Quecksilbersäule

A Quecksilbersäule, or mercury column, is a vertical column of liquid mercury used to measure pressure in devices such as barometers and manometers. The height of the column reflects the pressure of the surrounding gas or the pressure difference being measured.

The physical principle is simple: the atmospheric pressure (or applied pressure) pushes on the mercury reservoir and balances the weight of the mercury column. This is described by P = ρ g h, where ρ is the density of mercury and g is the acceleration due to gravity. Mercury’s density is about 13,546 kg/m³, so the height of the column corresponds to the supporting pressure. At sea level and standard temperature, atmospheric pressure balances a mercury column of roughly 0.760 meters, i.e., 760 millimeters of mercury (mmHg). The mmHg unit derives from this principle and is still used in several disciplines.

Historically, the mercury barometer was invented by Evangelista Torricelli in 1643 and provided a reliable method to measure atmospheric pressure. Mercury columns are also used in manometers to measure pressure differences in gases. In many modern instruments the top of the column approaches a near-vacuum, and alternative technologies (such as aneroid barometers or electronic sensors) are used today, though the mmHg unit remains common in meteorology, medicine, and physics.

Mercury is toxic and requires careful handling and containment. Environmental and health concerns have driven the development of safer alternatives, but the concept of a mercury column remains foundational in the study of pressure measurement.