CLAYS OF NEW YORE 749 



4 The bricks slioiilcl be soaked for 48 bours, completely im- 

 mersed, in pure water. 



5 After soaking, and before weighing, the bricks must be wiped 

 dry from surplus water. 



6 The difference in weight must be determined on scales sensi- 

 tive to 1 gram. 



Y The increase in weight due to water absorbed shall be calcu- 

 lated in percentage of the initial dry weight. 



The commission which drew up these specifications considers 

 that any brick which will satisfy the requirements of reasonable 

 mechanical tests will not absorb sufiicient water to prove injurious 

 to it in service, and that for such brick the absorption test should 

 be abandoned as unnecessary, if not actually misleading. 



Specifications for cross-breaking tests 



1 Support the brick on edge, or as laid in pavement, on hard- 

 ened steel knife edges, rounded longitudinally to a radius of 12 

 inches and transversely to a radius of one eighth of an incii, and 

 bolted in position so as to secure a span of 6 inches. 



2 Apply the load to the middle of the top face through a hard- 

 ened steel knife edge, straight longitudinally and rounded trans- 

 versely to a radius of yV inch. 



3 Apply the load at a uniform rate of increase till fracture 

 ensues. 



4 Compute the modulus of rupture by the formula 



„_3 w 1 



in which 



f= modulus of rupture in pounds a square inch 

 w = total breaking load in pounds 

 1 = length of span in inches = 6 

 b := breadth of brick in inches 

 d = depth of brick in inches 



5 Samples for test must be free from all visible irregularities 



