COLOURS FROM URIC ACID. 169

Since nitrous acid is simultaneously set free, the urea is immediately destroyedand converted into carbonic acid, water, and nitrogen—

C 2 H 4 N 2 0 2 + 2 N 0 3 = 2 C 0 2 -f- 4 H 0 -i- 4 N,

Urea.

so that the result of the rea&ion of nitric acid is the formation of alloxan, asubstance capable of crystallisation, soluble in water, of an unpleasant odour,and staining the skin red. Alloxan is one of those substances the molecules ofwhich are cn mouvcment perpetuel, and, hence, prone to ready conversion intoanother substance called alloxantin, containing 1 atom less of oxygen—Csf^N^; C 8 H 2 N 2 0 7 + 3 H 0 ,

Alloxan. Alloxantin.

This conversion of the former into the latter substance is effected by the adfcionof reducing agents ; for instance, nascent hydrogen, and also when alloxan issimply boiled with water. In the latter case parabanic acid is also formed,and carbonic acid given off; when a small quantity of an acid is added to thewater wherein the alloxan is boiled alloxantin is also generated, but urea,oxalic, and carbonic acids are simultaneously formed. Alloxantin, accompaniedby some alloxan, is diredtly formed when uric acid is treated with dilutenitric acid ; from alloxantin, when treated with chloride of ammonium, isformed dialuramide, and from that substance murexide, or purpurate ofammonium (NH 4 0,C I 6H 4 N 5 0 1 i + 2H0) is generated under the followingcircumstances:—(a) By the oxidation of dialuramide by means of the oxidesof mercury or silver; (6) By the adtion of ammonia upon alloxantin;(c) By the adtion of ammonia or of carbonate of ammonia upon alloxan, orbetter, a mixture of alloxan and alloxantin; (d) By destrudlive distillation ofalloxan by itself, or of that substance mixed with an organic body. For themanufacture of murexide on the large scale guano is chiefly employed as thesource of uric acid, and the process adopted may be described in the followingterms :—Peruvian guano* of best quality is placed in a suitable leaden vessel,and mixed with hydrochloric acid at 18 0 Tw., boiled therewith for one hour,while the mixture is kept well stirred up. The mass is next filtered throughcoarse linen and washed with water; the acid removes from the guano aquantity of inert salts, decomposing the combination of the uric acid andammonia, setting the former free, since that substance in its free state is verysparingly soluble in water, and especially so when it contains an acid. Theuric acid remains on the filter among the sand and other nondescriptsubstances insoluble in hydrochloric acid of the above strength ; the pastymass left upon the filter is placed in a large porcelain dish, and mixed with itsown weight of HC 1 at 40° Tw., and heated to 40°; when the action of the acidhas been continued for a short time there is added to the mass the T l g th partof the weight of the substance as when taken from the filter, of nitric acid,and the temperature kept steadily between 44 0 and 62°. This proceeding hasthe effect of converting the uric acid contained in the guano into alloxantineand alloxan; after a while an equal bulk of water is added to the fluid in thebasin, and the whole left quietly standing to deposit insoluble matters, the

* This guano contains a pretty large quantity of urate of ammonia, in addition to a host ofother substances.