244 ART OF BUILDING. 



If the oxides of iron or burnt clay are used, the mortar 

 has the property of not being acted upon by water, and 

 thus forms a cement. 



Most persons must have observed that buildings formed 

 of masonry, require to have their joints pointed over or 

 refilled, the old mortar having become rotten; this is ow- 

 iug to the action of moisture and the carbonic acid gas 

 ' which is in the air, the gas having united to the lime and 

 formed limestone, and thus destroying the attraction which 

 the hydrate of lime had for the sand, which causes the 

 mortar to crumble and fall to pieces. 



From the above principles we may explain the cause 

 why lime exposed to the air, becomes slacked and finally 

 loses its properties the moisture of the atmosphere 

 combines with the lime and slacks it, or forms a hy- 

 drate ; the carbonic acid gas from the same source, then, 

 combines with the slacked lime or hydrate, and forms a 

 carbonate of lime. This may again be made quicklime 

 by heating it violently, which expels the water and gas. 



FOUNDATIONS. 



Having described the materials used by the mason, and 

 explained the principles of their action on each other, we 

 now proceed to describe some of his operations in erect- 

 ing a building or other work. 



The laying of the foundation is the first operation in 

 constructing a building, and is the most important part 

 of the whole work ; without a firm foundation it is in vain 

 for the mason to attempt to produce a permanent building. 

 Almost every city in our country can show the pernicious 

 effects of masonry constructed without a due regard to 

 the foundation. Boston can show some lamentable 

 instances, where rents and settlings are to be seen from 

 the cellar to the ridgepole. 



Wherever it is intended to erect masonry, the ground 

 should be examined with an iron bar, or a well diggers' 

 auger, which will not only show the composition of the 

 earth, but the depth at which solid ground is found, 

 which will determine whether the earth can be excavated 

 to the solid bottom or not. 



