CHEMICAL BASIS OF THE ANIMAL BODY. 169 



ii. Haycrafls method^. When uric acid is precipitated by 

 ammoniacal solution of nitrate of silver in presence of the ammonio- 

 magnesic mixture as above described the precipitate is stated to contain 

 one atom of silver to each molecule of uric acid. The uric acid is hence 

 determined by dissolving the precipitate in nitric acid, in which solution 

 the silver is then estimated volumetrical]y with a standard solution of 

 potassium sulphocyanate 2 . 



Chemical constitution of uric acid. Notwithstanding the frequent 

 and careful investigation of uric acid and of the extremely numerous 

 products of its decomposition, its constitution has until recently been a 

 matter chiefly of surmise and conjecture, and many constitutional 

 formulae have been assigned to it. When uric acid is treated with 

 concentrated hydriodic acid at 160 170 it is decomposed into glycin, 

 ammonia and carbonic anhydride 



C 5 H 4 N 4 O 3 + 5H 2 O - CH 2 (NH 2 ) . COOH . + 3CO 2 + 3NH 3 . 



By reversing this decomposition as it were, namely by fusing together 

 at 200 230 glycin and urea, uric acid was for the first time obtained 

 artificially 3 ; when sarkosin is used instead of urea methyl-uric acid is 

 obtained. Uric acid has also been prepared by fusing together trichlor- 

 lactamide or trichlor-acetic acid and urea 4 . The high temperatures at 

 which the above reactions were conducted and the uncertainty as to 

 the nature of the products intermediate between the reagents and the 

 finally formed uric acid precluded them from being regarded as 

 syntheses in the strict sense of the word. A true synthesis of uric 

 acid has been recently discovered by Behrend and Rooseii 5 , from which 

 it appears that the constitutional formula first assigned to the acid by 

 Medicus 6 , is a true representation of its constitution. This view had 

 been previously stated by E. Fischer as a result of his analytical 

 investigations of uric acid 7 . 



NH CO 



Uric acid. CO C 



[H C NH 



An inspection of the above formula shows at once that uric acid 



1 Brit. Med. Jl. 1885, p. 1100. Jl. of Anat. and Physiol. Vol. xx. p. 695. Zt. f. 

 anal. Chem. Bd. xxv. (1885), S. 165. Zt.f. physiol. Chem. Bd. xv. (1891), S. 436. 



2 Volhard, Jn. f. pr. Chem. (2) Bd. ix. (1874), S. 217. 



3 Horbaczewski, Monatsh. f. Chem. Bd. in. (1882), S. 796. Ber. d. deutsch. chem. 

 Gesell. Jahrg. 1882, S. 2678. 



4 Horbaczewski, Monatsh. f. Chem. Bd. vi. (1885), S. 356; Bd. vm. (1887), Sn. 

 201, 584. 



5 Ann. d. Chem. u. Pharm. Bd. CCLI. (1889), S. 235. 



6 Ibid. Bd. CLXXV. (1875), S. 230. 



7 Ber. d. deutsch. chem. Gesell. 1884, Sn. 328, 1785. 



