Density determination is an important quality parameter for raw materials and finished products. Several techniques enable accurate density measurement of solid, viscous and liquid materials such as metals, plastics, chemicals, lubricants and food.

Density for Quality Control

A change in density indicates a change in raw materials that may adversely affect the function or quality of the final product. Density measurement of raw materials can confirm material purity: if a substance is adulterated with a cheaper substitute, the measured density of the composite will differ from that of the pure material.

Density can be used to ensure homogeneity. If a manufactured part is not homogeneous, critical properties such as strength and crack resistance may be compromised. For example, a small internal air bubble may eventually cause part failure under stress. Random sampling of parts is a simple, cost-effective way to continuously monitor quality.

Why Accurate Weighing Matters

Gravimetric density determination methods commonly used in laboratories include the buoyancy method, the displacement method and the pycnometer method.

The most common buoyancy method is based on Archimedes' principle: the weight loss of an object immersed in a fluid equals the weight of the fluid it displaces. This ancient principle, dating back to around 200 BC, is still used today for accurate gravimetric density determination. Accurate density determination therefore depends heavily on accurate weight values.

Workflow of a Density Balance

Buoyancy Method – Archimedes' Principle in Practice

Archimedes' principle states that an object partially or fully immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.

The solid is first weighed in air (A) and then in an auxiliary liquid of known density (B). The density ρ of the solid is calculated as follows:

ρ = Density of the Sample

A = Mass of the Sample in Air

B = Mass of the Sample in the Auxiliary Liquid

ρ0 = Density of the Auxiliary Liquid

ρL = Density of Air

The temperature of the liquid must be taken into account, as each °C can cause a density change on the order of 0.001 to 0.1, an effect visible in the third decimal place of the result.

Scope, Advantages and Disadvantages of Density Methods

Gravimetric Method, Buoyancy

Gravimetric Method, Displacement

Gravimetric Method, Displacement

Gravimetric Method, Displacement

Standards for Density Determination

There are many standards and specifications for density determination. The most commonly used include:

Challenges in Accurate Density Determination

Air Bubbles

By far the largest source of error in density determination is the limited wettability of the sample. When the sample is immersed in liquid, all air bubbles adhering to the sample and equipment must be removed. Any residual bubble creates a buoyancy effect that distorts the density calculation. (A 1 mm bubble produces 0.5 mg of buoyancy.) We recommend:

Temperature

Solids are generally insensitive to ambient temperature changes, and the corresponding density change is negligible. When using an auxiliary liquid for density determination, however, temperature must be considered: liquids are far more affected, with density changes on the order of 0.1–1‰ per °C.

This visibly affects the accuracy of the third decimal place of the weighing result. For precise results, we recommend always accounting for the temperature of the auxiliary liquid in every density determination. Corresponding values can be found in dedicated tables. The densities of the most important reference liquids (H2O and ethanol) are stored in the balance.

Weighing

As noted above, weighing plays a key role in accurate density determination, so the balance used must meet the requirements of density applications. For small samples, the balance's minimum weight must be considered—samples below the minimum weight cannot guarantee the required accuracy.

Data Processing

Manual transcription of sample data, weight values and density calculations is time-consuming and error-prone.

VicoMeter Density Determination Solutions

VicoMeter density balances easily determine the density of solids and liquids via the buoyancy method, delivering more reliable results than other methods.

VicoMeter provides detailed step-by-step instructions that even untrained operators can follow with ease. Additional benefits include: