The New Haven Clock Company heat their springs in a furnace burning wood, the springs being kept in the flames only, and quenched in a composition of the following proportions:—“To a barrel of oil 10 quarts of resin and 12 quarts of tallow are added.”
If the springs “fly,” that is, break, more tallow is added, but if the fracture indicates brittleness or granulation of the steel, rather than excessive hardness, a ball of yellow beeswax, of about 6 inches in diameter, is added to the above.
These springs are tempered, singly, to a reddish purple by being placed on a frame having horizontally radiating arms like a “star,” which is attached at the end of a vertical rod. The spring is laid on the “star” and lowered into a pot of melted lead, being held there a length of time dictated by the judgment of the operator.
The star-shaped frame is termed a sinker, and if upon being lifted from the lead the colour of the spring is too high, a second immersion is given.