I had some black powder containing charcoal, sulfur, and sodium nitrate, which I added some magnesium powder to. After mixing, I started to compress some in preparation for ignition, but as soon as I started to press it together, it became suddenly warm. Yikes! What is the magnesium reacting with that is causing this to happen?

 

BTW, the amound of powder was very small so don't worry about me blowing myself up. When you experiment with explosives, ALWAYS START SMALL!

Do you know what the 3 compounds in black powder do?

Well, charcoal is the fuel, so it wasn't reacting with the magnesium; sodium nitrate is the oxidizer, but I know for a fact it doesn't spontaneously react with magnesium; sulfur becomes sulfide to allow more oxygen to leave the nitrate, and I have considered that it might form a sulfide with magnesium, but I tried mixing magnesium and sulfur powders and nothing happened. I can't figure out what this reaction would be but it seems logical that it involves both the sodium nitrate and the sulfur. My powder was also slightly damp, so I should really go test magnesium with sulfur and sodium nitrate again with a little water added to really eliminate those possibilities.