A Dictionary of Arts: Catechu.

CATECHU, absurdly called Terra Japonica, is an extract made from the wood of the tree mimosa catechu, which grows in Bombay Bengal, and other parts of India. It is prepared by boiling the chips of the interior of the trunk in water, evaporating the solution to the consistence of sirup over the fire, and then exposing it in the sun to harden. It occurs in flat rough cakes, and under two forms. The first, or the Bombay, is of uniform texture, of a dark red color, and of specific gravity 1.39. The second is more friable and less solid. It has a chocolate color, and is marked inside with red streaks. Its specific gravity is 1.28.

According to Sir H. Davy, these two species are composed as follows: -
................. Bombay | Bengal
Tannin 54.5 | 48.5
Extractive 34.0 | 36.5
Mucilage 6.5 | 8
Insoluble matters, sand and lime 5 | 7
.................. 100.0 | 100.0

Areka nuts are also found to yield catechu; for which purpose they are cut into pieces watered in an earthen pot with solution of nitre, and have a little of the bark of a species of mimosa added to them. The liquor is then boiled with the nuts, and affords an inspissated decoction.

Good catechu is a brittle, compact solid, of a dull fracture. it has no smell, but a very astringent taste. Water dissolves the whole of it, except the earthy matter, which is probably added during its preparation. Alcohol dissolves its tannin and extractive. The latter may be oxidized, and thus rendered insoluble in alcohol, by dissolving the catechu in water, exposing it for some time to a boiling heat, and evaporating to dryness.

The tannin of catechu differs from that of galls, in being soluble in alcohol, and more soluble in water. It precipitates iron of an olive color, and gelatin in a mass which gradually becomes brown.

It has been long employed in India for tanning skins, where it is said to effect this object in five days. I have seen a piece of sole leather completely tanned by it in this country in ten days, the ox-hide having been made into a bag, with the hair outside, and kept filled with the solution of catechu. In India it has also been used to give a brown dye to cotton goods, and of late years it has been extensively introduced into the calico print works of Europe. The salts of copper with sal ammoniac cause it to give a bronze color, which is very fast; the proto-muriate of tin, a brownish yellow; the per-chloride of tin, with the addition of nitrate of copper, a deep bronze hue; acetate of alumina alone, a reddish brown, and, with nitrate of copper, a reddish olive gray; nitrate of iron, a dark brown gray. For dyeing a golden coffee brown, it has entirely superseded madder; one pound of it being equivalent to six pounds of this root.

A solution of one part of catechu in ten parts of water, which is reddish brown, exhibits the following results: with -
Acids - - - A brightened shade.
Alkalis - - - A darkened shade.
Proto-sulphate of iron - - - Olive brown precipitate.
Per-sulphate of iron - - - Olive green do.
Sulphate of copper - - - Yellowish brown.
Alum - - - A brightening of the liquor.
Per-nitrate of iron - - - Olive green precipitate.
Nitrate of copper - - - Yellowish brown do.
Nitrate of lead - - - Salmon do.
Proto-nitrate of mercury - - - Milk-coffee do.
Muriate of alumina - - - Brown-yellow.
Muriate of tin - - - Do. do.
Per-chloride of tin - - - Do. darker.
Corrosive sublimate - - - Light chocolate do.
Acetate of alumina - - - Brightening of the liquor.
Acetate of copper - - - Copious brown precipitate.
Acetate of lead - - - Salmon coloured do.
Bichromate of potash - - - Copious brown do.

Pure tannin may be obtained from catechu, by treating it with sulphuric acid and carbonate of lead; but this process has no manufacturing application.