CHEMICAL BASIS OF THE ANIMAL BODY. 199 



and 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 otf 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 crystalline 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 nitroprusside 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. Indol 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 2 + 2KHS0 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 (N0 2 ) - CH = CHOI. When this is reduced with 

 tin and hydrochloric acid it yields C 6 H 4 (NH 2 ) -CH = GHC1, and this when heated 

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

 alcohol and indol 8 . 



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

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

 Pniiger's Arch. Bd. xn. (1876), S. 78. Baumann, Zt. f. physiol. 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 Udranszky, Zt. f. 

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



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



5 E. Salkowski, loc. cit. 



6 Legal, Bresl. drtzl. 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. 



