Gas interferometer calibration

The Rayleigh-Zeiss gas interferometer has found numerous applications in high-precision gas analysis. However, it requires preliminary calibration, and its accuracy is limited by the accuracy of the calibration, even though the precision of reading be considerably greater. This interferometer and its uses have been described in detail by Haber and Lowe, 1 L. Stuckert, L,. H. Adams, 3 and others. This type of gas interferometer measures the difference in refractivity of two samples of gas contained in two gas chambers which, in the laboratory type of apparatus, are ioo cm long. Light from an illuminated slit passes through both chambers, after which the two beams combine to produce interference fringes which are observed through an eyepiece. The optical path of the two beams can be brought to equality by tilting a glass compensator plate which is placed in the path of one of the beams. If the temperature, pressure, or composition of the gas in one of the chambers is changed, the optical paths are