722 PHYSIOLOGICAL CHEMISTRY. 



of color is attained ; add chloroform, which is colored blue. (Care 

 should be taken to add the hypochlorite slowly, as an excess destroys 

 the color ; highly colored urine should be decolorized with basic lead 

 acetate ; in doubtful cases the mixture of urine, hydrochloric acid, one 

 or two drops of bleach ing-powder solution, and chloroform should 

 be set aside for several hours.) 



2. ObermayeSs test depends on the conversion of indican into indigo 

 by ferric chloride ; and as this reagent has no further action on indigo, 

 the method has a great advantage over the previous ones. The test 

 is made by following the directions given in the above test, using an 

 equal volume of strong HC1 containing 0.2 per cent, of ferric 

 chloride and no bleaching-powder solution. 



Indigo-red appears in the urine in the same conditions in which 

 indican is found. It is recognized by Rosenbach's reaction : Urine 

 is boiled, and, while it is still boiling, nitric acid is added drop by 

 drop, when a deep red color appears if indigo-red is present. The 

 foam on shaking the test-tube is bluish red. 



Skatole (skatoxyl-sulphuric acid) is rarely present in the urine. Its 

 formation is analogous to that of indole. 



Phenol, C 6 H 5 OH, and paracresol, C 6 H 4 .CH 3 .OH, occur in urine 

 in combination with potassium acid sulphate. The combined quan- 

 tity of the two substances is about 0.002 per cent. The quantity is 

 increased during intestinal putrefaction from all causes (except simple 

 obstruction), when there is absorption of pus from abscess or wounds, 

 and after ingestiou of carbolic acid. 



Experiment 101. (Determination of phenol.} 



a. Qualitative determination. Render alkaline 100 c.c. of urine with sodium 

 carbonate, evaporate to a syrup, add 20 c.c. of hydrochloric acid, and distill. 

 To the distillate apply the tests for phenol. 



b. Quantitative determination. To 500 c.c. of urine add 25 c.c. of hydrochloric 

 acid and distill 200 c.c. Neutralize distillate with sodium hydroxide, in order 

 to convert benzoic and possibly other acids present into salts, and again distill 

 200 c.c. Determine the quantity of phenol in the distillate by means of deci- 

 normal bromine solution, as directed on page 424. 



Pyrocatechin, ortho-dioxy benzene, C 6 H 4 (OH) 2 , occurs in urine as 

 pyrocatechin sulphuric acid. It is derived from the putrefaction of 

 vegetable food, and is found in large quantity in urine after taking 

 carbolic acid. Urine containing pyrocatechin turns dark on exposure 

 to air, especially if it is made alkaline. 



To show the presence of pyrocatechin, add a little sulphuric acid 

 to the urine, boil, and when cool extract with ether. Evaporate the 

 ether, dissolve the residue in a little water, and apply tests. 



