Scientific and applied pharmacognosy intended for the use of students in pharmacy, as a hand book for pharmacists, and as a reference book for food and drug analysts and pharmacologists . -compound; tracheae few, reticulate, occasion-ally spiral. The powder is colored reddish with alkalies. A com-mon adulterant is wheat middlings. The exhausted drug is fre-quently added to the powder and may be detected by the somewhataltered starch grains and the decrease in the amount of the aqueousor dilute alcoholic extract, which in genuine rhubarb is about 35per cent. Constituents.—The principal constitu
Scientific and applied pharmacognosy intended for the use of students in pharmacy, as a hand book for pharmacists, and as a reference book for food and drug analysts and pharmacologists . -compound; tracheae few, reticulate, occasion-ally spiral. The powder is colored reddish with alkalies. A com-mon adulterant is wheat middlings. The exhausted drug is fre-quently added to the powder and may be detected by the somewhataltered starch grains and the decrease in the amount of the aqueousor dilute alcoholic extract, which in genuine rhubarb is about 35per cent. Constituents.—The principal constituent appears to be a gluco-side (possibly the chrysophan of some authors) or an undeterminedsubstance which yields successive oxidation products, viz.: chry-sophanic acid (di-oxy-methyl-anthraquinone), emodin (tri-oxy-methyl-anthraquinone), and rhein (tetra-oxy-methyl-anthraqui-none). Chrysophanic acid crystallizes in golden-yellow, clinorhombicprisms and dissolves in alkalies and in concentrated sulphuric acid, 190 SCIENTIFIC AND APPLIED PHARMACOGNOSY the solutions having a deep-red color. It is reformed in rhubarbafter extracting it by exposing the moistened root to air. Emodin. Fig. 80.—Rheum officinale, growing in the Chelsea Physic Garden (London).—^ After Perredes. occurs to the extent of per cent and forms orange-red needleswhich are soluble in hot toluene and give with alkalies and alkali RHUBARB 191 carbonates purplish colored solutions. Rhein forms yellowish-brownscales which are insoluble in hot toluene, soluble in hot acetic acidand produce purplish-red solutions with the alkalies or alkali car-
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