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Comparing gas pressures using a manometer

A manometer measures the difference in pressure between two supplies of gases.

A manometer consists of a U-shaped tube filled with a liquid such as mercury. Each end of the tube is connected to a supply of gas.

The liquid will always be pushed towards the side with the gas that has the lower pressure.

If the two gases have equal pressure, the level of the liquid will be the same on both sides.

A manometer can be used to measure the pressure difference between the atmosphere and a controlled supply of oxygen.

A barometer is a special kind of manometer. One end is connected to the atmosphere and the other is connected to a vacuum.

Left: gas 1 has a higher pressure than gas 2. Right: gas 1 has a lower pressure than gas 2.
Left: gas 1 has a higher pressure than gas 2. Right: gas 1 has a lower pressure than gas 2.