SURFACES OF DISCONTINUITY 



579 



precautions appear to have been taken against every conceivable 

 source of error. 



The following results of preliminary trials indicate the very 

 satisfactory agreement now obtained between T calculated and 

 observed. It is no longer a matter of agreement of order of 

 magnitude, or a ratio between 2:1 and 4:1. 



Substance 



p-Toluidine 



p-Toluidine 



Phenol 



Caproic Acid 



Caproic Acid 



Caproic Acid 



Hydrocinnamic Acid 

 Hydrocinnamic Acid 



r X 10* calo. 



5.2 

 4.9 

 4.8 

 6.3 

 6.5 

 6.3 

 5.1 

 7.9 



XI. Adsorption of Gases and Vapors on Liquid Surfaces 



29. Form of Gihbs' Equation for Adsorption from a Gaseous 



Phase 



Hitherto we have considered the experimental tests on ad- 

 sorption from the liquid side of a gas-liquid interface; but we 

 must make some reference to the work carried out on adsorption 

 from the other side. In such experiments it is convenient to 

 replace the potential of the gaseous component by its pressure 

 in the adsorption equation. The theory of such transformation 

 of variables is given very completely by Gibbs (I, 264-269). 

 For our purpose we need only consider the part on pages 267- 

 268 which leads to equation [581]. We shall suppose that the 

 single accent phase is the liquid, the double accent the gaseous, 

 that component 1 is the liquid, ai-i component 2 the gas or 

 vapor adsorbed. From equation [581] we see that if <r is re- 

 garded as a function of the temperature and pressure, then 



dp 



C 



— . > 



