Density scales, such as the Gram FD, are precision instruments used to measure the density of a material. Density is defined as the ratio of the mass of an object to the unit volume. Density scales use the concept of gravity and buoyancy to make this measurement.
The operation of a density balance is based on Archimedes’ principle, which states that a body immersed in a liquid or gas experiences a buoyant force equal to the weight of the displaced liquid or gas. The density balance requires a sample of the material whose density is to be measured and a reference substance with a known density. Typically, the sample is placed in a liquid, often referred to as the “measuring liquid.”
The density measurement works as follows:
- Sample preparation: The sample of the material is prepared so that it has a uniform shape and size. This ensures consistent measurements.
- Immersion in the measuring liquid: The sample is immersed in the measuring liquid, which is located in a container on the density scale. In the process, the sample displaces a certain amount of liquid, which creates a buoyancy force.
- Measurement of buoyancy force: The density balance measures the buoyancy force experienced by the sample. This buoyancy force is proportional to the amount of liquid displaced, which in turn depends on the density and volume of the sample.
- Measurement of the weight force: The density balance simultaneously measures the weight force of the sample. This is achieved by a precise weighing mechanism.
- Calculation of density: Measuring the weight of the sample in the air and recording the buoyancy force (weight in the air – weight in the liquid) when the density of the liquid is known, enables the density of the solid to be calculated (Archimedes’ principle).
- Reference substance: A reference substance with a known density is used to check the accuracy of the measurement and to calibrate the measuring device.
Here you can see the Gram FD in action:
