Page:Text-book of Electrochemistry.djvu/234

 XIII.

��ELECTROMOTIVE FORCE.

��Hg I Hga I 01 KCl I 001 KCl I 001 Ha I 01 HCl

01 KCl I HgCl I Hg

the two electromotive forces at the ends exactly balance each other, since they are equal, but act in opposite directions.

Furthermore, the electromotive force between 01 HCl | 01 KCl must be equal to that between 001 KCl | 001 HCl, but with the opposite sign, since the electromotive force depends on the ratio of the concentrations of two solutions, and not on the absolute values. The remaining electromotive forces are therefore —

0-1 KCl I 001 KCl, and 001 HCl | 01 HCl,

which can be calculated according to the above formulae. Nernst (/^y) has made a large number of observations with such elements, and we give below some of his results. The experiments were carried out at 18°, and in this case we obtain —

^ = 86r.l0-*r-'^'-"'-^'}lnl0.

in + V Ui + Oi'

from which we find —

��Electrolytes.

��KCl, NaCl. .

KCl, LiCl. .

KC1,NHX1. .

NH.Cl, NaCl.

KCl, HCl. .

KCl, HNO3. . KCl, HO3SC9H,,

��U — P «i — *•] 0+1' Ml + ri

��IT (observed). w (calculated).

��The calculated values are all about 12 per cent, higher than those observ'ed. A deviation of about 5 per cent, can be explained by incomplete dissociation, but the cause

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