263 



potential of the dissolved iiydrogen in e' is more strongly negative, 

 and the same must, tlierefore, hold for the Pd. It is now, however, 

 the question in what way the potential of tlie palladium has under- 

 gone this change. 



It is clear that the Pd must have become richer in P(/-ions and 

 electrons. We have already seen that this phase has become richer 

 in electrons through addition of hydrogen in a state of formation, 

 so that only the question is still to be answered how the 

 concenlration of the A/-ions can have been increased. This must 

 have taken place through the reaction 



2H's + Pds -^ Pds + 2Hs 



in which, therefore, hydrogen ions have ceded their charge to 

 Pd-Siioms. We, therefore, come to the conclusion that the palladium 

 boundary layer, which coexists with hydrogen in a state of formation, 

 will possess too many hydrogen ions, palladium ions and electrons, 

 or in other words, that it will contain both hydrogen and palladium 

 in a state of formation. 



If palladium could coexist in the same state of formation with a l.N. 

 solution of a palladium salt, the electric potential would, of course, 

 possess a more strongly negative value than corresponds to point b in 

 fig. 2. This more strongly negative potential is indicated by b'. 

 And when, therefore, the same state of formation of /\/ could continue 

 to exist also in contact with the whole series of solutions, the line 

 b'e' would indicate the solid solutions which can coexist with the 

 electrolytes lying on the line h'c'. The new three-phase equilibrium 

 that is found when P;/ is made cathode at a definite density of current, 

 and in which hydrogen escapes in a state of formation, is denoted 

 by the points d'c'e'. The line a' c' g' rising very little throughout 

 the greater part of the concentration region, it is clear that the 

 value of the negative potential in this new three-phase equilibrium 

 would be equally great when the point c' lay on the prolongation 

 of the line be, and the point e on the prolongation of the line be, 

 but as we demonstrated above, the points c' and e' belong to other 

 lines than those that are mentioned here. It follows from these 

 considerations that in the case of electrolytic generation of hydrogen 

 the state of formation of the hydi'Ogen in the coexisting hydrogen and 

 palladium phases are very closely related. This makes it clear that 

 the cathode metal can exert influence on the degree of super-tension. 

 The state of formation is a state of non-equilibriun), and the differ- 

 ent cathode metals will, to a different degree, accelerate the con- 

 version of this state of noneqiiilibrinm in the direction of the inner 



