257.], who purified the potash salt and decomposed this with sulphuric
acid. Pelouze [Footnote: Liebig's _Ann._, 1843, 47, 358.], later on,
observed the formation of the crystalline gallic acid from tannin, when
the latter is boiled with sulphuric acid; this had already been observed
by J. Liebig.[Footnote: _Ibid._1843, 39, 100.] Both had noticed the
absence of nitrogen. In addition to the methods of preparation of tannin
then in vogue neutral solvents were mainly employed by subsequent
investigators; Pelouze [Footnote: _Jour. Prakt. Chem._, 1834, 2, 301,
and 328.] treated powdered galls with ether containing alcohol and
water, and considered the upper layer to be a solution of gallic acid
and impurities, the bottom layer to contain the pure tannin.

The EMPIRICAL FORMULA of tannin has also been the subject of much
speculation by the different investigators, the difficulty here being
that of obtaining a pure specimen of the substance free from sugars, and
which could be submitted to elementary analysis. Whereas these early
purified substances were thought to correspond to the formula of
digallic acid (galloylgallic acid), C_14H_10O_9, Fischer and Freudenberg
[Footnote: _Ber._, 1912, 915 and 2709.] were able to show, with
approximate certainty, that the constitution of tannin is that of a
pentadigalloyl glucose.

Early attempts at _hydrolysing tannin_ gave varying results, some
investigators claiming the presence, and others the absence of
sugars. Here, again, E. Fischer and Freudenberg [Footnote: _Ibid._] were
able to conclusively prove that on hydrolysing tannin with dilute acids,
7.9 per cent. glucose is dissociated, and that hence glucose forms part
of the tannin molecule. Fischer and Freudenberg also determined the
optical activity of pure tannin in water: [Greek: a]_D was found to lie
between +58 and +70 .