SURFACES OF DISCONTINUITY 571 



page 65.) Indeed an equation analogous to Amagat's has been 

 shown by Schofield and Rideal (ibid., page 66) to represent with 

 some exactitude the behavior for all but the most dilute con- 

 centrations. It is 



FiA - B) = xRt , 



where B is the limiting area of the unit mass of molecules when 

 crowded together in the unimolecular film, and x is a measure of 

 the lateral molecular cohesion, having a definite value not 

 greater than unity for each solute, and being smaller the larger 

 the cohesion. The values of B agree quite well with the values 

 suggested from other considerations. The equation is well 

 supported by its application to about a dozen solutes which 

 include the shorter-chain fatty acids and some alcohols. In so 

 far as it is valid it leads to an interesting equation as follows. 

 By the exact Gibbs' equation 



dF = — d<x = Vdn . 



Therefore 



fFB\ 

 a = CF-exp(-). 



Rideal states that this equation is in good accord with the 



