You would need 8 cubic centimeters of water to get the same mass as 1 cubic centimeter of iron. This is why the core of the earth is made of iron, and why the continents, made mostly of rock, are on the crust. The earth as a planet has a density of 5.52. This is because of the iron core. If the earth were just made of rock, its density would be close to 3.
Density is related to volume .
Whatever fits into a cubic centimeter can be given a density. If you beat the egg whites into fluffy peaks, the density of the beaten egg whites per cubic centimeter will be less than a cubic centimeter of the liquid egg whites in the bowl. The mass of the actual egg whites does not change, however. Sometimes rock coming out of a volcano is full of gas bubbles. A volcanic rock called pumice has so many bubbles in it that it will actually float on water.