RHEUM 157 



comparatively regular, radiate structure of red medullary rays travers- 

 ing a whitish parenchyma and extending into the cortical layer when 

 present; its odor is less aromatic, is less gritty, and its taste more 

 mucilaginous and astringent. Rumex hymenosepalus, Canaigre, has 

 been used, in powder, to adulterate powdered rhubarb. For detec- 

 tion, follow general directions for examination of powders, see 

 Part iv, Chap. I. 



Choice of Rhubarb. Select the moderately heavy and compact 

 pieces, which should break with a brittle fracture, presenting a lively, 

 mottled appearance of yellowish and reddish fibers intermingled 

 with white parenchyma; odor decidedly aromatic; taste bitter, 

 astringent, and gritty, not mucilaginous, tingeing the saliva orange- 

 yellow when chewed. Very light, rotten, or worm-eaten pieces should 

 be rejected. The yield of extractive using dilute alcohol should 

 not be less than 30 per cent. The yield of ash should not exceed 

 13 per cent. It should be stored in air-tight containers with a few 

 drops of chloroform to prevent the development of insects. 



Powder. Characteristic elements: See Part iv, Chap. I, B. 



CONSTITUENTS. Seemingly a mixture of different coloring principles of 

 a somewhat resinous quality, each having a peculiar solubility of its 

 own: Chrysophan, C 2 7H 30 Oi4 (and chrysophanic acid), emodin, 

 aporetin, phaeoretin, erythroretin, rheumic acid, and rheo-tannic 

 acid ; also starch, calcium oxalate, pectin, and arabic acid. Chryso- 

 phan is a yellow glucoside yielding, with acidulated water, sugar and 

 chrysophanic acid, CioHioC^, yellow crystals, one of the best solvents 

 for which is hot benzol. According to Hagar, by proper extraction 

 with chloroformic solvent, etc., rhubarb yields not less than 3 per 

 cent, of chrysophanic acid. Chrysophanic acid, or dioxy-methyl- 

 anthraquinone (CuHsCHstOH^CM is closely related to emodin, 

 which is a trioxy-methyl-anthraquinone (Ci4H 4 CH 3 (OH)3O2). 

 Cathartic acid represents the cathartic principles of rhubarb in a crude 

 but concentrated form. For its preparation, see Senna (240). 



EMODIN TEST, in Rhubarb. Boil o.ioo Gm. of powdered rhubarb with 

 10 mils of an aqueous solution of potassium hydroxide (i in 100), 

 allow it to cool, filter, acidulate the filtrate with hydrochloric acid 

 and shake it with 10 mils of ether; on standing, the ethereal layer 

 should be colored yellow. On shaking this ethereal solution with 5 

 mils of ammonia water, the latter should be colored cherry-red 

 (presence of emodin) and the ethereal layer should remain yellow 

 (presence of chrysophanic acid) U.S.P. 



Preparation of Phaoretin. Wash alcoholic extract with water; dissolve residue 

 in a little alcohol; add ether. This precipitates crude phaeoretin. 



