PREPARATIONS 209pump and wash well with water.Aminoazobenzene is freely soluble in methylated spirit,although insoluble in water. For recrystallisation, therefore,dissolve the crude substance in boiling methylated spirit, removefrom the water-bath, and then add water drop by drop until thesolution becomes just cloudy owing to the separation of the solute:replace the solution momentarily on the water-bath until thecloudiness disappears, and then at once remove the solution, andallow it to cool slowly. (Alternatively, the crudedrymaterialcan be recrystallised from carbon tetrachloride in the usualway.) Aminoazobenzene is thus obtained as yellowish-browncrystals, m.p. 126°: yield, 5 g.To prepare the hydrochloride, add about i g. of amino-azobenzene to 200 ml. of dilute hydrochloric acid and boil untilnearly all the solid material has dissolved. Filter hot and allow tocool slowly. Aminoazobenzene hydrochloride separates asbeautiful steel-blue crystals: filter and dry. If a small quantity
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