145 



silver, and on gold i.e. so tliat the potentials tor cliroininm on 

 copper are the most negative, it nuist be assnmed that chroniiiini 

 deposited on coppei contains more hydrogen than chrominm on 

 silver, and this more than chromium on gold. 



In the same way the existence of a retrogressive cnrrent potential 

 line can be explained, as has been drawn in tigui-e 11 of the second 

 commnnication. These lines refer to the formation of chromate, and 

 we shall, therefore, have to assume that also the potential of 

 chromate formation will be de|>en(lent on the hydi-ogen content. This 

 dependence is e.g. given by the line i\() in ligure 1. 



Here too, in case of anodic polarization the concentration of the 

 hydrogen at the boundary layer will l)e small, hence the potential 

 high. On increasing current density the ditfusion layei- becomes 

 thinner, so that in case of interruptions of the cnrrent by the 

 commutator the hydrogen charge at the boundary surface after the 

 curi-ent has been broken will be the greater as the current density 

 was greater. 



Hence for greater current density tlie potential is more negative 

 after the current has been interrupted than for small current density. 

 Moreover it is clear that the retrogressive cnrrent potential line can 

 only be found when we work with a commutator. When the potential 

 is measured with continual passage of the cnrrent, the potential is 

 the more positive as the current density is greater, because then 

 only the hydrogen charge at the boundary surface is to be reckoned 

 with as it is dnriiui the polarization. 



Accordingly the activation after anodic polarization can be satis- 

 factorily accounted for by means of the hydrogen theory. 



It remains, however, to explain the phenomenon tliat on anodic 

 polarization of electrolytic chrominm and of activated chromium of 

 GoLDSCHMiDT, the potential becomes more negative also during the 

 passage of the current. 



An explanation of this may be arrived at when it is borne in 

 mind, that not immediately after the current is broken or started 

 the state in the ditTusion layer is stationary. 



When in figure 3 /^C' represents the concentration of the hydrogen 

 in the diJïusion layer of a piece of chronn'um which has been in 

 contact for a long time with an electrolyte, the hydrogen at the 

 boundary surface has the concentration FC. When this electrode is 

 now anodically polarized, the concentration of the hydrogen will 

 descend to F' ('/ in consequence of this. Now the concentration of 

 the hydrogen in the diffusion layer will have the course B' C' . This 

 will be the state when the current has just been started, and the 



• 10 



Proceedings Royal Acad. Amslerdain. Vol XXI. 



