62 



Dr. W. C. McC. Lewis on Internal 



It has also been shown that K itself can be calculated, but as 

 the basis of the method consists in applying an equation of: 

 the van der Waals' type, I do not think that it presents 



a 



much advantage over the method of setting K=~2 in van 



der Waals' equation itself. The temperature coefficient 

 being, however, a much smaller quantity, is no doubt given 

 by Davies' expression with a considerable degree of ac- 

 curacy, the simplicity of the expression rendering it par- 

 ticularly useful. 



Thus starting with equation (1) 





and substituting Davies' 

 finally 



K= 



expression 



for FT , 



one obtains 



1 + Ta' 



this being identical with Davies' equation (24) (I. <?.). 



Davies himself has calculated the value of K in a few cases 

 employing the above expression, in which I is taken as the 

 latent heat of vaporization of unit volume of the liquid. 

 The results obtained are given in the second column of the 

 following table, the third column containing the values 

 obtained by Davies' alternative method without introducing 

 equation (1). The last column is the van der Waals' 

 value *. 



Substance. 



K atraos. 



K atmos. 



ll = \ 



Benzene 



912 

 1042 

 1315 



686 



1102 



1188 



1176 



661 



1380 

 1180. 



Toluene 



Aniline 



Cyinene 





The agreement between columns 2 and 3 is fairly good. 

 In the above I is taken to be the latent heat of vaporization 

 of 1 c.c. of the liquid. It seems of interest to see what sort 



* Calculated by Traube, Zeitsch. Phys. Chem. lxviii. p. 293 (1909). 



