1895

Liquid Air

Carl von Linde (1842–1934), James Prescott Joule (1818–1889), William Thomson (1824–1907)

German scientist Carl von Linde hit on what some people would call the perfect business. In 1895, he took air and turned it into a range of worthwhile products. He developed an ingenious refrigeration process that cooled gases until they liquefied, using the thermodynamic properties worked out by previous investigators. Compressing a gas heats it, and allowing it to expand cools it (the Joule-Thomson effect, after the English physicists James Prescott Joule and William Thomson, Baron Kelvin of Largs). Linde’s device took compressed air and cooled it back to room temperature and below using groundwater-chilled pipes. It was then allowed to expand through a nozzle into a larger insulated space, which lowered its temperature sharply—the technique is still used in refrigerators and air conditioners today.

The key step, though, was that this chilled air was then pumped back around to cool down the air in the earlier stages, running through a jacket around the outside of the apparatus (an arrangement called a heat exchanger), which meant that the next batch was even colder when it hit the expansion chamber, which allowed it to cool down the batch after it even further, and so on. Eventually the air would start to condense into liquid in the collection chamber, and whatever didn’t was sent back around to the heat exchanger until enough liquefied air had been produced.

Liquefied air was an industrial novelty as it was, but Linde did not rest on his business model. The next stage was fractional distillation, which separated out the nitrogen from the oxygen. Those two elements had very different uses indeed—oxygen could be used for breathing-gas mixtures and to make high-temperature furnaces—and they were worth paying for either in their chilled form or in pressurized bottles of the now-purified gases. Argon was next, and when the other noble gases were discovered a few years later, neon became still another valuable commodity.

A factory producing liquefied air for separation into the various industrial gases.