3298. To Case-Harden with Charcoal

3298.   To Case-Harden with Charcoal. The goods, finished in every respect but polishing, are put into an iron box, and covered with animal or vegetable charcoal, and cemented at a red heat, for a period varying with the size and description of the articles operated on.

3299. Moxon's Method of Case-Hardening

3299.    Moxon's Method of Case-Hardening. Cow's horn or hoof is to be baked or thoroughly dried, and pulverized, in order that more may bo got into the box with the articles. Or bones reduced to dust answer the same purpose. To this add an equal quantity of bay salt; mix them with stale chamber-lye, or white wine vinegar; cover the iron with this mixture, and bed it in the same in loam, or enclose it in an iron box; lay it on the hearth of the forge to dry and harden; then put it into the fire, and blow till the lump has a blood-red heat, and no higher, lest the mixture be burnt too much. Take the iron out, and immerse it in water.

3300. To Case-Harden

3300.    To Case-Harden. Make a paste with a concentrated solution of prussiate of potash and loam, and coat the iron therewith; then expose it to a strong red heat, and when it has fallen to a dull red, plunge the whole into cold water.

3301. To Case-Harden Polished Iron

3301.   To Case-Harden Polished Iron. The iron, previously polished and finished, is to be heated to a bright red and rubbed or sprinkled over with prussiate of potash. As soon as the prussiate appears to be decomposed and dissipated, plunge the article into cold water. When the process of case-hardening has been well conducted, the surface of the metal proves sufficiently hard to resist a file. The last two plans are a great improvement upon the common method. By the application 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

3302.    Improved Process of Hardening Steel. Articles manufactured of steel for the purposes of cutting, are, almost without an exception, taken from the forger to the hardener without undergoing any intermediate process; and such is the accustomed routine, that the mischief arising has escaped 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 every razor manufactured; this is evidently a positive defect; and so long as it contiuues to exist, great difference of temper must exist likewise. Instead, therefere, of hardening the blade from the anvil, let it be passed immediately from the hands of the forger to the grinder; a slight application of the stone will remove the whole of the scale or coating, and the razor will then be properly prepared to undergo the operation of hardening with advantage. It is plain that steel in this state heats in the fire with greater regularity, and that, when immersed, becomes equally hard from one extremity to the other. To this may bo added, that, as the lowest possible heat at which steel becomes hard is indubitably the best, the mode here recommended will be found the only one by which the process of hardening can be effected with a less portion of fire than is, or can be, required in any other way. These observations are decisive, and will, in all probability, tend to establish in general use what cannot but bo regarded as a very important improvement in the manufacturing of edge steel instruments.