BRICK AND BUILDING STONE 273 



building stone, especially for bridge piers and other structures where 

 large masses of stone are needed. This particular limestone, unlike 

 most others, is easily worked, being almost equal to sandstone in 

 this respect. 



When limestone is subjected to the atmosphere of a large city, where 

 great quantities of coal are used, it is acted upon by the sulphuric 

 acid in the air. To determine the effect of this action, a small piece of 

 stone, well cleaned, is placed in a 1 per cent solution of sulphuric 

 acid and left for several days. If no earthy matter appears, it may be 

 concluded that the stone will withstand the action of the atmosphere. 



222. Sandstone. Sandstone consists very largely of grains of sand 

 (silicon) cemented together. It has been deposited from water, making 

 it homogeneous in structure, and as it occurs in vast beds, it is very 

 suitable for building purposes. The ease with which it may be carved 

 and worked makes it a much more valuable building material than 

 limestone. Various foreign substances, such as iron, manganese, etc., 

 give to the stone a variety both in color and texture. Sandstone 

 absorbs water much more readily than limestone, and were it not for 

 the fact that it occurs in such thick layers, and is therefore almost 

 free from sedimentary planes, this might be a serious objection to its 



The mean weight of sandstone is 140 lb./ft. 3 ; that of limestone 

 is 160 lb./ft. 8 . 



223. Compression tests of stone. The most common test for a 

 building stone is that of subjecting it to a direct crushing force in 

 an ordinary testing machine. To prevent local stresses, the specimen, 

 whi.-li is ^em-rally a well-finished cube, is usually bedded in plaster 

 of Paris, thin pine boards, or thick paper, and the load at first 

 <-ra.-k and the maximum load are noted. The friction of the bedding 



:ist the heads of the machine tends to prevent the spreading of 

 tin- specimen near these heads and thus adds to the strength of the 

 rul.c. (ireat care is necessary in preparing the specimen, in order to 

 be two bearing faces exactly parallel. The stone fractures along 

 the 30 line approximately, giving the characteristic fracture of two 

 inverted pyramids (Figs. 161 and 162). 



Fn.m a series of tests made by Buckley on the building stones of 

 Wisconsin,* the average of ten tests on limestone gave an ultimate 



* Buckley, Building Stones of Wisconsin. 



