40 BULLETIN 407, U. S. DEPARTMENT OF AGRICULTURE. 
Since the work was done with convicts and the conditions were favor- 
able, the cost is probably considerably lower than it would have been 
under ordinary conditions. 
EXPERIMENT AT WEST PALM BEACH, FLA. 
In May, 1914, a series of seven experimental sections involving the 
use of coralline rock and bituminous materials was constructed on 
the Miami-Quebec Highway, about 2 miles south of West Palm Beach. 
The details of construction are given in U. S. Department of Agri- 
culture Bulletin No. 257. In order to determine the wearing quali- 
ties of a sand-asphalt or bituminous-sand surface in comparison with 
the seven experimental surfaces, a section of this material was added 
to the series in January, 1915. It is continuous with the other experi- 
ments and adjoins section 7. 
Experiment No. 8. — Bituminous Sand Mixing Method. 
The original coralline rock road was scarified and reshaped for the 
foundation. The cross section of the foundation was parallel to the 
finished surface and 2 inches below it. During the time which 
elapsed between the preparation of the foundation and the laying of 
the wearing course, the former was thoroughly compacted by traffic 
and had become slightly dusty. 
In order to secure a sand which was fairly well graded, it was nec- 
essary to mix two sands in approximately equal proportions. This 
was done while they were being screened to remove twigs and other 
undesirable matter. The mechanical analyses of the original sands 
and the graded combination are given in Table 42, and the analysis 
of the fluxed native asphalt, B, is the same as given in Table 41. 
The bituminous sand was prepared by mixing heated sand and 
asphalt on a mixing board with rakes and shovels. A heater having 
about 90 square feet of heating surface was improvised to bring the 
temperature of the sand up to from 350° F. to 400° F. and two 1 -barrel 
asphalt kettles were used to heat the bitumen to 300° F. 
Beginning at the south end of the section for the first 52 linear feet 
the sand and asphalt are mixed in the proportions of 10 cubic feet of 
sand to 10 gallons of asphalt; in the next 27 linear feet the propor- 
tions are 10 cubic feet of sand to 11 gallons of asphalt; and in the 
remaining 3 linear feet the surface consists of a mixture of 10 cubic 
feet of sand No. 1 to 11 gallons of asphalt. The sand-asphalt mixture 
was spread 2\ inches thick and was held in place with 2 by 4 inch 
timber while it was being rolled with a 6-ton tandem roller. 
The work was interrupted by a succession of showers. The section 
was so short that an organization of competent labor could not be 
perfected and the equipment was of the crudest kind. 
