Nitrogen triiodide, NI3, is a black powder produced when iodine crystals are added to a solution of concentrated aqueous ammonia. While the crystals of NI3 are wet, they are stable, but when the substance dries off, the NI3 is touch-sensitive, and decomposes explosively to produce nitrogen gas and iodine vapor:
2NI3(s) ——> N2(g) + 3I2(g)
In the following demonstrations, a small amount of nitrogen triiodide has been prepared, and allowed to dry on a paper towel in a fume hood. It is then "tickled" with a feather at the end of a long stick, which causes it to explode. The purple smoke is caused by the molecular iodine in the vapor.
Video Clip 1:
This video consists of two film clips, which are different
camera angles on the same reaction.
Video Clip 2:
In this version, I placed moist nitrogen triiodide on four
pieces of filter paper, separated from each other by metal
o-rings, and allowed the material to dry for about an hour.
Touching the bottom pile caused a cascade of exploding NI3.
The video shows the same cascade from two different camera
angles; the last segment is the same camera angle as the
second, with the playback in slow motion.
Video Clip 3:
In this video, the pile of nitrogen triiodide was still slightly moist,
and took a little longer to detonate
!!! Hazards !!!
Although it is not a very powerful explosive, a sufficiently large amount of nitrogen triiodide can do a lot of damage. The material should never be handled when it is dry, since the slightest touch can cause it to explode. The best thing is to allow it to dry in the location where it will be detonated. A long stick should be used to set it off. (To demonstrate how light a touch is needed, a feather taped to the end of a long stick works best.)
Explosive Decomposition of Nitrogen Triiodide: Bassam Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 1. Madison: The University of Wisconsin Press, 1983, p. 96-98.
F. Albert Cotton and Geoffrey Wilkinson, Advanced Inorganic Chemistry, 5th ed. New York: John Wiley & Sons, 1988, p. 331-332.
Martha Windholz (ed.), The Merck Index, 10th ed. Rahway: Merck & Co., Inc., 1983.