Rolling Rods.—Round rods, and those of a square or flat shape, that are required more perfect in their figure, and with a smoother surface than those which are split by the process described, are made by rolling with small rolls that are case-hardened, and have their grooves very nicely formed. They are usually from six to seven inches in diameter, and make from 230 to 260 revo lutions per minute, and the rods, whilst between the rolls, are drawn through them at the same velocity. They are rolled of great lengths, sometimes upwards of forty feet, and are afterwards cut to the required lengths, and tied into bundles of 56 lbs. each. Round rods are thus rolled so small (about three sixteenths of an inch), as to form a very useful and cheap substitute for wire. It is extensively used by wire-workers, and in making "invisible fences ;" also by tinmen, coppersmiths, and other trades; but especially in those cases where it is covered over, and employed to stiffen flexible substances.
' Red-Short, is a term given to bar iron that has the defect of cracking or breaking, when punched or bent, while at a red heat. It is generally very strong when cold, and therefore useful in that state; and when it is worked, care should be taken by the smith not to subject it to severe strains at that peculiar heat in which it is disposed to give way.
Cold-Short, is that kind of iron that readily breaks when cold, but is easily wrought under the hammer when heated.
Testing the Quality of Iron is usually performed by cutting a nick on one side of it with a cold chisel, then bending it down, or giving it a blow with a sledge hammer. If the iron be bad, or cold-short, it will break, and exhibit a re splendent, crystallized fracture; if, on the contrary, the uncut part bends hack, and exhibits the appearance of a bundle of silky-looking fibres, such iron will probably stand the heated test of bending it double whilst at a cherry-red heat, first in the direction of the pile, and afterwards at right angles to it. If the iron does not crack by these tests, it is neither cold-short nor red-short, but of a tough good quality. We have now given a pretty general outline of the process of making common malleable iron, but there remains to be expl-ined in what respect the processes differ in the preparation of the superior kinds.
Best Malleable Iron.—The correct meaning of the term " best " is very different to the signification of it in the iron trade, in which it now implies the next better quality than common ; and it is usually said to be made by a repetition of the process at the balling furnace, the forge, and the rough rolls; that is to say, the rough bar of the common iron already described, is cut, piled, and made into a bloom once more, which confers upon the metal a more fibrous texture, and considerably increases its toughness and elasticity. We believe,
however, that much of the iron that is sold under this denomination undergoes a different process, which does not improve the quality to the same extent. We are informed that best iron is more commonly prepared from pig metal of a better quality, namely, the dark grey, whose fracture is brilliant, and of a silvery white colour. These are carefully refined and puddled, without any admixture of inferior materials ; the bloom is well hammered, and when rolled out into rough bar, it is made thinner than for common iron; this is afterwards cut into short lengths, piled, reheated, and rolled out to the required size, as in common iron.
Scrap Iron.—There is another kind of best iron, distinguished by the name of "scrap-iron," being made up of all the Scraps, short lengths, ends cut off the finished bars, as before explained, and all the little bits of wrought iron that can be collected together. Of these there is always a considerable quantity accumulating in an iron work ; the larger pieces are made up into piles, and the smaller into balls. The piles may be heated to a welding heat, and rolled at once into finished bars, but the balls, consisting of smaller pieces, are shingled under the great hammer, to consolidate them and bring them into the form of a bloom. This bloom is reheated, and when rolled, produces excellent tough iron, superior to the piled scraps that have not been shingled. Scrap-iron, thus reworked, often produces so excellent a quality, as to fall under the denomination of the next described quality of iron, namely, Best-best Iron, No. 3, Chain-cable Iron.—These names, and various others intended to denote the superlative degree, are given by manufacturers to that kind of iron which is deemed to be, in reality, of the best quality, prepared with mineral coal. This metal is chiefly manufactured for the purpose of enabling it to resist most effectually a longitudinal strain or tension ; and the property is best acquired by the careful selection of the best materials, and repeatedly cutting, piling, shingling, and rolling, as before explained. In the preparation of this superlative quality of iron, the utmost attention to the process is necessary; and any bloom or bar that may be incidentally injured in its tenacity should be rejected by the manufacturer, whose reputation might be injured by such iron receiving the mark that properly belongs only to the primest quality. It is this kind of iron which is chiefly employed in the making of chain-cables, in tie-rods and bolts, that are subjected to a powerful strain.