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construction of roads and canals throughout the kingdom, the circumvallation of Lisbon for fiscal purposes, &c. The Company has deposited 600 cantos (about 150,000l.) of forfeit money, and of course as there are two parties to every contract, the company may not choose to forego the railway portion of its agreement. The several parties are now in negotiation, and the result will be speedily known Senhor Silva Cabral is of opinion that the terms offered by the English company, as compared with those offered by the Portuguese company, are so advantageous to the Government, that the latter has the right of option. General Bacon, in fact, makes the most extensive offers, and appears rather to be on the side of offering too much. Herapath's Jour. & Railway Mag.
FOR THE JOURNAL OF THE FRANKLIN INSTITUTE.
The Wire Suspension Aqueduct over the Allegheny River, at
This work, recently constructed under the superintendence of John A. Roebling, the designer and contractor, has supplied the place of the old wooden structure which originally was built by the State of Pennsylvania at the western termination of the Pennsylvania Canal.
The Council of the city of Pittsburgh, by whom, in consequence of an arrangement with the State, the tolls on this aqueduct are of late received, and who are bound to keep the work in repair, decided on re-building, and after considering various plans, adopted that of Mr. Roebling, and entered into contract with him to re-construct the communication, for the gross sum of $62,000, including the removal of the old ponderous structure and the repair of the pier and abutments; a very small sum indeed for a work of such magnitude. As this work is the first of the kind ever attempted, its construction speaks well for the enterprize of the city of Pittsburgh.
The removal of the old work was commenced in September, 1844, and boats were passed through the new aqueduct in May, 1845.
This work consists of 7 spans, of 160 feet each, from centre to centre of pier. The trunk is of wood, and 1140 feet long, 14 feet wide at bottom, 16 feet on top, the sides 8 feet deep. These, as well as the bottom, are composed of a double course of 24 inch white pine plank, laid diagonally, the two courses crossing each other at right angles, so as to form a solid lattice-work of great strength and stiffness, sufficient to bear its own weight and to resist the effects of the most violent storms. The bottom of the trunk rests upon transverse beams, arranged in pairs, four feet apart; between these, the posts which support the sides of the trunk are let in with dove-tailed tenons, secured by bolts. The outside posts, which support the sidewalk and tow-path, incline outwards, and are connected with the beams in a similar manner. Each trunk-post is held by two braces, 24 × 10 inch, and connected with the outside posts by a double joist of 21 × 10. The trunk-posts are 7 inches square on top, and 7× 14 at the heel; the transverse beams are 27 feet long and 16 x 6 inches; the
space between two adjoining is 4 inches. It will be observed, that all parts of the framing are double with the exception of the posts, so as to admit the suspension rods. Each pair of beams is supported on each side of the trunk by a double suspension rod of 18th inch round iron, bent in the shape of a stirrup, and mounted on a small cast-iron saddle, which rests on the cable. These saddles are connected, on top of the cables, by links, which diminish in size from the pier towards the centre. The sides of the trunk set solid against the bodies of masonry, which are erected on each pier and abutment as bases for the pyramids which support the cables. These pyramids, which are constructed of 3 blocks of a durable, coarse, hard-grained sand-stone, rise 5 feet above the level of the side-walk and tow-path, and measure 3 5 feet on top, and 4 x 6 feet at base. The side-walk and tow-path being 7 feet wide, leave 3 feet space for the passage of the pyramids. The ample width of the tow and foot-path is therefore contracted on every pier, but this arrangement proves no inconvenience, and was necessary for the suspension of the cables next to the trunk.
The caps which cover the saddles and cables on the pyramids rise 3 feet above the inside or trunk railing, and would obstruct the free passage of the tow-line; but this is obviated by an iron rod which passes over the top of the cap and forms a gradual slope down to the railing on each side of the pyramid.
The wire cables, which are the main support of the structure, are suspended next to the trunk, one on each side; each of these two cables is exactly 7 inches in diameter, perfectly solid and compact, and constructed in one piece from shore to shore, 1175 feet long; it is composed of 1900 wires of th inch thickness, which are laid parallel to each other. Great care has been taken to insure an equal tension of the wires. Oxidation is guarded against by a varnish applied to each wire separately, their preservation, however, is insured for certain by a close, compact, and continuous wrapping, made of annealed wire and laid on by machinery in the most perfect manner. A continuous wrapping is an important improvement, which, in this case, has been for the first time successfully applied.
A well-constructed and well-wrapped cable presents the appear
ance of a solid cylinder, which in strength greatly surpasses a chain, made of bars of the same aggregate section or weight. It is not only the great relative strength of wire which renders it superior to bar iron, but its greater elasticity, which enables it to support strong and repeated vibrations, add still more to its value as a material for bridge building.
The extremities of the cables do not extend below ground, but coanect with anchor chains, which, in a curved line, pass through large masses of masonry, the last links occupying a vertical position. The bars composing these chains average 14×4 inch, and are from 4 to 12 feet long; they are manufactured of boiler scrap and forged in one piece without a weld. The extreme links are anchored to heavy castiron plates of 6 feet square, which are held down by the foundations, upon which the weight of 700 perches of masonry rests. The stability of this part of the structure is fully insured, as the resistance of the anchorage is twice as great as the greatest strain to which the chains can ever be subjected.
The plan of anchorage adopted on the aqueduct varies materially from those methods usually applied to suspension bridges, where an open channel is formed under ground for the passage of the chains. On the aqueduct, the chains below ground are imbedded and completely surrounded by cement. In the construction of the masonry, this material and common lime mortar have been abundantly applied. The bars are painted with red lead. Their preservation is rendered certain by the known quality of calcareous cements to prevent oxidation. If moisture should find its way to the chains, it will be saturated with lime and add another calcareous coating to the iron. This portion of the work has been executed with scrupulous care, so as to render it unnecessary on the part of those who exercise a surveillance over the structure to examine it. The repainting of the cables every 2 or 3 years, will insure their duration for a long period.
Where the cables rest on the saddles, their size is increased at two points by introducing short wires and thus forming swells, which fit into corresponding recesses of the casting. Between these swells, the cable is forcibly pressed down by three sets of strong iron wedges, driven through openings which are cast in the side of the saddle.
When the merits of the suspension bar were discussed previous to the commencement of the structure, doubts were raised as to the stability of the pyramids and the masonry below, when unequal forces should happen to disturb the equilibrium of adjoining spans. It was then proved by a statistical demonstration, that any of the arches with the water in the trunk, could support an extra weight of 120 tons, without disturbance to any part of the work. In this examination, no allowance at all was made for the great resistance of the wood-work and the stiffness of the trunk itself. During the raising of the frame-work, the several arches were repeatedly subjected to very considerable unequal forces, which never disturbed the balance, and proved the correctness of previous calculations.
The stiffness and rigidity of the structure is so great, that no doubt is entertained that each of the several arches would sustain itself in
case the wood-work of the next one adjoining should be consumed by fire. The wood-work in any of the arches separately may be removed and substituted by new material, without affecting the equilibrium of the next one.
The original idea upon which the plan has been perfected, was to form a wooden trunk, strong enough to support its own weight, and stiff enough for an aqueduct or bridge, and to combine this structure with wire cables of a sufficient strength to bear safely the great weight of water.
The plan of this work, therefore, is a combination which presents very superior advantages, viz., great strength, stiffness, safety, durability, and economy.
This system, for the first time successfully carried out on the Pittsburgh aqueduct, may hereafter be applied, with the happiest results, to railroad bridges, which have to resist the powerful weight and great vibrations, which result from the passage of heavy locomotives and trains of cars.
REMARK.-The quantities in the following table are calculated for a depth of water of 4 feet, which has been in the aqueduct ever since the opening. The depth contemplated was 34 feet; a greater depth is at present required on account of the raising of the bottom of the canal by bars and sediment, which have to be removed before the level can be lowered.
Pressure resulting from weight of water upon 1 pyramid, 1374 tons.
" 1 superfi
List of American Patents which issued in the month of Febry ary, 1845, with Remarks and Exemplifications. By CHARLES M KELLER, late Examiner of Patents in the U. S. Patent Office. 1. For improvements in the Cultivator; R. H. Springsteed, Wooster, Wayne county, Ohio, February 12.
In this cultivator, which is adapted to the planting of seed, the frame is made to expand and contract, like the expansion harrow. The ploughs are arranged diagonally across the frame, and are con nected with it by means of journals, to admit of adjustment as the frame is expanded or contracted. The seeds are dropped in two rows, one on each side, by means of cams on the shaft of a running wheel that supports the back of the machine, which cams operate two slides for dropping the seeds.
Claim. I do not claim a cultivator with the side beams of the frame moveable, nor do I claim the spreading contracting seed planters, or the extension of shafts as described in my machine, as it has been before used for various purposes; but what I do claim as my invention and desire to secure by letters patent, is the arrangement of the ploughs as herein described, by means of the curved side pieces of the frame, said side pieces being made so that they can be expanded for the purposes herein set forth.
"I also claim in combination with the above, the shaft constructed so as to extend as herein described, combined with, and operating the slides in the hoppers.
"I further claim the construction of the back of the plough as herein described, so as to fasten all the parts by hooking the land slide into the cutter, as described."
The shaft that carries the cams for operating the slides for dropping the seeds are made with sliding coupling boxes.
2. For an improvement in the method of Evaporating Brine in the Manufacture of Salt; James S. O. Brooks, Kanawha county, Virginia, February 12.
The object of this improvement is to apply heat to the brine at the top, as it is believed that this improves the crystalization.
Claim." I do not claim applying heat to the surface of the brine for the purpose of crystalizing the salt, as that has before been done, but I confine my claim to the mode herein described of applying the heat to the surface of the brine as that surface rises or falls, by means of the revolving or floating pipe, constructed and operating substantially as herein described. Its advantages are two-fold: 1st preserves a low degree of heat in all parts of the cistern; 2nd is a convenient mode of preventing the currents in the lower strata of brine."
9. For an improvement in Door Hinges; Robert B. Varden, Baltimore, Maryland, February 12.