Wikipedia:Reference desk/Archives/Science/2010 January 31

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January 31

take a solution of enantiomerically pure lactic acid in water ... pH 4-5

The lactic acid will start racemising slowly, right, until an equilibrium is reached between the two isomers? How long will this take? Racemisation of chiral sugars seems pretty rapid -- so why does the optical purity of your lactic acid matter?

Or is it harder to racemise a carboxylic acid versus an aldehyde/ketone? The enol form seems stabilised by the alpha-hydroxy group though. I could imagine the hydroxy group becoming a carbonyl and carboxylic acid carbon bearing two hydroxy groups (as one of the tautomers). John Riemann Soong (talk) 00:00, 31 January 2010 (UTC)

Thinking about other things and performance in minesweeper while tired

I have noticed that, while tired, I get better times in 16x30 99 mines minesweeper when I'm thinking about other things. I would get 1:50 or a few seconds over two minutes most of the time, but when thoughts start to wander I hit 1:30 - 1:40, about the same as when in a state of full awareness. What's happening and could you name something similar? Are the events both effects or this there causality? Wild speculation is wished. --194.197.235.240 (talk) 02:21, 31 January 2010 (UTC)

Are you writing down the times for every single game you play? Otherwise it could be Confirmation bias or Illusory correlation. Ariel. (talk) 02:29, 31 January 2010 (UTC)

This is purely WP:OR but personally I find that my limiting factor at most points during a given game is my click speed rather than the rate I can process the information. My times are around where yours are (typically 85-110s). My level of concentration doesn't seem to make much difference (although I don't have any data to back that up). However when I try really hard to achieve fast click speed I tend to make more mistakes and it ends up slowing me down compared to when I'm "loose", including when I'm not paying attention. Many times that I've gotten a high score have been when I wasn't expecting it. As for tiredness, I do have data for time of day versus completion time, and I seem to do worst in the few hours after I wake up and then fairly steady for the rest of the day with a slight improvement late at night. Rckrone (talk) 03:56, 31 January 2010 (UTC)

(OR) I have noticed a similar effect when solving Sudoku puzzles and I attribute it to subconscious Pattern recognition (psychology). Cuddlyable3 (talk) 16:41, 31 January 2010 (UTC)

Yes, and I've noticed this effect in Minesweeper specifically. For example, if I have uncovered a "1" and one adjacent mine has already been marked, I can either consciously think that this means the other 7 squares must not have mines, or my subconscious can do that for me. Apparently, the subconscious is significantly faster at such tasks, and seems to take over more when the conscious mind is either fatigued or busy. I believe this is because the conscious only works on a single thought at a time, while the subconscious is capable of multiprocessing. As I write this, it's probably thinking about scratching that itch on my leg and several other things, all at once.

So, then, if the subconscious is actually faster at certain "no-brainer" tasks, perhaps we should think about how to use it more for such things. I've noticed that most of car driving seems to operate on a subconscious level, which is normally good, but can be bad when you mysteriously arrive at the wrong destination. Getting just the right mix of conscious and subconscious brain activity involved in every task is quite important, it seems to me, and significant research should be devoted to this topic. Thus, your seemingly trivial Q may give us a very important insight into an much bigger and more important Q. StuRat (talk) 18:08, 31 January 2010 (UTC)

It seems to me that the ability of the 'sweet spot' of human awareness to really focus on a task at hand is generally limited. There are other parts of our awareness that are paying better attention than us. This is evident to me when I can't find something that I set somewhere. As long as I consciously look and look for it, it's impossible to find. But then when I stop seeking it myself and let that part of me that knows right where it is show me where it is, all of a sudden I will realise I am looking right at it. --Neptunerover (talk) 20:26, 31 January 2010 (UTC)

I would even compare a human to the Starship Enterprise, where, while we might be the captain, we cannot keep track of everything going on around us. And so we have a crew too who monitor the sensors and alert us if there's need. The onboard computer keeps track of everything, and tapes can all be reviewed (memory). --Neptunerover (talk) 23:38, 31 January 2010 (UTC)

Sleep and creativity may be of interest. ~AH1^(TCU) 02:34, 1 February 2010 (UTC)

I asked a similar question last month, please see this discussion and the VERY useful external links provided therein:Wikipedia:Reference desk/Archives/Science/2009 December 18#Autonomous behaviour on Guitar Hero. Regards. Zunaid 12:54, 1 February 2010 (UTC)

No matter how much I eat, I don't gain weight.

Request for medical advice (and some highly irresponsible advice) removed. If you wish to debate this removal, please start a thread on the talk page - not here. SteveBaker (talk) 16:24, 31 January 2010 (UTC)

Polyethylene foam bed vs Urethane

breathing? —Preceding unsigned comment added by 67.246.254.35 (talk) 05:55, 31 January 2010 (UTC)

Breathing? --Neptunerover (talk) 09:09, 31 January 2010 (UTC)

BREATHING? --124.157.247.221 (talk) 09:40, 31 January 2010 (UTC)

Both of these polymers are watertight and impervious to air, you cannot breath through them. Whether they will suffocate you will depend on the structure, whether there are holes that connect. However a firm foam is likely to be closed cell. Graeme Bartlett (talk) 10:52, 31 January 2010 (UTC)

So then, Polyethylene foam bed vs Urethane: Not for breathing, no. --Neptunerover (talk) 11:06, 31 January 2010 (UTC)

i mean which will breathe better so i dont sweat —Preceding unsigned comment added by 67.246.254.35 (talk) 15:26, 31 January 2010 (UTC)

They could only stop you from sweating by keeping you cool...so the question becomes one of how to get the heat out. Maybe less bedclothes? SteveBaker (talk) 16:20, 31 January 2010 (UTC)

no —Preceding unsigned comment added by 67.246.254.35 (talk) 16:24, 31 January 2010 (UTC)

For breathing (porosity to air), try a feather bed, but if you want air to circulate below you, then perhaps just a wire mesh would be best, though not most comfortable. As Steve said, if you want to avoid sweating, just reduce the thermal insulation above you. Dbfirs 17:34, 31 January 2010 (UTC)

While keeping the body cool will limit the moisture released from the skin, it will not eliminate it. Thus, the circulation of air and/or absorption of moisture by the bedding material is important. Note, however, that the "bedding material" also includes the sheets and perhaps a "feather top", etc. Thus, the mattress itself may be completely impervious to water, so long as enough absorbent material is between it and the occupant. This might be a good way to do things, as a mattress may be ruined if someone has an "accident", while other bedding may be more washable. I myself use a comforter as a "bottom sheet" (although I haven't had an accident in several decades now :-) ). StuRat (talk) 17:48, 31 January 2010 (UTC)

We do not provide medical advice. However materials such as those mentioned and even nylon can cause overheating (this is how a sleeping bag works). Cotton does not restrict heat flow as much and therefore may have better air flow. ~AH1^(TCU) 00:57, 1 February 2010 (UTC)

Horrible Insects

Inspired by Red imported fire ant, what prevents an insect species from evolving that would prey on mammals, entering by the ears, feeding on the brain and using the scull as protection? 95.115.151.113 (talk) 15:05, 31 January 2010 (UTC)

Evolution is a slow, incremental process. You'd first have to imagine an insect that would be interested in clambering around inside a mammalian ear without somehow getting through the skull and into the brain - and then imagine incremental benefits to each step. Expect this change to take maybe a million years to happen. Bear in mind that the mammals in question will also be evolving ways to keep these pesky insects out of their ears in the meantime. It's not a simple matter. SteveBaker (talk) 16:19, 31 January 2010 (UTC)

The eggs of parasites are microscopic and can be passed sexually, through shaking hands, walking barefoot, from a pet, eating or drinking from someone else's glass, bottle, can, fork etc., swimming in polluted lakes, rivers or streams, going to the beach, etc. Entamoeba Histolytica[1] can get into the liver, the lungs and the brain. Cuddlyable3 (talk) 16:34, 31 January 2010 (UTC)

This would be catastrophic for whatever insect species decided to try to prey on mammals. We are thinking, feeling, revenging creatures that would, upon discovery of this new predation, seek out and destroy every nearby colony! Vranak (talk) 16:51, 31 January 2010 (UTC)

Um, no. Plenty of insects prey on living mammals—mosquitos and fleas being two obvious ones, not to mention all of the parasitic worms and larvae that would love to get inside us and burrow around. Even us mighty revenging, thinking human beings have been shown to have limited capacity to deter such activities (it has taken until the 20th century to even start to get a handle on the worst of such pests in the most developed parts of the world). And of course if we get beyond the mistake that "mammals" and "humans" are identical, there are even bug-sized creatures that eat small mammals, birds, and fish (army ants, certain large spiders). The issue, here, is that insects don't seem to outright hunt and kill large animals. The reason for this is probably both ecological (it would be a tremendous waste of biomass, and such an insect would probably deplete its food supply rather quickly) and evolutionary (it is evolutionary easier to feed on carrion than it is to try and hunt a big animal, when you are that small). --Mr.98 (talk) 19:24, 31 January 2010 (UTC)

Mmm, as I read the initial question, I inferred a sort of nightmarish glint about, well, horrible insects actively going after healthy individuals. Everything you point out is true of course, but these infestations are inevitability spawned out of disease. The prime mover is a lack of health, not hungry little insects. Vranak (talk) 22:10, 31 January 2010 (UTC)

Not true for botflies, an article I fond after posing the question. Guessing from the answers raising up every god and reason (like that a dog could make its paw scratch behind the ear-hole already inside the scull) to make believe this cannot happen, I must have hit some severe archetypical nightmare. 95.112.190.236 (talk) 17:43, 1 February 2010 (UTC)

I disagree that evolution has to be slow and incremental. When the barrier to selection is low, evolution is very, very, very rapid, like tossing water into a solution of acid chloride. A selection barrier is a bit like activation energy -- when high enough, it will prevent selection in a certain direction even though that direction may be favourable to the species and thus selection in that direction will be slow. John Riemann Soong (talk) 16:56, 31 January 2010 (UTC)

It wouldn't work. The inner ears are extremely sensitive, and if a bug gets in there (which happens occasionally), people will do whatever it takes to get it out, even if it means pushing sticks in and damaging sensitive tissues. There was an African explorer (Stanley?) who lost hearing in one ear due to an episode of that sort. Looie496 (talk) 17:02, 31 January 2010 (UTC)

What could a cow, a dog, a cat do to get such a bug out of the ear or at least kill it? 95.115.151.113 (talk) 17:24, 31 January 2010 (UTC)

A dog or cat could maybe get a claw in there and do some damage. As for cows, there are birds, like oxpeckers, which specialize in removing parasites from them. Also, animals would be under evolutionary pressure to develop a defense, like a thick, poisonous earwax. StuRat (talk) 17:38, 31 January 2010 (UTC)

The dog or cat would probably do more damage to themselves than the bug. They have limited ability to remove pests from themselves, even if they are bothered by them. Ear mites drive dogs crazy but there isn't much they can do other than shake and scratch ineffectively. The thing is, it is better for the mite to not be fatal—the affected dog then can spread more mites to other dogs, and so on, and the mite has plenty of food as it is (what would a mite do with a whole dog?). --Mr.98 (talk) 19:24, 31 January 2010 (UTC)

What provides the bugs/mites/critters with such wisdom? Imagine a mutant putting (nearly) all available resources into reproduction. A brain even as small as from a cat can provide large amounts of nutrients (yummy fat and proteins). Having more offspring is a primary trait in natural selection. As insects have far more generations than mammals do have in the same timespan, the mammals would not have enough time to adapt. Such a mutant would spread explosively, killing off their pray nearly entirely in a short time, than die out or establish an equilibrium with the more hardy and resistant specimens of their pray. Is there any evidence/hint that this ever happened in the history of live? 95.112.190.236 (talk) 17:09, 1 February 2010 (UTC)

There's some sort of cat disease that a large proportion of people are said to be infected with and includes cysts in your brain. 92.24.73.102 (talk) 21:43, 31 January 2010 (UTC)

Toxoplasmosis? --Dr Dima (talk) 22:48, 31 January 2010 (UTC)

There's also Baylisascaris sp., and Taenia solium. Note that these three are very different critters: Toxoplasma gondii is a protozoan, Baylisascaris is a roundworm (class Nematoda), and Taenia is a tapeworm (class Cestoda). None of them is an insect, though :) . The only insects I can think of that live in the relative safety of the mammalian skull are the fly larvae that live in the sinuses of the sheep. Their Latin name will come back to me in a moment. --Dr Dima (talk) 22:56, 31 January 2010 (UTC)

The sheep nasal bot-fly is Oestrus ovis. Nasty, nasty critter. We don't have an article on it, much to my surprise. --Dr Dima (talk) 23:07, 31 January 2010 (UTC)

However, we do have an article on the gnat in the Titus' brain (which Titus entirely deserved for what he did). Mysterious are the ways of the Editors. --Dr Dima (talk) 23:14, 31 January 2010 (UTC)

I saw a doco recently which would have been great to post here. It was of a herd of African cattle of some sort, they were all peacefully grazing, relatively still, except for their ears which were wildly gyrating, no doubt because of the insects, it actually made me laugh it looked a bit ridiculous. Even Darwin in Origin of Species recognised that insects play a not insignificant role in the success or failure of larger mammal species. He said even the small tail of the giraffe may seem superficially quite ridiculous and pointless to evolve but even if it provides a little relief as a swatter from the constant harassment of insects, it makes the animal more fit, not just less likely to be killed by insects, but being so worn down by them as to succumb to diseases or even other predators. Vespine (talk) 23:43, 31 January 2010 (UTC)

And of course immediately relavant to this topic is myiasis, I thought someone would have mentioned it already. Vespine (talk) 23:46, 31 January 2010 (UTC)

The tsetse fly's bite causes African trypanosomiasis, where the infection spreads to the brain. Naegleria fowleri is a form of "brain-eating amoeba". Also, under certain circumstances microorgaisms and species in smaller niches can evolve rather quickly, and the effects of global warming on most of those species are currently not known. ~AH1^(TCU) 00:53, 1 February 2010 (UTC)

Earwig. 124.157.247.221 (talk) 01:35, 1 February 2010 (UTC)

This has been recorded, although through the nose, not ear, and I'm not certain we'd regard it as a scientifically rigorous report, as the objectivity of the source is somewhat in doubt. --Dweller (talk) 12:06, 1 February 2010 (UTC)

Depth and temperature

Why is it very cold six miles underwater, but very hot six miles underground? 213.122.14.252 (talk) 18:38, 31 January 2010 (UTC)

Water is a liquid. Hot water tends to be less dense than cold so will float on top if it. Hence water will colder as you go deeper. Rock OTOH is a solid plus the source of heat is radioactivity in the rock itself plus primordial heat. The earth is slowly cooling down, but is doing it from the outside in, so the surface is cooler than the core. Theresa Knott | token threats 18:55, 31 January 2010 (UTC)

Why then does ice form at the top of lakes? 213.122.14.252 (talk) 19:16, 31 January 2010 (UTC)

Because it's lighter than the water, see water: The maximum density of water occurs at 3.98 °C (39.16 °F).[13] Water becomes even less dense upon freezing, expanding 9%. This results in an unusual phenomenon: water's solid form, ice, floats upon water... --Ayacop (talk) 19:23, 31 January 2010 (UTC)

OK. Why isn't the deep ocean heated up by pressure? 213.122.14.252 (talk) 19:26, 31 January 2010 (UTC)

It probably is, but again, hotter water is less dense, so any water heated by pressurization will tend to rise. --Ludwigs2 20:04, 31 January 2010 (UTC)

1. Is it naive of me to think of thermal energy as molecules jiggling around?
2. When a fluid expands, do the molecules jiggle around less, and if so, why?
3. Alternatively, does the fluid get colder simply because the molecules are further apart, meaning less jiggling per unit of volume, in which case how is the fluid any more able to absorb heat from its surroundings than it was before? 213.122.14.252 (talk) 20:28, 31 January 2010 (UTC)

1) No, that's precisely what thermal energy is (well, molecules and atoms jiggling around). I'll let somebody else tackle 2 and 3. --Tango (talk) 20:41, 31 January 2010 (UTC)

For 2, the answer is yes, if the expansion does work. When you let compressed air out of a bottle, the air does work against the atmosphere, and the nozzle gets cold. Similarily, water expanding against the weight of the ocean would also do work (of course, the expansion would come from an input of thermal energy, so the actual temperature of the water would rise. But the rise in temp would be less than expected from the amount of thermal energy put in). If, on the other hand, you let a gas expand into a vaccuum (some 17th or 18th century science guy did this, but I'm not sure who or why. Perhaps it was to test the phlogiston theory?), the temperature doesn't change. For point 3, the temperature article has some good stuff, though it's quite dense. Short answer is: temperature is not equal to thermal energy. Additionally, heat capacity (how much the temperature changes when thermal energy is added) is measured on a per mass or per mole basis, not a per volume basis. Buddy431 (talk) 21:26, 31 January 2010 (UTC)

Have I got this right? I have some gas in an expandable container, like bellows (yes, with the nozzle sealed). I forcibly expand the container: the gas stays the same temperature, because I did the work. If I instead I was forcibly holding the container compressed, and let go, letting it work to expand against atmospheric pressure, the gas cools down. If I let go of it in a vacuum, and we imagine the container expands until it stops expanding without offering any resistance along the way, the gas doesn't cool down. 213.122.14.252 (talk) 21:57, 31 January 2010 (UTC)

When you pull open the bellows, you're only doing some of the work; the air inside's doing some of the work, and the temperature will decrease. If you don't believe that the air is doing some work, try to immagine pulling apart a bellows with nothing in it (that is, a vaccuum) verses one that has some air in it. Buddy431 (talk) 22:55, 31 January 2010 (UTC)

OK, that works. :) Bit surprising. 213.122.48.165 (talk) 23:03, 31 January 2010 (UTC)

Having some trouble visualizing this. So far I'm at: water on the bottom of the ocean is heated by the pressure. It expands from the heat. It does work against the pressure as a result of expanding, so it doesn't heat up all that much. So water on the bottom of the ocean basically expands and rises. That doesn't sound right... is it constantly convecting, or does it just find its level, which I suppose would be the at bottom despite the heating? What if it's a system with a really compressible fluid and a lot of pressure, like the atmosphere of Jupiter - would the gas at the bottom of the atmosphere be heated up massively and become, er, much less dense, and rush to the top? Is there a bit of a delay between heating and expanding, which would cause constant frantic convection just because of pressure, or am I making up a lot of nonsense? 213.122.14.252 (talk) 22:09, 31 January 2010 (UTC)

Trouble is, pressure doesn't heat up the water. Pressure plus a decrease in volume heats up the water. Water at the bottom of the ocean is already compressed (what little amount it does), so the pressure doesn't affect its temperature. If water was heated up by a different means (like a hydrothermal vent) then convection currents would be set up, though probably not all the way up to the surface. Buddy431 (talk) 22:50, 31 January 2010 (UTC)

What happens to some ice-cold (OK, nearly ice-cold) water added at the surface? Does it sink to the bottom? Does it then compress and heat up and rise again? 213.122.48.165 (talk) 23:11, 31 January 2010 (UTC)

It will sink, and as it does, the increasing pressure will compress it a tiny amount, heating it up a tiny amount. So it's not like the liquid sinks to the bottom, then compresses and heats up; it's doing that all the way down, until it reaches a layer of water that's the same density (and same temperature), where it will stay (barring currents, etc.). Buddy431 (talk) 00:05, 1 February 2010 (UTC)

It is compressed as it sinks, which makes it heat up, which makes it expand again, canceling out the compression, canceling out the heating, leaving it no denser than it was at the surface. It can only reach the level where the water is the same density as very cold water at the surface. It won't end up any denser (or hotter, or colder). Is that right? (Edit: I've concluded that it would in fact end up both denser and hotter, as Buddy said. The "hot water rises" remarks from earlier threw me off.) 213.122.48.165 (talk) 00:59, 1 February 2010 (UTC)

I think this must be a mistake ("hotter water is less dense, so any water heated by pressurization will tend to rise"). If it's heated by being compressed, it's not expanding. I think this contradiction has been confusing me for a while now, and the answer is that it just gets slightly hotter and doesn't rise because it doesn't get less dense. In fact it should get more dense and sink. Pressurization means getting more dense, right? 213.122.17.58 (talk) 01:39, 3 February 2010 (UTC)

No, both your scenarios are essentially the same thing. In the 1st scenario you decrease the pressure and the temperature will drop. In the second scenario you first inscrease the pressure which will raise the temperature, but then presumably you wait for the increased temperature to dissipate which means when you release it again the temperature will drop. What you have described of course is the simplest kind of heat pump. Water is NOT being heated by the pressure, you have to be careful: pressure is NOT Work (physics), it's an easy mistake to make, for the same reason you can't just get energy out of a magnet, a magnet can make pressure. Vespine (talk) 22:18, 31 January 2010 (UTC)

Excuse me but what is this first scenario where I decrease the pressure? Can't relate this to what I wrote, sorry. 213.122.14.252 (talk) 22:27, 31 January 2010 (UTC)

I was referring to your previous comment, when you forcibly expand the bellows (I presume with the nozzle sealed) you decrease the pressure and the temperature will decrease. Vespine (talk) 22:36, 31 January 2010 (UTC)

Oh, OK. I was confused by your answering down here with random indentation and by the word "both" when there are three scenarios. In the third one, the gas is essentially expanding in a vacuum so I take it you agree with Buddy431 that it doesn't heat up. Why is the first one different - my muscles do the work of decreasing the pressure in the gas, the gas doesn't do the work, so why should the gas lose energy? (Am I right in thinking that Buddy431's stipulation about doing work is because the work provides somewhere for the heat energy to go? It's a little confusing since many things, such as muscles, heat up when they do work.) 213.122.48.165 (talk) 22:55, 31 January 2010 (UTC)

Read the comment I made under your scenerios. When you pull open the bellows, the air does do some work; it's not all you. When you let it expand in a vacuum, with no resistance, it does no work. Buddy431 (talk) 22:59, 31 January 2010 (UTC)

Sorry it starts getting confusing when you are talking about so many related topics, by the time I replied there were already 2 other posts in between. Work is energy transferred by a force through a distance, your muscles provide the force, the gas provides the distance. Does that clear it up a bit? Part of the confusion might be that you think heating something up takes "work" so the opposite: cooling something down takes the opposite of work: (lack of work?) but what you are actually doing is not heating something up or cooling something down, it's heat transfer, all that is changing is the direction of that transfer, either case takes work. Vespine (talk) 23:18, 31 January 2010 (UTC)

Er, I thought the gas provides some of the force, by resisting less than a vacuum would. I get the heat transfer bit alright (the heat is transferred to the atmosphere, which you wouldn't notice since the atmosphere is very large). 213.122.48.165 (talk) 23:32, 31 January 2010 (UTC)

You're right 213. Vespine doesn't know what he's talking about. (Although "resisting less than a vacuum would" probably isn't the best way to put it. Better would be: "helping out more than a vacuum would"). Buddy431 (talk) 23:53, 31 January 2010 (UTC)

And just for the record, when I said the gas provides the "distance" I did actually mean "and the associated resistance across that distance." I was just simplifying. Of course opening bellows with the end closed takes more work then flapping your arms. Vespine (talk) 00:36, 1 February 2010 (UTC)

And importantly, the gas does NOT lose energy when you expand it, it loses temperature but increases volume, the energy remains the same!Vespine (talk) 23:20, 31 January 2010 (UTC)

NO. Gas can lose energy in expansion, and usually does. For an ideal gas, the volume has no effect at all on the internal energy. I think you mean that the total energy doesn't change (energy of gas + energy of everything else, including what the gas transferred energy to when it did work), which is just the First law of thermodynamics. And No to the post above your last one too. When pulling open the bellows with air in them, your muscles apply a force, and the gas does too. If you pulled apart a bellows with a vaccuum inside, the same amount of work would be done (same total force, same distance), but you would do all of the work. Buddy431 (talk) 23:50, 31 January 2010 (UTC)

So am I alright with "the work provides somewhere for the heat energy to go"? 213.122.48.165 (talk) 23:56, 31 January 2010 (UTC)

Well come on Buddy, that's not playing nice. I don't think you are correct either, where is the expanded gas losing energy to? Won't it GAIN energy? Such that if you release the force you used to expand the bellows the gas will be warmer than when it started? Also, if you really had a vacuum in the bellows, you wouldn't be able to expand it no matter how great a force you apply! That's how those glass holding suction cups work that can lift tons of weight. Unless you are also in a vacuum of course, which is a bit of a big detail to leave out. ;) Vespine (talk) 00:11, 1 February 2010 (UTC)

The gas is losing energy to whatever it's doing work on. For the case of a gas expanding against the atmosphere, it's transferring energy to the atmosphere (which will just heat up the atmosphere a tiny bit). And you certainly can pull against a vacuum, it's just hard when you're pulling against atmosphere. Atmospheric pressure is 14 lb/sq inch, so a suction cup even 7 inches square (a 3 inch diameter) could lift 100 lb. But in a barometer, just 30 inches of mercury can pull against a vacuum. Buddy431 (talk) 01:35, 1 February 2010 (UTC)

The Thermohaline circulation shows how complex the convection and advection currents in the ocean are. ~AH1^(TCU) 00:25, 1 February 2010 (UTC)

In reply to 165's last comment, the work doesn't really PROVIDE the place for the heat to go, the place was there all along, I would instead say the work provides a temperature gradient for the heat transfer to occur across. Vespine (talk) 01:08, 1 February 2010 (UTC)

I was thinking about a fridge. The refrigerant is compressed at the back of the fridge, it goes through a radiator, then it is squirted through a narrow gap into pipes inside the fridge. It expands a lot in these pipes. Presumably the particles in the refrigerant are jiggling less at this point than before it was squirted in. Why is that? I was thinking along the lines of "the particles are jiggling less because they've done some work", though it doesn't seem like they've done very much work. (I'm leaving out the phase change, I hope I can get away with that.) 213.122.48.165 (talk) 01:25, 1 February 2010 (UTC)

I think I've worked out where my confusion stems from, I was taking atmospheric equilibrium as the reference point, where as you guys are all talking about vacuum being the reference point which I admit is more correct, however in thought experiments I think it is easier to sometimes use the atmosphere as the reference point. Case in point the fridge example above: The refrigerant is compressed, as the volume decreases the temperature and pressure increases but the ENERGY effectively remains the same. What changes the energy is that the radiator takes the heat away and the energy of the refrigerant decreases at that point. Now you have compressed refrigerant at the same temp as the ambient atmosphere. Then when the refrigerant is squirted back into the pipes inside the fridge and expands the volume increases and the temperature decreases but the energy is STILL the same. At this point the "heat" in the fridge can transfer into the refrigerant until both are equal. Then the refrigenrant with more energy is taken out of the fridge and the cycle is repeated. The real work that is done here is done by the compressor, all the other work by the gas expanding and all that only confuses the issue IMHO. Vespine (talk) 01:47, 1 February 2010 (UTC)

(ec)It is mostly the phase change of the refrigerent that's pulling heat out of the frige, so you can't ignore it. See vapor-compression refrigeration for how the whole process works. Vespine's right, in that it's the compressor doing work, and when it does, the vapor comes out at a higher temperature, and higher internal energy, than when it came in. It then loses that energy from the compressor, plus the energy from cooling the frige, in the condenser. It's squirted into the coils in the frige, where it evaporates, which requires energy, which comes from the air inside the fridge (which is why it cools down inside). Buddy431 (talk) 02:03, 1 February 2010 (UTC)

Yep, I read that article a while back. I'm trying to comprehend how the energy in the fridge can transfer into the refrigerant. I find it necessary to go into detail, because I figure the heating of the refrigerant by the air inside the fridge consists of the evening-out of the jiggling of particles. Therefore I want to know what it was about expansion of the refrigerant that caused the particles in it to jiggle less. I could just say "the same energy occupies more volume, and therefore it can now accept some energy from inside the fridge," but if I imagine the individual particles, this explanation doesn't work, because the spreading out of the particles doesn't explain why each particle has less energy. 213.122.48.165 (talk) 02:13, 1 February 2010 (UTC)

Each particle doesn't have less energy. Pressure and temperature are two different things but are correlated, you can't change one without changing the other. The temp is like the "jiggling" and the pressure is more like "jostling against each other". When you decrease the pressure, the particles spread out and jostle against each other less but they still jiggle with the same energy they had before, it is the decrease of "jostling against each other" that accounts for the drop in temperature, not the individual particles losing any energy. Now that the particles aren't "jostling against each other" so much, they need more jiggle to bring them up to the same temperature they were before the pressure was decreased. Vespine (talk) 03:28, 1 February 2010 (UTC)

Yes you can reduce pressure without affecting temperature: release a gas into a vacuum (like I said, there was some guy who did just that to prove something or other). And in a gas anyway, temperature is related to the kinetic energy of the particles (the "jiggling", I think), NOT to how often they collide (the "jostling"). A gas with particles moving at the same average speed is a given temperature, regardless of what the pressure is. When a gas cools down while expanding, it is because the particles have lost energy in doing work, and they are moving at slower speeds. See the Kinetic theory article, especially the pressure and temperature sections. Buddy431 (talk) 04:18, 1 February 2010 (UTC)

Would the fridge not work without the phase change? (Something like a backwards stirling engine?) Would evaporation in a vacuum cause cooling? 81.131.48.166 (talk) 05:17, 1 February 2010 (UTC)

For your second question, yes, evaporating in a vacuum would cause cooling. A phase change from liquid to gas absorbs energy: see enthalpy of vaporization. I'm not sure about a compression fridge without a phase change, but I think it certainly wouldn't be as effective at cooling as the ones typically used. Buddy431 (talk) 17:01, 1 February 2010 (UTC)

I'm still uncertain about the original question. Let's try this: suppose we collect a lot of water and put it on a bare planet to make an ocean. Imagine it's insulated above and below. It was all originally the same temperature, and now suddenly it's an ocean, and subject to gravity. So the bottom of this new ocean is getting compressed. There is no heat input from anywhere. When everything has settled down, is the ocean the same temperature throughout, or cold at the bottom, or hot at the bottom? Does everything ever settle down? 213.122.17.58 (talk) 01:27, 3 February 2010 (UTC)

These "planet" scale questions I think are going to have different issues affecting them. You can't just say "bare planet" because I think for liquid water you have to have at least an atmosphere of some sort, otherwise it would freeze or evaporate away, I think. So as far as I know, planets including the earth, form as molten balls due to the forces of accretion but once that is settled down and new material isn't being added, they gradually cool. After that point the pressure of gravity does not "add" any more heat to this process, the planet slowly cools until it geologically "dies", which means there is no heat left in the core. You could call that "settled down". For example it is believed that Mars is geologically inactive. So if you added water to that, even if there was enough pressure to heat something up, the heat would dissipate and that too would eventually settle down. The pressure down there is not what creates the heat, the only reason the earth has heat deep down inside is because it is still cooling. Once it has cooled down you could drill all the way to the core and it would be the same temp as the crust, the "pressure" is not adding extra heat.Vespine (talk) 00:46, 4 February 2010 (UTC)

This is archived now, but I'm pissy enough to observe here that you ignored my "imagine it's insulated above and below" sentence. Just straight out ignored it. 81.131.60.13 (talk) 19:17, 7 February 2010 (UTC)

What gas is green?

What gas is green in nature, without electrical charges or other tricks to make it glow? I remember in science class in high school talking about one specific gas that naturally occurs green. Maybe there's more than one.

People might not know the answer offhand, so can you recommend a good way to search? Or an article topic or category or something I could use? Thanks 24.20.200.67 (talk) 19:52, 31 January 2010 (UTC)

Chlorine gas is said to be green, looks more greeny/olive/brown to me. Nanonic (talk) 19:56, 31 January 2010 (UTC)

Fluorine too. But neither of these gases occur in nature. Buddy431 (talk) 20:20, 31 January 2010 (UTC)

I think its Fluorine I was thinking of. Thanks wikipedia!! 24.20.200.67 (talk) 21:31, 31 January 2010 (UTC)

As far as I know, the dihalogen gases (eg. Cl2, and F2 mentioned) are not coloured as a diatomic molecule. The colour that is observed is due to tiny amounts of radicals formed from the dissociation of the diatomic (Cl_2 -> 2 .Cl). The diatomic and radical species are in an equilibrium (the diatomic side is heavily favoured over the radical side). —Preceding unsigned comment added by 24.150.18.30 (talk) 02:42, 2 February 2010 (UTC)

Order of reaction Mg + HCl

How does the rate of the reaction Mg(s)+HCl(aq) depend on the concentration of HCl? Is it first order or second order? My class did an experiment in which both my group's data, and the averaged data of the entire class, clearly show that it is first order. However, the teacher claims this was wrong and gave us "real" data which showed the reaction to be second-order. I searched on the Internet and found some sources claiming it's first-order and some claiming it's second-order.

Which one is right? --99.237.234.104 (talk) 19:58, 31 January 2010 (UTC)

What is the balanced chemical equation for this reaction? What is the coefficient of the HCl (or the ionic part of it that is really reacting)? Often the coefficients are Order of reaction of each reactant. DMacks (talk) 21:18, 31 January 2010 (UTC)

This and this suggest that the mechanisms not really known, and that different concentrations and different types of acid can give different rate dependences, and that different people have gotten results that can't be reproduced. That sure inspires confidence. They cite an article claiming that it's second order though. You can download the article, and it becomes clear that even real scientists with lots of experience are getting different results based on how exactly the experiment is set up. I think the conclusion is that this probably isn't the best experiment to be teaching high school chemistry students about rate laws. Buddy431 (talk) 04:04, 1 February 2010 (UTC)

One thing this does illustrate is the importance of careful experimental procedures (and documentation of them) to make sure all variables are controlled. The results don't sound random/non-reproducible, but rather are just highly affected by experimental details. DMacks (talk) 06:51, 1 February 2010 (UTC)

Reactions don't have to be one or another. For example, the substitution reactions of secondary alkyl halides can proceed through SN1 or SN2 pathways depending on the solvent and other experimental conditions (like say, the presence of nucleophilic catalysts). Whether the HCl was added as a gas or was added dilute or added in concentrated form or maybe added as a solution in ether (as opposed to water) would all affect the mechanism. Reactions aren't often only first order or second order -- sometimes they can go through both types of pathways (to give the same product). John Riemann Soong (talk) 23:02, 1 February 2010 (UTC)

There are all sort of side reactions that can take place because the reaction actually occurs by multiple steps and multiple mechanisms. You have an aqueous solution and solvent effects are very important. Is the magnesium effectively protonated, forming a polar covalent Mg+-H bond, or does magnesium reduce protons to free hydride ions? The latter would be a first order reaction -- hydrides are so reactive that they will pull off other protons right away, forming hydrogen gas.

But if Mg+-H is formed instead, then protonation would be a "fast step" and the Mg+-H species is vulnerable to nucleophilic attack by water or chloride. It could be protonated again to yield hydrogen and Mg2+, but this may be "slow" because it is difficult to protonate an already protonated species (think of the equilibrium between HMg+ and H3O+ and Mg2+ and HOH). Water is actually a better nucleophile than chloride so it competes and bind to HMg+ as a ligand; this relieves positive charge on the Mg (magnesium-bound water becomes a little more acidic) and then H3O+ finds it more easy to react with the magnesium hydride. (This step produces H2). But now you have HOH-Mg2+ <---> H+ , OH-Mg+ which might react with chloride or bind with water and you have to turn this into MgCl2. Which is actually thermodynamically favourable but chloride will find it difficult to displace hydroxide by a direct substitution so it will actually have to go through a roundabout pathway first.

But if you use a solvent that might not bind magnesium as well, then a different mechanism might occur.

Some metals also like to react by single electron transfer and the metal could release an electron first, releasing a solvated electron. This means sometimes radical mechanisms are involved, especially in redox reactions. There are multiple pathways to be pursued and some pathways have two rate-limiting steps, thus complicating the calculation of the rate laws for the reaction. John Riemann Soong (talk) 16:45, 2 February 2010 (UTC)

Chemical formula of cellulose

Should the chemical formula of cellulose be (C
₆H
₁₀O
₅)
_n·H
₂O? --84.61.165.65 (talk) 20:44, 31 January 2010 (UTC)

No, the use of a dot in the formula suggests it is specifically a monohydrate (contains a single actual molecule of water bound in the structure). Are you perhaps thinking about the ends of the polymer chain, one of which has an H and one an OH? Those are a total of H
₂O but they are not "together as a water molecule". This is a general concern for the chemical formula of any polymer. WP:Chem would be the place to see if there is a need to adjust the infoboxes...I spot-checked a few polymer articles and none of them include end-groups in their chemical formula. DMacks (talk) 21:13, 31 January 2010 (UTC)

Energy from reversing desalination

The desalination article says that desalination requires large amounts of energy. Why then, if I pour some salt into a glass of fresh water, do I not get any energy back? 92.24.73.102 (talk) 21:40, 31 January 2010 (UTC)

Actually, dissolving table-salt in water absorbs energy (it has a positive Heat of solution). The desalination process does not result in overall addition of energy into the water (i.e., the products having more energy, which could be recovered by remixing). For example, distillation consumes lots of energy to boil the salt-water, but then that energy is released when the water-vapor condenses and the salt and water cool back to room temperature--the cooling water winds up containing the energy that was transiently in the pure water vapor, and is then discarded into the environment. Problem is that it's difficult to recover that energy efficiently--the products do not have a higher energy content, just a lot of energy was wasted (in a net sense) to get them separated. Is reverse osmosis energy-efficient (other than perhaps having to pump the water)? DMacks (talk) 21:53, 31 January 2010 (UTC)

The large amounts of energy required are either to evaporate the water (in distillation, including multi-stage flash distillation) or to force it through a semipermeable membrane (in reverse osmosis). In the first instance, energy is released when the steam condenses, but as DMacks pointed out, it's hard to recover this. In the second instance, you (in theory) could get back some of this energy by allowing normal osmosis to occur and capturing energy from the water movement created across the membrane. Needless to say, it's not worth wasting using fresh water like this to generate electricity. Buddy431 (talk) 22:06, 31 January 2010 (UTC)

There have actually been suggestions on capturing the energy of freshwater/saltwater mixing. See, for example "Energy Recovery from Controlled Mixing Salt and Fresh Water with a Reverse Electrodialysis System" Environ. Sci. Technol., 2008, 42 (15), pp 5785–5790, or "Extracting Renewable Energy from a Salinity Difference Using a Capacitor" Physical Review Letters 103, 058501 (2009). or any number of the news articles from last year, e.g [2] [3] [4] [5]. The thought is that the generation plants would be located at the mouth of rivers, where there already is substantial mixing of salt and fresh water. -- 174.21.224.109 (talk) 22:45, 31 January 2010 (UTC)

The first "salination" power plant in the world (or so the owners argue) opened last year~in Norway, see this page Jørgen (talk) 13:40, 1 February 2010 (UTC)

Perpetrual-reality

understanding the theroy of perpetual reality and its consept in to continues energy? —Preceding unsigned comment added by Angeldell (talk • contribs) 23:13, 31 January 2010 (UTC)

Sorry, I don't understand. Could you define "perpetual reality"? Are you perhaps referring to perpetual motion machines? Comet Tuttle (talk) 23:22, 31 January 2010 (UTC)

I refer to if reality as we know it! is continues and by understanding the way it works can we creat a machine based on it's machnics? —Preceding unsigned comment added by Angeldell (talk • contribs) 23:30, 31 January 2010 (UTC)

I think you're asking whether a machine might be made that does some useful work based on the simple fact that time advances. I'd suggest that this is unlikely, because entropy always increases (see Second law of thermodynamics). Comet Tuttle (talk) 23:48, 31 January 2010 (UTC)

If you are correct, then it sounds like, yes. You might look at the mathematical links under mobius for a model of something which could be considered continuous. I'm not sure Science has anything beyond possible speculation in the area of reality, and creating such a machine could prove the existence of reality having a continuous shape, which would be an interesting discovery for science. --Neptunerover (talk) 23:54, 31 January 2010 (UTC)

This response from NeptuneRover is a clear breach of the WP:NOR rule. It is not true - I advise our OP to ignore it. SteveBaker (talk) 02:42, 1 February 2010 (UTC)

I have this idea in mind for years that an active formal that is not yet seen that might prove that such a machine might be created. --Angeldell (talk) 00:00, 1 February 2010 (UTC)

Sorry, the phrase "active formal" doesn't mean anything in English — could you try a rephrasing? Comet Tuttle (talk) 00:08, 1 February 2010 (UTC)

(edit conflict x2)Are quantum mechanics, chaos theory and illusion partially relavent? ~AH1^(TCU) 00:06, 1 February 2010 (UTC)

Maybe he's wondering if it's possible to create a machine to simulate the entire universe. It's very hard to understand the question.

Angeldell: try posting the question in your native language. There are many editors here, maybe someone will know your language. Ariel. (talk) 01:00, 1 February 2010 (UTC)

possibly he's wondering if he can keep us guessing what he's after for the rest of eternity... --Ludwigs2 02:01, 1 February 2010 (UTC)

More suggestions: end of the Universe, vacuum energy, expansion of the universe, supercomputer, reality, perception of time, spacetime, Special Relativity, out of body experience, Eschatology, Large Hadron Collider, The Quantum Prophecy, Kali Yuga, Infinity, hypercube, information, self-reference. ~AH1^(TCU) 02:23, 1 February 2010 (UTC)

We need a clearer statement of this question before we can attempt to answer it. It is pointless to guess at what our original poster is asking and the answers presented so far are as likely to mislead as they are to inform. We should cease to comment until/unless the questioner can expand a little on what we're being asked. SteveBaker (talk) 02:44, 1 February 2010 (UTC)

If you don't even know what the question is, Steve, how can you decide which answer might be wrong? --Neptunerover (talk) 03:12, 1 February 2010 (UTC)

Steve's ". . . as likely to mislead as . . . to inform" is not equal to "wrong" in my understanding of English. The very point is that we can't decide right or wrong based on what is here. Bielle (talk) 03:24, 1 February 2010 (UTC)

I understood what the question was though. Steve doesn't. I gave the guy an answer fitting his question. --Neptunerover (talk) 04:58, 1 February 2010 (UTC)

If Steve doesn't understand the question, then he cannot judge how my answer relates to it. --Neptunerover (talk) 05:03, 1 February 2010 (UTC)

"I'm not sure Science has anything beyond possible speculation in the area of reality, and creating such a machine could prove the existence of reality having a continuous shape"? This is nonsense from beginning to end. Comet Tuttle (talk) 05:37, 1 February 2010 (UTC)

I see what you misunderstand, but you are misunderstanding what that statement says. Did you read the OP's question? It was a question mentioning perpetual reality as if it were a fact. I pointed out that science is not aware of such being a fact. As the OP mentioned a machine based on perpetual reality, I informed him that if there were to be such a machine, that would be quite a discovery for science. I didn't tell him to run build a machine! I didn't even tell him any such thing was possible. All I said was yes, if the OP was correct in all the statements he said about reality being perpetual and continuous, then yes, a perpetual reality-based machine would be a yes, or at least it sounds like it, for how would I know? --Neptunerover (talk) 06:06, 1 February 2010 (UTC)

Guys, let it go. the question was confused, and there's no need to go over whether the answers are confused as well. I think what we all need to do is go home, take some heavy-duty mind expanding drugs, and reconsider the issue from an altered state of perception. sound like a plan? --Ludwigs2 06:14, 1 February 2010 (UTC)

No. Mind-expanding drugs are not even the only way to acheive an altered state of mind.

It was an accident. ~AH1^(TCU) 04:00, 3 February 2010 (UTC)