328 



Dr. A. E. Everest. 



The red acid solutions of the glucosides obtained by the author, when made 

 neutral by shaking with excess of calcium carbonate, pass to violet or red- 

 violet, and rapidly become decolorised. On nitration, and addition of a few 

 drops of acid (HC1 used) to the decolorised solution — either soon after 

 decolorisation, or even after standing over night in that condition — they 

 quantitatively regain their red colour, thus behaving as true anthocyanins. 



The acid solution of the non-glucoside examined, on shaking with excess of 

 calcium carbonate became violet. After filtration, the solution on warming, 

 loses the violet colour, but on addition of a few drops of acid and warming 

 the red colour reappears, but not quantitatively. A solution of cyanidin 

 yielded exactly parallel results. As already mentioned, unless the pigment 

 be pure, or nearly so, the complete recovery of colour is difficult to obtain in 

 the case of the non-glucosides. 



Besides the examination of the observations of Willstatter, the comparison 

 of the absorption spectra of the pigments obtained by the author with those 

 of cyanin and cyanidin — in acid solution — has been carried out. 



The pigments all show one characteristic band, resembling in every respect 

 that shown by cyanin and cyanidin chlorides, and agreeing with that 

 described by AVillstatter for the characteristic band of the anthocyans in acid 

 solution, as a broad band which becomes flatter towards the violet, and 

 extends over a great portion of the green and blue regions. 



The author has therefore been able to show that by reduction of flavonol 

 glucosides — the yellow pigments present in many flowers — a series of red 

 pigments may be obtained whose properties agree with those of the- 

 anthocyanins. A brief summary of the points of agreement may be given. 



(1) The glucosides remain quantitatively — the monoglucoside from 

 quercitrin is apparently an exception — in dilute (about 2N) sulphuric acid 

 solution when shaken with amyl alcohol, whereas the hydrolysed products- 

 pass quantitatively into the alcoholic layer, yielding a red solution which 

 shaken with sodium acetate solution becomes violet or red- violet, the pigment 

 remaining in the alcohol, and their solution on shaking with sodium 

 carbonate solution turns blue or blue-green and at the same time the pigment 

 descends quantitatively to the aqueous layer. All these changes are exactly 

 similar to those observed with anthocyanins. 



(2) In acid solution — aqueous or alcoholic — they are stable, and their 

 absorption spectra .are similar to those of the anthocyanins. 



(3) By oxidation — e.g. hydrogen peroxide — their acid solutions may be 

 decolorised. By reduction — e.g. Zn and HC1 — the red colour of their acid ■ 

 solutions is discharged, but reappears on careful addition of hydrogen 

 peroxide. Anthocyanins react in an exactly similar manner. 



