ASTM D2386 standard test method for freezing point of aviation fuels
7. Procedure
7.1 Measure out 25 more or less 1 mL of the fuel and transfer it to the clean, dry, jacketed sample tube. Close the tube tightly with the cork holding the stirrer, thermometer, and moisture proof collar and adjust the thermometer position so that its bulb does not touch the walls of the tube flask and is approximately in the center. The bulb of the thermometer should be 10 to 15 mm from the bottom of the sample tube.
7.2 Clamp the jacketed sample tube so that it extends as far as possible into the vacuum flask (Warning - Implosion hazard) containing the cooling medium (Note 5). The surface of the sample should be approximately 15 to 20 mm below the level of the coolant. Unless the medium is cooled by mechanical refrigeration, add solid carbon dioxide as necessary throughout the test to maintain the coolant level in the vacuum flask.
NOTE 5 - Acetone and either methyl, ethyl, or isopropyl alcohols are suitable. All of these require cautious handling. Liquid nitrogen may also be used as a coolant instead of liquids cooled with solid carbon dioxide for fuel samples which have a freezing point below -65°C. Mechanical refrigeration is permitted. Where used the refrigerant temperature should be -70°C to 80°C.
7.3 Stir the fuel continuously, moving the stirrer up and down at the rate of 1 to 1.5 cycles/s, except when making observations, taking care that the stirrer loops approach the bottom of the flask on the downstroke and remain below the fuel surface on the upstroke (Note 6). Disregard any cloud that appears at approximately -10°C and does not increase in intensity as the temperature is lowered, because this is due to water. Record the temperature at which hydrocarbon crystals appear. Remove the jacketed sample tube from the coolant and allow the sample to warm, stirring it continuously at 1 to 1.5 cycles/s. Record the temperature at which the hydrocarbon crystals completely disappear.
NOTE 6 - Because the gases released by the coolant can obscure vision, the sample tube can be removed to observe the appearance of the wax crystals. The tube can be removed for periods no longer than 10 s. If crystals have already formed, the temperature should be noted and the sample allowed to be reheated to 5°C above the point where the crystals disappear. The sample should then be reimmersed and allowed to cool.
Remove the sample slightly above the noted temperature and observe the wax appearance point.
