171 



and tlie three-phase eqnilibriiim, which therefore finally is established, 

 is here indicated by the points d' c' e' . Accordingly also in this case 

 the potential difference of the nickel electrode is equal to that 

 of the hydrogen electrode. 



When we now consider the metals of which the nnat- 

 tackable electrodes consist, we need oidy remark that because as 

 was just now demonstrated, these metals are ideally inert, the 

 potential difference metal-electrolyte is in almost all cases exclusively 

 determined by the electron-concentration in the electrolyte. Hence, 

 when e.g. a platinum electrode is immersed in an electrolyte through 

 which hydrogen is led, the platinum shows the hydrogen potential 

 almost immediately, which was the case for nickel only after some 

 time had passed. When we want to express this graphically in a 

 A, A'-fig., we get, of course exactly the same representation as for 

 the case nickel-hydrogen. 



That in aqueous solutions we cannot determine the equilibrium 

 potential of platinum, whereas this is still possible for nickel is 

 owing to this that the electrolyte c has such an one-sided situation 

 for platinum-hydrogen, that an aqueous solution of a platinum salt 

 always possesses a concentration on the riglithand side of the point 

 c as regards the platinum and the hydrogen ions, so that a disturb- 

 ance must always take place. 



In a subsequent communication I hope to enter into a fuller 

 discussion of the phenomenon of the "super-tension", which has 

 already been repeatedly referred to in our considerations without 

 having been named. 



Amsterdam, March 1918. General Anory. Chemical Laboratory 



of the University. 



