Galvanic Pile, and Electromotive Forces. 439 



quantity of heat is produced than the galvanic which is caused 

 in the voltameter by the passage of the current; and this 

 happens notwithstanding it might be supposed, in consequence 

 of the chemical decomposition of the liquid, that the result 

 would be a cooling. 



Raoult is of opinion that the cause of the heating in this 

 case is to be sought in secondary chemical processes occurring 

 in the voltameter, which have nothing to do with the current. 

 He supposes that the constituents of the electrolyte, which 

 cover the electrodes and cause the polarization, are easily de- 

 composable, and on their decomposition give rise to a heat- 

 production in the same manner as takes place with the hyper- 

 oxide of hydrogen — that the decomposition of these products 

 first takes place after they have left the electrodes and begin 

 to ascend through the liquid, in consequence of which this is 

 heated by them without the current being at all afFected. In 

 my view, this explanation is unsatisfactory; on the other 

 hand, heat-production is in this case a necessary consequence 

 if we start from representation No. 2. 



According to this way of representing it, if a current passes 

 through an electromotor in the direction required by its elec- 

 tromotive force, a quantity of heat is consumed which is pro- 

 portional to the electromotive force, multiplied by the inten- 

 sity of the current ; but if the current goes in the opposite 

 direction, just as great a quantity of heat is generated. If, 

 therefore, the current is permitted to traverse the electromotor 

 during so long a, time that an equivalent of the electrolyte is 

 decomposed, the quantities of heat consumed or generated 

 become proportional to the electromotive force. Consequently 

 there arises in the voltameter a source of heat, because the 

 electromotive force of the polarization acts in the opposite di- 

 rection against the current which is passing through. It has 

 been mentioned above that the galvanic heat-development in 

 a closed Daniell pile during the liberation of an equivalent of 

 copper amounts to 23900 heat-units ; and according to No. 2, 

 exactly so much heat must, during the same time, be con- 

 sumed by the electromotive force of the pile. With the help 

 of this datum it is easy to calculate the magnitude of the 

 above-mentioned source of heat in the various experiments 



e 

 instituted by Raoult ; for we need only multiply - with the 



last-mentioned number. But, moreover, heat is consumed by 

 the chemical decomposition in the voltameter. For each 

 equivalent, 34462 thermal units are consumed, according to 

 Favre and Silbermann, in the decomposition of the water ; 

 and, according to Raoult, 29605 in the decomposition of the 



