

EQUILIBKIUM OF HETEROGENEOUS SUBSTANCES. 353 



Surfaces of discontinuity between solids and fluids. 



PAGE 



Preliminary notions, 314 



Conditions of equilibrium for isotropic solids, 316 



Effect of gravity, - * 319 



Conditions of equilibrium in the case of crystals, - - - 320 



Effect of gravity, - -323 



Limitations, 323 



Conditions of equilibrium for a line at which three different masses meet, one of 



which is solid, - - 326 



General relations, 328 



Another method and notation, - 328 



ELECTROMOTIVE FORCE. 



Modification of the conditions of equilibrium by electromotive force, - - 331 

 Equation of fluxes. Ions. Electro-chemical equivalents, 331 

 Conditions of equilibrium, - - 332 

 Four cases, - 333 

 Lippmann's electrometer, - - 336 

 Limitations due to passive resistances, - 337 

 General properties of a perfect electro-chemical apparatus, - - 338 

 Reversibility the test of perfection, . - 338 

 Determination of the electromotive force from the changes which take place 

 in the cell. Modification of the formula for the case of an imperfect 

 apparatus, - - 338 

 When the temperature of the cell is regarded as constant, it is not allowable " 

 to neglect the variation of entropy due to heat absorbed or evolved. This 

 is shown by a Grove's gas battery charged with hydrogen and nitrogen, 339 

 by the currents caused by differences in the concentration of the electrolyte, 340 

 and by electrodes of zinc and mercury in a solution of sulphate of zinc, 341 

 That the same is true when the chemical processes take place by definite 

 proportions is shown by a priori considerations based on the phenomena 

 exhibited in the direct combination of the elements of water or of hydro- 

 chloric acid, - 342 

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

 in a galvanic or electrolytic cell, - - 345 

 The different physical states in which the ion is deposited do not affect the 

 value of the electromotive force, if the phases are coexistent. Experiments 

 of M. Raoult, - . - 347 

 Other formulae for the electromotive force, - 349 



G.I. 



