2Q2 URINE. [CH. XII. 



has evaporated away. Pour off the acetone into a dry watch glass 

 and allow it to cool. Crystals of urea separate out as silky needles. 

 Demonstrate that they are urea crystals by evaporating to dryness, 

 taking up in a small amount of water and applying the urease test 

 (Ex. 343). 



F. Uric Acid. 



Uric Aci, C 5 H 4 N 4 O 3 , is 2-6- 8-tri-oxy-p urine. 

 NH-CO 



CO C - NH^ 



I! CO 



NH - C - 



Its relationship to certain of the other purines is 

 indicated on page 63. 



When pure it crystallises in microscopic rhombic 

 plates, but when impure it assumes a variety of forms, 

 such as whetstones, dumb-bells, sheaves, rosettes, butchers 1 

 trays, etc. 



It dissolves to the extent of i part in 16,000 parts of 

 cold water and i ,600 parts of hot water. It dissolves in 

 alkalies, and the alkali salts of carbonic, phosphoric, boric, 

 lactic and acetic acids, but not in the ammonium salts of 

 these acids. It dissolves in warm concentrated sulphuric 

 acid to form a sulphate, which is decomposed by the addi- 

 tion of water. 



It is precipitated by phosphotungstic acid in the 

 presence of hydrochloric acid, slowly by lead acetate, and 

 completely by picric acid, mercuric chloride and ammonia- 

 cal silver nitrate. 



By oxidation, allantoin, alloxan, parabanic acid and 

 urea are formed, depending on the reaction and the reagent 

 employed. 



NH a NH - CO NH - CO 



CO CO - NH^ CO CO CO 



NH - CH - NH- NH - CO NH - CO 



Allautoin. Alloxan. Parabanic acid. 



