270 Dr. S. A. Shorter on the Constitution 



the question in the light of the above theory. Initially we 

 have 



Mo^oV + po'V' + IV, 



and, finally, 



M = Po (V + AY) + Po '(V> + AY') + T (a + A*), 

 M 1 + AM 1 = / o 1 (V + AV)+/) 1 '(V' + AV , ) + ri(cr + Acr); 

 and since the total volume is constant 

 AV + AV' = 0. 

 From these equations we readily find that 



AM!_ r pi-pi v _ r nv 



~r— — L i — - — — ri — « i(o)i • • • y*-^) 



i. e. that the value of the surface excess of C x deduced from 

 the experimental data is the value relative to the " zero- 

 plane " of C . 



§ 4. Special Cases of a Binary System. 



Case I. Two Immiscible Liquids. 



The simplest case of a binary system is that in which each 

 phase consists of a single substance, i. e. that formed by two 

 immiscible liquids. Let us suppose that the <f> phase contains 

 only the component C , and the <f>' phase only the com- 

 ponent Ci. Equation (10) then takes the form 



I\ , T /dr\ 



7 + - 



Pi Po \dp)e 



(a w 



r ««—'ii), <16) 



This equation may also be written in the forms 



'dr 



.dp/ 

 and 



r »<»= -'»(!)„ ( i7 > 



This result is of importance in relation to the question of 

 the composition of the surface-layers of pure liquids. It is 



