ELECTROCHEMICAL THERMODYNAMICS 717 



which shows how, by means of a reversible process, the heat 

 [Q] absorbed at constant temperature t" may replace that ab- 

 sorbed at a series of temperatures denoted by i. The tempera- 

 ture ^" is the highest at which all the heat may be supplied to 



f dQ 

 the system. Eliminating / — from equation (21) by means 



of equation (23), we obtain 



V" -r = ^—^ [Q] + [W] + Wp. (24) ([6] p. 410) 



This equation can be derived from the usual form of reversible 

 cycle in which the cell is discharged isothermally at t', heated to 

 t", then the changes produced reversed isothermally at t" 

 without the flow of electricity, and finally cooled to t'. The 

 above equation would be true for such a process if the heat 

 absorbed during the heating from t' to t" cancelled that evolved 

 during the cooling from t" to t'. This may not be true for a 

 specific case, but if we define t" by equation (23), then equation 

 (24) is strictly valid. We shall find later that this definition 

 considerably simplifies theoretical discussion. 



The remainder of the letter which we have been discussing is 

 devoted to showing that the equations developed are in accord 

 with those derived by Helmholtz. Gibbs proceeds to deduce 

 the equation of Helmholtz, 



Yt = -~t (25) ([11] p. 411) 



by simple transformations of equation (22), and thus shows that 

 his methods lead to the same conclusions as those of this 

 investigator. 



II. On the Question of the Absorption or Evolution of Heat 

 during Galvanic Cell Processes 



As we have shown by consideration of equation (15), there is 

 every reason to beHeve that during charging or discharging of 

 a galvanic cell at constant temperature, heat may be absorbed 

 or evolved. Gibbs uses three lines of argument to show the 



