Galvanic Pile, and Electromotive Forces. 435 



lowering of temperature 1288, and, in the zinc-platinum pile, 

 1051 thermal units. 



Favre * has also, with the aid of the mercury calorimeter, 

 determined how much chemical and galvanic heat is liberated 

 in some piles of another construction during the solution of 

 one equivalent of zinc f. 



We will here take into consideration only the numerical 

 values obtained by Favre for the piles of Daniell and Grove. 

 If Jew denote all the chemical, and gio all the galvanic heat, 

 he obtained for Darnell's pile kw = 25060, ^it? = 23993, and 

 consequently kiv—giv = 1067 thermal units; for Grove's pile 

 &w = 41490, ^10= 46447, and consequently hv—cjiv=— 4957 

 units ; so that in Daniell's pile the chemical heat is only about 

 1000 units greater than the galvanic, while in Grove's pile 

 the galvanic is greater than the chemical heat. Consequently, 

 when this pile is closed with a conducting wire of great resist- 

 ance, the pile itself is cooled during the passage of the current, 

 while the conducting wire is heated. 



We may add that Eaoult also has determined by direct ex- 



* Connies JRendus, t. lxix. p. 34. 



t The following- was the method of observation here employed : — The 

 pile to be investigated was enclosed in one muffle of the calorimeter. As 

 the progress of the chemical processes could "be determined with great 

 accuracy by measuring the hydrogen which was evolved in the Smee's 

 pile, such a pile was also placed in the calorimeter, and connected with 

 the other pile, so that the current passed through both. The rheostat, 

 which connected the two poles, was also enclosed in the calorimeter. 

 Thus the calorimeter gave the chemical heat developed in both piles. 

 The quantity of heat shown by the calorimeter while half an equivalent 

 of hydrogen was being evolved in the Smee pile was now observed — that 

 is, during the time that the chemical processes in the two piles together 

 corresponded to one equivalent. When a Daniell's and a Smee's pile were 

 placed in the calorimeter, 22447 heat-units were in this way obtained. 

 The quantity of chemical heat for one equivalent of hydrogen, in the 

 Smee's pile employed, was determined, by special trial, at 19884 thermal 

 units, or 9917 for a half-equivalent. Consequently, if the quantity of che- 

 mical heat corresponding to 1 equivalent for the Daniell's pile be called x, 

 we shall have 



x 



+9917=22447, whence *=25060. 



A fresh experiment was then made, in which the Smee ? s pile and the 

 rheostat resistance were taken out of the calorimeter, so that the Daniell's 

 pile alone remained within. The outer resistance was so great, that the 

 heating caused by the current in consequence of the resistance in the pile 

 itself could be neglected. With this arrangement, the calorimeter now 

 gave the difference between the chemical and the galvanic heat, or gJc—gw. 

 In this way was obtained, during the evolution of one equivalent of hydro- 

 gen in the Smee pile, gk—gw = 1087 thermal units. Subtracting this 

 number from 25060, we get 23993, which denotes the galvanic heat of 

 the Daniell pile. Favre proceeded in the same manner in his investigation 

 of the other piles. 



2F2 



