﻿van 



der Waals Formula. 597 



liquids, the differences between the two series of calculated 

 values of latent heat are quite as likely to be due to a 

 divergence of Biot's formula from the facts as to such a 

 divergence of the modified van der Waals' relation. 



Consequently it will be seen that this modified van der Waals' 

 relation, and the derived expression (B) for the latent heat 

 of vaporization, hold good for all the non-associated liquids 

 examined and for none of the associated liquids ; hence the 

 agreement between the two series of calculated latent heats, 

 and the variations in the value of Mills' constant (see above) 

 give delicate tests of association in a liquid. 



My thanks are due to Professor Young for supplying 

 some data I had overlooked, and for kindly offering to read 

 the proofs of this paper. 



The University, 

 Melbourne. 



Appendix, 



In the following it is shown in detail that the methods of 

 calculation used by Mills- Young and by Applebey-Chapman 

 are essentially the same. 



The data employed in the Mills- Young and the Applebey- 

 Chapman calculations are the measurements of the vapour- 

 pressure and the vapour-density of thirty-two pure liquids 

 made by or under the direction of Dr. Sydney ^oung. 

 These have been collected and revised, and are published in 

 the Scientific Proceedings of the Royal Dublin Society, 

 1910, pp. 412-443. With them appear Dr. Mills' series of 

 calculated latent heats that we are about to discuss. 



In each case the process of reduction has consisted of — 



(1) Finding some formula connecting the temperature 

 with either the vapour-pressure or the specific volume 

 of the saturated vapour. Determining the constants 

 of this formula over a range extending to the critical 

 temperature. 



(2) Differentiating this formula and substituting the value 



of -77- so found in the Clausius-Clapeyron relation 

 h=t(v 2 —' i>i)-£> 



where v 2 and Vi are the molecular volume of vapour and 

 liquid respectively, t the absolute temperature, j) the satura- 

 tion-pressure, and Lthe molecular latent heat of vaporization. 



