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an inch. This powder is thoroughly incorporated with hot mineral tar, in the usual way, in the proportions of about three hundred and thirty pounds of tar to four thousand four hundred pounds of powder. This mixture, termed mastic, , can be cast into moulds of suitable size and kept for use.

To one hundred pounds of this mixture five or six pounds of mineral tar are added. A portion, about three per cent. of the mastic, of the mineral tar is first heated in an iron cylinder, and then one-third of the mastic thoroughly incorporated with it by stirring with an iron rod, one per cent. more of the tar is then added, and next another third of the mastic, and the remaining portions are stirred in in like manner. When the whole is melted one-half the gravel is stirred in, and then the remaining half in the same way.

In warm climates the mixture may receive a larger dose of gravel.

When the subsoil is compact and dry a layer of concrete of one inch and a half in thickness is spread over it, and covered by a layer of mortar half an inch thick; and over this, when thoroughly dry, a coat of one inch and six-tenths of the prepared mastic concrete.

When the soil is not hard, it should be rammed or rolled to make it so before receiving the hydraulic concrete, which, in this case, is three inches and a half thick, the other two courses being the same as before.

The mastic, whilst hot, is spread uniformly with wooden trowels over the mortar bed; and before it has cooled fine sand is sifted over the surface.

In some cases, instead of a bed of hydraulic concrete and mortar to receive the mastic concrete, one of hot gravel, mixed up with a small dose of mineral tar, is laid, and over this a layer of concrete mastic, formed of the fine siftings of mineral coal ashes, mixed up with heated mineral tar, is laid to form the top coating. This, in like manner, may receive a sifting of fine sand. Rollers are used in this case to give compactness to the bed and the upper layer.

729. Materials and Repairs. The materials for brokenstone roads should be hard and durable. For the bottom layer a soft stone, or a mixture of hard and soft, may be used, but on the surface none but the hardest stone will withstand the action of the wheels. The stone should be carefully broken into fragments of nearly as cubical a form as practicable, and be cleansed from dirt and of all very small fragments. The broken stone should be kept in depots at convenient points along the line of the road for repairs.

Too great attention cannot be bestowed upon keeping the road-surface free from an accumulation of mud and even of dust. It should be constantly cleaned by scraping and sweeping. The repairs should be daily made by adding fresh material upon all points where hollows or ruts commence to form. It is recommended by some that when fresh material is added, the surface on which it is spread should be broken with a pick to the depth of half an inch to an inch, and the fresh material be well settled by ramming, a small quantity of clean sand being added to make the stone pack better. When not daily repaired by persons whose sole business it is to keep the road in good order, general repairs should be made in the months of October and April, by removing all accumulations of mud, cleaning out the side channels and other drains, and adding fresh material where requisite.

The importance of keeping the road-surface at all times free from an accumulation of mud and dust, and of preserving the surface in a uniform state of evenness, by the daily addition of fresh material, wherever the wear is sufficient to call for it, cannot be too strongly insisted upon. Without this constant supervision, the best constructed road will, in a short time, be unfit for travel, and with it the weakest may at all times be kept in a tolerably fair state.

730. Cross Dimensions of Roads. A road thirty feet in width is amply sufficient for the carriage-way of the most frequented thoroughfares between cities. A width of forty, or even sixty feet, may be given near cities, where the greater part of the transportation is effected by land. For cross roads and others of minor importance, the width may be reduced according to the nature of the case. The width should be at least sufficient to allow two of the ordinary carriages of the country to pass each other with safety. In all cases, it should be borne in mind that any unnecessary width increases both the first cost of construction, and the expense of annual repairs.

Very wide roads have, in some cases, been used, the centre part only receiving a road-covering, and the wings, termed summer roads, being formed on the natural surface of the subsoil. The object of this system is to relieve the road-covering from the wear and tear occasioned by the lighter kind of vehicles during the summer, as the wings present a more pleasant surface for travelling in that season. But little is gained by this system under this point of view; and it has the inconvenience of forming during the winter a large quantity of mud, which is very injurious to the road-covering.

There should be at least one foot-path, from five to six feet wide, and not more than nine inches higher than the bottom of the side channels. The surface of the foot-path should have a pitch of two inches, towards the side channels, to convey its surface-water into them. When the natural soil is firm and sandy, or gravelly, its surface will serve for the foot path; but in other cases the natural soil must be thrown out to a depth of six inches, and the excavation be filled with fine clean gravel.

To prevent the foot-path from being damaged by the current of water in the side channels, its slide slope, next to the side channel, must be protected by a facing of good sods, or of dry stone.

As it is of the first importance, in keeping the road-way in a good travelling state, that its surface should be kept dry, it will be necessary to remove from it, as far as practicable, all objects that might obstruct the action of the wind and the sun on its surface. Fences and hedges along the road should not be higher than five feet; and no trees should be suffered to stand on the road-side of the side-drains, for independently of shading the road-way, their roots would in time throw up the road-covering.

731. Plank-Roads. Plank-roads were very popular a few years since. The road was carefully graded, then stringers -one on each side-were imbedded in the earth, and upon these were laid planks, three or four inches thick, forming a continuous floor. When the planks are new and well laid this makes a very agreeable road for haulage and for pleasure rides, but when the planks become worn and displaced it makes a very disagreeable road. As a general thing they have been abandoned, except in certain localities where they are maintained on account of peculiar circumstances. A good gravel road has been found to be more profitable, and in the long run makes a much better road. Many plankroads have been changed to McAdam or to Telford roads.

II.

RAILWAYS.

732. A railway, or railroad, is a track for the wheels of vehicles to run on, which is formed of iron bars placed in two parallel lines and resting on firm supports.

733. Rails. The iron ways first laid down, and termed tramways, were made of narrow iron plates, cast in short

lengths, with an upright flanch on the exterior to confine the wheel within the track. The plates were found to be deficient in strength, and were replaced by others to which a vertical rib was added under the plate. This rib was of uniform breadth, and of the shape of a semi-ellipse in elevation. This form of tramway, although superior in strength to the first, was still found not to work well, as the mud which accumulated between the flanch and the surface of the plate presented a considerable resistance to the force of traction. To obviate this defect, iron bars of a semi-elliptical shape in

Fig. 227-Represents a cross-section a, of the fish-bellied rail of the Liverpool and Manchester Railway, and the method in which it is secured 'to its chair. The rail is formed with a slight projection at bottom, which fits into a corresponding notch in the side of the chair b. An iron wedge c is inserted into a notch on the opposite side of the chair, and confines the rail in its place.

elevation, which received the name of edge-rails, were substituted for the plates of the tramway. The cross-sections of these rails are of the form shown in Fig. 227, the top surface being slightly convex, and sufficiently broad to preserve the tire of the wheel from wearing unevenly. This change in the form of the rail introduced a corresponding one in the tires of the wheels, which were made with a flanch on the interior to confine them within the rails of the track.

The cast-iron edge-rail was found upon trial to be subject to many defects, arising from the nature of the material. As it was necessary to cast the rails in short lengths of three or four feet, the tract presented a number of joints, which rendered it extremely difficult to preserve a uniform surface. The rails were found to break readily, and the surface upon which the wheels ran wore unevenly. These imperfections finally led to the substitution of wrought iron for cast iron.

734. The wrought-iron rails first brought into use received nearly the same shape in cross-section and elevation as the cast-iron rail. They were formed by rolling them out in a rolling-mill so arranged as to give the rail its proper shape. The length of the rail was usually fifteen feet, the bottom of

Fig. 228-Represents a side elevation of a portion of a fish-bellied rail.

it (Fig. 228) presenting an undulating outline so disposed as to give the rail a bearing point on supports placed three feet apart between their centres. This form, known as the fishbelly rail, was adopted as presenting the greatest strength for

the same amount of metal. It has been found on trial to be liable to many inconveniences. The rails break at about nine inches from the supports, or one fourth of the distance between the bearing points, and from the curved form of the bottom of the rail they do not admit of being supported throughout their length.

735. The form of rail at present in most general use is known by the name of the parallel, or straight rail, the top and bottom of the rail being parallel; or as the T, or H rail, from the form of the cross-section.

A variety of forms of cross-section are to be met with in the parallel rail. The more usual form is that (Fig. 229) in

b

Fig. 229-Represents a cross-section a

of a parallel rail of the form generally adopted in the U. States. The rail may be confined to its chair by two wooden keys c on each side, which are formed of hard compressed wood. At the present time two iron straps are used instead of the keys c e, which are firmly bolted to the rails. This form is called a fish-joint. In this case the projection b is omitted. A very great variety of splices are in

use.

which the top is shaped like the same part in the fish-belly rail, the bottom being widened out to give the rail a more stable seat on its supports. In some cases the top and bottom are made alike to admit of turning the rail. The greatest deviation from the usual form is in the rail of the Great Western Railway in England (Fig. 230), and the Grand Trunk in Canada; but this form is rapidly going out of use. ·

Fig. 230-Represents a cross-section of the rail of the Great Western Railway in England. This rail is laid on a continuous support, and is fastened to it by screws on each side of the rail. A piece of tarred felt was inserted between the base of the rail and its support.

The dimensions of the cross-section of a rail should be such that the deflection in the centre between any two points of support, caused by the heaviest loads upon the track, should not be so great as to cause any very appreciable increase of resistance to the force of traction. The greatest deflection, as laid down by some writers, should not exceed three-hundredths of an inch for the usual bearing of three feet between the points of support. The top of the rail is usually about two and a half inches broad, and an inch in depth. This has been found to present a good bearing surface for the wheels, and sufficient strength to prevent the top from being crushed

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