52 THE PROPERTIES AND [CH. 



reaction (see below) ; are precipitated and give a bright red colour 

 with concentrated hydrochloric acid; and turn green on addition of 

 alkalies. Ex. Pigments from Vitis, Ampelopsis quinquefolia, Rhus 

 typhina, Cornus sanguined, etc. 



The ' Riibenroth' group, of which the pigments give a red precipitate 

 with basic lead acetate, do not give the Erdmann reaction ; turn dark 

 violet with concentrated hydrochloric acid; violet with ammonia, but 

 with other bases yellow. Ex. Pigments from Beta, Iresine Lindeni, 

 Achyranthes Verscliaffeltii, Amaranthus, Atriplex hortensis, Pliytolacca 

 decandra. According to Gertz (19), the following should be added to 

 Weigert's ' Riibenroth ' group : several Chenopodiaceae (Blitum virgatum, 

 Atriplex litoralis, Corispermum canescens), Amarantaceae (except 

 Mogiphanes brasiliensis), Nyctaginaceae (Oxybaphus nyctagineus), 

 Phytolaccaceae (Phytolacca decandra, leaves), Aizoaceae (Tetragonia 

 crystallina, Mesembryanthemum nodiflorum), Portulacaceae (Portulaca 

 grandiflora) and Basellaceae (Basella rubra). The remaining families 

 of the group Centrospermae, i.e. Polygonaceae and Caryophyllaceae, 

 seem to be distinguished by anthocyanin of the 'Weinroth' group 

 as also the greater number of the Chenopodiaceae. 



The reaction of Erdmann (618) was originally employed in order 

 to detect true wine pigment and may be described as follows : The 

 pigment solution (wine) is diluted with four times its volume of water, 

 eight drops of concentrated hydrochloric acid are added, and the 

 mixture shaken up with 16 c.c. of amyl alcohol. The amyl alcohol 

 separates out with a fine violet-red colour, the underlying acid solution 

 being yellow or cherry-red. If the amyl alcohol is separated off, and 

 an equal volume of water added, together with two drops of concentrated 

 ammonia, the amyl alcohol decolorises and the underlying solution 

 becomes bright green. If the original acid solution below the amyl 

 alcohol is placed in a porcelain dish and carefully neutralised with 

 dilute ammonia, at neutralisation point an indigo-blue colour is produced 

 which afterwards becomes green. 



The reactions of anthocyanins with acids and alkalies, the Erdmann 

 reaction, etc., have received a new interpretation through the recent 

 researches of Willstatter (245). These views are based upon work 

 devoted in particular to the anthocyanin of Centaurea but also to 

 anthocyanins in general. As far as can be gathered from a preliminary 

 publication, the following represents, in the main, the views of Will- 

 statter (see also Chapter v). 



1. Red, purple and blue pigments occur in the plant entirely as 



