9. Procedure
9.1 Fill a test cup with sample by pressing the larger opening into the grease to be tested until the cup is filled. Remove excess grease with a spatula. Gently press the cup, held in a vertical position with the smaller opening at the bottom, down over the metal rod until the latter protrudes about 25mm. Press the rod against the cup in such a manner that the rod makes contact at both upper and lower peripheries of the cup. Maintain this contact, rotating the cup on the rod along the index finger to give a spiral-like motion down the rod to remove a conical section of the grease which adheres along the rod. As the cup approaches the end of the rod, carefully slip the rod out of the cup so that a smooth film, free of air bubbles and of reproducible thickness, remains inside the cup. See Fig.4.
9.2 Place the corks on the thermometer to be used in the test tube as shown in Fig.2. With the thermometer depth gage in position in the test tube, adjust the position of the upper cork on the thermometer so that the thermometer bulb bottoms snugly in the depth gage. Observe the relative position of the top edge of the upper cork to the thermometer stem as well as the relative position of the top edge of the test tube to the cork. Care must be taken to be certain that the thermometer is inserted to the same depth when the apparatus is reassembled with the grease cup in position.
9.3 Replace the depth gage with the grease cup as shown in Fig.2 so that the thermometer is inserted to the previously gage ddepth. When properly inserted, the bulb of the thermometer does not touch either the grease sample or the cup.
9.4 Suspend the test tube in the oil bath to a depth corresponding to the 76mm immersion mark on the thermometer. This should leave the test tube rim at least 6mm above the oil level.
9.5 Suspend the second thermometer in the oil bath so that its bulb is at approximately the same level as the bulb of the test tube thermometer.
9.6 Stir the oil bath and heat at a rate of 4 to 7°C/min until the bath reaches a temperature of approximately 17°C below the expected dropping point of the grease. At this point reduce the rate of heating so that the temperature difference between the test tube and the oil bath is maintained between 1 and 2°C. This condition is established whe the oil bath is heated at a rate of about 1 to 1.5°C/min. As the temperature increases, material will gradually protrude through the orifice of the grease cup. When a drop of material falls, note the temperatures on the two thermometers and record their average to the nearest degree as the dropping point of the grease.
NOTE 2 - Certain greases form a drop with a tailing thread upon melting, which can break off or which can hold until the drop reaches the bottom of the test tube; in any case, the observed dropping point is the temperature when the drop reaches the bottom of the test tube.
NOTE 3 - The dropping points of some greases, particularly those containing simple aluminum soaps, are known to decrease upon aging, the change being much greater than the deviation permitted in results obtained by different laboratories. Therefore, comparative tests between laboratories should be made within a period of six days.
9.7 Two determinations can be made simultaneously in the same bath, provided both samples have approximately the same dropping points.
