URIC ACID. 



587 



residues on to a nucleus derived from lactic acid. This Horbaczewski 

 succeeded in doing by heating urea with trichorlactamide : 



CC1. 3 CH.OH.CO.NH 2 4-2(NH 2 ) 2 CO=C 5 H 4 N 4 3 + NH 4 C1 + 2HC1+H 2 



The simple changes involved in this reaction will be more clearly seen on 

 examination of the following graphic scheme : 



HNH 



CO 



HNH 



(urea) 



Cl 



C1.C.C1 



I 



CH(OH) 

 CONH 2 



(trichlorlactamide) 



HNH, 

 HNH 



(urea) 



)CO 



The groups printed in thick type unite to form uric acid ; the atoms repre- 

 sented in thinner type split off to form respectively a molecule of ammonium 

 chloride, two molecules of hydrochloric acid, and one of water. 



Uric acid is formed also when glycine is heated with urea (Hor- 

 baczewski), but the molecular changes involved are not so simple 

 as those shown above, and the yield is not so good. In Behrend and 

 Eoosen's synthesis the nucleus is primarily derived from acet-acetic 

 ether, and the urea residues are linked on separately at two different 

 stages in the synthetic process. 



Properties. Pure uric acid forms a white powder, which is made up 

 of small rhombic crystals, of more or less prismatic or tabular type. Its 

 crystalline forms become very diverse in the presence of impurities, 

 and when it separates from the urine, the crystals, which are then always 

 coloured, take shapes which depend to a large extent upon the nature of 

 the pigment associated with them 1 (Figs. 50 and 51). 



In cold water it is very in- 

 soluble, only dissolving to the ex- 

 tent of about 1 part in 15,000. 

 A litre of boiling water takes 

 up about half a gramme. Ether 

 and alcohol do not dissolve it. It 

 dissolves in oil of vitriol without 

 decomposition, and from the solu- 

 tion a crystalline sulphate separates 

 on freezing the mixture. By this 

 process pure uric acid may be 

 obtained from contaminated speci- 

 mens, the sulphate being resolved 

 into its constituents when treated 

 with water. 



It acts as a somewhat weak 

 dibasic acid, but forms three orders 

 of salts. 



1. The neutral urates, M' 2 U, have an intense caustic taste and are 

 very unstable. They are decomposed by carbonates and even by the 

 carbonic acid of the air. As they are only produced in the presence of 

 caustic alkalies, and cannot exist in the presence of carbonates, it is un- 



1 A. E. Garrod. 



FIG. 50. Uric acid. 



