On the Manchester and Liverpool railway, the rails are each five yards in length, and weigh thirty-five pounds each yard. The rails are supported every three feet upon stone blocks, each block containing nearly four feet of stone. Two holes, six inches deep, and one inch diameter, are drilled into each block, and into these are driven oak plugs ; and the cast-iron chairs, to which the rail is immediately fastened, are firmly spiked down to the oak plugs, forming a construction of great solidity and strength. On the embankments, where the foundations may be expected to subside, the rails are laid on oak sleepers; thus there are thirteen miles of the rail resting on oak, and the remaining eighteen miles on stone sleepers. There are two double lines of rails, four feet apart, elevated above the ground rather more than an inch. The sectional form of the rail is represented in the subjoined cut at r: this figure is designed to exhibit the mode adopted by Mr. Stephenson in joining the rails to the chairs, which is deserving of notice. In pass ing the bars through the rollers, a lateral projection is rolled upon one side of the rail ; and, on one side of the cheek of the chair, a cavity is cast, equal in size with the projec tion, as seen at a in the annexed figure. On the opposite aide of the chair another cavity b is cast, for the purpose of receiving an iron key. When the rail is laid into the chair, the key is driven into the cavity b, which, pressing against the aide of the rail, forces the projection a into the cavity on the opposite side, and thus effectually secures the rail from rising up.
Mr. Losh has a different mode of effecting this object. In this plan the pro jection is rolled on both sides of the rail, as shown in the annexed section ; one of these projections enters a cavity, a, in the chair, as in Mr. Stephenson's. On the other cheek of the chair a longitudinal cavity is cast to receive a key, but, as shown in the figure, it is a double one, acting at the same time upon the upper part of the projection on the rail, to force it down upon the chair, and against the side of the rail, to steady it, and force the projection on the other side of the rail into the cavity. By this mode of keying, if the rail works loose upon the chair, by driving the key, it can again be tightened.
The plan of fastening the rails by keys is infinitely pereferable t3 pins; as the latter are apt to work loose, and to secure them again permanently has been found a difficult task.
An opinion having been extensively promulgated by the advocates for cast-iron rails, that those made of wrought iron, from their softness and fibrous texture, were liable to exfoliate and wear away fast, an investigation into the facts was very generally instituted, the result of which was decidedly favourable to the eligibility of the malleable rails. Mr. George Stephenson's report on this subject, corroborated as it is by other indubitable testimony, is deserving of attention.
" In my opinion," says Mr. Stephenson, " Bilkinshaw's patent wtought-iron rail possesses those advantages in a higher degree than any other. It is evi.
dent that such rails can at present be made cheaper than those that are cast, as the former require to be only half the weight of the latter to afford the same security to the carriages passing over them, while the price of the one material is by no means double that of the other. Wrought-iron rails, of the same
expense, admit of a greater variety in the performance of the work, and em ployment of the power upon them, as the speed of the carriages may be increased to a very high velocity without any risk of breaking the rails; their toughness rendering them less liable to fracture from an impulsive force, or a sudden jerk. To have the same advantages in this respect, the cast-iron rails would require to be of enormous weight, increasing, of course, the original cost.
" From their construction, the malleable iron rails are much more easily kept in order. One bar is made long enough to extend over several blocks; hence, there are fewer joints or joining., and the blocks and pedestals assist in keeping each other in their proper places.
" On this account, also, carriages will pus along such rails more smoothly than they can do on those that are of cast-iron.
"The malleable iron rails are more constant and regular in their decay, by the contact and pressure of the wheel ; but they will, on the *hole, last longer than cast-iron rails. It has been said by some engineers, that the wro ht-iron exfoliate, or separate in their laminae, on that part which is ex to the pressure of the wheel. This I pointedly deny, as I have closely examined rails which have been in use for years, with a heavy tonnage passing along them, and on no part are such exfoliation, to be seen. Pressure alone will be more destructive to the cohesive texture of cast iron than to that of wrought iron. The true elasticity of cast iron is greater than that of malleable iron ; L e. the former can, by a distending power, be drawn through a greater space, without permanent alteration of the form ; but it admits of very little change of form without producing total fracture. Malleable iron, however, is suscep tible of a very great change of form, without diminution of its cohesive power; the difference is yet more remarkable, when the two substances are exposed to pressure ; for a force which in consequence of its crystalline texture would crumble down the east-iron, would merely extend or flatten the other, and thus increase its power to resist the pressure. We may say, then, that the property of being extensible, or malleable, destroys the possibility of exfoliation as long as the substance remains unchanged by chemical agency. A remarkable difference, as to uniformity of condition or texture in the two bodies, produces a corresponding wasit,of uniformity in the effects of the rubbing or fraction of the wheel. All the particles of malleable iron, whether internal or superficial, resist separation from the adjoining particles, with nearly equal forces. Cast, iron, however, as is the ease with other bodies of similar formation, is both harder and tougher in the exterior part of a bar than it is in the interior. This, doubtless, arises from the more rapid cooling of the exterior. The con sequence is, that when the upper surface of a cast-iron rail is ground away by the friction of the wheel, the decay becomes very rapid.