What a gunpowder magazine looked like at Fort Macon during the Civil War!

Chloride of Lime, which as you can see was suspended in a box above the powder, is Calcium hydrochlorite. This was a powder that was used as a dessicant for well over a hundred years, in all walks of life. Used to suck moisture out of the air, much as those little silica gel ("Do not eat!") packets are used today in any product you buy in a box that might be damaged by atmospheric moisture.

This box would have been changed on a frequent basis, as not only are casemates notoriously damp, dank places, but the Atlantic Ocean was only a few hundred feet away...and gunpowder isn't any good to anybody when it's damp.