﻿Molecular Theory of Solution. 899 



energy, he Failed to explain why the solutions of many other 

 substances, which increase the surface tension of water, 

 decrease with increasing surface tension of their solutions. 

 AVhen all the factors are considered, as above, it is found 

 that the solubilities of substances generally, whether solid, 

 liquid, or gaseous, can be accounted for, and that when 

 substances are arranged in the order of their solubilities they 

 are in the order of every other property of solutions. It was 

 pointed out that exceptions may be expected when the 

 distances of the electric charges of the particles may be 

 influenced by the configurations of the unlike particle*, so 

 that the adhesive forces may differ from those calculated 

 from the respective cohesions according to formula (iii). 

 In this May, however, the theory gives a picture of the 

 processes of solution and crystallization, and indicates for 

 the first time the cause of the widely differing solubilities 

 and solvent powers of different substances. 



On the assumption of molecular fields of force, it may 

 be easy to understand why such properties of solutions 

 as solubility, degree of hydration, heat of solution, molecular 

 volume and compressibility, should follow the order of their 

 surface tensions. But, at first sight, it may be surprising 

 that the same 1 should be true of the depression of the 

 freezing-point, elevation of the boiling-point, vapour pressure, 

 and electrical conductivity, with the suggestion that, were 

 sufficient determinations available, osmotic pressure wouid be 

 included. The inference can hardly be avoided that these 

 properties, also, are influenced by the molecular fields. As 

 with solubilities, Traube attempted, unsuccessfully, to account 

 for the coincidence by considering only the adhesion of solute 

 and solvent. That these properties are affected by the mole- 

 cular attractions is, however, a direct result of the present 

 theory. 



A solution may be considered as a liquid in which a number 

 of its ultimate particles have been replaced by others 

 having the same average kinetic energy but exerting 

 different fields of force. The concentration of solvent will 

 be less and the internal pressure of the solution will differ 

 from that of the solvent. Kleeman* has shown that the 

 intrinsic pressure of a solution is given by the relation 



x n = x nw 2 + -x nws -\- x ws 2 , 



where Y nw * and F nS 2 are the attractions exerted, respectively, 



across a plane by. the molecules of the kinds w and s on the 



molecules of the same kind in a cylinder of unit cross-section 



• <A Kinetic Theory of Gases and Liquids,' p. 202 (1920). 



