Ammonium Cobalti-nitrite, 4(NH₄)₃Co(NO₂)₆

Ammonium Cobalti-nitrite, 4(NH₄)₃Co(NO₂)₆.3H₂O, was first prepared in 1856 by Gibbs and Genth. Erdmann obtained it by the action of ammonium nitrite upon cobalt chloride solution acidulated with acetic acid. It may also be obtained by adding semicarbazide to a solution of sodium cobalti-nitrite and by double decomposition of solutions of ammonium chloride and sodium cobalti-nitrite; or by addition of nitrous acid to a suspension of cobalt carbonate in the requisite quantity of ammonium nitrite solution. In all three cases the salt is precipitated out.

Ammonium cobalti-nitrite is a yellow powder, almost insoluble in cold water, yielding on warming a yellow solution, which simultaneously decomposes. When dry the salt is quite stable, and may be kept for months without decomposition.