INDICAN. 177 



Let the chloroform settle to the bottom. If indican is pres- 

 ent in the urine it will be thus oxidized to indigo blue, and 

 this colors the chloroform. A second piece of the hypo- 

 chlorite may be added and the shaking repeated. An ex- 

 cess will destroy the blue color. Instead of calcium hypo- 

 chlorite, a few drops of chlorin water, bromin water, or 

 hydrogen dioxid can be used. This is Jaffe's test. . 



377. Obermayer's reagent for indican contains 2 to 

 4 grammes of ferric chlorid in a liter of concentrated hy- 

 drochloric acid. An excess does not destroy the indigo. 

 Mix equal volumes of the reagent and urine and shake. 

 Indican is oxidized to indigo-blue. This can be taken up 

 by a drop of chloroform, as in the preceding test. 



After the internal use of iodin compounds the iodin is ex- 

 creted largely through the urine. The reagents of either Jaffe's 

 or Obermayer's tests will set it free and it will dissolve in the 

 chloroform with a color which simulates or conceals the indican 

 reaction. A few drops of sodium thio-sulphate solution will, how- 

 ever, destroy the iodin color, but not that of indican. 



378. Add to 10 cubic centimeters of urine a few drops of a 

 solution of potassium iodid and make Jaffa's or Obermayer's test, 

 following this with sodium thio-sulphate. 



379. THE QUANTITATIVE DETERMINATION OP URINARY 

 INDICAN: WANG'S METHOD. This depends upon the conversion 

 of indican to indigo by Obermayer's reagent and, after extracting 

 it with chloroform, determining its amount by titration with 

 standard potassium permanganate. The quantity of urine em- 

 ployed for each test should be modified according to the amount 

 of indican as revealed by a preliminary test, 50 cubic centimeters 

 being enough when much is present and 250 or more when very 

 little is found. 



If the urine is alkaline acidify with acetic acid and precipi- 

 tate with a 20-per-cent. solution of basic lead acetate, avoiding an 

 excess. Find the volume of this mixture, filter, measure off most 

 of the filtrate and to it add as much of Obermayer's reagent. 

 Shake this with renewed portions of chloroform until the latter is 



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