days for conversion, are not profitable; because the charcoal cement works but for a certain time in a certain heat, and all additional time and heat is useless waste. Bars which require more carbon than can be given to them in a week's time, like those for cast-steel, had better be converted a second time with fresh cement.

THE FIRING OF A FURNACE

Is to be conducted with intelligence, particularly at a large establishment. Too rapid firing not only injures the furnace and boxes, but exhausts the cement before the iron is sufficiently heated to absorb the carbon thus liberated. The cement or charcoal is a very bad conductor of heat; and the heat of the most intense fire would scarcely reach the centre of the box before that of a more moderate character. Two or three days are required before a cherry or bright-red heat is given to the boxes; and after this it is gradually increased to a white heat, which is kept up regularly and constantly without diminution until the operation is finished.

Small furnaces require four or five days and nights -large ones, from that to ten days. The kind of fuel has some influence on the time of conversion.

Anthracite appears to be the best fuel; and bituminous coal is superior to wood.

A good steel-maker knows pretty nearly when a heat is done, if he is acquainted with his materials. To assist his judgment, the trial-bars are drawn when he thinks the process has been completed. These bars may be either of the whole length of the box, or but two or three feet long; the iron is to be of the same quality as the other iron in the box. The breakage of the bar will of course show whether the whole of the metal has been converted into steel, or whether a core of iron is left in the centre. If the latter should be the case, the heat is continued until another trial shows a sufficiency of carbon throughout the bar. Spring-steel may be good enough for the purposes for which it is used, even if it has an iron core in the centre; but the other varieties of steel, such as that for saw-blades, shear-steel, millsteel, &c., are of but little value unless thoroughly cemented. Blistered steel, to be suitable for conversion into cast-steel, must have an abundant supply

of carbon.

CLOSING OF A HEAT.

When the conversion is sufficiently advanced, the furnace doors are closed, the chimney-top and the flues in the arch stopped up, and the furnace left to cool, which will require from two to five days, or half as long as the conversion. If the furnace is cold, or so far cooled as to admit of the entrance of a man, the doors and flues are reopened, and the workmen remove the converted bars. The size and form of the blisters on the surface show very nearly the kind of iron used, and the quality of the steel made from it. The best steel shows small blisters of uniform size; coarse and imperfect iron shows both small and large blisters in great profusion; a sound iron has but few blisters, and those of a large size; coarse fibrous or puddled iron shows hardly any blisters. Blistered steel, on coming from the chest, if well converted, is very brittle; if strong, it generally contains iron; but there is no rule to be depended on: short iron makes short steel, even if imperfectly converted. The produce of a box, if designed for caststeel or refining, is assorted according to the size of its crystals in the fracture, and laid by for either the one or the other purpose.

THE TILTING OF STEEL,

As described in Chapter IV., has been sufficiently explained, and requires no addition here. Steel for springs and saw-blades, if made directly from blistered steel, is rolled like sheet-iron, and not subjected to tilting or refining. A few remarks, however, are needed in reference to the chemical characteristics of cast-steel.

CAST-STEEL.

In former years, many experiments were made by Europeans, and in America also, to make cast-steel in a more simple way, with the hope of avoiding the converting process. It was thought that cast-steel could be made directly from the iron, without resorting to the use of blistered steel. These experiments, however, have utterly failed, and are now scarcely thought of. We will enumerate some of them as a matter of curiosity: The melting of wrought-iron together with carbon, or lampblack; the melting of protoxide of iron with lampblack; protoxide of iron and

grey cast-iron; and the melting of pure wroughtiron. These experiments were so erroneous in prin.

ciple, that success can hardly have been expected. Even if this were not so, the practical difficulties are so great, as to render success almost impossible. If too much carbon were used, the product would be cast-iron; if too little carbon, we should have wrought-iron; and if the admixture were precisely correct, the burning of a part of the carbon, which would be almost unavoidable, would destroy or injure the steel.

The inexperience of some metallurgists, inducing them to pronounce hard brittle wrought-iron to be steel, has been the cause of many errors. Some of these learned men insisted upon making good steel by melting grey and white cast-iron together, or, as before remarked, grey cast-iron and wrought-iron; or carbon, plumbago, or diamond dust, together with wrought-iron. All these and numerous other experiments show that the nature of steel never was understood by these men. They assumed that any iron combined with a certain amount of carbon would make steel, which is not true. They did not discriminate between pure and impure wrought-iron-did not know that most iron is too impure ever to make steel. How absurd to recommend the melting of volatile carbon and refractory wrought-iron together! Even if the iron is of pure quality, it is almost im