Ries — Physical Tests of Devonian Siiaj.es. 



685 



Stiff-mud brick are frequently repressed, as it is considered to improve 

 the quality of the product and, indeed, this is true within certain limits. 



In a series of experiments recently made by Professor E. Orton, Jr., it 

 was found that end-cut bricks were tougher than side-cut ones, and when 

 repressed they were still more so. These experiments are important and 

 interesting and worth mentioning in detail. A number of bricks were made 

 from the same lot of shale, but molded on different machines. They were, 

 however, all burned together in the same kiln. These brick were tested in a 

 rattler and it was found that the loss by abrasion was least in the case of the 

 end-cut repressed brick. 



Soft-mud process. This method is sometimes used for shales or clays 

 which can not be molded in stiff -mud machines, and works well. It is being 

 used at one locality in New York state for the manufacture of paving brick. 

 The soft-mud process gives a brick of thoroughly uniform texture, but on 

 account of its limited capacity the cost of production is greater than with 

 stiff-mud machines. 



Drying. Paving brick are generally dried by artificial heat. Two 

 general systems of drying may be noticed, viz., floor-dryers and tunnel-dryers. 

 The latter have the most extended application. 



Floor-dryers. These may be of brick, heated by flues underneath them, 

 which conduct the heat from the fire-place at one end. Such floors are cheap, 

 but the heat is very unequal at the two ends, and the use of such floors 

 involves considerable labor in handling. Slatted floors, such as those used 

 for drying sewer pipe, may be used, but their cost of installation is great, and 

 the bricks also require much handling. 



Tunnel-dryers. The tunnels are made of brick or wood and heated by 

 hot air, steam or flues running under them. The bricks are piled on cars, 

 which are run on tracks into the tunnel. The cars are run in at one end 

 and always taken out at the other. The hot air is introduced at the end 

 where the bricks are taken out. 



A recent improvement is the drawing of hot air from the cooling kilns 

 and blowing -it through the tunnels. Though still in the experimental stage, 

 this method will no doubt be widely used before long. 



Burning. Paving brick are generally burned in down-draft kilns, 

 These are of rectangular or circular shape, the former having a capacity of 

 160,000 to 200,000 and the latter about 30,000. The rectangular ones are 

 quite generally used now, and it is only in a few districts that the manu- 

 facturers cling to the circular ones. 



