9. Procedure
9.1 Dry a clean filter membrane for 15 min in a desiccator, place in a labeled aluminum weighing dish, and weigh to the nearest 0.1 mg.
9.2 Place a 50 mL graduated cylinder on the balance, and tare it.
9.3 Remove the oil from the oven. Vigorously shake the sample by hand for a minimum of 30 s.
9.4 Using a medicine dropper, weigh approximately 0.25 g of oil sample into the graduated cylinder. Record the weight to the nearest 0.1 mg.
9.5 Add 10 mL pentane and agitate gently until the oil sample is fully dissolved.
9.6 Bring the volume in the graduated cylinder up to the 50 mL mark with fresh 1 % coagulant solution. Stopper and shake gently, inverting the graduated cylinder four times in 4 to 5 s. Allow to stand for 30 min. Shake the solution similarly every 10 min of the 30 min.
9.7 Mount the filter on a dry holder and apply a vacuum. Mount and securely clamp the filter funnel to the filter holder. Ensure a minimum vacuum of 50.653 kPa (15 in. Hg) is attained and held.
9.8 Shake the sample gently one last time, pour into the filter funnel, and using the stopwatch or other timing device immediately start timing the flow rate.
9.9 Rinse the graduated cylinder twice using a minimum of 35 mL pentane and pour the rinsings into the filter funnel.
9.10 Stop timing when the last of the free liquid on the filter disappears. Record the flow time to the nearest second.
9.11 Iffilter flow time exceeds 5 min, re-run 9.4 to 9.10 with 0.1 mg sample.
9.12 Rinse the funnel wall with pentane from a squirt bottle.
9.13 Remove the filter funnel from the filter holder and rinse the filter membrane with a stream of pentane from the squirt bottle. Ensure the edges of the filter funnel are rinsed well to remove any oil trapped beneath the funnel.
9.14 Release the vacuum, and using the smooth-tip forceps transfer the filter membrane to its original weighing dish, and dry in the oven at 100 +/- 3°C for 1 h +/- 5 min.
9.15 Remove the weighing dish and filter membrane and cool to room temperature in a dessicator for a minimum of 1 h.
9.16 Weigh the filter membrane and weighing dish and record the stabilized weight to the nearest 0.1 mg.
10. Calculation
10.1 Calculate the percent coagulated pentane insolubles in the used oil as follows:
where:
I = coagulated pentane insolubles, %,
A = mass of filter and deposit, mg,
B = mass of filter, mg, and
C = mass of oil sample, mg.