Sulphuric acid when concentrated dissolves uric acid, and forms a crystalline compound with it; it is decomposed on the addition of water ; concentrated hydrochloric acid dissolves it in greater quantity than water.
Uric acid, when submitted to destructive distillation, yields the same products as urea, namely, cyamelide, cyanic acid, cyanuric acid, hydrocyanic acid, a little carbonate of ammonia, and a brown carbon aceous residue containing much nitrogen. In this decomposition the hydrated cyanic acid and ammonia combine in the neck of the retort and form urea. The cyamelide dissolves in potash, and yields cyanurate of potash.
When uric acid is heated with a little water to 392° Fahr. in a closed tube, it is converted, without any disengagement of gas, into a yellow transparent liquor, which becomes a yellow gelatinous mass when it cools; this is soluble both in cold and hot water : the alkalies evolve ammonia from it, and with the acids it produces gelatinous precipitates ; with hot nitric acid it effervesces, and the solution by evaporation yields a reddish yellow mass, which ammonia renders purple.
Hydrate of potash when fused with uric acid produces carbonate of potash, cyanate of potash, and cyanide of potassium. When boiled in water with peroxide of lead, it is converted into allantoin and oxalic acid, urea being set free.
Saline combinations of Uric Acid.—Uric acid is dibasic, and forms neutral and acid urates. The uratea of the alkaline metals and of the alkaline earths are but slightly soluble in cold water, but very soluble in boiling water ; an excess of alkali increases the solubility; the uratea are generally colourless, and are all decomposed by acids, even by the acetic acid ; the uric acid, which is set free, is at first gelatinous, but soon assumes the form of fine brilliant L3minse.
Urate of Ammonia acid salt is the only one known. Urinary calculi occasionally consist of this com pound. [CALCULI.] i'rates of Potash.—The neutral salt (2K0,C„II,N,0,) is prepared by dissolving the excrements of serpents in a weak boiling solution of potash ; the insoluble portion being separated by filtration, urate of potash is obtained as a white crystalline mass by evaporating and cooling the solution; this, after washing with cold water, is converted by drying into a brilliant powder, composed of very fine needles.
This salt is very slightly soluble in cold water ; the solution has an alkaline reaction. On passing carbonic acid through its solution, acid urate if potash (KO, HO, is deposited.
rrates of Soda.—According to Dr. Wollaston, gouty concretions consist principally of these salts. They may be prepared in the same way as the urates of potash ; the reactions are similar. Urate of soda is also formed when uric acid i3 boiled with borax.
Uroxanic add (2110, When uric acid is boiled for a long time with caustic potash a small quantity of it, by assimilation of six equivalents of water, is converted into a new acid termed uroxanic. Uroziote of potash (2 KO, 6 Aq.) is very soluble in water, but may be °brained in rhombic tables; from its solution hydrochloric acid precipitates uroxanic acid in microscopic tetrahedra; boiling water decomposes it, carbonic acid being evolved.
slUostart (C,H,N,0,+ 2 and 8 Aq.) This is the chief product of the action of cold nitric on uric acid. The latter is added to the former in small quantities at a time, carbonic acid and nitrogen escape, pro ducing brisk effervescence, heat is evolved, so that it is sometimes necessary to artificially prevent undue elevation of temperature, 120° Fahr. being the maximum point to which the mixture should rise. After a time crystals begin to form in the liquid and, on repose, octo bedra of alloxan separate out. They contain two equivalents of water, but from resolution in water crystallise in prisms containing eight equivalents of water.
Alloxan is colourless, of faint odour, unpleasant astringent taste, stains the akin pink, is very soluble in water, and has an acid reaction. By the action of sulphuretted hydrogen and similar reducing agents it yields dialuric acid (C,H,N,0,) and free sulphur :— The dialurie acid is crystalline, and forms crystallisable salts. Gregory's uramilic acid seems to be the bidialurate of immonia.