of the Surface Layers of Liquids, 273 



surface-layer, we obtain a value of drjdp opposite in sign to, 

 and arithmetically more than a hundred times as large as, 

 the value obtained experimentally. 



A similar discrepancy between theory and experiment 

 exists in the case of the ether-mercury interface, Lynde's 

 experiments giving for drjdp a small positive value, and 

 Lewis's theory a relatively large negative value. Our theory 

 shows, therefore, that the theory of surface compression is 

 inconsistent with experimental data relating to the effect of 

 pressure on the interfacial tension. 



Case II. Two Partially Miscible Liquids. 



Suppose that the two phases are the liquid layers formed 

 by two partially miscible liquids, the </> phase being the C 

 layer. If we write c =(j 'Jp and c 1 = /3 1 //o 1 / , we have 



r "--'-^($), — < i9 > 



*=d^)(i). • • • • <*» 



Lynde's results for three pairs of partially miscible 

 liquids, together with the calculated values of h, r 0( i), and 

 r^o) are shown in the following table. 



dr 



o - Oi. r dp n r o(l) r l(o) 



in dyne/cm. in ju/i. in /*/*. in 10~ 8 gin./cm. 2 in 10~ 8 gm./cm. 3 



Water. Ether. 9'7 --060 -'068 +-6 +-4 



Water. Chloroform. 27 --006 --006 -f'06 +09 



Water. Carbon bi- 42 + 037 +'041 -'4 -"5 



sulphide. 



It will be seen that in two cases drjdp is negative. The 

 distance between the " zero-planes " is, however, much too 

 small to justify any assumption of surface compression. 



Case III. Liquid Phase in contact with Vapour Phase (both 

 components volatile). 



In this case we may in general neglect the densities in the 

 vapour phase in comparison with those in the liquid phase. 

 Phil. Mag. S. 6. Vol. 31. No. 184. April 1916. U 



