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seed oil before shipment from the works, and all bright parts shall be protected by a coat of tallow and white lead.

After erected in place it shall be painted two good coats of lead and oil of such color as the engineer in charge shall direct.

Quality of the iron.-All iron used in the bridge shall be "best best" quality of double refined iron with an elastic limit not less than 25,000 pounds per square inch, and an ultimate strength as great as can be attained with that elastic limit in the best iron for bridge purposes.

All wrought irou must be tough, fibrous, and uniform in character. Finished bars must be thoroughly welded in rolling, and free from injurious seams, blisters, buckles, cinder spots, or imperfect edges.

For all tension members the muck-bars shall be rolled into flats and again ent, piled, and rolled into finished sizes. No scrap shall be used. They shall stand the following tests:

Tension tests. When tested in specimens of uniform sectional area of not less than half nor more than one square inch for a length of ten inches, taken from members to be used in the bridge, the iron shall show an ultimate strength and elongation as follows:

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Full sized pieces of flat, round, or square iron used for tension members, and not over 3 square inches in sectional area shall have an ultimate strength of 50,000 pounds per square inch, and bars of larger sectional area will be allowed a reduction of 1,000 pounds per square inch, down to a minimum of 46,000 pounds per square inch.

Bending tests.-All iron for tension members must bend cold, for about 90 degrees to a curye whose diameter is not over twice the thickness of the piece, without cracking. At least one sample in three must bend 180 degrees to this curve without cracking. Then nicked on one side, and bent by a blow from a sledge, the fracture must be nearly all fibrous, showing but few crystalline specks.

Specimens from angle, plate, and shaped iron must stand bending cold through 90 degrees, and to a curve whose diameter is not over three times its thickness, without cracking.

When nicked er bent its fracture must be mostly fibrous.

All facilities for inspection of iron and workmanship shall be furnished by the contractor. He shall furnish, without charge, such specimens, or full sized pieces of the several kinds of iron to be used as may be required to determine their character.

Sizes of iron.-In case the sizes of iron or members herein specified, or stated on the strain sheets, shall be found by the engineer to be insufficient to meet the strains arising from the specified loads, the sizes of such iron or member shall be increased so as to meet the required strain per square inch.

Wood work.--All lumber shall be of sound, well-seasoned, Georgia or North Carorina long-leaved pitch pine, to be all heart-wood, free from shakes, large or unsound knots, or any other defects.

Roadway plank.-The roadway plank shall be 3 inches thick, 6 to 12 inches wide, and laid diagonally. They shall be spiked to each joist by two 7-inch spikes, and with two spikes at each end.

Sidewalk plank. The sidewalk plank shall be 2 inches thick, 6 to 12 inches wide, laid crosswise, with two 5-inch spikes at each intersection with joist, and two in each end. The grade of the sidewalks shall be 4 inches above that of the roadway.

Roadway joist.-The roadway joist shall be 15 inches deep, 4 inches wide, placed 2 feet apart.

Sidewalk joist.-The sidewalk joist shall be 3 inches thick, 15 inches deep, and placed 2 feet apart.

Wheel guard.-To the end of roadway plank shall be spiked a 6 by 8-inch wheel guard, raised on blocks, placed 4 feet apart to a level of the sidewalk plank. The inner edge of wheel guard to be bound with an 1 inch by inch flat bar of iron secured to same by 14-inch wood screws driven after wheel guard is set, In case the floor system above

specified shall be found insufficient to bear the specified panel and wheel loads the sizes of beams shall be increased as required by the engineer. If in case it shall be deemed best by the contractor, upon a further examination of the natural conditions of the site, to change the location of the bridge, within the limits specified in the original advertisement, from the site herein noted, or to make any changes in the length of the spans from those herein stated, they shall base their unit strains the same as herein specified, and the capacity per square foot of roadway and walks as per the following table, subject in all cases to the approval of the engineer in charge:

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Provided that the loads per square foot herein indicated are to be taken for a width of bridge of 30 feet. In case the width is reduced to 25 feet the loads per linear foot of bridge shall be the above units multiplied by 30 feet.

85 feet and 55 feet spans.-The sizes and section for 85 feet and 55 feet spans are given on strain diagram sheet, and in all respects they shall conform in quality to that specified above for the 187-foot spans.

False works.-The false works for the bridge shall be erected by and at the expense of the contractor, and upon the completion of the bridge shall be entirely removed.

APPROACHES.

Virginia shore. The approaches to the bridge on the Virginia side are to be of such extent and length as will permit a connectiou to be readily made therewith by the county roads. The width of the approach shall not be less than the combined width of the footways and roadways, and the grade shall not exceed 3 feet in 100 feet.

The slopes of the embankment or excavation of the approach shall not be less than 14 horizontal to 1 vertical.

The character of the road-bed shall be fully equal to that of the roads connecting therewith.

Georgetown approach.-The north or Georgetown end of the bridge will cross the canal and terminate at the north abutment, to be built as already specified on the north side of the canal, so as to make a direct connection with the canal road by raising the grade of the same.

The grade of the road will be raised to the level of the bridge at the end of the same, and the approaches to a grade of 2 feet in 100 in either direction from this level. The filling shall be made in layers, with suitable material such as is found in the immediate vicinity, and the work is to be done so as not to interfere with travel. The width of the roadway will be 50 feet, and the side slopes 13 to 1, and the roadway will be macadamized to the same depth as the existing canal road.

The wall along the canal is to be raised so as to be at the same height above the new grade as it is above the present grade of the road.

On the north side of the embankment of approach a suitable wooden railing shall be put up, if deemed necessary by the engineer, to prevent accidents to vehicles.

B.

CORRUGATED METAL COMPANY TO MR. S. T. ABERT, UNITED STATES CIVIL ENGI

NEER.

BINGHAMTON, N. Y., February 13, 1882.

SIR: Referring to your esteemed favor 31st ultimo, would say: We beg to decline to accept the modified specifications there with inclosed to us, as a basis for a contract for building the proposed bridge at Georgetown, D. C., in the particular matter of the height of the piers.

It is not necessary to the stability of the structure to carry up the masonry of the piers to the center of the trusses.

The iron end part and braces, which you prefer to omit, are amply sufficient for the purpose as designed, for the particular reason that the brace (acting as a strut or tie)

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affords a sufficient safe resistance as against wind or other force longitudinally applied to the extent and amount of a force which would overturn the pier. The exact amount of strain exerted under various conditions upon the foot brace is not determinable, but the amount of force required to overturn the pier, when applied to its top and longest side is determinable in amount, and the foot brace is in design and section sufficient to resist that amount of strain, whether acting as a strut or tie. We deem it quite unnecessary to provide for a condition of resistance of the character under consideration greater than the resistance offered by the piers themselves. With the exception of the height of the piers (they to be as proposed by us as to height) and their thickness at top (to be reduced by 1 foot) from that stated in your specifications, we accept all of the conditions named in your specifications of January 31, 1881, as the basis of a contract to build the bridge.

Referring to the postscript of your favor of January 31, 1880, would say, the weight per linear foot or yard determines the net section of an angle or channel bar.

Referring to your favor of 4th instant would say, in calculating strains graphical method has been used. We waive any error in calculations, and will submit detailed calculations if desired and if contract is awarded to us. We are, sir, very respectfully, your obedient servants,

Mr. S. T. ABERT,

United States Civil Engineer.

THE CORRUGATED METAL COMPANY, By WM. O. DOUGLAS, Agent.

P. S.-We here with return your specifications of 31st ultimo, as requested. The piers to be 7 feet wide, measured on top of coping.

C.

CORRUGATED METAL COMPANY TO THE CHIEF OF ENGINEERS.

BINGHAMTON, N. Y., February 16, 1882.

GENERAL: We regret that under date of the 14th instant we were compelled to decline the final specifications concerning the proposed free bridge, submitted by Mr. Abert, principally in the matter of the increased height of the piers, which were increased from 26 feet to 46 feet above low-water.

This increased amount of masonry would cost $50,000, for which amount, in addition to our former bid of $140,000, we would subscribe to Mr. Abert's last specifications in full, and in every particular, as the basis of a contract to do the whole work. We are, general, very respectfully, your obedient servants,

THE CORRUGATED METAL COMPANY, By WILLIAM O. DOUGLAS, Agent.

Bvt. Maj. Gen. HORATIO G. WRIGHT,

Chief of Engineers, U. S. A.

D.

THE KING BRIDGE COMPANY TO MR. S. T. ABERT, UNITED STATES CIVIL ENGINEER.

CLEVELAND, OHIO, January 28, 1882.

DEAR SIR: Your favor of 23d received. We also have received a Washington paper,with inclosed clipping. We presume there is some mistake about it, and that we will be allowed to modify our bid if Corrugated Company are allowed to modify theirs. We think we should have that privilege. As we understand Mr. Lewis, onr bid is for a bridge such as we understood you desired for the place, and nearly twice as wide as the Corrugated Metal Company's plan. If we are allowed to bid on a bridge no wider than theirs, our price, of course, would be considerably less than on the plan we submitted last fall.

We think the fair plan would be to readvertise on a specified width, and length of spans and load, which would put all bidders on same footing. We think more companies would now compete, and the bids be lower.

Yours truly,

Col. S. T. ABERT,

JAS. A. KING.

United States Engineer.

E.

CLEVELAND, OHIO, February 2, 1882. DEAR SIR: Your favor 30th duly received. You must have forgotten the request of our Mr. Lewis while there to modify his plan and bid. He says he made such a request. We will now make a further request to be allowed to modify our plan and bid, and secure bid substructure to accompany it.

Please advise us if this will be considered, and much oblige us.

Yours truly,

Col. S. T. ABERT,

JAS. A. KING.

United States Engineer.

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