PROPERTIES OF URIC ACID. 673 



If a little uric acid in substance is treated on a porcelain dish with 

 a few drops of nitric acid, the uric acid dissolves on warming, with a 

 strong development of gas, and after thoroughly drying on the water- 

 bath a beautiful red residue is obtained, which turns a purple-red (ammo- 

 nium purpurate or murexide) on the addition of a little ammonia. If 

 instead of the ammonia we add a little caustic soda (after cooling), the 

 color becomes deeper blue or bluish violet. This color disappears quickly 

 on warming, differing from certain purine bodies. This reaction is called 

 the murexide test. 



If uric acid is converted into alloxan by the careful action of nitric 

 acid and the excess of acid carefully expelled, on treating this with a few 

 drops of concentrated sulphuric acid and commercial benzene (contain- 

 ing thiophene) a beautiful blue coloration is obtained (DENIGES' reaction 1 ). 



Uric acid does not reduce an alkaline solution of bismuth, while, on 

 the contraiy, it reduces an alkaline cupric-hydroxide solution. In the 

 presence of only a little copper salt we obtain a white precipitate consist- 

 ing of cuprous urate. In the presence of more copper salt red cuprous 

 oxide separates. The compound of uric acid with cuprous oxide is formed 

 when copper salts are reduced by dextrose or a bisulphite in alkaline 

 solution in the presence of a sufficient amount of urate. 



If a solution of uric acid in water containing alkali carbonate is treated 

 with magnesium mixture and then a silver-nitrate solution added, a 

 gelatinous precipitate of silver-magnesium urate is formed. If a drop 

 of uric acid dissolved in sodium carbonate is placed on a piece of filter- 

 paper which has been previously treated with silver-nitrate solution, 

 a reduction of silver oxide occurs, producing a brownish-black or, in the 

 presence of only 0.002 milligram of uric acid, a yellow spot (SCHIFF'S 

 test). 



If a weak alkaline solution of uric acid in water is treated with a 

 soluble zinc salt, a white precipitate is produced, which on the filter in 

 the presence of alkali is oxidized by the air, and becomes sky-blue in 

 color, especially in sunlight. Potassium persulphate causes a blue 

 coloration immediately (GANASSINI'S reaction 2 ). 



The precipitation of free uric acid from its alkali salts by means of 

 acids can be prevented to some extent by the presence of thymic acid 

 or nucleic acid (GOTO). According to SEO S we are here dealing with 

 combinations of 1 molecule nucleic acid and 2 molecules uric acid, which 

 protects the uric acid within the body against destruction or transforma- 

 tion into allantoin. 



1 Journ. de Pharm. et de Chim., 18. Cited from Maly's Jahresber., 18. 



2 Cited f. Bioch. Cenetralbl., 8, 250. 



3 Goto, Zeitschr f. physiol. Chem., 30; Seo, Arch. f. exp. Path. u. Pharm., 58. 



