“Negative X” is the nickname given to a dry mixture of finely ground metallic zinc powder (69% by weight), ammonium nitrate (NH₄NO₃, 28%), and ammonium chloride (NH₄Cl, 3%). This mixture, kept dry and ground together, has the unusual property that adding a drop of water or even picking up moisture from the air will cause it to heat up in a runaway exothermic reaction which eventually bursts into flame. In the presence of water, the ammonium chloride dissociates into ions, with the chloride ions acting as a catalyst to decompose the ammonium nitrate, which then oxidizes the zinc, releasing heat, nitrogen gas, and more water, which makes the reaction run away.
Here is more about Negative X from that essential resource for mad scientists, United Nuclear, “Start a Fire with a Drop of Water”.
But what happens if you cool Negative X down to liquid nitrogen temperature? Let’s see….
