In article , betwys1
@sbcglobal.net says...
On Mon, 8 Oct 2007 18:22:14 -0700, Mark Borgerson
wrote:
...
If you pump both the fresh and salt water to the top of the U-Tube,
then switch from the pumps to the reservoirs at the bottom,
you won't get a siphon. The boiling of water at the top will
break the siphon action.

Mark Borgerson


I am regretting this already.
But If I repeat this little test, pumping mercury up an inverted
U-tube to 35 inches, when I stop the pump and open the tubes to a
mercury pool, the mercury levels in the two tubes drop to a 29.92
inch column each side. The mercury does not boil.

29.92 inches is 760 mm of mercury, by the way. So boiling is not
essential to breaking a syphon.
Excess height is all that is needed.

That is correct. The difference is that water will boil at
room temperature because the vapor pressure is much higher. Mercury
will not---or at least the evaporation to produce the equilibrium vapor
pressure will not require visible boiling.

Mark Borgerson