Ultrasonic Velocity in Carbon Dioxide and Ethylene in the Critical Region

Measurements of the velocity of ultrasonic waves in carbon dioxide and ethylene are presented; the velocity was obtained while the gas was allowed to follow a p—v isothermal. For carbon dioxide the pressure range is 5 to 98 atmospheres at temperatures of 28.0°, 30.0°, 31.0°, 32.0°, 33.0°, 35.0° and 38.0°C. For ethylene the pressure range is 35 to 75 atmospheres at temperatures of 9.7°, 18.7° and 23.0°C. For both gases, as pressure increases, the velocity decreases, falls to a sharp minimum, and then rises steeply on the high pressure side of this minimum. The minima have a discontinuity of slope for isothermals below the critical isothermal, which persists for a limited temperature range above the critical temperature. Above this range the curves become continuous in slope through the minimum. The curve log p vs. 1/T for the minima is linear through the critical point and, below the critical point, coincides within experimental error with standard vapor pressure data. Some calculations of ratio of specifi...