FED-STD-228A
3.2.9.2 Method B. Twenty-five ml. of 0.1 N arsenous acid solution shall be added to a 400-ml. beaker,
10 ml. of 1 to 1 sulfuric acid, 3 drops of osmium tetroxide (2.5 grams per liter of 0.1 N sulfuric acid), as a
catalyst, and 1 drop of ortho-phenanthroline ferrous complex indicator added. The solution shall be
titrated to a pale blue or colorless end point with the standard ceric sulfate solution.
3.2.10 Citric acid, 20 percent solution.
3.2.11 Copper nitrate anolyte solution. The anolyte solution shall be prepared by dissolving 4 grams of
metallic copper in nitric acid, sp. gr. 1.43, evaporating just to dryness, adding 30 ml. of nitric acid, and
diluting to 1 liter.
3.2.12 Copper sulfate standard solution. The solution shall be prepared by dissolving 1.0000 gram of
metallic copper in 15 ml. of 1 to 3 nitric acid, adding 5 ml. of sulfuric acid, sp. gr. 1.83, and evaporating to
white fumes. The beaker shall be cooled, the walls washed down with 20 ml. of distilled water and the
solution again evaporating to dense white fumes. Two hundred ml. of 1 to 1 sulfuric acid shall be added
and the solution made to 1 liter in a volumetric flask.
3.2.13 Copper sulfate, 04 percent solution.
3.2.14 Formic acid, specific gravity 1.20.
3.2.15 Formic acid mixture. The solution shall be prepared by mixing 200 ml. of formic acid, specific
gravity 1.20, 970 ml. of distilled water and 30 ml. of ammonium hydroxide, specific gravity 0.90.
3.2.16 Formic acid mixture wash solution. The solution shall be prepared by diluting 25 ml. of formic acid
mixture, 3.2.15, to 1 liter with distilled water and saturating the solution with hydrogen sulfide.
3.2.17 Hydrazine sulfate.
3.2.18 Hydrogen peroxide, 3 percent solution.
3.2.19 Hydrogen sulfide wash solution. The solution shall be prepared by saturating sulfuric acid
solution, 2 to 98, with hydrogen sulfide.
3.2.20 Iodine, 0.1 N solution. The solution shall be prepared by dissolving 12.7 grams of iodine and 40
grams of potassium iodide in 25 ml. of distilled water. When solution is complete it shall be diluted to one
liter and stored in a cool place in a dark bottle. The solution shall be standardized as follows: Ten ml. of
a tin solution (1 ml. equal to 0.001 gram of tin) shall be pipette into a 500-ml. flask, 10 ml. of sulfuric acid,
specific gravity 1.83, 20 grams of sodium chloride, 75 ml. of hydrochloric acid, specific gravity 1.19, and 5
grams of test lead added. The solution shall be reduced and titrated with the iodine solution as described
in 4.3.4.
3.2.21 Iron, standard solution. The solution shall be prepared by dissolving 0.100 gram of iron (National
Bureau of Standards standard sample No. 55b of ingot iron is satisfactory) in 10 ml. of 1 to 1 hydrochloric
acid and 1 ml. of bromine water, boiling to remove the excess bromine, adding 20 ml. of the hydrochloric
acid, and diluting to 1 liter in a volumetric flask.
3.2.22 Manganese nitrate, 10 percent solution.
3.2.23 Manganese sulfate, 10 percent solution.
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