SAMPLING AND TESTING HIGHWAY MATERIALS. 89 
7. The speed of compression should be slow, not exceeding 0.1 Speed of 
inch per minute. Near the elastic limit and yield point the load compression. 
should be increased very slowly. 
Note. — A lower speed than that stated might be advisable if per- 
mitted by the testing machine. Evidently a bibber spef-d may be 
allowed with a long specimen than with a short one. 
8. For determining modulus of elasticity, the linear compres- 
sion of the specimen should be observed by a precise compress- 
ometer which is attached to the specimen anad does not touch the 
bearing blocks of the machine. Readings of the compressometer 
should be taken for three loads, the first at about one-fourth, the 
second at about one-half, and the third at about three-fourths of 
the elastic limit. 
Note. — It is believed that these measurements are sufficient for 
most commercial work. Nothing is said about the release of the 
specimen from load, since opinions differ as to its advisability. 
9. To determine the elastic and also the proportional limit, sev- 
eral readings of the compressometer should be taken as that limit 
is approached for load increments of 1,000 pounds per square 
inch. 
Note. — This requirement seems sufficient to determine the pro- 
portional limit, for materials in which such a limit exists. It does 
not seem wise to require the first permanent set to be observed for 
ordinary commercial work. 
10. The yield point is to be noted as corresponding to that load 
for which the compressometer shows a linear compression with- 
out an increase in load. In the absence of a compressometer this 
point may be noted, for ductile materials, by the drop of the 
scale beam. 
Note. — This requirement corresponds to the usual practice of 
testing laboratories. It is regarded as important that the term 
" elastic limit " should not be used to designate the yield point. 
11. Measurements for the modulus of elasticity, elastic limit, 
proportional limit, and yield point may be made, if desired, on a 
specimen ranging in length from 10 to 15 diameters. 
Note. — This clause is inserted because it may often be difficult to 
apply a compressometer in a length shorter than 4 inches. 
12. The record of the test should mention any phenomena ob- 
served near the elastic limit, proportional limit, and yield point. 
The manner of final failure should also be noted when the test 
is carried to this limit. 
Note. — This requirement furnishes data for comparing the be- 
havior of brittle and ductile metals near critical points of molecular 
change. 
III. METHOD FOR TRANSVERSE TESTS OF METALS 
1. In the case of cast metals, when transverse tests are to 
be used to aid in determining the quality of the material, 
the specimen used shall be cast vertical, shall be 1| inches in 
diameter, and long enough to use a span of at least 15 times the 
diameter. 
Note. — It is important that a definite and uniform standard be 
adopted so that the results may be comparable with each other ; 
hence the diameter specified above (sectional area corresponding 
to practically 1 square inch). The determination of span is at 
present the subject of international tests to decide upon a definite 
distance to replace the present standard of 12 inches. It will 
probably be from 16 to 18 inches. The circular section will best 
secure a uniform thickness of skin, and thus avoid this irregularity 
when other sections are employed. 
In the case of ductile materials (except in impact tests) trans- 
verse tests shall never be used to determine the quality of the 
material, tension tests being those suitable for the purpose. 
Note. — In small round or square bars of ductile material both the 
modulus of rupture and the transverse elastic limit vary considerably 
with the span. 
In the case of tests made for determining constants to be used 
for designing, the specimen shall conform as nearly as possible 
