The oil yielded by these seeds is, in physical and chemical properties, practically the same, the range of fluctuations not being greater than would be found in the oil of any specific seed under similar varying conditions of production. Colza seed is, in general, the richest in oil, and the winter varieties of all the seeds are more productive than the summer varieties. In summer rape and riibsen the proportion of oil averages from 30 to 35 per cent., the winter seeds have from 35 to 40, and winter colza contains from 40 to 45 per cent. Newly pressed rape oil has a dark sherry colour with, at first, scarcely any perceptible smell; but after resting a short time the oil deposits an abundant mucilaginous slime, and by taking up oxygen it acquires a peculiar disagreeable odour and an acrid taste. Refined by the ordinary processes (see Oils, vol. xvii. p. 743), the oil assumes a clear golden yellow colour. In specific gravity it ranges between 09112־ and 09117־ in the raw state, and from 09127־ to 09136־ when refined; the solidifying point is from - 2° to - 10’ C. Rape oil consists of a mixture of three simple fats or glycerides of fatty acids—the glyceride of oleic acid (olein), of stearic acid (stearin), and of brassic acid, the latter being a fat found hitherto only in oils from the Crucifei'se and from grape seeds. The olein of rape oil differs from ordinary olein in not yielding sebacylic acid on destructive distillation.

The principal uses of rape oil are for lubrication and lighting; but since the introduction of mineral oils for both these purposes the importance of rape has considerably decreased. It is but little employed in soap-making, as it saponifies with difficulty and yields only an indifferent product. In Germany it is very considerably used as a salad oil under the name of Schmalzöl, being for that purpose freed from its biting taste by being mixed with starch, heated till the starch is carbonized, and filtered after the oil has cooled. The offensive taste of rape oil may also be removed by treatment with a small proportion of sweet spirit of nitre (nitrous ether). In the East Indies rape oil and its equivalents, known under various names, are the most important of oils for native use. They are largely consumed as food instead of ghi under the name of “metali” or sweet oil, but for all other purposes the same sub-stance is known as “kurwah” or bitter oil. Most natives prefer it for the preparation of their curries and other hot dishes. Rape oil is the subject of extensive adulteration, principally with the cheaper hemp oil, rosin oil, and mineral oils. These sophistications can be most conveniently detected, first by taste and next by saponifica-tion, rosin oil and mineral oil remaining unsaponified, hemp oil giving a greenish soap, while rape oil yields a soap with a yellow tinge. With concentrated sulphuric acid, fuming nitric acid, nitrous acid, and other reagents rape oil gives also characteristic colorations; but these are modified according to the degree of purity of the oil itself. The presence of sulphur in rape and other cruciferous oils also affords a ready means for their identification. Lead plaster (emplastrum lithargyri) boiled in rape oil dissolves, and, sulphide of lead being formed, the oil becomes brown or black. Other lead compounds give the same black coloration from the formation of sulphide.