FED-STD-791D
NOTE 1. Moisture may be removed by heating MoS2 powder in a drying oven at
105C for 1 h.Oil may be removed by extraction with acetone and petroleum ether.
6.2 Add l mL of distilled water to the sample and moisten particles of MoS2.
Add with caution 30 mL of a saturated solution of potassium chlorate in nitric acid.
6.3 After vigorous action ceases, place the beaker on a hot plate and digest the
sample slowly until the solution becomes pale yellow or almost white. Add 0.5 g of
potassium chlorate to the solution and evaporate it to dryness.
6.4 Add 15 mL of conc. HCl, and boil solution until all brown fumes are
expelled. Allow solution to cool and while stirring dilute with distilled water to 50 5
mL.
6.5 To this solution add 40 mL of concentrated ammonium hydroxide (this will
precipitate iron). Heat to boiling and while hot filter through Whatman No. 40 (or
equivalent) paper. Paper pulp may be added to aid filtration. Collect filtrate in 600-mL
beaker and retain.
6.6 Wash residue on filter paper 5 times with 10-mL portions of hot distilled
water, collecting the filtrate in the 600-mL beaker containing first filtrate. Retain
combined filtrate.
6.7 Transfer filter paper with residue to clean 400-mL beaker, add 10 mL of
hydrochloric acid. Stir until filter paper is pulped.
6.8 To this solution add 40 mL of distilled water and while stirring add 40 mL of
concentrated ammonium hydroxide. Bring solution to a boil. While the solution is hot,
filter through Whatman No. 40 (or equivalent) paper, and collect the filtrate in the 600-
mL beaker containing the previous filtrate. Wash residue on filter paper with 25-mL
portions of hot distilled water 8 times, collecting filtrate in the 600-mL beaker with the
combined filtrate.
6.9 Discard filter paper and residue (see Note 2) and retain combined filtrate.
The filter paper and residue can be used to determine percent total
NOTE 2.
insoluble matter. Place filter paper and residue in a previously ignited and
weighed porcelain crucible, carefully burn off filter paper and then place
in muffle furnace at 600C for l h. Remove crucible and place in
desiccator for l h, when cooled remove and weigh. Repeat ignition to
constant weight. Calculate percent total insoluble matter (see 7.1).
6.10 Transfer the combined filtrate from the 600-mL beaker to a 500-mL
volumetric flask, dilute with distilled water to 500 mL.
250
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