Gum, Insoluble. See Bassora Gum, Cherry-tree Gum, and Gum Tragacanth.
Gum, Seed. Syn. Gummi seminum, L. A species of soluble gum extracted from the seed of the flax (linseed), quince, &c.
Gum, Senegal. This product, which is largely exported from Portendie, Sierra Leone, and the French settlements on the Senegal, ranks next in quality to gum acacia, and for many purposes, as calico-printing for instance, it answers equally well. The transparent and light-coloured pieces are frequently picked out and sold as gum Arabic.
Gum Trag′acanth. Syn. Tragacanth, Gum dragon; Gummi tragacantha, G. draconis, Tragacantha (Ph. L.), L. The gummy exudation of the Astragalus verus, hardened by the air. When digested in water, it swells considerably, a portion is dissolved, and the whole combines to form a thick mucilage. It is totally soluble in boiling water, when some change is supposed to take place
in it; a great portion, however, afterwards separates. Sp. gr. 1·384. It is chiefly employed in calico-printing, and by shoemakers and lozenge-makers; by the latter to give toughness to the saccharine mass.
Powdered tragacanth is often adulterated with flour of starch, and not unfrequently with the commoner varieties of gum Arabic. According to M. Planche, a mixture of pulverised tragacanth and gum Arabic forms, with water, a thinner mucilage than the same quantity of either of these gums alone. This fraud may be detected as follows:—Make a mucilage of the suspected gum, and add thereto a few drops (2 or 3 to the dr.) of alcoholic tincture of guaiacum, taking care to stir it all the while. If the sample contains any gum Arabic, the mixture, in the course of a few minutes, assumes a fine blue colour, whilst it does not change colour if the gum tragacanth is pure, 5% of gum arabic can be thus detected. When the quantity is very small, one to four hours may elapse before the colour is developed. Starch and flour are detected in the manner noticed under Gum Arabic.
Gum, Turkey. Various qualities of gum acacia are sold under this name.
GUM RES′INS. Syn. Gummi resinæ, L. Vegetable products in which the properties of gum and resin are combined. They are partly soluble in water, and partly in alcohol. Many of them form a species of emulsion when triturated with the former fluid. The principal gum resins are AMMONIACUM, ASSAFŒTIDA, BDELLIUM, GALBANUM, GAMBOGE, MYRRH, OLIBANUM, OPOPONAX, SAGAPENUM, and SCAMMONY.
GUN BAR′RELS. See Browning.
GUN COT′TON. See Pyroxylin.