the folks behind the fountain nowadays are young women in jeans and T-shirts, not soda jerks in white paper caps; and the tall, elegant soda glasses have given way to disposable plastic cups.

When you trigger a soda fountain dispenser, a carbon dioxide tank infuses the water coming into the machine with carbonation. Both the carbonated water and a flavored syrup combine in your cup.

Bubbles and soda will quickly shoot out of the bottle in a high fountain. The carbon dioxide molecules attach to the surfaces of the Mentos like they did in the cup of soda. All those Mentos in a lot ...