Difference Between Alcohol and Mercury Thermometers

Main Difference – Alcohol vs Mercury Thermometers

A thermometer is a device that is used to measure the temperature. The temperature is expressed from thermometer as a number of a particular unit. A thermometer is composed of two components: a sensor to detect temperature, and a visible scale to get the numerical value for the temperature measured. Some thermometers use a bulb filled with a chemical such as mercury as the temperature sensor. But some thermometers also use digital sensors. The visible sale is often a glass tube marked with a temperature range. Sometimes, it is a digital readout. Alcohol thermometer and mercury thermometer are two types of thermometers which are composed of a bulb and a marked glass tube. The main difference between alcohol and mercury thermometer is that the bulb of mercury thermometer is filled with mercury whereas the bulb of alcohol thermometer is filled with an alcohol.

Key Areas Covered

1. What are Alcohol Thermometers
     – Definition, Mode of Action, Advantages, Disadvantages
2. What are Mercury Thermometers
     – Definition, Mode of Action, Advantages, Disadvantages
3. What is the Difference Between Alcohol and Mercury Thermometers
     – Comparison of Key Differences

Key Terms: Alcohol, Alcohol Thermometer, Mercury, Mercury Thermometer, Sensor, Temperature, Thermometer

Difference Between Alcohol and Mercury Thermometers - Comparison Summary (1)

What are Alcohol Thermometers

Alcohol thermometer is a type of thermometer that uses a bulb filled with alcohol as the temperature sensor. The liquid inside the bulb can be pure ethanol, toluene, kerosene or any other suitable component depending on the application.

Alcohol thermometers are used to measure temperatures from -115°C to78.5°C. The maximum temperature that can be measured depends on the boiling point of the liquid inside the bulb. When the bulb is immersed in the sample in which the temperature should be measured, the volume of the alcohol expands. The bulb is connected to a sealed capillary tube which is filled with a mixture of nitrogen gas and the vapor of the alcohol. This capillary tube is made of the same glass used to make the bulb, and it is inside a glass tube which has the temperature scale marked on.  When the volume of alcohol expands, the liquid enters the capillary tube and rises. The position of the meniscus of the liquid is read using the temperature scale marked on the glass tube.

Since alcohols are colorless, they are dyed before filling the bulb. If not, the rise of the meniscus cannot be seen clearly. When the dyed alcohol rises upward the capillary tube, the position of the meniscus can be clearly located. The most commonly used colors as dye are blue or red.

Difference Between Alcohol and Mercury Thermometers - 1

Figure 1: An Alcohol Thermometer

Alcohol thermometers are used in the place of mercury thermometers considering the safety of the chemical compound. Unlike mercury in the mercury thermometer, alcohol is less toxic and evaporates quickly. But the maximum temperature measured by an alcohol thermometer is 78.5°C; hence this thermometer is suitable for measuring lower temperatures. It is a better choice to measure daytime and nighttime temperature, body temperature, etc.

Advantages of Alcohol Thermometer

  • It can measure low temperatures.
  • It measures the temperature precisely.
  • The expansion of alcohol is regular.
  • It is less toxic and less hazardous.

Disadvantages of Alcohol Thermometer

  • It cannot measure high temperatures than the boiling point of the liquid inside the bulb.
  • The capillary wall gets wet by
  • The liquid should be dyed before filling the bulb.
  • It is less durable because alcohol evaporates quickly.

What are Mercury Thermometers

Mercury thermometer is a type of thermometer that uses a bulb filled with mercury as the temperature sensor. It is also known as mercury-in-glass thermometer. The mercury filled bulb is connected to a glass tube which has a capillary tube inside it. On the surface of the glass tube, temperature scale is marked in order to get the value for a particular temperature. The space of the capillary tube (above mercury) is filled with nitrogen gas.

Difference Between Alcohol and Mercury Thermometers

Figure 2: Bulb of Mercury Thermometer

When the bulb is immersed in the sample in which the temperature should be measured, the mercury rises up the capillary tube due to the expansion of the volume as a response to the change in temperature. The position of the meniscus of the mercury on the temperature scale gives the temperature of the sample.

The temperature range that can be measured by a typical mercury thermometer is −37 to 356 °C. But if the capillary tube is filled with nitrogen gas, then the temperature range can be further increased since nitrogen is an inert gas and the pressure exerted by the gas on the mercury can increase the boiling point of mercury.

Main Difference - Alcohol vs Mercury Thermometers

Figure 3: A Mercury Thermometer

Below −37°C, mercury is a soli. Therefore, this thermometer is not suitable for such low temperatures. The boiling point of mercury is 356.7 °C, hence the maximum temperature that can be read from a mercury thermometer is 356 °C.

Advantages of Mercury Thermometer

  • It can measure high temperatures
  • Mercury is visible without any dye
  • Expansion of mercury is regular
  • Mercury does not wet the capillary tub wall
  • It gives precise results

Disadvantages of Mercury Thermometer

  • Cannot measure low temperatures
  • Hazardous if the bulb is broken and mercury leaks out
  • High price
  • Slow response

Difference Between Alcohol and Mercury Thermometers

Definition

Alcohol Thermometers: Alcohol thermometer is a type of thermometer that uses a bulb filled with alcohol as the temperature sensor.

Mercury Thermometers: Mercury thermometer is a type of thermometer that uses a bulb filled with mercury as the temperature sensor.

Liquid inside Bulb

Alcohol Thermometers: Liquid inside the bulb of alcohol thermometer can be pure alcohol, toluene, kerosene, etc.

Mercury Thermometers: Liquid inside the bulb of mercury thermometer is Mercury.

Toxicity

Alcohol Thermometers: Alcohol is less toxic.

Mercury Thermometers: Mercury is highly toxic.

Measurement

Alcohol Thermometers: Alcohol thermometer is suitable for measurement of low temperatures.

Mercury Thermometers: Mercury thermometer is suitable for measurement of high temperatures.

Temperature Range

Alcohol Thermometers: Alcohol thermometers are used to measure temperatures from -115°C to78.5°C.

Mercury Thermometers: Mercury thermometers are used to measure temperatures from −37 to 356 °C.

Durability

Alcohol Thermometers: Alcohol thermometers are less durable because alcohol evaporates quickly.

Mercury Thermometers: Mercury thermometers are highly durable because Mercury does not evaporate easily.

Wetting the Wall

Alcohol Thermometers: Alcohol thermometer wall get wet by alcohol.

Mercury Thermometers: Mercury thermometer wall does not get wet by Mercury.

Using a Dye

Alcohol Thermometers: Alcohol thermometer uses alcohols colored with a dye.

Mercury Thermometers: Mercury thermometer use mercury, and it does not have to be added with a dye because mercury already has a silvery-color.

Conclusion

Alcohol thermometer and mercury thermometer are two types of thermometers that are composed of a bulb filled with a liquid and a capillary tube connected to the bulb. When these thermometers are placed in warm solutions, they can measure the temperature of that solution using the expansion of the liquid inside the bulb through the capillary tube. The capillary tube is located inside a glass tube on which the temperature values are marked on. The main difference between alcohol and mercury thermometer is that the bulb of mercury thermometer is filled with mercury whereas the bulb of alcohol thermometer is filled with alcohol.

References:

1. “Mercury-in-Glass thermometer.” Wikipedia, Wikimedia Foundation, 12 Dec. 2017, Available here.
2. “Notions of English Disciple.” Comparison of Alcohol and Mercury Thermometer, Available here.
3. “Alcohol thermometer.” Wikipedia, Wikimedia Foundation, 22 Nov. 2017, Available here.

Image Courtesy:

1. “SpiritTherm02″ By Chemical Engineer – Own work, Public Domain) via Commons Wikimedia
2. “Mercury-thermometer” By Jurii – (CC BY 3.0) via Commons Wikimedia
3. “Rtuťový teploměr; Mediacal mercury-in-glass thermometer” by Da Sal (CC BY 2.0) via Flickr

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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