AQUEOUS SOLUTIONS.—ARCHIBALD. ys) 
It was thought, therefore, that it would be interesting to see 
to what extent a mixture of equal volumes of equi-molecular 
solutions of the constituents of the double sulphate of Potassium 
and Copper corresponded to a solution of the double salt of the 
same concentration. For that purpose mixtures were prepared 
of the same concentration as the solutions of the double salt 
previously examined. Table III gives the concentrations 
common to the mixtures and the solutions of the double salt, 
the observed conductivity of each, and the differences between 
the two values expressed as percentages. Concentrations and 
conductivities are expressed in terms of the same units as in 
Table IT. 
The results given in Table III show that in the case of the 
weaker solutions the differences are within the limits of experi- 
mental error, but that in the case of the first four solutions the 
errors of observation would need to be of opposite sign for the 
two solutions in each case in order to account for the. differences 
observed. In the stronger solutions, therefore, the conductivity 
of the mixture would appear to be greater than the conductivity 
of the equally concentrated solutions of the double salt. This 
might be due to the molecules of the double salt not having 
become broken up in solution, to the extent that they are in a 
mixture of solutions of its constituents. Similar results for 
Potassium Chrome Alum have been observed by Jones and 
Mackay.* 
Observations on Solutions containing Zine aud Copper 
Sulphates. 
As the large differences between the calculated and observed 
values of the conductivity, in the case of the double sulphate 
solutions, were still unaccounted for, I thought it advisable to 
see how closely it was possible to predict the conductivity of 
mixtures of equi-molecular solutions of each of the constituents 
of the double salt with some other sulphate with which it does 
not form a double salt of the same nature as the Potassium 
* Am. Chem. Jour., Vol. XIX,, No. 2, p. 83. 
