An Experimental Determination of Ultrasonic Velocity in Several Gases at Pressures Between One and One Hundred Atmospheres

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Abstract
An acoustic interferometer of the resonator or driven type has been developed for the study of the behavior of ultrasonic waves in gases under pressures ranging from vacuum to several hundred atmospheres; measurements of acoustic velocity at several frequencies and in several gases at pressures ranging from one to 100 atmospheres have been made. Increase of velocity with pressure was found for air, N2, He, and H2, a decrease for CO2, the approximate pressure and velocity ranges being respectively as follows: air, 1–101 atmos., 347–371 m/sec.; N2, 1–102 atmos., 353–380 m/sec.; CO2, 1–63 atmos., 270–198 m/sec. The He and H2 were known to be impure. For them an increase in velocity nearly linear with pressure was found. Using frequencies from 88 to 499 kc dispersion was found for CO2 at atmospheric pressure, but almost entirely disappeared above 8 atmospheres. The availability of this method for the indirect determination of specific heats is shown.