Science Questions

How can I boil water without killing the fish that lives in it?

Sun, 14th Jun 2009

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Neeraja Raghavan asked:

A glass jar is half filled with water. There is a live fish swimming in it. How can we boil the water that is inside the jar, without killing the fish?


Chris -   I love that question.  What is he doing?  It’s basically fish bowl…

Dave -   He’s apparently got a live fish swimming in the fish bowl and he wants to boil the water without harming the fish.

Chris -   He wants to boil the water without harming the fish.  Well, thinking about it.  I mean, what we know about the boiling point of water.  You can make water boil by raising the temperature that gives the water molecules more energy so they can escape from the body of water against the force being applied to the water surface by atmospheric pressure.  You can also make water boil at the same temperature by reducing the pressure above the water.  So, I suppose if you put the fish bowl into a very large space that he could evacuate very abruptly - so in other words, take all of the air out so the fish bowl is sitting in a vacuum, the water would boil without getting hot and therefore, wouldn’t harm the fish through heat.  The problem is all the dissolved gases would presumably boil out instantly so the fish would asphyxiate very quickly unless you did it transiently, just quickly make it boil and then stop again.  Just as a party trick to prove that this is possible.

Dave -   I guess the other problem is if the water is boiling around the fish even if its not damaging the proteins because it’s not hot. the fish is probably going to get the bends because any water or gases...

Chris -   Indeed because fishes have swim bladder, don’t they? This is how they regulate their buoyancies like a diver’s BCD, which makes them buoyant, neutral buoyancy in the water.  So, if you had a fish that has a swim bladder, it could explode.  I presume under those circumstances.

Dave -   Even if you have a little shark or something which didn’t and then it’s gonna get the bends, so it’s probably not going to be a happy fish.

Kat -   Horrible people.

Chris -   But, it may not die straight away.  So, there you go, there is the solution to your problem. 


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Neeraja Raghavan asked the Naked Scientists: Dear Naked Scientists:   A glass jar is half filled with water. There is a live fish swimming in it. How can we boil the water that is inside the jar, without killing the fish?   Regards, Neeraja.   Dr Neeraja Raghavan What do you think? Neeraja Raghavan , Wed, 10th Jun 2009

Take the fish out! Don_1, Wed, 10th Jun 2009

Presumably you mean "boil SOME OF the water"?
You could plunge a red hot iron rod in and boil some of it without frazzling the poor ol' fish.

Or do you put an insulated container with cold water in it into the glass (the other half) and put the fish in that?

Is the clue in "half"? lyner, Wed, 10th Jun 2009

Have you discovered some kind of super heat resistant fish species? Chemistry4me, Wed, 10th Jun 2009

Drop in a furuncle! Don_1, Wed, 10th Jun 2009

Boiling point depends on external pressure...
If you connect your jar's opening to a void pump, at 4.58 mm of Hg (for example) your water will boil at 0.01 °C. At greater pressure the boiling point will increase.
At ~ 17 mm Hg, the water will boil at 20°C.
lightarrow, Wed, 10th Jun 2009

Compression and decompression would have to be done slowly otherwise the fish would die from “the bends”
RD, Wed, 10th Jun 2009

A fish with a swim bladder would be in real trouble. Also, dropping the pressure until the water boiled would draw all the dissolved oxygen out of the water.
If there are fish that live near the volcanic vents at the botom of the sea they might just survive  the heat but there's still a problem with oxygen. One of the best ways to remove dissolved gases from liquids is to boil them. Bored chemist, Wed, 10th Jun 2009

I'll go along with Don_1's answer. Madidus_Scientia, Wed, 10th Jun 2009

lightarrow,  you are a clever lad!!!! lyner, Wed, 10th Jun 2009

I'm not getting into the debate on boiling fish alive just to check, so here's a related  observation.
If you wrap an ice cube in metal wire so it sinks you can put it in a narrow tube full of cold water then heat the water near the top of the tube until it boils, without melting the ice.
Water is a fairly poor conductor of heat and, with this setup there's no convection current to distribute the heat. Bored chemist, Thu, 11th Jun 2009

lightarrow, Thu, 11th Jun 2009

Which one?

I'd go with the first one myself. fishytails, Thu, 11th Jun 2009

Use a little shark, then - no swim bladder afaik. lyner, Thu, 11th Jun 2009

So it dies of anoxia rather than trauma. Bored chemist, Fri, 12th Jun 2009

Ok, what about steam distillation
but used at the reverse, that is, instead of using water to lower the boiling point of an organic liquid, use an organic liquid to lower the water's boiling point? If you use more different phases, you can add the various vapour pressures and so you lowers even more every substance' boiling point. 
lightarrow, Fri, 12th Jun 2009

Are you suggesting getting the fish pissed during the exercise?
Just to prove the point, you'd only need to do it briefly and - hell, it's only a fish! You could eat it afterwards. lyner, Fri, 12th Jun 2009

You could use inert chemicals, like perfluoropentane:
which has a boiling point of 29°C. (If you are worried for oxygen loss, you can add it to the mix). lightarrow, Sat, 13th Jun 2009

That would spoil the taste! lyner, Sat, 13th Jun 2009

  It's impossible raghavendra, Mon, 15th Jun 2009

A rather odd assertion after several of us have said how it can be done. Bored chemist, Mon, 15th Jun 2009

His arguement doesn't boil down to much in the end. Chemistry4me, Mon, 15th Jun 2009

Does Dr Neeraja Raghavan have a great secret he will be sharing with us some time? And why does he wish to boil some poor fish's life support system anyway? Don_1, Mon, 15th Jun 2009

Another solution of the problem could be this: take the fish and transfer it to another jar with water, than boil the water in the first one.   lightarrow, Mon, 15th Jun 2009

Don already said that, first reply! Madidus_Scientia, Mon, 15th Jun 2009

Gulp! Haven't even seen it!   lightarrow, Tue, 16th Jun 2009

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