Students of University Physics utilize an experimental apparatus like the one shown, except, of course, the cut-away section to aid visualization is only in the drawing. A cylinder with a d=13.13cm inner diameter and an hmax=11.81cm height is placed on a heating plate. A weighted circular disc fits snugly into the cylinder, creating a gas-tight seal; the combined mass of the disc and the weights it supports is 17.22kg. What is the purpose of the weighted circular disc in the experimental apparatus?
1) To create a gas-tight seal
2) To aid visualization
3) To measure the inner diameter of the cylinder
4) To support the heating plate