﻿Law of Molecular Attraction. 103 



ntom of chlorine is far greater than any molecular force of 

 attraction, while the attraction between a molecule of hydrogen 

 and a molecule of chlorine is extremely small. Furthermore, 

 it is impossible to discover any additive law resolved to atomic 

 attractions, to represent the attraction between two molecules. 

 It is necessary to assume that the atomic attractions neutralize 

 one another, whereas there is every evidence for the suppo- 

 sition that the attraction exerted on an external molecule by 

 two adjacent moleeules is double the attraction between the 

 external molecule and one of the molecules. Kieeman * has 

 sought evidence for the relation between atomic and mole- 

 cular attraction by deducing certain relationships between 

 the physical properties of members of homologous series. 

 But it can be shown that almost every physical property or 

 combination of properties of the members of a homologous 

 series is proportional to some function of the molecular 

 weight. As far as latent heats of vaporization and their 

 relation to molecular attraction are concerned, it will be 

 shown in this paper that it is not necessary to assume that 

 the formula representing the law of molecular attraction 

 includes a temperature function. 



Let us suppose for the present that the force of attraction 

 between two like molecules depends only upon their distance 

 of separation. We may represent it by 



K 2 



S"' 

 where K is a constant dependent only on the nature of the 

 molecules, S is their distance of separation, and n is a small 

 number to be determined. Consider a finite mass of a normal 

 unassociated liquid, with the molecules evenly distributed in 

 space. The attraction between any pair of molecules is 



K 2 . K 2 



m qw anc ^ between a second pair of molecules /pi g , sav. 



Suppose now that the liquid expands isothermally until the 

 distance betweeti two adjacent molecules is S : . It is obvious 

 that if the geometrical form of the mass of liquid remain the 

 same, the terms G l} 2 , . . . &c. are constants. 



The total work done by the separation of all the pairs of 

 molecules is 



K 2 P s «dS K 2 pdS K^C 



jr'Js s* crOs s n cr l js 

 c »-ij a s^i^)-^ 



* Phil. Mag. xx, p. 9a5(1910> 



-»S' ,/a 



8" 



say. 



