Liquid-in-Glass Thermometers

Liquid-in-Glass Thermometers

We discuss liquid-in-glass thermometers in some detail. Commonly there are two main types of liquid-in-glass thermometers. They are

(a) Mercury-rn-glass thermometer

(b) Alcohol-in-glass thermometer

Here we give a list of main features of mercury and alcohol.

Mercury

It is a good conductor of heat. It expands uniformally on increasing its temperature and contracts on decreasing its temperature. Hence mercury is used in a liquid-in-glass thermometer

1. Freezing and boiling point

Mercury freezes at —39°C and boils at 360° C. Hence it can be used to measure a relatively long range of temperature.

2. Colour of Mercury

It has a shining silvery colour. Hence no colouring is needed to read the temperature in the thermometer.

3. Non-wetting Property

Mercury does not wet the glass surface of the thermometer tube. Hence the reading can easily taken. Since the meniscus is convex, the reading is taken at the top of the meniscus.

4. Thermal Conductivity

Since mercury has high thermal conductivity, it responds quickly to the change of temperature.

5. Thermal Expansion

Although mercury is a good conductor of heat, its thermal expansion is only one fourth of that of alcohol. Hence alcohol expands 4 times more than mercury for the same rise in temperature.