PROPERTIES OF URIC ACID. 709 



lateritium. Whether these quadriurates, which have recently been studied 

 by RINGER, KOHLER and ScHMUTZER, 1 are chemical combinations of 2 molecules 

 uric acid and 1 atom of K or Na or are mixtures, so-called solid solutions of uric 

 acid in monourates, is still a disputed question. 



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. 



A solution of phosphotungstic acid, prepared according to certain 

 directions, gives with a solution of uric acid, when treated with an excess 

 of sodium carbonate, a beautiful blue solution. This extremely delicate 

 reaction (1:500,000) was suggested by FOLIN and DENis. 2 



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

 the contrary, 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 glucose 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 3 ). 



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 we are here dealing with combinations of 1 molecule nucleic 



1 Ringer, ibid., 67 (literature) and 75; Kohler, ibid., 70 and 72; Ringer and Schmut- 

 zer, ibid., 82. 



2 Journ. of biol. Chem., 12. 



3 Cited f. Bioch. Centralbl., 8, 250. 



