176 THE URINE. 



372. Test a solution of this organic sulphate with 

 barium chlorid. There is no precipitate. Compare the 

 result with that obtained from an inorganic sulphate, like 

 magnesium sulphate, with barium chlorid. 



373. Acidify a solution of an organic sulphate with 

 hydrochloric acid, boil, and add barium chlorid. The acid 

 has decomposed the sulphate; so that a precipitate of ba- 

 rium sulphate is now obtained. 



374. Show that a mixture of the two classes of sul- 

 phates, as in urine, can be detected in this way. First 

 acidify by acetic acid, then, after adding barium chlorid, 

 let the test-tube stand at least half an hour in a beaker of 

 boiling water. The inorganic sulphates are thus precipi- 

 tated as barium sulphate, but not the organic. Filter, and 

 test the nitrate with a drop of barium chlorid. If enough 

 was added at first there will be no precipitate. If there is, 

 more barium chlorid must be used, and the heating re- 

 peated. When the filtrate remains clear, acidify with hy- 

 drochloric acid and boil. The precipitate is from the de- 

 composed organic sulphates united with the barium chlorid 

 previously added. 



375. Insert into a rabbit's stomach a wide, flexible 

 catheter or rubber tubing, passing it through a short piece 

 of glass tubing held between the animal's teeth. Intro- 

 duce by this tube a gramme of ortho-nitro-phenyl-propiolic 

 acid and collect the urine for twenty-four hours. It will 

 contain a large quantity of indican. Eead the literature 

 on the relationship of the above acid to indigo, and explain 

 the formation of indican. 



376. Test urine for indican by adding to half a test- 

 tubeful an equal volume of concentrated HC1. Then add 

 a minute fragment of calcium hypochlorite ("chlorinated 

 lime") and a few drops of chloroform and shake gently. 



