Apparatus for sound velocity measurements in gases up to 10 kbar: Experimental data for argon

An apparatus for the measurement of sound velocity in gases up to pressures of 10 kbar and down to temperatures of 77 K is described. Important features of the experimental setup include a specially designed ultrasonic cell with double reflectors, based on the phase comparison pulse-echo technique, and a vacuum type of cryostat using a cold finger system for temperature control. Detailed measurements on argon down to the melting line show that the method is capable of giving a precision of 0.02% for the sound velocity.