FED-STD-791D
a. Pour 25 mL of 0.00322 M barium chloride into a 250-mL volumetric flask [0,0,2].
b. Add 125 mL of 0.0050 N sulfuric acid, and shake well to insure complete
precipitation [3,0,2].
c. Add approximately 25 mL of l N sodium hydroxide to make solution alkaline
[3,0,1].
d. Add distilled water to bring total volume to 250 mL.
e. Pour solution into a sample bottle, and seal it tightly with stopper.
NOTE: For red hydraulic liquids, in place of plain distilled water, use distilled water
containing 200 ppm red dye (National Erie Bordeaux B, manufactured by National Aniline
Division of Allied Chemical and Dye Corp., or equivalent).
6. PROCEDURE.
6.1 Clean sample bottles, and dry at approximately 100C for a minimum of 24 h.
6.2 Pour sample into bottle, and seal bottle tightly with stopper.
6.3 Store sample for the specified number of hours at a temperature no warmer than
-54C (-65F).
6.4 Before end of storage period, cool the methanol-glycerol solution to -54C (-65F).
6.5 Within 5 min of making comparison, shake the turbidity standard vigorously for 10 s,
and pour into the other sample bottle.
6.6 At the end of the storage period, remove sample from cold storage, and shake
vigorously for approximately 10 s.
6.7 Dip sample into methanol-glycerol solution to eliminate frosting (if necessary), and
within one minute of removal from cold storage, compare sample visually with the turbidity
standard.
6.8 Note the turbidity of the sample.
7. CALCULATIONS
7.1 This section is not applicable to the test procedure.
8. REPORTING.
8.1 Report turbidity of sample relative to standard as less than, more than, or equal to the
standard.
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