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