Pressure experiments are experiment

Experiment

An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

s performed at pressure

Pressure

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

s lower or higher than atmospheric pressure

Atmospheric pressure

Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

, called low-pressure experiments and high-pressure experiments, respectively. Pressure experiment are necessary because substances behave differently at different pressures. For example, water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 boils at a lower temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 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

Vacuum pump

A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...

 is used to remove the air out of a vacuum

Vacuum

In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

 vessel for low-pressure experiments. High-pressures can be created with a piston

Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

-cylinder

Pneumatic cylinder

Pneumatic cylinders are mechanical devices which utilize the power of compressed gas to produce a force in a reciprocating linear motion....

 apparatus, up to and . The piston is shifted with hydraulics

Hydraulics

Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...

, decreasing the volume inside the confining cylinder and increasing the pressure. For higher pressures, up to , a multi-anvil

Anvil press

An anvil press is related to a machine press, and is used to create extraordinarily high pressures on small items.They are often used in artificial diamond creation and research, as they mimic the pressures and temperatures that exist deep in the Earth....

 cell is used and for even higher pressures the diamond anvil cell

Diamond anvil cell

A diamond anvil cell is a device used in scientific experiments. It allows compressing a small piece of material to extreme pressures, which can exceed 3,000,000 atmospheres ....

. The diamond anvil cell is used to create extremely high pressures, as much as a million atmospheres

Atmosphere (unit)

The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...

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