summer varieties are sometimes recognized in trade. There is, however, no difference in the other characteristics of the oil.
The specific gravity of rape oil at 15.5 degrees C., compared with water at the same temperature, is about .916. The variations from this mean number are not very great. Rapeseed oil absorbs almost its exact weight of iodin,—the average iodin number being not far from 99.
The Chief Adulterations of Rape Oil—The chief adulteration of rape oil consists in the admixture of cheaper or flavoring oils. Among those which are often used in the adulteration of rape oil are linseed oil, hempseed oil, poppy-*seed oil, chamomile oil, cottonseed oil, the various mustard oils, refined fish and blubber oils, rosin oil, and paraffin. Some of these adulterations, it is seen, cannot be added to rapeseed oil when used for edible purposes. The chief adulteration of rapeseed oil, when intended for edible purposes, is the addition of cottonseed oil. The detection of these various adulterations, with the exception of that of cottonseed oil, can be accomplished only by an expert chemist. The presence of cottonseed oil can be detected by the application of the Halphen test already described.
Technique of Extraction.—The extraction of oil from the rape seed is not different from that of other oily seeds. It is either extracted by pressure, which is the proper way always when it is to be used for edible purposes, or when used for technical purposes it may be extracted by means of carbon bisulfid or petroleum ether. When extracted by pressure for edible purposes the oil should be refined by a similar treatment to that applied to cottonseed oil and finally filtered, preferably after mixing with fuller's earth or other similar material, in order that it may be perfectly pure and bright and free from suspended matter which interferes with its utility as an edible oil.
A very common treatment of the expressed oil, in order to coagulate and separate the mucilaginous matter which it contains, is with sulfuric acid. This acid has the very valuable property of coagulating this class of bodies. When treated with sulfuric acid it is necessary that the oil be thoroughly washed many times in pure water in order to remove the last trace of the acid.
The residue or oil cake is prized as a cattle food or as a fertilizer. The average content of oil in rape seed is about 37 percent.
Sesamé Oil.—Sesamé oil is very commonly used for salad oil and for the other purposes to which the edible oils are devoted. It is also known as gingili oil and teel oil. Sesamé oil is obtained by pressure from the seed of the sesame plant,—Sesamum orientale L.
Sesamé oil possesses a light amber color when properly made, is free from any unpleasant odor, has an agreeable taste, and when expressed cold produces what is known as the cold-drawn oil which is regarded by many as of equal palatable value with olive oil. Sesamé oil, in addition to containing stearin, palmitin, and olein, also contains a small quantity of a glycerid which exists in large quantities
