1132 



O) ■» ^ ^ 



temperature. 



If this is too great, e.g. 50 inA, the electrode becomes passive on 

 cooling. 



Figure 16 gives the course 

 of the potential as function 

 of the temperature on heating 

 and cooling of a chromium 

 electrode, when this is ano- 

 dically polarized with 1 mA 

 and 25 mA. 



After the current had been 

 broken, the potential was very 

 active, at 1 mA —0.60 V, 

 at 50 mA - 0.66 V. 



When the electrode has 

 remained active after cooling 

 ~' ~ "^ during the anodic polarisation, 



Fig- 16. and the current is broken, 



a very active potential is found. When after a short time e.g. after 

 20 sec. the current is closed again, the electrode cannot bear this 

 current, but becomes passive, in harmony with this is the phenomenon 

 that a chromium electrode which has become active through heating 

 in a solution of KCl, on anodic polarisation, and is cooled then 

 after the current has been broken, preserves indeed an active 

 potential, but can resist only a very feeble anodic current without 

 becoming passive. 



Finally the influence of molecular hydrogen and of hydrogen that 

 had been generated cathodically on the passifiability of chromium 

 was examined. Molecular hydrogen has no influence here, as was 

 already known from earlier researches. When a chromium electrode 

 is brought in an atmosphere of hydrogen in a saturate KCl-solution, 

 the chromium gets a potential of about — 0.5 V, a platinum-electrode 

 presenting — 0.68 V under the same circumstances. The chromium 

 is, therefore, not able to assume the hydrogen potential. When the 

 chromium is cathodically polarized, so that hydrogen is vigorously 

 generated, the metal at first shows a strongly negative potential, 

 which is the consequence of the acquired hydrogen charge. The 

 chromium pretty soon loses this hydrogen charge, at which the 

 potential gradually rises to — 0.5 V. Both before and after cathodic 

 polarisation, this electrode became passive on anodic polarisation 

 with 0.2 mA. Accordingly the cathodic polarisation had not been 

 able to activate the electrode perceptibly. This electrode did become 

 active when brought in strong hydrochloric acid. Now the potential 



