FED-STD-228A
4.3.3 Antimony by bromate titration. Glass beads shall be added to the titrated solution reserved in 4.3.2
and the solution boiled until the volume is reduced to 100 ml. The solution shall be transferred to a 250-
ml. glass-stoppered iodine flask, the 500-ml. Erlenmeyer flask rinsed with 40 ml. of hydrochloric acid and
the washings added to the iodine flask. Two ml. of 0.4 percent copper sulfate shall be added, the solution
cooled to room temperature, 5 ml. of metallic mercury added (if mercurons chloride is precipitated more
hydrochloric acid should be added), and the flask stoppered and shaken vigorously for 5 minutes. The
solution shall be decanted into the 500-ml. Erlenmeyer flask and the mercury washed, adding the wash to
the solution. The solution shall be diluted to about 350 ml. and, with air bubbling, slowly through it,
heated to 90°C (194°F). The air stream shall be discontinued, 1 drop of methyl orange indicator added,
and the antimony titrated slowly at 90°C (194°F) with 0.01 N potassium bromated. The titrated solution
shall be reserved for tin determination in 4.3.4. A blank determination shall be made using the same
amounts of reagents and following the same procedure. The number of milliliters of potassium bromate
required to titrate the antimony (B) is equal to the total titration minus the blank titration.
4.3.4 Tin by iodine titration. Thirty milliliters of hydrochloric acid, specific gravity 1.19, and sufficient 0.2
percent antimony chloride solution to make the total antimony chloride solution to make the total antimony
content of the flask equal to about 10 mg. shall be added to the titration solution reserved in 4.3.3. Five
grams of test lead shall be added and the solution boiled gently for 15 minutes. When the deposition of
noble metals is complete, the solution shall be filtered through cotton or glass wool into a wide-mouth
500-ml. Erlenmeyer flask containing 5 grams of test lead and 20 grams of sodium chloride. The flask
shall be assembled into a tin reduction apparatus as described in 3.1.15. A stream of carbon dioxide
shall be passed through the flask, the solution gradually heated to boiling, and boiled for 1 hour. The
flask shall be transferred to an ice bath and the carbon dioxide regulated so that no air will be sucked
back into the flask. The solution shall be cooled to about 10°C (50°F) under an atmosphere of carbon
dioxide, the plug removed from the third hole of the rubber stopper, and 5 ml. of 10 percent potassium
iodide solution and 5 ml. of 1 percent starch solution added. The tip of the burette containing 0.1 N iodine
solution shall be immediately inserted into the other hole of the rubber stopper and the solution titrated to
the first permanent shade of blue. A blank determination shall be made using the same amounts of
reagents and following the same procedure. The number of milliliters of iodine solution required to titrate
the tin (E) is equal to the total titration minus the blank titration.
4.3.5 Arsenic by distillation. The solution of arsenic, antimony, and tin shall be prepared as described in
4.3.1. This solution shall be cooled to room temperature, 50 ml. of hydrochloric acid, specific gravity 1.19,
and 8 to 10 grams of sodium chloride added. The 500-ml. Erlenmeyer flask shall be connected to the
distillation apparatus, 3.1.1, 200 ml. of water placed in the receiving flask, the distillation flask heated to
boiling, and continued until the temperature of the distilled vapor reaches 105°C (221°F). The distillation
flask shall be unstoppered, the hot plate removed, and the solution reserved for antimony determination
in 4.3.6. The delivery tube shall be rinsed into the receiving flask and the distillate heated nearly to
boiling. The solution shall be titrated at 85° ± 5°C (185° ± 9°F) with 0.01 N potassium bromate solution,
adding methyl orange indicator near the end of the titration. A blank determination shall be made using
the same amounts of reagents and following the same procedure. The number of milliliters of potassium
bromate solution required to titrate the arsenic (A) is equal to the total titration minus the blank titration.
4.3.6 Antimony determination. Two hundred ml. of water shall be added to the solution in the distillation
flask reserved in 4.3.5 and the solution boiled to dissolve all of the salts. The hot solution shall be titrated
with 0.01 N potassium bromate, adding methyl orange indicator near the end of the titration. The titrated
solution shall be reserved for tin determination in 4.3.7. A blank determination shall be made using the
same amounts of reagents and following the same procedure. The number of milliliters of potassium
bromate solution required to titrate the antimony (B) is equal to the total titration minus the blank titration.
4.3.7 Tin by iodine titration. The solution reserved in 4.3.6 shall be diluted to 250 ml., 75 ml. of
hydrochloric acid, specific gravity 1.19 added, and the tin determination completed as described in 4.3.4,
adding only 10 grams of sodium chloride instead of the 20 grams specified in the procedure.
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