Theory of Surface Forces. 143 



On the other hand from 



-=^2— Vl follows -jjrji — rf=C 2 — Cx ; . . (16) 

 (15) and (16) give in this way : 



T 2 dT l dT ^ } 



In the particular case when the curvature is zero p 2 ^=p v 

 and we get from (17) the known equation : 



r mdjh 



1 ,7T ' 



v 2 — V\ dT 



in which p x represents the ordinary vapour pressure. 

 The equation (17) may be written in this way : 



2r dpx dp 2 vi + t\ (dp 2 dp t \ ( 



[v 2 -v v )T ~ dT + dT + v 2 -v 1 \dT ~~ dT )' ' [L0) 

 After Kelvin we have further : 



Pl -p 2 = (19) 



JA 'K 



If we differentiate at constant E K and take E K in the 

 equation (18) as second parameter we find from (19): 



dpi dp 2 _ 2 dK .~ ~. 



Ir^dT-RzdT' ' ' * ' ( U) 

 and (18) becomes : 



in which 



P1+P2 Pi+Pv 

 v ~ 2 ~ 2 ' 

 For R K = oc 9 i. e . if liquid and vapour are separated by a 

 plane capillary layer, p 1 —p 2 =^ 9 and the last member of (21) 

 disappears, and we get the known equation : 



If p' represents the pressure of the theoretical isotherm, 

 we put 



V 



1 t 



or as 



1 C 2 

 I p'dv, 



i 2 ^'p 1 Vi= I p'dv, 

 Ji 



we have p 2 v 2 — p^ _ 



v 2 -v l 



