Residue Volume Method of Solubility J
Determination THO3IAS H. V.-IUGHN
AND
EUGENE G. SUTTING, J R . , The J. B. Ford Company, T?alidotte, Mich.
upon prolonged agitation the solute n ill no longer die:ippe:ii, but if insoluble impurities contaminate the material under eyamination, this method fails. Other factors may also affect this method, as for example, the color and opacity of the solutions or the presence of fluorides or other materials which attack vessels used to carry out the determinations. Thermal methods, such as the cooling of unsaturated solutions to determine the highest temperature of separation of solid phase, with or without seeding, haTTe obvious limitation.
A new method of determining solubility by measuring the volume of residues left by mixtures of solute and solvent has proved successful in cases where speed of determination combined with reasonable precision and simplicity is required. The method is particularly useful on commercial mixtures and on substances containing insoluble impurities. The solubility of pure substances may also be determined by this new method, but it is not applicable to volatile solutes or solutes of lower density than the solvent.
III
t
1 - 1
I
t
T
1.0
HE best solubility data are commonly obtained by the usual methods of phase rule investigation whereby the compositions of the liquid and solid phases in equilibrium are determined and verified by their mutual relations to the equilibria found to exist for systems of slightly altered composition. Solubility relations become vastly more complex and slower to establish as one progresses from two- to three- and then to four-component systems. I n systems of three or more components, a variable excess of solid phase beyond that required for saturation in many cases affects the composition of the solution with which it is in equilibrium. This paper deals with the more limited problem of determining the quantity of a soluble solid composition of any number of components in fixed ratios which will enter completely into solution. It is sometimes possible, of course, to secure the required data by adding known amounts of solute to the system until
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W
E
0.8
k 0.6 w
t J i
0.4
'
0.2
i
0
PERCENT NAHC03 FIGCHI.: 2.
SOLUBII.ITY O F SODIUM BICARBOS.~TL .
