Wikipedia:Reference desk/Archives/Science/2010 December 20

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December 20

Add salt to hot water bottle?

Can I make the heat in my hot water bottle last longer (I mean increase the heat capacity of the water) by adding salt? How much salt? How much difference would it make? I can reuse the water by pouring it from the bottle into a pan and pouring it back with a funnel. Of course I don't want the initial temperature to be increased (that would perish the rubber) but I do want more heat in there. —Preceding unsigned comment added by 78.148.143.201 (talk) 00:39, 20 December 2010 (UTC)

Boiling point elevation is a real effect, but too small to make much of a difference here. Yes, you can marginally raise the maximum temperature of hot water by adding salt to it before heating it, but ultimately we're talking about a difference of about 1-2% here, and that 1-2% difference might mean adding maybe 30 seconds or so to the effective usable time of your hot water bottle. In other words, not enough to bother. --Jayron32 01:17, 20 December 2010 (UTC)

Adding salt to water lowers the specific heat capacity, i'm not sure exactly how this is related to Boiling point elevation, or cooling time, but I agree with the above, getting a few minutes of an extra few degrees is not going to make any noticeable difference. Hot water bottles have been around for a long time, if it was worth filling them with brine, i'm sure it would be common practice. Get an extra blanket. Vespine (talk) 01:23, 20 December 2010 (UTC)

You could try to experiment with molten salts, these are also used for thermal storage. Count Iblis (talk) 01:30, 20 December 2010 (UTC)

Also consider that wattle bottles often leak, and salt-water is a worse spill to clean up, especially if it gets into electronics (like the alarm clock you pushed onto the floor when it went off :-) ). StuRat (talk) 02:47, 20 December 2010 (UTC)

You specifically mentioned that you didn't want to increase the initial temperature, so adding salt would actually reduce the thermal capacity from the same starting temperature (Fresh Water: 4186 compared with Sea Water: 3993 J kg⁻¹ K⁻¹; mainly offset by the fact that sea water is about less than 3.5% heavier). Buy a bigger bottle! Dbfirs 08:35, 20 December 2010 (UTC)

Since seawater is denser then freshwater, you might not need to get a bigger bottle. Googlemeister (talk) 19:14, 20 December 2010 (UTC)

Yes, I realised that fact and checked that it is always less than 3.5% denser (typically 2% heavier for a fixed volume), so you would need a bigger bottle whatever concentration of salt you used. I must admit that I don't know why salty water stores less heat per unit volume. Perhaps someone can explain the fact? I have a theory, but this is not an area where I have any expertise, so I don't know whether my guess is correct. Dbfirs 22:00, 20 December 2010 (UTC)

You could try a brick heated in the oven and wrapped in a towel - probably a wastful way to heat it. I didnt think people needed hot water bottles anymore. 92.29.124.17 (talk) 22:34, 20 December 2010 (UTC)

Well now you know how the other half live. It's more cost-effective to heat the person(s) directly than to heat every nook of a house. Such economy may never cease to be necessary for many people. --129.215.4.98 (talk) 23:53, 20 December 2010 (UTC)

I've heard of them being used for someone who is sick, and having chills, so you don't have to overheat everyone else in the house to make the sick person comfortable. It could also be used if one person in the bed likes it warmer than the other(s). StuRat (talk) 01:15, 21 December 2010 (UTC)

Why not use an electric blanket instead, if you can still buy them, although they seemed scarily dangerous to me. With central heating now being universal in the UK, nobody uses them anymore. I'm not sure they'd work with the lower North American voltages. Or buy an additional high tog duvet - probably safer. 92.24.188.27 (talk) 15:34, 21 December 2010 (UTC)

You seem to have answered your own Q; an electric blanket is inherently dangerous, that's why people would prefer to use a hot water bottle. And yes, they do work in North America. StuRat (talk) 17:56, 21 December 2010 (UTC)

Central heating now universal? We don't all have such luxurious houses! Also, overblankets, the most effective type of electric blanket, doesn't seem to be made any more in the UK, though the cheap and less-effective underblanket, with extra safety cut-out circuitry that often goes wrong, is still sold. Dbfirs 19:12, 21 December 2010 (UTC)

What place are you in where central heating is not the norm? In the UK houses are only without central heating where there isnt a gas supply and the owners don't want to go to the expense of oil heating at it is almost as expensive as electricity. I understand that in snowy Scandinavia, electric heating is most common, perhaps due to having lots of hydroelectric and heavily insulated homes. 92.15.5.196 (talk) 19:38, 21 December 2010 (UTC)

A place exactly as you describe. The nearest gas supply is five miles away, and older houses here have little insulation. In the house where I was born, I can remember when a glass of water by the bedside was frozen by morning, though the house where I now live is not quite as cold as that. Dbfirs 21:32, 21 December 2010 (UTC)

And did the house also lack plumbing ? Otherwise, I'd expect the pipes to freeze. StuRat (talk) 21:34, 21 December 2010 (UTC)

Strange you should ask that, because I've just thawed out some frozen pipes here. The house where I was born had very limited plumbing. Dbfirs 22:26, 21 December 2010 (UTC)

Not so strange, really, since the one is an inevitable result of the other. And, since water damage from burst pipes can cost far more, it doesn't make sense to keep it so cold that this becomes a possibility. StuRat (talk) 15:49, 22 December 2010 (UTC)

Well the house and plumbing have survived for over a hundred years without central heating, but this frozen bit was a later addition very near to an outside wall. It is more than 25 years since it was last frozen. Dbfirs 21:37, 22 December 2010 (UTC)

There's a big difference between being "the norm" and "universal". StuRat (talk) 21:32, 21 December 2010 (UTC)

Put 165 grams of Caesium-137 in your hot water bottle and it will generate about 100 Watts of heat for many years. Count Iblis (talk) 23:06, 22 December 2010 (UTC)

And an added benefit would be that you would feel warmer, due to the radiation burns. :-) StuRat (talk) 07:26, 24 December 2010 (UTC)

Drinks when sick

I have heard various advice over the years that clear liquids are better for you when you are sick than colored liquids, usually under the pretense of "needing to stay hydrated". However, my mom has always seemed to press on me something like 7-up (which is decisively clear), which raises to me the question what could be the benefits of a clear soft drink versus cola or some other colored soft drink? Why are clear fluids better for you than non-clear fluids (or are they)? Ks0stm ^(T•C•G) 00:49, 20 December 2010 (UTC)

I think the idea is to not drink stuff which is going to be heavy on your stomach; so something like milk or orange juice is probably too much for a sick stomach to take. Water or dilute tea or something like that. Functionally, it probably doesn't make much difference which brand of carbonated sugar water you drink, if you are drinking carbonated sugar water. Not sure whether that puts the whole class of drinks under "clear" or "not-clear", but I can't imagine being able to cut the line that finely. --Jayron32 01:15, 20 December 2010 (UTC)

I was always told it had to do with the caramel coloring being heavier on the stomach. Dismas|^(talk) 01:37, 20 December 2010 (UTC)

Maybe the caregiver is thinking ahead, and thinks clear vomit will cause fewer stains ? StuRat (talk) 02:44, 20 December 2010 (UTC)

Do you have personal experience of that? 92.15.13.152 (talk) 12:30, 20 December 2010 (UTC)

this is probably closer to the truth than it appears at first glance. --Jayron32 02:47, 20 December 2010 (UTC)

While it may be easier on the stomach, for some reason it seems to have been extended to all illness, anything from strep throat to stomach flu. Is there any particular advantages it would confer in a situation where the stomach was not a part of the illness? Ks0stm ^(T•C•G) 02:52, 20 December 2010 (UTC)

I believe "clear liquid" is meant to rule out milk or coffee. My mother would give me stirred (de-fizzed) Coke when I was sick as a child, and it was just fine. I suspect that was an old Southern remedy. Ginger ale is a mild anti-nauseant (as are all ginger products). Acroterion _(talk) 04:26, 20 December 2010 (UTC)

Perhaps Adam's Ale is what is preferred. 92.15.13.152 (talk) 12:32, 20 December 2010 (UTC)

Found a source that appears to be related (but I can't access it), titled "Soft Drinks, electrolytes and sick children", from the Lancet 1983 Jun25;1(8339):1450 - Although, there are far more sources that point to problems associated with soft drinks in areas such as obesity, diabeties etc... (Thats a bit of a non-answer though isn't it). I was often given flat 7-up as a child if I had been quite ill and vomited. I was always under the impression that it helped to re-hydrate, and that the sugars and salts in the drink helped to replenish what I had lost while vomiting Darigan (talk) 15:38, 20 December 2010 (UTC)

That's actually a response to a formal comment to an earlier report on the treatment of diarrhea in infants. The gist of the response is to compare and contrast the electrolyte content of certain soft drinks and juices with the standard medical intervention. The standard treatment is very high in sodium and low in potassium but the comment article notes this may be undesirable in some cases. Juices provide high potassium and low sodium, while soda provides medium sodium and low potassium. It isn't really about judging what is best, but merely showing alternatives that may be more appropriate depending on a patient's condition. Dragons flight (talk) 16:40, 20 December 2010 (UTC)

The history of the popular UK soft drink Lucozade may be of interest, as it was originally produced specifically for the mildly ill. Although our article contains no images, the original version at any rate (I haven't drunk any for some years) was clear, very pale orange in colour and carbonated. This may have been made in deliberate accordance with the OP's recalled proscriptions, or may have helped to form them. Common wisdom has it that (strength-for-strength and volume-for-volume) lighter-coloured alcoholic drinks cause less hangover than darker ones, because the colour is caused by congeners that may contribute to the ill effects: this might also apply to the substances responsible for darker colorations in soft drinks. 87.81.230.195 (talk) 01:22, 22 December 2010 (UTC)

I expect just plain water is best for you when ill, as it puts less strain on your body to digest it. Things like Lucozade or Seven-Up are just sugary water with fizz and colouring. If you are suffering from severe dehydration, which is unlikely in the West, then this advice may not apply. 92.29.126.195 (talk) 12:00, 22 December 2010 (UTC)

Augmented Nasal Passages?

When your nasal passages are congested, perhaps because of a cold, the linings become a bit inflamed and the amount of mucus increases, thereby making it difficult or impossible to breathe through your nose, correct? What if you threaded a bit of piping through the entire passage? Suppose it started at the nostrils and terminated, I dunno, above the throat? Would that provide you with guaranteed clear breathing? I realize it completely defeats the sanitation/filtration aspect of breathing through one's nose, but I'm just curious about the idea in general. I can't recall ever hearing of someone doing this, but it doesn't seem impossible... The Masked Booby (talk) 01:26, 20 December 2010 (UTC)

There is the Nasal cannula which serves that purpose, but is a bit extreme. The inventor of "Breath Right" nasal strips said he tried the straws; and the strips apparently worked better for him. You should, of course, consult a doctor for medical problems, but you may want to research those nasal strips. --Jayron32 01:36, 20 December 2010 (UTC)

Sure, it's possible, but why do it ? Are you thinking of a case where the mouth is wired shut or otherwise unavailable for breathing ? StuRat (talk) 02:42, 20 December 2010 (UTC)

The mouth being wired shut would not interfere with breathing -- can't you breath through your mouth when you're in sustained maximum intercuspation? DRosenbach ^{(Talk | Contribs)} 04:19, 20 December 2010 (UTC)

Not if you read mouth to mean lips not jaw. But I would tend to disagree that there is NO benefit to this, I sleep on my front and find it much harder to sleep with a blocked nose and I'm pretty sure a blocked nose can also significantly contribute to snoring. Vespine (talk) 04:25, 20 December 2010 (UTC) Vespine (talk) 04:25, 20 December 2010 (UTC)

Nasal spray is available in small squeeze bottles. It clears the nasal passages. It can be obtained as over-the-counter medication at drug stores.173.189.136.110 (talk) 04:34, 20 December 2010 (UTC)

Alternatively, in case of persistent problems, you can also remove part of the nasal concha via surgery. Count Iblis (talk) 12:58, 20 December 2010 (UTC)

How does quantum entanglement / quantum mechanics "know" that you know the positions of their particles?

Apparently you're not allowed to know the positions of particles when it comes to the quantum realm. But how does the quantum realm "know" whether you know this? I've been having a hard time wrapping my head around that notion, but hopefully you can change this situation. --70.179.178.5 (talk) 07:31, 20 December 2010 (UTC)

It's not if you know it, but if you measured it. Measuring a particle changes its state (because in order to measure it you have to interact with it). But see Quantum eraser. Ariel. (talk) 08:14, 20 December 2010 (UTC)

What happens mathematically is that, to find the probability of a given final state in quantum mechanics, you compute a sum over possible intermediate states then square the result. The "given final state" is the state of the system and environment. The environment includes the experimental apparatus, the experimenter, and everything else in the world. If you learn something about the system, say whether a particle went through slit A or B, then the final environment where you know it was slit A differs from the final environment where you know it was slit B (by slightly different electrical activity in your brain, for example). Since the final states are different, you have to compute two different sums and square them separately to get the probabilities of each outcome. On the other hand, if there's no unambiguous information in the final state of the system+environment regarding which slit the particle went through, you add up histories for both slits and square the result, which gives you a different answer. So it is, effectively, a matter of what you know (or, more precisely, what information is retained anywhere in the universe). Why the universe works that way is not really understood. -- BenRG (talk) 09:14, 20 December 2010 (UTC)

To clarify, it is incorrect to say that quantum measurement requires interaction. See interaction-free measurement. Looking for a particle and failing to find it tells you something about the particle's location (it's not there), even though no interaction took place. -- BenRG (talk) 09:19, 20 December 2010 (UTC)

Expect to keep having trouble wrapping your head around it. The two major revolutions of the early 20th century were relativity and quantum mechanics. Both were, at first, highly counterintuitive.

But there's a huge qualitative difference between the two. Relativity is counterintuitive at first, but you can retrain your intuitions to accommodate it. QM, not so much. That's because QM is virtually impossible to square with realism, and we are hard-wired realists.

The usual solution on the part of working physicists is to stop thinking about these things. I think it was Richard Feynman who said "shut up and calculate". John von Neumann claimed that "in mathematics, you don't understand things; you just get used to them" — that would be much more appropriate applied to QM. --Trovatore (talk) 08:38, 20 December 2010 (UTC)

The Many-Worlds interpretation is by far the simplest explanation. You simply get entangled with the particle when you measure it. It's no different than how one particle gets entangled with another. I suggest reading the Less Wrong Quantum Physics Sequence. If that's too long for you, just read Classical Configuration Spaces and Decoherence. — DanielLC 18:13, 20 December 2010 (UTC)

"Simplest" is subjective. Personally, I subjectively feel the many-worlds interpretation is pretty close to bat-shit insane, even though I know it is not provably any more right or wrong than any of the other mainstream interpretations of quantum mechanics. Of course, on the other hand, lots of things that are provably correct in quantum mechanics also feel insane, so maybe there is no accounting for subjective taste.  ;-) Dragons flight (talk) 18:37, 20 December 2010 (UTC)

Normally it's somewhat subjective. In this case, it's just the Copenhagen interpretation with wave-form collapse missing. Entanglement has been experimentally proven on small scales, and it's really all the Many Worlds Interpretation uses. Adding a law couldn't possibly make things simpler, especially when it's the only nonlinear, non-unitary, non-differential, discontinuous, non-local, CPT-asymmetric, Liouville's Theorem violating, or indeterministic law in all of quantum mechanics. It does require more universes, for a certain definition of more, but given that there's about 10^80 particles in the visible universe, and all the known laws of physics can fit on an index card, complexity of laws is clearly what matters. Also, it's theoretically possible to prove right, just obscenely difficult. If you want to actually test it, you can't prove it, but if you're wondering if there's a difference philosophically speaking, there is. — DanielLC 00:54, 21 December 2010 (UTC)

I like the MWI because the first time somebody explained it to me was the first time I understood the mathematical structure of quantum mechanics. I think it's helpful in understanding how the QM rules lead to the universe "knowing what you know", as the OP asked. It's not necessary to believe in it to get that benefit. I don't personally believe it, or disbelieve it, I suppose. I trust the well-tested quantum rules more than I trust untested rules added with the apparent purpose of avoiding MWI, but that's not at all the same as believing in MWI. -- BenRG (talk) 08:25, 21 December 2010 (UTC)

there a movement back and forth in time so the two partical are conected and afected . thanks —Preceding unsigned comment added by 212.117.145.118 (talk) 06:52, 21 December 2010 (UTC)

No, not at all. -- BenRG (talk) 08:25, 21 December 2010 (UTC)

That sounds like the Transactional interpretation.

Think of it if you like as what you might see if you were running a 4D simulation in a computer of a kind of minimum principle, with some of the boundary condition information specified at the end-time of the simulation, rather than the start time. So you start by propagating a 'best guess' forward from your incompletely specified initial conditions till you get to the end-time of the simulation, at which point you discover there's a mismatch, which you can patch up by propagating a 'correction' back towards the start-time of the simulation. You can see, at least for a simulation in a computer, how that might make some sense.

If I remember correctly, TI doesn't make any predictions that are different from the Copenhagen Interpretation (there was a paper, I think about 1990 in Foundations of Physics, that showed this in some detail). Rather, it's a way of creating a consistent possible intermediate picture for what Copenhagen says you're not allowed to picture. For those of a more realist disposition, it's a way of coping with non-local information and constraints in a way that is at least instantaneously local, albeit one that's build-up includes these back-in-time correction waves.

Perhaps best not to take it too seriously; but to see it as a way to develop intermediate-time pictures in a consistent way that develop smoothly, which can be a useful additional perspective to be able to add, when trying to think about some of the odder thought experiments, that are trying to push you into giving a realistic picture for "What was happening there?" Jheald (talk) 09:46, 21 December 2010 (UTC)

If QM applies to observers, then the MWI is correct. A simple argument by David Deutsch can be invoked in which a measurement is performed by an observer such that observer plus measured system is a closed system. Then, there always exists a unitary map that will erase the memory of the measurement result and restore the original state of the measured system, but such that the observer remembers having performed the measurement (but of course, unable to remember the result). But if the CI is true, this won't work; the wavefunction of the measured sytem won't be restored, because after the measurement, the unitary map that would restore it, would only act on the "real sector" of the state, the other sector where a different result is found, supposedly does not exist according to the CI so it cannot contribute to the final state. It is easy to verify that the state is always restored to the original state by repeatedly performing this procedure and performing a new measurements on the final states.

So, MWI can actually be experimentally distinguished from CI, but in practice that would require implementing observers within large scale quantum computing simulations. That's a bit far fetched as we can't even implement observers using ordinary computer simulations. But being able to actually implement a thought experiment is irrelvant in physics, all that matters is that there are no theoretical obstacles to be able to implement it. So, what is relevant here is that all unitary mappings can be implemented using quantum computers, as they can all be reduced to sequences of CNOT and Hadamard transforms. So, there is nothing in theory that would prevent one from actually performing Deutsch's thought experiment. I.m.o. this proves that if the MWI is not correct then QM itself is not correct. Count Iblis (talk) 14:27, 21 December 2010 (UTC)

First of all, Deutsch does not strike me as a very smart guy. He got famous by accident, by proposing a model of quantum computation that became popular, but his creation was not all that interesting. It's like Larry Wall and Perl, to take a completely random example. I think that some of what Deutsch writes about QM is correct, and some of it is wrong, but none of it is very interesting.

Second, this experiment can't be performed in practice, and to argue that it's performable in principle you have to make philosophical assumptions that effectively imply the MWI already. For starters, you have to assume that measurements of the sort that invoke the Born rule can be thermodynamically reversible. But Copenhagen supporters can always say that thermodynamics has an essential role in the collapse process, and how are you going to respond to that? It might even be true. The fact is we have no idea what happens to the quantum rules when they're extrapolated that far from the regime where they've been tested. We know something happens to them because we see general relativity in the classical regime, and we don't understand how that works. It's not even clear what unitary evolution means in a GR universe. The MWI starts with an equation (the Schrödinger equation) describing unitary evolution in terms of an a priori time coordinate. That equation makes accurate predictions in the lab so far, but the philosophy behind it is seriously at odds with the philosophy behind GR. The path-integral formulation of QM seems a bit closer to GR, and MWI doesn't seem so natural there. The path-integral formulation suggests that it's just as natural to constrain the end of the universe as to constrain the beginning. So much for all the worlds that don't meet the constraint. It's just ridiculous to pretend that we understand physics at this level well enough to say anything about the MWI. -- BenRG (talk) 00:34, 22 December 2010 (UTC)

Hmmm, I thought that in case of quantum gravity you have the Wheeler-deWitt equation H|psi> = 0. Count Iblis (talk) 22:44, 22 December 2010 (UTC)

Parallel RLC network

Can someone please tell me why the impedance of a parallel RLC network is at maximum in resonance ? With the aid of mathematical equations. — Preceding unsigned comment added by Randeep d (talk • contribs) 07:43, 20 December 2010 (UTC)

See RLC circuit#Parallel RLC circuit and that whole article. Since the impedance of a parallel RLC circuit is the reciprocal of the corresponding series RLC circuit, and the "resonance frequency [for series RLC and most other circuits] is defined as the frequency at which the impedance of the circuit is at a minimum," it follows that the impedance of a parallel RLC network at the resonance frequency will be its maximum. Ginger Conspiracy (talk) 12:05, 20 December 2010 (UTC)

embryology

if left umbilical vein is obliterated and remains as ligamentum teres in adults then why it is on the right side of the body instead of left side? — Preceding unsigned comment added by Afsawal1 (talk • contribs) 11:22, 20 December 2010 (UTC)

Because it went all the way across before the left side was obliterated. See Umbilical vein. Ginger Conspiracy (talk) 12:13, 20 December 2010 (UTC)

Lots of things start on one side of the body, then cross over to the other side. I'm not sure why, though, as this implies a longer route. StuRat (talk) 17:35, 20 December 2010 (UTC)

Evolution isn't perfect. ;) --71.240.162.87 (talk) 06:06, 22 December 2010 (UTC)

Propsopagnosia and specific face parts

My understanding after reading the article is that people with propsopagnosia have problems putting all the pieces together to recognize a face, but if they focus on or are only shown parts, can they perceive basic traits such as size and shape? For instance, if a person with this disorder were shown two pictures, one of Karl Malden's nose and one of Michael Jackson's nose near the end of his life and then asked which nose is thinner and which is more bulbous, could most propsopagnosics tell that? 20.137.18.50 (talk) 14:15, 20 December 2010 (UTC)

That would depend on the extent of the disorder and is likely to vary on a case-by-case basis. Anyone living with an agnosia might have practice overcoming it with concentration and effort, so I would guess yes, over time. If [1] (from page 79; call around to find a library that carries that) has prognosis information, you might consider please adding a Prognosis section to our article. Ginger Conspiracy (talk) 15:12, 20 December 2010 (UTC)

The question that really puzzles me here is why the OP used [[Prosopagnosia|propsopagnosia]] as a wikilink, linking to the correct article prosopagnosia but deliberately misspelling it as propsopagnosia. I don't understand why anybody would do that. Looie496 (talk) 18:00, 20 December 2010 (UTC)

I'd like to say I did it just to screw with you but the truth is that I looked at the word too quickly and saw three 'p's where there were only two in the word and typed it out for the word and copied and pasted the URL for the link using the link tool. 20.137.18.50 (talk) 18:37, 20 December 2010 (UTC)

Aha, thanks for the explanation. It didn't seem like the kind of thing anybody would do out of malice, but I just couldn't figure out a chain of events that would get there. Looie496 (talk) 18:50, 20 December 2010 (UTC)

I think the answer is that even a severely face-blind person could tell those noses apart, unless they have something more severe than mere face blindness. Even Oliver Sacks's Dr. P (the man who mistook his wife for a hat) could recognize such simple differences of shape, and he was much more than just face blind. The difficulty for prosopagnosiacs is recognizing people who have no unusual facial feature. -- BenRG (talk) 08:13, 21 December 2010 (UTC)

I think the Subtypes section of the article linked to by the OP answers the question: Associative prosopagnosiacs probably could tell the difference, still without being able to identify anyone by face; Apperceptive prosopagnosiacs probably could not.

See also the The Man Who Mistook His Wife for a Hat and the Visual agnosia articles. WikiDao ☯ (talk) 15:46, 21 December 2010 (UTC)

Except in a very severe form, I don't think there's any need for a flaw in basic recognition of visual features. The thing about facial recognition is that so many people are ridiculously, almost supernaturally, good at it. I mean, they can look at a snapshot of somebody on a TV broadcast and recognize that someone in their part of the country is the exact same person 25 years later and be so confident that they're actually willing to call the police about it. By comparison, you can hardly program a mechanical face recognition system so that it won't spot Osama bin Laden on an average day at the football stadium. Wnt (talk) 19:29, 21 December 2010 (UTC)

best thing for teeth after vomiting

I overheard a "debate" recently regarding whether, after vomiting, it was better to brush your teeth, rinse with baking soda, or rinse with mouthwash. I've done a little looking around and apparently the bad thing about brushing your teeth afterwards is that it helps the acid scratch away teeth enamel. Would toothpaste not satisfactorily neutralise? How valid is the "scratching away by brushing" theory? And baking soda seems most recommended, because it neutralises the acid, preventing it from damaging your teeth—does science verify this? I couldn't find any reasoning on the 'net for the mouthwash suggestion though . . . some are pro, some are anti, but no one says why. Any ideas? I have no personal need to know, really, I haven't vomited in years, but I'm interested in hearing what some science heads have to say on the topic. Thanks. 92.17.190.111 (talk) 16:21, 20 December 2010 (UTC)

Rinse well with water, then brush, and then mouthwash if available. (Do not swallow mouthwash unless the manufacturer has given you permission to do so. This is not medical advice.) Then figure out why you vomited? Then floss. Ginger Conspiracy (talk) 18:56, 20 December 2010 (UTC)

It depends on how much vomiting a person is doing. If this is an issue of vomiting daily, they should see a doctor ASAP. If its once every few years, as the OP states, then your teeth are perfectly resilliant enough to avoid any damage from such a rare occurance. --Jayron32 17:14, 20 December 2010 (UTC)

Vomit is normally quite acidic, and baking soda is alkaline, so, yes, they should neutralize each other (you would get bubbling when this happens). However, just getting the vomit out of your mouth quickly, by rinsing with water, is probably the quickest way to get rid of the acidity. If you want to brush with baking soda after, that's fine. StuRat (talk) 17:32, 20 December 2010 (UTC)

Chewing an antacid tablet would also help in the same way. WikiDao ☯ (talk) 18:23, 20 December 2010 (UTC)

Drink some milk, it acts as a chemical buffer that neutralises acids or alkalis. 92.15.27.229 (talk) 18:50, 20 December 2010 (UTC)

When I asked my dentist about something similar (brushing after drinking acidic, but sugar-free drinks), he said that it was better to brush before drinking than after, because the acid did effect the enamel, and it was possible to "brush it off". Acid erosion#Prevention and management says, "No brushing immediately after consuming acidic food and drink as teeth will be softened. Leave at least half an hour of time space. Rinsing with water is better than brushing after consuming acidic foods and drinks." (sources provided)--Kateshortforbob _talk 10:33, 22 December 2010 (UTC)

If you decide to drink milk, homogenized milk may not be quite the best thing. This is anecdotal but it twice made me vomit. ~AH1^(TCU) 17:32, 22 December 2010 (UTC)

What I should have written above was drink, swirl, and then spit out the milk. 92.15.31.212 (talk) 22:33, 23 December 2010 (UTC)

Probably the best thing to do is treat it like any other chemical spill: flush the affected area with copious amounts of water. --Carnildo (talk) 02:53, 24 December 2010 (UTC)

Metallic vs. nonmetal antimony

The antimony in question

In the article antimony, it states that this picture is the nonmetal black form of antimony. The description of the picture states that it is metallic antimony. Which one is it?Chemicalinterest (talk) 16:47, 20 December 2010 (UTC)

Browsing around http://www.google.com/images?q=antimony makes me think it's the nonmetalic form in the vial. Ginger Conspiracy (talk) 17:12, 20 December 2010 (UTC)

FWIW the caption in the article was added here I'm guessing by looking at the image, the description in the image was added here by the same person I think as a translation of the Czech text added by the uploader (from wiktionary:kovový it does mean metal. Nil Einne (talk) 17:18, 20 December 2010 (UTC)

I see some shiny bits in the picture which look somewhat like a metal. It could be the light reflecting, though. --Chemicalinterest (talk) 17:24, 20 December 2010 (UTC)

I'd say it's impossible to tell from the photo. You really need a big solid crystalline lump of antimony for it to look like a "metal" as you'd normally think of a metal. Physchim62 (talk) 20:39, 20 December 2010 (UTC)

Tobacco

do tobacco companies wash off tobacco before putting it in cigarettes — Preceding unsigned comment added by Kj650 (talk • contribs) 18:08, 20 December 2010 (UTC)

Start at Tobacco#Production and follow links from there to get the full story of how Tobacco gets from the ground into cigarettes. It is a bit more complex than just stuffing it into cigarettes. --Jayron32 18:11, 20 December 2010 (UTC)

While it is being grown, I suppose it is washed by the occasional rain. It is dried in various ways to "cure" it, after which the tobacco companies buy it at auction. If it were washed after curing, the curing process would have to be repeated in some fashion, with some nicotine lost in the re-washing, so, no. Edison (talk) 02:27, 21 December 2010 (UTC)

Dawn chorus (birds)

Do birds raised in captivity sing a dawn chorus (suggesting it is cultural rather than genetic)? Does it happen wherever in the world there are birds, or not? Have scientists discovered any reasons for it yet? Thanks 92.15.27.229 (talk) 19:06, 20 December 2010 (UTC)

Birds of many species sing. Our article explains how there are many reasons: attracting mates, defending territory, etc. Many species start singing at dawn simply because they are diurnal and sleep at night. Singing in captivity would not suggest that the vocalization is cultural. In fact, the opposite: if a bird can be raised in captivity, isolated from others of the species, and still sing, this would indicate a genetic component, because the bird cannot have learned the song from other birds. SemanticMantis (talk) 19:20, 20 December 2010 (UTC)

I guess you have never heard a dawn chorus, because the point is that all the birds sing at once, so there is a thousand times or more intensity of birdsong in the dawn chorus than at any other time throughout the day. 92.29.124.17 (talk) 22:29, 20 December 2010 (UTC)

A quick look at the literature, I can see several theories as to why birds sing at dawn (honest signals, optimal atmospheric conditions for song, dawn is not a good time to forage, for example) but I don't see any studies to suggest it was learned behaviour, although it appears that many songbirds learn their song from parents or other of their own species. -- JSBillings 20:02, 20 December 2010 (UTC)

Lunar eclipse on Winter solstice

Is it a coincidence that the the pending lunar eclipse is on the solstice or does it happen more often then? Ariel. (talk) 23:21, 20 December 2010 (UTC)

A coincidence. The last time it happened was in 1638, apparently [2]. Physchim62 (talk) 23:38, 20 December 2010 (UTC)

(e/c) According to December 2010 lunar eclipse "it will be the first total lunar eclipse to occur on the day of the Winter Solstice since 1638, and only the second in the Common Era." WikiDao ☯ (talk) 23:41, 20 December 2010 (UTC)

Figures that just after I asked this every news headline emphasizes how rare it is. Thanks for the replies. Ariel. (talk) 02:51, 21 December 2010 (UTC)

It's not the winter solstice around here anyway. It's the height of summer! I do wish that people would take a global view of these things. Believe it or not, we can see the moon here in the souther hemisphere too. HiLo48 (talk) 00:08, 21 December 2010 (UTC)

Hu! I thought it was called that there too despite it not being winter, it's still Dec 21 over there. (Or did you guys shift your calendar months too? :) Anyway the article on it says that's not the case, and I didn't know that. Ariel. (talk) 00:48, 21 December 2010 (UTC)

The winter solstice is still called the winter solstice of course. But that's not for another 6 months... Nil Einne (talk) 14:56, 22 December 2010 (UTC)

Yup. 372 years. I'm staying up to see it :) Crimsonraptor (talk) 01:02, 21 December 2010 (UTC)

I guess our article should mention the fact that it isn't winter in one half of the world, and it shouldn't really be called winter solstice, but December solstice, rather. --Lgriot (talk) 11:16, 21 December 2010 (UTC)

It doesn't call it the winter solstice. It says "Northern Winter Solstice (Southern Summer Solstice)". -- Jack of Oz [your turn] 11:22, 21 December 2010 (UTC)

In any case, the solstice is at 2338 UTC, by which time it'll be the 22nd in much of the world. The eclipse is only on the same day as the solstice in timezones west of Greenwich. Algebraist 11:37, 21 December 2010 (UTC)

Antimony trifluoride

Won't the reaction of the elements make the pentafluoride? --Chemicalinterest (talk) 23:47, 20 December 2010 (UTC)

Not according to the Wikipedia articles. It would appear that in the case of excess Antimony, you get the trifluoride. In the case of excess fluoride, you can generate the pentafluoride. That's how I read it. There are references in those articles, if you have questions you could consult those. --Jayron32 01:03, 21 December 2010 (UTC)