178 Professor Sir James Deivar [Jan. 20, 



de Saussure. Subsequently Graham and Stenhouse added valuable 

 contributions to the inquuy. The thermal evolutions of some 

 gaseous absorptions in charcoal were determined by Faure and 

 Silbermann ; and later, Hunter showed the advantage of using cocoa- 

 nut charcoal, and made a long series of investigations on the absorp- 

 tion of organic vapours and gases by this variety of charcoal. 



In de Saussure's experiment a piece of red-hot charcoal was 

 plunged under mercury, and introduced into the gas to be absorbed 

 after it was cool, without allowing it to come in contact with air. He 

 made use of box-wood charcoal, about which he remarks that it 

 absorbed so little mercury during the cooling that it would readily 

 swim on water. His experiments were conducted at ordinary tem- 

 perature and pressure, and gave the results in the annexed table, the 

 unit volume being that of the absorbing charcoal. For comparison, 

 similar experiments made by Hunter with cocoa-nut charcoal are 

 given. 



Boxwood Cocoa-nut 



(Saussure) (Hunter) 



Ammonia 90 172 



Hydrochloric acid 85 — 



Sulphurous acid 65 — 



Sulphuretted hydrogen .... 55 — 



Nitrous oxide 40 86 



Carbonic acid 35 68 



Olefiant gas 35 75 



Carbonic oxide 9*42 21 



Oxygen 9-25 18 



Nitrogen 7-5 15 



Hydrogen 1 • 75 4 



He found that even if the charcoal were moistened with water, it 

 was still capable of absorbing one-third to one-half the amount of gas 

 absorbed when quite dry. 



During these experiments he called attention to the evolution of 

 heat during absorption, and remarked that it appeared to increase with 

 the absorbability of the gas. 



In further experiments he considered the effect of pressure on the 

 amount of absorption, and found that absorption by volume is far 

 greater in a rare than in a dense atmosphere, but that if reckoned by 

 weight it is more considerable in the latter than in the former state.* 



He continued similar experiments with meerschaum, asbestos, and 

 other substances, and also examined the effect of mixed gases. 



Hunter examined the absorption of vapours by cocoa-nut charcoal 

 at or above their boiling points with interesting and suggestive results 



* Saussure's results for carbonic acid may be represented by the formulae — 



. = i5-3 + ^-^i:Z 



V 

 v = 19-1 + -53 i>; 



where v is the volume absorbed, measured as above, and p is the pressure in 

 inches of mercury. 



