'2l6 



NATURE 



[Mi\Y i6, 1918 



tferrhdns use a 40° angle of safety ; that means that 

 On a given straight portion of the' front the wind direc- 

 tion must lie between the two directions which make 

 :angles of 40° with the neighbouring sections of the 

 front. The most suitable type of country is where 

 the ground slopes gently away from where the gas is 

 being discharged. If the country is flat like that about 

 Ypres, and the wind direction is right, there is little 

 difficulty about making an attack. German gas 

 attacks are made by two regiments of pioneers, with 

 highly technical officers, including engineers, meteoro- 

 logists, and chemists. The first attack was made with 

 chlorine. If a gas attack is to be made with gas- 

 clouds, the number of gases available is limited. The 

 gas must be easily compressible, easily made in large 

 quantities, and should be considerably heavier than 

 'air. If to this is added the necessity of its being very 

 toxic and of low chemical reactivity, the choice is prac- 

 tically reduced to two gases : chlorine and phosgene. 

 "Pure chlorine did not satisfy quite all the requirements, 

 as it is very Active chemically and therefore easily 

 absorbed. 



The first protection was primitive. It consisted 

 largely of respirators made by women in England in 

 response to an appeal by Lord Kitchener. Then came 

 the helmet made of a flannel bag soaked in thiosulphate 

 and carbonate, with a mica window in it. A modified 

 form of this device with different chemicals is still 

 used in the British Army as a reserve protection. The 

 outcome of attempts to counteract the effects of phos- 

 gene was a helmet saturated with sodium phenate. 

 The concentration of gases when used in a cloud is 

 small, and i to 1000 by volume is relatively very 

 strong. The helmet easily gave protection against 

 phosgene at a normal concentration of i part in 10,000. 



The element of surprise came in an attack by night. 

 The meteorological conditions are much better at night 

 than during the day. The best two hours out of the 

 twenty-four, when steady and downward currents 

 exist, are the hour between sunset and dark and the 

 hour between dawn and sunrise. Gas attacks have 

 therefore been frequently made just in the gloaming 

 or early morning, between lights. This took away one 

 of the easy methods of spotting gas, that of seeing it, 

 and we had to depend upon the hissing noises made 

 by the escaping gas, and upon the sense of smell. 



Another element of surprise was the sending out of 

 more than one cloud in an attack. After the first 

 cloud the men would think it was all over, but ten 

 minutes or half an hour later there would come another 

 cloud on exactly the same front. Efforts were also 

 made to effect surprise by silencing the gas. But 

 silencers reduced the rate of escape so greatly that the 

 loss of efficiency from low concentration more than 

 made up for the gain in suddenness. Another method 

 was to mix the gas up with smoke, or to alternate 

 gas and smoke, so that it would be difficult to tell 

 where the gas began and the smoke ended. 



There was a long search for materials that would 

 absorb phosgene. The substance now used very 

 extensively is hexamethylenetetramine (urotropine), 

 .(CH2)6.N4, which reacts very rapidly with phosgene. 

 Used in conjunction with sodium phenate, it will pro- 

 tect against phosgene at a concentration of i : 1000 

 for a considerable period. An excess of sodium 

 hydroxide is used with the sodium phenate, and a 

 valve is provided in the helmet for the escape of 

 exhaled air. 



A high concentration for a gas-cloud is i part in 

 '1000, whereas concentrations of 2 or 3 per cent, can 

 be met by respirators depending on cherhical reactivity. 

 One such respirator is a box of chemicals connected 

 by a flexible tube with a face-piece fitting around, the 

 contours of the face, and provided with a mouthpiece 

 and a noseplece. As regards the chemicals used there is 

 NO. 2533, VOL. lOl] 



no secret, for the Germans have many of the sam6 

 things. Active absorbent charcoal is one of the main 

 reliances, and is a suggestion that we - owe to 

 the Russians. Wood charcoal was used in one of 

 their devices and was effective, but most of the Rus- 

 sian soldiers had no protection at all. We wanted to 

 protect against chlorine, acids and acid-forming gas^s, 

 phosgene, etc., and at one time were fearful of meet- 

 ing large quantities of hydrocyanic (prussic) acid 

 (HCN). The three things that then seemed most im- 

 portant were: — (i) Chlorine and phosgene; (2) prussic 

 acid; (3) lachrymators. Charcoal and alkaline per- 

 manganate will protect against nearly everything used, 

 even up to concentrations of 10 per cent, for short 

 periods. 



As regards the future of the gas-cloud, it may be 

 looked upon as almost finished. The case is different 

 with gas shells. The gas shells are the most impor- 

 tant of all methods of using gas on the Western 

 front, and are still in course of development. The 

 enemy started using them soon after the first cloud 

 attack. He began with the celebrated "tear" shells. 

 The original tear shells contained almost pure xylyl 

 bromide or benzyl bromide, made by brominating the 

 higher fractions of coal-tar distillates. The German 

 did his bromination rather badly. It should be done 

 carefully or much dibromide is produced, which is solid 

 and inactive. Some of the shells contained as much 

 as 20 per cent, dibromide, enough to make the liquid 

 pasty and inactive. 



When the Germans started using highly poisonous 

 shells, the substance used was trichloromethyl-chloro- 

 formate, but not in great strength. 



The use of gas out of a projectile has a number of 

 advantages over its use in a gas-cloud. First, it is 

 not so dependent on the wind. Secondly, the gunners i. 

 have their ordinary job of shelling, and there is no w 

 such elaborate and unwelcome organisation to put into * 

 the front trenches as is necessary for the cloud. Thirdly, 

 the targets are picked with all the accuracy of artillery 

 fire. Fourthly, the gas shells succeed with targets that 

 are not accessible to high explosives or to gas-clouds. 



Among the effective materials used by the Germans 

 for gas shells were mono- and tri-chloromethyl-chloro- 

 formate. Prussic acid never appeared ; the Germans 

 rate it lower than phosgene in toxicity, and reports 

 concerning it were obviously meant merely to produce 

 fear and distract the provisions for protection. 



During the last months of 1917 the actual materials 

 and the tactics used by the Germans have undergone a 

 complete change. 



One substance used for the method of simultane- 

 ously harassing and seriously injuring was dichloro- 

 diethylsulphide (mustard gas). It has a distinctive 

 smell, rather like garlic than mustard. 



Up to the present time there has been no material 

 brought out on either side that can be depended on to 

 go through the other fellow's respirator. The casual- 

 ties are due to surprise or to lack of training in the 

 use of masks. The mask must be put on and adjusted 

 within six seconds, which requires a considerable 

 amount of preliminary training, if it is to be done 

 under field conditions. 



Among other surprises on the part of the Germans 

 were phenylcarbylamine chloride, a lachrymator, and 

 diphenylchloroarsine, or "sneezing gas." The latter 

 is mixed in with high-explosive shells, or with other 

 gas shells, or with shrapnel. 



As regards the future of gas shells, it should be 

 emphasised that the " gas shell " is not necessarily a 

 gas shell at all, but a liquid or solid shell, and it 

 opens up the whole sphere of organic chemistry to be 

 drawn upon for materials. The material placed inside 

 "the shell is transformed Into vapour or fine droplets .by the 

 explosion, and a proper adjustrpent between the bursting 



