VII. ON SOLUBILITY. 845 
From a study of the distribution of iodine between pairs of non-mis- 
cible organic solvents, Landaw**° concluded that when the solute exists 
1910 in the same state in both solvents, then the distribution ratio is 
* a constant, but, if in one of them the state of aggregation of the 
iodine is different from its state of aggregation in the other, then the 
ratio is dependent upon the concentration of the solute. 
Herz and Kurzer**® studied the more complex case of the distri- 
bution ratio of various solutes as between two liquids of which one was a 
mixture of two solvents. In general the mixture was found to behave 
as a homogeneous liquid when allowance was made for association or 
dissociation of solute in the solvents. 
1911 Sidgwick 400 and others found that the distribution of aniline 
* hydrochloride between aniline and water varies very considerably 
with change of concentration. The distribution ratio of ammonia be- 
tween water and chloroform was found by Bell and Field *°* to be much 
lower in concentrated than in dilute solutions and the ratio to be 
changed but slightly by the addition of ammonium chloride. Kolos- 
sovsky,*?* on the other hand, found the distribution ratio of acetic acid 
between water and ethylic ether to be generally lowered by the addition 
of salts. 
VII.—Theoretical Considerations. 
In Part I. of this Report* reference was made to the view expressed 
by Arctowski, that when one substance dissolves in another it does so by 
virtue of its property of forming molecular compounds with the solvent. 
1896 In a subsequent communication this author '* urged the desira- 
* bility of studying the simplest cases of dissolution, namely, that 
of a solid substance dissolving in a gas, as the best means of obtaining 
knowledge respecting the laws of solubility. From this point of view he 
contributed results of measurements of the velocity of sublimation of the 
three mercuric halogen salts, and expressed the opinion that such 
measurements, being measures of the vapour tension of the solid 
substances, may be regarded as indicative of their solubility in the gas. 
Speyers ™ published a discussion of the nature of liquids in which 
he approved the practice of viewing a liquid as a condensed gas, at the 
same time recognising that besides being compressed into smaller com- 
pass it carries gaseous activity—pressure—with it into the liquid con- 
dition. He looked upon a dissolved substance as being brought into 
the same condition as the liquid, and capable also of exerting a pres- 
sure. 
An investigation of the distribution of iodine and bromine between 
water and certain organic solvents led Jakowkin * to recognise a change 
in the distribution coefficient with increased concentration, and this he 
attributed to the existence in the organic solvent of associated molecules. 
The non-obedience of Henry’s law of solutions of carbon-dioxide was 
also attributed to the existence of duplex molecules of solute when jn the 
gaseous state, and only simplex molecules when in solution, 
* Vide Part I, R. 209. 
