MIL-DTL-82655A
4.5.2 Calcination loss. The calcination loss shall be determined on a dry basis in accordance with the
following:
a. Remove the cover from the crucible with sample from 4.5.1c and place the crucible in a muffle
furnace at 800 to 900°C for 30 minutes, minimum.
b. Remove the crucible from the furnace and allow to cool for 2 to 3 minutes. Replace the cover,
place the crucible in a desiccator and cool to room temperature. Weigh the covered crucible to the nearest 0.1
mg. Retain covered sample for use in the iron content test of 4.5.3.
c. Calculate the calcination loss on a dry basis as follows:
Calcination loss, wt% =
B-C
x 100
B-D
where: B = Weight of crucible, cover and dried sample (from 4.5.1e), g
C = Weight of crucible, cover and ignited sample, g
D = Weight of crucible and cover (from 4.5.1e), g
d. Report the results of 2 determinations and their average.
4.5.3 Iron content. The iron content as weight percent Fe2O3 shall be determined on a calcined basis in
accordance with the following:
a. Prepare or obtain the following reagents:
1. Hydrochloric acid, concentrated
2. Stannous chloride solution - prepare fresh by dissolving 12.5 g, weighed to the nearest 0.1
mg, of stannous chloride in 25 ml hot concentrated hydrochloric acid and diluting to 250 ml with
distilled water.
3. Mercuric chloride, saturated solution - dissolve 100 g of mercuric chloride in 1 liter of distilled
water by heating.
4. Sulfuric -phosphoric acid mixture - made by adding 150 ml concentrated sulfuric acid to 500
ml distilled water, adding 150 ml of 85 percent phosphoric acid and diluting to 1 liter with distilled
water.
5. Barium diphenylamine sulfonate indicator, 0.2 percent.
6. Standard potassium dichromate solution, 0.1 normal (N).
b. Weigh 0.28 to 0.32 g of ignited sample from 4.5.2b to the nearest 0.1 mg into a 400 ml beaker.
.
c. Add 20 ml of concentrated hydrochloric acid and cover the beaker. Heat on a hot plate until the
sample is completely dissolved. Remove the cover and rinse the cover and the sides of the beaker with 15 to
20 ml of distilled water.
d. With the beaker still on the hot plate, slowly add stannous chloride solution dropwise until the last
drop makes the solution colorless or free from any tinge of yellow, then add an additional 1 or 2 drops.
Remove the beaker from the heat and rapidly cool to room temperature. Quickly add 10 ml of mercuric
chloride solution, swirl a few seconds until uniform in appearance, then set aside for 2 or 3 minutes to allow a
slight white precipitate to form. If precipitate does not form or if a heavy grayish precipitate forms, discard
and perform another determination using more or less stannous chloride, as indicated.
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