Electrolysis cell with samples of cryolite and fluorspar, 1886.
© Science Museum / Science & Society Picture Library
A reproduction of the electrolysis cell with which the chemist Henri Moisan (1852-1907) first isolated the element fluorine in 1886. It is shown together with specimens of cryolite (left) and fluorspar (right) . Although fluorine had been known to exist since the end of the 18th century, it was to be a further 100 years until it was actually isolated. Moisan electrolysed a solution of potasium fluoride (KF) in anhydrous hydrofluoric acid (HF) (whose raw material is fluorspar), using a cell made from platinum. Cryolite is a rare mineral which contains fluoride. The supplies from Greenland, where the only known reserves of it were found, are now exhausted and it is made synthetically.