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A McLeod gauge is a scientific instrument used to measure very low pressures, down to 10 −6 Torr (0.133 mPa). It was invented in 1874 by Herbert McLeod (1841–1923). [ 1 ] McLeod gauges were once commonly found attached to equipment that operates under vacuum , such as a lyophilizer .
Thermal: Uses the changes in thermal conductivity of a gas due to density changes to measure pressure. A common example of this type is the Pirani gauge. Ionization: Measures the flow of charged gas particles (ions) which varies due to density changes to measure pressure. Common examples are the Hot and Cold Cathode gauges.
Inch of mercury (inHg and ″Hg) is a non-SI unit of measurement for pressure. It is used for barometric pressure in weather reports , refrigeration and aviation in the United States . It is the pressure exerted by a column of mercury 1 inch (25.4 mm) in height at the standard acceleration of gravity .
The parent of all mercury pressure gauges is the mercury barometer invented by Evangelista Torricelli in 1643. [15] An early engineering application of the mercury pressure gauge was to measure pressure in steam boilers during the age of steam. The first use on steam engines was by James Watt while developing the Watt steam engine between 1763 ...
Stating the molar volume of a gas without indicating the reference conditions of temperature and pressure has very little meaning and can cause confusion. The molar volume of gases around STP and at atmospheric pressure can be calculated with an accuracy that is usually sufficient by using the ideal gas law. The molar volume of any ideal gas ...
And finally, the centimetre and square centimetre are used in the normal way to measure thickness and area. The cm corresponds in the permeability equations to the thickness of the material whose permeability is being evaluated, the cm 3 STP cm −2 s −1 to the flux of gas through the material, and the cmHg to the pressure drop across the ...
Similarly, a eudiometer uses water to release gas into the eudiometer tube, converting the gas into a visible, measurable amount. A correct measurement of the pressure when performing these experiments is crucial for the calculations involved in the PV = nRT equation, because the pressure could change the density of the gas.
So, for any particular measurement of pressure head, the height of a column of water will be about [133/9.8 = 13.6] 13.6 times taller than a column of mercury would be. So if a water column meter reads "13.6 cm H 2 O ", then an equivalent measurement is "1.00 cm Hg".