water suddenly boiling?

taken from this post on a bulletin board…

puzzled in portland
has anyone heard of such a thing?
Wed Nov 3 20:19:51 1999

I put on a pot of water to boil today at luchtime. I have a gas stove, so it usually takes about 7 or 8 minutes for water to start boiling. I put the water on the stove and went about doing other things, checking back occasionally to see if my water had started boiling yet. 5 minutes… no boiling. 10 minutes… nothing. 15 minutes later, the water is still just sitting there. Thinking this was a bit odd, I looked closer and was startled to see that although the flame was fiercly licking at the bottom of the pot, there wasn’t a trace of steam and there weren’t any little air bubbles forming beneath the water. Here’s this pot of water that has been sitting on a strong flame for 15 minutes and it looks exactly like a pot of cold water, just sitting there. I take the pot by the handle and before I can move it, half the water literally jumps straight out of the pot into the air, while the rest erupts into a mad boil. I don’t know if this sounds odd the way I’ve described it, but it was without doubt the strangest thing I have seen in my life. Can anyone explain it?


Maybe. (Disclaimer: IANAP). Hard to say for sure. But before boiling happens, one has to have nucleation sites, or some physical disturbance that can start the nucleation process. It’s possible (but rare, I think, on stoves?) to have water above its boiling temperature, but not boiling. Bumping the pan or doing something that adds nucleation sites (like maybe sprinkling some sugar into it) will then cause it to erupt in a mad boil.

I have always been under the (perhaps mistaken) impression that this happens more with microwave heating, and is extemely rare with stoves. Usually stove heating is uneven enough to set up a bunch of currents in the water that one would think sufficient to initiate boiling once the right temp is reached. But again, I am not a physicist, so take that for what it’s worth.

peas on earth

I’ve had that happen with microwaves. Put in a cup of coffee and nuke it for 3 minutes. It doesn’t boil. Put in a teaspon of sugar, or, better yet an envelope of NutriSweet and it goes bananas.

Lex Non Favet Delicatorum Votis

JBENZ, putting anything into hot water lowers the boiling point of it, thus, this is what you saw.

We used to use things called ‘boiling stones.’ Little rocks you would put in your lab mixture to get it to boil sooner. There were always those would couldn’t hear that like me, & put them in after the water was pretty hot.

As for the first post, I would assume the same thing occured. The water was indeed at the boiling temperature but he may have dropped in a tiny piece of something like dirt, causing the water to boil quickly.

sorry Handy, but this is wrong.
A nonvolatile solute elevates the boiling point of the solvent. Putting boileezers in your hot water just provided nucleation sites.

As I recall Chem 101, the instant violent boil is called “bumping”.

Last night I watched “@discovery.ca” (a Canadian science show, kind of magazine format), and they had a demo of that very thing.

Either they’re stretching coincidence a long way, or somebody there is a Doper.

Anybody got a confession to share?

Bob the Random Expert
“If we don’t have the answer, we’ll make one up.”

The correct answer is that it created nucleation sites. My question is how do I recreate this… it sounds pretty col.

“C’mon, it’s not even tomorrow yet…” - Rupert

If you need a graphic solution, http:\ alk.to\Piglet

Bantmof you are totally correct on all points. Your also right… it is very common in microwaves. I beleive the water at the point before instant eruption is “superheated”

“Boy, wouldja get a load of the cloaca on that one”? -Cecil Adams, october 8 1999