CITRIC ACID (C,,ILO,,, or Is a powerful tribasic acid, which crystal lizes in large transparent colorless prisms. These crystals are readily soluble in water and alcohol, but are insoluble in ether. The crystals contain two atoms of water of crystallization (not expressed in the above fornittlie), which are expelled at a tempera ture of 212'. Citric acid has a strongly acid taste and reaction, and displaces carbonic acid from the carbonates. Its watery solution quickly becomes moldy on exposure to the air, and the acid is then found to be converted into acetic acid., When heated to about no°, vapor of acetone and carbonic oxide are given off, and a residue of aeon itic acid (0,21160,2), an acid occurring in the leaves and roots of monkshood and other species of aconite, is left; and when fused with potash, it assimilates the elements of water, and is decomposed into oxalic and acetic acids, as shown in the equation.
Citric Acid. Oxalic Acid. Acetic Acid.
+2110 = + 2C411404.
These reactions illustrate the changes which organic acids naturally undergo in the vegetable kingdom. It is to the presence of C. A. that a great many fruits owe their agreeable acidity. It occurs in a free state either alone or associated with malic and tar taric acids in oranges, lemons, cherries, currants, raspberries, gooseberries, strawber ries, wim•tleberries, etc.. and in several tubers and bulbs, as in the potato and onion. It also exists in combination with potash or lime in potatoes, onions, and artichokes.
This acid, which is almost always prepared from lemon or lime juice, is thus obtained. The juice, after undergoing incipient fermentation, is filtered, and neutralized with chalk; and the insoluble citrate of lime thus formed is decomposed with very dilute sulphuric acid. On the removal of the sulphate of lime that is thus formed by filtra tion, the solution of C. A. must be concentrated till a film begins to form, when the crystals readily separate on cooling. Citric acid has also been prepared from unripe gooseberries, whose juice is allowed to ferment; and after the removal of the alcohol by distillation, the acid is separated in the way already described: 100 lbs. of goose
berries yield 10 lbs. of spirit of spec. gray. 0.028, and 1 lb. of crystallized acid.
Citric acid is used largely in manufactures; calico-printers employ it for discharging the mordant from the cloth in patterns; and it is used in dyeing silk with safflower, and for heightening the tint of cochineal. The raw material from which the acid for these purposes is obtained "is a black fluid-like thin treacle, which comes from Sicily, and is obtained by inspissating the expressed juice of the lemon after the rind has been removed for the sake of the essential oil."—Watts's Dictionary of Chemistry, vol. i. p. 005.
The most important of the numerous salts of C. A. are the citrates of lime, potash, ammonia, and iron. Citrate of lime 4Aq) is formed in the preparation of C. A., and is a tine white crystalline powder, more soluble in cold titan in hot water. Citrate of potash +2Aq) is formed by neutralizing the acid with carbon ate of potash, and crystallizes in clear deliquescent needles, insoluble in alcohol. Citrate of ammonia can only be obtained in solution. Citrate of iron is prepared by dissolving freshly precipitated peroxide of iron in a warm solution of C. A.; a reddish-brown solution is formed, which, on evaporation, yields brilliant scales of a light-brown color. Excepting the first, all these salts are employed in medicine— the citrates of potash and ammonia as diaphorctics and febrifuges (see Al RATED WATERS), and the citrate of iron as a tonic. Lemon juice, in which C. A. is the most active ingre dient, is a most valuable medicine in scurvy, active hemorrhage, rheumatism, etc.•, and when it cannot be obtained, C. A. is the best substitute. The general uses of C. A. in combination with an alkali have been already noticed.