HYDROMETERS

Laboratory Hydrometers

Hydrometers are instruments used to determine the density or relative density of liquids by means of flotation. Their operating principle makes it possible to take measurements easily based on the position reached by the instrument when it is immersed in a liquid sample.

For this reason, laboratory hydrometers are used in a wide range of analytical, quality control and liquid characterisation procedures. Depending on the scale incorporated and the type of instrument, they can be used to work directly with relative density or with specific scales related to the concentration and characteristics of a particular solution.

At Pobel, you can find different types of hydrometers for laboratory applications, including Baumé hydrometers and Bouyoucos hydrometers.

What is a hydrometer and what is it used for?

A hydrometer is a measuring instrument typically consisting of a glass body with a weighted lower section and a narrow stem containing a graduated scale. When placed in a liquid, it remains upright and sinks to a greater or lesser extent depending on the characteristics of the sample.

Its operation is based on Archimedes’ principle. The liquid exerts an upward buoyant force on the instrument equal to the weight of the volume of liquid displaced. As a result, the depth to which the hydrometer sinks varies according to the density of the medium in which it is floating.

This allows the user to obtain a reading directly from the instrument’s scale, provided that a model with a suitable range for the sample is used and the measurement conditions specified for that hydrometer are followed.

What does a hydrometer measure?

The quantity indicated by a hydrometer depends on the scale for which it has been manufactured. Some models are designed to measure density or relative density, while others are intended for use with specific scales employed in particular industries or analytical methods.

This means that not all hydrometers are interchangeable. Before taking a measurement, it is important to check which scale the instrument uses, its measuring range and the type of analysis for which it has been designed.

Hydrometers can be used, among other applications, for monitoring liquid solutions, checking concentrations using specific scales, or carrying out analyses in which density or particle flotation provides information about the sample.

Difference between a hydrometer and a density meter

The terms hydrometer and density meter are closely related and, in certain contexts, may both be used to refer to instruments for studying the density of a liquid. However, a density meter is a broader concept that includes different density measurement systems.

A hydrometer specifically belongs to the group of instruments that take measurements by floating directly in the liquid. The depth reached by the instrument provides the corresponding reading on its graduated scale.

Other methods for determining density operate differently. Therefore, if you specifically require instrumentation for measuring this parameter, you can also consult our range of laboratory density meters.

Types of laboratory hydrometers

There are different types of hydrometers depending on the scale used and the application for which they have been designed. The options available from Pobel include:

• Baumé hydrometers: these feature a scale in degrees Baumé, used to express the relative density of different solutions. Different scales and ranges are available, so it is important to select the appropriate model for the liquid being analysed.

• Bouyoucos hydrometers: these are mainly associated with soil analysis using sedimentation procedures. They allow readings to be taken based on the particles that remain suspended during the test.

The availability of different scales and applications makes it particularly important to check the specifications of each instrument before use.

Applications of hydrometers

Hydrometers are used in laboratories and control processes where measurements related to density or scales derived from density are required. Depending on the model selected, they can be useful in chemical, industrial, educational or research environments.

Their applications include the control of liquid solutions and mixtures, checking certain concentrations, monitoring processes in which density is used as a control parameter, and carrying out certain laboratory analyses based on sedimentation methods.

To obtain a valid measurement, it is essential that the hydrometer used is compatible both with the expected range of the sample and with the analytical method being followed.

How is a hydrometer used?

To take a measurement, the sample is placed in a container that is tall and wide enough for the instrument to float freely. The hydrometer is slowly lowered into the liquid and allowed to stabilise before the reading is taken.

Several factors should be considered during the process:

• The hydrometer must float freely, without resting against the walls or touching the bottom of the container.

• The sample must allow a clear reading and be representative of the liquid being analysed.

• Air bubbles attached to the instrument should be avoided, as they may affect its buoyancy.

• The reading should be taken once the hydrometer has stabilised.

• The reading method and meniscus criterion specified for the instrument or method being used should be followed.

Careful handling is particularly important with glass hydrometers, both to protect the instrument and to avoid affecting the measurement.

The importance of temperature in measurement

Temperature affects the density of liquids, so it must be taken into account when using a hydrometer. These instruments are manufactured and graduated according to specific reference temperature conditions.

If the sample is at a temperature different from the reference temperature used for the instrument, the result may require correction depending on the procedure followed and the level of accuracy required.

For this reason, before starting a test, it is advisable to check the reference temperature, measuring range and instructions corresponding to the selected model.

How to choose a hydrometer

When selecting a suitable laboratory hydrometer, it is not enough simply to choose any instrument designed for liquids. The specific characteristics of the analysis to be carried out must be taken into account.

The main factors to consider include:

• Type of scale: this must correspond to the quantity or method to be used.

• Measuring range: it must include the expected values of the sample.

• Graduation: this determines the resolution at which readings can be taken.

• Reference temperature: this is important for correctly interpreting the result.

• Application: certain tests require hydrometers specifically designed for that particular procedure.

Selecting these parameters correctly ensures that the analysis is performed using an instrument suited to the actual working conditions.

Frequently asked questions about hydrometers

What is a hydrometer used for?

A hydrometer is used to take measurements related to the density or relative density of a liquid by means of flotation. Depending on the scale of the instrument, it can also be used in procedures designed to determine other parameters related to the composition or concentration of a sample.

How does a hydrometer work?

The instrument floats in the liquid and reaches a specific depth depending on the density of the sample. Once it has stabilised, the result is read from the graduated scale located on the stem.

Can all hydrometers be used with the same liquids?

No. It is necessary to choose a model with a scale, range and specifications that are suitable for the liquid and the test method being used.

Why does temperature need to be taken into account?

Because the density of a liquid can change with temperature. To interpret the reading correctly, the instrument’s reference conditions and the instructions corresponding to the method being used must be taken into account.

Find the right hydrometer for your laboratory

Explore our selection of laboratory hydrometers and choose the model that best suits the range, scale and type of analysis you need to perform. If you are unsure which instrument is most suitable for your application, contact the Pobel team and we will help you find the most appropriate option for your laboratory.