705 



need not necessarily abvays be valid, and here loo exceptions may 

 be expected, when viz. the nietastal)le and stable solid phases dilfer 

 only little in concentration. 



5. We have discussed the phenomenon of electrolysis here on 

 the sup[)Osition that the internal equilibrium in both phases sets in 

 with so great a velocity that at any moment internal equilibrium 

 prevails, but this is a limiting case, and it is certain that the setting 

 in of the internal equilibrium at least at the ordinary temperature, 

 requires an appreciable space of time. It is therefore of importance 

 to ascertain what the phenomena will be when (he setting in of the 

 internal equilibrium cannot keep pace with the changes of concen- 

 tration caused by the electrolytic process. 



For this purpose it is simplest first of all to assume the other 

 limiting case, viz. that the internal transformations are ^/i^/r^-A/ wanting 

 during the experiment. We think two rods of the same metal .1/, 

 which have somehow assumed internal equilibrium at the temperature 

 and the pressure for which Fig, 1 holds. These rods are used as 

 electrodes, and placed in some salt solution of the same metal, and 

 of a concentration, for which Fig. 1 also holds. Suppose internal 

 equilibriuui also to exist in the solution, then both metal electrodes 

 are in electromotive equilibrium with the solution and the coexisting 

 phases are indicated in Fig. 1 by the points S and L. Then we 

 think a negative catalyst to be added, after which there can be no 

 question any more of the setting in of internal equilibrium. 



Fig. 2 represents the potential differences, which exist between 

 the two electrodes and the electrolvte. The distance c/> = rAnndicates 



cc L 





n 



■/ 



V\% 2. 



the |)otential of the solution with respect to the metal electrodes. 

 So the situation of cd agrees with the potential of the electrolyte, 

 and that of the lines ab and e./ with the potentials of the two metal 

 electrodes 1 and II. So the potential of the electrolyte is here positive 

 with respect to that of the metal electrodes. 



Let us now connect the two metal electrodes with the poles of a 

 battery ; let us put 1 to be the positive, and II the negative pole, 

 then electrode 1 ^vill be dissolved, whereas metal fi'om the elecli-olyle 

 deposits on the electrode II. If we again imagine ihe total metal ion 



