120 BUTLER art. d 



compared with the quantities of Sa, ■ ■ . Sg, can be expressed 

 by equations of the form 



, , , Chnih 

 Hh = Ah log 



Ilk = Ak log 



V 



Ckirik 



(119) [217] [218] 



where A//, Ch. ■ -Ak, Ck are functions of the temperature, the 

 pressure and the ratios of the quantities nia, . . . mg. 



17. Derivation of the Potentials of a Solution from Their Values 

 in a Coexistent Vapor Phase* The part of the memoir which 

 deals with the values of the potentials in gases does not come 

 within the scope of this article, but since it is necessary for us to 

 show how the potentials of the volatile components of a solution 

 can be determined from the partial vapor pressures in a co- 

 existent vapor phase we must first give a short derivation of 

 the equation representing the variation of the potential of a 

 gas with its pressure. 



According to the laws of Charles and Boyle the pressure, 

 volume and temperature of unit weight of a perfect gas are 

 related according to the equation 



pv = at, 



where a is a specific constant for each gas. For a weight m of 

 the gas, we have 



pv = amt, 



and since, according to Avogadro's law, equal numbers of 

 molecules of all perfect gases occupy the same volume at the 

 same temperature and pressure, this equation becomes 



Amt , _ 



p. = — > (122) 



where A is a universal constant and M the molecular weight of 

 the gas. 



*Gibba, I, 164-165. 



