The different forms in which bricks are made for special purposes are almost innumerable.
It would not be worth while, even if space were available, to describe them all; but a few of the principal varieties may be mentioned.
Ordinary Bricks are of rectangular section, both longitudinally and transversely, and solid throughout. They have already been described.
Purpose-made Bricks are those which are specially moulded to shapes suited for particular situations, such, for example, as the voussoirs of arches struck to a quick curve, the corners of obtuse-angled structures, etc. etc.
There are several advantages in having the bricks thus purpose-moulded : cutting is saved, and the surface-skin of the brick is left intact, which enables the brick to resist the weather far better than if the surface were removed by cutting.
Arch Bricks are shaped as voussoirs of arches.
Compass Bricks taper in one direction at least. If they taper in thickness they are suitable for the voussoirs of an arch, and are called Arch bricks or Side-wedge bricks. If, however, the thickness is constant, and they vary gradually in width, they are useful for steining walls, and are sometimes called Bullheads.
The name Compass bricks is sometimes applied only to bricks tapering in both directions, as in Fig. 13. Such bricks are used for parts of furnaces etc. etc.
Perforated Bricks (Fig. 14) have cylindrical holes through their thickness, which makes them easier to burn (because the fire can penetrate them more thoroughly), and lighter to handle, such bricks are often made from the denser and heavier clays.
An objection sometimes stated against them is that they transmit sound readily.
Splits are bricks of the ordinary area, but of reduced thickness, being 9 inches by 41/2 inches wide, and 1, l1/2, or 2 inches in thickness.
Soaps are bricks 9 inches long, 21/4 inches wide and 21/4 inches thick.
Fig. 15. Fig. 16. Angle Brick. Stretcher.
Fig. 17. Header.
Hollow Bricks should be moulded from the best and most homogeneous clay. They may be of large size, as their shape enables them to be thoroughly burnt, and makes them lighter to handle.
There are a great many forms of these bricks used for building hollow walls.
Figs. 15, 16, 17 show hollow bricks made by Messrs. Clayton, Son, and Howlett's machines.
The three figures show an angle brick, stretcher, and header in position as for the angle of a wall, but spread out so as to show their construction. They are so arranged that a solid side or end is always presented on the face of the wall.
In other forms the perforations are somewhat different; for example, as in Figs. 18, 19 -
Fig. 18. Fig. 19. Header. Stretcher.
The form and use of other hollow bricks are shown by the section, Fig. 27.
Tubular Bricks are hollow bricks in which there is one large perforation running through the length of the brick.
Tubular bricks are also made in the form shown in Fig. 20, so that several of them built up together form a pillar.
Somewhat similar bricks, but flat, instead of round, are made for building up pilasters.
Plinth, Cornice, and String-Course Brides are made of several patterns.
Fig. 22. Fig. 23. Fig. 24.
They have to be arranged so as to be built in as headers and stretchers, and also for angles.
Thus Figs. 21 to 24 are all plinth bricks: a is a stretcher, b a header, c an external angle, d an internal angle.
Those that are intended to project should have a throat on the lower side, as in Fig. 25.
Sometimes several different forms of moulded bricks are combined to form a cornice, as in Figs. 26, 27, which are from an advertisement by the Broom-hall Company.
Bricks shaped like 0, Fig. 26, are known as Hollow Cornice; those of section like p are Full Cornice, while q and r are Moulded Cornice bricks.