CHANGES IN PRACTICE
In the extraction of zinc from its ores the most important changes in practice during recent years have been adaptations of retort smelting for the purpose of utilizing zinc concentrates from complex ores, the increased production of zinc oxide and lithopone through the application of volatilization methods to the re-treatment of retort residues and base ores, and the electrolytic and electro-thermic processes of extraction of the metal.
The most revolutionary advance has been the development of the oil flotation, the electro-magnetic, and electro-static processes for the concentration of ores. These processes are being widely introduced and in connection with electrolytic reduction are particularly adapted to the production of spelter of the highest quality from complex ores. As the electrolytic and electro-thermic processes find their field only where power is relatively cheap, the tendency is to put installations where hydro-electric power is available, effecting a redistribution of zinc-smelting centers.