USE A THERMOMETER
The only safe procedure in melting glue is to use a thermometer. If glue is melted in an open pot, or one in which the contents of the glue chamber can be reached easily, an ordinary drop thermometer, encased in a frame for protection, may be used.
It is preferable, however, to have the thermometer a part of the apparatus, with the mercury tube extending into the glue chamber. In this way it is easy to keep watch on the temperature of the glue mass at all times.
An improvement even on this method is found in the automatic temperature controller that may be had with some glue-melting appliances, by which the supply of heat is automatically regulated. When the temperature in the glue chamber passes 150° F.—the absolute maximum of safe temperature—the valve automatically closes and shuts off the heat, re-opening again when the temperature has lowered from 5° to 10°. By the use of the automatic temperature controller the temperature is kept at the proper point, and there is no necessity of making observations with the thermometer except to verify your controller.
The temperature controller not only permits the scientifically correct preparation of glue, preventing overheating and ruined work, but saves also in expense of supervision.