Fischer and Freudenberg [Footnote: _Ibid._, 1912, 45, 2717; 1913, 46, 1127.] subsequently elaborated a method of purifying tannin, and on investigating the purified substance, arrived at the conclusion that no other hydroxybenzoic acid than gallic acid was present in tannin. On repeating Strecker's hydrolysis they obtained 7-8 per cent, sugar, and hence concluded that 1 molecule of glucose was combined with about 10 molecules of gallic acid. Owing to the difficulty of isolating the intermediary hydrolysis products, and the subsequent impossibility of drawing any conclusions as to the constitution of tannin, the latter investigators decided to adopt the methods offered by synthesis. Their basic idea was the absence of carboxylic groups in tannin, and that hence the total gallic acid must be present in ester form. These conditions are fulfilled if one views tannin as being an ester compound of 1 molecule of glucose and 5 molecules of digallic acid, of similar construction as, for example, pentacetyl glucose. Fischer and Freudenberg succeeded in preparing the former by shaking a mixture of finely powdered glucose, chloroform, and quinoline with an excess of tricarbomethoxygalloyl chloride for twenty-four hours and precipitating the resulting product with methyl alcohol; suitably purified, a light amorphous colourless substance was obtained which proved to be penta-(tricarbomethoxygalloyl) glucose. Careful saponification with excess alkali in acetone-aqueous solution at room temperature yielded a tannin very closely resembling tannin, identified as pentagalloyl glucose. It is doubtful, however, whether this substance is homogeneous, and it is probably a mixture of two stereoisomers. Fischer and Freudenberg, therefore, further concluded that tannin is mainly an ester compound of glucose and 5 molecules _m_-digallic acid. Elucidation on this point offered itself advantageously in Herzwig's methylotannin, [Footnote: _Ber._, 1905, 38, 989.] which is obtained by the interaction of diazomethane and tannin. The first step was then to prepare pentamethyl-_m_-digallic acid CH_3.O_______ ______COOH CH_3.O{_______}--CO.O--{______} CH_3.O CH_3.O O.CH_3 from trimethylgalloyl chloride and the _m-p_-dimethyl ether of gallic acid; the chloride of this substance, coupled with [Greek: a]- and [Greek: b]-glucose, yields-- _CH.OR | | | CH.OR H_______O.CH_3 | | R=CO{_______}O.CH_3 O{ CH.OR H O | | H_____O.CH_3 | CH CO{_____}O.CH_3 | | H O.CH_3 |_CH.OR CH_2.OR [Illustration: Penta-(pentamethyl-_m_-digalloyl)-glucose.]