VEGETABLE OILS [B. VOLATILE AND ESSENTIAL].
fruits of Quercus robur (see Timber—Oak), when distilled with water, yield an essential oil of buttery consistence, and peculiar, strong odour.
Albahaca-oil.—The IllyroxYlon peruiferum (see Resinous Substances—Tolu balsam) affords an essential oil of sp. gr. 0.892 at 13° (55° F.), with a pleasant, aromatic, sassafras-odour.
Allspice- or Pimento-oil.—Both the fruit and leaves of several kinds of allspice or pimento (see Spices—Pimento) afford essential oil. The oil is most commonly extracted from the fruits, These, dried before they are quite ripe, are ground, and distilled with water. The product amounts to about 3-4i per cent., rarely almost 6 per cent. ; analysis reveals the presence of 10 per cent. in the husks, and 5 per cent. in the kernels. The yield of oil from the leaves has not been ascertained, but it is said to be considerable, and that the leaves and young shoots, destroyed while gathering the crop of berries, would repay distillation. The oil has a sp. gr. of 1.037, and very closely resembles clove-oil. It is frequently used as a substitute for or adulterant of the latter, both in medicine, and in combination with other oils for scenting soap. The small yield of oil renders it incapable of competition with clove-oil (p. 1420), except as a substitute.
essential oil known as " bitter-almond-oil " is obtained from the bitter almond (see Fruit—Almonds, p. 1022), which also yields a fatty oil, described on p. 1377. Though bitter almonds are the only commercial source of the oil, it is also afforded by many plants of the Pruned and Pomeal tribes, by a species of Vida, and probably some others. It does not exist ready-formed, but is a product of the decomposition of amygdaline in the presence of water and emulsine. The process is as follows. The unpeeled almond-kernels are first pressed to extract their fatty oil (p. 1377); the residual cake is then placed in salt water for about 24 hours, prior to distillation. Without due precaution, there is some difficulty in the distillation, owing to the presence of much albuminous matter, Pettenkofer avoids this by immersing 12 parts of powdered almonds in boiling water, by which the albuminous matters are coagulated, and the amygdaline is dissolved. The addition of an emulsion of only 1 part of either sweet or bitter almonds
will then suffice to effect the decomposition at a temperature not exceeding 40° (104° F.). The yield by this process from small quantities will sometimes reach per cent. Some manu facturers force steam through the cake enclosed in coarse sacking. In dealing with large quan tities of cake, the yield of essential oil varies widely ; the yearly average may fall to per cent., or rise to per cent., which, reckoning 57 lb. of cake to represent 100 lb. of almonds, means per cent. on the latter. This fluctuation is due partly to the want of uniformity in the bitter almonds used, and partly to the admixture of sweet almonds. The action of the emulsine on the amygdaline iu the presence of water is very rapid, 200 lb. of cake being completely exhausted by a 3-hours' distillation. The crude oil contains a proportion of hydrocyanic (prussic) acid, feebly combined, and which is gradually set free. This crude oil is employed by perfumers ; but the oil for medicinal use is sometimes deprived of the hydrocyanic acid by a process of purification. Maolagan's process oofisists in shaking up with lime and sulphate of iron (ferrous), and rediatilling ; the loss is 10 per cent. The purified oil is very liable to oxidize, unless carefully freed from water by agitation with fused chloride of lime. The oil ie colourless and thin, of peculiar odour, and burping aromatic flavour ; its sp. gr. is 1.061-1.065 when crude, and when purified ; its boiling-point is 180° (356° F.); it dissolves in 300 parts of water, and readily in alcohol and ether ; by exposure to the air, it is oxidized, and converted into benzoic acid.