| | H_____O.CH_3
| CH CO{_____}O.CH_3
| | H O.CH_3
|_CH.OR

CH_2.OR

[Illustration: Penta-(pentamethyl-_m_-digalloyl)-glucose.]

The [Greek: a]- and [Greek: b]-derivatives thus obtained differ in their
behaviour towards polarised light, and are, again, probably mixtures of
two stereoisomers, _i.e._, mixtures of derivatives of [Greek: a]- and
[Greek: b]-glucose. Compared to methylotannin, these preparations
exhibit very close resemblance to the former, from which it may be
concluded that they are closely related to this substance, and probably
possess the same or a very similar structure; the result of the above
experiments has, therefore, brought us at least in close proximity to
the structure of tannin. It must, however, be borne in mind that the
analysis and hydrolysis of tannin does not afford an explanation of the
question as to whether tannin is a compound of glucose and 10, 9, or 11
molecules of gallic acid; it is also possible, though not probable, that
tannin would contain a polysaccharide instead of glucose
itself. Similarly to sugar, the true glucosides can be coupled with
hydroxybenzoic acids, which is proved by the preparation of
tetra-galloyl-[Greek: a]-methyl glucoside; this substance, also,
exhibits tannoid character.


2. DIGALLIC ACID