236 



Journal of the Asiatic Society of Bengal. [May, 1907. 



General character of the 'phenomena of ahsorjption. 



We may consider the absorption of vapours by solid or amor- 

 phous substances to be due to one of three causes : 



(a) Chemical action. 



(6) Surface condensation or capillary action. 



(g) Solution. 



■ 



Cases involving chemical action hai^dly come within the 

 sphere of the discussion, unless, as possibly may be the case, the 

 absorption of water by soils is in any degi^ee due to the presence 

 of hydrates of such substances as alumina. The influence of 

 chemical affinity would in any case be very slight. 



As to whether the absorption of water by cotton^ etc., or of 

 gases by other amorphous substances, such as charcoal, is due to 

 solution or to surface condensation, has been the subject of a discus- 

 sion between Professor Trouton, of University College, London, 

 and myself. I am in favour of attributing it to solution, and for 

 the following reasons. We are concerned with systems which 

 consist of a gas or vapour and an amorphous substance, which as 

 we have seen is physically a liquid, though it possesses rigidity, 

 and is therefore capable of forming solutions, as are ordinary 

 liquids. It is true that crystalline solids are capable of forming 

 homogeneous mixtures, which Van t'HofB has termed 'solid solu- 

 tions ' ; but the constituents of such solutions nmst necessarily be 

 igomorphous, and hence the possibility of forming them is limited. 

 The fact that amorphous substances, such as gut, undergo a change 

 of form and volume when they absorb water, is distinctly in 

 favour of the solution theory. 



For my first investigation on the nature of absorption I select- 

 ed tbe simple case of carbon dioxide and charcoal, and as no very 



Pin 

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79 



Fig. 1. — Absorption of carbon dioxide by charcoal. 



