SAMPLING AND TESTING HIGHWAY MATERIALS. 79 
the pipe to equalize the lower bearing before the upper one is 
brought into contact. 
Both of the bearings shall be sufficiently rigid to transmit and 
receive uniform loads throughout their lengths without deflec- 
tion, and shall he so attached, to The machine as to transmit and 
receive the maximum stresses produced by the tests without lost 
motion, vibration or sudden shock. 
At the option of the consumer or purchase]- the crushing test 
may he applied with sand bearings or with two or three edge 
bearings. 
The crushing strength shall he calculated by dividing the total 
load required to break each pipe by the net inside length of the 
barrel of the pipe, measuring from the bottom of the socket to the 
end of the spigot, and by then multiplying the quotient by the fol- 
lowing factors : 
For knife or two-edge bearings -V 1 
For three-edge bearings V 1 
For sand bearings LOO 
8. When three-edge bearings are used, the ends of each speci- 
men of pipe shall he accurately marked in halves of the circum- 
ference prior to the test. 
The two lower hearings shall consist of two wooden strips with 
vertical sides, each strip having its interior top corner rounded to 
a radius of approximately one-half inch. They shall he straight 
and shall be securely fastened to a rigid block with their in- 
terior vertical sides 1 inch apart. 
The upper bearing shall be a wooden block, straight and true 
from end to end. 
The test load shall be applied through the upper bearing block 
in such a way as to leave the bearing free to move in a vertical 
plane passing midway between the lower bearings. 
In testing a pipe which is " out of sight." the lines of the 
bearings chosen shall be from those which appear to give most 
favorable conditions for fair bearings. 
0. "When sand bearings are used, the ends of each specimen of 
pipe shall be accurately marked prior to the test in quarters of 
the circumference. Specimens shall be carefully bedded, above 
and below, in sand, for one-fourth the circumference of the pipe 
measured on the middle line of the barrel. The depth of bedding 
above and below the pipe at the thinnest points shall be one-half 
the radius of the middle line of the barrel. 
The sand used shall be clean, and shall be such as will pass a 
No. 4 screen. 
The top bearing frame shall not he allowed to come into con- 
tact with the pipe or with the top be;irinsr plate. The upper sur- 
face of the sand in the top bearing shall be struck level with a 
straightedge, and shall be covered with a rigid top hearing; plate, 
with lower surface a true plane, made of heavy timbers or other 
rigid material, capable of distributing the te^t load uniformly 
without appreciable bending. The test load shall be applied at 
the exact center of tin's top bearing plate in such ;i manner as to 
permit free motion of the plate in all directions. For this pur- 
pose a spherical hearing is preferred, but two rollers at righl 
angles may be used. The test may he made without the use of a 
testing machine, by piling weights directly on a platform resting 
on the top bearing plate, provided, however, that the weights 
shall be piled symmetrically about a vertical line through the 
center of the pipe and that the platform shall not be allowed to 
touch the top bearing frame. 
The frames of the top and bottom bearings shall be made of 
timbers so heavy as to avoid appreciable bending by the side 
pressure of sand. The interior surfaces of the frames shall be 
