Auri-iodic Acid, HAuI₄

Hydrogen iodide converts aurous iodide, auric iodide, and gold in presence of free iodine into auri-iodic acid. It forms small, black crystals.

Crystallization of a solution containing auric chloride and potassium iodide in the molecular proportions 1: 4 yields potassium auri-iodide, KAuI₄. It forms black crystals which begin to decompose at 66° C., and on strong heating leave a residue of crystalline gold. Water decomposes it, forming auric iodide. Johnston has also prepared an auri-iodide of sodium, ammonium, barium, and ferrous iron respectively; and a strontium auri-iodide in solution.