256 Dr. 0. K. A. Wright on the Determination of 



1-501 volt and 29,951 %J== 1-321 volt. The former number 

 closely agrees with the above-cited results of Joule, Kiechl, 

 and Favre, and with the number deduced by direct combus- 

 tion of hydrogen (§ 32) ; the latter is somewhat larger than 

 the values deducible from the observations of Joule, Julius 

 Thomsen, and Favre, given in § 21. 



The mode of calculation employed by Kaoult, however, was 

 far less simple than would appear from this brief account of 

 his results. He complicated the work by attempts to measure 

 the amount of polarization set up in the voltameter; and from 

 the numbers thus obtained, together with the strengths of the 

 derived currents and the amounts of heat actually generated 

 as such, he calculated certain amounts of heat, to which he 

 applied the terms " local heat" and "voltaic heat of the vol- 

 tameter," the difference between which represented the heat 

 equivalent to the chemical decomposition — i. e. the above 

 numbers. On revising his formulae, however, it becomes evi- 

 dent that the determination of the amount of polarization of 

 the voltameter-plates (a determination the accuracy of 

 which is open to some criticism) is in no way involved in 

 the determination of the heat equivalent to the chemical de- 

 composition, inasmuch as the terms involving the amount of 

 polarization in the expressions for the " local heat " and the 

 "voltaic heat of the voltameter" are identical, and conse- 

 quently become both eliminated in the expressions represent- 

 ing the difference between these two quantities — i. e. the che- 

 mical decomposition. 



24. It is evident that any method that will give a direct 

 valuation by electrical measurements of the work done in the 

 formation of a given compound in terms of E.M.F. will, 

 when compared with the direct determination of the " heat of 

 formation" of the same compound by means of the calori- 

 meter, enable a new valuation to be deduced for J, the mecha- 

 nical equivalent of heat ; for the work done in the formation 

 of a gramme-equivalent of the compound being found by the 

 one method to be measured by e C.G.8. units, and by the 

 other by h gramme-degrees, the relationship 



AJ=eQ= * 

 X 



holds, where Q is the quantity of electricity requisite to decom- 

 pose a gramme-equivalent of substance, i.e. where Q = — (§ 7); 

 whence T _ e 



~~ h X 



