Gold monoxide, AuO

An Gold monoxide, AuO, is said to be formed by the action on gold of a small proportion of aqua regia containing excess of hydrochloric acid, addition of sufficient primary carbonate to the solution to redissolve the precipitate first formed, and heating the solution. The product separates as an olive-green hydrate, which dries in the air to a hard mass. It is doubtful whether the oxide is a true chemical compound or not.

A hydrated gold oxide of the formula Au₃O₂(OH)₂ is prepared by the action of boiling water on the monosulphate, AuSO₄. It is a deep-black powder, decomposed at 160° to 205° C.