18 BULLETIN 105, XJ. S. DEPARTMENT OF AGRICULTURE. 
The road selected for the experiments is commonly known as the 
Kockville Pike and extends from the District of Columbia line to the 
corporate limits of Rockville, Md., a distance of approximately 9 
miles. It was a macadam road originally constructed with quartzite 
and patched with limestone from time to time. At the time of these 
experiments it had become rough and badly worn, and was therefore 
resurfaced before any surface treatments were applied. This work 
was done on three contracts, the first two of which, including the 
portion from station + 15 at the District line to station 210, were 
completed in July, 1913, and the third, extending from station 210 
to the corporate limits of Hockville, in October, 1913. The old sur- 
face was loosened with spikes in the roller wheels and further broken 
up with a 3-ton scarifier. The surface was then reshaped and rolled, 
after which from 3 to 3 J inches of new limestone was added and the 
surface was finished as water-bound macadam. The road was graded 
25 feet wide in both cuts and fills, and the surface of the finished 
macadam had a width of 15 feet and a crown of 0.6 inch per foot. 
The cost of this work averaged 52 cents per square yard or $4,676 per 
mile of 15-foot road. A section of 10-foot road on Bradley Lane, 1,500 
feet in length, was also scarified and resurfaced with limestone as water- 
bound macadam on a separate contract. This was a limestone road 
which had become badly worn and rutted. The total cost for resur- 
facing was $1,285.72, or 75.6 cents per square yard. 
Surface treatment was started on September 5 at the District line 
on the macadam which had been longest completed. The surface 
was thoroughly swept with a horse-drawn street sweeper, and any 
hard cakes of dust were removed with shovels. As the work 
progressed over macadam which had been more recently completed, 
these cakes of dust became more numerous, and were removed with 
considerable difficulty. The advisability of permitting traffic to con- 
solidate and wear a new macadam surface to a reasonable extent 
before surface treating was thereby demonstrated. All the bitumi- 
nous materials were delivered in tank-car lots of from 5,600 to 5,800 
gallons with an average haul of 1 J miles from the road. The material 
was heated at first by a small portable boiler, but as colder weather 
developed it was found necessary to engage a 40-horsepower traction 
engine in order to heat the heavier materials properly. 
The application was made by means of two 600-gallon distributors 
which were each drawn by one team. They were equipped with a 
gasoline pump developing about 40 pounds pressure at the nozzles. 
The material was ejected from slotted nozzles in fan-shaped sprays 
so spaced as to cover half the width of the road on each passage of 
the machine. 
