(1) Harden right out, and then temper by flaring off in oil. If they are flat springs, a good way to harden them would be to get them red hot, and lay them on a fiat iron surface, covered with water, quickly bringing another piece of flat iron (of about 7 lb. in weight) down on top of it. This will prevent them warping. If they are curved or bent, this cannot be done. If bent, put them into water (or oil, which is better than water for small springs) edgewise. To produce a nice spring temper, place them in a .shallow sheet - iron dish, cover them with lard oil (this is important - mineral oils will not do), and hold them over the gas with a Bunsen flame until the whole of the oil has burned or flared away; then turn them out, and let them cool of themselves.
(2) First harden right out by making red hot, and cooling in water; then, to temper, have a bright, clear, arched fire, and move the spring to and fro in it until it is hot enough to scorch a stick or make sparks fly off a stick when rubbed along it, care being taken that it will do this all along the spring, and yet not be hot enough to set fire to the stick; then let it cool of itself.
(4) For long springs get a piece of 1-in. wrought - iron gas - pipe, put your spring inside, place the pipe in furnace. When hot enough, get hold of pipe with tongs, tip the pipe up over tank with oil or other tempering fluid in, and the spring will slip out into tank. If you have 2 or 3 pipes, you will temper over a gross per hour.