J 65 



or also from tlie equations Tor the product of solubility of zinc and 

 hydrogen : 



Lz„=z{Zn){6y 

 and 



Lu^ = {UY{dy 



by putting {6)zn == (<9//,), in consequence of which : 

 or 



{Hl,y 102X-48 



When we put for a moment {Ziii)=^l, then: 



We see therefore, that the point 6' lies so much on one side that 

 practically it coincides with the zinc-axis. Hence the line (/, c, e or 

 (he line for the three-phase equilibrium zinc-hydrogen-electrolyte lies 

 practically on the same level as the point a, so that the measured 

 potential difference of the zinc, which contains a little dissolved 

 hydrogen, and is besides covered with a layer of hydrogen, is 

 certainly pi-actically equal to (he potential difference of the pure 

 hydrogen-free zinc, the measurement of which is impossible here. 



Let us now suppose that we immerse zinc in an electrolyte, the 

 composition of which, as regards the zinc- and hydrogen ions, is .t'l ; 

 we then see, that zinc cannot be in stable electi-omotive equilibrium 

 with this liquid, but that hydrogen can. 



If, how^ever, the hydrogen did not appear as a new phase, but 

 only dissohed in the zinc, a melastable electromotive equilibrium 

 would, indeed, be possible, viz. g f, but (he po(ential difference 

 would be more strongly negative than (hat of the three-phase 

 e([uilibrium represented by the line </, c, e. 



This metastable electromofive equilibrium does not appear, however; 

 on the contrary, we observe a generation of hydrogen, and we will 

 point out here in a few words, how the experimental fact is to be 

 explained that under these circumstances the potential difference 

 zinc-elec(roly(e is equal to that which corresponds with d, c, e, or 

 what is practically (he same thirig, with a. 



The explanation is this-, when zinc is immersed in the electrolyte 

 of the concentration .^i, (he es(ablishment of the three-phase ecpiili- 

 brium between the zinc phase, the electrolytes, and the hydrogen 

 phase takes immedialely j)lace in the boundary layer. 



