aluable dye-wood is imported in logs;
the heart-wood is the most valuable, which is cut up into chips or
ground to powder for the use of dyers by large powerful mills
constructed especially for the purpose. Logwood, when boiled in water,
easily imparts its red colour. If a few drops of acetic acid (vinegar)
is added, a bright red is produced; and when a little alum is added for
a mordant, it forms red ink. If an alkali, such as soda or potash, is
used instead of an acid, the colour changes to a dark blue or purple,
and with a little management every shade of these colours can be
obtained. Logwood put into polish or varnish also imparts its red
colour.

=Fustic= (_Maclura tinctoria_).--This tree is a native of the West
Indies, and imparts a yellow dye. Great quantities are used for dyeing
linens, etc. The fustic is a large and handsome evergreen, and is
imported in long sticks.

=Turmeric= (_Curcuma longa_).--Turmeric is a stemless plant, with
palmated tuberous roots and smooth lance-shaped leaves. It is imported
from the East Indies and China. The root is the part which affords the
yellow powder for dyeing. It is also a condiment, and is largely used in
Indian curry-powder. Paper stained with turmeric is used by chemists as
a test for alkalies, and it is also used in making Dutch, pink, and
gold-coloured varnishes.

=Indigo= (_Indigofera tinctoria_).--Indigo is a shrub which grows from
two to three feet in height, and is cut down just as it begins to
flower. It is cultivated in almost all the countries situated in the
tropics. The dye substance is prepared from the stems and leaves, and is
largely used in calico-printing.

=Persian Berries= (_Rhamnus infectorius_).--These berries are the
produce of a shrub of a species of buckthorn common in Persia, whence
they derive their name; but large quantities are also imported into
England from Turkey and the south of France. The berries are gathered in
an unripe state, and furnish a yellow dye.

=Nut-galls.=--These are found upon the young twigs of the Turkish dwarf
oak (_Quercus infectoria_), and are produced by the puncture of an
insect called Cynips. The supply is principally from Turkey and Aleppo.
Nut-galls contain a large quantity of tannin and gallic acid, and are
extensively used in dyeing.

=Catechu.=--This is obtained from the East Indies, and is the extract of
the _Acacia catechu_, a thorny tree. The wood is cut up into chips
similar to logwood, a