FLAVONES AND ANTHOCYANINS 241 



in plants, but in Indian yellow obtained from camel's urine; 

 it has the formula 



HO 



CO OH 



Gentisin is a yellow colouring matter occurring in Gen- 

 tiana lutea. 



CO OH 



Properties of Flavones and XantJiones. 



1. These colouring matters are mostly yellow crystalline 

 solids. 



2. In water the crystals are hardly soluble, in acids they 

 dissolve readily giving yellow to red solutions, and in alkalis 

 they also are soluble, yielding the same coloured solutions. 



3. From their solutions they may be precipitated by lead 

 acetate, the precipitate being yellow, orange or red. 



Aniline or toluidine nitrate and potassium nitrite give a 

 cinnabar red precipitate. 



With ferric chloride a dull green or sometimes a red- 

 brown coloration results. 



4. On fusion with alkali, decomposition ensues, phloro- 

 glucinol and protocatechuic acid being commonly formed, and 

 sometimes resorcinol, resorcylic or hydroxybenzoic acids. 



It has been suggested by Wheldale that a close relation- 

 ship exists between the flavones and the anthocyanins. It 

 is assumed that the red pigments known as anthocyan are 

 produced from flavones by two distinct changes ; first the 

 hydrolysis of the glucosidic flavone, and secondly the oxida- 

 tion of the resulting free flavone, with formation of a more 

 complex red colouring matter. A similar series of changes is 

 known to occur in certain plants when the glucoside indican 

 is hydrolysed to indoxyl, which on oxidation yields indigo. 



The theory is to some extent borne out by experiments 

 16 



