URINE 277 



residue with boiling 3% sulphuric acid. This dissolves the xan- 

 thine bases and leaves the uric acid as a residue. Allow to stand 

 over night, filter, and make the filtrate strongly alkaline with 

 ammonia. Reprecipitate xanthine bases as above with silver 

 nitrate. Filter, suspend the precipitate in boiling water acid- 

 ulated with HC1. Boil vigorously a few minutes and decom- 

 pose the silver salts with H 2 S. Filter, and evaporate to dryness. 



(2) Reactions of Xanthine Bases. 



i. Test solubility in water, alcohol, acids and alkalies, 

 ii. Murexid test. Perform this test as described under 

 uric acid. Note the method of distinguishing xanthine from uric 

 acid. 



(d) CREATININE. 



(1) Preparation. Creatinine may be prepared from urine by 

 precipitation as the zinc salt. Its reactions may be studied, 

 however, without isolation from the urine. 



(2) Reactions. 



i. Weyl's test. To about 10 c.c. of normal urine add 2-3 

 drops of sodium nitroprusside and then 2-3 drops 10% sodium 

 hydrate. A red color which soon fades to yellow shows the pres- 

 ence of creatinine. ( Compare with Legal 's test for acetone. See 

 below.) On the addition of glacial acetic acid to this test, a pure 

 solution of creatinine gives a greenish color, which serves to dis- 

 tinguish it from acetone. In urine, however, this reaction with 

 acetic acid is not easily recognized. 



A second simple way to determine to which of these substances 

 a positive test is due is to distill the urine. Acetone will pass 

 over in the first few cubic centimeters of distillate, whereas crea- 

 tinine will not distill. 



ii. Jaffe's test. To 10 c.c. of urine, add about 1 c.c. picric 

 acid, and then 1-2 c.c. of 10% sodium hydrate. Observe the red 

 color. This test serves as the basis for the quantitative estima- 

 tion of creatinine. (See below). 



(e) OXALIC ACID. To 200 c.c. urine in a beaker add 5 c.c. 

 saturated solution of calcium chloride, acidify with acetic acid 



