1903.] Xantlwphyll Group of Ydlow Colouring Matters. 165 



" The Xanthophyll Group of Yellow Colouring Matters." By 

 C. A. SCHUNCK. Communicated by HORACE T. BROWN, F.R.S. 

 Received April 17, Read May 14, 1903. 



[PLATES 6 AND 7.] 

 Tlie Xanthophyll Group of Yellow Colouring Matters. 



The group under consideration comprises those colouring matters 

 occurring in flowers, leaves, fruits, etc., which are insoluble in water 

 but soluble in alcohol, ether, carbon-bisulphide and other organic 

 solvents, to which collectively the name of xanthophyll has been 

 applied. It is to these colouring matters that the characteristic yellow 

 colour of flowers, autumnal leaves and fruits in the majority of cases 

 is due. There are, however, present, varying in amount but generally 

 in considerably less relative quantity, other yellow colouring matters 

 which are soluble in water and alcohol, sparingly soluble in ether but 

 insoluble in carbon-bisulphide ; they, however, absorb the violet and 

 ultra-violet rays without giving any absorption bands, whereas the 

 members of the xanthophyll group transmit the ultra-violet rays and 

 give definite absorption bands in the less refrangible region of the 

 spectrum, whereby they may be distinguished from one another, and 

 which is their chief characteristic feature. The present memoir is 

 mainly a spectroscopic investigation of this group, whereby I have 

 endeavoured to distinguish the different yellow colouring matters 

 present in various flowers, leaves and fruits, and to show their spectro- 

 scopic relationship one to another, and which may, perhaps, be an aid 

 to elucidate their chemical constitution, of which so little, if anything, 

 is known so far. 



The spectroscopic observations, as in a former investigation,* were 

 made by means of photography, an Iceland-spar prism, and quartz 

 lenses being used, the source of light being a Welsbach incandescent 

 gas mantle. 



Flowers. 



In all, twenty common yellow flowers were examined. The method 

 of procedure was to obtain an alcoholic extract of the pigment con- 

 tained in the petals, boiling for a short time being generally necessary 

 to extract the whole. On cooling the hot filtered extract a fatty 

 waxy deposit forms, in most cases, which carries down a certain 

 quantity of the pigment with which it is deeply impregnated. The 

 extract, filtered from this deposit, is now agitated with carbon- 

 bisulphide which takes up the greater portion of the xanthophyll, 

 leaving in the alcohol those colouring matters which obscure the violet 



* ' Eoy. Soc. Proc.,' vol. 63, p. 391. 



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