Pressure

A gas uniformly fills any container, is easeily compressed, and mixes compoletely with any other gas. One of the most obvious properties of a gas is that it exerts pressure on its surroundings. For example, when you blow up a balloon, the air inside pushes against the elastic sidse of the balloon and keeps it firm.

 

A device used to measure atmospheric pressure is called the barometer. It was invented by a Italian scientist named Evangelista Torricelli, who was a student of Galileo. Torricelli's barometer is constructed by filling a glass tube with liquid mercury and inverting it in a dish of mercury.

 

Instruments used for measuring pressure, such as the manometer often contain mercury, the most commonly used units for pressure are based on the height of the mercury column that the gas pressure can support. The unit mm Hg is often called the Torr in honor of Torricelli.

 

This is a barometer used to measure air pressure

 

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The gas laws