400 REPOKTS ON THE STATE OF SCIENCE. — 1919. 



were made to modify the respirators, and within a few weeks the fighting troops 

 had been re-equipped with the new pattern. Less than three months after the 

 change had been recommended three attacl^s were made by the Germans which 

 would certainly have had very serious consequences if our troops had not been 

 in possession of the improved respirator, as the older pattern would not have 

 withstood the concentration of gas employed. 



This was only one of many changes that were made in the respirator to meet 

 new developments, with the result that our troops always found themselves fully 

 protected, and the confidence they placed in the respirator became an important 

 factor in the success of our gas defence. 



Development of the Respirator. 



The respirator sent to France a few days after the first gas attack consisted 

 of a pad of cotton wool which was to be dipped in a solution of sodium 

 thiosulphate and sodium carbonate and held over the mouth. This was super- 

 seded in May 1915 by the ' black veil ' respirator composed of a pad of cotton 

 waste impregiiated with the same solution, with the addition of glycerine, and 

 enclosed in black veiling by which it could be tied over the mouth. By this 

 means protection against a low concentration of chlorine was obtained for a short 

 time, provided that the pad was carefully adjusted. 



By the end of May the manufacture of the ' Hypo Helmet ' was begun. 

 This consisted of a flannel bag impregnated with a solution of sodium thio- 

 sulphate, sodium carbonate and glycerine, and provided with a small celluloid 

 window. The bag was worn over the head and tucked in under the collar so 

 that the inspired air was freed from chlorine by passing through the fabric. The 

 protection, however, was limited to chlorine and strongly acid gases, and the 

 ' P Helmet ' was adopted for use in July 1915, and issued to the troops in August, 

 in view of the possible employment of phosgene and hydrocyanic acid by the 

 enemy. It was a bag similar to the ' HyiX) Hehnet,' made of fiamielette 

 impregnated with a solution of sodium phenate, sodium hydroxide and glycerine. 

 In order to prevent the carbonation of the alkali by the passage of expired air 

 through the fabric, the helmet was provided with a mouthpiece and rubber outlet 

 valve through which air was exhaled, and it was consequently kno^^-n sometimes 

 as the 'Tube Helmet.' Phosgene was first employed by the enemy in the cloud 

 attack on December 19, 1915, foui- months after the new helmet had been issued. 



Early in 1916 it was thought necessary to increase the protection against 

 phosgene in case clouds of higher concentration should be used, and the ' P.H. 

 Helmet ' was issued in February 1916, in which hexamethylene tetramine 

 (hexamine) was added to the phenate solution. Hexamine reacts rapidly with 

 phosgene, and the new helmet gave a greatly improved protection against this gas. 



However, by this time the possibility of the employment of a wide range 

 of chemical substances in gas warfare had been foreseen, and it w"as recognised 

 that a more general type of protection was needed than that which could be 

 obtained by means of a helmet impregnated with various solutions. The limita- 

 tion of the helmet was seen in its failure to keep out lachrjnnatory gases such as 

 xylyl bromide, in consequence of which the ' P.H.G. Helmet' was introduced 

 shortly after the ' P.H. Helmet,' containing rubber sponge goggles to be -vvom 

 over the eyes to protect them against any traces of lachrymator that might 

 penetrate the helmet. 



A large box respirator, giving a high degree of protection against all gases 

 likely to be employed, had already been devised for the use of the Special 

 Brigade, who always ran the risk of being exposed to high concentrations of gas 

 when they were carrying out operations. This had to be reduced in size to make 

 it suitable for g'eneral issue to the troops, and a satisfactory design was obtained 

 in June, and issued to the troops in August. 1916. The respirator consisted 

 originally of a metal container filled with layers of animal charcoal and of the soda- 

 lime permanganate granules devised by Major Bertram Lambert at Oxford in 

 June 1915, as an absorbent for cblorine, phosgene, hydrocyanic or other acids, 

 and arsine. The container is carried in a haversack on the chest, and is con- 

 nected by a corrugated rubber tube to a mouth-piece attached to a mask made 

 of material impervious to gas and fitted with glass eyepieces. The mask is 



