Tantalum Pentoxide: Potassium Tantalum Fluoride Heated with Sulphuric Acid to 400 °C and Ignited (Roscoe 1913)

Hot sulphuric acid drives the fluorine out of potassium tantalum fluoride; boiling with water leaves a tantalum oxide-sulphate, and igniting it with a little ammonium carbonate leaves pure tantalum pentoxide. Result: white tantalum pentoxide (Ta2O5). Source: Roscoe and Schorlemmer, A Treatise on Chemistry vol. 2 (1913), p. 948. Hydrogen fluoride comes off: work outdoors or under a strong draught. Picture drawn by Youblob.