163 



and hydrogen is passed (hrotigli, the electron conoeiilration of the 

 platinum equilibrium in the electrolyte 



PtL ^ PtL + ^Ol 

 has almost immediately become equal to the electron concentration 

 of the hydrogen e(|uilibrium, 



corresponding to the pressure of the hydrogen that passes through, 

 so that e. g. the platinum electrode has almost immediately become 

 electromolively equal to the hydrogen electrode. 



For these metals, which behave idealhf inert, the potential differ- 

 ence is, therefore, governed by the existing electron concentration 

 in the electrolyte. This is also the reason why these exceedingly 

 inert metals may serve not only as gas-electrodes, but also for the 

 determination of the so-called oxidation, resp. reduction potentials. 



When e. g. platinum is immersed in a solution in which the 

 equilibrium -. 



prevails, the electron concentration of the platinum equilibrium in 

 the solution has almost immediately become equal to the electron 

 concentration of the above feiro-ferri equilibrium, so that in the 

 electron equation for the potential difference of the platinum 



A = In 



F {Ol) 



the electron concentration of the ferro-ferri equilibrium may be 

 written instead of {di), in consequence of which we get: 



^ ^ {Fe) 



as was already stated before. 



The peculiar feature of these platinum metals is therefore their 

 extraordinary inertia, which causes them to behave ideallj/ passive in 

 most electrolytes. 



6. Considerations in the Light of the Theory of Phases. 



It is clear that for the explanation of the phenomena discussed 

 here, considerations as have been introduced by us of late, are 

 indispensable. 



Phase-theoietical considerations are inadeipiate here, but all the 

 same it may be of use lo represent the obtained results gra[)hically 

 by means of A,ci'-diagrams. 



11* 



