606 



URIC GROUP. 



URIC GROUP. 



EDO 



pigment, urin 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, &c. ; 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, parabanic acid, 

 ammonia, 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. 



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 

 th;m water. 



Uric acid, when submitted to destructive distillation, yields the 

 game 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 (ombinatiom of Uric Acid. Uric acid is dibasic, and forms 

 neutral and acid urates. The urates 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 

 urates 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 laminae. 



Urate of Ammonia (NH 4 0,HO,C 10 H. I N,0,). The acid salt is the 

 only one known. Urinary calculi occasionally consist of this com- 

 pound. [CALCULI.] 



I'mta of Potah. The neutral salt (9KO,C,AK t <X) " prepared 

 by dissolving the excrements of serpents in a weak boiling solution of 

 potash ; the insoluble portion being separated by nitration, 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. 

 Thin salt is very sh'gbtly soluble in cold water ; the solution has an 

 alkaline reaction. On passing carbonic acid through its solution, acid 

 if potath (KO, HO, C.oHjN.,0,) is deposited. 



<. 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 is boiled with borax. 



I'l-nxanic acid (2HO,C 10 H 8 N,0 10 ). When uric acid is boiled for a 

 long tune with caustic potash a small quantity of it, by assimilation of 

 six equivalents of water, is converted into a new acid termed uroxanic. 

 Uroxante of jiatatk (2 KO, C 10 H,N 4 10 + 6 Aq.) is very soluble in water, 

 but may be obtained in rhombic tables ; from its solution hydrochloric 

 acid precipitates uroxanic acid in microscopic tetrahedra; boiling 

 water decomposes it, carbonic acid being evolved. 



AUojcan (C,H,N,0 9 + 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 

 .all 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 Uquid and, on repose, octo- 

 hedra 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, 



the skin 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 : 



C.H,N,0. + SHS = C.H.N.O. + 8, 



The dialuric acid is crystalline, and forms crystallisable salts. 

 Gregory's uramilic acid (C 10 H 10 N 5 15 ) seems to be the bidialurate of 

 ammonia. 



Alloxantin (C-JLl^O,, + 6 Aq.) is formed on adding together 

 solutions of equivalent proportions of alloxan and dialuric acid, and 

 would seem to be a compound of those substances. It may also be 

 formed by the action of several reducing agents on alloxan. It occurs 

 in small colourless rhomboidal prisms, slightly soluble in cold water, 

 rather more so in boiling water ; oxidising agents reconvert it into 

 alloxan. Boiled with hydrochloric acid it yields white, pulverulent, 

 allituric acid (C H 3 N,;0,) and diliturie acid, which has not been fully 

 examined. The dimethyl derivative of alloxantin is identical with 

 amalic acid. [CAFFEINE.] 



Alloxanic Acid (C 8 H,N,0 10 ) may be considered as alloxan plus two 

 equivalents of water. It is a product of the action of bases upon 

 alloxan, and may be isolated on treating an alloxanate with a stronger 

 acid. By evaporation it is obtained as a semi-crystalline mass, of 

 unstable character. Its aqueous solution, by ebullition and evapora- 

 tion to near dryness, splits up into leucoturic acid (C e H 3 N.,0 6 ?) which 

 dissolves on rediluting with water, and a white, insoluble, slightly acid 

 powder termed ditwtn. Some of the alloxanates crystallise readily. 



Mycomdic Acid (HO, C S H 3 N,0 3 , Aq.), or aUoxanamide.-is formed 

 when a solution of alloxan in ammonia is boiled and cooled slowly. 



C.H.N.O, + -2NH 3 = HO, 



+ 4HO 



Alloxan. 



Mvcomelic acid. 



Mttoxalie Acid (2HO,C 8 0,). Where solutions of alloxanates are 

 boiled for some time, they break up into urea and mesoxalic acid : 



2EaO, CjHjNjOu 

 Alloxanate of baryta. 



2HO = 2BaO, C O 8 + C,H 1 N ! ,O 1 

 Mcsoxalate of baryta. Urea. 



Alloxan. 



Dialuric acid. 



Mesoxalic acid may be isolated from the baryta salt by sulphuric acid 

 or from the lead salt by sulphuretted hydrogen. It is very soluble in 

 water, but may be obtained in crystals. The silver salt is decomposed 

 when heated, brisk effervescence of carbonic acid and carbonic oxide 

 occurring. 



Parabanic Acid (C a H,f! t O e ) may be obtained in flat colourless 



?risms on evaporating the nitric acid with mother liquor of alloxan. 

 t is permanent itself, but forms unstable compounds with bases. The 

 parabanate of ammonia, for example, decomposes during evaporation 

 the ammonia salt of oxaluric acid (NH,0,C 8 H 3 N.,0 7 ) being formed. 

 The latter occurs in brilliant crystals, and is interesting from the fact 

 hat dumb-bell crystals of oxaluric acid at first mistaken for oxalate 

 of lime are sometimes met with in urinary deposits. 



P/ienyl-oxalitramide or oxaluranilide, (C n H > i l O ( ) is a white crystal- 

 ine powder. 



Thionuric Acid (2HO, C.H,N,0 W 2S0 2 ). Solutions of alloxan, 

 sulphite of ammonia, and ammonia, combine together when boiled, 

 .hionurate of ammonia crystallising out on cooling in brilliant leaflets. 

 Che lead salt decomposed by sulphide of hydrogen furnishes an acicular 



las of thionuric acid. 



Uramil (NH,,C,H,N,0,) murexan or dialuramide. When a hot 

 saturated solution of thionurate of ammonia is treated with hydro- 

 chloric acid in excess, the mixture is converted into a semifluid mass. 

 The uramil thus obtained is in the form of plumose acicular crystals, 

 which are permanent in the air, and become of a pink colour when 

 ueated ; they are insoluble in cold and but slightly soluble in boiling 

 water. The alkalies dissolve uramil, and acids precipitate it from them 

 unchanged. The solutions in ammonia and potash become of a purple 

 colour by exposure to the air, and deposit green acicular crystals of a 

 brilliant metallic lustre. If the potash solution be boiled, ammonia is 

 evolved and uramilic acid is formed; dilute acids produce similar 

 decomposition. It is soluble in concentrated sulphuric acid, and is 

 precipitated from it by water ; by concentrated nitric acid it is resolved 

 into alloxan, with the evolution of hyponitrous acid, and the formation 

 of nitrate of ammonia. 



Muraeid (C 2 ,H,jN 10 O i() !), purpurate of ammonia of Dr. Prout. This 

 substance may be obtained by several processes. The least operose is 

 probably that of dissolving uric acid in dilute nitric acid, evaporating 

 the solution till it assumes a reddish colour; after the liquor has 

 cooled to 158 Fahr., add excess of ammonia ; then dilute it with half 

 its volume of boiling water, and allow it to cool. Care must be taken 

 not to employ too much or too little nitric acid. Whilst ammonia 

 continues to give a red precipitate, when added to small portions, the 

 nitric acid is insufficient. If, on the contrary, ammonia produces a 

 glairy yellow precipitate, murexide cannot be obtained without passing 

 a current of hydrosulphurie acid into the liquor. 



Murexide crystallises in short four-sided prisms, which exhibit a 

 green metallic reflection. They are garnet-red by transmitted light. 

 It is very little soluble in cold water, and gives it a magnificent purplish 

 red colour. It dissolves readily in water at 158, and crystallises from 

 the solution unaltered. It is insoluble in alcohol and in ether. It is 

 insoluble also in solution of carbonate of ammonia, but dissolves in a 

 solution of potash, producing a superb indigo-blue colour, which 

 disappears by heat, with the evolution of ammonia. 



Purpurate of Potaik. According to Fritzehe, this ia best obtained 



