156 



Dr. A. E. Everest and Mr. A. J. Hall. 



solution of (I) or (11), the colour is immediately discharged, due to the 

 pseudo-base formation. This clearly indicates that the acetates of these 

 metals have not the power of forming stable addition complexes with the 

 oxonium group. In the absence of any phenolic hydroxyls, no second 

 colour change takes place. In contrast to the above, when sodium acetate is 

 added to an alcoholic solution of cyanin chloride, the first colour change (red 

 to purple) due to colour base formation, is followed by a second colour 

 change (purple to blue) due to phenolic salt formation. The blue phenolic 

 salt thus produced decolorises when allowed to stand in dilute solution. 



The above observations have brought the authors to the conclusion that, 

 in the fine blue complex iron salts of anthocyans, the blue colour itself is 

 due to an interaction of the metal with a phenolic group (or groups), whilst 

 the stability of the colour in dilute solution is due to the attachment of the 

 metallic salt to the oxonium complex. In the case of the blue alkali, or 

 alkaline-earth salts of anthocyans, the blue colour is due to a phenolic 

 grouping, whilst the lack of stability in dilute solution is due. to the inability 

 of these salts to form stable complexes with the oxonium group. 



The authors consider that it is most probable that all the anthocyan 

 pigments form additive salts with ferric chloride, in which the iron salt is 

 attached to the oxonium group, but that characteristic colours are only 

 produced when suitably placed phenolic OH groups also react. 



Conchtsiom concerning the Constitution of Blue Anthocyan Pigments in 



Flowers. 



From the above it will be seen that the blue colours of anthocyan- 

 containing flowers may be due to the presence of either — 



(i) Anthocyan phenolates of alkali or alkaline-earth metals ; or 



(ii) Complex anthocyan-iron salts. (It is unlikely that copper or tin will 

 take part.) 



In deciding under which of these heads we must classify the actual blue 

 pigments occurring in flowers, observations as to whether or no dilute 

 solutions of their colouring matters become decolorised on standing should 

 serve as a reliable guide. 



In the case of at least three blue flowers (cornflower, iris, and violet), 

 there is definite recorded evidence* that solutions of the blue pigments 

 present in each of these flowers decolorise on standing. As there is also 

 record that the decolorisation in each case is due to pseudo-base formation, 

 and not to decomposition, the conclusion must be drawn that no complex 



* Fremy and Cloez, ' J. f. pr. Chem.,' vol. 62, p. 269 (1854) ; Willstiitter and Everest 

 ' Ann.,' vol. 401, p. 189 (1913). 



