BUILDING AND ORNAMENTAL STONES. 



491 



The specific gravity or density of stone having been considered by 

 many as sufficiently indicative of their strength to be authoritative, the 

 series of tests given below were made by Dr. Bohine. The results ob- 

 tained seem to show that while with limestones this might be true, with 

 sandstones such tests could not be relied upon. A moment's reflection 

 will be sufficient to show us the cause of this, since the strength of any 

 stone, which is but an aggregate of minerals, is necessarily dependent 

 not upon the hardness, density, or toughness of the individual miner- 

 als themselves, but upon the tenacity with which they adhere to one 

 another. (See ante p. 306.) 



(a) Limestone ivith a specific gravity of 2.68. 



Five wet 

 samples. 



Five dry 

 samples. 



Lowest strength . 

 Highest strength 



7, 154. 16 

 9, 984. 54 



7, 267. 95 

 10,581.91 



(&) Limestone with a specific gravity of 2.70. 



Lowest strength . 

 Highest strength 



Eleven wet 

 samples. 



8, 050. 22 

 10, 738. 36 



Eleven dry 

 samples. 



8, 050. 22 

 12, 515. 80 



(c) Limestone with a specific gravity of 2.71. 



Lowest strength . 

 Highest strength 



Six wet 

 samples. 



7, 196. 83 

 12, 316. 72 



Six dry 

 samples. 



7, 879. 54 

 13, 668. 60 



after careful weighing, saturate them with water, and subject them to freezing and 

 thawing by artificial temperatures; weighing them again, at the conclusion of the 

 experiments, to learn the loss of material, if any. After the freezing tests are con- 

 cluded the same cubes should, in their saturated condition, be submitted to crushing 

 tests. By a comparison of the results thus arrived at it is believed a better knowl- 

 edge of the durability of any stone could be obtained than would be possible in any 

 other way than by the actual exposure of the stone for a period of many years. 

 Where stones are to be subjected to the action of the acid gases of cities or liable to 

 be subjected to high temperatures from burning buildings, artificial atmospheric and 

 fire tests can readily be applied after the plan adopted by Professor Winchell (Geol. 

 of Minn., final rep., Vol. i). The actual cost of such a series of experiments need not 

 necessarily be great after the apparatus has once been established. Had such a series 

 been inaugurated by the National Government years ago, we might have been spared 

 the infliction of the painted walls of the White House and Capitol. 



