Why is mercury used in thermometer? - QS Study
QS Study

Mercury is used in thermometer because it have lot of advantages. The advantages of using mercury in a thermometer are as follows:

  • Mercury is a good conductor of heat. So mercury level indicates the temperature as quickly as possible and accurately.
  • Mercury is available in pure form.
  • Mercury is opaque and bright; so movement of mercury inside the capillary tube is easily visible.
  • Mercury does not stick to the glass surface. So it can move freely inside the capillary glass tube.
  • Expansion of mercury is uniform along the whole range of temperature. So it gives correct temperature.
  • for a small change of temperature, the expansion of mercury is quite large. Hence it is convenient to make marks on the thermometer surface.
  • The freezing point of mercury is  – 39oC and the boiling point is 357oC, So for a long span mercury remains in the liquid form.
  • Mercury is less volatile. So a small amount of mercury vapor which remains above the liquid mercury in the thermometer does not hinder the rise and fall of mercury.