Analytical 



of growth-substance was estimated by them at about 2 mg. 

 per day, of which only about a fifth is indolyl-acetic acid, the 

 remainder consisting chiefly of auxin-a. In the case of their 

 special patient, "E.W.V.", who excreted 8-10 mg. of growth 

 substance per day, at least three-quarters of that amount 

 consisted of indole-acetic acid. 



The oat assay of the successive urine fractions showed very 

 satisfactory agreement with the determinations of indole- 

 acetic acid by weight, allowance being made for losses and for 

 the presence of auxin in the original urine. (The oat-test 

 activities of the two auxins and of indole-acetic acid are very 

 similar). 



Weise (loc. cit. ) gives the following method of preparation 

 of indole-acetic acid from urine. It may perhaps serve as a 

 basis of a method of isolation from agricultural materials. 



Several litres of urine are evaporated down, and the residue 

 extracted with absolute alcohol. The extract is distilled, and 

 the residue is dissolved in a little water and acidified with sul- 

 phuric acid. It is then shaken with ether. The ether extract 

 is separated, and is shaken with a sodium hydroxide solution 

 to remove the indole-acetic acid. The alkaline solution is 

 evaporated down, and the residue is repeatedly extracted with 

 absolute alcohol to a total volume of about 100 ml. Ether is 

 then added, and a precipitate forms. The precipitate is 

 separated from the liquid, the latter is evaporated down, and 

 the residue is acidified with hydrochloric acid. After an ether 

 extraction of the acid mixture, the ether is evaporated off. 

 This gives an impure product (containing traces of hydro- 

 chloric acid) which can be dissolved in hot benzene and re- 

 crystallized. 



Kogl and others (1934, and other papers) have improved on 

 Weise's method in several respects, notably by taking up the 

 indole-acetic acid on an absorbent, thus avoiding the tedious 

 evaporation. They have also made use of a chromatographic 

 technique to separate the indole-acetic acid from auxin. Their 

 papers should be consulted for details. 



E. Salkowski's original methods of isolation of indole- 

 acetic (1884) and indole-propionic acid (1899) from decom- 



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