Curiously, the current Friends of the Hunley (of which I'm a Charter Member) website refers to a "magnesium" blue light. However, the lantern with a blue lens that was recovered was a small, handheld carbide lamp -- similar in principle to those used by miners -- and certainly bright enough for the purpose of signaling over 4-5 miles.
When the X-rays of the recovered lamp were made available, I immediately located a very similar carbide lantern online. I hope to be able to examine that recovered lantern -- once it is freed from its incrustation...
There is a replica of the Hunley lamp on display at
http://travel.webshots.com/photo/2638440590103680599DJwFEh.
BTW, "carbide" lamps are technically acetylene lamps, since they meter water into a chamber containing solid calcium carbide, thus releasing acetylene gas, which burns as a brilliant white jet.
My grandfather used to be a coal miner. After he passed away I played with the carbide lamp he had worn. Started the drip then cupped my hand over the reflector & flicked the ignitor. Later my Dad gave me a Big Bang carbide cannon. Later still I took welding class and we were taught how acetylene gas is manufactured & bottled.
Having said all that, I now learn for the first time that acetylene lamps date back to the time of the Civil War. Always wondered how a candle lantern could have been seen that far from shore. Like the old saying goes,
“The ancients are stealing our wisdom again!”
The lantern which was recovered from the H.L. Hunley submarine was not a carbide, or acetylene lamp. The carbide technology for lights was not invented until several decades after the American Civil War. The lantern found aboard the Hunley was an oil burning lamp, likely sperm whale oil; it had a bullseye lens, and was properly called a “dark lantern” due to its sliding shade which could reveal or hide the flame at the operator’s will. The “blue light” which was mentioned in the historical record of the engagement between the H.L. Hunley and the USS Housatonic was a pyrotechic firework signal in long use in both military and civilian sectors. It was not a magnesium light. The original formulae for its manufacture are listed in period US military texts, and I have reproduced it and tested it under conditions similar to those during the Hunley-Housatonic engagement. See YouTube: “Burning Blue Light” and “Making Civil War-Era Blue Light”