PREPARATIONS 257 bath in a fume-cupboard and add slowly down the condenser, from a calibrated dropping-tube, 2 ml. of acetyl chloride. Shake the flask after each addition (about 0-5 ml. at a time). When all the acetyl chloride has been added, fit the top of the condenser with a calcium chloride tube bent downwards (cf. Fig. 61, p. 105), and heat the flask in the water-bath at 50° for about 30 minutes. This usually suffices to remove all the hydrogen chloride. When no more hydrogen chloride is evolved pour the mixture into a ioo ml. flask containing 20 ml. of water. Shake the flask vigorously: aluminium chloride and hydrogen chloride are thus extracted by the water. Now pour the mixture into a small separating-funnel and run off the lower aqueous layer. Wash the benzene layer with dil. NaOH solution and again run off the lower layer. Transfer the benzene layer to a small dry flask and dry with anhydrous calcium chloride for 15 minutes. Transfer the dry benzene solution (or a portion of it at a time) to a 10 ml. pear-shaped flask
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