474 Mr. C. A. Schunck. The Yellow Colouring Matters 



of stimulus being placed in round numbers 2 per cent, below the 

 arbitrary zero, that of physiological response in round numbers 20 per 

 cent, below the arbitrary point of origin (0') of the empirical curve. 



At the same time this 20 per cent, estimate is little better than a 

 guess. I am of opinion that the time for an absolute scale is not 

 yet, and that an empirical generalisation in close touch with observa- 

 tion and experiment, such as that on which my own curve is based, is 

 more likely to be helpful as a guide to further investigation than a 

 wider law involving assumptions the validity of which is doubtful. 



The Yellow Colouring Matters accompanying Chlorophyll and 

 their Spectroscopic Relations. Part II." By C. A. Schuxck. 

 Communicated by Dr. E. Schunck, F.RS. Beceived June o, 

 — Bead June 20, 1901. 



[Plates 5, 6.] 



In the former investigation* the yellow colouring matters, generally 

 known as the xanthophyll group, which accompany chlorophyll in the 

 healthy green leaves, and which are extracted along with it by means 

 of alcohol, were separated from the chlorophyll by treating the 

 alcoholic extracts with an excess of animal charcoal in the cold, by 

 which means the chlorophyll is absorbed by the charcoal, leaving the 

 yellow colouring matters in the alcohol. On investigating this crude 

 yellow solution it became evident that more than one colouring matter 

 was present, and I now give the results of the experiments I have 

 made in the endeavour to further isolate the constituents of this group 

 by means of carbon bisulphide, which method was adopted by Sorbyt 

 in his investigation of the differ ent colouring matters present in plants. 

 The crude alcoholic extracts of the accompanying yellow colouring 

 matters, which I will for the future term the xanthophylls, can be 

 obtained either by the above method or by boiling the chlorophyll 

 extracts for three or four hours with caustic potash or soda (10 grammes 

 to 1 litre of solution), allowing to stand, and shaking up with ether, 

 which takes up the xanthophylls unaltered, whereas the chlorophyll is 

 changed to an alkali compound of alka-chlorophyll, which is insoluble 

 in ether, but soluble in water ; the ethereal solution is then evaporated, 

 and the residue dissolved in alcohol. From either method of prepara- 

 tion the same results are obtained. 



These crude yellow alcoholic solutions of the xanthophylls show, as 

 a general rule, four distinctive absorption bands in the violet and ultra- 

 violet situated between the lines F and L (Plate 5, C, 2), any indication of 



* < Roy. Soc. Proc.,' vol. 65, p. 177. 

 f 'Roy. Soc. Proc.,' vol. 21, p. 456. 



