689 



Crelectrode in 100 cm3 i/io norm. CrCI^-solution. 



Observations 



Potential of the Cr-electrode with 

 respect to Vio norm. Calomelelectrode 



Initial state with active chromium ') 

 with 3 drops of Br-water 



with 1 cm3 of Br-water 



with 2 cm3 of Br-water 



with I cm3 of N. KBr solution 



— 0,26 V 



— 0,08 „ 



then slowly descends to 



— 0,24 V 

 + 0,62 „ 



rises in a few minutes to 

 + 0,79 V 

 + 0,79 „ 

 + 0,78 „ 



Then the preceding experiment was repeated with a solution of 

 Cr (NOjj witi) the following result : 



Observations 



Potential of the Cr-electrode with 

 respect to '/loNorm. Calomelelectrode 



In the first place we see from this that the chromium electrode 

 undergoes an exceedingly strong enobling, in which the metal beco- 

 mes passive, as could be demonstrated. By 1 cm\ of bromine water 

 the potential rises more than 1 Volt. Further we see that addition 

 of KBr has no influence on the Cr-potential, which proves both 

 that chromium does not behave here as bromine electrode, and 

 that Br'-ions do not exert a catalytic influence on the setting in of 

 the metal equilibrium. The metals Co, Al gave a smaller rise of the 

 potential when attacked by Bromine. 



We shall revert to this behaviour later on. 



^) The commercial chromium is passive, and can as Hittorf states, be activated 

 by heating with strong HGl. Z. f. phys. Ghem. 25, 729 (1898) and 30, 481 (1889), 



