t method, the seeds are first cleaned, then "decorticated"
(hulls removed), crushed or ground, then subjected to intense pressure in
an hydraulic press. In the commercial process, the ground seeds are first
pressed at ordinary temperature, which yields "cold-drawn" oil, then the
press cake is heated and pressed again, whereby "hot-drawn" oil is
obtained. The crude oil is refined by heating it to coagulate any albumin
which it may contain, and is sometimes bleached by different processes
before it is marketed. The press cake from many seeds, such as flaxseed
(linseed), cottonseed, etc., is ground up and sold for use as stock feed.

In the second method, the finely crushed seeds are treated with solvents
such as gasoline or carbon bisulfide, in an apparatus which is so arranged
that the fresh material is treated first with solvent which has already
passed through various successive lots of material and has become highly
charged with the oil, followed by other portions which contain less oil,
and finally by fresh solvent, whereby the last traces of oil are removed
from the material. The saturated solvent is transferred to suitable boilers
and the solvent distilled off and condensed for repeated use, leaving the
oil in the boiler in very pure form.

Extraction by boiling with water is sometimes used in the preparation of
castor oil and olive oil. In such cases, the crushed seeds are boiled with
water and the oil skimmed off as fast as it rises to the surface.

IDENTIFICATION OF FATS AND OILS

Fats and oils are identified by determinations of their physical
properties, such as specific gravity, melting point, refractive index,
etc., and by certain special color reactions for particular oils; or by
measurements of certain chemical constants, such as the percentage of free
fatty acids which they contain, the saponification value (i.e., the number
of milligrams of KOH required to completely saponify one gram of the fat),
the iodine number (percentage by weight of iodine which is absorbed by the
unsaturated fatty acids present in the fat), percentage of water-insoluble
fatty acids obtained after saponification and acidifying the resultant
soap, etc., etc. Most of these tests must be carried out under carefully
controlled conditions in order to insure reliable identifications, and need
not be discussed in detail here. Full directions for making such tests,
together with tables of standard values for all c