[ 645 ] 



LX. On the Polarization at a Metallic Anode. By S. R. 

 Milner, D.Sc, Lecturer in Physics, University College, 

 Sheffield *, 



THE theory of the electromotive force of concentration- 

 cells developed by Nernst affords a simple explanation 

 of the polarization which results in cells or voltameters from 

 the pas-age of a current through them. In his Theoretische 

 Chemie, p. t>76. Nernst points out that the current will 

 produce alterations, either in the concentrations at the surfaces 

 oi the two electrodes of the metallic ions present in the 

 solution, or in that of the hydrogen or oxygen occluded in 

 the two electrodes. In either case a "concentration-cell" is 

 produced : its electromotive force, which is always in the 

 opposite direction to that which produces the polarizing 

 current, constitutes the polarization. 



AVhile this theory is in excellent qualitative agreement 

 with mo>t of what is known about polarization, so far as I am 

 aware no direct quantitative comparisons of the theory with 

 experiment have been carried out. Such a comparison is of 

 value since, in certain simplified types of cells, the polarization 

 is calculable on the theory entirely in terms of known 

 quantities, so that a comparison of absolute values is possible. 

 It i- also of interest that the mathematical development of 

 the theory leads to a simple expression, which may be 

 experimentally tested, for the polarizations produced not 

 only by a constant current, but by any arbitrarily varied 

 current however complex ; in other words, for the polarizations 

 as dependent on the whole previous history of the cell with 

 regard to the current which has passed through it. The 

 calculation of the polarization developed in a certain type of 

 cell by an arbitrarily varied current, and a comparison of the 

 results with those of experiment, form the subject of the 

 present communication. 



The kind of cell considered is one in which the anode 

 (A. fig. i. p. 646) is a metal plate surrounded by a vertical glass 

 tube of the same sectional area as the plate, and immersed in 

 a solution which contains the metal ion-. For the sake of 

 definiteness suppose the plate to be silvcr,and the solution to 

 consist of nitric acid containing a very small quantity of 

 silver nitrate mixed with it. The cathode C is a large silver 

 plate suspended in a similar solution in another beaker, the 

 solution in the two beakers being connected by a siphon. 

 Th«' observed polarization of such a cell when a current is 

 i through it from A to C may be looked upon as being 



* Communicated by the Author. 



