138 STEAM BOILERS, ENGINES, AND TURBINES
chimneys-perhaps the most important point is the foundation. The foundation of the chimney must be of a certain definite depth and width, in proportion to its height and sectional area. In the building of brick chimneys it is of great importance that the bricks should be of a very high class, and that very much greater care should be taken in laying the bricks than with ordinary building. In fact, chimney building is a special art in itself. Special forms of bricks have been designed for the building of chimneys, and amongst them may be noted the perforated radial bricks made by the Alphons Custodis Construction Company. The chimney is designed on paper, exactly as a machine is, and the bricks for the chimney are also designed to occupy their proper sectorship of the cylinders they go to make up. It is claimed for chimneys built with these bricks that they stand better, and that better provision is made for expansion, while the chimney itself is more of a solid structure than can be obtained with the ordinary brick. With the ordinary brick, it will be understood, the angles formed by laying the bricks together to form a cylinder must be filled in with mortar; while with radially designed bricks the bricks themselves form the cylinder, the only office of the mortar being to hold the bricks together. It is usual to build an outer protective shell with ordinary bricks, though it is claimed that this is not neces- sary with the perforated radial bricks. It is sometimes arranged to fix water tanks about halfway unp the chimney, the tank taking an annular form, the lower portion being inclined to the vertical, and being supported by special ledges of bricks, a cover being provided for the water above. This arrangement has the advantage of a water tower at a considerable height above the ground, with only a small expense for the support of the tank, where the ordinary water tower would be a somewhat expensive matter. Steel chimneys are now built very much on the lines of steel boilers, except that, as they have not so much pressure to withstand, it has not been found necessary to take such great care in the forma- tion of the cylinders, the joints, etc. The chimney is built up in sections, each section being made of sheets from 8 to 10 feet in length, the sheets being riveted together in the usual way, the rivct-holes being punched instead of drilled. Steel chimneys are made either to be supported by guys, or to be self-supporting. Where there is a difficulty in obtaining a good foundation, it is necessary to support the chimneys at two or three portions of their height by guys or stays in all directions, the stays consisting of wire ropes, ending in rods attached to anchors in the ground. Where a good foundation is obtainable, the chimney is made self-supporting, by giving it a broad, deep foundation, and by anchoring its base by means of bolts.
