Preparation of sodium manganate decahydrate
Two grams of very finely powdered potassium permanganate are added to 50 ml of a 30% (by weight) solution of sodium hydroxide at 0° C. 3.5 g of finely divided sodium sulfite 7-hydrate (or 1.8g of the an hydrous salt) are stirred in and the mixture agitated at 0° C for 10 minutes. The purple liquid turns blue and the similarly colored product separates during this time. The crystals are suction-filtered and washed with 15 ml of 30% of ice-cold sodium hydroxide, then dried rapidly on a porous plate in vacuo over potassium or sodium hydroxide. Sodium manganate is unstable and it is best to store the material in a dry, well-sealed, non-vitreous vessel, out of contact with heat and moisture.
Inorganic laboratory preparations, by G. G. Schlessinger, 38, 1962