Message-Id: <v01540b23af4353158f33@[192.174.2.173]>
Date: Wed, 5 Mar 1997 08:46:01 -0800
To: pinhole@exploratorium.edu
From: pauld@exploratorium.edu (Paul Doherty)
Subject: liquid nitrogen over bunsen burner
Sheldon,
I tried the liquid N2 over the Bunsen burner demo, but instead of a tea
pot I just made a little bowl out of aluminum foil and supported it with
a ring stand. Interesting effect:
If you don't turn the burner on, the thing drips liquid O2, which
coincidentally was mentioned in a recent Chem 13 News feature on Ron
Perkins. Placing a wood splint w/ ember against the cold (O2-rich) foil
instantly rekindles the flame... even more impressive with a rolled up
paper towel w/ember.
If you place the burner beneath, you can immediately see a snow white
sheet of ice forming there. It does not grow very thick, however, since
it insulates itself from the cold (if you know what I mean). After a
while, you can remove the burner and pour out the liq N2, and straighten
out the foil to losen the ice from it, and you will see it doesn't
behave like ice at all, it is more like a flexible papery film than
anything brittle or crystalline. Then I looked up H2O's phase diagram
and discovered that normal (hexagonal) ice-1 forms from water vapors
down to -140C, cubic ice-1 forms from -140 to -160C, and then below
-160, "vitreous ice" (ie: amorphous) forms. Since the Al foil was at
about -200C, I can only imagine that we are forming vitreous ice!
That's exciting. Shall we do a joint write-up for chem 13??
Also, If you light the burner beneath the Al foil before you add the liq
N2, then no ice will form. The foil gets hot and the liq N2 is never
able to make good enough contact with it to cool it down sufficiently,
In the above, the Al was being insulated from the heat below by the
layer of ice... here the Al is being insulated from the cold beneath by
a layer of gaseous N2! And the N2 (ironically) lasts a lot longer in
the second scenario, even though (or actually, because) the foil is so
hot! Fascinating. Thanks Sheldon for this great lead.
chow4now becker