Liquid-filled thermometer

Einschluss thermometer analychem All-glass, liquid-filled thermometer, temperature range -201 to +360°C, used for laboratory test work. Tn.shlus thor.mam-... 

The measuring range with liquid-filled thermometers (mercury with a glass stem) is situated between —200 and +370°C, with an accuracy of +1% of full scale, usually less than +0.5°C [4]. 

In filled thermometers the thermal expansion of a gas or a liquid is transmitted through a thin capillary tube to a bellows or helix, where the deformation indicates the temperature. The temperature range of filled thermometers is very wide, approximately -200 to +700 °C. They are extremely robust but are not very high in accuracy. The application is mainly for process instrumentation and as stand-alone control devices. 

In liquid-filled thermal systems, mercury or various organic fills are used. In vapor-filled systems, a number of hydrocarbons, including ethane, ethyl chloride, ethyl ether, chlorobenzene, and propane, among others, are used. Nitrogen or other fully-dried and purified gases may be used in a gas thermometer. 

Liquid-in-glass thermometers used mercury or alcohol as the liquid that expands as it gets warmer. Most countries mandate the removal of any mercury-filled devices due to its extreme toxicity, but alcohol and other fillings are still used. The expansion rate is linear with temperature and can be accurately calibrated. Bimetallic thermometers bond two dissimilar metals with different coefficients of expansion to produce the bimetallic element in thermometers, temperature switches, and thermostats. Filled System Thermometers can be filled with either liquid or vapor. Liquid-filled units are the most popular although they require compensation for the weight of the liquid head and for capillary length. Vapor-filled elements cannot be used if the operating temperature crosses the vapor/liquid point. 

D Any mercury-filled thermometer will reveal the silver-gray color. Also note that mercury is a metal that is in the liquid state. 

Pressure thermometers may be sub-divided into vapor-pressure, liquid-filled and gas-filled instruments. 

For temperatures down to -200°C, organic liquids can be used as the working fluid. Thermometers filled with organic liquids, however, are not considered as reliable as mercury-filled thermometers. 

F = correction factor. For approximate work and when the liquid in the thermometer is mercury a value for F of 0.00016 is generally used. For more accurate work with mercury filled thermometers values as given in the following table are used. For thermometers filled with organic liquids it is customary to use 0.001 for the value of F. 

A(r) 200.59 density (at 20°C), 13.55 g/cm m.p., -38.8°C mercury and many of its compounds are toxic and tend to accumulate in the bodies of higher animals named for the planet Mercury, Latin hydrargyrum, liquid silver known since prehistoric times used in dental fillings, thermometers. 

The density determination may be carried out at the temperature of the laboratory. The liquid should stand for at least one hour and a thermometer placed either in the liquid (if practicable) or in its immediate vicinity. It is usually better to conduct the measurement at a temperature of 20° or 25° throughout this volume a standard temperature of 20° will be adopted. To determine the density of a liquid at 20°, a clean, corked test-tube containing about 5 ml. of toe liquid is immersed for about three-quarters of its length in a water thermostat at 20° for about 2 hours. An empty test-tube and a shallow beaker (e.g., a Baco beaker) are also supported in the thermostat so that only the rims protrude above the surface of the water the pycnometer is supported by its capillary arms on the rim of the test-tube, and the small crucible is placed in the beaker, which is covered with a clock glass. When the liquid has acquired the temperature of the thermostat, the small crucible is removed, charged with the liquid, the pycnometer rapidly filled and adjusted to the mark. With practice, the whole operation can be completed in about half a minute. The error introduced if the temperature of the laboratory differs by as much as 10° from that of the thermostat does not exceed 1 mg. if the temperature of the laboratory is adjusted so that it does not differ by more than 1-2° from 20°, the error is negligible. The weight of the empty pycnometer and also filled with distilled (preferably conductivity) water at 20° should also be determined. The density of the liquid can then be computed. 

Wells should slope downwards into the pipe, so that they can be part filled with liquid to provide better thermal contact. Where a pipe temperature is a critical factor in the operation of a system, it is usually worth fitting a permanent thermometer. 

---