Thermos flask

The thermos flask is a special kind of bottle in which hot liquids like tea and milk remain hot and cold items like ice, cold water etc. remain cold for a long time. It was invented by Sir James Dewar in 1892. That is why it is called Dewar flask also. It consists of a double-walled glass bottle. These walls are silvered from inner side. The space between the walls is evacuated with the help of a vacuum pump and sealed. This bottle is protected by a metal case. A cork is fitted on its mouth.