<P> In 1896 Italian inventor Arturo Malignani (1865--1939) patented an evacuation method for mass production, which allowed obtaining economic bulbs lasting 800 hours . The patent was acquired by Edison in 1898 . </P> <P> In 1897, German physicist and chemist Walther Nernst developed the Nernst lamp, a form of incandescent lamp that used a ceramic globar and did not require enclosure in a vacuum or inert gas . Twice as efficient as carbon filament lamps, Nernst lamps were briefly popular until overtaken by lamps using metal filaments . </P> <P> On 13 December 1904, Hungarian Sándor Just and Croatian Franjo Hanaman were granted a Hungarian patent (No. 34541) for a tungsten filament lamp that lasted longer and gave brighter light than the carbon filament . Tungsten filament lamps were first marketed by the Hungarian company Tungsram in 1904 . This type is often called Tungsram - bulbs in many European countries . Filling a bulb with an inert gas such as argon or nitrogen slows down the evaporation of the tungsten filament compared to operating it in a vacuum . This allows for greater temperatures and therefore greater efficacy with less reduction in filament life . </P> <P> In 1906, William D. Coolidge developed a method of making "ductile tungsten" from sintered tungsten which could be made into filaments while working for General Electric Company . By 1911 General Electric began selling incandescent light bulbs with ductile tungsten wire . </P>

Why is tungsten metal used to make the filament of the bulb
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