4 BULLETIN 370, U. S. DEPARTMENT OF AGRICULTURE. 
TOUGHNESS TEST. 
Toughness is determined by subjecting a cylindrical test specimen 
25 by 25 millimeters (1 by 1 inch) in size to the impact produced by 
the fall of a 2-kilogram (4.4-pound) hammer upon a steel plunger 
whose lower end is spherical and rests upon the test piece. The 
energy of the blow delivered is increased by increasing the height of 
fall of the hammer 1 centimeter (0.39 inch) after each blow. The 
height of blow in centimeters at failure of the specimen is called the 
toughness. 
DEVAL ABRASION TEST. 
A test devised by the French for measuring the combined action 
of abrasion and impact is as follows: Five kilograms (11 pounds) 
of freshly broken rock between 2 and 2J inches in size is tested in a 
special form of cylinder so mounted on a frame that the axis of 
rotation of the cylinder is inclined at an angle of 30° with the axis 
of the cylinder itself. The fragments of rock forming the charge 
are thus thrown from end to end twice during each revolution, caus- 
ing them to strike and rub against each other and the sides of the 
cylinder. After 10,000 revolutions the resulting material is screened 
through a T V mcn sieve and the weight of the material passing is used 
to calculate the per cent of wear. The French coefficient of wear is 
calculated from the per cent of wear as follows : 
40 
French coefficient of wear=T^ 1 • 
Fer cent wear 
CEMENTING- VALUE TEST. 
To determine the binding power, or cementing value, as it is usually 
called, 500 grains (1.1 pounds) of the material to be tested is crushed 
to pea size and ground with water in a ball mill until it has the con- 
sistency of a stiff dough. It is then molded into cylindrical briquettes 
25 by 25 millimeters (1 by 1 inch) in size, which, after thorough dry- 
ing, are tested to destruction in a special form of impact machine. 
A 1-kilogram (2.2-pound) hammer falls through a constant height 
of 1 centimeter (0.39 inch) upon an intervening plunger, which in 
turn rests upon the test piece. By means of a suitable arrangement a 
graphic record of the number of blows required to destroy the speci- 
men is obtained. The number of blows producing failure is called 
the cementing value of the material. 
SPECIFIC GRAVITY— WEIGHT PER CUBIC FOOT— WATER ABSORPTION. 
The specific gravity, weight per cubic foot, and the water absorp- 
tion in pounds per cubic foot are obtained on samples of rock which 
are tested to determine their road-building qualities. The weight 
