The new International Temperature Scale of 1990 (ITS-90).

A new international temperature scale, the ITS-90, will replace the International Practical Temperature Scale of 1968 (amended edition of 1975), IPTS-68(75), on 1 January 1990. Temperatures on the ITS-90 will agree more closely with thermodynamic temperatures; therefore, the ITS-90 represents a substantial improvement over the IPTS-68(75). Fortunately for the clinical laboratory community, the change in the scale will be at most only 0.05 degrees C or less in the range from 0 to 60 degrees C, but corrections in primary calibrations should be made so that the calibrations are based on the ITS-90.

Calorimetric determination of the deviation between the International Practical Temperature Scale 1968 and the Thermodynamic Temperature Scale

A flow calorimeter was constructed to measure the isobaric heat capacity cp for dilute fluids for pressure [Formula: see text] and for temperature [Formula: see text]. The special design features of the calorimeter facilitate measurements at extremely high accuracy. In this paper the measurements have been used to explore the metrology of the temperature. Measured values of cp were compared with corresponding theoretical values calculated via statistical mechanics. From the comparison, the deviation between the International Practical Temperature Scale of 1968 and the (theoretical) Thermodynamic Temperature Scale has been obtained. The results of this metrology are in good agreement with those obtained with the PVT gas thermometer and those obtained by radiometry. The comparison establishes the accuracy of the calorimeter and, more important, the feasibility of cp metrology, especially for probing local stretching or contraction of the International Practical Temperature Scale. The integration of this distortion, starting from the triple point of water, yields the deviation between the scales. It is, e.g., between 30 mK and 40 mK at the boiling point of water, according to our results.

The specific heats of copper, silver, and gold below 300 K

Specific-heat measurements on silver and gold in the 15–320 K range are reported and compared with earlier measurements on these metals. The present results together with recent measurements on copper (D. L. Martin, Rev. Sci. Instrum. 58, 639 (1987)) are analyzed in terms of the Debye temperature. The results suggest a negative anharmonic contribution to specific heat for silver and gold. Structure in the results for all three metals below 60 K is consistent with known imperfections in the International Practical Temperature Scale of 1968.

The Basis of Temperature Measurement

Measurement activity in the UK is estimated to cost about £18,000 million per annum, and yet the principles which underlie measurement processes are frequently ignored or misunderstood. In the case of temperature, one of the four or five most important parameters in industrial process control, the difficulties are compounded by the obscure nature of the quantity that is being measured. Starting with the definition of the unit, this article outlines how the temperature scale is built up and how the standards are established which form the basis of temperature measurement in the UK and internationally. Progress with improvements for the future, including the revision of the International Practical Temperature Scale, are discussed.