Mentos and Diet Coke Geysers II

In the interest of advancing the pursuit of scientific truth I will report on the results from the Mentos and Diet Coke investigation that I described in the last post. As I said our  control conditions were 24 oz. (700 milliliters) of Diet Coke with 5  mint Mentos introduced through a “geyser tube.” The average standard conditions were 7.8 feet with 234 mL of liquid left in the bottle. Using regular Coke or Sprite instead of Diet Coke reduced to geyser height to 5.3 and 5.1 feet respectively. Diet Coke that had been left open for 24 to 48 hours a room temperature gave an average height of 5.1 feet, but their was a large variation in the results suggesting that the Diet Coke should have been more rigorously degassed. Substituting fruity Mentos or cinnamon Mentos for mint Mentos gave geysers of 6.6 and 8.4 feet respectively. Crushing the Mentos decreased the fountain significantly – 2.0 feet. However, scraping or halving the Mentos gave heights of 5.1 and 7.5 feet respectively. Scraping Mentos gave widely varying results presumably because the scraping method was not uniform. Adding a marble on top of the Mentos gave an average of 7.6 feet. It is my personal observation that adding a weight on top of the Mentos is a good practice because it keeps the Mentos from getting stuck in a wet tube or getting forced back up into the geyser tube by the eruption. Some issues that contributed to inconsistent results were: 1) the tubes need to be screwed on securely each time, 2) the tube should be as dry as possible inside, and 3) the tube has vents in the side so that if something does obstruct the tube, the froth just shoots out the sides instead of erupting from the top.

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