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gas thermometer[¦gas thər′mäm·əd·ər]
a device for measuring temperature. Its principle of operation is based on the dependence in an ideal gas of the pressure or volume on the temperature. Constant-volume gas thermometers are used more often than constant-pressure. Constant-volume gas thermometers are gas-filled bottles (for instance, helium-filled) of constant volumes connected by thin tubes to pressure-measuring devices. In such gas thermometers, gas temperature changes in the bottle are proportional to pressure changes. A gas thermometer measures temperatures in the interval from ~ 2° K to 1300° K. The maximum attainable accuracy of a gas thermometer, depending on the temperature measured, varies from 3 × 10-3 °K to 2 × 10-2 °K. A gas thermometer of such high precision is a complicated device; the deviation of the properties of the gas filling the device from the properties of an ideal gas, the change in bottle volume with temperature changes, the presence of gas impurities and especially condensed gas impurities, gas sorption and desorption by bottle walls, gas diffusion through bottle walls, and temperature distribution along the connecting tube must be taken into account when using such a device.
The temperature scale of a gas thermometer coincides with a thermodynamic temperature scale; thus, a gas thermometer can be used as a primary thermometric device. The temperature of the fixed point (reference point) of the International Practical Temperature Scale was determined with the aid of a gas thermometer.
REFERENCEPopov, M. M. Termometriia i kalorimetriia, 2nd ed. Moscow, 1954.
D. N. ASTROV