Temperature of the Metal.
It is essential that the temperature of the metal should be kept uniform. If the temperature is too high, porous or spongy slugs will result, also defective faces and a weak surface, which allows the letters to sink in printing.
A temperature that is too low causes the metal to adhere to the mouthpiece and prevents the free flow of the metal to the mold.
We recommend that the metal in front of the well be kept at a temperature anywhere between 536 and 563 degrees Fahrenheit. The temperature can be kept uniform by means of the gas governor attached to each machine, and can be supplemented by a gas pressure governor attached to supply pipe. (See Fig. 10.)
The temperature can be ascertained by plunging a thermometer reading up to 600 degrees Fahrenheit into the molten metal in front of the well and readings taken when the mercury remains constant. Heat the thermometer before plunging it into the metal. The bulb should be wholly covered by the molten metal.
When no thermometer is at hand the temperature may be obtained approximately by plunging a piece of paper into the molten metal. If it turns brown the metal is in a proper condition to cast. The temperature is too low if only a slight color is imparted to the paper; too high if a deep brown or black.
No other metal, such as brass, zinc, or stereotype metal should be mixed with linotype metal. It has been found that better results are obtained if the slugs are melted in a proper furnace and cast into ingots or blocks.
The pot will be kept more free from dross by this method than by melting the slugs in the metal pot of the machine.