1121 



The potential was at 5 mA A, descended on transition to 1 mA to 

 £, and tlien rose slowly to C. The lower line was found when the 

 current was rapidly changed from 5 mA to 0.1 mA. This line 

 exhibits the same course, but more pronounced. The course of the 

 lines in figure 3 can be accounted for by the assumption (hat the 

 anodic polarisation has two kinds of intluence on the potential. In 

 the first place the potential is much more positive than the end- 

 potential (hiring anodic polarisation ; in the second place the potential 

 is more negative than the end-potential after anodic polarisation. 

 There is, therefore, a passivating action, which manifests itself during 

 the polarisation, and there is at (he same time an activating action, 

 which shows itself after the polarisation. Both actions are the stronger 

 as the strength of the polarising current is the greater, as will be 

 more fully discussed later. 



When the current is broken after anodic polai-isation, the potential 

 descends to about — 0.8 V, then a sloiv rise to — 0.55 V takes 

 place again. 



This course is shown by 

 line I in figure 4. Here 

 the current was brought 

 from 5 mA to 0. 



In the same figure line 

 II gives the course of ihe 

 potential after cathodic po- 

 larisation with 5 mA. Here 

 the potential is very strongly 

 negative at first, after one 

 or two minutes the potential 

 has already risen to — 0.75 V, 

 and from this point the 

 line for cathodic polarisation 

 coincides about with that 

 for anodic polarisation. I.e. 

 through anodic polarisation 

 the potential is at first too positive, through cathodic polarisation 

 too negative, after a few minutes, however, (he condi(ion after 

 anodic and cathodic polarisation has become the same. 



As was already observed, it follows from line I in figure 1 that 

 two different reactions take place on anodic polarisation of chromium. 

 One at about +0.1 V, another at about -|- 0.7 V. The latter is 

 undoubtedly the anodic formation of chromate. What reaction takes 



