A two-gram sample was oven-dried and placed into a 250 mL Erlenmeyer flask with 100 mL of distilled water. A reflux condenser was attached to the flask and the apparatus was placed in a gently boiling water bath for three hours. Special attention was given to insure that the level of the solution in the flask remained below that of the boiling water. Samples were then removed from the water bath and filtered by vacuum suction into a fritted glass crucible of known weight. The residue was washed with hot tap water before the crucibles.
