Page 9 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL II

6 FIXED OILS, FATS, AND WAXES.
In the case of liquids containing oil in the form of emulsion, a separa-
tion may often be effected by agitation with ether. For the extraction
of unsaponifiable matter F~rster has devised an apparatus which is
figured and described in Vol. 1, page 82.
Purification of Oils.--The methods used in the refining and puri-
fication of crude oils have often considerable influence upon the analy-
tical characteristics of the final products.
Action of Heat.--Simple application of heat may effect coagulation
of protein impurities in an oil.
Mechanical Attraction and Filtration.--Substances such as Spanish
clay, fuller's earth, and the like are used as mechanical precipitants of
the suspended matter in oils. The clarified oil, which is not chemi-
cally altered by this treatment, is subsequently decanted or passed
through a filter.
Treatment with Acids.-Rape, linseed, and some fish oils are fre-
quently refined by treatment with a small proportion of sulphuric acid,
which chars the impurities and causes them to subside without
materially attacking the oil itself. The objection to the process is that
traces of free mineral acid may remain, even after the subsequent
washing with water, and, if the oil is used as a lubricant, may lead to
corrosion of bearings, etc,, or to charring of the wick in the case of
lamp oils. Treatment with sulphuric or hydrochloric acid is also em-
ployed in the removal of the lime which is present in bone fat.
Treatment with Alkalies.--Certain oils, notably cottonseed, olive,
and sperm oils, are frequently purified by treatment with a solution of
caustic soda, the quantity of which depends upon the amount of free
fatty acids and impurities to be removed. Cottonseed oil contains a
notable proportion of a resin-like substance which gives a blue colora-
tion with the alkali. Ammonia, sodium carbonate, magnesium car-
bonate, milk of lime, and sodium peroxide are also employed in certain
refining processes. Oils, which have been treated with alkali usually
contain a much smaller amount of free fatty acids than even the
freshly-expressed crude oils, and cottonseed oil used for cooking pur-
poses is often practically neutral.
Treatment with Oxidising Agents.Fish oils are purified, and to
some extent deodourised, by treatment with a current of steam followed
by a current of hot air. Excessive treatment of this kind will alter
the character of the oil itself, so that it becomes heavier and more
viscous, and acquires other characteristics of "oxidised" or "blown"