because it is heated beyond tempering. This mode of tempering tools is practical, and based on correct principles; but it requires care on the part of the blacksmith that he does not go beyond the colour which he intends to impart. The degree of hardness is tested by scratching the article with a file; but the test is uncertain, and shows merely if the hardening is too soft, but not if it is too hard.

Sometimes the tempering is performed by covering the steel with a film of oil or fat, and heating the steel until this oil or fat is inflamed. This is a very imperfect method, and cannot be depended upon; it generally makes the steel too soft. Small objects are very well tempered by putting the steel between the jaws of the fire-end of a pair of blacksmith's tongs, which are heated beyond the tempering point. As soon as the steel shows the desired colour, it is dropped in cold water. This is perhaps one of the most successful methods of tempering steel.

A somewhat scientific, but at present not much practised mode of tempering, is to heat the glasshard steel in a bath of fusible metal, kept at a certain heat, the objects being laid on an iron plate. This way is best adapted to temper knife-blades and saw-blades in masses; but we should hesitate to recommend it for general use.

CHARACTERISTICS OF STEEL.

The signs by which to distinguish good from bad steel are very difficult to describe; however, we shall endeavour to do so. If there is an opportunity of forging some of the steel, it is advisable to do so; for there is no better means of ascertaining its true nature. A bar is gently heated to cherry-red, and drawn out into a gradually tapering square point. The operative who performs this labour, if familiar with working in steel, will judge of the quality from the manner in which it forges. If it is cast-steel, it forges harder than any other; after this follows good German steel, then shear-steel, and at last blistered. steel. Hard wrought-iron is the softest. If the trial is performed, and cannot be depended upon for want of experience, the forged point is heated to cherryred, and cooled in cold water; if possible, ice or snow-water. After this hardening it is tried by a file, and, if it should be found to be soft, it may be concluded that it is either iron or German steel. It is then heated again to a higher degree of heat, and hardened; if it is not hard after this heat, which may be a white heat, it is iron. In either case, the steel is to have a uniform heat; for the thin point

will naturally be hotter than the thicker portions. The hardened point is then screwed between the jaws of a vice, and just enough broken off to show the fracture. The power used in breaking forms the rule by which to judge of the tenacity of the steel under trial. The broken point may be tried by crushing it under the face of a hardened hammer, when laid upon a dull but hard file. If the steel is good, it will resist the crushing, and will cut the hammer-face and the file. The degree of resistance of this grain of steel to the crushing power is the best rule by which to judge of it; for many kinds of steel feel hard to the file, and even cut glass, or other hardened steel, and yet show no tenacity. Here we find the true criterion of good cast-steel, and natural or German steel. The latter may be as hard as the first, but is never as tenacious when glass-hard. As tenacity in steel is of greater importance than hardness, it is an object to attend to this trial most carefully. Hard iron will be found to be easily ground to dust in the experiment. Some kinds of steel, particularly those which have been forged a great deal, or which never had much carbon, or in which other matters predominate over carbon, will not bear to be drawn into fine points. It may be quite strong when in large pieces, or even tenacious; but still it will

that is not sufficient. Steel which is really good will take a fine point, and be tenacious if not tempered, unless it has been overheated. If the steel will not take a point, it of course will not receive an edge, and is therefore useless for any of the finer articles of manufacture. The white crude steel-iron of the Germans is harder in a body than the hardest caststeel, or the hardest German steel; but it will not take a strong point, nor receive a fine, smooth edge.

The marks by which to know good steel, by sight, sound, or strength, are fallacious, and cannot be depended upon unless assisted by long experience; and even then the result is always uncertain. The fresh fracture of steel is of a silver-grey colour, inclining in many instances to white, particularly in shear and German steel. Certain kinds of cold-short wroughtiron have a similar appearance and bright fracture; but they are far from being steel.

Hardened, refined, or much-forged steel is always more bright in its fracture than cast, annealed, or tempered steel. The lustre of a fresh fracture in steel, however, is as uncertain as its colour. Phosphorus and silicon have the property of imparting a rich lustre to iron as well as steel, and hence the difficulty of distinguishing steel by this test. Hardened steel has more lustre than that which is tem

pered, and hammered steel more than that which is annealed. Cast-steel not hardened frequently shows a fracture similar to that of fine-grained cast-iron. Baltimore pig-iron has more the appearance of good cast-steel in its fracture, than many kinds of shea and natural steel.

TEXTURE.

The most characteristic feature of steel is its texture, or grain. The grain of good steel, when hardened or soft, is uniformly round when viewed through the microscope; no flickering of light, as if broken by the planes of small crystals, is visible. The fracture shows a velvety uniformity, of a more or less white colour, and of more or less lustre; but always of great regularity and uniformity; no spots which are more bright or more dull than others.

Good steel does not look like mottled cast-iron, or cold-short bar-iron. The fracture of good steel has the appearance of deadened silver; it is of a uniform colour, grain and lustre, with the entire absence of sparkling particles.