532 



Albert P. Mathews 



in the liquid; and ^'/V^ 8 is that in the vapor. If now we 

 divide the first by V l and the second by V w we obtain the 

 cohesive pressure per unit surface in the liquid and vapor, 

 respectively, or ///V] /3 and /*'/V* /3 . But we know that the 

 cohesive pressure is a/V 2 , hence the original assumption must 

 be incorrect. 



If, on the other hand, the difference in the cohesive 

 energy in the liquid and vapor is equal to a(i/V 1 - - i/V v ), 

 and all the latent heat is used in overcoming external and 

 cohesive pressure, then L E should equal this expression. 

 If, however, some of the heat, I, is used in expanding the 

 molecules then the equation should be : L E I = a(i/V l - 

 i/VJ. Near the critical temperature I becomes very small 

 and hence (L E)/(^ - - DJ, near the critical temperature, 

 must be very nearly equal to a/Wt, where Wt is the weight 

 taken in grams; but at temperatures below the critical, 

 (If - - E)/(^ - - DJ should be progressively greater than 

 a/Wt by the amount l/(d l - - DJ. Table 4 shows that this 

 expectation is realized, since in all cases the value (L -- E)/- 

 (</! - - D v ) is greater below the critical temperature, but be- 

 comes very nearly equal to a/Wt at the critical temperature. 

 The value "a" used in these calculations was calculated from 

 the surface tension in the manner described. 1 j * 



The values diverge as the temperature'falls. 



TABLE 4 ERGS FOR GRAM MOLECULAR QUANTITIES 

 Diisobutyl Methyl acetate 



1 Mathews: Jour, Phys. Chem., 17, 154 (1913). 



