524 J. W. Gibbs — Equilibrium of Heterogeneous Substances. 



SURFACES OF DISCONTINTTITY BETWEEN SOLIDS AND FLTTIDS. 



Page 



Preliminary notions, 482 



Conditions of equilibrium for isotropic solids, 485 



Effect of gravity, 488 



Conditions of equililirium in the case of crystals, 489 



Effect of gravity, 492 



Limitations, 493 



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



which is solid, 495 



General I'clatious, 49*7 



Another method and notation, 497 



ELECTEOMOTIVE FORCE. 



Modification of the conditions of equilibrium by electromotive force, 501 



Equation of fluxes. — Ions. — P]lectro-chemical equivalents, 501 



Conditions of equilibrium, 502 



Four cases, . 503 



Lippmann's electrometer, 506 



Limitations due to passive resistances, 507 



General properties of a perfect electro-chemical apparatus, 508 



Reversibility the test of perfection, 508 



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, 509 



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, 510 

 by the currents caused by differences in the concentration of the electrolyte, 511 



and by electrodes of zinc and mercury in a solution of sulphate of zinc, 511 



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

 proportions is shown b}' a priori considerations based on the phenomena 

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

 chloric acid, -_ 513 



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



in a galvanic or electrolytic cell, 516 



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, '- 518 



Other formulae for the electromotive force, 520 



