SAPONIFIABLE OILS, FATS AND WAXES 181
first group contains appreciable quantities of the glycerides of
butyric, caproic and caprylic acids, in addition to those of oleic,
palmitic and stearic acids, which make up the bulk of most other
oils and fats. The lower molecular weights of these acids raises
the saponification number of butter to about 227 and that of
cocoanut fat to 255.
The .true waxes are not glycerides but esters of mono- and
di-hydric alcohols, usually of higher molecular weights than that
of glycerol and always of higher equivalent weights. Most
waxes contain also acids of higher molecular weight than that of
stearic acid, as constituents of the essential esters. This gives
lower saponification numbers to waxes, as will be noted from an
inspection of Table XII on page 198.
It will thus be seen that the determination of saponification
number will be useful chiefly in identifying materials of the
classes just named. In most other cases this constant will fall
between the approximate limits of 190 and 210.
Insoluble Acids (Hehner Value) and Soluble Acids.—The
determination of the saponification number may be conveniently
combined with the determination of soluble acids and insoluble
acids. Among the most important of the acids of smaller
molecular weight than oleic acid, combined as glycerides, are
butyric, caproic, caprylic and capric acids, discussed above.
These acids are soluble in water, the solubility decreasing as the
molecular weight increases, so that, while butyric acid is infi-
nitely soluble, capric acid dissolves only to the extent of 1 part in
1000 parts of boiling water. The next acid in the series, lauric
acid, is almost insoluble while the still higher acids are prac-
tically insoluble. An approximate separation of the lower
acids from the higher ones may be accomplished by saponifying
the oil, decomposing the resulting soap with sulphuric acid and
washing the fatty acids with water. The per cent of insoluble
acids is called the Hehner value.
An inspection of the formula for a typical triglyceride, as that
of palmitin, CsH^CieHgiC^s, shows that the acid residue
comprises the greater part of the compound. Also since the
variation in the molecular weights of the three acids, palmitic,
stearic and oleic, which make the greater part of the acids of
most oils and fats, is small as compared with the molecular