As a part of preparatory work for the establishment of the new ITS-90 temperature scale, measurements of thermodynamic temperature by means of a gas thermometer without "dead space" were performed. The deviation of the NPL-75 scale from thermodynamic temperature was found to lie between zero and 0.7 mK. The value for the thermodynamic temperature of the hydrogen normal boiling point was found to be only 0.6 mK higher than that of Berry. The deviation of our scale, referenced to 273 K, from that of Steur and Durieux does not exceed 0.4 mK from 4.2 K to 27 K. Independent values of the second virial coefficient in the range 2.5 K to 27 K were found. In agreement with the results of other workers the deviations of the IPTS-68 from thermodynamic temperature were found to be - 8 mK near 20.3 K and +11 mK near 83 K. The maximal deviation of the IPTS-68 from thermodynamic temperature, viz 15 mK, was found near 150 K. This result is 4 mK higher than that of Kemp et al and lower by the same amount than was measured by the total radiation thermometer of Martin et al. The new values found for the thermodynamic temperatures of the fixed points are in good agreement with the results of other workers. The reference function W(T) for a standard platinum resistance thermometer is calculated.

New measurements of the thermal expansion of the copper used to manufacture the VNIIFTRI gas thermometer were performed and the temperature scale was corrected. The deviations of recalculated (gas) scale from the IPTS-68 scale and from the ITS-90 scale in the range 13 K to 308 K were found.

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