O-S-801F
and dilute to about 20 ml. The blue color shall not be deeper than that produced by 0.83 mg of copper in an equal volume of solution containing 4 ml of ammonium hydroxide.
4.3.13 Zinc. (If the percent fixed residue does not exceed 0.0060 for class 1, 0.0032 for class 2,
0.0024 for class 3, or 0.0019 for class 4, determination of zinc is to be omitted.) As applicable, dilute 20 ml of class 1, 49 ml of class 2, 72 ml of class 3, or 104 ml of class 4 specimen to approximately 110 ml and neutralize with ammonium hydroxide. Dilute the solution to 200 ml, add 10 ml of 6 N sulfuric acid, and saturate with hydrogen sulfide gas. Filter the solution and
boil the filtrate to remove the hydrogen sulfide. Cool the solution and neutralize with ammonium hydroxide using methyl red as the indicator. Pipette 1 ml of 1 N sulfuric acid for each 100 ml of solution into the solution and pass a rapid stream of hydrogen sulfide through the solution for
20 minutes. Collect any precipitate formed on ashless filter paper, wash with water, ignite in a tared crucible, cool to room temperature in a desiccator, and weigh the collected precipitate. Calculate the percentage weight zinc as follows:
Percent Zinc = 100A/BW
where: A = Weight of collected precipitate in grams, B = Milliliters of specimen, and
W = Specific gravity of the specimen
4.3.14 Arsenic. As applicable, dilute 20 ml of class 1, 49 ml of class 2, 58 ml of class 3, or
78 ml of class 4 specimen to 100 ml in a volumetric flask. As applicable, dilute a 20 ml aliquot of the class 1 or class 2 specimen dilution or a 25 ml aliquot of the class 3 or class 4 specimen dilution to 50 ml and determine arsenic by modified Gutzeit procedure. The stain produced shall not exceed that produced by 0.0075 mg of arsenic. (Note: Also compare the stain with that produced by 0.00075 mg of arsenic in reference 4.3.15.)
4.3.15 Antimony. If arsenic content has been found to be not greater than one-tenth of the permitted limit (see note of 4.3.14), antimony is determined without first removing arsenic; proceed as specified in 4.3.15.1 below. If the arsenic content has been found greater than one-tenth the permitted limit, proceed as specified in 4.3.15.2 below.
4.3.15.1 Antimony - arsenic content is less than or equal to 0.0001 percent. As applicable, evaporate 11 ml of class 1, 27 ml of class 2, 40 ml of class 3, or 57 ml of class 4 specimen to
4 or 5 ml. Transfer to a Gutzeit apparatus, make up to 50 ml with water, and proceed as in the determination of arsenic except that the solution is finally warmed to 60 °C and kept at
60 ° ± 3 °C for 1 hour. Develop the stain by immersing the paper strip (mercuric bromide paper) in 20 percent by volume ammonium hydroxide solution. The stain developed shall not exceed that produced by 0.02 mg of antimony following the same procedure.
4.3.15.2 Antimony - arsenic content is greater than 0.0001 percent. As applicable, evaporate
55 ml of class 1, 110 ml of class 2, 162 ml of class 3, or 225 ml of class 4 specimen to 4 or 5 ml in a 250 ml beaker. Cool to room temperature and cautiously add 10 ml of water containing
0.25 g of sodium sulfite. Mix and evaporate until the solution begins to fume. Cool and add
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