84 MODERN GASWORKS PRACTICE
(accompanied by clinker formation.), also inferior quality of producer gas, it is usually advisable to breeze-up the open space above the top plate. The plates forming th.e grate may be of cast-iron or steel, but th.e most satisfactory method is to make them of cast-iron, to th.e underside of which a couple of thin (-^-inch.) strips of mild steel (IJ-inches wide) are riveted across both diagonals.
A development of the inclined grate principle is the author’s “ Grille ” grate, which is operated by taking in the primary air under vacuum through, door slides in the ordinary way ; or, preferably, by impelling the air thiougli specially con-
structed cast-iron duets placed one on either side of the furnace. By means of these duets, the air (thoroughly admixed with. steam) is delivered at a point adjacent to the grate bars. The grate (Fig. 35) consists of specially-designed cross bars and Langer bars, arranged in the form of a grille so as to yield a maximum of grate area. The whole is constructed of special heat-resisting iron, the primary air being injected as explained above. If the air is taken in under vacuum, however, a small supply of steam, issuing from pipes let through the furnace cheeks, is arranged for.
The hanger bars are of S shape, the upper portion of which forms a hook