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Q & A: Adding a little alcohol to a barometer?

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Most recent answer: 12/23/2013
Q:
what will be the effect of adding a little alcohol in the vacuum top of a mercury barometer?
- mohammed (age 16)
port louis,Mauritius
A:

Hi Mohammed,

Adding a little amount alcohol to the top of a mercury barometer is like adding a huge amount of alcohol to the driver of an automobile.  It will completely screw up the ability of both of them to function properly.

In the barometer case the operating premise is that the atmospheric pressure must be compared to the vacuum pressure of the mercury column.   It you add the smallest amount of alcohol to the empty space of the barometer it will immediately increase the vacuum pressure that is close to the PV=nRT value of every day life. The reason is that alcohol, unlike mercury, has a large vapor presure near room temperature.

LeeH


(published on 12/23/2013)

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