How do Trees Really lift Water to their Leaves?

You know Sophie, you must be correct. I must be a complete idiot for showing you that water can be placed under tension when you refuted it. But where does that leave you?

Tension is brewing
Of course every molecule in the columns is under tension. Each and every single one of them. The downward pull from gravity on the water must also have an effect on the walls of the stiff nylon tubing, but not sufficient to account for the water springing up the tube when the ends are removed from the water container at ground level.

Add a pinch of salt to one side and water is drawn up under tension. Not because of pressure changes either. 1 grain of salt will trigger this flow! How can you account for this in pressure changes? Surely this flow is responsible for generating the pressures and not the other way around. What drives the circulation before a heart forms? Gravity is a good starting place! This is not the same as a siphon. I keep trying to explain that there is a huge difference between a siphon flow and a density flow. Thought experiment. Coloured salt solution added to upward flow side of a siphon in sufficient quantity to generate a density flow in the upward flowing side. Here we have a downward density flow in the same side as an upward flowing siphon flow. Seen it done it!

Do I have a laboratory and unlimited funds to go with my cohesion and adhesion measuring device? Perhaps an entire university behind me even as you do?

You avoid most of my questions and ignore most of my answers and concentrate on what is happening to the molecules inside the tube? I do not understand what you want from me other than for me to become a verbal punch bag that is?

Lyner:
I did try to deal with all the issues in your last post. Did I avoid any of them?
I am surprised that you don't think the behaviour of molecules is relevant to the way substances behave. To my mind that is a crucial issue upon which all other things in this topic must hinge. Any explanation just has to include the molecular consideration or we are back in the middle ages.

Have you given some thought to my chewing gum idea? Is that not relevant to the situation with water?

One grain of salt will cause a flow? Of course it will. The solution around it is more dense and will drop through the fresh water, albeit quite slowly. It would be a real surprise if it stayed there or went up.

What is 'surely' about the flow generating the pressure? You can measure a pressure difference with out needing any flow. As I suggested, try raising the salty side and you will get a balance point (equalise the pressure difference) with no flow. Why do you muddle up cause and effect so often? What do you suppose started the flow in the first place? Everything needs energy from somewhere to make it happen. Where does the energy come from for your flow if not from the salt having been lifted, by some means or another and gaining Gravitational Potential.

How about my question regarding the space that you saw above the column of water? Did it stay there? Was it air? How did it get there? There is an interesting practical question here.

The fact that an open-bottomed U tube doesn't stay full is very well explained in terms of small pressure difference. You have not replied to my general comments about your latest trials. I think they were mostly good-willed comments??

What is a "density flow"? It is not a term in common use.

I fully believe you saw what you saw but the girl saw the tooth fairy's money too. Was she right to believe in the tooth fairy? She could have found the real cause by the appropriate experiment - staying awake all night- or asking someone who knows.

Ok let me ask you to state what you know about the Brixham experiment.

Lyner:

There's no point in going into too much detail but what it has actually 'proved', rather than what you have 'seen in it' is as follows. Water, under reduced pressure, will not boil instantly. It exhibits cohesion and adhesion. The forces of adhesion and cohesion, as a pair, sustain a siphon process when you increase the density of the liquid on one side of a U tube.
That, in itself, makes the Brixham Experiment well worthwhile having been done. It is a surprising result but reasonable with hindsight. There is, elsewhere, work which shows and measures the 'dynamic (temporary) tensile strength' of water under negative pressures.
You have not yet answered my objections / questions regarding the results of your recent single tube experiment. They are the same questions that I would have asked myself if I had done the work myself - I was not trying to give you a hard time about it.

Your explanation and the undefined terms you use (such as density flow, for instance) are not the only ones possible.

My explanation uses conventional and well tested ideas and tries to use as much of the existing knowledge as possible.

If you really had a convincing package of explanations for the phenomenon then you should be able to reconcile your ideas with such fundamental questions as mine regarding how the molecules behave at the top. You have still not managed to answer this in any depth. You just cannot ignore the problem or dismiss it as obvious - it isn't.

Remember - you are the one who is introducing a new idea and rejecting the established one. The burden of proof lies with you. That is, if you want it to be taken seriously.
Are you still not prepared to discuss the molecular situation and the nature of the forces all through the water?
Rather than just getting upset that your ideas haven't been accepted without argument, you need to substantiate them better.

Stefan:
I'd really like to see Andrew answer whether the column of water would remain intact if the tube were removed.

SophieCentaur.

Thank you for your reply

However, you have not stated anything I have not already stated other than mentioning the adhesion of water to the inside of the tube, which to me at least was obvious. In other posts, I have mentioned this, as soft walled tubes collapse when tension is applied. Again it is obvious that the water is still stuck to the tube and that the tension is pulling on those molecules which in turn pull on the tube. One could also argue that the adhesion inside the tube, coupled with the applied tension lowers the pressure inside a soft-walled tube to the point where atmospheric pressure pushes the tube in and that it does so because air molecules are in contact with the outside of the tube. I have also stated time and time again that the water resists the tendency to boil over the 10 metre mark, even adding when you take the experiment considerably higher than 24 metres the water boils as would expect it to. Even stating that adhesion in certain previous experiments was the reason for failure when cohesion in an unbroken column of water succeeds. Somewhere, I have also stated about my friend Adrian Van Sweden, a brilliant physicist, and former water engineer from South West Water sat on a step with his hands covering his face saying this is not possible after witnessing my experiments. He added water cannot exist in a negative pressure environment but here it is. Why have I not been taught this?

Remember what I said about working with a siphon over 10 metres
As you lower one vessel it stretches the water on the side that you are lowering causing cavitation and eventual failure. It does not induce a flow from one vessel to another. This is worth considering because had it ever have done so it would have been in the literature by now, as many engineers, plumbers, pipe fitters, boilermakers, fire fighters, irrigation experts, have all entertained this problem.

The spinning Z tube where water is injected at the centre of the Z causes the water to cavitate when sufficient tension has been applied. As water passes over the elbows of the Z tube rotating clockwise it induces tension that can be measured accurately.

Hindsight is an easy word to say after an event, but a difficult word to comprehend before an event.

The 6 mil bore tubing capped and swung around gently caused the water to empty from the tube without any deliberate whipping or flexing in the tube. I wanted this experiment to succeed by the way as I have to admit there was a chance it could have, albeit slim. Even using degassed, pre-boiled water it made little to no difference. The spinning Z tube on the other hand confirms the huge tensile strength of water and as the Z tube is of a very small size, adhesion provides the stability of the injected water preventing it from necking. In a soft tube this necking is illustrated. In a solid walled tube not so obvious.

This is why IBT is important for varicose veins shrinking and oedema being drawn from the surrounding tissue back into the circulation. The density flow through the arteries induces the tension in the veins causing the fluids to pull the veins in as the pressure is relieved that causes them to bulge.

Studying trees on the other hand is more difficult due to the rigidity of the tubes, except in the stages of tube production just beneath the bark. This is where pressures and adhesion count in the liquids before they become solid tubes. The pressure in the liquid caused by the gravity induced downward flow resulting from solute free evaporation at the leaf enables a flow without tubes under a positive pressure, essential for maintaining the inside diameter of the forming tubular cells. And lignifications strengthen the walls around the flow by attracting and hanging on to the molecules of resin suspended in the sap. So here lies the answer to yours and Stefan’s valid question about whether a flow can exist without tubes. In fact circulation in all creatures begins long before any tubes are formed.

Andrew K Fletcher

Why do you bother to include comments about trees and IBT in your reply?
The fact that you can observe certain effects does not justify your explanations of one simple effect. You just cloud the issue.

You will notice a scattering of posts from other members amongst our dialogue. They all include the same basic question as mine regarding the basics of what happens at the surfaces of the tubes, in molecular terms.

I assure you that we are not all 'ganging up' on you about this. You should take it as a sign that the question really does need answering.

You keep doing exactly what you complain that teachers of Science do. You expect us to believe in something and refuse to look outside your particular model. Just consider, for a moment, that you could be wrong in this particular aspect of what you (think you) understand.

You went to the trouble of experimenting with the single tube - that's good. But why don't you reply to my queries about experimental details? I am a pretty experienced experimenter and my points are valid.

If you have something to add about molecular behaviour in tubes then spit it out man. You appear not to be asking a question but to be implying you know the answer to your own question so get on with it.

I mentioned the tubular growth in trees because I was asked how this flow system could be there without tubes. The reference to soft walled tubes was required to explain how a flow could cause tubes to form with the flow maintained inside them once they have formed.

Perhaps you would like to explain why water inside the tube does not conform to the phase diagram of water to people viewing this thread too?

Lyner:
I'll spit it out, 'man'.

If the water is to stay in contact with the top of your U tube or my single tube, the molecules at the very top must be attracted to the top or they will move away from it. They must behave in exactly the same way. How can they tell whether they are at the top of your tube or at the top of my tube? They have no brains and no eyes. The same forces must be acting on them. Can you suggest why they should behave any differently? Are you suggesting that no force is needed in your U tube where a force is needed in my tube?
The answer to this question must contain no mention of trees or sick people or how bad Science teaching is.

We can't get anywhere near your flow system until you justify something far more fundamental.

You won't answer my perfectly understandable questions about your latest experiment. Why not? Does it threaten your integrity or don't you understand them?

I haven't mentioned your Xylem tubes for ages. I am not interested in your tubes until we get the first bit sorted out. Is it really too hard for you?

I have to explain nothing - you are the one who is making the claims.
I just need some valid justifications for your new opinion - not paranoia.

This is a Science Forum. Why don't you treat it as such? Please apply some logic.

Andrew
I suggest you try reading through this article and some of the references in it.
www.lps.ens.fr/~caupin/fichiersPDF/CRPhys_2006_7_1000-1017.pdf

You may find it instructive. If you can read it and understand what it says, it will tell you a lot of what you need to know about trees, the conditions under which tension in water becomes relevant and how cavitation occurs.
Basically, some of your ideas work for trees but they won't work for firemen.
Before anyone thinks they have found something new, it is a good idea for them to trawl through the literature.
Your 'revolutionary' ideas are very fragmented and seem to contain a lot of half-understood notions. Your very worthwhile experiment on the cliffs has been a bit wasted because of your interpretation of the results.