Determination of the differences between the Kelvin Thermodynamic Temperature Scale (KTTS) and the International Practical Temperature Scale of 1968 (IPTS-68) in the range from 230 "C to 660 "C has been accomplished by gas thermometry. The estimated random uncertainty of the results ranges from & 0.005 "C to frO.008 "C; the major uncertainties appear to lie in the determination of the volume of the gas bulb and the determination of its IPTS-68 temperature. The present results differ noticeably from earlier gasthermometric determinations in the range of temperature overlap. The value found for the thermodynamic temperature of the freezing point of A1 is (660.342f 0.01 5')"C.

The range oyer which thermodynamic temperatures have been realized by gas t hermometry at the NBS has been extended to 730 K. The results are preserved by measu ring the corresponding international practical temperatures. The difference b etween them is ex pressed as the foll owing polynomial : 8= -120,887.784/ T.i + 1213.53295/ T 68 -4.3159552 + 6.44075647 X 10-3 T 68 -3.56638846 X 1 0-6 T6~ which is valid in the range 273 to 730 K.The difference found and the es timated uncertainties at the t h ree defining fixed points in the range covered arc

A mercury manometer using capacitance sensing of meniscus positions has been refined to give an accuracy within 2 parts in 108 of the pressure in the range from 1 x lo4 to 1.3 x 105 N/ma. The determination of pressure ratios is accurate within 1.5 parts in 1 0 6 for pressures in the same range.

The investigation of the effects of sorption in a gas thermometer used to realize the Thermodynamic Kelvin Temperature Scale has been continued. By eliminating sorbable material more completely from the gas thermometer. we attained higher gas purity. So little contaminant re mained that further cleanup produced no significant effect on the values of thermodynamic temperatures measured between 0 °C and 142°C. The results are presented by giving the differences between the values on the thermodynamic scale and the International Practical Temperature Scale of 1968. The value of the steam point was deter· mined to be 99.970 °C(therm} with an uncertainty of ± 3.5 mK at the 99 percent confidence level (based on 3 times the estimate of the standard deviation).

Erratum: Equation (22) contains an error. It should read 100 ɛ(t, 0 °C) = 8.79 × 10 −4 t + 0.805 × 10 −7 t 2 .