My kids have been begging me to do the Mentos and Diet Coke experiment for years. When my eldest needed two liter bottles for her Food Science class, I relented, because the bottles were needed and the soda was not. I rigged a delivery system out of a 1” PVC pipe by cutting channels on the sides for a trap door and sanding out the inside to fit over the top of the soda bottle. The “trap door” was a small plastic ruler with a hole in one end (I intended to use a popcicle stick. Where are all my popcicle sticks?) To make sure it was an experiment and not just an excuse to make a mess, I bought a bottle of Diet Sprite and a bottle of Diet Coke. We took the supplies out into the meadow and loaded the tube with Mentos, and pulled the trap door from a safe distance using a thread tied to the ruler. Fail. The trap door worked, the soda bubbled up, but there was no epic geyser. We repeated with Diet Coke. Still a fail. The video is rather off center. I really anticipated a high fountain and framed for it.

So what happened? I believe that only a couple Mentos actually made it into the bottle, and the others were stuck on the bottle lip then were pushed out of the tube by the lack luster bubble surge. In addition, the channels for the trap door acted as additional exits and reduced the pressure, resulting in a lower than expected eruption. So it really was an experiment, although a disappointing one for the kids. We’ll see if more 2 liter bottles are needed in the future, and we may even purchase a better delivery system that reduces the flow to cause a higher geyser. And find a different area for the experiment that doesn’t involve running across a chigger infested field. (By the way, Texas A&M has a great resource on chiggers here.) So itchy.