Theory of Galvanic Polarization. 429 



the distance between neighbouring particles. But when we 



compare two points on opposite sides at distances from it 



great compared with this latter distance, it is immaterial 



whether the distribution is supposed to be in isolated points or 



uniformly spread over the surfaces. Therefore, as regards 



points not in the immediate molecular neighbourhood of the 



electrode, the effect of this polarization is still to produce 



simply a difference of potential on the two sides, which is just 



the same as if the charges were uniformly spread over the 



surfaces at the actual distance apart. 



These considerations, then, give a reason for the fact which 



is brought out by the table given above, deduced from Lipp- 



mann's experiments with the capillary electrometer, and also 



independently by Helmholtz from direct measurement of the 



capacity of platinum electrodes in fluid with no dissolved gas 



(which would disturb the action); viz. that the polarization 



capacity is constant for all values of the applied electromotive 



force up to limits of considerable magnitude. 



6. In order to form an estimate of the nearness of the 



neighbouring molecules on a face of the double sheet when 



they begin to exert an influence on one another comparable 



with that exerted by the opposite charges, we must assign a 



limit to the interval of potentials within which the capacity 



remains constant. The table in § 4 shows that we shall attain 



the correct order of magnitude by taking it to be, say, 1 volt 



in the case there considered. 



We may now make the following calculation, bearing in 



mind that the sign = is to be interpreted as meaning that 



the quantities are of the same order of magnitude. 



Let t be the thickness of dielectric layer ; 



d the distance between neighbouring atoms when their 



effective mutual action becomes comparable to that 



between opposed atoms (the important part of this 



action being that between any atom and the 



neighbours of its opposed charge) ; 



tf the mean molecular distance in the electrolyte ; 



e the constant aggregate charge of a single atom or 



radical ; 



so that 



^- 3 ^ = the electro- chemical equivalent of 1 cubic centim. 



of water, 



10 5 

 = -q- coulombs, approximately, 



10 5 

 = -q- x 3 . 10 9 electrostatic C.G.S. units, 



and d~ e = surface density. 



