164 THE URINE. 



354. To a small quantity of uric acid in a porcelain 

 dish add a few drops of dilute nitric acid and evaporate 

 to dryness, holding the dish over a small flame with the 

 hand in order to avoid heating too highly. A reddish-yel- 

 low residue is left. Pour into the dish a drop of ammonia 

 without at first letting it come directly into contact with 

 the residue. In a short time the residue becomes colored 

 reddish purple. The ammonia may be added directly to 

 the residue if an excess is not used. An excess destroys 

 the color. The addition of a drop of' sodium hydrate 

 changes the color to a bluish purple, which is destroyed on 

 warming. The test is called the murexid test. 



355. PREPARATION OF AMORPHOUS ACID URATES. Dissolve 

 uric acid in a slight excess of sodium hydrate, and then pass carbon 

 dioxid into the cold solution until it is saturated. Acid sodium 

 urate separates in amorphous masses. 



356. Test the solubility of the acid sodium urate by 

 warming with a small quantity of water. It will dissolve, 

 and, if not too much water has been used, will separate out 

 again when it cools. 



357. Prepare crystallized acid urates by dissolving a 

 little uric acid in a warm solution of sodium phosphate. 

 Filter, if necessary, and allow the filtrate to stand and 

 evaporate. The sodium urate will crystallize as masses of 

 acicular crystals. 



358. FOMN'S METHOD FOR THE QUANTITATIVE DETERMINA- 

 TION OF URIC Acnx Prepare a solution in water, one liter of 

 which shall contain 500 grammes of ammonium sulphate, 5 

 grammes of uranium acetate and 6 cubic centimeters of glacial 

 acetic acid. Of this add 75 cubic centimeters to 300 cubic centi- 

 meters of urine in a 500 cubic centimeter flask, mix, and after five 

 minutes filter through a plaited filter. Take two portions of the 



