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PROPERTIES OF STEEL,

Remark. ..There are several varieties of this iron arisingfrom the intermixture of other substances. There is one kind offorged iron, which,'when cold, possesses ductility; but whenheated, is extremely brittle; it is also fusible: this is termedhot short iron. Another variety, the cold short iron, possessesprecisely the opposite properties, being highly ductile while hot,but when cold extremely brittle. The causes of these peculiaritieshave not perhaps been perfectly explained. Chemists are gene-rally agreed that the property of cold short iron depends on thepresence of a .substance termed siderite, once considered as apeculiar metal, but now known to be a compound of phosphoricacid and iron : that of hot short iron has been ascribed to theintermixture of arsenic, Sulphur, or sulphureous acid, but thereal cause is not well ascertained.

. PROPERTIES OF STEEL.

Steel is of a light grey colour; its fracture is finely granulated,and brilliant, and it is susceptible of a very' high polish. It isfusible by itself. It is both ductile and malleable, and u-henhammered, has a specific gravity greater than that of iron. Theproperty by which it is eminently distinguished is, that ofacquiring a degree of hardness by being hastily immersed in coldwater when red hot; the hardness being proportioned to theheat of the steel, and the coldness of the water. This is what istermed tempering of it, the requisite degree of hardness beinggiven by attending to the degree of heat which the metal acquires,and suffering it to cool accordingly. It may be made so hard asto scratch glass, and at the same time it becomes more brittleand elastic. Steel thus hardened may have its softness and duc-tility restored to it, by again heating it, and suffering it to coolslowly. '

The colours which a polished piece of steel acquires by beingheated with access of air, are far brighter than those with which