SAMPLING AND TESTING HIGHWAY MATERIALS. 35 
whole inch of the shoot wires. The diameter of the wire should 
be 0.0165 inch and the average diameter shall not be outside the 
limits of 0.0160 and 0.0170 inch. 
The No. 30 sieve shall have between Ui*.-~i and 30.5 wires per 
whole inch of the warp wires and between 28.5 and 31.5 wires per 
whole inch of the shoot wires. The diameter of the wire should 
he 0.0110 inch and the average diameter shall cot he outside 
the limits 0.0105 to 0.0115 inch. 
54. Immediately after mixing, the standard mortar shall bo 
placed in the molds, pressed in firmly with the thumbs, and 
smoothed off with a trowel without ramming. Additional mortar 
shall be heaped above the mold and smoothed off with a trowel : 
the trowel shall be drawn over the mold in such a manner as t" 
exert a moderate pressure on the material. The mold shall then 
be turned over and the operation of heaping, thumbing, and 
smoothing off repeated. 
55. Tests shall be made with any standard machine. The bri- 
quets shall he tested as soon as they are removed from the water. 
The bearing surfaces of the clips and briquets shall be free from 
grains of sand or dirt. The briquets shall be carefully centered 
and the load applied continuously at the rate of 600 pounds per 
minute. 
56. Testing machines should be frequently calibrated in order 
to determine their accuracy. 
57. Briquets that are manifestly faulty, or which give strengths 
differing more than 15 per cent from the average value of all 
test pieces made from the same sample and broken at the same 
period, shall not be considered in determining the tensile strength. 
XV. STORAGE OF TEST PIECES. 
58. The moist closet may consist of a soapsrone. slate, or con- Storage, 
crete box. or a wooden box lined with metal. If a wooden box 
is used, the interior should be covered with feH 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being so arranged that they may be withdrawn readily. 
59. Unless otherwise specified all test pieces, immediately after 
molding, shall be placed in the moist closet for from 20 to 24 
hours. 
60. The briquets shall be kept in molds on glass plates in the 
moist closet for at least 250 hours. After 24 hours in moist air 
the briquets shall be immersed in clean water in storage tanks 
of noncorroding material. 
61. The air and water shall be maintained as nearly as practica- 
ble at a temperature of 21° C. (70° F. | . 
RATTLER TEST FOR PAVING BRICK. 
(A. S. T. ML standard method, serial designation, C 7-15. slightly 
modified.) 
THE CONSTRUCTION OF THE RATTLER. 
1. General design. — The machine shall be of good mechanical The rattler. 
construction, self-contained, and shall conform to the following 
details of material and dimensions, and shall consist of barrel. 
frame, and driving mechanism as herein described. 
2. The barrel. — The barrel of the machine shall bo made up of 
the heads, head liners, staves, and stave liners. 
The heads may be cast in one piece with the trunnions, which 
shall be 2\ inches in diameter, and shall have a bearing 6 inches 
in length, or they may be cast with heavy hubs, which shall be 
bored out for 2&-inch shafts, and shall be keyseared for Two 
keys, each one-half by three-eighths inch and spaced 90° apart. 
The shaft shall be a snug lit and when keyed shall be entirely 
