MISSABLE ACHIEVEMENT/TROPHY ALERT!
If you can catch the bouncing Cube before it touches the ground, you'll earn yourself the 'Schrodinger's Catch' Achievement/Trophy!
Now catch the Cube and carry it under the water to clean it up. Drop it onto the red floor switch to lower the lift that's up on the ledge behind you.
Now bounce up to the lift, turn around and place the exit portal on the ceiling directly above the Wooden Test Cube. The gel will coat the Cube again, causing it to bounce off the switch, raising the lift and allowing you to exit the chamber.