The Phase and Group Velocity Apparatus (oscilloscope not included) uses sound waves in the ultasonic region to clearly illustrate and distinguish the often poorly understood phase and group velocity concepts. It permits precise measurements of the velocity of sound in up to three different liquids to be made using three different measurement techniques. This allows the characteristics and advantages of each material and technique to be examined and compared. The apparatus consists of a frame carrying a fixed ultrasonic transmitter and a movable receiver. The transmitter and receiver are immersed in a trough of liquid. Three troughs are supplied for testing different liquids. Distilled water, salt water, and denatured alcohol are suitable examples. A precision lead screw and scale provide for accurate positioning of the receiver. A control unit supplies a frequency-adjustable ultrasonic sine wave signal between 500kHz and 900kHz, or a series of 3µs pulses. The signals are displayed on a user-supplied dual channel oscilloscope. Any wave system displays two different propagation velocities, depending on what is being measured. The phase velocity refers to the propagation of an endless stream of identical waves, while the group velocity refers to the propagation of a wave packet or pulse. The group velocity may be higher or lower than the phase velocity, depending on the wave system and the medium. The distinction is important for transmitting information in pulses.