EQUILIBRIUM OF HETEROGENEOUS SUBSTANjCES. 349 



pressures or by gravity. But the relations expressed by (693), (694), 

 and (696) may be put in a briefer form. 



If we set, as on page 89, 



i/r = e-fy, 



we have, for any constant temperature, 



d\/s de tdri\ 



and for any perfect electro-chemical apparatus, the temperature of 

 which is maintained constant, 



F '_ F= _^ + ^o + d ^p ; (697) 



de de de 



and for any cell whatever, when the temperature is maintained uni- 

 form and constant, 



(F'-F^^-ety + dW Q + dW P . (698) 



In a cell of any ordinary dimensions, the work done by gravity, as 



well as the inequalities of pressure in different parts of the cell may 



be neglected. If the pressure as well as the temperature is main- 



tained uniform and constant, and we set, as on page 91, 



where p denotes the pressure in the cell, and v its total volume (in- 

 cluding the products of electrolysis), we have 



dg = de t dr\ +p dv, 

 and for a perfect electro-chemical apparatus, 



F'-F=-^, (699) 



or for any cell, 



-d (700) 



[SYNOPSIS. 



