Riddle of the Rhine | Page 9

produced a sufficient concentration of gas to be of military value. It was a kill or cure compound, for recovery was rapid from any concentration which did not produce death.
A prominent Cambridge physiologist, in the heat of the controversy on this matter, made a very brave and self-sacrificing experiment. He entered a chamber of prussic acid which was sufficiently concentrated to cause the death of other animals which were present. They were removed in time, and he escaped because the concentration was not a mortal one for man. This was, in a sense, an _experimentum crucis_ and, although it did not disprove the extreme danger of prussic acid, if employed in high concentrations, it showed, on the other hand, that it was difficult to gauge the military value by field experiments; battle results were necessary. The Germans' disappointment with the use of arsenic compounds confirms this need for battle evidence.
Lachrymators.--There is hardly need to dwell on the next class, the lachrymator. These compounds were employed on a large scale to produce temporary blindness by lachrymation, or weeping. We give later some interesting examples of their use on the front. It is an arresting thought that even as early as 1887 Professor Baeyer, the renowned organic chemist of Munich, in his lectures to advanced students, included a reference to the military value of these compounds.
Vesicant or Blistering Compounds.--It was the introduction of the fourth, the vesicant class, which revealed, more than any other enemy move, the great possibilities inherent in chemical warfare. These compounds, the chief of which was mustard gas, produced vesicant, or skin burning, effects, which, although rarely mortal, were sufficient to put a man out of action for a number of months. Mustard gas resulted from pure scientific investigation as early as 1860. Victor Meyer, the famous German chemist, described the substance in 1884, indicating its skin-blistering effects. There is evidence of further investigation in German laboratories a year before the outbreak of war, and whatever the motive for this work, we know that mustard gas must have received the early attention of the German War Office, for it was approved and in production early in 1917. Although the Medecin aide-major Chevalier of the French services drew attention to its importance in 1916, the French had no serious thought of using mustard gas, and did not realise its possibilities until the German battle experiment of July, 1917. It is not generally known, however, that other vesicant compounds were employed, notably some of the arsenic compounds, and the Germans were researching on substances of this nature which gave great promise of success. Mustard gas provides a striking example of the organic way in which chemical warfare is bound up with the dye industry. The compounds required for its manufacture were those which had been made on a large scale by the I.G. for the production of indigo. World indigo monopoly meant possession of a potential mustard gas surprise on the outbreak of war.
Sneezing or Sternutatory Substances.--The last class, the sternutatory substances, produced the familiar sneezing effect which was accompanied by intense pain and irritation of the nose, throat, and respiratory channels. They were mostly arsenic compounds and were not only sternutatory but also toxic, producing the after effects of arsenic poisoning.
The Tactical Classification.--From the point of view of our account of chemical warfare, however, the physiological classification of these substances is not so important as the tactical and, indeed, once this grouping of the substances is understood, a profound knowledge of their chemical nature is not necessary.
Persistent Substances.--Two main classes exist from the tactical Point of view. There are those "persistent" substances which remain for a long time on the soil or on the object on which they are sprayed by shell, while retaining their dangerous effect. Mustard gas was the chief example, but some of the lachrymators were just as persistent. By their use it is possible to render ground uninhabitable or ineffective for military movement. The combination of the vesicant and persistent properties of mustard gas rendered it a powerful military factor.
Non-Persistent Substances.--On the other hand, there are the relatively volatile substances, such as phosgene, which can be used immediately before an attack. The chief sternutatory compound, diphenylchlorarsine, although not volatile, could also be used in this way, for, being a solid and in a very finely pulverised state, its presence on the ground was not a distinct danger, and it invited chemical decomposition.
Penetrants.--The Germans introduced an additional tactical group. This comprised pulverised substances able to penetrate the mask on account of their existence as minute particles. The Germans expressed these tactical conceptions by their shell markings. The familiar Green Cross represented the slightly persistent, volatile, lethal compounds, such as phosgene and diphosgene. The German gunner had no need to know the content of his gas shell