A: To a solution of 5 g in 10 mL of 3 N hydrochloric acid add 5 drops of methyl red TS, heat to boiling, add 6 N ammonium hydroxide until the color of the solution changes to deep yellow, then continue boiling for 2 minutes, and filter: the filtrate responds to the tests for Magnesium 191.

B: Wash the precipitate obtained in Identification test A with hot ammonium chloride solution (1 in 50), and dissolve the precipitate in hydrochloric acid: the solution responds to the tests for Aluminum 191.

0.55(0.0385A) + 0.8(0.0343 M)

Edetate disodium titrant— Prepare and standardize as directed in the Assay under Ammonium Alum.

Assay preparation— Transfer an accurately measured quantity of Oral Suspension, previously well shaken in its original container, equivalent to about 1200 mg of aluminum hydroxide, to a suitable beaker. Add 20 mL of water, stir, and slowly add 10 mL of hydrochloric acid. Heat gently, if necessary, to aid solution, cool, and filter into a 200-mL volumetric flask. Wash the filter with water into the flask, add water to volume, and mix.

Procedure— Pipet 10 mL of Assay preparation into a 250-mL beaker, add 20 mL of water, then add, in the order named and with continuous stirring, 25.0 mL of Edetate disodium titrant and 20 mL of acetic acid–ammonium acetate buffer TS, and heat near the boiling point for 5 minutes. Cool, add 50 mL of alcohol and 2 mL of dithizone TS, and mix. Titrate with 0.05 M zinc sulfate VS until the color changes from green-violet to rose-pink. Perform a blank determination, substituting 10 mL of water for the Assay preparation, and make any necessary correction. Each mL of 0.05 M Edetate disodium titrant consumed is equivalent to 3.900 mg of Al(OH)3.

Assay preparation— Prepare as directed in the Assay for aluminum hydroxide.

Procedure— Pipet a volume of Assay preparation, equivalent to about 40 mg of magnesium hydroxide, into a 400-mL beaker, add 200 mL of water and 20 mL of triethanolamine, and stir. Add 10 mL of ammonia-ammonium chloride buffer TS and 3 drops of an eriochrome black indicator solution prepared by dissolving 200 mg of eriochrome black T in a mixture of 15 mL of triethanolamine and 5 mL of dehydrated alcohol, and mix. Cool the solution to between 3 and 4 by immersion of the beaker in an ice bath, then remove, and titrate with 0.05 M edetate disodium VS to a blue endpoint. Perform a blank determination, substituting 10 mL of water for the Assay preparation, and make any necessary correction. Each mL of 0.05 M edetate disodium consumed is equivalent to 2.916 mg of Mg(OH)2.