in succession are required under one shed; their form must be nearly square-that is to say, their extent, lengthwise and crosswise, should be equal to that of a rail. On the first platform, the rails are overhauled by means of coarse files, and any imperfection or unsoundness of iron exposed. Those which cannot well be improved by patching are removed. Between the first and second platform a very heavy cast iron anvil is placed, on which the final straightening of the rails is performed; for that purpose, heavy iron sledges weighing from twenty to thirty pounds are used. Between the second and third, fourth and fifth scaffold, the rails are patched. This consists in fitting in small pieces of iron into the defective parts. In the rolling of rails, there is sometimes. difficulty in bringing out their flanches; in this case, we succeed far better with cold-short, or impure, dirty iron, than with pure, strong, and fibrous iron. This difficulty increases with the diminished thickness of the flanches, and cannot be avoided if the iron is very strong, or free from cinder. Weak iron, or cold-short iron can be worked to great perfection, if the pile is turned in such a way that the joints of the mill bars fall perpendicularly upon the bases of the rail. If taken in the opposite direction, even the weakest iron will not make full, broad, and thin flanches. To what extent the quality of a rail is impaired, in consequence of these practical difficulties, it is not our province to investigate. But we may say that the quality of rails might, in most cases, be made, from the same materials, far superior to what it now is. If the constructing engineer of a railroad would reflect upon the best practical form of a rail, and alter its section accordingly, there is no doubt that great advantages might be realized. With respect to rails, or rails with equally thick flanches, the above difficulty does not exist, at least not to so great an extent. The making of rails may be considered the most pleasant and easy branch in the whole extent of the iron manufacturing business.

VI. Sheet Iron.

The making of sheet iron is a branch full of intricacies and difficulties; but once thoroughly understood, it is very simple and agreeable. The main difficulty we encounter depends upon the quality of iron from which it is made. Charcoal iron generally works well; but some kinds of puddled iron do not make good sheet iron. We alluded to this in our remarks on puddling, but propose to speak of it again at the close of this chapter. Sheet iron was

made in ancient times by means of forge hammers; it was flattened down by broad-faced hammers on large anvils. This method is still practiced in the eastern parts of Europe. At the present day, and in our own country, sheet iron is rolled. It is made partly from charcoal blooms, and in some places from puddled iron.

a. In all cases where thin sheet iron is to be made, the iron must first be converted into flat mill bars. Charcoal blooms, as well as puddled iron, undergo the same treatment, with this difference, however, that good charcoal blooms do not require a welding heat.

Puddled iron is to be piled, and a pack of rough bars welded and rolled down into flat mill bars. These bars are from four to six inches wide, varying in thickness, according to the number of sheets to be made from them. Heavy sheet iron and boiler-plate are to be made from mill bars, if we want a good article. Sheet iron is principally made from charcoal blooms shingled down into slabs; sometimes from puddled rough bars, piled, welded, and shingled by the T hammer into slabs. By neither method is good boilerplate made; a second reheating is, in all cases, to be resorted to, if we want the best article the material is capable of producing. In the manufacture of sheet iron, our main attention must be concentrated upon the quality of the iron, and the power at our service. All other matters are of subordinate importance, and have little bearing upon the success of our operations. Clean, white, fibrous iron, and a surplus of power, are the most essential elements in making good and cheap sheet iron.

b. The machinery for making sheet iron does not materially vary, except as regards strength, from that used in making bar iron. The housings are generally heavier, in Europe often made of wrought iron; the junction shafts and coupling boxes stronger; the flywheels heavier. The length of the rollers is, in most cases, but three feet between the gudgeons; seldom three and a half feet for thin sheet. For the rolling of boiler-plate, we find rollers four and even five feet long in use. The diameter varies according to the length. A short roller may be of smaller diameter than a long one; and weak cast iron, of course, will make a larger diameter necessary than strong castings. In Fig. 120, a set of sheet rollers is represented. The pinions and pinion standards are not generally employed; they are unnecessary, and even disadvantageous, for making thin sheet. But for roughing down, when the plates are thick, or for making boiler-plate, they are advantageous, and save a great deal of breakage. Slabs which are one and a half, or two or more inches

thick, lift the top roller very high, and suddenly drop it; this, of course, produces a heavy shock all through the machinery. To avoid this shock, the top ought not to touch the bottom roller: but

Fig. 120.

Rollers and pinions for sheet iron.

then the pinions are necessary; without them the top roller will not move, and unless this moves, the rollers will not bite. In cases where the top moves independently of the bottom roller, the first is generally balanced by counter weights, applied either below or above the rollers; these weights keep the top and bottom rollers apart. We think that the arrangement indicated in Fig. 109, for keeping the top roller up, is far preferable to any other. The wrenches on the top screws form a cross, so as at any time to expose a handle to the workmen before the rollers. The distance between the rollers must be perfectly controlled by the foreman, because he regulates the thickness of the sheet by these screws. Of all the improvements made relative to the regulation of the distance between the rollers, none is preferable to the above simple mode.

c. For making very thin and polished sheet iron, cast iron housings are not sufficiently strong, unless very heavy, and of the best kind of iron. In this case, wrought iron standards are preferable; and, as there is no difficulty in obtaining heavy and good wrought iron, at reasonable prices, in Eastern Pennsylvania, where it is manufactured up to seven inches in diameter, it may, in many instances, be advantageous to employ such standards. In

Fig. 121, a, a represent wrought iron pillars; these are fastened by being cast into the bottom plate. Each of these pillars is

Fig. 121.

AMLET

provided with a screw and nut; the advantage of taking small, very minute grades of pressure, decrement, upon the top roller is thus secured. For the making of thin sheet iron, this is a very convenient and essential arrangement. The aprons are broader than at bar iron rollers, which is indispensable. If heavy plates are to be rolled, even small friction rollers in the apron are to be added on the work side. The friction of heavy iron upon the apron is great, and the employment of additional hands would be necessary, if this friction were not diminished by the above friction roller. Sheet rollers move with various speed, and the foreman ought to have it in his power to give to them just the degree of speed required. The speed necessary for these rollers is from twenty to forty revolutions. In a well-conducted establishment, there are roughing-rollers, finishing rollers, and hard or chilled rollers. We generally find only the first two, and in very few establishments the last.

d. For making boiler-plate, but one pair of rollers is needed, and the slab rolled down in one heat. The slab, as received from the T

hammer, is generally from twelve to eighteen inches long, from seven to ten inches wide, and from two to three inches thick. It is heated, in a reheating furnace, to a bright red, but not welding heat. The dimensions of the sheet to be rolled from a given slab are produced by turning the slab more or less, and increasing in one direction. The surface of the iron is repeatedly chilled by sprinkling cold water on it by means of a broom; this loosens the adhering scales, which may then be removed by turning the plate, or by the broom. This operation must be particularly attended to when the plate is nearly finished. Polish and great smoothness are not required for boiler-plate. Uniform thickness and good quality of iron are the main requisites.

e. Sheet iron thinner than boiler-plate is generally rolled from platines, or from cuttings of flat merchant bars. That which is heavier may be made from one length of the flat mill bar; and two, or even three thicknesses, when sufficiently heated, are welded together in the sheet rollers. Common sheet iron, as No. 15 and higher numbers, is made from one thickness of the mill bars, which, heated to a cherry-red heat, is run through the rollers in single sheets. At subsequent heats, two or even three may be rolled together. When heated, the mill bars or platines are brought from the oven in pairs, which are pushed singly through the rollers. This keeps the workmen actively employed; for, while one plate is between the rollers, the other is returned over the top roller, the one thus closely following the other. If three plates are at once in motion, still more active manipulation is required, for, while one plate is between the rollers, the two other plates are in the tongs on each side of them. In the first heat, the iron is reduced as much as possible; and to what extent it may be brought to the desired form, depends on the power of the engine, and the dexterity of the workmen. In this heat, the breadth of the sheet is determined, in case the platines are not already cut to the proper length.

After this operation, the iron, which already assumes the appearance of sheet iron, is returned to the heating oven, or, as in wellconducted establishments, it is heated anew in a more advantageous oven. From this second heat, two sheets are taken and rolled together, with the caution that after passing them two or three times through the rollers, they are separated, and their sides reversed, partly to prevent the adhesion of the plates, and partly to impart a smooth surface to both sides of the sheets. Sheet iron for