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CITRIC ACID

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Originally appearing in Volume V06, Page 398 of the 1911 Encyclopedia Britannica.
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CITRIC See also:

ACID , Acidum citricum, or OXYTRICARBALLYLIC ACID, C3Hi(OH) (CO.OH)3, a tetrahydroxytribasic acid, first obtained in the solid See also:state by Karl Wilhelm See also:Scheele, in 1784, from the juice of lemons. It is See also:present also in oranges, citrons, currants, See also:goose-berries and many other fruits, and in several bulbs and tubers. It is made on a large See also:scale from See also:lime or See also:lemon juice, and also by the See also:fermentation of See also:glucose under the See also:influence of Citromycetes pfefferianus, C. glaber and other ferments. Lemon juice is fermented for some See also:time to See also:free it from See also:mucilage, then boiled 2 Cf. the name Kathian in a Ramessid See also:list of cities of See also:Cyprus, Oberhummer, See also:Die Insel Cypern (See also:Munich, 1903), p. 4. ' Gen. x. 4; Num. See also:xxiv. 24; Is. See also:xxiii. 1, 12; Jer. ii. Io; Ezek. See also:xxvii. 6. See also:Dan. xi.

30; I See also:

Mace. i. 1; viii. 5. See also:Schrader, " Die Sargonstele See also:des Berliner Museums," in Abh. d. k. Preuss. Akad. Wiss. (1881); Zur Geogr. d. assyr. Belches (See also:Berlin, 1890), PP. 337-344 (c. 1700 B.c.). and filtered, and neutralized- with powdered See also:chalk and a little See also:milk of lime; the precipitate of See also:calcium citrate so obtained is decomposed with dilute sulphuric acid, the See also:solution filtered, evaporated to remove calcium sulphate and concentrated, preferably in vacuum pans.

The acid is thus obtained in colourless rhombic prisms of the See also:

composition C6H807+H20. Crystals of a different See also:form are deposited from -a strong boiling solution of the acid. About 20 gallons of lemon juice should yield about to lb of crystallized citric acid. The acid may also- be prepared from the juice of unripe gooseberries. Calcium citrate must be manufactured with care to avoid an excess of chalk or lime, which would precipitate constituents of the juice that cause the fermentation of the citrate and the See also:production of calcium acetate and butyrate. The See also:synthesis of citric acid was accomplished by L. E. Grimaux and P. See also:Adam in 1881. See also:Glycerin when treated with hydrochloric acid gives propenyl dichlorhydrin, which may- be oxidized to s-dichloracetone. This See also:compound combines with hydrocyanic acid to form a nitrile which hydrolyses to dichlorhydroxy iso-butyric acid. See also:Potassium See also:cyanide reacts with this acid to form the corresponding dinitrile, which is converted by hydrochloric acid into citric acid.

This See also:

series of operations proves the constitution of the acid. A. See also:Haller and C. A. Held synthesized the acid from See also:ethyl chlor-acetoacetate (from See also:chlorine and acetoacetic ester) by See also:heating with potassium cyanide and saponifying the resulting nitrile. The See also:acetone dicarboxylic acid, CO(CH2CO2H)2, so obtained combines with hydrocyanic acid, and this product yields citric acid on See also:hydrolysis. Citric acid has an agreeable sour See also:taste. It is soluble in 4ths of its See also:weight of See also:cold, and in See also:half its weight of boiling See also:water, and dissolves in See also:alcohol, but not in See also:ether. At 15o° C. it melts, and on the continued application of See also:heat boils, giving off its water of See also:crystallization. At 175° C. it is resolved into water and aconitic acid, CSH606, a substance found in Equisetum jiuviatile, Monks-See also:hood and other See also:plants. A higher temperature decomposes this See also:body into See also:carbon dioxide and itaconic acid, C5H5O4, which, again, by the See also:expulsion of a See also:molecule of water, yields citraconic anhydride, C5H403. Citric acid digested at a temperature below 4o° C, with concentrated sulphuric acid gives off carbon monoxide and forms acetone dicarboxylic acid.

With fused potash it forms potassium oxalate and acetate. It is a strong acid; and dissolved in water decomposes See also:

carbonates and attacks See also:iron and See also:zinc. The citrates are a numerous class of salts, the most soluble of which are those of the alkaline metals; the citrates of the alkaline See also:earth metals are insoluble. Citric acid, being tribasic, forms either acid monometallic, acid dimetallic or neutral trimetallic salts; thus, mono-, di- and tri-potassium and See also:sodium citrates are known. On warming citric acid with an excess of lime-water a precipitate of calcium citrate is obtained which is redissolved as the liquid cools. The impurities occasionally present in commercial citric acid are salts of potassium and sodium, traces of iron, See also:lead and See also:copper derived from the vessels used for its evaporation and crystallization, and free sulphuric, tartaric and even oxalic acid. Tartaric acid, which is sometimes present in large quantities as an adulterant in commercial citric acid, may be detected in the presence of the latter, by the production of a precipitate of acid potassium tartrate when potassium acetate is added to a cold solution. Another mode of separating the two acids is to convert them into calcium salts, which are then treated with a perfectly neutral solution of cupric chloride, soluble cupric citrate and calcium chloride being formed, while cupric tartrate remains undissolved. Citric acid is also distinguished from tartaric acid by the fact that an See also:ammonia solution of See also:silver tartrate produces a brilliant silver See also:mirror when boiled, whereas silver citrate is reduced only after prolonged ebullition. Citric acid is used in See also:calico See also:printing, also in the preparation of effervescing See also:draughts, as a refrigerant and sialogogue, and occasionally as an antiscorbutic, instead of fresh lemon juice. In the form of lime juice it has See also:long been known as an antidote for See also:scurvy. Several of the citrates are much employed as medicines,the most important being the scale preparations of iron.

Of these iron and ammonium citrate is much used as a haematinic, and as it has hardly any tendency to cause gastric irritation or See also:

constipation it can be taken when the See also:ordinary forms of iron are inadmissible. Iron and See also:quinine citrate is used as a See also:bitter stomachic and tonic. In the See also:blood citrates are oxidized into carbonates; they therefore See also:act as remote alkalis, increasing the alkalinity of the blood and thereby the See also:general See also:rate of chemical See also:change within the body (see See also:Ace= See also:Acne). CI.TRON; a See also:species of Citrus (C. medics), belonging to the tribe Aurantieae, of the botanical natural See also:order Rutaceae; the same genus furnishes also the See also:orange, lime and See also:shaddock. The citron is a small See also:evergreen See also:tree or See also:shrub growing to a height of about 10 ft.; it has irregular straggling spiny branches, large See also:pale-See also:green broadly oblong, slightly serrate leaves and generally unisexual See also:flowers purplish without and See also:white within. The large See also:fruit is ovate or oblong, protuberant at the tip, and from 5 to 6 in. long, with a rough, furrowed, adherent rind, the inner portion of which is thick, white and fleshy, the See also:outer, thin, greenish-yellow and very fragrant. The pulp is sub-acid and edible, and the seeds are bitter. There are many varieties of the fruit, some of them of See also:great weight and See also:size. The See also:Madras citron has the form of an oblate See also:sphere; and in the " fingered citron " of See also:China the lobes are separated into See also:finger-like divisions formed by separation of the constituent carpels, as occurs sometimes in the orange. The citron-tree thrives in the open See also:air in China, See also:Persia, the See also:West Indies, See also:Madeira, See also:Sicily, See also:Corsica, and the warmer parts of See also:Spain and See also:Italy; and in conservatories it is often to be seen in more northerly regions. See also:Sir See also:Joseph See also:Hooker (See also:Flora of See also:British See also:India, i. 514) regards it as a native of the valleys at the See also:foot of the See also:Himalaya, and of the Khasia hills and the Western Ghauts; Dr Bonavia, however, considers it to have originated in See also:Cochin China or China, and to have been introduced into India, whence it spread to See also:Media and Persia.

It was described by See also:

Theophrastus as growing in Media, three centuries before See also:Christ, and was See also:early known to the ancients, and the fruit was held in great esteem by them; but they seem to have been acquainted with no other member of the Aurantieae, the introduction of oranges and lemons into the countries of the Mediterranean being due to the See also:Arabs, between the loth and 15th centuries. See also:Josephus tells us that " the See also:law of the See also:Jews required that at the feast of See also:tabernacles every one should have branches of See also:palm-tree and citron-tree" (Antiq. xiii. 13. 5); and the See also:Hebrew word tappuach, rendered " apples " and " See also:apple-tree " in Cant. ii. 3, 5, Prov. See also:xxv. ri, &c., probably signifies the citron-tree and its fruit. Oribasius in the 4th See also:century describes the fruit, accurately distinguishing the three parts of it. About the 3rd century the tree was introduced into Italy; and, as Gallesio in-forms us, it was much grown at See also:Salerno in the 11th century. In China citrons are placed in apartments to make them fragrant. The rind of the citron yields two perfumes, oil of cedra and oil of citron, isomeric with oil of See also:turpentine; and when candied it is much esteemed as a dessert and in See also:confectionery. The lemon (q.v.) is now generally regarded as a subspecies Limonum of Citrus medics. Oribasii Sardiani, Collectorum Medicinalium Libri X VII. i. 64 (De citrio); Gallesio, Traite du citrus (1811); See also:Darwin, Animals and Plants under Domestication, i.

334-336 (1868); See also:

Brandis, See also:Forest Flora of See also:North-West and Central India, p. 51 (1874) ; E. Bonavia, The Cultivated Oranges and Lemons, &'c., of India and See also:Ceylon (189o).

End of Article: CITRIC ACID

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