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What is thermometry?

Thermometry The branch of heat relating to the measurement of the temperature of a body is called thermometry. The thermometer is an instrument used to measure the temperature of a body. The essential requisites of a thermometer are given as under:  1) Construction, 2) Calibration, and 3) Sensitiveness. For the construction of a thermometer, the proper choice of a substance, whose physical property varies uniformly with rising in temperature, is essential. 1) Construction The physical property of a substance plays an important role in the construction of a thermometer. In a mercury thermometer, the principle of expansion of mercury with rising temperature is used. The platinum resistance thermometer is based on the principle of the change in resistance with a change in temperature. The gas thermometer is based on the principle of change in volume or pressure with a change in temperature. 2) Calibration  When a thermometer is constructed, it should be properly calibrated. The standa

Liquids which are miscible

If miscible liquids are to be separated, then this can be done by fractional distillation. The apparatus
used for this process is shown in the photo and diagram in Figure, and could be used to separate a mixture of ethanol and water. 

Fractional distillation relies upon the liquids having different boiling points. When ethanol and
the water mixture is heated the vapours of ethanol and water boil off at different temperatures and can be condensed and collected separately. 
Ethanol boils at 78 °C whereas water boils at 100 °C. When the mixture is heated the vapour produced is mainly ethanol with some steam. Because water has a higher boiling point of the
two, it condenses out from the mixture with ethanol. This is what takes place in the fractionating column.
The water condenses and drips back into the flask while the ethanol vapour moves up the column and into the condenser, where it condenses into liquid ethanol and is collected in the receiving flask as the distillate. When all the ethanol has distilled over, the temperature reading on the thermometer rises



steadily to 100 °C, showing that the steam is now entering the condenser. At this point, the receiver can be changed and the condensing water can now be collected.


Fractional distillation is used to separate miscible liquids such as those in crude oil, and the technique can also separate individual gases, such as nitrogen, from the mixture we call air.



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