49 



TABLE 8. 

 Iron electrode, immersed in ' 2 NFeS04-solution. 



It is now remarkable that, as has also been fonnd by others, 

 contact with hj^drogen can annihilate the passivity. When we reversed 

 the cnrrent and made the passive anode the cathode for a moment, 

 and then reversed the current again at a density of 400 m.A., the 

 difference of tension with the auxiliary electrode amounted at lirst 

 only to 0,12 Volt, but this tension rose at first riither slowly to 

 0,6 Volt and then rapidlj to 2,27 Volts. 



It therefore a|)pears from this experiment that hydrogen is a 

 positive catalyst for the setting in of the internal equilibrium of 

 iron,, which also accounts for the fact that the cathodic polarisation, 

 as appears fiom the last table, is extremely small in comparison 

 with the anodic i)olarisation. The difference between anodic and 

 cathodic polarisation is therefore so great here, because for the 

 ano.dic polarisation a negative catalyst, and for the cathodic polarisa- 

 tion a positive catalyst come into pla} . 



That for nickel the anodic and the cathodic polarisation are about 

 the same pro^■es that the oxygen and the hydrogen do not act 

 noticeably catalytically on this metal. 



It should finall}' still be pointed out that when at the moment 

 that the passive iron had reached an anodic tension of polaristxtion 

 of 2.27 Volts, the current was broken, still a tension of polarisation 

 was observed of 1,07 Volts, which tension, however, pretty quickly 

 fell to 0. So it appeared just as for nickel that the iron without 

 |)assage of the current soon assumes internal equilibrium by the aid 

 of the electrolyte, and becomes active. We see from this that the 

 negative catalytic action is maintained by the current : when the 

 curi-ent is broken the active iron above the liquid will, however, 



Proceedings Royal Acad. Amsterdam. Vol. XVll. 



