Pumice
»Pumice is a substance of volcanic origin,consisting chiefly of complex silicates of aluminum,potassium,and sodium.
Packaging and storage—
Preserve in well-closed containers.
Labeling—
Label powdered Pumice to indicate,in descriptive terms,the fineness of the powder.
Powdered Pumice meets the following requirements:
“Pumice Flour”or “Superfine Pumice”:not less than 97.0%of pumice flour or superfine pumice passes through a No.200standard mesh sieve.
“Fine Pumice”:not less than 95.0%of fine pumice passes through a No.150standard mesh sieve and not more than 75.0%passes through a No.200standard mesh sieve.
“Coarse Pumice”:not less than 95.0%of coarse pumice passes through a No.60standard mesh sieve and not more than 5.0%passes through a No.200standard mesh sieve.
Water-soluble substances—
Boil 10g with 50mLof water for 30minutes,adding water from time to time to maintain approximately the original volume,and then filter:the filtrate is neutral to litmus,and one-half of this filtrate,when evaporated and dried at 105
for 1hour,yields not more than 10mg of residue (0.20%).
for 1hour,yields not more than 10mg of residue (0.20%).
Acid-soluble substances—
Boil 1g of Pumice with 25mLof 3Nhydrochloric acid for 30minutes,adding water from time to time to maintain approximately the original volume,then filter the liquid.Add 5drops of sulfuric acid to the filtrate,evaporate to dryness,ignite,and weigh the residue:not more than 60mg of residue is obtained (6.0%).
Iron—
Acidify the remaining half of the filtrate from the test for Water-soluble substanceswith hydrochloric acid,and add a few drops of potassium ferrocyanide TS:no blue color is produced.
Auxiliary Information—
Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 1678
Phone Number:1-301-816-8251