Checking your thermometers accurate

[Cory]

When you do an ice cube and water to test your thermometer, do i need to wait an hour or so for the surrounding water to get to 0 C? Also, does the ice need to be cubed or little peices are better?

Basically whats important?

 

[Reef.]

No, you can do it within seconds.

doesn’t matter the shape, just use a lot of ice and enough water to cover the thermometer probe.

 

[Cory]

No, you can do it within seconds.

Is this an accurate way? Do you trust it?

 

[Reef.]

Is this an accurate way? Do you trust it?

yes, in a past job I was responsible for checking the probes we used and this was the way we did it.

Now though I just have 3 different probes I use to check against each other, far easier, they are all within .1 of each other, if any were way off, then yes I would check using the above method.

 

[sp1187]

Is this an accurate way? Do you trust it?

yes & yes
it's how chef/professional cooks do it. think food poisoning prevention. kind of important.

 

[Cory]

What about boiling water and seeing it boils at 100c. Good way too? Get an up and down reading.

 

[sp1187]

What about boiling water and seeing it boils at 100c. Good way too? Get an up and down reading.

nope, water boils at different temp depending on altitude.

Boiling point of pure water at elevated altitudes

Altitude, ft (m)	Boiling point of water, °F (°C)
5,000 (1524 m)	203°F (95°C)
6,000 (1829 m)	201.1°F (94°C)
8,000 (2438 m)	197.4°F (91.9°C)
10,000 (3048 m)	193.6°F (89.8°C)

 

[Reef.]

What about boiling water and seeing it boils at 100c. Good way too? Get an up and down reading.

I believe it’s not as accurate, any impurities will affect the result, also the temp is also hard to actually take, as if you take in on the heat source I.e the stove top, the heat from the stove will affect the result, if you remove the water from the stove, the drop in heat is extremely fast, so again the result is not reliable...do the ice one first then give it a try straight after, see what you get.

 

[Randy Holmes-Farley Verified Community Expert]

The answer to how accurate this is depends on the type of thermometer and if it is made correctly. It is certainly accurate at 0 deg C and also, I think, at 100 deg C. Whether that translates exactly to other temperatures is not certain. Impurities move both the freezing point and the boiling point, but not by much unless you are talking seawater levels of salts.

But I expect it is better than nothing, and if you do both, it should be quite good.

 

[Cory]

The answer to how accurate this is depends on the type of thermometer and if it is made correctly. It is certainly accurate at 0 deg C and also, I think, at 100 deg C. Whether that translates exactly to other temperatures is not certain. Impurities move both the freezing point and the boiling point, but not by much unless you are talking seawater levels of salts.

But I expect it is better than nothing, and if you do both, it should be quite good.

Okay so ideally id use ro water. So at 650 meters above sea level water boils at about 97.5 c correct?

Also is the size of ice cubes important? I have two glass thermometers scientific ones i want to double check. I can take pics when im home from work.

 

[Randy Holmes-Farley Verified Community Expert]

Okay so ideally id use ro water. So at 650 meters above sea level water boils at about 97.5 c correct?

Also is the size of ice cubes important? I have two glass thermometers scientific ones i want to double check. I can take pics when im home from work.

Yes. Maybe 97.7. If there is an airport nearby with a weather station, you can use the barometric pressure report to get it more exactly if you want.

Water - Boiling Points vs. Altitude

Elevation above sea level and the boiling point of water.

www.engineeringtoolbox.com

 

[Cory]

Yes. Maybe 97.7. If there is an airport nearby with a weather station, you can use the barometric pressure report to get it more exactly if you want.

Water - Boiling Points vs. Altitude

Elevation above sea level and the boiling point of water.

www.engineeringtoolbox.com

Thanks. One last question, when fresh water starts to boil, will the temperature stay at 100c (or in mine 97.7c), or does the temperature keep increasing after bubbles start. (Im worried i might miss the bubble point lol-smack)

 

[Cory]

Oh and i must know- does ice size/amount matter?

Reason- if ice is actually colder than the surrounding water, and your thermometer is touching the ice, it would read colder than 0 C, correct? But if your thermomter doesnt touch the ice, but touches just the cold water the ice is making, then technically your getting a read from just the cold water and not the ice.

Sooo, basically what are we measuring the cold water or the ice? Whats actually at 0C the ice or water? Maybe im over thinking it.

 

[sp1187]

put some ice in a glass.
fill with water.
wait 30 seconds.
place thermometer in ice water.
check temp.
the end.

 

[Cory]

put some ice in a glass.
fill with water.
wait 30 seconds.
place thermometer in ice water.
check temp.
the end.

I think it would be more correct:
Put some ice in a glass
Let some of the ice melt making icewater
Place thermometer in actual ice water
Check temp.
The end

 

[sp1187]

I think it would be more correct:
Put some ice in a glass
Let some of the ice melt making icewater
Place thermometer in actual ice water
Check temp.
The end

What do you think happens in the 30 seconds. It’s rhetorical. No need to answer.
Have a nice day.

 

[Cory]

What do you think happens in the 30 seconds. It’s rhetorical. No need to answer.
Have a nice day.

Well I think what happens is the temperature of the tap water or ro water placed into a cup of ice is different than ice water made from melting ice. Thus 30 seconds may be enough time for the surrounding water to reach ice temperature or it may not and your test will mess with your mind. Lol. However if you melt ice that surrounding water should be nearly the same as the temperature which ice forms-32 f. No?

Reason- melting ice has water that has reached less than 32f or 0C. Because usually ice freezes at 0C. So the water should be close to 0 c.

 

[Biglew11]

Thanks. One last question, when fresh water starts to boil, will the temperature stay at 100c (or in mine 97.7c), or does the temperature keep increasing after bubbles start. (Im worried i might miss the bubble point lol-smack)

Having done maple syrup myself once water starts to boil the temperature does not keep increasing unles the concentration of contaminated become high enough.

 

[jccaclimber]

The reason this works so well is that both of these points are at a phase change. (All statements are sea level with pure water.)

For the ice we don’t know the temperature when we take it out of the freezer, but we know that it will not melt until it warms up to 0 *C. So, if it’s in a cup of water long enough that the edges start melting off the cubes, then the cubes are at 0 *C, at least at the outside which is what we care about. If the inside of the cubes is still is a tad colder we don’t care, because we only touch the outsides. We are making the assumption that the water has been cooled down to 0 *C. With a large amount of ice and little water this doesn’t take long, but you can check by noting that the temperature on your thermometer will stop falling. There is no way for the ice to make the liquid water colder, because it wouldn’t be liquid any more.

Same sort of thing with boiling water. Once you are at a rolling boil it is a safe assumption that the entire pot is all one uniform temperature. The water cannot go above 100 *C because at that point it turns to steam, which rises away from the heat source and thus the steam bubble stops getting warmer.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks. One last question, when fresh water starts to boil, will the temperature stay at 100c (or in mine 97.7c), or does the temperature keep increasing after bubbles start. (Im worried i might miss the bubble point lol-smack)

As noted above, the temperature does not rise until so much water has evaporated that the salt concentration rises substantially, raising the boiling point.