55 2 STUDIES FOR STUDENTS 



EXPLANATION OF PLATE V 



The samples numbered i, 3, 6, 7, 13, and 16 are granite; those 

 numbered 8, 9, 10, and 11 are limestone; and numbers 2, 3, 4, 12, 14, 

 and 15 are sandstone. Samples numbered 5, 6, and 13 were cooled 

 suddenly by immersing them in cold water, while the remaining were 

 cooled gradually. Number 6 is fine grained, number 5 medium 

 grained, and number 13 coarse grained granite. It is simply neces- 

 sary to direct attention to these samples, for one to see how the dif- 

 ference in grain influenced the manner of cracking. 



The limestone samples were partly calcinated. Where the quick- 

 lime has been removed the samples have the rounded edges noticed 

 in numbers 9 and 10. 



The sandstone samples are, to all outward appearances, uninjured, 

 as shown in samples numbered 2 and 15. The chipping of the cor- 

 ners and edges in numbers 4, 12, and 14 was occasioned by pressing 

 the thumb against the parts broken off, which in spite of the uninjured 

 appearance of the samples, indicates the friable character of the stone 

 after heating to the extreme temperature of i3oo°-i5oo° F. 



