Wikipedia:Reference desk/Archives/Science/2009 February 5

= February 5 =

Prism's and white LED's.
I'm doing a presentation at UT Austin in a couple of weeks - and I'm going to be talking to a bunch of budding computer geeks about color. My mission is to entertainingly undo the mess that people are usually taught on the subject of color. All the wierd stuff we talk about here all the time basically. It's called "How to successfully argue that black is white, magenta is a shade of green and yellow probably isn't yellow". Anyway, one thing I want to do is to split some white light into a spectrum using first an incandescent lamp and then a white LED flashlight - and I'm hoping to get a relatively smooth rainbow out of the incandescent lamp flashlight and some nice, narrow red, green and blue lines out of a white multi-LED flashlight. I don't YET have a prism - that's on order (gotta LOVE the Internet!). But I won't have a lot of time between it arriving and needing to do the talk - so experimentation needs to be minimized. Hence I have a few questions of an 'optical' nature...


 * 1) I presume I need to use a fairly narrow 'slit' of light going into the prism.  Any advice on how narrow?  I'd like the spectrum to be as big and as bright as possible - it doesn't matter if it's a bit blurry so long as it's really obvious that not all "white" light is made up of "all the colors of the rainbow" as we're all (incorrectly) taught in school.
 * 2) According to our various articles, there are two kinds of white light LED's - one is a blue LED with a yellow phosphor, the other is an infrared LED with red, green and blue phosphors.  I want the latter type.  I have a white LED flashlight - which kind is it likely to be?   Is there a way to tell before my prism arrives?  I tried looking at it through a red filter...but I rather doubt how good the filter really is at excluding yellow.  If I'm actually going to get a yellow and a blue line - I'll have to resort to PLAN B and buy some of the correct kind of LED's and wire them up myself.
 * 3) I'd like to capture the light from a computer monitor and produce a spectrum - I guess I need to converge the light somehow onto my slit and thence into the prism...but how to do that in practice seems a little tricky.
 * 4) I'm also looking for a source of pure yellow light (ie the kind that WON'T split into red and green through the prism).  I know a sodium lamp would do it - but I don't have one of those sitting around anywhere.   I have one of those yellow emergency lights that you 'snap' to mix two chemicals...is that going to do what I want?

Any ideas?

SteveBaker (talk) 00:23, 5 February 2009 (UTC)

1. Two slits was the way it used to be done - problem - you lose >99% of the light - so make sure the lecture room has curtains (most have?) and suggest getting a low light video camera to capture the small image - then project it using a DLP onto the big screen.
 * Alternatives - very short focal length lens.
 * Better alternative - use a 'laser prism' to capture the light - eg a cylindrical prism with one end silvered and the other polished - put the led inside a silver foil bag illuminating the side of the prism, and just let one end of the prism poke out of a hole. (It can help if the sides of the prism are rough like frosted glass)
 * The above method is approximate and may not work very well..
 * OOPS sorry misread the question - ignore the above then... —Preceding unsigned comment added by 87.102.126.244 (talk) 01:13, 5 February 2009 (UTC)

2. Use the dvd/cd as diffraction grating (again in a darkened room) - this does work (so persevere) - I can see quite clearly what the energy saving light bulb I'm using is made up of using this method - you need to look off the axis of the main reflection...

3. dunno - maybe the silver foil and cylinder trick above may help. NOTE that the circular disc at the end of the prism will act as a 'point source' of light with diameter (blurry-ness) similar to the diameter of the disc - therfore placing a lens with the disc at the focal length of the lens should produce a roughly parallel beam. (thin cylinders and short focal length lens help here to reduce the width of the beam.)

4. as a rusty chemist the answer is almost certainly (probably) see Chemiluminescence - the article suggests that often the reaction (when you break the stick mixing the chemicals) produces uv light, and a sensitiser (uv fluorescence) makes the coloured light - the fluorescents can be expected to be likely to be monochromatic - but not as narrow a range of frequencies as the sodium d-line - ie a braod peak.87.102.126.244 (talk) 00:58, 5 February 2009 (UTC)


 * Sorry I don't have much to add here, except that I would definitely plan to have some slides showing your best results from practice sessions. It your plans work in the room, you can skip those slides, but if the demo fails you have something cool to show.  I've done enough demos to know that you need something "in the can".  --Scray (talk) 02:14, 5 February 2009 (UTC)


 * Oh...WOW! Thank you *SO* much '87 !!  The CD trick works great!  I should have thought of that.  So I could have saved myself some money and not bothered with the prism. The trick is not to look for the reflected light on the ceiling or the wall opposite but instead to look directly at the CD surface.  It's like having your own personal spectrograph!   The best part is that I bet 90% of the kids at the lecture will bring laptops - so I just have to hand out a bunch of blank CD's and we can do it "live".  And exactly as predicted, the LED flashlight produces red, green and blue lines - and the incandescent lamp makes a full spectrum.


 * Per User:Scray - I've taken photos, but the trouble is that a digital camera has it's own 'spin' on color. So the photos I took of green light coming off of the screen - that looks green to my eyes - looks green with a blue fringe to the camera.  So I suppose the camera's blue sensor is sufficiently sensitive to the higher frequencies of green coming off of my LCD monitor such that it's seeing a blue fringe that's not there "in reality".


 * The "yellow" glow stick (well, it's yellow on the package) turned out to be red. Argh!  The orange-ish colored streetlamps in my neighbourhood are modern high pressure sodium lamps so they don't come out as pure orange.  And the orange turn signals on a 2007 MINI Cooper are white bulbs filtered through orange plastic and show mostly red light with a dash of green. The box of yellow LED's I bought at Fry's are evidently a red and a green LED packaged in the same housing...the CD spectrometer proves it.


 * So - the new (and rather important) question is:
 * What source of pure yellow (NOT RED + GREEN) light can I find cheaply and easily? (Of course I could always cheat and use photoshop!)
 * SteveBaker (talk) 03:26, 5 February 2009 (UTC)
 * The thing that pops to mind is a low-pressure sodium-vapor lamp. I don't know how cheaply they're available, or how easily. --Trovatore (talk) 03:31, 5 February 2009 (UTC)
 * Yeah - they used to be in street lamps - but people hated the color - so now we have the high-pressure variety that produce a whiter light. I'm heading out soon to cruise the local malls and see if I can find some old parking lot with an old-fashioned low pressure lamp. SteveBaker (talk) 04:19, 5 February 2009 (UTC)


 * Oh — but if you have access to a Bunsen burner in the classroom, you could make your own version. Just hold some rock salt in the Bunsen flame to get the sodium line.  Obviously I take no responsibility for the safety of this suggestion; that's your lookout. --Trovatore (talk) 03:52, 5 February 2009 (UTC)
 * Yes - but I bet you get all sorts of other colors from the gas and the chlorine in the salt. SteveBaker (talk) 04:19, 5 February 2009 (UTC)
 * I don't know; the sodium line is pretty bright. My dad was a ChemE and I think I recall him telling me that one of the things you had to watch out for, when identifying substances by their flame color, was to keep all the sodium out of them, because the sodium line would just dominate everything else.
 * On the thing about people hating the low-pressure color — do you get that? I don't, really; I think the nice cheery yellow is much more attractive than that sickly pink.  OK, so you don't really have color vision under the yellow ones, but somehow in a parking lot that just doesn't seem so important to me. --Trovatore (talk) 05:15, 5 February 2009 (UTC)
 * I guess that depends on how unusual your car is! I have a MINI and no matter the color distortions, it's shape makes it easy to find in a large parking lot.  But if you had something really common then the loss of color discrimination might be a problem!  Thanks for the info about the dominance of sodium in the flame color.  I'll play around with a candle and some salt and see if I can get a decent spectrum out of it.  This $0.50 spectrometer is a really handy gadget to have around!  I'm going around looking at spectra from all sorts of sources now...it's fascinating. 14:48, 5 February 2009 (UTC)
 * I'll be interested to hear your results. To be honest I'd be a little surprised if the sodium were bright enough to dominate a candle flame, plus I'm not sure it's hot enough.
 * If that doesn't work, what about one of those little kitchen torches, the ones you use to finish off a cr&egrave;me brul&eacute;e? Might be a tiny bit more than you wanted to spend, but afterwards you could make cr&egrave;me brul&eacute;e. --Trovatore (talk) 19:46, 5 February 2009 (UTC)
 * A candle flame is about the same temperature as a Bunsen burner or blowtorch flame, isn't it? Things put in all of them tend to glow a reddish-yellow colour, which should mean they are the same temperature. Don't be confused by some of the flames being blue - that's chemical emission lines, not thermal emissions (as I learnt on this desk a few weeks ago). --Tango (talk) 20:01, 5 February 2009 (UTC)
 * As an aside - I really like the sodium yellow - I think it's also more effecient than the high pressure lamps. But if you have a blue or red car (or outfit) they appear black - so I guess safety is on reason to replace the lovely yellow lights.87.102.126.244 (talk) 16:22, 5 February 2009 (UTC)
 * Incidentally - I found this: - very cool. SteveBaker (talk) 04:19, 5 February 2009 (UTC)


 * Very nice! Regarding a source for pure yellow, I did find this description of pure-yellow LEDs, but I doubt they're on the market yet.  I don't suppose you have an old yellow street lamp handy? BTW Steve, chapeau - your questions on RD/S are as interesting as your answers. --Scray (talk) 04:28, 5 February 2009 (UTC)


 * I drove around for a while last night looking for an old, run down parking lot that might have old-fashioned low-pressure sodium lamps - and found one fairly quickly.  The "CD spectrometer" did a great job and I go a nice orange-only CD reflection.  Unfortunately, my digital camera does weird things with these spectra - which is not entirely surprising because it's an RGB device with sensitivity into the infrared range and a propensity for adding a little blue that I don't see with my naked eyes.   So I'm still looking for a cheap/portable way to get some real orange/yellow light into the classroom.  Maybe the salt+candle trick will do the job. SteveBaker (talk) 14:48, 5 February 2009 (UTC)


 * You might want to check out this site:, which displays a large collection of spectra from a lot of "common" light sources. Someone42 (talk) 08:43, 5 February 2009 (UTC)

In the days of Newton, experiments requiring monochromatic light passed sunlight through stained glass windows, which apparently produces sufficiently bright and monochromatic light to see first order diffraction lines in simple setups. I don't know how true this is across different colors, or if the stuff that's sold today transmits as narrow a spectrum as the old stuff, but it's pretty cheap to buy in small amounts. Someguy1221 (talk) 08:56, 5 February 2009 (UTC)


 * You may also wish to consider the Shakespearian premise that "a rose by any other name will smell as sweet" and "there is nothing either good or bad but thinking makes it so". In other words, names are not absolutes and black means whatever we choose it to mean. (Ooops sorry that one's from Alice in Wonderland!) --TammyMoet (talk) 10:51, 5 February 2009 (UTC)


 * Well, yes.
 * But from the title of my talk:
 * The "Black is White" part is easy - I'm planning to show the Same color illusion to illustrate that one - check out our article and you too will believe that black IS white. In the context of computer graphics (which is REALLY what I'm there to talk about), this feeds into issues of how human vision adapts to different lighting levels: scotopic versus photopic vision - and how computer games should render nighttime scenes.
 * "Magenta is a shade of green" comes about because the two kinds of yellow (a mixture of red+green and a frequency midway between red and green) are roughly as "different" as magenta (a mixture of Red+Blue) and green (a frequency midway between red and blue). Since we pathetic humans can't distinguish the two kinds of yellow and give those two DRAMATICALLY different colors the same name - it seems reasonable to argue that magenta and green are the same color (which they are to people with green-deficient color blindness).
 * "Yellow isn't always yellow" is a reference to the fact that goldfish, some kinds of freshwater shrimp, and one particular little old lady in England (who is a tetrachormat) have better color vision than us - and for them, the two kinds of yellow must seem as different as magenta and green are to us! It's this part of the talk that really demands that I show something like a sodium lamp next to a CRT displaying "the same color".
 * I also want to talk about why physicists show the spectrum as a linear progression from red to blue - yet artists always show the spectrum as a wheel where the blue and the red merge through violet and magenta...and how this relates to the little 'bump' in the red cone receptor's sensitivity in the blue area of the spectrum. (That's something I learned about right here in the WP:RDS).
 * If I have time, I want to sneak in the IEC chromaticity diagram and show that the color gamut of a CRT is smaller than our eyes - so there are colors you can't display on a computer screen.
 * SteveBaker (talk) 14:48, 5 February 2009 (UTC)
 * I don't see that black is white... I see that the human brain compensates for shadows. Black is the absence of light, white is light with the same frequency distribution as the sun (or something the human eye can't distinguish from that distributions). How are they the same? The bump in the red cone's sensitivity thing really is fascinating, though, I too learnt that here and am just waiting for a dinner party where I can bring it up in conversation... --Tango (talk) 14:58, 5 February 2009 (UTC)
 * That's why nobody invites me to dinner parties anymore!
 * Well, it's obviously a bit of a stretch - but you get to do that in your lecture titles to get people interested. There is no doubt that under some lighting levels, the color/brightness that you would name "white" would be something that you would name "black" in another lighting situation.  In the picture in Same color illusion this exact thing becomes evident.  You have one square on the chessboard that is "White" and another that is "Black" and they are the exact same color. SteveBaker (talk) 16:57, 5 February 2009 (UTC)
 * They're blatantly not black, though, they're grey. If you used a real chess board with actual black squares, it wouldn't work. Grey is just dark white, black is the limit as you get darker and darker greys, but it's also the limit as you get darker and darker with any colour. The human brain perceives brightness in relative terms, that's all that's going on. "Light is dark" would be reasonable, but "black is white" seems wrong to me... --Tango (talk) 17:30, 5 February 2009 (UTC)

Incidentally, Steve, if you're looking for a quick-and-dirty "colour is in the eye of the beholder" demonstration, I doubt anything is simpler than showing the CCD in your cameraphone can see the the flashing IR LED in a tv remote control where the eye can't (I think that should also be true of a UV source, although I can't immediately think of a household UV source). 87.113.74.22 (talk) 15:33, 5 February 2009 (UTC)
 * Blacklights aren't that difficult to come by - I expect ebay will have them. --Tango (talk) 16:24, 5 February 2009 (UTC)
 * Yes - the TV remote is another good one. I'll see if I have time to work it in.  Blacklights ought to work too - but all of the ones I've seen produce a soft violet glow so it's a lot less convincing than a TV remote. SteveBaker (talk) 16:57, 5 February 2009 (UTC)
 * Yeah, you would probably need to get quite an expensive blacklight. --Tango (talk) 17:30, 5 February 2009 (UTC)


 * Actually, your digital camera can't see UV -- between the low natural sensitivity and the filtering effect of the glass, you need a very bright source to get the camera to respond. --Carnildo (talk) 22:49, 5 February 2009 (UTC)
 * Presumably it can see really near UV? Maybe too near for a blacklight to be useful, you would need something with a very narrow emission band. It seems highly unlikely that the cut-off point for a camera is the same as for the human eye, given their completely different methods of detection, and presumably the designers made sure the camera can detect everything a human can see, which would suggest some near UV must be visible. (I guess it's possible cameras can't see certain extreme shades of violet, but I would have thought I'd have heard of that were it true...) --Tango (talk) 23:30, 5 February 2009 (UTC)
 * Yellow light. Maybe get some from an "overdriven" LED, where the voltage is too high. The led will burn out, though I have heard of people chilling them to get very bright light output. Polypipe Wrangler (talk) 09:28, 6 February 2009 (UTC)


 * Digital cameras are sensitive to near-UV, but the sensitivity is between three and five orders of magnitude weaker than the visible-light sensitivity. That means that in order to get a visible color shift, your light source needs to be putting out at least an order of magnitude more UV light than the ambient visible light, or you need to be using a UV-bandpass filter and a long exposure.


 * And yes, cameras do have trouble with extreme violet. It usually shows up either as pink or as deep blue. --Carnildo (talk) 23:00, 6 February 2009 (UTC)

Sinkholes - Geology
Looking at locations of sinkholes in the pennines I notice that many occur in lines close together on contour lines (eg~same height) - as I think that sinkholes are made by collapse of underground caverns caused by erosion of the limestone bedrock this seems wrong - I would expect the sinkholes to go downhill, or occur in a fashion unrelated to the overlying height map.

Can someone explain what is going on. Thanks.87.102.126.244 (talk) 00:48, 5 February 2009 (UTC)
 * In ignorance of the actual geology there, it is possible that the limestone only forms a bed of limited vertical extent, then the sinkholes only appear along the bed of limestone on the contour. Another possible cause is faults or formation when the sea level was at this level (Probably not this as these are mountains). Graeme Bartlett (talk) 03:37, 5 February 2009 (UTC)


 * The place that they will appear is at the top of the bed of limestone and, if the dip is low, this boundary will roughly follow the contour lines. Mikenorton (talk) 09:16, 5 February 2009 (UTC)


 * And, on a small scale, they do often occur in a series going downhill.   D b f i r s   10:05, 5 February 2009 (UTC)
 * Statistically (in the area I'm looking at) they are along the countours - and definately not uphill. A small number are in scattered clusters.
 * I didn't really understand "at the top of the bed of limestone" - They are holes in the limestone (is this correct) and must occur in the limestone (the top part is the bit visible) - what causes them to appear at a particular place in the limestone? —Preceding unsigned comment added by 87.102.126.244 (talk) 16:45, 5 February 2009 (UTC)

Update - they seem to often occur between the boundary of the river valley (flattish) and the hills surrounding. Would OS coordinates help?

It's possible that I need a basic lesson in geology - are the sinkholes formed by surface water running off through cracks or flaws already existing in the limestone - or are they due to underground collapse.? Also are they new (ie made after glaciation) or old (uncovered by glacial activity).? Does/do flaws in the underlying millstone grit have something to do with it - such as cracks or step formations.? Is the process well understood. (I'm refering to sinkholes in the pennines - around Howgill fells in particular) Thanks/ Here's an example- (shake holes) http://www.multimap.com/s/dWF6DVqH —Preceding unsigned comment added by 87.102.126.244 (talk) 17:47, 5 February 2009 (UTC)


 * That's a really nice image. AFAIK the lines of shake holes that you can see are formed where there is just a thin cover of younger sediments on top of a limestone layer. On a nice flat limestone pavement you get regular dissolution features. In the area you're referring to, water running along the base of the overlying sediment layer also causes small-scale dissolution in the top of the limestone but, where the layer on top is thin enough, it collapses into these holes. Elsewhere there is still dissolution going on but you don't see it so clearly because the beds above are thick (and therefore strong) enough not to collapse into a relatively small hole. Mikenorton (talk) 19:35, 5 February 2009 (UTC)
 * ok thanks - I think that made sense to me.
 * It's starting to make sense to me. Thank you very much.

Science related to Neuorlogy
HOW DOES THE NUMBER OF NEURONS IN THE BRAIN INCREASE? WHAT IF WE USE OUR BRAIN MORE EFFECTIVELY OR MUCH MORE CONCERN THE QUANTITY OF NEURON? —Preceding unsigned comment added by Mustekke6184 (talk • contribs) 02:52, 5 February 2009 (UTC)
 * (I edited your post to remove the awful formatting). I think long-term potentiation may be what you are after. I'm not aware of any ways of increasing the number of neurons in the brain, why would you want to do that exactly? --Mark PEA (talk) 03:12, 5 February 2009 (UTC)


 * For increasing number of neurons you may look at Neurogenesis. For learning processes that do not involve neurogenesis (most don't) see synaptic plasticity, Long-term potentiation, long-term depression. You may also want to look at synaptogenesis. As far as efficiency of neural "computation" in biological systems is concerned, I can't think of any publication that is understandable to the general audience. Just ask questions and we'll try our best to answer. --Dr Dima (talk) 04:32, 5 February 2009 (UTC)
 * Here's an interesting paper about a TrkA receptor agonist found in Garcinia hanburryi. --Mark PEA (talk) 17:01, 5 February 2009 (UTC)

Calculating Molality
I'm working on some Chemistry homework and for one problem I have to calculate the molality of concentrated Sulfuric acid. The information I am given is the density: 1.84 g/mL and the mass percent of solute: 95%.

I assume for calculation's sake that I have 1000g of solution. Because of the mass percent, I should have 950g of H2SO4 and 50g of water. Thus from that I calculate the moles of solute to be 9.69 mols. Since the density of water is 1 g/mL, I calculate I have .050L of water. Thus the molality is calculated as 9.69mols solute /.050L of solvent = 194 mols/kg. Is this correct? It seems like a ridiculously high number to me compared to those in the other examples. Have I done something wrong? I guess what I'm also having trouble wrapping my head around is dissolving nearly a kilogram of H2SO4 in only 50 mL of water. According to the density, my total solution volume should be 543.5 mL. I feel like I have misstepped somewhere but I cannot figure it out.

Help is appreciated 198.82.110.57 (talk) 03:13, 5 February 2009 (UTC)
 * You should be dividing by the volume of the solution not the solute, after all the molarity of a 100% substance is not infinite. Graeme Bartlett (talk) 03:33, 5 February 2009 (UTC)
 * Molarity and Molality are not the same. There is no molality for a pure substance.  Nimur (talk) 05:21, 5 February 2009 (UTC)
 * Dimensionally analyze what you did by writing everything out as multiplication with labels next to the values. If what you get at the end is x moles of solute/1 kg solution, then you have done it correctly. 96.242.34.226 (talk) 03:48, 5 February 2009 (UTC)
 * I just got more confused by the first reply. I divided my moles of solute (9.69 mols) by the mass of my solvent (.050 kg)to find my molality, which came out to 194 mols/kg. If I divide by the volume of the solution, that just gives me molarity, not molality. Or were you referring to a different step? If so, please elaborate. Thanks. I can't find any error in my calculations.198.82.110.57 (talk) 03:55, 5 February 2009 (UTC)
 * The major problem I think you're having is dividing by mass of solvent, when you should be dividing by mass of solution. However, (as suggested above by 96.242.34.226) I also think you should go back to the beginning using the density and mass percent provided, and dimensionally analyze from beginning to end (using specific units like "kg H2SO4", "kg solution", etc).  --Scray (talk) 04:08, 5 February 2009 (UTC)
 * But my textbook and everything else I have found online explicitly state that molality = moles of solute/kilograms of solvent, not kilograms of total solution 198.82.110.57 (talk) 05:07, 5 February 2009 (UTC)
 * Sorry - this was my mistake - it is moles of solute divided by kg of solvent (a little rusty hinge in my brain). --Scray (talk) 05:33, 5 February 2009 (UTC)


 * I'm not sure what the textbook question actually asked, but I would verify that your mass fraction is the right way around. It seems a lot more likely to put 50 grams of acid into 950 grams of water.  Even that would be pretty concentrated.  950 grams of acid into 50 milliliters sounds implausible.  On the other hand, the 1.84 grams/mL is pretty dense (actually it's exactly the density of pure H2SO4...), so your original work may be correct.  There's nothing which explicitly forbids having 194 moles per kilogram, as far as I know... you might want to check the solubility constants for H2SO4 to see if that's a plausible solution.  Sulfuric acid says it is miscible with water, which I assume means can form a solution in any ratio.  "Although nearly 100% sulfuric acid can be made, this loses SO3 at the boiling point to produce 98.3% acid. The 98% grade is more stable in storage, and is the usual form of what is described as concentrated sulfuric acid." Nimur (talk) 05:23, 5 February 2009 (UTC)


 * I'll second Nimur's analysis. The problem is that you have a rediculously concentrated solution, at 95% H2SO4 and only 5% water.   You don't really have a water solution, what you really have is a little bit of water dissolved in a sulfuric acid solution.  At that level, the really high molality (of the acid in the water) makes sense.  --Jayron32. talk . contribs  05:41, 5 February 2009 (UTC)

Chemical Content
Hey, I'm doing some research and I'd like some help finding the articles I'd need! I'd like to know...What ingredients in the liquids (orange juice, Coke, Red Bull, milk, salt water) are considered "chemicals"? For example...salt water has salt; milk has calcium. —Preceding unsigned comment added by 69.178.20.243 (talk) 04:51, 5 February 2009 (UTC)


 * Every ingredient in every food or beverage is a chemical. If you meant to ask "what ingredients have scientific-sounding names," then the answer is probably still ... "everything" - even water is known by a few scientific names (oxidane? That's a new one for me!).  If you're looking for natural or synthetic food additives, Food additive article is a good place to look.  You can also look up orange juice, Coca-Cola, Red Bull, milk, salt water.  Chances are, there is an article for any food item you can think of.  Nimur (talk) 05:07, 5 February 2009 (UTC)


 * Just read the label on the food or drink container. FDA regulations require that you be informed of what is in the things you eat or drink. The chemicals listed on a candy-bar wrapper will make your hair stand on end! - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 16:01, 5 February 2009 (UTC)
 * (The FDA only regulates certain consumables, and only in the United States. Nimur (talk) 16:55, 5 February 2009 (UTC)
 * There's nothing wrong with that. For example, what do you think of the chemical deoxyribonucleic acid? I wouldn't recommend eating anything without that in it, except ice, though even that will have trace amounts. — DanielLC 16:48, 5 February 2009 (UTC)
 * And aren't viruses composed primarily of that kind of acid and of simply ribonucleic acid? This is sounding almost as dangerous as dihydrogen monoxide, which will kill you if you breathe too much of it.  Nyttend (talk) 07:25, 6 February 2009 (UTC)

Alkali = ?
The second half of A Study in Scarlet (the first appearance of Sherlock Holmes) takes place primarily in the western USA, beginning in a region (consisting essentially of the Four Corners states, Wyoming, and Nevada) that Conan Doyle describes as extremely desolate (it's a bit fictionalised). This region he names the "great alkali plain" (read the relevant part of the story here), a description that confuses me. Why "alkali"? It's not as if the region was composed solely of francium, lithium, and the elements in between, and there's nothing in the story that suggests that it would have a strongly basic pH. Any ideas what this might mean? Nyttend (talk) 05:52, 5 February 2009 (UTC)


 * Alkali flat redirects to playa, which explains that what we're talking is not really the whole desert, but dry lakebeds. The evaporite on the surface of the ground contains salts of alkali metals.  --Anonymous, 06:10 UTC, February5, 2009.

Membership of American Academy of Arts and Sciences as compared to Royal Society
A related question to my last one.

How does the membership of AAAS compare to FRS(Ramanathan) —Preceding unsigned comment added by 212.247.70.129 (talk) 07:58, 5 February 2009 (UTC)
 * In what way? Numbers?  Professions?  Demographics?  Learnedness?  The AAAS is 3 times as large and admits artists and writers whereas the RS is purely for scientists.  Try --Maltelauridsbrigge (talk) 12:14, 5 February 2009 (UTC)

I do not think that is entirely accurate!If you look through the membership of the Royal Society you find people like Samuel Pepys and Robert Darwin to quote two!People who have nothing to do with science have been members throughout the history of the Society eg.Lord Brougham,John Locke in the past!Even when you look at the membership in the last 50 years people like Margaret Thatcher who despite having studied chemistry is no scientist!What about Quentin Hailsham,a lawyer!And the present list has Partha Dasgupta,an economist!

AAAS has always been open that it recognises excellence in all human endeavours.And US has 4-5 times the population of UK!Therefore the size of the membership is roughly commensurate. The reason I felt AAAS membership would be propbably more prestigious internationally is: 1.Royal Society bars people from becoming fellows unless you are a Commonwealth or an Irish citizen(Foreign Membership apart which is very rare in any case!).Besides the by laws as on the site state that if you hold a second nationality other than Commonwealth or Irish you are automatically debarred from becoming a member(except a Foreign Member).

2.As far as I know AAAS has more Nobel Laureates on its rolls than any other learned society in the world in all disciplines.

I would like the researchers to correct me if I am wrong.(Ramanathan)
 * Re. your first point, I think Maltelauridsbrigge used the present tense for a reason. Algebraist 12:53, 5 February 2009 (UTC)

'To my inexperinced eye,AAAS has 171 Nobel laureates and Royal Society has 8.I also counted the Nobels in science for AAAS-118!That surely would make it the most prestigious learned society!(Ramanathan)'

Parallel Universes
If we can't really be sure that the laws of physics are the same in our own universe, don't even know if parallel universes exist, how can we say that they are inaccessible? Seems to me like an awfully arrogant statement considering our current level of ignorance.Bastard Soap (talk) 08:52, 5 February 2009 (UTC)
 * Well if they don't exist, they are inaccessible by definition (except in our imagination), but if they do exist then we should say that they are inaccessible via any of the known laws of physics in our own universe.   D b f i r s   10:00, 5 February 2009 (UTC)

To quote Donald Rusmfeld...There are known knowns, there are things we know that we know. There are known unknowns. That is to say, there are things we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.

It doesn't seem like ignorance to me - it is making statements/theories based on the best available knowledge, and then being prepared to revise those as further information becomes available. 194.221.133.226 (talk) —Preceding undated comment was added at 10:04, 5 February 2009 (UTC).


 * Rumsfeld quoting Socrates!! Wow! --pma (talk) 11:25, 5 February 2009 (UTC)


 * What about the completely ignored "orthogonal universe" first proposed by Robert Heinlein, notably in his treatise Glory Road? Perhaps there are universes at right angles to everything else, including your precious parallel ones. And shouldn't we be paying more attention to the possibilities inherent in the "retrograde universe" inhabited by Benjamin Button? I can dream up a dozen impossible things before breakfast, far faster than the world of science can refute them with its small-minded insistence on verifiability, reproducibility, and evidence. --Milkbreath (talk) 12:18, 5 February 2009 (UTC)


 * I would argue that if they are accessible, they aren't a separate universe. How do you define "universe" in such a way that accessible alternative universes isn't a contradiction in terms? --Tango (talk) 14:04, 5 February 2009 (UTC)

I think I would define universe as the place where our physical constants hold true, even though I think it's trivial what we do call our little bubble. So do we have any real reason to assume they would be inaccessible except semantics?Bastard Soap (talk) 18:54, 5 February 2009 (UTC)
 * Do we have reason to believe that are no accessible regions of space with different physical constants? The main reason is that we haven't found any. Astronomers have studied distant galaxies in ways that allow us to determine certain physical constants there and the evidence is all consistent with them being the same. --Tango (talk) 19:41, 5 February 2009 (UTC)
 * I would define universe as everything observable, so if we found a region of space with different constants, it would be part of our own universe, however difficult or impossible we might find it to live there. Thus I would define a parallel universe (if I had reason to imagine it) as one which could not be observed from our universe, or reached by any present or future scientific method.  In this sense, my parallel universes are inaccessible by definition.  Not arrogance, just my definition.  How do you define parallel universe?  Perhaps you have a better imagination!    D b f i r s   13:11, 7 February 2009 (UTC)

English language
Moved question to the Language Desk. --Milkbreath (talk) 11:31, 5 February 2009 (UTC)

Cork taint
In Cork taint:


 * Andrew Waterhouse, professor of wine chemistry at University of California, Davis has stated that the offensive flavor of corked wine can be removed by pouring the wine into a bowl with a sheet of plastic wrap. Effective within a few minutes, the 2,4,6-trichloroanisole molecule is chemically similar to polyethylene and will stick to the plastic.

Does polyethylene remove other good aromatic chemicals as well? How does polyethylene absorb 2,4,6-trichloroanisole? The chlorine? -- Toytoy (talk) 11:51, 5 February 2009 (UTC)


 * The relevent article is Lipophilicity, which in a broad sense is the ability of a non-polar substance to dissolve another non-polar substance. Basically, substances whose molecules lack distinct positive and negative regions will mix well with other similarly "non-polar" molecules.  --Jayron32. talk . contribs  12:38, 5 February 2009 (UTC)


 * Unless you are refering to the other definition of taint. --Jayron32. talk . contribs  12:39, 5 February 2009 (UTC)


 * Ah yes, as in "itaint the one, and itaint the neither". StuRat (talk) 20:22, 5 February 2009 (UTC)
 * So when you spit out a sip of bad wine and and exclaim "this wine tastes like ass!" you really mean it? DMacks (talk) 21:42, 5 February 2009 (UTC)

"drawing" letters and words by moving your eyes
Ever since I was young I used to look at bulbs, and by moving my eyes in different directions I could form letters and even words using the bulb as a pen.

For example if you look at a bulb and move your eyes down, that would 'move' the bulb 'up', forming a stroke. Looking left moves the bulb right. Closing your eyes allows you to move the 'pointer'.

I've never encountered anybody else that ever does this. Do you have any references or anecdotes about this? Perhaps I can control my eye ball muscles in a very controlled way. Rfwoolf (talk) 12:15, 5 February 2009 (UTC)


 * Anecdotally, you're not alone. --Scray (talk) 13:41, 5 February 2009 (UTC)
 * I suspect everyone can do that. It's easier to move the light source, though - sparklers are fantastic for that. --Tango (talk) 14:06, 5 February 2009 (UTC)


 * Sure, I can do that. Well, I used to be able to do that -- I just tested it, and clearly I'm way out of practice. -- Captain Disdain (talk) 14:48, 5 February 2009 (UTC)


 * I'm a bit mystified about "bulbs". Do you mean light bulbs?  (It's just that in my country we never refer to a light bulb as simply a "bulb".  A bulb would usually refer to a part of certain types of plant.) --  JackofOz (talk) 21:38, 5 February 2009 (UTC)


 * It's not a country JackOfOz, it's an island... ;) Rfwoolf (talk) 22:18, 5 February 2009 (UTC)

Wine aging
I learned the hard fact that some wines are so bad that you don't even use them for cooking while I was in college. If properly aging for years or decades may improve the tastes of good wines, can the taste of a regular cooking wine, when "cooked" with aeration and under low heat separately from the food, be improved?

Is it possible to improve the taste of a large batch of cheap wine by hiring a chemical expert and "cook" the wine strategically (e.g, aeration, heating, adding sugar, adding so-called "liquid smoke", removal of unpleasant sulfur compounds) so its final chemical profile may match a much better wine that has been aged?

Is it possible to salvage over-aged wine by blending in young wine? -- Toytoy (talk) 12:37, 5 February 2009 (UTC)
 * Aging of wine may be of use. Algebraist 12:51, 5 February 2009 (UTC)


 * Perhaps something like an oloroso sherry could be produced this way. The Wikipedia article calls sherries "underappreciated" :^) --Digrpat (talk) 14:29, 5 February 2009 (UTC)

mass-energy equation
can someone explain how einstein got this formula? $$       E = mc^2 \,

$$ the wikipedia article doesn't explain how he got this thing $$       K.E. = \frac{m_0 c^2}\sqrt{1-\frac{v^2}{c^2}} - m_0 c^2,

$$ please explain that also. And the article says that he omitted the second term just because he wanted that. How can he do so without changing the value of the equation?--Harnithish (talk) 15:54, 5 February 2009 (UTC)


 * The second equations says that kinetic energy is total energy minus rest energy, which is quite intuitive. Getting the formulae for total energy and rest energy is a little more complicated - there is some discussion of it in our article, here. --Tango (talk) 16:31, 5 February 2009 (UTC)

Water flouridation and the crank estate
Why is it that certain groups of people believe that water flouridation is a conspiracy to keep the hoi poloui stupid? Is there any particular reason for this belief? What is its origin and who first proposed it? Why is it not taken seriously by the scientific community or society at large? 86.132.243.243 (talk) 17:11, 5 February 2009 (UTC)
 * http://www.google.co.uk/search?hl=en&q=fluoridation+mental+retardation&meta= should help to get you started. —Preceding unsigned comment added by 87.102.126.244 (talk) 17:14, 5 February 2009 (UTC)
 * A majority of the links that come up after that google search contain no scientific information whatsoever. This chart needs a statistical test applied to it, because from looking with my naked eye, there is no significant correlation there. In fact all of the charts (Mortality, Arthritis, Tooth Loss, Tooth Decay) seem to have no correlation. --Mark PEA (talk) 17:44, 5 February 2009 (UTC)
 * We have an article about Opposition to water fluoridation. DMacks (talk) 19:06, 5 February 2009 (UTC)


 * Theres no reason why not. How can peoples teeth be so bad anyway? International relations, national flouridation, ancient history... Who are you going to see tomorrow that can accurately prove the information of the world? Nobody. You don't have to beleive any of it. ~ R . T . G  18:41, 6 February 2009 (UTC)


 * If water fluoridation is used only for helping to strengthen teeth, it shouldn't have to go through your bloodstream to get there. ~ A H  1 (TCU) 16:15, 7 February 2009 (UTC)


 * Why not? You eat carrots to improve your night vision. You don't pour carrot juice on your eyeballs. There are a lot of things people consume to help with skin conditions. Et al. As it turns out, the systemic role of flouride is apparently limited so there is a difference but it highlights the simplisticness of what you are saying. However the key point you're missing is that while the benefit of flouride is primarily topical, the benefit comes from a constant low level. Unless you brush your teeth every 30 minutes, the only logical way to achieve that is to ensure the water you consume has a low level of flouride. The ingestion of flouride is a secondary and relatively harmless secondary effect. The flouride is not going through your bloodstream to get to your teeth, contrary to your belief Nil Einne (talk) 11:44, 8 February 2009 (UTC)


 * Dental caries is a problem worldwide and for some people it can be a major problem. My mother from example had difficulty eating for a long time due to poor teeth. She eventually got dental implants combine with a partial denture but it was still far from having a good set of teeth and is not something most people can afford Nil Einne (talk) 11:48, 8 February 2009 (UTC)

Life without plants
If all plants went extinct, could animals continue to live? When would carnivorous species start to go extinct? 86.8.176.85 (talk) 18:50, 5 February 2009 (UTC)


 * What about the poor herbivores? In any event, plants help regulate oxygen in the atmosphere as well as in the sea - so no plants would have a chain reaction that would affect life in all kinds of ways - whiping out entire ecosystems. Rfwoolf (talk) 19:02, 5 February 2009 (UTC)


 * Autotrophs form the basic root of the food chain. There are plenty of non-plant autotrophs such as protists and bacteria but it is unlikely that all ecosystems could readjust to use these as the new food sources.  Nimur (talk) 19:23, 5 February 2009 (UTC)


 * There are non-plant algae and cyanobacteria that also produce oxygen, although I'm not sure in what quantities (most oxygen is produced by algae, but I think that's mostly green algae, which are usually classed as plants). It's possible they would produce enough oxygen to allow animals to keep breathing, and would also provide food for at least some herbivores (which would provide food for some carnivores). With all the plants gone, there would be a lot of room for these algae and cyanobacteria to grow, so they may well replace the plants sufficiently to keep the oxygen levels about where they are now. I think they mostly grow in water, though, so land animals might suffer. Sea life would probably continue well enough (kelp could serve as the root of plenty of food chains). --Tango (talk) 19:38, 5 February 2009 (UTC)


 * To clarify a bit, there are many things which the common observer would call "plants", which scientists classify as something else. Kelp would be a good example. StuRat (talk) 19:55, 5 February 2009 (UTC)


 * Herbivores would be likely to die off quickly, as all plant sources of energy were depleted. Now, as for carnivores, they would need to eat each other to stay alive, which would obviously reduce their numbers quickly.  If we just take the case of human cannibalism, and assume that those vitamins and minerals missing from the all-meat diet could be supplied in some way, we can do some calculations.  Let's say that a  average person could live for a year on the corpse of another (refrigeration is allowed, right ?).  That would cut the human population in half every year, and to about 1/1000th in a decade.  That would mean one millionth in two decades and one billionth in three decades.  So, given a starting population of about 7 billion, we would be down to around 7 by then.  They could maybe survive for another 4 years after that, giving us 34 years.


 * However, this assumes that people are allowed to die of starvation or are only killed as necessary to provide food for others. If, on the other hand, you kill off most of the human population immediately, and refrigerate them for later use as food, you could keep a million people alive for 7 thousand years, 1000 people alive for 7 million years, or 1 person (at a time) for 7 billion years.  This last approach may meet with considerable resistance from the majority of the population, however. StuRat (talk) 20:08, 5 February 2009 (UTC)


 * It might be better to start off eating non-human carnivores..--Tango (talk) 20:12, 5 February 2009 (UTC)


 * Adult humans need about 2 pounds (1 kg) of food per day. Given that an average human might be 150 pounds, and allowing for indigestible bits like bones, a cannibal probably would need a new food source every 60 days or so, not a year.  Dragons flight (talk) 22:39, 5 February 2009 (UTC)


 * I wasn't able to find nutritional information for eating humans, but pork bellies are probably similar, and have some 2349 calories per pound. That's more than is needed to survive. StuRat (talk) 05:36, 6 February 2009 (UTC)


 * Hmmmm, well I suppose there might be more energy per pound of flesh than there is in the average food stuff that people ordinarily eat. For example, I have a one pound pasta dinner in my freezer that says it is only 400 Calories.  Dragons flight (talk) 07:42, 6 February 2009 (UTC)


 * Yes, with fat being the densest source of calories, at 9 calories per gram, or 9000 per kg. StuRat (talk) 15:23, 6 February 2009 (UTC)


 * These estimates of cannibalism assume that humans can easily find each other. But as the population thins out, it will become harder and harder to find a meal. Especially because, when they are not hungry, humans will hide from each other. It will reach a point where humans will die of starvation even though there are others lurking around somewhere in the vicinity. - GlowWorm.

If stuff like kelp isn't classified as a plant, then I guess it doesn't fall under the criteria of my question (although I did think it was one). I asked about carnivores because I figured they'd be able to eat each other for a awhile at least. What sort of life would start filling the gap left by plants? What would happen to the atmosphere? Or would pretty much all interesting life be doomed (above ground, anyway)? Your answers are fascinating, thanks. 86.8.176.85 (talk) 20:59, 5 February 2009 (UTC)


 * I thought it was one until I looked it up in order to answer your question! I reckon algae would replace plants pretty quickly and keep the atmosphere topped up with oxygen - it's pretty fast growing stuff. Plants evolved out of algae once, so they can do it again given a billion years! I expect there would be a lot of confusion among the animal kingdom for a time, during which many species would die out. I expect some would survive though and spread into new niches and evolve into new interesting life over time - just like an asteroid falling from the sky and killing a bunch of terrible lizards makes room for some bipedal rodents to create freely accessible encyclopaedias! --Tango (talk) 22:55, 5 February 2009 (UTC)


 * Yeah and the deadly plant killer disease will have to leave yeast alone too, as it's a not classed as a plant either, so Free Beer all round WooHoo. ~ R . T . G  18:30, 6 February 2009 (UTC)
 * Yeast needs a source of sugar to ferment... Barley is a plant, so no beer. I wonder what you would get if you mushed up kelp, mixed in some yeast and left it on a low heat for a while... --Tango (talk) 18:39, 6 February 2009 (UTC)


 * Beer! ~ R . T . G  21:30, 6 February 2009 (UTC)


 * When a mass extinction wipes out the plants, you'd expect herbivores to go extinct before the carnivores. However, a fossil hadrosaur (herbivorous dinosaur) was found in rock created about half a million years after the K-T extinction, according to Wikipedia, later than any carnivourous dinosaur fossils (excepting birds). ~ A H  1 (TCU) 16:10, 7 February 2009 (UTC)


 * Kew Gardens, one of the world's first and still one of the greatest botanical gardens, has as its slogan, visible on all information plaques "All life depends on plants." BrainyBabe (talk) 20:43, 8 February 2009 (UTC)

Eggs in candleflames
I remember seeing an experiment years ago where you place an egg over a candle flame until the suit collects upon it, then you place it in a glass of water and it produces a shiny, silver effect. Is this just air bubbles accululating on the egg, producing a shiny effect, or is there something else going on? —Cyclonenim (talk · contribs · email) 20:27, 5 February 2009 (UTC)
 * http://www.google.co.uk/search?hl=en&q=egg+soot&meta=
 * eg http://www.eggs.ab.ca/kids/Tricks/eggtrick008.htm
 * Yes it's (one big) bubble s ... —Preceding unsigned comment added by 87.102.126.244 (talk) 02:44, 6 February 2009 (UTC)

Homeopathic medicine
The wonderful Tim Minchin, in his beat poem Storm, has the line: Water has memory! And whilst its memory Of a long lost drop of onion juice is infinite, It somehow forgets all the poo it's had in it. How do homeopaths explain this? Of all the impurities and previous things the water cycle has had in it? -- MacAddct1984 (talk &#149; contribs) 21:24, 5 February 2009 (UTC)


 * They use distilled water, so presumably the distillation process works as a water memory eraser. Also, the repeated shaking ("succussion") is purported to be crucial: the "vital energy of the diluted substance is activated and its energy released by vigorous shaking of the substance". It's all hand-waving, prescientific nonsense, but these are the excuses they'll trot out. &mdash; Scientizzle 21:37, 5 February 2009 (UTC)


 * I don't think they explain it. I don't think it really enters into the equation. I mean, logic dictates it should, but logic also dictates that you can't get powerful medicine by diluting something until nothing remains of it and shaking the container repeatedly. When you've forced yourself to be dumb enough to believe in homeopathy -- or ruthless enough to profit from it even though you know it's crap -- things like "logical proof" aren't that high on your list of priorities. -- Captain Disdain (talk) 21:39, 5 February 2009 (UTC)


 * This is addressed in the article under "High Dilutions": Homeopathic - and by addressed I mean talked about. Rfwoolf (talk) 22:24, 5 February 2009 (UTC)


 * They explain it by adding "Poo removal: $10" to your receipt. --Tango (talk) 23:35, 5 February 2009 (UTC)


 * Surely by "poo removal" you mean colonic irrigation? BrainyBabe (talk) 20:59, 8 February 2009 (UTC)