3292. Bath for Hardening Mill Picks

3292.    Bath for Hardening Mill Picks. Take 2 gallons rain water, 1 ounce corrosive sublimate, 1 of sal-ammoniac, 1 of saltpetre, 11 pints rock salt. The picks should be heated to a cherry red, and cooled in the bath. The salt gives hardness, and the other ingredients toughness to the steel; and they will not break, if they are left without drawing the temper.

3293. Composition for Tempering Cast - Steel Mill Picks

3293.     Composition for Tempering Cast - Steel Mill Picks. To 3 gallons of water, add 3 ounces each nitric acid, spirits of hartshorn, sulphate of zinc, sal-ammoniac, and alum; 6 ounces salt, with a double handful of hoof-parings; the steel to be heated a dark cherry red. It must be kept corked tight to prevent evaporation.

3294. Tempering Steel

3294.    Tempering Steel. Mr. N. P. Ames, late of Chicopee, Mass., after expending much time and money in experiments, found that the most successful means of tempering swords and cutlasses that would stand the United States Government test, was by heating in a charcoal fire, hardening in pure spring water, and drawing the temper in charcoal flame. (See No. 3285 (Tempering Tools).)

3295. To Straighten Hardened Steel

3295.    To Straighten Hardened Steel. To straighten a piece of steel already hardened and tempered, heat it lightly, not enough to draw the temper, and you may straighten it on an anvil with a hammer, if really not dead cold. It is best, however, to straighten it between the centres of a lathe, if a turned article, or on a block of wood with a mallet. "Warm, it yields readily to the blows of the mallet, but cold, it would break like glass.

3296. To Restore the Power of Horseshoe Magnets

3296. To Restore the Power of Horseshoe Magnets. To restore horseshoe magnets that have lost their power from disuse, proceed as with new ones. Place the poles of the magnet to be charged, against the poles of another, making opposite poles meet. Then draw a piece of soft iron, placed at right angles upon the magnet to be charged, from the poles to the bend. Do this a number of times on each side of the magnet. If the magnet is of good steel, this produces a maximum power. It is the method of Jacobi, and is considered one of the best.

3297. Case-Hardening

3297.     Case-Hardening is the operation of giving a surface of steel to pieces of iron, by which they are rendered capable of receiving great external hardness, while the interior portion retains all the toughness of good wrought-iron. This is accomplished by heating the iron in contact with animal carbon, in close vessels. George Ede says: - The articles intended to be case-hardened are put into the box with animal carbon, and the box made air-tight by luting it with clay. They are then placed in the fire and kept at a light red heat for any length of time, according to the depth required. In half an hour after the box and its contents have been heated quite through, the hardness will scarcely be the thickness of a half dime; in an hour, double; and so forth, till the desired depth is acquired. The box is then taken from the fire, and the contents emptied into pure cold water. They can then be taken out of the water and dried (to keep them from rusting), by riddling them in a sieve with some dry saw-dust; and they are then ready for polishing. Case-hardening is a superficial conversion of iron into steel. It is not always merely for economy that iron is case-hardened, but for a multitude of things it is preferable to steel, and answers the purpose better. Delicate articles, to keep from blistering while heating, may be dipped into a powder of burnt leather, or bones, or other coaly animal matter.