﻿Theory of Surface Forces. 5G5 



For the capillary layer equation (3) becomes : 



y=9* y +**fp en) 



If we multiply this equation by 2-— , after replacing q by 

 - and replacing f by j- r-j and integrate, we find : 



Uv — ^— + vj/ i7 - • • • ^ 



The equilibrium between the thermic pressure and the 

 forces o£ cohesion demands (for every direction) 



J0 = - P dV, (13) 



whence 



where X is the thermic pressure in the interior of the liquid. 

 We have further for the liquid phase : 



V 1 =-2a/> 1 . . . (14) (Gauss 



and and van der Waals) 



Hence equation (12) gives : 



or 



%=l£y/—^. . . . (15) 



Now, dd= —pdV (equation 13) yields, noting that 



V 1 =-2ap, (14) 



Ji p Ji p . 



whence, replacing in (15) V by its value, we see : 

 Phil. Mag. S. 6. Vol. 12. No. 72. Bee. 1906. 2 P 



