Chemical Affinity in Terms of Electromotive Force. 173 



wise) the two quantities, conclusions may be drawn as to the 

 general nature of the phenomena connected with the " nascent 

 state." If the difference of potential between the electrodes 

 of an electrolytic cell be E, during the passage of a quantity 

 of electricity Q sufficient to decompose a gramme of electro- 

 lyte in a time t (thereby giving rise to a current C = — ) a 







total amount of workEQ = EC* is done, of which C 2 R£ = CQR 

 represents the work done as heat due to the resistance of the 

 cell R (Joule's law, Part I. §§ 1 & 2); consequently an 

 amount EQ — C 2 Ri = (E — CR)Q of work is done in decompo- 

 sing the electrolyte into the nascent products of decomposition. 

 The E.M.F. E — CR representing this amount of work is 

 readily measurable by electrical means ; for it is the quantity 

 sometimes spoken of as the "counter E.M.F. set up during 

 electrolysis/' being the value of e in Ohm's theorem 



2(E)- g 



2(R) + R ? 



where 2(E) is the sum of the electromotive forces of the bat- 

 tery, e the counter E.M.F. set up, 2(R) the total resistance 

 in circuit less that of the electrolytic cell, and C the cur- 

 rent produced. For if r be the " resistance of a wire obstruct- 

 ing the current equally with the electrolytic cell " (i. e. what 

 may be conveniently termed the apparent resistance of the 

 voltameter, equal to that of a wire through which the current 

 C would pass when a difference of potential E subsisted between 

 its ends), we have 



2(E)-« _ 2(E) 



c=5 



V 



whence* 



and 



C also = 



2(R) + R 2(R) + 

 2(E)-E_ 



E 

 r-U 



E 



2(R) 



R 



e=E-CR. 



* These relationships may 

 be represented graphically 

 thus : — On a base-line A B H F 

 let fall perpendiculars AC, 

 B D, representing respectively 

 2(E) andE, the length AB 

 representing 2(R). Join D, 

 and produce the line C D till 

 it cuts AB produced in F. 

 Cut off from BD at the end 

 D a length D G representing e, 

 and through G draw GH 



Phil. Mag. S. 5. Vol. 11. No. 67. March 1881. 



