Packaging and storage—
Preserve in tight containers.
Identification—
A:
To 5 mL of a solution (1 in 250) in a test tube add 1 mL of 5 N sodium hydroxide and 10 drops of 30 percent hydrogen peroxide, and heat gently for about 2 minutes: a yellow color develops.
B:
To 5 mL of a solution (1 in 250) in a test tube add 5 drops of
silver nitrate TS: a white, curdy precipitate is formed, and it is insoluble in nitric acid.
Insoluble matter—
Transfer 10 g to a 250-mL beaker, add 100 mL of water, cover the beaker, and heat to boiling. Digest the hot solution on a steam bath for 30 minutes, and filter through a tared filtering crucible of fine porosity. Rinse the beaker with hot water, passing the rinsings through the filter, and wash the filter with hot water until the last washing is colorless. Dry the filter at 105
: the weight of the residue does not exceed 1 mg (0.01%).
Substances not precipitated by ammonium hydroxide—
Dissolve 2.0 g in 80 mL of water, heat the solution to boiling, and add a slight excess of ammonium hydroxide. Continue heating to remove the excess ammonia, cool, dilute with water to 100.0 mL, and mix. Pass through a retentive filter, and transfer 50.0 mL of the clear filtrate to an evaporating dish that previously has been ignited and tared. Add 0.5 mL of sulfuric acid to the filtrate, evaporate on a steam bath to dryness, heat gently to remove the excess acid, and ignite gently: the weight of the residue does not exceed 2.0 mg (0.20% as sulfate).
Sulfate 
221
—
Prepare a test solution by dissolving 2.0 g in 10 mL of water. Add 1 mL of 3 N hydrochloric acid, filter if necessary to obtain a clear solution, wash the filter with two 5-mL portions of water, and dilute with water to 40 mL. Prepare a control solution in a similar manner, but use 1.0 g of the substance under test, and after the filtration step add 0.10 mL of 0.020 N sulfuric acid. To each solution add 3 mL of
barium chloride TS, mix, and allow to stand overnight. Decant most of the supernatants, without disturbing the precipitates, but leaving twice the volume of liquid in the control solution as in the test solution. Dilute each solution with water to 25 mL, and sonicate for 1 minute: any turbidity in the test solution does not exceed that in the control solution (0.01%).
Iron 241—
Dissolve 1.0 g in 100 mL of water, and mix. Transfer 10 mL of this solution to a 100-mL color comparison tube, dilute with water to 45 mL, add 2 mL of hydrochloric acid, and mix (
Test Preparation). Proceed as directed for
Procedure, except to add 15 mL of butyl alcohol to the
Test Preparation and the
Standard Preparation at the same time that the
Ammonium Thiocyanate Solution is added. Shake for 30 seconds, and allow the layers to separate: the color in the upper butyl alcohol layer from the
Test Preparation is not darker than that from the
Standard Preparation. The limit is 0.01%.
Assay—
Dissolve about 0.4 g of Chromic Chloride, accurately weighed, in 100 mL of water contained in a glass-stoppered, 500-mL conical flask, add 5 mL of 5 N sodium hydroxide, and mix. Pipet, slowly, 4 mL of 30 percent hydrogen peroxide into the flask, and boil the solution for 5 minutes. Cool the solution slightly, and add 5 mL of nickel sulfate solution (1 in 20). Boil the solution until no more oxygen is evolved, cool, and add 2 N sulfuric acid dropwise until the color of the solution changes from yellow to orange. Add to the flask a freshly prepared solution of 4 g of potassium iodide and 2 g of sodium bicarbonate in 100 mL of water, then add 6 mL of hydrochloric acid. Immediately insert the stopper in the flask, and allow to stand in the dark for 10 minutes. Rinse the stopper and the sides of the flask with a few mL of water, and titrate the liberated iodine with 0.1 N sodium thiosulfate VS to an orange color. Add 3 mL of starch TS, and continue the titration to a blue-green endpoint. Each mL of 0.1 N sodium thiosulfate is equivalent to 8.882 mg of CrCl3·6H2O.
