Chem. [f. as THORIUM + -a, after alumina, magnesia, silica, etc.] An oxide of thorium, ThO2; a very heavy white substance discovered in the mineral thorite by Berzelius, 1828, and named by him in Swedish, Thorjord, Ger. Thorerde, lit. Thor-earth. Now important in the manufacture of incandescent gas mantles. Also attrib.
1847. in Webster.
1881. Watts, Dict. Chem., VIII. 1967. Thorium Oxide, or Thoria,… is insoluble in dilute acids.
1899. Westm. Gaz., 10 June, 6/3. The expiry of the master patent this year, and the thoria patent next spring. Ibid. (1904), 16 April, 7/1. About [1888], experiments on incandescent mantles gave to thoria considerable commercial value. A mantle of pure thoria gives a very little light; but, on the other hand, it gives a stability to the fragile mantle which no other body yet discovered is able to do.
