CHEMICAL BASIS OF THE ANIMAL BODY. 203 



(CH 3 ) 2 CH . C 6 H 3 (N0 2 ) . COOH l and clearly proved by its synthetic production 

 from, propylidene-phenylhydrazin C 6 H g . NH.N = CH.CH 2 . CH 3 , the product of the 

 action of propionic aldehyde (CH 3 . CH 2 . COH) on phenylhydrazin (C 6 H 5 . NH. NH 2 ). 

 When this substance is heated with zinc chloride it loses NH 3 and yields skatol 2 



NH 



CH a 



Since the condition of the occurrence and formation of skatol are 

 on the whole the same as those for indol, and since these substances 

 further resemble each other in being both volatile and hence passing 

 over in the vapours arising from their heated solutions, the method 

 previously described for the preparation of indol from putrefactive 

 products may be applied for the preparation of skatol. The separation 

 of the two depends chiefly on the fact that skatol is much less soluble 

 in water than is indol, so that if the mixed substances are dissolved 

 in a minimal amount of absolute alcohol, then on the addition of 8 

 10 volumes of water, indol remains in solution while skatol is pre- 

 cipitated 3 . Skatol is unaffected by being boiled with moderately 

 strong caustic soda, whereas indol is decomposed. This difference in 

 behaviour to caustic alkalis provides a further means by which the 

 former may be obtained free from the latter. 



Skatol is a crystalline substance which melts when heated to 93, 

 and has a powerfully unpleasant odour, somewhat like that of indol. 



Reactions. Many of the reactions of skatol resemble so closely 

 those of indol that they provide no means for distinguishing between 

 the two substances. Skatol is however characterised by yielding only 

 a milky opacity instead of a red colouration on the addition of fuming 

 nitric acid to its aqueous solutions (see sub indol), in not giving the 

 reaction with a strip of pine- wood dipped in hydrochloric acid which 

 indol does 4 , by its lesser solubility in water and greater resistance to 

 the action of caustic soda. 



5. Skatoxyl-sulphuric acid. C 9 H 8 N.O.SO 2 OH. 



The close relationship between indol and skatol is further shown by 

 the fact that the latter, like the former, after absorption from the 

 alimentary canal is oxidised, the product being skatoxyl C 9 H 8 N.OH 

 which unites, as does indoxyl, with the elements of sulphuric acid and 



1 Fileti, loc. cit. p. 356. Abst. loc. cit., S. 2927. 



2 E. Fischer, Ber. d. d. chem. GeselL Bd. xix. (1886), S. 1563. Liebig's Ann. 

 Bel. ccxxxvi. (1886), S. 116. 



3 Brieger, Ber. d. d. chem. GeselL Bd. xn. (1879), S. 1985. Zt. f. physiol 

 Chem. Bd. iv. (1880), S. 414. 



4 When however a strip of pine-wood is dipped into an alcoholic solution of 

 skatol and subsequently into strong hydrochloric acid, it is coloured first crimson, 

 which turns to bluish- violet. Fischer, Liebig's Ann. Bd. ccxxxvi. (1886), S. 140. 



