278 CLAYS AND CLAY INDUSTRY. 



long, the other two dimensions may vary. Thus, of the blocks 

 which are 12 inches long, the other dimensions may be 6 by 3 in., 

 6 by 4 in., 6 by 5 in., 6 by 6 in., 6 by 7 in., etc., or perhaps 3 by 8 

 or 3 by 12 in., etc. A large number of the fireproof shapes made 

 are for floor arches, and in such cases the architect commonly 

 specifies the depth of the arch while the width of the blocks is gov- 

 erned by the width of the span. The weight of the arch will 

 depend on its depth. 



Thus, 6-inch floor arches weigh about 25 pounds per square foot. 



7 do. do. do. 



do. 



do. 



28 



do. 



do. 



do. 



do. 



10 do. do. do. 



do. 



do. 



35 



do. 



do. 



do. 



do. 



12 do. do. do. 



do. 



do. 



42 



do. 



do. 



do. 



do. 



3-inch book tile 



do. 



do. 



15 



do. 



do. 



do. 



do. 



3-inch partition tile 



do. 



do. 



15 



do. 



do. 



do. 



do. 



6 do. do. do. 



do. 



do. 



21 



do. 



do. 



do. 



do. 



8 do. do. do. 



do. 



do. 



28 



do. 



do. 



do. 



do. 



2 do. wall furring 



do. 



do. 



8-5 



do. 



do. 



do. 



do. 



3 do. do. do. 



do. 



do. 



10.5 



do. 



do. 



do. 



do. 



2 do. column covering 



do. 



do. 



13 



do. 



do. 



do. 



do. 



3 do. do. do. 



do. 



do. 



15 



do. 



do. 



do. 



do. 



The cost of fireproofing is commonly figured by the ton. 



Hollow blocks are usually made in 8-inch lengths, but vary in 

 their other two dimensions, being 4 by 16, 6 by 16, 8 by 16, 10 

 by 16, 12 by 16, etc. They are used quite extensively in the 

 central States, but not so much in the eastern ones. Hollow 

 blocks are made with either smooth, corrugated or ornamented 

 surfaces. 



Sizes 8 by 4 by 16 in. are sold for about $0.07 each, and 8 by 

 8 by 16 in. at $0.10 each. Hollow bricks are often used for the 

 interior course of exterior walls, and the plaster can be laid 

 directly on them without the use of lathing. 



Raw materials. — The clays used for making fireproofing and 

 hollow bricks are often a grade of fire clay, but those manufac- 

 tured in New Jersey are made from a mixture of an impure red- 

 burning clay, to which a certain proportion of fire clay is some- 

 times added. The former is obtained in great abundance from 

 the laminated clay in the upper part of the Woodbridge clay bed, 

 as well as from Clay Marl II. While the different classes of 



