SAMPLING AND TESTIXG HIGHWAY MATERIALS. 
59 
Method of 
test- 
materials of 
high softening 
points. 
timeters (2 inches) below the surface of the water. Allow 
it to remain in the water for 15 minutes before applying heat 
Suspend the thermometer so that the bottom of the bulb is 
level with the bottom of the ring and within 0.635 centimeters 
(one-quarter inch) but not touching the ring. 
Note. — More than one ring may be used at one time. 
5. Apply the heat in such a manner that the temperature of 
the water is raised 5° C. (U° F. ) each minute. 
6. The temperature recorded by the thermometer at the in- 
stant the bituminous material touches the bottom of the glass 
vessel shall be reported as the softening point. 
7. The rate of rise of temperature shall be uniform and shall 
not be averaged over the period of the test. The maximum per- 
missible variaton of any minute period after the first three 
shall be ±0.5° C. (0.9° F. ). All tests in which the rate of rise 
in temperature exceeds these limits shall be rejected. 
(A) Bituminous Materials Having Softening Points Above 
80° C. (176° P.)- 
8. To use the same method as given under (A), except that 
glycerin shall be used instead of water, and that the thermome- 
ter shall conform to the following specifications : 
Total length : 370 to 400 millimeters (14.57 to 15.75 inches). 
Diameter: 6.5 to 7.5 millimeters (0.256 to 0.295 inch). 
Bulb length: Not over 14 millimeters (not over 0.55 inch). 
Bulb diameter: 4.5 to 5.5 millimeters (0.177 to 0.217 inch). 
The graduations shall be from 30° to 160° C. in 0.5°C. and 
shall be clear-cut and distinct. The 30° mark shall be at least 
75 millimeters above the bottom of the bulb. The length be- 
tween the 30° mark and the 100° mark shall be between 230 
and 275 millimeters. 
The thermometer shall be furnished with an expansion cham- 
ber at the top and have a ring for attaching tags. It shall be 
made of a suitable quality of glass and shall be so annealed as 
nut to change its readings under conditions of use. It shall 
be correct to 0.25° C. (0.45° F.) as determined by comparison 
at full immerson with a similar thermometer calibrated at full 
immersion by the United States Bureau of Standards. 
IV. PRECAUTIONS. 
9. The use of freshly boiled distilled water is essential, as 
otherwise air bubbles may form on the specimen and affect the 
accuracy of the results. Rigid adherence to the prescribed rate 
of heating is absolutely essential in order to secure accuracy 
of results. 
A sheet of paper placed on the bottom of the glass vessel 
and conveniently weighted will prevent the bituminous ma- 
terial from sticking to the glass vessel, thereby saving consid- 
erable time and trouble in cleaning. 
V. ACCURACY. 
10. The limit of accuracy of the test is ± 0.5° C. (0.9° F.). 
METHOD FOR DETERMINATION OF SPECIFIC VISCOSITY. 
The viscosity of fluid bituminous road materials may be de- Engler 
termined at any suitable temperature by means of the Engler viscosimeter. 
viscosimeter. This apparatus is shown in Figure 4. and may be 
described as follows: a is a brass vessel for holding the material 
to be tested, and may be closed by the cover b. To the conical 
bottom of a is fitted a conical omil<>\\ tube, e, exactly 20 milli- 
meters long, with a diameter at the top of 2.9 millimeters and at 
the bottom of 2.8 millimeters. This tube can be closed and opened 
