An Instrument for Determining the Partial Pressure of Oxygen in a Gas

Abstract

Operation of the instrument depends upon the fact that the magnetic susceptibility of O2 is very much greater than that of any other common gas. The indication of the magnetic susceptibility of the gas in the test chamber of the meter depends upon the behavior of a small test body surrounded by the gas in an inhomogene-ous magnetic field; the force on the test body due to the magnetic field is proportional to the difference in volume magnetic susceptibility of the test body and the gas surrounding it. The test body in the meter is a small dumbbell consisting of 2 small glass spheres about 3 mm. in diam. connected by a small glass rod or tube about 4 mm. long. This dumbbell, which weighs about 2 mg., is cemented, together with a small mirror, to a silica fiber about 3 [mu] in diam. and about 10 mm. long which is stretched across a silica fork. By rotating around the silica fiber, which serves as a torsion balance, the spheres of the dumbbell may move in an inhomogeneous magnetic field which is produced by permanent magnets with suitably shaped soft iron pole pieces. The magnetic susceptibility of the gas in the chamber (with gas volume about 4 ml.) surrounding the test body may be indicated on a scale by a beam of light reflected from the small mirror.