ASTM D938 Method for Congealing Point of Petroleum Waxes, Including Petrolatum
7. Procedure
7.1 Adjust the thermometer through the stopper so that the bottom of the bulb will be 10 to 15 mm above the bottom of the Erlenmeyer flask when the stopper is fitted snugly in the flask. After making this adjustment, remove the thermometer and stopper from the flask, being careful not to change the position of the stopper relative to the thermometer stem.
7.2 Place approximately 50 g of sample, which is representative of the material under inspection, in a porcelain evaporating dish or other suitable container.
7.3 Place the empty Erlenmeyer flask (without the thermometer assembly) and the container holding the specimen in a temperature-controlled oven set at 99 more or less 3°C (210 more or less 5°F) until the specimen and the flask reach oven temperature.
NOTE 2 - For nonreferee, routine testing of samples known to have low congealing points, the oven may be set at a lower temperature, but it must be at least 11°C (20°F) above the expected congealing point of the sample.
7.4 Remove the specimen from the oven and completely immerse the thermometer bulb in it without covering any part of the thermometer stem with specimen. Gently stir the specimen with the thermometer until the mercury column has stopped rising.
7.5 While holding the thermometer bulb in the molten wax specimen, remove the heated flask from the oven, using a towel or gloves to protect the hands. Now carefully remove the thermometer from the specimen, taking care to retain a relatively large drop of specimen adhering to the bulb. Holding the thermometer in a horizontal position, firmly fit the thermometer and stopper into the flask. Keep the assembly in a horizontal position.
7.6 While observing the drop on the thermometer bulb at an eye level position, rotate the thermometer and flask about a horizontal axis. Use a steady and even rate for each continuous full revolution, and complete each revolution in not less than 2 s, nor more than 3 s. Do not pause at the completion of each revolution any longer than required to reindex the fingers for the next full and continuous rotation (Note 3). When the drop is observed to rotate with the bulb, immediately read the thermometer to the nearest 0.2°C (0.5°F) and record this determination. Make a repeat determination on the wax specimen. If the variation of these two determinations does not exceed 1°C (2°F), record the average of these determinations as the congealing point of the specimen under test. If the variation of two determinations is greater than 1°C (2°F), make one additional determination and record the average of the three determinations as the congealing point.
NOTE 3 - Operators should periodically check themselves for compliance with this turning rate. The brief pause time is not to be included in the 2 to 3-s rotation time.
