Thorium

Thorium (sym. Th, equiv. 231·5) is a rare metal resembling aluminium, but taking fire below a red heat, and burning with great brilliancy. Thoria, $\backslash text\{ThO\}\_2$, the oxide, is remarkable for its high specific gravity, 9·2. Thorium was discovered in 1829 by Berzelius in an earth to which he had given the name Thoria, and which occurs in a rare black Norwegian mineral termed Thorite. A use was found for it in making the mantles for incandescent gas-light (see GAS-LIGHTING).