110 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



iodine. A part of the indigo carbonizes, another part sub- 

 limes; in this process, however, some of the indigo blue is 

 always transformed into the isomeric indigo red (Rosin). 



3. Heat a little indigo with some chloroform: blue solu- 

 tion. 



4. Heat a little indigo with concentrated sulphuric acid, 

 let cool completely, and then pour into water: blue solution 

 of indigo mono- and di-sulphonic acids. Filter the solution 

 and examine with the spectroscope: strong absorption-band 

 between C and D, nearer to D. 



(6) Detection of Indican. 



1. JafiVs Indican Test. Add to some of the urine an equal 

 volume of hydrochloric acid, then, drop by drop, with con- 

 stant shaking, a dilute solution of chloride of lime (bleaching- 

 powder) (1:20). Then, add about 1 cc. of chloroform and 

 shake gently : the chloroform becomes colored blue, owing to 

 its dissolving the indigo formed. The quantity of the chlo- 

 ride of lime is difficult to estimate, and an excess may oxidize 

 the indigo blue. The reaction always takes place slowly and 

 requires some time. Urine which is rich in indican turns 

 green or even blue directly, while urine poor in indican does 

 not do this. Frequently, instead of a blue, a violet color 

 results, which is not taken up by the chloroform. This is due, 

 according to Rosin, to indigo red or to urorosein. Normal 

 urine as a rule turns violet to red-violet, but it gives up indigo 

 blue to the chloroform. Strongly colored urines, e.g., icteric, 

 must be decolorized by the addition of a little basic lead ace- 

 tate and filtered before making the test. 



2. Modification of the Indican Test according to Obermayer. 

 Precipitate the urine with the basic lead acetate solution, tak- 

 ing care not to use an excess, filter through a dry filter, shake 

 the filtrate vigorously for one to two minutes with an equal 

 volume of fuming hydrochloric acid (containing in 1000 



