22 
CHEMISTRY: NO YES AND MacINNES Proc. N. A. S. 
drogen chlorides, by Harned^ on potassium chloride, and by Linhart^ 
on hydrochloric acid. As the results of Harned supplement at higher 
concentrations those for potassium chloride here presented, it may be 
stated that, assuming a constant transference-number of 0.497 for the 
potassium ion and an activity-coefficient of 0.745 at 0.1 molal as given 
in the table, his data lead to the following values : 
Normal concentration 0.2 0.3 0.5 0.7 1.0 2.0 3.0 
Activity-coefficient 0.688 0.657 0.624 0.608 0.593 0.572 0.586 
The results presented in the table may be summarized as follows: 
1. In the case of all four substances the activity-coefficient decreases 
with increasing concentration much more rapidly than does the conduc- 
tance-viscosity ratio, the differences amounting to from 7 to 15% at 0.1 
molal, and from 5 to 18% at 0.5 molal. 
2. In the case of all the substances except potassium chloride the 
activity-coefficient, unlike the conductance-viscosity ratio, passes through 
a pronounced minimum in the neighborhood of 0.5 molal, afterwards in- 
creasing rapidly at the higher concentrations. Even potassium chloride, 
according to Harned' s data, has a minimum activity-coefficient in the 
neighborhood of 2 -normal. 
3. The activity-coefficient even at moderate concentrations varies con- 
siderably with the nature of the substance; thus its value at 0.5 molal 
is 64% for potassium chloride, 73% for lithium chloride, and 77% for hydro- 
chloric acid and for potassium hydroxide. 
From these facts we may draw the general conclusions that the con- 
ductance ratio can no longer be regarded as even an approximate measure 
of the activity of the ions of largely ionized substances in their mass-action 
and thermodynamic relations; that this activity varies with the concen- 
tration, differently in the case of different substances; and that for the pres- 
ent it can be determined only empirically for each substance, with the 
aid of measurements of chemical equilibria, electromotive force or freezing- 
point.'^ 
It is, moreover, evident that the activity-coefficient of the ion-constit- 
uents cannot be proportional to and mainly determined by the fraction of 
the substance ionized, for this fraction could not increase with increasing 
concentration unless the ionizing power of the medium becomes much 
greater at moderate concentrations; and even then, it could not become 
greater than unity, as is actually the case with the activity-coefficient of 
hydrochloric acid above 2-molal. 
The results here presented do not show whether or not the conductance- 
ratio is equal to the degree of ionization. But these two quantities can 
hardly be equal in view of the fact that the conductances of the two ion- 
constituents of most uniunivalent substances seem to vary by different 
percentage amounts with increasing concentration, as may be seen from 
