The manufacture of this article is interesting from the wonderful rapidity of its execution; and that it is of great importance in its results, it need only be stated that in the neighbourhood of Birmingham alone, it furnishes the highly-convenient raw material to upwards of sixty thousand people, men, women, and children, who are employed in nail-making, besides being applied to an infinite variety of other purposes. The slitting is performed by what we would define to be a series of circular shears, formed by the continued contact of a pair of deeply-grooved steeled rollers, which cut by the intersection of their angular edges, as will be clearly understood by reference to the subjoined engraving, which exhibits a pair of slitting rolls, adapted to slit a flat bar or slab, of about seven inches wide, into thirteen equal parts. An end view of this slab is intended to be represented at a, and by presenting it between the two rolls at b b it is obvious that the edges, as they intersect each other in their revolution, will divide the slab in the manner shown at a, and force them into the cavities between them, in which manner they will pass out of the rolls in a finished state, requiring only to be tied up into bundles afterwards, of the usual weight of 56 lbs.

To facilitate the operation of slitting, the bar passes from the rolls where it has been formed of the required dimensions, in its red-hot state, directly between the slitters. In this manner upwards of thirty rods, of a small size, are made at once by a single revolution of a pair of rolls. As the sizes and forms of the rods required are extremely various, it is necessary in a slitting mill to have, at the least, two pair of rolls for each size, that a freshly-turned pair may be in readiness to supply the place of those which become worn or damaged. Slit rods are always more or less ragged at their edges, but this is of trifling import compared to the advantage of their great cheapness, especially in the making of nails, where they have to be drawn out under the hammer. To prevent any considerable burr, or ruggedness of edge in the rods, the slitting rolls are turned with great care and truth, so as accurately to fit each other

Rolling of Plate or Sheet Iron is performed between perfectly plain rolls, as before mentioned, for hoops; but the rolls are necessarily of greater dimensions, frequently as wide as five feet; and of course a very great power is required to compress at once so extensive a line of surface. For ordinary sheet iron, such as is called "double and single plate," only one pair of rolls is employed at a time, the rolls being set nearer together by regulating screws, each succeeding time that a sheet is passed through. In rolling boiler plates, which are often more than half an inch in thickness, and weigh more than 2 cwt. each, the manual labour is very severe. The iron for these plates is prepared by making a pile of rough bars, which is heated in an air furnace, and then subjected to the action of the great forge hammer, already described, which reduces the pile to a thick slab, the forgers moving it under the hammer, so as to give it somewhat of the figure, as to length and breadth, required for the finished boiler plate.

It is then heated again in the furnace, and rolled to the required thickness by repeatedly passing the plate between the rolls, the rollers adjusting the rolls nearer together each succeeding time, and taking due care to present the plate in such positions as will extend it to the required shape and dimensions, sometimes making it enter the rolls corner ways, sometimes lengthways, and sometimes breadth ways; the skill and efforts of the workman being directed to bringing the plate to the required form and dimensions at one heat, and so as to require but very little superfluous edging to be subsequently taken off" by the shears.