Re: Money to burn?

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

On Mon, 28 Jun 1999 11:38:33 -0400 Robert A Cohen <bbq@ESU.EDU> writes:
> On Sun, 27 Jun 1999, Herbert H Gottlieb wrote:
>
> > [snip]
> >
> > CONDENSATION OF WATER VAPOR. A simple cloud chamber can be made >>from
a gallon jug fitted with a one-hole stopper with a short piece of
> > glass tubing.  Blow into the jug through the glass tubing to increase
> > pressure.  Put finger over end of tube and pull stopper, suddenly
> > reducing the pressure.  No cloud is formed.  If some smoke is
> > introduced into the jug it provides nuclei about which water vapor
condenses.
> > Repeat the performance and watch the clouds form in the jug.
> > [snip]
>
> Some words of caution regarding the "cloud in a jar" demo.  The
> implication is that there are no nuclei in the jug until the smoke is
> introduced.  This is not right, for even in smoke-free environments,
> only very slight supersaturations are needed to form clouds.  In
> fact, meteorologists assume that "any" supersaturation will form a
cloud,
> as there is an abundance of cloud condensation nuclei in the air.
> Perhaps someone on the list can offer an explanation for why smoke is
> needed at all then.  My guesses are that either (a) the water vapor
> prefers the sides of the jar itself to the "natural" nuclei or (b)
> that supersaturation isn't obtained at all and that the smoke (like
salt)
> can attract the water vapor at subsaturation (creating something more
> like haze than clouds).

According to the International Dictionary of Physics and Electronics, 2nd
Edition 1961, Van Nostrand Company, p. 237......

"CONDENSATION IN THE ATMOSPHERE. .........
Nuclei upon  which condensation can take place are absolutely necessary.
Non-ionized and pollution-free air will become up to 400% supersaturated
before condensation occurs. On the other hand, clouds sometimes form
before the air becomes 100% saturated. Nuclei upon which condensation
begins at the approach toward saturation are highly hygroscopic and
encourage condensation. Minute salt crystals, primarily sodium, magnesium
and calcium chlorides, carbonates and sulfates, smoke particles and ions
serve as condensation nuclei.  Lowering the temperature of air below its
dew point, or adding water vapor beyond the holding capacity of air, is a
second requirement for the formation of clouds."

Herb Gottlieb from New York City
(Where dust and smoke nuclei deposits are left on our windows whenever
rain evaporates)