SPECIFIC GRAVITY OF AQUEOUS SOLUTIONS.—ARCHIBALD. 9345 
of sign is not to be expected in the differences as was observed 
in the differences between observed and calculated values for 
the simple solutions. In any case in which variation of sign 
might be expected, as in the case of mixtures of the Copper 
and Potassium Sulphates where the solutions mixed were equi- 
molecular, alternation of sign in the differences is quite satis- 
factory. 
The results of the above tables would seem to warrant the 
conclusion that it is posssible by aid of the dissociation theory 
of electrolysis, to predict the surface tension and specific gravity 
of mixtures of moderately dilute solutions of Sodium Sulphate 
with Potassium Sulphate and Potassium Sulphate with Copper 
Sulphate within the limits of the error of observation, by means 
of data obtained by observations on simple solutions of these 
salts. 
Observations on the Specific Gravity of Solutions containing 
Potassium Sulphate and Sodium Chloride. 
As it appears from the above results to be possible to predict 
the specific gravity of a mixture of two solutions of sulphates, 
and from Prof. MacGregor’s results in the case of mixtures of 
two chiorides also, I thought it would be interesting to see if a 
similar prediction was possible in the case of a mixture of a 
swphate solution with that of a chloride of a different metal 
In such a case there will be four electrolytes present in the: 
solution. Hence the formula for calculating, expression (2) on 
page 335, will involve four each of the quantities h, /, @, 7, v, and 
the calculation is thus extremely difficult. Prof. MacGregor has 
found it practically impossible to calculate even the conductivity 
in the ease of mixtures of any two solutions taken at hap- 
hazard. I therefore did not attempt to do so in the case of the 
specific gravity. The plan adopted was that of my paper on 
the conductivity of solutions containing Potassium Sulphate 
and Sodium Chloride,* viz., to prepare simple solutions of the 
four salts having the same concentration of ions and to mix 
7 1G0G. Cte. 
