149 



the hydrogen ion concenhation was JO •'', tliere has been formed 

 0.003 mgr. aeq. of hydrogen ions, 3 niF iiaving gone through 

 the solution. Hence the ciironiiuin would have to contain 0.1 '/, 

 hydrogen in order to give the above mentioned degree of acidity to 

 the solution. In reality this must be slightly more, because part of 

 the OH ions has moved from the cathode space to the anode space, 

 and has, therefore, partly neutralized the acid formed. 



It also appeared in these experiments that the potential which the 

 chromium electrode presents, is really a chromium potential, or at 

 least no hydrogen potential. In the acid solution the potential was 

 namely — 0.59 V. When the solution was then made feebly alcalic, 

 the potential rose to ^0.58 V, whereas a hydrogen electrode in 

 the same liqnids would have to present a decrease of about 0.2 V. 

 In this and in other experiments the chromium developed liydrogen. 

 This cannot be hydrogen that the chrominm developed spontaneously 

 from the liquid, for in this case the potential of the chromium 

 electrode would have to be more negative than that of a hydrogen 

 electrode in the same liquid. This was not the case hei-e ; the 

 potential of the hydrogen electrode was — 0.58, that of the chi'omium 

 electrode — 0.52. Besides the hydrogen generation took just as well 

 place in a feebly alcalic solution as in a feebly acid solution, 

 whereas the [)Olential of the chromium electrode was often pretty 

 much more positive than —0.52 V. It is possible that the chromium 

 contains more hydrogen than dissolves anodically, and that part of 

 it escapes in gaseous form. 



Hence it must be assumed that the examined chromium always 

 contained hydrogen. In the case of electrolytic chromium this has 

 been sepai'ated at the same time with the chromium in a considei-- 

 able quantity, whereas the chromium of Goldschmidt contains a 

 slight quantity. By treatment with molten KCI -f- NaCl oi* ZnCI, 

 the chromium can absorb more hydrogen in consequence of (he 

 decomposition of the water present in it by (he chromium. On the 

 action of chromium on these molten salts development of a com- 

 bustible gas and formation of chromium oxide was always observed. 

 That ZnOI, activates more strongly than KCI -)- NaCI could be ex- 

 plained by this, that the hygroscopic ZnCI.^ contained more watei", 

 and can, therefore, vield more hydrogen. The activity' which chi'omium 

 obtains by treatment with hydrochloric acid and by increase of 

 temperature must, however, chiefly or exclusively be attributed to 

 the hydrogen which is naturally present in the metal. 



With regard to the hydrogen generation at chromium during the 

 anodic polarization it should still be pointed out that this ceases 



