GLUE

Syn. Gluten , Glutinum , L.; Colle , Colle forte , Fr. Inspi ated animal jelly, or gelatin, used as a cement. Prep. Glue is principally prepared from the parings and waste-pieces of hides and skins, the refuse of tanneries, and the tendons and other offal of slaughter-houses. These substances, when intended for the glue-maker, are steeped for 14 or 15 days in milk of lime, then drained, and dried by exposure to the air. This constitutes what is termed the ‘cleansing’ or ‘preparation,’ and in this state the ‘glue pieces,’ as they are called, may be kept for a long time, and transported to any distance without suffering decomposition. Before conversion into glue, they are usually again steeped in weak milk of lime, and next well washed and exposed to the air for 24 to 30 hours. They are then placed in a copper boiler two thirds filled with water, and furnished with a perforated false bottom, to prevent them from burning, and as much is piled on as will fill the ve el and rest on the top of it. Heat is next applied, and the whole gently boiled or simmered together, until the liquor on cooling forms a firm gelatinous ma . The clear portion is then run off into another ve el, and a very small quantity of alum (di olved) added; here it is kept hot by a water bath, and allowed to repose for some hours to deposit its impurities, after which it is run into the ‘congealing boxes,’ and placed in a cool situation. The next morning the cold gelatinous ma es are turned out upon boards wetted with water, and are cut horizontally into thin cakes with a stretched piece of bra wire, and then into smaller cakes with a moistened flat knife. The latter are placed on nettings to dry. The dry cakes of glue are next dipped one by one into hot water, and slightly rubbed with a brush wetted with boiling water, to give them a glo ; they are, lastly, stove-dried for sale. This furnishes the palest and best glue. As soon as the liquor of the first boiling has drained off, the undi olved portion of skins, ., left in the copper is treated with fresh water, and the whole operation is repeated again and again, as long as any gelatinous matter is extracted. In this way a second and other inferior qualities of glue are obtained. The product from dried glue-pieces is about 50%. Var. These chiefly depend on the care with which the proce is conducted. Hatmakers’ glue is prepared from the tendons of the legs of neat cattle and horses. It is brown, opaque, and soft; and grows moist in damp weather, but it does not render felt brittle like the other varieties. Fish glue is made in like manner from various membranous and solid parts of fishes. Parchment glue is prepared from shreds or shavings of parchment, vellum, white leather, ., di olved by boiling them in water. It is scentle , and nearly colourle . Qual. The best glue is transparent, nearly colourle , and tastele , has very little smell, even when melted, and is extremely adhesive. The presence of more than a trace of alum is objectionable; an undue quantity may be easily detected by the usual tests. The strongest glue is that obtained from skins, more especially from the hides of oxen and cows. That obtained from the bones, cartilages, and tendons, is weaker.