Ultrasonic Relaxation in Freon Vapors

From the point of view of their use in supersonic wind tunnels in which it is desired to obtain a high Mach number without great expenditure of power, the substitution of the air by vapors having a low velocity of sound is of interest. The freons (halogen‐substituted methanes) suggest themselves for this. It is shown that these vapors have ultrasonic relaxation times in the neighborhood of 10⁻⁷ sec coupled with high absorption coefficients in the ultrasonic range, a fact which may limit their usefulness in wind tunnels. The relation between relaxation times measured by other methods and by the present one are discussed.