1122 



place at -}- 0.1 V is still to be investigated. There exist here three 

 possibilities. 1. the chromium can go iiere into solution as chromous-ion 

 (perhaps also as chromic-ion). 2. oxidation can take place in the 

 solution from Cr" to Cr", 3.. the copper on which tlie chromium 

 has been precipitated, can go into solution. This last possibility must 

 be considered, as the chromium does not very firmly adhere to the 

 copper. The chromium might, therefore, present cracks, and this 

 might be the reason that the copper went into solution. 



That the reaction at -f- 0.1 V is not an oxidation from chromons- 

 to chromic-ion appears from this, that pretty much the same course 

 was found for the current potential line when as electrolyte a 

 solution of KCl was used. Only the potential, for which a great 

 increase of the strength of the current was found, lay somewhat 

 lower, viz. at from —O.J lo 0.0 V. The same thing appears from the 

 following experiment : A naked, and a [)latinized electrode were 

 anodically polarized in a solution of chromous-sulphale. No rise was 

 noticeable at -}- 0.1 V. The strength of the current rose at once 

 with a potential of — 0.5 V; hence oxidation evidently takes place 

 here from Or* to Cr--. The limiting current had ahead} been 

 reached at 2 mA, and a fnither rise of ihe strength of the current 

 did not set in t)efore -[- ^ -^ V (oxygen generation). For comparison 

 the anodic oxidation of PVSO^ was examined. Here the limiting 

 current was not reached before 90 miV. In figure 5 the current 



potential lines of platinum in 

 chromous sulphate and ferrous- 

 sulphate have been drawn. 



When an electrode of copper 

 is anodically polarized in a 

 solution of KCl, a current 

 potential line is found, which, 

 as regards the first portion, 

 agrees pretty well with the 

 line for chromium precipitated 

 on copper. Hence it is pos- 

 sible that the first verti'cal 

 'part in the chromium line 

 Fig. 5. is caused by the going into 



solution of copper. 



That the metal on which the chromium has been electrolytically 

 precipitated, plays a part in anodic polarisation, appears from the 

 following observations. Chromium that has been deposited on silver, 

 presents about the same current potential line as chromium on copper. 



