750 NEW YORK STATE MUSEUM 



of surface or deformities of shape, and their upper and under 

 faces must be practically parallel. 



6 Not fewer than 10 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 edge- 

 wise, or as they 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 100,000 pounds' 

 capacity should be used, and the specimen should not be reduced 

 below 4 square, inches of area in cross-section at right angles to 

 the direction of load. 



2 The upper and lower surfaces should preferably be ground 

 true and parallel planes. If this is not done they should be 



redded in plaster of paris while in the testing machine, which 

 should be allowed to harden 10 minutes under the weight of the 

 crushing planes only, before the load is applied. 



3 The load should be applied at a uniform rate of increase to 

 the point of rupture. 



4 'Not less than an average obtained from five tests on five dif- 

 ferent bricks shall constitute a standard test. 



It was resolved by the commission that " from the experimental 

 work done so far by this commission, or by others so far as is 

 known to us, in the application of the cross-breaking and crushing 

 tests to paving brick, it is not possible to show any close relation- 

 ship between the qualities necessary for a good paving material 

 and high structural strength as indicated by either of these tests ". 



Effect of structure on wearing power of paving brick ^ 

 Recent experiments by Prof. Edward Orton jr on bricks made 

 from the same shale, but molded on different machines and burned 



^ Clayworker, February and March 1897. 



