Formerly, wrought-iron was obtained either directly from the ore, or from cast iron, by a process still in extensive operation abroad, in which wood charcoal is required. In 1783 and 1784 Mr. Cort took out patents for the processes of puddling and rolling, which have been continued with successive improvements, and are now conducted in the following manner.

The crude cast iron is remelted in quantities of from half a ton to one ton, in a furnace called the chafery, or refinery, blown with blast; it is kept fluid for about half an hour, and then cast into a plate about four inches thick, which is purer, finer in the grain than pig metal, and also much harder and whiter, it is then called refined metal. The plate when cold is broken up, and from two to four hundred weight of the fragments, with a certain proportion of lime, are piled on the hearth of the puddling furnace, which is a reverberatory furnace without blast.

In about half an hour the iron begins to melt, and whilst it is in the semi-fluid state, the workman stirs and turns it about with iron tools; he also throws small ladles full of water upon it from time to time. In this condition the metal appears to ferment, and heaves about from some internal change; this is considered to arise from the escape of the carbon in a volatilised form, which ignites at the surface with spirits of blue flame; in about twenty minutes the pasty condition gives way, and the iron takes a granulated form without any apparent disposition to cohesion; the fire is now urged to the utmost, and before the metal becomes a stiff conglomerated mass, the workman divides it into lumps or balls of about fifty pounds in weight.

These balls are taken out one at a time, and shingled, or worked under a massive helve or forge-hammer, that weighs six or eight tons, and is moved by the steam engine, this compresses the ball, squeezes out the loose fluid matter, and converts it into a employed. In reference to the above experiment, (No. 8 of a series of 12,) Mr. Musbet says "that duriug the 24 hours, in which each of the foregoing experiments and observations were made, the furnace was supplied with a continual discharge of air equal to 2500 cubical feet per minute, amounting, in the 24 hours, to 3,600,000 cubical feet upon the whole, each cubic foot weighing 555 grains, we shall find (page 289) the immense total quantity of 1274 tons of atmospheric air !" or upwards of thirty-seven times the weight of all the solid materials introduced into the furnace.

bloom, or short rudely-formed bar. The bloom is then raised to the voiding heat in a reheating furuace, and again passed under the hammer, of through grooved rollers, or it is submitted to both processes, by which it is elongated into a rough bar called No. 1. The shingling is sometimes performed by large squeezers, somewhat like huge pliers, or by roughened rollers that also serve to compress the iron; hut the ponderous flat-faced helve is considered the more effectively to expel the dross and foreign matters from the bloom, and to weld the same more perfectly at every point of its length. See Note Q, Appendix, Vol. II., p. 958.

The No. 1 bars are next cut into short pieces, and piled in groups of four to six; they are again raised to the welding heat in a reheating furnace, and passed through other rollers to weld them throughout their length, and reduce them to the required sizes, when the bars are called No. 2: and sometimes the processes of cutting and welding arc again repeated in the manufacture of still superior kinds called No. 3 Iron.

A similar process of manufacture is still occasionally carried on, partly with wood charcoal, in place of coals and coke; the iron thus manufactured, called charcoal iron, is much purer, but it is also more expensive; it is sometimes, by way of distinction, left in ridges from the hammer, when it is called dented iron.

Fig. 76.

The rollers or rolls of the iron works are turned of a variety of forms, according to the section of the iron that is to be produced; in general one pair is used exclusively for each form of iron required; although in the imaginary sketch, fig. 76, it is supposed that the shaded portion represents the upper edge of the bottom roll; and that the top roll, which is not drawn, almost exactly meets the bottom one, with the exception of the grooves, and which are in general turned partly in each roll, in the mat: denoted by the black figures.

One pair will have a series of angular grooves for square iron, gradually less and less, as a, b, c, fig. 76, so that the bar may be rapidly reduced without the necessity for altering the adjustment of the rolls, which would lose much valuable time; the flat bars, are prepared square, and then flattened in grooves, such as that at d; round, or bolt iron, requires semicircular grooves e; but round iron often shows a seam down one side, from the thin waste spread out between the rolls being afterwards laid down without being welded, when the iron is turned one quarter round and sent again through the rollers; therefore the best round works are mostly forged from square bars.

Figs. f and g are described as angle, and T iron; these are particularly used in making boilers, the ribs of iron steam-vessels; also frames, sashes, and various works, requiring strength with lightness. Plain cylindrical rollers serve for producing plate and sheet iron, which vary in thickness from one inch to that of writing-paper, and rolls turned like fig. i, are employed for curvilinear ribbed plates, or the corrugated iron, an elegant application lately patented for roofs. Other rollers composed of two series of steeled discs, placed upon spindles, are used to slit thin plates of iron about six inches wide, into a number of small rods for the manufacture of nails, and similar rods are also made of larger sizes called slit iron; they always exhibit two ragged edges, and from being tied up in small parcels, are also known as bundle iron.