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A Thermal Conductivity Recorder for Oxygen and Carbon Dioxide For Clinical Atmosphere Control.

1930; Volume: 27; Issue: 6 Linguagem: Inglês

10.3181/00379727-27-4860

0071-3384

Grace Lubin, Jesse G. M. Bullowa,

Biomedical and Engineering Education

Thermal conductivity instruments, which in the past 10 years have been increasingly applied in industry and in medicine, have hitherto not been available for the measurement of oxygen in air, since it was assumed that the thermal conductivity of oxygen was too close to that of nitrogen, and hence to that of air, for the practical application of the method to this type of mixture. Recent studies at Harlem Hospital have indicated, however, that the thermal conductivity instruments used to determine the carbon dioxide content of alveolar air are more sensitive to changes in oxygen concentration than has generally been assumed to be the case. Indeed, the galvanometer deflection caused by a 10% increase in oxygen concentration is about the same as that caused by a 1% decrease in carbon dioxide concentration. This observed effect is held to be consistent with the relation between the accepted thermal conductivity values for oxygen, air and carbon dioxide. These preliminary experiments showed that a thermal conductivity instrument cannot be used for carbon dioxide measurement in the presence of a varying oxygen concentration, unless the thermal cell is rendered indifferent to these variations in oxygen by passing the gas stream to be tested through both the analyzing and the standard or reference compartments of the cell, the reference mixture being freed from carbon dioxide with a suitable scrubber. The tests also suggested that the single-flow thermal cell, with normal air in the fixed reference mixture, which is used to measure carbon dioxide in air to within +0.05%, could be directly calibrated to indicate within 0.5% the concentration of oxygen in a stream of air mixture, freed from carbon dioxide. Prompt and generous cooperation on the part of Chas. Engelhard, Inc., of Newark, N. J., and especially of Dr. W. F. Hamilton, research director, resulted in the construction and calibration of a 2-cell instrument, which yields on a single chart the quasi-continuous record of the concentration of carbon dioxide on the one hand and of oxygen on the other hand.