Bouteille isotherme

A vacuum flask (also known as a Dewar flask, Dewar bottle or thermos) is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. Invented by Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which significantly reduces heat transfer by conduction or convection. When used to hold cold liquids, this also virtually eliminates condensation on the outside of the flask. Vacuum flasks are used domestically to keep beverages hot or cold for extended periods of time, and for keeping cooked food hot. They are also used for thermal cooking. Vacuum flasks are also used for many purposes in industry. The vacuum flask was designed and invented by Scottish scientist Sir James Dewar in 1892 as a result of his research in the field of cryogenics and is sometimes called a Dewar flask in his honour. While performing experiments in determining the specific heat of the element palladium, Dewar made a brass chamber that he enclosed in another chamber to keep the palladium at its desired temperature. He evacuated the air between the two chambers, creating a partial vacuum to keep the temperature of the contents stable. Dewar refused to patent his invention; this allowed others to develop the flask using new materials such as glass and aluminium, and it became a significant tool for chemical experiments and also a common household item. Dewar's design was quickly transformed into a commercial item in 1904 as two German glassblowers, Reinhold Burger and Albert Aschenbrenner, discovered that it could be used to keep cold drinks cold and warm drinks warm and invented a more robust flask design, which was suited for everyday use. The Dewar flask design had never been patented but the German men who discovered the commercial use for the product named it Thermos, and subsequently claimed both the rights to the commercial product and the trademark to the name.