70 THE ISOLATION AND [CH. 



to the flower-colour used. The crude pigment is filtered off through 

 as small a funnel as possible by means of a vacuum pump, washed, 

 and dried over calcium chloride. The well-dried pigment is then 

 finely ground, and placed in a Soxhlet thimble. The thimble is sus- 

 pended just above the surface of ether contained in a wide-necked 

 Erlenmeyer flask fitted with a condenser, and the ether kept boiling 

 upon an electric heater. This process is continued until the ether 

 ceases to extract any yellow colour. In this way the anthocyanins are 

 obtained practically free from flavones, since the latter are soluble 

 in ether. The anthocyanin residue in the thimble is then taken up in 

 absolute alcohol, and filtered, and is, in this way, freed from a quantity 

 of brown substance, which is insoluble in alcohol, and which is probably 

 formed during the hydrolysis of the glucoside with sulphuric acid. 

 The absolute alcohol solution, evaporated to its minimum bulk, is 

 then poured into a large volume of ether, and the anthocyanin is 

 precipitated, but any flavone present as impurity is retained in solution. 

 The dried precipitate of anthocyanin is again extracted with ether 

 to remove traces of flavone. The method of precipitation gives better 

 results, as regards the purity of anthocyanin, than crystallisation, for, 

 on crystallising a mixture of anthocyanin and flavone, both substances 

 crystallise out together, and one is unaware of the presence of flavone 

 in the product obtained. 



The two forms of anthocyanin, red and magenta, were extracted 

 and purified in this way from the flowers of different varieties of 

 Antirrhinum mentioned above. 



Pure red anthocyanin is an indian-red powder. It is readily 

 soluble in absolute alcohol, almost insoluble in water, and slightly 

 soluble in dilute acids and ethyl acetate; insoluble in ether, chloro- 

 form and benzene. In concentrated sulphuric acid it forms a reddish 

 solution with a slight green fluorescence. It is soluble in alkalies 

 to a greenish-yellow solution. With ferric chloride it gives a 

 brownish-green coloration. With lead acetate, a brownish-yellow 

 precipitate. 



Pure magenta anthocyanin is a magenta-red powder with similar 

 properties and solubilities to the red. In concentrated sulphuric acid 

 it gives a red solution with a slight greenish fluorescence. It is soluble 

 to a green solution in alkalies. With ferric chloride solution it gives 

 a brownish-green coloration. With lead acetate it forms a greenish- 

 black precipitate of a lead salt. In alkaline solutions it is strongly 

 fluorescent, green by transmitted, red by reflected light. 



