CHEMICAL THEORY OF SOLUTIONS. PART I. VJ 



properties such as the absorption of light or the rotation of the 

 plane of polarisation are probably also additive. The molecular 

 surface tension of such solutions has been shown to be of the 

 same nature by Kamsay and Aston (Zeits. pliysik. Chem., 15, 

 89 ; 1894). Xo doubt with the extension of exact measurements 

 of various properties such examples would be greatly increased. 



§ 2. The Equilibrium between Gaseous and 

 Liquid Phases. 



[a) Vapour Pressure at a Constant Temrperature. 



In the following the gas phases are assumed to be so rare- 

 fied that the gas law^s are applicable without restriction. In 

 such case the relations obtaining are remarkably simple. 



The chemical potential of the components in the liquid 

 phase may, under the circumstances, l)e considered as constant 

 at a constant temperature and independent of pressure. The 

 chemical potential of the components in the gas phase varies of 

 course with pressure. For the component @i it is 



/V = z,' + RTlnP+RTlnC\', (4) 



where 0/ is the molecular thermodynamic potential of the isolated 

 component in the gaseous state at the temperature T and under 

 the unit pressure, w^hile Cî is tlie molar fraction of the com- 

 ponent in the gas phase. 



If the isolated component ©1 has the vapour pressure Pj at 

 the temperature Ji then we have 



?;, =z/ + JlTliiP,. 

 When the solution is in equilibrium with its vapour 



