Temperature Scale

Based on zeroth law of thermodynamics, the temperature of a group of bodies can be compared by bringing a particular body (a thermometer) into contact with each of them in turn. To quantify the measurement, the instrument should have thermometric properties. These properties include: The length of a mercury column in a capillary tube, the resistance (electrical) of a wire, the pressure of a gas in a closed vessel, the emf generated at the junction of two dissimilar metal wires etc. are commonly used thermometric properties.

To assign numerical values to the thermal state of a system, it is necessary to establish a temperature scale on which temperature of a system can be read. Therefore, the temperature scale is read by assigning numerical values to certain easily reproducible states. For this purpose, it is customary to use

1. Ice Point: The equilibrium temperature of ice with air saturated water at standard atmospheric pressure which is assigned a value of 0^oC.
   
2. Steam Point: The equilibrium temperature of pure water with its own vapor at standard atmospheric pressure, which is assigned a value of 100^oC.

This scale is called the Celsius Scale named after Anders Celsius.