mon coke-dust. These ingredients should be perfectly mixed, and subjected to strong pressure in the potpress. A saving in fuel may be effected by making the pots of a conical form; but, on the other hand, they do not last so well if too much tapered, and the quality of the steel is also injured. The cylindrical form is the best for quality and durability; but these are obtained at a greater expense of fuel. Pots are generally of three and a half to four inches diameter at the bottom, and from four and a half to five inches at the top; the height varies from twelve to sixteen inches. It is not advisable to melt more than fifty pounds in one crucible at a time; the usual charge is but thirty or forty pounds. FLUX. The flux used to cover the melted steel, and protect it against the air and flame of the furnace, is glass-powder. It is not indifferent what kind of glass this powder is made of; glass which contains much iron, lead, arsenic, manganese, or, in fact, any metallic oxides, will not answer for the purpose, and should be carefully avoided. So also of crystal, crown, and coloured glass. What we require is a hard, strong, soda glass, such as is generally used for good window-panes; it is white when in thin sheets. but assumes a light-green appearance as it increases in thickness. A flux is not absolutely necessary if the pot-covers fit well; indeed, if good glass cannot be bai̟ it is better to use none at all. Any other fax, such as potash, soda, or glass compositions, must be scrupulously avoided; they are all positively injurious to the steel. We have said enough to show the importance of providing good pot-covers. How long a pot should be exposed to heat, is not very easy to say. If the steel is not very fluid, it may require five or six hours before the operation can be completed; and if so, the steel will not be good. In Sheffield, from three to four and a half hours is considered sufficient. Steel which melts in less than three hours is brittle, and not strong. A perfectly limpid, and not a slimy, pasty state of the liquid steel, is necessary, and should continue at least a quarter or half an hour, under repeated stirring. The mould after casting is covered with fine sand or clay, to protect the hot steel from the air. TILTING OF STEEL Is one of the most important operations in the manufacture. Good tilting improves the steel, while imperfect work degrades it. Experience is the only safe guide here. The force-hammers should strike in rapid succession, even if the blow is slight. The degree of heat in the bars varies according to the quality of the steel; cast-steel bears the least, and natu ral steel the highest heat. Too hot or too cold tilting makes the steel brittle. CHAPTER VI. NATURE OF STEEL. HARDNESS. WHEN heated to redness and suddenly plunged into cold water, or suddenly cooled in any other way, steel becomes hard-so hard, if of good quality, as to scratch glass. The degree of hardness depends not only on the quality of the steel, but also on the degree of heat to which it has been exposed, the medium in which it is cooled, and the manner in which that cooling is performed. FINE CAST-STEEL Is susceptible of a high degree of hardness, almost equal to that of the diamond; but it is then too brittle to be of practical use. Shear-steel is less hard, if hardened in the same manner as cast-steel, and is still more brittle. Spring-steel is not capable of so great a degree of hardness as either of the above varieties, and, if manufactured from hot-blast or impure iron, is very brittle. GERMAN STEEL Is frequently found to be very hard and tenacious, equal to good cast-steel; but the quality of German steel is so irregular, that no dependence can be placed upon it. We frequently find very hard and tenacious steel, and very soft and brittle steel, in the same bar of but a few feet long. We often also find fibrous iron and good steel in the same fracture of a bar. The hardest iron or steel known is the white cast-iron or steel-iron of Germany, of which German steel is made. It is, however, so brittle when hardened, that it will not serve for any practical purpose. Some kinds of wrought-iron may also be hardened, but the metal is never sufficiently tenacious to assume a fine edge; for the edges formed of it are so brittle as to break when exposed to slight pressure. The hardness as well as the nature of steel are greatly affected by exposure to too much or too little heat. A dark cherry-red heat is sufficient to give to |