261 



acid solution, and the palladium was and remained in inner 

 equilibrium, this metal would dissolve a little, till tlie palladium 

 concentration of JO^x ^*-^ was readied, while a corres|)ondiiig in- 

 appreciable quantity of hydrogen would have been generated. In 

 this it is assumed that both platinum and hydrogen continue to be 

 in inner equilibrium, for the value used for Ljj, agrees with the value 

 for hydrogen in inner equilibrium, and we shall for the moment 

 assume the value used for Lpj also to agree with the condition of 

 inner equilibrium of Pel. Pd is, howevei-, an inert metal, so that 

 the solubility product of this metal will in reality have decreased 

 through the slight attack, and the dissolving will have already stopped, 

 before the palladium ion concentration lO^x 15.2 [i^g been reached '). 

 For the sake of simplicity we shall, however, assume here that 

 no disturbance of the Pd takes place, and that Ihe three-phase 

 equilibrium is established, in which the iV-phase e coexists with the 

 electrolyte c and wilh the hydrogen phase J at a piessure of one 

 atmosphere. When now the PJ-electrode is made cathode, or in 

 other words, when electfons are added to the Pd, hydrogen and 

 palladium ions in the ratio of 1 ; iO'^-x.—^^'^ or practically only 

 hydrogen ions will be separated at this electrode. It will now depend 

 on the velocity with which the inner equilibrium 



sets in, if the hydrogen formed will coexist in a slate of internal 

 equilibrium or in a state of formation. In this condition the solubi- 

 lityproduct of the hydrogen is greater, and the point that now 

 denotes the coexisting hydrogen phase, will lie on a potential curve 

 that lies at more negative values, and is represented by a'g' in fig. 2. 

 We must, however, not forget that this line could only be realised 

 when the state of formation of the hydi'ogen discussed just now could 

 coexist unchanged in electro-motive equilibrium with a series of solutions. 

 This is, however, not the case; only one point can be realised on 

 this curve, and this is the point indicating the liquid layer that 

 coexists with the hydrogen phase d', which is in a state of formation, 

 and with the palladium phase e'. The heterogeneous equilibrium 

 between the metal boundary layer and the hydrogen boundary layer, 

 just as that with the liquid boundary layer, having been immediately 

 established, the palladium boundary layer will also contain too many 

 hydrogen ions and electrons, which means that also the hydrogen 

 dissolved in this metal boundary layer, will be in a state of formation. 



1) The potential + 0.82 V., from which the solubility product Lpd = 10^ ^ ""^^^ 

 has been calculated, is most probably already a potential of a disturbed state of 

 the metal palladium. 



