He studied the compression and expansion of air and other gases, and formulated Boyle's law. This law states that the volume of a gas at constant temperature varies inversely with its pressure.
Boyle also improved the air pump, and studied the boiling and freezing of liquids at reduced pressure in a bell jar.
He also developed Dalton's law of partial pressures - that the total pressure of a mixture of gases equals the sum of the pressures exerted by each gas independently - and found that gases expand as their temperature is raised.
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