By observing the barometric pressure across a weather system, forecasters can determine the movement and severity of the system. Barometers can be made using a wide variety of technologies, but many are archaic and obsolete. This blog will concentrate on the most common barometer technologies in use today. A mercury barometer, also called a manometer, is a glass tube filled with mercury that is closed on one end and opened on the other. The seal on the open end is removed, which causes a portion of the mercury to flow out of the tube forming a near-vacuum at the closed end of the tube.
It is a near-vacuum because of the mercury vapor present in that portion of the tube. The remaining mercury in the tube represents the balance between the atmospheric pressure pushing on the surface of the mercury in the cistern, the weight of the mercury, and the vacuum in the tube.
This is the absolute atmospheric pressure measured in units corresponding to the height of mercury above the surface of the mercury in the cistern. A common pressure unit for barometric pressure is millimeters of mercury mmHg or inches of mercury inHg. Mercury manometers were one of the first barometers to be used and were instrumental in the discovery of principles governing the atmosphere. The accuracy of mercury barometers depends on the accuracy of the height measurement, density and vapor pressure of the mercury used.
Mercury barometers are impractical for many industrial applications and their use has diminished over time due to their size, cost, delicate nature, and toxicity of mercury. An aneroid barometer is made without the use of mercury or any other fluid. The chamber is sealed with most of the air pumped out of it. The difference in pressure between the inside of the chamber a near-vacuum and the outside causes it to expand or contract, depending on the change in atmospheric pressure. Mechanical linkages transfer this movement to a calibrated dial that shows the atmospheric pressure.
Aneroid barometers range in price and accuracy based on the manufacturer and quality. Aneroid barometers are typically used aboard ships and sailing vessels for the purpose of monitoring the weather, in homes for the same purpose, or as a novel decoration. So, we cannot replace mercury by water in the barometer. What are the factors that affect the atmospheric pressure at a place? Factors Affecting Air Pressure: Temperature: As the temperature increases, air expands because of which its density decreases which results in low pressure.
Which liquid is used in aneroid barometer? How do we measure atmospheric pressure? A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. A simple barometer consists of a long glass tube closed at one end, open at the other filled with mercury and turned upside down into a container of mercury. Why mercury is used in sphygmomanometer?
Mercury is used in blood pressure measurement in blood pressure monitors or sphygmomanometers. This means that, in comparison to water, mercury will expand less as pressure changes and a column of reasonable and portable height can be used for pressure measurements. What do you mean by pressure? Pressure is defined as the physical force exerted on an object.
The force applied is perpendicular to the surface of objects per unit area. Unit of pressure is Pascals Pa. Does Mercury have a high vapor pressure? Elemental mercury i. Hydrometers measure the specific gravity of liquids. Mercury was often used in hydrometers as a weight but research indicates that mercury hydrometers are no longer manufactured and sold as new.
However, schools and laboratories may still have mercury hydrometers in use. Non-mercury hydrometers that contain lead ballast as a weight are now used.
For more information, go to: www. Manometers measure the difference in gas pressure. Mercury manometers are generally U-shaped glass or plastic tubes containing elemental mercury with one end of the tube closed and the other open to the atmosphere. The difference in the levels of mercury in each side of the tube indicates the pressure of the gas being measured. Manometers are frequently used to measure air pressure within air ducts or compressed air lines.
Pyrometers measure the temperature of extremely hot materials and are primarily used in foundry applications. Mercury is contained in the temperature-sensing device. There still may be mercury pyrometers in use; however, research indicates that mercury pyrometers are no longer manufactured and sold as new.
New non-mercury pyrometers are either digital or optical. Psychrometers and Hygrometers are instruments used for measuring humidity. They contain two mercury thermometers - a "dry bulb," or ordinary thermometer, and a "wet bulb" thermometer, which is kept constantly wet. A sling psychrometer is a psychrometer encased in a swiveling mechanism that is swung around rapidly to record an accurate reading for relative humidity.
These devices function similarly but the names differ due to the applications in which they are used. In each device, the humidity is determined by comparing the difference in the temperatures shown by the two thermometers. Sphygmomanometers are a type of mercury manometer that is used for measuring blood pressure. Sphygmomanometers measure both maximum arterial pressure, when the heart beats and sends blood through the arteries, and minimum pressure, when the heart relaxes and fills with blood again.
Mercury is contained inside a plastic or glass tube. Strain Gauges measure forearm blood flow, or arterial inflow, using a technique called strain gauge plethysmography. Mercury is contained in a fine rubber tube, which is placed around the forearm. The gauge measures the increase in forearm circumference as pressure is applied.
These products are not common, and only one manufacturer has informed the IMERC-member states that they manufacture mercury strain gauges. Therefore, these products are included in the "other" category in Table 2. Thermohydrometers are a specific type of hydrometer that contains a mercury thermometer for measuring the temperature of liquids.
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