1856 Henry Bessemer develops an efficient process for producing steel by blowing air through molten iron. The image of a Bessemer Converter is shown. 1886 Charles Hall and Paul Héroult independently develop a method for using electricity to obtain aluminum from aluminum oxide. 1908 Henry Ford uses vanadium steel (an alloy of iron with carbon and vanadium) extensively in his Model T Fords. A Ford car is shoown and a label for Vanadium steel is shown with the text 'This alloy becomes popular in car manufacturing because it is lightweight and strong.' 1914 The start of World War I leads to the widescale use of welding techniques, such as gas welding with acetylene, for ship building. A man with a gas torch is shown with the label 'Hot gas flame' and the text 'The flame from a burning gas melts the surfaces where two metal parts will join.' 1931 The 102- story Empire State Building in New York City is completed. Skyscrapers would be impossible without steelframed construction. The image of the Empire State building is shown and the text with it is titled 'Steel-framed structure' and reads 'The Empire State building is supported by a framework of steel column and beams that weigh 60,000 tons.' 1942 Making small, complex parts from metal powders is less wasteful than machining. World War II spurs advances in iron powder metallurgy. The image of a diagram captioned 'Metal parts from powder' is shown and the text with it is 'Metal parts, such as the gears in this gold watch, are made by applying heat and pressure to powdered metal in a mold. 1991 New alloys containing rhenium are introduced. These superalloys are capable of retaining their strength at very high temperatures. The image of an airplane with the lable reading 'Superalloys containing rhenium are used in jet engines' is shown.