Wikipedia:Reference desk/Archives/Science/2010 May 5

= May 5 =

Fucking Magnets!
HOW DO THEY WORK? —Preceding unsigned comment added by 69.180.172.142 (talk) 00:12, 5 May 2010 (UTC)

Are you asking how magnets fuck? Or are you just interested in magnetism? 71.104.119.240 (talk) 00:27, 5 May 2010 (UTC)

Both. —Preceding unsigned comment added by 69.180.172.142 (talk) 00:37, 5 May 2010 (UTC)

It has to do with all the electrons in the magnet being aligned a certain way so the subatomic forces don't cancel each other out. Why it is that the subatomic forces exist in the first place, I can't say. 71.104.119.240 (talk) 00:53, 5 May 2010 (UTC)
 * They exist because if they didn't we wouldn't be here to notice it. (See anthropic principle - it's the best answer to "why" questions we have. Science is good at "how" but it doesn't really do "why".) --Tango (talk) 01:09, 5 May 2010 (UTC)
 * Sure you're not just interested in ICP lameness? DMacks (talk) 01:22, 5 May 2010 (UTC)


 * For those not in on the joke, see Miracles (Insane Clown Posse song). Incidentally the New York Times had an amusing article on this meme. Regarding magnets:
 * VIOLENT J: I think we might have misused the word miracle. These things we mentioned in the song, they can all be explained. But what we’re doing is appreciating them. Even the infamous line “Magnets, how do they work?” I mean, yeah, we know how magnets work. But they’re still incredible. You can push something across the table without touching it.''
 * SHAGGY 2 DOPE: Come on, man. The North and South Pole makes a rock magnetic, and if you touch a piece of metal with it, that becomes magnetic? That’s crazy.''
 * I kind of agree, to be honest. I find magnetism pretty magical, scientific explanation be damned! --Mr.98 (talk) 01:54, 5 May 2010 (UTC)


 * The reason a magnet attracts iron/steel is basically because when you bring it toward an iron/steel object, it induces an electric current in the object, which interacts with the object's magnetic domains (if they're lined up right) such as to produce a magnetic field of the opposite polarity, which creates an attracting force. As for your question specifically about how fucking magnets work, I got no clue -- I'm pretty conventional in my love life, so I've never tried using magnets for it.  Perhaps you could find out more on this use of magnets if you take a look at the article Sex toys...  :-D 67.170.215.166 (talk) 04:11, 5 May 2010 (UTC)
 * I thought only a moving magnetic field induces a current. When a magnet is motionless near a piece of iron, there is still the same attractive force present. DMacks (talk) 05:04, 5 May 2010 (UTC)
 * I think that's because the magnetic lines of force are a different density at different points in the metal object. But honestly, I'm not so sure about the induction part anymore... 67.170.215.166 (talk) 05:45, 5 May 2010 (UTC)
 * It's not usually induction (eg magnet/metal attraction). The Magnetic reluctance / Permeability (electromagnetism) are the factors in whether or not a material is attracted to a magnet (see below).Sf5xeplus (talk) 09:04, 5 May 2010 (UTC)
 * As for fucking magnets, I've checked out the article on sex toys -- there's no mention of magnets anywhere in it. I suppose you could put a pair of magnets on your cock for more female stimulation, but I don't think it would give much of an advantage vs. all those other toys, or simply improving your technique.  FWiW 67.170.215.166 (talk) 05:52, 5 May 2010 (UTC)
 * Motors that are present in vibrators contain magnets. This would potentially make these magnets "fucking magnets" ;) Sjschen (talk) 15:45, 5 May 2010 (UTC)

Well, I've known more than a few guys who thought they were magnetically fuckable. And despite my asexuality, these losers seem to hit on me constantly. Subatomic forces aside, sometimes opposites just don't attract. 71.104.119.240 (talk) 08:11, 5 May 2010 (UTC)

One route to the explanation: Magnets in their interactions will move the position of lowest energy (like everything else - gravity, electric fields etc) - this explains both magnet-magnet and magnet-metal interactions - for 'part 2'; an explantion of how energy levels change with magnetism is required...Sf5xeplus (talk) 08:57, 5 May 2010 (UTC)

When two magnets meet at opposite poles, is their overall magnetic field lowered than when they were separated? John Riemann Soong (talk) 18:23, 5 May 2010 (UTC)
 * The easiest way to answer this is to treat the two magnets each as simple dipoles (assume an inverse square law if you wish) - what happens is that the shape of the field changes - along the axis there is some cancelling of field - yes. perpendicular to axis the field shape will be different from a single magnet - and slightly stronger along the center line.77.86.68.186 (talk) 18:08, 6 May 2010 (UTC)

Also I'm curious in the thermodynamics of how magnets reproduce, i.e. magnetise other materials. Generally delta-S is negative. How about delta-H? Do the calories expended in moving your arm provide the free energy required? John Riemann Soong (talk) 18:23, 5 May 2010 (UTC)
 * delta H is negative for magnetic attraction - energy levels are split into opposed and alligned states (eg for paramagnetic materials) - electrons will tend to drop from opposed states to alligned states (emmitting hv) and creating a net magnetic property.
 * As you note - delta S is negative - so thermal energy tends to demagnetise in general.77.86.70.220 (talk) 19:20, 5 May 2010 (UTC)
 * As a better attempt at a (simple) answer - a big strong magnet will magnetise a smaller weaker magnetic substance.. any energy required (from your hand/arm combination) will be to separate them afterwards..! 77.86.68.186 (talk) 20:18, 5 May 2010 (UTC)


 * Is delta-H negative for magnetic induction? And is delta-S still negative when two magnetic poles come together by attraction, without induction? John Riemann Soong (talk) 21:00, 5 May 2010 (UTC)
 * ok. So magnetic induction isn't a chemical process.. H=E+pV .. there's no pV change I can think of in induction so H=E for this. If you don't do any work in magnetic induction (ie no electrical load ) then delta H is zero. Maybe I'm missing something obvious? 77.86.68.186 (talk) 16:55, 6 May 2010 (UTC)
 * Surely there is some sort of ordering because of magnetisation though. Besides pV is just to describe work done by a gas, you can convert it to other forms. John Riemann Soong (talk) 17:19, 7 May 2010 (UTC)

It is interesting to hear Richard Feynman's take on the OP's question: Feynman argues that the questions is currently unanswerable in terms of anything "simpler". (To be pedantic, his argument applies to magnetism rather than magnets, but leaving such cavils aside it's an interesting counter-intuitive viewpoint anyway). Abecedare (talk) 17:12, 6 May 2010 (UTC)

Gulf war oil spill
Is the claim that 36 billion gallons of oil was released in the Gulf War oil spill as ridiculous as it sounds to me? I'm ready to remove the quotation, reliable sources be damned, considering how silly it sounds. Thoughts? Magog the Ogre (talk) 01:04, 5 May 2010 (UTC)


 * As our article says, it is orders of magnitude bigger than all the other estimates we have. My guess is that the Times article is getting confused between the Gulf War oil spill and the Kuwaiti oil fires. The latter may well have burnt 36 billion gallons of oil, but I don't think that much has ever been spilt at sea. --Tango (talk) 01:15, 5 May 2010 (UTC)

For the record, it takes the entire US a month a half to consume that much oil. Magog the Ogre (talk) 01:22, 5 May 2010 (UTC)

Medical question
What is the name of the disease when the body has trouble keeping fat and storing it, and the sufferer is underweight as a result? I saw it describled on a medical TV show, but I didn't quite pick up the name. ```` —Preceding unsigned comment added by 76.229.150.6 (talk) 01:34, 5 May 2010 (UTC)


 * You may be thinking of Cachexia. Dauto (talk) 02:55, 5 May 2010 (UTC)
 * You might also be thinking of hyperthyroidism. Dismas |(talk) 05:11, 5 May 2010 (UTC)
 * None of the above. You saw a description of lipodystrophy which occurs in both congenital and acquired forms, and both generalized and partial. Quite striking and in the severe forms associated with several other severe problems. alteripse (talk) 10:38, 5 May 2010 (UTC)
 * And to sign, use ~ rather than ````. ~ is on the same key as `, SHIFT+` gives you ~ (on a US keyboard, at least) --Psud (talk) 06:58, 6 May 2010 (UTC)

Silver mineral
How does this type of silver form? 149.169.218.250 (talk) 01:49, 5 May 2010 (UTC)


 * By precipitation from hot sulfurous solution (such as in geysers, fumaroles, those kinds of places) due to the action of the dissolved hydrogen sulfide (generally upon cooling of the solution -- the stuff is slightly soluble in hot water, but completely insoluble in cold water). FWiW 67.170.215.166 (talk) 02:29, 5 May 2010 (UTC)
 * aka Hydrothermal synthesis 77.86.70.220 (talk) 15:58, 5 May 2010 (UTC)
 * as well as Ore_genesis 77.86.70.220 (talk) 16:00, 5 May 2010 (UTC)

What is the current state of Computer text to speech compare to human readers?
Two question: is good/modern computer TTS system better reader then "average Joe" who is a human native speaker reading same text aloud? If yes, is computer TTS as good as professional announcer (TV, radio etc.)? 1) Sounds as good as human pro. 2) Very close. 3) Still far away, but better then average Joe.

As to give an example of good TTS, I generated mp3 on my computer from reading few paragraphs of introduction to Bird article. http://www.autohotkey.net/~TePe/BirdsIntro.mp3 TTS I used probably not the best one out there, but still quite good IMHO. And the reason I'm asking, I'm very curious, but ESL here, and computer sounds totally perfect for me. But my judgment could be clouded, plus once again, mine English is far from perfect. PS. Lets not go into acting and emotion, sure computer could mimic them, but there is too much room for good or bad taste opinions etc. Lets stick with reading informational articles like most on Wikipedia etc. 70.48.64.135 (talk) 01:52, 5 May 2010 (UTC)


 * It still sounds like a computer to me, regarding the tone. It still has something of a Stephen Hawking quality, and the timing of some words is off. Some of the words are a bit wrong to my ear (e.g. the second "i" in "fertilizer" is pronounced wrong), but it's not bad. What throws it off is the pitch at the end of words, and the timing between words, which is not very natural. It is definitely not as good as a professional announcer to a native English speaker. I have definitely heard better text to speech than that, though. --Mr.98 (talk) 02:29, 5 May 2010 (UTC)


 * I don't think the bird recording comes anywhere near to even an average native speaker in terms of quality. --99.237.234.104 (talk) 02:38, 5 May 2010 (UTC)


 * Thank you Mr.98! Much appreciated! Could you please point me to the system that sounds more natural then the one I choose as an example? Sure, if it is available online. Or, if that is not possible, make a recording of the same paragraphs for comparison. Thank you once again. 70.48.64.135 (talk) 03:26, 5 May 2010 (UTC)


 * I'm not a linguist, but I believe that getting the timing and emphasis perfect is AI-complete. Consider the sentence "Fruit flies like a banana.".  To read that sentence aloud correctly requires recognizing that "fruit flies" is one noun phrase, and needs to be grouped tightly, so that it doesn't get parsed the same way as "Time flies like an arrow.", in which "flies" is the verb, not "like".  (Time flies like an arrow; fruit flies like a banana)  So, in order to get a sentence to sound just right, it's necessary to understand it.  Paul (Stansifer) 02:50, 5 May 2010 (UTC)


 * The point is valid but the example is not a very good one. One of the reasons Chomsky chose "fruit flies like a banana" is that it actually sounds the same for both parsings, even though the meanings are completely different. Looie496 (talk) 03:00, 5 May 2010 (UTC)
 * I say the two parsings differently, although you would only notice if you were listening really carefully. The difference is in the pauses between the words "fruit" and "flies" and between "flies" and "like". --Tango (talk) 03:05, 5 May 2010 (UTC)
 * I'm with Tango. I say them they way he does.  -- Jayron  32  03:08, 5 May 2010 (UTC)
 * They can be said the same if you're trying to make a point, but a normal human reading that line would emphasize it for clarity, depending on the intended meaning. APL (talk) 03:14, 5 May 2010 (UTC)
 * Interestingly, system I used got the phrase from |TTS article "My latest project is to learn how to better project my voice" right, but ""Time flies like an arrow. Fruit flies like a banana" was very unnatural. 70.48.64.135 (talk) 03:30, 5 May 2010 (UTC)

I just noticed that spellchecker highlighted the word "fertiliser" from bird article. The phrase is "Some species, particularly songbirds and parrots, are popular as pets. Other uses include the harvesting of guano (droppings) for use as a fertiliser." Could it be misspelled? When I have changed it to "fertilizer" TTS sounded much more natural :( 70.48.64.135 (talk) 03:39, 5 May 2010 (UTC)
 * You can pick even worse examples: "Green flies like a lettuce", for example is semantically reasonable spoken both ways. You need a much bigger context than that sentence.  Since there are no such things as "Time flies", you'd at least have a chance at that one. SteveBaker (talk) 18:39, 5 May 2010 (UTC)
 * How does the colour green flying make any more sense than fruit flying? I would say it makes less sense - at least fruit is tangible. --Tango (talk) 20:21, 5 May 2010 (UTC)
 * See American_and_British_English_spelling_differences. The -ize/-ise are both equally acceptable spellings.  Americans tend to exclusively use -ize endings, while the British tend to have a much more nuanced approach towards deciding when to use each of them.  -- Jayron  32  03:55, 5 May 2010 (UTC)


 * (ec)Fertiliser is the British spelling and is just as correct, and is also consistent with the rest of the article (see the words specialise, characterise, categorise... in the same page). If your software can't read British-English spelling, it isn't very good. --Lgriot (talk) 04:02, 5 May 2010 (UTC)
 * So if a human make mistake while reading an article you will also claim that "humans are not very good"? Or just particular person? Have you tried to listen to WikiProject Spoken Wikipedia articles? Even on the project page they are talking about "incorrect pronunciation" in the problem section. And BTW, could you please point at better software? Thank you in advance. 70.48.64.135 (talk) 04:17, 5 May 2010 (UTC)


 * We've come a long way since the "Stephen Hawking" era of text-to-speech. He's been offered vastly better voice synths (some, even based on analysis of recordings of his own voice before he lost the ability to speak) - but he turns them down because he's become used to it.  My Amazon Kindle has pretty good text to speech (the male voice seems superior to the female for some reason).  There are a few words it gets wrong - but they are pretty rare and it seems to react to punctuation better than some that I've heard.  Some of the best stuff I've heard is done by analysis of actual, specific people talking - and some of those are incredibly lifelike.  But the limit comes (as others have observed) when the text doesn't contain enough information by itself to convey how it should be read.  Since it would take a full-scale AI system with a vast knowledge of humanity and all of it's quirks to get that right.  Figuring out when something should be read sarcastically - and when it's real requires a lot of smarts.  The way you read "The dog was wearing pink and green spotted hat!" is quite different from "The man was wearing a pink and green spotted hat!" - my emphasis helps - but the reason that sentence is surprising is different because dogs don't often wear hats - but men do - and because pink and green spots would be remarkable on a man - but relatively unremarkable on a dog.  The amount of culture, knowledge and so forth needed to artificially generate the highlighting I added to those sentences is incredible - way beyond the current ability of our best AI systems. SteveBaker (talk) 18:39, 5 May 2010 (UTC)


 * The example sounds like sampled speech (recorded speech) played back as a collection of phonemes, with rising and falling inflections added manually or by a clever program. It is better than early purely synthesized text-to-speech, which to Americans sounded a bit like a Russian reading from phonetically written Scottish English. It was full of unusual phonemes, and this sample is less so. Perhaps the earlier system sounded more natural to inhabitants of some other English speaking countries. Edison (talk) 19:04, 5 May 2010 (UTC)

File:Sirius A and B Hubble photo.jpg
On this File's description, it says "The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system.".

Hadn't the mirror been replaced, and the battery replaced, by this time?174.3.123.220 (talk) 04:24, 5 May 2010 (UTC)


 * Diffraction spike has half your answer. Also, I don't think the mirror was actually replaced, our Hubble Space Telescope article describes what was done to correct the spherical aberration present in the original mirror. I suspect the concentric rings are also an artifact of part of the telescope's design, or limitation of the design, rather then a "fault" with some part of it. There is an example of a star imaged with the "uncorrected" mirror in the HST article, it looks a lot worse then the photo you link. Vespine (talk) 05:42, 5 May 2010 (UTC)
 * I think the other half of your answer might be Diffraction it self. Vespine (talk) 06:05, 5 May 2010 (UTC)
 * More specifically, see Airy disk. TenOfAllTrades(talk) 12:35, 5 May 2010 (UTC)

Using TNT or dynamite instead of smokeless powder in guns
According to this, http://en.wikipedia.org/wiki/Trinitrotoluene#Energy_content TNT and dynamite contain more energy per unit of mass than gunpowder. I don't know if the article means modern day smokeless powder or old day black powder. But why don't we use TNT or dynamite in smaller quantities (so energy content released is the same while mass used is reduced) instead of smokeless powder as propellant? Or maybe even gasoline?

Or perhaps to rephrase the question, what advantages does smokeless powder have over those other explosives when used in guns? Presumably reduced smoke is one. Is it possible to make guns using those propellants? ScienceApe (talk) 04:27, 5 May 2010 (UTC)


 * High explosives would blow the gun to bits and pieces instead of propelling the projectile. 67.170.215.166 (talk) 04:32, 5 May 2010 (UTC)


 * Smokeless powder deflagrates, while dynamite detonates. That is, the first goes "whoosh" while the second goes "bang".  See USS Vesuvius (1888) for an unusual approach to keeping projectiles from going "bang" in the barrel. PhGustaf (talk) 04:40, 5 May 2010 (UTC)

TNT or any other higher explosives hav got a very high burning rate sometimes it being a few hundred meters per second! Now at such high speeds you have to provide small length barrels to maintain the pressures. just refer to this.. http://thefiringline.com/forums/showthread.php?p=2351433 Prady.. —Preceding unsigned comment added by 116.73.242.109 (talk) 05:16, 5 May 2010 (UTC)

Consistent, safe, controllable burning is important in a firearm. Modern smokeless powder can already easily produce the maximum allowable pressure (if desired) in any particular cartridge, so there is little advantage to a propellant with more power. Friday (talk) 15:14, 5 May 2010 (UTC)


 * Put another way: If you have an explosion then all of the explosive gets converted into gas pretty much instantly. The pressure in the barrel goes up insanely high and the bullet gets an extremely violent initial acceleration.  As the bullet moves along the barrel, the space behind it gets bigger - and since no more gas is being produced, the pressure can only drop.  The bullet is therefore no longer being accelerated as fast as it could be.  For relatively slow burning propellants, the gas pressure builds up more slowly (although still pretty darned fast!) and the bullet gets a chance to start accelerating more slowly - and as the volume behind it increases, the propellant generates enough gas to fill it and keep the pressure up.  So the bullet gets a more smooth and gradual acceleration down the barrel.   For a given muzzle velocity, you need much lower pressures with a slow burning charge than with an explosive.  So the gun doesn't have to be as strong - and can therefore be lighter and easier to handle.  As far as the user of the gun is concerned, you can get the same muzzle velocity with a lighter weapon if you use a slower burning charge...or to put it another way - for the same pressure-resistance in the gun, you get a higher muzzle velocity with gunpowder than with dynamite - which gives you a longer range and better accuracy.  A perfect charge would be one that produces exactly constant pressure from the moment it's triggered until precisely the moment when the bullet leaves the end of the barrel, and no more after that.  Since the volume to be filled is at it's largest at the end, you ideally want a charge that gradually increases the amount of gas it produces until the bullet leaves the barrel...pretty much the opposite of an explosive. SteveBaker (talk) 18:18, 5 May 2010 (UTC)


 * An analogy might help. Think of a bow and arrow instead of a gun.  The string of the bow accelerates the arrow over a distance of a foot or two.  How hard would you have to hit the end of the arrow with a hammer to make it go as far?  If I were to hit the end of the arrow as hard as I possibly could, it might go a few feet - but that would be it!  But whacking the end of the arrow hard enough to make it go 100 feet would certainly smash it to bits!  So a gentler (but more prolonged) force is better. SteveBaker (talk) 18:22, 5 May 2010 (UTC)
 * So even if the cannon or gun were invincible and wouldn't blow up, the gunpowder is still better to use? ScienceApe (talk) 00:00, 6 May 2010 (UTC)
 * The answer to that isn't very meaningful though. How much dynamite am I allowed to use versus how much gunpowder?  Dynamite is an energetically more concentrated explosive than gunpowder - so if there is zero risk of harming the gun then stuff the barrel almost full of dynamite and get a really HUGE bang!  But if you have a gun with a limited tolerance for pressure - then you can do better with gunpowder than dynamite. SteveBaker (talk) 03:35, 6 May 2010 (UTC)
 * Well the reason why I asked is because the example you gave seemed to indicate that no matter how hard you hit the arrow, it won't be as effective as the bow string. ScienceApe (talk) 05:29, 6 May 2010 (UTC)
 * Even if the gun barrel is strong enough to contain the initial pressure of the dynamite explosion, there is a limit to how much energy the explosion can impart to the bullet, because the bullet does not seal perfectly against the inside of the barrel. Some explosive gas will leak around the bullet. The leakage rate will be a function of the pressure difference from the back to the front of the bullet. Since the TNT will create a tremendously high pressure behind the bullet initially, before the bullet has time to get going, a lot of the combustion gas will leak around the bullet. In any case, it is possible to launch a projectile using high explosives without any barrel at all; see Project Orion (nuclear propulsion). If you adapted the same principle to firing a projectile out of a gun barrel, using high explosives, it would almost certainly be more effective to divide the explosive charge into multiple small charges that could detonate in sequence, for example by placing the charges in side chambers off the main barrel, each one exploding just when the bullet passes. See Supergun, Project Babylon, and V-3 cannon. However, even in supergun designs, the propellant is always gunpowder or cordite rather than a high explosive. Read the lead section of the cordite article for an explanation. I'd also guess that high explosives would not work well with gas-operated automatic firearms. And of course if the projectile contains an explosive warhead, using high explosive for the propellant might detonate the warhead too, by imparting too much shock to the projectile. Also see base bleed for another way to increase the range of a cannon-fired projectile. --Teratornis (talk) 00:24, 9 May 2010 (UTC)

Proximity of brain structures?
How close is the hypothalamus (especially the suprachiasmatic nucleus) to the hippocampus and amygdala? —Preceding unsigned comment added by 71.104.119.240 (talk) 10:02, 5 May 2010 (UTC)


 * Fairly close. There is a good schematic drawing on this page. --Dr Dima (talk) 10:31, 5 May 2010 (UTC)

Since the hypothalamus and hippocampus/amygdala don't actually touch, what is it exactly that's between them? 71.104.119.240 (talk) 19:34, 5 May 2010 (UTC)


 * Parts of hypothalamus are bounded by the third ventricle, optic tracts, and cerebral peduncles. Hypothalamus is fairly compact. Hippocampi, on the other hand, are fairly large, curving structures in the human brain. They go almost all the way around the thalamus, and join up in a fornix, adjacent to the third ventricle. The fornix projects down towards mamillary bodies, which are the part of the hypothalamus. So they do actually touch. --Dr Dima (talk) 23:19, 5 May 2010 (UTC)


 * Well, they are connected, but I wouldn't say that they touch. Looie496 (talk) 23:37, 5 May 2010 (UTC)


 * From Grey's anatomy (29th American edition), page 863: "The body of the fornix lies above the tela choroidea and ependymal roof of the third ventricle... Anteriorly, above the interventricular foramina, the body [of the fornix] divides again into the columns or anterior pillars of the fornix. They bend downward, forming an anterior boundary of the interventricular foramina, become buried behind the wall of the third ventricle and end in the mamillary bodies". So they do touch. --Dr Dima (talk) 01:15, 6 May 2010 (UTC)


 * Yes, the fornix touches the hypothalamus, but the fornix is not usually considered part of the hippocampus. It is a nerve bundle connecting the hippocampus to the hypothalamus and septum. Looie496 (talk) 03:51, 6 May 2010 (UTC)

Sleep before Exams
I feel more sleepy whenever I wish to avoid sleep the night before my exams. Why is that so? 'Interest' matters? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 10:51, 5 May 2010 (UTC)


 * Perhaps this is because studying at night is more demanding for the brain than going out with your friends at night or watching a movie? Count Iblis (talk) 13:57, 5 May 2010 (UTC)


 * Wait, wait, waaaiiit! Staying up late the night before an exam is really seriously dumb!  It's much more important that you are relaxed and well rested than that you cram facts into a sleep-deprived brain!  You won't retain much of what you revise that late at night anyway - and being alert through the exam is critical to your performance. SteveBaker (talk) 18:06, 5 May 2010 (UTC)


 * Usually, yes. Although if you've just found that you only had access to half the course over the last couple of months, and the exam is in the morning, and you slept the night before, you might consider hours spent cramming outweighed hours sleeping. But usually, yes, it is much better to sleep than do last-minute revision. 86.178.228.18 (talk) 21:07, 5 May 2010 (UTC)

Well, We will speak about last minute preparation and not last minute revision! Why do i feel sleepy when i intend to avoid it? Not just in case of sleeplessness and exams but at many occasions, "I should not do that...Oops, I did that" happens. Something which I wish to avoid is mostly confronted. Why? —Preceding unsigned comment added by 125.21.50.214 (talk) 03:51, 6 May 2010 (UTC)
 * Inability to delay gratification? Sleep when you're tired is gratification, where as studying is not. If you figure out how to solve this problem, there are probably tens of millions of students who'd like to know it. --Mark PEA (talk) 21:05, 6 May 2010 (UTC)

Plastics & half-life periods
DO all entities have half-life periods? Why do they say that plastics are non-degradable (non-biodegradable)? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 10:56, 5 May 2010 (UTC)


 * Theoretically, the entire universe has a "half life" in that it itself is degrading (see heat death of the universe). So yes, anything in the universe is, by definition, "temporary" and "degrading".  If the half-life of a substance is, say, measured in the millions of years, its going to be here a while.  Even though it may be "technically" degrading, on any scale reasonable for human life, it isn't.  -- Jayron  32  13:23, 5 May 2010 (UTC)
 * Yeah...I once had a comb that said indestructible on it, and I made it my business to destroy it. In your case, perhaps it's supposed to be like a plastic bag in relation to, like, an apple core.  The latter will be gone way before the former.  DRosenbach  ( Talk 17:33, 5 May 2010 (UTC)
 * Plastics do degrade in sunlight, and you may find that some are slowly degraded by fungi or bacteria over thousands of years.. Also In theory proton decay could destroy all the matter you like. Graeme Bartlett (talk) 22:22, 5 May 2010 (UTC)

Right-hand writing & Left-leg tumbling
It is easy to write/draw (not with pen or pencil) using the right leg for a right-hander/right-hand-writer even though the one has never been exposed to practice for writing using legs. BUT, It is difficult for the same person to use the left leg for writing/drawing (not with pen or pencil). Does the left-brain hemisphere train the right-leg covertly when one practices to write using right-hand? - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 11:08, 5 May 2010 (UTC)
 * I can't answer your question directly, but suggest that, to the extent that the left side of the brain does exercise preferential control over the opposite side of the body - bearing in mind (Ha!) that theories of brain lateralization have sometimes been exaggerated - the pre-existing brain functions for controlling the right hand to write and draw will be more easily applied to the novel use of the right leg for those tasks than to the left. A brief self-trial seems to indicate that this is true even for someone like myself who is naturally right-handed but also naturally left-footed. 87.81.230.195 (talk) 16:33, 5 May 2010 (UTC)

Can light be heard?
Can light be heard by any creature? What is the essential factors for an organism to 'hear' light? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 11:56, 5 May 2010 (UTC)
 * Sound is caused by mechanical vibrations in the air, which is detected by an organ (usually in the ear) which is designed to detect those vibrations. See hearing.  On the other hand, light is caused by electromagnetic radiation and does not cause mechanical vibrations, so no organ which can be described as a "hearing" organ would be able to detect it.  See sight.  -- Jayron  32  13:19, 5 May 2010 (UTC)
 * In certain ways, yes. When pulses of light at select frequenciecs strikes certain objects, the interaction may cause the object to emit sounds (photoacoustic effect). However you can't really "hear" the sound the the traditional sense of the word. Sjschen (talk) 14:42, 5 May 2010 (UTC)
 * Another "not really" answer... Some people with brain damage have a side effect of hearing noise when they see certain lights (or seeing light when they hear certain sounds). This is not hearing light.  It is brain damage causing signals caused by perceiving light to trigger sensations in the part of the brain that should only be activated by hearing something. --  k a i n a w &trade; 14:46, 5 May 2010 (UTC)
 * Well...it both can and can't be heard...radio waves, microwaves, and I'm assuming visible light (as it's in the same spectrum) can be converted into sound, but cannot be heard outright. Also, some forms of synaesthesia may cause light to be heard, but this is, again, not hearing them in the true sense. Ks0stm (T•C•G) 15:11, 5 May 2010 (UTC)
 * You get on a slippery slope with some of these answers:
 * Sound and light are very different things - organs designed to pick up vibrations in the air (our ears) can't pick up electromagnetic waves (which is what light is). So in truth, it's impossible to use an organ of hearing to detect light.
 * However, light can sometimes cause sounds - which you could hear. If you attach a sensitive microphone to a tree - then as the sun rises and lights up the leaves, they will start to transpire water and you can hear the flow of that water up the trunk.  Are you "hearing light"?  Well, not really - you're hearing the consequences of the light.
 * But then, our ears don't exactly transmit sound to the brain - they convert the sound waves into the vibration of little hairs which in turn create nerve impulses that are a combination of electrical signals and chemical reactions. In a sense, we aren't really "hearing" the sound - we're hearing the consequences of the sound hitting our ears.
 * People who have synesthesia mistakenly interpret one sense as another - so they might get the sensation of sound from light - or vice-versa - but they aren't truly hearing the light. If you blindfold them, so their eyes can't see the light - but leave their ears wide open - then stop "hearing" the light immediately.  So this doesn't count.
 * There is a demonstration of sound being carried by a laser beam in the Dallas Science museum - but that's not really "hearing light" either because the light has to be converted back into sound by a bunch of electronics.
 * Short, direct answer: "No". SteveBaker (talk) 18:01, 5 May 2010 (UTC)
 * A few thoughts on this
 * We don't know how bats and dolphins interpret their sonar.
 * Some blind people report feeling an object in front of them brushing their face, before they actually touch it; it is believed that they hear the echos from their footfalls, see Human echolocation.
 * There has been an experiment with a blind person. They wore a camera, connected to a computer. It scanned the image in horizontal lines, top to bottom. Pixels on each line were converted to a pure sine wave, low frequency to the left, high frequency to the right. The brightness of each pixel. controlled the intensity of each sine wave. Thus a thin vertical line gave a continuous pure tone, a thin horizontal line gave a short burst of white noise, a diagonal line gave either a rising or lowering tone. The subject could recognise simple shapes after a little practise. I'm not sure how successful the experiment was in the long run.
 * CS Miller (talk) 18:28, 5 May 2010 (UTC)
 * I'd be inclined to say the answer is just: no. I think it's a primarily semantic question. By definition, "hearing is the sense by which sound is perceived", I'd argue it doesn't matter if you do that with your eyes, visual cortex, or your backside; you hear sound, not light. Synaesthesia is a neurological condition which does "funny" things to perception, if EVERYONE was synesthetic, then our definitions of normal sight and hearing would be different. Vespine (talk) 22:50, 5 May 2010 (UTC)
 * See Environmental effects of wind power. Evidently bats are able to detect and avoid microwave transmitters. The mechanism is unknown.
 * --Teratornis (talk) 00:52, 9 May 2010 (UTC)
 * --Teratornis (talk) 00:52, 9 May 2010 (UTC)
 * --Teratornis (talk) 00:52, 9 May 2010 (UTC)

Chromate Reactions
The chromates I formed by the reaction of chromium hydroxide with sodium hypochlorite were yellow. When I reacted them with hydrogen peroxide (3%), they immediately turned dark purple-black. After a while, the hydrogen peroxide started sizzling (from catalytic decomposition), and the solution began lightening. It turned into a shade of yellow just darker than the previous one (more purple). I added more hydrogen peroxide and it repeated the reaction. The hydrogen peroxide was not finished up when it turned yellow again, because an addition of sodium hypochlorite made it fizz oxygen gas still. What is the purple-black substance. It is about as dark as solid potassium permanganate. --Chemicalinterest (talk) 11:59, 5 May 2010 (UTC)
 * Could it be something like or related to Potassium tetraperoxochromate(V) which is red-brown?77.86.70.220 (talk) 12:58, 5 May 2010 (UTC)
 * or Chromium : "Chromium(VI) compounds in solution can be detected by adding an acidic hydrogen peroxide solution. The unstable dark blue chromium(VI) peroxide (CrO5) is formed, which can be stabilized as an ether adduct CrO5·OR2" 77.86.70.220 (talk) 13:05, 5 May 2010 (UTC)

It could be the chromium peroxide. It was dark blue and decomposed soon. --Chemicalinterest (talk) 13:44, 5 May 2010 (UTC) The formula would be CrO6 though, because the chromium is 6+ and 3 peroxide ions would be 3 O2(2-). --Chemicalinterest (talk) 14:37, 5 May 2010 (UTC)
 * I did some figuring and got these reactions.
 * Na2CrO4 + 3 H2O2 + 2 HCl → CrO6 + 12 H2O + 2 NaCl
 * CrO6 + 6 NaCl + 2 H2O → 4 NaOH + Na2CrO4 + 3 Cl2
 * 4 NaOH + 2 CrO6 → 2 Na2CrO4 + 2 H2O + 3 O2

Overall reaction:
 * 3 Na2CrO4 + 9 H2O2 + 6 HCl → 3 Na2CrO4 + 12 H2O + 3 Cl2 + 3 O2
 * As you can see, the Na2CrO4 is not consumed. It is a slow acting catalyst for the reaction of H2O2 with HCl. They do not react normally. That is why the yellow color comes back after the reaction is over.
 * Thanks for the information on the chromium peroxide. It helped me figure out what I wrote here. --Chemicalinterest (talk) 14:37, 5 May 2010 (UTC)
 * What I mean by slow acting is that the intermediate states do not instantly decay, as in an ordinary catalyst. --Chemicalinterest (talk) 14:38, 5 May 2010 (UTC)
 * If it is CrO5 that would be 2 x O22- (peroxide) and 1 x O2- (oxide) - that's the often reported structure eg - explaining why it is two peroxide and not three is quite difficult.77.86.70.220 (talk) 15:33, 5 May 2010 (UTC)
 * So its not a pure peroxide, its chromium peroxide oxide? --Chemicalinterest (talk) 16:32, 5 May 2010 (UTC)
 * Then I have to refigure my reactions. --Chemicalinterest (talk) 16:33, 5 May 2010 (UTC)

Collagen-proline-triple helix
Might be an old question. Collagen is rich in proline. Collagen is triple helical for which the three strands should be 'tightly' wounded to each other, at the same time, proline distorts the structure (tertiary) of a protein. Paradoxical??? Are prolines present in the periphery of the helical structure? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 12:09, 5 May 2010 (UTC)
 * The article collagen discusses this, and the picture in the article (unfortunately in French, so you'd have to translate it), this one, clearly shows the formation of crosslinking between collagen triple helices. Thus, coupled with the non-standard amino acids present in the chain probably explins the tertiary structure yoy note.  -- Jayron  32  13:14, 5 May 2010 (UTC)


 * Proline does not disrupt the tertiary structure of a protein - on the contrary, the unique structural properties of prolines can be critical for a protein to fold into its final conformation. And it's not that prolines disrupt all secondary structure. For example a polyproline helix is actually remarkably stable. Proline is thought of as "secondary structure disrupting" because it does disrupt the two most common secondary structures (the alpha helix and the beta strand). -- 140.142.20.229 (talk) 22:48, 5 May 2010 (UTC)


 * What proline does is force the protein chain to adopt the right amount of twist, thus actually stabilizing the collagen triple helix. Note that the triple helix must also contain hydroxyproline to be adequately stabilized.  BTW, the hydroxylation of proline requires vitamin C as a cofactor -- not having any vitamin C in your system weakens your collagen, which is responsible for the symptoms of scurvy.  FWiW 67.170.215.166 (talk) 01:12, 6 May 2010 (UTC)

Space random movements vs planets
While every object in space moves in a random manner, how are planets and satellites moving in orbits? - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 12:26, 5 May 2010 (UTC)

Macroscopic objects in space never move in a random manner. Perhaps you are thinking of thermal motion. Macroscopic objects (satellites, planets) are too massive to move in such a random manner, there is insufficient thermal energy available. 157.193.175.207 (talk) 12:37, 5 May 2010 (UTC)


 * You might want to read Formation and evolution of the Solar System. Dismas |(talk) 12:55, 5 May 2010 (UTC)


 * The only force big enough to move large objects like this is gravity. Because gravity is an attraction force that acts as if the source is a point (at the "Center of gravity"), that forces nearby objects into elliptical orbits (strictly, they are conic sections).  However, even gravity gets weak at intergalactic scales so you'd expect galaxies to have motion that's all over the place - except that at those colossal scales, the expansion of the universe starts to dominate motion and is seems like everything at those distances are moving directly away from wherever you happen to be.  It's only at really small scales (around the size of dust grains, bacteria, stuff like that) where the forces involved are much more complex (electromagnetic, weak and strong nuclear forces) and truly random quantum effects come into play that the motion is truly random.  Between those limits, there are some things (like winds and storms and stuff) that are not strictly random - but so complicated that they are "chaotic" (in the mathematical sense) and are therefore unpredictable beyond very short intervals of time...so they might as well be random for all practical purposes.  SteveBaker (talk) 17:52, 5 May 2010 (UTC)
 * Gravity only acts as though from a point-source if the source is a shell (including spheres). At sufficient distance, any object is roughly spherical, so it is actually at large scales that you would expect elliptical (and other conic sectional) orbits. The reason you don't get that is because a conic section is the solution for the 2-body problem. At large distances you usually have to consider more than just two objects, which can result in very complicated motions. Within a cluster of galaxies, they do sometimes move in roughly elliptical orbits. At larger scales it can be difficult to determine the movement beyond current speed and direction (and even that isn't easy) - all paths are approximately straight on a small enough scale, and you don't need a very small scale when you are talking about clusters of galaxies. --Tango (talk) 20:34, 5 May 2010 (UTC)

Grass cuttings
I know stuff about slow and fast baterial decomposition of compost and the like but I have noticed that newly cut grass gets very warm very quick (e.g. in 15C ambient reaching 50C+ in the time it takes to finish mowing the lawn, so say an hour). Whether this cools off quick depends on the heap size, it can stay hotter for a few days. An hour seems very fast for bateria to multiply, is it possible that there is direct oxidation of some of the chemicals in the grass sap on that timescale? It is much more pronounced when (as at this time of year) the grass is fast growing and sappy. --BozMo talk 17:40, 5 May 2010 (UTC)
 * Are you sure its bacterial growth and not merely absorbing sunlight which is causing the additional heating? -- Jayron  32  18:25, 5 May 2010 (UTC)
 * Yes, sunlight causes much heat addition. Probably some oxidation is occurring, but there would need to be large quantities of a strong reducing agent in the phloem of the plant, which I don't hear of. --Chemicalinterest (talk) 18:38, 5 May 2010 (UTC)
 * There was no sun this afternoon. The grass was cut cold and went hot in a heap in about an hour, possibly two from the first blade cut. The pile of lawn cutting from cutting the lawn once must be at least 200 kg with an incident surface area in the pile of say 4 sq metres. So say 200 kg of grass contains what 100kg of water heated by 0.5C a minute I make about 20kW of heat. Also the heat is much more pronounced from about 10cm deep in the surface, the very surface is losing heat to air and feels about ambient. Not sun. Very fast fermentation of some sort or direct oxidation? --BozMo talk 18:50, 5 May 2010 (UTC)


 * Could be. Each blade of grass has a cut end and smashed cells of fatty acids, phospholipids, oils and enzymes splashed all over the place. Perhaps it could simply be due to the rapid oxidation of these volatile components taking place, multiplied millions of times. --Aspro (talk) 18:50, 5 May 2010 (UTC)


 * The O2 isn't present deep in the grass pile though, limiting the amount of oxidation and the heat. It would be used up very quickly (only a little can seep through the grass), limiting the heat output. --Chemicalinterest (talk) 18:59, 5 May 2010 (UTC)


 * Diffusion and the partial pressure of oxygen will insure will ensure there is no shortage (after all, an anaerobic heap would become black and stagnate -would it not).The smell of cut grass is due to a rapid chemical reaction --Aspro (talk) 19:25, 5 May 2010 (UTC)


 * Nitrates and sulfates are other potential electron acceptors. You could culture the bacteria on an agar plate to see what type of species you get ... John Riemann Soong (talk) 19:01, 5 May 2010 (UTC)


 * Bit technical for me culturing something. And is it definitely a bateria not, say, a yeast? Only really smells grassy mind you. But certainly there will be a lot of nitrates. --BozMo talk 19:06, 5 May 2010 (UTC)
 * If it is oxidising something then I reckon it needs to release about 70MJ for my 200kg pile in an hour say which corresponds to oxidising a bit over a kg of sugar, or 1% of the total weight being an oxidisable mixture. S'pose thats vaguely plausible. --BozMo talk 19:10, 5 May 2010 (UTC)


 * If it's a yeast, you should see some of the colonies too. Why don't you smash up some of the cuttings and put it in a little bit of water in a test tube (or some sort of small see-through container). Cover the top of the solution with oil to prevent O2 entry. Or have two containers and cover one to see what oxygen presence does. (Seal both.) I'm a bit curious if any gas will evolve. (You could make a homemade gas test... basically any evolved N2, NO2, SO2, H2S etc. will bubble into an overturned glass dome inside the container and show up as a bubble.) John Riemann Soong (talk) 19:10, 5 May 2010 (UTC)


 * Getting dark here. Might have to wait until the next cut next week. Should I warm the crushed grass in water? Couple of centrimetres thickness of pestled grass? Presumably I don't need to use boiled water because disolved gas will be negligible? --BozMo talk 19:20, 5 May 2010 (UTC)


 * I don't think you have to warm it. Lukewarm water might do (25C - 37C), but plain tap water will work. I've never done a microbiological experiment in a drinking glass. Basically enough water to make a liquid suspension. We're being really unrigourous about the concentration and skipping buffering the solution, but I'm just curious what type of things will show up.
 * I wonder if you could also do a pH sample across time. Sample the pH of freshly cut grass, grass in a grass heap after 1h, 4h, 24h, etc. (Use a large sample of cuttings per time period to prevent sampling error). and use the same amount of liquid each time. John Riemann Soong (talk) 19:25, 5 May 2010 (UTC)


 * I don't think boiled water is necessary. The gas solubility for produced gases will be very low. On the other hand, dissolved O2 in water might retard the growth of any microbes causing the heat. You have a large sample of grass, I assume.
 * Some species causing the heat, e.g. Pseudomonas can turn a previously yellow/colourless culture a nice green. ;-) John Riemann Soong (talk) 19:27, 5 May 2010 (UTC)
 * Silage says fermentation takes 48 hours to establish. If that's true the heat might be respiration . For some reason although I googled "grass" first googling "silage" did not immediately occur to me. But I have not found what "respiration" is beyond that it is immediate, heat releasing and uses carbohydrates. --BozMo talk 19:34, 5 May 2010 (UTC)
 * Note the reference refers to "a potential silo fire" from allowing too much respiration. This all sounds quite plausible now. --BozMo talk 19:37, 5 May 2010 (UTC)


 * The only issue is the oxygen. Maybe it's microbes using nitrates / sulfates. Fermentation might not be in full swing for 48 hours, but other forms of anaerobic respiration might be used before then. John Riemann Soong (talk) 19:59, 5 May 2010 (UTC)


 * Interesting. Hmm. I didn't know the browning reaction reduced the amount of available protein. I thought it just made proteins tastier by glycating them to sugars. John Riemann Soong (talk) 20:02, 5 May 2010 (UTC)
 * The initial heating may not be due to microbes at all but due to the living (about to die) grass. This is metabolising too, and it suddenly has a lot of repair work to do, so there will be a lot of activity in the damaged cells. Graeme Bartlett (talk) 22:13, 5 May 2010 (UTC)


 * I think there's too much thinking going on here. Did you cut the grass into a bag or was it all raked up afterwards? Given the relatively short amount of time you gave for cutting such a large amount of grass, I've got to think you used a bag. A bag held not too far away from a very hot electric motor or gasoline engine, which in fact probably got hotter and hotter the longer it was run. I'm thinking the grass is hot because the mower is hot; it's just retaining the heat well because the mass of cellulose is good insulator. Matt Deres (talk) 14:00, 6 May 2010 (UTC)


 * How often do you cut the grass? ;-) Grass in the collector/catcher has always been, as far as I can remember,  nice and cool -regardless of the type of mower. By the next morning however, the grass heap is noticeably warm. I can't say I've noticed the same thing when harvesting rows of  cauliflowers in the snow.--Aspro (talk) 16:13, 6 May 2010 (UTC)


 * Yep @Aspro Nope @ Matt. For the benefit of people who don't mow.. the dual fabric grass collection bags on a John Deere 54in mower hang in free air at the rear of the tractor whilst the (diesel) motor is at the front, with exhaust to one side. In between the motor and the bags there is a couple of metres plus a driver. On top of which when I lift off the heavy bags to empty them (say every 15 minutes) they are cool. An hour later the heap is hot. --BozMo talk 00:35, 7 May 2010 (UTC)

I have a compost bin in my back yard made from four discarded wooden pallets tied together. It's roughly a cube five feet on a side. When I add fresh grass cuttings to the bin it gets noticeably hot, although I haven't paid attention to how fast it heats up. I notice the heat the following day when I dig down into the pile a bit to make a hole in which to dump kitchen scraps. Covering the putrescible material such as kitchen scraps with a thick layer of grass or leaves blocks odors and keeps the flies off. I can rule out other sources of heat because I mow with a human-powered reel mower, with no grass bag, and I rake the grass up. By the time I collect the grass, any heat it could have gained from the mowing itself would be dissipated. I also usually mow in the evening when there is little sun. The pile also gets noticeably hotter after a rain, which uniformly wets the upper layer of material that tends to dry out otherwise. Incidentally, Appropedia has some articles about using compost to heat domestic water, and a greenhouse. There is a lot of usable heat from biomass decay that currently gets wasted. If someone wanted to be systematic about this, a compost thermometer would be good to have. I have not bought one yet. I might buy one, if only to reassure myself that I am not risking a compost fire. That is, to check the pile for excessive internal temperature rise, particularly after I add a large amount of fresh material from the autumn leaf drop. --Teratornis (talk) 01:16, 9 May 2010 (UTC)

Copper oxidation
When copper metal is added to a solution of copper(II) nitrate, does the copper(II) nitrate oxidize the copper metal? The silver-potassium nitrate discussion in the reference desk archive is similar. If a small amount of HCl is added to it, does it oxidize it? Thanks. --Chemicalinterest (talk) 18:16, 5 May 2010 (UTC)
 * If it is of sufficiently low pH, then yes it will. See Standard electrode potential (data page) and find the half reaction for the reduction of nitrate.  The reaction requires H+ ions, which means that at low enough pH, the nitrate ion will sufficiently oxidize additional copper metal.  One could calculate the necessary concentration of H+ necessary to do so; converting the Eo for the overall reaction to an equilibrium constant is trivial, and from the equilibrium constant and the concentration of copper nitrate, you can calculate the concentration of H+ needed to oxidize additional copper.  I suspect you will need a small amount of additional acid, either HCl or H2SO4 should be sufficient.  You should see the brown NO2 gas as a product; the counterion of the acid (either chloride or sulfate) effectively replaces the nitrate in the solution as the additonal copper is oxidized.  -- Jayron  32  18:23, 5 May 2010 (UTC)


 * Does the counterion for the nitrate really matter for the oxidation to work? I assume that existing Cu(II) will tip the equilibrium slightly towards the reverse reaction. Unless the reaction is autocatalytic -- Cu2+ oxidises copper metal? (But two Cu(I) ions I recall, are less stable than Cu(0) and Cu(II). But maybe this represents a good intermediate...) John Riemann Soong (talk) 18:29, 5 May 2010 (UTC)


 * See above. The Cu(II) is irrelevent, excepting that it will lower the pH of the water by forming complex ions via lewis acid-base reactions.  Basically, you will get some Cu(OH)42- complexes in any solution with Cu(II) ions, and thus will also produce an excess of H+.  I am not certain this excess H+ is of sufficient concentration to be useful in the nitrate reduction half-reaction, which is why you probably need a little bit of extra acid.  -- Jayron  32  18:36, 5 May 2010 (UTC)


 * I don't have any nitrates, but I saw a demonstration of a Daniell cell using copper nitrate and copper electrodes, and I wondered if the copper got oxidized. --Chemicalinterest (talk) 18:41, 5 May 2010 (UTC)


 * Copper seems to need an acidic environment to oxidize. When copper metal is added to hydrogen peroxide, no black CuO is formed; but when HCl is added, green CuCl2 solution is formed (green because of HCl prevalence). --Chemicalinterest (talk) 18:43, 5 May 2010 (UTC)


 * I'm wonder if it's out of a need to have a counterion more than anything. You're generating Cu2+ from Cu(0) -- you're generating OH-, which will accumulate unfavourably. What if you add a weak acid like ammonium chloride or acetic acid? John Riemann Soong (talk) 18:52, 5 May 2010 (UTC)

My possibly incorrect reaction on paper was: Cu(NO3)2 + Cu → 2 CuO + 2 NO2. In this reaction, the OH- as O2- is precipitated from solution. --Chemicalinterest (talk) 18:57, 5 May 2010 (UTC)


 * I wonder if you can "guide" the reduction to other things, e.g. nitrogen, imines, amines... Also NO doesn't last long by itself in solution. In the presence of oxygen it becomes NO2. John Riemann Soong (talk) 18:59, 5 May 2010 (UTC)
 * In general yes - adding a reagent that will complex the oxidised copper helps - one v. good example from old A level course if the use of thiourea - it complexes Cu+ strongly enough to allow the reverse disproportionation reaction to happen. For Cu2+ - yes amines et al help - eg Copper and water - fairly non 'rusty', but copper + water + ammonia - increase rate of corrosion.77.86.70.220 (talk) 19:45, 5 May 2010 (UTC)
 * I said before that I didn't complete this reaction, so it might not occur. --Chemicalinterest (talk) 19:04, 5 May 2010 (UTC)


 * No, your reaction is wrong. For the correct reaction, you need to use the correct half-reactions from Standard electrode potential (data page).  The relevent half reactions are:
 * Cathodic: NO3−(aq) + 2H+ + e− NO2(g) + H2O
 * Anodic: Cu(s) Cu2+ + 2e−
 * Now, just balance the electrons by doubling the nitrate half reaction, and combine the two reactions, to get:
 * 2NO3−(aq) + 4H+ + Cu(s) 2NO2(g) + 2H2O + Cu2+
 * Notice that the reaction equilibrium depends on the concentration of H+ on the reactant side, so you need a sufficiently low pH to drive the equilibrium to the product side. As I noted above, Cu2+ will generate some acid via lewis acid-base reactions with the water; however this is probably not sufficient to make the reaction extensive if you are just adding copper metal to copper nitrate solution.  Remember, there is already Cu2+ ions present in the solution, so via the common ion effect, the equilibrium is unlikely to move forward.  What you need to do is to overcome the common ion effect by adding something additional to the reactant side.  Adding more copper metal does no good, since solids do not effect equilibrium, so you need to add either additional nitrate OR additional acid.  The acid is easy enough to do, and you could easily figure out for yourself what the maximum pH is to have an extensive reaction by converting the total Eo for the above reaction to an equilibrium constant, and then using your initial concentration of copper(ii) nitrate.  If doing that gives you trouble, I can help you with that too.  -- Jayron  32  19:38, 5 May 2010 (UTC)


 * One of two things ie either Cu2+ or NO3- as the oxidant.
 * 1.
 * Cu + Cu2+ >>> 2Cu+
 * This is called Symproportionation (opposite of Disproportionation)
 * This reaction doesn't happen in water - the reverse reaction does..
 * The overall reaction doesn't occur in major amounts in water ... but this is mainly due to hydration energy, right? But I wonder if Cu(I) can form intermediates. e.g. Cu + Cu2+ ---> 2 Cu(I) ---> 2 Cu(II). John Riemann Soong (talk) 19:56, 5 May 2010 (UTC)
 * 2.
 * Cu + NO3- + H+ >>> yes ... products vary can be NO2, N2 , N2O maybe others.
 * Jayron already covered this above - it only happens if you add acid (in general enough and strong enough to generate some free nitric acid).77.86.70.220 (talk) 19:45, 5 May 2010 (UTC)

Chromate reduction
What is a good chemical to reduce chromates to Cr2O3? --Chemicalinterest (talk) 19:03, 5 May 2010 (UTC)
 * Just about metal will do. Chromates have a very high standard reduction potential, see Standard electrode potential (data page), Cr2O72- has a reduction potential of +1.33 volts, more than sufficient to oxidize most any metal.  The end product is Cr3+, which in a base will precipitate Cr(OH)3.  A hydroxide is just the hydrated oxide, If you heat a hydroxide in a crucible, you can drive off water and generate the oxide, in this case Cr2O3.  -- Jayron  32  19:27, 5 May 2010 (UTC)
 * On the organic side, if you find metals a little expensive, you could try sugar, alcohols (vodka comes to mind), formaldehyde ... Organic reactions might be a little more chaotic though. If you don't care about the identity of what spread of sugar products you might get, e.g. you care only qualitatively about the production of Cr2O3 (or black/brown products from oxidation of sugar), then you're good. John Riemann Soong (talk) 19:35, 5 May 2010 (UTC)

endodermal cell solution
My biology question paper has the following multiple choice question: Four solutions, with different water potentials are listed. 1 endodermal cell solution 2 root hair cell solution 3 soil water solution 4 solution in a xylem vessel Which list has the solutions in order from the highest (least negative) water potential to the lowest (most negative) water potential? highest-> lowest A 1  2   3   4 B 2  4   1   3 C 3  2   1   4 D 4  1   3   2

Link: http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9700%20-%20Biology/9700_w08_qp_1.pdf Question no. 23 —Preceding unsigned comment added by 116.71.40.176 (talk) 20:20, 5 May 2010 (UTC)

I cant seem to find anything regarding the endodermal cell solution in either my textbook or the internet. What is it? And what would be the answer to the question? This is not a homework problem, and I have tried it. Thanks. --116.71.40.176 (talk) 20:18, 5 May 2010 (UTC)

heat capacity units and calculation
I find heat capacity units are confusing. (K = kilogram or K for Kelvin?. °K instead of °C.)

I would appreciate if someone would check if I have interpreted and calculated this correctly.

According to this table Heat capacity, the heat capacity of water (under constant pressure) at 25 degrees C is 4.18 J/(g·K). Same at 100 degrees C.

Suppose I want to heat water from 25 to 75 °C, at atmospheric pressure

So to heat a gram of water takes 50 x 4.18 = 209 joules.

And to heat a kilogram of water takes 50 x 4.18 x 1000 = 209,000 joules.

And 1 kWh = 3.6 x 10**6 joules. So 1 kWh would heat 3.6 x 10**6 /209000 = about 17 kilograms of water. And 17 kilograms of water is 17 litres.

So to heat a 175 litre tank of water requires just over 10 kWh of energy.

Therefore a water tank that was one cubic meter in volume could be heated from 25 to 75 °C with 1000/175 = 57 kWh of energy. Please is this all correct?

Thank you, Wanderer57 (talk) 21:36, 5 May 2010 (UTC)
 * According to Google, your calculation is correct, (with a slight rounding error).
 * Three points, the specific heat capacity of water is slightly dependant on the temperature, the units are normally 4.18 kJ/kg/K (kg is the base unit of mass, but its the same as J/g/K. Lastly K is kelvin, kg is kilogrammes. CS Miller (talk) 22:11, 5 May 2010 (UTC)


 * ... and °K is just wrong. (While Celsius, Fahrenheit and Rankine get degree symbols, Kelvin does not.) -- 140.142.20.229 (talk) 22:42, 5 May 2010 (UTC)
 * It's wrong now, that is. The kelvin (no capital letter, symbol capital K) was previously called the degree Kelvin (with capital K, symbol °K) just like all the other "degrees" of temperature.  It changed in 1968, but some people took a long time to notice.  --Anonymous, 01:50 UTC, May 6, 2010.


 * (edit conflict) :The calculations seem correct, but how many liters (or litres) are in a 1 m3 tank? --Chemicalinterest (talk) 22:15, 5 May 2010 (UTC)
 * 1 liter = 1 cubic decimeter. Since a decimeter is 1/10th of a meter, 1 liter is 1/10^3 = 1/1000 of a cubic meter. -- Jayron  32  22:25, 5 May 2010 (UTC)

Electric spacecraft drives
Why do Variable Specific Impulse Magnetoplasma Rocket drives have the ability to get spacecraft around the solar system better than Ion thrusters? The articles go on about the workings of each, but the main advantage claimed in the VASIMR article is less electrode erosion. Is that really the basis for the recent wild hype about VASIMR that it could get astronauts to Mars in 45 days? If they were both operated for the same burn duration in spacecraft of similar mass, would the VASIMR drive produce greater acceleration? Edison (talk) 23:45, 5 May 2010 (UTC)


 * Both Ion drives and VSIMR deliver varying amounts of force. So I can't answer your last question. Obviously if the force, mass, and burn duration are the same the two will do the same. But I think Ion drives have reached their limit for force, but VSIMR is just getting started. To increase the force on the ion drives lowers the lifespan of the electrode too much. But VSIMR can still be scaled up to even higher power levels. (i.e. ion drives topped out at 200Kw, while VSIMR started at 200Kw.) Ariel. (talk) 07:18, 6 May 2010 (UTC)


 * Ion drives I remember reading about had negligible thrust, .01 Newton or the weight of a sheet of paper on Earth, but could continue it for a very long time. The VASIMR article implies far more thrust, like 5 Newtons or more. Is the mass of the propulsion unit similar, or is it proportionately greater, mostly cancelling the advantage? Edison (talk) 19:17, 6 May 2010 (UTC)


 * Don't forget, in an ion drive the gas is ionized and accelerated using electrostatic feilds, in Vasimr it is ionized, super heated, then accelerated. The gas is much more energetic in a vasimr, boncing around much faster providing more power. —Preceding unsigned comment added by 74.67.89.61 (talk) 22:12, 7 May 2010 (UTC)