Packaging and storage—
Preserve in well-closed containers.
Identification—
Mix 1 g with 10 mL of water and 5 mL of sulfuric acid in a porcelain dish. Evaporate the mixture until the excess water is removed, and continue heating the residue until dense, white fumes of sulfur trioxide appear. Cool, cautiously add 20 mL of water, boil for a few minutes, and filter: there remains on the filter a gray residue (
impure silica). The filtrate responds to the tests for
Aluminum 
191
.
Acid-soluble substances—
Digest 1.0 g with 20 mL of 3 N hydrochloric acid for 15 minutes, and filter: 10 mL of the filtrate, evaporated to dryness and ignited, leaves not more than 10 mg of residue (2.0%).
Carbonate—
Mix 1.0 g with 10 mL of water and 5 mL of sulfuric acid: no effervescence occurs.
Iron—
Triturate 2.0 g in a mortar with 10 mL of water, and add 0.50 g of sodium salicylate: the mixture does not acquire more than a slight reddish tint.
Lead—
To 1.0 g contained in a centrifuge tube add 10 mL of 1 N nitric acid, and digest for 1 hour in a boiling water bath. Centrifuge until the solids are completely separated, and pour the supernatant into a 100-mL volumetric flask. Add 5 mL of 1 N nitric acid to the Kaolin, mix, and digest for 15 minutes in a boiling water bath. Centrifuge, and add the supernatant to the previous extract in the volumetric flask. Dilute with water to volume. A 50-mL portion of this solution contains not more than 5 µg of lead (corresponding to not more than 0.001% of Pb) when tested as directed in the test for
Lead 251, using 3 mL of
Ammonium Citrate Solution, 1 mL of
Potassium Cyanide Solution, and 500 µL of
Hydroxylamine Hydrochloride Solution.
Organic volatile impurities, Method IV 467:
meets the requirements.
and 600