Hardening Liquids
If water is used for hardening, 32 deg. F. will be found about right for the sized articles hardened by watchmakers, and if the article is very small, ice may be added to the water. A solution composed of 1 quart of water, 1 1/4 lbs. of sal-ammoniac, 10 oz. of refined borax, 1 1/4 ozs. red wine, is used extensively for fine cutlery. A mixture of 1 lb. of resin, 3 ozs. of lard, 1/2 lb. train oil and 1/2 oz. of assafoetida is said to be excellent for fine steel work.
Directions for Plunging when Hardening. Thin articles, as steel plates, or articles of small diameter, such as drills, should always be plunged into the hardening compound, end or edge foremost to avoid warping. If an article is thicker on one side than the other, as a knife blade, the thick side should enter the compound first. Heat the article only as far as you wish to harden it and immerse it as far as it has been made red hot. Tempering by Electricity. Watch springs have of late years been successfully tempered with the aid of electricity. The steel ribbon is passed through a bath of oil and an electric current of sufficient strength to keep it at the proper heat is passed through the ribbon. The heating is thus effected without contact with the atmosphere and the spring is not liable to blister as in ordinary methods. The temper is drawn in the same manner and the heat can be controlled to a nicety and is uniform throughout. The spring is then finished by means of rolls.
Glass Polisher for Steel. French plate glass, ground on one side, makes a good polisher for flat work. A piece four inches square, nicely finished on the edge, is about the right size.