Oleum Limonis (U. S. P.)—Oil of Lemon.
Related entry: Limon.—Lemon
"A volatile oil obtained by expression from fresh lemon peel. It should be kept in well-stoppered bottles, in a cool place, protected from light"—(U. S. P.).
Preparation.—Oil of lemon is obtained by lightly grating the fresh rind of the lemon, placing it in a fine cloth bag, and then subjecting it to pressure; the sediment is allowed to settle, and the clear oil is poured off (C.). It may also be obtained by distillation, but this mode is not advisable, because the distilled oil readily decomposes. Other methods, such as the process of rupturing the oil glands and gathering the product upon sponges, etc., are likewise followed (see Oleum Aurantii Corticis). The oil is imported from the southern parts of Europe, as Italy, Portugal, etc.
Description and Tests.—Oil of lemon as officially described as "a pale yellow, limpid liquid, having the fragrant odor of lemon, and an aromatic, somewhat bitterish taste. Specific gravity, 0.858 to 0.859 at 15° C. (59° F.). Its optical rotation should not be less than 60° to the right in a 100 Mm. tube, and at a temperature of about 15° to 20° C. (59° to 68° F.). Soluble in three times its volume of alcohol, the solution being neutral or slightly acid to litmus paper; also soluble, in all proportions, in absolute alcohol, carbon disulphide, or glacial acetic acid. When kept for some time, the oil should not develop a terebinthinate odor or taste (absence of oil of turpentine, or other oils consisting chiefly of pinene)"—(U. S. P.). When exposed to light and air, oil of lemon readily decomposes, becoming thicker, and forming a brown, sticky sediment.
Oil of lemon is frequently adulterated by alcohol, the fixed oils, or more frequently oil of turpentine. Alcohol may be detected by the milky fluid which forms upon agitating the oil with water. The fixed oils may be known by leaving a residue of more than 5 per cent upon evaporation of the oil. Well rectified coal oil has its odor entirely covered when added to oil of lemon, but the adulteration may be detected by the difference in specific gravity, and by the almost complete insolubility of the coal oil in alcohol. Oil of turpentine may be detected by the turpentine odor evolved when the impure oil is evaporated from heated paper. Its presence can be more accurately established by its diminishing influence upon the optical rotation of the oil. Oil of lemon contains no pinene (Schimmel &, Co., 1897).
Chemical Composition.—Ninety per cent of oil of lemon consists of terpenes, the chief constituent of which is dextro-limonene (Wallach, 1885; Tilden's citrene, 1877), with a small quantity of phellandrene (Schimmel & Co., 1897). The highest fractions contain a sesquiterpene (Olivieri, 1891). The agreeable fragrance of lemon oil is due to oxygen compounds, especially citral (C10H16O, or CH3.C[CH3]CH.CH2.CH2.C[CH3]:CH.CHO), a doubly unsaturated aldehyde, present in the quantity of about 7 to 10 per cent (J. Bertram, 1888). Its chief occurrence is in lemon-grass oil (70 to 80 per cent). It is a golden-yellow fluid, optically inactive, boiling with slight decomposition at 228° to 229° C. (442.4° to 444.2° F.), under atmospheric pressure. It is the aldehyde of geraniol (see Oleum Rosae), and forms a crystallizable compound with sodium bisulphite. It is convertible into ionone, an isomer of irone, both possessing the essential odor of orris root (see Gildemeister and Hoffmann, Die Aetherischen Oele, p. 215). Oil of lemon furthermore contains the fragrant aldehyde citronellal (C10H18O), and small amounts of the esters geranyl-acetate (in Messina and Palermo oils), and linaloyl-acetate in the latter oil alone (Umney and Swinton, Pharm. Jour. Trans., Vol. VII, 1898, pp. 196 and 370). The non-volatile lemon camphor is not a uniform substance.
Action, Medical Uses, and Dosage.—Stimulant and aromatic. Its chief use is in perfumery, and to impart an agreeable flavor to medicines. It has been recommended in certain affections of the eye, as a local application. A very agreeable drink for the summer and for febrile patients may be made of white sugar, 4 ounces; oil of lemon, 10 drops; triturate together, and add citric acid, 2 drachms; a teaspoonful of this to a tumbler of water forms a pleasant, refreshing draught. Tartaric acid may be substituted for the citric, if desired.