Introduction:

Ammonium triiodide is a dark purple crystal that forms when iodine crystals are dissolved in aqueous ammonia.  Although the crystals decompose rapidly from the application of heat or pressure, they are not considered explosives.  Ammonium triiodide is instead, a rapidly decomposing compound.  Ammonia, when dissolved in water, produces ammonium hydroxide.  The ammonium, ion, NH₄^-1 has one extra electron to donate to an iodine atom.  Iodine will readily receive an extra electron, and will even receive electrons that aren't readily donated from the nitrogen atom.  The result is NH₄I₃^-2, which is extremely unstable.  This compound rapidly decomposes to NH₄I, a stable compound, and I₂ gas.  The gas is easily recognized by its brilliant purple color, and NH₄I is a waste material.  As ammonium triiodide decomposes, it releases energy in the form of a loud report.

A word about the purity of ammonia:  The quality of the explosion produced from this compound's decomposition  is dependent on well-formed, pure crystals.  If the crystals are crushed as they are forming, a poor report will be heard.  If the crystals are impure, a poor report will be heard.  However, if the crystals are well-formed and very pure, the compound will be too unstable, and unable to be handled.  The product is generally detonated by the brush of a twig or a feather, but an overly pure product will be detonated by a wind current.  In order to obtain crystals of the correct quality, clear household ammonia must be used, as scented or sudsy ammonia will produce crystals of insufficient purity, and reagent grade ammonium hydroxide will produce crystals of superior quality.

Preparation:

1. Gloves and eye protection should be worn throughout this experiment. Ammonia and ammonium hydroxide are nasal and airway irritants.  Elemental iodine, in crystal form, stains objects easily, and is corrosive.  Iodine gas irritates the nasal and airway, and is corrosive.  Ammonium iodide stains objects easily.
2. Place about an inch of ammonium hydroxide (NH₄OH) in a glass container or beaker.
3. Add a small amount (less than a teaspoon) of iodine crystals (I₂) and stir the mixture well.
4. Allow the mixture to react, until the solvent turns yellow.  If the solvent does not turn yellow, react for about a half an hour.  The reaction can be sped by heating it very slightly, by putting it in the sun.
5. The result should be purple crystals in a yellow or clear solution. This is the safest way to store ammonium triiodide, although it should not be stored for a long period of time.
6. To separate the crystals from solution, pour off the liquid, or filter the crystals.  A small amount off ammonium hydroxide can be used to wash the crystals, if desired.
7. Separate the crystals onto small amounts and scoop them onto filter paper before they dry.  Try to preserve the delicate crystal structure.
8. Do not store ammonium triiodide when dry.

Cleanup:

Do not store ammonium triiodide crystals when dry- they are easily decomposed.  Ammonium iodide can be disposed of in the trash can, and iodine gas should escape to the atmosphere.