198 INDOL. 



skatol (see below), by acidulating and distilling the products of a 

 not too prolonged alkaline putrefactive pancreatic digestion of 

 proteids, preferably of liver or fibrin. Indol passes over into the 

 distillate, from which it is extracted by shaking up with ether, 

 and is left behind as an impure oily liquid when the ether is 

 driven off by heat. 1 It may also be prepared by heating moist 

 proteids slowly to a red-heat with excess of caustic potash, the 

 indol as before passing over into the distillate. 2 Indol is a crys- 

 talline body which when pure melts at 53. It is soluble in 

 boiling water, alcohol, and ether. 



Reactions. A strip of pine-wood moistened with hydrochloric 

 acid is coloured bright crimson when dipped into an alcoholic 

 solution of indol. 3 Its alcoholic solution turns red when treated 

 with nitrous (fuming nitric) acid, and its aqueous solution gives a 

 copious red precipitate with the same reagent. 4 This reaction is 

 more delicate if carried on by the addition of strong nitric acid 

 first, and of a 2 p.c. solution of potassium nitrite subsequently. 5 

 When indol in dilute solution is mixed with a little sodium nitro- 

 prusside and then with a few drops of caustic soda it turns at 

 once violet-blue, and pure blue on subsequent acidulation with 

 acetic acid. 6 Skatol yields neither of the above reactions. Iridol 

 also forms a well-marked crystalline compound with picric acid 

 (trinitro-phenol) when added in benzolic solution to a solution of 

 the acid in benzol, so also does skatol. 



It has been already stated that a part of the indol formed in the 

 alimentary canal leaves the body in the urine as a potassium salt of 

 indoxylsulphuric acid; by oxidation this may be readily decomposed 

 into indigo-blue and acid potassium sulphate: 2C 8 H 6 NKS0 4 -\- 2 

 = C 16 H 10 N 2 O2-h2KHSO 4 . 7 By the action of powerful reducing 

 agents indigo-blue may be made to yield indol, which by oxidation 

 may be again converted into indigo-blue. This shows that indol is 

 the mother substance of the indigo series. The constitution of indol 

 is elucidated by its formation from orthonitrophenylchlorethylene 

 C 6 H 4 (NO,) - CH = CHC1. When this is reduced with tin and hydro- 

 chloric acid it yields C 6 H 4 (NH 2 ) CH=:CHC1, and this when 

 heated to 160 170 with sodium-ethylate (NaO . C 2 H 5 ) yields 

 sodium chloride, ethyl-alcohol and indol. 8 



1 Neiicki, Ber. d. d. chem. Gesell. Bde. vn. (1874), S. 1593, vni. S. 336, 722. 

 Brieger, Zt. f. physio!. Chem. Bd. in. (1879). S. 134. Cf. Koukol-Yasnopolsky, 

 Pfluger's Arch. Bd. xii. (1876), S. 78. Baumann, Zt. f. phi/siol. Chem. Bd. i. 

 (1877), S. 63. Weyl, Ibid. S. 339. See specially E. Salkowski, Ibid. Bd. vm. 

 (1884), S. 417. 



2 Kiihne, Ber. d. d. chem. Gesell. Bd vm. (1875), S. 206. Nencki, Jn. f. prakt 

 Chem. (N. F.), Bd. xvn. (1878), S. 97. 



3 This reaction depends on the presence of coniferin in the pine-wood. Phenol 

 under similar conditions yields a blue colouration. But see Udrauszky, Zt. f. 

 physiol Chem. Bd. xu. (1888), S. 367. 



* Cf. Nencki, Ber. d. d. chem. Gesell. Bd. vm. (1875), S. 722. 



5 E. Salkowski, loc. cit. 



6 Legal, Bresl. artzl. Zeitsch. Nrn. 3 u. 4, 1883. 



7 Baumann u. Brieger, Zt. f. physiol. Chem. Bd. in (1879), S 254. 



8 Lipp, Ber. d. d. chem. Gesell. Bd. xvn. (1884), S. 1067. 



