The Internal Pressures of Liquids 



627 



It will be seen by an inspection of Tables 8 and 9 that all 

 the formulas, i. e., those from the latent heat; from van der 

 Waals' equation, assuming that b c is 2V C /S; from the surface 

 tension; from Young's formula and that involving the molecu- 

 lar weight and number of valences, give practically the same 

 result. The confirmation of the values from the surface 

 tension and van der Waals' equation by the computation from 

 the latent heat close to the critical temperature is, I think, 

 conclusive evidence that these results are correct, within the 

 limits of error of the data from which they are computed. 

 The internal pressures of such liquids as benzene and ether are, 

 therefore, about 14 per cent, higher than have been calculated 

 by van der Waals' formula: a --= 27^/64 X 273 2 P C . As a 

 result the co-volume, or the volume of the molecules, the value 

 "6," must be taken larger both in the liquid and vapor than 

 has been customary. 



The values for "a" and M 2 K given in my earlier papers 

 should be multiplied by i .085 approximately to bring them to 

 these new and correct values. 



The internal pressures at zero degrees centigrade computed 

 by Lewis, by the method of van der Waals and by formula 

 (7) compare as follows (Table 10) : 



10 INTERNAL PRESSURES IN ATMOSPHERES AT ZERO DE- 

 GREES 



The values obtained from the surface tension and from the 

 latent heat of expansion as computed by Lewis, agree pretty 

 well except in the case of carbon bisulphide; they are widely 



