles of magnet

\JcAar

Copper electrodes ^--C . Wdtir

Copper_e/ectrot/es

A ^ Poles of magnet

FIG. 8. Obtaining nitric oxide from the air. An electric arc is struck between water-cooled electrodes. The arc is spread into a disk of flame by means of the powerful electro-magnets, so that when air is forced through, some of

the nitrogen and oxygen combine

Section. External Vicvu. Birkcland.-Eydc Furnace

FIG. 9. The air enters at AA and passes in through holes in the refractory lining B. The electric flame plays down the disk-like space CC and the burnt

gases come out at D. EE is the wiring of the electro-magnets (From Chemical Lecture Diagrains, by permission of Messrs. Sampson,

Low & Co.)

turn is made to react either with lime to form calcium nitrate or with soda to produce nitrate of soda. Only a very small percentage of the atmospheric nitrogen passing through the arc is oxidized to nitric oxide, and

file:///JcAar

68 CHEMISTRY AND THE SOIL so the process is commercially successful only in places where plenty of water-power is available to provide cheap electricity.

Another method of fixing atmospheric nitrogen which has proved successful consists in heating calcium carbide to a high temperature in contact with atmospheric nitrogen, resulting in the production of calcium cyan-amide or nitrolime. This process also is practically confined to places where water-power, and consequently electric power, is cheap, for the electric discharge is required for the production of the calcium carbide irom hme and anthracite, as well as for the final reaction.

wifh^^ ^ T •'P^^^h-^^aking developments, however, Tf n ^ S u * ° ?'*''°gen fixation, resulted from the work method n f ' ^^.^^^"^any. In 1913 he discovered a Ammonia ' ' ' ' ' ' ^ ""^'"^^"^ °^ '^^ atmosphere to make

h f ^ r Z r r ? ' " ' ' ^ '^"'P^^ compound of nitrogen and

could b e W r t o T o X e ' ^ " ' " ^ ' " ^"^ '^^^"^'"

m i X s S X l t r ^ n r ' ^ ' - ^^ ^ ^ - ^ ^ ^ ^^ a high W e ^ f u r e rrhf,'^"^^'^^^^^^ ^^^ ^^^^^^ ° pound of iron, c o m b T n e t e r ' ' °^ " '^^^^" '^°"' '

The keystone of the 1 . "^ ammonia. iron, withLt w 4 h no a m o t ? ? , * ^ ^^^^^^^^^ ° ' would be effective. Catalysts^4°f/^^^^ and pressure among the mysteries of science A i,^''^^^,''^''^''^^'^^'^ certain substances possess the pr'optlTf ^^"^ ' I w ' speed up, or even in some e a s e T ^ ^'""^ '' ^ ^° action without undergoing anvnprl ^ ' ^ chemical selves. Many kinds of substIncer?r^'^fS^'^^"^-

axices—solids, hquids, or

CHEMISTRY AND THE SOIL 69 gases—may act as catalysts, but generally a particular reaction requires a particular catalyst, and Haber's triumph lies in having discovered a catalyst capable of promoting the union of nitrogen and hydrogen.

One rather interesting point about a catalyst is that it can be poisoned and put out of action by many of the common poisons as well as by various other substances. For this reason a catalyst used in any industrial process must be carefully guarded from contamination.

In Haber's process nitrogen fi'om air is mixed with three times its bulk of hydrogen and compressed to 200 atmospheres (3,000 lb. per sq. in.), after which it is heated to a temperature of 500° C. in contact with the catalyst. The engineering difficulties in the construction of the plant were enormous, for the construction of steel converters strong enough to withstand the great pressure necessitated forgings on a scale hitherto unheard of.

The immediate result of Haber's discovery was that during the Great War, when the nitrate supriies of Chile were closed to her, Germany was able tfj manufacture sulphate of ammonia for agricultural i)urposes and compounds of nitrogen for conversion into explosives, and thus became independent of outside sources.

In this covmtry a factoiy for the production of synthetic ammonia was established after the War at Billingham-on-Tees. This is now under the control of Imperial Chemical Industries, and is able to manufacture nitrogen compounds at a price which competes successfully with similar compounds from other sources. The fear of a wheat famine, on the score of nitrate starvation at any rate, need no longer worry us.

The task of the chemist in regard to the provision of

70 CHEMISTRY AND THE SOIL fertilizers containing potassium has been much simpler. All fertile soils contain potassium, and this stock is being

I870 I 8 8 0

F I G . IO . Showing the increase in nitrate products since 1870

1890 I 9 0 0 I910 I9EO I 9 3 0

VEAR

slowly added to by the weathering of certain rocks, notably the felspars, which are essentially compounds of potassium. Under natural conditions this weathering is sufficient to provide all the potassium required by plants, but modern crop yields are now so great that

CHEMISTRY AND THE SOIL 7

potassium compounds are taken from the soil more quickly than they become available as a result of the breakinsr down of rocks. . r

Fortunately there are large, easily worked deposits oi potassium compounds in various parts of the world, ana these come on the market generally in the form ot sulphate of potash, a cr>'stalline compound easily applied. Potassium as an element is rarely seen by the layman^ it is a soft, silvery-white metal which has such a great affinity for oxygen that on exposure to air it quickly turns to a white rust or oxide. T h e oxide is known as potash, although the term is often loosely applied to any simple compound of potassium. .

As has already been stated, potash is concerned with the production of carbohydrates, and on this account is used largely in the manuring of potatoes and also of fruit-trees.

If ever mineral sources of potassium fail us, and there is no early prospect of this, chemists will have to invest!-, gate the possibilities of the ocean beds, for it. is estimated that more than 50,000,000 tons of potash salts are carried by rivers each year to the sea. *

Rather more romance is attached to the history of the phosphorus compounds.

Phosphorus itself is a non-metallic element with a wax-Hke appearance. I t burns spontaneously in air to a white oxide, which, with metals, forms compounds known as phosphates. T h e match industry makes enormous demands on the world's supply of phosphorus, and this demand helps to keep up the price ot agncui-tural phosphorus. , . ^^-..^^o that

I t was in connexion w i * pho^P*'""^ " S, " ri ul-Sir John Lawes began Us long ^^°^ZJnl!lr/it was tural chemistry. Early in the nmeteent

72 ^ CHEMISTRY AND THE SOIL

realized among agriculturalists that heavily cropped soils were losing their fertiUty on account of the loss of phosphates. A crop of wheat, reaped when the grain IS ripe, may remove from the ground as much as 200 lb. of calcium phosphate per acre.

The use of bones as manure became general, for bones consist partly of calcium phosphate. It was, however, found that the action of bones, even when ground to powder, was very slow on account of the inso uble nature of calcium phosphate. Lawes, in his lertUizer factory, treated bones with sulphuric acid, mereoy producing a readily soluble phosph orus com-

The success of this new product was great, and large quantities were manufactured, not only from bones, bu from mineral phosphates also. Since the time of iâwes superphosphate of lime, as his product was called, torld ° ' ' ' '^^'^ phosphatic fertilizers of the

s te IwS7° ' ' ^^ ' ' ' " " ^° ^^ ^ " ^ connexion between the latter hi?/ Zt "§"^^^^^^^1 fertilizers. Yet during the a new n;^ nineteenth century the introduction of a further. "" '^V'"''' ^"^ ''^^^ industry provided a further source of phosphatic fertilizers.

to ts conver? ' ' " ' ° ' ^ ' phosphorus from pig-iron, prior he L m r e ° ' ' """XT'^' '^^^"^^^ ^"d Gilchrisi L e d v h a h . l r ' ^ ' ^ ' ' ^ ' ^^ ^^î^h the iron was melted

of Ae UnZ ^^^"S' ^^^rîng largely of lime. Some car^W^.^fh"^. r.^ ^l^ ^°^^^^ °n the molten iron th f h ^ L ' phosphatic impurities. At first ca L H I f'^' T '' '?' '^"^^' ^^« ^^n off and discarded but was later found to be a valuable source of phosphorus.

To-day basic slag in a finely ground condition is

CHEMISTRY AND THE SOIL 73 extensively used as a fertilizer. It is insoluble in water, although slightly soluble in the weak acids which may be present round the roots of plants. Thus it is slower in action than superphosphate but none the less certain.

No review of soil fertility would be complete without reference to the use of lime in agriculture. When limestone or any other form of calcium carbonate is strongly heated, carbon dioxide is given off, and calcium oxide, or quicklime, is left. Quicklime on exposure to air first absorbs moisture and becomes slaked lime or calcium hydroxide. This in due course combines with the carbon dioxide of the air to form calcium carbonate again. The term lime is often loosely applied to all three substances.

The early Celtic inhabitants of this country, in their search for flints, dug out vast quantities of chalk, which in due course became scattered over and incorporated with the soil.

During the subsequent Roman occupation it was observed that these chalked fields were able to produce heavy crops of wheat. The chalking or liming of land IS practised to this day, although there was 'a period ^vhen the practice fell into disrepute. This was when chalking was found to assist crop production so much that it was looked upon as a cheap substitute for manure. For a time this simple treatment gave good results and farmers made good profits. Later on the chalked land became so impoverished that many farmers were faced ^ith ruin. Thus arose the saying, 'Lime enriches the ^^i^^ 3nd impoverishes the son'. . The fault lay, not in the lime, but in the misconcep

tion of its function. Lime (or chalk) is not m itselt a plant food to any extent. It is able, however, to unlock and make more readily available the plant food

74 CHEMISTRY AND THE SOIL already in the soil. Once this food is exhausted there will be no more crops xmless more food is supplied in the form of natural or artificial manures. Liming and manuring are complementary and must go hand in hand.

Since lime quickly becomes chalk after being spread on the land, it is immaterial which form is used, except that quicklime is likely to scorch existing crops. Apart from this, fineness of grinding, availability, price, and cost of transport will decide the matter. In taking the above factors into consideration, it should be noted that 56 lb. of quicklime spread on the land turns into 100 lb. of chalk.

Lime is useful also in correcting a sour soil and in improving the texture of clay.

The task of the chemist is not yet finished, but, working in collaboration with the biologist, he is daily extending his knowledge of the soil, and helping the farmer to increase his returns for labour and money • expended.

CHAPTER V

CHEMISTRY AND T H E HOUSEWIFE. I

IF 'the policeman's lot is not a happy one', the lot of the housewife is certainly vei7 much happier than used to be the case, and for this improvement chemistry can claim quite a large share of the credit. Especially is this so since the development of chemistry has helped to remove much of the drudgeiy inseparable from tlie management of the household. Gone are the days when to light a fire one had to resort to flint, steel, and tinder; the matches we nowadays use are available only because chemistry has made them so. Matches were first introduced tothis country, from France, about the year 1810. They consisted, then, of thin strips of wood, the ends

. of which were coated with a mixture of potassium chlorate, sugar, and gum. Some years previously Pelle-tier had discovered that such a mixture ignited when-

> "'bought into contact with concentrated sulphurfc acid, so the latter material was required to ignite these matches. One therefore had to purchase, alsfl, an ' Instantaneous Light Box' which contained a small bottle

o . \ ^ asbestos fibre soaked in sulphuric acid. In J 526 'friction lights' were invented by John Walker of Stockton-on-Tees. The heads of these matches consisted of potassium chlorate, antimony sulphide, and

' n ? ' ^^^ ^^^^ ^^^^ ignited by holding the head between olcjs of sandpaper and giving a vigorous pull at tlie

^ther end. These matches seem to have been put /^^the market by Samuel Jones, a London match-^^^^J^- Jones had previously made and sold a kind «t match requiring sulphuric acid for its ignition snd known as the 'Promethean Match', but he sold

76 CHEMISTRY AND THE PIOUSEWIFE his imitation of Walker's matches under the name JLucifers'.

T h e modern match has been developed from the s tudy of phosphorus and its compounds. This element appears to have been discovered by Brand, a Plamburg doctor, who died in 1674. ^ specimen of it was seen

F I G . I I . Jolin W.Îkc^'s 'friction liglit'

by Boyle, who, in 1680, rediscovered the method of making it. . .

I t was, however, very rare and expensive until, in 1770, it was discovered to be present in bone as , which is now known to consist largely of calcium p ôs phate . Shortly after this Scheele discovered how

—— make it from bone ash. h rus Ordinary phosphorus, known as white P^^^^P, g^J

is a solid of waxy consistency, very inflarnma ^ ^ exceedirf^ly poisonous. If, however, it is ii^^ ^^ ^ closed iron vessels, from which air is exclu e ' , temperature of 230° C , considerable heat is ^ . ^^^^ . j and tlie waxy-white phosphorus turns into ^J^°^^^ of powder known as red phosphorus. The re ,^^j^|^gn phosphorus is non-poisonous and less easily ign the white variety. briefly---

T h e manufacture of p h o s p h o r u y s a ^ - f i ^ - ^ - ^ J ^ ^ ^

| - b ^ I S r k m i n e j i L p h ^ ^ of the ' f ^ d b ^ ^ ^ n S ^ ^ ^ a worm conveyor (liJê tn ^^^^^ - fur-domestic mincing machine) ^ ^ ^ ^ t . ^ve rv high tem-nace. Here the mixture is heated to a very

electrodes T L T ? ' ' ' ' ' ' ^ ' " ' ^ ^^^'^^^^ ^^° carbon ^nd the carbon ^'TS^^^'J^^ ^'^^'^^^' phosphoric oxide, ^^^"ing from t?.f f'^ '"^"""^ '^"^' ^° ^ ^ ^ ^he vapour ^"^ carbon m o n o x i r % r " ' " ' " ' phosphorus vapour

lunoxide. This vapour is condensed by

Sand $f Cofca + \~7— Phosphate Kock. \ <,'cO;'>f / or Bone A S K . \ > % y

Wabir

f)5Ml

• Vopoar i; • and -Ji

J Carbon ^ Monoxidcj ! '

. sC\

li»»^

^ 830 anri • '^"""s pnosphorus were lu-stmade aboui of a p f ^^ *^^ earliest of these, the heads were made ehlorat ^ consisting of white phosphorus, potassium tended^' ^^^ S^^, the potassium chlorate being in-bur °- ^^PP^y oxygen to enable the phosphorus to ^ / ^ , rapidly and so ignite the match stem. These

" ehes could be 'struck' by rubbing on any hard or

78 CHEMISTRY AND THE HOUSEWIFE rough surface, but they were apt to ignite rather explosively as a result of the sudden decomposition of the potassium chlorate. This substance was consequently replaced by less dangerous sources of oxygen, such as red lead or manganese dioxide,

'Safety'-matches, designed to strike only on the box, were first made in 1855 in Sweden, where so many are still made. In these there is no phosphorus, the match-head consisting of a mixture of gum, antimony sulphide, and an oxidizing agent such as potassium chlorate or red lead. The phosphorus in this case, instead of being on the match, is on the box, and is of the red non-poisonous variety.

Antimony sulphide burns readily when ignited but does not take fire so easily as phosphorus. Thus a safety-match cannot be struck on sandpaper or other similar surface as the heat of friction is not sufficient to cause ignition. I t , however, lights easily when struck gn a prepared surface consisting of a coating of red phosphorus, antimony sulphide, powdered glass, and gum. As the head of the match is drawn across this surface it obtains a thin coating of phosphorus, which, with the gentle heat of friction, takes fire and ignites the match-head.

Safety-matches, besides being non-poisonous, are not likely to become ignited accidentally. I t is, however, possible to ignite a safety-match by drawing it quickly in a wide sweep across a sheet of glass. This is because the glass is such a poor conductor of heat that little or no heat of friction is conducted away from the match-head, which consequently becomes hot enough to take

fire. , V • T h e use of white phosphorus m match-making has

now ceased, as it is extremely poisonous, and work-

CHEMISTRY AND THE HOUSEWIFE 79

people exposed to its vapour are liable to develop a curious disease of the bones, this disease frequently attacking the jawbones and giving rise to the condition known as 'phossy jaw' . T h e heads of the modern 's tnke-anyxvhere' match usually contain phosphorus sulphide, \vhich is non-poisonous but easily ignited by friction.

Apart from the changes that have taken place in the match-head, another and more recent improvement has resulted in the wood of a match ceasing to glow immediately the flame is blown out. T h e struck match, carelessly thrown down, is not now so likely to cause trouble as was formerly the case. Another advantage of these matches is that the burnt part of the wood does not fall off so easily, or if it does fall, is 'dead . I h i s improvement is the result of soaking the wood, before the actual match-making, with solutions of various salts and then diying it. T h e match-making is, of course, carried out by machines that are almost automatic m their action. T h e splints are fed mechanically inio holes in a long travelling band, which carries them along, dips them into melted paraffin, and then dips the head into the striking mixture. The tipped^splmts are next dried, removed from the travelling band, and packed automatically into boxes.

Our grandmothers usually had a brass or copper kettle and took a pride in having it always sparkling and bright. This was no small matter either, tor a copper kettle soon became coated with soo^ ^ ^ ^ " P " '

. . - ^n the fire to boil. Of course, the kettle could be cbaned up a g a i n - t h e chemist having made a s^^^able rnetal-polish for this p u r p o s e - b u t what a ^ ^ f °f ^^^^^^"4' How much better to use an aluminium kettle which we can get quite cheaply nowadays as the result ot chemical developments. Aluminium was hardly known

file:///vhich

8o CHEMISTRY AND THE HOUSEWIFE

fifty years ago, though it is present in all varieties of clay, so that the raw material would appear to be plentiful. In fact, however, it has not been found possible easily to prepare the metal from clay.

A mineral known as 'bauxite', an impure form of aluminium oxide, is used. T h e bauxite has first to go

v.

"^//////////////////////////////////TM^ FIG. 13. Illustrating the manufacture of aluminium.

A. Iron tank which acts as cathode B. Copper rod with carbon rods attached = the anode C. The fused electrolyte D. Fused aluminium E. Tapping hole arid plug

through a chemical process, the main object of which is the removal of such impurities as iron oxide, and the purified material is then electrolyzed, after being dissolved in fused cryolite (a double fluoride of sodium and aluminium). This calls for a large expenditure of electrical energy, so that the works of the British Aluminium Company are situated where electricity can be cheaply obtained from water-power, namely, in North Wales and in Scotland. Although aluminium retains in use its silvery appearance and never appears to rust, yet in fact, its surface has always a very thin film of oxid' which thus protects the metal from further injury S ^ water, or water containing salt, corrodes the m T l quickly; aluminium is also quite rapidly dissolved by

PLATE 12

The scum Above: Tapping a steel furnace.

the smaller slag ladle ^ ,„d put into bags Be/ow: Basic slag being we.gn ^^^^^ 5LAG

rhe lip of the steel ladle into . basic slag is running over the hp ° or basic siag ^ .__ ^^^^ ^^^ Photos:

kr

Sp

lint-

cutt

ing

or

chop

ping

mac

hine

r—

>

H

m

On

e o

f th

e M

atch

Hal

ls

MA

TCH

MA

KIN

G

Pho

tos:

Bry

ant

& M

ay,

Ltd.

CHEMISTRY AND THE HOUSEWIFE 8i

liquids containing soda, a point which must not be forgotten in using or cleaning aluminium utensils. There are people who maintain that aluminium vessels should never be used for cooking, as small amounts of the metal may dissolve into the food. This is a possibility which one must not overlook, but the evidence on the point is somewhat conflicting, and the probability seems to be that though traces of aluminium do sometimes get into food prepared in aluminium vessels, yet the quantity is very rarely enough to do any harm, and usually there is none whatever dissolved.

Of course, even an aluminium kettle would be difficult to keep clean if always used on a coal fire, but in most houses of to-day the coal fire has been superseded by the gas-stove. Coal-gas manufacture is one of our most important chemical industries, for not only is the gas a useful substance, but other products of the gas industry are coke (or other smokeless fuels), coal-tar, and ammonia. Coal-tar alone contains hundreds of individual substances almost all of them of some use, which eventually brings them back into the household, e.g. as drugs, disinfectants, or colours.

Coal-gas was at first manufactured solely for illuminating purposes and was burnt with one of the old-fashioned bats-wing or fish-tail burners, which gave a flat yellow flame. This was a great improvement on the candle or oil-lamp which had formerly been used, but was not very much better when used in the chemical laboratory for heating purposes. In order to improve the illuminating power of the gas it was formerly the custom in gas-works not to remove many of the hydrocarbons which nowadays are separated from the gas indeed, the manufacturers often went even further ana added hydrocarbons to increase the luminosity ot tne

Complcta Oxidation

^ParKal OxidaKon

Unburnt C a s

82 CHEMISTRY AND THE HOUSEWIFE

gas In order to make coal-gas burn with a clean, non-luminous flame, air must be mixed with it before combustion and appreciation of this fact led Bunsen, a German chemist, to invent the type of burner which s commonly named after him. This was invented with

the object of securing a clean, non-luminous flame suitable for laboratory use as a heating agent.

The Bunsen burner is very simple. It is so constructed that a jet of gas emerges into a wider tube having holes for the admission of air. The size of these holes can be regulated. The quickly moving stream of gas issuing from the jet causes a reduction of pressure in the wider tube so that air enters, and having mixed with the coal-gas, the mixture passes to the end of the tube where it is

supply pf air for the 'S^^tJ^^^^'"''^'^^ ^ sufficient which thus gives a hot K ! combustion of the gas, flame. The only drawback to .K^ t^ ' ' " ' ^ " " ' ^^^ ^ < ^ to 'strike back' when t h e t I 3 ^ ^ ^ " ^ ' ^ ^ '^' ^^^^^^^^ a certain limit. The flame burn S ^ ' ' ' '' ^°^^^ '^^yo^^ rate which, in general, is less t L ^ T ' ' ^ ' ' ' ^ ' ^ ^ ^^^"^'^ ward moving stream of air and ^ T?^^"^ °^ ^^^ "P-upward speed is reduced by cuttin5!f * ' however, the the flame may strike back to the l ? r \ * ^ ^ ^^^ ^"PP^y* there is incomplete combustion th . t 'u ''^^- ^hen and a most unpleasant, poisonous smeH ' ' ' J ' ^ ^ ° ' ' It IS on this account that the dome^t^u ' ' *^^ result. IS Still heated by means of the oIr^f•?^^^te^ geyser

"^a-tashioned fish-tail

Collar fcr 'sgulal ing flow of air

FIG. 14. Bunsen burner


burner, as there is no possibihty of striking back with this flame. Thus, the Bunsen burner, invented as a piece of laboratory apparatus, has become the standard gas burner of to-day, being used wherever gas is used for heating purposes, as in gas-cookers and gas-fires, but not in geysers.

Some years after Bunsen invented his burner, Carl von Auer, afterwards Baron von Welsbach, working in the very same laboratory, made another discoveiy which resulted in a revolution in methods of gas lighting, and ultimately caused a complete change in the composition of the domestic gas supply. Welsbach, who was engaged in examining the spectra of various elements, used as the source of light for his spectroscope cotton threads soaked in various metallic salts and heated with a Bunsen burner. As the result of his observations he invented the incandescent gas mantle, which, as is well known, looks like a knitted cotton sleeve suspended over a non-luminous flame. These mantles are made of cotton or ramie fibre soaked in salt solutions containing chiefly thorium nitrate and cerium nitrate. Before the mantle can be used it has to be 'burnt oflt', that is, the collodion put in as stiffening has to be burnt away, and the same operation converts the nitrates into the oxides (thona and ceria), which when heated become incandescent.

When coal-gas was first used, not much more than a century ago, its chief value lay in the fact that it gave a luminous flame. After the inventions of Bunsen and Welsbach the character of the domestic gas supply gradually changed as it was required to give heat rather than light. Had it not been for these inventions, tnen electricity would certainly have replaced gas entirely for all kinds of illumination. This change in the gas has been fully recognized by Parliament, and the laws now

84 ^ CHEMISTRY AND THE HOUSEWIFE

requure companies manufacturing coal-gas to supply the^ customers with a gas of a certain standard heat-

tem 1 ? ^ ? ' ' ' '}''' "^^^g^ ° " thi«- When the sys-T Z ^ I introduced it caused a little confusion, as undTri ' M I T ' - ^ r ' ^°ns^niers apparently did not unde stand the method by which the price vvas fixed. t i n n \ ! ' ^ ^ \ T ' ^ ^^"^Ple, and perhaps a short explanation here will be useful. ^ ^ ^

m e l l / l ^ K l^^ ^°'^^ '^^^^"'^ °f gas supplied that is T e ore in t^ ^ ' P " " " ' ' ^ ^ - ^^^^^^ ^ê introduction of

according to the nY^K ' ' ^ ' ^''''''' ^y^^^^' ^^ P^^^ burning ^the gas ' °^ ^"^'^ "^ ^^^^ ^^ S^ ^ ^^

t o T S t e m p T r a r I V ' ^ ^ ° ' ^ ^ " ^ ' ^^^ • known as the Brkbh T h t ^^ ^/^^^^^^ ^° ^- This is B.T.U., and the l t comn^ ^^^' ' "^ "^°^^ ^^"^P^^' somuchper iocoooBTU TK ^ ° ^ '" ^ '^^^^ g^^ ^' will provide this amonnt (i • quantity of gas which

The actual i^::^]^'^':^:, - " ^ ^ ^ ™ M of gas. rally will vary according toTt."?,,"^ ^P ^ '^^^"^ ^^^"-the neighbourhood of 200 cnK^^'f ^y' ^""^ '^ "^^^lly in mg, a therm of gas will heat t^l"" Roughly speaker light an avera'ge roorîlltZZr'^' ""^ ' ° ^ '^^ '^

Each gas company is now • "^^• analyst, called a 'Gas Examin!?^''û *° "^î^tain an heat value of all the gas made ' H f ° "^^^sures the the average value over anv pivl,f" • "^ ^ ^ records When, therefore, the conLêr receive V^^'-^-'-<^-not only does he know the volume f I ' ^""^ ^ ^ ' consumed, but is also told its ave I ^^^ ^^ ^^^ which the price is calculated. ^^^^ value, on

CHEMISTRY AND THE HOUSEWIFE 85 Domestic life has changed very considerably, and

one of the biggest changes has been in the prodigal way we use water. Coupled with the growth of our cities and urban districts, this has resulted in our water companies having to provide very much more water than would, at one time, have appeared likely to be required. All the water we use comes down as rainwater at first, but before it can be collected it has drained from the surface soil into rivers or passed through the ground to reappear as spring water. Thus before it reaches storage reservoirs it has acquired a greater or less degree of contamination. In the normal course of events, during the storage and filtration of the water, the oxygen necessary to purify it is obtained from the air, for the purifying process is really nothing but a kind of slow combustion. The process is slow, however, and with the ever-growing demand for water, chemistry has had to be called in to shorten the time of purification.

The substance used is chlorine, which, as is generally known, is a greenish-coloured gas; it is the same gas that for a period during the European War had a considerable vogue as a poison gas, for if inhaled m any quantity it produces a choking sensation, and causes such damage to the lungs and bronchial passages as niay lead to death. It may seem strange that such a poisonous substance can be used as a water puriiier. The theory of its action is very simple. Chlorine acts on the hydrogen, which forms a part of the water ana produces hydrochloric acid, but at the same time me IS set free an equivalent quantity of oxygen. ^ ^^^^^^ purification is really brought about by the release or this oxygen. In using chlorine for this purpo e it is very necessary, of course, to regulate the amount.

86 CHEMISTRY AND THE HOUSEWIFE much chlorine gives the water that horrid flavour which all old soldiers will know, as it is usually present in water supplied to troops on active service. Conditions are such in the field that there is not time to test all

V1?l'^•^'l^'TPl-^''^ ' ° ^^ ^"^y' so it is usual to chlorinate all of it, and for safety's sake the chlorina-

tion IS usually rather overdone. Chlorination in this case IS done by adding a small amount of 'bleaching-powder (often called chloride of lime) to each water-^ n r l """^Y,^^^^ companies perform this operation more carefuUy, using cylinders of chlorine. These tfon h ? '°J?^^^,chlorine in its liquid form, liquefac-o n l v n ^ ^ ° ' '^^ ' " ^ ° ^ ' ^y compression, and it is to t h r r r " ^ ' ° ' ° ^ ^ ^ ' ^ ^^y^^^^^ «f l q^^d chorine escane TuT.^^'"' ' ^ ^ ' " ° ^ '^' tiniest of trickles to chlorfne W t^' " " f ' ^^^ introduction of a trace of ?ron a'nd th ^ ^ ^ '^' '^''' °f speeding up the purifica-

chToriTac d o t c r s e " t \ V ^ - ^" T ^ ^ ^ ^ ^ ' ^ ^ ^ ' ^ ^ ^ ^ ° -quantities, and t S r i , t^'r^^P^^'^"^^^^^"^^^^^^ some substances that,eu, ^ ^ ^ ^ ^ f ^^e water if it remained unchanged 1 ? ' ' " " ' " °^""^- ^^"" amount to be o b ' S b l e " ' ' ' '' ^' ^°° ^"^^" ^"

Although in the household we i,c« water than did our grandmrem! ' ° """^^ "^° '^ using even larger q u a n t i S for ^ "If " '" ' ^^directly, household wash has gone ;nd M " ^ °^ '^^ weekly that do not send at least a part of ?1? " '" ^ ' ^ ^^^^^^^ or table linen to the laundry We r"" P^''^^"^^ ^^^^n increasing specialization, and in snJt^ / ,? ^^ ^^^ of the way in which laundries ruin th! ° , i ^^^ J^^^s at remains that they do the work better t i • ^^' ^^^ ^^"^^ mto consideration, than it can be don T^ ^ ^ *^"Ss the standard of laundry work alr^ ^ ^ °"^e. Also,

' ^^^y improved out


of recognition in the last thirty years, is continually getting better.

The chief laundry materials are soap and water. Bleaching agents also find a place in all laundries, of course, for their judicious use solves many problems, as, for example, the removal of stains caused by tea, coffee, or fruit-juices. Water is frequently 'hard'; that is, it is reluctant to give a lather when soap is added. In this case, before a lather can be formed, a good deal of soap has to be used, and apart from the waste of soap, such water forms a disagreeable curdy scum (known as lime-soap). This scum sticks to fabrics in the water with remarkable tenacity, and frequent washing of clothes in such conditions causes them to become grey instead of white. Hard water, then, leads to waste of soap and discoloured clothing. The enlightened laun-dryman turns to the chemist, for not only can he not afford to waste soap, but his reputation as a good craftsman is at stake. The chemist provides him with a water-softening plant.

To understand fully why water softening is desirable we need to know something of the causes of hardness in water, and also- how, by chemical action, the dissolved solids which cause the hardness are treated so as to be converted into harmless substances. Water is hard when it prevents soap from lathering. Soap is a chemical substance produced by long boiling together of soda and an oil of animal or vegetable origin (not a mineral oil). AH such oils are similar in composition, containing glycerine united to acids which are callea fatty-acids. The soda combines with the acids to form soap, and the glycerine is set free. (J^'^/l^l^''^' which the chemL prefers to call glycerol, and which we use medicinally, for toilet purposes, and also tor tne


manufacture of explosives, is thus a by-product of soap manufacture. Not very many years ago it used to be thrown away as its value was not realized.) Soap is thus seen to be a mixture of chemical compounds; it is the mixture of salts produced by the soda combining with the fatty acids, and thus its properties will differ to some extent according to the type of fat or oil used in making it: whether tallow or olive-oil, for instance. Whatever kind of soap it may be, however, if we try to dissolve it and use it in water that contains chalk or similar bodies, the first thing that happens is that the chalk forms what has already been referred to as lime-soap, so we have to go on adding more of our soda-soap till there is enough left over to give us our lather. The amount of soap thus wasted is much more than is commonly realized; for instance, with London water it is not less than four-fifths of the whole amount used. Many water supplies, especially in chalk or limestone districts, are still harder, and so cause even more waste. It would appear, then, that the problem of water softening is to convert the chalk into something that does not cause precipitation of the soap.

This desirable state of affairs is brought about in one of the following ways:

(a) by the addition of caustic soda and/or washing soda,

(b) by the addition of lime and washing soda, (c) by what is called the Base-Exchange method. Method (a) is only suitable with certain types of

water, and, like method (i), which is very much used industrially, requires the use of large settling tanks or filters for the collection of the chalk which separates. It also calls for frequent expert supervision and control. Method (c) requires no supervision, and the apparatus

CHEMISTRY AND THE HOUSEWIFE 89 is almost automatic in action. In addition, it gives a soft water having qualities specially suitable for laundry-work. I t is also the method used for the domestic water-softeners now obtainable and hence has additional interest for us. The softening material is a bed of zeolite, a mineral substance the natural supplies of which are somewhat limited. That which is used in softeners is made artificially by fusing together felspar, china-clay, pearl ash, and soda. It is interesting to note that the peculiar properties of the zeolites were discovered by a scientist of the German Geological Survey in the course of an inquiry into the composition of various minerals—an apparently very useless quest not likely to be of more than academic interest. The natural zeolites are of complicated composition but have a base' of potash or soda. Now hard water contains com

pounds having lime (or magnesia) as their base. When hard water percolates through a layer of zeolite, the zeolite and the dissolved solids in the water exchange their bases. Thus, water containing chalk (lime base) after being filtered through zeolite contains salts having a soda base, and since these salts cause no precipitation of soap, the water is soft. This base-exchange continues until the zeolite has lost all its soda, and the time needed for this to happen will depend on the quantity of water filtered and the original degree of hardness of the water. The zeolite need not then be thrown away, as it can be regenerated by soaking it in some liquid from which it can recover its soda base. Such a liquid is easily made by merely dissolving common salt in water so as to make a strong brine, and when the zeolite is left for a short time in this liquid it releases the lime it has acquired, takes in soda, and is ready for softening more water.


This type of water-softener, it will be seen, needs no settling tanks, nor is it necessary to measure the quantity of chemicals needed for softening, as the water helps Itself to the exact amount required. All the user has to do IS to see that the required substance is there when wanted by regenerating the zeolite sufficiently frequently. A further advantage is that the softener can be attached directly to the main water supply, and the pressure of the main will assist the passage of the water through the zeolite bed. Such a softener leaves in the water compounds having a soda base, and the amounts of these substances will depend on how hard the water was before being softened. The salts left in will usually be the sulphate and the bicarbonate of soda. The former of these is also known as Glauber's salt and the latter as bakmg soda. Whether the amounts of these salts will be enough to be objectionable will depend on circumstances. One reason why some users like these water softeners is that they say they economize on tea and coffee. Water containing alkaline substances such as baking soda will most decidedly cause more colour to be extracted from the tea or coffee, but whether or not the flavour is improved is an open question. If a very hard water were softened by zeolite the soft water would certamly be so alkaline as to dissolve traces of aluminium from any such vessels in which it was boiled. Opimon, again, is very divided on the degree of importance to be attached to this fact.

CHAPTER VI

CHEMISTRY AND THE HOUSEWIFE. II

IT was the rapid expansion of chemical knowledge in the second half of the nineteenth century that brought to light the wonderful wealth of materials obtainable from coal-tar, that is to say, indirectly from coal. Conversely, it was the discovery and study of the many remarkable new substances that proved a wonderful stimulus to chemical research. The facts unearthed have accumulated, snowball fashion, till they are to-day beyond the power of any individual to appreciate to the full. We can, however, study some aspects of the science and see how, in particular, the study of coal-tar led to the discovery of new coloured substances capable of replacing the old and rather crude dyes formerly ^fed. The study of these early dyes in turn led to the discovery of dyes of new types, and these discoveries reacted in such a fashion as to make it essential to know more of the nature and properties of the common textile materials. Thus chemists worked to understand and to improve upon nature's products, and eventually produced the modem artificial fibres which are now Jâde so cheaply that the most sumptuous lookmg tabrics have become sufficiently common to be accepted ^vithout further thought. ^ , , , , A hundred years ago the variety of colours that could °^ applied to fabrics was much less than is the case *°-day, and though the dyes then popular can still be ^btained, they are hardly ever used; indeed it vvould be ^ârly true to say that, with the exception of mdigo they X' never used now. The chief reason is, of <ôjrse^^ll ^he old dyes cannot compare for brilliance with those

92 CHEMISTRY AND THE HOUSEWIFE now used. In general, too, modern dyes stand up to wear and tear better than the old ones. Some of the old dyes were very good as regards being 'fast' to light, &c., but they were Hable to annoying variations in quality which made their use much more uncertain than IS the case with their successors. One hears a complaint occasionally that the modem colours are not so good as the old ones, but such complaints are not well founded. When a dye to-day proves unsatisfactory the reason will generally be found to lie in its unsuit-ability; m such a case the fabric is probably being used for a purpose that the dyer did not anticipate.

i he process of dyeing varies in details, but the essen-tial part remams the same. The dye is first dissolved in water, and the material to be dyed is immersed in the r^ V nT ' T f ' ^ f ^^^'^^- I^ °^der that colour n e e d f h . n f " I'^^u'T ' ° '^' ^^^ric the dye must ^hTst ZfZ ^^^^ ^^l ^^^^^^ h^« ^^ attraction; if this is not the case, then it becomes necessarv to chinVe the properties of the fabric by giving it . n r^ !^ to change ^.-„„t-^„_. rp, . '"- "^y giving It some preliminary treatment. This preparatory treatment is called mordanting, a term derived from the French morire - to bite. It was supposed long ago that the substtnce~we describe as a mordant actually bit the surface of the fibres, so enablmg the colour to penetrate

We speak of the 'art' of dvein? nnH u • • , more correct to call it an art than f'science VV' '^"^^^ it is found that there are so many types of dv ^ ^ f' ^ many variations in the details of their applic ? ^^ , ^° no single theory has been put forxvard that'ofT' adequate explanation of all the facts. There h \^ ^^ for example, chemical theories of dyeing wh' h^^ °^en, that the dyed fabric is a chemical compound 7 fil^^^ and dye; mechanical theories, which attempt to° l • ^

CHEMISTRY AND THE HOUSEWIFE 93 dyeing as due to a penetration of dyestuff into the pores of the fibre; and many others. None of the suggested explanations does more than explain a fraction of the facts.

Before the discovery of the coal-tar dyes, the dyer's choice of materials was comparatively limited. He could, for example, choose between cochineal and madder if he needed red; between prussian blue, indigo, and log\vood if he required blue; and with other colours his ânge was similarly restricted. Since the discovery of coal-tar dyes an almost countless number of such dyes has been made, and though many of these proved worthless when tried, there remain hundreds of excellent dyes. From these the dyer may choose those that appeal to him on account of price, or some special property they may possess that makes them particularly suitable for the class of work in which he specializes. - 11 dyers are specialists, and confine their attention to goods of one type, for example, to articles made of cotton, or to silks, or perhaps to yams or to worsted goods only.

The first coal-tar dye, 'mauve',' was made-in 1856 by W. H. Perkin, who obtained it unexpectedly when oxidizing crude aniline. Although the discovery was, n a sense, accidental, yet Perkin appreciated its value,

and so did other chemists, who immediately began a fêrish search for similar substances. The activities ^f the colour-chemists also included research into the chemical composition of the colour principles ot tne "ôre satisfactory amongst the old natural dyes- Ahei êfarchessucceedcdinidentifyingtheindividualchemi

âl substances that were present; for example, madder

th^ e ^ r ^ - " ^ - - d in use as the colouring of the penny postage stomp till na of Queen Victoria's reign.

94 CHEMISTRY AND THE HOUSEWIFE root was found to owe its dyeing power to the presence of a coloured substance to which the name alizarin was given, and the colour of indigo was shown to be due to a different substance that was given the name of indigo-tin. Now the amounts of these colours found in various samples of madder root or indigo vary according to the conditions of growth, the climatic conditions at the time of harvesting, &c., so that the dyer who used them had always, as it were, to feel his way. Clearly here was an invitation to the chemist to synthesize these colours, for if this could be done, quality could be standardized and prices would be more stable; but, of course, the people -who grew madder and indigo would find theu: markets gone. Madder used to be grown in large quantities chiefly in France, and more than 70,000 tons was produced in 1868 though none is grown now. Indigo was produced chiefly in India, where a little, is still made, but thousands of acres of land had to be put to new uses. Thus one result of chemical developments was to cause temporary unemployment in France and India.

Alizarin is now made exclusively from the hydrocarbon called anthracene, a solid yellow substance separated from coal-tar. Although the discovery of the chemical constitution of alizarin took several years, and a further long period was needed before a successful manufacturmg process was evolved, by a remarkable coincidence, Caro, Graebe, and Liebermann in Germany and Parkin in England all discovered the same method. The former group filed their patent application on the 25th June 1869, and Parkin filed his application on the very next day!

I t was no less than forty-three years from the time the first experiments on indigo were begun to the day

CHEMISTRY AND THE HOUSEWIFE 95 when its constitution was finally established by Baeyer, and another twenty years elapsed before a commercially satisfactory manufacturing process was m operation. It is said, probably truly, that the makers had spent no less a sum than £500,000 before they were able to sen any synthetic indigo. The greater part of the indigo used at the present day is this synthetic product, ana the quantities used are very large. Most of the navy-blue suitings for men and such things as blue dungarees are indigo dyed, or have a basis of indigo, 'topped wim some other dye to vary the shade. . ,

As long ago as 1844 John Mercer had experimented to observe the effect of various chemical substances on cotton fibres, and amongst the materials he used were solutions of caustic soda of various concentration, m effects of which he had noted at a number of difterent temperatures. Cotton fibres when viewed througn "Microscope can be seen to look like flattened or co-lapsed tubes. The general effect of caustic soda solutions on these fibres is to cause them to swell as thougn the tubes had been inflated, while at the same time tne

fibres appear translucent --^f'^'^l^^f^/Xlc^ Thomas and Prevost repeated some of Mercer s ^ nênts but with this important difference, that tn^ ^^ ^vere prevented from shrinking by bemg kept stre ^ ^ during the application of the caustic s°da' ^ the ^hile water was afterwards used to .âsn ^ ^ _ ^kali. This gave the fibres a ^^f^J^^tsigncd The method was developed and machme y^^ ^^^ ^

tor treating cotton, both in the ^^'"^ ^lîe ]iceping yoven fabric, with caustic soda solution ^^^^^îâtion t under tension. The process was caii jy[ercer,

in recognition of the foundation laid uy j ^^^ ions and has become one of the most important P


to which cotton materials are subjected during the finishing stages of their manufacture.

Mercerizing is seen to be a chemical process, and in like manner chemistry is intimately concerned in all textile manufactures, particularly in those processes known by the general name of 'finishing', a term that would also include such diverse operations as shrinking, making unshrinkable, water-proofing, fire-proofing, dyeing, printing, sizing, silk-weighting, and others too numerous to catalogue. The chemist, having supervised the production of every kind of fabric from the heaviest carpet to the flimsiest crepe de chine, has in recent years solved the problem of producing new fibres that in one respect resemble silk, and which, in consequence, have come to be called artificial silk. This name is somewhat unfortunate, the term artificial suggesting an imitation of inferior quality, whereas the materials thus made are in a class apart and can well afford to stand or fall on their own merits.

The natural fibres fall into two classes. The first contains animal fibres such as silk and the various kinds of wool .(botany, merino, alpaca, etc.); the second class comprises the vegetable fibres, viz. cotton, flax, jute, hemp, etc. Now all these fibres except silk are relatively short (say from | to 6 inches) and have to be made into yarns by spinning, that is, by twisting a large number of fibres together so that they grip each other and form a continuous thread. The filaments of silk are sometimes hundreds of yards in length, so that in this case all that is required is that a number of such filaments be used together as one thread, very little twisting together being necessary. Thus we see that in this respect it is much easier to make silk yarns than yarns of other kinds, and, further, the almost completd absence of spinning enables

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PLATE 15

Mercerizing machine through ^ i t h cloth passing

Photo: Mather & P,ott. Ltd.

Apparatusforchlor inat ingwater : this 'Chloro-nome' is for water flows up to2,000,000 gallons per day

Photo: Paterson Engineering Co., Ltd.

CHEMISTRY AND THE HOUSEWIFE 97 the natural lustre of the silk to show to advantage. It is in this one respect that the so-called 'artificial' silks resemble the natural product, for they also are continuous filaments. All the artificial silks, which we shall in future refer to by the name 'rayon', are made from cellulose. This substance is very widely distributed in the vegetable world, and in fact is the material of which the walls of living plant-cells are made. It is thus present in such things as cotton, linen, flax, and wood, forming in fact, the greatest part of these substances.

Rayon is of two types, one similar in composition to the cellulose which is the raw material, and the other a rather different substance, a derivative of cellulose, called cellulose acetate. There is no visible difference between the two types, but the difference in composition does mean differences in their properties, e.g. the acetate rayons cannot be dyed with the same dyes as can be used for the other type, and also they are more easily affected by heat, which softens or even melts them, and by certain solvents such as might be used in removing stains. Acetone, for example, dissolves this kind of rayon. Hence greater care is necessary in Ijandling fabrics made of this rayon at the laundry or dry-cleaning estabhshment.

The first kind of rayon to be produced was that manufactured in France by the Chardonnet' process, samples of it being shown at the Paris Exhibition in 1899. In this process the cotton is first 'nitrated', that is, treated with a mixture of concentrated nitric and sulphuric acids until it has much the same composition

• The process was invented by Comte Hilaire do Chardonnet who is said to have been inspired by watching silk-worms feeding on mulberry leaves (composed chiefly of cellulose), and spinning silk from the digested cellulose by their 'spitmereta'.

G


as gun-cotton. The nitrated cotton is then dissolved in a mixture of alcohol and ether, and the solution is filtered and then squirted through fine capillary tubes into warm air. The solvent evaporates rapidly leaving a filament of nitrocellulose, and several of these filaments are collected together to form threads and wound on a spool. This nitrocellulose thread has the appearance of silk, being very smooth and lustrous, but owing to its composition it is dangerously inflammable. To get over this difficulty the threads are passed through a bath of ammonium sulphide solution, which 'de-nitrates them and produces cellulose. Hence the final product is a cellulose thread consisting of a number of smooth, continuous filaments, having the appearance of silk but the composition of cotton. This Chardonnet rayon is not now used very much, having been replaced by other varieties.

In making rayon of all varieties the same general principle is employed for producing each single filament, i.e. the solution is squirted through very fine nozzles either into warm air (the Chardonnet and acetate processes) or in the other cases into a trough of some coagulating solution. Viscose rayon is made usually from wood-pulp, a purified cellulose being made from spruce wood. The wood cellulose, by a rather complicated chemical process, is converted into cellulose-xanthate, which is dissolved in water, squirted and coagulated, and at the same time reconverted into cellulose by passing the filaments through weak sulphuric acid. This is the variety of rayon most frequently used in Great Britain.

Another kind of rayon is that known as Glanzstoff, Bemberg Silk, or Brysilka. In making this rayon either cotton cellulose or wood-pulp is used and dissolved in


a liquid which is a solution of copper hydrate in ammonia. As in the viscose process, the coagulating bath is a sulphuric acid solution. It will be noted that the three varieties of rayon so far mentioned are all similar in composition to cotton.

The last kind of rayon to be mentioned is of a different composition. This variety is known generally as Cela-nese in this country, and the raw material for its production is cellulose in the form of cotton linters. Linters are the short cotton-hairs which remain attached to the cotton-seeds when these are separated by the ginning machine from the newly harvested cotton. The cellulose is first converted to cellulose acetate, a white substance looking much like cotton-wool. This is then dissolved in acetone, and from this solution the filaments are formed. Coagulation in some factories takes place by passing the filaments through solutions of various salts; in other factories the acetone is simply evaporated by warm air.

At first sight there would appear to be only a very slight connexion between rayon, even in the form of 'silk' stockings, and chocolate boxes, but in tliese days the btter are nearly always wrapped in a tra'hsparent tissue called cellophane. This remarkable substance is used for wrapping an enormous variety of different articles, such as cigarette cartons, cake boxes, &c., and is even used for making artificial flowers. No doubt many of the public who saw artificial flowers, apparently made of paper, being used for street decoration before ICing George's Jubilee, must have speculated as to what they would look like after rain. They need not have worried for the flowers were nearly all made of cellophane, and, as events showed, rain had very little effect. Cellophane is the same material as rayon, but in sheet


form, and is of two kinds. One kind burns readily, just as cotton does, and is made by the viscose process; the other kind does not burn easily. This is made of cellulose acetate, and when heated it goes soft, almost melts, and turns black before burning very slowly.

The study of the chemistry of metals has had very remarkable results. Many metals which were rarely seen only a few years ago are now quite commonplace, not merely in chemical factories or engineering shops but even in the household. Aluminium has been mentioned already. Tungsten and tantalum are used in making the filaments of our electric lamps; platinum in jewel setting; nickel and chromium in plating other metals; chromium with iron for making rustless alloys, and so on. If we include the family automobile as a part of the household furnishing, which in these days it often is, then we should be able to make a very long list of the various alloys that have been discovered and studied mainly with a view to their use in connexion with the internal-combustion engine.

Our grandparents kept their cutlery bright by using a knife-board—a leather-faced board on which it was usual to sprinkle powdered bath-brick, the knives being rubbed on this till all stains were polished away. The result was excellent, but the method laborious. The first time- and labour-saving knife-cleaners allowed a number of knives to be cleaned at the same time; the knives were held in slots between two flat, circular rubber disks which were revolved carrying powdered emery with them, thus rubbing both sides of several knives in one operation. Chemists were at work, however, studying the conditions under which steel corrodes, and whispers of 'rustless' steel were heard. About this time there appeared knives which the sellers claimed

PLATE 16

H which has removed impurities Above, Left: Extracting sheets of wood-pulp from a l="[^ °[,'^lo"f' 'R°/K; A cake of Rayon, the form in and formed an entirely new compound called alkali cenuio . s . which the thread comes from the spinning machme Photos: CourtauWs, Ltd. 6e/ow: Rayon thread wound into hanks

RAYON MANUFACTURE

PLATE 17

CHEMISTRY AND THE HOUSEWIFE loi were rustless, but they were made so merely by platmg with nickel, which had the unfortunate result of making the edge quite blunt; any attempt at sharpening spoiled the plating, so buyers were warned against attempting to improve the edge, being told that rusdess steel could not be sharpened. In consequence, when genuine rust-

FiG. IS- Ivnifc-cleaning macliine

less or stainless steel was produced, many potential buyers were prejudiced against its use, their prejudice being strengthened to some extent by the fact that it was some time before stainless steel knives capable o taking a good edge were produced. Many people still think stainless knives must not be sharpened, bu ot course they can be sharpened when necessary just ii^e any other kind of knife, since the non-stammg power o the metal is inherent in its composition and does not depend on an added surface layer Ordinary stamless steel is made by alloying iron with some 15 ^ cent, of chromium. , , „,ct;n(T of iron

It would seem a. firs, sight that he ^^^if^^^^ (or steel) was quite a simple matter ano oi


explained. Rust is iron oxide, and iron when exposed to the air goes rusty; hence one might conclude that rusting is a simple case of oxidation. It is easy to show, however, that air alone will not cause rust; neither will water which has been boiled to expel all dissolved air, so that one cannot conclude that iron which rusts in presence of water does so because the metal decomposes the water and takes oxygen from it. The problem, in fact, is quite complex, and the solution of it is quite a recent discovery. It appears that for rusting to occur, in addition to oxygen, there must be present also water containing in solution something that will permit the passage of small currents of electricity (the land of substance known to chemists as an electrolyte). Further, some parts of the iron must be more aerated than other parts—^there must be 'differential aeration'. Then rusting will take place, not where the supply of oxygen

^ is greatest, but where it is least. This is in agreement \ with the commonly observed fact that it is usually the ; re-entrant angles of hinges or girders which show the ' most rusting. It also explains why, when rusting has

begun, it generally continues at the same point, for the layer of oxide formed is sufficient partly to pro te^ tKe metal there and so cause differential aeration. ^ " " ^

The study of corrosion, fortunately, is not wholly a study of its harmful effects. Metals do not always corrode when they might be expected to do so, and it

; ,, / I S possible to treat them in various ways to prevent '^ ^ s t i n g . Suppose, for example, that a metal were tmi-

formly coated with a layer of oxide, this layer would tend to prevent further corrosion. Aluminium is one example of such a metal; if its surface be scraped free of oxide, more is immediately produced (hence arises the difficulty in soldering aluminium). Sea-


water or water containing washing soda dissolves this protective film.

Iron can be prevented from excessive corrosion m several ways. One method is to heat it in an atmosphere of ammonia gas. This gives a surface film of iron nitride which is very hard and protective. Another way is to dip the iron into a solution of phosphoric acid, which forms a thin coating of iron phosphate. The most usual manner, however, is to make the iron, as it were, seir-protective. (This brings us back to our stainless steel.) Chromium is a metal on which a film of oxide forms spontaneously; this film is extremely thin, and so is invisible, but it has the power to renew itself automatically when broken. It is found that when iron is alloyed with chromium in sufficient amount, the hlm-forming power is also conferred on the iron which thus becomes, as we say, 'rustless'. It would, of cour e be more accurate to regard the alloy as P^nnanent y rusted, but the film of rust is so thin as to be mvisib e - i t merely protects against further ô^ ^ ^ ^ .' \ ^ ^ ' chromium is used in the household alloyed with iron as stainless steel. We also make extensive "^^ ot tê metal, by the electro-plating method, as a Protf^^^_ agent to prevent the tarnishing of ^^ter- t^ . b ^ * room fittings, door-handles, reflectors for electric radia tors, the plated work on motor-cars, &c. .j j^

Aluminium in the form of household utensUs already been discussed. In the form of comp,^ ^^^ containing the metal, we meet it m om j ^ ^ ^^^^ household. Alum is the base of tê styp F ^ ^^^^ the male members of the family find ô u ^ . ^ .^ ^j^^ the bleeding of small scratches or û^s s _ . ^^ ^ j ^ ^ . _ daily effort to keep the chin smooth. - ^ ^ . ^ nium is the chief substance used in maKi g


shower-proof. Fabrics can only be made impervious to rain by coating with some such substance as rubber or oil. In our climate, however hard it may be raining, we can count on an early change, and so the oilskin or heavy rubber mackintosh is not often required in the ordinary vocations of life. A fabric which is not very easily wetted is sufficient, and since such a fabric is not air-tight it is usually preferred. It is thus only necessary to treat the fabric so as to make it water-repellent. To do this aluminium acetate is first applied to the cloth, by passing the cloth through troughs containing a solution of this compound, squeezing out the excess by means of rollers working like the domestic wringing-machine. The cloth is then dried by heating, when the aluminium acetate is decomposed, and there is left in the pores of the fabric a deposit of aluminium oxide, such that, when the material has once been thoroughly dried, it will afterwards be difficult to wet. The process is sometimes extended by applying a further solution —this time of wax dissolved in some such solvent as benzene.

Aluminium acetate solution for shower-proo&ig is made by adding a solution of aluminium sulphate to one of lead acetate. When the mixture is made, lead sulphate, which is insoluble, is formed and is allowed to settle out, the clear aluminium acetate solution being decanted. This solution finds another use in textile work, being employed as a mordant. It is used particularly in dyeing with alizarin (see p. 94). Any red cotton fabric may therefore turn out, on examination, to have been dyed on an aluminium mordant.

There are few households to-day that do not possess one or more articles made of the material spoken of, although sometimes erroneously, as bakelite. This ver-


satile material may appear in the form of door-knobs, lampshades, wireless panels, electric switches, combs, tea-cups, and even tables and chairs.

There appears to be scarcely any limit to its possibilities, and the growth and development of the plastics industry, as the industry concerned in these productions is called, is one of the romances of chemistry.

Bakelite was the first material of this kind to be manufactured, but now many other materials, of different composition but similar properties, are made and used. It may seem incredible that two colourless liquids can be made to react together to form a hard and durable solid, but, in the case of bakelite at least, this is the case. The two liquids are phenol, and formaldehyde, dissolved in water. Phenol is the chemist's name for carbolic acid, and formaldehyde is probably familiar to most people under the name of formalin.

If the two hquids are mixed together and heated nothing much happens, but if, before heating, a tew drops of ammonia are added, a surprising change takes place after heating for a short time. All at once the mixed liquids froth up, and then settle o^J 'nto two layers, one yellow and the other colourless. The colourless layer turns out to be water, while the yellow hquid when separated from the water and allowed to cool, is seen to be a resin-like solid. It has, in if^'^^'f.^^^'l properties of a natural resin of gum obtained trora .

' ' T h i s is the first stage in the " J ^ ^ f ?f * 4 ' f f i t r material. The next operation is to rmx it ^^^^^^.^^ such as fine sawdust or wood Hour, a ^_^^ ^^^ matter if desired, and heat gently o ; ^°"^^^ ^^ded to filler plays much the same P ^ ^ ^ y ^ ' j heated the cement in concrete making. vVnue uc &

io6 CHEMISTRY AND THE HOUSEWIFE

whole mass is made to undergo constant churning and mixing in a kind of large mincing machine. During this treatment a further chemical action takes place, producing a hard material, which, however, can be softened by heat. When finely ground the substance is known as moulding powder, and is ready to be moulded into any required shape.

The moulding of plastics calls for a special technique. These materials cannot, like wax or metal, be melted to a liquid and poured into a mould to set. They must be moulded in a semi-fluid or pasty condition, and pressure is needed in closing the mould to force the material into all parts of it.

One type of plastic is known as a 'thermo plastic', which means a substance that softens sufficiently on heating to be moulded and sets hard again on cooling. Vulcanite and celluloid belong to this class, and they can be softened again and remoulded if necessary. Thus a defective vulcanite dental plate can be heated and then remoulded into any desired shape.

Another type, known as a 'thermo-setting' plastic, behaves rather differently. Heat first of all softens it, but while it is still hot the material undergoes a chemical change and turns into a permanently hard substance. Bakelite moulding powder belongs to this class, and, once it has set, cannot be again softened by heating.

Thus we can suin up the stages of bakelite formation as follows: The initial operation produces a resin which can easily be melted. More heat converts this into a substance less easily melted but still more or less fusible. Further heating continues the chemical change, and produces at last a material that is permanently hard and cannot again be softened.


Hence it is necessary for the final heating and the moulding process to take place together, so that the finished material is produced in the shape of a tea-cup, ash-tray, or other moulded article.

The moulds are of steel, massive in construction, highly polished, and chromium plated inside, so as to give a smooth finish to the moulded product. They are made hot before use, the required amoimt of powder is filled into them, and then the two halves are squeezed tightly together in a heated hydraulic press.

After a few minutes the pressure is released, the moulds are opened, and the moulded article ejected, ready for the market without any further treatment.

Since the introduction of bakelite, chemical research has enabled the manufacturer to produce plastics from various kinds of chemical substances.

One type of plastic is made from formaldehyde and urea, another from glycerine and phthalic anhydride, and a third from the casein precipitated from milk. Even some of the processes for making rayon have been modified in order to produce plastics from cellulose. Most of the early plastics could be produced, only m dark colours, but now they can be made white or of any desired tint. It is possible even to make a colourless plastic that is as transparent as glass. Although this, as made at present, is more easily scratched than glass, ye it is less fragile and more flexible, and bemg non-inflammable, has undoubted possibilities.

A further application of plastics, or of synthet resins, as some of them are called, is m the m kmg^t varnishes, wherein they replace the natural gums ana resins. . . • („nrv

The plastics industry is stiU P"ba"y - • s » t o y ; the future will no doubt see more progress an

io8 CHEMISTRY AND THE HOUSEWIFE

applications, and it is at present impossible to see where these will lead. Time only will justify or condemn the sanguine prophet who says that we shall one day build our houses—^walls, floors, roofs, and windows—entirely of plastics, and then fill them with furniture of the same material.

PLATE 18

-•'— .;.

f' ' 'A ' J \

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f»H the other unproofed, immersed shower-proofed, the otn^^^ ^v^^^ ^^^ unproofed , . the other unprooiea, I , . M . , - . - -

Above.; Two hanks of the same yarn, one shower-proofed t ^^^^ ^^^^ ' '^^", i ^ las°s to 'n a glass of water, leading to two empty i^^''f^^^°A the water from the f"" g' ^s ^° yarn, by saturation and capillary attraction has conv^eye . except where «mnner ed water level in the previously empty glass. The prooleo y pi^^j^^. Barberry, Ltd. and the glass to which it leads remains empty

PLATE 19

Sorting rough diamonds Photo: General Photographic Agency

CHAPTER VII

CHEMISTRY AND THE BOUDOIR WE have stated elsewhere that agriculture is one of the world's oldest arts. Another art must be nearly as old— that of the adornment of the feminine person. Jewellery, cosmetics, and other forms of embellishment are no new things, and, as in the case of agriculture, have only m modem times become associated with and dependent on the art of the chemist.

So far as precious stones are concerned, one might think that chemistry has been associated largely with the production of imitations.

While this is true to some extent, it must be pointed out that investigations into the chemical composition of gem stones have resulted in a store of knowledge that enables the expert more easily to detect the real from the spurious gem.

Also, as will be seen, the chemist has in certain cases been able to manufacture gems possessing so nearly the composition and properties of the natural stope that they must be regarded as reproductions rather than imitations.

Some of the reproductions can compete successfully with the natural products, but others have only a scientific interest and no commercial value. To this latter class belongs the diamond, which is generally looked upon as the most valuable of precious stones. It possesses to a high degree the properties of beauty and durability, which, when combined with rarity, are otten the deciding factors in the value of a particular type of gem.

Pride of place for beauty has not always been held by

no CHEMISTRY AND THE BOUDOIR

the diamond, for in its natural state it has a dull and • uninteresting appearance.

Only when it is cut and polished with the facets at definite angles does it appear in all its scintillating brilliance. The art of cutting and polishing belongs to modern times, and for this reason rubies, sapphires, and emeralds were formerly more highly prized than the diamond.

Chemically the diamond is the simplest of all precious stones. It is a crystalline form of carbon, and except for a minute trace of impurity contains no other element. It is hard to believe that the diamond, with its extreme hardness and brilliance, is made of the same element as the graphite of a drawing-pencil or the soot from a smoky chimney.

It is, however, easy to demonstrate its composition. A small diamond is put in a little platinum cage that can be heated by an electric current. The cage is hung in a sealed jar containing only oxygen and a little lime-water. The cage is now made white-hot and the diamond swells up and bums away completely. Then, on shaking the jar, the lime-water becomes chalky white, showing the presence of carbon dioxide. This carbon dioxide can only have been made by the combination of the substance of the diamond with oxygen, and as no other substance is found afterwards in the jar, the experiment shows the diamond to be composed of carbon only.

Exactly how diamonds are made in nature we do not know, but they are apparently formed deep down below the surface of the earth imder conditions of great heat and pressure.

In 1897 the French chemist Moissan attempted to reproduce these conditions artificially. He dissolved

CHEMISTRY AND THE BOUDOIR " i

• pure carbon in molten iron in a crucible, and then by plunging the crucible into cold water hoped to solidify the iron on the outside of the mass so that as it shrank on cooling it would exert an enormous pressure on the unsolidified interior.

His first experiment was a failure, for the hot iron immediately vaporized the water around it, and this non-conducting cushion of vapour prevented the rapid cooling of the molten mass. Moissan was not dis-coui-aged but repeated his experiment, this time using molten lead instead of water to cool the molten iron. (Molten lead at 326° C. is, of course, sufficiently cool o cause iron to soHdify and, moreover, it does not easily vaporize.) ., ^„„i

When the contents of his crucible were quite cool and solid, Moissan dissolved away the iron with acid and to his delight found among the residue a tew small splinters of diamond. Although a great scientihc achievement, Moissan's experiment was not a commercial success, nor was it expected to be, tor ac ai enormous cost a few imperfect diamonds worth no more than a shilling or two were produced. .

From time to time other people have claimed to have made synthetic diamonds, but the claims have al ^ays turned out to be fraudulent. i.„«„m but

The diamond is the hardest substance kno^ 'n, the ruby and the sapphire mn it f ^J^^/^J'^-^position,

Both these coloured gems have a ^'^P^^^^^ ^hich being varieties of a mineral kno^^ as ^^^^^ j . ^ ^ no is a form of aluminium oxide, ru ^ ^ . colour colour, the stones valued as gems °^jJ^^j.gj.coIoured to traces of other metallic oxides- j^^^j stone corundum is kno\vn as ruby and the D as sapphire.

112 CHEMISTRY AND THE BOUDOIR

Colourless and opaque stones are used for abrasive purposes, the common emery paper of the household being made with a very impure form of corundum.

Considering the value of the ruby and the simplicity of its composition it is not surprising that attempts have been made to reproduce the gem artificially. The attempts met with indifferent success until early in this century, when a Frenchman, Vemeuil, by means of a blowpipe of his own invention, was able to fuse a mixture of pure aluminium and chromium oxides into a clear liquid drop, which on cooling became a pear-shaped solid with practically all the characteristics of the natural ruby. The manufacture of artificial rubies is now an established industry, and it is probable that many artificial rubies are bought and sold unknowingly as natural gems.

A further class of precious stones are the beryls. These are double silicates of aluminium and beryllium. When pure, beryl is quite colourless, but it is more often tinted by traces of other metals. Beryl with a deep green colour is known as emerald, a stone which from the time of Cleopatra has been much prized for its beauty. A paler tinted variety, often with a bluish cast, is the aquamarine, which is in many cases a stone of unusual beauty. Attempts have been made to manufacture artificial emeralds and aquamarines by the same process as that used for rubies, but with rather less success.

The mineral kingdom is not the only source of jewels, for some few are made by animal or vegetable agency. Chief among these is t|ie pearl, a product of tribulation which becomes a source of delight.

A small speck of grit or other foreign body lodges inside the shell of an oyster and sets up irritation. The bivalve, being unable to eject the unwelcome visitor,

CHEMISTRY AND THE BOUDOIR 113

• covers it over with a thin layer of smooth material. This probably stops the irritation, but the oyster seems to be unable to let well alone. Probably the pressure of the foreign body is now the cause of the reflex action, and the oyster continues to deposit layer after layer until a pearl is formed.

The layers appear to consist alternately of calcium carbonate and of a horny substance known as conchi-olin. Pearls require no cutting or poHshing for they owe their iridescent beauty to the action of light on the thin superimposed layers. These gems have not the durability of mineral gems, for the calcium carbonate of which they are largely composed is easily attacked by acids. They are, moreover, easily scratched or crushed and so require careful handling.

An industry has arisen in Japan for the production of so-called 'culture' pearls. A small piece of mother-of-pearl or other substance is introduced within the shell of a living mollusc in the hope that the oyster will, in course of time, produce a pearl. The best of these pearls are not easily distinguished, except by experts, from the natural products, as they are in a sense natural products themselves. There is no eventual difficulty in making the distinction, however, for G. F. H. Smith and E. Hopkins discovered in 1921 that when viewed in ultra-violet light 'culture' pearls showed a green fluorescence as distinct from the sky-blue efl 'ect of the Indian pearl.

Manufactured or synthetic stones must not be confused with imitation gems. The former resemble the real stones not only in appearance but in other physical and chemical properties, while imitation stones have nothing but outward appearance to recommend them.

What are kno^vn as 'paste' stones are made of glass H

114 CHEMISTRY AND THE BOUDOIR

moulded into the required shape and polished. Fof coloured gems the glass is tinted with various metallic oxides. It is unfortunate from the point of view of the imitator that the most suitable glass for his purpose, that is to say, one with high refracting power, is also a soft glass. On this account paste gems are easily scratched m wear and so soon lose their brilliancy. Nevertheless, some of the imitations show in appearance a marvellous resemblance to the real gems.

Second only to jewellery as adornments of antiquity come cosmetics, substances chosen for their supposed power of beautifying the skin, hair, eyes, and limbs, in early tunes many of the paints and face powders used were chosen for the appearance they produced, with small regard for their effect on the skin.

In modem times chemistry has at any rate been able to point out the dangers of unsuitable applications, and devise methods of ensuring the purity of the products

There is yet much to be done, for it is no simple matter to mterfere with the natural functions of the hymg sbn and cosmetics are not yet subject by law to the careful scrutiny given to food and drugs

One of the first books on chemistry, as distinct from alchemy, was written in 1675 by Nicholas Lemery, a French medical man. In it he gives recipes for cosmetics consisting of preparations of lead, tin. and antimony. One IS inclined to wonder how many cases of lead poisomng resulted from the use of the lead compounds. In this connexion it is interesting to note that a century later William Nicholson, in his book on chemistry, refers to these substances and condemns their use as likely to cause injury to the skin.

Lemery also recommends, among other things, snail


water and frog's-spawn water for whitening the skin and removing spots.

In considering the effect of a cream, powder, or other preparation on the skin, it is necessary to take account of the structure of the skin and the functions of its parts. Perspiration tal<es place almost constantly from a healthy skin, and if this is impeded both skin and body suffer. Perspiration consists partly of water containing certain waste products from the body, and partly of an oily material which comes from the sebaceous glands. The oily material serves to lubricate the skin and to prevent it from becoming dry and hard. The watery matter, evaporating from the surface, coois the skin and helps to regulate the temperature of the body.

The use of face powders containing materials insoluble in water or in the slightly acid perspiration is likely to lead to the clogging of the pores of the skin and so interfere with the proper functioning of the sweat glands. Powders designed to stay on the face for a long time are more likely to contain insoluble materials, and for this reason may be not so innocuous as the less permanent ones. Otherwise there does not appear to be much danger, for the materials used are generally inert and are not known to have any irritating action on the skin. Some of the substances used are talc (magnesium silicate),precipitated chalk,magnesiumcarbonate,kaolin, zinc oxide, titanium oxide, rice starch, and salicylic acid.

Talc itself, although perfectly smooth and non-gritty, is insoluble, but some so-called talc powders consist of a mixture of magnesium carbonate and bone acid. These latter are especially suitable for tender skins and for use on babies, for magnesium carbonate is soluble in perspiration, and boric (or boracic) acid is soothing and antiseptic.

ii6 CHEMISTRY AND THE BOUDOIR

Tinted face powders and rouges are said to be harm-" ful, as they may contain insoluble ingredients which clog the pores, or colouring materials of an irritating nature. The old-time rouge was a form of iron oxide, used also for polishing silver, but carmine, a product prepared from cochineal, finds greater favour to-day.

Face creams are preparations with a fatty or oily base, and may or may not contain mineral ingredients.

A favourite base for a face cream is lanolin, a fatty material excreted from the skin of sheep and absorbed by the wool. In the preparation of sheep's wool for textile purposes this material is extracted and purified.

Petrolatum, a white, purified form of vaseline, is another face-cream base. Oil of almonds, witch-hazel oil, and paraffin wax may also be used.

Anti-perspiration creams may contain either substances capable of absorbing moisture or astringent products designed to contract the pores. Zinc oxide, alum, alcohol, glycerine, salicylic and boric acids are among the products used.

A modern development of the face cream is the cleansing cream, designed for the use of those who for one reason or another, prefer not to wash in the ordinary way with soap and water. These creams contain a mineral oil to dissolve perspiration grease and suspend dirt particles in order that they may be easily removed by a towel or by absorbent paper. The action is helped by the use of a modern chemical product known as tri-ethanolamine which acts as an emulsifier. (An emulsifier helps in the mixing of liquids, such as oil and water, which do not naturally mix.) Chemically, triethanol-amine is allied partly to alcohol and partly to ammonia.

Another constituent of some cleansing creams is car-bitol; its chemical name is diethyleneglycolmonomethyl

LIME BURNING

PLATE 21

o

o

l->

c e


' ether. This acts as a solvent, and is said also to have a soothing effect on the skin.

The chemical history of depilatory preparations is rather curious. Arsenic sulphide has for long been used in the leather industry for the dehairing of hides, and it was known that this substance was also capable of removing living hair from the body.

In Eastern countries especially, arsenic sulphide, made into a paste, had an almost universal use as a depilatory agent.

The dangers involved in the use of such a poisonous preparation are obvious. There are, in fact, cases on record where a woman has found an alternative use for her depilatory paste in the removal of an unwanted husband.

Later it was found that the hair-removing property lay not in the arsenic but in the sulphide part of the material. This discovery led to the use of less dangerous sulphides, and sulphur compoimds of barium, calcium, strontium, or sodium are now used. Unfortunately none of these substances affects the roots of the hair, only the portion above the skin being attacked. The hair grows again, generally more luxuriantly than before.

Therp is a certain irony in the fact that while there is no safe preparation which will prevent the growth of hair in unwanted places, neither is there any preparation which is definitely known to promote the growth, of hair on the head. It is said that in all cases wh^e a hair restorer appears to give results, the effect is due to the scalp massage entailed in the application rather than to the lotion itself.

CHAPTER VIII

CHEMISTRY AND THE BUILDER SAND and clay are two of the most important raw materials of the building industry. They are the basic materials for the mud walls of simple dwellings, the more elaborate buildings of bricks and mortar, or the massive concrete structures of the present day.

Both sand and clay are compounds of silicon, the second most common element in the earth's crust, and both have been formed by the breaking down or weathering of ancient rocks.

Sand is a form of sihca, or silicon dioxide. When pure It is white, but in general it has a yellow or reddish tint due to the presence of small quantities of iron compounds.

^ Clay is a complex compound of sihcon and alumin-mm, and is not, as a rule, found in so pure a condition as sancl.

^ Geologically, it is classed as a sedimentary rock-that is to say. It has been carried as fine particles by water and deposited as the motion of the water became more quiet-and its form and composition may vary according to Its origin and the changes it has undergone since It was deposited. *

In some cases the other materials of the parent rock h a ^ been washed away and the clay left behind as resftiual clay ; m other cases the clay itself has been

carried away by water until it has been deposited on the bed of a river, lake, or sea. It is then known as 'transported clay'.

Clay particles are very small and do not easily settle out when mixed with water. Where a clay has been

CHEMISTRY AND THE BUILDER 119

carried for some distance by a swiftly moving stream, the larger particles of sand and grit with which it may be mixed will sink to the bottom while the fine clay particles will remain in suspension, to be deposited only after reaching the comparative calm of a lake or ocean. Even then many fine particles of other substances remain and so the clay is rarely pure. The actual clay substance is chemically a mixture of hydrated silicates of aluminium, and the impurities may consist of particles of limestone, chalk, silica, and other materials according to the origin of the clay and the nature of the ground over which it has been transported.

One of the best-known characteristics of clay is its property of becoming plastic when wet.

This property is made use of in the moulding of bricks and other articles. When clay is dried at a moderate temperature it undergoes shrinkage and loses its plasticity, but can be brought back to its former state on re-wetting.

If, however, it is heated to a temperature of 700° C , its chemical composition changes; it loses combined water and becomes a hard, stone-like mass. It is now brick and cannot be brought back again to it's former state.

Bricks for building are made on these lines, the clay being first moulded while plastic, then dried in air, and subsequently heated or 'fired' in a suitable kiln. Such bricks are porous and are suitable for general building purposes. If non-porous bricks are required the iiring is done at a much higher temperature, whereby the material undergoes partial fusion into a glassy mass, which on cooling cements the unfused particles together and fills up the pores.

The colour of a clay is no guide to the colour of the

120 CHEMISTRY AND THE BUILDER finished brick. The colour of a natural clay is largely due to the carbonaceous impurities it contains, and these always burn away on firing. The ordinary red brick owes its colour to the red oxide formed by the heating of iron compounds present in the clay.

FIG. 16. Section of lime kiln

The use of mortar is presumably as old as, if not older than, the use of bricks. The simplest form of mortar is a mixture of slaked lime and sand, worked up R» a stiff paste with water. Several chemical reactions are concerned with the making and setting of mortar.

The lime is usually manufactured by the burning of limestone, although it may be made by burning either chalk or marble. All these three substances are forms


" of calcium carbonate, and apart from the possible presence of impurities, there is no difference in their chemical composition.

The term 'burning', applied to lime making, although in general use, is rather a misnomer, for the process is not one of burning but of decomposition by heat.

Lumps of limestone rock are filled into a kiln and strongly heated, either by a coal fire or by producer gas. The limestone is thereby decomposed into carbon dioxide, which escapes as a gas, and calcium oxide, which remains in the kiln as hard lumps known-as quicklime, and as such is delivered to the builder.

The effect of water on quicklime is curious. When water in moderate quantities is poured over quicklime no wetting takes place but great heat is developed, and the hard, rock-like quicklime crumbles down into a fine dry powder. This is called calcium hydroxide or slaked lime. The heat formed in the slaking of lime is the result of chemical action, water combmmg with the calcium oxide to form the hydroxide.

In making mortar, a builder uses excess of water, thus not only slaking the lime but turning it into a thick paste. The paste, spoken of in the buildihg trade as 'putty', but having no connexion with or resemblance to glazier's putty, is left in pits to mature, when any particles of quicklime that have escaped slaking become converted to slaked lime. The 'putty' when mixed with sand is used as mortar. , • 1 j r^iJlv

The setting of mortar is partly a physical ^ d p&t y a chemical process The first part of the setting is due d Liicniicdi pruccbb. xnv. r evaporation to the drying out of excess water bo^h by^v p ^^^^^ and by absorption into the Voro^^^J"^^^^ ^^^.^^ the chemical part of the process, the c a l a ^ > slowly reacting with carbon dioxide from the

122 CHEMISTRY AND THE BUILDER

sphere to form calcium carbonate, more moisture being given off in the process.

Thus the lime in the mortar has once more become calcium carbonate, and although it may not be so hard as the limestone from which it was made, it is a dry solid of the same chemical composition. A fair amount of shrinkage takes place, and, if it were not for the sand, the mortar would develop cracks. The sand undergoes no chemical change, but being present in the proportion of about four parts of sand to one of lime, acts as a filler and so minimizes shrinkage.

The first stage in the drying of lime mortar is comparatively rapid and may, under good conditions, take only a few days. The final setting may take months or even years, for it depends on the carbon dioxide of the atmosphere obtaining access to all parts of the mortar, and this, in the case of thick walls, is likely to take some time. During recent repairs to St. Paul's Cathedral it was found that the mortar in the interior of one of the massive pillars, after two and a half centuries, contained much unchanged slaked lime.

It has already been pointed out that moisture is eliminated, not only in the initial drying stage, but also as a result of the chemical change involved in the final setting of a lime mortar. This is especially noticeable in the case of wall plaster, which is a kind of mortar bound together by hair or fibre.

^ h e interior walls of a new building, even after the rooms have been well dried out by fires and ventilation, may show signs of sweating for a year or more. Only when there is no further action between the carbon dioxide of the air and the lime of the plaster will the exudation of moisture cease. The occupier of a new house, seeing damp patches appear on the walls, is apt


' to think that his house is not weatherproof, especially as the dampness is more evident in wet weather.

In many cases, however, his fears are groundless, for the water has not come from outside but is chemical in origin and is a sign of the setting of the plaster. It is, of course, more likely to show in damp weather when evaporation is very slow.

Pure lime mortars have little binding power, and act rather as a bed for the bricks to lie on than as a medium for holding the bricks together. It was at one time thought that in the course of years a slow chemical action took place between the sand and the calcium carbonate to form a hard rock-like calcium silicate. This assumption appeared to be borne out by the fact that the mortar in many ancient buildings is harder and more tenacious than a newly set lime mortar. Modem investigation has, however, shown the assumption to be wrong, the hard-setting mortars of the Middle Ages having been made by the burning of Hmcstone containing accidental impurities wliich gave to the mortar a cement-like property.

The modern builder achieves a similar result by mixing a small amount of cement with his mortar.

Most of the cements used in present-day buildmg are known as 'hydraulic cements' because they possess the property of setting under water. They set by tiie absorption of and combination with water instead o by its elimination. Many of the ^ ^ " d ^ ' J . ' ; ° ; f ^es mortars which have resisted from the M'd^e ^^ ^ undoubtedly contained ^V^^^l^l^:^^^^^ presence was more a matter or cnani-of applied science. ^ ^ .t,„ first people

It is thought that the Romans we« * e j r s P y^^ deliberately to make hydrauUc cements, and


them the art was lost and rediscovered only in modern times.

The Romans added to their lime mortar certain crushed or ground siliceous materials known as puzzo-lanas. Some of the silica in puzzolanas has the property,

F I G . 17. Horizontal section of the lower and solid part of the Eddy-stone Lighthouse, showing the mode in which the courses of stone are

dovetailed together

unlike the silica of sand, of combining with lime to form a hard calcium silicate.

The modern history of hydraulic cements begins soon after the burning down of the second Eddystone Lighthouse in 1756. The following year Smeaton was asked to replace the destroyed wooden structure by one of stone. He realized that the success of his operations would depend largely on the binding material used be^een the blocks of stone. Ordinary lime mortar wasbut of the question, for he required a material which would set under water, become hard and smooth and have great adhesive properties. He accordingly set to work to collect information and perform experiments. Limes from different parts of the country were tried, notably one produced by the burning of a stone found

PLATE 22

Rotatory kiln in which the raw matcfial is burnt

Cooling drum into which the hot clinker passes from the kiln

Chemists testing the raw material Photos; The Cement Marketing Co.. Ltd.

IN A CEMENT WORKS

PLATE 23

E^L:-^^^^.^^i^^:K... Above: A paint-grinding laboratory at the Borough Polytechnic, London below: Varnish running n, „ ^ i,^

S Photo: Pinchin, Johnson & Co., Ltd.


^ at Aberthaw, on the coast of Glamorganshire. With the help of his friend Mr. Cookworthy, who was a chemist, Smeaton made rough analyses of the different limes, and came to the conclusion that the burning of a limestone mixed with clay gave a lime with hydraulic properties.

The fact that Smeaton's lighthouse lasted for more than a hundred years, and was replaced only when the rock on which it stood began to be undermined by the sea, was some justification of this conclusion.

In 1827 a Yorkshire bricklayer named Aspdin started to manufacture a hydraulic cement by burning a mixture of clay and chalk. This was known as Portland cement, from its resemblance when set to Portland stone. Modern Portland cement is made in a similar way, but under controlled conditions and with materials selected as the result of chemical analysis. An intimate mixture of finely ground clay with chalk or limestone is heated in a rotatory kiln to clinkering temperature, that is to say, until the whole mass softens and fuses together. The resulting clinker is ground in a ball-mill or other type of grinder until it will pass through a sieve of 900 meshes per square centimetre. u A f

According to the materials used and the method ot manufacture the cement may be 'quick' or 'slow' setting, the time necessary for setting varying from less than half an hour for a 'quick'-setting to seven hours tor a 'slow'-setting cement. , r pAric

Another form of hydraulic cement is plaster of P^ns which is made by heating gypsum M^^^J^ .^"/f ^ ^ ^ to a temperature of 120° C. At this temperature gyp_ sum loses part of its water of rystaUizati ^^ J ^ ^ ^ ^ comes a fine white powder. On mixing ^^^^^^ of water the powder takes up again tne 10


crystallization, and quickly sets to a hard white solid ' consisting of fine needle-shaped crystals. Plaster of Paris sets too quickly to be of much use in building operations, although the setting time can be retarded

F I G - 1 8 . Section of ball-mill grinder

somewhat by the addition of a small quantity of gly-cenne to the mixing water.

If gypsum is heated to a much higher temperature than 120 C. It loses all its water of crystaUization. and is then known as 'dead burnt' or 'overburnt' plaster. This sets more slowly but is harder when set.

Overburnt gypsum, or some modification of it, is used to some extent on inside work in the building industry. The final, or skimming, coat of wall plaster generally contains some form of gypsum.

All the building materials so far mentioned can be regarded as permanent and not subject in any great measure to the processes of decay. It is otherwise with


•• the wood and iron used for such parts of buildings as doors, window frames, gutters, and rain pipes. These are lilcely to suffer deterioration unless they are protected from the elements in some way.

The usual method of protection is by the use of paint and varnish, and here again chemistry plays a part.

Paint has not only a protective value but may have decorative qualities also, and it is fortunately possible to make much of the decorative aspect of painting without interfering with its protective value.

Essentially paint consists of a coloured powder called the 'pigment', mixed to a more or less thin paste with a liquid called the 'vehicle*. Broadly speaking, it can be said that the pigment, on account of its colour, provides the decorative part of the paint, while the protective value depends largely on the nature of the liquid used as a vehicle.

In the water-colour of the artist, for example, the vehicle is simply a watery solution of gum. The paint dries by the evaporation of the water and leaves a thin film of gum over the painted surface. This has little protective value, and for this reason a water-colour picture is usually given the extra protection of a sheet of glass. A cheap distemper is similar in composition, glue instead of gum being used as the binding medium. This may stand washing with cold water, but hot water will quickly soften and dissolve away the protective film of glue. The real washable distemper, known as 'tempera', contains some oil in the vehicle, and is much more permanent when dry.

None of the paints so far mentioned has much protective value and would be unsuitable for exterior work. Outdoor paints are nearly always oil paints; that is, they have a vehicle consisting chiefly of oil and on this


account are much more durable. These paints are of '^ such great importance that it is usual in general practice to take the word paint to refer to oil paint unless another type is definitely specified.

The majority of oils, on exposure to air, undergo no chemical change. Others turn rancid, and a small class, known as the 'drying oils', absorb oxygen from the atmosphere, lose their oily nature, and turn into hard, elastic, resin-like substances. It is oils of this latter class, of which linseed oil is the most important, that alone are suitable for making oil paints.

The drying of an oil paint, then, is the result of a chemical change in the oil, producing a tough, impermeable film which binds the particles of the pigment together and protects the painted surface from the action of the weather.

In the case of linseed and other drying oils used in the paint industry, the oxidation process, although varying with the condition of the atmosphere, takes many days to give a hard surface. This does not suit the house painter, who requires his paint to set sufficiently within eight or nine hours to prevent dust sticking to it', and to be hard enough after twenty-four hours to take another coat.

Fortunately it is possible in a simple way to hasten the chemical process known as drying. It happens that compounds of certain metals, notably lead, manganese, and cobalt, when added in small quantities, act as catalysts and accelerate the oxidation process and consequently the drying of the oil. Hence in the preparation of paint advantage is taken of this property. The metallic compounds, spoken of in the trade as 'driers', are added in small quantities to the oil before it is mixed with the pigment.


*» Sometimes oxides of the metals are used as driers, but more frequently use is made of a compound of the chosen metal with the fatty acids of linseed oil or rosin, as these compounds are more readily incorporated with the drying oil.

Raw linseed oil, as extracted from the seed, is prepared in a variety of ways for use in the paint industry. In some cases the raw oil is refined to get rid of moisture and gummy matter. The transparent liquid thus produced is known as 'refined' linseed oil. A large amount of raw oil is converted to 'boiled oil' by keeping it at a temperature of 400° F. to 500° F. in contact with air and with the admixture of a small quantity (not more than 2 per cent.) of driers.

Boiled oil dries quickly and forms a hard film, hence its great value in paint mixing. It is not, however, used alone as a rule, but is mixed with some raw oil; otherwise the film may be too brittle and lead to cracking of the paint surface.

The old-time craftsman generally made his own paint, first of all rubbing up the finely ground pigment with linseed oil on a glass or marble slab by means of a palette knife or muller. The rubbing was laboriously continued until a stiff homogeneous paste of the consistency of putty was obtained. "

When required for use, this paste paint was thinned with the requisite quantity of oil and driers.

Such a process is too slow and costly to satisfy modern requirements, and to-day the paint manufacturer prepares his paste paint by first roughly mixing together oil and pigment in a suitable mixing machine, and then grinding and further mixing the rough paste m a roller-mill or other form of grinder. The paste may then be worked up in the factory into paint ready for use, m

I30 CHEMISTRY AND THE BUILDER

which case it is sold to the painter as ready-mixed paint. Some painters, on the other hand, hke to buy paste paint and do the requisite thinning themselves.

Artists'oil-colours are simply paste paints put up in

FIG. 19. Roller-mill used for grinding paint

tubes, poppy-seed oil being used instead of linseed on account of Its paler colour. "nseed ^ Where a paint is too thick or viscous for easy spreading by a brush, an organic solvent knou^ as a K e r IS added. The thinner, as its name implies, th nsThe paint down but It takes no part in the formation of a prctective film for bemg volatile, it evaporates from the painted surface soon after appHcation.

Tui-pentine and white spirit are the thinners com monly used. Turpentine is obtained from the resinous exudation of various types of pine trees. The tr are 'tapped' or 'gashed' and the gummy sap collected


» in pots. This material, known as an oleo resin, is subjected to distillation, giving turpentine as the distillate, and leaving behind in the still a solid resin known as rosin or colophony.

White spirit is a petroleum product and is sometliing like petrol but not so volatile. It is sometimes called mineral turpentine or turpentine substitute, and was at one time looked upon by painters as being a cheap and inefficient substitute for turpentine. It has, however, been taken into extensive use as a paint thinner, and appears to be as satisfactory as turpentine for ordinary oil paint, although it is not so good for thinning varnishes. For cleaning painters' brushes and paint-making machinery it is preferable to turpentine.

The gloss with which an oil paint dries depends to some extent on the proportion of thinner used. If a paste paint is worked up with linseed oil containing a small amount only of thinner the paint dries with a smooth finish; but if about four parts of thinner to one of linseed oil is used, a dull surface or 'flat' finish is obtained.

Where a more shiny finish is required the painted surface, after drying, is given a coat of varnish, which not only improves the appearance but provides an additional protection.

Varnishes are solutions of resins, gnms, or lacs m a suitable solvent. A spirit varnish is simply a solution of a suitable resin in alcohol or similar solvent. Such a varnish dries by the evaporation of the solvent, leaving a thin, lustrous film of resin over the painted surface. Spirit varnishes have the advantage that they diy quickly, generally in a few minutes, but the fi m they give is easily destroyed, so they are not as a n^e - e d for outside work. Spirit varnishes are frequently made


with shellac and are known as lacquers. Shellac is an / exudation from certain oriental trees, produced by a species of insect known familiarly as the lac insect. These insects feed on the sap of the tree after puncturing the bark and excrete large quantities of lac, which forms deposits over the twigs. The twigs, known as stick lac, are collected and the lac is separated and purified. Both knotting varnish, used for covering the knots in new wood, and French polish are solutions of shellac in spirit.

The varnish used by the house decorator is usually an oil varnish, made by the incorporation of a gum or resin with a drying oil.

The making of an oil varnish calls for skill and judgement, and was until recently an operation performed by a specialist workman. These operators were usually regarded as possessing secret knowledge, and their so-called secrets were carefully guarded. Chemical control has now reduced the practice of varnish-making to questions of temperature and measurement, enabling a greater variety of materials to be used and resulting in standardized products suited to various purposes.

A res?n is not normally soluble in linseed oil, and the first process in varnish-making is that known as gum-running. This consists of heating the resin until it melts and undergoes certain chemical changes, losing water and gaseous decomposition products in the process.

While this is going on the oil is heated separately to aboi^t 500° F., and is then slowly added to the melted resin, with careful mixing. The mixture is then reheated to ensure thorough incorporation of the oil and resin. The skilled varnish-maker tests the melt from time to time to see if it strings, that is to say, if a drop placed between thumb and finger remains in long strings


'» when thumb and finger are separated. The amount of stringiness aimed at depends on the type of varnish. Driers are added either during the heating process or afterwards, and when the varnish has cooled somewhat it is thinned to a suitable consistency with turpentine.

The resins used vary according to the type of varnish required. All the natural resins are secretions from trees and come mostly from tropical countries. African copals, manilla, kauri, dammar, sandarac, and mastic are the names of some of the resins used in vatnishes. Some varnishes are made with tung oil or China wood oil in place of linseed. This oil is being increasingly used in the manufacture of varnishes, particularly those made with synthetic resins. It differs from linseed oil in that on heating it easily sets to a stiff jelly, and on this account special precautions are required in order to use it successfully.

Although it is usual to apply a coat of varnish over a painted surface, paints are sometimes prepared by thinning down a paste paint with a varnish. When a high-grade, elastic varnish is used, the product is known as an enamel, but manyso-called varnish paints are made with cheaper and less clastic varnish and are known as varnish paints. These dry with a high gloss, but have little durability and are only suitable for interior work.

With regard to the pigments used in paint manufacture, it is only possible here to give a brief summary. These are in many cases coloured compounds of various metals, either prepared from natural products by careful grinding, or chemically prepared in a finely divided form by precipitation and other processes. Fe^v paints except artists' colours, contain single P^S^'f'/'^^^_ coloured paints being usually prepared with an admix ture of a white inert base.


White lead is one of the oldest white pigments, and ' is prepared by the combined action of vinegar fumes and the atmosphere on sheets of lead. It has good covering power and opacity and great durability, but is regarded with suspicion by many authorities on account of its poisonous properties. Painters inhaling the fine particles, caused by rubbing down with sandpaper a surface painted with white lead, have been known to suffer from lead poisoning, which in acute cases causes serious illness or even death. In some countries the use of this pigment is forbidden by law, and in Great Britain, where white lead is still a standard article, it is now compulsory to use some wet method of rubbing down in order to avoid the production of the poisonous dust. One other drawback is that white lead, which is chemically a basic carbonate of lead, is apt to darken on exposure to the atmosphere of towns. This is due to the action of sulphurous gases, from factory and domestic chimneys, acting on the paint to produce black lead sulphide. In spite of these drawbacks, white lead is still in great demand on account of its great efficiency as a pigment.

Zinc oxide, or zinc white, the Chinese white of the artist, has replaced white lead to some extent, notably in the preparation of enamels. It is non-poisonous and does not form a black sulphide.

Another white pigment of outstanding quality is titanium white, which is an oxide of the metal titanium. Not. very long ago titanium and its compounds were looked upon as rare substances, but chemical progress has now resulted in the manufacture of the oxide on a commercial scale, and it is probable that this pigment has an important future.

Various oxides of iron provide us with red, brown,


and yellow pigments; lead oxide (red lead) is a valuable red pigment much used in priming paints, especially for the initial coating of iron work.

Of chemically prepared colours we might mention Prussian blue, made from an iron salt and potassium ferrocyanide; the chrome yellows, which are double compounds of chromium with various other metals; and also the lake colours. These latter colours are made by the precipitation of an aniline dye on an inert white base such as oxide of aluminium, and provide the painter with a variety of colours and tints unknown to previous generations of craftsmen.

CHAPTER IX

CHEMISTRY AND THE DETECTIVE

IN fiction, the scientist-detective is a common character, as witness the popularity of Sherlock Holmes and Dr. Thomdyke; and, as all the world knows, every large police organization cither maintains its own laboratory and staff or retains scientific advisers. It is our purpose here to refer to some of the questions that arise where the chemist is especially interested.

There was a time when the detective requiring information on any scientific point would turn for help to the medical man, for the latter was regarded as expert, not only in such matters as medicine and surgery, but also in such things as poisons and the analysis of food, fabrics, and water. This is no longer the case, though the medical profession still provides a majority of the expert witnesses to be met with in the Law Courts, because its members are most frequently in contact with questions of birth and death, legitimacy, and so on. Since the growth of chemistry as an exact science, the chemist has played an increasingly large part in the detection of crime and in bringing criminals to justice

The detection of poisons is one of the first things which comes to mind. In this respect it would seem natural to turn to the medical man, since the majority of substances used as poisons are also, in smaller doses, used' medicinally. We must remember, however, that though the medical man may be familiar both with the medicinal effects and use of small doses, and the lethal effects of excessive doses, yet the final irrefutable proof by analysis that a given poison was used is a matter for the chemist—or at any rate, it is a chemical problem.

CHEMISTRY AND THE DETECTR^ 37 • This fact is being more and more recognized. (A

Public Analyst may only be appointed nowadays by selection from those Fellows of the Institute of Chemistry who have passed the prescribed examination in the analysis of food and drugs.)

At one time, to the criminally imnded. ^Îf^^^ the favourite poison, usually ^^^q"^^''^^,û^fd c op or rat poison, and cases where it has been used crop up from time to time even now-the Seddon c se in 1912 and the Armstrong case m Ô^^J'^^Jl stancis. In these cases arsenical poisonswe e ^^^^^^^^^ spite of the fact that it is one of the P° ^;"^, ^ ^ ^ detected-the word 'easily' meaning here hat the

are very definite and conclusive. ^ ^ f^^^^ poison used can be separated Ê^^-^^^'^J Vhe test

- to allow of its production "^ / ° "^^^^ ;X , fed material is carried out by Vêp^nn, i^^^^^^^^^ ,,hich (viscera, hair, finger-nails, and s°jm^^" ^^^^^^^ is then introduced mto '-^^/PP^^^f ^^rogen may be hydrogen is being produced 'Ihe ny ^ ^^ ^^ ^^.^ made by electrolysis of water o the a ^ ^^^3 on zinc. The hydrogen reduces the arsem _ ^ F ^ ^ ^ present and combines with the eic ^ ^ ^ ^^^ arsine (or arseniuretted hydrogen), whicn^P^^ ^^^^^^ of the apparatus through a narrow g . deposited that the arsine is decomposed and tne^ ^ ^ ^ ^^^^^ • farther along in the cool P^ '^^ •__,.'. the amount ot thus formed a metallic lookmg nii^r ^ -^^^ with

; \ which can be visually ^stjm^^^'gentical condition i' ^ standard mirrors produced under r^ ^^^^^^^,y ^âll

with known amounts of/rsemc. J , estimated m amount can be^detecte - ^ ^ ^ ^ ^ ^ this manner, as little as one J ^ ^ , _ , This an ounce giving a definitely

mirror. This:

138 CHEMISTRY AND THE DETECTIVE

or even more, might quite easily be foimd in a legal' sample without necessarily being criminally administered, for most foodstuffs contain minute quantities of arsenic; hence in suspected poisoning cases one looks for much larger quantities. It is clear, then, that the test is of a delicacy adequate for the purpose. Not all

FIG. 20. Apparatus for detecting the presence of arsenic

poisons are so easily detected or measured as arsenic, though even this comparatively straightforward case is one for expert handling. The responsibility resting on any-one making the analysis is very grave, and no one should be expected to do such work without that training and detailed knowledge of the requisite conditions for such a test which alone can ensure reliable results.

Many other poison tests need to be carried through from time to time, and to prevent, so far as possible the inadvertent destruction of evidence, the law in some countries (e.g. India) insists on the analyst being supplied with as much information as possible before beginning his work. Information on such points as the number of persons suspected of being poisoned; the

CHEMISTRY AND THE DETECTIVE 139

t symptoms observed; and whether all persons who might perhaps have been poisoned showed these symptoms, is all helpful to the analyst as a preliminary guide in his work. Without such knowledge the chemist, in making one test, may destroy material which will later be required.

The manner m which the analyst searches for all possible poisons cannot even be indicated briefly in the limits of this book. The common poisons, other than arsenic compounds, include alkaloids (such as morphine, strychnine, hyoscyamine, cocaine, etc.); such drugs as aspirin, phenazone, antifebrin, veronal, sul-phonal, and many other hypnotics all of which act poisonously in too large doses; metals such as antimony, lead, copper, mercury, and their compounds such chemical substances as carbolic acid, oxalic acia and its salts, chloroform, chloral, prussic acid, etc.

Besides the detection of poisons, chemistry rendeis many other services to the forces of law and order Consider how often an examination of such things as blood-stains, fabrics, string, rope, dust, and stams or various kinds has been helpful in the adrmmstrauon ot justice. We might mention also the use ^^ * c micr scope, photography and micro-photography, and l e use of ultra-?iolet light m the examination ^j^^^^^^^ ments, ink, and paints. Though such ^ ^ ^ ^ ^ sarily chemical, it is usually P^f ^y'^'^^.rial is almost for an analysis of some part of the mai sure to be required. Umhted to chemical

Corns are quite frequently snom^^^ ^^^ ^^^^^^^l analysis. With the exception ot go ^ ^^^ly heard, jingle of which is now, ^"^^fT'^il^ae, and the coins the coin in circulation is a'token c o i n | . ^ ^ ^ ^ j^^^ . have not the actualintrinsic value ass g

I40 CHEMISTRY AND THE DETECTIVE

Bronze, of course, it does not pay to counterfeit, but the ^ larger 'silver' coins are very tempting to the coiner, since the cost of the actual metal is considerably below face-value. Coimterfeit coins sometimes are cast in moulds, but more frequently are struck from dies much in the same manner as the genuine coins, and, indeed, except for slight differences in composition, may be indistinguishable from the products of the Royal Mint. It is here, however, that the analyst has helped, for an analysis of the material of forged coins has often been found sufficient to establish the guilt of some 'working jeweller' upon whose premises suspicious metal and apparatus suitable for coining has been seized.

In the examination of stains suspected to be blood the chemist has first to decide whether a particular stain is likely to be blood or not; that is to say, he applies a preliminary test, as a result of which he can often say at once, 'That is not blood'. There is no simple, purely chemical test that is absolute proof of the presence of blood, but there are a number of tests by means of which a stain may be excluded as not being blood. In the event of a stain not being excluded, it is first examined by the onicroscope to see if blood corpuscles can be observed; then follows a micro-chemical test, and next examination by the micro-spectroscope. These tests are sufficient to establish that a stain is of blood; then, by the application of a biochemical test, it is usually possible to demonstrate the origin of the blood (i.e.. whether human, ox-blood, and so on); and if human, to which one of the four groups into which human blood can be classified the specimen belongs.

It has happened not infrequently that an analyst has been required to examine portions of various textiles, clothing, sacking, etc., with a view to throwing


Jight on their previous history. This apparently hopeless quest has sometimes yielded important results, for every kind of fibre, thread, or fabric has certain measurable characteristics from the study of which much may be learnt; and in addition, adherent dust and stams, when their nature or cause has been discovered, Jire often helpful. This kind of work, however, is only tor the specialist. A textile expert, familiar, let us say, witn the microscopic appearance of fibres, can see far more through his microscope than can a trained microscopist unfamiliar with various fibres. He would certainly be able to distinguish at first glance animal fibres (woo, etc.) from vegetable or artificial fibres, and mde^d with an animal fibre, would probably be able to give its origin, i.e. upon what kind of animal it g^f , and even possibly, upon what part of the ammals body. He would distinguish readily such things as human hair, cow's hair, cat's hair, and so on. jntPn^e

The study of fibres and fabrics has been so mten ^ that the exact composition of the ash left after combus tion of each type of fibre is well 1- own, so tl at^he analysis of the a^h in any given -^^l^^l^g^^^ry surprising information regardmg the pre .^^^ of the material. Thus, to g'^e a simple^ 1 ^ ^ ^^^^ suppose two identical pieces ot imen ^ ^ ^^^^^, washed, the one in hard and the °^^.^, , g yeen them, chemical analysis would easily distinguisi^^^ ^ ^ ^ ^ ^^

An interesting example of the evi ^ ^^^ jj in the examination of clothing f^? gj-j Arnold & Co.). Forensic Chemistry, by A. Lucas (li ^ ^ arrested m It appears that during the war a ^ ^^^^ ^^^^l. His suspicious circumstances ^^f^ -^ examination, as waistcoat was

submitted to cnenu.^^^ ^^ ^^^ ^,,veiieu result of which it was suspecte


to Egypt from Batavia (probably by a Dutch steamer^ since these were the only ones then using the canal and calling at Batavia); that he had jumped overboard (at night, probably), and after swimming to land had come ashore on certain sand-dunes. (This theory was suggested by the nature and style of the material of the garment; the buttons; the sea-salt which analysis revealed still in the fabric; the type of sand-grains found in the pockets.) As a result of inquiries based on this supposition, the theory was found to be correct in all details.

Dust, as well as sand, is frequently submitted to chemical examination. Cases are known where dust scraped from finger-nails has been analysed, and ashes have been tested where a crime has been committed and the murderer suspected of having burnt his victim. There are, too, many cases where, following injury by shooting, examination of the clothing immediately surrounding holes made by bullets or slugs has proved useful in deciding the type of bullet or shot—^whether lead, nickel-coated, etc.; and also the nature of the charge used—black-powder, smokeless powder, etc.

In a- recent case a man was found murdered, but it was some days before his identity could be established, careful examination of the body showing no distinguishing marks, his finger-prints not being Imown to the police, and no one coming forward who was able positively to recognize the man from photographs. Under the hollow of one shoe were traces of a dark red substance, which was analysed. Its composition was such as might be expected had the deceased trodden upon a floor where newly laid cement was still soft. Now within a short distance of where the body was found was a newly constructed 'road-house' where the entrance hall


• had jus t that kind of cement, and on this it was easy to see a footprint which fitted the murdered man's shoe exactly. The proprietor on viewing the body not only recognized the man, but was able to give information regarding the two men who were with him when he took what turned out to be his last ride. From this link sufficient circumstantial evidence was collected to bring to book his two companions by whom he had been *bumped-off'.

The ordinary person probably thinks of paper as thick or thin, rough or glazed, white or coloured, plain or ruled; to the chemist, paper is much more, and a chemical examination of paper will rarely fail to throw light on its origin. Paper, as distinct from parchment or vellum, was originally made from rags, and while at first these were always of linen, later cotton was used. Linen alone was used till about A.D. IOOO, and the earliest known English manuscript on cotton paper is dated A.D. 1049. From then till the beginning of the nineteenth century linen and cotton were both used; but about this time straw was introduced, though it was not much used till 1850. Esparto grass was first used in i860, and various kinds of wood-pulp were intl-oduced between 1870 and 1890. Before 1800 all paper was hand-made. Blotting-paper is known to have been in use since the fifteenth century.

By a systematic examination of paper its constituent fibres can be separated and identified, as can also the materials used in sizing it, which may include such things as glue, gelatine, resin, casein, and starch or mineral matter. It wiU be seen, then, that paper has well-defined characteristics which ^^^unately are not always known to those who attempt forgery and other fr^^s^ What could besaid,forexample.oftheman ^vho claimed

144 CHEMISTRY AND THE DETECTIVE to be the heir to a large estate and supported his claim--with much documentary evidence, when the principal document, which was dated 1728 and appeared quite genuine, was shown by analysis to be made of a wood-pulp paper of a type not known before 1880! The judge's remarks included something about penal servitude.

Often associated with paper is ink, another very characteristic substance. The principal kinds (used for visible, as distinct from invisible, writing) are carbon-ink, logwood-ink, iron-gall ink, and 'aniline' ink (so called because it contains a synthetic dye, the earhest of which was made from aniline). Carbon-ink is the oldest of these, and in oriental countries is still much used. The carbon is obtained in various ways, but it is usually lamp-black, and is mixed with gum and water. Iron-gall ink has certainly been known for more than one thousand years. Originally, sulphate of iron was dissolved in an infusion of gall-nuts. This gives only a faintly coloured Hquid, but after use, oxidation causes the writing to turn quite black. This ink was formerly improved by adding some colour such as indigo, which served to show up the writing at once and did not interfere with the subsequent darkening. Later, various coal-tar dyes were used in place of indigo, and the present-day blue-black ink is of this type. After the middle of the eighteenth century a decoction of logwood was occasionally added to iron inks, and in later times logTVOod extract was used to which had been added a solution of alum or of bichromate of potash. Such inks are rarely met with nowadays. In England we do not often use (except as red ink) inks made wholly or even chiefly of coal-tar dyes. Coal-tar dyes are only found in inks made after the year 1861, for in that year they were


first used; the first dye of the kind was made from aniline by W. H. Perkin in 1856.

Claims for Old Age Pensions are frequently supported by the evidence of entries in the Family Bible. In one such case, where the claimant seemed exceptionally well preserved, the entry was examined closely, and it was seen that the date of birth had been 1862, but that it had been altered to 1852. Unfortunately for his claim, the applicant had used an aniline ink of a type unknown in 1852, so he had to wait ten years longer for his pension.

Alterations and erasures can sometimes be done so skilfully as to defy detection with the unaided eye, but the microscope will nearly always disclose them, while under ultra-violet light erasures, especially, show up very clearly, for it is impossible to make an erasure and leave no sign of it. The surface layer of the paper, where is most of the size, is damaged irrevocably, so that an attempted forgery of this kind cannot fail to be detected if sufficient suspicion is aroused to cause an examination of the document to be made. Mere wetting of the surface causes a redistribution of the size which shows quite distinctly, while any kind of friction also leaves its mark. Ultra-violet lamps are becoming quite common, as many uses have been found for them in routine work in laboratories.

An interesting case where the chemist was able to give important evidence is reported to have occurred in Germany. It is said that a workman in an explosives factory disappeared one day, and since he might have fallen into a tank containing a mixture of sulphuric and nitric acids, his wife claimed on his insurance company. The zealous local representative of the company refused to authorize payment, maintaining that


the man could not be dead as no body was forthcoming. Kjiowing the wife, he put forward the suggestion that the man had absconded, probably to America, where he would be out of her reach. However, an analysis of the acids was made, and it was found that they contained just such a quantity of dissolved phosphorus compounds as might result from the dissolving of a man's body; so the wife was recognized as a widow and received the money.

CHAPTER X

ATOMS AND MOLECULES

OUR knowledge of the constitution of matter, although not yet complete, has become considerably more exact in recent years.

Boyle, in 1661, suggested that all matter was made up of elements, that is to say, of simple substances which are the ingredients of which all other bodies are made.

Lavoisier, in 1789, gave us our modern definition of an element as a body that cannot be split up into simpler bodies.

The elements are, so to speak, nature's building material. Just as a builder can use bricks, stone, iron, wood, and glass to build a bridge, a house, or a church, so nature, with the elements at her disposal, gives us a piece of gold, a lump of chalk, or a block of amber.

Only twenty-eight elements were known to Lavoisier. At the present time the number of known elements is ninety, and, strange though it may sound, "we have every reason to believe that only two more elements remain to be discovered.

A detailed account of the researches and discoveries that provided the clues to the number of possible elements is outside the scope of this book, but we may say that the first clue was the realization that certain groups of elements showed a sort of family resemblance in properties.

In 1863 Newlands found that if the names of the elements were written down in order of their atomic

K 2

'^^ A TOMS AND MOLECULES

^<Jch mention at the time It"^''^- did not attract Law of Octaves was tru™^',' i * ' "^ '"SS^^'^d that the 'eading in otJiers. ^ ' " '^^«''"' «ses and mis-

Six years Jater fh» D •

; e a W that there wassoleZZ • ' ' ^ ' 1 ^^' '^ '^^ff 'arrangement, but thatitr!"^^'"'"'*'^ octave

T ^" "-^plVV''"' ">' 'a«y of fft" 7 '" '^' day, squares of a I: J^'^'^'^S to their „ " " ' " a m e s of

Columbus, before to™^°"" element : ' " " ^°"P«. • stated his beliefl ,r ' S^'"' ™yage of !i- " ' '"*«• Jf

»dhadgiven; r" i fe2 :" ; ' "^^° '^^ wes t t r ' ^ -^ ' ^^^ • •nouMains, th. 1™11 ' ' ' ' ' '•^SardinrZ?^ 5°"tine„t, ' "f^" i" ' .ni . ,^!i '°8*^ »£ ite rivets f'^^^^'ghta of ite J"adman. Yet the p r T p t c ' ' " " '=-" W & * - - S ess remarkable. I n * / . " ' , °^ IWendefe/P"" as a

he gave details of ,he ' „ ' ' ' ° * ^ ^ ' « l e t t ! f r " < = "o undiscovered e/en! °"''' f"™^. and d l • " §=Ps

and c h e m i c t ' a c ^ . ; ' ^ ' ' ^ f " ^ ^ P o f e ^ ' h e

- t s . e r e d i s c o v e r f d . h ^ ' j S J L t ^ T S ' ^ ^ ^ ^ ^ ^ •

ATOMS AND MOLECULES

^ prophecy adirutted of no criticism. Hcreisanexsmph'. or one or these cases:

Property Mend^'f Prophecy I

Atomic weight Specific gravity Colour Effect of heating in air

Germamm, dt'sc iSS6

Action on water

Action of acids „ alkalies

Properties of the oxide

Properties of the chloride

72 5-5

dirty grey element will turn to white oxide

element wilJ decompose / Steam with difficulty

/ slight

I no pronounced action refractory (i.e. hard to melt), specific gravity 4 7

a liquid boiling at less than 100° C. and with a speciiic gravity of 1 -9

white

723 5-47

greyish white element gives a oxide

element does not decom pose water

: tlight I no pronounced action refractory, specific gravity 4703

boils at 86° C , specific gravity 1-887

When the gaps of the Periodic Table, as MendeI6eff's arrangement was called, began to be filled, the usefulness of the table became apparent. Apart from giving a clue to the existence of new elements, the table showed up errors in the determination of the atomic weights oi certain existing elements. It also made the study of chemistry much easier, for now the properties of groups or families of elements could be studied, and knowledge of such things as valency and the formation of compounds could be systematized. There were some ano-maVies iTv \!he tafek as. certain elements did not seem to fit in satisfactorily anywhere. lniacX,'6&teii rare earth elements, not all known to Mendel^eff, appeared to require a place on the same square. Subsequent knovv-ledge, however, has sho^vn how the table can be modified to take in all the elements, -^rnr^sup-

The brilliant work of Henry Moseley m 1J14 suP plied the last piece of evidence required for

148 ATOMS AND MOLECULES

weight, every eighth element showed some sort of resemblance to the first, just as the eighth note on a'' piano is a kind of repetition of the first. Newlands's suggestion, known as the Law of Octaves, did not attract much attention at the time, it being suggested that the Law of Octaves was true only in certain cases and misleading in others.

Six years later the Russian chemist Mendel^eff realized that there was some value in Newlands's octave arrangement, but that it required modification. Not more than sixty-seven elements were known in his day, and Mendeleeff felt that the tally of the elements was not yet complete. He therefore arranged the names of the elements, according to their properties, in the squares of a kind of chess-board, in such a way that the elements of any vertical column showed a resemblance in properties, or, as we now say, belonged to the same group.

But Mendeleeff's chess-board table contained certain empty spaces, and he boldly stated that these gaps represented undiscovered elements. He went even further, and by reference to elements in the same groups, prophesied what the unknown elements were like. If Columbus, before his great voyage of discovery, had stated his belief in the existence of a western continent, and had given precise details regarding the heights of its mountains, the lengths of its rivers and the character of its inhabitants, he would have been looked upon as a madman. Yet the prophecies of Mendeleeff were no less remarkable. In the case of three at least of his gaps he gave details of the colour, forms, and density of the undiscovered elements, their melting-point, hardness, and chemical activity. When in due course these elements were discovered, the justification of Mendeleeff's

ATOMS AND MOLECULES

prophecy admitted of no criticism. Here i;

• of one of these cases:

149,

is an example

Property^

Atomic weight Specific gravity

S e T o f heating in air

Action on water

Action of acids

PropertiesoftheOK.de

p^opertiesofthechlor-

ide

72 72-3

5-47 greyish white ^

element gi^es a

eS t tdoesno tdecom-

pose water

vity 4-703 oe.o C specific boils at 86 C.. P

gravity I-887

f"' rspecW!!!! ! ^ - _ - - — ^^ ' T T T i b l e asMendel6eff's " " ^ ^ «f the Periodic 1 abie, ^^g.

W ' ' - n C s ^ ^ > = ^ " : : t A p ^ ^ t n . giving arrangement was apparent- ' P 3t,„,ed fulness of the tabk ^ elemems, h ^ . . „t acluetotheexist^n i„„tionof theat ^ ^ ^ <,f up errors in th^d^rm ^ also madM f certain existing e'^^ for now the proP^" yi„„ledge ch^-^;^:?de":S'couldbestudi^^^^^^^ „f co . -or families of f ^ ,,„ey and the t ^^„, ano

^l^'"^"''' ola e on the sa»^ ^""die table can be «> reauire a place w ^ j ow

plied the last pie

http://PropertiesoftheOK.de

150 ATOMS AND MOLECULES comprehension of the Periodic Table and all that it impUed. He found that each element, under certain'-conditions, could be made to emit X-rays of a certain wave-length, and that there was such a simple numerical relationship between the wave-lengths from the different elements that he was able to give to each element a number according to its wave-length. Thus hydrogen, the lightest element, has atomic number i, and uranium, the heaviest, atomic number 92. There is good reason for the behef that no elements exist outside these limits; that is to say, there is no element with an atom lighter than the hydrogen atom or heavier than the uranium atom.

Most of the ninety-two elements are metals, and the greater number of these are so rare as to be of no direct interest to the ordinary man. Fully half the weight of all the land, water, and air of the world consists of oxygen, and half of the remainder is sihcon. After these, in order, come aluminium, iron, calcium, sodium, potassium, magnesium, hydrogen, titanium, chlorine, and carbon.

These twelve elements form 99 per cent, of the total weight of the earth's crust, the other eighty forming only I per cent, between them. The composition of the earth's interior is unknown, but it is thought to be much richer in metallic elements, notably iron and nickel.

One of the most interesting developments of modern times has been the gradual change in our conception of the solidarity of matter. After the general acceptance of Dalton's Atomic Theory, a lump of solid material was regarded as being composed of a number of tiny particles, something like infinitely small billiard balls, packed together. A diagrammatic representation of a

^TOMS AND MOLECULES j - ,

FIG. :

From such a diagram it was possible to deduce the fact of empty spaces between the atoms, and so in some measure account for the porosity of soHds.

In 1811 the Italian physicist Avogadro made a suggestion which was to serve as a basis not only for our modem theory of chemistry, but also for the understanding of many properties of solids, liquids, and gases. He suggested that the ultimate particle of matter was , a group of atoms rather than a single atom. The name molecule was given to such a group, and we now think of a molecule as the smallest particle of matter, whether element or compound, that can exist in a free state, and of an atom as the smallest particle of an element that can take part in a chemical reaction.

Although we carmot prove its existence by seeing and handling it, yet the molecule is a very real thfng to the scientist. How many atoms go to make up a molecule we cannot tell, but we usually think of a molecule of an elementary gas as being made up of tvvo atoms. Perhaps this number should be four or six or eight or any even number, but it makes no difference to the theory.

Whatever the number, all tht atoms m a molecule of an element are alike, while a molecule oi a compound is made up of atoms of different element. A rnok ule

of water,^r ^^^-^^^'-:^^,t^^ hydrogen and one atom ot oxygtu,

many people appear to think, shorthand or cryptic signs for the names of substances. H2SO4, for example, stands for a molecule of sulphuric acid, and states that this molecule is composed of two atoms of hydrogen, one atom of sulphur, and four atoms of oxygen.

The molecules of a solid are close together but not touching. They are held together by a force which is known as the force of cohesion. They are in a constant state of vibration, and the hotter the body becomes the more rapid is the vibration of the molecules. Only when a body loses all its heat—^that is to say, when it is cooled down to absolute zero (—273° C.)—does the motion of the molecules cease.

Another effect of heat is to overcome the force of cohesion and so allow the molecules to get farther apart. The expansion of a solid on heating is due, not to an increase in size of the molecules, but to a widening of the spaces between them.

By adopting the molecular theory, a lump of solid matter has to be considered as being more open in structure than is shown by Fig. 21. Assuming two atoms to the molecule, a highly magnified speck of solid could be represented like Fig. 22.

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(2) (?) (D ® (D F I G . 22

The circles represent the boundaries, so to speak, of the molecules, the actual material part of the solid being

modihcation. In a liquid the molecules, although stUl under the

mfluence of cohesion, have more freedom of movement A tumbler filled with fine dry sand or small shot gives an idea of the molecular state in a liquid, the molecules being able to roll over one another. Thus a liquid can be poured, and a hand thrust in pushes masses of molecules out of the way.

When a liquid is heated to its boiling-point cohesion is overcome to such an extent that the molcules separate entirely and the liquid becomes a gas, A swarm of bees let loose in a large hall would be a crude representation of the state of the molecules of a gas, except that the bees might alight on walls or floor, while the molecules •-of a gas are never stationary but move always with the speed of rifle bullets in straight lines, changing direction only on collision with other molecules or with the walls of the containing vessel.

It has been found possible to compute the sizes of molecules, but the ordinary mind can obtain no clear idea of the meaning of the actual measurements. If a molecule of oxygen were about 5,000 times as big in every direction as it actually is, it would still be quite invisible to the naked eye, but it might be just possible to see it with the aid of a powerful microscope capaWe of magnifying up to 5,000 diameters.

From what is known of the molecules xveget Bstnkmg conception of the restlessness of nature. The iwmo able mountain, the placid waters of a P^^^^'fJ^l,^ air on a calm day, are at rest on y ^ J ^ ^ , "S i^ s . tell us. In reality the molecules of ai «ohds, and gases are in a state of ceaseless motion.

154 ATOMS AND MOLECULES

A chemical reaction between two substances is a coUeciion of reactions between individual molecules,' just as a battle in ancient times was a collection of fights between individuals. When oxygen and hydrogen are mixed together and the mixture ignited there is an explosion, and steam is produced. This reaction is prosaically represented in chemistry by the equation

2 H0+O2 = 2 H2O

It could be represented pictorially as in Fig. 23.

Two molecules of hydroRcn and one molecule of oxygen

Explosion = chemical reaction

Result: two molecules of steam produced

F I G 23

Since the discovery of radium, chemists have been led to believe that atoms are not the solid, unalterable particles pictured by Dalton.

In 1896, some months after the discovery of X-rays by Professor Rontgen of Wiirzburg, Henri Becquerel in Paris began a series of experiments with phosphores-

ATOMS AND MOLECULES 155

cent bodies. Among other substances he used crystals ot a uranmm compound, and discovered to his surprise that these crystals, even in the dark, had the property ot foggmg a photographic plate, although they gave off no visible light. Moreover, the fogging took place even although the plate was protected by a wrapping of light-proof paper, suggesting to Becquerel that the crystals gave off rays similar to Rontgen's X-rays. Professor and Madame Curie then set to work to examine other uranium compounds, and found that the mineral pitchblende, an oxide of uranium, possessed this property in a greater degree than other compounds.

As a resplt of a brilliant and painstaking series of researches, they discovered that the X-ray effect was due, not so much to the pitchblende itself, as to a substance always present in natural pitchblende. Using . an enormous quantity of pitchblende, they succeeded in extracting a small amount of a compound of the very active substance. Thus was a further secret wrested from nature, for the new substance was the bromide of an imknown element henceforth to be kno^vn as radium. The element itself was isolated in 1910 by Madame Curie, who, after the unfortunate death by accident of Professor Curie, continued the work she and her husband had previously shared.

Radium is a soft, white metal belonging to the same group as calcium, barium, and strontium, and havmg similar chemical properties to these elements. The grea difference bet^veen radium and other "êmbeiôt tne group lies in its radio-activity. A - - f j ^ / ^ r a the metal or of one o/^^s 3 0 7 ^ ^ ^ ^ ^ ^ microscope, appears to be ^^^^J ^jêse radiations out rays or radiations in all ^^^^l^.\.. render the air from radium affect a photographic plate, ren

156 ATOMS AND MOLECULES round about capable of conducting electricity, and cause certain other substances to become phosphorescent. They also have a corroding or disintegrating action on bodily tissue, and thus cause painful sores in any part of the skin exposed for a few hours to their action. Properly controlled and directed, this property of radium is made use of in the treatment of cancer.

The most remarkable thing about radium, however, is that it is continually sending out energy in the form of light, heat, and electricity. Now, it is one of the axioms of science that energy can neither be created nor destroyed, and so, if each atom of radium is continually producing energy, it follows that this energy is being freed as a result of some change in the constitution of the atom. In other words, the atom of radium

. must be dissociating into atoms of another kind. Actually this has been shown to be the case, for one set of radiations consists of particles of helium carrying a positive charge. This means that the atom of radium is actually disintegrating, producing, among other things, atoms of helium, and leaving behind atoms of another element. The element left behind when a helium atom breaks off from a radium atom is called radon, and this in turn breaks up, the process of degradation going on until what was once an atom of radium has become an atom of lead.

In the year 1921 the women of America presented Madame Curie with a gramme of radium. The value of this large amount of metal was £20,000, and the reader may wonder how long it will be before the valuable gift will have changed to an almost worthless speck of lead. As a matter of fact, a definite proportion of the atoms in any mass of radium disintegrates each second. It will take 2,000 years for the gramme of radium to be

ATOMS AND MOLECULES iS7

reduced to half a gramme; another 2,000 years for half othe remainder to disappear, and so on. Ihus even

10,000 years hence the gramme of radium will possess one-thirty-second of its present activity.

Once the complex nature of t he ; . f ^'i^^.^^T J ^ reahzed, it because necessary to modify ^^ on s con ception of atoms. The modern view ^\^f'^J^^ although still indivisible so far as chemica ~ ^ concerned, is made up of a number of ^ ^ ^ " ^ ^ two kinds. One part of the ^^om is co^PO^^j;* ^ or more particles called ^r./o«^, whic^ are real y^^^^^ tive units of electricity, and the other part

tary electrons rev°l;^,„S„3 ^ j s« nucleus of melve^P^^

This suggests an inn or negative units of electncity- J ^ ^^ electricity, anj mate relationship between m^^e^ j Ip3 to acc unt the modern theory of a tor"^/ ' ' " for many electric P h - o - ^ ^ ^ ^

It is considered that the P remaining e J ^^,

form the nucleus of the atom ^^^^^^ orbit^s^ ^^.

revolving round this ^^^^,, solar syst^^- ^ revolving rouna un= • j^ture the atom resembles a nun

158 ATOMS AND MOLECULES gen atom consists of one proton and one electron, a helium atom of four protons and four electrons, and a.p sodium atom of twenty-three protons and twenty-three electrons.

The number of protons (and of electrons) is the same as the number representing its atomic weight, and the number of orbital or planetary electrons is the same as the atomic number, the rest of the electrons being in the nucleus.

A proton is more than 1,800 times as heavy as an electron, so that practically the whole of the mass of an atom is centred in its nucleus (Fig. 24).

Reverting for a moment to our diagrams of a speck of solid matter on pages 151 and 152, it is evident that a still further modification is necessary, and that we must henceforth think of a piece of solid as being chiefly empty space, the material part consisting of particles of electricity (Fig. 25).

F I G . 25

Although such a conception may at first be rather bewildering, yet it really helps us to a clearer view of many scientific phenomena. The splitting up of the radium atom now becomes the separating and escape of a certain number of protons and electrons. Also, the passage of X-rays through opaque bodies is understandable. X-rays have a much smaller wave-length than ordinary light. We can think of them as rays capable of passing through the space between the units of electricity which form the opaque body, ordinary

ATOMS AND MOLECULES 159

light rays being unable to find a passage. We can also • understand why lead, the atoms of which consist of more

than 400 particles of positive and negative electricity, is practically opaque even to X-rays.

The dream of the alchemist was the transmutation of metals. Now, long after the death of alchemy, we find that nature, so far as the radio-active elements at least are concerned, practices transmutation. It is thought that uranium, the heaviest element, is slowly disintegrating and producing radium, but a million times more slowly than radium itself disintegrates. If there is a general tendency for elements to break down into simpler bodies, with the eventual arrival at helium or hydrogen, the process is so slow as to be beyond measurement, and the alchemist's idea of lead turning into gold in the depths of the earth is not likely to be •• realized in the lifetime of the human race.

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