The cupola platform or charging floor of the foundry is of 2«-inch planks laid on 3 × 12 inch joists, placed 12 inches from center to center, and supported in their centers by a 10 × 12 inch beam, whose ends rest in the brick walls, and its center upon an 8 × 8 inch post. The floor, at least in the vicinity of the cupola, should be protected by sheet iron smoothly nailed down.

If preferred, the floor may be constructed entirely of iron. In this case, plate girders or I-beams should carry cross supports and the floor be composed of cast iron plates reaching from one support to the other, and having supporting ribs cast on their under sides.

This form would, of course, make a much better method of construction, and in such a situation, much safer from the danger of fire, although more expensive.

The floors of the washrooms in the power house are of 1« × 6 inch matched planks, planed on both sides, and laid on 2 × 12 inch joists placed 16 inches from center to center. Iron or steel floors may be here used to advantage on account of the disagreeable odors produced by saturated wood floors.

Floors in the office building, including the drawing room and pattern shop, are laid with a lining of ordinary pine ⅞-inch thick, and covered by 1⅛-inch hard pine, planed and matched, and not over 3« inches wide, with the grain of the wood as shown in Fig. 47.

The floors are laid on 3 × 12 inch joists placed 16 inches from center to center and supported by 10 × 12 inch beams set 12 feet from center to center.

For the second floor these beams are supported on iron columns in the office and on 8 x 8 inch posts in the tool room, set 16 feet apart, making four posts or columns in the building 50 feet square, outside measurement.

The timbers of the ground floor are supported on brick piers rising from the ground, which is excavated to a depth of at least three feet below the floor. One of these piers is under each post or column.

In place of wooden beams and joists, iron or steel girders or I-beams may be introduced, making a construction more nearly fire-proof, particularly for the second floor, but adding materially to the expense.

The floor of the pattern storage loft is of 1«-inch matched planks laid on 3 × 12 inch joists placed 16 inches from center to center and supported by I-beams 15 inches deep, one end resting in the front wall and the other on an 18-inch box girder carrying the rear wall and resting on iron columns, as shown in the plan.

As to the kind of lumber used in the floors of manufacturing buildings, spruce is by far the most common, and if properly selected is best for all ordinary purposes. Hard pine makes an excellent floor and is preferable where extra expense is not an obstacle.

Occasionally, when cost is a secondary consideration, and a perfectly smooth surface is necessary, floors of hard maple are laid and carefully surfaced off by hand-planing. This makes probably the most durable of any of the wood floors.

The author saw a floor about 125 × 250 feet, prepared with a concrete bed and then laid on the wet flowing coat with hard maple blocks 2×4×12 inches, laid on edge, and in the "herring-bone pattern" shown for bricks in Fig. 43. After the concrete had thoroughly set the surface was hand-planed and oiled.

Of whatever kind of wood floors are made the material should be well seasoned, and if shrinkage cracks are to be avoided, the narrower the planks are the better, although 3 inches may be the minimum width.

If they are 3 inches thick or more, then 6 inches should be the minimum width.