i2 4 PRACTICAL ORGANIC CHEMISTRY water, and add 2 ml. of concentrated nitric acid. White crystals of the nitrate separate almost immediately. Filter at the pump, drain thoroughly, reject the filtrate, and then wash with a few ml. of ethanol and ether in turn. The oxalate is prepared in a similar way, using a solution of !•2 g. of oxalic acid in about 15 ml. of water. On stirring the mixed solutions with a rod, the oxalate crystallises out. The chief disadvantage of the above preparation of urea is the long time required for the complete evaporation of the mixed solutions, particularly as occasional stirring is required throughout this operation. A more rapid evaporation is obtained if ammonium chloride is used instead of the sulphate, as the potassium chloride formed is more soluble in water than potassium sulphate: the chloride is, however, slightly soluble in ethanol, and an impure sample of urea is thus obtained. The following preparation of monophenyl-urea (Method i) may well be substituted for that of urea, as the reaction in-
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