This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The lemon is the fruit of Citrus Medica, Linne, var. β-Limonum, Hooker filius (N.O. Butaceoe), a small tree which, like the orange, is probably a native of northern India. It is cultivated in all countries bordering on the Mediterranean, especially in Sicily and southern Italy, in Spain and Portugal, and in the Riviera.
The fruits are gathered whilst they are still green; the finest are wrapped in paper and exported in cases of 200 (Murcia lemons) to 360 (Messina lemons); less sightly fruits are packed in barrels and preserved with salt water. The finest lemons are those imported from Sicily (Messina and Palermo); those from Murcia are also of high quality, while Naples and Malaga lemons are less esteemed.
The lemon resembles the orange in development and in structure, but it is easily distinguished by its more elongated, ovoid shape and pale yellow colour; at the apex it is crowned by a distinct nipple. The pulp has a strongly but agreeably acid taste; the peel is aromatic and bitter.
The following parts of the fruit are official: the fresh peel, the juice, and the volatile oil obtained from the peel.
1. Lemon peel is pale yellow and more or less rough on the outer surface, whitish on the inner. The transverse section shows numerous large oil-glands embedded in the tissue. The peel has a strong fragrant odour and aromatic, bitter taste. It contains volatile oil and hesperidin, and is used chiefly as an agreeable flavouring agent.
Lemon Juice. Fresh lemons yield about 30 per cent, of juice, which, for pharmaceutical use, should be pressed from the fresh fruit. It is a turbid yellowish liquid with a characteristic odour and acid taste. The principal constituent is citric acid, of which it contains from 6.7 to 8.6 per cent. (30 to 40 grains in each fluid ounce). The amount of citric acid in the juice is largest in lemons imported in December and January, and smallest in August, both the fruit and the juice itself gradually diminishing in acidity when kept.
Large quantities of lemon juice are pressed in Sicily from the pulp that is left in the production of the volatile oil, the residual cake being used as cattle food. The juice is concentrated to a specific gravity of 1.233 to 1.235 and exported, chiefly to England, for the manufacture of citric acid; or the citric acid is precipitated as calcium citrate from which the citric acid is subsequently regenerated.
Oil Of Lemon. Various methods are used for the production of oil (essence) of lemon, but the following appears to be largely adopted in Sicily, whence most of the oil is exported: -
Fig. 54. - Lemon. Transverse section. (Planchon and Collin).
The lemons are first cut lengthwise into three or four pieces, the pulp removed and pressed, and the peel set aside in a cool place for some hours. The workman holds in his left hand a medium-sized sponge, smaller ones being placed between the fingers. With the right hand he takes a piece of peel and squeezes it in such a way as to break the oil-glands and discharge their contents on the sponges. When sufficient has accumulated the sponges are pressed; the liquid thus obtained separates on standing into a lower watery stratum and an upper clear oily layer which can be poured off. The oil thus obtained is filtered and exported in coppers of varying sizes. This hand-pressed peel is then pickled in brine and sold to the manufacturers of candied lemon peel. This method of separating the volatile oil from the peel is termed the ' sponge ' process; 1,000 lemons yield about 800 gm. of volatile oil. That which is obtained during the winter from lemons that are not fully ripe is considered the best.
In the south of France a different procedure is adopted, of which the following description has been given: ' The object being to set free and to collect the oil contained in the vesicles of the peel, an apparatus is employed which may be thus described: a stout saucer or shallow basin of pewter, about 25 cm. in diameter, with a lip on one side for convenience of pouring; fixed in the bottom of this saucer are a number of stout, sharp, brass pins standing up about half an inch; the centre of the bottom is deepened into a tube about an inch in diameter and five inches in length, closed at its lower end. This vessel, which is called an ecuelle a piquer, has therefore some resemblance to a shallow, dish-shaped funnel, the tube of which is closed below.
' The workman takes a lemon in the hand and rubs it over the sharp pins, turning it round so that the oil-vessels of the entire surface may be punctured. The essential oil which is thus liberated is received in the saucer, whence it flows down into the tube; and as this latter becomes filled it is poured into another vessel that it may separate from the turbid aqueous liquid that accompanies it. It is finally filtered, and is then known as Essence de Citron au Zeste ' (Fliickiger and Hanbury).
A machine (scorzetta), constructed on a similar principle, has been devised by which the scarification of the lemons is much more rapidly effected than is possible by the tedious hand process, and by which at the same time an increased yield of oil is obtained; it has not, however, as yet been generally adopted.
Oil of lemon is also prepared by distilling the peel with water, but this distilled essence is inferior in fragrance to that prepared by either of the foregoing processes.
Oil of lemon is a pale yellow liquid of sp. gr. 0.857 to 0.860 and optical rotation + 58° to + 64°, consisting of about 90 per cent, of the terpene limonene and about from 4 to 6 per cent, of the aldehyde citral, C10H1 60, the latter being the chief odorous constituent of the oil. Other odorous constituents are citronellal, geranyl acetate, linalyl acetate, octyl and nonyl aldehydes, etc. ' Terpeneless ' essence of lemon is prepared by distilling off the terpene in vacuo, and consists mainly of citral (50 per cent.) together with the above-mentioned esters and aldehydes.
The fruit of Citrus Bergamia, Risso, cultivated in southern Italy and Sicily. The volatile oil is obtained by rotating the fruits in a machine against sharp copper points, collecting and filtering the mixture of volatile oil and cell sap and decanting. The pulp is pressed and the juice used for the production of calcium citrate or citric acid. The oil contains linalyl acetate (34 to 40 per cent.), d-limonene and bergaptene.
The fruit of Citrus Medica, var. acida, Brandis (West Indian Lime) or of Citrus Limetta, Risso (Italian Lime). The volatile oil of the former has an odour of citronella and contains citral and limonene; that of the latter an odour of bergamot and has a com-position similar to bergamot oil but contains less linalyl acetate (26 per cent.). The pulp of both contains citric acid (about 7 per cent.).