1919] on Liquid Oxygen in Warfare 605 



These results showed that asbestos and silica dust (kiesel^^'uhr) 

 absorbed the largest amoimts of liquid. Relatively to the liquid 

 oxygen capacity of the same space without absorbent, asbestos held 

 80 per cent, and kieselguhr 70 per cent., while the hguie for the 

 best form of charcoal (dust) was only 53 per cent. Moreover, sihca 

 suffered from the disadvantage of weight : the proportion absorbed on 

 this basis being : — 



Silica ...... Equal weight. 



Asbestos ...... Three times its weight. 



Thus the weights of the same vessel filled respectively with the 

 two substances and saturated with liquid oxygen are, in grams : — 



I I solid I Liquid I ,T0t^-,;^ 



But the really effective basis of com- 

 parison is that of equal weights of liquid ;. 

 in this case the proportions are : — | 



Silica 225 225 t 450 



Asbestos 97 j 290 I 387 



Silica I 290 290 580 



Asbestos I 97 290 387 



so that the charged asbestos has only two-thirds of the weight of 

 kieselguhr carrying the same weight of liquid. 



Such masses, when in a vacuum vessel, retain a constant tempera- 

 ture and rate of ebullition until almost the last trace of liquid has 

 boiled away. This was determined by immersing the gas bulb of a 

 small helium thermometer, carrying a capillary mercury manometer,"' 

 into the centre of a cooled mass of silica contained in a silvered 

 vacuum flask. In contrast to this, a similarly saturated mass of 

 powdered charcoal shows a gradual rise of temperature with a steadily 

 decreasing rate of evaporation. This follows from the exceptional 

 gas absorption of cooled charcoal. The method has been applied to 

 the study of this subject, among others connected with low-tempera- 

 ture radiation. 



For the purpose of either the electrical heating or metallic con- 

 duction methods of evaporation already described, there is no objection 

 to the use of a proper absorbent for the liquid oxygen, since the 

 heating coil or metallic rods are readily embedded therein ; but for 

 the syphon method a modified arrangement is necessary. 



The method adopted was to use a pure lead tube, which is flexible 

 in liquid air or oxygen, weighted at the lowest part to keep it below 

 the surface of the liquid. A double conical spiral of lead tube gave 

 good results when connected to the rigid delivery tube cut-off just 



Proc. Roy. Inst., xx. 583. 



