INDICAN 191 



Prepared in this way the natural indigo contains, in addition, 

 to indigotin, varying proportions of indirubin (a red colouring 

 matter), indigo brown, etc., produced as by-products in the 

 oxidation of the indoxyl. 



Until a few years ago, Indigofera was the only source of 

 the blue colouring matter indigo, for the obtaining of which 

 large tracts of country were under cultivation in India. With- 

 in recent years, however, the natural production of indigo has 

 suffered from very severe competition with the synthetic 

 product and the planters have been compelled to improve 

 their output. The importance of attention to fertilizing the 

 soil has been shown by the fact that superphosphate manuring 

 has considerably increased the yield and improved the quality 

 of the resulting indigo.* 



* Davis: "Agric. Res. Inst. Pusa.," Indigo Publ., No. 4, 1918. 



FURTHER REFERENCES. 



Armstrong: "The Simple Carbohydrates and Glucosides," London, 1919. 



Henry: "Science Progress," 1906, I, 39. 



Kobert : " Beitrage zur Kenntniss der Saponinsubstanzen," Stuttgart, 1904. 



Robinson : " Science Progress," 1909, 3, 575. 



Van Rijn: "Die Glykoside," Berlin, 1900. 



