' GLUE is :Substance gelaL tineio a dry'state.' • The preparation and preservation of the skin and other animal matters employed' in' the manufacture of glue, constitute ti peculiar branch of in dustry. Those who exercise it should study to prevent the fermentation of the substances, and to diminish' the cost of carriage by depriVing as much water as can conveniently be done. They may then be put in preparation by mace rating them in milk of lime, renewed three or four time in the course of a fortnight or three weeks.• This process is performed in large, tanks of masonry. They are next taken out With all the ad hering lime, and laid in a layer, 2 or 8 inches thick, to 'drain; and dry, upon a sloping pavement; where they are turned Over by prongs two or three times a day. The action of theliine disSolves the blood and certain soft gartS; attacks the epider mis, and disposes the gelatinous matter to dissolve more When the cleansed matters are dried, they may be packed in sacks'or hog,sheads, and trans ported to the glue manufactory at any distance. The Principal substances. of which glue is made are the parings of ox and other thick! hides, which form the strongest article ; :the 'refuse of the lea ther-dresser; both 'afford from 45 to 55 per cent. of glue.) The tendons, and many other offals of slaughter-houses, also afford materials, though of an inferi or quality, for the purpose. The refuse tinneries, 'Such as the ears of oxen, calves, sheep, &c., are better articles ; but parings of parchment; old gloves, amid, in fact' animal skin, in every form, uncombined, with tannin, may be made into glue.
These various matters arc first rinsed, then drained, and afterwards boiled in 'large shallow' copper vessels for some hours, during which they are well stir red. • The solution must be drawn off in suc cessive portions ; a method which frac tions the products, or subdivides them into articles of various value, gradually decreasing from the first portion drawn off to the last. It has been ascertained by careful experiments that gelatine gets altered over tlae fire very soon after it is dissolved, and it ought therefore to be drawn off whenever it is sufficiently fluid and strong for forming a clear gelatinous mass on cooling, capable of being cut in to moderately firm slices by the wire.
This point is commonly determined by filling half an egg-shell with the liquor, and exposing it to the air to cool. The jelly ought to get very consistent in the course of a few minutes ; if not so, the boiling_ must be persisted in a little long er. When this term is attained, the fire is smothered up, and the contents of the boiler to settle for a quarter of an hour. The stop-cock being partially turned, all the thin gelatinous liquor is run off into a deep boiler, immersed in a warm water bath, so that it may continue hot and fluid for several hours. At the end of this time, the supernatant clear liquid is to be drawn off into con gealing boxes, in which the solution as it cools into a jelly takes the shape of the space. It is then exposed to the air, or a stove heat, to dry, and receives a gloss by being dipped in water and brushed. It is finally dried, and rendered fit for pack ing.
was first extracted by Bee caria from wheat flour, and was long re garded as a proximate principle of plants, till Einhof, Taddei, and Berzelius, suc ceeded in showing that it may be' re solved by means of alcohol Into three different substances, one of which re sembles closely animal albumine, and has been called Zgmome, or vegetable albu mine ; another has been called Gliadine; and a third, Macke. The mode of sepa rating gluten from the other constituents of wheat flour has been described to wards the end of the article BREAD.
Gluten, when dried in the air or a stove, diminishes greatly in size, becomes hard, brittle, glistening, and of a deep yellow color. It is insoluble in ether, in fat, and essential oils, and nearly so in water. Alcohol and acetic acid cause gluten to swell and make a 'sort of milky solution. Dilute acids and alkaline leys dissolve gluten. Its ultimate constitu ents are not determined, but mote is one of them, and accordingly when moist glu ten is left to ferment, it exhales the smell of old cheese.