Procedure:
Stack the Mentos candies (approx. half a roll) in the test tube
Cover the opening of the test tube with an index card or similar slim, small paper.
Invert the test tube, holding the cover in place.
Place the soda bottle outside in and area that can get dirty.
Open the soda and place the index card over the bottle opening.
Pull the index card away swiftly, dropping the candies into the soda. Be prepared: the eruption happens quickly, so back up fast!
Observe the eruption—height, trajectory, duration, etc. Record your observations in a logbook.
Repeat the process, varying the opening that the soda erupts from. For example, cut the bottle top to increase the diameter an inch or more. Alternatively, dispense the soda into a vase or pitcher. Or, attach plastic piping or tubing to extend the opening’s neck. Be sure to measure the diameters for each eruption.
Observe each eruption, recording the details and compare the results