"Lemon Juice is the freshly expressed juice of the ripe fruit of Citrus Medica, Linn., var. ß Limonum, Hook. f." Br.
Limonis Succus, U. S. P. VIII; Succus Citri; Sue de Citron (de Limon), Fr. Cod.; Citronensaft, Limonensaft, G.; Succo di limone, It.; Zumo de limon, Sp.
We are supplied with lemons and limes chiefly from the West Indies, the Mediterranean and California. Though the former of these fruits only is directed by the Br., lime juice is recognized by the N. F., and both kinds are employed indiscriminately for most medicinal purposes, and the lime affords a juice at least equal, in proportional quantity and acidity, to that obtained from the lemon.
The seed of the lime contains 58 per cent. of fixed oil, which is said to equal in flavor the best olive oil. Its tendency to resist rancidity is reputed to be very great. ((, 1894, 411.) Lime juice is official in the N. F. IV under the title of Succus Citri .
As lemons rapidly deteriorate on keeping, if exposed to the air, the suggestions of protecting them by dipping them in melted paraffin, or by using a varnish of shellac dissolved in alcohol, made by George Mee, of London, are not without value. Mee found that lemons thus covered with varnish continued sound for a period of many months. (See A. J. P., 1866, p. 474.)
The juice is the part for which the fruit is most esteemed. It is sharply acid, with a peculiar grateful flavor, and consists chiefly of water, citric acid (from 6 to 10 per cent.), gum and sugar (from 3 to 4 per cent.), and inorganic salts (2.28 per cent.). It sometimes has in it a little volatile oil, derived by pressure from the rind. It is " a slightly turbid, yellowish liquid. Taste sharply acid. Specific gravity 1.030 to 1.040. 20 millilitres require for neutralisation not less than 20 and not more than 25.7 millilitres of N/l solution of sodium "hydroxide, corresponding to a proportion of not less than 7 and not more than 9 grammes of citric acid in 100 millilitres. The residue obtained on evaporation, dried at 110° C. (230° F.), yields not more than 3 per cent. of ash. 100 millilitres of Lemon Juice are neutralised by about 11.4 grammes of Potassium Bicarbonate, by about 9.5 grammes of Sodium Bicarbonate, and by about 16.5 grammes of Sodium Carbonate." Br.
The U. S. P. IX does not recognize lemon juice, the U. S. P. VIII provided the following tests: "It reddens blue litmus paper and should contain from 7 to 9 per cent. of citric acid. If a few drops of barium chloride T.S. be added to filtered Lemon Juice, no turbidity or white precipitate should be produced (absence of sulphuric acid or sulphates). If an equal volume of sulphuric acid containing a few drops of alcohol be added to Lemon Juice, and the liquid heated, no odor of acetic ether should be developed (absence of acetic acid). Upon the addition of solution of potassium acetate (1 in 3) and alcohol in excess, no white crystalline precipitate should form after allowing the liquid to stand fifteen minutes (absence of tartaric acid). At least 10 mils of normal potassium hydroxide V.S. should be required to neutralize 10 mils of Lemon Juice, phenolphthalein T.S. being used as indicator." U. S. VIII.
As lemons cannot always be obtained, the juice is often kept in a separate state, but, from its liability to spontaneous decomposition, it speedily becomes unfit for medicinal use, and, though various means have been resorted to for its preservation, it can never be made to retain for any length of time its original flavor unaltered. One of the most effectual methods of preserving the juice is to allow it to stand for a short time after expression, until a coagulable matter separates, then to filter, and introduce it into glass bottles, with a stratum of almond oil or other sweet oil upon its surface. It will keep still better if the bottles containing the filtered juice be permitted, before being closed, to stand for fifteen minutes in a vessel of boiling water. Another mode is to add one-tenth of alcohol and to filter. The juice may also be preserved by concentrating it either by evaporation with a gentle heat, or by exposure to a freezing. temperature, which congeals the aqueous portion and leaves the juice much stronger than before. When used, it may be diluted to the former strength, but though the acid properties are retained, bottled lemon juice is frequently found to be preserved with sulphur dioxide, which dissolves in it to form sulphurous acid. The presence of this preservative interferes with some of its pharmaceutical uses and such a product should not be employed for medicinal purposes. The flavor of the juice is found to have been deteriorated. Lemon syrup is another form in which the juice is preserved.
The proportion of citric acid in lemon juice varies greatly, ranging from 4.5 to nearly 9 per cent. Stoddart found the acidity to diminish rapidly with the advance of summer, with little change in the sp. gr. of the juice. (P. J., Oct., 1868.) H. H. Robins, after examining large consignments of lemons, states that the average yield of citric acid taken from a year's receipts was 35.23 grains in a fluidounce. (C. D., 1896, 742.) A solution of tartaric acid in water, with the addition of a little sulphuric acid, and flavored with the oil of lemon, has been fraudulently substituted for lemon juice, particularly as an antiscorbutic on long voyages, for which purpose it is quite useless. An application of the test for tartaric and sulphuric acids will at once detect the fraud.
The proportion of citric acid in lime juice is required by the N. F. IV to be not less than 5 Gm. nor more than 10 Gm. to each 100 mils. It is required to be free from sulphuric acid, but is permitted to contain 0.04 Gm. of 802 in each 100 mils. Other preservatives are prohibited as are also artificial colors.
Uses.—Lemon juice is refrigerant, and, properly diluted, forms a refreshing and agreeable beverage in febrile and inflammatory affections. It may be given with sweetened water in the shape of lemonade, or may be added to the mildly nutritive drinks, such as albumen water, barley water, etc., usually administered in fevers. It is also much employed in the formation of those diaphoretic preparations known by the names of neutral mixture and effervescing draught. One of the most beneficial applications of lemon juice is to the prevention and cure of scurvy, for which it may be considered almost a specific. For this purpose, ships destined for long voyages should always be provided with a supply of the preserved juice. In England every foreign-going ship is required by law to take such a supply of lemon or lime juice that every seaman shall have a daily allowance of an ounce after having been ten days at sea. Its antiscorbutic effects have been found to be due to the presence of one of a class of chemical activators called vitamines. It has been employed with advantage in acute rheumatism in doses of from one to four fluidounces (30-120 mils) from four to six times a day. Locally applied it acts as an astringent and has been used with benefit in pruritus of the scrotum, in uterine hemorrhage after delivery, in sunburn, and as a gargle in diphtheritic sore throat.
Off. Prep..—Syrupus Limonis, Br.; Trochiscus Acidi Carbolici, Br.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.