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Thermometer- Clinical and Laboratory Thermometer

Thermometer- Clinical and Laboratory Thermometer


The device that measures temperature is the thermometer. The Greek word thermos means hot and, metron indicates measure. A tapering glass tube makes up a thermometer with a bulb at one end. Mercury (a liquid metal) is present inside the channel. It stays in a liquid state while at room temperature. A minimum alteration in the temperature can lead it to expand or contract. Heat is a form of energy, and the thermometer's primary function includes heat measurement. The mathematical depiction of heat is the temperature. The thermometer has different types according to its uses.

Heat, Temperature, and Thermometer

For temperature measurement, there are three units: Celcius (C°), Fahrenheit (F°), and Kelvin (K).

  • Celcius: °C represents degree celsius. For example, 15°C is read out as fifteen degrees celsius.
  • Fahrenheit: °F depicts degree Fahrenheit. For example, 31°F is read as thirty-one degrees Fahrenheit.
  • Kelvin: K represents kelvin. 50K represents fifty kelvin.

According to their needs, thermometers are of different types. This guide addresses two significant ones: Clinical thermometer and Laboratory thermometer.

Clinical Thermometer

Clinical thermometer

A clinical thermometer serves clinical purposes and measures human body temperature. The standard human body temperature is 37°C that might swing between 35°C and 42° C and, the mercury level determines the body temperature in °C. Considering the toxicity of mercury, digital thermometers are more in use nowadays in place of clinical ones. Note: It is compulsory to sterilize the clinical thermometer before usage to ensure a safe check- up.

How does a Clinical Thermometer Work?

The working methodology of a clinical thermometer is simple. After sterilizing, a person places the thermometer inside the patient's mouth to measure the temperature. The body heat leads the mercury inside the tube to expand and, it flows through the capillary cord at a particular level. The kink restricts the mercury flowing back after the thermometer is taken out from the patient's mouth. Bringing back the mercury at its original position requires a steady jerk for a few minutes.

Mercury Advantages and Disadvantages


  • Mercury expands immediately after coming in contact with heat since it is a good conductor of heat.
  • Even at a broad temperature range between -39°C and 357°C, the mercury can remain in the liquid state.
  • The metal is non-adhesive to glass.


Mercury is a poisonous metal. Accidentally, if the glass tube breaks during the temperature reading, the liquid can leak inside the mouth. It is the reason why most people use Digital thermometers or scanner thermometers nowadays.

Activity: Taking a Clinical Thermometer Reading

  • The first step is to clean and sterilize the thermometer.
  • Then jerk the thermometer for a few minutes to get the mercury back in place in the glass tube.
  • There are two colossal marks on the scale, note down the temperature difference between them.
  • Assume the difference to be 1°, and there are ten divisions between the marks. Hence, the tinier division equals 0.1°C.
  • Keep the thermometer into the mouth of the patient under his tongue to get the body temperature. When you take the reading, hold the thermometer vertically to your eyes. The eyes must level the top of mercury in the capillary string.

Laboratory Thermometer

Better known as a lab thermometer, this device helps measure any temperature other than the human body. It ranges between -10°C and 110°C. Laboratory thermometers primarily serve lab purposes like measuring freezing and boiling points and checking the temperature of other substances. The temperature of a solvent is also measured with a laboratory thermometer. Even weather reporters prefer using laboratory thermometers to measure the minimum and maximum temperature of a place.

Laboratory Thermometer

  • Laboratory thermometers possess a high resolution.
  • The kink is not present in these thermometers, and they are used in a constant method. Acquiring perfect results requires constant monitoring all along.
  • A Laboratory thermometer is bigger in size and measures a broad range of temperatures.

Differences between Clinical and Laboratory Thermometer

Clinical Thermometer

Laboratory Thermometer

The temperature range is between 35°C and 42°C. 

The temperature range is between -10 and 110°C. 

Serves clinical purposes and measures human body temperature. 

Serves lab purposes and measures anything other than human body temperature. 

Did you know?

The German physicist Daniel Gabriel Fahrenheit is the father of the thermometer and inventor of the modern mercury thermometer. He was a worshipper of science and inventions. Fahrenheit also invented the mercury-in-glass thermometer.


1: What are the similarities between a clinical and laboratory thermometer?
Ans: Both the thermometers comprise a narrow glass tube having mercury at the extreme point. Even, Celsius scale is also present in these thermometers.

2: What does the kink do in a clinical thermometer?
Ans: The kink prevents the mercury from flowing back to the bulb after the thermometer comes out of the patient's mouth.

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