ALWAYS SOAK GLUE IN COLD WATER BEFORE MELTING
The function of soaking is to get back into the glue the liquid it originally contained.
Soaking in cold water gets the glue into proper condition to dissolve readily when heat is applied. If glue is soaked in warm water, or if melted without soaking, the glue on the outside will dissolve at once, and this will coat the remainder with a film, so that it will not readily dissolve, except when heat is applied in a degree that is harmful.
Glue has an affinity for cold water. Good glue will absorb from 1½ times to 2½ times its weight of cold water.
If glue is in flakes or strips, break up into small pieces. Soak the pieces from 10 to 12 hours in cold water. Soak ground glue 1 to 4 hours in cold water. Naturally the thinner the glue the less time required for thorough soaking. The glue should be soaked through thoroughly and not merely moistened on the outside. You can determine whether the soaking has been completed by breaking a piece in two and noting conditions at the centre. If pieces are permitted to stick out beyond the level of the water, the natural result is that such pieces will be only partially softened. As the melting proceeds, these will slip to the bottom of the kettle, and in order to melt them long heating and high temperature are required. This means damaging the strength and adhesiveness of the glue.
In soaking ground glue it is a good plan to keep stirring as the glue is added to the water in the soaking vessel, as this helps to keep the fine particles of glue immersed in the water, instead of floating on the top. This is true also of thin-cut, high test glues.