Packaging and storage—
Preserve in tight containers, and prevent exposure to excessive heat.
Labeling—
Label it to indicate whether it is Type I-A or Type I-B.
Identification—
A:
Transfer 0.5 g of Magnesium Aluminometasilicate to a suitable container, add 5 mL of a sulfuric acid solution (1 in 3), and heat until white fumes are observed. Cool, add 20 mL of water, and filter. Neutralize the filtrate with
ammonia TS, and retain for use in
Identification test
B. Collect the precipitate, and dissolve in 3 N hydrochloric acid: the solution meets the requirements of the tests for
Aluminum 
191
.
B:
The filtrate retained from
Identification test
A meets the requirements of the tests for
Magnesium 191.
C:
Prepare a bead by fusing a few crystals of sodium ammonium phosphate on a platinum loop in the flame of a Bunsen burner. Place the hot, transparent bead in contact with Magnesium Aluminometasilicate, and again fuse: silica floats about in the bead producing, upon cooling, an opaque bead with a web-like structure.
Acid-consuming capacity—
Transfer about 0.2 g of Magnesium Aluminometasilicate, accurately weighed, to a glass-stoppered flask, and add 100.0 mL of 0.1 N hydrochloric acid VS. Stopper the flask tightly, shake at 37 ± 2
for 1 hour, and filter. Transfer 50.0 mL of the filtrate to a beaker, and while stirring, titrate the excess hydrochloric acid with 0.1 N sodium hydroxide VS to attain a pH of 3.5. Perform a blank determination, and make any necessary correction. Not less than 210 mL of 0.1 N hydrochloric acid is consumed per g of Magnesium Aluminometasilicate, calculated on the dried basis.
pH 791—
Transfer 2 g of Magnesium Aluminometasilicate to a suitable container, and add 50 mL of water. While stirring, immerse the pH electrodes in the suspension, and after 2 minutes, record the pH: between 6.5 and 8.5 for Type I-A, and between 8.5 and 10.5 for Type I-B.
Loss on drying 731—
Dry it at 110
for 7 hours: it loses not more than 20.0% of its weight.
Soluble salts—
Transfer 10.0 g of Magnesium Aluminometasilicate to a suitable container, add 150 mL of water, and boil gently for 15 minutes, with shaking. After cooling, dilute with water to 150 mL, and centrifuge. Dilute 75 mL of the clear filtrate with water to 100 mL, and retain the diluted filtrate for use in the tests for
Alkalinity,
Chloride, and
Sulfate. Evaporate 25 mL of the diluted filtrate on a water bath, and heat at 700
for 2 hours. The residue weighs not more than 0.020 g: not more than 1.6% is found.
Alkalinity—
Add 2 drops of phenolphthalein TS to 20 mL of the diluted filtrate retained from the test for Soluble salts, containing 1 g of Magnesium Aluminometasilicate: if a pink color is produced, not more than 0.50 mL of 0.1 N hydrochloric acid is required to discharge it.
Chloride 221—
A 20-mL portion of the diluted filtrate retained from the test for
Soluble salts shows no more chloride than corresponds to 0.75 mL of 0.020 N hydrochloric acid: not more than 0.053% is found.
Sulfate 221—
A 2-mL portion of the diluted filtrate retained from the test for
Soluble salts shows no more sulfate than corresponds to 0.5 mL of 0.020 N sulfuric acid: not more than 0.480% is found.
Iron 241—
Test Preparation—
To 0.11 g of Magnesium Aluminometasilicate add 8 mL of 2 N nitric acid, boil for 1 minute, and cool. Dilute with water to 100 mL, and centrifuge. Dilute 30 mL of the supernatant with water to 45 mL: the limit is 0.03%.
Heavy metals, Method I 231—
Test Preparation—
Transfer 2.67 g of Magnesium Aluminometasilicate to a suitable container, add 20 mL of water and 8 mL of hydrochloric acid, and evaporate to dryness on a water bath. To the residue add 5 mL of 1 N acetic acid and 20 mL of water, boil for 2 minutes, add 0.4 g of hydroxylamine hydrochloride, and heat to boiling. Cool, dilute with water to 100 mL, and filter. Use 25 mL of the filtrate as the Test Preparation.
Monitor Preparation—
Transfer another 25 mL of the diluted filtrate to a suitable container, and add 2.0 mL of Standard Lead Solution.
Standard Preparation—
Transfer 2 mL of hydrochloric acid to a suitable container, and evaporate to dryness on a water bath. To the residue add 2.0 mL of Standard Lead Solution and 0.1 g of hydroxylamine hydrochloride. Dilute with water to 25 mL: the limit is 30 µg per g.
Assay for aluminum oxide—
Edetate disodium titrant—
Prepare and standardize as directed in the
Assay under
Ammonium Alum.
Assay preparation—
Transfer about 1.25 g of Magnesium Aluminometasilicate, accurately weighed, to a conical flask, add 10 mL of 3 N hydrochloric acid and 50 mL of water, and heat on a water bath for 15 minutes. To this solution add 8 mL of hydrochloric acid, and heat on a water bath for 10 minutes. After cooling, transfer the solution to a 250-mL volumetric flask, rinse the conical flask with water, and add the washings to the volumetric flask. Dilute with water to volume, and mix. Centrifuge, and use the supernatant as the Assay preparation. Retain a portion of the Assay preparation for use in the Assay for magnesium oxide.
Procedure—
Transfer 20.0 mL of the
Assay preparation to a beaker, and add 20.0 mL of
Edetate disodium titrant. To this solution add 15 mL of acetic acid–ammonium acetate buffer TS and 20 mL of water, and boil for 5 minutes. After cooling, add 50 mL of alcohol and 2 mL of
dithizone TS, and titrate with 0.05 M zinc sulfate VS until the color of the solution changes from green-violet to rose-pink. Perform a blank determination, and make any necessary correction. Each mL of 0.05 M
Edetate disodium titrant is equivalent to 2.5490 mg of Al
2O
3.
Assay for magnesium oxide—
Transfer 50.0 mL of the
Assay preparation retained from the
Assay for aluminum oxide to a suitable container, add 50 mL of water and 25 mL of a trolamine solution (1 in 2), and shake well. Add 25 mL of ammonia–ammonium chloride buffer TS and 0.04 g of
eriochrome black TS trituration as the indicator. Titrate with 0.05 M edetate disodium VS until the red-purple color changes to blue and persists for 30 seconds. Each mL of 0.05 M edetate disodium VS is equivalent to 2.0152 mg of MgO.
Assay for silicon dioxide—
Transfer about 1 g of Magnesium Aluminometasilicate, accurately weighed, to a suitable container, add 30 mL of 3 N hydrochloric acid, and evaporate on a water bath to dryness. Moisten the residue with hydrochloric acid, and again evaporate on a water bath to dryness. To the residue add 8 mL of hydrochloric acid and 25 mL of hot water, and stir. Allow to stand, and then decant the supernatant through an ashless filter paper. To the residue in the container add 10 mL of hot water, stir, and decant the supernatant through the filter paper. Wash the residue in the container with three additional 10-mL portions of hot water, stir, and decant as described above. Treat the residue in the container with 50 mL of water, and heat on a water bath for 15 minutes. Filter, and rinse the residue on the filter paper with hot water until no precipitate is obtained when 1 mL of
silver nitrate TS is added to 5 mL of the washing. Transfer the filter paper and its contents to a tared platinum crucible, heat to dryness, incinerate, and continue to heat at 800 ± 25
for 1 hour. Cool, and weigh. Moisten the residue with 6 mL of hydrofluoric acid, evaporate to dryness, and ignite for 5 minutes. Cool, and weigh. The loss in weight represents the weight of silicon dioxide (SiO
2).
