Page:Text-book of Electrochemistry.djvu/231

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216

ELECTROMOTIVE FORCE.

CHAP.

solutions of potassium chloride, sodium chloride, and hydrochloric acid. According to the results obtained by Loomis and Hausrath, we may set $i=1+\alpha$ (approximately), where a is the degree of dissociation calculated from the conductivity. In the following table Jahn's experimental values (E, observed) are given along with those calculated (E, calculated). The concentrations (in gram-molecules per litre) of the solutions used are given in the columns headed $x_{1}$ and $x_{2}$ .

Electrolyte.	x1.	X2.	E (observed).	E (calulated).	Difference.
КСl	0.03349	0.00167	0.07028	0.07173	-2.0%
KCl„	0.01669	0.00167„	0.05424	0.05539	-2.1
KCl„	0.01114	0.00167„	0.04497	0.04579	-1.8
KCl„	0.00833	0.00167„	0.03844	0-03885	-1·1
KCl„	0.00670	0.00167„	0.03330	0.03364	–1.0
KCl„	0.00557	0.00167„	0.02895	0.02920	-0.9
HCl	0.03342	0.001665	0.11955	0.12122	-1.4
HCl„	0.01665	0.001665„	0.09235	0.09334	-1·1
HCl„	0.01113	0.001665„	0.07664	0.07710	-0.6
HCl„	0.00831	0.001665„	0.06487	0.06534	-0.7
HCl„	0.00669	0.001665„	0.05614	0.05652	-0.7
HCl„	0.00556	0.001665„	0.04884	0.04906	-0.4
NaCl	0.03344	0.001674	0.05614	0.05679	-1.1
NaCl„	0.01673	0.001674„	0.04360	0-04395	-0.8
NaCl„	0.01117	0.001674„	0.03608	0.03636	-0.8
NaCl„	0.00836	0.001674„	0.03073	0.03089	-0.8
NaCl„	0.00669	0.001674„	0.02652	0.02663	-0.4

The agreement between the observed and calculated values is very satisfactory. The observed values are always somewhat smaller (on the average about 1 per cent.), which points to a constant experimental error.

The formulæ given above for V are perfectly exact, but they are more or less inconvenient, since they cannot be directly integrated. They can, however, be integrated if we assume that they are constant, and that the law of mass action—

{\frac {g^{r}}{c-g}}={\text{const}}