Gravimetric Buoyancy

VWR Analytical Balance
Mass Range: 10mg - 160g
Precision: 0.1mg (0.0001g)

The VWR Balances provide maximum weighing performance and are used for the accurate weighing of samples and precipitates. They are designed to measure small masses in the sub-milligram range. They are useful for determining density via the Archimedes method and can be used to take measurements over time.  For example, it could be used to measure the rate at which a liquid evaporates.

Archimedes Method

The Archimedes method is used to determine the density of samples without needing to measure the sample’s physical dimensions. The difference in mass between the dry and submerged samples (in g) is equal to the volume of water displaced by the submerged sample (in mL or cm^3) because water has a density of 1gm. The density of the sample can then be found by taking the dry mass and dividing it by this volume. This method should only be used with samples that will not dissolve in water, as it will not work properly with water-soluble samples.

<math> \rho = \frac{m_d}{V} \frac{m_d}{m_d-m_w}

Take the dry mass of the sample and divide it by the difference between the dry and wet masses of the sample to get the sample’s density

Dry Mass)(Dry Mass - Wet Mass)= Sample density (g/cm^3)

If a solvent other than water is used, or you need to take very precise density measurements based on liquid temperature, the formula becomes:

[(Dry Mass)(Dry Mass - Wet Mass)] * Solvent Density