400 



tration of the hydrogen equilibrium is smaller than that of the 

 nickel equilibrium. We shall, therefore, have to make the H-ion 

 concentration as small as possible by the addition of a base. In this 

 case a few nickel ions and electrons will go into solution, and, no 

 hydrogen separating on the metal, the internal equilibrium can set 

 in. In the determination of the equilibrium potential, however, we 

 may have no hydrogen atmosphere, for hydrogen of a pressure of 

 1 atmosphere would render the electron concentration of the hydrogen 

 equilibrium too large. Nor may we have an oxygen atmosphere, 

 because when there is oxygen present in the solution, the equilibrium 



0, -^ 2i7,0 + 4 6*^4 0//' 

 exists, in which case the electron concentration is much smaller than 

 would correspond with the unary nickel equilibrium. The conse- 

 quence is then that electrons are withdrawn from the nickel equi- 

 librium, and the nickel sends ions and electrons into solution. The 

 nickel is therefore attacked, and it results from the inertia of the 

 nickel, together with the negative catalytical action of the dissolved 

 oxygen that this disturbance is not negatived, and the nickel is super- 

 licially in such an ennobled condition that the corresponding electron 

 concentration is in agreement with the electron concentration of 

 the oxygen equilibrium. Accordingly the potential of Ni with respect 

 to a nickel salt solution measured in contact with the air, lies at a 

 much less negative value than would correspond with the equilibrium 

 potential. 



It is therefore cleiw that to jind the unary equilibrium potential 

 of nickel, ive shall have to loork in 'a solution, in which for 

 (Ni") = 1 the H-ion concentration is <^ 10~-^, and in an atmos- 

 phere free from H^ and 0^ or in vacuum. 



Thus we really easily find the unary equilibrium potential. 



ScHOCH ') and in imitation of him later on Schildbach ") are the 

 only investigators who as far as we know, have also worked in 

 vacuum. They have, however, not succeeded in finding the true 

 explanation of the disturbing influence of H, and 0,. 



In a determination of the equilibrium potential in a IN. NiSO^- 

 solution boiled out in vacuum, the following values were found: 



Potential — 0.453 V — 0.477 V — 0.480 V — 0.480 V 



of the nickel: after 4 hours after 47 h. after 52 h. after 70 h. 



Then hydrogen was led through the same solution, and the H,- 

 potential was measured. After 48 hours we found : 



^) loc. cit. 



3) Z. f. Electr. Chera. 22 [1910J 977. 



