VOLATILE OILS, or ESSENTIAL OILS, vegetable oils distinguished by the pos session of pungent, characteristic odors, and by the fact that they can be vaporized without de composition, and usually without any consider able residue. The volatile oils differ from the "fatty oils,o or "fixed (Ale" (of which olive oil is an example), from a chemical point of view, in containing little or no true fat The known volatile oils are very numerous, and are obtained from plants, or parts of plants, or from vegetable exudations, mainly by the action of heat or pressure, or by the solvent action of fats, chloroform, petroleum ether or carbon tetrachloride. In some cases, as in the extraction of the essential oil in orange peel, a portion of the oil may be obtained by plac ing the material containing it in horse-hair bags, and subjecting it to pressure. Distillation is also commonly employed, the plants or parts of plants containing the oil being placed in a still with water, the contents of the still being constantly stirred and heated by means of a steam-jacket. The boiling points of the volatile oils are mostly higher than that of water, but as they possess a considerable vapor tension at the boiling point of water, they distil over at that temperature in sufficient quantity to make the process commercially practicable. In some cases it is found to be advantageous to raise the boiling point of the water in the still some-. what by the addition of salt. When the oil that is to be prepared is injured by exposure to the temperature of boiling water, it is customary to extract the oil by macerating the plant with grease. In the preparation of perfumes, for example, it is common to treat the flowers con taining the oiI with pure lard or paraffin, which is kept fluid by a water-bath. The fat extracts the volatile oil, and when the charged fat is afterward shaken up with akohol it gives up the oil, in large measure, to the alcohol. The process known as "enfleuragep is essentially the same as the one just indicated, except that it is not conducted by the aid of heat, the grease being allowed to remain in contact with the flowers for a longer time, at a lower tempera ture; the oil then being recovered from the fat by means of alcohol, as before.
The following are some of the more familiar of the essential or volatile oils: Oil of Bitter Prepared by Cis tilling the pulp that is left after the fixed oil contained in the almonds has been expressed by pressure. As at first prepared it contains a considerable quantity of prussic acid, and in this stage it is very poisonous. After it has been freed from the prussic acid it is lcnown, commercially, as gOil of bitter almond, S. P. Al) (without prussic acid). When thus
purified the oil consists mainly of benzaldehyde, C.H.CHO, and boils at 179° C.
Oil of Bergamot—Prepared from the unripe fruit of Citrus bergamia., by squeezing the rind by hand and wiping the expressed oil off with a sponge, the sponge being squeezed at intervals into a collecting vessel. It contains a consider able quantity of the hydrocarbon citrene. together with other compounds whose precise nature has not yet been thoroughly investigated. The oil is extensively used in perfumery. Oil of bergamot is also made synthetically.
Oil of Obtained by distilling the flower buds of Caryophyllus aro;naticus. It consists of a mixture of sesquiterpene and euge nol and is heavier than water.
Oil of Prepared by distilling the leaves of the eucalyptus tree. It is pale yellow in color and is used in medicine and in perfumery. Its chief constituent is eucalyptol or cineol, Ci0H00.
Oil of Prepared by the distilla tion of lavender flowers, the best quality being made from Lavandula vera. Oil of spike is an inferior variety, prepared from Lavandula spica. Oil of lavender is used in perfumery and oil of spike is extensively employed in porcelain paintuig.
Oil of Lemon.-- Prepared from scarcely ripe lemon rinds by the sponge method, de scribed above under Oil of Bergamot. An in ferior variety is also prepared by distilling the residues remaining from this process. Oil of lemon consists chiefly of limonene, C.H., a hydrocarbon which resembles the citrene of oil of bergamot, but which differs from it in certain particulars. Oil of lemon is used in confectionery and perfumery.
Oil of Origanum, Oil of Thyme, or Mar joram Oil.— Obtained by distillation from cer tain species of marioram.
Oil of Peppermmt— Prepared by distilling the herb Mentha piperita. It consists chiefly of a solution of menthol in various terpenes and is used in medicine and as a flavoring, espe cially in confectionery.
Attar (or Otto) of Roses.-- Prepared by the distillation of certain species of roses and especially from Rosa dansascena, which is culti vated in Turkey. It is used extensively in per fumery and, on account of its high coirunercial value, is often (and perhaps always) adul terated. The most common adulterant is "geranium which is manufactured expressly for adulterating attar of roses, by distilling a species of grass that grows in India.
Oil of Prepared by distilling the resinous exudations from certain species of pine trees. American oil of turpentine is prepared chiefly from Pima australis and con sists mainly of dextro-pinene, a hydrocarbon having the formula CaoHlit, and boiling at 156° C.