The density of a solution can be measured manually or digitally. For more detailed information on how to measure density with pycnometers, hydrometers and digital density meters please see our 3 Ways to Measure Density guide.Manual methods like pycnometers and hydrometers are widely used for the determination of density and related values, e.g. specific gravity, alcohol%, BRIX°, API degrees, Baumé, Plato, etc. Although these methods are easy to use and quite inexpensive, they require expertise in every step of manual operation protocols, which often affects the accuracy and reliability of the results.
A pycnometer is a glass beaker of defined volume. It is weighed without the sample (M1), then filled with the sample and weighed again (M2). The difference between M1 and M2 divided by the volume of the beaker is the density of a sample.
A hydrometer is a glass body which is dipped into the sample. After a short equilibration time it will float a certain level. The higher the density of the sample, the less the hydrometer will float. The level of equilibration reads the density.
A density kit is used with a balance. A glass body of defined volume is weighed in air (M1), dipped into the sample and weighed again in the sample (M2). The difference between M1 and M2 (buoyancy) divided by the volume of the glass body is the density of the sample. A special holder can also be used to measure the density of solids using a reference liquid (water, ethanol or user defined).
Digital density meters, also known as specific gravity meters or densimeters, are available as benchtop and handheld instruments. They use oscillation tube technology to very accurately measure the density of a sample in a short timeframe. A hollow glass tube vibrates at a certain frequency. This frequency changes when the tube is filled with the sample: the higher the mass of the sample, the lower the frequency. This frequency is measured and converted to density. In addition, benchtop digital density meters use a built-in Peltier thermostat to control the temperature of the sample.
For more information on digital density meters and how they compare to manual methods, please see our comparison of different measuring techniques.