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 so long as he could identify the cross. Yellow Cross, representing mustard gas, was the most highly persistent type. It is interesting to speculate whether a new persistent compound, whose military value was due to some other property than the blistering, would have been grouped under Yellow Cross. Logically, this should have been done. Blue Cross covered the arsenic group of compounds, which were non-persistent and were expected to penetrate the mask. So strong was this tactical conception that the Allies were on the verge of adopting a uniform shell marking based on this principle throughout their armies.

Special Gas Weapons and Appliances.—It is a popular misconception that gas was only discharged from cylinders in huge clouds, or used as artillery shell. A number of special weapons developed, which were particularly adapted for gas. Thus, the Livens projector, which was a great Allied advance, produced a gas cloud a long distance from the point of discharge, while the Stokes and other short range guns were used for rapid fire of large numbers of gas shell.

The primary conceptions with regard to protection have been brought home to so many, through the fact that the mask was a part of the equipment of every soldier, that we need not dwell on them here. It is not generally realised, however, that every modification introduced by either side was a vital and direct counter to some enemy move planned to render the protection of the opponent ineffective.

Gas Shell.—A word is necessary to define the use of gas shell. The point which must be realised is that gas, and in particular gas shell, fulfilled a special purpose in warfare, from which it was much more suitable than explosives. The use for neutralising batteries, cross roads, and rendering whole areas uninhabitable, is developed fully in our reference to the great German attacks in 1918.

With this brief sketch to clear the ground, we can embark more freely upon the account of chemical warfare which follows. CHAPTER II

THE GERMAN SURPRISE

Ypres, April, 1915, to the Somme, August, 1916.

The First Cloud Gas Attack.—The critical factor of surprise in war was never nearer decisive success than on April 22nd, 1915. Of this, the occasion of the first German gas attack at Ypres, Field-Marshal Sir J. D. P. French Stated:

"Following a heavy bombardment, the enemy attacked the French Division at about 5 p.m., using asphyxiating gases for the first time. Aircraft reported that at about 5 p.m. thick yellow smoke had been seen issuing from the German trenches between Langemarck and Bixschoote. What follows almost defies description. The effect of these poisonous gases was so virulent as to render the whole of the line held by the French Division mentioned above practically incapable of any action at all. It was at first impossible for any one to realise what had actually happened. The smoke and fumes hid everything from sight, and hundreds of men were thrown into a comatose or dying condition, and within an hour the whole position had to be abandoned, together with about fifty guns. I wish particularly to repudiate any idea of attaching the least blame to the French Division for this unfortunate incident."

The Element of Surprise.—The enemy just missed colossal success rendered possible by the use of an entirely new war method; one contrary to engagements entered into by them at the Hague Convention.

There were elements in this first gas attack which were absent even from the situation created by our first use of tanks. Unfamiliarity amongst the troops, or the staff, for that matter, created an atmosphere of unparalleled confusion. Men attempted to protect themselves by burying their mouths and nostrils in the loose earth. Those chemists, on the spot, not immediately struck down, made frantic efforts to bring up supplies of any suitable and available chemical or material which might assist resistance and movement in the affected zone. Paying every homage to the heroic sacrifices and brave actions which characterised the Allied resistance, we cannot ignore the fact that morale must have been very severely shaken locally, and that a general disquiet and uneasiness must have permeated the whole front until measures were known to be effectively in progress, not only for protection, but for retaliation. The enemy had but to exploit the attack fully to break through to the channel ports, but failed to do so. The master mind behind this new and deadly attack was not, let us remember, that of a soldier. It was very strongly rumoured that this monstrous conception and its execution were due to one or, at the most, two renowned German Professors. The first hammer blow in the enemy chemical campaign was a two-party conspiracy, led by world-famous scientists and the powerful I.G. with the German army unconvinced but expectant, little more than a willing dupe.

Lord Kitchener's Protest.—In his spirited protest in the House of Lords, Lord Kitchener stated: "The