Gas and flame in modern warfare

by Samuel James Manson Auld

Another story which commenced to make its appearance at that time and which we have heard a great deal about ever since was that the Germans were busy making prussic acid in enormous quantities for a huge offensive which was to finish the war. It was stated that the Kaiser had at last been persuaded to use this terrible weapon in order by its use to finish the war at once and prevent needless suffering.

When they first made their appearance stories with regard to prussic acid had to be taken a great deal more seriously than those like the “little black bubbles.” For one thing we were unprotected against prussic acid, and for another it was known of course to be an extremely deadly poison. Indeed before the war it was regarded as the most poisonous vapour known, so a great deal of weight was attached to these statements, and experiments were at once put on foot to find protection against prussic acid and to see exactly how poisonous it was compared with other gases.

As a matter of fact prussic acid has not been used by the Germans simply because it is not poisonous enough. It is not so poisonous, for example, as phosgene, and a lot of captured German documents showing the relative toxicity of different vapours always put it on a rather low basis. It was this and not a desire to avoid utter barbarity which decided the Germans not to use it. The ordinary German soldiers, just like ourselves, still consider prussic acid as the most dangerous possible material, and whenever they have a story to tell of a new gas being invented or being got ready to use against us they will tell you in awestruck tones that it is prussic acid.

The most valuable piece of information which we got was a complete set of notes of some very secret lectures given to specially selected senior officers at a conference in Germany. We gathered that this conference was held behind closed doors and triple lines of sentries, and all that kind of thing, and I cannot of course indicate how the information came into our hands, but there it was. It described a lot of new gases which had been considered, and stated among other things that they intended to make a big gas attack against either the French or ourselves in Flanders in December, 1915, some time before Christmas when the wind was favourable. For this purpose they were going to use a mixture of chlorine with another gas, phosgene—the amount of phosgene to be twenty per cent of the whole.

Now phosgene had been realised by our own chemists as a very likely gas to be used. I cannot say that it is more poisonous than chlorine, but it is infinitely more deadly because it is much more difficult to protect against and is more insidious in its nature. For one thing, though it is an asphyxiant like chlorine it is possible for a man to be only slightly gassed and think he is all right, and then, especially if he takes any exercise in between, to fall dead several hours later from heart failure.

The information was so complete that our arrangements to provide a helmet which would protect against phosgene were hastened as much as possible; and it was as well that they were, for the attack actually did come off just about the time and place mentioned, in the Ypres salient.

It was realised of course that any change in protection would have to include both prussic acid and phosgene; and this is not nearly so easy as it sounds. Phosgene is peculiarly chemically inert for such an active poison, and it was some time before a reasonable protection was found which could be incorporated in a smoke helmet. The substance actually decided upon was a solution of sodium phenate—that is, carbolic acid dissolved in caustic soda, the mixture containing an excess of caustic. This solution is quite capable of dealing with reasonable concentrations of phosgene and would successfully protect against three parts of phosgene to ten thousand of the air, which in the circumstances was quite good enough. The French also altered their protection at the same time and used sodium sulphanilate as the basis of protection against phosgene. The objections against the sodium phenate were that it could not be absorbed into a flannel helmet owing to its destruction of the fabric, and on account of its being strongly caustic it would tend to burn the faces of the men it came in contact with. These difficulties were overcome by making the helmet of two layers of flannelette instead of one layer of flannel, and by mixing with the sodium phenate a large quantity of glycerin. This kept the fabric moist and prevented the caustic from exerting its corrosive action.

It was realised from the start that a smoke helmet containing free alkali would deteriorate considerably on exposure to air, and it was found advantageous to provide a breathing tube in the mask so that a man would breathe in through the helmet and out through an outlet valve; in this way the breath, which contains a lot of carbonic acid, would have no bad effect on the chemicals. The use of an outlet valve was also found to have the advantage of keeping the air purer inside the helmet and preventing the stuffy feeling which accompanied the older types of helmet.

This additional complication to the helmet was not looked upon favourably at first by the troops, but it was very quickly realised that only a little practice was required to make a man breathe quite normally in the way mentioned above, and that the advantages accruing from the alteration were very great indeed. We found that we could carry on for much longer stretches of time without being fagged out, and more exact trials by the scientists showed that a man’s temperature, pulse and rate of breathing did not increase nearly so rapidly if he used an outlet valve as when breathing out and in through the same material. This is largely due to what is called “dead space,” which means the volume of air in between the lungs and the atmosphere and in which the air is largely composed of breath exhaled from the lungs. The smaller this space the easier it is to breathe.

This principle of using an outlet valve has been retained in all the British respirators which have been invented since and is regarded as one of the very highest importance.