[ 266 ] 
XXV. The Solubility and Diffusion in Solution of Dissociated 
Gases. By O. W. Ricuarpson, M.A., 6.Se., Clerk 
Maxwell Student and Fellow of Trinity College, Cambridge”. 
HE solubility of gases which act chemically on the solvent, 
or which dissociate in solution, is treated in Van t’ Hoff’s 
Lectures on Theoretical Chemistry, pt. ii. p. 28 et seg.\ It 
is there pointed out, on theoretical grounds, that gases which 
dissolve without chemical action, or which associate with the 
solvent in such a way that each aggregate contains only one 
molecule of the dissolved gas, obey Henry’s Law of pro- 
portionality between the pressure and the mass of gas 
dissolved. As all gases which have been examined appear 
to obey Henry’s Law, with the exception of ammonia, 
sulphur dioxide, and hydrochloric acid in water, this subject 
has not hitherto attracted much attention. Phenomena of 
this kind appear, however, to characterize the absorption of 
hydrogen by palladium and platinum, and, probably, of other 
gases by other metals (for instance, carbon monoxide by 
iron). The recent experiments of Winkelmann on the 
variation of the rate of diffusion of hydrogen through hot 
palladium} and platinuin {, with the driving pressure, led 
him to the conclusion that the hydrogen was partly dissociated 
into atoms, and that only the atoms were capable of passing 
through the hot metal. A series of experiments on the rate 
of diffusion of hydrogen through platinum at different 
pressures and temperatures has just been carried out by. the 
author in conjunction with Messrs J. Nicol and T. Parnell, 
and will shortly be published. This investigation, so far as 
the pressure relations are concerned, has yielded results 
similar to those of Winkelmann, and most of the phenomena 
appear to be capable of explanation on the view that the 
hydrogen dissolves in the platinum and then dissociates 
(partially, at any rate) into atoms. It was in seeking an 
explanation of these results that the author was led to 
examine into the theory of the solubility of a dissociating 
gas and to the results which are given in the present 
communication. 
§ 1. Solubility Relations. 
We shall confine our attention to the case of a gas in 
which each molecule dissociates into » similar molecules. 
The same methods could, of course, be applied to a more 
complicated case if it should occur. The reaction which we 
are considering is symbolized by a chemical equation of the 
* Communicated by the Author. 
+ Drude’s Annalen, vol. vi. p. 104. { bid. vol. viii. p. 388. 
