336 ON THE SURFACE TENSION AND 
where the n’s are the numbers of equivalent gramme-molecules 
contained in unit volume of the original simple solutions, the «’s 
are the ionization coefficients in the mixture of the respective 
electrolytes mixed, the v’s the respective volumes of the original 
simple solutions mixed, and the l’s and k’s the ionization con- 
stants found for the simple solutions of the several electrolytes. 
Prof. MacGregor applied the above expressions to the caleu- 
lation of the density, thermal expansion, we., of some simple 
solutions and mixtures of Potassium and Sodium Chlorides, and 
found it possible to calculate the various properties of these 
solutions within the limits of experimental error. 
At his suggestion I have carried out the observations and 
calculations described in this paper, to see if it is possible to 
represent by the first of the above expressions the density and 
surface tension of simple solutions of Sodium, Potassium and 
Copper Sulphates, salts of more complex molecular structure 
than those previously examined, and then, by means of the 
ionization constants thus obtained, to predict the values of the 
same properties for mixtures of solutions of these salts. I have 
also thought it well to test the possibility of predicting the 
specific gravity of solutions containing Potassium Sulphate 
and Sodium Chloride, and consequeatly also Sodium Sulphate 
and Potassium Chloride. 
Data for the Calculations.—Kaperimental Methods. 
The methods employed in puritying the water and salts used, 
and of preparing and mixing solutions and determining their 
concentration and conductivity, were the same as described in 
the papers I have read before the Institute during the present 
session.* 
Observations of Surface Tension. 
I have made no observations of surface tension myself, but 
have used those made by Rother.+ His measurements were made 
at 15°C, and are there therefore not strictly comparable with 
* Tran. N S. Inst. Sci., Vol. [X., p. 291, and 307. 
t Wied. Ann., 21 (1884), p. 576. 
