ASTM D61 Standard Test Method for Softening Point of Pitches (Cube-in-Water Method)
9. Procedure
9.1 Pitches Having Softening Points Between 110 °F and 176 °F (43 °C and 80 °C):
9.1.1 Assemble the apparatus as shown in Fig. 1. Fill the container to a depth of about 100 mm with freshly boiled distilled water cooled to 60 °F (15 °C) (Notes 4 and 5). Place two cubes of pitch on hooks as shown in Fig. 1, warming the hooks slightly before inserting them in the center holes if necessary. Suspend the specimens in the bath so that the lower edges are 1 in. (25 mm) above the bottom of the container. Position the thermometer so that the bulb is between the cubes and within 6 mm, but not touching either cube. The bottom of the bulb should be level with the bottom of the cubes. Allow the specimens to remain in the bath at 60 °F (15 °C) for 15 min before applying heat.
NOTE 4 - The use of freshly boiled water is essential to prevent the formation of air bubbles on its surface which may retard the sinking of the cube.
NOTE 5 - A sheet of filter paper that will sink when wet may be placed on the bottom of the container to prevent the pitch from sticking to the glass.
9.1.2 Apply heat in such a manner that the temperature of the water is raised 9 °F (5 °C)/min. The rate shall be uniform and shall not be averaged over the period of the test. The maximum permissible variation for any 1 min period, after the first three, shall be +/- 1 °F (0.5 °C). Reject all tests in which the rate of rise is outside these limits.
9.1.3 The softening point is the average of the temperatures at which the two cubes touch the bottom of the container. Estimate individual readings to the nearest 0.5 °F (0.2 °C). Repeat the determination if the individual values differ by more than 2 °F (1 °C).
9.2 Pitches Having Softening Points Below 110 °F (43 °C) - Follow the procedures described in 9.1, but cool the water bath to 40 °F (5 °C). After immersing the specimens in the bath, maintain the temperature for at least 15 min before applying heat.
