356 STUDIES FOR STUDENTS 
the essential qualities of a good building stone. In the conflagra- 
tions which have occurred in many cities, brick, stone, and 
wooden structures have suffered alike. Granite and brick walls 
have crumbled into shapeless masses, while iron beams and 
girders have been melted and twisted into all conceivable shapes. 
A comparatively low temperature destroys some materials, 
while others are barely affected at a temperature above the melt- 
ing point of copper. Most building materials, however, are 
destroyed when subjected to a very high heat. 
It is known that rocks are poor conductors of heat, and for 
this reason the outer shell of a block may be very highly heated 
while the interior is comparatively cold. If a block is quickly 
cooled after heating, contraction of the outer shell takes place, 
and the differential stresses occasioned thereby rupture the rock. 
The destruction caused by a conflagration is largely increased 
by streams of water which are thrown onto the burning buildings 
in an attempt to extinguish the flames. If the fire occurs in 
winter the effect is still further intensified by the freezing of the 
water. 
Few experiments have thus far been performed to determine 
the temperature which the different kinds of stone will stand 
without injury. It has, however, been demonstrated that stone 
will withstand a much higher temperature when heated and cooled 
slowly than when heated and cooled rapidly. 
The easiest method to test the capacity of a stone to with- 
stand heat is to place two-inch cubes in a muffle furnace and 
gradually heat them from a low to a high temperature. By 
using a standard pyrometer the temperature can be gauged and 
the visible effect of any increase in heat can be noted. Samples — 
should be tested not only to ascertain the effect of gradual heat- 
ing and cooling, but they should also be removed from the 
furnace and suddenly cooled by plunging into cold water. 
Limestone and dolomite are injured mainly through calcina- 
tion, although when suddenly cooled they flake at the corners. 
Coarse grained granite is often shattered throughout its mass. 
Medium grained granite flakes at the corners, while the compact, 
