﻿of Vaporization and Expansion. , r > ( ,U 



From (1) we have, at constant volume, 



T (dA\ __HT_1 da r 



RT a T 



/_ 1 da\ 

 { U =adT)- 



Hence, substituting in the equation 



A-U = T 



/dA 

 \dT 



), 



-U=-A + T^ = ^(l-c7T) .... (2) 



= \ ex ., the latent heat of the expansion. 



Now Da vies (Phil. Mag. [6] xxiv. p. 421) has obtained the 

 following expression for 7r, the initial pressure in a fluid: — 



tt= 4 -(2T c -T) 

 v c 



(v c and T c are critical volume and temperature). 

 Hence 



1 /dir\ 1 



ttUtA" 2T c -T' 



Davies has also shown (Phil. Mag. [6] xxiii. p. 415) that 

 z^n — m = *> the coefficient of cubical expansion, so that 



Kft).--- • • • • • ^ 



But, if 7r= --g, we get from (3) : 



1 /da\ 

 a \dTJ v ~~ 



Substituting in (2) 



A«.= -n+«T) (4) 



When T = 0, we find A ex . = — ; in other words, at the 



absolute zero the expression becomes identical with Bakker's 

 expression for the latent heat of vaporization. 



