Schunck . — The Chemistry of Chlorophyll . 75 
reference to this question Professor Stokes 1 says : ‘ I find the 
chlorophyll of land-plants to be a mixture of four substances, 
two green and two yellow, all possessing highly distinctive 
optical properties. The green substances yield solutions 
exhibiting a strong red fluorescence, the yellow substances do 
not. The four substances are soluble in the same solvents, 
and three of them are extremely easily decomposed by acids 
or even acid salts ; but by proper treatment each may be 
obtained in a state of very approximate isolation, so far at 
least as coloured substances are concerned. . . . Green sea- 
weeds agree with land-plants except as to the relative pro- 
portion of the substances present ; but in olive-coloured sea- 
weeds the second green substance is replaced by a third 
green substance, and the first yellow substance by a third 
yellow substance, to the presence of which the dull colour of 
those plants is due.’ Mr. Sorby’s experiments confirm those 
of Professor Stokes. According to Mr. Sorby 2 — whose 
definition of chlorophyll is the same as that which I have 
given — the chlorophyll of land-plants is a mixture of two 
substances — ‘ blue chlorophyll 5 and ‘ yellow chlorophyll 
while sea-weeds contain two colouring matters belonging to 
the chlorophyll-group, blue chlorophyll and chlorofucin, the 
latter replacing the yellow chlorophyll of land-plants. In order 
to separate these substances one from the other Mr. Sorby 
agitates alcoholic extracts holding two or more of them in 
solution with other solvents, such as carbon disulphide and 
benzol. This method, though it may effect an approximate 
separation of several substances, having distinct absorption- 
spectra, can never, when no other means are employed, lead 
to the isolation of a chemically pure substance. No chemist, 
moreover, can rely absolutely on the absorption-spectrum of a 
compound as a means of identification ; other tests must be 
applied as well, and the behaviour of the substance in more 
than one direction must be examined before complete 
1 Proceedings of the Royal Society, XIII. 144. 
2 Ibid. XXI. 451. 
