ester willow, eleven
of Spanish chesnut, eighteen of elm, and twenty-one of common willow
bark. Tannin obtained from these sources, however, differs materially
in some of its characters. The tannin of nutgalls, which is that
generally employed for chemical purposes, is sometimes called
gallo-tannic acid, to distinguish it from other species.

Notwithstanding the number of different substances which have from
time to time been introduced for the use of tanners, it is,
nevertheless, pretty generally acknowledged that there is nothing
superior, or even equal, to good oak bark, and that all attempts to
hurry the process beyond a certain point by the use of concentrated
solutions of tan, &c., are for the most part failures, as the
manufacture of good leather, to a great extent, depends on the process
being conducted in a slow and gradual, but--at the same time--thorough
and complete matter.

Oak bark is, however, by no means the only astringent bark well suited
to the use of the tanner, and in various parts of the world other
similar substances are used with very great success. All these tanning
materials, though they may not be considered by the English tanner
equal to the best oak bark, are, nevertheless, of great value to him;
they may be employed in conjunction with oak bark, or even as a
substitute in times of scarcity, or when the price of oak bark is
high; in fact the very existence of such substances tends to keep down
and equalise the price of bark, and to prevent it from undergoing
those great fluctuations in value which would necessarily occur were
it the only tanning material available to our manufacture--("Prof.
Solly in Jury Reports of Great Exhibition.")

There are a vast number of bark and other substances useful for
tanning purposes, which are found in the tropics, that are
comparatively unknown or little regarded in Europe; but which might be
readily obtained in large quantities and at a trifling cost. The bark
of many species of _Acacia_ furnishes the tanning principle in a great
degree, particularly that of _A. arabica_, which, under the name of
Babul wood, is largely used about Scinde, Biliary, Gruzerat, and other
parts of India; where it is regarded as a powerful tonic. The fruit of
_A. vera_, termed Egyptian and Senegal "bablah," has been employed in
tanning and dyeing. Numerous species of this tribe are found abundant
in New South Wales and the Cape Colony, and these, particularly the
wattle bark