336 ON THE SURFACE TENSION AND 



where the n'a are the numbers of equivalent gramme-molecules 

 contained in unit volume of the original simple solutions, the as 

 are the ionization coefficients in the mixture of the respective 

 electrolytes mixed, the vs the respective volumes of the original 

 simple solutions mixed, and the Ts and k's the ionization con- 

 stants found for the simple solutions of the several electrolytes. 



Prof. MacGregor applied the above expressions to the calcu- 

 lation of the density, thermal expansion, &c , 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 fir.it 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 consequently also Sodium Sulphate 

 and Potassium Chloride. 



Data for the Calculations. Experimental Methods. 



The methods employed in purifying 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.f His measurements were made 

 at 15C, and are there therefore not strictly comparable with 



* Tran. N S. Inst. Sci., Vol. IX., p.^91, and 307. 

 t Wied. Ann., 21 (1884), p. 576. 



