» Ferric Oxide contains not less than 97.0 percent and not more than 100.5 percent of Fe2O3, calculated on the ignited basis.
Packaging and storage Preserve in well-closed containers.
Identification Dissolve 0.5 g in 50 mL of hydrochloric acid, and dilute with water to 200 mL: the solution so obtained responds to the test for Ferric Salts under Iron 191.
Water-soluble substances Digest 2.0 g in 100 mL of water on a boiling water bath for 2 hours, filter, and wash the filter with water. Evaporate the filtrate and washings, and dry the residue at 105 for 1 hour: the weight of the dried residue is not more than 20 mg (1.0%).
Acid-insoluble substances Digest 2.0 g in 25 mL of hydrochloric acid by boiling for 20 minutes. Add 100 mL of hot water, and filter quantitatively through a tared filtering crucible, with the aid of hot wash water, until the filtrate tests negative for chloride. Dry the crucible and contents at 105 for 1 hour: the residue weighs not more than 6 mg (0.3%).
Organic colors and lakes Place 1.0 g in each of 3 beakers, and add 25 mL of each of the following reagents, respectively: 1-chloronaphthalene, alcohol, and chloroform. Heat the beakers containing alcohol and chloroform just to boiling. Heat the other beaker on a boiling water bath for 15 minutes, with occasional swirling. Filter the contents of the beakers through retentive, solvent-resistant filter paper. If any of the filtrates shows visible turbidity, centrifuge for 15 minutes. Record the spectra against respective solvent blanks in 1-cm cells from 350 to 750 nm. No peak, above the noise level, with a slope greater than +0.001 absorbance unit per nm is found.
Mercury, Method IIa 261 Transfer 0.67 g of Ferric Oxide to a beaker, add 35 mL of 0.5 N hydrochloric acid, and heat to boiling. Allow to cool, and proceed as directed for Test Preparation beginning with Add 2 drops of phenolphthalein. The limit is 3 µg per g.
Limit of arsenic
Lead acetate cotton Immerse absorbent cotton pledgets in a mixture of lead acetate TS and 2 N acetic acid (10:1). Free the cotton pledgets from excess liquid by expression, and allow to air-dry.
Sodium borohydride solution Dissolve 3 g of sodium borohydride in 0.25 N sodium hydroxide, dilute with 0.25 N sodium hydroxide to obtain 100 mL of solution, and mix. Store in a loosely covered container protected from direct sunlight.
Mercuric bromide paper Immerse several 15-mm diameter filter paper disks in alcoholic mercuric bromide TS, remove the disks from the solution, and allow to dry, protected from light. Store in a glass-stoppered container protected from light.
Arsenic trioxide stock solution Transfer 132.0 mg of arsenic trioxide to a 100-mL volumetric flask, dissolve in 2.0 mL of 2 N sodium hydroxide, dilute with water to volume, and mix.
Standard solution On the day of use, transfer 1.0 mL of the Arsenic trioxide stock solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. Dilute 1.5 mL of this solution with hydrochloric acid to 10.0 mL, and mix. This solution contains 0.15 µg of arsenic per mL.
Test solution Dissolve 0.5 g of Ferric Oxide in several mL of hydrochloric acid with the aid of heat, dilute with hydrochloric acid to 10.0 mL, and mix.
Apparatus Prepare a 300-mL side-arm conical flask containing a magnetic stirring bar. Attach to the conical flask a ground-glass stopper through which passes a 20-cm long glass tube with an internal diameter of 5 mm. The lower end of the tube is inside the conical flask, and has been drawn to a tip with an internal diameter of 1 mm. About 15 mm from the tip and at least 3 mm below the lower surface of the stopper is an orifice about 2.5 mm in diameter. The upper end of the tube has a flat ground surface at a right angle to the axis of the tube. A second glass tube of the same internal diameter and 30 mm long, with a similar flat ground surface, is placed in contact with the ground surface of the first tube and is held in position by a clamp and springs. Into the lower tube insert about 55 mg of loosely packed Lead acetate cotton. Between the flat surfaces of the tubes place a disk of Mercuric bromide paper.
Procedure Before placing the tube assembly into the flask, transfer the Test solution to the flask, and add 5.0 mL of potassium iodide TS and 20 mL of water. Assemble the apparatus immediately, and stir while slowly adding through the side arm of the flask, over a period of about 20 minutes, 40 mL of Sodium borohydride solution. Examine the stain produced on the Mercuric bromide paper. Perform the same procedure using the Standard solution. The stain produced on the Mercuric bromide paper from the Test solution is not more intense than that from the Standard solution (3 µg per g).
Limit of lead
Lead nitrate stock solution Transfer 159.8 mg of lead nitrate to a 100-mL volumetric flask, dissolve in and dilute with 0.5 M nitric acid to volume, and mix. Prepare and store this solution in glass containers free from soluble lead salts.
Standard solution On the day of use, transfer 5.0 mL of the Lead nitrate stock solution to a 100-mL volumetric flask, add 10 mL of 1 N hydrochloric acid, dilute with water to volume, and mix. Transfer 1.0 mL of this solution to a second 100-mL volumetric flask, add 10 mL of 1 N hydrochloric acid, dilute with water to volume, and mix. This solution contains 0.5 µg of lead per mL.
Test solution Transfer 2.5 g of Ferric Oxide to a 100-mL glass-stoppered conical flask, add 35 mL of 0.1 N hydrochloric acid, and stir for 1 hour. Filter, collecting the filtrate in a 50-mL volumetric flask, dilute with 0.1 N hydrochloric acid to volume, and mix.
Procedure Concomitantly determine the absorbance of the Standard solution and the Test solution at the lead emission line of 217.0 nm with an atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a lead hollow-cathode lamp, a flow spoiler, and an airacetylene oxidizing flame. The absorbance of the Test solution does not exceed that of the Standard solution (0.001%).
Assay Digest about 1.5 g of Ferric Oxide, accurately weighed, in 25 mL of hydrochloric acid on a water bath until dissolved. Add 10 mL of hydrogen peroxide TS, and evaporate on a water bath almost to dryness in order to volatilize all hydrogen peroxide. Dissolve the residue by warming with 5 mL of hydrochloric acid; add 25 mL of water; filter into a 250-mL volumetric flask, washing the filter with water; and add water to volume. Transfer a 50-mL aliquot to a glass-stoppered flask, add 3 g of potassium iodide and 5 mL of hydrochloric acid, and insert the stopper into the flask. Allow the mixture to stand for 15 minutes, add 50 mL of water, and titrate the liberated iodine with 0.1 N sodium thiosulfate VS, using starch TS as the indicator. Perform a blank test with the same quantities of reagents and in the same manner, and make any necessary corrections. Each mL of 0.1 N sodium thiosulfate is equivalent to 7.985 mg of Fe2O3. Ignite about 2 g of Ferric Oxide at 800 ± 25 to constant weight as directed under Loss on Ignition 733, to enable calculation of the percentage of Fe2O3 on the ignited basis. [noteIgnited Ferric Oxide is hygroscopic.]