Density

Density is given as mass per unit volume (e.g. grams per ml) and can be measured in a variety of ways.  The most basic method is to take a fluid and measure the weight and volume to perform a simple calculation.  Another way to determine a fluid density is to use a mud balance.  The mud balance can be “pressurized” thus reducing entrapped air and the correlating error;  It can also be “atmospheric” which is often used for cement foams, in which removing the air would give a wrong result.  For solids, a stereopycnometer is often used for granular solids.  A granular solid is placed in the “pycnometer” which is then flushed with a non-compressible gas; this correlates change in pressure with volume using the ideal gas law.  Solids of unusual shape are often measured using “Archimedes Principle” in which the solid’s buoyant ability can be used to directly measure the change in weight of water and correlated to a change in weight.  This is done by suspending the object by a thread of minimal weight in a body of water without touching the sides of the vessel.