Wikipedia:Reference desk/Archives/Science/2010 June 9

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June 9

Lightbulb question

Just now I heard a quiet, high pitched noise in my room. At first I wasn't sure where it was coming from, and my wife couldn't even hear it at all. This might sound funny, but it reminded me of the almost non-existent sound my Nintendo DS makes when the battery's charging. I discovered it was coming from my lamp and when I touched the bulb, it was extremely hot (more than usual) and when I twisted it, it died. Is that sound normal? What does it mean? I've never heard a noise coming from a dying light bulb before. Thanks!  ?EVAUNIT^{神になった人間} 06:45, 9 June 2010 (UTC)

I've heard this before, and I've guessed that the interior is a partial vacuum and that corrosion has caused a tiny inward leak of outside air, including oxygen which causes the filament to burn out. Our article Incandescent light bulb says that the bulb contains a low-pressure inert gas. Dbfirs 06:55, 9 June 2010 (UTC)

What kind of lamp? Incandescent, or fluorescent? Ariel. (talk) 07:18, 9 June 2010 (UTC)

I've seen some bulbs where the part of metal filament was not well secured and could vibrate at twice the power frequency or a multiple of it. Some brands and styles are more prone to it than others. Visible vibration has long been noted in bulbs, and might be observable with a microscope as an apparent "broadening" of the filament when lit with alternating current. I have not noticed it being an indication the bulb was near its end of life, but I suppose local erosion of the filament might make it more flexible and prone to vibration. The cause of the vibration might be the slight expansion and contraction as it heats up and cools off slightly twice per cycle of the alternating current. If it were near a strong magnetic field, there could have been a 'motor effect" from the passage of current in the field causing motion, as in this 1896 "Nature" report. I think it may be more of a problem if the bulb is on a dimmer circuit which chops the current off at some spot in every half cycle. Oxygen in the bulb would cause a darkening of the glass and a swift burnout. How confident was the OP that the bulb was "hotter than usual" versus "hot to the touch?" An incandescent bulb normally gets way too hot for sustained contact with the finger. Edison (talk) 13:18, 9 June 2010 (UTC)

I think this is likely to be where the filament has got so thin it can no longer carry the current, and the electricity effectively arcs from one side of the filament to the other. The noise heard is the arcing. When the buld is shaken or turned off, the arc is broken and the filament falls away. --Phil Holmes (talk) 17:35, 9 June 2010 (UTC)

No, the noise I've heard (twice in the fifty years since electricity first came to this area) was a high-frequency "whistle" that I assumed was what the OP was describing. At well above above 10KHz, it is unlikely to be generated by mains frequencies in an incandescant light-bulb, though I accept that the other sounds described above are possible, and higher frequencies are generated in other light fitting types, but they are all "buzzes" not "whistles". Dbfirs 20:24, 9 June 2010 (UTC)

The whistle you describe could easily be the sound make by an arc. --Phil Holmes (talk) 20:51, 9 June 2010 (UTC)

I've heard lots of arcs and none of them sounded like the light bulb fault. Dbfirs 23:01, 9 June 2010 (UTC)

The light is incandescent, and I guess it may have been a normal temperature, as I'm used to changing bulbs when they have not been on for awhile, whereas this bulb was on for hours when I touched. Do you think there could be anything wrong with my lamp?  ?EVAUNIT^{神になった人間} 09:50, 10 June 2010 (UTC)

Probably not (though you should check that the new bulb fits firmly). If it happens again, then look for arcing in the switch or elsewhere in the lamp, but the probability is perhaps 99% that the fault was in the bulb, whatever the cause of the sound. If you know a friendly electrician, then get the lamp checked just to be sure. Dbfirs 12:10, 10 June 2010 (UTC)

Nodules on high tension lines

What is the name/purpose/etc of the nodules I sometimes see on high tension lines? I've seen a few different styles (north-east US), but vast majority are the one one in red in the image to the right (click to see greater detail--thumb here for context/placement relative to tower). DMacks (talk) 07:00, 9 June 2010 (UTC)

This is just a guess, but for line maintenance, linemen will sometimes hang a harness on the line, and pull themself along while dangling from it. So my guess is that those things prevent the lineman from accidentally pulling himself too far. Ariel. (talk) 07:17, 9 June 2010 (UTC)

For video of such work, see this YouTube video. Dismas|^(talk) 07:37, 9 June 2010 (UTC)

That's the one! But watch this version. (That video has been re-uploaded so many times, it's nuts, some of the later ones are pretty blurry, this is the earliest one I could find.) Ariel. (talk) 08:37, 9 June 2010 (UTC)

Wow! incredible. Those scary sparks as he approaches the line and then if you look closely there are more sparks leaping across as the helicopter draws away from the line. whoa, some people live on the edge. 86.4.183.90 (talk) 15:32, 9 June 2010 (UTC)

But the most incredible thing about this is, most of their accidents come from helicopter crashes rather than electrocutions -- those folks are so well-equipped and highly trained that their chances of getting zapped while working on a live 100-kV power line are less than those of you or me getting zapped while fixing the fuse box in the home. 67.170.215.166 (talk) 03:02, 10 June 2010 (UTC)

Isn't it a Stockbridge_damper (a type of tuned mass damper), to dampen wind-induced vibrations in the lines? CS Miller (talk) —Preceding undated comment added 09:31, 9 June 2010 (UTC).

Just to second CS Miller, this is definitely a vibration damper. Take it from someone in the industry ;) More images at this Google search. Zunaid 11:32, 9 June 2010 (UTC)

Thanks! DMacks (talk) 19:21, 9 June 2010 (UTC)

Red liquid in sprinkler

What's the red liquid?

I can find a bunch of sources on the net that explain that the red liquid will break the glass at 68 C but nothing that says what the liquid actually is. So, what is it? Some sort of alcohol? Dismas|^(talk) 07:49, 9 June 2010 (UTC)

I can't find an answer, but it seems that it's not any one standard thing - each manufacturer can choose any liquid he wants, as long as it meets the specs. One place mentioned they mix two liquids, which lets them pick any temperature between a range. Ariel. (talk) 08:56, 9 June 2010 (UTC)

I pulled up the (delightfully retro) datasheet for the "Type 817" bulb from Day-Impex, and as Ariel suggests, they just refer to a "special blend of thermally expansive liquids." But as to the red color, note that the color corresponds to the temperature at which the sprinkler activates. You can see the different colors and temperatures at the aforementioned site or our fire sprinkler article. -- Coneslayer (talk) 11:45, 9 June 2010 (UTC)

Many thermometers use red-coloured alcohol, which expands with rises in temperature. So its probably that. 92.24.182.110 (talk) 11:52, 9 June 2010 (UTC)

I've never seen any discussion of what the liquid is either, and I review sprinkler submittals routinely. "Special blend of thermally expansive liquids" is all I see too, but alcohol is a good bet - it would be immediately diluted by the water flow. The heads are usually color-coded according to the activation temperature, with higher-temperature heads used in places like boiler rooms, attics, or in high places near large banks of windows. Acroterion _(talk) 15:44, 9 June 2010 (UTC)

Titanium Cup

how come this same Titanium Cup has a rough edge is a single wall design but a smooth one in the Double-Wall design please compare and click on zoom

http://www.cabelas.com/cabelas/en/templates/links/link.jsp?id=0013258514880a&type=product&cmCat=froogle&cm_ven=data_feed&cm_cat=froogle&cm_pla=1510203&cm_ite=0013258514880a

http://www.rei.com/product/659999?preferredSku=6599990014&cm_mmc=cse_froogle-_-datafeed-_-product-_-6599990014&mr:trackingCode=EE734FFE-FB85-DE11-B7F3-0019B9C043EB&mr:referralID=NA —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 08:33, 9 June 2010 (UTC)

If you are talking about the "bumps" on the upper left corner, those are caused by whoever edited the photo. They were in a hurry and did a bad job of cutting the photo away from the background. Ariel. (talk) 08:45, 9 June 2010 (UTC)

Muntjacs

We are plagued by Muntjacs in our garden but they are mainly very shy of people and retiring. However they make a din with very loud barking noise; enough to bring everyone out of the house (most recently giving birth a week ago). So why so noisy? If they are so fearful the noise must attract more danger at a rather vulnerable point with a baby deer (which now beds down with mother everynight under a brushwood pile). Any idea what the advantage is to them in the load bark? --BozMo talk 11:06, 9 June 2010 (UTC)

According to our article on the Indian Muntjac, they bark when disturbed to tell the predator that they know it is around. Their main predators seem to be stalkers, so they predators, hearing they have been detected probably look for an easier animal to sneak up on. Googlemeister (talk) 19:25, 9 June 2010 (UTC)

Curved horizon?

It is asserted above that "the horizon is curved not straight". I do not think that is true. The horizon, if you were standing on a boat in the middle of an ocean on a calm day, would be a straight horizontal line which wraps around you 360 degrees (since the angles and distances involved are identical in all directions). Anyone who has been to the seaside can tell you that the sea horizon is a straight line. On the other hand, photographs from spacecraft show that if you get far enough away from earth, then the horizon is curved. So what determines when the horizon is curved or not? Since there is unlikely to be a sudden cut-off point, how much curvedness would you get for a observer with an eye-level five or six feet above sea level? Thanks. 92.24.182.110 (talk) 11:49, 9 June 2010 (UTC)

See the horizon article. 92.24.182.110 (talk) 12:08, 9 June 2010 (UTC)

Actually, if the horizon were a line then if you look in different directions the horizon would farther in some directions than others. The fact that it's the same distance in every direction shows that it's a circle. To answer the height question, it's probably the hight of the smallest cone that can fit over the earth without going through it. At that point you will be able to look "down" on the earth, and clearly see it silhouetted against space. Ariel. (talk) 12:19, 9 June 2010 (UTC)

The point is, from the point of view of an observer as described above it is a straight line that wraps around the observer 360 degrees. If you traced this line on the earth with a giant pen and then looked at it from above, then it would be a circle as you say. But this big circle is not the horizon, its a big circle. 92.24.182.110 (talk) 12:43, 9 June 2010 (UTC)

It's the same view from the boat and from space, just with a different perspective. Consider: the astronaut looks directly at the Earth (i.e. straight down) and observes that the horizon is a circle. The sailor looks directly at the Earth (again, straight down) and observes that the horizon is a circle. The only difference is the relative position and apparent size of that circle, and that's a function of altitude. Characterizing the horizon as a straight line is a function of (a) only observing a portion of the horizon and (b) using only an approximation of a line. There is no absolute "cut-off point", as the horizon is never a truly straight line*, and personal interpretations of when curvature is apparent will vary.

*With the possible trivial exception of the distance-zero horizon from a plane tangent to the surface. — Lomn 14:16, 9 June 2010 (UTC)

That is mostly repeating what was said in the question. 92.15.21.24 (talk) 20:06, 9 June 2010 (UTC)

Nope - you are 100% wrong. Imagine you are way out in space, looking back at the earth - the horizon is undoubtedly a circle. As you get closer, the circle gets bigger and bigger. When you are a mile up, it's still a circle around you. When you are 5 feet above the water in your boat, it's STILL a circle - although it's so edge-on, that it looks only very subtly curved. Only when your eye is actually precisely at the height of the water (at 'sea level') is the circle perfectly edge-on - and therefore could be considered to be 'straight'. However - in the perfectly idealised spherical world - with no waves disturbing that line, the distance from your eye to the horizon gets smaller, the lower you are. When your eye is perfectly on the surface of the sphere - the distance to the horizon is zero - so there is no horizon and you can't argue that it's straight. So no! Categorically, the horizon is NEVER a straight line - not even in a perfectly spherical world with idealized-everything. It's either curved or non-existent. In the 'real' world, things like waves make it not-straight, so you can't win that way either. SteveBaker (talk) 16:14, 9 June 2010 (UTC)

If the horizon you see standing in a boat is curved, then this would imply that when you turn 180 degrees, the horizon should be lower, due to the curve forcing it down. Part of the curve would have to be convex, and part concave, otherwise it would never join up. But it is not, it is just the same. And why would there be a difference between the upper and lower parts of the curve? The horizon is all the same - same distance, same angle of declination. 92.15.21.24 (talk) 20:06, 9 June 2010 (UTC)

The horizon is straight if your camera takes a picture that's a cylindrical projection of the environment (I don't know any physical cameras that do this, but my raytracer is happy to simulate them for me). In a cylindrical projection (which doesn't have to have a 360-degree field of view, but typically does), as you rotate the camera on a vertical pole, the position of objects doesn't change vertically. But with an ordinary perspective camera (or your eyes), as you rotate the camera, objects on the horizon will appear lower if they are further towards the edge. The next question to ask is "what about objects behind you -- what height are they?", but that's a trick question; an ordinary perspective projection makes no sense with a 180-degree field of view or higher (and as you get closer to that, the image will look increasingly weird).

For a similar phenomenon, see how spheres don't look like circles unless they're in the center of your view. Usually, our cameras (and, effectively, our eyes) have narrow enough fields of view that we don't notice this or the curvature of the horizon. Paul (Stansifer) 21:13, 9 June 2010 (UTC)

Photo stitchers like hugin can make cylindrical projections, and most of the stitched panoramas on Commons, for example, are cylindrical. The discussion at the Povray wiki that you linked is not very accurate. The issue is not which way you're looking, it's where you are. If the location of your eye relative to the on-screen image is the same (up to an overall scaling) as the location of Povray's virtual aperture relative to its virtual film, then all objects in the frame will appear undistorted. If your eye is elsewhere, there will be distortion. Right now, my eyes and the sides of my display screen form about a 30–75–75 triangle, so full-screen images with a horizontal FOV of 30° will be undistorted. The trouble shows up when people render with high FOVs like 60° or 90°. This distortion only exists when an image is recorded, projected, and then viewed from the wrong location. There is no such distortion if you view the original scene directly, because there is no viewing of a projected image (homunculus argument). -- BenRG (talk) 03:07, 10 June 2010 (UTC)

I think that you and the FAQ are saying the same thing, but I'm not sure. To go back the the OP's question: The special thing about about the way that cameras and raytracers usually work is that 2D image looks like the 3D scene when displayed on a flat surface (provided that you view it from the exact right point). If the camera was above the ground, the image of the horizon will be slightly curved. The horizon does appear straight in 2D in a cylindrical projection, but in order to make the image "look right", you need to display it on a curved surface. So there's no way to take an accurate (in some sense) picture of the horizon without it being curved (in some direction). Paul (Stansifer) 00:22, 11 June 2010 (UTC)

This whole business of picking a cylindrical projection is cheating - I can grind a lens or craft specialised ray-tracing software or build image distortion software that would turn a pretzel into a straight line! Does that make a pretzel "straight"? Only by some very curious use of the language! I can make literally anything look "straight" by these kinds of techniques - so are we going to say that absolutely everything in "nature" is straight - or that nothing is? You can't have it both ways! SteveBaker (talk) 01:29, 11 June 2010 (UTC)

You're arguing semantics. The horizon is curved in the sense that it does not trace a straight line in three dimensional space. It joins up with itself. If you're at a low enough altitude (ie: Standing on the ground) then the horizon appears to be a circle that completely encircles you.

If I had a glass cylinder and drew a line around its equator, no one would argue that the line was straight in 3d space. However, if I placed a camera in the center of the cylinder, exactly level with the line, it would be easy to get a 2d image of the line that was perfectly straight.

Of course, you're not exactly level with the horizon, you're slightly above it. So even a 2D photo would betray some slight curvature if it were possible to magnify it enough. (This isn't too hard to understand if you visualize it right, and it does not show the "never joining up" effect you describe. Imagine holding a hoola-hoop at waist level. It looks curved. Now turn around, it still looks curved, in the same direction.) APL (talk) 01:30, 10 June 2010 (UTC)

The horizon would only appear (very slightly) curved under normal conditions if you have a disability that prevents you ffom moving your eyes or your neck. If you do not have this disability, then you move your eyes along the horizon, and its straight. 92.15.4.200 (talk) 14:41, 11 June 2010 (UTC)

Vernier calipers

How is the least count of the vernier calipers calculated? —Preceding unsigned comment added by Camusrajmohan (talk • contribs) 12:19, 9 June 2010 (UTC)

Are you asking how to use and read a vernier caliper? -- 58.147.55.151 (talk) 12:58, 9 June 2010 (UTC)

Photons

If photons are their own antiparticle, why doesn't shining two lights toward each other make an explosion? --76.77.139.243 (talk) 12:45, 9 June 2010 (UTC)

Very low collision Cross section (physics) for foton-foton interations, and the energy that is released when it does happen is no larger than the photon energies were in the first place (i.e. not nearly large enough to create an explosion, photons have no rest mass thus no energy is released from mass-energy equivalence, unlike massive particle-antiparticle collisions). 157.193.175.207 (talk) 13:01, 9 June 2010 (UTC)

But shouldn't they still make everything dark when they annihilate, even if they don't release any energy? --76.77.139.243 (talk) 13:02, 9 June 2010 (UTC)

"Everything dark" is taking the concept too far, but yes, photons can destructively interfere. This phenomenon can be observed easily in many settings -- however, the destructive interference of two photons has no effect at all on the untold legions of other photons. — Lomn 14:08, 9 June 2010 (UTC)

Particle-antiparticle annihilation turns the particles into photons, so if two photons annihilate each other and turn into photons, you still have two photons left - there is no significant change. --Tango (talk) 16:24, 9 June 2010 (UTC)

The photons can't simply disapear into nothing (Keep in mind that energy conservation must be preserved). They can either do nothing at all (pass each other), produce more photons (scattering of light by light has a fairly low cross section), or follow an inverse anihilation reaction and produce (for instance) electrons and positrons. The last possibility requires the photons to have enough energy to begin with (at least about ten billion kelvins), so visible light cannot do it. Dauto (talk) 18:18, 9 June 2010 (UTC)

Another important point implicit in what I said above is that anihilation doesn't necessarily turn particles into photons. For instance, when a proton and an anti-proton anihilate they are far more likely to produce a meson shower. Dauto (talk) 00:53, 10 June 2010 (UTC)

Mushroom cloud

Would any large-enough explosion make a mushroom cloud, or only atomic explosions? --76.77.139.243 (talk) 12:47, 9 June 2010 (UTC)

See our article on mushroom cloud. In short, large explosions often produce mushroom clouds—they are caused primarily by a ball of heated gas rising and cooling. --Mr.98 (talk) 12:57, 9 June 2010 (UTC)

Any large enough explosion can do it. --Tango (talk) 16:59, 9 June 2010 (UTC)

Do deep underwater explosions create mushroom clouds? (underwater ones, not in the air above the water) Googlemeister (talk) 18:28, 9 June 2010 (UTC)

No, because there's no such thing as a cloud underwater. If you tracked the convective movement of the explosion-heated water, I'm sure it would form the shape of a mushroom due to entrainment, but there would be no way to visualize it.-RunningOnBrains^(talk) 19:08, 9 June 2010 (UTC)

The relevant article, I suppose, is underwater explosion. It sounds like in some circumstances it has a mushroom like appearance but it is not quite the same thing at all as the surface mushroom cloud. --Mr.98 (talk) 19:16, 9 June 2010 (UTC)

Check out the article about Operation Crossroads, it's got a pretty impressive picture of an underwater nuclear explosion. 67.170.215.166 (talk) 03:05, 10 June 2010 (UTC)

Though as the article I linked to pointed out, it was a very shallow one. The only images of a deep underwater explosion that I've found are in Operation Wigwam, but they are just the result of the bubble formed hitting the surface. I couldn't find any images of what such an explosion would look like from under water before it hit the surface. ---Mr.98 (talk) 12:26, 10 June 2010 (UTC)

The question is probably academic since anything close enough to view a deep underwater explosion form a mushroom cloud would be totally crushed by the shockwave. I mean usually good visibility underwater is measured in hundreds of feet, not miles. Googlemeister (talk) 13:30, 10 June 2010 (UTC)

I'm not sure it's entirely academic—knowing how the shockwave would form and what it would do to the water around it is surely something that the nuclear strategists have studied (indeed, it is probably why they detonated the Wigwam blast in the first place). I am sure that in one of the Wigwam reports they have diagrams of this. --Mr.98 (talk) 16:27, 11 June 2010 (UTC)

Endurance of an unused automobile

I know that if one is preserving a classic automobile, it's wise to drain it of all fluids so as to minimize corrosion. But perhaps because that's such reasonable advice, I can't find any hard numbers on how long an automobile will last if you don't drain it. What are the best-case and worst-case scenarios for how long I could leave an automobile (let's say, a brand new American-made sedan, if that matters) with gas, motor oil, etc., completely unattended and ignored in a garage? What are the odds that it would start up again with just the turn of a key, or just some minor tune-ups, after a month, a year, or a decade? Thanks for any help. --M@rēino 14:19, 9 June 2010 (UTC)

As you've noted, there's not going to be much in the way of hard numbers. However, I can say that the first wear item you'll have to deal with is the battery -- depending on the condition of the battery and the storage conditions, even a month could be enough time for the battery to be no longer capable of starting the car. After a year I'd guess that odds are better than not that the battery won't be able to start the car. On the other hand, replacing the battery probably lands under "minor tune-ups". — Lomn 14:26, 9 June 2010 (UTC)

Well assuming your vehicle is gasoline powered, after a couple of years, I would imagine that the gasoline would have gone bad (the best volatiles will have evaporated) and you would not get a start. It is pretty easy to take a battery out of the car, but as noted above, leaving the battery in will drain it over the course of months. Googlemeister (talk) 14:28, 9 June 2010 (UTC)

I've restored cars that have been left in a garage for 10 years. I'm not convinced that draining the fluids makes much difference either way. The worst problem I see is that the tyres go flat and the weight of the car on the deflated tyre bends the steel belting and produces a 'flat spot' - making the tyres useless. It's really frustrating to have to junk four nearly new tyres! So the most important thing (IMHO) is to put the car up on blocks so the wheels are off the ground. I agree that the issue with the volatile fractions of the gasoline evaporating is all too real - when you come to restart the car, you'll certainly want a couple of gallons of fresh gas in the tank - and since disposing of the old stuff is a pain, it's better to drain the gas tank and actually use the gas for something else before you abandon the car.

Replacing the battery is also a good idea - lead-acid batteries are not designed to run completely dead flat - and that's going to happen after just a few months of not driving it. If you can't arrange to periodically recharge the battery - expect to have to replace it after a year or two. As for the other fluids, you could drain the radiator - but the biggest corrosion issue is inside the engine block and with most cars, there isn't a handy drain plug to get the water out of there. Having lots of antifreeze in the water is important because it contains corrosion inhibitors...and you don't want the water in the block to freeze and crack it! Brake & clutch fluids, transmission and engine oil can be left in place - they don't cause corrosion - if anything, they prevent it.

Don't park with the car in gear or in park or with the parking brake on. Leave it with the brakes off and the shifter in neutral - since it's going to be up on blocks anyway, that's unnecessary and brake pads/drums tend to seize up and lock on - and the parking brake cable will stretch because it's under tension. I'm not sure why leaving it in neutral is important - but many people whom I trust on car matters have assured me that it matters. With cars in long storage, rubber hoses and seals tend to 'dry out' and they often fail only after you have the car running again when the pressures go up and vibration sets in - there isn't much you can do to prevent that - but just be aware that just because the car starts, that doesn't mean that you can immediately head off on a 100 mile road-trip! If you can, you should lubricate everything before you try that though...the engine may run, but there are lots of other things that may have seized up.

Cars left in a garage can also attract rats and mice - so it's worth popping the hood and pulling out any obvious nests and doing a cursory check for chewed wiring and/or hoses before you attempt to run the car.

As for starting, I've found that cars that were running OK when they were put away can usually be started with not much more than a new battery and fresh gas...but all too often, people put their cars away when they WEREN'T running (for whatever reason) - so you first have to diagnose and fix the original problem BEFORE you can start work on improving it's condition. If you are putting a car up like this for decades - you might want to do yourself/your ancestor a favor and buy a set of the most obvious spare parts for the car...in 10 or 20 years time, they might be almost unobtainable...or at least horribly expensive! (Also buy an owner's manual while you still can!) SteveBaker (talk) 15:50, 9 June 2010 (UTC)

We bought our current car when it was 21 years old, with just 6000 miles on the clock. Now it hadn't just sat in the garage, but it had only been taken out a couple of times a year for many many years. You need to be careful with anything that's rubber – tubes, seals and, obviously, tyres – the rubber will harden with age whether the car is used or not, and if it's not used then there won't have been any incentive to change anything. We found a rubber seal on the steering column which was about to break, which could potentially have caused the steering to lock, and one of the tyres (we changed all four) that was about to blow through hardening-cracking. Otherwise, we've had the car for three years now, and it runs fine. Physchim62 (talk) 17:42, 9 June 2010 (UTC)

In addition to rubber cracking, you can also have the insulation on your electrical items dry out. This can cause electronics problems in the car and can be fairly difficult to repair. Whether it would interfere with the engine running, or just make your radio not work is going to depend on which wires wear out. Googlemeister (talk) 18:27, 9 June 2010 (UTC)

I think you would like this story of a brand new car that was buried in a time capsule for 50 years. Water got in the capsule and the car was pretty rusty when removed. Ariel. (talk) 19:27, 9 June 2010 (UTC)

• Thanks, everyone -- this is a wealth of good information! --M@rēino 17:47, 10 June 2010 (UTC)

All the above is very true and one other thing to add is that environment plays a big role in how fast all that stuff wears out. Just as museums diligently maintain constant temperatures and humidities, so too do you need to keep these at stable levels or things will wear a LOT faster. From personal experience I can attest to this; gasoline in a garage without much fluctuation will likely be as good as new in two or three years' time (I have proven this on two occasions) but sitting outside left to the elements it will be "sour" in less than a year. --144.191.148.3 (talk) 20:22, 10 June 2010 (UTC)

I once owned an old Buick that vandals had slashed the tires of, and I could not at the time replace them. It was in a bitter cold northern US winter, but I went out every month, chipped away the ice from the driver's door and started it and ran it for a few minutes to keep the battery charged and the engine lubricated. It started fine with this once per month activation. In the Spring, after 5 months of this regimen, I replaced the tires, started it and put it in gear. The transmission made funny noises, but it went around the block ok and drove fine afterwards. If attempting that again, I would add Sta-Bil to the gas to prevent it gumming up. Edison (talk) 02:37, 11 June 2010 (UTC)

how to functionalise a carbohydrate with acetylene?

This is not for a problem set... it's for a real life problem. Many many things will turn out excellently if I can functionalise a carbohydrate with acetylene (most notably I can perform the click reaction)... conveniently. Preferably this involves reagents that aren't too terribly toxic. If I have a polymer of saccharides, perhaps I can use the straight-chain / cyclic equilibrium of one of the terminal ends and use sodium acetylide there to attack the aldehyde form? John Riemann Soong (talk) 15:20, 9 June 2010 (UTC)

^{Way over my}_head.--Chemicalinterest (talk) 17:44, 9 June 2010 (UTC)

There are some reactions of Lithium acetylyides here [1] they do react with ketones and aldehydes.

Sodium acetylide could work too eg [2]

For either reaction you'll need to protect any potentially acidic groups - if you are thinking of explotting this reaction - there's a OH produced in the ring opening reaction of sugars.

There are alternative ways to add an alkyne group - eg Propargyl chloride , propynoyl chloride (HCCCOCl) etc.87.102.13.111 (talk) —Preceding undated comment added 18:11, 9 June 2010 (UTC).

I think zinc acetylides are tolerant of hydroxyls (still nucleophilic towards aldehydes, but not nearly as basic as lithium/sodium ones). DMacks (talk) 19:18, 9 June 2010 (UTC)

Thanks guys. Do you know of an adaptable protocol I could use ... my supervisor sort of wants that (as opposed to me trying to design a completely new one). John Riemann Soong (talk) 19:34, 9 June 2010 (UTC)

I'm not sure but are Zinc acetylides safe? (copper acetylides aren't, and zinc alkyls aren't so...) - all I can find is that it's water sensitive though.83.100.132.26 (talk) 19:43, 9 June 2010 (UTC)

Propargyl chloride or bromide should functionalise your sugar (there are numerous ways)

One example here [3] see Scheme 1 , reaction e using: CH≡CCH2Br, NaH, THF / DMPU - note the sugars where already protected with OAc.83.100.132.26 (talk) 20:19, 9 June 2010 (UTC)

Reading a book similar to this https://doi.org/10.1007%2F3-540-06649-7_3 should give many possibilities.83.100.132.26 (talk) 20:23, 9 June 2010 (UTC)

Uh.... I don't like the use of acyl chlorides and the use of alkyl halides sounds potentially problematic. Could I use an acetylene-functionalised carboxylic acid and toss in some EDC and HOBT? (Does that work less well with alcohols?) John Riemann Soong (talk) 21:48, 10 June 2010 (UTC)

Carbodiimides can be used to make both esters and amides...87.102.13.41 (talk) 22:39, 10 June 2010 (UTC)

Blue and red cobalt(II) hydroxide

Why does the article say the red form is more stable when every time I form it, it is blue. Is it because I only use ammonium hydroxide to react with cobalt(II) chloride(forms blue-green precipitate)? Also, the cobalt carbonate article says that it is a red powder. When I react cobalt chloride with sodium carbonate, I obtain an indigo-colored compound. Why isn't it red? --Chemicalinterest (talk) 15:22, 9 June 2010 (UTC)

Cobalt hydroxide

With hydroxide and Co²⁺ the initial product is blue, this should change (on boiling) or after ~8hrs to the pink/red form - there are two forms with different structures. It's described here [4] - to save you the trouble of reading that the initial form is called the alpha form, or α-Cobalt (II) hydroxide, the more stable form that forms later is called the beta form or β-Cobalt hydroxide.

Suggest using NaOH (caustic soda) instead of ammonia , and waiting to see the other form - avoid mixing the hydroxide with air since this will oxidise it.87.102.13.111 (talk) 16:06, 9 June 2010 (UTC)

Cobalt carbonate

Cobalt carbonate is usually 'violet' (is that the same as your indigo?) (yes--Chemicalinterest (talk) 17:37, 9 June 2010 (UTC))

See these images http://www.google.co.uk/images?hl=en&q=cobalt+carbonate&um=1&ie=UTF-8&source=og&sa=N&tab=wi

If your produce is blue possibly you are forming the hydroxide due to the basicity of sodium carbonate .. as before allow time for the reaction or boil - this should give the carbonate eventually.87.102.13.111 (talk) 16:29, 9 June 2010 (UTC)

It should be pink usually though - eg images 87.102.13.111 (talk) 16:58, 9 June 2010 (UTC)

There's some instructions for making the basic carbonate here from Cobalt (II) chloride and sodium carbonate. [5] 87.102.13.111 (talk) 17:13, 9 June 2010 (UTC)

I dried the hydroxide in air and it turned dark green. --Chemicalinterest (talk) 17:39, 9 June 2010 (UTC)

Its blue probably because of the mixture of the red carbonate and the greenish-blue hydroxide. I boiled that mixture and it did not turn red. I think the carbonate resists conversion. --Chemicalinterest (talk) 17:43, 9 June 2010 (UTC)

Look on cobalt carbonate for the picture. --Chemicalinterest (talk) 18:33, 9 June 2010 (UTC)

Yes that's the right stuff (probably) - colour is also known as Mauve 87.102.13.111 (talk) 18:50, 9 June 2010 (UTC)

I boiled the blue hydroxide (still using ammonia) and it stayed blue. As I have no NaOH for the time being, I have to use my KOH/K₂CO₃ mixture. Hope it works. --Chemicalinterest (talk) 18:33, 9 June 2010 (UTC)

The ammonia will affect the reaction. You can get pure (99% or better) NaOH from hardware stores - usually in 'pearl' or 'flake' form for about the same price as bleach. eg google shops - similar price in rest of world Check the label though - some versions (intended for drain cleaning) contain aluminum - don't buy that stuff. (It's very caustic - and does hurt a lot if you get it on your hands - it also has a tendency to heat water to boiling if you add a lot of it to water - the dissolution reaction is very exothermic.)87.102.13.111 (talk) 18:50, 9 June 2010 (UTC)

When I precipitated the Co²⁺ with the KOH/K₂CO₃ mixture, there was some fizzling (probably acidity of Co²⁺ and HCl impurities in the test tube) and a red precipitate was formed. I am drying it now. It may be a mixture of beta-cobalt(II) hydroxide and cobalt carbonate.--Chemicalinterest (talk) 19:02, 9 June 2010 (UTC)

using a car 12 volt alternator as a generator when its removed from the car

what problems are likely if i periodically spin a small 12 volt car alternator, at approx. 1000 rpm, with a 12 volt motor (eg a battery screwdriver) which is itself connected to one of the 12 volt batteries that im charging with the alternator. i intend for the outfit to be mounted on a 36 volt power assisted pushbike correctly wired in parallel to charge the 3 times 12 volt batteries, as im riding. also can you point any pitfalls in the above idea generally as i would like to power small 240 volt appliances via invertors using the same type of outfit. thanks —Preceding unsigned comment added by 85.189.247.67 (talk) 16:03, 9 June 2010 (UTC)

It's not clear to me what is your source of energy. Dauto (talk) 16:42, 9 June 2010 (UTC)

An alternator generates electricity. Spinning it with a battery-operated screwdriver doesn't make any sense to me - you'll get more energy back just by taking the batteries out of the screwdriver and attempting to use them to power the appliances. That being said, I don't think that those batteries contain enough energy to make that practical, even with inverters, though since I'm not an electrician I could be wrong. Okay, nevermind... I see now that that's not what you are trying to do, but I'm extremely confused as to the nature of your setup now. Falconus^{p t c} 17:05, 9 June 2010 (UTC)

Your statement may not be what you intend to say... You state that you have a generator charging a battery. The battery is connected to an electric screwdriver. The electric screwdriver is spinning the generator... which is charging the battery. The effect is simple: You will reduce the charge in the battery because it is not a perfect system. There is loss. So, the amount of electricity used to turn the screwdriver and the generator is less than the amount of electricity being charged back into the battery. -- kainaw™ 17:13, 9 June 2010 (UTC)

People have tried many times in the past to make these perpetual motion machines but they never work. Even the earth is slowly slowing down.--Chemicalinterest (talk) 17:36, 9 June 2010 (UTC)

If you are saying you've got 3 12V batteries in series, and you want to charge one of those batteries whilst still in the circuit - then yes you can do that.. though your charging device will also have to supply current to drive the main circuit if it's on, and will need to provide a sufficient overvoltage to charge.

It doesn't seem likely that a 12V screwdriver will have sufficient power to do that. But it might. The 12V screwdrivers I'm thinking of definately wouldn't be able to turn a car alternator at the required speed. Also you would need a rectifier to convert the AC output from the alternator to DC. 87.102.13.111 (talk) 18:26, 9 June 2010 (UTC)

(EC) It sounds to me like 85.189.247.67 is trying to power things with a bicycle (in which case their muscles or food or whatever are the source of energy). However I don't get why the set up is so complicated. I'm also not sure what the 'power assist' is for. Are they trying to make some sort of 'regenerative breaking'? Or to help them go up hills by doing more work (to charge the batteries) while on flat bits? P.S. Be aware that you shouldn't expect good returns from whatever you do do. It wouldn't surprise me if you get an efficiency of less then 10% Nil Einne (talk) 18:28, 9 June 2010 (UTC)

One problem you will have is that alternators need to be energized with current before they will do anything. (As opposed to generators that just need to be spun.) The strength of the current being fed into them determines the voltage. They do that to keep the voltage steady even when the alternator spins at varying RPMs. They need rather a lot of current. Ariel. (talk) 19:35, 9 June 2010 (UTC)

I didn;t realise that - you could try this [6] - also it seems that car alternators have a built in rectifier (so ignore my comment above, now crossed out)>83.100.132.26 (talk) 19:59, 9 June 2010 (UTC)

If your motor and alternator are 80% efficient, then about 36% =(1 -.8²) of the energy will be lost converting mechanical rotation of the motor to the generation of electricity, and the power originally stored in the battery will not be replenished by the alternator, so the system will fail in short order. In addition, the wires will dissipate energy as heat. This is a best case scenario. Edison (talk) 02:30, 11 June 2010 (UTC)

Question about birth change

Lets imagine someone is making sex and some months later a baby is born. Now lets imagine that is this example the couple started make sex just 3 seconds later. My question is, in the second example, a another baby could be born in the place of the baby that I said before or no baby be born at all?

Before you ask: Why you want to know this? I am just curious if a time traver woud be able to create a paradox so easily.

PS: Because of the extreme chains of changes that those new things on the second example will create this would easily create a paradox. 187.89.81.94 (talk) 16:19, 9 June 2010 (UTC)

(ec) You may find the article human fertilization useful to analyze the extremely complex and largely random set of events that lead to (usually) a single human sperm fertilizing the egg. Clearly, even a slight perturbation in any way could permit a different sperm to be the one that reaches the egg. Biologically, the result would be an individual that is genetically distinct from the (now hypothetical) individual who would have otherwise been born. Whether those biological distinctions result in a "different" human individual is a matter of philosophical debate; but undoubtedly, even a tiny perturbation in conditions would, with overwhelming certainty, result in a different sperm reaching the egg. Nimur (talk) 16:43, 9 June 2010 (UTC)

(ec) The key question here is whether the particular sperm that happens to fertilize the egg would make it back to that egg again. My understanding (based mostly on a "competitive sperm" graphic from my sex education days) is that if you varied the conditions slightly, that the odds that another sperm would "make it" is probably fairly high. I'm not sure if 3 seconds would make a large difference but some amount of time would. As for whether the other baby is "another baby", it depends on your interpretation of the philosophy behind this. In any case, it's worth remembering that the egg would be the same in either case.

That being said, I'm not sure how the time travel connection plays in. Would said time traveler show up, delay his parents having sex by five minutes, and thus a paradox is formed? It's kind of an awkward situation to imagine. (Especially since time travel and potential paradoxes created by it is not exactly a subject that current science can explain meaningfully.) --Mr.98 (talk) 16:46, 9 June 2010 (UTC)

I endorse Nimur's answer about the butterfly effect. Yes, the time traveler could destroy his own existence by delaying the sex act for a second. Since you're interested in speculative fiction involving this, I should point you to Watchmen, in which Dr. Manhattan has an insight related to this whilst on Mars. Comet Tuttle (talk) 16:56, 9 June 2010 (UTC)

It just strikes me that delaying sex for just a second would be quite difficult from a practical point of view. "Oh, hi there, didn't realize someone was in here! Please continue!" --Mr.98 (talk) 19:04, 9 June 2010 (UTC)

Not so difficult. When I said delaying a sex for just some seconds. Some very small changes like the time traveller killing a fly could trigger this. In the original timeline this fly was not killed, making the father arrive one second later in the house (the fly bothered the father for about 1 second while he was walking on the street and this makes he arrive one second later in sex).This second later would influence on the kid he would have.

Something about this kid: When I said a different kid, I was talking about a kid that is at least a little different (personality, body skills, or appearance) from the other kid, those littles difference would create chain reaction that would later create a father paradox, or sometimes other paradox.

A little different kid could lead to a different name, kids in school not creating a nickname based on something about him he would have on the other timeline[...], and this would lead to bigger changes that would lead to changes that would create the paradox.

If this father is the father of the time traveller, this is even more simple. This new kid, would not be him, and BANG!, father paradox.

I asked this question, because if this birth thing was true, this would make paradox almost impossible to avoid, because tiny changes would (in a direct way or because of buttlefly effect) make someone (that would later have a kid) make sex earlier or later, resulting a different kid, then the bigger changes woud start to happen or small changes that would led to big changes.187.89.177.139 (talk) 21:14, 9 June 2010 (UTC)

The thing about the infamous "butterfly effect" is that we do not have a scientific model of human behavior that is sufficiently accurate that we could make meaningful predictions. If you want to consider a human to be an enormously complex state machine, and then presume that we could conduct a controlled experiment where the two hypothetical stimuli are simulated (with and without a fly, for example), we would need some way to generate a reliable model of human behavior, compute a predicted outcome based on all the circumstantial and situational inputs, and then observe some set of responses. This level of accurate and rigorous modeling for human behavior does not exist. Similarly, we can't accurately model the rest of the universe to the level of accuracy that would be needed to precisely predict such complex states. As such, it is useless to analyze whether killing a fly (or similar "insignificant" changes of state due to hypothetical time-travel scenarios) would or would not change some perceivable/measurable outcome. For these reasons, "butterfly effect" speculations remain fairly philosophical and are rarely subject to any kind of actual physical or mathematical analysis. Nimur (talk) 22:14, 9 June 2010 (UTC)

Given enough time, I think the time traveller could drastically change his future time by doing nothing more than sending a single photon back in time. The consequence of change is usually more change - and chaotic systems are rather more common than self-correcting ones - so eventually, any change - no matter how small - will have 'macroscopic' consequences that would be noticable. SteveBaker (talk) 00:36, 11 June 2010 (UTC)

Sinkhole debris

I'm looking at pictures of this massive 300-foot-deep sinkhole from Guatemala. That is a lot of sediment - a lot of material. Hundreds of thousands of cubic meters of debris. Where does it go? Is there so much pore space between the overburden material that it can just compress at the bottom and form a denser sediment, or is there actually a large void, cavern, or geological water-pipe that the sediment all piles into at the bottom? I see a lot of discussion about "eroded" limestone, which makes me wonder if there were actually large cavernous hollow spaces that the sediment rested above. Nimur (talk) 18:30, 9 June 2010 (UTC)

Similar question not long ago Wikipedia:Reference_desk/Archives/Science/2010_June_1#Sinkhole

It's actually described at sinkhole I'm sure. The limestone underneath is dissolved over time by underground streams, a relatively thin lid is on top of the hole.

See http://www.change.freeuk.com/learning/geog/caves.html for info on the underground geology of limestone areas .. (87.102.13.111 (talk) 18:42, 9 June 2010 (UTC)

By the way the examples seen are extreeeeeme examples - in the UK in limestone areas sinkholes are common - but they are usually less than 1m accross, and usually don't result in a huge pipe, and may only go down a few metres.83.100.132.26 (talk) 19:03, 9 June 2010 (UTC)

You can read my old question on sinkholes here http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_February_5#Sinkholes_-_Geology

google maps Here's some more modest sinkholes - they're the line that looks like someone has pricked the ground with a pin.83.100.132.26 (talk) 19:16, 9 June 2010 (UTC)

Awesome. This topic has clearly been addressed thoroughly. It seems like the consensus then is that there are actual large limestone caverns underneath the surface. Sorry for my failure to check the archives - I've just reconnected to the Internet after a long absence and am slow to catch up on my Science Desk archives... Nimur (talk) 19:31, 9 June 2010 (UTC)

Actually, there is some suggestion that the Guatemala sinkhole was not caused by limestone dissolution but by the washing away of soft rock (loose pumice) according to this article. Mikenorton (talk) 22:25, 9 June 2010 (UTC)

See this article. Do we have an article on cenotes? DuncanHill (talk) 22:29, 9 June 2010 (UTC)

Cobalt compounds yet again!!!

Left, solution containing the Co(H₂O)₆²⁺ ion. Center, a solution containing the CoCl₄^2- ion. Right, a solution containing the (fill in the blank) ion.

Heating of concentrated sodium chloride and cobalt(II) chloride

A little later, it turns back into a pink solution

I reacted red cobalt(II) chloride with hydrochloric acid to get the blue-purple tetrachlorocobalt(II) complex. I reacted a tiny amount of the blue-purple tetrachlorocobalt(II) complex with 10 times its amount of hydrochloric acid to get a blue-green solution. It looks like a clear version of alpha-cobalt(II) hydroxide. Is it a hexachlorocobalt(II) complex? --Chemicalinterest (talk) 19:11, 9 June 2010 (UTC)

I'm not sure (it doesn't seem that likely) - what happens if you take a similar tiny amount of CoCl₄^2- and just dilute it. or use NaCl solution instead of HCl.83.100.132.26 (talk) 19:24, 9 June 2010 (UTC)

If you dilute a tiny amount of the CoCl₄² in water, you will get an extremely faint pink color of the Co²⁺ hydrate ion. The color is very vibrant; a microscopic amount of cobalt compound, such as cobalt(II) hydroxide, will react with concentrated HCl to form that color. --Chemicalinterest (talk) 19:28, 9 June 2010 (UTC)

Mmmh - but isn't that what you've just done in "test tube 3" and got green.. I'd try two things:

• Do it again to double check (making sure the test tube is super clean)
• Try with a NaCl solution of the same molar concentration as the HCl you used, eg this reaction is valid too:

CoCl₂ + 2NaCl >> CoCl₄^2- + 2Na⁺

If the product/colour from the above reaction is different on diluting the above reaction compared to the reaction of CoCl₂ with HCl_(aq) then it must be due to the acidity.83.100.132.26 (talk) 19:49, 9 June 2010 (UTC)

It forms when any cobalt compound, CoCO₃, Co(OH)₂, CoCl₂ is added in small quantities to concentrated HCl. It also forms when blue CoCl₄^2- is reacted with HCl. Here is the pattern: red + HCl → purple + HCl → blue + HCl → blue-green. I will try NaCl now, but NaCl is not as soluble and so will not be concentrated (12 molar) like HCl; probably won't get green coloration. --Chemicalinterest (talk) 20:17, 9 June 2010 (UTC)

It was a little greener when heated because the equilibrium toward blue is driven by heat and away from blue is driven by cold. It isn't as green as the HCl reaction though, but it is a brighter blue than the "normal" CoCl₄^2-. --Chemicalinterest (talk) 20:27, 9 June 2010 (UTC)

If you use dilute sodium chloride (e.g. in a test for chloride ions) it forms a blue-purple solution. --Chemicalinterest (talk) 20:29, 9 June 2010 (UTC)

It follows the same pattern as the spectrum on a "Create Custom Colors" section on a computer graphics program. --Chemicalinterest (talk) 20:31, 9 June 2010 (UTC)

The CoCl₂ + 2NaCl went green when hot? but not as much as the HCl CoCl₂ reaction?83.100.132.26 (talk) 20:34, 9 June 2010 (UTC)

See pics on right. --Chemicalinterest (talk) 20:43, 9 June 2010 (UTC)

This [7] and others agree that increasing Cl^- concentration as well as increasing temperature favour tetrahedral (blue) complexes. So that matches what you found.

I still can't find anything about the green colour though.83.100.132.26 (talk) 21:29, 9 June 2010 (UTC)

So the question is:What is the green color formed when small amounts of cobalt(II) salts are added to large amounts of concentrated hydrochloric acid? --Chemicalinterest (talk) 21:31, 9 June 2010 (UTC)

My guess would be [CoCl₅]³⁻, or possibly [HCoCl₅]²⁻. It won't be the hexachloro complex if it has a bright colour. Physchim62 (talk) 21:51, 9 June 2010 (UTC)

Phenol

If it's only mildly acidic, why is it so corrosive if you touch it by mistake? --75.25.103.109 (talk) 22:52, 9 June 2010 (UTC)

For the record, it's a popular misconception that all corrosives are acids. See Corrosive#Common types of corrosive substances. Regards, --—Cyclonenim | Chat  22:57, 9 June 2010 (UTC)

I know that bases are also corrosive, but I don't think that a single chemical can simultaneously be both an acid and a base. --75.25.103.109 (talk) 23:00, 9 June 2010 (UTC)

A corrosive is only a substance that hastens or causes the destructive decomposition of a material. --Chemicalinterest (talk) 23:56, 9 June 2010 (UTC)

Exactly, some oxidative molecules are corrosive, as are electrophilic salts. It doesn't have to be an acid or a base, but it often is. I'm afraid I can't answer the question directly regarding it's mechanism.

Ironically, one reason why phenol is so corrosive is precisely because it is a weak acid. A strong acid such as hydrochloric acid is completely dissociated in solution: that is, a solution of hydrochloric acid contains H⁺ and Cl⁻ ions. These ions cannot cross the epidermis, the top layer of dead skin cells: they have to burn their way through the epidermis before the acid can do any serious harm to living tissue. So, if you spill hydrochloric acid on yourself, you have a couple of seconds or so to wash it off before it starts doing real damage. Phenol, on the other hand, is most C₆H₅OH molecules in solution; that is, there is very little dissociation into ions. The neutral molecules can diffuse across the epidermis so, even if you wash the spill off, some phenol will already have reached the living tissue below and can continue doing damage. There are many other compounds which show a similar risk of corrosion through skin absorption, such as hydrofluoric acid, bromine and mustard gas. Note as well that phenol is quite toxic by skin absorption, and several deaths have been reported [8].

I couldn't find a good discussion about the mechanism of tissue damage (ie, corrosion) – most reference source just state that it is corrosive as well as toxic – but looking at some of the biochemical studies that have been carried out, I would guess that it acts by reacting with the proteins which hold cells together to form skin tissue, and so weakens the cohesion of the skin in that way. This is similar to the mode of corrosion with mustard gas, although obviously phenol is less corrosive than mustard gas. Physchim62 (talk) 00:51, 10 June 2010 (UTC)

Actually, that's almost the exact opposite of irony, but being the Science desk I'll let it slide :P

Being the non-chemist that I am, I'm a bit confused by this discussion. Everyone (including the article) seems to agree that the chemical is highly corrosive and damaging to biological tissue, yet there is a section which talks about its use in preserving tissue. Now that is irony (okay not exactly, I just wanted to link to that video):-D -RunningOnBrains^(talk) 14:41, 10 June 2010 (UTC)