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 Subject: triple point?Posted Aug 21, 2002 by Fire Bat Post: 1

I'm not shure i understood it completely- you say that on 0.01 degrees celsius and on the same pressure you can have steam, liquid water and ice alltogether?

 Subject: triple point?Posted Aug 28, 2002 by Euan - † - Getting a new laser to play with - woohooThis is a reply to this Posting. Post: 2

Yes.

For (almost?) all substances, there is a single unique point where all three states of matter can coexist. For water, this occurs at 0.01 deg. Celcius at the particular pressure.

It is possible to get two states to coexist over a range of temperature and pressure; these points form a line, and there are three such lines, for transitions between solid-liquid, liquid-gas and solid-gas. The triple point sits at the junction of these three lines.

 Subject: triple point?Posted Sep 1, 2002 by seaThis is a reply to this Posting. Post: 3

is that the point where dry ice starts to give off... fog-like stuff? love the scientific terminology in that sentence.

have a look at the entry and let me know what you think about the changes, okay?

 Subject: triple point?Posted Sep 2, 2002 by Euan - † - Getting a new laser to play with - woohooThis is a reply to this Posting. Post: 4

Looks fine to me, sea.

"is that the point where dry ice starts to give off... fog-like stuff?"

Actually, not as daft a comment as it might be, given that the fog-like stuff is... fog! Well, water vapour anyway

So don't forget your

 Subject: Observing triple pointsPosted Oct 2, 2002 by Sea ChangeThis is a reply to this Posting. Post: 5

I am a practical person who thinks about things I can see and touch. Since science is about the observable, this is a good thing.

The triple point for dry ice is at about 5 times atmospheric presure, and at about minus 50 C. Unless you went to a dry ice distiller, you wouldn't be able to see this state.

One might suppose that most things go from solid to liquid to gas in a regular pattern, because on Earth, where most observers are, that's what water, which is the substance most observers deliberately change the state of, does. Carbon Dioxide goes directly from solid to gas when you see it, and the sudden cooling that is created when it outgasses cools down the water that is already in the air down, and you get fog.

 Subject: Observing triple pointsPosted Oct 3, 2002 by Chitinid the ChaoticThis is a reply to this Posting. Post: 6

I'd just like to add that dry ice usually sublimes, which means it goes directly from a liquid to a gas. This relates directly to the triple point also. Most people assume that matter goes from solid to liquid to gas. This is not the case, as much depends on pressure. http://snobear.colorado.edu/Markw/SnowHydro/Phases/triple_point.gif>
This picture demonstrates this well. Note that depending on the pressure the liquid state may be skipped altogether.