768 THE INDIGO SERIES. [App. 



THE INDIGO SERIES. 



Indican. C 8 H 7 NS0 4 . 



A body was long ago described * as occurring in the urine and sweat 

 of men and other animals which yielded by the action of acids the 

 blue colouring matter indigo as one of the products of its decom- 

 position. Schunk considered this substance to be identical with the 

 indican known to occur in several plants (Indigofera, Isatis). Hoppe- 

 Seyler 2 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. Bauinann has shown 3 that the two 

 are really different, and has confirmed his earlier statements in a more 

 recent publication 4 . 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.SO 2 .OH, and regards it as indoxylsulphuric acid. The acid 

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

 as that of potassium, C 8 H 6 N.S0 4 K. It occurs largely in the urine 

 as the result of the presence of indol in the alimentary canal. In this 

 way Baumann and Brieger 5 were enabled to obtain large quantities by 

 giving indol to a dog. For its preparation 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 + O a ~ 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 colour 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 

 colour, in alcohol and aether. Chloroform also dissolves them to a slight 

 extent. Indigo is soluble in strong sulphuric acid, forming at the same 



1 Schunk, Phil. Mag. Vol. x. p. 73; xiv. p. 228; xv. pp. 29, 117, 183. Chem. 

 Centralb. 1856, S. 50; 1857, S. 957; 1858, S. 225. Hoppe-Seyler, Arch. f. path. 

 Anat. Bd. xxvii. S. 388. Jaffe", Pfliiger's Arch. Bd. in. (1870), S. 448. 



2 Handb. d. path. chem. Anal. Ed. iv. (1875), S. 191. 



3 Pfliiger's Arch. Bd. xm. (1876), S. 301. Zeitschr. f. physiol. Chem. Bd. i. 

 (187778), S. 60. 



4 Zeitschr. f. physiol. Chem. Bd. m. (1879), S. 254. 



5 Zeitsch. f. physiol. Chem. Bd. in. (1879), S. 254. See also Ber. d. deutsch. 

 Chem. Gesell, xii. (1879), Sn. 1098, 1192 ; 2166, ami xm. (1880), S. 408. 



