Getting water to zero degrees celsius

[cmsapms]

Say you've just had a cook's temperature probe delivered and you want to find its accuracy. Using items normally available in the average (non-scientist's) kitchen, how would you check the accuracy at zero degrees celsius?

Initially, I thought of ice cubes from the freezer, but these could easily be several degrees cooler than zero.

If ice cubes were left in a glass, would the melt water be at zero just as the last of the ice disappeared.

I'm stumped . Over to the PH eggheads...

[The Nur]

Put salt in it?

eta: I may have demonstrated how retarded I am with this post.

[Simpo Two]

Hmmm....

...

..

.


Conclusion: I'd buy an accurate thermometer

[Odie]

You will need a mixture of ice and water to get 0 degree's C.


http://www.canadacutlery.ca/download/calibrate-a-t...

[prand]

Why not test it at 100C instead? boil a pan of water with the thermometer dipped in it shouldn't get hotter than 100.

Your fridge/frezer might have a temperature setting?

Or try the oven at a set temperature?

[cmsapms]

The Nur said:

Put salt in it?

Salt, you say? How much?

The Nur said:

eta: I may have demonstrated how retarded I am with this post.

I keep seeing the words "heat", "latent" and "fusion". But all that was 30 odd years ago.

[The Nur]

cmsapms said:

The Nur said:

Put salt in it?

Salt, you say? How much?

The Nur said:

eta: I may have demonstrated how retarded I am with this post.

I keep seeing the words "heat", "latent" and "fusion". But all that was 30 odd years ago.

*puts foot out on limb, hears it creak*

Now, bearing in mind I didn't read the question properly and only realised this after posting my reply..

I was thinking that you could put salt in some water, chuck it in the freezer until it is below the regular freezing point of water and then give it a little dip with the thermometer. Then I realised that you would have no reliable way (unless you have another thermometer that is a known quantity) of testing to see what the actual temperature of the salt water mix is.

I don't generally think before I speak.

[JDiz]

prand said:

Why not test it at 100C instead? boil a pan of water with the thermometer dipped in it shouldn't get hotter than 100.

This is the normal way to test.

[steveT350C]

Insert in rectum and look for 37 degrees. A mirror may help

[Mr Sparkle]

steveT350C said:

Insert in rectum and look for 37 degrees. A mirror may help

Feck, I wanted to make that joke.

[Simpo Two]

Odie said:

You will need a mixture of ice and water to get 0 degree's C.

http://www.canadacutlery.ca/download/calibrate-a-t...

True but now much of each and after what time? You don't know the starting temps of each. To know this you'd need an accurate thermometer, and if you had one, you wouldn't need to do the test

Or maybe the ice warms up until it gets to 0, and the water cools down until it gets to 0, and they sit like that at 0 and think for a bit while the rest of the ice thinks about melting. Yes, that must be it.

Some days I feel like Einstein, at others, Winnie-the-Pooh. This is a Winnie-the-Pooh day.

[davepoth]

How about freezing the bulb of the thermometer into water, and then leaving it to melt? The melting should take place at zero if you use pure water.

[richwig83]

steveT350C said:

Insert in rectum and look for 37 degrees. A mirror may help

LOL

[cmsapms]

steveT350C said:

Insert in rectum and look for 37 degrees. A mirror may help

Would "post dump" or "touching cloth" give a more accurate result?

[witko999]

I believe an ice/water mix will remain at 0 degrees until either all the ice melts or all the water has frozen (depending on which way it's going)

[RealSquirrels]

crushed ice, water, stir constantly very well, insulate very well, leave it a decent amount of time, and then measure it, there should still be ice present.

[Halmyre]

Ice/water mix is what we were told at school. It stays at zero degrees for as long as there's a reasonable quantity of ice and you stir it up every so often. I think you need to use crushed ice as well.

[cmsapms]

Thanks very much chaps. I'll crush some ice tonight.

I'm also going to test it at 100 degsC so any inaccuracy will show as either an absolute offset or a percentage - between 0 and 100, anyway. I shall just wing it outside that range

[RealSquirrels]

of course you will need to use distilled water and ice made from distilled water

[tapkaJohnD]

Agree with above.
An ice cube straight from the fridge might be below 0C.
But Physics is your friend!
1 calorie will change the temperature of one gram of water by one degree C. This is the Specific Heat of Water
But to freeze that gram of water, already at 0C, another 80 calories must removed. And adding 80 calories to a gram of ice (ignoring the reduced density of ice) will melt it, but not change its temperature. This is the Latent Heat of Crystalisation, the finite amount of heat that must be extracted to cause a liquid to become a solid.

So your cubes start to melt as soon as the temperature rises to 0C. Any more heat melts ice, and the ice/water mixture stays in temperature equilibrium with the added heat, until all the ice has gone.

Adding salt to ice will lower the freezing point of any water in there, and distort this picture, so that the melting takes place at a lower temeprature than 0C. So you want pure frozen water to achieve zero.

And the same physics makes the boiling point another fixed point to calibrate your gauge. At 100C any added heat goes into the Latent Heat of vapourisation, so that water boiling briskly will always be at 100C. BUT do this at sea level! If the air pressure is low, the water will boil at a lower temperature. If you live in Denver, Colorado, Mile-High City, or Kabul, Mexico City or Nairobi your water will boil at about 95C, but in the UK don't worry about weather highs and lows!

John