erra
japonica_, is produced from the leaves of _Uncaria gambir_ and _U.
acida_, cinchonaceous plants growing in the East Indian Archipelago. A
third product to which the name catechu is also applied, is obtained
from the fruits of the areca or betel palm, _Areca catechu_.

Ordinary black catechu is usually imported in three different forms. The
first and best quality, known as Pegu catechu, is obtained in blocks
externally covered with large leaves; the second and less pure variety
is in masses, which have been moulded in sand; and the third consists of
large cubes packed in coarse bags. The wood of the two species of
_Acacia_ yielding catechu is taken for the manufacture when the trees
have attained a diameter of about 1 ft. The bark is stripped off and
used for tanning, and the trunk is split up into small fragments, which
are covered with water and boiled. When the extract has become
sufficiently thick it is cast into the forms in which the catechu is
found in commerce. Catechu so prepared is a dark brown, or, in mass,
almost black, substance, brittle, and having generally a shining lustre.
It is astringent, with a sweetish taste. In cold water it disintegrates,
and in boiling water, alcohol, acetic acid and strong caustic alkali it
is completely dissolved. Chemically it consists of a mixture of a
peculiar variety of tannin termed catechu-tannic acid with catechin or
catechuic acid, and a brown substance due to the alteration of both
these principles. Catechu-tannic acid is an amorphous body soluble in
cold water, while catechin occurs in minute, white, silky, needle-shaped
crystals, which do not dissolve in cold water. A very minute proportion
of quercetin, a principle yielded by quercitron bark, has been obtained
from catechu.

Gambir, which is similar in chemical composition to ordinary catechu,
occurs in commerce in the form of cubes of about an inch in size, with a
pale brown or yellow colour, and an even earthy fracture. For the
preparation of this extract the plants above mentioned are stripped of
their leaves and young twigs, and these are boiled down in shallow pans.
The juice is strained off, evaporated, and when sufficiently
concentrated is cast into shallow boxes, where, as it hardens and dries,
it is cut into small cubes.

Gambir and catechu are extensively employed in dyeing and tanning. For
dyeing they have been in use in India from the most remote period, but
it was only during the 19th century tha