Cobalt burns in nitric oxide at 150° C. giving the monoxide.
It dissolves readily in strong nitric acid, and the helium contained is thus liberated.
On oxidation with chromic or nitric acids, or potassium permanganate, it yields nicotinic acid or (3-pyridine carboxylic acid, C 5 H 4 N CO 2 H; alkaline potassium ferricyanide gives nicotyrine, C10H10N2, and hydrogen peroxide oxynicotine, C10H14N20.
It is an indigo-blue powder, soluble in hydrochloric acid, but insoluble in dilute nitric and sulphuric acids.
Iridium tetrachloride, IrC1 41 is obtained by dissolving the finely divided metal in aqua regia; by dissolving the hydroxide in hydrochloric acid; and by digesting the hydrated sesquichloride with nitric acid.