502 Proceedings of Royal Society of Edinburgh. [sess. 
already stated, these were calculated from the work of Kohlrausch, 
using his newer values for the conductivity at infinite dilution 
( Wied. Ann., 1893, 1. 408). 
The calculation of the degree of dissociation of sulphuric acid, and 
of a neutral sulphate in a solution containing them in definite pro- 
portions was carried out in the following manner. 
The dissociations of sulphuric acid and of each neutral sulphate 
at a number of dilutions were calculated. From these the concen- 
trations of the ions at each dilution was obtained, and a curve was 
then drawn for each substance, in which ionic-concentration was 
plotted against dissociation. As a first approximation, the dissocia- 
tions of the acid and of the salt in any mixture were made equal to 
the value which they would have, if the concentration of each was 
equal to the sum of the concentrations of the acid and salt. 
(Arrhenius, Zeit. physikal. Cliem., 1890, v. 1). From the dissocia- 
tions thus obtained, the concentrations of the ions, due to the acid 
on the one hand, and to the salt on the other, were calculated. 
The sum of these gave the total concentration of the ions, which 
corresponded to a certain dissociation on the ionic-concentration 
dissociation curves referred to above. This gave a second approxi- 
mation to the real dissociations of the acid and of the salt 
(Macgregor, Phil. Mag. 1896, xli. 276), which did not, as a rule, 
differ very much from the first. 
If the difference was comparatively great, the above process was 
repeated, and a third approximation obtained, but this was seldom 
necessary, and only when the dissociations of the acid and salt were 
very different. An example is appended. 
C = concentration, a = degree of dissociation. 
cq Concentration a 2 
C 
(when (7 = 0*15). 
of ions. 
(from curves). 
h 2 so 4 
0*05 
0*547 
0*0274 j 
0*544 
+ 
Na 2 S0 4 
0T 
0*645 
+ [=0*0919 
0*0645 ) 
0*652 
A third approximation gives the same result. 
The degrees of dissociation of the acid sulphates were assumed 
to be equal to those of the corresponding acetates. This assumption 
is justifiable if we consider the acid sulphate to be, in the first 
