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To Temper Old Files

Grind out the cuttings on one side, until a bright 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 is the operation of giving a surface of steel to pieces of iron, tion of the prussiate, as in the last receipt, any part of a piece of iron may be case-hardened, without interfering with the rest. 3302. Improved Process of Hardening Steel. Articles manufactured of steel by which they are rendered capable of receiv- for the purposes of cutting, are, almost withing great external hardness, while the interior out an exception, taken from the forger to the portion retains all the toughness of good hardener without undergoing any intermewrought-iron. This is accomplished by heat- diate process; and such is the accustomed ing the iron in contact with animal carbon, in routine, that the mischief arising has escaped 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 observation. The act of forging produces a strong scale or coating, which is spread over the whole of the blade; this scale or coating is unequal in substance, varying in proportion to the degree of heat communicated to the steel in forging; it is almost impenetrable to the action of water when immersed for the purpose of hardening. Hence it is that different degrees of hardness prevail in nearly thickness of a half dime; in an hour, double; every razor manufactured; this is evidently a and so forth, till the desired depth is acquired. positive defect; and so long as it continues to The box is then taken from the fire, and the exist, great difference of temper must exist contents emptied into pure cold water. They likewise. Instead, therefere, of hardening can then be taken out of the water and dried the blade from the anvil, let it be passed im- (to keep them from rusting), by riddling them mediately from the hands of the forger to the in a sieve with some dry saw-dust; and they grinder; a slight application of the stone will are then ready for polishing. Case-hardening remove the whole of the scale or coating, and is a superficial conversion of iron into steel. the razor will then be properly prepared to It is not always merely for economy that iron undergo the operation of hardening with adis case-hardened, but for a multitude of things vantage. It is plain that steel in this state it is preferable to steel, and answers the pur- heats in the fire with greater regularity, and pose better. Delicate articles, to keep from that, when immersed, becomes equally hard blistering while heating, may be dipped into from one extremity to the other. To this may a powder of burnt leather, or bones, or other be added, that, as the lowest possible heat at coaly animal matter.