Packaging and storage—
Preserve in tight containers.
Residue on ignition 
281
—
To 20 mL add 2 drops of sulfuric acid, evaporate to dryness, and ignite: the weight of the residue does not exceed 2 mg.
Sulfate—
To a mixture of 3 mL of it and 5 mL of water add 5 drops of
barium chloride TS: neither turbidity nor precipitate appears within 1 hour.
Sulfite—
On the completion of the test for
Sulfate, the further addition to the liquid of 2 drops of 0.1 N iodine produces neither turbidity nor decolorization of the iodine.
Heavy metals 231—
To 3.8 mL (4 g) add 5 mL of water and 1 drop of
phenolphthalein TS. Add 6 N ammonium hydroxide until the solution assumes a faint pink color. Add 2 mL of 1 N acetic acid, then add water to make 25 mL: the limit is 5 ppm.
Free bromine or chlorine—
To 10 mL add 1 mL of
potassium iodide TS and 1 mL of chloroform, and agitate the mixture: the chloroform remains free from any violet coloration for at least 1 minute.
Assay—
Transfer 10.0 mL of Diluted Hydrochloric Acid to a conical flask, and add about 20 mL of water. Add 3 drops of
methyl red TS, and titrate with 1 N sodium hydroxide VS. Each mL of 1 N sodium hydroxide is equivalent to 36.46 mg of HCl.
to make