Pumice

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Pumice is a substance of volcanic origin, consisting chiefly of complex silicates of aluminum, potassium, and sodium.

2 IMPURITIES

2.1 Iron

Sample solution: The remaining one-half of the filtrate from the test for Water-Soluble Substances

Analysis: Acidify the Sample solution with hydrochloric acid, and add a few drops of potassium ferrocyanide TS.

Acceptance criteria: No blue color is produced.

3 SPECIFIC TESTS

3.1 Water-Soluble Substances

Sample: 10 g

Analysis: Boil the Sample with 50 mL of water for 30 min, adding water from time to time to maintain approximately the original volume, and then filter. The filtrate is neutral to litmus. Evaporate one-half of this filtrate, dry at 105° for 1 h, and weigh the residue.

Acceptance criteria: NMT 10 mg (NMT 0.20%)

3.2 Acid-Soluble Substances

Sample: 1 g

Analysis: Boil the Sample with 25 mL of 3 N hydrochloric acid for 30 min, adding water from time to time to maintain approximately the original volume, then filter. Add five drops of sulfuric acid to the filtrate, evaporate to dryness, ignite, and weigh the residue.

Acceptance criteria: NMT 60 mg (NMT 6.0%)

3.3 Powdered Pumice

Pumice flour or superfine pumice: NLT 97.0% of pumice flour or superfine pumice passes through a No. 200 standard mesh sieve.

Fine pumice: NLT 95.0% of fine pumice passes through a No. 150 standard mesh sieve, and NMT 75.0% passes through a No. 200 standard mesh sieve.

Coarse pumice: NLT 95.0% of coarse pumice passes through a No. 60 standard mesh sieve, and NMT 5.0% passes through a No. 200 standard mesh sieve.

4 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

Labeling: Label powdered Pumice to indicate, in descriptive terms, the fineness of the powder.