FED-STD-228A
3.2.7 Bismuth sulfate, standard solution. The solution shall be prepared by dissolving 1.0000 gram of
metallic bismuth in a small excess of nitric acid, specific gravity 1.43, adding 20 ml. of sulfuric acid,
specific gravity 1.83, evaporating to dense white fumes, cooling, rinsing the sides of the vessel with water
and evaporating again to dense white fumes, and diluting to 1 liter with distilled water in a volumetric
flask. This primary solution shall be diluted 1 to 10 for bismuth standards.
RESERVOIR
(50 TO 75 ML., APPROX.)
PERFORATED
PORCELAIN
PLATE
AMALGAMATED SILVER
(20 TO 30 MESH)
X
19 MM
120-150 MM
GLASS WOOL
PERFORATED
PERCELAIN
PLATE
GLASS BEADS
STOP COCK
100 MM
8 MM
TO SUCTION FLASK
FIGURE 7231D. Silver reductor.
3.2.8 Bismuth colorimetric standards. These standards shall be prepared by transferring to 100 ml.
colorimetric tubes, 0.2 to 1.4 mg. of bismuth, in increments of 0.1 mg., from the standard solution in 3.2.7,
adding 2 ml. of 40 percent potassium iodide, 2 ml. of 20 percent sodium thiocyanate solution, 0.5 ml. of
starch solution, and 2 ml. of 0.1 N sodium thiosulfate solution to each tube, diluting to 90 ml. with distilled
water, adding 1 ml. of 1 to 1 sulfuric acid, and diluting to 100 ml. These standards should be prepared
just before the test is conducted.
3.2.9 Standard ceric sulfate solution, 0.1 N. This solution shall be prepared by dissolving 54 grams of
Ce(HWO4)4 in 500 ml. of distilled water containing 16 ml. of sulfuric acid, sp. gr. 1.83, and diluting to 1
liter. The solution shall be standardized by either of the following methods:
3.2.9.1 Method A. Approximately 0.2 gram of iron of known composition shall be transferred to a 250-ml
beaker and dissolved in 20 ml. of 1 to 1 hydrochloric acid and 1 to 2 ml. of saturated bromine water. The
solution shall be boiled to expel excess bromine, stannous chloride solution (150 grams of SnCl22H2O in
1 liter of 1 to 2 hydrochloric acid) added dropwise while stirring, until the yellow color just disappears, and
exactly 1 drop in excess. The solution shall be cooled to room temperature and 10 ml. of 5 percent
mercuric chloride added all at once. The precipitate should be white and milky. (If it is gray, the solution
shall be discarded.) One drop of ortho-phenanthroline ferrous complex indicator shall be added and the
solution titrated with ceric sulfate to a pale blue or colorless end point.
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