554 STUDIES FOR STUDENTS 



EXPLANATION OF PLATE VI 



Fig. i. — A sample of medium-grained granite heated to a tempera- 

 ture of from i3oo°-i5oo° F., and suddenly cooled by immersing in 

 cold water. This figure is a good illustration of the result of throwing 

 a stream of water on the walls of a burning building, which is con 

 structed out of granite of this texture. 



Fig. 2 — The sample in the upper left hand corner is sandstone 

 which has become so friable by being heated to a temperature of 

 i3oo°-i5oo° F., that it crumbles when pressed between the fingers. 

 The remaining samples are limestone. They have flaked off at the 

 corners, due to having been quickly cooled from a very high tempera- 

 ture. Such results may frequently be noticed in the limestone walls 

 of buildings which have been destroyed by fire. 



