After the reading of the note on chlorophyll at the meeting of the society on December 13th, I was reminded by Professor Stokes that e and others had succeeded in separating the complex to which the erm chlorophyll had previously been applied into two substances, or ather groups of substances, one characterised by its green colour and ed fluorescence, the other showing a more distinctly yellow colour without fluorescence, and he suggested to me that it would be advisable to ascertain whether the property of yielding glucose by decomposition with acids might not belong to one of these substances or groups of substances only. Professor Stokes at the same time kindly communicated to me the details of the process whereby he succeeded n effecting the separation referred to, a process depending on the action of carbon disulphide in' removing some of the bodies contained n an alcoholic solution of crude chlorophyll in preference to others. The process employed for the same purpose by Mr. Sorby is essentially the same. Before applying disulphide of carbon to an alcoholic extract of green leaves according to the process of Professor Stokes, it was necessary first to remove the ready-formed glucose, tannin, and other matters soluble in water, which almost always exist in such extracts, and which would by their presence have rendered the result of the experiment quite uncertain. This was done in the way I have already described. An ethereal solution of chlorophyll prepared by my method was evaporated, and the residue having been dissolved in alcohol, the solution was mixed with a quantity of carbon disulphide larger than the alcohol would dissolve, and the mixture well shaken. The carbon disulphide acquired a dark green colour, while the supernatant alcoholic liquid, containing principally the xanthophyll of Professor Stokes and Mr. Sorby, was yellow with a tinge of green. The two liquids having been separated, the lower dark green one was washed several times with alcohol to remove any of the xanthophyll that might still be present, and having then been mixed with a large quantity of alcohol, a current of air was passed through it to remove the excess of carbon disulphide as directed by Professor Stokes. In this way I obtained two liquids, one intensely green, the other deep yellow with only a tinge of green. The two liquids were found to contain substances essentially different so far as regards their products of decomposition with acids. The yellow liquid having been mixed with dilute sulphuric acid was evaporated in the waterbath, water being added during evaporation, until the liquid had lost nearly all its colour. A quantity of yellow fatty matter separated during evaporation, and this having been filtered off the liquid was found to contain an abundance of glucose. The yellow fatty matter insoluble in water, dissolved easily in alcohol, but the yellow solutio showed none of the characteristic absorption bands of “acid chloro phyll.” The dark green liquid, treated in exactly the same way yielded a dark green product insoluble in water. The filtrate Iron this gave a slight reaction with Fehling’s solution, but so trifling comparatively that I am inclined to attribute it to the presence o some substance not completely removed from the disulphide of carboi solution by washing with alcohol. The dark green product of tin action of acid insoluble in water was soluble, though with difficultyin boiling alcohol, the solution being dull green and showing the absorption bands due to “acid chlorophyll.” If, therefore, chloro phyll be defined as the constituent of the green parts of plants, which gives a spectrum showing the well-known bands at the red end, and yields by decomposition with acids the product or products going by the name of “acid chlorophyll,” of which Fremy’s phyllocyanin is the most important and most characteristic, then chlorophyll is not a glucoside. The glucoside which accompanies it and resembles it as regards solubility in various menstrua may have to be sought among the group of bodies to which the generic name of xanthophyll has been applied.
Negative after-images and successive contrast with pure spectral colours
