[DoctorBeaver (OP)]

Why is it that when I boil eggs more bubbles rise around the eggs than anywhere else in the pot?

[daveshorts]

Unless you get water really hot it will not spontaneously boil beacuse in order to create a buble of steam you have to create a water surface, now water molecules are held together by relatively strong hydrogen bonds, so to create the bubble you have to break some of these bonds, and this takes a lot of energy.

What normally happens in a saucepan is that there is some dirt or some scratches in the pan. The water will not bond to this dirt so well as itself, so it is a lot easier to start a bubble here. This is called nucleation, and is the same reason that if you have a glass of coke and add a spoonfull of sugar to it, it fizzes like crazy.

I would guess that the egg provides extra nucleation points where the bubbles can start, so the water prefers to form steam bubbles under the egg.

Interestingly if you use a very clean container and there is nowhere for the steam to nucleate you can get water to exist at above it's boiling point, this is called superheating. This can occur when heating liquids in the microwave, and when you put the spoon in to stir it, you can trigger all the superheated water to boil at once, shooting boiling hot liquid at your face... which is nice

 This means that you can actuall

[DoctorBeaver (OP)]

Ahh, now I see. Thank you. It's been puzzling me for ages. I assume the same principle applies to boiling potatoes (incidentally, why do they congregate together?)

[daveshorts]

You will probably have a convection current with hot water going up in the middle and cold water going down the outside. this means that at the bottom of the pan there will be a current of water going into the centre of the pan. This may have something to do with it.

[DoctorBeaver (OP)]

They congregate at the side. But, yeah, it's probably to do with a current of some kind

[chris]

Dave is right.

The surface of the egg is rough (at least on the scale of a water molecule to which it looks like a mountain range) and these sharp points act as nucleation centres - points where water molecules are surrounded by (and hence hydrogen-bonded to) fewer other water molecules than elsewhere in the pan.

As Dave has suggested, this means that water molecules at these points have to pick up less energy to turn into steam - which is why the steam - bubbles - originate from these points.

In the context of the glass of fizzy drink, the bubble of gas coming out of solution finds it easier to open up a gas pocket in the water at a nucleation point for exactly the same reason.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx

[neilep]

DoctorBeaver...I think everyone here is really missing the most important fundamental point.....How were the eggs ?...and did you have soldiers with them ?

Men are the same as women.... just inside out !!

[Exodus]

quote:Originally posted by neilep

DoctorBeaver...I think everyone here is really missing the most important fundamental point.....How were the eggs ?...and did you have soldiers with them ?

Men are the same as women.... just inside out !!

i was thinking exactly the same thing... were the soldiers brown or white bread? and how do you have your yokes?

[neilep]

...and were the soldiers toasted with butter, or were they just plain ?...i hope the yokes were runny, soldiers don't like glutinous yokes.

Men are the same as women.... just inside out !!

[DoctorBeaver (OP)]

The eggs were done to perfection (soft yolk) & I had white bread soldiers with them