158 THE NEW WORLD OF SCIENCE 



from lampblack, powdered coal and other suitable materials 

 (Carbonite). 



Soda Lime. Charcoal alone is not a satisfactory all-round 

 absorbent because it has too little capacity for certain highly 

 volatile acid gases, such as phosgene and hydrocyanic acid and 

 also because an oxidizing agent is the best means of handling 

 certain gases. It has, therefore, been found that the use of an 

 alkaline oxidizing agent in combination with the charcoal is 

 advisable. The material actually used was a soda lime con- 

 taining sodium permanganate. The ratios used were 60 per 

 cent. 6-14 mesh cocoanut shell charcoal and 40 per cent. 8-14 

 mesh soda lime permanganate granules. The last mixture sug- 

 gested, which would have had a distinctly greater all round 

 efficiency, was composed of 75 per cent, specially impregnated 

 cocoanut charcoal and 25 per cent, soda lime containing no per- 

 manganate. 



Due to the inherent nature of soda lime, it was a very difficult 

 and complicated problem to determine the best balance of the 

 requirements. The activity is not of vital importance except 

 in the case of phosgene. Capacity is of the greatest importance 

 since the soda lime is relied upon to hold in chemical combina- 

 tion a very large amount of toxic gas. The question of 

 chemical stability and mechanical strength demanded much 

 serious thought before they were satisfactorily secured. 



A typical formula for gas mask soda lime is : 



Hydrated lime 45 parts 



Cement 14 parts * 



Kieselguhr 6 parts 



Sodium hydroxide , I part 



Water 33 (approx.) 



The lime constitutes over 50 per cent, of the finished dry 

 granule and is responsible in a chemical sense for practically all 

 of the gas absorption. The cement furnishes a degree of hard- 

 ness adequate to withstand service conditions. The loss in 

 porosity due to its use is counterbalanced by the introduction of 



