GLUE: is obtained from the hides and hoofs of oxen and a great variety of other animal refuse.
The raw material is first steeped for fourteen or fifteen days in milk of lime, then drained and dried by exposure to the air. This constitutes what is called the "cleans ing" or "preparation"; and, after being so treated, the "glue stock," as it is called, may be kept for a long time and transported to any distance without suffering decomposi tion. Before conversion into glue, the "stock" is generally again steeped in weak milk of lime, and then well washed and exposed to the air for twenty-four to thirty hours. It goes next to copper boilers, two-thirds full of water and fitted with per forated false bottoms to prevent burning, each boiler being filled and piled up with it. Heat is then applied and the whole is gently boiled or simmered until the liquor on cooling shows firm, gelatinous consistence. The clear portion is next run off, a very small quantity of dissolved alum being added, into another vessel, where it is kept hot by a water bath, and allowed to remain for some hours to deposit its impurities, then being passed into the "congealing boxes" and allowed to cool.
The next morning, the cold gelatinous masses are turned out upon wet boards and cut horizontally into thin cakes with a stretched piece of brass wire, and then into smaller cakes with a moistened fiat knife. These small cakes are placed on nettings
to dry and are later dipped one by one into hot water and slightly rubbed with a brush wetted with boiling water, to give them a gloss. Finally comes a stove-drying process and the glue is ready for market.
As soon as the liquor of the first boiling has drained off, the undissolved portion of the skins, etc., left in the copper is treated with fresh water, and the whole opera tion is repeated again and again as long as any gelatinous matter can be extracted— the product grading as second and lower qualities.
Fish glue is made from fish-sounds and other parts of fish membrane.
Liquid glue is made by dissolving dry glue and adding nitric acid in the proportion of one ounce to a pound, or by adding to it three times its weight of strong vinegar.
Light, clear glues are considered the best and are always preferred, irrespective of strength, for special purposes such as joining light woods, etc., where transparency is of paramount importance, but the only certain means of ascertaining the comparative strength of glue of any color is by a practical test.