Re: latent heat of evaporation

[Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU>]

On Wednesday, Sep 29, 2004, at 12:38 America/New_York, John Denker
wrote:

> Ludwik Kowalski wrote:
> > What would one need  "to measure the cooling?"
>
> Turn off the heater and measure dT/dt.
>
> Or just design the apparatus as others have suggested (dewars
> etc.), so that heat leaks are negigible in comparison to what
> you're trying to measure.
>
> ================
>
> This whole thread seems to revolve (implicitly or perhaps
> explicitly) around the hypothesis that energy might not be
> conserved.
>   -- If you end up with a null result, nobody is going to be
>    surprised.  Nobody is going to care.
>   -- If you end up with a non-null result, you are going to
>    need a reeeeeally well-designed experiment if you expect
>    to convince anybody.  As James Randi likes to say, extraordinary
>    claims require extraordinary levels of proof.

I was thinking about a student experiment.
How can a claim about a violation of the
first law be taken seriously? I am not aware
of any scientist making such  claim.

The experiment that Robert suggested seems
to be suitable for the purpose of testing the effect
of bubbling on L (latent heat of evaporation). I do
not think that one has to measure the rate of
cooling, except that loses of thermal energy by
conduction and convection should be minimized
(or accounted for). What has to be measured is
by dT/dm, where T is the temperature and m is
the mass of vapor. It is a clever way to show that
L does not (or perhaps it does) depend on the
intensity of bubbling. That intensity will depend
on the pressure in the vessel. The dT/dt, by the
way, would would also depend on pressure.
Ludwik Kowalski