17-1 Dr. G. R. A. Wright on the Determination of 



58. Very many experiments have been made during the last 

 thirty or forty years on the values of e under varying condi- 

 tions, on a somewhat closely allied thing, viz. the E.M.F. 

 existent between the electrodes of an electrolytic cell after 

 rupture of the current*, and on the E.M.F. of gas-batteries 

 (and especially those with hydrogen and oxygen as gases) |. 

 From these researches it results that, other things being equal, 

 the counter E.M.F. set up during electrolysis increases with 

 the current-strength as the size of the electrodes is diminished 

 and as the temperature is lowered, at least within certain limits. 

 The observations made have almost invariably been performed 

 with currents of moderate or considerable magnitude ; with 

 such currents in no case has a value for e been obtained less 

 than the E.M.F. corresponding to the decomposition into the 

 final products, whilst with powerful currents much largei\values 

 have been obtained : thus with water, all values of e registered 

 lie above 1*50 volt, and sometimes exceed 3 volts (when reduced 

 to that unit). Certain experiments of Andrews (Phil. Mag. 

 [3] x. p. 433), and Buff {Ann. Chem. Pharm, xciv. p. 1), made 

 by decomposing water with a feeble battery-power (less than 

 1*50 volt), appear, however, to show that a less value for e 

 may exist when a very minute current only is employed, in 

 which case simultaneous evolution of hydrogen and oxygen 

 does not take place ; if the one or the other be prevented from 



parallel to CDF, cutting A F in H. Then B F represents r, and B H 

 represents K. And by similar triangles, 



or 



2(E) _2(E)-E_ 2(E)-e_E_E- 



■e e 



2(E) +r 2(E) 2(E) +E r E r-R 



* The term " polarization " is sometimes applied to mean the counter 

 E.M.F. of an electrolytic cell e as above defined, sometimes the E.M.F. 

 set up between the electrodes after the current has ceased to How (a quan- 

 tity always less than the value of e existent whilst the current passes), 

 and sometimes (perhaps most frequently of all in a vague undefined sense), 

 to express the fact that something or other takes place tending to diminish 

 the current : thus the silver plate of a Smee's cell is said to become " pola- 

 rized."' In the subsequent parts of this paper the terms " counter E.M.F. 

 of an electrolytic cell " and a subsequent polarization " respectively are 

 used to indicate the first two of these meanings. 



t At the request of the Publication Committee of the Physical Society 

 a discussion of the results obtained by many previous observers bearing in 

 these directions is omitted, together with the numerous references to their 

 work. The best resume of this work that the writer is acquainted with 

 is in Wiedemann's Lehre vom Galvanismus, which, however, does not in- 

 clude a considerable number of researches published within the last few 

 years. 



