DENSITY AND SPECIFIC GRAVITY

101

Applications.—For the application of specific gravity deter-
minations to the quantitative analysis of solutions, two condi-
tions are necessary: The solution must be a binary one (having
only two components, solvent and solute) and the variation of
specific gravity with concentration must be great enough to
make possible calculations of concentration to a reasonable
degree of accuracy. Accurate tables have been worked out in a
limited number of cases and for these the specific gravity deter-

FIG. 27.—Westphal plummet as used with an analytical balance.

mination frequently offers the most convenient method for the
analysis. Examples of such cases are solutions of ethyl alcohol,
methyl alcohol, various sugars and various acids in water. If it
is known that only one of these compounds is present in a solu-
tion, the concentration can readily be determined. Of course a
good thermostat is necessary, in order to a void temperature errors.
Such tables as those mentioned above are found in many of
the standard handbooks. Quite elaborate tables are contained
in "Methods of Analysis/7 published by the Association of Official
Agricultural Chemists, and in U. S. Bureau of Standards Circular
19. The latter may be obtained from the Superintendent of
Documents at small cost,