148 PRACTICAL ORGANIC CHEMISTRY In this preparation, the (+) or dextro-rotatory (natural) cam-phor or the (±) or racemic (synthetic) camphor can be used. Perform the oxidation in a fume-cupboard. Place a mixture of 5 g. of camphor, 6 g. of powdered selenium dioxide and 5 ml. of acetic anhydride in flask fitted with a reflux water-condenser. Heat the flask in an oil-bath for 3 hours at 140-150° so that gentle boiling occurs: shake the mixture from time to time. Then cool the reaction-mixture, filter it at the pump, leaving a black residue of selenium, and wash out the flask twice with 2x 5 ml. of acetic acid, passing the washings also through the filter. Dilute the united filtrates with water, and make the solution alkaline with 10% aqueous sodium hydroxide, which precipitates the camphorquinone. Cool, filter off the yellow camphorquinone at the pump, wash with water and drain thoroughly. The camphorquinone can be purified in either of two ways,
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