Glue, a tenacious, viscid mat-ter, serving as a cement to unite or connect substances together.
The common or string-glue, which is chiefly used by carpenters, joiners, etc. is prepared sometimes from the whole skins of oxen, cows, and other animalsj but more generally from the parings or scraps, sinews of the legs, etc.
The parings are steeped for two or three days in water, when they are washed out, and boiled to the consistence of a jelly, which is passed, while hot, through osier baskets, in order to separate the impure particles. It is then left to subside and filtrate : when all feculent matters are settled at the bottom, the jelly is dissolved and boiled a second time ; after which it is poured into flat vessels or moulds, whence it is taken out in solid masses, and cut into square pieces or cakes. - Lastly, it is suspended in a kind of coarse net, fastened to a frame, or strings, where it is suffered to remain till completely dry. - The best glue for common purposes used in this country is generally imported from Ireland, and is exempt even from the convoy-duty; whereas the glue obtained from foreign markets pays to the customs 9s. 3d1/2. per cwt.
A very superior, but expensive, glue may be prepared from the hides of the oldest cattle, especially those of bulls. Its quality is likewise much improved by long keeping ; and its strength may be easily determined, by immersing a piece in water for three or four days; at the expiration of which, if it swell considerably without dissolving, and resume its former dry state, on being exposed to the air, it may be considered as excellent.
Glue is also manufactured from the skins, fins, heads, tails, and cartilages of porpoises, cuttls-fish, and other sea-monsters. For this purpose, the parts above men-tioned should be boiled in water, being carefully preserved from smoke, and whatever may discolour the liquor, or render it turbid. When all the substance of the fish has been boiled down, the jelly is strained through a sieve, and suffered to cool. It is then again boiled with the same precaution, till the drops, when dried in the • open air, concrete on cooling. Af-ter having acquired a proper consistence, it is twisted in a manner similar to paste, and suspended on strings for drying in the. shade. Glue, thus prepared, is more or less perfect, in proportion to the care with which it is clarified : it should be completely soluble in water.
Another very powerful, glue may be prepared by a spirituous solution of isinglass, which Mr. BoUYLEdirects to be first steeped for twenty-four hours in common brandy; when the isinglass is opened and softened, the whole should be gently boiled together, and stirred till it forms a perfect; solution, and till a drop of the cold liquor indicates a strong jelly. It is then to be strained while hot, through a clean linen cloth, into a vessel, which ought to be closely stopped. A gentle heat will be sufficient to dissolve this glue into a colourless, and nearly transparent fluid, which is said to be so adhesive, that pieces of wood glued with it, separate elsewhere sooner than in the place where they are joined. - See Isin-glass.