Table of contents

Oxygen vapor pressure measurements reported in the literature have been critically evaluated and the most consistent and reliable of the data sets have been correlated with a vapor pressure equation. However, the data were first adjusted for temperature scale differences to conform with the IPTS-68 temperature scale. "Best" values for the oxygen triple point and critical point parameters were selected for use as indirect constraints in the equation. Pressures obtained from this equation are compared to corresponding values calculated from other published oxygen vapor pressure equations. A new value for the critical pressure of oxygen of 5.043₂ MN/m² (49.77₂ atm) is given.

A description is presented of the establishment of the IPTS68 from 1064.43 °C to 2200 °C on vacuum and gas-filled tungsten blackbody lamps using the NSL photoelectric pyrometer. The apparatus, experimental technique and computational methods, including a method for calculating the effective emissivity of the walls of blackbody cavity radiators, are described and the components of all significant uncertainties are stated. The total uncertainties (99% confidence limits) obtained are ±0.10 °C at 1064.43 °C and ±0.25 °C at 1627 °C for vacuum lamps, and ±0.4 °C at 1627 °C and ±1.6 °C at 2200 °C for the gas-filled lamp.

Apparatus design and procedures are described for the determination of the vapor pressures of naturally occurring neon (^natNe) and the pure isotopes ²⁰Ne and ²²Ne from their triple points (TP) to their normal boiling points (NBP). The data have been fitted to vapor-pressure equations with root-mean-square deviations of ± 2.5 to ± 4.7 N/m² (± 0.019 to ± 0.035 mmHg). The TP pressures (P) and the TP and NBP temperatures (T) were found to be:

(The temperatures are in terms of the NBS-1955 provisional temperature scale. The figures after the ± symbol indicate estimated uncertainties). The calculated vapor pressures of the isotopic ^natNe, based on Raoult's law of solution and the observed vapor pressures of the pure isotopes, are in agreement within the combined precision of the measurements with the observed values of ^natNe.

The influence of the atomic velocity distribution in cesium beam atomic frequency standards on the frequency shift due to Ramsey cavity phase difference is discussed. The atomic resonance is shifted and its shape distorted to a degree dependent not only on the exciting power level and cavity phase difference, but also on the actual velocity distribution which exists in the standard. Calculations carried out for the NRC 2.1 metre primary standard show that, for the velocity distribution which probably exists in this standard, the resonance distortion gives rise to a power dependence of the frequency shift of about an order of magnitude less than that expected for a Maxwellian velocity distribution in the beam. Experimental measurements tend to support this result.