PREPARATIONS 173 crystallised from hot water alone, it almost invariably separates first as a fine emulsion, which subsequently crystallises.) For properties and reactions of o-and />-nitrophenols, see p. 386. OH NO 2 /\ NO 2 Picric Acid (2,4,6-Trinitrophenol). 1 I^J, NO 2 Required: Phenol, 8 g.; sulphuric acid, 10 ml.; nitric acid 30 ml. Weigh out 8 g. of phenol into a dry 750 ml. flat-bottomed flask, add 10 ml. (18-5 g.) of concentrated sulphuric acid, and shake the mixture, which becomes warm. Now heat the flask on a briskly boiling water-bath for 30 minutes to complete the formation of the phenol-sulphonic acid, and then chill the flask thoroughly in an ice-water mixture. Place the flask on a wooden block (or on some similar non-conducting surface) in an efficient fume-cupboard, and without delay, i.e., whilst the phenol-sulphonic acid is still a cold viscous syrup, add 30 ml. of concen-trated nitric acid and at once thoroughly mix the liquids by shaking for a few seconds. Then allow the mixture to stand undisturbed.
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