202 SKATOL. 



Indigo as ordinarily seen possesses a pure blue colour; it leaves 

 a reddish copper-coloured mark when pressed with a hard body and 

 the crystals exhibit the same colour if seen in reflected light. 



Treated with reducing agents in strongly alkaline solution indigo 

 is decolorised, being reduced to indigo-white. The latter contains two 

 atoms of hydrogen more than indigo, is reconverted into indigo-blue by 

 exposure to the air and thus provides a convenient reaction for the 

 detection of either indigo or of reducing substances such as dextrose. 



r X NH X -i 



4. Skatol. C 9 H 9 K C 6 H 4 OH. Methyl-indol. 



^ C ' 



CH 3 



Skatol was first noticed and definitely described by Brieger as 

 occurring in human faeces together with indol, the latter usually being 

 less in amount than the former 1 . Later researches have shown that 

 the conditions of its production are in general the same as those for 

 the formation of indol so that the two substances occur mixed in 

 variable proportions among the products of the putrefactive decompo- 

 sition of proteids 2 or brain-substance 3 and of the action of caustic 

 potash at high temperatures on proteids 4 . In the former case it 

 appears to be produced at a later stage than is indol, so that on the 

 whole it is most preponderant the longer the putrefactive change is 

 allowed to proceed. Its presence in the faeces is thus due to causes 

 similar to those which account for the presence of indol, and the 

 resemblance is further shown by the fact that a portion of the first- 

 formed skatol is absorbed, oxidised, and appears externally in the 

 urine as skatoxyl-sulphuric acid (see below). 



Skatol is formed in small quantities during the preparation of indol by 

 reduction from indigo 5 . It may be partly converted into indol by passing its 

 vapours through a red-hot porcelain tube 6 . The constitution of skatol was 

 foreshadowed by its preparation from the barium salts of ortho-nitrocuminic acid, 



1 Ber. d. d. chem. Gesell. ~BA. x. (1877), S. 1027. Jn. f. prakt. Chem. (N.F.), 

 Bd. xvn. (1878), S. 124. A closely similar, if not identical, substance had 

 previously been noticed, but not clearly characterised, by Nencki as among the 

 products of the putrefactive decomposition of gelatin and by Secretan among those 

 of a similar decomposition of proteids. See Maly's Jahresb. 1876, Sn. 31, 39. 



2 Nencki, Centralb. f. d. med. Wiss. 1878, S. 849. E. u'. H. Salkowski, Ber. 

 d. d. chem. Gesell. Bd. xn. (1879), S. 648. Zt. f. physiol. Chem. Bd. vm. (1884), 

 g. 417 466. Contains very full references to previous literature. 



3 Nencki, Ibid. Bd. iv. (1880), S. 371. Stockly, Jn. f. prakt. Chem. (N.F.), 

 Bd. xxiv. (1881), S. 17. 



4 Nencki, Jn.f. prakt. Chem. (N.F.), Bd. xvn. (1878), S. 97. 



5 Baeyer, Ber. d. d. chem. Gesell. Bd. xin. (1886), S. 2339. 



6 Fileti, Gazz. Chim. T. xm. (1883), p. 378. See abstr. in Ber. d. d. chem. 

 Gesell. 1883, S. 2928. 



