Titanium Tetra-iodide, TiI₄

Titanium Tetra-iodide (Titanic Iodide), TiI₄, is obtained when iodine vapour is passed over heated titanium, when hydrogen iodide is passed into titanium tetrachloride while the latter is gradually raised to its boiling-point, and by the action of iodine vapour and hydrogen on titanium tetrachloride at a dull red heat. Titanic iodide forms a reddish brown, brittle, metallic-looking mass which melts at 150° C., and then crystallises in large octahedra. It boils at 360° C., forming an orange vapour, and distils unchanged. Its vapour density at 440° C. is 18.054 (air = 1) or 260 (H = 1), indicating a molecular weight of 520, theory requiring 556. It fumes in the air, is combustible, and dissolves in water, forming a solution whence titanic acid soon separates by hydrolysis. Titanic acid dissolves in hydriodic acid, forming a deep red solution which probably contains hydriodotitanic acid; the acid and its salts are, however, too unstable to be isolated.