RHEUM (Rhabarbs Afedieal Properties of As the particular species which yields the officinal rhubarb, and even the precise place of its growth, are not known, the varieties met with in commerce are here described, without attempting to ensign them to any ascertained species. There are six well-marked varieties, namely, Russian or Turkey, Dutch-trimmed, Chinese, Himalayan, English, and French. Of the first sort the greater portion at present comes from St. Peters burg, and is denominated Muacovite, Bokharian, or Siberian rhubarb, while a " part has always formed one of the imports from China into Bokhara, whence paving to Smyrna, it is known In Europe as Turkey rhubarb" (Hoyle, ' Flues of the Himalaya), which name it commonly bears in the shops. This kind varies much in size and appearance, the pieces being cylindrical, spherical, flat, or irregular, from two to three inches lung, one to three broad, and one to three thick. "The smaller pieces are picked out, being preferred, while the larger pieces and the dint are employed for powdering?' Holes are remarked in many of the pieces, of which one occasionally extends entirely through, the others only partially ; the former having been made in order to suspend the piece in drying, the others in examining the quality. This kind, and probably the other sorts, is frequently worm-eaten, owing to the ravages of a small beetle, Simodetsdrum pontlam. (Kirby and Spence,' Ento mology,' I., p. 252.) Externally the pieces are covered with a bright yellow:coloured powder, which either results from the friction of the pieta during their passage to this country, or from the process of rouncing (that is, shaking in a bag with powdered rhubarb), previous to its exportation. The odour Is strong, both of the root and fresh powder, peculiar, somewhat but not pleasantly aromatic. When chewed, it feels gritty, owing to the presence of numerous raphidee (or crystals of oxalate of lime, which are present to the amount of between 30 and 40 per cent); it communicates a bright yellow colour to the saliva, and has a bitter, slightly astringent taste, which to some persons is not unplea sant, as they are in the habit of chewing rhubarb to obtain he tonic effects on the stomach; but this practice is objectionable from the yellow colour it imparts to the teeth and gums.
When the dug which covers the surface is removed, It exhibits a more or less reddish-yellow hue with white lines interspersed, which firm beautiful reticulations, best seen on a vertical section, while a transverse section exhibits small star-like spot. and depressions of a
darker colour. The transverse fracture is uneven, the longitudinal still more so. " The powder of genuine Russian rhubarb Is of a bright yellow colour, verging to red, but as met with in the shops it le almost invariably mixed with the powder of English rhubarb," which gives it a much lighter colour.
The analysis of this sort by Hornernann shows it to consist: of— Rhubirberin In also called chrysophanie acid, or yellow crystalline granulated matter of rhubarb, According tO Schlifeaberger and Dipping, rhubarb contains three resins : Aporetine, Phaeoretine, and Erythore tine. It is supposed to contain some volatile oil, to which the peculiar odour is due.
The chief chemical distinction between this and English rhubarb is the presence in the latter of a principle termed rhaposticin, and 14 per cent. of starch, with a smaller portion of rhubarberin, of yellow colour ing matter and extractive : iodine furnishes a ready distinguishing test, for a " decoction of Russian, Dutch-trimmed, or Chinese rhubarb becomes, with a solution of Iodine, greenish-blue (iodide of starch); after a few minutes the colour disappears, and no iodine can be detected in the liquor by starch, unless nitric acid be previously added ; a decoction of English rhubarb is rendered by a solution of iodine intensely blue (iodide of starch), the colour not completely dis appearing by standing." (Pereira.) This difference is clearly dependent on the much greater portion of starch existing in English rhubarb. Inferior rhubarb, or roots cut to resemble rhubarb, and sprinkled over with powdered turmeric, or dyed with it, may be detected by means of bomcic acid, or any berates rendered acid, since the colour of genuine rhubarb, or paper dyed with it, Is not affected by these re-agents, whereas turmeric-paper is reddened by them. Yellow ochre, with which black and worthless pieces are covered, or which is used to fill the holes in worm-eaten pieces, may be detected by heat, as it burns with a brownish red appearance, and exhibits the characters of a ferruginous earth.