Assay—
Weigh accurately a quantity of Barium Sulfate for Suspension, equivalent to about 0.60 g of barium sulfate (BaSO
4), in a tared platinum crucible, and ignite over a low flame until any organic matter is thoroughly carbonized. Cool, cautiously add 0.5 mL of nitric acid and 0.5 mL of sulfuric acid, and continue the ignition over a low flame until the residue becomes gray in color, then ignite over the full heat of a blast burner. Allow the contents of the crucible to cool to room temperature.
NOTE 1—If the specimen contains a silicate, such as bentonite, proceed as follows. Add 10 mL of water and 1 mL of sulfuric acid to the residue in the crucible, mix, and add 10 mL of hydrofluoric acid. Heat gently over a low flame until fumes of sulfur trioxide appear. Add 5 mL more of hydrofluoric acid, heat again over a low flame to the appearance of dense fumes, and continue heating until the sulfuric acid has been completely volatilized. Allow the contents of the crucible to cool.
NOTE 2—If the specimen does not contain a silicate, omit the treatment of the specimen with hydrofluoric and sulfuric acids.
Add to the treated or untreated specimen in the platinum crucible 10 g of anhydrous sodium carbonate, fuse over a blast burner until a clear melt is obtained, and heat for an additional 30 minutes. Proceed as directed in the
Assay under
Barium Sulfate, beginning with “Cool, place the crucible in a 400-mL beaker.”
791
:
between 3.5 and 10.0, in a 60% (w/w) aqueous suspension, or constituted for its intended use as directed in the labeling.
for 4 hours: it loses not more than 1.0% of its weight.