ASTM D61 Standard Test Method for Softening Point of Pitches (Cube-in-Water Method)
4. Summary of Test Method
4.1 Two cubes of pitch, supported on wire hooks, are heated at a controlled rate in water in a glass container. The softening point is defined as the mean of the temperatures at which the cubes sag downwards a distance of 25 mm.
5. Significance and Use
5.1 Pitch does not go through a solid-liquid phase change when heated, and therefore it does not have a true melting point. As the temperature rises, pitch softens and becomes less viscous. The softening point is arbitrarily defined and shall be established by a closely controlled method which shall be carefully followed if test results are to be reproducible.
5.2 This test is useful in determining the consistency of pitch as one element in establishing the uniformity of shipments or sources of supply.
