APDC Extraction Method

Lead Determine as directed in the APDC Extraction Method under Lead Limit Test, Appendix IIIB. 

Chloride Content (as Cl) Transfer about 1 g of sample, previously dried in vacuum for 1 h and accurately weighed, into a 250-mL beaker, and add sufficient water to make 100 mL. Equip a pH meter with glass and silver electrodes, and set it on the + millivolt scale. Insert the electrodes and a motor-driven, glass stirring rod into the sample beaker. Add 1 to 2 drops of methyl orange TS. Stir, and add, drop wise, 10% nitric acid until a pink color appears, then add 10 mL in excess. Titrate the solution with 0.1 A silver nitrate to a reading of +1.0 millivolt on the pH meter. Each milliliter of 0.1 A silver nitrate is equivalent to 3.545 mg of chloride. Lead Determine as directed in the APDC Extraction Method under Lead Limit Test, Appendix IIIB. 

Fluoride Determine as directed under Fluoride Limit Test, Appendix IIIB, using 1.0 g of sample, accurately weighed. Lead Determine as directed in the APDC Extraction Method under Lead Limit Test, Appendix IIIB. 

Assay Dissolve 250 mg of sample, accurately weighed, in 100 mL of water and 4 mL of 2.7 N hydrochloric acid, boil to effect solution, and cool. While stirring, preferably with a magnetic stirrer, add about 30 mL of 0.05 M disodium EDTA from a 50-mL buret, then add 25 mL of 1 N sodium hydroxide and 300 mg of hydroxy naphthol blue indicator, and continue the titration to a blue endpoint. Each milliliter of 0.05 M disodium EDTA is equivalent to 6.807 mg of CaS04. Fluoride Determine as directed under Fluoride Limit Test, Appendix IIIB, using 1.67 g of sample, accurately weighed. Lead Determine as directed in the APDC Extraction Method under Lead Limit Test, Appendix IIIB. 

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