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# Density measurement applications

The density of liquids is an important physical parameter that plays an essential role not only in consumer protection, trade, safety and healthcare, taxation, and environmental protection but also in research and development. It is needed, for example, for the characterization of oils and fuels as well as for determination of alcohol concentration in alcoholic beverages for fiscal purposes or the determination of sugar content in non-alcoholic beverages. Knowledge of the density is also needed to quantify large amounts of liquid goods when converting a mass flow into a volume flow or vice versa.[1]

## Concentration determination

The determination of the concentration of binary solutions is one of the most important applications of density measurement. Binary solutions are mixtures of two components, such as alcohol-water solutions or sugar/water solutions. The density of a solution depends on the concentration of the dissolved substance (“solute”). If the interrelationship is known, the density of the solution can be measured and then be converted into the respective concentration.

One example of a typical application is the determination of sugar content in the soft drink industry. A soft drink is considered a sugar-water solution and by density measurement the sugar content can be determined.

Concentration determination is also possible if a mixture contains several components and only one of them varies while all other ingredients are constant.

## Material characterization

In industries like the petrochemical industry the density of a product is a very important characterization number or quality parameter. Norms including the ASTM norm define a certain density for every product, e.g. fuels, lubricating oils, or crude oils. Using density measurement these materials can be characterized and the quality of each product can be defined.

Density is also used in general as a standard parameter in professional academic research to get to know the special physical behavior of a product. In petrochemistry, scientists are used to measuring the density of gasoline at different pressures and temperatures in the laboratory to find out how it will react once injected into an engine.

## Quality control

Another important application of density measurement is quality control, not only in the soft drink or petrochemical industry, but also in the production of alcoholic beverages (beer, spirits, wine ), fuels (including biodiesel and bioethanol ), cosmetics, personal care products, pharmaceuticals, and many more .

## Filling volume control

Whereas some products are quantified by their weight, others are filled, paid, or even taxed by their volume. A well-proven procedure is to measure the weight of a fluid product with a balance, followed by calculating the filling volume by using the density of the sample. This procedure is applied wherever the measurement of volumes is not possible, e.g. in the beverage industry, petroleum industry, or chemical industry.

The filling volume of a certain sample weight can be calculated based on the sample’s apparent density:

$$V = { W \over \rho _{app}}$$

Equation 1: The filling volume V is defined as weight in air W divided by apparent density ρapp of the sample.

## Conclusion

Countless analytical methods prevail in today’s laboratories, whether at research facilities or in industry plants. Density measurement is used to specify and describe a pure substance, but also determines concentrations of binary mixtures and therefore gives information about the composition of mixtures. It is, for example, useful during quality control or helps determine the filling volume during the bottling of a product.

## References

1. H. Fehlauer and H. Wolf Density reference liquids certified by the Physikalisch-Techische Bundesanstalt Meas.Sci.Technol. 17 (2006) 2588-2592