THE MANUFACTURE OF BUILDING BRICK. 223 



factories in the State making enameled brick, and both employ a 

 mixture of fire clays from the Middlesex county district. 



Glazed brick are made only to a slight extent in New Jersey. 

 The clays used are similar to those employed for enameled brick. 



Methods of Manufacture. 



The methods employed in the manufacture of common and 

 pressed brick are usually very similar, the differences lying chiefly 

 in selection of material, the degree of preparation, and the amount 

 of care taken in burning. The manufacture of bricks may be 

 separated into the following steps : preparation, molding, drying 

 and burning. 



PREPARATION. 



In brickmaking some preparation o>f the clay is commonly 

 necessary, since few clays can be sent direct from the bank to the 

 molding machine, although some common brick manufacturers in 

 New Jersey reduce the preparation process to- a minimum. 



Weathering. — Many clays are prepared by weathering, espe- 

 cially if they are to be used in the manufacture of pressed brick. 

 This is done by distributing the clay in a thin layer over some flat 

 surface not more than 2 or 3 feet in thickness and allowing it to 

 lie there exposed to frost, rain, wind, and sun. This results in a 

 slow but thorough disintegration or slacking. Iron nodules, if 

 present, tend to' rust, and are thus more easily seen and rejected, 

 while pyrite, if present, may also decompose and give rise to 

 soluble compounds, which form a white crust on the surface of 

 the clay. Although some clays are weathered, yet in great part 

 their preparation is done by artificial means. 



Dry crushing. — When the clay or shale is to be disintegrated 

 or crushed, it is commonly done dry, and the machine employed 

 varies with the character of the material. Hard' shale is usually 

 disintegrated in a jaw crusher, which consists: of two* movable jaws 

 that interact, and are set closer together at their lower than at 

 their upper ends. Where a soft shale, or a hard, tough, dry clay 



