Dissolve 10 g of potassium hydroxylamine disulfonate in hot 25-30 mL of water with stirring. Dissolve 2 g of potassium permanganate in about 15 mL of water. Combine both solutions, magnetically stir rapidly for 5 minutes and filter. Collect the liquid, flush with inert gas and cover then chill the solution down to freezer temperature for 24h. Filter, dry and use the fremy’s salt immediately. Fremy’s salt will decompose fast in the presence of oxygen.
Potassium permanganate solution
Potassium hydroxylamine disulfonate solution
Both solutions combined
Filtering, manganese dioxide precipitated.
Graduated beaker was flushed with nitrogen gas and put in a freezer
Fremy’s salt crystallizing out from the solution in a freezer