39 
1917-18.] Thermodynamics of Adsorption. 
2. Expressions are developed for three isothermal heats of adsorption 
of a gas and for the heat of immersion of a powder in a liquid. 
3. The effect of the variation of the surface of an adsorbent when 
adsorbing is examined, and it is shown from Ti toff’s observations (assum- 
ing, of course, the adsorption to be reversible) that the divergence between 
calculated and observed values of the heat of adsorption can be explained 
on the assumption of a change of surface area. The fractional change of 
surface per c.cin. adsorbed can be calculated, and also the surface energy 
per grm. adsorbent in vacuo. 
The author wishes to express his thanks to Professor James Walker, 
F.R.S., for his kindness in reading and helping him in the presentation of 
this paper. 
(Issued separately February 28 , 1918 .) 
