FED-STD-791D
test is to be made. Allow the block to maintain the temperature of the test at least 2 h before
beginning the test. During this period, allow clean air to flow through the cell at the prescribed
rate, 2.58 " 0.02 g/min (2 L/min at standard temperature and pressure), as indicated by the
rotometer. Then remove the cover, thread the weighed hood and sample cup into place, and
replace the cover. Tighten the three knurled cover- tightening screws securely to prevent air
leakage under the cover. Pass clean air through cell for 22 h " 5 min.
6.1.4 At the end of the 22-hour period, remove the assembled sample cup and hood from
the cell, and allow to cool to room temperature. Determine the net weight of the sample to the
nearest mg.
6.2 Oils.
6.2.1 Clean the oil-sample cup and hood as described in 6.1.1.
6.2.2 Weigh the clean oil-sample cup and hood to the nearest mg. Transfer, by means of
a pipet, 10.00 " 0.05 g of sample to the cup. Assemble the cup and hood, being careful not to
splash oil on the underside of the hood. Weigh the assembly and record the net sample weight to
the nearest mg.
6.2.3 Evaporate the sample as described in 6.1.3 and 6.1.4.
7. CALCULATION
7.1 Calculate the evaporation loss of the sample as follows:
S -W
* 100
Evaporatio n loss, percent by weight =
S
where:
S = initial weight of sample, in grams.
W = weight of sample, in grams, after the test.
8. REPORTING
8.1 Report the evaporation loss percentage.
9. PRECISION
9.1 Results should not differ from the mean by more than the following amounts:
Repeatability: 2.5% of mean
Reproducibility: Not established
Method prepared by:
Navy - NADC 1986
36
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