Wikipedia:Reference desk/Archives/Science/2009 September 11

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September 11

Blood Glucose Nanotcehnology

Hi. I was looking for information & links on the workings of blood glucose monitoring devices, but on a very detailed level. Like "Chemical X reacts with Y" or "These bonds are broken/deformed in the reaction," and I have a particular interest in the reactions/mechanisms on a nano level.

Many thanks =) Cuban Cigar (talk) 00:41, 11 September 2009 (UTC)

There are a few systems: the basic schema is that glucose passes through a selectively permeable membrane controlling the transport of analytes to a metabolizing enzyme system that generates a response on interaction with the glucose, leading to an electrical signal generated by the transducer and eventually amplified and translated into glucose concentration on the meter screen. Details can be found here. You may also find this of interest. - Nunh-huh 00:49, 11 September 2009 (UTC)

Blood glucose meter#Technology has some relevant information. --Tango (talk) 00:50, 11 September 2009 (UTC)

Need help understanding American sports gambling notation...

Redskins (+6.5) over GIANTS // SEAHAWKS (-8.5) over Rams // PACKERS (-3.5) over Bears

I've read the relevant Wiki article, but it just left me more confused. Are the above "lines" discussing the spread or the odds?

For example, if I choose to place a bet on the Redskins in the first example, do I win if they score 7 more total points than the Giants? Or do I just get $6.50 for every $1 I bet on them if they win? If the former is true what happens if I choose the Giants?

I feel like I'm the only person in the world who doesn't understand this :-/ 218.25.32.210 (talk) 01:08, 11 September 2009 (UTC)

Far as I know, those numbers are the "spread". If the Skins win by only 6 over the Giants, then they failed to "cover the spread" and someone betting the spread on the Skins loses, even though the Skins won the game. The spread is a way of "leveling the playing field", meaning, yeh, the Skins should win, but by at least 7, or they didn't cover. The 1/2's are to ensure that you can't "tie" the spread. You can only cover it or not cover it. Of course, you can also lose, in which case you obviously didn't cover. Baseball Bugs ^{What's up, Doc?} carrots 01:23, 11 September 2009 (UTC)

Some of those spreads are negative - doesn't that mean you can lose and still cover the spread? --Tango (talk) 01:31, 11 September 2009 (UTC)

Well, ya got me on that one. Spread betting doesn't seem to explain it, either. You might have to resort to Google if a real expert doesn't turn up here soon. Baseball Bugs ^{What's up, Doc?} carrots 01:37, 11 September 2009 (UTC)

This site [1] doesn't explain the system, but it does give the spreads, all of them as negatives, and it lists the Giants as favorites over the Skins (which is what I would have expected, actually) at -6 1/2. I guess the way to look at that is, take the final score (assuming Giants do win) and subtract 6 1/2 from the margin. If the Giants still come out on top, then they've covered the spread. Baseball Bugs ^{What's up, Doc?} carrots 01:43, 11 September 2009 (UTC)

That would make sense. Perhaps the OP's "+6.5" is just a typo. Presumably you can get bet in either direction? --Tango (talk) 01:45, 11 September 2009 (UTC)

Not a typo, just how to think of it from the other team's perspective. You'd buy the Redskins and if their score + 6.5 is greater than the Giants, you'd win. I think I finally understand this now... 218.25.32.210 (talk) 01:50, 11 September 2009 (UTC)

No, not quite, I don't think so. The Giants are favored to beat the Skins. If you bet on the Skins, it's + 6 1/2, which I interpret to mean that you add 6 1/2 to the Skins score at the end and see if it results in a winner for the Skins or not. It's the flip of the same idea - if the Giants fail to cover the 6 1/2 spread, the ones betting the spread on the Skins win. Baseball Bugs ^{What's up, Doc?} carrots 01:55, 11 September 2009 (UTC)

(ec)That's it. If you take Redskins, then (Redskins score) + 6.5 > (Giants score) gives you a win and the opposite gives you a loss. If you take Giants, then (Giants score) > (Redskins score) + 6.5 gives you a win and the opposite gives you a loss. When you win, it's typically referred to as "covering the spread." Hope that helps. Makeemlighter (talk) 01:56, 11 September 2009 (UTC)That's not what I meant. Makeemlighter (talk) 01:58, 11 September 2009 (UTC)

Covering the spread is when the winning team wins by more than the spread. So, if the Giants win by 7 or more points, they've covered the spread. Makeemlighter (talk) 01:59, 11 September 2009 (UTC)

In your example, betting on the Giants, I think you would actually say (Giants score) - 6.5 > (Redskins score) gives you a win. Hence the minus figure used with the favorite. Arithmetically, of course A - C = B is the same thing as A = B + C Baseball Bugs ^{What's up, Doc?} carrots 02:04, 11 September 2009 (UTC)

Yeah, exactly. Vegas probably counts on gamblers getting confused by all of this. Makeemlighter (talk) 02:14, 11 September 2009 (UTC)

And not too surprisingly, the largest spreads involve potential winners over the Chiefs and the Lions. Place yer bets! Baseball Bugs ^{What's up, Doc?} carrots 02:20, 11 September 2009 (UTC)

(undent). Just a little more on spread betting. It is often (incorrectly) assumed that the spread is somehow set by an "expert" who has studied the teams and determines who should be favored to win. In actuallity, the spread is set by the market. It's pure free market economics. As more people put money down on one team, the spread shifts to compensate until betting is aproximately even between the two teams. The bookmakers are looking for perfect 50/50 betting between the two teams; since they are paying out full on whoever wins (if you win, you double your money, less the vig), they do best when there is approximately even betting between the teams. The "favorite" is thus the one the market favors, and not necessarily the better team. Often, teams with popular followings tend to get better spreads than their skill level would dictate. --Jayron32 05:32, 11 September 2009 (UTC)

It is not quite that they do best when there is even betting, it is that they have the least risk. Businesses don't like risk. They would make more profit if they had a 75%/25% split and the 25% side won, but they would rather guarantee a small profit than have a chance at a large profit and a risk of a large loss. --Tango (talk) 14:48, 11 September 2009 (UTC)

The "market" definining the betting odds is what tips the experts off that a fix might be in. Such was the case in the 1919 World Series, where everyone expected the Sox to win, but the betting favored the Reds. As well it should have - since the fix was in. Baseball Bugs ^{What's up, Doc?} carrots 16:47, 11 September 2009 (UTC)

Battery leak query

Hi, I have a pinhole leak in a deep cycle acid battery. I was wonderin if their was a common susstance ie tape,glue etc I could use to block it & not be dissolved by the sulphuric acid cheers. —Preceding unsigned comment added by 219.88.82.92 (talk) 01:51, 11 September 2009 (UTC)

Considering how dangerous sulphuric acid is - either safely dispose of the battery and obtain a replacement or seek specialist advice. See Sulphuric_acid#Safety. Exxolon (talk) 02:39, 11 September 2009 (UTC)

Sulfuric acid is extremely corrosive and rapidly degrades all organic substances (including duck tape and all kinds of adhesives), as well as most metals. The ONLY way to fix your battery is to WELD THE LEAK SHUT (and no, soldering won't do, the acid will eat right through solder before you can blink). So, either get your welding torch, or turn in the battery for toxic waste disposal. 98.234.126.251 (talk) 06:23, 11 September 2009 (UTC)

Really? Sulfuric acid eats solder instantly? I find that very unlikely; Lead is pretty resistant to sulfuric acid. The all-inclusive statements are probably inaccurate; this company says PVC is "excellent" for storing sulfuric acid up to 60% concentration. I don't think it's a good idea to recommend welding torches and sealed acid batteries in the same sentence, though. Nimur (talk) 13:50, 11 September 2009 (UTC)

Sorry, can't resist anymore. Epoxy resin.[2] But you should talk to a battery specialist before doing anything. Find a battery shop and call them up. Real life people who deal with that stuff every day will always be willing to give you advice, and it will often be better than the advice you get from the internet. Franamax (talk) 06:46, 11 September 2009 (UTC)

Of course, all of this advice for repairing the battery may not be worth the time, materials, and effort. It may be better just to recycle the faulty battery and buy a new one. --Jayron32 07:06, 11 September 2009 (UTC)

Acres of rice

How many acres of rice does it take to feed one person for one growing cycle (assumed to be one year)? -- Taxa (talk) 02:33, 11 September 2009 (UTC)

Rice is 370 kcal/100 grams, and the average person needs something like 2000 kcal/day. Assuming that all of the various micronutrients could be provided in pill form (so we could avoid scurvy and beri-beri and that stuff) a person would need 2000/370*100 = 540 grams of dry rice. Yields of rice probably vary significantly, but here's one data point: [3] which indicated that in 2006, rice in Texas was averaging yields of about 7200 pounds/acre. That's about 16000 kilograms/acre. Putting it all together, from a caloric standpoint, a person eating nothing but rice would consume 540 * 365 / 1000 = 197 kilograms of rice in a year. That means that, given that an acre of rice could produce 16000 kilograms, one acre could feed 81 people (assuming no wastage, and assuming that those 81 people ate nothing but rice for their caloric intake). ANother measure of productivity is Edible protein per unit area of land, of which rice produces roughly 224 lbs/acre or 493 kg/acre. A person needs roughly 50 grams of protein per day, so that's 50 * 365 /1000 = 18 kg per year. 493/18 = 27 people per acre of land could subsist on nothing but rice from a protein point of view. --Jayron32 07:01, 11 September 2009 (UTC)

Er, 7,200 pounds is about 3,200 kilograms. You need to divide by 2.2, not multiply. Matt Deres (talk) 13:46, 11 September 2009 (UTC)

Er, oops. Lets do that one again. Redoing the math with the CORRECT factor results in 16 people being supported on 1 acre of rice from a caloric point of view, and 5 people being supported on 1 acre of rice from a protein point of view. Blame the fact that it was after 1:00 AM local time...

That's a bit misleading, though, since rice sucks as a protein source -- it's a much better carb source. Probably even a little bit of protein supplementation would push the numbers way up. Looie496 (talk) 01:36, 12 September 2009 (UTC)

Even if you eat enough rice to get the right quantity of protein, that still won't be your protein needs met. There are various types of protein you need and rice doesn't have them all. You need a pulse (eg. some kind of bean) in addition to a cereal to get the full range. (There are some exceptions - quinoa is like a cereal, but with all the protein, for example - and animal products tend to have all the protein you need, but cereal+pulse is a good general rule for vegetarian meals.) --Tango (talk) 02:06, 12 September 2009 (UTC)

REQUEST FOR INFORMATION ON UGCA 292 (DDO 125) GALAXY

Hi,

I request you to help me get some information about UGCA 292(DDO 125)GALAXY.

Regards Lakshmi —Preceding unsigned comment added by Nagasethu (talk • contribs) 02:41, 11 September 2009 (UTC)

According to our list of nearest galaxies, it is the 89th nearest galaxy to the Milky Way; the list has a table that contains other information. Looie496 (talk) 03:05, 11 September 2009 (UTC)

How far can your cat see into the universe?

This is a list of galaxies that have been seen with the naked-eye by humans. So, humans can see 14.7 million lightyears into the universe, unless you believe in the rumors about M101 being seen with the naked eye. M101 is 27 million lightyears away.

I've read that the eye of a cat can collect about 20 times more light than the eye of a human. Then, given the brightness of the dimmest galaxies that have been seen by humans, that seems to imply that all the galaxies listed here should be visible to a cat.

So, can your cat really see 100 million lightyears into the universe in case of very dark sky (i.e. Bortle class 1)? Count Iblis (talk) 03:11, 11 September 2009 (UTC)

Sound weird, but I'd go along with it. If cats can see in rooms where humans are virtually blind, then there is no reason why they could not see many stars not visible to humans. In the same way, humans would be able to see many more stars than a dog could. Birds could probably make out far better colour variations amongst stars than humans can. Myles325a (talk) 03:52, 11 September 2009 (UTC)

On the other hand cats have 20/200 vision which for a human is considered legally blind. They're good for catching mice but not for anything too discriminating. So yes they collect the photons but what actually would someone with that sort of vision see if they went out on a clear night? The sky would be lighted up but they wouldn't be able to pick out many details besides the moon. Dmcq (talk) 12:03, 11 September 2009 (UTC)

It is not just the absolute amount of light from an object that determines whether or not we can see it, it is that light relative to the light around it. The smallest a human with 20/20 vision can resolve is 1 arcminute. If the galaxy in question is smaller than that then it will be blurred with the surrounding sky. If that surrounding sky is too bright, you won't be able to make out the galaxy, even with very sensitive eyes. --Tango (talk) 16:41, 11 September 2009 (UTC)

If Tango's argument is correct, then no ground based telescopes would be able to see much better than a human could, seeing as those telescopes are basically simple large artifical versions of human eyes. Also, I gather from the previous interesting comments on cat's poor visual acuity, that they are made to see movement rather than discriminating small details. That makes sense to me. Being a cat lover, I have often noticed how cats behave myopically, ignoring stuff you put out for them on the carpet. UNLESS IT MOVES. In which case they pounce on it. Myles325a (talk) 08:40, 15 September 2009 (UTC)

I just had a quick work out of the figures and as far as I can see they'd collect 20 times more light but it would be spread over 10x10 more area, so they need 5 times the flux from a star as us. Each magnitude needs 2.5 times as much flux so they'd only see stars of about 1.5 less magnitude han a human. In an urban setting we only see down to about magnitude 4 so they'd see just the stars in List of brightest stars but not much more. In ideal conditions they'd see those of about 2 magnitudes more. Dmcq (talk) 18:37, 11 September 2009 (UTC)

What Australian plants relate to American ones from the time of Gondwana?

As an Aussie, I am interested in the fauna and flora connection between America and Australia, which were once joined together with what is now Antarctica. For example, the New World tomato has its distant relative the uncultivated bush tomato, and I yesterday I read that the well-known Australian plant Monstera deliciosa has its distant cousin in Mexico. The (only?) marsupial find outside of Australia is the American opussum. Interestingly, Australia does not have the cactus succulents of the American deserts, although we have a lot of similar deserts. Would that mean the continents drifted apart after the evolution of marsupials but before the evolution of cacti? Has there been any research done on this? Myles325a (talk) 04:12, 11 September 2009 (UTC)

There are actually close to 100 species of opossums in the Americas, plus one other marsupial called the Monito del Monte. Anyway, my understanding is that the split-off of Australia happened about 140 million years ago, as described in our Pangaea article, while the main radiation of flowering plants happened around 100 million years ago. So, although flowering plants had probably already existed for a long time, they were still at a relatively limited level of diversity back then. Some of them no doubt reached Australia after the land-split, carried by wind and wave from Southeast Asia or other places. (I'm stretching my limits here, there's tons of research on this stuff but it's well outside my usual domain.) Looie496 (talk) 04:47, 11 September 2009 (UTC)

Path through Earth

For a physics assignment, I was able to show that the time it takes to circle the earth at an orbit near the earth's surface is equal to the time it takes for a mass passing through the earth to return to it's original position (T=sqrt(4*Pi^2*R/g)). Is this a coincidence or is there a deeper reason behind the equality? —Preceding unsigned comment added by 76.68.245.247 (talk) 05:34, 11 September 2009 (UTC)

Well, we're not supposed to do your homework for you, but I'm not sure how much to give away before it starts being unfair... To make it easier, imagine the earth as a circle instead of a sphere. Now imagine two points at 12 o'clock, one will accelerate towards the middle then decelerate back to a stop at the 6 o'clock position purely by gravity. The other will orbit half way around the circle at a constant speed and also stop at 6 o'clock. Compare both vertical components of their velocity vectors and you'll hopefully find your answer. The journey back to 12 from 6 will just be the same thing again. Vespine (talk) 06:11, 11 September 2009 (UTC)

I struggled with that for a few minutes, but yeah, that's beautiful. Both objects are falling freely under the influence of gravity. Is it true then that both objects would be at the same position in the vertical plane? Or would one (through) need an integral function to calculate it's instantaneous position, and the other one (orbiting) use a cosine rule? Sorry to step on the OP's question (and it seems like they already did the homework) but this is interesting to me too! Franamax (talk) 06:39, 11 September 2009 (UTC)

The question is simply a more complex version of The Monkey and the Hunter problem, except this time the hunters bullet is fired with enough force to make it into orbit and the monkey if falling through a giant hole though the center of the earth. But otherwise, the exact principles that hold true in The Monkey and Hunter Problem hold true here. --Jayron32 06:46, 11 September 2009 (UTC)

The monkey and hunter problem only works in a uniform gravitational field, which this isn't. This behavior actually depends on the specific properties of the gravitational field at work here. For example it wouldn't work for a hollow spherical shell or more generally a sphere with non-uniform density. Rckrone (talk) 07:05, 11 September 2009 (UTC)

(ec)It can be shown that the gravitational field inside a sphere of uniform density is proportional to the displacement vector from the center. Therefore your acceleration in the vertical direction only depends on your vertical position. Note that both paths initially have zero vertical velocity so they behave the same along the vertical axis. Rckrone (talk) 06:55, 11 September 2009 (UTC)

I would also have accepted "yes" or "no" as an answer. ;) But yeah, vectors, I'd forgotten about them. I thought Vector was either a running shoe or an energy drink. Why did I ever think that the horizontal component of velocity had anything to do with the vertical? Thanks and d'ohh! :) Franamax (talk) 07:16, 11 September 2009 (UTC)

Well both are oscilators about the same centre of mass , one circular, one linear, and involve the same force. So there should be a close connection between the two - as to whether both are the same for a good reason...83.100.250.79 (talk) 11:16, 11 September 2009 (UTC)

Why not consider the motion of the rotating object in two axises - is the equation obtained the same as the linear oscillator? And is there a reason for this? (eg consider circular motion as two oscillators, one sin the other cos)..<hint>try the differential equations for the circular motion expressed as separate for the two axis</hint>

It is intereesting isn't it, I got the exact same problem too a while ago as a physics assignment83.100.250.79 (talk) 11:55, 11 September 2009 (UTC)

I think a key point here is that the force stopping the object that is going through the Earth from orbiting is the reactive force with the sides of the tunnel. That force will obviously be perpendicular to the motion of the object, and such a force does not change the energy of the object. That means you can calculate everything using energy really easily, since it is constant for both objects. The initial energy of each object will be the same (assuming they start travelling at the same speed, which I think is part of the problem). The angular speed depends on the linear speed and the distance from the centre, the linear speed gives you kinetic energy and the distance from the centre gives you potential energy, which must add up to that total energy. When you work out the maths you should (I haven't actually tried) get that the average angular speed is the same for both objects (ie. it takes the same amount of time for each to get from start to finish). --Tango (talk) 18:04, 11 September 2009 (UTC)

I don't think conservation of energy simplifies the problem. Also the two objects have different total energy so I'm not really sure what you mean.

As I mentioned before, and as 83.100.250.79 hinted at, the force law here (gravity inside a sphere with uniform density) has a particularly nice form, that of a 3D harmonic oscillator, which is the key to the problem since as a result the equations of motion in each dimension are independent from each other. a = -(g/R)r, which means a_z = -(g/R)z. A close orbit just above the surface acts the same as an orbit just below the surface, so both paths can be treated as following the force laws in the interior of the sphere. Rckrone (talk) 18:51, 11 September 2009 (UTC)

If they start at the same place with the same speed, they have the same total energy. Are they not supposed to start at the same speed? --Tango (talk) 19:12, 11 September 2009 (UTC)

The one that goes straight through has to start at rest for it to work.

On an unrelated side note, I think it's worth pointing out that the Earth doesn't have uniform density and so this wouldn't work on the actual Earth. The one going straight through would make the trip faster. Rckrone (talk) 19:21, 11 September 2009 (UTC)

Really? But in the limit as the two points on the surface get closer together the distance travelled will be same and the one travelling in a straight line won't have any time to accelerate, the one in orbit will have a speed independent of the distance. I don't see how they can have the same travel time under those conditions. --Tango (talk) 19:31, 11 September 2009 (UTC)

It doesn't work for any path through the sphere, only one through the center (otherwise gravity isn't the only force acting on the object and so it won't behave like a harmonic oscillator). Rckrone (talk) 19:37, 11 September 2009 (UTC) Edit: No wait that's wrong, it would still behave like a harmonic oscillator, and so the period for any straight path through the sphere is equal, which is an interesting result of its own. Note that that period is the time it takes for the orbiting object to make a full orbit.

Comment - Tango as I remember the orbiting object has just enough speed to orbit, but the through the earth object starts with v=0 as I remember the period for the orbit is sqrt(4pir³/Gm_earth) , and you need to pick the uniform density version of the earth (I think) - which is described in good detail at shell theory (God bless newton) (It's also described by Gausses law but I won't recommend that).

Usually the teacher gives just enough detail so that you work out the one that has the 'cool' result...83.100.250.79 (talk) 21:49, 11 September 2009 (UTC)

One of the curiosities is that the force inside the solid sphere = -kx_displacement - which is just like that of a simple spring (eg Hookes law ) - this gives a chance to suggest that the students work out the neat solution by "assume that the force is like a spring" - before actually covering the whole shell theorem thing.. The odd consequence of this is that the adage "simplify = lie to children" - actually turns out to be "not lie to children" since the more thorough analysis gives exactly the same result (until you consider non-uniform earths...)83.100.250.79 (talk) 22:16, 11 September 2009 (UTC)

Orbital velocity at the Earth's surface (for a circular orbit) is about 8km/s. I can't see how an object can start at rest, roll along a near horizontal path and accelerate up to almost 16km/s at the half way point (which is what would be required for a short journey through the Earth). That's just an absurd speed. --Tango (talk) 22:30, 11 September 2009 (UTC)

Looking at the equations in harmonic oscillator the k in F=-kx is "Gm_earthm_object / r³" - which when placed into the equation for period of oscillation gives the same equation as that given above for the time it takes a thing to orbit the earth. I don't know what is going wrong with the numbers.?83.100.250.79 (talk) 23:03, 11 September 2009 (UTC)

For any straight path between two points on the Earth, the amount of time it takes for the object to get from one end to the other is the same as the time it takes for the orbital object to get halfway around the Earth. If the path is very shallow, it's also much shorter than the distance traveled by the orbital object, so the straight line object doesn't need to approach the orbital speed. (The max speed is (L/2)*sqrt(g/R) where L is the length of the path. The equation of motion is x(t) = (L/2)cos(sqrt(g/R)t), where x is the distance from the center of the tunnel.) If the path is through the center of the Earth, then the max speed of the straight line object is exactly the same as the orbital speed, which shouldn't come as a surprise. The straight line object under goes a large acceleration, but he change in velocity of the orbital object over the same period of time is even larger, by a factor of sqrt(2) since it's had to make a 90 degree turn. Rckrone (talk) 02:12, 12 September 2009 (UTC)

The orbiting ball always going halfway around the Earth? That is the bit I was missing. I interpreted the OP's description as the orbiting ball going between the same points the straight path went between, which didn't seem at all plausible. Your version is entirely believable (I'll work through the maths another time). --Tango (talk) 16:47, 12 September 2009 (UTC)

If you were to drill from the USA straight through the earth, you would find yourself boring a hole into the bottom of a 13,000 foot deep tub of water called the Indian Ocean. Once you broke through, I wonder how fast that water would push you back through to the USA, and how much of the USA would then be inundated. Baseball Bugs ^{What's up, Doc?} carrots 02:51, 12 September 2009 (UTC)

Assuming you could keep the magma from collapsing in on the tunnel and you could keep the tunnel cool enough that there could be liquid water in it, then some water would shoot out of the tunnel initially, but it would settle at sea level, so unless you started at Death Valley it wouldn't flood anything for long. Rckrone (talk) 03:17, 12 September 2009 (UTC)

I think this result is less surprising if you kinda sneak up on the orbiting thing. Imagine a gun is fired horizontally - if you dropped a bullet onto the ground at the precise moment that someone fired the gun - both bullets would hit the ground at the exact same instant. Some people find that surprising. Now mentally transition to the classic thought experiment where you fire the gun at progressively higher muzzle velocities so the bullet goes further before it hits the ground each time. At long enough ranges (and at correspondingly high enough muzzle velocity), the curvature of the bullet's path starts to more and more follow the curvature of the earth. until it completely misses the surface and orbits. But at no point did the bullet you dropped behave any differently. If you dig a hole for the dropped bullet to fall into - it'll continue to accelerate at the same rate as the shot bullet. SteveBaker (talk) 04:05, 12 September 2009 (UTC)

Laxative

Does laxative show up in a blood tests? —Preceding unsigned comment added by Clmac99 (talk • contribs) 06:52, 11 September 2009 (UTC)

Laxatives are not one but a wide range of substances. AFAIK there is none that shows up in a blood test. Cuddlyable3 (talk) 12:28, 11 September 2009 (UTC)

It depends what tests you run on the blood, but I think most drugs show up on a toxicological screen. --Tango (talk) 20:20, 11 September 2009 (UTC)

UTIs in history

Today, a UTI can be easily treated with proper prescription medication (assuming it's not severe). Though, I've always been curious as to how such infections were treated before modern medicine came into play. Or, better yet, how do people treat such infections where proper medical supplies are not available? 76.121.122.191 (talk) 07:04, 11 September 2009 (UTC)

People used herbs by and large for medication: things such as rose hips, saw palmetto berries, cranberries, goldenseal, cleavers, marshmallow. And they drank lots. --TammyMoet (talk) 08:42, 11 September 2009 (UTC)

Many bacterial infections that are now treated with antibiotics would most likely be cleared by the body's immune system. This is how it worked for millenia. Some people (perhaps those with compromised immune systems or specific susceptibility to certain infections) would develop more serious infections, such as a urinary tract infection turning into pyelonephritis or otitis media extending into mastoiditis or meningitis. Bacterial illnesses sometimes enter the blood at which point there can be sepsis. But most minor bacterial illnesses can be dealt with effectively by the body. Antibiotics help to clear an infection more quickly, prevent complications, and keep the infection from progressing in those who might otherwise develop a serious illness. I have no doubt that some of the compounds in "natural products" are useful or bacteriostatic (some people swear by cranberry juice for prevention of UTIs) which is probably why folk remedies have been passed down for ages. --- Medical geneticist (talk) 13:16, 11 September 2009 (UTC)

Note that rose hips and cranberry juice are high in Vitamin C, which helps the immune system fight infections. 146.74.230.81 (talk) 22:04, 11 September 2009 (UTC)

Many vitamin therapies have been disproven. I'm not sure it's true that vitamin C would help a great deal in UTIs. I do know that antibiotics are a major reason for the substantial global increase in life expectancies. 98.14.222.248 (talk) 22:39, 11 September 2009 (UTC)

I thought the idea of cranberry juice was to raise the acidity in the bladder and kill the bugs, not a vitamin thing. 70.90.174.101 (talk) 08:05, 12 September 2009 (UTC)

chemical engeneering

Q WHAT DO THE FOLLOWING TERMS MEAN

COSTS OF INVERSION COST OF PRODUCTS RETURN OF INVESTMENT —Preceding unsigned comment added by 196.2.73.6 (talk) 08:56, 11 September 2009 (UTC)

Please don't type in ALL CAPS, it's the equivalent of shouting and is considered rude. Could you please give some context to your question? Rate of return and cost may help to answer your question. — QuantumEleven 09:18, 11 September 2009 (UTC)

We also have a policy of not doing your homework for you. Vimescarrot (talk) 10:56, 11 September 2009 (UTC)

Hammett equation and (normalised?) constants

Okay, I'm having issues with interpreting the constants. Is rho for a particular type of reaction (e.g. base-induced hydrolysis) constant across a range of substituents, or does it change depending what type of substituents you put on it? Conversely, does sigma change depending on the reaction involved? Is it simple as matching constants for the substituents with a constant for the reaction?

The other thing I'm working out is that whole affair when both constants are negative ... I mean yeah, cool, mathematically the equilibrium constant increases, but why does it work out that way in real life?

(Lastly, and my least important question, what happens when you have several substituents?)

Thanks as always. John Riemann Soong (talk) 11:35, 11 September 2009 (UTC)

Oh, can I confirm that the rho constant for most basic hydrolyses of substituted benzoic acid esters will be positive? John Riemann Soong (talk)

electron withdrawing in two directions (induction only)

Can two electron withdrawers connected (directly or indirectly) to say, a carbon atom, end up having opposing effects on the partial charge on that oxygen? This is purely for the inductive effect, so take meta-fluorobenzene as an example or something (but I meant EWGs in general). So let's say I have some electronegative substituent, X. So let's have a symmetric molecule X-R2-R1-CH2-R1-R2-X. Would the central carbon be in fact less positive than it would be if it were H3C-R1-R2-X?

The other thing is why does the inductive effect usually exceed the mesomeric effect (except for say, alkoxy substituents) when the inductive effect would be presumably weak across so many bonds, and resonance stabilisation/destabilisation would presumably have more influence? John Riemann Soong (talk) 12:08, 11 September 2009 (UTC)

Are you, by any chance, taking a course on organic chemistry? Nimur (talk) 14:04, 11 September 2009 (UTC)

If I pull on your left hand, you become strained a bit. If Numur pulls your right hand, you're proposing that you become less strained overall. Either we're both pulling in the same direction, in which case you're strained even more strongly that way, or we're pulling in opposite directions, in which case you're being pulled twice as strongly apart. The inductive effect is a vector, so you need to do vector math. Or even do simple partial-charge addition: two partial-positives make even more positive (it's not literally added numerically, but qualitatively they do reinforce each other). Every intro-orgo text I've read has a whole section about dipoles. DMacks (talk) 16:26, 11 September 2009 (UTC)

Well yes, but carbon tetrachloride has no dipole moment. Directly attached to the carbon, I can see a stronger effect yes, but perhaps a better example is something with sp2 geometry. Let's say, attach an EWG group on one of the sp3 arms of the carbonyl... doesn't that strengthen the C=O bond and make the resonance structure where the has 3 lone pairs contribute less greatly? Suppose you have an aryl ring with some EWG on it. To remove the mesomeric effect contribution (and just look at induction effects), let's put this EWG say on meta position. But wouldn't this make the ring more electron dense, thus increasing the contribution of the resonance structure where the carbonyl carbon forms a double bond with the connecting aryl carbon? John Riemann Soong (talk) 17:25, 11 September 2009 (UTC)

CCl₄ has no net (molecular) dipole moment because the vectors cancel each other out for the molecule as a whole. But looking closer, they reinforce each other to make the carbon more δ⁺. CCl₄ has a central positive surrounded (symmetrically) by negative, not "no partial charges anywhere". Putting an inductively withdrawing group on an sp² side of a carbonyl makes the carbon more δ⁺ by adding its own vector to the existing one of the C=O. Our acyl chloride article discusses that as the reason why these types of molecules are particularly electrophilic at the central C compared to other carbonyls. DMacks (talk) 18:59, 11 September 2009 (UTC)

Yes, but in reactions it matters what the nucleophile "sees". Aren't nucleophiles attracted towards dipole moments? I mean, I'm sure the chlorine atom of perchlorate is extremely electrophilic but its reactivity is stymied by the fact that reactants have little access to that positive charge. John Riemann Soong (talk) 05:26, 12 September 2009 (UTC)

"Yes but"? This is the first you've mentioned any context of reactivity in a certain reaction type rather than just structure analysis. Please ask questions specifically or be careful not to sound critical when we don't read your mind. DMacks (talk) 17:03, 12 September 2009 (UTC)

Let's take this back to the carbonyl question. If the two =O are attached to the same carbon, then yes they DO cancel, which explains the structure of Carbon dioxide which has no net dipole moment. However, in nearly all other situations, the =O's will not be 180 deg away from each other, meaning that they will always work additively. Consider a molecule like Acetylacetone (aka 2,4-pentadione). The two carbonyl groups are so electron withdrawing that the hydrogens on Carbon 3 are measurably acidic, and the corresponding ion is a useful thing. --Jayron32 06:02, 12 September 2009 (UTC)

Note that CO₂ is an excellent electrophile for Grignards and other nucleophiles even though there is no molecular dipole: the partial-positive in the middle is visible from afar and the direction of nucleophilic attack is unhindered. DMacks (talk) 17:10, 12 September 2009 (UTC)

Fly energy; really quite impressive

I've had one housefly buzzing around my apartment for two days. Yes, it's annoying, but at the same time I've been thinking about the energy required to do what it's doing. There's nothing to eat here. I have no food scraps lying around at all. Just really quite sterile. This things is in constant motion, flying around seemingly nonstop. It would seem superhuman (well, supermusca domestica); the equivalent of a human doing ten marathons. I don't really have a targeted question exactly. I'm just wondering if anyone can comment on the little bastard's incredible energy output.--162.84.164.115 (talk) 12:38, 11 September 2009 (UTC)

Maybe it's stopping momentarily to eat dead skin cells that may be in the vicinity. Bus stop (talk) 12:53, 11 September 2009 (UTC)

It takes surprisingly little food to fuel movement. A large portion of the food humans eat actually goes to thermoregulation and cognitive functions. Flies, obviously, do not have the same issues. -- 128.104.112.179 (talk) 14:38, 11 September 2009 (UTC)

Are you calling me slow? -- The Fly 98.14.222.248 (talk) 22:36, 11 September 2009 (UTC)

Also, consider how little the fly weighs and how well-optimized it is. It's fantastically lighter and more energy efficient than any sort of machine we could make at the moment. --98.217.14.211 (talk) 00:13, 12 September 2009 (UTC)

I don't think it's that amazing. You could easily walk around your apartment (stopping periodically as the fly does) for two days without food or water. You wouldn't enjoy it - and maybe the fly doesn't either - but you could definitely do it. And consider that you have to generate heat internally (which means you have to eat literally ten times as much as a cold-blooded animal) - and you have to run your big brain (20% of your food energy goes to running that gadget!). Admittedly, you aren't flying - but proportionate to body size/mass/whatever, the air is thick and gloopy stuff for a fly - for a tiny insect, it's more like swimming in thick treacle than flying - the air supports it quite well - it doesn't take much energy to stay airborne. But that's nothing! According to (for example) this, a crocodile can survive for two years without eating. SteveBaker (talk) 03:22, 12 September 2009 (UTC)

Please excuse me, but I'm skeptical of the reported observations here. I've never personally seen a fly last that long without running out of steam -- how do you know it was the same fly? Looie496 (talk) 01:31, 12 September 2009 (UTC)

There's a general answer to this question here. More specifically, starved houseflies can live for 2 1/2 days, by which time the respiration of their flight muscles will have dropped to 50% of the usual level. The average housefly has 14 micrograms of glycogen in its thorax, but only 2ug is left after 2 1/2 days of starvation.[4] Also see Insect flight. Fences&Windows 23:51, 12 September 2009 (UTC)

decreased electrophilicity of diacetyl?

Is diacetyl more electrophilic or less eletrophilic (towards hydration) than formaldehyde? The carbonyl carbons both have methyl groups on them, which can stabilise the partial charge via hyperconjugation, but I'm thinking placing two carbonyl groups next to each other would destabilise them (by synergistically making each their carbons even more positive). John Riemann Soong (talk) 13:30, 11 September 2009 (UTC)

Ninhydrin is an interesting extension of this question. DMacks (talk) 16:29, 11 September 2009 (UTC)

iodine test

iodine test performed on starch on heating the blue colour formed dissappears why? —Preceding unsigned comment added by Srikishore (talk • contribs) 14:26, 11 September 2009 (UTC)

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems. Please attempt to solve the problem yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

The article Iodine test may be a place to start. -- 128.104.112.179 (talk) 14:34, 11 September 2009 (UTC)

Allergy to chemical element

Many of people tell about allergy to iodine, chlorine or other chemical element (not substance). Is it theoretically possible to have an allergy to chemical element (not substance containing this element) which is essential to human organism? Renaldas Kanarskas (talk) 15:42, 11 September 2009 (UTC)

Iodine is typically used as a radiocontrast agent in medical imaging. The adverse reaction you are probably referring to is more of a pseudoanaphylaxis reaction caused by stimulation of Mast cells by the complement system (anaphylatoxins), as opposed to an allergy caused by excessive stimulation of Mast cells by IgE. --- Medical geneticist (talk) 16:14, 11 September 2009 (UTC)

Some people exhibit type IV hypersensitivity to metals, see MELISA test. --Dr Dima (talk) 17:05, 11 September 2009 (UTC)

An allergy is when your immune system overreacts to something harmless. A sensitivity to iodine, or something, isn't likely to be caused by the immune system, so isn't an allergy. --Tango (talk) 17:51, 11 September 2009 (UTC)

Type IV hypersensitivity is mediated by a kind of lymphocytes called T cells. They are definitely a part of the immune system. --Dr Dima (talk) 20:58, 11 September 2009 (UTC)

I stand corrected, thank you. --Tango (talk) 15:46, 12 September 2009 (UTC)

I know it's not an element, but it is possible to develop an allergy to water. Fences&Windows 23:33, 12 September 2009 (UTC)

I had an imaginary friend that was allergic to oxygen. Needless to say, he no longer exists. DRosenbach ^{(Talk | Contribs)} 03:27, 14 September 2009 (UTC)

Our article on Nickel states that it's part of urease, so the body would need nickel. At the same time, nickel allergy is common. EverGreg (talk) 13:04, 16 September 2009 (UTC)

albedo

Ther is two types of albedo, visual and geometric albedo, but I have no idea about both of them, and what they mean? Article we have don't make sense to me.--209.129.85.4 (talk) 16:51, 11 September 2009 (UTC)

Unless we re-write the articles entirely, a more specific question might be useful. What about the topic is not clear? // BL \\ (talk) 17:05, 11 September 2009 (UTC)

According to Geometric albedo - it is the ratio of reflected to incoming light ASSUMING the object is a flat surface at right angles to the incoming light rays. The "visual geometric albedo" is the exact same thing but with the narrower definition of the word "light" to mean only light within the visual spectrum. So, if an object looked very white to the naked eye, it would have a high visual geometric albedo - but if it failed to reflect infra-red and ultraviolet light very well then it's overall "Geometric" albedo would be much lower. Worse still, there is the "Bond albedo" which refers not to a perfectly flat surface - but instead to the net reflection from a spherical object such as a planet or moon. SteveBaker (talk) 02:50, 12 September 2009 (UTC)

electropotential of esters

Can someone get me an electropotential map of an ester versus an electropotential map of a ketone? I don't have a Hartree-Fock calculator right now and google images is being unhelpful. John Riemann Soong (talk) 17:37, 11 September 2009 (UTC)

Did you mean "electron density ...." - google images gives a few results for this term, but nothing amazing, both cross sections and '95% cutoff' images found.83.100.250.79 (talk) 22:28, 11 September 2009 (UTC)

Here you go, electrostatic potential surfaces for formaldehyde and methyl formate:

• http://www.benjamin-mills.com/Wikipedia/formaldehyde-vs-methyl-formate-elpot.png

• http://www.benjamin-mills.com/Wikipedia/formaldehyde-vs-methyl-formate-elpot-seethrough.png

I could do a proper ketone like acetone (instead of formaldehyde, which is an aldehyde but is symmetrical) if needed.

Ben (talk) 22:53, 13 September 2009 (UTC)

Heavy Metals in the Earth's Crust

Why is it uranium or even gold can be found near the surface? It seems like when the Earth first formed from a molten state each element would settle into individual layers ordered by density. Why isn't this the case? TheFutureAwaits (talk) 18:03, 11 September 2009 (UTC)

To an extent, that does happen, but it isn't perfect. There would be all sorts of convection currents and things that keep moving the heavy elements back towards the surface. --Tango (talk) 18:06, 11 September 2009 (UTC)

Also note that most of them form compounds with other lighter elements such as Pitchblende a uranium oxide. Others, such as gold, are soluble in high temperature aqueous solutions and tend to be transported towards the surface and deposited from these hydrothermal systems as the temperature falls. Mikenorton (talk) 18:55, 11 September 2009 (UTC)

Also the billions of years of volcanoes, earthquakes, plate tectonics, comets, wind, hurricanes, floods, glaciers, fire, landslides, tsunamis, erosion...--Patton123 (talk) 17:29, 17 September 2009 (UTC)

The Perfect Mirror

Why is a perfect mirror (which reflects 100% of the light going into it) impossible? Regards. AtheWeatherman 18:53, 11 September 2009 (UTC)

Light pressure means the mirror must be pushed backwards by the light. That is going to accelerate the mirror, and the energy for that has to come from the light, so the reflected light must have less energy. --Tango (talk) 19:27, 11 September 2009 (UTC)

What if you fix the mirror and the light source in a box so neither can move? This way the light pressure isn't converted to energy. 95.112.165.86 (talk) 08:49, 12 September 2009 (UTC)

The pressure has to do something - the energy will be used deforming whatever you have used to fix them in place. --Tango (talk) 19:17, 12 September 2009 (UTC)

You could reach an equilibrium where the mirror (or its mounting) was distorted but was not gaining any energy from the (constant) illumination. Remember that it takes energy to put it into a distorted state, but no further power to hold it there. (You might also owe Steve a dollar, but I'm not sure.) --Tardis (talk) 21:01, 12 September 2009 (UTC)

True. I was thinking of a light pulse rather than a continuous beam, but you are right that a continuous beam could overcome the light pressure issue. Maybe it isn't theoretically impossible, then? (It is practically impossible for the reasons given below, of course.) --Tango (talk) 22:57, 12 September 2009 (UTC)

It would also have to be perfectly smooth to prevent any diffusion. Livewireo (talk) 19:31, 11 September 2009 (UTC)

It could also not have any foreign objects land on the mirror (such as dust) which would absorb light. Googlemeister (talk) 19:39, 11 September 2009 (UTC)

You can get very close to 100% reflection at some angles, and/or at some wavelengths, but never to a perfect 100%. --Dr Dima (talk) 20:43, 11 September 2009 (UTC)

Total internal reflection is how fiber optics work and comes awfully close. 70.90.174.101 (talk) 08:06, 12 September 2009 (UTC)

Green Pretzels

My girlfriend and I made soft pretzels a couple of days ago using this recipe. We decided to put cinnamon-sugar on some of them. However, when these pretzels came out of the oven the cinnamon had turned a deep grayish green, a quite unappealing color! We ate them anyway, and they tasted like cinnamon-sugar pretzels. We suffered no ill effects. What could have caused this though? We've made the same recipe before without incident. Could our cinnamon be bad? Or could it have something to do with the baking soda the pretzels are dipped in before baking? --S.dedalus (talk) 20:51, 11 September 2009 (UTC)

Lots of colored foods are actually decent acid-base indicators, for example red cabbage and tumeric are two classic examples I can think of, but there are likely others. I am not sure on cinnamon one way or the other, but I would not be surprised if it turned out that the basic sodium bicarbonate (baking soda) caused the color to change. Such changes are not harmful in any way, if the pH was the source of the color change, then any change is reversable when the pH is lowered again, as it would be in your stomach. --Jayron32 00:05, 12 September 2009 (UTC)

May have found the culperit. Almost ALL of the cinnamon you are going to get in the western world is Cinnamomum aromaticum or Cassia Cinnamon. Cassia Cinnamon contains relatively high amounts of a compound called Coumarin, which turns a light green fluorescent color at around pH 10.5 apparently. It is likely that the baking soda wash you used for the browning caused the coumarin in the cinnamon to take on a green palour. As noted above, however, such changes are harmless, as the coumarin will revert back to its previous form with no ill effects, in the low pH of your stomach. --Jayron32 04:22, 12 September 2009 (UTC)

Use some pandan extract, to get a nice pastel green instead of an unappealing one. Have you seen the colour of pandan chiffon? mmm... John Riemann Soong (talk) 07:08, 12 September 2009 (UTC)

This is fascinating! :) One of the most interesting answers I've ever gotten on the reference desk. Thank you. . . A quick followup question if I may: do you have any idea how pretzel stands avoid this change in color? Presumably green food wouldn't be good for business. Many pretzel chains sell normal colored cinnamon sugar pretzels somehow though. Would using a slightly less basic wash be enough? --S.dedalus (talk) 17:14, 12 September 2009 (UTC)

But what's wrong with green food? A lot of cultures have green pastries. Now that you mention it though, I have seen slightly green pretzels before. John Riemann Soong (talk) 17:57, 12 September 2009 (UTC)

The answer, of course, is that they add the cinnamon AFTER they come out of the oven. Acording to your description, you added the cinnamon immediately AFTER the baking soda wash, bringing the cinnamon into contact with wet, basic, sodium bicarbonate solution, which is why it turned green. After baking, the bicarb has chemically reacted with the dough, doing its job in browning, so it likely isn't going to be availible to react with the coumarin in the cinnamon. --Jayron32 22:03, 13 September 2009 (UTC)

vortex and the third law

Hello

This new non lethal weapon the vortex ring gun, is planned to be mounted on a hand held system the Gl-6. It produces an explosion that is then channeled into a vortex, which is fired at the target and knocks it down. my question is how can it do this without violating the law of action and reaction. Surely a force strong enough to knock down the target would have just as strong a reaction and knock down the person fireing it?

Thank you —Preceding unsigned comment added by 79.67.205.215 (talk) 21:01, 11 September 2009 (UTC)

Do you have a link to this thing? --S.dedalus (talk) 21:13, 11 September 2009 (UTC)

(after ec): I guess firing this thing does not knock you down for the same reason as punching a punchbag does not knock you down. In both cases there is a reaction force pushing you back, and in both cases you are ready for it and adjust your posture accordingly in advance. --Dr Dima (talk) 21:16, 11 September 2009 (UTC)

I agree, it probably works because you brace for it. Alternatively, it could be that you feel a weak force for a prolonged period and the target feels a strong force for a short period (with the air acting as a buffer). --Tango (talk) 21:38, 11 September 2009 (UTC)

http://en.wikipedia.org/wiki/Vortex_ring_gun

Here the link which has more links underneath.

Thanks —Preceding unsigned comment added by 79.67.205.215 (talk) 21:18, 11 September 2009 (UTC)

I'd generally agree with the other answers above. The "recoil effect" is the reaction force of the explosion on the fixture. You would definitely be trained to anticipate the initial reaction force. The widening barrel is a good clue that the reaction force will be lessened as the charge expands. Also, it seems that the reaction energy is channeled into a vortex, which proceeds to the target. Production of a vortex is a very efficient way of transferring energy to a different medium, and the reactive force is exerted in a largely radial direction (or maybe tangential in the case of tuna fish and seagulls?). Sorry I can't source this, but it seems to me that if you are holding something that derives its driving force by acting outwards in its chamber, it will have much less backwards force than, say, a bullet, which pushes mostly backwards to make itself go forward. This device seems to push itself circularly, which is a whole different thing, but delivers the same amount of energy at the other end. I realize that's pretty garbly. :) Franamax (talk) 04:28, 13 September 2009 (UTC)

Human hermaphrodites

What are their sex genetic makeup X- and Y- wise? The articles are pretty vague on this point. 98.14.222.248 (talk) 23:20, 11 September 2009 (UTC)

Intersexuality#Typical sex development is extremely specific and has pretty much everything I think you want. ~ Amory (user • talk • contribs) 23:29, 11 September 2009 (UTC)

It varies. There are different types of intersex people. They can have unusual genetics, such as XXY, or perfectly normal genetics but have something unusual happen during gestation, such as odd hormones. This can result in someone with XY genes, say, ending up with female sexual characteristics. I suggest you read the intersex article, it has a list of various types of intersexuality. If you are interested in Caster Semenya, we don't know the details of her case yet. --Tango (talk) 23:33, 11 September 2009 (UTC)

As stated above, it really depends on the case. There is no single cause for intersex conditions (by the way, the term "hermaphroditism" is not really used in the mainstream to describe most of these disorders any more). There are 46,XX individuals who have a chromosomal translocation of the SRY gene onto one of the X's and develop as males. Likewise, there are 46,XY individuals with a mutation of SRY who develop as females. One of the more common intersex disorders is androgen insensitivity syndrome, where the body does not respond to androgens during development, leading to a 46,XY female. Another common disorder is congenital adrenal hyperplasia where the adrenal glands produce excessive sex hormones during development leading to virilization of a 46,XX female. I'd echo what Tango said - that details of Caster's case are unknown and we couldn't really speculate about the cause in her case. IMHO the disclosure of this information to the press was a deplorable breach of Caster's privacy. --- Medical geneticist (talk) 01:36, 12 September 2009 (UTC)

It appears that the case in question has to do with XY/androgen insensitivity. It was a horrific way to find out. 74.64.121.56 (talk) 17:17, 14 September 2009 (UTC)

Fossil Fuels and CO2

How does the burning of fossil fuels create carbon dioxide? Someone was trying to tell me that burning fossil fuels doesnt create carbon dioxide, it creates carbon monoxide. I knew that wasnt true but i couldnt explain how burning fossil fuels creates CO2 —Preceding unsigned comment added by 71.98.64.15 (talk) 23:52, 11 September 2009 (UTC)

If it created just carbon monoxide then everybody with a gas cooker would be dead by now. The initial burning of fossil fuels (for instance gas, petrol, diesel, etc. - they are just hydrocarbons - compounds of just carbon and hydrogen) creates carbon monoxide (which is more stable when very hot), but at the outer parts of the flame (where it is relatively cooler) the carbon monoxide burns to give carbon dioxide. The other component of burning such fuels is water - which is why car exhaust pipes sometimes drip when just started. Car engines run very hot - hence make carbon monoxide, which (these-days) has to be removed by the catalytic converter.  Ronhjones  ^(Talk) 23:59, 11 September 2009 (UTC)

Most fossil fuels consist mostly of carbon and hydrogen. When you burn them, you add oxygen. The hydrogen reacts with the oxygen - gives off heat and produces water (H2O) - and the carbon reacts with the oxygen to produce more heat and to produce a MIXTURE of CO and CO2 (carbon monoxide and carbon dioxide, respectively). Carbon monoxide is a nasty poison and a greenhouse gas - but it can react with more oxygen to make CO2 - Carbon dioxide is pretty inert - but also a greenhouse gas. The precise mixture of CO and CO2 that you get depends on a lot of factors - which fuel you started with - how much oxygen was available - what temperature the reaction happened at...lots of complicated stuff. In a car, for example, burning gasoline produces mostly CO2 with a fairly small amount of CO. The catalytic converter in your exhaust system adds the extra oxygen so that the CO emissions are cut fairly drastically. If you burn propane, however - you get almost no CO at all. That's why you'll see many fork-lift trucks that have to be run inside warehouses using propane as a fuel - it means that the machine doesn't emit poisonous CO in the confined space of a building. So the person who told you this was talking complete nonsense. SteveBaker (talk) 00:38, 12 September 2009 (UTC)

haha im very aware that is was complete nonsense, hes notorious for that. —Preceding unsigned comment added by 71.98.64.15 (talk) 01:04, 12 September 2009 (UTC)

Why doesn't propane produce CO? Is this because of the radical mechanism of combustion? Is this characteristic of alkanes? What about methane and butane? I do think that when you start to burn alkenes with double bonds, because of their existing unsaturation, they tend to form sooty particles...(hence why oils smoke). I also don't get why CO is stable at higher temperatures.... CO has a higher Gibbs free energy, so is it due to entropy or something? John Riemann Soong (talk) 21:42, 12 September 2009 (UTC)

Can't help with the thermodynamics, but I'm pretty sure that if you burn (oxidize carbon) anything in O2-insufficient conditions, you will get CO in preference to CO2. In conditions of excess oxygen, you will get CO2 as a primary end-product, and CO as a by-product. Hydrocarbons are quite commonly split in O2-deficient environments to get the very useful syngas - a mixture of H2 and CO. Franamax (talk) 03:51, 13 September 2009 (UTC)

Or to continue with my qualtitative argument, lighter hydrocarbons require less oxygen to achieve complete combustion. The lowest-energy products are water and CO2 (CO can be further oxidized to CO2). Any one oxygen atom "uses up" two hydrogen atoms, whereas a carbon atom "needs" two oxygens. Methane has a H:C ratio of 4:1, propane is 8:3, octane is 18:8. It seems to me that combusting methane will need the fewest number of of oxygen molecules per methane molecule, so it will have a lower probability of producing CO due to incomplete combustion. And yet every single gas burner in an enclosed space (i.e. a dwelling) is recommended to have a CO alarm close by. I'll have to leave you to work out the energetics which result in preferential CO in O2-deficient conditions. (And of course, in excess-air conditions, there's the problem of NOx, but that's different) Franamax (talk) 04:13, 13 September 2009 (UTC)

I wrote this before the last two posts so forgive any discontinuity.

Its not a concern over saturation in all likelihood a flame sees every sort of saturation and doesn't much care if it starts with a saturated or unsaturated molecule (although some aromatics are especially hard to get to burn well). I can't account for CO being "more stable when very hot", although I would readily assume the inside of a flame is oxygen staved. What I think matters more in the propane vs. gasoline debate is the molecular mass of the hydrocarbon. As you pointed out its harder to get oils to burn clean and I assume that because oils are heavy hydrocarbons. (By burning clean I mean taking O2 and a hydrocarbon to CO2 and H2O. I consider soot, mostly carbon, and CO to be product of an unclean burn.)

Part of getting a gasoline internal combustion engine to run right is vaporizing the fuel before igniting the air-fuel mixture. This isn't a concern with propane since it is a gas at much lower temperatures and higher pressures than gasoline. So its easier to a get a propane engine to burn more efficiently.

To make this clearer lets think about camp stoves two of the most common types are white gas and some sort of butane/propane mixture. The white gas generally runs the fuel line through the flame to vaporize the fuel before igniting the fuel to get a vaporized fuel that burns hotter and more completely. In contrast a butane/propane camp stove will run the fuel straight from the canister to the flame. Now its commonly known/believed that the propane/butane stoves are better for high altitude since they burn cleaner even in low oxygen environments. This is a rule of thumb and doesn't account for badly designed propane/butane stoves and well designed liquid fuel stoves. The important point is that it is really important to burn your fuel completely when cooking in tent above 20K' since CO is even more dangerous in confined spaces with low levels of O2. Even when using a Propane/Butane stove a lot of these mountaineer folks still end up getting quite a bit of CO into their system especially if they do most of the cooking. Hope that helps.--OMCV (talk) 04:18, 13 September 2009 (UTC)