Pressure experiments are experiments performed at pressures lower or higher than atmospheric pressure, called low-pressure experiments and high-pressure experiments, respectively. Pressure experiment are necessary because substances behave differently at different pressures. For example, water boils at a lower temperature at lower pressures. The equipment used for pressure experiments depends on whether the pressure is to be increased or decreased and by how much. A vacuum pump is used to remove the air out of a vacuum vessel for low-pressure experiments. High-pressures can be created with a

piston-cylinder apparatus The piston-cylinder apparatus is a solid media device, used in Geosciences and Material Sciences, for generating simultaneously high pressure (up to 6 GPa) and temperature (up to 1700 °C). Modifications of the normal set-up can push these lim ...

, up to () and . The piston is shifted with hydraulics, decreasing the volume inside the confining cylinder and increasing the pressure. For higher pressures, up to , a multi-anvilcaltech.edu - Multianvil
/ref> cell is used and for even higher pressures the diamond anvil cell. The diamond anvil cell is used to create extremely high pressures, as much as a million

atmospheres The standard atmosphere (symbol: atm) is a unit of pressure defined as Pa. It is sometimes used as a ''reference pressure'' or ''standard pressure''. It is approximately equal to Earth's average atmospheric pressure at sea level. History The s ...

(), though only over a small area. The current record is , but the sample size is confined to the order of tens of micrometres ().

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