"It was evident that it was much^ more economical to renounce the lighting power of the open flame"
Carl Auer von Welsbach
In 1807 Pall Mall in London became the first public street to be lit with coal gas, and other countries soon followed. Although gaslight was much cheaper than oil lamps or candles, it also produced smoke, bad smells, and lots of heat. These problems were resolved by an Austrian chemist.
Carl Auer von Welsbach (1858-1929) had studied chemistry at the University of Heidelberg under Robert Bunsen (co-inventor of the Bunsen burner). In 1885, Welsbach discovered the rare-earth elements neodymium and praseodymium. In the course of his research he found that some rare-earths produced a bright light when heated in a Bunsen burner.
In 1885, he patented a mantle, a sheath of metallic threads, made of 60 percent magnesium oxide, 20 percent yttrium oxide, and 20 percent lanthanum oxide. It was not a commercial success. Five years later, he developed a mantle made of 99 percent thorium dioxide and 1 percent cerium dioxide. These mantles lasted longer, produced a brighter white light, and were soon used to light streets, factories, and homes.
Welsbach mantles still produced soot and heat. The solution to this was found in incandescent electric lamps, and most gaslights were replaced by electric lights in the early twentieth century. Welsbach mantles are still used today for camping.
