🚀 go-pugleaf

You can't siphon a gas.

The gas in the upper reservoir would simply disperse into the atmosphere. 
You could enclose the gas at each end in some flexible membrane, but this 
would cause the pressures at each end to equalise and there would be no 
force to push the gas through the "siphon".

BTW, siphons work because atmospheric pressure pushes the liquid through the 
siphon. That is why they don't work in a vacuum. If the atmospheric pressure 
is low enough at the receiving end, siphons can pump water up hill (ie 
against the force of gravity).



"terryc" <newsninespam-spam@woa.com.au> wrote in message 
news:hscssf$3ii$1@speranza.aioe.org...
> On Tue, 11 May 2010 19:47:54 +0000, Don H wrote:
>
>> It seems the Oxford dictionary (and others?) has an incorrect definition
>> of "siphon"; attributing the agent involved as atmospheric pressure, not
>> gravity.
>>   But the key aspect of a siphon is surely that it is a tube with one
>>   leg
>> longer than the other - but makes a "fluid' (liquid; gas) go upwards,
>> before descending.
>>   Hence, the fluid "defies" gravity, before succumbing to it.  How?
>>   Presumably, because of internal cohesion of the fluid concerned - the
>> molecules drag each other along (viscosity?); otherwise, the whole
>> system just wouldn't work.
>>   The agent involved may well be gravity - but can you siphon a gas?
>
> Yes. Think of pools of gas, e.g. cold air. The critical part of the
> gravity siphon explanation is that both legs/tubes of te siphon are
> filled with the gas that you are siphonig.