EXAMINATION OP *L'H& >&klWBs V. ' 101 



If snake urine, so-called excrement, is available, 10 g. of 

 this and 20 cc. of caustic sod^ solution are sufficient. 



Uric acid, C 5 H 4 N 4 3 , forms a crystalline powder extremely 

 difficultly soluble in water (in 1800 parts of hot, 14,000 1 parts 

 of cold water), insoluble in alcohol. 



Reactions of Uric Acid. 



1. Place a small quantity of uric acid with a little water 

 on a microscope-slide and treat with some caustic soda 

 solution or piperazine solution (10 per cent.); the crystals 

 difsilve. When all or nearly all has dissolved add a little 

 hydrochloric acid: the uric acid separates in characteristic 

 spindle-shaped crystals. Examine under the microscope. 



2. Murexide Test. Pour upon a very small quantity of 

 uric acid on a porcelain crucible-cover some drops of nitric 

 acid, dissolve by warming and evaporate cautiously, avoid- 

 ing heating too strongly: there remains a yellow to red resi- 

 due. Let cool and moisten the residue with an extremely 

 small quantity of ammonia: purple-red color due to the 

 formation of murexide. Now add a drop qf caustic soda 

 solution: deep-blue color. If now we heat again, the color 

 becomes paler and disappears even before the mass becomes 

 completely dry. If the purple-red residue or the blue residue 

 be moistened while still hot with a few drops of water, it dis- 

 solves to an almost colorless fluid. If this is evaporated by 

 heating with a very small flame the color is not restored, as 

 the murexide is very easily destroyed (distinction from the 

 reaction of the xanthine bases, especially of guanine). 



3. Dissolve some uric acid in a solution of sodium car- 

 bonate and moisten with it a strip of paper which has pre- 

 viously been saturated with a solution of silver nitrate : spots 



1 According to His and Paul, Zeitschr. f. physiol. Chern. 31, 1 (1900- 

 1901), 1 part dissolves in 39,500 parts of pure water at 18. O. 



