Re: does a siphon work in vacuum?

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

> Sunday, March 14, 2004 1:36 PM, John Denker wrote:

> It *is* possible to have negative pressure in a liquid.  I 
> get 600 hits from
>   http://www.google.com/search?q=homogeneous-nucleation+liquid+bubble
>
> Such a state is only metastable against phase-separation.  
> But sometimes metastability is good enough.  A "D" battery is 
> at best metastable against self-discharge, but people buy "D" 
> batteries all the time.
>
> Siphoning in a vacuum is presumably somewhat tricky, but I 
> would not be at all surprised to see it done.  I can't think 
> of any law of physics that would prevent it.

Could you define "negative pressure"?

I thought "negative pressure" meant a pressure less than atmospheric.
To syphon a liquid in a hose where one end is at atmospheric pressure,
one needs to create "negative pressure" at the other (where "negative"
means less than atmospheric).  To syphon a liquid in a hose where one
end is at a vacuum, one needs to create "negative pressure" at the other
(where "negative" means less than zero).

Unless you are "grabbing" the liquid in a manner similar to "grabbing" a
rock, and letting the cohesion between the molecules "bring" the rest of
the liquid along with it, I don't see how it is possible to get a "less
than zero" pressure.

Or, have I misunderstood Josip Slisko's question...

Josip Slisko <jslisko@FISMAT1.FCFM.BUAP.MX>:
...
> According to the (1), the maximum lenght of the short arm is the 
> barometric height of used liquid and a siphon would not work in 
> vacuum.
>
> According to the (2), for a very cohesive liquid, the maximum lenght 
> can be bigger than the barometric height and a siphon would work in 
> vacuum.
____________________________________________________
Robert Cohen; 570-422-3428; www.esu.edu/~bbq
East Stroudsburg University; E. Stroudsburg, PA 18301