Packaging and storage—
Preserve in tight containers.
Identification—
A 1 in 20 solution in 3 N hydrochloric acid responds to the tests for
Magnesium 
191
.
Loss on ignition 733—
Ignite it at 800
, increasing the heat gradually, to constant weight: it loses between 30.0% and 33.0% of its weight.
Soluble salts—
Boil 2.0 g with 100 mL of water for 5 minutes in a covered beaker, filter while hot, cool, and dilute the filtrate with water to 100 mL. Titrate 50 mL of the diluted filtrate with 0.10 N sulfuric acid, using
methyl red TS as the indicator: not more than 2.0 mL of the acid is consumed. Evaporate 25 mL of the diluted filtrate to dryness, and dry at 105
for 3 hours: not more than 10 mg of residue remains.
Carbonate—
Boil a mixture of 0.10 g with 5 mL of water, cool, and add 5 mL of 6 N acetic acid: not more than a slight effervescence is observed.
Limit of calcium—
Test preparation—
Transfer 250 mg of Magnesium Hydroxide, previously dried, to a beaker, add 30 mL of
Dilute hydrochloric acid, and stir until dissolved, heating if necessary. Transfer the solution so obtained to a 200-mL volumetric flask containing 4 mL of
Lanthanum solution, dilute with water to volume, and mix.
Heavy metals, Method I 231—
Dissolve 1.0 g in 15 mL of 3 N hydrochloric acid, and evaporate the solution on a steam bath to dryness. Toward the end of the evaporation, stir the residue frequently, disintegrate it so that finally a dry powder is obtained, dissolve the residue in 20 mL of water, and filter. To the filtrate, which should be neutral to litmus, add 2 mL of 1 N acetic acid, and dilute with water to 25 mL: the limit is 20 µg per g.
Lead 251—
Prepare a
Test Preparation by dissolving 1 g of Magnesium Hydroxide in 20 mL of 3 N hydrochloric acid. Use 10 mL of
Diluted Standard Lead Solution (10 µg of Pb) for the test: the limit is 0.001%.
Assay—
Transfer about 75 mg of Magnesium Hydroxide, previously dried and accurately weighed, to a conical flask. Add 2 mL of 3 N hydrochloric acid, and swirl to dissolve. Add 100 mL of water, adjust the reaction of the solution to a pH of 7 (using pH indicator paper; see
Indicator and Test Papers under
Reagents in the section
Reagents,
Indicators,
and Solutions) with 1 N sodium hydroxide, add 5 mL of ammonia-ammonium chloride buffer TS and 0.15 mL of
eriochrome black TS, and titrate with 0.05
M edetate disodium VS to a blue endpoint. Each mL of 0.05
M edetate disodium is equivalent to 2.916 mg of Mg(OH)
2.
