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Changes to the text (to correct typographical errors) are listed [at the end of the book]. A few cases of missing punctuation have been regularised in the advertisements without comment.

There are extensive blocks of publisher's advertising material included both [before] and [after] the title page, [after the index] and in a [sixteen page catalogue at the end], which has (duplicate) page numbers 1-16, but may be referenced with unique page anchors 1C-16C.

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THE IAN HARDY SERIES
by
COMMANDER E. HAMILTON CURREY, R.N.

Each Volume with Illustrations in Colour. 5s. each

Ian Hardy's career in H.M. Navy is told in four volumes, which are described below. Each volume is complete in itself, and no knowledge of the previous volumes is necessary, but few boys will read one of the series without wishing to peruse the others.

IAN HARDY, NAVAL CADET

"A sound and wholesome story giving a lively picture of a naval cadet's life."—Birmingham Gazette.

"A very wholesome book for boys, and the lurking danger of Ian's ill deeds being imitated may be regarded as negligible in comparison with the good likely to be done by the example of his manly, honest nature. Ian was a boy whom his father might occasionally have reason to whip, but never feel ashamed of."—United Service Magazine.

IAN HARDY, MIDSHIPMAN

"A jolly sequel to his last year's book."—Christian World.

"The 'real thing.' ... Certain to enthral boys of almost any age who love stories of British pluck."—Observer.

"Commander E. Hamilton Currey, R.N., is becoming a serious rival to Kingston as a writer of sea stories. Just as a former generation revelled in Kingston's doings of his three heroes from their middy days until they became admirals all, so will the present-day boys read with interest the story of Ian Hardy. Last year we knew him as a cadet; this year we get Ian Hardy, Midshipman. The present instalment of his stirring history is breezily written."—Yorkshire Observer.

IAN HARDY, SENIOR MIDSHIPMAN

"Of those who are now writing stories of the sea, Commander Currey holds perhaps the leading position. He has a gift of narrative, a keen sense of humour, and above all he writes from a full stock of knowledge."—Saturday Review.

"It is no exaggeration to say that Commander Currey bears worthily the mantle of Kingston and Captain Marryat."—Manchester Courier.

"The Ian Hardy Series is just splendid for boys to read, and the best of it is that each book is complete in itself. But not many boys will read one of the series without being keenly desirous of reading all the others."—Sheffield Telegraph.

IAN HARDY FIGHTING THE MOORS

"By writing this series the author is doing national service, for he writes of the Navy and the sea with knowledge and sound sense.... What a welcome addition the whole series would make to a boy's library."—Daily Graphic.

"The right romantic stuff, full of fighting and hairbreadth escapes.... Commander Currey has the secret of making the men and ships seem actual."—Times.

"By this time Ian Hardy has become a real friend and we consider him all a hero should be."—Outlook.

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THE LIBRARY OF ROMANCE

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POPULAR SCIENCE FOR YOUNG PEOPLE

By CHARLES R. GIBSON, F.R.S.E.

"Among writers for boys on science, easily the most skilful is Mr. Charles Gibson. He writes so clearly, simply and charmingly about the most difficult things that his books are quite as entertaining as any ordinary book of adventure. Mr. Gibson has a first-rate scientific mind and considerable scientific attainments. He is never guilty of an inexact phrase—certainly, never an obscure one—or a misleading analogy. We could imagine him having a vogue among our young folk comparable with that of Jules Verne."—The Nation.

"Mr. Gibson has fairly made his mark as a populariser of scientific knowledge."—Guardian.

JUST PUBLISHED

THE STARS & THEIR MYSTERIES (Vol. III. Science for Children Series). With Coloured Frontisp. & other Illustrations. 3s. 6d.

OUR GOOD SLAVE ELECTRICITY (Vol. I. Science for Children Series). With Illustrations. 3s. 6d.

"An exquisitely clear book for childish beginners."—The Nation.

"Told in simple and remarkably clear language, and with such ingenuity that many pages of it read like a fairy tale."—Glasgow Herald.

THE GREAT BALL ON WHICH WE LIVE (Vol. II. Science for Children Series). With Coloured Frontispiece and other Illustrations. 3s. 6d.

"Capital."—Field.

"A most fascinating and suggestive story of the earth. Mr. Gibson not only knows his subject thoroughly, but has the capacity of conveying the knowledge to young folk."—Church Family Newspaper.

THE ROMANCE OF MODERN ELECTRICITY. Describing in Non-technical Language what is known about Electricity and many of its interesting applications. With 41 Illustrations. Extra crown 8vo, 5s.

"Admirable, clear and concise."—Graphic.

"Very entertaining and instructive."—Queen.

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THE ROMANCE OF MODERN PHOTOGRAPHY. Its Discovery and its Applications. With Illustrations. Extra crown 8vo, 5s.

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"The narration is everywhere remarkable for its fluency and clear style."—Bystander.

THE ROMANCE OF SCIENTIFIC DISCOVERY. A Popular Account of the most important Discoveries in Science. With 30 Illus. 5s.

"The most curious boy of mechanical bent would find such a book satisfying."—Westminster Gazette.

THE ROMANCE OF MODERN MANUFACTURE. A Popular Account of the Marvels of Manufacturing. 5s.

"A popular and practical account of all kinds of manufacture."—Scotsman.

"Just the sort of book to put into the hands of senior boys as a school prize."—Sheffield Telegraph.

HEROES OF THE SCIENTIFIC WORLD. An Account of the Lives, Sacrifices, Successes, and Failures of some of the greatest Scientists in the World's History. With 19 Illustrations. Extra crown 8vo, 5s.

"The whole field of science is well covered.... Every one of the 300 odd pages contains some interesting piece of information."—Athenæum.

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THE ROMANCE OF WAR INVENTIONS

A Tank.

These weird-looking engines are literally moving forts, and are the evolution of a peaceful agricultural machine fitted with "caterpillar" wheels, that is, a broad band encircles the driving wheels, and so the whole construction moves as it were on its own revolving platform and is thus prevented from sinking into the soft ground. The principle itself is not new, as it was adapted to transport carts during the Crimean War.

THE
ROMANCE
OF
WAR INVENTIONS

A DESCRIPTION OF WARSHIPS, GUNS, TANKS,
RIFLES, BOMBS, AND OTHER INSTRUMENTS
AND MUNITIONS OF WARFARE, HOW
THEY WERE INVENTED & HOW
THEY ARE EMPLOYED

BY
T. W. CORBIN

AUTHOR OF "THE ROMANCE OF SUBMARINE ENGINEERING,"
"MECHANICAL INVENTIONS OF TO-DAY,"
&c., &c., &c.

With many Illustrations

LONDON
SEELEY, SERVICE & CO. LIMITED
38 GREAT RUSSELL STREET
1918

THE LIBRARY OF ROMANCE

Extra Crown 8vo. With many illustrations. 5s. each.

"Splendid Volumes."—The Outlook.

"The Library of Romance offers a splendid choice."—Globe.

"Gift Books whose value it would be difficult to over-estimate."—The Standard.

"This series has now won a considerable & well deserved reputation."—The Guardian.

"Each Volume treats its allotted theme with accuracy, but at the same time with a charm that will commend itself to readers of all ages. The root idea is excellent, and it is excellently carried out, with full illustrations and very prettily designed covers."—The Daily Telegraph.

By Prof. G. F. SCOTT ELLIOT, M.A., B.Sc.

• The Romance of Savage Life
• The Romance of Plant Life
• The Romance of Early British Life

By EDWARD GILLIAT, M.A.

• The Romance of Modern Sieges

By JOHN LEA, M.A.

• The Romance of Bird Life

By JOHN LEA. M.A. & H. COUPIN, D.Sc.

• The Romance of Animal Arts and Crafts

By SIDNEY WRIGHT

• The Romance of the World's Fisheries

By the Rev. J. C. LAMBERT, M.A., D.D.

• The Romance of Missionary Heroism

By G. FIRTH SCOTT

• The Romance of Polar Exploration

By CHARLES R. GIBSON, F.R.S.E.

• The Romance of Modern Photography
• The Romance of Modern Electricity
• The Romance of Modern Manufacture
• The Romance of Scientific Discovery

By CHARLES C. TURNER

• The Romance of Aeronautics

By HECTOR MACPHERSON, Junr.

• The Romance of Modern Astronomy

By ARCHIBALD WILLIAMS, B.A. (Oxon.), F.R.G.S.

• The Romance of Early Exploration
• The Romance of Modern Exploration
• The Romance of Modern Mechanism
• The Romance of Modern Invention
• The Romance of Modern Engineering
• The Romance of Modern Locomotion
• The Romance of Modern Mining

By EDMUND SELOUS

• The Romance of the Animal World
• The Romance of Insect Life

By AGNES GIBERNE

• The Romance of the Mighty Deep

By E. S. GREW, M.A.

• The Romance of Modern Geology

By J. C. PHILIP, D.Sc., Ph.D.

• The Romance of Modern Chemistry

By E. KEBLE CHATTERTON, B.A.

• The Romance of the Ship
• The Romance of Piracy

By T. W. CORBIN

• The Romance of Submarine Engineering
• The Romance of War Inventions

By NORMAN J. DAVIDSON, B.A. (Oxon.)

• The Romance of the Spanish Main

SEELEY, SERVICE & CO., LIMITED.

CONTENTS

LIST OF ILLUSTRATIONS

THE ROMANCE OF WAR INVENTIONS

CHAPTER I
HOW PEACEFUL ARTS HELP IN WAR

In the olden times warfare was supported by a single trade, that of the armourer. Nowadays the whole resources of the greatest manufacturing nations scarcely suffice to supply the needs of their armies. So much is this the case that no nation can possibly hope to become powerful in a military or naval sense unless they are either a great manufacturing community or can rely upon the support of some great manufacturing ally or neutral.

It is most astonishing to find how closely some of the most innocent and harmless of the commodities of peace are related to the death-dealing devices of war. Of these no two examples could be more striking than the common salt with which we season our food and the soap with which we wash. Yet the manufacture of soap furnishes the material for the most

furious of explosives and the chief agent in its manufacture is the common salt of the table.

Common salt is a combination of the metal sodium and the gas chlorine. There are many places, of which Cheshire is a notable example, where vast quantities of this salt lie buried in the earth.

Fortunately it is very easily dissolved in water so that if wells be sunk in a salt district the water pumped from them will have much salt in solution in it. This is how the underground deposits are tapped. It is not necessary for men to go down as they do after coal, for the water excavates the salt and brings it to the surface.

To obtain the solid salt from the salt water, or brine as it is called, it is only necessary to heat the liquid, when the water passes away as steam leaving the salt behind.

Important though this salt is in connection with our food, it is perhaps still more important as the source from which is derived chlorine and caustic soda. How this is done can best be explained by means of a simple experiment which my readers can try in imagination with me or, better still, perform for themselves.

Take a tumbler and fill it with water with a little salt dissolved in it. Next obtain two short pieces of wire and two pieces of pencil lead, which with a pocket lamp battery will complete the apparatus. Connect one piece of wire to each terminal of the battery and twist the other end of it round a piece of pencil lead. Place these so that the ends of the leads dip into the salt water. It is important to keep

the wires out of the solution, the leads alone dipping into the liquid, and the two leads should be an inch or so apart.

In a few moments you will observe that tiny bubbles are collecting upon the leads and these joining together into larger bubbles will soon detach themselves and float up to the surface. Those which arise from one of the leads will be formed of the gas chlorine and the others of hydrogen.

It will be interesting just to enumerate the names of the different parts of this apparatus. First let me say that the process by which these gases are thus obtained is called electrolysis: the liquid is the electrolyte: the two pieces of pencil lead are the electrodes. That electrode by which the current enters the electrolyte is called the an-ode, while the other is the cath-ode. In other words, the current traverses them in alphabetical order.

Now it is familiar to everyone that all matter is supposed to consist of tiny particles called Molecules. These are far too tiny for anyone to see even with the finest microscope, so we do not know for certain that they exist: we assume that they do, however, because the idea seems to fit in with a large number of facts which we can observe and it enables us to talk intelligibly about them. We may, accordingly, speak as if we knew for a certainty that molecules really exist.

Now when we dissolve salt in water it seems as if each molecule splits up into two things which we then call "ions." Salt is not peculiar in this respect, for many other substances do the same when dis

solved in water. All such substances, since they can be "ionized," are called "ionogens."

Now the peculiarity about ions is that they are always strongly electrified or charged with electricity.

At this stage we must make a little excursion into the realm of electricity. You probably know that if a rod of glass be rubbed with a silk handkerchief it becomes able to attract little scraps of paper. That is because the rubbing causes it to become charged with electricity. In like manner a piece of resin if rubbed will become charged and will also attract little pieces of paper. A piece of electrified resin and an electrified glass rod will, moreover, attract each other, but two pieces of resin or two pieces of glass, if electrified, will repel each other. This leads us to believe that there are two kinds of electrification or two kinds of electrical charge. At first these two kinds were spoken of as vitreous or glass electricity and resinous electricity, but after a while the idea arose that there was really one kind of electricity and that everything possessed a certain amount of it, the electrified glass having a little too much of it and the electrified resin a shade too little of it. From this came the idea of calling the charge on the glass a "positive" charge and that on the resin a "negative" charge. Recent investigations seem to show that we have got those two terms the wrong way round, but to avoid confusion we still use them in the old way.

It will be sufficient for our purpose, therefore, if we assume that every molecule of matter has a certain normal amount of electricity associated with it and

that under those conditions the presence of the electricity is not in any way noticeable. When a molecule becomes ionized, however, one ion always seems to run off with more than its fair share of the electricity, the result being that one is electrified positively, like rubbed glass, while the other is negatively charged, like rubbed resin.

Thus, when the common salt is dissolved in water, two lots of ions are formed, one lot positively charged and the other lot negatively. Each molecule of salt consists of two atoms, one of sodium and one of chlorine: consequently, one ion is a chlorine atom and the other is a sodium atom, the latter being positive and the former negative.

Now the electrodes are also charged by the action of the battery. That connected to the positive pole of the battery becomes positively charged and the other negatively. The anode, therefore, is positive and the cathode negative.

It has been pointed out that two similarly charged bodies, such as two pieces of glass or two pieces of resin, repel each other, while either of these attracts one of the other sort. Hence we arrive at a rule that similarly charged bodies repel each other, while dissimilarly charged bodies attract each other.

Acting upon this rule, therefore, the anode starts drawing to itself all the negative ions, in this case the atoms of chlorine, while the cathode gathers together the positive ions, the atoms of sodium. Thus the action of the battery maintains a sorting out process by which the sodium is gathered together around one of the electrodes and the chlorine round the other.

Those ions, by the way, which travel towards the an-ode are called an-ions, while those which go to the cath-ode are termed cat-ions.

Thus far, I think, you will have followed me: the chlorine is gathered to one place and the sodium to the other. The former creates bubbles and floats up to the surface and escapes. But where, you will ask, does the hydrogen come from, which we found, in the experiment, was bubbling up round the cathode. Moreover, what becomes of the sodium?

Both those questions can be answered together. The sodium ions, having been drawn away from their old partners the chlorine ions, are unhappy, and long for fresh partners. They therefore proceed to join up with molecules of water. But water contains too much hydrogen for that. Every molecule of water has two atoms of hydrogen linked up with one of oxygen, but sodium does not like two atoms of hydrogen: it insists on having one only. Accordingly the oxygen atom from the water, together with one of the hydrogen atoms, join forces with the sodium atom into a molecule of a new substance, a most valuable substance in many manufactures, called Caustic Soda, while the odd atom of hydrogen, deprived of its partners, has nothing left to do but to cling for a while to the cathode and finally float up and away.

The sum-total of the operation therefore is this: when we pass an electric current through salt water, between graphite electrodes, chlorine goes to the anode and escapes, while caustic soda is formed round the cathode and hydrogen escapes. Let us see now how this is applied commercially.

For the production of Chlorine the apparatus need be little more than our experimental apparatus made large. The anode can be covered in such a way as to catch the gas as it bubbles upwards. In times of peace this gas is chiefly used for making bleaching powder. It is led into chambers where it comes into contact with lime, with which it combines into chloride of lime, a powder which is sometimes used as a disinfectant, but the chief use of which is for bleaching those cotton and woollen fabrics for the manufacture of which this country is famous throughout the world.

The Germans, however, have taught the world another use for chlorine. Those gallant Canadians who were the first victims of the attack by "poison gas" who suddenly found themselves fighting for breath, and a few of whom, more fortunate than the rest, have reached their homes shattered in health with permanent damage to their lungs, those brave fellows suffered from poisoning by chlorine.

We cannot obtain the other product, the caustic soda, by the same simple means. In our little experiment we succeeded in manufacturing some of it in the region around the cathode, and had we drawn off some of the liquid from there we would have been able to detect its presence. But it would have been mixed up with much ordinary salt, and for commercial purposes we need the caustic soda separate from the salt. The principle is, however, just the same, as you will see.

Imagine a large oblong vat divided by vertical partitions into three separate chambers. These

partitions do not quite reach the bottom of the vessel, so that there is a means of communication between all three chambers. This is closed, however, by filling the lower part of the vat with mercury up to a level a little higher than the lower ends of the partitions.

Thus we have three separate chambers with communication between them but that communication is sealed up by the mercury.

The two end chambers are filled with salt water, or brine, while the centre one is filled with a solution of caustic soda. In each end compartment is a stick of graphite, both being electrically joined together and so connected up that they form anodes, while in the centre compartment is the cathode.

When the current flows from the anodes it carries the sodium ions with it, just as it did in our little experiment. But its course, this time, is not straight, since in order to travel from anode to cathode it has to pass through the openings in the partitions, in other words through the mercury.

On arrival at or near the cathode the ions of sodium cause the caustic soda to be formed just as in our experiment, but in this case, you will notice, the formation takes place in a chamber from which the salt brine is completely excluded by the mercury.

Brine is continually fed into the outer chambers and the solution of caustic soda is drawn from the centre one, while the chlorine is collected over the anodes.

And now we can go a step further on our progress from common salt to explosive.

In the soap works there are enormous coppers in which are boiled various kinds of fat. The source of the fat may be either animal or vegetable, many kinds of beans, nuts and seeds furnishing fats practically identical with that which can be got from the fat flesh of a sheep, for instance. To this fat is added some caustic soda solution and the whole is kept boiling for some considerable time. This protracted boiling is to enable the soda thoroughly to attack the fat and combine with it, whereby two entirely new substances are formed.

At first the two new substances are not apparent, for they remain together in one liquid. The addition, however, of some brine causes the change to become obvious for something in the liquid turns solid, so that it can be easily taken away from the rest. That solid is nothing else than soap. It remained dissolved in the water which forms part of the liquid until the salt was put in, but as it will not dissolve in salt water, as you will discover if you attempt to wash in sea water, it separates out as soon as the salt is added.

But still a liquid remains: what can that be? It is mainly salt water and glycerine, that sticky stuff which in peace times we put on our hands if they get sore in winter, or take, in a little water, to soothe a sore throat. That it has other and very different uses was brought home to me when, during the war, I tried to buy some at a chemist's, only to learn that it could not be sold except in cases of extreme need under the orders of a doctor.

The mixed liquid is distilled with the result that the water is driven off and the salt deposited, which

with other minor purifying processes gives the pure glycerine.

The next step takes us to the explosives factory, where the glycerine is mixed with sulphuric and nitric acids. Now glycerine, as you will have observed, comes from the animal or vegetable sources and therefore is one of those substances known as "organic," and, like many other of the organic compounds, it consists of carbon, hydrogen and oxygen. Nature has a marvellous way of combining these same three things together in many various ways to form many widely different substances and if, to such a compound, we can add a little nitrogen, we usually get an explosive. Thus, the glycerine, with some nitrogen from the nitric acid, becomes nitro-glycerine, a most ferocious and excitable explosive, the basis of several of those explosives without which warfare as we know it to-day would be impossible.

CHAPTER II
GUNPOWDER AND ITS MODERN EQUIVALENTS

The origin of gunpowder appears to be lost in antiquity. At all events it has been in use for many centuries and is still made in many countries.

Most boys have tried to make it at some time or other and with varying degrees of success. Such experiments generally lead to a glorious blaze, a delightfully horrid smell and no harm to anyone, the experimenter owing his safety to his invariable lack of complete success, for although other and better explosives have superseded it for many purposes it is capable of doing a lot of harm when it is well made.

It consists of a mixture of charcoal, sulphur and saltpetre ground up very fine and mixed very intimately together. The mixture is wetted and pressed into cakes and dried, after which it is broken up into small pieces. The precise proportions of the various materials seem to vary a great deal in different countries, but generally speaking there is about 75 per cent of saltpetre (or to give it its scientific name, nitrate of potash), 15 per cent of charcoal and 10 per cent of sulphur.

Now gunpowder, like all explosives, is simply

some thing or mixture of things which is capable of burning very quickly. When we light the fire we set going the process which we call combustion, or burning, and, as we know from our own experience, that process causes heat to be generated.

What takes place in the fire-grate is that the carbon of the coal enters into combination with oxygen from the air, the two together forming a new compound called "carbonic acid gas." There is nothing lost or destroyed in this process, the carbon and oxygen simply changing into the new substance, and could we weigh the gas produced we should find that it agreed precisely with the weight of the carbon and oxygen consumed. For the purpose for which we require the fire, namely, to heat the room, the chief feature about this process is not what is formed in the shape of gas, for that simply goes off up the chimney, but the heat which is liberated. We believe that in some mysterious way the heat is locked up in the coal. Latent is the term we use, which means hidden: in other words we believe that the heat is hidden in the coal: we cannot feel it or perceive it in any way, but it comes out when we let the carbon combine with the oxygen.

Why these two things combine at all is one of those mysteries which may never be solved. We have theories on the subject, but all we really know is that under certain conditions if they be in contact with one another they will combine, apparently for the simple reason that it is their nature so to do.

When we apply the match to the fire all we do is to set up the conditions under which the carbon and

oxygen are able to follow their natural instincts, so to speak.

A coal fire, as we all know, burns slowly, for the simple reason that it is only at the surface of the lumps that carbon and oxygen are in contact. If we grind up the coal into a fine powder and then blow it into a cloud, so that every tiny particle is surrounded with air, a spark will cause an explosion. That is how these terrible explosions in coal-pits are caused.

This is sometimes seen on a small scale when one shakes the empty fire-shovel after putting coal on the fire to get rid of the fine dust adhering to it and to save making a mess in the fender. That little cloud of fine dust will often burst into flame like a mild explosion.

We see from this that to make an explosion we require fuel, just as we do to make a fire: but we need that it shall be very intimately mixed with oxygen, so that all of it can burn up in practically a single instant. Now in gunpowder we get these conditions fulfilled. We have the carbon in the shape of charcoal, we also have some sulphur which likewise burns readily, and we have saltpetre which contains oxygen.

Thus, you see, we do not need to go to the air for the oxygen, for the gunpowder possesses it already, locked up in the saltpetre. Moreover, we can see now why it is so important for all the materials to be ground up very fine, for it is only by so doing that we can ensure that every particle of charcoal or sulphur shall have particles of saltpetre close by ready to furnish oxygen at a moment's notice.

Another thing to be observed, for it lets us into the great key to the manufacture of nearly all explosives, is the scientific name of saltpetre. It is "nitrate of potassium," and all substances whose names begin with "nitr-" contain nitrogen: while the termination "ate" signifies the presence of oxygen. We need the oxygen to make the explosion but we do not need the nitrogen, yet the latter has to be present for without it the oxygen would be too slow in getting to work.

Nitrogen is one of the strangest substances on earth. Extremely lazy itself, it has the knack of hustling its companions, particularly oxygen, and making them work with tremendous fury. Whenever we get the lazy gas nitrogen to enter into a combination with other things we may confidently look for extraordinary activity of some sort.

So when we put a light to a quantity of gunpowder we set up those conditions under which the carbon and oxygen can combine, and at the same moment our lazy friend the nitrogen turns out his partner oxygen from the nitrate in which they were till then combined and a sudden burning is the result. The solid gunpowder is suddenly changed into a volume of hot gas 2500 times as great. That is to say, one cubic inch of gunpowder changes suddenly into 2500 cubic inches of gas. That sudden expansion to 2500 times its volume is what we term an explosion. If it takes place in an enclosed space so that the gas formed wants to expand but cannot, the result is a pressure of about forty tons per square inch.

If that enclosed space were the interior of a gun, that force of forty tons per square inch would be available for driving out the projectile.

Now, gunpowder is still used for sporting purposes and also for some special purposes in warfare, but it has the great disadvantage that it makes a lot of smoke, so that the enemy would be easily able to locate the guns were it to be used in them. As we know so well, by the messages from France, guns and rifles drop their shells and bullets apparently from nowhere and are extremely difficult to locate. That is owing to the use of improved powders one of the great features of which is their smokelessness.

The reason why gunpowder makes a dense smoke, is because the burning which takes place is very incomplete. Therefore, by some such means as a more intimate mixture of the materials a better and more complete burning must be brought about.

One of the best known of the new powders (they are all spoken of as powders, whatever their form, since they have taken the place of the old gunpowder) is nitro-glycerine, the basis of which is glycerine.

The way in which we obtain this useful material has already been explained. It consists of carbon, a lot of hydrogen and some oxygen. These are not merely mixed together but are in combination, just as oxygen and hydrogen are combined in water. Carbon and hydrogen will both combine with oxygen and will give off heat in the process, but in glycerine they are already happily united together and so glycerine itself is no use as an explosive. If, however, we bring

nitric acid and sulphuric acid into contact with it a pair of new partnerships is set up, one being water and the other a compound containing carbon and hydrogen, a lot of oxygen and, most important of all, some of that disturbing, restless though lazy nitrogen.

This is nitro-glycerine, a particularly furious explosive, for that curious nitrogen seems to be so uncomfortable in his new surroundings that at the smallest provocation he will break up the whole combination and then there will be a mass of free atoms of carbon, hydrogen and oxygen, all seeking new partners, just right for a glorious explosion.

So furious and untamed is this stuff that it was almost useless until the famous Nobel hit upon the idea of taming it down by mixing it with an earth called Kieselguhr, which reduces its sensitiveness sufficiently to make it a very safe explosive to use. To this mixture Nobel gave the name of dynamite.

It is interesting at this point to compare the action of this typical modern explosive with that of the older gunpowder. The latter is only a mixture: the former is a chemical compound. The smallest particle of material in the gunpowder is a little lump containing millions of molecules and still more of atoms: when the nitrogen has broken up the original nitro-glycerine, just before the explosion actually takes place, we have a mixture of single atoms. Thus the mixture is far more intimate in the latter case and the burning is therefore quicker and more thorough.

Machine-gun versus Rifle.

This illustrates the rapidity and accuracy with which the modern rifle can be used. Sergeant O'Leary, V.C., tackled a gun crew of five and killed them all before they had time to slew their gun round—a striking contrast to the "Brown Bess" of a hundred years ago.

Another well-known explosive is gun-cotton. Surely

this must be a fancy name, for what can harmless, simple cotton have to do in connection with guns. It is a perfectly genuine descriptive name, however. It seems very strange at first, but it is perfectly true that nitrogen, as it turned glycerine into dynamite, can also turn cotton into gun-cotton. Cotton consists mainly of cellulose, a compound of carbon, hydrogen and oxygen, happily combined together and therefore showing, as we well know from experience, no tendency whatever to change into anything else, least of all to "go off bang." But that state of things is very much changed when we have induced nitrogen to take a hand in the game.

In actual practice, cotton waste, pure and clean, is dipped into a mixture of sulphuric and nitric acids whereby the cellulose becomes changed into nitro-cellulose, just as a similar process changes glycerine into nitro-glycerine. The whole process of manufacture is of course far more than that simple dipping, but that is the fundamental fact of it all. The rest is concerned with getting rid of the superfluous acid, tearing the stuff into pulp and pressing it into blocks. It is probably the safest of explosives, since it can be kept wet, in which case the danger of an accidental explosion is practically nil, provided reasonable care be taken. Even when dry, it behaves in a very kindly way. If hit with a hammer, it only burns for a moment just at the point struck. If ignited with a red-hot rod, it burns but does not explode, unless it is enclosed. The burning, that is to say, is not sufficiently rapid to constitute an explosion.

On the other hand, if it be exploded by a detonator, by which is meant a small quantity of a very powerful explosive, such as fulminate of mercury, fired close

to it, it then goes off with a violence which leaves little to be desired.

It would be better still could we persuade a little more oxygen to enter into its composition, for as it is there is not quite enough to burn up the other matters completely. That, however, does not cause smoke, since the combustion is complete enough to change everything into invisible gases. With more oxygen more heat might be generated and the power of the explosion be made greater. Still, even as it is, the explosion of gun-cotton has been estimated by a high authority to produce a pressure of 160 tons per square inch, four times as much as gunpowder. Nitro-glycerine has the advantage of a rather larger proportion of oxygen to carbon, resulting in its being rather more energetic.

Yet another class of explosive is made from Coal Tar. This is a by-product in the manufacture of gas for lighting and also in the manufacture of coke for industrial purposes. It comes from the retorts along with the gas in a gaseous form but condenses into a black liquid in the pipes and more particularly in an arrangement of cooled pipes called a condenser specially placed to intercept it.

In the chemist's eyes it is the most interesting of liquids, for it is full of mysteries and possibilities. The most wonderful achievements of chemistry have it for their raw material and there is still scope for much more in the same direction.

If the tar be gently heated in a closed vessel it will evaporate and the vapour can be led to another vessel, there cooled and converted back into a liquid. This

looks rather like doing work for nothing, but the various liquids, of which tar is a mixture, evaporate at different temperatures, so that this furnishes a means of separating them. The first liquid thus procured is known as coal tar naphtha, and if it be again distilled it can be subdivided further, the first liquid separated from it being known as Benzine. This, again, is another of those almost numberless things which consist of carbon and hydrogen. Also, like the other similar substances which we have been discussing, it can, if treated with nitric acid, be made to take into partnership a quantity of oxygen and nitrogen.

Thus we get nitro-benzene. We can repeat the process, when it will take more and become di-nitro-benzene. Again we can repeat it, thus producing tri-nitro-benzene.

The second liquid separated from coal tar naphtha is called Toluene, which again is composed of carbon and hydrogen in slightly different proportions. Like its confrère benzene it, too, can be treated with nitric acid, becoming nitro-toluene and then di-nitro-toluene and finally tri-nitro-toluene, the deadly explosive of which we read in the papers as T.N.T.

After the naphtha has been removed from the tar another substance is obtained called Phenol, which in a prepared form is familiar to us all as the disinfectant Carbolic Acid. It also can be treated with nitric acid, to produce tri-nitro-phenol, otherwise known as Picric Acid, which after a little further treatment becomes the famous "Lyddite."

Most of the actual explosives used in warfare are

prepared from one or more of the above-mentioned compounds. For example, nitro-glycerine and gun-cotton, having been dissolved in acetone (another compound of carbon, hydrogen and oxygen) and a little vaseline added, form a soft gelatinous substance which on being squeezed through a fine hole comes out looking like a cord or string, and hence is called Cordite.

Other explosives are finished in the form of sheets, the dissolved gun-cotton or whatever it may be being rolled between hot rollers which give it the convenient form of sheets and at the same time evaporate the solvent.

By combining these various substances various characteristics can be given to the finished explosive. For instance, the one which drives the shell from the gun, known as the propellant, must not be too sudden in its action. It must push steadily. Its purpose is to drive the shell not to burst the gun, wherefore its action must be comparatively slow and continuous so long as the shell is still in the gun. It must "follow through" as the golf player would put it.

The charge in the shell, however, needs to go off with the greatest possible violence so as to blow the shell to pieces and to scatter the fragments so that they do the maximum of damage.

Those explosives, whose function is thus to burst with a sudden shock, are called High Explosives, as distinguished from the propellants which produce a more or less sustained push.

The great fundamental principle which enables

large quantities of these powerfully explosive substances to be handled with comparative safety involves the use of two different substances in combination. That which is used in quantity and which actually does the work is made comparatively insensitive, indeed in some cases it is very insensitive, so that it can safely travel by train, by ship and by road and also may be handled by the soldiers and sailors with very little risk. Some of these compounds can be struck or set on fire with impunity. They are none the less violent, however, when, by the agency of a suitable detonator they are caused to explode.

The detonator, of course, has to be very sensitive indeed, but it need only be used in very small quantities, so that by itself it, too, is comparatively safe. Fulminate of mercury is often employed for this purpose—a compound based upon mercury but in which nitrogen of course figures largely.

Thus, there are two things necessary for the successful explosion, one of which is powerful but insensitive, while the other is highly sensitive but relatively harmless since it is never allowed to exist in large quantities, and as far as possible these are kept apart until the last moment.

One other thing may be mentioned in regard to this matter which is of the greatest importance. That is the necessity for the utmost uniformity in these various compounds, so that when the gunners put a charge into a gun they can rely upon it to throw the shell exactly as its predecessor did. Modern artillery seeks to throw shell after shell within a small area which would clearly be quite impossible if one charge

were liable to be stronger or weaker than another, for we can easily see that the more powerful the impetus given the farther will the shell go.

To secure this uniformity the greatest care is taken at all stages of the manufacture, and various batches of the same stuff are tested and mixed, and any of them turning out a little too strong are placed with some a little too weak, so that their faults may neutralize each other. By such methods as these a remarkable degree of uniformity is attained, the result of which we see when we read in the papers of the wonderfully accurate gunnery of which our soldiers and sailors are capable.

In conclusion, a word of warning may be appropriate. Reference has been made above to the safety of modern explosives in the absence of the detonators, but do not let that lead anyone to take liberties. Should any reader come into possession of any of these materials, even in the smallest quantities, let him treat it with the utmost respect, for although what has been said about safety is quite correct, it only means comparative safety, there can be no absolute safety where these substances are concerned.

CHAPTER III
RADIUM IN WAR

When we remember how all forms of scientific knowledge were called upon to help in the great struggle, it is not surprising to hear that, although in a comparatively humble way, Radium has had to do its share.

Now radium is one of the most, if not actually the most, remarkable substance known. About a generation ago scientific men, or some of them at all events, were getting rather cocksure. Of course they were quite right when they realized how much was known about things and what great strides had been made during the years through which they had lived. They were proud of the achievements of their scientific friends, for I am not imputing personal vanity to anyone, and they had reason to be proud. They made the mistake, however, of thinking that in one direction at least they had learnt all that there was to be known. The present generation of scientific men seem to be almost too prone to go to the other extreme and to dwell rather much on how little we know now and the wonderful things which are going to be discovered in time.

But that is by the way. A generation ago men seem to have pretty well made up their minds that

they knew all about atoms. They said that everything was made up of atoms, that the atoms could not be subdivided nor changed into anything else except temporarily by combination with other atoms, and that when these combinations were broken up the atoms remained just as before, quite unchanged. They believed that the atoms were unchangeable and everlasting. Professor Tyndall, in a famous address, referred to this in somewhat flowery language, telling his hearers that the atoms would be still the same when they and he had "melted into the infinite azure of the past," which a wag translated into the slang expression of the time, "till all is blue."

Now not very long after Professor Tyndall made this historic speech Professor Henri Becquerel, of Paris, was trying some experiments with phosphorescent materials, that is, materials which glow in the darkness. In the course of these experiments he used some photographic plates upon which, to his surprise, he found marks which he thought ought not to have been there. Thinking at first that he had accidentally "fogged" his plates, as every photographer has done at some time or other, he tried his experiments again with special care but still he got the mysterious marks.

Those marks were caused by some of those "unchangeable and everlasting" atoms deliberately and of their own accord blowing themselves to bits.

For the celebrated Frenchman was not content to let the matter of those mysterious marks rest: he wanted to know what caused them and he did not desist until he was on the track of the secret. It

appeared after careful investigation that they were made by the action of something in some of the ore of the metal "uranium" which he had been using. Moreover, this something evidently had the power of penetrating through the walls of the dark-slide to the plate within. Finally, it was tracked down to the uranium itself which was unquestionably proved to be giving off something in the nature of invisible light, or at all events invisible rays, of strange penetrative power. A little later it was observed that certain ores of uranium seemed to give off these rays more freely than would be accounted for by the amount of uranium present, from which fact it was inferred that there must be something else present in the ore capable of giving off the rays much more powerfully than uranium can. Madame Curie ultimately found out two such substances, one of which she called, after her native land, Polonium (for she is a Pole), and the other Radium. It is the latter which is responsible for by far the greater part of the rays formed.

The rays are invisible, but they affect a photographic plate in the same way that light does. They also make air into a conductor of electricity and if allowed to impinge upon a surface coated with a suitable substance they cause it to glow.

This spontaneous giving off of rays is now spoken of by the general term of "radio-activity," and it has grown into an important branch of science. A number of other substances have been found to exhibit the same peculiar ray-forming powers, notably Thorium, one of the components of the incandescent

gas mantle by the prolonged application of a fragment of which to a photographic plate an impression can be obtained due to the rays.

What, then, are these rays? It is found that they are of three kinds, not that they vary from time to time, but that they can be sorted out into three different sorts of rays which are given off simultaneously all the time.

The first sort are stopped by a sheet of paper, the second passing easily through a thick metal plate, while the third appear to be identical with X-rays.

For convenience the three sorts are termed Alpha, Beta and Gamma rays, respectively, after the first three letters of the Greek alphabet.

Further, the Alpha rays prove to be a torrent of tiny particles about the size of atoms, indeed if they be collected the gas Helium is obtained, so that evidently they are helium atoms, and since that is one of those substances whose molecules consist of a single atom each they are also molecules of helium. No doubt the reason why they are so easily stopped by a piece of paper is because being complete atoms they are large, huge indeed, compared with the particles which form the Beta rays, for they are apparently those same electrons which are found in the X-ray tube, and which are at least 2000 times smaller than the smallest atom.

When the electrons in the vacuum tube are suddenly brought to a standstill X-rays are given off and in like manner X-rays no doubt would be given off when they start on their journey, providing that they started suddenly enough. Hence it is the starting

or sudden explosion-like ejection of the Beta particles which is believed to give rise to the Gamma rays.

The strength or intensity of the rays can be measured very conveniently by their action in making air conductive to electricity, for which purpose a very beautiful but simple instrument called an Electroscope is employed. It consists generally of a glass-sided box or else a bottle with a large stopper, consisting of sulphur or some other particularly good insulator. Through this a wire passes down into the inside of the vessel terminating in a vertical flat strip to the upper end of which is attached a similar strip of gold leaf or aluminium foil. Normally the leaf hangs down close to the strip, but if the wire above the stopper be electrified by touching it with a piece of sealing-wax rubbed lightly against the coat sleeve the charge of electricity passes down into the inside and causes both strip and leaf to become so electrified that they repel each other.

Owing to the non-conductivity of the air in its normal condition the leaf will, if the insulation of the stopper be good, remain projecting almost horizontally for some time until, as it loses its charge by a slow leakage, it gradually settles down close to the strip.

If, however, a piece of radium be brought near while it is sticking out, the leaf will fall almost instantly. X-rays have a similar effect even from several feet or yards away.

The intensity of the radio-activity of different substances can be compared by noting the difference

in the rate at which the leaf falls under the influence of each.

What is happening, then, to the atoms of radium, which causes them to show these curious effects and to give off these strange rays? To give any intelligent answer to that question we are bound to assume that which the older generation of scientists thought impossible, namely, that atoms can be broken up. Then we are forced to believe that the atoms of this particular substance radium are of a peculiarly flimsy unstable sort, so that they cannot permanently hold their parts together but are liable to break up, as far as we can see through their own inherent weakness and under the influence of disruptive forces at work within themselves.

We must remember, however, that the tiniest speck of matter which we can see contains a number of atoms of such a size as to be quite beyond the grasp of our minds. To give a rough idea of it in figures is useless as no one can comprehend the real value of a figure or two followed by probably from a dozen to twenty "noughts." It is best to content ourselves with the general statement that a speck of matter only just visible to the eye contains an exceedingly vast number of atoms. Of course a speck of radium is no exception to this and we must remember, too, that all of them do not break up at once. Indeed, the number breaking up at any time are actually countable by means of a very simple contrivance and a sensitive electrometer. Consequently, in view of the enormous number present and the comparatively small number breaking up

at any moment, it is not surprising to hear that, so it is estimated, the process can go on for an almost indefinite number of years, certainly for hundreds. There are, moreover, certain facts which we need not go into here from which the above fact can be clearly inferred, quite apart from what has been said about the vast numbers of the atoms.

It seems as if the uranium atoms break up first, giving off helium atoms and electrons and leaving an intermediate substance called Ionium which in its turn breaks up giving off the same things again and leaving radium. That in its turn goes through a complicated series of changes still giving off the same alpha particles or atoms of helium and electrons until, it is suggested, it finally settles down into the simple commonplace metal lead of which we make bullets and water pipes and such-like ordinary things.

We see then that all through its history—its radio-active history at any rate—this stuff is throwing off atoms of helium at a very high velocity (about 50,000 miles a second), and if it be enclosed in anything this enclosing vessel or substance will be subjected to a continual bombardment by the alpha particles. Now just as a piece of iron gets hot if we hammer it, so the enclosing matter is heated by the continual blows which it is receiving night and day, year in and year out, from the alpha particles.

Consequently the immediate surroundings of a speck of radium are always slightly raised in temperature.

Moreover, if a speck of radium be placed against a screen covered with suitable materials each particle

which strikes it will make a little splash of light. At least that is what it looks like when seen through a magnifying glass, but to the naked eye there only appears a beautiful steady glow.

Suppose, then, that instead of putting the speck of radiant matter in front of a screen we mix it up intimately with a fluorescent substance such as sulphide of zinc, we then get the same conditions in a slightly different form. Each particle of the substance serves as a tiny screen which glows every time a particle hits it. Thus is produced a luminous paint which glows by night, suitable for painting the dials of instruments which have to be used in the dark.

No doubt some of my readers will have experienced the strangely mingled delight and horror of seeing a Zeppelin in the night sky intent on dropping murder and death on the sleeping civilians of a peaceful town or city. Some too may have witnessed the later acts in that wonderful drama, when, beside the silvery monster illuminated by the beams of the searchlight there must have been, though quite invisible, a little aeroplane manned by one man or at most two. That aeroplane was, no doubt, fitted with instruments at which the pilot glanced now and then and which he was able to see and read because of the tiny speck of radium mixed into the paint. The little alpha particles gave him the light by which to see, but they gave no help to the Germans on the Zeppelin. Hence, in due time he did his work and the gigantic balloon, the pride of the Kaiser and his hordes, fell to the ground, a blazing wreck. How he did it I cannot

tell, but of this I am sure, that most probably radium helped him by making luminous and visible the instruments which guided him.

But probably it has rendered and will still render us even greater services in the way of helping to repair the damages to our injured manhood. How many men came back from the war crippled with rheumatism because of the hardships through which they went. That disease is believed to be due to a substance which mingles with the blood and which, although usually liquid and harmless sometimes changes into a solid and settles in the joints. Now it is believed that radium properly administered will act upon that solid and cause it to change back into its liquid form again, thereby curing the disease. Certainly many of the mineral springs at such places as Bath and Buxton give forth a water which shows a certain amount of radio-activity and it may be that which gives those waters their healing properties. If so, we may look forward with confidence to the time when radio-activity will be induced to play a still more successful part in meeting this painful and widespread illness.

Then, of the other ills which will inevitably arise in our men through the hardships which they have endured are sure to be some of the cancerous type, many of which appear to succumb to treatment by radium. If a very small quantity indeed be carried for a few days in a pocket it will imprint itself upon the skin beneath as if it burnt the tissues. It is never advisable, therefore, to carry radium in the pocket without special precautions. One cannot help

feeling, however, that in that little fact is a hint of usefulness when the best modes of application have been discovered, for as a means of safely and painlessly burning away some undesirable growth it would seem to be without a rival. It is said, too, that it has the strange power of discriminating between the normal and the abnormal, attacking the latter but leaving the former, so that when applied, say, to some abnormal growth like cancer it may be able to remove it without harmful effect upon the surrounding tissues.

Of this, however, it is too soon to write with confidence. It has not been known long enough for our doctors to find out the best modes of use, but that will come with time: meanwhile there are indications that in all probability it will render good service to mankind.

CHAPTER IV
A GOOD SERVANT, THOUGH A BAD MASTER

One morning during the war the whole British nation was startled to learn that Mr. Lloyd George, then the Minister of Munitions, had taken over a large number of distilleries. Could it be that he, a teetotaller and temperance advocate, was going to supply all his workers with whiskey? Or was he going to close the places so as to stop the supply of that tempting drink?

Neither of these suggestions was his real reason. What he wanted the distilleries for was to make alcohol for the war, not for drinking purposes but for the very many uses which only alcohol can fulfil in most important manufactures.

Probably alcohol is the next important liquid to water. For example, certain parts of shells have to be varnished and the only satisfactory way to make varnish is to dissolve certain gums in alcohol. The spirit makes the solid gum for the time being into a liquid which we can spread with a brush, yet, after being spread, it evaporates and passes off into the air, leaving behind a beautiful coating of gum. That is how all varnishing is done, the alcohol forming the vehicle in which the solid gum is for the moment

carried and by which it is applied. It is far and away the most suitable liquid for the purpose, and without it varnishing would be very difficult and unsatisfactory. Hence one need for alcohol, to carry on the war.

Then again some of the most important explosives are solid or semi-solid, and yet they require to be mixed in order to form the various "powders" in use by our gunners. The best way to bring about this mixture is to dissolve the two components in alcohol, thereby forming them both into liquids which can be readily mixed. Afterwards the alcohol evaporates; indeed, one of its great virtues for this and similar purposes is that it quietly takes itself off when it has done its work like a very well-drilled servant.

What then is this precious liquid and how is it produced? In order to answer that question it is necessary first to state that there are a whole family of substances called "alcohols," all of which are composed of carbon, hydrogen and oxygen in certain proportions. There are also a number of kindred substances also, not exactly brothers but first cousins, so to speak, which because of their resemblance to this important family have names terminating in "ol."

They owe their existence to the wonderful behaviour of the atoms of carbon. In order to obtain some sort of system whereby the various combinations of carbon can be simply explained chemists picture each carbon atom as being armed with four little links or hooks with which it is able to grapple, as

it were, and hold on to other atoms. Each hydrogen atom, likewise, has its hook, but only one instead of four.