Floors constructed with rolled-iron beams and brick arches are proof against fire only to a limited degree; for experience has shown that the heat, in an extensive conflagration, is sufficiently intense to deprive the iron of its rigidity, and consequently of its strength. Singular as it may seem, it is nevertheless true that wood, under certain circumstances, has a greater fire-resisting quality than iron. Floors of timber constructed, as is usual, with the beams set apart, have but little power to resist fire, but if the spaces between the beams be filled up solid with other beams, which thus close the openings against the passage of the flames, and the under surface be coated with plastering mortar containing a large portion of plaster of Paris, and finished smooth, then this wooden floor will resist the action of fire longer than a floor of iron beams and brick arches. The wooden beams should be secured to each other by dowels or spikes.