(M.P. 275 -280 C) by coupling tricarbomethoxygalloyl chloride with
dicarbomethoxygallic acid.

Nierenstein [Footnote: _Ibid_., 1910, 43, 628.] obtained, from the
carbethoxy compound of tannin, a crystalline, optically active digallic
acid, M.P. 268 -270 C. The pentacetate of this substance, obtained by
reduction and acetylisation, yielded hexacetylleucotannin. A
pentamethyldigallic acid methyl ester of the composition

((O.CH_3)_3)C_6H_2----COO-----C_6H_2((OCH_3)_2)COO.CH_3

was obtained by Mauthner [Footnote: _Jour. f. prakt. Chem_., 1911, 84,
140.] from the chloride of trimethylgallic acid and the methyl ester of
the acid from the glucoside of syringin; on saponification with caustic
potash the former compound yielded trimethylgallic acid and syringic
acid.

Fischer [Footnote: _Ber_., 1913, 46, 1116.] synthesised the so-called
_m_-digallic acid by coupling tricarbomethoxygalloyl chloride with
carbonylgallic acid and subsequent splitting off of CO_2. The
_m_-digallic acid appears as rather thick, colourless, microscopic
needles containing about 16 per cent. water of crystallisation,
M.P. 271 C. They are slightly soluble in cold, soluble in hot water,
and very soluble in methyl and ethyl alcohols. Their aqueous solution
gives dark blue coloration with ferric chloride, and precipitates
gelatine and quinine.

Fischer and his students [Footnote 5: _Ibid_., 1912, 45, 915, 2709;
1913, 46, 1116.] prepared quite a number of digallic acid derivatives,
amongst which are the following:--