1126 



hence 0.39 V ; at 5 mA it descends only 0.1 V, viz. from -j-103 

 to -\- 0.93 V. With these potentials formation of chromate takes 

 place. But also when the chromium goes into solution as chromous ion, 

 the activation is very apparent after interruption of the current. 

 Here e.^. the potential that is found according to Le Blanc, is for 

 10 mA about 0.1 V more negative than when measured with a 

 siphon. In the first case the current potential line up to J 8 mA has 

 the course of a normal line, in the second case the current potential 

 line proves that also the anodic solution in hydrochloric acid as 

 chromous ion is a reaction that proceeds slowly. 



In virtue of the difference found here between the current potential 

 line that is determined with a commutator and one that is determined 

 by means of a siphon, it might be imagined that the above described 

 activation by anodic polarisation takes only place during the moments 

 that the current is broken, hence only after, not during the polari- 

 sation. That activation takes place also JM?'my the anodic polarisation 

 ap|)ears from the experiments with chromium of Goldschmidt 

 described below. 



3. Anodic polarisation of chromium of Goldschmidt. 



The passivation and activation of chromium of Goldschmidt has 

 been closely examined by Hittorf, especially with regard to the 

 different factors that act in a passivating or activating way. It then 

 appeared, as was already said in the introduction of the preceding 

 paper, that oxidizers (HNO,, bromine water), like anodic polarisation, 

 make chromium passive. Cathodic polarisation on the other hand 

 makes chromium active. In the same way the hydrogen generation, 

 which chromium gives in active state in diluted acids (especially 

 HCl) is able to make the active state permanent. Chromium is also 

 made active by being placed in melted chlorides, (Zn CI,, KCl -|- NaCl). 

 Chlorine ions have a specific activating action, hence chromium is 

 more strongly active in hydrochloric acid than in sulphuric acid of 

 the same concentration. 



In the first place a quantitative comparison was then made between 

 the activating action of hydrochloric acid and sulphuric acid by 

 determination of the strength of the current required to make the 

 metal in these solutions passive. It then appeared that the current 

 strength required for passivation was about proportional to the 

 concentration of the acid, as figure 12 shows. The values found for 

 the current strength of passivation, are rather divergent; this causes 

 the points in figure 12 to lie rather scattered. 



It appears clearly from the lines found that hydrochloric acid 



