44 NEW YORK STATE MUSEUM 



Strength. The crushing strength is determined by applying a 

 gradually increasing pressure upon a cube placed between two steel 

 plates until the stone breaks down. It is usual to note also the 

 pressure at which the first crack occurs. The value of the results 

 depends upon the care used in preparing the cubes, which should 

 be sawed, not dressed to size with the hammer, and also upon 

 the relation of the faces of the cube to the structure of the stone in 

 the quarry. In sedimentary rocks, the pressure should be applied at 

 right angles to the bedding. In granites and other igneous rocks 

 that have rift and grain, tests should be made upon three samples 

 of each rock, so as to find the strength perpendicular respectively 

 to the rift, grain and heading. Even with the greatest care in the 

 selection of samples and their preparation, the tests will show wide 

 variations in the crushing strength of rock from the same quarry. 

 Nearly any quarry material, however, has sufficient strength to 

 withstand any compressive force that is likely to develop in the 

 walls of a building. Buckley states that a stone with a crushing 

 strength of 5000 pounds to the square inch is sufficiently strong for 

 any ordinary building.^ 



The transverse strength is determined on rectangular pieces which 

 are supported at the ends on knife edges and subjected to a pressure 

 in the middle from another knife edge. The test has some value for 

 stone to be used in arches, lintels, and similar purposes. 



Tensile strength is seldom determined on stone, although com- 

 monly tested in cements. It is equally, if not more important, 

 however, than the compressive strength, as it measures the bonding 

 power and gives some indication as to the behavior of stones under 

 the internal stresses of contraction and expansion. Shearing 

 strength is measured by the resistance the stone ofifers to forces 

 tending to displace the particles with reference to each other. Tests 

 for it are rarely made. 



Wear or abrasion. The resistance to wear by abrasion may be 

 said to be dependent upon the qualities, of hardness and toughness. 

 It is useful to determine such resistance in macadam and paving 

 stones. The method employed in the State Department of High- 

 ways is to prepare with the aid of a breaking press, cubical samples 

 of from i^ to 25^ inches diameter, of which 50 will approximate 

 5 kilograms in weight. The pieces are then washed, dried, and 

 placed in a cast-iron cylinder, mounted at an angle of 30° with 

 the axis of rotation, and revolved for 10,000 revolutions at the rate 



1 Building Stones of Wisconsin, p. 59. 



