Packaging and storage—
Preserve in well-closed containers.
Identification—
A:
Treat 1 g with 10 mL of 3 N hydrochloric acid, and filter: the filtrate responds to the tests for
Zinc 
191
.
B:
Treat 1 g with 10 mL of 3 N hydrochloric acid, heat to boiling, and filter: the filtrate assumes a reddish color upon the addition of
ammonium thiocyanate TS.
Microbial limits 61—
It meets the requirements of the tests for absence of
Staphylococcus aureus and
Pseudomonas aeruginosa.
Loss on ignition 733—
Weigh accurately about 2 g, and ignite at 500
to constant weight: it loses not more than 2.0% of its weight.
Acid-insoluble substances—
Dissolve 2.0 g in 50 mL of 3 N hydrochloric acid. If an insoluble residue remains, collect it on a tared filter, wash with water, dry at 105
for 1 hour, cool, and weigh: the weight of the residue does not exceed 40 mg (2.0%).
Alkaline substances—
Digest 1.0 g with 20 mL of water on a steam bath for 15 minutes, filter, and add 2 drops of phenolphthalein TS: if a red color is produced, not more than 0.20 mL of 0.10 N sulfuric acid is required to discharge it.
Calcium—
Digest 1 g in 25 mL of 3 N hydrochloric acid for 30 minutes, filter to remove the insoluble ferric oxide, and add 6 N ammonium hydroxide to the filtrate until the precipitate first formed is redissolved, then add 5 mL more of 6 N ammonium hydroxide. To 10 mL of this solution add 2 mL of
ammonium oxalate TS: not more than a slight turbidity is produced.
Calcium or magnesium—
To another 10-mL portion of the solution prepared for the test for
Calcium add 2 mL of
dibasic sodium phosphate TS: not more than a slight turbidity is produced.
Lead—
To 1 g add 15 mL of water, stir, then add 3 mL of glacial acetic acid, and warm on a steam bath until dissolved. Filter, and add 5 drops of
potassium chromate TS: no turbidity is produced.
Assay—
Digest about 1.5 g of freshly ignited Calamine, accurately weighed, with 50.0 mL of 1 N sulfuric acid VS, applying gentle heat until no further solution occurs. Filter the mixture, and wash the residue on the filter with hot water until the last washing is neutral to litmus paper. To the combined filtrate and washings add 2.5 g of ammonium chloride, cool, add
methyl orange TS, and titrate with 1 N sodium hydroxide VS. Each mL of 1 N sulfuric acid is equivalent to 40.69 mg of ZnO.
