cut and melted in a high cupola furnace with a certain proportion of pure cast-iron. The fuel must be of good quality. The resulting highly carburized steel, or rather white metal, is then further purified in a Bessemer converter. This last operation is somewhat difficult, on account of the small proportion of carbon and silicon in the material used; nevertheless the material has been fined twice, and the process is a step in the right direction for using inferior materials, the low cost of which allows of more extended manipulations.

We now pass to the methods by which carbon is added to wrought-iron. First in importance is that by cementation and fusion, already described in this work. We shall simply remark that it presents all the features necessary for the production of a perfect steel, provided, however, that the wrought-iron used is of good quality, and the operation is well performed. In this case, the metal has been fined until it cannot be fined any more, that is, until it has become wrought-iron. A good cementation imparts to it the proper proportion of carbon, and the fusion in pots renders it thoroughly homogeneous, and separates the small proportion of cinders and other impurities that had not been removed by the hammer or rolls.

Lastly, wrought-iron, cut into fragments, is melted in pots with a certain proportion of charcoal, part of which

combines with the metal, while the remainder is burned by the gases which penetrate the pot from the fire-place. Peroxide of manganese is generally added to the mixture, and, as its action is complex, we shall devote, further on, a special paragraph to this substance. This method is extensively followed, and requires a good wrought-iron, since there is.very little fining. It is open to the objection that the percentage of carbon in the steel, and therefore its hardness, is variable, since the crucible covers only fit more or less closely, and allow of the burning of a greater or less proportion of the carbonaceous material. This inconvenience is not so great with cemented steel, because the carbon is already combined with the metal, and is not so easily burned off as wood charcoal.

Cast steel has also been made from puddled steel, by simple fusion in pots. The metal becomes more homogeneous, but there is little further fining, and if the raw material is impure, the product is also impure.

We see, from what precedes, that under the name of cast-steel, many qualities of metal may be found, differing in purity, hardness, and tenacity.

Homogeneous metal, a newly coined name, is a low kind of steel, with a very small percentage of carbon. It is often quite impure; but, as it has been obtained by fusion, its quality is the same throughout. It is homogeneously good, bad. or indifferent, according to the nature of the raw

material used. Many kinds of so-called "Bessemer steel rails" are nothing more than homogeneous metal. In fact, when impure pig is employed, it is preferable to make this article rather than a more highly carburized one.

The manufacture of steel, direct from the ore, has often been attempted, with more or less satisfactory results. The apparatus is generally a fire similar to that of the Catalan forge, bloomery, or run out fire. The ores must, of course, be rich and perfectly pure, since the fining is but partial. We have examined several samples of steel made of pure titaniferous ores, which were remarkable for their hardness and tenacity. As in similar operations, it will be difficult to stop the carburization or decarburization just at the desired time, for a given quality of steel.

We now come to the Bessemer and Martin processes, in which the pig-iron is decarburized partly, or entirely, and afterwards recarburized to a given point. Or, the pig-iron is melted with wrought iron, or with oxide of iron, then recarburized, etc. The chemical reactions are the same as those we have already examined; but the apparatuses and modes of operation are different, and remarkable for the quantity of the materials which can be worked in a very short time.

For persons interested in patent office matters, the history of these processes cannot fail to be found very interesting. Let it be sufficient in this place to state that

many have been the co-workers, and that in many instances, their failures were due to the employment of impure raw materials. Indeed, the success of Mr. Bessemer dates from the time he began to employ pure Swedish pig-metal.

BESSEMER PROCESS.

When a blast of air is passed through molten cast-iron, the chemical action of the oxygen upon the silicon, carbon, and even the iron itself, is sufficient to raise the temperature to such a point that, after complete decarburization, the metal is liquid enough to be cast into ingots. The Bessemer process is based essentially upon the entire or partial decarburization of molten pig-iron by a blast of air passing through it.

Two kinds of converting vessels are used, one which is stationary, and the other movable. The former is still retained in Sweden, and consists of a kind of cupola, which receives the molten metal from another cupola, or direct from the blast furnace. The air is injected near the bottom through several fire-clay tuyeres, which are inclined at a certain angle, so as to impart to the fused mass a rotary motion. In order to prevent the obstruction of the tuyeres by the metal, the blast is given before the metal is poured in, and until it is run out. The method by partial decarburization is followed out, and notwithstanding the difficulty of stopping the opera

tion at the proper time, and the incomplete fining, the products are a superior Bessemer steel, which is used for fine wires, tools, razors, etc. Such superiority is evidently due to the remarkable purity of the Swedish raw metal, and to its percentage of manganese, which allows of the non-employment of Spiegeleisen.

The movable apparatus is, in every respect, superior to the preceding one, even with equally pure materials, as it has been proven in comparative trials made in Styria.

For impure materials, which require a complete decarburization or fining, followed by a partial recarburization, it is necessary to be able to stop and restore the blast when desired, and this cannot be done with the stationary apparatus.

The movable converting vessel, or Converter, revolves on two trunnions (Fig. 29); one of them is hollow and connected by a coupling box with the blowing machine,