Gold parting in 1860's Australia. It is able to refine gold up to 99.5% purity. The process involves blowing a stream of chlorine gas over and through a crucible filled with molten impure gold. Impurities in the gold form chlorides before the gold does and these insoluble salts are removed from the melt by skimming the surface. Invented by Emil Wohlwill in 1874, this produces the highest purity gold (99.999%). It is an electrolytic process using pure gold for the cathode (or titanium as a starter cathode) and chloroauric acid (gold chloride-hydrochloric acid) as the electrolyte; this is made by dissolving gold
Ultra-high-purity steam for oxidation and annealing high temperature combustion. Within its optimal operating range, torches deliver good purity. Pyrolytic systems can support a middle range of flow but have a difficult time with very low flow rates and low steam to hydrogen ratios when adding water vapor to a carrier gas. Also, thermal management of the heat profile of the furnace and incomplete combustion affect furnace performance. In selective oxidation processes, water vapor is needed with hydrogen and without molecular to oxygen. This allows for the oxidation of specific metals. Torches and catalytic system are not 100% efficient so low levels of oxygen may still enter