THE public mind has to a large extent reacted against the opinions impressed on it during the war by official propaganda. Some of these have been overcome by counter-propaganda in the press and on the platform, others have been dropped because they led to effects which, though admirable during a war, were undesirable in peace-time. But as chemical warfare will not assume importance until the outbreak of the next serious war, and figures on the programme of no party, people still think about it as they were told to think by the newspapers during the Great War.

Now I am to some extent a chemist, so I can no more be expected to be impartial in my estimate of the value of chemistry than a politician or a clergyman can be expected to give an unbiased view of the value of politics or religion. I can only plead that, unlike the average clergyman or politician, I have warned my audience in advance, and shall attempt - though no doubt vainly to be impartial.

A few of my readers hold the view that while war in itself is a noble occupation the use of poisonous gas is an innovation as cruel as it is unsoldierly. The majority are probably

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pacifists in the sense that they prefer almost any peace to almost any war, support the League of Nations or other devices for the prevention of international strife, and look askance at preparations for future warfare, more particularly for future chemical warfare. If so, I certainly share their objection to war; but I doubt whether by objecting to it we are likely to avoid it in future, however lofty our motives or disinterested our conduct. War will be prevented only by a scientific study of its causes, such as has prevented most epidemic diseases.

For many centuries people had guessed that epidemic diseases constituted a punishment for human misconduct of some kind. They tried to prevent them by prayer and almsgiving. Christians gave up washing; Hindus liberated rats captured during plague epidemics. Religious orders and priests of the church gave the most magnificent examples of self-sacrifice in times of pestilence. But that was not the way in which pestilences can be prevented. Besides good intentions a special type of accurate thinking was needed. We have not yet made a scientific study of the causes of war and, until we do, may expect more

wars. If we are to have more wars, I prefer that my country should be on the winning side.

In general, pacifists are a very great military advantage to Britain. On the outbreak of war, the large majority of them become intensely patriotic, whereas beforehand they lead our own military authorities, and also those of our potential allies and enemies, to underestimate our strength. This keeps us out of some wars and leads to our showing unsuspected power in others. After a few years of war, when the originally bellicose politicians, like Lord Lansdowne, are getting tired, ex-pacifists, like Lloyd George and Pitt, have just got into their stride. The national staying-power is thus greatly increased.

I need hardly remark that future governments will not enter on war without first persuading the vast majority of the people of its justice. This appears to be an extremely simple process under modern conditions.

At the present moment, however, pacifists are combining with the less competent soldiers in an attempt to check the progress of chemical warfare. This I believe to be neither in our national nor in the international interest.

Until 1915 the soldier's business was to push or throw pieces of metal at the enemy. Various devices had been employed for throwing them fast or far, and some of them threw other pieces on arrival at their destination, thanks in the main to the genius of the unforgotten Major-General Shrapnel. It is true that in the late seventh century A. D. the appropriately named Syrian, Callinicus, had prolonged the life of the Eastern Roman Empire for another 750 years and saved a large part of Christendom from Mohammedan domination by his invention of 'Greek fire,' an inflammable liquid

which was later superseded by gunpowder. In the fifteenth century the defenders of Belgrade against the Turks had hit upon a similar device, under the direct inspiration, it was claimed, of the Holy Ghost, but these weapons had fallen into desuetude, their effect being largely psychological.

Chemical warfare had been so far foreseen by statesmen that in 1907 the signatories of the Hague Conference agreed to renounce the use of projectiles the sole object of which was the diffusion of asphyxiating or harmful gases. They were thus debarred from using lachrymatory gas, the most humane weapon ever invented, but were permitted to discharge gas from cylinders on the ground, an exceedingly cruel practice. This regulation was well meant, but the path to August 1914 was paved with good intentions. In 1914 none of the Great Powers had made any preparation for poison-gas warfare, and it was not till April 22, 1915, more than eight months after the beginning of the war, that the Germans began its use.

During the war twenty-five different poisonous weapons were employed. Of these, three are gases at ordinary temperatures and can be discharged from cylinders in which they are stored under pressure. The remainder are liquids which gradually evaporate, yielding a poisonous vapor, or solids which are poisonous in the form of smoke.

These poisonous substances so far used fall into four classes according to their effect on men. First come gases and vapors which are poisonous when breathed, but have no effect on the skin, and affect only the eyes or nose when present in concentrations which are poisonous to the lungs. They can all be kept out by respirators, and were only of military value against unprotected troops, or in local surprise action.

This group, which included chlorine and phosgene, is probably almost as obsolete as muzzle-loading cannon.

A second group is poisonous only in very high concentrations, but irritates the eyes when present in amounts so small that one part in five million may render a man blind with weeping in a few seconds. There is no evidence, so far as I know, that anyone was killed or even permanently blinded by these substances, but they had a great momentary effect. They can be kept out by respirators or even goggles.

The third group of poisonous smokes, mostly arsenic compounds, was little developed during the war. They are, however, weapons of very great efficiency, and it is well known that they would have been used, by the British at any rate, on a very extensive scale in 1919. In small amounts these smokes

merely make one sneeze. In somewhat larger amounts they cause pain of the most terrific character in the head and chest. The pain in the head is described as like that caused when fresh water gets into the nose when bathing, but infinitely more severe. These symptoms are accompanied by the most appalling mental distress and misery. Some soldiers, poisoned by these substances, had to be prevented from committing suicide, others temporarily went raving mad and tried to burrow into the ground to escape from imaginary pursuers. And yet within forty-eight hours the large majority had recovered, and practically none became permanent invalids. These substances, when in the form of smoke, will penetrate any of the respirators used in the late war, though the British box respirator would stop all but a little of them in the concentrations then used. In future they will

1 The American 'Lewisite,' of which so much was heard in 1918 and 1919, is a substance of this class.

probably be used in much larger concentrations and in finer particles than those formed by the German smokeshells.

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or

It is extraordinarily difficult to produce a respirator which will completely stop very fine smoke, for the following reason. In a gas the molecules ultimate particles are moving very rapidly with speeds of several hundred yards per second, continually colliding and rebounding. A gas molecule therefore will probably hit the sides of a fairly narrow passage through which it is drawn. But a smoke particle is moving at a speed measured in inches per second, and is far less likely to hit the wall of the respirator and be held by its absorbent surface. If we try to make the passages through which air is drawn very narrow, as by sucking in our air through cotton wool, - which will stop most smokes, we find that we have created an appalling resistance to breathing. There is an electrical method of removing smoke particles completely, but it would probably more than double the weight of respirators and does not appear to be either waterproof or foolproof.

The fourth group of blistering gases contains only one substance used during the war, dichlorethyl sulphide, or 'mustard gas.' This is really a liquid, whose vapor not only is poisonous when breathed, but blisters any part of the skin with which it comes in contact. To take an example, a drop of the liquid was put on a piece of paper and left for five minutes on a man's sleeve. The vapor penetrated his coat and woolen shirt, causing a blister the effects of which lasted six weeks. And yet evaporation is so slow that ground contaminated by the liquid may remain dangerous for a week. Mustard gas caused more casualties to the British than all other chemical weapons put together.

II

Such are the weapons which chemistry has given us. It is often asked why chemists cannot produce something which will put our foes comfortably to sleep and allow us to take them prisoners. The answer is that such substances exist, but that when used in small amounts they are harmless, in large amounts, fatal. It is only over a moderate range of concentrations that their effect is merely stupefying. One has only to think of the familiar case of chloroform vapor and the skill required to give neither too much nor too little.

It would be logical to speak of explosives under the heading of chemical warfare, but there is curiously little chance of explosives becoming any more effective. We know fairly well the maximum amount of energy which can possibly be got out of a chemical action, and, though explosives might perhaps be made which were about twice as destructive as our best or worstto-day, they would probably be far less. stable and therefore less safe to their

users.

Of course, if we could utilize the forces which we now know to exist inside the atom, we should have such capacities for destruction that I do not know of any agency, other than divine intervention, which would save humanity from complete and peremptory nullification. But the remoteness of the day when we shall use these forces may best be judged by an analogy. Some thousands of years ago someone first realized that the sun, moon, and stars were not mere bodies the size of a plate or a house, but very large and moving very fast. It was an obvious idea that their motions might be exploited in some way. Wise men observed them and hoped, for example, to increase the probability of success in their own enterprises by beginning them when

Jupiter was in the ascendant. These attempts were unsuccessful, though far more valuable to humanity than most of the methods successfully employed for the same purposes, such as fraud, violence, and corruption. They led to astronomy and so to all modern physics.

We now know that the only probable way of harnessing the energy of the heavenly bodies is to employ tidal power to create electric currents. But five thousand years ago hitching one's wagon to a star was a reasonable project, and not a poetic metaphor. The reason we cannot do it is a simple matter of scale. And the reason why we cannot utilize subatomic phenomena is just the same. We cannot make apparatus small enough to disintegrate or fuse atomic nuclei, any more than we can make it large enough to reach to the moon. We can only bombard them with particles of which perhaps one in a million hit, which is like firing keys at a safe door from a machine-gun a mile away, in an attempt to open it. We do occasionally open it, but the process is very uneconomical. It may be asked why we cannot bring our machine-gun nearer or improve our aim. To do this would require the construction of apparatus on the same infinitesimal scale as the structure of the chemical atom. Now we can arrange atoms into various patterns. For example, we can arrange carbon, hydrogen, and oxygen atoms in patterns which constitute the molecules of sugar, glycerine, or alcohol at will. This is called chemical synthesis. We have been doing it by rule-of-thumb methods for thousands of years, and are just beginning to learn a little about it. But even chemical molecules are much too large for our purposes. We can no more ask a chemist to build our apparatus than expect a theatrical scenepainter or a landscape gardener to do us a miniature. We know very little