32 Surface Energy, Latent Heat, and Compressibility. 



obviously take into account the variation of e with 

 temperature. 



Summary. 



(1) If the van der Waals constant "a" is independent of 

 volume, it is shown that the compressibility /? ota liquid 

 should be connected with the internal latent heat by the 

 relation 



^•j=-2X 1 5 (xii.) 



If a is a function of v, then 



1 1 ^ e -s 



-^j=e\ 1( ?, (xm.) 



where e= ( P — - stt : coefficient of variation of surface 

 a V p 01 



energy with temperature : 



a= - ^r~: coefficient of cubical expansion). 

 v Ol L J 



It is found, for the limited number of liquids for which data 

 are available, that (xii.) is approached at higher temperatures 

 (the relation holding as such for some liquids at the boiling- 

 point), and that (xiii.) becomes progressively applicable at 

 low temperatures. 



(2) Lewis's empirical approximation, that heat of com- 

 pression is very nearly equal to latent heat of vaporization 

 per unit volume at 0° 0., is deduced. 



(3) The approximate constancy of the product of com- 

 pressibility and surface energy at 0° 0. is deduced, and 

 the observed lack of constancy at other temperatures 

 accounted for. 



The Chemical Laboratory, 



The College, Winchester. 



