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Co 6-Nh Co

acid, uric, urate, soluble and sodium

CO 6-NH > CO, occurs in the urine of carnivorous ani mals, and in much larger quantities in the ex creta of birds, reptiles, snails and insects. It may be present either in the free state or as acid ammonium or sodium salt. It ousts nor mally in the blood of birds, and as a pigment it has been detected on the wings of certain but terflies. In small quantities uric acid is a con stituent of normal human urine in which it was first detected by Scheele in 1776. It is produced in the human organism in large quantities when foods rich in nucleo-proteids are used, although the enzymes present in the liver convert the bulk of this product into urea. Under certain abnormal conditions it accumulates in the sys tem forming urinary calculi, chalkstones, and other concretions. The tissues and joints of gouty patients contain the sparingly soluble acid sodium urate.

Uric acid may be prepared from the excreta of reptiles or birds by treatment with a boiling solution of caustic soda. The product is filtered and the clear hot liquid is strongly acidified with hydrochloric acid. The precipitated uric acid is washed with water and dried. Prepared in this way the acid is a white powder which shows the crystalline structure under the micro scope. It dissolves in glycerine, piperazine, propylamine and caustic alkalies, but is only sparingly soluble in water (one part in about 15,000 parts at 20° C., and in 1,800 parts at 100° C.). It dissolves in concentrated sulphuric acid without decomposition, and its molecular weight has been determined by the cryoscopic method, with this acid as the solvent. When

uric acid is suspended in nitric acid, or chlorine water, and then evaporated to dryness, a yellow residue is formed which changes into purple-red when moistened with ammonia. or into violet with caustic soda; this is known as the aMu rexide Test"' and is employed for the detection of the acid.

Uric acid is a weak dibasic acid and may form a series of salts with the same metal. With sodium, for example, it forms 1) neutral sodium urate Na3C4121440.; 2) di-sodium urate NaHC4H,N40.• and 3) quadrisodium urate NaH (GH,NA). N (GH2402). The neutral urate is quite insoluble; the quadriurate is quite soluble ; while the diurate may exist in a and b modifications. The a form is soluble and un stable, readily passing into the b form which is stable and less soluble. This property of diu rates and some other characteristics of uric acid have led investigators to the belief that the com pound has two structural formulas, the "lactam' formula given above, and the •lactiiri* formula which is tautomeric with the lactam structure.

Although uric acid is almost exclusively a product of animal metabolism, its close rela tion to compounds of vegetable origin has been clearly demonstrated. Chemically it is related to caffeine, the active principle in coffee, to theophylline, found in tea, and to theobromine, present in the cocoa bean. This keenship is strikingly illustrated by the relatively simple methods which have been successfully employed for the conversion of uric acid into these com pounds.