504 Dr. W. C. McC. Lewis on the Nature of the 



Bakker s Relationship. 



Bakker *, in 1888, was the first to point out that the latent 

 heat o£ vaporization is given by the expression 



-1 



Kc?r-fp(v ga9 — Vfl), 



where v& denotes the specific volume o£ the liquid. In 

 view of the considerations advanced above one can no longer 

 speak of magnitudes as pertaining to the liquid state only, 

 but must further specify whether bulk or surface. Evidently 

 here we are dealing with surface quantities, so that with 

 corresponding notation 



-J" 



gas 



(\ is the latent heat, external and internal, per gram). 

 Further, van der Waals' equation gives us for the surface 

 laver 



K — — 



s ~ Vs 2 ' 



so that on integration the above expression becomes 



X = a (-- — )+ P ("*»-".), 



or approximately, 



a , RT a /ax 



X = ^ s + M or **"7,' • • • • (3) 



where M is the molecular weight of the liquid in the state 

 of vapour. 



The connexion between Bakker's relationship and Dupre's 

 expression is obvious. 



By means of equation (3) we can calculate v s knowing 

 \i and a. This has been done for a number of chemical 

 compounds given in the following table, which is partly taken 

 from a list compiled by J. Traube f. The values refer to the 

 boiling-point of the respective compounds. 



* G. Bakker, Dissertation, Schiedam, 1888. 



t J. Traube, Ann. d. Physik [4] xiii. p. 300 (1902). 



