The manufacture of wrought iron, by means of bituminous coal, is executed at three successive processes, and is facilitated by very great improvements in the machinery. Where hammers are still used, they are much increased in weight, and driven with greater velocity; but by far the greater part of the operation of drawing the bars is effected by means of rollers. The plan of these is in some measure borrowed from the slitting mill, in which bar iron is reduced into rods and thin rolls for various uses. These rollers are in sets, composed each of two of equal diameter, lying in a horizontal position, and placed one vertically above the other. Grooves corresponding to each other are cut in the two rollers, between which the heated iron is drawn by their revolution, and forced to assume a section that just fills up the two grooves. By passing in succession through grooves gradually decreasing in size, any form or magnitude may be given to the bars; and the operation is so rapid, that the bar may be drawn from the loup at a single heat. The first operation to which the pig iron is subjected, consists in melting it in a fire called a finery, similar in form and character to the bloomeries and refineries of which we have spoken, but in which the fuel is coke. The melted metal is drawn off by tapping the furnace from beneath, and is cast into thin plates. In this way it assumes the characters of the white cast iron, which has been described as formed, when the reduction of the metal is complete, a form that cannot be given when the blast furnace in which it is made is supplied with coke. The rapidity of the cooling is increased, by throwing water on the surface of the plates. It thus appears, that this operation is adopted in order to bring the cast iron into a slate that it may often assume when manufactured by charcoal, and which cannot be given to it by coke. In conformity with this view of the subject, it has been found, that when wrought iron is manufactured by puddling, from American pig prepared by charcoal, this preliminary operation is unnecessary.