Alcohol Thermometer

What is an Alcohol Thermometer?

An alcohol thermometer is a thermometer which uses alcohol as thermometric fluid in the bulb. Bulb of thermometer is filled with alcohol as the temperature sensor. It utilizes the expansion and contraction of alcohol in response to change in heat to measure the temperature.

A number of different alcohols can be used, depending on the environment where the thermometer is being used. Ethanol is the most common liquid used in this type of thermometer. However, some other type of liquids are also used such as toluene, kerosene or any other suitable component depending upon the application.

Advantages of Alcohol Thermometer

Alcohol thermometers has certain advantages which makes its use wide as an alternative of mercury thermometers. It has following advantages –

  1. Mercury used in the bulb of a thermometer is hazardous, poisonous and unsafe. Unlike mercury, alcohol is less toxic and so safer to use as clinical thermometers.
  2. Alcohol evaporates more quickly than mercury. Thus it gives better reading for a very low change in temperature.
  3. It measures the temperature more precisely.
  4. This type of thermometer can measure low temperatures up to -115 \degree \ C .
  5. The expansion of alcohol is regular and linear with rise in temperature.

Disadvantages of Alcohol Thermometer

Alcohol Thermometers has following disadvantages –

  1. The maximum temperature measured by an alcohol thermometer is 78.5 \degree \ C , where as mercury thermometer can measure up to 356.7 \degree C .
  2.  Unlike mercury thermometer, it wets the walls of capillary which may bring errors in measurement.
  3. Alcohol is colorless, so it should be dyed before filling in the thermometer bulb.
  4. It is less durable because alcohol evaporates quickly.

Working principle of Alcohol Thermometer


A typical alcohol thermometer is shown in figure. It is constructed of a capillary tube and a bulb made of glass and sealed at both ends as shown in figure. The capillary tube is connected to the bulb which contains alcohol. As the alcohol is colorless, it is mixed with a dye to make it visible in the capillary tube. The most commonly used colors as dye are blue or red.

The capillary tube which is filled with a mixture of nitrogen gas and the vapor of the alcohol. The whole system i.e. capillary tube and the bulb is placed inside another glass tube which has the temperature scale marked upon outer surface.

When the bulb is immersed in the sample for measurement, the volume of the alcohol in the bulb expands. When the volume of alcohol expands, the liquid enters the capillary tube and rises. The position of the meniscus of the raised colored liquid column is read using the temperature scale marked on the glass tube.

Range of Alcohol Thermometer

At atmospheric pressure, the freezing point temperature of alcohol is -115 \degree \ C and its boiling point temperature is 78.5 \degree \ C . Hence, alcohol thermometers are used to measure temperatures from -115 \degree \ C \text {to} \ 78.5 \degree \ C .

If other type of liquid is used in the bulb, the maximum temperature that can be measured depends on the boiling point of that liquid used inside the bulb.

Difference between Alcohol and Mercury Thermometers

Alcohol thermometer and mercury thermometer are two main types of thermometers which are composed of a glass bulb and a marked glass capillary tube. The basic difference between these two types of thermometers are summarized as follows –

Sl. No.Mercury ThermometerAlcohol Thermometer
1Thermometer bulb is filled with liquid mercury.Thermometer bulb is filled with alcohol, toluene or kerosene or other liquid.
2Mercury thermometer is suitable for measurement of high temperatures.Alcohol thermometer is suitable for measurement of low temperatures.
3Mercury thermometers are used to measure temperatures from - 37 \degree \ C \text {to} \ 365 \degree \ C .Alcohol thermometers are used to measure temperatures from -115 \degree \ C \text {to} \ 78.5 \degree \ C .
4Mercury thermometers are highly durable because Mercury does not evaporate easily.Alcohol thermometers are less durable because alcohol evaporates quickly.
5Thermometer wall does not get wet by Mercury. So, correct meniscus reading is ensured.Thermometer wall get wet by alcohol. So, accuracy of meniscus reading is affected.
6Mercury used in the bulb is toxic and hazardous.Alcohol used in the bulb is non-toxic and safe.
7It is risky to use as clinical thermometer.It is safe to use as clinical thermometer.
8Mercury is bright, silver colored and easy visible. No dye is required to mix.Alcohol is clear and transparent. So a dye is added to make it visible.
9No colored background is required.Usually colored background is used for accurate reading of meniscus.

Hicks Mercury free Thermometer

Mercury is a hazardous substance. So, it is risky to be used in a clinical thermometer. It is poisonous and harmful too. It will be fatal if the thermometer bulb breaks inside mouth, and someone swallow the mercury.

So, to prevent health risks, Hicks India offers a mercury free thermometer. Instead of mercury, it contains in bulb a non-toxic substance named “Galinstan”. It is made up of an alloy of low reactive metals like Gallium, Indium, and Tin. A typical Hicks mercury free thermometer is shown in figure.


It has following features –

  1. This thermometer has all the readings and accuracy similar to that of a mercury thermometer.
  2. It has similar scale divisions to that of an usual mercury thermometer.
  3. These thermometers are eco-friendly and non-toxic. Therefore, this makes it safe for usage.
  4. The use of this device are oral, rectal and axillary.
  5. This device is durable, 100 \% accurate and hygienic.
  6. Hicks Mercury Free Thermometer comes with an enclosed glass scale. It has a magnifying case. Hence, this makes it an easy to use device.
  7. One more essential thing about this mercury-free thermometer is its usage similarity with a normal thermometer.