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a device used to measure the change in volume of substances that occurs as a result of hydrostatic pressure. Piezometric measurements are used to obtain data on the compressibility, or volume elasticity, of substances and to investigate phase diagrams, phase transitions, and other physical and chemical processes.
The design of piezometers is determined by the range of pressures and temperatures to be applied, by the state of aggregation of the substance to be investigated (gaseous, liquid, or solid), and by the compressibility of the substance. There are two main types of piezometers. In those of the first type, the mass M of the substance being investigated is constant, but its volume V changes with pressure ρ and temperature T. Such piezometers are thick-walled vessels in which pressure is applied to solids, liquids, or gases in order to determine their compressibility. During the experiment, the relationship between the change in V and that in ρ is measured; the temperature of the substance is usually kept constant. In piezometers of the second type, M is a variable quantity, and the volume of the vessel containing the substance to be studied is constant. Here, an allowance must be made for any deformation in the piezometers caused by the application of pressure. Piezometers of the second type are not used in the study of liquids with high viscosity or of solids. In working with such piezometers, p is measured and each change in M is determined either by weighing or, after removal of the load, by such methods as measuring the volume of the discharged gas under standard conditions.
Plunger- or piston-type piezometers are used for determining the compressibility of liquids and solids at pressures in the high range of 108-1010 newtons per square meter (N/m2). During the process of compression, the volume V is determined by noting, either optically or with the aid of electric sensors mounted inside the vessel, the piston’s displacement; a value for ρ is arrived at by measuring the force applied to the piston or by resorting to electric sensors. In a number of cases, the substance under investigation itself serves as a pressure-transmitting medium. For the pressure range ρ ≳ 109-1010 N/m2 (10–100 kilobars), compressibility is determined by other methods, such as X-ray structural analysis. The change in the linear dimensions of bodies acted upon by hydrostatic pressure is measured by linear piezometers.
The term “piezometer” was introduced during the 1820’s in connection with the work done by the British physicist J. Perkins and by H. C. Oersted on the compressibility of liquids. At that time, the piezometer was a vessel that contained the liquid to be investigated. The open end of this vessel was immersed in mercury, which in turn was located at the bottom of a high-pressure vessel. If pressure was applied above the mercury by, for example, water or oil, the mercury would be displaced into the vessel containing the liquid under investigation. The height of the mercury’s rise, which depended both on the applied pressure and the compressibility of the liquid being studied, was recorded visually (in glass piezometers) and by using such means as measuring the resistance change in a platinum wire. Further development of piezometers during the 19th century is associated with the Russian scientists G. F. Parrot, E. Kh. Lents (H. F. E. Lenz), and D. I. Mendeleev and the French physicists E. Amagat and H. V. Regnault; in the 20th century major contributions were made by G. Tammann and the American physicists T. Richards and P. Bridgman.
In the technology of physical experiments at high pressures, the term “piezometer” sometimes denotes thick-walled, high-pressure vessels with a cylindrical channel that are not designed for measurements of compressibility. In English reference sources, the term is also applied to devices used to measure pressures found in flow systems, in the bore of artillery pieces, and at ocean depths.
REFERENCESBridgman, P. W. Fizika vysokikh davlenii. Moscow-Leningrad, 1935. (Translated from English.)
Bridgman, P. W. Noveishie raboty v oblasti vysokikh davlenii. Moscow, 1948. (Translated from English.)
Tsiklis, D. S. Tekhnika fiziko-khimicheskikh issledovanii pri vysokikh i sverkhvysokikh davleniiakh, 3rd ed. Moscow, 1965.
Kornfel’d, M. “Metody i rezul’taty issledovaniia ob”emnoi uprugosti veshchestva.” Uspekhifizicheskikh nauk, 1954, vol. 54, issue 2.
L. D. LIVSHITS