Thursday, December 4, 2008

Where Will Water Not Boil?

Water will boil anywhere, but it boils at different temperatures in different places. For example, it will boil at a lower temperature up a mountain than at sea level.

The boiling point of water is the temperature at which its vapour pressure becomes equal to the outside atmospheric pressure. As the atmospheric pressure is always changing so the boiling point of water will vary from day to day. Water boils at 100 degree Centigrade only when the atmospheric pressure outside is at the "standard value".

At Quito in Ecuador, which is about 2700 meters (8800 feet) above sea level, water boils at 90 degree centigrade.

People who explore in mountainous regions find a pressure cooker very useful. The time required to cook food can be greatly reduced if the boiling point of the water is raised. The pressure cooker does this, since it is an aluminum container fitted with a sealing ring but with a loaded pin-valve which allows steam to escape. The valve can be set at varying pressures, enabling the food to be cooked at a temperature of about 120 degree Centigrade.

No comments: