Potassium Hydrogen Fluoride and Anhydrous Hydrogen Fluoride: Moissan's Purification of Commercial Acid (Thorpe 1912)

Moissan's way to the dry acid he needed for fluorine: distil commercial hydrofluoric acid from lead (silica stays behind), turn it into potassium hydrogen fluoride, dry that completely, then heat it in platinum; the dry hydrogen fluoride that comes off is condensed in ice and salt. Result: dry potassium hydrogen fluoride, and anhydrous liquid hydrogen fluoride boiling at 19.4 °C. Source: Moissan, as given in Thorpe, A Dictionary of Applied Chemistry vol. 2 (1912), p. 585. Hydrogen fluoride is deadly and burns through skin: full protection, calcium gluconate at hand, never work alone. Picture drawn by Youblob.