ABSTRACT BY THE AUTHOR. 371 



the term tdq will vanish. But in the calculation of electromotive 

 forces, which is the most important application of the equation, it is 

 convenient and customary to suppose that the temperature is main- 

 tained constant. Now this term tdr\, which represents the heat 

 absorbed by the cell, is frequently neglected in the consideration of 

 cells of which the temperature is supposed to remain constant. In 

 other words, it is frequently assumed that neither heat or cold is 

 produced by the passage of an electrical current through a perfect 

 electro-chemical apparatus (except that heat which may be indefinitely 

 diminished by increasing the time in which a given quantity of 

 electricity passes), unless it be by processes of a secondary nature, 

 which are not immediately or necessarily connected with the process 

 of electrolysis. 



That this assumption is incorrect is shown by the electromotive 

 force of a gas battery charged with hydrogen and nitrogen, by the 

 currents caused by differences in the concentration of the electrolyte, 

 by electrodes of zinc and mercury in a solution of sulphate of zinc, by 

 a priori considerations based on the phenomena exhibited in the 

 direct combination of the elements of water or of hydrochloric acid, 

 by the absorption of heat which M. Favre has in many cases observed 

 in a galvanic or electrolytic cell, and by the fact that the solid or 

 liquid state of an electrode (at its temperature of fusion) does not 

 affect the electromotive force. 



