158 THE PROTEIN SUBSTANCES. 



C.CH 3 



are formed in variable quantities from pro- 



NH 



tein compounds under different conditions. Hence they occur habitually 

 in the human intestinal canal, and, after oxidation into indoxyl and 

 skatoxyl respectively, pass, at least partly, into the urine as the cor- 

 responding ethereal sulphuric acids, and also as glucuronic acids. 



Indol and skatol crystallize in shining leaves, and their melting- 

 points are 52 and 95 C. respectively. Indol has a peculiar excremen- 

 titious odor, while skatol has an intense fetid odor. Both bodies are easily 

 volatilized by steam, skatol more easily than indol. They may both be 

 removed from the watery distillate by ether. Skatol is the more insoluble 

 of the two in boiling water. Both are easily soluble in alcohol and give 

 with picric acid a compound crystallizing in red needles. If a mixture 

 of the two picrates be distilled with ammonia, they both pass over with- 

 out decomposition; while if they are distilled with caustic soda, the indol 

 but not the skatol is decomposed. The watery solution of indol gives 

 with fuming nitric acid a red liquid and then a red precipitate of nitroso- 

 indol nitrate (NENCKi 1 ). It is better first to add two or three drops 

 of nitric acid and then a 2-per cent solution of potassium nitrite, drop 

 by drop (SALKOWSKI 2 ) . Skatol does not give this reaction. An alcoholic 

 solution of indol treated with hydrochloric acid colors a pine chip cherry- 

 red. Skatol does not give this reaction. Indol gives a deep reddish-violet 

 color with sodium nitroprusside and alkali (LEGAL'S reaction). On 

 acidifying with hydrochloric acid or acetic acid the color becomes pure 

 blue. Skatol does not act the same. The alkaline solution is yellow 

 and becomes violet on acidifying with acetic acid and boiling. With a 

 few drops of a 4-per cent formaline solution and concentrated sulphuric 

 acid indol gives a beautiful violet color while skatol gives a yellow or 

 brown color (KoNDO 3 ). On warming skatol with sulphuric acid a 

 beautiful purple-red coloration is obtained (CIAMICIAN and MAGNANINI 4 ) . 

 According to SASAKI skatol, in methyl alcohol free from aldehyde, 

 gives with concentrated sulphuric acid containing ferric salt a violet- 

 red ring at the juncture of the two liquids. Indol and tryptophane 

 do not give this reaction. DENIGES has carefully studied the behavior 

 of these two bodies with EHRLICH'S reagent, dimethylaminobenzaldehyde, 

 or with cinnamic aldehyde and vanillin. Comparative investigations on 



1 Ber. d. d. deutsch. chem. Gesellsch., 8, 727, and ibid., 722 and 1517. 



2 Zeitschr. f. physiol. Chem., 8, 447. In regard to newer reactions for indol and 

 skatol, see Steensma, ibid., 47, and Deniges, Compt. rend. soc. biol., 64. 



3 Zeitschr. f. physiol. Chem., 48. 



4 Ber. d. d. chem. Gesellsch., 21, 1928. 



