The temperature controller not only permits the scientifically correct preparation of glue, preventing overheating and ruined work, but saves also in expense of supervision.
HEAT GLUE SLOWLY
Glue should be heated slowly, requiring about 30 minutes. Rapid heating dissolves the outer portions of the glue quickly, and a scum is then formed over the rest of the glue, preventing its proper melting.
The following precautions will be found useful to put into practice.
CLEANING THE MELTING POT
Dirt enters the melting-pot through the glue itself, the introduction of dirty brushes, or the exposure of the pot to dust, etc. If glue is melted in a dirty pot, the skin forming on the surface of the glue liquor gradually accumulates at the sides of the kettle and slowly decomposes. This may or may not fall into subsequent melts, thus contaminating them. The only way to make sure that it will not do so is to clean the pot.
Much unnecessary waste of glue may be avoided through observance of the following procedure. The contents of the melting-pot exhausted, scraps of dried glue, as well as scraps of partially dried jelly adhering to the sides should be detached mechanically, as thoroughly as possible, and examined. If clean, they may be replaced in the bottom of the kettle; if dirty, they are to be set aside temporarily.
In the first instance, they are covered with the minimum of water necessary to soften, and the sides of the kettle swabbed with a little water in order to soften any glue that has dried and has not been detached mechanically. The pot is then gently heated in order to bring the scraps into solution, this solution used in work, and the pot thoroughly washed out with hot water and cooled before soaking a fresh portion of glue.
If the scraps have proved dirty, but not sour, they may be kept warm enough to permit the dirt to settle, when the glue may be used without risk. If sour they must be thrown away. If the glue-pot is properly cleaned there is no danger of souring and all the glue may be used without waste.
It may be contended that much labor may be saved by adding sufficient water for the next melt, and through this means soften all glue adhering to the kettle in connection with that added fresh. It will be found, however, that the freshly added glue will absorb the bulk if not all of the water, leaving adhering scraps practically unsoftened, which in this way continue to accumulate, interfering with the proper working of the glue.