USES OF MONAZITE
Practically the only use of monazite has been as a source of thorium salts. In extracting these, by-products are recovered, such as cerium, lanthanum, and other rare earths. Thorium salts are used almost exclusively for the manufacture of Welsbach mantles, which consist of 99 per cent. thorium oxide and 1 per cent. cerium oxide. For this use there is no known substitute. The one other use of thorium salts is in ordinary chemical laboratories, but this use is very limited. The fluoride and other salts of cerium are used in connection with the flaming arc, their presence giving increased luminosity.
Mesothorium is a radio-active element always found in thorium minerals. Until quite recently it has been thrown away in the manufacture of thorium nitrate; but it is now being produced as a by-product, and is useful as a substitute for radium in luminous paints, and for therapeutic purposes.