D2386_1 (15e1)

Collar assemble the collar (5.2 of the written standard), thermometer (5.5 of the written standard) and stirrer (5.3 of the written standard) into the cork. To prevent the ingress of water into the test portion, it is important that an effective moisture-proof collar as prepared in accordance with 8.1.1 or 8.1.2 of the written standard is used. Collar type A, flush with nitrogen or dry air before fitting to the jacketed sample tube and throughout the entire determination. The air can be effectively dried by passing through absorbent tubes filled with dehydrating agents (6.8.1 and 6.8.2 of the written standard). Collar type B, fill with fiberglass (6.7 of the written standard) and a suitable dehydrating agent (6.8.1 and 6.8.2 of the written standard) as shown in Figure 2 of the written standard. The fiberglass shall be replaced every fourth test. The dehydrating agent should be renewed at intervals of not more than three months or when a color change shows it to be ineffective. Measure out 25 milliliters, plus or minus 1 millimeter 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 it's bulb does not touch the walls of the tube flask and is approximately in the center. The bulb of the thermometer should be 10 millimeters to 15 millimeters from the bottom of the sample tube. (Warning do not add solid carbon dioxide to liquid nitrogen.) Performance of this test method can be difficult, since the specimen tube is immersed in a coolant medium that evolves gas bubbles during the test. This can interfere with visual observations. In addition, the crystals that are formed in the specimen can be difficult to recognize, And they can appear in a variety of manifestations. It is strongly suggested that operators seek guidance from experienced operators of this test method to assist them in the correct recognition of these crystals. This test method should be performed under laboratory conditions where there is an ample supply of light. Some crystals can be very faint in appearance and difficult to observe under inadequate lighting conditions. 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 7 of the written standard). The surface of the sample should be approximately 15 millimeters to 20 millimeters 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. 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 degrees Celsius. Mechanical refrigeration is permitted. Where used, the refrigerant temperature should be -70 degrees Celsius to 80 degrees Celsius. Stir the fuel continuously, moving the stirrer up and down at the rate of 1 cycle per second to 1.5 cycles per second, taking care that the stirrer loops approach the bottom of the flask on the downstroke and remain below the specimen surface on the upstroke. It is permissible for momentary interruption of stirring while performing some operations of the procedure (see Note 8 of the written standard). Observe the specimen continuously for the appearance of hydrocarbon crystals. Disregard any cloud that appears at approximately -10 degrees Celsius and does not increase in intensity as the temperature decreases, because this cloud is due to water. Record the temperature at which hydrocarbon crystals appear. Remove the jacketed sample tube from the coolant and allow the specimen to warm by ambient air, stirring it continuously at 1 cycles per second to 1.5 cycles per second. Continue to observe this specimen continuously for the disappearance of hydrocarbon crystals. Record the temperature at which the hydrocarbon crystals completely disappear. Because the gases released by the coolant can obscure observations, the sample tube can be removed from the coolant for observations. The tube can be removed for periods no longer than 10 seconds. If crystals are observed to have already formed, the specimen temperature should be noted and the specimen allowed to be warmed by ambient air, with continued stirring to at least 5 degrees Celsius above the temperature at which the crystals disappeared. The specimen should then be re-immersed in the coolant and allowed to cool. Remove the specimen from the coolant slightly above the noted temperature, and observe for appearance of the crystals. It is recommended to compare the crystal appearance temperature with the crystal disappearance temperature. The appearance temperature should be colder than the disappearance temperature. If this is not the case, this is an indication that the crystals were not correctly recognized. Also, the difference between these temperatures should typically be no greater than 6 degrees Celsius.