252 



CLAYS AND CLAY INDUSTRY. 



bricks was 555 pounds and 16,675 pounds, respectively. For a 

 brick measuring 8 inches in length by 4 in width, this would mean 

 a crushing strength for the whole brick of from 21,152 to 443,936 

 pounds. 



Transverse strength. — This is more important even than the 

 crushing strength, for while a brick is rarely loaded to' its crush- 

 ing limit, it is sometimes exposed to its limit of elasticity and 

 cracked. This can perhaps be better understood if the manner 

 of making the test is first explained. In the cross-breaking test a 

 whole brick was placed on two rounded knife-edge bearings 

 (Fig. 37), which in the tests made on the New Jersey brick were 

 6 inches apart. Pressure was then applied from above, as in- 



Fig. 37. 



Diagram showing method of testing the breaking strength of brick. 



dicated by the arrow, until the brick broke in two, and the num- 

 ber of pounds pressure at which this occurred was noted. It is 

 evident that in two bricks of exactly the same degree of strength, 

 the amount of pressure necessary to break them will depend 

 upon, 1) the distance between the supports, and 2) the cross 

 section of the brick. The farther apart the supports the less 

 the pressure necessary to break the brick, and the greater the 

 cross section, the greater the pressure necessary. Since this is 

 so, it is necessary that for purposes of comparison all results of 

 the breaking strength be reduced to some uniform expression, 

 which shall take account of the differences in length, width and 

 thickness of the brick. The most accurate expression is that 



