TUTIN AND CLEWER: THE CONSTITUENTS OF RHUBARB. 947 a product called " rhabarberin." This wm shown by Schlossberger and Dijpping (Annulen, 1844, 50, 214) t o be identical with chrysu phanic acid, which had, in the meantime, been described by Rochleder and Heldt, but it would appear probable that it was a mixture of this compound and emodin monomethyl ether. De la Rue and Miiller (Journ. Chem. SOC., 1857, 10, 298) examined a deposit from " Extracturn Rhei," from which they obtained " chrysophane " and a new compound, designated its emodin. Heme (Pharm. J., 1895, [iv], I, 352; and ,4nnaZen, 1899, 309, 32) recorded the occurrence in rhubarb of rhein and "rhabarberon" (an isomeride of emodin), but was unable to isolate pure chrysophanic acid, this being always associated with a methylated constituent, which wm assumed t o be a methyl ether of chrysophanic acid. The next communication of importance on Chinese rhubarb was by Tschirch and Heuberger (Arch. Pharm., 1902, 204, 596), who failed to obtain the " rhabarberon " of Hesse, but isolated gallic acid, a substance giving the reactions of a cholesterol, impure chrysophanic acid, emodin, rhein, and two amorphous, glucoeidic products, namely, rheotannoglucoside and rheomthraglucolside. The former of these products, on hydrolysis, gave a laevorotatory sugar and small amounts of gallic and cinnamic acids, together with amorphous products, whilst the latter " glucmide " yielded a dextrorotatory sugar, small amounts of the acids mentioned, a mixture of anthraquinone derivatives, and amorphous material. Eyken (Phwm. V'eekblad, 1904, 41, 177) isolated impure chrysophanic acid, emodin, " isoemodin," and rhein, together with (' anthraglucwides," and Tschirch and Eyken (Schweiz. Woch. Pharm., 1904, Nos. 40 and 41) stated that " isoemodin " is probably identical with Hesse's " rhabarberon." Gilson (Compt. rend., 1903, 136, 385) claimed to have isolated two crystalline glucmides, '(glucogalline " and " t 6 t r a h e. " The former of these was stated t o yield dextrose and gallic acid, whilst the latter gave the same sugar, gallic and cinnamic acids, and " rh6usmine." Quite recently, Oesterle and Johann (Arch. Pharm., 1910, 248, 476) showed in an indirect way that the methylated substance with which the chrysophanic acid from rhubarb is invariably wociated was emodin monomethyl ether, identical with that wociated with chrysophanic acid in Rurnex Ecklonianus, Meisaner (Tutin and Clewer, Trans., 1910, 97, 1). I n addition to the compounds mentioned in the foregoing review of the literature, most of the abovementioned investigators also describe, under various names, a number of amorphous products, which were obviously of indefinite composition. Mention is several times made, however, of the presence in rhubarb of ((glucose " and of a neutral fat.
