MASONRY. 277 



EXAMPLE. How many perches of stone contained in a 

 wall 4:0 feet long, 20 feet high, and 18 inches thick ? 



SOLUTION. 40 feet, length, x 20 ft., height, x 1 feet, 

 thick,=1200-r-22=:54.54 perches. Ans. 



NOTE. To find the number of perches of masonry, divide 

 the product, as above, by 24.75, instead of 22. 



Brick-work. 



The dimensions of common bricks are from 7f to 8 inches 

 long, by 41 wide, and 2J thick. Front bricks are 8 J inches 

 long, by 4^- wide, and 2J thick. 



The usual size of fire bricks is 9& inches long, by 4f wide, 

 by 2| thick. 



Twenty common bricks to a cubic foot when laid ; 15 

 common bricks to a foot of 8-inch wall when laid. 



To find the number of common ~bricks in a wall. 



RULE. Multiply the length of the wall in feet by the 

 height in feet, and that by its thickness in feet, and that 

 again by 20, and the product will be the number of bricks 

 in the wall. 



EXAMPLE. How many common bricks in a wall 40 feet 

 long by 20 feet high and 12 inches thick ? 



SOLUTION. 40 ft., length, x 20 ft., height, x 1 ft., thick, 

 x 20=16000. Ans. 



NOTE. For walls 8 ins. thick, multiply the length in feet 

 by the height in feet, and that by 15, and the product will 

 be the number of bricks in the wall. 



