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Celsius and Centigrade

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37995.  Fri Dec 09, 2005 6:56 pm Reply with quote

So after watching this evenings episode on BBC4


I was wondering about how Stephen took points off Dara for being 0.01 off when defining the triple point of water (Dara said 0 degrees Celsius ina previous series and then QI took points off him).

I was wondering because Stephen said 0.01 degrees centigrade is the triple point of water is he is wrong... slightly in a QI sort of way?

From Wikipedia

In 1948 the system's name was officially changed to Celsius (a third name which had also been in use before then) by the 9th General Conference on Weights and Measures (CR 64), both in recognition of Celsius himself and to eliminate confusion caused by conflict with the use of the SI centi- prefix. While the values for freezing and boiling of water remain approximately correct, the original definition is unsuitable as a formal standard:

I know sometimes Wikipedia is wrong and also have this from [url]
This definition makes values on the Celsius and centigrade scale agree within less than 0.1 degree. For everyday purposes, the scales are identical.

So is the actual answer 0.01 Celsius or between 0.019 and 0.01 Centigrade?

I found this out because there was a question recently in a magazine that asked what was zero degrees and I remembered, I thought, from a previous episode of QI that zero degrees was the point at which ice melts not when water freezes.

38005.  Fri Dec 09, 2005 7:21 pm Reply with quote

Nice quibble, safers. We should have said 'celsius'. But, since we are quibbling, this must be a typo, surely:
between 0.019 and 0.01 Centigrade

38006.  Fri Dec 09, 2005 7:21 pm Reply with quote

I believe the triple point of water, if I remember anything from A-level Physics (1991, fluked an E) apart from how gorgeous Linda Atkinson was, is 273.16 kelvins - and given that a single degree celsius is of exactly the same magnitude as a single kelvin, and that Absolute Zero is -273.15C, it would be 0.01C.


38007.  Fri Dec 09, 2005 7:24 pm Reply with quote

Yes, the triple point of water is 0.01C, as a matter of definition.

38013.  Fri Dec 09, 2005 7:49 pm Reply with quote

Surely it depends what pressure the water is under. I imagine that you all mean that the triple point of water at standard atmospheric pressure (1.013 x 10^5 pascals) is...whatever you eventually agree it is!

It may be specified at some other pressure of course (1 bar say, ie 10^5 Pa) but the higher the pressure the less water will exist as vapour and if you're talking about the triple point then if you raise the pressure then it's no longer the triple point.

On this basis everybody else is wrong Dara (twice), Stephen (twice), all of you (at least once) and I alone am right and pure and good and just and I should recieve the points whilst you all suffer forfeits.


Last edited by Celebaelin on Sat Dec 10, 2005 5:06 am; edited 2 times in total

38014.  Fri Dec 09, 2005 7:55 pm Reply with quote

For anyone who doesn't know what we're on about: the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium. The triple point of water is used to define the kelvin, the SI unit of thermodynamic temperature. The number given for the temperature of the triple point of water is an exact definition rather than a measured quantity. The single combination of pressure and temperature at which water, ice, and water vapour can coexist in a stable equilibrium occurs at exactly 273.16 kelvins (0.01 C) and a pressure of 611.73 pascals (ca. 6 millibars). At that point, it is possible to change all of the substance to ice, water, or steam by making infinitesimally small changes in pressure and temperature.

Nicked off the wiki, naturally.

38052.  Sat Dec 10, 2005 5:19 am Reply with quote

Flash wrote:
Nice quibble, safers. We should have said 'celsius'. But, since we are quibbling, this must be a typo, surely:
between 0.019 and 0.01 Centigrade

Damn. My own pedantic-ism turned back onto me. Cheers Flash.

38064.  Sat Dec 10, 2005 6:08 am Reply with quote

safers wrote:
Damn. My own pedantic-ism turned back onto me

A pedant writes:

Surely you mean pedantry, as pedantic-ism is not a word ;)

38105.  Sat Dec 10, 2005 7:50 am Reply with quote

Yes, what exactly do you mean by 'pedant'?

38238.  Sat Dec 10, 2005 4:53 pm Reply with quote

This is getting embarrassing. I'm just going to slip away quietly without making any more mistakes. Well I'll try.

38246.  Sat Dec 10, 2005 5:16 pm Reply with quote

That'd be: "Well, I'll try" - strictly speaking.

38248.  Sat Dec 10, 2005 5:27 pm Reply with quote

Actually I was thinking more: "Well... I'll try." :)

38253.  Sat Dec 10, 2005 5:41 pm Reply with quote

Oh, I see. However, it raises another question:

"Well... I'll try."


"Well... I'll try".


Jiggered if I know.

39260.  Wed Dec 14, 2005 7:54 am Reply with quote

Is there another word for the triple point? I only ask because I have learned about the idea before but I don't remember the phrase.

41210.  Wed Dec 21, 2005 4:54 pm Reply with quote

Strictly speaking the triple point of water can be at any temperature between 0.01 degrees celsius and an as yet undetermined higher value that is lower than 100 degrees celsius unless you specify the triple point as being the lowest temperature. I say this because passing an electric current (actually a very small current as well) can cause the water to form into ice even at room temperature.

In this weeks New Scientist this is described in an article ("As hot as ice" on page 38) concerning research by Eun-Mi Choi at Seoul National University. The idea of ice at room temperature has been known for a long time using computer models to show the arrangement of water molecules when a small current is passed through it. The molecules line up and form the same cohesive structure as ice. This had never been put to test until this year but has been finally proven in experimentation. The surprising thing is that the size of the current needed to create the ice is very small. Small enough that the charge created by charged proteins could create small volumes of ice nearby. In fact some of the water in your body at this very moment may be in a frozen state.

Of course, finding evidence for naturally occurring ice in this manner is difficult (although not impossible) and the remains controversial.

Read the start of the article here:;jsessionid=KMBJIDNBOBEF


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