54 EQUALITY OF THE HEATS. 



in decomposing the elements. The former including the 

 force necessary to overcome the joint affinities of the oxide 

 for the acid and the acid for water, as well as the affinity 

 of the oxygen for the metal, so that while the total heat in 

 the cell is as the product of the total electromotive force, 

 multiplied by the current, the heat due to decomposing the 

 electrolyte is the product of the electromotive force to 

 overcome the last affinity multiplied by the current. 



He then adopts a method of eliminating the effect on 

 the heat of the two former affinities, when he finds the 

 corrected theoretical quantities of heat, that is the quan- 

 tities equivalent to the electric action, agree very closely 

 with the experimental heats of combustion, in every case 

 except that of hydrogen, where there is still a discrepancy 

 of some five per cent, which now he attributes to still un- 

 determined actions in the cell. 



In concluding his paper, he says, " I conceive that the 

 correctness of the idea, entertained, I believe, by Davy, and 

 afterwards more explicitly mentioned by Berzelius, that the 

 heat of combustion is an electrical phenomenon is now 

 sufficiently evident. I have shown that the heat arises from 

 the resistance to the conduction of electricity between the 

 atoms of combustibles and oxygen at the moment of their 

 union. Of the nature of this resistance we are still ignorant." 



This remark, in which Joule clearly over-states his case, 

 shows that at this date, June, 1842, he had not conceived 

 the idea of the heat developed by chemical union being 

 a measure of the mechanical potency of chemical separa- 

 tion, and thus being the same by whatever agency it is 

 developed. The remark is also interesting as containing an 

 expression of a conviction which was not sanctioned by 

 his scientific instinct. That he is not satisfied with his 

 proofs is shown in his next paper. 



