822 



For chromium out of chromium chloride these values were 5 7o> 

 76% and 20 7o- The mean of all the observations lies at — 0.75 V 

 for the first kind of chromium, at —0.71 V for the second. 



This potential is not only presented by the electrodes when they 

 are brought in fresh condition into CrSO^, but also when after the 

 end potential has been reached, they are polarized cathodically or 

 anodically in chromoussulphate, or cathodically in sodium hydroxide 

 or are treated with bromine water, or are brought once more in an 

 acid solution of CrSO^. 



The above mentioned operations have as result a renewal of the 

 chromium surface. In case of anodic polarisation and treatment with 

 bromine water hydrogen could also be withdrawn from the metal. 

 In case of cathodic polarisation in CrSO^, and action of diluted 

 acids hydrogen can also be added to the metal. Only the cathodic 

 polarisation in sodium hydroxide does not give a renewal of the 

 surface, but only hydrogen charge. 



In this last case the negative potential, w^hich the metal takes, 

 might be ascribed to a strong hydrogen charge, in which then the 

 hydrogen, not the chromium, was electro-motively active. In the 

 same way the negative potential which electrolytic chromium gets 

 on renewal of the surface, might be the hydrogen potential of the 

 hydrogen [)resent in electrolytic chromium. In contact with the liquid 

 this chromium might lose its hydrogen, till the hydrogen pressure 

 corresponds with one atmosphere, in which the potential might rise 

 to — 0,53. Against this view, that the potential of about — 0,75 V 

 is the potential of hydrogen which has been dissolved in the metal 

 under a high pressure, different objections may be advanced, how- 

 ever. In the first place it would then be strange that the electrodes 

 after anodic polarisation, in which hydrogen is withdrawn from the 

 metal, present the same potential as after cathodic polarisation, in 

 which hydrogen is added. 



A greater difficulty is, however, this, that a piece of chromium 

 of GoLDscHMiDT in hydrochloric acid spontaneously generates hydrogen 

 at a potential of about — 0,75 V. In this there is no question of a 

 hydrogen charge which the metal gets through external influences, 

 but the metal itself is able to generate hydrogen at this potential. 

 The potential of chromium itself must, therefore, be — 0.75 V or 

 higher negative here. In hydrochloric acid the potential can still be 

 considerably more negative. In 25 "/o hydrochloric acid — 0,84 was 

 found, in 6 7, —0,76, in 1,5 7„ —0,74. 



In general a metal, that generates hydrogen out of an acid, will 

 present a potential lying between that of the metal itself and of a 



