820 



in a solution of chromous sulphate, electrolytical chromium presents 

 an almost constant potential of — 0,55 V., lohen the metal has been 

 in contact with the solution for some days. For shortness we shall 

 call this potential the end potential. 



Bj anodic or cathodic polarisation the potential of the chromium 

 can be temporarily modified. When then the metal in the solution 

 is left to itself, the potential returns to — 0,55, as appears from table III. 



TABLE III. 



3 and 5 had been anodieally polarized, 4 and 6 cathodicallj, 

 with 7 m.A. for 40 sec. It appears that electrolytic chromium is 

 activated not only by cathodic, but also by anodic polarisation. In 

 this, however, the metal is more positive immediately after the 

 breaking of the current than at first, and then falls rapidly to a 

 negative value. 



When the electrodes are subjected to different previous treatments, 

 they have at first different potentials, which, however, approach to 



— 0,55 again after some days. 



Four chromium electrodes which had been in contact with a 

 solution of CrSO« for a week, and which had then been exposed 

 to the air for a quarter of an hour, immediately gave potentials of 



— 0,54 to — 0,55, when brought into a new solution of CrSO^, which 

 potentials remained constant in further observations. 



Four other electrodes, which had been chromated electrolytically, 

 the same day and had been exposed to the air for some hours, 

 gave at tlrst potentials of — 0,27 to —0,53. After ten days they had 

 become constant and amounted to from — 0,55 to — 0,57. 



Four newly chromated electrodes were cathodically polarized in 

 sodium hydroxide. In CrSO^ they at first presented potentials of 



— 0,70 to —0,75, after ten days 'of —0,55 to —0,57. 



Four electrodes of electrolytic chromium, which had been in 

 diluted bromine water for some hours, gave — 0,65 to — 0,76 in 

 chromous sulphate. After ten days from - 0,55 to — 0,56. 



One would be inclined to consider this final potential, which 



