M. Eaoulf 07i Chemical Heat and Voltaic Heat. 523 



produce in the spiral the same current as the pile P, and which 

 for an equivalent of metal dissolved would disengage a quantity 



of heat equal to — . As the quantities of heat produced 



by the current in the same circuit for one equivalent of metal 

 dissolved are proportional to the electromotive forces, an element 

 of no resistance and electromotive force F, that is, producing in 

 the compass a current of the intensity F, would disengage in the 

 spiral, from the solution of an equivalent of metal, a quantity of 

 heat represented by 



w ex 31-6 F 



P f 



as I haye advanced. 



The following are the data of an experiment made to deter- 

 mine the voltaic heat of a DanielPs element — copper in sulphate 

 of copper, zinc in sulphate of zinc. The pile P is composed of 

 six large DanielFs elements : 



/ = 0-5281. 



c = 502*3 thermal units. 



p = 223 milligrammes. 



F = 0-1752. 

 Duration of the experiment 5 minutes. Temperature of the air 

 25°. From which data 



W= 23614 thermal units. 



I have modified the experiments by replacing several elements 

 of the pile by Bunsen's elements, varying their number, work- 

 ing for a longer or shorter time, and have always obtained con- 

 cordant results, the extremes of which were 22859 and 24012. 

 The mean of twenty experiments, where all the data varied from 

 the simple to the double, is 



W= 23602 thermal units. 



The calorimeter which I used is the mercurial calorimeter of 

 Favre and Silbermann, a little simplified. I measured directly 

 the heat disengaged by the substitution of zinc for one equivalent 

 of copper in a concentrated solution of sulphate of copper, and I : 

 found 



23564 thermal units. 



Favre and Silbermann's number is 23205. It follows from 

 this, that in a Daniell's element the heat produced by the current 

 is very nearly equal to the heat produced by chemical action. 



Daniell's element is the only one in which it is so. In other 

 elements, the heat produced by the current in the entire circuit 

 and the heat produced by chemical action are often remarkably 

 different. The following are some of the results obtained ;— 



2M2 



