76 THE ISOLATION AND [CH. 



If there is excess of acid in the cell-sap, a red oxonium salt with an 

 organic acid is formed. The crystalline salts with hydrochloric acid 

 are regarded as artificial compounds of this kind : 



oci 

 ^\ > 



HO-f 



o = 



N^ 



OH 



In the presence of excess of water, both the red and the blue forms 

 will pass to the colourless isomer, but in the case of the blue the tauto- 

 meric change can be prevented by adding a neutral salt which forms an 

 additive compound : 



ONO 3 



S\ y. 

 NaO, 



The chief argument against the above hypothesis is that flavones 

 of the above constitution are at present unknown. The analyses so 

 far made only point to the existence of a definite hydrochloric acid 

 compound, and indicate nothing as regards the constitution, the above 

 suggestions being purely hypothetical. Variations in this hypothesis, 

 based upon later work, will be considered in the following paragraphs. 



Willstatter, in conjunction with Bolton, Nolan, Mallison, Martin, Mieg 

 and Zollinger (256, 257), 1914. The flower -pigments of Centaurea, 

 Delphinium, Malva, Pelargonium and Kosa gallica; the fruit- 

 pigments of Vaccinium Myrtillus, Cranberry and Vitis vinifera. 



Flower-pigment of Centaurea. 



The statement made previously that the cyanin of Centaurea is 

 decomposed on hydrolysis into one molecule of cyanidin and two 

 molecules of glucose is confirmed. But the formula C 16 H 13 7 C1, originally 

 given for cyanidin chloride, is found to be incorrect owing to the fact 

 that the product was insufficiently dried. It is found that reliable 

 numbers can only be obtained after long drying in a high vacuum at 



