Crystallise it from water (3mL/g) by partial evaporation in a desiccator. It forms a pentahydrate at low temperatures, but the crystals filtered from a saturated solution at 80o are the monohydrate; the transition temperature is 62.5o. [Lumsden J Chem Soc 81 359 1902.] Ithas a dissociation constant of 0.31 [Colman-Porter & Monk J Chem Soc 4363 1952]. [Beilstein 2 H 290, 2 II 290, 2 IV 845.]
