146 Dr. G. Bakker on the 



A second thermodynamic relation we find in the following 

 manner. If we evaporate a quantity of the liquid phase 

 given by the expression 



l, fa Wt-P» (see above), 



we get precisely the complex of the two homogeneous 

 phases, which can form unit of mass of the capillary layer. 

 The corresponding heat of vaporization is expressed by 



VP\P2 — P2 / \ r 



P1 — P2 u 



If we further convert the complex into the matter of the 

 capillary layer, we must still add a quantity of heat per unit of 



mass, expressed by — T /r rrS. We have therefore : 



In the same manner we have : 



Hence : 



v 2— " S 5T + ( V --2~J^T' * * (28) 



where u = v 2 — Vi represents the difference between the specific 

 volumes of the liquid and vapour. 



From the equations (27) and (28) we can now deduce the 

 equation of energy in the following way : by differentiation 

 of (27) we find : 



+ d|^^-^l±^U=HiS + Sc/H. . (29) 



By substitution of the expression (28) for rj ~r~^ •> anc * 



as: * 



de — Tdrjx — —pidv x an d de 2 — Tdrj 2 — —p 2 dv 2 : 



de, - Td v - HdS = - i Pl d Vl - i p 2 dv 2 + fv - ^y^ 2 ) 



* In another way I have deduced this relation in Ann. d. Phys. xvii. 

 p. 496 (1905;, formula (37). 



