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4.13 DETERMINATION OF INSOLUBLE MATTER

      Dissolve the quantity of the sample specified in the monograph in 100 ml of water, heat to boiling unless otherwise directed, in a covered beaker, and warm on a water-bath for 1 hour. Filter the hot solution through a filtering crucible with an asbestos mat or a crucible with a sponge platinum mat or a sintered-glass crucible of fine porosity or a porous porcelain crucible, which has been tared. Wash the beaker and the filter thoroughly with hot water, dry at 105º to constant weight, cool in a desiccator, and weigh.