250 PIGMENTS 



light is of importance ; the pseudobase is due to the photo- 

 chemical reduction of the oxidation product of the original 

 pigment. In the dark, on the other hand, anthocyanidin is 

 oxidized, a process accelerated by heat. 



CONNECTION BETWEEN ANTHOCYANINS AND 

 ANTHOXANTHINS. 



A comparison of the formula of cyanidin chloride on page 

 248 with that of quercetin on page 243 reveals a close relation- 

 ship between these two substances, and consequently between 

 the flavones or anthoxanthins and the anthocyanins. Theo- 

 retically it should be possible to pass from anthoxanthins to 

 anthocyanins by reduction, or conversely from anthocyanins 

 to anthoxanthins by oxidation. In the plant no doubt this 

 is effected readily enough by enzymes, but in the laboratory it 

 is more difficult, and so far the only transformation effected 

 has been the reduction of quercetin to cyanidin.* These facts 

 provide a confirmation of the views put forward by Wheldale 

 and others previous to this definite experimental evidence. 

 Further evidence for the close relationship between the two 

 classes of compound is provided by the fact that cyanidin is 

 isomeric with luteolin and fisetin while delphinidin is isomeric 

 with quercetin and morin. 



EXTRACTION OF ANTHOCYANINS. 



The method of extracting anthocyanins varies with the 

 material employed, f The method recommended in the case 

 of grape skins is as follows : Extract the skins in the cold 

 with glacial acetic acid and precipitate the dark red filtrate 

 with ether ; by heating the deposit so obtained with a solution 

 of picric acid a crystalline picrate is formed which separates 

 out on cooling. 



* Willstatter and Mallison : " Sitzungsber. K. Akad. Wiss., Berlin," 1914, 

 769. 



fCf. Willstatter and Mieg : "Annalen," 1915, 408, 61 also Willstatter 

 and Bolton: id., 1915, 408, 42. 



