266 



Dr. S. A. Shorter on the Constitution 



heterogeneity). A simple type of such a curve is shown in 

 fig. 4. It is evident that the position of the surface of 



Fiff. 4. 





© i 



A 



/v | v 



4— > 

 00 



i 



i 



1 ; 



l 



i N 



i 

 i 

 i 





c^ 



« 



B 1 



Posit/ on. 



separation may be assigned quite arbitrarily within the limits 

 of the region of heterogeneity. If we assign a position AB, 

 the surface excess is given by 



T= area C'N'R-area CNR. 



The value of Y may vary within wide limits with the 

 arbitrarily assigned position of the surface of separation. 

 If we choose the position of AB so that 



area CNR == area C'N'R, 



the surface excess is zero. We will call the plane, relative 

 to which the surface excess of a component is zero, the 

 " zero-plane " of that component. If the density assumes in 

 the surface-layer values greater than in either phase, the 

 position of the " zero-plane" is fixed (see fig. 5) by the 

 relation 



area CED + area C'N'R= area RDN. 



If the increase in density in the surface-layer is very great 

 the " zero-plane " may lie in the interior of one of the phases 

 (as in fig. 6). 



