A: To 1 mL of a saturated solution of it add 1 mL of nitric acid: a light red color appears.

B: To 1 mL of a saturated solution of it add 1 mL of bromine TS: a yellow, flocculent precipitate is formed. Add 2 mL of 6 N ammonium hydroxide: the precipitate dissolves, producing a yellow solution.

Standard preparation— Transfer 34.0 mg of mercuric chloride to a 250-mL volumetric flask. Add 1 drop of hydrochloric acid, add water to dissolve, and dilute with water to volume. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, add 1 drop of hydrochloric acid, and dilute with water to volume. Transfer 1.0 mL of this solution to a 500-mL volumetric flask, add 1 drop of hydrochloric acid, and dilute with water to volume.

Test preparation— Transfer 134 mg to a 250-mL beaker, and cautiously add 10 mL of 11 N nitric acid and 10 mL of 18 N sulfuric acid. Digest, with the aid of heat, in a well-ventilated hood until the evolution of brown fumes ceases. Cautiously add an additional 10 mL of 11 N nitric acid, and continue heating until no more fumes are evolved. Cool, transfer to a 200-mL volumetric flask, and dilute with water to volume.

Procedure— Transfer 100 mL of Standard preparation to a 300-mL mercury analysis reaction vessel, add 2 drops of potassium permanganate solution (1 in 20), and mix (the solution should be purple; add additional permanganate solution dropwise, if necessary). Add 5 mL of 11 N nitric acid, stir, and allow to stand for not less than 15 seconds. Add 5 mL of 18 N sulfuric acid, stir, and allow to stand for not less than 45 seconds. Add 5 mL of hydroxylamine hydrochloride solution (3 in 200), stir, and allow to stand until the solution turns light yellow or colorless. Add 5 mL of stannous chloride solution (1 in 10) [note—Disregard the presence of insoluble matter in this solution; mix prior to use], immediately insert the aerator connected to the air pump, and determine the maximum absorbance of the treated Standard preparation at the mercury resonance line of 253.65 nm, with a suitable atomic absorption spectrophotometer equipped with a mercury hallow-cathode lamp and an absorption cell that permits the flameless detection of mercury. Connect in a closed system with a circulating air pump, a calcium chloride drying tube, and an aerator inserted in a 300-mL reaction vessel so that air passed through the treated preparation contained in the reaction vessel evaporates any metallic mercury present. In a similar manner, treat 100 mL of the Test preparation and 100 mL of water (reagent blank), and determine the maximum absorbances at the same wavelength [note—Check the zero setting of the instrument frequently]. The absorbance of the solution from the Test preparation does not exceed that of the solution from the Standard preparation (3 ppm).