Opalescent suspension— Dissolve 1 g of hydrazine sulfate in sufficient water to produce 100 mL, and allow to stand for 4 to 6 hours. Add 25 mL of this solution to a solution containing 2.5 g of methenamine in 25 mL of water, mix well, and allow to stand for 24 hours.

Primary reference suspension— Dilute 15.0 mL of the Opalescent suspension with water to 1000.0 mL. [note—This suspension is freshly prepared, and may be stored for at most 24 hours.]

Reference suspension— To 30 mL of the Primary reference suspension, add 70 mL of water, and mix. [note—Shake before using.]

Test solution— Dissolve 1.5 g at room temperature in carbon dioxide-free water, and dilute with the same solvent to 150 mL.

Procedure— Compare the opalescence of equal volumes of the Test solution and the Reference suspension. The Test solution is not more opalescent than the Reference suspension.

A: Ignite 0.1 g in a crucible. Take up the residue with 5 mL of nitric acid, heat on a water bath for 1 minute, and filter. Mix 1 mL of the filtrate with 2 mL of ammonium molybdate TS: a yellow color develops.

B: Dissolve about 20 mg of the substance being examined in 5 mL of 5 M acetic acid, and add 0.5 mL of potassium ferrocyanide solution (53 g in 1000 mL). The resulting solution remains clear. To the clear solution, add about 50 mg of ammonium chloride: a white crystalline precipitate is produced.

Mercury (II) sulfate solution— Dissolve 1 g of mercuric oxide in a mixture of water and sulfuric acid (5:1).

Procedure— Mix 5 g with 20 mL of carbon dioxide-free water, and filter. To the filtrate, add 0.15 mL of sulfuric acid, and filter. To the filtrate, add 5 mL of Mercury (II) sulfate solution, and heat to boiling. Add 0.5 mL of 0.2 M potassium permanganate, and heat to boiling. No precipitate is formed.

Standard solution— Dilute 1 volume of Standard Iron Solution, prepared as directed under Iron 241, with water to 10 volumes (1 ppm).

Procedure— Dissolve 0.20 g in 10 mL of water. Add 2 mL of a 20% (w/v) solution of citric acid to 0.1 mL of thioglycolic acid, mix, make alkaline with 10 M ammonia, dilute with water to 20 mL, and allow to stand for 5 minutes. Any pink color produced is not more intense than that obtained by treating 4 mL of the Standard solution in the same manner.

Chloride standard solution— Dissolve an accurately weighed quantity of sodium chloride in water to obtain a solution having a concentration of about 0.824 mg per mL. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Test solution— Dissolve 0.125 g in a 10-mL mixture of water and 5 M acetic acid (8:2), and dilute with water to 15 mL.

Procedure— To the Test solution, add 1 mL of 2 M nitric acid, then add the resulting solution to 1 mL of a silver nitrate solution (17 g in 1000 mL), and allow to stand for 5 minutes protected from light. To 10 mL of the Chloride standard solution, add 5 mL of water and 1 mL of 2 M nitric acid. To this solution, add 1 mL of silver nitrate solution (17 g in 1000 mL), and allow to stand for 5 minutes protected from light. When viewed against a dark background, the Test solution is not more turbid than the Chloride standard solution: not more than 400 ppm.

Sulfate standard solution— Dissolve an accurately weighed quantity of potassium sulfate in water to obtain a solution having a concentration of about 1.81 mg per mL. Transfer 2.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Test solution— Use the Test solution prepared as directed in the test for Appearance of solution.

Procedure— To 15 mL of the Sulfate standard solution, add 0.5 mL of 5 M acetic acid and 1 mL of barium chloride solution (250 g in 1000 mL). Repeat, using 15 mL of the Test solution. Allow the solutions to stand for 5 minutes protected from light. When viewed against a dark background, the Test solution is not more turbid than the Sulfate standard solution: not more than 0.2%.

Arsenic trioxide stock solution— In a 250-mL volumetric flask, dissolve 330 mg of arsenic trioxide in 5 mL of 2 N sodium hydroxide, and dilute with water to volume. Transfer 1 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Arsenic standard solution— Transfer 1 mL of the Arsenic trioxide stock solution to a 10-mL volumetric flask, dilute with water to volume, and mix.

Tin (II) chloride solution— Heat 20 g of tin with 85 mL of hydrochloric acid until no more hydrogen is released. Allow to cool. Dilute 1 volume of this solution with 10 volumes of dilute hydrochloric acid (20 g of hydrochloric acid in 100 mL of water).

Test solution— In a 25-mL volumetric flask, dissolve 330 mg of Calcium Glycerophosphate in water, dilute with water to volume, and mix.

Apparatus— Prepare a 100-mL side-arm conical flask containing a magnetic stirring bar. Attach to the conical flask a ground–glass stopper through which passes a 20-cm long glass tube with an internal diameter of 5 mm. The lower end of the tube is inside the conical flask and has been drawn to a tip with an internal diameter of 1 mm. About 15 mm from the tip, and at least 3 mm below the lower surface of the stopper, is an orifice about 3 mm in diameter. The upper end of the tube has a flat ground surface at a right angle to the axis of the tube. A second glass tube of the same internal diameter and 30 mm long, with a similar flat ground surface, is placed in contact with the ground surface of the first tube and is held in position by a clamp and springs. Into the lower tube insert about 55 mg of loosely packed lead acetate cotton. Between the flat surfaces of the tubes place a disk of mercuric bromide paper.

Procedure— Before placing the tube assembly into the flask transfer the Test solution to the flask, and add 15.0 mL of hydrochloric acid, 0.1 mL of Tin (II) chloride solution, and 5 mL of potassium iodide TS. Allow to stand for 15 minutes, and add 5 g of activated zinc. Assemble the apparatus immediately, and immerse the flask in a water bath at a temperature such that a uniform evolution of gas is maintained. After not less than 2 hours examine the stain produced on the mercuric bromide paper. Perform the same procedure using the Arsenic standard solution. The stain produced on the mercuric bromide paper by the Test solution is not more intense than that produced by the Arsenic standard solution (1 ppm).

Sulfomolybdic solution— Dissolve with heating 2.5 g of ammonium molybdate in 20 mL of water. Dilute 28 mL of sulfuric acid in 50 mL of water, and cool. Mix the two solutions, and dilute with water to 100 mL.

Tin (II) chloride solution— Prepare as directed in the test for Limit of arsenic.

Phosphate standard stock solution— Dissolve an accurately weighed quantity of monobasic potassium phosphate in water to obtain a solution having a concentration of about 1.43 mg per mL. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Phosphate standard solution— Transfer 50.0 mL of the Phosphate standard stock solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Test solution— Transfer 2.5 mL of the Test solution from the test for Appearance of solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Procedure— To 100 mL of the Test solution, add 4 mL of Sulfomolybdic solution, mix, and add 0.1 mL of Tin (II) chloride solution. To 100 mL of the Phosphate standard solution, add 4 mL of Sulfomolybdic solution, mix, and add 0.1 mL of Tin (II) chloride solution. Allow the preparations to stand for 10 minutes, then examine 20 mL of each preparation. Any color produced by the Test solution is not more intense than that produced by the Phosphate standard solution (400 ppm).