Tension and Chemical Interaction. 419 



where P x is the intrinsic pressure of the saturated solution 



forming one layer, 

 P 2 „ „ ,, the other layer, 



P 12 resultant inward pressure at the interface, 

 a Y = surface tension of one layer, 

 Pi = number of molecules per unit volume in the same 



layer, 

 « 2 and p 2 — corres P on ding quantities for the second 



layer. 

 It was shown that the expression must conform with 



Pu ■■=/(*) «u 

 or 



or 



«12 = «1— «2 (2) 



The result (2) is only possible if p\=p2- 



It can be seen that the above results would remain the 

 same whatever the law of molecular action, whether it varies 

 inversely as the fourth, fifth power of the distance, or other- 

 wise. It can be shown that assuming the inverse nth power 

 law our expressions for surface tension a and internal pressure 

 P respectively would be 



n+l 



ex. — kp 3 , 



n+2 



F = 2kp~ ir . 



Thus the formula connecting both quantities will be the 

 same as indicated on p. 382 of my former paper, i. e. 



F = kccp 1 < s , 

 where k = 2. 



Thus the relation (2) does not depend upon the law of 

 molecular attraction, but is a result of a certain chemical 

 interaction between the liquids forming the solutions, which 

 enables the heterogeneous system to become stable and pre- 

 vent both layers from mixing. The essential condition of 

 this equilibrium is the equality of molecular concentrations 

 (p 1 =p 2 ). This is based on some physico-chemical evidence 

 briefly mentioned in the previous paper. On p. 394 two 

 typical curves were reproduced to this effect. They were 

 borrowed from a theoretical paper by G. Tarn man *, which 

 reference was by mistake omitted in the previous paper. 

 Some experimental results of that kind together with more 

 complete theory will be published in a subsequent paper. 



6 Featherstone Buildings, 

 High Holborn. 



* Z. An. Ch. xlvii. p. 274 (1905). 



