FED-STD-228A
3.2.43 Zinc turbidity standards. The standards shall be prepared by transferring to 50-ml. colorimetric
tubes portions of the zinc solution prepared in 3.2.42 containing from 0.01 to 0.1 mg. of zinc, in
increments of 0.01 mg., and adding 15 ml. of 1 to 9 hydrochloric acid and 45 ml. of distilled water to the
tubes. Five ml. of 0.7 percent potassium ferrocyanide solution shall be added and the solution mixed.
The standards should be prepared just before the test is conducted.
4. PROCEDURE
4.1 Copper and bismuth in leads containing over 0.02 percent bismuth.
4.1.1 Specimen size. The size of the specimen used will depend on the copper and bismuth content and
shall be as indicated in the following table:
Weight of specimen
Type of lead
Copper
Bismuth
Copper
Bismuth
determination determination
Percent
Percent
Grams
Grams
Common desilverized lead A
0.0025 max
0.15
20
10
Acid lead
0.04 to 0.08
0.025
20
20
Copper lead
0.04 to 0.08
0.1
10
10
4.1.2 Determination of copper and bismuth. A specimen of suitable size as determined in 4.1.1 shall be
transferred to a 600-ml. beaker and 1 gram of tartaric acid, 20 ml. of 1 to 4 nitric acid, and an additional 5
ml. of nitric acid per gram of specimen added. The mixture shall be heated gently until solution is
complete and then boiled to expel the brown fumes. The solution shall be diluted to 250 ml., cooled to
40°C (104°F), and a 1 percent solution of potassium permanganate added while stirring until the solution
remains colored for at least 1 minute. The solution shall be allowed to stand or heated gently to expel the
color, the temperature adjusted to 37° ± 3°C (100° ± 5°F), 2 ml. of 10 percent potassium iodide added
while stirring, and then set aside for about 10 minutes, avoiding exposure to direct sunlight. The solution
shall be filtered through a Gooch into a 600-ml. beaker, washed with distilled water, and the precipitate
discarded. The solution shall be boiled until the iodine is expelled and the solution becomes colorless,
and then the boiling continued for 10 minutes longer. It shall be diluted to 350 ml. and 50 mg. of urea
added. The temperature shall be adjusted to 68 ± 3°C (154° ± 5°F) and then electrolyzed while stirring at
850 to 1,000 RPM in the apparatus described in 3.1.13 using 3 percent nitric acid as the anolyte. During
the electrolysis the anode chambers shall be flushed, the sides of the beaker and the anode shall be
rinsed down, and approximately 50 mg. of urea added once or twice. After the copper and bismuth are
completely deposited most of the electrolyte shall be removed by siphoning while adding slowly 1 liter of
water. The beaker shall be removed and quickly replaced with one containing distilled water. The beaker
shall be removed, the electrode detached, rinsed with distilled water, and then dipped twice into separate
portions of ethyl alcohol or methyl alcohol. The electrode shall be dried at 110° ± 1°C (230° ± 2°F) for 5
minutes, cooled, and weighed. This weight minus the weight of the clean electrode is the weight of the
copper bismuth deposit (A). The weighed electrode shall be transferred to a 250-ml. wide-mouth flask
and the copper-bismuth deposit dissolved in a mixture of 5 ml. of 3 percent hydrogen peroxide and 2 ml.
of sulfuric acid, sp. gr. 1.83. The electrode shall be well rinsed and removed from the flask, the solution
evaporated to dense white fumes to remove all the hydrogen peroxide, the residue cooled, and diluted to
25 ml. with distilled water. Five ml. of 40 percent potassium iodide and 5 ml. of a 20 percent solution of
sodium thiocyanate shall be added and the solution titrated with 0.1 N sodium thiosulfate. When the end
point is reached, 1 ml. of 1 percent starch solution shall be added and the solution titrated to the
disappearance of the blue color. The number of milliliters of sodium thiosulfate used shall be recorded as
B. (In the titration of solutions containing bismuth the starch indicator must be added after the addition of
the sodium thiocyanate and before the beginning of the titration.)
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