[kenny1999]

there is question
where there is a student directly heating the bottom part of a thermometer (does not specify if it is mercury-made)
with bunsen burner
it asks what is the dangerous of this act? actually i can't think of this.

first, i think mercury is inside the glass of thermometer, while it is a closed system so i think the mercury can't escape from the glass tube of thermometer
second, glass bulb of the thermometer should have a high melting point, so I can't think of any
dangerous situation will occur while direct heating of a thermometer under bunsen burner.

[nj_bartel]

Bunsen burner flame is WAY WAY hotter than max temperature any thermometer I've seen read.  In lab, we were actually determining melting points and someone forgot to turn the instrument off - the thermometer exploded after some time.  I'd expect similar results.

[typhoon2028]

The mercury could flash and explode the thermometer

[Sceak]

If you think of the thermometer in its constituents, you should be able to figure out the reason for this.

- You have a graduated, hollow, closed and vacuumed, glass cylinder.

- You have mercury or alcohol, which will expand or contract, depending on the temperature, within the space allotted in the glass cylinder.