Hydrolysis of digallic acid yields gallic acid; oxidation, on the other hand, ellagic acid and luteic acid (Luteo Säure), which can be separated by shaking with pyridine. The reduction of digallic acid yields, by different methods, the same reduction compound, [Footnote: Nierenstein, Abderhalden's "Handb. d. biochem. Arbeitsm.," vi. 154.] viz., the racemic leucodigallic acid, which differs from digallic acid by being devoid of any tannoid properties; the latter distinction may be ascribed to the transformation of the tannophor group--CO.O--, to the tannoid-inactive group CH(OH)--O--. The successful resolving of racemic leucodigallic acid into both of its optically active components can only be brought about through the _d_- or _l_-hexacarbethoxyleucodigallic acid on introducing the latter into a 1 per cent. pyridine solution and heating to 45°-50° C., whereby the _d_- or _l_-acid is formed accompanied by a strong evolution of carbon dioxide. Hydrolysis of leucogallic acid yields gallic acid and gallic aldehyde; oxidation by means of hydrogen peroxide yields ellagic acid and luteic acid, and oxidation with potassium persulphate and sulphuric acid, in acetic acid solution, yields purpurotannin (see below) [Footnote: Liebig's _Ann_., 1912, 386, 318.]. Another distinct difference between digallic acid and leucodigallic acid is the fact that the formaldehyde condensation product of the former resembles gallic acid, whereas that of the latter resembles tannin; it is therefore probable that the leucodigallic acid part of the tannin molecule imparts this characteristic property to tannin. ---CO.O--- ^ ^ | | | | HO V OH COOH V OH OH OH [Illustration: Digallic Acid becomes...] ---CO.O--- ^ ^ OH | | | | HO V OH COOH V OH OH OH [Illustration: Luteic Acid becomes...] ---CO.O--- ^ ^ OH | | | | HO V --O.CO-- V OH OH OH [Illustration: Ellagic Acid becomes...] COOH COOH ^ _______ ^ | | | | HO V ---O--- V OH OH OH [Illustration: Purpuro Tannin.] 3. Ellagic Acid