Chemical Affinity in terms of Electromotive Force. Ill 



amount of work actually performed by the curent whilst 

 causing electrolysis, in such a way that the algebraic sum of 

 the energy gained by these other actions is subtracted from the 

 energy that would otherwise be required to break up the elec- 

 trolyte into nascent products. 



This theorem may be put in the form of the following- 

 equation. — Suppose that the quantity of total products of elec- 

 trolysis at the negative electrode be called 1, and out of this 

 amount let 1 — n x parts be evolved "nascent," whilst n ± parts 

 are so affected by the condensing or attractive action of the 

 electrode as to be evolved ab initio not in the " nascent " con- 

 dition, but in a more condensed form, viz. in the ordinary phy- 

 sical condition of the substance, if non-gaseous, but, if naturally 

 gaseous, in the form of a more or less condensed form of 

 gaseous matter (occluded gas, quasi-liquefied gas, or gas 

 strongly attracted to the surface of the electrode). Let H x be 

 the heat evolved per gramme-equivalent of product in its 

 transformation from the " nascent" to the ordinary free con- 

 dition, and let h x be the heat evolved in further condensing a 

 gramme-equivalent of the substance to the more condensed 

 form in which the fraction n Y of total product is evolved. Simi- 

 larly let n 2 , H 2 , and h 2 be the values corresponding respectively 

 to n v H 1? and h v referring to the products at the + eleqtrode 

 taken as unity. Then the amount of energy to be subtracted 

 from that corresponding to the decomposition into the nascent 

 products due to the attractive action of the electrodes is given 

 in terms of E.M.F. by the expression 



{n 1 (H i +h 1 ) + n 2 (E. 2 + h 2 )} X J. 



The energy corresponding to the work done in the decom- 

 position into nascent products being expressed in terms of 

 E.M.F. by Ej, let 2(H) represent the heat-evolution per 

 gramme-equivalent of substance decomposed, due to the 

 algebraic sum of the chemical actions taking place between 

 the products and the electrodes, &c, and of the diffusive 

 action of the differently constituted liquids surrounding the 

 two electrodes; then the final E.M.F. corresponding to the 

 work done in electrolysis will be 



e =B ( -K(H 1 +A 1 )+^(H 2 +^)+S(H)} x J. 



If now E 2 represent the E.M.F. corresponding to the work 

 done in decomposing the electrolyte into the final products, 

 supposing them to escape in the ordinary free condition, 



E, = E,-(H l + H 2 ) % J: 



