Question

What happens to the density of a given substance if you increase the amount of the substance that you have?

Answer 1

Have you ever looked up the density of a substance ?  You ought to try it.  Go ahead. Pick a substance, then go online or open up an actual book and find its density.  You will never see any particular volume mentioned along with the density . . . because it doesn't matter.  The whole idea of density is that it describes the substance, no matter how much or how little you have of it.  The density of a tiny drop of water under a microscope is the same as the density of a supertanker-ful of water.

Answer 2

The density stays the same because it's all one substance