Ammonium dichromate

Ammonium dichromate is the inorganic compound with the formula (NH4)2Cr2O7. This salt is sometimes known as Vesuvian Fire, because of its use in the formation of tabletop "volcanoes". It has been used in pyrotechnics and in the early days of photography.

The volcano demonstration involves igniting a pile of the salt, which initiates the following conversion:
 * (NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + 4H2O(g)

Like the well-known explosive ammonium nitrate, ammonium dichromate contains both an oxidizer (dichromate) and a reducer (ammonium). The reaction proceeds to completion once initiated. This demonstration finds only limited use because the chromium(III) oxide ash produced by this reaction is toxic, possibly carcinogenic.