Limestone kiln. Glow from the heating zone of a limestone kiln. This is a rotating cylinder kiln. 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 used as slaked lime (calcium hydroxide), an alkaline material used in farming to neutralise acidic soils. Photographed in Seilles, Belgium.