Posted in Kafevend Blog

With the new year upon us, the excesses of Christmas will no doubt be weighing heavily, if not upon our minds, then certainly on our stomachs. For those who like to make a new year's resolution or several, the most prominent of them may well be to cut back on the feasting of yesteryear and engage in healthy exercise, perhaps by walking somewhere other than to the fridge and back. For those folks, the vacuum flask may well come in handy as they venture out into winter's frigid grasp.

The invention of the vacuum flask was originally made to support scientific studies. It was first made by the Scottish chemist and physicist Sir James Dewar in 1892. Dewar had been studying the properties of liquid gases for some time, and came upon the idea of using a vacuum flask to keep the liquid gases in this state for a longer period of time, giving him longer to work with them. His design incorporated two flasks, with one placed inside the other and joined at the neck. There was a gap inbetween the two which contained a partial vacuum. This meant that liquids placed inside, whether hot or cold, took longer to reach the outside ambient temperature as heat transfer by conduction and convection were limited by the lack of air. The use of a silver lining on the inner flask also helped by reducing thermal radiation.

It isn't a perfect solution of course- the vacuum is only partial, meaning there is still some heat transfer due to the remaining air, and the join at the neck and any internal supports for the glass inner flask also provide more ways for heat to get around. There's no denying its effectiveness though. Vacuum flasks are still a very useful tool in science and industry today, and of course for those of us not engaged in those fields, they serve as a great way to keep our drinks hot (or cold). Dewar missed out on this aspect of his design however. He chose not to patent it, and instead a pair of German glassblowers claimed the rights to commercialise it under the brand Thermos- such is the cut throat world of business! Thermos has of course gone on to be perhaps the most recognisable brand when it comes to vacuum flasks for use at home, so much so that their name is commonly applied to the device.

For those of us who aren't very good at keeping our thermos flasks whole what with that fragile glass core, you might be interested in buying a Stanley bottle. Unlike a traditional vacuum flask, it is made completely out of steel, lending it a rugged durability suitable for countryside hikes or just for those who have a habit of dropping things. The idea was hit upon by William Stanley Jr. Who was working on transformers at the time. In 1913, he realised that a particular welding technique he used during for his job could be also be used to create a vacuum flask made entirely of steel. Many Stanley bottles have become family heirlooms thanks to their strength!

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