of said rollers, but never enough to involve the possibility of collision with the draw-span during its revolution and when the top chords thereof are thirty (30) degrees Fahrenheit warmer than the bottom chords.

All parts of the end-lifting machinery must be finished in accordance with the best machine-shop practice, and all sliding surfaces shall be provided with oil-holes that are easily accessible.

In all cases end floor-beams with double webs shall be used, in order to provide proper support for the end-lifting machinery.

Whenever spans are to be floored for highway traffic, all keyholes for applying hand-levers are to be provided with suitable cast-iron caps.

Whenever practicable, the end-lifting toggle machinery is to be assembled in the shops to make sure that it will work satisfactorily.

HOUSES AND SUPPORTS.

Wherever mechanical power of any kind is to be used for operating any draw-span, a suitable house is to be provided for same. The size of the house required will depend upon the kind of power to be used, and the amount thereof. All parts of the house shall be durable and strong, and shall be finished in a first-class and workmanlike manner. A sufficient number of windows is to be put in to light properly all parts of the building. The house shall be placed high enough in the tower to give the required clearance beneath its supports, and, where shallow trusses are used, it shall be placed entirely above the span. The supports for the house shall be designed to carry the weight of the latter and that of all machinery to be placed therein, together with a proper allowance for live load. In general, steel beams shall be used for the joists supporting the floor, and all parts of the latter shall be made strong enough to carry three hundred and fifty (350) pounds per square foot.

The weight of the house and its machinery must always be