Experiment 2: Huygens Engine
Christiaan Huygens designed a blueprint for a gunpowder-powered piston in a cylinder 300 years ago. In Huygens' design, blackpowder ignites inside the chamber and forces air out one-way valves. The resulting vacuum sucks the piston down. The design was never actually realized by Huygens.
Despite upping the amount of powder from 15 to 20 grains, they weren't able to generate vacuum power. Their seal and one-way valves weren't tight enough -- the design was a bust. It seemed unlikely to the MythBusters that the Huygens design could have been built in Huygens' time.