8 BULLETIN 257, U. S. DEPARTMENT OF AGRICULTURE. 
The sand used, from which roots and grass were removed by the use - 
of a 2-inch screen, was a clean, white silica obtained at the roadside. 
Dustless screenings, so-called, were obtained by rescreening on a 
1-inch screen all rock that had passed the 4-inch screen. All material 
passing the }-inch mesh was classed as ‘‘extra fines.” About 33 per 
cent of the rock passed the 34-inch screen, of which one-half was 
recovered on the }-inch screen. There was no appreciable change 
in volume between the pit run and the screened rock above one-half 
inch. 
It was found necessary to extend the width of the subgrade from 
12 feet to 15 feet on account of the thin depth of the original rock 
outside the former width. This was done by trenching the sides and 
backfilling with sufficient rock to give the required grade. About 15 
per cent. of the total cost of the work was expended in this manner. 
EXPERIMENT No. 1 (Resrpuau AspHattTic PETROLEUM—PENETRATION METHOD). 
Location: Station 0+00 to station 14+02=—102 feet. 
Area: 170 square yards. 
TABLE 4.—Analysis of residual asphaltic petroleum. 
meppeitic eravity 25°/25° C25. fo owe Ges ee ee Oe re ere me ey ee eee 0. 989 
Plashspolmtet.cm 2. aes es eS rh I ee a eS cn Ar Of 130 
WENA ON... 2 eo eee ee SA a aie eens Meee ai OS 155 
Viscosity; Wavler’ 100 «.-c) at 1002 specine.< 2 ea a ee 9.8 
Piloat test Ab 32°°0- (hime Oke es ee eee es ee ee 44/7 
Pigat test-at BO° ©, (dame) ses oath See, See eed Se eee nar 
Toss; 5 hoursiat 163°C | 20 cxramay 2, Benen? SN. obs eae eee per cent.. 13.74 
Wioat fest on-residue at 32° Cs Game). 6. 40 Ske Be, oe eee alee 
Float test on‘residue at.50° C. Gime): <<: 2.22 5:2 Pee ye et ga ee eee | Ge 
Percentage of total bitumen insoluble in 86° B. naphtha...................- 10. 05 
Buxedcarbon 262020 Sei SE SERA ee ie Bie Been CN AME Wp cae percent.. 4.68 
Solubice in CS; Gotal bitumen) si ee ee eee eee ee eee do... 5 99552 
Greanie mattersnpoluble: 200 eee a ecg ere a eee do. 4 . 05 
Jnercanic matter insoluble.) ose: PURO ee eae 70 ede . 03 
DOAN oe so Se oa eS oe SR ee eae ee te 100. 00 
Method.—The screened-rock course was lightly rolled to bring the 
suriace to a smooth cross section and leave an open surface which 
would allow deep penetration of the bitumen. The rate of applica- 
tion for the penetration course was 1.76 gallons per square yard, at 
an average temperature of 95° C. No excess of bitumen remained 
on the surface, which was then covered with sand and thoroughly 
rolled. Before applying the seal coat all free sand was swept from 
the surface with rattan brooms. The rate of application of the seal 
coat was 0.56 gallon per square yard. A top dressing of sand was 
applied and the surface thoroughly rolled. 
A. From stations, 0+00 to 0+50, the seal-coat application was 
allowed to stand two hours before sanding. 
