3 g of sodium sulfite and 1 g of sulfite are suspended in 30 mL of water with stirring, the mixture is left to reflux and stir for 2 hours. The mixture is filtered and the filtrate is concentrated on a hot plate till crystals form. The crystallized slurry is then cooled down in an ice bath and some ethanol is added to crystallize the product out and then filtered. The procedure is repeated twice. The product is obtained in a pentahydrated form.
Na2SO3 + S = Na2S2O3
The mixture of reflux
Removal of the unreacted sulfur
Spontaneous crystallization of the filtrate
Crystallization of the filtrated solution
Addition of the ethanol
The crystallized product