APRIL 5, 1912] 
a useful road material; that best results require 
a dense mixture, preferably proportioning the 
aggregate for maximum density; that some doubt 
may be attached to the complete durability of 
bituminous surfaces made by the penetration proc- 
ess, and suggesting that the grading of stone 
in this method, rather than having a uniform size, 
is desirable; that a moderately coarse aggregate 
should be brought to the surface, to overcome 
slipperiness and take up wear; that tar-concrete is 
less durable under concentrated wear than is sheet 
asphalt; that broken stone will provide a more 
stable structure than will water-rounded gravel 
when bonded by tar; that a paint and grit coat is 
necessary as a preservative as frequently as signs 
of surface wear or oxidation appear. 
Surface Treatment of Park Roads: 
CrosBy, Washington. 
In building and rebuilding park roads in Wash- 
ington in the last few years a heavy oil or tar 
binder, applied by the penetration method, has 
been used with most satisfactory results. For the 
surface treatment of existing macadam roads, 
emulsions, waste sulphite liquors, coal gas and 
water gas tars, and asphaltic oils have been ex- 
perimented with and last have been found to 
give best results. One application per year is 
sufficient to keep the surface in excellent condition. 
During the last fiscal year 166,000 square yards of 
park roads were given surface application of oil 
or tar at an average cost of 24 cents per square 
yard, not including cost of screenings. This com- 
pares with an average cost of 3.2 cents per square 
yard for watering in previous years. 
Oyster Shell Roads: W. W. CrosBy, Johns Hop- 
kins University. 
General remarks on arguments for and limits to 
use of shells for road purposes. Descriptions of 
results in Maryland. Particular points to be ob- 
served in construction and specifications recom- 
mended. Use of bituminous material in connec- 
tion with shells. Costs of construction and of 
treatment with bitumen. (Six photographs show- 
ing shell roads treated and untreated.) 
Changes in Pitch under Exposure and Traffic: W. 
W. CROSBY. 
Description of construction and analysis of tar 
used. Description of traffic conditions and record 
of traffic census. Description of results apparent. 
Analysis of tar surface after three years of use and 
of tar extracted from samples of this surface. 
Conclusions as to changes in tar that have appar- 
ently occurred. 
SPENCER 
SCIENCE 
551 
The Chemistry of Modern Highway Engineering: 
Prevost HUBBARD, Institute for Industrial Re- 
search. 
The necessity of chemical training for modern 
highway engineers is discussed at some length, 
and an outline is given of what the author believes 
to be the essentials of such training. Columbia 
University has already made the chemistry of road 
materials a part of its new post-graduate course 
in highway engineering. It is believed that this 
training will establish closer relations between the 
highway engineer and the chemist. Modern con- 
ditions demand the work of specialists in highway 
construction as in many other branches of engi- 
neering, and it is not reasonable to expect that 
the man whose training has been primarily devel- 
oped along engineering lines can satisfactorily 
apply the principles of other highly specialized 
subjects to his work without the assistance of 
those who have specialized in such subjects. There- 
fore, the highway engineer should not attempt the 
chemical testing of road materials, but should 
cooperate with the chemist in this matter. 
A Review of the Use of Bituminous Materials in 
the Construction and Maintenance of American 
Highways during 1911: A. H. BuancHarD, Co- 
lumbia University. 
The following table shows the characteristic 
developments in the use of bituminous materials 
during the years 1908, 1909, 1910 and 1911 under 
the supervision of the highway departments of 
Maine, New Hampshire, Massachusetts, Rhode 
Island, New York, New Jersey, Pennsylvania and 
Maryland. The quantities are square yards. 
SURFACE TREATMENT OF ROADS 
Fluxed Native As- 
phalts Oil Asphalts 
Tars and Tar- and Residual As- 
Asphalt Com- phaltic and Semi- 
pounds asphaltic Oils Light Oils 
1908. 57,700 1908. 239,500 UNOS. d¢oboda. 
1909. 95,500 1909. 910,600 1909 . 4,125,900 
1910.123,400 
1911.433,000 
1910.2,434,200 
1911.7,980,000 
1910 .9,890,400 
1911.3,765,000 
BITUMINOUS PAVEMENTS CONSTRUCTED BY 
PENETRATION METHODS 
Fluxed Native As- 
phalts Oil Asphalts 
Tars and Tar- and Residual As- 
Asphalt Com- phaltic and Semi- 
pounds asphaltic Oils Light Oils 
1908.. 37,800  1908.. 25,200 1908........ 
1909..170,200  1909..2,077,400 1909........ 
1910. .339,300 1910. .4,840,200 1910. .26,500 
1911..122,000  1911..8,600,000 1911...... he 
