If you want to run a tube with 10 mL of liquid, put another tube with 10 mL of water in the opposing hole on the rotor (see photo, below). If the liquid has a higher or lower density than water, you must balance the tubes by mass, not volume. The total mass of each tube should be as close as possible this becomes increasingly important at very high rotor speeds. Running a centrifuge with unbalanced load could permanently damage the centrifuge. It could also cause injury to you or someone else.