AQUEOUS SOLUTIONS. ARCHIBALD. 315 



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 II. 



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 Zinc aud Copper 



Sulphates. 



As the large differences between the calculated and observed 

 valuer 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. 



