flange of the iron joist by means of a cement (bituminous preferred), and the combination is then fixed in position, the edges of the slabs adhering to, or rather supported by, the iron joist being rebated so as to receive and support intervening slabs, the heading joints of which are laid to break with those of the slabs supported by the joists.  For double floors the iron joists are made with a double flange on their lower edge, and are fitted to iron girders, which cross in the opposite direction.  This provision secures the covering of the cross girders on their undersides by the ceiling slabs.  The concrete having been deposited upon the slabs, its upper surface may be finished off in any of the usual ways, while the ceiling may be treated in any of the ways described for the walls.  This system does not exclude the ordinary methods of constructing floors and roofs, although it supplies a fireproof system.  Where required, bricks, stone, and, in fact, any other building material, may be used in conjunction with the slabs.

The system of building construction is intended, as in the case with all concrete, to supersede brickwork and masonry in the various uses to which they have been applied, and, at the same time, to offer a more perfect system of building in concrete.  Hitherto slab concrete work has never been erected in a perfectly finished state (i.e., with mouldings, etc., complete), but has either been left in a rough state or without ornament, or else has been constructed so as never to be capable of receiving good ornamental treatment.  Hitherto the great difficulty in constructing concrete walls of concrete and other slabs has been to prevent the slabs from being forced outward or from toppling over by the pressure of the plastic filling-in material from the time of its deposition between the slabs until it has become hard enough to form, with the slabs, a solid wall.  Besides the system of forming the slabs of L (vertical or horizontal) section, or with a kind of internal buttress and shoring them up from the outside, or of supporting the slabs upon framing fixed against the faces of the wall, several devices have been used to obviate this difficulty.

In the first place, temporary ties, or gauges, connecting the slabs forming the two faces of the wall, have been used, and as soon as the plastic filling-in material has set or become hard (but not before), these have been removed.  Secondly, permanent ties or cramps have been used, and, as their name implies, have been allowed to remain in the wall and to be entirely buried in the plastic filling-in material.  These permanent transverse ties or cramps have been of two kinds:  those which were affixed as soon as the slabs were placed in position, and those which were made to form part of the manufactured slab, as, for instance, slabs of Z or H horizontal section.  Thirdly, a small layer of the plastic filling-in material itself has been made to act as a transverse tie by depositing