Miller Process for Gold Refining.

The Miller process, patented in 1867 by Francis Bowyer Miller, is an industrial-scale chemical parting gold procedure used to refine gold to a purity of 99.5%. This method involves blowing chlorine gas through molten, slightly impure gold, causing other metal contaminants to form chlorides or slag, leaving the gold unaffected. Once impurities are removed, the resulting gold is 99.5% pure but of lower purity than the gold produced by the Wohlwill process. The Miller process is preferred for its relative ease, quicker turnaround times, and the absence of a large gold tie-up in chloroauric acid, which the Wohlwill process permanently requires for the electrolyte.