ASTM D87 standard test method for melting point of petroleum wax (Cooling Curve)
6. Apparatus
6.1 The necessary apparatus is described in Annex A1.
7. Test Specimen
7.1 Obtain a sample of wax representative of the shipment to be tested. From each test unit obtain a portion of wax weighing at least 25 g for each melting point determination.
8. Procedure
8.1 Support the air bath in its proper position in the water bath. Fill the water bath to within 13 mm (1/2 in.) of the top with water at a temperature of 16 to 28°C (60 to 80°F). The bath temperature is kept within these limits throughout the test.
8.2 Heat the wax sample to at least 8°C (15°F) above its expected melting point (see Note 3). To heat the wax sample use a suitable container in an oven or water bath which is held at a temperature not exceeding 93°C (200°F). Avoid the use of direct heat such as flame or hot plate. Do not keep the sample in the molten state longer than 1 h.
NOTE 3 - If no estimate of the melting point is available, heat the wax sample to 10°C (15°F) above the temperature at which the wax is completely molten, or to from 90 to 93°C (195 to 200°F) before proceeding to the next step.
8.3 Fill the test tube to a height of 51 mm (2 in.) with the melted sample. Insert the melting point thermometer through the center of a cork so that the 79-mm (3 1/8-in.) immersion line is at the lower surface of the cork. Insert the cork into the test tube so that the bottom of the thermometer bulb is 10 mm (3/8 in.) from the bottom of the test tube. Support the test tube assembly in the air bath as shown in Fig. 1 while the temperature of the molten wax is still at least 8°C (15°F) above its expected melting point (Note 3).
8.4 Read the melting point thermometer every 15 s. Record each reading to the nearest estimated 0.05°C (0.1°F). Observe the progress of these sequential readings to determine the appearance of the plateau. Identify the plateau as the first five consecutive readings all of which agree within 0.1°C (0.2°F). Discontinue the test after obtaining these five plateau readings.
NOTE 4 - If no plateau appears as defined above, the reading procedure is continued until either (1) the temperature reached 38°C (100°F) or (2) the temperature reaches a point 8°C (15°F) below a temperature where the wax has solidified (as may be observed through a transparent bath). In either of these cases the test is discontinued and the method is judged Not Applicable to the sample (see Note 1 for other methods).
