It was an ancient concoction called "Greek Fire", a mixture of sulfur, naphtha and quick lime, put in a jar which when opened and exposed to air/oxygen, would ignite. There were about 20 of these fires and were quickly put out.
Edit - Correct, JohnnyClair. Welcome to the trivia game and to CivilWarTalk.
Hope you'll come back and play again. If you haven't done so already, you're invited to stop by the New Recruits Meet and Greet forum and introduce yourself to some more CivilWarTalkers.
Hoosier