164 



Let us first consider the case that the metal zinc is iranmersed in 

 a hydrochloric acid solution of ZnCl, ; then it is the A-A'-figure of 

 the system Zn-H^ that may serve for the gi-aphical elucidation of 

 the found result. 



z\=o 



Fig. 1. 



Zinc. 



A A-,?Nfigure holds for constant T, P, and a constant total ion- 

 concentration ; for T we choose here the ordinary tem[)érature, and 

 for P the pressure of 1 atm., the total ion-concentration being put 

 here at 2 norm. 



The sitnation of the point C, which represents the electrolyte 

 which coexists with the zinc phase and the hydrogen phase of the 

 pressure of 1 aim., is found from the equation: 



R2\ Kzn Rl\ Kir 



In — r^ — = in — ; — 



2F (Zul) F (Hl) 



from which follows 



KZn 



H 



ifiiy 



