The next operation is the placing and firmly bedding the sleepers, which generally consist of solid blocks of stone, weighing from one to two or more hundred weights each. There is no particular shape neoessary, provided their bases be broad, and pretty even ; it is also particularly that the upper surfaces should present an even and solid batisfer the iron plates or rails to rest upon. The sleepers are generally placed along each side of the road, measuring about three feet distant from eaoh other, from centre to centre, the opposite ones being separated by the width between the opposite rails. In such situa tions, where the ground under them is of a soft nature, it is usual and proper, in the first instance, to lay on a coat of gravel, small stones, or metallic scoriae ; and this is well beaten down in order to form a firm foundation. Each stone, when laid down, is carefully gauged, both in respect to its distance from the adjoining ones, and the level or declivity of its upper surface, on which the plates or rails are intended to rest. The sleepers being thus correctly placed, the spaces between them are filled up with either gravel, metallic scoria, or some other hard road materials, in order that the whole may consolidate into a hard and firm mass.
The foregoing is a sketch of the process adopted in forming metallic lines of road, whatever may be the form of the rail or wheel-tracks laid down. Of these, theripare two principal kinds, namely, tram-plates (already noticed) and edge-rails, both of which are very extensively adopted, though the latter is, at the present time, the most approved by engineers. Nevertheless, it is unques tionable that tram-plates, when correctly formed, and laid down with the same attention to accuracy of adjustment and solidity of bearing as is now practised with the best edge-rails, answer their purpose admirably. They are commonly employed in Wales, and in the neighbourhood of blast furnaces, on account of the greater facility and cheapness of their construction. They are especially usefil in forming new roads, in the working of mines, quarries, in digging canals, in conveying large stones for buildings, and numerous other temporary as well as per manent purposes; chiefly for this reason,— that the ordinary wheels of carts and waggons can run upon them, and with a surprisingly increased power of draught, while the carriages are kept steady in their tracks, by the upright flanges, as shown in the annexed section, where B represents the flat bearing surface of the tram-plate, which, as now practised, is fas tened by a spike, driven into an oaken plug previously inserted into the stone sleeper C; the horse-path or gravelled road is partly shown at A. These tram-plates are made of cast-iron, are usually about three feet long, from three to five inches broad, and from half an inch to an inch thick, extending from sleeper to sleeper, and the turn-up flange from two and a half to four inches high. The plate usually bears on the sleepers about three inches at each end, where its thickness is for that purpose increased ; between these bearing-points the plate has no support but what it derives from the ground, which, though not very permanent or secure, is infinitely more so than the sup port thus derived by an edge-rail : indeed, the extensive bearing surface of the plate upon the ground is often found quite sufficient for temporary uses, without any sleepers at all ; and in other cases, where a little more stability is required, to spike down the opposite ends of the tram-plates, on each side of the road to a transverse piece of wood, which remains useful for a longer period, without taking up for re-adjustment.
Tram-rails are decidedly of a weak form, considering the quantity of iron in them ; and in some works it has been found necessary to strengthen them, by adding a rib on the under aide, as shown in the annexed perspective view of a section of half a rail, in which A is the guiding flapge; B the bed of the rail on which the wheels run ; C is the rib on the under side to strengthen it.
The tram-plates used for repairing the Surrey trammed were of this form, and it certainly renders them very stiff.
The mode of fastening down tram-plates by bolts or spikes was found to be attended with several inconveniences, owing to the occasional projection of their heads, their becoming loose, and hence both the plates and bolts being fre quently stolen, to the entire stoppage of the traffic upon the road. To remedy these evils, Mr. Charles le Caan, of Llanelly, in South Wales, contrived a mode of forming the so that no bolting or nailing was requisite, but each plate in succession fastened down the previous one. Fig. 1 represents a plan of the junction of two plates, placed on a stone sleeper D; and Fig. 2 shows a longitudinal section of the same. The plates are joined by a dove-tailed notch and tenon, and an oblique plug is cast on each plate, which is let into the stone sleeper; but for the advantage of taking up the plates to repair any defect, there are plates at every thirty yards, with perpendicular plugs; such plates are called stop-plates. The diameter of the plug near the shoulder is one inch and three quarters, at the point one inch, its length two inches and a half, and its obliquity, shown in Fig. 2, about eight degrees. A small groove in the whole length of the exterior of such plug is made to allow the water in the hole to expand in freezing; and it also serves to admit a wire to draw a broken plug out by it. The holes for the plugs should be cut to the depth of three inches by a standard gauge of cast-iron, and countersunk so as to allow the end of the plate to bed firmly on the block which supports it. Fig. 3 is one of the ends of a tram-plate, in which II shows the flange or upright edge; I the flat part or sole, in which the wheels of the waggon run; D one of the plugs ; and H a projection behind, to render the plates firmer upon the blocks. The usual length of one plate is three feet ; the flanch H is one and a half inch high ; the sole, or bed, three and a half, or four inches broad, and three-fourths of an inch thick ; but these dimensions are varied according to circumstances. The most approved weight has been forty-two pounds for each plate ; the ends from which the plugs project, under which the tenons. and notches are made, should be a quarter of an inch thicker than the other parts of the plate. The weight of the blocks or sleepers should not be less than about 120 pounds each; and some kinds of ground will require heavier. In this method the wheels of the waggons cannot be obstructed by the heads of the nails rising above the surface, and the blocks are not disturbed by fixing the plates ; and when repairs are necessary, the plates must be formed for the purpose. When tram plates are fixed by spikes to stone sleepers, there is some difficulty in keeping the joint even and in its place; but it seems to be successfully obviated, by using a saddle-pin to receive the ends of the nails at the joints, an improvement which was introduced by Mr. Wilson on the Troon tramroad.