Have you ever kept icy cold liquids in a thermos? They stay colder a lot longer than they would in an ordinary bottle.
Even better, have you ever kept hot coffee or cocoa piping hot in a thermos?
A thermos of hot cocoa or coffee can be a beautiful thing at a nighttime football game or concert under-the-stars—and we have James Dewar to thank for it!
Dewar (born on this date in 1842) was a Scottish chemist and physicist who studied atomic and molecular spectroscopy and the liquefaction of gases. He needed something to store liquid gases—something that would keep heat out—and the idea occurred to him to build a double bottle—a bottle inside a bottle—with a vacuum between the two. We call this invention a Dewar flask.
A Dewar flask has very reflective surfaces (mirrors) facing each other to prevent heat from being transmitted by radiation. In other words, the inner surface of the outer bottle has a reflective surface, and the outer surface of the inner bottle also has a reflective surface. In between these two reflective surfaces is...nothing at all! A vacuum is a space with almost no atoms at all—no air, nothing. The vacuum prevents heat being transmitted by conduction.
This great idea was exploited for commercial use by the Thermos company. By the way, Dewar didn't get any money from this commercial use of his idea because he failed to file a patent on it.
Learn more about a Dewar flask or Thermos from How Stuff Works.
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