1916-17.] The Adsorption of Sulphur Dioxide by Charcoal. 171 
of the adsorbent. The Pouillet effect,* which is simply the heat given out 
on adsorption of a liquid by a powder, has been attributed to the com- 
pression of the “ films ” of liquid in contact with the powder. But in view 
of recent work on compression, the heat effect appears too large to be 
attributable solely to this cause. Thus the greatest loss of energy in com- 
pressing ether was found by Bridgman f to be 14 per cent, of the heat of 
condensation ; and moreover, after a certain compression the total heat effect 
diminished. In the adsorption studied above (cf. also Titoff and Chappuis) 
the initial heat effect exceeds by more than 80 per cent, the heat of con- 
densation, and only after a great amount is adsorbed does it fall much 
below an excess of 40 per cent. It seems, therefore, unlikely that it is only 
the adsorbate which loses a considerable amount of energy on adsorption, 
and it looks very probable that initially at any rate the adsorbent loses 
energy on what may be not contraction but expansion of surface in 
embracing the adsorbed particles. J 
* See Williams, Trans. Far. Soc., x, p. 167 (1914). 
f Proc. Amer. Acad., xlix, 1 (1913). 
I Gf. Donnan’s negative surface tension of colloids. 
