Types of Thermometers: Characteristics, Functions and Uses

We know by thermometer, that instrument capable of measuring temperature, either body or environmental. Initially, they were manufactured taking advantage of the phenomenon of dilation, making the stretching of the material easily detectable at high temperatures. The most widely used substance at the time was mercury, enclosed in a glass tube with a built-in graduated scale.

The passing of the years and technological improvements have given rise to different thermometers that currently exist. The best known are:

  • The mercury thermometer, made up of a sealed glass tube containing mercury.
  • Pyrometers, which are high temperature thermometers that are used in factories, baking ovens, etc.
  • Bimetal foil thermometer: consisting of two metal foils with different coefficients of expansion.
  • Gas thermometer: they are very accurate thermometers that can be at pressure or at constant volume.
  • Resistance thermometer: formed by a metal wire whose electrical resistance changes with temperature.
  • Thermocouple: used to measure temperatures based on the electromotive force generated by heating the two-metal weld.
  • Digital thermometer: they use integrated circuits that convert the technical variations obtained into numbers.

The Evolution of the Thermometer

As we have previously commented, the basis of the thermometer’s operation is that the fluids dilate with the increase in temperature.

Prior to the use of mercury, alcohol was used, and it was Galileo Galilei, who in 1610 created a thermometer made of a glass tube that ends in a closed sphere. The open end was immersed upside down in a mixture of alcohol with water and when heating the liquid, it went up the tube until it reached the sphere depending on the temperature.

The first sealed thermometer was designed for the Grand Duke of Tuscany in 1641, which used alcohol and had degree marks, but did not use a standardized mark. It was not until 1714 that the first modern thermometer arrived at the hands of the physicist Fahrenheit, who was commissioned to create the mercury thermometer and introduce the standard temperature scale that bears his name today. This scale divides the freezing and boiling points of water by 180 degrees. Initially, the human body temperature was 100ºF, but since now it has been adjusted to 98.6ºF.

The first practical medical thermometer that was used to take a person’s temperature, appeared at the hands of the doctor, Sir Thomas Allbutt in the year 1867. This thermometer was 6 inches long and took 5 minutes to record the temperature of a patient.

The latest advance is the ear thermometer, invented by Theodore Hannes Benzinger during World War II. David Philips made a series of improvements to this latest version, turning it into an infrared ear thermometer in 1984.

The latest improvements have brought the forehead thermometer, a thermometer that projects points that facilitate remote temperature measurement with a laser beam. The emission ranges can be adjusted and they are capable of measuring from -50 to 1,000ºC. Its use is mainly private and industrial.

Mercury in the Thermometer

We know that one of the best-known models within thermometers is the mercury-type thermometer. These thermometers are used to measure both body temperature and a different material. The mercury inside them expands and contracts with changes in temperature.

This thermometer is able to measure the temperature of the air, without the result being affected by any object around it.

In 2007, these models of thermometers were banned for use due to mercury poisoning that could be caused if the object were to accidentally break. In Spain, its marketing was banned in 2009.

Mercury is a toxic material that can cause serious problems if large amounts are inhaled. Breathing this material can cause neurological and behavioral disorders, such as insomnia, memory loss, or headaches.

If you still have a mercury thermometer and it accidentally breaks, you should be aware that to clean it you have to use rubber or latex gloves and pick up the broken glass pieces carefully. When you visualize the mercury drops, use a dropper to collect them and place them on damp kitchen paper. Subsequently, store the kitchen paper in a zip lock bag and close it. Go back to the area where the thermometer has broken, and with a brush with shaving cream on top, clean the affected area to collect those drops that are not seen but are there. Once finished, put the brush in the same zip lock bag and label it correctly specifying “Contains Mercury”.