atjld: methods of gas warfare 51 



cine-lined glass cap, were distributed, but the only one that 

 came back was an unopened tube found in a hedge, and marked 

 by the finder "Dangerous; may contain cholera germs." In 

 a gas attack everybody keeps quiet or else has a job on hand, 

 and conditions are not conducive to the taking of gas samples. 

 The original types of vacuum tube were smaller than those now 

 used. 



There was a long search for materials that would absorb 

 phosgene, as there are few substances that react readily with it. 

 The successful suggestion came from Russia. The substance 

 now used very extensively by all is hexamethylenetetramine 

 (urotropine) (CH2)8N4, which reacts very rapidly with phosgene. 

 Used in conjunction with sodium phenale, it will protect against 

 phosgene at a concentration of 1 : 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. The valve was originally devised so that the hydroxide 

 would not be too rapidly carbonated, but it was found in addi- 

 tion that there is a great difference in ease of breathing and 

 comfort if a valve is placed in the mask. The helmet is put 

 on over the head, grasped with left hand around the neck and 

 tucked into the jacket. This form is still used in reserve. 



By this time gas shells were beginning to be used in large 

 numbers, and it became evident that protection by a fabric 

 could not be depended on with certainty. The box type of 

 respirator was the next development. Respirators have to ful- 

 fill two requirements which are quite opposed to one another. 

 In the first place they should be sufficiently large and elaborate 

 to give full protection against any concentration of any gas, 

 whereas military exigency requires that they be light and com- 

 fortable. It is necessary 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 really very 

 low. As has been said, a high concentration for a gas cloud is 



