266 Dr. 0. R. A. Wright on the Determination of 



direct E.M.F.), and decreases in magnitude with the rate of 

 current-flow. 



This decrease in magnitude, although a phenomenon well 

 known under the name of "polarization of the cell," has never- 

 theless been less thoroughly investigated than is desirable. 

 Thus, for instance, in the case of a given Daniell cell it is un- 

 known to what relative extents the diminution is due to each 

 of three entirely different possible causes, viz.: — first, the for- 

 mation, in consequence of the electrolytic actions going on, of 

 a stronger zinc-sulphate solution round the zinc plate, and of a 

 weaker copper-sulphate solution round the copper plate, than 

 were there originally ; secondly, the more or less incomplete 

 action as regards setting up E.M.F. of the energy gained by 

 the solution of the zinc, and displacement thereby of copper 

 from the copper-sulphate solution; and, thirdly, the somewhat 

 analogous want of completeness in transformation into E.M.F. 

 (and quantity of electricity jointly) of the energy gained by 

 the transformation into ordinary copper of the nascent metal 

 thus set free. In order to refer briefly to this possible want 

 of completeness in development of E.M.F., it will be conve- 

 nient to term that portion of the energy due to the various 

 actions taking place in the cell that does contribute to the 

 setting-up of difference of potential, the "adjuvant " portion of 

 this energy; whilst the remainder is spoken of as the "non- 

 adjuvant " energy. Of course the non-adjuvant energy in 

 practice makes its appearance in the form of heat developed 

 ah initio, and not in accordance with Joule's law — i. e. not due 

 simply to the passage of a current through a resistance. 



As regards the possible non-adjuvancy of energy thus indi- 

 cated, it is to be noticed that whilst the observations of nume- 

 rous experimenters agree in showing that, under certain con- 

 ditions, at least an approximate equality subsists between the 

 electromotive forces actually developed in a Daniell cell, and 

 in various analogously constructed cells, and those corre- 

 sponding to the net chemical changes taking place therein 

 (viz., in the case of a Daniell cell, the displacement of copper 

 from copper sulphate by zinc), this approximate equality 

 does not exist under all conditions even in a Daniell cell, inas- 

 much as, first, considerable discrepancies exist between the 

 values obtained by different observers working under different 

 conditions, and, secondly, the same cell exhibits values vary- 

 ing with the rate of current-flow through so-called " polari- 

 zation;" whilst, on the other hand, with certain forms of cell 

 the maximum E.M.F. developed falls considerably short of 

 that corresponding to the net chemical action. These discre- 

 pancies and amounts of falling short appear to be in certain 

 cases considerably greater than can be accounted for by the 



