In the bottom of a vessel with mercury there is a round hole of diameter `d = 70 mu m`. At what maximum thickness of the mercury layer will the liquid still not flow out through this hole ?

Explanation

The pressure just inside the hole will be less than the outside pressure by `4 alpha//d`. This can support a height `h` of `Hg` where
`rho gh = (4 alpha)/(d)` or `h = (4 alpha)/(rho g d)`
=`(4 xx 490 xx 10^-3)/(13.6 xx 10^3 xx 9.8 xx 70 xx 10^-6) = (200)/(13.6 xx 70) ~~ .21 m of Hg`.