246 ART OF BUILDING. 



Where a foundation is laid upon piles, it is important 

 that they are not overloaded, which will cause their rup- 

 ture and the overthrow of the building. In order to de- 

 termine the weight which each pile should support with- 

 out bending, we must know the total weight of the mass 

 of masonry which is to be placed upon them, together with 

 the dimensions of the piles, from this we may determine 

 the number of piles. The total weight of the building 

 may be asceitained by calculating the solid contents of 

 the walls from the bottom of the foundation to the top of 

 the building, to which the weight of the wood- work &-C, 

 must be added, and the doors, windows and other open- 

 ings must be subtracted. Having found the cubic con- 

 tents of the masonry, we may find their weight by knowing 

 the weight of one cubic foot of the stone or brick, or 

 what is the same thing, the specific gravity. Specific 

 gravity may be defined as the relative weight of any 

 body when compared with some other of which we know 

 the weight, one cubic foot of pure rain water weighs just 

 1000 avoirdupois ounces, and this is the substance with 

 which we compare the weight of solid bodies. Example. 

 How much will one cubic foot of Chelmsford granite 

 weigh more than one cubic foot of water 1 The deter- 

 mination of this is determining the specific gravity of 

 Chelmsford granite. If we could cut out a block of this 

 stone, exactly one foot oh each side, we could easily 

 weigli it, but this cannot be done for practical purposes, 

 and if it could, we may arrive at the same conclusion 

 much easier. 



It is evident, that if we drop a piece of stone or brick 

 into a tumbler or other vessel filled with rain water, the 

 stone will displace apart of the water just equal in bulk 

 to itself, and if the stone be weighed in the water it will 

 be found to have lost just as much in weight as the water 

 displaced will weigh, therefore we have the weight of the 

 piece of stone and the weight of an equal bulk of water, 

 which is the specific gravity. Suppose the stone weighed 

 3i pounds out of water, and one pound in the water, 

 here the bulk of water equal to that of the stone weighs 

 ' 2^ pounds, and the specific gravity in the relation or pro- 

 portion between 2^ and 3iV which is li or 1. 4. In this 



