250 PIGMENTS 



salts of the type illustrated by the following structural formulae 

 of a few anthocyanidins : 



Cl Cl 



CH O ,, CH O 



nH 



HOC C C{ \OH C < >OH 



CH C COH CH C COH 



V X\ X \ 



COH CH COH CH 



Cyanidin chloride Delphinidin chloride 



Cl 



CH O 



OH 



1 1 



CH C 



COCH-, 



COH "CH 



CEnidin chloride 



It will be seen from these formulas that the oxygen is 

 tetravalent and that the molecules contain phenolic hydroxyl 

 groups capable of forming salts with alkalies. Moreover, by 

 replacing the chlorine by the hydroxyl group on addition of 

 caustic alkalies the possibility of eliminating water from the 

 molecule arises as follows : 



OH '> 



CH O OH 



i / \S \ 



HiOC C C ^ \OH - OC C C / >OH 



CH 6 



O// \// \ / V 



OH - OC C C < > 



1 t ' 



CH C COH CH C COH 



COH CH COH CH 



I. II. 



These considerations explain the colour variations produced 

 by the same cyanidin occurring in the same or in different 

 flowers, it having been found, for example, that the same 

 cyanidin was responsible for the colour of the cornflower and 

 of the rose.* 



Thus when combined, as in the case of cyanidin chloride, 

 with mineral acid or in the plant with organic acids, the com- 



* Willstatter and Nolan ; " Annalen," 1915, 408, i. 



