DYE WOODS 303 



with ferric chloride, and when warmed with alkali gives a 

 deep indigo blue which changes through green to yellow ; 

 this latter reaction is responsible for its name — cyanomaclurin 

 — but as may be seen from the formula given below it is 

 a more complex substance than maclurin (for formula see 

 p. 280) and is in fact regarded by Perkin * as a reduction 



product of morin : — 



OH 



HO— /\/\r {" \— OH HO—/ \/\c / VO^ 



OH 

 I. Morin, CijHjoO^ II. Cyanomaclurin, CuHijOg 



This relationship would thus be just the same as that 

 between quercetin and catechin which occur together in 

 catechu (see p. 294). 



Quercitron Bark. 



This is the bark of Qttercus discolor or Q. tinctoria, which 

 grows in the United States of America ; it contains a glucoside 

 quercetrin which may be extracted by dilute ammonia solu- 

 tion after a preliminary boiling with a fairly strong salt 

 solution to remove gummy impurities ; on adding acid a 

 flocculent precipitate is formed which is removed and the 

 filtrate on further boiling is hydrolysed, yielding the free 

 quercetin which crystallizes in colourless needles. Quercetin 

 is soluble in alkali to give a yellow solution and gives various 

 shades of yellow and brown with chromium, aluminium, tin, 

 and iron mordants ; similar shades are given by the gluco- 

 side itself. 



OTHER REFERENCES. 



Freudenberg : " Die Chemie der naturlichen Gerbstoffe," Berlin, 1920. 

 Gnamm : " Die Gerbstoffe und Gerbmittel," Stuttgart, 1925- 

 Perkin and Everest : " The Natural Organic Colouring Matters," 

 London, 1918. 



* Perkin : " J. Chem. Soc," 1905, 87, 715. 



