Calculating Air Column Length in a Capillary Tube Using Boyle's Law

[Machodog]

Homework Statement

A uniform capillary tube (with one end sealed) contains air trapped by a mercury thread 40mm long. When the tube is placed horizontally, the length of the air column is 36 mm. When placed vertically, with the open end of the tube downwards, the length of air column is now x mm (the mercury is still 40mm).

Calculate x if the atmospheric pressure is 760 mmHg, assuming that the air obeys Boyle's law.

Homework Equations

Boyle's law, pV = constant.
density = mass/volume perhaps?

The Attempt at a Solution

I really have no clue how to start, any hints would be great.

 

[Chestermiller]

The initial pressure of the air is 760 mm Hg. When placed vertically, the air pressure is 800 mm Hg. So the new length of the air column, according to Boyle's law is $x=\frac{(760)(36)}{800}=34.2 mm$