Re: latent heat of evaporation

[Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>]

Ludwik Kowalski wrote:
> What would one need  "to measure the cooling?"

I'm not sure.  As JD wrote, though, you'd have to do it
very precisely to convince someone of a non-null result
and I don't have the expertise to come up with a way to do
that.

> I was thinking about a student experiment.

Again, I don't know of a simple student experiment.  My
suggestion was more of a "thought" experiment.  However,
perhaps you can take a large syringe filled with
water (no air).  Insert a temp probe, seal the tip, and then
quickly pull the plunger out.  The water will then "boil"
until saturation is reached.  Compare that temp drop
with what happens if you do the same thing but don't seal
the tip and instead allow the syringe to draw in very dry
air.  Just keep in mind that there is air in the second
case, which will lead to less overall cooling since the air
will cool also.

Warning: My "back of the envelope" calculation predicts
the change in temperature would be very small unless the
volume of air is much greater than the volume of liquid.
And, given the precision of the experiment, I doubt you'll
be able to show the difference in L, if any exists.  I
much prefer the thought experiment. :-)

____________________________________________________
Robert Cohen; 570-422-3428; www.esu.edu/~bbq
East Stroudsburg University; E. Stroudsburg, PA 18301