Analytical 



of indole-acetic acid, and then a few drops of 2 per cent, 

 potassium nitrite solution are added, a cherry-red colour 

 appears ; if the dilution is not too high, a red colouring- 

 matter is precipitated, which is easily soluble in ethyl acetate 

 and in amyl alcohol. Caustic soda solution discharges the 

 colour from ethyl acetate solution and acquires a yellow 

 tinge. The alkaline solution is rendered colourless after 

 addition of zinc dust and remains colourless on exposure 

 to air. (Distinction from indole; nitroso-indole after 

 reduction becomes blue on standing — Salkowski.)" 



The same test is given by Ellinger on p. 792 of Teil 7, Abt. 

 I, of Abderhalden's Handbuch. (Urorosein may often be 

 formed from urine by simply adding hydrochloric acid; its 

 formation requires the presence of nitrite, which is often 

 present in urine owing to bacterial activities). The following 

 will now be understandable. 



"For the demonstration of urorosein, 5-10 ml. of con- 

 centrated hydrochloric acid are added to 50-100 ml. of 

 urine. If no red colour appears after a few minutes, a little 

 0-2 per cent, sodium nitrite is cautiously added, drop by 

 drop. The red colour then appears if the chromogen is 

 present. 



"The dyestuff thus formed can be separated out by 

 shaking with amyl alcohol: this operation is especially 

 necessary when other red or yellowish-red colouring- 

 matters are present. The amyl alcohol solution should be 

 examined spectroscopically. 



"Urorosein dissolves to a reddish solution in water, ethyl 

 alcohol, amyl alcohol, but is insoluble in ether and in 

 chloroform (distinction from indirubin and skatole red). 

 The colour of the solutions is discharged by addition of 

 alkaUs, and restored on acidification. The amyl alcohol 

 solution shows a sharp absorption band in the green, 

 about 557 A.U." 



From Weise's account of the indole-acetic acid tests with 

 acid and nitrite, it looks as if nitroso-indolyl-acetic acid 



125 g^ 



