In this lab, I slid my body across a classroom chair and gave it a negative electric charge. This occured because electrons that reside on the chair were rubbed off on my body causing a negative electric charge. I then placed my finger inside a Faraday pail and used a charge sensor to determine how much charge it had.
When my finger was placed in the Faraday pail, the reading was consistantly around 5.1 nanocoulombs.
I believe that the purpose of the cage is to act as a shield against the postive and negative charges that may be interacting inside the enviroment in which the test occured. I could test this by sending a charge aimed at the center of the cage, and the measuring the charge that occurs inside that cage. The result would make the charge inside the cage unchanged because the cage absorbed all of it.