FED-STD-791D
6.11.3 Note the color of any stains present on the copper square.
6.12 Examine the sample in the test tube as follows:
6.12.1 Inspect for any evidence of insoluble or gummy material as required by
the specification and record.
6.12.2 Determine the acid number by method ASTM D 664 or D 974, whichever
is applicable, and calculate the change from the original acid number (see 6.1 and 7.3).
6.12.3 Determine viscosity in centistokes by method ASTM D 445 at 40C
(104F) (unless otherwise specified), and calculate the percentage change from the
original centistoke viscosity (see 6.2 and 7.4).
7. CALCULATIONS
7.1 Evaporation loss:
-
L = W 1 W 2 * 100
W1
where:
L = percentage evaporation loss
W1 = initial weight
W2 = final weight
7.2 Change in metal square weight:
(
-
)* 1000
M = M2 M1
2 * (W * L )2
where:
M = change in metal weight per surface area (mg/cm2)
M2 = final weight in g
M1 = original weight in g
W = width of metal square in cm
L = length of metal square in cm
7.3 Change in acid number:
299
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