408 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and after standing and shaking, unless indeed it be due to the formation 

 there of some new substance. 



When we compare series of experiments conducted on different days 

 and at different temperatures, ranging from 20° to 40°, we find that all 

 give curves similar in every respect to the one shown in Figure 2. In 

 every case the points obtained on the way up to the maximum potential 

 lie on a straight line, while those obtained on the way down form an 

 irregular curve lying above the line. Let us confine our attention to the 

 former points and consider the theoretic grounds upon which the loga- 

 rithmic formula is based. They are briefly as follows : 



We assume that all true polarization (excepting the apparent polariz- 

 ation caused by an electric resistance at the electrode) is due to a counter- 

 electromotive force caused either by the exhaustion of the substances 

 used in the electrolytic reaction faster than they can be replaced, or by 

 the accumulation of the products of this reaction faster than they can be 

 removed. The degree of polarization is therefore a measure of the 

 slowness of some irreversible process or processes, these being either 

 processes of diffusion to or from the field of action (situated at or near 

 the electrode surface), or chemical processes which supply the factors or 

 destroy the products of the electrolytic action. From this point of view, 

 the potential of the electrode, when the current is passing, differs from 

 that of the unpolarized electrode by the potential of a concentration cell. 

 From the Nernst equation, therefore, we are able to write for the poten- 

 tial of an electrode through which a current is passing the equation, 



_i_ _i_ 



E = —=- In \ " / " + constant, (2) 



Where c x ', c 2 ', etc., represent the concentrations of the factors, c x , etc., 

 those of the products of the electrolytic reaction, n x ', etc., and n u etc., are 

 whole numbers, each of which represents the number of gram-equivalents 

 in a gram-molecule of the substauce in question. 



Let us assume as a special case that the polarization is due solely to 

 the accumulation of the products of the reaction. Let us further assume 

 as a more special case that the polarization is due to the accumulation of 

 only one of the products, and that the process by which this product is 

 removed is a chemical one, obeying the law of Guldberg and Waage. 

 Accordingly, equation (1) becomes 



7? T i 

 J3=y-lnc&, (3) 



