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7.21 TOTAL SOLIDS

         The term “total solids” is applied to the residue obtained when the prescribed amount of the preparation is dried to constant weight under the conditions specified below.

Apparatus

         A shallow, flat-bottomed, flanged dish, about 75 mm in diameter and about 25 mm deep, made of suitable metal of high heat conductivity and low specific heat and which is not affected by the preparation such as nickel or stainless steel, with a well-fitting cover.

Method

         Place the quantity stated in the monograph in a tared dish, evaporate at as low a temperature as possible until the ethanol is removed and heat on a waterbath until the residue is apparently dry. Transfer to an oven operating without a fan and dry to constant weight at 105º unless otherwise stated in the monograph. It may be necessary, for residues of a hygroscopic nature, to use a dish provided with a well-fitting cover and to cool in a desiccator.