258 INDOXYL-PIGMENTS. SKATOXYL-PIGME^TS. 



6. Indoxyl-pigments. 



Of the total indol formed in the alimentary canal, a portion is 

 excreted with the faces, while the remainder is absorbed and re- 

 appears in the urine united with potassium as ethereal compounds 

 of indoxyl with either glycuronic acid (p. 107) or sulphuric acid 

 (p. 199), the latter being known as urinary indican. When 

 warmed with hydrochloric acid these compounds are decomposed, 

 yielding indoxyl and the potassium salt of the corresponding acid. 

 If the decomposition is effected in the absence of oxygen, the in- 

 doxyl may be in part gradually changed into an amorphous red- 

 dish substance, indigo-red, which is insoluble in water, but yields 

 a red solution when dissolved in alcohol, ether, or chloroform. 1 

 These solutions show no certainly characteristic absorption bands. 

 In presence of oxygen and with most certainty by the action of 

 an oxidising agent, the indoxyl is readily converted into indigo- 

 blue, whose properties and solubilities have been already suffi- 

 ciently described. Dilute solutions of indigo-blue exhibit in thin 

 layers one absorption band in the red lying between a and B 25 

 C ; if the thickness of the solution be increased this band widens 

 out towards D and at the same time a second faint band makes 

 its appearance in the green lying between D 50 E and D 77 E? 



The numbers just given refer to the method (Vierordt's) frequently 

 used for indicating the position of an absorption band. In this the 

 distance between any two of the fixed lines of the solar spectrum is re- 

 garded as being divided into 100 equal parts and the extent of the 

 band is given by reference to these divisions. Thus if a band is de- 

 scribed as lying between D 50 E and D 77 E it implies that the band 

 begins half way (-fifa of the distance) between D and E and extends 

 to -j 7 ^ of the distance between the same two lines. 8 (See also above, 

 note I, p. 228.) 



Variable accounts of the above pigments may be obtained from 

 urines during their spontaneous decomposition or when treated 

 with hydrochloric acid or oxidising agents, the amount being 

 greatest in herbivorous urine and especially great in certain 

 pathological urines (see p. 199). They have also been met 

 with in urinary sediments and calculi. 4 



7. Skatoxyl-pigments. 



The skatol formed in the alimentary canal gives rise, like in- 

 dol, to compounds of skatoxyl with either sulphuric acid or glycu- 



1 Cf. Nencki, Ber. d. d. chem. Gesell. Bd. ix. (1876), S. 299, and see MacMunn, 

 Proc. Roy. Soc. Vol. xxxv. (1883), p. 370. 



2 Vierordt, Zt.f. Biol. Bde x. (1874), S. 27, xi. (1875), S. 192. 



8 A table for the conversion of these data into wave-length limits is given by G. 

 n. H. Kriiss, Kolorimetrie u. quant. Spe.ktra/ana/yse, 1891, S. 290. 



* Ord, Berl. klin. Wochensch. 1878, S. 365. Chiari, Prager med. Wochensch. 

 1888, S. 541. 



