312 ON THE CALCULATION OF THE CONDUCTIVITY OF 
The foregoing table, I, contains the necessary data for the 
drawing of the ionic concentration-dilution curves for each salt. 
Dilutions are expressed in terms of litres per equivalent gramme- 
molecule of anhydrous salt at 18°C. The conductivities are 
specific molecular conductivities (7. e. per gramme-equivalent) at 
18°C, expressed in terms of 107° times the specific conductivity 
of mercury at 0°C. The concentrations of ions are the ratios 
of the specific molecular conductivity, to specific molecular con- 
ductivity at infinite dilution, divided by the dilution. 
Observations on the Double Sulphate Solutions. 
Table II contains both the data for, and the results of, the 
calculation of the conductivity of each solution of the double 
sulphate examined, together with the observed values, and the 
differences between observed and calculated values, expressed 
as percentages. The concentrations of solutions are expressed in 
terms of equivalent gramme-molecules of anhydrous salt per 
litre at 18°C. The conductivities are specific conductivities at 
18°C, expressed in terins of 10~* times the specific conductivity 
of mereury at O°C. The concentration of ions common to the 
two electrolytes in a solution, and the dilutions of the electro- 
lytes in the solution, are obtained by Prof. MacGregor’s graphical 
method, on the assumption that a solution of double salt may 
be made by mixing equal volumes of equi-molecular solutions of 
the simple salts, and that, on mixing, the double salt does not 
form The former is the number of dissociated gramme-equiva- 
lents of either electrolyte, which on that assumption would be 
present in the solution, divided by the volume in litres of the 
portion of the solution occupied by it. In any one solution it 
will have the same value for both electrolytes. The latter are 
the volumes in litres of the portions of the solution occupied by 
the respective electrolytes, divided by the number of gramme- 
equivalents present. In each solution they will have different 
values for the two electrolytes. The product of the former into 
the value of the latter, in the case of either electrolyte gives the 
ionization coefficient for that electrolyte in the solution. 
