iv] REACTIONS OF ANTHOCYANINS 47 



there are definite exceptions, such as those of the Amarantaceae, 

 Chenopodiaceae and Phytolaccaceae which are entirely insoluble in 

 this solvent. To these may be added the blue pigment of Centaurea 

 (Willstatter, 245), the glucosidal pigment of Althaea (Grafe, 197) and 

 probably others. In many flowers it is difficult to extract the petals 

 completely with alcohol. This is possibly due in some cases to the 

 presence of several pigments, certain of which are insoluble in alcohol ; 

 or there may also be retention of the pigment to some extent by the 

 coagulated cell-contents. A curious phenomenon is connected with 

 the alcohol solutions of most anthocyanins ; such solutions, though 

 at first coloured red or purple as the case may be, somewhat rapidly 

 lose their colour and eventually become quite colourless ; the same 

 effect is produced by immersing petals in strong alcohol. The colour 

 returns on evaporation of the alcohol or, in many cases if the solution 

 is sufficiently strong, on adding water. A few drops of acid, also, 

 restore the colour completely ; similarly a few drops of alkali produce 

 the green (or yellow) reaction characteristic of anthocyanin. This 

 phenomenon was first remarked upon by Nehemiah Grew (1): "Again 

 though no Blew Flowers, that I know of, will give a Blew Tincture to 

 Spirit of Wine : yet having been for some days infused in the; said 

 Spirit, and the Spirit still remaining in a manner Limpid, and void of 

 the least Ray of Blew, if you drop into it a little Spirit of Sulphur, 

 it is somewhat surprizing to see, that it immediately strikes it into a 

 full Red, as if it had been Blew before: and so, if you drop Spirit of 

 Sal Armoniac or other Alkaly upon it, it presently strikes it Green.... 

 It is likewise to be noted, That both Yellow and Red Flowers give a 

 stronger and fuller Tincture to Water, than to Spirit of Wine; as in 

 the Tinctures of Cowslip, Poppys, Clove- July-Flowers and Roses, made 

 both 'in Water and Spirit of Wine, and compared together, is easily 

 seen." Loss of colour in alcohol \vas also mentioned by Morot (122), 

 Filhol (125) and Fremy & Cloez (126). In 1884, Hansen (11) commented 

 on it, and suggested that anthocyanin, in absolute alcohol, forms a 

 colourless anhydride. Keeble & Armstrong (239) have recently offered 

 another, though unsatisfactory, explanation of this, decolorisation (see 

 p. 120). Willstatter (245) considers the loss of colour to be due to 

 the formation of a colourless isomer (see p. 72). 



As regards the appearance, colour, melting point, crystalline form, 

 etc., of solid anthocyanin, the accounts of the few workers who have 

 prepared the pigment are so varied that information is best obtained 

 by reference to individual cases quoted in the next chapter. 



