Ether, Peroxide-free

Shake 1000 mL of ether with 20 mL of a solution of 30 g of iron(ii) sulfate in 55 mL of water and 3 mL of sulfuric acid. Continue shaking until a small sample no longer produces a blue colour when shaken with an equal volume of a 2% w/v solution of potassium iodide and 0.1 mL of starch mucilage.