RAPE OIL. This important fatty oil, known also as " sweet oil," is obtained from seeds of cultivated varieties of the cruciferous genus Brassica, the parent form of the whole apparently being the wild navew, B. campestris (Lin.), the B. pr.wcox of De Candolle. From the same stock, it is generally assumed, have sprung the Swedish turnip and the common turnip ; but the oil-yielding plants have developed in a special dire,ction and are exclusively culti-vated for the oil they yield. Under the general name " rape oil " is included the produce of several plants having distinct and fairly constant characters, and one of these oils CoLzA (q.v.) - is a very well-known commercial variety. In Germany, where the production of rape oil centres, three principal oil-seeds--colza (Koldsaat), rape, and riibsen are well recognized. Colza. is the produce of the parent stock B. campestris and is the form principally cultivated in France and Germany. Rape seed, the variety produced by B. campestris, var. napus, and riibsen seed, yielded by B. campestris, var. rapa, are extensively cultivated in the valley of the Danube and eastwards through Persia into India. These plants are principally distinguished from each other by the colour of their radicle leaves and the form of inflorescence, but also by the size and appear-ance of the small ovoid seeds. The seed of the colza is ruddy brown, rape is blue-black, and riibsen is almost black in colour. It has been found that 1000 seeds of colza weigh 29.3 grains, the same number of riibsen weighing 34.5 g-rains and of rape 71.75 grains. Each_ of these plants has summer and winter, or annual and biennial, varieties ; and as there are numerous intermediate forms in cultivation the varietie,s merge into each other.

The oil yielded by these seeds is, in physical and chemi-cal properties, practically the same, the range of fluctua-tions not being greater than would be found in the oil of any specific seed under similar varying conditions of pro-duction. 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 mpe 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 On.s, vol. xvii. p. 743) the oil assumes a clear golden yellow colour. In 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 nanie of Schmalzill, 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 larg-ely consumed as food instead of ghi under the name of "metah " 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 th'e 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.