THE MANUFACTURE OF BUILDING BRICK. 233 



DRYING. 



Bricks made by either the stiff-mud or soft-mud process have 

 to be freed from most of their water of tempering before they can 

 be burned. This is done by drying them in 1 ) open yards, 2) cov- 

 ered yards, 3) on pallet racks, 4) tunnel driers, or 5) floors. 



Open yards. — These are used at most soft-mud brick plants, 

 and are simply smooth flat floors of earth or brick, on which the 

 bricks are dumped as soon as molded, and allowed to dry in the 

 sunlight. (PI. XXVII, Fig. 1.) They are cheap, but require 

 much space, and in case of a sudden shower the green bricks are 

 washed from lack of cover. After being spread out for a day the 

 bricks are generally piled in double rows several courses high 

 along the sides of the yard. These rows, called "hacks," are often 

 covered with planking as protection from rain (Plate XXVII, 

 Fig. 2). 



Covered yards. — Covered yards differ from the preceding in 

 having a sectioned roof that can be opened in fair weather. They 

 are not used to any great extent, for when some form of protec- 

 tion against weather is desired, the type of drier next mentioned 

 is more commonly used. 



Pallet driers. — These are covered frames for holding the boards 

 or "pallets," on which the bricks are dumped from the mold at the 

 machine. They are used at many soft-mud yards and even some 

 stiff-mud plants, and possess the advantage of cheapness, large 

 capacity, economy of space and protection against rain. 



One disadvantage common to 1 all three of the above methods is 

 that they cannot be used in cold weather. Dampness in summer 

 may also interfere with them, and therefore sunlight and wind 

 are the most favorable weather conditions in most cases. Some 

 clays are quite susceptible to air currents, however, and crack 

 easily when exposed to them. 



Drying tunnels. — Many brickyards dry their product by this 

 method, especially if they continue in operation throughout the 

 year. With this system the bricks, after molding, are piled on 

 cars, which are run into a tunnel heated artificially. Several of 

 these tunnels are generally constructed side by side, and the green 



