Ammonium dichromate, also known as ammonium bichromate, has the chemical formula of (NH4)2Cr2O7. It is also sometimes known as “Vesuvian Fire”, due to its use in demonstrations as tabletop volcanoes. However, due to its carcinogenic nature, its used in schools has decreased in popularity over the years. This compound exist as orange-red, needle-shaped crystals at normal room temperature and pressure. It is also soluble in water and alcohol.\
It can by synthesized by adding chromic acid to ammonium hydroxide, followed by crystallization. Alternatively, it can be prepared by reacting sodium dichromate with ammonium chloride.
It is commonly used as a source of pure nitrogen in the laboratory, and occassionaly, as a catalyst.
Ammonium dichromate is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, leather tanning, chrome alum, and in oil purification.