294 PRACTICAL ORGANIC CHEMISTRY remove the external cooling so that the mixture slowly attains room temperature. After 3 hours, replace the separating-funnel by a reflux condenser, and the thermometer by a stopper. Add n g. of zinc dust in small portions by rapid removal of the stopper at such a rate that the liquid is first brought to the boil (usually about 2 portions of 2 g. each) and is then maintained gently boiling. Avoid too rapid addition of the zinc^ otherwise the reaction will become too vigorous, and rapid immersion of the flask in ice-water will be necessary to control the effervescence. When the reaction is complete, heat the stirred mixture care-fully under reflux over a Bunsen burner and asbestos gauze for i hour: if the mixture becomes too thick for efficient stirring, add up to 15 ml. of acetic acid. Now decant the hot mixture into 500 ml. of vigorously-stirred ice-cold water: wash the residual zinc thoroughly with glacial acetic acid (2 portions each of 1-2 ml.), decanting the acid also into the stirred water.
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