Theory of Elect i oca pillar it ij. 371 



between these two limits. Obviously in such a case 

 equation (2) cannot be verified by means of a dropping 

 electrode, and it would be advisable to use a slowly increasing 

 surface. 



Let us now consider the transition from equation (2) to 

 the classical equation (1). We shall admit that the change 

 of the potential difference solution / mercury caused by 

 surface increase, depends only on the change of the concen- 

 tration of mercury. This is not quite correct, as the value 

 of the potential difference may also be influenced by other 



dc 

 components of the solution, but as dyjr is proportional to - 



and the concentration of mercury in the solution is very 

 small as compared with the concentrations of oilier com- 

 ponents, we may neglect their influence. 



Let us suppose that there are M gram-equivalents of 

 mercury in the solution when s and E are zero ; if a quantity 



E 

 of electricity eqoal to E passes through the solution T \ eram- 



equivalents of mercury are removed from the solution ; 



likewise _ +1^ gram-equivalents are removed if the surface 



is increased by unity, where F Hg is the excess of mercury in 

 gr.eq. per cm. 2 of the dividing* surface ; where 



M-|-£(p+r Hg )* 



and (* E \ V w 



r^E 



On substituting this value of -^— in (2) we obtain 



OS 



ij=* +r ^ F ' w 



an equation which can be regarded as a generalized equation 

 of Krueoer. 



It is easy to show that the second term of the right-hand 

 side of equation (4) may sometimes be of importance. Let 

 us consider a drop of zinc amalgam immersed in a solution 

 of zinc sulphate. In the solution and in the surface-layer 



* The position of the dividing surface is chosen as to make r H zero. 



