ANTHOCYANINS 345 



a few drops of 75 per cent acetic acid and rolling a glass rod 

 over it to crush the tissues. The preparation is covered with 

 a cover glass and set aside ; after a few hours, needle-shaped 

 aggregates of deep red crystals will be formed along the edge 

 of the cover glass. 



Reactions and Properties. 



1. The anthocyanins are soluble in water and in alcohol,* 

 but are insoluble in ether. 



2. Solutions are turned red by acid and blue by alkalis ; 

 owing to the almost universal contamination with flavonols, 

 the crude aqueous extracts of anthocyanins from plants 

 usually give a green coloration with alkali due to the simul- 

 taneous production of blue and yellow. 



The red juice of an unboiled beet and the anthocyanins of 

 the Chenopodiacese generally, give a purple colour with acid 

 and a yellow with alkali. 



3. Lead acetate or basic lead acetate give with antho- 

 cyanins bluish-green or green precipitates ; with beet juice and 

 similar anthocyanins basic lead acetate produces a red pre- 

 cipitate. 



CHEMICAL CONSTITUTION. 



The anthocyanidins or non-carbohydrate moiety of the 

 anthocyanins are derivatives of benzo-pyrilium which, as may 

 be seen from the appended formula I. — 



CH O- CH O 



CH C CH CH C CH 



I I II i II II 



CH C CH CH C CH 



\ /\/ \ /\/ 



CH CH CH CO 



I. Il- 



ls closely related to benzo-pyrone II., the mother substance of 

 the fiavones. Both these substances contain a so-called basic 

 oxygen atom which by becoming tetravalent can form addi- 

 tive compounds with acids producing oxonium salts. These 



* In some cases, e.g. pelargonium, the pigment loses its colour in 

 alcohol, but the colour may be restored by the addition of acid, or by 

 evaporating off the alcohol and taking up the residue in water. 



