Uses of Laboratory Thermometers and their Functions in Chemistry Lab

The word ‘thermometer’ includes ‘thermo’ of heat and ‘meter’ of measuring, of determining. Therefore, the thermometer is a device with which the magnitude of the vibratory energy presented by the molecules of a substance can be determined. This energy is manifested in heat and its intensity is determined by a specific value of temperature.

Laboratory thermometer. Source: Lilly_M / CC BY-SA (

The thermometer is an instrument of very frequent use in research laboratories, routine laboratories, clinical centers, the pharmaceutical industry, and food, among other areas.

The most commonly used is that of liquid in glass (upper image), which has a temperature sensor or thermometric substance, which expands or contracts with the increase or decrease in temperature. An example of this is alcohol dyed red or mercury, among others depending on the type of thermometer.

Laboratory Thermometer Features

Laboratory thermometers. Source: Polimerek / CC BY-SA (

The most widely used laboratory thermometer is the liquid-in-glass thermometer. There are several characteristics that it possesses and the following stand out:


The most commonly used laboratory thermometer is a glass tube about 30 cm long. It is triangular or round in shape, and contains the thermometric scale on its outer surface. Inside it contains the stem or capillary through which the mercury or alcohol travels.

These thermometric substances are stored at one end called the bulb. The thermometer has one end opposite the bulb, which ends in a hollow circular ring. By means of this ring, the thermometer can be held to keep it immersed during the measurement process or test.


The laboratory thermometer is characterized by its high sensitivity. A small increase in heat will cause the liquid contained in the bulb to expand, resulting in a proportional change in the length of the wire up the capillary of the thermometer.

The function of the bulb is to contain the thermometric substance. It is the part that must be in contact with the solution to be measured. Laboratory thermometers are characterized by having a fine bulb, which makes them more sensitive to changes in temperature.


With the laboratory thermometer you can determine temperatures that oscillate within a wide range: from -10 ° C to 200 or even 357 ° C approximately. The range is determined by the freezing and boiling point of the thermometric substance.

Temperature scale

The laboratory thermometer has a temperature scale or thermometric scale expressed in Fahrenheit (° F), in Celsius (° C), which is the scale most used today, or in some with the Kelvin (K) scale.

Without valve

The laboratory thermometer is characterized in that it does not have a valve or connection folds between the bulb and the stem. This valve causes the mercury or alcohol to slowly sink or return to the bulb.

Without this valve the thermometric liquid drops rapidly, providing an unreliable reading when withdrawn from the measuring substance. For this reason, the laboratory thermometer has to stay in contact with the substance to correctly measure the temperature.


They are resistant to temperature fluctuations since in their elaboration they are subjected to processes such as thermal tempering.


An electronic laboratory thermometer

Measure temperature

The fundamental use of the laboratory thermometer is to measure the temperature with high precision of different substances, whether they are in a liquid, solid or gaseous state.

There are thermometers that have alcohol dyed red inside in order to facilitate the observation of the mark that reaches the temperature. As the mercury or alcohol traverses the numerical scale in proportion to the heat it receives, the temperature can be accurately determined.

For these purposes, thermometers are used in industry, in quality control laboratories, in experimentation laboratories, or in diagnostic routines.

Measure physical properties

Laboratory thermometers are used to determine the physical properties of substances such as freezing and boiling points, among others.

Control chemical processes

The laboratory thermometer is also used in order to control and regulate at a certain temperature the development of different processes or chemical reactions, such as enzymatic determinations, for example.

It is useful to monitor experiments, to measure the temperature of different metals, to test materials, among other scientific procedures.

How is the laboratory thermometer used?

To measure the temperature, the laboratory thermometer must be placed vertically. It should not be inclined and can be partially immersed. It is recommended to immerse the thermometer at half the height of the solution at which the temperature is to be determined.

Avoid touching the walls, bottom, or base of the container with the thermometer, especially when the substances to be measured are being boiled. This is because the temperature of the walls or the bottom in general is usually higher than that of the material contained.

The bulb must be kept within the substance or material while the temperature is required to be measured. It should not be removed for the reading process as the temperature would fluctuate rapidly reflecting that of the surrounding medium.

The thermometer needs to be very clean before use. Maintenance and care are essential as all laboratory equipment, and must be calibrated to avoid errors in its use.

Usage examples

Some examples of its use are listed to finalize:

-The laboratory thermometer is used to measure the temperature in different processes of monitoring experiments, and testing materials, among others.

-It is an instrument of mandatory presence in the different research laboratories, quality control, and sample processing, among many more.

-It is used to determine the boiling point of substances, the freezing point, or to verify the temperature of solvents.

-It is required to measure the maximum and minimum temperatures of certain environments or physical spaces in which it is important to maintain sterile working conditions.

-The calibrated laboratory thermometer is used in the verification or calibration processes of another thermometer.

There are other types of more specialized thermometers, such as radiation, which is used to measure the temperature of those substances with which it is convenient not to come into contact.

The nature of the investigation will determine what type of laboratory thermometer should be used, since there are digital, and infrared thermometers, among others.

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