EXAMINATION OF THE URINE. 109 



or less marked turbidity or precipitate of nitrotribromphenol. 

 Normal urine, when treated in the same way, either remains 

 clear or gives' a faint turbidity. Make the rest of the liquid, 

 obtained after heating with nitric acid, alkaline with caustic 

 soda solution: orange-red color due to the formation of 

 sodium nitrophenolate. 



IX. PYROCATECHIN, C 6 H 4 (OH) 2 .(o.) 



Use an aqueous solution (0.1 g. : 25-50 cc.) of the com- 

 mercial product for the reactions. 



1. Add cautiously some dilute ferric chloride solution: 

 green color. If now a trace of ammonia be added or, better, 

 a trace of tartaric acid and then ammonia, the green color 

 changes to violet. Acidifying with acetic acid restores the 

 green color. 



2. Add to some of the solution a little ammonia and then 

 a few drops of silver nitrate solution: almost immediate re- 

 duction to metallic silver results. 



3. On the addition of caustic soda solution the liquid takes 

 up oxygen and becomes colored green, then brown and black, 

 especially on shaking. 



4. Pyrocatechin is completely precipitated by lead acetate 

 solution, as the filtrate gives none of the above reactions. 



X. INDIGO BLUE. INDICAN (POTASSIUM INDOXYL 



SULPHATE), 



(a) Indigo Blue, C 16 H 10 N 2 2 . 



1. Heat cautiously some finely powdered commercial 

 indigo, spread out in a porcelain or metal dish. The upper 

 surface becomes covered with purple crystals of indigo blue. 



2. Heat a small portion in a dry test-tube. The tube 

 becomes filled with a purple vapor, resembling the vapor of 



