AQUEOUS SOLUTIONS. MCKAY. 331 



The conductivity of the water used in making up the above 

 solutions did not need to be taken into account. The water 

 used in making up the weakest NaCl solution had a conductiv- 

 ity equal to less than two-tenths of one per cent of the conduc- 

 tivity of the solution itself. 



Density. 



Recurring to the formula for the conductivity of a mixture 

 of two electrolytes, given at the beginning of the paper, it will 

 be seen that the ratio of the volume of the mixture to the sum 

 of the volumes of the constituent solutions is required. When 

 equal volumes are mixed as was the case in the present deter- 

 minations, this ratio is equal to the ratio which the mean density 

 of the constituent solutions has to the density of the mixture. 

 The ratio is generally so nearly equal to 1 as to be negligible. 

 Still its value was calculated for the mixtures of solutions above 

 0.2 gramme-equivalent per litre. The greatest difference from 

 unity in the mixtures studied was .0017. The densities of the 

 simple solutions were taken from Kohlrausch and Hallwachs' 

 determinations in the case of NaCl, and from the British 

 Association report before referred to in the case of BaCl 2 . The 

 densities of the mixtures were determined by the writer by 

 means of Ostwald's form of Sprengel's pycnometer. The error 

 might be about 1 in the fourth place of decimals. 



Preparation of Mixtures. 



The mixtures examined were in all cases mixtures of equal 

 volumes. They were made either with the same pipette or with 

 pipettes of equal volume. These were filled with the respective 

 solutions at the temperature 18C, and delivered into dry flasks 

 or bottles. 



Procedure in Calculation. 



In making a calculation of the conductivity of any mixture, 

 the conductivities and concentrations of the single solutions were 

 first plotted on coordinate paper. From the curves thus obtained 



