MERCURY BAROMETER: CHARACTERISTICS AND OPERATION - CHEMISTRY - 2024

The mercury barometer is an instrument for use in meteorology by means of which the value of atmospheric pressure is measured. It is made up of a column of mercury located inside a tube that rests vertically on a container filled with mercury.

The tube is made of glass and is located upside down or inverted; that is, its opening is in contact with the container. The word barometer comes from the ancient Greek, which means baro "weight" and meter "measure." The mercury barometer is one of the two main types of barometers that exist.

Source: By GOKLuLe 盧 樂, from Wikimedia Commons

Atmospheric pressure is the weight or force of gravity that acts on an object, per unit of surface or area exerted by the atmosphere. The operation of the barometer is based on the fact that the level reached by the mercury column is equivalent to the weight exerted by the atmosphere.

With this scientific instrument the pressure changes caused by the climate are measured. By analyzing subtle changes in atmospheric pressure, short-term changes in weather or climate can be forecast.

Invention of the mercury barometer

The Mercury Barometer was invented in 1643 by the Italian physicist and mathematician Evangelista Torricelli.

This instrument is very old. However, it was preceded by the water barometer, a larger device also created by this scientist. Torricelli was a student and assistant to the astronomer Galileo Galilei.

In Torricelli's experiments related to creating a vacuum, Galileo intervened and suggested that he use mercury. In this way Torricelli is recognized as the first scientist who created a vacuum and who described the foundation or theory of the barometer.

Torricelli observed that the height of the mercury in the glass tube varied closely with the change in atmospheric pressure. Atmospheric pressure is also called barometric pressure.

There is historical controversy, since it is pointed out that another Italian scientist, Gasparo Berti, was the creator of the water barometer. Even René Descartes was interested in determining atmospheric pressure long before Torricelli, but he did not consolidate his experimental phase.

characteristics

- The mercury barometer is much smaller in size than the water barometer.

- This instrument has a glass tube that only has a downward opening, immersed in a container containing mercury.

- The tube contains a column of mercury that adjusts its level according to the pressure that the mercury receives from the container.

- A vacuum is created by the weight of the mercury in the upper part of the tube, which is known as the torricellian vacuum.

- The container is a round plate that has little depth, and contains mercury that is kept in close contact with that of the tube.

- The tube is graduated, that is, it has a scale marked that allows you to see the increase or decrease in the level of mercury.

- The pressure can be determined by observing the mark on the scale at which the mercury level stops.

- The effect of elevated temperature on the density of mercury does not interfere with the scale reading. The barometer scale is adjusted to compensate for this effect.

Mercury level

The level that reaches the column of mercury in the tube will correspond to the increase or decrease in atmospheric pressure. The higher the atmospheric pressure of a certain place, the higher the mercury column of the barometer will reach.

How does it work?

The layer of air that surrounds the Earth is the atmosphere. It is made up of a mixture of gases and water vapor. The force of gravity exerted by the Earth causes the atmosphere to "compress" on the surface.

Precisely by using the mercury barometer, it is possible to measure the pressure exerted by the atmosphere in a certain geographical location. As the pressure on the mercury in the container increases, the level of the mercury contained in the tube increases.

That is, the pressure of the air or the atmosphere pushes the mercury in the container down. This pressure in the container simultaneously pushes up or raises the level of the mercury column in the tube.

Changes in the height of the mercury column caused by atmospheric pressure can be accurately measured. Also, the accuracy of the mercury barometer can be increased by taking into account the ambient temperature and the local value of gravity.

Units of atmospheric pressure

The units in which atmospheric pressure can be expressed are variable. With the mercury barometer, atmospheric pressure is reported in millimeters, feet, or inches; these are known as torr units. One torr is equal to 1 millimeter of mercury (1 torr = 1 mm Hg).

The height of the mercury column in millimeters, for example, will correspond to the value of atmospheric pressure. One atmosphere of mercury is equal to 760 millimeters of mercury (760 mm Hg), or 29.92 inches of mercury.

Design variations

Different designs of the mercury barometer have been created in order to improve its sensitivity more and more. There are wheel, basin, siphon, cistern barometers, among others.

There are versions that have a thermometer added, such as the Fitzroy barometer.

Restriction on its manufacture

To end this point, it is important to note that since 2007 the sale and handling of mercury has been limited. Which translates, unsurprisingly, into a decline in the production of mercury barometers.

Usefulness of the mercury barometer

-Using the mercury barometer it is possible, based on the result of atmospheric pressure, to make predictions about the weather.

-Also with atmospheric pressure measurements, high or low pressure systems can be detected in the atmosphere. With the use of this instrument you can even announce rains, storms, if the sky will be clear, among other predictions.

-Atmospheric pressure has been determined to be a parameter that varies with atmospheric height and density. It is usual to take the sea level as a reference point to determine the pressure in a certain place.

It is specified if the distance of interest to assess the pressure is above or below sea level.

-With the mercury barometer you can also measure the altitude of a certain site in relation to sea level.

References

1. The editors of Encyclopaedia Britannica. (February 3, 2017). Barometer. Encyclopaedia Britannica. Recovered from: britannica.com
2. History of Chemistry. (sf). Evangelista Torricelli. Recovered from: chemed.chem.purdue.edu
3. Turgeon A. (June 19, 2014). Barometer. National Geographic Society. Recovered from: nationalgeographic.org
4. Wikipedia. (2018). Barometer. Recovered from: en.wikipedia.org
5. Bellis, Mary. (June 14, 2018). The History of the Barometer. Recovered from: thoughtco.com