The cork will already be wrapped in copper wire and will be soaking in water.  As the cork will be wetted it will not trap air in your eudiometer tube.  Overfill your eudiometer tube until a slight reverse meniscus formed by the surface tension of water is observed.

This lab is very straightforward if you pay attention to the unknown metal you are using and the reaction conditions assigned to your unknown.  If you use cold water and dilute acid for an unknown requiring hot water and concentrated acid you will not finish in time.   The literature in the text is an excellent source for both your discussion and how to accomplish the calculations.

You will perform two runs using a metal ribbon (magnesium) prepared as you did for Exp. 17.
Calculate the Molar Volume of a gas using the data collected from these first two runs.
 

You will be assigned an unknown metal and perform two runs on the unknown.
Calculate the Atomic weight of the unknown metal using the data from the second two runs.