403 



equilibrium, and the remarkable feature in the behaviour of nickel 

 is this that tiie influence of these negative catalysts is exceedingly 

 great. 



This is accompanied with something \ery remarkable, viz. this 

 that when hydrogen of e.g. 1 atm. is conducted through an NiSO^- 

 solution, in which Ni-electrodes stand, the metal through the deposition 

 of electrons -|- nickel-ions resp. through the going into solution of 

 these compeuents, is disturbed so far in base resp. noble direction 

 till the electron-concentration of the metal equilibrium in the liquid 

 has become equal to that of the hydrogen equilibrium in the 

 electrolyte. 



It can be demonstrated that in this case the potential difference 

 Of the nickel with respect to the electrolyte, with exception of the 

 Volta-effect, must become equal to the potential difference of the 

 hydrogen electrode. 



Experimentally it was found that under the circumstances given 

 here, practically equality of the two potential differences is found. 



The theoretical considerations led us further to expect that the 

 unary equilibrium potential for nickel was only to be expected in 

 the experiment in an atmosphere free from 0,- and H, or in vacuum, 

 and when an Ni-salt solution was used in which the H-ion 

 concentration is smaller than 10"^ for an Ni-ion concentration ofl. 



Experiments made in this direction gave as result — 0,480 V. 

 with respect to the In. calomel-electrode, a value that agrees entirely 

 with the value calculated by Wilsmore and also with that found 

 by ScHOCH in an experiment in vacuum. 



In the many potential measurements of the metal nickel which 

 ivei^e carried out in the air or in a hydrogen atmosphere, the equili- 

 brium potential of the unary nickel has not heeii measured, but the 

 potential of a state of this metal that was disturbed in base or in 

 noble direction. 



Amsterdam, June 29 1917. 



Lidioratory for Anorg. and General 

 Chemistry of the University. 



