FED-STD-228A
4.2 Copper and bismuth in leads containing 0.02 percent bismuth and under. A specimen containing 20
grams shall be used for lead sheaths made of soft undesilverized lead and chemical lead. A specimen
containing about 20 grams of the lead sheath shall be transferred to a 600-ml. beaker, the specimen
dissolved, the copper and bismuth deposited, and the copper titrated as described in 4.1.2. The number
of milliliters of sodium thiosulfate required to titrate the copper shall be recorded as B. Two ml. of sodium
thiosulfate in excess shall be added. Macerated filter paper shall be added, the solution diluted to 100 ml.
in a graduated cylinder, and then filtered through a close-texture, dry paper. An aliquot of the filtrate
containing 0.2 to 1.4 mg. of bismuth shall be transferred to a 100-ml. colorimetric tube and diluted to 100
ml. with distilled water. The color shall be compared with a series of freshly prepared bismuth colorimetric
standards. The comparisons may be made by visual observations of the solutions in tubes placed
against a white background. If available, a colorimeter or a spectrophotometer may be used for making
the color comparison.
4.3 Arsenic, antimony, and tin.
4.3.1 Preparation of solution of arsenic, antimony, and tin. A specimen containing about 50 grams of the
lead sheath shall be transferred to a 500-ml. Erlenmeyer flask and 200-ml. of 1 to 8 nitric acid added.
The mixture shall be heated gently to dissolve the lead and then boiled to expel the brown fumes. The
solution shall be diluted to 300 ml. heated to boiling, 10 ml. of 2 percent potassium permanganate and 20
ml. of 10 percent manganese nitrate added, and then boiled gently for about 2 minutes. The hot solution
shall be filtered through a rapid filter paper and the precipitate washed with hot water. The filtrate shall be
labeled (a) and reserved. The paper containing the precipitate shall be returned to the original
Erlenmeyer flask, 15 ml. of sulfuric acid, sp. gr. 1.83 and 35 ml. of nitric acid, sp. gr. 1.43, added, and the
solution heated gently to boiling to destroy the filter paper. The solution shall be labeled (b) and reserved.
One-hundred ml., or enough to remove all of the lead of 35 percent ammonium sulfate, shall be added to
the filtrate labeled (a) while stirring, the solution cooled to room temperature, filtered through a close-
textured paper on a Buchner funnel, and washed once with distilled water. The precipitate of lead sulfate
shall be discarded. The filtrate shall be neutralized with ammonium hydroxide, 15 ml. added in excess,
heated to boiling, 10 ml. of 10 percent ammonium persulfate added, and then boiled vigorously for 1
minute. The solution shall be filtered through a rapid filter paper, the precipitate transferred to the paper,
washed four times with hot water, and the filtrate discarded. The paper and precipitate shall be
transferred to the solution in the 500-ml. Erlenmeyer flask labeled (b). This flask contains all the arsenic,
antimony, and tin plus some manganese, lead, and a trace of copper. Thirty-five ml. of nitric acid, specific
gravity 1.43, shall be added to the flask and the solution heated gently to destroy the carbonaceous
material, adding more nitric acid if necessary. The solution shall be evaporated to dense white fumes, the
residue cooled, 3 grams of potassium bisulfate and 0.1 gram of hydrazine sulfate added, and the sides of
the flask washed down with water, making certain that no hydrazine sulfate remains on the walls. The
solution shall be evaporated to dense white fumes, and then heated over an open flame until the volume
has been reduced to about 10 ml. The arsenic, antimony, and tin shall be determined as described in
4.3.2, 4.3.3, and 4.3.4, or in 4.3.5, 4.3.6, and 4.3.7.
4.3.2 Arsenic and antimony by bromated titration. The solution from 4.3.1 shall be cooled to room
temperature, the sides of the flask washed down with 150 ml. of distilled water, 20 ml. of hydrochloric acid
added, and the solution heated to about 90°C (194°F) to dissolve all of the lead salts. One drop of methyl
orange indicator shall be added and the solution titrated with 0.01 N potassium bromated until the red
color weakens. A second drop of methyl orange shall be added and the titration continued slowly until the
color changes to yellow or colorless. The titrated solution shall be reserved for use in 4.3.3. A blank
determination shall be made using the same amount of reagents and following the same procedure. The
number of milliliters of potassium bromate required to titrate the arsenic and antimony (A) is equal to the
total titration minus the blank titration.
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