AQUEOUS SOLUTIONS.—MCKAY. 3381 
The conductivity of the water used in making up the ahove 
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,. 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 18°C, 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 
