iv] REACTIONS OF ANTHOCYANINS 51 



die Losung nun auch die farblose Modifikation enthalt. Dies ist das 

 Verhalten eines wassrigen Bliitenauszugs, worin sich iiberdies noch 

 gelbe FarbstofTe befinden, deren Alkalisalze intensiv gelb sind.) The 

 blue colour given by alkalies with the pure anthocyanin pigment will, 

 Willstattei found, become green or yellow by decomposition on standing, 

 or with excess of alkali. Further consideration will be given below 

 (pp. 52-54) to these reactions. With anthocyanins from other plants 

 Willstatter notes various reactions with alkalies (see p. 56). Hence 

 we have at present the following suggestions. Pure anthocyanin from 

 Centaurea gives a blue colour with alkalies; the green colour given in 

 solutions and crude extracts is due to mixture with the yellow colour 

 produced by the colourless isomer or accompanying flavones, or both. 

 Pure anthocyanin from Antirrhinum gives a green colour with alkalies, 

 and this cannot be due to admixture with flavones, as the latter are 

 removed by purification ; nor can we suppose it due to admixture with 

 a colourless isomer, since this is not formed in a strongly acid solution 

 such as that from which the pigment separates out in preparation. 

 Thus, whether the green or blue reaction is given by pure anthocyanin, 

 or whether it is green in some cases, and blue in others, remains undeter- 

 mined until anthocyanins from many other species have been purified 

 and tested. In many cases the green reaction either rapidly or slowly 

 changes to yellow, and the original colour does not return on neutralisa- 

 tion, so that evidently some anthocyanins are completely destroyed by 

 alkalies. 



The same difficulty arises with regard to the precipitates with lead 

 acetate, for the accompanying flavones produce yellow or orange- 

 yellow precipitates with lead acetate, and hence the actual lead salt 

 of anthocyanin is not identifiable except from the pure pigment with 

 which the results are the same as with alkalies. The colour of the 

 lead precipitate varies very considerably in crude solutions. In extracts 

 from white flowers containing little anthocyanin, it is greenish-yellow ; 

 from flowers containing much anthocyanin, bright green or blue-green, 

 whereas from red varieties (Wheldale, 211), it is practically red with a 

 greenish tinge. The latter must be distinguished from the red preci- 

 pitates given by the special pigments of the Amarantaceae and Phyto- 

 laccaceae which are mentioned below. 



On the basis of qualitative reactions, Weigert (179), in 1895, 

 attempted a classification of anthocyanins into two groups: 



The 'Weinroth' group, of which the pigments give blue-grey or 

 blue-green precipitates with basic lead acetate; give the Erdmanu 



42 



