Dewar vacuum flask

Contributed by Faraday Museum - Royal Institution

This is one of the first ever vacuum flasks. While we generally use them to keep our drinks hot, vacuum flasks were invented by James Dewar in 1892 to keep things very cold.

Dewar was interested in cryogenics, the science of extreme cold and in 1898 he was the first person to make liquid hydrogen, which at the time was the coldest substance ever produced.
Cooling gas to the point where it liquefies was an expensive process and Dewar needed to find a way to prevent very cold liquids evaporating while he worked with them. He built boxes insulated with cork, hay or crumpled newspapers, but none kept the liquids cold enough. Eventually he designed a double-walled glass flask and removed the air from the space between the two walls, creating a vacuum. Liquid put inside the flask stays at the same temperature because there are no air molecules through which heat can transfer.

This is one of the earliest trial flasks, later vessels had a silver coating to stop the heat being directly transmitted. Nowadays space rockets are fuelled by super-cooled gases stored in modern Dewar vessels that can keep liquids cold for nearly three years.

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