Recrystallise it three times from conductivity H2O and dry it in air to constant weight over the partially dehydrated salt. [James Trans Faraday Soc 45 855 1949.] Alternatively the Ca salt can be purified by precipitation with absolute EtOH in the cold (to avoid oxidation) from an air-free saturated aqueous solution. The pure lemon yellow crystals are centrifuged, dried in a vacuum desiccator first over dry charcoal for 24hours, then over partly dehydrated salt and stored in a dark glass stoppered bottle. No deterioration occurred after 18 months. No trace of Na, K or NH4 ions could be detected in the salt from the residue after decomposition of the salt with conc H2SO4. Analyses indicate 11mols of H2O per mol of salt. The solubility in H2O is 36.45g (24.9o) and 64.7g (44.7o) per 100g of solution. [Farrow J Chem Soc 50 1926.]
