ANTHOXANTHINS 247 



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

 it has the formula 



o 



HO 



CO OH 



Gentisin is a yellow colouring matter occurring in Gen- 

 tiana lutea. 



aX)"' 



HO 



CO OH 



Datiscetin occurring in the form of a glucoside, Datisdn, in 

 Datisca cannabina. 



Properties of Anthoxantkins. 



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 alkalies 

 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. 



4. Aniline or toluidine nitrate and potassium nitrite give 

 a cinnabar red precipitate. 



5. With ferric chloride a dull green or sometimes a red- 

 brown coloration results. 



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

 glucinol and protocatechuic acid being commonly formed, and 

 sometimes resorcinol, resorcylic, or hydroxybenzoic acids. 



The solubility of the anthoxanthins in acids is due to the 

 peculiar basic properties of the oxygen atom taking part in 

 the ring formation. The basic nature of the oxygen atom in 

 such circumstances was first observed in the case of the simpler 

 substance pyrone 



