2 BULLETIN 347, U. S. DEPARTMENT OF AGEICULTUEE. 
since that time in the actual routine of testing has shown the neces- 
sity of strictly adhering to many apparently minor details the 
importance of which was not formerly fully emphasized. Particular 
stress has been laid upon these details, in order that others engaged 
in, or about to engage in, this line of work may, with the least amount 
of preliminary experimentation, obtain results of practical value. 
The first systematic attempts to determine the value of rock for 
road-building purposes by means of laboratory tests were made in 
France, where in 1878 a road-material laboratory was founded in the 
French School of Bridges and Roads at Paris. Here the Deval abra- 
sion test was adopted, and this test with slight modification has been 
accepted as standard throughout the United States. The test is 
named from its inventor and was first used in connection with con- 
tract work in the city of Paris. Many valuable data were also col- 
lected in this laboratory on the hardness and toughness of rock, and 
tests for these properties were developed which were, in principle, 
the same as those in use to-day. 
Outside of France very little work was done in road-material test- 
ing in either Europe or America until 1893, when the Massachusetts 
Highway Commission established a laboratory in the Lawrence 
Scientific School of Harvard University, under the direction of Logan 
Waller Page. The Deval abrasion test was adopted and a test to 
determine the binding power of rock dust was developed by Mr. Page 
in this laboratory. 
In December, 1900, the United States Government established a 
laboratory in the Bureau of Chemistry of the Department of Agri- 
culture, under the direction of Mr. Page. This laboratory became in 
1905 a part of the Division of Tests of the newly organized Federal 
Office of Public Roads. On July 1, 1915, during a general reorganiza- 
tion, it was placed in the Division of Road Material Tests and Re- 
search of the new Office of Public Roads and Rural Engineering. The 
recent general interest in road improvement has also resulted in the 
establishment of many laboratories in technical and scientific insti- 
tutions both in this country and abroad, as well as in the various 
State highway commissions. 
PHYSICAL PROPERTIES OF ROAD-BUILDING ROCK. 
The suitability of rock for use in highway construction is largely 
determined in the laboratory by tests of certain physical properties 
which have a direct bearing upon the behavior of the rock under 
service conditions. In the case of rock intended for use in water- 
bound macadam construction, experience has shown that the 
qualities most essential to success are those of hardness, toughness, 
and binding power. These properties may be briefly defined as 
follows : 
