192 GLUCOSIDES 



Glacial acetic acid 2 c.c. 



Strong sulphuric acid i c.c. 



Ammonium persulphate "5 gram. 



Water to 100 c.c. 



As this fluid penetrates the cells, the indigo is precipitated in 

 blue granules. When penetration is effected fully, the material 

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

 may be cut and stained in the usual way. 



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 artificial synthesis of this sub- 

 stance has been effected in a variety of ways and the days of 

 natural indigo are numbered, unless the planters can produce 

 it at a cheaper rate than the chemists. 



Indicane, if boiled with mineral acids or hydrolysed by 

 means of an enzyme contained in the plant, breaks up into 

 glucose and indoxyl. 



COH 

 C^HsNC-O-CeHiiOs + H,0 = Q^li^.O^ + Q,^Yi/^Q,\l 



NH 



Indicane Indoxyl 



The latter substance on exposure to atmospheric oxygen 

 undergoes oxidation with the formation of the deep blue 

 colouring matter indigo. 



FURTHER REFERENCES. 



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



De Jong: " Ann. Jard. Bot. Buit.," igo8, 7, i. 



Faust: "Arch. Exp. Path, and Pharm.," 1907, 56, 236. 



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



Jorissen: " Bull. Soc. chim. Belg.," 1912, 26, 199. 



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



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



Van der Haar : "Chemisch. Weekblad,," 1914, 11, 214. 



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



