and Surface Energy. 45 



d(p\i) 



necessary. It is of interest, however, to calculate 



from latent beat data. Three examples of such calculation 

 are therefore given in Table V. The data used are Young's. 



Table V. 



Substance. °C. .= ~ |I. \ ^ ■ ' 07M (— ~ X ^) " d ( P ~) 

 (Jaeger J- 



Benzene 80° -00125 86-5 -"28 -1-73 -T85 



Ether 35 '00172 75'7 --26 -160 -1"70 



Ethyl acetate... 80 -00160 83'96 -'203 -1'53 -130 



Matthews (Jour. Phys. Ohem. xx. p. 554 (191b')) has 

 derived an expression for the Ramsay-Eotvos relation by a 

 method that bears some resemblance to that employed above. 

 He obtains a connexion between surface energy, latent heat, 

 and Bakker's equation ; he assumes, however, that van der 

 Waals' " a " is independent of temperature. His reasoning, 

 moreover, involves certain rather indeterminate assumptions 

 in connexion with the intra-molecular energies of liquid 

 and gaseous molecules, and depends on Goldhammer's 

 empirical relation between liquid and gaseous densities and 

 temperature (Zeit. Phys. Chem. lxxi. p. 577 (1910). His 

 calculations of " K " are nevertheless remarkably exact. 



The empirical relationships that have been shown above to 

 have a theoretical justification have been used to calculate 

 the association of liquids with which marked deviations from 

 the empirical constants have been obtained. The usual 

 procedure has been, when an " abnormal " constant is 

 obtained, to find a number n by which M, the molecular 

 weight of the simple or gas molecule, must be multiplied 

 in order that the average or normal constant may be obtained. 

 A glance at the expressions derived for Trouton's Rule,. 

 Walden's relations, and the Ramsay-Eotvos " law " shows 

 that such procedure is quite unjustifiable. Where the ex- 

 pressions involve the molecular diameter d, the assumption 

 would be involved that the diameter of the associated 

 complex is the same as that of the simplest gas molecule. 

 This of itself might not involve serious error, since d varies 

 but slowly with increasing molecular complexity ; equations 

 (3) and (4) might therefore be expected to give approximate 

 degrees of association Trou ton's Rule and the Ramsay- 

 Eotvos law, as given by (2) and (5), contain, however, both 

 d and critical data, which refer to the non-associated vapour 

 (c/. Tyrer, Zeit. Phys. Chem. lxxx. p. 50 (1912)). 



