214 Prof. E. F. Herroun on the Divergence of 



of a difference of temperature, the effect of which would be 

 to cool the cold cell and heat the hot one ; or heat would be 

 transferred from the cold to the hot body, and be made 

 capable of performing- mechanical Avork, instead of requiring 

 its expenditure. It does not appear to me that this could be 

 adequately explained by the different heats of dilution of the 

 salt at different temperatures, so that the result of believing 

 that a Latimer Clark cell works partly " at the expense of 

 sensible heat "is a direct contradiction of the principle of 

 the second law of thermodynamics, as this would require 

 that its E.M.F. should rise with rise of temperature. That 

 it is the postulate with regard to mercury cells, and not the 

 second law, which is fallacious, I hope to show later in this 

 paper. 



If two plates of zinc, one amalgamated and the other plain, 

 be immersed in a solution of zinc sulphate, on completing 

 the external circuit a current is found to flow from the 

 amalgamated to the non-amalgamated plate through the cell ; 

 but Prof. J. Willard Gibbs in his paper " On the Equilibrium 

 of Heterogeneous Substances,'^* remarks that such a current 

 could not have the effect of dissolving zinc from the amalga- 

 mated plate and depositing it on the non-amalgamated plate, 

 as this deposited zinc might be immediately redissolved in 

 mercury to form an amalgam with merely the absorption of 

 sensible heat. 



By the use of pure zinc foil in solutions of zinc sulphate, 

 free from oxygen, I have found that the difference of poten- 

 tial between amalgamated and plain zinc becomes exceedingly 

 small ; and in the case of a cell freely exposed to air the 

 current on a circuit of only 1'5 ohm's resistance did not 

 deposit any weighable quantity of zinc on the plain zinc 

 electrode after passing for seven days. This, therefore, is in 

 confirmation of the theoretical conclusion from the second 

 law put forward by Willard Gibbs, and renders it more im- 

 })erative to stringently examine any reputed case of the pro- 

 duction of electrical energy at the expense of thermometric 

 heat. 



It therefore became important to examine on an experi- 

 ment;il basis the theory that reversible heat effects are associated 

 with cells giving anomalous electromotive forces. 



Method. 

 The method usually adopted may be briefly described as 

 follows : — The experimental cell was constructed of a thin 



* Trans. Connect. Acad. vol. iii. pts. 1 and 2. 



