﻿T he Law of Molecular Attraction. 101 



against the arc, tlie only result observed being a weakening 

 of: the oxide spectrum. The experiments described above 

 are of a preliminary nature, and it is hoped to continue the 

 work. 



I wish to express my indebtedness to Mr. Morris-Airey 

 for suggesting the experiments and for his valuable advice. 



Physical Department, Armstrong- College, 

 Newcastle-upon-Tyne. 



VIII. The Law of Molecular Attraction. 

 By D. Tyrer, M.Sc* 



THE nature of molecular attraction is a problem which 

 has at various times attracted a considerable amount 

 of attention. The question is involved in the study of energy 

 changes connected with surface tension and isothermal volume 

 changes. Knowing the law of molecular attraction, it is 

 easily possible to deduce a formula to represent the relation 

 between the potential energy of a liquid and its density, as 

 for example the relation between latent heat of vaporization 

 of a liquid and its density. Assuming that the attraction 

 between two molecules varies inversely as the square of the 

 distance between them, an equation involving the latent heat 

 was deduced by J. E. Mills f which holds remarkably well. 

 This equation may be written 



■L-E 



i* -IV 



where L is the latent heat of vaporization, E is the external 

 work done during vaporization, D L and D v are the densities 

 of liquid and saturated vapour respectively, and //, is a 

 constant dependent only on the nature of the liquid. Because 

 this relation fits the facts it was thought bv Mills that the 

 assumed law of attraction was the true one ; but this by 

 no means follows J. 



Kleeman § has deduced the following formula for the law 



of molecular attraction: 



Hil)^ 



where z is the distance of separation of the molecules, X\/n 



* Communicated by the Author. 



t Journ. of Phys. Chem. vi. p. 209 : viii. pp. 385, 593; ix. p. 402 

 xi. pp. 594, 132. 



X ride Kleeman, Phil. Masr. Jan. 191 I, p. 83. 

 § Phil. Mag. xix. pp. 78:5 809 (1910). 



