Emergent stem correction for liquid-in-glass thermometers

Emergent Stem Corrections for Liquid-in-Glass Thermometers 75 Ed. 

EMERGENT STEM CORRECTION FOR LIQUID-IN-GLASS THERMOMETERS... 

The accuracy attainable with a liquid-in-glass thermometer is limited by the characteristics of the thermometer itself. Instability of the thermometric liquid, nonuniformity of capillary bore, and inaccuracies in scale graduation are the important factors. Uncertainties in corrections for the emergent stem may greatly limit the accuracy of partial-immersion thermometers. Generally, partial-immersion thermometers are assigned an uncertainty of 0.3°C in their calibration, whereas total immersion thermometers may have an uncertainty as small as 0.03°C. Observer errors add to the uncertainty but with care these can usually be made relatively small. 

With aU these corrections discussed, it may be useful to practice an actual loss calculation, using the data in Table 4.2 (answer AT = 1.3710 K). If the temperature is measured with a calorimetric mercury-in-glass thermometer, an emergent stem correction becomes necessary if the thermometer extended out of the bath liquid. This emergent stem correction can be made as the last correction for the calculated AT, using the equation derived in Fig. 4.4. 

The most frequently encountered source of error when using liquid-in-glass thermometers is the misuse or complete neglect of the emergent-stem correction. This correction derives from the use of the thermometer with a portion of the stem exposed to a different temperature from that of calibration. A common example is the use of partial immersion of a thermometer calibrated for total immersion. For detailed information on this correction, see the American Society of Mechanical Engineers Power Test Codes Temperature Measurement. 

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