The Colouring Matter of Red Roses. 



197 



exposure to air (a possible explanation of this oxidation is given later). 

 The alkaline solution was acidified, extracted with ether, and the ether 

 extract evaporated to dryness. The residue, on being dissolved in absolute 

 alcohol, to which a small quantity of hydrochloric acid had been added, 

 yielded, on the addition of a small piece .of magnesium ribbon, a fine red 

 coloration, similar to an alcoholic solution of cyanidin chloride. It is 

 possible that the yellow pigment present in the petals is a quercetin 

 glucoside, but it was not possible to make further tests, as the quantity of 

 pigment available was very small. In order to add additional weight to the 

 assumption that a glucoside of quercetin is present, the above-mentioned 

 tests were carried out with a known glucoside of quercetin, viz., " myrti- 

 colorin." A small quantity was boiled with acid and hydrolysed, and the 

 resulting sugar-free pigment " quercetin" treated, in alcoholic solution, with 

 hydrochloric acid and magnesium ribbon in the same manner as with the 

 sugar-free pigment from the rose, exactly similar results were obtained. 

 Tests made with both pigments in a glucoside form also agreed. It is 

 hoped that further work on this rose will result in sufficient of the yellow 

 flavonol sap-pigment being isolated to confirm its identity, by means of 

 derivatives. For the sample of " myrticolorin " used in the above tests, 

 I am indebted to Mr. H. G. Smith, of the Technological Museum, who very 

 kindly supplied me with it ; it is a rhammo-glucoside of quercetin, and was 

 isolated from eucalyptus leaves. 



-Possible Cause of the Rapid Darkening of the Alkaline Solution of the YellovJ 

 Sap-pigment from the Rose. 



Although it is the property of the flavonols to undergo oxidation on 

 exposure to air in alkaline solution, the very rapid oxygen absorption of the 

 solution previously mentioned would appear to be due to some other cause. 

 It was thought that this might possibly be due to tannin matter. An 

 examination of the petals of the rose revealed the fact that both pyrogallol and 

 catechol tannins were present, the former (probably gallo-tannin), being 

 present in the greater quantity. The alcoholic extract of the petals would 

 contain the tannin matter in solution, and the boiling with acid, to hydrolyse 

 the glucosides, as previously mentioned, would also hydrolyse the gallo-tannin, 

 with the production of gallic acid ; the subsequent extraction of the acid 

 solution with ether, to obtain the hydrolysed glucosides, would also extract 

 the gallic acid, and this would accompany them into the alkaline solution ; 

 the presence of a small quantity of gallic acid would be quite sufficient to 

 cause a rapid darkening of the solution, on exposure to air. 



