Phase Composition of Commercial "Ammonium Carbonate".

A unique crystalline phase was the sole constituent in newly opened containers of commercial reagent-grade "ammonium carbonate." The chemical composition, optical constants, x-ray powder diffraction pattern, infrared absorption spectrum, and density indicate a double salt, ammonium bicarbonate-carbamate (NH(4)HCO(3).NH(4) CO(2)NH(2)), which is unstable in air at ambient temperature and decomposes rapidly to ammonium bicarbonate.