Packaging and storage—
Preserve in well-closed, light-resistant containers, and store at controlled room temperature.
Clarity and color of solution—
Dissolve 1 g in 20 mL of water, and transfer 10 mL to a 20- × 150-mm test tube. Compare with water in a similar test tube: the liquids are equally clear and, when viewed transversely by transmitted light, exhibit no apparent difference in color.
Identification—
A:
Dissolve about 4 g in 10 mL of water in a test tube, and add 1 mL of silver-ammonia-nitrate TS: metallic silver is produced, either as a finely divided, gray precipitate or as a bright metallic mirror on the inner surface of the tube.
B:
Dissolve about 40 mg of salicylic acid in 5 mL of sulfuric acid, add about 50 mg of Sodium Formaldehyde Sulfoxylate, and warm very gently: a permanent, deep red color appears.
Alkalinity—
Dissolve 1.0 g in 50 mL of water, add phenolphthalein TS, and titrate with 0.10 N sulfuric acid: not more than 3.5 mL is required for neutralization.
pH 
791
:
between 9.5 and 10.5, in a solution (1 in 50).
Loss on drying 731—
Dry it at 105
for 3 hours: it loses not more than 27.0% of its weight.
Sulfide—
Dissolve 6 g in 14 mL of water in a test tube, and wet a strip of lead acetate test paper with the clear solution: no discoloration is evident within 5 minutes.
Iron—
Transfer 1.0 g to a suitable crucible, and carefully ignite, initially at a low temperature until thoroughly charred, and finally, preferably in a muffle furnace, at 500
to 600
until the carbon is all burned off. Cool, dissolve the residue in 2 mL of hydrochloric acid, and dilute with water to 50 mL. Add about 50 mg of ammonium persulfate and 5 mL of
ammonium thiocyanate TS, mix, and transfer to a color-comparison tube. Treat in the same manner 5.0 mL of a solution of ferric ammonium sulfate, prepared by dissolving 43.2 mg of ferric ammonium sulfate in 10 mL of 2 N sulfuric acid and adding water to make 1000 mL, each mL representing 5 µg of Fe. The color of the test solution is not deeper than that of the solution containing the standard iron solution (0.0025%).
Sodium sulfite—
Transfer 4.0 mL of the solution prepared for the
Assay to a conical flask containing 100 mL of water. Add 2 mL of formaldehyde TS, and titrate with the same 0.1 N iodine VS that is used for the
Assay, adding 3 mL of
starch TS as the endpoint is approached. Calculate the percentage of Na
2SO
3 in the Sodium Formaldehyde Sulfoxylate taken by the formula:
(1.25)(63.02)(
V2 
V1)(
N /
W),
in which 63.02 is the equivalent weight of sodium sulfite;
V1 and
V2 are the volumes, in mL, of 0.1 N iodine VS consumed in this titration and in the titration performed in the
Assay, respectively;
N is the exact normality of the iodine solution; and
W is the weight, in g, of Sodium Formaldehyde Sulfoxylate taken for the
Assay: not more than 5.0% of Na
2SO
3, calculated on the dried basis, is found.
Assay—
Transfer about 1 g of Sodium Formaldehyde Sulfoxylate, accurately weighed, to a 50-mL volumetric flask, dissolve in about 25 mL of water, dilute with water to volume, and mix. Reserve a portion of this solution for the test for
Sodium sulfite. Transfer 4.0 mL of this solution to a conical flask containing 100 mL of water, and titrate with 0.1 N iodine VS, adding 3 mL of
starch TS as the endpoint is approached. Each mL of 0.1 N iodine is equivalent to 1.602 mg of SO
2.
;)
