169 



only a trace of hydrogen, so that the found potential difiference will 

 practically very certainly agree with that of the purely unary metal. 

 It is supposed here that the potential ditference between nickel 

 and the nickelsalt solution with the exceedingly small hydrogen-ion- 

 concentration, is measured after the electrolyte has been heated with 

 the nickel electrode in vacuum, after the whole apparatus has been 



JA=0 



Fig. 4. 



tilled with the electrolyte and connected with the 1 N. Calomel 

 electrode by means of a siphon and a liquid circuit, so that the 

 pressure umier which the electrolyte is, amounts to 1 atm. also in 



this case. 



An entirely different result is obtained when the foregoing measure- 

 ment does not take place in vacuum, but in a hydrogen current. 



In this case the nickel electrode is disturbed, but the disturbance 

 does not take place now in a noble direction, but in a base direction, 

 and as we showed before the potential ditference of the nickel has 

 again become equal to that of the hydrogen-electrode. This result 

 can again be bi-ought to expression in an exceedingly simple way 

 by means of a A,A'-rig. 4. 



