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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 .
Thereafter, research into the partial vacuum lapsed until 1850 when August Toepler invented the Toepler pump and in 1855 when Heinrich Geissler invented the mercury displacement pump, achieving a partial vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, which renewed interest in further ...
A pump of this type is capable of producing high vacuum in which the pressure is 1 mPa. [1] The Sprengel pump is a vacuum pump that uses drops of mercury falling through a small-bore capillary tube to trap air from the system to be evacuated. [Note 1] It was invented by Hanover-born chemist Hermann Sprengel in 1865 while he was working in ...
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 ...
Heinrich Geissler invented the mercury displacement pump in 1855 [10] and achieved a record vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, and this renewed interest in vacuum. This, in turn, led to the development of the vacuum tube. [11]
So, for example, pressure head might be written "742.2 mm Hg" or "4.2 in H 2 O at 59 °F" for measurements taken with mercury or water as the manometric fluid respectively. The word "gauge" or "vacuum" may be added to such a measurement to distinguish between a pressure above or below the atmospheric pressure.
This is a list of vacuum tubes or thermionic valves, ... 10–19 – Y8A 8-pin steel tube ... 5 A Half-wave mercury-vapor rectifier with a 2-pin base and an anode ...
The resistance can be set using a bridge circuit. The current required to achieve this balance is therefore a measure of the vacuum. The gauge may be used for pressures between 0.5 Torr to 1×10 −4 Torr. Below 5×10 −4 Torr, a Pirani gauge has only one significant digit of resolution. The thermal conductivity and heat capacity of the gas ...