The 1962 He3 scale of temperatures. I. New vapor pressure comparisons

Abstract

A comparison of He³ and He⁴ vapor pressures, (<i>P</i> ₃, <i>P</i> ₄), has been made in an apparatus designed to reduce the number and magnitude of corrections associated with the refluxing film in the He⁴ pressure sensing tube and the attached bulb. The critical pressure of He³ has been redetermined to be at 873.0 ±1.5 mm Hg at 0° C and standard gravity; the corresponding temperature as measured by a He⁴ thermometer is 3.3240±0.0018° K on the 1958 He⁴ scale. These (<i>P</i> ₃, <i>P</i> ₄) comparisons and the 1958 He⁴ scale are the basis of the 1962 He³ scale of temperatures derived and evaluated in the papers following this one. Empirical interpolation equations containing only <i>P</i> ₃ and <i>P</i> ₄ are described by means of which existing <i>P</i> ₄ measurements may be converted to an equivalent <i>P</i> ₃. A comparison has been made between this interpolation and a conversion in which the 1958 He⁴ and 1962 He³ scales are used as parameters. Deviations between the two procedures are within the estimated errors of the (<i>P</i> ₃, <i>P</i> ₄) measurements. In subsidiary experiments on techniques for He⁴ thermometry a typical vapor pressure bulb arrangement was tested. It is shown that the refluxing film introduces a heat flux, <i>Q̇</i>, and a resulting Kapitza temperature drop, Δ<i>T</i> _<i>k</i> , between the He ii and its container, which may amount to many millidegrees. The feasibility of calculating ΔT _<i>K</i> for a particular He⁴ vapor pressure bulb was studied. The necessity of measuring Δ<i>T</i> _<i>k</i> <i>/Q</i> _<i>f</i> at least once <i>in situ</i> is pointed out. In addition, it is necessary to redetermine the film flow rate periodically at the same time that He⁴ vapor pressure measurements are being made.