PHYSICAL PROPERTIES OE ROAL>-BUILDING ROCK. 15 
METHOD. 
A core of the rock which is to be tested is first drilled, as described 
under the hardness test. In many cases the core which has already 
been subjected to the hardness test may be used. A cylinder a little 
over 25 millimeters long is next cut from the rock core by means of 
the diamond saw. The ends are then ground plane on the grinding 
lap, making the length of the specimen when completed exactly 25 
millimeters. Although it is not necessary that the two ends of the 
specimen be exactly parallel, one surface at least should be as nearly 
perpendicular to the axis of the cylinder as it is possible to make it. 
After drying, the specimen is placed on the anvil (W ) of the Page 
impact machine, taking extreme care that when in position the 
specimen rests with a perfect bearing on the anvil and that the 
spherical end of the plunger touches the specimen exactly in the 
center of its upper surface. The small thumbscrew used for sepa- 
rating the clips which hold the specimen in place should be so adjusted 
that the clips hold the specimen firmly without any undue pressure 
on the spring. Attention to these details is very important if accu- 
rate results are to be obtained. When the specimen is in position 
the current is turned on the magnet and the upper crosshead is 
lowered until the rod projecting from it just comes in contact with 
the rod projecting up from the lower crosshead (M). This occurs 
at the instant the pilot lamp, in series with the magnet circuit, flashes 
out. The dial (Q) is then adjusted to (0), the upper crosshead 
raised 1 centimeter, and the motor started. After each blow the 
fall of the hammer is increased 1 centimeter until failure of the test 
piece occurs. 
COMPUTATIONS. 
The height in centimeters of the blow at failure is recorded as the 
toughness of the material. The average of two determinations is 
taken. 
VALUE OP TEST. 
This test is useful in determining the comparative resistance of 
rock to the impact of traffic produced by the action of horses' hoofs, 
etc., on the stones forming the wearing course of a macadam road. 
Toughness in rock varies through a wide range of values from as low 
as 2 or 3 in the case of some limestones and sandstones to as high 
as 60 in rare instances. 
This test was standardized in 1908 by the American Society for 
Testing Materials. 
CEMENTING VALUE TEST. 
OBJECT. 
To determine the ability which the rock powder, when wet, pos- 
sesses of binding the larger fragments together 
