Thermometer correction

Tn addition to the error due to the exposed stem, ordinary chemical thermometers of low cost are subject to errors due to irregularities in the bore and sometimes the scale graduations may not be very accurate. " It is therefore essential to check the thermometer at several temperatures against the melting points of pure solids or the boiling points of pure liquids as described below. The application of an exposed stem correction will of course be unnecessary if the thermometer is calibrated in this way. A calibration curve may then be drawn upon graph " paper from the data thus obtained. Temperatures at intervals of about 20° are marked as abscissae and the corrections to be added or subtracted as ordinates the points thus obtained are then connected by a smooth curve. The thermometer correction at any temperature may be read directly from the curve. 

P° = 101.325 kPa (= 1 atm). At reduced pressures the solvent boils at Twater boils at 97°C), by certain weather conditions, or on the application of a partial vacuum. Since the boiling point is strongly pressure dependent, and since the usual determination with a mercury-inglass thermometer suspended in the vapour depends on the position of the thermometer, corrections to P° and for the thermometer stem-length have... 

Thermometer Scale Correction. An NBS thermometer was used for the adiabatic jacket and a Beckmann differential thermometer for the calorimeter water. The Beckmann thermometer was calibrated against the NBS thermometer. Corrections were made to the initial and final temperatures recorded on the Beckmann thermometer. 

Thermometer correction. The temperature which is read on the thermometric scale must be corrected because there are several errors in such determinations. One source of error arises from the construction and calibration of the thermometer. The bore of the capillary may not have the same diameter throughout further, the scale graduation and the calibration of low-priced thermometers are not very accurate. A second source of error is the method used in the common melting point apparatus. The common thermometer has been calibrated while totally immersed in a bath. In the melting-point apparatus described, only a part of the stem is immersed. The column of mercury above the oil bath has a lower temperature than that at which the thermometer was calibrated. Therefore either a thermometer calibrated by partial immersion should be used or a correction must be made for the unequal heating of the mercury in the stem of the thermometer. Although thermometers calibrated by partial immersion are available, the latter practice is the more common. 

Physical Constants of Liquids The Boiling Point and Density, Part A. "Boiling Points and Thermometer Correction"... 

Technique 13 Physical Constants of Liquids, Part A, Boiling Points and Thermometer Correction New Technique 16 Vacuum Distillation... 

A2.2.3.4 Record the ice-point readings and determine the thermometer correction at this temperature from the mean reading. If the correction is found to be higher or lower than that corresponding to a previous calibration, change the correction at all other temperatures by the same value. 

---