688 



Report of the State Geologist. 



6. The difference in weight must be determined on scales sensitive to 

 one gram. 



7. The increase in weight due to w ater absorbed shall be calculated in 

 percentage of the initial dry weight. 



Specifications for Cross-Breaking Tests. 



1. Support the brick on edge, or as laid in pavement, on hardened steel 

 knife-edges, rounded longitudinally to a radius of twelve inches and trans- 

 versely to a radius of one-eighth inch, and bolted in position so as to secure a 

 span of six inches. 



2. Apply the load to the middle of the top face through a hardened 

 steel knife-edge, straight longitudinally and rounded transversely to a radius 

 of one-sixteenth inch. 



.'5. Apply the load at a uniform rate of increase until fracture ensues. 

 •1. Compute the modulus of rupture by the formula 



3 w 1 



f = 



1 b d* 



in which 



f = modulus of rupture in pounds per square inch. 

 w = total breaking load in pounds. 

 I = length of span in inches = 6. 

 J> = breadth of brick in inches. 

 «J = depth of brick in inches. 



5. Samples for test must be free from all visible irregularities of surface 

 or deformities of shape, and their upper and under surfaces must be perfectly 

 parallel. 



6. Not fewer than ten bricks shall be broken, and the average of all be 

 taken for a standard test. 



Specifications for Crushing Test. 



1. The crushing test .should be made on half bricks, loaded edgewise, 

 or as thev are laid in the street. If the machine used is unable to crush a 

 full half brick, the area may be reduced by chipping off, keeping the form of 

 the piece to be tested as nearly prismatic as possible. A machine of at least 

 1 00,000 pounds capacity should be used, and the specimen should not be 

 reduced below four square inches of area, in cross-section at right angles to 

 the direction of the load. 



