Thus, when iron is heated, its pores are opened, the carbon on the outside is carried away by the air, and more is liberated from within, to pass off in the same way; the object of the frequent meltings and the hammering is to expose new surfaces to contact with the oxygen of the air, and get rid of the carbon, just as the farmer turns his hay, and brings new surfaces to the sun, to dry off the dew.
As the result of this we have wrought iron, soft, tough, of close and fibrous, instead of a crystalline or granular texture, that may be made red hot and quenched in water without hardening or becoming brittle; may be welded, split, punched, made into wheel-tires, hoes, shovels, axes, hammers, pitchforks, knives, or razors. But there is one grand defect in this iron, although it is so tractable that it may be worked under the hammer into a thousand different shapes at the will of the smith; may be drawn into wire so fine as to be woven in a loom or made into a watch spring that weighs only the tenth of a grain, and rolled into leaves as thin as paper, insomuch that a pound of raw iron costing a cent affords steel sufficient for seventy thousand watches, worth one hundred and seventy-five thousand dollars. It is, however, too soft to form a cutting edge that will stand. Make a pitchfork of it, it is harder work to stick it into the hay than it is to pitch the hay, as we know from experience; an axe, it will take all your strength to cut through the bark, and you must grind it every hour; a razor, you can shave but once, and then with tears of agony. Make a hammer of it, and it batters up forthwith; a punch, it bends; a drill, at the first stroke of the sledge it turns.
What next?
Troughs are made of fire-brick, from eight to sixteen feet in length, and two or three feet in depth. The troughs are placed in a furnace, and on the bottom of each of them a mixture of powdered charcoal, ashes, and salt. Bars of wrought iron are laid upon this mixture half an inch apart, to the amount, perhaps, of twelve tons, and covered with charcoal; then another layer of iron and more charcoal, till the trough is full. The top is covered with cement that has been used before, and damp sand. The fire is then made in such a manner that the heat passes all around the troughs, and is kept up from six to ten days, according to the size of the bars and the purposes for which the contents of the troughs are wanted.
The heat of the furnace opens the pores of the iron, and sets free the carbon contained in the charcoal; and as the cement prevents it from escaping and uniting with the oxygen of the air, it enters the pores of the iron and impregnates it. The fire is now suffered to die out, and the metal is taken from the troughs. It is no longer iron, but steel. We now have that which is the "king of metals," and by the aid of which the skilful mechanic can do what would once have been thought miraculous.
The surface of this material is covered with blisters, hence it is called blistered steel. It resounds when struck. Iron once bent remains so; but steel is so elastic that it may be bent to an angle of forty-five degrees, and will spring back to its original position. It is said that Andrew of Ferrara manufactured swords so elastic, that the point of the blade would bend to touch the hilt, and spring back again uninjured. The quality of steel depends upon the quality of the iron from which it is made. The English have carried the art to great perfection, nevertheless are obliged to import the iron from which their razor-steel is made from Sweden. This blistered steel is the kind that lay upon the floor of William Richardson's shop, and in the possession of which he so exulted.
Now you have an article that gives to the axe its temper, the fork its point, the mainspring of the watch its elasticity, and to all tools an enduring edge that may be so attempered as to pierce the hardest rocks and crush the hardest stones; that may be welded to iron, and thus economized. Do you think it strange that Will Richardson rejoiced at the acquisition in his circumstances, or reflected long and seriously in respect to the manner in which he should use his treasures to the best advantage?
And now, perhaps, some thoughtful boy may say,—
"Why be at so great expense of labor and material to take carbon from iron, and then set right at work to put it back again?"
Because there is too much in the cast iron, and so it is all taken out, and just the right amount put in.