My Siphon Challenge FINALLY!!! I've thought over my remarks concerning the theory by Dr. Stephen Hughes, Lecturer in Physics at Queensland University of Technology, concerning gravity, rather than differential air pressure, as being the primary source of motive energy for a siphon system. (See: http://www.guardian.co.uk/science/blog/2010/may/10/dictionary-definition-siphon-wrong" [Broken] : Notes & Theories science blog Dictionary definition of 'siphon' has been wrong for nearly a century A schoolboy error in the Oxford English Dictionary's definition of 'siphon' has come to light after nearly 100 years in print Dictionary definition of 'siphon' has been wrong for nearly a century A schoolboy error in the Oxford English Dictionary's definition of 'siphon' has come to light after nearly 100 years in print The Oxford English Dictionary gives the definition of siphon as a tube for 'drawing off liquids by means of atmospheric pressure'. Photograph: Roger Tooth/Guardian Perpetuated by dictionaries for nearly a century, it's surely the most persistent scientific howler in the history of the English language. Siphons – those ingenious plastic tubes we use to fill or drain everything from aquariums to petrol tanks – move liquid by "the force of atmospheric pressure". Except, how could a siphon possibly work by a difference in pressure when atmospheric pressure is the same for the liquid at both ends of the tube? Bleeding obvious when you think about it. Even I can figure that out 25 years after I scraped through A level physics. And yet according to the Guardian science desk's own coffee-stained Collins, a siphon is "a tube placed with one end at a certain level in a vessel of liquid and the other end outside the vessel below this level, so that atmospheric pressure forces the liquid through the tube and out of the vessel". *** I've concluded that I was totally wrong, but that Dr. Hughes was only partially right. Believe it or not, my experiences with juice boxes led me to this conclusion. I've noticed that once I've stuck a straw into a juice box, the juice flows out spontaneously, and my only explanation for this observation was that, as I live at sea level, the juice boxes must have been filled at a higher altitude (with lower ambient air pressure) than my own home. Then I realized that what I was actually observing here was the massive power of the capillary action of water. I then realized that, when siphoning gasoline, the initial suction at the end of the longer length of the tube (that being the end of the tube aimed into your jerry can, while the end of the shorter length is immersed into the gas tank of the car you're siphoning) is required to create an air pressure differential sufficient to get the flow going, but neither that suction (as the atmospheric pressure at the higher level of gasoline in the car's tank is actually a bit lower than the pressure pressing down upon the surface of the gasoline in your jerry can) nor gravity (as it cannot explain the tendency of the gasoline in the car's tank to rise up (i.e., AGAINST the force of gravity) into the shorter length of the hose) can explain the continuous flow of the gasoline through the hose. Only capillary action can explain that. And only the fact that the surface tension/capillary action of gasoline is far weaker than that of water (combined with the possibility that my juice boxes may have been filled at an altitude higher than my own (which, seeing as I live at sea level, is hardly implausible)) explains the differential results between my juice boxes and a teenager trying to earn favor with the mob, in that ambient air pressure is sufficient to create a continuous flow in the former, whereas some degree of negative atmospheric pressure (i.e., suction) is required to create a similar flow with respect to gasoline. Gravity is only sufficient to maintain the flow by pulling down on the mass of liquid within the longer length of hose emptying into your jerry can if the volume of liquid within that longer length of hose can pull along the upward-flowing liquid behind it in the shorter length of hose due to hydrogen bonding (i.e., surface tension/capillary action). Otherwise, the upward-bound liquid within the shorter length of tube would simply fall back out of the tube back into the tank, interrupting the flow. Ethanol exhibits no hydrogen bonding capillary action, and, therefor, should be impossible to siphon, should my hypothesis be correct. I'll try to get my hands on some pure EtOH in the near future, in order to test my hypothesis (and to celebrate my results if I'm right, and to drown my tears if I'm wrong). *** Here's my source as to capillary action in gasoline versus that of EtOH: Susan E. Powers (Clarkson University, Potsdam, NY), Ph.D., P.E.: Transport and dissolution of ethanol and ethanol-blended gasoline in the subsurface Workshop on Ethynol and Alkylates in California Automotive Fuels (April 11, 2001) "www-erd.llnl.gov/ethanol/proceed/etohf_t.pdf"[/URL] Please scroll down to Page 17: "Ethanol does not spread by capillary action. Gasoline continues to move in advance of ethanol front. Capillary fringe is depressed."