Prepared Calamine
Action and use
Antipruritic.
Preparations
Aqueous Calamine Cream
Calamine Lotion
Calamine Ointment
Calamine and Coal Tar Ointment
DEFINITION
Calamine is a basic zinc carbonate suitably coloured with iron(III) oxide.
CHARACTERISTICS
An amorphous, impalpable, pink or reddish brown powder, the colour depending on the variety and amount of iron(III) oxide present and the process by which it is incorporated.
Practically insoluble in water. It dissolves with effervescence in hydrochloric acid.
IDENTIFICATION
A. Yields the reactions characteristic of carbonates, Appendix VI.
B. To 2 g add 5 mL of hydrochloric acid and heat to boiling; if necessary, add hydrochloric acid drop wise until a bright yellow solution is obtained. Cool and add 13.5M ammonia until the first sign of precipitate (solution A). The solution yields reaction B characteristic of iron salts, Appendix VI. Dilute 1 mL of solution A to 5 mL with water; the solution yields the reaction characteristic of zinc salts, Appendix VI.
TESTS
Calcium
Dissolve 0.50 g in a mixture of 10 mL of water and 2.5 mL of glacial acetic acid and filter. To 0.5 mL of the filtrate add 15 mL of 5M ammonia and 2 mL of a 2.5% w/v solution of ammonium oxalate and allow to stand for 2 minutes. The solution remains clear.
Soluble barium salts
To the remainder of the filtrate obtained in the test for Calcium add 2 mL of 1M sulfuric acid and allow to stand for 5 minutes. The solution remains clear.
Lead
Not more than 150 ppm when determined by atomic absorption spectrophotometry, Appendix II D, Method II, measuring at 283.3 nm or 217 nm and using an air-acetylene flame. Carefully add 5 g of the substance being examined to 25 mL of hydrochloric acid and allow to stand for 18 hours. Add 5 mL of nitric acid and sufficient water to produce 200 mL. Use lead standard solution (100 ppm Pb) suitably diluted with a 3.5% v/v solution of nitric acid to prepare the standard solution.
Chloride
Dissolve 0.15 g in water with the addition of 1 mL of nitric acid, filter and dilute to 30 mL with water. The resulting solution complies with the limit test for chlorides, Appendix VII (0.07%).
Sulfate
Dissolve 0.1 g in water with the addition of 3 mL of 2M hydrochloric acid, filter and dilute to 60 mL with water. The resulting solution complies with the limit test for sulfates, Appendix VII (0.6%).
Ethanol-soluble dyes
Shake 1.0 g with 10 mL of ethanol (90%) and filter. The filtrate is colourless, Appendix IV B, Method II.
Matter insoluble in hydrochloric acid
Dissolve 1 g in 20 mL of warm 2M hydrochloric acid and filter. The residue, when washed with water and dried to constant weight at 105°, weighs not more than 10 mg.
Water-soluble dyes
Shake 1.0 g with 10 mL of water and filter. The filtrate is colourless, Appendix IV B, Method II.
Residue on ignition
68.0 to 74.0%, when ignited at a temperature not lower than 900° until, after further ignition, two successive weighings do not differ by more than 0.2% of the weight of the residue. Use 1 g.
