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Glue.—This is made, by boiling, from horns and bones; it is essentially the same as gelatine. It is the most generally known of all adhesives, and may be modified by certain admixtures to suit almost any substance. It has the peculiarity that it must always be boiled in a balneum mariæ, or in a kettle in hot water in another kettle. Its strength is vastly increased by admixture with nitric acid or strong vinegar. On the subject of glue in all its relations, the reader may consult Die Leim- und Gelatine-Fabrikation, or “The Manufacture of Glue and Gelatine,” by F. Dawidowsky; Vienna, price 3s.

Flour-Paste and Starch-Paste.—These mixtures, though generally used for weak work, such as to make papers adhere, can be very much strengthened by admixture with glue and gums. Combined with certain substances, such as paper, mineral powders, and alum, they, when submitted to pressure, become intensely hard, and resist not only water but heat, when not excessive. Also combined with varnishes they are decided resistants. Lehner speaks of them as if they were perishable in any condition.