Reason why Mecury is preferred to alcohol as thermometric liquids

Mercury is preferred to alcohol as thermometric liquids because

1. Mercury has a much greater conductivity than alcohol and expands rapidly, and thus indicates a temperature change quickly. Alcohol being a relatively poor conductor, expands slowly and thus responds to temperature changes slowly.
2. Its silvery surface makes mecury opaque, and hence it can be easily seen. Alcohol has to be coloured to be easily seen.
3. Mercury does not wet glass but alcohol because of its concave meniscus tends to cling to the walls of stem of the thermometer. This leads to an inaccurate reading when the thread is falling.
4. Mercury is not easily vaporized whereas alcohol is very easily vaporized even at low temperatures.
5. Mercury boils at 357°C while alcohol boils at 78°C. Mercury can therefore be used to measure higher temperatures than alcohol.

Alcohol has the following advantages over Mercury as a thermometric liquid:
1. It freezes at -115°C whereas Mercury freezes at -39°C. Alcohol can therefore be used for measuring very low temperatures.
2. The expansivity of alcohol is about six times that of Mercury for the same temperature rise