56 THE PROPERTIES AND [CH 



did not return on treatment with oxidising enzymes. Grafe (222) 

 holds the view that the loss of colour is due to changes brought about 

 in the aldehyde groups (which he postulates) by the action of nascent 

 hydrogen. The fact that the return of colour in air is not equally 

 great with all acids (Wheldale & Bassett, 621) may indicate that the 

 reaction is not a simple reduction process. 



Compounds with acids. In some cases anthocyanins appear to form 

 definite compounds with acids (Willstatter's oxonium salts), since such 

 compounds occur in crystalline form. Grafe (222) obtained the antho- 

 cyanin from Pelargonium in combination with two molecules of acetic 

 acid as a crystalline substance. Willstatter (245) also obtained both 

 anthocyanin, and the corresponding anthocyanidin. in combination 

 with hydrochloric acid as crystalline compounds. 



Spectrum of anthocyanin. A considerable amount of attention 

 has been devoted to the spectroscopic examination of flower and leaf 

 pigments. Sorby (139, 144), Miiller (169), Engelmann (394), Lepel (151) 

 and Formanek (186) may be mentioned as workers on these lines; 

 but the results are of little value for identification, or otherwise, on 

 account of the impurity of the products employed, that is the doubt 

 as to the number of pigments present, etc. 



Willstatter (245) has distinguished various groups of anthocyanins 

 by their different behaviour to reagents, though the observations do 

 not pretend to include any kind of systematic classification. The 

 following represent some of the classes : 



1. Red in acid solution, blue with soda and a blue precipitate 

 with lead acetate ; pigment readily isomerises to a colourless modifica- 

 tion (Centaurea, Rosa, Lathyrus). 



2. Red in acid solution, blue with soda and a blue precipitate with 

 lead acetate; pigment decolorises less readily or not at all (Grapes, 

 Bilberries, flowers of Delphinium). 



3. Yellowish-red in acid solution, blue with soda, red precipitate 

 with lead acetate (Radish). 



4. Yellowish-red in acid solution (Pelargonium) and blue-red 

 (Papaver) ; both violet with soda and decolorised by isomerisation. 



5. Red in acid solution ; with soda red in dense layers, blue-green 

 in thin layers (Pinks) or red-violet to red-brown (Aster). 



6. Violet in acid solution, red with soda, red precipitate with lead 

 acetate (Beet-root, Atriplex). 



The author (211, 212) has also made observations on crude extracts 

 of anthocyanins from a very large number of flowers, using the colour 



