Published online by Cambridge University Press: 05 August 2012
There are two levels of concern with temperature in scientific experiments. One is the control of temperature to achieve some secondary (but essential) aim in the apparatus. Examples are the use of a cold trap in a vacuum line, and the use of heaters and coolants in a distillation column. For such needs, the temperature needs only to be known and kept constant to within a few kelvins. In the second case, the measurement of the dependence of physical parameters on temperature is a primary aim of the experiment. A physicist learns about the nature of a material by measuring such properties as density or heat capacity as a function of temperature. An organic chemist studies the kinetics of a chemical reaction by measuring its rate of reaction as a function of temperature. For these experiments, the temperature must be varied over a range and controlled at any point in that range, at resolutions better than 1 K.
Sometimes the temperature must be known accurately. That is, the measurement must be closely calibrated to the International Temperature Scale. Accurate measurements are necessary if the new data are to be used with other measurements on the system under study. If measurements of the density of water are to be combined with measurements of its kinematic viscosity to calculate its shear viscosity as a function of temperature, then the temperature must be measured with the same accuracy in both the density measurements and the kinematic viscosity measurements.