46 THE PROPERTIES AND [CH. 



method, using acetic acid instead of water, Molisch (104) obtained good 

 crystals from petals of garden roses and of Anemone fulgens. Several 

 other investigators have crystallised anthocyanin from extracts ; the 

 cases may be mentioned here though the methods of preparation will 

 be given in the next chapter. From the red pigment of Vine leaves, 

 Gautier (175) isolated two substances termed by him a- and /3-ampelo- 

 chroi'c acids. From a solution in hot water, the ct-acid was obtained 

 on cooling as a red crystalline powder. The ^8-acid also was deposited 

 from water in red crystals on slow evaporation. Griffiths (191) prepared 

 crystals from pigment of 'Geranium' (Pelargonium) flowers. From 

 flowers of Althaea rosea, Grafe (197) isolated a deep red pigment which 

 separated out from alcohol in minute crystalline plates. Portheim & 

 Scholl (204) also succeeded in crystallising the anthocyanin from the 

 testa of seeds of Phaseolus multiflorus. Later, Pelargonium flowers 

 were again employed by Grafe (222) as material for the purification 

 and analysis of anthocyanin, and like Molisch, Grafe found that this 

 pigment very readily crystallised. The facility with which Pelargonium 

 pigment may be made to crystallise, as compared with other antho- 

 cyanins, is no doubt due to the difference in its chemical nature. Not 

 only as regards the scarlet colour, but also in its reactions towards 

 reagents, the Pelargonium pigment differs from the more universally 

 distributed purples and purplish reds. 



Before describing the solubilities of anthocyanin, it should be 

 mentioned that the pigment usually exists in the plant in the form 

 of a glucoside. In this form it has been isolated from fruits of the 

 Bilberry (Heise, 178), and from flowers of Althaea, Pelargonium (Grafe, 

 197, 222) and Centaurea (Willstatter, 245). There is little doubt, as 

 will be shown in later chapters, that anthocyanins are aromatic sub- 

 stances containing hydroxyl groups, and, as is well known, hydroxyl 

 groups in plant products are frequently replaced by sugars. As a 

 glucoside, anthocyanin is readily soluble in water, and since it is in 

 this form that the pigments chiefly occur in the cell, they can be 

 extracted with water. After hydrolysis, in the non-glucosidal state, 

 the pigment is far less soluble in water, and in some cases almost or 

 quite insoluble, i.e. Antirrhinum (Wheldale & Bassett, 254) and Bilberry 

 (Heise, 178). To the consideration of these glucosides we shall return 

 again later in the chapter. 



In ether, anthocyanin is insoluble, as also in benzene, carbon bisul- 

 phide, chloroform and similar solvents in which plastid pigments are 

 soluble. In alcohol, the greater proportion of anthocyanins are soluble ; 



