1131 



that has been first activated by ZnCl^, becomes passive throiigii 

 HNO,. 



In the experiment the potential rose from — 0.65 to -|- 0.1. 

 After vigorous anodic polarisation the electrode had become active 

 again and presented a potential of — 0.49. 



When a piece of chromium is brought into hydrochloric acid, it 

 becomes active, and generates hydrogen. After it has been rinsed 

 and conveyed into a saturated KCl-solution the activity continues, 

 but is by no means so strong as the activity obtained in molten 

 ZnCl,, so. that the electrode already becomes passive e.g. at 1 mA. 

 When, however, the current is slowly made stronger, the activity 

 continues to exist. Thus a strength of current of 12 mA could be 

 reached for a potential of — 0.35 V in ten days. Here too it was 

 always observed that on increase of the strength of current the 

 potential first increased greatly, and diminished later again. The 

 electrode continually developed hydrogen, sometimes with a crackling 

 sound. The liquid contained a large quantity of chjomhydroxide 



and had become alcaline in conse- 

 quence of the cathodic formation 

 of NaOH. After breaking of the 

 current the electrode was active 

 — 0.66 V. When after 8 minutes 

 the current was suddenly brought 

 to 3 mA, the electrode became 

 passive. After interruption of the 

 current the activity returned. In 

 F'ig. 15 the passivation with 3 mA 

 and the activation after the current 

 had been broken off, is represented 

 as a function of the time. 

 When chromium of Goldschmidt, which had not been previously 

 activated, is anodically polarised in a saturate solution of KCl with 

 a current strength of J mA, it becomes passive. When we begin to 

 heat, activation sets in at a certain temperature. With a strength of 

 current of 1 mA this took place at about 60°. Then the potential 

 fell to — 0.55 V. When the temperature is lowered during passage of 

 the current, the electrode remains active, during which the potential rises 

 to — 0.4 V. With higher current strength the same behaviour is 

 found ; here the temperature at which activation occurs, lies higher, 

 for 25 mA e.g. at 75°. With lowering of the temperature the 

 electrode remains active in this case; the potentials found here, 

 are the more positive as the strength of the current is the greater. 



