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 92 cotton), both of which can be obtained commercially in slabs, as cloth, or in the form of loose fibre or wool. The loose wool is useful for filling up the spaces between the joists as a pugging to deaden sound (as already described), as well as affording protection against fire. A convenient method of attaching the slabs is shown in Fig. 385. The slabs are formed by enclosing silicate cotton between sheets of galvanised wire netting, and are made of thicknesses varying from 1 in. to 3 in. They are secured to the under side of the joists, as shown at, by wooden fillets nailed underneath, the nails passing through the slabs. To these fillets are secured the laths, when a lath-and-plaster ceiling  is desired. Additional security can be obtained by placing other slabs between the joists, resting on triangular fillets as shown in Fig. 386. Owing to the comparative cheapness of these methods of construction, and the measure of security they afford, they are worthy of more general adoption in dwelling-houses and office buildings.

Fig. 385.—Asbestos Slabs under Wooden Floor.

Fig. 386.—Asbestos Slabs between Joists.

Solid Wooded Floors.—Woodwork, when used in solid masses, is an excellent material for fireproof construction. It is extremely difficult to destroy timber in bulk by fire, and in America, partly on this account, and also on account of the cheapness of timber, floors and walls are constructed of planks nailed together side by side. The walls of many of the large grain elevators and station buildings are constructed in this way. The system of forming floors by close timbering instead of the ordinary use of joists and flooring boards, was introduced into England by Messrs. Evans and Swain between 1870 and 1880. The joists, instead of being placed at some distance from each other, were laid close together, so that air could not penetrate between them, the planks being then spiked as shown in Fig. 387. As an alternative method, the spikes could be driven in diagonally, and, if thought necessary, the under side of the planks could be protected with a plaster ceiling keyed into grooves formed in the planks. As a test of the capability of this system, a building was erected 14 ft. square inside of 14-in. brick walls, and measuring 7 ft. from the ground to the ceiling. The flooring was laid as described above, of deal battens 7 in. deep by 2½ in. thick, spiked together side by side. One-third of the under side was plastered, the joists being grooved for this purpose; one-third was plastered on nails partly driven into the planks, and the remaining third was left unprotected. The chamber underneath was packed almost full of timber, which was then lighted, and it was not until after five hours' continuous exposure to the flames that the unprotected portion of the floor gave way. The system was afterwards adopted in large warehouses for the East and West India Docks, London, and in other buildings.

Fig. 387.—Floors of Solid Wood.

Other Systems.—A modification of the system just described has been patented by Messrs. Hinton and Day, and is illustrated in Fig. 388. The joists are spaced apart in the ordinary way, but the spaces are filled in with solid blocks, having the grain placed vertically, tongued and grooved together in such a manner that the passage of air between them is prevented. The blocks are carried by fillets nailed to the sides of the joist. A test of this system of flooring was made at Westminster. Four walls of 9-in. brickwork were erected, and the under side of the floor to be tested was 9 ft. 6 in. from the ground. The lower part of the building