ART OF BUILDING. 247 



way we may determine the specific gravity of any body 

 which is heavier than water. 



Knowing the specific gravity of any body we know 

 the weight of one cubic foot of it. As a cubic foot of wa- 

 ter is just 1000 ounces, if we multiply this number by the 

 specific gravity, we have the weight in ounces and from 

 thence in pounds, Sec. 



The following table of specific gravities of several bo- 

 dies will answer for all practical purposes, instead of 

 calculating them as above. 



Iron, wrought, - 7645 



Iron, cast, - - 7425 



Granite, Maine, - 2731 



Do, Chelmsford, 2910 



Sienite, Quincy, - 3000 



Limestone, - 2635 



Clay, - - - 2160 



Brick (impressed) 1980 



Brick (pressed) - 2050 



Earth, common about 1*J89 



Sand, - - 1520 



Sea water, - 1030 



Marble, - - 2840 Common water, - 1000 



Sandstone (Freestone) 2435 Slate, - - 2541 



Note. The specific gravity of water is here called 

 1000, which is just its weight in ounces, therefore the 

 numbers in this table express the weight of one cubic 

 foot of each substance in ounces. 



From the above principles we may find the solid con- 

 tents of any irregular body, provided we know the weight 

 and specific gravity. The above numbers in the table 

 are the weights of one cubic foot or 1728 cubic inches 

 in ounces ; therefore if we find how many times the num- 

 ber of ounces in one cubic foot is contained in any given 

 weight, we find how many cubic feet there are in that 

 given weight, the remainder, if any, reduced to inches 

 and divided will give the cubic inches. 



Example. Required the solid contents of an irregular 

 block of sienite which weighs 281^. 



Answer, I! cubic feet. 



The reverse of the above rule we have explained, that 

 is, to find the weight, knowing the dimensions and specific 

 gravity, multiply the solid contents in feet by the spe- 

 cific gravity, and it will give the weight in ounces. 



Having determined the weight to be supported by the 

 piles, we may determine their number and size. It has 

 been found from experiments, that each pile should not 



