Extremely Dilute Acid and Alkali Solutions. 9 
impurity of the water, the association which occurred through the 
addition of a strong acid would involve the disappearance of some 
of the hydrogen ions added, and not of the ammonium ions 
originally present. The loss of conductivity would consequently 
be greater than the original conductivity of the solvent, inasmuch 
as the velocity of the hydrogen ion is greater than that of the 
ammonium ion. 
For example, in Fig. 4 the loss of conductivity AB is about 
08 x10-% ‘This is due, we shall suppose, to the combination of 
carbonate ions (from the solvent) with hydrogen ions (from the 
acid added). The amount of (ionised) ammonium carbonate 
required to bring about this loss of conductivity on the addition 
of strong acid would itself possess a conductivity of 
70 + 50 
320 + 50 
(where the numbers 320, 70 and 50 are the velocity numbers of 
the H, NH, and 4 CO, ions respectively). The initial conductivity 
of the water is of this order. 
It will be seen, therefore, that the loss of conductivity in any 
particular instance is readily accounted for quantitatively on the 
assumption that the residual conductivity of the water is due to 
the absorption of ammonia and carbonic acid from the air in 
suitable proportions. The proportion would naturally vary with 
the actual conditions attending each distillation, Just as the 
conductivity of the water itself varies. The important point is 
that the quantities which the acid curve makes it necessary to 
assume are always such as can be fitted in with the conductivity 
of the solvent itself. 
(3) There is another important conclusion to be noticed. 
These results provide us with a method of deducing the ‘true 
value’ of k/m, the equivalent conductivity, for these solutions at 
infinite dilution. The straight line indicates that ionisation is 
complete (within the limits of observation) for the concentrations 
included. Hence the value of dk/dm, the tangent of this straight 
line, is the limiting value of &/m for ‘infinite dilution.’ These 
quantities are given in the last column of Table I]. In a similar 
way, using Kohlrausch’s results (Fig. 1), we obtain dk/dm = 0°364. 
The maximum value of k/m in the equivalent conductivity curve 
of Kohlrausch is 0355. 
(4) An illustrative series of experiments was carried out with 
avery dilute solution of ammonium carbonate. Successive quan- 
tities of sulphuric acid were added in the same manner as for the 
previous experiments, and the conductivities of the solutions were 
measured. The initial solution contained about 7 x 10~> gram- 
molecule of pure (NH,).CO, per litre, and had a conductivity of 
x 0°8 x 10-6 =0°3 x 10~ reciprocal ohm, 
