﻿J 02 Mr. D. Tyrer on the 



is the sum of the square roots of the atomic weights of the 

 atoms of the molecule, x c is the distance between the mole- 

 cules at the critical temperature T c . The function $( — .,w ) 



is unknown, but is constant at corresponding temperatures. 

 This formula makes the law of attraction dependent both on 

 the distance of separation of the molecules and on the 

 temperature. 



Van der Waals in his equation of state 



(p+^VV-&)=RT, 



a 



by introducing the term ~ 2 supposes the attraction of the 



molecules to vary inversely as the fourth power of their 

 distance of separation. But, as is well known, this is in- 

 sufficient, as the term — 2 does not, with liquids, adequately 

 represent the facts. 



Now, as has been already mentioned, it is supposed by 

 Kleeman that the law of attraction varies with the tem- 

 perature. It is, however, very difficult to see how a force of 

 attraction acting between two molecules should be in any way 

 influenced by their velocity or kinetic energy, which of course 

 really represents their temperature. Kleeman has sug- 

 gested * that the atoms in a molecule are in a state of rapid 

 motion round the centre of gravity, and that the centrifugal 

 forces thus set up are balanced by atomic attractions, and 

 further that the effect of increase of temperature is to disturb 

 this balance and to alter in this manner the force of attraction 

 at a given external point. This hypothesis is untenable from 

 two considerations. In the first place, it is highly improbable 

 that the atoms in a molecule are in a state of rapid motion 

 relative to one another ; for it is hardly conceivable that in a 

 very complex molecule under normal conditions, the atoms 

 could maintain their relative positions with such perfect 

 regularity as the theory of stereochemistry demands. It is 

 probable that, at ordinary temperatures, the molecules of 

 stable substances have no other kinetic energy than that of 

 rotational and trans] ational motion. In the second place, the 

 explanation involves the assumption that atomic attraction is 

 identical with molecular attraction, but there appears to be 

 little or no connexion between the two. The force of attraction 

 which causes the union of. sav. an atom of hvdroo'en with an 



* Phil. Mag. Jan 1911, p. 93. 



