CHARLESTON, SOUTH CAROLINA—The H.L. Hunley, a Civil War-era submarine, will be immersed in a caustic bath that will remove the concretion of sand and shell that accumulated on its 40-foot-long iron hull. The procedure will also extract salt from the hull so that the Hunley can eventually be displayed without immersing it in water. Once the sediment has loosened the scientists at the Warren Lasch Conservation Center will begin to scrape it off. “Under that concretion is the possibility of new information about the attack,” archaeologist Michael Scafuri told The Post and Courier. The submarine sank and disappeared in 1864 after it rammed a torpedo into the USS Housatonic.