This is a large glass bottle with a glass tube fitted to it. The tube is open at the top and the bottom and it has a piston inside it. It's a stop at the bottom to keep the piston from falling out of the tube. The first part challenging is to figure out how to get the piston to the top of the tube. There's a hole in the attached to the thing so I can just blow air into the volume and raise the piston. It's clear to see the piston makes a nice fit inside the tube and I'll just leave it to open and drop it. Now what's what happens when I lock off the end of the tube and seal off, close off the volume of air inside the apparatus. Let's see that again.