﻿Law of Molecular Attraction. 113 



of the molecules in the true law of attraction must not be less 

 than 5 about. 



Since the function F(T, V,— V) must become equal to zero 

 at the critical temperature, it must follow that the value of 

 C in the equation 



-4-T 



k) 



V,-r- V v 3 



must increase with rise of temperature. Now the equations 

 obtained by putting n in the law of attraction equal to 5 

 and 6 give values of C which decrease as temperature 

 increases; and when 7i = 7, remains constant with rise of 

 temperature, and for all values of n greater than 7, C increases 

 with rise of temperature. It would seem therefore probable 

 that the true value of n is greater than 7. The value of C 

 in the above equation may, however, at first decrease at low 

 temperatures and increase at higher temperatures. Un- 

 fortunately, there is not sufficient experimental evidence to 

 test this point. 



Summarising, it may be concluded that : — 



(1) So far as latent heat considerations are concerned, it 

 is not necessary to assume that the law of attraction includes 

 a temperature function ; but it is impossible to determine 

 completely the law of attraction from considerations of 

 energy changes accompanying the change of volume of a 

 liquid or gas. 



(2) When a liquid or gas undergoes isothermal expansion, 

 some intramolecular energy is liberated. This is entirely 

 apart from energy changes due to molecular attraction. 



(3) Assuming that the law of attraction can be represented 



by a— t where K 2 is constant for a given pair of molecules 



and S is the distance between them, the value of n cannot be 

 less than 5, and is probably greater than 7. 



It is hoped in a subsequent paper to discuss the problem 

 in its relation to other physical properties of liquids. 



The Chemical Department, 

 The University, Manchester. 

 Auffust 1911. 



Phil. Mag. S. 6. Vol. 23. No. 1.33. Jan. 1912. 



