16 BULLETIN 1216, U. S. DEPARTMENT OF AGRICULTURE. 
shall ho loaded continuously to failure. The moving head of the 
testing machine shall travel at the rate of not less than 0.05 
or more than 0.10 Inch per minute. 
11. Testing machines should he frequently calibrated in order 
to determine their accuracy. 
12. Cylinders thai are manifestly faulty, or which give strengths 
differing more than 15 per cent from the average value of all 
test pieces tested at the same period and made from the same 
sample, shall not he considered in determining the compressive 
strength. 
III. STORAGE OF TEST PIECES. 
Storage. 13. The moist closet may consist of a soapstone, slate, or con- 
crete box, or a wooden box lined with metal. If a wooden box 
is used, the interior should be covered with felt or broad wicking 
kept wet. The bottom of the moist closet should be covered with 
water. The interior of the closet should be provided with non- 
absorbent shelves on which to place the test pieces, the shelves 
being so arranged that they may be withdrawn readily. 
14. Unless otherwise specified, all test pieces, immediately af- 
ter molding, shall be placed in the moist closet for from 20 to 24 
hours. 
15. Cylinders or briquets shall be kept in molds on glass plates 
in the moist closet for at least 20 hours. After 24 hours in moifll 
air the briquets or cylinders shall be immersed in clean water in 
storage tanks of noncorroding material. 
16. The air and water shall be maintained as nearly as prac- 
ticable at a temperature of 21° C. (70° F.) 
Note. — It is recommended that thp laboratory method of propor- 
tioning fine aggregate viz, by weight or by volume, for either the 
compression or tension test shall be the same as the method used 
in proportioning concrete in the field. 
When the mortal' is proportioned by volume the required quan- 
tity of fine aggregate and cement shall be determined from the unit 
weight of the material. 
Example : 
Weight of sand, 100 pounds per cubic foot. 
Weight of cement, 94.0 pounds per cubic foot. 
Required, 75 cubic inches of mortar. 
75 
Quantity of sand, p^s X 100X453.6= 1,969 grams. 
25 
Quantity of cement, -ry^g X 94.0X453.6=617 grams. 
METHOD OF SAMPLING AND TESTING SEMIGRAVEL, 
TOPSOIL, AND SAND-CLAY AGGREGATE FOR ROAD 
SURFACING. 
I. DEFINITION. 
1. The terms, clay. silt. sand, and coarse material, used herein. 
are defined as follows: 
Xote. — The definitions here given are intended t f > apply to these 
termi only when used in connection with rouds of these types. 
Clay. — Material separated by subsidence through water and 
possessing plastic or adhesive properties, generally less than 0.02 
millimeter in diameter. 
Silt. — Fine material, other than clay, which passes a 200-mesh 
sieve, generally from 0.07 to 0.02 millimeter in diameter. 
Sand. -Hard material, usually siliceous, which passes a 10- 
mesh sieve and Is retained on a 200-mesh sieve, generally from 
1.85 to 0.07 millimeter in diameter. 
Coarse material. — Hard material of gravelly nature, retained 
on a 10-mesh sieve, i. e.. more than 1.85 millimeters in diameter. 
