Have you ever heard of liquid air? The process of liquifying air was a major scientific achievement that took place over 100 years ago. Even after 100 years there are only a few companies that liquify air, which is probably why you've never heard of it before. Liquifying air is a cheap way to isolate different gasses like oxygen and nitrogen.
The task of liquefying air began in 1892, when Frenchman Georges Claude began working with acetylene. At time, acetylene was thought to be a very promising substance as it was used in lighting fixtures, but it was very difficult to produce and transport. Georges Claude worked out a method for liquefying air in order to remove its different components and isolate oxygen. Oxygen had nothing to do with acetylene at time, except Claude felt that using oxygen could help reduce costs of producing fires necessary to separate acetylene.
When Georges Claude heard that a scientist named Carl von Linde had managed to liquefy air, Claude set out to do it himself but vowed to do it faster and more efficiently. During day he worked as an engineer at Thomson-Houston and he spent his nights conducting tests in an old warehouse. For two years he worked with a second-hand expansion engine, conducting experiments by trial and error to solve all his technical problems. When he needed to lubricate refrigerated moving parts he replaced oil with petroleum ether so it would remain liquid down to 140 degrees. To seal moving parts he used dry leather packing between piston and cylinder liner.
And finally, after all these small tricks were put in place, he succeeded! He created a system using cold air from expansion cylinder to liquefy pre-cooled pressurized air at exchanger outlet. It was a simple and inexpensive matter to extract oxygen from this liquefied air. If liquifying air sounds like a mystical process now, in an age full of advanced technology, just imagine what people thought of Georges Claude when he told world he was going to form a company that liquified air!