vn] THE FORMATION OF ANTHOCYANINS 123 



Tswett (243) also found that an 'artificial anthocyanin ' could be 

 prepared from apple juice by the action of strong mineral acids in the 

 presence of formaldehyde or acetic aldehyde. The artificial anthocyanin 

 had properties and reactions very like the natural pigment, but was 

 soluble in ether, whereas natural anthocyanins are insoluble in this 

 solvent. Tswett produced similar pigments, though he did not study 

 them in detail, from extracts of white grapes, bananas, flesh of purple 

 grapes, white petals of Rosa and Cyclamen. He failed however to get 

 any formation of pigment on treatment of the following: leaves of 

 white Cabbage, mesophyll of red Cabbage, leaves of Pelargonium, Orange 

 skins, petals of white Pinks, white petals of buds of red Pinks, flowers of 

 Lily of the Valley, Carrots, Potatoes, Kohlrabi and Barley seedlings. 



Artificial anthocyanin resembles natural anthocyanin in the following 

 respects. It is soluble in alcohol, gives a green reaction with alkalies, 

 red with acids and a green precipitate with lead acetate ; it is decolorised 

 by sodium bisulphite, but the colour returns again on acidifying with 

 sulphuric acid. It differs from the natural product in its solubility in 

 ether and also its ready solubility in water, the natural pigments being 

 only slightly soluble in water, except in the condition of glucosides. 

 The work of Everest (248, 249) in this direction has been more 

 elaborate. Mention has been previously made of the fact that Everest 

 has prepared from the flavones, substances which give some of the 

 qualitative reactions of anthocyanin. Everest's methods are as follows : 

 He reduces an alcoholic solution of flavones, to which is added 2 N acid 

 solutions, by means of nascent hydrogen formed by (1) addition of 

 granulated zinc, (2) sodium amalgam, (3) electrolysis, using sulphuric 

 acid and lead electrodes, and (4) magnesium ribbon. The materials 

 employed were cjuercetin, quercitrin and extracts from various flowers 

 and tissues. In many cases a red pigment is obtained as reduction 

 proceeds. When quercetin was employed, the product could be 

 extracted quantitatively from the acid solution by amyl alcohol showing 

 it to be an anthocyanidin. When quercitrin, a monoglucoside of quer- 

 cetin, was used, anthocyanidin, contrary to expectation, was also 

 obtained. Extracts, however, from flowers and other tissues, in which 

 the flavones are presumably in the glucosidal state, gave anthocyanins 

 in the cold and anthocyanidins on hydrolysis. 



Everest also lays stress upon the fact first noted by Keeble, Arm- 

 strong & Jones (240), that the artificial anthocyanin is reduced to a 

 colourless substance by vigorous reduction with nascent hydrogen. 

 This is also the case with the natural pigment (see p. 55). This similarity 



