A narrow vessel is preferable to a wide vessel. The ultrasonic energy is generated from the tip and is directed downward. As a sample is processed the liquid is pushed down and away in all directions. If the vessel is too wide it will not mix effectively and some sample will remain untreated at the periphery. Twice the volume in a narrow vessel takes a shorter time to process than the same volume in a wider vessel. In addition, the probe should never touch the sides or bottom of a vessel.