Mercury Chromicyanide

The addition of potassium chromicyanide to a solution of mercurous nitrate gives a yellowish-white precipitate, which rapidly darkens and finally becomes grey. The original precipitate is probably mercurous chromicyanide, Hg₃[Cr(CN)₆], which decomposes, yielding mercurous cyanide, which in its turn splits up into mercuric cyanide and mercury.