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How to make the perfect boiled egg… - Page 2

post #31 of 42
Answer to Chris -- Yes to pretty much everything. You started wandering a little when you talked about the absorptive nature of salt, but otherwise ...

The formula holds up as long as the solute can be absorbed into solution. Is that linear? Yes. When the solute precipitates out, the formula only applies to the amount still in solution. Supersaturates aren't a problem, molality includes and doesn't reject them -- so you didn't need to put them in the subset of exceptions.

Another way of thinking about it, is that you get an ~0.5* C increase in BP per mole of ions added to each kg (liter) of water. Because salt breaks up into two ions (one sodium and one chloride), you get 1* C for every mole of salt in every liter of water.

People want salt to have more of an effect on BP than it does, but there you go.

BDL
post #32 of 42
Okay. Now we know that salt raises the boiling point of water; does that mean that, all other things being equal (same size vessel, same heat source, same amount of water and salt, etc), unsalted water will boil sooner than salted water ?
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post #33 of 42
Yes, I'm pretty sure that's right.

But how much sooner? Trivially so.

I'm sure BDL can give this precisely, but if memory serves it's a question of calories, which are units of energy: 1 kCal is the amount of energy required to raise 1 liter of water by 1 degree C; these days you're supposed to use joules, and 1 kCal is 4.184 kJ. So how much energy does your rangetop put out? Well, 1 BTU is about 0.25 kcal, and the big boiler on the front right of my range at home in America is 15,000 BTU (properly BTU/hr), so that's about 3750 kCal/hr, or a hair over 1 kCal/second.

If I'm doing this math at all correctly, this means that if you add 1/3 cup of salt to 1 liter of water, and bring it to the boil over high heat, it will boil about half a second later than would the plain water.

Half a second... even bakers don't work to that level of precision!
post #34 of 42
Why salt? How does salt aid the process?
Lance
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Lance
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post #35 of 42
It doesn't. It will raise the boiling-point of the water, but by so little that you'd need a very precise scientific thermometer to tell the difference. Specifically, if I'm doing the math right, I believe it will raise the boiling-point by 1/10 of 1 degree Fahrenheit. Since you're not boiling the water rapidly, the temperature is entirely up to you anyway, and .1 degree F is trivial when compared to the imprecision of "boiling" or "room temperature." The only reason to salt boiling water is for taste, as with pasta.
post #36 of 42
That's the part that doesn't make sense to me. The eggs are boiled in their shells which are discarded before eating. Does the salted water permeate the egg shells? I tried boiling eggs in salted water and could not taste any difference compared to boilig eggs in unsalted water.
Lance
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post #37 of 42
I'd be extremely surprised if the salt could penetrate the shells. Eggshells are amazingly tough things, actually. My point is that the thing about adding salt to the water when boiling eggs is an old wives' tale. The only time it'll make any practical difference to add salt is if it will change the taste of something, as it will with pasta, and even then you have to add quite a bit of salt to be able to tell.
post #38 of 42
Thanks for the clarification. Pretty much my thinking as well.
Lance
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post #39 of 42

2 questions about salt

Two questions
- one is, isn;t the salt in the water to keep the white from coming out of any cracks that may be in the shell? I'm not sure how it would work, but that;'s what i've read many times. It wouldn;t be to salt the egg, which wouldn;t absorb enough salt, and i imagine it would remain mostly outside the membrane. Anyway, is it true that this keeps the white from leaking out if there are cracks?

- the second is a question completely unrelated to eggs, but to salt in water in general:
When making pasta sometimes, i remember just before the water boils that i forgot to put in the salt. When i do the whole thing boils up suddenly - i thought it was because maybe salt water boils at a LOWER temp, but now you say it;s at a higher temp? What's going on then? Why does it suddenly boil up furiously (i may regret this question if it involves molecules and space between them or something).
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"Siduri said, 'Gilgamesh, where are you roaming? You will never find the eternal life that you seek...Savour your food, make each of your days a delight, ... let music and dancing fill your house, love the child who holds you by the hand and give your wife pleasure in your embrace.'"
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post #40 of 42
Good questions. I've heard the thing about the white not leaking, and certainly seen the apparent "foaming up" with boiling water. I have some offhand guesses about both, but I don't actually know the answers. Anyone?
post #41 of 42
Even though salt doesn't do much to change the boiling point, it does lower the "heat capacity." That means, it requires less energy to raise each unit volume of water a unit temperature. So, water won't boil at as low a temperature, but will boil quicker. If I remember correctly, the freshman, physics for majors version of boiling is "ebulliscopic." If you were to google it, or "ebulliscopic + point" you'd probably come up with some fairly sophisticated explanations.

In theory, eggs cooked in salted water peel more easily. Salted water does coagulate egg white more efficiently than plain , but not as well as acidulated (vinegar, usually).

BDL
post #42 of 42
Rather than just edit...

It's ebullioscopic rather with an "o," rather than ebulliscopic which is just plain ignorant; and the google for "ebullioscopic constant" is a lot more interesting than for "ebullioscopic point."

Which goes to show something, but I'm not sure what other than my spelling of and memory for words scientific is not quite what my hubris thought it was; and one (another way of saying "I") probably oughtta do his own googling before recommending a particular search to others.

Oops,
BDL
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