Catechu, Bombay. Firm, brittle, dark brown, of a uniform texture, and a glossy,
semi-resinous, and uneven fracture, Sp. gr. 1·39. Richness in tannin, 52%.
Catechu, Bengal. Rusty brown colour externally; porous, and more friable than the preceding. Sp. gr. 1·28. Richness in tannin, 49·5%.
Catechu, Malabar. Resembles the last in appearance, but is more brittle and gritty. Sp. gr. 1·40. Richness in tannin, 45·5%.
Of the above varieties the first is the one generally employed in medicine, and which commonly passes by the name of catechu. The second popularly passes under the name of terra Japonica (Japan earth), from the old belief that it was of mineral origin.
Catechu, Pale, is prepared at Singapore and in the Eastern Archipelago. It generally occurs in cubical reddish-brown pieces, porous, bitter, and astringent in taste. Entirely soluble in boiling water; the solution, when cold, is not rendered blue by iodine. Of 100 parts, only 60 are dissolved by cold water, and the solution is bright. Thirty parts of isinglass precipitate the whole of the astringent matter.—Test. Sp. gr. 1·39. “The pale catechu being already in the Edin., the B. P. 1864 retained it with the black; but the black is the one adopted by all other pharmacopœias, and is preferred in the arts and manufactures; it is well known to be far superior to the pale in astringency, and is always to be had of good quality; it is therefore a matter of surprise and regret that it has been rejected from the ‘British Pharmacopœia.’” (Squire.)
Estim. It is often of importance to the tanner and dyer to determine the richness of this article in tannic acid or tannin. The following are two simple methods:—
1. Exhaust a weighed sample (in powder) with ether, and evaporate by the heat of a hot-water bath. The product, which is the tannin, must then be accurately weighed.
2. Dissolve the sample (in powder) in hot water, let it cool out of contact with the air, filter, and add a solution of gelatin as long as a precipitate falls. The precipitate, after being washed and dried at a steam heat, contains 40% of tannin.
Uses, &c. Catechu is extensively employed in medicine, both internally and externally, as an astringent. It is used to flavour British brandy, and by the tanners as a substitute for oak bark. With it the dyer produces, inexpensively, many of his most pleasing browns. Alum mordants are mostly employed in dyeing with catechu. “The salts of copper with sal-ammoniac cause it to give a BRONZE COLOUR, which is very fast; the protochloride of tin, a BROWNISH YELLOW; the perchloride 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 GREY; nitrate of iron, a DARK-BROWN GREY. For dyeing a GOLDEN COFFEE-BROWN, it has entirely superseded madder; 1 lb. of it being equivalent to 6 lbs. of this root.” (Ure.)—Dose, 10 gr. to 30 gr. in solution, in water, or made into a bolus, or sucked as a lozenge.