## Section 4: Gas - The Basics

First Discoveries of Gas
Units of Pressure

#### First Discoveries of Gas

Gas is one of the three phases and its properties include the ability to be easily compressed, and theability to fill containers with odd shapes. A Flemish physician named Jan Baptista Van Helmont was the first scientist to realize that "air" was not an element, but actually a mixture of different gases. This set the pace for an Italian physicist named Evangelista Torricelli who determined that air exerts a pressure. This discovery led him to the creation of the first barometer.

The first barometer was a long tube that was closed at one end and filled with mercury and then inverted into a pool of mercury. From the barometer, Torricelli notied that the mercury was always in the tube at around 760 mm. He determined that this was due to the atomospheric pressure.

#### Units of Pressure

Torricelli determined that the standard atmospheric pressure was 760 mm Hg or 760 torr (named for Torricelli). Also 760 mm Hg is equal to 1 atm (standard atmospheric pressure)

1 atm = 760 mm Hg = 760 torr

Pressure is defined as force / area. In the metric system there is another unit for pressure and it is the pasca (Pa). There are 101325 Pa is every atm, so:

1 atm = 760 torr = 760 mm Hg = 101325 Pa