Limestone kiln. This is a rotating cylinder kiln. The white powder is lime and limestone dust. The glow (upper centre) is where limestone (calcium carbonate) is heated until it dissociates to form lime (calcium oxide) and carbon dioxide. Lime is used to make cement in the construction industry. It is also converted to slaked lime (calcium hydroxide), an alkaline material used in farming to neutralise acidic soils. Photographed in Seilles, Belgium.