Suitable guide-chairs for the rails near the ends of the span are to be provided beneath the same on at least fifteen (15) ties from each end of the span. These chairs must be either spiked or bolted to the ties, and must hold the rails firmly in place. Guide-rods such as are employed in ordinary switchwork are to be used every six feet between the portions of the rails resting in the guide chairs.

The strength of all parts of the rail-lifting machinery is to be determined by computing the force necessary to deflect the two rails the required amount in a distance of twenty (20) feet, and adding fifty (50) per cent thereto for friction.

If considered necessary for any particular span, latches are to be provided for holding the ends in place; but under ordinary conditions the track-rails and the end rollers are all that will be required.

In double-track drawbridges special attention must be paid to the designing of not only the lifting-gear, but also the trusses themselves, in order to ensure that, under the most unfavorable circumstances possible, there shall be no lifting of the ends of trusses off their supports. If such a lifting were possible, the result would certainly be the derailment of an entering train, and consequently disaster to the span. To prevent such uplifting the trusses must be deep and very rigid, and the lift of the ends must be from one (1) to two (2) inches, according to the length of the span.

SHOES AND END-BEARING ROLLERS.

Rollers are to be provided beneath the end-pins of trusses and attached to the span by means of links which form a part of the toggle. The rollers must be bored so as to fit over the pins at the bottom of the links. Both the pins and the inside of the rollers must be finished very smooth; and provision must be made for oiling the bearings between them. The allowable intensity for bearing between rollers and pins shall be ten thousand (10,000) pounds per square inch of horizontal projection of pin inside of the roller.

No roller shall be less than six (6) inches in diameter, and the pins inside of same shall not be less than three and seven-