Oleum Rosae (U. S. P.)—Oil of Rose.
"A volatile oil distilled from the fresh flowers of Rosa damascena, Miller (Nat. Ord.—Rosaceae). It should be kept in well-stoppered vials, in a cool place, protected from light. When dispensed, it should be completely liquefied by warming, if necessary, and well mixed by agitation"—(U. S. P.).
SYNONYMS: Otto of roses, Attar of roses, Essence of rose.
History and Source.—The earliest nations gave attention to the rose aroma, and employed oil of rose in many of their religious ceremonies. This oil consisted for centuries merely of some fatty oil saturated with the aroma of the flower. Arab writers mention the distillation of the oil of rose in the eighth and ninth centuries. In the middle ages Persia was the principal country of its production. It gradually extended to India and westward, and gained a foothold in Bulgaria early in the seventeenth century. Since about 1850 the French, and in more recent years the German rose industries, have become important. Adulteration with santal-wood oil was practiced in Persia (E. Kämpfer, 1682-1684), and with East Indian geranium (Palma rosa) oil in Kashmir (Polier, 1788). (See Dr. Hoffmann in Die Aetherischen Oele, p. 556.) Rose oil is distilled in Bulgaria as well as in Germany, from the fresh leaves of Rosa damascena, Miller; in southern France from Rosa centifolia, Linné. The yield of German oil is 1 pound from 5,000 to 6,000 pounds of flowers, or about 0.02 per cent.
Description.—The official oil of rose is thus described: "A pale-yellowish, transparent liquid, having the strong, fragrant odor of rose, and a mild, slightly sweetish taste. Specific gravity, 0.865 to 0.880 at 20° C. (68° F.). It is but slightly soluble in alcohol, and neutral to litmus paper moistened with alcohol. The congealing and melting points of the oil are subject to some variation, depending upon the amount of stearopten, but, when slowly-cooled to a temperature, usually between 16° and 21° C. (60.8° and 69.8° F.), it becomes a transparent solid, interspersed with numerous slender, shining, iridescent, scale-like crystals. Upon the application of the heat of the hand, the crystals should float in the upper portion of the liquefied oil"—(U. S. P.). It is combustible, and its vapor is said to form an explosive mixture with oxygen. The pharmacopoeial description is that of the Bulgarian oil. The German oil is stated to have a much stronger rose odor than the Bulgarian, and to be of absolute purity (see Power, Essential Oils, p. 30). At ordinary temperatures, it is a semisolid, soft mass, congealing between 27° and 37° C. (80.6° and 98.6° F.), and containing from 26 to 34 per cent of stearopten, while Bulgarian oil contains from 10 to 15 per cent.
Chemical Composition.—Rose-stearopten, or rose camphor, is odorless, and was recognized by Flückiger (1869) to be a paraffin hydrocarbon. It may be differentiated, by distillation in vacuo, into two paraffins, one melting at 22° C. (71.6° F.), the other at 40° and 41° C. (104° and 105.8° F.). The presence of this paraffin renders the oil partly insoluble in alcohol. The liquid portion of oil of rose contains as its chief constituent the alcohol geraniol (Bertram and Gildemeister, 1894; U. Eckart's rhodinol, 1891).
GERANIOL is a colorless liquid, boiling at 230° C. (446° F.), of a rose-like odor, having the formula C10H18O or (CH3.C[CH3]:CH.CH2.CH2.C[CH3]:CH.CH2OH). It is a primary alcohol, and yields, upon oxidation, the aldehyde citral (C10H16O). It is likewise the principal constituent of East Indian geranium, rose geranium, citronella, and lemon-grass oils. It forms a characteristic, crystallizable addition compound with dry calcium chloride, insoluble in the usual organic solvents, but decomposable by water; this regenerates therefrom geraniol, which may be obtained chemically pure by this method. Oil of rose furthermore contains about 20 per cent of l-citronellol (Tiemann and Schmidt, 1896). Both geraniol and citronellol are, for the smaller part, combined in the form of ester (about 3 per cent). The exact honey-like odor of rose oil has not yet been obtained by a combination of the constituents enumerated.
Adulterations and Tests.—Owing to its high price, oil of rose is subject to adulteration; the additions to it are mostly the oils of palma rosa (East Indian geranium from Andropogon) and of rose geranium (from Pelargonium). A deficiency in rose camphor, resulting from the addition of these oils, is sometimes made up by adding spermaceti. The addition of these oils, if carried out intelligently, is very difficult to detect. Crude adulterations may be recognized by determining the following constants: Specific gravity, optical rotation, congealing point, amount and chemical nature of stearopten, saponification, and acetylation (see details of these determinations in Gildemeister and Hoffmann, Die Aetherischen Oele, pp. 566-570). The U. S. P. gives the following color tests for the purity of oil of rose: "If to 5 drops of the oil, contained in a test-tube, 5 drops of concentrated sulphuric acid be added, a reddish-brown, thick mixture will be produced, but no white fumes or tarry odor should be developed, and the fragrant odor of the oil should not be destroyed. If this mixture be then shaken with 2 Cc. of alcohol, the resulting liquid may be turbid, but should be nearly colorless, and should not at once assume a red or reddish-brown color (absence of oil of ginger-grass or Turkish oil of geranium, from Andropogon Schoenanthus, Linné [Nat. Ord.—Gramineae], and from oil of rose geranium, from Pelargonium Radula [Cavanilles], Aiton, Pelargonium capitatum [Linné], Aiton, and Pelargonium odoratissimum [Linné], Aiton [Nat. Ord.—Geraniaceae])"—(U. S. P.). Power (loc. cit.) suggests that the foregoing test is rather reliable if 5 Cc. of alcohol is employed instead of 2 Cc., and if the adulterant is present in considerable quantity. The oils mentioned in the above test all have an acid reaction, as well as the oil of rhodium (from roots of Convolvulus [Rhodorrhiza, Webb] Scoparius, Linné, and Convolvulus floridus, Linné, of Canary Isles), which is occasionally an adulterant. The latter has the combined odor of rose, copaiba, and cubeb, and is bitter.
Uses.—Oil of rose is used altogether as a perfume, and is frequently added to cerates, ointments, liquors, etc., for the purpose of rendering them fragrant.