Posted on 05/11/2010 9:03:35 AM PDT by Gomez
An Australian physics prof has discovered a 99-year-old error in the Oxford English Dictionary - repeated in most dictionaries worldwide - and is having it corrected.
The error is in the definition of the noun "siphon", a tube used to draw fluid from a higher location to a lower one - as when emptying a vehicle fuel tank, an aquarium or other vessel difficult to empty by other means.
Liquid is, of course, drawn up the shorter limb of the siphon by the weight of that in the longer downward one: thus the operating force is gravity. However most dictionaries follow the OED in stating that atmospheric pressure drives the process.*
Dr Stephen Hughes of Queensland University of Technology noted the error after visiting a massive siphon project in South Australia which was being used to transfer gigalitres of water into a depleted lake.
On returning, the prof decided to write an article about the siphon for use by school science teachers, and discovered to his dismay that most dictionaries described the process wrongly.
"An extensive check of online and offline dictionaries did not reveal a single dictionary that correctly referred to gravity being the operative force in a siphon," grumbled the physicist.
The OED currently says:
A pipe or tube of glass, metal or other material, bent so that one leg is longer than the other, and used for drawing off liquids by means of atmospheric pressure, which forces the liquid up the shorter leg and over the bend in the pipe.
"The OED entry for siphon dates from 1911 and was written by editors who were not scientists," explained Margot Charlton of the Dictionary's staff. Amazingly, it seems that in 99 years nobody had ever queried the definition.
The next edition of the OED will be corrected.
According to Hughes some encyclopaedias - though not the Encyclopaedia Britannica - repeat the error. The doc has written a paper with more detail on siphons which the interested can read here.
*This may be true during the process of starting the siphon off, which is usually done by creating a temporary suction on the outflow end of the pipe so as to draw fluid up and over the hump. This works by the action of atmospheric pressure on the surface in the to-be-emptied vessel: but once the siphon is flowing this force is countered by atmospheric pressure at the other end of the pipe.
The government right now is siphoning off huge amounts of job creating capital from the private sector into government coffers to fund an unbalanced budget. The government is a black hole. I therefore vote with the professor and go with gravity.
Thanks, I can sleep now.
Gravity causes liquid in the lower leg to fall, lowering the pressure above it, causing atmospheric pressure to force liquid from the reservoir up into the shorter leg.
The longer leg of liquid causes a continuous “sucking” on the column of liquid above the shorter leg.
So the dictionary has been describing a toilet??
For those who must siphon a liquid using a hose, if you don’t want the fluid about to be siphoned getting in your mouth, fill the hose with water, first, then make a crimp near the end about to be placed in the target liquid and empty that short section of the hose, plug the other end so the water remains in the hose from the crimp to the plug; push the short length into the target liquid then release the plug ... gravity will pull the water out, creating a suction of the target liquid which will flow through the vacated hose where a suction vacuum has been created.
Sure, but what’s the definition of “is”?
Your explanation is, in fact, the correct description of the process. Gravity causes the liquid in the long end of the tube to fall, which creates a pressure differential along the length of the tube, which atmospheric pressure on the to-be-emptied liquid attempts to "correct".
You’re right. The power of the siphon is limited to the amount of atmospheric pressure in which it’s operated, i.e. about 14.7 psi at sea level.
Pass the hose to your friend and let him do it....because he’s just been standing there telling YOU how to do it....
Me too!
It’s kept me sleepless for years.
Are you sure siphons don’t work in a vacuum?
FreeRepublic has the correct answer to ANY question.
When you show this technique to children, they see it as magic! Place the hose in the target liquid so that the hose fills. Then plug the end through which you want liquid to run and pull that end out and place it lower than the liquid to be siphoned. Release the plug and watch the eyes light up on the children ... works every time!
Where do you find children who are so easy to amuse?
Or you can get an ingeneous device called a jiggle siphon. Basically, the end you put in the higher tank has a wide spot that has a ball inside it that acts like a check valve. If you jiggle the hose a few times, it will let liquid into the tube, but not let it back out. After a few jiggles, there will be enough liquid in the tube to go over the U, start falling, and thus pulling vaccuum.
Walla, easiest way on the planet to drain a 5 gallon gas tank.
Who gives a crap and who uses a syphon?
Incorrect. It's all gravity. Water seeks its own level, and if the longer leg of the siphon is below the surface of the standing liquid, the siphon will flow. Atmospheric pressure has nothing to do with it (it does, though, for the short term one might suck on the siphon to get it started).
As an aside, this word has been horribly misused by the media recently, claiming oil would be "siphoned" from the containment dome over the oil leak in the Gulf. "Pumped" is the word that is correct.
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