Powdered magnesium is so reactive that it will burn in an atmosphere of nitrogen gas. If you light a pile of the powder and cover it with a beaker, after all of the oxygen in the air has been exhausted it will continue to burn, reacting with the remaining nitrogen to form magnesium nitride (Mg₃N₂). The reactivity of magnesium is such that it can break the triple bond between gaseous nitrogen molecules, the strongest bond between any two identical atoms.
Guess that’s why it’s in thermite grenades. Lecturer at Harvard Chem 1 lit all his burning demos with magnesium.
He also happened to be the inventor of napalm. All the napalm bombs in WWII had magnesium fuses. That way when you put the fire out, as soon as it dried a bit the fire started over again. Or at least that’s how he described it.
That sounds more like phosphorous or another pyrophoric substance. Magnesium burns fiercely, but the reaction has a high activation energy, which means you have to put in a lot of heat to get it going, after which it is self-sustaining. But if you quench a magnesium fire and cool the burning part, it will not re-ignite.
You may well be right. I’m trying to remember a class from 58 years ago that I wasn’t crazy about in the first place. But I DO remember the point that it restarted when dried.