Rubia, Madder, allied to Galiums, which are almost the only English representatives of the family. The coffee- and cinchona-plants are foreign representatives.
Nauclea, or Uncaria gambir. East Indies. ([Fig. 56].) A climbing shrub, source of “gambier,” or “Terra Japonica”; also called “Catechu,” in common with several other solid extracts. Gambier is first described by the Dutch trader Couperus, in 1780; plant introduced in Malacca, 1758; plantations established in Singapore in 1819.
Culture is mainly by Chinamen, and is very rude; it yields rapid return, but under the treatment to which it is subjected a plantation is worn out in ten to fifteen years. Cropping commences three years after planting, and is continued two to four times annually, with little regard to fitness of shrubs, the plant being cropped till it has barely leaves left to support existence. It is found advantageous to combine pepper-culture with that of gambier, the spent leaves form a good protection for the pepper-plant roots, but they have little actual manurial value.
Fig. 56.—Gambier Shrub (Nauclea gambir).
Cropping is done with a knife called a parang, while a larger knife is used for chopping the leaves and twigs before they are put in a boiler, in which they are heated with water till the liquid, which is constantly stirred during the operation with a wooden five-pronged stirrer, becomes syrupy. The leaves are then brought out with a wooden fork, and allowed to drain on a tray, so that the liquor runs back into the boiler. The coarser matter still remaining in the boiler is removed with a strainer like a racquet, and the finer by straining the liquor through a perforated cocoanut shell into small shallow tubs, where it is allowed to cool with constant stirring with a cylindrical wooden bar, which is worked up and down with a rotary motion until the catechin crystallises. When quite cool the pasty mass is turned out of the tub, cut into cubes with sides 1 inch long with a hoop-iron knife, and dried on bamboo trays in racks under sheds, or sometimes smoke-dried with wood fires.
Good cube gambier is an earthy-looking substance and is dark outside, but pale within from crystallisation of catechin. Catechin is not itself a tanning material, but is apparently converted into a tannin by drying at 110°-126° C., when it parts with a molecule of water. It is very probable that a similar change occurs in the tannery. The tannin is a catechol-phloroglucol derivative, less astringent than most of this series, and of pale colour. (See [p. 297].)
A commoner quality, called “block-gambier,” instead of being cut into cubes, is run into large oblong blocks of about 250 lb. weight, which are wrapped in matting and exported in a pasty condition. These contain 35-40 per cent. of tannin, as estimated by the hide-powder method, while the best cubes reach 50-65 per cent. Besides the forms named, various others are made, principally for native use in chewing with betel-nut in the form of small biscuits, or in thin discs (“wafer gambier”) by running the pasty mass into bamboos and cutting the cylinder so formed into thin slices. These forms are usually light in colour, and very rich in catechin.
For details of the chemistry and employment of gambier, see [pp. 228], [231], [239], etc.