Thorium Nitrate, Th(NO₃)₄

By the crystallisation of a dilute nitric acid solution of thorium hydroxide or carbonate large deliquescent tablets of the salt Th(NO₃)₄.12H₂O are produced, which are very soluble in water and alcohol. By the crystallisation of a warm aqueous solution the hydrate Th(NO₃)₄.6H₂O has been obtained, and from a strongly acid solution the hydrate Th(NO₃)₄.5H₂O. A dilute solution of the nitrate is slowly hydrolysed with separation of a basic salt. Thorium nitrate is employed for the manufacture of incandescent-gas mantles. For this purpose it is obtained in granular masses containing about 48 per cent, of thoria, which corresponds nearly to the formula Th(NO₃)₄.4H₂O. When strongly ignited the nitrate leaves a residue of pure white oxide. This is dense and harsh when the nitrate is quite pure, but if 1 to 2 per cent, of sulphuric acid is present in the nitrate the salt swells like "Pharaoh's serpents" during ignition, and yields a soft, voluminous ash from six to ten times as bulky as that obtained from the pure nitrate. Most mantle-makers prefer a nitrate that yields the bulky ash, and hence commercial thorium nitrate almost invariably contains from 1 to 2 per cent, of sulphuric acid.