324 ON THE CALCULATION OF THE CONDUCTIVITY OF 
a concentration of 0.6 gramme-equivalent per litre. Above that. 
concentration the solutions, which were to be used in obtaining 
data for the calculations, were made up outside the cell. Two 
sets of solutions made in the cell in which the concentrations of 
the final solutions were calculated by a comparison of their con- 
ductivity with the conductivity of other solutions of approxi- 
mately the same, and of known, concentration, were used to give 
an idea of the course of the conductivity-concentration curves 
between 0.7 and 1 gramme-equivalents per litre, but in none of 
the mixtures calculated and tabulated at the end of the paper 
does the determination of the ionisation coefficients require the 
use of these portions of the curves. 
To test the validity, within the limits of experimental error, 
of the assumption, that, in the case of dilute solutions, the 
volumes of the latter are increased by the volume of water 
added, I made use of Kohlrausch and Hallwachs’ observations 
of the specific gravity of solutions of sodium chloride.* For 
solutions whose concentration is not greater than 0.2 gramme- 
molecule per litre, the specific gravity may be represented to 1 
in the fifth place of decimals by the equation 
s=1+4+.04244m — .00872, 
where s represents the specific gravity at 18°C and m the 
concentration in gramme-molecules per litre. The following is. 
a comparison of the values obtained by this equation with those. 
obtained by Kohlrausch and Hallwachs.:— 
Mm. Ss (by formula). SLES fs'6) 18 5)) 
2 1.008268 1.008358 
wl 1.004214 1.004202 
.05 1.002115 1.002111 
Writing then & for the first constant in the formula, and / for 
the second, W for the weight of water in grammes, w for the 
weight of salt when divided by a the value of the molecular 
* Wied. Ann., 53 (1894) p. 14. 
