CITRIC ACID (Fr. citrique. Lat. cit•ieus, from citrus, citron) , ( 011 ) (('00H + -' crystalline organic substance found in various plants, especially in the fruits of the lime (Citrus b•rgamin) and the lenum (('itrus kmonum). The citric acid of commerce is obtained from the lemon's juice. which is made in large quantities in southern Italy, in northern Africa, in the West Indies, etc. 'l'o obtain citric acid, lemon is boiled (to coagulate all proteid matter), and neutralized with chalk and lime: the precipi tate of calcium citrate thus obtained is decom posed by boiling with dilute sulphuric acid; on filtering. and evaporating the filtrate, citric acid crystallizes out in the form of colorless rhombic prisms. freely soluble in water, and having an agreeable acid taste. Citric acid has the property of preventing the precipitation by potash or ammonia of the hydroxides of iron and certain other metals. This property is utilized in calico printing. citric acid being employed to prevent the formation of certain colors where they are not called for. Citric acid is also used in making refreshing effervescent drinks; the pure acid, or preferably lenmn-juice, is very beneficial in scur vy: formerly it was popularly believed to be an excellent remedy for rheumatism: it is also used to increase the secretion of saliva and to allay thirst in fever. It is often used in medicine in
combination With iron. magnesium, lithium. quinine. etc. Chemically, as its constitutional formula shows, it is a monoxy-tribasic acid. and is therefore capable of forming three series of salts, in which one, two, or all the three of the acid ]hydrogens are replaced by metals. It is somewhat similar to tartaric acid, from which it may. however, be readily distinguished by testing the solubility of its calcium salt, which is insoluble in potash. and is more solulde in cold than in hot water. Citric acid melts at 100° C. in its water of crys tallization, which it loses at 130°. If heated further to 175' C., citric acid loses the elements of water, and is transformed into aeonitie acid— an unsaturated tribasie acid, having the formula )3. Citric acid was discovered by Scheele. in 17S4; its properties were investigated by Berzelins and Lieldg.