Thermometric scales Kelvin

Lord Kelvin, On an Absolute Thermometric Scale Founded on Carnot s Theory of the Motive Power of Heat, and Calculated from Regnault s Observations. Philos. Mag., 33, 313-317 (1848). Online at http //zapatopi.net/kelvin/papers/. 

All thermometers, regardless of fluid, read the same at zero and 100 if they are calibrated by the method described, but at other points the readings do not usually correspond, because fluids vary in their expansion characteristics. An arbitrary choice could be made, and for many purposes this would be entirely satisfactory. However, as will be shown, the temperature scale of the SI system, with its kelvin unit, symbol K, is based on the ideal gas as thermometric fluid. Since the definition of this scale depends on the properties of gases, detailed discussion of it is delayed until Chap. 3. We note, however, that this is an absolute scale, and depends on the concept of a lower limit of temperature. 

It will be seen in Chapter VII ( 18k) that it is possible to develop an absolute temperature scale, also independent of the nature of the thermometric substance, based on the second law of thermodynamics. This is sometimes called the Kelvin scale, in honor of its originator. Lord Kelvin (William Thomson). Actually, the thermodynamic scale can be shown to be identical with the absolute ideal gas scale, as defined above hence, temperatures on the latter, as well as the former, scale are represented by the symbol K. The ice point is consequently 273.16 K. It may be noted, incidentally, that the thermodynamic derivation of the absolute temperature scale provides a more definite interpretation of the absolute zero, i.e., the lowest limit of temperature, than is possible by means of the ideal gas thermometer. ... 

The most common method of measuring temperature is with a thermometer, which has a fluid inside that expands when heated. In the International System of Units (SI), temperature is measured on an absolute scale. The unit is called Kelvin (K), and the ideal gas is considered a thermometric fluid. A Kelvin corresponds to approximately 1.38 x 10 J per particle. Degrees Celsius are related to the Kelvin absolute scale as... 

---