Germanium Dioxide: Argyrodite Fused with Nitre and Potash, Purified through Potassium Germanofluoride (Winkler, Roscoe 1913)

Argyrodite, the Freiberg silver ore in which germanium was found, is fused with nitre and potash. The germanium goes into the upper layer, comes out of solution as oxide, and is cleaned by passing it through the fluoride and the sulphide before roasting back to pure oxide. Result: germanium dioxide, a dense white powder. Source: Roscoe and Schorlemmer, A Treatise on Chemistry vol. 2 (1913), p. 839, after Winkler. Not given: amounts and temperatures. Hydrogen sulphide is a poison gas; hydrofluoric acid burns deep. Picture drawn by Youblob.