68 CONTEMPORARY SCIENCE 



to one another. In the first place they should be suffi- 

 ciently large and elaborate to give full protection against 

 any concentration of any gas, whereas military exigency 

 requires that they be light and comfortable. It is neces- 

 sary to strike a balance between these two. Upon a 

 proper balance depends the usefulness of the respirator. 

 Oxygen apparatus will not do on account of its weight 

 and its limited life. Two hours' life is excessive for that 

 type. The side that can first force the other to use oxygen 

 respirators for protection has probably won the war. 



The concentrations of gas usually met with are realty 

 very low. . As has been said, a high concentration for a 

 gas cloud is I part in 1,000, whereas concentrations of 

 two or three per cent, can be met by respirators depend- 

 ing on chemical reactivity. One such respirator is a box 

 of chemicals connected by a flexible tube with a face- 

 piece fitting around the contours cf the face, and provided 

 with a mouthpiece and nosepiece. 



As regards the chemicals used there is no secret, for 

 the Germans have many of the same things. Active ab- 

 sorbent charcoal is one of the main reliances, and is an- 

 other suggestion that we owe to the Russians. Wood 

 charcoal was used in. one of their devices and was effec- 

 tive, but most of the Russian soldiers had no protection 

 at all. 



We wanted to protect against chlorine, acids and acid- 

 forming gases, phosgene, etc., and at one time were fear- 

 ful of meeting large quantities of hydrocyanic (prussic) 

 acid (HCN). At one period every prisoner taken talked 

 about the use of prussic acid, saying that the Kaiser had 

 decided to end the war and had given permission to use 

 prussic acid. Protection was evidently needed against it. 

 The three things that then seemed most important were: 

 (i) chlorine and phosgene; (2) prussic acid; (3) lachry- 

 mators. Charcoal and alkaline permanganate will protect 

 against nearly everything used, even up to concentrations 

 of ten per cent, for short periods. 



