MIL --- DTL --- 150E
4.4.9 Bromates.
4.4.9.1 Starch indicator solution. Mix 2 g of soluble starch and several milligrams of mercu-
ric iodide, CP grade, (as a preservative) with a little water. Add the mixture slowly to 500 mL
of boiling water. Allow the liquid to boil for 5 minutes; then cool to room temperature.
4.4.9.2 Procedure. To a 200 mL aliquot of solution from 4.4.5 in a 500 mL iodine flask, add
5 mL of freshly prepared 10 percent potassium iodide solution, 10 mL of 1N hydrochloric acid
and 15 mL of the starch indicator solution prepared as specified in 4.4.9.1. Stopper the flask,
swirl to mix, and set aside in the dark for one hour. Prepare a reagent blank as follows: Place
200 mL of freshly boiled and cooled water in a 500 mL iodine flask. Add 10 mL of 1N hydro-
chloric acid and 15 mL of the starch solution prepared as specified in 4.4.9.1. Stopper the flask,
swirl to mix, and set aside in the dark for one hour. Titrate the specimen and the blank against
0.05N sodium thiosulfate solution to the starch end --- point, using a microburet calibrated in
0.01 mL divisions. Calculate the percent bromates as KBrO3 as follows:
2.78A(B - C)
Percent bromates =
W
where: A =
Normality of sodium thiosulfate solution,
B=
Milliliters of sodium thiosulfate solution required to titrate specimen,
C=
Milliliters of sodium thiosulfate solution required to titrate blank, and
W=
Weight in grams of specimen in aliquot from 4.4.5.
4.4.10 Heavy metals. To 25 mL of the solution from 4.4.5, add 1 mL of a 0.1N hydrochloric
or sulfuric acid solution, and pass hydrogen sulfide through the solution for 30 seconds. No pre-
cipitate or coloration shall result.
4.4.11 Alkaline earths. To a 25 mL aliquot of the specimen solution from 4.4.5, add 1 mL of
a 1 + 9 solution of ammonium hydroxide and 5 mL of a 10 percent solution of ammonium oxa-
late. Heat the solution nearly to boiling. No precipitate shall be found when the liquid is cooled
to room temperature. (Not applicable to grade C).
4.4.12 Sodium. Determine the sodium content of the specimen in accordance with the
method for determining sodium in potassium chlorate in the ACS reference titled Reagent
Chemicals. For Grade C, if Tricalcium Phosphate is used to prevent caking, the sodium level in
the Potassium Chlorate should conform to Table I before the Tricalcium Phosphate is added.
4.4.13 Magnesium carbonate (grade C only).
4.4.13.1 Standard magnesium solution. Dissolve exactly 0.5000 g of polished magnesium
metal ribbon in 50 mL of a 1 + 10 solution of hydrochloric acid and dilute to 500 mL with water.
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