"Moment of nature" on CBS Sunday Morning on 11 October 2015
DeSoto Caverns located on 5181 DeSoto Caverns Pkwy Childersburg, AL 35044.
Of relevance to Civil War history, DeSoto Caverns became a gunpowder-mining center toward the end of the Civil War.
Cave soil, often rich in calcium nitrate (Ca (NO3)2 " 4H20), called saltpeter, can be processed into potassium nitrate, or niter (KNO3). Niter makes up 75% of what we call gunpowder. The mining of saltpeter required a lot of water, which DeSoto Caverns with its spring-fed well had, in abundance.
A wooden vat was constructed so that when water was added, the soil in the vat became thoroughly saturated. The nitrate-enriched water would filter out the bottom of the vat into a leaching trough. The water was allowed to stand so that the soil's impurities would settle out. The nitrate water was then carried in buckets out of the cave and boiled in large kettles where it was mixed with potash or wood ashes.
This process converted the calcium nitrate into potassium nitrate or niter. Finally, the water was boiled off leaving niter crystals usable, after drying, for making gunpowder. The actual well, leaching trough, and a reconstructed vat used in this operation are on display in the caverns.
Wikipedia also notes an issue in the history of Desoto Caverns as to lower-priced labor in Mexico:
Studies were made and the caverns proved to be a "gold mine" of onyx. All the partners expected to become millionaires from the mining operation. However, Mexican Onyx became popular about this time, and labor costs in Mexico were very low.
In passing, one notes the definition of saltpeter is a bit ambiguous. From Britannica:
Saltpetre, also spelled Saltpeter, also called Nitre, or Niter, any of three naturally occurring nitrates, distinguished as (1) ordinary saltpetre, or potassium nitrate, KNO3; (2) Chile saltpetre, cubic nitre, or sodium nitrate, NaNO3; and (3) lime saltpetre, wall saltpetre, or calcium nitrate, Ca(NO3)2. These three nitrates generally occur as efflorescences caused by the oxidation of nitrogenous matter in the presence of the alkalis and alkaline earths.
And, as to the patent connection, recall US Patent No. 1, issued in 1790 to Samuel Hopkins, for a better way to make potash.
Potash was a war material.