ON CHEMICAL WARFARE. 395 



Owing to its slight smell it is less easily detected than other gases, and, although 

 it produces no immediate sensations of discomfort, exposure to a very low 

 concentration is sufficient to put a man out of action owing to the effects of the 

 gas on the eyes and the lungs. As the liquid has a low vapour pressure at 

 atmospheric temperature and reafts very slowly with water, it may remain for 

 days on the surface of the soil and continue to produce a dangerous concentration 

 of gas. In addition to its effects on the eyes and lungs, serious blisters are 

 produced either by splaslies of the liquid or contact with any objects con- 

 taminated _ with it. Blue Cross shell contained bottles of diphenylchlorarsine, a 

 solid melting at 46° C, which when finely divided causes sneezing, irritation of 

 the nose and throat, nausea and intense pain. The bottles of this substance were 

 embedded in high explosive, and it was expected that the burst of the shell 

 would scatter the arsenic compound as a fine dust, which would penetrate our 

 respirators and cause such violent sneezing as to make the wearing of the mask 

 impossible. However, the Blue Cross shell failed almost entirely to achieve its 

 object, and in 1918 diphenylcyanoarsine (M.P. 23° C.) was substituted for 

 diphenylchlorarsine without any noticeable changes in the efficiency of the shell. 

 It is probable that favourable results had been obtained with these substances 

 in the laboratory, which could not be reproduced under field conditions. The 

 failure of the Blue Cross shell, many millions of which were fired, is a striking 

 proof of the necessity of having an experimental station at which thorough 

 field^ trials of any new developments can be carried out before these are put into 

 service use. 



Two other substances were used in large quantities by the enemy, phenyl- 

 carbylamine chloride, a strong lachrymator fiB.P. 209° C), first used in 

 September 1917, and dichlorethyl arsine (B.P. 156° C), first used early in 1918, 

 which causes irritation of the nose and throat, headache, and temporary loss of 

 feeling in the extremities. 



Thus by the beginning of 1918 the German.s had a number of different gas 

 shells which could be divided into two main classes from the point of view of 

 their tactical employment : — 



(a) Those containing liquids such as dichlorethyi sulphide which persist for 

 long periods in the soil and can therefore only be used on ground which it is 

 not intended to attack or occupy. 



{b) Those containing relatively volatile liquids such as trichlonnethyl chloro- 

 formate or ethyl dicMorarsine, or solids such as diphenylchlorarsine, which can 

 be used immediately before an attack. 



In his preparation for the offensive of March 1918, the enemy relied to a 

 considerable extent on the use of gas projectiles, which had never been iised before 

 in such large numbers. Eighty per cent, of the ammunition allotted for some 

 purposes contained gas, and it was estimated that several million rounds of gas 

 shell were fired on March 21. From that date until the end of the war a large 

 proportion of gas shell was used by the enemy in all offensive and defensive 

 operations. 



British Use of Gas Projectiles. 



Gas shell and trench mortar bombs containing lachrymators were first used 

 by the British during the battle of the Somme, but it was not until the battle 

 of Arras in April 1917 that our supplies of gas shell were sufficient to make 

 them effective. Large quantities both of lachrymatory and of lethal shell were 

 used for harassing purposes during the night before the attack at Arras, and 

 their success in interfering with artillery fire and in preventing the movement 

 of troops and transport is described in the following extract from a confidential 

 report, dated 11.4.17, from the General Commanding the First German Army, on 

 ' Experiences in the Battle of Arras ' : — 



The enemy made extensive use of gas ammunition against our front 

 positions as well as against batteries. It has not yet been established 

 whether they employed a new gas. Our gas masks afforded complete pro- 

 tection ; however, the fighting resistance of the men suffered considerably from 

 wearing the mask for many hours. Horses were greatly affected by the gas — 



