312 M. P. A. Favre's Thermal Researches on the Battery. 



gether, I measured the gases which they separately disengaged. 

 One of these elements, having served for various operations before 

 being used for the present experiment, was covered with all the 

 hydrogen it could condense, while the other, working for the 

 first time, had not been able to condense hydrogen on its surface. 



I then took a new couple, the platinum of which had been 

 treated with boiling nitric acid, then heated to redness, and im- 

 mersed in a considerable mass (about 2 litres) of my normal 

 acid*. The intensity of the current did not appreciably vary in 

 the numerous successive experiments, and the quantity of heat 

 indicated by the calorimeter containing a rheostat was virtually 

 the same. Hence the hydrogen condensed on the surface of the 

 platinum does not exercise any appreciable influence on the phe- 

 nomenon in question, and the variations observed should be at- 

 tributed to the differences of chemical composition which the 

 liquid of the couple experiences under ordinary circumstances. 



Lastly, it is sufficient to renew the liquid of the couples of 

 Smee's battery which have worked for some time, in order to 

 recover the original intensity and the corresponding thermal 

 result. 



The influence of the other causes above mentioned has still to 

 be investigated. 



I will first observe that in the first of the experiments II. the 

 local phenomenon of the solution of the zinc deposited on the 

 platinum in the acid can only play a very small part in the 1816 

 thermal units indicated by the calorimeter in which is the battery. 

 In fact, at the beginning of the experiment there is no sulphate of 

 zinc in the liquid; and the absolute quantity at the end is very 

 small, while the sulphuric acid which remains free is in a relatively 

 large proportion (only about J^ of the sulphuric acid has been 

 changed into sulphate of zinc). Hence I have necessarily been led 

 to attribute the heat which remains in the couples whenever the 

 acid liquid is renewed, almost exclusively to the local phenomenon 

 of the change of condition of the hydrogen. May we consider 

 the number adduced of 1816 units as representing even approxi- 

 mately the effect due to the change Gf state of the hydrogen ? I 

 think not ; for the quantity of heat corresponding to the che- 

 mical action, which is not met with in the circuit R-f?* and 

 which is confined to the couples, is greater (other things being 

 equal) the shorter the time in which the electrolysis of sulphuric- 

 acid is effected. 



IV. The following numbers justify this assertion ; they corre- 

 spond to experiments in which the liquid of the battery was re- 

 newed each time, and in which the length of the platinum wire 

 in the external part of the circuit was successively reduced : — 

 * The quantity of acid ordinarily employed is 90 cubic centims. 



