FED-STD-791D
NOTE 1.
Caution. n-Hexane is both toxic and extremely flammable. Use only in a
well ventilated area. Do not breathe its fumes nor allow it to come in
contact with the skin. Keep all flames away from the Hexane.
d. Remove the thimble from the extraction tube and dry in an oven at 100C.
Allow to cool in a desiccator. After cooling, remove and weigh to
constant weight. Subtract the weight of the thimble from the latter weight
to determine the weight of the solids in the grease. Calculate the percent
solids (see 7.1).
6.2 Determine percent molybdenum disulfide in the grease as follows:
a. Ignite a clean crucible (50 mL) in the blue oxidizing flame of a Meker burner.
Cool in a desiccator. Remove and add approximately 2 g of Eschka's mixture
and weigh to the nearest 0.1 mg.
b. Add approximately 0.1 g of the grease solids (6.1 d) and reweigh to the nearest
0.1 mg (throughly mix by stirring sample using a wire rod).
c. Place a layer 0.6 cm (0.25 in) of Eschka's mixture on the sample from 6.2 b. Do
not mix.
d. A blank determination using 4 g of Eschka's mixture is conducted in a separate
crucible.
e. Place both crucibles in a cold muffle furnace and slowly raise the temperature to
760C. Maintain a temperature of 760C for 2 h. Remove the crucibles from
the muffle furnace and allow to cool.
f. Remove the contents of each crucible into separate 600-mL beakers and place
the crucibles in a horizontal position in the beakers. Cover the crucibles with
distilled water.
g. Place on heated steam bath for 30 min. Remove and rinse each crucible so that
the rinse water is deposited in the beakers.
h. Pass the contents of beaker through filter paper (Whatman No. l or equal) and
rinse the residue 2 or 3 times with distilled water. Discard residue and paper.
i. Add 10 mL of saturated bromine water to the filtrates. Heat gradually to
boiling. Continue to boil until the volume is reduced to 200 mL.
j. Cool the solution and add 5 mL of concentrated hydrochloric acid to each
beaker and boil until colorless.
k. While boiling, add at a very slow rate 10 mL of 10% solution of barium
chloride. Heat on a steam bath for at least 3 h, and allow to stand for 24 h.
l. Pass the solutions through filter paper (Whatman No. 40 or equal). Remove all
barium sulfate adhering to the surfaces of the beakers by means of a rubber
policeman. Wash the precipitates and discard the filtrates.
m. Clean the crucibles by fusing 50-50 mixture of sodium and potassium
carbonates. Do not use potassium bisulfate. Dry and cool the crucibles and
weigh to the nearest 0.1 mg.
n. Fold the filter paper and precipitates, and place in the clean weighed crucibles.
o. Place the crucibles in a cold muffle furnace and heat gradually to a temperature
of 400C. Hold at 400C until the filter papers are thoroughly charred. Slowly
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