What Liquid is in a thermometer | Mercury or Ethanol

liquid in a thermometer

The liquid in the thermometer can be 

1- Mercury

2- Ethanol/Alcohol

1- Mercury: it’s silver in color. It is used at room temperature. The bulb is formed at the end of the thermometer which constitutes the largest part of mercury. The expansion and contraction of this mercury size are then further increased in the thin bore of the glass tube. It aids in the sensitivity of the thermometer. The area over the mercury is filled with inert gases like nitrogen. The freezing point is -38.83C and the boiling point is 356.62 C. The mercury absorbs the heat so the temperature of mercury would be the same as that of an object. The expansion of mercury is stable or linear to the changes of heat, except for the high temperature.

  • Expands easily on heating.
  • Responds quickly to temperature.
  • A high boiling point, so used in high places
  • It does not wet
  • It’s poisonous
  • Expensive
  • A high freezing point, so not used in cold places.


2- Alcohol or ethanol: the red liquid is alcohol. It is dyed red because alcohol is colorless. The freezing point of the alcohol is -115C and the boiling point is 78.5C. alcohol being a volatile substance may result in the parting of the column due to mechanical shock. It is used in the freezing region because it has a lower freezing point than mercury. Alcohol thermometer works by enclosing a narrow capillary attached to the bulb of reserve fluid. As the temperature rises it expands as the temperature drops it contracts to drop down the capillary.


They are not as accurate as mercury because alcohol evaporates. The liquid in the thermometer goes up while the thermometer is heated because heating makes the alcohol molecules of the liquid flow quicker. The greater velocity of the molecules competes for one another and causes them to move slightly. Since the molecules flow in addition, an equal amount of alcohol takes up more room inside the skinny tube of the thermometer. The liquid inside the thermometer goes down when the thermometer is cooled due to the fact cooling makes the alcohol molecules of the liquid flow more slowly.


When they move more slowly, they come closer together Since the molecules come nearer together, the same quantity of alcohol takes up much less room within the thin tube of the thermometer and goes down. simpler to look the liquid pass up and down. Since the volume of the liquid simplest increases or decreases a small amount when heated or cooled, it might be harder to peer these adjustments if the tube changed wider. The cause of the outer wider tube at the thermometer is to shield the thinner internal tube. Another cause might be to magnify the road that the pink liquid makes

  • Low freezing point -115C.
  • Safe liquid.
  • Cheap
  • Non-uniform expansion
  • Sticks to glass
  • Slow reaction to temperature changes.
  • Low boiling point 78C.


The alcohol and the mercury thermometers go up with different amounts because the molecules that make up alcohol and the atoms that makeup mercury are one of a kind. Since they’re different, their attraction is different and the manner they respond to heating and cooling are also different. So even though they each move up and down whilst heated and cooled, they do it utilizing specific amounts.

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