German scientist Carl von Linde (1842-1934) first invented a way to turn gases into liquid. His discovery would form the basis of modern refrigeration and liquid air production.
From the 1600s scientists had known that temperature affects whether a substance is in a gaseous or liquid state. By cooling and pressurizing a gas, it is possible to slow the molecules down and compress them until they collapse and form a liquid. French mathematician Gaspard Monge first produced liquid sulfur dioxide in 1784, and by the late 1800s most gases had been successfully liquefied. However, it was still not possible to produce large quantities suitable for commercial use.
Von Linde had the bright idea of using air itself as a coolant. In 1894, in response to a request from the Guinness brewery in Dublin, Ireland, to create a new refrigeration system, von Linde succeeded in liquefying air by first compressing it and then letting it expand quickly, causing it to cool. The cold air was constantly recycled to cool more incoming air until eventually the gas liquefied.
The "Linde technique" allowed the continuous production of large quantities of liquid gases such as oxygen and nitrogen, and became an immediate commercial success. The biggest use of liquid oxygen was initially for the oxyacetylene torch, invented in France in 1904 and used for cutting and welding metal. This revolutionized the construction of ships, skyscrapers, and other ironworks during the early twentieth century.
Later applications of liquefaction of air included liquid oxygen for distribution to hospitals and industries, and liquid nitrogen for cooling blood and tissues in biological applications.
