METHODS OF GAS WARFARE 67 



The protection that had been devised against phosgene 

 proved effective at the time, but provision was made to 

 meet increased concentration of phosgene. We never had 

 any actual evidence during the attack that phosgene was 

 being used, as no samples were actually taken from the 

 cloud, but cylinders of phosgene were captured later. 

 Glass vacuum tubes, about 10 by 30 cm., with a tip that 

 could be broken off and then closed by a phasticine-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 ab- 

 sorb 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) (CH 2 ) 6 N 4 , which 

 reacts very rapidly with phosgene. Used in conjunction 

 with sodium phenate, it will protect against phosgene at 

 a concentration of i : 1000 for a considerable period. An 

 excess of sodium hydroxide is used with the sodium phe- 

 nate, 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 addition 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 fulfill two requirements which are quite opposed 



