Barium Sulfate
BaSO4 233.39

Sulfuric acid, barium salt (1:1).
Barium sulfate (1:1) [7727-43-7].
» Barium Sulfate contains not less than 97.5 percent and not more than 100.5 percent of BaSO4.
Packaging and storage— Preserve in well-closed containers.
A: Mix 0.5 g with 2 g each of anhydrous sodium carbonate and anhydrous potassium carbonate, heat the mixture in a crucible until fusion is complete, treat the resulting fused mass with hot water, and filter: the filtrate, acidified with hydrochloric acid, meets the requirements of the tests for Sulfate 191.
B: Dissolve a portion of the well-washed residue from Identification test A in 6 N acetic acid: the solution meets the requirements of the tests for Barium 191.
pH 791: between 3.5 and 10.0, in a 10% (w/w) aqueous suspension.
Heavy metals 231 Boil 4.0 g with a mixture of 2 mL of glacial acetic acid and 48 mL of water for 10 minutes. Dilute with water to 50 mL, filter, and use 25 mL of the filtrate: the limit is 0.001%.
Limit of sulfide— To 10 g in a 500-mL conical flask add 100 mL of 0.3 N hydrochloric acid. Cover the mouth of the flask with a circle of filter paper that has been moistened at the area over the mouth of the flask with 0.15 mL of lead acetate TS, the paper being held in place with a string tied around the neck of the flask. Boil the mixture gently for 10 minutes, taking care to avoid spattering the paper. Any darkening of the paper is not greater than that produced by a similarly treated control consisting of 100 mL of 0.3 N hydrochloric acid containing 5 µg of sulfide: not more than 0.5 µg per g is found.
Limit of acid-soluble substances— Cool the mixture obtained in the test for Limit of sulfide, add water to restore approximately the original volume, and filter it through paper that previously has been washed with a mixture of 10 mL of 3 N hydrochloric acid and 90 mL of water, returning the first portions, if necessary, to obtain a clear filtrate. Evaporate 50 mL of the filtrate on a steam bath to dryness, and add 2 drops of hydrochloric acid and 10 mL of hot water. Filter again through acid-washed paper, prepared as directed above, wash the filter with 10 mL of hot water, and evaporate the combined filtrate and washings in a tared dish on a steam bath to dryness. The residue, when dried at 105 for 1 hour, weighs not more than 15 mg: not more than 0.3% of acid-soluble substances is found.
Limit of soluble barium salts— Treat the residue obtained in the test for Limit of acid-soluble substances with 10 mL of water, pass the solution through a filter previously washed with 100 mL of 0.3 N hydrochloric acid, and add 0.5 mL of 2 N sulfuric acid. Any turbidity formed within 30 minutes is not greater than that produced in a similarly treated control consisting of 10 mL of water containing 0.5 mL of 2 N sulfuric acid and 50 µg of barium: not more than 0.001% of soluble barium salts is found.
Assay— Accurately weigh not less than 0.58 g and not more than 0.62 g of Barium Sulfate in a tared platinum crucible, add 10 g of anhydrous sodium carbonate, and mix by rotating the crucible. Fuse over a blast burner until a clear melt is obtained, and heat for an additional 30 minutes. Cool, place the crucible in a 400-mL beaker, add 250 mL of water, stir with a glass rod, and heat to dislodge the melt. Remove the crucible from the beaker, and wash with water, collecting the washings in the beaker. Rinse the inside of the crucible with 2 mL of 6 N acetic acid and then with water, again collecting the washings in the beaker, and continue heating and stirring until the melt is disintegrated. Cool the beaker in an ice bath until the precipitate settles, decant the clear liquid through filter paper (Whatman No. 40, or equivalent), taking care to transfer as little precipitate as possible to the paper. Wash twice by decantation as follows. Wash down the inside of the beaker with about 10 mL of cold sodium carbonate solution (1 in 50), swirl the contents of the beaker, allow the precipitate to settle, and decant the supernatant through the same filter paper as before, transferring as little precipitate as possible. Place the beaker containing the bulk of the barium carbonate precipitate under the funnel, wash the filter paper with five 1-mL portions of 3 N hydrochloric acid, and wash the paper with water. [note—The solution may be slightly hazy.] Add 100 mL of water, 5.0 mL of hydrochloric acid, 10.0 mL of ammonium acetate solution (2 in 5), 25 mL of potassium dichromate solution (1 in 10), and 10.0 g of urea. Cover the beaker with a watch glass, and digest at 80 to 85 for not less than 16 hours. Filter while hot through a tared, fine-porosity, sintered-glass crucible, transferring all of the precipitate with the aid of a rubber-tipped stirring rod. Wash the precipitate with potassium dichromate solution (1 in 200), and finally with about 20 mL of water. Dry at 105 for 2 hours, cool, and weigh: the weight of the barium chromate so obtained, multiplied by 0.9213, represents the weight of BaSO4.
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