TEST OF THE QUALITY OF STEEL.

The indications by which we distinguish good from bad steel are difficult to describe. Blistered steel, when the blisters are uniform in size, may generally be considered as of the best quality. Where there are but few blisters, and those of an irregular size, we should pronounce the steel of an inferior description. Natural steel, German steel, and shear and cast-steel, are always bad if single sparkling crystals show themselves in a fresh fracture. Generally speaking, any sparkling steel is bad; it is merely hard, impure iron. Good hardened steel, on fracture, presents a dead silvery appearance, and is of a uniformly white colour; in soft shear-steel, the fracture has a bluish tint; and in soft cast-steel, it is of a greyish hue. In German and natural steel, the fracture has a soft bright grey tint, often inclined to fracture in the centre of the bar.

THE HARDENING OF STEEL

Is an operation which requires the exercise of some judgment. The usual method is to heat the steel to a certain point, and then plunge it suddenly

into cold water, tempering it afterwards. This method is undoubtedly the correct one; but the degree of heat to which steel is to be exposed before cooling, is a matter of vast importance. Some steel — the natural, for instance—will bear a strong white heat, and a plunge into cold water, before it assumes its greatest hardness. Other steel, particularly fine cast-steel, will not bear more than a brown or cherryred heat; beyond that point it burns, and becomes brittle in hardening. It may safely be concluded, that steel which does not bear heat in forging, will not bear it in hardening. The heat at which steel falls to pieces, or melts, is too high for hardening, as steel hardened in such heat will fly or crack. The alterations manifest in steel after hardening, as compared with annealed steel, are the following:-Its volume is a little increased; the black scales which adhere to its surface fly off, and the surface appears clean, and of the colour and lustre of iron; the fracture is brighter, and crystals are visible. Good steel, as we have said before, is silver-white, and is so hard that it will scratch pane-glass, and even a file. The cohesion, relative and absolute, is increased if the heat has not been too high before cooling. These are the chief characteristics of good steel, when hardened.

The phenomenon of hardening by sudden cooling is not peculiar to steel; it belongs to all the alloys of metals, but is perhaps more characteristic of iron. There is not a bar of puddled iron in market which does not show all the phenomena of hardening and tempering as clearly as they are perceived in steel. Most of the charcoal wrought-iron, particularly the hot-blast, shows the same phenomena. There is no difference in kind, but in degree.

None but the best and purest charcoal wroughtiron is uninjured after cooling. It is a true test of the quality of pure fibrous iron, if a bar, heated to the welding-heat, and suddenly plunged in cold water, does not harden or become brittle. Most of the bariron, on subjection to such a process, becomes as brittle as glass, and presents the appearance of an accumulation of crystals, without apparent connection. Such iron may be made more fibrous and strong by being fagoted, welded, and drawn.

The assertion of some writers and artisans that any iron which hardens by cooling is to be considered steel, is unfounded in reality; for every variety of iron in the market has this property. It is the tenacity and fine grain, or rather absence of grain, which distinguishes hardened steel from hardened iror Bar-iron, hardened, does not derive much

strength from tempering; while steel, on the other hand, does so to a high degree.

While it is true that bar and wrought-iron are very sensitive to the process of cooling, it is so in a far higher degree with cast-iron. This description of metal, if suddenly chilled, becomes, in most cases, so highly excited as to crack, or fly. The hardest castiron, if pure, may be converted into malleable iron, almost equal to wrought, by judicious tempering. Such tempered cast-iron, however, cannot be welded; it becomes brittle again if heated, and cooled in the air. Slow tempering, however, will restore such rehardened cast-iron to its malleable condition. The best and purest varieties of cast-iron become so excessively hard on refrigeration, that the finest caststeel, in its hardest condition, can be scratched by it; but this hardened cast-iron is very brittle in its smallest particles, and flies to pieces when in large

masses.

It is not possible to give any distinguishing mark between steel, wrought-iron, and cast-iron. A chemical test is even inadmissible. As a general feature, however, we may say, that cast-iron cannot be forged or welded, or at least very imperfectly; that wrought-iron feels softer under the hammer than steel, in forging; and that both impure wrought and cast

iron become very brittle in hardening. The united hardness and tenacity of steel are its characteristics. Good cast-steel, or any other variety, if not freshly annealed or hardened, and if free from fissures, will emit a sonorous silvery tone when a suspended bar is struck. Iron, particularly if good, emits a dull, leaden sound; while cast-iron gives out a tone like that of a cracked instrument.

Steel is superior to wrought or cast-iron in all the characteristic qualities of that metal; it is stronger, tougher, harder, and more elastic than either cast or wrought-iron indeed, it is iron in its highest perfection.

TEST OF STEEL.

The surest test of the quality of steel is to draw a rod into a tapered point, harden it by a gentle heat, and break off pieces from the point. The degree of resistance to the hammer, which of course should be a very small one, is the test of the value of the steel. The best steel is that which, under this treatment, is found to be the toughest and strongest.