URIC GROUP, a cluster of chemical compounds, derivatives, or congeners of uric acid. Next to uric acid itself, the product,' of ita artificial oxidation claim chief interest, inasmuch as they illustrate some of the changes which oxygen effects upon the exhausted tissues of the human frame prior to their elimination as urea. Thus uric acid plus moisture and oxygen yields urea and a body termed alloxan. Alloxan plus moisture furnishes urea and mesoxalic acid; and mesoxalic acid contains no nitrogen, the latter element having thus artificially been thrown out from uric acid as urea. It is probable that this change, or a similar one, occurs naturally in animals; for although uric acid is nearly always present in human urine, its quantity is much modified by diet. It does not occur in the urine, but does in the spleen, of the dog; and Professor Haughton, who has paid considerable attention to the physiology of this body, says that "no uric acid what ever should occur in the urine of man in perfect health, but all tho nitrogen of the urine should pass off in the form of urea,—a more highly oxidated product than uric acid." The following list includes nearly all the members of the uric group. The consideration of those of them derived from uric acid is supposed to be simplified by assuming that body to contain the radical twit (uryl) or cyanoxalic add (C„N,0,=C,O,Cy,) ; that is, oxalic anhydride, in which two equivalents Of oxygen are replaced by two of cyanogen : but uril has not been isolated, and its usefulness is very slight.
Uric Acid (2HO, substance, sometimes called laic add, was discovered by Scheele ; Vauquelin efterwards found it in the excrements of serpents, Brugnatelli in that of silkworms, and Roublquet in oantharides.
Uric acid is secreted by carnivorous animals, birds, and by several insects. When in excess, it Is deposited from human urine as a brownish-yellow powder, which is usually a compound of uric acid and ammonia. It occurs, in combination with soda or ammonia, in those gouty concretions commonly called clialk-stonc, and it constitutes the principal portion of the calculi deposited in the human bladder. The
semi-solid urine of serpents and birds is chiefly composed of urate of ammonia; and guano, the decomposed excrement of aquatic birds, and which is imported from some islands in the South Sea and extensively used as a manure, contains a largo quantity of urate of ammonia.
This acid in conveniently obtained by dissolving the excrement of serpents--the boa constrictor, for example—in a solution of potash, and decomposing the clear solution by the addition of hydrochloric acid. It may also be obtained from the excrement of pigeons and other birds by the same process. According to Liebig, it is better to employ borax as a solvent than a caustic alkali, it dissolving less of the animal matter. On the large scale, as a source of unirexia as a pigment, uric acid is obtained from guano, which is treated first with hydrochloric acid to remove carbonates and phosphates of lime, mag nesia, and ammonia, then with boiling caustic soda, which dissolves the uric acid from sand, clay, gypsum, kc. ; and the alkaline solution is finally treated with hydrochloric acid, which precipitates the uric acid, in a state sufficiently pure for conversion into murexia.
Uric acid occurs in small, fine, white, silky, crystalline scales ; it is inodorous and insipid, heavier than water, and nearly insoluble in it when cold, and only slightly dissolved by it when hot ; the solution reddens litmus-paper, but feebly. It is insoluble in alcohol or ether.
Nitric acid, even diluted, dissolves uric acid with brisk effervescence; the gases evolved consist of equal volumes of nitrogen and carbonic acid. The solution contains alloxan, alloxantin, urea, parahanic acid, and other variable products. When the solution is evaporated to dryness, the residue is 'of a fine purple colour : the formation of this residue is a test of the presence of uric acid, its colour is much intensified on the addition of ammonia.