EXAMINATION OF THE URINE. 



103 



the mark with the same liquid. Let stand till the next day, 

 filter through a dry filter, and add to the filtrate about twenty 

 drops of an alcoholic solution of zinc chloride. After stand- 

 ing for one or two days crystals of creatinine zinc chloride, 

 (C 4 H 7 N 3 0) 2 ZnCl 2 , will be deposited. Examine these under 

 the microscope. Filter, and wash with alcohol. 



For identification Weyl's reaction may be used: Grind 

 the creatinine zinc chloride to a fine powder, boil a small 

 quantity of this with water in a test-tube, let cool and filter. 

 Add to the filtrate a few drops of a very dilute solution of 

 sodium nitroprusside (freshly made) and then some caustic 

 soda solution: deep-red color, which quickly fades to a 

 straw-yellow. 



FIG. 9. Creatinine Zinc Chloride from Urine. 



The Weyl reaction may also be used directly with the 

 urine. As the urine often contains acetone in considerable 

 quantity and this gives a very similar test, it is advisable 

 before trying the reaction to boil the urine for a few minutes, 

 thus driving off the acetone and then cool. 



JafiVs reaction with picric acid may also be used directly 

 with the urine: Add to the urine some aqueous picric acid 

 solution and then a few drops of caustic soda: deep-red color. 



