Page 7 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL II

4 FIXED OILS, FATS, AND WAXES.
mechanically retained by the tissues, and hence a larger yield can be
obtained by the use of carbon disulphide or petroleum spirit, which,
on being distilled off, leaves the fat behind.
The proportion of oil or fat yielded by any particular material de-
pends on many conditions,
Tables of the yields usually obtained from different seeds, nuts, etc.,
are given in Schaedler's Untersuchungen der Fette, Oele und Wachsarten,
1892, p. 25, and in Wright and Mitchell's
Oils, Fats and Waxes, 1903, 297.
Oils obtained by the use of solvents are
more likely to contain impurities than those
obtained by pressure.
Estimation of Oils and Fats. the
I
n
laboratory, the estimation of the oil in
solid animal and vegetable matters is
effected by treating the finely divided and
previously dried substance' with a suitable
solvent under such conditions as to ensure
complete extraction. Carbon disulphide or
petroleum spirit may be employed for the
purpose, but ether or carbon tetrachloride
is, as a rule, preferable.
The exhaustion of seeds, bones, shoddy,
oil-cakes, milk residues, etc., by simply
digesting the substance with the solvent at
F16, 1. the oinary temperature, with frequent
agitation, in a closed flask, is unsatisfactory, as it requires a consider-
able quantity of the solvent, of which a notable proportion is likely to
be lost. The apparatus devised by Szombathy (see Vol. 1, p. 77)
obviates these drawbacks, The substance to be exhausted of oil is
enclosed in a plaited filter or cylinder of filter-paper; or if it be
coarse, it is sufficient to place it loose in a large test-tube having an
aperture at the bottom closed by a plug of glass-wool.
A very simple and convenient form of exhauster, adapted either for
extraction or re-percolation, has been described by Dunstan and Short
(Pharm. J., [3], 1882, 13, 66.4).
A form of exhauster (Fig. 1), suitable for the extraction of very

fa the case of linseed and other substances containing drying oils, the desiccation must
either be omitted or conducted in an atmosphere of hydrogen or illuminating gas.