MIL-PRF-23950B(AS)
j. Refill the buret with the standard acid. Add 25 mL of 50 percent potassium fluoride
solution to the beaker. The released hydroxyl ions activate the delivery unit and the titration will
automatically start and will terminate at exactly 10.5 pH.
k. Calculate as follows:
(mL of standard HCl)(Standardization factor)(250)
percent Aluminum = X 100
(Sample weight in mg)(mL of aliquot)
l. The apparatus can be changed to a continuous pH measurement device such as a Beckman
zero-matic pH meter. In that case, a magnastirrer is used for thorough mixing during titration,
and the acid is manually added from a 50-mL buret with 0.1-mL graduation.
4.4.2.1.4 Alternate procedure.
a. Weigh 0.9 +0.05 g, accurate to 0.1 mg, of the sample into a 400-mL beaker and add 50
mL of distilled water.
b. Add 20 mL concentrated HCl in 5 mL increments and heat to boiling to obtain complete
solution of the aluminum.
c. Cool, transfer to a 1-liter volumetric flask and dilute to the mark with distilled water.
d. Mix solution thoroughly and pipette a 50 mL aliquot into a 400-mL beaker.
e. Warm the solution to 70°C to 80°C (158°F to 176°F) and add approximately 25 mL of
the precipitating agent (5 percent solution of 8 hydroxyquinoline in 2N acetic acid).
f. Slowly add 30-40 mL 2N ammonium acetate. If the liquid above the precipitate is yellow,
enough reagent has been added.
g. Allow to stand for one hour.
h. Collect the precipitate in a previously dried and weighed filter crucible (Selas, 3001 or
equivalent) and wash well with distilled water.
i. Dry the precipitate (ppt) in an oven at 115°C (239°F) for one and one-half hours.
j. Allow to cool in a desiccator.
k. Weigh and record as residue.
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