man knows by the bearing of his steel under the hammer what degree of heat is most suitable for the kind of steel under his management, and will harden and temper according to his own convictions.

DAMASCUS STEEL.

To imitate or make Damascus steel in the forge by welding together steel and iron which has been bound in fagots, or any other form composed of thin rods, is an experiment generally attended with but ill success. The quality of steel, as we shall explain hereafter, depends so much upon the quality of the ore and iron from which it is made, as not to offer any hope of success in the attempt to make good steel in the forge. Damascus gun-barrels are made by welding strips of iron and steel together; but in hardening such compositions, the advantages are small in respect to tenacity, and the loss is considerable in hardness.

Gun-barrels, which are of course not hardened, are certainly superior when made in this way to those forged in any other manner; but this is not the case with edged instruments. A kind of Damascus steel for weapons is still imitated by some French cutlers;

but it is so expensive a process, and the blades are so slightly, if at all, superior to those of the ordinary manufacture, that this is more of a curiosity than anything else.

CASE-HARDENING

Is that process by which the surface of iron is converted into steel. This is a very useful art, and deserves to be more cultivated than it is at present. In this process, the surface of iron may be made harder than the hardest steel, and still retain all its malleability. Steel, when hardened, is brittle, and tools or keys of steel are liable to break. If casehardened, however, they combine all the advantages of steel and iron.

The articles to be case-hardened are to be well polished; and if the iron is not quite sound, or shows ash-holes, it is hammered over and polished again— the finer the polish, the better. The articles are then imbedded in coarse charcoal powder, in a wrought-iron box, or pipe, which should be air-tight. A pipe is preferable to a box, because it can be turned, and the heat applied to it more uniformly. The whole is then exposed for twenty-four hours to a gentle cherry-red heat, in the flue of a steam-boiler,

or in some other place where the heat is uniformly kept up. This makes a very hard surface, and, on large objects, one-eighth of an inch in depth may be thus obtained. If so much time cannot be given to the operation, and no deep hardening is required, the articles are imbedded in animal charcoal, or in a mixture of animal and wood coal; four or five hours' heat will make a good surface of steel. If a single article, a small key, or any other tool, is to be hardened, the coal must be finely pulverized, and mixed into a paste with a saturated solution of salt; with this paste the iron is well covered and dried. Over the paste is laid a coating of clay, moistened with salt water, which is also gently dried. The whole is now exposed to a gradually increased heat, up to a bright red, but not beyond it. This will give a fine surface to small objects. In all cases, the article is plunged in cold water when heated the proper time, and up to the proper degree.

A quick mode of case-hardening small objects is that by prussiate of potash. The iron is well polished, and heated to a dark-red heat; it is then rolled in a box containing powder of the yellow prussiate of potash, or sprinkled with it; the powder will melt on the surface, and the iron is then heated to a bright-red, and plunged in cold water. The powder

of the prussiate is obtained by exposing the crystals to a gentle heat in an open iron box, or pot, for the purpose of evaporating the water contained in them; the remainder is a white powder. Some persons recommend the mixing of one-third camphor with the prussiate. As the camphor melts at a lower heat than the prussiate, and causes it also to melt, the whole operation can be performed at a lower heat, which is certainly an improvement. Calcined borax has also been proposed to be mixed with the prussiate; but we do not know with what effect it operates. To mix prussiate in clay, as recommended by some, is not of much use, as it requires too much labour to put the clay around the article; in these cases, the above recipe of coal, salt and clay, is all-sufficient.

In the operation of case-hardening there is not the slightest difficulty; any degree of hardness may be given, and almost any depth. The addition of salt, bone-ashes or bone-black, animal charcoal, hoof, horn or leather, to the charcoal powder, will regulate the degree of hardness; and the time of its exposure to the action of heat must be governed by the depth of steel required.

While the performance of the operation is simple, it is not so easy to select the proper kind of iron. If the iron is of coarse fibre, the hai lened and pol

ished surface will be unsound; if it is impure, it will be brittle after being hardened. The surest way is to select a very fine, close-grained iron, heat a piece of it a little beyond the heat by which it is to be hardened, and plunge it into cold water. If it retains its fibre and malleability, and is free from ashholes, it may be selected as fit for the purpose.

Edges, however hard they may be, are never good if made of case-hardened iron; it is not in the nature of the materials, nor of the process, to produce such a result.

The most expeditious method of case-hardening is to imbed the article in borings of grey cast-iron, in a sheet-iron box, which may be open at the top, and covered with fine dry sand. These borings are a better conductor of heat than charcoal, and the article is therefore very soon covered with a coating of steel. A very little salt may be added to the borings; or a mixture of borings, charcoal, bone-coal, animal coal, scraps of horn, hides, leather, and other materials of the kind, may be used to advantage.