Mercury barometer discussion

Question

anonymous · Answer

The tallest column of water that atmospheric pressure can support is 
10.3 m. If you try to "suck" water up an 11 m straw, it will not reach your mouth. Even if you remove all the air from the straw, a feat that you can't actually do with your mouth, atmospheric pressure will only lift the water 10.3 m up the straw.

anonymous · Answer

Guys be aware you are not sucking in water you are reducing pressure in the straw.

mrnood · Answer

|dw:1439741255687:dw|

The space above the mercury is filled with saturated mercury vapour.

the saturated vapour  pressure of mercury is very low

the open end has atmospheric pressure

to balance the pressure the mercury level is different in each tube 

the pressure difference due to the height difference is rho * g * delta h

so - as the atmospheric pressure changes - so does the delta h in the 2 sides of the  tube