Anthocyanins and Anihocyanidins. 



155 



action of iron salts and those of the alkali and alkali-earth metals on antho- 

 cyan pigments. 



Confirmation and additional information concerning this difference has now 

 been obtained by adding a trace of the salts of various metals to decolorised 

 solutions of violanin or cyanin chlorine. In the case of iron, copper, and 

 tin, although no immediate colour change occurred, a full intense blue 

 gradually developed and was stable, whereas in the case of the salts of 

 sodium, calcium, and magnesium, even on long standing, no return of colour 

 at all occurred. (The presence of the anthocyan in the colourless form was 

 proved in each case after the experiment by the addition of acid, whereby 

 the oxonium salt was regenerated in full.) 



In connexion with the complex iron salts, Willstatter's observations con- 

 cerning the methylation of delphinidin upon the colour changes produced 

 when the oxonium salts of delphinidin, or its various methyl ethers, are 

 treated with iron chloride have made it abundantly clear that the final 

 change from purple (or violet) to blue is, in these instances, dependent upon 

 the reactivity of certain phenolic hydroxy groups. 



The present authors have found that when iron chloride is added to the 

 solutions of the compounds 



Cl Cl 

 i i 



(I) I I || \ /and (II) / 



\y\/^~^ \/%/^~^ OH 



c c 



I I 



H H 

 there is no colour change beyond slight intensification, although definite iron 

 compounds are formed, and the tendency to decolorise in dilute solution is 

 very greatly reduced. This absence of marked colour change on passing from 

 the oxonium chloride to the iron double salts has also been recorded in a 

 number of cases, including the following : — 



FeCl4 FeCl4 FeCL FeGi4 



' o o o o 



I I II ' I ' I •* 



CO c c 



41 I I 



H H H H 



On the other hand, the present authors have observed that, when a trace 

 of the acetates of an alkali or alkaline-earth metal is added to an alcoholic 

 * Cf. Decker and Fellenberg, ' Ann.,' vol. 364, p. 1 (1909). 



