8 INTRODUCTOKY [OH. 



and they have helped to draw the attention of chemists to the subject; 

 for much of the earlier chemical work on anthocyanin, notably of a 

 group of French chemists (1800-1825), Braconnot (110), Payen & 

 Chevallier (113, 114, 115) and Roux (116), centred round these reactions, 

 especially in some cases round their role as indicators. But the idea 

 of anthocyanin as an indicator was fully conceived long before 1807 

 by Robert Boyle (107). '' When," he says, " we have a mind to examine, 

 whether or no the Salt predominant in a Liquor or other Body, wherein 

 'tis Loose and Abundant, belong to the Tribe of Acid Salts or not... 

 if such a Body turn the Syrrup of a Red or Reddish Purple Colour, 

 it does for the most part argue the Body (especially if it be a distill'd 

 Liquor) to abound with Acid Salt. But if the Syrrup be made Green, 

 that argues the Predominant Salt to be of a Nature repugnant to that 

 of the Tribe of Acids." After the reactions of anthocyanin with acids 

 and alkalies, other reactions were noticed with iron salts and various 

 reagents, many of which modify the colour as it is modified in nature. 

 These reactions gave rise to views among some chemists, Fremy & Cloez 

 (126) and Wigand (136), that natural blue, purple and red pigments 

 are modifications of the same substance, brought about by the presence 

 of other compounds in the cell-sap. But as analyses and investigations 

 proceeded, the view of a certain multiplicity of pigments gained the 

 ascendency. 



One of the first actual analyses of anthocyanin was carried out 

 in 1849 by Morot (122) who isolated the blue pigment of the Corn- 

 flower, and found it to contain carbon, hydrogen and oxygen, with 

 nitrogen as impurity. Ten years later Glenard (129, 130) isolated the 

 pigment of wine, found it also to contain carbon, hydrogen and oxygen, 

 and gave it a percentage formula. 



An early suggestion as to the chemical nature of anthocyanin and 

 its mode of formation was that of Wigand (136) in 1862. This author 

 suggested that anthocyanin arises by the oxidation of a colourless 

 tannin-like chromogen, a substance widely distributed in plants and 

 giving a green reaction with iron salts and a yellow reaction with alkalies. 

 The same substance obviously had been noted at an earlier date by 

 Filhol (125, 132) who observed it to be widely distributed, and main- 

 tained that the green coloration of anthocyanin with alkalies was due 

 to a mixture of a blue anthocyanin reaction plus the yellow reaction 

 of these accompanying substances; a view also held by Wiesner (135). 

 The idea of the formation of anthocyanin from a tannin-like chromogen 

 by oxidation was, from this time onward, generally accepted by botanists 



