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Doris Kolb (J. Chem.
Educ. 1996, 73, A189) regretted the error that appeared in the June 1995 issue of the
Journal regarding the real reasons for reducing the
internal pressure in a bottle after the flame of a burning paper
inside is extinguished. Not the loss of oxygen inside the
bottle, but the cooling of the gas (inclusive of the produced
carbon dioxide!) and the condensation of water vapor allow the
egg to be pushed into the bottle. In the reply the error was
explained as a mix-up with a related demonstration in
which an inverted drinking glass is lowered over a burning
candle, which is floating in a cork on a dish of water.
In the cited demonstration, mostly the same effects
as in the experiment with the egg reduce the pressure
inside the drinking glass, even though in this demonstration
the gas is in contact with water. Under the described
circumstances (without shaking), carbon dioxide is not very
water soluble. Besides, the candle flame goes out before the
oxygen inside the glass gets used up. Concrete tests come
to 16% of remaining oxygen.
You can check my claim about the solubility of
carbon dioxide in a very simple way: fill the drinking glass
with pure carbon dioxide at the same temperature as the
water; cover the drinking glass, then open it when the rim is
below the surface of the water. The level inside the glass
rises only a little during one hour, although there is pure
carbon dioxide inside and not a mixture of mainly nitrogen, a lot
of remaining oxygen, and only a little bit of carbon dioxide
as in the demonstration with the candle. When the dish
is filled with limewater, the level inside the glass rises faster, of course. But in this case the reduced pressure is due
to the formation of solid calcium carbonate.
Nevertheless, the note about getting the egg out of
the bottle with vinegar and baking soda is very useful.
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