QI, the BBC show about comedians coming to grips with trivia that's even funnier than they are, has added a regular science installment. This means we get to watch everyone's favorite Harry Potter audiobook narrator make a bargain-basement lava lamp.
Three parts vegetable oil, one part water, a little food coloring, some alka-seltzer and an empty tennis ball tube is all it takes to make yourself a cheap lava lamp. Getting four comedians to come over and intentionally try to screw it all up will probably cost you a little more. Also they will heckle you while you tell them what to do.
Stephen Fry is always entertaining but my favorite part of the piece is David Mitchell, who says exactly what I was thinking from the moment Fry puts a lid on the top of the tube, trapping the gases inside: "Won't it explode now?"
According to an outline of the experiment, yes, it most certainly will explode if too much alka-seltzer liberates too much gas, and if the lid is sealed. It should at least blow the lid off. That doesn't happen on camera — but fortunately we have another disaster to entertain us at the end.