1124 



course of these lines is as follows: When the current 'is interrupted, 

 the chromium is still somewhat passive, the potential moves however 

 quickly to more negative values, and finally approaches a value of 

 about —0.5 V. 



The way in which this value of — 0.5 V is reached, is however 

 different for different strengths of current. For feeble anodic polari- 

 sation, 1 mA, the potential falls gradually from 0.0 V. At 5 mA 

 a faint minimum is reached, after which the line begins again to 

 ascend slowly. For 10 mA this minimum lies lower, for 20 and 

 50 mA still somewhat lower ( — ^0.75 Vj. For these last two lines 

 the rise following on the minimum, is much slower than for the 

 others. Hence it appears from this, that the activation of chromium 

 on silver is the stronger and the more prolonged as the strength of the 

 current, with which the anodic polarisation takes place, is the greater. 

 The same phenomenon is observed for chromium that has been 



precipitated on gold, but the 

 potentials are much more 

 positive here. In figure 8 

 these lines are drawn, which 

 indicate the course of the 

 potential with the time, when 

 the current is suddenly broken 

 off. Here too the potential 

 that is reached, lies at the 

 more negative values as the polarising current has been the stronger. 

 Hence it appears here, that activation 

 makes its appearance after anodic pola- 

 risation with chromium that has been ^ - 

 deposited on copper, silver, or gold. ©^ 



The potentials that are reached in 

 this, are most negative for the least 

 noble of these metals^). 



It was noticed in these experiments 

 that chromium on gold or on platinum, 

 after anodic polarisation, becomes less 

 active when it has been cathodically 

 polarised shortly before. Lines 1 and 

 2 in figure 9 give the potential after 



Fig. 9. 



the current has been interrupted, when the electrode had not been 



1) Rathert. Zeitschr. f. physik. Chemie 86, 567 (1914) observed the same 

 phenomenon for Gr that had been precipitated on Gu and on Pt. 



