THE CHEMICAL WARFARE SERVICE 157 



a type which can be relied upon to give protection against prac- 

 tically any toxic gas. The absorbents must be mechanically 

 strong in order to retain their structure and porosity under very 

 rough handling and jolting. They also must not be subject to 

 abrasion, for the fines would plug up the canister or cause 

 serious channeling. The materials used as absorbents must 

 possess a very considerable degree of chemical stability; this 

 stability is composed of many factors, and places a very serious 

 limitation upon the materials which can be satisfactorily used. 

 The result of a very extensive series of investigations, having 

 as their object a low breathing resistance canister, has shown 

 that, in general, the use of large cross-sectional area of rela- 

 tively fine granules gives the best all round results. Then, of 

 course, such questions as ease of manufacture, and cheapness 

 and availability of raw materials must be considered. 



The only single substance which even approximately fulfills 

 all the above requirements is charcoal. From a theoretical 

 study, it has been shown that the essential characteristics of 

 active charcoal are : it must have high and fine-grained porosity ; 

 it must consist of amorphous base carbon ; it must be free of 

 absorbed hydrocarbons. On the basis of these considerations 

 the preparation of active charcoal resolved itself into two steps : 

 the formation of a porous, amorphous base carbon at relatively 

 low temperatures, and the removal of the absorbed hydrocar- 

 bons from the primary carbon and the increase of its porosity. 

 The first step involves the destructive distillation of a material 

 (cocoanut shell was found the most suitable wood) at relatively 

 low temperatures, in thin layers so that the deposition of in- 

 active carbon from the cracking of hydrocarbons, would be 

 avoided. The second step is much more difficult, and was 

 finally accomplished by oxidation with air, steam or carbon 

 dioxide steam, all of which were used in the manufacture of 

 gas mask carbon. 



In addition to the use of cocoanut shell (Dorsite), other 

 sources were developed, such as anthracite coal (Bachite), and 

 a synthetic product made by carbon manufacturing process 



