440 On the Thermal Phenomena of the Galvanic Pile. 



salt of copper. If from the quantity of heat developed by the 

 electromotive counterforce the last-mentioned quantity of heat, 

 consumed by the decomposition, be subtracted, we actually 

 obtain, as the following Table shows, the values observed by 

 Raoult of the surplus heat L. 



In the decomposition of water. 



A (2-04x23900). 48756-34462= +14294 

 B „ „ 41825-34462=+ 7363 

 C „ „ 51624-34462= +17162 



In the decomposition of sulphate of copper. 



A (1-59x23900). 38001-29605= +8396 

 B „ „ 37762-29605= +8157 

 C „ „ 32504-29605= +2899 



Indeed the calculated do not differ more from the observed 

 numbers than can be accounted for from the unavoidable 

 errors of observation occurring in experiments of this sort. 

 Hence it follows that, to account for the thermal phenomena 

 occurring in the voltameter, there is no need to have recourse 

 to the secondary chemical processes which may take place 

 there, the nature and amount of which are more or less un- 

 known * ; the theoretical view above presented under No. 2 

 perfectly suffices for their explanation. 



5. Some experiments made by Favre, on the development 

 of heat in the voltameter, fully confirm what is here alleged f . 

 In a mercury calorimeter (No. 1) provided with seven muffles, 

 in the first five muffles five equal Smee's elements were en- 

 closed, and in the sixth a rheostat consisting of a platinum 

 wire with so great a resistance that the resistance of the 

 remaining parts of the circuit, in comparison with it, 

 could almost be neglected. On the solution of one equi- 

 valent of zinc in each element, the calorimeter indicated 

 the quantity of chemical heat k developed in the five elements. 



* Raoult, in order to show that the occurrence of secondary chemical 

 processes is necessary for the production of the heat in this case, makes an 

 inference which might he rendered in the following manner : — When the 

 voltameter is inserted in the circuit, the electromotive force of the series 

 is thereby diminished by e, and the entire circuit is thus deprived of a 



e 

 quantity of heat which is equal to 23900 X ~. This heat is expended in 



the production of chemical decomposition in the voltameter. But as the 

 quantity of heat expended for this is less than that above-mentioned, the 

 difference must be made good by the occurrence of secondary chemical 

 processes. 



t Comptes JRendus, t. lxvi. p. 252; Pogg. Ann. vol. exxxv. p. 300 

 (1868). 



