388 Prof. G. N. AntonofT on Interfacial 



We will take it for granted that when two liquids which 

 do not completely mix are in equilibrium at the limit of 

 separation, the following must hold good : 



P12 = Pi ~~ ?2> 



where P 12 is the resulting normal pressure at the interface, 

 Pj and P 2 the normal pressures of the solutions 1 and 2. 



According to the present theory there must be a definite 

 relation between such quantities as P and a. For the 

 solution 1 there must be 



Pj = &* lPl l/3. 



For the solution 2, 



P 2 == ka 2 p 2 V 3 ; 



and similarly at the interface of the two layers an expression 

 must hold good of the following type : 



P 12 =^a 12 p 1 /3. 



Thus 



P 12 = Pi-P 2 =K«iPi 1/3 -^2 1/3 ). • . • (3) 



We will show in the subsequent paragraph that when two 

 liquid layers are in equilibrium both superposed solutions are 

 equimolecular, i. e. contain an equal number of molecules per 

 unit volume, or we may put 



Pi- Pi- 



From the expression (3) we shall then obtain 



Pi2 — kpVZfa— « 2 ), 



but since Pi2 = ^ a i2 j p 1/3 5 



therefore « 12 =a 1 — a 2 . . (4) 



This is perhaps the most fundamental result required by 

 the theory outlined above. 



The equations (3) and (4) are identical provided that 



Pi=P2 ; 

 which means that in two layers there are an equal number of 



