Although discovering oxygen and investigating its role in chemical reactions proved to be of crucial importance in changing the science of chemistry, initially oxygen could be produced only in the laboratory and in limited quantities, by chemical or electrolytic means: it had little importance outside the laboratory. It was the achievement of Carl von Linde (1842–1934) in 1902 to take oxygen from the air itself—and he was soon extracting it in quantities approaching one thousand cubic feet per hour. Oxygen became a common commodity that was supplied to hospitals and industries and was later used in rocket fuel, but this was not the German engineer's first important contribution.
Linde, the son of a Lutheran minister, was educated in science and engineering at the Federal Polytechnic in Zurich, Switzerland. After working for locomotive manufacturers in Berlin and Munich, he became a faculty member at the Polytechnic in Munich. His research there on heat theory, from 1873 to 1877, led to his invention of the first reliable and efficient compressed-ammonia refrigerator. The company he established to promote this invention was an international success: refrigeration rapidly displaced ice in food handling and was introduced into many industrial processes.
After a decade Linde withdrew from managerial activities to refocus on research, and in 1895 he succeeded in liquefying air by first compressing it and then letting it expand rapidly, thereby cooling it. He then obtained oxygen and nitrogen from the liquid air by slow warming. In the early days of oxygen production the biggest use by far for the gas was the oxyacetylene torch, invented in France in 1904, which revolutionized metal cutting and welding in the construction of ships, skyscrapers, and other iron and steel structures.
One company formed to use Linde's later patents was the Linde Air Products Company, founded in Cleveland in 1907. In 1917 Linde Air Products joined with four other companies that produced acetylene, among other products, to form Union Carbide and Carbon Corporation. Recently, Linde Air again became an independent company—Praxair.