346 SILI S WHOM SINGS OLIN IES 
position of the rupture should be carefully recorded. The 
modulus of rupture is then computed from the following formula: 
a 
ee ame 
31 
jeaass 
2bhd Me 
W— concentrated load at center in pounds. 
6 =breadth in inches. 
a@ —depth in inches. 
Z —length. 
# —=modulus of rupture in lbs. per sq. in. 
Modulus of elasticity—Vhe modulus of elasticity is synonymous 
with coefficient of elasticity, and is sometimes defined as the 
weight that would be required to stretch a rod one square inch 
in section to double its length. The result is generally expressed 
in pounds per square inch. It is ‘‘valuable in determining the 
effect of combining masonry and metal, of joining different 
kinds of masonry, or of joining new masonry to old; in calcu- 
lating the effect of loading a masonry arch; in proportioning 
abutments and piers of railroad bridges subject to shock,” etc. 
Baker. ) 
One method of measuring the modulus of elasticity is by 
recording the amount of compression which a two-inch cube of 
stone undergoes for each increment of 500 to 1000 pounds up 
to the limit of elasticity. From the data thus obtained the 
modulus of elasticity is computed by use of an empirical 
formula. 
The value of such determinations from a commercial stand- 
point are somewhat doubtful, owing to the fact they are seldom 
reterreds tom by architects) ihe sparcitymomsthemcetenmina. 
tions in this country is undoubtedly one reason for their 
uselessness. 
FHlardness—The hardness of a stone may be determined 
quantitatively by the use of an abrading machine, and the results 
expressed as the coefficient of wear. .The abrasion test is used 
mainly for determining the wearing qualities of crushed rock for 
