DUST PREVENTION AND ROAD PRESERVATION, 1916. 7 
description of experiments. 
Experiment No. 1. — Bituminous Macadam: Trap Rock with Refined Water- 
Gas Tar. 
Location, station 1+81 to station 17+81. 
Total length, 1,600 feet. 
Total area, 2844. 4 square yards. 
The gravel base, as mentioned, had been under traffic for 4 months 
before the experimental surface was begun. The base was in good 
condition and required only a small amount of trimming and reshap- 
ing. One and one-half inch trap rock, having the physical properties 
and the mechanical analysis shown in Tables 4 and 6, was hauled 
in dump wagons and spread by hand to a depth of 3 inches. The 
spread stone was rolled until well keyed for two or three stations 
in advance of the pouring of the bituminous material which was 
heated in 500-gallon kettles mounted on trucks. The tar, at a tem- 
perature of 250° to 300° F., was drawn off into 4-gallon hand-pouring 
pots and applied at the rate of 1| gallons to the square yard. The 
distribution was controlled by pouring in longitudinal strips with as 
little lapping as possible. 
Clean stone chips were spread on the surface while the bituminous 
material was still hot and were broomed to an even distribution 
while the surface was being rolled with a 10-ton macadam roller. 
A seal coat of the hot tar, slightly in excess of one-half gallon per 
square yard, was applied. Chips then were spread in such quantity 
as to cover all visible bituminous material and rolled immediately. 
The mechanical analysis of the chips is shown in Table 6. 
Experiment No. 2 — Bituminous Macadam: Trap Rock with Refined Water- 
Gas Tar as Binder and Oil Asphalt for the Seal Coat. 
Location, station 17+81 to station 35+91. 
Total length, 1, 810 feet. 
Total area, 3,217.7 square yards. 
The construction of this experiment was exactly as described for 
experiment No. 1, except that an oil asphalt at a temperature of 
275° to 350° F. was used as the seal coat and applied in the same 
quantity and manner as the tar seal coat in experiment No. 1. 
Experiment No. 3: Bituminous Macadam: Trap Rock with Refined Coal Tar 
for Binder and Seal Coat. 
Location, station 35+91 to station 54+55. 
Total length, 1,804 feet. 
Total area, 3,313.7 square yards. . 
This experiment differs from experiments 1 and 2 only in the 
bituminous material. 
