ANIMAL AMIDES. 



Glue, This well known substance has been long manufac- 

 tured in most countries, and employed to cement pieces of wood 

 together. It is extracted by water from animal substances, and 

 differs in its qualities according to the substances employed. 

 Bones, muscles, tendons, ligaments, membranes, and skins, all 

 yield it ; but the quality is best when skins are employed ; and 

 those of old animals yield a much stronger glue than those of 

 young animals. English glue is considered as the best, owing 

 to the care with which it is made. The parings of hides, pelts 

 from furriers, the hoofs and ears of horses, oxen, calves, sheep, 

 &c. are the substances from which it is extracted in Britain, and 

 quantities of these substances are imported for the purpose. 

 They are first digested in lime-water to clean them, then steeped 

 in clean water, laid in a heap till the water runs off, and then 

 boiled in brass caldrons with pure water. The impurities are 

 skimmed off as they rise ; and when the whole is dissolved, a lit- 

 tle alum or finely powdered lime is thrown in. The skim- 

 ming having been continued for some time, the whole is strained 

 through baskets, and allowed to settle. The clear liquid is gently 

 poured back into the kettle, boiled a second time, and skimmed 

 till it is reduced to the proper consistency. It is then poured 

 into large frames, where it concretes on cooling into a jelly. It 

 is cut by a spade into square cakes, which are again cut by 

 means of a wire into thin slices ; these slices are put into a kind 

 of coarse net- work, and dried in the open air.* The best glue is 

 extremely hard and brittle ; it has a dark brown colour, and an 

 equal degree of transparency without black spots. When put 

 into cold water, it swells very much, and becomes gelatinous, but 

 does not dissolve. When glue is soluble in cold water, it is a 

 proof that it wants strength. Dry glue, according to Dr Bos- 

 tock, contains 10^ per cent, of water.f 



Size. This substance differs from glue in being colourless 

 and more transparent It is manufactured in the same way, but 

 with more care ; eel skins, vellum, parchment, some kinds of 

 white leather, and the skins of horses, cats, rabbits, are the sub- 

 stances from which it is procured. It is commonly inferior to 

 glue in strength. It is employed by paper-makers to give 



* Clennell. See Johnson's History of Animal Chemistry, i. 315, 

 j- Nicholson's Jour. xxiv. 7* 



