( 131 ) 



The imperfect agreement between the real course of the vapour 

 tension and tliat derived from the equation of state willi a and h (con- 

 stant, lias induced us to assume that a is a function of the tem- 

 perature. It appears however that this agreement is not satisfactorily 

 established by the modification proposed by Claüsius. It will there- 

 fore be of no use to {proceed further in this way — S[)ecially be- 

 cause this moditication in itself is certainly insuilicient to account for 

 the fact that liquid volumes occur which are even smaller than b. 



If we had not supposed a to increase so quickly with decreasing 



T 



Tic 1-^ 



temperature as agrees with a -;r7 ; if we had chosen ae * for in- 

 stance, then the greater part of the above difficulties would have 

 vanished. 



We should then have found: 



T dp ^^ ^ T^ a e^~ Tk 



(-1) 



pdT V ■ TkJ RTv, 



1- — 

 The expression | 1 + — - j e ^* is equal to 2 at T = Tk and at 



7^=10 it would have increased to <?:= 2,728 etc. ; so the increase is 



relatively small. But the term which should be found equal to 



Io(/ 27', would also have remained far below the required value. For 



this reason it seems desirable to me to inquire, in how far the 



variability of b alone can account for the course of the vapour 



tension. 



As I dared not expect that the variability of b could explain the 



course of the vapour tension as it is found experimentally, and in any 



case not being able to cakmlate this variability, I have often looked 



for other causes, which might increase the value of the factor ƒ from 



27 . a 



— to about twice that value. The quantity — representing the amount 



8 V 



with ^vliich the energy of the substance in rare gaseous condition 



surpasses that of the same substance in liquid condition, and this 



Tdp 

 quantity seeming ^ — from the value of — ^, — to be only half of what 



it should be, I have thought that the transformation of liquid into 

 vapour ought perhaps to be regarded as to consist of two transforma- 

 tions. These two ti-ansformations would be: that of liquid into 

 vapour and that of complex molecules into simple gasmolecules. 

 If this really happened then the liquid state would essentially differ 

 from the gaseous state even for substances which we consider to be 



