FED-STD-791D
NOTE 1:
Caution. Petroleum ether and n-hexane are both flammable. Use these
materials in a well ventilated area. Do not breathe their fumes nor permit
them to come in contact with the skin. Keep all flames away from these
materials.
6.7 Cap the bottle (with inert seal in place), and mount it in the tumbling
mechanism in the oven.
6.8 Allow the mechanism to rotate the container end-over-end at 5 rpm for the
time required by the specification.
6.9 After the container has rotated for the required time, filter the liquid contents
through a tared Gooch crucible lined with a thin layer of asbestos. Save the filtrate. (The
operator should wear heavy asbestos gloves and a face shield while handling the hot
beverage bottle). Rinse the copper strip and beverage bottle with 50 mL of distilled water
and 50 mL of petroleum ether and filter through the Gooch crucible. Save only the water
washings and add them to the filtrate.
6.10 Process any insolubles that remain in the crucible, as follows:
a. Wash the precipitate with 50 mL of distilled water, and add the washings to the
filtrate.
b. Wash the precipitate with 50 mL of petroleum ether, and dry the crucible at 66
to 93C (150 to 200F).
c. Determine and record the increase in weight of the crucible to within 0.2 mg.
6.11 Process the filtrate as follows:
a. Weigh a clean centrifuge tube to within 0.2 mg.
b. Transfer the filtrate to the tube, and centrifuge the tube for 15 min at 1500 rpm
(min.).
c. After centrifuging, decant the oil and water layers to suitable separate
containers.
6.12 Process the oil layer from the centrifuge tube as follows:
a. Wash the oil with 25 mL portions of distilled water until the water is neutral to
litmus. Save the water from this washing.
b. Examine the oil for insolubles, and remove any that still exist, using a
combination of filtration, centrifuging, and solvent extraction as necessary.
c. When all insolubles have been removed, dry the oil with anhydrous sodium
sulfate.
d. Determine the acid number of the oil by ASTM D 974, and calculate the change
from the original acid number.
e. Determine the kinematic viscosity of the oil by ASTM D 445, and calculate the
change from the original viscosity.
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