122 REACTIONS INVOLVED IN [cm. 



As a converse to the above experiments, Combes oxidised antho- 

 cyanin and obtained a flavone. The method employed consisted in 

 taking Ampelopsis anthocyanin and purifying it by crystallisation, 

 first from, alcohol, and secondly from water. The pure product is 

 dissolved in alcohol, and an equal volume of hydrogen peroxide is 

 added. The purple colour of the anthocyanin gradually disappears, 

 and a yellow solution is left which deposits crystals of a flavone identical 

 in properties and melting point with the natural product derived from 

 the plant. Hence he concludes that the anthocyanin has been oxidised 

 with the formation of flavone. 



A criticism of this last experiment and the deduction therefrom may 

 be made at this point. It is not mentioned in Combes's paper whether 

 the crystalline anthocyanin had been tested in order to ascertain if 

 it were free from flavone. It is the experience of the author (Wheldale, 

 254) that when a mixture of flavone and anthocyanin obtained from 

 Antirrhinum is allowed to crystallise from alcohol, both pigments 

 crystallise out together in plates which, in spite of the fact that they 

 may consist largely of flavone, are deep red in colour, and very careful 

 purification is necessary before anthocyanin can be obtained entirely 

 free from flavone. When pure anthocyanin from Antirrhinum is treated 

 with hydrogen peroxide, the pigment is destroyed but no flavone is 

 found. Hence it is possible that the flavone derived from Combes's 

 anthocyanin may have been present as impurity. If, however, this 

 were not the case, it still may be possible that the action of the hydrogen 

 peroxide is not necessarily one of oxidation. 



Before making any criticism upon the question of the action of 

 sodium amalgam, the work of Keeble, Armstrong & Jones, Tswett 

 and Everest on similar lines, must be considered. 



Keeble, Armstrong & Jones (240) have obtained red pigments, 

 giving, in some cases, the anthocyanin reaction by treating alcoholic 

 extracts of a number of plants with zinc dust and hydrochloric acid. 

 Under these conditions, extracts from the following plants gave red 

 pigments: pale yellow 'primrose' variety of Cheiranthus, yellow 

 Daffodil, yellow Crocus, cream Polyanthus, and the dominant white 

 variety, but not recessive white variety, of flowers of the Chinese 

 Primrose (Primula sinensis). The red pigment which is first formed 

 will, after continued treatment with nascent hydrogen, become colourless, 

 the colour returning on exposure to air. This phenomenon led the 

 authors to conclude that a preliminary reduction, followed by oxidation, 

 is the sequence of events. 



