IL.As ON SOLUBILITY. 799 
which forms on admixture of stronger solutions. In general, the values 
thus determined—for instance, for AgCl and AgBr—are higher than 
those obtained by the conductivity method. 
In determining the solubility of stearic acid in ethylic alcohol, 
Emerson *°? found it necessary to use a large excess of the solid; other- 
wise highly supersaturated solutions are formed and constant results 
are not obtainable. 
Osaka *1* used a refractometric method in determining the com- 
position of saturated solutions. The method depends upon the validity 
of the relationship ax + bz? =§—38, in which z is the concentration of 
the solution, § and 8! are the refractometer readings for the solution 
and solvent respectively, and a and b constants which can be calculated 
from observations made upon two solutions of known concentration : 
thus, if the refractometer readings be taken for a saturated solution, 
1908 the concentration z can be calculated. In a subsequent paper 
* the author confirmed the applicability of this refractometric 
method.**§ 
The solubilitres of a large number of sparingly soluble salts were 
recalculated by Kohlrausch *?° from data which had been obtained from 
conductivity measurements. 
Hill *** gave a method for estimating the relative solubilities of two 
sparingly soluble salts, which, however, depends upon a knowledge of 
the degree of dissociation of both salts in their saturated solution. By 
this method he determined the relative solubilities of the halides and 
thiocyanate of silver. ; 
Interesting observations were made on the rate of dissolution by 
Gaillard,*?* who found that substances of equal solubility often take 
widely different times to dissolve. 
1909 Schréder **? described an apparatus wherewith the solubility 
* of a solid can be measured at the boiling point of the saturated 
solution, the distinguishing feature being that all junctions were made 
of fused glass. He also described another apparatus for measuring 
solubility at room temperature which was specially designed to guard 
against loss due to evaporation of the solvent during filtration. 
A form of apparatus suitable for use in estimating the solubility of 
very small quantities of substance was described by Stolzenberg.**1 
Getman and Wilson **® tested Osaka’s refractometric method of 
determining solubility, and were only able to obtain approximate results 
when using sucrose, potassium chloride, bromide, iodide, nitrate and 
chromate. 
An apparatus for measuring solubility at high pressures was 
described by Cohen and. Sinnige,*** and in a later paper *°* these authors 
described the estimation of the solubility of zine sulphate and cadmium 
sulphate at different pressures. The method used was somewhat novel: 
cells of the Weston type were set up and the E.M.F. of the cell 
measured, (1) using in the cell a saturated solution of the salt in 
question in contact with solid; (2) a saturated solution not in contact 
with solid; (3) a solution of known concentration. The solubility was 
calculated from the results of these measurements. 
