252 GLUCOSIDES 



is washed for twenty-four hours in water, after which sections 



may be cut and stained in the usual way. 



Indican is hydrolysed by indimulsin, with which it is 



associated in the plant, into glucose and indoxyl according 



to the equation — 



COH 



C,H,NC . O . CfiHiiOs + H,0 = CeHiPe + C^H^^ ^CH 



NH 

 Indican Indoxyl 



The same reaction can also be effected, though more slowly, 

 by emulsin. 



The resulting indoxyl, by exposure to air, is oxidized to 

 the deep blue colouring matter indigotin — 



COH CO CO 



2C«H,^^CH + O = CeH,^\c : C(^^C,Y{, -f H,0 



NH NH NH 



Indoxyl Indigotin 



The production of indigotin from the indigo plant is based 

 on these two reactions and consists in fermenting the plant 

 material by steeping it in slightly acidified water for a few 

 hours, and then exposing to the air the fermented extract to 

 which a little ammonia has been added to facilitate oxidation. 



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. 



