What is Density – Definition, Applications, Instruments and More
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What is Density?

Know How

Density definition, applications, instruments for measuring density and more

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What is density?

How is density measured?

What are the applications of density measurement?

Below you can find answers to your density related questions!

 

Click on the picture on the right to learn more about the principle of digital density measurement.

In a digital density meter, density is measured with a U-shaped hollow glass tube. The glass tube is put into oscillation and 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.

Download our Density Measurement Guide to learn how to measure density, specific gravity or concentration of liquids, and how to achieve accurate results while avoiding errors!

What is density?

Density is the mass of a substance per unit of volume. It is used to measure the compactness of a substance, and is commonly expressed in g/cm³, or lb/ft³.

The density of a sample is expressed with the Greek letter "ρ" (the Latin letter D can also be used) and is calculated as:

ρ = m / v

For example, if you fill 500cm³ of a sample into a glass beaker, and the mass weighs 1000g, then the density would be:

ρ = 1000g/500cm³ = 2g/cm³

What is the difference between density and mass?

Mass is a measure of how much matter there is within an object or liquid while density expresses how much mass there is per a certain amount of volume.

For example, 10kg of steel and 10kg of feathers have the same mass, but different volumes therefore they have different densities.

What are some everyday examples of density?

Helium filled balloons fly because the density of helium is lower than the density of air.

Oil floats in water because it has a lower density. This property is helpful if an oil spill happens in seawater. The fact that the oil floats makes it easier to clean up.

What is the relationship between density and temperature?

The density of a sample is very much dependent on the temperature, therefore the temperature must be recorded and controlled very precisely.

The graph below shows changes in the density of water based on the temperature it is measured at.

Usually, density is measured at a reference temperature of 20°C.

The density of water at 20°C is:

Water ρ 20= 0.99821 g/cm³

What is specific gravity?

What is density and is it the same as specific gravity?

Density and specific gravity are not the same. Specific gravity, or relative density, is the density of a sample divided by the density of a reference substance. The reference substance for liquids and solids is usually water at its densest (4°C), and for gasses, it is air at 25°C.

The density of water at 4°C is 1g/cm3 so for example, if a liquid sample has a specific gravity less than 1, which means that it is less dense than water and it will float.  If the sample has a specific gravity greater than 1 it is denser than water and it will sink in it.

Why can density be used to identify a sample?

What is density? Why can it be used to identify  sample?

Density can easily be used to identify a pure sample because each element has a unique density. After a measurement, the density of the sample in question can be looked up to see what it corresponds to.

How is the density of solutions measured?

What is density and how can it be measured in dissolved solutions?

Let's take a solution of ethanol in water as an example.

As shown before, at 20°C pure water has a density of ρ=0.9982 g/cm3, and pure ethanol has a density of ρ=0.9839 g/cm3 at 20°C. A solution of ethanol/water will have a density value which depends on the concentration of the solution.

Let's see what is the density of an ethanol/water solution with 20% ethanol concentration:

Density at 20°C

(g/cm3)

% Ethanol in Water

0.9982

0.00

0.9963

1.00

0.9945

2.00

0.9927

3.00

0.9910

4.00

0.9893

5.00

0.9878

6.00

0.9862

7.00

0.9847

8.00

0.9833

9.00

0.9819

10.00

0.9687

20.00

0.9539

30.00

0.9352

40.00

0.9139

50.00

0.8911

60.00

0.8676

70.00

0.8436

80.00

0.8180

90.00

0.7893

100.00

The density of an ethanol/water solution with 20%ethanol concentration is ρ20=0.9687 g/cm3

What is viscosity?

What is density? Are density and viscosity related?

Density and viscosity are not related. Viscosity is simply a measure of a fluids resistance to flow.

For example, honey is more viscous than saline water, but it is less dense.

The SI unit for viscosity is the pascal second (Pa·s)

Which instruments are used to measure density?

What is density and how can it be measured?

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 the 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 together 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 density of solids, using a reference liquid (water, ethanol or user defined).

Digital Density Meters are available as benchtop and handheld instruments. They use oscillation tube technology to very accurately measure the density of a sample in a short time. 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

 

What are some typical applications of density measurement?

For applications, methods, and instructions in density measurement visit our Applications Library.

 

Brix Measurement

Brix is the measurement in percentage by weight of sucrose in a pure water solution. For sugars others than sucrose it is called "apparent Brix" and is always a relative value. Brix measurements are mostly done in the food industry for quality control reasons e.g. sucrose solution in beverages. Sugar syrup intended for beverages and similar products is sold by weight and sugar content. The exact determination of Brix is therefore very important for cost and quality control. Although the designation of Brix is valid strictly for solutions which are entirely sucrose, the food industry uses the measurement to refer to any sweet solids in a product. Most often High Fructose Corn Syrup (HFCS) is measured and expressed in Brix°.

What is HFCS?

High Fructose Corn Syrup (HFCS) is a liquid sweetener that is extracted from cornstarch containing mainly fructose and D-glucose. HFCS is used to replace sucrose in beverage and food industries. HFCS is available in three different fructose levels: HFCS 42%, 55%, and 90% weight percent, and is mainly used in the USA.

Alcohol Measurement

Density measurement is a reliable method for determining alcohol content. On digital density meters, the measured density is directly converted into alcohol in Vol% with the built-in table OIML R-22 (International Organization of Legal Metrology, Recommendation 22: alcohol tables). For straight-forward measurement of distillates an accurate measurement system is required, and careful sample preparation.

Applications in Beer Production

Beer is mainly made by fermenting water, malts, and hops. During the fermentation process the major part of the malt (sugar) is converted into alcohol. During the brewing process the value of sugar concentration (called wort) is one major control parameter as this will be directly relate to the end value of alcohol concentration. For the end product, the values of sugar (original wort) and alcohol are the major control values.

Applications in Wine production

The sugar in wine juice, also called must, directly affects the alcohol concentration of the final product and therefore must be monitored in order to achieve optimal results. This monitoring of sugar content, as well the alcohol concentration in the final product, can be performed using density measurements.

Oils and Paraffins

Density is a fundamental physical property that can be used in conjunction with other properties to characterize the quality of crude oils. Therefore, it is used during the exploration process to monitor the quality during production and to establish the price in trading.

The density and derived quantities such as the specific gravity and API gravity are used worldwide to characterize liquid petroleum products and to compare their quality. Many heavy oils, lubricating oils and paraffins are highly viscous or solid at room temperature. Density meters are sometimes combined with heating devices to perform these measurements more rapidly, accurately and reproducibly.

Flavors and Fragrances

The flavor and fragrance industry produces ingredients for a wide range of products. In some cases, the fragrance is the final product (e.g. perfumes), in other cases a small amount of fragrance or flavor is added to the final product (e.g. soaps, creams, snack foods). Certain raw materials, particularly natural substances, have a high price per kg, therefore, strict quality control is essential. Techniques such as GC, GC-MS, HPLC or IR-technology are able to differentiate every single compound within a complex mixture; however, such techniques require a lot of time and highly skilled operators. Many producers therefore rely on density, among other physical values, for the quality control of raw materials, bulks, and finished products.

Battery Acid

The lead acid battery used in the automobile industry is made of plates, lead, lead oxide, and a solution of electrolyte. Specific gravity measurements are used to determine the density of the battery solution which consists of 65% water and 35% sulfuric acid. The higher the specific gravity of the battery solution, the lower the remaining charge in the battery.

Fertilizers

Nitrogen is the most important nutrient for the healthy growth of plants and is a common component of most fertilizers. Density, combined with refractometry, can be used to measure the nitrogen (N) concentration in the fertilizer solution Urea Ammonium Nitrate (UAN).

 
 
 
 
 
 
 
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