FED-STD-228A
3.2.24 Methyl orange indicator. The solution shall be prepared by dissolving 0.1 gram of methyl orange
in 100 ml. of distilled water and filtering off any residue.
3.2.25 Metallic mercury.
3.2.26 Nitric acid-tartaric acid wash solution. The wash solution shall be prepared by dissolving 20
grams of chloride-free tartaric acid in 200 ml. of 1 to 9 nitric acid and diluting to 1 liter.
3.2.27 Ortho-phenanthroline indicator solution. The solution shall be prepared by dissolving 6.95 grams
of ferrous sulfate (FeSO47H2O) in 1 liter of distilled water and adding 14.85 grams of ortho-phenanthroline
monohydrate (C12H2N2H2O).
3.2.28 Potassium bisulfate.
3.2.29 Potassium bromated, 0.01 N solution. The solution shall be prepared by dissolving 0.2784 grams
of potassium bromated (KBrO2) in distilled water and diluting to 1 liter in a volumetric flask.
3.2.30 Potassium ferrocyanide, 0.7 percent solution.
3.2.31 Potassium iodide, 1, 10, and 40 percent solutions.
3.2.32 Potassium permanganate, 1 and 2 percent solutions.
3.2.33 Sodium chloride.
3.2.34 Sodium thiocyanate, 20 percent solution.
3.2.35 Sodium thiosulfate, 10 percent solution.
3.2.36 Sodium thiosulfate, 0.1 N solution. The solution shall be prepared by dissolving 24.8 grams of
sodium thiosulfate (Na2S2O25H2O) in 1 liter of freshly boiled and cooled distilled water. The solution shall
be standardized as follows: Ten ml. of standard copper sulfate solution shall be transferred to a 250-ml.
wide-mouth flask, the solution diluted to 25 ml. with distilled water, cooled to room temperature, and
titrated with the standard sodium thiosulfate solution as described in 4.1.2. If sulfur precipitates during
preparation or on standing, the solution shall be discarded.
3.2.37 Starch, 1 percent solution, prepared fresh, as required.
3.2.38 Talc suspension. The suspension shall be prepared by suspending 50 grams of talc in 1 liter of
distilled water.
3.2.39 Tartaric acid-chloride-free.
3.2.40 Test lead.
3.2.41 Urea.
3.2.42 Zinc chloride solution. The solution shall be prepared by dissolving 4.0000 grams of pure zinc in
200 ml. of 1 to 4 hydrochloric acid and diluting to 1 liter.
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