8 



NEW YORK STATE MUSEUM 



the samples were taken out; most of them were allowed to cool 

 slowly and some were cooled suddenly by being plunged into cold 

 water. He states: 



Different building stones show a considerable^difference in the 

 capacity which they have to withstand high temperatures. Other 

 things being equal, it appears that a rock having a uniform texture 

 and a simple mineralogical composition has the greatest capacity 

 to withstand extreme heat. It is known that rocks are poor con- 

 ductors of heat, and for this reason the outer shell of a rock may be 

 very highly heated while the interior remains comparatively cold. 

 If, after heating, the rock be quickly cooled, contraction of the 

 outer shell takes place. The differential stresses occasioned thereby 

 ruptures the rock and the outer shell is thrown off. 



Buckley 1 continues: 



As a result of theljexperiments ... it was discovered 

 that all the samples, when struck by the hammer or scratched with 

 a nail, after being taken from the muffle furnace, emitted a sound 

 similar to that which would be given off by a brick. This sound 

 was characteristic not only of the sandstones, but also of the gran- 

 ites and some of the limestones. 



The planes of lamination of the originally stratified samples were 

 brought out more distinctly as the temperature was increased. 

 But few of the limestone samples, which were tested in the muffle 

 furnace, were injured by gradual heating and cooling, except when 

 the temperature reached a point where calcination occurred. This 

 temperature was generally from iooo° to i2oo°F. When the 

 limestone samples were suddenly cooled they always flaked off at 

 the corners. 



The very coarse grained granite broke into a great many pieces, 

 and may be said to have exploded. The cracks were so numerous 

 that the stone was broken into fragments not much larger than 

 the individual grains. The medium grained granite . . . de- 

 veloped cracks through the middle of the sample. 



In contrast with the limestone and granite samples, the sand- 

 stones were, to all outward appearances, little injured by the ex- 

 treme heat. The samples which were taken from the muffle fur- 

 nace and allowed to cool gradually were apparently as perfect as 

 when first placed in the furnace. But after they had cooled, one 

 could crumble any of them in the hand, almost as readily as the 

 softest incoherent sandstone. In fact, when they were heated to a 

 temperature of i5oo°F. some of the samples had become so inco- 

 herent that it was barely possible to pick them up after cooling, 

 without their falling to pieces. 



G. P. Merrill 2 summarizes the effect of heat on stones as follows : 



The injurious effects of artificial heat, such as is produced by a 

 burning building, are, of course, greater in proportion as the tem- 

 perature is higher. Unfortunately, sufficient and reliable data are 



ildem. i8q8. 4:385. 



2 Stones for Building and Decoration. N.Y. 1003. p. 424- 



