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D381_11 (12 Reapproved 2017) 08-2017

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Wash the beakers, including the tare, with the gum solvent until free of gum. Rinse thoroughly with water and immerse in a mildly alkaline or neutral pH laboratory detergent cleaning solution. The type of detergent and conditions for its use need to be established in each laboratory. The criterion for satisfactory cleaning shall be a matching of the quality of that obtained with chromic acid cleaning solutions on used beakers (fresh chromic acid, six hour soaking period, rinsing with distilled water and drying). For this comparison visual appearance and mass loss on heating the glassware under test conditions may be used. Detergent cleaning avoids the potential hazards and inconveniences related to handling corrosive chromic acid solutions. The latter remains as the reference cleaning practice and as such may function as an alternate to the preferred procedure-cleaning with detergent solutions. Remove the beakers from the cleaning solution by means of stainless steel forceps or tongs (see section 6.10 of the written standard) and handle only with forceps or tongs thereafter. Wash the beakers thoroughly, first with tap water and then with distilled water, and dry in an oven at 150 degrees Celsius for at least one hour. Cool the beakers for at least two hours in the cooling vessel placed in the vicinity of the balance. Select the operating conditions, corresponding to the aviation and motor gasoline or aircraft turbine fuel under test, from the data given in Table 1 of the written standard. Heat the bath to the prescribed operating temperature. Introduce air or steam to the apparatus and adjust the total flow to that established in section 8.1 or 9.2 of the written standard. If an external preheater is used, regulate the temperature of the vaporizing medium to give the predescribed test well temperature. Weigh the tare and test beakers to the nearest 0.1 milligrams. Record the masses. If suspended or settled solid material is present, mix or shake the contents of the sample container thoroughly using an appropriate method. At atmospheric pressure, immediately filter a quantity of the sample through a centered glass funnel of coarse porosity (see section 13.3 of the written standard). Treat the filtrate as described in Section 11.5 through 11.7 of the written standard. Measure a 50 plus or minus 0.5 milliliter test specimen in a graduated cylinder (see section 6.9 of the written standard) and transfer it to a weighed beaker (see section 6.2 of the written standard). (See practice D4057 regarding sample handling.) Use one beaker for each test specimen to be tested, and fill each beaker except the tare. Place the filled beakers and the tare in the evaporation bath, keeping the elapsed time between placing the first and last beaker in the bath to a minimum. When using air as the evaporation medium in an evaporation bath without a mechanical means to raise and lower the conical jets, use forceps or tongs (see section 6.10 of the written standard) to replace the conical jets as each individual beaker is placed in the bath. When using steam, allow the beakers to heat for three to four minutes before using forceps or tongs to replace the conical jets (or lowering the conical jets by mechanical means), which shall be preheated either in the steam stream by placing on the steam outlet and positioning the jet between the beaker wells, or on top of the hot evaporation bath prior to attaching to the outlets. Using forceps or tongs (if needed), center each conical jet above the surface of the liquid, and start the flow of air or steam, adjusting it to the specified rate. Maintain the temperature and rate of flow, and allow the test specimen to evaporate for 30 plus or minus 0.5 minutes. When introducing the flow of air or steam, care should be taken to avoid splashing of the test specimen as this may lead to erroneous low results. At the end of the heating period, remove the conical jets using forceps, tongs, or other suitable means, and transfer the beakers from the bath to the cooling vessel. Place the cooling vessel in the vicinity of the balance for at least two hours. Weigh the beakers in accordance with section 11.3 of the written standard. Record the masses. Segregate the beakers containing the residues from motor gasolines for finishing as described in Section 11.8 through 11.12 of the written standard. The remaining beakers may be returned for cleaning and reuse. Qualitative evidence of motor gasoline contamination can be obtained by weighing the residue at this point if retained samples of the original finished gasoline are available for reference testing. This reference testing is essential since motor gasoline may contain deliberately added materials that are nonvolatile. If evidence of contamination is obtained, further investigation is indicated. For non-aviation fuels that have unwashed results that are less than 0.5 milligrams per 100 milliliters, it is not necessary to perform the washing steps identified in this section, as well as those that follow, since the washed gum values will always be less than the unwashed gum value. See section 11.6, section 12, and section 13.2 of the written standard. See section 11.9 to section 11.12 of the written standard. If the unwashed results are not less than 0.5 milligrams per 100 milliliters to each of the beakers containing the residues from non-aviation fuels, add approximately 25 millimeters of heptane and swirl gently for 30 seconds. Allow the mixture to stand for 10 plus or minus one minute. Treat the tare beaker in the same manner. Decant and discard the heptane solution, taking care to prevent the loss of any solid residue. Repeat the extraction with a second portion of approximately 25 milliliters of heptane as described in (section 11.8 and 11.9 of the written standard). If, after the second extraction, the extract remains colored, repeat the extraction a third time. Do not perform more than three extractions. (See note six of the written standard). Further extractions (after the third extraction) are not to be performed, since portions of insoluble gum may be removed due to mechanical action, which can lead to lower solvent washed gum contents being determined. Place the beakers, including the tare, in the evaporation bath, maintained at 160 to 165 degrees celsius and, without replacing the conical jets, allow the beakers to dry for five plus or minus 0.5 minutes. At the end of the drying period, remove the beakers from the evaporation bath using forceps or tongs (see section 6.10 of the written standard). Place them in a cooling vessel and allow them to cool in the vicinity of the balance for at least two hours. Weigh the beakers in the same manner as described in section 11.3 of the written standard. Record the masses.

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Posted by: abuckmaster on Aug 23, 2018

D381_11 (12 Reapproved 2017) 08-2017

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