168 UKIC ACID. 



of nitrate of silver is added to a solution of uric acid, to which an 

 ammoniacal mixture of magnesium chloride and ammonium chlo- 

 ride has been previously added, the uric acid is precipitated as a 

 magnesio-silver salt. This is collected, washed, and decomposed 

 by sodium or potassium hydrosulphide, whereupon the uric acid 

 passes again into solution as a urate of the alkali. On the addi- 

 tion of an excess of hydrochloric acid to this solution the urate is 

 decomposed, uric acid separates out and is collected and weighed. 



ii. Hay craft's method. 1 When uric acid is precipitated by am- 

 moniacal 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 volumetrically 

 with a standard solution of potassium sulphocyanate. 2 



Chemical constitution of uric acid. Notwithstanding the fre- 

 quent 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 formula? 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 = CH 2 (NH 2 ) . COOH . -f 3C0 2 + 3NH 8 . 



By reversing this decomposition as it were, namely by fusing to- 

 gether 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 Koosen, 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 pre- 

 viously stated by E. Fischer as a result of his analytical investiga- 

 tions of uric acid. 7 



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

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



2 Volhard, Jn. f.pr. Chem. (2) Bd. ix. (1374), S. 217. 



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

 Gesell. Jahrg. (1882), S. 2678. 



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

 201, 584. 



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



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



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



