Oleum Limonis. U. S., Br. Oil of Lemon.
Ol. Limon. [Lemon Oil]
"A volatile oil obtained by expression from the fresh peel of the ripe fruit of Citrus medica Limonum (Risso) Hooker filius (Fam. Rutaceae), and yielding not less than 4 per cent. of the aldehydes from Oil of Lemon, calculated as citral [C10H16O =152.13]. Preserve it in well-stoppered, amber-colored bottles, in a cool place, protected from light. Oil of Lemon having a terebinthinate odor is not to be dispensed." U. S. " Oil of Lemon is the oil obtained from Lemon Peel by various methods of expression." Br.
Oleum Limonum; Huile volatile de Citron, Fr. Cod.; Essence de Citron, Fr.; Oleum Citri, P. G.; Citronenöl, G.; Olio da limone, It.; Esencia de limon, Sp.
The exterior rind of the lemon abounds in a volatile oil, which, being contained in distinct cells, may be separated by simple expression. The rind is first grated from the fruit, and then submitted to pressure in a bag of fine cloth. The oil thus obtained is allowed to stand till it becomes clear, when it is decanted, and kept in stoppered bottles. By a similar process, the oil called by the French huile de cedrat is procured from the citron. (See Oil of Bergamot and Succus Limonis.) These oils may also be obtained by distillation, but thus procured, though clearer, and, in consequence of the absence of mucilage, less liable to change on keeping, they have less of the peculiar flavor of the fruit, and the mode by expression is generally preferred. A third method of separating the oil, used in Calabria and Sicily, is to put the grated rind into hot water and skim off the oil as it rises to the surface. (A. J. P., 1868, p. 27.) The method employed to obtain the finest oil is, however, that known as the ecuelle process. The ecuelle is an instrument usually made of tinned copper, bowl-shaped, and armed with concentric rows of short spikes. Attached to the bottom of the bowl is a hollow handle, closed at the bottom. This acts as a reservoir for the oil as the fruit is rubbed by the workmen over the sharp teeth. The oils are brought from Italy, Portugal, or Southern France.
The oils of lemons and oranges, as well as those of the other Aurantiaceae, will keep indefinitely upon admixture with a small proportion of alcohol (one ounce to a pound of the oil). When wanted for use, a quantity of water equal to that of alcohol, added to the mixture, will unite with the alcohol, and subside, leaving the oil free of the alcohol for all practical purposes. (Carl Fruh, A. J. P., 1871, 201.) E. J. Parry (Ch. & Dr., 1913, p. 378) discusses at some length the relative advantages of terpene-less and sesquiterpeneless oils and normal oils. The ordinary terpeneless oils contain from 42 to 45 per cent. of citral, while those that are sold as sesquiterpeneless contain from 65 to 72 per cent. citral. He states that the latter products lack the sweetness and softness of odor of those containing less citral, the overpowering odor of the latter constituent destroying the balance of harmony in the odor of the oil. He states that users of these products claim to get the best results from oils containing slightly less than 40 per cent. of citral and from which the whole of the terpenes have not been removed. The characters of the commercial terpeneless oil are as follows: sp. gr. at 15° C. (59° F.), 0.8935 to 0.899; optical rotation, -5° to -8° 30'; refractive index, 1.4810; citral, 42 to 48 per cent. The sesquiterpeneless oils are slightly higher in specific gravity, lower in optical rotation and always run above 65 per cent. of citral.
The great extent of the production and export of Sicilian and Calabrian essential oils (lemon, orange, bergamot, etc.) may be seen from the Italian official statistics, according to which the number of trees producing in 1896 was 17,084,-569, yielding 3,337,000,000 fruits. Of these 1,897,000,000 were exported, leaving 1,439,555,000 fruits for home consumption inclusive of those used in the manufacture of essences. (Schim. Rep., Oct., 1897, 23.)
Parry (Schim. Rep., Apr., 1912, p. 78) reports several shipments of lemon oil which upon investigation were found to be adulterated with Greek turpentine oil. They were noted by their low optical rotation, +50° to +54°, and their low citral content, 3.3 to 4.1 per cent.
Oil of lemon contains a small amount of pinene, with dextrogyrate limonene, about 7 to 8 per cent. of citral, C10H16O, an aldehyde yielding geraniol upon reduction, and a small amount of citronellal, C10H18O, also an aldehyde. Pinene, phellandrene, higher aldehydes, as octyl and nonyl, terpineol and geranyl acetate have also been reported in small amounts. Of these the citral is the constituent to which the oil chiefly owes its aroma and value. Umney and Swinton (P. J., 1898, 196) state that citral, citronellal, and an ester of geraniol are all necessary to form the true odor of oil of lemon. Citral boils under normal atmospheric pressure ,at from 228° to 229° C. (442.4°-444.2° F.) without decomposition if pure, and, like aldehydes, forms stable compounds with alkaline bisulphites. Schimmel & Co. now prepare the citral in a pure state, and recommend its use for enriching the ordinary oil of lemon.
Oil of lemon is often adulterated by the fixed oils and by alcohol, and sometimes with purified oil of turpentine, which is difficult of detection from its similar composition and specific gravity except with the polariscope. One of the tests for the presence of this oil is the terebinthinate odor produced when the adulterated oil is evaporated from heated paper; the official quantitative test defining the percentage of citral will be of service in detecting these adulterations. The most dangerous adulteration of oil of lemon is the use of citrene, the terpene left after the extraction of citral from oil of lemon which has been used in making terpene-less oil. Oil of lemon procured by expression is apt to precipitate and to undergo chemical change. J. S. Cobb has found no method so effectual to obviate this result, and at the same time to retain unimpaired the flavor of the oil, as to shake it with a little boiling water and allow the mixture to stand. A mucilaginous matter separates, and floats on the surface of the water, from which the purified oil may be decanted. (Ann. Pharm., ii, 86.) The best method of preservation is to add 10 per cent. of a bland fixed oil such as olive or cottonseed, which must subsequently be allowed for in measuring the oil for use.
Adulteration of Lemon Oil with Pinene.—In consequence of some seizures of lemon oil alleged to be adulterated with turpentine, in 1906, a number of importers stated their belief that pinene was normally present in appreciable amounts in some lemon oils. In consequence of this the U. S. Dept. of Agriculture undertook a special investigation of the subject, sending a trained observer and analyst to the producing countries, and published the results of the investigation in a special bulletin called "Circular 46, by E. M. Chace." The investigation showed conclusively that lemon oil shows no appreciable amount of pinene.
Spirit of Lemon (Spiritus Limonis, U. S. 1890) is no longer official. It was made by dissolving 50 mils of oil of lemon in 900 mils of deodorized alcohol, to which 50 Gm. of freshly grated lemon peel were added, the whole macerated for twenty-four hours, filtered, and enough deodorized alcohol added through the filter to make the whole measure 1000 mils.
Uses.—The oil of lemon is much less active than most of the other official volatile oils, and is used almost exclusively for its flavoring properties.
Dose, two to five minims (0.12-0.3 mil).