Figure 57.
How to Temper Mainsprings.—If it be a single spring that is to be tempered, heat it carefully or evenly in a fire that is well burned to free it from sulphur, or preferably in a charcoal fire, and when at a light-red heat, harden by plunging it in any animal oil. An iron pan may be used to contain the oil, and any refuse or poor oil that may collect may be used. Lard oil is good, but if oil be wanting, use common lard or even tallow. If hard, melt before using.
Figure 58.
To temper the spring, remove from the oil, and hold it all dripping with the oil over a clear fire until the oil takes fire and blazes off. It is best to dip it in the oil and blaze off the second time.
Figure 59.
If there are a number of springs enclose them in a piece of gas pipe to heat them, and when hot, turn them into the oil. To temper, remove them, put them in an old wrought-iron frying pan, add a little oil, heat the pan over the fire, shaking it in the meantime, until the oil takes fire and blazes off. Let the work cool without putting it in water or oil.
Figure 60.