Wildwood, Missouri
This is a lime kiln. It is in Rockwoods Reservation, a Missouri forest and wildlife conservation area in Wildwood, Missouri, just west of St. Louis and north of Route 50.
This kiln was built in the mid-1850s by a businessman who needed powdered lime to use in mortar for houses he was building in the area. It is 20 feet on a side and about 40 feet tall, roughly the height of a four-story building.
The kiln is at the base of a hill and is open at the top so limestone rocks could be dumped into it from above. Openings on the sides allowed firewood to be put inside. Burning the wood produced temperatures reaching 800 degrees Fahrenheit, which broke down the limestone rocks into powdered lime. The arch you can see at the bottom was used to shovel the powdered lime out.
The wood that was burned was harvested near the kiln. This resulted in clear cutting, and the trees you see are part of a second-growth forest.
The vertical line on the wall of the kiln is an expansion joint, allowing the walls to expand and contract as the temperature within changed. The kiln itself was built of the same limestone it rendered. To protect it from the heat, the inside walls were lined with firebrick brought from St. Louis. Firebrick is made from a type of clay, often mixed with minerals. It, too, is produced by firing in a kiln. Firebricks are still used today to help contain molten metals and in other applications.
This kiln is the lone survivor of several that were built in the area at about the same time.