Gum, Bleached. See Gum Arabic (above).
Gum, Brit′ish. Syn. Dextrin, Starch gum. Starch converted by the action of acids, diastase, or heat, into a soluble substance resembling gum.
Prep. 1. Malt (crushed small), 1 lb.; warm water, 2 galls.; mix, heat the whole to 145° Fahr., add of potato starch 5 lbs., raise the heat to 160° or 165° Fahr., and mash for about 25 minutes, or until the liquid becomes thin and clear; it must then be instantly run off, and raised to the boiling point to prevent the formation of sugar; after boiling for 3 or 4 minutes the whole must be filtered, and evaporated to dryness by a steam heat.
2. By exposing dry potato starch, in a stove, to a heat of about 400° Fahr. Yellow and inferior.
3. (M. Payen.) Dry starch, 1 ton, is moistened uniformly with concentrated nitric acid, 41⁄2 lbs. (diluted with), water, q. s., and the paste or dough is made up into small bricks or loaves, and dried in a stove; it is next reduced to coarse powder, and exposed in a stove-room for some time to a current of air at 160° to 165° Fahr.; it is next ground, sifted, and exposed, as before, to a heat of about 228° Fahr.; it is, lastly, ground, and passed through the ‘bolting machine.’ Very white and superior. This process has been patented in France by M. Henzé.
4. (Pinel.) Water, 100 galls., nitric acid, 1⁄2 gall., and hydrochloric acid, 1⁄2 pint, are mixed together, and so much potato starch is mixed as will form a thin paste; in two hours the liquid is drained off, and the solid matter is made up into lumps, which are dried by a gentle heat in a stove-room; they are next coarsely pulverised, and the powder is exposed on three successive days to the respective temperatures of 100°, 150°, and 190° Fahr.; the whole is then sifted, and, lastly, exposed to a heat ranging from 300° to 350° Fahr. Darker coloured than the last. To give it the appearance of gum Arabic, it is made into a paste with water containing 1% of nitric acid, and after being spread on copper plates in layers 3⁄4 to 1 inch thick, it is exposed to a stove heat ranging from 240° to 300° Fahr.
Prop., &c. White; insipid; transparent; friable; soluble in cold water, and in dilute spirit; insoluble in alcohol and ether; its solution yields a precipitate with acetate of lead. Iodine commonly turns commercial dextrin blue, but does not affect the colour of pure dextrin. It is distinguished from ordinary gum by its right-handed polarization of light, and by yielding oxalic but not mucic acid, when treated with nitric acid.
Dextrin is nutritive, emollient, and agglutinant. In France it is largely employed by the pastry-cooks and confectioners, and in medicine as a substitute for gum. The French surgeons also commonly employ it as a ‘stiffening’ for the splints used for fractured limbs. In this country it is chiefly used as a fine dressing for muslins, silk, and other textile fabrics, and in calico printing. Recently it has been made up into tear-like masses, and sold for gum Arabic, to which, however, it is vastly inferior as an agglutinant. See Dextrin.
Gum, Cherry-tree. Syn. Fruit-tree gum, Plum-tree g.; Gummi cerasi, G. pruni, L. An exudation from the stems of cherry, plum, and some other of the Rosaceæ. It is only partly soluble in water. It contains CERASIN (which see).
Gum, East India. This product, which consists of inferior kinds of gum acacia, is chiefly exported from Bombay, having been previously conveyed there from the coast of Arabia. It varies greatly in quality. Some samples are quite unfitted for making gum-water.