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mad* 1 of ordinary machine cast-iron. The shot are of two sixes. The 

 larger sixe (_?A by -1 A inches) weigh V..") pounds each and have slightlv 

 rounded edges; the smaller shot ( 1 ..Vinch cubes) weigh about seven- 

 eighths of a pound each. The charge is composed of 7." pounds of the 

 larger and :>_!.'> pounds of the smaller sixe. The individual shot are 

 replaced by new ones when they have lost about one-tenth of their 

 original weight. The loss in weight undergone by a sample of the 

 brick under test at the end of 1,800 revolutions is found by comparing 

 the original weight of the brick with its weight after test. The l<s 



FIG. 9. Brick rattler. 



in per cent of the original weight is the factor determining the quality 

 of the brick. For the best paving brick this lo>-* should not be in 

 excess of 18 per cent. The above conditions are those demanded in 

 the standard specifications recommended by the National Hriek Manu- 

 facturer's Association. 



In order to collect data which will give a knowledge of the degree 

 of variation in the quality of individual brick this laboratory deter- 

 mines the loss of weight of individual brick as well as the average loss 



