752 KEW YORK STATE MUSEUM 



3 Removing the irregularities of surface and crushing between 

 straw boards. 



4 Removing irregularities, coating with plaster of paris and 

 placing under slight pressure till set (12-24 hrs), and then 

 crushing. 



5 Coating with plaster of paris which was afterward ground 

 down, on a sand paper disk, to the surface of the brick so as to 

 leave a minimum thickness with a perfectly flat surface, and then 

 crushing. 



After a number of experiments no great diifererice was found 

 between the first three, but difficulties connected Avith the last 

 two rendered them worthless. With a uniform grade of brick 

 the first three methods gave TOGO to 9000 pounds as the crushing 

 strength of cubes. Some samples of the same lot of brick were 

 prepared on a rubbing bed at marble works, and the strength of 

 these carefully prepared cubes ranged from 16,000 to 21,000 

 pounds a square inch, showing that a very small difference in flat- 

 ness of surface makes a great difference in the apparent strength. 



At a recent meeting of the JSTational brick manufacturers asso- 

 ciation, Gomer Jones, city engineer of Geneva, IST. Y., advocated 

 the following method for testing the resistance of paving brick to 

 abrasion. 



A rattler of the usual type has the staves fitted with two longi- 

 tudinal pockets each, in which the bricks are inserted and held end 

 to end. These pockets are 3 inches deep, leaving about one inch of 

 brick protruding. " When all the staves are in place, the interior 

 of the rattler is virtually solid brick lined. During rotation the 

 attack of the abrading material is at right angles to the length of 

 the brick, and confined to the surfaces and edges which are ex- 

 posed in actual use; there is suflicient space between the brick for 

 the escape of any dust or waste, and incidentally allowing the 

 abrading material free access to the unsupported edges of the' 

 brick under test, thus establishing the conditions of position and 



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