Historically the term flue meant the chimney itself. Wastewater streams include flue-gas desulfurization, fly ash, bottom ash and flue gas mercury control. The space inside a chimney is called the "flue". This results in low firebox temperatures and low flue temperatures. It used water and alkaline sprays over scrubbers of steel and timber in flue ducts. Modern incinerators include pollution mitigation equipment such as flue gas cleaning. The locomotive comprised a boiler with a single return flue mounted on a four-wheel frame. Early ideas for flue gas desulfurization were established in England around 1850. Because of possible problems with corrosion by flue gases, such constructions are very rare. The moisture content of the flue gas stream also affects particle resistivity. Legislation in Europe has been efficient to reduce flue gas pollution. The recorder produces sound in the manner of a whistle or an organ flue pipe. The London Power Company developed an experimental technique for washing flue gases in 1925. Special tiles are used for roofing, siding, flooring, ceilings, pipes, flue liners, and more. Coal can contain significant amounts of cadmium, which ends up mostly in flue dust.