Mammoth Cave saltpeter

In the War of 1812, when British blockade cut imported saltpeter, operators worked the Rotunda and nearby passages at industrial scale—leaching cave soil in wooden vats, pumping liquor to the surface, and converting it to potassium nitrate. Enslaved laborers did most of the hauling and filtering; remnants of vats, pipes, and pump works still stand just inside the Historic Entrance. After the war, when prices fell, the workings were abandoned and the cave became a minor tourist attraction.