Talc »Talc is a native,hydrous magnesium silicate,sometimes containing a small proportion of aluminum silicate. Packaging and storage— Preserve in well-closed containers. Identification— Mix about 200mg of anhydrous sodium carbonate with 2g of anhydrous potassium carbonate,and melt in a platinum crucible.To the melt add 100mg of the substance under test,and continue heating until fusion is complete.Cool,and transfer the fused mixture to a dish or beaker with the aid of about 50mLof hot water.Add hydrochloric acid to the liquid until effervescence ceases,then add 10mLmore of the acid,and evaporate the mixture on a steam bath to dryness.Cool,add 20mLof water,boil,and filter the mixture:an insoluble residue of silica remains.Dissolve in the filtrate about 2g of ammonium chloride,and add 5mLof 6Nammonium hydroxide.Filter,if necessary,and add dibasic sodium phosphate TSto the filtrate:a white,crystalline precipitate of magnesium ammonium phosphate separates. Microbial limits á61ñ The total bacterial count does not exceed 500cfu per g. Loss on ignition á733ñ Weigh accurately about 1g and ignite at 1000to constant weight:it loses not more than 6.5%of its weight. Acid-soluble substances— Digest 1.00g with 20mLof 3Nhydrochloric acid at 50for 15minutes,add water to restore the original volume,mix,and filter.To 10mLof the filtrate add 1mLof 2Nsulfuric acid,evaporate to dryness,and ignite to constant weight:the weight of the residue does not exceed 10mg (2.0%). Reaction and soluble substances— Boil 10g with 50mLof water for 30minutes,adding water from time to time to maintain approximately the original volume,and filter:the filtrate is neutral to litmus paper.Evaporate one-half of the filtrate to dryness,and dry at 105for 1hour:the weight of the residue does not exceed 5mg (0.1%). Water-soluble iron— Slightly acidify with hydrochloric acid the remaining half of the filtrate obtained in the test for Reaction and soluble substances,and add 1mLof potassium ferrocyanide TS:the liquid does not acquire a blue color. Arsenic,Heavy metals,and Lead— Test solution— Transfer 10.0g to a 250-mLflask,and add 50mLof 0.5Nhydrochloric acid.Attach a reflux condenser to the flask,heat on a steam bath for 30minutes,cool,transfer the mixture to a beaker,and allow the undissolved material to settle.Decant the supernatant through thick,strong,medium-speed filter paper into a 100-mLvolumetric flask,retaining as much as possible of the insoluble material in the beaker.Wash the slurry and beaker with three 10-mLportions of hot water,decanting each washing through the filter into the flask.Finally,wash the filter paper with 15mLof hot water,cool the filtrate to room temperature,dilute with water to volume,and mix.Use this Test solutionfor the following tests. Arsenic ,Method Iá211ñ—Use 10mLof the Test solutionin preparing the Test Preparation.The limit is 3ppm. Heavy metals á231ñ —Use 5mLof the Test solutionin preparing the Test Preparation.The limit is 0.004%. Lead á251ñ —A5-mLportion of the Test solutioncontains not more than 5µg of lead (0.001%). Auxiliary Information— Staff Liaison:Justin Lane,B.S.,Scientific Associate Expert Committee:(EMC)Excipients:Monograph Content USP28–NF23Page 1846 Pharmacopeial Forum:Volume No.30(5)Page 1857 Phone Number:1-301-816-8323