When the opening of the glass tube is upward, the pressure of the air column is:

p 1 = P0+L2 = 1 14 cmhg？

When the glass tube is in a horizontal position, the air column pressure is P0.

Let the length of the air column be l and the cross-sectional area of the glass tube be s,

From Boyle's law: P 1? L 1S=PoL？ S

Substituting the data, the result is: L= 18cm.

When the opening of the glass tube is downward, some of the original mercury will flow out. Let the length of the air column be L'.

P2 = 76-(60-L') cm Hg = 16+L'

Then from Boyle's law: P 1? L 1S=P2？ L-shaped

Substituting the data, the result is: L'=30cm.

Answer: The length of the gas column is18cm; When it rotates to the horizontal position; The length of the air column in the tube is 30cm. When the opening is down.