which they begin varies from 97.5 to 100, the latter being the height fixed by the original plans, and adopted on Piers 1 and 6, but subsequently changed on observing the exceedingly low stage at which the ice went out in 1868. The ice-breaker nose is protected by a heavy plate of cast-iron, and the shoulders are carefully dressed to a curve; this cutting being done after the stones were laid in the pier. The overhang of the cornice is one foot on each side of the pier, and two feet on the starlings, making two feet and ten inches on the angle of the nose. All the oblong piers have the same total length, the difference being in their thickness. Piers 1 and 3 finish eight feet thick at the neck, and ten feet broad on top; Piers 4, 5, and 6 finish seven feet thick at the neck, and nine on top; and Pier No. 7, six feet at the neck and eight on top. As Pier No. 7 is situated within the line of the shore it was built without an icebreaker. All of those piers finish at an elevation of 145.6.

The pivot-pier is of circular form, 29 feet in diameter, and built plumb without a batter. The cornice has an overhang of one foot and a-half, making the diameter on top 32 feet. This pier finishes four inches higher in the centre than on the circumference, this difference being made to accommodate the dimensions of the turn-table; its elevation on the outside is 142.24. The two pillars on the bank are of square section, measuring seven feet and eight inches on top and finishing at the same height as the oblong piers. The south abutment is built with its ends parallel to the trusses of the 68 foot span, and finishes at an elevation of 147.10.

These sizes make the actual clear openings of the draw 160.38 feet, at an elevation of 100, the lowest navigable stage of water; 162.8 feet at the neck of the piers, where the piers are narrowest, and 160.25 feet between the copings. The first stone laid was in the south abutment, on the 21st of August, 1867; work was suspended here during the building of Pier No. 1, and the abutment was not completed till the latter part of December. The pillars were begun in December immediately after the completion of the abutment, and finished in the following month. The time occupied in building the several piers is shown by the following table:

Pier No. 1, First stone set October 16, 1867. Pier completed November 30, 1867.

This does not include the masonry laid in Pier No. 4 during the sinking of the foundation.

The masonry of Piers 1, 2, and 3 was laid entirely with floating derricks, which were also used to some extent at Pier No. 4.* These tools were found among the most serviceable parts of the bridge outfit, and admirably adapted for use on the Missouri river; by chaining them to the sides of the caissons, or lashing to them spars which rested on the bed of the river, all difficulty from lurching under heavy loads was obviated. The three northern piers, as well as the south abutment and pillars, were built with land derricks of the ordinary pattern.

The amount of masonry and beton in the several piers is given below. These quantities are the actual amounts returned in the contractor's final estimates, but include only what forms a part of the permanent work, taking no account of the rubble masonry used in weighting the caissons for Piers 2, 3, and 5, nor of the beton placed in the draw rests:

South Abutment,...... 197 cubic yards Masonry.

CHAPTER V.

SUPERSTRUCTURE.

In the early part of August, 1867, letters were sent to a number of prominent American bridge-builders, inviting proposals for the superstructure of the Kansas City Bridge. These letters were accompanied by sets of specifications of general character, which were intended to serve rather as an indication of the quality of bridge wanted, than to contain the precise requirements of a contract. The lengths of the several spans, and the uses for which the bridge was building, were given in these specifications; they also stated that it was designed to build the draw entirely of iron, and the fixed spans of a combination of iron and wood, the latter material being used used only to resist compressive strains; the moving loads to be assumed in the calculations were specified, as well as the strains to which the iron might be subjected, and the factor of safety to be used in the wooden parts. The builders, however, were invited to propose any form of truss which they might select, submitting plans of the same if novel, and to suggest such departure from these specifications as might in their judgment seem wise, with the reasons for the change, and a statement of the benefit resulting therefrom. At the same time a set of plans for the fixed spans was prepared by Mr. Tomlinson, under the direction of the chief engineer, which were to be adopted only if, on a fair examination, they were found to be preferable to those submitted by outside parties. It had been intended to prepare plans for the draw as well, but in consequence of the mass of detail which this would involve, and the shortness of the time, it was found impossible to do so.

Nine sets of proposals were received from five different parties, two being on the common Howe truss plan, with both chords of wood; of the other plans, three were adaptations of the Pratt truss, one being entirely of iron, and the

remaining four were respectively examples of the Post, the double and the single triangular, and the Fisk suspension trusses. On the 30th of October the contract was let to the Keystone Bridge Company, of Pittsburg, Pa.; the fixed spans were to be built according to the plans supplied by the chief engineer, the iron in them being paid for by the pound, and the timber by the foot; the draw was to be built, according to the contractors' design, for a fixed sum; subject, however, to such alterations as might be suggested by the chief engineer, the Company to have the benefit of any saving which might result from such changes, and to pay any extra cost which they might involve. Under this provision certain changes were suggested in the depth of the truss and arrangement of panels, which resulted in a material reduction of the cost. By a subsequent arrangement a pony truss of wrought-iron, made by the contractors from their own designs, was built, in place of the composite structure proposed by the engineer for the shore span of 66 feet.

The general design of the fixed spans is that of a double triangular truss or trellis girder, in which the top chord, posts, and braces are of wood, and the other members of wrought-iron, cast-iron being used in the details and connections. This combination, which has been used as yet only to a limited extent, is believed to overcome the most objectionable features of a wooden bridge, avoiding the wasteful connections which accompany the use of wood in tension, and disposing of the bulk of the perishable material in places where it can easily be protected; besides this, the character of the butt-joint connections, used to take compression, is such, that worn out parts can be removed and replaced by others without disturbing the remaining parts of the structure; it is also possible to replace the wooden parts by iron, and thus gradually convert the bridge into an iron structure without the expense of false-works or the intermission of traffic. The braces, which are always open to the air on all sides, are exposed to moisture only during the actual prevalence of a storm, and would therefore be well protected by a thorough coating of paint. The top chord can be covered in, and thereby thoroughly protected from the weather, without perceptibly increasing the wind surface of the bridge. The only danger to which such a bridge can be exposed is that of fire, and if the wood-work be painted throughout with mineral paint, and a watch kept, which is always

necessary at Kansas City, men being constantly needed to tend the draw, and collect tolls, this danger is reduced to almost nothing.

The trusses of the five fixed spans measure respectively 130, 198, 248, 198, and 176 feet, the difference between these distances and the lengths of spans, given in the preceding chapters, being the allowance made for pedestals, wall-plates, and clearance room. The two shortest of these have straight parallel chords, the depth of truss being 22 feet; the same depth is retained at the ends of the larger spans, but in them the upper chord is arched so as to increase the central depth to one-eighth of the length, the inclination of the braces being kept nearly constant by varying the lengths of the panels. The upper chord of the 130 foot span is formed of three pieces, packed in the usual manner; in the other spans the chord is of five parts, and supplemented at the centre by a sub-chord of two parts. The lower chords are of wrought-iron upset links with pin connections, made under the Linville and Piper patent. The end posts and braces bear upon a cast-iron pedestal, which rests on a wallplate likewise of cast-iron, carefully fitted to the masonry, and well bedded with mortar; at one end of each span a set of rollers is placed between the pedestal and the wall-plate. In place of the ordinary square ends the braces are cut with two end faces, which make an obtuse angle with one another, and the angle blocks are cast to correspond; this device makes it impossible for a brace to slip upon its bearing. The ties are of square iron, with a welded loop at the lower end, passing around the chord pin, and a screw cut on the upper end, which is previously upset, so as to leave an equivalent area after the cutting of the screw. In the 130 foot span both the main and counter braces are single, the counters bearing upon cast-iron brackets placed on the sides of the main braces; the main and counter ties are in pairs running along the sides of the braces. In the other spans the main braces are in pairs, and the counters, which are single, pass between them. In the 176 foot span both sets of ties are in pairs, the main ties passing outside of the main braces, and the counter ties between the main and counter braces. The arrangment of ties is the same in the central panels of the 198 and 248 foot spans, but in the panels near the ends there are four main ties, two passing outside the main braces, and two between them and the counter. In all the spans the counter ties are carried