A New Green Vegetable Colouring Matter1

Abstract

THE seeds of the Trichosanthes palmata are inclosed in a rounded scarlet fruit and embedded in a green bitter pulp. The bitter principle has been shown by Mr. D. Hooper to be a glucoside differing from colocynthin, and he has named it trichosanthin. The green colouring matter, when freed from the trichosanthin and fatty matter, yields a solution closely resembling a solution of cholorophyll. It is green in thin and red in thick layers, and has a red fluorescence. The spectrum, however, is very different. Taking the thickness and strength yielding the most characteristic spectrum, it may be described thus:—The first band begins (penumbra) at W.L. 654 and ends about W.L. 615; from this there is a small amount of absorption till the second band begins at W.L. 593˙4, and continues to W.L. 566˙8, with the maximum absorption near the less refrangible end; from this there is no perceptible absorption till the third band, which extends from W.L. 548˙4 to 534˙8; there is a fourth band, very faint, with its centre about W.L. 510˙6, and a fifth extending from about W.L. 485 to W.L. 473˙4. Comparing this with the chlorophyll spectrum, it will be seen that the first band has its centre almost midway between the two chief chlorophyll bands, but that bands III., IV., and V. are probably coincident with chlorophyll bands. When the trichosanthes colouring matter is treated with ammonia sulphide the spectrum is completely changed. The first and most prominent band slowly decreases in strength and finally disappears, two new bands appear in the space between bands I. and II. of the original spectrum; band II. is apparently displaced towards the violet end and intensified; and band IV. is greatly widened. Chlorophyll under the same treatment behaves in a totally different manner, and the two spectra become almost complementary. When, however, the trichosanthes colouring matter and chlorophyll are both treated with hydrochloric acid the result is very different, for the two spectra have now three bands in common. The first band in the trichosanthes spectrum has disappeared, and the spectrum is practically reduced to one of three bands corresponding in position with bands II., III., and IV. of the altered chlorophyll spectrum. Band I. of the chlorophyll spectrum has no representative in the trichosanthes spectrum. The conclusions to be derived from a study of these spectra seem to be that we have in the trichosanthes colouring matter a substance in which the “blue chlorophyll” of Sorby or the “green chlorophyll” of Stokes is replaced by some other substance easily decomposed by reducing agents and acids. Farther, if we assume with Schunck that the product obtained by acting on chlorophyll with hydrochloric acid is the same as Frémy's phyllocyanin, this, too, must be a mixture, one constituent of which is obtained by acting on the trichosanthes colouring matter with acid, while the other is, apparently, the unaltered substance yielding band I. in the chlorophyll spectrum.