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7.13 RESIDUE ON EVAPORATION OF VOLATILE OILS

         The residue on evaporation is the percentage by weight of the oil that remains after evaporation when determined by the following method. Unless otherwise specified in the monograph, place 5 g of the oil, accurately weighed, in a heat-resistant glass evaporating dish, which has been weighed after heating on a waterbath for 1 hour and cooling in a desiccator; place the evaporating dish over a water-bath on a cover with holes 70 mm in diameter and maintain the water level in the water-bath so that it is about 50 mm below the cover throughout the test. Vigorously boil the water in the water-bath in a draught-free atmosphere for the time specified in the monograph. Allow the evaporating dish to cool in a desiccator and weigh.