916 APPENDIX. 



indigo as one of the products of its decomposition. Schunk considered this sub- 

 stance to be identical with the indicari known to occur in several plants (Indigofera, 

 Isatis). Hoppe-Seyler, 1 on the other hand, having regard to the greater ease with 

 which the indican from plants undergoes decomposition, regarded them as most 

 probably different substances. Baumann has shown 2 that the two are really differ- 

 ent, and has confirmed his earlier statements in a more recent publication. 3 

 According to him, the indican obtained from urine is not a glucoside (so also 

 Hoppe-Seyler) and yields sulphuric acid by the action of hydrochloric acid. He 

 assigns to it the formula C 8 H 6 N.O.S0 2 .OH, and regards it as indoxy-sulphuric acid. 

 The acid itself is not yet known in the free state, but it yields stable salts such as 

 that of potassium. CgHeN.SCXK. It occurs largely in the urine as the result of 

 the presence of indol in the alimentary canal. In this way Baumann and Brieger * 

 were enabled to obtain large quantities by giving indol to a dog. For its prepara- 

 tion their original paper must be consulted. 



When treated in aqueous solution with hydrochloric acid in presence of oxygen 

 it yields indigo-blue. 



2C 8 H 6 NS0 4 K + 2 - 2C 8 H 5 NO + 2KHS0 4 . 



It is always estimated in urine by conversion into indigo-blue. 



Indigo. C 8 H 5 NO. 



It is formed, as stated above, from indican, and gives rise to the bluish color 

 sometimes observed in sweat and urine. 



It may, by slow formation from indican, be obtained in fine crystals; these are 

 insoluble in water, slightly soluble, with a faint violet color, in alcohol and ether. 

 Chloroform also dissolves them to a slight extent. Indigo is soluble in strong sul- 

 phuric acid, forming at the same time two compounds with this acid ; these are 

 soluble in water. It possesses a pure blue color ; when pressed with a hard body 

 a reddish copper-colored mark is left, and the crystals exhibit the same color if seen 

 in reflected light. 



The soluble compounds with sulphuric acid give an absorption band in the spec- 

 trum which lies close to the D line and to the red side of it. This may be used to 

 detect indigo. 



Treated with reducing agents, indigo is decolorized, being reduced to indigo- 

 white. The latter contains two atoms more hydrogen than indigo. 



Indol. C 8 H 7 N. 



To this body the specific odor of the feces is partly due. It is obtained as the 

 final product of the reduction of indigo, and also by the distillation of proteid 

 matter with caustic alkalies. 5 



It often occurs among the products of the action of pancreatic ferment on pro- 

 teids ; its presence in such cases appears, however, to be due, not to the action of 

 the trypsin, but to a simultaneous putrefaction under the influence of bacteria, 

 etc. 6 If the pancreatic digestion be carried on in the presence of salicylic acid, 

 indol does not make its appearance. Indol is a crystalline body, soluble in boiling 

 water, alcohol, and ether. It passes over in the steam when its aqueous solution 

 is boiled. It is characterized by the following reactions : A strip of pine-wood 

 moistened with hydrochloric acid is colored bright crimson when dipped into a 

 solution of indol. Its alcoholic solution turns red when treated with nitrous acid, 

 and its aqueous solution gives a copious red precipitate with the same reagent. It 

 also yields a characteristic crystalline compound with picric acid. 



i Handb. d. path. chem. Anal., ed. iv. (1875), S. 191. 



8 Pfliiger's Arch , Bd. xiii. (1876), S. 301. Zeitschr. f. physiol. Chem., Bd. i. (1877-78), S. 60. 



3 Zeitschr. f. physiol. Chem., Bd. iii. (1879), S. 254. 



* Zeitschr. f. physiol. Chem., Bd. iii. (1879), S. 254. See also Ber. d. Deutsch. chem. Gesell., xii. 

 (1879), Sn. 1098, 1192, 2166; and xiii. (1880), S. 408. 



5 Kuhne. Ber. d. deutsch. chem. Gesell., viii. (1875), S. 206. 



e Kuhne, Verhand. Heidelb. naturhist.-med. Ver., N.S., Bd. i., Hft. 3. Ber. d. Deutsch. chem. 

 Gesell. (1875), S. 206. 



