Torricelli barometer

Mercury Manometer. An open-end U-tube mercury manometer, known historically as the Torricelli barometer, can typically be read to 0.05 mmHg, but should be corrected for the capillary depression of mercury in glass and for residual gases in the "vacuum" above the column these two small effects are usually corrected for by the manufacturer s scale next to the column. The isoteniscope is just a fancy term for a U-tube of the Torricelli type, containing a liquid, which measures pressure differences by different heights of the liquid in the two arms, one open to the system under study, the other open to air. 

Torricelli Barometer Instrument to measure absolute atmospheric pressure, consisting of a graduated tube closed at the top end, containing a vacuum at the top above a column of mercury, and standing in a reservoir of mercury. 

The initial weather-forecasting barometer, the Torricelli barometer, measured the height of a liquid column that the pressure of air would support, with a vacuum at the closed top end of a vertical tube. This barometer is an absolute pressure instrument. Atmospheric pressure is obtained as the product of... 

In 1643, Italian physicist and mathematician Evangelista Torricelli proved that atmospheric pressure would support the weight of a thirty-five-foot water column leaving a vacuum above that in a closed tube and that this height would change with the weather. Later Torricelli barometers used liquid mercury to reduce the size of the column and make such instruments more practical. 

FIGURE 9.6 The Torricelli barometer with a meter stick. (From Kenkel, J., Kelter, P., and Hage, D., Chemistry An Industry-Based Introduction with CD-ROM, CRC Press, Boca Raton, FL, 2001. With Permission.)... 

In the late fifteenth century AD mercury was successfully used as a treatment for syphilis. In the late sixteenth century the development of the Patio process for the recovery of silver by amalgamation (see Silverand silveralloys) greatiy increased the consumption of mercury. Usage of mercury increased in 1643 when Torricelli invented the barometer, and again in 1720 when Fahrenheit invented the mercury thermometer. Other scientific and medical appHcations foUowed. Industrial usage after 1900, particularly in electrical appHcations, expanded rapidly, offsetting the sharp decline in its use in amalgamation. 

The torr i.s a unit of pre.s.snre named for Torricelli, inventor of die barometer. 1 torr corre-.spond.s to 1 mm Hg (l/760dr of an atmo.sphere). 

A mercury barometer. This is the type of barometer first constructed by Torricelli. The pressure of the atmosphere pushes the mercury in the dish to rise into the glass tube. The height of the column of mercury is a measure of the atmospheric pressure. 

A device commonly used to measure atmospheric pressure is the mercury barometer (Figure 5.1), first constructed by Evangelista Torricelli in the seventeenth century. This consists of a closed gas tube filled with mercury inverted over a pool of mercury. The pressure exerted by the mercury column exactly equals that of the atmosphere. Hence the height of the column is a measure of the atmospheric pressure. At or near sea level, it typically varies from 740 to 760 mm, depending on weather conditions. 

The pressure of the atmosphere can be measured with a barometer, an instrument invented in the seventeenth century by Evangelista Torricelli, a student of Galileo. Torricelli (whose name coincidentally means little tower in Italian) formed a little tower of liquid mercury. He sealed a long glass tube at one end, filled it with mercury, and inverted it into a beaker (Fig. 4.4). The column of mercury fell until the pressure that it exerted at its base matched the pressure exerted by the atmosphere. To interpret measurements with a barometer, we need to find how the height of the column of mercury depends on the atmospheric pressure. 

Although mercury is known from early times and was used hy alchemists, its first modern scientific applications date hack to 1643 when Torricelli used it in the barometer to measure pressure and about eight decades later Fahrenheit used it in the thermometer to measure temperature. Before this, mercury s use was confined to decorative work, gold extraction and medicines. The element was named after the planet mercury and its symbol Hg is taken from the Latin word hydrargyrum, which means hquid silver. 

He inverted the tube in a pool of mercury. Torricelli noticed that the mercury in the tube fell, creating a vacuum at the top of the tube. The final height of the mercury in the tube was roughly 28 inches. Because mercury has 13.5 times the density of water, Torricelli proposed that water should rise about 13.5 X 28 inches or about 32 feet. Torricelli reasoned that atmospheric pressure placed a limit on how high a liquid could raise in the tube. His inverted mercury-filled tube was the first barometer (Figure 9.1). 

The height of the mercury column in a barometer on a typical day at sea level is about 760 mm, which we have seen corresponds to 101 kPa. This pressure could be reported as 760 mmHg. The unit 1 mmHg has been largely replaced by the unit 1 Torr (named for Torricelli), with 1 Torr = 1 mmHg so normal atmospheric pressure is about 760 Torr. Atmospheric pressure varies with altitude and weather. The pressure of the atmosphere at the cruising height of a commercial jetliner (10 km) is only about 200 Torr, so airplane cabins must be pressurized. 

He took a long glass tube open at one end and filled it fully with mercury. Closing the open end of the glass tube with his thumb, he inverted it into a glass dish containing mercury. When his thumb was removed, the mercury dropped to 76 cm level. The length of the tube or its cross section did not matter. The vacuum above the mercury column is still called Torricelli s vacuum . Modem barometers are based on this principle. 

Volume may be expressed in a variety of units—liter (L), milliliter (mL), cubic meter (m3), cubic centimeter (cc or cm3). Similarly, pressure can be expressed in a variety of units, but the standard unit of pressure is the atmosphere (atm) one atmosphere (1 atm) is defined as the pressure needed to support a column of mercury 760 mm in height at 0°C at sea level. In honor of Evangelista Torricelli, the Italian inventor of the barometer, the unit torr is used and is equal to 1 mm Hg. Thus... 

He designed the apparatus which we now know as the barometer, shown in Figure 11.10. Torricelli filled a glass tube of 1 cm diameter, closed at one end, with mercury. He then inverted the tube in a dish of mercury. Some of the mercury ran out of the tube. But about 760 mm of mercury remained in the tube. This is about 13.6 times less than the height of water that Galileo could pump. It is the air pushing on the mercury in the dish that keeps this 760 mm of mercury in the tube. 

Torricelli makes the first barometer using mercury in a sealed glass tube The Dutch scientist Anton van Leeuwenhoek develops a microscope Isaac Newton invents a reflecting telescope... 

A unit of pressure equal to that exerted by a column of mercury 1 mm high at 0°C and standard gravity (1 mm Hg). Named after Evangelista Torricelli (1608-1647), inventor of the mercury barometer. 

At sea level, the atmosphere keeps the mercury in a barometer at an average height of 760 mm, which is 1 atmosphere. One millimeter of mercury is also called a torr, after Evangelista Torricelli, the Italian physicist who invented the barometer. Other units of pressure are listed in Table 1. 

The device that Torricelli invented is called a barometer. A barometer is an instrument used to measure atmospheric pressure. As Torricelli showed, the height of the mercury in a barometer is always about 760 mm. The exact height of the mercury is determined by two forces. Gravity exerts a constant downward force on the mercury. This force is opposed by an upward force exerted by air pressing down on the surface of the mercury. Changes in air temperature or humidity cause air pressure to vary. An increase in air pressure causes the mercury to rise a decrease causes the mercury to fall. 

Units of pressure The SI unit of pressure is the pascal (Pa). It is named for Blaise Pascal, a French mathematician and philosopher. The pascal is derived from the SI unit of force, the newton (N), which is derived from three SI base units the kilogram, the meter, and the second. One pascal is equal to a force of one newton per square meter 1 Pa = 1 N/m. Many fields of science still use more traditional units of pressure. For example, engineers often report pressure as pounds per square inch (psi). The pressures measured by barometers and manometers can be reported in milhmeters of mercury (mm Hg). There also is a unit called the torr, which is named to honor Torricelli. One torr is equal to one mm Hg. 

FIGURE 9.2 (a) In Torricelli s barometer, the top of the mercury in the tube is approximately 76 cm higher than that in the open beaker, (b) The mass of mercury in the column of height h exactly balances that of a column of air of the same diameter extending to the top of the atmosphere. 

The unit torr was named for Evangelista Torricelli (1608-1647), who invented the mercury barometer. 

One of the first instruments used to measure gas pressure was designed by the Italian scientist Evangelista Torricelli (1608-1647). He invented the barometer, an instrument that measures the pressure exerted by the atmosphere. His barometer was so sensitive that it showed the difference in atmospheric pressure between the top and bottom of a flight of stairs. Figure 11.4 explains how Torricelli s barometer worked. The height of the mercury column measures the pressure exerted by the atmosphere. We live at the bottom of an ocean of air. The highest pressures occur at the lowest altitudes. If you go up a mountain, atmospheric pressure decreases because the depth of air above you is less. 

One unit used to measure pressure is defined by using Torricelli s barometer. The standard atmosphere (atm) is defined as the pressure that supports a 760-mm column of mercury. This definition can be represented by the following equation. 

Propose a reason why Torricelli used mercury in his barometer rather than some other liquid such as water. 

Pascal established the final proof with his experiment du vide dans le vide , the vacuum within the vacuum (see (c) in Fig. 1.1) in 1647 the Torricelli apparatus shows no evidence of gas pressure or no special ether above the mercury level [5], Further experiments at various heights above sea level prove that the 20 km high column of air balances out a 760 mm elevation of a mercury column at sea level and by normal air pressure. This apparatus became useful for measuring air pressure, the first mercury barometer was built, and the unit of 1 mmHg got the unit 1 torr - due to the famous scientist Torricelli ... 

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