Page:The American Cyclopædia (1879) Volume IV.djvu/627

CITRIC ACID CITRON 615 so long as the effervescence continues. Citrate of lime (an insoluble powder) forms, and after being separated by drawing off the watery liquor is well washed with warm water. This salt is then intimately mixed with strong sul- phuric acid diluted with six parts of water. After some hours the citrate is decomposed, the sulphuric acid having taken up the lime and formed an insoluble sulphate, setting the citric acid free. This, separated by decanting and filtering, is evaporated in leaden pans till it attains the specific gravity 1-13. The eva- poration is afterward continued by a water or steam bath till the liquor begins to be sirupy, or to be covered with a thin pellicle. It is then instantly removed from the fire, and put aside to crystallize, the mother liquor after a few days being evaporated as above, and again set to crystallize, and so on as long as clean crystals are obtained. To obtain pure citric acid, all the crystals should be redissolved and recrystal- lized, it may be several times, and the solution digested with bone black. A gallon of lemon juice should make about eight ounces of crys- tals; more than this is sometimes obtained. Attempts have been made to prepare the citrate of lime for exportation instead of the lemon juice, to reduce the cost of transportation; but its liability to ferment, which destroys the citric acid by converting it into acetic and butyric acids, prevents this method from being employed. Citric acid was first obtained by Scheele in 1784. The crystals are trans- parent, in the form of rhombic prisms, with summits of four trapezoidal faces. The salt is soluble in water, warm or cold, as also in alco- hol, but not in ether. Its specific gravity is 1'6. Its taste is intensely acid, and almost caustic, but still agreeable. It is distinguished from other vegetable acids by its depositing an insoluble citrate when heated with lime water, by the form of its crystals, and also by forming a deliquescent salt with potassa. The crystals are combinations of 1 equivalent of citric acid with either 3, 4, or 5 of water, according to the method and temperature by which they have been obtained. The anhydrous acid, as it exists in the citrate of silver, is represented by the formula CgHsOT ; but it has never been isolated. Citric acid is much used at sea as an antiscorbutic, but the raw lemon juice is thought to be more efficient. English ves- sels are all required by law to carry a certain quantity of the latter for each man employed. It goes to the manufacture of citric acid, as already stated, in a concentrated form ; but that intended for the use of ships is protected from fermentation by the addition of some spirit. Citric acid is largely adulterated, some- tunes to an almost incredible percentage, with tartaric acid. Acetate of potassa, added to its solution in cold water, will, if tartaric acid be present, throw down a white crystalline precip- itate of bitartrate of potassa (cream of tartar). It sometimes also retains some sulphuric acid. Besides its use as an antiscorbutic, citric acid is employed instead of lemon juice for the prep- aration of refreshing drinks, and in the arts it is of value to calico printers. CITRON, the fruit of a low, evergreen tree (citrus medica, Linn.), which belongs to the same genus as the lime, lemon, shaddock, and orange trees, attains in its wild state a height of about 8 ft., and is erect and prickly, with long reclining branches. Its leaves are alter- nate, oblong-acute, subserrate, and pale green ; its petioles are naked, and its flowers 40-androus and externally purple ; and its fruit is ovate, about 6 inches long, furrowed, with a pro- tuberance at the tip, and with two rinds, the outer thin, greenish yellow, with numberless miliary glands, full of a most fragrant oil, and the inner thick, fungous, and white. The trees of this genus are among the most brilliant of fruit-bearing trees, are indigenous in the East, and are supposed to be alluded to in the golden apples which the Greeks attributed to the gar- Citrus medlca. dens of the Hesperides. There is, however, no evidence that any of them were cultivated either by the Greeks or earlier Romans. The citron tree, the most beautiful of them, and the first in- troduced into Europe, was obtained from Media and perhaps Assyria, and was first cultivated in Italy by Palladius in the 2d century. In the East it is constantly in blossom, flowers and fruit always hanging upon the tree together; at Nice, Genoa, and Naples, and also in the West Indies, it endures the open air, but at Florence and Milan it requires protection in the winter, and in more northern climates it is cul- tivated in conservatories. In China there is a splendid variety, with large and solid fruit, divided at the end into five distinct lobes, whence it is called by the Chinese the fingered citron. It is kept for its agreeable fragrance on fine porcelain dishes in sitting rooms. The citron is a somewhat acid fruit, rarely eaten raw, and highly valued for its very fragrant rind, which by being preserved in sugar be-