Mercury-in-glass thermometers

The temperature of air as indicated by a dry sensing element such as a mercury-in-glass thermometer. 

Temperature is measured indirectly, by observing its effect on the properties of a substance. A mercury-in-glass thermometer takes advantage of the fact that mercury, like other substances, expands as temperature increases. When the temperature rises, the mercury in the thermometer expands up a narrow tube. The total volume of the tube is only about 2% of that of the bulb at the base. In this way, a rather small change in volume is made readily visible. 

Mercury (II) oxide, 3-4 Mercury-in-glass thermometers, 7-8 Mercury thermometers, 2 Metabolic energy, 218 Metal A substance having characteristic... 

Measuring body temperature is important for the detection of disease and assessment of the response to treatments. The first thermometer was developed by Galileo in 1603. Thermometers for measuring body temperature have been in use since about 1870. The first measurements taken were axillary, and later oral and rectal measuring methods were introduced. The working principle of those thermometers, the expansion of matter by temperature increase, is still used for body temperature measurement in mercury-in-glass thermometers. Electronic thermo-... 

For a more dense liquid, such as mercury, the relationship between l and T is linear - at least over a relatively narrow range of temperatures - so a viable mercury-in-glass thermometer may be constructed. But, because the temperature response is only linear over a narrow range of temperatures, we need to exercise... 

The boiling point temperature was maintained within 0.02°C of the selected temperature, and measured by using a mercury-in-glass thermometer. The equilibrium pressure was measured by means of a mercury-in-glass manometer, and was readable within an accuracy of 0.1 mm. 

The ordinary mercury-in-glass thermometer as covered by ISO 177014 is in such common use that it is rather badly taken for granted. In practice, much of the variability associated with testing at a set temperature can be traced to the misuse of thermometers. They should be calibrated frequently, carefully inspected for separation of the mercury, and immersed to the correct depth. The worst errors are usually found with low temperature thermometers and, hence, particular care should be taken when conditioning or testing at sub-zero temperatures. Precision thermometers are covered by ISO 653 - 65615 18 and there is a British standard for laboratory thermometers19. 

G. Temperature Determinations. In vacuum line work it is frequently necessary to measure low temperatures. While the mercury-in-glass thermometer is convenient, it does not extend below the freezing point of mercury, — 38.9°. Pentane-in-glass thermometers have a similar convenience and may be used down to about — 150°C, but they are only useful for rough work (an error of 5°C is common). For more precise determinations, a calibrated thermocouple or thermistor, or a vapor pressure thermometer, is useful. 

The most commonly used thermometers in a laboratory are alcohol-in-glass. However, mercury in-glass thermometers can be used but should be handled with great care. The mercury inside them is poisonous and should not be handled if a thermometer breaks. The units of temperature are those of the Celsius scale. This scale is based on the temperature at which water freezes and boils, that is ... 

One source of error in this method (ASTM D-3286) is in temperature measurement. If a mercury-in-glass thermometer is used, it must be calibrated accurately and consistent readings must be made. Many calorimeters are equipped with digital thermometers with thermistor probes and microprocessors to control the firing and record the temperatures at prescribed intervals. This alleviates most of the human error in recording the temperature changes. 

The Jerguson gage is immersed in a constant temperature bath with silicon fluid as the heat-transfer medium, that also thermostats the density meter. The bath temperature is controlled to . 01 K with a Thermomix 1460 temperature regulator and temperature is measured with a calibrated mercury-in-glass thermometer to within. 01 K. The lines external to the bath are maintained at the bath temperature with the help of heating tapes and temperature at several points is monitored with thermocouples. Pressure is measured with two calibrated Heise pressure indicators to within .16 bar for pressures up to 160 bar and to within .4 bar for pressures up to 350 bar. 

The clear point, also called the clear melting point, complete melting point, complete fusion point or capillary melting point, is the temperature at which a sample of fat becomes visibly completely clear, indicating the disappearance of all traces of solid fat (Rossell, 1986 Stauffer, 1996). Its measurement is specified by the American Oil Chemists Society (AOCS) Official Method Cc 1-25 (Firestone, 1998). Samples of the tempered fat contained in at least three vertical glass capillary tubes, sealed at their lower ends, are attached to a vertical mercury-in-glass thermometer such that their lower ends are level with the lower end of the thermometer s bulb. This assembly is immersed in a water bath and heated, and the... 

Liquid in Glass Thermometers. Mercury-in-glass thermometers (or better yet, mercury-in quartz) function well between -25°C and 360°C their typical precision is 0.1 K. They must be corrected for (1) relatively small pressure effects and (2) a relatively large "exposed-stem correction," due to the different coefficients of thermal expansion of mercury and glass in the part of the thermometer not immersed in the system being measured. 

The Beckmann96 mercury-in-glass thermometer is very sensitive By a change in bore of the container, it can be used to determine temperatures to a precision of 0.001 K. 

A mercury-in-glass thermometer having e 0.9 hangs in a metal building and indicates a temperature of 20°C. The walls of the building are poorly insulated and have a temperature of 5°C. The value of h for the thermometer may be taken as 8.3 W/m °C. Calculate the true air temperature. 

A mercury-in-glass thermometer is inserted in a duct to measure the temperature of an air flow stream. The thermometer indicates a temperature of 55°C and the temperature of the walls of the duct is measured with a thermocouple as 100°C. By the methods of Chap. 6 the convection heat-transfer coefficient from the thermometer to the air is calculated as 30 W/m2 °C. Calculate the temperature of the air. 

In addition to the mercury-in-glass thermometer, other temperature-sensing elements may be used for psychrometers. These include resistance thermometers, thermocouples, bimetal thermometers, and thermistors. 

Introduction.—High-temperature thermometry deals with instruments used to measure temperature in the range 100 to 550°C. This temperature range is more or less arbitrary, although the upper limit (550 C.) is fairly definite and coincides with the approximate upper limit of use of the mercury-in-glass thermometers. ... 

All thermometers must be verified against a certified thermometer before being placed into use. For example, the NIST SRM 934 is a mercury-in-glass thermometer with calibration points at 0 °C, 25 °C, 30 °C, and 37 °C. Some manufacturers supply hquid-in-glass thermometers that have ranges greater than the SRM thermometer and are verified to have been calibrated against the NIST thermometers. Details of the verification of the calibration of a thermometer have been described in a NCCLS standard. ... 

A mercury-in-glass thermometer is standardized at 0 and 100 C. The change of volume of mercury between these temperatures is represented by... 

Temperatures can be measured with mercury-in-glass thermometers. A mercury thermometer consists of a reservoir of mercury at the base of a glass tube, open to a very thin... 

Figure 1-16 At 45°C, as read on a mercury-in-glass thermometer, d equals 0.45 iQ where d is the distance from the mercury level at 0°C to the level at 100°C.

If somewhat better accuracy and/or a sensor smaller (with a shorter response time) than the mercury-in-glass thermometer is required, then an industrial-grade PRT may be used. Normally, one can expect such PRTs to have an uncertainty of 0.02°C, plus whatever statistical uncertainty is present, if the PRTs are calibrated periodically (Mangum and Evans, 1982 Connolly, 1982).Some industrial PRTs are capable of giving better results than this and some much worse (Mangum and Evans, 1982). A few can be stable and reproducible to 0.005°C, but that represents a small percentage of PRTs and they must be specially selected. 

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