54 BULLETIN 949, U. S. DEPARTMENT OF AGRICULTURE, 
The scale shall be engraved upon the stem of the thermometer, shall be clear cut 
and distinct, and shall run from 0° to 80° C. (32° to 176° F.) in i° centigrade divisions. 
It shall commence not less than 7.5 cm. (2.95 inches) above the bottom of the bulb. 
The thermometer shall be furnished with an expansion chamber at the top and have 
a ring for attaching tags. It shall be made of a suitable quality of glass and be so 
annealed as not 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 immersion with a similar 
thermometer calibrated at full immersion by the United States Bureau of Standards. 
II. PREPARATION OF SAMPLE. 
(3) The sample shall be melted and stirred thoroughly, avoiding incorporating air 
bubbles in the mass, and then poured into the ring so as to leave an excess on cooling. 
The ring, while being filled, should rest on a brass plate which has been amalgamated 
to prevent the bituminous material from adhering to it. After cooling the excess 
material shall be cut off cleanly with a slightly heated knife. 
III. TESTING. 
(A) Bituminous Materials Having Softening Points 80° C. (176° F.) on Below. 
(4) Assemble the apparatus as shown in figure 29. Fill the glass vessel to a depth 
of substantially 8.25 cm. (3.25 inches) with freshly boiled, distilled water at 5° C. 
(41° F.). Place the ball in the center of the upper surface of the bitumen in the ring 
and suspend it in the water so that the lower surface of the filled ring is exactly 2.54 
cm. (1 inch) above the bottom of the glass vessel and its upper surface is 5.08 cm. 
(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 cm. ({ inch), but not touch- 
ing, the ring. 
(5) Apply the heat in such a manner that the temperature of the water is raised 
5° C. (9° F.) each minute. 
(6) The temperature recorded by the thermometer at the instant 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 permissible variation for 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. 
(B) Bituminous Materials Having Softening Points Above 80° C. (176° F.). 
(8) Use the same method as given under (A) except that glycerine shall be used 
instead of water and that the thermometer shall conform to the following specifications: 
Total length 370 to 4Q0 mm. (14.57 to 15.75 in.) 
Diameter of stem 6.5 to 7.5 mm. (0.256 to 0.295 in.) 
Bulb length, not over 14 mm. (not over 0.55 in.) 
Bulb diameter 4.5 to 5.5 mm. (0.177 to 0.217 in.) 
The graduations shall be from 30° to 160° C. in |° C. and shall be clear cut and dis- 
tinct. The 30° mark shall be at least 75 mm. above the bottom of the bulb. The 
length between the 30° mark and the 160° mark shall be between 230 mm. and 275 mm. 
The thermometer shall be furnished with an expansion chamber at the top and have 
a ring for attaching tags. It shall be made of a suitable quality of glass and so annealed 
as not to change its readings under conditions of use. It shall be correct to 0.25° 0. 
as determined by comparison at full immersion with a similar thermometer calibrated 
at full immersion by the Bureau of Standards. 
