CATECHU. This is a substance which has been long known under the name of terra japonica, being believed to be an earth that came from Japan. It is, however, now known, to be an inspissated vegetable juice, which its name is said to indicate, cate signifying a tree, and chu Juice.
There are two varieties of catechu, one comes from Bengal, and the other from Bombay. These differ from each other very slightly in their chemical characters, but may be distinguished by the particular appearance of each. In general, catechu has a pale reddish brown colour, is friable, possesses a lamellar structure and rough fracture ; specific gravity about 1.39 ; taste bit terish and astringent, leaving a disagreeable sweetness ; it is infusible, does not deliquesce, and does not exhibit any sensible change in consequence of exposure to the action of the atmosphere. The Bengal catechu may be distinguished from that which comes from Bombay, by being of a darker colour, more nearly resembling choco late on its exterior surface, and by exhibiting a streaked appearance of chocolate and reddish brown internally. The texture is more uniform, and the fracture more resinous and shining. Its specific gravity is somewhat less, and it is also more friable.
Sir Ilumphry Davy, at the suggestion of Sir Joseph Banks, analysed both varieties, and the results nearly correspond. We shall give a general statement, which may be considered equally applicable to both, previous to the details of the analyses. Catechu is almost soluble in hot water ; the solution is of a deep reddish brown, and reddens the infusion of litmus. By long decoction a solution is formed, which yields, by evaporation, about nth of its whole weight of solid matter.
The presence of gallic acid and tannin were also dis tinctly proved, by the black colour produced by sul phate of iron, and by the copious precipitate by animal gelatine.
Catechu contains a peculiar extractive, and a sub stance resembling mucilage. The last is left pure by the action of alcohol, which dissolves all the other mat tors. The extractive, when completely freed by washing from the tannin, is slightly astringent, and very sweet \Olen chewed for some time. It is soluble both in water and alcohol, and acquires a deep colour by exposure to the air.
The following are the exact results of the analyses. 200 grains gave, Bengal. Bombay.
Tannin 97 109 Extractive 73 68 Mucilage 16 13 Residual sand and calcareous 10 matter 200 200 It has been said to be derived from various trees ; but it is certain, that it is most usually obtained from the Acacia catechu of \Villdenow, which grows abundantly on the mountains of Hindostan, and which is there called Coira.t It seldom exceeds twelve feet in height, and one foot in diameter. It is covered with a thick coarse bark, and divides into many branches at its top. The
leaves arc alternate on the young ltranches, and are com posed of from 15 to 30 parts of partial pinnx, nearly two inches long, each having about forty pairs of linear leaflets beset with short hairs, with a small gland on the leaf stalk between the bases of each pair of the pinnx. There are two short recurved spines at the base of each leaf.
The flowers arc male and hermaphrodite, and spring from the axillx of the leaves on close spikes four or five inches long. The calyx is tubular, hairy, dividing into five oval pointed segments. The corolla tubular, mono petalous, and twice the length of the calyx. The fila ments are numerous, twice the length of the corolla ; anthers roundish ; germen oval, supporting a slender style of the same length with the stamens, and terminated by a simple stigma.
Fruit lanceolate, compressed, pod smooth, brown, gin thin. It contains six roundish flattened seeds.
The following is the mode of preparation, as narrated by INIr Kerr, who was formerly assistant surgeon to the civil hospital at Bengal.
" After felling the trees,'' says this gentleman, " the manufacturer carefully cuts off all the exterior white part of the wood. The interior coloured part is cut into chips, with which he fills a narrow-mouthed un glazed pot, pouring water upon them until lie sees it among the upper chips : when this is half evaporated by boiling, the decoction, without straining, is poured into a flat earthen pot, and boiled to one-third part : this is set in a place to cool for one day, and afterwards evapo rated by the heat of the sun, stirring it several times : when it is reduced to a considerable thickness, it is spread upon a mat or cloth, which has previously been covered ith the ashes of cow dung; this mass is divided into square or quadrangular pieces by a string, and complete ly dried, by turning them in the sun until they are lit for sale.
Catechu is imported into this country in bags, and occasionally in small chests that contain 3 or 4 cwt. each. Both varieties are mixed up together in the same package.
Catechu is used in India in some processes of dyeing. It is a chief ingredient in the betel composition, which is so generally chewed by the natives of the East. The Indians also use it as an ingredient of an ointment, in high repute for curing sores.
In Europe, it is chiefly employed for medicinal pur poses. Its astringency renders it peculiarly taluahle in sonic cases of dysentery and diarrhea, w hen astringents are indicated. Front the quantity of tannin which it con tains, it may become a very valuable article in the pre paration of leather.
Sec Medical Observations, vol. v. Phil. Trans. tip 1803. Aikin's Chemical Dictionary. Thomson's .System of Chemistry. Willdenow, edition of Linnaits Species Plantarum. (v.