1111 



phase equilibrium will be indicated by the point m, so that the 

 three-phase polential coincides with the potential of the hydrogen 

 electrode, as was already demonstrated before. 



Now it is perfectly clear from the considerations given here that 

 we are not justified in saying that when the hydrogen generates at 

 a metal of a potential which is baser than that of the hydrogen 

 electrode, the hydrogen presents the phenomenon of supertension. 

 F'ig. 2 e.g. refers to this case, here the generated hydrogen shows 

 no supertension, because the liquid lies in the boundary layer on 

 the line he. The point c' lies, indeed, above iii, but this is only 

 owing to tiiis that in consequence of the solution of the metal, the 

 concentration of the liquid, in the boundary layei', is different tVom 

 that outside it. 



In the cases represented by figures 1 and 3 the hydrogen presents 

 supertension, but this supertension is not equal to the potential dif- 

 ference between the potential of the generating hydrogen and the 

 hydrogen electrode, for in order to get to know the supertension it 

 would be necessary to have the hydrogen electrode also in the 

 boundary layer of the dissolving metal. 



The real supertension can be read from the figures 1 and 3 men- 

 tioned, it is not the distance from the point ni to the horizontal 

 line il'e', but equal to the distance in'c'. 



Laboratory of Anorg. and General Chemistry 

 of the University. 



Amsterdam, January 20^^, 1919. 



72 



Proceedings Royal Acad. Arasterdam. Vol. XXI. 



