Since then, we've had a fair amount of fun showing this to our friends at parties.

[Boring scientific explanation]

The effect seems to vary quite a bit. Sometimes the geyser only goes 4 or 5 feet high, and sometimes it is much more dramatic. Our top height is maybe 12 feet. We've seen it on the web as high as 18 feet.

There are all sorts of factors that may impact the height of the geyser: the temperature of the soda, the number of Mentos, and, possibly, the type of soda.

Then, he created a wire basket.

The idea was that he could put several (3 or 4?) Mentos in the basket, and put the basket through the opening of the bottle so that it would hang the Mentos in the airspace above the actual liquid.

A loop from the basket would be fit through the hole in the lid and the lid would be fastened back down.

Then, the Mentos could be dropped into the soda with the lid on, and a much smaller opening through which everything to escape.

Ah, but the basket proved to be too small to fit many Mentos and more importantly, too big to get through the opening.

It was back to the drawing board.

It didn't take long for Rob to come up with the idea of drilling a hole in the Mentos.

This would allow us to string the Mentos like beads on a wire, instead of putting them in a basket.

We had about 2 1/4", which was enough room for five Mentos.

Most people suggest that you use thirteen Mentos for the standard experiment. This is because there are thirteen Mentos in a standard roll. It's also because there are thirteen stripes on the American flag, thirteen witches in a coven, thirteen full moons in most years and thirteen people at the Last Supper.

But we knew from painful experience that just one or two Mentos could set off a fairly good reaction, so we figured five would be plenty.

It all paid off pretty well. The fountain went up over 20 feet, maybe even 25 feet. It also lasted a lot longer than the basic experiment, which is over in a couple of seconds. Our modified fountain went for 10-15 seconds.

This picture was taken too early to get the full effect. I was anticipating the rapid evacuation that happens without the lid.

Since we still had more soda bottles and more Mentos, and since the photo of the first one had been too early, we decided to try some other modifications.

The first modification was to make the hole in the lid even smaller. We decided that our minimum diameter was the guage of the wire, so we drilled a new lid so that the wire could just pass through it.

This was significantly smaller than the hole in our first lid.

The first lid had to be able to fit a knot through it. But we figured that with this lid, we'd just drop the wire straight down the hole by hand.

We went back to a bigger hole in the lid, but forewent the trouble of putting a loop on the wire. This meant that Rob was still going to drop it in manually, and that screwing on the lid was still a two-person job.

We also went for orange soda, because we thought it would look pretty. Rob wore saftey glasses. No one knows why.

The only thing left to do was to take the entire experiment to extremes.

We got a 3 liter bottle of diet cola and went with a 1/4" hole in the lid.

Because the 3 liter bottle had a wider neck, we rigged a double string of Mentos, thereby doubling the number of places the carbon dioxide could nucleate. (see boring scientific explanation).

This created a spectacular geyser.

Good volume. Good height (20-25 feet again). And great duration. It lasted around 30 seconds with good volume for the whole time.