Plant Qrowth'Suhstances 



amyl alcohol, in which the red substance is very 

 soluble. 



(2) If to the neutral solution of the acid is added an equal 

 volume of hydrochloric acid (D. 1-12) and a few drops of 

 about I per cent, "bleaching-powder solution", a purple-red 

 colour is produced. In concentrated solutions a precipitate is 

 formed, soluble in ethyl alcohol and in amyl alcohol. 



EhrlicKs test. — Resembling the usual diazotization reaction 

 in hydrochloric acid solution, this is performed with alcoholic 

 />-dimethylamino-benzaldehyde in hydrochloric acid in pre- 

 sence of nitrite. With indole-acetic acid a reddish colour is 

 produced, not very distinct from that given by indole. 



Lead acetate gives a crystalline precipitate with a o-i per 

 cent, solution of sodium or potassium indole-acetate, whereas 

 other heavy metals give little or no precipitate (Ellinger). 



Indole-acetic acid is not volatile in steam, is stable towards 

 alkalis, and is odourless. 



Link et al. (1937, H) used the Salkowski colour test as sole 

 chemical test for indole-acetic acid. They remark that it is 

 considered specific for that compound. Evidence for its 

 specificity is not quite satisfactory. An analytical scheme for 

 the detection of the principal indole-acids and related com- 

 pounds is badly needed. 



Urorosein is a derivative of indole-acetic acid. It was dis- 

 covered by Nencki and Sieber in 1882. Opinions differ about 

 its constitution. 



Weise in Abderhalden's Handhuch^ Abt. 4, Teil 5(1), gives 

 tests for the presence of indole-acetic acid (p. 767) and for the 

 production of urorosein (p. 768) which, though similar, diff"er 

 in detail. It has been suggested that urorosein is a derivative 

 of indolyl-aceturic acid (indolyl-acetoyl-glycine), the conjuga- 

 tion product (see p. 58) of indole-acetic acid, but it appears 

 uncertain that the glycine takes part in the production of 

 urorosein. 



The tests given by Weise [loc. cit) are as follows : 



"Indole-acetic acid (Salkowski's test). — If a few drops of 

 pure nitric acid (D. i '2) are added to a very dilute solution 



124 



