CHAP. X.] INDOL. 423 



peculiar, disgusting, faeculent smell. Indol is tolerably soluble in hot, 

 and less soluble in cold, water ; it is easily soluble in alcohol, ether, 

 chloroform, benzol, and petroleum ether. 



1. A watery solution of indol when treated with 

 strong yellow nitric acid, or better still with a 2 per 

 cent, solution of sodium nitrite and pure nitric acid, is either coloured 

 red or furnishes a red precipitate of nitrate of nitroso-indol 

 C 16 H 13 (NO)N 2 , HN0 3 , which is very slightly soluble in water, readily 

 soluble in alcohol, and insoluble in ether, and is readily decomposed. 

 If the solution is so dilute as not to yield a precipitate spontaneously, 

 this may be caused by shaking with chloroform, when at the line of 

 junction of the colourless chloroform and the red-coloured liquid a 

 red precipitate becomes visible. 



"The characteristic red colouration which cholera cultures in bouillon 

 exhibit when they are treated with dilute sulphuric acid ('Cholera-reaction') 

 depends upon the simultaneous production of indol and nitrous acid by the 

 cholera spirillum. The nitrous acid is set free by the dilute sulphuric acid 

 and then acts upon the indol, and the red nitroso.-indol is then formed, 

 which is identical with cholera-red. ' Vibrio Metschnikoffii ' also exhibits 

 the cholera reaction 1 ." 



" The nitrous acid test for indol enables us readily to detect the body 

 in the products of a pancreatic digestion which has not been aseptic. 

 With this object the fluid resulting from the digestion is distilled, and to 

 every 200 or 300 cc. of the distillate are added from 5 8 cc. of a reddish- 

 yellow nitric acid. The liquid thus treated assumes the colour of arterial 

 blood and in the course of some hours deposits the red precipitate, composed 

 of nitrate of nitroso-indol. By dissolving this precipitate in a little hot 

 absolute alcohol and then adding ether, the substance is obtained in the 

 form of beautiful red, microscopic, needles. The red colouration which 

 pancreatic juice exhibits when treated with impure nitric acid was first 

 observed by Claude Bernard 2 " (see p. 264). 



2. A small piece of pine wood moistened with strong hydro- 

 chloric acid and then plunged into an alcoholic solution of indol, 

 acquires a cherry-red colour. 



3. (Legal's reaction 3 ). When sodium nitro-prusside is added to 

 a solution of indol of 1 in 1000, so as to produce a yellowish coloura- 

 tion, and, thereafter, some drops of solution of caustic soda, the liquid 

 instantly becomes of a deep violet-blue. On acidulating with hydro- 

 chloric or acetic acid, the colour at once changes to a deep blue, 

 which is destroyed by an excess of acid. The second stage of the 

 reaction is so delicate that in a solution containing only 1 part of 

 indol in 10,000 of water, a deep blue colouration is observed 4 : 

 Hemala has studied the spectroscopic characters of Legal's reaction 5 . 



1 Dr Th. Weyl, Lehrbuch d. org. Chemie, Berlin, 1891, p. 452. 



2 Maly, Hermann's Handbuch, Vol. v. n. p. 225. 



3 Breslauer drtztliche Zeitschrift, 1884, Nos. 3 and 4, quoted by Salkowski. 



4 Salkowski, op. cit. Zeitschr. f. phys. Chem. Vol. vm. p. 447. 



5 Kich. Hemala, ' Zur Kenntniss der in der chemischen Physiologie zur Anwendung 



OF THE 



UNIVERSITY 



