166 



Accordingly the concentration c prevails in the boundarj' layer, 

 whereas the total concentration of the electrolyte is x^. 



The liydrogen ions now diffuse in the boundary layer, where for 

 the maintenance of the concentration c the reaction : 



takes place, in consequence of which, as we have already seen, 

 electrons and zinc ions from the metal j)hase go into solution. The 

 zinc phase assumes internal equilibrium with great velocity, and 

 consequently it remains unaltered during the liydrogen generation, 

 and the measured potential difference is that of the three-phase 

 equilibrium d, c, e, which practically agrees with that of pure zinc, a. 



When a platinum electrode is placed in the same electrolyte, it 

 indicates the hydrogen-potential which corresponds with the line 

 m n. The zinc electrode and the hydrogen electrode present therefore 

 entirely different potential differences in the same electrolyte. 



This is the graphical elucidation for our conclusion that the 

 potential difference of zinc with respect to a solution of ZnCl^ acidified 

 with hydrochloric acid is determined by the state of internal equili- 

 brium of the zinc. 



Nickel. 



Let us now proceed to the case that instead of zinc the metal 

 nickel is taken; then it is worthy of note in the first place that 

 under the same circumstances we then find for the composition of 

 the electrolyte c 



Kh Lh, (//>~102x-*« 



When we now put {Ni'[]) = J , we get {H' y = 10~l or {hi ) = 10~\ 

 Here, too, the electrolyte c has still a one-sided position. Let us 

 assume that the adjoined figure 2 again holds for 18°, and a pressure 

 of 1 atm. for a total-ion concentration of 2-norm.; then an entirely 

 different phenomenon is observed on immersion of a nickel-electrode 

 in the electrolyte of the concentration x^ than in the case with zinc 

 discussed just now, because the internal equilibrium in the metal 

 surface cannot maintain itself when electrons and nickel ions go 

 into solution. 



The metal is more and more disturbed in noble direction, and the 

 result is, as we demonstrated already', that the electron-concentration 

 of the nickel equilibrium in the solution has become equal to the 

 electron-concentration of the hydrogen-equilibrium in the electrolyte, 



