A saturated aqueous solution at 60o is decolorised with activated charcoal, and filtered. The filtrate is cooled in a water-ice bath, and the salt is precipitated by adding EtOH. After five recrystallisations from ethanol-water mixtures, it is dried overnight at 130o in air [Eden & Bates J Res Nat Bur Stand 62 161 1959]. [Beilstein 3 H 419, 3 III 915, 3 IV 1123.]
