Le 2011/09/05 11:52, Invisible a écrit :
> On 05/09/2011 04:43 PM, Jim Henderson wrote:
>> On Mon, 05 Sep 2011 10:35:45 +0100, Invisible wrote:
>>
>>> that water freezes at 0°C (actually no, it
>>> doesn't) and boils at 100°C
>>
>> It also doesn't always boil at 100C - reduce the atmospheric pressure and
>> see when it boils.
>
> Or increase it. Or add impurities. Or whatever.
>
> Yes, but under /normal/ circumstances, it boils at 100°C, which is why
> it's defined that way. :-P

Pure water at average sea level presure boils/condense at 100°C and 
melt/freeze at 0°C at the same presure level. Both by definition. In 
fact, it's the definition of 0°C and 100°C.
(0°F is defined as the freezing poing of sea water and 100°F as the body 
temperature of a "healthy" human male, but the "healthy" human male who 
was used for the original mesure was somewhat feverish at the time, and 
had the flue the next day...)

Change the presure and you also change freezing temperature.


Alain

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