A good practical test for glue is to soak it in water till it swells and becomes jelly-like.

The more it swells without dissolving the better the quality.

Poor glue dissolves.

Glue is sometimes bleached, becoming brownish white in color, but it is somewhat weakened thereby.
Fish glue is made from the scales and muscular tissue of fish.
Isinglass is a sort of glue made from the viscera and air bladder of certain fish, as cod and sturgeon.
Liquid glue may be made either from animal or fish glue.

The LePage liquid glue is made in Gloucester, Mass., one of the greatest fish markets in the country.