161 



difference metal-electrolyle will remain equal lo Ihe potential (iiflerence 

 of Ihe unary metal. 



In the second place (he case may present itself that (he internal 

 equilibrium of (he me(al surface does no( set in so rapidly as was 

 sujiposed a!)0\'e, and then it will be possible to dis(urb (he me(al 

 surface eidier in one direclion or in (ho other, i.e. it may become 

 either nobler or baser, hence (he potential difference can differ from 

 that of (he unai-y me(al in noble or base direction. 



A third case, whicjj like the firs(, represen(s a limiting case, is 

 this that the metal is so inert that (he velocity wi(h which it assumes 

 internal eqnilibi'ium is very small compared with the veloci(y wi(h 

 which the electrons and ions are withdrawn from (he me(al or 

 added to it. 



In the first limiting cafee the po(en(ial dilference is entirely governed 

 by the state of internal equilibrium of the metal, and in (he last 

 case (he po(en(ial difference is dominated by (he elec(ron coiicen- 

 (I'alion of the hydrogen equilibrium in the electrolyte. 



4. Nickel as Example of an Inert Metal, the Inertia of n^hich 

 Increases under the Injluence of the Dissolved Hydrogen. 



An example of the latter case with this particularity, however, 

 that (he jus( mentioned great inertia is only slowly reached, because 

 the metal is converted to this state after some time through (he 

 negative catalytic influence of the dissolving hydrogen, is furnished 

 by nickel. As was shown in a previous conimunicalion, (he case 

 presents itself (hat when (his metal is immersed in such an acid 

 solution that hydrogen generation would have to take place, this 

 phenomenon does not take place to an appi-eciable degree, and the 

 metal appears to l)e disturbed after some time so far in a noble 

 direction that its potential difference has become equal to that of (he 

 hydrogen electrode. 



On that occasion we already gave an explanation of this pheno- 

 menon, and pointed out (ha(, nickel being so inert, the electron 

 concentration of the nickel equilibrium in the electrolyte 



A'i/. ^ Nil + 2<9/, 

 becomes equal (o (he eleclron concentration of the hydrogen equi- 

 librium : 



so that finallj'^ 



This was demonstrated in (he following way. We poinled out 



11 

 Proceedings Royal Acad. Amsterdam. Vol. XXI. 



