Chemistry. — ''The Phenomenon Electrical Supertension" . II. By 

 Prof. A. Smits. (Conmmnicated by Prof. P. ZeeiMan). 



(Communicated in the meeting of Jan. 25, 1919). 



In the first coinmnriication on the phenomenon of electrical siipei- 

 tension the snpertension of the hydrogen etc. has been considered 

 which appears at nnattackable electrodes on the passage of an 

 electric cnrrent. Now we shall discnss the phenomenon of snper- 

 tension at the generation of hydrogen, whicii occurs when metals 

 act on water, or on solutions of acids without the aid of an electric 

 cnrrent, i.e. without entrance of electrons from outside. 



In the discussion of the hydrogen generation on immersion of 

 zinc in an acid zinc salt solution the adjoined figure 1 led us to 

 make the following remarks. 



When zinc (37") is placed in a liquid of the concentration x^, 

 the zinc can be electromotively in equilibrium with this solution, 

 but only metastable, at an electrical potential indicated by the dotted 

 line gf. 



In this case no hydrogen-generation should, however, take place. 



The metal zinc does acl, however, on the here supposed liquid, 

 and hydrogen is generated, whicli gives lise to a three-phase equili- 

 brium, consisting of a hydrogen-containing metal phase, a hydrogen 

 phase, and the electrolyte, in whicli we should bear in mind that 

 by. what is here indicated as electrolyte, the liquid phase in the 

 houndarif layer is meant. On action of the metal on the electrolyte 

 the concentration of the liquid in the boundary layer will differ 

 from that of the liquid outside the boundary layer. 



In consequence of the reactions 



m,^m;- + Ws 



\ \ \ 



Mz-»M/; +2ÖA 



\ 



\ \ \ 



26'a + 2HG-^H,c; 



the liquid in the boundary layer will be j)Oorer in hydrogen-ions 

 and richer in zinc-ions than the electrolyte outside the boundary 

 layer. 



