BUILDING AND ORNAMENTAL 8TONES. 



4yi 



The specific gravity or density of stone having- been considered by 

 many as snfficieutly indicative of their strengtlito be authoritative, the 

 series of tests given beh)w were made by Dr. Bohnie. Tbe 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 

 iu)t 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. 30(3.) 



(rt) Limestone with a specific f/ravify of 2.08. 



Lowest strength 8, 050. 22 



Highest strength 10, 738. 3(i 



Eleven wet 

 samples. 



Eleven dry 

 samples. 



8, 050. 22 

 12, 515. 80 



(c) Limestone with a specific (jravity of 2.71. 



Six wet 

 samples. 



Six dry 

 samples. 



Lowest strength . 

 Highest strength 



7, 19(), m 

 12, 316. 72 



7, 879. 54 

 13, ms. 60 



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

 thawing by artificial temperatures; weigliing 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 stjoue 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 bo applied after the plan ado[)ted by Professor Winehell (Geol. 

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

 necessarily be gr<!at after the apparatus has once been established. Had such a series 

 been inaugurate!!! b^' the National GoverniiuMit years ago, we might have been spared 

 the iniliction of the painted walls of the White House aud Capitol. 



