Wikipedia:Reference desk/Archives/Science/2010 October 10

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October 10[edit]

Practical way[edit]

Most manuals tell to use mix of nitric acid and sulfuric acid to glycerin to make nitroglycerin. But why is sulfuric acid to be there ? Isn't nitric acid enough to go through ? —Preceding unsigned comment added by (talk) 00:14, 10 October 2010 (UTC)

It is not. You have to take nitric acid, which normally likes to lose H+ (as all strong acids do) and add enough additional acid to force it back on, and then force another H+ to react with it. That is, exactly as Nitroglycerin#Manufacturing says: "The sulfuric acid produces protonated nitric acid species". DMacks (talk) 01:45, 10 October 2010 (UTC)
Can a superacid be used to protonate the nitrate ion? --Chemicalinterest (talk) 18:50, 10 October 2010 (UTC)
Yes, superacids and non-protic lewis acids can activate nitric acid in this way. Have to be careful of possible side-reactions such as redox and competing sulfonation. Sulfuric acid is nice because it's a good sponge for the water byproduct (I don't know if super-acids tend to decompose back to "normal" sulfuric-acid-like acids in water). But the general idea works fine, and the resulting nitration mixture is very reactive (like even at dry-ice temperatures). DMacks (talk) 19:19, 10 October 2010 (UTC)
Protonation of water is one decomposition route for superacids. The protonation is extremely exothermic, so not you only really want an acid that's just strong enough to protonate nitric acid for a reaction which is producing three moles of water for each mole of product and which has to be conducted in a strict temperature range. You can consider conc. sulfuric acid to be the weakest of the superacids: it works fine for this reaction and it's cheap, so there is no need to look any further up the acidity scale. Physchim62 (talk) 20:45, 10 October 2010 (UTC)

Map of direction of stellar and galactic motion[edit]

Where can I view a color coded map of stellar and galactic motion with color intensity adjusted for speed away from and speed toward the Earth or at least my position at any given moment in time and space upon the Earth? -- (talk) 00:16, 10 October 2010 (UTC)

There is the CFA redshift survey. [1]--Aspro (talk) 09:46, 10 October 2010 (UTC)

What is this on the roof?[edit]


What is this on the roof? It's a "stock image" from House, I've seen it many times, always the exact same pan/zoom shot. It looks like a pile of boxes near some metal panels. Ariel. (talk) 07:44, 10 October 2010 (UTC)

The panels look like replacement roofing panels (maybe solar???) for the other building up and to the right. The boxes look like... boxes. → ROUX  07:46, 10 October 2010 (UTC)
It reminds me a bit of the Stata Center. I bet those components are there for aesthetic reasons, but that they only make sense if you can see the rest of the building. Paul (Stansifer) 12:47, 10 October 2010 (UTC)
As it should, given that they were designed by the same architect. Buddy431 (talk) 15:51, 10 October 2010 (UTC)
The building used to depict the hospital is the Frist Campus Center, at Princeton University. You can see an aerial photo on Google Earth: [2]. There's also a campus map here. The building with the box things on top is apparently the Lewis Science Library [3] at Princeton, built by architect Frank Gehry [4]. Buddy431 (talk) 15:00, 10 October 2010 (UTC)
That's excellent sleuthing Buddy431! Thank you very much. Ariel. (talk) 23:50, 11 October 2010 (UTC)
That's not on the roof, that is the roof. That's just the design of the roof, with metal slanted sheets.-- (talk) 15:14, 10 October 2010 (UTC)

Insect identification[edit]

Could anyone tell me what type of insect is seen in this photo. It was taken in New Hampshire in July. Thanks--Captain-tucker (talk) 10:50, 10 October 2010 (UTC)

Well it looks very much like a Humming-bird Hawk-moth, but they don't occur in North America, so I go for a species of Hemaris, possibly Hemaris thysbe the Hummingbird clearwing. Mikenorton (talk) 11:06, 10 October 2010 (UTC)
Hmmm, how about Hemaris diffinis? [5] Wnt (talk) 21:42, 11 October 2010 (UTC)

Carbon footprint[edit]

Would it be possible to use household refuse without metal and glass in a coke oven . then use the producer gas to generate electricity then bury the carbon afterward? Tynyman (talk) 10:55, 10 October 2010 (UTC)

When you burn producer gas (or any carbon-containing material), the carbon winds up as carbon dioxide. Pretty hard to bury a gas. The solid residues of burning garbage (the ashes) are the non-burnable inert materials, not the "burned carbon". DMacks (talk) 14:38, 10 October 2010 (UTC)
There might be some carbon in the ashes, though in comparatively small amounts. The majority of the carbon, which burned (oxidized) and formed CO2, is in gaseous form and has escaped. This is the problem for carbon sequestration. It is difficult to "put the CO2 back" - if it remains in gas form, it is difficult to store effectively; and any chemical process to turn CO2 back into carbon would require energy. Because we get most of our energy (on industrial scales, at least) by burning carbon into CO2, it is implausible to reverse the process with present technologies. You might find this "Tactical Garbage to Energy Refinery" interesting - it is a garbage incinerator that has been deployed by the U.S. Army. It is fed a mixture of dry garbage and sugar-rich "wet waste," plus a dose of diesel fuel, and the mixture is set on fire to power an electric generator. One of its byproducts is a sort of syngas/bio-ethanol mixture which is fed back into the incinerator and burned for electric production. It is my opinion that this horrible contraption is only suitable for use in combat zones, where there is little concern for the noxious fumes it exhales - they are the least-worrisome features of its operation (in combat). Another news-story here: Army generators turn garbage into energy, energy into freedom. Nimur (talk) 16:18, 10 October 2010 (UTC)
In the UK we have several large household waste incinerators, the largest is the Edmonton Incinerator in North London. It burns 796,000 tonnes of solid waste annually (after any recyclable material has been removed) and generates 55 megawatts of power, 90% of which goes into the National Grid. The official website[6] describes this as "green energy", probably on the basis that they don't have to dig up new fossil fuels to generate it and the carbon in the organic materials would find it's way back into the atmosphere as it decayed anyway. Greenpeace don't think much of it though[7]. The big bonus for us is that we're only a little island and fast running out of places to bury our waste. Some residual ash is a lot easier to bury than a big heap of rubbish. Alansplodge (talk) 21:38, 11 October 2010 (UTC)
Me again; have a look at our Waste-to-energy article. Alansplodge (talk) 21:43, 11 October 2010 (UTC)

Lead toxicity[edit]

The lead powder burning, for the scientifically curious

Would burning 50 milligrams of lead in a flame on a kitchen stove have any harmful effects? --Chemicalinterest (talk) 11:17, 10 October 2010 (UTC) says lead will burn with a blue flame when heated and turn into a stinking toxic gas. The Oxidation numbers of lead are 4, 2, -4 (amphoteric oxide); see the articles Lead(II) oxide and Lead dioxide. Lead burning occurs daily in automobiles running on (deprecated) leaded gasoline and in burning off old lead-based paint, both regarded today as health hazards. As long ago as 1786 Benjamin Franklin wrote about "the bad Effects of Lead taken inwardly"[8]. I think you should use a fume cupboard not a kitchen for your experiment. Cuddlyable3 (talk) 12:24, 10 October 2010 (UTC)
The amount is not enough to poison a person at once although inhalation is one of the most efficient ways to get lead into the body. Lead is accumulating and at some point there will be a effect on your health if this experiment is not the only source of lead. Better do it in a fume hood or outside.--Stone (talk) 12:31, 10 October 2010 (UTC)
In case you are worrying (which you probably aren't), the lead fumes went up a range hood and outside. Too bad. --Chemicalinterest (talk) 18:51, 10 October 2010 (UTC)
How do you know that all the lead was "burned," i.e. oxidized, rather than merely melted? Generations of boys had toys with which they melted and cast lead into "toy soldiers." Others melted many times this much lead in soldering Heathkit electronic kits, also with no apparent ill effects. Cable splicers for electric utilities in New York, Philadelphia and Chicago melted many hundreds of pounds of tin-lead alloy solder in a career without apparent ill effects, given some ventilation. Edison (talk) 04:31, 11 October 2010 (UTC)
It was a fine powder, so it would have a hard time melting before burning. Any chunk of lead would melt in no time, never burn. --Chemicalinterest (talk) 11:05, 11 October 2010 (UTC)
Very nice gray-green lead flame! I liked the lithium-, boron- and copper-flame more. --Stone (talk) 05:40, 11 October 2010 (UTC)
To Edison: See the color change in the flame? That is evidence of actual oxidative burning, and not merely melting. --Jayron32 05:43, 11 October 2010 (UTC)
It was burnt. There was no lead left and nothing left on the wire. I took it out of the fire and I saw it still burning for a while, then extinguish. --Chemicalinterest (talk) 11:05, 11 October 2010 (UTC)
Some thoughts on your experiment: Lead melts at 327 deg C. The stove burner flames can't be higher than the 1100-1200 deg C quoted for a Bunsen burner flame. That is less than the boiling point of lead 1749 deg C so I conclude that it is the liquid phase of lead that is burning. Is that an endothermic or exothermic reaction, and if the latter can lead burn by itself? I would be interested to see the "soot" (cooled particles) from the flame; would it have the pink or black colour expected of an oxide of lead? We do care about your health. Cuddlyable3 (talk) 07:57, 11 October 2010 (UTC)
That would be nice, but I would not want to burn enough lead to collect the soot. It would be very dangerous to the stove, all that lead falling all over. Don't powdered metals burn easily? Even powdered copper is a flame hazard, although copper is one of the less reactive metals. --Chemicalinterest (talk) 11:05, 11 October 2010 (UTC)
They do with a bang if they are aluminium, see Thermite. The NFPA 704 ratings for lead granules are:
  • Flammability 1: Must be heated before ignition can occur. Flash point over 93°C.
  • Health 3: Short exposure could cause serious temporary or moderate residual injury.
  • Instability/Reactivity 0: Normally stable, even under fire exposure conditions, and is not reactive with water.
FWIW Lead dioxide and Lead tetroxide do not burn. Cuddlyable3 (talk) 11:42, 11 October 2010 (UTC)
Yes, it does burn. A small chunk of zinc metal can burn in a flame too. I haven't tried aluminium yet. What color does aluminium burn? --Chemicalinterest (talk) 16:55, 11 October 2010 (UTC)
How are you going to activate the aluminum? Aluminum has a thin (several atoms thick) layer of aluminum oxide. John Riemann Soong (talk) 16:56, 11 October 2010 (UTC)
Usual method is to wash with strong acid (several-molar sulfuric?) then rinse with degasses water and use while still wet (or else coat with mercury, but you probably don't want to be burning that). It's hard to light aluminium as a thermite mixture unless you use a pre-existing metal flame (a strip of magnesium, ignited with a bunsen burner, is common). Once you have that much energy, I'm not sure a thin oxide coating will matter--thermite has a huuuuuge surface area and does not require special surface cleaning. For igniting a piece or powder of aluminium in air, I'm not sure how much activation it takes to get a self-sustaining burn, or if the oxide matters. DMacks (talk) 17:06, 11 October 2010 (UTC)
I wanted to bypass the oxide coating by fiercely heating a small crumpled ball of aluminium foil attached to a steel wire in a flame. I have no clue whether that would work or not. --Chemicalinterest (talk) 17:28, 11 October 2010 (UTC)
Oxidizing and reducing flames might be an interesting read. DMacks (talk) 17:37, 11 October 2010 (UTC)
That is interesting, but I would not like to mess with my kitchen stove. My parents might not like it O-o --Chemicalinterest (talk) 18:11, 11 October 2010 (UTC)
Maybe you want two flames -- a reducing flame and an oxidising flame... the first flame reduces the aluminum oxide into CO2 and aluminum carbide (or some sort of aluminum-hydrocarbon mix). The second flame then oxidises the aluminum carbide and the aluminum underneath. John Riemann Soong (talk) 18:41, 11 October 2010 (UTC)
Why would that happen? I don't think the aluminium oxide can be reduced into anything as it is quite stable and very resistant to melting. --Chemicalinterest (talk) 18:43, 11 October 2010 (UTC)
Look at our article aluminum carbide. At high temperatures there are many pathways and many reactions as well, and also oxygen will still be somewhat present, but basically methane or a hydrocarbon will be oxidised, and aluminum oxide will be reduced. Heat will also drive the reaction forward, naturally. Remember, there's only about 40 nm of aluminum oxide to destroy, and imagine millions of high-energy methane molecules hitting the surface every second. The aluminum oxide layer cannot survive more than a few minutes, if not a few seconds.
Remember also the reactant is a solid and the product is a rapidly-escaping gas, and that at high enough temperatures, the kinetic barrier to transformation is low. John Riemann Soong (talk) 18:58, 11 October 2010 (UTC)
Here are some chemistry data you might be interested in. (Google doi:10.1016/ Tell me if you get full access to the paper -- otherwise I'll just send it to you. The kinetic barrier is breached at about 1800C, and the equilibrium barrier at around 2000C, but remember this is for bulk, not surface chemistry. Remember that at surfaces, compounds have surface energy which make them more reactive, and that surfaces take much less time to react than bulk materials. ;-) John Riemann Soong (talk) 19:18, 11 October 2010 (UTC)
An alternative reaction begins with alumina, but it is less favorable because of generation of carbon monoxide.
2 Al2O3 + 9 C → Al4C3 + 6 CO
Why would I want to make carbon monoxide?!?! That is not a good way to terminate my questions ;) Also, the aluminium oxide is not reduced. The carbon disproportionates into carbide and carbon monoxide. --Chemicalinterest (talk) 20:46, 11 October 2010 (UTC)
A gas stove (which I assuming) is likely to emit methane and polyaromatic hydrocarbons, which isn't quite pure graphite (it has a lot of pure C-H bonds); your products are more likely to be water, formaldehyde, alcohols, than outright carbon monoxide, which still will form, but that forms in any oxygen-poor flame! The aluminum oxide is reduced because the aluminum carbide bond is less polar. The aluminum gains a measure of its electrons back. In fact, this reaction is called the carbothermal reduction of alumina, and it is a competitor to the mainstream and energetically-expensive electrolytic Hall–Héroult process for producing aluminum. Carbon monoxide is dangerous if it builds up in a room without ventilation. You produce it all the time whenever you barbecue. ;-) John Riemann Soong (talk) 20:56, 11 October 2010 (UTC)
What makes you think I barbecue?This discussion is getting off topic. Not that it's bad, but if you have anything else to say, maybe you can open a new thread. --Chemicalinterest (talk) 22:18, 11 October 2010 (UTC)
Just a final note:The aluminium foil did not burn, but melted into a hard lump of oxidized aluminium metal. --Chemicalinterest (talk) 01:11, 12 October 2010 (UTC)
It is a really bad idea to breathe the fumes of burning heavy metal. In a real chem lab, such experiments would be done only under a vent hood. Lead poisoning is a big problem, despite my comments aboove about soldering and lead soldiers. The temperature for those activities is way lower than from the gas flame. Edison (talk) 18:56, 11 October 2010 (UTC)
Yes. That is why I only burned a small amount and probably won't do it again. --Chemicalinterest (talk) 20:41, 11 October 2010 (UTC)

Work/Power problem[edit]

Hey, so I'm trying to calculate the power needed to push a 95 kg chest at .62 m/s along a floor sloping upwards at an angle of 5 degrees, the coefficient of friction is .78 . Also I need to know how much work would be done pushing the chest 11 m.

I understand how to do this problem if it were a horizontal plane, the applied force would equal the frictional force, n=mg so the power would simply be the frictional coefficient times the mass times gravity times the velocity= 450 W. I'm confused where to start now that an angle has entered the equation...any tips? (talk) 17:45, 10 October 2010 (UTC)

So the key for both parts is finding the force needed to keep the thing moving. There are going to be two components, one from gravity and one from the friction. The friction is proportional to the normal force of the chest against the ramp, so you have to find what component of the weight is acting perpendicular to the ramp. For the gravity part you similarly have to find the component of the weight that's acting in the direction you're pushing the chest in (which is parallel to the ramp). Rckrone (talk) 18:08, 10 October 2010 (UTC)
To expand on Rckrone, a big help with this sort of question is drawing a diagram and marking on the forces. I imagine you have done this before, and have examples written down. You need to break the force due to gravity acting on the chest into two components: one parallel to the sloping plane, and one perpendicular to it. That will then tell you the normal force exerted by the plane on the chest, which allows you to work out the maximum force due to friction. You'll then know the force you're having to overcome, made up of the friction and the force due to gravity acting down the slope. (talk) 20:41, 10 October 2010 (UTC)
Power (see article) is equal to the pushing force times the object's velocity. Cuddlyable3 (talk) 09:03, 11 October 2010 (UTC)
Yes, and the OP already knows that. I don't understand your point. (talk) 20:28, 11 October 2010 (UTC)

backlighting digital cameras[edit]

My digital camera (which is a Canon EOS 350D a few years old now) doesn't like being backlit, as it tends to overexpose (much less than a film camera would). Which is a pity because backlighting can be quite dramatic. Do more recent cameras deal with this better (e.g. if I got a top end Canon EOS 1D Mk IV, or its modern equivalent Canon EOS 550D). Why is this? Can we expect to see better sensors in the future?

If I understand you correctly, you're not using the camera's built in exposer meter to (manually) set the best exposer. All the wizardry in the world will not do that. If so, then this might make sense to you and save me from a very long explanation.[9] & [10] & [11]--Aspro (talk) 19:53, 10 October 2010 (UTC)

I know how to set the exposure. I also know to use graduated filter, but I want to know why it overexposed more than film, and if the clever Japanese people are doing something about it —Preceding unsigned comment added by (talk) 20:30, 10 October 2010 (UTC)

That is just the point: If you really knew how to set the exposer properly, then the camera (which is only doing what you are telling it to do) would not over exposed the shot! Some film has a greater contrast range, so bad exposure is less of a disaster for the happy snapper. But if you were using 'slide' film it could look just as bad. Just looks more. In other words you are over exposing the shot. Perhaps a better idea would be: (1) Put the camera back in its box. (2) Take it to a charity shop. (3) Say to them: “this camera still works OK, but I am just too stupid to used it. Please take it, it's yours. Maybe you can find it a better home where it will be appreciated for what it is and loved. ” --Aspro (talk) 21:04, 10 October 2010 (UTC)
Please be nice when responding to questions. Nimur (talk) 07:50, 11 October 2010 (UTC)
What you should be doing is taking a spot metering reading of your subject, locking that in, then taking your shot and let the backlighting fall where it may. PЄTЄRS J VЄСRUМВА TALK 23:31, 10 October 2010 (UTC)
I think the OP is asking about the disparity between digital ISO settings and film ISO settings. In theory, an ISO-200 setting on your digital Canon should be equivalent to loading ISO-200 film into a camera. In practice, the degree to which these images/photographs will match depends. The Canons in particular are less "exact" in their lineup; Nikon, for example, prides itself in being essentially "identical" in image-quality to a film camera. But no digital camera will exactly match the exposure characteristics of analog, photo-chemical 35mm film. See our excellent explanation here - you can see that digital sensors are not the same as film; they have an amplifier gain which is calibrated to approximate a film ISO setting. But even film ISO numbers are loosely-interpreted parameters; they are approximations based on a complex exposure-time/saturation formula. Nimur (talk) 07:53, 11 October 2010 (UTC)
The deeper question is, is there any hope for developing sensors that have a dynamic range closer to that of the eye? Or, if I pay more for a camera now, can I get one with a better dynamic range? I've never done enough with film to know how it compares in this regard, but I don't care that much; the comparison that interests me more is digital-vs-human-eye. --Trovatore (talk) 07:56, 11 October 2010 (UTC)
Modern digital cameras have much more sensitive sensors than a film camera ever could. Again from our film speed article, digital cameras now have "ISO equivalent speeds of up to 102,400, a number that is unfathomable in the realm of conventional film photography..." Now, faster film means noisier pictures; but digital image processing and advanced de-noising algorithms are the mainstay of fancy cameras. (Here's a few good articles from Digital Photography Review: Noise and Noise Reduction). Combined with high-quality electronics (particularly, low noise amplifiers, and cooled sensors, the low-end (dark end) of the dynamic range is filling out very nicely. I still see better in a dark room than my Nikon D90 (even at top ISO), but with long exposures, it can perform quite well for night-time landscapes. On the high end (bright end), the camera can always operate without saturating by closing the shutter faster, reducing the aperture, or the photographer can place a filter in front of the lens to reduce incident light. Nimur (talk) 08:02, 11 October 2010 (UTC)
Well, but the point about dynamic range is to capture light and dark in the same photo. If I look towards a line of mountains, on a bright but cloudy day, say looking west in the late afternoon (but not near sunset), I can plainly see detail in both the clouds and the trees at the same time. If I take a photo of the same scene, I can't — I have to set the exposure for one or the other, or compromise on both. If I want to work really hard I can take a bracketed set of exposures and try to piece them together in a photo editor (the simple sort of HDR photography).
But I can't help but think that I shouldn't have to do that. My eye can see both things at once. Why can't my camera? --Trovatore (talk) 08:23, 11 October 2010 (UTC)
You perceive detail in both the clouds and the trees but perhaps not as simultaneously as you think. Detail vision is limited to the small central angle of the fovea. The eye turns to bring the image of whatever you look at on to the fovea, and keeps adjusting the iris to optimise the illumination of the fovea. A camera cannot scan to seek out detail in this way. The article Foveated imaging has images that demonstrate this limitation. Cuddlyable3 (talk) 08:53, 11 October 2010 (UTC)
I don't buy it. Sure, I can't see as much detail in the regions I'm not scanning over. But in the scenario I'm talking about, I can definitely see that there are trees, and that there are variations in the brightness of the clouds, even when I'm not scanning. In a photo, all of that is gone. --Trovatore (talk) 09:36, 11 October 2010 (UTC)
More: Suppose I even buy that I'm really scanning even when I think I'm not — just how fast do you think the eye adjusts to changing light? The time constant is on the order of at least a second, I think. That's far too slow to explain what I can see in a high-dynamic-range landscape. --Trovatore (talk) 09:46, 11 October 2010 (UTC)
Indeed, I overestimated the speed of Adaptation (eye). At a given moment in time the eye can sense a contrast ratio of one thousand (not cited). That's your trees and clouds. In a digital camera that corresponds to about 10 bits of grey scale resolution. Allow 30 minutes to adapt and you might adapt across 109 contrast ratio. (That would demand an impractical 30-bit brightness range.) Those Chilean miners will need that time. There is a different eye reflex that is fast: Accommodation (eye) (refocusing) in 350 milliseconds. Cuddlyable3 (talk) 11:06, 11 October 2010 (UTC)
To get back to one of the OP's original questions, digital cameras have improved over time with the dynamic range the sensors can handle. In general the more you pay, and the better (and bigger, that is more in terms of physical size than megapixels) sensor you get, the better it will handle a wider dynamic range. FWIW it seems that in-camera HDR processing will soon become quite common, thus effectively increasing the dynamic range of the sensor. Over time, as with other features, it should become better done and at some stage become quite effective when used properly. See here for news of a recent Canon patent. Additionally the Pentax K-7 has had a version of this technology available for over a year, though AFAIK it's not exactly brilliant at this stage. Some Sonys also have this built in, as may some other cameras quite possibly. I think the current systems essentially just do what HDR software does - combining a number of images taken at different exposures into a single final image, but just doing it in-camera. The Canon patent looks at doing it by mapping the exposure level by the pixel in-camera, which is quite a more advanced method and could be quite an improvement. So yes, clever people are working on this issue. --jjron (talk) 13:53, 11 October 2010 (UTC)
I really don't follow at all what the Canon scheme is supposed to be doing. Is it just software, or is it physically changing the amount of light that arrives at the brighter versus darker pixels?
If it's just software I don't see it as much of a help; I can take a RAW and do the same thing off-line, so big deal. What I want is a RAW file that gives accurate details of the exposure across a wide dynamic range; to get that you have to change something physically. Maybe Canon does, but it isn't clear from the linked article just what they're changing, or at least it isn't clear to me.
An idea that occurs to me is to scatter different-sized pixels throughout the sensor — large ones to record the darker parts of an image, and small ones to record the bright parts. Kind of like rods and cones, except they'd all be color-capable. Wonder if anyone's working on that. --Trovatore (talk) 18:03, 11 October 2010 (UTC)
As I read it - and I'm no expert on this - the idea is that the camera would take a preliminary 'test shot', meter the exposure by the pixel, then retake the photo with its calculated adjustments in place. In other words, say the camera detected pixels where the highlights were blown out, it would reduce the exposure at those pixels on the retake, and conversely pixels with crushed blacks would have the exposure lifted, to bring out details in both highlights and shadows in a single photo. I don't even know that they've got a working prototype of this yet, I think it's just an idea (undoubtedly there must be some development, but it seems they're understandably keeping the details as close to their chest as possible), so don't expect to see it too soon. If this works as planned though, it would largely render current HDR methods obsolete, though having said which it would seem to place a lot of the decision-making process onto the camera's processor as it would need to take the test shot and the HDR shot in pretty short time in case of rapidly changing light conditions. It would certainly be a big selling point though if worked well. --jjron (talk) 13:15, 13 October 2010 (UTC)
One can build a camera that contains a Beam splitter to share the image among 2 or more CCD chips. That technique is nothing new to manufacturers of colour TV cameras. Cuddlyable3 (talk) 15:52, 13 October 2010 (UTC)

Which preservatives are used in McDonald's french fires?[edit]

How much time will take them to became black?

Aw1010 (talk) 19:54, 10 October 2010 (UTC)

Des feux francaises de McDonald's?
Fat and salt HiLo48 (talk) 20:37, 10 October 2010 (UTC)
They probably don't have any artificial preservatives. IIRC, the french fries are cut an par-cooked at the processing plant, then frozen for shipping. They are then fried for you to eat. A little salt is added, and that's about it. They consist of simply potato and salt and whatever oil they picked up in the frier. Incedentally, the par-cooking this is how you get good french fries anyways... good french fry technique is to fry once, drain and cool for a few minutes, then fry again. McDonalds and other fast food restaurants simply freeze after the first fry. --Jayron32 02:54, 11 October 2010 (UTC)
Couple minor corrections. McDonald's actually does their initial blanching in water, not oil. According to Kenji Lopez-Alt over at A Hamburger Today, this seems to provide a lighter and fluffier end result. I do not have a reference handy because I cannot remember where I read it (though it was recent), but McDonalds also includes some sort of beef/substitute flavouring in the fries now to compensate for the fact that they are no longer fried in beef fat. However, a simple visit to the McDonalds website leads you here, which lists:

French Fries: Potatoes, canola oil, hydrogenated soybean oil, safflower oil, natural flavour (vegetable source),

dextrose, sodium acid pyrophosphate (maintain colour), citric acid (preservative), dimethylpolysiloxane (antifoaming agent) and cooked in vegetable oil (Canola oil, corn oil, soybean oil, hydrogenated soybean oil with THBQ, citric acid and dimethypolysiloxane).

(Source is the link above). → ROUX  03:03, 11 October 2010 (UTC)
Polydimethylsiloxane: "in general, is considered to be inert, non-toxic and non-flammable" John Riemann Soong (talk) 04:51, 11 October 2010 (UTC)
So why do their french fries always taste of soap? Is it just me?--Shantavira|feed me 08:58, 11 October 2010 (UTC)
Yes. There are some substances--one of the flavour compounds in cilantro is probably the most famous--which can only be tasted by certain people; there's a genetic marker for being able to taste it or not. Ferran Adria demonstrated this in Decoding Ferran Adria in 2002 with a compound that they didn't name; he and Anthony Bourdain couldn't taste it, but their interpreter could. So it's altogether possible that one of those chemicals tastes like soap to you. Beyond that, McDonald's fries are actually textbook-perfect pommes frites in the French style. Protip if you're making them at home: the freezing process, assuming you can do it rapidly (liquid nitrogen is good for this if you can get some) is a large part of why they are so crispy. Google 'kenji lopez-alt french fries' and you should find a how-to. → ROUX  09:08, 11 October 2010 (UTC)
To answer the original question: the MacDonalds fries could last a lot longer before mould sets in. I agree that fat and salt may have helped preserve them. But it's also likely that they have dried out. The jars used in the video aren't hermetically sealed. Try comparing rotting times of dry spaghetti and cooked spaghetti to see a similar effect. Itsmejudith (talk) 14:27, 11 October 2010 (UTC)
Regular fries have fat and salt too and the become black quickly. Aw1010 (talk) 18:07, 11 October 2010 (UTC)
I've seen it suggested before that one of the reasons McDonalds food doesn't go off so fast is because the staff tend to observe good hygiene practices, particularly compared to many home cooks as well as cheap non chain takeaway outlets so if you don't open the packet the food is relatively uncontaminated. Of course, selection bias may also play a factor. The video/picture of McDonalds food lasting several days or weeks is much more interesting to most of the people showing these things. Finally I cook chips at home from fresh potatoes and occasionally drop them particularly after re-heating in the oven. I don't even usually use salt. When I find them again they usually haven't gone black although they do dry out and I'm not saying they're safe to eat. Nil Einne (talk) 20:33, 11 October 2010 (UTC)
The notion of using silicon grease on fries doesn't seem so palatable to me. This compound has not enjoyed such a perfect reputation in regard to breast implants [12]. While this general sort of silicon when aerosolized is hard to convict [13] I still have to recognize that a relation of mine is quite sensitive to the stuff when sprayed, even at levels where I wouldn't be aware of it. Wnt (talk) 21:30, 11 October 2010 (UTC)
It's a molecule, not an atom. Different molecules containing silicon can have totally different effects. It's like how salt is made from a poisonous gas and a highly reactive/flammable metal, but once it's a molecule its properties change dramatically.Ariel. (talk) 23:47, 11 October 2010 (UTC)
Silicones are a general class of compounds. I doubt that the properties of a 5- or 10- membered ring are that different than those of a straight chain of greater length. Wnt (talk) 22:59, 12 October 2010 (UTC)
In the first video, the McDonalds french fries are the only ones not handled (I presume someone touched the other french fries to put them in the aluminium dish). So they are not contaminated by the skin flora from the hand, including moulds. (talk) 21:35, 11 October 2010 (UTC)
According to a few news sources, McDonald's may not be a reliable source for what they put on their own fries. If the reports are to be believed, there's a bit more there than potato and salt... Matt Deres (talk) 14:29, 12 October 2010 (UTC)
That's only one news source, not a 'few,' and it's from 2006. The ingredient list is posted above. Further, this is nothing new whatsoever. Ingredients are elided by manufacturers everywhere; 'natural flavour' can mean basically anything. Hydrolized soy protein is MSG. Etc etc etc. → ROUX  23:06, 12 October 2010 (UTC)
You can get several more by Googling, all with the basic complaint that McD's was caught having added high-risk allergens (milk and soy protein) and other substances that frequently cause distress (gluten from wheat) and then quietly added a note to their ingredient list. That note is no longer present (unless I'm missing it), so it's entirely up in the air whether they've ceased including that stuff or whether they're simply covering it up again (though you'd think they'd learn after getting sued over it). The law probably has enough loopholes to allow them to "get away" with including small amounts of high-risk allergens without specifying they're there, but the spirit of the law is clearly that they should mention those high-risk allergens (and gluten) and do so in accessible language. Heck, in Canada, the CFIA issues public health warnings when substances not generally known to contain milk are found to have some in it (example). Good point about the "natural flavour" (and colour) dumping ground, though they don't seem to come into play here. Matt Deres (talk) 00:24, 13 October 2010 (UTC)
But, if you were sensitive enough to gluten or milk proteins that trace amounts on the fries would cause you distress, why would you be eating at McDonalds? It's a food site that handles large quantities of gluten-containing bread and milk protein-containing cheese: it would be like someone with a peanut allergy eating food from a Thai restaurant. It is never going to be safe, even if the specific food ordered doesn't have the allergen purposely added. Soy protein seems more arguable, since you might not have a reasonable expectation that the site handles soy. I'm not saying they shouldn't declare the milk proteins and gluten, but the fries are always going to be at-risk of traces of those, unless McDonalds stops selling cheeseburgers! (talk) 17:58, 13 October 2010 (UTC)