DUST PEEVENTION AND ROAD PRESERVATION, 1916. 25 
manner similar to that employed on experiment No. 1, except that 
the rate at which the tar was applied was only 0.35 gallon per 
square yard, and only sufficient gravel top-dressing was used to pre- 
vent the wheels of the distributor from picking up the surface while 
making the second application. Two days were allowed to elapse 
between the first and second applications. 
Table 29. — Analysis of refined coal tar 1 used on experiment No. 3, second application. 
Specific gravity, 25°/25° C 1.207 
Float test, 32° C. (seconds) 117 
Per cent free carbon 11. 02 
Distillation : 
Per cent Per cent 
by volume. by weight. 
Water 0.0 0.6 
First light oils (110° C.) 0.0 0.0 
Second light oils (110-170° C.) 0.0 0.0 
Heavy oils (170-235° C.) 5.0 3.9 
Heavy oils (235-270° C.).... 12. 2 10. 2 
Heavy oils (270-300° C.) 7. 6 6. 4 
Pitch residue 75. 2 79. 5 
Total 100. 100. 
The tar for the second application is represented by the analysis 
shown in Table 29. This material was heated at the plant in George- 
town, so that when it reached the work the temperature was about 
205° to 220° F. It was spread at the average rate of 0.50 gallon per 
square yard. Immediately after the second application of tar the 
surface was covered with the gravel top-dressing, spread at the rate 
of 1 cubic yard to about 78 square yards of surface. The amount of 
top-dressing required for the two applications was 1 cubic yard of 
gravel to 53.7 square yards of surface. 
The places where a noticeable lack of uniformity occurred in the 
work are : 
(1) In making the first application the distributor moved too 
slowly on the east side of the road from station 98 + 50 to 100 + 00 
and the tar was applied over this area at the rate of about one-half 
gallon to the square yard. 
(2) In making the second application an excess of tar was deposited 
at station 85 + 45, where experiments 2 and 3 join. 
(3) The second application was made in cold weather and the tar 
chilled so that little of the gravel top-dressing sank into it. Later, 
when the road was opened to traffic, it was observed that much of 
the top-dressing had been swept off the road surface by passing 
vehicles. 
i Sticky, very viscous. 
4588°— 18— Bull. 586 4 
