244 Dr. C. K. A. Wright on the Determination of 



Hence the mean of this value and that deduced by Kohlrausch 

 from his own observations (viz. ^=0*00010527) may be taken 

 as probably the nearest approximation to the truth ; i. e. 

 % =0*000105005, or practically %=0*000105. 



10. If it were possible to obtain a current between the two 

 electrodes of a voltameter or other similar electrolytic cell 

 which would decompose the electrolyte without any disturb- 

 ance of the thermal equilibrium, then the difference of poten- 

 tial between the electrodes would represent the force of che- 

 mical affinity exerted between the products of decomposition 

 in the compound examined ; for if e be the potential-difference 

 (E.M.F. existing between the electrodes) during the passage 

 of a quantity of electricity q, eg units of work will be done. 

 If n grammes of substance are decomposed, and /is the work 

 done by the force of chemical affinity in the synthesis of a 

 gramme of substance from the products of decomposition, the 

 total work done is also expressed by nf, which, by the defini- 

 tion of electrochemical equivalents (§ 8), =«%^/. Hence 



af= — 

 J X 



Or " affinity," reckoned per gramme-equivalent, is measured 

 by electromotive force divided by a quantity which is constant ; 

 i. e. the work done in the synthesis of a gramme-equivalent of 

 substance is expressible by a value indicated in electromotive- 

 force units, just as it is expressible by a value indicated in 

 heat units — the one valuation involving the constant %, the 

 other J. 



11. In practice it is impossible to realize this supposition ; 

 for experiment shows that, in the passage of electricity between 

 two electrodes, work is done not only as chemical decomposi- 

 tion but also as heat ; by determining the amount of the latter, 

 however, it is easy to calculate how much of the total potential- 

 difference existent between the electrodes is due to the chemical 

 affinity of the constituents : thus, if h gramme-degrees are 

 evolved during the decomposition of n grammes of substance 

 of electrochemical equivalent ax by the transfer of a quantity 

 of electricity q, and if E represent the total potential-difference 

 existent between the electrodes, the total work done in the 

 electrolytic cell is E^, of which A J is done as heat. Hence 

 ~Eq—hJ is done as chemical decomposition. Let this be equal 

 to eg, where e is the E.M.F. representing the chemical affi- 

 nity to be measured ; then 



q n ; 



