[CHAPTER III.]
COMMERCIAL TANNING MATERIALS.
Algarobilla.—The seed-pods of Prosopis pallida and P. Algarrobo are known as algarobilla, the two kinds being distinguished as negro and blanco. The trees are abundant in mountainous parts of South America, notably Chili and the Argentine Republic. The pods contain up to 50 per cent. of a bright-yellow tannin, somewhat resembling that of myrobalans. The friable tannin is readily soluble in cold water, and is so loosely held in the fibrous network of the pod, that great loss is sustained by careless handling. The commerce in algarobilla does not figure in the official trade returns; but J. Gordon & Co., Liverpool, obligingly state that they imported 50 tons, at an average value of 18l. 10s. a ton, in 1880. Widow Duranty & Son, also of Liverpool, are good enough to add that they received 160 tons in 1881, the first that had reached them for a long time. Havre imported 50 tons in 1881. The name algarrobo is also applied to Balsamocarpon brevifolium in Chili, and to Hymenæa Courbaril in Panama.
Chestnut-extract.—The wood of the chestnut (Castanea vesca) contains 14-20 per cent. of a dull-brown tannin. It is quite different from the bark and bark-extract of the American chestnut-oak (Quercus sessiliflora). Its extract is used largely to modify the colour produced by hemlock-extract, and for tanning and dyeing. The pulverised wood is also extensively employed in France. The imports are included in barks and extracts, [p. 39].
Cork-bark. See [Oak-barks].
Cutch, Catechu, or Terra Japonica (Fr., Cachou; Ger., Catechu).—The term kát, kut, or "cutch," is applied to the dried extract, containing 45-55 per cent. of dark-coloured mimo-tannic acid, prepared chiefly from 2 trees:—(1) Acacia Catechu [Mimosa Catechu, M. sundra], a tree of 30-40 ft., common in most parts of India and Burma, growing also in the hotter and drier districts of Ceylon, and abundant in tropical East Africa—the Soudan, Sennar, Abyssinia, the Noer country and Mozambique, though the utilisation of its tannin is restricted to India; (2) A. [M.] Suma, a large tree inhabiting South India (Mysore), Bengal, and Gujerat.
The process for preparing cutch varies slightly in different districts. The trees are reckoned to be of proper age when their trunks are about 1 ft. diam. They are then cut down, and the whole of the woody part, with the exception of the smaller branches and the bark, is reduced to chips: some accounts state that only the darker heart-wood is thus used. The chips are placed with water in earthen jars, arranged in a series over a mud fire-place, usually in the open air. Here the water is made to boil, the liquor as it becomes thick and strong being decanted into another vessel, in which the evaporation is continued until the extract is sufficiently inspissated, when it is poured into moulds made of clay, or of leaves pinned together in the shape of cups, or in some districts on to a mat covered with the ashes of burnt cow-dung, the drying in each case being completed by exposure to the sun and air. The product is a dark-brown extract, which is the usual form in which cutch is known in Europe.
In Kumaon, North India, a slight modification of the process affords a drug of very different appearance. Instead of evaporating the decoction to the condition of an extract, the inspissation is stopped at a certain point, and the liquor is allowed to cool, coagulate, and crystallise over twigs and leaves thrown into the pots for the purpose. By this method is obtained from each pot about 2 lb. of kath or catechu, of an ashy-whitish appearance. In Burma, the manufacture and export of cutch form one of the most important items of forest revenue. The quantity of cutch exported from the province in 1869-70 was 10,782 tons, valued at 193,602l., of which nearly half was the produce of manufactories situated in British territory. The article is imported in mats, bags, and boxes, often enveloped in the large leaf of Dipterocarpus tuberculatus. It is brought down from Berar and Nepal to Calcutta. That of Pegu has a high reputation.
Our imports of cutch in 1880 were 5155 tons, value 173,040l., from the British East Indies; 539 tons, 15,572l., from other countries; total, 5694 tons, 188,612l. Our exports in the same year were:—892 tons, 28,527l., to Germany; 676 tons, 24,562l., to the United States; 478 tons, 15,505l., to France; 303 tons, 10,537l., to Holland; 177 tons, 5859l., to Russia; 141 tons, 4835l., to Belgium; 245 tons, 8719l., to other countries; total, 2912 tons, 98,544l. The approximate London market value of Pegu cutch is 21-42s. a cwt.
An astringent extract prepared from the areca nut (Areca Catechu) is said to contribute to commercial cutch; if so, it is a totally distinct product from those just described.