Here's why:

* Volume refers to the amount of space a substance occupies. A buret is designed to measure the precise volume of a liquid being dispensed.

* Mass refers to the amount of matter in a substance. A buret doesn't directly measure mass, though you could use the volume measured and the density of the liquid to calculate its mass.

Think of it this way: a buret tells you how much liquid you have, while a scale tells you how heavy that liquid is.