Calibration of thermometers

Table II, 9, A.—Reference Substances for the Calibration of Thermometers BY THE Melting Point Method...

Full experimental details for the determination of melting and boiling points are given in Sections 11,10 and 11,11 respectively. The Tables II, 9, A and II, 9, B list suitable substances for the calibration of thermometers by melting point or boiling point determinations respectively. Substances which are bracketed are alternative to each other. It need hardly be emphasised that only compounds of the highest pimity should be employed. 

Table 1 Corrected Melting Points of Compounds Suitable as Reference Materials in the Calibration of Thermometers...

Corrected melting points of compounds suitable as reference materials in the calibration of thermometers... 

Temperature °C (SI unit)3 Used in the standard uncertainty of V Certificate of calibration of thermometer used to monitor laboratory temperature... 

Calcium sulphate, as desiccant, 41, 141 Calibration curve of thermometer, 229 Calibration of thermometers, 72-75 reference substances for, by boiling point method, 74... 

Following is the procedure for calibration of thermometers intended to be used as "standards for plant control detns of sp s of TNT s a)... 

The transition temperature at which a hydrated salt liberates all or part of its water and passes into another less hydrated form is almost as definite as an ordinary melting-point, and can therefore be used as a standard for the calibration of thermometers thus the transition temperature for Glauber s salt, Na2S04.10H2O, occurs at 32 383° C., whilst that of sodium bromide, NaBr. 2H20, is at 50-674° C.3... 

In order to make corrections for errors due to construction, it is necessary to calibrate the thermometer. This is best accomplished the placing of the thermometer side by side with another thermometer already calibrated by the Bureau of Standards and then taking three to four readings over the entire scale. Another method of calibration is to compare the readings of the thermometer with the freezing or boiling points of reference compounds. Several compounds which are used for the calibration of thermometers are listed in the Appendix. 

National standard laboratories, such as the National Institute of Standards and Technology (NIST) in the United States, implement and maintain the practical temperature scale for their respective countries. They also help in the transfer of the scale by calibrating the defining standard thermometers These defining standard thermometers are costly to maintain and are primarily used in temperature calibration laboratories in industry or universities They are directly or indirectly used for calibration of thermometers used in actual applications. 

The ebullioscope of von Weber, shown in Fig. 32, operates in a similar manner. With this apparatus vapour pressure curves in the range of 10 to 760 mm Hg can be determined, whilst it can also be employed for other purposes, for instance for the calibration of thermometers, ebullioscopic measurements, the determination of vapour-liquid equilibria and the characterization of distillate fractions, such as those from petroleum and tar [33]. The apparatus consists of a vertical boiling tube A of 34 mm I.D. and 500 mm length. At its lower end the liquid is heated by an electric soldering iron element B of variable output, which is contained in a well C, the outer... 

Primary calibration of thermometers, such as the platinum resistance thermometer with well-defined and stable characteristics, is achieved by making measurements at a series of defined temperatures or fixed points and then fitting these data to an appropriate equation. These fixed points should be selected to be as close to the proposed operating temperature range as possible. A list of Primary and Secondary Fixed points is given... 

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